75 10 13233 https://digitalcollections.lakeheadu.ca/files/original/e93535ba9a7f7218964703f7fd8f6433.pdf 9907c8db5d636aa3e6933cfcb903ac20 PDF Text Text FORTY-FIRST ANNUAL MEETING ANNUAL MEETING INSTITUTE ON LAKE LAKE SUPERIOR SUPERIOR GEOLOGY Marathon, MarathonyOntario Ontario May May 13-18, 13-1aY1995 1995 PROCEEDINGS PROCEEDINGS VOLUME VOLUME 41 41 PART 1: I : PROGRAMAND PROGRAM AND ABSTRACTS ABSTRACTS �Annual Meeting 41st Annual Meeting Institute lnstitute on on Lake Lake Superior Superior Geology Geology Ontario Marathon, Ontario May 13-18, 13-18, 1995 1995 Organizing Committee Organizing Committee Genera! General Chairman: Mark Smyk (Ontario Geological Geological Survey) Survey) Secretary-Treasurer: Mark Secretary-Treasurer: Mark O'Brien (Ontario (Ontario Geological Geological Survey) Survey) Program Chair/Abstracts lenbeck Chair /AbstractsEditor: Editor:Manfred ManfredKeh Kehlen beck (Lakehead (Lakehead University) Additional assistance provided by: Bernie Schnieders, Doug Mckay McKayand and Maurice Maurice Lavigne Lavigne (Ontario (Ontario Geological Geological Survey) Survey) with the cooperation cooperation of of the the Ontario Geological Geological Survey and the Ministry Ministry of Northern Development and Mines Proceedings Volume Volume 41: 41 : 1: Abstracts Part I: Part 2: Field Field Trip Trip Guidebooks Guidebooks 2a. Alkalic Rocks Rocks of the the Midcontinent MidcontinentRift Rift 2b. Geology and Base Metal Deposits of the Manitouwadge Greenstone Belt Metal 2c. Geology of the Schreiber Schreiber Greenstone GreenstoneAssemblage Assemblage and its its Gold Gold and Base Base Metal Metal Mineralization Mineralization 2d. Geology Geology and and Gold Gold Deposits Depositsof of the the Hemlo Hemlo Area Area 2e. Kimberlite, Kimberlite, Base Base Metal Metal and and Gold Gold Exploration Exploration Using Using Overburden, Wawa Area Published and Distributed Distributed by by the Institute lnstitute on Lake Lake Superior Geology Mark Jirsa, Secretary-Treasurer Secretary-Treasurer Minnesota Minnesota Geological Geological Survey Survey 2642 University University Ave. Ave. 551 14-1057 U.S.A. U.S.A. St. Paul, MN 55114-1057 ISSN 1042-9964 ISSN 1042-9964 �Institute Institute on on Lake Lake Superior SuperiorGeology Geology Marathon, Ontario Ontario 1995 May 13-18, 13-18, 1995 Proceedings Volume 41 41 Proceedings Volume Part 1: Program Programand andAbstracts Abstracts Mark Smyk Smyk General Chairman, 41st I.L.S.G. I.L.S.G. Ontario Ontario Geological Survey Survey Field Services Services Section Section -- Northwest Ministry of Northern Development Development and Mines James St. St. Suite B002, 435 S. James Thunder Bay, ON ON P7E 6E3 CANADA CANADA Manfred Kehlenbeck Kehlenbeck Abstracts Editor, Editor, 41st 41st I.L.S.G. Program Chair I/ Abstracts Department of Geology Geology Lakehead University Thunder Bay, ON ON P7B 5El 5E1 CANADA CANADA Reference to material material in in Volume Volume 41, 4 1,Part Part1,1,should shouldfollow followthe theexample examplebelow: below: Lightfoot, P.C. P.C .The Therelationship relationshipbetween between mantle mantle plumes, flood basalts and mineralization [abst];; Institute on Lake Superior Geology, Geology, 41st 41st Annual Annual Meeting, Meeting, Marathon, Marathon, ON, [abst] 1995, v.41, part 1, 1, p.42-43. �Contents Part 11 Part Program and Abstracts Institutes Institutes on Lake SuperiorGeology Superior Geologyto to 1995 1995 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . i . .. Constitutionof ofthe theInstitute Instituteonon Lake Superior Geology Constitution Lake Superior Geology . . . . . . . . . . . . . . . . . . . . . . . . . ii ... By-Laws By-Laws of of the the Institute Instituteon on Lake Lake Superior SuperiorGeology Geology . . . . . . . . . . . . . . . . . . . . . . . . . . . . iii iii Goldich Medal Guidelines Guidelines . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . iv Goldich Medal Committee . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . v Past Goldich Medalists . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . v 1995 Goldich Medal Recipient/Citation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . v Banquet Speaker . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . vi Banquetspeaker Student Travel Award . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . vii Student Student Travel Award Application Form . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . vii ... Board of Directors . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . viii ... Local Committees . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . viii LocalCommittees Report of the Chair Chair of of the the 40th 40th Aimual Annual Institute Institute . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . x Calendar Calendar of Events Events and and Program Program . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . xii Abstracts Abstracts . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11 �INSTITUTE INSTITUTE ON LAKE SUPERIOR GEOLOGY INSTITUTE NUMBER 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 DATE PLACE CHAIRMAN 1955 1956 1957 1958 1959 1960 1961 1962 1963 1964 1965 1966 1967 1968 1969 1970 1971 1972 1973 1974 1975 1976 1977 1978 1979 1980 1981 1982 1983 1984 1985 1986 1987 1988 1989 1990 1991 1992 1993 1994 1995 Minneapolis, Minneapolis, Minnesota Minnesota Houghton, Houghton, Michigan Michigan East Lansing, Lansing, Michigan Michigan Duluth, Minnesota Minnesota Minneapolis, Minneapolis, Minnesota Minnesota Madison, Madison, Wisconsin Wisconsin Port Arthur, Ontario Ontario Houghton, Houghton, Michigan Michigan Duluth, Duluth?Minnesota Minnesota Ishpeming, Ishpeming?Michigan Michigan St. Paul, Minnesota Minnesota Sault Ste. Marie, Michigan Michigan East Lansing, Michigan Superior, Superior, Wisconsin Oshkosh, Wisconsin Thunder Bay, Ontario Duluth, Minnesota Houghton, Michigan Michigan Madison, Madison?Wisconsin Wisconsin Sault Sault Ste. Ste. Marie, Marie, Ontario Ontario Marquette, Marquette?Michigan Michigan St. Paul, Minnesota Thunder Thunder Bay, Ontario Ontario Milwaukee, Milwaukee, Wisconsin Wisconsin Duluth, Minnesota Eau Claire, Wisconsin East Lansing, Michigan International Falls, Minnesota Houghton, Michigan Wausau, Wisconsin Wausau7 Kenora, Ontario Kenora? Wisconsin Rapids, Wisconsin Wawa, Ontario Ontario Marquette, Michigan Michigan Duluth, Minnesota Thunder Thunder Bay, Bay, Ontario Ontario Eau Claire, Claire?Wisconsin Wisconsin Hurley, Wisconsin Eveleth, Minnesota Houghton, Michigan Marathon, Ontario Ontario C.E. Dutton Dutton A.K. Sneigrove Snelgrove BL Sandehr B.T.Sandefur R.W. Marsden E.N. Cameron & R.A. Hoppin E.N. Cameron Cameron E.G. Pye A.K. Sneigrove Snelgrove H. Lepp Lepp A.T. Broderick P.K. Sims Sims & R.K. Hogberg R.W. R.W. White White W.J. W.J. Hinze Hinze A.B. Dickas Dickas G.L. LaBerge M.W. Bartley & E. Mercy D.M. Davidson J. Kalliokoski M.E. Ostrom P.E. Giblin J.D. Hughes M. Walton M.M. Kehlenbeck Kehlenbeck G. Mursky D.M. Davidson Davidson P.E. Meyers Meyers W.C. Cambray D.L. Southwick Southwick T.J. Bornhorst G.L. LaBerge C.E. Blackbum Blackburn J.K. Greenberg E.D. Frey & R.P. Sage Sage J. S. Klasner J.C. Green M.M. Kehlenbeck P.E. Meyers A.B. Dickas Dickas D.L. Southwick Southwick T.J. Bornhorst M.C. Smyk 1 �____________ CONSTITUTION CONSTITUTION OF OF THE THE INSTITUTE INSTITUTE ON ON LAKE SUPERIOR GEOLOGY Article Article I Name Geology'. The name of the organization organization shall be the "Institute Ynstitute on Lake Superior Geology". Article I1 Article II Objectives Obiectives The objectives objectives of this organization organizationare: are: region may exchange ideas and A. To provide a means whereby geologists A. geologists in the Great Lakes region scientific scientific data. data. promote better better understanding understanding of of the the geology of the Lake Superior region. B. To. To promote C. C. To plan and conduct conduct geological geologicalfield field trips. trips. III Article 111 Status Status No part of the income income of the organization shall insure to the benefit of any member or individual. individual. In the event event of of dissolution dissolution the the assets assetsof of the the organization organizationshall shallbe be distributed distributedto to (some tax free free organization). organization). be not not only "scientific" or (To avoid Federal and State income taxes, the organization should be "educational, "educational,but also also "non-profit".) "non-profit".) Mum. Stat. Anno. 290.01, subd. Minn. subd. 4 Minn. Stat. Stat. Anno. 290.05(9) 290.05(9) 1954 Internal Revenue Code s.501(c)(3) S S O 1(c)(3) Article Article IV Membership members hi^ shall consist consistof ofthe theboard boardof ofdirectors. directors. Any Any geologist The membership of the organization shall interested the annual meetings. interested shall be permitted to attend and participate in and vote at the Article V Meetings Meetings The organization year, preferably preferably during duringthe themonth monthof ofApril. April. The place and organization shall meet once a year, exact exact date date of of each each meeting meeting will will be be designated designated by by the the board board of ofdirectors. directors. Article VI Directors Secretary-Treasurer, and and the the last last three three past past The board of directors shall consist of the Chairman, Secretary-Treasurer, than five five persons, persons, by by reason reason of Chairman; but if the board should at any time consist of fewer than directors, the the vacancies vacancies on the unwillingness or inability of any of the above persons to serve as directors, board may be filled membership of the board up to five filled by the annual annual meeting meeting so so as as to bring the membership five members. Article Article VII VII Officers Officers The officers officers of of this this organization organizationshall shall be be aa Chairman Chairmanand and Secretary-Treasurer. Secretary-Treasurer. A. A. The Chairman Chairman shall be elected each year by the board of directors, who shall give due consideration consideration to the wishes of any group that may be promoting the next annual meeting. His His the annual meeting meeting over which he term of office office as Chairman Chairman will terminate at the close of the presides or when his successor shall have have been been appointed. appointed. He will then serve for a period period of three years years as as aa member member of of the the board board of of directors. directors. 11 �B. The Secretary-Treasurer Secretary-Treasurer shall shall be elected at at the annual annual meeting. meeting. His Histerm termof ofoffice officeshall shallbe be B. The two two years years or or until untilhis hissuccessor successorshall shallhave havebeen beenappointed. appointed. Article ArticleVIII VIII Amendments Amendments This This constitution constitutionmay may be be amended amended by by aa majority majority vote vote of of those persons persons who who are are personally personally present present at, at, participating participatingin, in,and andvoting votingatatany anyannual annualmeeting meetingofofthe theorganization. organization. BY-LAWS BY-LAWS I. Duties Dutiesof of the the Officers Officersand andDirectors Directors A. A. It shall shall be the the duty duty of of the the Annual AnnualChairman Chairmanto: to: 1. I. Preside Preside at at the the annual annual meeting. meeting. 2. 2. Appoint Appointallallcommittees committeesneeded neededfor forthe theorganization organizationof ofthe theannual annualmeeting. meeting. 3. Assume Assumecomplete completeresponsibility responsibilityfor forthe theorganization organizationand and fmancing financing of of the the annual annual meeting meeting over which he presides. over which he presides. B. B. shall be be the the duty duty of of the the Secretary-Treasurer Secretary-Treasurerto: to: It shall 1. I. Keep Keepaccurate accurateattendance attendancerecords recordsofofall allannual annualmeetings. meetings. 2. Keep accurate records of all meetings of, 2. Keep accurate records of all meetings of,and andcorrespondence correspondencebetween, between, the the board board of of directors. directors. 3. 3. Hold Holdallallfunds fbndsthat thatmay mayaccrue accrueasasprofits profitsfrom !?om annual annualmeetings meetingsor or field field trips trips and and to to make make these funds available for the organization and operation of future meetings as required. these fbnds available for the organization and operation fbture meetings as required. shall be be the the duty duty of of the the board board of of directors directors to plan locations locations of annual annual meetings meetings and and to to advise advise C. C. ItIt shall on on the the organization organizationand andfmancing fmancingof ofall allmeetings. meetings. 11. II. Duties and Ex~enses Exlenses There shall shall be be no no regular regular membership membership dues. dues. I. 1. There consultation Registration fees for the annual annual meetings shall be determined by the Chairman in consultation 2. 2. Registration with the board of of directors. directors. ItItisisstrongly stronglyrecommended recommendedthat thatthese thesebe be kept keptatataaminimum minimumto to encourage encourageattendance attendanceof of graduate graduatestudents. students. 111. III. Rules Rules of of Order Order The The rules rules contained contained in in Robert's Rules Rules of Order shall govern this organization organization in all cases to which they are are applicable. applicable. IV. IV. Amendments Amendments These These by-laws by-laws may may be be amended amended by by aa majority vote vote of of those persons who are personally personally present present at, at, participating participatingin, in, and and voting voting at at any any annual annual meeting meeting of of the organization; organization;provided provided that that such such modifications modificationsshall shallnot not conflict conflictwith with the the constitution constitutionas as presently presently adopted adopted or subsequently subsequently amended. amended. 111 �Award Guidelines Guidelines SAM GOLDICH GOLDICH MEDAL MEDAL Preamble Preamble The Institute on Lake Superior Superior Geology Geology was born on or around 1955, 1955?as as documented by the fact that the 27th annual annual meeting was held 1. The Institutes are exemplary in aspects of of held in in 198 1981. in their their continuing objectives of dealing with those aspects geographically to Lake Superior; Superior; of encouraging encouraging the discussion of subjects and sponsoring sponsoring field field geology that are related geographically academia7government government surveys, surveys, and industry; industry; and and of of maintaining maintaining an an trips which will will bring bring together together geologists geologistsfrom from academia, exceedingly informal but highly effective effective mode of operation. the course course of of its its existence existence the the membership membership of of the the Institute Institute (that (that is, is,those thosegeologists geologistswho whoindicate indicate an an interest interest in in During the the objectives objectives of of the the I.L.S.G. I.L.S.G. by by attending) attending) has has become become aware of the fact that certain of their colleagues have made particularly noteworthy and meritorious contributions to to the the improvement improvementof ofunderstanding understandingof of"Lake 'Lake Superior" geology geology mineral deposits. and its mineral deposits. The exemplary award award was was made made by by I.L.S.G. I.L.S.G. to to Sam Goldich Goldich in in 1979 for for his his many many contributions contributions to to the the geology geology of of the the region extending extending over over about about 50 50 years. years. Award Guidelines Guidelines 1) by the the I.L.S.G. I.L.S.G.Board Board of ofDirectors Directorstotoaageologist geologistwhose whosename name is is associated associated The medal shall be awarded annually by with a substantial substantial interest in, or a major contribution contribution to, the geology of the Lake Superior region. 2) shall appoint appointthe theNominating NominatingCommittee. Committee. The The initial initial appointment appointment will will be be of of The Board of Directors, 1.L.S.G. I.L.S.G. shall three members, one one to to serve serve for for three three years, years, one one for for two, two7and and one one for for one one year, year, the member member with the briefest briefest incumbency to be chairman. After the first the Board Board of ofDirectors Directorsshall shallappoint appointatateach each spring springmeeting meeting one one fxst year the three years. years. In the third year year this this member member shall shallbe bethe thechairman. chairman. The Committee new member who will serve for three membership should geographic distribution of I.L.S.G. membership. membership should reflect reflect the main fields fields of interest and geographic 3) By November 1, the Goldich Medal Medal Nominating NominatingCommittee Committeeshall shallmake makeits itsrecommendation recommendationto tothe the Chairman Chairman of of the Board of Directors Directors who who will then inform the Board of the nominee. 4) The Board Board of of Directors Directors normally normally will will accept accept the the nominee nominee of of the theCommittee, Committee, will will inform inform the the medalist medalist immediately, engravedappropriately appropriatelyfor forpresentation presentationatatthe thenext nextmeeting meetingofofthe theInstitute. Institute. immediately,and and will will have have one onemedal medalengraved 5) recommended that Institute set aside annually from whatever such funds will betorequired to fiom whatever sources,sources, such funds as will be as required It is recommended that thethe Institute set aside annually support the continuing continuing costs of this award. April 4, 1981 198I Kalliokoski, Chairman J. Kalliokoski, Bill Cannon Fred Kehlenbeck G.B. Morey Morey Greg Mursky iv �GOLDICH GOLDICH MEDAL COMMITTEE COMMITTEE1994-95 1994-95 Glen Adams (1995) Crystal Exploration, Exploration, Inc., Inc., Crystal Crystal Falls, Falls, MI MI 44420 44420 Crystal Penelope. Morton (1996) (1996) Department Department of of Geology, Geology, University UniversiQ of of Mimiesota Minnesota Duluth, Duluth, Duluth, Duluth, MN MN Card (1997) Ken Card (1997) Geological Survey Survey of of Canada, Canada,Ottawa, Ottawa,ON ON K1A KIA 0E8 OE8 Geological GOLDICH GOLDICH MEDALISTS MEDALISTS 1979 1980 1981 1982 1983 1984 1985 1986 Samuel Samuel S. Goldich Goldich 1987 Henry HenryH. H. Halls Halls 1988 Walter WalterS. S.White White 1989 Jorma JormaKalliokoski Kalliokoski 1990 Kenneth KennethC. C. Card Card 1991 William J. Hmze Hinze 1992 William F. Cannon Cannon WilliamF. 1993 Donald DonaldW. W. Davis Davis 1994 Cedric CedricIverson Iverson not awarded Carl E. Dutton, Dutton, Jr. Jr. Ralph W. Marsden Burton Burton Boyum Richard Richard W. W. Ojakangas Ojakangas Paul K. Sims Sims G.B. Morey 1995 Gene 1995 Gene LaBerge LaBerge /9525 &A 77%ch//e4inn/ ne ta/ir1o Citation Citation Gene L. LaBerge, 1995 Goldich Medal Recipient am pleased pleased and and honored honored to to introduce introduce you you to to For all of you associated associated with the Institute on Lake Superior Geology, II am Gene L. LaBerge as this year's recipient geologist whose whose name name recipient of of the the Sam Sam Goldich GoldichMedal. Medal. The medal is awarded "to a geologist is associated with with aa substantial substantialinterest interestin, in,or oraamajor majorcontribution contributionto, to,the thegeology geologyofofthe theLake LakeSuperior Superiorregion". region". Gene is certainly worthy on both counts. counts. Gene was born and raised in Ladysmith, Wisconsin, appropriately, appropriately,the thehome homeof ofthe therecently recentlydeveloped developedFlambeau Flambeau mine. mine. V �After a stint in the the U.S. U.S. Marine Marine Corps, Corps,he hebegan beganhis hisgeology geology education education at at UW-Superior, UW-Superior, eventually eventually obtaining his B.S., related to the the origin origin of of magnetite magnetite M.S. and Ph.D. degrees in geology from from UW-Madison. UW-Madison. The topic of his dissertation related iron-formation. in iron-formation. first two two summer summer jobs, jobs, while while he he was was aagraduate graduate student, student, introduced introduced him to aspects aspects of of geology geology that that were were to to Gene's first 1957, he was hired Ishpeming, Michigan Michigan become his primary research interests. In 1957, hired by Ralph Marsden of U.S. Steel in Ishpeming, Ralph and and Stan Stan Tyler of UW-Madison, Gene's fhture advisors, would include include the the to explore for iron-formation. Ralph future Ph.D. advisors, summer help on regional field field trips trips to look look at at iron-formation. iron-formation.Gene Geneclaims claimsthat thatititwas wasaadirect directresult resultof ofthe thequestions questions this area. It has led international posed by Ralph and Stan Stan that inspired inspired his research interest i n t e r e ~in in4his led40 to 6 publications in international journals, numerous of aa book book on on Precambrian Precambrian iron-formations. iron-formations. In numerous presentations presentations at at national meetings, and the editing of 1958, Gene Gene worked worked for U.S. Steel as a field assistant to to Ced Ced Iverson Iverson doing doing aa pebble pebble survey survey in in Wisconsin. Wisconsin. After 1958? identif'ing several identifying severalbillion pebbles that summer, summer, Gene was convinced convinced that the Precambrian geology of Wisconsin was more than aa "green "greenblob" blob" on on the the map. map. InIn1969, 1969,he heconceived conceivedand andinitiated initiated aa regional regional mapping mapping and Natural History Onthe theadvice adviceof ofCarl CarlDutton, Dutton, the the project project was was begun begun in incentral central Survey under the direction of George F. Hanson. On Wisconsin near Wausau. Since Wisconsin Since1982, 1982,support supportfor for this this on-going on-going research research has has been been provided provided by by the the U.S. U.S. Geological Geological Society. This national publications, numerous reports and maps for both the This program program has has resulted in several national the WGNHS WGNHS and the USGS, and over 30 papers at professional meetings. In In 1994, 1994,this work was collated to form the basis of his book, Geology Geolom of the Lake Superior Su~eriorRegion. Region. I know Gene best the best in in the the role role of of educator. educator. InIn1965, 1965,he hejoined joined the the faculty faculty at at UW-Oshkosh as the third member of the department with the charge of designing and building the geology program. Since he began teaching, he has led in the charge of designing program. Since I remember Gene saying that he "walked over more of Wisconsin that almost excess of 100 Wisconsin almost 100ovemight overnightstudent studenttrips. trips. anyone -- from Baraboo to Lake Superior". Superiorv'.We Wedidn't didn't doubt doubtit, it,but but wondered wondered ifif he he meant meant to to add add "on "on the the same sametrip". trip". He sure seemed seemed to have have the the stamina. stamina. Recently RecentlyGene Geneconfided confided in in me me that that aa major major stimulus stimulus for for his his work work in in central central Wisconsin was the students' students' questions, questions, "So "So simple, simple, yet so difficult difficult to answer". As Asaatestament testamentto tohis hissuccess successin inacademia, academia, Gene has received received all all of of the teaching teaching and and research research awards that UW-Oshkosh offers, the only faculty member to have done done so. so. Gene also has has aa long long history history with with the the ILSG. ILSG. Gene in Duluth in 1958 Gene attended attended his first f ~ smeeting t 1958 and presented presented his first paper at the 1960 meeting meeting in inMadison. Madison. Since that time, he has presented over 20 20 papers papers and led or co-led 5 field trips with accompanying accompanying guides. guides. Through the years, years?Gene Gene and and IIhave haveinteracted interacted on onmany manylevels, levels,teacher, teacher,mentor, mentor, fellow fellow guitar guitar player, player?researcher, researcher, colleague and and most most rewardingly, rewardingly,as as aa fiiend. friend. As he joins joins an elite and colleague As the the 16th 16threcipient recipient of the Goldich Goldich Medal, Medal, he distinguished group. II am am pleased pleased to to present present to you, Gene LaBerge. LaE3erge. Tim Flood Natural Sciences Sciences Division, St. Norbert College DePere, Wisconsin Wisconsin BANQUET SPEAKER SPEAKER Peter Lightfoot Peter Lightfoot(Ontario (OntarioGeological GeologicalSurvey, Survey,Sudbury) Sudbury) relationship between mantle plumes, plumes,jlood flood basalts basalts and and mineralization The relationship vi �__________________________________________________________________ _________________________________ ____________________ _______________ ______ ______ STUDENT TRAVEL STUDENT TRAVEL AWARD The 1986 1986 Board of Directors Directors established established the I.L.S.G. Student Student Travel Award to support student participation at the annual Institutes. The purpose. This Theawards awardswill will be be made made from from aa special special fund set up for this purpose. This award award is intended intended to help defray some some of the direct direct travel travel costs to the Institute Institute and includes a waiver of registration fees, but excludes expenses for meals, lodging, and field trip trip registration. The number of awards and value are determined by by the the annual Chairman Chairman in consultation consultation with the Secretary-Treasurer and will be announced at the annual banquet. The following following general general criteria criteria will be considered considered by the annual Chairman, Chairman, who is responsible for the selection: selection: 1) 1) The applicants applicants must have active resident (undergraduate or graduate) student status at the time of the Institute, certified Institute, certified by by the the department departmenthead. head. 2) 2) Students Students who are the senior senior author author on either an oral or poster paper will be given favored consideration. consideration. 3) It is desirable desirable for for two two or or more more students studentsto to jointly jointly request requesttravel travelassistance. assistance. 4) 4) In general, general, priority priority will be given to those in the Institute region who are farthest away. with an explanation of 5) Each Each travel award request shall be made in writing, to the annual Chairman, with need, possible author status or other significant details. possible author status or other significant details. Successful Successful applicants applicants will will receive receive their their awards awardsatatthe the time timeof ofregistration registrationfor forthe theMeeting. Meeting. INSTITUTE INSTITUTE ON ON LAKE LAKESUPERIOR SUPERIORGEOLOGY GEOLOGY Student Travel Award Award Application Application Please Pleaseprint: print: Date: Date: Student Student Name: Name: Address: II certify that the the above named person is is an active resident student. 1I 1I1 Department Department Head Head -- Typed Typed Department Department Head Head -- Signature Signature Date Date Educational Educational Status: Are you the Senior Author of an oral or poster paper? Yes Yes Will any other students will be traveling with you? 1I - - No No - How many? many? Statement Statementof ofNeed: Need:(If(Ifyou youneed needmore moreroom, room,please pleaseuse usethe theback back of of the the page.) page.) Other Significant Significant Details: Details: return to: Please return vii �BOARD OF OF DIRECTORS DIRECTORS BOARD 1995 1995 MarkC. C.Smyk, Smyk,Chairman Chairman Mark Ontario OntarioGeological GeologicalSurvey, Survey,Thunder ThunderBay, Bay,Ontario OntarioP7E P7E6E3 6E3 1994 1994 TheodoreJ.J.Bornhorst Bornhorst Theodore MichiganTechnological TechnologicalUniversity, University,Houghton, Houghton,Michigan Michigan49931 4993 1 Michigan 1993 1993 DavidL. L.Southwick Southwick David Minnesota Minnesota Geological Geological Survey, Survey, St. St. Paul, Minnesota 55114 55 114 1992 1992 AlbertB. B.Dickas Dickas Albert University University of of Wisconsin-Superior, Wisconsin-Superior, Superior, Superior, Wisconsin 54880 54880 Secretary-Treasurer Secretary-Treasurer Mark ursa Jirsa Mark MinnesotaGeolgical GeolgicalSurvey Survey Minnesota 2642 University UniversityAve. Ave. 2642 MN55 551 14-1057 St.Paul, Paul,MN St. 114-1057 LOCAL LOCAL COMMITTEES COMMITTEES GENERAL CHAIRMAN MarkC. C.Smyk Smyk Mark Ontario OntarioGeological GeologicalSurvey, Survey,Field FieldServices ServicesSection Section Thunder Bay, Bay, ON ON P7E P7E6E3 6E3 Thunder PROGRAM CHAIR AND EDITOR PROGRAM CHAIR AND ABSTRACTS ABSTRACTS EDITOR ManfredKehienbeck Kehlenbeck Manfred Department of of Geology, Geology,Lakehead Lakehead University University Department Thunder Bay, Bay, ON ON P7B P7B5E1 5E1 Thunder SECRETARY-TREASURER Mark O'Brien O'Brien Mark Ontario Ontario Geological GeologicalSurvey, Survey,Field Field Services ServicesSection Section Thunder Bay, ON P7E P7E6E3 6E3 Thunder COMMITTEE ASSISTANCE Bernie Schnieders, Schnieders, Doug McKay and and Maurice MauriceLavigne Lavigne Ontario Ontario Geological GeologicalSurvey, Survey,Field FieldServices ServicesSection Section P7E 6E3 6E3 Thunder Bay, ON P7E viii �STUDENT PAPER COMMITTEE Mark Jirsa Jirsa (Chair) (Chair) Mark Minnesota Minnesota Geological GeologicalSurvey Survey St.Paul,MN St. Paul, MN55114-1057 551 14-1057 Virginia Virginia Peterson Peterson Department Departmentof ofGeosciences Geosciencesand andAnthropology, Anthropology, Western Western Carolina CarolinaUniversity Cullowhee, Cullowhee, NC 28723-9047 28723-9047 David Laderoute Laderoute Ontario Ontario Geological Geological Survey, Survey,Field Field Services Services Section Section Thunder Bay, ON P7E 6E3 P7E 6E3 SESSION CHAIRS Ted Ted Bornhorst Bornhorst Michigan Technological TechnologicalUniversity University Michigan Houghton, Houghton, MI 49931 4993 1 Mark Jirsa Jirsa Mark Minnesota MinnesotaGeological GeologicalSurvey Survey MN 55114-1057 St. Paul, Paul, MN 551 14-1057 St. Maurice Maurice Lavigne Lavigne Ontario Ontario Geological Geological Survey, Survey,Field Field Services ServicesSection Section Thunder Thunder Bay, ON P7E P7E6E3 6E3 Jim Jim Miller Miller Minnesota Minnesota Geological GeologicalSurvey Survey Paul, MN 55114-1057 MN 551 14-1057 St. Paul, St. Bernie Schnieders Bernie Schnieders Ontario Ontario Geological GeologicalSurvey, Survey,Field FieldServices ServicesSection Section Thunder Bay, Bay, ON ON P7E P7E6E3 6E3 Thunder Cliff Shaw Shaw Cliff Department Department of of Geology, Geology,University Universityof of Western Western Ontario Ontario London, London, ON N6A N6A5B7 5B7 Laurel Woodruff United United States States Geological Geological Survey Survey MN 55112 St. Paul, Paul, MN 55 112 St. Eva Zaleski Zaleski Eva Canada Geological Survey Survey of of Canada Geological Calgary, AB T2L T2L 2A7 2A7 Calgary, AB ix �REPORT OF OF THE THE CHAIRMAN CHAIRMAN GEOLOGY 40TH ANNUAL INSTITUTE ON LAKE SUPERIOR GEOLOGY HOUGHTON, MICHIGAN MICHIGAN The 40th Annual Institute on Lake Superior Superior Geology Geology was held May 11-14, 11-14, 1994 1994 on on the the campus campus of of Michigan Michigan Technological University The meeting meeting was was hosted by the Department of Geological University in in Houghton, Michigan. Michigan. The Engineering, Geology, and Geophysics with assistance assistance from from the the Division Division of of Education Educationand andPublic PublicServices. Services. The The meeting Chairman was Theodore Theodore J. J. Bornhorst Bornhorst who who handled handled all all aspects aspects of of the the meeting meeting including including the the technical technical sessions and the field trips. published in in 55 parts parts as as Volume Volume 40, 40, Part 1: Program and The Proceedings of the 40th Annual ILSG was published and Abstracts Abstracts by Theodore J. J. Bornhorst and S. Douglas McDowell, McDowell, and and aa series series of of 44 field field trips, trips, including; including; Part Part 2: 2: Selfedited by guided geological field trip to the Keweenaw Peninsula, Peninsula, Michigan Michiganby by Theodore TheodoreJ.J. Bornhorst Bornhorst and and William William I.I. Rose; Part 3: Volcanic Royale, Michigan Michigan by by William WilliamI.I. Rose; Rose; Part Volcanic geology of eastern Isle Royale, Part 4: 4: Michigan Michigan kimberlites kimberlites and by Shawn Shawn M. M. Carlson and and Wayde Wayde Floodstrand; Floodstrand; and and Part Part 5: 5: Lessons Lessons from from mining mining diamond exploration techniques by case histories: West Menominee Range, Range, Michigan Michiganby byAllan AllanM. M.Johnson. Johnson. For the field trip to the White Pine and Caledonia Mines no ILSG ILSG guidebook guidebook was published and instead the trip used Society of Economic Geologists Guidebook Series Volume 13 13 titled "Keweenawan "Keweenawan Copper Deposits of Western Upper Michigan" Michigan" edited edited by Theodore J. Bomhorst. ofthe theILSG. ILSG. The field trip to Isle Bornhorst. Field Fieldtrips tripscontinue continueto to be be an an important important component component of Royale National Park was the first ever ever geological geological field trip to the island. A total of 154 meeting. Field 154 people registered for the meeting. Fieldtrips trips attracted attracted121 121paid participants, including: 24 for Keweenaw Peninsula, 13 13 for Isle Isle Royale, 41 41 for for Michigan Michigan kimberlites, kimberlites, 13 13 for Menominee Menominee Range and 30 for White Pine/Caledonia. PineICaledonia. banquet was was attended attended by by about about 105 people. people. Cedric The annual banquet Cedric Iverson Iverson was was awarded awarded the Institute's Institute's prestigious prestigious Goldich Medal. Medal. The given by by Geoffrey GeoffreyS. S. Plumlee, Plumlee,U. U. S. S. Geological GeologicalSurvey. Survey. His topic was was Goldich The banquet banquet address was given "The crucial (but underutilized) role of the economic economic geologist in predicting and remediating the environmental effect of mineral resource development." development." Optional lunch was offered on both days of the technical sessions and featured speakers, speakers, Larry Larry Lankton Lanktonon on Keweenaw Peninsula mining mining history history and and Stan Stan Dyl Dyl on on minerals mineralsin in Russia. Russia. The Keweenaw The lunch program was well received received as a total of 140 140attended attended the the two two lunches. lunches. The best student paper awards went to Nicholas Van Wyck, University of of Wisconsin, Madison Madison and and Elizabeth Elizabeth Kropf, Macalester College for best oral or poster presentation, respectively. respectively. Student Student travel awards, awards, for for aa total total of of $375, were awarded awarded to to Elizabeth Elizabeth Kropf, Kropf, Leslie Leslie Magnus, Magnus, Gwendolyn Gwendolyn Miner, Micheal Micheal Rogers, Rogers, and and Mark Mark Schmitz. Schmitz. lengthy discussion discussionon onthe thefuture futureofofthe theILSG. ILSG. At this time they they directed the the In 1993, the Board of Directors had a lengthy incoming Chairman, Chairman, T.J. Bomhorst, component of ofthe the40th 40thAnnual Annualmeeting. meeting. In incoming Bornhorst, to to increase increase the "environmental" "environmental" component resulted in in 20% 20% of the abstracts being response to this directive, "environmental" "environmental" papers were solicited which resulted "environmental" as compared to a median of 2% 2% in in this topic category for past meetings (by far the 40 year high). A mining-related environmental environmental field trip was solicited solicited (Menominee Range) and the banquet speaker addressed a topic. These mining-related environmental topic. These changes changes in in topics topics covered by the ILSG seemed to be well received by the meeting participants. The Board of Directors of the Institute Houghton, Michigan Michigan on on May May 12, 1994. Institute on Lake Superior Superior Geology met in Houghton, In attendance were were T. T.J. Bornhorst (Chairman), A.B. Dickas, G.L. LaBerge for Paul Meyers, Jim Miller for for Dave Dave J. (Chairman), A.B. Dickas, G.L. for Meyers, Jim Miller Southwick, and and M.G. M.G. Mudrey, Jr. (Secretary-Treasurer). Guests included Mark Smyk, Bill Cannon, and R. (Secretary-Treasurer). Guests included Sage. Actions Actions taken taken were: were: 1. Approved Approved an offer offer by by the the Ontario OntarioGeological GeologicalSurvey Survey to to host host the the 41st 41st Annual Annual Institute Institute (1995) (1995) in in Marathon, Marathon, Ontario. Mark MarkSmyk Smykwill willbe be Chairman. Chairman. x �2. Approved Approved an anoffer offerby bythe theU. U.S.S.Geological GeologicalSurvey Surveytotohost hostthe the42nd 42ndAnnual Annual Institute Institute (1996) (1996) near near Cable, Cable, 2. Wisconsin. Laurel Wisconsin. LaurelWoodruff Woodruffwill willbe bethe thefirst firstever everwoman womanChair Chairofofthe theInstitute Instituteon onLake LakeSuperior SuperiorGeology. Geology. 3. Endorsed Endorsedan anoffer offerby bythe theOntario OntarioGeological GeologicalSurvey Surveytotohost hostthe the43rd 43rdAnnual AnnualInstitute Institute(1997) (1997)ininSudbury, Sudbury, 3. Ontario. Approval Approvalwill willbe benecessary necessaryatataafuture futuremeeting meetingof ofthe theBoard Board of of Directors. Directors. Ontario. 4. 4. Appointed Appointed Theodore Theodore J. J. Bornhorst Bornhorst to to the the post of Associate Secretary-Treasurer. This This action action was was taken taken to facilitate guidebookunder underthe the auspices auspicesofofthe theInstitute. Institute. The facilitate selling selling the popular popular Keweenaw Peninsula field guidebook Associate Secretary-Treasurer Secretary-Treasurer will willbe be backup backup the the signature signatureon onthe theInstitute Institute accounts. accounts. Associate 5. Received Received and and accepted a Financial Report from Secretary-Treasurer Secretary-Treasurer Mudrey. Mudrey. The 5. The net net assets assets of the Institute Institute on Superior Geology as of May 10, 10,1994 1994are are $9,965 $9,965.26. Studenttravel traveland andpaper paper awards awardsand and39th 39thAnnual Annual Lake Superior .26. Student meeting overrun accounted for $3411.27 $3411.27 net decrease in assets. To Tohelp helpavoid avoidfuture futuredecrease decreaseininassets assetsthe theBoard Board of Directors Directors agreed agreedthat thatStudent StudentTravel TravelAwards Awardsbe belimited limitedtotointerest intereston oninvestments investments(the (theChairman Chairmanshould shouldcontact contact the the Secretary-Treasurer Secretary-Treasurerto todetermine determinethe theamount amount to to be be awarded) awarded) and and that that Student Student Paper Awards should should be funded by the local local meeting meeting budget. budget. 6. Approved Approved Cedric Cedric Iverson Iverson for forthe the 1994 1994Goldich Goldich Medal Medal Award. Award. K. Card Card(representing (representinggovermnent) government) to to aa 33 year year term termon onthe theGoldich Goldich Medal Medal Conmiittee. Committee. 7. Appointed Appointed K. 7. 8. 8. Discussed Discussedownership ownershipof of Institute Institutefield fieldtrip tripguidebooks guidebooksand and agreed agreedthat that the the Institute Instituteowned owned the the guidebooks guidebooks only only when it paid for printing. printing 9. 9. Discussed Discussed the the future future of of the theInstitute. Institute.Agreed Agreedthat thatenvironmental environmentaltopics topicsneed neednot notbe besolicited solicitedfor forthe theMarathon Marathon meeting (41st ILSG) next year, but for the Cable, Wisconsin (42nd ILSG) it may be desirable to once meeting year, but for the Cable, Wisconsin (42nd ILSG) it may be desirable to once again again solicit solicit environmental environmental material for for the the ILSG. ILSG. 10. of Secretary-Treasurer for for aa term term of of two two years. years. The 10. Approved Approved an election for the position of TheBoard Board discussed discussed be held, at least, every the the need need to to have have elections elections on on aa more more regular regular schedule. schedule. It was agreed agreed that elections should be every 4 years. years. The election for a new Secretary-Treasurer was held on May May 12, 1994 at at the the annual annualbanquet. banquet. Mark Jirsa, Jirsa, Minnesota Geological Geological Survey, Survey, was was elected elected to to the the post. post. I am am sure the institutes institute'sfinances finances are are in in good good hands. hands. Financially the 40th Annual ILSG was an overwhelming success. success. The The combination combination of excellent budget help of Marty Banks Banks and Mary Mary Rouleau, Rouleau,Michigan MichiganTech TechDivision Division of of Education Education and and Public Public Services Servicesand and advice advicefrom fromDave Dave Southwick Southwick helped me avoid the deficit deficit which which occurred occurred from from the the meeting meeting last last year. year. I am pleased to report a profit of about $4,000 $4,000 from from the the 40th 40th Annual Annual meeting. meeting. Exact Exactnumbers numbersare arenot notpossible possiblesince sincepublications publications continue continue to to be be sold. The TheKeweenaw KeweenawPeninsula Peninsulaguidebook guidebook(Volume (Volume40, 40, Part Part2), 2),published publishedand anddistributed distributedby by the the Institute Instituteon on Lake Lake Superior Superior Geology, Geology, is is now now in in its its second second printing printing as as the the first first printing printing of 250 250 copies is sold out. Profits from sale sale of the guidebook guidebook will go the Institute's treasury. treasury. On a personal note, I'm I'mglad gladtotobe befinished finishedwith with the thetask taskof of being being Chairman Chairmanof of the the 40th 40th Institute Institute on on Lake Lake Superior Superior Geology. It is is easier easier being being Chairman Chairman the the second second time, time, but but itit still still requires requires aa lot lot of of work. work. I thank all all those who who Geology. have have given given me me positive positive feedback, feedback, since since this helps make all of the work more worth doing. Despite Despitethe the disappointment disappointment for the White Pine/Caledonia PineICaledonia field field trip trip when when aa totally totally unexpected unexpected mine fire fire precluded precluded going going underground at White Pine, II consider consider the the 40th 40th ILSG ILSG to to have been a very successful successful meeting. Respectively Submitted, Submitted, Bornhorst Theodore J. Bomhorst Chairman 40th 40th ILSG ILSG Chairman September September 19, 19,1994 1994 Houghton, Michigan Michigan Houghton, xi �PROGRAM PROGRAM �C A L E N D A R OF O F EVENTS E V E N T S AND A N D PROGRAM PROGRAM CALENDAR PRE-MEETING FIELD FIELD TRIPS TRIPS PRE-MEETING Field trips depart from the Marathon Marathon Recreation Recreation Complex at 8:OO return each 8:00 a.m. and return evening by about 6:00 6100 p.m. p.m. 1995 SATURDAY MAY MAY 13, 13.1995 TRIP lIaa FIELD TRIP (DAY ONE OF TWO DAYS) DAYS) ALKALIC ROCKS OF THE MIDCONTINENT MIDCONTINENT RIFT FIELD TRIP 2A (DAY ONE ONE OF TWO DAYS) DAYS) MANITOUWADGE GREENSTONE MANITOUWADGE GREENSTONE BELT BELT SUNDAY MAY 1995 MAY 14. 14,1995 TRIP lIaa FIELD TRIP (DAY TWO OF TWO DAYS) IDAY DAYS) ALKALIC ROCKS OF THE MIDCONTINENT RIFT FIELD FIELD TRIP TRIP 2a (DAY TWO OF TWO DAYS) lDAY DAYS) MAN ITOUWADGE GREENSTONE GREENSTONE BELT MANITOUWADGE BELT FIELD TRIP 3a GREENSTONE ASSEMBLAGE SCHREIBER GREENSTONE ASSEMBLAGE FIELD TRIP 4 HEMLO HEMLO GREENSTONE GREENSTONE BELT BELT I:I: REGIONAL REGIONAL GEOLOGY GEOLOGY 1995 SUNDAY MAY 14. 14,1995 REGISTRATION REGISTRATION MARATHON RECREATION MARATHON RECREATION COMPLEX COMPLEX 4:00 pm. 1O:OO pm. pm. 4:OO pm. - 10:00 - POSTER (authors POSTERSESSION SESSION (authorsatatposters) posters) - - - CASH BAR BAR MIXER MIXER MONDAY 1995 MONDAY MAY MAY 15. 15.1995 REGISTRATION REGISTRATION CONTINUES CONTINUES 8:00 8:OO am - 4:30 pm pm - xii �TECHNICAL PROGRAM PROGRAM MONDAY MAY 15. 15,1995 1995 - MORNING - SESSION SESSION II MORNING CHAIRS: Ted Bornhorst Born horst and Eva Zaleski Zaleski 8:45 8145 WELCOME WELCOME 1. 8:50 8:50 BERENDSEN, BERENDSEN, P. P. HISTORY AND AND DEVELOPMENT OF OF THE THE SOUTHERN EXTENSION EXTENSION OF THE MID-CONTINENT MID-CONTINENT RIFT RIFT IN IN KANSAS KANSAS 2. ** HALLS, HALLS, H.C. H.C. MANSON, MANSON, M.L. M.L. ZHANG, ZHANG, B. B. ARE THE MAJOR THRUST FAULTS OF THE MID-CONTINENT MID-CONTINENT RIFT RIFT TECTONIC AND THE KAPUSKASING KAPUSKASING ZONE PART OF THE SAME TECTONIC ZONE? ZONE? 3. 9:10 9110 CORFU, F. CORFU, F. STOTT, G.M. STOTT, G.M. U-Pb GEOCHRONOLOGY OF THE SHEBANDOWAN SHEBANDOWAN GREENSTONE GREENSTONE BELT, SUPERIOR PROVINCE ONTARIO PROVINCE ONTARIO 4. 9:30 9130 * KING, KING, D. D. FRALICK, FRALICK, P.W. P.W. DEPOSITIONAL SYSTEMS SYSTEMS ASSOCIATED DEPOSITIONAL ASSOCIATED WITH THE 3.0 GA FINLAYSON AND LUMBY LAKE LUMBY LAKE GREENSTONE GREENSTONEBELTS, BELTS, NORTHWESTERN ONTARIO NORTHWESTERN ONTARIO 9:50 9:50 COFFEE BREAK BREAKAND AND POSTER POSTER SESSION SESSION 5. 10:20 LaBERGE, LaBERGE, G.L. G.L. CANNON, W.F. CANNON, W.F. KLASNER, KLASNER, J.S. J.S. 6. 10:40 10:40 * PUFAHL, PUFAHL,P.K. P.K. FRALICK, FRALICK,P.W. P.W. 7. 11:00 * PETERSON, 1l:OO PETERSON,D.M. D.M. 8. 11:20 11:20 9. 9. 11:40 I 1:40 JIRSA, M.A. CHANDLER, V.M. CHANDLER, BOERBOOM, T.J. BOERBOOM, T.J. NOON NOON LUNCH BREAK BREAK * SHORE, SHORE, C. G. NEW OBSERVATIONS ON THE THE GEOLOGY OF THE WESTERN WESTERN GOGEBIC IRON RANGE, NORTHERN WISCONSIN PALEOGEOGRAPHIC RECONSTRUCTION OF THE GUNFLINTGUNFLINTMESABI-CUYUNA MESABI-CUYUNA DEPOSITONAL DEPOSITONAL SYSTEM: SYSTEM: A BASIN BASINANALYSIS ANALYSIS APPROACH APPROACH SULFIDE DEPOSITS DEPOSITS EXPLORATION EXPLORATION IN THE TARGETING MASSIVE SULFIDE WESTERN VERMILLION DISTRICT: VOLCANOLOGICAL CONTROLS DISTRICT: VOLCANOLOGICAL CONTROLS ON THE ORIGIN OF ALKALINE GABBROIC ROCKS ROCKS IN THE COLDWELL PENINSULA PENINSULA AREA, COLDWELL COLDWELLALKALINE ALKALINECOMPLEX, COMPLEX, ONTARIO ONTARIO THE WISCONSIN WISCONSIN MAGMATIC MAGMATIC TERRANES TERRANES INTO EXTENSION OF THE THE MINNESOTA SEGMENT OF THE PENOKEAN OROGEN OROGEN ** Student Student paper paper ** cancelled ** cancelled paper ... xlii X lll �MONDAY MAY 15. 1995 - AFTERNOON - SESSION SESSION III1 AFTERNOON Jim Miller Miller and Maurice CHAIRS: Jim Maurice Lavigne Lavigne 10. 10. 2:00 2100 * SCHNEIDER, SCHNEIDER, D.A. D.A. HOLM, HOLM, M. M. HISTORIES OF OF COMPARISON OF POST-PENOKEAN THERMAL HISTORIES THE WATERSMEET AND REPUBLIC DISTRICTS, DISTRICTS, NORTHERN NORTHERN MICHIGAN: MICHIGAN:RESULTS RESULTSAND ANDIMPLICATIONS IMPLICATIONSOF OF40 40 Arl39 Ar/39 Ar DATING MINERAL AGE DATING 11. 11. 2:20 HOLM, HOLM, D.K. D.K. THERMOCHRONOLOGY OF CENTRAL CENTRAL MINNESOTA MINNESOTA REVISITED: REVISITED: IMPLICATIONS IMPLICATIONS FOR THE THE POST-COLLISIONAL POST-COLLISIONAL EVOLUTION OF THE OROGENIC BELT PENOKEAN OROGENIC 12. 12. 2:40 * DARRAH, DARRAH, KS. KS. HOLM, HOLM, D.K. D.K. APPLICATION BAROMETER APPLICATION OF THE ALUMINUM-IN-HORNBLENDE ALUMINUM-IN-HORNBLENDE BAROMETER ON EARLY PROTEROZOIC, POST-PENOKEAN PLUTONS, PLUTONS, CENTRAL CENTRAL MINNESOTA MINNESOTA 3:00 3100 COFFEE BREAK BREAK AND AND POSTER POSTER SESSION SESSION 13. 13. 3:30 3:30 * KOEBERNICK, KOEBERNICK, C.F. NEOARCHEAN COASTAL COASTAL SEDIMENTATION SEDIMENTATION IN THE THE C.F. NEOARCHEAN FRALICK, SHEBANDOWAN GROUP, NORTHWESTERN FRALICK,P.W. P.W. NORTHWESTERN ONTARIO ONTARIO 14. 14. 3:50 3:50 NORTH, NORTH, J. J. 15. 15. 4:10 4110 * FEHER, FEHER, L. L. FLOOD, T. AND SUPERGENE SUPERGENE OXIDATION OXIDATION OF PREKEWEENAWAN UPLIFT AND PENOKEAN, SUPERIOR TYPE IRON IRON FORMATION FORMATION VESICLES AND BRECCIA DUE TO INJECTION INJECTION OF MAFIC MAFIC MAGMA MAGMA INTO PARTIALLY LITHIFIED SEDIMENTS OF THE EARLY PROTEROZOIC IRONWOOD IRON FORMATION FORMATION WESTERN GOGEBIC RANGE, RANGE, NW NW WISCONSIN 4:30 SESSION SESSION END END 6:00 6:OO HALL - MIXER - CASH BAR MOOSE HALL 7:30 7130 HALL -- BANQUET MOOSE HALL BANQUET AND AWARDS AWARDS PRESENTATION PRESENTATION Speaker: Peter The relationship relationshipbetween between mantle Banquet Speaker: Peter Lightfoot Lightfoot-- The plumes, flood basalts basalts and mineralization. mineralization. ** Student Student paper xiv �TUESDAY MAY MAY 16. 16.1995 TUESDAY 1995 - MORNING MORNING- SESSION SESSIONIIIIll CHAIRS: Laurel Laurel Woodruff Woodruff and and Bernie Bernie Schnieders Schnieders CHAIRS: 16. 8:30 8:30 LIN, LIN,S.S. SKULSKI, SKULSKI,T. T. PERCIVAL, PERCIVAL,J.J. STRUCTURALGEOLOGY GEOLOGYAND AND TECTONIC TECTONICEVOLUTION EVOLUTIONOF OFTHE THE STRUCTURAL VIZIEN GREENSTONE GREENSTONEBELT BELTIN IN MINTO MINT0BLOCK,NORTHEASTERN BLOCK,NORTHEASTERN VIZIEN SUPERIORPROVINCE, PROVINCE,NORTHERN NORTHERNQUEBEC QUEBEC SUPERIOR 17. 8:50 8150 PETERSON, PETERSON,V.L. V.L. ZALESKI, ZALESKI,E. E. BREEMEN, BREEMEN, 0. 0. STRUCTURALEVOLUTION EVOLUTIONAND AND AGE AGE RELATIONSHIPS RELATIONSHIPSOF OFTHE THE STRUCTURAL MANITOUWADGEGREENSTONE GREENSTONEBELT BELTAND AND WAWA-QUETICO WAWA-QUETICO MANITOUWADGE SUBPROVINCE,SOUTHWESTERN SOUTHWESTERNSUPERIOR SUPERIORPROVINCE, PROVINCE, SUBPROVINCE, ONTARIO ONTARIO 18. 9:10 9:lO ZALESKI, ZALESKI,E.E. GEOLOGICALSETTING SETTINGAND AND GEOCHEMISTRY GEOCHEMISTRYOF OFMASSIVE MASSIVE GEOLOGICAL SULFIDE DEPOSITS AND ALTERATION ZONES IN THE SULFIDE DEPOSITS AND ALTERATION ZONES IN THE MANITOUWADGE GREENSTONE BELT, BELT, NORTHWESTERN NORTHWESTERN MAN ITOUWADGE GREENSTONE ONTARIO ONTARIO 19. 9:30 9:30 FRALICK, FRALICK,P.W. P.W. PURDON, PURDON,R.R. NEOARCHEANTRANSUBPROVINCE TRANSUBPROVINCEDEPOSITIONAL DEPOSITIONALSYSTEMS: SYSTEMS: NEOARCHEAN TEMPORAL VS. SPACIAL VARIABILITY IN WESTERN SUPERIOR TEMPORAL VS. SPACIAL VARIABILITY IN WESTERN SUPERIOR PROVINCE PROVINCE 9:50 9:50 COFFEE COFFEEBREAK BREAKAND ANDPOSTER POSTERSESSION SESSION 20. 10:20 10:20 BORNHORST, BORNHORST,T.J. T.J. WHITEMAN, WHITEMAN,R.C. R.C. NATIVECOPPER COPPERAND ANDASSOCIATED ASSOCIATEDMINERALS MINERALSININBASALTS BASALTS NATIVE ATTHE THECALEDONIA CALEDONIAMINE, MINE,WESTERN WESTERNUPPER UPPERMICHIGAN MICHIGAN AT 21. 10:40 10:40 SHAW, SHAW,C.S.J. C.S.J. GEOCHEMISTRYAND ANDFRACTIONATION FRACTIONATIONOF OFTHE THEEASTERN. EASTERN. GEOCHEMISTRY COLDWELLALKALINE ALKALINECOMPLEX COMPLEX GABBRO,COLDWELL GABBRO, 22. 11:00 I1:OO LIGHTFOOT, LIGHTFOOT,P.C. P.C. FARRELL, FARRELL,K.K. MOORE, MOORE,M. M. PEKESKI, PEKESKI,D.D. CRABTREE, CRABTREE,D.D. KEAYS, KEAYS,R.R. R.R. GEOCHEMICALVARIATIONS VARIATIONSWITHIN WITHINTHE THESUBLAYER SUBLAYERAND ANDTHE THE GEOCHEMICAL MAFIC-ULTRAMAFICINCLUSIONS, INCLUSIONS,WHISTLE WHISTLEMINE, MINE,SUDBURY SUDBURY MAFIC-ULTRAMAFIC IGNEOUS IGNEOUSCOMPLEX, COMPLEX,CANADA CANADA 23. 11:20 11:20 LEE, LEE,I.I. RIPLEY, RIPLEY,E.M. E.M. MINERALIZATIONAT ATTHE THE GENESIS CU-NiSULFIDE SULFIDE MINERALIZATION GENESIS OF OF Cu-Ni SPRUCE SPRUCEROAD ROADDEPOSIT, DEPOSIT,SOUTH SOUTHKAWISHIWI KAWISHIWIINTRUSION, INTRUSION, DULUTH DULUTHCOMPLEX COMPLEX 24. 11:40 11140 MILLER, MILLER,J.D., J.D.,Jr. Jr. PREDICTIONAND ANDDISCOVERY DISCOVERYOF OFPGE PGEOCCURRENCES OCCURRENCESIN INTHE THE PREDICTION DULUTH DULUTHCOMPLEX COMPLEXAT ATDULUTH DULUTH NOON NOON LUNCH LUNCHBREAK BREAK POSTERSMUST MUSTBE BEREMOVED REMOVEDBY BYNOON NOONTODAY TODAY POSTERS xv �1995 TUESDAY MAY 16. 16.1995 - AFTERNOON - SESSION SESSION IV IV AFTERNOON Jirsa and Cliff Cliff Shaw CHAIRS: Mark Jirsa 25. 25. ZBIKOWSKI, D.W. ZBIKOWSKI, D.W. 2:00 2:OO A CONTINENTAL CONTINENTAL CRUST FRACTURE FRACTURE INITIATION INITIATION PATTERN PATTERN AND HYPOTHETICAL MECHANISM - HYPOTHETICAL MECHANISM A CURVILINEAR DERIVATIVE CONTINENTAL INDICATIONS OF A MANTLE CONVECTION CARIBBEAN MANTLE CONVECTION PLUME PLUME 2:20 2:20 ZBIKOWSKI, D.W. ZBIKOWSKI, D.W. 2:40 2 40 PRESENTATION OF STUDENT PAPER AWARDS PRESENTATION 2:50 2 50 COFFEE COFFEE BREAK BREAK AND AND POSTER POSTER SESSION SESSION 27. 27. 3:20 3:20 MORRIS, T.F. MORRIS, T.F. MURRAY, C. MURRAY, C. CRABTREE, D. CRABTREE, D. HEAVY MINERAL MINERAL INDICATORS, INDICATORS, WAWA AREA 26. 28. 3:40 3:40 RUDASHEVSKY, RUDASHEVSKY,N.S. N.S. WEIBLEN, WEIBLEN, P.W. P.W. STOYNOV, H. H. STOYNOV, PRODUCTS OF ELECTRIC PULSE DISAGGREGATION DISAGGREGATION OF SOME KEWEENAWAN KEWEENAWAN ROCKS ROCKS 29. 29. 4:00 4:OO FREY, B. FREY, 6. U.S.A. CORE CENTRAL MINNESOTA, U.S.A. CORE LOGGING LOGGING AND ASSAY DATABASES DATABASES 26. 26. - 10:00 10:oo pm. pm. 7:00 7:OO - WINE AND CHEESE AND CHEESE HOSTED: BY Hemlo Branch of the Canadian Institute of Mining and Metallurgy at the Royal Royal Canadian Canadian Legion Legion 4:20 4:20 CLOSING REMARKS CLOSING REMARKS 4:30 SESSION SESSION END END xvi �POSTER PRESENTATIONS PRESENTATIONS Authors are are requested requested to to be be present present at at their their posters posters during during scheduled scheduled times. times. Authors Senior Author ** CARD, CARD, K. K. Title ]je LITHO-TECTONIC PROVINCE LITHO-TECTONIC AND MINERAL DEPOSIT MAPS OF THE SUPERIOR PROVINCE DESAUTELS, P. DESAUTELS, P. DAVID BELL DAVID BELL MINE MINE GERE, GERE, M. M. CURRENT INVENTORY INVENTORY OF MICHIGAN'S GEOLOGICAL CORE AND SAMPLE REPOSITORY MARQUETTE REPOSITORY AT MARQUETTE * EVEREST, EVEREST,J. J. IGNEOUS CHARACTERISTICS BRECCIA, CHARACTERISTICS OF THE MATRIX TO TO THE FOOTWALL FOOTWALL BRECCIA, NORTH RANGE, SUDBURY STRUCTURE, CANADA * DAVIS, DAVIS, D. D. 1.IGA NORTH AMERICAN MID-CONTINENT MID-CONTINENTRIFT RIFT GEOCHRONOLOGY GEOCHRONOLOGY OF THE 1.1 GREEN, GREEN, J. J. * KARKKAINEN, KARKKAINEN, N. N. GEOLOGY OF THE NORTH SHORE STATE PARKS TITANIUM WESTERN FINLAND TITANIUM ORE ORE POTENTIAL POTENTIAL OF GABBROS: GABBROS: EXAMPLES EXAMPLES FROM FROM WESTERN FINLAND LAWLER, T. LAWLER, EVALUATION, CENTRAL MINNESOTA MINERAL POTENTIAL POTENTIAL EVALUATION, LIGHTFOOT, P.C. LIGHTFOOT, P.C. THE SUBLAYER, MAIN MASS, AND GEOCHEMICAL RELATIONSHIPS RELATIONSHIPS BETWEEN THE OFFSETS, SUDBURY IGNEOUS IGNEOUS COMPLEX, CANADA MORRIS, T. MORRIS, T. KIMBERLITE KIMBERLITE HEAVY MINERAL INDICATORS IN OVERBURDEN, MICHIPICOTEN RIVER-WAWA AREA, NORTHEASTERN NORTHEASTERN ONTARIO ONTARIO MUIR, T. MUIR, T IMPORTANCE THE CURRENT SETTING OF THE HEMLO GOLD DEPOSIT, ONTARIO: IMPORTANCE OF FUNDAMENTAL FUNDAMENTALRELATIONSHIPS RELATIONSHIPS * PETERSON, PETERSON,D.M. D.M. GEOLOGICAL, GEOPHYSICAL AND GEOCHEMICAL COMPILATION OF THE GEOLOGICAL, WESTERN WESTERN VERMILLION VERMILLION DISTRICT: DISTRICT: TARGETING TARGETING FOR FOR GOLD GOLD AND AND MASSIVE MASSIVE SULFIDE SULFIDE DEPOSITS DEPOSITS SAGE, SAGE, R. R. KIMBERLITE IN KIMBERLITE IN ONTARIO ONTARIO SEVERSON, SEVERSON, M. M. SOUTHERN PORTION GEOLOGY OF THE SOUTHERN PORTION OF THE DULUTH DULUTH COMPLEX COMPLEX SKRECKY, G. SKRECKY, G. WILLIAMS WILLIAMS MINE MINE VIITALA, VIITALA, R. R. EFFECTS EFFECTS OF LARGE LARGE METEORITE METEORITE IMPACTS IMPACTS ON CRUSTAL ROCKS -- SUDBURY BASIN BASIN IN IN THIN THIN SECTION SECTION WOLFSON, WOLFSON, I.I. MANITOUWADGE, ONTARIO: ONTARIO:AAVOLCANOGENIC THE GECO MINE, MANITOUWADGE, VOLCANOGENIC MASSIVE SULPHIDE SULPHIDE DEPOSIT DEPOSIT (see Lockwood, Lockwood, H. for abstract) WOODRUFF, WOODRUFF, L. L. PROPOSED FIELD TRIPS FOR THE THE 42ND 42ND ANNUAL ANNUAL INSTITUTE ON LAKE SUPERIOR GEOLOGY GEOLOGY * Student Paper Paper ** cancelled cancelled paper ** xvii �POST MEETING MEETING FIELD FIELD TRIPS TRIPS Field trips depart from the Marathon Recreation Complex Complex at at 8:00 8:00 a.m. a.m. All field trips, except trip number number 6, 6, return return to to Marathon Marathoneach each evening evening by by about about 6:00 6:00 p.m. p.m. 1995 WEDNESDAY. MAY 17. 17,1995 FIELD TRIP TRIP 1lb b (DAY ONE OF TWO DAYS) DAYS) ALKALIC ROCKS OF THE MIDCONTINENT RIFT FIELD TRIP 2b (DAY ONE OF TWO DAYS) DAYS) MANITOUWADGE MANITOUWADGE GREENSTONE GREENSTONE BELT BELT FIELD FIELD TRIP 3b 3b SCHREIBER GREENSTONE GREENSTONE ASSEMBLAGE FIELD TRIP FIELD TRIP 55 HEMLO HEMLO GREENSTONE BELT II: 11: DEPOSIT DEPOSIT GEOLOGY FIELD TRIP FIELD TRIP 66 (DAY ONE ONE OF OF TWO DAYS) DAYS) WAWA KIMBERLITE/GOLD EXPLORATION KIMBERLITEIGOLD EXPLORATION WAWA AT PARTICIPANT'S OVERNIGHT OVERNIGHT STAY STAY AT AT AT PARTICIPANT'S EXPENSE EXPENSE 1995 WEDNESDAY. MAY 17. 17.1995 TRIP 1lb FIELD TRIP b (DAY TWO OF TWO DAYS) IDAY DAYS) ALKALIC ROCKS OF THE MIDCONTINENT RIFT FIELD TRIP 2b FIELD (DAY TWO OF TWO DAYS) DAYS) MANITOUWADGE MANITOUWADGE GREENSTONE GREENSTONE BELT BELT FIELD TRIP FIELD TRIP 66 (DAY TWO OF TWO DAYS) IDAY DAYS) WAWA WAWA KIMBERLITE/GOLD KIMBERLITE/GOLDEXPLORATION EXPLORATION 6:00PM. PM. RETURN TO MARATHON MARATHON BY ABOUT 6:00 xviii �ORAL PRESENTATIONS ORAL PRESENTATIONS Senior Author Session Paper No. No. Session No. No. -.Paper BERENDSEN, BERENDSEN. PP. . . . . . . . . . . . . . . . . . . . . . . . . I—i BORNHORST, BORNHORST. T . . . . . . . . . . . . . . . . . . . . . . . . III- 20 CORFU, P CORFU. P. . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1-3 * DARRAH, DARRAH. K K. . . . . . . . . . . . . . . . . . . . . . . . . . . II - 12 * FEHER, FEHER. LL. . . . . . . . . . . . . . . . . . . . . . . . . . . . . II - 15 FRALICK, P FRALICK. P. . . . . . . . . . . . . . . . . . . . . . . . . . III - 19 FREY, FREY. B B. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . lV-29 ** HALLS, H **HALLS. H. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1-2 HOLM, HOLM. D D. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Il—Il JIRSA, JIRSA. M M. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1-9 **KING,D KING, D . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1-4 * KOEBERNICK, KOEBERNICK, C C. . . . . . . . . . . . . . . . . . . . . . . . II - 13 LaBERGE, G 1-5 LEE, II. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . LEE. 111-23 LIGHTFOOT, P. LIGHTFOOT. P. (1) (1). . . . . . . . . . . . . . . . . . . . . . IIIIll - 22 22 LIGHTFOOT, P. LIGHTFOOT. P. (2) (2). . . . . . . . . . . . . . . . . . . . . . Banquet Banquet Presentation Presentation UN, S LIN. S. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 111 - 1166 III MILLER, JJ. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 111-24 111 - 2 4 MILLER. MORRIS, T . . . . . . . . . . . . . . . . . . . . . . . . . . . . MORRIS. IV - 227 7 NORTH, JJ . . . . . . . . . . . . . . . . . . . . . . . . . . . . NORTH. III - 114 4 * PETERSON, D.M . . . . . . . . . . . . . . . . . . . . . . . "PETERS0N.D.M 1 -7 1-7 PETERSON,V PETERSON. V. . . . . . . . . . . . . . . . . . . . . . . . . 111 - 1177 III * PUFAHL, PUFAHL. PP. . . . . . . . . . . . . . . . . . . . . . . . . . . -1-6 6 RUDASHEVSKY, RUDASHEVSKY. N.S N.S. . . . . . . . . . . . . . . . . . . . IV -28 IV-28 * SCHNEIDER, SCHNEIDER. D D. . . . . . . . . . . . . . . . . . . . . . . . 11II - 110 0 SHAW, C SHAW. C. . . . . . . . . . . . . . . . . . . . . . . . . . . . . 111 21 III-- 21 * SHORE, SHORE. G G. . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1 -8 1-8 ZALESKI, E ZALESKI. E. . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11III1-18 - 18 ZBIKOWSKI, D. ZBIKOWSKI. D. (1) (1). . . . . . . . . . . . . . . . . . . . . . IV -25 IV-25 ZBIKOWSKI, D. D. (2) (2). . . . . . . . . . . . . . . . . . . . . . ZBIKOWSKI. IV - 2266 *Student 'Student Paper Paper **cancelled paper "cancelled xix �RACTS ABSTRACTS �HISTORY AND DEVELOPMENT OF T HE SOUTHERN EXTENSION THE EXTENSION OF OF THE THE MIDCONTINENT RIFT IN KANSAS. IN KANSAS. BERENDSEN, Pieter, BERENDSEN, Pieter,Kansas KansasGeological GeologicalSurvey, Survey,University University of of Kansas, Kansas, Lawrence, Lawrence, KS 66047. 66047. KS Igneous and sedimentary sedimentaryrocks rocks associated with the southern southern extension extension of the the (MRS) in regionally significant significant MidcontinentRift Rift System System (MRS) Midcontinent in Kansas Kansasterminate terminate against a regionally northwest-trendingstructural structuralzone zone(Missouri (MissouriGravity GravityLow) Low) at at the the Kansas-Nebraska Kansas-Nebraska northwest-trending border. To the south, south,an anequally equallypronounced pronouncedstructural structuralzone zone(Fall (FallRiver RiverTectonic Tectonic south of of which no rift-related igneous or sedimentary Zone) defines defines a boundary south sedimentary the basement basement surface. surface.The The southern southern boundary boundaryalso alsoroughly roughlycoincides coincides rocks occur at the suture between between the the older older (1.63-1.80 (1.63-1.80 Ga) metamorphic with the suture metamorphic and and granitoid rocks of of the Central Plains orogen (Sims and Peterman, 1986) and younger (1.35( 1.35orogen to the north (Sims 1.48 Ga) rhyolitic rhyolitic and dacitic volcanic rocks rocks and and associated epizonal granitic plutons plutons to the south south (Denison, (Denison, and others, others, 1984). 1984).North-northeast-trending North-northeast-trending faults identified NW-SEthe subsurface subsurface are are not notas aspronounced pronouncednorth northand andsouth southofofthese thesesutures. sutures.NW-SEin the and NNE-WSW-trending NNE-WSW-trending faults geologic time. The and faultshave havebeen beenreactivated reactivated troughout geologic distribution pattern patternof ofPrecambrian Precambrianand andPaleozoic Paleozoic rocks rocks within the area area comprising comprising distribution the trend trend of of the the rift rift has has been been greatly greatly influenced influenced by by motion along these faults. Renewed resulted in in complex complex sets sets of closely spaced Renewed movement movement along basement faults resulted spaced younger rocks, and and are referred referred to Nemaha and and faults affecting younger to as tectonic zones. The Nemaha Peace Creek tectonic zones are SWare the themajor majorNNE-trending NNE-trending rift-related rift-related structures. structures.SWNE-trending tectonic tectonic zones zonesare are believed believedto tobe beolder older (Clendenin, (Clendenin,and andothers, others, 1989) 1989) and and NE-trending tectonic zones and cross the the rift rift zone. zone.The TheFall Fall River, River, Chesapeake, Chesapeake, Bolivar-Mansfield tectonic and Loware arethe the better better known known structures. structures. the Missouri Gravity Low activity associated associated with with the the active phase of rifting was essentially Magmatic activity synchronous along of 1097.5 ±3 Ma Ma obtained obtained from synchronous along its its length. length.A A concordant concordantU-Pb U-Pb age of 1097.5 ± of published baddeleyite in gabbro from a depth of about about 900 m. is within the range of 1992). In In the post-igneous stages of of rifting rifting initially coarse and ages (Van Schmus, 1992). by finer finer grained grained and more mature strata immature sedimentary sedimentaryrocks rocks followed by strata were were deposited in axial and flanking basins. There is no no geologic geologicrecord recordindicating indicatingthat that deposited sedimentary or igneous rocks accumulated in in the time span span between between the the end end of of the sedimentary Keweenawanand and the the onset of the Paleozoic, but instead instead the area was subjected to a Keweenawan Paleozoic, but long period of erosion and peneplanation. peneplanation. Faulting, Faulting, as evidenced by considerable vertical vertical displacement displacement of of Proterozoic Proterozoic igneous and and sedimentary sedimentary rocks rocks (Woelk (Woelk and Hinze, 1991; Berendsen, Berendsen,in inpress) press) played played an an important important role in preserving younger Hinze, graben structures rocks in graben structures and andexhuming exhuming older older rocks rocks on on hortsted hortstedblocks. blocks. Rocks of ofPermian Permianage ageare arethe theyoungest youngestsedimentary sedimentarystrata strata to to be be deposited deposited in Rocks the area. with the western edge of of the the rift province Cretaceous area. Closely Closely coinciding with rocks are present. They are believed to have extended farther farther to the east, but were eroded back to their their present presentposition, position,possibly possibly related to reactivation reactivation of rift structures. structures. The The occurrence occurrenceof of numerous numerousCretaceous Cretaceous(90 (90Ma) Ma) kimberlites occurring occurring at at or near the the surface surface as as well well as non-deposition non-depositionor or erosion erosion of of several several pre-Permian sedimentary sedimentary rock rock units units indicate indicate that thatsignificant significanttectonic tectonic activity activity took took place at at various times stresses responsible various times during duringthe thePaleozoic Paleozoicand andMesozoic Mesozoic eras. The stresses responsible for for all all craton during this activity originated at the the eastern easternmargins margins of of the the North North American American craton during continent continent to to continent continentcollisions collisions beginning beginning during during Grenville Grenville time and shifting to affecting the the midcontinent mldcontinent during during the the south with a major period of activity affecting Ouachita-Wicbita-Marathon Since Permian Permian sedimentary sedimentary rocks are the Ouachita-Wichita-Marathonorogeny. Since youngest strata strata in in the thearea areaunder underdiscussion discussionititisisdifficult, difficult,ifif not notimpossible, impossible, to to document document Cenozoic Cenozoic and recent tectonic activity (probably (probably of lesser intensity) that that 1 �undoubtedly must must occurred. occurred.The The stresses stresses are are believed to have been transmitted undoubtedly primarily via Precambrian Precambrian basement basement rocks rocks and and mostly mostly along along pre-existing pre-existing fractures. fractures. primarily direction from from which the stresses stresses were applied resulted in complex and The shift in direction often often reversal reversal of of movements movements on on faults. faults. influenced by the Depositional patterns of stratigraphic units quite often are influenced tectonic events eventsas as evidenced evidenced for for example example by by the the location location of of paleo-stream paleo-stream previous tectonic channels, and and the the location location of of carbonate carbonate build-ups. build-ups. Of Of more more practical practical consequences, consequences, it channels, important to to remember remember that that the the distribution distributionof of energy energy and and mineral mineral resources, resources, is important migration of fluids or gases is responsible for the concentration concentration especially where migration and accumulation accumulationof of aa commodity, commodity, is directly influenced by the tectonic framework and of the the rocks. rocks. REFERENCES REFERENCES Berendsen, Berendsen, P., (in (in Press), Press), Tectonic evolution of the the Midcontinent MidcontinentRift Rift System in Kansas: Geological Society of America Special Special Paper. Paper. Clendenin, W., and and Niewendorp, C. C. A., A.,1989, 1989,Reinterpretation Reinterpretation of of faulting faulting in C. W., Clendenin, C. southeast 2 17-220. southeastMissouri: Missouri:Geology, Geology, v. 17, 17, p. 217-220. Denison, G., Bickford, Bicklord, M. M. E., F., and and Kisvarsanyi, Kisvarsanyi, E. B., 1984, 1984, Geology and and Denison,R. R. F., E., Lidiak, Lidiak, E. E. G., E. B., geochronology of of Precambrian Precambrian rocks rocksin in the the central central interior interior region of of the United Professional Paper United States: States:U. U. S. S. Geological Survey Professional Paper 1241-C, 1241-C,20 20 p. p. Sims, P. P. K., K.,and and Peterman, Peterman, Z. E., 1986, 1986, Early Early Proterozoic Proterozoic Central Plains Orogen: A A major major Z. E., buried buried structure structureininthe thenorth-central north-centralUnited UnitedStates: States:Geology, Geology,v. v. 14, 14,p. p.488-491. 488-491. Van Schmus, R., 1992, Tectonic setting Schmus,W. R., setting of of the theMidcontinent MidcontinentRift RiftSystem: System: Tectonophysics, Tectonophysics, 213, 213, p. p. 1-15. 1-15. Woelk, T. S., S., and and Hinze, W. W. JJ., 1991, Model of of the the Midcontinent Midcontinent Rift ., 199 1,Model Rift System in northeastern 2 77-280. northeasternKansas: Kansas:Geology, Geology, v. 19, 19, p. p. 277-280. �NATIVE COPPER COPPER AND AND ASSOCIATED ASSOCIATED MINERALS IN IN BASALTS AT THE CALEDONIA NATIVE MINE, WESTERN WESTERN UPPER UPPER MICHIGAN MICHIGAN BORNHORST, Theodore Theodore J., J., Department Department of Geological Engineering BORNHORST, Engineering and and Sciences, Sciences, Michigan Michigan Technological Technological University, University, Houghton, MI MI 49931 49931 and and WHITEMAN, WHITEMAN, Richard Richard C., C., Red Red Houghton, Metal Explorations, Explorations, Hubbell, Hubbell, MI MI 49934 49934 Metal The Caledonia Caledonia Mine Mine is is located located near near Mass Mass City City in in western western Upper Upper The Michigan. Michigan. It It lies lies within within an an area area of of native native copper copper deposits deposits some some 40 km krn southwest southwest of of the the major major deposits deposits of of the the Keweenaw Keweenaw Peninsula Peninsula 40 native native copper copper district. district. The The Caledonia Caledonia Mine Mine produced produced about about 33 million kg kg of of native native copper copper from from 1863-1881 1863-1881 and and 1951-1958. 1951-1958. Since Since million 1985 the the mine mine has has been been tested tested by by Red Red Metal Metal Explorations. Explorations. The The 1985 Caledonia Mine Mine provides provides access access to to continue continue studies studies of of native native Caledonia copper mineralization mineralization while while most most of of the the native native copper copper mines mines of of copper the the Keweenaw Keweenaw Peninsula Peninsula are are now now flooded flooded or or closed closed permanently. permanently. The Caledonia Caledonia Mine Mine intersects intersects the the Butler and Knowlton Knowlton flow flow The tops. tholeiitic tops. These These lava lava flows flows are are part part of of aa package package of of tholeiitic basalt basalt lava lava flows flows up up to to 210 210 mm in in total total thickness thickness within within the the Portage adit at at the the Portage Lake Lake Volcanics. Volcanics. For For most most of of its its length length the the adit Caledonia Mine Mine follows follows the the brecciated brecciated amygdaloidal amygdaloidal top top of of the the Caledonia Knowlton Knowlton flow flow which which dips dips at at about about 450 45' northwest. northwest. The The average average thickness of of the the stratabound stratabound Knowlton Knowlton lode lode (flow (flowtop) top) is is about about thickness 2.5 2.5 mm but but locally locally thickens thickens to to more more than than 66m. m. Native Native copper copper and and an an associated associated suite suite of of secondary secondary minerals minerals fill amygdules amygdules and and spaces spaces between between fragments fragments in in the the brecciated brecciated fill lava flow flowtop. top. Calcite Calcite is is the the most most abundant abundant secondary secondarymineral. mineral. lava Quartz, epidote epidote and and K-feldspar K-feldspar are are lesser lesser in in abundance abundance and and occur occur Quartz, in in subequal subequal amounts. amounts. Prehnite, Prehnite, pumpellyite, pumpellyite, and and chlorite chlorite are are present in in small small amounts. amounts. Native Native copper, copper, in in minor minor amounts, amounts, is is present associated associated with with even even less less abundant abundant native native silver. silver. Paragenetic Paragenetic sequence, sequence, based based on on filling filling of of amygdules amygdules and and open open spaces, spaces, is is KKfeldspar followed followed by by epidote epidote and and then then calcite+quartz. calcite+quartz. Native Native feldspar copper tends tends to to be be more more commonly commonly associated associated with with epidote, epidote, copper calcite, calcite, and and quartz. quartz. Rarely Rarely is is native native copper copper abundant abundant in in areas areas with with abundant abundant K-feldspar. K-feldspar. No No major major differences differences exist exist in in the the abundance abundance of of secondary secondary minerals averaged averaged over over the the scale scale of of 100's 100's of of meters. meters. In In minerals contrast, over the scale of a few meters the distribution contrast, over the scale of a few meters the distribution of of secondary secondary minerals minerals is is variable. variable. AA secondary secondary mineral mineral may may be be completely absent absent in in one one zone zone and and extremely extremely abundant abundant in in another. another. completely However, the the meter meter scale scale variation variation does does have have aa certain certain degree degreeof of However, regularity. regularity. In In some some areas areas the the occurrence occurrence of of secondary secondary minerals minerals is banded banded consistent consistent with with the the progressive progressive filling filling of of open open spaces spaces is indicated by by amygdule amygdule paragenesis. paragenesis. The The intensity intensity of of alteration alteration indicated footwall of of the the is highest highest near near both both the the hanging hanging wall wall and and footwall is brecciated brecciated flow flow top top lode. lode. Distribution Distribution of of secondary secondary minerals minerals also also correlates correlates with with the theoccurrence occurrenceof ofveins. veins. Veins Veins are are of of two two types. types. Some Some veins veins within within the the lode lode and and extending into into underlying underlying massive massive basalt basalt contain contain the the same same basic basic extending minerals minerals as as the the lode, lode, including including native native copper. copper. These These veins veins are are 3 �considered synchronous synchronous with with lode lode formation formation whereas whereas others others are are considered clearly clearly late-stage. late-stage. One One vein vein of of the the former former type type is is the the target target of of current current exploration. exploration. This This particular particular vein vein strikes strikes subparallel subparallel with with the the strike strike of of the the flow flow top top but but dips dips more more steeply steeply (about (about800 80' for the the vein) vein) and and has has been been traced traced for for over over 100 100m. m. The The vein vein is is for well well developed developed in in the the footwall footwall and and below, below, but but is is hard hard to to identify identify as as it it enters enters the the lode. lode. Within Within this this vein vein the the intensity intensity of of alteration alteration varies varies from from slight slight to to very very high. high. Original Original basalt basalt can can be be completely completely converted converted to to aa green green soft soft epidote+lesser epidote+lesser chlorite chlorite rock, rock, or or aa hard hard epidote+lesser epidote+lesserquartz quartz rock. rock. Overall Overall mineralogy mineralogy and and paragenesis paragenesis is is similar similarto to the thelode. lode. The The vein vein contains contains pockets pockets of of soft soft blue-green blue-green mineral mineral identified identified as as corrensite corrensite by by XRD XRD (mixed (mixed layered layered clay clay mineral mineral with with 50/50 50/50 chlorite chlorite and and smectite smectite unit unit cells cells stacked stacked in in perfect perfect alternation). alternation). This This vein vein has has recently recently yielded yielded outstanding outstanding world world class class quality quality specimens specimens of of crystalline crystalline native native silver silver which which was was originally originally encased encased in in white white calcite calcite (calcite (calcitewas was removed removed by by acid acid leaching), leaching),and and clusters clusters of of colorless calcite calcite crystals crystals internally internally laced laced with with native native copper copper in in colorless vugs. vugs. Several Several masses masses of of native native copper copper weighing weighing over over 100 100 kg kg and and small small groups groups of of copper copper crystals crystals originally originally encased encased in in white white calcite, calcite, some some coated coated with with very very small small cubic cubic native native silver silver crystals, crystals, have have also also been been recovered recovered during during exploration. exploration. Massive Massive datolite datolite is is associated associated with with native native copper, copper, occurring occurring on on and and within within native native copper. copper. This This vein vein is is quite quite similar similar to to veins veins described described by by Broderick Broderick (1931, (1931,Economic EconomicGeology, Geology,v. v.26, 26, p. p. 840840856) 856) in in the the Baltic Baltic and and Isle Isle Royale Royale Mines Mines about about 50 50 km km northeast northeast near near Houghton. Houghton. This This steeply steeply dipping dipping vein vein is is interpreted interpreted as as aa pathway pathway for for ascending ascending hydrothermal hydrothermalfluids. fluids. Other Other veins veins are are clearly clearly late-stage late-stageand and crosscut crosscut the the native native copper-mineralized copper-mineralized lode lode at at the the Caledonia CaledoniaMine. Mine. Late-stage Late-stage veins veins containing containing calcite calcite and and laumontite laumontite are are readily readily visible visible in in the the adit adit and and are are barren barren of of native native copper. copper. Adularia Adularia is is an an additional additional late-stage late-stage secondary secondary mineral mineral that that occurs occurs in in veins veins and and in in the the lode. lode. Veins Veins played played an an important important role role in in the the deposition deposition of of native native copper copper and and associated associated minerals minerals at at the the Caledonia CaledoniaMine. Mine. 4 �LITHO-TECTONIC THE SUPERIOR SUPERIOR LITHO-TECTONICAND AND MINERAL MINERALDEPOSIT DEPOSITMAPS MAPS OF OF THE PROVINCE PROVINCE K.D. Card, R.A. Frith, and K.H. Poulsen, Geological Survey Survey of of Canada, Canada, Ottawa Ottawa deposit maps Litho-tectonic and mineral deposit maps of Superior Province Province were were compiled compiled at 2.5 million million scale as part part of of aa contribution contributionto to Decade Decade of of North North American American Geology Geology (DNAG). (DNAG). Sources Sources induded includedpublished publishedand andunpublished unpublishedmaps mapscompiled compiledon onaaone onemillion millionscale scaleDigital Digital Chart Chart of the World base. base. Twenty maps were prepared, prepared, raster raster scanned and processed processed using usingArcArcInfo software over over aa two twomonth monthperiod. period. The TheMineral Mineral Deposit DepositMap Map was was prepared prepared from fromthe the Litho-tectonic Map and individual individualdeposits depositswere werekeyed keyed by by type, type, size sizeand andlocation locationfrom from dbase dbase files. files. Geological units were grouped grouped by by age age and and tectonic tectonic type, type, based based on on U-Pb U-Pb isochron isochron ages, inferred depositional sequence, in in order to depositional environments, environments, and and intrusive-orogenic intrusive-orogenic sequence, relate economic mineral mineral deposits deposits to toenvironments environmentsand andprocesses. processes. Supracrustal Supracrustal rocks rockswere were assigned to to late lateand andearly earlysuccessor successorbasins, basins,accretionary accretionarycomplexes, complexes, calc-alkaline calc-alkaline and and tholeiitic arc sequences, sequences,and and submarine submarine tholeiitic-komatiitic tholeiitic-komatiiticmafic maficplain plainsequences. sequences. Where Where regional metamorphism is high, high,bulk bulkcomposition, composition,metamorphic metamorphicand and "unknown" "unknown" affinity affinity designations designations were were used. used. 5 �GEOCHRONOLOGY OF OFTHE THESHEBANDO SHEBANDOWAN GREENSTONE BELT, BELT, U-Pb GEOCHRONOLOGY WAN GREENSTONE SUPERIOR PROVINCE, PROVINCE, ONTARIO ONTARIO SUPERIOR Corfu,F., F.,Jack Jack SatterlyGeochronology GeochronolosyLaborato,y, Laboratory,Royal Royal Ontario OntarioMuseum, Museum, 100 100 Queen's Park, Toronto Corfu, Satterly Pang Toronto M5S 2C6and and Stott, Stott, G.M., M5S 2C6 G.M., Precambrian Precambrian Geoscience Section, Ontario Ontario Geological GeologicalSurvey, Survey, 933 933 Ramsey Lake Road, Sudbuy, Sudbuy, Ontario OntarioP3E P3E 6B5 6B5 The Shebandowan Shebandowangreenstone greenstonebelt, belt,in inthe thewestern westernWawa Wawa Subprovince, Subprovince, is composed of Archean The Archean metavolcanic and composite batholith to to the the south southand andimpinging impinginginto intothe themetasedimentary metasedimentary metasedimentary rocks bound by a composite QueticoSubprovince Subprovinceto the the north. north. An An extensive extensive geochronological Quetico geochronological study studyhas hasbeen beenundertaken undertaken in in order order to constrain the stratigraphic stratigraphicrelationships relationshipsof of the the belt belt and anddate datethe theformation formationof of major majorplutonic plutonicsuites, suites,complementing complementingan an early early the U-Pb U-Pb study study carried carried out out in in the thebelt belt(Corfu (Corfuand andStott Stott1986). 1986). structural mapping mapping had had indicated indicated the the presence presence of of two two major major volcanic volcanic assemblages, assemblages, the Geological and structural north-facing Burchell assemblage in the northern northern part part of of the thebelt beltand andthe thesouth-facing south-facingGreenwater Greenwaterassemblage assemblage north-facing to the thesouth south(Williams (Williamsetetal. al.1991). 1991).Both Bothassemblages assemblages were were further furthersubdivided subdivided into into three threecycles cycles consisting consisting of to mafic and and minor minor komatiitic komatiitic volcanic volcanic successions successions capped intermediate to felsic felsic units. units. Our Ourpreliminary preliminary mafic capped by by intermediate geochronological data data show show that that most mostof of these thesevolcanic volcanic units units developed developed within within aa relatively relatively short short period period of of time time geochronological at around around2722 2722 to to 2718 2718 Ma. This time frame also includes the crystaffization crystallization of at frame also ofanorthosites anorthosites and and layered gabbroic gabbroic bodies such such the Haines Haines and and the the North NorthColdstream Coldstream gabbros. gabbros. A similar bodies similar age has also also been found found for for aa felsic felsic volcanic volcanic unit in the the Saganagon Saganagon belt belt to to the thesouthwest. southwest. An age ageof of 2733 2733 Ma, Ma, determined determinedin in the theprevious previoussurvey survey for aa porphyry porphyry sill sill intruding metabasalts metabasalts in the An northern part part ofofthe thebelt, belt,remains remainsunique uniqueand andcould couldindicate indicatethe thepresence presenceofofa atectonically tectonicallyinterleaved interleavedolder older northern verificationof ofthis thisage ageisisinin package or or ititcould couldbe beaaspurious spuriousage agebiased biasedby bya axenocrystic xenocrysticzircon zirconcomponent. component.AAverification package progress. The The only only older older unit unit found foundin inthis thisstudy studyisis2750 2750 Ma Ma tonalitic tonalitic gneiss gneiss of the the Northern NorthernLight LightComplex. Complex. progress. Zircons with with age agebetween between2750 2750 and and 2900 2900 Ma Ma occur, occur, however, however, as as detrital detritalcomponents componentsin inyounger youngersediments sedimentsor or Zircons as as xenocrystic xenocrystic grains grains in in granitic graniticrocks. rocks. A A young young volcanic episode at around around 2695 2695 Ma formed formed pyroclastic pyroclastic units located in northern northern segments segmentsof of the belt. belt. These Theseunits unitscorrelate correlatewith withthe thepreviously previously dated dated2696 26% Ma Ma synsyn- or or post post Dl D lShebandowan ShebandowanLake Lakepluton. pluton. the A previous previousage agedetermination determinationofof2689 2689Ma Mafor foran analkalic alkalicvolcanic volcanicrock rock isisnow nowsupported supportedby bynew newages agesofof 52692 A 2692 Ma for for aavolcanogenic volcanogenic unit of the Duckworth Duckworth group and for a breccia in the Strawberry Strawberry Hill area. An age of Ma about 2693 2693 was was also also obtained obtainedfor forthe thesyenitic syeniticTower Towerstock. stock.These TheseTimiskaming-type Timiskaming-type units units are arecoeval coevalwith with about emplacementof ofthe the2690 2690 Ma Ma Saganaga Saganagapluton pluton in in the the southwest, southwest, and and hence hence with with deposition deposition of of metasedirnentary metasedimentary emplacement units of of the the Knife KnifeLake Lakeassemblage assemblage in in Ontario Ontario and andMinnesota. Minnesota. The Theyoungest youngest ages ages of of 2683 2683 to 2680 2680 Ma were units obtainedfor forsyenitic syeniticto to granodioritic granodioriticphases phasesof of the the Kekekuab, Kekekuab, Icarus Icarusand andPerching PerchingGull GullLake Lakeplutons. plutons.These Theseages ages obtained 2684Ma Mapreviously previously obtained obtained for for the thepost-D2 post-D2Burchell Burchellpluton. pluton. overlap the the less lessprecise precisedate dateofof2684 overlap Amaximum maximum age ageof of deposition depositionof of about about2682 2682 Ma Ma isisprovided provided by by the the youngest youngest detrital detrital zircon zircon grains grains in in A conglomeraticunit unit in in the the northeastern northeasternpart partofofthe thebelt. belt.This Thisunit unitrepresents representsthe thelatest latestsedimentary sedimentarysuccession succession aa conglomeratic known in in the the region, region,postdating postdatingdeposition depositionand anddeformation deformationofofmuch muchofofthe theadjacent adjacentQuetico Queticosedimentary sedimentaryrocks rocks known and 1990). Deposition andof of the theSeine SeineGroup Group(Davis (Davisetetal.al.1989, 1989,1990). Depositionof ofthis thislate latesedimentary sedimentarysuccession successionprobably probablyreflects reflects some of of the thelatest latesttectonic tectonicadjustments adjustmentsoccurring occurringatatthe theboundary boundarybetween betweenWawa Wawaand andQuetico Queticosubprovinces. subprovinces. some References:Corfu Corfuand andStott Stott(1986). (1986).Can CanJ.J.Earth Earth Sci., 1075-1082. References: Sci., 23:23:1075-1082. Davis, and Kamo Kamo(1989). (1989).J.J.Geology, Geology,97: 97:279-398. 279-398. Davis,Poulsen Poulsen, ,and EarthPlant. Plant. Sci. Lett., 195-205. Davis,Pezzutto, Pezzutto,and andOjakangas Ojakangas(1990). (1990).Earth Davis, Sci. Lett., 99:99: 195-205. Williams, Stott, Stott,Heather, Heather,Muir, Muir,and andSage Sage(1991). (1991).Ont. Ont.Geol. Geol.Survey, Survey,Spec. Spec.Vol. Vol.4/1: 411:484-539. 484-539. Williams, 6 �APPLICATIONOF OF'THE THEALUMINUM-IN-HORNBLENDE ALUMINUM-m-HORNBLENDEBAROMETER BAROMETERON ONEARLY EARLY APPLICATION PROTEROZOIC,POST-PENOKEAN POST-PENOKEANPLUTONS, PLUTONS,CENTRAL CENTRALMINNESOTA. MINNESOTA. PROTEROZOIC, K.S.,and andHOLM, HOLM,D.K., D.K.,Department DepartmentofofGeology, Geology,Kent KentState StateUniversity, University,Kent, Kent, DARRAH,K.S., DARRAH, OH 2 16-672-4094; dholm@kentvm.kent.edu. dholm@kentvm.kent.edu. OH 44242; 44242; 216-672-4094; Archean and and Early Early Proterozoic Proterozoic metamorphic metamorphic rocks rocks in in central central Minnesota Minnesota record record relatively relatively Archean uniform uniform paleopressures paleopressures of of 5-6 5-6 kb kbassociated associated with with the thePenokean Penokean collisional collisional orogeny orogeny(1870-1830 (1870-1830 (18 12 Maand and—1770 -1770 Ma) Ma) tectonic tectonic Ma). These Theserocks rocksare areintruded intrudedby bysynsyn-(-1870 (-1870Ma) Ma)and andpostpost-(1812 Ma). Ma plutons, plutons, some some of of which which occupy occupy the the cores cores of of domal domalstructures structures in inthe thecountry countryrock rock(Southwick, (Southwick, and and others, others, 1988). 1988). InInorder ordertotoassess assessthe thepost-collisional post-collisional uplift uplifthistory history of of this this part part of of the the orogen orogen we we have have applied applied the theempirical empiricalAl-in-hornblende Al-in-hornblende igneous igneous barometer barometer of ofHammarstrom Hammarstrom and andZen Zen (1986) (1986) to to estimate estimateemplacement emplacementdepths depthsof ofthe themagmatic magmaticsuite. suite.This Thisbarometer barometercorrelates correlatesj,JtOt A P content content of of magmatic magmatic hornblende hornblende linearly linearly with with crystallization crystallization pressure of intrusion. Of Ofthe thesix six plutonic plutonic bodies bodies sampled sampled for for this this study, study, three three contain contain the theappropriate appropriatemineral mineral assemblage assemblage required for for the the barometer barometer and and yield yield relatively relativelyuniform uniform aluminum aluminumcontent contentfrom fromhornblende hornblenderim rim required microprobe microprobe analyses. analyses. The Theresults resultsofofmicroprobe microprobeanalyses analysesofofthe theundated, undated,moderately moderatelydeformed deformed Freedhem (iranodiorite Granodiorite(KA-F), (KA-F),and andthe the—1770 -1770 Ma Ma Isle Isle (K-4) (K-4) and and St. St. Cloud CloudGranites Granites(MN-35) (MN-35) Freedhem are are recorded recorded in in Table Table 1.1. The The barometer barometer has has been been verified verified experimentally experimentally by by Johnson Johnson and and Rutherford Rutherford (1989) (1989) and and more more recently recently by Schmidt (1992). The Theresults results of of our ourdata data using using both both of of these these calibrations calibrations isis given given below. below. Rock Rockunit unit St. St. Cloud Cloud Granite Granite Freedhem Freedhem Granodionte Granodiorite Isle IsleGranite Granite Johnson Johnson and andRutherford. Rutherford. 1989 1989 3.32 3.32 ±k0.5 0.5 kb kb 2.46 0.5 kb kb 2.46 ±k0.5 2.30 2.30±k0.5 0.5 kb kb Schmidt. 1992 1992 Schmidt. 4.62 4.62 ±k0.6 0.6kb kb 3.65 ± 0.6 kb 3.47 ± 0.6 kb TheJohnson Johnsonand andRutherford Rutherfordcalibration calibrationwas wasaccomplished accomplishedat at temperatures temperatures of of 740-780°C 740-780° The with with Pt0t Ptot == CO2 P c o 2 ++ F20, m 2 0 , whereas whereas the the Schmidt Schmidt calibration calibration was carried carried out out under under water water saturated saturated conditions conditions at at temperatures temperatures of of 700-655°C. 700-655OC. To Toour ourknowledge knowledgethere thereisisno noindication indicationfor for the thepresence presenceof ofaaCO2 C 0 2-bearing -bearing fluid fluid at at the the time time of of crystallization crystallization of of these these rocks, rocks, although although such such aa thing thing may may be, be, admittedly, admittedly, difficult difficult to to evaluate. evaluate. However, However,for forindependent independentreasons, reasons,we weconsider consider the the pressures pressures obtained obtained by by the theJohnson Johnsonand andRutherford Rutherford calibration calibration to to give givedepth depthofofintrusion intrusion estimates estimates that that are areunreasonably unreasonably low low (i.e., (i-e.,less lessthan than 10 10km kmfor forthe theFreedhem Freedhem Granodiorite Granodioriteand and Isle Isle Granite). Granite). Recent Recentthermochronologic thermochronologicdata data(see (seeHoim Holmand andLux, Lux,1995 1995ILSG ILSGabstract, abstract,this this volume) emplaced into into country country rock rock with withambient ambient volume) indicates indicates that that the the intrusions intrusions were were emplaced temperatures temperatures above above 300°C. 3OO0C. Considering Consideringan anupper-crustal upper-crustal geothermal geothermal gradient gradient in in the the range range of of 20-30°CIkm, 20-30°C/kmthis this indicates indicates aaminimum minimum depth depth estimate estimateof of 10-15 10-15km kmfor foremplacement emplacementof ofthese these plutons. plutons. Using (19921,the theSt. St.Cloud CloudGranite Graniteintruded intrudedatataapressure pressureofof Using the thecalibration calibration of of Schmidt Schmidt(1992), 4.62 0.6 kb. kb. Assuming Assumingananaverage averageoverburden overburdendensity densityofof2.7 2.7g/cc, gkc,this thiscorresponds correspondstotoaadepth depth 4.62 ±k0.6 of km. However, of —17 -17 km. However, the the comagmatic comagmatic (?) (?)Isle IsleGranite Graniteintruded intruded atataapressure pressureofof3.47 3.47±h0.6 0.6kb kb corresponding corresponding to to aa depth depthofof—13 -13 km. The Thefact factthat thatdifferent differentintrusions intrusionsofofthe the—1770 -1770 Ma Ma magmatic magmatic suite suite yield yield different differentemplacement emplacement pressures pressures suggests suggests that thatmagmatism magmatism occurred occurred simultaneously —1770 simultaneouslywith withpost-orogenic post-orogenicuplift. uplift.We Weinterpret interpretformation formationofofthethe -1770 Ma Mapost-tectonic post-tectonic plutons plutonsin ineast-central east-central Minnesota Minnesotato tohave haveresulted resulted from fromthermal thermal relaxation relaxation of of the theinternal internalzone zone of ofthe theorogen orogenwhich whichremained remainedoverthickened overthickenedfor for50-70 50-70Ma Ma after after collision. collision. We Weenvision envisionthermal thermal weakening weakening and andmelt meltproduction productionasasconcurrent concurrentwith withthe theonset onsetofofsignificant significantpost-orogenic post-orogenicuplift. uplift. Continued Continued unroofing unroofing is is suggested suggested by by the theabundant abundant 1760-1750 1760-1750 Ma Ma Rb-Sr Rb-Sr and andAr-Ar Ar-Arbiotite biotite cooling cooling ages ages throughout throughout central central Minnesota. Minnesota. Intrusion Intrusionand andcoeval coevaluplift upliftfollowed followedshortly shortlyby by orogen-wide orogen-widecooling coolingare areall allconsistent consistentwith withan anepisode episodeofoforogenic orogeniccollapse collapseproposed proposedby byHoim Holm and andothers others(1993). (1993). 7 �Although itit has has not notbeen beendated, dated?the thedeformed deformedFreedhem Freedhem Granodiorite Granodiorite has has been been Although commonly considered a syn-tectonic pluton associated with the Penokean collisional orogeny. commonly considered a syn-tectonic pluton associated with the Penokean collisional orogeny. However?its its shallower shallower depth depth of ofemplacement emplacement relative relative totothe thepost-tectonic post-tectonicSt. St.Cloud CloudGranite Granite However, suggests to us that it is also post-tectonic. We interpret deformation features in the Freedhem suggests to us that it is also post-tectonic. We interpret deformation features in the Freedhem Granodiorite (solid (solid state state foliation foliation and and cross-cutting cross-cutting shear shear zones), zones)?and and perhaps perhaps also also the the country country Granodiorite rock structural domes mentioned above? as features formed during uplift and collapse of the the rock structural domes mentioned above, as features formed during uplift and collapse of Penokeanorogen. orogen. Penokean Table1.1.Results ResultsofofMicroprobe Microprobeanalyses analysesononthe theFeedhem FeedhemGranodiorite Granodiorite(KA-F), (KA-F),the theIsle IsleGranite Granite Table (K-4)? and the St. Cloud Granite (MN-35). (K-4), and the St. Cloud Granite (MN-35). Sam~le Sample KA-F- 1 KA-F-1 KA-F-2 K-4-1 Si Ti A1 ME Si Ti Al Mg 6.891 0.147 0.147 1.335 1.335 2.724 2.724 6.891 1.329 2.708 2.708 6.915 0.143 0.143 1.329 6.915 6.761 0.142 1.511 2.510 6.843 0.148 1.424 2.597 6.850 0.128 1.356 2.790 6.822 0.147 1.439 2.641 6.845 0.158 1.340 2.721 6.832 0.160 1.401 2.709 6.819 0.142 1.455 2.659 6.853 0.109 1.381 2.552 6.808 0.117 1.470 2.488 6.857 0.117 1.407 2.522 6.927 0.083 1.360 2.642 6.891 0.104 1.391 2.539 K-4-2 6.942 0.101 1.319 2.574 7.008 0.086 1.290 2.587 6.991 0.091 1.275 2.633 K-4-3 MN-35-1 MN-35-2 6.955 0.093 1.314 2.567 6.974 0.073 1.320 2.640 6.833 0.112 1.453 2.529 6.590 0.224 1.640 0.242 6.552 0.217 1.643 0.248 6.580 0.212 1.627 0.221 6.712 0.159 1.542 0.214 6.735 0.143 1.530 0.234 6.642 0.161 1.630 0.219 MN-35-3 6.594 0.184 1.628 0.210 6.607 0.206 1.637 0.249 Ca Mn Ca Mn 1.897 0.077 1.897 0.077 1.876 0.071 0.071 1.876 Fe Na Fe Na KK 1.976 0.316 0.177 1.976 0.316 0.177 1.978 0.362 0.362 0.156 0.156 1.978 1.968 0.067 2.171 0.254 0.173 1.952 0.069 2.015 0.317 0.182 1.947 0.069 1.957 0.325 0.171 1.921 0.074 1.999 0.359 0.181 1.920 0.067 1.999 0.381 0.171 1.875 0.073 1.986 0.361 0.185 1.890 0.086 1.972 0.390 0.191 1.919 0.087 2.174 0.368 0.174 1.942 0.082 2.158 0.380 0.171 1.966 0.081 2.119 0.347 0.162 1.902 0.078 2.072 0.347 0.146 1.923 0.086 2.125 0.314 0.159 1.925 0.081 2.105 0.352 0.147 1.943 0.072 2.030 0.344 0.145 1.920 0.081 2.041 0.357 0.141 1.898 0.085 2.121 0.369 0.153 1.987 0.093 2.064 0.319 0.143 1.926 0.086 2.118 0.385 0.159 1.867 0.052 4.420 0.394 0.266 1.843 0.055 4.461 0.507 0.278 1.851 0.056 4.500 0.431 0.265 1.879 0.071 4.472 0.357 0.258 1.885 0.061 4.448 0.388 0.255 1.891 0.047 4.489 0.348 0.257 1.784 0.077 4.502 0.598 0.270 1.798 0.072 4.384 0.577 0.25 1 REFERENCES 1313. Hammarstrom J.M., and Zen, Zen7E-an, E-an71986, 1986?American American Mineralogist, Mineralogist?v. v. 71, 717p. p. 1297 1297-- 1313. Hamma.rstrom J.M., and Holm?D.K., D.K.? Holst, Holst, T.B., T.B., and and Lux, Lux7D.R., D.R., 1993, 1993?Canadian Canadian Journal Journal of of Earth EarthSciences, Sciences?v.v.30, 307p.p. Holm, 913-917. 9 13-917. 841. Johnson M.C., M.C.?and and Rutherford RutherfordM.J., M.J., 1989, 1989?Geology, Geology,v. v. 17, 17?p. p. 837 837-- 841. Johnson Schmidt? M.W.? 1992? Contributions to Mineralogy and Petrology7 v. 1lo7p. p. 304 304--310. 310. Schmidt, M.W., 1992, Contributions to Mineralogy and Petrology, v. 110, ., and McSwiggen? P.L., 198& Minnesota Geological Survey Southwick, D.L.? Morey, G.B Southwick, D.L., Morey, G.B., and McSwiggen, P.L., 1988, Minnesota Geological Survey Report of Investigations 37? scale 1:2507000. Report of Investigations 37, scale 1:250,000. 8 �Geochronology the 1.1 1.1 Ga North American Mid-Continent Geochronology of the Mid-Continent Rift D.W. Geology Dept., DepteIRoyal Royal Ontario Ontario Museum, Museum, Toronto, Torontol Ont., Onte1 D.W. Davisl Davis, Geology J. C. Greenl Geology Dept., Depts1Univ. Univ. of of Minn. Minn. Duluth, Duluthl Duluth, DuluthlMN, MNl Green, Geology M. Dept.# ROM, ROMl Toronto Toronto M. Manson# Manson, Geology Dept., Mid-Continent Rift Rift (MCR) The Mid-Continent (MCR) structure structure is is underlain underlain by by one one of the thickest crustal sections sections in in North North America America and and represents represents one one of of the the great great flood flood thickest crustal km3 of of basalt eruption of at at least least 1.5 1.5 million million km3 basalt provinces provinces of the world with eruption 1ava.The excellent much of of the igne0t.T~stratigraphy stratigraphy provides provides an an lava.The excellent preservation preservation 6f f much opportunity zircon geochronology and to opportunity to to test the resolving power of U-Pb zircon measure rates rates of of plume—driven plume-driven igneous igneous processes processes in the the Precambrian. Precambrian. Ages measure Ages discussed below are baddeleyite analyses discussed are based on on zircon zircon or baddeleyite analyses and are are given given with 95% confidence confidence errors. The The earliest earliest igneous igneous activity is is represented 95% represented by the the emplacement of +/- 11Ma)' ~a)'and and emplacement of alkaline alkaline plutons plutons such such as as the the Coldwell Coldwell complex complex(1108 (1108+/a syenodiorite within a syenodiorite within the the lower lower North North Shore Shore Volcanic Volcanic Group Group (NSVG, (NSVGI1107.0 1107.0 +/+/- 1.6 1.6 Ma); as well as as by the the emplacement emplacement of tholeiitic sills such such as the sills tholeiitic sills the Logan Logan sills +/- 0.6 0.6 Ma)3; ~ a ) ~and ; the the +4/-2 Ma)2 ~a)' and Nathan's Nathan's layered layered series series (1106.9 (1106.9 +1— (1109 +4/—2 eruption eruption of of felsic felsic lava lava in in the the Powder Powder Mill Mill group group (1107.5 (1107.5 +1— +/- 1.6 1.6 Ma), Ma) at at the the base base the Osler group group (1108 (1108 +41-2 +4/-2 Ma) Ma) and and in in the the lower lower part part of of the the NSVG NSVG (1108.0 (1108.0 of the +/-2.1 Ma). of these these units units are are paleomagnetically paleomagnetically reversed and appear to +/—2.1 Ma). All of represent an intense intense but short—lived short-lived episode episode of mantle mantle and and induced induced crustal crustal melting. AA significant significant time gap occurs occurs in in NSVG NSVG stratigraphy stratigraphy between between older older melting. paleomagnetically younger normal rocks. A sample sample from from the the Hovland paleomagnetically reversed and younger lavas collected collected near near the the top of of the the reversely reversely magnetized magnetized section section gives gives 1107.6 +/lavas 1107- 6 +/— 2.5 Ma, Ma, while while a sample sample from the Chicago Chicago Bay the 2.5 from the Bay lavas, l a v a ~near near ~ the base base of of the the normally normally magnetized section, gives gives 1100.5 1100.5 +/÷1- 1.9 1.9 Ma. Ma. This is followed followed by units aged aged magnetized 1097.9 +/1— 1.6 1.6 Ma, Mal 1098.1 +/-1.5 1.7 Ma Ma and and 1096.6 1096.6 ÷1— +/- 1.9 1.9 Ma Ma at at 1097.9 +/—l.5 Ma, Ma, 1098.5 +/1— 1.7 5 km. The The Duluth Duluth higher stratigraphic stratigraphic levels, comprising a thickness of about 5 layered gabbro complex was emplaced into the NSVG over a time span of at least 1099.3 +/1— 0.3 Lake 0.3 to to1098.6 1098.6 +1— +/- 0.5 0.5 Ma3.The ~ a ~ . T hPortage Portage e Lake Volcanics Volcanics (PLV) (PLV) comprise comprise 1099.3 structurally over 4 km of basalts and are faulted at the base but appear to be structurally above the the NSVG. Thick above Thick basalt basalt flows flows near near the the base base and and top top of of the the PLV PLV give give ages ages of of +1- 1.8 The PLV PLV is overlain by 1.8 Ma and and 1094.0 1094.0 +/+/- 1.5 1.5 Ma, MaI respectively4. respectively4. The 1096.2 +/sediments the Copper Copper Harbor Harbor Conglomerate sediments of the Conglomerate which which contain contain interlayered interlayered basaltic basaltic +/- 1.6 1.6 Ma4. Ma4. This This age age is is andesite flows, flowsI one of of which which gives gives an an age age of of 1087.2 1087.2 +1— coeval with emplacement of of a a felsic felsic porphyry on on Michipicoten Michipicoten Island Island at at 1086.5 1086.5 +1.3/—3.O and represents represents aa final the +I. 31-3.O Ma5 ~ a 'and final episode episode of of volcanism. volcanism. Thus, Thuslmagmatisxn magmatism in in the m.y. and appears to be MCR shows a total time span of slightly slightly more than 20 m.y. confined to three three main pulses, pulses, the the most most significant significant occupying occupying aa time time span span of of approximately approximately 77 m.y. m.y. Paleomagnetic studies of of MCR MCR rocks Paleomagnetic studies rocks have have furnished furnished the the most most reliable reliable apparent apparent polar polar wander wander curve curve for for the the Precambrian. Precambrian. Most Most sections sections show show aa single single R—N R-N polarity transition. polarity transition. The The age age of of this this reversal reversal is is constrained constrained between between the the 1100.5 1100.5 +1— +/- 1.9 Ma age age of of the the normally normally magnetized magnetized Chicago Chicago Bay Bay lavas lavas and and the the age age of of aa rhyo].ite sample from from Agate Agate Pointl Point, near near the the top top of the rhyolite sample the reversely reversely magnetized magnetized section of the the Osler Osler Group. Group. This section This age age was was formerly formerly reported reported as as 1098 1098 +1— +/- 44 Ma2 ~a'from from data data which had to to be be corrected corrected for for substantial substantial amounts amounts of of inheritance. inheritance. Recent Recent work small, apparently apparently inheritance-free inheritance—free zircon zircon fractions fractions gives a a preliminary preliminary work on smalll age age of of 1105 1105 +/— +/- 22 Ma. Ma. The within the The interpretation interpretation of of aa single single R-N transition transition within the MCR sequence sequence is is complicated the presence presence of of aa R-N-R—N R-N-R-N sequence sequence at at Mamainse Mamainse Point. Point. AA volcanic volcanic complicated by the from near near the the top unit top of the the lower reversed section section gives an age of 1096.2 1096.2 +/+1— unit from 1.9 Ma, implying a total 1.9 total of at at least least five five reversals reversals during during development development of of the the MCR. The Mamainse Point The Mamainse Point sequence sequence may may represent represent aa short short period period oscillation oscillation of of the the geomagnetic geomagnetic field field during during the the brief, briefl geochronologically geochronologically unresolved time time between between eruption +/- 33 Ma Ma from from eruption of of the the NSVG NSVG and and the the PLy. PLV. AA reversed reversed gabbro gabbro dated dated at at 1097.5 1097.5 +/— a drill in ~ a n s a smay ~ have The lower lower drill hole hole in Kansas6 may have also also been been emplaced emplaced during during this this period. The reversed section at Mamainse Mamainse Point Point shows shows aa coherent coherent geochemical geochemical and and isotopic isotopic that there there are are no significant age gaps gaps over over most most of this trend7,*implying implying that significant age this trend7'8 sequence. that the the reversed reversed paleomagnetic paleomagnetic poles poies determined determined from sequence. If If so, soI the fact that Mamainse Mamainse Point Point show show aa high high latitude latitude similar similar to to the the 1108 1108 Ma Ma poles poles implies implies that that at at least the early early part of of the the paleomagnetic paleomagnetic polar polar wander wander path path was was dominated dominated by by 9 �reversal reversal asymmetry asymmetry and there there may have been very little little continental continental drift. This This might explain explain why why plume—generated plume-generated volcanism9 volcanism9 in the the Lake Lake Superior Superior region region m.y. period when the degree of apparent persisted over a 20 20 m.y. apparent polar wander would suggest suggest a a continental continental drift drift of of several several thousand thousand kilometers. kilometers. '~eaman~ L.M. 'Heaman, L.M. and and Machador Machado, N. N. 1992. 1992. Timing Timing and origin origin of the Midcontinent Rift alkaline magmatismI North America: America: evidence evidence from from the the Coldwell Coldwell Complex. Complex. Contrib. Contrib. alkaline magmatism, North Mineral. Petrol. Petrol. 110: 110: 289—303. 289-303. '~avis~ SutcliffeI R.H. R.H. 1985. and 2Davis, D.W. D.W. and Sutcliffe, 1985. U-Pb U-Pb ages from the Nipigon plate and Am. Bull., Bull.I 96: 96: 1572—1579. 1572-1579. SOC. Am. northern Lake Lake Superior. Superior. Geol. Geol. Soc. northern 3Paces, J.B. -Mill-er, -'J.D. 3~acesI J.B.and and -MilkerI -3.D. -1993. 1993. - Precise .-U-Pbages -of of Duluth Precise-U—Pb Duluth Complex Complex and related mafic related maf ic intrusions, intrusionsI northeastern northeastern Minnesota: geochronological geochronological insights ins-ights to to physical, petrogenicI petrogenic, paleomagnetic tectonomagmatic processes with physicalI paleomagnetic and andtectonomagmatic processes associated associatedwith the 1,lGa the lIIGa Midcontinent Midcontinent Rift Rift system. system. J. J. Geophys. Geophys. Res. Res. 98: 98: 13997—14013. 13997-14013. 4Davis, D.W. D.W. and and Paces, Paces, J.B. J.B. 1990. 1990. Time Time resolution resolution of of geologic geologic events events on on the 4~avisI Keweenaw Peninsula and implications implications for for development development of of the the Midcontinent Midcontinent Rift Rift system. Earth Planet. Sci. Lett. Lett. 97: 97: 54—64. 54-64. Palmer, H.C. and U-Pb U-Pb geochronology geochronology of 'palmerI H.C. and and Davis, DavisI D.W. D.W. 1987. Paleomagrietism Paleomagnetism and of Island, Lake volcanic rocks from Michipicoten Superior, Canada: volcanic rocks Michipicoten IslandI Lake SuperiorI Canada: precise precise calibration of the Keweenawan Keweenawan polar calibration of the polar wander wander track. track. Precambrian Precambrian Res. Res. 37: 37: 157—171. 157-171. 6Van %an Schmus, SchmusI W.R. Tectonic setting of the 1992. 1992. Tectonic the Midcontinent Midcontinent Rift Rift System. System. Tectonophysics Tectonophysics 213: 213: 1—15. 1-15. 7K.W.Klewin and J.H.Berg J.H.Berg 1990. Geochemistry of the 7~.~.Klewinand the Mamainse Mamainse Point Point volcanics, volcanicsI Ontario, OntarioI and and their their implications implications for for the the Keweenawan Keweenawan paleomagnetic paleomagnetic record, recordI Can. Can. J.Earth Sci. 17: 17: 1194—1199. 1194-1199. 8Shirey, S.B., KlewinI Klewin, K.WSI K.W., Berg, Carison, R.W. 1994. *shireyI S.BeI BergI J.H. and and CarlsonI 1994. Temporal Temporal changes changes in the sources sources of flood flood basalts: Isotopic Isotopic and trace trace element element evidence evidence from from the the 1100 Ma old old Keweenawan Keweenawan Mamainse Mamainse Point Point Formation, FormationI Ontario, OntarioI Canada. Canada. Geochim. Geochim. Cosmochim. Acta Acta 58: 58: 4475—4490. 4475-4490. on the origin of the 9Cannon, W.F. and 9~annonIW.F. and Hinze, HinzeI W.J. W. J. 1992. 1992. Speculations on the North North American Midcontinent 213: 49—55. 49-55. American Midcontinent rift. rift. Tectonophysics Tectonophysics 213: 10 �DAVID BELL MINE MINE POSTER POSTER DISPLAY DISPLAY DESAUTELS, Pierre, Teck-Corona Operating Corporation, David David Bell Mine, P.O. Bag 11, 11, Marathon Marathon ON ON POT-2E0 POT-2E0 km east eastof ofMarathon, Marathon,Ontario Ontarioon onthe theTrans-Canada Trans-Canada Highway. Highway. The The mine mine lies lies The David Bell mine is is located located 35 35 km Belt and is jointly jointly own by Teck Corporation and Homestake Canada within the Schreiber-White River Greenstone Belt Ltd. f ~ sgold gold t pour took took place place Following the main ore zone discovery by consulting geologist David Bell in 1981, 1981, the first in May Since then, then, the mine has been May 1985 1985 after after two two years years of ofconstruction construction and and underground underground development. development. Since been in in continuous production production extracting extractingin inexcess excessof of2.0 2.0 million millionounces ouncesof ofgold. gold.Remaining Remainingreserves reservesasasofofDecember December31a, 3l', 1994 are estimated at 4.9 million million tonnes tonnes grading grading 10.85 10.85 grams grams per per tonne. tonne. The main ore group " A and and "D" "D" zone zone generally generally lies within within the the Moose Moose Lake Lake formation formation at the the group comprising comprising of the "A" contact between quartz feldspar porphyry rocks, often often in close porphyry and metasedimentary metasedimentary rocks, close relationship relationship with with a mafic mafic metavolcanjc unit. The lower "C" zone metavolcanic unit. zone lies lies within within the thelaminated laminated metasedimentary metasedimentary member member of the the Cache Cache Lake Lake formation. The ore horizons generally occur as tabular sheets striking at 102 102 degree and dipping between 50 and 61 degree north. Three workings and and in in the thedrill drillcore. core. Three distinct distinct ore ore characteristics characteristics were were observed observed in in the the underground underground workings The display plans, longitudinal projection of of the ore zones and aa typical display consists consists of of underground underground geology plans, longitudinal projection typical cross cross section. The sample collection includes a suite of representative representativemine samples samples and and drill drill core core specimens specimens covering covering the the ore horizons and and walirock wallrock lithologies. lithologies. 11 �IGNEOUS CHARACTERISTICS CHARACTERISTICSOF OF THE THE MATRIX TO THE FOOTWALL BRECCIA, NORTH IGNEOUS RANGE, RANGE, SUDBURY SUDBURYSTRUCTURE, STRUCTURE, CANADA CANADA 0.and andWatkinson, Watkinson,David DavidH., H., Department Department of of Earth Earth Sciences, Sciences,Ottawa-Carleton Ottawa-Carleton Everest, John 0. Everest, Geoscience Centre, Centre,Carleton Carleton University, University, Ottawa, Ottawa,Ontario, Ontario,Canada, Canada,Ki K1SS5B6; 5B6; Geoscience Farrow,Catherine., Catherine.,Ontario OntarioGeological GeologicalSurvey, Survey,Sudbury, Sudbury,Ontario, Ontario,Canada, Canada,P3E P3E6B6. 6B6. Farrow, Much Muchof ofthe theore orein inthe theNorth NorthRange Rangeof ofthe the1.85 1.85Ga GaSudbury SudburyStructure Structureisishosted hostedby by aa discontinuous discontinuous graniticunit unit knownas known asthe theFootwall FootwallBreccia. Breccia.Impact-generated Impact-generatedembayments embaymentshave haveprovided providedtopographical topographical granitic lows lowsfor forthe thecreation creationof ofaathickened thickenedheterolithologic heterolithologicbreccia brecciasequence sequenceoverlain overlainby by an an equally equally thickened thickened Sublayer unit. The Thexenoliths xenolithswithin withinthis thisbreccia brecciapile pileconsist consistof ofrandomly randomlyoriented, oriented,locally locallyderived derived Sublayer footwallgneisses gneissesas aswell wellas asexotic exoticclasts clastsof ofdiatexite, diatexite,diorite, diorite,gabbro, gabbro,pyroxenite, pyroxenite,anorthosite, anorthosite,diabase, diabase, footwall graniteand and Sudbury SudburyBreccia. Breccia. Depending Dependingon ontheir theirrefractory refractoryproperties, properties,these theseinclusions inclusionsmay mayhave havediffuse diffuse granite or sharp sharp contacts contactswith with the the matrix, matrix, and and may may be represented by a diverse range of sizes. Quite Quitefrequently frequently or these breccia breccia fragments fragmentsare areblanketed blanketedby byelongate elongatesulfide sulfideblebs, blebs,aatexture texturewhich whichmay mayhave haveformed formedduring during these the the initial initialmagma magmainjection. injection. The Thematrix matrixto tothese theseinclusions inclusionsisisaafine fine --to tomedium medium-- grained grainedgranitic graniticunit unit composed composeddominantly dominantly of ofgrains grainsof ofhornblende, hornblende,pyroxene pyroxeneand andlarge largeoptically opticallycontinuous continuousgrains grainsof ofpoikilitic poikiliticquartz quartzenclosing enclosing subhedral (Ano-.jo).Granophyric Granophyrictextures, textures, consisting consistingof of intergrowths intergrowthsof ofquartz quartzand and subhedralgrains grainsof ofplagioclase plagioclase(An050). fresh freshto to saussuritized saussuritizedalbite albiteare arevery verycommon, common,and andincrease increaseininabundance abundancetoward towardthe thecontact contactwith withthe the overlying overlyingnorite. norite. The Thematrix matrixisisalso alsoaamajor majorhost hosttotothe theNi-Cu-PGE Ni-Cu-PGEsulfides. sulfides.These Theseare arerepresented represented predominantly predominantlyby byblebs blebsofofpyrrhotite, pyrrhotite,chalcopyrite, chalcopyrite,pentlandite pentlanditeand andpyrite. pyrite.Characteristic Characteristicofofthe the mineralized breccia brecciaisisthe theincrease increaseininthe theoccurrence occurrenceof ofmafic maficminerals mineralswhich whichmay mayform formhalos halosaround aroundthe the mineralized sulfides. sulfides. Alteration Alterationof ofthe thematrix matrixby byinteraction interactionwith withformational formationalfluids fluidshas haslocally locallyproduced producedaamineral mineral assemblage quartz, calcic amphibole, biotite (XMgI(Mg+Fe) ==0.65), (XMg/(Mg+Fe) 0.65),chlorite chlorite (XMg/<Mg+Fe) 0.35-assemblageofofepidote, epidote, quartz, calcic amphibole, biotite (XMgI(Mg+Fe) ==0.35 0.5), 0.5),garnet, garnet, titanite, titanite,magnetite magnetite and and calcite calcite(Epidote (Epidote Zone, Zone, Fraser Mine). Fluid Fluidinclusion inclusionstudies studieshave have shown shownthat thatthese thesefluids, fluids,which whichwere weredriven drivenby bythe theheat heatof ofthe thecooling coolingSudbury SudburyIgneous IgneousComplex, Complex,formed formed this alteration assemblage and remobilized Cu, Ni, PGE, Au, Ag especially, at temperatures between this alteration assemblage and remobilized Cu, Ni, PGE, Au, Ag especially, at temperatures between210 210 and OC. and400 400°C. Petrographic albite(Ano) (Ano)patches patches and and veins veins with withcentrally centrally Petrographicstudy studyreveals revealsthe thepresence presenceof ofquartz quartz--albite located chloritefilled filledcavities. cavities.Quartz Quartzininthe thelatter lattercontains containsabundant abundant fluid fluid inclusions. inclusions. Locally, Locally, locatedquartz quartz--chlorite original originalalbite albitemineralization mineralizationwithin withinthe thegranophyric granophyricveinlets veinletshas hasbeen beenreplaced replacedby byaapink pinkpotassic potassic feldspar feldspar(orthoclase). (orthoclase). Themineralogy mineralogyand andtextures texturesthat thathave havebeen beenobserved observedindicate indicatethat thatthe theFootwall (1) FootwallBreccia Brecciawas was(1) The formed formedby by aamagmatic magmaticprocess processinvolving involvingassimilation assimilationof offootwall footwallrock, rock,and and(2) (2)subsequently subsequentlyaltered alteredby by hydrothermal hydrothermalfluids fluidsrelated relatedtotothe thecooling coolingSudbury SudburyIgneous IgneousComplex. Complex. 12 �VESICLES AND AND BRECCIA BRECCIA DUE DUE TO TO INJECTION INJECTION OF OF MAFIC MAFIC MAGMA INTO INTO VESICLES PARTIALLY LITHIFIED SEDIMENTS OF THE EARLY PROTEROZOIC IRONWOOD PARTIALLY LITHIFIED SEDIMENTS OF THE EARLY PROTEROZOIC IRONWOOD IRON-FORMATION, WESTERN WESTERN GOGEBIC GOGEBIC RANGE, RANGE, NW NW WISCONSIN WISCONSIN IRON-FORMATION, LEEANN FEHER, FEHER, Geology Geology Dept., Dept., St. St. Norbert Norbert College, College, DePere, DePere, LEEANN Wisconsin. Wisconsin. Tim Flood, Flood, Geology Geology Dept., Dept., St. St. Norbert Norbert College, College, DePere, DePere, Wisconsin. Wisconsin. Tim Detailed mapping mapping and and petrographic petrographic analysis analysis of of ironiron- and and Detailed silica-rich argillites argillites of of the the Ironwood Ironwood Iron-Formation Iron-Formationand and silica-rich associated mafic mafic and and felsic felsic intrusions intrusions was was undertaken undertaken in in the the associated Western Gogebic Gogebic Range Range near near Atkins Atkins Lake, Lake, Wisconsin. Wisconsin. The The purpose purpose Western of the the study study was was to to determine determine the the nature, nature, origin, origin, and and of relationships of of these these rocks. rocks. In In particular, particular, we we focused focused on on the the relationships The contact between between the the argillites argillites and and aa sill-like sill-likemafic mafic body. body. The contact contacts are are marked marked by by breccia breccia zones zones that that contain contain local local areas areas of of contacts argillite clasts clasts in in vesiculated vesiculatedbasalt basaltmatrix. matrix. argillite In places places the the In breccia resembles resembles aa peperite. peperite. breccia The study study area area is is approximately approximately 500 500 meters meters by by 500 500 meters meters and and The was mapped mapped at at aa scale scale of of 1:1000. 1:1000. The The rocks rocks trend trend approximately approximately was N70° and and have have an an average averagedip dipof of50°NW. 50°NW The The argillite argillite is is thinly thinly N70°E 45 meters. meters. bedded to to laminated laminated and and has has aa minimum minimum thickness thickness of of 45 bedded Concordant with with the the argillite argillite is is aa mafic mafic body body that that has has aa finefineConcordant grained diabasic diabasic to to medium-grained medium-grainedgabbroic gabbroic texture. texture. This Thismaf mafic grained Ic unit is is approximately approximately 50 50 meters meters thick. thick. The The contacts contacts between between the the unit argillite and and the the mafic mafic rocks rocks are are characterized characterized by by breccia breccia zones zones argillite up to to 20 20 meters meters thick. thick. The The breccia breccia consists consists of of angular angular to to up subangular, tabular tabular clasts clasts of of argillite argillite up up to to 11 meter meter In in subangular, diameter, some some of of which which are are bent. bent. Most Most of of the the clasts clasts are are silicasilicadiameter, rich, but but iron-rich iron-richclasts clasts have have been been observed. observed. Garnets Garnets up up to to 55 rich, 13 �mm in in diameter diameter are are common common and and unique unique to to the the breccia breccia zone. zone. mm Locally, lodestone lodestone occurs occurs in in the the iron-rich iron-richargillite argillite at at the the Locally, meter wide wide contact with with the thebreccia. breccia. Granitic Granitic dikes dikes up up to to 11 meter contact These granites granites are are intrude both both the the mafics mafics and andargillites. argillites. These intrude medium- to to fine-grained fine-grainedwith with chilled chilled margins. margins. medium22 thin thin sections sections Petrographic analysis analysis was was performed performed on on 22 Petrographic which included included textural texturaldescriptions descriptionsand and 500 500point point counts counts per per which The argillite argillite is is composed composed of of alternating alternating layers layersof of section. The section. fine-grainedmagnetite, magnetite, fine-grained fine-grainedbiotite biotite or or actinolite, actinolite,and and fine-grained The mafic mafic rock rock is is composed composed primarily primarily of of recrystallized quartz. quartz. The recrystallized medium-grainedamphiboles amphiboleswith with included included plagioclase plagioclaselathes, lathes, medium-grained probably aa relict relict ophitic ophitic texture. texture. Magnetite Magnetite is is common. common. probably Preliminary geochemical geochemical data data indicates indicatesaa tholeiitic tholeiitic composition. composition. Preliminary The breccia breccia consists consistsof of clasts claststhat that are are composed composedof of The recrystallized quartz quartz plus plus chlorite, chlorite, or or biotite biotite plus plus garnet garnet in in aa recrystallized basaltic matrix matrix that that is islocally locallyvesiculated. vesiculated. Vesicles Vesicles are are basaltic infilled with with chlorite, chlorite,with with or orwithout withoutquartz. quartz. Some Some vesicles vesicles infilled are composed composed of of quartz quartzwith withchlorite chloritecores. cores. The The granite granite is is are composed of of mediummedium- to to fine-grained fine-grainedpotassium potassium feldspar, feldspar,quartz, quartz, composed plagioclase,and and minor minor amounts amountsof of biotite. biotite. plagioclase, infer that that the the argillites argillites were were deposited deposited as as aa sequence sequenceof of We infer We thin, alternating alternating iron-rich iron-richand and silica-rich silica-richlayers. layers. The The sillsillthin, like mafic mafic body body intruded intruded into into these these water-rich water-richsediments sediments while while like Intrusion of the mafic magma lithified. they were wereonly onlypartially partiallylithif they led. Intrusion of the maf Ic magma into the the water-rich water-richsediments sediments resulted resulted in in the the formation formationof of the the into breccia, i.e. i.e.peperite. peperite. The The matrix matrix of of the the breccia breccia is is locally locally breccia, vesiculated due due to to interaction interaction of of the the mafic mafic magma magma with with water water vesiculated 14 �derived from from the the sediments. sediments. We We suggest suggest that that the the breccia breccia is is not not derived the result result of of aa mafic mafic lava lava flowing flowing onto onto or or into into unconsolidated unconsolidated the sediments because because of: of: 1) 1) development development of of aa medium-grained medium-grained gabbroic gabbroic sediments 2) capture capture of of angular, angular, texture in in the the interior interiorof ofthe themaf mafic body, 2) texture Ic body, 3) formation formation bent and and tabular tabular xenoliths xenoliths in in the the breccia breccia zone, zone, and and 3) bent of vesicles vesicles at at the the top top and and bottom bottomcontacts contactsof ofthe themaf mafic body with with of Ic body the breccia. breccia. Garnets Garnets only only occur occur in in the the breccia breccia zones zones and and most most the likely formed formed by by contact contact metamorphism metamorphism caused caused by by intrusion intrusion of of the the likely mafic sill. sill. mafic Significantly, emplacement emplacement of of the the mafic mafic magma magma into into partially partially Significantly, lithified igneous activity activity lithif led sediments sediments does does imply imply contemporaneous contemporaneous igneous and deposition deposition of of the the Ironwood Ironwood Iron-formation Iron-formation on on the the western western end end and of the the Gogebic Gogebic Range. Range. The The maf mafic now occurs occurs as as of Ic material material now metadiabase and and metagabbro, metagabbro, the the result result of of later later low-grade low-grade metadlabase metamorphism. Granitic Granitic dikes dikes that that intrude intrude concordantly concordantly to to metamorphism. discordantly into into the the mafic mafic and and argillitic argillitic rocks rocks have have chilled chilled discordantly margins and and lack lack metamorphic metamorphic features. features. In In addition, addition, the the margins surrounding country country rock rock does does not not appear appear to to have have been been contact contact surrounding metamorphosed by by the the granitic granitic intrusions. intrusions. We We infer infer that that these these metamorphosed emplaced after after cooling cooling of of the the mafic mafic sill sill and and the the dikes were were emplaced dikes argillites, and and are are likely likely related related to to nearby nearby Middle Middle Proterozoic Proterozoic argillites, granitic rocks. rocks. granitic 15 �Neoarchean Transubprovince Depositional Systems: Temporal vrs vrs Spacial Variability Systems: Temporal Variability in Province. Fralick, Western Superior Province. Fralick, P.W., P.W., and and Purdon, Purdon, R., R., Department Departmentof of Geology, Geology, University, Thunder Thunder Bay, Bay, Ontario, Ontario, P7B P7B 5E1. 5E1. Lakehead University, With the growing acceptance that plate tectonic tectonic processes similar to those operating operating the amalgamation amalgamation of of Superior Superior Province Province during the Late Late Archean Archean comes comes the the today led to the sequence stratigraphy stratigraphy techniques to analyze analyze tectonic control control of of basin basin opportunity to use sequence formation. formation. Application Applicationof ofthis thistechnique techniqueand andchemostratigraphy chemostratigraphyto tofour foursedimentary sedimentarybasins basins Wawa Subprovinces Subprovinces of of northwestern in the theWabigoon, Wabigoon, Quetico Quetico- and Wawa northwestern Ontario Ontario adds adds significantly to the the tectonic interpretation interpretation of significantly to of this this region. region. The Beardmore-Geraldton forearc basin, basin, located located in in the the southern southern Wabigoon Wabigoon Beardmore-Geraldton forearc Subprovince, and the Quetico Queticotrench trenchformed formedaayoked yokedsystem, system,with withvolcaniclastic volcaniclastic sediment sediment feed from the north north (see (seeEriksson Eriksson et etal, al,1994, 1994,and and references references therein). therein). Braided fluvial fluvial channels delivered delivered detritus detritus to to fan fan and and braid braid deltas, deltas, which in turn rerouted rerouted itit to to the theseafloor, seafloor, building sequence in forearc basin basin and and building aa submarine submarine fanlramp fan/ramp sequence in the distal portion of the forearc trench. Sediment Sedimentgeochemistry geochemistryof of the theforearc-trench forearc-trenchassemblage assemblageisisextremely extremely consistent, consistent, implying that a similar source terrain existed laterally for 300 kilometres, or a single area implying that provided most of the element ratios indicate that aacaic-alkaline provided most the sediment. sediment. Immobile Immobile element calc-alkaline extrusive-intrusive the extrusive-intrusivesuite suitepresent present in in the the Onaman-Tashota Terrane Terrane supplied sediment to the forearc and the portion portion of of the the trench trench to to its itssouth. south. Immobile Immobile element ratios and zircon zircon geochronology further further indicate that the volcanicthe western western trench trenchreceived received sediment sedimentfrom fromaavolcaniccratonic area to its its north. This Thisimplies impliesthat thatgeochemistry geochemistryof of the the arc arcsystem system was consistent from the continental arc in the west to the the eastern easternoceanic? oceanic? arc. arc. The sedimentary of an interarc interarc basin, present present in in the the Wawa Wawa Subprovince Subprovince sedimentary geochemistry of Terrace Bay, is very very similar similarto to the the Quetico Quetico trench. trench. This east of Terrace This basin basin is is dominated dominated by by distal distal submarine ramp turbidites, while the Quetico to the the north northisiscomposed composedof of proximal proximal ramp ramp turbidites. These turbidites. These data data imply imply that that the thedepositional depositionalsystem system overwhelmed overwhelmed the trench, trench, overflowed onto onto the the ocean floor and flooded into an interarc setting. setting. overflowed an interarc The fourth basin examined examined is in an intermontane intermontane setting setting within the Onaman-Tashota Onaman-Tashota Arc Terrane. It was filled by a mostly mostly subaqueous fan delta system system with local sources of variable composition supplying the detritus. Sediment supplying the Sedimentgeochemistry geochemistry confirms the variable nature of the source present in the area were source terrane terrane and and indicates indicates large granitic batholiths present intermontane basin the major contributors. The Thedifference difference in in sediment sediment source between the intermontane and other basins to to the south can only be be interpreted as as aa change change in in basin basin type type other synvolcanic synvolcanic basins through time reflecting cessation of volcanism volcanism in in the the area area and emplacement and unroofing emplacement and of later-stage later-stage batholiths. The Thebasin basin may may have been produced produced as a result of transpression but this conclusion awaits further structural structural studies. studies. FIGURE geologyofof portions portions of of the FIGURE 1: 1: Regional Regional geology the Wabigoon, Wabigoon, Quetico Quetico and and Wawa Wawa refer to areas Subprovinces, northwestern Ontario. Subprovinces, northwestern Ontario. Numbers Numbers refer areas samples samples for for sediment sediment geochemistry (Table). (Table). TABLE: Sediment geochemistry geochemistry of the areas areas indicated on Figure 1. 1. 16 �1 1 Wabigoon Forearc Forearc nn=7 = 7 Si02 Ti02 A1203 Fe203 MnO MgO CaO Na20 K20 P205 64.1 .54 15.4 530 .09 2.73 3.06 3.77 2.08 .14 22 Quetico Trench Trench 3 Quetico Quetico Trench Trench n=5 n =5 44 Quetico Quetico Trench n=1O n = 10 64.0 64.7 .56 15.4 6.60 .09 2.76 2.77 3.49 2.36 .17 64.4 .58 n=8 n = 8 36 152 5.77 .10 3.07 2.81 3.93 1.68 .15 152 6.06 .07 2.92 3.46 3.34 2.10 .14 55 Quetico Quetico Tench Tench n=14 n=14 64.1 .50 15.1 5.64 .12 231 3.80 3.32 2.16 .14 Ba Co Cr Cu Mo Nb Pb Rb 560 24 530 24 640 - - 21 106 35 1.1 170 48 1.1 5.9 94 73 175 142 119 - 38 50 Se Sr V Y 350 Zn Zr 5.2 85 68 274 89 10 61 103 350 390 97 540 - 6 15 83 66 620 7 6 Wawa Wabigoon Wabigoon Interarc Interarc Intermontane Intermontane n=6 nn=11 =ll n = 6 64.0 .58 153 5.23 .09 3.00 3.40 3.72 1.95 .19 6.0 26 57 - 369 - 300 94 13 13 78 127 lOi 14 78 138 3.56 2.44 .08 48 - 78 142 .05 .79 1.27 5.9 461 10 3.03 3.2 - 59 103 .32 14.8 550 340 108 16 71.8 1 and 2 - Fralick 1986; 4 -- Williams, 1 Fralick and Barrett, 1991; 1991; 3 -- Sawyer, Williams, 1978; 1978; Sawyer, 1986; 5 -- Stone Aniukun, 1980. Stone et aL, al., 1992; 1992; 6 -- Purdon, Purdon, in progress; 7 -- Amukun, 1980. 17 �CENTRAL CENTRAL MINNESOTA, U.S.A. U.S.A. CORE CORE LOGGING LOGGING AND AND ASSAY ASSAY DATABASES DATABASES Frey, Frey, Barry Barry A., A., Minnesota Dept. Dept. of of Natural Natural Resources, Resources, Minnesota Minerals Division, Division, P.O. P.O. Box Box 567, 567, Hibbing, Hibbing, Mn. Mn. 55746 55746 Minerals This work work includes includes the the relogging relogging and and assaying assaying of of existing existing DNR DNR Drill Drill Core Core Library Library This samples. planning and samples. The The purpose purpose is is to to provide provide data data for for land land use use planning and other other geologic geologic needs needs such such as as mineral mineral exploration. exploration. total of of 1241 1241 sample sample sets sets representing representing samples samples from from aa total total of of 850 850 drill drill AA total holes completion of of this thispoject, holes will will be logged at the completion project,and andapproximately approximately1500 1500 samples samples will will be be analyzed. analyzed. Many Many of of these these drill drill samples samples have have not not previously previously been been included on on the the DNR DNR Drill Drill Core Core Library Library Index Index (DCLI) (DCLI)(Ruhanen (Ruhanenand and Dzuck, Dzuck,1994). 1994). included Available historical historical information information has has filled filled many many previous previous data data voids voids for for drill drill Available samples samples previously previouslyon on the the DCLI. DCLI. The The DNR DNR Minerals InformationServices Services Minerals Management Management Information continues to to revise revise old old data data and and incorporate incorporate new new data data into into its its ever ever improving improving continues DCLI. DCLI Drill samples samples encountered encountered include include Proterozoic Proterozoic and and Archean Archean rocks, rocks, with with Drill scattered scattered Paleozoic, Paleozoic, Mesozoic, Mesozoic, lateritic lateritic weathering weathering products, products, and and glacial glacial materials, materials. Of Of the the lithologies lithologies encountered, encountered, the the iron iron formation formation(Proterozoic (Proterozoic Algoman Algoman type?) type?) related related rocks rocks (including (includingmetavolcanic metavolcanic schists) schists) are are typically typically deformed, deformed, metamorphosed metamorphosed (typically (typically low low grade), grade), altered, altered, and and recrystallized. recrystallized. Other Other rocks rocks include include gneiss, gneiss, Keweenawan Keweenawanrift rift material, material,and and some someschists schiststhat thatmay may represent the the continuation continuationof of the the Wisconsin Wisconsin Volcanic Volcanic Terrane Terrane that that hosts hosts Cu—Zn—Au Cu-Zn-Au represent deposits. deposits. Results for for the the 1300 1300 analyzed analyzed samples samples have have been been received received from from Bondar—Clegg Bondar-Clegg Results && Company Company Ltd. Ltd. of of Ottawa, Ottawa,Ontario. Ontario. Besides Besides being being (in (ingeneral) general) anomalously anomalously high high in in Mn Mn and and Fe, Fe, samples samples also also had had anomalous anomalous Ba, Ba, As, As, Hg, Hg, F, F, Li, Li, Nb, Nb, Zr, Zr, and and rare rare earths. earths. In In general general samples sampleswith withhigher higherTi02 Ti02also alsohad hadhigher higher1(20 K20 and and Al203. A1203. K-1 in in T47N T47N R2OW R20W Sec Sec Anomalous Zn Zn values values (with (withvisible visiblesphalerite) sphalerite)include includeDD}1 DDH K—i Anomalous 22 22 with with aa 5' 5' sample sample containing containing 2.25% 2.25% Zn. Zn. This This occurred occurred in in deformed deformed graphitic graphitic sulphide sulphide phyllite phyllite with with minor minor chloritic chloritic sericitic sericitic metatuff. metatuff. Drilling Drilling at at the the Arrowhead Arrowhead Mine Mine (graphite) (graphite) in in T48N T48N R18W R18W Sec Sec 32 32 produced produced brecciated brecciated graphitic graphitic sulfide sulfide schist schist samples sampleswith with several severalZn Zn values values over over 1300 1300ppm pprn (high 1916 ppm). pprn). (highof of 1916 Samples from from several several drill drill holes holes in in T43N T43N R32W R32W Sec Sec 12 12 had had anomalous anomalous base base and and Samples precious Perhaps the the most most interesting interesting values values came came from from drill drill hole hole 109. 109. precious metals. metals. Perhaps This 5' 5' sample sample contained contained 1383 1383 ppb ppb Au, Au, 1339 1339 ppb ppb Pd, Pd, 1156 1156 ppb ppb Pt, Pt, and and 1343 1343 ppm pprn Zn. Zn. This Another 2.3 ppm pprnAu. Au. Samples Samples (one (oneof of carbonate, carbonate, magnetite, magnetite, Another drill drillsample samplecontained contained2.3 silicate iron iron formation) formation) from from two two other other drill drill holes holes in in this this area area had had Cu Cu values values silicate of 1791 and and 1200 1200 ppm pprn respectively. respectively. In In T46N T46N R29W R29W Sec Sec 9, 9, DDH DDH 310 310 contained contained aa of 1791 sample with with chert(?), chert(?), hematite, hematite, quartzite(?) quartzite(?) iron iron formation formation with with aa Cu Cu value value of of sample 1622 1622 ppm, ppm, and and an an adjacent adjacent chert, chert, goethite, goethite, hematite, hematite, Mn Mn oxide(?) oxide(?) iron iron formation formation sample The highest highest As As value value was was 1362 1362 ppm pprn sample with with the the highest highest Li Li value value (1145 (1145ppm). pprn). The in tuffaceous tuffaceous carbonate, carbonate, chert, chert, goethite, goethite, magnetite, magnetite, red red hematite, hematite, silicate, silicate, in 280, located located in inT46N T46N R29W R29W Sec Sec sulfide iron iron formation formation (with (withtourmaline?) tourmaline?)in in DDH DDH 280, sulfide 2. The analyses analyses above above without without lithologies lithologiesindicate indicatethat thatthey theycame camefrom frompowdered powdered 2. The samples samples without without identifiable identifiablerock rockfragments. fragments. Pending Pending XRD XRD work work may may provide provide some some answers. =\Other locations locationsalso also contained contained anomalous anomaloussamples. samples. answers. =\Other The data data indicates indicates that that hydrothermal hydrothermal processes processes were were active active within within the the study study The area, area, and and that that there there may may be bea ahigh highprobability probabilityfor forundiscovered undiscovered economic economic mineralization. mineralization. Reconnaissancedrill drill core corelogging logginginformation informationhas has been been created createdand and stored stored Reconnaissance as This includes includesbasic basic information information about about rock rock types, types,alteration, as digital digitalfiles. files. This alteration, and Each database databaserecord record corresponds correspondsto to aa unique unique drill drill hole hole and and and mineralization. mineralization. Each footage footage interval. interval. A A separate separate"comments" "comments" database database contains contains aa brief brief synopsis synopsisof of each each drill drill hole hole and and notes notes on onunusual unusualfeatures. features. Other Other "related" "related" data data files files include include the theDCLI, DCLI, chemical chemical analyses, analyses,sample sample information, information,and andcore coregeophysical geophysical measurements. Combined, measurements. Combined, these these databases databases form form an an abundance abundance of of available available information information for forpossible possiblesynthesis synthesisby by users. users. The "constructed"using using aa data data manipulation manipulation system system The logging logging databases databases were were "constructed" called called WATFILE/Plus WATFILE/Plusand andSoftware SoftwareCarousel. Carousel. This This allowed allowed six six databases databasesto tobe be open open at at one one time, time, and and still still allow allow for for very very rapid rapid database database switching, switching, queries, queries, data data entry, entry, and and editing. editing. The The six six databases databases consist consist of of aa geographic geographic portion portion of of the the . 18 �DCLI, database, the lithologic code DCLI, the the logging logging database, database, the the logging logging comments comments database, code database, the alteration alteration code code database, database, and and the the database database containing containing sampling sampling information. While information. While not not being being truly truly "relational", "relational", the WATFILE the individual WATFILE databases databases were constructed constructed with the the common common fields fields necessary necessary for for linking linking after after importing importing into into aa relational relational database. database. The methodologies for utilization will will be dependent dependent upon upon The methodologies for data data synthesis synthesis and utilization hardware and hardware and software software limitations, limitations, and and the the ingenuity ingenuity of of the the user. user. One hope for for One hope a future future product product will be aa Paradox Paradox run—time run-time module that will make the the data data useable to to those those who-do who-do not not have have their .their own awn database database software. "software. Such Such "module" "module" users users should should be aware, aware, however, however, that that any packaged data queries will be limited to to those those of of the the developer's developer's preconceived preconceived notions. notions. Usage of this this data data can can make make geologic visits to to the the Drill Drill Core Core Library Library more more efficient. efficient. The The database database also also allows preliminary work allows preliminary work to to be be done done BEFORE BEFORE aa visit. visit. As database "development", this database database As in in any database "development", certain certain ideas ideas were were used used in in this formulation: formulation: 1) 1) TRY to convey to the the users users HOW HOW it was was put put together together and what what its its limitations limitations are; are; 2) TRY to be consistent consistent in in application application and and usage; usage; 3) 3) Create Create the data to support support anticipated anticipated queries; the queries; 4) 4) Convey uncertainty uncertainty as possible as best possible when it Lithology, alteration, and mineralization it exists; exists; 5) mineralization searches searches and and 5) Lithology, queries are are to make queries make use use of of text text string string matches; matches; 6) cognizant of the the 6) Be cognizant importance proper spelling as quantitative quantitative 7) Be Be as importance of of proper spelling and and spelling spelling variations; variations; and and 7) as possible possible within within the the context context of of the the data data structure. structure. THE THE MOST IMPORTANT IMPORTANT IDEA IDEA TO LET LET THE THE USER USER MAKE MAKE THE MOST MOST EFFICIENT EFFICIENT USE THE DATA. TO MAKE MAKE THE THE MOST MOST IS TO USE OF THE . TO OF THE DATA DATA WITHOUT WITHOUT BEING BEING LED LED ASTRAY! ASTRAY! certain concepts should be As in the the "utilization" "utilization" of of ANY ANY database, database, certain embraced; 1) Become familiar with the embraced; 1) the actual actual data, data, to to see see how how it it was was used, used, to to see possible, see how well it actually represents that see its its limitations, limitations, and if possible, which it queries that are supported supported by the the data; data; which it supposedly supposedly describes; describes; 2) Make queries 3) 3) In the case case of of descriptive descriptive data, be aware aware that that there there may may be be alternative alternative with similar meaning that should be included in making data queries; language with queries; 4) 4) Be cognizant cognizant of the specificity of your queries relative to the specificity of your data; data; and and 5) 5) Queries Queries done done on on the the "logging" "logging" database database should should also also be be done done on on the the "comments" "comments" database. database. samples exist from the study study area area of of An additional 2600 sets of drill samples Central Minnesota Minnesota and have These represent have not not been been logged. logged. represent samples samples from from approximately these samples 1600 drill drill holes. holes. Many of these samples are are drill drill core. core. Most of of approximately 1600 these samples these samples were were originally originally drilled drilled in in the the search search for for iron iron and and manganese manganese in in the the Cuyuna A lesser lesser number number Cuyuna Iron Iron Range Range area area during during the the first first half half of of this this century. century. of samples samples were drilled drilled for for base base metal, metal, uranium, uranium, precious metal, or diamond diamond drilled for or exploration. Additional samples samples were exploration. Additional were drilled for regional regional geologic geologic or engineering information. engineering information. with the data This work will 1995, with will be be published published in in July, July, 1995, data available available digitally in in a variety variety of of formats. formats. .. . The State State of of Minnesota Minnesota and and the the Department Department of Natural Natural Resources Resources neither endorse endorse products products or or services services listed listed nor nor accept accept any any liability liability arising arising from from the the use use products or of products or services services listed. listed. WATFILE WATFILE/Plus are are registered registered trademarks trademarks of of WATCOM WATCOM Systems Systems Inc. Inc. WATFILE and and WATFILE/Plus and WATCOM Publications Publications Ltd. Ltd. Software Carousel Software Carousel is is aa registered registered trademark trademark of of Softlogic Softlogic Solutions, Solutions,Inc. Inc. Paradox is Paradox is aa registered registered trademark trademark of of Borland Borland International, International, Inc. Inc. Index: Ruhanen, R. Dzuck, A., W., and and Dzuck, A., 1994, 1994, 1994 1994 Drill Drill Core Core Library Library Index: Ruhanen, R. Minnesota Minerals Division, Division,218 218 pages. pages. Minnesota Department Department of of Natural Natural Resources, Resources, Minerals 19 �CURRENT INVENTORY INVENTORY OF OFMICHIGAN'S MICHIGAN'S GEOLOGICAL GEOLOGICAL CORE AND SAMPLE REPOSITORY AT MARQUETTE MARQUETTE Milton Milton A. A. Gere, Gere, Jr., Jr., Regional RegionalGeologist Geologist William T. Swenor, William Swenor, Geological Geological Technician Technician Geological Survey Division, Division, Michigan DNR, Region I, Marquette, Marquette, Ml MI Survey Division Division (GSD) (GSD)of of the the Michigan Michigan Department Department of of Natural Resources Resources (DNR) (DNR) maintains maintains the The Geological Survey Geological This "Rock "Rock Library" Library" collection collectionof of core, core, cuttings cuttings Geological Core Core and and Sample Repository Repositoryat at Marquette, Marquette, Michigan. Michigan. This currently represents represents62 62of ofthe the83 83 counties countiesininthe the state. state. The materials are available for study to help and samples currently understand mineral resource resource potential potential of of the the state. state. understand the geology and mineral The collection continues to are submitted submitted to to grow grow in in an an effort to tobetter better represent representthe the geology geologyof ofthe thestate. state. Materials are the Repository Repository from a number number of sources: sources: 1) state metallic metallic and nonmetallic mineral leases; 2) various state sponsored projects; projects; 3) 3) company company donations; donations; 4) 4) other other state state and and federal federal government government agencies, agencies, such such as as the the U.S. U.S. Bureau Bureau of Mines. Since January January 1994, 1994, cuttings cuttings from from all all selected selected new new oil oil and and gas gas wells wells drilled drilled in Michigan have been sent to the the Repository. These Repository. These cuttings cuttings account for much of the material material currently currently being received. The most significant recent recent addition was was the early release release of of confidentiality of of the the deepest deepest all-cored all-cored Mineral Mineral Well in March, 1995. the confidentiality confidentiality on the core, well logs and file 1995. AJvIOCO AMOCO Production Company released the file data data for for their St. Amour #1-29 #1-29 and #1-29R #1-29R test test holes. holes. The #1-29R is a 7,238 foot hole hole that that was was drilled drilled in in late 1987 to learn more about the Midcontinent of Munising, Munising, near near Wetmore, Wetmore, in in Alger County in the MidcontinentRift. Rift. It was located southeast southeast of Upper Peninsula. Peninsula. The hole went through 110 110 feet of glacial glacial drift drift and and entered entered bedrock bedrock in in the thePaleozoic Paleozoicaged aged Autrain Autrain Formation Formation of Ordovician Ordovician time. time. The hole hole ended ended in inPrecambrian Precambrian aged aged Portage Portage Lake Lake Volcanics Volcanics of of Keweenawan time. time. This This core core should shouldbe be of of interest interestto to geologists geologistsfrom fromacademia, academia,the theoil oiland and gas gas industry, industry, and the Keweenawan mineral exploration exploration industiy. industry. On March 31, 1995, contained 766 complete complete drill drill hole cores totaling 246,679 feet; drill 1995, the Repository collection contained cuttings from 440 holes representing representing 491,735 feet of drilling, drilling, 424 424 holes holes represented represented by by abbreviated abbreviatedcore corefrom from 131,380 feet of of drilling, drilling, 2,229 feet of represented represented overburden overburden drilling, drilling, and many boxes of miscellaneous materials 13 1,380 feet This gives total of 1,685 (chip samples, samples, soils, outcrop outcrop samples, samples, assay assay pulps, pulps, etc.). etc.). This gives a collection collection total 1,685 drill drill holes holes representing representing872,023 872,023 feet (165 (165 miles) miles) of of drilling drilling plus plus numerous numerousboxes boxes of of miscellaneous miscellaneous materials. materials. The GSD's Metallic Mine Map and Data Collection is also also stored stored at at the the Repository. Repository. This collection also helps helps in Collection is the understanding being an aid to public understanding of the geology and mineral resource potential of the state, as well as being public safety safety and land use planning. ItItisisaarecord recordof ofpotential potentialmine minesubsidence subsidenceareas areas of of the the state statewhich whichshould shouldbe be avoided avoided when when construction is planned. planned. The Repository is open for for visitors visitors by byappointment appointmentto to study studythe thecontents. contents. Some sampling sampling and and loans loans of of material materialcan can be arranged for on a case-by-case case-by-casebasis. basis. Copies of of data derived derived from from the the use use of of the the collections are are to to be be submitted to be made part of the public record record for for future future use. use. For For information information or an an appointment, appointment, call Bill Swenor Swenor or Milt Gere at 906-228-6561. 906-228-6561. oil and and gas gas well well logs logs and and thousands thousands of of selected selected well well cuttings cuttings for oil oil and and gas gaswells wells The GSD also maintains all oil drilled prior to 1994 in in Lansing. Water Water well well records records for the entire state are kept in Lansing by the GSD, too. Call Call 517-334-6907 for for information. information. Copies of all Upper Peninsula, Region I, water well records and well cuttings from Office near Escanaba. Escanaba. Call Frank 610 selected water water wells wells are are maintained maintained by by the the GSD GSD at at the DNR's District 33 Office 906-786-2351 for more information. information. Chenier at 906-786-2351 20 �GEOLOGY OF THE THE NORTH NORTH SHORE SHORE STATE STATE PARKS PARKS GREEN, Geology GREEN, John C., C., Geology Department, Department, 211 211 Heller Heller Hall, Hall, University University of of Minnesota Minnesota Duluth, Duluth, Duluth, Duluth, MN MN 55812 55812 The bedrock geology of of the the nine North The bedrock geology nine State State Parks Parks along along Minnesota's Minnesota's North Shore of Lake Lake Superior Superior has been mapped, with funding funding from the the MN Shore Department of of Natural Natural Resources. Resources. Recent mapping by by the the author author augments earlier earlier work work published published by by the Survey. augments the Minnesota Minnesota Geological Geological Survey. Notable features icial geology, features of of the thesurf surficial geology, such as as abandoned abandoned shorelines,deltas, deltas, and and stream stream channels, channels, are are also also mapped. mapped. For For some some shorelines, parks, B. A. A. M. M. Phillips Phillips (personal (personal parks, the the recent recent work work of of B. communication, communication, 1994 1994 and Phillips Phillips et et al., al., 1994) 1994) on on surf surficial icial features has has been been very very useful. useful. Along with with the the geologic geologic maps, maps, an an features account account of of the the geologic geologic history history of of the the region region was was prepared, prepared, as as well well as a description of the the relation relation of of geology geology to to the the scenery scenery in in each each as description of park. park. project is is aimed aimed at at publication publication of a book book for for the the The project general general public. public. The parks parks at at the the two two geographical geographical extremes, extremes, Jay Jay Cooke Cooke and and The Grand Portage, Grand Portage, are are underlain underlain principally principally by by Lower Lower Proterozoic Proterozoic ("2.0 (2.O billion years years old) old) metasedimentary metasedimentary rocks rocks (cut (cut by by 1.1 1.1 b.y. b.y. diabase diabase billion dikes) b.y. dikes) whereas whereas the remaining remaining seven seven are are underlain underlain by by 1.1 1.1 b.y. volcanic and and intrusive intrusive rocks rocks of of the the Midcontinent Midcontinent Rift Rift System. System. volcanic The The major scenic scenic features features of of the the North Shore Shore are are a a legacy legacy of of its geological geological history, history, coupled coupled with with the the effects effects of of differential differential its erosion erosion of of rock rock layers layers or or intrusions intrusions of of differing differing resistance. resistance. The The "Sawtooth the slow erosional etching "Sawtooth Range" Rangen is is the the result result of of the slow erosional etching out out of of thick, thick, resistant resistant lava lava flows flows and sills sills that that are are interlayered interlayered with more more easily easily eroded eroded sandstones sandstones and and thinner thinner lava lava flows, flows, all all tilted tilted gently toward toward the the lake. lake. The The highest highest eminences eminences near near the the lake, lake, the thick thick Palisade Palisade rhyolite rhyolite flow flow in in Tettegouche Tettegouche S.P., S.P., are are beside the made of of concentrations concentrations of of large large (10-100 (10-100 mm across) across) blocks of of resistant resistant anorthosite, anorthosite,carried carriedup up in in diabase diabasemagma magma from from the the base base of of the the earth's earth's crust, crust, now now enveloped enveloped in in the the solid solid diabase. diabase. Examples Examples are are in in Split Split Rock Rock Lighthouse Lighthouse State State Park Park and and Carlton Carlton Peak, Peak, Temperance Temperance River River S. S. P. P. Thick Thick sequences sequences of of volcanic volcanic rock rock underlie underlie many many of of the the parks. parks. For For instance, instance, Cascade River River S.P. S.P. includes includes a nearly nearly 2200—foot 2200-foot sequence of basalt basalt flows flows and and sandstone; sandstone; Judge Judge Magney Magney S.P. S.P. is is underlain by an underlain by an estimated estimated 4800 4800 feet feet of of interbedded interbedded basalt basalt and and rhyolite rhyolite flows. flows. Some of of the the large large rhyolite rhyolite flows, flows, such such as as in in Tettegouche Tettegouche and Judge Judge Magney, Magney, were were erupted erupted in in violent, violent, explosive explosive events much larger Helens (1980) (1980) or or Pinatubo Pinatubo larger than than the the Mt. Mt. St. Helens (1991) (1991) eruptions. eruptions. All of of these these volcanic rocks rocks were were erupted on on aa broad, broad, gradually gradually subsiding subsiding continental continental plateau. plateau. The river river gorges gorges and and many many other other interesting interesting North North Shore Shore features were produced during and since since the the melting melting of of the the last last Pleistocene Pleistocene ice ice sheet, sheet,when when the the west west end end of of the the Lake Lake Superior Superior basin basin was was occupied occupied by by aa deep, deep, ice—dammed ice-dammed lake lake whose whose level level fell fell in in stages stages between between 11,000 11,000 and and 8000 8000 years years ago. ago. Some Some of of these these features features include include abandoned abandoned shorelines, shorelines, deltas, deltas, and and river river meanders meanders (Jay (JayCooke Cooke S.P.) S.P.) and Waterfalls and channels channels (e.g. ( e . g . Judge Judge Magney). Magney). Waterfalls developed developed where where resistant resistant igneous igneous rocks rocks were were encountered encountered (Split (splitRock, Rock, Tettegouche, Tettegouche, Cascade, Cascade, Grand Grand Portage Portage S.P.), S.P.), or or columnar columnar jointing jointing in in basalt basalt flows flows localized localized erosion erosion (Gooseberry (GooseberryFal1s). Falls). 21 �ARE THE THE MAJOR MAJORTHRUST THRUSTFAULTS FAULTSOF OFTHE THEMID-CONTINENT MID-CONTINENTRIFT RIFTAND ANDTHE THE ARE KAPUSKASING ZONE PART OF THE SAME TECTONIC ZONE? KAPUSKASING ZONE PART OF THE SAME TECTONIC ZONE? HALLS,H.C., H.C., M.L. M.L. MANSON, MANSON,and andB. B.ZHANG ZHANG HALLS, Departmentof ofGeology, Geology,Erindale ErindaleCollege, College,University Universityof ofToronto, Toronto,Mississauga, Mississauga,Ontario OntarioL5L L5L1C6 1C6 Department Regional variations variations in in paleomagnetic paleomagnetic polarity polarity and and feldspar feldsparclouding cloudingin inthe the2.45 2.45 Ga GaMatachewan Matachewandyke dyke Regional swarm have been used to delineate major faults across which the southern Superior Province has been swarm have been used to delineate major faults across which the southern Superior Province has been krnorormore1. more1.These Theseobservations, observations,originally originallyused used to todefme defineNENEdifferentially uplifted uplifted by by about about10 10km differentially trending faults associated with the Kapuskasing zone ( a ) ' ' have been extended to a region lying trending faults associated with the Kapuskasing zone (KZ)1' have been extended to a region lying KZand andthe the1.1 1.1Ga GaLake LakeSuperior SuperiorBasin. Basin.Here Herechanges changesininregional regional between the the southern southernend endofofthe theKZ between magnetic polarity have defined two new faults and extended a third one. The new results suggest that magnetic polarity have defined two new faults and extended a third one. The new results suggest that KZisisprogressively progressivelydepressed depressedand anddisplaced displacedsinistrally sinistrallyby byaasystem systemof of N-S N-S trending trending towardsthe theSW, SW,the theKZ towards faults, the western one of which is the Agawa Canyon fault. Changes in feldspar clouding intensity faults, the western one of which is the Agawa Canyon fault. Changes in feldspar clouding intensity between dykes dykessuggest suggestthat thatthe theblocks blocksbetween betweenthe thefaults faultsalso alsohave havebeen beentilted tiltedto tothe theeast. east.The The new new data data between NW faulted faulted margin margin of of the the KZ KZ continues continues westwards westwards to to within within about about 60km 60kmof of the theLake Lake indicate that that the the NW indicate Superior eastern shoreline. Here, gravity, magnetic, and geological studies have identified several ENESuperior eastern shoreline. Here, gravity, magnetic, and geological studies have identified several ENEtrending reverse reverse faults faultswith withvertical verticaldisplacements displacementsup uptotoseveral severalkilometres2. kilometres2.Magnetic, Magnetic,reflection reflection trending seismic and bathymetric data from eastern Lake Superior suggest that two of these faults represent an seismic and bathymetric data from eastern Lake Superior suggest that two of these faults represent an easterlycontinuation continuationof of the the Isle Isle Royale Royale and and Keweenaw Keweenaw faults faults between between which which the the inversion inversionof of the theMidMideasterly Rift (MCR) has taken place to form a pop-up structure. Lithoprobe seismic data suggest that Continent Continent Rift (MCR) has taken place to form a pop-up structure. Lithoprobe seismic data suggest that NWmargin marginof ofthe theKZ KZdips dipstotothe theSE3, S E ~and and , hence hencethat thatthe theKZ KZalso alsorepresents representsaapop-up pop-upstructure. structure.The The the NW the foregoing evidence suggests that the reverse faults of the KZ and MCR are part of the same structure foregoing evidence suggests that the reverse faults of the KZ and MCR are part of the same structure (Fig.1) 1) and major ENE ENE to to NNE-trending NNE-trending compressional compressionaltectonic tectonic zone zonemore morethan than2000 2000 (Fig. and together together define defme aa major km long. Parts of this zone km long. Parts of this zone have experienced experienced periodic periodic have MAJOR CRUSTAL FAULTING IN THE MCR-KSZ TECTONIC ZONE reactivation since the reactivation since the Major reverse faults Cross-structure faults - -. (upthrown side iadicated) Archean,the the last last significant significant Archean, phase of of which which was was in in phase response to the the Grenvile Grenville response orogen at about 1050 Ma. orogen at about 1050 Ma. ,( - References: References: 1: Halls Halls et et al., al., 1994. 1994.Can. Can. J.J. 1: Earth Sci., 31, p. 1182; Earth Sci., 31, p. 1182; 2:2: Manson, M.L. M.L. and and Halls, Halls, Manson, Earth H.C., 1994. 1994. Can. Can. J.J. Earth H.C., Sci., 31, 3 1,p. p. 640; 640; 3: 3: Percival, Percival, Sci., J.A. and and West, West, G.F., G.F.,1994. 1994. J.A. Earth Sci., Sci., 31, 31, p.p. Can. J. Earth Can. 1256. 1256. 22 �THERMOCHRONOLOGY OF CENTRAL CENTRALMINNESOTA MINNESOTA REVISITED: REVISITED: THERMOCHRONOLOGY OF THE IMPLICATIONS FOR THE THE POSTCOLLISIONAL POSTCOLLISIONAL EVOLUTION OF THE OROGENIC BELT. PENOKEAN OROGENIC D.K., Department Departmentof of Geology, Geology, Kent KentState StateUniversity, University, Kent, Kent, OH OH44242 44242(2 (216HOLM, HOLM, D.K., 16672-4094; dholm@kentvm.kent.edu); and LUX, D.R., D.R., Department of Geological Sciences, University of of Maine, Orono, Orono, ME ME 04469. 04469. Rocks exposed in central Minnesota represent deep-seated metamorphic metamorphic and plutonic plutonic rocks of the internal zone of the Penokean their classic classic Penokean collisional orogen orogen (1870-1830 (1870-1830 Ma). Ma). In their study of the geochronology of Minnesota, Goldich and others (1961) obtained obtained Rb-Sr and K-Ar mica and whole whole rock ages ages from from central central Minnesota Minnesota in the the range range of of 1500-1800 1500-1800 Ma Ma (see (see mica and histogram below). below). The histogram The wide wide scatter scatter in in ages ageshas hashindered hindered their their interpretation, interpretation, although although the the relatively relatively older Rb-Sr dates have been attributed to to the onset of regional regional post-Penokean post-Penokean uplift uplift whereas younger K-Ar commonly considered considered to reflect an orogen-wide, orogen-wide, lowwhereas the younger K-Ar dates are commonly grade metamorphic resetting In this this study, study, we we have have dated dated mica mica separates separates from from Archean Archean resetting event. event. In and metamorphic and central Minnesota Minnesota using using the the and Early Proterozoic metamorphic and plutonic rocks from central modem ^Ar/^Ar incremental modern 40Ar/39Ar incrementalheating heatingtechnique. technique. Mica Mica separates separates collected collected across a >I30 >130 km northeast-southwest Minnesota yield age populations populations (see (see northeast-southwest transect transect in in central central Minnesota yield two distinct age histogram below). below). The histogram Theyounger younger population population (1680-1700 (1680-1700 Ma) Ma) represents represents data data obtained obtained solely solely McGrath gneiss dome. dome. The from samples collected within the McGrath The older older population population represents represents data data obtained from samples samples collected collected outside outside the the dome dome (both (bothto to the the north north and and southwest). southwest). They obtained from include the Archean/Early ArcheanIEarly Proterozoic Hiliman Hillman migmatite, the Early Proterozoic Proterozoic Little Little Falls Falls and Denham Denharn Formations (and unnamed equivalent rocks to the the north), north), and and Early Early Proterozoic Proterozoic plutons which are intrusive into the metamorphic rocks. These results provide important new information on the post-collisional thermal thermal history history ^Ar/^Ar ages and tectonic development of the Penokean orogen. orogen. InIncentral centralMinnesota Minnesotamica mica40Ar/39Ar obtained from late and post-tectonic plutons are obtained are concordant with mica ages ages obtained obtained from from the the Penokean-metamorphosed country rock. This suggests that post-Penokean Penokean-metamorphosed post-Penokean plutons (1812(1812—1770Ma?) Ma?)thermally thermallyequilibrated equilibratedwith with the the country country rock rock at temperatures -1770 temperatures above above 300°C. 300°C Emplacement of the post-tectonic magmatic suite was followed by an episode of regional uplift and cooling through —300°C justprior priorto to -1755 —1755Ma. Ma.We We propose propose that that the the dome and basin -300° just structural style, which appear from aeromagnetic data to be associated with the plutons, may have developed during uplift. uplift. We have developed during We further further speculate speculate that that dome dome formation formation may have been been triggered by the plutonic activity and that that the intrusions intrusions were were aa contributing contributing factor factor to to continued continued isostatic uplift. The isostatic uplift. Theremarkably remarkably uniform uniform ages ages obtained obtained from rocks outside of the McGrath McGrath gneiss dome suggest moderate moderate to to relatively relatively fast fast uplift uplift rates rates (see (see Holm Hoim and and others, others, 1993). 1993). We interpret the younger ages obtained from within the McGrath interpret McGrath gneiss dome as reflecting reflecting the the time of dome formation during yet another younger episode of uplift. Research in the previous decade decade has has shown shown that that Phanerozoic Phanerozoic orogenic orogenic belts belts developed developed during convergence are commonly structurally modified during their demise demise by by gravitational gravitational collapse. In like like manner, manner, we we propose propose that that crust crust thickened thickened at at 1870-1830 1870-1830 Ma Ma during during the the Penokean collisional orogeny underwent structural modification during its collapse from the InMinnesota, Minnesota, collapse collapseof of the theorogen orogen appears appearsto to mid to late 1700 1700 Ma (Hoim (Holm and others, 1993). 1993). In begun around around 1760 Ma shortly shortly following following an an episode episode of of magmatism. magmatism. We argue that the have begun magmas may have contributed of an overthickened which led to contributed to thermal weakening weakening of overthickened crust which collapse driven by gravitational instability. instability. Orogenic Orogenic collapse collapse was was apparently apparently episodic episodic with with significant significant pulses pulsesoccurring occurringatat—1755 -1755 Ma Maand andatat—1700 -1700 Ma. As noted by Hoim (1993), the the late late low-grade low-grade metamorphic metamorphic event widely Holm and and others others (1993), recognized in Wisconsin and Michigan apparently apparently affected affected these rocks to to aa much much lesser lesser extent extent than previously thought. 23 �U) 5g f1 E % 5 1 zo 3'61'4- 1850 .0 after 961)) after Goldich Goldich and others (1 (1 961 ~ 6U 1800 I 1750 I 1700 I.1 - U-. Z 01- 1850 1850 I- 1800 1800 I 1650 I 1600 I 1550 K-Ar mica - ~ data, r mica El K and whole rock and whole rock data, all pZ I8Rb-Sr Rb-Sr data, all biotite biotite 1500 after Hotm Holm and others others (1 (1 993) 993) after study and this this study LL I.'.'.' I•IsI•I 1750 1750 1700 1700 I data, mica mica Ar-Ar data, and one one hornblende hornblende and I 1650 1650 1600 1600 1550 1550 1500 1500 AGE AGE (Ma) (Ma) Comparison of age histograms of thermochronologic Comparison of thermochronologic data from from Archean Archean and Early Proterozoic rocks rocks of central Early Proterozoic central Minnesota Minnesota (both histograms histograms cover cover the the area area from from southwest southwest of of Little LittleFalls Fallsto tonear nearMoose Moose Lake). Lake). Goldich, Goldich, S.S., S.S., Nier, A.O., A.O., Baadsgaard, Baadsgaard, H., Hoffman, Hoffman, J.H., J.H., and and Krueger, Krueger, H.W., H.W., 1961, 1961, The The Precambrian geology and geochronoiogy of Minnesota: Minnesota Geological geochronology of Minnesota: Minnesota Geological Survey Survey Bulletin p. Bulletin 41, 41, 193 193p. Hoim, D.K., Hoist, Holm, Holst, T.B., and and Lux, D.R., 1993, 1993, Postcoiiisionai Postcollisional cooling of the Penokean orogen in east-cental Minnesota: Canadian Journal v. 30, 30, p. p. 913-917. 913-917. in Canadian Journalof of Earth EarthScience, Science,v. 24 �EXTENSION THE WISCONSIN WISCONSIN MAGMATIC MAGMATIC TERRANES TERRANES INTO THE EXTENSION OF THE INTO THE MINNESOTA PENOKEAN OROGEN MINNESOTA SEGMENT SEGMENT OF OF THE PENOKEAN Mark A. Jirsa, Val W. Chandler, and Terrence J. Boerboom Boerboom Geological Survey Survey 2642 University Avenue, St. Paul, MN 55114-1057 55114-1057 Minnesota Geological (6121-627-4780 FAX FAX (612)-627-4778 (6121-627-4778 phone (612)-627-4780 Previous work established that the Wisconsin Wisconsin and Minnesota segments of the Early Proterozoic Penokean generally equivalent, equivalent,and strata strata north north of the Niagara fault fault in Wisconsin have been correlated correlated with with orogen are generally supracmstal the Malmo Malmo structural structural discontinuity in Minnesota. The TheNiagara Niagarafault faultseparates separatessupracrustal those north of the rocks of the Marquette Marquette Range Supergroup Supergroup to the north, which have continental chemical affinities, from those of the Wisconsin Wisconsin Magmatic Terranes (WMT) to the south, which have volcanic arc compositions. Parts of the Marquette Range strata are analogous with the epicratonic rocks rocks of of the the Mille Mille Lacs Lacs Group north north of the little was was known known of of the the rocks rocks south south of the the Malmo Malmo discontinuity discontinuity in in Minnesota. Minnesota. However, However, little the discontinuity, Much of of that that bedrock bedrock was was interpreted interpreted as Penokean granitoid discontinuity, largely because outcrops are rare. Much intrusions, although geophysical signatures signatures imply imply that thatrock rocktypes typesand andstructures structuresare aremore morediverse. diverse. Recent Recent results of test drilling drilling and and geophysical geophysical studies provide new insight on the southern part of the the Penokean Penokean orogen. orogen. Our current work south of the Malmo structural discontinuity in Minnesota divides divides the the area into five geophysically distinct, arc-shaped terranes. The Thearcuate arcuatepattern patternisisinferred inferredto torepresent representnorthwest-verging northwest-verging tectonic imbrication imbrication during the Penokean orogeny; however, however, details details about individual individual terranes terranes and their Quaternary deposits and thick saprolite, by post- and synsynbounding structures are obscured by cover of Quaternary kinematic plutons plutons which which make make up up as much much as 50 percent of the subcrop, and and by by several generations of kinematic generations of faults. Nevertheless, Penokean orogen orogencan canbe bedeciphered. deciphered. The The McGrath McGrath terrane, terrane, on Nevertheless, some some elements of the Penokean the north, is aa dome dome of of Archean Archean McGrath McGrath Gneiss Gneiss mantled mantled by clastic clastic and and volcanic volcanic strata strata of of the the Denham Denham Formation. ItItisisseparated separatedfrom fromthe theHillman-Little Hillman-LittleFalls terrane to the south by a sharp geophysical break discontinuity. The itic here named the Mille Lacs discontinuity. TheHiliman-Little Hillman-Little Falls Falls terrane terraneisiscomposed composedofoffoliated foliatedtonal tonalitic to granodioritic rocks of the Hiliman Hillman Migmatite and the Sartel Sartel Gneiss, Gneiss, which which are metamorphosed metamorphosed to the amphibolite to granulite amphibolite to granulite facies, and the the Little Little Falls Falls Formation—a Formation-a pelitic schist schist containing containing biotite, biotite, staurolite, garnet, and and sillimanite. sillimanite. The rocks of the terrane are intruded staurolite, garnet, The metamorphic metamorphic rocks intruded by at least least two two generations generations of post-metamorphic post-metamorphic plutons including including granodiorite granodiorite dated at 1868-1869 1868-1869Ma, and several oval to irregularly shaped irregularly shaped granitic granitic bodies bodies in the range range of of 1770-1812 1770-1812 Ma, Ma, together together with with many many small small plug-like plug-like intrusions of unknown age which vary in composition from peridotitic to charnockitic. The The arcuate arcuatewestern western of Early Early Proterozoic edge of the Hiliman-Little Hillman-Little Falls terrane appears to represent the western termination of thrust sheets, and and isis marked marked by by sharp sharpgeophysical geophysicalcontrast contrast between between Proterozoic Proterozoic metaclastic metaclastic rocks rocks and and Archean granitoid gneiss. gneiss. The Milaca terrane isisthe themost mostlithologically lithologica1ly diverse, diverse, and from an exploration perspective, perhaps perhaps the the most most promising. promising. The perspective, The eastern eastern part of the the terrane terrane is is composed composed of aa variety variety of of plutons separating screens of older supracrustal rocks. These These older older rocks rocks include include exposures exposures of basalt and and anorthositic gabbro, and several drill holes intersected amygdaloidal and and porphyritic porphyritic basalt basalt and and dacitic to andesitic crystal-lapilli tuff. All Allare aremetamorphosed metamorphosedto to atatleast leastgreenschist greenschistfacies, facies, and and intense intense shearing shearing isis locally loca1ly evident in both plutonic and supracrustal supracrustal rocks. The Thewestern western part part of of the theterrane terraneisisalmost almostentirely entirely contains schistose schistose rocks rocks of The narrow Princeton terrane narrow Princeton terrane contains obscured by post-kinematic obscured post-kinematic plutons. plutons. The undetermined protolith and and granite. granite. The terrane terrane is is sharply sharply bounded bounded by by ENE-trending ENE-trending geophysical geophysical undetermined discontinuities that intersect linear anomalies trending trending eastward. The The geophysical geophysical pattern of of the the southernsouthernBecker terrane isismarked most Becker markedby bysemicircular semicircularanomalies anomaliesthat that suggest suggest the the presence of gneiss domes, and samples from several drill cores cores confirm confirm that that gneissic gneissic rocks rocks are are present, present, together together with with strongly strongly schistose schistose rocks of supracrustal supracrustal protolith. protolith. Correlation between between the the two segments Correlation segments of the the orogen orogen across across the the intervening intervening Middle Middle Proterozoic Proterozoic Midcontinent rift system, based on gross Midcontinent gross attributes attributes of of the the structural structural terranes, terranes, is is shown shown schematically schematically on on Figure 1. 1. These Theseattributes attributesare areinferred inferredfrom fromoutcrop outcropand anddrill-hole drill-holedata data in in Minnesota, Minnesota, published published geologic geologic geophysical maps maps of of both both states. states. We maps of Wisconsin, and derivative geophysical We depict depict the the bounding bounding structures structures between terranes on the Minnesota side of Figure 1 as relict thrusts. This Thisinference inference is is speculative speculativebecause because geophysical modeling indicates indicates that most contacts dip steeply, geophysical modeling steeply, and that that most most sources sources within within individual individual terranes extend to depths of 2-5 km. However, However, drill drill cores cores of some some supracrustal and gneissic sequences show much shallower dips, locally locally in in the the 305O0 30-50' range, range, and and we we infer infer that that many many of of the the anomalies anomaliesare are bounded bounded by by steep faults and plutons. The Themost mostcompelling compellingcorrelation correlation is is based based on on strong strong lithologic (and geophysical) contrasts across the Niagara fault and and its its Minnesota Minnesota analog—the analog-the Mille Mi11e Lacs and Malmo discontinuities. These faults separate strata of of continental continental affinity to the the north north that that typically typically lack lack plutons, plutons, from from volcanic volcanic 25 �rocks to to the the south south that that are arecut cutby byabundant abundant postpost- to to syn-tectonic syn-tectonic granitoid granitoid intrusions. Previous Previous work work by by rocks Southwick and and Morey Morey (1991) (1991)inferred inferredaasouth-dipping south-dippingsubduction subductionzone zonealong alongwhich whichPenokean Penokeanrocks rocks were were Southwick thrust northwestward northwestward over over continental continental crust crust of of the the Superior Superior craton. IfIfthis thisisiscorrect, correct,the theboundary boundarybetween between thrust pluton-bearing and and pluton-absent pluton-absentrocks—the rocks-the Niagara Niagara and and Mule MilleLacs-Malmo Lacs-Malmostructures—may structures-may represent representthe the pluton-bearing southernmost southernmostextent extentof ofcontinental continentalcrust crustbeneath beneathPenokean Penokeanstrata. strata. voIcaniclastic rocks in the the Milaca Milaca terrane terrane invites correlation correlation with the The presence presence of of volcanic volcanic and and volcaniclastic The Pembine-Wausau terrane terrane of of the the WMT. WMT. The ThePrinceton Princetonterrane terraneisisinferred inferredtotobe bean anearly, early,complex complexshear shearzone zone Pembine-Wausau separating the the supracrustal supracrustal rocks rocks of of the the Milaca Milaca terrane terrane from from gneisses gneisses of the Becker terrane. The ThePrinceton, Princeton, separating therefore, may maybe becorrelative correlativewith withthe theEau EauPlaine Plaineshear shearzone zonewhich whichseparates separatesthe thePembine-Wausau Pembine-Wausauterrane terrane therefore, from Proterozoic Proterozoic and and Archean Archean gneisses gneisses of of the the Marshfield terrane to the south. Correlation Correlation of of the the HillmanHillmanfrom Little Falls Falls terrane terrane isismore moreenigmatic, enigmatic, because because ititisisintruded intrudedby bysynsyn-and andpost-tectonic post-tectonic plutons plutons like likethe the Little WMT and and Milaca Milaca terrane, terrane, but butititalso alsocontains containsmigmatitic migmatiticgneiss gneiss(of (ofunknown unknownage) age)and andpelitic peliticschist schistlike like WMT the Falls isis aa hybrid hybrid the terranes terranes north north of of the theNiagara Niagara fault. fault. We Wetentatively tentativelysuggest suggestthat thatthe theHiliman-Little Hillman-Little Falls containing lithic Iithicand andstructural structuralelements elementsof ofthe theterranes terranesboth bothnorth northand andsouth southofofthe theNiagara Niagarafault. fault. ItIt may may containing not not have havean ananalog analogin inWisconsin, Wisconsin,or orititmay maybe berepresented representedby by aa poorly poorly exposed exposed tectonic tectonic sliver. sliver. Correlating segments segments of of the theorogen orogenacross acrossthe theMidcontinent Midcontinentrift rift isisnot notonly onlyofofscientific scientificinterest, interest,but but Correlating WMThost hostdeposits depositsof ofbase-metal base-metalsulfides sulfidesand andassociated associatedprecious precious also of of economic economic interest interestbecause becausethe theWMT also metals, metals, including including those those of of the the Ladysmith Ladysmith mine. mine. InInan anearlier earlierpaper paper(Minnesota (MinnesotaProsnector, Prospector,January January1995), 1995), we we asked askedthe thequestion question"can "canthe theEarly EarlyProterozoic ProterozoicWisconsin WisconsinMagmatic MagmaticTerranes Terranesbe be traced traced into into Minnesota?" Minnesota?" The Thesimple simpleanswer answerisisaaguarded guarded"yes." "yes." REFERENCE REiFXWNCECITED CITED Southwick, Southwick, D.L., D.L., and and Morey, Morey, G.B., G.B.,1991, 1991,Tectonic Tectonicimbrication imbrication and and foredeep foredeep development development in in the thePenokean Penokean orogen, interpretation based based on on regional regional geophysics geophysics and and the results of orogen, east-central east-central Minnesota—An Minnesota-An interpretation of testtestdrilling, Sims, P.K,, P.K., and and Carter, Carter,L.M.H,, L.M.H.,eds., eds.,1991, 1991,Contributions Contributions to to Precambrian Precambrian geology geology of of Lake Lake drilling, inin Sims, Superior Superiorregion: region:U.S. US.Geological GeologicalSurvey SurveyBulletin Bulletin1904-C, 1904-C,17 17p.p. ACKNOWLEDGMENTS ACKNOWLEDGMENTS Test Test drilling, drilling,outcrop outcropmapping, mapping, and and geophysical geophysical studies studies were were supported supported in in large large part part by bythe theMinnesota MinnesotaState State Legislature Legislatureon onthe theadvice adviceofofthe theMinnesota MinnesotaMinerals MineralsCoordinating CoordinatingCommittee. Committee. EAST-CENTRAL MINNESOTA AlTRIBUTES NORTH-CENTRAL WISCONSIN t Flambeau Flowage fault Figure Figure1.1. Schematic Schematiccomparison comparisonand andproposed proposedcorrelation correlationof of major majorstructural structuralterranes terranesofofthe thesouthern southern Penokean Wisconsin. Penokeanorogen orogeninineast-central east-centralMinnesota Minnesotawith withthose thoseofofnorth-central north-central Wisconsin. 26 �TITANIUN TITANITJM ORE ORE POTENTIAL P O T E N T I A L OF O F GABBROS: GABBROS: EXANPLES EXAMPLES FROM FROM WESTERN WESTERN FINLAND FINL,AND KARKKAINEN, Nub, Geological ~ R K ~ I N E N Niilo, , GeologicalSurvey Surveyof of Finland, Finland! 02150 02150 J., Department Department of of Espool Finland; Finland; BORNHORST, BORNHORST, Theodore, Theodorel J., Espoo, Geological Geological Engrg. Engrg. and and Science, Science, Michigan Michigan Technological Technological University, university, Houghton, Houghton, MI MI 49931 49931 Early Proterozoic Proterozoic Svecofennian Svecofennian gabbros gabbros are are being being explored explored for for Early ilmenite by the the Geological Geological Survey Survey of of Finland. Finland. Two Two different different ilmenite Pohjanmaa, western western Finland. Finland. types of of Ti—enriched Ti-enriched gabbros gabbros occur occur at at Pohjanmaa, types Subeconomic, low low grade grade titanium titanium deposits, deposits, with with ilmenite ilmenite and and Subeconomic, apatite as as major major ore ore minerals and minor magnetite, are hosted by apatite smallsmall- to to medium—size medium-size layered layered gabbros gabbros located located between between late late orogenic orogenic and and synorogenic synorogenic granite granite complexes complexes (Kauhajoki) (Kauhajoki). Potentially economic economic titanium titanium ore, ore, with with ilmenite ilmenite as as the the major major ore ore Potentially mineral and and vanadiniferous vanadiniferous magnetite magnetite as as aa minor minor ore ore mineral, mineral, is is mineral hosted km north north of of hosted by by aa small small layered layered mafic mafic intrusion intrusion located located 200 200 km Kauhajoki Mid-Finland Kauhajoki in in the the western western margin of the synorogenic Mid-Finland Granite Granite Complex Complex (Kälvià). (Kalvia). Kauhajoki Kauhajoki gabbros gabbros occur occur as as lenticular lenticular bodies bodies along along the the eastern eastern contact contact of of the the late late orogenic orogenic Lauhanvuori Lauhanvuori microcline microcline granite. granite. These These gabbros gabbros were were previously previously studied studied as as aa possible possible source source for for phosphorous. phosphorous. The The large large Perämaa Peramaa deposit, deposit, averaging averaging 5.8 apatite, belongs belongs to to the the same same gabbro gabbro province. province. The The best best 5.8 %% apatite, Ti-enriched Ti-enriched gabbro gabbro of of this this type type is is at at Kauhajàrvi. Kauhajarvi. Here Here apatite apatite and and oxides oxides occur occur together. together. Most of the the Ti at Kauhajàrvi ~auhajarviis is sited sited in in ilmenite. ilmenite. Disseminated ~isseminatedoxides oxides are are more more abundant abundant in in mela— melagabbro-norites at at the the bottom bottom of of the the steeply steeply dipping dipping intrusion. intrusion. gabbro-norites Coarse-grained coarse-grained plagioclase-rich plagioclase-rich gabbro gabbro with with thin thin anorthositic anorthositic layers layers composes composes the the roof roof of of the the intrusion. intrusion. Kauhajàrvi Kauhajarvi contains contains grades grades of of 44 to to 77 % apatite apatite and and 77 to to 12 12 %% ilmenite, ilmenite, but but is is subeconomic, partially partially because because of of thick thick overburden. overburden. The The total total subeconomic, amount 18-22 wt.% wt.% and amount of of apatite apatite and and oxides oxides is is normally between 18-22 the the ilmenite/magnetite ilmenitelmagnetite ratio ratio is is about about 2. 2. There There are are also also magnetite-rich layers layers with with slightly slightly increased increased ore ore grade, gradelhowever, however, magnetite-rich these these layers layers have have much much lower lower ilmenite/magnetite ilmenitelmagnetite ratios ratios (0.5-1.2). (0.5-1.2). Good quality concentrations concentrations of of ilmenite ilmenite and and magnetite, magnetite, as as well well as as Good quality the the beneficiation beneficiation of of phosphorous, phosphorous, are are indicated indicated by by metallurgical metallurgical tests. tests. The Koivusaarenneva Koivusaarenneva ilmenite ilmenite deposit deposit at at Kälvià Kalvia is is hosted hosted The by km long long and and 500 500 m m thick, thick, almost almost vertical vertical by an an unexposured unexposured 33 -- 55 km sill—like sill-like intrusion intrusion surrounded surrounded by by tonalites tonalites and and granodiorites, granodiorites, at at the the contact contact of of the the mid mid Finland Finland Granite Granite Complex Complex and and the the Sykãrainen Sykarainen Volcanic Volcanic Belt. Belt. The The intrusion intrusion is is clearly clearly identified identified from from aeroaeromagnetic magnetic maps. maps. Detailed Detailed magnetic magnetic and and gravimetric gravimetric surveys surveys have have been been used used for for locating locating drill drill holes. holes. The The gabbro gabbro body body is is cut cut by by fault zones zones and and is is divided divided into into two two main main units units along along strike strike fault with with significant significant displacement. displacement. The The intrusion intrusion consists consists of of 55 lithostratigraphic zones zones with with gradual gradual contacts. contacts. From From bottom bottom to to lithostratigraphic 27 �top these these zones zones are are 1) 1) heterogenous heterogenous lower lower barren barren uralite uralite gabbro gabbro top zone; 2) 2) main main ore ore zone zone consisting consisting of of disseminated disseminated ore ore in in gabbro, gabbro, zone; massive ore ore layers, layers, and and metapyroxenite metapyroxenite layers; layers; 3) 3) zone zone of of barren barren massive uralite gabbro; gabbro; 4) 4) layered layered zone zone consisting consisting mainly mainly of of uralite ilmenomagnetite disseminated ore in gabbro and barren uralite ilmenomagnetite disseminated ore in gabbro and barren uralite gabbro layers; and 5) mainly' coarse-grained uralite gabbro. The gabbro layers; and 5) mainly coarse-grained uralite gabbro. The most mafic rock in the intrusion is almost totally uralized most mafic rock in the intrusion is almost totally uralized metapyroxenite,which which exists exists as as thin thin layers layers in in several several zones, zones, but but metapyroxenite, mostly in the main ore zone. Coarse-grained plagioclase cumulates mostly in the main ore zone. Coarse-grained plagioclase cumulates of the the uppermost uppermost zone zone contain contain minor minor enrichment enrichment of of apatite. apatite. of Prominent enrichment of phosphorous, 2 to 5 % apatite, exists in in Prominent enrichment of phosphorous, 2 to 5 % apatite, exists some zones of ilmenite-barren medium-grained uralite gabbro. some zones of ilmenite—barren medium-grained uralite gabbro. lun along along The ore ore zone zone has has been been followed followed for for over over 22 km The strike. The ore is both massive and disseminatedThe massive strike. The ore is both massive and disseminated. The massive ore is up to 15 m thick and contains 23 to 52 wt. % ilmenite, ore is up to 15 m thick and contains 23 to 52 wt. % ilmenite, 44 magnetite and and 11 to to 22 wt. wt. %% iron iron sulphides. sulphides. It It is is to 18 18 wt. wt. %% magnetite to surrounded by a few tens of meters of ilmenite-rich disseminated surrounded by a few tens of meters of ilmenite—rich disseminated oxides, averaging averaging over over 10 10 %% ilmenite ilmenite with with minor minor vanadiniferous vanadiniferous oxides, magnetite. Massive ore is hosted by almost totally uralitized magnetite. Massive ore is hosted by almost totally uralitized metapyroxenite, whereas disseminated ore is mostly in uralite metapyroxenite, whereas disseminated ore is mostly in uralite gabbro . gabbro. Common features features of of Ti-enriched Ti-enriched gabbros gabbros of of western western Common Finland are small size, distinct layering, compositional range Finland are small size, distinct layering, compositional range from minor pyroxenite, through dominant gabbro-norite, to coarsefrom minor pyroxenite, through dominant gabbro—norite, to coarse— grained leuco-gabbro leuco-gabbrowith with only only thin thin anorthositic anorthositic layers. layers. grained ~conomically, the most most significant significant feature feature is is that that Ti Ti is is sited sited in in Economically, the ilmenite and and there there is is only only aa minor minor amount amount of of ilmenomagnetite. ilmenomagnetite. ilmenite ~eochemically, the Ti-gabbros Ti-gabbros are are characterized characterized by by enrichment enrichment of of Geochemically, the phosphorous. phosphorous. 28 �mi-POSITIONAL SYSTEMS ASSOCIATED AS SOCIATEII WITH WIT11 THE Till': 3.0 3.0 GA. GA.FINLAYSON FINLAY SONAND ANDLIJMBY LUMBY DEPOSITIONAL LAKE GREENSTONE BELTS, BELTS,NORTHWESTERN NORTHWESTERN ONTARIO ONTARIO LAKE KING, David FRALICK Phillip, University KING, Davidand and FRALICK Phillip,Dept. Dept.ofof Geology, Geology, Lakehead Lakehead University Bay, Ontario OntarioP7B P7B 5E1, 5E1, Canada Canada Thunder Bay, The Late Lale Archean Archeiln Superior Province of the Canadian Canadian Shield Shield is known known to The Superior Province of the of alternating alternatinglinear linearbelts beltsofofgranite—greenstone granite-greenstone and andmetasedimentary iiietasedinientary consist of An accretionary accretionary model model has been been suggested, suggested, involving involving island island arcs a r c s and and terrains. An metasedimentar y complexes complexes colliding paired metasedimentary colliding with with older older cratonic cratonic masses masses (Langford and Morrin, Morrin, 1976). 1976). Support this model model has has come come from (Langford Support for this from recent of the t h e Quetico Quetico metasedimentary metasedimentary belt portions of of the the neighboring neighboring studies of belt and and portions Wabigoon Subprovince t o its i t snorth north (Williams,1986, 1986,1987; 1987;Devaney Devaneyand andWilliams, Williams, Wabigoon Subprovince to (Williams, 1989; Barret Fralick, 1989; 1989; Fralick Fralick et e t al., al., 1992). 1992). Quetico Quetico trench sediments sediments 1989; Barret and Fralick, a r e constrained constrained ininage a g ebetween betweenapproximately approximately 2710 2710 to to2690 2690 Ma Ma (Davis (Davis eett al., al., are 1990). 1990). The interior interior of ofthe t h eWabigoon Wabigoon Subprovince is is not notwell welldocumented. documented. Metasediments of tthe Metasediments of h e Finlayson Finlayson and and Lumby Lake within Lumby Lake greenstone greenstone belts, within t h e Wabigoon Wabigoon Subprovince, r e the the the Subprovince, aare focus of of this this study s t u d y (Fig. (Fig. 1). 1).Zircon Zircon ages from from the the volcanics volcanics and and + intr usiv es cutting cutting volcanics intrusives volcanics constrain constrain the the eruptive eruptiveepisode episodetoto2999 2999 Ma Ma and and greater than than2936 2936 Ma Ma for for the theLumby Lumby Lake Finlayson Belts Belts respectively respectively Lake and Finlayson (Stone et e t a!., al., 1992), 1992), and and overlying overlying sediments may be be related related to this sediments may this older volcanic volcanic episode episode (Fenwick, (Fen wick, 1976). The surrounding 1976). The surroundingMafic Mafic Tonalite Tonalite and Old Old Tonalite Tonalite of of the t h eMarmion Marmion Lake Lake Batholith and Tonalite of the Batholith and Tonali te Gneiss Gneiss of the Lumby Lumby Lake greenstone greenstone belts. belts. Lithofacies Lithofacies Dashwa Uashwa Gneiss complex complex are a r e3001, 3001,2953 2953 symbols symbols are the same same as as Figure Figure2. 2. and 2928 respectively (Davis, 2928 Ma, Ma, respectively (Davis, in in Stone et e t al., al., 1992) 1992) Sedimentary facies within Sedimentary facies within the the Finlayson Finlayson belt beltconsist consistofofmetaconglomerate, metaconglomerate, course—pebbly sandstone,medium-grained medium-grainedsandstone, sandstone,and andfine fine sand sand and and silt course-pebbly sandstone, silt turbidite deposits. deposits. Lesser Lesser chemical chemical sediments sediments include include cherty iron iron formation formation and and sulfide facies facies iron iron formation. formation. The lake clastic clastic sediments The Lumby Lumby lake sediments consist of of matrix matrix supported supported conglomerate, fine sand sand and and silt turbidites, conglomerate, fine turbidites, and andgraphitic graphiticslates. slates.Chemical Chemical sediments, including, including, ferrugineous ferrugineouschert, chert,chert—magnetite chert-magnelite IF, IF,chert—siderite chert-siderite IF, IF, sulfide sulfide facies facies IF, IF, and andmarble, marble,are a r edominant dominantininthe t h eLumby LumbyLake Lakemetasediments. metasediments. Well developedlateral lateraland and vertical vertical ttrends Well developed r e n d s are a r e recognized recognized within wilhin the the Finlayson Lake metasediments. metasediments.The TheLittle LittleFalls Fallslake lakearea, area, in in the extreme Finlayson Lake extreme southwest of of the t h ebelt, belt,isi dominated s dominatedbybycourse—pebbly course-pebbly sandstone, sandstone,medium medium sandstone sandstone and conglomeratic beds. Traveling north, along conglomeratic beds. Traveling north, along strike, strike, finer finer grained grainedsediments sediments become increasingly mimore prevalent, withonly onlyfine fine sand-sill sand—siltturbidity turbidity ccurrent become increasingly more prevalen t, with urrent deposits Verticalttrends deposits found found in the the north—east. north-east. Vertical r e n d s aare r e recognized recognized by by an an i t + + + increase; in average average grain grain size size as a s one one moves moves p upsection sectiontoward towardthe thedominant dominant increase synclinal axes running through the main running north—south north-south through main sedimentary sedimentary belt belt of of 29 �Finlayson Lake. Finlayson Lake. Trends within the t h e Lumby Lumby Lake Lake belt belt are a r esimilar. similar. Metasediments Metasedimenls grade grade Trends within along s t r i k e from dominantly fine sand-silt turbidites with minor chemical along strike from dominantly fine sand—silt turbidites with minor chemical sedi~ncm ts, in t11c west, west, to .topredominantly predomiriantly chemical chemical sediments h e east. east. A A sediments, in the sediments in in tthe clmnge from from chemical chemical dominated h e lower lower section, progressive change dominatedsediments sedimentsinin tthe section, to clastic dominance do~ninanceinin upper vertical trend trend recognized. recognized. elastic upper sections, sections, isis the vertical Similarities Similarities in lgneou% Roc<, sedimentary facies facies the sedimentary P1 MoStly F present, and in present, in lateral lateral voIccnw, and vertical vertical trends, trends, and Mostly Mot,c L_J volcanic, suggest that t h a t the the suggest roOcl;tC Finlayson and arid Lumby Lumby Finlayson Lake metasediments metasediments Lake Me to sed rn en a ry indicates sedimentation within a sedimentation within I3cando r gso m~e m~ t e, A '~' owon ,,,,inor ~ ~ ccr!,,.::. stngle single basin. The basin. The Sondsoon Corbonts ;~;;r;oter~~ corbon,:te% c,: tsnoltornwcteJ I r o n Formclion of felsic felsic predominance of Sandstone " " (deeper water) volcanic clasts within wit hi11 c:onglomeratic facies facies conglomeratic may represent I i1gure Figure 2 Paleogeographic sketch of of the Finlayson and subaerial volcar~isni to Lumby prograde north, from a Lumby Lake area. Clastic sediments prograde ttte soutli. the south. ~t is is vokanic source region, distal chemical sediments. volcanic over distal chemical sediments. suggested elastic suggested that elastic sediments were were derived from from a higher higher derived relief in the relief source source in the south, south, and and prograded prograded through through aashallow shallow water water environment in Little Falls Falls and and southern southernFinlayson Finlayson Lake Lake area. area. Deeper Deeper environment in the the Little water in the more water turbidity current c u r r e n t deposits deposits and and chemical chemical sediments sediments aare r e found found &the more distal northern Finlayson and Lumby Lake area. Figure 2 represents distal Finlayson and Lumby Lake area. Figure 2 r e p r e s e n t s a possible paleogeographic reconstruction. possible paleogeographic a fl F O ~ ~ C ~ ~ C - * saamsni to REFERENCES Barret, T.J. and Fralick, P.W., 1989. nehea. iedi.e.tatis. ii the learture—Gerattt,i Terral., hum: claitic aid chealcal &itp.aitiii ii a carrie iibaariae eralimie aargia. Zedi.e.t.l.pi, vii. U, p. 211—114. Davis, D.W., Pezzutto, F., and Ojakangas, R.W., 1990. The ale aid pr.,e.aece .1 .etiieLi.eutary cecil ii the Qeelico E.ipr.viuce, Oitarj., fri. ziule cite.. a.aiyaia: iaplieatieia fir Archeai ae&iie.tati,i aid teeticice ii the Eiperi.r Pr.eiice; Earth &i& Ucietary Eciecce Letteri, vii. 11, p. 111—225 b...dary aa aedi.eitiispieai if ac 1989. E,.I.tii. Devaney, J.R. J.R. and and Wiliams, ll.R., 1989. Wiliams, H.R., t v a l ~ t i a nat I . AAreheal ~ C ~ Smbpravimte C Xihpr.,iie ~ I bommiary: ~ c ~ i m c m t 0 1 a r i c aaid 4I 1 4 ii uertheri Jiurial if vet. IIt,G l etedy af if part aitractiral t r u c t ~ r a l almir par1 ifafthe Q ~ e t i c abh..dary o ~ i m r y im martberm hitari.. Omlaria. Caiadiau Canaiiam Jaarmal af Earth tarti Eciecee., S e i e m e c # ~ val. lbcVahig,.. Wabiraom— Queue. - 1111—lIlt. p, p. 1811-1116. Ii.ei, Ge.aeieece Dietriet af if laimy Fiii&piiu Lake the FimIayaam ate area, area, Dialriel h i m y li,er;Oitari. IivcriOmIaria Divicie. Biviaian .1 0 1 himcn1 Gcaaeicmcc 1976.Ge.l.gy ~ c a 1 a ~if aty the Fenwick, F.F. F.F. 1976. lcpart S l Up. 16p. Depict1 4ill, laui. dep.uila aid aispe Trcmck am& aIapc basin icpamita iiima.amArehea. Arekcam 1992. Truth Fralick, P.W., P-W-, Wu, WU, J., and a n d Williams, Williams, H., H., 1992. belt,Saptriar tuperi.r troiimce, trevilee, Ca.adia, Shield.C taia&ia. it Earth 9 , 2SSl—155. p . 2551-ISST. maetaaediaeitary e h a c i i m c ~ t a r ybeltl Camaiiam Siieli, a m t i a m J Jeirial a w m a 1 a1 tartb *cie.cea, Scicmceal vii. val. ii.1 p. hurt. bg if the Eiperi.r Pr,,iaee J.A., 1976. Langford, F-F. a n d Mori.11, J.A., 1976.The t i c devel.p.eit i e v e i a p m c m ~ at the Smpcrier Iravimce etif iirth.eater. martiwcalcrm omlaria b, .crgi.g Z. tei. vii. 111 mcrtimt lucid ialamtarea. area.1..Am. J. Sci. val. p. 2761112—1114 p. 1121-1834 Preeaahria. Ge.1. Stone, D., Kamine~ii,D.G. a n d Jackson, M.G., 1992. trecanbriam G C ~ I * WifafthetheAtik.ka. AlitatamArea. Area, lirt,eateru Ccii.Smrv. lit,. Ca.. I a r l w e ~ l c r mOetari.. Onlaria. Gcal. Can. liii. 1111. 421, 4 0 S l hIp 186p Ii the belt,muertheru laurie; Ii ~ t r m e l a r a l atadlee atttiea in the leatd.ue—Ceyildtei 1 ~ a r t m a r e - h a i i t a m beltl a r t k m m tataria; im taaaatj $amnary .1ofFIeld Fie14hoth, Workl Williams, ll.R., 1986. 1986.ttr.tturat W i i h I n ~ ,II.l<., 11*1, GeileglealS nlirvey, taper1 3Ill, r v c r ~~liaeellauciau i a c c l l a m e a a ataper 8 1 p. p. 1*$14I. 188-146. 191tl Octane Oataria Gcalaricai thi Q.etici aid i~ ii lbe Williams, ii tie ll.R., 1987. 1987.itnueterat Slraclurai autediec l d i e a in lkele&nda.re—Giraldt.e Ieardmare-Geralilan belt bell am4 Q ~ e l i c aid aa m 4Va.a Wawa aubpr.vieeea ambpravimtc#; ia w i u a m ~ ,II-R., 121, p.11—Il. li..any if Field S ~ r v t y ,IlaeelIaie... hiaccllamcau# taper taper l3Il p.18-92. sum mar^ ar riel& link, Workl ilti, 198IlOutari. Omlaria Ge.i.gical Gcalarical 1.rvey, Fralick, F.F. and Morin, Stone, D., Kamineni, D.G. and Jackson, M.G., 1992. 30 �NEOARCHEAN COASTAL SEDIMENTATION IN IN THE THE SHEBANDOWAN SHEBANDOWAN GROUP, GROUP, NORTHWESTERN ONTARIO NORTHWESTERN ONTARIO KOEBERNICK, Christa Christa F. and FRALICK, W., Dept. Geology, Lakehead FRALICK, Philip W., Lakehead 5E1, Canada. Canada. Bay, ON, ON, P7B P7B5E1, University, Thunder Bay, Many present day tidal environments, such as the Bay of Fundy and the Dutch Dutch Wadden Sea, Sea, have have been been the the objects objects of of broad broad and comprehensive comprehensive studies. studies. Such environments in the Phanerozoic have also been extensively studied, studied, and and as a result, Although there exists a wealth of information on tidally influenced environments. environments. Although represented in the rock record, record, very little little work has has been been done done on on tidal tidal settings settings in inthe the Precambrian. The The majority majority of of studies studies have have concentrated concentrated on on such such environments environments in in South Africa, Africa, with little emphasis on Precambrian rocks elsewhere in the world. Canadian Shield Shield of northwestern northwesternOntario, Ontario, there there exists existsan anexcellent excellentexample example In the Canadian of a Precambrian tidal environment. The section section containing containing this this example example is is located located environment. The approximately 50 50 kilometres west west of of Thunder Thunder Bay, Bay, near near Finmark. Finmark. The rocks, approximately rocks, which which are are Neoarchean in age, age, belong to the Shebandowan Group and occur within exposures exposures of the Shebandowan Shebandowan - Wawa greenstone A lack lack of of bioturbation bioturbationhas has allowed allowed for the the greenstone belt. belt. A superb preservation presetvation of sedimentary structures structures within these units. A variety of primary sedimentary structures such as herringbone cross-bedding, ladderback ripples and flaser to lenticular bedding are present. These These structures structuresare are environments. Many of the sedimentary considered characteristic of tidally-influenced environments. structures closely resemble those that are are present present in in Phanerozoic Phanerozoic and and present-day present-day tidal flat environments. Moving Movingoffshore offshorefrom fromthe thetidal tidalflat flat environment environment into intothe the dominates. Trough subtidal, coarse grained material dominates. Trough cross-stratification cross-stratificationand and parallel parallel lamination are present. present. There There isisno noevidence evidencein inthe the sequence sequence that that there there were were lengthy lengthy periods periods of emergence emergence above abovesea sealevel. level. trends are are present present throughout throughout the the section. section. The majority of Fining and coarsening trends layers fine fine upwards upwards into silts and muds from aa coarse individual layers coarse grained grained sandy sandy base. base. On a larger scale, scale, the the section section exhibits exhibits an an overall overall coarsening coarsening trend trend when when moving moving tidal towards the subtidal and and nearshore nearshore environment, or towards the centre of aa tidal channel. Occasionally, fining trend trendisissuperimposed superimposedupon uponthis thisoverall overallcoarsening coarsening Occasionally, aafining into the tidal flat trend, such as when moving out of aa tidal channel and back into environment. environment. There are also unique features features present present in in the the rocks rocks of of this this area. area. For For example, example, 10 I0 to 20 20 centimetre centimetre thick thick parallel parallel laminated laminated coarse coarse grained grained sand sand layers, layers, which which grade grade into into thin fine-grained tops tops are present. present. The The sand sand layers, layers, which are light in colour, stand stand in in marked contrast to the darker coloured rocks of the section. section. These These layers layers are to represent wave wave deposition deposition of of sand on a beach during believed to during a storm, and and appear appear with regularity throughout the section. The presence of storm layers in in the tidal flat environment differ storms usually usually move move sediment sediment differ from from the prevailing thought that storms offshore. The Thestorm stormlayers layersmay maybe beindicative indicative of of storms storms which which occurred occurred during during periods periods of high high spring spring tides. tides. - 31 �Tidal channels present throughout the section differ from those that are commonly described described in in the the literature. literature. Typically, tidal tidal channels are meandering, but in this case, the tidal channels show very few features that are diagnostic of either meandering or braided channels. Herring-bone Herring-bonecross-stratification cross-stratification and and parallel parallel lamination are present in the channels, with sediments sediments fining towards towards the the centre centre of of the thechannel. channel. (1988) outlined characteristics of supratidal supratidal deposits, such such as as the the Terwindt (1988) of plant remains, remains, gypsum gypsum or or salt salt pans. pans. None presence of Noneof of these these features features are present, present, in fact the supratidal environment environment appears appearsto to be be completely completelyabsent. absent. The absence of supratidal deposits is is often often noted notedin indescriptions descriptionsof ofPrecambrian Precambriantidal tidalsethngs, settings, and and may be a reflection reflection of environmental environmental conditions conditions that were prevalent prevalent during during this this time time period period The excellent preservation of sedimentary structures enables the determination determination of aa for this ancient tidal environment. environment. A paleotidal range for A minimal minimal tidal range range of 3.5 3.5 metres metres was calculated, using methods Terwindt (1988). (1988). This methods outlined by Klein Klein (1971), and Terwindt This comparable to to other other determined determined paleotidal paleotidalranges ranges of of Precambrian Precambriantidal tidal value is comparable environments, which range from 0.5 to to 12.5 12.5 metres. metres. References References Klein, G. deV., deV., 1971, 1971,Sedimentary Sedimentary Model Modelfor for Determining DeterminingPaleotidal Paleotidal Range. Range. Geological Geological Society Society of of America America Bulletin, Bulletin, v.82, v.82, p.2585-2592. p.2585-2592. J.H.J., Terwindt, J. H.J., 1988, Palaeo-tidal Palaeo-tidalReconstructions Reconstructions of of inshore inshoretidal tidal depositional environments, in P.L. P.L. de de Boer et. a/., a!., eds, eds, Tide-Influenced Tide-Influenced Publishing Company. Company. p.233-263. Environments and and Facies. Facies. D. Reidel Publishing p.233-263. 32 �NEW OBSERVATIONS OBSERVATIONSON ON THE THEGEOLOGY GEOLOGY OF OFTHE THEWESTERN WESTERN GOGEBIC GOGEBIC IRON IRON RANGE, NORTHERN WISCONSIN WISCONSIN Gene L. LaBergel LaBerge, Geology Geology Deptm1 Dept., University University of Wisconsin-Oshkosh, Wisconsin-Oshkoshl Oshkosh, Oshkoshl WI, Wll Gene L. and U.S. Geological Geological Survey W. F. F. Cannon, Cannonl U. S; Geological Geological Survey, Reston, Reston#VA Dept., Western Illinois University, John S. Klasner, Klasnerl Geology DepteI Universityl Macomb, Macomb#IL, lLl and and U.S. U.S. Geological Survey. Survey. From 1992 1992 to t o 1994 1994we wereexamined reexaminedthe theGogebic Gogebic Iron lron Range Range between Tyler From Forks River River and the western termination termination of ofthe therange rangenear nearLake LakeNamekagon. Namekagon. Several aspects of the stratigraphy Several aspects stratigraphy and and structure structure of ofthe therange rangehave havebeen beenrevised. revised. River Dolomitel Dolomite, at the base of the Early section, attains The Bad River Early Proterozoic sectionl a maximum thickness of about 300meters metersnear near the the Marengo Marengo River River south of of Grand Grand about 300 View, Wisconsin. It is typically aa dolomitic Viewl dolomitic marble marble with with abundant abundant lenses lenses and and beds beds Farther east, from near Penokee Gap to of chert, chertl partly partly replaced replaced by by tremolite. tremolite. Farther eastl near Penokee t o near near Ballou Creekl Creek, the the Bad Bad River River is is much much thinner thinner and and is is mostly a monolithic chert Ballou chert breccia and and conglomeratel conglomerate, locally locallywith with lenses lenses of of dolomite dolomite near nearthe the base. base. This breccia lithology is interpreted interpreted to t o be be aa residuum residuum of chert chert nodules nodules and and beds beds formed as the during the the weathering weathering interval interval prior prior tto deposition of the dolomite was dissolved dissolved during o deposition unconformably overlying Palms Formation. The residuum Palms Formation. residuum was variably reworked into conglomerate with with clastic clastic quartz quartz grains grains interspersed interspersed in otherwise cherty cherty matrix. Local Localconcentrations concentrationsof ofmagnetite magnetiteand and hematite, hematitel explored explored in in numerous numerous test pits, pitsl may may be be either either placers placers or or hydrothermal hydrothermal iron iron concentrations. concentrations. Near Atkins Lakel Lake, in the the far far western part of the Near Atkins the range, rangel the Ironwood Ironwood IronlronFormation grades grades laterally laterally from from typical typical cherty banded iron-formation into magnetic magnetic argillite and non-cherty silicate iron-formation. iron-formation, Large Largesills sills of ofmetadiabase metadiabase are are also also contrast tto common in the iron-formation in contrast o the situation in the central central part part of of the the range where igneous rocks rocks are are rare. rare. In the Atkins Atkins Lake Lake area the iron-formation iron-formation also contains two t w o interlayers, interlayersl up up I0meters meters thick, thickl of ofan anunusual unusualbreccia breccia consisting consisting of of angular angular slabs slabs of tto o about 10 banded siliceous siliceous sedimentary sedimentary rock rock that that are as as much much as as aa meter meter long. long. Some banded Some slabs slabs are bent and may not have been fully lithified lithified when when incorporated incorporated in in the the breccia. breccia. The slabs slabs superficially superficially resemble resemblenearby nearbyiron-formationl iron-formation,but butwith with only only aa ffew The ew exceptions, we have not observed fragments that that are are iron rich or or magnetic. magnetic. The exceptions, observed fragments The matrix is is a dark gray-green, gray-greenl mostly massive rock, at least least partly partly of of igneous igneous origin. origin. Although metamorphism obscured much much of of the original texturesl textures, in metamorphism has obscured in places places a basaltic texture texture and and small small euhedral euhedral plagioclase plagioclase phenocrysts are are well well preserved, preservedl as as It are amygdules. amygdules. The The origin of of this this rock rock isis controversial, controversiall even even among among the authors. authors. It are may be aa "pepperite" "pepperite" intruded at shallow level in the iron-formation prior tto o 33 �lithification. Alternatively, Alternativelyr itit may may be be an an extrusive extrusive that that has has incorporated incorporated sediments sediments over which itit flowed. features arguing for an extrusive origin are: over flowed. Salient Salient features arguing for an extrusive origin are: I1)) perfectly concordant contacts with with thinly thinly laminated laminated iron-formation iron-formation well exposed exposed at several outcropsl outcrops, and and the the lack lack of of any any observed observed cross-cutting cross-cutting contactsl contacts, 2) the several exotic nature of virtually virtually all all fragments fragments in in the the breccia breccia and and the absence absence of fragments 3)marked marked lithologic lithologic of iron-formation with with which whichthe thebreccia brecciaisisinterlayered, interlayered! and and 3) contrast between between the the breccia breccia and and undoubtedly undoubtedly intrusive intrusive sifls sills of coarse-grained, coarse-grained! massive! inclusion-free metadiabase metadiabase.within massive, within the same outcrops. Regardless of whether whether the breccias are extrusive or very shallow Regardless of shallow intrusions, intrusions, they indicate that abundant abundant igneous igneous activity was was occurring occurring contemporaneously contemporaneously with iron-formation iron-formation deposition deposition in the western part part of the the Gogebic Gogebic Iron lron Range. Range. The The situation is similar to that that of of the theeastern eastern part part of ofthe therange, range! where where the theEmperor Emperor Volcanic Complex Complex is is interlayered interlayered with with the Ironwood Iron-Formation. Iron-Formation. Apparently Apparently the platform-like conditions of the the central central part part of of the the range, range, where where volcanic volcanic rocks rocks are limited tto o a few f e w thin thin ash ash beds, beds! grade grade both both east east and and west into into more more volcanically volcanically active regions regions at both both ends ends of of the theGogebic Gogebic Iron lronRange. Range. Although volcanism contemporaneous with ironvolcanism appears appears tto o have have been been contemporaneous ironformation deposition deposition on on the the Gogebic Gogebic Iron lron Range, Range! we have have found no no Early Early Proterozoic mafic rocks rocks cutting the overlying Tyler Formation. Proterozoic mafic Formation. This This observation, observationl coupled with the the prominent prominent unconformity unconformity at at the the base base of of the the Copps Copps Formation, Formation! the Tyler equivalent on on the the eastern eastern Gogebic Gogebic Iron lron Range, Range! suggests a time gap gap between between iron-formation deposition and accumulation accumulation of the overlying graywacke-slate sequence during which which volcanic volcanic activity sequence during activity ended. ended. The Penokean structural history of the Penokean structural the area area has has also been clarified. Penokean deformation increases increasesin in intensity intensity from from the Tyler Forks area, area! where Penokean deformation deformational features features are are limited limited tto folds, to o a few outcrop-scale outcrop-scale folds! t o the the Mineral Mineral Lake Lake area, where where the the iron-formation is repeated repeated by by large, large, nearly nearlyisoclinal isoclinalfolds. folds. Those area! folds were originally originally upright, upright! but but because because of northward northward rotation rotation during during development of the Midcontinent rift, development of rift! they they are are now now recumbent, recumbent! and and the south south overturned, limbs of synclines are overturned. From the the east east end end of of Mount Whittlesey to the the west west end end of of the therange, range! Early Early Proterozoic strata are are structurally structurally detached detached from from underlying Archean Archean rocks. rocks. The The Proterozoic strata basal decollement decollement is is well well exposed exposed on on the the east east end end of of Mount Whittlesey! Whittlesey, where basal where Bad Bad River lies on on aa shear shear zone zonedeveloped developedininArchean Archeandacitic daciticbreccia. breccia. A A River Dolomite lies decollement within the sedimentary Marengo decollement sedimentary section is is also also well exposed exposed along the Marengo River where an intensely sheared zone several several tens tens of meters wide sheared zone wide separates separates Bad Bad River and Palms Palms Formation. Formation. Second-order faults splay splay upward from the River Dolomite and Second-order faults decollement, generally climbinghigher higherininthe thesection sectiont otothe theeast. east. On On Mount d e ~ o l l e m e n tgenerally ~ climbing Whittlesey, the Ironwood repeated by by one one of of those those faults faults which Whittlesey! Ironwood Iron-Formation Iron-Formation is repeated results in the unusually wide outcrop belt belt of of iron-formation. iron-formation. 34 �INSTITUTE ON LAKE SUPERIOR GEOLOGY GEOLOGY 1995 1995 MINERAL POTENTIAL POTENTIAL EVALUATION, EVALUATION, CENTRAL CENTRALMINNESOTA MINNESOTA MINERAL Tom Lawler, Lawler, Minnesota Department Department of of Natural Resources, Division of Minerals, Hibbing, Minnesota Minnesota 55746, (218)262-6767 (218)262-6767 1525 3rd Ave. Ave. E., Hibbing, ABSTRACT: ABSTRACT: ~esources,Minerals Division, Division, has h& completed a low-cost The Minnesota Department of Natural Resources, tow-cost program program using computer computer enhanced contemporary methods to evaluate the mineral potential of a large enhanced contemporary methods to evaluate the mineral potential of a largepart part of of This project project isis oriented oriented toward toward identifying identifying nonferrous Central Minnesota Proterozoic greenstone belts. belts. This metallic mineralization, mineralization, associated lithologic units structures permissive permissive of such such metallic associated alteration alterationor or lithologic units and and structures partof ofthe theCentral CentralMinnesota Minnesotageographic geographicinformation information mineralization. This Thisinformation information will will become become aa part mineralization. system. The 2. To To encourage encourageprivate Theobjectives objectivesare: are: 1. To serve land land use planning planningwithin withinthe theD.N.R.; D.N.R.; 2. exploration through better data access, and; 3.3.To Toserve servegovernment governmentagency agencyplanning planning of future programs. programs. exploration Creating Listing mineral Creating an improved improved data data base base for for regional regional mineral mineral potential potential evaluation evaluation was done done by: 1. Listing occurrences, and and defining defining lithologic lithologic units and and structures structures permissive permissive of mineral mineral deposits. deposits. 2. Describing Describing and analyzing analyzing bedrock lithologies from existing drill core. 3. Creating Creating 1:62,500 1:62,500 scale scale inferred inferred geologic geologic maps, which which display display interpreted interpreted mineral mineral potential. potential. 4. Re-evaluating Re-evaluating existing existing geochemical surveys using contemporaneous statistical statistical analytical analytical methods. methods. 5. 5. Testing Testinggeophysical geophysical interpretations interpretations with drill holes. A contract was completed by Dr. Dr. Don L. Shettel Jr. and Dr. Patrick completed by Patrick O'Hara O'Hara to to interpret interpret three three existing existing ground water and and lake lake sediment sediment geochemical geochemical data sets using computer driven state of the art statistical statistical and geochemical modeling modeling methods. methods. From From these these models models Drs. Drs. Shettel Shettel and and O'Hara O'Hara constructed constructedanomaly anomaly maps for gold, base base metals, metals, iron iron and and uranium. uranium. Contracts were also completed by Dr. Allan Contracts were completed by Allan Spector Spector to to make make inferred inferred geologic geologic maps maps of of sixty-two sixty-two contiguous at aa scale scaleof of 1:62,500, 1:62,500, using usinggeophysical geophysical(primarily rimarily aeromagnetic contiguous townships at aeromagneticand and gravity gravity data), data), also geologic geologic data. data. Detailed magnetic ground traverses and and geophysical geophysical measurements measurements of density density and and magnetic magnetic susceptibility susceptibilitywere were made made on on selected selected logged logged samples samples for for computer computermodeling modeling of of geologic geologicfeatures features based based on on geophysical geophysical data. data. Dr. Spector's Spector's maps maps display display structurally structurally deformed, deformed, folded folded and and faulted, faulted, greenstones with associated associated metasedimentary metasedimentaryunits unitsand andintrusives. intrusives. An important of this contract important aspect of was construction constructionof of maps maps displaying displayingmineral mineral potential potential areas areas as as modeled modeled from fromgeophysical geophysicalcharacteristics characteristics of known known mines located in similar Precambrian terrains, based based on on the the contractor's contractor's experience experiencewith with such such features. Several areas of mineral features. Several mineral potential potential are are coincident coincident or or partially partiallycoincident coincident with with anomalous anomalous geochemical results defined defined by by Drs. Drs. Shettel Shettel and and O'Hara. O'Hara. InInthe geochemical results theShephard ShephardArea Area these these Mineral Mineral Potential Potential Areas include MPA2a, MPA5c MPA5c and and MPA6b; MPA6b; In In the the Shephard Shephard Area Area Extension Extension they include areas A3, A4 AlO. On Onthe theCamp CampRipley Ripleymap map there there are areMineral Mineral Potential Potential Areas, Areas, MPA3 MPA3 and MPA4, close to drill and A10. holes with anomalous anomalous gold and platinum group elements, Section 12, 12, T43N, T43N, R32W. R32W. In summary significant results include: Improved Improved definition definition of of geologic geologic features; features; Lithologic units and of areas features permissive of economic ore deposits; Detailed inferred geologic maps with definition of having mineral potential; potential; Multi element element geochemical geochemical anomalies anomalies with significant significant pathfinder pathfinder element element anomalies anomalies coincident coincident with with favorable favorable inferred inferred geologic geologic features. features. To test test the the inferred inferred geology, geology, in in cooperation with the Minnesota cooperation with Minnesota Geological Geological Survey, Survey, six vertical vertical holes holes were were drilled drilledthrough throughglacial glacial overburden to obtain bedrock samples. Examination Examinationof of the the core core confirms confirms inferred inferred geologic bedrock map lithologies P295lithologies in most of the drill holes. Native Nativecopper copperininaaKeweenawan Keweenawanlike likeconglomerate conglomeratefrom from hole hole P295Minnesota DNR DNR Report Report 284 284 records 960 ppb gold 6 suggests suggests mineral mineral potential. potential. Minnesota gold in in aa heavy heavy minerals minerals concentrate for for sample sample 23949. 23949. This T44N7 R31W, R31W, near concentrate This sample sample came from a gravel pit in Section 36, T44N, the trend of of aa mafic mafic volcanic-sediment volcanic-sediment contact contact where where Spector Spector maps maps several mineral mineral potential areas on the Shephard Area. 35 �GENESIS OF CU-NI CU-NI SULFIDE SULFIDE MINERALIZATION MINERALIZATION AT THE SPRUCE SPRUCE ROAD DEPOSIT, DEPOSIT, SOUTH KAWISHIWI INTRUSION, DULUTH COMPLEX Science Center, Center, Isotope Research Group, Yeoeun Dong 224-1, Yusung Ku, LEE, Insung, Korea Basic Science Yusung P.O. Box 41, Taejean 305-333, Korea. RIPLEY, RIPLEY, Edward Edward M., M., Department of Geological Sciences, Indiana University University Bloomington, Bloomington, Indiana Indiana 47405, 47405, U.S.A. U.S.A. Sciences, The South Kawishiwi Kawishiwi intrusion is one of several intrusions within the Duluth Complex, Minnesota - the principal exposed plutonic component of the Spruce Spruce Road Road of the 1.1 Ga Midcontinent Rift Rift system. system. In the area the South Kawishiwi Kawishiwi intrusion intrusion is divisible into seven distinct troctolitic troctolitic to to gabbroic gabbroic units, units, four four of of which contain 11 to 55 volume volume percent percent of of disseminated disseminated pyrrhotite, pyrrhotite, cubanite, cubanite, chalcopyrite, chalcopyrite, and pentlandite. 6S values S^S valuesofofthe themineralized mineralized units units range from 3.8 to 10.2%, 10.2%0,and and are are distinctly distinctly different from those of of non-mineralizedrocks rockswhich whichrange rangefrom from-3.4 -3.4toto2.8%0 2.8% (Figure (Figure 1). 1). The non-mineralized The proposed proposed model for the genesis of the sulfides involves the mixing mixing of sulfur sulfur derived derived from from two two sources, sources, accumulation accumulation of immiscible immisciblesulfi4e sulfide liquid, and emplacement of Twenty percent percent batch partial melting of a spinel spinel of sulfide-saturated sulfide-saturated magmas. magmas. Twenty Iherzolite mantle source source with with —20 -20 pprn pprn SS yields yieldsaaderivative derivativemelt meltwith with—76 -76 ppm pprn Cu Cu (65 (65 lherzolite mantle ppm Cu and 200 ppm ppm pprn from sulfide sulfide arid and 11 11 pprn total sulfur sulfur content content of of —1000 -1000 ppm. ppm from silicate) and a total ppm. In order to produce the relatively evolved, high-Al high-A1 olivine tholeiite tholeiite parental parental magmas magmas of of the theintrusive intrusive sequence, sequence, extensive extensive crystallization of of a primary melt in a lower crustal or mantle chamber is required. During fractional crystallization Duringthis this process sulfide saturation would have been achieved achieved and chalcophile elements removed from the magma liquid. Emplacement melt into into a higher level staging into a coexisting coexisting sulfide liquid. Emplacement of the the sulfide-saturated sulfide-saturated melt chamber permitted the assimilation assimilation of sulfur sulfur from from metasedimentary metasedimentary country country rocks. rocks. Reaction between externally-derived sulfur or neutral neutral species, species, would would externally-derived sulfur and metals metals initially present in the melt as silicate, oxide, or have produced a second liquid that that mixed mixed with with that that of mantle origin. second generation of immiscible immiscible sulfide liquid Sulfide-rich rocks of the South South Kawishiwi Kawishiwi intrusion represent melts derived from the high-level chamber chamber contamination with with sulfur of of crustal origin. origin. Because that had experienced contamination Because of of the the wide wide range range in in possible possible contaminant 34S values contaminant S^S values (e.g. (e.g. 00 to to 29% 29%0ininsulfides sulfidesfrom frommetasedimentary metasedimentary country country rocks), it is difficult to accurately assess the proportion of country rock sulfur sulfur present in the mineralized units, but a range of of to 70% 70% isisconsistent consistentwith with available availabledata. data. Sulfide assemblages are mineralogically zoned, such such from 30 to pyrrhotite-rich layers layers are are overlain overlainby bycubanite-chalcopyrite-rich cubanite-chalcopyrite-rich layers. layers. In situ situ crystallization, crystallization, that pyrrhotite-rich controlled by boundary layer layer fractionation fractionation and upward expulsion expulsion of of CuCu- and and Ni-enriched Ni-enriched residual residual liquid liquid proposed to explain explain the zonation. zonation. Upward Upward increases increases in in Cu Cu and andNi Nicontents, contents,as aswell wellas asincompatible incompatible is proposed elements such as Zr, Y, and P, may or possibly possibly as as a may be be controlled controlled either by aa filter-pressing filter-pressing mechanism, mechanism, or result of the decrease in density density of of an an interstitial interstitial liquid liquid related related to to enrichment enrichment of of volatiles. volatiles. 36 �34 -4 -2 0 2 S (°Ioo) 4 6 8 10 0 100 200 E -C 300 a) 400 500 600 Figure of sulfide minerals in the South Kawishiwi intrusion, Spruce Figure 1.1.S 5values s values of sulfide minerals in the South Kawishiwi intrusion, SpruceRoad Road area, MN. area,Duluth DuluthComplex, Complex,MN. 37 �Sublayer, Main Mass, and and Offsets, Sudbury Sudbury Geochemical relationships between the Sublayer, Igneous Complex, Canada Canada Lightfoot, P C . ' Farrell, Farrell, K.2, K., Moore, Moore, M.2, M.,, Pekeski, Pekeski, D.2, D., Crabtree, Crabtree, D.3, D . ~and ,andKeays, Keays,R.R.2 R.R.' Lightfoot, P.C.1. 1 Ontario Geological Geological Survey, Survey, Sudbury, Sudbury, Ontario OntarioP3E P3E 6B5 6B5 Mineral Deposits Section, Ontario 2 2 Department of Earth Earth Sciences, Sciences, Laurentian Laurentian University, University, Sudbury, Sudbury, Ontario OntarioP3E P3E2C6 2C6 Department 3 Geoscience Survey, Sudbury, Sudbury, Ontario, Ontario, P3E P3E 6B5 Geoscience Laboratories, Laboratories, Ontario Geological Survey, major element element oxide and trace element concentrations in samples samples from the Analyses of the major Main Mass felsic norite, quartz quartz gabbro, gabbro, and and granophyre granophyre of of the the Sudbury Sudbury Igneous Igneous Complex Complex (SIC) confirm t . % Si02, SiO,, (SIC) confirm that that there there is aa compositional compositional gap gap between between norites norites (e.g: (e.g: 55-60 55-60 w wt.% 3.5-5.5 wt.% (e.g: 65-74 65-74 w wt.% ppm Nb) Nb) and and granophyres granophyres (e.g: t.% 3.5-5.5 w t . % MgO, MgO, 5-8 5-8ppm ppmTh, Th, and and 5-10 5-1 0ppm SiO2; 0.5-1.6 0.5-1 .6wt.% wt.% MgO 13-17 SO2; 13-17ppm ppmTh, Th, and and112-1 2-1 8ppm Nb). Despite the differences differences in in elemental concentrations, rare earth concentrations, there is a remarkably remarkably narrow narrow range range of of ratios of the rare overlying elements (REE), (REE),Ba, Ba,Rb, Rb,Th, Th,U, U,Nb, Nb,Ta, Ta,Hf, Hf, Zr, Zr, and and YY in in the the felsic felsic norite and the overlying granophyre LaISm = dNb = -2.6, ThINb .I ). These similarities granophyre (e.g. (e.g. La/Sm = 5.4-7.0, 5.4-7.0, G Gd/Yb = 2.1 2.1-2.6, Th/Nb =0.9-1 =0.9-1 .1). simi'arities in ratios of elements are unlikely ttoo be be explained if the granophyre granophyre and felsic norite crystallised from magmas derived sources; rather, these data support models derived from from different sources; magma. We where the felsic norite norite and and granophyre granophyre are derived from a common magma. We explore explore the implications for this data for the the formation formation of of the the Main Main Mass Mass of of the theSIC, SIC, and and suggest suggest variations are are inconsistent inconsistent with with in-situ crystallisation of aa single intrusion that the observed observed variations or melt sheet. The reason for this is suggested to t o be be the compositional compositional gap between between the the which is not readily explained explained by by fractional fractional crystallisation crystallisation felsic norite and the granophyre granophyre which of one one pulse pulse of of magma. magma. The composition of quartz quartz diorite diorite from from the the Parkin Parkin and and Whistle Offsets Offsets and and leucocratic norites from the embayment structure at Whistle Mine, at the the north-eastern north-eastern margin of the SIC occupy occupy tight similar fields (quartz diorite: diorite: 55-64wt.% 55-64wt.% SIO2; SiO,; leucocratic norite: 59-62 for 59-62wt.% wt.%SiO2). SiO,). The The ratios ratios of of the theREE REE and other incompatible trace elements for these rocks are are very very similar similar tto those of of the the Main Main Mass Mass (e.g. (e.g.ThINb Th/Nb=0.8-1.2, these o those =0.8-1.2, La/Sm LaISm =5.36.6; Gd/Yb = 2.3-3.0), 2.3-3.0), although although in in detail, detail, when whenthese thesesamples samples are are normalised normalised to t o average average 6.6; GdNb = felsic norite, of the data for the norite, they they are are slightly slightly enriched enriched in inthe the light lightREE. REE. Comparison of the Parkin Offset Offset tto Parkin o other offsets offsets around around the the SIC SIC suggest that there is is aa broad broad compositional difference between those formed north of the SIC compared w with SIC compared i t h those formed tto o the south. With With the the exception exception of of the the Manchester Manchester Offset, Offset, those those formed formed to t o the thesouth southhave have TiO2 =0.65-0.80 wt.%, Sr = 150-350ppm, ppm, La/Sm LaISm==5-6 5-6and and La/Yb Lamb =10-15, = 10-15, whereas whereas those those TiO, =0.65-0.80 Sr =150-350 =0.8-1 .1, Sr = = 350-550 350-550 ppm, = 5.8-6.8, 5.8-6.8, and formed ttoo the north north have have TiO2 TiO, = 0.8-1.1, ppm, La/Sm LaISm = La/Yb = = 16-23. 1 6-23.The TheManchester Manchester Offset Offset has llow Lamb o w Ti02 TiO, and and Sr Sr with with elevated elevatedSiO2, SiO,, La/Sm, LaISm, and and La/Yb. Although the trace element ratios of most of the Offsets LaNb. Although Offsets overlap overlap with w i t h the the Main Main differences between those those tto Mass of the SIC, SIC, the small differences o the north and south of the SIC may be consistent w with i t h contamination contamination by by compositionally different country country rocks. rocks. Our new data for the the Sublayer Sublayer at Whistle Whistle Mine Mine suggest suggest that that there there is is aa compositional compositional spectrum between orthopyroxene-poor norites through norites containing up ttoo 40 4 0 modal modal percent cumulate orthopyroxene; orthopyroxene; the the more more orthopyroxene-rich orthopyroxene-rich samples samples sometimes sometimes contain contain olivine.The Theportion portionofofthe theembayment embaymentclosest closestt to the Whistle Whistle Offset Offset contains fresh Fo6567 Fo65.67olivine. o the leucocratic norite and quartz diorite. We believe that the classification of either the quartz quartz diorite. believe that quartz diorites of the Offsets Offsetsor orthe theleucocratic leucocraticnorite noriteof ofthe theembayment embayment as asSublayer-type Sublayer-typerocks rocks may be inappropriate, and w we inappropriate, and e suggest that they they are are more more closely related to t o the the magma magma Main Mass Mass of of the the SIC. SIC. giving rise ttoo the Main Compositional data data for the noritic noritic matrix matrix of of the theSublayer Sublayer in in the the embayment embayment structure structure at Whistle Mine indicate that the bulk composition of the Sublayer is more more mafic mafic (45-53 Sublayer is (45-53 1 38 �wt.% w t , % Si02; SiO,; 5-12 5-1 2 wt.% w t . %MgO) MgO)than thanthe thefelsic felsicnorite noriteand andheterogeneous heterogeneous with with respect respect to to major and trace element abundance. abundance. Much of the the heterogeneity heterogeneity may may be be due due to t othe thevariable variable amount of assimilation assimilation of of diabase diabase and and gabbro inclusions. The composition composition of of inclusion-free inclusion-free Sublayer markedly different when compared to Sublayer norite is markedly t o average felsic norite of of the the Main Main Mass. The Sublayer Sublayer from the Whistle Whistle embayment embayment has has Ti/Y T i N=1 175, =1 1.4, 75, DyIHf Dy/Hf = .4, LaISm La/Sm =3.9, = 3.9, and La/Ta La/Ta == 105, 105, which which contrasts contrasts with the felsic norite 0.9, norite which which has has Ti/Y T i N= = 220, Dy/Hf DyIHf = =0.9, La/Sm = = 6.2, 6.2, and and LLa/Ta =661. Compositionally, the the diabase and gabbro inclusions inc'usions have ana = 1. Compositionally, LaISm Ti/Y= T i N =192, 192, Dy/Hf DyIHf =2.8. La/Sm LaISm =3.2, and and La/Ta L a n a =44. ItItis is shown shown that that the the composition composition of of the Sublayer matrix reflects reflects aa component component of of assimilation assimilation of of hornfelsed hornfelsed diabase diabase inclusions, inclusions, and the composition of the the Sublayer Sublayer is inconsistent inconsistent with withthe theassimilation assimilationof oflarge largeamounts amounts of footwall footwall granitoid. granitoid. The The compositional compositional difference difference between betweenthe theSublayer Sublayer norite noriteand and the the suggests that they were emplaced different batches Main Mass norite suggests emplaced as different batches of of magma, magma, one one of of which was laden with partially assimilated inclusions of diabase. The presence of inclusions was laden with partially assimilated inclusions of diabase. The presence inclusions and footwall footwall breccias suggest suggest that that the breccias in the the massive massive suiphides sulphides and of Subayer Sublayer norite norite in In sulphides were formed after at and sulphides at least least some some of of the theSublayer Sublayer magma magma had had crystallised. crystallised. In detail, a more complete understanding of the geochemical variations variations in the Sublayer will detail, Sublayer will come from detailed microprobe studies of the the accessory accessory mineral mineral phases phases such such as as apatite, apatite, zircon, baddelyite, zircon, baddelyite, and biotite. 39 �Sublayer and the mafic-ultramafic mafic-ultramafic inclusions, Whistle Geochemical variations variations within within the Sublayer Mine, Sudbury Sudbury Igneous Igneous Complex, Complex, Canada Canada Lightfoot, P.C.1. P.c.', Farrell, Farrell, K.2, K . ~Moore, Moore, , M.', Pekeski, Pekeski, D.2, D . ~Crabtree, Crabtree, , D . ~and and , Keays, Keays,R.R.2 R.R.* Lightfoot, M.2, D.3, 1 Deposits Section, Section, Ontario Ontario Geological Geological Survey, Survey, Sudbury, Sudbury, Ontario OntarioP3E P3E6B5 6B5 Mineral Deposits 22 Department of Earth Earth Sciences, Sciences, Laurentian Laurentian University, University, Sudbury, Sudbury, Ontario OntarioP3E P3E2C6 2C6 Department 3 Geoscience Laboratories, Laboratories, Ontario Ontario Geological Geological Survey, Survey, Sudbury, Sudbury, Ontario, Ontario, P3E P3E 6B5 6B5 Geoscience i n the embayment embayment structure structure at at Whistle WhistleMine, Mine,Sudbury SudburyIgneous Igneous The Sublayer norites in orthopyroxene-poor to t o cumulate cumulate orthopyroxene-rich orthopyroxene-rich non-poikititic non-poikilitic Complex (SIC) consist consist of orthopyroxene-poor norites with w i t h up up to t o55modal modalpercent percent sulphide sulphide and and 10% 1 0 % inclusions. inclusions. The The Sublayer Sublayer textured norites often contains contains inclusions inclusions and and tends tends to t o be be heterogeneous; heterogeneous; multiple samples from the norite often t o analytical analytical same outcrop showing 1-10 1-10 times more variation than is attributed to The inclusion-free inclusion-free norites norites are less heterogeneous, heterogeneous, mostly i t h 1-5 1-5 times times more more uncertainty. The mostly w with t o analytical analytical uncertainty. uncertainty. A A small small number number of of samples samples of variation than can be attributed to norite contain contain fresh fresh olivine olivineofofcomposition compositionFo6567 Foc5-^ w i t h 970-1 970-13lOppm 3 1OppmNi. Ni. Sublayer norite with population at at Whistle Whistle isisequally equally split splitbetween betweenhornfelsed hornfelseddiabasediabaseThe inclusion population i t h anhedral anhedral porphyritic gabbro inclusions inclusions w with porphyritic clusters of feldspar, feldspar, and and poikilitic-textured poikilitic-textured melanorites It is is shown shown that that compositional compositional data data for for the thediabase-gabbro diabase-gabbro melanorites and pyroxenites. It o inclusions indicate broad broad similarities in major and trace element composition tto inclusions Matachewan diabase diabase dykes. The melanorite inclusions contain cumulate magnetite, Matachewan magnetite, apatite, apatite, zircon, baddelyite, baddelyite, orthopyroxene, orthopyroxene, ±Âolivine, olivine, and andintercumulus intercumulusaugite, augite, plagioclase, plagioclase, biotite, biotite, zircon, rocks and and are are unusual unusual in having having very high high apatite apatite(0.3 (0.3modal modal and sulphide. They are fresh rocks %), Fo7274 and 270-1490 %), and and biotite biotite(5-10 (5-10modal modal%) %)contents, contents,olivine olivinewith with and 11270-1 4 9 0 ppm ppm Ni, Ni, yet yet whole-rock MgO MgO contents contents of of 15-22 15-22wt.% w t . %MgO MgOand and50-80 50-80time timechondrite chondriteLREE LREE whole-rock 1 abundances. abundances. The melanorite and pyroxenite inclusions range range in composition corn positionfrom from88t to 28 wt.% wt.% o 28 MgO; the the least least mafic mafic poikilitic-textured poikilitic-texturedmelanorites melanoriteshave havetrace traceelement elementabundances abundancesand and ratios which, on on average, average, are are similar similar to t o the the Sublayer Sublayer norite norite matrix. matrix. The Theolivine-bearing olivine-bearing melanorite melanorite inclusions and pyroxenites have have elevated Ti/Y, Tim, Dy/Hf, DyIHf, La/Ta, Lana, and and low lowLa/Sm LaISm which which are are all features of the the Sublayer Sublayer matrix, but but the the most most ultramafic ultramafic samples samples show strong strong depletion in compared tto the Sublayer Sublayer matrix. matrix. Nd isotopic analysis of the in the the HREE HREE compared o the the melanorites .8SGa)isisbetween between -6 and -7 which which compares melanorites indicate that €Nd eNd (1 (1.85Ga) compares with with the the Sublayer matrix which which has has eNd eNd (1 (1.85Ga) -7.5 to t o-8. -8. Sublayer .85Ga)of of between between -7.5 There There is is aa significant significant range range in intrace traceelement elementabundance abundance and and ratios ratiosin i nthe themelanorites melanorites and and pyroxenites, pyroxenites, and and in detail, much much of of this this appears appears not not to t o be be linked linked to t oany anysingle single fractionating we fractionating mineral mineral phases phases such as olivine or hypersthene. hypersthene. Rather, Rather, w e suspect that the the compositional compositional variations are more a function function of of variations variations in in the the modal modal accessory accessory mineralogy of the rocks, rocks, and and we w e therefore therefore suggest suggest that that mineralogical mineralogical studies studies represent represent an an important next-step next-step in in unravelling unravelling the origin origin of of the the Sublayer. Sublayer. In the course of our our studies, studies, we w e have have acquired acquired compositional compositional data data from from aa number number of of embayment embayment structures structures around around the SIC, SIC, and we w e find find that that each each embayment embayment contains contains noritic noritic Sublayer Sublayer matrix with w i t h aa distinctive distinctivetrace traceelement elementsignature. signature. For For example, example, analysis analysis of of Sublayer matrix matrix from from the the Fraser Fraser and McCreedy McCreedy Mine areas on the northern northern margin margin of of the the SIC more closely resembles the composition of the the main main mass mass norite; norite; at at Crean Crean Hill Hill Mine Mineat at the Tim the southwestern southwesternmargin marginof of the theSIC, SIC, the thetrace traceelement elementsignature signaturehas has marked marked low low Ti/Y accompanied by low La/Ta La/Ta which is different different to t o both boththe the Whistle Whistle embayment embayment and and the Fraser-McCreedy em bayments.. These differences between embayments suggest Fraser-McCreedy embayments.. These between embayments suggest contributions contributions from from differing differingcrustal crustalreservoirs, reservoirs, and and suggest suggest that thatthe theSublayer Sublayer magmas magmas 40 �equilibrated andlor different different inclusion inclusion equilibrated at at depth depth and and in-situ in-situ with with either either different conduit walls and/or populations. populations. 41 �BANQUET TALK TALK - ABSTRACT ABSTRACT The relationship between between mantle mantle plumes, plumes, flood flood basalts basalts and and mineralization mineralization Peter C. C. Lightfoot Lightfoot 6B5. Mineral Deposits Deposits Section, Section, Ontario OntarioGeological Geological Survey, Survey, Sudbury, Sudbury, Ontario OntarioP3E P3E6B5. Mineral remarkable wealth of of information information on on the the chemostratigraphy chemostratigraphy of the basaltic basaltic rocks rocks found found in in A remarkable n o w available. available. Studies Studies of continental continentalflood floodbasalt basalt(CFB) (CFB) large igneous igneous provinces is now sequences sequences of the the Karoo, Karoo, Parana, Parana, Deccan, Deccan, Keweenawan, Keweenawan, West Westand andEast EastGreenland, Greenland, and and 1-15 k m thick thick successions successions of basaltic basaltic rocks rocks can can be be erupted erupted Siberian Traps Traps indicate indicate that that 1-15km close to t o continental continentalmargins marginsonto ontoyoung youngepicontinental epicontinentalsedimentary sedimentarysequences sequences and and ancient ancient close amphibolitic to t o granulitic granuliticterrains. terrains.These Thesegiant giantCFB CFBrecord record the the eruption eruptionof oflarge largevolumes volumes(up (up amphibolitic t o 2x106 2x1 O6 km3) km3) of magma over in some cases very short time time intervals intervals (e.g. (e.g. Deccan Deccan to Trap: < < 1 Ma.). Single Single lava flows flows may may extend extend for forseveral severalhundred hundred kilometers kilometerslaterally, laterally,and and chemical stratigraphy stratigraphy of of the the lavas lavas can can be be matched matched over over these these distances, distances, and and the the the chemical basalts can be be grouped grouped into into Formations. Formations. An A n important importantissue issue concerns concerns the the relationship relationship of of these these CFB CFB ttoo mantle plumes or hot spots. In In oceanic oceanic settings, mantle mantle plumes plumes are believed tto o control the distribution distribution of of ocean ocean Hawaiian chain. chain. Some Some of of these these island island chains chains converge converge with withCFB CFB island chains such as the Hawaiian continentalmargins, margins, and andthe theReunion-Chagos-Lacadive Reunion-Chagos-Lacadive system system is is one one example example where where the the at continental age of the the rocks rocks becomes becomes progressively progressively older older away away from fromthe thepresent-day present-day Reunion Reunion Island Island hot spot towards the 60 6 0 Ma. Ma. Deccan Deccan Trap. In detail, detail, recent work has shown that even the within the the Deccan Deccan appear appear tto o have migrated from o south as the eruptive centers within from north tto Indian Subcontinent Subcontinent migrated migrated northwards northwards over over the the Reunion Reunion hot hot spot. spot. In other settings, eruption more directly directly related tto rifting of eruption of of CFB CFB appears more o passive rifting of (c.30 3 0Ma.) Ma.)Parana Parana CFB. CFB. In In continental margins. margins. An A n example example of of this this is is the the more more protracted protracted(c. continental detail however, fall close close tto however, both both the the Parana Parana and Etendeka fall o the pre-rifting location location of of the the Tristan Tristan de Cunha Cunha hot spot, spot, and and so so even even in in these these cases cases plumes plumes appear appear to t o have have played played aa role. role. These features features are are all all very very satisfying satisfying confirmations of of the effects effects of of continental continental migration over mantle plumes, but the really exciting implications of these data comefrom from migration over mantle plumes, but the really exciting implications of these data come application in in mineral mineral exploration exploration strategies. strategies. One One of the the largest largest deposits deposits of of magmatic magmatic their application Ni, with the Ni, Cu, Cu, and and platinum platinum group group elements is associated with the Noril'sk Noril'sk Region Region of of the the Siberian Siberian Trap. Other major deposits are associated w with i t h the Keweenawan, Keweenawan, and and extensive extensive exploration programs programs have have been been pursued around the Insizwa Complex of the Karoo Karoo and and the Greenland Greenland CFBs. CFBs. At A t Noril'sk Norilfskininthe theSiberian Siberian Trap, Trap, the the lavas lavas are are split into into two t w osequences. sequences. The The Lower Lower Sequence has high high TiO, Ti02 (>1 .7) and ( > 1.7) and Gd/Yb (>2) ( >2)relative relativeto t othe theUpper UpperSequence, Sequence, but but both both Sequence has sequences contain picritic picritic basalts. basalts. The The Lower LowerSequence Sequence appears appears to t o have have been been derived derived from from deep asthenospheric mantle as the geochemical composition of the least contaminated deep asthenospheric composition of the least contaminated rocks rocks closely closely resembles resembles ocean ocean island island basalt basalt remobihsed remobilised from the mantle by by aa hot hot spot. spot. The The Upper Sequenceconsists consists of of aa ffew Upper Sequence e w picritic flows flows overlain overlain by by tholeiites, and and these rocks have geochemical signatures suggesting derivation from aa combination combination of of shallow shallow asthenospheric and the the continental mantle lithosphere. Basalts from from the the lower part asthenospheric mantle and lithosphere. Basalts of the the Upper Upper Sequence Sequence have havehigh highSi02, SiO,, LILE, LILE, LREE, LREE, and elevated elevated Th/Nb, ThINb, La/Sm, LaISm, and and radiogenic Sr-isotopic compositions. compositions. Basalts Basaltswwith 52-56wt.% Si Si02, La/Sm>3, > 3, and and SrSrradiogenic Sr-isotopic i t h 52-56wt.% O,, LaISm isotope signatures greater greater than than 0.707 0.707 have interacted w with i t h upper upper continental crust, and and become contaminated. Importantly, these lavas are also long bereft of their Ni, Cu, and become these lavas their Ni, Cu, and PGE, and have have CuIZrC0.2 Cu/Zr<0.2 and and Ni/MgO< NiIMgO <10; 10; these these are are features attributed to t o the the PGE, and equilibration of the magma with magma w i t h aa sulphide sulphide liquid. Upwards in the basalt stratigraphy, the degree of contamination contamination recorded in the rocks rocks is is progressively progressively less and this couples with with 42 �an increase in the tenor of of Ni, Ni, Cu, Cu, and and PGE. PGE. These features are found in the Nadezhdinsky Nadezhdinsky Formation lavas, lavas, and and these these lavas lavas were were erupted erupted in the Noril'sk Noril'sk Region close tto Region close o the Noril'skof Ni, Ni, Cu, Cu, and andPGE PGE missing from from the the Nadezhdinsky Nadezhdinsky Kharaelakh Fault. The amount of o account and Formation lavas lavas is is more more than than enough enough tto account for for the mineralisation at Noril'sk and and Talnakh intrusions consist of of at at most most several several hundred hundred meters meters of Talnakh. The Noril'sk and picritic to t o gabbroic gabbroic rocks, rocks, yet yethost hostthick thicklenses lensesofofmassive massiveNi-Cu-PGE Ni-Cu-PGEmineralisation. mineralisation. The The basalts in in this this context contextisisthat thattheir theirlow lowNi, Ni,Cu, Cu,and andPGE PGEcontents contentsare are importance of the basalts presumably due due tto o the extraction of of the the metals metals by by the the same same suiphide sulphide that that is is found found at at Noril'sk; Noril'sk; the the compositions compositions of of the the basalts basalts then become become important exploration tools. In In detail, the combination combination of of the the elemental elemental and and isotopic isotopic composition composition of of Sr Sr in inthe theintrusions intrusionsand andlavas, lavas, the together with w i t hthe theS-isotopic S-isotopic composition composition of of the the suiphides sulphides suggest suggest that that much much of of the the sulphur sulphur in the Talnakh ores was was derived derived from from Devonian Devonian evaporites. evaporites. This This suggests suggests that thatevaporite evaporite sulphur played a very important part in in the the genesis genesis of the Noril'sk Noril'sk deposits. deposits. In the Keweenawan, Keweenawan, aa thick thicksequence sequence of of lavas lavason onthe theBlack BlackBay BayPeninsula Peninsula and and St. St. In Ignace Island (the Osler Group) record many of the same same features as the Noril'sk Noril'sk basalts. basalts. lgnace Lower Formation Formation of of the the Osler Osler Group Group have have many many similarities similarities to t o the theLower LowerSequence Sequenceat at The Lower Noril'sk and and may be linked ttoo a mantle plume that initiated rifting. rifting. The The Central Central Formation of the Osler and ThINb, Th/Nb, and these these same same lavas lavas have have very very low SiO,, La/Sm, LaISm, and Osler Group has elevated Si02, Ni/MgO and moderate basalts of of Noril'sk. Noril'sk. Unfortunately moderate tto o low Cu like the Nadezhdinsky Nadezhdinsky basalts Cu was mobile during alteration, and therefore this this criterion criterion is is less less diagnostic diagnostic than than the the Ni/MgO ratio. The presence of abundant gabbroic rocks along the northern margin of NiIMgO ratio. The presence of abundant gabbroic rocks along the northern margin ofLake Lake Superior and and iin Plate, combined combined with with the presence n the Nipigon Plate, presence of giant Ni-Cu deposits at Duluth Duluth and and smaller deposits in in the the Crystal Crystal Lake Lake Gabbro Gabbro and Port Coldwell Coldwell Complex Complex encourage further exploration for Noril'sk-type Noril'sk-type targets targetsininthe theKeweenawan. Keweenawan. 43 �STRUCTURAL GEOLOGY GEOLOGYAND TECTONIC TECTONICEVOLUTION EVOLUTION OF OF THE THE VIZIEN VIZIEN GREENSTONE GREENSTONE STRUCTURAL BELT IN IN MINTO MINT0BLOCK, BLOCK,NORTHEASTERN NORTHEASTERNSUPERIOR SUPERIORPROVINCE, PROVINCE, NORTHERN NORTHERN BELT QUEBEC QUEBEC LIN, LIN, *Shoufa, *Shoufa,SKULSKI, SKULSKI,Tom, Tom,and andPERCIVAL, PERCIVAL,John JohnA., A.,Geological GeologicalSurvey Surveyof of Canada, Canada,601 601 Booth St., St., Ottawa, Ottawa,ON ONK1A KIA 0E8, OE8,Canada Canada Booth The Minto MintoBlock Blockin in the thenortheastern northeasternSuperior SuperiorProvince Provinceisis characterized characterizedby by north-northwesterly north-northwesterly structural structural The aeromagnetic trends trends that that contrast contrastwith with easterly easterly to to east-southeasterly east-southeasterlytrends trendsin in the the southern southern part part of of the the and aeromagnetic province. ItItconsists consistsmainly mainlyof ofplutonic plutonicrocks, rocks,but butalso alsocontain contain some some greenstone greenstone belts belts with with well-preserved well-preserved province. supracrustal sequences, sequences,including including the Vizien, Kogaluc, Payne our supracrustal Payne Lake Lake and and Qalluviartuuq Qalluviartuuq belts. belts. During our studyof of the the Minto MintoBlock, Block,we we paid paid special specialattention attention to to the the greenstone greenstone belts, belts, because because they they generally generally contain contain study more complete complete structural record than associated granitoid aa more granitoid rocks. rocks. Here we report results of a detailed structuralstudy studyof of one oneof of the thebelts, belts,the theVizien Vizienbelt, belt,and anddiscuss discusstheir their tectonic tectonicimplications. implications. structural C, D and X). PanelXXconsists consistsof of The Vizien belt consists of five structural panels (A, B, The Vizien belt consists of five structural Panel pillowed,nonvesicular, nonvesicular,low-K low-Ktholeiitic tholeiiticbasaltic basalticandesites andesitesintruded intrudedby byperidotite peridotiteand andgabbro gabbrosills sills(—2786 (-2786 pillowed, Ma), and and isisinterpreted interpretedto to be beaafragment fragmentof oftransitional transitionaloceanic oceaniccrust. crust.Panel PanelAAconsists consistsof ofupwardupwardMa), shoalingcalc-alkalic calc-alkalic(submarine (submarineto to shallow-marine shallow-marineor or subaerial) subaerial) mafic, mafic, intermediate intermediate and felsic felsic volcanic volcanic shoaling rocks(—2724 (-2724 Ma) formed in in aa continental continentalarc arc rocks Ma) and and minor minor sedimentary sedimentary rocks, and is interpreted to have formed environment.Panel PanelCCconsists consistsofofa abimodal bimodalsequence sequence subaerial high-Ktholeiitic tholeiitic lava flows -2722 environment. ofofsubaerial high-K lava flows ofof —2722 Ma, interpreted interpreted to to have have formed formed in in aa continental continental extensional environment Panel BB consists consistsof of aa basal basal Ma, environment. Panel conglomerate(<—2718 (<-27 18 Ma) tonalitic basement basement of of conglomerate Ma) and and greywacke greywacke that lie unconformably unconformably on saprolithic saprolithic tonalitic -2940 Ma. shear —2940 Ma. The The top of panel panel B consists of enigmatic enigmatic mafic tholeiitic tholeiitic lavas and a melange that is in shear Panel D D consists consists of of highly highly strained strained rocks of panels B, zone contact contact with, and contains clasts of, panel X. zone X. Panel CandX. C and X. Detailed Detailedstructural structuralanalysis analysisof of the theVizien Vizienbelt beltdemonstrates demonstratesfive fivegenerations generationsof of ductile ductile D5),asaswell wellas asbrittle brittlefaulting. faulting.Dl D lisisindicated indicatedby bythe thepresence presenceof ofaapre-D2 pre-D2foliation foliation deformation (Dl (Dl totoD5), deformation and D2isis and deformed deformed melange melange fragments. fragments. ItItisisinterpreted interpretedto to be be related related to to the the thrusting thrusting of panel X over B. D2 responsible for the main penetrative foliation (S2), axial-planar to tight to isoclinal F2 folds. The S2 responsible for the main penetrative foliation (S2), axial-planar foliation foliation generally generallystrikes strikessubparallel subparallelto to the thepanel panel boundaries boundariesand and lithological lithologicalcontacts, contacts,and anddips dipssteeply. steeply. On On the the S2 S2foliation, foliation,steeply steeplyplunging plunging mineral mineral and/or and/or stretching stretchinglineations lineations are are well well developed. developed. The TheD2 D2 deformation panels X X and and AIC. A/C. Kinematic deformationis is concentrated concentrated in a shear zone between panels Kinematic indicators indicate indicate that that panel panel X X was was thrust thrust over over both both panels panels A A and and C C during during D2. F3 F3and andF4 F4folds foldsare areopen opentototight, tight,with with NNW-SSEIncontrast contrastto tothe theF2 F2folds, folds, they they lack lack an an axial axial NNW-SSE-and and E-W-trending E-W-trendingaxial axial planes, planes, respectively. In planar F3and andF4 F4folds foldswarp warpthe theS2 S2foliation, foliation,panel panelboundaries boundariesand andlithological lithologicalunits. units. They They planar foliation. foliation. F3 dominate D5isisassociated associatedwith withdextral dextraltranscurrent transcurrentmovement movementalong alongaaNNW-SSE NNW-SSE dominatethe themap mappattern. pattern.D5 trending trending shear shear zone. zone. Analysis Analysisof ofthe thestructural structuraldata dataindicates indicatesthat thatthe theS2 S2foliation foliationwas wasplanar planarbefore beforebeing beingfolded foldedby by F3. F3.Therefore, Therefore,the thepre-F3 pre-F3geometry geometryofofthe thebelt beltcan canbeberestored restoredby byreorienting reorientingS2 S2into intoaaplanar planargeometry. geometry. The Therestored restoredgeometry geometryof ofthe theVizien Vizienbelt beltisismuch muchsimpler, simpler,with with panel panel BB on on one one side, side,and and panels panels A A and and CC on on the the other other side, side, of panel panel X. This Thisregular regulargeometry geometrysuggests suggeststhat that panels panels A A and and C C were were probably probably part part of of the same block when they were juxtaposed with panels B/X. Similar La/Nb ratios and Nd isotope the same block when they were juxtaposed with BJX. Similar LafNb ratios and Nd isotope compositions supportaamodel modelin inwhich whichpanel panelCCformed formedin inaarift riftwithin withinthe thepanel panelAA compositionsin inpanels panelsAAand andCCsupport continental continentalarc. arc. The Thearc arcwas wasseparated separatedfrom fromthe thebasement basementof ofpanel panelBBby by oceanic oceaniccrust, crust,anomalous anomalous fragments aspanel panelX. X. The Thecollision collisionrelated relatedtotothe theclosure closureofofthe theocean oceanwas was fragmentsof ofwhich whichmay maybe bepreserved preservedas responsible wasthrust thrustover overpanel panel B. B. Deposition Depositionofofpanel panel responsiblefor forthe theDl D ldeformation, deformation,during duringwhich whichpanel panelXXwas B sedimentary rocks is tentatively interpreted to have occurred in a foreland basin; geochronological data B sedimentary rocks is tentatively interpreted to have occurred in a foreland basin; geochronologicaldata on on panel panel BB volcanics volcanicswill will resolve resolvewhether whetherthey they are are autocbthonous autochthonousor or exotic. exotic. D2 D2deformation deformationwas wasrelated related to to back-thrusting, back-thrusting,during duringwhich whichpanels panelsX/B X/Bwere wereoverturned overturnedand andthrust thrustover overpanels panelsA/C. A/C. 44 �PREDICTION AND AND DISCOVERY DISCOVERYOF OFPGE PGEOCCURENCES OCCURENCESIN INTHE THEDULUTH DULUTH COMPLEX COMPLEX AT AT DULUTH DULUTH PREDICTION MILLER, James JamesD., D., Jr., Jr., Minnesota MinnesotaGeological GeologicalSurvey, Survey,2642 2642University UniversityAve., Ave., St. St. Paul, 55114 MILLER, Paul, MN MN 55114 Two intervals intervals of of anomalous anomalousPGE PGEconcentrations concentrationshave haverecently recentlybeen been discovered discovered in in the the medial medial part part of of the the Two series of of the the Duluth Duluth Complex Complex at at Duluth. Duluth. These Thesediscoveries, discoveries,though though far far from from economic, economic, validate validate layered series earlier speculation speculation (Miller, (Miller,1993) 1993)that thatCu-Ni Cu-Nisulfide sulfideand andPGE PGEmineralization mineralization might might be be associated associated with with earlier changes in cumulate cumulate mineralogy mineralogy and texture that are are thought thought to to represent represent interruptions interruptions to to the the abrupt changes steady-statecrystallization crystallization of of the the magma. magma. steady-state The layered layered series seriesat at Duluth Duluth (DLS) (DLS)isisaa4-km-thick 4-km-thickmafic maficlayered layeredintrusion intrusionthat that was was emplaced emplacedin in the the The lower part of of the the North Shore Shore Volcanic Volcanic Group Group (NSVG). Preceeding Proceedingthe theemplacement emplacementof of the the DLS DLS was was the the lower formation of an approximately 1-km-thick accumulation of gabbroic anorthositic rocks of the anorthositic formation of an approximately 1-km-thick accumulation of gabbroic anorthositic series. Despite Despiteaasharp sharpchilled chilledcontact contactbetween betweenthe theDLS DLSand andthe theoverlying overlyinganorthositic anorthositicseries, series,the thetwo two series have identical U-Pb U-Pb ages ages of 1099±0.5 1099kO.5 Ma (Paces and Miller, 1993). Overall, Overall,the the internal internalstructure structure series sheet-like DLS DLS dips dips 25400 25-40Âtotothe theeast, east,roughly roughlyconformable conformablewith with the the enclosing enclosingvolcanic volcanic rocks. rocks. of the sheet-like The cumulate cumulatestratigraphy stratigraphyand and cryptic cryptic layering layering of of the the DLS is consistent with bottom-up fractional fractional The crystallization crystallizationof of aashallow shallow(4-8 (4-8km) km)tholeiitic tholeiiticmagma magmabody bodythat thatwas wasintermittently intermittently open open to recharge recharge and and eruption. The TheDLS DLScan canbe bedivided dividedinto into55stratigraphic stratigraphiczones zones (Miller (Miller and others, 1993). 1993). Above Above aa 200200- to to eruption. 300-m-thick, heterogeneous basal contactzone zoneofofcoarse-grained coarse-grainedolivine olivine gabbro gabbro and and medium-grained medium-grained 300-rn-thick, basal contact troctolite, troctolite, the the DLS DLS passes passes into into to to aa 11-to to 1.5-km-thick 1.5-km-thick troctolite troctolitezone zoneofofmostly mostlyhomogeneous homogeneoustroctolitic troctolitic (Pl+01) cumulates. Marked Markedby by an an abrupt abrupttransition transition to to aa coarse coarse ophitic ophitic olivine olivine gabbro gabbro at its base, a 1-km1-km(P1+01) thick thick cyclic cycliczone zoneisischaracterized characterizedby by atatleast leastfive, five,5050-to to 200-rn-thick, 200-m-thick, macrolayered macrolayered couplets couplets of troctolitic and and gabbroic gabbroic(Pl+Aug+Ox±Ol) (Pl+Aug+Ox*Ol) cumulates. cumulates. Typically Typicallyabrupt abruptreversals reversalsto totroctolitic troctoliticcumulates cumulatesmark markthe the base base of of the the next next cycle. cycle.The Thegabbroic gabbroiccumulate cumulateintervals intervalslocally locallycontain containcmcm-to torn-scale m-scalelayers layersand andlenses lenses of of fine-grained fine-grainedilmenitic ilmeniticolivine olivinegabbro gabbro(microgabbro), (microgabbro),which whichare areclosely closelyassociated associatedwith withthe thePGE PGE mineralization. mineralization.The Thecyclic cycliczone zonegives givesway way to toaa11-to to 1.2-km-thick 1.2-km-thickgabbro gabbrozone zonethat thatisiscomposed composedmostly mostly of with locally locally abundant abundantanorthositic anorthositicseries seriesinclusions. inclusions.The Theupper upper contact contact of iron-rich iron-rich gabbroic cumulates with zone definedby by aaloss lossof of cumulate cumulatetexture textureand and isis very very uneven uneven in in thickness thickness owing owing to the irregular irregular nature nature zone isisdefined of of the the contact contactwith with overlying overlyinganorthositic anorthositic series. series. The Thezone zoneisiscomposed composedof ofaahybrid hybridrange rangeof of rock rocktypes types from from apatitic apatiticquartz quartzferromonzodiorite, ferromonzodiorite,which whichmakes makesup upmost mostof ofthe thezone zonewhere whereititisisthickest, thickest,totobiotitic biotitic ilmenite ilmeniteferrodiorite, ferrodiorite,which whicheverwhere everwhereforms formsthe the"chill" "chill"against againstthe theanorthositic anorthositicseries. series. Many Many models models of of sulfide-hosted sulfide-hostedPGE PGE mineralization mineralization in in mafic mafic layered intrusions (e.g., Campbell and others, 1983; Boudreau and McCallum, 1992) stress the importance others, 1983; Boudreau and McCallum, 1992) stress the importance of disruptions to the steady-state fractional fractionalcrystallization crystallizationby by such suchprocesses processes as as magma magma recharge, recharge, country country rock assimilation, volatile fluxing, and eruption. With recent mapping and petrologic studies fluxing, and eruption. With recent mapping and petrologic studies(Miller (Millerand andothers, others,1993) 1993)indicating indicating such an openness to the DLS system, the Minnesota Geological Survey, with funding from such an openness to the DLS system, the Minnesota Geological Survey, with funding fromthe theMinerals Minerals Coordinating CoordinatingCommittee Committeeof of the the Minnesota MinnesotaState StateLegislature, Legislature, has has set set out out to evaluate evaluate its potential for baseand and precious-metal precious-metal mineralization. mineralization.AAparticular particulartarget targetfor forstudy studywas wasthe themacrolayering macrolayeringof ofthe thecyclic cycliczone. zone. At At intermediate intermediatestages stagesof offractional fractionalcrystallization crystallizationand andunder underlow-pressure low-pressureconditions conditions(1-2 (1-2kb), kb),the theDLS DLS magma magmawas wassaturated saturatedininolivine olivineand andplagioclase plagioclaseand andwas wasevidently evidentlynearing nearingsaturation saturationiningabbroic gabbroicphases phases of of augite augiteand andilmenite. ilmenite.Although Althoughthe thetransitions transitionsfrom fromtroctolitic troctolitictotogabbroic gabbroiccumulates cumulateswithin withinthe thecyclic cyclic zone may have formed from normal crystallization differentiation causing saturation in these phases, the zone may have formed from normal crystallization differentiation abruptness of the transitions and the lack of noticeable cryptic variation across the units suggest that abruptness of the transitions and the lack of noticeable cryptic suggest abrupt abrupt changes changesin in physical physical conditions conditions of of crystallization crystallization also also may have played a role. Such Suchaachange changemay may have been an increase in pressure resulting from volatile (CO2 and perhaps 1120) saturation of have been an increase in pressure resulting from volatile (CO2 and perhaps H20) saturation of the themagma magma in in the the roof roof zone. zone. The Thebuild buildup upofofvolatiles volatilesininthe theroof roofzone zoneisisconsistent consistentwith withthe thepervasive pervasivehydrothermal hydrothermal alteration of the anorthositic series and could have caused failure of the cupola leading to volcanic alteration of the anorthositic series and could have caused failure cupola eruption eruption and and decompression decompressionof of the the chamber. chamber. Evidence Evidenceofofsuch suchdecompression decompressionisissuggested suggestedby bythe thesimilar similar ferrodioritic ferrodioriticcomposition compositionand andfine-grained fine-grainedtexture textureofofthe themicrogabbro rnicrogabbrolayers layerswithin withinthe thegabbroic gabbroic cumulates cumulatesof of the the cyclic cycliczone zoneand and of of the the "chill" "chill"against against the the anorthositic anorthositic cap. cap. Because Becauseof ofthe thestrong strongpositive positive effect effectof of pressure pressureon on water watersolubility solubilityin inmafic maficmagma magma at at low low total total pressures, pressures, decompression decompression may result in water-saturated water-saturatedconditions conditionswhich whichhas hasthe theeffect effect of of dramatically dramatically raising raising the the solidus solidus temperature temperature of the the magma magmaand andthereby therebyquenching quenchingit. it.Such Sucha aprocess processcould couldhave havecaused causedsimultaneous simultaneousrapid rapidcrystallization crystallizationofof 45 �the DLS "chill" "chill"zone zone and and microgabbro microgabbro layers. layers. Water-saturated Water-saturatedconditions conditionsare areindicated indicatedby by the the common common the occurrence of biotite biotite phenocryts phenocryts in in the the DLS DLS "chill". "chill".AAdecompression-quench decompression-quenchorigin originfor forthe theDLS DLS"chill", "chill", occurrence opposed to aa thermal thermal quench, quench, better explains explains the similar similar age of the DLS and anorthositic series and the as opposed the "chill", "chill",which which is is too evolved evolved to be parental to the entire DLS. The Thereturn returnto totroctolitic troctolitic composition of the cumulate crystallization crystallization may have have resulted resulted from from recharge and reinflation of the magma chamber by new new cumulate magma or or may may simply simplyindicate indicateaa return return to tolithostatic lithostaticpressures pressuresfollowing followingcessation cessationof ofvolcanic volcaniceruption. eruption. magma Decompression also also appears appears to have have a negative effect on sulfide sulfide solubility in silicate magmas, at least Decompression (Poulson and and Ohmoto, Ohmoto, 1990). 1990). Evidence Evidencethat thataasulfide sulfidesegregation segregationevent eventaccompanied accompanied at low pressures (Poulson decompression quenching quenching is is given by the discovery discovery of an anomalous concentration of sulfide (0.5 wt %) decompression at the base of aa microgabbro microgabbro layer. layer. Moreover, Moreover,the theconcentration concentrationof of sulfide sulfide(0.10-0.07 (0.10-0.07 wt wt %) %) in in the theupper upper at "chill" zone zone is is in in the the range range expected expectedfor forsulfide sulfidesaturation saturationof of an aniron-rich iron-rich(>10 (>lowt wt%) %)melt meltatatlow lowpressure pressure "chill" (Poulson and and Ohmoto, Ohmoto, 1990). 1990).Finally, Finally,the theobservation observationthat thatthe theaverage averagesulfide sulfideconcentration concentrationin in cumulates cumulates (Poulson below the the cyclic cycliczone zone isis about about 0.02 0.02wt wt %, %, compared compared to to about about 0.06% in the upper part of the intrusion, is below consistentwith with the the magma magmabecoming becoming sulfide sulfidesaturated saturated at at the the time time of cyclic zone formation. Sulfide Sulfide consistent decompression would cause cause segregation segregation of a dense sulfide melt thoughout much of the saturation by decompression magma system system that that could could then then scavenge scavengethe the magma magma of of PGE PGE as as it settled settled to the floor floor of the chamber. chamber. The The magma first occurrence occurrenceof of sulfide sulfidemelt melttotoform formininthis thisway wayshould shouldproduce producethe thehighest highestconcentration concentrationofofPGE. PGE. first Recognizing the the potential potential for for Cu-Ni Cu-Ni sulfide sulfideand and PGE PGE mineralization mineralization to be associated with horizons Recognizing representing perturbations perturbations to to the the steady-state steady-statecrystallization crystallization of the DLS, a suite suite of 50 handsamples were representing selected for for whole whole rock rock and and Pt-Pd-Au Pt-Pd-Au assay analysis. analysis. As Aspredicted predictedby by the themodel modeloutlined outlinedabove, above, selected anomalousPGE PGEconcentrations concentrationswere werefound foundassociated associatedwith withabrupt abruptchanges changesininrock rocktype typeininthe thecyclic cycliczone. zone. anomalous The two two most most PGE-nch PGE-richsamples samplesare aresituated situatedatatsimilar similarinterfaces interfacesbetween between gabbroic gabbroic cumulate cumulateand and The microgabbro and and at at approximately approximatelythe the same samestratigraphic stratigraphic level level within within the second second macrocyclic unit of the microgabbro cyclic zone. zone. The Themost mostanomolous anomoloussample samplehas has444 444ppb ppbPt, Pt,443 443ppb ppbPd, Pd,56 56ppb ppbAu, Au,whereas whereasthe theother otherhas has cyclic 44 ppb ppb Pt, Pt, 108 108ppb ppb Pd, Pd, and and 56 56ppb ppb Au. Au. The Thetwo twosamples samplesdiffer differgreatly greatlyinintheir theirCu-Ni Cu-Nisulfide sulfide 44 concentration with with the the high high PGE PGE sample samplecontaining containing 0.028% 0.028% S, S, 163 163ppm Cu, and 568 ppm Ni and the concentration lower PGE PGE sample samplecontaining containing0.50% 0.50% S, S, 5392 5392ppm ppm Cu, Cu, and and 852 852 ppm Ni. Average AveragePGE PGEconcentrations concentrationsfor for lower the the other other48 48 samples samplesare areapproximately approximately10 10ppb ppbPd, Pd,77ppb ppbPt, Pt,and and44ppb ppbAu. Au. Follow-up studies studiesare are in in progress progress to to confirm confirm and and more more fully fully chararacterize chararacterize the extent and nature of Follow-up this PGE PGE mineralization. mineralization.Nevertheless, Nevertheless,the theimportance importanceofofthis thisdiscovery discoveryisisthat thatititwas waspredicated predicatedon on this detailed characterization characterization of of the theigneous igneousstratigraphy stratigraphyof of the the DLS DLS and and petrologic petrologic interpretations of that detailed stratigraphy. Similar Similardetailed detailedstudies studiesalong alongthe thenorthwestern northwesternmargin marginofofthe theDuluth DuluthComplex Complex(Severson (Severson stratigraphy. and Hauck, Hauck, 1990; 1990;Severson, Severson,1994) 1994)reinforce reinforcethe the contention contention that that such such an an approach approach is the most effective effective and means meansof of evaluating evaluatingthe themineral mineralpotential potentialofoflayered layeredintrusions. intrusions. References References Cited Cited Boudreau, Boudreau,A.E., A.E., and and McCallum, McCallum,I.S., I.S.,1993, 1993,Concentration Concentration of of platinum-group platinum-group elements elements by magmatic fluids fluids in layered intrusions: intrusions:Economic EconomicGeology, Geology,v. v. 87, 87,p. p. 1830-1848. 1830-1848. Miller, Miller, J.D., J.D., Jr., Jr., 1993, 1993,Evidence Evidenceof of interruptions interruptionsduring during fractional fractional crystallization crystallizationof the Duluth Complex layered layered series Inst.on onLake LakeSuperior SuperiorGeology, Geology,v.v.39, 39,part part1,1,p.p.58-59. 58-59. seriesatatDuluth: Duluth:39th 39thInst. Miller, Miller, J.D., J.D., Jr., Jr.,Green, Green,J.C., J.C., and andChandler, Chandler,V.W., V.W., 1993, 1993,Field Field Trip Trip 4: 4: The The geology geology of of the the Duluth Complex Complex at at Duluth: Duluth: 39th 1-157. 39thInst. Inst.on onLake LakeSuperior SuperiorGeology, Geology,v.v.39, 39,part part2,2,p.p.13131-157. Campbell, Campbell,I.H., I.H., Naldrett, Naldrett,A.J., A.J.,and andBarnes, Barnes,S.J., S.J.,1983, 1983,A A model model for for the the origin origin of of platinum-rich platinum-richsulfide sulfide horizons horizons in the Bushveld Bushveldand andStillwater Stillwatercomplexes: complexes:Journal JournalofofPetrology, Petrology,v.v.24, 24,p.p.133-165. 133-165. Paces, Paces,J.B. J.B. and andMiller, Miller,J.D., J.D.,Jr., Jr.,1993, 1993,Precise PreciseU-Pb U-Pbages agesof of Duluth Duluth Complex Complex and and related mafic intrusions, intrusions, northeastern northeasternMinnesota: Minnesota:new newinsights insightsfor forphysical, physical, petrogenetic, petrogenetic, paleomagnetic paleomagnetic and and tectono-magmatic tectono-magmaticprocesses processes associated associatedwith with1.1 1.1Ga GaMidcontinent Midcontinentrifling: rifting:Journal JournalofofGeophysical GeophysicalResearch ResearchV.98, V.98,No NoB8, B8,13,997-14,013. 13,997-14,013. Poulson, H., 1990, 1990,An Anevaluation evaluationof of the the solubility solubility of of sulfide sulfidesulfur sulfur in in silicate silicate melts from from Poulson,S.R. S.R.and andOhmoto, Ohmoto,H., experimental experimentaldata dataand andnatural naturalsamples. samples.Chemical ChemicalGeology, Geology,v.v.85, 85,p.p.57-75. 57-75. Severson, Severson,M.J., M.J.,and andHauck, Hauck,S.A., S.A.,1990, 1990,Geology, Geology,geochemistry, geochemistry, and and stratigraphy stratigraphy of of aa portion of the Partridge Partridge River River Intrusion.University Universityof ofMinnesota-Duluth, Minnesota-Duluth,Natural Natural Resources Resources Research Research Inst. Inst. Technical Technical Report Report 89-11, 89- 1 1 ,236p. 236~. Intrusion. Severson, Severson,M.J., M.J.,1994, 1994,Igneous Igneousstratigraphy stratigraphyof ofthe theSouth SouthKawishiwi Kawishiwiintrusion, intrusion, Duluth Duluth Complex, Complex,northeastern northeastern Minnesota.University UniversityofofMinnesota-Duluth, Minnesota-Duluth,Natural NaturalResources ResourcesResearch ResearchInst. Inst.Technical TechnicalReport Report93/94, 93194,210~. Minnesota. 2 lOp. 46 �Kimberlite indicators in overburden, Michipicoten Xinberlite heavy mineral mineral indicators Michipicoten RiverArea, Northeastern River- Wawa Area, Northeastern Ontario. Ontario. Morris T.F., Morris T.F., Murray Murray C. C. Ontario Ontario G e o l o g i c a l Survey, Survey,933 9 3 3Ramsey R a m s e y Lake Lake Road, R o a d , Sudbury S u d b u r yON ON Geological P3E P 3 E 6B5, 6B5, Canada Canada AND D. Crabtree, D. Crabtree, Ontario Geosciences O ntario G e o s c i e n c e s Centre, C e n t r e , 933 9 3 3Ramsey R a m s e y Lake LakeRoad, R o a d , Sudbury S u d b u r yON ON P3E P 3 E 6B5, 6B5, Canada Canada Two diamonds, and Two diamonds, and possibly aa third, third, were were recovered recovered from from the the Wawa Wawa area area by by C. C. Clement Clement (local (local prospector) prospector) during during the the summer summer of of 1991. 1991. exact location location of of the the discovery discovery site site cannot cannot be be positively positively The exact identified. It is however, that identified. It is thought, thought, however, that the diamonds diamonds were were collected from collected from either either older older alluvium alluvium (sand (sand and and gravel) gravel) in in aa point point bar of of the the Dead Dead River, River, near near the the Michipicoten Michipicoten River Rivermand/or modern bar and/or modern alluvium alluvium (sand (sand and and gravel) gravel) associated associated with with Wawa Wawa Creek. Creek. The The diamond discovery discovery was reported reported to to the the Ontario Ontario Geological Geological Survey Survey (OGS) (OGS) in in the fall the fall of of 1993. 1993. Two diamonds were loaned then forwarded forwarded to Two of of the the 33 diamonds loaned to to the the OGS and then the Royal the Royal Ontario Museum, Department of Mineralogy, Mineralogy, for Ontario Museum, Department of for confirmation. confirmation. The stones stones were were identified identified as as industrial industrial grade grade diamonds diamonds with with carat carat weights weights of of 1.05 1.05 and and 1.13. 1.13. A sampling sampling program program was was initiated initiated by by the the OGS OGS in in September September of of 1993, 1993, in order to establish authenticity authenticity of diamond find. Ten, 25 kg in order to establish of the the diamond find. Ten, 25 kg samples were modern samples were collected collected from from the the reported reported discovery discovery sites: sites: 55 modern alluvium Wawa Creek samples from alluvium samples samples from from Wawa Creek and and 55 older alluvium samples a a point point bar bar associated associated with with the the Dead Dead River. River. Kimberlite indicator minerals (KIM'S) Kimberlite indicator minerals (KIM'S) isolated isolated from from these these samples samples include one "Gb" nG1Ongarnet garnet with with aa kelyphite kelyphite rim, rim, and 99 chrome chrome include one diopsides. Most of these indicators were recovered from the diopsides. these indicators were recovered from the Dead Dead River River point point bar bar and and verified verified that that the the 22 industrial industrial grade grade diamonds diamonds could could have have been been recovered recovered from from this this site. site. As preliminary discoveries, discoveries, the OGS OGS undertook undertook As aa follow-up follow-up to to these preliminary regional sampling program in the Michipicoten Michipicoten RiverRiver- Wawa Wawa area in a regional sampling program in the the the summer summer of of 1994. 1994. The The area area was was considered considered optimal optimalfor forkiinberlite kimberlite exploration as: a) a) it includes includes the the area area where the the 22 diamonds diamonds and and exploration as: associated heavy minerals were were recovered; recovered; b) bedrock bedrock and and overburden overburden associated heavy minerals geology is understood (Morris 1992a, 1992b; 1992b; Sage Sage geology is well understood (Morris 1990, 1990, 1991, 1991, 1992a, area is Kapuskasing structural 1994); the area 1994); and and C) c) the is close close to to the the Kapuskasing structural zone, zone, (Boland and an area area thought thought to to be be aa favourable favourable kimberlite kimberlite host host (Boland and 1989). Ellis Ellis 1989) 47 �Methodology, recommendations for kimberlite e~~loration exploration Methodology, results results and and recommendations for kimberlite from the 1994 1994 summer summer field field program program are are presented presented in in Morris Morris et et al. al. from (1994). (1994). indicators identified from from the the Michipicoten Michipicoten Kimberlite indicators RiverRiver- Wawa Wawa area area include: include: a) a) 44 "Gb" "GIOHchrome chromepyrope.garnets pyrope garnets and and 37 37 1G911 chrome garnets; b) 44 high chrome chromites chromites and and 104 104 low low "G9" chrome pyrope pyrope garnets; high chrome chrome magnesium rich chrome chrome chromites; chromites; c) c) 121 121 magnesium rich ilmenites; ilmenites; and and d) d) 39 39 chrome diopsides. diopsides. Several Several areas areas were were identified identified as as favourable favourable' for for kimberlite kimberlite exploration from: from: a) a) the the distribution of total total KIM'S; b) evaluating exploration distribution of evaluating site site results results e.g. e.g. the presence presence or or absence absence of of significant significant KIM'S KIM1s ( "GIO1 s and chrome chromites); chromites); and and C) c) the the variety variety of of KIM's. KIM'S. ("GlO's and high chrome All All of of the the favourable favourable areas areas exist exist on, on, or or southeast southeast of, of, the the northern northern margin margin of of the the Kapuskasing Kapuskasing structural structural zone. zone. References References Cited Cited Boland A.V. and and Ellis Ellis R.M. R.M. 1989. 1989. Velocity Velocity structure structure of of the the . Kapuskasing Kapuskasing uplift, uplift, northern northern Ontario, Ontario, from from seismic seismic refraction refraction studies; studies; Journal Journal of of Geophysical Geophysical Research, Research, v.94, v.94, n.B6, n.B6, p.7189p.71897204. 7204. Morris T.F. 1990. 1990. Quaternary Quaternary geology geology of of the the Wawa area, northern northern Morris Wawa area, Ontario; in in Summary Summary of of Field Field Work Work and and Other OtherActivities Activities1990,. 1990,. Ontario; Ontario Ontario Geological Geological Survey, Survey, Miscellaneous Miscellaneous Paper Paper 151, 151, p.149-151. p.149-151. Morris northern Morris T.F. T.F. 1991. 1991. Quaternary Quaternary geology geology of of the the Dog Dog Lake Lake area, area, northern Ontario; Ontario; in in Summary Summary of of Field Field Work Work and and Other Other Activities Activities 1991, 1991, Ontario Ontario Geological Geological Survey, Survey, Miscellaneous Miscellaneous Paper Paper 157, 157, p.149-151. p.149-151. Morris Morris T.F. T.F. 1992a. 1992a. Quaternary Quaternary geology geology of of the the Wawa Wawa area; area; Ontario Ontario Geological Geological Survey, Survey, Open Open File File Map Map 192, 192, scale scale 1:50 1:50 000. 000. Morris 1992b. Quaternary Quaternary geology, geology, Dog Dog Lake Lake area, area, northern northern Morris T.F. 1992b. Ontario; Ontario; Ontario Ontario Geological Geological Survey, Survey, Open Open File File Map Map 199, 199, scale scale 1:50 1:50 000. 000. Morris overburden Morris T.F., T.F., Murray Murray C. C. and and Crabtree Crabtree D. D. 1994. 1994. Results Results of of overburden sampling sampling for for Kimberlite Kimberlite heavy heavy mineral mineral indicators indicators and and gold gold grains, grains, Michipicoten Michipicoten RiverRiver- Wawa Wawa area, area, northeastern northeastern Ontario; Ontario; Ontario 69p. Ontario Geological Geological Survey, Survey, Open Open File File Report Report 5908, 5908, 69p. Sage Sage R.P. 1994. 1994. Geology Geology of of the the Michipicoten Michipicoten Greenstone Greenstone Belt; Belt; Ontario Ontario Geological Geological Survey, Survey, Open Open File File Report Report 5888, 5888, 592 592 p. p. 48 �Heavy mineral mineral indicators, indicators, Wawa Wawa Area Area Heavy Morris T.F.', T.F.*~Murray Murray C. C. Morris Ontario G e o l o g i c a l S u r v e y f 933 Ramsey Lake Roadf Sudbury Sudbury ON ON Ontario Geological Survey, 933 Ramsey Lake Road, P3E 6B5, 6B5/ Canada Canada P3E AND Crabtree# D. D. Crabtree, O n t a r i o Geosciences Geosciences Centre, C e n t r e , 933 933 Ramsey Ramsey Lake Lake Road, Roadf Sudbury Sudbury ON ON Ontario P3E 6B5, 6B5, Canada Canada P3E Two diamonds, diamondsI and and possibly possibly aa third, thirdl were were recovered recovered from from the the Wawa Wawa Two area by by C. C. Clement Clement (local (local prospector) prospector) during during the the summer s m e r of of 1991. 1991. area The exact exact location location of of the the discovery discovery site site cannot cannot be be positively positively The identified. It is is thought, thoughtl however, howeverl that that the the diamonds diamonds were were identified. It collected from from either either older older alluvium alluvium (sand (sandand and gravel) gravel) in in aa point point collected bar of of the the Dead Dead River, Riverl near near the the Michipicoten Michipicoten River River and/or and/or modern modern bar alluvium (sand (sandand and gravel) gravel) associated associated with with Wawa Wawa Creek. Creek. The The diamond diamond alluvium discovery was was reported reported to to the the Ontario Ontario Geological Geological Survey Survey (OGS) (OGS)in in discovery the fall fall of of 1993. 1993. the diamonds were were loaned loaned to to the the OGS OGS and and then then forwarded forwardedto to Two of of the the 33 diamords Two the Royal Ontario Museuml Department of Mineralogyl for the Royal Ontario Museum, Department of Mineralogy, for confirmation. The The stones stones were were identified identified as as industrial industrial grade grade confirmation. diamonds with with carat carat weights weights of of 1.05 1.05 and and 1.13. 1.13. diamonds , sampling program program was was initiated initiated by by the the OGS OGS in in September September of of 1993, 1993# AA sampling in order to establish authenticity of the diamond find. Tenl 25 kg kg in order to establish authenticity of the diamond find. Ten, 25 samples were collected from the reported discovery sites: 5 modern samples were collected from the reported discovery sites: 5 modern alluvium samples samples from from Wawa Wawa Creek Creek and and 55 older older alluvium samples from from alluvium alluvium samples a point bar associated with the Dead River. a point bar associated with the Dead River. 6 Kimberlite indicator indicatorminerals minerals(KIM'S) (KIM'S)isolated isolatedfrom fromthese thesesaxiples samples Kimberlite include one ItGlOt1 garnet with a kelyphite riml and 9 chrome include "Gb" garnet with a kelyphite rim, and 9 chrome diopsides. Most of these indicators were recovered from the Dead diopsides. Most of these indicators were recovered from the Dead industrial grade diamonds River point bar and verified that the 2 River point bar and verified that the 2 industrial grade diamonds could have have been been recovered recovered from from this this site. site. could As aa follow-up follow-upto to these these preliminary preliminary discoveries, discoverieslthe the OGS OGS undertook undertook As a regional sampling program in the Michipicoten RiverWawa areain in a regional sampling program in the Michipicotn River- Wawa area the s m e r of 1994. The area was considered optimal for kimberlite the summer of 1994. The area was considered optimal for kimberlite exploration as: as: a) a) it it includes includes the the area area where where the the 22 diamonds diamonds and and exploration associated heavy minerals were recovered; b) bedrock and overburden associated heavy minerals were recovered; b) bedrock and overburden geology is is well well understood understood (Morris (Morris1990, 199011991, 199111992a, 1992a11992b; 1992b; Sage Sage geology 1994) ; and c) the area is close to the Kapuskasing structural zonel 1994); and c) the area is close to the Kapuskasing structural zone, an area area thought thought to to be be aa favourable favourable kimberlite kimberlite host host (Boland (Boland and and an Ellis 1989) 1989). Ellis 49 �Methodologylresults resultsand and recommendations recommendationsfor for kimberlite kimberlite exploration exploration Methodology, from the 1994 summer field program are presented in Morris et al. al. from the 1994 summer field program are presented in Morris et (1994). Kimberlite Kimberlite indicators indicators identified identified from from the the Michipicoten Michipicoten (1994). 4 nGIOn chrome pyrope garnets and 37 37 RiverWawa area include: a) River- Wawa area include: a) 4 "Gb" chrome pyrope gamete and 4 high chrome chromites and 104 low 11G911 chrome pyrope garnets; b) "G9" chrome pyrope gamnets; b) 4 high chrome chromites and 104 low chrome chromites; chromites;C) c) 121 121 magnesium magnesium rich rich ilmenites; ilmenites;and and d) d) 39 39 chrome chrome chrome diopsides. diops ides. Several areas areas were were' identified identified as as favourable favourable for for kimberlite kimberlite Several exploration from: a) the distribution of total KIM1s; b) evaluating exploration from: a) the distribution of total KIM'S; b) evaluating site results e.g. the presence or absence of significant KIM1s site results e.g. the presence or absence of significant KIM'S (llGIO1s and high chrome chromites) ; and c) the variety of KIM1s. ("GlO's and high chrome chromites); and c) the variety of KIM'S. All of of the the favourable favourable areas areas exist exist on, onl or or southeast southeast of, ofl the the northern northern All margin of the Kapuskasing structural zone. margin of the Kapuskasing structural zone. References Cited Cited References Boland A.V. A.V. and and Ellis Ellis R.M. R.M. 1989. 1989. Velocity Velocity structure structure of of the the Boland Kapuskasing upliftl northern Ontario, from seismic refraction Kapuskasing- uplift, northern Ontario, from seismic refraction n.B6 p.7189p. 7189studies; Journal Journal of of Geophysical Geophysical Research, ~ e s e a r c hv.94, v. ~ 94 n.B6, studies; 7204. 7204. Morris T.F. T.F. 1990. 1990. Quaternary Quaternary geology geology of of the the Wawa Wawa area, arealnorthern northern Morris Ontario; in in Summary Summary of of Field Field Work Work and and Other OtherActivities Activities1990, 19901 Ontario; Ontario Geological Geological Survey, Surveyl Miscellaneous Miscellaneous Paper Paper 151, 1511p.149-151. p.149-151. Ontario Morris T.F. T.F. 1991. 1991. Quaternary Quaternary geology geology of of the the Dog Dog Lake Lake area, areal northern Morris northern in Summary Summary of of Field Field Work Work and and Other OtherActivities Activities1991, 19911 Ontario; in Ontario; Ontario Geological Geological Survey, SurveylMiscellaneous MiscellaneousPaper Paper157, 1571p.149-151. p.149-151. Ontario Morris T.F. T.F. 1992a. 1992a. Quatemnary Quaternary geology geology of of the the Wawa Wawa area; area; Ontario Ontario Morris Geological Survey, Surveyl Open Open File File Map Map 192, 192# scale scale 1:50 1:50 000. 000. Geological Morris T.F. T.F. 1992b. 1992b. Quaternary Quaternary geology, geologyl Dog Dog Lake Lake area, area, northern northern Morris Ontario; Ontario Ontario Geological Geological Survey, Surveyl Open Open File File Map Map 199, 19g1 scale scale Ontario; 1:50 000. 000. 1:50 Morris T.F., T.F.! Murray Murray C. C. and and Crabtree Crabtree D. D. 1994. 1994. Results Results of of overburden overburden Morris sampling for for Kimberlite Kimberlite heavy heavy mineral mineral indicators indicators and and gold gold sampling grainsl Michipicoten Michipicoten RiverRiver- Wawa Wawa area, arealnortheastern northeasternOntario; Ontario; grains, Geological Survey, SurveylOpen Open File File Report Report 5908, 5908169p. 69p. Ontario Geological Ontario Sage R.P. R.P. 1994. 1994. Geology Geology of of the the Michipicoten MichipicotenGreenstone GreenstoneBelt; Belt; Sage Ontario Geological Geological Survey, Surveyl Open Open File File Report Report 5888, 58881 592 592 p. p. Ontario * Denotes Denotes speaker speaker * 50 �THE CURRENT CURR.ENT SETTING SETTING OF OF THE THE HEMLO HEMLOGOLD GOLDDEPOSIT, DEPOSIT, ONTARIO: ONTARIO: THE IMPORTANCE OF FUNDAMENTAL RELATIONSHIPS IMPORTANCE OF FUNDAMENTAL RELATIONSHIPS Muir, T.L., Ontario Ontario Geological Geological Survey, Sudbuiy, Sudbury, Ontario, P3E 6B5 The deformed Hemlo Gold Deposit (HGD) occurs occurswithin within moderately to strongly strongly strained, strained, folded, transposed, and metamorphosed metamorphosedvolcano-sedimentary volcano-sedimentary rocks rocks of of the the Hemlo-Schreiber greenstone greenstone transposed, and Lithologicinterpretation interpretationininthis thispart partofofthe thebelt beltisisimpeded impededby by polyphase polyphase strain, strain, possibly belt. Lithologic hydrothermal events. Many Many of of the the polyphase metamorphism, and bcally locally extensive, extensive, complex complexhydrothermal interrelationships among these these events events are are not not well well constrained. constrained. Strain superposed on the HGD is (medium grade) grade) or or Metamorphismhas hasaffected affected the the deposit depositin in11(medium of one, and likely 2, generations. Metamorphism events. The Thedeposit depositappears appearstotopredate predatefelsic felsicplutonism, plutonism,which whichpredates predatesaaD3 D3dextral dextralshear shear more events. event. event. nor strata bound. Much The HGD is neither stratiform nor Much of of the the deposit deposit currently: currently: -occurs on the hanging wall side of the south limb of a large-scale, large-scale, S-shaped fold, fold, delineated delineated,,in part, quartz-plagioclase-phyric rocks; part7by bymassive massiveand andfragmental, fragmental,felsic, felsic, quartz-plagioclase-phyric -lies largely within within 22 or or more, closely spaced, 290'-striking 290°-striking high-strain high-strain zones, zones, that that occur within most pervasive, pervasive, highly highly strained part part of of an an otherwise otherwisewesterly westerlystriking strikingbelt; belt; and and the most -transgresses transposed units units such suchthat thatititisishosted hostedlargely largelyby by highly highly altered altered sedimentary sedimentary rocks rocks in in -transgresses transposed quartz-plagioclase-phyricrocks in east and and central central parts, parts, and and by by altered altered sedimentary sedimentary rocks rocks and and quartz-plagioclase-phyric the east part. the west part. Ore-grade mineralization and at least some types of alteration are presently structurally controlled at various scales. Notable Notablechanges changesininalteration alterationand andmineralization mineralization occur occur from from one one part part deposit to to another, another,particularly particularlyspatially spatiallyassociated associatedwith with an aninflection inflection in in the the greenstone greenstonebelt, belt, of the deposit from W-striking There is is an an extensive envelope of altered rocks W-striking to to WNW-striking. WNW-striking. There rocks in in the the west west Strain,metamorphism, metamorphism, end of the deposit and a narrow alteration envelope towards the east end. Strain, superposed on on the the HGD HGD have have modified modified various aspects aspects of the primary alteration and alteration superposed country rocks, rocks, and and and mineralization characteristics, which has resulted in additional alteration of country remobilization of Au, Mo, Hg, As, and and Ba. Ba. Hg, As, Various depositional to the HGD. Establishing depositional models have been applied to Establishingfundamental findamental field relationships is of paramount importance importance for evaluating evaluating the appropriateness appropriatenessof of aa given given model. model. Particular attention attention must be given to: -- iidentifying d e n t i ~ n gprotoliths protoliths and establishing contact relationships, both both of which are are critical to to some depositional models; depositional models; -determining which are synchronous synchronous with which generations generations of of structural structural elements predate, predate, postdate, postdate, or are the deposit; deposit; -distinguishing features hydrothermal features resulting from regional metamorphic events as opposed to hydrothermal alteration events, and putting into context their relative timing with respect to structural context their structural elements; and current features -characterizing what current features of the deposit deposit reflect reflect modification by events subsequent to emplacement. emplacement. Other sites within the Hemlo--Schreiber greenstone greenstone belt, belt7which which contain contain barite barite and and display display to that of the HGD, may reflect large-scale, synchronous or diachronous alteration similar to hydrothermal events. events. 51 �KEWEENAWAN UPLIFT UPLIFT AND AND SUPERGENE SUPERGENE KEWEENAWAN SUPERIOR-TYPE IRON FORMATION SUPERIOR-TYPE IRON FORMATION OXIDATION OXIDATION OF OF PRE-PENOKEAN? PRE-PENOKEAN, Jon North North Jon 22 Gurdwara Gurdwara Road, Road, Nepean, Nepean? Ontario, Ontario? WMC International Limited, Limited? 22 WMC International Canada K2E 8A2 Canada K2E 8A2 The Riverton Riverton and and Negaunee Negaunee Iron Iron Formations Formations are are lower lower The Proterozoic Superior-Type Iron Formation respectively within the Proterozoic Superior-Type Iron Formation respectively within the Paint River and Menominee Groups, Marquette Range Supergroup, Paint River and Menominee Groups, Marquette Range Supergroup, Michigan (Figure (Figure 1). 1). The The primary primary iron iron formation formation is is carbonate carbonate or or Michigan oxide facies and contains 20 to 30% iron. The Marquette Range oxide facies and contains 20 to 30% iron. The Marquette Range Supergroup was was deformed deformed and and metamorphosed metamorphosed during during the the Ca. ca. 1.85 1.85 Ga Ga Supergroup Penokean orogeny and subsequently intruded and overlain by rocks of Penokean orogeny and subsequently intruded and overlain by rocks of the Keweenawan Rift at ca. 1.1 Ga. Stratabound bodies of secondary, the Keweenawan Rift at Ca. 1.1 Ga. Stratabound bodies of secondary, massive hematite-goethite hematite-goethite containing containing greater greater than than 50% 50% iron iron were were massive The orebodies orebodies mined as as high high grade grade direct direct shipping shipping soft" "soft"iron iron ores. ores. The mined occupy axes axes of of plunging plunging synclines synclines or or other other upward-opening upward-opening occupy structures in in contact contact with with footwall footwallaquicludes, aquicludes, they they are are not not structures deformed, and of lower metamorphic grade than their host rocks. deformed, and of lower metamorphic grade than their host rocks. Riverton Iron Iron Soft iron iron ore ore is is at at maximum maximum depths depths of of 800 800 mm in in the the Riverton Soft Formation and 1800 m in the Negaunee Iron Formation. Formation and 1800 m in the Negaunee Iron Formation. i) Formation of of soft soft iron iron ore ore is is aa two two stage stage process process of of i) Formation widespread pseudomorphism of siderite by hematite and goethite and widespread pseudomorphism of siderite by hematite and goethite and ii) dissolution dissolution of of chert by hematite hematite and and goethite. goethite. ii) chert and and replacement replacement by Mn is is fractionated fractionated from from iron iron and and depleted depleted in in iron iron ore ore relative relative to to Mn primary iron iron formation. formation. The The isotopes isotopes of of oxygen oxygen in in iron iron oxide oxide primary minerals imply imply that that the the iron iron oxides oxides interacted interacted with with waters waters with with minerals variable18°sNow 618~sMow of -6.85 -6.85 to to 16.69 16.69 per per mil. mil. Present Present meteoric meteoric waters waters of variable latitude of of the the Paint Paint River River Group Group are are ca. ca. -10 -10per per mil. mil. at the the latitude at Hence, the the soft soft iron iron ores ores probably probably formed formed by by the the interaction interaction Hence, of meteoric meteoric water water with with primary primary iron iron formation formation but but not not present present of meteoric water. water. Because Because Mn Mn and and Fe Fe can can be be dissolved dissolved in in waters waters of of low low meteoric pH but but ferric ferric oxides oxides or or hydroxides hydroxides precipitate precipitate at at high high Eh Eh whereas whereas pH manganous ions ions can can be be transported transported at at high high Eh, Eh, the the fractionation fractionationof of manganous Mn from Fe in the iron ores implies that they formed at low pH and Mn from Fe in the iron ores implies that they formed at low pH and high Eh Eh as as in in acidic acidic supergene supergene weathering weatheringprofiles. profiles. high The soft iron ores most likely formed when the water water table table was was The soft iron ores most likely formed when the lowered because of uplift of the Marquette Range Supergroup on the lowered because of uplift of the Marquette Range Supergroup on the south ridge and flank of the Keweenawan Rift at about 1.1 Ga and, south ridge and flank of the Keweenawan Rift at about 1.1 Ga and, meteoric water water descended descended through through the the iron ironformations, formations, along along aa meteoric footwall aquiclude to the static water table. Hence they represent footwall aquiclude to the static water table. Hence they represent supergene oxidation oxidation of of primary primary chert-siderite chert-siderite iron iron formation formation supergene analogous to karstification with an iron oxide residue. The analogous to karstification with an iron oxide residue. The differential maximum depths of the oxidation of the iron formations differential maximum depths of the oxidation of the iron formations to soft soft iron iron ores ores is is evidence evidence of of differential differential uplift uplift of of the the rift rift to 2). flanks across a profile resembling a fedora hat (Figure flanks across a profile resembling a fedora hat (Figure 2). 52 �______ EXPLANATION Main Iron Formations L0I 1.1 volcanic rocks Duluth Gabbro, Nipigon CoIdwell Complex Ga.— Sibley Group 1.5 Ga.— Anorogenic Granite 1.8 Go.— Ii ,1 2.7 Keweenawai, Rift sedimentary rocks Keweenawan Rift Wisconsin Magmatic Terrane Marquette Range Supergroup Archean FIGURE South outcrop of rift rocks 1 North Rift Axis 0 NEGAUNEE IRON —2 KILOMETRES FORMATION Soft Orebodies 1o o V.,tcaI £xogg.roton 25X FIGURE 2 FIGURE 2 53 �Targeting Massive Massive Sulfide Sulfide Deposit Deposit Exploration Exploration Targeting in in the the Western Western Vermilion Vermilion District: District: Volcanological Controls Controls Volcanological Peterson,DeanM., M. ,Department DepartmentofofGeology, Geology,University University of of Peterson,Dean Minnesota, Duluth Minnesota, Duluth The last last ten ten years years has has been been aa period period of of rapid rapid growth growth in in the the The understanding of of the the formation formation of of volcanogenic volcanogenic massive massive sulfide sulfide understanding deposits. deposits. Numerous Numerous detailed detailed studies studies in in established established mining mining camps camps ~ l i n Flon, Sturgeon Lake, etc.) provides data data that that (Noranda, (Noranda, Fun Flon, Sturgeon Lake, etc.) provides allows deposit deposit characteristics characteristics and and volcanic volcanic facies facies changes changes to to be be allows observed observed and and correlated. correlated. These These studies studies have have made made it it possible possible to: to: 1) 1) Describe Describe characteristics characteristicsand and facies faciesof ofvolcanic volcanicrocks, rocks, 2) 2) Discuss Discuss methods methods of of deposition depositionand and eruption, eruption, 3) 3) Describe ~escribemineralogy mineralogy and and zoning zoning patterns patterns of of alteration, alteration, 4) 4) Describe Describe the the significance significanceof of synvolcanic synvolcanicintrusions, intrusions, 5) 5) Discuss Discuss depositional depositional environments environments of of massive massive sulfide sulfide deposits. deposits. In In the the western western Vermilion Vermilion District District (Figure (Figure1), I), volcanic volcanic reconstruction reconstruction is is the the key key to to targeting targeting favorable favorable volcanic volcanic successions successions for for massive massive sulfide sulfide deposit deposit exploration. exploration. Detailed Detailed mapping mapping by by the the author author over over the the last last two two years years indicates indicates two two areas areas have favorable favorable volcanic volcanic characteristics characteristics for for hosting hosting such such have deposits. These These areas areas include: include: 1) 1) The The uppermost uppermost two-mile two-milesection section deposits. of the the Lower Lower Ely Ely Greenstone Greenstone (LEG), (LEG),and and 2) 2) The The informally informally named named of Gafvert Gafvert Lake Lake Felsic Felsic Complex. Complex. Previous Previous mapping mapping in in the the Lower Lower Ely Ely Greenstone Greenstone indicated indicated that that the the formation formation is is composed composed of of roughly roughly 99% 99% massive massive and and pillowed pillowed basalt. basalt. Recent Recent mapping mapping (1:1,250 (1:1,250to to 1:10,000) 1:10,000)in inthe the Fivemile FivemileLake Lake area area (Figure (Figure2) 2) of of the the LEG LEG documented documented many many classic classic features features associated associated with with massive massive sulfide sulfide deposits. deposits. These These features features include: include: 1) semi-conformable 1) Regional, ~egional, semi-conformablealteration, alteration, 2) 2) Cross-cutting, Cross-cutting,base-metal base-metal bearing bearing chlorite chlorite alteration alterationpipes, pipes, 3) 3) Four Four mafic-felsic mafic-felsic volcanic volcanic cycles cycles (the (thetwo two mile mile section sectionis is 30% 30% felsic felsic breccias, breccias,lavas, lavas,and andtuffs), tuffs), 4) 4) Synvolcanic ~ynvolcanicfaults faults with with associated associated debris debris flow flow deposits. deposits. The The informally informally named named Gafvert Gafvert Lake Lake Felsic Felsic Complex Complex(Figure (Figure3) 3) is is aa north north facing, facing, composite composite dacitic dacitic volcanic volcanic complex complex overlying overlying the orm mat ion. The The complex complex is is cored cored by by large largemasses masses the Soudan Soudan Iron Iron Formation. of of quartz-feldspar quartz-feldspar porphyry porphyry and and blocky blocky dacitic dacitic lava lava flows. flows.Course Course blocky blocky pyroclastic pyroclastic flow flowdeposits deposits grade grade outward outwardand and interdigitate interdigitate with epiclasticrocks. rocks.Thick Thicksillsillwith fine-grained fine-graineddacitic dacitic tuffs tuffs and and epiclastic like like masses masses of of quartz-feldspar quartz-feldsparporphyry porphyry occur occur throughout throughout the the complex. complex. The The complex complex is is capped capped by by aa large large mass mass of of carbonate carbonate fades faciesiron ironformation formationthat that grades grades outward outward into into oxide oxide fades faciesiron iron formation. formation. Lenses Lenses of of massive massive pyrite pyrite occur occur directly directly above abovethe the complex complex within within basalts basalts of of the theUpper Upper Ely Ely Greenstone. Greenstone.The TheGafvert Gafvert Lake Lake Felsic Felsic Complex Complex has has many many volcanic volcanic features featuresanalagous analagouswith with Kuroko Kuroko Type Type Massive Massive Sulfide Sulfidedeposits. deposits. 54 �N -A' — sir - Basalt + + + + + + + + + I!I + + + + +++ w.r9Yore.n.ton>6 + + + + + + + + + + + ÷ + + + + +__---/VVV' + I - Mdsalt. Fdelc + 2j-c'vvvVvVvvvvv' I ,IUP ? s+o1: + ++ + + +++ MeSa + + IVVVVVVVVVVVVVVVV + ;I2S? Miles Figure 1 - — - Quartz Quartz Feldspar FeldsparPorphyry Porphyy — Felsic Pyroclastic PyroclosticFlow flow Deposits Deposits - — luff and - Felsic Felsic Tuff ondEpiclastic EpiclaaticRocks Rock — Oxide Oxide Facies Focies Iron Iron Formation Formotion - — - Felsic Felsic Lava Lava flows flow [] — Basaltic Volcanic - Basoltic VolcanicRocks Rocks - Rhycilte — I MeSa — Manly. Basalt Gabbro/Dlodt. Pillow Basalt Felule - MeSs -Ba Folsic Xl Tuff — Fslslc Br.ccla - Bedded Scorla L Figure I - —Carbonate Focies lron Formation DiabaseSills Sills [11111 Carbonate Fades Iron Formation [] — Diabase - FiUlo 0 •A Gafvert Lake Lake Felsic Felsic Complex Complex — Massive Massive Pyrlte Pyrite — FelsIc Brsccla I SoudwJronFormdtioj++,/v v v v v v v v v v v v v v v' + — F.lsc Brsccla - RhyolBe lo Miles w LI 55 �Geological, Geophysical and Geochemical Compilation of the Western Vermilion District: Targeting for Gold and Massive Sulfide Deposits Peterson, Dean M., Department of Geology, University of Minnesota,- Duluth Mineral exploration for gold and massive sulfide deposits in the Western Vermilion District has occurred sporadically since the late 1960's. No minable deposits have been discovered, however, these efforts have greatly increased the understanding of the geological characteristics of the district. A digital compilation of all available geological and geochemical data has been integrated into a mineral potential interpretation of the District. The data includes 7573 assays from 2097 outcrop samples and 176 drill holes, integrated geology from the authors mapping, terminated lease files, thesis maps, and government maps. Contoured aeromagnetic data for the area is part of the statewide 1/4 mile spaced Aeromagnetic Program of the Minnesota Geological Survey. Over the last thirty years, 145 holes have been drilled for gold in the western Vermilion District. Gold mineralization discovered to date is concentrated within three structurally controlled domains. These domains include: 1) The wedge shaped block between the Vermilion Fault and the Mud Creek Shear Zone. Mineralization generally occurs at the brecciated contacts of iron formations and quartz-feldspar porphyry bodies. Gold is concentrated in the breccia zones with quartz-pyrite-arsenopyrite matrix. 2) The wedge shaped block between the Shagawa Lake Deformation Zone and Burntside Lake Fault. 3) within sheared and carbonatized basalt and porphyries along the Murray Shear zone Exploration for massive sulfide deposits has generally been targeted upon geophysical anomalies (EM conductors and magnetic highs) within the Upper Ely Greenstone and Soudan Iron Formations. The vast majority of this work occurred during the late 1960's and early 1970's. Recent mapping by the author indicates that large, well exposed areas of the western Vermilion District have yet to be explored for massive sulfide deposits. These areas include the Gafvert Lake Felsic Complex and the Lower Ely Greenstone Formation. 56 �STRUCTURAL EVOLUTION RELATIONSHIPS OF THE MANIMANISTRUCTURAL EVOLUTION AND AND AGE AGE RELATIONSHIPS OF THE TOUWADGE GREENSTONE GREENSTONE BELT BELT AND AND WAWA-QUETICO WAWA-QUETICO SUBPROVINCE, SUBPROVINCE, TOUWADGE SOUTHWESTERN SUPERIOR SUPERIOR PROVINCE, PROVINCE, ONTARIO ONTARIO Peterson, Department DepartmentofofGeosciences, Geosciences, Western Western Carolina Carolina University, University, Cullowhee, Cullowhee, North V.L. Peterson, Carolina, Carolina, 28723, 28723, U.S.A.; U.S.A.; E. Zaleski Zaleski and 0. 0.van vanBreemen, Breemen,Geological Geological Survey Survey of of Canada, Canada, Ottawa, Ottawa, Ontario, Ontario,K1A KIA 0E8 OE8 preferred structuraJ structural model model for for the theManitouwadge Manitouwadge greenstone greenstone belt belt (northern (northern Wawa Wawa subsubOur preferred ductile deformation deformation (Fig(Figthe adjacent adjacent Quetico Queticosubprovince subprovinceinvolves involves four four phases phases of ductile province), and the 2720Ma Mamafic-to-felsic mafic-to-felsic volcanic volcanic sequence, sequence, repeated Thegreenstone greenstonebelt beltcomprises comprisesaa2720 ure). The repeated across an easterly-trending syncline with with aa central centralcore coreof of metagreywacke. metagreywacke. Interlayered Interlayered metamormetamoreasterly-trending D2 syndine the volcanic volcanic sequence sequence north of of the the phosed felsic volcanic volcanic rocks, rocks, iron iron formation formation and and altered rocks in the syncline are are host host to t ovolcanogenic volcanogenic Cu-Zn ductile faults and folds, folds, interpreted from D2 syncine Cu-Zn deposits. deposits. D Dll ductile detailed mapping in the the area area of of known known base-metal base-metal deposits, deposits, repeat repeat mineralized mineralized horizons. horizons. D3/D4 D3/D4 detailed progressive dextral transpression produced produced the distinctive distinctive synformal synformal structure structure of of shortening and progressive D land andD2 D2structures, structures,and andinvolved involvedQuetico Queticometasedimentary metasedimentary the Manitouwadge Manitouwadge belt, reoriented reoriented Dl the rocks rocks in map-scale map-scale folds. folds. The Thetiming timingofofstructural structuralevents eventsand andaccompanying accompanyingamphibolite-facies amphibolite-facies metamorphism is is partly partly constrained constrainedby bythe theresults resultsofofan anongoing ongoingU-Pb U-Pbgeochronological geochronological study. study. metamorphism --- - Foliated K—feldspar porphyritic granitold Foliated trondjbemlte, tonalite. felsic meta— volcanic rocks, slllimanfte—mnscovit,e schist E: Metagreywacke Black Plc batholith Orthoainphibole—cordlerite—garnet gnelss Metamorphosed Iron formation Intermediat, to me! Ic metavolcanic rocks Fold anial trace Aeromainetic or foliation trend - Geology and location map of the Manitouwadge Manitouwadge greenstone G=Geco mine, mine, W=Willroy W=Willroy mine, mine, Geology greenstone belt. G=Geco NC=Nama NC=Nama Creek Creek mine, mine, E=Willecho E=Willecho mine. mine. D l faults faults(shear (shearzones) zones)are arerecognized recognized from from the thecoincidence coincidence of of truncated truncated lithological lithological units, units, Dl repeated mineralized mineralized sequences, sequences, and zones of gneiss interpreted annealed mylonite. mylonite. In In repeated of straight gneiss interpreted as annealed addition D lplanar planarfabrics fabricsare arepreserved preservedlocally locallyininthe thehinge hingeregions regions addition to t ozones zones of of straight straightgneiss, gneiss, Dl of D2 folds. folds. Although Althoughno nosense senseofofkinematics kinematicsororoffset offsethas hasbeen beenobserved, observed,sequence sequencerepetitions, repetitions, of D2 geometries consistent consistent with low angle early relative relative age age of of these these structures structures is is geometries with low angle truncation, truncation, and the early suggestive suggestive of of thrusting. thrusting. D2 structures structuresinclude include the thedominant dominantplanar planarand andlinear linearfabrics fabricsand andmany manyof ofthe theoutcrop-scale outcrop-scalefolds, folds, D2 D2fabrics fabricsare aretypically typicallydefined defined by by high high grade grade metamorphic metamorphic minerals, minerals, locally with with sheath sheathgeometry. geometry. D2 locally D2map-scale map-scalefolds, folds, suggesting deformation deformationbroadly broadly synchronous synchronouswith withpeak peakmetamorphism. metamorphism.Among AmongD2 suggesting sheath fold fold repeats repeats aamajor majorDl D lfault faultand andthe themineralized mineralizedsequence sequence in in the thehinge hinge region region of of the the aa sheath D3 Manitouwadge Manitouwadge synform. synform. D2 D2 shortening shortening resulted resulted in in repetition repetitionofofthe thevolcanic volcanicsequence sequence across across D3 theeasterly easterlytrending trendingsyncline synclineon onthe thesouthern southernlimb limbofofthe theManitouwadge Manitouwadgesynform. synform.Metagreywacke Metagreywacke the D2fabrics. fabrics. D2 D2shortening shorteningmight might also alsoaccount account in the thecore coreof of the thesyncine synclineisisfolded foldedand andcontains containsD2 in 57 �for for the the presence presence of of volcanic volcanic rocks in the the Dead Dead Lake Lake (central (central to t othe theManitouwadge Manitouwadge synform) synform) and and Banana-Otter areas areas (east (east of of Thompson Thompson Lake). Lake). Older Older phases phases of of the theBlack Black Plc Picbatholith batholithenclosing enclosing Banana-Otter the the Manitouwadge Manitouwadge belt, belt,and andK-feldspar K-feldsparporphyritic porphyriticintrusions, intrusions,have haveD2 D2fabrics fabrics and and were interpreted interpreted as as prepre- to t osyn-D2 syn-D2intrusions. intrusions. Blackman Lake Jim folds, including including the Manitouwadge Manitouwadge synform, synform, Blackman D3 map-scale folds, Lake antiform, antiform, and Jim Lake belt and the boundary. The Lake synform, fold fold the Manitouwadge Manitouwadge belt the Wawa-Quetico Wawa-Quetico subprovince subprovince boundary. The supracrustal supracrustalsequence sequence is is thickest thickest in in the thehinge hinge of of the theManitouwadge Manitouwadge synform, synform, which which plunges plunges northnortheasterly easterly at at 25°. 25'. D3 D3 fabrics fabrics include include map- and and outcrop-scale outcrop-scale folds folds and moderately to t o poorly poorly and aa moderately developed developed axial planar cleavage. cleavage. Relationships Relationships between between metamorphic metamorphic minerals, minerals, migmatitic migmatitic segresegregations, that D3 gations, and and deformation deformation fabrics fabrics indicate indicate'that D3was wasbroadly broadly coeval coeval with with peak metamorphism metamorphism in in the Quetico Quetico subprovince. subprovince. Map-scale Map-scale D4 D4 structures structures modify modify the the geometry geometry of of the the D3 D3 folds. Examples Examples the are the the Nama NamaCreek Creek shear shearzone zone along along the thenorthwest northwestlimb limbof of the theManitouwadge Manitouwadge synform synform and and open open are Blackman Lake Lake antiform antiform and and Jim Jim folds in the the Wawa-Quetico Wawa-Quetico boundary and the the axial axial traces traces of of the the Blackman folds Lake synform. synform. In In addition, addition, the theBanana BananaLake Lakeantiform antiformmay mayhave haveformed formed by byfolding folding and andshearing shearing Lake during during D3/D4 D3/D4 deformation. deformation. Outcrop-scale Outcrop-scale D4 D4structures structuresinclude includelocal localkink kinkfolds folds and andcrenulation crenulation cleavage, for example, outcrop-scale outcrop-scale asymmetric folds and associated associated crenulation crenulation cleavage cleavage in in the the cleavage, area area of of the the Geco Geco mine. The The dominantly dominantlyZ-asymmetry Z-asymmetryof of D3/D4 D3/D4 folds, folds, and and dextral dextralD3/D4 D3/D4kinematic kinematic indicators, indicators, are areinterpreted interpretedasasaaresponse responsetot oprogressive progressive dextral dextral transpression. transpression. Zircon provenance provenance ages constrain constrain the the maximum maximum depositional depositional age ageofofManitouwadge ManitouwadgemetametaZircon greywacke to t o 2693 2693 Ma (Zaleski (Zaleski et al., al., 1995), 1995),at atleast least25 25Ma Mayounger youngerthan than2720 2720Ma Mafelsic felsicvolcanism volcanism greywacke (Zaleski (Zaleski et al., al., 1994; 1994; Davis Davis et et al., al., 1994). 1994).Field Fieldobservations observations are areequivocal equivocal regarding regarding the therelationrelationship ship of of Dl D ldeformation deformation and andsedimentation; sedimentation; however, however, uplift uplift resulting resulting from from Dl D ldeformation deformation may may have contributed contributedsediment sediment sources. sources. Thus, Thus,Dl D is l istentatively tentativelyconstrained constrainedtotthe o the interval 2720-2693 have interval 2720—2693 2680A2 Ma Ma and and 2687±3 2687A3 Ma. U-Pb U-Pbzircon zircon ages, ages, determined determined for for three three prepre- to t osyn-D2 syn-D2 plutons plutons gave gave 2680±2 Ma. Ma Ma for for the the Nama NamaCreek Creekand andLoken LokenLake LakeK-feldspar K-feldspar porphyries porphyries respectively, respectively, and 2687+3/-2 2687+3/-2 Ma Ma for for the the oldest oldest diorite diorite of of the theBlack Black Pic Pic batholith. batholith.Hence, Hence,D2 D2deformation deformationand andpeak peakmetamorphism metamorphism in in the theManitouwadge Manitouwadge belt belt are areyounger younger than than2680 2680 Ma. Ma. AAfoliated foliated(D2?/D3?) (D2?/D3?)monzodiorite monzodioritephase phase of of the the Black Black Plc Pic batholith batholithhas hasan anage ageofof2677±3 2677±Ma, Ma,within withinerror errorofofthe themaximum maximumage agelimit limit on onD2 D2 deformation. deformation. Based Basedon onthe theinvolvement involvementofofthe theManitouwadge Manitouwadgemetagreywacke metagreywacke in inD2 D2folds, folds, the theage age of of sedimentation sedimentation is is bracketed bracketed by by 2693 2693 and and 2680 2680 Ma. Given Given the the similarity similarity in in lithology lithology and and age, age, we we interpret interpretthe theManitouwadge Manitouwadgemetagreywacke metagreywacke as as aa tectonic tectonicoutlier outlier of of the theQuetico Queticosubprovince. subprovince. Monazites Monazites from from intrusive intrusive and and altered alteredvolcanic volcanic rocks rocks in the the Manitouwadge Manitouwadge belt belt give give metamorphic metamorphic and and post-metamorphic post-metamorphicU-Pb U-Pbages agesofof2669-2676 2669-2676 Ma, and and 2661 2661 Ma Ma (Schandi (Schandl et al., al., 1991; 1991;Davis Davis et et a!., al., 1994; 1994; Zaleski Zaleski et a!., al., 1995). 1995). U-Pb U-Pbisotopic isotopicanalyses analysesofoftitanite titanitefrom fromfive fiveintrusive intrusiverocks rocksgive give two distinct distinct age agegroupings groupings of of circa circa 2673 2673 and 2655 Ma. 2680 Ma Nama Creek pluton and the the two Ma. The 2680 2672A2and and2674±2 2674k2Ma, Ma,respectively, respectively, which which 2677 Ma Ma Black Black Pic Pic monzodiorite monzodiorite have have titanite titaniteages agesof of 2672+2 2677 we 600°closure closure temperature temperature we tentatively tentatively interpret interpret as asthe thetime timeofofregional regionalcooling cooling through through the the600°C of of titanite titanite (Heaman (Heaman and and Parrish, Parrish,1991). 1991). Titanite Titanitefrom fromthe the2687 2687Ma MaLoken Loken Lake Lake pluton pluton has has an an age age of of about about 2652 2652 Ma, Ma, and andtitanite titanitefrom fromprepre-tot osyn-D3 syn-D3dykes dykesgives gives2658+4/-2 2658+4/-2 and and2655±3 2655k3Ma, Ma, suggesting suggesting aa widespread widespread retrograde hydrothermal hydrothermal event that that locally locally crystallized crystallized or reset reset titanite. titanite. Davis, Davis, D.W., D.W., Schandi, Schandl, E.S., E.S., and and Wasteneys, Wasteneys, H.A. H.A. 1994. 1994. U-Pb dating of of minerals minerals in alteration alteration halos halos of of Superior Superior Province Province massive massive sulphide sulphide deposits: deposits: syngenesis syngenesis vs. vs. metamorphism: metamorphism: Contributions Contributions to 115, 427—437. t oMineralogy Mineralogyand andPetrology Petrology 115, 427-437. Heaman, U-Pb geochronology Heaman, L., L., and andParrish, Parrish,R.R.1991. 1991. U-Pb geochronologyofofaccessory accessoryminerals. minerals.Mineralogical Mineralogical Association Association of of Canada, Canada,Short ShortCourse CourseHandbook Handbook19, 19,Applications Applications of ofRadiogenic Radiogenic Isotope Isotope Systems Systems to 59—102. t oProblems ProblemsininGeology, Geology, 59-102. Schandi, Schandl, E.S., E.S., Davis, Davis, D.W., D.W., Gorton, Gorton,M.P., M.P.,and andWasteneys, Wasteneys,H.A. H.A.1991. 1991.Geochronology Geochronology of ofhyhydrothermalalteration alterationaround aroundvolcanic-hosted volcanic-hosted massive massive suiphide sulphide deposits deposits in inthe theSuperior SuperiorProvince. Province. drothermal Ontario 156, 105—120. OntarioGeological GeologicalSurvey, Survey,Miscellaneous MiscellaneousPaper Paper 156, 105-120. Zaleski, 1994. 1994.Geological, Geological,geochemical, geochemical, and andage ageconconZaleski, E., E., Peterson, Peterson, V.L., V.L., and andvan vanBreemen, Breemen,0.0. straints straintson onbase basemetal metalmineralization mineralization ininthe theManitouwadge Manitouwadge greenstone greenstone belt, belt, northwestern northwestern Ontario. Ontario. Current 225—235. CurrentResearch Research1994-C, 1994-C,Geological GeologicalSurvey SurveyofofCanada, Canada, 225-235. Zaleski, 1995. Zaleski, E., E., Peterson, Peterson, V.L. V.L. and andvan vanBreemen, Breemen,0.0. 1995.Geological Geologicaland andage agerelationships relationships ofof the themargins marginsof ofthe theManitouwadge Manitouwadge greenstone greenstonebelt belt and andthe theWawa-Quetico Wawa-Queticosubprovince subprovince boundary, boundary, northwestern Geological 35—44. northwesternOntario. Ontario.Current CurrentResearch Research1995-C, 1995-C, GeologicalSurvey SurveyofofCanada, Canada, 35-44. 2 58 �PALEOGEOGRAPHIC RECONSTRUCTION OF THE GUNFLINT-MESABI-CUYUNA GUNFLINT-MESABI-CUYUNA DEPOSITIONAL BASIN ANALYSIS ANALYSIS APPROACH APPROACH DEPOSITIONAL SYSTEM: A BASIN and FRALICK, FRALICK, Philip W., Geology, Lakehead Lakehead PUFAHL, Peir K. and W., Dept. Geology, University, Thunder Bay, ON, P7B P7B 5E1, Canada Canada The depositional depositional system system responsible responsible for the the genesis genesis of of the the Proterozoic Proterozoicbanded banded iron formations in Minnesota Minnesota and Ontario has been hotly debated since the mid mid 1950's. Recent 1950's. Recent exploratory exploratory drilIing,the drilling,-the acquisition acquisition of of high high resolution resolution aeromagnetic aeromagnetic data and a better better understanding understanding of the the regional regional stratigraphy of the Biwabik Biwabik and and Trommald iron formations in Minnesota during the 1980's has provided provided insight insight into into the style of deformation deformation that that affected affected the the iron ironbearing bearingstrata strata during duringthe thePenokean Penokean Orogeny, 1860 m.y. ago. Researchers have since speculated, based m.y. Researchers have since speculated, based on on this this data, data, that that the deposition deposition of the chemical chemical and and clastic clastic sediments which comprise the Animikie Group in in Minnesota Minnesota occurred occurred in in aa migrating migrating peripheral peripheral foreland basin (Southwick and Morey, 1991). 1991). This problems that that have haveyet yetto to be be resolved. resolved. Most Morey, This model poses several several problems troubling, the model model is is incapable incapableof of explaining explaining the the observed observedlateral lateral distribution distributionof of facies facies in iron formation and associated strata. strata. There There is is an an apparent apparent lack lack of of coarse coarse turbiditic, turbiditic, deltaic and fluvial sediments adjacent adjacent to to the the fold-thrust fold-thrust belt. belt. Also, Also, ifif iron ironformation formation deposition occurred occurred in in aa migrating migrating foreland, foreland, sedimentation would have been restricted restricted deposition to the the outer outer platform platform(Hoffman, (Hoffman, 1987) 1987) and and consequently consequently the the chemical chemicalsediments sedimentswould would only be represented by facies characteristic of the distal shelf. shelf. The observed lateral The observed lateral fades within distribution of facies within correlatable units of iron iron formation are to the the contrary, contrary, aa complete shelf sequence, not just the distal portion portion is is present. present. These Theseinconsistencies inconsistencies to the need for the re-examination of iron formation in Ontario and have lead to re-examination of Minnesota. The The current current study study uses uses aa process process oriented oriented approach approach combined combined with with basin basin analysis to perform perform aa paleogeographic paleogeographicrecOnstruction reconstructionof of the the Gunflint-Mesabi-Cuyuna Gunflint-Mesabi-Cuyuna depositional system. depositional Twenty drill holes holes were logged logged from from the the Gunflint, Gunflint, Biwabik Biwabik and and Trommald Trommaldiron iron formations. Great Greatcare carewas wasexercised exercisedininrecording recordingchanges changesiningrainsize, grainsize, bed bed thickness, and sedimentary structures present present within within drill drillcore. core. This procedure procedure provides critical insight as to whether the organization of iron formation facies was process controlled allocyclic mechanism mechanism such such as as fluctuating fluctuating sea sea controlled or or governed governed by by an an allocyclic level, or both. Intrabasinal Intrabasinalcorrelations correlationsbetween betweenthe the Gunflint Gunflint and and Mesabi Mesabi iron iron ranges ranges were assisted by the presence presence of aa volcanic volcanic ash ash layer, layer, which served as aa stratigraphic stratigraphic marker, and by by comparison comparison of of sea sea level level curves generated from core core logs. logs. Stratigraphic correlations indicate that iron formation facies within the Gunflintdepositional system system exhibit exhibit aa marked fining fining and thickening of the Mesabi-Cuyuna depositional entire section to to the southwest. The The Gunflint Gunflint is is dominated dominated by medium medium to coarse coarse grained cross-stratified chert grainstone beds 5 to 50cm thick with abundant abundant rip rip ups. ups. Hummocky cross-stratified well sorted fine grained chert beds beds are are interbedded interbedded with with parallel and wavy bedded bedded magnetite-rich magnetite-rich slaty iron iron formation packages packages 33 to to 10cm 10cm Stratawithin within packages packages are are graded and 11 to 3mm thick. Chemical Chemicalsedimentary sedimentary thick. Strata comprising the Biwabik iron formation of the Mesabi iron facies comprising iron range are distinctly to medium grained grainstones 3 to finer grained than those those in in the the Gunflint. Gunflint. Fine to 30cm thick dominate, dominate, and and are are interbedded interbeddedwith withwavy wavy and andparallel parallellaminated laminated magnetite magnetite rich slaty iron iron formation packages, 10 10 to to 30cm 30cm thick. thick. Rip ups are present at the base base 59 �of of many many medium medium grained grained cross-stratified cross-stratified chert grainstones. The TheBiwabik Biwabikiron iron formation of of the the Emily Emily district district in in the the northern northern segment segment of of the the Cuyuna Cuyuna range rangeisis formation 10cmthick thickand andparallel parallel composed of of interbedded interbeddedfine fine grained grainedchert chert grainstones grainstones11to to 10cm composed and and wavy wavy laminated laminated slaty iron iron formation. Iron Ironformation formationfacies faciesininthe theTrommald Trommaldiron iron formation from from the the Cuyuna Cuyuna North Northrange rangeare are finer finer still, still, and and are are dominated dominated by by graded graded formation parallel laminated slaty iron formation. Slatybeds bedsrange rangeininthickness thicknessfrom from11to to4mm 4mm parallel formation. Slaty and and resemble resemble DE DE turbidites. This Thislateral lateraldistribution distributionof ofchemical chemicalsedimentary sedimentary facies facies parallels shelf ttoo slope parallels facies transitions observed observed in in modern modernshelf slopeenvironments. environments. Examination of vertical vertical fades facies trends trends ininiron ironbearing bearingstrata stratareveals revealsthe thepresence presence Examination of of both bothfirst first order order(sea (sealevel) level) and andsecond secondorder order(process (processcontrolled) controlled)depositional depositional cycles. Gunflintand and Biwabik Biwabik iron iron cycles. Three Threefirst firstorder ordercycles cyclesare arepresent presentininthe theGunflint formations; formations; aabasil basiltransgressive transgressive cycle, cycle, aa middle middle regressive regressive cycle, and and an an upper upper transgressive cycle. Each Eachextends extends 60 60 to to 80 80 meters meters upwards upwards through the sequence. sequence. AA transgressive pulse pulse of of volcanism volcanism is is preserved preserved in in the the lower lower portion portion of of the the upper uppertransgressive transgressivecycle cycle as as aa 3m 3mthick thickash ashlayer. layer. Its Its bottom bottomcontact contactisissharp sharpand andindicates indicatesaarapid rapidand andalmost almost instantaneous instantaneousinflux influx of of volcaniclastic volcaniclasticmaterial material into intothe thedepositional depositionalsystem. system. Its Itsupper upper contact contact isisgradational gradationalininplaces placesand andrepresents representswaning waningdelivery deliveryof ofvolcaniclastics volcaniclasticsto tothe the Animikie Animikie Basin. Basin. The Thepresence presenceofofsimilar similarallocyclic allocyclictrends trendshave havebeen beenrecorded recordedby by Morey Morey(1983). (1983). However, However,their theirrelative relativestratigraphic stratigraphicpositions positionsdiffer differsignificantly significantlyfrom from those those observed observedin inthis this study. study. Superimposed Superimposedwithin withinfirst firstorder ordercycles cyclesare aresmaller, smaller, coarsening coarsening upwards, upwards, second second order order cycles. cycles. These Thesepreviously previouslyunrecognized unrecognizedtrends trends in in the vertical distance of of 5 to to 10 meters. They They Gunflint and Mesabi Mesabi iron iron ranges span a vertical the Gunflint coarsen coarsengradationally gradationallyfrom fromparallel parallel laminated laminated slaty slaty iron iron formation formation to to medium mediumand and coarse-grained, coarse-grained, cross-stratified cross-stratified grainstone successions. Their Their top topcontact contactisis gradational gradational but but sharp sharp into into the the base base of of the the overlying overlying cycle. Similar Similarsequences sequences present present withinthe the iron ironbearing bearingstrata strataof ofthe theGogebic Gogebiciron ironrange rangeininWisconsin Wisconsinhave havebeen been within interpreted as as representing representing offshore offshore bar bar complexes. complexes. Their Theirpresence presenceisissignificant significantas as interpreted depositionalprocesses processesresponsible responsiblefor foroffshore offshorebar bardevelopment developmentprovide provideanother another depositional mechanism mechanismfor for the thegenesis genesisof ofinterbedded interbeddedcherty chertyand andslaty slatyiron ironformation. formation. References References Hoffman, Hoffman,P.F., P.F., 1987. 1987. Early EarlyProterozoic Proterozoicforedeeps, foredeeps,foredeeps foredeepsmagmatism magmatismand and Superior-type shield, in in Kroner, Kroner, A., A., ed. ed. Proterozoic Proterozoic Superior-type iron-formations iron-formations of the Canadian shield, lithospheric evolution. lithos~heric evolution. American AmericanGeophysical GeophysicalUnion UnionGeodynamics GeodynamicsSeries, Series,v.v.17. 17. p.85-98. p.85-98. Morey, Morey,G.B., G.B., 1983. 1983. Animikie AnimikieBasin, Basin,Lake LakeSuperior SuperiorRegion, Region,U.S.A.. U.S.A.. in in A.F. A.F.Trendall Trendall and Iron-Formation:Facts Factsand andProblems. Problems.Elsevier, Elsevier,New NewYork. York. andR.C. R.C. Morris, Morris,eds. eds. Iron-Formation: p.13-68. p. 13-68. Southwick, Southwick, D. D. LL.and andMorey, Morey,G.B., G.B., 1991. 1991. Tectonic Tectonicimbrication imbricationand andfordeep fordeep development developmentininthe thePenokean Penokeanorogen, orogen,east-central east-centralMinnesota-An Minnesota-Aninterpretation interpretation based basedon onregional regionalgeophysics geophysicsand andthe theresults resultsdrilling: drilling: U.S. U.S. Geological GeologicalSurvey Survey Bulletin Bulletin1904-C, 1904-C,17p. 17p. 60 �PRODUCTS PRODUCTS OF O F ELECTRIC ELECTRIC PULSE PULSE DISAGGREGATION DISAGGREGATION OF O FSOME SOMEKEWEENAWAN KEWEENAWAN ROCKS. ROCKS. RUDASHEVSKY, N. N.S., Saint Petersburg Petersburg Russia; Russia; RUDASHEVSKY, S., Mechanobr Mechanobr Technical Technical Corporation, Saint WEIBLEN WEIBLEN P.W. and and STOYNOV, STOYNOV, H., Department DepartmentofofGeology Geologyand andGeophysics, Geophysics, University of of Minnesota, Minnesota, Minneapolis, Minneapolis, MN MN 55455, 55455, and andSAINI-EIDUKAT, SAINI-EIDUKAT, B., B., University Department FargoND, ND,58105. 58105. Department of of Geosciences Geosciences North North Dakota Dakota State StateUniversity, University, Fargo A A new new facility facility atatthe theUniversity University of of Minnesota Minnesota for fordisaggregating disaggregating rocks rocks and and minerals minerals with with high high voltage voltage electrical electrical pulses pulses (Weiblen, (Weiblen, 1994) 1994) is is currently currently being being used used to to obtain obtain mineral mineral separates separates from Keweenawan Keweenawan rocks rocksofofthe theDuluth DuluthComplex, Complex,the theCopper CopperHarbor HarborConglomerate Conglomerate and andthe the from Nonesuch Previous research research at at the the Mechanobr Mechanobr Technical Technical Corporation Corporation in in Saint Saint Nonesuch Formation. Formation. Previous Petersburg, Petersburg, Russia Russia has hasdemonstrated demonstratedthe theefficacy efficacyofofelectric-pulse electric-pulsedisaggregation disaggregation to to separate separate minerals minerals of of contrasting contrastingdielectric dielectricproperties properties along alonggrain grainboundaries boundaries(Rudashevsky (Rudashevskyand andothers). others). The The electric-pulse electric-pulse method method of of comminution comminution preserves preserves the the original original grain-size grain-size distribution distribution of of liberated This phenomenon, phenomenon, which which contrasts contrasts with decrease in grain-size grain-size in in with the decrease liberated minerals. minerals. This mechanical mechanical comminution, comminution, facilitates facilitates recovery recovery of of fine-grained fine-grained minerals. minerals. Careful Careful materials materials handling handling of of the thedisaggregated disaggregatedproduct productremains remainsan animportant importantaspect aspectofofmineral mineralrecovery. recovery. Electric-pulse Electric-pulse disaggregation disaggregation of of Cu-Ni Cu-Ni bearing bearing samples samplesfrom from the the INCO, INCO, Spruce Spruce Road, Road, Test Test Pit Pit atat the the base base of of the theDuluth Duluth Complex Complex is is being being conducted conducted as as aa part part of of on-going on-going studies studies of of the the distribution and and petrogenesis petrogenesis of of platinum-group platinum-group minerals minerals (PGM's) (PGM1s)and their recovery. To-date, To-date, distribution several here-to-for here-to-for unreported unreported PGM's PGM's as as well as gold and silver alloys have have been been recovered. recovered. The The several PGM's PGM1sinclude: include: the the platinum-antimony-bismuth platinum-antimony-bismuth alloys sudburyite and froodite, and grains grains of of platinum-silver-selenide. The Theliberated liberatedgrains grainsretain retaindelicate delicatesurface surfacegrowth growthfeatures featuresand and have have aa platinum-silver-selenide. limited limitedgrain-size grain-size distribution distribution(0.01 (0.01 - - 0.1 0.1 mm). mm). Although Althoughsamples samplesfrom fromthe theINCO INCOSpruce SpruceRoad Road site site were were extensively extensively studied studied by by aanumber number of of investigators investigators in in the the past, past, discrete discrete grains grainsof of PGM's PGM's have The recovery recovery of of PGM PGM have not, not, to toour ourknowledge, knowledge, been been previously previously reported reported from fromthis thissite. site. The grains grains strengthens strengthensthe the view view that that aasignificant significantportion portion of ofthe theubiquitous ubiquitousabove abovebackground backgroundtoto 11 ppm assay assay values values for forplatinum platinum group group elements elements (PGEs) (PGE1s)ininthe theCu-Ni Cu-Niores oresofofthe theDuluth DuluthComplex Complex ppm are are due due to to discrete discretePGM PGM grains. grains. Further Furtherstudies studiesare arebeing beingdirected directedtoward towardproviding providingpreviously previously unobtainable unobtainable mineralogical mineralogical and and textural textural data on PGM's PGM's that that are are needed needed to to devise devise new new and and efficient efficientmethods methodsof ofmetal metalrecovery recoveryfrom fromDuluth DuluthComplex Complexores. ores. - The Themineralogy mineralogy and andtextures texturesof ofthe thefine-grained fine-grainedphases phasesininthe theCopper CopperHarbor HarborConglomerate Conglomerateand and the the Nonesuch Nonesuch Formation Formation of of the theWhite WhitePine Pinedistrict, district,Keweenaw KeweenawPeninsula, Peninsula,Michigan Michiganare arebeing being studied studied by by one one us us(Stoynov) (Stoynov) as aspart partofofa agraduate graduateresearch researchprogram. program. Electric-pulse Electric-pulse disaggregation of samples from these rocks has resulted in the recovery of fine-grained disaggregation of samples from these rocks has resulted in the recovery of fine-grained (<0.1 (< 0.1 mm) mm)barite baritecrusts, crusts,detrital detritalzircon, zircon,and andnative nativecopper coppergrains grainswith withdelicate delicatesurface surfacegrowth growthfeatures. features. Textural Textural and and compositional compositionaldata dataon on these thesematerials materials are arebeing being used used totoevaluate evaluatemodels modelsof ofcopper copper mineralization mineralizationprocesses processesininthese theserocks. rocks. The The electric-pulse electric-pulse facility facilityatatMinnesota Minnesota isisavailable available to to investigators investigators for for exploratoiy exploratory research. research. References References cited. cited. Rudashevsky, Rudashevsky, N.S., N.S., Burakov, Burakov, B.E., B.E., Lupal, Lupal,S.D, S.D,Thalhammer, Tlialhammer, O.A.R., O.A.R.,and andSaini-Eidukat, Saini-Eidukat,B, B,inin review, review, Liberation Liberation of of accessory accessory minerals minerals from from various various rock rock types typesby byelectric electricpulse pulse disintegration disintegration -- methods methods and and applications, applications, Transactions Transactions of of the the Institute Institute of of Mining Miningand and Metallurgy, Metallurgy,London. London. Weiblen, spearatesfor for Weiblen, P.W., P.W., 1994, 1994,AAnovel novelelectric electricpulse pulsemethod method for forobtaining obtainingclean cleanmineral mineralspearates geochemical 75,No. No.16, 16,p.p.70. 70. geochemicaland andgeophysical geophysicalresearch, research,EOS, EOS,Trans., Trans.,v.v.75, 61 �Kimberlite in in Ontario Ontario Xiinberlite Sage R. R. and and Morris MorrisT.F. T.F. Sage 933 Ramsey LakeRoad, Road,Sudbury SudburyOn On Ontario Geological Survey, Ontario Geological Survey, 933 Ramsey Lake P3E 6B5, Canada P3E 6B5, Canada To evaluate evaluate the the presence presence of of diamond diamond deposits deposits in inOntario, Ontario, the To the Ontario Geological Survey (OGS) initiated an investigation of known Ontario Geological Survey COGS) initiated an investigation of known kimberlitepipe pipeoccurrences occurrenceswithin withinthe theprovince. province. Each pipe will be kimberlite Each pipe will wilibe classified, it's exploration history defined and and models be classified, it's exploration history defined models will be developed to outline areas where other kimberlite pipes may exist developed to outline areas where other kixnberlite pipes may exist within the the province province (Sage (Sage1994). 1994). within Presently,there thereare are22areas areaswithin withinthe theprovince provincewhere wherekixnberlite kimberlite Presently, These are the Attawapiskat area and the area has been discovered. has been discovered. These are the Attawapiskat area and the area 1 ) . Kimberlite along the Lake Timiskaming Structural zone (Figure along the Lake Timiskaming Structural zone (Figure 1). Kimberlite core has has been been generously generously donated donatedto tothe the OGS OGS by by companies companiesworking workingin in core these areas. these areas. KWG Resources Resources and and Monopros Monopros Limited Limited have have provided provided core from the KWG core from the, Attawapiskat area. Dan Scholtz (University of Toronto) Attawapiskat area. Dan Scholtz (University of Toronto), Falconbridge Ltd., Ltd., Findore Findore Minerals Minerals Inc., Inc., Geological Geological Survey Survey of of Falconbridge Canada, KWG Resources Inc , Monopros Limited, Portland Firth, Canada, KWG Resources Inc., Monopros Limited, Portland Firth, Seymour Sears Sears (Consulting (Consulting Geologist), Geologist), Strike Strike Minerals Minerals Inc. Inc. and and Seymour Sudbury Contact Mines Ltd. provided core from the Lake Timiskaming Sudbury Contact Mines Ltd. provided core from the Lake Timiskaining StructuralZone. Zone. Examples Examples of of kimberlite kimberlite core corefrom from each each of of these these Structural areas are available for viewing. areas are available for viewing. . In addition addition to to the thecore, core, heavy heavy mineral mineral concentrates concentrates are are also also In KWG Resources donated chrome diopsides and available for viewing. available for viewing. KWG Resources donated chrome diopsides and it's C-14 pipe, Lake Timiskaming Structural pyrope garnets from pyrope garnets from it's C-14 pipe, Lake Timiskaming Structural Zone area. area. Monopros Monopros Limited Limited donated donated kiniberlite kimberlite core core from from the the Zone Guigues Pipe, Lake Timiskaming Structural Zone and KWG Resources Guigues Pipe, Lake Timiskanting Structural Zone and KWG Resources Inc. donated donated heavy heavy mineral mineral concentrates. concentrates. Inc. For each each area, area, kimberlite kimberliteand and heavy heavy mineral mineral concentrates concentrates available available For for display are listed in alphabetical order and in no way reflect for display are listed in alphabetical order and in no way reflect the level of importance of the contribution. the level of importance of the contribution. Two industrial industrialgrade gradealluvial alluvialdiamonds diamonds(1.05 (1.05and and 1.13 1.13 carat caratweight) weight) Two were recovered from the Michipicoten River-Wawa area in the summer were recovered from the Michipicoten River-Wawa area in the summer (C. Clement) who discovered the of 1991. The local prospector of 1991. The local prospector (C. Clement) who discovered the diamonds donated them to the Royal Ontario Museum who, in turn, has diamonds donated them to the Royal Ontario Museum who, in turn, has The story storybehind behind the the diamonds diamonds loaned them themto tothe theOGS OGSfor fordisplay. display. The loaned and follow-up work is summarized by Morris et al. (1994; this and follow-up work is summarized by Morris et al. (1994; this volume). volume) . 62 �References Cited References Cited Morris T.F., Murray C. and Crabtree D. 1994. Results of overburden Morris T.F., Murray C. and Crabtree D. 1994. Results of sampling for kimberlite heavy mineral indicators and gold overburden sampling kiniberlite heavy Wawa mineral grains, for Michipicoten Riverarea, northeastern Ontario; indicators and gold grains, River- Wawa northeastern Ontario; OntarioMichipicoten Geological Survey, Open area, File Report 5908, 69p. Ontario Geological Survey, Open File Report 5908, 69p. Sage R.P. 1994. Kimberlites of Ontario; in Summary of Field Work Sage and R.P.Other 1994.Activities Kirnberlites of Ontario; in SunnarySurvey, of Field Work 1994, Ontario geological and Other Activities Ontario geological Survey, Miscellaneous paper 1994, 163, p.113-115. Miscellaneous paper 163, p.113-115. 96 W + 76 N " ' 56 N Klznberljtes 0 L. 300 km Structuraj Zone 47 N__\ 96 W kche&n Supenor Provinc. Protrozo,c Soutbero ProTlig. (paxt of PeDokeaj OrogeA) Greovifle Protjic. (part of CrenvIIIe Oroge) Pbeoeroioic / \.. P.Ieozo1e Irid )IeIo2oIc baTiD sequecce. Figure 1. Index map showing the location of known kimberlite Figure 1. Index map showing the (from location known kimberlite clusters in Ontario Sageof1994). clusters in Ontario (from Sage 1994). 63 �COMPARISON POST-PENOKEAN THERMAL THERMAL HISTORIES HISTORIES OF OF THE THEWATERSMEET WATERSMEETAND AND COMPARISON OF POST-PENOKEAN REPUBLIC DISTRICTS, DISTRICTS, NORTHERN NORTHERN MICHIGAN: MICHIGAN: RESULTS RESULTSAND AND IMPLICATIONS IMPLICATIONSOF OF REPUBLIC 4 0 ~ r 1 3 9MINERAL ~r AGE 40ArI39Ar MINERAL AGE DATING D.A., HOLM, HOLM,D.K., D.K., (both (both at at Dept. Dept. of of Geology, Geology, Kent State University, Kent, OH SCHNEIDER, SCHNEIDER, D.A., 44242; 216-672-4094; 216-672-4094; dhoIm@kentvm.kent.edu) dholm@kentvm.kent.edu) and LUX, D.R. (Dept. of Geology, University Orono, ME 04469). of Maine, Orono, northern Michigan, Michigan, Archean Archean and and Paleoproterozoic Paleoproteroz~icrocks were were deformed deformed and and metamorphosed metamorphosed In northern during the 1870-1830 orogeny. Attoh 1870-1830 Ma Penokean orogeny. Attoh and andKiasner Klasner (1989) (1989) determined determined that that rocks rocks of of the the Watersmeet district reached pressures of 5-6 kbars and temperatures of 500-600OC, 500-600°C, whereas rocks of the Republic district attained similar temperatures but much lower pressures (2-3 (2-3 kbars). kbars). This pressure consistent with with the the contrasting contrasting ductility in the the rocks rocks of of these these two two regions. regions. variation across the orogen is consistent Paleoproterozoic ductile deformation fabrics fabrics are well-developed well-developed in in nearly nearly all all the rocks exposed in the Watersmeet area. In Incontrast, contrast,Paleoproterozoic Paleoproterozoicductile ductile fabrics fabrics are are only only well-developed in late mafic dike rocks of the Republic district. The Thecontrasting contrastingductility ductility and and pressure pressure determinations determinations from these regions suggests they would have experienced experienced different different cooling histories following the peak of metamorphism. In In assess this, this, we we have have applied appliedthe the40Ar/39Ar 40Ar139Arincremental order to assess incremental dating dating method method on on hornblende and biotite Thesedata dataallow allowcomparison comparisonof ofthe thethermal thermalhistories historiesbetween betweenthe thetwo tworegions regionsas aswell well from both regions. These as comparison of Ar/Ar RblSr biotite ages obtained obtained previously in other studies. ArlAr biotite ages ages with Rb/Sr Results from dated twotwo hornblende from the theWatersmeet Watersmeetdistrict. district.WeWe dated hornblendeseparates separatesfrom from the the Watersmeet district. An AnArchean Archeanamphibolite amphibolitecollected collected within within the the Watersmeet Watersmeet gneiss dome gave a welldefined plateau age of 1822±18 Weinterpret interpretthis this age ageas asrepresenting representing l822kl8 Ma (total gas age age == 1793A12 1793±12 Ma). We (the closure closure temperature temperature for hornblende). homblende). simple post-Penokean cooling of these these rocks rocks through through—500°C -5W° (the Hornblende obtained from a mylonitized mylonitized Archean Archean amphibolite amphibolite outside the dome dome gave gave no no plateau plateau age. age. Ma, similar similar to to aa UFb U/Pb zircon zircon However, a significant significant amount amount of of the the total total gas gas released released gave gavean anage ageof of —1750 -1750 Ma, age obtained on aa highly highly sheared sheared Paleoproterozoic Paleoproterozoic rock from within within the the Watersmeet Watersmeet gneiss gneiss dome dome Both ages probably represent the the time time of of shearing (Peterman and others, 1986). (Peterman 1986). Both probably represent shearing of these rocks at at temperatures temperaturesbelow below—500°C. -500OC. We obtained four biotite Ar/Ar ArlAr plateau ages from rocks within and adjacent to the dome which range Ma RblSr Rb/Sr biotite biotite ages obtained by Peterman range fronl from 1760 1760to to 1740 1740Ma, Ma,concordant concordantwith withthe thetwo two—1750 -1750 Ma and others (1980) and Sims and others (1984). One Onebiotite biotiteseparate separatefrom from aa rock collected collected 10 10km from from the dome yielded a somewhat somewhat disturbed disturbedspectrum spectrum with withaatotal totalgas gasage ageofof—1700 -1700 Ma (oldest increments increments were were Ma). Our 1720 Ma). Our biotite biotite ages agesare aresomewhat somewhatolder olderthan than Ar/Ar ArlAr biotite biotite ages ages obtained obtainedby by Winnett Winnett(1981) (1981) from from the same same rocks. The Thediscordance discordance between between the the two two studies studies reflects reflects the difference difference in the number number of increments analyzed per sample sample together with the fact fact that that low low temperature temperatureincrements increments are are considerably considerably younger than higher temperature temperatureincrements. increments. Interpretation. The ages obtained here Interpretation. The ages obtained here(see (seehistogram histogrambelow) below)support supportthe theinterpretation interpretationof of Sims Sims and others (1984) and Peterman and and others others (1980) (1980) that that the the Watersmeet Watersmeet district district experienced experienced significant significant cooling/uplift and concomitant deformation Ma, probably probably related related to to gneiss dome formation. coolinghplift deformation at at —1750 -1750 Ma, However, our 1822 1822 Ma homblende hornblende plateau age age indicates indicates that that metamorphism metamorphism in the the Watersmeet Watersmeet node node is is not related to heat transfer associated with rise of the dome rocks. We Weattribute attributegneiss gneissdome dome formation formation (and deformation of Penokean-aged isograds) to an episode of extensional collapse superimposed on an earlier history of crustal shortening (Schneider and Holm, 1994). Following Following uplift uplift and and stabilization stabilization at at —1750 Ma,this thisarea areahas hasnot not experienced experienced any significant thermal reheating. -1750 Ma, reheating. district. Three hornblende separates separates were dated from the Republic Republic Results from the Republic district. district, including two amphibolite amphibolite gneisses gneisses of probable probable Archean age and aa Paleoproterozoic Paleoproterozoic mafic mallc dike. One of the gneisses gneisses gave a plateau age of 1695±19 1695519 Ma and the dike rock gave a slightly older plateau age at 1720±13 Ma. AAsimilar ± 14 14 Ma) Ma) was was obtained on a dike dike rock rock by by 1720513 Ma. similar hornblende hornblende plateau age (1704 k on the the north north side side of of the the Winnett (1981). The Thethird third hornblende hornblende separate, separate, obtained from a rock collected on Marquette syncline north of Republic, did not give a plateau age; it yielded yielded aa disturbed disturbed spectrum specmm with a total gas Ma. Similar gas age age of of —1660 -1660 Ma. Similar disturbed disturbed ages ages were were obtained obtained by Winnett Winnett (1981) (1981)for for rocks rockscollected collected along the Marquette syncline. While Whileititisisdifficult difficulttotointerpret interpretthese thesedata, data,their theirlocation locationalong alongthe thefaultfaultbounded Marquette syncline syncline suggests suggests their disturbance disturbance might be related related to reactivation reactivation of of this this zone zonewell well Penokean orogeny. after the Penokean orogeny. 64 �____ were obtained obtained from from two two different different Paleoproterozoic Paleoproterozoicdikes. dikes. One gave an Two biotite separates were unreasonably old 27 old age attributed to to excess excess argon. argon. The other gave a well-defined well-defined plateau plateau age ageof of 1678 1678k±27 Ma. This Thisage ageisissimilar similartotothe theoldest oldestbiotite biotiteages agesobtained obtainedfrom fromthis thisarea areain inprevious previousthermochronologic thermochronologic studies using both the Ar/Ar ArIAr and Rb/Sr RblSr methods (see histogram below). Interpretation. The Interpretation. Thehornblende hornblendeplateau plateauages agesobtained obtained from from the the Republic Republic area area are are 100 100 Ma Ma younger than the hornblende age from the Watersmeet area. Given Giventhe therelatively relativelyshallow shallowdepth depthof of this this region, itit is is very very unlikely unlikely that that temperatures temperaturesin in the theRepublic Republicarea arearemained remained above above500°C 50O0Cuntil until 1720 1720Ma Maor or region, so following the. Penokean orogeny. We reflect. a significant fol1owing.the.Penokean -Wefeel feelthat thatthese theseages. ages.reflect significant thermal thermal resetting resettingevent, event, homblendes, well after the Penokean orogeny. orogeny. Schulz strong enough to reset hornblendes, Schulz and and others (1988) recently identified a —1733 -1733 Ma be responsible, responsible, Mapluton plutonlocated locatednortheast northeastof ofthe theRepublic Republicsyncline. syncline. This body may be in part, for the the existence existence of of aa near nearsurface surfacenegative negative gravity gravity anomaly anomaly in in the the Republic Republic area area (Attoh (Attoh and and Klasner, 1989). 1989). If so, so, we we speculate speculate that this this pluton pluton may also also be the the heat heat source source responsible responsible for the isotopic resetting. Maisis not not directly directly responsible responsible for for formation of the Republic resetting. If plutonism at at —1730 -1730 Ma node, it seems at least to be the cause metamorphic node, cause of aa major major thermal thermal perturbation superimposed on a pre-existing high regional temperature temperature distribution (cf. Peavy metamorphic metamorphic node; Attoh Attoh and and Vander Vander pre-existing Meulen, 1984) 1984) The 1680 1680 Ma Rb/Sr RblSr and Ar/Ar ArIAr biotite ages from the Republic area probably represent the time of 30O0C following the thermal reheating cooling through 300°C reheating event. event. The younger scatter in the biotite data is of partial partial resetting resetting associated associated with with the the long recognized recognized low-grade metamorphic event at about the result of 1630 Ma. 1630 gneiss dome formation gneiss post-Penokean cooling cooling I through through -500°C -5OO0C Lh g 51 5 .26 e% u/pb zir~ons U/Pb data, zircons • Peterman PetermanetetaL, al., 1986 1986 Rb/Sr data, biotite Rb/Sr data, biotite Peterman and and others, others. 1980 1980 9ms Slms and and others, others, 1984 1984 I I Ar/Ar data, Ar/Ar data, biotite biotite e 1j 0 nntt, 1981 Winnett, 1981 2 0 ' 1850 850 1800 lao0 II I I 1750 1750 1700 1700 AGE AGE (Ma) (Ma) This study This stMy 1650 Ar/Ar data, data, hornblende hornblende 1650 Ar/Ar l1 This Thisstudy study Age histogram of thermochronologic thermochronologic data from the the Watersmeet Watersmeet Area. Area. Rb/Sr data, biotite Rb/Sr data, and Sim, SIms, 1988 1988 Peterman and ' VanSchmusandWoolsey,1975 Van Schmus and W w b y , 1975 -1733 Ma plutonism 5 5 a rn i E ii I e-o0 1i ZE? z kQ . Ar/Ar Ar/Ar data, data, biotite biotite I Winnett, 1981 1981 0 Winnett, I c, I 1750 1750 is.. [] • 1 1700 1700 1650 1650 AGE (Ma) AGE (Ma) 1600 1600 1550 1550 This study study Ar/Ar data, data, hornblende hornblende Ar/Ar • l1 winnett, 1981 lg81 Winnett, This This study s t ~ y Age histogram of of thermochronologic thermochrono~ogicdata data from fromthe theRepublic RepublicArea. Area. Attoh, K., and Vander Meulen, Meulen, 1984, 1984,Journal Journal of of Geology, Geology,v. v. 91, 91, p. p. 417-432. 417-432. Attoh, K., and Kiasner, 911-933. Klasner, J.S., 1989, 1989, Tectonics, Tectonics, v. 8, 8,911-933. Peterman, Z.E., and others, others, 1980, 1980, Geological GeologicalSociety Societyof ofAmerica AmericaSpecial SpecialPaper Paper182, 182,p. p. 125-134. 125-134. Peterman, Z.E., and others, Peterman, others, 1986, 1986, U.S. U.S.Geological GeologicalSociety Societyof ofAmerica AmericaBulletin Bulletin1622-F, 1622-F,p. p. 51-64. 51-64. Peterman, Z.E., and Sims, Sims, P.K., 1988, 1988, Tectonics, v. 7, p. 1077-1090. 1077-1090. Schneider, D.A., D.A., and Holm, D.K., Schneider, D.K., 1994, 1994, Eos, v. 75, p. 691. Schulz, Schulz, K.J., K.J., and others 1988, 1988, ILSG, 34th 34th Annual Meeting, Marquette, Michigan, p. 95-96. 4.lp. Sims, P.K., and others, others, 1984, 1984, U.S. US. Geological Geological Survey Profesional Paper 1292-A, 1292-A, 41p. Van Schmus 1975, Canadian Canadian J. Earth Earth Sciences, Sciences,v. 12, 12,p. 1723-1733. 1723-1733. Schmus ,,W.R., and Woolsey, L.L., 1975, Winnett, T.L., 1981, 1981, [Master's [Master's thesis], thesis], Ohio State State University, lO6p. 106p. 65 �COMPLEX GEOLOGY OF THE SOUTHERN PORTION OF THE DULUTH DULUTh COMPLEX SEVERSON, MARK J.l J., Natural Resources Research Institute, SEVERSONl MARK Institutel University University of of Minnesota, Minnesotal Duluth, MN Duluthl MN 55811 5581I The Duluth plex (Middle (Middle Proterozoic Proterozoic -- 1099 1099 Ma) Ma) is isaalarge largeintrusive intrusivebody bodythat thatcontains contains Duluth Corn Complex numerous Recent work work has has shown shown that numerous smaller intrusions intrusions that collectively comprise comprise the Complex. Recent igneous stratigraphic sections can can be igneous stratigraphic sections be delineated delineated within these these intrusions intrusions through through detailed detailed relogging of drill corel core, e.g., Riverintrusion intrusionand andSouth SouthKawishiwi relogging e.g.l for the Partridge River Kawishiwi intrusion. More More I 4 0 drill holes are located located in in the the "South "South Complex" CompIeY study study area (Figure (Figure 1), I ) $which is an area than 140 between the Wyrnan Wyman Creek Cu-Ni Prospect (to the north) north) and and the the Boulder BoulderLake Lake area area (to (to situated between the south). south). Most of these holes holes (112 ( I 12 holes; holes; 88,000 881000feet of of core) core) have have been been relogged relogged and and correlated into several troctolitic troctolitic to to gabbroic gabbroic stratigraphic sections. While While each indMdual individual drilled drilled area exhibits good correlative units do do not extend into an area exhibits correlative units in drill hole, holel these correlative correlative units adjacent drilled area area that that is located adjacent drilled located aa few few miles miles distant. distant. This lack lack of of large-scale large-scale continuity continuity suggests suggests that either: either: 1) I )the the "South "SouthComplex" Complex"study studyarea area constitutes constitutesan an area area that actually actually includes includes several smaller smaller intrusive intrusive bodies; 2) several 2) drilling drilling is not not detailed detailed enough enough to to delineate delineatelarge-scale large-scale correlative units; 3) the effects of contamination contamination related to assimilation of footwall rocks rocks close close to to the contact hampers hampers large-scale correlations; or 4) combinations combinations of the above. above. In addition to exploration exploration for Cu-Ni Cu-Ni sulfide mineralization, mineralization1many of the holes holes drilled drilled in in the "South "South Complex" Complex" area intersected intersected smaller smaller plug-like plug-likebodies bodiesof of Oxide-bearing Oxide-bearingUltramafic UltramaficIntrusions Intrusions (OUl); the distribution distribution of large OUI OUl bodies are shown in Figure 1. (OUI); the I.The The OUI OUI are characterized by coarse-g rained to to pegmatitic pegmatitic clinopyr~xenite~ clinopyroxenite, picrite, coarse-grained picrite! peridotite, peridotitel and and dunite dunite that that are are intrusive intrusive into into troctolitic rocks. OUIvaries variesfrom from 15-20% 15-20Y0(disseminated) (disseminated)to thick thick massive massive the troctolitic rocks.Oxide Oxidecontent contentininthe theOUI oxide zones. Ilmenite llmeniteisis the the dominant dominant oxide oxidein insome some OUI; OUI; whereas, whereas1titanomagnetite titanomagnetiteis is dominant dominant in others. In Inalmost almostall allinstances, instancesl the the OUI OUI are are spatially spatially arranged arranged along along linear linear trends suggesting suggesting that structural control control was important important to their their genesis. At Atsome somelocalities, localitieslaagenetic geneticlink linkbetween between iron-formation assimilation assimilationat at the the basal contact and OUI OUI formation formation isisapparent apparent(Longnose, (Longnosel iron-formation Longear, and Section 17 This suggests that the OUI were initially formed at depth Longearl 17 bodies). bodies). This suggests that depth followed followed by by upward upwardinjection injectionof of OUI OUI material material along along fault zones. However, Howeverlother otherOUI OUI are are situated situated within, withinl or immediately immediately below, below1layered layered oxide-rich gabbroic rocks rocks (Boulder (Boulder Lake Lake area) suggesting that the OUI OUI formed by by aa differentiated differentiated iron-rich melt that drained down into into the the cumulate cumulate pile pile OUI do do not notshow showany anyimmediate immediaterelationships relationshipsto oxide-rich oxide-rich rocks rocks along fault zones. Still Stillother other OUI present within either the footwall or surrounding surrounding troctolitic rocks rocks and and possible possiblegenetic geneticlinks linksare are the 'South "South Complef Complex" area. area. The The Sulfide-mineralized zones are generally rare within the unknown. Sulfide-mineralized highest amount amount of sulfides associated associated with with troctolitic troctolitic rocks are are present present in holes drilled in the highest Water Hen and Whiteface Whiteface Resermir Reservir areas areas (Figure (Figure 1). I). of rock types on a geochemical basis is ongoing. The Comparison of TheOUI OUI are are the the most most interestingofof this this group group as each interesting each of of the the specific specific OUI OUI bodies bodies has has aadistinct distinctgeochemical geochemical 'Yingerprintl'relative relative to to each each other. other. Each of the OUI OUI also also has has significant significant variations variations in in overall owrall 'ingerprint" content of Ti02, TiO2! V2OS, V 2 m 1 Cr, Cu, Cul Ni, Nil and graphite graphite due to dominant dominant rock rock type, type1mineralogy, mineralogyl and and geographic location. location. For example the southernmost OUl OUI bodies generally have much much higher higher V2O5 contents contents than than the the northernmost OUls which which contain contain higher concentrations concentrations of of Crl Cr, Cu and and V205 Ni. While While graphite graphiteisiscommon commonto tomost mostOUI, OUI,the theWater Water Hen HenOUI OUI is is the the only only OUI OUI that contains contains thick thick massive graphite graphite (present (present in in the upper upper half half of of the the body). body). In some cases cases these these intersections of massive variations reflect the dominant mineralogy; mineralogy; however, howeverl in some some cases cases they they may mayreflect reflect different different modes of origin origin (or (or differences differences in in the the footwall footwall source source rock rock or or Complex Complexhost hostrock). rock). 66 �- Edge of D u l u t h Complex Cu-Ni DEPOSIT OXIDE-BEARING ULTRAMAFIC INTRUSION (OUI) 0EXPLORATION AREA 10 kilometers 0 OUTLINES ENLARGED AREA 1 Geology and ACAD by Mark J. Severson Februaw. 1994 67 �Geochemistry and and fractionation fractionation of of the the Eastern Eastern Gabbro, Gabbro,Coidwell Coldwell Geochemistry Alkaline Complex. Complex. Alkaline Shaw, Cliff Cliff S.J. S.J. Shaw, Department of of Earth Earth Science, science, University university of of Department Western Ontario, Ontario, London, London,Ontario, ~ntario, N6H 5B7. 5B7. Western N6H The Eastern Eastern Gabbro Gabbro is is the the oldest oldest major major intrusion intrusion in in the the 1108±1 1108± Ha Ma The Coldwell Alkaline Alkaline Complex Complex (CAC). (CAC). It It forms forms aa ring-dyke ring-dyke surrounding surrounding Coidwell variety of of lithologies lithologies ranging ranging from from quartz quartz syenite syeniteto to nepheline nepheline aa variety syenite. syenite. It is is part part of of the the first first intrusive intrusive center center in in the the CAC CAC and and It is associated associated with with iron—rich iron-rich augite augite syenite, syenite, monzodiorite monzodiorite and and is basaltic xenoliths. xenoliths. basaltic The Eastern Eastern Gabbro Gabbro consists consists of of four four subunits, subunits, in in order order of of The Gabbronorite (GN), (GN), Two Two Duck Duck Lake Lake Intrusion Intrusion emplacement these these are, are, Gabbronorite emplacement (TDLI), Layered Layered Gabbro Gabbro (LG) (LG)and and Malpas Malpas Lake LakeIntrusion ~ntrusion (MLI). (TDLI), (MLI). The The rocks are are plagioclase—rich plagioclase-rich cumulates cumulates that that contain contain variable variable amounts amounts rocks of of ilmenite, magnetite magnetite and and olivine, clinopyroxene, clinopyroxene, biotite, biotite, ilinenite, olivine, orthopyroxene. orthopyroxene. Rock and and mineral mineral Mg# Mg# and and compatible compatible elements elements decrease decrease in in Rock abundance in in the the sequence sequence GM GN - TDLI TDLI — LG LG — HLI. MLI. Incompatible Incompatible abundance - - - elements eg eg alkalis, alkalis,Ba, BatZr Zr and and REE REE increase increasein inthe thesame samesequence. sequence. elements There is is however however aa great great deal deal of of overlap overlap in in the the compositions compositions of of the the There GN, TDLI TDLI and and LG LG indicating indicatingthat thatthey theycrystallised crystallisedfrom fromiuagmas magmas with with GN, similar compositions. compositions. similar The composition composition of of the the magmas magmas which which crystallised crystallised to to form form the the The rocks of of each each subunit subunit was was estimated estimated by by analysis analysis of of fine—grained fine-grained rocks Theestimated estimatedmagma magmacomposition compositionof of samples and and weighted weighted averaging. averaging. The samples 68 �the TDLI TDLI and and LG LG are are similar similar to to typical typical Keweenawan Keweenawan olivine olivine the tholeiites. tholelites. The MLI MLI estimate estimate is is rich rich in in Si02 SiO, and and alkalis alkalis and and is is The akin to to aa Keweenawan Keweenawan basaltic basaltic andesite. andesite. The The estimate estimatefor forthe theGN GN is is akin not used used because because it it may may have have been been contaminated contaminated by by silica. silica. not Modelling of of fractionation fractionation in in the the Eastern Eastern Gabbro Gabbro suggests suggests that that Modelling there is is aa differentiation differentiation trend trend from from TDLI TDLI to to LG LG and and MLI. MLI. there The The similarities in in major major oxide oxide composition composition of of the the TDLI TDLI and and LG LG magmas magmas similarities and difference difference in in trace trace elements elements rules rules out out simple simplefractionation. fractionation. and more complex complex model model of of fractionation fractionation in in aa replenished replenished and and erupting erupting AA more In this this model model fractionation fractionation is is achieved achieved magma chamber chamberis is proposed. proposed. In magma by crystallisation crystallisationof of olivine, olivine,clinopyroxene clinopyroxeneand and plagioclase plagioclasein in the the by 1:4:6.7. ration 1:4:6.7. ration The magma magma removed removed is is evolved evolved and and the the replenishing replenishing The magma is is the the same same composition composition as as the the original originalstarting startingmaterial. material. magma This model model causes causes fractionation fractionation of of trace trace elements elements but but leaves leaves the the This major elements elements relatively relatively unaffected. unaffected. major 2-8 cycles cycles Using this this model model the the LG LG was was derived derived from from the the TDLI TDLI by by 2-8 Using of of fractionation, fractionation, eruption eruption and and replenishment. replenishment. Continued Continued fractionation of the LG LG leads leads to to the the MLI MLI and and eventually eventually to to the the fractionation of the iron-rich augite augite syenite syenite which which intrudes intrudes the the Eastern Eastern Gabbro. Gabbro. iron-rich 69 �ON THE THEO1UGIN ORIGIN OF OFALKALINE ALKALINE GABBROIC GABBROIC ROCKS ROCKS IN IN THE THE COLDWELL COLDWELL PENINSULA PENINSULA AREA, AREA, COLD WELL ALKALINE COMPLEX, COLDWELL COMPLEX,ONTARIO. ONTARIO. Shore, Geoff T., Department Department of of Earth Earth Science, Science, University of Western Ontario, Ontario, London, Ontario, Ontario, N6A N6A 5B7. 5B7. The Coidwell Coldwell Peninsula Peninsula Area Area (CPA) (CPA)represents representsthe thesouthernmost southernmostextension extensionof ofthe theKeeweenawan KeeweenawanCoidwell Coldwell Alkaline Complex Complex (CAC) (CAC) into intoLake LakeSuperior. Superior.Arcuate Arcuatebodies bodiesofofnepheline nephelinesyenite syeniteand andalkaline alkaline gabbro gabbro dominate dominate the CPA and together comprise the main lithologies within the second intrusive centre of the CAC. A of together comprise the within the second intrusive centre of the CAC. zone of heterogeneous-textured alkaline alkalinegabbroic gabbroicmegaxenoliths, megaxenoliths,varying varyinginincomposition compositionfrom fromgabbro gabbro to to olivine olivine gabbro, occupies occupies the thecentral centralportion portionof ofthe thepeninsula peninsulabounded bounded to to the the north north and and south southby by later laterintrusions intrusionsofofnepheline nepheline syenite. The xenolithsoccur occurasasblocks blocks(c (<1m Imtoto> lOOm)formed formedby by disruption, disruption, brecciation brecciation and > 100m) and The alkaline alkaline gabbroic xenoliths assimilation of an early assimilation early layered layered gabbroic gabbroicbody body by by later later syenitic syeniticphases. phases. Several large vicinity of of Port Coidwell. largelayered layered alkaline alkaline gabbro gabbro megaxenoliths megaxenoliths occur in the vicinity Coldwell. The Thelayered layered heterogeneous-textured gabbroic gabbroic rocks. rocks. gabbroic sequences sequences are are cut cut by by chemically chemically and mineralogically similar, heterogeneous-textured fractionated with with decreasing decreasing compatibles compatibles (Ni, Early, rhythmically layered alkaline gabbroic megaxenoliths are fractionated Cr, Co) and increasing increasing incompatibles incompatibles(Zr, (Zr, Y, Y, Th, Th, Nb, Ba) and alkali elements towards the south. south. Spectacular breccia breccia zones, zones, comprised comprised of of lobe lobe and and cuspate cuspate microgabbroic microgabbroic enclaves enclaves surrounded surrounded by a nepheline nepheline host, are are the the result result of of nepheline nepheline syenite syenite magmatism magmatismand andsynplutonic synplutonicmicrogabbroic microgabbroicdykes. dykes. Whole rock syenite host, and mineral geochemistry is is consistent consistentwith withderivation derivationofofthe thesynplutonic synpiutonicmicrogabbroic microgabbroic enclaves enclaves through througholivine olivine (Fo87), clinopyroxene (En43Wo48Fs8) andplagioclase plagioclase(Anw) (An67)fractionation fractionationofofa aprimitive primitivealkali alkali basaltic basaltic parent. parent. (Fog,), clinopyroxene (En43W040Fss) and Microgabbroic enclaves enclavesand andsyenites syenitesform formlinear lineartrends trends on on Mg# Mg# versus versus major major element (Na, K, Ca, Microgabbroic Ca, Al) Al) and andtrace trace element (Ni, Co, Zr, Nb, Ba, Ba, Rb) Rb) plots plots suggesting suggesting that that at at least least some some of the enclaves are related to the syenites assimilation. by assimilation. A four-stage four-stagemodel model isisproposed proposedtotoexplain explainthe theemplacement emplacement history of the main units within the CPA: 1) emplacement of centre I1 lithologies lithologiesand and initiation initiation of of alkaline alkaline gabbro gabbro fractionation; fractionation; 2) disruption disruption of the layered layered alkaline gabbro 3) nepheline nepheline syenite syeniteintrusion intrusionand and gabbro sequence sequenceand and intrusion intrusionby by cognate cognatealkaline alkalinegabbro gabbromagma; magma; 3) synpiutonic microgabbroic dyke intrusion. in situ differentiation; differentiation; 4) 4) amphibole amphibolenatrolite natrolite nepheline syenite and synplutonic 70 �WftUAMS MINE By: Gordon Gordon Skrecky, Gray, and Allan Skrecky, James JamesGray, Allan Guthrie Guthrie REGIONAL GEOLOGY The The Williams Williams Mine Mine lies lies on onthe thesouth southside sideofofthe theessentially essentiallyeast-west east-west trending trending Schreiber-White Schreiber-White River River Greenstone Belt Belt of of Archean volcanic Greenstone volcanic and and sedimentary sedimentary rocks. rocks. The belt has has been been subjected subjected to to regional regional s interpreted metamorphism, o amphibolite metamorphism, up up tto amphibolite grade. grade. It It iis interpreted as asbeing beingsynclinally synclinallyfolded. folded. Granitic Granitic intrusions and gneissic bodies bodiesbound boundthe thebelt belttto the north and south and intrude the synclinal axis gneissic o the axis of the the belt. belt. In the vicinity vicinity of of the theWilliams WilliamsMine Minethe thesupracrustal supracrustalrocks rocks are divided divided into into the the Playter Playter Harbour Harbour Group Group and and Heron Bay Group. The The former former is primarily primarily composed of maf Icvolcanic volcanic rocks rocksand andthe the latter latter primarily primarily of Bay Group. composed of mafic of felsic volcanic rocks and metasedimentary rocks with minor intrusive rocks. The Heron Bay Group dips to rocks rocks with minor intrusive rocks. The Heron Bay Group dips t o the north, structurally structurally overlies overlies the the Playter Playter Harbour Harbour Group, Group, and and contains contains all the the economic economic gold gold deposits deposits found to t o date date near Hemlo. Hemlo. PROPERTY GEOLOGY GEOLOGY PROPERTY The major rock rock units units on on the the property property strike strike 108° The major 108O and dip from 60° 60Âto to700 70Âto tothe thenortheast. northeast. The The general general property stratigraphy maficmetavolcanic metavolcanicrocks, rocks, lower lowermetasedimentary metasedimentaryrocks, rocks, an an stratigraphy from from south south to to north northisi smafic altered altered felsic felsic prophyry prophyryrock rockunit, unit,the thegold goldmineralized mineralizedrocks, rocks,and andthe theupper uppermetasedimentary metasedimentaryrock rocksequence. sequence. An intermediate to the upper upper metasedimentary metasedimentaryunit unitfrom fromthe thefelsic felsic porphyry porphyry to felsic fragmental fragmental unit unit separates separates the western portion portion of the the property. property. lower unit on the western Lowerand and upper upper denote the relative structural positions of the metasedimentaryrock rockunits units as asthe theyounging youngingdirections directionsare areunclear. unclear.An Anintermediate intermediateintrusive intrusive unit unit divides metasedimentary the felsic porphyry unit end of of the property. All of unit into intotwo twosegments segments at the east end of the the major majorrock rockunits unitsare are highly deformed. The major major intrusive rocks, order of age, are intermediate intermediate to to felsic dikes and felsic porphyry The rocks, in decreasing decreasing order age, are dikes, altered, altered, biotite-rich biotite-rich dikes, Iamprophyre. All All of these dikes, dikes, diabase, diabase, and lamprophyre. these intrude intrude the the orebody orebody and and the the basic basic stratigraphy. A mafic intrusive body cuts cuts the the felsic felsic porphyry porphyry rocks iin 'C' zone intrusive pipe-shaped pipe-shaped body n the 'C' zone pit pitand and is i s in in turn cut cut by by later later diabase diabase diking. diking. diabasedikes dikesand andyounger youngerlamprophyres lamprophyresare areProterozoic. Proterozoic.I In contrastto tothe theintermediate intermediate and and felsic felsic dikes dikes The diabase n contrast which are conformable to the stratigraphy, fill joints stratigraphy, they fill joints trending trendingnorth northand anddipping dippingvery verysteeply steeply east east and cut the earlier earlier dikes. dikes. MAIN THE M A I NOREI3ODY OREBODY The main main orebody orebody has hasaastrike strikelength lengthof ofabout about 1200 1200 m, m, dips dipsat at60 60° to to 70 70° to to The to the the northeast northeast and and plunges to the northwest at approximately approximately 45O. 450 ItItoutcrops to a vertical vertical depth of about 1300 outcropsat at surface surface and continues to m on the Williams property. property. Upon Uponcrossing crossing a claim claim line line to to the the east east ititbecomes becomes the Golden Giant deposit of Hemlo Gold. The maximum thickness thicknessof of ore ore iis 45 metres metresand andi sislocated locatedadjacent adjacentto tothe the Hemlo Hemlo Gold Gold boundary. boundary. Moving s 45 Moving The west declines iin width and grade. grade. The portion of west from that property boundary, boundary, the ore generally declines n width The western portion of 'B' zone reserves, reserves,from from about about the the provenlprobable proven/probable line category, incorporates 'B' line through through the the possible possible category, incorporates two two oreoregrade zones zoneswithin within the typical typical host lithology. waste pillar pillar of at lithology. These These are are separated separated by an internal waste at least least 10 10 metres horizontal horizontal thickness. thickness. This This mineralization mineralizationrepresents represents the fringe fringe of of the the'Hemlo 'HemloDeposit' Deposit'and andas assuch, such, continuity of erratic. continuity of ore oregrade grade and and thickness thickness become increasingly erratic. Williams Operating Corporation treated treated 2.3 2.3 million million tonnes of gold gold iin tonnes of ore to to produce produce 445,000 445,000 ounces ounces of n making itit one gold mines. Total Proven totalled at 30.9 1994, making one of Canada's Canada's largest largest gold Proven and Probable Probable Ore Ore Reserves Reserves totalled 30.9 million milliontonnes tonnes grading grading 5.7 5.7 grams grams of gold per per tonne tonne at at the the end end of of 1994. 1994. 71 �EFFECTS OF O NCRUSTAL. CRUSTAL ROCKS ROCKS EFFECTS OF LARGE LARGE METEORITE IMPACTS ON - N THIN THINSECTION SECTION - SUDBURY BASIN IIN Viitala, Reino Viitala, Reino L., Department of Geology, Geology, Lakehead Lakehead University, University, Thunder Thunder Bay, Bay, L., Department Ontario, P7B P7B5E1, 5E1, Canada Canada The origin of The of the theSudbury Sudbury Igneous Igneous Complex Complex (SIC), (SIC), in central Ontario, Ontario, has has been been aa subject of controversy for over subject over ninety ninety years. years. Since 1 1962 laboratory studies studies by Dietz, Dietz, Guy-Bray, Guy-Bray, Since 962 more more recent recent detailed detailed field and laboratory Peredery, the impact theory as Peredery, Dence, Dressier Dressler and many others have greatly strengthened the as the trigger mechanism mechanism for the the Sudbury Sudbury event. event. The Sudbury Sudbury impact occurred occurred during during an an active Penokean orogeny orogeny about about 1.85 1 .85b.y. b.y.ago ago[I]. [1]. One of of the the interesting interesting questions arising from the impact-theory impact-theory is is how how much much of of the the SIC SIC might be be impact impact melt melt rather rather than internally internally derived igneous igneous rock rock material? material? Presence of shock metamorphic features Presence of features have been observed by recent recent research research in in the footwall footwall of of the theSIC SIC (Dence (Dence 1972, 1972, Guy-Bray Guy-Bray and INCO INCO Geological Geological staff staff 1966, 1966, DressIer Dressier 1984) and in i n the the breccias breccias of the the Onaping Onaping Formation Formation (French (French 1968, 1970, 1970, 1972, 1972, Peredery Peredery 1 972, Muir Muir and Peredery 1984). 1 984). These These features featuresinclude: include: shatter cones, cones, microscopic microscopic planar 1972, feldspar, kink bands in biotite elements in quartz and feldspar, feldspar, plastic deformation of feldspar, biotite mica, mica, severe fracturing fracturing of garnet, recrystallized and incipient incipient melt bodies. severe recrystallized quartz and glasses, glasses, and bodies. Commonly found Commonly foundassociate associatefeature featurenear nearimpact impactsites sitesare areShatter-cones. Shatter-cones. Shatter-cones Shatter-cones are radial with striae 968, 11972). 972). The radial fracture fracture surfaces surfaces with striae that that fan fan from from an an apex apex (Dietz (Dietz11968, Thestriae striae are sharp grooves grooves between between intervening, rounded upon roundedridges ridges developed developedby bypressure pressure releases upon impact. Shatter-cones 7 km away. Shatter-conescan can be be found foundaround aroundthe theSIC SIC for fordistances distances as as much much as as 117 et al. al. 1969, Stoffer Stöffer 1967, 1967, Chao Chao 1968, DressIer Dressler 1970) Studies indicate (von Engelhardt et that weakerthan than 100 100 kilo-bars do not that shock shock pressures pressures weaker kilo-bars do not produce produce any any typical typicalshockshockmetamorphic features. features. Shock Shock experiments experiments using using plagioclase plagioclase feldspar [2] produced produced planar planar between 150 and 300 kilo-bars pressure. features between pressure. Between Between 300 300 and and 500 500kilo-bars kilo-barspressure, pressure, whole whole plagioiclase plagioiclasecrystals crystalsbecame became diaplectic diaplecticglass glass (maskelynite) (maskelynite) and above above 500 500 kilo-bars, kilo-bars, normal glass glass of plagioclase plagioclase composition composition was was formed. formed. The The corresponding corresponding working temperature reached reached during during the active stage stage of of the the SIC SICcan canbe be estimated estimatedfrom fromthe thework work of temperature 967)[3]. They at its norite intrusion They concluded concluded that that the the SIC at intrusion activity activity Naldrett and Kullerud Kullerud (1 (1967)[3]. level reached temperaturesofof 1000° 1000°C with with aa 20°C reached temperatures 20° per per 11km kmgeothermal geothermal gradient gradient at at an an emplaced emplaced depth of 55 km. km. From Fromthe theextent extentofofthe thepyroxene-hornfels pyroxene-hornfelsfacies facies of of 220 220metres metres from the estimated that that the SIC remained at temperatures of about the SIC, SIC, these these researchers researchers estimated SIC remained 600°C 600° for for more morethan than720,000 720,000 years years after after the the norite norite intrusion. intrusion. 72 �Some representative field with Some 23 23 representative field samples samplesfrom from the the SIC SIC [4] [4] were were collected along with several examination. several samples samples of of Shatter-cones Shatter-conesfor forthin-sectioning thin-sectioningfollowed followed by microscopic examination. Shatter-cones (Map #1,2), Sudbury SudburyBreccia Breccia North-range North-range (Loc (Loc #4), Field samples samples include: include: Shatter-cones (Map Loc bc #1,2), ry Breccia South-range (Loc #6), Footwal l Breccia (Loc #8,9,1 O), Nort h-range Onaping Sud bu Sudbury South-range (Loc #6), Footwall Breccia (Loc#8,9,10), North-range Onaping Basal Member (Loc (Loc #1 #111A), A), Gray Member Member (Loc (Loc#1 #11 B), Melt Melt Body Body(Loc (Loc#1 #11 C), Formations Basal 1B), 1C), Black (Loc #13), #13), South South Range-Basal Range-Basal Member (Loc #16), #16), Black Member (Loc Member (Loc (Loc #14), #14), Chelmford (Loc Onwatin Formation Formation(Loc (Loc#17), #17), SIC SICmember member Norite Norite(Loc (Loc#19), #19),SIC-member SIC-member Sublayer Sublayer (Loc (Loc Onwatin #20), and Nickel-copper sulphide sample from the discovery site at Murray Mine Open #20), suiphide sample from thediscovery site at Murray Mine Open pit pit (LOC (Loc #23). Shock metamorphic metamorphic features featurescan can be be viewed viewed in thin Shock thin sections sections ofofthese thesesamples. samples. Sections of Shatter-cones showthe theextent extentof of the the obliteration obliteration of quartz Sections of Shatter-cones show quartz grains grains along along the the pressure fractures fractures occurring occurring in arenite pressure arenite material. material. Similar features features as shatter-cones shatter-cones but not not formed formed in the the usual usual conical conical pattern pattern were were found found in in the the Basal Basal member member of of the the Onaping Onaping Formation on the south range sample site site #14 #14 south south of of Vermillion Vermillion Lake. range at sample Lake. This Thishands-on hands-on to some some of of the the Sudbury Sudbury Igenous Igenous Complex rock rock units units and and poster display provides a window window to their unique unique inherent inherent mineralogy. mineralogy. Cited References Cited [1] [I] Krogh T.E. et al. (1984) In T.E. et In The Geology Geology and and Ore Ore Deposits Deposits of of the theSudbury SudburyStructure Structure (E.G. Pye Pye et et al., at., eds.), eds.), Ministry Ministry of Natural (E.G. Natural Resources, Resources, Toronto. [2] Engelhardt. W.von, W.von, Arndt, J., Stöffler, D., D., Muller, W.F., J., Stoffler, W.F., Jeziorkowski, Jeziorkowski,H., H., and andGubser, Gubser, R.A. (1967) des Ries Riesvon von Nordlingen Nordlingen als R.A. (1 967) Diaplebtische Diaplebtische Gäser Gaser in den Breccien des als Anzeichen für Stosswellenmetamorphose; Contributions to Mineralogy and Mineralogy and fur Stosswellenmetamorphose; Contributions Petrology, 02. Petrology, Volume 15, 15, p.93-i p.93-102. [3] Naldrett, A.J., and and Kullerud, Kullerud, G. G. (1967) A study Mine and its Naldrett, A.J., (1967) A study of the the Strathcona Strathcona Mine its bearing on the Origin of the Nickel-Copper Ores of the Sudbury District, bearing on of the Nickel-Copper Ores of the Sudbury District, Ontario; Journal Journal of Petrology, Petrology, Volume 8, 8, Part Part 3, 3, p.453-531. p.453-531. [4] [4] DressIer B.D., B.D., Peredery Peredery W.V., W.V., Muir Muir T.L. 992)Geology Geology and andMineral Mineral Deposits of the Dressier T.L. (1992) Sudbury Structure, Structure, Ontario Ontario Geological Survey, Survey, Field Guidebook 8. 13 �The Geco Mine, Manitouwadge, Manitouwadge, Ontario: a volcanogenic volcanogenic massive massive suiphide sulphide deposit deposit H.Lockwood H. Lockwood by: I. I . Wolfson Wolfson presented by: Hemlo Gold Mines, Inc. Golden Golden Giant Giant Mine, Mine, Hemlo, Ontario Ontario The Geco Division of Noranda Mining and Exploration Inc. began production in 1957. To date, over 53 million tons of ore grading 1.85% 1.85% copper, 3.78% zinc, 0.30% lead, 1.64 1.64 ounces per ton silver silver and and 0.004 0.004 dollars at 1994 1994prices. prices. The The orebody orebody was was ounces per ton gold have been produced, worth over 5 billion dollars discovered by 3 prospectors prospectors in in 1953. 1953. now consists of of an underground mine with with 125 miles miles of of lateral drives serviced by by two shafts, a Geco now underground mine concentrator concentrator and and supporting supporting plant plant installations. installations.The Themine minecurrently currentlyproduces produces80,000 80,000tons tonsofof ore ore per per month. Most Most ore now comes month. comes from from remnants remnants and pillars using the the Geco Geco Running Running Tight Tight Fill Fill stoping stoping which uses uses immediate rock rock fill to stabilize weak stope walls as ore is removed. 260 people are method, which are employed. Copper and zinc concentrates averaging 29% copper and 55% zinc respectively are shipped by rail to Noranda's smelters smelters in Rouyn Rouyn and and Valleyfield, Valleyfield, Québec. Quebec. The The mine mine will will close closein in late late 1995. 1995. Geco's main ore zone pyrite-pyrrhotite-sphalerite-chalcopyritecore zone consists consists of of aamassive massive coarse-grained coarse-grained pyrite-pyrrhotite-sphalerite-chalcopyrite enveloped by stringer stringer pyrite-pyrrhotite-chalcopyrite pyrite-pyrrhotite-chalcopyrite ore in in aa silicified silicified sericite sericite schist schistunit. unit. The Thestringer stringerore ore margins are defined by assay, currently 2% copper. The main ore zone has a surface strike length of 2,400 feet, an average width of 65 feet, and plunges east at 40 degrees to 3450 feet below surface. The sulphiderich orebody grades laterally laterally into into aa siliceous siliceous magnetite-rich magnetite-rich iron iron formation. formation. Two Two narrow narrow copper copperand andzinczincrich stringer stringer zones(4/2 zones(412 copper and 8/2 812 zinc zone) total 3 million tons of marginal marginal ore ore and are are found found on on the the lower and upper contacts contacts of of the the sericite sericiteschist schist unit unit respectively. respectively. The main ore ore zone zone grades grades laterally laterally eastward eastward into into aasiliceous siliceousbanded bandedquartz-magnetite quartz-magnetite iron iron formation formation zones(Willroy, Willecho which has been followed for 15 15 miles miles with with diamond diamond drilling; drilling; several several other other ore ore zones(Willroy, and Nama Creek) have been located to the west on or near the Geco productive horizons in the 10 by 15 15 mile area of folded supracrustal supracmstalrocks that that comprise comprise the the Manitouwadge Manitouwadge Camp. Camp. The silicified orthoamphibole-biotite-gametorthoamphibole-biotite-gametsilicified sericite sericite schists schists that that host hostGeco's Geco'sore oreare areunderlain underlainbyby cordierite cordierite gneisses, which are interpreted as hydrothermally altered mafic to intermediate volcanics. This group extends several miles laterally, and there does not appear appear to to be be any anyparticular particular alteration alteration pattern pattern within it immediately immediately underlying the Geco ore zone. The deposit is overlain by varying textures of quartzfeldspar-biotite gneisses, gneisses, interpreted interpreted as as volcaniclastic volcaniclasticmetasediments, metasediments,with with intercalated intercalatedvolcanics, volcanics,quartzquartzmagnetite magnetite iron formation(locally formation(local1yzinc-rich) zinc-rich) and and tonalitic tonalitic intrusions. intrusions. 74 �PROPOSEDFIELD FIELD TRIPS TRIPS FOR FOR THE THE PROPOSED 42nd ANNUAL ANNUAL INSTITUTE INSTITUTEON ONLAKE LAKE SUPERIOR SUPERIOR GEOLOGY 42nd LaurelG. G.Woodruff woodruff1, William F. Cannon2 Cannon2 and andGene GeneL. L.LaBerge3 LaBerge3 Laurel 1, William U. S. S. Geological GeologicalSurvey; Survey;1St. 1st.Paul, Paul, MN, MN, 2Reston, *Reston, VA; 3UW WI U. 3UW Oshkosh, Oshkosh, Oshkosh, Oshkosh, WI The 42nd Annual Institute Institute on on Lake Lake Superior Geology Geology will The will be be held in Cable, Wisconsin from from 15 15 May to 19 May, tradition, two two Cable, May, 1996. 1996. In In keeping keeping with tradition, days of of technical technical session session on on May May 16 16 and 17 will days will be be bracketed bracketed by by pre-meeting pre-meeting and post-meetingfield fieldtrips. trips.The Thefield fieldtrips tripswill willcover coveraawide widerange rangeof of interests, interests,from from post-meeting Archean to to the the most mostrecent recentgeological geological the metamorphosed metamorphosed and and deformed deformed Archean the manifestations of the last last glaciation. glaciation. The The field field trips trips will will highlight highlight results results of of manifestations U.S. S.Geological Geological Survey, Survey, the the recentgeologic geologicefforts effortsin innorthern northernWisconsin Wisconsinby bythe theU. recent Wisconsin Geological Geological and staff at at the the active active Wisconsin and Natural History Survey, and the staff Flambeau massive massivesulfide sulfide mine. mine. Six Six possible field trips are currently planned but but Flambeau the final final selection selectionwill will depend depend on onthe the interest interestlevel level for for each each trip. trip. All Allof ofthe thefield field the trips are arewithin within easy easytravel traveldistance distance from from the the Institute Institute headquarters headquarters at atthe the trips TelemarkLodge, Lodge,Cable, Cable,Wisconsin, Wisconsin, allowing allowingmaximum maximumtime timein inthe thefield. field. Telemark Geologyof ofthe theSouth SouthLimb Limbof of the the Midcontinent MidcontinentRift, Rift, North-Central North-CentralWisconsin Wisconsin Geology U.S. S.Geological GeologicalSurvey Survey Bill Cannon, Cannon,Suzanne SuzanneNicholson, Nicholson,Laurel LaurelWoodruff, Woodruff,U. Bill Rocks of the the Midcontinent Midcontinent Rift Rift dated at at 1.1 1.1 Ga Ga cover cover much much of of northern northern Rocks Wisconsin. Geologists Geologistsatatthe theU. U.S. S.Geological Geological Survey have remapped the region region Wisconsin. remapped the as as part partofofthe theMetallogeny Metallogenyofofthe theMidcontinent MidcontinentRift RiftProject, Project, providing providing new new insight into intothe the structure, structure,geochemistry, geochemistry, and stratigraphy stratigraphy of the rift. The The area area of of insight this this field fieldtrip tripnear nearMellen, Mellen,Wisconsin, Wisconsin, provides providesaacomplete completestratigraphic stratigraphiccross cross section section of of the the rift, rift,from frompre-rift pre-riftBessemer Bessemer Quartzite Quartzite through through the thesyn-rift syn-riftFreda Freda Sandstoneand andincludes includesthe theintrusive intrusiveMellen MellenComplex, Complex,which which strongly stronglyinfluenced influenced Sandstone thedevelopment developmentofofthe therift riftininthis thisregion regionas asboth bothaavolcanic volcanicsource sourceand andaathermal thermal the and andstructural structuralhigh. high. From Archean:AA25 25km kmsection sectionof of the thecrust crust Fromthe theMiddle MiddleProterozoic Proterozoictotothe theArchean: Bill Cannon, Cannon,U.S. U.S. Geological Geological Survey Survey Bill AA25-km 25-km thick thick monoclinal monoclinalsuccession succession of vertical to steeply steeply dipping dippingstrata strataisis exposed between between the the shore shore of of Lake Lake Superior Superior and the the Gogebic Gogebic iron range range in in exposed northern northern Wisconsin. Wisconsin. The Themonocline monoclinewas wascreated createdby bycrustal-scale crustal-scale thrusting thrusting shortly shortly after after formation formation of of the theMidcontinent Midcontinent rift. rift. The The trip trip will willtraverse traverse 'downward' 'downward'through throughthe thecrust crustfrom fromthe theFreda FredaSandstone, Sandstone,through throughthe theMiddle Middle ProterozoicKeweenawan KeweenawanSupergroup, Supergroup,Early EarlyProterozoic Proterozoicstrata strataofofthe theGogebic Gogebic Proterozoic Archean volcanic volcanic rocks. rocks. This iron range, range, and andend endininLate LateArchean iron This is is one one of of the the most most complete completesections sectionsof of the the upper upperand andmiddle middlecrust crustexposed exposedon onearth. earth. Geologyand andEnvironmental EnvironmentalImpact Impactofofthe theFlambeau FlambeauMine, Mine,Ladysmith. Ladysmith,WI WI Geology Staff Staff Geologists Geologistsof of the the Flambeau FlambeauMine Mine The The open openpit pitFlambeau Flambeaumine, mine,operated operatedby byFlambeau FlambeauMining MiningCompany, Company,aa whollyowned ownedsubsidiary subsidiaryofofthe theKennecott KennecottCorporation, Corporation,isisdeveloped developedininaazone zoneofof wholly 75 �Late Proterozoic supergene enrichment on an an Early Early Proterozoic Proterozoic volcanogenic volcanogenic massive sulfide deposit. deposit. Copper chalcocite, bornite, Copper is extracted from chalcocite, bornite, and chalcopyrite in the supergene Gold is mined separately separately from an overlying, supergene zone. Gold gold-rich gossan. gold-rich gossan. The The development development of the project project employs employs the latest latest of the environmental controls of massive sulfide exploitation. environmental controls exploitation. The mine is scheduled scheduled to close in in 1997 1997and and the the area area restored restored to to its itspre-mining pre-mining condition. condition. This field trip will include detailed look include a visit to the working face of of the the open open pit pit and and a detailed look at the environmental aspects of of the the mine. mine. environmental aspects and WI WI Early Proterozoic Proterozoic Strata of the Marquette Range Supergroup, Supergroup. MI and Gene John Klasner, Gene LaBerge, University of Wisconsin, Oshkosh, John Western Illinois University, University,and andBill Bill Cannon, Cannon,U.S. U.S. Geological Survey Western Illinois Survey 2compriseaa 2Early Proterozoic Proterozoic strata strata of the Marquette Marquette Range Supergroup Supergroup comprise 3 km-thick sedimentary sequence recording sedimentation successively successively on on a stable craton, passive margin, margin, and and compressional compressional foreland. foreland. Recent detailed mapping has led to to new new insight insight about the depositional environments and postdeformation of Bad River River depositional deformation of the various units, which include the Bad Dolomite, the Palms Formation, the Ironwood Iron-Formation, Iron-Formation, and the Tyler Tyler Dolomite, Formation. As As many many as as three three possible possible trips may be developed from the recent work; examine the eastern part of of the the section section in in Michigan, Michigan, the work; these would examine near the Penokee western part part of of the the section section in in Wisconsin, Wisconsin, and aa cross-section cross-section near the structural structuraldeformation deformation and and stratigraphic stratigraphicrelations. relations. Gap, emphasizing emphasizing the Geology of of Northwestern Northwestern Wisconsin Glacial Geolo~v Adolphus College Mark Johnson, Gustavus Adolphus This field field trip will investigate the margin of This of the Superior Superior lobe lobe of of late late Wisconsinan age in northwestern looking at at landforms (tunnel Wisconsinan age northwestern Wisconsin, Wisconsin, looking (tunnel ice-walled-lakeplains) plains)and and typical typical sediment sediment types types channels, eskers, hummocks, ice-walled-lake Falls till, till, outwash, outwash, and and lake lake sediment). sediment). The trip will (Cooper Falls will also also look look at at the the Spooner eroded hills, built by catastrophic Spooner Hills, a band band of of high-relief, eroded catastrophic releases releases of one stop stop will will be be devoted to highlighting subglacial meltwater. Finally, Finally, one highlighting the the history history of of glacial glaciallakes lakes in inthe theClam-Yellow-River Clam-Yellow-River lowland. lowland. Sulfide Mineralization Mineralization in of the the Midcontinent Rift in Basalts of Cannon and Bill Cannon and Laurel Laurel Woodruff, Woodruff, U. U. S. Geological Survey Preliminary field field studies studies on on the north limb of Preliminary of the Ashland syncline syncline in isc cons in has revealed widespread copper sulfide mineralization in northern Wisconsin basalt basalt quarries quarries of of the theMiddle MiddleProterozoic ProterozoicChengwatana Chengwatana Volcanics. Volcanics. Mineralization has has been been found in numerous quarries Mineralization auarries and and natural natural exposures. exnosures. occurmostly mostlyin inamygdules amygdules and and open open space Chalcopyrite, bornite, and chalcocite occur filling in in altered fragmental basalt flow flow tops, tops, in in much much the the same same manner manner that filling fragmental basalt of the the Keweenaw Keweenaw Peninsula. Peninsula. This field native copper copper occurs occurs in correlative basalts of trip will visit several several exposures exposures displaying displaying various aspects of this little-known type type of mineralization. mineralization. 1 1 . 76 �GEOLOGICAL GEOCHEMISTRY OF OF MASSIVE MASSIVE SULPHIDE SULPHIDE DEDEGEOLOGICAL SETTING AND GEOCHEMISTRY AND ALTERATION ALTERATION ZONES ZONES IN THE THE MANITOUWADGE MANITOUWADGE GREENSTONE GREENSTONE POSITS AND ONTARIO BELT, NORTHWESTERN ONTARIO E. Zaleski, Zaleski, Geological KIA OE8 V.L. Peterson, GeologicalSurvey SurveyofofCanada, Canada, Ottawa, Ottawa, Ontario, K1A 0E8 and V.L. Department of of Geosciences, Geosciences, Western Carolina Carolina University, University, Cullowhee, Cullowhee, North Carolina, Carolina, 28723, 28723, U.S.A. The base-metal belt provide of the base-metal deposits deposits of the the Manitouwadge Manitouwadge greenstone greenstone belt provide a classic classic example example of difficulties encountered of mineralization mineralization in in complex complex metamorphosed metamorphosed and and difficulties encountered in in petrogenetic studies of polydeformed terranes. The Manitouwadge belt is a highly polydeformed Manitouwadge belt highly deformed deformed remnant of of supracrustal supracrustal rocks in in the volcano-plutonic Wawa subprovince, subprovince,immediately immediatelysouth southof ofthe the major major tectonic tectonic boundboundrocks volcano-plutonic Wawa the figure figure in in Peterson Peterson et et al., metasedimentary-migmatitic Quetico Quetico subprovince subprovince (see see the ary with the the metasedimentary-migmatitic this volume). volume). The The map map pattern patternisisdetermined determinedby byregional regionalD3 D3folds, fo ds, including including the the Manitouwadge Manitouwadge synform. Dl synform. D l and and D2 D2 structures structures repeat repeat mineraiized mineralized and and altered altered horizons. horizons. Our Our understanding understanding of of the depositional setting and genetic relationships relationships of of the base-metal deposits, alteration zones and host rocks, depends on unravelling the effects of of ductile ductile deformation deformation and metamorphic recrystallization. The belt belt comprises comprises aamafic-to-felsic mafic-to-felsic volcanic volcanic succession, succession, in which which felsic felsic rocks rocks are are interleaved interleaved with iron previously assumed assumed to iron formation formation and and massive massive sulphide sulphide deposits. deposits. Greywackes, Greywackes, previously t o reflect reflect 25 Ma Ma clastic sedimentation sedimentation (Friesen least 25 a transition from from volcanism volcanism tto o clastic (Friesenetet al., al., 1982), 1982), are are at least younger younger than the the2720 2720 Ma Ma felsic felsic volcanism volcanism and probably probably aa tectonic tectonic enclave enclave of of Quetico Quetico rocks rocks (Za(Zaleski al., 1995). 1995). AAsynvolcanic synvolcanic trondjhemite trondjhemite intrusion intrusion was was aareservoir reservoir for for felsic felsic volcanism volcanism and leski et al., heat source source for hydrothermal activity. All All rocks rocks have have been metamorphosed metamorphosed tto o upper amphibolite amphibolite facies, including including two zones zones of of synvolcanic synvolcanichydrothermal hydrothermal alteration, alteration, now now characterized by by metamorfades, phic phic minerals. minerals. Orthoamphibole+garnet±cordierite Orthoamphibole&garnet±cordieritgneiss gneiss forms a stratabound strataboundsheet sheet of ofregional regional extent, mantling trondjhemite in the stratigraphic mantling synvolcanic synvolcanic trondjhemite stratigraphic footwall footwall (structural (structuralhanging hangingwall) wall) to t o the the mineral mineral deposits. deposits. The Theunit unitisisprimarily primarilydefined definedon onthe thepresence presence of of orthoamphibole-bearing orthoamphibole-bearing assemblages, which are interleaved sillimanite-cordierite-biotite±garnelayers. layers. HornblendeHornblendeassemblages, which interleaved with sillimanite-cordierite-biotite+garnet plagioclase±orthamphibole±cummingtonite±garnet assemblages plagioclase&orthamphibole~cummingtonite~garnet assemblagesbecome becomemore morecommon commonaway away from known mineral deposits deposits and are interpreted as known mineral as less less intensely intensely altered altered mafic mafic rocks. rocks. The Theprecursers precursors to t o alteration, alteration,recognizable recognizable in inless lessaltered alteredenclaves, enclaves,were weremafic maficand andinterlayered interlayeredmafic-felsic mafic-felsicrocks rocks near the transitional sillimanite-muscovite-quartz transitional mafic-felsic mafic-felsic contact. The The second second alteration alteration unit, unit,sillimanite-muscovite-quartz schist, occurs in close proximity proximity to massive suiphide deposits, deposits, mostly mostly in in the stratigraphic massive sulphide stratigraphic hanging hanging wall orebodies including includingthe the largest largest in in the the belt, the wall (structural footwall). footwall). It It also also envelopes envelopes some orebodies Geco main orebody. orebody. The precurser found along-strike Geco main precursor to t o alteration alterationwas wasfelsic felsic volcanic volcanic rock found along-strike and in less altered enclaves. less enclaves. The Geco, massive sulphide suiphide deposits deposits lie lie in in the the northern part Geco, Willroy, Willroy, Nama Creek and Willecho massive part of the the southern limb and synform (see (see the the figure figure in in Peterson Peterson of and hinge hinge region region of the D3 D3 Manitouwadge Manitouwadge synform et al., this this volume). volume). A A Dl D l fault fault divides divides the the area area into into two two tectonic tectonic blocks blocks and repeats part of of the mineralized sequence. sequence. In the Willecho area, original original stratigraphic stratigraphic relationships relationships are further obscured mineralized Willecho area, by D2 folds folds of of the the Dl by D l fault fault and and mineralized mineralized sequence. sequence. The The structural structural complexity complexity can be be partly partly resolved by by examining examining the the characteristics of orebodies and mineralized horizons. Based resolved characteristics of orebodies and mineralized horizons. Based on on CuCuZn-Pb proportions, proportions, nature of and relationships Zn-Pb of mineralization, mineralization, and relationships tto o iron formation formation and alteration zones, orebodies of Manitouwadge camp divided into three main main types. types. Firstly, zones, the the orebodies of the Manitouwadge camp can can be be divided Cu-rich stringer/disseminated orebodies orebodies lie in the the orthoamphibole-garnet-cordierite Cu-rich stringer/disseminated orthoamphibole-garnet-cordieritefootwall footwall and, Secondly, the Geco Geco area, area,surround surroundthe themain mainorebody orebodyininsiffimanite-muscovite-quartz sillimanite-muscovite-quartz schist. schist. Secondly, in the massive and and semi-massive Zn-Cu-(Pb) orebodies orebodiesare are hosted hosted by by iron iron formation formation and enveloped by massive semi-massive Zn-Cu-(Pb) enveloped by siffimanite-muscovite-quartz schist, or or interleaved interleaved with with schist schist and quartz-phyric felsic rocks. rocks. This sillimanite-muscovite-quartz schist, group includes includes the largest orebodies; orebodies; the Geco Geco main main and Willroy Willroy #3 orebodies. orebodies. Thirdly, group the two largest massive and semi-massive Zn-Pb-(Cu)orebodies, orebodies,interpreted interpretedasashighest highestinin the the stratigraphy, are massive and semi-massive Zn-Pb-(Cu) hosted by iron formation sillimanite-muscovite-quartz schist. formation that thatoverlies overlies sillimanite-muscovite-quartz Despite Despite the unusual unusual extent extent and andcorcordance corcordance of ofalteration alterationzones zonesatatManitouwadge, Manitouwadge,geochemgeochemical trends from 'least-altered' ical 'least-altered7 to t o intensely intensely altered, altered, such such as as increase increase in FeO+MgO FeOf+MgOand andA1203, A1203, and depletion and CaO, CaO, are similar recorded in in alteration alteration pipes pipes in in the Abitibi depletion in alkalis alkalis and similar tto o those recorded Abitibi camp (Riverin and and Hodgson, Hodgson, 1980). 1980). All All felsic felsic extrusive extrusive rocks rocks show show evidence evidence of potassic alteration; alteration; whereas, synvolcanic trondjhemite preserved its primary primary sodic sodiccomposition. composition. Similar whereas, synvolcanic trondjhemite apparently preserved observations of of alkali alkali exchange exchangehave havebeen beenmade madeinin the the Abitibi Abitibi camp camp with with respect observations respect to t o the the synvolsynvolcanic canic Flavrian pluton and and its its extrusive extrusive equivalents equivalents (Goldie, (Goldie, 1979). 1979). 'Immobile' 'Immobile' elements in altered altered \ 77 �rocks at Manitouwadge tend to define bimodal populations that mimic element abundances in mafic and felsic precursers. The bimodal distribution shows that orthoamphibole-garnet-cordierite rocks and sillimanitic interlayers had both mafic and felsic protoliths; the metamorphic assemblage was determined by small variations in (FeOt+MgO)/A1203, apparently due to alteration and not inheritance from the protolith. The unusual extent of orthoamphibole-bearing gneiss at Manitouwadge may be partly due to the high metamorphic grade. With increasing grade, orthoamphibole-hornblende stability expands the range of orthoamphibole-bearing assemblages to more calcic bulk-rock compositions (Spear. 1993, pages 478—489). By inference, bulk-rock compositions that produced orthoamphibole-bearing rocks at Manitouwadge might, at lower metamorphic grade, be considered incipient alteration. The closest analogues for the stratabound regional orthoamphibole-bearing alteration are found in the Bergslagen area of the Svecofennian Baltic shield. At Bergslagen, exhalative base-metal deposits and iron formation are underlain by conformable stratabound Mg-rich alteration zones of regional extent (TrAgtrdh, 1988; Itipa, 1988; Baker et al., 1988). Amphibolite-facies metamorphism at Bergslagen may play a role, as at Manitouwadge, in facilitating identification of altered rocks. However, in both areas, it appears that alteration was partly focussed on aquifer horizons possibly consisting of permeable, poorly consolidated volcaniclastic deposits. Baker, J.H., Hellingwerf, R.H. and Oen, 1.5. 1988. Structure, stratigraphy and ore-forming processes in Bergslagen: implications for the development of the Svecofennian of the Baltic Shield. Geologie in Mjinbouw 67, 121—138. Friesen, R.G., Pierce, GA., and Weeks, R.M. 1982. Geology of the Geco base metal deposit. Geological Association of Canada, Special Paper 25, 343—363. Goldie, It. 1979. Consanguineous Archaean intrusive and extrusive rocks, Noranda, Quebec: chemical similarities and differences. Precambrian Research 9, 275—287. Ripa, M. 1988. Geochemistry of wail-rock alteration and of mixed volcanic-exhalative fades at the Proterozoic Stoilberg Fe-Pb-Zn-Mn(-Ag)-deposit, Bergslagen, Sweden. Geologie in Mjinbouw 67, 443—457. Riverin, G. and Hodgson, C.J. 1980. Wall-rock alteration at the Millenbach Cu-Zn mine, Noranda, Quebec. Economic Geology 75, 424—444. Spear, P.S. 1993. Metamorphic Phase Equilibria and Pressure-Temperature-Time Paths. Mineralogical Society of America, Monograph, Washington, D.C., 799 pages. Trägá.rdh, 3. 1988. Cordierite-mica-quartz schists in a Proterozoic volcanic iron ore-bearing. terrain, Riddarhyttan area, Bergslagen, Sweden. Geologie in Mjinbouw 67, 397—409. Zaleski, E. and Peterson, V.L. 1995. Geology of the Manitouwadge greenstone belt overlain on shaded relief of total field magnetics. Geological Survey of Canada, Open File 3034, scale 1:25000. Zaleski, E., Peterson, V.L. and van Breemen, 0. 1995. Geological and age relationships of the margins of the Manitouwadge greenstone belt and the Wawa-Quetico subprovince boundary, northwestern Ontario. Current Research 1995-C, Geological Survey of Canada, 35—44. 2 78 �DERIVATIVECONTINENTAL CONTINENTALINDICATIONS INDICATIONSOF OFAACURVILINEAR CURVILINEARCARIBBEAN CARIBBEANMANTLE MANTLE DERIVATIVE CONVECTION CONVECTIONPLUME PLUME ZBIKOWSKI,Douglas DouglasW., W.,Geological GeologicalSociety Societyof ofMinnesota, Minnesota,7833 7833Able AbleSt StNE, NE,Spring SpringLake LakePark, Park, ZBIKOWSKI, MN MN 55432 55432 Inextricably Inextricablyinterrelated interrelatedto tothe therecurved-bow recurved-bowinterpretation interpretationof ofthe theMRS MRSdevelopment, development,isisintroduced introducedaa second secondhypothesis, hypothesis,proposing proposingthat thatwhen whenthe theIowa Iowabow bowinitially initiallyfractured, fractured,its itscontinental continentalterritory territorywas was positionedover overaadistinctively distinctivelycurvilinear curvilineararray arrayofofrelated relatedmantle mantleconvection convectionupwelling, upwelling,which whichoriginally originally positioned establishedand andcontinues continuesto todefine definethe the perimeter perimetermargins margins of of the the eastern eastern end end of the Caribbean Caribbean plate. The The established ancientformation formationof ofthis thiscurvilinear curvilinearplume's plume'scharacteristic characteristicarc arcshape shapeisisreasoned, reasoned,by byrationale rationaleand and ancient evidence, evidence,to toexhibit exhibitaacoriolis coriolisinfluence, influence, upon upon its its early early convection's convection's melt meltflow. flow. The Theemergent emergentscenario scenarioisisthat thatafter afterthe theIowa Iowabow bowfracturing fracturingofofthis thisfirst firstcontinental continentalsuperposition, superposition,the the plumeremained remainedstationary stationarywhile whilethe thecontinent continentwas wasmoved movedabout about160 160km, km,possibly possiblyby bythe thecollision collisionofofthe the plume GrenvilleProvince. Province.Subsequently, Subsequently,the themovement movementsubsided subsidedand andaasecond secondrift riftsystem systemdeveloped, developed,which whichisis Grenville indicated indicatedtoday todayby bythe theclear cleardelineation delineationofofthe thesame sameplume plumeprofile profileby byderivative derivativeaeromagnetic aeromagneticeffects effectsfrom from the theattendant attendantsurface surfacerifting; rifting;and andby byaasecond secondrecurved recurvedbow bowininsouthern southernMichigan, Michigan,which whichisissymmetrically symmetrically coincident 90 degree degree alignment alignment to to the Iowa Iowa coincidentto tothe therift riftpattern, pattern,and andexhibits exhibitsboth both aastressfully stressfullysignificant significant90 bow, bow,and andisisconcordant concordantwith withititinincurvature curvaturephase phasewith withrespect respecttotothe theinterior interiorside sideofofthe thesame samerift riftpattern. pattern. This Thisunique uniqueorientation orientationisisan anextremely extremelysignificant significantevidential evidentialcorrelation correlationbetween betweenthe therecurved-bow recurved-bow hypothesisand andthe theCaribbean Caribbeanconvection convectionplume plumehypothesis, hypothesis,asasititlends lendsvalidity validitytotoboth boththe theproposed proposed hypothesis mechanisms mechanismsby bygraphically graphicallyillustrating illustratingthe theinterrelationship interrelationshipbetween between the the two two developments. developments. Also, Also, supporting supportingconsistent consistentpattern patterncorrespondence, correspondence,the thepaleogeographic paleogeographicposition positionofofthe thelength lengthaxis axisofofthe theIowa Iowa bow, bow,paleomagnetically paleomagneticallymatches matchesthe theCaribbean Caribbeanplate's plate'snorthern northernmargin. margin. Could Couldaacurvilinear curvilinearmantle mantleconvection convectionplume, plume,positioned positionedunder underthe theCaribbean Caribbeanplate, plate,have havecreated createdthese these continental continentaland andoceanic oceaniccrustal crustalpattern patternreplications? replications?ItItisissuggested suggestedthat, that,asasaacomposition compositionimplies impliesaa history, history,the thecoincidence coincidenceof ofthree threephysical physicalmatchings matchings of of derivative derivativeeffects effects in in accessible accessible proximity, proximity, begs begs for for thoughtful consideration of a common causal source. thoughtful consideration of a common causal source. 79 �CONTINENTAL CRUST FRACTURE INITIATION PATTERN AND A CONTINENTAL AND HYPOTHETICAL HYPOTHETICAL MECHANISM MECHANISM Douglas W., Geological Geological Society Society of of Minnesota, Minnesota, 7833 7833 Able Able.St Spring Lake Lake Park, Park, ZBIKOWSKI, Douglas St NE, Spring MN MN 55432 55432 A A careful careful observation observation of of the the North North American American Midcontinent MidcontinentRift Rift System System (MRS) (MRS) as as detailed detailed on on aa Bouguer Bouguer gravity map map filtered filteredto to exclude excludefeatures featureswith withwavelengths wavelengthsgreater greaterthan than 250 250 km, km, reveals reveals aa distinctive distinctive gravity symmetry and and geometric geometric regularity regularity between southern Minnesota and southeastern Nebraska. The symmetry Nebraska. The SE,and andaa symmetry expressed expressedisis reflected reflectedrelative relativeto to both both aaprimary primaryaxis axisoriented orientedfrom fromthe the NW NW to tothe theSE, symmetry secondary axis axis oriented oriented orthogonally. orthogonally. The Theaxes axesof ofsymmetry symmetryon on the the map's map's surface, surface, are are interpreted interpreted to to secondary represent the the intersections intersectionsof of two two orthogonal orthogonalradial radialplanes planes of of reflection reflectionwith with the the spherical sphericalcrustal crustalsurface. surface. represent The observed observed symmetrical symmetricalpattern patternof of rift rift curvature curvaturesuggests suggestsaa causal causalrelational relationalinfluence influencesuperimposed superimposed The fracture formation formationprocess processby by some somecompelling compellingfeatures featuresor or events eventslocated locatednearby, nearby,and andwithin within upon the fracture these two two radial radial planes planes of of reflection. reflection.This Thisisisbecause, because,mechanistically, mechanistically,simple simplenatural naturalsymmetry symmetryisisthe the these physicalmanifestation manifestationof ofspatial spatialpattern patternthat thatreflects reflectsan aninvariance invarianceofofdistance distancedependent dependentcausal causal physical relationship. relationship. It is is hypothesized hypothesizedthat that the the crust crustfracture fracturecurvature curvatureisisthe the product product of ofaa curvilinear curvilineararray arrayof ofrelated relatedmantle mantle It convection upwelling upwelling aligned alignedunder under the the secondary secondaryaxis, axis, that that produces producestension tension and and other otherconvection convection convection related stresses stressesin in the the crust. crust.The Thesymmetrical symmetricalcurvature curvatureproduced producedby bythe theinitial initialpropagation propagationof ofcrustal crustal related This figure figure isis aa fracture under under these stresses, stresses, exhibits exhibits a profile very similar to an archer's recurved bow. This fracture surface surface expression expression of of an an extensional extensionalcrust crustfracture fractureregime, regime, and and delineates delineatesan an initial initialpenetrating penetratingnormal normal fault which which later later bounded bounded an an upwelling upwelling decompression melt. ItIt isisfurther furtherproposed proposed that that the the entire entire rift rift fault fracture started startedwith with this this figure, figure,that thatthe thecurvature curvatureresults resultsfrom froman anelastic elasticstrain strainrelease releaseof ofregional regionalcrustal crustal fracture material materialduring duringits itsfracture, fracture,and andthat thatsimilar similarsignature signatureprofiles profileshave havepast pastrecorded recordedoccurrences occurrencesworldwide. worldwide. A tensive, tensive,adjunctive adjunctiveemergence emergenceof ofaatriple triplejunction junctionof offracture fractureisisoffered offeredtotosupplant supplantits itspreviously previously A imagined imagined role role in in the the rift's rift's creation creation and and growth. growth. The Thesignature signaturebow bow fracture fracturehypothesis hypothesis isis further further supportedby by evidence evidenceof of the the regular regularappearance appearanceof of several severalcollateral collateralfeatures featureswhich whichare arelogically logicallyrelated related supported to the the bow's bow's development developmentand and have have been been noted noted at at other other suspected bow fracture locations. Thus, Thus,from fromthe the to creative application applicationof ofpattern patternrecognition recognitionwith with aamechanistic mechanisticunderstanding understandingof ofsimple simplenatural naturalsymmetry, symmetry, creative andgiving givingconsideration considerationtotogeometric geometricmaterial materialstress stressprojection, projection,aahypothetical hypotheticalfracture fracturedevelopment developmentisis and presented. presented. 80 � https://digitalcollections.lakeheadu.ca/files/original/81d7f8c9cd4ef4122e13d1b6328bd71c.pdf 0ffa2b160f299d59ab6be01138109912 PDF Text Text o f the Midcontinent Rift Rift Alkalic Rocks of Institute Instituteon onLake LakeSuperior SuperiorGeology Geology 41st 1995 41st Annual AnnualMeeting, Meeting,May May13-18, 13-18,1995 Marathon, Marathon, Ontario Ontario Proceedings Part 2a 2a Proceedings Volume Volume 41: Part Field Field Trip TripGuidebook Guidebook 4JStJISC l_ Ii /—% — / 4I / I �Alkalic Rocks of the Midcontinent Rift by Ronald P. Sage' Sage1and andDavid. David.H. H. Watkinson2 Watkinson2 'Mineral 'MineralDeposits Deposits and and Field Field Services Services Section Section Ontario Geological Ontario Geological Survey Ministry of Northern Northern Development and Mines 8th Floor, Floor, 933 933 Ramsey Lake Road Sudhury, ON ON P3E 6B5 Sudbury, 6B5 2Department of of Earth Earth Sciences 'Department Carleton University Carleton University Ottawa, ON K1S 5B6 Frontispiece: Orbicular Orbicular jolite ijolitefrom the the Prairie PrairieLake Lake carbonatite, carbonatite, the the world's world's only only known occurrence of this texture occurrence texture in in aa rock rock of of this this composition composition (photograph (photograph courtesy of John Scott) Scott) �CHAIRMAN'S NOTE: Due to sudden illness, co-author co-author and and field trip trip co-leader co-leaderDr. Dr. David David Watkinson Watkinson could could not not take take part ininthese thesefield trips tripsthat thatfeature featurethe thealkalic alkalicrocks rocksassociated associatedwith withthe theMidcontinent Midcontinentr?ft rift in inthe the part vicinity Dr.Watkinson Watkinson's vicinity of of Marathon. Marathon. Dr. 's continuing research research into the petrology petrology and metallogeny of twenty-fiveyears. years. He He has expressed his his regrets regrets about not being able to these rocks dates back twenty-five G.. I.L.S.G.. attend but has has wished wished all all meeting meeting and and trip tripparticipants participants the thebest bestof ofluck luck during during the the 41st 41stIL.S. I'm that you will will join me in extending our best wishes for to I'm sure that join me for a speedy and complete recovery to Dr. Watkinson. Watkinson. In the absence of Dr. Watkinson, ClffShaw Watkinson, Dr. Cliff Shaw(Post-Doctorate (Post-DoctorateFellow, Fellow,University Universityof of Western Western field trips trips with with Dr. Dr. Ron RonSage. Sage. Dr. Shaw has just just Ontario) has graciously offered offered to co-lead thesefield completed his Ph.D. thesis on the gabbros of complex and and has has taken part part in the of the Coldwell complex recent 1:20 definitely be be an asset 1:20 000 000 scale scale mapping mapping project project of of the the complex. complex. This Thisknowledge knowledge will definitely during these trips. trips. On Onbehalf behalfofofthe theIL.SG. I.LSG.organizing organizingcommittee, committee,IIwould wouldlike like to toexpress express my my for stepping in on such such short short notice notice and and wish wishall allofyou ofyou aa great greatfield field trip! trip! gratitude to to Dr. Shaw Shaw for Mark Smyk Chairman, 41st Chairman, 41stI.L.S. I. L.S.G. G. April 23, 1995 �2 ACKNOWLEDGEMENTS ACKNOWLEDGEMENTS The The authors authors were were helped helped in in preparation preparation of of trails trails and and sites sites by by Mr. Mr. Duncan Duncan Michano Michano of of Heron Heron Bay, Bay, Ontario. Ontario. Permission Permission to to examine examine outcrops outcrops of of the the Dead Dead Horse Horse Creek Creek Diatreme Diatreme was was granted granted by by Mr. Mr. John John Ternowesky, Ternowesky, Prospector, Prospector, Thunder Thunder Bay, Bay, Ontario. ~ntario.Mr. Mr. J. J. McGoran, McGoran, President, President, Fleck Fleck Resources Resources Ltd., Ltd., Vancouver, Vancouver, agreed agreed to to display display diamond diamond drill drill core core and and samples samples from Coldwell from the the Two Two Duck Duck Lake Lake intrusion intrusion within within the the Port Port Coidwell Complex. Complex. The The Ontario Ontario Geological Geological Survey Survey donated donated copies copies of of Geological ~eological Studies 27, 45 and 46 and Geological Report 264 to the the Studies 27, 45 and 46 and Geological Report 264 to Institute Institute of of Lake Lake Superior Superior Geology Geology in in support support of of the the alkalic alkalic rock These reports reports provide provide the the background background data data rock field field trip. trip. These and and more more detailed detailed maps maps for for the the Slate Slate Islands, Islands, Killala Killala Lake Lake Complex, Complex, Prairie Prairie Lake Lake Carbonatite Carbonatite and and Diatreme Diatreme structures structures found in the region. found in the region. �3 ALKALIC ROCKS OF THE MIDCONTINENT RIFT Introduction Introduction intrusions occur in an area that extends extends from Alkalic rock intrusions the north shore of Lake Superior in a north to east of north km. The The diatreme structures direction for approximately 140 km. Slate Islands(Sage, Islands(Sage, 1991) 1991) and and the the carbonatite carbonatite found on the Slate dikes with associated associated fenite fenite in in the the Geraldton Geraldton area(Sage, area(Sage, excluded from from the the present tour tour due due to to 1985) will be excluded access(Slate Islands) or distance(Chipman distance(Chipman difficulty of access(S1ate Lake)(Figure examine the the Lake) (Figure 1). 1). An An attempt attempt will will be be made made to examine types in in the the alkalic rock, carbonatite and major rocks types diatreme structures near Marathon, Marathon, ~ntario. Ontario. By necessity the visits to individual individual outcrops will be brief. Whenever Whenever possible, economic aspects aspects of the the alkalic alkalic rocks rocks will will be be emphasized. Some optional optional stops stops are included included in in the the guidebook for those who wish wish to to spend spend additional additional time on their own in the area examining exposures exposures which which time time does does not permit this this tour tour to to visit. visit. Regional Reuional setting settinq The Midcontinent Rift is is represented by aa horseshoe horseshoe shaped shaped gravity and aeromagnetic aeromagnetic anomaly open to to the the south south that that is is exposed in the region(Figure 2) the Lake Superior Superior region(Figure 2) and and lies lies east east of the Kapuskasing Structural Zone(KSZ) Zone(KSZ) and and northwest northwest of of the the (Figure 3). western Grenville Front Front Tectonic Tectonic Zone(GFTZ) Zone(GFTZ)(Figure 3). The western this gravity and aeromagnetic anomaly strikes limb of this strikes southwest southwest into Kansas and it it has been postulated postulated by by Adams Adams and Keller(1994) to to extend as far far south south as as west west Texas Texas and and eastern New Mexico. Mexico. The eastern arm of the the Midcontinent Midcontinent Rift Rift strikes strikes southeast southeast into into southern southern Michigan and and has has been been extended into Ohio and Kentucky by Dickas et al.(1992). al.(1992). The The Dickas et rift has been interpreted interpreted to to be a triple triple junction junction formed formed by by a rising and Dewey(1973); however, rising mantle mantle pluine(Burke plume(Burke and however, junction has has not not Green(1983) concluded concluded that a triple junction the usual sense sense due to the the U-shape of of the the rift developed in the and the abrupt abrupt termination termination of activity along along it. it. The The model model of decompression decompression melting over an upwelling upwelling mantle mantle plume plume in in an extensional extensional lithosphere lithosphere environment is is the the favored favored model model at present(Nicho1son present(Nicholson and and Shirley, Shirley, 1990; 1990; Hutchinson Hutchinson et et al. al. 1990). Nicholson Nicholson and Shirley(1990) indicated 1990). indicated that large large volumes of magma of dominantly tholeiitic tholeiitic composition composition extruded over a short short period is is consistent consistent with with the the mantle mantle model. Tre'hu plume model. Trethu et al.(1991) al.(1991) stated stated that that the the Midcontinent Rift resembles resembles a passive continental continental margin models of which is in marked contrast to to many models of active active and and extinct Phanerozoic rift zones. zones. Behrendt et al. (1988) (1988) have also noted that the Midcontinent Rift is different different from �4 :•::: 5O•OO. .. . . . . ...'. ..•. I komes al 4 a - B/ I I' LAKE SUPER/Cl? N Granitic rocks Supracrustil rocks Aikalic rock and carbonatite intrusions Major Major carbonatite—alkalic carbonatite-alkalic Intrusions Intrusions and and major major regional regionalfaufts fault8 48) 30) 30) Chlpman ChipmanLake Lakefenitea fenites 48) McKeflar McKeflarCreek Creekdiatreme diatrerne 49) 49) Gold GoldRange Rangediatreme diatreme dikes and carbonatite dikes diatreme 31) KIllala Klllala Lake Lake aliaflc a l k a kcomplex comdex 50) 50)Neys Neys diatrenr 31) 32) 32) Prairie PrairieLake Lakecarbonatite carbonattte 33) 33) Port PortCoidwelt ColdwellaNaNc alkaRccomplex complex A) 36) Slate SlateIslands Islandsdiatremes diatremes A) Michipicoten MichipicotenIsland Islandfault fault 30) B) and carbonattte carbonatit. dik. dike B) Big BigBay Bay- -Ashburton AshburtonBay Bay fault 47) Dead DeadHbrse HbraeCreek Creek dlatrem. diatreme fault and and Its its extrapolated extrapolated 47) northern northern extension extension Figure 1: 1: Index map showing showing the the location location of features features Figure associated associated with with Keweenawan Keweenawan alkaline alkalineinagmatism(from mag-matism(from Sage, Sage, 1986). 1986). �5 ID 92 56• / 88 / 84 so. 4UOSON a4Y / 52• i. ac ONTARIO 041(07.4 I MINNso - WISCONSIN 38 KIL.OMTERS a Figure2: 2: Index Indexmap mapshowing showinggeneral generallocation locationof ofthe the Figure includes Rift System (Shaded Area). Shaded area Midcontinent Rift System (Shaded Area). Shaded area includes Midcontinent high associated with the rift that that part of the gravity high associated with the rift that that part of the gravity the portion extending into is greater than -20 milligals; the portion extending into is greater than -20 milligals; Kansasisisdrawn drawnalong alongthe the-40 -40 milligal milligalcontour. contour. The Thegravity gravity Kansas defines location of dense high roughly, but not uniquely, defines location of dense high roughly, but not uniquely, Midcontinent Rift System. The rift crust associated with the Midcontinent Rift System. The rift crust associated with the although the gravity high is extends beneath Lake superior, although the gravity high is extends beneath Lake Superior, because of structural not continuous in this area because of structural not continuous in this area complexities.Modified Modifiedfrom fromKiasner Klasneretet al. al. (1982). complexities. (1982). �C' :: i.. II rP I• m H o i-i. •— • . mil WU)O 03 II Crap' H'< U. pa i-.. o tn '0 I-I. 0 40 Pa 03 rI —. r1 I-• l.a- I-m n ilH mm 0 Pa —. Jil pam Pa (DH II H U) P1 - ilL.3 Oil Oil t:-rtø Pfl) '11 Figure 3: Index map showing relationship of major regional structural features to the Midcontinent Rift System(Modified from Lumberst 1978; Brummert 1978; from Sage, 1986). �7 Phanerozoic rifts rifts in in that that it it has has aa crustal crustal thickness thickness equal equal Phanerozojc to or or greater greater than than the the surrounding surrounding unextended unextended terrane. terrane. to high-velocity lower lower crustal crustal layer layer is is thickest thickest beneath beneath the the AA high-velocity rift graben graben under under Lake Lake Superior Superior and and is is interpreted interpreted to to be be rift magmatic material material underplated underplated during during rifting(Behrendt rifting(Behrendt et et magmatic et al., al., 1991; 1991; Shay Shay and and Tre'hu, Trerhu,1993). 1993). al., 1990; 1990; Tre'hu Trefhu et al., Gravity modeling modeling requires requires large large buried buried masses masses of of mafic mafic Gravity igneous rocks rocks of of assumed assumed Keweenawan Keweenawan age age beneath beneath the the igneous Midcontinent Rift Rift whose whose distribution distribution is is asymmetric(Mariano asynunetric(Marian0 Midcontinent and Hinze, Hinzer 1994b; 1994b; Thomas Thomas and and Teskey(l994). Teskey(l994)- This This asymmetry asymmetry and implies that that the the northern northern margin margin of of the the rift rift is is dominated dominated by by implies plutonic rocks rocks and and the the southern southern margin margin by by volcanic volcanic plutonic rocks(Thomas Complex rocks (Thomas and and Teskey, Teskey, 1994)1994). The The Port Port Coldwell Coidwell Complex and Duluth Complex are manifestations of the dominant and Duluth Complex are manifestations of the dominant plutonic northern northern margin. margin. Allen Allen et et al. al. (1992) (1992) suggested suggested that that plutonic a topographic dome centered on Lake Superior represents the a topographic dome centered on Lake Superior represents the effect of the mantle plume active in the Keweenawan time of effect of the mantle plume active in the Keweenawan time of rifting which is now maintained isostatically by changes to rifting which is now maintained isostatically by changes to These changes changes consist consist of of magmatic magmatic the lithosphere. lithosphere. These the underplating and depletion of the upper mantle. Paces and and underplating and depletion of the upper mantle. Paces Miller(1993) compiled existing U-Pb geochronological and Miller(1993) compiled existing U-Pb geochronological and paleomagnetic data data for for volcanic volcanic and and intrusive intrusive rocks rocks within within paleomagnetic the Lake superior Basin. A simplified version of their data the Lake Superior Basin. A simplified version of their data is given in Table 1 which demonstrates that the Duluth is given in Table 1 which demonstrates that the Duluth U-Pb isotopic isotopic Complex and and Port Port Coldwell Coldwell Complex Complex have have similar similar U-Pb Complex ages and were emplaced just before and after a paleomagnetic ages and were emplaced just before and after a paleomagnetic reversal; from from reverse reverse polarity(Port polarity(P0rt Coidwell) Coldwell) to to normal normal reversal; polarity(Du1uth Complex). Samson and West(l994) reported polarity(Duluth Complex). Samson and West(1994) reported that this this reversal reversal occurred occurred at at approximately approximately 1097 1097 Ma. Ma. During During that this polar reversal the composition of the volcanic rocks this polar reversal the composition of the volcanic rocks changes from from those those displaying displaying crustal crustal contamination(Osler contamination(Os1er changes series) to those displaying typically uncontaminated series) to those displaying typically uncontaminated asthenospheric mantle—derived mantle-derivedmelts melts(Mamainse asthenospheric (Mamainse Point)(Lightfoot et al. 1994). series evolved evolved Point) (Lightfoot et al. 1994). Both Both volcanic volcanic series from high-Mg primitive basal members to those of tholeiitic from high-Mg primitive basal members to those of tholeiitic composition; the the earlier earlier flows(Osler flows(Os1er series) series) may may represent represent composition; series(Mamainse Point; deeper partial melts than the later deeper partial melts than the later series(Mamainse Point; Lightfoot et a1.(1994). Lightfoot et al.(1994). TABLE 11 TABLE (Simplified from Paces and and Miller, Miller, 1993) 1993) (Simplified from Paces Rock Unit Unit Rock Polarity Polarity Unnamed Unnamed Copper City City Flow Flow Copper Greenstone flow flow Greenstone Lake Shore Shore Trap Trap Lake Nathanfs Layered Layered Nathan's Series Series Complex Duluth Duluth Complex Bay Complex Complex Beaver Bay Beaver RR NN Age(Ma) (Ma) Age ++++++— ++— ++- Reference Reference NN NN RR 1097.5 1097.5 1096.2 1096.2 1094.0 l094.0 1087.2 1087.2 1106.9 1106.9 33 1.8 1.8 1.5 1.5 1.6 1.6 0.6 0.6 11 22 22 22 33 NN NN 1099.0 ++- 0.5 0.5 1099.0 +1096.0 1096.0 +- 11 33 33 �8 Logan Sills Sills Osler Porphyry Porphyry Agate point Rhyolite Rhyolite Port Coidwell Coldwell Complex Michipicoten Island Michipicoten Island Formation Formation R R R R +4 —2 -2 1108.8 +4 1107.5 1107.5 +4 +4 -2 -2 1097.6 1097-6 ++- 3.7 3-7 1108 ++- 11 1108 4 4 4 5 N 1086-5 +13 —3.0 -3.0 1086.5 6 S c h u s et al.(1990); ale(1990); 2) 2) Davis Davis and and Paces(1990); Paces (1990);3) 3) 1) Van Schmus Paces and Miller(1993); Miller(l993); 4) 4) Davis Davis and and Sutcliffe(1985); Sutcliffe(l985); 5) 5) Paces Heaman and Machado(1992); Machado(l992); 6) 6) Palmer Palmerand andDavis Davis(l986) Heaman and (1986) In the Lake Lake Superior Superior region separation separation along the the rift axis axis was on the the order of 50 to 60 60 kn(K1asner ale 1982; km(Klasner et al. the resulting resulting Chandler, 1983; Shay and Trerhu, Tre'hu, 1993) and the graben filled with 30 to 32 km of volcanic and sedimentary sedimentary graben rocks(Trerhu et al., al., 1991; Behrendt et al., al., 1988; Cannon Cannon et et rocks(Tre'hu 1989). Gravity Gravity modeling modeling is is consistent consistent with with the the Keweenaw, Keweenaw, al. 1989). Isle Royal, Thiel(Big Bay-Ashburton Bay), Bay), Douglas and Michipicoten l?aults being growth faults faults controlling controlling Michipicoten Island Faults rift development(Thoiuas development(Thomas and Teskey, 1994)(Figure rift Teskey, 1994) (Figure 4). 4). Cannon Cannon al.(l989) interpreted regional seismic seismic data to to suggest suggest et al.(1989) Superior changes changes that the central graben beneath Lake Superior attitude along strike strike and thus the the rift is segmented attitude segmented and requires requires accommodation zones zones between the segments. segments- Sexton Sexton Henson(l994), using using an an interpretation interpretation of of seismic seismic data, data, and Henson(1994), the modeling of accommodation zones and suggested suggested questioned the accommodation zones closer inspection inspection zones zones of accomodation that upon closer accommodation may not required to to account account for for changing changing attitudes attitudes along along strike. strike. be required data, the depth depth to the Moho Moho beneath western From seismic datat Lake Superior Superior is is 37-46 km, central Lake Superior Superior Superior 42-49 approximately 55 km and in eastern Lake Superior kin(Behrendt et al. al. (1988). Trerhu Tre'hu et km(Behrendt et et al. al. (1991) (1991) and Shay and Tre'hu(1993) Trefhu(1993) used seismic data to to interpret interpret the crustal thickness thickness beneath the Midcontinent Rift as diminishing diminishing rapidly to the the south from 55 to to 60 60 km at the centre of the the rift to 35 km and gradually gradually to to the the north north to to 40 40 km. km. Bisecting the the gravity anomaly of the horseshoe-shaped Midcontinent Rift is the Trans-Superior Tectonic Zone Zone that contains the Thiel or Big Bay-Ashburton Bay-Ashburton Bay Bay Fault(Sage, Fault(Sage, 1978, (Figures 3, 1978, Kiasner Klasner et et al., al., 1982) 1982)(Figures 3 t 5, 6, and 7). This This zone of deformation is represented by by changes in isomagnetic isomagnetic and isomilligal contouring of aeromagnetic and gravity data(Figures 6 6 and 7) 7) and is also represented as a topographic topographic high on lake lake bottom contours(Hough, 1958, Wold (Figure 8). 8). The The Slate Slate Island Island Diatremes Diatremes and and the the et al. 1982) 1982)(Figure Port Coldwell Complex occur where this zone impacts impacts on the the north shore shore of Lake Superior and is is proximal to the Proterozoic—Archean contact. contact. Extrapolating faults related to Proterozoic-Archean this zone to the region of Chipman Lake(Sage, Lake(Sage, 1985), 19851, a distance of approximately 140 km, reveals a change distance 140 reveals change in the �_____ ______ I. ca, II Go Kopka cone sheets 2. i o , 11 Go Beordmwe cone sheets 3 ca, II Ga Fox Mountain dike 4. co, I1 Go Pigeon River dike swarm 5. co, II Ga hkoskwo 6 1.54 Ga 7. co, 2.lGo Paleozoic Paleozoic Illinois and Illinois ond Michigan Michigan basins basins dike sworm Mesoproterozoic Midcontinent Rift Midcontinent Rift a English Bay Gronile Clastic Clostic sedimentary sedlmentory rocks rocks Kenoro-Fort Frances (Kubetogoma) dike sworm 0 j Volcanic Volcan~crocks rocks(1.11-109 (1.11-109Go) 601 [ Intrusive rocks ricks (1.11-109 (1.11- 1.09Ga) GO) Anorogenic/Post - orogenic suites Anorogenlc/Post-orogenic suites Sibley Group-sandstone, Sibley Group - sondslane, carbonate carbonate >1.54 > l , 5 4 Ga Ga FTTg Granilold rocks Granitold rocks (148-177 (140- I 7 7Ga) Gal 2 Paleoproterozolc I%leoproterozolc Ponokean Penokeon Orogen Orogen and Related Related Rocks Rocks 1111111G~anitold Gionitoldond and volcanic volcanic arc orc rocks racks LLIJILJ(189-184 (18 9 - 184 Gal GO) u.ull nimikie Group Animlk~e Groupand andMarquette MarquetteRange Ronge Siipergroup St~pergroup(Ca. (ca 2.1-1.85 2 I- 185 Ga) Go) Archean Archeon 0 '.' - ** International boundary bcundory tic complexes Selected alka olkol~c complexes (see Sage, Soge, this this volume volume for more more detail) deta~l) Dikes lll1~\1'[ D~kes I , ' Faults Faulfs 'P geological features found in the the 4: Proterozoic geological 4: Major Proterozoic Lake ~ a k esuperior superior region(from region (from Sutcliffe, ~utclif%e,1991). 1991) Figure . faults Thrust foults �10 0 0 Figure 5: 50 50 * 100 100 , 2P 200 3 W KILOMETERS 300 KILOMETERS Diagram indicating the amount of separation that Figure 5: occurred Diagram indicating the amount separation that may have during development ofof the Midcontinent may have occurred during development of the Midcontinent Tectonic Zone Rift System, location of the Trans-Superior Rift System, location of alkaline the Trans—Superior Tectonic Zone and the position of two features associated with and position of two alkaline featureset associated with the the tectonic zone(modified from Klasner al., 1982). the tectonic zone(modjfjed from Kiasner et al., 1982). Figure 6: Regional Bouguer gravity anomaly map over Lake Figure 6: with Regional Bouguer gravityTectonic anomaly Zone map over Lakesites Superior the Trans-Superior and two Superior with the Trans-Superior Tectonic Zone andHinze two sites of alkaline magmatism superimposed(modified from et of alkaline al., 1982). magmatism superimposed(modifjed from Hinze et al., 1982). �1966). al., et Hinze from superimposed(modified maginatism alkaline of sites two and Zone Tectonic Trans—Superior the with region Superior Lake of map intensity magnetic Total 7: Figure &— 5#_. — - — — ----. — - ,..l.,..k o ., .. t— ...,.., WNIS ,.n. so F00 no 500 - XA( COt-DWELL PORT MAP CONTOUR INTENSITY MAGNET/C TOTAL �12 SLATE ISLANDS \ I Figure Contour map map of of lake lake bottom bottom topography topography of of Lake Lake Figure 8: 8: Contour Superior(From Hough, 1958; Wold et al., 1982). Superior(From Hough, 1958; Wold et al., 1982). �13 scale activity. The scale of of alkalic alkalic inagmatic magmatic activity. The Port Port Coidwell Coldwell superimposed ring ring complexes complexes exposed exposed complex consists consists of of 33 superimposed complex along along the the shore shore of of Lake Lake Superior; Superior; the the smaller smaller Killala Killala Lake Lake Complex, Complex, 40 40 km km north north of of the the lake, lake, consists consists of of aa single single ring ring km complex. The The much much smaller smaller Prairie Prairie Lake Lake Carbonatite Carbonatite is is 30 30 km complex. north of of the the lake lake and and the the Chipman Chipman Lake Lake alkalic alkalic units, units, at north at aa distance km, consist consist of of carbonatite carbonatite dikes dikes and and fenite. fenite. distance of of 140 140 km, What structural structural or or tectonic tectonic significance significance this this change change from from What alkalic rock rock to to carbonatite carbonatite magmatism, magmatism, and alkalic and presumably presumably much much lower lower degrees degrees of of partial partial melting melting at at greater greater depths, depths, may aay have have is is unclear. unclear. Interpretation Interpretation of of the the aeromagnetic aeromagnetic data data in in eastern eastern Lake Lake Superior Superior by by Hinze Hinze et et al.(1966) al.(1966) indicates indicates that that the the Thiel Thiel or or Big Big Bay-Ashburton Bay-Ashburton Bay Bay fault fault offsets offsets the the Michipicoten Michipicoten Island Island fault fault left-laterally left-laterallyfor forapproximately approximately5.0 5.0miles(8.O miles(8.0kin). km). This This left-lateral left-lateral offset offset has has been been recognized recognized along along the the northern northern extension extension of of this this structure structure in in the the Chipman chipman Lake Lake area area where where offset offset of of approximately approximately 0.8 0.8 km km has has been been mapped(Sage, mapped(Sage, 1985). 1985). The The age age relationships relationships between between the the younger younger Thiel Thiel or or Big Big Bay-Ashburton Bay-Ashburton Bay Bay fault fault and and the the older older Michipicoten Michipicoten Island Island fault fault are are consistent consistent with with recent recent structural structural interpretations interpretations using using seismic seismic data(Mariano data(Mariano and and Hinze, Hinze, 1994). 1994) . Linear Linear trends trends in in the the topography topography approximately approximately 1.5 1.5 km km southeast southeast and and southwest southwest of of the the Slate Slate Islands Islands estimated estimated to to be be approaching approaching 240 240 metres metres in in depth, depth, are are consistent consistent with with the the fault fault trends trends established established by by Hinze Hinze et et al.(1966) al.(1966) and and Sage(1991). Sage(1991). These These trends trends likely likely represent represent subsidiary subsidiary faulting faulting related related to to the the two two regional regional fault fault trends. trends. The The Michipicoten Michipicoten Island Island fault fault follows follows the the margin margin of of the the Lake Lake Superior Superior Basin Basin and and is is likely likely to to have have been been active active during during basin basin formation. formation. The The water-filled-linear water-filled-linear southeast southeast of of the the Slate Coldwell Slate Islands Islands can can be be extrapolated extrapolated to to the the Port Port Coldwell Complex Complex where where it it joins joins with with the theLittle LittlePlc PicRiver Riverlineament, lineament, aa zone zone of of possible possible faulting. faulting. This This linear linear feature feature is is therefore therefore likely likely to to be be related related to to the the Thiel Thiel or or Big Big Bay— BayAshburton Ashburton Bay Bay fault faultsystem systemwhich whichcuts cutsthe thePort PortColdwe].l Coldwell Complex, Complex, dated dated by by U-Pb U-Pb techniques techniques as as 1108 1108 ++- 11 Ma(Heaman Ma(Heaman and and Machado, Machado, 1992). 1992). Some Some movement movement along along the the Thiel Thiel or or Big Big Bay— BayAshburton Ashburton Bay Bay fault fault thus thus postdates postdates the the emplacement emplacement of of the the Port Port Coidwell Coldwell Complex Complex and and likely likely represents represents reactivation reactivation of of earlier earlier regional regional structural structuralpatterns. patterns. Soon Soon after after extension extension and and rifting, rifting,between between1109 1109and and 1094, 1094, closing closing of of the the rift rift began(Cannon, began(Cannon, 1994). 1994). The The southwest— southwesttrending trending arm arm of of the the Midcontinent Midcontinent Rift Rift closed closed by by an an estimated estimated 30 the central central portion of the the graben graben was was inverted inverted along along 30 kin, km, the thrust thrust faults faults and and the the southeast—trending southeast-trending arm arm was was dominated dominated by by strike-slip strike-slip motion(Cannon, motion(Cannon, 1994). 1994). Rifting Rifting of of the the lithosphere lithosphere caused caused weakening weakening in in an an otherwise otherwise strong strong continental continental lithosphere lithosphere and and focused focused this this deformation deformation into into the in eastern eastern Lake Lake SuperiOr Superior the Midcontinent Midcontinent Rift. Rift. The The graben graben in �14 is 30 km wider than than in western Lake Superior, consistent thrusting in in the the west and strike-slip strike-slip faulting faulting in in the the with thrusting east(Cannon, 1994). 1994). Tectonic Tectonic transport transport was perpendicular to to east(Cannon, the Grenville ~renvilleFront Front with the transition transition between between thrusting thrusting the strike slip slip movement occurring where the the Midcontinent and strike changes trend(Cannon, trend(Cannon, 1994). 1994). The abundance abundance of eastRift changes faults and displacements in the the Midcontinent Rift north-east faults displacements in suggests accommodation accommodation perpendicular perpendicular to to the the axis axis of of the the suggests rift(Marian0 and and Hinze, 1994a). 1994a). The Thiel Fault or Big Bayrift(Mariano Ashburton Bay Bay Fault Fault is is the the most notable notable transform transform fault fault Ashburton separating separating distinct distinct segments of the the rift: rift: symmetrical symmetrical graben in haif—graben in in the the east, asymmetrical asymmetrical half-graben in the the west(Mariano west(Marian0 1994a). This accommodation zone is is the the Trans— Transand Hinze, 1994a). accommodation zone superior Tectonic Tectonic Zone Zone into which alkalic alkalic magma was emplaced Superior north of of Lake Lake Superior. Superior. Mariano and Hinze(1994a) Hinze(l994a) indicated that this this compression compression is demonstrated by drag faults faults along that the Keweenawan Keweenawan Fault, Fault, folds and anticlinal anticlinal structures in the the main basin, basin, and and reverse reverse faults faults to to the the north north and and south south of main Mariano and Hinze(1994a) report the central Lake Superior. central Lake Superior. Mariano and Hinze(1994a) report the presence of of an an anticlinal structure structure in in eastern eastern Lake Superior Superior bisecting and and paralleling the trend of the the rift which has as much of relief on the basalt layer. much as as 55 km km of relief the basalt layer. The The rapid rapid evolution of the Midcontinent Rift from an extensional to aa evolution of the Midcontinent Rift from an extensional to compressional feature feature occurred occurred at at approximately approximately 1080 1080 compressional Ma(Cannon, 1994). 1994). Ma(Cannon, Midcontinent Midcontinent Rift Rift and and the Grenville Grenville Front Front Tectonic Tectonic Zone (GFTZ1 Zone (GFTZ It It was was suggested suggested by by Gorden Gordon and and Hempton(1986) Hempton(1986) on on the the basis basis of of isotopic isotopic ages ages that that the the Midcontinent Midcontinent Rift Rift was was formed formed as as aa result result of of convergence convergence related related to to the the synchronous synchronous Grenville Grenville orogeny. orogeny. Cannon(1994) Cannon(1994) noted noted that that the the Midcontinent Midcontinent Rift Rift developed developed adjacent adjacent to to the Grenville Front Tectonic Zone and that that the the evolution evolution from from extension extension to to compression compression at at approximately approximately 1080 1080 Ma Ma was was coincident coincident with with renewal renewal of of northwest-directed northwest-directed thrusting thrusting in in the the Grenville Grenville Province, Province, probably continent—continent collision. probably in in response response to continent-continent collision. A reversal reversal of of movement movement occurred occurred along along the the major major graben graben faults faults of of western western Lake Lake Superior, Superior, and and in in eastern eastern Lake Lake Superior Superior the the compression compression was was taken taken up up in in reverse reverse faults faults oriented oriented normal normal to to the the Midcontinent Midcontinent Rift Rift axis axis and and parallel parallel to to the the Grenville Grenville Front (Manson and and Halls, Halls, 1994). 1994). In In most most cases cases Front Tectonic Tectonic Zone Zone (Manson these these faults faults reactivated reactivated pre-existing pre-existing faults faults within within the the Archean and Halls, 1994). Archean baseinent(Manson basement (Manson and 1994) Cannon(1994) Cannon (1994) has has interpreted interpreted geophysical geophysical data in in southern southern Michigan Michigan as as suggesting suggesting that that the the Grenville Grenville Front Front Tectonic Tectonic Zone Zone is is thrust thrust over over the the Midcontinent Midcontinent Rift(Figure Rift(Figure 9). 9). . Midcontinent Rift Rift and and the the Kapuskasinci Kawuskasincr Structural Structural Zone(KSZ) ZonefKSZ1 Midcontinent The The Kapuskasing Kapuskasing Structural Structural Zone(KSZ) Zone(KSZ) strikes strikes north north of of east east from from the the east east shore shore of of Lake Lake Superior, Superior, but but quickly quickly becomes becomes more more northerly northerly in in strike strike east east of of the the Lake. Lake. This This more more �15 Grenville Province Midcontinent Rift Midcontinent Rift s Magmotic Belt Seismic profile Seismic pofile Killarney / Provincial or State bou-biy - International boundary —. International undory Figure 9: Regional sketch map showing the positions of the Figure 9: Regional sketch map showing the positions of the Grenville Front, Grenville Front Tectonic Zone, Central Grenville Front, Grenville FrontZone. Tectonic Zone, Central Metasedimentary Belt Boundary The southeastern Metasedimentary Belt southeastern idcBoundary continentZone. Rift The in areas covered by extension of the extension of the Midcontinent Rift in areas covered by Paleozoic are geophysical interpretations.(From Easton, Paleozoic are geophysical interpretations. (From Easton, 1992). 1992). �16 northern strike strike is is closely closely parallel parallel to to the the trend trend of of the the northern 3, 10). The KSZ is aa Trans-Superior Tectonic Zone(Figures Trans-Superior Tectonic Zone(Figures 3, 10). The KSZ is broad zone of faulting at the east coast of Lake superior broad zone of faulting at the east coast of Lake Superior and aa very very narrow narrow zone zone near near Hudson Hudson Bay Bay to tothe thenorth. north. The The and zone is characterized by positive aeromagnetic and gravity zone is characterized by positive aeromagnetic and gravity anomalies and and west—dipping west-dipping zones zones of of high high refraction refraction anomalies velocities(Percival and West, 1994). The zone contains contains west— westvelocities(Percival and West, 1994). The zone Ion thick section dipping faults exposing an approximately 20 dipping faults exposing an approximately 20 km thick section of Archean Archean crust(Percjva]. crust(Perciva1 and 1983) related related to to of and Card, Card, 1983) transpressive tectonics(Perciva1 and West, 1994). Uplift transpressive tectonics(Perciva]. and West, 1994). Uplift took place place prior prior to to 2.45 2.45 Ga(Bursnall Ga(Bursnal1 et. et. al. al. 1994; 1994; Heaman, Heaman, took 1988), since relatively undeformed Matachewan dikes cut the the 1988), since relatively undeformed Matachewan dikes cut structure, and perhaps as early as 2630 Ma(Krogh and structure, and perhaps as early as 2630 Ma(Krogh and Moser(1994). and other other Moser (1994). ~ranulite-facies Granulite-facies metamorphism metamorphism and deformations took place prior to this KSZ event(Bursna11 et deformations took place prior to this KSZ event(Bursnall et al., 1994; Krogh and Moser, 1994). The ~apuskasing al., 1994; Krogh and Moser, 1994). The Kapuskasing Structural Zone Zone is is an an intracratonic intracratonic uplift uplift representing representing 27 27 Structural km of crustal shortening through brittle upper crustal km of crustal shortening through brittle upper crustal thrusting(Perciva1 and and West, West, 1994). 1994). Within Within the the KSZ KSZ the the Moho Moho thrusting(Percival compared to values near 45 occurs at a depth of about 53 km occurs at a depth of about 53 km compared to values near 45 km near Wawa and approximately 35 km near ~immins(~erciva1, km near Wawa and approximately 35 km near Timmins(Percival, 1990). 1990). Manson and and Halls(1994) Halls(1994) traced traced faults faults from from Mamainse Mamainse Point Point to to Manson the Keweenaw Peninsula and suggested that the Michipicoten the Keweenaw Peninsula and suggested that the Michipicoten Island Fault Fault may may be be traced traced into into Grindstone Grindstone Point Point Fault. Fault. Island mapped a large northeast-trending fault along Grunsky(1991) Grunsky(199l) mapped a large northeast-trending fault along the Montreal River which separated the Chapleau Gneiss the Montreal River which separated the Chapleau Gneiss Domain from from the the Batchawana Batchawana Volcanic Volcanic Domain—Ramsy Domain-Ramsy Gneiss Gneiss Domain ~omain. This fault contained gouge, breccia and quartz veins Domain. This fault contained gouge, breccia and quartz veins and was correlated with faulting associated with the KSZ. and was correlated with faulting associated with. the KSZ. Other northeast-trending northeast-trending faults faults with with aa brittle brittle style style of of , Other deformation occur along the Batchawana and Goulais rivers deformation occur along the Batchawana and Goulais rivers but their their relationship relationship to to the the KSZ KSZ is is not not as as clear clear but (Grunsky.1991). Sage(1994) correlated the Wawa-Hawk(Grunsky, 1991). Sage (1994) correlated the Wawa—Hawk— Manitowik Lake Lake Fault Fault with with the the Kapuskasing Kapuskasing Structural Structural Zone Zone Manitowik and suggested that it was rooted in Archean tectonics. The and suggested that it was rooted in Archean tectonics. The extension of this fault toward Lake Superior may account for extension of this fault toward Lake Superior may account for the straight coastline of Lake superior west of Wawa. the straight coastline of Lake Superior west of Wawa. km east east of of the the shoreline shoreline of of Lake Lake Superior superior ~pproximately15 15 km Approximately the Wawa-Hawk-Manitowik Lake Fault is cut by a smaller local the Wawa-Hawk-Manitowik Lake Fault is cut by a smaller local fault known as the Firesand River Fault(Sage, 1994). At this fault known as the Firesand River Fault(Sage, 1994). At this intersection, the mantle-derived Firesand River Carbonatite intersection, the mantle-derived Firesand .River Carbonatite was emplaced, emplaced, which which on on the the basis basis of of imprecise imprecise age age dating dating is is was prairie Lake ~arbonatite(~age and likely coeval with the likely coeval with the Prairie Lake Carbonatite(Sage and Watkinson, 1991). 1991). Numerous Numerous alkalic alkalic rock rock and and carbonatite carbonatite Watkinson, Zone which which complexes occur along the Kapuskasing Structural complexes occur along the Kapuskasing Structural Zone were emplaced at about 1.1 Ga(Sage and Watkinson, 1991; were emplaced at about 1.1 Ga(Sage and Watkinson, 1991; Bursnall et. et. al. al. 1994; 1994; Percival Percival and and West, West, 1994). 1994). Within within the the Bursnall alkalic constraints of existing isotopic age dating, constraints of existing isotopic age dating, alkalic magmatism along along the the Trans Trans Superior Superior Tectonic Tectonic Zone Zone and and magmatism ~apuskasing Structural Zone appear to be contemporaneous. Kapuskasing Structural Zone appear to be contemporaneous. The alkalic alkalic rock rock and and carbonatite carbonatite complexes complexes along along the the The Kapuskasing Structural Zone should also be considered Kapuskasing Structural Zone should also be considered �17 * Proterozoic, Phanerozoic cover Proterozoic Alkalic rock complex Archean Moose Quefico Metasedlmentary r: River Basin Belt Metavolcanic rx Granitoid rx Anorthositlc rx Granulites • 4• • ••••• CobaltT-- Figure 10: 10: Geologic Geologic sketch sketch map map of of the the Kapuskasing Kapuskasing Structural Structural Figure Zone Zone and and surrounding surrounding parts parts of of the the central central Superior Superior Province, Province, showing showing major major geological geological and and geographical geographical features. features. BLFZ, BLFZ, Budd Lake Lake fault fault zone; zone; BRF BRF Bad Bad River Riverfault; fault;FF, FF, Foxville Foxville Budd fault; ILFZ, ILFZ, Ivanhoe Ivanhoe Lake Lake fault fault zone; zone; KF, KF, Kineras Kineras fault; fault; fault; SLF, Saganash Saganash Lake Lake fault; fault; WRF, WRF, Wakusimi Wakusimi River River fault; fault; WHMF, WHMF, SLF, Wawa-Hawk-ManitoWik Wawa-Hawk-Manitowik Lake Lake fault; fault; rx, rxf rock rock types(modified typesfmodifiedfrom from Percival and and West, West, 1994). 1994). Percival �18 manifestations tectonic activity associated with the manifestations of tectonic development Rift. It It is also likely that development of of the the I4idcontinent Midcontinent Rift. late Archean faulting faulting associated with with the the KSZ KSZ was was reactivated at 1.1 Ga and played a major role in the development of the Midcontinent Rift in the the Lake Superior Superior region. region. Summarv of of Reczional Regional Settinq Summary Setting The locations locations of alkalic alkalic rock intrusions intrusions north and northeast northeast Superior are not haphazard or random. The intrusions intrusions of Lake Superior Trans—Superior Tectonic Zone occur within the Trans-Superior Zone and its northern extension extension with the largest intrusion occurring at the Proterozoic-Archean intersection of Proterozoic—Archean contact close to the intersection the Michipicoten Michipicoten Island and the Big Bay-Ashburton Bay—Ashburton Bay Faults. The Trans-Superior Trans—Superior Tectonic Zone bisects the Midcontinent Rift and has aeromagnetic, gravity and topographic topographic expression. The Trans-Superior Tectonic Zone is accommodation zone an accommodation zone separating the Lake Superior basin into two contrasting tectonic domains. domains. Development of the Midcontinent Rift is is intimately related to developments developments along the GFTZ and KSZ and likely strongly influenced by early structures structures in in the the Archean Archean basement. basement. The unique positions of the diatreme structures structures on the Slate Islands Islands is is more consistent with the tectonic development of the Midcontinent Rift impact(Sage, 1978; Rift than than meteorite meteorite impact(Sage, 1978; Halls and Grieve, Halls Grieve, 1976). 1976). �19 DAY11 DAY KILLALA LAKE COMPLEX The The Killala Killala Lake Lake Complex Complex is is an an alkalic alkalic complex complex consisting consisting of of an outer ring of troctolite troctolite followed followed inward inward by nepheline nepheline syenite(Figure syenite and then an inner core core of of amphibole amphibole syenite(Figure syenite 11). The interior syenites syenites are are coarse—grained, coarse-grained, equigranular, equigranular, 11). part of of the grey to buff on fresh surface in the southern part complex and red complex red to to reddish reddish brown, brown, coarse—grained, coarse-grained, inequigranular, seriate senate to to porphyritic, porphyritic, in in the northern part. Several part. Several minor lithologies lithologies are are also also locally locally present. In In the centre centre of the intrusion intrusion on on the the shores shores of Kentron Kentron and and Blank Lakes mafic banding is is very well well developed developed in in the the syenites(Sage, 1988). 1988). The size size and and number number of xenoliths xenoliths increase to the north as do the number of septa of enclosing enclosing wall wall rocks rocks projecting projecting into into the the syenite syenite mass. mass. The Killala Lake complex has been been dated by Rb-Sr techniques techniques as being 1050 1050 +— +- 35 Ma(Bel1 and Blenkinsop, Blenkinsop, 1980). 1980). This age 35 Ma(Bell with more more precise U-Pb isotopic is essentially coeval with isotopic age age dating at at the the Port Port Coidwell Coldwell Complex. Complex. Kila1a The Ki lalaLake Lake Complex Complex has has aa surface surface area area of of approximately approximately prevalence of 110 km The large number of xenoliths and prevalence wall rock septa suggest that the the northern northern part of the the ring ring complex is is exposed at a higher structural structural level level than than is is the the southern part and the intrusion intrusion which may plunge south southern south to to southwest toward the Lake Superior Basin. The isomagnetic isomagnetic contours contours on aeromagnetic aeromagnetic maps of of the the complex complex outline outline aa circular circular pattern in contrast contrast to to the the tear—drop tear-drop shape shape defined defined by mapping(ODM-GSC mapping(0DM-GSC 1963f, 1963f, g; g; Coates, Coates, 1970; 1970; Sage, Sage, 1988) (Figure 12). 12). The The northern northern projection projection of of the the ring 1988)(Figure complex complex has been interpreted interpreted as as aa sheet-like sheet-like or petal—like petal-like laccolithic laccolithic mass extending north of, and overlying the the outer outer gabbro ring which on the basis basis of of aeromagnetic aeromagnetic data data likely likely completely encloses encloses the the complex(Coates, complex(Coates, 1970; 1970; Sage Sage 1988). 1988). The arcuate, open-to-the-north horseshoe horseshoe shaped shaped lithologic lithologic distribution distribution suggests suggests the possibility of of a former former caldera caldera structure(Sage, 1988). 1988). Coates Coates (1967, (1967, 1970), 1970), Bathe Bathe (1977), (1977), Wanless (1976) Wanless (1976) and Sage, (1988) (1988) described described detailed detailed geology geology of the Killala Killala Lake Lake Complex. Complex. i The Killala Lake Complex Complex lies lies at at the the intersection intersection of of topographic topographic and aeromagnetic aeromagnetic linears. linears. A prominent aeromagnetic linear connects the Killala Lake Complex with the Prairie Lake Carbonatite, of similar age, to the southwest. Williams(1989) has identified a zone several several kilometres kilometres wide of deformed rocks rocks along along this this aeromagnetic aeromagnetic �20 o o kilomstr,. I 2 r • nwles Thur SItS- •.* * _j_,O,,,,.,., • •_o'-• .• • • I-. - •.&++**.+_ S.' KILLAL.A LAKE ALKAUC COMPLEX PROTEROZOIC r.::.:j Brn syenft. I°ó°°I NepheUns $yenits Buff syenite I] Syenodiont. Gobbro I .'lDiobose ARCHEAN Quartz monzonifs I. . • . , to gronodicdts Metosedirnents ~ i g u r e11: Geologic sketch map of the Killala Lake Alkalic Figure 11: GeologicSage8 sketch198G8 map of the Killala Lake Alkaljc Rock Complex(from 1988) Rock Complex(from Sage, 1986, 1988) �3 JEIoi. -4 I I-i DI I-' 1-d. CD I.,) 0 '— DI 0S(D DI C)0 GHD (DCD —.1-a I-P1 OIa. Figure 12: Aeromagnetic map of the Killala Lake Alkalic Rock CO~P~~X(ODM-GSC, 1963e, f). �22 trend which which he he referred referred to to as as the the Killala Killala Lake Lake Deformation Deformation trend ZoneA prominent topographic linear along the east side side of of Zone. A prominent topographic linear along the east Coates(l970) the complex has been interpreted by as aa the complex has been interpreted by Coates(1970) as fault(Bo0merang Lake Lake Fault) Fault) and and this this fault fault may may be be fault(Boomerang interpreted from from air air photographs photographs to to join join with with the the Little Little Pic Pic interpreted River lineament on the west side of the Port Coldwell River lineaiuent on the west side of the Port Coldwell Complex. The The Killala Killala Lake Lake Complex Complex lies lies within within the the northern northern Complex. part of the Lake Superior Tectonic Zone and along the part of the Lake Superior Tectonic Zone and along the interpreted extensions of the Big Bay-Ashburton Bay interpreted extensions of the Big Bay-Ashburton Bay Fault(Sage, 1978) 1978) or or Thiel Thiel Fault(Klasner Fault(K1asner et et al. al- 1982). 1982)- The The Fault(Sage, trend of this tectonic zone parallels approximately the trend of this tectonic zone parallels approximately the Kapuskasing Structural Structural Zone. Zone. The The topographic topographic linear linear Kapuskasing connecting the Port Coldwell and Killala Lake complexes may may connecting the Port Coldwell and Killala Lake complexes be extrapolated northward to the Chipman Lake area where be extrapolated northward to the Chipman Lake area where fenite and and carbonatite carbonatite dikes dikes are are widespread(sage, widespread(sage, fenite 1985)(Figure 13). Offset of lithologies across this this 1985) (Figure 13). Offset of lithologies across lineament at Chipman Lake is 0.8 -(Sage, 1985)lineament at Chipman Lake is 0.8 km(Sage, 1985). ~conomicGeology Geology Economic The Killala Killala Lake Lake complex complex has has been been prospected prospected for for its its copper copper The and nickel content in the early 195Os(Sage, 1988). and nickel content in the early 1950s(Sage, 1988). examined some some of of the the drill drill core coreremaining remainingfrom. from Bath(l977) examined Bath(1977) this effort and recognized pyrrhotite, chalcopyrite, this effort and recognized pyrrhotite, chalcopyrite, cubanite, pentlandite, pentlandite, and and valleriite. valleriite- The The complex complex remains remains cubanite, relatively untested for PGE. Within the area of Blank Lake, relatively untested for PGE. Within the area of Blank Lake, intrusion, zircon and pyrochlore are near the centre of the near the centre of the intrusion, zircon and pyrochiore are present within narrow pegmatite dikes(Sage, 1988). present within narrow pegniatite dikes(Sage, 1988). interest only. only. Pyrochlore and and zircon zircon are are of of mineralogical mineralogical interest Pyrochiore The complex is currently undergoing examination as a The complex is currently undergoing examination as a possible source source of of building building stone. stone. possible The road road log log is is from from the the intersection intersection of of Highway Highway 17 17 and and the the The Dead Horse Creek access road. Recent logging activities in Dead Horse Creek access road. Recent logging activities in the region now permit access to the margins of the Killala the region now permit access to the margins of the Killala Lake Complex. ComplexLake 18.4 Km Km @@ 18.4 Jackpine Road, Road, turn turn right right Jackpine 33.7 Km Km Prairie Lake Lake Carbonatite Carbonatite intersection intersection on on left. left. @@ 33.7 Prairie Continue north and cross the Little Pic River bridge and Continue north and cross the Little Pic River bridge and stay to to the the righthand right hand branch branch of of the the road. roadstay 55.2 Km Km @@ 55.2 Turn right right on on skid skid road. road. This This road road is is located located Turn just north north of of Sandspit Sandspit Lake. Lake. just 0-40 Km Km @@ 0.40 Park in in cleared cleared area. area. Park �23 CHIPMAN CHIPMAN LAKE LAKE AREA AREA PROTEROZOIC PROTEROZOIC I [ *Tj Fenite I Feniteandandcorbonotite c a r b m t i t edikes dikes ARCHEAN ARCHE AN p r d Diorite Diorite totoquartz quartzmonzonite mnzonite intrusive intrusiverocks rocks to syenodiorite intrusive rocks 1['J -1 DioriteDiorite to syenodbrite intrusive rocks I:1 iafic Mafic rnetavoicanics metavolcanics fault — —rood Figure 13: 13: Geologic ~eologicsketch sketch map map of of the the Chipman chipman Lake Lake area area Figure showing faulting faulting along alongthe thelong longaxis axisof ofChipiuan Chipman Lake. Lake. This This showing fault may may be be the the northern northern extension extension of of the the Boomerang Boomerang Lake Lake fault fault that that passes passes along along the the east east side fault side of of the the Killala Killala Lake Lake Alkalic Rock Rock Complex(from Complex(from Sage, Sage81985, 1985#1986). 1986). Alkalic �24 Stop Stop la la Walk approximately approximately 470 470 mm along along skid skid road road in in aa SE SE Walk direction and and up up hill(See hill(See Figure Figure 14; 14; Sage, Sage, 1988). 1988). direction Medium- to to coarse—grained coarse-grained equigranular equigranular olivine olivine gabbro gabbro to to Medium— troctolite occurs along the north side of road as rounded troctolite occurs along the north side of road as rounded grey outcrops. outcrops. Outcrop Outcrop is is cut cut by by dikes dikes of of pink pink to to red red grey Bathe(l977) described described samples samples syenite and and nepheline nepheline syenite. syenite. Bathe(1977) syenite from similar similar gabbro gabbro outcrops outcrops as as being being composed composed of of 45 45 to to 50 50 %3 from plagioclase(An56 plagioclase(An56 — An65), -651, augite augite clinopyroxene clinopyroxene 20 20 to to 25 25 %, %, olivine olivine 55 to to 30 30 %% and and accessory accessory apatite, apatite, biotite, biotite, green green amphibole, oxides oxides and and suiphides. sulphides. Noritic Noritic gabbro gabbro and and amphibole, larvikite are are described described by by Bathe(1977) Bathe(l977) as larvikite as being being associated associated with phase. In thin with the the olivine olivine gabbro gabbro to to trocto].ite troctolite phase. thin section section corona structure structure where where in the olivine—plagioclase olivine-plagioclase have have aa corona the in reaction with with water water under under middle middle to to contact, attributed attributed to to aa reaction contact, upper amphibolite-facies amphibolite-faciesconditions conditions(Laderoute, 1984). upper (Laderoute, 1984). - Stop Stop lb lb approximately approximately 130 130 mm east east of of la la Small outcrop outcrop of of coarse—grained coarse-grained nepheline nepheline syenite syenite with with up up to to Small 10 to 15 nepheline. The The nepheline nepheline syenite syenite has has been been I0 .to 15 %% nepheline. estimated to to contain contain approximately approximately 10 10 to to 15 15 %3 nepheline, nepheline, 00 estimated to dark green green to to green green brown brown amphibole, amphibole, 30 30 to to 70 70 %% to 25 25 %% dark perthite perthite and and 00 to to 65 65 %% sodic sodic plagioclase(Sage, plagioclase(Sage, 1988). 1988). Minor Minor amounts amounts of of clinopyroxene clinopyroxene and and biotite biotite are are present present with with accessory accessory sphene, sphene, magnetite, magnetite, apatite, apatite, sericite sericite and and carbonate. carbonate. Stop Stop lc lc approximately approximately 70 70 mm east east of of lb. lb. Nepheline Nepheline syenite syenite with with lower lower nepheline nepheline content. content. Stop Stop ld ld approximately approximately 145 145 mm east east of of lc lc Some Coarse—grained Coarse-grained equigranular equigranular buff buff to to pink pink syenite. syenite. Some pitting pitting of of the the surface surface may may be be due due to to weathering weathering of of nepheline nepheline but but most most is is due due to to the the mafic mafic mineral mineral content. content. The The buff buff syenite plagioclase(An2845 %% plagioclase(An28syenite contains contains approximately approximately 55 to to 45 An39), An39), 55 to to 25 25 %% amphibole, amphibole, and and 15 15 to to 95 95 %% perthite(Sage, perthite(Sage, 1988). 1988). Minor Minor amounts amounts of of olivine olivine 00 to to 11 %, %, biotite biotite 00 to to 10 10 %3 and and clinopyroxene clinopyroxene 00 to to 55 %% may may also also be be present present in in some some specimens. specimens. The The accessory accessory minerals minerals are are apatite, apatite, magnetite, magnetite, sericite, sericite, carbonate, carbonate, zircon, zircon, sphene, sphene, chlorite chlorite and and quartz(Sage, quartz (Sage,1988). 1988) . Stop Stop le le approximately approxinately 55 55 mm east east of of id ld Small Small outcrop outcrop as as previously previouslydescribed. described. �25 1 FROM: Ontario Qeologlcal Survey Study 4 5 FROM: Ontario 4 Chart Chart A SANDSPIT LAKE LAKE SANOSPIT 5 14 / LEOEI4D LEGEND 5 R.d Sy.nht. Red Synlte 4 SyenIt. &It Buff Buff $y.nIts Nepholin. Nephellne Syenlte Synlte Gabbro — — — 500 m•tr•s 500 metres / 2 GranIttc Rock Granitic Rock 1 M.tas.dlm.ntary Rock Metasedlment8ry Roek 3 J Figure 14: 1 4 : Geologic ~ e o l o g i csketch s k e t c h map map showing showing field f i e l d trip t r i p sites, sites, Killala K i l l a l a Lake Lake Alkalic A l k a l i c Rock Rock Complex. Complex. Base Base map map from from Sage(1988, Sage(1988, Chart Chart A). A). �26 Stop if If approximately approximately 125 125 m east of le; skid skid road road has has deteriorated. deteriorated. Coarse—grained Coarse-grained equigranular equigranular amphibole amphibole syenite. syenite. Feldspar Feldspar somewhat lath-like and mafic mineral content approximately approximately somewhat lath—like 15 to to 20 20 %. %. Outcrop similar similar to to id. Id. main road. road. Turn Turn Return to parking area and go back to the main 21.5 km to to intersection intersection of left back the way you came. Drive 21.5 a skid skid road road and and Jackpine Jackpine Lake Lake Road. Road. Turn right tan. right onto onto skid skid road road and continue continue to to 25.6 25.6 km. Turn right right onto onto partially overgrown overgrown skid skid road road and and continue continue this point the the road road splits. splits. until odometer odometer reads reads 26.6 26.6 km. At this Take the the right-hand fork fork and continue continue to to the the odometer odometer reading f to 26.7 km. km. An An overgrown overgrown skid skid road road leads leadsof off to the the reading of of 26.7 right up a a steep steep hill. Park Park at the the road road junction junction or or drive drive the the short short distance distance to to the the base base of of the the hill hill and and park. park. �27 PRAIRIE PRAIRIE LAKE LAKE CARBONATITE CARBONATITE The Prairie Prairie Lake Lake Carbonatite Carbonatite consists consists of of arcuate arcuate units units of of The sovite, sovite, silicocarbonatite, silicocarbonatite, ijolite ijolite and and wollastonite wollastonite ijolite(Figures ijolite(Figures 15, 15, 16a,b). 16a,b). Minor Minor amounts amounts of of biotitite(g1immerite) may The complex complex biotitite(glimxnerite) may locally be present. The forms forms aa prominent prominent hill, hill, which, which, in in spite spite of of its its topographic topographic relief, relief, has has only only rare rare outcrops. outcrops. Weathering weathering is is deep deep and and samples samples of of fresh fresh rock rock may may be be obtained obtained only only through through diamond diamond trenching or or in in logging logging skid skid roads roads where where lumps lumps drilling, drilling, trenching resistant resistant to to weathering weathering have have been been exposed exposed by by heavy heavy equipment. equipment. The carboatite carbo atite complex of complex has has aa surface surface area area of approximately approximately 8.8 8.8 km Ion 9. The The complex complex has has been been dated dated at at 1033 1033 ++- 59 59 Ma Ma by by the the Rb-Sr Rb-Sr technique(Bel1 and and Blenkinsop, ~lenkinsop,1980) 1980) and and is is considered considered to to be be technique(Bell essentially coeval coeval with with the the Killala Killala Lake Lake and and Port Port Coidwell Coldwell essentially Alkalic Alkalic rock rock complexes. complexes. The The Prairie Prairie Lake Lake Complex Complex has has aa prominent aeromagnetic aeromagnetic anomaly anomaly approximately approximately 2.5 2.5 km km in in prominent diameter(0DM-GSC, 1963a). 1963a). The The aeromagnetic aeromagnetic anomaly anomaly is is diameter(ODM-GSC, approximately approximately 1400 1400 gammas gammas absolute absolute total total field field above above the the surrounding background background area area which which is is underlain underlain by by granitoid granitoid surrounding rocks(Sage, rocks (Sage,1987) 1987)(Figure (Figure17). 17) . North-trending topographic topographic linears linears from from the the north north shore shore of of North-trending Lake Lake Superior Superior intersect intersect northeast—trending northeast-trending topographic topographic and and aeromagnetic linears at at the the site site of of the the Prairie Prairie Lake Lake aeromagnetic linears Carbonatite. Carbonatite. The The northeast northeast trending trending linear linear connects connects with with the the Killala Williams(1989) recognized recognized aa Killala Lake Lake Complex. Complex. Williams(1989) deformation deformation zone zone between between these these two two complexes complexes which which he he referred referred to to as as the the Killala Killala Lake Lake deformation deformation zone. zone. This This zone zone is is several several kilometres kilometres wide wide and and defines defines the the boundary boundary between between the the Wawa Wawa and and Quetico Quetico subprovinces(Williams, subprovinces(Williams, 1989). 1989). The The complex complex lies lies within within the the northern northern part part of of the the Trans-Superior Trans-Superior Tectonic Tectonic Zone(Klasner Zone(K1asner et et al, al, 1982) 1982) and and along along linear linear trends trends subparallel subparallel to to the the Big Big Bay—Ashburton Bay-Ashburton Bay Bay Fault Fault or or Theil Theil Fault trend(Sage, 1978; 1978; Kiasner Klasner et et al, al, 1982). 1982). The The geology geology Fault trend(Sage, and and mineralogy mineralogy of of the the Prairie Prairie lake lake Carbonatite Carbonatite have have been been described described by by Watkinson,(1971, Watkinson,(1971, 1973, 1973, 1976), 1976), Melnik(1984) Melnik(1984) and and Sage(1987). Sage(1987). Sage(1987) Sage(1987) ôites cites numerous numerous unpublished unpublished company company reports reports on on the the complex, complex, most most of of which which can can be be obtained obtained from from the Thunder the Assessment Assessment Files, Files, Resident ~esidentGeologist's ~ e o l o g i s t ~Office, office, s Thunder Bay. Bay. Economic Economic Geology Geology Uranium Uranium mineralization mineralization was was discovered discovered at at "Jim's "Jim's Showing" Showingwby by J. J. Gareau Gareau working working for for Newmont Newmont Mining Mining Corporation Corporation of of Canada Canada Ltd. Ltd. in in 1968 1968 and and the the company company completed completed radiometric, radiometric, magnetic magnetic and and geochemical geochemical surveys surveys over over the the intrusion. intrusion. At At "Jim's "Jim's �28 ••:•:•:•:•::. Stop metres 0 P00 4 q•• .tut. 200' • 890 Stop 4 PRAIRIE F'RAIRE LAKE LAKE CARBONATITE CARWATIE PROTEROZOIC PROTEROZOIC AlkalicDike DikeRocks Rocks. Alkalic E1: Sovite SovileSilicocarbonate Silicocarbonale IjoIite LiJ Ijolite E:.j Fenite Fenite a ---- .—-——fault fault LIJ Archecn 0 Archem - stream stream Figure Figure 15: 15: Geological Geological sketch sketch map map of of the the Prairie Prairie Lake Lake Carbonatite Carbonatite showing showing field field trip trip sites sites and and potential potential sites. sites. (Modified (Modified from from Sage, Sage, 1986, 1986, 1987). 1987). �1986). Figure 16a: Idealized plan view of a carbonatite intrusion showing the idealized distribution of rock types(from Sage, Figure 16b: Idealized cross section through a carbonatite intrusion illustrating an idealized distribution of rock typ.s(froa Sag., 1986). %0 t..J �30 1.6 km Figure 17: Prominent aeromagnetic anomaly that outlines the Figure 17:Lake Prominent Carbonatite(0DM-GSC, 1963e).that outlines the prairie aeromagnetic anomaly Prairie Lake Carbonatjte(oDM-Gsc, 1963e). �31 Showingw the the company company outlined outlined 109,024 109,024 tons tons grading grading 0.12 0.12 %% Showing" U3O8 in in aa deeply deeply weathered weathered ferruginous ferruginous dolomite. dolomite. This This was U308 expanded by by Nuinsco Nuinsco Resources Resources Limited Limited in in 1975 1975 to to 200,000 200,000 expanded tons grading grading 18 1.8 pounds pounds U308 U3O8 and and 5.0 5.0 pounds pounds Nb205 Nb205 per per ton ton in in tons aa zone Watkinson(l976), zone 300 300 feet feet long long and and 275 275 feet feet deep. deep. Watkinson(1976), using the the microprobe, microprobe, identified identified the the uranium-bearing uranium-bearing mineral mineral using as pyrochiore pyrochlore which which displayed displayed increasing increasing uranium uranium contents contents as from from core core to to rim. rim. Uranium Uranium may may comprise comprise up up to to 30 30 %% of of pyrochlore (Watkinson, (Watkinson, 1976). 1976). In In 1975 1975 the the complex complex was was pyrochiore examined for for possible possible residual residual apatite apatite deposits deposits by by the the examined ~nternationalMinerals Minerals and and Chemical Chemical Corporation(Canada) Corporation(Canada) Ltd. International Ltd. and and in in 1983 1983 New New Insco Xnsco Mines Mines Ltd. Ltd. tested tested the the carbonatite carbonatite complex for for its its wollastonite wollastonite potential. Sage(1987) Sage(l987) provided complex additional information information regarding regarding these these exploration exploration efforts. efforts. additional Walk Walk approximately approximately400 400in m up up the the skid skid road. road. Stop 2. MediumMedium- to to coarse-grained coarse-grained inequigranular inequigranular ijolite ijolite is is Stop 2. present as as weathered weathered lumps lumps and and outcrop. outcrop. This This exposure exposure is is present typical of of the the coarser-grained coarser-grained phases phases of of the the Prairie Prairie Lake Lake typical Carbonatite. Carbonatite. In In addition addition to to the the pyroxene pyroxene and and nepheline, nepheline, calcite, calcite, magnetite magnetite and and garnet garnet are are present present in in this this outcrop outcrop and and titanite titanite has has been been observed observed in in similar similar rocks rocks within within the the complex. complex. The The outcrop outcrop is is deeply deeply weathered weathered with with secondary secondary carbonate carbonate along along joint joint surfaces. surfaces. This This exposure exposure is is much much larger larger than than most most exposures exposures within within the the intrusion. intrusion. Return You may may note note the the presence presence of of Return to to the the vehicles. vehicles. You phiogopite in the skid road as you return to the vehicles. phlogopite in the skid road as you return to the vehicles. Drive Drive back back approximately approximately 0.1 0.1 km km where where the the road road splits splits and and take the right hand fork. Drive along this partially Drive along this partially take the right hand fork. overgrown for approximately approximately 0.8 0.8 km km overgrown skid skid trail trail up up the the hill hill for and and park. park. Stop Stop 33 Wollastonite Wollastonite ijolite. ijolite. This This site site displays displays deeply deeply weathered weathered wollastonite wollastonite ijolite ijolite which which has has been been torn torn up up during during logging logging operations. operations. The The material materialisispegniatitic pegmatitic and and prismatic prismatic crystals crystals of of wollastonite wollastonite up up to to 15 15 cm cm or or more more have have been been found found here. here. The The wollastonite wollastonite will will sometimes sometimes appear appear as as veins veins cutting cutting the the ijolite. ijolite. The The wollastonite wollastonite crystals crystals are are perpendicular perpendicular to to the the vein vein trend. trend. Return f to Return or or drive driveback back0.35 0.35 km. km. AAflagged flaggedtrail trailleads leadsofoff to the in. m. the left left into intothe thebush bushfor forapproximately approximately100 100 Stop Stop 44 Orbicular Orbicular ijolite(optional). ijolite(optiona1). The The orbicular orbicular ijolite ijolite never in solid solid outcrop outcrop projecting projecting above above ground ground never occurred occurred in level level but but consisted consisted of of large large frost—heaved frost-heaved blocks. blocks. Collectors Collectors �32 have dug dug aa pit pit at at the the discovery discovery site site and and over over the the years years have large large quantities qyantities have have been been removed. removed. The The site site was was overgrown overgrown and the the pit pit filled filled in in the the fall fall of of 1994 1994 and and it it will will have have to to and be exposed additional sampling. AA equipment for for additional exposed with heavy equipment visit to to the the site site will will be be depend depend on on whether whether arrangements arrangements can can visit be be made made to to expose expose deeper deeper material. material. This material material is is one one of of the the finest finest examples examples of of orbicular orbicular This texture this is the only known known occurrence texture known known arid and this occurrence of of this this texture 1987). The The texture in in rocks rocks of of this this composition(Sage, composition(Sage, 1987). orbicules orbicules consist consist of of aa multitude multitude of of concentric concentric bands bands consisting consisting of of varying varying proportions proportions of of aegirine—augite, aegirine-augite, nepheline melanite garnet. garnet. Apatite Apatite and and biotite biotite are are also also nepheline and and melanite present present as as well well as as aa white white alteration alteration mineral, possibly melilite(Sage, 1987). 1987). The The orbicules orbicules are are up up to to 33 cm former melilite(Sage, em in in former diameter diameter and and the the largest largest have have aa medium—grained medium-grained equigranular equigranular ijolite core. core. It It is is assumed assumed that that all all orbicules orbicules will will have have ijolite this equigranular equigranular core core if if they they have have been been cut cut through through the the this centre. Several Several large large blocks blocks of of the the material material recovered recovered in in centre. initial initial sampling sampling suggest suggest that that the the orbicules orbicules may may occur occur along along distinct distinct bands bands within within equigranular equigranular ijolite. ijolite. Return Return to to vehicles vehicles and and return return to to the the main main road road (Jackpine (Jackpine Road). Turn Turn right right on on the the main main road road and and go go 15.2 15.2 km km to to the the junction junction with with the the Dead Dead Horse Horse Creek Creek access access road. road. Turn 10.1 km km and and park park at at the the side side of of the the Turn right right and and go go north north 10.1 road. small lake lake will will lie lie to to the the west west and and aa steep steep hill hill road. AA small occurs occurs to to the the east east across across aa flat flat area area used used as as aa storage storage area area for for logs. logs. Walk to the the east east and and along along the the skid skid Walk approximately approximately 100 100 metres metres to road This hill hill is is the the west west side side of of the the road up up the the steep steep hill. hill. This Prairie Prairie Lake Lake Carbonatite. Carbonatite. Various Various cobbles cobbles and and boulders boulders of of sovite sovite and and silicocarbonatite silicocarbonatite have have been been turn turn up up by by logging logging equipment into the the deeply deeply equipment in in the the skid skid road. road. In In deep deep cuts cuts into weathered weathered carbonatite-rich carbonatite-rich soil soil relict relict primary primary banding banding may may sometimes sometimes be be observed. observed. At At the the top top of of the the hill hill aa partly partly overgrown overgrown skid skid road road leads leads into into the the interior interior of of the the carbonatite carbonatite and and aa former former campsite campsite near near Centre Centre Lake. Lake. This This trail trail is is not not aa difficult difficult walk walk and and is is approximately the length approximately 1.2 1.2 kin km in length. Due to the length of of the the walk walk and and time time involved involved these these sites sites will will not not be be visited visited unless gained-toall allsites sitesdescribed described for for Stops Stops unless access access can can be gainedto 5 5 thru thru 7. 7. �33 Optional Optional stops stops 5, 5, 6, 6, and and 77 Stop Stop 55 Sovite Sovite and and banded banded sovite. sovite. This This is is the the largest largest natural natural outcrop on on the the Prairie Prairie Lake Lake Carbonatite Carbonatite and and occurs occurs in in the the outcrop stream stream bed bed of of the the small small stream stream connecting connecting Centre Centre and and Anomaly Anomaly Lakes. Lakes. The The outcrop outcrop is is weathered weathered and and thickly thickly mantled mantled with with moss. moss. The The stream stream bed bed contains contains abundant abundant rhombs rhombs of of carbonate carbonate as as well well as as grains grains of of phiogopite phlogopite and and magnetite. magnetite. This This mineral mineral assemblage assemblage is is typical typical of of sediment sediment found found in in streams streams flowing flowing through carbonatite. through aa deeply deeply weathered weathered carbonatite. Stop Stop 66 Frost—heaved Frost-heaved sovite. sovite. Some Some specimens specimens may may contain contain some some ijolitic ijolitic material material as as elongated elongated clots clots or or irregular irregular masses. masses. This frost—heaved frost-heaved material material occurs occurs on on the the south south shore shore of of This Centre Lake Lake but but the the exposure exposure was was flooded flooded out out in in the the fall fall of of Centre 1994. 1994. Stop Stop 77 Trench Trench in in deeply deeply weathered, weathered, radioactive, radioactive, ferruginous ferruginous dolomite This dolomite of of "Jim's *@Jim's Showing". Showingt8. This trench trench was was caved caved and and poorly poorly exposed exposed during during mapping mapping in in the the 1970's 1970's and and could could not not be be relocated relocated in in the the fall fall of of 1994. 1994. This This trench trench contains contains material material typical typical of of weathered weathered ferruginous ferruginous dolomite dolomite that that hosts hosts U-Nb U-Nb minerals. minerals. Return Return to to the the vehicles vehicles and and drive drive back back down down the the Dead Dead Horse Horse Creek Access Road toward Highway 17. At approximately 24.9 At approximately 24.9 Creek Access Road toward Highway 17. km park in the open area on the east side of road on the km park in the open area on the east side of road on the north At the the far far north side side of of the the bridge bridge over over Dead Dead Horse Horse creek. creek. At end of this partially overgrown parking area is a trail end of this partially overgrown parking area is a trail leading leading to to the the U-Y U-Y showing showing at at Dead Dead Horse HorseWest. West. �34 DEAD HORSE HORSE CREEK CREEK DIATREME DIATREME DEAD The Dead Dead Horse Horse Creek Creek Diatreme Diatreme is is the the largest(1600 largest(1600 xx 400 400 m) m) The of several several diatreme diatreme structures structures occurring occurring east east of of the the Port Port of Coldwell complex(Sage, 1982, 1991)(Figure 18). The complex Coidwell complex(Sage, 1982, 1991) (Figure 18). The complex consists of of aa broad broad spectrum spectrum of of heterolithic heterolithic breccias breccias that that consists have undergone varying degrees of alteration and are have undergone varying degrees of alteration and are variably radioactive(Sage, radioactive(Sage, 1982). 1982). The The diatreme diatreme was was variably discovered by Mr. Gordon Yule while completing field discovered by Mr. Gordon Yule while completing aa field assignment at Lakehead University in 1976(Mitchell and assignment at Lakehead University in 1976(Mitchell and Platt, 1977; Gordon Yule, personal communication, 1995). Platt, 1977; Gordon Yule, personal communication, 1995). Since the the diatreme diatreme was was radioactive radioactive prospectors prospectors working working for for Since Gulf Minerals Canada Ltd. investigated the diatreme Gulf Minerals Canada Ltd. investigated the diatreme structure for for its its uranium uranium content. content. The The complex complex occurs occurs within within structure the thermal thermal aureole aureole of of contact contact metamorphism metamorphism of of the the Port Port the Coldwell Complex(Walker, Complex(Walker, 1967) 1967) and and rare rare granitoid granitoid fragments fragments Coldwell found in the eastern part of the breccia may be from the found in the eastern part of the breccia may be from the Port Coldwell Complex(Sage, 1982). Preliminary unpublished Port Coldwell Complex(Sage, 1982). Preliminary unpublished U-Pb isotopic isotopic ages ages on on zircons zircons from from the the Dead Dead Horse Horse Creek Creek West West U—Pb +6 Ma(1.82% subcomplex have given values of 1128.7 subcomplex have given values of 1128.7 +— 6 Ma(l.82% +- 44 Ma(—2.49% Ma(-2.49% discordant) discordant)(Krogh and discordant) and and 1112.7 1112.7 +discordant) (Krogh and Wilkinson, 1995, personal communication). These preliminary Wilkinson, 1995, personal communication). These preliminary ages suggests suggests the the possibility possibility that that the the Dead Dead Horse Horse Creek Creek ages diatreme is slightly older than the Port Coldwell Complex diatreme is slightly older than the Port Coldwell Complex dated at at 1108 1108 ++- 11 Ma Ma by by Heaman Heaman and and Machado Machado(1992). Until the the dated (1992). Until isotopic investigations are completed the age relationship isotopic investigations are completed the age relationship between the the diatreme diatreme and and the the alkalic alkalic rock rock complex complex remain remain between somewhat speculative since critical outcroppings needed to somewhat speculative since critical outcroppings needed to establish a relationship are lacking. The age dating does establish a relationship are lacking. The age dating does indicate that that the the mineralization mineralization within within the the Dead Dead Horse Horse Creek Creek indicate diatreme is Keweenawan in age and related to alkalic rock diatreme is Keweenawan in age and related to alkalic rock magmatic events events of of the the Midcontinent idc continent Rift. ~ i f t .Failure ~ a i l u r eto to magmatic correlate lithologies across Dead Horse Creek have prompted correlate lithologies across Dead Horse Creek have prompted Walker(1967) and Sage(1982) to propose that a fault may Walker(1967) and Sage(1982) to propose that a fault may occur along the trend of the creek. The minor subcomplexes occur along the trend of the creek. The minor subcomplexes generally have have aa northwest—trending northwest-trending long long axis axis suggesting suggesting generally structures(Sage, 1982). that they may occupy crosscutting that they may occupy crosscutting structures (Sage, 1982). The diatreme diatreme lies lies at at the the northern northern end end of of the the Big Big BayBayThe Ashburton Bay Fault(Sage, 1978) or Thiel Fault(K1asner et Ashburton Bay Fault(Sage, 1978) or Thiel Fault(Klasner et al. 1982) within the Trans Superior Tectonic Zone. The al. 1982) within the Trans Superior Tectonic Zone. The diatreme lies lies within within north, north, to to east east of of north, north, trending trending diatreme regional linears, some of which are likely to be faults. faults. regional linears, some of which are likely to be On the the basis basis of of the the anomalous anomalous concentrations concentrations of of K, K, Nb, Zr, Nb, Zr, On and LREE elements, Sage(1982) interpreted the Dead Horse and LREE elements, Sage(1982) interpreted the Dead Horse Creek Diatreme Diatreme to to be be the the high high level level expression expression of of aa Creek possibly coeval with the emplacement of the the carbonatite, carbonatite, possibly coeval with the emplacement of prairie Lake carbonatite. Smyk et al. (1993) came to Prairie Lake Carbonatite. Smyk et al. (1993) came to aa similar conclusion conclusion and and proposed proposed that that the the carbonatite— carbonatitesimilar emplacement event was followed by a later mineralizing event event emplacement event was followed by a later mineralizing �_______ _____IMETASEDIMENTS 35 DEAD HORSE ::: +++ + •+ + + + + + + ± + + + + + + + +.+ + + + +_+ + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + +++ + + + + -1- +4+4+ + + + + 4 + + + + + + + + + + + + + + . + + + . + + + + + •. . ...... . . . . AD HORSE CENTRAL ++1+. + . + DEAD HORSI . + 4 + HORSE NORTH + + + + + .I .. + + II EAST.::::::::::::::::::: + + + + + + + + + + + + + I*l'I—Iu + 200m + + + + 4 + —. --' ++++++4 'DEAD HORSE SOUTH + + + + + + ,II 4$t4)+ +4+4++'.iPROTEROZOIC ++Ij+++BREccIA fault' + :::: :::::::. INTRUSIVE CWTACT ::••..•. :: : :::::::::::::::::::::::::::::::::::::. ' MONZONITE, .1V///// QUARTZ MONZONITE —. ,. ' /''7c'1/$/I"E. t'1,V7AC7 1 DIABASE ARCHEAN INTR(.IS/VE CONTACT -''.i' MAFIC TO : INTERMEDIA1E METAVOL.CANICS Figure Figure 18: Geological sketch map of the Dead Horse Creek Diatreme Diatreme with with field field trip trip sites sites indicated(modified indicated(m0dified from from Sage, Sage, 1982). 1982). �36 an agpaitic agpaitic nature. nature. This of an This suggestion suggestion is is based based on on the the observation that that HREE(Gd-Lu) HREE(Gd-Lu) are are concentrated concentrated in in the the observation shear cutting the Dead Horse Creek West diatreme mineralized shear breccia(Smyk et al., al., 1993). 1993). This This HREE-enrichment is more more characteristic of agpaitic agpaitic syenites syenites and and peralkaline peralkaline granites granites characteristic carbonatites that are typically typically LREE-enriched. LREE-enriched. Smyk than carbonatites than Smyk et et al. (1993) (1993) correlated this late-stage HREE mineralization al. mineralization with the the possible possible emplacement emplacement of of the the Port Port Coidwell Coldwell complex. complex. Economic Economic Geology Geology The The complex complex was prospected for its uranium content by Gulf Minerals Canada Ltd. Ltd. who found the best mineralized area at the the Dead Horse Creek West subcomplex. The company completed mapping, sampling, diamond drilling and radiometric surveys over over the the complex complex in in 1977-1978. 1977-1978. Unocal Unocal Canada Canada Ltd. Ltd. examined examined the Diatreme in in the the late late 1980's 1980's principally principally the Dead Dead Horse Horse Creek Creek Diatreme for its its I Y content. content. The diatreme has has very high high concentrations concentrations of Zr Zr and and Be Be which have not been been examined examined for for their their economic economic potential. potential. Take Take the the trail trail SW SW for for approximately approximately 750 750 mm from from the the parking parking area. This trail trail is is up and down down and and numerous numerous wet wet and and rocky rocky area. This areas areas exist. exist. - Stop The U-YU-YStop 88 Unocal Unocal YY prospect prospect - Dead Horse Horse Creek Creek West. The Be-Zr mineralization mineralization found found within within the the Dead Dead Horse Horse Creek Creek Diatreme Diatreme is is most highly concentrated concentrated in in the the Dead Dead Horse Horse West West subcomplex subcomplex breccia breccia and is is associated associated with with shearing shearing trending trending 290 290 with with vertical vertical dip. dip. The The mineralization mineralization is is best best exposed exposed at at the in aa narrow narrow zone zone the west west end end of of the the stripped stripped area area in approximately The richest richest mineralization mineralization occurs occurs approximately 15 15 cm wide. The as as very very fine— fine- grained, grained, chocolate-brown, chocolate-brown, vitreous vitreous material. material. Silicification Silicification accompanied accompanied the the mineralization. mineralization. Highest Highest assays assays occur occur over a width of 1.5 1.5 m and and length length of of 82 82 m(Smyk et et al., al., 1993). 1993). The The main minerals minerals are are calcium calcium zirconosilicate zirconosilicate with subordinate subordinate zircon, zircon, uraninite, uraninite, thorite, thorite, monaZite—(Ce) monazite-(Ce) and xenotime-(Y)(Smyk xenotime-(Y)(Smyk et al., al., 1993). 1993). Phenakite(Be2SiO4) Phenakite(Be2Si04) is is the et al., al., 1993). 1993). Smyk Smyk the Be-bearing mineral (Sage, (Sage, 1982, 1982, Smyk Smyk et et et al.(1993) al.(1993) reported reported that that xenotime xenotime occurs occurs as as inclusions inclusions in in niobjan niobian rutile rutile and and that that the the monazite monazite is is associated associated with with calcite, calcite, K-feldspar K-feldspar and riebeckite. riebeckite. Assays Assays range range up up to to 11.6 11.6 %% Zr, Zr, 0.6 0.6 %% Be, 2.5 2.5 % Th, 250 250 ppm Sc, Sc, 1850 1850 ppm 1, Y, 300 300 ppm ppm Nb, 903 903 to to 1004 1004 ppm HREE(sum of of Gd Gd to to Lu) Lu) and and 4600 4600 ppm ppm U(Smyk U(Smyk et et al. al. 1993). 1993). In In the the central central stripped stripped area area of of Dead Dead Horse Horse Creek Creek West West aa heterolithic heterolithic breccia breccia is is well exposed. exposed. This This breccia breccia contains contains subrounded ite subrounded to to subangular subangular clasts clasts of of white whiteto topink pinkquartz quartzite �37 rocks of of the the Sibley sibley Group, Group, the the nearest nearest outcrops outcrops of of which which now now rocks exist 60 km to the west on islands in Lake superior near exist 60 km to the west on islands in Lake Superior near Rossport. The The clasts clasts are areup upto to0.3 0.3 in m in in diameter diameter and and have have Rossport. been exposed by stripping(~age, 1982). At the south end of been exposed by stripping(Sage, 1982). At the south end of the stripped area a 10 to 15 cm wide quartz vein trending the stripped area a 10 to 15 cm wide quartz vein trending phenacite(~e~sio~)(not 115 and and dipping dipping south south contains containsphenacite(Be2SiO4) 115 (not visible to the naked eye). visible to the naked eye). At the the eastern eastern end end of of the the stripped stripped area area exposures exposures of of At heterolithic breccia and a lamprophyre(carbonatite) dike are are heterolithic breccia and a lamprophyre(carbonatite) dike present. present. Follow aa flagged flagged trail trail from from the the partially partially stripped stripped area area Follow below the main stripping for a distance of approximately 550 below the main stripping for a distance of approximately 550 m to south. in to the the south. 9: Cliff Cliff face face of of heterolithic heterolithic breccia. breccia. This This is is one one of of Stop 9: Stop the larger exposures of breccia close to the western contact the larger exposures of breccia. close to the western contact of the the Dead Dead Horse Horse Creek Creek South South subcomplex. subcomplex. The The cliff cliff is is of approximately1010inm high high and and 100 100inm long long and and gives gives aa strong strong approximately channel. response on on aa scintillometer, scintillometer, particularly particularly on on the the KK channel. response The clast-supported, angular to subangular breccia is red to to The clast—supported, angular to subangular breccia is red brick red red with with clasts clasts commonly commonly displaying displaying concave concave centres centres brick and raised raised rims rims suggesting suggesting silicification silicification of of the the margins. margins. and Clasts up up to to 11 mm occur occur but but most most are are less less than than 0.3 0.3 m. m. The The Clasts matrix consists consists of of carbonate, carbonate, biotite, biotite, amphibole amphibole and and quartz quartz matrix and because because of of the the high high carbonate carbonate content content weathers weathers and recessively, leaving leaving the the clasts clasts in in relief. relief. Exposed Exposed within within recessively, is aa carbonate-rich carbonate-rich lamprophyre lamprophyre dike dike the face face of of the the cliff cliff is the his dike dike 28 cm cm wide, wide, trending trending 250 250 and and dipping dipping 75 75 south. south. This 28 sharply cross cross cuts cuts the the breccia breccia and and is is visually visually estimated estimated to to sharply opaque minerals, minerals, 50 50 to to 70 70 percent percent contain 10 10 to to 15 15 %% opaque contain carbonate and and 30 30 to to 40 40 %% biotite(Sage, biotite(~age,1982). 1982). carbonate km and and Return to to the the vehicles vehicles and and continue continue south south to to 25.7 25.7 km Return park on on the the east east side side of of the the road. road. This This is is on on aa curve curve so so be be park careful careful. . Walk aa few few metres metres east east of of the the road road to to the the outcrop outcrop of of Walk side of of the the hill. hill. heterolithic breccia breccia exposed exposed on on the the side heterolithic - Scapolite-replaced heterolithic heterolithic breccia breccia - Discovery Discovery Stop 10: 10: Scapolite—replaced Stop is the the first first outcrop outcrop on on the the Dead Dead Horse Horse outcrop. This This outcrop outcrop is outcrop. Creek Diatreme Diatreme examined examined by by prospectors prospectors working working for for Gulf Gulf Creek Minerals Canada Canada Ltd Ltd searching searching for for the the cause cause of of radioactivity radioactivity Minerals in the the area. area. The The breccia breccia weathers weathers grey, grey, is is clast—supported, clast-supported, in and has has aa "ragged "ragged jagged" jaggedw surface(Sage, surface(Sage, 1982). 1982). The The fragments fragments and are angular angular to to rounded rounded and and generally generallyless lessthan than0.3 0.3inm in in are �38 maximum dimension. The clasts clasts are extensively altered along the margins margins and scapolite scapolite in in fibrous fibrous crystals crystals up to 5 cm may the replace parts of some some clasts. clasts. On weathered surface surface the replace scapolite is easily recognizable recognizable by by its its white white fibrous fibrous habit; habit; scapolite is however, on fresh fresh surface surface it is extremely difficult to recognize in in hand sample. sample. In thin section section the the matrix recognize consists of quartz, carbonate, amphibole, opaques opaques and consists scapolite and and the the clasts clasts show scapolite show replacement replacement by by carbonate, carbonate, amphibole amphibole and and scapolite(Sage, scapolite(Sage, 1982). 1982). to the the vehicles and continue continue south south to Highway 17 at Return to 28.6 km. km. 28.6 Time Time permitting we will go to the optional stop, the McKel].ar Creek Creek diatreme. diatreme. From From the the Junction Junction of of the the Dead Dead Horse McKellar Creek km to to McKellar McKellar Creek. Creek. Creek access access road road turn turn right(west) right(west) 2.2 2.2 km The trail is on on the the west west side trail to to the the McKellar McKellar Creek Creek Diatreine Diatreme is of McKellar Creek Creek and and one one must must park park on on the the shoulder shoulder of of Highway 17 17 so so be careful. There is a skid road going south the east east side side of of McKellar McKellar Creek Creek which which may may also also be be used used as as on the a parking parking site. site. Walk approximately approximately 430 metres north along the skid road and the the two two outcrops outcrops of of breccia breccia representing representing this this diatreme diatreme occur occur the east on the east side side of of the the trail. trail. Stop 11: McKellar Creek diatreme. This This diatreme diatreme was was located located interpreted it it to to be be aa possible possible Animikie Animikie by Walker(1967) who interpreted conglomerate. The fact fact that that it it was was radioactive radioactive and and most most likely intrusive intrusive into into the the enclosing enclosing rocks rocks was was recognized recognized much later(Sage, later(Sage, 1982). 1982). The The McKellar McKellar Creek Creek Diatreme Diatreme is is aa clast supported supported heterolithic heterolithic breccia breccia similar similar to to that that exposed exposed at stop stop 99 on the the Dead Horse Horse Creek Creek South South subcomplex. subcomplex. The The clasts clasts are are red from alteration, alteration, angular angular to to subrounded, subrounded, and and generally 0.3 0.3 m or less less in in maximum dimension. dimension. Sibley Sibley Group Group clasts clasts are are abundant and in in thin thin section section the the quartz quartz displays displays Sibley Group Group curved deformation deformation lamellae. lamellae. In In addition addition to to Sibley clasts and clasts clasts from the the surrounding surrounding Archean Archean rocks, rocks, Rove Rove Formation Formation clasts clasts have also also been identified identified by by thin thin section section examination(Sage, examination(Sage, 1982). 1982). The The space space between between the the clasts clasts is is carbonate—rich carbonate-rich and generally generally weathers weathers low low leaving leaving the the clasts clasts outcrops exposed in relief. Behind the outcrops exposed by the the road, a 22 x 33 m clast clast of rounded Sibley Sibley Group Group rock rock may may be be examined. examined. On On the the basis of outcrop outcrop and soil soil composition composition the the McKellar McKellar Creek Creek Diatreme in size size and and on on the the Diatreme is is estimated to to be 240 240 xx 60 60 mm in basis basis of similar similar alteration alteration styles, styles, interpreted interpreted to to be be coeval coeval 1982). At with the the Dead Horse Horse Creek Creek Diatreme(Sage, Diatreme(Sage,1982). At present, present, the the closest closest outcroppings outcroppings of of Sibley Sibley Group Group rocks rocks are are 60 60 km west, on on islands islands in in Lake Lake Superior Superior near near Rossport. Rossport. �39 DAY DAY 22 The second day is is devoted devoted to to the the Port Coldwell Coldwell Alkalic Alkalic Rock Rock Complex and will consist consist of aa west to east traverse traverse through through the complex along Highway Highway 17. 17. The tour starts starts at at the the Dead Creek access access road road and and distances distances are are given given from from that that Horse Creek The Port Port Coidwell Coldwell Alkalic Alkalic Rock Rock Complex Complex has has been been the the point. The subject of many field trips trips in in the the past and the the reader reader may wish to to refer refer to to these these guidebooks guidebooks for for additional additional information(Puskas, 1970; 1970; Mitchell Mitchell and and Platt, Platt, 1977, 1977, 1982, 1982, information(Puskas, Several stops stops described described by by Mitchell Mitchell and and Platt, Platt, (1994) (1994) 1994). Several are revisited and the the reader should refer to to their their guidebook guidebook for supplementary supplementary detailed detailed mineral mineral chemistry. chemistry. General Geology Geology Coldwell Complex Complex occurs occurs within within the the Trans Trans Superior Superior The Port Coldwell Tectonic Zone(Klasner Zone(K1asner et et al. al. 1982) 1982) where where the the Big Big BayBayTectonic Ashburton Bay(Sage, 1978) 1978) or or Thiel Thiel Fault(Klasner Fault(K1asner et et al. (1982) intersect intersect Archean Archean rocks rocks of of the the Superior province al.(1982) on the the north north shore shore of Lake Lake Superior. Superior. This This fault fault may may be be 140 km north, as as far far as as Chipman Chipman Lake Lake using using extrapolated 140 airphotographs, LANDSAT and and local local geologic geologic mapping(Coates, mapping(Coates, airphotographs, LANDSAT 1970; Sage, 1985). 1985). The Port Coidwell Coldwell Complex occurs occurs on the the northern flank flank of the the Lake Lake Superior Superior Basin Basin at at or or close close to to the the northern Proterozoic—Archean Proterozoic-Archean contact(Sage, contact(Sage, 1991). 1991). The The Slate Slate Islands, Islands, located approximately 10 km southwest of the the Port Port Coldwell Coldwell Complex, have Keweenawan Keweenawan volcanic rocks of the the Osler Osier Group exposed on the shoreline shoreline and as isolated isolated blocks blocks in in diatreme diatreme structures(Sage, 1991). 1991). These islands islands occur very close close to the the intersection intersection of the the Michipicoten Island Island Fault Fault and and the the Fault or or Thiel Thiel Fault. Fault. The The Michipicoten Michipicoten Big Bay-Ashburton Bay Fault Island Fault appears to closely follow follow the the Proterozoic— ProterozoicArchean contact. The Port Port Coidwell Coldwell Complex Complex has has been been mapped (1967), Currie(1980) Currie (1980) and and more more recently recently by by Walker by Tuominen Tuominen(1967), al.(1993a,b). The Port Coidwell Coldwell Complex is is one one of the the et al.(1993a,b). largest alkalic rock complexes complexes in in the world having a surface area of diameter of approximately approxim tely 25 km and a surface 2 (Figure19). km(Figure approximately 490 km 19). Milne(1967) Milne(1967) and and Muir(1982) Muir(1982) completed a limited amount of mapping along the the eastern eastern margin of the the intrusion intrusion and and Walker(1967) completed completed aa similar similar area of mapping along along the the western western margin. margin. Walker(1967) Walker(1967) defined a thermal aureole of contact metamorphism of approximately 1.6 approximately 1.6 km width along the western margin which would envelope envelope the the Dead Dead Horse Horse Creek Creek Diatreme Diatreme structure. structure. Aubut(1977) determined determined that that this this thermal thermal aureole aureole attained attained pyroxene hornfels facies facies where in direct contact contact with the intruding intruding gabbro. gabbro. The Port Coidwell Coldwell Complex consists consists of 3 ring coinplexes(Mitchell and and Platt, Platt, 1978; Currie, 1980) complexes(Mitchell 1980) superimposed superimposed on each other and younging systematically to �Figure 19: Geology nodi4ed Fr-on Volker et at., Colwel1 Alkalic Rock Complex. 1993a,b. Geological_sketch map_oC the Port Mafc Metavotcanic Rocks Rocks Inter-mediate to Fetsic Metavoconc Metasedimentary Rocks Massive to Foloted Grantod Rocks A RC HE AN rELSIC TO INTERMEDIATE P1JTliNIC ROCKS Macc Vo1canc, Subvotcarc and Hypabyssal Intrusive Rocks c3abro Aka1ne Gabbro 0 Recr'ysta1tzed Arphiboe Quartz Syenite Iron-Rich Aug;te Syente Amphbote Syente NepheUne Syenite Amphbo(e Natro1te-NepheLne Syerte AmphiboLe Quartz Syente CDLDWELL LKALIC COMPLEX PRECAMBRIAN LEGEND �41 the southwest southwest along along the the trend trend of the the Trans Trans Superior Superior Tectonic Tectonic the Zone(Figure 19). 19). The oldest ring complex is centered centered north north Craddock Cove, Cove, the the next north north of the the town town of of Port Port of Craddock Coldwell and the the youngest is is centered on on Pic Pic Island(Currie, Island(Currie, Coidwell 1980). 1980). Mitchell and Platt(1994) classified these centres as Centre 11 - Saturated Saturated alkaline rocks with follows: Centre rocks oversaturated residue; Centre Centre 2 — Miascitic oversaturated residue; Miascitic alkaline rocks undersaturated residue residue and and Centre Centre 33 — Alkaline Alkaline rocks with undersaturated with with oversaturated oversaturated residue. residue. - - - The oldest consist dominantly dominantly of an an oldest rocks rocks of Centre 11 consist olivine gabbro gabbro outer outer ring and a ferroaugite ferroaugite centre. The The gabbros have been studied studied as a consequence consequence of their their sulfide sulfide content and are are described below under economic economic geology. Shaw(1994) subdivided subdivided the eastern eastern gabbro into into four four intrusions; Gabbronorite, Two Duck Lake Intrusion, Layered Gabbro Gabbro and and Malpas Malpas Lake Lake Intrusion. Intrusion. The The most primitive primitive gabbro gabbro is the Two Duck Lake Lake Intrusion Intrusion which is equivalent equivalent to to a high-Al in composition(Shaw, composition(Shaw, 1994). 1994). The The ferroaugite ferroaugite high-A1 basalt basalt in syenites syenites have have been been classified classified as as laurvikite laurvikite by by Puskas(1967) Puskas(1967) and have undergone undergone detailed detailed study study by by Jago(1980), Jago(1980), McGill (1980), Mitchell Mitchell and and Platt(1978) Platt(l978) and Whittaker(1976). McGill(1980), The detailed composition composition of the amphiboles amphiboles in centres centres 11 and 3 have been 146—149). The been summarized summarized by by Mitchell, Mitchell, (1990 (1990p. p.146-149). augite syenite augite syenite contains contains minor amounts amounts of fayalite fayalite olivine(Fa83—98)(Whittaker, 1976; olivine(Fa83-98)(Whittaker, 1976; Mitchell Mitchell and and Platt, Platt, 1978). 1978). The ferroaugite ferroaugite syenite syenite was highly evolved at the the time time of by fayalitic olivine, olivine, diopsidicintrusion as revealed by hedenbergite and (Mitchell and hedenbergite and ferro-hastingsitic ferro-hastingsitic hornblende hornblende(Mitchel1 Platt, 1978). The The REE mineralogy of the syenites syenites and associated associated pegmatites pegmatites was was studied studied by by Nicol(1990). Nicol(1990). The centre centre 22 rocks rocks consist dominantly of an outer outer ring ring of alkalic biotite gabbro and a inner core of nepheline nepheline syenite. The syenite syenite has been studied studied by by Whittaker(1976), Whittaker(1976), McGill(1980), Clark(1983) McGill(1980), Clark(1983) and Mitchell and Platt(1982). Platt(1982). Mitchell and Platt(1982) interpret the nepheline nepheline syenite syenite to to be the the product of fractional fractional crystallization crystallization of a basaltic magma. Centre Centre 33 syenites syenites have have been been studied studied in in detail detail by by Jago(1980), Jago(1980), Lukosius—Sanders(1988) Lukosius-Sanders(1988) and Mitchell et al.(1993). al.(1993). The The REE rare—metal minerals associated with centre 3 were and rare-metal concentration of examined by Nicol(1990) who documented the concentration REE REE and rare rare metals metals in in the residual residual liquids liquids of these these syenitic inagmas. Mitchell et et al. al. have have interpreted interpreted the centre syenitic magmas. Mitchell 3 syenites to be the differentiation products of more than mantle—derived basalt magma. magma. These syenites one batch of mantle-derived syenites now represent represent the the product product of multiple intrusion, intrusion, contamination contamination and brecciation giving rise to complex field and petrologic relationships(Mitchell et al. 1993). relationships(Mitchel1 1993). �42 Lainprophvres Lamprophyres are are abundant abundant'within the centre centre 11 rocks, rocks, Lamprophyres within the in the the western western part part of of the the complex. complex. They They have have particularly in been studied studied by by Aubut(1977), Aubut(1977), Evans Evans(1984), Laderoute(1987), been (1984), Laderoute(1987), Mitchell et et al. al. (1991) (1991) and and those those external external to to the the complex complex at at Mitchell McKellar Harbour Harbour by by Platt Platt and and Mitchell(1979, Mitchell(1979, 1982a,) 1982a,) Platt Platt McKellar 1983). The The lamprophyres lamprophyres have have aa variety variety of of strikes strikes but but et al. 1983). the dominant trend trend is is approximately approximately east-west east-west with with greatly greatly the subordinate NW and and NE trends. The subordinate The lamprophyres lamprophyres are are generally generally less than than 1.0 1.0 m in in width width and and are are interpreted interpreted to to be be less dominantly related to centre22 magmatism(Mitchell magmatisin(~itchel1et et al., al., dominantly tocentre Mitchell and Platt(1994) summarized summarized classification classification of of 1991). Mitchell the lamprophyres lamprophyres and and one one alkalic alkalic basalt basalt dike dike in in their their order order the of emplacement emplacement as as follows: follows: of MAFIC OCELLAR OCELLAR LAMPROPHYRES o foftthe h e camptonitic c a m p t o n i t i c variety, variety, MAFIC LAMPROPHYRES These These rocks rocks contain c o n t a i n phenocrysts phenocrys t s of o f olivine, 01ivine, aluminous a 1uminous pyroxene, pyroxene, 1. 1. with w i t h or or without w i t h o u t carbonate-rich c a r b o n a t e - r i c h ocelli, o c e l l i , are a r e widespread. widespread. k a e r s u t i t e and and titanian t i t a n i a n ferroparg'asite f e r r o p a r g a s i t e set n aa matrix kaersutite set iin matrix o off magnesian hastinsgite, h a s t i n s g i t e , augite, a u g i t e , plagioclase, p l a g i o c l a s e , biotite, biotite, magnesian m a g n e t i t e , sphene sphene and and minor minor nepheline. n e p h e l i n e . The The ocelli ocelli are are magnetite, commonly commonly concentrated c o n c e n t r a t e d bby y f flow l o w ddifferentiation i f f e r e n t i a t i o n in i n the the centers centers of o f the the dikes. d i k e s . In a d d i t i o n t o c a l c i t e , the ocelli ocelli contain contain scapolite, and f l u o r i t e . s c a p o l i t e , epidote e p i d o t e and In addition to calcite, the fluorite. 2. 2 . QUARTZ-BEARING QUARTZ-BEARING MAFIC MAFIC LAMPROPHYRES LAMPROPHYRES which w h i c h are are camptonites, camptonites, o f quartz q u a r t z with w i t h aa hexagonal hexagonal c h a r a c t e r i z e d by b y phenocrysts p h e n o c r y s t s of characterized habit. The phenocrysts p h e n o c r y s t s are a r e typically t y p i c a l l y resorbed resorbed and and mantled m a n t l e d by by h a b i t . The c l i n o p y r o x e n e . Carbonate Carbonate ocelli o c e l l i are a r e commonly commonly present. p r e s e n t . The The clinopyroxene. p r i n c i p a l exposures e x p o s u r e s of o f these these dikes dikes are a r e to t o be be found found within within principal the the gabbros gabbros and and ferroaugite f e r r o a u q i t e syenites syenites located l o c a t e d on on the the lakeshore (see Aubut, l a k e s h o r e to t o the the west w e s t of o f the t h eLittle L i t t l ePic p i cRiver River(see Aubut, 1977). 1977). 3. 3 . SANNAITE-TYPE SANNAITE-TYPE LAMPROPHYRES LAMPROPHYRES characterized c h a r a c t e r i z e d by b y the the presence presence of o f euhedral e u h e d r a l phenocrysts p h e n o c r y s t s of o f aluminian a l u m i n i a n and and chromian chromian diopside. diopside. These These pyroxenes p y r o x e n e s exhibit exhibit complex complex zonation z o n a t i o n and and mantling m a n t l i n g due d u e to to the The groundmass groundmass is i s composed composed of of the effects e f f e c t s of o f magma magma mixing. m i x i n g . The ferroan f e r r o a n paragasite, p a r a g a s i t e , aluminian a l u m i n i a n diopside, d i o p s i d e , biotite, b i o t i t e , albitized albitized plagioclase p l a g i o c l a s e and and epidotized e p i d o t i z e d alkali a l k a l i feldspar. feldspar. 4. 4 . MONCHIOUITIC-TYPE MONCHIOUITIC-TYPE LAMPROPHYRES LAMPROPHYRES with w i t h silicate s i l i c a t e and and carbonate c a r b o n a t e ocelli. o c e l l i . These These rocks rocks are a r e characterized c h a r a c t e r i z e d by b y the the presence p r e s e n c e of o f brown brown titaniferous t i t a n i f e r o u s ferro—paragasite f e r r o - p a r a q a s i t e phenocrysts phenocrysts The silicate s i l i c a t e ocelli ocelli set set in i n aa matrix m a t r i x of o f devitrified d e v i t r i f i e d glass. g l a s s . The consist c o n s i s t of o f paragasitic p a r a g a s i t i c amphibole, amphibole, alkali a l k a l i feldspar f e l d s p a r and and analcime. a n a l c i m e . The The monchiquites m o n c h i q u i t e s are a r e considered c o n s i d e r e d to t o be be heteromorphs heteromorphs of o f the the camptonites(Mitchell c a m p t o n i t e s (Mitchell et e t al. a1 1991). 1991) . . �43 5 . FELDSPAR FELDSPAR GLOMEROPORPHYRY GTJOMEROPORPHYRY MID AND ALKALI ALKALI BASALT BASALT DIKES DIKES. These These 5. n o t been been studied s t u d i e d extensively e x t e n s i v e l y but b u t may may be be not r e p r e s e n t a t i v e of o f contemporaneous contemporaneous basic b a s i c magmas. magmas. representative r o c k s have have rocks . 6 . ANALCIME ANALCIME TINGUAITE(heronites). TINGUAITE ( h e r o n i t e s ) Porphyritic P o r p h y r i t i c salic s a l i c dikes dikes 6. commonly of o f an an orange orange or o r reddish—brown reddish-brown colour. c o l o u r . Phenocrysts commonly Phenocrysts be found, found, set set o f analcime, analcine, alkali a l k a l i feldspar f e l d s p a r and and nepheline nepheline can can be of iinn aa fine f i n e grained grained m a t r i x o f a l t e r e d a l k a l i f e l d s p a r s and matrix of altered alkali feldsparè and a c n i t i c pyroxene. pyroxene. The The least l e a s t altered a l t e r e d occurrences occurrences of o f this this acmitic s u i t e are are found found in i n the t h e country country rocks r o c k s close c l o s e to t o the t h e eastern eastern suite margin of o f the t h e complex complex and and along along railroad r a i l r o a d tracks t r a c k s in i n the t h e Heron Heron margin Bay region. r e g i o n . Modern Modern mineralogical mineralogical studies s t u d i e s of o f these t h e s e rocks r o c k s have have Bay n o t been been undertaken. undertaken. not The lamprophyres lamprophyres are are common common in in centre centre 11 rocks rocks less less common common in in The centre 22 and and rare rare in in centre centre 3( 3( Mitchell Mitchell et et al., al., 1991; 1991; centre Mitchell and and Platt, Platt, 1994). 1994). Mitchell Mitchell et et al.(1991) al.(1991) interpreted interpreted Mitchell the lamprophyres to be the product of centre 2 magmatism and the lamprophyres to be the product of centre 2 inagmatism and their absence within a given lithologic unit may be used as their absence within a given lithologic unit may be used as rocks from from centres centres 11 one criterion criterion for for separating separating centre centre 33 rocks one and 2 . The Marathon lamprophyre dikes dated as 1.65 +- 0.12 0.12 and 2. The Marathon lainprophyre dikes dated as 1.65 +Ga by the Rb-Sr technique(P1att and Mitchell, 1983) and the Ga by the Rb-Sr technique(Platt and Mitchell, 1983) and the Slate Island lamprophyre dated as 282 +11 Ma to 310 +18 Slate Island lamprophyre dated as 282 +- 11 Ma to 310 +— 18 Ma by the K-Ar technique(Sage, 1991) have been redated by Ma by the K-Ar technique(Sage, 1991) have been redated by Heaman(persona1 communication, communication, 1994) 1994) as as 1145 1145 +15/—b +15/-10 Ma Ma and and Heaman(personal 1141 +9 Ma respectively using the U-Pb technique on 1141 +- 9 Ma respectively using the U-Pb technique on perovskite. The The Marathon Marathon dikes dikes and and the the Slate Slate Island Island dike dike perovskite. intrude the Archean supracrustal assemblage west of the Port Port intrude the Archean supracrustal assemblage west of the Coldwell Complex and may represent a pro-Port Coldwell Coidwell Complex and may represent a pre-Port Coidwell Complex alkalic alkalic event event since since the the Complex Complex has has been been dated dated by by Complex +1 MafHeaman and Machado, 1992). the same method at 1108 the same method at 1108 +- 1 Ma (Heaman and Machado, 1992). Diatremes Diatremes On the the west west coast coast of of the the Coldwell Coldwell peninsula, peninsula, 4.0 4.0 km km south south of of On the Neys Provincial Park headquarters, is a diatreme the Neys Provincial Park headquarters, is a diatreme structure described described in in detail detail by by Balint(1977). Balint(1977). This This diatreme diatreme structure is approximately 75 x 240 m and contains rounded to angular is approximately 75 x 240 and contains rounded to angular clasts of of Port Port Coidwell Coldwell Complex Complex rocks. rocks. The The long long axis axis of of the the clasts intrusion strikes north of east and it appears to have a intrusion strikes north of east and it appears to have a vertical dip(Sage, dip(Sage, 1982). 1982). The The rounding rounding of of the the clasts clasts vertical suggests turbulent flow in a high velocity gas-solid suggests turbulent flow in a high velocity gas-solid system(Balint, 1977, considered the the systein(Balint, 1977, Sage, Sage, 1982). 1982). Sage(1982) Sage(1982) considered diatreme to be a high-level feature similar to those found diatreme to be a high-level feature similar to those found in porphyry porphyry copper copper systems systems exposed exposed at at high high structural structural in The origin of the this diatreme is not comparable to to levels. levels. The origin of the this diatreme is not comparable the Dead Horse Creek and McKellar Creek diatremes on the the Dead Horse Creek and McKellar Creek diatremes on the east flank flank of of the the Port Port Coidwell Coldwell Complex Complex which which are are likely likely the the east high level expression of mantle-derived carbonatite high level expression of mantle-derived carbonatite magmatism(Sage, 1982). 1982) magmatism(sage, . Hornfelsed CaD Cap Rocks Rocks Hornfelsed �44 In In the the Wolf Wolf Camp Camp Lake Lake area area and and at at aa number number of of sites sites on on the the north flank flank of of the the Port Port Coidwell Coldwell Complex Complex subhorizontal subhorizontal north massive to to amygdaloidal amygdaloidal flow massive exposed(Wa1ker flow rocks rocks are are exposed(Walker 1993a,b). 1993a,b). These These volcanic volcanic remnants remnants have have been been preserved preserved by by fracturing and down—dropping down-dropping of the the former former volcanic ring fracturing edifice above the the intrusion(Sage, intrusion(Sage, 1986). 1986). The The basaltic rocks edifice vary from from fresh fresh andesine—oligoclase andesine-oligoclase basalt, basalt, hornfelsed hornfelsed vary to metasomatized metasomatized basalt in in flows flows up to to 55 m basalt to thick(Mitchel1 and Platt, 1994). 1994). Nicol(1990) Nicol(1990) has studied studied the the thick(Mitchell flows and considers considers them to be of tholeiltic tholeiitic lineage. lineage. The flows hornfelsed flows flows contain contain some some orthopyroxene orthopyroxene and and the the amygdule amygdule hornfelsed fillings greenish caic—silicate calc-silicate fillings were were metamorphosed metamorphosed to to aa greenish mineral mineral assemblage. assemblage. Xenoliths Xenol iths In Nicol(1990), In addition addition to to the the study study of of xenoliths xenoliths by by Nicol(1990), Mitchell Mitchell and and Platt(1979) Platt(1979) examined examined feldspar feldspar porphyry xenoliths xenoliths in in nepheline nepheline syenite syenite displaying displaying nephelinenephelineplagioclase plagioclase intergrowths intergrowths and determined that the the nepheline has has likely likely resulted resulted from a Na—K Na-K cation exchange. This metasomatism metasomatism caused caused desilication desilication of of the the andesine andesine phenocrysts phenocrysts but did did not not form form nepheline nepheline in in the the groundmass(Mitchell groundmass(Mitche1l and and Platt, developed alkali alkali feldspars of Platt, 1979). 1979). The The nietasomatism metasomatism developed aa wide wide range range of of compositions(Mitchell compositions(Mitche11 and and Platt, Platt, 1979). 1979). Isotone Studies Studies Isotope Excluding isotopic isotopic studies studies directed directed toward toward age age determinations, determinations, Heaman and Machado(1992) examined Sr, Nd and Pb Pb isotopes isotopes and and determined determined that that Midcontinent MidcontinentRift Riftmagnias magmas have aa uniform uniform Nd isotopic isotopic composition. composition. Heaman and have Machado(1992) compared 1.1 1.1 Ga carbonatites carbonatites with Port Coldwell Coldwell Complex Complex data data and and found found that that carbonatites carbonatites have have lower lower Rb/Sr Rb/Sr and and higher higher U/Pb U/Pb and and Sm/Nd Sm/Nd ratios. ratios. This This means means that that there there were were two two isotopic isotopic reservoirs reservoirs present present at at 1.1 1.1 Ga; Ga; an an enriched plume—component plume-component represented represented by by most most Midcontinent Midcontinent Rift Rift magmatisiu magmatism and a carbonatitic carbonatitic coniponent(Heaman component(Heaman and and Machado, (1992) interpreted Machado, 1992). 1992). Heaman Heaman and and Machado Machado(1992) interpreted the the presence presence of of nonradiogenic nonradiogenic Pb Pb compositions compositions and negative negative Nd values Coldwell magmas magmas as as values in in silica—saturated silica-saturated Port Port Coldwell documenting documenting the the interaction interaction of of plume—derived plume-derived mantle mantle melts melts lower crust. crust. with with low low U/Pb U/Pb granulite-facies granulite-facies lower Geochronolocrv Geochronolociy Currie(1980) provided some some K-Ar isotopic isotopic ages ages and and Rb/Sr Rb/Sr isotopic isotopic ages ages have have been been provided provided by by Platt Platt and and Mitchell(1982b) Mitchell(1982b) and and Bell Bell and Blenkinsop(1980). Blenkinsop(1980). The means of determining determining the the Rb/Sr Rb/Sr isochron isochron of of Platt Platt and and Mitchell(l982b) Mitchell(1982b) �45 was discussed discussed by Blenkinsop was (1983) and Platt Platt and and Blenkinsop and Bell (1983) Mitchell(1984). isotopic ages ages were were first first Mitchell(1984). Uranium-lead isotopic et al. al. (1985) (1985) and and the the results results discussed discussed undertaken by Turek Turek et undertaken by Thorpe(1986) Thorpe(l986) and Turek Turek et et al(1986). al(1986). Heaman Heaman and and Machado(1992) reported reported aa U-Pb isotopic isotopic age age of of 1108 1108 +— +- 11 Ma which is age. Heaman and is now accepted accepted as the the most accurate accurate age. could not not distinguish distinguish the the three three intrusive intrusive Machado(1992) could isotopic ages. ages. The The distinction distinction centres on the basis of isotopic between these intrusive intrusive centres centres rests rests on on field field observations. observations. Local Structure Structure The Port Coidwell Coldwell Complex Complex occurs occurs at at the the Proterozoic—Archean Proterozoic-Archean contact just north of the the intersection intersection of the the Michipicoten Michipicoten 1978) Island Fault and the the Big Bay-Ashburton Bay Fault(Sage, 1978) Fault(Klasner et al., or Thiel Fault(K1asner al., 1982). 1982). The The Michipicoten Michipicoten Island Fault parallels and may mark the the limits limits of the the Proterozoic basin. The The Port Port Coldwell Coldwell Complex Complex lies lies within within the the Proterozoic Trans Superior ZonefKlasner et et al., al., 1982). 1982). Within Within Superior Tectonic Tectonic Zone(Klasner the Port Coidwell Coldwell Complex Complex mafic mafic banding, banding, trachytoidal trachytoidal textures textures and xenolith xenolith preferred preferred elongation elongation may may locally locally be be used to outline outline the the configuration configuration of of parts parts of of the the various various centres centres of intrusion. These These planar planar features features have have been been used used by Currie(1980) to to speculate speculate on on the the centres centres of of emplacement emplacement Coldwell for the three ring complexes complexes that make up the the Port Coldwell Complex. The three three intrusive intrusive centres centres young young in in aa southwest southwest Complex. direction toward the the Slate Slate Islands(Sage, Islands(Sage, 1991) 1991) and and along along the the Big Bay-Ashburton Bay Fault Fault trend. trend. The The successive successive emplacement of superimposed superimposed ring ring complexes complexes accompanied accompanied by by repeated faulting faulting and and stoping, sloping, multiple multiple intrusion, intrusion, metamorphism and metasomatic metasomatic activity activity has has created created very very complex petrographic, petrologic complex petrographic, petrologic and and field field relationships. relationships. The presence of abundant abundant xenoliths xenoliths in in some some lithologies lithologies and and large roof pendants indicate indicate that the the complex complex is is barely unroof ed and and is is thus thus exposed exposed at at a a very very high high structural structural unroofed level. Lilley(1964) proposed that that the the Port Port Coldwell Coldwell Complex Complex is is aa funnel-shaped intrusion funnel-shaped intrusion and Puskas(1967) has proposed that it is a lopolith. Currie(1980) considers the complex complex to to consist of an interlocking interlocking group group of of cone cone sheets sheets and and ring ring dikes. The arcuate outer outer gabbro gabbro unit unit of centre centre 11 may be be interpreted as a ring dike as may the alkaline biotite 2. Arcuate Arcuate faults faults and and large large down—dropped down-dropped gabbro of centre centre 2. roof pendants are are consistent consistent with with ring ring fracturing fracturing and subsidence, subsidence, characteristic characteristic of of caldera caldera emplacement(Sage, emplacement(Sage, Mitchell and (Figures 1986, Mitchell and Platt, Platt, 1982b, 1982b, 1994, 1994, Walker, Walker, 1993) 1993)(Figures 20, 21). 21). Each intrusive intrusive centre centre has has likely likely undergone undergone aa similar Platt(1994) similar series series of of intrusive intrusive events. events. Mitchell Mitchell and and Platt(1994) consider intrusive intrusive centres centres 22 and and 33 to to be exposed exposed at at aa higher higher level than centre one one due due to to the the abundance abundance of of xenoliths; xenoliths; however, the large large xenoliths xenoliths or or roof roof pendants pendants near near Wolf Camp Camp �-4 c 4 c u 3 a 0 -4 -4 JJ h Q 6 >I10 JJ m a- dr-1 A Figure 20: Idealized ap of rock type distribution in a ciaple ring coaplex(froa sage, 1986). a 0 & a 0> u a H N -4-4 hi - on 2!3 N à -44 4 ^ a a a o a Â¥ 0 04 .. B> c 6  h 2tna% a 1986). Figure 21: Idealized vertical section displaying rock type in a siaple alkalic ring complex(from Sage, distribution * NAN?%.I MAPIC ANO %L,mAMA,,c øocs �47 Lake and and in in the the northern northern parts of of the the complex are largely Lake centered on on centre centre 1. 1. The The difference difference in in the level of centered structural exposure between the three centres is not likely to be very very great. great. Sage(1986) Sage(1986) suggested suggested that the southern to of the the Port Port Coldwell Coldwell Complex Complex may be exposed at a part of slightly deeper deeper level slightly level than than that that of of the the north due to the the abundance abundance of of xenoliths xenoliths and and rook rook pendants in the northern part part of of the the intrusion. intrusion. Geophysics Geophysics and and LANDSAT LANDSAT Imagery Imauerv The The Port Port Coldwell Coldwell Complex Complex is is covered covered by by LANDSAT LANDSAT imagery(Canada Centre Centre for for Remote Remote sensing, Sensing, 1987) 1987) and and the the imagery(Canada large large Port Port Coldwell Coldwell Complex Complex is is easily easily recognized. recognized. Local Local faults be faults and and linears linears are are easy easy to to trace trace and and often often can can be extended beyond beyond the the limits extended limits of of the the complex. complex. Meru(1965) studied studied the the angle angle of of emergent emergent seismic seismic P waves at Meru(1965) Marathon, Marathon, Ontario Ontario and and interpreted interpreted his his data to indicate that the the Moho Moho below below Marathon Marathon dips dips southwest southwest under under the the Lake Lake Superior Superior Basin Basin at at 44 degrees. degrees. He He also also concluded concluded that that the the crust crust was was much much thicker thicker to to the the southwest southwest of of Marathon Marathon than than to to the the northeast(Meru, northeast (Meru, 1965). 1965) . Lilley(1964) Lilley(1964) examined examined the the aeromagnetic aeromagnetic expression expression of of the the Port Port Coldwell Coldwell Complex Complex and and observed observed intense intense negative negative anomalies anomalies over over the the eastern eastern gabbros gabbros of of centre centre (Figure (Figure 22). 22). The atat 1108 -F-+- 11 The emplacement emplacement of ofthe thePort PortCoidwell ColdwellComplex Complex 1108 ina(Heaman and Machado, Machado, 1992), therefore, took ma(Heaman and took place place just just prior prior to to aa magnetic magnetic reversal reversal that that occurred occurred between between 1096.2 1096.2 +— +1.8 1.8 Ma and and 1097.6 1097.6 Ma(Davis Ma(Davis and and Paces, Paces, 1990). 1990). The The age age of of reversal reversal may may closely closely approximate approximate the the age age of of reversal reversal for for the the Osler Osier Group(Davis Group(Davis and and Paces, Paces, 1990, 1990, Paces Paces and and Miller, Miller, 1993). 1993). Isomagnetic Isomagnetic contouring contouring of of the the aeromagnetic aeromagnetic data data clearly clearly distinguishes distinguishes the the Port Port Coldwell Coldwell Complex Complex from from the the surrounding surrounding Archean Archean rocks rocks and and reveals reveals aa prominent prominent circular circular pattern(Figure pattern (Figure 22). 22) . Currie(1980) Currie(1980) cites cites gravity gravity data data as as indicating indicating that that the the Port Port Coidwell Coldwell Complex Complex has has aa mafic mafic component component at at depth(Figure depth(Figure 23). 23). Since Since mostly mostly light light syenitic syenitic rocks rocks are are exposed exposed at at surface surface postulation Ic rocks rocks beneath the postulation of of maf mafic the syenites syenites is is required required to to explain explain the the positive positive gravity gravity anomaly. anomaly. Mitchell Mitchell et et al. al. (1983) modeled the gravity data and suggested that the (1983) modeled felsic to 55 km—thick km-thick layer layer over over aa felsic rocks rocks represent represent aa 33 to differentiated differentiated basic basic intrusion intrusionconsisting consistingof of3 3toto5 5kin km of of gabbro The presence presence gabbro underlain underlain by by peridotite peridotite or or pyroxenite. pyroxenite. The of of large large volumes volumes of of mafic mafic rocks rocks at at depth depth supports supports the the concept concept that that some some of of the the Port Port Coidwell Coldwell Complex Complex felsic felsic rocks rocks are are differentiates differentiates (Figure (Figure 23). 23). During During Keweenawan Keweenawan rifting rifting upper Ic magmas magmas migrated from the upper mantle-derived mantle-derived maf mafic the southwest southwest to to the the northeast northeast and and came came to to rest rest at at Port Port Coldwell(Mitchell Coldwell(Mitchel1 et et al., al., 1983). 1983). �48 Figure 22: 22: Aeromagnetic Aeromagnetic map of of the the Port Coldwell Alkalic Figure Alkalic Rock Complex(ODM—GSC, Complex(0DM-GSC, l963a,b,c,d). 1963a,b,c,d). Rock Figure Coidwell Alkalic Figure 23: 23: Bouguer Bouguer anomaly anomaly map map of of the the Port Coldwell Rock Rock Complex. Complex. The The solid solid straight straight line line is is the location of a gravity profile(fr0m Mitchell Mitchell et et al., al., 1983). gravity profile(from 1983). �49 The The Port Port Coidwell Coldwell Complex Complex and and surrounding surrounding Archean Archean terrane terrane has has been been covered covered by a reconnaissance reconnaissance airborne airborne gamma—ray gamma-ray spectrometer survey(Graham and Bonham-Carter, Bonham-Carter, 1993). 1993). The The spectrometer in the the Port Port Coidwell Coldwell Complex Complex concentration concentration of of radioelements radioelements in is high in in contrast to the enclosing Archean supracrustal supracrustal rocks. rocks. Graham Graham and and Bonham-Carter (1993) (1993) indicated indicated that that in in general each each lithologic lithologic unit may be distinguished on on the the general basis basis of of its its gross gross radiometric radiometric signature signature and and that that the the three three intrusive intrusive centres centres display display minor minor correlatable correlatable differences. differences. The Port Port Coldwell Coldwell Complex Complex is is also also covered covered by side-scanning side-scanning The radar radar imagery imagery completed completed by the the Canada Canada Centre Centre for for Remote Remote Sensing Bonham— Sensing and these these data were merged by Graham and BonhamCarter(1993) Carter(l993) in in their their study study of the the radiometric radiometric data. The The radar imagery imagery reflects reflects the the rugged rugged topography topography of the the Port Port radar Coidwel]. Complex area. Coldwell Complex area. Economic Geolow Economic Geoloqy The The Port Port Coidwell Coldwell Complex had several several small small quarries quarries developed developed for for building building stone stone in in the the ferroaugite ferroaugite syenite syenite close close to to the the CPR CPR tracks tracks and the the town town of Marathon in in the the early early l930's(Puskas, 1930fs(Puskasf 1967). These efforts efforts failed failed to to be commercial and and the the efforts were soon soon abandoned. The Port Port commercial Coldwell Complex Complex has has repeatedly repeatedly been been evaluated evaluated as as aa Coidwell potential source source for for building stone stone due due to to the the pronounced pronounced potential blue to gold schiller texture of the feldspars in the blue to gold schiller texture of the feldspars in the ferroaugite syenite. syenite. In the late late 1930's 1930fs efforts were made to to ferroaugite evaluate evaluate the the titaniferous titaniferous magnetite magnetite showings showings in in the the gabbros(Puskasf 1967). 1967). Other Other than than surface surface peripheral gabbros(Puskas, peripheral trenching and and pitting pitting little little work work was was completed completed and and no no trenching tonnage tonnage was was outlined. outlined. The The titaniferous titaniferous magnetite magnetite at at Stop Stop 15 15 occurs in in the the area area where where most efforts efforts were were expended expended in in occurs search search of of titaniferous titaniferous magnetite magnetite deposits. deposits. 1950fs porphyritic syenite syenite dikes were prospected for for In the the 1950's In their Nb Nb and and Zr Zr content. content. The their The principal principal areas areas of of investigation were Port Port Munro Munro near near the the former former siding siding of of investigation Angler on on the the CPR CPR and and north north of of west west from from the the west end end of of Angler Craddock Lake Lake within within the the interior. interior. None None of of these these efforts efforts Craddock proved sufficient sufficient grade grade or or tonnage tonnage to to be be of of economic economic proved interest. One of these dikes was tested for for U and Th without interest. success. success. In In the the 1960's l96Ofs the the nepheline nepheline syenites syenites on on the the Neys Neys Peninsula Peninsula and Pic Pic Island Island were were evaluated evaluated as as aa possible possible source source of of and ceramic grade grade nepheline. nepheline. This This work work proved proved unsuccessful unsuccessful ceramic because the the impurities impurities could could not not be be removed removed from from the the because nepheline. nepheline. The The poikilitic poikilitic nepheline nepheline commonly commonly contains contains tiny tiny inclusions of of ferromagnesian ferromagnesian minerals minerals which which cannot cannot be be inclusions removed removed in in milling, millingf thus thus the the desired desired ceramic ceramic grade purity purity could could not not be be obtained. obtained. �50 The Port Port Coldwell Coldwell Complex Complex offers offers the the best potential potential as as aa The source source for for Cu-Ni-PGE. Cu-Ni-PGE. Exploration Exploration of of the the suiphide sulphide mineral mineral assemblages assemblages in in the the peripheral peripheral gabbros gabbros of of centre centre 11 on on both both the western western and and eastern eastern flanks flanks of of the the intrusion intrusion started started in in the the the 1950's 1950fs and and peaked peaked in in the the 1960's. 1960fs. Most Host of of this this work work was was done in in the the eastern eastern gabbro gabbro north north of of Marathon Marathon by by Anaconda Anaconda done American TWODuck Duck American Brass Brass Ltd. Ltd. on on aa deposit deposit now known known as as the the Two Lake Occurrence. Occurrence. Watkinson Watkinson and and Ohnenstetter(1992) Ohnenstetter(l992) indicated indicated Lake that Two Duck Duck Lake Lake Occurrence Occurrence occurs occurs in in aa separate separate that the the Two gabbroic intrusion intrusion within within the the outer outer ring ring of of centre centre 11 gabbro. gabbro. gabbroic The mineralization mineralization occurs occurs in in coarse coarse gabbro gabbro and and pegmatite pegmatite and and The is is interpreted interpreted to to be be the the product product of of interaction interaction of of aa magmatic mineral mineral assemblage assemblage with with fluids fluids of of mixed mixed magmatic magmatic magmatic origin and and fluid fluid generated generated by by the the breakdown breakdown of of abundant abundant origin xenoliths8 principally principally felsic felsic metavolcanic metavolcanic rocks(Watkinson rocks(Watkinson xenoliths, and Ohnenstetter, Ohnenstetter, 1992). 1992). Good Good and and Crocket(1994b) Crocket(1994b) have have and proposed that that the the Two Two Duck Duck Lake Lake Occurrence Occurrence was was intruded intruded as as aa proposed plagioclase-rich crystal crystal mush mush which which had had fractionated fractionated at at plagioclase-rich depth depth and and contained contained suiphide sulphide droplets. droplets. The The suiphide sulphide mineral mineral assemblage precipitated precipitated after after rapid rapid solidification solidification of of the the assemblage crystal crystal mush mush with with little little Cu Cu or or PGE PGE migration(Good migration(Good and and Crocket, Crocket8 1994b). 1994b). Good Good and and Crocket(1994b) Crocket(1994b) suggested suggested that that the the origin origin of of the the mineralization mineralization is is analogous analogous to to that that of of the the Duluth Duluth Complex. Complex. Shaw(1994) Shaw(l994) has has interpreted interpreted the the Two Two Duck Duck Lake Lake Intrusion Intrusion to to be be the the most most primitive primitive unit unit of of 44 subunits subunits within within the the eastern eastern gabbro gabbro and and similar similar to to high—Al high-A1 basalt. basalt. This This magma magma underwent underwent fractionation fractionation in in an an open open system system with with removal removal and and recharge 10 cycles cycles in in an an expanding expanding magma magma recharge in in 33 — 10 chainber(Shaw, chamber(Shaw8 1994). 1994). The The reader reader should should refer refer to to Shaw(1994) Shaw(l994) for for details. details. In In the the 1980's l98Ofs interest interest in in the the Two Two Duck Duck Lake Lake deposit deposit was was revived revived by by Fleck Fleck Resources Resources Ltd. Ltd. who who have have outlined Cut0.04 0.04 %%Ni, ~i~ outlined 37,000,000 3780008000tons tons grading grading 0.31 0.31 %% Cu, 251,000 2518000 oz oz Pt, Pt8 1,001,000 l8OOl8O0Ooz oz Pd, Pd8 84,000 848000 oz oz Au Au and and 43,000 43#000oz oz Rh(Canadian ( See %(Canadian Nines MinesHandbook, Handbook81993—1994, 1993-1994#p.p.145) 145)( See Stops Stops 25, 25# 27). 27). Platinum—group—element Platinum-group-element mineralization mineralization is is also also present present in in association association with with aa large large block block of of gabbro gabbro within within the the north north central central part part of of the the Port Port Coidwell Coldwell Complex. Complex. This his is is known as as the the Geordie Geordie Lake Lake Occurrence Occurrence and and grade grade and and tonnage tonnage known have have not not been been determined. determined. The The Geordie ~ e o r d i eLake Lake Occurrence Occurrence has has been interpreted as a late-stage hydrothermal been interpreted as a late-stage hydrothermal product product of of the the final crystallization of a plagioclase-rich intrusion of final crystallization of a plagioclase-rich intrusion of gabbroic gabbroic magma(Good magma(Good and and Crocket, Crocket8 1994a). 1994a). The The dominant dominant sulphides are chalcopyrite, pyrrhotite, pyrite, sulphides are chalcopyrite8 pyrrhotite8 pyrite8 cubanite cubanite and and rare pentlandite. Table 2 lists other minerals found rare pentlandite. Table 2 lists other minerals found in in studies completed completed over over the the years years in in these thesemineralized mineralized rocks. rocks. studies The reader should refer to the references for details and The reader should refer to the references for details and to to Walker(1993c) Walker(l993c) for for another another brief brief discussion discussion of of the the economic economic geology. geology. - Table 2: Mineralogy Mineralogy of of the the mineralized mineralized gabbros gabbros of of the the Port Port Table 2: Coldwell Coldwell Complex Complex �51 Mineral Reference Altaite(PbTe) Atokite(Pd3Sn) Bornite(Cu5Fes4) Electrum(Au,Ag) Guanglinite(pd3As) Galena(Pbs) Ressite(Ag2Te) Hollingworthite (RhAsS) Irasite(IrAsS) 2 12 5 2 112 2 4 Kotuiskite (PdTe) Si and Pb-bearing Kotuiskite Mackinawite((Fe,Ni)958 Majaicite(NiPdAs) 1,2 1,2 1,2 5 2 Merenskyite, solid solutions, (PbTe2) Mertieite—II(Pd35b3) Palladoarsenide(Pd2As) Ag—Pentlandite(p'e,wi)958 with Ag Platarsite (PtAsS) 1,2 1,2 1,2 2 1,2 Rhenium sulphide Sopcheite, solid solutions, (Pd2Ag4Te4) Sperrylite(PtAs2) Telargpalite((Pd,Ag)3Teçp) Troilite(Fes) Unnamed (PdsAs?), Pd—bearing nickeline Unnamed Pd16N].As15 4 1,2 1,2 2 5 1,2 3 Zvyaginskite(pd3pb) 1,2 1) Ohnenstetter et al., 1991; 2) Watkinson and Ohnenstetter, 1992; 3) Mulja and Mitchell(199o); Mitchell et al., 1989; 5) Lum, 1973 Field Trip Log At 2.0 km from the Dead Horse Creek access road Stop 12: Molybdenite along fractures in hornfelsed wacke. Molybdenite occurs throughout the Port Coldwell Complex as tiny isolated grains and rosettes along joint planes. Ho concentration of molybdenite has been found which warrants further testing. The outcrop is locally cut by gabbro and syenite. At this site the molybdenite occurs as tiny grains and rosettes up to 2 mm along joint planes which may display some alteration to yellow ferrimolybdite. The syenite dikes contains abundant xenoliths of both wall rock and phases of the complex. East of the exposure, the road cut reveals various phases of syenite with abundant xenoliths. The general trend of the bedding in the wacke is 050 with a �52 steep but extreme extreme variation variation in in bedding bedding steep southerly southerly dip, dip, but attitudes attitudes occur. occur. At 2.9 Jan Stop Stop 13: 13: Optional: Optional: Rheomorphic Rheomorphic breccia. breccia. This his stop stop requires requires at 20 minute minute walk walk over over aa skid skid trail trail that that is is at least least aa 20 overgrown overgrown and and often often wet. wet. Park Park the the vehicles vehicles on on the the north north side side of Be careful careful and and be be sure sure that that you you of the the curve curve in in the the highway. highway. Be can the highway highway safely and that can get get on on and and of offf the that the the shoulder shoulder of of the the road road is is not not soft. soft. The The skid skid trail trail was was made made for for power power line line construction construction and and leads leads off off into into the the bush bush from from the the top top of of the the outcrop outcrop on on the the south south side side of of the the highway. highway. At 795 mm the the power power line line tower tower to to the the east east of of At approximately approximately 795 the the trail trail is is on on aa syenite syenite outcrop outcrop containing containingvery very fine— finegrained grained gabbro gabbro xenoliths xenoliths with with concentric concentricrings ringsof of alteration. alteration. The The reaction reaction rings rings are are 0.5 0.5 to to 1.0 1.0 cm cm wide wide and and weather weather high high compared compared to to the the core core of of the the xenolith. xenolith. The The xenoliths xenoliths are are in in coarse—grained coarse-grained syenite syenitecut cutby by aa fine— finegrained aplite up up to to 20 grained syenitic syenitic aplite 20 cm cm wide wide that that trends trends165. 165. Between Between this this tower tower and and Highway Highway 17 17 to to the the east, east, the the outcrops outcrops are are dominantly dominantly layered layered gabbro. gabbro. The The very very fine-grained fine-grained gabbro gabbro is is the the oldest oldest gabbroic gabbroic phase phase and and often often has has aa knobby knobby weathered weathered surface surface which which may may be be observed observed in in outcrops outcrops on on the the trail trail beneath beneath the thepower powerline. line. . Continue Continue walking walking to to approximately approximately 1270 1270 mm The skid skid trail trail The takes wide loop loop to to the the south south and and comes comesout out at at the the base base of of takes aa wide aa tower tower on on the the power power line line east east of of the the earlier earlier stop. stop. The The exposure exposure beneath beneath the the tower tower and and aa few few metres metres to to the the east east is is one of rheomorphic rheomorphic breccia breccia observable observable one of of the the best best examples examples of on Coldwell Complex. Complex. Angular Angular to torounded roundedclasts clastsof of on the the Port Port Coidwell metasediiuentary metasedimentary rock occur occur in in aa fine fine grained grained remobilized remobilized anatectic 0.3 mm and and some someare are anatectic matrix. matrix. Some Some clasts clastsare are up up to to0.3 rusty. rusty. The The clasts clasts have have contorted contortedbanding banding in inaamatrix matrix displaying displaying aa fluxion fluxion structure structuresuggesting suggestingthe thefragments fragmentswere were ductile The xenoliths xenoliths are are randomly randomly ductile in in aa flowing flowing medium. medium. The oriented oriented and and angular angular to to rounded rounded fragments fragmentsof of vein vein quartz quartzare are locally locally present. present. From From the the exposure exposure beneath beneath and and just just east east of of the the tower tower walk walk west west along along the the skid skid road road beneath beneath the thepower power line line and and note note the the rapid rapid change changefrom from rheomorphic rheomorphicbreccia brecciainto into less less and and less lessdeformed deformedmetasedimentary metasedimentaryrocks. rocks. • At At 60 60 to to 70 70 mm convoluted convolutedbedding beddingas aswell wellas assegmented segmentedquartz quartz veins are easily recognized. There are good examples veins are easily recognized. There are good examplesof of boudinaged boudinaged quartz quartzveins veinsat atthis thissite sitedirectly directlybelow belowthe the power line. At approximately 100 m good compositional power line. At approximately 100 m good compositional convolutionbut but the the layering(bedding) layering(bedding) displays displaysmuch much less less convolution quartz veins are still boudinaged. The bedding is trending quartz veins are still boudinaged. The bedding is trending approximately 295with with aa 75 75 south southdip dipand andthere thereis isopen open approximately295 kinking of the bedding. The kink bands 345and and dip dip kinking of the bedding. The kink bands trend trend 345 �53 vertically. The The plunge plunge of of the the fold fold axis axis in in the the kink kink band band is is vertically. approximately 35 35 NW. NW. approximately At approximately approximately165 165inm the the bedded bedded metasedinientary metasedimentary rocks rocks are are At much less less contorted contorted and and bedding bedding trending trending 300 300 and and dipping dipping 70 70 much north north is is easy easy to to recognize. recognize. Some Some open open folding folding in in the the metasedimentary rocks rocks and and some some minor minor faulting faulting trending trending 345 345 inetasedimentary dipping 75 75 north north offset offset the the bedding bedding by by as as much much as as 20 20 - 25 25 dipping cm. The fault trend is parallel to the trend of the kink cm. The fault trend is parallel to the trend of the kink bands. bands. - To To observe observe even even less less deformed deformed rocks rocks continue continue west. west. After After of your your observations observations return return to to the the vehicles. vehicles. completion of completion At 3.2 km Stop 14: 14: Mineralized Mineralized western western gabbro. gabbro. Park Park at at the the entrance entrance to to Stop the trail trail to to Middleton Middleton siding siding on on the the south south side side of of the the road. road. the The trail trail is is aa good good walking walking trail trail which which leads leads to to the the CPR CPR The tracks. tracks. At At approximately approximately925 925in m an old trench trench in in rusty, rusty, mediummediumgrained grained gabbro gabbro occurs occurs on on the the west west side side of of the the trail. trail. The The gabbro 0.5 to to 1.0 1.0 %% gabbro is is massive massive and and locally locally contains contains 0.5 chalcopyrite chalcopyrite and and pyrrhotite. pyrrhotite. This This exposure exposure is is typical typical of of mineralized mineralized western western gabbro gabbro and and differs differs from from the the mineralized mineralized eastern eastern gabbro gabbro in in the the lack lack of of well well developed developed pegmatitic pegmatitic textures. textures. This This trench trench was was probably probably made made in in the the late late 1950's. 1950fs. Wilkinson(1983) Wilkinson(1983) reported reported that that the the olivine olivine from from this this site site is is Fo Fo 49 49 to to 51 51 and and that that plagioclase plagioclase is is An An 47 47 to to 52. 52. The The western western gabbros gabbros are are less less evolved evolved than than the the eastern eastern gabbros gabbros which which have have olivine olivine compositions compositions of of Fo Fo 43 43 to to 46 46 and and plagioclase An 51 51 to to 57 57 (Wilkinson, (Wilkinson,1983). 1983). plagioclase compositions compositions of of An At 3.3 km to Remain Remain parked parked at at stop stop 14 14 and and walk walk east east along along Highway Highway 17 17 to the the large large outcrop outcrop on on the the north north side side of of the the road. road. This This is is stop Platt(1994) stop 10 10 of of Mitchell Mitchell and and Platt(l994) Stop Stop 15: 15: This This site site is is noted noted for for its its spectacular spectacular 'hydronephelinite" (natrolite) syenite llhydronephelinite"(natrolite) syenite pegmatite pegmatite enclosing enclosing medium medium grained grained gabbro gabbro xenoliths. xenoliths. The The outcrop outcrop is is cut cut by by aa late late lamprophyre lamprophyredike. dike. The Theniedium-grained medium-grained angular angular gabbro gabbro xenoliths xenolithsupuptoto1.0 1.0inm in in size size have have aa wide wide 11 to to 22 cm cm dark dark reaction reaction rim rim with with the the enclosing enclosing syenite syenitepegmatite. pegmatite. The The natrolite natrolitesyenite syenitepeginatites pegmatites contain contain patches patches of of red red to to orange-red 15 cm, cm, perthitic perthitic feldspars feldspars orange-red natrolite natrolite up up to to 10 10 - 15 up up to to 30 30 cm cm and and dark dark green green to toblack black amphibole amphibole up up to to20 20 to to25 25 cm. cm. Mitchell Mitchell and and Platt(l994) Platt(1994) reported reported the the presence presence of of pleochroic titaniteand and biotite. biotite. pleochroic clinopyroxene, clinopyroxene,zircon, zircon,titanite - �54 The fine-grained fine-grained lamprophyre lamprophyrethat thatcuts cutsthe thenatro].ite natrolite The pegmatite pegmatite trends trends 040, 040, dips dips 55 55 north north and and is is approximately approximately 40 40 cm cm wide. wide. Mitchell Mitchell and and Platt(1994) Platt(1994) indicated indicated that that most most lamprophyres lamprophyres in in this this area area may may be be classified classified as ascamptonites. camptonites. Continue continue east east along along the the face face of of the the outcrop outcrop from from the the natrolite pegmatites. pegmatites. The The rock rock is is aa finefine- to to medium-grained medium-grained natrolite nepheline syenite syenite with with nepheline nepheline indicated indicated by by the the chalky chalky nepheline weathering. Occasionally Occasionally aa grain grain of of reddish reddish orange orange weathering. "hydronephelinite" (natrolite) is **hydronepheliniteg~(natrolite) is recognizable. recognizable. continue east east along along the the face face of of the the outcrop outcrop to to almost almost the the Continue end end of of the the exposure exposure to to examine examine various various syenite syenite and and syenite syenite pegmatite pegmatite units. units. Near Near the the end end of of the the outcrop outcrop medium-grained medium-grained titaniferous titaniferous magnetite magnetite with with minor minor clinopyroxene, clinopyroxene,plagioclase plagioclase and and apatite apatite is is exposed exposed in in the the road road cut. cut. This This material material has has been been prospected prospected in in the the past past as as aa source source for for titaniferous titaniferous luagnetite. The best best outcropping outcropping is is approximately approximately 150 150 mm east east magnetite. The of of the the lamprophyre lamprophyre dike dike that thatcuts cutsthe thenatrolite natrolitepegmatite. pegmatite. The The various various rock rock types types exposed exposed in in this this road road cut cut have have been been assigned assigned to to various various intrusive intrusive centres centres by by Mitchell Mitchell and and Platt(1994). Platt(1994). The The gabbro, gabbro, and and ferroaugite ferroaugitesyenites syenites are are related activity, amphibole amphibole syenites syenites to to centre centre 33 related to to centre centre 11 activity, and the the natrolite natrolitepeginatites pegmatites to to centre centre 2(Mitchell 2(Mitchell and andPlatt, Platt, and 1994). 1994). McGill(1980) McGill(1980) has has examined examined the the natrolite natrolite pegmatites pegmatites and titaniferous titaniferousmagnetite magnetite accumulations accumulationsin inthe thegabbro. gabbro. and Return Return to to vehicles vehicles At 5.5 km Stop Stop 16: 16: Intrusive Intrusive breccia breccia on on the the east east side side of of the the Little Little Pic Park at at the the large largeturn turnout out at at the the east east end end of of the the Pic River. River. Park bridge bridge and and walk walk along along the the highway highway to to the the first first outcrop outcrop on on the the south southside sideof ofthe theroad. road. Angular Angular blocks blocks of of fine— fine- to to medium—grained medium-grained equigranular equigranular oligoclase oligoclase gabbro gabbro occur occur in in aa matrix matrix of of medium—grained medium-grained pink pink quartz quartz syenite. syenite. The The gabbro gabbro appears appearsto to be be shattered shattered and and veined veined by by the the syenite syeniteand and some someof of the the fragments fragmentsmay may visually visually be The quartz quartz be refitted refittedas as one one would would aa jig jig saw sawpuzzle. puzzle. The syenite syenite filling filling in in around around the the fragments fragmentslocally locally contains contains miarolitic miarolitic cavities cavities up up to to several severalcentimetres centimetresin in width width which which may may contain contain euhedral euhedral quartz quartz and and feldspar feldsparcrystals. crystals. White White calcite calcite may may partially partially fill fill some someof of these these cavities. cavities. This This oligoclase oligoclase gabbro gabbro occurs occurs only only in inthis this area area of of the the Little Little Pic Pic River lookout(Stop 17) 17) where where River and and up up to to the the Little Little Plc Pic River River lookout(Stop Mitchell referto toit itas as an an oligoclase oligoclase Mitchell and and Platt(1994) Platt(1994) refer basalt. basalt. Volcanic Volcanic textures textureshave have not not been been observed observed in in this this unit. The Little Little Plc Pic River River occupies occupiesaa strong strong lineament lineament which which unit. The may may be be traced traced on on airphotos airphotosto to the thewest west flank flank of of the the Killala Killala Lake Thelineainent lineament is is likely likely aa fault fault zone zone LakeComplex Complexand andnorth. north.The �55 but offset offset cannot cannot be be determined determined at at this this location. location. The The Little Little but Pic River River lineament lineament can can be be interpreted interpreted to to be be the the onshore onshore Pic extension of of aa deep deep water—filled water-filled linear linear located located southwest southwest of of extension the Slate Slate Islands(Sage Islands(Sage 1991) 1991) which the which probably probably represents represents the the onshore expression expression of of faulting faulting related related to to the the Thiel(Klasner Thiel(K1asner onshore et et al. al. 1982) 1982) or or Big Big Bay-Ashburton Bay-Ashburton Bay Bay Fault(Sage, Fault(Sage, 1978). 1978). Laws(1983). Parts of of the the breccia breccia zone zone have have been been studied studied by by Laws(1983). Parts of the the intrusive intrusive breccia, breccia, weakly weakly At the the extreme extreme western western end end of At trachytoidal ferroaugite ferroaugite syenite syenite occurs occurs in in outcrop. outcrop. The The trachytoidal spectacular cliff cliff faces faces observed observed on on the the west west side side of of the the spectacular Little Pic Pic River River consist consist of of ferroaugite ferroaugite syenite. syenite. Little At 6.3 km Stop 17: 17: Little Little Pic Pic River River turn turn out. out. This This is is aa frequent frequent stop stop Stop for visitors visitors to to the the Port Port Coidwell Coldwell Complex Complex as as it it provides provides for safe safe parking parking of of the the vehicles. vehicles. Be Be careful careful and and watch watch for for vehicles vehicles while while you you examine examine exposures exposures along along Highway Highway 17. 17. This This is is stop stop 17 17 of of Mitchell Mitchell and and Platt(1994). Platt(1994). Walk Walk from from the the parking parking area area to to Highway Highway 17 17 and and examine examine the the intrusive intrusive breccias breccias and and xenolith—rich xenolith-rich syenite. syenite. Oligoclase Oligoclase gabbro gabbro veined veined with with quartz quartz syenite syenite occurs occurs along along the the south south side of the road and various syenitic rocks with side of the road and various syenitic rocks with xenoliths xenoliths occur syenites are are pyroxene-amphibole pyroxene-amphibole occur on on the the north north side. side. The The syenites syenites syenites containing containing xenoliths xenoliths of of alkali alkali gabbro, gabbro, alkali alkali diorite diorite and and various various syenites. syenites. The The syenitic syenitic xenoliths xenoliths vary vary from from coarse-grained coarse-grained equigranular equigranular blocks blocks to to porphyritic porphyritic phases. ratio of of alkali alkali gabbro gabbro to to diorite diorite increases increases to to phases. The The ratio the the east east toward toward the the entrance entrance to to the the lookout. lookout. The The alkali alkali gabbro is cut cut by by grey grey nepheline nepheline syenite syenite with with some some gabbro to to diorite diorite is reddish reddish orange orange "hydronephelinite" "hydronephelinite" toward toward the the entrance entrance to to the the lookout. lookout. The The amphibole amphibole tends tends to to be be somewhat somewhat acicular acicular in in the the nepheline-rich nepheline-rich phases phases and and locally locally they they have have somewhat somewhat gradational gradational contacts contacts with with the the alkali alkaligabbro gabbroto todiorite. diorite. Pegmatitic Pegmatitic dikes dikes of of quartz quartz syenite syenite outcrop outcrop opposite opposite the the entrance entrance to to the the lookout. lookout. East East of of the the turn turn off off to to the the lookout lookout the the mediummedium- to to coarse— coarsegrained amphibole-pyroxene syenite is inequigranular senate grained amphibole-pyroxene seriate and the number of xenoliths has greatly diminished. and the number of xenoliths has greatly diminished. The The syenites syenites at at this this location location have have been been related related to to centre centre 33 and Mitchell Mitchell intrusive intrusive activity activity and and Lukosius-Sanders(1988) Lukosius-Sanders(1988) and et et al.(1993) al.(1993) described described these these syenites syenites in in detail. detail. In In the the order Platt(1994) list list the the order of of emplacement emplacement Mitchell Mitchell and and Platt(1994) syenites syenites as as follows: follows: magnesio—hornblende magnesio-hornblendesyenite, syenite, contaminated contaminated ferro-edenite ferro-edenite syenite, syenite, ferro—edenite ferro-edenite syenite syenite and and quartz quartz syenite. syenite. Sannaite Sannaite lamprophyre lamprophyre and and ocellar ocellar camptoniticlamprophyre arereported reportedto tooccur occur in in the the camptonitic lamprophyreare area(Mitchell 1994). Lukosius—Sanders(1988) area(Mitchel1and andPlatt, Platt.1994). Lukosius-Sanders(1988) �56 classified classified the the syenites syenites as as miaskitic, metaluminous metaluminous enriched enriched in in U, Th, Th, REE REE and and Zr Zr due due to to the the presence presence of of zircon, zircon, chevkinite((Ca,Ce,Th)4(Fe,Mg)2(Ti,Fe)3si4022}, REEchevkinite{(Ca,Ce,~h)~(Fe,~g)~(Ti,~e)~~ REEi~O~~), carbonates, carbonates, Nb—rutile Nb-rutile and and aeschylite aeschylite {(Y,Ca,Fe,Th)(Ti,Nb)2(O,OH)6}. { (Y ,Ca,Fe,Th) (Ti,Nb) 2 (0,OH) G>. The centre centre 33 syenites syenites have have affinities affinities to to A-type A-type granites granites and and have have been been interpreted interpreted to to be be the the result result of of fractional fractional crystallization crystallization of of mantle— mantlederived itche ell et et magma(Lukosius-Sanders, 1988; 1988; Mitchell derived basaltic basaltic magma(Lukosius-Sanders, al. al. 1993). 1993). At 9.8 km Stop to Neys Neys Provincial Provincial Park. This Stop 18(Optional): 18(Optional): Turn Turn of offf to This will to this this area area will be be the the site site of of an an optional optional stop. stop. Access Access to may may not not be be possible possible in in the the early early spring spring since since the the park park is is This stop stop has has been been described described as as stop stop 15 15 closed closed to to visitors. visitors. This by by Mitchell Mitchell and and Platt(1994). Platt(1994). Drive along park park access road km along road and and park park Drive approximately approximately 2.8 2.8 kin at at Neys Neys Park Park headquarters. headquarters. Walk east east and and south south along along the the beach beach for for approximately approximately400 400in m to to the the first first large large outcrop outcrop on on the the shore shore of of Lake Lake Superior. Superior. SAMPLE AT THIS SAMPLE COLLECTING COLLECTINGAT THIS SITE SITE IS IS PROHIBITED PROHIBITED MediumMedium- to to coarse—grained coarse-grained biotite biotite gabbro gabbro of of centre centre 22 outcrops outcrops on on the the eastern eastern part part of of the the exposure exposure and and nepheline nepheline syenites syenites of of centre centre 22 are are exposed exposed on on the the western western part part of of the the outcrop. outcrop. The The texture texture and and composition composition of of the the nepheline nepheline syenites syenites are are heterogeneous heterogeneous and and possibly possibly represent represent magma magma mixing process not not yet yet studied studied in in detail detail mixing and and hybridization, hybridization, process within within the the Port Port Coidwell Coldwell Complex. Complex. One One may may continue continue walking walking south south along along the thecoast coastfor forseveral several100 100inm and and observe observe nepheline nepheline syenites syenites with with well well developed developed layering layering and and structures structures reminiscent reminiscent of of "soft—sediment" wsoft-sediment**deformation. deformation. The The layered layered syenites syenites are are divided divided into into large large blocks blocks by by aa later later intrusion The earlier earlier syenites syenites were were intrusion of of nepheline nepheline syenite. syenite. The subjected wsedimentationm and and then then subjected to to current current action action and and "sedimentation" subsequently subsequently forcibly forcibly intruded intruded by by younger younger syenites syenites of of similar similar composition. composition. The Theinafic mafic mineral is is hastingsite(Mitchell hastingsite(Mitchel1 and and Platt, Platt, 1994). 1994). The The general general trend trend of of the the banding banding is is NNW NNW with with aa highly highly variable variable dip. dip. Return Return to to Highway Highway 17 17 and and continue continue east east Stop Stop 19 19(Optional): (Optional): At f to former At 14.6 14.6 km km turn turnof off former townsite townsite of of Port Port Coidwell. Coldwell. Distance Distance remains remains from from the the Dead Dead Horse Horse Creek Creek access accessroad. road. Drive Drive approximately approximately 0.2 0.2 km km and and park park near near the the CPR CPR tracks. tracks. �57 THISISIS A VERYDANGEROUS DANGEROUS LOCATION. LOCATION. THE THE SHAPE SHAPE OF OF THE THE HILLS HILLS THIS A VERY AND ONE MAY NOT HEAR MODIFY THE SOUND OF APPROACHING TRAINS MODIFY THE SOUND OF APPROACHING TRAINS AND ONE MAY NOT HEAR BE ALERT AT ALL TIMES. A TRAIN UNTIL IT IS EXTREMELY CLOSE. A TRAIN UNTIL IT IS EXTREMELY CLOSE. BE ALERT AT ALL TIMES. Amphibole-nepheline syenites syenites of of centre centre 2. 2. Walk Walk east east for for Amphibole-nepheline approximately 700 700 mm along along the the CPR CPR tracks tracks to to the the high high cliff cliff approximately faces along the west side of the railroad opposite Echo faces along the west side of the railroad opposite Echo Lake. These These cliffs cliffs are are composed composed of of nepheline nepheline syenite syenite and and Lake. there is abundant loose rock above so be careful. The there is abundant loose rock above so be careful. The nepheline syenite syenite is is generally generally aa massive massive equigranular equigranular rock rock nepheline The with local reddish orange spots of whydronephelinite". with local reddish orange spots of "hydronephelinite". The rock surface is highly stained and fresh surfaces may only rock surface is highly stained and fresh surfaces may only be obtained obtained from from breaking breaking open open pieces pieces that that have have fallen fallen from from be the cliff. the cliff. continuing beyond beyond this this cliff cliff face face one one may nay examine examine Stop Stop 88 of of Continuing Mitchell and Platt(1994). This stop is on the shore of Mitchell and Platt(1994). This stop is on the shore of Redsucker Cove Cove 1.6 1.6 km km from from Port Port Coldwell Coldwell village. village. At At aa Redsucker concrete embankment leave the tracks and go down to the lake lake concrete embankment leave the tracks and go down to the nepheline syenite veins and a shore to examine diorite, shore to examine diorite, nepheline syenite veins and a analcite trachyte trachyte dike(Mitchell dike(Mitchel1 and and Platt, Platt, 1994). 1994). To To the the analcite east various varieties of nepheline syenite may be observed, east various varieties of nepheline syenite may be observed, and to to the the west, west, breccias breccias of of gabbro, gabbro, diorite diorite and and nepheline nepheline and syenite may be examined. A number of camptonitic syenite may be examined. A number of camptonitic lamprophyres and and one one sannaite sannaite lamprophyre lamprophyre occur occur at at this this lamprophyres site(Mitchel1 and Platt, 1994). For details of this stop site(Mitchell and Platt, 1994). For details of this stop refer to to Mitchell Mitchell and and Platt, Platt, (1994). (1994). refer Return to to the the vehicles vehicles and and continue continue east east along along Highway Highway 17 17 Return At 16.1 16.1 km km highway highway 17 17 crosses crosses Mink Mink Creek. Creek. There There is is aa At waterfall in in syenite syenite approximately approximately 100 100 mm south south of of the the waterfall You may may park park on on the the small small logging logging access access road road highway. You highway. 17 west west of of Mink ink Creek Creek and and take take aa leading north north from from Highway ~ighway17 leading short trail trail south south of of the the highway highway to to the the falls. falls. short At 19.2 km Biotite gabbro gabbro intruded intruded by by various various types types of of Stop 20: 20: Biotite Stop nepheline syenite. syenite. nepheline This stop stop is is at at aa broad broad curve curve in in highway highway 17 17 and and one one should should This be very CAREFUL OF VEHICLES. be very CAREFUL OF VEHICLES. 18.8 km km outcrops outcrops on on the the east east side side starting at at approximately approximately 18.8 Starting of the highway of grey to buff pyroxene amphibole syenite of the highway of grey to buff pyroxene amphibole syenite contain orange orange fluorescing fluorescing hackmanite, hackmanite, aa variety variety of of contain W This mineral can only readily be seen with sodalite. This mineral can only readily be seen with aa UV sodalite. lamp. The The syenite syenite contains contains numerous numerous mafic mafic xenoliths xenoliths up up to to lamp. 25-30 cm cm in in maximum maximum length. length. The The xenoliths xenoliths are are subangular subangular to to 25—30 subrounded and the mafic minerals within the syenite tend to subrounded and the mafic minerals within the syenite tend to �occur occur in in clots. clots. The The larger larger xenoliths xenoliths may nay have have feldspar feldspar phenocrysts or or porphyroblasts porphyroblasts up to to 1.0 1.0 cm. The phenocrysts The phenocrysts phenocrysts or porphyroblasts porphyroblasts display or display aa seriate senate size size distribution distribution and and comprise comprise up up to to 55 %% of of the the rock. rock. km an an alkalic alkalic biotite biotite At the the centre centre of of the the curve curve at at 19.2 19.2 kin At gabbro is is exposed exposed on on the the north north side side of of the the highway. highway. The The gabbro mediummedium- to to coarse—grained coarse-grained gabbro cut by by gabbroisis extensively extensively cut medium— medium- to to coarse—grained coarse-grained syenite syenite and and some some of of the the nepheline nepheline has has been been altered altered to to reddish reddish orange orange "hydronephelinite". Hhydronepheliniten. There There may be be two two ages ages of of alkalic alkalic gabbro gabbro with the the older older coarser coarser may grained gabbro gabbro displaying displaying dark dark selvages selvages up up to to 77 or or 88 cm cm wide wide grained more and an an irregular irregular shape shape suggesting suggesting that that it it behaved behaved in in aa more and or less less ductile ductile manner. or manner. The The alkalic alkalic gabbros gabbros have have aa clotty dotty mafic mineral mineral assemblage. assemblage. The The surface surface of of the the coarser coarser grained grained mafic biotite gabbro gabbro is is pitted pitted from from the the weathering weathering of of mafic mafic clots. clots. biotite Dikes of of nepheline nepheline syenite syenite pegmatite pegmatite occur occur on on the the north north side side Dikes of the the highway highway at at the the inflection inflection in in the the curve. curve. At At this this site site of two two ages ages of of nepheline nepheline syenite syenitepeginatite pegmatite of of essentially essentially identical identical composition composition cut cut each each other. other. The The trends trends of of these these dikes dikes are are approximately approximately 340 340 dipping dipping 60 60 south south and and 090 090 dipping dipping 50 50 north. north. The The dike dike trending trending 090 090 cuts cuts the the dike dike trending trending 340 340 and both both are are on on the the order order of of 20 20 to to 30 30 cm cm in in width. width. The The dikes dikes and have Puskas (1970). Both dikes have been been sketched sketched by byPuskas(1970). dikes are are zoned zoned from from an an amphibole-rich amphibole-rich margin margin to to aa feldspar— feldsparnatrolite(hydronephe1inite)-rich core. core. The The central central parts parts of of natrolite(hydronephelinite)—nich these these dikes dikes are are commonly commonly relatively relatively rich rich in in reddish reddish orange orange "hydronephelinite". 18hydronepheUniten.West West from from the the two two dikes dikes toward toward the the hackinanite-beaning outcrop, coarse-grained coarse—grained alkalic hackmanite-bearing outcrop, alkalic biotite biotite gabbro gabbro is is intruded intruded by by medium medium to to coarse coarse grained grained pyroxene, pyroxene, amphibole amphibole syenite syenite with with traces traces of of nepheline. nepheline. Both Both of of these these rock rock types types are are in in turn turn cut cut by by coarse—grained coarse-grained nepheline nepheline syenite syenite dikes. dikes. Brecciation Brecciation is is so so intensive intensive that that the the outcrop outcrop is an an igneous igneous breccia. breccia. West West toward toward the the hackmanite—bearing hackmanite-bearing is outcrop outcrop the the syenite syenite is is pink pink to to grey, grey, fine— fine- to to medium— aedium- grained, senate with grained, inequigranular inequigranular seriate with dotty clottyassemblages assemblagesof of mafic mafic minerals. minerals. On On the the south south side side of of the the highway highway coarse-grained coarse-grained alkalic alkalic gabbro gabbro appears appears to to be be cut cut by by medium-grained medium-grained alkalic alkalic gabbro gabbro which which is is in in turn turn intruded intruded by by mottled mottled pink pink to to grey, grey, inequigranular inequigranular senate seriateamphibole amphibolesyenite. syenite. There There is is aa slight slight coarsening coarsening in in texture texture next next to to the the medium—grained medium-grained gabbro gabbro and and aa dike material projects projects from from the the contact contact with with dike of of similar similar material the the medium-grained medium-grained gabbro gabbro through through both both phases phases of of alkalic alkalic gabbro. gabbro. At 24.4 km Stop Stop 21: 21: Hornfelsed Hornfelsed roof roof pendants, pendants, Wolf Wolf Camp Camp Lake Lake �59 This is Tot is stop 7 of Mitchell Mitchell and and Platt(1994). Platt(1994). Hornfelsed Hornfelsed rocks rocks overlying the the Port Port Coidwell Coldwell Complex were recognized recognized early in in overlying the mapping mapping of of the the intrusion intrusionby by Tuoininen(1967) Tuominen(1967) and and the Puskas(1970) and and are are likely likely representative representative of a former former Puskas(1970) volcanic edit edifice(Sage, volcanic ice(Sage, 1986). 1986). Mitchell Mitchell and and Platt(1994) and studied these rocks in in detail and consider Nicol(1990) have studied these basalts to to be contemporaneous contemporaneous with the Port Coldwell these to represent represent a tholeiitic lineage. The basalts Complex and to are fresh, fresh, inetasomatized are and hornfelsed hornfelsed andesine-oligioclase andesine—oligioclase metasomatized and basalt flows flows estimated estimated to to have a thickness thickness of of up up to to 55 m basalt (Nicol, Mitchell and (Nicol, 1990, Mitchell and Platt, Platt, 1994). 1994). At this this stop stop amygdaIoidal amygdaloidal basalt basalt with calc-silicate calc-silicate amygdule amygdule fillings is is well well exposed. exposed. The fillings The ameboid ameboidaniygdules amygdules are are unlike unlike amygdules found found in in Archean Archean metavolcanic metavolcanic rocks rocks of of the the region region amygdules and more more typical typical of of those those found found in in Keweenawan Keweenawan flows. flows. The The and greenish caic-silicate calc-silicate amygdule amygdule fillings fillings are are interpreted interpreted to to greenish represent the the metamorphic metamorphic product product of of former former calcite, calcite, quartz quartz represent etc. fillings fillings of of the the amygdules. amygdules. Exposures Exposures of both massive etc. and amygdular amygdular flows flows may may be be found found on on the the hills hills and and cliffs cliffs and southwest of of Wolf Wolf Camp Camp Lake Lake and for for aa short short distance distance along along southwest Highway 17 17 east east of of this this stop. stop. Hornfelsed Hornfelsed mafic flows flows are are Highway also present present in in the the northern northern part of of the the complex complex also (Tuominen,1967) where they have been observed observed to to overlie overlie (Tuominen,1967) syenitic rocks rocks of of the the Port Port Coldwell Coldwell Complex. Complex. These These flows flows are are syenitic thought to to be be the the remnants remnants of a once once former former volcanic edifice edifice thought that have have been been preserved preserved due due to to ring fracturing fracturing and caldera caldera that subsidence. subsidence. At At 33.9 33.9 km km Turn of offf to Turn to the the town town of Marathon Marathon At 35.6 km Stop 22: 22: Layered Layered gabbro. gabbro. This This is is stop stop 44 of of Mitchell Mitchell and and Stop Platt(1994). Platt(1994). The The gabbros gabbros of of the the eastern eastern contact contact area area are are well well exposed exposed at at this this site site and and considered considered to to represent represent centre centre is part part of of an an outer outer ring ring 11 intrusive intrusive activity. activity. This This gábbro gabbro is that that encompasses encompasses the the eastern eastern and and most most of of the the northern northern parts parts of Coldwell Complex Complex separating separating the the external external Archean Archean of the the Port Port Coldwell rocks rocks from from the the internal internal syenitic syenitic rocks rocks of of the the intrusion. intrusion. These These gabbros gabbros are are reversely reversely magnetized magnetized and and form form prominent prominent lows lows on on aeromagnetic aeromagnetic maps(Lilley, maps(Lilley, 1964). 1964). This This stop stop is is close close to to the the ferrosyenite—gabbro ferrosyenite-gabbro contact contact and and there there is is aa lack lack of of intermediate compositions compositions between between these these two two rock rock types types intermediate implying implying two two distinctly distinctly different different magmas. magmas. Relationships Relationships between between these these two two magma magma types types are are unknown. The ferroaugite ferroaugite syenite syenite is is best best observed observed at at the the western western end end of of the the outcrop outcrop miarolitic cavities cavities up large miarolitic where where pegmatitic pegmatitic phases phases contain contain large to to 22 mm lined lined with with euhedral euhedral feldspar, feldspar, quartz quartz and and amphibole. amphibole. McLaughlin, McLaughlin, (1990) (1990) reports reports the the presence presence of of fluorocarbonates (bastnaesite, parisite, parisite, synchysite) fluorocarbonates(bastnaesite, synchysite) Nb— Nb- �60 futile, Nb—bearing Nb-bearing ilmenite, ilmenite, columbite, columbite, pyrochlore pyrochlore and and rutile, zircon zircon in in these these pegmatites. pegmatites. The best best exposure exposure for for viewing viewing the the layered layered gabbró gabbro is is in in the the The east central central part part of of the the road road cut cut at at the the top top of of the the outcrop. outcrop. east Small Small pegmatitic pegmatitic dikes dikes of of quartz quartz syenite syenite cut cut the the outcrop. outcrop. The The rhythmic rhythmic layering layering is is due due to to variation variation in in the the plagioclase-mafic mineral mineral content content and and individual individual layers layers of of plagioclase—mafic plagioclase-rich plagioclase-rich rock rock are are 0.5 0.5 to to15 15cm cmthick thickand andniafic mafic The banding banding mineral-rich mineral-rich layers layers are are 0.2 0.2 to to 2.0 2.0 cm cm thick. thick. The strikes roughly roughly parallel parallel to to the the road road and and dips dips approximately approximately strikes 45 45 west. Mitchell Mitchell and and Platt(1994) Platt(1994) believe believe this this rhythmicrhythmiclayered layered gabbro gabbro is is aa rafted rafted block. block. The The trend trend of of banding banding in in this this area area is is somewhat somewhat erratic, erratic, dips dips are are consistently consistently west west Outcrops west west of of this this stop stop on on the the north north side side but but variable. variable. Outcrops of of the the highway highway display display aa less less distinct, distinct, wispy, wispy, streaky streaky banding banding due due to to slight slight variations variations in in mafic—felsic mafic-felsic mineral mineral contents. contents. The The reader reader may may wish wish to to refer refer to to Shaw(1994) Shaw(1994) for for aa detailed petrological petrological study study of of the the eastern eastern gabbro. gabbro. detailed At 37.3 km Stop Stop 23: 23: Eastern Eastern gabbro gabbro in in contact contact with with rheomorphic rheomorphic breccia breccia at at the the eastern eastern contact. contact. This This is is aa deeply deeply weathered weathered outcrop outcrop of of suiphide-bearing sulphide-bearing gabbro gabbro at at the the contact contact with with Archean Archean wall wall rocks. rocks. The The gabbro gabbro contains contains abundant abundant xenoliths xenoliths of of the the wall wall rock rock and and very very fine fine grained The gabbro gabbro is is cut cut by by irregular irregular dikes dikes of of grained gabbro. gabbro. The quartz quartz syenite syenite pegmatite. pegmatite. The The rheomorphic rheomorphic breccia breccia is is identical contact(Stop 13) 13) identical to to that that observed observed at at the the western western contact(Stop where where the the exposure exposureis is better. better. The Therheoiuorphic rheomorphic breccia breccia is is characterized characterized by by convoluted convoluted flow flow lines lines and and xenoliths xenoliths in in random random orientation, orientation, some some of of which which appear appear to to have have been been ductile ductile and and partially partially assimilated. assimilated. Some Some xenoliths xenoliths retain retain aa somewhat somewhat angular angular outline outline and and some some display display aa boudinage boudinage structure structure as as they they underwent underwent further further fragmentation. fragmentation. The The contact rocks may may be be observed observed contact between between the the gabbro gabbro and and wall wall rocks but but due due to to its its irregular irregular trend trend its its attitude attitude is is uncertain. uncertain. The The sulphide-bearing sulphide-bearing gabbro gabbro has has been been prospected prospected north north and and south south of of highway highway 17 17 at at this this point. point. The The suiphides sulphides are are principally principally chalcopyrite chalcopyrite and and pyrrhotite. pyrrhotite. Return Return to to the the vehicle vehicle and and return return to to the the intersection intersection of of the the road road to to Marathon Marathon and and Highway Highway 17. 17. From From the the intersection intersection of of the the Marathon Marathon road road with with Highway Highway 17 17 take take the the following followingroute: route: Go f, cross the CPR tracks tracks and and turn turn Go 5.3 5.3 km km from from the theturn turnof off, right right toward toward Lake Lake Superior. Superior. Go km and and pass pass the the hotel hotel on on the the right, right, Moose Moose Lodge Lodge on on Go to to 5.7 5.7 km the the left left and and turn turnright right on on Winston Winston St. St. �61 Go Go to to 6.0 6.0 km km crossing crossing the the CPR CPR tracks tracks and continuing continuing to to the the right. right. Go to to 6.7 6.7 km km where where the the road road splits. splits. Take Take the the left left hand fork fork Go along along the the shore shore of of Lake Lake Superior. Superior. At 7.2 Km small quarry quarry in in Stop 24: 24: Ferroaugite Ferroaugite syenite. syenite. This This is is aa small Stop ferroaugite syenite syenite on on the the shore shore of of Lake Lake Superior Superior where where ferroaugite coarse grained grained equigranular equigranular specimens specimens of of the the syenite syenite may may be be coarse This quarry quarry was was probably probably made made in in the the 1930's 1930's and and collected. collected. This is typical typical of of centre centre 11 ferroaugite ferroaugite syenite syenite referred referred to to as as is laurvikite (1967). Puskas(1967). laurvikiteby byPuskas At 7.8 km Stop Stop 25: 25: Layered Layered ferroaugite ferroaugitesyenite. syenite. Park Park at at the the end end of of the the road road which which is is aa boat boat landing landing and and walk walk north 680 in. north along along the theshore shoreline linefor forapproximately approximately 680 m. There There is is aa partial partial trail trail for for most most of of the the distance. distance. The The broad broad expanses expanses of of ferroaugite ferroaugite syenite syenite exposed exposed along along the the shoreline shoreline display display excellent excellent glacial glacial grooving grooving and and polishing. polishing. Be Be careful careful where where seepage seepage from from the the surrounding surrounding bush bush onto onto the the rocks rocks has has permitted his green green algae algae is is very very permitted green green algae algae to to grow. grow. This slippery. slippery. Also Also be be careful carefulafter afterwalking walkingthrough througha'a sandy sandy area area and then then stepping stepping onto onto outcrop. outcrop. Sand Sand on on the the sole sole of of the the boot boot and may may act act like like ball ball bearings bearings on on the the glacially glacially polished polished outcrop outcrop surface surface and and you you may may slip. slip. At 340 mm along along this this traverse traverse near near the the bushbushAt approximately approximately 340 outcrop outcrop line line of of demarcation demarcation aa fine-grained fine-grained inequigranular inequigranular porphyritic porphyritic senate seriatesyenite syenitedike dike1.5 1.5inm wide, wide cuts cuts the the ferroaugite ferroaugite syenite. syenite. The The dike dike trends trends 150 150 and and has has aa vertical vertical dip. dip. The The dike dike locally locallycontains contains10, 10 to to 15 15 %% feldspar feldspar phenocrysts phenocrysts up up to to 1.0 1.0 cm cm in in long long dimension. dimension. Similar Similardikes dikesin in the the region region have have been been prospected prospected for for their their niobium(pyrochlore) content. zirconium(zircon)content. niobium(pyroch1ore)and andzirconium(zircon) Continue Continue north north to to the the banded banded ferroaugite ferroaugite syenite. syenite. The The banding banding is is wispy, wispy, discontinuous discontinuous and and may may bifurcate. bifurcate. The The general general trend trend is is 070 070 with with aa 60 60 north north dip. dip. The The banding banding is isdue due to Ic mineral content. The to varying varying maf mafic The glacial glacial grooving grooving has has aa general 240 degrees. degrees. This This is is the the second second best best general trend trend of of 240 location location to to study study mafic mafic banding banding in in the the pyroxene pyroxenesyenites. syenites. The The best best site site is is east east of of Marathon Marathon on on the the shore shore of of Lake Lake Superior walk(Stop27). 27). longwalk(Stop Superior and and involves involvesaa long �62 Return to to the the core core shack shack of of Fleck Fleck Resources Resources Ltd. Ltd. Marathon. Marathon. Return building on the the west side side of the the road This is is a blue-grey building This into into Marathon. Marathon. Stop Stop 26: 26: Mr. Mr. J. McGoran, President, President, Fleck Fleck Resources Resources Ltd. Ltd. will place place on on display display drill drill core core from from the the Two Two Duck Duck Lake Lake will Gabbro. The The PGE-rich PGE-rich sulphides sulphides are are cubanite, cubanite, pyrrhotite pyrrhotite and and Gabbro. chalcopyrite interstitial interstitial to to the the rock rock forming forming minerals minerals of of chalcopyrite the gabbro. gabbro. The The pegmatitic pegmatitic phases phases of of the the gabbro gabbro are are the the most the suiphide-rich. sulphide-rich. End End of of formal formal tour. tour. Optional 27: For For the the connoisseur connoisseur of igneous igneous petrology Optional Stop Stop 27: or the better or of of the the geology geology of of the the Port Coldwell Coldwell Complex, the part part of of aa day day should should be be spent spent walking walking along along the the shore shore of of Lake Superior east of Marathon to observe analcite Lake Superior east of Marathon to observe analcite tinguaite tinguaite dikes dikes cutting cutting the the Archean Archean wall wall rocks, rocks, excellent excellent exposures exposures of of banded banded ferroaugite ferroaugite syênite syenite and and fine-grained fine-grained hybrid hybrid gabbro. gabbro. These wave-washed outcrops outcrops are are excellent excellent These glacially glacially polished, polished, wave—washed to reasonably calm calm Lake Lake Superior Superior to study. study. Good Good weather weather and and aa reasonably are are highly highly desirable. desirable. The The trail trail along along this this shore shore line line starts starts at at the the end end of of Howe Howe St. St. in in Marathon Marathon and and these these outcrops outcrops have have itche ell and and Platt(1994) Platt(1994) as as been described described in in some some detail detail by by Mitchell been stop stop 6. 6. Optional Optional Stop Stop 28: 28: For For the the economic economic geologist geologist aa visit visit to to the the Cu-Ni-PGE Cu-Ni-PGE deposits deposits at at Two Two Duck Duck Lake Lake is is advisable. advisable. This This is is private private property property and and requires requires the the permission permission of of Fleck Fleck Resources Resources Ltd. Ltd. to to visit. visit. The The road road to to these these deposits deposits begins begins and the the road road to to opposite opposite the the junction junction of of highway highway 17 17 and Marathon. Marathon. The The distance distance to to the the Cu-Ni-PGE Cu-Ni-PGE deposits deposits is is in in excess 12 km km and and the the road road is is often often impassable impassable even even with with aa excess of of 12 4-wheel 4-wheel drive drive vehicle. vehicle. At At this this site site aa sill-like sill-like gabbro gabbro body body referred referred to to as as the the Two Two Duck Duck Lake Lake Gabbro Gabbro intrudes intrudes earlier earlier eastern eastern gabbros gabbros of of the the centre centre 11 intrusive intrusive centre. centre. This This gabbro gabbro is is medium— medium- to to coarse— coarsegrained grained and and contains contains pegmatitic pegmatitic phases. phases. The The Cu Cu and and PGE PGE enrichment enrichment is is considered considered to to be be of of hydrothermal hydrothermal origin(Watkinson origin(Watkinson and and Ohnenstetter(1992) Ohnenstetter(1992) and and is is represented represented by by platinum—group platinum-group minerals, minerals, chalcopyrite, chalcopyrite, and and cubanite. cubanite. The The Canadian Canadian Mines Mines Handbook(1993-1994, Handbook(1993-1994, p. p. 145) 145) lists lists the the reserves Cut 0.04 0.04 %% Ni, Nit reserves as as 37,000,000 37,000,000 tons tons grading grading 0.31 0.31 %% Cu, 251,000 251,000 oz oz Pt, Pt, 1,001,000 1,001,000 oz oz Pd, Pd, 84,000 84,000 oz oz Au Au and and 43,000 43,000 oz 02 Rh. Rh. One One should should refer refer to to Ohnenstetter Ohnenstetter et et al. al. (1991), (1991), Watkinson Watkinson and and Ohnenstetter(1992), Ohnenstetter(1992), Good Good and and Crocket(1994b) Crocket(1994b) and and Shaw(1994) Shaw(1994) for for details details on on the the mineralization mineralization and and petrology petrology of of eastern eastern gabbro. gabbro. �63 SELECTED SELECTED BIBLIOGRAPHY BIBLIOGRAPHY Adams, D.C. D.C. and and Keller, Keller, G.R., G.R., 1994. 1994. Possible possible extension extension of of Adams, the Midcontinent Midcontinent Rift Rift in in west west Texas Texas and and eastern eastern New New Mexico; ~exico; the Canadian Canadian Journal Journal of of Earth Earth Sciences, sciences, v. v. 31, 31, P. p. 709-720. 709-720. Allen, Allen, D.J.; D.J.; Hinze, Hinze, W.J. W.J. and and Cannon, Cannon, W.F., W.F., 1992. 1992. 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Laws, G.Ref 1983. 1983* Geology Geology of of aa portion portion of of the the Little Little Plc Pic Lawsf G.R., River River Breccia Breccia Zone Zone within within the the Coidwell Coldwell Complex; Complex; unpublished unpublished B.Sc. B.Sc. Thesis, Thesisf Lakehead Lakehead University, University, Thunder Thunder Bay, Bayf Ontario Ontario 82p. 82p. Lilley, Lilleyf F.E.M., F.E.Mef 1964. 1964. An analysis analysis of of the the magnetic magnetic features features of the the Port Port Coldwell Coldwell intrusion; intrusion; unpublished unpublished M.SC. M.Sc. Thesis, Thesis, University University of of Western Western Ontario, Ontariof London, Londonf Ontario, Ontariof 89p. 89p. Lightfoot, Lightfootf P.C.; P*C.; Doherty, Dohertyf W.; W.; Naldrett, Naldrett, A.J. A.J. and and Sutcliffe, Sutcliffef R., R., 1994. 1994. 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Petrology Petrology of of the the eastern gabbro associated sulphide mineralization of the Coldwell Alkalic associated suiphide mineralization of the Coidwell Alkalic Complexf Ontario; unpublished B.Sc. Thesis Carleton Complex, Ontario; unpublished B.Sc. Thesis Carleton University, Ottawa, Ottawa, Ontario, Ontario, 65p. 65p. with with appendix. appendix. University, Lumbersf S.B., S.B., 1978. 1978. Geological Geological setting setting of of alkalic alkalic rockrockLumbers, carbonatite complexes complexes in in eastern eastern Canada; Canada; p. p. 81—89, 81-89, carbonatite Proceedings of of First First International International Symposium Symposium on on Proceedings carbonatites: Pocos Pocos de de Caldas Caldas Minas Minas Gerias, Gerias, Brazil: Brazil: carbonatites: Ministerio Ministerio Das Das Minas Minas EE Energia. Energia. Department Department Nacional Nacional de de Producao Producao Mineral. Mineral. Manson, Manson, M.L. M.L. and and Halls, Hallsf H.C., H.C., 1994. 1994. Post—Keweenawan Post-Keweenawan compressional compressional faults faults in in the the eastern eastern Lake Lake superior superior region region and and their tectonic tectonic significance; significance; Canadian Canadian Journal Journal of of Earth Earth their v. 31, 31, p. p* 640—651. 640-651. Sciences, v. Sciences, Mariano, Mariano, J. J * and and Hinze,, Hinzef, W.J., W.Jef 1994a. 1994a. Structural Structural interpretation interpretation of of the the Midcontinent Rift in in eastern eastern Lake Lake superior superior from from seismic seismic reflection reflection and and potential—field potential-field studies; V * 31., 3 1 e fp. p. 619619studies; Canadian Canadian Journal Journal of of Earth Earth Sciences, Sciences, V. . 628. 628 Mariano, J. J. and and Hinze, Hinzef W.J., W.Jef 1994b. 1994b. Gravity Gravity and and magnetic magnetic models models of of the the Midcontinent Midcontinent Rift Rift in in eastern eastern Lake Lake Superior; Superior; Canadian Canadian Journal Journal of of Earth Earth Sciences, Sciences, v. v. 31, 31, p. p. 661-674. 661-674. - McGill, M.K., M.K., 1980. 1980. The The coldwell coldwell complex complex western western margin margin petrology petrology and intrusive intrusive relationships; relationships; unpublished unpublished B.Sc. B.Sc. Thesis, Thesisf Lakehead Lakehead University, University, Thunder Thunder Bay, Bayf Ontario. Ontario. McLaughlin, McLaughlinf R.M., R.M., 1990. 1990. Accessory Accessory Rare Rare Metal Metal Mineralization Mineralization in Northwest Ontario; Ontario; Coldwell Alkaline Alkaline Complex, Complex, Northwest in the the Coidwell unpublished unpublished M.Sc. M.Sc* Thesis, Thesis, Lakehead Lakehead University, University, Thunder Thunder Bay, Bayf Ontario; Ontario; 123p. 123p. with with appendix. appendix. Melnik, Melnikf N. N. 1984. 1984. Textural Textural Evidence Evidence for for the the Origin Origin of of the the Prairie Ontario Prairie Lake Lake Carbonatite Carbonatite - Alkalic Alkalic Rock Rock Complex, Complex, Ontario Canada, Canada, unpublished unpublished B.Sc B.Sc Thesis, Thesisf Queen's Queen's University, University, Kingston, Kingston, Ontario, Ontariof 81p. alp. - Mereu, Mereuf R.F., R.FOf 1965. 1965. AA Study Study of of Apparent Apparent Angle Angle of of Emergence Emergence at at Marathon Marathon Ontario Ontario from from the the Lake Lake Superior Superior Data; Data; Seismological Seismological Society Society of of America America Bulletin, Bulletin, v. v. 55., 55.f p. p. 405—416. 405-416. �68 Milne,V.G., V.G., 1967. 1967.Geology Geologyofofthe theCirrus CirrusLake-Banioos Lake-Bamoos Lake Iake Mime, area; Ontario Ontario Department Department of of Mines Mines Geological Geological Report Report 43. 43. area; R.H. and and Platt, Platt, R.G., R.GO8 1977. 1977. Field Field Guide Guide to to aspects aspects Mitchell, R.H. of of the the geology geology of the the Coidwell Coldwell alkaline alkaline complex; complex; Field Field guide guide prepared for for the the 23rd. 23rd. Annual Annual meeting meeting of of the the Institute Institute on on prepared Lake 34p. Lake Superior Superior Geology, Geology8 34p. R.H. and Platt, Platt8 R.G., R.G., 1978. 1978. Mafic mineralogy mineralogy of of Mitchell, R.H. ferroaugite syenite syenite from from the the Coidwell Coldwell alkaline alkaline complex, complex8 ferroaugite 0ntario8 Canada; Canada; Journal Journal of of Petrology, Petrology, v. v. 19., 19*, p. p. 627-651. 627-651. Ontario, Mitchell, Mitchell, R.H. R.H. and Platt, Platt, G.R., G * R O 81979. 1979. Nepheline-plagioc].ase ~epheline-plagioclase and intergrowths of of inetasomatic metasomatic origin Coldwell intergrowths origin from the Coidwell complex8 Ontario; Ontario; Canadian Canadian Mineralogist, Mineralogist, v. v. 17., 17.' p. p. 537-540. 537-540. complex, Mitchell, Mitchell, R.H. R.H. and and Platt, Platt8 G.R., G.R., 1982a. 1982a. Mineralogy Mineralogy and and petrology petrology of of nepheline nepheline syenites syenites from from the the Coidwell Coldwell alkaline alkaline complex, Ontario, Ontario, Canada; Canada; Journal Journal of of Petrology, Petrology, v. v. 23, 23, p. p. complex, 186—214. 186-214. Mitchell, R.H. and and Platt, Platt, G.R., G.RO81982b. 1982b. The The Coldwell Coldwell Alkaline Alkaline Mitchell,R.H. Complex; p. 42-71; 42-71; Field Trip Trip Guidebook, Guidebook8 Trip Trip 4, 4, Complex; p. Field Proterozoic Proterozoic Geology Geology of of the the northern northern Lake Lake Superior Superior Area; Area; J.M. J.M. Franklin F'ranklin editor; editor; Geological ~eologicalAssociation of CanadaCanadaMineralogical Mineralogical Association Association of of Canada. Canada* Mitchell, Mitchell, R.H.; R.H.; Platt, Platt, G.R G.R and and Cheadle, Cheadle, S.P., S.PO8 1983. 1983. AA gravity Coldwell complex, complex8 northwestern northwestern Ontario Ontario gravity study study of the the Coidwell and and its its petrological petrological significance; significance; Canadian Journal Journal of of Earth Earth Sciences, Sciences, v. v. 20, 20, p. p. 1631—1638. 1631-1638. Mitchell, R.H.; Laflamme, Laflame, J.H. J.H. and and Cabri, Cabri, L.J., L.Je8 1989. 1989. Mitchell8 R.H.; Rhenium Rhenium suiphide sulphide from from the the Coidwell Coldwell alkaline alkaline complex, complex, northwestern northwestern Ontario, Ontario8 Canada; Canada; Mineralogical Mineralogical Magazine, Magazine, v. v. 53, 53, p. 635—637. 635-637. p. Mitchell, Mitchell, R.H., review of of the the compositional compositional R.H., 1990. 1990. AA review variation of amphiboles in alkaline variation of amphiboles in alkaline plutonic plutonic complexes, complexes8p. p. 135-156, jn Alkaline igneous rocks and carbonatites, 135-156, Alkaline igneous rocks and carbonatites, A.R. A.R. Woolley M. Ross Ross editors; editors; Lithos, Lithost v. v. 26. 26. Woolley and and M. Mitchell, Mitchell, R.H.; R.H.; Platt, Platt, G.R.; G.R.; Downey, Downey, M. M. and and Laderoute, Laderoute, D.G., D.G., 1991. Petrology of alkaline lamprophyres from 1991. Petrology of alkaline lamprophyres from the the coidwell coldwell alkaline alkaline complex, complex, northwestern northwestern Ontario; Ontario; Canadian Canadian Journal Journal of of Earth 28, p. p. 1653—1663. 1653-1663. Earth Sciences, Sciences, v. v* 28, Mitchell, J.; ArtistArtistMitchell, R.H.; R.H.; Platt, Platt, G.R.; G.R.; Lukosius-Sanders, Lukosius-Sanders, J.; Downey, s., 1993. 1993. Petrology Petrology of of Downey, M. M. and and Moogk-Pickard, S., syenites syenites from from Centre Centre III I11 of of the the Coidwell Coldwell alkaline alkaline complex, complex, northwestern northwestern Ontario, Ontario, Canada; Canada; Canadian Canadian Journal Journal of of Earth Earth Sciences, Sciences8 v. v. 30, 30, p. p. 145—158. 145-158. �69 Mitchell, R.H. R.H. and Platt, G.R., 1994. Mitchellf Plattf G.Ref 1994. Aspects of the Geology of the Coidwell Coldwell Complex; Complex; Field Trip Trip A2; prepared prepared for for the the Geological Geological Association Association of Canada and and the the Mineralogical Mineralogical Association Association of of Canada, Canadaf 36p. 36p. Muir, Muirf T.L., T.Lef 1982. 1982. Geology Geology of the the Heron Bay Bay Area, Areaf District District of Thunder Thunder Bay; Ontario Ontario Geological Geological survey survey Report Report 218, 218# 89p., 89p., accompanied accompanied by map 2439, 243gf scale scale 1:31,680. 1:3lf68OO Mulja, T. Mitchell, R.Haf RH., 1991. . and Mitchellf 1991. The The Geordie Geordie Lake Lake Muljaf T Intrusion, Palladium- and and Intrusionf Coidwell Coldwell Complex, Complexf Ontario: A PalladiumTellurium—rich Tellurium-rich disseminated sulfide sulfide occurrence derived from v. 86., 86.# p. p. 10501050tholeiitic magma; Economic Geology, v. evolved tholeiitic 1069. 1069. Nicholson, Midcontinent Rift Nicholsonf S.W S.W and Shirley, Shirleyf S.B., S.Bef 1990. Hidcontinent volcanism in Region: Sr, in the the Lake Superior Region: Srf Nd and Pb isotopic evidence evidence for isotopic for a Mantle Plume; Journal Journal of of Geophysical Geophysical Research, Researchf v. v o 95, 95# n. n. B7, Byf P. P. 10,851—10,868. 10f851-10f868. Nicol, Nicolf D.N., D.NOf 1990. 1990. Assimilation Assimilation of of basic basic Xenoliths Xenoliths with with Centre of the the Coidwell Coldwell complex, complexf Ontario; Ontario; Centre 33 syenites syenites of unpublished M.Sc. M.Sc. Thesis, Thesisf Lakehead Lakehead University, Universityf Thunder Thunder Bay, Bayf Ontario, Ontariof 59p. 59p. with with appendix appendix ODM-GSC, ODM-GSCf 1963a. 1963a. Slate Slate Islands, Islandst Ontario Ontario Department Department of of MinesMinesGeological Survey Survey of of Canada, Canadaf Aeromagnetic Aeromagnetic Map Hap 2146G, 2146Gf scale scale 11 Geological inch inch to to 11 mile(1:63,360). mile(l:63f 360). ODM-GSC, ODM-GSCt 1963b. 1963b. Ashburton Ashburton Bay, Bayf Ontario Ontario Department Department of of MinesMinesGeological Survey of Canada, Aeromagnetic Map 2147G, Geological Survey of Canadaf Aeromagnetic Hap 2147Gf Scale Scale 11 inch 360). inch to to 11 mile(1:63, mile(1:63f360). ODM-GSC, ODM-GSCf 1963c. 1963c. Heron Heron Bay, Bayf Ontario Ontario Department Department of of MinesMinesGeological Survey of Canada, Aeromagnetic Map 2156G, Geological Survey of Canadaf Aeromagnetic Xap 2156Gf Scale Scale 11 inch to 1 mile(1:63,360). inch to 1 mile(l:63f360). ODM-GSC, ODM-GSCf 1963d. 1963d. Goodchild Goodchild Creek, Creekf Ontario Ontario Department Department of of Mines-Geological Survey of Canada, Aeromagnetic Mines-Geological Survey of Canadat Aeromagnetic Map Map 2157G, 2157Gf Scale Scale 11 inch inch to to 11 mile(1:63,360). mile(l:63,360). - ODM-GSC 1963f. 1963f. Killala Killala Lake; Lake; Ontario Ontario Department Department of of Mines Mines Geological Aeromagnetic Map Geological Survey Survey of of Canada, Canadaf Aeromagnetic Hap 2148G, 2148Gf Scale Scale 11 inch inch to to 11 mile(1:63,360). mile(l:63t360). - ODM-GSC ODM-GSC 1963g. 1963g. Vein Vein Lake; Lake; Ontario Ontario Department Department of of Mines Mines Geological Geological Survey Survey of of Canada, Canadaf Aeromagnetic Aeromagnetic Map Xap 2158G, 2158Gt Scale Scale 11 inch inch to to 11 mile(l:63,360). mile(l:63f360). Ohnenstetterf D.; D.; Watkinson, Watkinsonf D.H. D.H. and and Dahi, Dahlf R., R o t1991. 1991. Zoned Zoned Ohnenstetter, from the the Two Two Duck Duck Lake Lake intrusion, intrusionf Coidwell Coldwell hollingsworthite from hollingsworthite complex, complexf Ontario; Ontario; American American Mineralogist, Mineralogistf v. v o 76, 76# p. p. 169416941700. 1700. �70 Paces, Pacesl J.B. J.B. and and Miller, Millerl Jr., J r e 1J.D., J.Def 1993. 1993. Precise Precise U—Pb U-Pb Ages Ages of Ic Intrusionsf Intrusions, Northern of Duluth Duluth Complex Complex and and Related Related Maf Mafic Northern Minnesota: Geochronological Geochronological Insights Insights to to Physical, Physicall Minnesota: Petrogeneticl Paleomagnetic Paleomagnetic and and Tectonomagmatic Tectonomagmatic Processes Processes Petrogenetic, Associated Midcontinent Rift Rift System; System; Journal Journal Associated with with the the 1.1 1.1 Ga Ga Midcontinent of of Geophysical Geophysical Research Research Letters, Lettersl v. v. 98, n.B8, n.Bgf p. p. 13,997— 13199714,013. 141013. Paces, Pacesl J.B. J.B. and and Davis, Davisl D.W., D e w a l1988. 1988. Implications Implications of of high high precession precession U-Pb U-Pb age age dates dates on on zircons zircons from from Portage Portage Lake Lake volcanic volcanic basalts basalts on on Midcontinent Midcontinent Rift Rift subsidence subsidence rates; rates; lava lava flow flow repose repose periods periods and and magma magma production production rates; rates; p. p. 85—86, 85-861 .jfl Program with with Abstracts Abstracts 34th 34th Annual Annual Meeting Meeting of of the the Institute Institute Program on on Lake Lake Superior Superior Geology. Geology. Palmerf H.C. H.C. and and Davis, Davisf D.W., D.W.# 1987. 1987. 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P. 227-283, 227-2831.jn Exposed Cross-sections Cross-sections of of the the Continental Continental Crust; Crust; M.H. M.H. Salisbury Salisbury and and D.M. D.M. Fountain Fountain editors; editors; Kiuwer Kluwer Academic Academic Publishers, PublisherslNetherlands. Netherlands. Percival, Percivall J.A. J.A. and and Card, Cardl K.D., K.DeI 1983. 1983. Archean Archean Crust Crust as as revealed revealed in in the the Kapuskasing Kapuskasing Uplift, Upliftl Superior Superior Province, Provincef Canada; Canada; Geology, Geologyl v. v. 11, llfp. p. 323—326. 323-326. Platt, Plattl G.R. G.R. and and Mitchell, Mitchellf R.H., R.H.# 1979. 1979. The The Marathon Marathon Dikes. Dikes. I: I: Zirconium-rich Zirconium-rich titanium titanium garnets garnets and and manganoan manganoan magnesium magnesium ulvospinel—inagnetite ulvospinel-magnetite spinels; spinels; American American Mineralogist, Mineralogistl v. v. 64, 64# p. p. 546—550. 546-550. Platt, Plattl G.R. G.R. and and Mitchell, Mitchelll R.H., R.H.# 1982a. 1982a. The The Marathon Marathon Dikes: Dikes: ultrabasic ultrabasic lamprophyres lamprophyres from from the the vicinity vicinity of of McKellar McKellar Harbour, Harbourl NW. N.W. Ontario; Ontario;American AmericanMineralogist, Mineralogistfv. v. 67., 67.# p. p. 907—916. 907-916. PLatt, PLattl G.R. G.R. and and Mitchell, Mitchell! R.H., R.Hef1982b. 1982b. Rb-Sr Rb-Sr geochronology geochronology of of the the Coidwell Coldwell complex, complexl northwestern northwestern Ontario, Ontariof Canada; Canada; Canadian Canadian Journal Journal of of Earth Earth Sciences, Sciencesf v. v. 19, 1glp. p. 1796—1801. 1796-1801. Platt, PlattlG.R.; G.R.; Mitchell, MitchellfR.H. R.H. and andHolin, Holml P.M., P.Me1 1983. 1983. Marathon Marathon dikes: Rb-Sr and and K-Ar K-Ar geochemistry geochemistry of of ultrabasic ultrabasic dikes: Rb-Sr lamprophyres lamprophyresfrom from the the vicinity vicinity of of McKellar McKellarHarbour, Harbourl northwest Journal of of Earth Earth Sciences, Scienceslv. v. northwest Ontario; Ontario; Canadian Canadian Journal 20, 201p. p. 961—967. 961-967. �71 Platt, G.R. and Mitchell, R.H., 1984. Rb-Sr geochronology of the coldwell complex, northwestern Ontario, Canada: Reply: Canadian Journal of Earth Sciences, v. 21, p. 126. j Puskas, F.W., 1970. The Port Coidwell Alkali Complex; p. 87100, Proceedings for the 16th Annual Meeting of the Institute on Lake Superior Geology. Puskas, F.P., 1967. Geology of the Port Coldwell Area, Ontario Department of Mines Open File Report 5014, 94p. Sage, R.P., 1978. Diatremes and Shock Features in Precambrian Rocks of the Slate Islands, Northeastern Lake Superior; Geological Society of America Bulletin, v. 89., p. 1529—1540. Sage, R.P. 1982. 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Imaging using using large large aperture aperture seismic seismic data; data; Geophysical Geophysical Research Research Letters, Letters, v. v. 18, 18, n.4, n.4, p. p. 625—628. 625-628. Tuominen, Coldwell Area, Area, Ontario Ontario Department Department Tuominen, H.V., H.V., 1967. 1967. Port Port Coldwell of of Mines Mines map map P114, P114, Scale Scale 11 inch inch to to1/4 114 mile(1:15,840). mile(l:15,840). Turek, Turek, A.; A. ;Smith, Smith,P.E. P. E. and andSynions, Symons, D.T.A., D.T.A., 1985. 1985. U-Pb U-Pb geochronology geochronology of of the the Coidwell Coldwell complex, complex, northwestern northwestern Ontario, Ontario, Canada; Canada; Canadian ~anadianJournal Journal of of Earth Earth Sciences, Sciences, v. v. 22, 22, n. n. 4, 4, p. p. 621—626. 621-626. Turek, D.T.A, 1986. Smith, P.E. P.E. and Symons, D.T.A., 1986. U-Pb U-Pb Turek, A.; A. ; Smith, geochronology northwestern Ontario, Ontario, geochronology of of the the Coldwell Coldwell complex, complex, northwestern Canada: Canada: Reply; Reply; Canadian Canadian Journal Journal of of Earth Earth Sciences, Sciences, v. v. 23, 23, p. p. 127—128. 127-128. Van Martin, M.W.; M.W.; Sprowl, Sprowl,D.R.; D.R.; Geissman, Geissman,J. J. Van Schumus, Schumus,W.R.; W.R.; Martin, and and Pb Pbisotopic isotopic composition composition and Berendsen, Berendsen, P., P., 1990. 1990. Age, Age, Nd Nd and �73 and magnetic Midcontinent Midcontinent Program Program with with polarity polarity for for subsurface subsurface samples samples of of the the 1100 1100 Ma Ma Rift; p.Al74, Geological Society Society of of America Rift; p.A174, Geological Abstracts, Abstracts, v. v. 22. 22. Walkert E.C.; E.C.; Sutcliffe, Sutcliffe, R.H.; R.H.; Shaw, Shaw, C.S.J.; C.S.J.; Shore; Shore; G.T. G.T. and and Walker, P e n m a k t R.S., R.S.t 1993a. 1993a. Precambrian Precambrian geology, geology, Port Port Coidwell Coldwell Penczak, Complex, east east half; half; Ontario Ontario Geological Geological Survey Survey Preliminary Preliminary Complex, Map P3233, P3233# scale scale 1:20,000. 1:2Ot0O0. Walker, E.C.; E.C.; Sutcliffe, Sutcliffet R.H.; R.H.; Shaw, Shawl C.S.J.; C.S.J.; Shore, Shoret G.T. G.T. and and Walker, Penczakt R.S., R.S.t 1993b. 1993b. Precambrian Precambrian geology, geology, Port Port Coldwell Coldwell Penczak, Complext west west half; half; Ontario Ontario Geological Geological survey, surveyt Preliminary Preliminary Complex, Map Map P3232, P3232, scale scale 1:20,000. 1:20,000. Walkert E.C.; E.C.; Sutcliffe, ~ u t c l i f f eR.H.; R.H.; ~ Shawl C.S.J.; C.S.J.; Shore, Shoret G.T.; G.T.; Walker, Shaw, Penczak, R.S., R e S o l1993c. 1993c. Precambrian Precambrian geology geology of of the the and Penczak, Coldwell Alkalic ~ l k a l i ccomplex; complex; Ontario Ontario Geological Geological Survey, Survey, Open Open Coidwell File 30p. File Report Report 5868, 5868, 30p. Walker, J.W.R. J.W.R. 1967. 1967. Geology Geology of of the the Jackfish Jackfish Middleton Middleton Area; Area; Walker, Ontario Ontario Department Department of of Mines, Minest Geological Geological Report Report 50, 50, 41p. 41p. Wanless, Wanlesst P. P. 1976. 1976. Petrology Petrology and and Geochemistry Geochemistry of of the the Killala Killala Lake Alkali Alkali Complex; Complex; unpublished unpublished B. B. Sc. Sc. thesis, thesist Queen's Queents University, University, Kingston, Kingston, 66p. 66p. Watkinsont D. D. H. H. 1971. 1971. Petrology Petrology and and U-Nb U-Nb mineralization mineralization of of Watkinson, the the Alkalic Alkalic Rock-Carbonatite Rock-Carbonatite Complex Complex at at Prairie Prairie Lake, Laket Ontario; Ontario; (abstract) (abstract) Canadian Canadian Mineralogist, Mineralogist, v. v. 10, lotpt. pt. 5, 5, p.921. p.921. Watkinson, Watkinsont D.H. D.H. 1973. 1973. Pseudoleucite Pseudoleucite from from Plutonic Plutonic Alkalic Alkalic Rock-Carbonatite Rock-Carbonatite Complexes; Complexes; Canadian Canadian Mineralogist, Mineralogisttv. v. 12, 12,p. p. 129—134. 129-134. Watkinson, Watkinsont D.H. D.H. 1976. 1976. Geology Geology of of the the Uranium—Niobium Uranium-Niobium Mineralization Rock-Carbonatite Complex, Complext Mineralization of of the the Alkalic Alkalic Rock-Carbonatite Prairie Prairie Lake, Laket Ontario; Ontario; unpublished unpublished report. report. Watkinson, Watkinson, D.H. D.H. and and Ohnenstetter, Ohnenstettert D., D.! 1992. 1992. Hydrothermal Hydrothermal origin origin of of platinum group group mineralization mineralization in in the the Two Two Duck Duck Lake Lake intrusion, intrusiont Coldwell Coldwell complex, complex, northwestern northwestern Ontario; Ontario; Canadian Canadian Mineralogist, Mineralogistt v. v. 30, 30t P. p. 121—136. 121-136. Whittaker, Whittaker, P.J., P.J., 1976. 1976. Geology Geology of of the the East East Central Central Port Port Coidwell Coldwell Complex Complex from from the the Pic Pic River River to to Red Red Sucker Sucker Cove; Cove; unpublished unpublished M.Sc. M.Sc. Thesis, Thesist MacMaster MacMaster University, University, Hamilton, Hamilton, Ontario. Ontario. Wilkinson, Wilkinson, S.J., S.Jet 1983. 1983. Geology Geology and and sulphide sulphide mineralization mineralization of the the marginal marginal phases phases of of the the Coidwell Coldwell complex, complext northwestern northwestern Ontario; Ontario; unpublished unpublished M.Sc. M.Sc. Thesis, ThesistCarleton, Carleton, University, Universityt Ottawa, Ottawat 129p. 129p. with with appendix appendix �74 Williams, WilliamsI H.R. H.R* 1989. 1989. Geological Geological studies studies in in the the Wabigoon, WabigoonI Quetico Quetico and and Abitibi—Wawa Abitibi-Wawa subprovinces, subprovincesI Superior Superior Province Province of of Ontario, Ontario, with with emphases emphases on on the the structural structural development development of of the the Bearbore-Geraldton Belt; Belt; Ontario Ontario Geological Geological Survey, SurveyI Open Open Beardmore-Geraldton File File Report Report 5724, 5724, 189p. 189p. Wold, WoldI R.J.; R o s e ;Hutchinson, HutchinsonI D.R. D - R . and and Johnson, Johnson, T.C., T . C * , 1982. 1982. Topography icial structure structure of Lake Superior Topography and and surf surficial Superior bedrock bedrock as as based on on seismic seismic reflection reflection profiles; profiles; p. p. 257-272, 257-272, ft Geological Geological Society Society of of America America Memoir Memoir 156 156 �75 �NOTES NOTES �NOTES NOTES � https://digitalcollections.lakeheadu.ca/files/original/157c2078900a8fba2519d21214d63003.pdf d696c36d2d38bf5d60590b38819e07da PDF Text Text Geology, Structure Sfructure and Age Relationships of Manitou wadge Greenstone Greenstone Belt and the the Manitouwadge Wawa-Quetico Subprovince Boundary, Boundary, Wawa-Quetico North western Ontario Ontario North Institute Instituteon onLake LakeSuperior SuperiorGeOlogy Geology 41st 1995 41st Annual AnnualMeeting, Meeting,May May13-18, 13-18,1995 Marathon, Marathon, Ontario Ontario Proceedings ProceedingsVolume Volume 41: Part Part2b 2b Field Field Trip TripGuidebook Guidebook 41$t JJSG —7' I 'P �Geology, structure structure and age relationships Geology, relationships of the Manitouwadge greenstone belt and the the Wawa-Quetico Wawa-Quetico subprovince boundary, northwestern northwestern Ontariol Ontario1 Field guidebook guidebook by by Peterson3, H. Lockwood4 E. Zaleski2, Zaleski2, V.L. Peterson3, Lockwood^ and 0. 0.van vanBreernen2 Breemen2 1Geological Survey of of Canada Canada Contribution Geological Survey Contribution 13995 13995 Project funded funded by by the the Canada-Ontario Canada-OntarioSubsidiary Subsidiary Agreement Agreement on Northern Ontario OntarioDevelopment Development (1991-1995), (1991-1995), Canada-Ontario Canada-OntarioEconomic Economic and and Regional Region al Development Development Agreement 2Continental Survey ooff Canada, Canada, Continental Geoscience Geoscience Division, Geological Survey 601 Booth Booth Street, Ottawa, K I A 0E8 OE8 Ottawa, Ontario, Ontario,K1A 3Department Departmen t of o fGeosciences Geosciences and Anthropology, Western Carolina Carolina University, University, Cullowhee, North Carolina, Carolina,28723, 28723, U.S.A. U.S.A. 4Hemlo ^Hemlo Gold Mines, P.O. Box Box 40, 40, Marathon, Ontario, Ontario,POT POT 2E0 2E0 Marathon, (formerly of o f Geco Mining Division, Noranda Minerals Inc.) (formerly Sillimanite knots in in metamorphosed metamorphosed altered altered felsic felsic rocks near Willroy mine (left). Folded and and Frontispiece: Sillimanite near the Willroy (left). Folded brecciated right). Mafic Mafic to tointermediate in termediatemetavolcanic metavolcanic inclusions in tonalite tonalite along along the the brecciated iron formation formation (upper right). folded at ten tuated extensions extensions of o f the theManitouwadge Manitouwadge greenstone belt (lower (lower right). folded attentuated �TABLE OF OF CONTENTS CONTENTS INTRODUCTION INTRODUCTION 11 Methodology ........................................................................................ Methodology REGIONAL REGIONAL SETTING SETTING -22 Relationships in in the theWawa Wawasubprovince subprovince Relationships 33 Structural and and tectonic tectonic setting setting ....................................................................... Structural Metamorphism .....................................................................................-44 Geochronological constraints constraints ........................................................................ -44 Geochronological HISTORICAL BACKGROUND BACKGROUND OF OF THE THEMANITOUWADGE MANITOUWADGEBELT BELT HISTORICAL - 55 History of deposits ................................................................................. 66 interpretations ............................................................... Previous mapping and interpretations 66 Historical nomenclature, the the 'Mine 'Mine Series' Series' ........................................................... DESCRIPTION OF OFUNITS UNITS DESCRIPTION rock units units .............................................................................-77 Supracrustal rock 77 3) ............................................................... Mafic metavolcanic rocks (Unit 3) 99 Mixed mafic-felsic mafic-felsic metavolcanic rocks (Unit 4) 4) ................................................... 99 Intermediate to tomafic maficmetavolcanic metavolcanic rocks (Unit 5) 5) ............................................... Intermediate 10 Felsic to intermediate intermediate metavolcanic metavolcanic rocks rocks (Unit (Unit 6) 6) ..............................................10 11 7) ......................................................11 Aphyric felsic metavolcanic rocks (Unit 7) 11 11 felsic metavolcanic rocks (Unit 8) 8) ................................................ Quartz-phyric felsic 12 12 (Unit 9) 9) ........................................................ Metamorphosed iron formation (Unit rocks (Unit (Unit 10) 10) ..............................................................13 13 Metasedimentary rocks 13 Tectonic rock units ................................................................................. 13 13 Straight gneiss gneiss (Unit (Unit 11) 11) ....................................................................... 13 Straight 13 rock units units ................................................................. 13 Metasomatically altered rock 13 Orthoamphibole-garnetkordierite gneiss gneiss (Unit (Unit 2) 2) .............................................. 13 Orthoamphibole-garnet±cordierite Sillimanite-muscovite-quartz Sillimanite-muscovite-quartzand sillimanite-knot sillimanite-knot felsic felsic schist (Unit (Unit 1) 1) ..........................14 14 15 Synvolcanic Synvolcanic intrusions intrusions .............................................................................. 15 (Unit 12) 12) ........................................15 15 Foliated trondhjemite-hornblende granodiorite (Unit 15 Syn- to post-tectonic intrusions intrusions ..................................................................... 15 15 granitoid (Unit (Unit13) 13) ............................................. 15 Foliated K-feldspar porphyritic granitoid Undivided foliated intrusive rocks rocks (Unit (Unit 14) 14) .................................................... 16 16 Pegmatite, aplite aplite and and foliated foliated granite granite (Unit (Unit 15) 15) ................................................16 16 17 Alkalic Alkalic rocks (Unit (Unit 16) 16) ......................................................................... 17 17 Quetico Quetico subprovince subprovince ................................................................................ 17 17 Metasedimentary rocks rocks (Unit (Unit lOq) lOq) 17 Proterozoic Proterozoic intrusions intrusions ..............................................................................18 18 dykes .................................................................................18 18 Diabase dykes STRUCTURAL GEOLOGY D1 Dl deformation deformation ....................................................................................18 18 D2 deformation ....................................................................................19 19 Da deformation deformation ....................................................................................24 24 D3 D4 D4 deformation deformation ....................................................................................25 25 Late faults faults .........................................................................................26 26 Late GEOCHRONOLOGY Zircon—Metavolcanic and metasedimentary metasedimentary rocks Zircon-Metavolcanic and rocks ....................................................26 26 Zircon and rocks and and brackets on deformation and monazite—Intrusive monazite-Intrusive rocks deformation ...................................28 28 31 Titanite ............................................................................................ 31 Titanite SETTING OF OFMINERALIZATION MINERALIZATION SETTING Relationships Relationships of orebodies and host host rocks rocks ...........................................................32 32 Structural Structural complications—DuD2 complications-Di/D2 folds folds and faults faults ...................................................33 33 GEOCHEMISTRY GEOCHEMISTRY 34 Metavolcanic and and subvolcanic subvolcanic rocks rocks ................................................................. 34 rocks ....................................................................................... 38 Altered rocks 38 DISCUSSION DISCUSSION setting and and deformation deformation of of massive massive sulphide sulphide deposits deposits and and alteration alterationzones zones ..............41 41 Depositional setting ............................................................. ............................................................. 11 �Structuraland andtectonic tectonicsynthesis synthesis ................................................................... 4242 Structural REFERENCES ......................................................................................... 4444 REFERENCES FIELD-TRIPSTOPS STOPS FIELD-TRIP ............................................................................................ Introduction 49 Introduction Knowneconomic economicdeposits, deposits.inner innervolcanic volcanicbelt belt .......................................................49 -49 A .Known A. A1-A8 . Willroy-Geco Willroy-Gecoarea area .........................................................................4949 A1—A8. SlimLake Lakesection section ......................................................................... 5555 A9-A20 . Slim A9—A20. A21.Nama NamaCreek Creekdeposit deposit ..........................................................................5656 A21. metavolcaniccontact contact ....................................57 57 A22-A23 . Da A22—A23. D2 folds folds of of iron formation/felsic formation/felsic metavolcanic and inner inner hinge hingeof ofthe theManitouwadge Manitouwadgesynform synform .............................59 59 A24-A26 . Willecho A24—A26. Willecho 33 pit pit and B.Outer Outervolcanic volcanicbelt belt ................................................................................. -606 0 B. B l Northern . Northerncontact contactzone zone .........................................................................6060 Bi. B2-B10 . Gaug area, comparison comparisonto toinner innervolcanic volcanicbelt belt .........................................61 61 B2—B10. Gang Lake area, B11-B21 . Hinge Manitouwadgesynform synformnear nearSwill SwillLake Lake ...............................64 64 Bi 1—B2 1. Hingeregion region of of the the Manitouwadge C .Inner InnerManitouwadge Manitouwadgesynform, synform,Dead DeadLake Lakesuite suite .......................................................67 67 C. D .Eastern Easternextension extensionofofthe the'Geco 'Gecohorizon' horizon' .............................................................. 70 70 D. Dl-D2 . Eastern inner inner volcanic volcanic belt, belt. 'Geco 'Gecohorizon' horizon' .................................................70 70 D1—D2. 70 D3-D4 . Orthoamphibole-cordierite-garnet rocks, rocks, Banana Banana area area ....................................... D3—D4. 70 E .Quetico Queticosubprovince, subprovince.Jim JimLake Lakesynform synform .............................................................. 72 72 E. El-E3 . Quetico subprovince, subprovince. eastern eastern Manitouwadge Manitouwadgearea area ........................................... 73 73 E1—E3. E4-E6 . Jim Lake Lake synform, synform. Jim/Davis JimIDavisLakes Lakesarea area ................................................... 7373 E4—E6. BlackPic Picbatholith, batholith.supracrustal supracrustalscreens screensand andmajor majorfolds folds .............................................74 74 F.F .Black Pic batholith batholith ......................................................................... 74 74 F1-F5 . Black Pic F1—F5. F6-F12 . Western Blackman Blackmail Lake antiform antiform (D3), (D3). Janet JanetLake Lakeroad road ...................................75 75 F6—F12. G .Quetico Queticosubprovince, subprovince.western western and andcentral centralManitouwadge Manitouwadgearea area ........................................ 76 76 G. 77 ACKNOWLEDGEMENTS ............................................................................. 77 ACKNOWLEDGEMENTS iii 111 �Manitouwadge greenstone belt belt Introduction INTRODUCTION Despite its its relatively relatively small small size, size, the the Manitouwadge Manitouwadge greenstone belt is is host host to tosignificant significant economic economic Cu-Zn deposits, the most most productive productive being being Noranda's Noranda's Geco Geco mine. mine. ItIt isisamong amongthe thelargest largestof ofCanadian Canadianvolcanogenic volcanogenic massive suiphide deposits, deposits, with with total lifetime production production projected projected at 55.9 tonnes. The massive sulphide 55.9 million tonnes. Thedeposits deposits of of the belt belt have have been been known known since since the the 1950's, 1950's, and and early early theories theories of of their their origin origin and and geological geological history history are aa microcosm microcosm of the major major debates debateson onmassive massivesulphide sulphide petrogenesis. petrogenesis. In Inmore morerecent recentyears, years,aavolcanogenic volcanogenicorigin origin has has been been generally generally accepted accepted for for the the Manitouwadge Manitouwadge deposits deposits (Friesen (Friesen et et al., al.,1982; 1982;Bakker Bakker et et al., al.,1985; 1985;Williams Williams et et al., al., 1990), 1990), although although their their stratigraphic, stratigraphic, structural structural and andtectonic tectonic setting, setting,their theirrelationships relationships and and detailed detailed petrogenesis petrogenesis were were largely largely unknown unknown or or controversial. controversial. In interest of of the area In recognition recognition of the economic economic interest area and and the theimpending impendingclosure closure of of the the Geco Geco mine, mine, the the Manitouwadge project was conceived to further further understanding of mineralization, alteration, metamorphism Manitouwadge project conceived to metamorphism and camp. Within this mandate, and deformation deformation and their their relationships relationships in the Manitouwadge Manitouwadge camp. mandate, the the project project has has focussed on 1) 2) the theinfluences influences of of primary primary depositional depositional setting, setting, focussed on 1) the the evolution evolution of of the theManitouwadge Manitouwadge belt; belt; 2) deformation, on the the belt belt and its mineral deposits; deposits; and and 3) 3) the relationship of the the belt belt to deformation, and metamorphism metamorphism on relationship of the the enclosing enclosing plutonic rocks rocks and the the adjacent adjacentWawa-Quetico Wawa-Quetico boundary. boundary. The The Manitouwadge Manitouwadge project is is still still ongoing; ongoing; although most of of the the field field component component has has been been completed, completed, laboratory laboratory and andfollow-up follow-up investigations continue. The The first first part partof ofthis thisvolume volumeisis intended intended as asaacomprehensive comprehensive interim report of of our our results results to to date. date. Some Someofofthe thematerial materialisisofofa apreliminary preliminarynature naturealthough, although,we wehope, hope, presented backgroundand andinterpretation interpretationto to stimulate stimulate discussion. discussion. The second presented with sufficient sufficient background second part of of this this volume is a field field guide guide to to the Manitouwadge area, consisting of of stops, stops, outcrop descriptions and and maps maps arranged arranged as as aa series series of day or part-day part-day field field trips. The Theorganization organization of of the field field trips is is mostly mostly thematic, with stops stops selected selected to to demonstrate demonstratecritical criticalororrepresentative representativeobservations. observations. Methodology Methodology Our Our approach approach in inthe theManitouwadge Manitouwadgeproject project has hasbeen beenprimarily primarilyfield-based, field-based,entailing entailing mapping mapping varying varying in in scale scale from from 1:5000 1:5000 in in the thearea areaofofknown knowneconomic economicCu-Zn Cu-Zndeposits, deposits, toto1:10000 1:10000and and1:20000 1:20000mostly mostlyalong along the the extensions extensions of the belt belt and and ininperipheral peripheral areas. areas. In In detailed detailed mapping, mapping, we we made madeuse useofofexisting existinggrids, grids, cut for for mineral mineral exploration exploration purposes purposes and and varying varying greatly greatly in in age, age, condition condition and and utility. utility. The Theco-operation co-operationof of cut private-sector companies, prospectors, prospectors, and Ontario Ontario government government geologists geologists contributed success of of the the private-sector contributed to the success project. Unpublished Unpublished data, data,mostly mostlyininthe theform formofofgeological, geological,geophysical geophysical and and grid grid maps, maps,drill drilllogs, logs,reports reports project. A. Turner Turner and geochemical geochemical analyses, analyses, were Noranda Inc., Granges Granges Inc., Minnova Minnova Inc., and and A. and were contributed contributed by by Noranda (prospector). (prospector). F. F. Breaks Breaks and andH. H.Williams Williams(Ontario (OntarioGeological GeologicalSurvey) Survey) allowed allowed access access to their field field notes, notes, station location locationmaps mapsand andthin thinsections, sections,providing providinguseful usefulsupplemental supplementalobservations observationsininareas areasofofplutonic plutonicrock rock station and (1957),Milne Milne and near near the theQuetico Queticoboundary. boundary.InIncombination combinationwith withthe thepublished publishedgeological geologicalmaps mapsofofPye Pye(1957), (1974) and Williams Williams and Breaks Breaks (1990b), (1990b), we used this information to direct direct mapping mapping and, and,ininsome somecases, cases, to to (1974) interpolate or orextrapolate extrapolategeological geological contacts. contacts. Our Ourfield fieldobservations observations were were compiled compiled in digital maps maps and and data data interpolate bases. bases. Aeromagnetic information, in in combination combination with with field field observations, observations, proved to be be aapowerful powerful tool tool ininrereAeromagnetic solving the complex complex structure of of the the Manitouwadge Manitouwadge belt. The Theaeromagnetic aeromagnetic data datawere were collected collected during during high high solving resolution surveys, surveys, flown flown by Dighem Surveys and Processing Inc. for Noranda Exploration Exploration Ltd., Ltd.,and andreleased released resolution by Noranda Noranda to tothe theGeological GeologicalSurvey Survey of of Canada Canada for for compilation compilation by the Geophysical Geophysical Data Centre. Centre. Published Published by (Geological Survey of Canada, 1993a, 1993b; Zaleski (Geological Canada, 1993a, Zaleski and and Peterson, Peterson, 1995) and and unpublished unpublished aeromagnetic maps based on on these these surveys surveys were were invaluable invaluable for for focussing focussing our contacts in in areas areas of of poor poor based our mapping, extrapolating contacts 1:25000map, map,showshowexposure, and and interpreting interpretingthe thelocations locationsofoffaults faultsand anddiabase diabasedykes. dykes.The Theaccompanying accompanying1:25000 exposure, ing ing geology geology draped draped over over shaded shaded relief relief of of total totalfield field magnetics, magnetics,demonstrates demonstratesthe theclose closecorrespondence correspondencebetween between map-scale map-scale structure structure and andaeromagnetic aeromagneticexpression. expression. Field observations observations and and interpretations interpretationswere were followed followed up by by laboratory laboratorystudies, studies,including includingpetrographic petrographic Field observations, in in particular particularpetrofabric petrofabricstudies studiesofoforiented orientedsamples samplesand anddocumentation documentationofofmetamorphic metamorphicminminobservations, eral assemblages. assemblages. In Inconjunction conjunctionwith withmetamorphic metamorphicstudies, studies,electron-microprobe electron-microprobe determination determinationof of mineral mineral eral compositions has been initiated. initiated. Whole-rock Whole-rockgeochemical geochemical analyses, analyses, including including major, trace and and rare-earth rare-earth compositions elements, were were done on a sample sample suite suite representing representing apparently apparently unaltered unaltered or or'least-altered' 'least-altered' metavolcanic metavolcanicrocks rocks elements, and their theiraltered alteredequivalents, equivalents,-metasedimentary metasedirnentary rocks rocks from from the theManitouwadge Manitouwadge belt beltand andQuetico Queticosubprovince, subprovince, and iron formation, formation, and and intrusive intrusiverocks. rocks. Geochronology Geochronology samples samples were were collected primary iron collected with with the the aim of dating primary volcanism, bracketing bracketing deformational deformational events and and metamorphism, metamorphism, bracketing bracketing sedimentation sedimentation and anddetermining determining volcanism, provenance, provenance, and dating dating intrusive intrusiveactivity. activity. 1 �Manitouwadge Manitouwadge greenstone greenstone belt belt Regional Regional setting setting FIG. FIG.1.1.Tectonic Tectonicmap mapofofthe thesouth southcentral centralSuperior SuperiorProvince Provinceshowing showingthe theWawa, Wawa,Quetico Queticoand andWabigoon Wabigoon subprovinces subprovinceswith with the thearea areaof of Figure Figure 22 outlined. outlined. 11==Rainy RainyLake Lake area; area; 22 ==Vermilion Vermiliondistrict, district,Minnesota; Minnesota; 33 ==Shebandowan Shebandowangreenstone greenstone belt; belt; 44 ==Max MaxCreek Creek conglomerate; conglomerate;55==Beardmore-Geraldton BeardmoreGeraldton belt; belt; 66 == Schreiber-Hemlo Schreiber-Hemlogreenstone greenstone belt; 77 == Michipicoten Michipicoten greenstone greenstone belt; 88 == Dayohessarah-Kabinagami Dayohessarah-Kabinagami greenstone greenstone belt; belt; 99 ==Kapuskasing Kapuskasingstructural structuralzone; zone;QQ ==Quetico Queticofault; fault;AA ==Atikokan; Atikokan;TB TB ==Thunder Thunder Bay; Bay;SS==Schreiber; Schreiber;GG==Geraldton; Geraldton;M M==Manitouwadge; Manitouwadge;W W==Wawa; Wawa;LL==Lepage Lepagefault faultzone. zone. Adapted Adapted from fromWilliams Williams et etal. al. (1991) (1991) and and Percival Percival (1989). (1989). The heinset insetshows showsthe thesubprovinces subprovincesof of the thesouthern southern Superior Superior Province Provinceafter afterCard Cardand andCiesielski Ciesielski(1986), (1986),and and the thearea areadetailed detailedininthe thetectonic tectonicmap. map. REGIONAL REGIONALSETTING SETTING Relationships Relationshipsin inthe theWawa Wawasubprovince subprovince TheManitouwadge Manitouwadge greenstone greenstone belt belt lies liesininthe thevolcano-plutonic volcano-plutonicWawa Wawasubprovince subprovince ofofthe theSuperior Superior The Province, near near the theboundary boundarywith withthe themetasedimentary-migmatitic metasedimentary-migmatiticQuetico Queticosubprovince subprovince(Fig. (Fig.1). 1).The Thebelt beltisis Province, aaremnant remnantofofvolcanic volcanicand andsedimentary sedimentaryrocks, rocks,highly highlydeformed deformed and and metamorphosed metamorphosed to to upper upper amphibolite amphibolitefafar cies. cies.Williams Williamsetetal.al.(1991) (1991)proposed proposedcorrelations correlationswith withthe theDayohessarah-Kabinakagami Dayohessarah-Kabinakagamiand andSchreiber-Hemlo Schreiber-Hemlo greenstonebelts, belts,and andsuggested suggestedthat thatthese theseare aredismembered dismemberedparts partsofofananoriginally originallycontinuous continuousgreenstone greenstonetertergreenstone rane.Regional Regionalmapping mappingestablished establishedthat thatsupracrustal supracrustalrocks rocks(mostly (mostlymafic maficmetavolcanic metavolcanicrocks) rocks)extend extendeast east rane. of ofManitouwadge Manitouwadge to to the the Moskinabi Moskinabi belt, and and southeast southeast to tothe theFaries FariesLake Lake belt belt (Fig. (Fig.2), 2),asasaasemicontinuous semicontinuous unitand andasasinclusions inclusionsininfoliated foliatedplutonic plutonicrocks rocks(Williams (Williamsand andBreaks, Breaks,1989; 1989;1990a, 1990a,b; b;Williams Williamset etal., al.,1992). 1992). unit The a layered complex comprising TheMoshkinabi Moshkinabiand andFaries FariesLake Lakebelts beltsare areintruded intrudedbyby a layered complex comprisinggabbro, gabbro,leucogabbro, leucogabbro, anorthosite Breaks, 1989; 1990b). anorthositeand andperidotite peridotite(Williams (Williamsand and Breaks, 1989; 1990b). The TheManitouwadge Manitouwadgebelt beltisisbounded boundedtotothe thewest westand andsouth southbybyfoliated foliatedmultiphase multiphaseplutonic plutonicrocks, rocks,colleccollectivelyknown known as as the theBlack Black Pic Picbatholith batholith(Fig. (Fig.2). 2).To Tothe thesouth, south,foliations foliationsininthe theBlack BlackPic Picbatholith batholithdefine defineaa tively structuraldome dome(Williams (Williamsand andBreaks, Breaks,1990a, 1990a,b), b),and andplutonic plutonicrocks rocksextend extendtotothe theSchreiber-Hemlo Schreiber-Hemlogreengreenstructural stone thethe west of of thethe Manitouwadge greenstone inclusions stonebelt belt(Williams (Williamsetetal., al.,1991). 1991).ToTo west Manitouwadge greenstonebelt, belt,abundant abundant inclusions ofofmafic mafictotointermediate intermediatesupracrustal supracrustalrocks rockswere werelikely likely derived derived from from the the belt. belt. On Onaeromagnetic aeromagneticmaps, maps,the the corresponding area areashows shows aapronounced pronouncedstriping stripingparallel paralleltotofoliation foliationtrends trends(accompanying (accompanying1:25000 1:25000map), map), corresponding interpretedtotoreflect reflectthe thepresence presenceofofdiscontinuous discontinuoussupracrustal supracrustal septa. septa.Areomagnetic Areomagneticlineaments lineaments that thattrend trend interpreted southwesttoward towardthe theSchreiber-Hemlo Schreiber-Hemlogreenstone greenstonebelt beltsupport supportlinkage linkageofofthe thegreenstone greenstoneterranes terranes(Williams (Williams southwest al.,1991). 1991).InIncontrast, contrast,the the BlackPic Pic batholith south Manitouwadge containsfew fewsupracrustal supracrustalinclusions inclusions etetal., Black batholith south of of Manitouwadge contains and andthe theaeromagnetic aeromagneticsignature signatureisislow lowand andfiat. flat. 2 �_____ Regional setting greenstone belt Manitouwadge greenstone — Proterozoic/Paleozoic Rocks Quetico subprovrnce Metasedimentary/ — intrusive rocks Quetco — Wawa & Wabigoon subprovinces •. Metavolcanic & Granitoid rocks related rocks . Isograd ——-Faults . •. .. Opz _vz C — I. FIG. 2. greenstone belt belt and 2. The TheWawa, Wawa,Quetico Quetico and andWabigoon Wabigoon subprovinces subprovinces with the Manitouwadge Manitouwadge greenstone the area greenstonebelt; belt;FF = = Faries belt; Mo = Schreiber-Hemlo greenstone Faries Lake Lake belt; MO = area of of Figure Figure 33 outlined. outlined. SH SH ==Schreiber-Hemlo Moshkinabi greenstonebelt; belt; DK DK = greenstonebelt; belt;BPb BPb = = Black Moshkinabi greenstone = Dayohessarah-Kabinakagami Dayohessarah-Kabinakagami greenstone Black Pic Pic batholith; isograd; SS = = Schreiber; M= = batholith; Pb ==Pukaskwa Pukaskwa batholith; batholith; Opx Opx ==orthopyroxene orthopyroxene granulite granulite isograd; Schreiber; M Manitouwadge; WL WL = = Winston Winston Lake Lake Zn-Cu mine; H = = Hemlo Hemlo Au camp. Adapted Adapted from fromWilliams Williams et et al. al. (1991). (1991). Structural Structural and tectonic setting Stockwell (1964)originally originallyused usedstructural structuraltrends trends and and style style to subdivide Stockwell (1964) subdivide the Superior Superior Province Province (Fig. 1), contrasting with the curvilinear trends of the I), contrasting the linear linear east-west east-west trends trends of the the Quetico Quetico subprovince subprovince with curvilinear trends Wawa and and Wabigoon subprovinces, subprovinces, the the latter latter defined by by remnants of greenstone belts lying between between domical Wawa Subsequently, lithological lithologicalfeatures featureswere werealso also used used to to define subprovinces, by by contrasting the batholiths. Subsequently, define subprovinces, dominantly supracrustal rocks in the volcano-plutonic dominantly volcanic volcanic origin of supracrustal volcano-plutonic terranes with with the thesedimentary sedimentaryorigin originof of the Quetico Quetico subprovince subprovince (Stockwell, (Stockwell, 1970; 1970; Card and and Ciesielski, Ciesielski, 1986). 1986). In some some cases, cases, boundaries boundaries were were defined defined rocks from from the the Quetico subprovince subprovince (Williams, (Williams, 1991). Supracrustal Supracrustal sequences to exclude mafic metavolcanic rocks sequences in subprovinces resemble resemblearc-type arc-type deposits deposits in in modern modern orogenic orogenicbelts belts (Card, (Card, 1990). Among the volcano-plutonic subprovinces the recent recent tectonic tectonic models models for for the theWabigoon, Wabigoon,Quetico Quetico and andWawa Wawa subprovinces, subprovinces, an an arc-accretionary arc-accretionary model model (1990). In has been favoured by Percival Percival (1989), (1989), Percival Percival and Williams (1989) (1989) and Williams (1990). In this thisscenario, scenario, the Quetico Quetico subprovince subprovince represents accretionary complex complex that accumulated southward from the margin margin represents an accretionary that accumulated of the Wabigoon Wabigoon arc, above a northerly dipping dipping subduction subduction zone. zone. Collision Collision of the Wawa arc from the south amalgamated the the three three subprovinces. subprovinces. The Therelatively relativelyhigh high temperature-low temperature-low pressure pressure metamorphic metamorphicassemblages assemblages preserved preserved within the the Quetico Quetico and and northern northernWawa Wawasubprovinces subprovinces could could be explained by ridge subduction subduction or or by by post-subduction post-subduction thermal thermal relaxation relaxation (Percival, (Percival, 1989). 1989). identification of structures produced by dextral dextral transcurrent transcurrent motion motion isisaafeature featurecommon commonto tovarious various The identification structural studies of the Quetico and its its boundaries. boundaries. Both Quetico subprovince subprovince and Both ductile ductile and brittle structures structures have have been typically in shear zones or deformation zones near subprovince subprovince boundaries boundaries (Fig. (Fig. 1). Exambeen identified, typically zones near Examinclude the Quetico fault (Borradaile (Borradaile et al., al., 1988), 1988), the Vermilion Vermilion district (Hudleston et 1988), the ples include district (Hudleston et al., 1988), l986), Beardmore-Geraldton belt (Devaney and Williams, Williams, 1989), l989), the Shebandowan Shebandowan belt and Stott, Stott ,1986), Beardmore-Geraldton belt (Devaney belt (Corfu and Shebandowan-Quetico boundary (Borradaile and Spark, Spark, 1991), 1991), and the the Hemlo-Schreiber Hemlo-Schreiber belt (Williams, (Williams, the Shebandowan-Quetico 1989). Zones Zones of of distributed distributed dextral motion have have been been noted noted in the western 1989). western Quetico (Bauer et al., al., 1992), 1992), as as have dextral shear shear zones zones well well within the the Wawa Wawa subprovince, for example in the Dayohessarah-Kabinakagami Dayohessarah-Kabinakagami greenstone belt (Leclair, 1990). In the the Shebandowan Shebandowan belt, the the timing timing of of dextral dextral transcurrent transcurrentmotion motion(local (localD2) Da) is constrained 2689+3/-2 and and 2684+6/-3 2684+6/-3 Ma Ma (Corfu (Corfu and andStott, Stott,1986); 1986);however, however, temporal temporal correlacorrelaconstrained to between 2689+3/-2 tion with dextral dextral motion motionelsewhere elsewhere in in the theWawa-Quetico-Wabigoon Wawa-Quetico-Wabigoon region the timing timing region isisuncertain. uncertain. Although the of dextral dextral motion motion varies varies widely, widely, in several several areas it isis associated associated with with later laterphases phasesofofdeformation deformation and style of 3 �Regional setting setting Manitouwadge greenstone belt Bauer et et al., 1992). In the western Quetico (Hudleston et al., 1988; 1988; Devaney and Williams, 1989; Bauer Quetico subprovince, subprovince, dextral motion has been been attributed attributedtotodextral dextraltranspression transpressionfollowing followingoblique oblique arc arccollision collision (Hudleston (Hudleston et al., al., 1988; Borradaile Borradaile and and Spark, 1991; 1991; Bauer et al., al., 1992). 1992). Evidence of thrusting thrusting prior prior to dextral Evidence of dextral transcurrent transcurrent motion motion has has been been observed observed in several several areas of the Wawa-Quetico-Wabigoon region.In In the the BeardmoreGeraldton Beardmore-Geraldton belt, belt, stratigraphic stratigraphic packages are separated by Wawa-Quetico-Wabigoon region. by dip-slip faults faults attributed attributed to dip-slip to thrust thruststacking stackingininan anaccretionary accretionarywedge wedge (Devaney (Devaney and Williams, Williams, 1989). 1989). Early Early (local Dl) Di) thrusting (local thrusting and andnappe nappeformation formationininthe theVermilion Vermiliondistrict districtof ofthe thewestern westernWawa Wawasubprovince subprovince may may have been been associated with accretion (ursa associated with (Jirsa et etal., al.,1992). 1992).Along Alongthe theWawa-Quetico Wawa-Quetico boundary boundary near near Schreiber, Schreiber, Williams (1989) (1989) identified identifiedstructures structures possibly possiblyrelated relatedto toearly earlydip-slip dip-slipthrusting. thrusting. Early Early (D2 (D2 and and earlier) earlier) thrust thrust structures in by Arias and Helmstaedt in the theMichipicoten Michipicoten greenstone greenstone belt were were described described by Helmstaedt (1990) (1990) and McGill McGill (1992). Detailed mapping in the Manitouwadge greenstone belt belt has also led led to to the recognition of of ductile ductile shear shear (1992). zones, interpreted as the the loci loci of of early thrusting thrusting (Zaleski (Zaleski and Peterson, Peterson, 1993a). 1993a). Williams et a!. al. (1992) interpreted interpreted the theManitouwadge, Manitouwadge,Moshkinabi Moshkinabi and and Faries Faries Lake Lake greenstone belts belts (Fig. (Fig. 2) as a semicontinuous easterly trending supracrustal supracrustalsuite suite(Manitouwadge-Hornpayne (Manitouwadge-Hornpayneassemblage), assemblage),belonging belonging to a discontinuous layer along along the the northern northern margin of the Wawa subprovince, traceable to discontinuous mafic metavolcanic layer the east to to the the Lepage Lepage fault fault zone zone (Williamset (Williamset al., al., 1991) 1991) (Fig. 1). 1). In In the thearea areaof of the the Manitouwadge, Manitouwadge, Moshkinabi belts and the Quetico and Faries Lake belts Quetico subprovince to the north, north, Williams Williams and and Breaks Breaks (1989; (1989; 1990a) 1990a) described a 5-phase sequence of of deformation deformation in in which which D2 D2was wasthe themain mainfabric-forming fabric-formingevent. event.The The easterly easterly regional regional trend trend of the greenstone belts is modified by by D3 northeasterly northeasterly trending Z-shaped from west west to to east; east; Blackman Z-shaped folds, from Lake antiform, Manitouwadge Manitouwadge synform, Banana Lake Lake antiform antiform and andMoshkinabi MoshkinabiLake Lake synform synform(Williams (Williamsand and Breaks, 1990b). The axial parallel with with the east-west regional trends of axial traces traces of of the the Z-folds Z-folds curve, becoming parallel the Quetico Quetico subprovince to the north north (Williams (Williams et et a!., al., 1992). 1992). Metamorphism There is a regional regional metamorphic metamorphic gradient gradient from from amphibolite amphibolitefacies facies in in the theSchreiber-Hemlo Schreiber-Hemlogreenstone greenstone belt belt (Corfu and Muir, 198gb), at Manitouwadge, Manitouwadge, to upper amphibolite amphibolite and and granulite granulite 1989b), through upper amphibolite amphibolite at facies in in the Quetico subprovince immediately north of Manitouwadge (Williams (Williams and and Breaks, 1989) (Fig. 2). facies facies kb) in in the ManiThermobarometric results are areconsistent consistentwith withupper upperamphibolite amphibolite facies(600—700°C, (600-700°C3—6 3-6 kb) Maniand facies (680—770°C, kb)in in the the Quetico touwadge belt (Petersen, (Petersen,1984; 1984;Pan Panand andFleet, Fleet,1992), 1992), andgranulite granulite facies (680-77O0C14—6 4-6 kb) subprovince to to the the north (Pan subprovince (Pan et et al., al.,1994). 1994). In Inthe theManitouwadge Manitouwadgebelt, belt, metamorphic metamorphic grade grade increases increases to the north, with with muscovite-sillimanite-quartz muscovite-sillimanite-quartzschists schists near the the Geco Geco mine on the southern southern limb limb of the Manitouwadge synform, giving giving way way to to sillimanite-microcline-quartz sillimanite-microcline-quartzschists schists(Fig. (Fig.3). 3).Migmatites Migmatitesare are ubiquitous ubiquitous north north of of the Blackman Lake antiform. Metagreywackes along the southern limb of Blackman Lake Metagreywackes along of the the Manitouwadge Manitouwadge synform contain garnet-sillimanite-biotite in pelitic pelitic layers, layers, but but are are not migmatitic. garnet-sillimanite-biotite in migmatitic. Similar Similar rocks near the Quetico Quetico boundary boundary contain tonalitic segregations, in some cases caseswith withcordierite cordieriteand andgarnet. garnet. In the Manitouwadge belt, dominant Manitouwadge belt, D2 fabrics are defined D2 fabrics defined by high high grade grade minerals minerals and and deformed deformed by by D3 Da folds; folds; hence, hence, peak peak metamorphism metamorphism was was broadly synchronous synchronous with D2. D2. Petrographic Petrographicevidence evidenceof ofdecompression decompression reactions reactions (e.g. (e.g. cordierite cordierite mantling mantling cooling was high temperatures temperatures persisted persisted sillimanite and orthoamphibole) orthoamphibole) suggests suggests that that cooling was protracted protracted and that high during D3 D3 deformation. Along most of its its length, length, the theQuetico Queticosubprovince subprovinceisissymmetrically symmetrically zoned zoned from from low low grade margins margins adjaadjacent to the the Wawa Wawa and and Wabigoon Wabigoon subprovinces, to central high grade migmatites (Percival, 1989). 1989). The ManManitouwadge area area is unusual unusual in two respects. respects. Firstly, the Manitouwadge boundary itouwadge Manitouwadge belt and the the Wawa-Quetico Wawa-Quetico boundary preserve amphibolite-facies assemblages, assemblages, and secondly, secondly, amphibolite-facies assemblages preserve upper amphibolite-facies assemblages are are transitional to orthopyroxene-bearing orthopyroxene-bearing granulites, found in aa lensoid lensoid area area (about (about 80 80x10 granulites, the the latter found x 10 km) km) near near the southern 1994) (Fig. 2). Moreover, Moreover, sammargin of the Quetico subprovince (Williams and Breaks, 1990a, b; b; Pan et al., 1994) pling study shows shows that that orthopyroxene-bearing orthopyroxene-bearing rocks rocks in the the Quetico Quetico subprovince subprovince extend somewhat pling during this study south of the Williams Williams and Breaks Breaks (1990b) (1990b) isograd, to within 1.5 1.5 km of the subprovince boundary. boundary. Geochronological constraints Geochronological constraints In the Manitouwadge Manitouwadgebelt, belt,felsic felsicmetavolcanic metavolcanicrocks rockshave have primary primaryvolcanic volcanicages agesof ofcirca circa2720 2720 Ma Ma(Zaleski (Zaleski al., 1994; 1994; Davis Davis et et al., al.,1994), 1994),as asdoes doesaasubvolcanic subvolcanic trondhjemite trondhjemite north of of the the Willroy Willroy and and Geco Geco mines mines et al., (Zaleski 1994). In In the theSchreiber-Hemlo Schreiber-Hemlobelt, belt, felsic felsic volcanism volcanism ranges in age from 2772±2 2772&2 Ma Ma (Hemlo(Hemlo(Zaleski et et al., 1994). Black Hemlo gold 26952~2Ma for the the Heron Heron Black River River assemblage, assemblage,Williams Williamsetetal., al., 1991) 1991) near near the the Hemlo gold camp camp to to 2695±2 Muir, 1989a). 1989a). Felsic Felsic metavolcanic metavolcanic rocks rocks (Schreiber (Schreiber assemblage, assemblage, Williams Bay volcanic complex (Corfu and Muir, al., 1991) 1991) associated associated with with the the Winston Winston Lake Lake Zn-Cu Zn-Cu mine mine are are 2723±2 2723&2 Ma Ma (Schandl (Schandl et et al., al.,1991), 1991),within within et al., at Manitouwadge. Manitouwadge. The Theages ages suggest suggest that that'Manitouwadge-Hornpayne' 'Manitouwadge-Hornpayne' assemblage assemblage is related error of those at related to Schreiber assemblage, assemblage, rather than thanthe theHemlo-Black Hemlo-BlackRiver River assemblage assemblage as as originally originally proposed by Williams the Schreiber et al. al. (1991). (1991). InInthe thewestern westernAbitibi Abitibisubprovince, subprovince, east east of of the theKapuskasing Kapuskasing structural structural zone zone (Fig. (Fig. 1), I),felsic felsic rocks base-metal mineralization mineralization at Timmins, Timmins, Abitibi Abitibi greenstone greenstone belt, belt, have have been been bracketed bracketed rocks associated associated with with base-metal at 2710—2717 2710-2717 Ma Felsic tuff underlying the Shunsby Shunsby base-metal base-metal Ma(Bleeker (Bleekerand andParrish, Parrish,pers. pers. comm., 1994). Felsic occurrence in the Swayze Swayze greenstone belt is is 2724±2 2724&2 Ma Ma (Heather (Heather etetal., al.,1995). 1995).Evidently, Evidently,circa circa2710—22 2710-22 Ma Ma 4 �Historical background Manitouwadge greenstone belt felsic volcanism volcanisminin the the Wawa Wawa and and western western Abitibi Abitibi subprovinces tended to be associated felsic subprovinces tended associated with with hydrothermal hydrothermal activity and mineralization. mineralization. The U-Pb systematics systematicsof of metavolcanic metavolcanic rocks from the Manitouwadge belt do not suggest suggest any any inheritance inheritance of older crustal components. AA model modelage age of of 3000 3000 Ma Ma based based on on Pb Pbisotopic isotopicanalyses analysesof of galena galena from fromthe theGeco Geco mine (Tilton (Tilton and and Steiger, Steiger,1969) 1969)reflects reflects the the inadequacies inadequaciesof of early models of Pb isotopic evolution; recalculation recalculation gives model ages ages near near or slightly younger (i.e. by circa Ma)than than the the 2720 2720 Ma Ma age age of of the volcanic host host gives model circa 5—15 5-15 Ma) rocks (R. Thorpe, Thorpe, written written comm., comm., 1994). 1994). The Theslight slight discrepancy discrepancy could be the result of limited isotopic resetting during regional regional metamorphism metamorphism (ibid.), (ibid.), an an interpretation interpretation supported by the presence Pb-bearing amazonite presence of of Pb-bearing in pegmatites in in contact contact with withmassive massivesulphide sulphide (Stevenson, (Stevenson, 1985). 1985). U-Pb zircon geochronology of various variousphases phasesofofthe the Black Black Pic Pic batholith continues geochronology of continues under the theauspices auspices of the Manitouwadge project. Two Manitouwadge project. Two dioritic dioritic phases phases of the Black Black Pic batholith batholith have have ages ages of of 2687+3/—2 2687+3/-2 and 2677±2 2677&2 Ma (see (see Geochronology). Geochronology). Two prepre- to to syn-D2 syn-Da bodies bodies of of K-feldspar K-feldspar porphyry, porphyry, the the Loken Loken Lake Lake and and Nama Creek Creek plutons, near the the margins margins of of the theManitouwadge Manitouwadge belt belt (Zaleski (Zaleski et a!., al., 1995), 1995), have have zircons zircons that that yield intrusive ages of of 2687+2/-3 2687+2/—3Ma Maand and 2680zk3 2680±3 Ma, Ma, respectively. respectively.Titanites Titanites from from the the Nama Creek Creek pluton yield intrusive and from the 2677 2677 Ma Black Black Pic diorite have U-Pb ages of 2672±3 2672&3 and 2674±2 2674&2 Ma, respectively, tentatively interpreted as of as metamorphic metamorphiccooling cooling ages. In In comparison, comparison, south of of the Schreiber-Hemlo Schreiber-Hemlo belt, marginal rocks of the Pukaskwa Pukaskwa batbolith batholithwere were intruded intrudedatat2719+6/—4 2719+6/-4 Ma Ma(Corfu (Corfuand andMuir, Muir,1989a), 1989a),broadly broadlycoeval coevalwith withfelsic felsic volcanism at Winston Lake Hemlo,several severalgranodiorite granodiorite plutons plutonscluster cluster volcanism at Lake and Manitouwadge Manitouwadge (Fig. 2). Near NearHemlo, closely Ma,whereas whereasamphibolite-facies amphibolite—facies metamorphism datedbybytitanite titanite peaked around closely around 2687—2688 2687-2688 Ma, metamorphism dated around 2676—2678 Ma,coeval coeval withthe thelate latetectonic tectonicGowan GowanLake Lakepluton plutonatat 2678dz2 2678±2 Ma Ma (Corfu (Corfu and Muir, 2676-2678 Ma, with Muir, 1989b). 1989b). Synmetamorphic monazites have ages of of 2675k1 2675± 1Ma MaatatGeco Gecoand and2677&1 2677±1Ma MaatatWinston Winston Lake Lake (Schandl (Schandlet et al., al., Synmetamorphic youngermonazite monazite(2661&1 (2661±1Ma) Ma)in inbiotite biotite schist schist at at Geco Geco was wasinterpreted interpreted to to date local K-metasomatism 1991); younger (Davis et aL, (Davis et al., 1994). In In general, general, metamorphic metamorphic titanite and and monazite monazite ages ages suggest suggest that metamorphism metamorphism was was nearly synchronous, synchronous, or or diachronous diachronousover overabout about55Ma, Ma,throughout throughout this this part part of the Wawa subprovince. In the nearly Wawa subprovince. subprovince, Percival Percival (1989) (1989) suggested suggested that that metamorphism was approximately approximately coeval with with granitic Quetico subprovince, plutonism from2670—2650 2670-2650 Ma. plutonism from Metagreywackes of of the the Quetico Quetico subprovince subprovince have havebeen beeninterpreted interpreted as an accretionary complex Metagreywackes complex continuous with the Ma (Percival (Percival and Williams, 1989). the Wawa Wawasubprovince subprovince atatleast leastsince since2689—2684 2689-2684 Ma 1989). Geochronological Geochronological studies of Quetico metasedimentary rocks have have been been mainly mainly confined confinedto towest westand and north north of of Thunder Thunder Bay (Fig. sedimentation to to 27023Z4 2702±4 Ma Ma for for the the southern southern Quetico near near 1). Detrital Detrital zircons zircons constrain the the maximum maximum age age of sedimentation Thunder Bay Bay (Percival (Percival and and Sullivan, Sullivan, 1988), 1988), and to to 2698±3 2698&3 Ma Ma for the the northern northern Quetico Queticonear nearAtikokan Atikokan(Davis (Davis et al., al., 1990). 1990). Minimum Minimumdepositional depositional ages ages were were constrained constrained by by intrusions intrusions of of 2687+19/-13 2687+19/-13 Ma and and 2688±4 2688&4 Ma, respectively for each each area. area. in respectively for In both bothcases, cases,zircons zircons older older than than 3000 3000 Ma Ma indicated indicated input input from fromold oldsources sources (ibid.). In sources to to the north, In the theAtikokan Atikokanarea, area,the thezircons zirconscould couldhave have relatively relatively proximal proximal sources north, including including the the 3003±5 Ma Marmion Marmion Lake Lakebatholith batholith (Davis (Davisetet al., al., 1990). 1990). In the case greater than 2800 Ma in 3003k5 Ma case of of zircons zircons greater 2800 Ma the southern Quetico, Quetico, no no local localpotential potentialsources sources are areknown known (Percival (Percival and and Sullivan, Sullivan, 1988). 1988). The TheCoutchiching Coutchiching metagreywackesinin the the Rainy metagreywackes Rainy Lake area of of the the Wabigoon Wabigoon subprovince subprovince contain detrital detrital zircon zircon populations populations similar to those of similar of Quetico Quetico rocks (Davis et al., al., 1989). 1989). The Themaximum maximumdepositional depositional age age was was established established at 2704±3 2704k3 Ma and the the minimum minimum age age at at 2692±2 2692zk2Ma, Ma, the theage ageof of aa cross-cutting cross-cutting intrusion. intrusion.The Thepresence presenceofofzircons zircons as old as 3059 3059 Ma indicated indicated aaMesoarchean Mesoarchean source. source. sequences are are comparable comparable to Timiskaming In both the the Wabigoon Wabigoonand andWawa Wawa subprovinces, subprovinces, conglomeratic conglomeratic sequences rocks facies associations These sequences sequences include (Fig. 1); 1); the the Max Max Creek Creek conglomerate conglomerate with with rocks in in facies associations and and age. age. These a maximum depositional age of 2687±3 2687&3 Ma (Percival (Percival and Sullivan, Sullivan, 1988), 1988), the Seine Seine group near near Rainy Rainy Lake Lake and 2686+2/-i 2686+2/-1Ma Ma(Davis (Daviseteta!., al.,1989), 1989),and and the theShebandowan Shebandowan group (Borradaile (Borradaile bracketed between 2696+5/-3 and and Brown, 1987) with depositional age depositional contact with a maximum depositional age of of 27043~2 2704±2 Ma Ma and and in depositional contact with alkalic 1986). volcanic rocks rocks of of 2689+3/-2 2689+3/-2 Ma Ma (Corfu (Corfu and Stott, Stott, 1986). THE MANITOUWADGE MANITOUWADGE BELT BELT HISTORICAL BACKGROUND OF THE History of deposits Department of Mines, Mines, while of 1931, JJ.E. In 1931, .E. Thomson, Thomson, Ontario Department while engaged engagedinin mapping mappingthe the north north shore of Lake Superior, was local Ojibway Ojibway Indians of rusty rocks near Manitouwadge Manitouwadge Lake Lake was told told by the local Lake to to the north (Brown, 1963). Thomson and and his his guide, guide, M. M. Fisher, completed completed a canoe traverse to t o the the area areaand andfound foundsuiphide sulphide mineralization and 'considerable 'considerable magnetic disturbance' (Thomson, (Thomson, 1932) 1932) on the future future sites sites of of the the Geco Geco and and mineralization Willroy returned in in 1943 1943and and staked staked the the showing, showing, but but he he was was unable unable to tofind findfinancial financial Willroy mines mines (Fig. (Fig. 3). 3). Fisher returned backing during the war years and allowed allowed his his claim claimto tolapse lapse(Pye, (Pye, 1957). 1957).Ten Tenyears yearslater, later,interest interest in in base base metal metal potential was heightened and the the showings showings on Thomson's map were staked by 'weekend 'weekend prospectors', prospectors', Dawd, Barker Forster (ibid.). (ibid.). Within Withinthe theyear, year,drilling drillingintersected intersected an anorebody orebodyand andGeco GecoMines Mines Limited Limited was was Barker and Forster incorporated. In In the theensuing ensuingstaking stakingrush, rush,the theWillroy, Willroy,Nama NamaCreek Creekand andWillecho Willechodeposits depositswere werediscovered, discovered, all of Willroy and Geco Geco mines went in 1957. 1957. of which which were were eventually eventually mined. mined. The Wiliroy went into production in 5 �Historical background background Manitouwadge greenstone belt The is the the only mine mine currently currently active in the area. Geco The Geco Geco mine, scheduled to close in late 1995, is Geco was was by tonnes with an overall far the largest deposit; total total production production for for its its lifetime lifetime is projected to to be be 55.9 55.9 million tonnes of 1.85% Cu, Cu, 3.76% 3.76%Zn Znand and 46.9 46.9 gramltonne gram/tonne Ag. Ag. Minor grade of Minor amounts of Au, Cd and and Bi Bi are arerecovered recovered and, and, until 1988, of 0.30% 0.30%Pb Pb was wasextracted extracted (Williams et et al., 1990) as as aa by-product of purification of CU Cu 1988, an average of concentrate. Combined concentrate. Combined production production from from the the Willroy, Willroy, Nama Nama Creek Creek and and Willecho Willecho deposits, deposits, until until the theclosure closure of the Wiliroy mine in 1977, was was 8.0 8.0 million milliontonnes tonneswith withaa grade grade of of 0.9% 0.9%Cu, Cu, 4.9% 4.9%Zn Znand and 50 50 gram/tonne gram/tonne of Willroy mine Ag. Exploration continues in the area, on identifying identifyingtargets targets at at depth and Ag. area, mainly mainly focussed focussed on and along along the the folded folded extensions of of the the belt. extensions Previous m mapping and interpretations interpretations Previous a p p i n g and The The first systematic systematic mapping mappingof of the the Manitouwadge Manitouwadge greenstone belt was undertaken by by Pye Pye (1957) (1957) for the Ontario Department Departmentof of Mines, Mines, from from1954 1954 to 1957. 1957. He outlined the the general general shape shapeof of the the Manitouwadge Manitouwadgesynform synform rocks along along the the inner inner and outer margins supracrustal sequence. and recognized mafic metavolcanic rocks margins of the the folded folded supracrustal sequence. At the time time of Pye's mapping, mapping, most most of of the the presently presently known known economic deposits had already been discovered and, in many cases, his detailed maps maps of of mine mine properties properties are are the theonly onlypublished publishedrecord recordofofgeological geological relationships relationships replacement that postthat were were obliterated by by mining. mining. Pye Pye regarded regarded all all the themineralization mineralization as as Algoman-age Algoman-age replacement postof diabase diabase dykes. dykes. He He interpreted most supracrustal dated intrusive activity, activity, with the the possible possible exception of supracrustal rocks rocks Mime (1974) (1974)remapped remappedthe the area area of of major economic economic interest interest for for the the as metasediments. metasediments. From From 1968 1968 to 1970, 1970, Milne Ontario Division of Mines, reinterpreting most of of the the felsic felsic rocks as as volcanic or volcanogenic. The base-metal base-metal deposits deposits of of the the Manitouwadge Manitouwadge greenstone greenstone belt are are aaclassic classicexample example of of the theproblems problemsenencountered in petrogenetic studies of mineralization in complex polydeformed polydeformed terranes. terranes. Early studies countered studies tended tended to focus on evidence of local replacement, replacement, remobilization and and structural structural control control (Pye, (Pye,1957; 1957;Timms Timmsand andMarMarshall, 1959; 1959; Brown Brown et al., al., 1960; 1960; Watson, Watson, 1970). 1970). Associated Associated orthoamphibole-cordierite-garnet orthoamphibole-cordierite-garnetgneiss gneisshas hasbeen been interpreted as metasediment et al., 1960; Watson, 1970), restite from from the extraction of metasediment (Pye, 1957; 1957; Brown Brown et 1960; Watson, 1970), restite partial melt melt (Robinson, (Robinson,1979), 1979),and andmetamorphosed metamorphosedaltered alteredvolcanic volcanicor orvolcaniclastic volcaniclasticdeposits deposits with withpossible possible pelitic interbeds (James Sillimanite-muscovite-quartz schist in proximity to (James et et al., al.,1978; 1978;Friesen Friesen et al., al., 1982). 1982). Sillimanite-muscovite-quartz orebodies has also been been variously interpreted as metasediment, metasediment, with the the most mostmuscovitic muscovitic zone zone corresponding corresponding to aa concordant altered metasediment Brown et a!., concordant fault fault (Milne, (Milne,1974); 1974);epigenetically epigenetically altered metasediment (Pye, 1957; 1957; Brown al., 1960); 1960); metamorphosed altered volcanic and volcaniclastic rock rock (Friesen (Friesen et et al., a!., 1982; Bakker Bakker et et al., 1985); metamorphosed 1985); and synsynalteration (Schandl et al., 1991; metamorphically altered rock, possibly with a prehistory of synvolcanic alteration 1991; Davis et a!., al., 1994). 1994). Suffel Suffel et et al. al.(1971) (1971)were were the the first first totopropose proposeaavolcanogenic volcanogenic origin, interpreting textures and and microstructures the result result of of superimposed superimposed metamorphism metamorphism and and remobilization. remobilization. More More recently, recently, aa syngenetic syngenetic for the the base-metal deposits and origin for and altered altered rocks rocks has has been been increasingly increasingly accepted (James (Jameset eta!., al.,1978; 1978;Friesen Friesen et al., al., 1982; 1982;Bakker Bakker et al., al., 1985). 1985). Historical h e 'Mine Series' Series' Historical nomenclature, nomenclature, tthe Most previous detailed mapping has been who have have adopted the Most previous detailed been done done by by private-sector private-sector geologists geologists who the hishistorical 'Mine Series' lithological units (Table 1). 1). This Thisconfusing confusing nomenclature nomenclature is is of of wide wide use locafly locally and has found its way way into the the literature. literature. The The'Mine 'MineSeries' Series'consists consistsofofaafour-fold four-fold subdivision subdivision of supracrustal rocks rocks (Friesen et et al., 1982; (Friesen 1982; Williams et al., al., 1990) 1990) into; into; Granite Granite Gneiss Gneiss group, group, Sericite Sericite Schist Schist group, group, Grey Grey Gneiss Gneiss group and Hornblende Schist group. group. The group The 'Granite 'GraniteGneiss Gneissgroup' group'refers referstotoorthoamphibole-cordierite-garnet orthoamphibole-cordierite-garnet gneiss, interpreted as as metamorphosed metamorphosed synvolcanically synvolcanically altered rocks lying in the stratigraphic stratigraphicfootwall footwall (struc(structural hanging hanging wall) to the the mineral mineral deposits deposits (ibid.). (ibid.). The Themisleading misleading name name dates dates back back to to the thediscovery discovery drill holes of the Geco mine; mine; by by a quirk of nature and holes of and karma, karma, the the holes holes penetrated penetrated foliated foliated granite granitebefore before emergemerging into massive sulphide, sulphide, and and hence, hence, all the rocks of of the structural hanging grouped as as 'granite hanging wall wall were were grouped 'granite gneiss'. 'Sericite muscovite-quartzksillimanite schist, and (although (although gneiss'. 'Sericite schist' schist' was was originally originally Pye's field field term for muscovite-quartz±sillimanite corrected by Pye (1957) on on the basis of of petrography) petrography) the misnomer persists persists in the 'Mine Series'. The The 'Sericite 'Sericite Schist group' has been been viewed viewed as the the lateral lateralequivalent equivalentof of the the'lower 'lower Grey Grey Gneiss Gneiss group', group', representing representing either either a sedimentary facies (Milne, (Milne, 1974) 1974)or or an an alteration alteration product product (Friesen (Friesen et al., 1982; 1982; Bakker Bakker et al., 1985). 1985). The The 'Grey Gneiss group' corresponds to Pye's metasedimentary metasedimentary unit, later later subdivided subdivided into into lower lower (northerly) (northerly) and and upper (southerly) (southerly) members. members. The The'lower 'lowerGrey GreyGneiss Gneissgroup' group'isisapproximately approximatelyequivalent equivalenttotofelsic felsicto tointermediintermediate metavolcanic interlayered with with iron formation, extending extending from from Geco Geco to to north north of the Willecho metavolcanic rocks, interlayered Willecho area (Fig. 3). The The'upper 'upperGrey GreyGneiss Gneissgroup' group'mainly mainlyincludes includesmetagreywackes metagreywackes and and foliated foliated tonalite tonaliteoccupying occupying (Fig. synform. The The contact contact between between the the 'lower' 'lower' and and 'upper 'upper the centre of the southern southern limb limb of the Manitouwadge Manitouwadge synform. Grey Gneiss' has been been considered considered as transitional, reflecting reflecting a change change from a depositional depositional regime dominated dominated sedimentation (iron formation and suiphide by volcanism and chemical sedimentation sulphide mineralization), to one dominated dominated by by clastic 1982; Bakker al., 1985). Our Our U-Pb U-Pb dating datingof of detrital detritalzircons zirconsshows shows clastic sedimentation sedimentation (Friesen (Friesen et et al., 1982; Bakker et et a!., that the the 'upper 'upper Grey GreyGneiss Gneiss group' group' is is at at least least 25 25 Ma Ma younger younger than 'lower Grey than the 'lower Grey Gneiss Gneissgroup', group',and andthat that the former is likely metagreywackes of likely correlative with migmatized metagreywackes of the the Quetico subprovince (Zaleski (Zaleski et et al., 1995; see Geochronology). The 'Hornblende 'Hornblende Schist Schistgroup' group'corresponds correspondstotomafic maficmetavolcanic metavolcanicrocks, rocks,now nowrecognized recognized to lie at the the stratigraphic stratigraphicbase baseof ofthe theentire entiresequence. sequence. 6 �Description of units Manitouwadge greenstone belt TABLE 1 1.. Comparison of of M Map TABLE a p Units and Historical 'Mine Series' -- - Mine series series Upper Grey Grey Gneiss Gneiss -- Map units, this this work work Metasedimentary rocks (and tonalite) tonalite) (Unit (Unit 10) 10) depositional age depositional <2693 Ma'a ' <2693 ~ unconformity or fault . . . . . . . . . . . .. .. .. ... .. unconformity Lower Grey Gneiss Gneiss Felsic metavolcanic metavolcanicrocks rocks (and (and iron formation), Felsic formation), quartzitic variant quartzitic variant of of sillimanite-muscovite-quartz sillimanite-muscovite-quartz schist (Units 1, 6, 7, 8, 9) 2720 ~Ma'a ' Sericite Sericite Schist Schist Sillimanite-muscovite-quartz schist, schist, altered altered felsic Sillimanite-muscovite-quartz felsic rocks (Unit 1) volcanic rocks 2720 Ma2 ~a~ Granite GraniteGneiss Gneiss Ortboamphibole-cordierite-garnet gneiss, gneiss, altered Orthoamphibole-cordierite-garnet altered mixed rocks (Unit (Unit 2) mixed mafic-felsic mafic-felsic volcanic rocks 2) 2720 Ma Hornblende Schist Hornblende Mafic metavolcanic metavolcanic rocks rocks (Unit (Unit 3) Mafic 1ZnIeski et al. (1995) l ~ a l e a k iet (1995) 2720 22720Ma Ma 22Davia ~ a v i aet at. al. (1994) (1994) Contradictions exist in the literature literature with with respect respect to tothe thestratigraphic stratigraphicsuccession successionand andyounging younging direction direction of the 'Mine 'Mine Series'. Series'. The Theconfusion confusionisisrelated related totothe thepresence presenceofofan anearly earlyfold, fold,originally originallyproposed proposedby bySuffel Suffel et al. al. (1971) (1971) and and Touborg Touborg (1973), (1973), that that repeats repeatsthe theaupracrustal supracrustalsuccession succession across across the southern southern limb limb of of the the Manitouwadge synform. Pye Pye (1957) (1957) assumed assumednortherly northerlyyounging youngingfor forthe theentire entirebelt. belt. Reinterpretation of the Manitouwadge synform. massive sulphide deposits as as volcanogenic volcanogenic implied a southerly southerly younging younging sequence sequence for the the Wiliroy-Geco Willroy-Geco area (Suffel et et al., al., 1971) and, and, in some cases, cases, southerly southerly younging youngingwas wasextrapolated extrapolatedto to the the entire entire belt (Friesen et al., (Suffel 1982). 1982). DESCRIPTION D E S C R I P T I O N OF O F UNITS UNITS The Manitouwadge Manitouwadge greenstone greenstone belt beltcomprises comprisesaamafic-to-felsic mafic-to-felsicsuccession, succession, the thefelsic felsiccomponent componentof ofwhich which is circa 2720 pattern isisdominated dominatedby byD3 D3folds, folds, and and the the greatest greatest thickness thicknessof of supracrustal supracrustalrocks rocks 2720 Ma. Ma. The map pattern D3Manitouwadge Manitouwadge synform (Fig. 3). Away Away from from lies hinge region region and along along the the southern southern limb limb of of the theD3 lies in the hinge the hinge region, and invaded invaded by plutonic rocks. rocks. On On the the southern southern limb, limb, region, supracrustal supracrustal units units are attentuated and the volcanic succession north and andsouth southby byaaD2 D;syncline synclinewith withaacentral centralzone zoneofofmetagreywacke metagreywacke succession is is repeated repeated to north The northern northernsequence sequence is is here referred referred to as the 'inner' volcanic volcanic belt, and the the southern southern as as the the (see Structure). The 'outer' volcanic belt, with with respect respect to tothe theinner innerand andouter outerregions regionsofofthe theManitouwadge Manitouwadgesynform. synform. All Allknown known 'outer' volcanic Cu-Zn deposits, including the the Geco, Geco, Willroy, Willroy, Nama Creek and and Willecho Willecho deposits, lie lie in the the inner inner volcanic volcanicbelt belt along the southern limb limb and andinner innerhinge hingeregion region of of the theManitouwadge Manitouwadgesynform. synform. Our definition of map units units partly partlyreflects reflectsdifferences differences in scale of mapping, exposure and accessibility; accessibility; for example, mafic, example, mafic, mixed mixed mafic-felsic, mafic-felsic,and andfelsic felsictotointermediate intermediatemetavolcanic metavolcanicrocks rocks(Units (Units3,3,44and and 6) 6) in in the inner volcanic belt belt give way way to to undifferentiated undifferentiated intermediate intermediate to to mafic mafic metavolcanic metavolcanicrocks rockstotothe thenorth north (Unit All supracrustal supracrustal rocks rocksare aremetamorphosed, metamorphosed, although although the the prefix prefix 'meta' 'meta' isissometimes sometimes omitted omitteddepending depending 5). All on the context. context. 'Alteration' 'Alteration'isisused usedtotomean meanmetasomatic metasomatic changesininwhole-rock whole-rockcomposition, composition,inferred inferredfrom from changes metamorphic and metamorphic mineral mineral assemblages assemblagesand and abundances. abundances. Unless Unlessstated, stated, timing timing isis not not implied implied by by 'alteration' 'alteration' and it could could be be synvolcanic synvolcanic (premetamorphic), (premetamorphic), synmetamorphic numbers, synmetamorphicor or post-peak post-peak metamorphic. metamorphic. The unit numbers, locations, geographic geographic names references to aeromagnetic aeromagnetic trends in the the following following discussion discussion refer locations, names and references refer to to the refer to field stops accompanying 1:25000 1:25000map, map, generalized generalizedin infigure figure3.3. Stops Stops and and figures figures prefixed prefixedby by aa letter letter refer and maps found in in the the field-trip field-trip section section of of this this volume. volume. Supracrustal rock units units Mafic rnetavolcanic is Mafic metavolcanicrocks rocks(Unit (Unit3)3)occur occurininboth boththe the inner inner and and outer outer volcanic volcanicbelts. belts. The outer belt is mafic rocks, comprising a steeply dipping section of up to to 33 km km of of interleaved interleaved hornblende-rich hornblende-rich dominated by mafic mafic mafic schists, schists, laminated laminated rocks rocks and and foliated foliated gabbros. gabbros. These are folded folded around around the hinge of of the Manitouwadge synform near in aa zone zone of high strain along the northwestern margin margin near Mills Mills Lake, Lake, and and continue continue to to the northeast in of the Manitouwadge Manitouwadge belt Nama Creek Creek pluton of beltuntil untiltruncated(?) truncated(?) by by the Nama pluton (Unit (Unit 13a). 13a). To the east east on on the the limb of the the Manitouwadge Manitouwadge synform, synform, the unit thins thins and andisisincreasingly increasingly engulfed engulfed by by plutonic plutonic rocks. rocks. southern limb 7 �Manitouwadge greenstone belt 8 --\\ LEGEND Foliated K-feldspar porphyritic granitoid Foliated tonalite felsic to intermediate meta volcanic rocks,sillimanite-muscovite schist Metasedimentary rocks Ij [ [ IOrthoamphibole-cordierite-garnet gneiss Metamorphosed iron. formation - Intermediate to mafic melavolcanic rocks - Fold axial trace Fault # - Aeromagnetic or foliation trend (t a) C' a)U) l) d o U) o a).— .4-i ' Cl) Q) 0 a) 0 0 'a)Oa) d U) -4-, a) 1.OO U) C) 0I- C) .4-' C) a) cj.c .— (j._ 0 C) _U)U)C) •U) U) — a) ' a)4_' N a)r-.,C )0r .4-, a) -' o C) C) . a) - a) -E'4-. OI.a) — I C) ., a) c' Cl) C) Q --'.0 Cl) '4_l) O o C C)O a) • —000 ) 0 C) Description of units o O-'0 — FIG. 3. Generalized geology of t h e Manitouwadge greenstone belt, omitting diabase dykes (see the accompanying 1:25000 map for details). The regional structure is dominated by major Dn folds; the Manitouwadge synform, Blackman Lake antiform and Jim Lake synform. The inner and outer volcanic belts a r e correlative, repeated by a Dg syncline, the axial trace of which lies in metasedimentary rocks on the southern limb of t h e Manitouwadge synform (Fig. 5). Asterisks mark economic and subeconomic base-metal deposits. The area detailed in Figure 4 is outlined. A-A' is t h e trace of the projection in Figure 7. �Description of units Manitouwadge greenstone belt of the the Banana Lake antiform is poorly exposed, but foliation trends in in the the enclosing enclosing tonalite tonalite The hinge region of suggest a possible connection to to the Faries Lake Lake belt belt (Fig. (Fig. 2). 2). Aeromagnetic trends are more consistent with an easterly continuation continuationof of the the mafk maficunit, unit,although althoughweak weak trends trendsobscured obscuredby by diabase diabase dykes dykes may be consistent with by the the Banana Lake antiform. In trondjemite folding by In the theinner innervolcanic volcanic belt, belt,mafic mafic inclusions inclusions in synvolcanic trondjemite (Unit 12), near-continuous screens screens traceable traceable in in outcrop outcrop for for distances distances of of 3.5 3.5 km km (from (from the the 12), in some some cases, form near-continuous Mose Lake Lakefault fault to to the the road road east of Wowun Lake). Mafic Maficrocks rocksofofUnit Unit33are are transitional transitionalto to the the south south to Mose Wowun Lake). interleaved mafic-felsic mafic-felsic metavolcanic rocks (Unit 4). 4). Mafic metavolcanic rocks rocks are are strongly strongly foliated, fine grained, grained, homogeneous homogeneousto to thinly thinly layered Mafic metavolcanic layered schists, and medium to coarse grained grained metagabbro, typically interlayered. interlayered. In the area of medium of detailed detailed mapping mapping between between Mills and Swill Swill Lakes, Lakes, layers layers of schist schist and and metagabbro metagabbroare are50—100 50-100 metres (Fig. B3). B3). Near Near Gaug Gaug Lake, Lake, metres thick thick (Fig. metagabbro forms forms aa larger metagabbro larger body in fine fine grained schist. The Themetagabbro metagabbroisiscommonly commonly aa hornblende-augen hornblende-augen cmininsize), size),locally locallywith with well welldeveloped developedasymmetric asymmetrictails, tails, lie lie in in a fine schist in which lenticular augen augen (0.5—1 (0.5-1 cm matrix. In some high strain zones, metagabbro or augen schist schist is is transitional transitional to fine grained grained schistose matrix. homogeneous schist, schist, suggesting suggesting that that some schist could could have have originated originated as gabbro, homogeneous some homogeneous schist gabbro, commmuted comminuted by deformation (Stop B15). B15). In both the theinner innerand andouter outervolcanic volcanicbelts, belts,mafic maficschists schistsare arelocally locallypillowed pillowed but, but, with with few few exceptions, exceptions, deformation makes makes younging younging or or structural structural facing determinations suspect. In deformation In an anexposure exposurebetween between Swill Swill and and Mills Lakes, Lakes, pillow pillowshapes shapessuggest suggestsoutherly southerly younging younging(Stop (Stop B14), B14), and and northerly northerly younging has been reported west of of Gaug Gaug Lake Lake (W. (W. Bates, Bates, Granges Inc., pers. pers. comm., 1992). In view in the west Granges Inc., comm., 1992). view of the polyphase polyphase folding folding in Manitouwadge belt, belt, these these few few younging youngingdeterminations determinationscontribute contributelittle little to to regional regional interpretation. interpretation. Manitouwadge schists consists consists of ofhornblende-plagioclasekgarnet&biotite&clinohornblende-plagioclase±garnet±biotite±clinoThe typical mineral assemblage assemblage in mafic schists pyroxene with with quartz, magnetite, titanite, titanite,sulphide sulphideminerals minerals and and apatite apatiteininaccessory accessory or or trace trace amounts. amounts. LamiLaminations Iamellae. Epidote occurs in calc-silicate calc-silicate lenses lensesor orboudins. boudins. Garnetiferous Garnetiferous nations are are defined defined by plagioclase-rich lamellae. zones (up to 40% garnet), in some cases cases with with quartz, quartz, magnetite and cummingtonite, cummingtonite, are particularly particularly common common in mafic schists schists in the outer outer volcanic volcanic belt. Near Near the thenorthern northerncontact contacttotometagreywacke, metagreywacke,mafic mafic rocks rocks of the outer belt interleaved felsic felsicschist, schist,foliated foliatedtonalite, tonalite, garnetiferous garnetiferous hornblendebelt are areinvolved involved in in aa complex complex zone of interleaved biotite±magnetite biotitehmagnetite gneiss, gneiss, iron iron formation formationand andorthoamphibole-plagioclase±garnet±magnetite±hornblende orthoamphibole-plagioclase&garnet&magnetite&hornblende gneiss (Stops (Stops B Bil and gneiss and B20). B20). The intensity intensity of of deformation deformation generally generally makes it difficult difficult to unambiguously identify the physical protolith to mafic interlayered with with schists may be mafic rocks. rocks. Metagabbros Metagabbros interlayered be massive massive flows, flows, massive massive bases bases of flows, flows, or sills. Some origin, but highly sills. Some laminated laminated mafic mafic schists may have have had aa tuffaceous tuffaceous or or volcaniclastic volcaniclastic origin, highly strained strained pillowedflows flowscould couldalso alsobebepresent. present. Orthoamphibole-bearing Orthoamphibole-bearingrocks rocksnear nearthe thenorthern northern contact contact of of the the outer pillowed orthoamphibole-cordierite-garnet gneiss gneiss of the belt are are interpreted interpreted as asequivalent equivalentto tothe themuch muchmore moreextensive extensiveorthoamphibole-cordierite-garnet inner belt, and alteration (see (see Unit Unit 2). 2). However, inner and hence hence as as metamorphosed metamorphosed synvolcanic synvolcanic alteration However, at least some some of the garnet±cummingtonite zones zones of ofthe the outer outer belt belt are apparently discordant of garnetkcummingtonite discordant to tectonic tectonic fabrics, fabrics, and hence, hence, of later origin (Stop B20). B20). Mixed mafic-felsic mafic-felsicmetavolcanic metavolcanicrocks rocks(Unit (Unit4)4)ofofthe theinner inner volcanic volcanicbelt beltlie liemostly mostlyalong alongthe the transitional transitional contact between mafic rocks north, and and felsic felsic (Units 6 and 8) and orthoamphibole-bearing rocks rocks rocks (Unit 3) to the north, trondhjemite (Unit 2) 2) to to the thesouth. south.Mixed Mixedmafic-felsic mafic-felsic rocks rocks also also form form inclusions inclusions and screens in synvolcanic trondhjemite (Unit 12) 12) north north and andeast eastofoforthoamphibole-bearing orthoamphibole-bearingrocks. rocks.Layering Layeringofofmafic maficand andfelsic felsiccomponents components(cm—i (cm-1 m width) might might suggest suggest contemporaneous contemporaneous mafic mafic and and felsic felsic volcanism, volcanism, or tectonic tectonic interleaving. interleaving. Mafic Maficlayers layers are more abundant than thanfelsic, felsic,and andconsist consistofofdark, dark,fine finegrained, grained,strongly stronglyfoliated, foliated,hornblende-plagioclase hornblende-plagioclase without magnetite, magnetite, quartz, quartz,cummingtonite, cummingtonite, biotite biotite and and garnet garnetand andgenerally generallysimilar similar to tomafic mafic schist, with or without schist Layers rich rich in in biotite, and garnet garnet are more schist of Unit 3. 3. Layers biotite, cummingtonite cummingtonite and more common common near the the southern southern contact. Intercalations Intercalationsofofquartz-rich quartz-richfelsic felsicand andleucofelsic leucofelsicschist contain plagioclase, plagioclase, biotite and, and, locally, locally, quartz quartz phenocrysts, phenocrysts, magnetite and and garnet. garnet. West WestofofFox FoxCreek, Creek,outcrops outcropsofoffelsic felsicschist schist with withelongate elongatehornblendehornblendericher patches or 'clasts' are inclusions in in aa trondhjemite trondhjemite areinterpreted interpretedasasan anintrusion intrusionbreccia brecciaof ofmafic mafic volcanic volcanic inclusions matrix. of Garnet Garnet Lake Lake and and west west of of orthoamphibole-bearing orthoamphibole-bearing Unit 2 were were also also Two areas of mafic rocks north of grouped with mixed mafic-felsic mafic-felsic rocks. the rocks rocks are are charchargrouped rocks.These Theseare are somewhat somewhatatypical atypicalofofthe theunit unit in in that the acterized by abundant abundant calc-silicate calc-silicate minerals minerals including including Ca-amphibole, Ca-amphibole, epidote, epidote, clinopyroxene, clinopyroxene, titanite and acterized titanite and plagioclase, as Microcline, garnet and calcite are present in in minor minor amounts. amounts. Diffuse Diffuse semiconsemiconplagioclase, as well well as as quartz. quartz. Microcline, lenses (typically (typically 0.5—30 0.5-30 cm and grain grain tinuous layers or lenses cmininwidth) width)are are defined definedby byvariations variations in in the the abundance and size of of calc-silicate calc-silicate and and felsic felsicminerals. minerals. In In some some cases, cases,quartz quartz eyes eyes resemble resemblerelict relictphenocrysts. phenocrysts. The The origin origin of of these they are are the the result result of of these rocks rocks and and their relationship relationship to to more more typical typical Unit Unit 44 isis uncertain; uncertain;but but itit may may that they alteration of of felsic felsic volcanic volcanic rocks, rocks, possibly possibly with with interleaved interleaved mafic mafic rocks. rocks. calc-silicate alteration Intermediate mafic metavolcanic metavolcanic rocks rocks (Unit (Unit 5) 5) comprise comprise aaheterogeneous heterogeneous group group of of undifferentiundifferentiIntermediate to mafic ated rocks, rocks, dominantly dominantlyhornblende-plagioclase, hornblende-plagioclase,hornblende-plagioclase-biotite hornblende-plagioclase-biotite and andhornblende-plagioclasehornblende-plagioclasegarnet±clinopyroxene±magnetjte garnet&clinopyroxene&magnetite schists, and and foliated foliated diorites. diorites. The unit defines defines the attenuated attenuated northern northern 9 �Manitouwadge greenstone belt Description of units limb folds to to the north (Blackman limb of the the Manitouwadge Manitouwadge synform and related map-scale folds (Blackman Lake Lake antiform, Jim Lake synform). Between Between Rabbitskin RabbitskinLake Lakeand andthe therailway railwaywest westofofFox FoxLake, Lake,exposure exposureisispoor poorand andinaccessible; inaccessible; however, aeromagnetic trends trends suggest that that the however, aeromagnetic the unit unit isis continuous continuous east to to One One Otter OtterLake. Lake.West WestofofRabbitskin Rabbitskin Lake, fine fine to medium medium grained, grained, mafic mafic to to intermediate intermediateschist schistand andminor minorfelsic felsicschist schistare arehomogeneous, homogeneous,lamilaminated nated or or layered, layered, and and host host many manyintrusions intrusions of of foliated foliated pegmatite, pegmatite, granite granite and and tonalite. tonalite.Garnetiferous Garnetiferouszones zones and patches, garnet porphyroblasts porphyroblasts and and lesser lesser amounts amounts (<lo%) (<10%) of magnetite, patches, in in some somecases cases with with30—40% 30-4076 garnet are are common. common. South SouthofofFox FoxLake, Lake,laminated laminatedtotolayered layered(1(1mm—10 mm-10 cm), cm), fine fine grained, grained, mafic mafic to to intermediate intermediate metavolcanic rocks rocks are are present present both north and asinclusions. inclusions. The Theminminand south south of of the the Nama Nama Creek Creek pluton, pluton, and andas eral hornblende-plagioclase±clinopyroxene±quartz±biotite, with eral assemblage assemblage includes hornblende-plagioclasekclinopyroxenekquartz&biotite, withepidote epidotelocally locallyininknots, knots, and and accessory accessory titanite, titanite, magnetite magnetiteand andapatite. apatite.Southeast SoutheastofofFox FoxLake, Lake,exposures exposuresofofheterogeneous heterogeneousinterleaved interleaved (1 cm—i m) foliated foliated pegmatitic pegmatitic granite, biotite cm-1 m) biotite and andhornblende-biotite hornblende-biotitefelsic felsic schist schist locally locally grade grade to togarnetifgarnetiferous strongly magnetic magnetic gneiss. gneiss. Garnet Garnetporphyroblasts porphyroblastscomprise compriseup uptoto50% 50%ofofthe thegneiss, gneiss,occurring occurringininlenses lenses (2—3 cmwide) wide)between between anastomosing anastomosing mafic layers of of fine grained hornblende, (2-3 cm hornblende, clinopyroxene clinopyroxene and and magnetite. magnetite. In some some cases, cases, quartz eyes eyes and aggregates aggregates are abundant. The Themagnetic magneticgneisses gneisses undoubtably contribute contribute to to the the high high aeromagnetic aeromagnetic signature signature of of the the area. area. In the thevicinity vicinityof of the theBlackman BlackmanLake Lake and andJim JimLake Lakefolds, folds,the theManitouwadge Manitouwadgebelt beltcomprises comprisesthinly thinlylayered, layered, fine to medium grained, mafic to intermediate well as as foliated foliated diorite and gabbro that intermediate metavolcanic metavolcanic rocks, as well that may rocks. The rocks are commonly strongly magnetic may be be recrystallized recrystallized homogeneous homogeneous volcanic or subvolcanic rocks. and, in in addition, addition, are areinterleaved interleaved with with minor minor iron iron formation formation (Stop E6). E6). The TheJim JimLake Lakesynform synformisisdefined defined by mappable mappable zones zones of mafic to intermediate intermediate screens screens and inclusion inclusion swarms in foliated tonalite and and pegmatite. pegmatite. mafic to intermediate intermediateblocks blocks (with (with discordant discordant foliation foliation trends) trends) in inan anintrusive intrusivematrix matrixresemble resemble Locally, rotated rotated mafic agmatite agmatite or or intrusion intrusion breccia. breccia. At At least leasttwo twonearly nearlycontinuous continuouszones zonesof ofmafic maficrocks rocks can can be bemapped mappedinside insidethe theManitouwadge Manitouwadgesynform, synform, zones of high variable variable aeromagnetic aeromagnetic relief. relief. These These rocks, rocks, here here called called the theDead DeadLake Lakesuite, suite, corresponding to zones comprise aa complex complex association association of of interleaved foliated gabbro, diorite, diorite, and and layered layered mafic mafic to to intermediate intermediaterocks rocks comprise of probable supracrustal origin. origin. The TheDead DeadLake Lake suite suiteincludes includes aa distinctive distinctive group group of of strongly strongly magnetic magnetic rocks rocks of characterized by by hornblende-magnetite±plagioclase±garnet±clinopyroxene±sulphicie hornblende-magnetitekplagioclasekgarnetkclinopyroxeneksulphide minerals, with with variable variable characterized amounts irregular lenticules (Stops C3—C5). amounts of of quartz quartz (minor (minortoto50%) 50%)ininquartz quartzeyes eyesand and irregular lenticules (Stops C3-C5). Titanite Titanite and and apatite are arepresent presentininminor minoramounts amounts(1—3%), (1-3%), and monazite in trace trace amounts. amounts. apatite and allanite/epidote, zircon and monazite hornblende-magnetite&garnet rocks rocks are usually fine fine to medium grained grained and homogeneous, homogeneous, at The hornblende-magnetite±garnet at least at hand-sample scale. Themore moreleucocratic leucocratic varieties varieties resemble resemble synvolcanic synvolcanic trondhjemite with hand-sample scale. The trondhjemite (Unit (Unit 12), but with disseminated hornblende, and/or magnetite. magnetite.However, However,ininmany manycases, cases,thin thinlayering layering(1—5 (1-5 cm) cm) and and disseminated hornblende, garnet garnet and/or grading, interpreted interpretedasasmodified modifiedbedding, bedding, isis defined defined by by variations variations in in grain grain size size and mineral mineral abundances abundances (Stop (Stop grading, C4). C4). Layered Layered rocks rocks are associated with magnetite-bearing quartzites (metachert?) (metachert?) or or with withmafic maficmetavolcanic metavolcanic rocks with with garnet-cummingtonite(?) garnet-cummingtonite(?)concentrated concentratedinininterconnected interconnectedganglions. ganglions.Field Fieldobservations observationssuggested suggested rocks an origin origin as asmetamorphosed metamorphosed and and digested digested (by (by intrusion) intrusion) ferruginuous ferruginuous chert (G. (G. Stott, Stott,Ontario OntarioGeological Geological an Survey, Survey, pers. comm., comm., 1994) 1994) and iron formation. formation. These These proposals proposals are are supported supportedby by an an exposure exposure on on the thewestern western shore of of Wowun Wowun Lake, in which foliated granite contains contains inclusions inclusions of mafic rock shore rock and and weakly weakly magnetic magnetic quartzrich layered layered iron formation, the latter latter dispersed dispersed over over a width of of 2 to 33 metres. metres. However, However, the high TiO2 TiOs and rich Zr Zr geochemistry geochemistry of magnetite quartzite, quartzite, hornblende-magnetite±garnet hornblende-magnetitekgarnet rocks rocks and and garnet-horublende-bearing garnet-hornblende-bearing trondhjemiteare aremore moreconsistent consistentwith withsedimentary sedimentaryconcentration concentrationof of heavy heavy minerals, minerals, rather rather than thaniron ironformation formation trondhjemite (see (see Geochemistry). Geochemistry). The The relationship relationship of of the the Dead Dead Lake Lake suite suitetotothe themain mainsupracrustal supracrustalassemblage assemblageisisproblematic. problematic. The The two two zones zones of of the the suite suiteare areindistinguishable indistinguishable and and may mayrepresent represent aastructural structuralrepetition. repetition. They They are aresimilar similar to mafic maficrocks rockselsewhere elsewhere in in the theManitouwadge Manitouwadgebelt, belt,especially especiallygarnetiferous garnetiferousmafic maficrocks, rocks,but buthornblendehornblendeto magnetitekgarnet rocks rocks and andassociated associated layered layered magnetite magnetite quartzite quartzite are are unusual. unusual. Aeromagnetic Aeromagnetic trends trends corcormagnetite±garnet responding to to the theDead DeadLake Lakesuite suitecontinue continue easterly easterly both both north northand andsouth southofofthe thecentral centralLoken LokenLake Lakepluton pluton responding 13b). On On the thesouthern southern side, side, the theaeromagnetic aeromagnetic trend tends to to converge converge with the main main southern southern limb limb of of (Unit 13b). (Unit the Manitouwadge Manitouwadge synform. synform. Rocks Rocks similar to the garnet-hornblende garnet-hornblende 'trondhjemite' 'trondhjemite' occur occur east east of of Banana BananaLake Lake the orthoamphibole-garnet-cordierite screens in plutonic plutonic rocks rocks (Stop (Stop D4). D4). North Northof of in association association with with mafic mafic and and orthoamphibole-garnet-cordierite in screens the Loken Loken Lake Lake pluton, pluton, aa pronounced pronounced aeromagnetic aeromagnetic anomaly extends north of of Straight, Straight, Loken Loken and Thompson Thompson the Lakes, Lakes, and apparently apparently continues continues around around the the hinge hinge of of the the Blackman Blackman Lake antiform. The The same same distinctive distinctiverock rock exposedeast eastofofLarry LarryLake, Lake,enclosed enclosedby bytrondhjemite trondhjemite type (grouped (grouped with with the theDead DeadLake Lakesuite suiteofofUnit Unit5)5)isisexposed type to the thenorth northof ofthe themain mainsupracrustal supracrustalbelt. belt.Along Alongthe thenorthern northerncontact contactofofthe theLoken LokenLake Lakepluton, pluton, aazone zone of of to mafic rocks rocks associated associated with with subeconomic subeconomicZn Zn mineralization mineralization (Noranda's (Noranda's Straight StraightLake Lakezone) zone) may may also alsobelong belong mafic to tothe theDead DeadLake Lakesuite. suite. 6) are are among among the the most most unsatisfying unsatisfying and and frustrating frustratingof of Felsic to to intermediate intermediatemetavolcanic metavolcanic rocks rocks (Unit (Unit 6) Felsic units totomap, map,consisting consistingofofsubtly subtlyheterogeneous heterogeneousand andtransitional transitionallithologies lithologiesincluding: including: fragmental fragmentalrocks; rocks; units calc-silicate, sillimanite-muscovite, sillimanite-muscovite, and and felsic-intermediate felsic-intermediate schists; straight gneiss gneiss (see (see Unit Unit 11); 11); and and foliated foliated calc-sihcate, 10 �Description of units Manitouwadge greenstone greenstone belt tonalite, but but generally generally without without marker marker units units to toallow allow useful useful subdivision. The unit unit contains contains lithologies lithologies typical of Units 1, as minor minor exposures exposures typical typicalofofUnits Units22and and 3, 3, but but not on a mappable scale. 1, 7, 8, 11 11 and 14, 14, as well well as of some of of the complexity is probably probably due due to In the the inner inner hinge hinge region region of of the theManitouwadge Manitouwadge synform, synform, some complexity is cryptic early faults faults and and folds folds (see (see Structural StructuralGeology). Geology). Homogeneous Homogeneous to to weakly weakly layered, layered, quartz-phyric quartz-phyric and Microcline is heterogeneously aphyric schists with with minor biotite±muscovite aphyric felsic felsic schists biotiteztmuscovite are predominant. predominant. Microcline heterogeneously disdislayers. In tributed, in in some some cases cases absent absent entirely, entirely, or or in inothers, others,confined confined to tomillimetre-wide millimetre-wide microcline-rich microcline-rich layers. the vicinity vicinity of of the thetwo twoiron ironformation formationlayers layerssouth southofofthe theWillecho Willechodeposit, deposit,felsic felsicrocks rockssporadically sporadicallyconconbetain large large zoned sillimanite sillimanite knots identical to those those of of Unit Unit lbl b(aillimanite-knot (sillimanite-knotfelsic felsic schist) schist) described described be" zoned low. Fragmental-looking enclaves in in an intermediate matrix low. Fragmental-looking rocks have lenticular aphyric felsic enclaves matrix containing containing biotite±hornblendegarnet±magnetite. The biotite&hornblende&garnet&magnetite. Thefragmental fragmentalappearance appearance may may be be partly partly an an artifact artifact of of tectonism tectonism or alteration. alteration. Where Wherethe thematrix matrixisismore morefelsic felsicinincomposition composition(less (lessaltered?), altered?),felsic felsicenclaves enclavesare aremore moredefined defined and resemble clasts in an volcaniclastic or epiclastic breccia. breccia. The outer outer hinge hinge region from Nama Creek to Swill Lake, is underlain by felsjc felsic to intermediate intermediate metavolcanic metavolcanic rocks and biotite biotite schist schist (mostly (mostly metasedimentary?) metasedimentary?) invaded by by foliated tonalite. Aphyric felsic felsic metavolcanic metavolcanicrocks rocks(Unit (Unit7)7)are are present present in in the the outer volcanic Aphyric volcanic belt in three three main mainareas; areas; interlayeredwith with mafic maficrocks rocks(Unit (Unit3) 3) in in the Swill-Mills Lakesarea, area,north northofofGaug Gaug Lake, Lake,and and north north of of interlayered Swill-Mills Lakes Lake near near the Fox Manitouwadge Lake Fox Creek fault. In Inthe theSwill-Mills Swill-MillsLakes Lakes area, area, two two semicontinuous semicontinuous felsic felsic units markers outlining map-scale map-scale symmetrical symmetrical and and asymmetrical asymmetrical folds folds near near the hinge region of the form useful useful markers synform (Fig. (Fig. B3). B3). The southernmost Manitouwadge synform southernmost unit, unit,up uptoto50 50metres metresthick, thick,can canbe berecognized recognizedlocally locallyas as of fine grained to aphanitic a highly deformed deformed monolithologic monolithologic felsic breccia, consisting of aphaniticlapilli-size lapilli-size felsic felsic clasts clasts B12 and and1313). B13). The The breccia brecciaisisassociated associated in a matrix matrixof of biotite-muscovite biotite-muscovite or or garnet-hornblende garnet-hornblende schist schist (Stops (StopsB12 disseminated pyrite pyrite and and pyrrhotite (Stop B14). with minor iron formation and, locally, disseminated B14). North of Gaug Lake, aphyric felsic rocks and and interleaved interleavediron ironformation formation (Unit (Unit 9) 9) lie lie along along or or near the North felsic rocks metavolcanic rocks rocks (Unit (Unit 3) and metagreywacke (Unit 10). The contact between mafic metavolcanic metagreywacke (Unit Thefelsic felsicrocks rocks include include homogeneous schist, and monolithologic monolithologic and heterolithic volcaniclastic volcaniclastic breccias. Monolithologic Monolithologicclasts clasts mostly mostly vary from 2 to to10 10centimetres centimetres ininsize, size,but butsome somebreccias brecciashave havelarge large(cm—m (cm-m scale) angular clasts clasts (Stop (Stop B4). B4). Some large clasts have reentrant reentrant angles, angles,and andsome somenearest nearestneighbours neighbourshave havecomplementary complementaryshapes shapessuggestive suggestive of in situ fragmentation fragmentation of larger blocks. blocks. The The matrix matrix isisfelsic felsic to to intermediate, intermediate, normally normally containing containing biotite, but in and garnet garnet porphyroblasts. interpreted as in some some cases, cases, dominated dominated by hornblende hornblende and porphyroblasts. The breccias breccias were were interpreted Granges Inc., pers. pers. comm., comm., 1992) 1992) or or proximal volcanic volcanic deposits, deposits, possibly possibly derived derived from from phreatic phreatic (W. Bates, Granges hydrothermal limited transportation. transportation. Heterolithic hydrothermal explosions involving limited Heterolithic breccias breccias contain contain felsic felsic and hornblendegarnet-rich garnet-rich clasts clasts (generally (generally 2 to to 10 10centimetres centimetres in in size), size),typically typically inina abiotite-hornblende-garnet-bearing biotite-hornblende-garnet-bearing that matrix. The Thehornblende-garnet hornblende-garnet clasts clastsresemble resemble matrix matrix material materialofofmonolithologic monolithologic breccias, suggesting suggesting that reworked proximal deposits were a source for heterolithic breccias (Stop B5). reworked B5). North of Manitouwadge Lake and south of the Agam Lake fault, fault, exposures of of white white laminated laminated quartz-rich felsic schists schists are are interpreted interpreted as volcanic volcanicor orintrusive intrusiverocks. rocks.To Tothe thenorth, north, they they are bounded bounded by by a topographic felsic depression markingthe thetrace traceofofthe the Agam AgamLake Lakefault. fault. On On the the north north side side of of the the fault, fault, the biotite schist depression marking schist is typical of metasedimentary metasedimentary rocks rocks of of Unit Unit 10. The have aa strong fabric, possibly related to the typical of The felsic felsic rocks rocks have possibly related the fault, defined by partially annealed quartz quartz ribbons, ribbons, minor minor biotite biotite and andmuscovite. muscovite. Quartz-phyric feisic met avol canicrocks rocks(Unit (Unit8), 8),ininthree threebodies bodiesininthe theinner inner volcanic volcanicbelt, belt, are are spatially felsic metavolcanic associated with with the known with iron formation (Unit associated known mineral deposits. Quartz-phyric Quartz-phyric rocks are interlayered interlayered with sulphide deposits deposits hosted hosted by iron formation, and sillimanite-muscovite-quartz schist (Unit (Unit 1); at 9), massive massive sulphide sillimanite-muscovite-quartz schist least some of of the the interlayering interlayering isis interpreted interpreted to to be due to structural least structural repetition repetition by by early early faults faults and and folds folds (see (see 20%,typically typically1—3 1-3 Structural Geology). Geology). The The unit unit isischaracterized characterized by byabundant abundantquartz quartzphenocrysts phenocrysts(up (uptoto20%, forming lenticular lenticular augen, augen, in in a fine grained grained biotite felsic matrix. The mm in size), commonly forming felsic to leucofelsic leucofelsic matrix. matrix consists consists of quartz, quartz, plagioclase, plagioclase, microcline and biotite, with with accessory accessory or trace trace amounts amountsof of muscovite, muscovite, epidote and garnet. garnet. Magnetite Magnetiteporphyroblasts porphyroblasts(1—3 (1-3 mm in size) are prominent. As As in in felsic felsic rocks rocks of of Unit Unit 6, 6, microcline and and muscovite muscovite are are heterogeneously heterogeneouslydistributed, distributed, even evenon on aa thin-section thin-section scale, scale,suggesting suggestingthat that their their microcline presence is is related related to potassic alteration rather presence rather than thanprimary primarymagmatic magmaticcomposition composition(see (see Geochemistry). Geochemistry). In In some cases, quartz-phyric rocks grade to to aphyric aphyric rocks, rocks, especially especially toward contacts. The three schists and and fragmental fragmental rocks, rocks, the the latter both monothree quartz-phyric quartz-phyric bodies bodies include include homogeneous homogeneous schists monolithologic and heterolithic. heterolithic. In Inone onelocation, location,angular angularmonolithologic monolithologic quartz-phyric quartz-phyric felsic felsic clasts, ranging from large large (>0.5 (>0.5 m) m) to to small small (<1 (<1cm), cm),are areunsorted unsortedand andapparently apparentlymatrix-supported, matrix-supported, ininaamicrocline-biotitemicrocline-biotiteepidote-horublende matrix (Stop A18). epidote-hornblende matrix A18). The The breccia breccia could could be be aa proximal proximal volcaniclastic volcaniclastic deposit, or aa flow-top flow-top (<I-30 cm cm or flow-foot flow-foot breccia. More Moretypically, typically,volcaniclastic volcaniclasticrocks rockscontain containlenticular lenticularlapilli-size lapilli-sizefragments fragments(<1—30 long), and both fragments and matrix long), matrix contain contain quartz quartz phenocrysts phenocrysts (Stop A3). The The clasts clasts show show subtle variavariation in colour and grain size that could could be be attributed attributed totovariable variableresponse response to to alteration alteration (e.g. (e.g. devitrification, devitrification, Willroy-Geco diagenesis, alkali-exchange) of oforiginally originallycomagmatic comagmaticcrystalline crystallineand and glassy glassycomponents. components. In In the Wiliroy-Geco area, the the matrix matrixcontains contains muscovite, muscovite, biotite, biotite, garnet garnet and andmagnetite. magnetite.North NorthofofWillecho, Willecho,fragmental fragmentalrocks rocks are are \ 11 �Description of units Manitouwadge greenstone belt more difficult to identify unambiguously. calcunambiguously. Diffuse Diffuse lenticular quartz-phyric quartz-phyric felsic felsic enclaves are present present in in aacalcmatrix including plagioclase, Ca-amphibole, Ca-amphibole, epidote epidote and and garnet, garnet, as well as magnetite, muscovite silicate-rich matrix and microcline. microcline. In all three quartz-phyric bodies, bodies, the the abundance abundanceof of caic-silicate calc-silicate minerals tends to to increase increase toward contacts contacts with formation. In the the Willroy Willroy area, area, outcrops outcrops dominated dominated by bythe thecaic-silicate calc-silicateminerals; minerals; plagioclase, plagioclase, with iron formation. clinopyroxene,Ca-amphibole, Ca-amphibole,garnet, garnet,epidote epidoteand and titanite, titanite, can be clinopyroxene, be traced traced laterally laterallyinto intoquartz-phyric quartz-phyricfelsic felsic rocks (Stop A4). The rocks The calc-silicate calc-silicate rocks rocks were interpreted as as metasomatically metasomatically altered. altered. Metamorphosed iron iron formation (Unit (Unit 9) three subunits; a) quartz-magnetite 9) includes three quartz-magnetite iron iron formation, formation, b) b) Metamorphosed silicate iron iron formation, formation, and and c) c) sulphidic suiphidic iron iron formation. formation. These These occur occur in in both both the inner silicate inner and and outer outer volcanic volcanic rocks (Units (Units 6, 7 and and 8) and sillimanite-bearing schist (Unit belts, interlayered mostly with felsic felsic metavolcanic rocks 1). Most associated with with quartz-magnetite iron iron formation that that grades laterally to Most of the Cu-Zn Cu-Zn orebodies are associated to sulphidic iron formation and and to to massive massive sulphide sulphide (Pye, (Pye, 1957; 1957; Timms Timms and and Marshall, Marshall,1959; 1959;Friesen F'riesen et et al., al., 1982). 1982). Quartz-magnetite iron formation, formation, by by far the most abundant type, Quartz-magnetite type, isis characterized characterized by by alternating alternating white white coarse grained (recrystallized) (recrystallized)quartz quartzlayers layersand anddark darkmagnetite~grunerite~actinolite~garnet&clinopyroxene magnetite±grunerite±actinolite±garnet±clinopyroxene coarse grained layers. The relative minerals is is variable variable and and even even magnetite magnetite is is present present only only in in trace layers. relative proportions proportions of of iron-rich minerals amounts, or absent, in in some some cases. cases. Suiphide Sulphide minerals minerals (pyrrhotite, pyrite, pyrite, sphalerite, sphalerite, chalcopyrite) chalcopyrite) and carcarbonate may be present present in minor minor or or trace trace amounts, amounts, as aswell well as as stilpnomelane, stilpnomelane, apparently of retrograde origin. Layering, interpreted interpreted as aa modification precipitated bedding, bedding, varies varies from from dark lamellae Layering, modification of chemically chemically precipitated lamellae in aa quartz-dominated rock to to dark dark and andlight lightlayers layersof of 10 10 centimetres centimetres or or more more in in width. width. Iron Ironsilicate silicateminerals, minerals,esescmlength), length), typically with weakly developed pecially grunerite, vary vary from from medium medium to tovery verycoarse coarsegrained grained(1—5 (1-5 cm at least in D2 folds. tectonic fabrics. However, However, at in some some localities, grunerite defines a foliation axial planar to to D2 is commonly commonly disrupted disrupted by by breccia breccia zones zones and and outcrop-scale outcrop-scale folding. folding. A A tectonic tectonic origin is indicated indicated Layering is for minor folds by by the observation that systematic systematic changes changes in asymmetry asymmetry are related related to tomap-scale map-scale D2 D2 folds. folds. Breccia zones zones of ofangular angular and and rotated rotated quartzose fragments in a dark Breccia dark magnetite-silicate magnetite-silicate matrix matrixare aresandwiched sandwiched between coherent layers layers (Stop A22), features features typical of intraformational breccias. between coherent breccias. However, However, the apparently apparently competent behaviour behaviour of of quartzose fragments fragments suggests that that brecciation brecciation occurred occurred after afterdiagenesis diagenesisor or low low grade grade metamorphism. Tectonic Tectonic fragmentation fragmentation isis also also suggested suggested by by local local breccia breccia zones zones in the the hinges hinges of of minor minor folds, folds, and by quartzose quartzose fragments that that preserve preserve fold fold hinges. hinges. In In the the case case of of breccias breccias related to to folds, folds, dark dark iron-rich iron-rich material encloses encloses quartzose fragments, fragments, evidently evidently having having migrated migrated into intothickened thickened hinge hingeregions. regions. Silicate iron iron formation is dark the dark layers Silicate dark and and homogeneous, homogeneous, resembling resembling the layers in in quartz-magnetite quartz-magnetite iron iron formation, except except that that garnet garnet tends to be formation, be coarser coarser and and more more abundant. abundant. Minor Minor amounts amounts of of quartz quartz may may be be present, dispersed Silicate iron iron formation formation occurs occurs mainly mainly near near the contacts present, dispersed among the iron-rich iron-rich minerals. minerals. Silicate contacts of quartz-magnetite quartz-magnetite iron iron formation. formation. It may unit or stratiform alteration of may represent represent an an original original depositional depositional unit related to iron formation contacts. Alternatively, related Alternatively, its similarity to iron-rich material in quartz-magnetite iron evidence of of outcrop-scale outcrop-scale remobilization, remobilization, suggest silicate iron formation formation may may represent represent formation, and evidence suggest that that silicate large-scale large-scale remobilization remobilization and and segregation segregation of of material material derived derived from from quartz-magnetite quartz-magnetite iron formation. Suiphidic iron iron formation is generally generally similar similar to to quartz-magnetite iron formation, but with Sulphidic with disseminated disseminated or stringer rarely forms forms a mappable unit, occurring mainly stringer pyrite, pyrrhotite or sphalerite. ItIt rarely mainly in in the the transition iron formation formation to to massive massive suiphide sulphide (Stop A3). from quartz-magnetite iron the inner inner volcanic volcanicbelt belt along alongthe thesouthern southernlimb limbofofthe theManitouwadge Manitouwadgesynform, synform,iron ironformation formationdefines defines In the Southwest of of the theNama NamaCreek Creek deposit, deposit, the themost mostsoutherly southerlyiron ironformation formationisisthickened thickened by by four main belts. Southwest D2 folding (see (see Structural Structural Geology). formation is is present present along along its its northern contact D2 folding Geology). Silicate iron formation contact and and forms forms west side of a sliver of Lake. The The sliver sliver is is a thicker zone on the west of iron iron formation formation that that extends toward Garnet Lake. separated from formation by Some of iron formations in separated from the the main main belt belt of iron formation by an an early early fault. fault. Some of the thin iron in the Willroy area west Willroy area similarly similarly represent representstructural structural repetitions repetitions (see (see Structural Structural Geology). Geology). In In the Geco area and west of Fox Fox Creek, southernmost iron iron formation formation isis heavily heavily invaded invaded by concordant concordant sheets sheets of of foliated foliated tonalite, tonalite, Creek, the southernmost mostly at the thescale scaleof of mapping; mapping; hence, hence, the the true truevolume volumeof of iron iron formation formation is is exaggerated. exaggerated. The The mostly not separable at southern contact contact between between iron iron formation formationand andmetagreywacke metagreywackeis is mostly mostly obscured obscured by by tonalite tonalite sheets. sheets. North of Garnet Lake, Lake, iron formations formations are tectonically tectonically thinned, in in some some cases occurring occurring as boudin trails or pinching out entirely. In the the Willecho Willecho area and and to to the thenorth, north,iron ironformation formationdefines definesmap-scale map-scale folds folds and is thickened by folding. Iron formation the hinge hinge of the Blackman Lake antiform. North North of of formation was also mapped on the limbs and near the Straight Lake, Lake, zincian suiphidic sulphidic quartz-rich rocks (Noranda's Jim Jim Lake Lake zone), associated with orthoamphibolebearing rocks, were interpreted formation. West West of of One One Otter Otter Lake Lake and andbetween between Jim Jimand andDavis DavisLakes, Lakes, interpreted as iron formation. magnetic rocks rocks grouped grouped with withiron ironformation formationare arehornblende-plagioclase-rich hornblende-plagioclase-rich with withthin thinlayers layers(mm—cm (mm-cm width) width) magnetic defined by defined by varying varying proportions proportions of of fine fine grained grained mafic maficand andfelsic felsicminerals mineralsand andmagnetite magnetite(Stop (Stop E6). E6). They are mainly associated with with mafic mafic to to intermediate intermediatemetavolcanic metavolcanicrocks rocks and and may may represent represent chemical chemical precipitates precipitates with with considerable detrital or or tuffaceous tuffaceous component, component, or altered altered volcanic volcanic rocks. Minor Minor exposures exposures of more typical a considerable quartz-magnetite iron iron formation formationare arelocally locallypresent present in in the the area, area,and andalso alsoin in the theDead DeadLake Lakesuite suite in in an an exposure exposure quartz-magnetite 12 �Description of units Manitouwadge greenstone belt on Wowun Lake. West of the Manitouwadge belt and Wowun Lake. and Kern Kern (Blackman) (Blackman) Lake, Lake,two two lenses lenses of of quartz-magnetite quartz-magnetite batholith in iron formation are present as as inclusions inclusions in tonalite of the Black Pic batholith in an an area areaof of strong strong aeromagnetic aeromagnetic striping. Metasedimentary rocks (Unit (Unit 10) lie between Metasedimentary rocks between the inner and and outer outer metavolcanic metavolcanic belts belts along along the thesouthsouthcentral to the ern limb of the the Manitouwadge Manitouwadge synform, synform, central the D2 D2'Manitouwadge 'Manitouwadge syncline' syncline' (see Structural GeolGeology). Mostly Mostly comprising comprising monotonous monotonous metagreywacke, metagreywacke, they are are dominated dominatedby byhomogeneous, homogeneous,grey, grey,foliated, foliated, fine grained, grained, poorly to strongly layered, schist. biotite-quartz-feldspar~hornblende~muscovite schist. Locally, Locally, more more fine layered, biotite-quartz-feldspar±hornblende±muscovite pelitic layers contain garnet and/or and/orsillimanite. sillimanite.Layering Layeringorormodified modifiedbedding bedding(0.5—30 (0.5-30 cm in width) width) isisdedefined by by variation variation in mafic and locally locally graded. graded. Concordant fined mafic mineral abundance,abundance,. and Concordant and and semiconcordant semiconcordant intruintrusions of of plagioclase-phyric plagioclase-phyrictonalite tonalite are are common. common. East of contains quartz- and sions of Agam Agam Lake, Lake, metagreywacke metagreywacke contains and plagioclase-crystal clasts, plagioclase-crystal clasts, interpreted interpretedasasevidence evidencefor foraa tuffaceous tuffaceousvolcanogenic volcanogenic component. component. Chaotic Chaoticfolds, folds,some some cm) and and sandwiched between undisturbed eye-shaped, spanning aa thickness thickness of of several several layers layers (totalling (totalling5—20 5-20 cm) layers, are are interpreted interpreted as the result of transposed soft-sediment deformation (Stop (StopAl). Al). layers, soft-sediment deformation age of of the Manitouwadge metagreywackesisisatat least least 25 25 Ma Ma younger younger than than The maximum maximum depositional depositional age Manitouwadge metagreywackes associated with with Cu-Zn mineralization mineralization (Zaleski et a!., the age of of felsic volcanism associated (Zaleski et al., 1995). 1995). The The metagreywackes metagreywackes in map-scale map-scale D; D2folds foldssouth southof ofthe the Nama Nama Creek Creek deposit deposit and and the dominant foliation are involved involved in foliation is ascribed ascribed metavolcanic rocks rocksto to north north and south, The contact contact between between metagreywackes metagreywackes and metavolcanic south, largely to D2 deformation. The obscured by by intrusions intrusions and and deformation, deformation,isisinterpreted interpretedtoto be be either either an an unconformity unconformityoror an an early early (pre(pre- to obscured syn-D2) fault. fault. Tectonic nits Tectonic rock rock uunits Straight gneiss (Unit Straight (Unit 11), l l ) ,or or laminated laminatedfelsic felsicgneiss, gneiss, was was identified identified in isolated exposures exposures and and in insemiconsemicontinuous map-scale between quartz-phyric quartz-phyric felsic felsic bodies bodies (Unit (Unit 8) in in the Wiliroy map-scale layers or lenses between Willroy area, associated with iron formation (Unit 9) and sillimanite-knot felsicschist schist(Unit (Unit lb) ib) in the Willecho Willecho area, and associated with sillimanite-knot felsic with iron formation and sillimanite-muscovite-quartz schist (Unit (Unit la) south of Lake. In the sillimanite-muscovite-quartz schist of Wowun Wowun Lake. the Wiliroy Willroy area, zones map-scale truncations truncations of of iron formation and repetition zones of straight gneiss gneiss coincide coincide with map-scale repetition of of aa disdis(see Structural Geology). tinctive lithological sequence sequence (see Geology). Locally, Locally, straight gneiss is associated with high high strain strain in iron formation, manifested either straight alternating manifested as either alternating quartz-rich quartz-rich and and dark dark magnetite-rich magnetite-rich laminations laminations (Stop Dl) Dl) or orconcordant concordant zones zones of of iron iron formation formation slivers slivers and boudins. On Onthe thebasis basisofofthese theseobservations, observations, straight gneiss straight gneiss was interpreted interpreted as asannealed annealed mylonite mylonite (see (see Hanmer, Hanmer, 1988 1988 for a definition) lying on early ductile faults. Straight gneiss gneiss is fine fine grained to to aphanitic, aphanitic,and andcharacterized characterizedby bycontinuous continuoustotostreaky streakylamellae lamellae(<1—1 (<I-1 mm width) of quartz and and feldspar, feldspar, and andat atsome somelocalities, localities,micaceous micaceous or hornblende-rich lamellae. Petrographic Petrographic shows that that straight gneiss examination shows gneiss has an annealed annealed granular texture but, but, in insome somecases, cases, strained strained quartz quartz ribbons were interpreted as as remnants remnantsof of an anoriginal originalmylonitic mylonitic fabric. fabric. felsicrocks rocksand andpegmatite. pegmatite.On On the the north north The protolith to to straight straight gneiss gneiss apparently apparently mostly comprised comprised felsic of the Willecho Willecho 33 pit, pit, a transition side of transition from from pegmatite pegmatite to tostraight straightgneiss gneissisisexposed exposedover over several several metres metres (Stop (Stop A26). With increasing A26). increasing intensity of strain, strain, near-massive near-massive pegmatite grades to sheared pegmatite with with strongly strongly lineated sillimanite on on shear shear surfaces, pegmatite, to streaky fine lineated surfaces, to porphyroclastic porphyroclastic pegmatite, fine grained grained straight straight gneiss. gneiss. In porphyroclastic porphyroclastic pegmatite, pegmatite, enclaves enclaves of coarse grained grained quartz and and feldspar feldspar are areenclosed enclosed by by fine fine grained grained gneiss containing lineated sillimanite. sillimanite. laminated gneiss Metasomatically Metasomatically altered rock units units Extensive orthoamphibole-bearing gneiss sillimanite-bearing schist themafic-felsic mafic-felsic Extensive zones zones of orthoamphibole-bearing gneiss and sillimanite-bearing schist near the transition belt and, to transition in the the inner inner volcanic volcanic belt to aa limited limited extent, extent, in in the theouter outervolcanic volcanic belt, belt, are are interpreted interpreted as as zones of of synvolcanic synvolcanichydrothermal hydrothermal alteration, alteration, modified by high grade regional metamorphism metamorphism and deformation. deformation. Orthoamphibole-garnetdicordieritegneiss the basis basis of of surface surface observations observations and and subsurface subsurface Orthoamphibole-garnet±cordierite gneiss (Unit (Unit 2), on the data, data, forms forms aa sheet sheet of of regional regional extent, extent, mantling mantling synvolcanic synvolcanic trondhjemite (Unit 12) 12) and folded folded by the ManMangneiss extends continuously for 30 km km from from Rabbitskin Rabbitskin itouwadge synform. synform. Orthoamphibole-garnet gneiss for at at least 30 northern limb limb of of the theManitouwadge Manitouwadge synform, synform, around the the hinge hinge of of the thefold fold to tothe theWillroy-Geco Willroy-Geco Lake on the northern and east east to tothe theHucamp Hucampand andFalconbridge Falconbridgezones zones of of subeconomic subeconomic mineralization of the the area, and mineralization(Fig. (Fig. 3). 3). East of however, aa prominent and Hucamp zone, exposure is poor; however, prominent aeromagnetic aeromagnetic anomaly anomaly continues continues the the same trend and the unit was was intersected intersected in in drill drill holes. holes. North North of of Straight StraightLake, Lake,orthoamphibole-garnet orthoamphibole-garnet rocks and sphaleritebearing attentuated northern northernlimb limbofofthe theManitouwadge Manitouwadgesynform, synform, are are correlated correlated with with bearing iron formation, on the attentuated the same horizon. East East of of Thompson Thompson and andBanana BananaLakes, Lakes,orthoamphibole-cordierite-garnet orthoamphibole-cordierite-garnet gneiss, gneiss, defining a series of same of map-scale map-scale folds foldswith with aanortherly northerly trending enveloping enveloping surface, surface,isisinterpreted interpreted as a repetition of the same horizon, possibly in the 'keel' 'keel' of of aa D2 D2 fold involved in (Peterson and andZaleski, Zaleski, in aa Dz/Da D2/D3 fold fold interference interference pattern pattern (Peterson Orthoamphibole-garnet rocks by deep deep drill drill 1994b; Zaleski Zaleskietet al., al., 1995). 1995). Orthoamphibole-garnet rocks have have also also been been intersected intersected at at depth by holes penetrating plutonic rocks rocks inside the the Manitouwadge Manitouwadge synform. For For example, the the 'Geco 'Geco deep deep hole', hole', drilled drilled penetrating plutonic 13 �Manitouwadge greenstone belt of units Description of test the thedown-plunge down-plungeprojection projection of of the the Willroy Willroy deposits, deposits, intersected intersected about about 300 300 metres metres of of orthoamphiboleorthoamphiboleto test or sillimanite-bearing rocks. rocks. the area areaof of known known economic economic mineralization, orthoamphibole-garnet rocks lie north of of mineral deposits deposits In the Nama Creek, Creek, Willroy Willroy and and Geco, Geco, along along the the contact contact between between synvolcanic synvolcanic trondhjemite trondhjemite and andextrusive extrusivevolcanic volcanic at Nama rocks. The The precursers precursors to toalteration, alteration,still stillrecognizable recognizable in in less less altered altered enclaves enclaves mostly mostly on on the the margins margins of of the the rocks. unit and and to tothe thenorthwest northwestfurther furtherfrom fromknown knowndeposits, deposits,were were mafic mafic (Unit (Unit 3)3)and andinterlayered interlayeredmafic-felsic mafic-felsic rocks the transitional transitional mafic-felsic mafic-felsic contact. the outer outer volcanic volcanic belt, belt, orthoamphibole-garnet orthoamphibole-garnet rocks (Unit (Unit 4) near the contact. In the assemblages are are found found locally locally in in mafic mafic metavolcanic metavolcanicrocks rocksininaa discontinuous discontinuouszone zonenear near the the northern contact to felsic felsic metavolcanic rocks and metagreywacke metagreywacke (Stop B1). Bl). Orthoamphibole-bearing Orthoamphibole-bearing zones zones are much much less less extensive in the outer belt belt than thanininthe theinner; inner:however, however,,garnetiferous earnetiferous zones are common in mafic rocks. zones are common in mafic rocks. " The unit isis defined defined primarily primarily by by the thepresence presence of of orthoamphibole. orthoamphibole. Orthoamphibole-bearing Orthoamphibole-bearing rocks are astypically with first-order first-order metre-scale metre-scale layering metamorphic mineral astypically layered, layered, with layering defined defined by by variations variations in metamorphic semblages, size (Stops (Stops A6, A13, A14, D4). Second-order Second-order layering layering semblages, proportions, proportions, textures textures and and grain size A6, A13, A14, D3 and D4). consists of semi-continuous auartz-rich which locally locallv define define rootless intrafolial intrafolial quartz-rich lamellae or fine felsic bands. bands, which isoclinal the Wiliroy willroy area, area, garnet-orthoamphibole garnet-orthoamphibole layers layers that that anastomose anastornosearound aroundhornblende-rich hornblende-rich isoclinal folds. folds. In the resemble deformed deformed altered altered pillow pillow selvedges selvedgesor orfracture-controlled fracture-controlled alteration. alteration. Local enclaves resemble Local exposures exposures of of semisemiconcordant hornblende-cummingtonite-plagioclase hornblende-cummingtonite-plagioclase layers, and linear linear swarms swarms of of lenticular lenticular felsic felsic enclaves enclaves in an an orthoamphibole-garnet matrix, have been interpreted as orthoamphibole-garnet as remnants remnants of of dykes. dykes. In Insome someareas, areas,orthoamphiboleorthoamphibolesnake-like garnetiferous garnetiferous enclaves enclavesin inaastructure structure suggesting segmented layering garnet rocks enclose lenticular or snakelike and reminiscent of of aa coarse coarse breccia breccia (Stop (Stop D4). D4). In In general, general, the the layering layeringisisinterpreted interpreted as as the the result result of of transpotranspoor early fractures, dykes or sills, sition of syngenetic structures including including tuffaceous tuffaceous bedding, possible pillows or and domains domains of more and less less altered rocks. rocks. The orthoamphibole orthoamphibole commonly commonly displays blue iridescence, iridescence, characteristic of of cryptocrystalline cryptocrystalline exsolution exsolution from a composition above the the gedrite-anthophyllite gedrite-anthophyllitesolvus solvus(Robinson (Robinsonetetal., al.,1982). 1982).ItIt occurs occurs in in a variety variety of of composition above whichinclude includegarnet&cordierite&sillimanite&plagioclase garnet±cordierite±sillimanite±plagioclase and and cummingtonite&hornblende&plagcummingtonite±hornblende±plagassemblages, which ioclase±garnet. ioclasekgarnet. Hornblende-plagioclase±cummingtonite±garnet Hornblende-plagioclase&cummingtonite~garnetassemblages assemblages interlayered with orthoamphiborthoamphibole-bearing assemblages are are interpreted as indicative indicative of of lower intensity hydrothermal alteration alteration of ofmafic maficvolvolrocks. Orthamphibole-garnet-cordierite area, interleaved (on Orthamphibole-garnet-cordierite assemblages assemblages dominate in the Willroy-Geco area, canic rocks. a 10 scale)with withsillimanite-cordierite-biotite&garnet sillimanite-cordierite-biotite±garnetlayers layers(Stop (StopA5). A5).Quartz Quartz and and magnetite are 10 cm—10 cm-10 mmscale) ubiquitous, and and small small amounts amountsof of sulphide minerals, staurolite, staurolite, and and gahnite gahniteare arecommon. common.More Moreexotic exoticminerals minerals are found in the [(Ti,Sn)(Fe,Mg,Zn,Mn)e(Al,Fe)ie032] the Geco Geco mine, mine, including including corundum, corundum,cassiterite, cassiterite,högbomite hogbomite[(Ti,Sn)(Fe,Mg,Zn,Mn)6(Al,Fe)16032] (Spry, 1982; 1982;Petersen, Petersen, 1986). 1986). In orthoamphibole-bearing and nigerite [(Sn,Ti)2(Zn,Mg,Fe,Mn)4(Al,Fe)16032J [(Sn,Ti)2(Zn,Mg,Fe,Mn)4(Al,Fe)i6032] (Spry, rocks, biotite habits suggest both metamorphic and retrograde generations, the latter of latter forming forming pseudomorphs of coarse orthoamphibole sprays (Stop AS). A5). Plagioclase small amounts amounts in in orthoamphiboleorthoamphibolePlagioclase is absent or present in small bearing assemblages, assemblages, particularly particularly in in the theWillroy-Geco Willroy-Gecoarea. area. Sillimanite-muscovite-quartz schist (Unit 1) Sillimanite-muscovite-quartzand and sillimariite-knot sillimanite-knot felsic schist 1) are subdivisions representing 'endmembers' of Unit 1, orebodies in in the the Willroy-Geco Willroy-Gecoarea, area,and and the the latter latter 1, the former found mainly to the south of orebodies area and north. The in the Willecho area Theunit unitalso alsoincludes includestransitional transitionalquartzites quartzitesinterleaved interleavedwith withmicaceous micaceousschist. schist. Sillimanite-muscovite-quartz schist occurs occurs in in close proximity to to massive suiphide deposits deposits and envelopes the Sillimanite-muscovite-quartz schist close proximity massive sulphide Geca Geco main orebody. Abundant muscovite and/or sillimanite sillimanite and quartz quartz are are typical of the unit, and and plagioclase, plagioclase, biotite, K-feldspar, K-feldspar, garnet and and magnetite magnetite may may also alsobe be present. present. Felsic Felsic volcanic volcanic rocks lying along strike and in less altered altered enclaves enclaves are are interpreted interpreted as the protolith to to alteration. alteration. Along the southern southern limb limbof of the theManitouwadge Manitouwadgesynform synformin inthe theWiliroy-Geco Willroy-Gecoarea, area,two twozones zonesof ofsillimanitesillimaniteschist converge convergetotothe the east east near near the Geco mine, mine, where where they they are are separated by an early fault (see bearing felsic schist (see Structural Geology). schist (Stop (Stop A19) A19) to quartzGeology). The The northern northern zone zone grades grades easterly easterly from from sillimanite-knot sillimanite-knot schist muscovite-sillimanite schist schist consisting consisting of of finely finely interlayered interlayered quartz quartz and muscovite with sillimanite muscovite-sillimanite sillimanite sprays sprays on on the foliation surface (Stop A6). Near schist that that Near Wiliroy, Willroy, the southern belt consists consists of a thinly thinly layered layered felsic schist becomes more muscovitic muscoviticand andsilicic silicictotothe theeast, east, merging mergingwith withthe the northern northern belt belt and grading to aa suiphidic becomes more sulphidic muscovite-biotite quartzite in the Geco muscovite-biotite quartzite Geco area. area. Near the the hinge hinge region region of of the the Manitouwadge Manitouwadge synform synform in in the theWillecho Willecho area, area, sillimanite-knot sillimanite-knot felsic felsic schist schist is is interleaved (on a metre scale) felsic schist, schist, straight straight gneiss gneiss and and sheared sheared pegmatite pegrnatite (Stop interleaved scale) with with non-sillimanitic non-sillimanitic felsic A24). Similar rocks occur sporadically sporadically to to the south of associated with with iron iron formation formation that can A24). of Willecho, Willecho, associated can be be traced continuously to the the Willroy Willroy area. area. The Thesillimanite-bearing sillimanite-bearingrocks rocks contain contain quartz, quartz,plagioclase, plagioclase,microcline microcline and biotite and and are aregenerally generally more more feldspathic feldspathic than those those in in the theWiliroy-Geco Willroy-Geco area. Sillimanite occurs in cminindiameter), diameter), typically typically zoned zoned with with greenish greenish cores cores mantled mantled by by white fibrous sillimanite. sillimanite. coarse knots (1—8 (1-8 cm and vary from sparse sparse to to about about 20 percent. In general, general, the knots are are disseminated disseminated and vary in abundance abundance from percent. At At aafew few tuff or ortuffaceous tuffaceousmetasediment metasedimentcontains containsabundant abundant sillimanite that that localities, thinly layered quartz-phyric felsic tuff coalescesinto intosillimanitic sillimaniticlayers. layers. In In these these cases, cases, the the distribution distribution of of sillimanite sillimanite isis stratabound, stratabound, concentrated coalesces concentrated from near the tops(?) tops(?) of of modified modified beds. A A northward northward increase increase in metamorphic metamorphic grade is indicated by a change from 14 �Description of units units Manitouwadge greenstone belt sillimanite-muscovite sillimanite-muscovite to to sillimanite-microcline sillimanite-microclineassemblages. assemblages. Synvolcanic intrusions Synvolcanic intrusions Foliated trondhjemite-hornblende 12)underlies underlies aa large large area area inside inside the theManitouwadge Manitouwadge trondhjemite-hornblende granodiorite granodiorite (Unit (Unit 12) synform, forming forming an elliptical ring cored by the younger Lake pluton pluton (Unit 13b). cored by younger Loken Loken Lake 13b). Granodiorites Granodiorites and and tonalites of of similar appearance extend around around the the Blackman Blackman Lake Lake anticline, to the the hinge hinge region region of of the the Jim Jim Lake synform. The Lake synform. The area area of of the theunit unitdisplays displaysaahigh highvariable variableaeromagnetic aeromagnetic signature, signature, probably probably related to to the abundance abundance of of magnetite magnetite and andtotothe thepresence presenceofofsupracrustal supracrustalscreens, screens,for forexample examplethe theDead DeadLake Lakesuite. suite. A deep deep drill hole, hole, collared about one one kilometer north of the Geco Geco mine, penetrated mostly mostly trondhjemite trondhjemite to to granodiorite granodiorite for for the the uppermost uppermost1470 1470metres, metres,before beforeencountering encounteringfine finegrained grainedmafic maficmetavolcanic metavolcanicschist. schist. Along Along its its outer outer perimeter, perimeter,trondhjemite trondhjemiteintrudes intrudesmafic mafic(Unit (Unit3)3)and andmixed mixedmafic-felsic mafic-felsicmetavolcanic metavolcanic rocks rocks (Unit gneiss (Unit (Unit 2). 2). The outermost trondhjemite is a quartz-rich (Unit 4), 4), and and orthoamphibole-cordierite-garnet orthoamphibole-cordierite-garnet gneiss quartz-rich (30—50%) leucocratictonalite tonalitewith withminor minorbiotite, biotite, magnetite magnetite and, locally, garnet. ItItvaries (30-50%) leucocratic variesfrom fromfine fine to tocoarse coarse grained, grained, but but typically typically contains contains coarse coarse quartz grains up to to 55 millimetres millimetres in diameter. Minor Minor or trace amounts amounts of titanite, apatite, allanitelepidotemay mayalso alsobe bepresent. present.InInthe theWillroy-Geco Willroy-Gecoarea, area,the the of microcline, titanite, apatite,zircon zircon and andallanite/epidote abundance of biotite and garnet garnet tends tends to toincrease increase toward toward the the southern southern contact contact with with orthoamphibole-bearing orthoamphibole-bearing rocks, rocks, and and locally, locally, the trondhjemite trondhjemite isishost host to tonarrow narrowseams seamsof of biotite, biotite,orthoamphibole, orthoamphibole,cordierite cordieriteand andgarnet garnet (Stop A7). A7). The Theseams seamswere were interpreted interpreted as aspre-metamorphic pre-metamorphic fracture-controlled fracture-controlled alteration related related to tosynvolsynvolcanic hydrothermal activity, implying that that trondhjemite is a synvolcanic intrusion. Our field activity, implying synvolcanic intrusion. field interpretation of of synvolcanic synvolcanic intrusion intrusion was wasconfirmed confirmedby bygeochronology geochronology(2720±3 (2720h3Ma, Ma,see seeGeochronology). Geochronology). Despite some variations in modal abundances, Unit 12 is is characterized characterized by by abundant abundant coarse grained quartz, quartz, disseminated biotite, and disseminatedmagnetite magnetiteporphyroblasts porphyroblasts(1—3 (1-3 mm), minor biotite, and aa weakly weakly to to moderately moderately developed developed fabric. fabric. Away Away from its outer perimeter perimeter in in the thehinge hingeregion region of of the the Manitouwadge Manitouwadge synform, foliated trondhjemite grades to to more more granodioritic granodioritic and and granitic graniticcompositions, compositions, although although not not in inany anyregular regularor orsystematic systematicfashion. fashion.Younger Younger foliated foliated granites, granites, pegmatites pegmatites and and aplites aplites(and (andprobably probablyyounger younger foliated foliated tonalites) tonalites) are are also also present, present, and and these these are intrusion. In are not not always always easy easy to to distinguish distinguish from from the the synvolcanic synvolcanic intrusion. In the the inner inner synform, synform, the the Dead Dead Lake Lake suite suite isis intruded intruded by by foliated foliated multiphase multiphase tonalite, tonalite, granite granite and and pegmatite-aplite, pegmatite-aplite, and and at atleast leastsome someof of the thetonalite tonalite isis similar most tonalites tonalites in proximity similar to tothe thesynvolcanic synvolcanictrondhjemite trondhjemite (Stop (Stop C6). C6). However, However, most proximity to the the Dead Dead Lake resemblingthose thoseofofthe the outer outer margin margin in in textures, textures, and and in magnetite Lake suite, while while resembling magnetite and quartz quartz content, content, have have aa higher higher proportion proportionofofmafic maficminerals, minerals, including including hornblende. hornblende. Some Someof of the the hornblende, hornblende, present present as ascoarse coarse grained cm),randomly randomly to to moderately moderately oriented poikiloblasts, looks secondary. In the grained (0.5—1 (0.5-1 cm), the Dead Dead Lake Lakesuite, suite, leucocratic to to melanocratic melanocratichornblende-magnetite-plagioclase±garnet hornblende-magnetite-plagioclasehgarnetrocks, rocks,with withconspicuous conspicuousquartz quartzeyes eyesor or leucocratic lenticules, resemble altered or contaminated contaminated tonalite tonalite (Stops (StopsC3 C3and andC5). C5).InInsome somecases, cases,blocky blockyinclusions inclusionsof of lenticules, hornblende-magnetite-plagioclasehgarnetrock rockinintonalite tonalitehave havenarrow narrow(1—10 (1-10 cm) cm) transitional transitionalcontact contactzones, zones, hornblende-magnetite-plagioclase±garnet apparently apparently due dueto toreaction reactionorormixing mixingofofthe thetwo tworock rocktypes. types. In In general, general, although although the themore morepotassic potassic and andhornblende-bearing hornblende-bearing intrusive intrusive rocks toward the central central ManManitouwadge synform, west of of the the Loken Loken Lake Lake pluton, are are texturally texturally and and modally modally similar similar to to itouwadge synform, and and north north and west synvolcanic trondhjemite, it is not clear synvolcanic trondhjemite, clear in in outcrop outcrop whether whether they they are are comagmatic, comagmatic, or or belong belong to to different different and possibly younger intrusions. However, However, geochemical geochemical analyses least some some are are comagmatic comagmatic(see (see possibly analysessuggest suggestthat that at least Geochemistry). Foliated Foliated trondhjemite trondhjemite has hasnot notbeen beenobserved observedininthe theouter outervolcanic volcanicbelt; belt;however, however,amongst amongst Geochemistry). undivided foliated foliated intrusive intrusive rocks rocks (Unit (Unit14), 14),aalayer layerofofstrongly stronglymagnetic magneticfelsic felsic rocks, rocks, lying lying within within the the mafic mafic undivided sequence sequence striking through through Gaug GaugLake, Lake, has hassome sometextural texturaland andgeochemical geochemical(see (seeGeochemistry) Geochemistry) similarities similarities to to hornblende-magnetite-plagioclasehgarnet~clinopyroxene rocks and magnetite magnetite quartzite quartziteofofthe the the quartz-eye quartz-eyehornblende-magnetite-plagioclase±garnet±clinopyroxene the rocks Dead Dead Lake Lake suite. suite. Synpost-tectonic intrusions intrusions Syn- to post-tectonic 13)could could be be grouped grouped with the the Black Black Pic Pic batholith; batholith;howhowFoliated K-feldspar K-feldspar porphyritic granitoid granitoid (Unit (Unit 13) Foliated ever, two two mappable mappable bodies bodies can be be distinguished distinguished from the multiphase plutonic 3). These Theselie lienear near ever, plutonic suit (Fig. 3). the margins marginsof of the thegreenstone greenstonebelt belt(including (includingsubvolcanic subvolcanicintrusions), intrusions), and andhave havebeen beeninvolved involvedininD3 Dafolds. folds. the The northwestern northwestern contact contactbetween between supracrustal supracrustal rocks rocks and and foliated foliated tonalites tonalites of of the the Black Black Pic Pic batholith, batholith,inside inside The the Blackman Blackman Lake Lake antiform, antiform, isismantled mantledby byaalong longsinuous sinuousbody bodyofoffoliated foliatedhornblende-biotite hornblende-biotite (up (uptoto35%) 35%) the granitoid, granitoid, here here called called the the Nama Nama Creek Creek pluton pluton (Unit (Unit13a). 13a). Microcline Microcline phenocrysts, cm in in phenocrysts, typically typically 11 to 2 cm length, vary vary in in abundance abundance from sparse to about about 25%. 25%. The The matrix matrixvaries varies from from tonalitic to granitic granitic in in modal modal length, 10-20%, titanite composition, in some some cases, cases, containing containing little little K-feldspar. K-feldspar. Quartz Quartzcontent contentvaries variesfrom fromabout about10—20%, composition, is commonly commonly present (I%), and apatite, apatite, zircon, zircon, opaque minerals and allanite are are trace traceconconis present in minor amounts (1%), stituents.AAmoderate moderatetotostrong strongtectonic tectonicfabric, fabric,defined definedbybymafic maficminerals mineralsand andaugen-shaped augen-shapedphenocrysts, phenocrysts, isis stituents. D3 Blackman Blackman Lake Lake antiform antiform and and outcrop-scale outcrop-scale Z-folds Z-folds (D3). The folded fabric, and the the presence presence folded by by the the D3 folded of folded folded pegmatite-aplite pegmatite-aplite dykes, dykes, suggest suggest that that the theintrusion intrusionisisprepre-totosyn-D2. syn-Dg. of Anothermicrocline microclinephenocrystic phenocrysticgranitoid granitoidintrudes intrudesthe theinnermost innermostcore coreof of the theManitouwadge Manitouwadgesynform synform (Fig. (Fig. Another 3) the Wowun-Luckyshoe 3) and andisishere herecalled calledthe theLoken LokenLake Lakepluton pluton(encompassing (encompassing the Wowun-LuckyshoeLakes Lakes mass mass of of Williams Williams 15 �Manitouwadge greenstone belt of units Description of et al., 1992). 1992). With With the the exception exception of of the the western western part part of of this this body, body, exposure exposure is poor, poor, and and the thecontacts contacts were were tocoincide coincide with with an anelliptical ellipticalarea areaof oflow low flat flat aeromagnetic aeromagnetic expression. expression. The Thebody bodyisischaracterized characterized interpreted to to 15 15cm cm long, long, varying varying in in abundance abundance from from sparse to 25%. 25%. Large Large areas areas by microcline megacrysts, typically 5 to of the intrusion intrusion consist consist of of non-porphyritic non-porphyritic rock rock resembling resembling the matrix matrix of of porphyritic porphyritic varieties; varieties; however, however, Kfeldspar phenocrysts phenocrysts or augen have been been observed observed close closeto to contacts contacts to to the west west and northeast of of Dead Dead Lake, Lake, Thompson Lake. Lake. In comparison and south of Thompson comparison to the Nama Nama Creek Creek pluton, the the Loken Loken Lake Lake pluton has larger larger 5% biotite. Quartz Quartz isisabundant abundant(25—40%) (25-40%) and phenocrysts and is more leucocratic, containing about 5% and apatite, apatite, titanite, opaque opaque minerals, minerals, zircon zircon and, and, in in some some cases, hornblende titanite, hornblende are are typically typicallypresent present in intrace trace amounts. amounts. Where present, the therock rock looks looksdisconcertingly disconcertingly similar to to synvolcanic synvolcanic trondhjemite of K-feldspar phenocrysts phenocrysts are not present, 12, but but geochronology geochronology confirms a post-volcanic age of Unit 12, of 2687+2/-3 2687+2/—3 Ma Ma (see (see Geochronology). Geochronology). A A strong tectonic tectonic fabric, fabric, commonly commonlyL>S, L>S, isis delineated delineatedby by quartz, quartz, feldspars, feldspars,biotite, biotite, and and microcline microclineaugen augen(Stop (StopCl). Cl). Variations in fabric orientation suggest folding by by the the D3 D3 Manitouwadge Manitouwadgesynform synformimplying implyingthat, that, like likethe the Nama Nama Creek intrusion is is prepre- to to syn-D2. syn-Da. Creek pluton, the intrusion Undivided rocks of of the the Black Black Pic Pic Undivided foliated foliated intrusive rocks rocks (Unit 14) include foliated multiphase plutonic rocks batholith, as well well as foliated foliated tonalitic tonalitic intrusions intrusions within supracrustal suite of of the the Manitouwadge Manitouwadge belt. within the supracrustal Near the southern margin belt, at least Near margin of of the the Manitouwadge Manitouwadge belt, least 33intrusive intrusive phases phases can can be berecognised recognised in in the the Black rocks, diorite diorite and and Black Pic batholith. The Thecontact contactisisaatransitional transitionalzone zoneofofinterleaved interleaved mafic mafic metavolcanic metavolcanic rocks, younger tonalite, tonalite, all involved younger involved in tight tight intrafolial intrafolial folds. folds. The oldest oldest intrusive intrusive phase phase (2687+3/—2 (2687+3/-2 Ma, Ma, see see Geochronology), medium medium to to coarse grained, grained, foliated foliated hornblende-biotite hornblende-biotite diorite diorite to to monzodiorite with plagioclase augen, dominates dominatessome someoutcrops outcropsand andforms formsblocky blockyinclusions inclusionsininyounger youngerphases. phases.Quartz Quartzis is present from 5-20%, present from 5—20%, from <2-15%, <2—15%,and andhornblende hornblendeplus plusbiotite biotite comprise comprise 15-35%. 15—35%.The Therock rockcontains containsminor minorto to trace trace microcline from of titanite titanite and opaque amounts of opaque minerals, and trace amounts of apatite, allanite/epidote allanite/epidote and andzircon. zircon. AAstrong strong schistosity is defined by mafic minerals and plagioclase plagioclase augen. Younger Younger foliated foliated monzodiorite monzodiorite (2677±2 (2677zk2Ma) Ma) is predominant of the area north of predominant in much of of the the Banana Banana Lake Lake antiform antiform (distribution (distribution based based on on petrographic petrographic observations Ontario Geological Survey), that is is the the area area between between observations on thin thin sections sections made made available available by F. Breaks, Ontario the easterly easterly extensions extensions of the inner and and outer outer volcanic volcanic belts. Inclusions of the the oldest oldest diorite are engulfed by foliated foliated biotite biotite tonalite to granite, Inclusions of engulfed by granite, possibly possibly representing representing more than one one intrusive intrusive phase. The The youngest youngest phase phase on on the the southern southern margin margin of of the the Manitouwadge Manitouwadge belt cuts cuts across diorite, tonalite and granite, foliated granite, granite, aplite and pegmatite granite, as asdykes dykes of of weakly weakly foliated pegmatite and, and,locally locally as as more bodies. These rockshave haveminor minortototrace trace amounts amounts of of biotite, biotite, and and trace more discrete discrete bodies. These youngest youngest leucocratic leucocratic rocks amounts of opaque minerals and apatite. apatite. Diffuse Diffuse transitions between between granite granite and and pegmatitic pegmatitic enclaves enclaves can can be be observed locally. locally. Tonalitic rocks of of the the Black Pic batholith extend extend west west of of the the Manitouwadge Manitouwadge belt, belt, inside inside the the hinge hinge region region of the Blackman Blackman Lake Lake synform synform (D3). Near the the Blackman Blackman Lake Lake of Lake antiform antiform (D3) (D3) and and north north of of the Jim Lake (D3). Near antiform, weakly foliated to to massive, medium to to coarse grained grained tonalite tonalite is commonly present present on the short weakly foliated massive, medium short of minor folds and outcrop-scale shear zones. zones. Diffuse contacts to the limbs of Diffuse contacts the foliated foliated host host rocks rocks are aresuggestive suggestive of localized localized coarsening coarseningand and recrystallization, recrystallization,or or of of anatectic anatectic mobilizates mobilizatesthat that migrated into dilational of dilational zones. zones. Evidence of of migmatization migmatization increases increases northward northward toward toward the the Quetico boundary. boundary. Northwest of the Manitouwadge belt, septa septa of of mafic mafic to to intermediate intermediatesupracrustal supracrustalrocks, rocks,likely likely derived derived from from the the main mainsupracrustal supracrustalsequence, sequence, correspond to pronounced aeromagnetic quartz-magnetite aeromagnetic striping striping parallel parallel to to foliation trends. trends. AAfew few screens screens of quartz-magnetite iron formation are present; also are commonly commonlystrongly stronglymagnetic. magnetic. The The striping and the also mafic inclusions are the linear linear straighter and trending more nearly map pattern are are transitional transitional across across the theQuetico Quetico boundary, boundary, becoming becoming straighter east-west toward toward the north. east-west fine to to medium medium grained, granodiorite and tonalite Irregular bodies and and dykes dykes of of homogeneous, homogeneous, foliated, fine tonalite intrude the the main main supracrustal supracrustalbelt. belt.Tonalites Tonalitesare aremost mostcommon, common,typically typicallycontaining containingplagioclase plagioclasephenocrysts, phenocrysts, and accessory biotite and/or and/or hornblende. hornblende. The Thehinge hingeof ofthe theManitouwadge Manitouwadgesynform synform in the the vicinity vicinity of of Cadawaja Cadawaja Lake is dominated by granodiorite-tonalite granodiorite-tonalitecontaining containing inclusions inclusions of biotite schist (Unit (Unit 10) 10)and andfelsic felsic to to interintermetavolcanic rocks rocks(Unit (Unit 6). 6). In In general, general, the the contacts contacts of of this this body body are are gradational gradational and their position mediate metavolcanic is poorly near the contact poorly constrained. constrained. Tonalite Tonalite is is pervasive pervasive near contact between between iron formation and metasedimentary metasedimentary rocks in in the inner volcanic belt, and in mafic rocks of ofthe the outer outer belt belt near near their contact to metasedimentary rocks volcanic belt, mafic rocks metasedimentary rocks. Concordant to m)intrude intrude all all supracrustal supracrustal rock rock units, in rocks. to slightly slightly discordant discordant tonalite tonalitedykes dykes(<10 (<I0cm—i cm-1.5.5m) some cases, cases, cutting across straight straight gneiss tonalite foliations gneiss (annealed mylonite) or early folds. In most cases, tonalite are parallel parallel to the dominant dominant fabric fabric of of the host host rocks rocks and and at at least leastsome some tonalite tonalite dykes dykes can can be be interpreted interpreted as as syn-D2 syn-Dz (Stop A23). A23). Pegmatite, sheets and and Pegmatite, aplite and and foliated foliated granite (Unit (Unit 15) 15) are are present present as as foliated foliated and and massive massive dykes, sheets which can can be be shown shown at at the scale of of mapping. mapping. The irregular subconcordant bodies, bodies, aa few few of which The largest is is aa foliated foliated granite intruding north of of the Geco intruding supracrustal supracrustal rocks rocks and and synvolcanic synvolcanic trondhjemite immediately immediately north Geco mine. In In general, the unit comprises of quartz, K-feldspar general, comprises undivided undivided leucocratic leucocratic intrusions intrusions of of various various ages, composed composed of K-feldspar with accessory accessory muscovite muscoviteororbiotite. biotite. Garnet is and plagioclase, plagioclase, with is present present locally locally in pegmatite, pegmatite, mainly mainly near near 16 �Description of of units units Description Manitouwadge Manitouwadge greenstone greenstone belt belt contacts contacts to to iron iron formation. formation. North Northand andwest westofofthe theNama NamaCreek Creekdeposit, deposit,pegmatites pegmatiteshave havesheared sheared contacts contacts and surfaces for example example as as described describedin in the the transition transition to straight surfaces coated by aligned sillimanite, for straight gneiss gneiss north of of the the Willecho Willecho 3 pit pit (Stop (Stop A26). A26). InInmany manycases, cases,pegmatites pegmatitesshow show tectonic tectonic fabrics fabrics only only near near contacts contacts or or in Locally, discordant discordant pegmatite pegmatite dykes dykes and and dyke dyke swarms swarms show show little little evidence evidence of in fine fine grained grained aplitic aplitic zones. zones. Locally, deformation, gashesat at aa high high angle to contacts. deformation, excepting exceptingquartz—filled quartz-filled gashes contacts. Alkalic 16) including including hornblende hornblende syenite, syenite, hornblendite and and lamprophyre, lamprophyre, both bothmassive massiveand and Alkalic rocks (Unit (Unit 16) foliated, sporadically throughout throughout the the map area. These foliated, were were encountered encountered sporadically Thesegenerally generally form form dykes dykes or irregular irregular bodies, bodies, too too small small to to show show at atthe thescale scaleofofmapping, mapping,and andininsome somecases, cases,with withcomplex complex contacts contacts or or internal internal relationships massivehornblendite hornblenditebody bodyof ofabout about250 250metres metresinindiameter, diameter, relationships that thatwere were not notmapped mappedinindetail. detail.AAmassive lying lying northeast northeast of ofCadawaja CadawajaLake, Lake,isisthe theonly onlyone oneshown shownon on our our 1:25000 1:25000 map, map, but but other otherexposures exposuresof of the theunit unit were were observed observed southwest of of Swill Swill Lake, northwest of Willecho, near the the town town of of Manitouwadge, Manitouwadge, and and1.5 1.5km km south south of of Manitouwadge ManitouwadgeLake Lake just west west of of the the extension extension of of the the Fox Fox Creek fault. fault. The Theunit unitgenerally generallycorresponds corresponds to to the the'Appinite 'Appinitesuite' suite'ofofWilliams Williamsetetal. al.(1992) (1992)and andthe theFox FoxCreek Creeklocality localitywas was described described by by them. them. On On outcrop, outcrop,syenite-hornblendites syenite-hornblenditesare areusually usuallyheterogeneous, heterogeneous,pink pinkand andgreen greenvarying varyingfrom fromleucocratic leucocratictoto melanocratic, hornblende. Tectonic fabrics, where recognizable, are typically weaker than melanocratic, with withup uptoto80—90% 80-90% hornblende. than in D3 in adjacent adjacent host hostrocks. rocks.An Anexception exceptionisisaafine finegrained grainedsyenite syenitewith withaastrong strongfoliation foliationfolded foldedby byasymmetric asymmetricD3 folds, folds, exposed near the the Geco Geco gatehouse gatehouse (Stop (Stop Bi). Bl).The Therocks rocksare arecharacterized characterizedbybyhornblende hornblendephenocrysts, phenocrysts, up up to to15 15mm mmininlength, length,riddled riddledwith withinclusions inclusionsof oforiented orientedbiotite biotiteblades. blades.The Theorientation orientationofofinclusions inclusionsvaries varies between apparently being being related related to hornblende crystallographicstructure structure rather rather than to between phenocrysts, phenocrysts, apparently hornblende crystallographic to any any penetrative penetrative fabric. fabric. Minor Minorclinopyroxene clinopyroxene is is also also commonly commonly present, as skeletal or corroded corroded phenocrysts phenocrysts or or as as ragged hornblende. Titanite and apatite ragged relicts coring hornblende. apatiteare areeither either abundant abundantor orpresent presentinintrace traceamounts amountsalong along with with allanite, allanite, opaque opaque minerals, minerals, epidote and quartz. quartz. InInmany manycases, cases,the therocks rockslook looklike like hybrid hybrid mixtures mixtures of of leucocratic leucocratic and and melanocratic melanocratic material. material. Northwest of about 50 metre width Northwest of of Willecho, Willecho, a syenite-hornblendite syenite-hornblendite dyke of width was was traced traced for for 500 500 metres. metres. The Thedyke dykeconsists consistsof of dark, dark,medium mediumto tocoarse coarsegrained, grained,hornblende hornblendeporphyry, porphyry,with withhornblende hornblendephenocrysts phenocrystsininaa matrix matrixof of plagioclase plagioclase and/or and/or microcline microcline(up (up to to35%). 35%).Diffuse, Diffuse, medium medium grained grained to to pegmatitic, pegmatitic, feldspathic feldspathic net net veins veins cut cut the the porphyry. porphyry. The Theveins veinsare areflattened flattened and andhave haveaatectonic tectonic lineation. lineation. Inthe thetown townof of Manitouwadge, Manitouwadge, aafoliated lamprophyre dyke dyke (about (about 11m wide) cuts across diorite and aplitic aplitic In foliated lamprophyre dykes dykes of of the the Black Black Pic Pic batholith. batholith.The Thelamprophyre lamprophyredyke dykeconsists consistsofofbiotite biotiteand andclinopyroxene clinopyroxenephenocrysts phenocrysts (up (up to to55mm mmininsize) size) in in aaquartz+plagioclase quartz+plagioclase matrix matrixwith with minor minor horublende hornblende and apatite apatite (about (about 2%). 2%). The The Fox Fox Creek Creek occurrence occurrence (1.5 (1.5km kmsouth southofofManitouwadge ManitouwadgeLake) Lake)ofofsyertite-hornblendite syenite-hornblendite is is notable, notable, although althoughititwas wasnot notmapped mappedininany anydetail. detail.ItItintrudes intrudesBlack BlackPic Pictonalites tonalitesofoflow lowaeromagnetic aeromagneticresponse responseand andisis itself associated associated with with an anisolated isolatedhigh high aeromagnetic aeromagneticanomaly anomaly (partly (partlymasked maskedby bydiabase diabasedykes). dykes).The Theexposure exposure itself isis relatively relatively extensive (at (at least least 300 300 metres). Internal Internalstructures structuresinclude includeorbicular orbiculargabbro gabbro(Williams (Williamsetetal., al.,1992), 1992), rhythmiclayering layering(cm-scale) (cm-scale) defined defined by mafic and felsic mineral truncations of of layering layering that that rhythmic mineral abundance, and truncations resemblecross-bedding cross-bedding(Stop (StopF5). F5).Locally, Locally,the therock rockisisananintrusion intrusionbreccia brecciacomprising comprisinglithic lithicclasts clasts(1—10 (1-10 cm cm in in resemble size) in in aa hornblende-porphyritic hornblende-porphyritic matrix matrixtypical typicalofofthe theunit unit(Stop (StopF4). F4).The Theclasts clastsare aremostly mostlymafic mafic(hornblende(hornblendesize) biotite-plagioclase-titanitekepidotekopaque minerals), minerals),apparently apparentlywith withcoarse coarsegrained grainedhybridized hybridizedmargins, margins,inin biotite-plagioclase-titanite±epidote±opaque somecases, cases, with with aa fine fine grained grained core. core. Particularly Particularlynotable notableisisthe thepresence presenceofofaasingle single(observed) (observed)massive massivesulphide sulphide some clast, clast,22centimetres centimetres in inlength, length,consisting consistingof of pyrite, pyrite, magnetite, magnetite, ilmenite ilmenite and and chalcopyrite. chalcopyrite. Presumably Presumablythe theclast clast population of of the the breccia breccia represents represents rocks rocks sampled sampled by the the intrusion intrusion during during its itsascent ascentand andemplacement; emplacement; population however, the closest closest known known massive sulphide occurrence is Rock units unitsinin however, is the the Geco Geco mine mine 3.5 3.5 km km to to the north. Rock thisarea areaare aresteeply steeplydipping dippingand, and,according accordingtotoour ourcurrent currentunderstanding understandingofofthe thesubsurface subsurfacestructure, structure,unlikely unlikely this toextend extend below below the the intrusion intrusion breccia. breccia. The Thesubsurface subsurfacedips dips and and extent extent of of the the syenite-hornblende syenite-hornblende body are not to known, known, but but ititseems seemslikely likely that thatthe thebody bodysampled sampledsome someunknown unknownsulphide sulphidemineralization mineralization during duringits itsascent. ascent. Quetico Queticosubprovince subprovince Metasedimentary rocks rocks (Unit (Unit lOq) lOq) of of the theQuetico Queticosubprovince subprovince are aredominated dominatedby bymonotonous monotonousmetametaMetasedimentary greywacke and and biotite biotiteschist, schist,lithologically lithologicallysimilar similarto tometagreywacke metagreywackein in the theManitouwadge Manitouwadgegreenstone greenstone belt belt greywacke (Unit 10), lo),except exceptfor forthe theubiquitous ubiquitouspresence presenceofofmigmatitic migmatiticsegregations. segregations. Quetico Queticomigmatitic migmatiticmetasedimenmetasedimen(Unit taryrocks rocksextend extendacross acrossthe thenorthern northernpart partofofour ourmap, map, defininga broadly a broadlycurved curvedsubprovince subprovinceboundary, boundary, tary defining concave to to the thesouth. south.Similar Similarmetasedimentary metasedimentaryrocks rockscan canbe betraced tracedinindiscontinuous discontinuousoutcrops outcropsfrom fromJim JimLake Lake concave toeast eastofofAppelle AppelleLake, Lake,totoDavis Davisand andLarry LarryLakes, Lakes,folded foldedby bythe theJim JimLake Lakesynform synform(D3) (Da)and and aarelated related to map-scale Z-fold Z-fold in the the Davis Davis Lake Lake area. area. The Theposition positionofofthe thefolded foldedsubprovince subprovinceboundary boundaryisisbased based on onexexmap-scale posuresof of migmatitic migmatiticbiotite biotiteschist schist(Quetico (Queticosubprovince) subprovince)and andfoliated foliatedtonalite tonalitewith withmafic maficinclusions inclusions(Wawa (Wawa posures subprovince), especially especially between between Appelle Appelle Lake Lake and and the therailway railwaywest west of ofJim JimLake. Lake.The Themafic maficinclusions inclusionswere were subprovince), interpreted as asthe thecontinuation continuationofofmetavolcanic metavolcanic rocks rocks (Unit (Unit 5) 5) of of the the Manitouwadge Manitouwadge belt. Immediately Immediatelyeast east interpreted of Jim JimLake, Lake,exposures exposuresof of foliated foliated granitoid granitoidwith withinclusions inclusionsof of biotite biotiteschist schistwere weregrouped grouped with withQuetico Queticorocks. rocks. of Queticometagreywackes metagreywackesare arecompositionally compositionallylayered layered(typically (typically2—50 2-50 cm), locally with politic to psammitic psammitic Quetico pelitic to grading defined defined by by variations variations in in biotite, biotite, quartz quartzand andfeldspar feldsparproportions proportions(Stop (StopE3). E3).Pelitic Peliticlayers layerscommonly commonly grading 17 �Manitouwadge Manitouwadge greenstone greenstone belt belt Structural Structuralgeology geology contain contain garnet garnet and, and,less lesscommonly, commonly,sillimanite. sillimanite. In Insome somecases, cases, hornblende hornblende isis associated associated with with biotite biotiteininmafic mafic layers, layers, especially especially near near contacts contacts tototonalitic tonaliticrocks rockswith withmafic maficinclusions. inclusions.Ubiquitous Ubiquitousmigmatitic migmatiticsegregations, segregations, mainly mainly pegmatitic pegmatiticand andtonalitic tonaliticleucosome, leucosome,locally locally with with garnet garnet and andcordierite, cordierite,are arepreferentially preferentiallyconcentrated concentrated in (1—2 inpelitic peliticlayers. layers.North NorthofofDavis DavisLake, Lake,garnetiferous garnetiferousmetagreywacke metagreywackeisislocally locallyinterlayered interlayeredwith withthin thin (1-2 cm), cm), contorted contorted and andsegmented, segmented,quartz-rich quartz-richrusty rustyiron ironformation, formation,and andassociated associatedmigmatitic migmatiticsegregations segregationscontain contain coarse cm)grunerite gruneriteporphyroblasts porphyroblasts (Stop (StopE5). E5).AAsingle singlesample, sample,collected collectednorth northofofAppelle AppelleLake Lakeand and coarse (to (to11cm) about about200 200metres metresbeyond beyondthe thenorthern northernedge edgeofofour our1:25000 1:25000 map, map, contained contained orthopyroxene-biotite-garnet, orthopyroxene-biotite-garnet, while while another anothersample sampleabout about140 140metres metrestotothe thesouth southcontained containedbiotite-garnet-sillimanite-spinel. biotite-garnet-sillimanite-spinel.These Theseassemblages assemblages suggest suggest aa metamorphic metamorphic transition transition to togranulite granulitefacies facies just north north of of the the map maparea. area. The Thewestern western exposures exposures of of Quetico Quetico metasedimentary metasedimentary rocks, rocks, approximately approximately as as far far east east as asAppelle AppelleLake, Lake, are are interlayered interlayered with with medium medium to tocoarse coarsegrained grainedgabbroic gabbroic and anddioritic dioriticrocks. rocks.Foliated Foliatedgabbro-diorite gabbro-dioriteisisfound foundon on both both sides sidesof of the thesubprovince subprovinceboundary, boundary, but butisislocally locallydifficult difficulttotodistinguish distinguishunambiguously unambiguouslyfrom fromtonalitic tonalitic and mafic mafic (recrystallized (recrystallized metavolcanic) metavolcanic) rocks Wawa subprovince The and rocks typical typical of of the the northern northern Wawa subprovince in in the the area. The gabbro-diorite EverestLake Lake pluton, pluton, aalenticular lenticular gabbro-diorite (not aa separate separate unit unit on onour ourmap) map)isispartly partlyequivalent equivalent to to the theEverest intrusion km in width) lying intrusion (about (about1—1.5 1-1.5 km lying along along the the Wawa-Quetico Wawa-Quetico subprovince boundary grouped with the the Black Pic Pic batholith batholith (Williams (Williams and and Breaks, Breaks, 1990a; 1990a; Williams Williams et al., al., 1992). 1992). Our Ourobservations observations suggest suggest that that Black the the intrusion intrusioncomprises comprisessheets, sheets, varying varying considerably considerably in thickness, thickness, that that transgress transgress the thesubprovince subprovinceboundary. boundary. Interlayering (10 m m plus) to thin Interlayering with with Quetico Quetico metasedimentary metasedimentary rocks rocks apparently apparently varies varies from outcrop-scale outcrop-scale (10 thin (20 (20 cm) cm) concordant concordant sheets sheets (Stop (Stop G2). G2). Aeromagnetic Aeromagnetic striping in the the area, area, parallel parallel to toand andtransgressing transgressing the the Thegabbro-diorite gabbro-diorite isis subprovince subprovince boundary, boundary, isis inferred inferred totoreflect reflectthe thepresence presenceofofgabbro-diorite gabbro-dioritesheets. sheets. The foliated, foliated,but butsome somelow lowstrain strainenclaves enclavesare arenearly nearlymassive, massive,for forexample exampleininboudinaged boudinagedremnants remnantsofofextended extended layers layers(Stop (StopG2). G2).Locally, Locally,blocky blocky gabbroic gabbroicinclusions inclusions in aa matrix matrixof of contorted contorted migmatite migmatitemay mayhave haveoriginated originated as aspre-metamorphic pre-metamorphicdykes. dykes. Proterozoic Proterozoicintrusions intrusions Diabase Diabasedykes dykes (Unit (Unit17) 17)likely likely include include representatives representatives of of at at least least three threeProterozoic Proterozoicswarms; swarms;Matachewan, Matachewan, Biscotasing Biscotasing and and Marathon Marathon dykes dykes (K. (K. Buchan, Buchan, pers. pers. comm., comm.,1992). 1992).They Theyproduce producepronounced pronouncedaeromagnetic aeromagnetic lineaments. lineaments.The Themost mostvoluminuous voluminuousdykes dykesin inthe theManitouwadge Manitouwadgearea areaare arenorthwest-trending northwest-trending dykes dykesinferred inferredto to belongto tothe theMatachewan Matachewanswarm, swarm,dated datedatat2454±2 2454zt2Ma Ma(Heaman, (Heaman,1988). 1988).AAsecond secondset setof of northeasterly northeasterly trend, trend, belong probably probablybelonging belongingto tothe the2166.7±1.4 2166.7zt1.4Ma MaBiscotasing Biscotasingswarm swarm(Buchan (Buchanetetal., al.,1993), 1993),isismainly mainlyrepresented representedby by aawide widedyke dyke (up (upto to80 80m) m)striking strikingthrough throughSwill SwillLake. Lake. Northerly Northerly trending trending dykes dykes are are inferred inferred to to belong belong to to the the 2170 2170 Ma Ma Marathon Marathonswarm swarm(Fahrig (Fahrigand andWest, West,1986). 1986). STRUCTURAL STRUCTURALGEOLOGY GEOLOGY Ourpreferred preferred model model accounts accounts for for structural structuralobservations observations in in the theManitouwadge Manitouwadge belt belt inin aa4-stage 4stagehishisOur toryof ofductile ductile deformation. deformation. The Themap mappattern patternofofthe thebelt beltis is largelycontrolled controlledbybynortheasterly northeasterlyplunging plungingD3 D3 tory largely folds,including including the theManitouwadge Manitouwadge synform. synform. D1 Dl and and D2 D2folding folding and and faulting faulting produced produced much much of of the the internal internal folds, complexity of of the thebelt, belt,particularly particularlyapparent apparentininthethe hinge regionofofthe the Manitouwadgesynform. synform.HeterogeHeterogecomplexity hinge region Manitouwadge neously distributed distributedD4 D4deformation deformationlocally locallymodified modified the the map mappattern patternand andcaused causedsporadic sporadicdevelopment developmentofof neously outcrop-scale outcrop-scalestructures. structures. D1 deformation D 1 deformation D1 Dl encompasses encompasses all all structural structural features features that that pre-date D2 Dadeformation deformation and and ititmay mayrepresent representmore morethan than onephase phaseof ofdeformation. deformation. Most MostD1 Dlstructures structuresare areinterpreted interpretedfrom frommap-scale map-scaleobservations observationsand andare arecryptic cryptic one atatoutcrop-scale, outcrop-scale, due duetotooverprinting overprintingby bysubsequent subsequentmetamorphism metamorphismand andcomplex complexdeformation. deformation. The Themost most Dl map-scale map-scale structures structures isisin in the thearea areaof of known known mineralization mineralization (Fig. (Fig.4). 4).InInthe theWillroyWillroycompellingevidence evidencefor for D1 compelling Gecoand andWillecho Willecho areas, areas, aaprominent prominent discontinuity discontinuityisisassociated associated with with truncation truncationofofiron ironformation formationand andother other Geco units,and andwith withrepetition repetitionofofthethe lithological sequence;quartz-phyric quartz-phyricfelsic felsicrocks, rocks,iron ironformation formationand andmassive massive units, lithological sequence; sulphidemineralization, mineralization,sillimanite-muscovite-quartz sillimanite-muscovite-quartzschist. schist.The Thediscontinuity discontinuityisismarked markedby byseveral severalmappable mappable sulphide zones of of laminated laminated straight straightgneiss gneiss(Unit (Unit11), l l ) ,interpreted interpretedasasannealed annealedmylonite. mylonite.An Anadditional additionaldiscontinuity discontinuity zones expressed as asaa'finger' 'finger' dominated dominatedby bysilicate silicateiron iron formation formation that thatextends extendsfrom fromthe thethick thicksouthernmost southernmostiron iron isisexpressed formationnortherly northerlytoward towardGarnet GarnetLake Lake(accompanying (accompanying1:25000 1:25000map). map). formation Thestraight straightgneiss gneissisistypically typicallya ahard hardlaminated laminatedfelsic felsicrock, rock,characterized characterizedininthin thinsection sectionbybymillimetremillimetreThe scale scalequartz quartzand andfeldspar feldsparlamellae, lamellae,mostly mostlyannealed annealedtoto aagranular granulartexture. texture. Despite Despite annealing, annealing, the thegrain grain size asquartz quartzribbons. ribbons. North Northofof sizeremains remainsvery veryfine fineand, and,ininsome somecases, cases,vestiges vestigesofofmylonite mylonitefabric fabricsurvive surviveas the theWillecho Willecho 33pit pit(Fig. (Fig.4), 4),pegmatite pegmatiteisistransitional transitionaltotostraight straightgneiss, gneiss,asasalready alreadydescribed described(see (seeTectonic Tectonic rock rock units). units). InInthe theWillecho Willechoarea areainingeneral, general,straight straightgneiss gneissoccurs occurs adjacent adjacent to totruncated truncatedand andboudinaged boudinaged iron gneiss Willroy-Geco ironformation. formation.Straight Straight gneissininthethe Willroy-Gecoarea areaextends extendseasterly easterlyand andisisexposed exposednear nearthe thesouthern southern endofofWowun Wowun Lake, Lake, in in contact contactwith withhighly highlystrained, strained,straight-laminated straight-laminated iron iron formation formation (Stop (Stop Dl). Dl).These These end observations observationsled ledus ustotointerpret interpretstraight straightgneiss gneissasasannealed annealedmylonite mylonitelying lyingon ondiscontinuities discontinuitiesrelated relatedtotoearly early ductile ductilefaults. faults. 18 �______ Structural Structuralgeology geology Manitouwadge Manitouwadge greenstone belt belt Metaaediment.ry rock. — Iron Straight joel.. . granite to tonalite Orthoamphlbole—cordlerlte— : Quartz—phyric feteic Slflhnanlte—mu.covite—quartz EI garnet joel.. .1 ( ... ..• f. .. .. N. -' . . Foliated trondhjexnite Inner . . * metavolcanic rocks Mafic, mixed maflc—fel.ic metavolcanic rocks Massive .ulphide deposit Fold azial trace (02. 03) Fault — Interpreted • formaUon Felaic to intermediate met..— volcanic rock., foliated Dl thruat fault Schematic D2 - volcanic sheath fold belt / FIG. 4. Geology Geology of of the the area area from from the the Geco Geco mine mine (G) in in the the east, east, to tothe theWiliroy Willroyorebodies orebodies (1 (1 to to 6), 6), the Nama Nama Creek Creek mine mine (N) (N) and and the theWillecho Willecho orebodies (El (El to toE3) E3)ininthe thewest. west.All Allthe theknown knowneconomic economic Cu-Zn deposits lie in the the inner inner volcanic volcanic belt. The Theinset insetshows showsaaschematic schematicview view of of the theD2 D2sheath sheath fold fold interpreted interpreted to torepeat repeatthe theD1 Dlfault faultand andmineralized mineralizedsequence sequencebetween between the theNama NamaCreek Creek (N) (N)and andWillecho Willecho deposits deposits (El, (El,E2, E2,E3). E3). Straight gneiss gneiss mostly mostly lacks lacks any any well well defined defined lineation, lineation, and and where where aa lineation lineation isisobvious, obvious,for forexample example Straight sillimanite in sheared pegmatite, itit may may have have developed developed in lineated sillimanite in response response to to later later deformation. deformation. Due to the paucity of of lineations lineations and and kinematic kinematicindicators, indicators,and andthe thedifficulty difficulty in in interpreting interpretingoffsets offsets based based on on stratigraphy, stratigraphy, paucity transport direction directionofofearly earlyductile ductilefaults faultsisisnot notknown; known;however, however,the thelow lowangle angleofofthe thediscontinuities discontinuities the transport suggests thrust faults. faults. Straight gneiss gneiss layering layering is mostly parallel parallel to to dominant dominant D2 D2foliation, foliation, except except in in the thehinge hingeregions regions of of some some Straight D2 D2 folds. folds. Relationships Relationships suggesting pre-D2 age gneiss fabrics fabrics and associated associated faults are are best best suggesting aa pre-D2 age for for straight gneiss preserved in the hinge hinge region of the D2 map-scale preserved map-scale fold foldsouthwest southwestofofthe theNama NamaCreek Creekdeposit deposit(Fig. (Fig.4). 4). In In this Dz folds in felsic area, minor D2 felsicrocks rocksare aredefined definedby byan anearlier earlier(Dl) (Di)gneissosity gneissositythat thatwe weinterpret interpret to to be be related related to straightgneiss gneisslayering layering(see (seeStops StopsA22—A23). A22-A23). The fault that thatfollows followsthe thefinger fingerof of iron ironformation formation(see (seeabove) above) straight GarnetLake Lakeisisdeformed deformedby bymap-scale map-scaleD2 Dzfolds. folds. toward Garnet Willechodeposits, deposits,aamap-scale map-scaleisoclinal isoclinalfold fold is is defined defined by quartz-phyric quartz-phyric felsic felsic rocks, iron of the theWillecho Northeast of formation and and sillimanite-knot sillimanite-knot felsic The southern southern limb limb of of the the fold fold is is apparently apparently truncated truncated formation felsic schist schist (Fig. (Fig. 4). 4). The by aa D1 Dl fault, fault,suggesting suggesting that thatthe thefold foldwas wasproduced produced by by progressive progressive D1 Dl deformation. of by deformation. Irregular truncation of units along along D1 Dl fault fault traces traces in in general general could could be the the result result of of prepre- or or early early D1 Dl folding. The map map pattern pattern of of D1 Dl units structures isisalso alsocomplicated complicated by by later laterdeformation, deformation, particularly particularly during duringD2. D2. structures D2 D 2 deformation deformation The dominant dominant planar planar and andlinear linearfabrics, fabrics, and andoutcrop-scale outcrop-scale folds, ubiquitous The ubiquitous in in most most rocks, rocks, are are attributed attributed to D2 D2 deformation. deformation. The Thedominant dominantD2 D2foliation foliationisistypically typically aa pervasive pervasive moderate moderate to tostrong strongschistosity, schistosity,defined defined to by micas, amphiboles, amphiboles, and and deformed deformed quartz quartz and and feldspar. feldspar. Except Exceptininthe thehinge hingeregions regionsof of D2 Dz folds, the foliation by is aa composite composite D2-D1 Dg-Dl fabric, generally parallel lithological contacts. Early elements elements of the the fabric fabric include include is parallel to lithological contacts. Early 19 �Structural Structural geology geology Manitouwadge greenstone belt =:'!;;!*- I AXIAL SURFACE TRACES OF FOLDS FIG. 5. syncline' repeats repeats the 5. Axial Axial traces traces of ofD2 D2synclines, synclines, D3 D3 and D4 D4 folds. folds. The The D2 Dz 'Manitouwadge 'Manitouwadge syncline' belt) about aa central sequence (OVB = = outer volcanic volcanic belt, belt, IVB = = inner volcanic belt) central zone zone of of metametavolcanic sequence on the the southern limb greywackes on limb of the D3 Manitouwadge synform. The The Manitouwadge Manitouwadgemetagreywackes metagreywackes are interpreted to to be be correlative correlative with with Quetico Quetico rocks. rocks. Another Another D2 D2syncline syncline could could account account for the the two two of the the Dead Dead Lake Lake suite suite (DL) (DL) or, or, alternatively, alternatively, the the Dead Dead Lake Lake suite suite could couldbe beequivalent equivalentto toouter-belt outer-belt zones of mafic rocks rocks repeated repeated by the Orthoamphibole-cordieriteD2 syncline syncline centred centred on on the themetagreywackes. metagreywackes. Orthoamphibole-cordieritemafic the D2 garnet gneiss and mafic mafic rocks rocksinin the the One One Otter-Banana Otter-Banana Lakes Lakesarea areato to the the east (0-B) are garnet gneiss and areinterpreted interpreted as repetitions of of the thesupracrustal supracrustalsequence sequenceby byaaD2 D2synclinal synclinal'keel' 'keel'involved involvedininD2-D3 D2-D3fold foldinterference interference patterns. modified bedding, bedding, metamorphic layering, transposed intrusive modified intrusive sheets, sheets, and andshortened shortenedpillows, pillows,volcanogenic volcanogenic fragments, fragments, mafic clots in intrusive rocks and sillimanite knots. D2 D2 fabrics fabrics are are well well developed in most intrusive rocks, including including synvolcanic synvolcanictrondhjemite trondhjemite(Unit (Unit 12), 12),early earlyphases phasesofofthe the Black Black Pic Pic batholith batholith (Unit 14), rocks, 14), the the Lake and and Nama Nama Creek Creek plutons plutons (Unit 13), and undivided intrusive rocks (Unit 14) Loken Lake 14) within the supracrustal supracrustal sequence. sequence. In the Quetico Quetico subprovince to the north, the the dominant dominant planar planar fabric fabric is is correlated correlated with with D2 D2 fabrics in the the Manitouwadge and Jim Lake the Manitouwadge Manitouwadge belt. belt. D2 D2foliations foliations are aredeformed deformed by by D3 Da folds, including the synforms and the Blackman Blackman Lake antiform (Figs. 5 and 6). 6). Metamorphic minerals minerals characteristic characteristic of of upper amphibolite-facies, such as sillimanite, amphiboles Metamorphic amphibolite-facies, such amphiboles and micas, define the the orientation of the east-northeastly plunging plunging D2 D2 mineral lineation. In In some some places, unoriented sprays of of orthoamphibole orthoamphibole and and sillimanite are are present present in in the the same sameoutcrop outcropas aslineated lineatedgrains. grains. The Thejuxtaposition juxtaposition of lineated lineated and randomly oriented may reflect reflect patterns patterns of of strain strain partitioning, or it may oriented grains may may suggest suggest postkinematic recrystallization. Locally, Locally,strong strongelongation elongationof of sillimanite sillimanite knots, knots,feldspar feldsparaugen, augen,orormafic maficenclaves enclaves produced produced L>S tectonites. tectonites. InIngeneral generalacross acrossthe theregion, region,the therelationships relationships between between orientations orientations of of lineations lineations and later later folds folds are are variable. variable. In Inmany manyareas, areas,the theD2 D2lineation lineationisisnearly nearlycoaxial coaxialwith withD3 D3fold foldaxes; axes;however, however, in the inner of the inner volcanic volcanic belt, belt, the the orientation orientationof of the thelineation lineationvaries varies systematically, systematically, from the hinge hinge region of Manitouwadge synform, synform,to to the the southern limb (Figs. 5 and 6). Manitouwadge D2 foliations and east-northeasterly east-northeasterly plunging Dz foliations plunging mineral/stretching lineations lineations are are parallel parallel to toaxial axialsurfaces surfaces and axes folds. In the inner hinge synform, mapmap- and and outcrop-scale axes of local D2 folds. hinge region of the D3 Manitouwadge synform, D2 are defined by iron formation formation and D2 folds are and felsic felsic rocks. Locally, Locally, minor minor folds folds have circular circular eye eye shapes shapes produced produced by curving hinge lines. Southwest Southwest of the the Nama Nama Creek Creek deposit, deposit, aaprominent prominent map-scale map-scalefold fold of of iron iron formation formation inconsistent with with a parasitic relationship synform. In has S-asymmetry S-asymmetry inconsistent relationship to the the D3 D3 Manitouwadge Manitouwadge synform. In the the hinge hinge region of the axial surfaces surfaces of map-scale minor folds of the S-fold, outcrop-scale folds change change asymmetry across the axial of 20 �Manitouwadge Manitouwadge greenstone greenstone belt belt Structuralgeology geology Structural FIG. FIG.6.6. Structural Structural subareas subareas AAtotoKKofofthe theManitouwadge Manitouwadgearea, area,corresponding correspondingtotothe theaccompanying accompanying stereonets (this (thisand andfollowing followingpage). page). Equal Equalarea areanets nets(A—K) (A-K) show the distribution distribution of of the the dominant dominantD2 D2planar planar stereonets (filled linear (cross) (cross) fabric fabricelements. elements. The The structural structural data data was (filled circle) and linear wasparsed parsed into intoapproximately approximately30 30subareas subareas on on the thebasis basisofofsimilar similarorientation. orientation.The Thesubareas subareasononthe themap mapare arecomposites compositesshowing showingthe themajor majorchanges changesinin (S) and and linear linear (L) (L) data data points points isis structural trends trendsrelated related totomap-scale map-scale folding. folding. The The number number of data planar (S) structural shown best fit for planar data. shown for each net, and and the the great greatcircle circle and and pole pole (filled (filled square) is the cylindrical best data. 21 �Manitouwadge greenstone greenstone belt Structural Structuralgeology geology 22 �Structural Structuralgeology geology Manitouwadge greenstone belt ..... • . k :. .... : .. .. • . . .•• Foliated tondhjemlte Tonalite, metagreyweoke, felaic roake, a,llimanlte— muocov,t,e schiat ——————— 1- 1km . Orthoamphibole—garnet— cordierite gnei.a — — Interpreted Interpreted fault fault Quarto—phyrlc blab metavobcan,c rocka e.ni intermediate to maf Ic metavolcanic rocica ---,'- Da fold fold trace trace D2 FIG. 7. 7. Down-plunge Down-plunge projection projection of of the the inner inner hinge hinge region region of of the the Manitouwadge Manitouwadge synform. synform. The The line line of projection projection is the plunge plunge of the synform synform at 065°/25°. 065O/25'. A-A' A-A?isis the theline lineof of intersection intersection between between the projection plane plane and and the the horizontal horizontal at at350 350metres metres elevation. elevation. Topographic Topographic relief (about 140 140 metres) is not shown. trace of of the the projection. projection. G = shown. See See Figure 3 for the surface surface trace = Geco Geco mine, mine? 11 to 66 ==Wiliroy Willroy orebodies, =Nama Nama Creek Creek mine, mine?EE ==Willecho Willecho33 orebody. orebody. orebodiesl NC = the iron iron formation-felsic formation-felsiccontact contact (Stops (StopsA22—A23). A22-A23). The plungingD2 D2mineral mineral lineation lineation the The dominant northeasterly plunging gneissosityl interpreted axes of of minor folds. Felsic Felsic rocks have a folded folded gneissosity, is parallel to axes rocks near near the contact have interpreted to to be be a Dl fabric? Dl foliation D1 fabric, and local micaceous enclaves enclaveshave haveaaschistosity schistositythat that is is oblique obliqueto to the the D1 foliation and parallel parallel to the the theaxial axialplanes planesofoflocal localD2 D2folds. folds.To Tothe thesouth, southlmetagreywackes metagreywackesare areinvolved involved in in map-scale map-scale D2 D2 folds and the the the dominant dominantfoliation foliation isis ascribed ascribed to toaaD2 D2axial-planar axial-planar fabric. fabric. Between the Nama Nama Creek Creek and and Willecho Willecho deposits, deposits, lithological lithological units and and D1 Dl faults faultsdefine define aacomplex complexgegeBetween interpreted as the the result result of of folding folding by aa map-scale map-scale D2 sheath ometry interpreted sheath fold fold (Fig. (Fig. 4). 4). The Thegeometry geometry of of the the structures in in the theinner innerhinge hingeregion regionofofthe theManitouwadge Manitouwadgesynform synformcan canbe beviewed viewedinina adown-plunge down-plunge pre-D3 structures The mapped mapped D1 Dl faults are interpreted interpreted to be be part part of of aa single single ductile ductile thrust fault, fault?folded folded projection (Fig. 7). The projection map-scale D2 D2 sheath produced a continuous continuous fault northeast and and an an eye eye fold fold to to by aa map-scale sheath fold fold that produced fault trace trace to the northeast southwest. The Thesheath sheathfold foldrepeats repeatsmineralized mineralizediron iron formation formation (Willecho (Willecho deposits) the southwest. deposits) lying lying on on or near the Dl fault. Alternatively, Alternatively? the the map mappattern patternofofthe thearea areacould couldbebeexplained explainedby bymushroom-shaped mushroom-shaped D2/D3 D2/D3 fold fold D1 however? the nearly coaxial coaxial relationship relationship of of D2 D2 and and D3 D3 linear fabric fabric elements elements (see (see below) below) is more interference; however, plunging sheath fold. Also, the intrafolial repetitive consistent with a northeasterly plunging intrafolial character? character, rather than aa repetitive fold fold pattern, pattern?suggests suggests sheaths sheaths rather ratherthan thaninterference. interference. the southern southernlimb limbof of the theManitouwadge Manitouwadgesynform, synform?the the progression progression from from volcanic to sedimentary rocks On the syncline (Suffel (Suffel et al., al., was previously previously interpreted as as aa stratigraphic stratigraphicsuccession succession repeated repeated by by an an early earlysyncline (Fig. 3) was of the theGeco Gecoorebodies orebodiesfrom from north north 1971; Touborg? 1971; Touborg, 1973)? 1973), the the 'Manitouwadge syncline'. syncline'. An increase in Zn/Cu of to south, southland andthe thepresence presenceofoforthoamphibole-cordierite-garnet orthoamphibole-cordierite-garnet gneiss gneiss(metamorphosed (metamorphosed equivalent equivalent of of footwall footwall to synvolcanic alteration) the north, north?support supportsoutherly southerlyyounging youngingfor forthe theWillroy-Geco Willroy-Geco area area(Suffel (Suffel et et al., al.? synvolcanic alteration) to the 1971; Friesen al. 1982). 1982). Our Ourmapping mappingconfirms confirmsrepetition repetitionofofthe thelithological lithologicalsequence; sequence;mafic maficmetavolcanic metavolcanic 1971; Friesen et al., rocks?felsic metavolcanic rocks interlayered metasedimentary rocks rocks (Figs. (Figs. 33 and and 5). 5). The The rocks, interlayered with iron formationl formation, metasedimentary correlation of of volcanic volcanic sequences sequences is belts, the the correlation is strengthened strengthened by the ages of felsic felsic rocks rocksin in both both inner inner and outer belts, orthoamphibole-cordierite-garnet same within within error error atat2720 2720Ma Ma(see (seeGeochronology). Geochronology).The Theextensive extensiveunit unitofoforthoamphibole-cordierite-garnet same rocks in the the inner inner volcanic volcanic belt belt has has aacounterpart counterpartininthe theouter outerbelt beltininsporadic sporadicorthamphibole-bearing orthamphibole-bearingzones zones rocks in mafic mafic rocks rocks near their their northern northern contact. contact. InInour ourinterpretation, interpretation? volcanicand andsedimentary sedimentarysequences sequencesare are in volcanic repeated across across the the southern southern limb limbof of the theD3 D3Manitouwadge Manitouwadge synform by a D2 syncline with in repeated with an axial trace in the central central metagreywacke metagreywacke (Fig. (Fig. 5). 5). the our preferred preferred structural structural interpretation, interpretation?map-scale map-scale D2 D2 folding folding is is responsible responsible for repetitions repetitions of of In our supracrustal rocks along along the axial trace of of the the Manitouwadge Manitouwadge synform The two two zones zones of of supracrustal synform (Figs. (Figs.55 and and 8). 8). The 23 �Structural Structuralgeology geology Manitouwadge Manitouwadge greenstone greenstone belt belt nMafic meiavoicanic rocks Mafic metavolcmic rocks Iron formation El FIG. 8. 8. Block Block diagram diagram showing showing schematic schematic prepreD3 D3 relationships relationships of supracrustal supracrustal rocks, rocks, repeated repeated by D2 D2folds. folds. The The fold fold trace traceininmetagreywacke metagreywacke between between the inner (IVB) (IVB) and and outer outer (OVB) (OVB) volvolcanic belts belts represents represents the the'Manitouwadge 'Manitouwadge synsyndine' cline' (Fig. (Fig. 5). 5). The Thesheath sheathfold folddefined defined by by iron iron formation formation represents represents the Nama Nama Creek Creek to toWilleWillecho area in Figure 4. DL DL = = Dead Dead Lake Lake suite, 0-B 0-B ==One One Otter-Banana Otter-Banana area. area. Metagreywacke the Dead and orthoamphibolebearing orthoamphibole-bearing rocks rockseast eastof ofOne OneOtter Otter and and Banana Dead Lake Lake suite and and exposures exposures of mafic and Lakes Lakes may represent D2 D2 synclinal synclinal 'keels', 'keels', involved involved in in D2/D3 D2/D3 fold fold interference interference patterns. patterns. Alternatively, Alternatively, the the Dead Lake suite might might simply simply be be septa septaof ofmafic mafic volcanic volcanic and and associated associated rocks rocks that thatwere wereincluded includedinindeeper deeper levels of the synvolcanic synvolcanic trondhjemite intrusion. intrusion. levels D3 deformation deformation The regional D3 folds, folds,from fromnorth northto to south; south; the Jim regional map pattern is is dominated dominated by by easterly easterly plunging plunging D3 Lake synform, synform, the Blackman Blackman Lake Lake antiform and the the Manitouwadge Manitouwadge synform. The Banana BananaLake Lakeantiform antiform Lake synform. The could be either a D3 D3 or or aa D4 D4 fold fold or or shear shear zone. zone. There There isis aagradational gradational change change to the the south, south, from from tight tight could fold hinges and dominantly dominantly east-west eat-west structural structural trends, trends, totomap-scale map-scalefolds foldswith withbroader broaderhinge hingeregions regions and and northeasterly northeasterly traces. traces. The Thecrude crudeZ-asymmetry Z-asymmetryof ofmap-scale map-scale D3 D3 folds and the the curvature curvature of of their their axial axialtraces traces suggests formation during during oblique oblique dextral dextral transpression. transpression. The changes from from aa broad broad rounded rounded inner inner hinge hinge to to a tighter The shape shape of of the theManitouwadge Manitouwadge synform changes tighter outer outer hinge Lakes area area (Figs. (Figs. 33 and and B3). In the the inner inner hinge hinge region, region, the the synform synform has has aa shallow shallow to hinge in the the Swill-Mills Swill-Mills Lakes moderate northeasterly northeasterly plunge. plunge. The Theaxial axialsurface surface dips dips to tothe thesouth, south,based basedon onshallow shallowsoutherly southerly dips dipsof ofthe the northern limb, limb, and and near-vertical near-vertical to to moderate moderate southerly southerly dips of the southern southern limb. limb. D2 D2planar planar fabrics fabrics in in the the Willecho-Geco area define a girdle with a moderate to 6, area area A), A), generally generally to shallow shallow easterly plunging plunging axis axis (Fig. (Fig. 6, parallel to the from the hinge region region to to the southern the axis axis of of the the synform. synform. D2 D2lineations lineations vary vary systematically systematically from limb of the synform, small circle circle rotation rotation (Fig. (Fig. 6, areas synform, defining defining aa small areas A and B). B). This This suggests suggests aa component component of fiexural flexural slip during folding, possibly possibly due to mechanical mechanical anisotropy produced by iron formation formation or or altered altered rocks. rocks. In In the the outer outerhinge hingeregion, region,D2 D2foliations foliations in supracrustal rocks and in the Black Black Pic Pic batholith batholith define define aa girdle with aa moderately moderately to the D2 lineations lineations consistently consistently plunge moderately the moderately northeast-plunging northeast-plunging pole, pole, and and D2 northeast. northeast. InInagreement agreementwith withfield fieldobservations, observations,orientations orientationssuggest suggest that thatearly earlyfabrics fabrics are are strongly strongly transposed transposed by D3 folding. Local enclaves of of westerly westerly plunging plunging D2 D2lineations lineationsare are likely likelythe theresult result of of reorientation reorientation by minor to the theManitouwadge Manitouwadgesynform. synform. folds related to D3 map-scale minor folds folds are are identified identifiedacross acrossthe themap map area. area. In map-scale minor In the the outer outerhinge hingeregion region of of the theManiManitouwadge synform, D3 folds are defined defined by contacts contacts between between felsic felsic or intermediate intermediate and andmafic maficmetavolcanic metavolcanic rocks. rocks. In In the theinner innervolcanic volcanicbelt, belt,iron ironformation formation contacts contacts define define D3 D3 folds in the northern northern hinge hinge region region and southern limb of the Manitouwadge synform. In In the the One One Otter-Banana Otter-Banana area along along the the eastern eastern axial trace of of Manitouwadge synform. the the synform, synform, aa thin thinbelt beltofofsupracrustal supracrustalrocks rocksdefines definesseveral severalfolds folds which which also also deform deform the foliation foliation (Fig. (Fig. 5). 5). Underground Underground at at the the Geco Geco mine, mine, the the'Geco 'Gecodrag dragfold' fold'(Brown (Brownetetal., al.,1960; 1960;Friesen Friesen etetal., al.,1982) 1982)may mayalso alsobe be a D3 D3 structure. structure.The TheZ-shaped, Z-shaped,easterly easterlyplunging plungingfold foldpair pairisisdefined definedbybyquartz-muscovite-sillimanite quartz-muscovite-sillimaniteschist, schist, which hosts the main orebody which hosts orebody at at Geco Geco (see (see Setting of Mineralization). Mineralization). (Note (Note that Brown Brown et al. al. mistakenly mistakenly refer to S-asymmetry in their their figures.) S-asymmetry in their their discussion, discussion, but show show Z-asymmetry Z-asymmetry in figures.) The main main orebody orebody has has aa teardrop shape of the 'Geco shape and and lies lies within within the the synformal synformal axial axial region region of 'Geco drag fold' (ibid.). The Thegeometry geometry isis consistent with that synform and and similar similarto to that that of of that expected expected for for aa parasitic parasitic fold fold related to the the Manitouwadge Manitouwadge synform outcrop-scale folds folds (see (see below). below). D3 outcrop-scale Locally outcrop-scale D3 D3folds foldsvary varyin in character character depending depending on on rock rock type and position Locally developed developed outcrop-scale position with with respect to to larger larger structures. structures. InInthe theSwill SwillLake Lakearea areaininthe theouter outerhinge hingeregion regionofofthe theManitouwadge Manitouwadgesynform synform (Fig. B3), B3), two two felsic felsic layers layers in in the themafic maficvolcanic volcanic sequence sequence define define map-scale symmetrical and asymmetrical asymmetrical D3 folds (Stops B11—B21). The moderately moderately open D3 folds deform D2 foliation foliation and, locally, Bll-B21). The locally, layering. Fold Fold asymmetry changes changes from dominantly dominantly Z-asymmetry Z-asymmetry on the the southern southern limb limb of of the thesynform, synform,to toM-asymmetry M-asymmetryinin the the hinge hinge region, region, to to S-asymmetry S-asymmetry on on the the northwestern northwestern limb. limb. In Inthe thevicinity vicinityof ofthe theGeco Gecoand andWillroy Willroydeposits, deposits, both on on surface surfaceand andunderground, underground,micaceous micaceousrocks rockslocally locallypreserve preserveD3 D3folds, folds,typically typically with withshallow shalloweasterly easterly or westerly plunges and gently gently curving curving hinge hinge lines. Sulphide Sulphide mineral mineral are are commonly commonly concentrated in in the thehinge hinge 24 �Structural geology Structural geology Manitouwadge greenstone belt regions of of the the D3 folds folds in in the Geco regions Geco mine. In In aafew fewsurface surface exposures, exposuresl the the D2 D2mineral mineral lineation lineation isis evidently evidently folded at aa low low angle angle to to the thefold foldaxes. axes. In general, general) D3 axial planar planar fabrics fabrics are areweakly weakly developed. developed. Locally, Locally, a crenulation crenulation cleavage cleavage lies in the axial axial regions of of D3 D3 outcrop-scale outcrop-scalefolds, folds,and andan an associated associatedcrinkle crinklelineation lineationisisparallel paralleltotofold foldaxes. axes. On the limbs regions limbs of map-scale D3 folds, folds, schistosity schistosity in in micaceous micaceous layers layersisis locally locallyoblique obliqueatat aa low low angle angle to the dominant dominant D2 D2 foliation. The The absence absence of of aa pervasive pervasive D3 D3 axial axial planar planar fabric fabric may may reflect reflect post-peak post-peak metamorphic metamorphic conditions, conditions, the presence of a strong D2 D2 anisotropy and the the paucity paucityof ofmicaceous micaceous rocks. rocks. The Blackman Blackman Lake Lake antiform antiform is is defined defined by folded folded D2 foliation and mafic to intermediate intermediate rocks, rocks, which which mostly occur as screens in foliated plutonic rocks (Fig. 3). Along Along the the western western trace trace of of Blackman Blackman Lake Lake antiform in the foliated tonalite tonalite change orientation around the Janet JanetLake Lakearea area(accompanying (accompanying1:25000 1:25000 map), D2 fabrics in foliated define aa girdle girdlewith withan aneast-northeasterly east-northeasterly plunging plungingaxis axis(Fig. (Fig.6) 6,area areaF). F). On On the the northerly northerly trending trending the fold and define short limb limb of of the thefold, fold)D2 D2foliations foliationsin inmigmatitic migmatiticrocks rocksare arereoriented reorientedininoutcrop-scale outcrop-scaleshear shearzones zones(1—3 (1-3 m long) and in convolute folds. The shear zones have northerly northerly strikes) strikes, steep steep dips, dips, and and either either sinistral or convolute minor folds. zones have in plan plan view. view. The folds vary vary in in style styleand and orientation) orientation, but but most most have have S-asymmetry S-asymmetry and and moderate moderate dextral offset offset in they deform an an earlier earlier (D2?) (D2?) mineral mineral lineation. lineation. Along the the easterly trending northeasterly plunges, plunges) and locally, they long limb limb of of the Blackman long Blackman Lake Lake antiform, antiform) south of Blackman Blackman Lake Lake (or Kern Lake) Lake) (Fig. (Fig. 3), 3)$moderately moderately east-northeasterly plunging, plunging, Z-shaped Z-shaped folds folds are commonly commonly parallel to aa distinct distinctstretching stretchinglineation. lineation.Locally, Locally, pegmatites of folds. North pegmatites and and granitic graniticveins veins are are concentrated concentrated in in the the short shortlimbs limbsof North of of Blackman Lake, migmatitic segregations and veins increase toward toward the Quetico boundary. Abundant Abundant screens screens of of mafic mafic gneiss, gneiss, and locally, locally, iron formation could could be be an extension of the outer volcanic belt of of the Manitouwadge synform. In In the One extension of volcanic belt Manitouwadge synform. Otter area, area, the theBlackman BlackmanLake Lake antiform antiform is is defined defined by the attentuated attentuatedextension extension of of the theinner innervolcanic volcanic belt belt (Fig. 5). D2 girdle with with an east-southeasterly east-southeasterly plunging plunging pole pole (Fig. (Fig. 6) 6, area G). D2 fabrics define define aa girdle The The most most northerly northerly D3 D3fold, fold,the theJim JimLake Lakesynform, synform)isisdefined defined by by zones zones of of mafic mafic inclusions in tonalite tonalite and and by migmatitic metasedimentary rocks of of the Quetico (Fig. 3). Migmatitic Quetico subprovince subprovince (Fig. Migmatitic biotite biotite schist schist can can be be traced to traced to the the south southasasfar farasasLarry LarryLake Lakeand andisisinvolved involvedin inaaparasitic parasiticZ-fold Z-fold between between Jim Jim and andDavis DavisLakes Lakes (accompanying 1:25000 map). Away from fold fold hinges, hinges, dominant dominant D2 foliations foliations are are mostly mostly east-west east-west trending 1:25000 map). Away from and steeply steeply dipping, dipping, parallel parallel to to the theaxial axialsurfaces surfacesof of tight-isoclinal tight-isoclinal D3 D3 folds. folds, The Thefoliations foliationsdefine define aacrude crude girdle with a near-horizontal near-horizontal easterly easterly plunging plunging axis, axis, subparallel subparallel both both to tolineations lineationsand andD3 D3fold foldaxes. axes. Outcrop-scale structures in in migmatitic migmatitic rocks rocks in the Quetico subprovince and near the subprovince boundubiquitous Z-folds with easterly easterly to to northeasterly northeasterly plunging plunging axes axes that that fold the dominant ary include, include) ubiquitous Z-folds with dominant planar planar fabric (D2?), shear bands, bandsl foliation foliation fish, fish, and and rotated rotated boudinage, boudinage)mostly mostlyshowing showing dextral dextral kinematics kinematics and and ininterpreted to reflect dextral shear. shear. Their that they are terpreted reflect oblique oblique dextral Their relationship relationship to the dominant dominant fabric suggests suggests that are correlative with with D3 D3 deformation deformation in in the Manitouwadge belt. All correlative Manitouwadge belt. All of of the the minor minor structures structures deform deformmigmatitic migmatitic layering, but are are transected transected by by discordant discordant migmatitic migmatiticveins veins which, which, in some cases, casesl are subparallel to the axial axial surfaces of folds. folds. These observations suggest that that peak peak metamorphism metamorphismand andmigmatization migmatizationwere weresynchronous synchronous progressive deformation and the the D3 D3 map-scale map-scale folds near the subprovince subprovince boundary. with progressive D4 deformation deformation D4 deformation has limited limited map-scale map-scale expression, expression, in part part consisting consistingof of gentle gentle deflections deflections of the Blackman Blackman Lake antiform, Jim Lake synform and the Wawa-Quetico subprovinceboundary boundaryininthe the northeastern northeastern map area Wawa-Quetico subprovince (Fig. 5). 5). The Thegeometry geometryofofthe thedeflections deflectionsisisconsistent consistentwith withdextral dextraltranspression transpression focussed focussed on on the theWawaWawaQuetico boundary. Another D4 structure structure is a northeast-trending Quetico boundary. Another possible possible map-scale map-scale D4 northeast-trending shear shear zone zone along along the northwestern margin of supracrustal rocks northwestern rocks folded folded by the the Manitouwadge Manitouwadge synform. The Theshear shearzone zonefollows follows aa pronounced northeasterly northeasterly trending trendinglineament, lineament)defined defined by by truncated truncated aeromagnetic aeromagnetictrends, trends)and andgenerally generallycovered covered by recent deposits deposits in the Nama Nama Creek Creek valley. valley. Mafic Mafic rocks metavolcanic belt dramatically by recent rocks of of the the outer outer metavolcanic belt thin thin dramatically and show increasing increasing transposition transposition with with proximity proximity to to the the shear shear zone) zone, and and may may be be truncated truncated by the zone. High High plunging stretching lineation, lineation) strain is manifested by by spectacular spectacular L>S tectonites with a moderate northeasterly plunging defined by (especially in folded quartz veins), and streaky streaky mafic mafic lenses in intermediate defined by hornblende) hornblende, quartz rods (especially metavolcanic rocks. rocks. Earlier Earlier structures, folds, are are strongly strongly transposed, transposed, so that metavolcanic structuresl including including D3 and possible possible D2 folds) D4lineations. lineations. all linear features are are essentially essentially parallel to to the thelocal localD4 D4 kink folds and crenulation locally, particularly particularly in micaceous rocks associated D4 crenulation cleavage cleavage are developed developed locallyl with mineralization on on the the southern southernlimb limbof ofthe theManitouwadge Manitouwadgesynform. synform.Intersections Intersectionsof ofcrenulation crenulationcleavage cleavage and foliation produce intersection lineation cleavage has produce an intersection lineation with with a moderate easterly plunge. plunge. The cleavage has a variable variable northeasterly strike, strike, and and both bothkinks kinksand andcleavage cleavagetypically typically have have aa Z-asymmetry. Z-asymmetry. In In some someexposures exposures of of quartzmuscovite schist schist (Unit (Unit la), la), D4(?) A6). Crenulations muscovite D4(?) kinking kinking produced dextral asymmetric quartz lenses (Stop A6). are also present in retrograde retrograde biotite-rich biotite-rich zones zones in in orthoamphibole-garnet-cordierite orthoamphibole-garnet-cordierite gneiss gneiss (Unit (Unit 2). 2). the vicinity vicinity of of the the Jim JimLake Lakefold fold and and in in the theQuetico Queticosubprovince, subprovince, tight tight kink kink folds folds of of small small amplitude amplitude In the (<lo common1plunging plunging moderately and west. west. In Insome somecases, cases, small small northeast-striking northeast-striking (<10 cm) are common, moderately to to both east and shears shears of foliation foliation are transitional transitional to to kink kinkfolds. folds. West West of of Jim Lake Lake on on both both sides sidesofofthe theWawa-Quetico Wawa-Quetico an oblique oblique foliation, foliation, usually defined defined by biotite, strikes northwesterly across across the the dominant dominanteast-west east-west boundary, an 25 �Manitouwadge greenstone belt Geochronology Geochronology migmatitic migmatitic layering. layering. The The oblique oblique foliation foliation increases in intensity to to the the west west and and isisnearly nearly ubiquitous ubiquitous between between Appelle and Hourglass Hourglass Lakes. The The foliation foliation transects transects tight-isoclinal tight-isoclinal folds folds in migmatitic migmatitic rocks rocks and and is is deformed deformed by D4 D4 kinks; hence, it post-dates post-dates D3, D3, and and pre-dates predates D4, D4,deformation. deformation. Late Late Faults Faults A number of brittle-ductile to toductile ductilefaults faultsininthe theManitouwadge Manitouwadgearea areawere werepreviously previously identified identified by by Pye Pye (1957) and Milne (1974). The The Agam Agam Lake Lake fault fault (Pye, (Pye,1957) 1957)forms forms aapronounced pronounced strike-parallel strike-parallel topographic topographic lineament mostly in metasedimentary metasedimentaryrocks rocks on on the the southern southern limb limb of the Manitouwadge synform. It It is is primarily primarily a brittle brittle fault, fault,but butlocal localoccurrences occurrencesof of L-tectonites L-tectonites suggest suggest an an earlier earlier ductile ductile history. ItItappears appearstotocorrespond correspond to aa change change in in aeromagnetic aeromagnetic signature, signature, from from high high in the south south to tolow low ininthe thenorth, north,possibly possiblysuggesting suggesting involvement involvement of of subsurface subsurface volcanic volcanicrocks. rocks. High-angle faults associated associated with with brittle structures are High-angle faults are marked marked by by aeromagnetic aeromagnetic and and topographic topographic linealineaments. The TheMose Mose Lake Lake fault fault (Pye, (Pye, 1957) 1957)has has aanorthwesterly northwesterly strike, strike, parallel parallel to tothat thatofofMatachewan Matachewandykes, dykes, the oldest area. More oldest Proterozoic Proterozoic dyke swarm in the Manitouwadge Manitouwadge area. More nearly nearly north-south north-south faults faults include include the the Cadawaja fault (ibid.), (ibid.), interpreted interpreted totoextend extendacross acrossthe theWawa-Quetico WawsQuetico boundary boundary on onthe thebasis basisofofleft-lateral left-lateral displacement aeromagnetic aeromagnetic trends. trends. The Slim Lake Lakefault fault (ibid.) (ibid.) to to the east produced little apparent horizontal displacement. mineralization at at the Geco displacement. The The Fox Fox Creek Creek fault fault displaces displaces massive massive sulphide mineralization Geco mine, mine, apparently apparently with east-side east-side up and and 60 60metres metres of of left-lateral left-lateral movement movement(ibid.; (ibid.; Brown Brown et et aL, al., 1960). 1960). GEOCHRONOLOGY GEOCHRONOLOGY Our ongoing studies are focussed ongoing geochronology geochronology studies focussed on determining ages ages of of volcanism, volcanism, sedimentation, sedimentation, sedsedimentary and plutonism, and on events and and metamorphism in the imentary provenance, provenance, and on bracketing bracketing deformational deformational events metamorphism in Manitouwadge Manitouwadge greenstone belt and and the the adjacent adjacentQuetico Queticosubprovince subprovince(Fig. (Fig.9,9,Table Table2). 2). Black Pic batholith Orthoamphibole—bearing gneiss MaIlc—intermediate metavolcar,Ic rocks KM 5.0 0 Fold axial trace Fault 9. Locations Locationsof of 12 12geochronology geochronology samples. Table FIG. 9. samples. The numbered sample locations match those in Table IVB ==Inner Innervolcanic volcanic belt, belt, OVB OVB ==Outer Outervolcanic volcanic belt. belt. 2. IVB Zircon-Metavolcanic and metasedimentaryrocks rocks Zircon—Metavolcanic and metasedimentary The oldest oldest ages ages thus thusfar faremerging emergingfrom from the theManitouwadge Manitouwadge belt belt are areU-Pb U-Pb zircon zircon ages ages of of circa circa 2720 2720 Ma, Ma, The dating felsic felsic volcanism in the inner inner and and outer outervolcanic volcanic belts. belts. An Anaphyric aphyricfelsic felsic breccia breccia from the the barren barren dating in both the (unmineralized) sequence gave an age of 2722±2 2722k2 Ma 10, Stop Stop B5), B5), within within error of of (unmineralized) sequenceofofthe the outer outer belt belt gave Ma (Fig. 10, 2720h2 Ma muscovite muscovite schist the Geco Geco mine, mine, interpreted interpreted as as an analtered alteredfelsic felsicvolcanic volcanic rock rock (Davis (Davis et al., al., 2720±2 schist at the 26 �Manitouwadge greenstone belt Geochronology Geochronology 1994). Our age of 2720±3 foliated trondhjemite sampled north of 2720&3 Ma, for foliated of the Willroy Willroy and and Geco Geco mines mines (Fig. (Fig. 9, Stop A7), interpretation of subvolcanic intrusion (Fig. (Fig. 11). The A7), confirmed confirmed our field interpretation subvolcanic intrusion The 2720 2720 Ma Ma barren barren and and mineralized felsic rocks rocks stratigraphically stratigraphically overlie overlie mafic mafic metavolcanic metavolcanicrocks rocksinin the the inner inner and mineralized felsic and outer outer volcanic volcanic belts and, andlbarring barring unknown unknown structural structuralcomplications, complicationslmafic maficvolcanism volcanism was was either either contemporaneous contemporaneous (within (within analytical uncertainty), uncertainty), or orsignificantly significantly older. We We are in the process of testing these alternatives with aa sample sample of of felsic volcanic breccia interlayered with the themafic maficsequence sequencebetween between Swill Swill and and Mills MillsLakes Lakes (Stop (StopB13). B13). TABLE 2. Summary Summaryof ofGeochronology Geochronology Rock type type Mineral Mineral Relationships Relationships Age Age VOLCANISM VOLCANISM Felsic breccia, outer outer volcanic volcanic belt belt (1)1 (1)' zircon zircon Geco mica schist, inner volcanic volcanic belt zircon zircon 2722±2 2722&2Ma2 Ma2 2720±2 2720&2Ma3 Ma3 2720±3 2720&3Ma2 ~a~ Foliated trondhjemite, trondhjemite, inner volcanic volcanic zircon zircon belt (2) (2) felsic volcanic protolith protolith synvolcanic synvolcanic SEDIMENTATION SEDIMENTATION Manitouwadge Manitouwadgemetagreywacke metagreywacke (3) (3) zircon zircon 1eq2693 leg2693 Ma4 Ma4 depositional age, pre-D2 postD1 Dl Loken pluton (4) Loken Lake pluton (4) Black Pic diorite (5) Black diorite (5) Nama Nama Creek Creek pluton pluton (6) (6) Black Pic Pic monzodiorite(7) monzodiorite(7) FL PL UTONISM UTONISM 2687+2/—3 Ma prepre-to tosyn-D2 syn-D2 2687+2/-3 Ma 2687+3/—2 Ma preto syn-D syn-D2 2687+3/-2 Ma zircon zircon zircon zircon 2680±3 2680&3Ma4 Ma4 2677±2 2677&2 Ma Ma zircon zircon zircon zircon pre- to tosyn-D2 syn-D2 preprepre- to to syn-D3 syn-D3 METAMORPHISM METAMORPHISM and RETROGRESSION Geco Geco mica mica schist schist Black Pic monzodiorite Pic monzodiorite (7) (7) monazite monazite 2675±1 2675&1Ma3 Ma3 titanite 2674±2 titanite 2674&2 Ma Ma Nama Creek Creek pluton pluton (6) (6) titanite titanite Syn-D2 tonalite tonalite dyke dyke (8) (8) monazite 2671±3 2671&3Ma2 Ma2 monazite monazite monazite 2669±3 2669&3Ma2 Ma2 monazite 2661±1 2 6 6 l h l Ma5 ~a~ monazite PrePre- to to syn-D syn-Dlpegmatite pegmatite(9) (9) Geco Geco biotite biotite schist schist Syn-D3 Syn-D3 tonalite tonalitedyke dyke(10) (10) Syn-D3 Syn-D3 granite granitedyke dyke(11) (11) Loken Lake pluton pluton (4) (4) 2672&3Ma Ma 2672±3 titanite titanite titanite titanite titanite titanite Synkinematic granite dyke, Synkinematic granite dyke, Quetico Queticomonazite monazite metamorphic metamorphic regional regional cooling cooling through through cloclosure sure temperature temperature regional cooling cooling through through clocloregional sure sure temperature temperature retrograde? retrograde? retrograde 2658+4/-2 Ma retrograde 2658+4/—2 Ma retrograde 2655&3Ma Ma retrograde retrograde 2655±3 2652&4Ma Ma 2652±4 2642&2 Ma Ma 2642±2 retrograde retrograde? subprovince subprovince (12) (12) umbers in in paratheses parathesesrefer refer to to locations locations in in Figure Figure 9. 'Numbers 2Zaleski et al.(1994) (1994) 2~aleski et al. 3Davis al. (1994) (1994) 4~aleski al. (1995) (1995) 3 ~ a v i et s al. 4Zaleski et al. Schandi Schandl et et al. al.(1991) (1991) limb of of the the Manitouwadge Manitouwadge synform synform (Fig. 9), 91, contained contained aasuite suiteof ofconcorconcorMetagreywacke on the southern limb dant or or slightly slightly discordant discordant detrital detritalzircons, zircons,ranging ranging in in age age from from 2719±2 2719&2 Ma to 2679±11 2679kll Ma (Fig. 12, 12?Stop Al). dant The youngest youngest zircon, zircon, together together with with another anothergrain grainofofmore moreprecise preciseage ageof of2692±1 2692ztl Ma, Ma,provide provideaaconservative conservative The maximum limit on deposition deposition of 2693 Mal lea& 25 25 Ma Ma younger younger than than the theage ageofoffelsic felsicvolcanic volcanic rocks rocks to maximum Ma, at least north and and south. south.Zircon Zirconanalyses analysestend tendtotocluster clusteraround around2700 2700Ma, Ma,an anage agenot notknown knownelsewhere elsewhere in in the the the north belt. The Theoldest oldestzircon zirconofof2719±2 2719h2Ma Macould couldbebederived derivedfrom fromlocal localvolcanic volcanicrocks, rockslwhich whichwould would Manitouwadge belt. imply their exposure exposure at at or or before before the the time time of of sedimentation. sedimentation. In In general, general, the zircon zircon population and maximum imply depositional age age are are similar similar to tothose thosedetermined determinedfor forthe theQuetico Queticosubprovince subprovincewest west of of Thunder ThunderBay Bay(Percival (Percival depositional and Sullivan, Sullivan,1988; 1988; Davis Davis et et al., a].,1990). 1990).The TheManitouwadge Manitouwadgemetagreywacke metagreywacke is is lithologically lithologically indistinguishable indistinguishable and that of ofthe theQuetico Queticosubprovince, subprovincelthe themain maindifference difference being being in in the the higher higher metamorphic metamorphic grade grade and andprespresfrom that ence of migmatitic segregations We are attempting attempting to to bracket bracket the the minimum minimum depositional depositional age of ence segregations in in the the latter. latter. We Manitouwadge metagreywacke Manitouwadge metagreywacke by by dating dating a cross-cutting cross-cutting tonalite tonalite dyke (Stop Al). Al). 27 �Geochronology Geochronology Manitouwadge greenstone belt belt 0.64 0.64 0.53 o.53- v, Foliated Foliated trondhjemite trondhjemite A A Z992—P191Z ZB92—W24Z ZB92-W24Z 3 .0 0 Felsic Felsic breccia breccia C 2720 - 2720 .0 .0 a. Q- C 2722 ±2 Ma 2700 0.62 0.52 0.52 2720±3 Ma 0.50 13.2 13.6 207Pb/235U 207Pb/235U FIG. 11. Concordia Concordia diagram diagram with with zircon zircon analyses analyses FIG. from foliated subvolcanic trondhjemite in the the inner inner volcanic belt (Location (Location 2, 2, Fig. Fig. 9). 9). FIG. FIG. 10. Concordia Concordia diagram diagram showing showing zircon zircon analanalyses yses from felsic breccia breccia in the the outer outervolcanic volcanic belt belt (Location 1, 1,Fig. Fig. 9). 9). Manitouwadge metagreywacke 27 detrital zircon Concordia diagram diagram of detrital detrital zircons zircons FIG. 12. 12. Concordia from Manitouwadge metagreywacke between the the ininner and outer volcanic volcanic belts (Location 3, Fig. 9). All All analyses are from single single abraded abraded crystals, crystals, except 'A' which represents aa fraction fraction of of about 20 which represents 20 grains. The The maximum maximum age of deposition is constrained constrained to to 2693 2693 Ma by the the two two youngest youngest grains. grains. 207Pb/235U and monazite—Intrusive monazite-Intrusive rocks n d brackets on deformation deformation Zircon and rocks aand We have attempted to tobracket bracketdeformation deformation by by sampling sampling dykes dykes that that show show relative relative timing timing relationships relationships We with respect respect to to various various generations generations of tectonic fabrics and structures. In Ingeneral, general, we we had had limited limited success success at at with dating these these intrusions intrusions because, because, either either they they did did not notcontain containzircon, zircon, or orthe thezircon zirconwas washighly highlyfractured fractured and and dating vulnerable to secondary secondary Pb Pb loss. loss. In Inthose thosecases casesininwhich whichzircon zircon of of doubtful doubtful quality quality was was analysed, analysed, the the result result scatter of of discordant discordant points. points.Some Somedykes dykescontain containmonazite, monazite,apparently apparentlyofofigneous igneousmorphology, morphology,analysed analysed was a scatter the expectation expectation that thatititwould wouldgive giveprimary primarycrystallization crystallizationages. ages. Monazite, Monazite,including including some some prismatic grains in the pyramidal terminations, terminations, and and fractured fractured zircon zircon (not (not analysed), analysed), were were separated separated from from aa prepre- totosyn-Di syn-Dl with pyramidal transitional to tostraight straightgneiss gneissalong along an an interpreted interpreted D1 Dl ductile ductile fault (see (see Stop A26). Two Two monazite pegmatite transitional analyseslie lie above aboveconcordia concordia(Fig. (Fig.132, 13 ,suggesting suggestingthe thepresence presenceofofexcess excess206Pb ^Pb derived derivedfrom from230Th, "OTh, aa short-lived short-lived analyses intermediate daughter daughter product product of of2 8U W decay. The The preferential preferential incorporation incorporation of of230Th ^OTh into into monazite monaziteduring during lie above above concordia (Parrish, 1990). 1990). The The spread spread of of crystallization commonly results results in isotopic analyses that that lie concordia suggests subsequent minor Pb Pb loss; loss; hence, hence, the the concordance concordance of of aa single single grain grain (Fig. (Fig. analyses down to concordia 13, 'Z') isislikely likely due due to tocombined combinedexcess excess 206Pb ^Pb and Pb loss. loss. The Thebest bestage ageestimate estimateisisthe the207Pb/235U 2 0 7 ~ b / 2 model 3model 5~ 13, 2669k3 Ma Ma defined defined by by the theslightly slightlydiscordant discordantgrains grainsabove aboveconcordia. concordia. age of 2669±3 Nama Creek Creek deposit deposit (Fig. (Fig. 9), 9), aa syn-D2 syn-Dz tonalite dyke, dyke, subparallel to the the axial axialsurfaces surfaces Southwest of the Nama of D2 D2 folds of between iron iron formation formation and and felsic felsic rocks planar foliation. foliation. of of the contact between rocks (Stop (Stop A23), has an axial planar The dyke dyke contained contained only only monazite, monazite,giving giving slightly slightly discordant isotopic analyses that define define an an age age of of 2671±3 2671± The Ma (Fig. (Fig. 14). 14).This Thisage ageisiswithin withinerror errorofofmonazite monazitefrom fromthe thesyn-D1 syn-Dl pegmatite pegmatiteand andofof2675± 2675± Ma 1 Ma age reported for metamorphic metamorphic monazite monazite from from the theGeco Gecomine mine (Davis (Daviset etal., al.,1994). 1994). for Two intrusions, intrusions, interpreted interpreted to tobe besyn-D3, syn-D3,were were sampled sampled in in the theSwill-Mills Swill-Mills Lakes the hinge hinge of of Two Lakes area near the the Manitouwadge Manitouwadge synform synform (Fig. 9). These These intrusions intrusions have have only yielded yielded useful ages (see below). below). A the useful titanite titanite ages third sample, sample, from from aa foliated foliated granitic granitic sheet sheet both both deformed deformed by, by, and and cutting, cutting,D3 D3 folds folds (Stop (Stop B18), B18), is is still being being third processed. processed. i 28 �- - Geochronology Geochronology Manitouwadge greenstone belt '.''- 0.515 FIG. FIG. 13. 13. Concordia Concordiadiagram diagramshowing showing monazite monazite analanalyses from pegmatite pegmatite involved in a D1 strain zone Dl high strain north of Willecho 3 deposit (Location (Location 9, 9, Fig. Fig. 9). 9). of the the Willecho Grains lying lyin above above concordia concordia suggest suggest the thepresence presence of 'excess' derived from from 2°Th 'excess' 206Pb '06Pb derived Th incorporated incorporated into the monazite during crystallization. crystallization. The The spread spread of analyses down down to grain 'Z' 'Z' on onconcordia concordiasuggests suggests subsequent minor Pb Pb loss and, hence, subsequent minor hence, that the the conconcordance of of grain grain 'Z' is is aa fortuitous fortuitous combination combination of of excess and Pb Pb loss. loss. In excess 206Pband In view view of of these these features features of U-Pb systematics in monazite, the best estimate estimate of of age age isis the the207Pb/235U 207Pb/235Umodel age of 2669±3 2669k3 Ma Ma defined by grains grains ''X' defined by X'and 'Y'. 'Y7. pegmafite pegmatite Pre— Pre- to to syri—D1 syn-Dl ZB91 ZB9 1—55Z -55Z 2670 C N Z -a 00 2669±3Ma C 0 N 12.7 2O7p b/235U 12.9 Syn-D tonalite dyke ZB9 1 - P I 3Z 3 FIG. 14. 14. Concordia Concordia diagram diagramshowing showing monazite analdyke (Location (Location8, 8,Fig. Fig.9). 9). yses from a syn-D2 tonalite tonalite dyke 2671 & 3 M8 27 2% CC 288O, Loken Loken Lake Lake pluton pluton Nama Creek pluton ZB93-87AZ 2660— Z893—417AZ ZB93-417AZ fl 5 0 2687 +2(3 M 0.50 'C 0.49 Ga n Ai 12.0 207Pb/235U FIG. 15. 15. Concordia Concordiadiagram diagramshowing showing zircon zircon and and titiFIG. tanite (TA, (TA, TB) TB) analyses analyses from from the the prepre- totosyn-D2 syn-D2 tanite ThezirzirNama Creek pluton (Location 6, Fig. 9). The con age of of 2680k3 2680±3 Ma Ma is is interpreted interpreted as the age of the intrusion intrusionand andthe themaximum maximumage ageofofD2 D2deformadeformathe tion. The Thetitanite titaniteage ageofof2672±3 2672&3Ma Maisisinterpreted interpreted tion. as the thetime timeofofregional regionalcooling cooling through through the theclosure closure as temperature of of titanite. titanite. temperature - 12.4 207Pb/235U 12.8 FIG. 16. 16. Concordia Concordia diagram diagramshowing showing zircon and tiFIG. tanite tanite(Ctit) (Ctit)analyses analysesfrom fromthe theprepre-totosyn-D2 syn-D2Loken Loken Thezircon zircon age age of of Lake pluton (Location 4, Fig. 9). The 2687+2/-3 Ma is the the age age of of intrusion, intrusion,whereas whereasthe the 2687+2/—3 2652~t4Ma is interpreted interpreted as a late late titanite age age of of 2652±4 titanite retrograde retrograde event that crystallized crystallized or reset titanite. titanite. In the theQuetico Quetico subprovince subprovince (Fig. (Fig. 9), 91,aamuscovite-biotite muscovite-biotite granitic granitic dyke dyke was was interpreted interpreted to to be becontemcontemIn with progressive progressive deformation (late D3 D3 or D4) D4) and, and, judging judging by by the thepresence presenceofofmuscovite, muscovite,late lateinin poraneous with 29 29 �Manitouwadge Manitouwadge greenstone greenstone belt belt Geochronology Geochronology Black Pic batholith Foliated diorite Black Pic batholith Foliated monzodiorite--.... 2~ 2680 J m ZB94-86BZ 207Pb/235U 207Pb/235U FIG. FIG.17. 17. Zircon Zircon concordia concordia diagram diagram of of the the oldest oldest phase phase of of the theBlack BlackPic Picbatholith, batholith,foliated foliatedplagioplagioclase clase porphyritic porphyritic diorite diorite (Location (Location 5, S1Fig. Fig. 9). 9). The The age ageof of 2687+3/—2 2687+3/-2 Ma is within error error of of that thatof ofthe the prep r e totosyn-D2 syn-D2Loken LokenLake Lake pluton. pluton. FIG. FIG. 18. 18. Concordia Concordia diagram diagram showing showing zircon zircon and and titanite(Atit, (Atit,Btit) Btit)analyses analysesfrom fromfoliated foliatedmonzomonzotitanite diorite of of the the Black Black Pic Pic batholith batholith(Location (Location7,7,Fig. Fig. diorite 9). The Thezircon zirconage ageof of2677±2 2677&2Ma Ma dates dates the theintruintru9). sionand andisiswithin withinerror errorof ofthe theNama NamaCreek Creekpluton. pluton. sion 2674&2Ma Maindicates indicatescooling cooling Thetitanite titaniteage ageofof2674±2 The through the theclosure closuretemperature temperature of oftitanite titanitesoon soon through after afterintrusion. intrusion. themetamorphic metamorphicand andanatectic anatectichistory. history.The Thedyke dykeisissubparallel subparalleltotothe theaxial axialplanes planesofofZ-folds Z-foldsininmigmatitic migmatitic the rocks and and has hasan anaxial axialplanar planarfoliation foliation (Stop (Stop E2). E2). Shear Shearbands bandsininthe thehost hostrock rockand andthe thedyke dykecut cut across across the the rocks contact.Zircons Zirconsfrom from the thedyke dyke gave gave scattered discordant discordant analyses, apparently in part due due to toinheritance. inheritance. Of Of contact. two monazite monazite grains grainsanalysed, analysed,one onewas washighly highlydiscordant, discordant,and andthe theother otherslightly slightlydiscordant discordantabove aboveconcordia concordia two (see 206Pbabove), giving an age age of of 2642±2 2642&2 Ma Ma (Table (Table2). 2). (seediscussion discussionof of excess excess 206Pb We had had better bettersuccess success inindating datinglarger largerplutonic plutonicbodies. bodies. InInsome somecases, cases,the therelative relativeage ageofofthese thesewith with We respect TwoK-feldspar K-feldspar porphyritic porphyritic granitoids, granitoidsl the the respect to todeformation deformation can can be beinferred inferredwith withsome someconfidence. confidence. Two Nama Creek Creek and and Loken Loken Lake Lake plutons plutons (Fig. (Fig. 9), 9))are are both both interpreted interpreted asasprepre-totosyn-D2 syn-D2intrusions intrusionsbased based on on Nama tectonic tectonicfabrics fabricsdeformed deformedby byD3 D3folds. folds.Analyses Analysesof ofzircon zircon from from Nama NamaCreek Creekpluton plutondefine definean anage ageofof2680±3 2680k3 Ma Ma(Stops (StopsF11—F12, F11-F121 Fig. 15), 15)! whereas those from the Loken Lake pluton are are slightly slightly older older at a t2687+2/—3 2687+2/-3 Ma Ma (Fig. (Fig. 16). 16).The Theoldest oldestdioritic dioriticand andthe theyoungest youngestaplitic aplitic(not (notprocessed) processed)phases, phasesl both bothfoliated, foliatedlof of the the Black Black Pic Pic batholithwere weresampled sampledsouth southofofthe theManitouwadge Manitouwadgebelt belt(Stop (StopF3). F3).Zircon Zirconanalyses analysesfrom fromthe thediorite dioriteyield yieldan an batholith age —2 Ma Ma (Fig. 17), ageof of2687+3/ 2687+3/-2 171, within error of of the the Loken Loken Lake Lake pluton. Foliated Foliatedmonzodiorite monzodiorite of of the theBlack Black Picbatholith, batholith,between betweenthe theeastern easternextensions extensions of of the theinner inner and andouter outervolcanic volcanicbelts belts (Fig. (Fig.9), 91,has hasananage ageofof Pic 2677±2 2677&2Ma Ma(Fig. (Fig.18). 18).The Theage ageisiswithin withinerror errorofofthe theNama NamaCreek Creekpluton, pluton,but butthe themonzodiorite monzodioritefoliation foliationcould could be beaaD2 D2ororD3 D3fabric. fabric. 1 0.532 Syn—D3 fonaIie dyke Syn-D3 tonalite dyke Z893—P1 ZB93-PIO2AZ 02AZ 0.508 2 ÷41-2 Ma -o ci- 0.504 FIG.19. 19.Concordia Concordiadiagram diagramshowing showingtitanite titaniteanalyanalyFIG. sesfrom fromaasyn-D3 syn-D3tonalite tonalitedyke dykenear nearthe thehinge hingeregion region ses theManitouwadge Manitouwadgesynform synform(Location (Location10, 10,Fig. Fig.9), 911 ofofthe defining definingan anage ageofof2658+4/—2 2658+4/-2 Ma. Ma. () ,,>v27%77, /€.2 Ga — 12.2 207Pb/235U 12.6 30 �Setting of mineralization Manitouwadge greenstone belt belt Titanite Titanite were done done on on titanite titanite from U-Pb isotopic analyses analyses were from intrusive intrusive rocks rocks in in order order to toplace placeminimum minimumage ageconconstraints on magmatism magmatism and and metamorphism. metamorphism. The The analyses analyses group group around around two two distinct distinct ages ages of of 2673 2673 and 2655 Ma. The titanite ages 2672k3 The 2680 2680 Ma Nama Creek pluton and and the the 2677 2677 Ma Ma Black Black Pic monzodiorite have titanite ages of 2672±3 Ma (Fig. 15) 15) and 2674±2 26744Z2 Ma Ma (Fig. (Fig. 18), 181, respectively. respectively. We tentatively interpret these these as as the the time timeof ofregional regional cooling through the 600°C closure temperature temperature of titanite titanite (Heaman cooling through 6OO0C closure (Heaman and and Parrish, Parrish,1991) 1991)and, and,for for the thecase case of of the the Nama Creek pluton, about about 88 Ma Ma after afterintrusion. intrusion.Titanite Titanitefrom fromthe the2687 2687Ma MaLoken LokenLake Lakepluton plutondefines definesan anage age of 26524Z4 2652±4 Ma (Fig. 16), of 161,whereas whereas syn-D3 syn-D3 intrusions intrusions in in the theSwill-Mills Swill-Mills Lakes area gave gave ages of 2658+4/—2 2658+4/-2 Ma from a tonalite dyke (Fig. 19), and 2655±3 from 26554~3Ma from a granitic sheet (Table 2). The The circa circa 2655 2655 Ma titanites titanites suggest aa widespread widespread late late hydrothermal hydrothermal event event that that locally locally crystallized crystallizedor orreset resettitanite. titanite. suggest SETTING S E T T I N G OF O F MINERALIZATION MINERALIZATION sulphide deposits deposits lie lie in the inner The Geco, Gecol Wiliroy, Willroyl Nama Creek and Willecho Willecho massive massive sulphide inner volcanic volcanic belt belt along the the southern limb and hinge region of the the D3 Manitouwadge Manitouwadgesynform synform(Fig. (Fig.3). 3). Our Our understanding understanding of of along region of deformation of of the the area and the complex complex pre-D3 pre-D3 deformation and of of the theprobable probable original original relationships relationships of of sulphide sulphide deposits deposits depends on detailed detailed lithological lithological and and structural structural mapping, as well as any any additional additional clues clues that that could be gleaned gleaned depends well as from features characteristic of of individual deposits. Except Except for for Nama Nama Creek, Creek, each each of of these these deposits deposits comprised comprised several massive, massive, semi-massive semi-massiveorordisseminated disseminatedsulPhid&orebodies sulphide orebodiesofofwidely widelyvarying varyingCu, Cu,Zn Znand and Pb Pb grades several and ratios (Table 3). On On the the basis basis of of Cu-Zn-Pb Cu-Zn-Pb proportions, nature of mineralization and relationship relationship to iron formation, the sulphide orebodies of the the Manitouwadge camp can can be be divided dividedinto into three three main main types. types. Firstly, orebodies of Manitouwadge camp Firstly, Cu-rich stringer and disseminated Cu-rich disseminated orebodies orebodies are are hosted hosted by by orthoamphibole-cordierite-garnet orthoamphibole-cordierite-garnet gneiss gneiss (footwall (footwall alteration) sillimanite-muscovite-quartzschist. Secondly, Secondly, massive massive and alteration) or or envelop envelop the the Geco Geco main main orebody orebody in insillimanite-muscovite-quartz semi-massive Zn-Cu-(Pb) orebodies orebodies are associated associated with iron formation horizons interleaved with sillimanitesemi-massive Zn-Cu-(Pb) schist or 6r quartz-phyric quartz-phyric felsic felsic rocks. Thirdly, Thirdlylmassive massive and and semi-massive semi-massive Zn-Pb-(Cu) orebodies orebodies muscovite-quartz schist sillimanite-muscovite-quartz schist. schist.With Withsome someexceptions exceptions(see (seebelow), below), by iron iron formation formation south southofofsillimanite-muscovite-quartz are hosted by the spatial spatial distribution distribution of of orebodies orebodies defines defines a tendency tendency to more Zn-rich Zn-rich and and Pb-rich Pb-rich deposits deposits toward toward the the south. In terms of of classification based Manitouwadge belt collectively collectively fits based on Cu-Zn-Pb, the Manitouwadge fits Franklin's Franklin's (1986) Cu-Zn Cu-Zn Group la, l a ,which which includes includes the the deposits deposits of of the the Abitibi Abitibigreenstone greenstone belt, belt,the theNorwegian Norwegian Caledonides Caledonides and and other other areas dominated by by basaltic basaltic volcanism volcanism (Fig. (Fig. 20). 20). TABLE 3. 3. Types aand TABLE n d Grades G r a d e s of Mineralization Orebody Orebody TYPe Type %Cu %Cu %Zn %Zn %Pb %Pb g/tAg Geco 412 4/2 Cu Cu disseminated disseminated 1 .8 1.8 0.3 0 .3 — 16 16 Geco Main massive massive 2.3 2 .3 8.2 8 .2 0.4 0.4 74 74 Geco Main stringer, disseminated stringer, disseminated 1 .5 1.5 0.1 0.1 — 0.2 0.2 4.9 4.9 — 36 36 Geco ZnIF massive, disseminated massive, disseminated semi-massive semi-massive - 22 22 8/2 Zn Geco 812 0.1 0.1 8.6 8.6 0.8 0.8 41 41 Willroy Willroy 11 disseminated, disseminated,stringer stringer 1.3 1 .3 - — 99 Willroy Willroy 22 semi-massive semi-massive <O.l <0.1 6.0 6.0 0.2 0 .2 64 64 Willroy Willroy 33 1.3 1 .3 4.5 4.5 0.2 0 .2 56 56 — - 8.0 8.0 1.2 1.2 168 168 — 6.0 6.0 0 .2 0.2 28 28 — — Willroy Willroy 44 massive massive massive* semi-massive massive, semi-massive Willroy 55 Willroy semi-massive semi-massive Willroy 66 stringer stringer 2.0 2.0 1.0 1.0 Willroy 77 massive 0.4 0.4 5.0 5.0 Nama Creek semi-massive semi-massive 0.8 0.8 3 .9 3.9 Willecho 11 Willecho semi-massive semi-massive 1.O 1.0 3.0 3 .0 Willecho 22 Willecho semi-massive semi-massive 0.2 0.2 5.8 5.8 Willecho 33 Willecho semi-massive semi-massive 0.6 0 .6 3 .8 3.8 - — 14 14 39 39 — 28 28 — 42 42 — 42 42 — 53 53 Datacompiled compiledby by -H. .H. Lockwood, Lockwoodl Noranda Inc. from from unpublished unpublishedcompany companyrecords. records. Data from an an unpublished unpublished report report by by Derry, Derry, Michener Michener and Booth Booth (1971) (1971)for Willroy data data from Willroy Mines Inc. Inc. Willroy Tiand Marshall Marshall (1959), (1959),or estimated estimated Willroy %Pb %Pb from Timms depositwas wasnever nevermined. mined. constant Zn/Pb. Zn/Pb.The TheWillroy Willroy77deposit assuming near constant The suiphide sulphide mineralogy is generally generally simple, simple, consisting consistingofofpyrite, pyrite,pyrrhotite, pyrrhotite, chalcopyrite, chalcopyrite,sphalerite sphalerite and and galena Marshall, 1959; 1959; Friesen Friesen et al., 1982). 1982). Many Many details detailsof ofindividual individual orebodies orebodies have have been been galena (Timms and Marshall, 31 �Manitouwadge greenstone belt Narna Nama Cree Creek Willecho Type 3 Type 2 Type Setting of of mineralization mineralization Setting Cu Wiflroy Geco Urn #4 A #2. J/5, #7 .0 #3 * #1 2 3 + orebody #6 #1 I ZnIF ZnIF 8/2 Zn zone main orebody *I main stringer, £ main orebody 4/2 Cu zone T FIG. FIG. 20. 20. Cu-Zn-Pb Cu-Zn-Pb ternary ternarydiagram diagram(weight (weight %) showing showing the metal metal composition composition of of the the %) In orebodies of of the theManitouwadge Manitouwadge camp. camp. In orebodies the key key and and the thedotted dottedfields, fieldsl orebodies orebodies the are grouped grouped into into Types Types 1,l l 22 and and 33(see (see are text). The The average averagebase-metal base-metal proportions proportions text). in the theAbitibi Abitibibelt, beltlNorwegian NorwegianCaledonides, Caledonidesl in Japanese Green Green Tuff Tuffbelt, belt, and and the the BathurstBathurstJapanese Newcastle area area of of New New Brunswick Brunswick are arefrom from Newcastle Lydon (1984). (1984). Lydon Coladonides Ablflbi Jopon Type2. V Pb V V V Bothursi. Type 3 V '.1 V V Zn described described by by Pye Pye (1957), (1957)>Timms Timms and and Marshall Marshall (1959), (1959)1Brown Brown et al. al. (1980) (1960) and and Friesen Friesen et et al. al. (1982) (1982) and and only only observations observations pertinent pertinent to toour ourreinterpretation reinterpretationare arereviewed reviewedhere. here. Relationships m d host host rocks rocks Relationships of of orebodies orebodies and The Geco 4/2 Cu zone, and Willroy 1 and depositslconsist consistof of Cu-rich, Cu-richldisseminated disseminatedor orstringer stringersulphides sulphides The Geco 412 Cu zonel and Willroy 1and66deposits, on on or or near near the the contact contactbetween between orthoamphibole-cordierite-garnet orthoamphibole-cordierite-garnet gneiss gneiss and and sillimanite-muscovite-quartz sillimanite-muscovite-quartz schist (Fig. (Fig. 4, 21). 21). On Onthe thesouth southside sideofofthe the4/2 412Cu Cuzone, zone,a aweakly weaklymineralized mineralized'breccia' 'breccia' of offlattened flattenedquartz quartzlenses lenses in in an anorthoamphibole orthoamphibolematrix matrixhas hasbeen beenvariably variablyinterpreted interpretedasasaltered alteredpyroclastic pyroclasticrock rock(Friesen (Frieseneteta!., al.l1982) 1982) or or disrupted disruptedaltered alterediron ironformation formation(Bakker (Bakkeretetal., al.?1985). 1985). The TheGeco Gecomain mainorebody orebodylies liessouth southofofthe the4/2 412Cu Cuzone, zonelenveloped envelopedby bysillimanite-muscovite-quartz sillimanite-muscovite-quartz schist schist and andquartzite. quartzite. ItItisisby byfar farthe thelargest largestand andhighest highestgrade gradeofofthe theorebodies, orebodieslalthough althoughthe theproportions proportionsof ofCuCuZn-Pb sillimanite-muscovite-quartz Zn-Pbare aresimilar similartotoWillroy Willroy33(Fig. (Fig.20). 20).AAhalo haloofofchalcopyrite chalcopyritedisseminated disseminatedininsillimanite-muscovite-quartz schist surrounds surroundsthe themassive massivezone zone (Table (Table3, Geco Geco main main stringer), stringer)>especially especially on on the the lower lower eastern eastern margin margin and and schist south 1982). south side side (Friesen (Friesen et al., ale$ 1982). The Themain mainorebody orebody has hasbeen been traced traced totothe theeast eastininunderground undergroundworkings, workings, where where itit grades grades and andthins thinstotoZn-rich Zn-richmassive massivesulphide sulphide interleaved interleaved with iron iron formation, formation, the the latter lattercorrelated correlated with iron ironformation formationformerly formerlyexposed exposedininthe theGeco Gecoquarry quarryatatsurface surface(Geco (Gecomine, minelunpublished unpublishedcross-sections). cross-sections). with We We are are not notable abletotoconfirm confirmthis thisrelationship relationshipand, andlfurthermore, furthermorelsurface surfacemapping mappingofofthe thesurviving survivingexposures exposures shows shows that the theGeco Geco main main orebody orebody lies lies to the the north north of of the thesouthernmost southernmost iron iron formation, formationl and and that that the theiron iron formation is is continuous continuous to the the quarry. quarry. The Thesubsurface subsurfacerelationships relationships imply imply that that the theeastern easternextension extensionofofthe the formation main orebody orebody crosses crosses stratigraphy stratigraphyatataalow lowangle angle(ibid.); (ibid.);but butwe weare areunable unabletotodiscriminate discriminatebetween betweenpossible possible main syngenetic syngenetic or or epigenetic epigeneticrelationships relationships(see (seebelow). below). Low grade economic and subeconomic Geco main orebody orebody to to Low grade economic subeconomic Cu mineralization is continuous from from the Geco the 1982), near transition from sillimanite-muscovite-quartz the8/2 812Zn Znzone zone(Friesen (Friesenetetal., al.> 1982)> nearthe the transition from sillimanite-muscovite-quartzschist schisttotomore more quartzitic varieties varieties of the same same unit. The The8/2 812Zn Znzone zoneand andiron ironformation formationon onthe thesame samehorizon horizon project project to to quartzitic surface south south of of the themain mainorebody. orebody.The Thesouthernmost southernmostorebody orebodyatatthe theGeco Gecomine mineisisa azincian zincianiron ironformation formation surface (Table (Table 3, 31ZnIF) ZnIF) in in micaceous micaceous quartzite, interpreted interpreted as asan analtered alteredvolcanic volcanic rock. rock. Zincian Zincian iron iron formation formation attains attains aL11985; 1985;Williams Williams economicgrades grades in in deeper deeper levels levels of of the the mine mine-near theMose Mose Lake Lake Fault Fault (Fig. (Fig. 4) 4) (Bakker (Bakkeretetal., economic near the etetal., aL11990). 1990). G&O main mainorebody orebodywas wasdisplaced displacedby by the thesteeply steeplydipping, dippinglhigh-angle high-angleFox Fox Creek Creek fault fault (Pye, (Pyel1957; 1957; TheGeco The Brown et et al., aL11960). 1960).Well Wellaway awayfrom fromthe theFox FoxCreek Creekfault, faultlevidence evidenceofoftectonic tectonicremobilization remobilizationofofsulphide sulphide Brown minerals is is ubiquitous, ubiquitous, in in part partrelated relatedtotolayer-parallel layer-parallelmovement movement(Friesen (Friesen et et a!., alm1 1982). For Forexample, example1wallwallminerals 1982). rock rock breccias breccias have have aa sulphide sulphide matrix, matrix, and anddisrupted disrupted segmented segmented pegmatite pegmatite and andtonalite tonalitedykes dykes can can be betraced traced across massive massive sulphide. All All orebodies orebodies are are conformable conformable to to the the nearly nearlyvertical vertical host hostrocks, rocks,and andelongate elongatewith with across shallow to to moderate moderate easterly easterly plunges, plungeslsubparallel subparallel to tothe thedominant dominantmineral minerallineation. lineation.The Themassive massivesulphide sulphide shallow zone of of the the Geco Geco main main orebody orebody isisthickest thickest ininthe thehinge hingeofofthe theeasterly-plunging easterly-plunging Z-shaped Z-shaped 'Geco 'Geco drag drag fold' fold' zone (ibid.), inferred inferred to tobe beaaD3 D3ororlater laterfold foldbased basedononthe theinvolvement involvementofoffolded foldedfoliation. foliation. The TheZ-asymmetry Z-asymmetryisis (ibid.), consistent with with the thegeometry geometryexpected expected for foraaparasitic parasiticfold foldon onthe thesouthern southernlimb limbofofthe theD3D3 Manitouwadge consistent Manitouwadge synform.Locally, LocallylCu Cugrades gradesare arehighest highestininfold foldnoses noses(Friesen (Friesenetetal., al.,1982) 1982)and andminor minor(less (lessthan thanmetre-scale) metre-scale) synform. folds foldshave havepods podsofofmassive massivechalcopyrite chalcopyriteinindilational dilationalzones. zones. TheZn-rich Zn-richWillroy Willroy2, 3,3,4, 55and The and7 7deposits depositslielieon oniron ironformation formationhorizons horizonssouth southofofthe theWiliroy Willroy1 1and and Cu-stringerdeposits, depositslintercalated intercalatedwith withquartz-phyric quartz-phyricfelsic felsicmetavolcanic metavolcanicrocks rocksand andsillimanite-muscovitesillimanite-muscovite66Cu-stringer 32 �Setting of of mineralization mineralization Manitouwadge greenstone belt Unconformity Unconformity or fault fault 1 Quartzite,felsic rocks -....- .,------I Reconstructed trace of of DDil fault. Reconstructed trnce fault Type Type 33 Zn—Pb—(Cu); Willroy 4, 4, Ceco Zn-Pb-(Cu); Willroy Ceco ZnIF ZnlF Quartzite *. '\, K-A1 alteration '\.(Sillimanite-muscovile)' / lkall-depleted Pe-Mg altera (Orthoarnphibole-cordierite- Type Type 22 Zn—Cu--(Pb); Zn-Cu-(Pb); Willroy Willroy 2,2 , 3, 3, 5, 5, Ceco Geco main main orebody, orebody, 8/2 812 Zn Zn Nama Nama Creek Creek WIllecho 3, Willecho 1, 22 , 3, Type Type I1 Cu Cu stringers; Willroy Willroy 1, 66 Geco 4/2 Cu Geco 412 Cu Trondhjemite FIG. FIG. 21. Schematic Schematic reconstructed reconstructed section section of of the the probable probable relationships relationships between between orebodies, orebodies, showing the trace trace of of the D1 showing the Dl fault that divides divides the area. area. Stringer/disseminated Stringer/disseminated zones zones are are shown and iron formations cross-hatching, and formations are stippled. stippled. Some ambiguity remains in in shown as cross-hatching, detailed correlations correlations of of mineralized mineralized horizons horizons between between the the Geco Geco main main and andWiliroy Willroyorebodies. orebodies. schist. The TheWiliroy Willroy33orebody, orebody, the thesouthernmost southernmost and and largest largest of of the theWiflroy Willroy deposits, deposits, is is zoned zoned from quartz schist. relatively Cu-rich Cu-rich core (Cu=Zn) to to aa Zn-rich Zn-rich margin, margin, to to barren barren pyrite-pyrrhotite pyrite-pyrrhotite sulphidic sulphidic iron iron formation formation a relatively 1957; Timms and Marshall, Marshall, 1959). 1959). The TheWiliroy Willroy 44 orebody orebody and andGeco Gecozincian zincian iron ironformation formationhave have the the (Pye, 1957; highest Pb Pb grades grades of of the the Manitouwadge Manitouwadge deposits deposits (Table 3, Fig. 20). The Nama Nama Creek Creek deposit, deposit, located located near near the thecontact contactbetween between orthoamphibole-cordierite-garnet orthoamphibole-cordierite-garnetgneiss gneiss and The sillimanite-muscovite-quartz schist, schist,consisted consistedof of marginally marginally economic economic Zn-rich mineralization (Table (Table 3), 31, hosted hosted sillimanite-muscovite-quartz by iron iron formation formation and and much much intruded intruded by by pegmatite. pegmatite.North Northofofthe thehinge hingeregion regionof ofthe theManitouwadge Manitouwadgesynform synform by 41, three three Willecho Willecho deposits deposits are arehighly highlydeformed deformed Zn-rich Zn-rich semi-massive semi-massive sulphide (Fig. 4), suiphide sheets interleaved with iron formation formation and and altered alteredrocks. rocks. S t r u c t u r a lcomplications—D1/D2 complications-Dl/D2 folds and a n d faults faults Structural The interpreted sillimanite-muscovite-quartz interpreted D1 Dl fault faultofofthe theWillroy-Geco Willroy-Gecoarea areacontinues continueseastward eastwardininsillimanite-muscovite-quartz schist schist to highly highly strained strained iron iron formation formation and and straight straight gneiss gneiss exposed exposed east of of Wowun Wowun Lake Lake (Fig. 3). Our Our allow some fault with with respect respect to tothe theGeco Gecomain mainorebody; orebody;ititcould could observations allow some latitude latitude in the position of the fault orebody. The TheWillecho Willecho deposits deposits lie lie near or on on the the D2 D2 fold repetition of of the D1 Dl fault, fault, or south south of of the theorebody. lie north or their original originalstratigraphic stratigraphicrelationship relationshiptotothe theWiliroy-Geco Willroy-Gecoorebodies orebodiesisisobscure. obscure. and their interpretation,the theD1 Dlfault faultdivides dividesthe theNama NamaCreek-Wiliroy-Geco Creek-Willroy-Gecoarea areainto into22tectonic tectonicblocks blocks (Fig. (Fig. In our interpretation, The Wiliroy Willroy 33 orebody orebody and and Geco Geco zincian iron formation lie Willroy 1, 1, 2, 21). The lie in in the southern block, and the Willroy orebodies, Nama Nama Creek Creek and and Geco Geco 4/2 412 Cu Cu zone zone lie lie in in the the northern northern block. block. The TheGeco Gecomain mainorebody orebody 4, 55 and and 66 orebodies, 4, 812Zn Zn zone zone could could lie either on on the the northern northern margin marginof of the the southern southernblock, block,or or the thesouthern southernmargin marginof of the the and 8/2 northern block. block. The TheCu-rich Cu-richdisseminated disseminatedand andstringer stringerzones, zones,the theGeco Geco 4/2 412Cu Cuzone, zone,Willroy Willroy 11and and 66 deposits deposits northern to lie lie on on the thesame samehorizon, horizon, and andare areprobably probably related related totothe thedisseminated disseminatedCu Cumineralization mineralization are interpreted to around the theGeco Gecomain mainorebody. orebody.Zn-rich Zn-richmassive massiveand andsemi-massive semi-massivesulphide bodies north north of of the theD1 Dl fault, fault,the the around Willroy 2, 5 and and Nama Nama Creek Creek deposits, deposits, could could lie lie on on the thesame sameiron iron formation formationhorizon horizon as asthe theWillroy Willroy33deposit deposit Willroy on the the south south side side of of the the fault. fault.The TheGeco Gecozincian zincianiron iron formation formation in in the the southern southern block block is is interpreted interpreted to to be be on correlative with iron iron formation formation hosting hosting the the Wiliroy Willroy 44 deposit deposit in in the the northern northernblock. block. correlative The Wiliroy Willroy 33 and and Geco Geco main main orebody orebody are are similar similar in in Zn-Cu-Pb Zn-Cu-Pb (Fig. (Fig. 20). 20). Cu-to-Zn Cu-to-Zn zoning zoning toward toward iron iron The formation, such such as as that thatexhibited exhibitedby bythe theWillroy Willroy33deposit, deposit,isischaracteristic characteristicofofvent-proximal vent-proximalmassive massivesulphide sulphide formation, bodies (Lydon, (Lydon, 1984). 1984). Similarly, Similarly, stringer stringer sulphide sulphide zones, zones, like like those associated associated with with the theGeco Gecomain mainorebody, orebody, bodies are typical typical of of subsurface subsurface feeder feeder zones zones of proximal deposits. These features features suggest suggest the the Wiliroy Willroy 33and andGeco Geco are deposits. These 33 �Manitouwadge greenstone belt belt Geochemistry Geochemistry main orebody precipitated close close to to a hydrothermal vent, and and that the orebody precipitated hydrothermal vent, the Geco Geco main main orebody orebody could could also also lie lie on or or near near the theWiliroy Willroy3,3,2,2,55and andNama NamaCreek Creekhorizon. horizon.However, However,we wecannot cannotdiscriminate discriminatebetween betweenseveral several possible interpretations of iron-formation-hosted eastern eastern of the the relationships relationships between between the the Geco Geco main orebody, its iron-formation-hosted extension in the Geco quarry (i.e. the southernmost iron formation), and early faults. Structural Structuralcomplications complications are possible juxtaposing the main possible including, early faulting juxtaposing main orebody orebody with with an an unrelated unrelatediron-formation-hosted iron-formation-hosted deposit and, and, remobilization remobilization of of sulphides sulphides along along early faults faults and and iron iron formation formation layers. layers. The TheCu-to-Zn Cu-to-Znzoning, zoning, reported in in the the sulphide-iron sulphide-iron formation formation transition transition in in the thequarry, quarry,argues arguesagainst againstremobilization, remobilization,as as does does the the observation observation that, that,atatGeco Gecoand andininother otherdeformed deformedmassive massivesulphide sulphidebodies bodies(e.g. (e.g.Valenta, Valenta,1994), 1994),remobilization remobilization generally generally involves involves redistribution redistribution of of chalcopyrite. chalcopyrite. The increase increase in Zn/Cu Zn/Cu of of the theGeco Gecoorebodies orebodies from from north north to to south, south.characteristically characteristicallv aa stratigraphicstratiffraohic". upwards sulphide deposits, deposits, and the upwards zonation zonation in in volcanogenic volcanogenic massive sulphide the presence presence of of orthoamphibole-cordieriteorthoamihibole-cordieritegarnet footwallalteration, alteration, to to the the north have garnet gneiss, gneiss, the the metamorphosed metamorphosed equivalent equivalent of synvolcanic synvolcanic footwall have both been been used area (Suffel et al., al., 1971; et al., 1982). used to to infer infer southerly southerly younging younging in the the Willroy-Geco Willroy-Geco area (Suffel et 1971; Friesen Friesen et 1982). The The northerly northerlyposition positionof ofthe thesynvolcanic synvolcanictrondhjemite trondhjemiteintrusion intrusionisisconsistent consistentwith withexposure exposureofofprogressively progressivelydeeper deeper levels of a volcanic edifice edificein in that that direction. Southerly levels of Southerly younging younging in the the Willroy-Geco Willroy-Geco area implies implies that the the northern northern tectonic tectonic block block is, is, in in general, general, stratigraphically stratigraphically lower lower than the the southern southern tectonic tectonicblock block (Fig. (Fig.21). 21). A A consequence consequence of D2-fold repetition of sequences on the southern southern limb limbof ofthe theManitouwadge Manitouwadgesynform synformisis that that the themineralized mineralizedand andaltered alteredintervals intervalsof ofthe theWillroy-Geco Willroy-Geco area area are are repeated repeated in inthe theouter outervolcanic volcanicbelt, belt, assuming younger greywackes. assuming that that they theywere werenot notremoved removedby byerosion erosionororfaulting faultingalong alongthe thecontact contactwith with younger greywackes. Sporadic orthoamphibole, garnet garnet and minor cordierite rocks of of the outer volcanic belt are Sporadic zones of orthoamphibole, cordierite in mafic rocks volcanic belt interpreted as asincipient incipient synvolcanic synvolcanic alteration alteration correlative correlative with with altered alteredrocks rocksin inthe theWillroy-Geco Willroy-Gecoarea. area. GEO CHEMISTRY GEOCHEMISTRY A A suite suiteof of 127 127samples samples was was collected collected to to represent represent supracrustal supracrustal and andplutonic plutonicrocks rocksofofthe theManitouwadge Manitouwadge greenstone belt, the the Black Black Pic Picbatholith, batholith,and andthe theQuetico Queticosubprovince. subprovince. These were greenstone were analysed analysed for for major major H20, C 0 2 and S, St,and andmost mostwere werealso alsoanalysed analysed for for trace traceelements, elements,including including rare-earth rare-earth elements, ferrous ferrous iron, iron, H2 elements, 0, CO2 elements from the area elements (REE). Our Our data dataare aresupplemented supplemented by bysome somemajor-element major-element analyses analyses of samples from area of of known mineral deposits, made made available available by Noranda Inc. Evaluation Evaluation of of results results of of our our geochemistry geochemistry program program known is is ongoing ongoing and many of the interpretations interpretations presented presented here here are areincomplete incomplete or or preliminary. preliminary. Metavolcanic Metavolcanic and a n dsubvolcanic subvolcanicrocks rocks A sample sample suite suite of of 54 54metavolcanic metavolcanic and and associated associated rocks rocks was was chosen chosen to to represent represent primary primarygeochemistry, geochemistry, A avoiding evidence evidence of retrogression as much much as as possible possible (with (withsome someexcepexcepavoiding of synvolcanic synvolcanic alteration alteration and and later retrogression tions discussed discussed below). below). The Thesuite suiterepresents represents55main mainrock rocktypes; types;aphyric aphyricfelsic felsicmetavolcanic metavolcanicrocks, rocks,quartzquartztions phyric metavolcanic metavolcanic felsic rocks, foliated mafic metavolcanic rocks, and hornblendephyric foliated trondhjemite-granodiorite, trondhjemite-granodiorite, mafic magnetite-garnet rocks/magnetite rocks/magnetite quartzites. quartzites. The Thelatter latterinclude includemagnetite-rich magnetite-rich layered layered rocks rocks (see (see Unit Unit 5), 5), magnetite-garnet resembling sedimentary concentrations of heavy minerals, and quartz-richer quartz-richer transitional rocks rocks interpreted as as resembling contaminated trondhjemite. trondhjemite. To Tofacilitate facilitatediscussion, discussion, the the suite suitecan canbe besubdivided subdividedinto into66geographic geographicgroups; groups; contaminated the inner inner and andouter outervolcanic volcanic belts, belts, and andthe theDead DeadLake, Lake,eastern eastern extension, extension, One One Otter-Banana Otter-Banana Lakes Lakes and and JimJimthe Davis Lakes Lakes areas (Fig. 22). The The foliated foliated trondhjemite-granodiorite trondhjemite-granodiorite in in the the inner inner volcanic volcanic belt belt isisinterpreted interpreted Davis as synvolcanic; synvolcanic; similar to test test their theircompositional compositional similarity similarity and and as similar rocks rocks were weresampled sampledtoto the the east east and north to the the extent extentofofpossibly possiblycomagmatic comagmaticintrusive intrusiverocks. rocks. Mafic metavolcanic rocks 23). The ThecompocompoMafic rocks throughout throughout the Manitouwadge belt belt are tholeiitic basalts (Fig. 23). sitions of of mafic rocks from attentuatedand andfolded foldedextensions extensions sitions from the the inner and outer volcanic belts, and from the attentuated of the the belt, belt,for forthe themost mostpart, part,are arepermissive permissiveofofcorrelation correlationand andsuggest suggestthat thatallallmafic maficrocks rockscould couldhave havebeen been of produced by the same same magma magma system. The The tendency tendency of of the outer outer belt belt to tohigh highMg, Mg,low low Ti02 Ti02 (Fig. (Fig. 24), 24),and and produced low light REE REE (Fig. (Fig.26) 26)contents, contents,isisdefined definedby bygabbros gabbrosand andsamples samplesfrom fromthe theSwill-Mills Swill-MillsLake Lake area area (near (near the the low hinge of the Manitouwadge Manitouwadge synform southwestern part Mafic compositions compositions in the inner inner hinge synform in in the southwestern part of Fig. 22). Mafic and outer outer belts beltsshow showconsiderable considerable overlap, overlap, and andthe theslight slightdifferences differences could could reflect reflect aa bias biasininwhich whichgabbros gabbros and and rocks rocks deeper deeper in the the stratigraphic stratigraphicsection section were were not sampled sampled in the inner inner belt. belt. The Thesingle singlesample sample from from the and inner belt belt that thatplots plotsininJensen's Jensen's(1976) (1976)field fieldofofbasaltic basaltickomatiite komatiite(Fig. (Fig.23) 23)isisassociated associated with with altered alteredrocks rocks inner (see below) and may may have have undergone incipient magnesian magnesian alteration. A sample sample (from (from the One One Otter-Banana Otter-Banana (see alteration. A area) area) that thatlies liesininthe thefield fieldofofcalc-alkaline calc-alkalineandesites, andesites,persistently persistentlyshows showsanomalous anomalousgeochemistry geochemistrywith withrespect respect toother othermafic maficrocks rocks in in the theManitouwadge Manitouwadge belt. belt. Hornblende-magnetite-garnet Hornblende-magnetite-garnet rocks rocks and magnetite magnetite quartzites quartzites to in the the Dead Dead Lake Lake suite, suite, and and aasingle single sample sample from the outer volcanic belt, Ti02, in belt, have have distinctive distinctive high high FeOt FeO and Ti02, and andlow lowMgO MgO contents contents(Figs. (Figs.23, 23,24). 24). Felsic volcanic volcanic rocks and synvolcanic trondhjemite are are transitional transitionalcaic-alkaline calc-alkalineto totholeiitic tholeiiticrhyolites rhyolitesand and Felsic dacites (Fig. (Fig.23), 23),mostly mostlycontaining containing65—80 65-80 percent quartz-phyric dacites percentSiO2 Si02(Fig. (Fig.24). 24). In In terms terms of of Al-(Fet+Ti)-Mg, Al-(Fe+Ti)-Mg, quartz-phyric felsic rocks show a somewhat wider compositional range that could be be due dueto to aa mafic mafic component component in in heterolithic heterolithic felsic that could breccias, breccias, and/or and/or incipient incipient alteration. alteration.The Thenarrow narrowcompositional compositionalrange rangeofofsynvolcanic synvolcanic trondhjemite trondhjemite in in the the 34 �Inner volcanic volcanic Felsic Felsic rnetavolcanic metavolcanic rocks rocks Quartz—phyric felsic rocks Quartz-phyric felsic Trondhjemite—granodiorite Trondhjemite-granodionte Mafic metavolcanjc rocks Mafic metavolcanic rocks Hornblende—magnetite—garnet Hornblende-magnetite-garnet rocks/magnetite rockslmagnetite quartzite quartzite belt belt (JVB) (IVB) 9 (2) (2) (6) (6) (8) (6) • •+ rn (6) •(6) Outer volcanic volcanic belt belt (OVB) (OVB) l @ Dead Lake Dead Lake (DL) (DL) One Otter— OtterBanana (OB) Banana (OB) Eastern extension (E) (E) extension Jim-Davis Jim—Davis (JD) (JD) Noranda suite suite (3) (3) (7) 0(7) .(1) e (1) 0 o (7) (7) •t) (5) (5) 13 (2) (2) (4) 4v 4 • (1) (1) • (3) (3) 0 6 (1) 0(3) 0 (3) rn (3) • (3) Gq CD jq '1 CD CD a4. 0 CD CCD 01 e e LEGEND Metasedimentary rocks Orthoamphibole-cordierite-garnet gneiss 0Intermediate to mafic metavolcanic rocks --- ----- Fold axial trace Fault FIG. 22. associated geochemical geochemical samples in in the t h eManitouwadge Manitouwadge greenstone greenstone FIG. 22. Locations Locations ofof metavolcanic metavolcanic and and associated The key key shows shows tthe h e symbols symbols used rock types types and and geographic geographic areas, and the the number number belt. The belt. used to to represent represent rock areas, and of samples samples is is in in parentheses. parentheses. Locations Locations of of samples samples analysed analysed by by Noranda Noranda Inc., Inc., all all from from the t h e inner inner volcavolcaof belt, are a r enot notshown. shown.'2'2pts' pts' indicates 2 samples f r othe m t same h e same location. Swill-Mills Lakes Lakes area area nic belt, indicates 2 samples from location. TheThe Swill—Mills most westerly westerly samples samples in in the the outer outervolcanic volcanic belt. belt. encompasses the t h e 33 most (see text) encompasses CD 0 CD E a '1 �__ Geochemistry Geochemistry Manitouwadge greenstone belt Fet+Ti Fe+Ti Fet+Ti A49 \ \ \ rhyolule Al \ \ docite V \ high—Mg \ \ thoisili. \ ' andesite V c&c—alkaline calc-alkaline bosailic komotlite \ ' \ \bOZOif \J • Mg Al A1 Mg rhyolite docite V \ \ high—Mg \ tholeilie \ \ ondesite V catc—olkalirie calc-alkaline basaltic komotlite ' \basait \/ V Mg FIG. 23. and associated associated rock rock compositions compositions in in terms of Jensen's (1976) 23. Metavolcanic Metavolcanic and (1976) definition definition of tholeiitic rhyolite to to basalt, basalt, and basaltic komatiite, based based on on Al-(Fet+Ti)-Mg Al-(Fe+Ti)-Mg (cation tholeiitic and and calc-alkaline calc-alkaline rhyolite (cation to be mobile during sea-floor sea-floor alteration alteration and regional metamorphism. Symbols %), elements elements less likely to Symbols %), as as in in Figure Figure 22. 22. The Thefields fieldsofofquartz-phyric quartz-phyric felsic felsic rocks rocks (dotted), (dotted)>and and innerinner- (dash-dot) (dash-dot) and andouterouterbelt (dashed) (dashed) mafic mafic rocks rocks are outlined outlined as as in in Figure Figure 24. 24. The Thesamples samplesare aredivided dividedbetween between 22 plots plots to to minimize minimize overlap. overlap. volcanic belt tends tends totoencompass, encompass,or ornearly nearlyso, so,analyses analysesofofsimilar-looking similar-lookingrocks rocks from from the theDead DeadLake, Lake, inner volcanic areasl suggesting suggesting aa comagmatic comagmatic relationship. relationship. Some Sometrondhjemite trondhjemite Otter-Banana, and andJim-Davis Jim-Davis Lakes Lakes areas, One Otter-Banana, samples in in the the vicinity vicinity of of the Dead Dead Lake Lake suite tend to to have have high FeOt and Ti02 Ti02 contents, contents,intermediate intermediatebetween between samples that of of hornblende-magnetite-garnet hornblende-magnetite-garnet rockslmagnetite that rocks/magnetite quartzites and inner-belt trondhjemite, consistent with with contamination. contamination. Mafic rocks distinguished from Mafic rocks in in the inner volcanic belt belt can be distinguished from felsic felsicrocks rockson onthe the basis basis of of Ti02 Ti02 and FeOt content, content, with with mafic mafic rocks rocks having TiO2>l% and FeO>10%, F'eOt>lO%, and and felsic felsic rocks rocks having having Ti02<0.4% FeO Ti02>1% and Ti02<0.4% and FeO<8% FeOt<8%(Fig. (Fig.24). 24).AAsingle singlefelsic felsicsample samplewith with Ti02=1.36% Tio2=1.36%isisaamicaceous micaceousquartz-phyric quartz-phyric heterolithic heterolithic breccia. breccia. The The majority majorityof ofquartz-phyric quartz-phyricfelsic felsicrocks rocks have have Ti02 Ti02between between0.27 0.27 and and0.39%. 0.39%. 'Unaltered1felsic felsic extrusive extrusive rocks rocks in in the theManitouwadge Manitouwadgebelt belthave haveundergone undergoneextensive extensivealkali alkaliexchange, exchange, 'Unaltered' Na20 and andCaO CaOcontent content(Fig. (Fig.25). 25).Quartz-phyric Quartz-phyricfelsic felsicrocks rocks are areprepreresulting in wide wide variations in K20, Na20 resulting potassic. In In contrast, contrast, synvolcanic synvolcanic trondhjemite is sodic and has a relatively relatively restricted restricted range of dominantly potassic. CaO, consistent consistent with with limited limitedsecondary secondary redistribution. redistribution. Trondhjemite Trondhjemitesamples samplesnear nearthe theDead DeadLake Lake alkalis and CaO, suite extend hornblende-magnetite-garnet extend to tomore morecalcic calciccompositions, compositions,again againsuggesting suggesting contamination contamination by by hornblende-magnetite-garnet rockslmagnetite quartzites quartziteswhich whichgroup groupwith withmafic maficmetavolcanic metavolcanicrocks. rocks. rocks/magnetite Chondrite-normalized REE in mafic rocks volcanic belts that are are Chondrite-normalized rocks in in the the inner inner and outer volcanic belts define define patterns patterns that have slightly elevated light REE, REE, with with weak weak negative or positive Eu anomalies anomalies (Fig. 26). 26). The The relatively flat or have haahigher higherlight lightREE REE levels (11-40 x chondrite) than than the theouter outerbelt belt(6—2 (6-255xxchondrite). belt has inner belt levels (11—40 chondrite). The lowest light REE REE contents contentsin inthe theouter outerbelt beltare areiningabbroic gabbroicrocks rocksand andsamples samplesfrom fromthe theSwill-Mills Swill-MillsLakes Lakes area, area, again again light possibly reflecting reflecting a sampling bias. Heavy REE levels levels in are nearly nearly identical. identical. possibly in both belts are In In contrast contrasttotomafic maficrocks rocksfrom fromthe theinner innerand andouter outervolcanic volcanicbelts, belts,which whichshow showconsiderable considerablecompositional compositional overlap, REE patterns patterns define define two two distinct distinct suites suites of of felsic felsic volcanic volcanic rocks. REE abundance abundance in in two two overlap, rocks. The total REE samples of of northernmost northernmost outer-belt outer-belt aphyric aphyricfelsic felsicrocks rocks isis relatively relatively low, low, and normalized REE REE define define a steeply samples sloped La/Yb == 8) sloped pattern from from light light to to heavy heavy (normalized (normalized LaIYb 8) and aa moderately moderately negative negative Eu anomaly anomaly (Eu/Eu* (EuIEu* == 0.65—0.83) 0.65-0.83) (Fig. (Fig. 27). 27). Zr/Y, ZrIY,which whichgenerally generallymimics mimics the the light light to toheavy heavyREE REEslope slope(Lesher (Lesheretetal., al.,1986), 19861,isis high at at 32—44. 32-44. REE outer-belt felsic felsic rocks are typical of barren (not (not mineralized) mineralized) high REE and and Zr/Y Zr/Y in northernmost outer-belt felsic volcanic volcanic suites Wabigoon and Abitibi Abitibi subprovinces subprovinces (ibid.). AAsingle singlesample sampleofoffelsic felsic breccia, breccial felsic suites in in the Wabigoon interleaved with with mafic mafic rocks rocks in in the theSwill-Mills Swill-Mills Lakes area, has REE REE contents contents between between those those of of felsic felsic rocks rocks in interleaved the inner inner and andouter outerbelts. belts.Inner-belt Inner-beltfelsic felsicrocks, rockslincluding includingboth bothvolcanic volcanicrocks rocks and and subvolcanic subvolcanic trondhjemite, trondhjemite, the 2.34.9)1 more more are characterized characterized by higher higher total REE, REE, moderately moderately sloping sloping patterns (normalized (normalized LaIYb are La/Yb == 2.3—4.9), 36 �Geochemistry Geochemistry Manitouwadge greenstone belt belt hO, 0.1 0.5 1.0 80 0 0 •0 70 0 0 m a. C,) 60 60 - Inner Inner volcanic volcanic belt belt(IVB) (IVB) Quartz—phyric Quartz-phyric felsic felsic metavolcanic rnetavolcanic rocks rocks (9) (9) - - Mafic Maf~cmetavolcanic rnetavolcan~crocks rocks (9) (9) Outer Outer volcanic volcanicbelt bell(OVB) (OVB) _— Mafic Mafic metavolcanic rnetavolcanic rocks rocks (7) (7) , ---- .- (• I I , I , , I I I ,-\ ' / — 50 50 - & -- - l l l l 31 '; l 20 00 0 - FIG. 24. Si02and andFeOg FeOt (weight (weight %) 24. Si02 %) as as functions functions of of Ti02 T i 0 2(weight (weight%, %, logarithmic logarithmic scale). scale), Mafic Maficand andfelsic felsicrocks, rocks,especially especially in in the the inner inner volcanic volcanicbelt, belt, can canbe bediscrimdiscriminated inated on on the the basis basis of of Ti02 T i 0 2abundance, abundance, aa valuable valuable observation as as Ti02 T i 0 2isisrelatively relatively immobile immobile during alteration alteration and and metamormetamorphism. phism. Symbols Symbolsas as in Figure 22. The The outoutlined lined sample sample fields in this and and other other plots plots are are intended intended as as aa visual visual aid, aid, without without stastatistical tisticalsignificance. significance. a 0a, ---- U- ,, @c 10 0 U 0 S • a S 0•00 • S 0 0.1 hO2 0.5 1.0 K20 FIG. FIG. 25. 25. CaO-K20-Na20 CaO-K20-Na20 (weight (weight %) %) proportions. proportions. The The compositional compositional variation variation of ofquartz-phyric quartz-phyric felfelsic sic rocks rocks (dotted (dotted field) field) suggests suggests alkali alkali exchange exchange dominated dominated by by potassic potassic alteration. alteration. TrondhjemiteTrondhjemitegranodiorite (symbols (symbols as in Fig. Fig. 22) 22) has has aarelatively relatively granodiorite restricted restricted range range of ofsodic sodiccompositions. compositions. HornblendeHornblendemagnetite-garnet magnetite-garnet rocks rocks and and magnetite magnetite quartzites quartzites lie lie with with calcic calcicmafic maficrocks. rocks. Ca 37 Na20 �Geochemistry Geochemistry Manitouwadge greenstone belt FIG. 26. 26. Chondrite-normalized Chondrite-normalized rare earth earth element element (REE) (REE) abundances abundances in in mafic mafic metavolcanic metavolcanic rocks. The The positive Eu anomaly in the the inner inner volcanic volcanic belt belt isisdedefined by a single fined by single sample; all others have have nearly nearly fiat flat or weakly negative Eu/Eu*. Eu/Eu*. Gd weakly negative Gd was was interpolated interpolated asassuming a linear distribution distribution between between normalized normalizedSm Sm and Yb. (Tb (Tbwas wasnot notused usedbecause because of ofits itsrelatively relatively high detection limit). limit). Normalization Normalizationvalues valuesare arethose those of Taylor and McLennan McLennan (1985). (1985). ID v d.t.clion dd.clian datactlan limit limit ilmil limit - 0Inner Inner volcanic volcanic belt—mafic belt-mafic rocks (6) (6) Outer (7) Outer volcanIc volcmic belt—maflc belt-mark rocks (7) • U 5 Z 0E a 0 U .0 — 0>. I a E — .0 >- ..j too FIG. 27. 27, Chondrite-normalized Chondrite-normalized REE abundances abundances in felsic rocks. Normalfelsic metavolcanjc metavolcanic and subvolcanic subvolcanic rocks. Normalization values and interpolated Gd Gd as as in in Figure Figure 26. 26. 10 Inner volcanic volcanic belt. belt Foliated trondhjemite Quartz—phyrlc felsic rocks (8) Quartz-phyric felslc (6) Aphyrlc felsic (2) Aphyric telsic rocks (2) Outer volcanic volcanic belt belt Aphyrlc felsic rocks (2) Aphyric felsic (2) - - doteelian ----- limIt - Swill-Mills Lakes Lakes felsic (1) — felsic breccia breeds (I) Swill—Mills d O "- LL zV i , ? , z f & 2 G : e 3 pronouncednegative negativeEu Euanomalies anomalies(Eu/Eu* (Eu/Eu8= = 0.20-0.58), and andZr/Y Zr/Yfrom from1.7—11. 1.7-11. Quartz-phyric Quartz-phyricfelsic felsicsamples, samples, pronounced 0.20—0.58), three lenses lenses in in close close proximity to to massive massive sulphide deposits deposits (Fig. (F'ig. 4), 41,form formaacoherent coherent collected from each of the three compositionally similar to synvolcanic trondhjemite (Fig. 27). On On the thebasis basisof of similarity similarity in in composition composition group compositionally and age, age, the the trondhjemite trondhjemiteisisinterpreted interpretedtotohave havebeen beenaareservoir reservoirfor forquartz-phyric quartz-phyric felsic felsic volcanism. volcanism. In In general, general, and inner-belt felsic felsicrocks rocks are aregeochemically geochemically comparable comparableto tofelsic felsic volcanic volcanic suites suites associated associatedwith withmassive massivesuiphide sulphide inner-belt mineralization in in the theWabigoon Wabigoon (Sturgeon (Sturgeon Lake Lake area), area), Abitibi Abitibi and andUchi Uchi subprovinces subprovinces (Lesher (Lesher et al., al., 1986), 1986), in in mineralization particular particular in in the themagnitude magnitudeofofnegative negative Eu Euanomaly. anomaly. Altered Altered rocks rocks In concordance Manitouwadge, In view view of of the theunusual unusualextent extentand and concordanceofofaltered alteredrocks rocksat at Manitouwadge,especially especially orthoamphibole-bearing rocks, rocks, geochemistry geochemistry was applied in order order to todefine define compositional compositional trends trendsassociated associated orthoamphibole-bearing with alteration, alteration, to totest testthe theconsistency consistencyofofour ourfield fieldidentification identification of of probable probable protoliths, protoliths, and and to tocompare compare with compositions of altered and and unaltered unaltered rocks rockswith withthose thosereported reportedfrom fromsimilar similarand anddissimilar dissimilargeological geologicalsetsetcompositions tings. In Inthis thisdiscussion, discussion,'alteration' 'alteration'and and'protolith' 'protolith'imply implytheir theirpremetamorphic premetamorphicequivalents equivalents and, and,although although tings. some element element mobility is likely likely during metamorphism, this is is presumed presumed to to have have occurred occurred on onaalocal localscale, scale, some not significant significant to to the the discussion discussion here. here. Altered Altered rocks rocks are are compared compared with with unaltered unaltered or or 'least' 'least'altered alteredvolcanic volcanic not rocks sampled in the the inner inner volcanic volcanic belt belt on on the thesouthern southernlimb limband andininthe thehinge hingeregion regionofofthe theManitouwadge Manitouwadge rocks synform. Samples Samples representing representing synvolcanic synvolcanic alteration, including including orthoamphibole-cordierite-garnet gneiss gneiss and synform. sillimanite-biotite-cordierite interlayers, interlayers,as aswell well as sillimanite-muscovite-quartz sillimanite-muscovite-quartz schist and associated quartzite, sillimanite-bjotite-cordjerite quartzite, were collected collected in the Wiliroy-Geco Willroy-Geco area. The Thesample samplesuite suitewas wassupplemented supplemented by bywhole-rock whole-rock major-element major-element were analyses made available by km north north of of the the analyses by Noranda Noranda Inc., extending extending from from the the Willroy Wiliroy 215 2/5 deposit deposit to about 11km axial trace trace of of the theManitouwadge Manitouwadgesynform synform (Fig. (F'ig. 4). 4).Orthoamphibole-bearing Orthoamphibole-bearingrocks rocksand andsillimanitic sillimaniticinterlayers interlayers axial 38 �Geochemistry Geochemistry Manitouwadge Manitouwadge greenstone belt belt Ti0, 0.1 80 * * * * A * + A + +A . 70 A ** N 0 (I) 1.0 0.5 o. Unaltered arid least altered and 'least' altered rocks rocks Quartz—phyrio felsic znetavolcanic Quartz-phyric felsic metavolcanic rocks (9) (9) o0 Felsic F e h c metavolcanic metavolcanic rocks rocks (2) (2) 60 — - .. Mafic metavolcanic -----Mafic metavolcanic rocks rocks (9) (9) a0 Slightly Slightly altered altered pillowed pillowed rocks rocks (1) (1) • t - + A A AA ,-, A A S. / iA Metamorphosed Metamorphosed altered altered rocks rocks * Sillimanite—muscovite—quartz Sillimanite-muscovite-quartz schist (8) (6) * ,' a, Orthoamphibole—cordierite—garriet Orthoamphibole-cordierite-garnet gneiss gnelss A A Orthoarnphibole—bearing. Orthoamphibole-bearing, Geco—Willroy Geco-Willroy (a) (8) A A Orthoamphibole—bearing. Orthoamphibole-bearing. Nama Nama Creek—west Creek-west (4) (4) 50 50 - , ++ Sillimanitic Sillimanitic interlayers interlayem (7) (7) I , , I I , , ( , , , , ,, \ .,', AA /,/ + ! '\, i i \', .', \'\ +A \ A ----<.------7-A - 20 20 - - A + + AA ) FIG. FIG. 28. 28. Si02 Si02and andFeOg FeOt(weight (weight %) %) as as functions of Ti02 Ti02 (weight (weight % % logarithmic logarithmic scale) scale) for samples samples from from the the inner inner volvolcanic canic belt. Ti02 Ti02abundance abundancein inunaltered unaltered or 'least' 'least' altered alteredrocks rocksdefines defines aa bimodal bimodal population population corresponding corresponding to felsic felsic and and mafic rocks. rocks. The The bimodal bimodal distribution distribution isis mimicked by altered rocks. rocks. The Thefields fields for for quartz-phyric quartz-phyric felsic felsicrocks rocks and andmafic maficrocks rocks are are from from Figure Figure 24. 24. A A..A I 0a) A A 10 + * A + -IA A +1 + 0 0 0.1 I 0* *-• Ti02 0.5 1.0 in the area represented by the Noranda in the theWillroy-Geco Willroy-Geco area are are mostly mostly intensely intensely altered, whereas whereas the represented by Noranda suite suite includes includes transitional transitional or or incipient incipient alteration. alteration. Both Both orthoamphibole-bearing orthoamphibole-bearingrocks rocksand andsillimanitic sillimaniticinterlayers interlayers have bimodal distributions distributions of of Ti02 Ti02 content content similar similar to to that thatofofmafic maficand andfelsic felsic rocks, rocks, suggesting suggesting that Ti02 Ti02was wasrelatively relatively immobile immobile during alteration and and that, that,ininmost mostcases, cases,the theprotolith protolithof ofaltered altered rocks rocks can can be be inferred inferred from Ti02 abundance (Fig. 28). In In low low Ti02 rocks (<0.5%), Ti02 Ti02 shows shows aa negative negative correlation correlation with Si02 Si02 that that could could be beinterpreted interpretedasasa adifferentiation differentiation rocks trend. of samples sampleswith with TiO2<O.1% Ti02<0. 1% suggests suggests either either Ti02 Ti02 loss and/or, and/or, trend.However, However,the thehigh highSi02 Si02content content(75—81%) (75-81%) of silicic alteration alteration accompanied accompaniedby by volume volume increase increase and and dilution dilution of of Ti02. Ti02.FeOt FeOtininmafic, mafic,felsic felsicand andaltered alteredrocks rocks silicic shows the same bimodal distribution as Ti02, and the the Fe0 FeOtcontent contentofofaltered alteredrocks rocksisisgenerally generallysimilar similar to, to, or or shows Ti02, and slightly slightly higher, higher, than than that thatofof'least' 'least'altered alteredrocks. rocks.These Theseobservations observationsare areconsistent consistentwith withfield fieldidentication identicationofof protolith, schist, protolith,that thatis,is,felsic felsicvolcanic volcanicrock rockfor forsillimanite-muscovite-quartz sillimanite-muscovite-quartz schist,and andinterlayered interlayeredfelsic felsicand andmafic mafic rocks for for orthoamphibole-cordierite-garnet orthoamphibole-cordierite-garnet gneiss. gneiss. Interestingly, Interestingly, the distribution distribution of of orthoamphibole-bearing orthoamphibole-bearing rocks layers orthoamphibole-cordierite-garnet gneiss gneiss is apparently apparently not not determined determinedby by layers and and sillimanitic sillimaniticinterlayers interlayers in in orthoamphibole-cordierite-garnet protolith. protolith. The alteration alterationtrends trendscan canbebesummarized summarizedbybyviewing viewingcompositions compositions of of 'least' 'least' altered alteredand andaltered alteredrocks rocks The (FeOt+MgO)-(A1203/2)-(K20)-(Na20+CaO) tetrahedron (Fig. (Riverinand andHodgson, Hodgson, in an an 'unfolded' 'unfolded' (Fe0+Mg0)-(Al203/2).(K20)-(Na20+Ca0) in tetrahedron (Fig. 29)29) (Riverin 1980; Luff Luff et al., 1992). 1992). The Themobility mobilityof of alkalis alkalisin in felsic felsic rocks is apparent apparent from from their their wide widecompositional compositionalrange range 1980; Sillimanite-muscovite-quartzschist schistshows showsconsiderable considerableoverlap overlap in projections projections showing showingK20-(Na20+CaO). K20-(Na20+CaO).Sillimanite-muscovite-quartz in with felsic felsic rocks, rocks, but but also alsoextends extendsto toproportionately proportionatelymore more(Fe0 (FeOt+MgO)-rich andAl203-rich A1203-richcompositions. compositions. with +MgO)-rich and 'Least' altered alteredmafic maficrocks rocksdefine defineaarestricted restrictedcompositional compositionalrange. range.Orthoamphibole-cordierite-garnet Orthoamphibole-cordierite-garnetgneiss gneiss 'Least' has proportionately proportionately higher higher (FeOt+MgO) (F'eOt+MgO) and Al203, A1203, and and lower lower (Na20+CaO), (Na20+CaO), than than 'least' 'least'altered alteredrocks. rocks. has (I?eOt+MgO)/A1203, the Orthoamphibole-bearing rocks and sillimanitic sillimanitic interlayers interlayers are mainly different different in Orthoamphibole-bearing in (Fe0 +MgO)/Al2 03, the latter latter being beingslightly slightlymore morealuminous. aluminous. Transitional Transitional altered altered rocks, rocks, mainly mainly from the the area area northwest northwest of of the the 39 �Geochemistry Geochemistry Manitouwadge Manitouwadge greenstone greenstone belt belt Na20+CaO Unaltered and and 'least' 'least" altered altered rocks rocks Unaltered A Average alteration trends, Average alteration trends, Noranda Noranda camp camp / \ / \ Millenbach quartz—feldspar quartz-feldspar porpi porphyry Millenbach - ---------Millenbach andesite andesite - Millenbach -.-.-.-.-.-.- \ / / \ Quartz—phyric telsic rnetavolcanic Quartz-phyric felsic metavolcanic rocks rocks (9) (9) oo Felsic Felsic u,etavolcanic metavolcanic rocks rocks (2) (2) r Mafic metavolcanic metavolcanic rocks rocks(8) (81 -_-Mafic Slightly altered alteredpillows pillows (1) (1) Slightly Metamorphosed Metamorphosed altered altered rocks rocks * * Sillimanite—muscovite—quartz Sillimanite-muscovite-quartz schist schist (6) (6) . Orthoamphibole—cordierite—garnet Orthoamphibole-cordierite-garnet gneiss gneiss - FeO+ Na20+CaO -willrOY(8) Orthoamphibole—bearing. Geco—Willroy @) Creek-west (4) Orthoainphibole—bearing, Name Creek—west Sillimanitic interlayers (7) Al K20 20 3/2 Na20+CaO FIG. FIG.29. 29.Unfolded Unfoldedtetrahedron tetrahedronshowing showingcompositional compositional trends trends (molar (molar proportions) proportions) associated associated with withununaltered, altered,'least' 'least'altered, altered,and andaltered alteredrocks. rocks.Orthoamphibole-bearing Orthoamphibole-bearingrocks rocksfrom fromthe theWillroy-Geco Willroy-Geco area area (filled (filled triangles) triangles) are are generally generally more more intensely intensely altered than than those those west west of of the the Nama NamaCreek Creek deposit deposit (open (open triangles). triangles).The Thefields fieldsofoforthoamphibole-bearing orthoamphibole-bearingrocks, rocks,quartz-phyric quartz-phyricfelsic felsicrocks rocksand andmafic maficrocks rocksare are outlined. outlined.Average Averagealteration alterationtrends trendsfor forthe theMillenbach Millenbachandesite andesite(dashed) (dashed)and andquartz-feldspar quartz-feldsparporphyry porphyry (dash-dot) (dash-dot)are areshown shownfor forcomparison comparison(analyses (analysesfrom from Table Table 3, 3, Riverin Riverin and and Hodgson, Hodgson, 1980). 1980). The Theform form of of the theplot plotisisbased basedononRiverin Riverinand andHodgson Hodgson(1980) (1980)and andLuff Luffetetal. al.(1992). (1992). Nama NamaCreek Creekdeposit, deposit,tend tendtotohave havecompositions compositionsbetween betweenmore morealtered alteredWillroy-Geco Willroy-Geco rocks and 'least' 'least' altered altered rocks, rocks,in insome somecases, cases, overlapping overlapping with 'least' 'least' altered alteredrocks. rocks.Alteration Alterationtrends trendsfor forthe theMillenbach Millenbachandesite andesiteand and quartz-feldspar porphyritic porphyritic rhyolite rhyolite associated associated with with alteration alterationpipes pipesininthe theMillenbach Millenbachmine mine(analyses (analysesfrom from quartz-feldspar Table Riverinand andHodgson, Hodgson,1980) 1980)are areshown shown for for comparison. comparison. Although Although alteration alterationzones zonesatatMillenbach Millenbach Table33ofofRiverin are aremuch muchsmaller smallerininextent extent(100's (100'sofofmetres), metres),compositional compositionaltrends trendsgenerally generallycorrespond correspond to to those thoseof ofaltered altered and'least' 'least'altered alteredrocks rocksatatManitouwadge. Manitouwadge.The Themost mostintensely intenselyaltered alteredfelsic felsicrocks rocksatatboth bothManitouwadge Manitouwadge and andMillenbach Millenbachare areconsiderably considerablyhigher higherin in(FeOt+MgO) (FeOt+MgO)and andA1203 AlaOathan thanchloritic chloriticand andsericitic sericiticaltered alteredquartzquartzand feldspar feldsparpyroclastic pyroclasticrocks rocksfrom fromthe theBrunswick BrunswickNo. No. 12 12deposit deposit of of the the Bathurst Bathurst camp camp(compare (compareFig. Fig.1515ofofLuff Luff etetal., al.,1992). 1992). termsofofAFM AFM(Fig. (Fig. 30), compositions of orthoamphibole-bearingrocks rocksfrom fromManitouwadge Manitouwadge InInterms 30), thethe compositions of orthoamphibole-bearing mostly cordierite-anthophylliterocks rocksderived derivedfrom fromaltered alteredvolcanic volcanicprecursers, precursors,asas mostlylie lieininthe thefield fielddefined definedbybycordierite-anthophyllite compiled by by Reinhardt Reinhardt(1987). (1987).Reinhardt's Reinhardt'sfield fieldofofevaporatic evaporaticclays claysand andmagnesian magnesianpelites, pelites,which whichencomencomcompiled passescordierite-anthophyflite cordierite-anthophyllite metasedimentary metasedimentary rocks rocks from from the the Rosebud Rosebud syncline, syncline, Australia Australia isis restricted restricted toto passes Cordierite-anthophylliterocks rocksfrom fromthe theHemlo Hemlogreenstone greenstone belt, belt, interpreted interpreted to tobe bethe the MgO/(MgO+FeO)>0.7. Cordierite-anthophyllite MgO/(MgO+FeO)>0.7. metamorphic metamorphicequivalent equivalentofofimmature immatureclastic clasticsedimentary sedimentaryrocks rocksderived derivedfrom fromaamafic-ultramafic mafic-ultramaficsource source(Pan (Pan etetal., al.,1991), 1991),are arepredictably predictablyindistinguishable indistinguishablefrom fromaltered alteredvolcanic volcanicrocks. rocks. 40 �Discussion Discussion Manitouwadge greenstone belt A plot of oforthoamphibole-bearing orthoamphibole-bearing alalFIG. 30. 30. AFM plot tered rocks at Manitouwadge. Manitouwadge. An An additional additional sample sample tered shown) lies at at negative negative FM FM proportions. proportions. The The (not shown) AFM values (molar proportions) proportions) are are calculated calculated after after the the method methodof of Reinhardt Reinhardt(1987) (1987)ininwhich; which; A=Al203—(Na20+K20+CaO), A=A1203-(Na20+K20+CaO), FFeO —6(1—m)K20, F=FeOt -6(l-rn)K20, F M £A ManiLouwadge orthoamphibole—bearing rocks (11) Manitouwadge orthoamphibole-bearing ( 1 1) + Hemlo Hemlo belt, belt, cordierlte—anthophyllite cordierlte-anthophyliite rocks rocks (5) (5) M=MgO—6mK2O, M=MgO-6rnK20, and and m=MgO/(MgO+FeOt )wholerock. m=MgO/(MgO+FeOt)who~erock. The calculation attempts to 'correct' calculation scheme scheme attempts 'correct' for for oxoxides present present in biotite biotite and and feldspars, feldspars, assuming assuming that MgO/(MgO+FeOg) MgO/(MgO+FeOt) of biotite can be approximated approximated by by the value value of of the whole whole rock. rock. Reinhardt's Reinhardt'sfields fieldsof of alaltered volcanics, volcanics, and evaporitic evaporitic clays clays and and magnesian magnesian pelites are are shown shown for for comparison, comparison, as as are are five five analyanalyses ses of cordierite-anthophyllite cordierite-anthophyllite metasedimentary metasedimentary rocks rocks from the the Schreiber-Hemlo Schreiber-Hemlo greenstone belt belt (from (fromTable Table 2, Pan Pan et et al., al.,1991). 1991). DISCUSSION DISCUSSION Depositional setting and suiphide deposits and alteration and deformation deformation of of massive sulphide alteration zones zones When the presence area is is taken taken into account (Figs. 4 presence of the D1 Dl fault that that dissects dissects the theWillecho-Geco Willecho-Geco area and 21), relationships to to stratigraphic 21), alteration alteration zones zones and and orebody orebody types types at at Manitouwadge Manitouwadge have systematic relationships level, despite remaining ambiguities about detailed correlations of of some some mineralized mineralizedhorizons. horizons. Cu Cu stringer stringer and disseminated orebodies orthoamphibole-cordierite-garnet orebodies (Wiliroy (Willroy 11and 6, 6, and and Geco Geco 4/2 412 zones, zones, Table 3) lie in orthoamphibole-cordierite-garnet gneiss of of the footwall alteration zone. zone. The Theenveloping enveloping Geco Geco main stringer zone zone lies higher in the the stratigraphy, stratigraphy, linking the largest main orebody, and possibly possibly the 8/2 812 Zn Zn zone, zone, with with footwall footwall alteration. These These zones zones have have features features characteristic characteristic of ofsubsurface subsurfaceconduits conduitsfor formineralizing mineralizingfluids fluids and and may maymark markthe thelocations locationsofoffocussed focussed cross-stratal that supplied cross-stratal flow flow that supplied deposits deposits higher in the the stratigraphy. stratigraphy. Zn-Cu-(Pb) Zn-Cu-(Pb)orebodies orebodiesassociated associated with with iron Willecho Gecomain mainorebody orebodyand and8/2 812ZnZnzone, zone,Nama NamaCreek Creekand and Willecho1—3) 1-3) are are iron formation formation(Willroy (Willroy2,2,33and and5,5,Geco sea-floor sea-floor precipitates precipitates or or near-sea-floor near-sea-floor replacement deposits. This Thisgroup, group,representing representingvoluminous voluminousbase-metal base-metal precipitation precipitation and and the thepeak peakofofhydrothermal hydrothermalactivity, activity, includes includes the the largest largest deposits, deposits, the theWillroy Willroy33and andGeco Geco main orebodies. orebodies. The The Cu-to-Zn Cu-to-Zn zoning zoning of the Willroy Willroy 3 orebody orebody toward main toward the hosting iron formation, and the stringer stringer zones zones associated associated with with the theGeco Gecomain mainorebody, orebody,are aresuggestive suggestiveof of proximal deposits centred centred on on areas areas of of hydrothermal upflow. upflow. In In other otherZn-Cu-(Pb) Zn-Cu-(Pb)orebodies, orebodies,possible possibleprimary primaryfeatures, features,such suchasaslayering layeringororzoning, zoning, have not been been reported. reported. However, However, comparison comparison with metal metal ratios ratios in in the theMillenbach Millenbach and and Amulet Amulet orebodies orebodies in in the the Noranda Noranda camp camp (Knuckey (Knuckey et et al., al., 1982), 1982), suggests suggests that their their higher higher Zn/Cu Zn/Cu isisaafeature featureofofdeposition depositionfurther further from the main main area area of of hydrothermal hydrothermalventing. venting. The Theiron-formation-hosted iron-formation-hostedZn-Pb-(Cu) Zn-Pb-(Cu)orebodies orebodies(Willroy (Willroy44and and Geco Geco zincian iron formation) are highest in the stratigraphy stratigraphy and and formed formed during during the thewaning waning of of hydrothermal hydrothermal activity. activity. A sedimentary sedimentary association association for for the thedeposits depositsof of Manitouwadge Manitouwadgebelt belt has hasbeen been previously previouslyemphasized, emphasized,largely largely the assumption assumption that thatthe theManitouwadge Manitouwadgegreywackes greywackes represent a transition transition from from volcanism volcanism to to clastic clastic based on the presence of iron formation and contact (Franklin (Franklin et et al., al., 1981; 1981; sedimentation, and on the presence and quartzites near the contact Friesen et al. et al., al. 1982; 1982;Williams Williamset al., 1990). 1990). Detrital Detritalzircon zirconages agesshow show that thatthe thegreywacke greywackeis is considerably considerably younger the underlying underlying volcanic rocks, unconformity or than the rocks, and and that that the contact is either an unconformity or aa fault. fault. The quartzite silicified felsic volcanic sillimanite-muscovite-quartz schist which it is is is aa silicified volcanic rock, rock, locally locally gradational gradational to sillimanite-muscovite-quartz schist (with which grouped as a map map unit) unit) and andiron ironformation. formation.We Weregard regardall allofofthese theserocks rocksasasthe theproducts productsofofsynvolcanic synvolcanic grouped alteration or or through through precipitation precipitation from from hydrothermal hydrothermal fluids. fluids. hydrothermal activity, either through alteration 'Least' 'Least' altered alteredfelsic felsicvolcanic volcanic rocks rocks atatManitouwadge Manitouwadgehave have all allundergone undergone alkali alkaliexchange, exchange, dominated dominated enrichment in K K and and with withlittle littleeffect effect on onother otherelements, elements,typical typicalofoflow low temperature temperaturesea-floor sea-floor alteration alteration by enrichment (Lagerblad and andGorbatschev, Gorbatschev,1985). 1985).Synvolcanic Synvolcanictrondhjemite trondhjemitewas wasnot notaffected affectedby bywidespread widespreadalkali alkaliexchange, exchange, (Lagerblad despite despite the the local localFe-Mg Fe-Mg alteration alteration near nearcontacts, contacts,asasinferred inferredfrom fromorthoamphibole-garnet orthoamphibole-garnet seams. seams. Similar Similar observations of of alkali exchange in the Abitibi camp, camp, involving involving the sodic Flavrian Flavrian pluton pluton and andits itsmore morepotassic potassic observations comagmatic volcanic volcanic rocks, were were interpreted as as the theresult resultofofsea-floor sea-floorpotassic potassic alteration alterationofofextrusive extrusiverocks, rocks, comagmatic and preservation preservation of of primary primarycompositions compositionsin inthe thesubvolcanic subvolcanicbody body (Goldie, (Goldie,1979). 1979). and The lateral lateraldistribution distributionand andgeochemistry geochemistryof ofsillimanite-muscovite-quartz sillimanite-muscovite-quartz schist suggest these rocks rocks The suggest that these 41 �Discussion Discussion Manitouwadge greenstone belt interacted interacted with with hydrothermal hydrothermalfluids fluidsand andare arenot notsimply simplyaamore moreextreme extremeexample exampleof ofsea-floor sea-floor alkali alkali exchange. In In the Manitouwadge Manitouwadge camp, camp, they they have have been regarded as as a favourable exploration tool indicating indicating proximity to to ore. ore. This reconcile with with the the stratigraphic stratigraphic position This is difficult to reconcile position of of sillimanite-muscovite-quartz schist in in the the hanging hanging wall to orebodies, and of iron iron formation. formation. Locally, the distribution and sandwiched sandwiched between between semi-continuous layers of distribution of thin sillimanitic rocks was was apparently apparently governed governed by by bedding bedding and and is most consistent with sillimanitic layers in tuffaceous rocks sea-floor alteration. The and 66 areas, areas,interpreted interpretedasaszones zonesof ofprobable probablehydrothermal hydrothermalupflow, upflow, sea-floor alteration. The Geco, Geco, Willroy Willroy 11and are an exception exception in that thatsillimanite-muscovite-quartz sillimanite-muscovite-quartz schist schist directly directly overlies overlies orthoamphibole-cordierite-garnet orthoamphibole-cordierite-garnet footwall alteration. The of hydrothermal hydrothermal fluids fluids from from this this area, area, either either footwall alteration. The observations observations suggest lateral percolation percolation of Geochemicallyand andmineralogically, mineralogically,the theschist schistresembles resembles the the in the the subsurface subsurface or or on on the thesea seafloor floorororboth. both.Geochemically muscovite-aluminosilicate suiphide camp (Walford and Franklin, muscovite-aluminosilicate rocks rocks in the the Snow Snow Lake massive sulphide Franklin, 1982; 1982; Zaleski, 1989) and and sericitic sericitic alteration alteration capping capping and peripheral peripheral to chioritic pipes of of Noranda-type Noranda-type deposits deposits (Franklin (Franklin et et 1989) chloritic pipes a!., interpreted as representing al., 1981), interpreted representing the outer cooler cooler parts of of aa hydrothermal hydrothermal system. system. It is is generally generally accepted that thatsubvolcanic subvolcanic intrusions intrusions provide provide the necessary necessary heat for for driving driving hydrothermal hydrothermal systems, and that deposits (Campbell (Campbell et et al., 1981). In the Snow that these these commonly commonly intrude their their own own volcanic volcanic deposits Snow Lake camp, camp, synvolcanic synvolcanicplutons plutonsboth both intrude intrude altered altered rocks rocks produced produced by by their their hydrothermal hydrothermal system, system, and show show Lake evidence of of alteration; alteration; however, the distribution distribution of intrusive contacts contacts (Fig. of alteration alteration zones zones oniy only crudely follows intrusive 11 in in Galley, Galley, 1993). 1993). The very close relationship between between the the trondhjemite trondhjemite contact contact and stratabound close spatial relationship stratabound alteration alteration at at Manitouwadge Manitouwadge is is unusual, unusual, and and the the stratigraphic stratigraphiccontrol controlisisperhaps perhapseven evenmore more pronounced pronounced when when the unaltered unaltered or or weakly weakly altered altered character character of of supracrustal supracrustal inclusions inclusions in trondhjemite trondhjemite is taken taken into into account. account. The semi-concordant contact and supracrustal semi-concordant contact supracrustal septa septa suggest suggest aa sill sillor orlaccolith, laccolith,or ormultiple multiplesemi-concordant semi-concordant intrusions, with alteration along the the upper upper contact. It that the alteration focussed focussed along It is is also also possible possible that the trondhjemite trondhjemiteinvaded invaded deeper parts of of the the hydrothermal hydrothermal system system and and that thatsurviving survivinginclusions inclusions of of altered altered rocks rocks are are not not exposed exposed at at the the surface. Regional semi-conformable alteration alteration zones associated with volcanogenic volcanogenic massive sulphide deposits typically involve involve alkali-exchange, alkali-exchange,silicification silicificationand andepidotization epidotization (Galley, (Galley, 1993), 1993),rather rather than than alkali-depleted Fe-Mg alteration. alteration. Despite Despitethe theunusual unusualextent extentand andconcordance concordanceofofalteration alterationzones zonesatatManitouwadge, Manitouwadge,the thegeochemical geochemical FeOt+MgO and andA1203 A1203and and depletion depletion in in alkalis alkalis trends from 'least-altered' 'least-altered' to to intensely intensely altered, altered, of of increase increase in FeO+MgO and CaO, CaO, are are similar similar to to those those recorded recorded in in alteration alteration pipes pipes in inthe theAbitibi Abitibicamp camp(Riverin (Riverinand andHodgson, Hodgson,1980). 1980). The bimodal bimodal grouping grouping of of altered altered rocks, rocks, defined defined by by 'immobile' 'immobile' element element abundances, abundances,mimics mimicsmafic mafic and andfelsic felsic volcanic precursers. precursers. Orthoamphibole-garnet-cordierite rocks and and sillimanitic interlayers interlayers had had both mafic Orthoamphibole-garnet-cordierite rocks mafic and and volcanic felsic protoliths and the the metamorphic metamorphicassemblage assemblagewas was determined determined by by small smallvariations variationsin in (FeOt (FeOt+MgO)/A1203, +MgO)/Al203, apparently due to alteration alteration and and not not inheritance inheritancefrom from the the protolith. protolith. There Thereisisno noevidence evidence to tosuggest suggest the the prespresence of politic pelitic rocks, although some and local redeposition redeposition of of some layering in altered rocks could reflect reworking and unconsolidated volcaniclastic material. unconsolidated The unusual gneiss at at Manitouwadge may be be partly partly due to the unusual extent extent of of orthoamphibole-bearing orthoamphibole-bearing gneiss Manitouwadge may the high high metamorphic grade. stabilityexpands expands the the range grade. With increasing increasing grade, orthoamphibole-hornblende orthoamphibole-hornblende stability range of of orthoamphibole-bearing assemblages pages 478—489). assemblages to to more morecalcic calcicbulk-rock bulk-rockcompositions compositions(Spear, (Spear,1993, 1993, pages 478-489). By inference, inference, bulk-rock bulk-rock compositions compositionsthat that produced orthoamphibole-bearing rocks rocks at Manitouwadge By Manitouwadge might, at aa lower lower metamorphic grade, be be considered considered incipient alteration. In Inthe thegreenschistgreenschist-and andamphibolite-facies amphibolite-facies metavolcanic rocks of of the Snow zonesofof chloritic chloriticalteration alteration have have aa lateral exmetavolcanic rocks Snow Lake area, semi-continuous semi-continuous zones extent of of up up to totwo twototothree threekilometres kilometres(Galley, (Galley, 1993). 1993). The Theclosest closest analogues analogues for the the stratabound stratabound regional regional orthoamphibole-bearing alteration at orthoamphibole-bearing alteration a t Manitouwadge Manitouwadge are found in in the the Bergslagen Bergslagen area area of ofthe theSvecofennian Svecofennian Baltic shield. At At Bergslagen, Bergslagen, exhalative exhalative base-metal base-metal deposits deposits and and iron ironformation formationare areunderlain underlainby byconformable conformable stratabound Mg-rich of several, several,to toseveral severaltens tensofofkilometres kilometres(Traghrdh, (Trägrdh, stratabound Mg-rich alteration alteration zones zones with a regional extent of Ripa, 1988; 1988; Baker Baker et et al., a!., 1988). Amphibolite-facies Amphibolite-facies metamorphism metamorphism at at Bergslagen Bergslagen may may play play a role, as at 1988; Ripa, Manitouwadge, in facilitating identification identification of of altered altered rocks. rocks. However, However,ininboth bothareas, areas,itit appears appears that alteration alteration was partly focussed focussed on on aquifer aquifer horizons horizonspossibly possibly consisting consisting of of permeable, permeable, poorly poorly consolidated consolidatedvolcaniclastic volcaniclastic deposits. Structural S t r u c t u r a l and a n d tectonic tectonic synthesis synthesis preferred structural structural model model for for the the Manitouwadge Manitouwadge greenstone greenstone belt, and the the adjacent adjacent Quetico Quetico subsubOur preferred province, involves Dl faults (shear (shear zones) zones) are are recognized recognized from the the coincicoinciinvolves four four phases phases of of ductile ductile deformation. deformation. D1 dence of lithological units, repeated mineralized mineralized sequences, sequences, and zones of truncated truncated lithological zones of of straight straight gneiss gneiss interpreted interpreted Although no no sense sense of of kinematics kinematics or or offset offset has been been observed, observed, sequence repetitions, geas annealed mylonite. Although ometries consistent the early early relative relative age age of of D1 Dl structures, structures, suggest suggest thrusting. thrusting. consistent with with low angle angle truncation, truncation, and the Dg planar and linear linear fabrics, fabrics, typically typically defined defined by high grade metamorphic minerals, suggest D2 deDominant D2 formation broadly synchronous synchronous with peak metamorphism. metamorphism. D2 D; shortening shortening resulted resulted in inrepetition repetitionofofthe thevolcanic volcanic formation 'Manitouwadge syncline' on the southern limb limb of of the D3 D3 Manitouwadge Manitouwadge sequence across across the the easterly trending 'Manitouwadge possibly accounts for the presence presence of volcanic volcanic rocks One Otter-Banana Otter-Banana synform, and possibly rocks in in the the Dead Lake and One Lakes 'Manitouwadge syncline' is folded and contains D2 Ds fabrics. Lakes areas. areas. Metagreywacke in in the core of the 'Manitouwadge 42 �Manitouwadge greenstone belt belt Discussion Discussion Temperature (°C) (OC) —,. + Geological Geological Event Event 600 600 > 2720 Volcanism Volcanism and and mineralization mineralization Dl Ductile faults (thrusts) 2700 Erosion? Erosion? *0Q'4y --' . 2680 st. I 2660- / 1 Sedimentation, Sedimentation, distal distal volcanism volcanism Loken Loken Lake Lake pluton, pluton, Black Black Pic Pic diorite diorite D2 D2 D3 D3 D4 Nama N a m e Creek Creek pluton pluton Peak metamorphism metomorphisrn (Manitouwadge (Manitouwadge belt) belt) Peak Black Black Plc Pic monzodiorite monzodiorite Titanite Titanite closure closure Peak Peak metamorphism metamorphism (Quetico (Quetico subprovince) subprovince) Local Local retrograde retrogradeK—metasomatism K-metasomatism Local Local retrograde retrograde hydrothermal hydrothermal activity activity FIG. FIG. 31. 31. Temperature-time Temperature-timeplot plotshowing showingrelationships relationships between between the thedeformation deformationsesequence, quence, metamorphism metamorphism and plutonism plutonism in in the the Manitouwadge Manitouwadge belt belt and andQuetico Queticosubsubprovince. province. Alternative Alternative paths pathsare areshown shownfor forthe theManitouwadge Manitouwadgebelt belt assuming assumingeither, either, unconformable unconformable deposition deposition of sedimentary sedimentary rocks (dashed) or, or, emplacement emplacement by by early early faulting faulting (dash-dot). (dash-dot). Da Manitouwadge Manitouwadge synform, Blackman Lake antiform, and Jim Jim Lake Lake synform, synform, fold the Manitouwadge Manitouwadge The D3 The belt and andthe theWawa-Quetico Wawa-Queticosubprovince subprovince boundary. Relationships Relationships between metamorphic minerals, migmatitic segregations, and deformation fabrics D3 was was broadly broadly coeval coeval with peak metamorphism metamorphism in the the segregations, fabrics suggest suggest that D3 Quetico subprovince. subprovince. Map-scale Map-scale D4 D4 structures structures modify modify the the geometry geometry of D3 Da folds. Quetico folds. The The dominantly dominantly Z-asymmetry D3/D4 folds, folds, and and dextral dextral kinematic kinematic indicators, indicators, are are interpreted interpreted as asaaresponse responsetotoprogressive progressive dextral dextral of the the D3/D4 of transpression. transpression. In In aapreliminary preliminary structural structuralmodel model(Peterson (Petersonand andZaleski, Zaleski,1994a), 1994a),we weproposed proposeda a5-phase 5-phase deformation sequence sequence for Manitouwadge area. The preliminary preliminary model model interpreted the the Blackman Blackman Lake Lake deformation for the the Manitouwadge area. The antiform and and Jim JimLake Lakesynform synform as as D4 D4 structures structures that thatfolded foldedthe theaxial axialtrace traceofofthe theD3 D3Manitouwadge Manitouwadgesynform. synform. antiform Although our our observations observationsstill stillpermit permitthe the5-phase 5-phasemodel, model,ititrequired requiredaamore morecomplicated complicateddeformation deformationscheme scheme Although than thanour ourpreferred preferredsimpler simpler4-phase 4phasemodel. model. The Wawa-Quetico Wawa-Quetico boundary the Manitouwadge Manitouwadge area transitional on on structural structural and andlithological lithological The boundary in the area is transitional criteria. criteria. Firstly, Firstly, there there is is aagradational gradational change change to to the thesouth, south,from fromdominantly dominantlyeast-west east-west structural structural trends, trends, to to map-scale map-scale folds folds with with broader broaderhinge hingeregions; regions;secondly, secondly, Manitouwadge Manitouwadge and and Quetico Quetico metasedimentary metasedimentaryrocks rocks are are indistinguishable. indistinguishable. Zircon Zircon provenance provenance ages ages constrain constrain the themaximum maximumdepositional depositionalage ageofofManitouwadge Manitouwadge metagreywacke to 2693 2693 Ma, at at least least 25 25Ma Mayounger younger than thanthe the2720 2720Ma Mafelsic felsicvolcanism volcanism (Zaleski (Zaleski et al., al., 1994; 1994; metagreywacke D2tectonic tectonic Davis et et al., al.,1994). 1994).The Themetagreywacke metagreywackecontains containsupper upperamphibolite-facies amphibolite-faciesassemblages assemblages and and aaD2 Davis fabric, hence hence the the minimum minimumage age of of deposition deposition can can be be inferred inferred to tobe becirca circa2680 2680Ma Ma(see (seebelow). below). Provenance Provenance fabric, studies on on Quetico Quetico metasedimentary metasedimentaryrocks rockshave have established established age agebrackets brackets of of circa circa2700 2700 to to2688 2688 Ma Ma (Percival (Percival studies and Sullivan, Sullivan, 1988; 1988; Davis et al., al., 1990), 1990), overlapping overlapping the Manitouwadge. In contrast contrast to tothe the and the age brackets brackets at Manitouwadge. detritalzircons zirconsof of Mesoarchean Mesoarchean age recovered recovered from detrital from Quetico Queticorocks rocks(ibid.), (ibid.), at at Manitouwadge, Manitouwadge, the the oldest oldest detrital zircon of of 2719±2 2719zt2 Ma Ma could could be be derived derived from from local local volcanic volcanic rocks. rocks. The The Quetico Quetico studies studies were were done done at atleast least200 200 zircon km west west of of Manitouwadge, Manitouwadge, and both both source source areas areas and and timing timingof of sedimentation sedimentation could could be be expected expected to tovary. vary. km In In the theManitouwadge Manitouwadgebelt, belt,uplift upliftresulting resultingfrom fromD1 Dldeformation deformationcould couldhave havecontributed contributedsediment sedimentsources, sources, although our our field fieldobservations observations are are equivocal equivocal regarding the relationship relationship between D1 Dl and sedimentation. The The although presence of of straight straight gneiss gneiss (annealed (annealed mylonite) mylonite) on D1 Dl thrust faults faults indicates indicates ductile ductile deformation deformation and andsomewhat somewhat presence elevated temperatures. temperatures. Two Twopost-D1 post-Dl pre-D2 pre-Dz time-temperature time-temperature paths pathsare arepossible possiblefor for the theManitouwadge Manitouwadge belt, belt, elevated one assuming assuming erosion erosion and and unconformable unconformable deposition deposition of of sedimentary sedimentary rocks, rocks, the the other otherconsistent consistentwith withtectonic tectonic one emplacement of of an anallochthonous allochthonoussequence sequence by by prepre- or orsyn-D2 syn-Da faulting faulting(Fig. (Fig.31). 31). emplacement A major majorepisode episode of of magmatic magmatic activity activityfrom from 2687 2687 to to 2677 2677 Ma Ma isis indicated indicated by by the theage ageofoffour fourplutonic plutonic A 43 �Manitouwadge greenstone belt References References rocks; Black Black Pic diorite (2687+3/—2 (2687+3/-2 Ma), the Loken Loken Lake pluton (2687+2/—3 (2687+2/-3 Ma), the Nama Nama Creek Creek pluton pluton (2680±3 (2680k3 Ma) and Black Pic monzodiorite (2677±2 (2677k2 Ma). The The first first three threeof of these these are areprepre- to tosyn-D2 syn-D; intrusions, intrusions, and hence, D2 deformation and contemporaneous peak metamorphism is constrained to hence, the the maximum maximum age age of of D2 2680 Ma. Ma. Magmatic activity could could have contributed to metamorphic metamorphic heating. heating. Peak metamorphic thebelt belt (Petersen, (Petersen, 1984; Pan Pan and Fleet, metamorphictemperatures temperaturesofof600—700°C 600-700° ininthe Fleet, 1992) 1992) are are close close to temperature of 600°C closure closuretemperature temperature to the the 700°C 700° closure temperature of the the U-Pb U-Pb system system in monazite, and exceeded the 600° of titanite titanite (Heaman (Heaman and andParrish, Parrish,1991). 1991).Metamorphic Metamorphicmonazites monazitesfrom frommetavolcanic metavolcanic and and altered altered rocks rocks range range in in age Ma(Schandl (Schandietetal., al.,1991; 1991;Davis Davisetetal., al., 1994; 1994;Zaleski Zaleskietetal., a!., 1995), 1995),and and encompass encompass the circa age from from 2675—2669 2675-2669 Ma 2673 Ma Ma titanite ages 2). We ages from the Nama Nama Creek Creek pluton and and Black Black Pic Pic monzodiorite monzodiorite (Table (Table 2). We tentatively tentatively interpret the the titanite titaniteages agesasasthe thetime timeofofregional regionalcooling cooling through 00°C 600°(Fig. (Fig.31); 31);however, however, itit isispossible possible that that the crystallization or the metamorphic metamorphicfluids fluids that thatallowed allowed the the crystallization crystallizationof of monazite monazite were were also also responsible for crystallization resetting of titanite. titanite. Field Fieldobservations observations indicate indicate that thatpeak peakmetamorphism metamorphismand andmigmatization migmatizationin inthe theQuetico Quetico subprovince was synchronous with progressive deformation and and the map-scale folds (D3) (Da) near the the boundary boundary progressive deformation (Peterson and and Zaleski, Zaleski, 1994a). 1994a). Peak Peakmetamorphism metamorphismininthe theQuetico Queticosubprovince subprovincecould couldhave havebeen beencoeval coevalwith with granitic magmatism Ma(Percival, (Percival,1989). 1989).The The regional regional distribution distribution of of metamorphic ages and magmatism at at2670—2650 2670-2650 Ma assemblages is consistent with progressively progressively later development development of peak conditions, conditions, and andincreasing increasinggrade, grade,from from south Maamphibolite-facies amphibolite-faciesmetamorphism metamorphism in in the the Schreiber-Hemlo south to tonorth; north;from from2676—2678 2676-2678 Ma Schreiber-Hemlo greenstone belt (Corfu and Muir, 1989b), 1989b),to to 2680 2680 Ma Ma upper upper amphibolite-facies amphibolite-facies metamorphism metamorphism in in the the Manitouwadge Manitouwadge belt, belt, to to and Muir, 2670—2650 Magranulite-facies granulite-faciesmetamorphism metamorphismininthe the Quetico subprovince (Fig. 2). 2670-2650 Ma 2). A transitional of the Superior transitional boundary boundary between between volcano-plutonic volcano-plutonic and metasedimentary metasedimentary subprovinces subprovinces of Superior Province have been described Province is not unique unique to to the theManitouwadge Manitouwadge area. area. Similar relationships relationships have described between between the Coutchiching metasedimentary rocks in the the Rainy Rainy Lake Lake area areaof of the theWabigoon WabigoonsubsubQuetico subprovince and Coutchiching province et al., 1989), and Kehienbeck (1985)considered consideredthe theBeardmore-Geraldton Beardmore-Geraldtonbelt belt to to be be a strucprovince (Davis et Kehlenbeck (1985) tural tural and and lithological lithologicaltransition transitionzone zonebetween between the theQuetico Queticoand andWabigoon Wabigoonsubprovinces subprovinces(Fig. (Fig.1). 1).Kehienbeck's Kehlenbeck's Beardmore-Geraldton belt beltdeveloped developedthrough throughdeformation deformationinvolving involving the themargins marginsof ofboth both theBeardmore-Geraldton conclusion that the Wawa-Quetico boundary the Manitouwadge Manitouwadge area. area. subprovinces is equally applicable to the Wawa-Quetico boundary in the Wawa-Quetico subprovince west Studies along the Wawa-Quetico subprovinceboundary boundaryindicate indicatethat that itit varies varies in in character. character. To the west Manitouwadge, rocks although in in some some of Manitouwadge, rocks of of volcanic volcanic and and sedimentary sedimentary origin origin are are mostly mostly in in fault contact, although earlier structures can can be be correlated correlated across across the the boundary boundary (Percival, (Percival, 1989). 1989). To To the the east, east,between between the the areas, earlier I),sedimentary sedimentary and andvolcanic volcanicrocks rocks are are apparently apparently (Fig. 2) 2) and and the theLepage Lepage fault faultzone zone (Fig. (Fig.1), Moshkinabi belt belt (Fig. interbedded along the subprovince subprovince boundary variation along-strike along-strike suggests interbedded boundary (Berger, (Berger, 1985). 1985). The variation suggests that that the subprovince boundary Manitouwadge area preserves preserves features subprovince boundary in the Manitouwadge features of of early early ductile ductile deformation deformation that that may lateral transition transition between between the the conformable conformable contact to the east and and fault fault juxtaposition juxtaposition to tothe thewest. west. represent a lateral REFERENCES REFERENCES Arias, Z.G., and and Helmstaedt, Helmstaedt, H., H.,1990: 1990:Structural Structuralevolution evolutionof ofthe theMichipicoten Michipicoten(Wawa) (Wawa) greenstone greenstone belt, belt, an Archean Archean fold fold and andthrust thrustbelt. belt.Ontario Ontario GeologicalSurvey, Survey,Miscellaneous Miscellaneous Superior Province: evidence for an Geological Paper Paper150, 150,p.p.107—114. 107-114. Baker, J.H., J.H., Hellingwerf, Hellingwerf, R.H. 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Sciences, 1992: Evidence alteration at at Luff, W.M., W.M., Goodfellow, Goodfellow,W.D., W.D., and and Juras, Juras, S.J., 1992: Evidence for for a feeder feeder pipe pipe and associated alteration 167-185. the Brunswick Brunswick No. No. 12 12massive-sulfide massive-sulfide deposit. deposit. Exploration ExplorationMining MiningGeology, Geology,v.v.1,1,p.p.167—185. Lydon, JJ.W., .W., 1984: Volcanogenic Volcanogenicmassive massivesulphide suiphidedeposits depositsPart Part 1: a descriptive model. Geoscience Canada, Geoscience Canada, 11,p.p.195—202. 195-202. v. 11, McGill, G.E., 1992: Structure Structure and tectonics of a major tectonic contact, contact, Michipicoten Michipicoten greenstone belt, Ontario. Ontario. Canadian JournalofofEarth EarthSciences, Sciences,v.v.29,29, 2118-2132. Canadian Journal p.p. 2118—2132. Milne, 1974: Mapledoram-Gemmell, Thunder District. Map Map2280, 2280,scale scale1:12000: 1:12000: Ontario OntarioDivision Division Mime, V.G., 1974: Thunder Bay District. of Mines. Mines. Pan, Y., and and Fleet, Fleet,M.E., M.E.,1992: 1992:Mineralogy Mineralogyand andgenesis genesisof of caic-silicates calc-silicates associated associated with with Archean Archeanvolcanogenic volcanogenic Manitouwadge mining camp, Ontario. Canadian Canadian Journal Journalof of Earth EarthSciences, Sciences,v.v. massive sulfide sulfide deposits deposits at the Manitouwadge 29, 29, p.p.1375—1388. 1375-1388. Pan, Y., Fleet, Fleet, M.E., M.E., and andStone, Stone,W.E., W.E., 1991: 1991:Geochemistry Geochemistry of metasedimentary metasedimentary rocks Archean rocks in in the late Archean Hemlo-Heron Hemlo-Heron Bay Bay greenstone greenstone belt, belt, Superior Superior Province, Province, Ontario: implications for for provenance provenance and and tectonic setting. Precambrian PrecambrianResearch, Research,v.v.52, 52,p.p.53—69. 53-69. ting. Pan, Y., Y., Fleet, Fleet, M.E., M.E., and andWilliams, Williams,H.R., H.R.,1994: 1994:Granulite-facies Granulite-facies metamorphism in the the Quetico Quetico subprovince, subprovince, Pan, of Manitouwadge, Manitouwadge, Ontario. Canadian Journal Journal of of Earth EarthSciences, Sciences, v. v. 31, 31, p. p. 1427—1439. 1427-1439. north of R., 1990: 1990: U-Pb dating dating of of monazite monazite and its its application application to to geological geological problems. Parrish, R., problems. Canadian Canadian Journal Journal of of Earth Earth Sciences, Sciences,v.v.27, 27,p.p.1431—1450. 1431-1450. Percival, J.A., 1989: A A regional regional perspective perspective of ofthe the Quetico Queticometasedimentary metasedimentary belt, belt, Superior Superior Province, Province, Canada. Canada. Canadian Journal JournalofofEarth EarthSciences, Sciences,v.v.26, 26,p.p.677—693. 677-693. 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Thesis, University Robinson, J., Klein, Klein, C., C., Evans, Evans, B.W., B.W., and and Doolan, Doolan,B.L., B.L., 1982: 1982: Phase Phase Robinson, P., Spear, F.S., Schumacher, J.C., Laird, J., metamorphic amphiboles: amphiboles: natural natural occurrence occurrence and and theory. theory.Reviews Reviews in inMineralogy, Mineralogy, Mineralogical Mineralogical relations of metamorphic Society of of America, America,v.v.9B, 9B,p.p.1—227. 1-227. Society Schandl, E.S., Davis, D.W., Gorton, Gorton, M.P., M.P., and andWasteneys, Wasteneys, H.A., H.A., 1991: 1991: Geochronology Geochronology of of hydrothermal hydrothermal alteration around around volcanic-hosted volcanic-hosted massive massive suiphide sulphide deposits deposits in in the theSuperior SuperiorProvince. Province.Ontario OntarioGeological GeologicalSurvey, Survey, Miscellaneous Paper156, 156,p.p.105—120. 105-120. Miscellaneous Paper Spear, F.S., 1993: 1993: Metamorphic Phase Equilibria and Pressure-Temperature-Time Pressure-Temperature-Time Paths. Paths. Mineralogical Mineralogical SociSociof America, America, Monograph, Monograph, Washington, Washington, D.C., D.C., 799 799 p. p. ety of Spry, P.G., 1982: Spry, 1982: An unusual unusual gahnite-forming gahnite-forming reaction, reaction, Geco Geco base-metal base-metal deposit, deposit, Manitouwadge, Manitouwadge, Ontario. Ontario. Canadian Mineralogist,v.v.20, 20,p.p.549—553. 549-553. Canadian Mineralogist, Stevenson, R.K., 1985: 1985: Implications of amazonite amazonite to tosulfide-silicate sulfide-silicateequilibria. equilibria. M.Sc. M.Sc. Thesis, Thesis,McGill McGillUniversity, University, Implications of 310 p. p. Stockwell, C.H., 1964: Fourth on structural structuralprovinces, provinces,orogenies orogenies and and time-classification time-classification of of rocks rocks of of Stockwell, C.H., 1964: Fourth report on Canadian Precambrian PrecambrianShield. Shield.Age Age Determinations Determinationsand andGeological Geological Studies, Studies, Part PartII, 11,Geological GeologicalSurvey Surveyof of the Canadian Canada, Paper Paper 64-17, 64-17, p. p. 1-21. 1-21. Canada, Stockwell, Geology and Economic Minerals Stockwell, C.H., C.H., 1970: 1970: Geology Geologyofofthe the Canadian Canadian Shield, Shield, introduction. introduction, in Geology and Economic Minerals of of 44-54. Canada, PartA, A,Geological Geological Survey Survey of Canada, Canada, Economic Economic Geology Canada, Part GeologyReport Report 1, (ed.) (ed.) R.J.W. Douglas, p. p. 44—54. Suffel, G.G., and Ridler, Ridler,R.H., R.H.,1971: 1971:Metamorphism Metamorphismof ofmassive massivesulfides sulfides at at Manitouwadge, Manitouwadge, G.G., Hutchinson, R.W., and Ontario, Canada. Canada.Society Society of of Mining Mining Geologists Geologists of Special Issue No. 3, p. p. 235—240. 235-240. of Japan, Special McLennan, S.M., S.M., 1985: 1985: The Continental Crust: Its Its Composition Composition and and Evolution. Evolution. Blackwell, Blackwell, Taylor, S.R., and McLennan, Oxford, 312 p. 1932: Geology Geology of Heron Bay-White Bay-White Lake Lake area. Ontario Department Department of of Mines, Mines, Annual Annual Thomson, J.E., 1932: of the Heron Report XLI(6), Report XLI(6),p.p.34—47. 34-47. Tilton,G.R., G.R.,and andSteiger, Steiger,R.H., R.H.,1969: 1969:Mineral Mineralages agesand andisotopic isotopic composition composition of of primary primary lead lead at atManitouwadge, Manitouwadge, Tilton, Ontario. Journal Journalof of Geophysical Geophysical Research, Research, v. v. 74(8), 74(8), p. p. 2118—2132. 2118-2132. Ontario. Timms, P.D., and and Marshall, Marshall, D., D., 1959: 1959:The The geology geology of Proceedings of of the Willroy mines mines base base metal deposits. Proceedings of 11, p. p. 55—65. 55-65. Geological Association of Canada, Canada, v. v. 11, the Geological 1973: Structural Structural and and stratigraphical stratigraphicalanalysis analysisof ofthe theGeco Gecosuiphide sulphidedeposit depositininManitouwadge, Manitouwadge, Touborg, J.F., 1973: Ontario[abs.]. [abs.].19th 19thAnnual AnnualInstitute Institute Lake Superior Geology, 38-39. northwestern Ontario onon Lake Superior Geology, p.p.38—3 9. Tragkrdh, 1988: Cordierite-mica-quartz Cordierite-mica-quartz schists schists in aa Proterozoic Proterozoic volcanic volcanic iron ore-bearing ore-bearing terrain, RidRidTrägârdh, J., 1988: darhyttan area, area,Bergslagen, Bergslagen,Sweden. Sweden.Geologie Geologie in in Mjinbouw, Mjinbouw, v. v. 67, 67, p. p. 397—409. 397-409. darhyttan Vallenta, Mount Isa. Economic Economic Vallenta, R., 1994: Syntectonic Syntectonic discordant discordant copper copper mineralization mineralizationinin the the Hilton Hilton mine, Mount Geology, v. v. 89, 89,p.p.1031—1052. 1031-1052. Geology, 47 �Manitouwadge greenstone belt References References and Franklin, Franklin, J.M., J.M.,1982: 1982:The TheAnderson AndersonLake Lakemine, mine,Snow SnowLake, Lake,Manitoba. Manitoba.Geological GeologicalAssociAssociWalford,P.C., and ation of of Canada, Canada,Special SpecialPaper Paper25, 25,p.p.481—523. 481-523. 1970: The geology geology and evolution of the Geco Geco massive massive sulphide deposit deposit at at ManiManiWatson, D.W., 1970: and structural evolution Ontario, Canada. Canada. Ph.D. Ph.D.thesis, thesis,University Universityof ofMichigan, Michigan,272 272 p. p. touwadge, northwestern Ontario, 1989: Geological studies in the the Wabigoon, Wabigoon, Quetico Quetico and and Abitibi-Wawa Abitibi-Wawasubprovinces, subprovinces,Superior Superior Williams, H.R., 1989: structural development development of Beardmore-Geraldton belt. Ontario Province of Ontario, with emphasis on the structural of the Beardmore-Geraldton Geological Survey, Open File Report Report 5724, 5724,188 188 p. p. 1990: Subprovince Williams, H.R., 1990: Subprovince accretion accretion tectonics tectonics in in the the south-central south-central Superior Province. Canadian Journal of of Earth EarthSciences, Sciences,v.v.27, 27,p.p.570—581. 570-581. Williams, H.R., H.R., 1991: 1991: Quetico Quetico subprovince. subprovince. in in Geology Geology of Ontario, OntarioGeological Geological Survey, Survey, Special Special Volume Williams, Ontario, Ontario 4(1), 4(1), p.p.383—403. 383-403. and Breaks, Breaks, F.W., F.W.,1989: 1989:Geological Geological studies in in the theManitouwadge-Hornpayne Manitouwadge-Hornpayne area. area. Ontario Ontario Williams, H.R., and Geological Geological Survey, Survey,Miscellaneous MiscellaneousPaper Paper146, 146,p.p.79—91. 79-91. and Breaks, Breaks, F.W., F.W., 1990a: 1990a:Geological Geological studies in the the Manitouwadge-Hornpayne Manitouwadge-Hornpayne area. Ontario Ontario Williams, H.R., and Geological Geological Survey, Survey, Miscellaneous MiscellaneousPaper Paper151, 151,p.p.41—47. 41-47. and Breaks, Breaks,F.W., F.W.,1990b: 1990b:Geology Geology of of the the Manitouwadge-Hornpayne Manitouwadge-Hornpaynearea. area. Ontario OntarioGeological Geological Williams, H.R., and Survey, Open File File Map Map142, 142,scale scale1:50000. 1:50000. Breaks, F.W., F.W., Schnieders, Schnieders,B.R., B.R., Smyk, Smyk, M.C., M.C., Charlton, Charlton,S.G., S.G.,and andLockwood, Lockwood,H.C., H.C.,1990: 1990:Field Field Williams, H.R., Breaks, the Manitouwadge Manitouwadge area. in in Franklin, Franklin, J.M., J.M., Schnieders, Schnieders, B.R., and Koopman, Koopman, E.R., E.R., eds., eds., Mineral Mineral DeDeguide to the in the the Western WesternSuperior SuperiorProvince, Province,Ontario: Ontario:8th 8thIAGOD IAGODSymposium, Symposium,Field FieldTrip TripGuidebook, Guidebook,Geological Geological posits in Survey of Canada, Canada, Open Open File File2164, 2164, p. p.7—25. 7-25. Stott,G.M., G.M.,Heather, Heather,K.B., K.B.,Muir, Muir,T.L., T.L.,and andSage, Sage,R.P., R.P.,1991: 1991:Wawa WawaSubprovince. Subprovince.Geology Geology Williams, H.R., Stott, of Ontario, Special Special Volume 4, Part 1, 1, p. p.485—539. 485-539. Breaks, F.W., F.W., and andMilne, Milne,V.G., V.G.,1992: 1992:Geology Geology of of the theManitouwadge-Hornpayne Manitouwadge-Hornpayneregion, region, DisDisWilliams, H.R., Breaks, tricts of of Thunder ThunderBay, Bay,Algoma Algoma and and Cochrane. Cochrane.Ontario OntarioGeological Geological Survey, Survey, unpublished report, report, 149 149 p. p. tricts Zaleski, E., 1989: 1989: Metamorphism, Metamorphism, structure and andpetrogenesis petrogenesisof ofthe theLinda Lindavolcanogenic volcanogenicmassive massivesuiphide sulphide Zaleski, Ph.D. thesis, thesis, Winnipeg, Winnipeg, Manitoba, Manitoba, Canada, Canada,University Universityof of Manitoba, Manitoba, deposit, Snow Lake, Manitoba, Canada. Ph.D. 344 p. p. 344 Zaleski, E., and and Peterson, Peterson, V.L., V.L., 1993a: 1993a: Lithotectonic Lithotectonic setting setting of of mineralization in the the Manitouwadge Manitouwadge greenstone greenstone Zaleski, belt, Ontario: Ontario: preliminary preliminary results. results. Current Current Research, Research, Part C, C,Geological Geological Survey 93-lC, p. p. belt, Survey of of Canada, Canada, Paper Paper 93-iC, 307—317. 307-317. and Peterson, Peterson, V.L., V.L.,1993b: 1993b:Geology Geology of of the the Manitouwadge Manitouwadge greenstone greenstone belt, belt, Ontario. Ontario.Geological Geological Zaleski, E., and Zaleski, Canada,Open OpenFile File2753, 2753,scale scale1:25000. 1:25000. Survey of Canada, and Peterson, Peterson, V.L., V.L., 1995: 1995:Geology Geology of of the the Manitouwadge Manitouwadgegreenstone greenstone belt belt overlain overlain on on shaded shaded relief relief Zaleski, E. and 1:25000. of total totalfield fieldmagnetics. magnetics.Geological GeologicalSurvey Surveyof ofCanada, Canada,Open OpenFile File3034, 3034,scale scale1:25000. of Peterson, V.L., V.L., and andvan vanBreemen, Breemen,0., O.,1994: 1994:Geological, Geological,geochemical, geochemical,and and age age constraints constraints on on base base Zaleski, E., Peterson, metal mineralization mineralization in in the theManitouwadge Manitouwadge greenstone greenstone belt, northwestern northwestern Ontario. Ontario. Current Current Research Research 1994-C, 1994C, metal Geological Geological Survey of Canada, Canada, p. p.225—235. 225-235. and Peterson, Peterson,V.L., V.L.,1995: 1995:Geology Geologyof of the theManitouwadge Manitouwadgegreenstone greenstonebelt beltoverlain overlain on shaded shaded relief relief Zaleski, E. and Zaleski, totalfield field magnetics. magnetics.Geological GeologicalSurvey Surveyof ofCanada, Canada,Open OpenFile File3034, 3034,scale scale1:25000. 1:25000. of total Zaleski, E., Peterson, V.L., V.L., and and van van Breemen, Breemen, 0., O.,1995: 1995:Geological Geological and age age relationships of the margins margins of the Zaleski, and the the Wawa-Quetico Wawa-Quetico subprovince boundary, Current Manitouwadge greenstone belt and boundary, northwestern northwestern Ontario. Current 1995-C, Geological Survey of Canada, p. 35—44. 35-44. Research 1995-C, Canada, p. 48 �A. Known deposits, inner volcanic volcanic belt Manitouwadge field guide FIELD-TRIP STOPS STOPS Introduction The field trips in this this guidebook guidebook are are organized organized thematically thematicallyand and geographically, geographically,to to represent represent the thegeology geology of of the the outcrop outcrop observations observations critical critical to to our our structural, structural, stratigraphic the Manitouwadge area, and give examples of stratigraphic interpretations. The and petrological petrological interpretations. The guidebook guidebook is partly intended intended for the field field trip to to the theManitouwadge Manitouwadge greenstone belt belt sponsored by the Forty-first of the the Institute on greenstone Forty-first Annual Meeting Meeting of on Lake Lake Superior Superior Geology Geology and, tours that can by anyone anyone interested. interested. A A short in the longer term, term, as as aa series series of of self-guided self-guided tours can be be easily easily followed followed by For more detail and introductory section summarizes of each each area. For introductory summarizes the geology geology and significance significance of and regional regional synthesis, the the reader reader is referred referred to the interim report that synthesis, that comprises comprises the the first first part part of of this thisvolume. volume. A. Known economic deposits, iinner n n e r volcanic belt All of the known economic massive sulphide deposits of the Manitouwadge greenstone belt, comprising known massive sulphide deposits of comprising Nama Creek Creek and and Willecho Willechodeposits, deposits,lie lieininthe the inner inner volcanic volcanicbelt belt of ofthe the southern southern limb limb of of the Geco, Geco, Willroy, Nama synform (1:25000 (1:25000map). map). The The Geco Geco mine, mine, scheduled scheduledto to close close in in late late 1995, is is the only the D3 Da Manitouwadge Manitouwadge synform currently currently producing deposit. In In the thecase caseofofmined-out mined-outorebodies, orebodies, some some spatial spatialrelationships relationships can can be beinferred inferred from the positions of open open stopes stopes and pits with formation from positions of with respect respect to to the thehosting hosting metavolcanic metavolcanic rocks, rocks, iron formation and metamorphosed inthe the area area metamorphosed alteration alterationzones zonesalongalong-and andacross-strike. across-strike.Detailed Detailed1:5000 1:5000mapping mapping(1991—92) (1991-92) in of known deposits was was critical critical to our of known deposits our definition definition of lithological lithological units, and interpretation interpretation of ofpre-D3 pre-Da deformadeformarelationships. To the north, supracrustal tion and probable probable depositional relationships. supracrustal rocks rocks are are bounded bounded by by aa synvolcanic synvolcanic trondhjemite which metavolcanic rocks. rocks. The trondtrondhjemite which also also engulfs engulfs screens screens of mafic and interlayered interlayered mafic-felsic mafic-felsic metavolcanic trondinterpreted as hjemite is mantled by by orthoamphibole-garnet-cordierite orthoamphibole-garnet-cordierite gneiss, interpreted as the the metamorphosed metamorphosed equivalent equivalent of a synvolcanic hydrothermal hydrothermal alteration zone, of zone, developed developed in a protolith protolith of of intercalated intercalatedmafic-felsic mafic-felsic rocks. To TO rocks and and mineralized mineralized iron iron formation formation the south of of orthoamphibole-garnet-cordierite orthoamphibole-garnet-cordierite gneiss, gneiss, felsic felsic metavolcanic rocks sillimanite-muscovite-quartz schist representing metamorphosed synvolcanically synvolcanically altered are interlayered with sillimanite-muscovite-quartz felsic rocks. rocks. The volcanic sequence sequence isis repeated repeated in in the outer volcanic volcanic belt by the the D2 Da 'Manitouwadge 'Manitouwadge syncline', D3Manitouwadge Manitouwadge the axial axial trace trace of of which lies in the metasedimentary rocks rocks central central to to the thesouthern southernlimb limbof ofthe theD3 synform (Fig. 5). Stratigraphic Stratigraphicyounging youngingininthe theWillroy-Geco Willroy-Gecoarea areaisissoutherly, southerly, based based on ongenerally generallysouthward southward increase increase in Pb/Zn and andZn/Cu Zn/Cuofoforebodies, orebodies,and andononthe theposition positionofoforthoamphibole-cordierite-garnet orthoamphibole-cordierite-garnet gniess gniess (footwall-type alteration) alteration) and synvolcanic trondhjemite trondhjemite to to the north. (footwall-type the The area area of of the the inner inner hinge hingeregion region and and southern southernlimb limbof of the theManitouwadge Manitouwadge synform synform (D3) preserves preserves the best map.. of the the pre-D3 pre-D3 structural structural history (see (see Structural Structuralcomplications—Dl/D2 complications-Dl/D2 map- and outcrop-scale outcrop-scale evidence of folds and faults). The Thenear-continuous near-continuous layers layers of of iron iron formation formation are are excellent excellent marker marker units, units, useful useful in in linking linking correlative our structural structural interpretation, interpretation, aa D1 Dl correlative stratigraphic horizons and outlining outlining structural structural features. features. In our ductile fault divides the area area into into upper (southern) (southern)and andlower lower (northern) (northern) tectonic tectonic blocks blocks and and isis responsible responsible for the repetition repetition of of mineralized mineralized horizons. horizons. Between Between the the Nama NamaCreek Creek and andWillecho Willecho deposits, deposits, the theD1 Dl fault faultsurface surface by a map-scale D2 sheath fold (Fig. 4). is deformed deformed by area has has many many hazards associated with previous mining operations. operations. Permission The Geco-Willecho Geco-Willecho area associated with previous mining Permission for access, via aa locked locked gate gate across across the the Willroy Willroymine mineroad, road,must must be be arranged arranged in in advance advance with with Noranda Noranda Inc. Inc. Many access, via stops in this this area area were were previously previously described in the the guidebook guidebook for the International International Association Associationon on the theGenesis Genesis of Ore Deposits (Williamsetet al., al., 1990), and IAGOD stop numbers numbers are are given given here here to facilitate of Deposits (IAGOD) (IAGOD) (Williams 1990), and IAGOD stop comparison with with our our descriptions descriptions and and reinterpretations. reinterpretations. Our station numbers comparison numbers with prefix prefix 'ZB' are are also also given for each stop as aa cross-reference to sample and analytical data cross-reference to data in in preparation preparation for for open open file file release. release. A1-A8. Al—A8. Willroy-Geco Wiliroy-Geco area The following field-trip stops stops (1:25000 map) generally generallyproceed proceedfrom fromyounger youngertoto older older (and (and deeper following field-trip (1:25000 map) deeper in the section) section) rocks, rocks, from from the the metagreywackes metagreywackes central to the the D2 D2'Manitouwadge 'Manitouwadge syncline', syncline', to to iron iron formation formation interlayered with felsic felsic volcanic rocks, to to sillimanite-muscovite-quartz sillimanite-muscovite-quartz schist and and orthoamphibole-cordieriteorthoamphibole-cordieritegarnet gneiss, gneiss, to to subvolcanic trondhjemite. The Thegeneral generalsequence sequence was interpreted as a stratigraphic stratigraphicsuccession succession by Snifel a!. (1971), based on comparison Suffel et al. comparison with with successions successions typical of other greenstonc greenstone belts. belts. Suffel Suffeletetal. al.were were also the first first to to interpret interpretthe theManitouwadge Manitouwadgedeposits depositsasasvolcanogenic volcanogenicmassive massive sulphides, sulphides, and and orthoamphiboleorthoamphibolebearing rocks as metamorphosed footwall footwall alteration. Stop metagreywacke, Z1391-10, ZB93-410, A l Manitouwadge , Manitouwadge metagreywacke, ZB91-10, ZB93-410,ZB94-87. ZB94-87. Starting Startingatatthe thelocked locked gate gateon on S t o p Al, the Wiliroy mine road, road, drive drive north north about 300 metres metres up up the short hill, turning west track Willroy mine west (left) on the gravel track near the hill hill top. About About200 200metres metresmore morebrings brings you you to to aaparking parking area areaon onthe theeast eastside sideof ofaasmall smalldam damacross across valley. Cross Cross the the foot foot bridge bridge and and rock rock dam dam to an outcrop on the west the Slim Lake valley. west side. The The dam dam contains contains tailings from the Willroy Willroy deposits that that were were dumped dumped into intoSlim SlimLake Lake (now (now mostly mostly aa meadow) meadow) from from 1950's 1950's to to 1970's. is periodically periodicallypumped pumped into into the the ponded ponded water water to to neutralize neutralize acidity acidity and and precipitate precipitate metals. metals. The 1970's. Lime is north-south lineament of the the Slim Lake Lake fault, fault, a high-angle north-south lineament is the topographic topographic expression expression of high-angle brittle fault with with minor dextral offset. offset. 49 �A. Known deposits, inner volcanic volcanic belt Manitouwadge field guide Manitouwadge guide The Manitouwadge rocks comprise comprise biotitekgarnetksillimanite biotite±garnet±sillimanite schist schist and and biotiteManitouwadge metasedimentary metasedimentary rocks biotitehornblende schist, mostly mostly homogeneous, homogeneous,but but also also with with layering layeringand and grading grading defined definedby by the the abundance of hornblende schist, abundance of mafic minerals. Metagreywackes rnm—2 Metagreywackes in in this thisexposure exposureare arethinly thinly(2(2 mm-2 cm) cm)totothickly thickly(10 (10cm—2 cm-2 m) m)layered layered (transposed bedding) and and contain contain plagioclaseplagioclase- and quartz-crystal quartz-crystal clasts, clasts, evidence evidence of of aa tuffaceous tuffaceous component. Some layers have possible lithic fragments (1—10 cmlong) long)with withdiffuse diffusemargins. margins.The The layering, layering, and and the sub(1-10 cm parallel parallel foliation foliation(1)2), (D2), are near-vertical and straight, straight, and and aastrong strongmineral minerallineation lineationplunges plungeseasterly. easterly. Locally Locally developed intrafolial folds, some eye-shaped, eye-shaped, probably probably originated as soft-sediment folds that were were subsequently subsequently transposed during further tectonic tectonic deformation. deformation. detrital zircon Based on U-Pb provenance study of detrital zircon from this site site (Fig. (Fig. 12), 12),the the maximum maximumage ageof of deposition deposition is 2693 Ma, Ma, at at least 25 Ma younger than felsic volcanism volcanism (circa (circa 2720 2720Ma) Ma)ininboth both the the inner inner and outer volcanic belts. The in D2 D3 folds folds indicates indicatesthat that sedimentation sedimentation predated pre-dated D2 D2 and and that Theinvolvement involvement of of metagreywacke metagreywacke in the contact contact isis either either an anunconformity unconformity or or aaprepre-totosyn-D2 syn-D2fault. fault.Field Fieldobservations observationsare areequivocal equivocalregarding regarding the relationship relationship of of D1 Dl deformation deformation and and sedimentation; sedimentation; however, however, uplift uplift resulting resulting from from D1 Dl deformation deformation may may have contributed sediment sources. We We interpret interpret the theManitouwadge Manitouwadgemetagreywackes metagreywackes as a tectonic tectonic outlier outlier of of Quetico Quetico rocks. rocks. Foliated tonalite width) intrude intrude metagreywacke at a low tonalite dykes dykes (25 (25cm—2 cm-2 mmininwidth) low oblique angles to layering, layering, and some show stretching and boudinage related to to layer-parallel layer-parallel shear. One One of of these these dykes dykes was was collected collected for geochronologytoto constrain constrain to to the minimum age of of sedimentation sedimentation (analysis (analysis in in progress). progress). A geochronology A nearly nearly massive massive but has concordant aplitic apophyses; the pegmatite muscovite-pegmatite cross-cuts foliation but pegmatite shows shows thickening in the hinge hinge region region of a minor minor fold. fold. Stop A2, Iron formation, ZB91-l1, ZB92-P18, IAGOD S t o p A2, I r o n formation, ZB91-11,ZB92-P18, IAGOD#2. #2.Return Returntotothe theWillroy Willroymine mineroad roadand andcontinue continue 200 metres metres north, north, turning west track. Continue tower and and a 200 west at another another gravel gravel track. Continue about 1.5 1.5 km km to to aa microwave microwave tower large outcrop outcrop area on on the hill top. The large The space space for parking and turning around is small, soft and sandy. From the rocky crest, looking to the east, east, the the Geco Geco headframe headframe and the the open open cuts cuts of of Willroy Willroy deposits deposits are visible, visible, situated in sillimanite-muscovite-quartz in aanarrow narrowinterval intervalofofiron ironformation, formation,quartz-phyric quartz-phyricfelsic felsicrocks rocksand andsillimanite-muscovite-quartz schist. The The outcrop outcrop on on which which you stand is is part part of of the the thick thick southernmost southernmost quartz-magnetite quartz-magnetite iron iron formation, with zincian zincian iron iron formation formation at at the Geco apparently unmineralized in the Willroy area, and possibly correlative with mine. mine. The iron cm)with withalternating alternating white white to to smoky smoky quartzose quartzose layers layers and and dark iron formation formation isis layered layered (1 (1 mm—10 mm-10 cm) layers rich in magnetite and and Fe-silicates. Fe-silicates. The Thelayering layeringis is tightly tightly folded folded (D2 (D2or or combined combined D2/transposed Da/transposed D1?) Dl?) about easterly-plunging axes, and and fold fold asymmetry asymmetry varies varies across acrossthe theoutcrop outcrop area. area. The mineral easterly-plunging axes, mineral lineation lineation is parallel to fold axes and, locally, grunerite defines defines an an axial axial planar planar foliation. foliation. The southernmost iron formation has been thickened thickened by by folding, folding, and and we we interpret interpret these theseoutcrop-scale outcrop-scalefolds foldsas asrelated relatedtotomap-scale map-scale1)2 D2folds foldsof of formation/felsic contact to the the west west (Stop (Stop A23, A23, Fig. A3). the iron formation/felsic The metamorphic metamorphic assemblage assemblage in dark layers layers consists of magnetite, grunerite with with epitaxial epitaxial overgrowtbs overgrowths of green amphibole clinopyroxene(ferrosalite), (ferrosalite),and and minor minor pyrrhotite and (ferroactinolite-ferrohornblende), clinopyroxene and amphibole (ferroactinolite—ferrohornblende), garnet (Alm/Sps/Grs/Pyp (Alm/Sps/Grs/Pyp = = 58/22/17/2). geochemical analyses 3 samples containing variable garnet 58/22/1712). Whole-rock Whole-rock geochemical analyses of 3of samples containing variable proportions of material, have Si02 from 68.2—90.7%, from 5.6—26.0%, proportions ofquartzose quartzoseand anddark dark material, have Si02 from 68.2-90.7%,FeO FeO from 5.6-26.0%,MnO MnOfrom from0.3— 0.3andTiOz<0.02%, Ti02<0.02%, Al2O3<0.53%, Al203<0.53%, Na20<0.08% Na2O<0.08%and and K20<0.08%, suggesting 1.3%, CaO from 0.70—2.25%, 0.70-2.25%, and suggesting negligibledetrital detrital or or volcanic volcanic component. component. The The base base metal metal content very low; low; CCu<8 ppm, Pb<9 ppm negligible content is also very u e 8 pprn, ppm and Zn<28 ppm. m in in width) including granodiorite with mafic The iron iron formation formation isis cut cutby byfoliated foliateddykes dykes(30 (30cm—i cm-1.5.5m mafic tonalite-granodiorite. The dykes subparallel to to the axial traces clots and plagioclase-porphyritic tonalite-granodiorite. dykes are generally subparallel of D2 folds with with very very long long limbs limbs (+lo (+10 m). In Da folds but, locally locally show asymmetric folds Infold foldhinges, hinges, the thefoliation foliation margins and and axial axial planar planar to folds. belongto to aa suite suite of of in the dykes dykes is discordant discordant to dyke margins folds. The The dykes dykes likely likely belong tonalite tonalite dykes, dykes, some some of of which which show show structural structural relationships relationships suggesting suggesting syn-D2 syn-Dz emplacement. emplacement. AAdiscordant discordant pegmatite cuts both iron iron formation formation and and dykes. dykes. Stop rocks and and iron formation nnear S t o p A3, Quartz-phyric Quartz-phyric felsic rocks e a r the t h e Wiliroy Willroy 2, 3, 4 aand n d 5 orebodies, ZB91-12—14,ZB92-P139, ZB92-P139,ZB92-P152-P153. ZBO2-P152—P153. Return Willroy mineroad roadand andproceed proceedabout about 800 metres ZB91-12-14, Return to to thetheWillroy mine north to decrepit core core racks, racks,all allthat that remains remains of ofWillroy WillroyMines Mines#1 #1and and#2 #2 to aa large large gravelled gravelled area with some decrepit shafts and millsite millsite (Fig. (Fig. Al). Al).On Onthe thesouth southside sideofofthe thegravelled gravelledclearing, clearing,aachain-link chain-linkfence fencerestricts restrictsaccess access to the map, Fig. Fig.Al). Al). The the open open stope stope of of the the Willroy Willroy 33 orebody orebody (1:25000 (1:25000 map, The road road continues continues to the the northwest northwest side of the clearing, clearing, and down down aa hill hill toward toward an an abandoned abandoned railway railway linking linking the Willroy Willroy and and Geco Geco properties. properties. On the hill-top plateau to to the theeast eastofofthe theroad, road,another anotherchain-link chain-linkfence fence restricts restricts access access to dangerous dangerous ground immediately above above the the Willroy Willroy 4, 4, 22 and and 5 orebodies. orebodies. Within 50 metres metres on both sides sides of the road, road, there there are are several pavement outcrops of of quartz-phyric quartz-phyric felsic felsicbreccias brecciasand andthin thin interleaved interleavediron ironformation formation(mostly (mostlytoo too thin thin to show on the 1:25000 1:25000 map). The more rocks in in which which both both matrix and fragments more southerly outcrops outcrops consist consist of of felsic fragmental rocks fragments (<1 (<1 cm—10 cm)have havequartz quartzphenocrysts. phenocrysts.The Thevariation variationininclast clastlithology lithologyisisnot notdramatic dramatic and and might might be be attributed cm-10 cm) 50 �A. Known Known deposits, inner inner volcanic volcanic belt Manitouwadge field guide ..,,... I 0 I 400 metres FIG. Al. FIG. Geology and field-trip Geology field-trip stops stopsof of the theSlim SlimLake Lakesection section(A9— (A9- A20), and andWiliroy WillroyStops StopsA3—A5. A3-A5. Structure Structure symbols symbols show show dominant dominant D2 Dz foliations foliations and lineations, lineations, and and asterisks are the locations asterisks are locations of the the Willroy 2 to 55 orebodies. orebodies. In this this Wiliroy and and the thefollowing following figures, the the figure figure locations are shown on the the accomaccompanying map and lithopanying 1:25000 1:25000 map lithological units are shown logical units shown by bold bold numbers numbers that match match the the map mapleglegend. Circled Circledalpha-numerics alpha-numerics refer refer to field-trip stops. Dotted Dotted lines lines are are topographic contours at at 10 topographic contours 10 metre metre intervals. variable alteration alteration of of crystalline crystalline and and glassy glassy materials materials in in aavolcaniclastic volcaniclastic deposit; deposit; but but some somebiotite-rich biotite-rich to variable streaks could represent represent more mafic clasts. Microcline Microcline and muscovite muscovite are both heterogeneously heterogeneously distributed, even thin section, section, suggesting suggesting that that the theK20 K 2 0abundance abundancewas wasdetermined determinedby byalkali alkaliexchange exchange even on on the scale of a thin rather than than primary primary magmatic magmaticcomposition. composition. Magnetite Magnetite porphyroblasts porphyroblasts are are ubiquitous ubiquitous and and garnet garnet isis present present locally. These breccias are part of locally. of the thesouthernmost southernmostlens lensofofquartz-phyric quartz-phyric metavolcanic metavolcanic rocks rocks in in the theWiliroy Willroy area. In scattered outcrops outcrops on the the north northside sideofofthe theplateau, plateau,semi-continuous semi-continuous and and discontinuous discontinuous thin iron iron the felsic felsic breccia are difficult difficult to Dl ductile fault is interpreted formations intercalated with the to trace laterally. A D1 rocks (not (not exposed). exposed). The to pass through through this this area, area,following following the northern northern contact contact of of quartz-phyric quartz-phyric felsic felsic rocks south are aremoderately moderatelymuscovitic muscoviticand andcontain containquartz quartzeyes eyesand andquartz quartzpods podsupuptoto 5-10 cm cm felsic rocks rocks to the south 5—10 long. In the ditch west outcrop of of iron iron formation formationininthe thefirst firstbushes bushesatat the the top top of of long. west of the road, a small small (2 m2) outcrop shows two two types types of of iron iron formation; formation; firstly, firstly, aa breccia breccia of of quartzose quartzosefragments fragmentsinin aa dark dark the north-facing slope shows matrix and, and, secondly, secondly, homogeneous homogeneoussilicate silicateiron ironformation. formation. The The iron iron formation formation lies lieson on the the north side of the on or or near near the thesame samehorizon horizonas asthe theZn-Pb-rich Zn-Pb-richWillroy Willroy44orebody orebody (Fig. (Fig.21, 21,Table Table3). 3).Two Twogeochemical geochemical fault, on samples from from the the outcrop showed showed elevated elevatedZn Zn(32 (32and and68 68ppm), ppm),and andlow lowCu Cu(4(4and and13 13ppm) ppm)and and Pb Pb (7 (7 and 11 11 ppm) abundances. Between the the road road and the Between the chain-link chain-link fence to the east, east, sulphidic sulphidic iron iron formation formation crops crops out out along-strike along-strike 215 orebodies. orebodies. This Thisisisone oneof of the thefew few exposures exposures of a transition from from quartz-magnetite quartz-magnetite iron iron from the Willroy 2/5 to sulphidic sulphidic iron iron formation formation associated associated with withan anorebody. orebody.Two Twogeochemical geochemical samples, samples, separated separated by by55 formation to 51 �Manitouwadge Manitouwadgefield field guide guide A. A. Known Known deposits, deposits, inner innervolcanic volcanicbelt belt metres levels of ofbase basemetals. metals. The more distant (western) metres of of strike-length, strike-length, show show elevated levels (western) sample sample has Cu=18 Cu=18 ppm, ppm, Pb=14 Pb=14 ppm pprnand andZn=431 Zn=431ppm; ppm;whereas whereasthe thenearer nearer(eastern), (eastern),more moresulphidic sulphidic sample sample has has Cu=132 Cu=132 ppm, ppm, Pb=88 Pb=88 ppm pprnand andZn=474 Zn=474 ppm. ppm. Along the the hilltop hill topback backtoward towardthe theWillroy Willroyroad, road,aasmall smallbranch branch road road leads leadsdown down hill to to the the northwest northwest (Fig. (Fig. Along Al). metres down down the the road road along along the the ditch on the north side, Al).About About20—30 20-30 metres side, aa biotitic biotitic variety variety of of silhmanitesillimanitemuscovite-quartz schist between the projected projected horizons horizons of the Willroy Willroy 44 and and 2/5 215orebodies. orebodies. In In muscovite-quartz schist crops out between the the schist, schist, numerous numerous sillimanite sillimaniteknots knotsare areassociated associatedwith withplagioclase, plagioclase,garnet, garnet,and andminor minorsulphide sulphideminerals. minerals. Monocrystalline and and polycrystalline polycrystalline quartz quartz eyes, eyes, observed observed in thin thin section, section, resemble resemble relict relict quartz quartz phenocrysts phenocrysts Monocrystalline and and suggest suggest that thatquartz-phyric quartz-phyric rocks rocks were were the protolith protolith to topremetamorphic premetamorphic alteration. alteration. S t o pA4, A4,Wiliroy Willroy millsite calc-silicate rocks, ZB91-171-175,ZB92-P318, ZB92-P318,P123, P123, IAGOD IAGOD #3. AAgroup group Stop milisite caic-silicate rocks, ZB91-17l—l75, of of stripped stripped glacially-polished glacially-polished outcrops, on the the north-facing north-facing slope slope leading leading down down from from the the plateau plateauofofStop StopA3, A3, can be be accessed accessed either either by by walking walking down down the brow brow of of the the hill hillor ordriving drivingdown down and andwalking walkingback back up up(Fig. (Fig. can Al). Al).These Theseenigmatic enigmaticexposures exposuresofofcalc-silicate calc-silicaterocks rocksalways alwaysgenerate generate much much discussion, discussion, although although they they are are not 1:25000map. map. InIngeneral generalininthe theManitouwadge Manitouwadgebelt, belt,caic-silicate calc-silicateminerals minerals are are not aaseparable separable unit uniton onour our1:25000 sporadically sporadically distributed distributedthroughout throughoutfelsic felsicto tointermediate intermediaterocks, rocks,and andparticularly particularlyconcentrated concentratedinincalc-silicatecalc-silicaterich rich zones zones adjacent to contacts contacts with with iron iron formation. formation. The TheWillroy Willroy millsite millsite outcrops are atpyical atpyical in structure structure (for (for example, example, fracture-control on caic-silicate calc-silicate distribution) and and in in their their evidently evidentlycomplex complex multistage multistage history, history, unusual unusual features features that thatmake makethem themdifficult difficultto toplace place in inaaregional regionalcontext. context. TheWillroy Willroymilisite millsite calc-silicate calc-silicate rocks lie in the stratigraphic stratigraphic footwall footwall of the Willroy Willroy 2/5 215orebodies, orebodies, and and The grade grade laterally laterallytotoquartz-phyric quartz-phyricfelsic felsicrocks rocks(the (thenorthernmost northernmostlens lenson onthe theWillroy Willroyproperty) property)which whichwe weconsider consider to tobe bethe theprotolith protolithtotometamorphism metamorphismand andcalc-silicate calc-silicatealteration. alteration.The Theabundance abundanceofofclinopyroxene, clinopyroxene,garnet, garnet,CaCaamphibole,plagioclase, plagioclase, epidote, epidote, calcite calcite and and titanite, titanite,asaswell wellasasquartz quartzand andmicrocline, microcline,isisvariable. variable.Locally, Locally,for for amphibole, example example in in exposures exposures high high on onthe theslope, slope,dark darkcalc-silicate calc-silicateminerals mineralsoccupy occupyaadeformed deformedconjugate-fracture conjugate-fracture8et set in which which flattened flatteneddiamond-shapes diamond-shapes(looking (lookingdown-plunge) down-plunge)outline outlinemore moreleucocratic leucocraticfelsic felsicdomains domainscomprising comprising in quartz, quartz, microcline, microcline, plagioclase plagioclase and minor minor hornblende, hornblende, biotite, garnet garnet and and epidote. epidote. Fractures Fractures oriented oriented at at high high angle angle to to foliation foliation are arefolded folded (shortened), (shortened), whereas whereas those those atatlow lowangle angletotofoliation foliation are are straight straightand andlook look extended. Pervasive Pervasivecalc-silicate calc-silicatezones zones (coarse (coarsegrained, grained, green green with with epidote, epidote,clinopyroxene clinopyroxene and and Ca-amphibole), Ca-amphibole), extended. of metrewidth, width,are aresubparallel subparallel to to local local foliation foliationtrends trends and cross the the fracture-controlled alteration. of 0.25—1 0.25-1 metre alteration.The The pervasive pervasive zones zones have have the the appearance appearanceofofbreccia brecciaand, and,locally, locally,some some'fragments' 'fragments'preserve preservelayering layering or orfracturefracturecontrolled calc-silicate alteration. cases, early at the thecontact contacttoto controlled alteration. In some cases, early structures structures look look rotated rotated or truncated at the thepervasive pervasivecalc-silicate calc-silicatematrix. matrix. Thisgroup groupofofoutcrops, outcrops,and anda asuite suiteofofcalc-silicate calc-silicaterocks rocksfrom fromthe theGeco Gecomine mine(Sufi'el (SuffelCollection), Collection), were were This (1992),who whoconcluded concluded that thatdispersed dispersedCa Cawas wasremobilized remobilized and and concentrated concentrated during during studied by by Pan Panand andFleet Fleet(1992), studied metamorphism. High High Cl Clinincalcic calcicamphibole amphibole from from the theGeco Gecomine minecould could indicate indicate aa memory memoryofofprevious previous metamorphism. synvolcanic enrichment during sea-floor sea-floor alteration (ibid.). In Inour ourview, view,the thelocalization localizationofofcalc-silicate calc-silicatezones zones synvolcanic near iron iron formation formation contacts contacts could could be be attributed attributedtotoeither eitherprimary primaryororsecondary secondaryprocesses. processes. One Onepossibility possibility near thatcaic-silicate calc-silicatezones zones formed formed during during metamorphic metamorphic redistribution redistribution of of Ca Ca during during decarbonation decarbonation reactions reactions of of isis that carbonate-facies iron formation. However, However, arguing arguing against against this this isisthe thelack lackofofevidence evidencefor forcarbonate-facies carbonate-facies carbonate-facies precursors for for metamorphosed metamorphosed iron iron formation formationatatManitouwadge, Manitouwadge,and and the thepaucity paucityof ofcarbonate carbonateminerals mineralsininthe the precursers calc-silicaterocks. rocks. Alternatively, Alternatively,ininaamodel-driven model-drivensyngenetic syngeneticscenario, scenario,the thedistribution distributionofofcaic-silicate calc-silicaterocks rocks caic-silicate could reflect reflect synvolcanic synvolcanic hydrothermal hydrothermal alteration alteration in inwhich which iron iron formation formationacted acted as asaacap caprock. rock. could From the theeastern easternbase baseof of the themain mainoutcrop, outcrop,walk walk east east along along the the road road to toanother anotheroutcrop outcropabout about1010metres metres From into intothe thewoods woods on on the thesouth southside. side.Here, Here,the therock rockisisdominated dominatedby by coarse coarse grained grained garnet garnet and andhornblende, hornblende, and and moretypical typicalof ofcaic-silicate calc-silicatezones zones in general. There There isislittle littleevidence evidence of of a felsic precursor short distance distance more precurser until, a short tothe theeast east(just (justbefore beforea agravel gravelroad roadbranching branchingtotothe the south), a pavement (ZB92-P123) quartz-phyricfelsic felsic to south), a pavement (ZB92-P 123) ofofquartz-phyric rocks,typical typical of ofthose thosealong-strike along-strikeofofthe theWiliroy Willroymilisite millsitecaic-silicate calc-silicaterocks. rocks. rocks, S t o pA5, A5,Wiliroy Willroy railway u t , ZB91-15, IAGOD (continued).Looking Lookingnorth northfrom fromthe theWillroy WillroymillmillStop railway cut,c ZB91-15, IAGOD #3#3 (continued). site,the therock rockwall wallofofthe theWiliroy-Geco Willroy-Gecorailway railway cut cut 150 150metres metres away away isissubparallel subparallel to tothe thedominant dominantfoliafoliasite, orthoamphibole-cordierite-garnet gneiss, gneiss,and andthe theeasterly-plunging easterly-plunginglineation lineationisisobvious obvious tionofofthe theexposed exposedorthoamphibole-cordierite-garnet tion andspectacular spectacular(Fig. (Fig.Al). Al).Orthoamphibole-cordierite-garnet Orthoamphibole-cordierite-garnet gneiss gneiss (Unit (Unit 2) 2) isisinterpreted interpreted totobe bemetamormetamorand phosed alteration in the deposits. The phosed synvolcanic synvolcanic alteration the stratigraphic stratigraphicfootwall footwall to to known known economic economic deposits. The unit unitisis concontinuous around around the theinner innerManitouwadge Manitouwadge synform synform from from ltabbitskin Rabbitskin Lake Lake in in the the north, north,totothe theFalconbridge Falconbridge tinuous zone of of subeconomic subeconomic mineralization distance of of about about 30 30 km km (1:25000 (1:25000 map). (Don't spend spend too too zone mineralization to to the east, aa distance map). (Don't long at at this thisoutcrop; outcrop;it's it'snice, nice,but butthere thereare aremuch muchbetter betterexposures exposuresofofaltered alteredrocks rocksatatStops StopsA6 A6and andA7.) A7.) long Theinterlayered interlayered (metre-scale) (metre-scale) orthoamphibole-garnet-cordierite±biotite±plagioclase±staurolite orthoamphibole-garnet-cordierite&biotite~plagioclase&stauroliteand and garnetgarnetThe biotite-sillimanitedxordieriteassemblages assemblages are typical of Orthoamphibole is is present present both both as asaligned aligned biotite-sjllimanite±cordierite of the unit. Orthoamphibole prismsand andlarge large(4—5 (4-5 cm) radiating radiating sprays, sprays,variation variationpossibly possiblyresulting resultingfrom fromheterogeneous heterogeneousdeformation deformationoror prisms post-kinematic post-kinematic recrystallization. recrystallization. Biotite, Biotite, atatleast leastininpart, part,is isfound foundininpseudomorphs pseudomorphsafter afterorthoamphibole, orthoamphibole, suggestingretrograde retrogradepotassic potassicmetasomatism. metasomatism.Quartz Quartzpods podslocally locallycontain contain very verycoarse coarse(10 (10cm cmplus) plus)crystals crystals suggesting 52 �Manitouwadge Manitouwadgefield field guide guide A. A. Known Known deposits, deposits, inner innervolcanic volcanic belt belt I 1 50 metres 0 -- streaky felsic layers Grt-Qtz knots, Bt-St \ e \ I ' - - ---- ,. ,' - - - , 2-X ' f pagmolltc ' Isoclinal rootless folds ; t / I ' \ 1 I I I ' I ' Cpy-Py-Mog ,stringers In I -----' Sll knots FIG. A2. A2. Detailed Detailedgeology geology of of the the Wiliroy Willroy 11 Cu stringer orebody (Table 3) and host host rocks. rocks. Structure Structure FIG. symbols show show dominant dominant D2 D2 foliations foliations and and lineations, lineations, except except for for post-D2 post-D2 kinks kinks (labelled). (labelled). Mineral Mineral symbols abbreviations are areafter afterKretz Kretz(1983). (1983).Dotted Dottedlines linesshow showoutcrop outcropareas. areas. abbreviations of of blue blue cordierite. cordierite. S t o pA6, A6,Wiliroy Willroy 1 alteration section, ZB91-146-147, 164-170, ZB92-P1--P7, ZB92-PI-P7, IAGOD From the the Stop 1 alteration section, ZB91-146--147, 164—170, IAGOD#4. #4. From Willroy milisite, millsite, take take an anovergrown overgrown gravel gravel road east east for for about about1.25 1.25km kmtotothe thechain-link chain-linkfence fenceon on the thenorth north Wiliroy side of of the theroad. road. From Fromthe thewestern westernend endofofthe thefence, fence,the theopen openstope stopeofofthe theWiliroy Willroy11stringer stringerCu Cuorebody orebodyisis side visible (Fig. (Fig. A2). A2). The Therocky rocky knolls knolls to to the the north northand andininthe thefenced fencedarea areaare aremostly mostlypegmatite. pegmatite.The Thefollowing following visible outcrop descriptions descriptions are are from from south south to tonorth, north,from fromstratigraphic stratigraphichanging hangingwall walltotofootwall footwallofofthe theWillroy Willroy11 outcrop orebody. orebody. Walk about about 50 50 metres metres southeast southeast along along aa gravel gravel track rock knoll knoll south The white white Walk track to to a rock south of of the the track. track. The asweathering felsic felsic schist, with with muscovite-rich muscovite-rich partings and shears, shears, is is aa highly highly strained strainedmetavolcanic metavolcanic rock rock asweathering sociated sociated with withthe theinterpreted interpretedD1 Dlfault faultthat thatpasses passesthrough throughthe theWillroy-Geco Willroy-Gecoarea. area. Relict Relictquartz quartzphenocrysts phenocrysts are are visible visible in in thin thin section, section, as aswell well as asabundant abundantmicrocline microcline and and minor minor biotite, biotite, garnet garnet and and epidote. epidote. Foliated Foliated tonalite dykes dykes that thatcut cutthe thefelsic felsicschist schistcould couldbelong belongtotothe thesyn-D2 syn-D2suite. suite.AAmassive massiveaplite-pegmatite aplite-pegmatitedyke dyke tonalite intrudes intrudesalong alongthe theaxial axialsurface surfaceofofa ahigh-angle high-anglekink kinkofofschistosity schistosityand andhas hasan anasymmetrical asymmetricaltail tailthat thatextends extends along alongaafoliation-parallel foliation-parallel shear. shear.The Thetiming timingrelationships relationshipsare areambiguous; ambiguous;either eitheraapre-existing preexistingshear shearinfluenced influenced the theintrusion intrusiongeometry, geometry,ororthe thedyke dykewas wasdeformed deformedduring duringlocal localreactivation reactivationofofshears. shears. Return toward toward the thefence fence to toaarusty rustypavement pavementon onthe thetrack. track.This Thisoutcrop outcropand andseveral severalalong-strike along-strikeare are Return examplesof of sillimanite-muscovite-quartz schist (Unit la), la),in inthis thisexposure, exposure, consisting consisting of of thin alternating alternatinglayers layers examples (1-5 mm) and coarse coarse grained grained muscovite. muscovite.Locally, Locally,the thelayers layersdefine defineisoclinal isoclinalfolds folds(mm(mm-totocm-scale). cm-scale). (1—5 mm) of of quartz quartz and Sillimaniteknots knots are arepresent presentinindiscontinuous discontinuouszones. zones.Several Severalfeatures featuresshow showdextral dextral sense sense of of motion motion in inplan plan Sillimanite view including, including,an anoblique obliquemuscovite muscovitefoliation foliationresembling resemblingaa C-S G S fabric fabric with with mainly mainlydextral dextralasymmetry, asymmetry,quartz quartz view 53 �A. Known deposits, inner volcanic volcanic belt Manitouwadge Manitouwadge field field guide guide lenses with asymmetric tails, and and Z-shaped Z-shaped folds folds and crenulations of the dominant dominant schistosity schistosity (D2). (D2). Muscovite Muscovite lineation (D2?) plunges to the the east, east,whereas whereas the the axes axesof of Z-folds Z-folds and crenulations (D3 or later?) plunge plunge to to the the west. Continue alongthe the south south side side of ofthe the fence fencefor forabout about50 50metres metrestotoaa pavement pavementjust justinin the the trees. trees. The Continue along sillimanite-muscovite-quartz schist has large elongate (easterly-plunging) (easterly-plunging) sillimanite knots, knots, locally locally coalescing coalescing layers. Dyke relationships interesting; a concordant foliated foliated tonalite dyke (50 cm into sillimanitic layers. relationships are again interesting; wide) is cut by several wide) several thin aplitic aplitic dykes. dykes. The Theaplitic apliticdykes dykeshave havesigmoidal sigmoidal traces traces in in the thetonalite tonalite(syn-D2?) (syn-Do?) and tail apophysesininthe the host host schist. schist. The tonalite tail off off into asymmetrical asymmetrical foliation-parallel foliation-parallel apophyses tonalite dyke dyke shows shows small amounts of offset offset along along the the cross-cutting cross-cutting aplites. aplites. In plan view, the asymmetry asymmetry and and offsets offsets are consistent with dextral motion. motion. Interestingly, Interestingly,- 8illimanite sillimanite knots are absent in the host host schist schist for for about about 30 30 cm cm on on each each side side of the tonalite sillimanite-muscovite-quartz schist schist of tonalite dyke. dyke. About About5050metres metresfurther furthereast, east,another anotheroutcrop outcropofofsillimanite-muscovite-quartz contains a foliated tonalite dyke and aplite-pegmatite aplite-pegmatite boudins. boudins. Continue around southeast corner corner of the fence fence and immediately immediately to the east, east, several several Continue around the the southeast of the the fence. fence. At the excellent of muscovite muscovite schist schist are are in in abrupt contact excellent outcrops of contact (covered) (covered) with with orthoamphibole-cordierite-garnet orthoamphibole-cordierite-garnet gneiss (Unit 2). The gneiss Themuscovite muscoviteschist schist isis silky silky white white and and has hasrosettes rosettesofoffine fineaillimanite sillimaniteon on foliation foliation surfaces. surfaces. Close to the contact, contact, the theschist schist isis quartz-rich quartz-rich with with aysmmetric aysmmetricquartz quartzlenticules lenticulesand andpods podsconsistent consistentwith withdcxdextral kinematics, kinematics, and and kinks, kinks,crenulations crenulationsand andfolds foldsof of the thedominant dominantfoliation foliationare arewell welldeveloped developedand andpervasive. pervasive. open stope is along-strike along-strike west westof ofthe the contact. contact. Orthoamphibole-bearing Orthoamphibole-bearing rocks rocks to to the the north are The Willroy 1 open overgrownby byporphyroblastic porphyroblasticminerals. minerals. Orthoamphibole Orthoamphibole displays streaky with semicontinuous quartz lamellae overgrown a blue iridescence, orthoamiridescence, characteristic of of the the presence presence of of exsolution exsolution lamellae lamellae in in an an originally originallysupersolvus supersolvus orthoamphibole. Magnetite and staurolite phibole. staurolite are are also also present, present, the the latter lattermantled mantledby bycordierite cordieriteor orby byaacordierite-gahnite cordierite-gahnite intergrowth, petrographic petrographic evidence evidence of of metamorphic metamorphic decompression decompression reactions. Metre-scale compositional compositionallayering layeringisisdefined definedby byvariation variation in in proportions, proportions, textures and Metre-scale and assemblages assemblages of metamorphic minerals; minerals;for forexample, example,on onthe the northern northern part part of of the outcrop, garnet-poor metamorphic garnet-poor rocks are transitional to to garnetiferous garnetiferous rocks. rocks. First-order First-order compositional compositionallayers layers and and second-order second-order lamellae probably represent aa comcombination of primary and tectonic tectonic structures. the trail to Continue to the north north side side of of the the fence, fence, and and follow follow the to the the outcrops outcrops between between the thefence fence and and Strike Strike Lake, comprising an excellent section typical of rocks in in the footwall of alkali-depleted alkali-depleted Fe-Mg Fe-Mg rocks footwall to to the theWillroyWillroyGeco deposits. There There isisaagradual gradualnorthward northwardincrease increaseininleucocratic leucocraticfelsic-looking felsic-lookinglenses lenses and and semicontinuous semicontinuous layers, in some cases, resembling attentuated hinge hinge zones zones of of isoclinal isoclinal folds. Quartz-rich Quartz-rich layers layers and andlamellae lamellae are overgrown by garnet garnet porphyroblasts showing differential differentialdextral dextralrotation. rotation. Some layers layers are are spotted by overgrown by porphyroblasts showing by staurolite with aa white plagioclasewhite mantle mantle of of partially partially pinitized pinitized cordierite. cordierite. The Thepresence presence of of the theassemblage, assemblage, plagioclasewide) suggests suggestseither, either, that that the dyke biotite-gedrite-cummingtonite, in a concordant intermediate dyke (20 cm wide) dyke was hydrothermally hydrothermally altered altered or, or, that itit exchanged was exchanged with altered host rocks rocks during metamorphism. and obliterates layering and and foliation. foliation. The biotite A local irregular discordant patch of of biotite biotite overgrows overgrows and biotite weakly or or randomly randomly oriented oriented but but shows shows aa poorly poorly developed developedcrenulation crenulationsuggesting, suggesting,asasatatStop StopA5, A5,that that at is weakly least some biotite is of retrograde origin. in biotite, biotite, extracted extracted from from mica mica schist schist at the least origin. Monazite Monazite inclusions inclusions in the Geco mine, define define aa U-Pb U-Pb isotopic age of of 2661&1 2661±1 Ma, Ma, possibly possiblydating dating aa retrograde retrograde event event (Schandl (Schandi et et al., Geco mine, isotopic age 1991). 1991). Stop trondhjemite, ZB91-20, ZB92-P191--P193. S t o p A7, A7,Synvolcanic Synvolcanic trondhjemite, ZB91-20, ZB92-P191-P193. Return Return totothe theWillroy Willroymilisite millsite and and railway cut, cut, and find the easiest map). Continue easterly railway easiest access access to the railway railway bed (1:25000 (1:25000 map). easterly along the old railway keeping keeping track track of of distances distances from fromthe the first first outcrop outcrop on on the the south south side side (just east of a fluorescent? bright green pond). Initially orthoamphibole-cordierite-garnet gneiss (Unit 2), foliated Initiallythe theroute routepasses passesexposures exposuresof of orthoamphibole-cordierite-garnet trondhjemite mafic and and felsic felsic rocks rocks(Unit (Unit 4), 4), the the latter interpreted trondhjemite (Unit 12), 12), and and enclaves enclaves of mixed mixed mafic interpreted to to be be protolith to tosynvolcanic synvolcanicalteration. alteration. After After400 400metres, metres,foliated foliatedtrondhjemite trondhjemitetypical typicalofofUnit Unit1212isisexposed exposed the protolith in several contains magnetite magnetite and and biotite biotite and, and, near the several outcrops. outcrops. In general, general, trondhjemite trondhjemite contains the contact contact with with orthoamphibole-garnet-cordierite gneiss, orthoamphibole-garnet-cordierite gneiss,garnet garnetisislocally locallyabundant. abundant. Our Our field field interpretation interpretation of of the the unit as a synvolcanic intrusion corroborated by by U-Pb U-Pb zircon zircon geochronology geochronology giving of 2720±3 2720&3 Ma, Ma, within within synvolcanic intrusion was corroborated giving an age of of the the age age of of felsic felsic volcanism volcanism (Figs. 10 10 and 11, 11,Table Table 2). 2). 'Immobile' 'Immobile'elements elementsiningeochemical geochemicalanalyses analyses error of of of trondhjemite from from this this and andother otherlocations locationsare areindistinguishable indistinguishablefrom fromthose thoseofofquartz-phyric quartz-phyricfelsic felsicrocks rocks 24 and 27), suggesting intrusive and extrusive equivalents of of the same magma. (Figs. 24 Continue to rock knolls knollson onthe the north north side side of ofthe the rail rail bed; bed; you you are are about about 100 metres metres north north to 750 750 metres to to low rock of Strike Lake (not visible) and Stop Stop A6. A6. Trondhjemite Trondhjemite isis host host to todiffuse diffuse 'seams' 'seams' of of garnet-orthoamphibolegarnet-orthoamphibolecordierite-biotite, some cordierite-biotite, someofofwhich whichare arefolded foldedand andhave havean anaxial axialplanar planar foliation. foliation. We We interpret interpret the seams as the result result of of synvolcanic synvolcanic alteration similar similar to to that thatofofadjacent adjacentorthoamphibole-garnet-cordierite orthoamphibole-garnet-cordierite gneiss gneiss and, and, by trondhjemite as as aa high-level high-level synvolcanic to by implication, we we interpret interpret the trondhjemite synvolcanicintrusion intrusionthat that contributed contributed heat to the hydrothermal system. Trondhjemite Trondhjemite intruded intruded its itsown own aureole aureole of hydrotbermally hydrothermally altered rocks and, upon subsequent cooling, was was subject subject to incursion by hydrothermal subsequent hydrothermal fluids. fluids. Stop rocks, ZB91-21, A8,Pillowed Pillowedmafic mafic rocks, ZB91-21,ZB92-P202. ZB92-P202. This Thisisisa aspecial specialstop stopfor forkeeners keenersand andsceptics sceptics S t o p A8, 54 �A. Known deposits, inner volcanic volcanic belt Manitouwadge field guide who need proof proof of of mafic mafic volcanic volcanicrocks rocksnorth north of of the the Willroy-Geco Willroy-Gecoarea. area. Continue Continue for for about about 1.5 km along who need the railway railway cut to to dark dark rocks rocks exposed exposed on both both sides. sides. On Onthe thenorth northside, side,some somehighly highlydeformed deformed pillows pillows are discernible. Geochemically, these rocks rocks are are tholeiitic tholeiitic basalts basalts similar to mafic rocks in the outer Geochemically, these outer volcanic volcanic belt belt of the the Manitouwadge Manitouwadgesynform synform(Figs. (Figs.23—26). 23-26). A9—A20. Slim Lake Lake section section A9-A20. Slim field trip trip visits visits many many rock rock units units already described, but but it is The Slim Lake Lake field already described, is useful useful as aa near-continuous near-continuous 'stratigraphic' section 'stratigraphic' section across across the Willroy Willroy area (Fig. (Fig. Al) Al)including including exposures exposures of of straight straight gneiss gneiss (annealed (annealed mylonite) associated with with the interpreted mylonite) associated interpreted D1 Dl fault. The Theoutcrops outcrops are aremainly mainly along along the themargins margins of of aatailings tailings meadow, formerlySlim SlimLake. Lake. The The trip trip is divided meadow, formerly divided into two parts; firstly, firstly, north of of the the Willroy Willroy road road along along the eastern exposuresare are described describedfrom fromnorth north to south; eastern side side of of the themeadow meadow(A9—A14), (A9-Al4), exposures south; secondly, secondly, south of of the road descriptionscontinue continuetotothe thesouth. south. The base road along along the thewestern western side sideof of the themeadow meadow(A15—A20), (Al5-A20), descriptions base of of the supracrustal supracrustal section section(to (tothe thenorth) north)comprises comprisesinterlayered interlayeredmafic maficand andfelsic felsicmetavolcanic metavolcanicrocks, rocks, invaded invaded by by trondhjemite to granodiorite. To synvolcanic trondhjemite To the the south, south, about about150 150metres metres of of orthoamphibole-garnet-cordierite orthoamphibole-garnet-cordierite gneiss (Unit 2) and rocks (Unit 4) are and enclaves enclaves of less altered mixed mafic/felsic mafic/felsic rocks are overlain overlain by aa discontinuous discontinuous belt or quartz-phyric felsic or lens lens of quartz-phyric felsic metavolcanic rnetavolcanic rocks (Unit 8). This Thisnortherly northerlylens lensofofquartz-phyric quartz-phyricfelsic felsicrocks, rocks, about 150 150 metres thick at at Slim Slim Lake, Lake, is is interpreted interpreted to tobe beequivalent equivalent to tothe thesoutherly southerlylens lensofofsimilar similarrocks rocks (e.g. Stop A3), repeated across across a D1 Dl fault (Zaleski (Zaleski and Peterson, 1993a). 1993a). Quartz-phyric Quartz-phyric rocks rocks are are overlain overlain by the iron formation (not exposed) that that hosts hoststhe theWiliroy Willroy22and and55deposits depositstotothe theeast, east,and andbyby50—100 50-100 metres (not exposed) of sillimanite-muscovite sjllimanite-muscovitefelsic felsjcrocks rocks(Unit (Unitla). la). The The southernmost southernmost unit unit on on the traverse is a laminated of laminated felsic felsic interpreted to lie on on the D1 fault that truncates some Dl fault some map units (notably (notably iron iron formation) and straight gneiss interpreted repeats part part of of the thesection section(quartz-phyric (quartz-phyricfelsic felsicrocks, rocks, iron iron formation, formation,sillimanite-muscovite-quartz sillimanite-muscovite-quartz schist). west on on the the Willroy Wiliroy mine mineroad roadfrom fromthe the millsite millsiteand andrailway railwaycut, cut,turning turning north north on on the dirt road Continue west that follows meadow. Stay on the high road over a containment dam (Stop that follows the east side of the tailings meadow. (Stop A12 A12 is short eastern eastern fork fork of of the the road road somewhat somewhatbelow belowthe thedam). dam).Although Althoughthe theroad roadpeters petersout out after after the the dam, along aa short you should should be be able to drive (at your own risk) to the north end own risk) end of of the meadow meadow to another dam. Be Be sure sure to to look down down over over the the steep steep northern northern side of the dam for a view of the remnants of Slim Lake and a perspective look on the thickness thickness of the tailings tailings pile. pile. Stop trondhjemite, ZB92-P99. S t o p A9, A9, Potassic Potassicvariant variantofofsynvolcanic synvolcanic trondhjemite, ZB92-P99.The TheStop Stopisiseast eastofofthe thetailings tailings dam along the edge edge of the woods woods (Fig. (Fig. Al); Al);more moreoutcrops outcrops of of the the same samerock rock lie lie along along the the west west side side of of the the dam. dam. The Thefoliated foliatedgranodiorite granodioriteisistexturally, texturally,modally modallyand andgeochemically geochemicallysimilar similarto to trondhjemite trondhjemite(e.g. (e.g.Stops StopsA7 A7 and Al2), A12), especially especially in the the abundance abundance of of coarse coarse grained quartz and and magnetite magnetite porphyroblasts. porphyroblasts. We We interpret interpret potassic variety variety of of the thesynvolcanic synvolcanic intrusion. foliated granodiorite as aa potassic Stop S t o p AlO, A10, Quartz-phyric Quartz-phyricfelsic felsicrocks rocksini nmixed mixedmafic-felsic mafic-felsicrocks, rocks,ZB92-Pl01. ZB92-PlOl. Retrace Retrace the the route to the south approximately approximately 300 300 metres to an old old drill road. Walk Walk 50 50 metres east along drill road to to some some small outcrops on on the north side with a few quartz quartz eyes is part of outcrops side of of the the road. road. The Thefelsic felsicmetavolcanic metavolcanic rock rock with eyes is of the the package of of interlayered mafic and felsic affected by by synvolcanic alteration. alteration. felsic metavolcanic rocks, elsewhere affected Stop mafic-felsic rocks, (optional), ZB92-Pl02. S t o p All, A l lMixed , Mixed mafic-felsic rocks, (optional), ZB92-PlO2.Retrace Retracethe theroute routefor foranother another100 100metres metres south of south of the drill road and and look look for an outcrop just in in the the woods woods to the the east. east. The Theexposure exposurebelongs belongs to to the the same map unit unit as asStop StopAlO, AlO,here herecharacterized characterizedby byintimitely intimitelyinterlayered, interlayered,fine finegrained grainedmafic maficand andfelsic felsicrocks. rocks. that mafic volcanism was waspartly partly coeval. coeval. The The numerous numerous thin thin cross-cutting The interlayering suggests that mafic and felsic felsic volcanism quartz-rich and granitic granitic veinlets veinlets have have been been folded. folded. Stop ZB92-P104, ZB91-4. A12,Foliated Foliatedtrondhjemite, trondhjemite, ZB92-PlO4, ZB91-4.Continue Continuesouth southover overtailings tailings dam damtotoaalower lower S t o p A12, eastern fork fork of of the the road; road; turn north and short distance outcrop on on the the east. eastern and continue continue down down aa short distance to a pavement pavement outcrop The exposure exposure is is typical typical of of synvolcanic trondhjemite, quartz-rich leucocratic and foliated, with magnetite magnetite and and local biotite-rich tonalite dyke dyke (20 (20 cm) probably biotite-rich patches. patches. A A foliated foliated plagioclase-porphyritic plagioclase-porphyritic tonalite probably belongs belongs to the syn-D2 syn-D2 suite. suite. Stop S t o p A13, Orthoainphibole-garnet-cordierite Ortho-phibole-gwnet-cor&eSte gneiss gneiss and andmixed mixedmafic-felsic mafic-felsic nietavolcanic metavolcanic rocks, ZB92-P106,P109, P109,P441. P441. Continue Continuesouth south to to a broad broad area of pavement pavement outcrops outcrops that that form the top ZB92-PlO6, top of of the the low low knoll east of Slim Lake and north of knoll east Lake and of the the Willroy Willroy road. These These extensive extensive outcrops are part of of the thefootwall footwall alteration zone zone characterized characterized by byorthoamphibole-garnet-cordierite orthoamphibole-garnet-cordierite gneiss; gneiss; however, however, hydrothermal hydrothermal alteration alteration was apparently apparently heterogeneous, protolith. Compositional heterogeneous, leaving leavinghints hints of of the the interlayered interlayered mafic-felsic protolith. Compositionallayering layeringis is defined by by metamorphic metamorphic assemblages that that include; quartz, quartz, orthoamphibole, garnet, cordierite, cummingtonite, cummingtonite, hornblende, sillimanite,staurolite, staurolite, gahnite gahuite and and plagioclase. plagioclase.IfIftime timepermits, permits,aa visit visit to to the the eastern eastern end of of the hornblende, sillimanite, interesting. The fold limb limb isistruncated truncated outcrops is interesting. The metamorphosed metamorphosed altered altered rocks rocks are are folded and in one place, a fold by a broad, of the the same minerals, suggesting local metamorphic metamorphic redistribution redistribution of broad, diffuse diffuse zone of of orthoamphiboleorthoamphibolebearing assemblages. assemblages. Stop gneiss, ZB92-P108 (optional). S t o pA14, A14, Orthoaxnphibole-garnet-cordierite Orthoamphibole-garnet-cordierite gneiss, ZB92-PI08 (optional).Return Returntotothe theWillroy Willroyroad road about 50 50 metres to to an an outcrop outcrop on on the the east east side. side. In Inthis thisexample exampleof of metamorphosed metamorphosed altered altered and continue south about 55 �A. Known deposits, inner volcanic volcanic belt Manitouwadge field guide rocks, layering is defined defined by sillimanite-cordierite sillimanite-cordierite and orthoamphibole-cordierite-staurolite orthoamphibole-cordierite-staurolite assemblages. assemblages. AA biotite-rich zone is interpreted to to be be the the result result of of local local potassic retrogression. Note Note the the somewhat somewhat disorganized, disorganized, D3 or D4crenulations crenulations and and kink folds, preferentially preferentially developed developedin in the the micaceous micaceouszone. zone. Note Note also also the the spectacular sprays of orthoamphibole nearest nearest to the the road. road. Stop ZB92-P37. S t o p A15, A15,Felsic Felsic metavolcanic metavolcanicrock rockwith withorthoamphibole-garnet, orthoamphibole-garnet, ZB92-P37.Take Takethe theWillroy Willroyroad road to the second leg leg of of section. section. The first brief stop is the west west side side of of the the Slim SlimLake Lake tailings tailings meadow meadow to to commence commence second is a pavement outcrop thethe following stops (A15—A20) outcrop along alongthe thesouth southside sideofofroad. road.This Thisand and following stops (Al5-A20) are areeasily easilyaccessed accessed by walking along the western margin margin of of the the meadow. meadow. We have back-tracked back-tracked to to the north and We have and are areonce onceagain againininUnit Unit4,4,interlayered interlayeredmafic-felsic mafic-felsic rocks, rocks, here amounts of biotite, hornblende, by heterogeneous heterogeneous felsic felsic metavolcanic metavolcanic rock. rock. Minor Minor amounts hornblende, magnetite, magnetite, represented by garnet, zones of of garnet, and and local local quartz quartz and andplagioclase plagioclasephenocrysts(?) phenocrysts(?) define define aa weak weak compositional compositional layering. A few zones orthoamphibole-garnet alteration, although much of the orthoamphibole orthoamphibole-garnet are typical of synvolcanic alteration, orthoamphibole has been been replaced replaced by biotite. The Themetavolcanic metavolcanic rocks rocks are are intruded intruded by by foliated foliated tonalite. tonalite.Some Someminor minorfolds foldsare arepresent, present, and there there isis an anindication indication of of dextral, dextral,north-side-down north-side-down kinematics kinematics from porphyroblasts porphyroblasts with asymmetric asymmetric tails of matrix material. S t o p A16, A16, Contact Contactofoftrondhjemite t r o n d G e m i tand e a naltered d altered rocks, ZB92-P77. Walk southalong alongwest west side side of of Stop rocks, ZB92-P77. Walk south meadow, keeping keepingtrack track of of the the distance distance from from the the first first outcrop beyond beyond Stop A15. A15. At 60 metres, just before before an outcrop of fine grained hornblende schist, schist, head west west up into the the woods. woods. After After climbing climbing up up aa steep steepslope slopeover over deadfall (50—60 m),go gototothe the north north end of a low (50-60 m), low ridge of outcrop. The north end end of of the the outcrop outcrop isis medium medium to to coarse coarse grained trondhjemite; trondhjemite; the contact between between this and altered rocks is exposed exposedin inthe the central central part part of of the the outcrop outcrop under under aa tree limb. limb. At the contact, the the trondhjemite trondhjemite finer grained, grained, more more strongly stronglyfoliated foliatedand andcontains containsmore moregarnet garnetand andbiotite biotitethan than usual. usual. The altered is finer altered rocks rocks grading from from very very coarse coarse grained grained garnet-biotite garnet-biotite schist schist near near the contact to are heterogeneous, heterogeneous, grading tofiner finer grained grained felsic rocks, rocks,to to intermediate intermediate rocks rocks with with hornblende hornblende and and cummingtonite layers. layers. The garnetiferous felsic The relationships relationships suggest that incipient incipient alteration alteration affected affected trondhjemite along the contact. Carefully scramble scramble back back down downtoto the the meadow meadowand and continue continuesouth. south. Take Take aa quick quick look look at at the hornblende Carefully schist previously noted, a less of the rocks just visited. less altered altered equivalent equivalent of some of visited. Stop synvolcanic alteration, ZB92-P56, P79. Continue S t o p A17, A17,Metamorphosed Metamorphosed synvolcanic alteration, ZB92-P56, P79. Continuetotoa alarge largeoutcrop, outcrop,about about 150 metres metres south, south, dominated by pegmatite but with with aa sheet sheet of of garnet-orthoamphibole-biotite garnet-orthoamphibolebiotite schist schist with very coarse garnet. garnet. About coarse About 40 40 metres metres further further on on (190 (190 m), m),ininaasmall smallpavement pavement outcrop outcrop fresh fresh blue blue cordierite cordierite is is present, with sprays sprays of of orthoamphibole, and tiny staurolite staurolite grains. grains. Stop felsic rocks, ZB92-P81—P83, S t o pA18, A18,Quartz-phyric Quartz-phyric felsic rocks, ZB92-P81-P83,P54. P54.Continue Continuetotoseveral severallow lowoutcrops outcropsbetween between about 300 300 to to 400 metres south. south. These Theserocks rocks are arepart partofofthe thenorthern northernbody bodyofofquartz-phyric quartz-phyricfelsic felsicmetavolcanic metavolcanic rocks, characterized characterized by by abundant abundant (to 20%) porphyroblasts. 20%) quartz phenocrysts and ubiquitous magnetite porphyroblasts. Optional for keeners head up up into woods near near the northernmost keeners and breccia breccia lovers; lovers; head northernmost exposures exposures of the quartz-phyric felsic felsic rocks rocks looking looking for the the cut cutlines lines(somewhat (somewhatovergrown) overgrown)of of the theWillroy Willroygrid. grid.Find FindL130+OOE L130+00E at approximately and a small stripped stripped outcrop approximately25+OON 25+00N and outcrop of of monolithologic monolithologic quartz-phyric felsic breccia. Angular Angular fragments, ranging ranging in in size size from from very very small small to to metre-scale, metre-scale, are are supported supported in in a pale green fragments, green matrix enriched enriched in biotite, hornblende and epidote. Stop felsic schist, ZB92-P86, P87. Several small outcrops S t o p A19, A19,Sillimanite-knot Sillimanite-knot felsic schist, ZB92-P86, P87. Several small outcropsbetween between500 500and and600 600 1. metres document the presence presence of Unit 1. Stop (annealed mylonite), ZB92-P88. At At approximately S t o p A20, A20,Straight Straightgneiss gneiss (annealed mylonite), ZB92-P88. approximately600 600metres, metres,go go10 10metres metres with some some thin thin biotitebiotite- and into the woods to a large outcrop. The The pink pink to to white, white, quartzose quartzose laminated gneiss, with hornblende-rich layers, example of straight gneiss, gneiss, forming part of of a zone zone hornblende-rich layers, isis very very hard hard and flinty. flinty. This is an example of laminated rocks, lying on on the interpreted D1 Dlfault that that passes passes through the the Willroy-Geco Willroy-Geco area. In In this this case, case, the straight granoblastic texture. texture. Some Somegarnet garnetisispresent presentlocally, locally,and andvery very straightgneiss gneiss is is completely completely annealed to to aa granoblastic fine magnetite porphyroblasts are surrounded surrounded by by leucocratic leucocratic halos. A21. Naina N a m a Creek Creek deposit deposit S t o p A21, A21,Naina N a m aCreek Creek Mines deposit, ZB91-110, IAGOD#5. #5.From F'romthe thewestern westernmargin margin of of the tailings tailings Stop Mines deposit, ZB91-110, IAGOD meadow, drive continuation of Willroy road Nama Creek Creek and and Willecho Willecho meadow, drive northwest northwest on on the continuation of the Willroy road leading leading to to the Nama (1:25000 map). 600 metres from the meadow, turn off off on a gravel road to the the southwest southwest and and deposits (1:25000 map). About 600 flooded open cut of of the the Nama Nama Creek Creek deposit deposit (Fig. (Fig. A3). A3). continue 500 metres metres to the flooded Nama Creek Creek Mines Mines deposit deposit (also (also known known as the the Big Big Nama Nama deposit) deposit) was was aa marginally marginally economic economic ZnThe Nama (Table 3) hosted hosted by by iron iron formation formationimmediately immediately south south of of orthoamphibole-garnet-cordierite orthoamphibole-garnet-cordierite gneiss gneiss rich orebody (Table The iron iron formation formation can can be be traced traced east east to to that thathosting hosting the theWiliroy Willroy 2/5 215 orebodies. orebodies. As As traced traced by by (Unit 2). The subeconomic extension of the Nama Nama Creek Creek mineralization mineralization apparently apparentlyplunges plungeseasterly easterlytotoconverge converge drilling, the subeconomic in the subsurface subsurface with the Willroy Willroy 3 horizon horizon (1:25000 Dl fault, (1:25000map). map). The The two two zones zones are are separated separated by by the D1 56 �A. A. Known Known deposits, depositsl inner inner volcanic volcanic belt belt Manitouwadge Manitouwadgefield field guide guide I L 22 r 22 Dl DI gneissosity gneiss0sit.y D2 D2 foliation foliation -21 D2 D2 lrneation lineation . \\\40 40 D2 D2 fold f o l d axial a x i a l plane plane x22 D2 fold f o l d axis axis 22 D2 FIG. A3.Geology Geologyand andfield-trip field-tripstops stopsininthe thearea areaofofananS-shaped S-shapedD2 D2fold foldofofiron ironformation formation(Unit (Unit9)9) FIG.A3. andfelsic felsicmetavolcanic metavolcanic rocks rocks (Unit (Unit 6). 6). Dashed Dashedlines linesare arecut cutlines linesofofNoranda's Noranda'sWiliroy Willroygrid. grid. and interpreted deposit extensively interpreted totolie liesouth southofofthe theNama NamaCreek Creekdeposit. deposit.The The depositis is extensivelyinvaded invadedby bypegmatite-aplite pegmatiteaplite sheets sheets which which tend tendtotoobscure obscurefield fieldrelationships. relationships. On flooded orthoamphibole-garnet-cordierite On the thenorth northside sideofofthethe floodedcut, cutl orthoamphibolegarnet-cordieritegneiss gneisshas has minor minor amounts amountsof of magnetite?ilmenite, ilmenite, chalcopyrite, chalcopyritel pyrrhotite pyrrhotite and and biotite, biotite?asaswell wellasasstaurolite stauroliteinclusions inclusionsinincordierite cordieriteand and magnetite, garnet.Orthoamphibole-bearing Orthoamphibolebearinggneiss gneissisisintercalated intercalatedwith withsillimanitic sillimaniticlayers layersand, and,ininsome somecases, cases?sillimanite sillimanite garnet. occurs in in orthoamphibole-bearing orthoamphibolebearing assemblages. assemblages. However, However? sillimanite or occurs sillimanite isis mantled mantled by by cordierite cordierite or or quartz, or engulfed engulfed by by skeletal skeletal garnet, garnet?textures texturessuggestive suggestiveofofmetamorphic metamorphicdecompression decompressionreactions. reactions. At pegmatite is is interleaved Atthe theeastern easternend endofofthe thecut, cut, pegmatite interleavedwith withchlorite-mica chloritemicaschist, schist?foliated foliated tonalite tonaliteand and semi-massive pyrite and and magnetite. magnetite. In Inthe theconcordant concordantpegmatite pegmatitedyke, dyke,coarse coarsegrained grainedquartz, quartz?plagioclase plagioclaseand and semi-massive sprays sprays of of sillimanite sillimanite (to (to 55cm) cm)tend tendtotobebeoriented orientedperpendicular perpendicular totodyke dykemargins, margins?looking looking as as though though they they nucleated nucleated on on the thewall wall rock rock and and grew grew into into the the pegmatite, pegmatite, apparently apparentlywithout withoutsubsequent subsequent deformation. deformation. A22—A23. D2 foldsof ofiiron formation/felsic metavolcanic A22-A23. D 2 folds r o n formation/felsic metavolcanic contact contact Southwest of of the the Nama NamaCreek Creek deposit, deposit?the thethick thicksouthernmost southernmost iron ironformation formation(the (thesame sameas asthat thatofofStop Stop Southwest A2) A2) of of the theinner innervolcanic volcanicbelt beltdefines definesaamap-scale map-scaleS-fold S-fold (1:25000 As). Interdigitations Interdigitationsofoffelsic felsic (1:25000 map, mapl Fig. Fig. A3). rock and andiron ironformation formationrelated relatedtotoparasitic parasiticfolds foldsininthe thehinge hingeregion regionare arewell wellexposed. exposed.Locally, Locally,aagneissic gneissic rock fabric (Dl)ininthe thefelsic felsicrocks rocksisisinvolved involvedin in folding. folding.The Thedominant dominantD2 D2foliations foliationsand andlineations lineations are areparallel paralleltoto fabric(D1) theaxial axialplanes planesand andfold foldaxes, axes?respectively, respectivelylofofoutcrop-scale outcrop-scale folds. folds. The Theaxial axialtrace traceofofthe themap-scale map-scaleS-fold S-foldisis the 57 �A. Known Known deposits, deposits, inner innervolcanic volcanicbelt belt A. Manitouwadgefield field guide guide Manitouwadge D2 folds of D l fabric tonalite dyke with D 2 schistosit~ FIG. A4. A4. Sketch Sketchof ofoutcrop outcroprelationships relationships(Stop (StopA23) A23)between betweenD2 D2folds foldsof ofDi Dlgneissosity gneissosityininfelsic felsic FIG. metavolcanic rock, rock, and and D2 D2 schistosity schistosity in in aa syn-D2 syn-D2 tonalite tonalitedyke. dyke. metavolcanic D3Manitouwadge Manitouwadgesynform synform and and the theS-asymmetry S-asymmetryisisinconsistent inconsistentwith withwhat whatwould wouldbe beexpected expected deformed by by the theD3 deformed for aa D3 D3 parasitic parasitic fold fold related related to tothe thesynform. synform.On Onthe thebasis basisofofthese the= observations, observations,the theS-fold S-fold isis interpreted interpreted to to for be a D2 fold that reorients vestiges of Dl fabric preserved in felsic rocks in the strain shadow near the hinge be a D2 fold that reorients vestiges of D1 fabric preserved in felsic rocks in the strain shadow near the hinge region. A A major majorD2 D2sheath sheath fold fold isis interpreted interpreted to torepeat repeatthe theD1 Dl fault faultand andmineralized mineralizediron iron formation formation of of the the region. Willroy-Geco area between the the Nama Nama Creek Creek and and Willecho Willecho deposits deposits (Fig. (Fig. 4). 4). Wiliroy-Geco area between Access to to the the exposed exposed contact contactinvolves involves about about 700 700 metres metres (one (one way) way) of of bushwacking bushwacking on on the the somewhat somewhat Access overgrown cut lines of the Willroy grid. The exposures are worth viewing for those interested in the pre-D3 overgrown cut lines of the Willroy grid. The exposures are worth viewing for those interested in the pre-D3 structuralhistory historyof ofthe thearea. area.On Onthe thesouth southside sideofofthe theflooded floodedcut cutofofthe theNama NamaCreek Creekdeposit, deposit,look lookfor forL95E L95E structural (17+00N, English Although the the picket picket may may be be fallen fallenand andillegible, illegiblelitit should should be be possible possible to tospot spotthe theold old (17+OON, English units). units). Although (218') about 530 metres to the Willroy baseline. Remember that your compass cut and follow it southwest cut and follow it southwest (2 18°) about 530 metres to the Willroy baseline. Remember that your compass may not notbe bereliable. reliable. may S t o p A22, Foldsinin iron formation, ZB91-46. Continue northwest(308°) (308O)170 170metres metres on on the the Willroy Willroy Stop A22, Folds iron formation, ZB91-46. Continue northwest baseline to about 20 metres beyond L90E and some excellent stripped outcrop. In the quartz-magnetite baseline to about 20 metres beyond L9OE and some excellent stripped outcrop. In the quartz-magnetite iron formation formation some some groups groups of of layers layers define define S-folds S-folds (D2) are disrupted disrupted by by stratabound strataboundbreccia breccia iron (D2) and and others others are zones. The Thebreccias, breccias,consisting consisting of of segmented segmented quartzose quartzose layers layers in dark matrix, matrix,tend tendtotobebelocalized localizedwhere where zones. in aa dark quartzose layers layers are are thin thin and/or and/orproportionately proportionatelyless lessabundant abundantthan thandark darklayers layersofofmagnetite magnetiteand andFe-silicates. Fe-silicates. quartzose Quartzose fragments fragments are are preferentially preferentially oriented oriented subparallel subparallel to to the the axial axial traces traces of of folded folded layers. layers. The The apparently apparently Quartzose competent behaviour of quartzose fragments suggests that brecciation occurred after diagenesis or lowgrade grade competent behaviour of quartzose fragments suggests that brecciation occurred after diagenesis or low metamorphism, conditions conditions under A pegmatite pegmatite cuts cuts across across the the iron iron metamorphism, under which which quartz quartz is is relatively relatively competent. competent. A formation and and contains contains aa discontinuous discontinuous (<5 (<5 mm) mm) garnetiferous garnetiferous zone zone at the contact. contact. formation at the S t o pA23, A23,D2 D folded 2 folded contact, ZB91-50, ZB92-Pl3.Continue Continuenorthwest northwest on on the thebaseline baselineanother another 50-60 Stop contact, ZB91-50, ZB92-P13. 50—60 metres to to the the crest crest of of aa hill hill with with aaview view down down to to Garnet Garnet Lake Lake and and along along the the hill hill top top and and metres the baseline. baseline. On On the northwest-facing slope, there are are good good exposures exposures of of interfingering interfingering iron felsic rock. Scattered northwest-facing slope, there iron formation formation and and felsic rock. Scattered outcrops of of folded folded iron iron formation formation in in the the thick thick bush bushshow show changes changes between between ZS-asymmetry related to the the outcrops Z- and and S-asymmetry related to axial traces traces of ofD2 D2 minor minorfolds folds(Fig. (Fig.A3). A3). axial Continue just over the the hill hill crest crest north north of of the thebaseline baseline and and along along L87+50E L87+50E to to exposures exposures of of the thefolded folded Continue just over contact between between iron iron formation formation and andfelsic felsicrock rock (with (withsparse sparsequartz quartzeyes). eyes). Locally, Locally, the the felsic felsic rock rock has has aa contact crenulated gneissic gneissic layering layering (D1) (Dl) defined defined by by quartz quartz lamellae lamellae and and biotite-garnet-rich biotite-garnet-rich zones. zones. The Thebiotite biotitehas has crenulated a crystallographic-preferred orientation parallel to crenulation traces. Near the folded contactl felsic gneiss a crystallographic-preferred orientation parallel to crenulation traces. Near the folded contact, felsic gneiss contains odd odd irregular irregularmuscovite-schist muscovite-schistenclaves enclaves (some (some look look angular, angular, some some like like rootless rootless isoclinal isoclinal folds). folds). The The contains gneissosity in in the the host host rock rock isisfolded, folded,whereas, whereas, muscovite muscovite in in the the enclaves enclaves has has an an axial axial planar planar orientation orientation(Fig. (Fig. gneissosity A4). We We interpret interpretthe thegneissosity gneissositytotobe bea aD1 Dlfoliation foliationpreserved preservedin inthe thehinge hingeregion regionof ofthe themap-scale map-scaleD2 D2fold. fold. A4). A tonalite dyke subparallel to the axial traces of D2 folds (of somewhat variable orientation) near the A tonalite dyke subparallel to the axial traces of D2 folds (of somewhat variable orientation) near the iron formation/felsic contact has an axial planar foliation, parallel to that in the irregular muscovite-schist iron formation/felsic contact has an axial planar foliation, parallel to that in the irregular muscovite-schist enclaves in adjacent felsic felsic rocks Ad). The Therelationships relationships suggest suggest that that the thedyke dyke was was intruded intruded during during enclaves in adjacent rocks (Fig. (Fig. A4). D2 deformation, deformation, interpreted interpreted to to be bebroadly broadlycoeval coeval with with peak peak metamorphism. metamorphism. On Onthe thebasis basisofoflithology, lithologylfield field D2 relations and geochemistry, the dyke is one of a suite of tonalite dykes, other probable examples of which relations and geochemistry, the dyke is one of a suite of tonalite dykes, other probable examples of which were seen seen at at Stops StopsAl, Al,A2 A2and andA5. A5.AAsample sampleofofthe thedyke, dyke,collected collectedfor forgeochronology, geochron~logy~ contained no noseparable separable were contained 58 �A. Known deposits, inner volcanic volcanic belt Manitouwadge field guide zircon. Monazite, definesaa U-Pb U-Pb age age of of 2671k3 2671±3 Ma Ma (Fig. 14, Table zircon. Monazite, including including grains of of igneous igneous morphology, defines 2), from the the Geco mine (Davis (Davis et et al., 1994), 21, within error of of both both 2675±1 2675kl Ma Ma metamorphic metamorphic monazite monazite from Geco mine 19941, and 2669±3 Ma monazite monazitefrom fromaa prepre- to to syn-Di pegmatite (Stop (Stop A26). A26). The 2669h3 Ma syn-Dl pegmatite The estimated estimated temperature temperature of of peak peak metamorphism (650°C (650°C) in in the Manitouwadge belt is is less lessthan than the the closure closure temperature temperature of of the the U-Pb system in Manitouwadge belt monazite Heaman and and Parrish, 1991). (7OO0C, Heaman 1991). Nevertheless, Nevertheless, it would would appear that monazite monazite ages ages are are dating dating monazite (700°C, metamorphic or late metamorphic metamorphic events, eventsl or that that monazite monazitecontinued continued to toexchange exchange isotopes isotopes during during protracted protracted regional cooling and and decompression. decompression. A24—A26. Willecho3 3pit pitaand inner hinge hinge of of tthe A24-A26. Willecho n d inner h e Manitouwadge synform D1/D2 folding folding and and faulting faulting near the hinge region of of The three three Willecho Willecho orebodies orebodies lie in an area of complex D1/D2 synform (1:25000 (1:25000mapl map,Fig. Fig.4)> 4),and andititisisdifficult difficulttotoreconstruct reconstructtheir theirexact exactstratigraphic stratigraphic the D3 Ds Manitouwadge synform relationship relationship to orebodies orebodies in the the Wiliroy-Geco Willroy-Geco area. North NorthofofWillecho Willecho3, 3,the thesequence; sequence;quartz-phyric quartz-phyric felsic felsic rocks, iron formation, schist, is repeated in formationl sillimanite-knot sillimanite-knot felsic felsic schist, in aamap-scale map-scale isoclinal isoclinal fold, fold, possibly possibly aa Dl fold. In the the Wiliroy-Geco Willroy-Geco area, we interpret a similar sequence as a stratigraphic succession. succession. Sillimanite-knot felsic schist schist in in the Willecho area (Unit ib) Willecho area lb)is, is,iningeneral, generallmore morefelsic felsicthan thansillimauite-muscovite-quartz felsic sillimanite-muscovite-quartzschist schist in the Wiliroy Willroy area (Unit la, la,Stop StopA6), A6),although although the thelatter latteralso alsohas hasfelsic felsic variants. variants. Typically, Typically, layers layers with layers, and sillimanite-biotite-garnet large disseminated sillimanite knots are interleaved with non-sillimanitic layersl schists are of of local local occurrence. occurrence. In general, from muscovite-sillimanitegenerall toward toward the north north ininthe theWillecho Willechoarea, area,there thereisisa transition a transition from muscovite-sillimaniteassemblages, consistent consistent with with northerly northerly increase in metamorphic microcline to sillimanite-microcline assemblages, metamorphic grade. grade. Stop felsic schist, ZB91-2, ZB92-228. A24,Sillimanite-knot Sillimanite-knot felsic schist, ZB91-2, ZB92-228.From F'romthe theNama NamaCreek Creekjunction, junction, continue continue S t o p A24, west about about 2.25 km on on the gravel road toward toward the the Willecho deposit. Where Where the the road road starts uphill on the west 2.25 km gravel road Willecho deposit. northwest side of of Garnet Lake, stop at some outcrops in in the ditch on the north northwest some low outcrops north side side(1:25000 (1:25000 map). The The outcrops are typical of of Unit Unit ib; lb;diffuse diffuselayering layering in in the thedominantly dominantlyfelsic felsic rocks rocks is is defined defined by concentrations of disseminated large large (to 2 cm) zoned white-green sillimanite knots knots and and local local garnet. garnet. The disseminated white-green sillirnanite The sillimanite sillimanite knots knots are are strongly elongate, plunging northeasterly. northeasterly. Zoning Zoning in the the knots knotscommonly commonlyconsists consists of of aa muscovite-sillimanite muscovite-sillimanite oriented by by sprays of of fine finesillimanite, sillimanite, in in turn turn mantled by strongly oriented sillimanite core mantled by weakly oriented sillimanite fibres engulfed engulfed or or overgrown overgrownby bycoarse, coarse,either eitheroriented orientedor or random random muscovite. muscovite. In one sample, the cores fibres cores of of sillimanite knots knots contain contain relict relict andalusite. andalusite. The sillirnanite The matrix matrix has has aafew few quartz quartzeyes eyesand andisiscomposed composed of of quartz, quartz, plagioclasel Muscovite mostly looks like late unoriented overgrowths, overgrowths, but plagioclase, microcline, microcline, biotite biotite and muscovite. Muscovite commonly some blades, interleaved with foliated biotite, biotitel are are concordant concordanttotoschistosity. schistosity. Boudins of pegmatite wrapped strain, possibly wrapped by by gneissic gneissic layering indicate high strain, possibly related to tostraight straightgneiss gneiss exposed at the exposed south of the road, exposed the Willecho Willecho pit (Stop (StopA26). A26). Sillimanite-knot Sillimanite-knotfelsic felsic schist is also also well exposed along an overgrown overgrown track Garnet Lake. Lake. track angling southeast toward Garnet Stop Driveononabout about500 500 metres of Stop to a gravelled ZB92-87. Drive metres westwest of Stop A24 A24 to a gravelled S t o p A25, A25,Limb Limbof ofD1 D l (?) ( ? ) fold, ZB92-87. clearing shaft, which clearing and the remains remains of of building building foundations marking marking the location of the the former former Willecho Willecho shaftl which intersected the down-plunge extension of of the the Willecho orebody. Continue Continue on on the road west of the Willecho 33 orebody. the clearing clearing intersected down-plunge extension about 100 100 metres to to an overgrown track branching to the north, north, and andwalk walk about about 50 50 metres metres to to excellent excellent stripped stripped outcrops near L5N L5N (may or may not be be visible) visible) of the Willecho grid. The The stripping stripping exposes exposes the the folded folded contact contact between quartz-magnetite (?) map-scale quartz-magnetite iron ironformation formationand andsillimanite-knot sillimanite-knotschist schiston onthe thelimb limbofofthe theD1 Dl(?) map-scale fold. fold. The enveloping surface of of the contact enveloping surface contact trends trends about about260°; 260°whereas, whereas,metre-scale metre-scale isoclinal isoclinal S-shaped S-shaped folds folds of the contact contact and andlayered layered iron ironformation formationhave haveoblique obliquewesterly-trending westerly-trending axial axial traces. traces. Schistosity (composite D1/D2?) defined asymmetry Dl/Dz?) defined by biotite biotite and and flattened flattened sillimanite sillimanite knots is axial axial planar planar to to the thefolds. folds. The asymmetry of minor folds and and of fabrics with a parasitic relationship to the map-scale D1 fold, fold, but but the minor folds fabrics is consistent consistent with relationship to map-scale Dl schistosity defined by high grade minerals may be a D2 transposition of D2 fabric developed during transposition of the the early early fold. fold. S t o p A26, A26,Willecho Willecho33pit pitand and straight gneiss, ZB92-551 IAGOD#6. #6.The The Willecho33pit pitisison on the the south south Stop straight gneiss, ZB92-55, IAGOD Willecho of the gravel grave1 road about 3.5 3.5 km km west west of of the the Nama Nama Creek Creek (Stop (Stop A21) A21) junction. AAgravel graveltrack trackslopes slopes side of pit. Watch Watchfor forhazardous hazardousloose looserocks rocks on on the the steep steep pit pitwalls. walls. The Thepit pitwalls wallscomprise compriselenticular lenticular gently into the pit. layered sillimanite-garnet-biotite sillimanite-garnet-biotite schist, iron formation, minor minor orthoamphibole-garnet orthoamphibole-garnet gneiss to layered gneiss and semimassive to disseminated sulphide mineralization (pyrite-pyrrhotite-sphalerite-chalcopyrite). (pyritepyrrhotite-sphalerite-chalcopyrite). Locally, rotated garnet porphyroblasts wrapped wrapped by by biotite-sillimanite biotite-sillimanite suggest suggest north-over-south north-over-south sinistral kinematics. Along the top of the northern northern side side of of the the pit, pitlfrom from about aboutmidway midwayalong along its its length length and andcontinuing continuingeasterly, easterly, it is possible to walk gneiss over walk out out a transition from sheared pegmatite to straight gneiss over about about 100 metres metres (at low low angle to strike, true width may < l o m). m). The Thewesternmost westernmost outcrops outcrops of of pegmatite are are cut cut by by anastomosing anastomosing may be <10 discrete shears with abundant abundant coarse coarse strongly strongly lineated lineated sillimanite sillimanite on shear surfaces. Sheared Sheared pegmatite pegmatitegrades grades to porphyroclastic porphyroclastic pegmatite pegmatitewith withcoarse coarsequartz-K-feldspar-plagioclase quartz-K-feldspar-plagioclase enclaves enclaves (2—5 (2-5 cm) cm)in in aa fine grained matrix; lineated sillimanite sillimanite coats shear surfaces. Closer to the eastern end end of the pit, pit, very very fine fine grained layered rocks of gneiss (annealed mylonite), mylonite), possibly possibly of of aa mixed mixed felsic felsic of felsic felsic composition composition were were grouped grouped with with straight gneiss metavolcanic Thepresence presenceof of concordant concordant and andlow low angle angle pegmatite pegmatitedykes dykessuggests suggests metavolcanic and pegmatitic parentage. The 59 �_________ Manitouwadge field guide B. Outer Outer volcanic volcanic belt multiple of pegmatite pegmatite intrusion. multiple generations generations of intrusion. Immediately Immediately below below in the the wall wall of of the thepit, pit,mineralized mineralizedsheets sheets lenses of Willecho 33 deposit north and and plunge plunge northeasterly, northeasterly, underneath underneath the the and lenses of the Willecho deposit dip moderately moderately to the north straight gneiss. with the D1 gneiss. We We interpret the the straight straightgneiss gneiss as as lying lying on a D1 Dlfault, correlative correlative with Dl fault of the Willroy-Geco area, repeated repeated by by a map-scale D2 sheath fold fold (Fig. 4). By Willroy-Geco area, By implication, implication, the the pegmatite pegmatite involved involved straight gneiss gneiss transition transition was was intruded before before or during Dl sample of pegmatite pegmatite in the straight or during D1 deformation. deformation. In In a sample geochronology, only 2669k3 Ma collected for U-Pb geochronology, only monazite monazite was was suitable suitable for for isotopic isotopic analysis. aflaly8is. The The age of 2669±3 (Fig. 13) 13) is apparently apparently aa metamorphic metamorphic age subject to the the same same ambiguities ambiguities as the monazite monazite age from the syn-D2 tonalite tonalite dyke dyke (Stop (Stop A23). A23). B. Outer O u t e r volcanic volcanic belt Bi. Bl. Northern N o r t h e r ncontact contact zone zone Although the volcanic volcanic sequences correlative, the outer belt belt lacks lacks vovoAlthough sequencesofofthe theinner inner and and outer outer belts belts are correlative, luminous luminous synvolcanic synvolcanic intrusions, intrusions, extensive extensive units unitsof oforthoamphibole-bearing orthoamphibole-bearingororsillimanite-muscovite-bearing sillimanite-muscovite-bearing rocks and (known) (known) massive sulphide belt, the the northern northerncontact contactbetween betweenmafic mafic rocks sulphide deposits. deposits. Throughout Throughout the outer belt, metavolcanic rocks and felsic and metasedimentary metavolcanic rocks metasedimentary rocks rocks is aa complex complex zone zone that thatincludes includessemicontinuous semicontinuous garnetiferous domains (locally (locally with orthoamphibole-cordierite), orthoamphibole-cordierite), tonalite and minor minor iron ironformation. formation. garnetiferous tonalite sheets and orthoamphibole-garnet-cordierite zones the distal distal equivalent equivalent of of the theextensive extensivezones zones of of The orthoamphibole.-garnet-cordierite The zones are are interpreted interpreted as the metamorphosed synvolcanic alteration in the the inner inner belt. belt. 100 metres metres 61 90 Unit Unit 10. 1C Cm Cm quartzite quartzite m eta sedimentary? metasedimentary? JiotedHblsyen,e -72 Hbl syenite ,-foliated \ \c_____ 72 89 89 \ / Unit 22 k_______ — (.: —— Cr1 caic—silicate gate j \ N . gabbro high strain disrupted pillows? pillows 69 FIG. FIG. Bi. Bl. Outcrop geology geology of the the Geco Geco gatehouse section, section, showing showing exposures exposures of of mafic and and orthoamphibole-bearing orthoamphibole-bearing rocks rocks of the the outer outer volcanic volcanic belt and and the theconcontact tact with with metagreywacke. metagreywacke. Structure Structure symsymbols bols show show dominant dominant D2 D2 foliations and unlineations, and and the the axial axialsurface surfaceof of aa post-D2 post-D2 eations, Minfold in foliated hornblende syenite. Minabbreviations from from Kretz Kretz (1983). (1983). eral abbreviations 74 Grt /I \ Unit 3 380 Foliated Foliated tonalite tonalite Metagreywacke .:1 Metagreywacke r l Mafic Mafic rnetavolcanic rnetavolcanic rocks rocks Iron Iron formation formation and/or and/or orthoamphibole odhoamphibole gneiss gneiss B lGeco , Geco gatehouse section, ZB92-P249-P251,ZB93-P306, ZB93-P306, IAGOD IAGOD #I. Thisstop stop encompasses encompasses S t o pBi, Stop gatehouse section, ZB92-P249--P251, #1. This extend along along the the east eastside sideof of the theroad roadtotothe theGeco Gecomine, mine,starting startingacross acrossfrom fromthe thegatehouse gatehouse outcrops that extend at the the Geco Geco main main entrance entrance (Fig. (Fig. B1). Bl). Many Many units units typical typical of of the the outer outer volcanic volcanic belt, and the the intruded intruded and and at to younger younger metagreywacke, are tectonized contact to are exposed exposedover overaashort shortdistance. distance. Begin Beginat at the the southern southern end of of 60 �B. Outer Outer volcanic volcanic belt belt B. Manitouwadge Manitouwadgefield field guide guide the the outcrops outcrops (south (south of of the the gate) gate) and andwork work north to to the the eastward eastward curve curve in the the road sign-posted to the Geco Geco #4 shaft. shaft. The Thesection sectionbegins beginsininthe thenorthern northernpart partofofmafic maficmetavolcanic metavolcanicrocks rocksof ofthe theouter outerbelt belt(1:25000 (1:25000map). map). The Thehighly highlydeformed deformedpillows pillows and and pillow pillow breccias in the the first first outcrop outcropwere werethe themain mainfocus focusofofprevious previousfield fieldtrips trips (Williams (Williams et al., al., 1990). 1990).The Thepillows pillows are arebest bestexamined examinedon onthe theglacially glaciallypolished polished top topsurface surfaceof of the theoutcrop. outcrop. The The pillows pillows appear significantly significantly shortened on both top top and andfront frontsurfaces surfacesof of the theoutcrop. outcrop.Pillow Pillowselvedges selvedgesare are dark of garnet. garnet. Interpretation dark in in colour colour and and have have local local concentrations concentrations of Interpretation of of structural structural facing facing is is tempting, tempting, but but ambiguous ambiguous (go (go ahead, everybody everybody does does it). it). Moving Moving north along along the theoutcrop, outcrop,mafic Aaficmetavolcanic metavolcanicrocks, rocks,mostly mostlywithout withoutrecognizable recognizablepillows, pillows,are are interleaved interleaved with with foliated foliated tonalite tonalite sills sills (Fig. (Fig. Bi). Bl).InInthe thevicinity vicinityofofthe thefence, fence,foliated foliatedcoarse coarsegrained grained hornblendehornblendeplagioclase with mafic mafic schist. schist. The gabbro thickens to the west plagioclase gabbro is interleaved interleaved with west in the the Gaug Gaug Lake Lake area. area. North North of of the thefoliated foliatedgabbro, gabbro,mafic maficmetavolcanic metavolcanicrock, rock, with with garnetiferous garnetiferouslayers layersand andcalc-silicate calc-silicateboudins, boudins,and and foliated foliated tonalite continue continue to the end end of of the the first first outcrop. outcrop. Note Note the the steep steep easterly easterly plunging plunging lineation. lineation. A A thin thin layer layer of of rusty, rusty, locally locally magnetic rock, interpreted as as iron iron formation, formation, is exposed exposed at the thecontact contactbetween between mafic mafic rocks rocks and and tonalite tonalite near near the the northern northern end endof of the theoutcrop. outcrop. Along outcrop includes Along the road road about about 25 25metres, metres, the the southern southern part part ofofthe thenext next outcrop includesinterlayered interlayered orthoamphibole-plagioclase-biotite orthoamphibole-plagioclase-biotite gneiss and iron formation. formation. Along Along strike strike just just west westof ofManitouwadge ManitouwadgeLake, Lake, orthoamphibole contain cordierite, cordierite, garnet, garnet, staurolite, and gahnite, orthoamphibole gneisses gneisses contain gahnite, similar similar assemblages assemblages to those in in altered altered rocks rocks near near the theWillroy Willroydeposit deposit (Stops (Stops A5, A5, A6). A6). The Thecentral central outcrop outcroparea areaisisdominated dominatedby byfine finegrained, grained, foliated syenite, possibly belonging foliated hornblende-microcline hornblende-microcline syenite, belonging to aahornblendite-syenite hornblendite-syenite suite suitesporadically sporadicallyexexD3Z-fold Z-fold ofofthe thedominant dominantsyenite syenite posed posed throughout throughout the the Manitouwadge Manitouwadge area (compare (compare Stops F4, F5). F5). AAD3 foliation foliation is exposed on the top surface surface of the outcrop. The The northern northern end endof of this, this,and andall allofofthe thenext nextoutcrop, outcrop, The are possibly due due to silicification. are cummingtonite-bearing cummingtonite-bearing rocks rocks of intermediate to felsic felsic composition, composition, possibly silicification. The cummingtonite-bearing cummingtonite-bearing rocks rocks were were grouped with metasedimentary metasedimentary rocks; rocks; however, however, their origin origin is is uncertain. uncertain. The The remaining remaining outcrops outcrops to to the thenorth northalong alongthe theinside insidecurve curveofofthe theroad roadare aremore moretypical typicalbiotite-quartzbiotite-quartzplagioclase plagioclaseschist schist interpreted interpretedasasmetagreywacke. metagreywacke. B2—B1O. Lakearea, area, comparison comparison to inner inner volcanic volcanic belt belt B2-B10. GGaug a u g Lake TheGaug GaugLake Lakearea arealies liesininthe theouter outervolcanic volcanicbelt belton onthe thesouthern southernlimb limbofofthe theManitouwadge Manitouwadgesynform synform The (1:25000 map) and, and, like like the the inner inner belt, belt,comprises comprisesmafic mafic and and felsic felsic rocks and iron formation (Fig. (Fig. B2). B2). Much Much (1:25000 of the the area areabelongs belongs to to the the'Central' 'Central'Granges GrangesInc. Inc.claim claimgroup group and andgrid. grid.Felsic Felsicrocks rocks and andiron iron formation formation are are of less abundant abundantthan thanininthe theinner innervolcanic volcanicbelt, belt,although althoughthis thismay mayreflect reflectpreservation preservationrather ratheroriginal originalvolumes. volumes. less Felsic Felsic rocks are are of of the the same sameage agein inboth bothbelts belts(circa (circa2720 2720Ma), Ma),but butdiffer differinincomposition, composition,comprising comprisingaphyric aphyric rhyodacites and and dacites dacites in inthe theouter outerbelt. belt.Garnet-hornblende Garnet-hornblendeassemblages assemblagesininmafic maficand andfelsic felsicrocks rocks could could be be rhyodacites the theresult resultofofsynvolcanic synvolcaniccaic-silicate calc-silicate alteration alteration and andsubsequent subsequentregional regionalmetamorphism. metamorphism. Inthe theGaug GaugLake Lakearea, area,foliations foliations are are generally generally steep and lineations lineations plunge The area area In plunge east east to to northeast. northeast. The encompasses enclaves enclaves of relatively low strain strain where where volcaniclastic volcaniclastic deposits deposits are are remarkably remarkably well well preserved. preserved. encompasses Thepresence presence of of outcrop-scale outcrop-scale D2, D2, and and D3 D3 or or later laterfolds, folds, suggests suggests that that atatleast leastsome someintercalation intercalationofoffelsic felsic The rocks and and iron iron formation formationisisdue duetotofolding. folding.The TheAgam AgamLake Lakefault faultforms formsaapronounced pronouncedeast-west east-westtopographic topographic rocks lineament,mainly mainlywithin withinmetasedimentary metasedimentaryrocks, rocks,but butlocally locallyjuxtaposing juxtaposingmetavolcanic metavolcanicand andmetasedimentary metasedimentary lineament, rocks. Evidence Evidenceof of an anearly earlyductile ductilehistory historyisisrecorded recordedininisoclinal isoclinalfolds folds and and aastrong strongstretching stretchinglineation lineation near near rocks. thefault faultzone. zone.Locally, Locally,rocks rocks preserve preserve mylonitic mylonitic textures, unusual unusual in that that straight straightgneiss gneissassociated associatedwith withlow low the angle angle faults faults(Di) (Dl)ininthe theinner innerbelt beltisismostly mostlyannealed. annealed.There Thereisisalso alsoevidence evidenceof oflater laterbrittle brittlemovement movementon onthe the Agam Agam Lake Lake fault fault(W. (W.Bates, Bates,Granges GrangesInc., Inc.,pers. pers.comm., comm.,1992). 1992). Theaccess access isis along along ATV ATV trails trails and andcat cattracks tracksleaving leavingfrom from the thebase baseof ofthe theManitouwadge Manitouwadgeski ski hill. hill. For For The those intending intending to use use an an ATV, ATV, the the ATV ATV trail trail starts starts from from the the road road about about500 500 metres metres east east of of the theski skihill hill those parking parking lot. lot. Note, Note,however, however, that that the thecat cattrack trackthat thatbranches brancheswest westtotothe theGranges Granges area areamay may not notbe besuitable suitable for forATVs. ATVs. The TheGaug GaugLake Lakearea areaitself itselfisisabout about1.5 1.5km kmbeyond beyondthe theski skihill, hill,and andthe thestops stops are arelocated located using usingthe the cut lines linesof of the the Granges Granges grid grid (metric (metric units). The Thecondition condition of of the the grid grid and and pickets pickets is variable and it is best to cut measure distance distancealong alongthe thecat cattrack trackinincase casesome somegrid gridlines linesare aredifficult difficultto tospot, spot,ororpickets picketsillegible. illegible. measure S t o pB2, B2,Deformed Deformed pillow basalt, ZB93-408.Beyond Beyondthe therope ropetow, tow,head headup upthe themost mosteasterly easterly ski skirun run Stop pillow basalt, ZB93-408. forabout about500 500metres metrestotowhere wherethe therun runcrosses crossesa apowerline powerlineclearing clearingnear nearsome somesmooth smoothsloping slopingoutcrops outcrops(Fig. (Fig. for B2). The Thepillow pillowbasalts basaltsbelong belongtotothe theouter outermafic maficmetavolcanic metavolcanic belt. belt. The Thepillows pillows are are small small (<0.5 ( ~ 0 .m) 5m)and and B2). flattenedwith withselvedges selvedgesand andinterstices intersticesdefined definedby bycoarse coarsegrained grainedhornblende hornblendeporphyroblasts porphyroblastsoriented orientedparallel parallel flattened totoschistosity. schistosity. S t o pB3, B3,Mafic Mafic schist, ZB93-382. Continue runabout about200 200metres metrestotothe thenext nextgood goodoutcrop, outcrop,more more Stop schist, ZB93-382. Continue upup thethe skiskirun typicalof ofmafic maficmetavolcanic metavolcanic rocks rocks in in the theManitouwadge Manitouwadgebelt. belt.Here, Here,medium mediumgrained grainedgabbroic gabbroicaugen augenschist, schist, typical possibly originally originally aa massive massiveflow flow or or base base of of aaflow, flow,grades gradestotolaminated laminated(1(1mm—i mm-1 cm) cm)fine finegrained grainedhighly highly possibly strainedmafic maficschist. schist.InInthe thehigh-strain high-strainzone, zone,layer layertruncations truncationsresulting resultingfrom fromboudinage boudinagehave have aasuperficial superficial strained 61 �B. Outer Outer volcanic volcanic belt Manitouwadge field guide Geology and and field-trip field-trip stops stops(B2—B10) (B2-BlO) ofofthe Dashed FIG. B2. Geology the Gaug Gaug Lake Lake area, area, outer outer volcanic belt. belt. Dashed lines are cut lines lines of the Granges Granges grid. grid. Structure Structuresymbols symbolsshow show dominant dominant D2 D2 foliations and lineations. resemblance to cross-bedding. Layering Layering also also shows subtle rootless isoclinal folds. The The layering layering looks somewhat tuffaceous, but but could be entirely of tuffaceous, of tectonic origin. origin. Return down the ski run to to the thepowerline powerline and and follow follow the rough Return down rough trail leading northwest northwest under under the line 200 metres Follow the crossing the stream at the the east east end end for 200 metres to to join join the ATV trail. Follow the ATV ATV trail trail to to the north, crossing continuing up Leave the of Gaug Lake Lake after after 1 km, and continuing up the hill on on the north side for 100 metres. metres. Leave the ATV ATV trail trail and take the cat track track (drill (drill road) road) heading heading west. The The cat cat track track crosses crosses cut lines (azimuth=OO) (azimuth=0°) of the 'central at 100 100 metre metre intervals, intervals, the the ATV ATV trail trail being being at at approximately approximately L5W. L5W. Granges grid' at Stop rocks and iron formation, S t o p B4, B4, Felsic Felsic metavolcanic rocks ZB93-366. Find L13W L13W on formation, ZB93-366. on the the cat cat track track at edge of a drill-site drill-site clearing clearing and continue on the northern edge and continue on the the line line to to 5+40N 5+40N (about 40 metres north of the clearing). The The stripped stripped patch patchofoffelsic felsicmetavolcanic metavolcanic rocks, rocks, and another another of of quartz-magnetite quartz-magnetite iron iron formation formation clearing). 25 metres to the the north-northeast north-northeast (15 (15metres metres east east of of L13W Ll3W at 5+65N), are typical of intercalated about 25 intercalated units in Continueeast east about about40 40metres metresin inrelatively relatively open open bush bush to to aa long long (20 (20 m) northeasterly trending ledge the area. Continue exposures of with excellent exposures of felsic felsic breccia. breccia. Angular Angular monolithologic monolithologicfelsic felsicclasts clasts(up (upto to 30 30 cm) cm) are supported darker matrix matrix rich rich in in garnet, garnet, horublende hornblende and biotite. The The large large size size and and angularity angularity of of the the clasts clasts is is in a darker and biotite. characteristic of proximal volcaniclastic deposits, Bates, Granges Granges Inc., Inc., characteristic deposits, possibly possibly fragmented fragmented by by phreatic (W. Bates, pers. comm., 1992) or hydrothermal explosions. The The abundance abundance of of calc-silicate calc-silicate minerals in the matrix matrix suggests suggests preferential synvolcanic alteration alteration of permeable unconsolidated matrix material. S t o p B5, B5,Felsic Felsicbreccia, breccia,mafic-felsic ma&-felsiccontact, contact, ZB93-367.OnOn track near L15W, monolithologic Stop ZB93-367. thethe catcat track near L15W, monolithologic felsic clasts are are similar, similar, except felsic breccia brecciaisisexposed exposedon onledges ledgesand andflat fiatoutcrops. outcrops. In In this this case, case, the the matrix and clasts that the thematrix matrixisismore morebiotitic. biotitic.U-Pb U-Pbzircon zircongeochronology geochronologyon onaasample samplefrom fromthis thisoutcrop outcropconstrains constrainsfelsic felsic 2722~t2Ma Ma (Fig. (Fig. 10), lo), within within error error of of the the mineralized mineralized sequence sequence in the volcanism volcanism in in the the outer volcanic belt to 2722±2 inner belt. 62 �Outer volcanic volcanic belt belt B. Outer Manitouwadge Manitouwadge field field guide guide On On L15W L15W immediately immediately south of of the the cat cattrack track(6+OON), (6+00N), there there are aremore moreexcellent excellent exposures exposures of of both both monolithologic cm) felsic felsic clasts clasts are are supported by aa monolithologic and heterolithic breccias. In Inthe thefirst firstcase, case,coarse coarse(2—10 (2-10 cm) matrix B4,suggesting suggesting preferential preferential alteration alteration matrixwith with variable variableamounts amountsof of hornblende hornblende and and garnet, garnet,again again as as at atStop StopB4, of of the the matrix. matrix. The Theheterolithic heterolithicbreccias brecciascontain containboth bothfelsic felsicand and garnet-hornblende-rich garnet-hornblende-rich clasts, clasts, the the latter lattersimilar similar The clast clast types types suggest suggest that thatthe theheterolithic heterolithicbreccias breccias represent represent to to the thematrix matrixofofmonolithologic monolithologic breccias. breccias. The erosion breccias, and and by implication, that erosion and redeposition redeposition of clasts and matrix matrix material materialof ofmonolithologic monolithologic breccias, alteration alteration of of matrix matrixmaterial materialpredated predatedits itsincorporation incorporationinto intoheterolithic heterolithic deposits. deposits. Continue ledge that that trends southerly Continue west west of of the grid grid line line about about 15 15metres metres to toaalow low west-facing west-facing ledge southerly for for about about 100 100 metres to to Leach Leach Lake Lake and and crosses crosses the the contact contact between between felsic felsic and and mafic mafic rocks. rocks. Initially, Initially,there thereisisaasequence sequence (north-to-south) (north-to-south) from from felsic felsic rocks, rocks, to to about about55metres metresofofweakly weaklyrusty rustyvery verymagnetic magneticsilicate silicateiron ironformation, formation, to clasts. The iron formation has about to heterolithic heterolithic breccias breccias again again with with felsic felsic and hornblende-garnet-bearing hornblende-garnet-bearing clasts. 25—35% garnetup upto to 1 cm, hornblende, 25-35% garnet hornblende, magnetite, minor grunerite grunerite and and disseminated disseminated quartz. quartz. Follow Follow the the ledge ledge to the the south south to toaasharp sharpcontact contactofoffelsic felsicrock rock and andmafic mafic schist, schist, the the latter lattertypical typicalof ofmost most of of the themafic mafic metavolcanic metavolcanic unit. Tightly Tightlyfolded folded tonalite tonalitedykes dykeshave have an an axial axialplanar planar foliation foliation parallel parallel to tothe theschistosity schistosity(D2) (D2) of of the the mafic mafic host rock. rock. The The folds folds and tonalite tonalite fabric fabric are are interpreted interpreted to to be be D2 D2structures. structures. Stop iron formation andand felsic rock, ZB93-409. thethecatcattrack foldofof iron formation felsic rock, ZB93-409.OnOn track3030metres metreswest west S t o pB6, B6,D3(?) D3(?)fold of 9W, a flat rock (volcanic or or subvolcanic) subvolcanic) and and a thin of Li LlgW, flat outcrop outcropconsists consistsof of homogeneous homogeneous white felsic rock thin (<1 (<I m) m) iron iron formation. formation. The Theiron ironformation formation and and aastrong strongfoliation foliation in in the the felsic felsic rock rock are both both deformed deformed by an isoclinal interpreted to be D3 of the the dominant (D2) fabric. fabric. The axial trace of isoclinal fold, interpreted D3 or later, based based on folding of of the limb, a 20-cm the fold fold is is subparallel subparallel to to the thedominant dominantfabric fabricin inthe thearea. area.On Onthe thesouthern southern limb, a 20-cmzone zoneofoffelsic felsicrock rock penetrates penetrates through through the theiron ironformation, formation, apparently apparently in in an an intrusive intrusive relationship. relationship. AAthin thin(10 (10cm) cm)concordant concordant strongly stronglyfoliated foliated tonalite tonalitedyke dykealso alsolies lieson onthe thefold foldlimb. limb. Stop dyke, garrietiferous mafic rocks, ZB93-336. Outcrops lielienear S t o pB7, B7,Folded Foldedzoned zonedgabbroic gabbroic dyke, garnetiferous mafic rocks, ZB93-336. Outcrops nearL21W L21W and the thecat cattrack, track,and andnorth northononL21W L21Wnear near6+90N 6+90N(15 (15mmfrom fromtrack), track),the thelatter latterananexcellent excellentpavement. pavement.The The and immediate area area isisdominated dominatedby byfelsic felsicrock, rock,locally locallybreccia breccia with with recessive recessive weathering weathering clasts clasts (up (up toto1010cm). cm). immediate The The felsic felsic rock rock is is cut cut by byaafolded folded(D2?) (D2?)composite-zoned composite-zoned gabbroic gabbroic dyke dyke (1.25 (1.25 m m in in width). width).The Thedyke dykedefines defines an an asymmetric asymmetricfold fold in in which which the the northern northern limb limbcuts cutsacross acrossthe thelocal localdominant dominantfoliation, foliation,and andthe thesouthern southernlimb limb generally concordant. concordant. Foliation Foliation in the the dyke dyke is is parallel to that that ininthe thehost. host.The Thesouthern southernlimb limbshows showssome some isis generally odd features; features;the thedyke dykeisisapparently apparentlyrepeated repeated against againstthe thesouthern southernlimb limbininwhat whatlooks lookslike likeaasinistral sinistraloffset. offset. odd The Thecomposite composite and and zoned zoned nature natureofofthe thedyke dykeare arealso alsounusual, unusual,asasisisthe thepresence presenceofofananintermediate-mafic intermediate-mafic dyke dykein inthe thefelsic felsicrocks. rocks. Continueon onthe thecat cattrack trackabout about5050 metreswest westofofL21W, L21W,crossing crossingthe thecovered coveredcontact contactinto intomafic maficrocks. rocks. Continue metres The first first exposure exposure isisof of rusty rustygarnetiferous garnetiferous (25% (25% to to 22cm), cm),locally locally strongly strongly magnetic, magnetic, mafic mafic rock. To Tothe the The west and andsouthwest, southwest, the themafic maficrock rock isisstreaked streaked with with quartz quartzveinlets veinletsand andmottled mottledwith withirregular irregularepidosite epidositeand and west bleached patches. patches.Buff Buffleucotonalite leucotonalitedykes dykescontaining containingsome somemafic maficinclusions inclusionsare are tightly tightlyfolded folded(D2) (Dz)and andhave have bleached thickened thickened hinges. hinges. S t o pB8, B8, Deformed pillow basalt, ZB93-337. Continue metreswest westofofL24W L24Watat3+50N 3+50N(160 (160 mm Stop Deformed pillow basalt, ZB93-337. Continue to to 1010 metres southof ofthe thetrack) track)totoa alarge largestripped strippedoutcrop, outcrop,unfortunately unfortunatelymossing mossingover. over.The Thefine finetotomedium mediumgrained grainedmafic mafic south rock has haspillows, pillows,0.4—1 0.4-1 metres quartz-rich, selvedges. selvedges. A A few few pillow pillow shapes shapes give give hints hints of of rock metres in in length, length, with rusty, quartz-rich, northerly northerlyyounging, younging,but butthe thepillows pillowsare arestrongly stronglydeformed deformedand andsome someselvedges selvedgesdefine definelocal localS-folds. S-folds. Tenmetres metreswest westof ofL24W L24Watat3+1ON, 3+10N, on on aastripped strippedoutcrop, outcrop,mafic maficrocks rocksand andtonalite tonalitedykes dykesdefine definetight tight Ten folds (D2) (D2) with with straight straightlimbs limbsparallel paralleltotoschistosity. schistosity.About About15 15metres metresfurther furtherwest, west,the themafic maficrock rockcontains contains folds minor (<10%)garnet. garnet. minor (<10%) S t o pB9, B9,Unusual Unusual magnetic rocks, ZB93-338. Continue southononL24W L24Wtoto2+75N 2+75N to to aastripped strippedoutcrop outcrop Stop magnetic rocks, ZB93-338. Continue south about30 30metres metres west west of of the the line. line. These Theseare areunusual unusual and andenigmatic enigmatic rocks. rocks. To To the the north, north,about about33metres metresofof about fine grained grained rusty rusty intermediate intermediate rock rock has has thin thin (<15 (<I5cm) cm)dykes dykesof of 22types; types; irregular irregular boudinaged(?) boudinaged(?) gabbroic gabbroic fine dykes and, and,hybrid hybrid dykes dykescontaining containing 30% 30% tonalitic tonalitic streaks streaks and andpatches patcheswith withhornblende hornblendeporphyroblasts, porphyroblasts, inin dykes gabbroic matrix. matrix. The Thetextures texturesofofhybrid hybriddykes dykesresemble resemble those those of of magma magma mixing. mixing. To To the the south, south,about about66 aagabbroic metres rock containing 20—80% metresisisexposed exposedofofvery veryheterogeneous heterogeneousmagnetic magnetic rock(hornblende-clinopyroxene-bearing) (hornblende-clinopyroxene-bearing) containing 20-80% ovoid ovoid or or annular annular dark dark1-cm 1-cmspots spotsininaaleucocratic leucocraticmatrix. matrix.The Thespots spotsconsist consistofofhornblende-magnetite hornblende-magnetite cores cores orrings ringsininaafelsic felsicmatrix. matrix.Could Couldthese thesebe bemetaspherulites metaspherulitesorormetavarioles? metavarioles?Locally, Locally, the the spotted spottedrock rock grades grades or (northerly) to tosomething somethingthat thatlooks lookslike likeaafracture fracturebreccia breccia cut cutand andveined veinedby bydark darkmagnetite-rich magnetite-rich material. material. (northerly) Thedark darkmaterial materialisissimilar similartotosilicate silicateiron ironformation, formation,containing containingmagnetite, magnetite,grunerite(?) grunerite(?)and andminor minorpyrite pyrite The and andpyrrhotite. pyrrhotite. S t o pBlO, BlO,Again AgamLake Lake fault, ZB93-420.North Northofofthe thecat cattrack track(100 (100m) m) on onL27W L27W at at6+60N 6+60N isisaalarge large Stop fault, ZB93-420. outcroparea areanear neara astream streamononthe theAgam AgamLake Lakefault faultlineament. lineament.Laminated Laminatedtoto lensy felsicrocks rocksimmediately immediately outcrop lensy felsic southofofthe thestream streamhave haveintrafolial intrafolialisoclinal isoclinalfolds, folds,apparently apparentlysteeply steeplyplunging plungingto toboth bothwest westand andeast, east,possibly possibly south relatedtotoductile ductilemovement movementon onthe theAgam AgamLake Lake fault. fault. About About15 15metres metres to tothe thesouth, south,there thereisisaacontact contacttotomore more related 63 �B. Outer volcanic volcanic belt Manitouwadge Manitouwadge field guide intermediate to to mafic mafic rocks which are cut by by tonalite tonalite dykes dykes that thatdefine defineS-shaped S-shapedfolds folds (D2). (D2).Schistosities Schistositiesin in the host rock rock and and tonalite tonalite have have an an axial axial planar planar orientation. orientation. B11—B21. Hingeregion regionof oftthe Bll-B21. Hinge h e Manitouwadge synform near n e a r Swill SwillLake Lake In the folded in in the hinge region the Swill Swill Lake area, the the outer outer belt beltofofmafic maficand andfelsic felsic metavolcanic rnetavolcanic rocks is folded of the D3 map). The D3 Manitouwadge synform (Fig. B3, 1:25000 1:25000 map). The southernmost southernmostunit unitisisaathick thicksequence sequenceofofmafic mafic metavolcanic rocks that include include homogeneous schist, laminated and layered schist (tuffaceous?), and deformed pillowed flows. As As in in the Gaug pillowed flows. Gaug Lake Lake area, area, foliated foliated gabbroic gabbroic rocks, rocks, interlayered interlayered with the the fine fine grained grained mafic mafic schists, may be massive or bases bases of offlows, flows,ororsills. sills.High Highstrain strainzones zonesininmetagabbro metagabbro are are characterized characterized by by massive flows or grained homogeneous homogeneousschist schistand and cloud cloudthe the distinction distinction between between tectonic tectonic and and stratigraphic stratigraphic units. Highly fine grained Highly strained strained pillows pillows are are recognized locally and, and, in one location, location, deformed deformed pillow shapes suggest southerly younging. In view of the folding in the area, area, this thisisolated isolatedyounging younging determination determinationdoes doesnot nothave haveregional regionalsignificance. significance. Garnetiferous zones (less (less that that 15 rocks, particularly particularly near the northern 15 metres in width) occur in the mafic rocks, contact to units(compare (compareStop Stop Bl). Bi). Locally, to felsic—intermediate felsic-intermediate units Locally, garnet is is concentrated concentrated in inpillow pillow selvedges, selvedges, and just west and west of of Swill Swill Lake Lake (Fig. (Fig. B3), B3), aathick thickgarnetiferous garnetiferous zone zone is is associated associated with with minor minor exposures exposures of orthoamphibole-bearing rocks. In some zones are are discordant discordant to tectonic fabrics or are orthoamphibole-bearing rocks. some cases, cases, garnetiferous garnetiferous zones are concentrated along along the the traces traces of of fold fold hinges, hinges, suggesting suggesting synkinematic metasomatism. Within Withinthe thethick thicksequence sequenceofofmafic maficrocks, rocks,two two semi-continuous semi-continuousfelsic felsic units units are areuseful useful markers markersdefining definingmapmapscale symmetrical symmetrical and and asymmetrical asymmetricalfolds. folds. The The southern southern unit, up to to 50 50metres metres wide, wide, isis aahighly highlydeformed deformed monolithologic felsiclapilli lapillituff(?), tuff(?),with withfine finegrained grainedto to aphanitic aphanitic felsic felsic clasts clasts in a matrix monolithologic felsic matrixof ofmica micaschist. schist. The unit unit isisassociated associated with with thin, thin,discontinuous discontinuousexposures exposures of of iron iron formation formation and and locally locally hosts hosts disseminated disseminated pyrite and pyrrhotite. pyrrhotite. North Northofofthe themafic maficmetavolcanic metavolcanicrocks, rocks, fine fine grained grained felsic felsic to intermediate intermediate rocks are strongly deformed and commonly commonlylaminated. laminated. The dominance of hornblende hornblendeover overbiotite biotitesuggests suggeststhat that they they strongly deformed and dominance of had aa metavolcanic metavolcanic protolith. protolith. Felsic Felsic to tointermediate intermediaterocks rocksare areextensively extensivelyinvaded invaded by by foliated foliated tonalite, tonalite, which which dominates in the northeast. The dominant dominant D2 D2planar planarfabric, fabric,well well developed developed in in the the Swill Swill Lake Lake area, area, isis folded folded by the the D3 D3 Manitouwadge Manitouwadge synform. D2 folds folds with with axial axial planar planar fabrics fabrics are are preserved preserved locally locallyininthe the east. east. There is aa dramatic synform. dramatic westward westward in post-D2 post-D2 strain (Fig. B3), which transposes transposes all earlier fabrics. fabrics. High increase in High strain fabrics, best exposed exposed in synform, include include spectacular spectacular L>S L>S tectonites and the hinge region of the Manitouwadge synform, and folds folds with aa moderate moderate northeasterly plunge, plunge, parallel paralleltoto lineations. lineations. The The tectonites tectonites may, may,inin part, part, be the result northeasterly result of of transposition transposition of of D3 structures during on the western contact of supracrustal rocks D3 during deformation deformation focussed focussed on rocks with with the the Black Black Pic Pic batholith. The Two coarse diabasedykes dykescut cutthrough throughthe the area area (Fig. Two coarse grained, grained, plagioclase-megacrystic plagioclase-megacrystic diabase (Fig. B3). B3). The exposed and probably belongs to the Biscotasing swarm of of about 2167 Ma Ma northeasterly-trending dyke dyke is is well well exposed (Buchan et al., al., 1993). 1993). The Thelocation location of of the thenorthwesterly-trending northwesterly-trending dyke dyke isis inferred inferred from from one one outcrop outcrop exposure exposure Ma It probably probably belongs belongs to the the Matachewan Matachewan swarm of about 2454 Ma and aeromagnetic aeromagnetic and topographic trends. It (Heaman, 1988). (Heaman, 1988). in the the area are held by by Noranda Noranda Inc. Inc. in in the the northwest, northwest, A1 Al Turner Turner in in the the central central area, area, and Granges Granges Claims in Inc. in the east. east. Access Accessisis by by old old logging roads north of the Caramat Caramatroad roadleading leadingto toextensive extensiveareas areasof of variably variably overgrown clear cut. cut. Deep overgrown clear Deep streams streams and and washouts washouts on on most most of of the themain mainlogging logging roads roads severely severely limit limit vehicular vehicular access. Some outcrops f i r n e r claim claim group. To To reach reach the the access. outcrops are are located located using using aa cut cut grid (metric units) on the Turner Swill Lake Lake area, area, follow followthe the Caramat Caramat Road west west from Highway Highway614 614approximately approximately7.5 7.5km kmand andturn turn north north on on a logging road just just beyond beyond the landfill-site entrance entrance on on the the south side of of the the Caramat Caramat Road. Road. The Thefirst firstwashout washout logging road at at 0.8 0.8 km may or or may may not not be be passable; passable;ifif the theroad roadisiswet, wet,the theslope slopeon onthe thefar farside sideof of the thewashout washoutwill willprobably probably Continue north along along the the road. road. be greasy mud. Continue Stop flu, mafic metavolcanic At 750 750 metres metres north north of of the the first first Stop B l l , Folded m&c metavolcanicrocks, rocks,ZB93-2, ZB93-2, ZB93-P50. ZB93-P50. At washout, several several outcrops outcrops lie lie on on a small knoll washout, knoll to the the east, east,beginning beginning approximately approximately 80 metres metres from the mafic schist schist and foliated gabbro, road. The Themafic m d cmetavolcanic metavolcanic rocks rocks comprising comprising laminated laminated mafic mafic gneiss, gneiss, mafic S-foldswith withassociated associatedcrenulation crenulationcleavage cleavage are typical of of the the southern southern Swill SwillLake Lake area. area. Structures Structuresinclude includeS-folds (D3), a possible D2/D3 fold fold interference interferencepattern, pattern, ductile shear zones in in the the foliated gabbro with indeterminate (possibly dextral) shear sense, sense, and and brittle brittlefractures, fractures,typically typicallyfilled filled with with epidote epidote and andhaving havingdextral dextraloffset offsetin in plan view. view. B12,Felsic Felsicbreccia, breccia, ZB93-Pl75.Continue Continueanother another400 400metres metres northward northward along along the road road and then S t o p B12, Stop ZB93-P175. northeast across across a clear clear cut cut for for 200 200 metres metres to to the thelarge largelight-coloured light-coloured outcrop at at the thebase baseof ofthe thecliff cliff clearly clearly visible from from the the road. This visible Thisisisan anexcellent excellent exposure exposure of of the the southern southernfelsic felsic unit, unit,aahighly highlydeformed deformed but butwell well preserved mono1ithologic monolithologicfelsic felsicbreccia. breccia. AA geochemistry geochemistrysample samplefrom fromthis this outcrop, outcrop, prepared prepared by extracting preserved clasts and carefully avoiding be aa caic-alkaline calc-alkaline rhyolite, avoiding the the high high angle angle brittle brittle fractures, shows shows the the unit unit to be rhyolite, in in contrast to the the tholeiitic tholeiitic basalts basalts to to north north and andsouth. south.There Thereisisa afine, fine,streaky streakylineation lineationon onfoliation foliationsurfaces, surfaces, and small Z-folds Z-folds are common across the outcrop, although at at least leastone oneS-fold S-fold was was also also observed. observed. 64 �30 '- 1)2 —p" 1)2 23 Fold axial plane Fold axis. Z—asymmetry Fold axis, S—asymmetry foliation lineation axis, symmetrical Fold axis, unknown symmetry Cabbrolc interlayers Fold 14 S '-9. '• , L 3 0' 2YJ 23 '4 S "a •3i• 3, ".r •2 / 0.5 32 9 1.0 kn FIG. B3. Geology and field—trip stops (B11—B21) of the Swill—Mills Lakes area near the hinge region of the D3 Manitouwadge synform. Dashed lines are the cut lines of A. Turner's Swill Lake grid. 0 2+ '1 2+ �B. B. Outer Outervolcanic volcanicbelt belt Manitouwadge Manitouwadgefield field guide guide Stop lineation, ZB93-P71, P72. Return to to thethe road and S t o pB13, B13,Felsic Felsicbreccia, breccia,stretching stretching lineation, ZB93-P71, P72. Return road andcontinue continueanother another 200 200 metres, then follow follow a drill road branching branching to the southwest. southwest. After After about about 100 100metres, metres, take take the thenorthern northern fork fork of of the the drill drillroad road and andcontinue continuewesterly westerly 350 350 metres metres to to aalow low open open area areawhere where several several tracks tracks branch branch off off and northerly L7W. and the thedrill drillroad roadintersects intersectsL7W L7Wofofthe theTurner Turnergrid. grid.Continue Continue northerly(0100) (010')along along L7W.AtAt6+OOS 6+OOSand and about about 50 50metres metres to tothe theeast, east,the thesouthern southernunit unitofofmonolithologic monolithologicfelsic felsicbreccia breccia crops crops out. out. Note Notethe thepronounced pronounced stretching stretching lineation. lineation. The Thenorthern northernend endofofthe theoutcrop outcroparea areaisismafic maficschist. schist. Just Justwest westofofthe theline lineatat6+OOS, 6+OOS, the felsic felsic unit, unit, here here containing containing some some garnet garnet (rimmed (rimmed by by plagioclase) plagioclase) and and with with clasts clasts less less distinct, distinct,isisinterlayered interlayered with with rocks rocks of of more more intermediate intermediate composition. composition. The Thenorthern northerncontact contactwith withmafic maficschist schistisisexposed. exposed. Stop pillows, suiphidic felsic rocks, ZB93-P77—P78, Continue westerly S t o pB14, B14,Deformed Deformed pillows, sulphidic felsic rocks, ZB93-P77-P78,P82. P82. Continue westerly200 200metres, metres, following the crude drill road to outcrops along along north north side of of an open area following the to east-west-trending east-west-trending outcrops area just west west of of LOW. These are are the best LOW. These best preserved preserved pillows pillows that we we have have seen seen in in the the Manitouwadge Manitouwadge area, area, some some with with cusps cusps suggesting suggesting southerly southerly younging, younging, although although of of questionable questionable regional regional significance. significance. The The pillows pillows are are zoned zoned from from dark dark hornblende-rich hornblende-richselvedges selvedges to to lighter lightercores. cores. Walk Walk 50 50 metres metres north north to toaatrenched trenchedarea areaof ofrusty rustysulphidic sulphidic(mostly (mostlypyrite) pyrite)rocks rocksgrouped groupedwith withthe thesouthern southern felsic with plagioclase, biotite biotite and hornblende. In felsic unit. unit. The Thevery veryfine finegrained grainedsiliceous siliceous rocks rocks have have some layers with In aa second second trench, trench, visible visible to to the thenorthwest, northwest,felsic felsicrock rock isis intruded intrudedby byfoliated foliatedleucocratic leucocratictonalite. tonalite. Continue and an outcrop Continue northeast northeast from from the the trench, trench, finding finding LOW L9W and outcrop that that crosses crosses the theline linenear near6+50S. 6+50S. The The exposure exposure shows shows aa contact contact between between very very highly highly deformed deformed (mylonitic), (mylonitic), garnet-bearing garnet-bearing felsic felsic breccia and garnet-rich mafic maficschist. schist. garnet-rich Continue LlOW, 6+50S and another another exposure exposure of of the the felsic felsic breccia of the southern southern felsic felsic unit, unit, in in Continue west west to to L1OW, this this case, case, represented represented by by aaribbon ribbonmylonite. mylonite.Strongly Stronglyelongate elongateclasts clastsare arestill stillrecognizable recognizabledefining definingaalineation lineation that that plunges plungesmoderately moderately to tothe thenortheast. northeast.As Aspreviously, previously,garnet garnet tends tendstotobe berimmed rimmedby byplagioclase. plagioclase. Stop in metagabbro, ZB93-P81. Follow L1OW ZB93-P81. Follow L10Wnorthward northwardtotoananoutcrop outcropwest west of of S t o pB15, B15,High Highstrain s t r a izones n zones i n metagabbro, the of metagabbroic metagabbroic layers layersin inthe the thick thick mafic maficsequence. sequence.In In the the transition transition to theline lineatat6+OOS, 6+OOS, a beautiful example of high high strain strainzones, zones,the thegabbro gabbroisismedium mediumtotocoarse coarsegrained, grained,foliated foliatedand andcontains containshornblende hornblendeporphyroclasts. porphyroclasts. In In zones zones of of high high strain, strain,the thetextures texturesand andfabrics fabricsare aresimilar similartotothose thoseofofthe thefine finegrained grainedhomogeneous homogeneous mafic mafic schist schist common common throughout the thearea, area,suggesting suggestingthat thatsome someofofthe thehomogeneous homogeneousmafic mafic schist schist may maybe behighly highly strained metagabbro. metagabbro. strained Stop hinge of of thethe Manitouwadge synform, ZB93-P151, S t o p BiG, B16, Symmetrical SymmetricalM-folds M-foldsininthe the hinge Manitouwadge synform, ZB93-P151,P135. P135. Continue Continue north north on on L1OW L10W about 200 200 metres metres until until ititintersects intersectsaalogging loggingroad. road. Note Note in in passing passing the themafic mafic metavolcanic metavolcanic rocks and metagabbro along along the way. way. Follow Follow the road road west west for for 700 700 metres to to where where the the main main road road makes makes aa broad broad turn turntotothe thenorth northand anda aside sideroad roadcontinues continueswestward. westward.Follow Follow the the side side road road for for about about 60 60 metres metres and and then thentake takethe theright-hand right-handnorthwesterly northwesterly(less (lesstravelled) travelled)fork forkfor for300 300 metres metres to toaasmall smallpavement pavement on on the the south southside sideof of the thetrail. trail.The Thefirst firstoutcrop, outcrop,intended intendedasasvery verybrief briefstop, stop,isisdominantly dominantlyhomogeneous homogeneousfine fine grained, grained, mafic mafic schist (highly (highly strained strained gabbro?) gabbro?) with withan aninclusion inclusionof oflayered layered quartz-magnetite quartz-magnetiteiron ironformation, formation, both cut cutby byfoliated foliated granite. granite. both Continue metresto toan anoutcrop outcrop area area extending extending south of the road. Continuewest west along alongthe thetrack trackfor for100—120 100-120 metres road. The Thearea area lies lies in the the hinge hinge region region of the Manitouwadge Manitouwadge synform. Garnetiferous Garnetiferous mafic mafic metavolcanic rocks are interlayered with with rocks rocks of more intermediate intermediate composition. composition. The Thelayering layeringand anddominant dominantfoliation foliation(D2) (D2)are areextensively extensivelyfolded, folded, mostly although some some S-folds S-foldsoccur occuratatthe the northern northern end of the outcrop mostly into into symmetrical symmetrical M-shaped M-shaped D3 D3 folds, although area. area. Some Somelayers layers have have abundant abundantcoarse coarse(cm-scale) (cm-scale)magnetite magnetiteporphyroblasts. porphyroblasts. Stop folds and lineation, ZB93-P134 (optional). Continue 150—170 S t o pB17, BIT,Felsic Felsicrocks, rocks,D3D3 folds a nstrong d strong lineation, ZB93-PI34 (optional). Continue 150-170 metres metres west metressouth south of of the the track, climbing over over logs logs and and brambles brambles to find the west of of Stop Stop B16 B16 and and30—40 30-40 metres the outcrop. outcrop. Felsic intercalated with Felsic metavolcanic rocks belonging to the northern northern felsic felsic unit of of the the Swill Swill Lake area are intercalated with more more intermediate intermediate hornblende-bearing hornblende-bearing rocks. rocks. Tight Tightfolds folds (D3) (D3) of of the the dominant dominant foliation foliation (D2) (D2) plunge moderately to the the northeast, northeast,parallel parallel to toaavery very strong strongstretching stretching lineation. lineation. Stop rocks and ZB93-P154, P155, ZB94-84. Return S t o pB18, B18,D3 Dafolds foldsofofmetavolcanic metavolcanic rocks a ngranite, d granite, ZB93-P154, P155,ZB94-84. Returneast east(about (about 550 m) to where the main road turns turns north. north. Continue Continuenorthward northwardfor for220 220 metres metres to to aa westerly westerly branching track. Follow the track for 150 Follow the 150 metres to to the thetop topofofaahill hilland andextensive extensiveoutcrops outcropsofofstrongly stronglylineated lineatedand andfolded, folded, plagioclase-hornblende-bearing intermediate metavolcanic metavolcanic rocks. rocks. From From the the hill top, continue northerly to plagioclase-hornblende-bearing intermediate to the the base of the steep steep north north slope, slope, then then head headwesterly westerly (about (about 300 300 m) m)in inthe thelow lowcleared cleared area, area,keeping keeping the the slope slope and and log log piles to your your left. You You are are heading heading for for the the top top of of aa low low hill, hill, on the the southeast southeast side sideof of which which lies a small clean clean pavement visible in the distance. distance. The Thehill hillisisabout about200 200metres metres north northofofaalong longwood wood pile. pile. Intermediate rocks. Many Intermediate metavolcanic metavolcanic rocks rocks are dominant, dominant, thinly thinly interlayered interlayered with magnetite-rich mafic mafic rocks. tight folds folds (D3) (Da) reorient reorient the the foliation foliation (D2) (D2) and and plunge plunge northeasterly, northeasterly, parallel parallel to to aavery verystrong strongstretching stretching lineation. At and 30—40 Atthe thesouthern southernend endofofthe thehill hilltop, top, and 30-40 metres metreswest, west,mafic mafic metavolcanic metavolcanic rocks rocks and sheets sheets of foliated granite granite are are both bothinvolved involvedin inoutcrop-scale outcrop-scaleM-folds. M-folds. The Themafic maficrock rock has hasaastrong strongfolded foldedschistosity schistosity 66 �C. Dead Dead Lake Lake suite suite Manitouwadge field guide (D2), and a moderately developed axial axial planar fabric. fabric. The granite forms sheets parallel to the D2 D2 schistosity of the host rock and its of its most most obvious obvious fabric is axial planar to to the the D3 D3folds. folds. in an an attempt to The granite, interpreted as aa pre-D3 pre-Ds intrusion, was collected collected in to bracket bracket the theage ageof of D3 D3 Analyses of ofzircon zircongave gaveaascatter scatter of of discordant discordant points, points, whereas whereas titanite deformation by U-Pb geochronology. geochronology. Analyses defines an an age age of of 2655h3 2655±3 Ma Ma (Table 2), within error of of the the age age of of titanite titanitefrom fromaasyn-D3 syn-Datonalite tonalitedyke dykeless less defines and also within error error of of titanite from Lake pluton. pluton. The circa Ma than aa kilometre kilometre away, away, and also within from the Loken Loken Lake circa 2655 2655 Ma titanite. titanite ages ages are interpreted as as dating dating aa late late hydrothermal hydrothermal event that that crystallized crystallized or recrystallized recrystallized titanite. Stop metavolcanic rock, ZB93-P157 intermediate metavolcanic rock, ZB93-P157(optional). (optional).Retrace Retracethe theroute route B19, Lineation Lineationininintermediate S t o p B19, eastward to the main large wood wood pile pile and eastward main road. road. Continue Continue northward northward along along the the main main road road for for 200 200 metres metres to to aalarge metres to to a small clean clean outcrop on the south side an easterly branching side road. Follow Follow the side road for 70 metres of the the road. Thin of Thinstreaky streakyhornblende-rich hornblende-richand andfelsic felsiclayers, layers,and andthe thedominant dominantfoliation foliation(D2), (D2),define definesmall smallfolds folds (D3) with a weak weak Z-asymmetry. Z-asymmetry. A A beautiful beautiful lineation, lineation,strongly strongly developed, developed, plunges plunges northeasterly northeasterly parallel parallel to to fold axes. axes. Stop ZB93-4, S t o p B20, B20, Garnetiferous Garnetiferousmafic maficrocks, rocks,diabase, diabase, ZB93-4,P54. P54.Return Return(south (southand andthen then east) east) along along the main road for about 1.5 1.5 km, km, crossing crossing a narrow narrow deep washout washout and stream just before before intersecting intersecting a major major northwest-trending logging logging road. road. This is the road northwest-trending road on on which which the the vehicle(s) vehicle(s) are are parked parked somewhere somewhere (depending how many many washouts washouts were werenegotiated) negotiated)to to the the south. Cross follow how Cross the the intersection intersection with with the themain mainroad, road,and andfollow by the deep long gully gully that that has the road road leading leading uphill and northward, northward, also also identifiable identifiable by has been been eroded eroded into into it. it. After 150 metres, metres, the the road road curves curves to to the the east. Continue to the end of the road where it branches to the east east of Swill SwillLake. Lake. The The southeast southeast branch branch leads leadsto to aa trench trench 50 50 metres metres distant. The and south, 150 150 metres metres west west of The stripped outcrop outcrop area areaand andtrench trenchare aredominated dominatedbybydark darkmafic maficmetavolcanic metavolcanicrocks rockswith withgarnetiferous garnetiferouszones. zones. cmwidth, width,that that anastornose anastomose through through the the dominant foliation while while Garnet is is most most abundant abundantininseams seamsof of10—30 10-30 cm maintaining a generally cm in in diameter, and generally concordant concordant orientation. orientation. Grain Grainsize sizeranges ranges from from pinhead pinhead to to1—2 1-2 cm shape from equant to &type tails tails indicate indicate aanorth-side-up to lensoid, lensoid, parallel to foliation. In thin thin section, section, 6-type north-side-up shear shear sense with a slight of motion motion (also (also discernible discernibleon onoutcrop). outcrop). The abundance of of garnet garnet sense with slight sinistral sinistral component component of implies metasomatic alteration of of the the mafic mafic protolith; protolith; however, however, relationships between between tectonic fabrics, garnet porphyroblasts and anastomosing seams are are most most consistent consistent with with synkinematic synkinematic alteration alteration and anastomosing garnetiferous garnetiferous seams garnet crystallization. crystallization. Walk southeast to the outcrops in in the vicinity of the beaver Walk southeast the shore shore of of Swill Swill Lake. Lake. Water-washed Water-washed outcrops vicinity of beaver dam are dominated dominated by by coarse coarsegrained grained diabase diabasewith withmegacrysts megacrystsofofplagioclase, plagioclase,one one of of many manyexposures exposuresof of the thewide wide northeast-trending dyke dyke that thatcuts cutsacross acrossthe theSwill SwillLake Lake area. area. Return to to the the branch branch in in the theroad road and, and,just justwest west of of the thebranch, branch, head head south south on on L1W L1W to to aa small small outcrop outcrop 25 25 metres west schist with with minor minor garnet garnet is interinterwest of the line at at 0+75S. 0+75S. Dark Dark fine fine grained grained hornblende-plagioclase hornblende-plagioclase schist calated with schist. This is is one one of of with lighter-coloured lighter-coloured orthoamphibole-cummingtonite-plagioclase-garnet-biotite schist. the few orthoamphibole-bearing orthoamphibole-bearing rocks in the Swill Lake Lake area area and and suggests aa link link with with similar similar orthoamphiboleorthoamphibolenear Manitouwadge Manitouwadge Lake bearing rocks rocks to the east near Lake (e.g. (e.g. Stop Stop Bl). Bi). Stop metavolcanic rocks, ZB93-P179. metavolcanic rocks, ZB93-P179.Return Return5050metres metrestotothe theroad roadand andhead headwest, west, S t o p B21, B21, Intermediate Intermediate then follow follow L5W several outcrops then L5Wnorth north to to 2+25N 2+25N and and several outcropsscattered scatteredabout about35 35metres metreswest westofofthe the line. line. The rocks vary vary from from thinly thinly layered layered to to laminated and, are Uintermediate metavolcanic metavolcanic rocks are locally locally quite quite felsic. felsic. The TheUshaped northwestern part of the outcrop area may may be aa D2 D2 fold, based observation that shaped fold fold in in the northwestern based on on the observation that it folds layering, layering,whereas whereasthe the dominant dominantfoliation foliationappears appearsto to be be axial axial planar. planar. An interesting with straight folds interesting dyke, with sharp margins, cuts across across foliation in the southern southern part part of of the theoutcrop outcroparea. area.ItItcontains containspillow-like, pillow-like,medium medium mafic blobs blobs in in aa leucocratic leucocratic matrix matrix dominated grained, hornblende-rich hornblende-rich mafic dominated by microcline microcline and plagioclase. plagioclase. The dyke can can be be traced for about 200 200 metres to the the east-northeast east-northeast and andthere thereare aresimilar similarexposures exposures south south of of Swill Swill Lake. C. Inner Inner Manitouwadge Manitouwadge synform, Dead Lake suite The Dead foliated gabbro, diorite, and Dead Lake Lake suite suite comprises comprises aa complex complex association association of interleaved foliated and laylayered mafic grouped with with mafic ered mafic to intermediate intermediate rocks rocks of of probable probable supracrustal supracrustal origin origin collectively collectively grouped mafic to interintermediate metavolcanic metavolcanicrocks rocksofofUnit Unit5.5. The suite mediate suite can can be be mapped mapped in in atatleast leasttwo twonearly nearlycontinuous continuouszones zones within the within the Manitouwadge Manitouwadge synform synform corresponding corresponding to to high high variable variableaeromagnetic aeromagnetic relief relief (1:25000 (1:25000 map). map). It hornblendeincludes a group of distinctive homogeneous homogeneous or layered, strongly magnetic rocks rocks characterized characterized by by hornblendemagnetite±plagioclase±garnet±clinopyroxene±sulphide minerals mineralswith with variable variableamounts amountsofofquartz quartz (minor (minor to to magnetite&plagioclase&garnet&clinopyroxene&sulphide in eyes eyesor orlenticules. lenticules. Layered Layered varieties, varieties, in in particular, particular, resemble metamorphosed iron formation 50%), commonly in or ferruginous ferruginous chert; however, however, their their geochemical geochemicalcomposition composition(high (highFeOt, FeOt,TiOz Ti02 and and Zr) Zr) suggests sedimentary sedimentary concentration of heavy minerals. The The extent extent of of synvolcanic synvolcanic trondhjemite trondhjemite and andcomagmatic comagmaticrocks rocks in in the the inner innerManitouwadge Manitouwadgesynform synform is is not not easily answered answered on on the the basis of of outcrop outcrop and and petrographic petrographic observations. observations. At least some tonalite tonalite and granodiorite 67 �C. Dead Dead Lake Lake suite suite Manitouwadge field guide intruding the the Dead Dead Lake Lake suite suite isis texturally texturallyand andcompositionally compositionallysimilar similarto tosynvolcanic synvolcanic trondhjemite trondhjemite (Figs. (Figs. 23 23 and 24). However, However, most quartz-rich quartz-rich tonalites in the the area areahave have aahigher higher content contentof ofmafic mafic minerals, minerals, including including hornblende, than coarse grained (0.5—1 than those thosenear nearthe theWiliroy-Geco Willroy-Gecoarea. area.Some Someofofthe thehornblende, hornblende,present presentasas coarse grained (0.5-1 cm), randomly to moderately moderately oriented oriented poikiloblasts, poikiloblasts, appears appears secondary. secondary. The mafic rocks of of the Dead Dead Lake Lake suite suite are are tholeiitic tholeiitic basalts, basalts,geochemically geochemically very like like mafic rocks in the regard them to be inner and outer volcanic volcanic belts, with which which we we regard be correlative. correlative. The The two two zones zones of of the the suite suite are are indistinguishable and could couldrepresent representaastructural structural repetition. repetition. The structural relationship of the suite to the indistinguishable and relationship of the main main supracrustal supracrustalsequence sequencein inthe theManitouwadge Manitouwadgebelt beltisisbest bestexplained explainedby bysome somevariation variationon onaamodel modelinvolving involving major D2 D2 folds. folds. One One possibility possibility is that that the theentire entiresequence sequence between between the the Loken Loken Lake Lake pluton pluton and and the theBlack Black Pic batholith is is folded folded by the the D2 Dz 'Manitouwadge 'Manitouwadge syncline', syncline', the axial trace of of which which lies in metasedimentary metasedimentary rocks on the southern that the D3 Manitouwadge Manitouwadge synform (Fig. 5). This This model implies that theDead DeadLake Lake southern limb limb of of the the D3 suite is equivalent of the outer volcanic belt, and that equivalent to the the lower lower stratigraphic levels levels of volcanic belt, that trondhjemite trondhjemitepinches pinches out in of the the fold. Trondhjemite might might be be represented represented in in the outer belt in the the subsurface subsurface between between the two two limbs of of the the thin concordant units of map). A by some of of tonalite, for for example, striking through Gaug Lake (1:25000 (1:25000 map). second possibility is that that the thetwo twozones zones of of the the Dead Dead Lake Lake suite suite represent represent aa D2 Dz synclinal synclinal 'keel', 'keel', analogous analogous to to the the 'keel' of the D2 syncline' (Figs. (Figs. 55 and and 8). 8). This implies that the D; 'Manitouwadge 'Manitouwadge syncline' the Dead Dead Lake Lake suite suite isis equivalent equivalent screens included included in in trondhjemite trondhjemite in the Willroy-Geco area (and north to metavolcanic screens Willroy-Geco area north to toR.abbitskin Rabbitskin Lake) Lake) and the presence presence of a D2 anticlinal trace within the the trondhjemite. trondhjemite. The The Loken Loken Lake pluton, occupying the innermost area of the Manitouwadge Manitouwadge synform, is a biotite tonalite tonalite to long. It has aa strong to granite granite characterized characterized by by microcline microcline megacrysts, 5 to 15 cm long. strong tectonic tectonic fabric, fabric,commonly commonly represented represented by L>S tectonites. tectonites. The Theabundance abundanceofofmegacrysts megacrysts varies varies from from sparse sparse or or none none to to25%, 25%,although although near the to find find at least one the contacts contacts (based (based on on aeromagnetic aeromagnetic signature and mapping), it is usually usually possible to one megacryst depending depending on the the size size of the area exposed. Large Large areas of non-porphyritic rock, mainly more central to the the pluton, pluton,would would otherwise otherwise be be difficult difficult to to distinguish distinguish on outcrop outcrop from synvolcanic trondhjemite. However, However, the rocks Loken Lake Lake pluton plutonisissignificantly significantlyyounger younger atat2687+2/—3 2687+2/-3 Ma Ma rocks are are geochemically geochemically distinct, and and the theLoken (Fig. 16). Layering and the dominant dominant foliation foliation (D2) (D2) in the the Dead Dead Lake Lake area, including including foliations in the Loken Loken Lake axis (110°/250) (110°/25°), interpreted interpreted to to be the axis Lake pluton, are folded folded about an an east-southeasterly east-southeasterly plunging plunging axis axis of of the D3 synform. On this basis, the Loken Lake pluton pluton was was interpreted interpreted to be aa preD3 Manitouwadge synform. Loken Lake pre- to tosyn-D2 syn-Da intrusion. The Dead road north north from the Camp Dead Lake Lake area is reached reached by taking a logging logging road Camp 70 70 road road east east of of ManiManitouwadge. touwadge. The Camp Camp 70 70 road road intersects intersects the the Geco Geco mine road 22 km km east of of town, town, and and 11km km further, further,crosses crosses aa lumber lumber yard and railway railway line. Follow Follow the Camp 70 70 road for about about 99 km km from from the the railway railway line, line, crossing crossing the bridge across across the the Black Black River, River,passing passingaasign-posted sign-postedturn turnfor forTwist Twistroad roadand andaasand sandpit pit on on the the north, the bridge garbage dump dump and and you you will will latter about about 1.7 1.7km km before before the the logging logging road. The Thelogging logging road road also also leads leads to to aa garbage know you you made madethe the right right turn turn by by the garbage on the road road and to the west. know garbage on west. About About 300 300 metres metres north north of of the the turn and and on on the the north north side side of of the the dump, dump,aadirt dirtroad roadthat thatbranches brancheswest west totoWowun Wowun Lake Lake leads to Stop Stop Dl. Dl. Drive on past past the branch Drive on branch road road and and keep keep track track of of your your distance distance from it. Watch Watch out outfor forprobable probable washouts, washouts, hopefully negotiable with care. Stop ZB94-27. Continue Continue on on the logging road for for 6 km, winding around east C l , Loken Loken Lake Lake pluton, pluton, ZB94-27. logging road winding around S t o p Cl, Lake (not visible), making no no turns turns off off the the main main road road (1:25000 map). The stop is aa and north of of Wowun Wowun Lake visible), making (1:25000 map). low rocky rocky knoll knoll on on the the north side of the road, ditch. The low road, immediately immediately north of of the the water-filled water-filled ditch. The location location isis 400 metres metres east east of a railway (which you you will willnot not see see unless unlessyou youovershoot). overshoot). In In this exposure, 400 railway crossing crossing (which exposure, the Loken Lake Lake pluton pluton contains contains about 5% megacrystic megacrystic microcline microclineaugen, augen,ofofabout about 10 10cm cmin inlength, length, in in aa tonalitic Loken Thestrong strongsoutheasterly southeasterlyplunging plunging lineation lineation matrix with minor biotite and and trace trace amounts amounts of of hornblende. hornblende. The D2/D3?) is (L>S, composite composite Dz/D3?) is partly partly defined defined by asymmetrical asymmetrical (both oa- and 6-type, &type, Hanmer Hanmer and and Passchier, Passchier, 1991) tails tails on microcline augen. augen. Most of these are consistent with dextral, dextral, north-side-down, north-side-down, sense sense of rotation, rotation, show sinistral sinistral kinematics. kinematics. The conflicting rotations could could be due to variations although some show conflicting rotations variations in in the the original original orientation orientation of of long long axes axes of of phenocrysts. phenocrysts. C2, High Highstrain strain zone, contact t o Dead Lake suite, ZB93-360, ZB94-30.Cross Crossthe therailway railway at at 6.4 6.4 S t o p C2, Stop zone, contact to Dead Lake suite, ZB93-360, ZB94-30. continue on pavement outcrop of the road. km and continue on to 8 km stopping at aa pavement outcrop that extends from from the north side of This is the the first first exposure exposure of of the theDead DeadLake Lake suite, suite,here hererepresented represented by by interleaved interleaved white white quartzofeldspathic, quartzofeldspathic, intermediate (30—40% hornblende+biotite), and mafic (60—70% hornblende)layers, layers,0.5 0.5to to 30 30 cm cm in width. (3040% hornblende+biotite), (60-70% hornblende) width. Abundant to 3 mm, is concentrated in some some layers. layers. The Abundant magnetite, either fine grained grained or porphyroblastic porphyroblastic to concentrated in general appearance is that thatofofhighly highlyrecrystallized recrystallized and andcoarsened coarsened mafic mafic to tointermediate intermediatevolcanic volcanicrocks rocks with with tonalite sheets. sheets. rocky ledge ledge (3—4 (3-4 mmhigh) The Cross to aa rocky high)visible visibleabout about50 50metres metresaway awayon onthe the south south side side of of the the road. The very strong strong foliation foliation and and some some streaky quartz quartz ribbons, ribbons, could could be be aahighly highlystrained strained leucocratic tonalite, with aa very equivalent of either either synvolcanic synvolcanictrondhjemite trondhjemiteor or aa non-porphyritic non-porphyritic variety variety of of the the Loken Lake pluton. pluton. The equivalent of Loken Lake The presence of and magnetite magnetiteininsome somelayers layerssuggests suggests the the former. former. presence of pinhead pinhead garnet and 68 �C. Dead Lake suite Manitouwadge Manitouwadge field guide Stop rocks, ZB93-361, ZB94-108. qumtz-gmnet-magnetitehomblmde rocks, ZB93-361, ZB94-108. ConConS t o p C3, C3, Dead DeadLake Lakesuite, suite,quartz-garnet-magnetite-hornblende tinue to where the road bends to the just past the the southwest southwest (8.3 km) just the top top of of aa small small hill, hill, and and down down hill to aa gravelly area west westoff offthe theroad roadat at 99 km. km. The stop further along the road road on the first gravelly area stop is is 150 150 metres further first knoll knoll on the west west side, just beyond beyond aa swampy swampy area. area. Several Several rock rock types types are are exposed exposed including; including; 1) 1) strongly strongly magnetic, medium to coarse rock,locally locallywith withup upto to 50% 50% quartz quartz and coarse grained, grained, garnet-magnetite-hornblende-plagiocla.se garnet-magnetite-hornblende-plagioclase rock, minor sulphides suiphides and titanite, minor titanite, 2) 2) fine fine grained grained hornblende hornblende schist with with local local biotite biotite porphyroblasts, porphyroblasts, 3) 3) fine fine to to disseminated magnetite, magnetite, and 4) aa discordant medium grained, weakly weakly foliated, foliated, white white tonalite tonalitewith with2—5% 2-5% disseminated discordant pegpegmatite dyke. dyke. In Insome someplaces, places,quartz-garnet-magnetite-hornblende quartz-garnet-magnetite-hornblende rock forms a transitional transitional zone zone along along the the contact between hornblende hornblende schist schist and more leucocratic leucocratic rocks. rocks. The orientation of the dominant dominant fabric fabric (D2) (D2) and biotiteporphyroblasts porphyroblastsininhornblende horublendeschist schistlook look to to be defining is somewhat variable variable (038—075°/18—34°), (038-075°/18-340) and biotite a weak oblique foliation. From the south end of the outcrop, outcrop, climb climb up the hill hill to to several several outcrops along its crest about 80 80 metres west of of the road. quartz-garnet-magnetitewest road. The Therock rocktypes typesare aresimilar similartotothose thoselisted listedabove, above,with withmore morequartz-garnet-magnetitehornblende rock, rock, locally cut by weakly hornblende weakly foliated tonalite and forming forming angular angular inclusions inclusions in strongly strongly foliated foliated tonalite (trondhjemite?). (trondhjernite?). Biotite porphyroblasts porphyroblasts and selvedges selvedges in hornblende schist are developed developed mostly mostly might include include both both D2 and D3 folds, folds, the the near contacts with tonalite. tonalite. Tight Tightoutcrop-scale outcrop-scale folds folds of layering might with axial planes planes parallel parallel to to the the dominant foliation foliation (D2), (D2), and and the the latter latter with a weak weak axial planar fabric former with developed only in biotite selvedges developed selvedges at tonalite-hornblende tonalite-hornblende schist schist contacts. contacts. Stop rocks, ZB94-101. S t o p C4, Dead Dead Lake Lake suite, suite,layered layeredquartz-garnet-magnetite-hornblende qumtz-gmnet-magnetite-hornblende rocks, ZB94-101.Continue Continue south on the road, passing aajunction junction at at9.6 9.6 km km with with aa road road heading heading uphill to the west and, and, at at 9.9 9.9 km, km, reaching vehicles and and drivers. drivers. The next a muddy flooded stretch which may not be drivable drivable depending on water levels, vehicles stop, aa long of the road, is 450 long (150 (150 m) pavement pavement outcrop along the west side of 450 metres further on on and and worth worth a short hike. hike. The Theoutcrop outcropisisdominated dominatedbybyfine finegrained grainedhomogeneous homogeneous foliated foliated biotite tonalite tonalite with with some some thin (5 at the southern (5 cm) cm)concordant concordant aplitic aplitic layers. layers. On scattered scattered exposures exposures at southern end of of the the outcrop outcrop area, area, it isis possible possible to totrace tracea avery verymagnetic magnetic1—2 1-2 metre layer layer through aa series series of of complex complex folds. The Themagnetic magnetic layer of quartz, quartz, plagioclase, plagioclase,magnetite, magnetite,hornblende, hornblende,epidote, epidote,garnet garnetand andtitanite. titanite. The proportions layer consists consists of proportions of these minerals layering and and grading that minerals define define second-order second-order (cm-scale) (cm-scale) layering that looks lookslike likemodified modified bedding bedding and and suggests protolith. Locally, layer is is cut cut by diorite and pegmatite. Geochemical suggests a sedimentary protolith. Locally, the magnetic magnetic layer Geochemical analysis of addition to to high high FeOt FeOt (18.0%) (18.0%) and and CaO CaO (8.31%), (8.31%), analysis of a sample of of the magnetic layer shows shows that, that, in addition it is is relatively relatively high in Ti02 T i 0 2(1.36%) (1.36%) and and Zr Zr (2900 (2900 ppm). Ti02 T i 0 2and andZrZrare aretypically typicallyvery verylow lowininchemical chemical precipitates, their presence normally attributed to presence being normally to aa detrital detritalor orvolcanic volcaniccomponent. component. However, However, the high values here to the the enigma, enigma, values here may be more suggestive of of sedimentary sedimentary concentration concentration of of heavy heavy minerals. minerals. To add to preliminary of geochemical geochemical analyses preliminary interpretation of analyses of of quartz-garnet-magnetitehornblende quartz-garnet-magnetite-hornblenderock, rock,such suchas asthat that seen at Stop C3, and and hornblende-bearing hornblende-bearing trondhjemite, trondhjemite, suggest suggest that that these these represent represent synvolcanic synvolcanic trondhjemite trondhjemite by aa component component similar similar to to the the magnetic magnetic layer layer here. contaminated or altered(?) by diorite relationships, ZB943, ZB94-229. C5, Dead D e a dLake Lakesuite, suite,metagabbro, metagabbro,trondhjemite, trondhjemite, S t o p C5, Stop diorite relationships, ZB94-3, ZB94-229. Continue along the road 800 metres beyond the mud bath bath (10.7 (10.7 km km cumulative cumulative distance if you are still in your vehicle), to to another another extensive extensive outcrop outcrop in in the the ditch ditch on on the west. and tonalitic rocks rocks similar similar to to vehicle), west. Among dioritic and those seen at previous previous stops, stops, aavery very dark darkmafic maficvariety varietyof of magnetic magnetic hornblende-magnetite-plagioclase-garnet hornblende-magnetite-plagioclase-garnet rock Locally, the magnetic rock is veined veined by rock contains contains only minor minor amounts of of quartz. Locally, by fine and coarse grained grained felsic rocks, latter resembling resembling synvolcanic synvolcanic trondhjemite. felsic rocks, the the latter Continue south for another another 300 300 metres (11 km cumulative) to 100 metres Continue to another extensive outcrop outcrop about 100 west from the road road for for 50 50 metres. metres. The Therock rocktypes typesinclude; include;1)1)medium mediumtotocoarse coarsegrained grained long and stretching west metagabbro varying varying from from 80—90% 80-90% hornblende metagabbro hornblendetotoplagioclase-spotted plagioclase-spotted(30% (30%toto55mm, mm,phenocrysts? phenocrysts? or blasts?), fine to to medium medium grained grainedmagnetic magnetichornblende-magnetite-garnet hornblende-magnetite-garnet rock rock also alsolocally locallyplagioclase-spotted plagioclasespotted (up (up 2) fine 50%), 3) 3) fine fine to tocoarse coarsegrained grained trondhjemite, trondhjemite, 4) 4)fine finegrained grainedfoliated foliated diorite dioritewith with50% 50%hornblende hornblende and and to 50%), minor biotite porphyroblasts, and aplitelpegmatite. The Themetagabbro metagabbro isisinterpreted interpreted as asthe theoldest oldestrock; rock; minor biotite porphyroblasts, and 5) aplite/pegmatite. is cut cut by by trondhjemite trondhjemite and andboth bothmetagabbro metagabbroand andtrondhjemite trondhjemite are areengulfed engulfed by by foliated foliated diorite. diorite. Diorite Diorite it is contain local local inclusions inclusions of magnetic that the themetagabbro metagabbrolocally locallyhas hasnearly nearly5% 5% and trondhjemite contain magnetic rock. rock. Note that brown spots (1—3 (1-3 mm) section, looks looks like wormy aggregates. Although Although brown mm)ofoftitanite, titanite, which which in in thin section, wormy pods pods and aggregates. geochemically basalt, itit has hasrelatively relativelyhigh highTi02 Ti02(2.80%) (2.80%)and andanomolously anomolouslylow low geochemicallythe the metagabbro metagabbro is a tholeiitic basalt, Zr/Ti02. S t o pC6, C6,Foliated Foliatedgranodiorite, granodiorite, synvolcanic?, ZB94233. Continue southalong alongthe theroad roadfor for1150 1150 Stop synvolcanic?, ZB94-233. Continue toto thethe south metres metres (12.15 (12.15 km km cumulative), cumulative),just just 300 300metres metresnorth northofofthe thehairpin hairpinbend bendatatthe the southern southern end end of ofthe the road. road. An An outcrop area area stretches stretcheswest west of ofthe theroad roadfor for50—60 50-60 metres, coarse grained homogeneous homogeneous foliated metres, dominated by coarse granodiorite with disseminated disseminated magnetite porphyroblasts The strong strong porphyroblasts (up to 4 mm in size) and minor biotite. The foliation (D2) (Dz) undulates Therock rock isisrepresentative representative of of exposures exposures south from from here here foliation undulates in small folds and shears. The and, in texture, texture, and andgeochemical geochemical and andmodal modalcomposition, composition,resembles resembles synvolcanic trondhjemite, except for the the microcline. presence of of 10—15% 10-15% microcline. 69 �Eastern extension extension D. Eastern Manitouwadge Manitouwadge field guide D. Eastern extension extension of the t h e 'Geco 'Geco horizon' horizon' The The easternmost easternmost exposure, exDosure. of of what whatisislocally locallvcalled called the the'Geco 'Gecohorizon', horizon'.,crops crom outeast eastofofWowun WowunLake Lake . out near (1:25000map). map). Straight gneiss near the the Hucamp Hucamp zone zone of Lf subeconomic subkonomic mineralization mineralfzation (1:25000 gneiss in this this exposure exposure is is interpreted interpreted to tolie lie on on the thecontinuation continuation of ofthe theD1 Dl fault faultthat thatdissects dissectsthe theWillroy-Geco Willroy-Geco area area (Stops (StopsA3, A3, A6 A6 and and A20). A20). East East of ofthe theHucamp Hucampzone, zone,exposure exposure is is poor, poor, but but aaprominent prominentaeromagnetic aeromagneticanomaly anomaly continues continues on on the the same same trend, trend, and andthe the'Geco 'Gecohorizon' horizon'was wasintersected intersectedinindrill drillholes holes extending extending east east totothe theFalconbridge Falconbridgezone zone of of subeconomic mineralization. Orthoamphibole-garnet-cordierite mafic rocks rocks and and minor iron formation subeconomic mineralization. Orthoamphibolegarnet-cordierite gneiss, mafic east east of of Banana Banana Lake Lake (Noranda's (Noranda's East EastOne OneOtter Otterand andBanana Bananaclaim claimgroups, groups,Stops StopsD3—D4) D3-D4) are interpreted to to be be correlative correlative with the 'Geco horizon', horizon', but their structural structural relationship relationship is subject to to interpretation. interpretation. They Theyare are involved of map-scale map-scale folds, folds, that that also deform the the dominant foliation (D2), (D2), with aa northerly northerly trending trending involved in a series of enveloping surface. In In aa preliminary preliminary interpretation, interpretation, we we correlated correlated the the East East oOne Otter and enveloping surface. n e otter and Banana Banana zones zones with the the Falconbridge Falconbridge zone, zone, across across aa fault faultwith withsinistral sinistraloffset offset(Zaleski (Zaleskiand andPeterson, Peterson,1993b; 1993b;Peterson Petersonand andZaleski, Zaleski, 1994a). This model interpretation, as it implies that the model has ramifications ramifications to regional regional interpretation, the northern northern limb, limb,axial axial trace trace and and the theinner innervolcanic volcanicbelt beltofofthe thesouthern southernlimb limb(including (includingthe the'Geco 'Gecohorizon') horizon')ofofthe theManitouwadge Manitouwadge synform by the Blackman antiform and and the Jim synform (D3) are refolded refolded by Blackman Lake antiform Jim Lake Lake synform, synform, making making these latter latter D4 elements of of the preliminary D4 folds folds (see (see Structural StructuralGeology). Geology). Several Several elements preliminary model proved proved to be be problematic, problematic, among among them the thepostulated postulatedsinistral sinistralfault, fault,requiring requiring2.5 2.5km kmofofmap-view map-viewdisplacement, displacement,for forwhich whichwe wecould could find neither field nor aeromagnetic aeromagnetic evidence. evidence.In In our our preferred preferredrevised revisedmodel, model,the theEast EastOne OneOtter Otter and and Banana zones represent a D2 'keel', involved in in aa D2/D3 D2/D3 fold fold interference interferencepattern pattern along the the axial trace of the D2 synclinal 'keel', D3 map). This model allows for for aa simpler simpler more more elegant elegant interpretation interpretation D3 Manitouwadge synform (Fig. 5, 1:25000 1:25000 map). of the regional structure in that determine in which which the major folds that determine the the map map pattern patternofofthe thebelt belt(Manitouwadge (Manitouwadge synform, synform, Blackman Lake Lake antiform, antiform, Jim Jim Lake Lake synform) synform) are areall allD3 D3folds. folds. The Thefirst firsttwo twostops stops(D1—D2) (Dl-D2) are accessed from the logging road on the the east east side sideof of Wowun Wowun Lake, Lake, the thesame same road that C1—C6). thatwas wasused usedtotoaccess accessthe theDead DeadLake Lakesuite suite(Stops (Stops Cl-C6). The Thelast lasttwo twostops stops(D3—D4) (D3-D4) are areaccessed accessed by by continuing continuing east east on onthe theCamp Camp70 70road roadfor for1717km kmbeyond beyondthe theDead DeadLake Lakelogging loggingroad. road. D1—D2. Eastern inner inner volcanic volcanic belt, belt, 'Geco horizon' horizon' Dl-D2. Eastern Stop exposure of of thet h'Geco horizon', ZB93-P16. S t o p Dl, D l ,Easternmost Easternmostsurface surface exposure e 'Geco horizon', ZB93-Pl6.Take Takethe theCamp Camp70 70 road road and turn turnnorth northon ontotothe theDead DeadLake Lakelogging loggingroad road(see (seeC. C.Dead DeadLake Lakesuite, suite,for for more more detail), detail), after after300 300metres, metres, and turn turn west west off off the Dead Dead Lake Lake road on to aa dirt dirt road road around around the thenorth northside sideof of aagarbage garbage dump. dump. Drive Driveon on700 700 metres until until aapavement pavementoutcrop outcropisisjust just visible visiblethrough throughaastrip stripofofbushes busheson onthe thesouth southside sideof ofthe theroad road(1:25000 (1:25000 metres map). map). On Wowun Lake, Lake,an anattentuated attentuated sequence comprising comprising (north (north to to south); south); trondhjemite trondhjemite (synOn the the west west side of Wowun (synvolcanic), orthoamphibole-garnet orthoamphibolegarnet (or (orcummingtonite-garnet) cummingtonite-garnet)and andsillimanite-cordierite-biotite-garnet sillimanitecordieritebiotitegarnetgneisses, gneisses, volcanic), iron formation formation and metagreywacke, metagreywacke, crops the east east side side iron crops out out over over an an interval interval of of about about 200 200 metres. metres. Here, on the of Wowun Wowun Lake, 'Geco horizon' is marked by (north (north to tosouth); south);1)1)felsic felsicstraight straight of Lake, near near the Hucamp zone, the 'Geco thin (2 (2m) m)straight straightstreaky-layered streaky-layeredhighly highlystrained strainediron ironformaformagneiss containing containing some elongate elongate garnet, 2) aa thin gneiss tion, tion, 3) 3) <5 <5metres metresofofaahighly highlystrained strainedquartz-eye quartz-eyerock rock(possibly (possiblyquartz-phyric quartz-phyricfelsic felsicmetavolcanic metavolcanic rock) rock) with with fine grained grained garnet-magnetite in the the matrix, matrix, and and4) 4)rusty rustyfelsic felsic rock. rock. We We correlate correlate this high high strain strain zone zone with with fine interpreted D1 Dl fault fault in inthe theWillroy-Geco Willroy-Geco area. Throughout Throughout the theoutcrop, outcrop,there thereare areconcordant concordantfoliated foliated the interpreted Thedykes, dykes,although although plagioclase-porphyritic tonalite dykes, probably plagioclase-porphyritic tonalite dykes, probably belonging belonging to to a syn-D2 tonalite tonalite suite. The highly strained, strained, look look less less so than the the host host rocks. rocks. Note Notethe thesoutherly southerlydip dipofofthe thedominant dominantfoliation foliation(D2); (Dz);here, here, highly the the southern southernlimb limbofofthe theManitouwadge Manitouwadgesynform synformisisoverturned. overturned. S t o pD2, D2, Eastern Easterncontinuation continuation maficrocks rocksofof inner volcanic belt, ZB94-60.Return Returntotothe the Stop ofofmafic thethe inner volcanic belt, ZB94-60. Dead Lake Lake logging logging road, road, turn turnnorth northand andcontinue continuefor for650—700 650-700 metres east side side Dead metres to to an extensive outcrop on the east of coarse of the the road. road. The Thesouthern southernpart partofofthe theoutcrop, outcrop, coarsegrained grainedhomogeneous homogeneousfoliated foliatedtrondhjemite trondhjemitewith withlocal local magnetite and and biotite, biotite,isistypical typicalofofsynvolcanic synvolcanic trondhjemite. To To the the north, north,trondhjemite trondhjemiteisisinterleaved interleavedwith with magnetite mafic rocks rocks in a transitional transitional contact contact zone zone to to fine fine grained grained mafic mafic and laminated schist, the latter latter correlated correlated mafic with mafic mafic metavolcanic metavolcanic screens screens in the west. west. The Themafic maficschist schistlocally locallycontains containsplagioclase plagioclase with in trondhjemite to the porphyroclasts(?),possibly possibly derived derived from from dismembered dismembered veins, veins, and biotite biotite porphyroblasts, porphyroblasts, apparently apparentlydefining defining porphyroclasts(?), weak near-horizontal near-horizontal foliation. Stop Dl, Dl,layering layeringand and the thedominant dominantfoliation foliation (D2) (D2)dip dip moderately moderately to to aa weak foliation. As at Stop the the south. south. D3-D4. Orthornphibole-garnet-cordierite Banana area area D3—D4. Orthoamphibole-garnet-cordierite rocks, Banana The Banana Banana and and East EastOne OneOtter Ottergrid gridareas areasare aredominated dominatedby bymultiphase multiphase granitic granitic tototonalitic tonaliticrocks rocks The with variably variablydeveloped developed(mainly (mainlyweak) weak)fabrics. fabrics.AtAtleast leastsome someintrusive intrusiverocks rockscontain containabundant abundant ( 1 ~ 5 %disdis) with (1—5%) seminatedmagnetite magnetiteporphyroblasts porphyroblastsand, and,texturally texturally and compositionally (Figs. 23-25), resemble resemblesynvolcanic synvolcanic seminated and compositionally (Figs. 23—25), trondhjemitenorth northofofthe theWillroy-Geco Willroy-Gecoarea. area.Supracrustal Supracrustalrocks, rocks,including includingorthoamphibole-garnet-cordierite orthoamphibole-garnet-cordierite trondhjemite rocks, mafic mafic metavolcanic metavolcanic rocks and iron iron formation, formation, are arepresent presentasasscreens screensand andinclusions inclusionsdefining defining aa narrow narrow rocks, (about 50 50m) m)zone zoneof ofmap-scale map-scale folds folds related related to to the theD3 D3Manitouwadge Manitouwadge synform (Fig. Dl). Dl). InIn our ourpreferred preferred (about 70 �D. Eastern Easternextension extension D. Manitouwadge Manitouwadgefield field guide guide FIG.Dl. Dl.Geology Geologyand andfield-trip field-tripstops stopseast eastofofBanana BananaLake Lakealong dongthe theeastern easterntrace traceofofthe theD3 D3 FIG. Manitouwadgesynform. synform. Dashed Dashed lines linesare are cut cutlines linesof of Noranda's Noranda's Banana Bananagrid. grid.Structure Structuresymbols symbols Manitouwadge show show dominant dominantD2 D2foliations foliationsand andlineations. lineations. D28ynform synform(Fig. (Fig.5). 5).Folded Foldedfabrics, fabrics,interpreted interpretedasas D2, structuralmodel, model,the the zonefollows followsthe thefolded foldedtrace traceofofa aD2 structural zone D2, are areeasiest easiestto tosee seeand andmeasure measurewithin withinthe thesupracrustal supracrustalscreens. screens.The Thearea areawas wasthe thefocus focusofofmineral mineralexploration; exploration; however, however, aa drill drillhole hole in in the theEast EastOne OneOtter Otterzone zoneintersected intersectedonly onlyminor minordisseminated disseminatedsuiphide sulphidemineralization, mineralization, and andgeophysical geophysicalsurveys surveysofofthe theBanana Bananazone zonefailed failedtotoshow showany anyconductive conductiveanomalies. anomalies. Fkomthe thejunction junctionwith withthe theDead DeadLake Lakelogging loggingroad, road,follow followthe theCamp Camp70 70road roadfor forabout about1717km kmeast eastand and From north, ofofThompson north,turning turningtotothe theeast eastatata junction a junctioneast east ThompsonLake Lakeonon aagravel gravelroad roadsign-posted sign-postedfor forHillsport. Hillsport. Continue easterly easterly for for about about 33 km, km, taking taking aa dirt dirtroad roadto tothe thesouth southwhere wherethe themain mainroad road bends bends sharply sharply to tothe the Continue north.Continue Continuesoutherly southerlyfor for33km, km,ininpart partalong alongthe theeastern easternshore shoreofofa alake lake(which (whichmight mightbebeflooding floodingthe the north. road),until untilaacut cutline line(running (runningdown downthe thehill hilltotothe theeast) east)intersects intersectsthe theroad. road.The Theline lineisisthe the7S7stie tieline lineofofthe the road), Bananagrid. grid.The Thefollowing followinglocations locationsare arereferenced referenced to tothe thegrid grid(metric (metricunits). units). Banana S t o pD3, D3,Mafic, Mafic,orthoainphiboleorthoamphibolecummingtonite-bearing ZB93-313-315. Follow TL7S Stop andand cummingtonite-bearing rocks,rocks, ZB93-313--315. Follow TL7S theeast eastuphill uphillforfor 160 metres LO, and north to some rocky knolls ledges from 6+00S totothe 160 metres to to LO, and LOLOtotothethe north to some rocky knolls andand ledges from 6+OOS toto3+75S this distance from south to to north, thethe sequence; 3+75Son onboth bothsides sidesofofthe thegrid gridline line(Fig. (Fig.Dl). Dl).Over Over this distance from south north, sequence; trondhjemite,orthoamphibole-bearing orthoamphibole-bearingrocks, rocks,hornblende-biotite±cummingtonite hornblende-biotite&cummingtonite mafic maficrocks, rocks,trondhjemite, trondhjemite, trondhjemite, isisexposed. exposed.The Thetrondhjemite trondhjemiteisismedium mediumtotocoarse coarsegrained, grained,contains containsmagnetite magnetiteporphyroblasts porphyroblastsand andisisgeochemgeochemically contains inclusions ofofdioritic-looking icallyindistinguishable indistinguishablefrom fromthe thesame sameunit unitininthe theWillroy-Geco Willroy-Gecoarea. area.It It contains inclusions dioritic-looking fine finetotomedium mediumgrained grainedmetabasite metabasite(about (about50% 50%hornblende-biotite) hornblend+biotite) that thatmay maybe becoarsened coarsenedmetavolcanic metavolcanicrock. rock. Granitic Graniticrocks rockswith withassociated associatedpegmatite pegmatiteare arealso alsocommon, common,apparently apparentlyrepresenting representingyounger(?) younger(?)intrusions. intrusions. At relatively At5+65S, 5+65S,there thereisisa acontact contacttoto relativelyleucocratic leucocraticrocks rockswith withcoarse coarsesprays sprays(to (to5 5cm) cm)ofoforthoamphibole orthoamphibole (or (orcummingtonite?), cummingtonite?),and andlocally locallybiotite, biotite,inina aquartz-plagioclase quartz-plagioclasematrix. matrix.Locally, Locally,orthoamphibole orthoamphiboleand andbiotite biotite defineaastrong strongeasterly easterlyplunging plunginglineation. lineation.The Theorthoamphibole orthoamphibolerocks rocksstrike strikesubparallel subparalleltotothe thegrid gridline line(00) (0') define definingthe thehinge hingeofofan anopen openeasterly easterlyplunging plungingfold foldwhich whichwe weinterpret interpretasasthe thehinge hingeregion regionofofthe theManitouwadge Manitouwadge defining synform.Orthoamphibole-bearing Orthoamphibole-bearing rocks rocks can can be betraced tracedtotothe theeast easttotoorthoamphibole-garnet-cordierite orthoamphibole-garnet-cordieriterocks rocks synform. onthe thelimbs limbsofofthe thefold. fold.AtAt5+OOS 5+00S about about20 20metres metreseast eastofofthe theline, line,trondhjemite trondhjemiteand andgranite-pegmatite granite-pegmatite on 71 �Manitouwadge field guide E. Quetico, Jim Lake synform with abundant mafic (hornblende±cummingtonite) screens become dominant in the core of the fold until 3+80S. At 4+15S, a sample of fine to medium grained mafic schist (about 60% hornblende-curnmingtonite) has the major-element composition of a tholeiitic ferrobasalt, in contrast to mafic metavolcanic rocks from the supracrustal sequence to the west, which are high and low Mg tholeiites. The high Fe01 and presence of metamorphic cummingtonite may be due to alteration. At the base of the rocky hill at 3+80S, cummingtonite(+orthoamphibole?)-hornblende schists on the northern limb of the open fold strike at 070° and dip southerly underneath plutonic rocks, defining the northern limb of a synform. Stop D4, ZB93-287, Z894-93. Follow the trend (070°) of rocky ledges and knolls for about 130 metres to L1+25E, looking at the extensive exposures of orthoarnphibole-garnet-cordierite rocks. Plutonic rocks form the highest knolls to the south. The orthoarnphibole-garnet-cordierite rocks are coarse grained (locally with garnet to 10 cm and coarse orthoamphibole sprays) and heterogeneous with garnet-rich and orthoamphibolerich layering or enclaves (e.g. just west of L1+25E, 3+005). Garnet textures and distribution are fascinating, ranging to very coarse (to 10 cm) garnet porphyroblasts to fine grained garnetite, and local garnetiferous 'snakes' in an orthoaznphibole-riclj matrix. Locally, orthoamphibole-garnet-cordierite rocks are cut by irregular white veinlets (1—4 cm wide) characterized by quartz-sillimanite-garnet-cordierite. The margins to the host rock are diffuse and, although the veinlets have no systematic orientation and are discordant to the dominant foliation, the dominant foliation is found in both host rock and veinlet. The relationships suggest that the veinlets are the result of local channelling of metamorphic fluids. Orthoamphibole-garnet-cordierite rocks do not continue east of L1+25E beyond 40 metres; foliation trends indicate the presence of an antiformal hinge (Fig. Dl). At 2+755, on L1+25E and 20 metres to the west, plutonic rocks contain 2 layers (1 about S m thick) of an unusual strongly magnetic rock consisting of abundant (50%) quartz eyes in a matrixof fine grained magnetite, hornblende, clinopyroxene, garnet and minor plagioclase. The quartz eyes are monocrystalline, flattened and strained; locally, they are sufficiently abundant to coalesce into layers. The rock closely resembles quartz-garnet-magnetite-liornblende rocks of the Dead Lake suite, and possibly originated as a contaminated or altered quartz-phyric metavolcanic rock or trondhjemite. The quartz-eye magnetite-garnet rock tends to crop out to the east of orthoamphibole-garnet-cordierite rocks in the Banana area, including immediately to the east of the last exposure of orthoamphibole-garnet-cordierite rocks in the antiformal hinge. Orthoamphibole-garnet-cordierite rocks also crop out near L2+50E, 5+40S and L3-I-75E, 5+505 along the southern limb of the open fold. The road can be regained either by returning along tie line 75 or by continuing to base line 0 which also extends westerly to the road. Either of these routes crosses extensive outcrops of multiphase plutonic rocks, mainly magnetite-bearing trondhjemite and granite-pegmatite. E. Quetico subprovince, Jim Lake synform The Quetico subprovince in the Manitouwadge area is characterized by migmatitic biotite schists and metagreywackes, similar in texture, composition and depositional age, to those in the Manitouwadge belt (1:25000 map). The main difference is in metamorphic grade; rocks of the Quetico subprovince have been metamorphosed to granulite facies just north of the subprovince boundary and are extensively migmatized. Typically homogeneous or layered, they comprise biotite-plagioclase-quartz±garnet±cordieritethsilhimanite schist with extensive concordant, folded and cross-cutting tonalitic segregations. The dominant planar fabrics are interpreted to be correlative with D3 or D3 structures in the Manitouwadge belt. Northeasterly plunging Z-shaped folds of foliation, with a moderately developed, northeasterly striking axial-planar cleavage (in some cases, crenulation cleavage) are interpreted to be due to D3 deformation. Locally, the folds are associated with outcrop-scale structures (e.g. foliation fish) indicating dextral oblique shear. The D3 structures deform, and are cut by, migmatitic layers and veins, suggesting that D3 was approximately synchronous with peak metamorphism in the Quetico subprovince. The D3 Jim Lake synform is defined by mappable zones of mafic to intermediate metavolcanic screens and inclusions, with minor iron formation, enclosed in foliated to weakly foliated tonalite. Quetico metagreywackes can also be traced around the synform and along its southern limb as far as Larry Lake (1:25000 map). The Jim/Davis Lakes area lies near the hinge region, although most of the exposure lies along the southern limb and, in particular, near a map-scale 2-fold apparently parasitic to the Jim Lake synform. Quetico metasedimentary rocks in the Jim/Davis Lakes area are represented by migmatitic biotite schist with local thin iron formation. On the inside of the fold, northeast of Davis Lake, coarse grained trondhjemite to granodiorite resembles synvolcanic trondhjemite (Unit 12) in texture and composition (Figs. 23—25). South of the southern limb, foliated microcline porphyritic granitoid belongs to the Nama Creek pluton, which forms a sinuous body between supracrustal rocks and the Black Pic batholith folded by the Blackman Lake antiform. The Jim Lake synform is a tight fold and early fabrics are largely transposed and subparallel to the axial surface; however locally, dominant fabrics (D3) are folded around the hinge region and L-tectonites have a strong stretching lineation parallel to the axes of D3 minor folds. 72 �E. Quetico, Jim Lake Lake synform Manitouwadge field guide The The eastern eastern part partofofthe theQuetico Queticosubprovince subprovincein inthe theManitouwadge Manitouwadgearea areacan canbe beaccessed accessedfrom from the theHilisport Hillsport road (continuing from Stops Stops D3-D4). D3—D4).The Thesouthern southernlimb limbofofJim Jim Lake Lakesynform synformininthe the vicinity vicinity of of Jim Jim and road (continuing from Davis Lakes Lakes isis reached reachedby by continuing continuingto tothe the north north on the Camp 70 road beyond the Hillsport Hillsport junction east east of of Thompson Lake. El—E3.Quetico Quetico subprovince, subprovince, eastern eastern Manitouwadge Manitouwadge area area El-E3. S t o p El, E l ,Z-folds Z-foldsand a n kinks, d kinks, ZB93-P293.From Fromthe theBanana Bananaarea, area,return return 33km kmnorth north to tothe theHillsport Hillsport Stop ZB93-P293. road where where it curved sharply north north (1:25000 map). Continue Continue north north and and then northeast for road curved sharply (1:25000 map). for 4.5 4.5 km, turning turning right on to aa gravel right (southeast) (southeast) on gravel road. road. On On the thenorth northside sideofofgravel gravel road, road, 1.1 1.1 km km from from the the intersection, intersection, a pavement asediment ary rocks rocks shows showswell welldeveloped developedmigmatitic migmatiticlayering layeringparallel parallelto to aa fine finebiotite biotite foliation foliation pavement of of met metasedimentary (D2/D3). The The dominant dominant planar planar fabrics fabrics are areparallel parallel to tothe theaxial axialsurfaces surfacesof offolds foldswith with Z-asymmetry Z-asymmetry and, and, in in folded by by a kink (D4), also with Z-asymmetry. A coarse grained cordierite-bearing segregation one place, folded segregation cuts cuts discordantly across the outcrop. discordantly Stop indicators, ZB93-P294. Continue southeast ZB93-P294. Continue southeasttotoa alarge largepavement pavement outcrop outcrop S t o p E2, E2, Dextral Dextralkinematic kinematic indicators, north of the road road 1.7 1.7 km km from from the the intersection. intersection. The Themetagreywackes metagreywackes contain contain extensive extensive concordant and crosscrossD3, include include asymmetric asymmetric folds (most with cutting migmatitic segregations. Outcrop structures, interpreted interpreted as asD3, Z-asymmetry), foliation foliationfish, fish,rotated rotated boudins, boudins, and and incipient incipient shear shear bands, bands, all all indicating indicating a dextral sense Z-asymmetry), sense of of granitedyke dykeintrudes intrudessubparallel subparallelto to the the axial surfaces of D3 folds folds shear. A A coarse coarse grained grained muscovite—biotite muscovite-biotite granite of biotite schist, apparently rotated and has an axial axial planar planar foliation. foliation. ItItcontains containswall-rock wall-rock inclusions inclusions of rotated during during incorporation intruded during during incorporation into the dyke, dyke, and and folded folded migmatitic migmatitic schist. schist. The dyke dyke was interpreted interpreted as intruded progressive deformation late late in the metamorphic and anatectic progressive deformation anatectic history, history, hence, hence, contemporaneous with late late D3 D3 to D4. Zircon Zircon from from aa sample sample of of the the dyke dyke gave gave aa scatter scatter of ofdiscordant discordant analyses. analyses. AAsingle singleslightly slightlydiscordant discordant monazite grain with with an age of 2642±2 Ma (Table (Table 2), 2), is is difficult difficultto to interpret interpret in in isolation; isolation; itit could could date date the monazite grain 2642A2 Ma intrusion, or retrograde crystallization crystallization or resetting resetting of of monazite. Stop Z-folds, ZB93-P287. easy, but longish, S t o p E3, E3, Graded G r a d e layering, d layering, Z-folds, ZB93-P287.This This easy, but longish,walk walktotosee seea asingle singleoutcrop outcrop of of bedding) and spectacular graded layering (modified (modified bedding) spectacular folds folds in in Quetico Quetico metagreywacke metagreywacke is worth while, while, ifif time time permits. Return Return to tothe theHilisport Hillsportroad, road,turning turningsouthwest southwest to to retrace retrace the theroute routefor for 250 250 metres to an intersection road on on the north side with an overgrown overgrown road side of an an open open area. area. Walk Walk along along the theovergrown overgrown road north and and west west metres, crossing crossing aa small stream, stream, beyond which, continue south south 50 metres metres to an open area for 725 metres, area of of pavement pavement outcrop. The Theoutcrop outcropisisdominated dominatedby bylayered, layered,fine fine to to coarse coarse grained, grained, quartzofeldspathic quartzofeldspathic biotite biotiteschist, schist,locally locally with sillimanite and abundant abundantgarnet. garnet.Layers Layersofofmore morepelitic peliticcomposition compositionhave havemore moremigmatitic migmatiticsegregations. segregations. between the the coarse garnet-biotite-richtop(?) top(?) of A sharp folded contact (Z-asymmetry) (Z-asymmetry) between coarse garnet-biotite-rich of one layer, layer, and and the the quartz-plagioclase-rich of another, another, suggests suggests relict graded bedding with southward younging. younging. Folds Folds quartz-plagioclase-rich bottom(?) bottom(?) of various scales mostly mostly have Z-asymmetry Z-asymmetry and, locally, locally, are associated associated with an an axial axialplanar planarcrenulation crenulation on various cleavage. Folds Folds with with S-asymmetry S-asymmetry dominate dominateone onearea, area, indicating indicatingthat that the axial trace of cleavage. of aa larger larger scale scale fold fold crosses no closures closures are exposed. crosses the the outcrop, although no E4—E6.JJim Lakes area E4-E6. i m Lake synform, Jim/Davis Lakes S t o p E4, E4, Foliated Foliatedtrondhjemite, trondhjemite, ZB93-P270. From Hillsportjunction, junction,take takethe theCamp Camp70 70 road road northnorthStop ZB93-P270. From thetheHilisport westerly around the northern northern ends ends of of Thompson, Thompson, Loken Loken and Straight Straight Lakes Lakes (1:25000 (1:25000 map). At 77 km km beyond beyond westerly turn north northon onthe theJim JimLake Lakeroad; road;the thesingle-lane single-laneFox FoxLake Lake siding siding road road continues continues to the the west. west. the junction, turn Continue north Jim Lake Lake road, road, turning turning west west on on to to aagood gooddirt dirtroad roadwhich whichleads, leads, in in300 300 Continue north for 3.6 3.6 km on the Jim metres, area of of flooded flooded sand The road road isis visible visible beyond beyond the and metres, to an area sand pits. pits. The the flooded flooded area; area; it's it's best best to park and will be necessary (allowing for wade across as, 200 200 metres metres further further down the road, it will forthe the vagaries vagariesof ofnature) nature) to to 10 m m long). long). The Theroad roadcontinues continuesin in good good shape shape beyond beyond these these obstacles. obstacles. cross a beaver dam (less than 10 On the south south side side of of the the road, road,200 200metres metres west west of of the the beaver beaver dam, dam,aalarge largearea area(100 (100mmlong) long)of offiat-lying flat-lying outcrops consists of indistinoutcrops consists of homogeneous homogeneouscoarse coarsegrained grainedtrondhjemite trondhjemitewith with minor minor biotite biotite and magnetite, indistinguishable fabric is is foliated foliated to to gneissic gneissic and, and, guishable from from synvolcanic synvolcanictrondhjemite trondhjemiteinin the the Willroy-Geco Willroy-Gecoarea. area. The fabric deflected by by both both sinistral and dextral locally, deflected dextral minor minor shear shear zones. zones. S t o p E5, E5, Migmatitic Migmatiticbiotite biotite schist d iron formation, ZB94207. Continue alongthe theroad roadfor for540 540 Stop schist anda niron formation, ZB94-207. Continue along metres look for overgrown track 100 metres metres east low metres and and look for a very overgrown trackthat that heads heads off off to to the the south, south, about 100 east of a low Bushwack south for for 300 300 metres and and then thensouthwesterly southwesterlyfor for 100 100 metres metres following following the track, track, at at swampy area. Bushwack which point new growth is is very very thick. thick. Continue Continue westerly westerly about about 50 50 metres metres to toaalarge largeoutcrop outcrop(visible (visibleon on which point the new 37-15, Ministry road and and west west of of airphoto 90/2-4909 37-15, Ministry of of Natural Natural Resources, Resources, Ontario) Ontario) on on the the north side of the road small swamp. The Thebiotite biotiteschist, schist,containing containingpinhead pinhead garnet, garnet,was wasgrouped groupedwith withQuetico Queticometasedimentary metasedimentary a small rocks. Tonalitic Tonaliticleucosome leucosome is is more more abundant abundantininpelitic peliticlayers layersand andhas hasbiotite-garnet-rich biotite-garnet-richselvedges, selvedges,1—5 1-5 cm rocks. Leucosome apparently apparently shows shows 2 generations generations of of folding, folding, the of which which are east-southeasterly east-southeasterly in width. Leucosome the latest of plunging (121°/180 deform early plunging (121°/18°) folds foldsthat that deform early folds foldsand and have havean an axial axial planar planar biotite biotite schistosity schistosity (D3?). (D3?). Thin Thin (1-5 of iron formation, are (1—5cm) cm)rusty rustyquartzose quartzoselayers layerswith withminor minormagnetite magnetiteand andgrunerite, grunerite, the the remnants remnants of 73 �F. Black Black Pic batholith Manitouwadge field guide segmented and contorted in the the migmatitic migmatitic matrix. matrix. Leucosome Leucosome adjacent to to the the iron iron formation formationcontains contains some some coarse (to 11cm) cm) porphyroblasts porphyroblasts of of grunerite. grunerite. Stop formation, Nama Creek pluton, ZB94-197, ZB93-P281— S t o p E6, E6, Mafic Maficmetavolcanic metavolcanicrocks, rocks,iron iron formation, Nam a Creek pluton, ZB94-197, ZB93-P281282, ZB94210. ZB94-210. Make Make your your way wayback backto to the the road and continue passing the the remains of of an old cabin continue westerly, westerly, passing 1070 metres metres west west of of the the beaver beaver dam. dam. At 1070 At 1345 1345metres metres west west of of the thedam, dam,excellent excellent exposures exposures south south of of the the road comprise about 25% rocks included includedin in coarse coarse grained grained to to pegmatitic pegmatitic 25% mafic to intermediate metavolcanic rocks tonalite. Fine Finetotomedium mediumgrained grainedscreens screensofofmafic maficrock, rock,locally locallywith withepidote epidoteknots, knots,show showlayering layeringdefined defined by grain size The screens screenstend tend to to be boudinaged or segmented size and and hornblende hornblende abundance abundance (20—80%). (20-80%). The segmented and, in some cases, biotite-rich biotite-rich rims are related to to intrusive intrusive contacts. contacts. Intermediate Intermediatetotofelsic felsiclayered layered screens screens with with disseminated magnetite and possible quartz eyes are present present in lesser lesser amounts. Continue west 30 metres on the same outcrop area area to to aa weakly weakly magnetic quartzose iron iron formation formation (about (about 30 metres of strike-length strike-length is exposed) exposed) with minor minor sulphide sulphide minerals minerals associated associated with mafic mafic to to intermediate intermediate rocks. layer, up up to 55 metres rocks. The The iron iron formation formation is is aa semi-continuous semi-continuous layer, metres thick, thick, tracable tracable along-strike along-strike for about 150 metres metreson onboth both sides sidesofofthe theroad, road,and andcropping croppingout outagain again11km kmtotothe thewest. west.To Tothe thesouth, south,the the unit unit trends trends 150 south-southwesterly south-southwesterly around the the map-scale map-scale Z-fold Z-fold in the Davis Davis Lake area. Continue along the the road road for 1650 metreswest westofofthe the beaver beaverdam damto to an an outcrop outcrop on on the road itself Continue along 1650 metres itself and extending to the the north. north. The Theexposure exposureisistypical typicalof ofthe the2680 2680 Ma Ma Nama Creek pluton, pluton, medium medium to to coarse coarse grained granodiorite, strongly inicroclinephenocrysts phenocrystsabout about 11 cm cm long. long. The matrix strongly foliated foliated with with about about10—25% 10-25% microcline matrixhas has white chalky plagioclase and and about about 20% biotite biotite and and hornblende. hornblende. Fine grained biotite and hornblende inclusions outline growth zoning present, and an zoning in the phenocrysts. phenocrysts. Some Some minor minor mafic mafic screens screens are present, an extensive extensive network network of folded aplite-pegmatite aplite-pegmatite dykes. dykes. F. Black Black Pic P i c batholith, supracrustal supracrustal screens screens and a n d major m a j o r folds folds F1—F5. BlackPPlc batholith F1-F5. Black i c batholith Supracrustal rocks Supracrustal rocks of of the the Manitouwadge Manitouwadge belt belt are areenclosed enclosed by multiphase foliated foliated to to massive massive plutonic plutonic rocks rocks collectively knownas asthe the Black Black Pic Plc batholith batholith (1:25000 map). Foliations Foliations in in the the Black Black Pic batholith mimic collectively known (1:25000 map). mimic the the of the dominant D2 foliations foliations in in the supracrustal suite and are orientations of are folded folded by the the D3 Da Manitouwadge Manitouwadge synform. To the rocks are mainly mainly tonalitic tonalitic to granodioritic, synform. the south south of of the theManitouwadge Manitouwadge synform, synform, plutonic plutonic rocks granodioritic, but also also include dioritic and granitic phases, phases, commonly commonly on On the the basis basis of of cross-cutting cross-cutting on aa single single outcrop. outcrop. On relationships, mafic phases are generally generally older than than felsic felsic phases. phases. Stop contact zone,zone, ZB93-61—62. Fl,Black BlackPic/supracrustal Pic/supracrustal contact ZB93-61-62. Take Takethe theCaramat CaramatIndustrial Industrial road road west west S t o p Fl, from Highway Highway 614 614for for1.2 1.2km, km,turning turningsoutheast southeaston onaagravel gravelroad roadjust justwest westofofan anindustrial industrial area. area. In about 300 metres, a long pavement crops out north of the road under aa powerline (1:25000 (1:25000map). map). The The northern northern outcrops are dominated by by layered layered fine fine grained mafic mafic to intermediate intermediate hornblende-biotite hornblende-biotite amphibolite amphibolite (metavolcanic), (metavolcanic), locally with epidote hornblende-biotite 10—20% epidote knots knots and andgarnet. garnet.Foliated Foliated hornblende-biotitediorite, diorite,with with 10-20% plagioclase plagioclase augen augen (mostly 0.5 0.5 cm), cm), increases increasesinin abundance abundancetoward towardthe thesouth. south. The The diorite, diorite, typical typical of of the the oldest oldest phase phase of of the the (mostly Black Pic batholith, is cut Black Pic cut by by multiphase, multiphase, concordant concordant and discordant discordant granite, pegmatite and and aplite aplite dykes, dykes, Both diorite diorite and and granite graniteare areinvolved involved in in tight tight folds folds with metavolcanic metavolcanic varying from strongly foliated to massive. Both rocks. The The schistosity schistosity in the amphibolite amphibolite is is parallel parallel to axial axial plane plane traces and and also also undulates undulates in in broad broad open open rocks. S-folds (plan view). view). Continue 100 metres powerline clearing Here in aa high high strain strain metres south on the powerline clearingon onthe the east east side side of of the the road. Here mm) mafic mafic rocks rocks are are unusual in having zone, streaky laminated laminated (submm—10 (submm-10 mm) having aa westerly-plunging westerly-plunging lineation. lineation. diorite. Intercalated mafic The zone is cut by by plagioclase-porphyritic plagioclase-porphyritic diorite. mafic and dioritic rocks and pegmatite-aplite pegmatite-aplite dykes continue continue to to the south. south. Stop inclusions, ZB93-63. Retrace thethe route about S t o p F2, F2, Aplitic Apliticgranite g r a n i twith e w i tdiorite h diorite inclusions, ZB93-63. Retrace route about100 100metres metresfrom from the the first outcrop outcrop of of Stop Stop Fl Fl and first and turn turnon ontotoa aroad roadbranching branchingsoutheast southeastskirting skirtingthe theindustrial industrialarea; area;100 100metres metres further, there are are patchy patchy pavement pavement outcrops outcrops in in the the cleared cleared area area west west of of the the road. road. The Thewhite whiteweathering weatheringfine fine pegmatitic patches and more discrete veins. The to medium grained weakly foliated aplitic granite has diffuse pegmatitic The granite resembles the youngest phase of Stop Stop Fl F land andcontains containssome someminor minorinclusions inclusionsof offoliated foliatedplagioclaseplagioclaseporphyritic diorite. Stop PicPbatholith, ZB93-67, ZB94-86. S t o p F3, F3, Three Threephases phasesofofthe t hBlack e Black i c batholith, ZB93-67, ZB9486. Stops StopsF3, F3,F4 F4and and F5, F5, are are accessed at the the railway railway crossing crossing east of of Little Little Manitouwadge Manitouwadge Lake; 100 metres accessed from from the the Camp 70 road at metres east east (1:25000 of crossing, turn off the Camp Camp 70 road to to the the southwest southwest on on to to aaroad roadparalleling paralleling the thetracks tracks(1:25000 of the crossing, turn off map). After After 500 500 metres, large large rocky knolls slope slope down downon onthe the southeast southeast side sideof ofthe theroad. road. Three main plutonic youngest; 1) 1) strongly foliated (D2) coarse grained hornblende-biotite diorite rocks are exposed, from oldest to youngest; correlated with oldest phase phase of of Stops Stops Fl F land andF2, F2,2)2)fine finetotomedium mediumgrained, grained,buff buffweathering, weathering, foliated foliated correlated with the oldest granodiorite with <5% biotite and, and, 3) 3) weakly weakly foliated foliated pegmatitic-aplitic pegmatitic-aplitic granite, and granodiorite with <5% granite, similar similar to to Stops Stops FFll and plagioclase F2 but more more pegmatitic. pegmatitic. The Thediorite dioritecontains containssubtle subtle plagioclaseaugen augen(3—5 (3-5 mm) mm) and and locally locally approaches approaches 74 �F. Black Black Pic batholith batholith Manitouwadge Manitouwadge field guide monzodiorite with about about 10% 10%microcline. microcline. ItItcontains containssome somedark dark fine fine grained grained elongate elongate mafic mafic enclaves. Diorite, sampled on this outcrop, Ma (Fig. (Fig. 17, Table Table 2), 2), within sampled on outcrop, has has aa U-Pb U-Pb zircon zircon age age of of 2687+3/—2 2687+3/-2 Ma within error error of the Loken Lake microcline-megacrystic microcline-megacrysticpluton, pluton, and and both both are interpreted as as aaprepre- totosyn-D2 syn-D2intrusions. intrusions. The granodiorite granodiorite has has aastrong strongfoliation, foliation,locally locallygneissic, gneissic, and itit contains contains angular angularand andelongate elongateinclusions inclusions of diorite and minor exposures, and and it may be minor mafic mafic schist. This This phase phase is is difficult difficult to correlate correlate between between exposures, be that that there similar appearance appearance that that post-date diorite there are are several several granodioritic-tonalitic phases of similar diorite and and pre-date predate aplitic aplitic granite. Aplitic Aplitic granite granitedykes dykes cut cut the theolder olderphases phasesatatlow lowtotomoderate moderateangles anglestotofoliation, foliation,and andhave haveaaweak weak fabric apparently with the same same orientation as that that in inhost host rocks. rocks. AAsample sampleof of aplitic apliticgranite, granite, collected collected for for geochronology on this this outcrop, had only poor quality geochronology on quality zircon. zircon. Stop intrusion breccia, ZB93-69. Continue southwest S t o pF4, F4,Syenite-hornblendite Syenite-homblendite intrusion breccia, ZB93-69. Continue southwestalong alongthe theroad roadtoto1.8 1.8 km, on the the north side of the the road. Multiphase km, 100 100 metres east of of a powerline, to good outcrop ledges and knolls on Multiphase plutonic are olutonic rocks here are similar to those of Stop F3, F3. but the the relationships relationshi~s aremore more difficult difficult to see. see. Of Of note note are are the originating as as aa diatreme, diatreme, although the rubbly rubbly outcrops outcropsand and blocks blocks of an interesting intrusion breccia, possibly originating we have not mapped here here in in any any detail detail(see (see Alkalic Alkalic rocks (Unit 16), 16), Fox Creek occurrence). An assortment assortmentof of lithic fragments cm),mostly mostlyangular angular mafic mafic to to intermediate hornblende-biotite-rich, are embedded fragments (1—25 (1-25 cm), embedded in in aa coarse grained matrix hornblende and and biotite with hornblende matrix comprising comprising plagioclase, hornblende hornblende phenocrysts (euhedral (euhedral prisms to 1.5 apatite and titanite. 1.5 cm) and minor to trace amounts of quartz, microcline, apatite titanite. Locally, Locally, hornblende looks to be be of of metasomatic metasomatic igneous igneous origin, origin, forming radiating sprays or oriented oriented perpendicular perpendicular to to inclusion inclusion contacts, as though surfaces. Biotite is mainly mainly present present as laths within hornblende and though nucleated nucleated on on inclusion inclusion surfaces. tends to to be beuniformly uniformlyoriented orientedinineach eachphenocryst, phenocryst,locally locallylooking lookinglike likepartial partialreplacement replacementofofhorublende. hornblende. Although the breccia massive, itit is is cut by aplitic dykes. dykes. The breccia contains at least one breccia looks massive, one fragment fragment (2 (2 cm size) of massive sulphide suiphide (pyrite-chalcopyrite-magnetite) transported from depth? during (pyrite-chalcopyrite-magnetite) transported duringemplacement; emplacement; interesting concept, concept, as contact to supracrustal supracrustal rocks and the theclosest closest an interesting as the the contact rocks lies lies about about 1 km km to the north, and known massive the Geco Geco mine. The The area area of of the thebreccia breccia crudely crudely known massivesulphides sulphidesare aremore morethan than 33 km km to to the the north at the corresponds to several highs (1:25000 (1:25000map). map). The breccia was grouped by several isolated anomalous aeromagnetic aeromagnetic highs Williams Williams et al. (1992) (1992) in in an an 'appinite 'appinite suite', suite', with withother otherexamples examples intruding intruding the theRawluk Rawluk Lake Lake pluton to to the the east in in the the Faries Faries Lake Lake area area (Fig. (Fig. 2). 2). S t o p F5, F5, Syenite.hornblendite Syenite-hornblenditeinternal internal structures, Black batholith, ZB93-70. Continuedirectly directly Stop structures, Black PlcPic batholith, ZB93-70. Continue under the powerline, south of of the road, to an outcrop. The powerline, south an area area of of extensive extensive outcrop. The first first exposures exposures are apparently F4, here here represented represented by by aaheterogeneous heterogeneous suite suiteincluding including continuation of of the the syenite-hornblendite syenite-hornblendite of Stop Stop F4, a continuation of layering analogous rhythmically layered rocks, with truncations of analogous to to cross-bedding. cross-bedding. About About 200 200 metres metres further further powerline, two main plutonic rocks The uphill along the powerline, rocks more more typical typical of of the the Black Black Pic Pic batholith batholith are exposed. The oldest, medium medium grained grained well well foliated granodiorite with with about about15% 15%biotite biotiteand andhornblende, hornblende,isiscut cutby byaayounger younger oldest, network of pink massive aplite-pegmatite aplite-pegmatite dykes. dykes. F6—F12. Western Blackman Blackman Lake Lake antiform antiform (D3), (D3), Janet Janet Lake F6-F12. Western Lake road road In Manitouwadge In contrast contrast totothe theBlack BlackPic Picbatholith batholithsouth southofofthethe Manitouwadgebelt belt(Stops (StopsF1—F5), F1-F5), plutonic plutonic rocks rocks to to the thenorthwest northwestcontain containmany manysupracrustal supracrustalscreens, screens,including includingmafic maficmetavolcanic metavolcanic rocks rocks and and iron iron formation. formation. Outcrop-scale structures, foliation foliation and aeromagnetic aeromagnetic trends suggest the presence presence of major fold, fold, the theD3 Dg Outcrop-scale trends suggest of a major Blackman Lake antiform, Janet Lake Lake area area (1:25000 (1:25000 map). In Blackman antiform, with with a northeasterly trending axial trace in the Janet the accompany changes changesin in foliation foliation orientation. orientation. The the hinge hinge region, region, changes changes in in vergence vergence of outcrop-scale folds accompany limb of of the the Blackman Blackman Lake Lake fold forms the main main supracrustal supracrustal belt beltand andmay mayhave havebeen been eastern limb forms the contact to the the the locus locus of of post-D2 post-D2 shearing. shearing. The Theprepre-totosyn-D2 syn-D2microcline-porphyritic microcline-porphyritic Nama Nama Creek Creek pluton pluton was was intruded intruded contact. The Thesupracrustal supracrustalscreens screenson onthe thewestern westernlimb limbofofthe theBlackman BlackmanLake Lakeantiform antiformmay mayhave have along the contact. been derived derived from a highly attentuated attentuated hinge hinge region region of of the the Jim JimLake Lake synform synform or, alternatively, alternatively, they may may be be a continuation continuation of of the the outer outer volcanic volcanic belt to to the thesouth, south,displaced displaced by by apparent apparent dextral dextralshear. shear. The The Janet JanetLake Lakeroad roadisisreached reachedby byfollowing followingthe the Caramat Caramatroad roadwest westfrom fromHighway Highway614 614passing passing the thebridge bridge across Nama Creek Creek (14 the north, north, and andcontinuing continuing northerly northerly about about 7.5 7.5 across (14 km), km), where where the the Caramat Caramat road turns to the km. The TheJanet JanetLake Lakeroad roadisismostly mostlya agood goodsingle-lane single-lanegravel gravel track, track, but butrough roughand andslow. slow. S t o pF6, F6,Supracrustal Supracrustal screens in tonalite, ZB93-273. Drive eastfor for1.6 1.6km kmon onthe theJanet JanetLake Lake road road to Stop screens in tonalite, ZB93-273. Drive east extensive pavement outcrop outcrop on on the the south southside side(1:25000 (1:25000 map). map). The Thefoliated foliatedtonalite tonalitecontains containsmany manyscreens screens an extensive of cm),fine finegrained, grained, mafic maficto to intermediate intermediate metavolcanic rocks. rocks. Screens of homogeneous homogeneous to to layered layered (1—10 (1-10 cm), Screens up to to 1.5 metres in in width width comprise comprise about about25% 25%of of the theoutcrop. outcrop.Some Someofofthe thelayering layeringlooks lookslike liketransposed transposed veins veinsor or 1.5 dykes, and some screens have have intrafolial intrafolial (nearly) (nearly) folds foldsapparently apparentlytruncated truncated by by the the tonalite host rock. rock. ItItisis difficult to unequivocally unequivocally correlate sequence; but difficult correlate the the fabrics fabrics in in screens screens with with those those in in the main supracrustal sequence; the whereas the the foliation in in the tonalite may the screens screens may contain contain D1 Dl and D2 D2 fabrics and folds, whereas may be be aa D2 D2 or or D3 D3 fabric. fabric. S t o p F7, F7,Iron Ironformation formation tonalite, ZB93-K126.AtAt 4 km eastononthe theJanet JanetLake Lakeroad roadtake takethe theroad road Stop in in tonalite, ZB93-K126. 4 km east goodpavement pavementon onthe thewest west to the the north northfor for2.1 2.1km, km,then thenkeep keeptotothe theleft leftfork forkfor foraafurther further300 300metres. metres. AAgood to 75 �G. Quetico Quetico subprovince subprovince Manitouwadge field guide of the road exposes screens of of iron iron formation formationand and mafic mafictotointermediate intermediaterocks rocksininfoliated foliatedtonalite. tonalite. The The side of exposes screens layered quartz-magnetite quartz-magnetite iron formation, about 1.5 by layered 1.5 metres metres thick, thick, isisfolded folded and andsegmented, segmented, and andenclosed enclosed by which is also strongly strongly magnetic. magnetic. The amphibolite consists of streaky layered, medium medium to coarse amphibolite which grained, intermediate intermediate metavolcanic metavolcanic rock with local smeared-out pegmatite. pegmatite. Some Somemore more homogeneous homogeneous foliated hornblende-biotite The silicate silicate mineralogy mineralogy of iron hornblende-biotitediorite dioriteisis subconcordant subconcordanttoto the the supracrustal supracrustal rocks. rocks. The of the iron typical of of iron iron formation in in the Manitouwadge belt; belt; garnet, garnet, grunerite and clinopyroxene (bright formation is typical clinopyroxene (bright green mineral?). mineral?). Pegmatite green Pegmatite invading invading the the iron iron formation formationisis loaded loaded with with coarse coarsegrained grained magnetite, magnetite,suggesting suggesting crops out out about 11 km to the northeast. contamination. Iron formation also crops northeast. Stop F8,Z-fold, 2-fold,ZB93-137. ZB93-137. Return Return to tothe theJanet JanetLake Lakeroad, road, and andcontinue continue east east for for aa further further 2.8 2.8 km km to aa S t o p F8, pavement west of a small small stream. stream. Layering Layering in in the the fine fine grained grained foliated foliated pavement on on the the south south side side of of the road just west tonalite-diorite is is defined defined by the thehornblende hornblendeabundance, abundance,which whichvaries variesfrom fromabout about10—60%. 10-60%. A strong rodding rodding lineation is parallel to to the theaxis axisof ofaaZ-fold Z-fold (D3) (Ds) with with very very long long limbs. limbs. Locally, Locally, layers layers are are boudinaged boudinaged along alongthe the long limbs of folds. Pegmatite Pegmatite dykes dykes follow follow the the axial axialtraces tracesofofsome somefolds. folds. Stop rock tonalite, ZB93-133. Continue S t o p F9, F9, Mafic Maficmetavolcanic metavolcanic rockinifoliated n foliated tonalite, ZB93-133. Continuefor for3.8 3.8km km past past the the junction junction (Stop F7) to to good outcrop on both sides sides of the road. The The stop stop isis near near the thehinge hingeregion region of of the Blackman Blackman Lake antiform, and fabric fabric trends trends are aregenerally generally variable, variable, due due to to minor minor folds. folds. Medium Medium to to coarse coarse grained grained (coarsened?) (coarsened?) metavolcanic rocks (hornblende-plagioclase-quartz-biotite-clinopyroxene) (hornblende-plagioclase-quartz-biotite-clinopyroxene) are layered mafic metavolcanic areinvaded invadedby by foliated foliated either transected by tonalite to to diorite. diorite. The Themafic maficinclusions inclusionsshow show some some early folding either by foliation foliation or or with with axial axial planar foliation. inclusions in in foliated foliated coarse coarsegrained grainedtonalite tonalite show show some somerotation rotation of of planar foliation. Locally, Locally, blocky blocky mafic inclusions schistosity. schistosity. Stop Lake antiform, ZB93-129. 4.4 S t o p FlO, F10, Hinge Hingeregion regionofofthe t h Blackman e Blackman Lake antiform, ZB93-129. On Onthe theJanet JanetLake Lake road, road, 4.4 km past the the junction, junction, the the road road bends bends 90° 90' to tothe thesouth southand, and,after afteranother another300 300metres, metres,aapavement pavement lies lies east east of the road. road. The Thestop stopisisininthe thehinge hingeregion regionofofthe theBlackman BlackmanLake Lakefold. fold.Multiphase Multiphasefoliated foliatedplutonic plutonicrocks rocks with diffuse layering (5 (5 mm—10 are dominated dominated by bymedium mediumtotocoarse coarsegrained grainedtonalite tonalite with diffuse layering mm-10cm) cm)defined definedbyby5—40% 540% mafic minerals. The granite-pegmatite-aplite which whichvaries variesfrom from The tonalite tonaliteisisintruded intrudedbybyabout about10—20% 10-20% pinkish granite-pegmatite-aplite concordant and and folded folded dykes to net veins. veins. Pegmatite Pegmatitetends tendstotobe bepresent presenton onsmall smallshears shearsororshort shortlimbs limbsofoffolds folds on fold fold limbs. limbs. Locally Locally white white in tonalite, tonalite, and andlocally locallytonalite tonalitelooks lookscoarsened coarsened and andhomogeneous homogeneous in diffuse diffuse zones on tonalite is is either either massive massive or or has hasaaweak weakfoliation foliation(possibly (possiblyaxial axialplanar) planar)defined definedby byabout about30% 30%coarse coarse(3—8 (3-8 mm) hornblende porphyroblasts. Fabric Fabric trends trends are arevariable variableand andcommonly commonlyswirly, swirly, averaging about 300°/45°. 300°/45<' dominantly S-shaped S-shaped folds foldsin in the the southeast southeast to dominantly There is a general change across the outcrop from dominantly Z-shaped folds in in the northwest, accompanied Z-shaped accompanied by a change change in foliation trends from from northerly northerly to towesterly. westerly. Stop pluton, ZB93-91. Continue 2.52.5 kmkmbeyond S t o p Fil, F l lNama , N a mCreek a Creek pluton, ZB93-91. Continue beyondthe thesharp sharpbend bendtotothe thesouth southto toaahigh high knoll See Stop Stop F12 F12 for for aa description. description. knoll east east of of the road. See S t o p F12, F12,Nama N a m aCreek Creek pluton, ZB93-87. The stop kmsouth southononthe theroad roadbeyond beyondthe thesharp sharpbend; bend; Stop pluton, ZB93-87. The stop is is 4.64.6km however, itit will will probably probably be necessary the road is. however, necessary to to walk walk the thelast last1—2 1-2 km, depending on how overgrown overgrown the is. rocky knoll l l and F12 are both in The outcrop is a rocky knoll in in the the bush bush about about 50 50 metres metreswest westofofthe theroad. road.Stops StopsFFli the microcline-porphyritic Nama Creek pluton; Stop Stop F11 F l l is is more more easily easily accessed, accessed, but Stop StopP12 F12was wassampled sampled for geochronology. geochronology. Both outcrops outcrops are aretypical typicalofofthe therelatively relativelyhomogeneous homogeneousintrusion, intrusion,consisting consistingof ofcoarse coarse foliated hornblende-biotite hornblende-biotitegranodiorite granodioritetototonalite tonalite with 0-20% microcline microclinephenocrysts phenocrystsororaugen, augen,1—3 1-3 grained foliated with 0—20% Thepluton plutonisisinterpreted interpretedasasprepre-totosyn-D2, syn-Dg,on onthe thebasis basisofoffoliations foliationsfolded folded around around the thehinge hinge cm in length. The west of of One Otter Lake map). The strong linear and of the Blackman Lake antiform west Lake (1:25000 (1:25000 map). and planar planar fabrics fabrics south Lake may may be be related related to totransposition transposition during during post-D2 post-D2 deformation deformation near the south of Janet Lake near the the contact contact to the The geochronology geochronology sample Manitouwadge belt. belt. The sample of ofthe the Nama NamaCreek Creekpluton pluton contained containedboth both zircon zirconand and titanite, titanite, 2687 Ma the former giving an age of intrusion of 2680k3 2680±3 Ma (Fig. 15, Table 2), somewhat somewhat younger younger than than the 2687 presyn-Da Loken titanite age age of of 2672±3 2672k3 pre- to syn-D2 Loken Lake Lakepluton pluton and and oldest oldest diorite diorite of ofthe the Black BlackPic Picbatholith. batholith. The titanite regional cooling through the closure closure temperature of titanite titanite (600°C, (600°CHeaman Hearnan and and Parrish, Parrish, Ma suggests that regional 1991) 1991) occurred occurred about about 8 Ma after intrusion. G. Quetico subprovince, western n d central Manitouwadge aarea rea western aand In general, the the description description for for the theQuetico Queticosubprovince subprovincein in the theeastern easternManitouwadge Manitouwadgearea area(Stops (StopsE1—E3) El-E3) western and central central area. area. However, However, in in the the latter latterarea areanear nearthe theWawa-Quetico Wawa-Queticoboundary, boundary, also applies applies to the western is commonly interleaved with with gabbroic gabbroic and dioritic migmatitic metagreywacke metagreywacke is commonly interleaved dioritic rocks. rocks. Diorite Diorite apparently intrudes rocks along and field field observations observations suggest prealong the the subprovince subprovince boundary boundary and and to the north, and suggest that that itit predates migmatization migmatization (Stop G2). G2). Williams Breaks (1990a) (1990a) mapped lenticular unit unit of of melanocratic melanocratic Williams and and Breaks mapped a lenticular diorite (not (not differentiated differentiated on on our our 1:25000 1:25000 map) called called the the Everest Everest Lake Lake pluton pluton (Williams (Williamsand andBreaks, Breaks,1990b; 1990b; Williams 1992), extending along the western western subprovince Williams et et al., 1992), subprovince boundary boundary as as far east as Appelle Lake. They considered multiphase Black Much of the generally considered the the Everest Everest Lake Lakepluton pluton to to be be part of the multiphase Black Pic Pic batholith. batholith. Much aeromagnetic striping striping on on both both sides sidesof of the the western western subprovince subprovince boundary boundary could could be be related related east-west trending aeromagnetic to concordant diorite sheets. 76 �Manitouwadge Manitouwadge field field guide guide Quetico subprovince subprovince G. Quetico The western-central is most most easily easily accessed accessedfrom fromthe the Caramat Caramat Industrial road west western-central Quetico Quetico subprovince is west of the Manitouwadge belt. However for Stop Stop G2, G2, this this assumes assumesthat that a major washout, about 33 km However for km east east on on the the Husak road, has been repaired; the latest suggests that that the road latest information information (Feb. (Feb. 1995) 1995) suggests road is is passable. passable. S t o pGi, G l Migmatitic , Migmatitic metagreywacke, folds n d new fabrics, ZB9450. stop is reached following Stop metagreywacke, folds andanew fabrics, ZB94-50. TheThe stop is reached bybyfollowing CaramatIndustrial Industrial road road about about32 32km kmfrom fromHighway Highway 614 614 to to an an intersection intersection with with the the Michal Michal Lake Lake road road the Caramat (to the the west) west) and and the the Husak Husak road (to (to the the east). east). The Theintersection intersection isis about about 9.75 9.75 km km north north on on the the Caramat Caramat road from from the junction with with the theJanet JanetLake Lakeroad road(Stops (StopsF6—F12). F6-F12). Turn west west on on the the Michal Michal Lake Lake road road and and drive on for about 1.3 1.3 km to to an an extensive extensive area area of of pavement pavement outcrops outcrops in in an an old old clearing clearing or or road road leading leading south, south, between Hourglass and Slingshot Slingshot Lakes Lakes (1:25000 (1:25000 map). The Theexposure exposureof ofmigmatitic migmatiticmetagreywacke, metagreywacke,locally locally with with cordierite cordierite or or garnet garnetininleucosomes, leucosomes,shows shows multiple multiple folds folds and and complex complex structural structural relationships. relationships. Near Near the road, road, stretched stretched and andboudinaged boudinagedmigmatitic migmatiticsegregations segregationsdefine define isoclinal isoclinal folds, and some rotated boudins boudins show dextral kinematics kinematics (in (in plan plan view). view). Elsewhere Elsewhere on on the the outcrop, outcrop,layering layeringand andfoliation foliation show show both both ZZ- and and show S-shaped folds, folds, some some of of which which refold refold earlier folds folds of migmatitic segregations. segregations. In Inmicaceous micaceouslayers, layers,an anaxial axial S-shaped planar planar spaced spacedcleavage cleavageisiscommonly commonlydeveloped, developed, with with less less micaceous micaceous microlithons preserving preserving earlier earlier fabrics; fabrics; in in psammitic layers, layers, spaced spaced cleavage cleavage is less Locally, in psammitic less developed developed and and folded folded fabrics fabrics dominate. dominate. Locally, in the hinge of an S-fold, S-fold, asymmetric kink bands that that deform deformthe thespaced spacedcleavage cleavage were were interpreted interpreted as asthe theresult resultofofprogressive progressive deformation. deformation. S t o p G2, G2,Migmatitic Migmatiticmetagreywacke metagreywacke interleaved w i diorite, t h diorite, ZB94C45.Return Returntotothe theintersection intersection Stop interleaved with ZB94-C45. with with Caramat Caramat road road and and continue continue through to the the east east on on the theHusak Husak road road for for about about 13.5 13.5km km (about (about 1.5 1.5km km west of the junction with with the the Olson Olson Lake Lake road). road). Turn Turn left left on on to toaasmall smalltrack track leading leading northeasterly northeasterly and and up up west hill, as itit turns turns to the metres. About 70 metres further, the track hill, following following itit as the northwest northwest (left) after 360 metres. track is is crossed clear area area of ofoutcrops outcrops trending trending north-northeasterly. north-northeasterly. Three crossed by a large (200 m long) clear Three main main rock rock types types are are exposed; exposed; 1) 1) medium mediumto tocoarse coarsegrained grainedfoliated foliateddiorite, diorite,commonly commonlywith withup uptoto40% 40%plagioclase plagioclasephenocrysts phenocrysts(2—5 (2-5 mm) hornblendeand and biotite, biotite, 2) fine to medium grained layered mm) and and10—50% 10-50% hornblende layered heterogeneous foliated tonalite tonalite to hornblende-biotite hornblende-biotite diorite, diorite, and and 3) 3) migmatitic migmatiticbiotite biotiteschist schistwith withboudinaged boudinaged and andfolded folded layers layers of of tonalitictonaliticto pegmatitic leucosome. leucosome. These rock types are interleaved interleaved on The diorite diorite pegmatitic on a scale of of 10 cm cm to several metres. metres. The isis foliated, foliated,but butlow lowstrain strainenclaves enclavespreserve preserveigneous igneoustextures. textures.Diffuse Diffusecoarse coarseleucocratic leucocraticenclaves, enclaves,suggesting suggesting incipient migmatization, migmatization, are areheterogeneously heterogeneously distributed, distributed, in inpart, part,localized localizedinindilational dilationalzones zonessuch suchas asboudin boudin incipient necks. In Inmany manycases, cases,coarse coarseleucocratic leucocraticzones zonesform formananinterconnecting interconnectingnetwork networkofofganglions ganglionsenclosing enclosingenclaves enclaves necks. of dioritic dioritic protolith. The Theoverall overallimpression impression is is that thatthe thediorite dioritesheets sheetsshow showless lessstrain strainthan thanmetagreywacke, metagreywacke, of possibly a function function of of competency competency contrast. The Theheterogeneous heterogeneous and and patchy patchy distribution distributionof ofcoarse coarseleucocratic leucocratic possibly domains in diorite diorite suggests suggests that that migmatization migmatization may may have have partly partly been been driven driven by by the the introduction introductionof offluids fluids or or domains fluxing components. components. Note Note also also that thattight tighttotoisoclinal isoclinalfolds foldsof oflayering layering are are transected transected locally locallyby by an anoblique oblique fluxing southeasterly trending trending foliation foliation defined defined by hornblende hornblende and biotite. biotite. southeasterly ACKNOWLEDGEMENTS ACKNOWLEDGEMENTS Noranda Minerals Minerals Inc. (Geco (Geco Division), Division), Granges Granges Inc., contributed to this this Noranda Inc., Minnova Minnova Inc. Inc. and and A1 Al Turner Turner contributed project by by providing providing access access to unpublished maps and reports. Noranda NorandaMinerals Mineralsreleased released data dataacquired acquiredduring during project to Joan Joan Tod, Tod, GSC. GSC. The The data datawere were compiled compiled aa high resolution aeromagnetic survey (contracted to Dighem Inc.) to by Warner Warner Miles, Miles, and and the theresulting resultingaeromagnetic aeromagneticmaps maps(Open (OpenFiles Files2754, 2754,2755) 2755)were were valuable valuable aids aidsto tomapping mapping by and interpretation. interpretation.Our Ourspecial specialthanks thanksgogo Hugh Lockwood,Noranda NorandaMinerals MineralsInc., Inc.,for fordiscussions, discussions,ideas, ideas, and toto Hugh Lockwood, A1Turner Turnerand and and support supportofofour ourefforts effortsduring duringthe thefield fieldseason. season.Thanks Thanksalso alsogo goto toRob RobReukl, Reukl,Jody JodyHache, Hache,Al and Neil Poster. Poster. Rob RobReukl Reukland andJody JodyHache Hachecollected collectedthe thegeochronology geochronology sample sample of of the the Nama Nama Creek Creek pluton, pluton, and and Neil Doug McKay, McKay, Mark Smyk and Greg Greg Chariton Charlton helped helped in incollecting collecting various various other other problematic problematic samples. samples. We We Doug benefited from from field field trips trips and/or and/ordiscussions discussionswith withDoug DougMcKay, McKay,Mark MarkSmyk, Smyk,Bernie Bernie Schnieders, Schnieders, Fred Fred Breaks Breaks benefited and Howard Howard Williams, Williams, Ontario OntarioGeological GeologicalSurvey; Survey; Greg Greg Charlton, Charlton, Isobel Isobel Wolfson Wolfson and Paul Paul Degagne, Degagne,Noranda Noranda and Inc.; and and Warren Warren Bates, Bates, Granges Granges Inc. Inc. Our Ourfield fieldwork work was was greatly greatly aided aided by by the themapping mappingof of David David Copeland Copeland Inc.; and Katherine KatherineBoggs, Boggs, and andthe theassistance assistanceofofJoanne JoanneTreidlinger, Treidlinger,Andrea AndreaDorval, Dorval,Shannon ShannonWalsh Walshand andMike Mike and Thomas. The Themanuscript manuscriptwas wasimproved improvedby bythe thecomments commentsof of Jack Jack Henderson, Henderson, John John Lydon Lydonand andKen KenCard. Card. Thomas. 77 �NOTES �NOTES NOTES � https://digitalcollections.lakeheadu.ca/files/original/68bc76c7e587f90855b020ecc763137c.pdf 0139123474755ae9c5e522bc255dfb24 PDF Text Text Greenstone Geology of the Schreiber Greenstone Assemblage and and its its Assemblage Gold and Base Metal Mineralization r Institute Instituteon onLake LakeSuperior SuperiorGeology Geology 41st 1995 41stAnnual AnnualMeeting, Meeting,May May13-18, 13-18,1995 Marathon, Marathon,Ontario Ontario Proceedings 41: Part Part2c 2c ProceedingsVolume Volume 41: Field Field Trip TripGuidebook Guidebook I 1 �Geology of of the the Schreiber Schreiber Greenstone Greenstone Assemblage and and its its Gold and Base Metal Mineralization Mineralization by Mark Mark C. C. Smyk Smyk and Bernie Bernie R. Schnieders Schnieders Ontario OntarioGeological GeologicalSurvey, Survey, Field Field Services ServicesSection Section Ministry of of Northern Northern Development Development and Mines Suite 435 S. James Suite B002, BOO2,435 JamesSt. St. Thunder Thunder Bay, ON P7E 6E3 6E3 with contributions contributionsby: by: Steven A. A. Osterberg (BHP Minerals Minerals International International Inc.) Inc.) Rob Sim, Gerard Gerard Doiron, Doiron, Masood Masood Siddiqui Siddiqui and and Matthew Bliss (Winston Lake Division, Metal1 Metall Mining Corporation) Corporation) Frontispiece: 19166 Frontispiece:Trip Triptotothe theEmpress EmpressGold GoldMine, Mine,Syine Syine Township, Township,July July 29, 29,191 (photograph Bourguignon) (photographcourtesy courtesy of Msgr. G. Bo urguignon) �ACKNOWLEDGEMENTS ACKNOWLEDGEMENTS authors would would like like to to acknowledge acknowledgethe the support support of of the the Ontario Ontario Geological Geological Survey Surveyand and the the The authors st Institute on Lake Ministry of Northern Development and Mines in both the 41 41st Lake Superior Geology and its associated associated field field trips. trips. the staff staff of of the the Field Field Services Services Section Section -- Northwest for their administrative and We are indebted to the logistical support. Doug DougMcKay McKayprovided providedinvaluable invaluable assistance assistance in the drafting and generation generation of drawings in this report. Discussions Discussionswith withother othermembers membersof of the the Ontario Ontario the AutoCAD drawings Geological Survey, Survey, especially especially Dr. Andy Fyon, are gratefully gratefully appreciated. appreciated. Finally, Finally, we would like like to thank Rob Sim, Sim, Gerard Doiron, Masood Siddiqui and Matthew Bliss of Metall Mining Corporation's Winston Lake Division Mine for their their contributions contributions to to this this field field Metal1 guide as well as their support support in previous endeavours. Dr. Dr. Steven Steven Osterberg Osterberg has contributed contributed greatly to the understanding understanding of of Winston Winston Lake's Lake's geology geology and and this this has has been been so so noted. noted. The authors authors have tremendously tremendously benefitted benefitted from from the the work work and and ideas ideas of countless countless government governmentand and industry geologists North Shore. We geologists and prospectors that have worked on the North We wish wish the the best best of of luck to those those who who follow. follow. �. TABLEOF OFCONTENTS CONTENTS TABLE RoadLog Road Log . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22 Introduction GENERALGEOLOGY GENERAL GEOLOGY . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 66 Definitionof ofTerms Terms . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 66 Definition RegionalGeology Regional Geology . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 66 SupracrustalRocks Rocks . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 77 Supracrustal GranitoidRocks Rocks . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 88 Granitoid StructuralGeology Geology . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 99 Structural EconomicGeology 11 Economic Geology . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11 STOPDESCRIPTIONS: DESCRIPTIONS: STOP SteelRiver RiverTurbidites Turbidites . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15 15 STOP 1: 1:Steel STOP . . . 17 STOP 2A: 2A: Steel SteelRiver RiverKomatiites Komatiites ... . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17 STOP STOP 2B: 2B: Jackfish JackfishPillowed PillowedBasalts Basalts . . . . . . . . . . . . . . . . . . . . . . . . . . . 28 28 STOP 35 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 35 STOP 3: Terrace TerraceBay Bay Batholith Batholith .... STOP Gold Mineralization Mineralizationin inthe the Schreiber SchreiberArea Area Gold . 38 . . . . . . . . . . . . . . . . . . . . . . . . . . . . 38 41 STOP 4: 4: Gold GoldRange RangeProspect Prospect . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 41 STOP LocalGeology 42 Local Geology . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 42 Geologyof ofthe theNo. No .77Vein VeinShaft ShaftArea Area . . . . . . . . . . . . . . . . . . . . . . . . . 46 46 Geology �. STOP 5: 5: Winston Winston Lake Lake Cu-Zn Cu-Zn Mine Mine . . . . . . . . . . . . . . . . . . . . . . . . . . . Exploration Exploration and Mining History . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Mine Geology . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . MineGeology Hydrothermal Alteration . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Massive Massive Suiphide Sulphide Ore Ore . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Individual Individual Stop Stop Descriptions Descriptions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 48 48 48 48 51 51 57 62 62 64 64 REFERENCES 73 REFERENCES . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 73 �LIST LIST OF OFFIGURES FIGURES Figure Figure1:1:Tectonic Tectonicassemblages assemblagesmap mapof ofthe theWawa Wawasubprovince subprovince . . . . . . . . . . . . 33 Figure Figure 2: 2: Regional Regionalgeology geologyofofthe theSchreiber SchreiberAssemblage Assemblage . . . . . . . . . . . . . . . . 55 Figure 3 :Geology Geologyand andStop Stoplocations, locations.Jackfish Jackfisharea area Figure 3: . . . . . . . . . . . . . . . . . . . . 13 13 Figure Stops 2Aand and2B 2B . . . . . . . . . . . . . . . . 22 22 Figure 4: 4: Detailed Detailedflow flowcross-sections, cross~sections. Stops2A Figure Figure 5:5: Jensen JensenCation CationPlot Plotof ofSteel SteelRiver Rivermafic maficvolcanic volcanic rocks rocks . . . . . . . . . 25 25 Figure Figure 6: 6: Map MapofofGold GoldRange RangeProspect, Prospect.showing showingvein vein locations locations . . . . . . . . . . 43 43 Figure 7:Geology Geologyofofthe theWinston WinstonLake LakeMine Minearea area . . . . . . . . . . . . . . . . . . . . . 56 56 Figure7: Figure 8A:Geochemical Geochemicalchanges changeswith withalteration, alteration.Ladder LadderFlow Flow Figure 8A: . . . . . . . . . . . 60 60 Figure 61 Figure8B: 8B:Geochemical Geochemicalchanges changeswith withalteration, alteration.QFP QFPRhyolite RhyoliteFlow Flow . . . . . 61 Figure Figure9A: 9A:Detailed Detailedsurface surfacegeology, geology.Winston WinstonLake Lakefootwall footwallsection section . . . . . . 65 65 Figure Figure9B: 9B:Composite Compositecross crosssection, section.Winston WinstonLake Lakefootwall footwallsection section . . . . . . . 66 66 �LIST OF OF TABLES TABLES Table 1: 1: Geochemistry, Geochemistry,tholeiitic tholeiiticand andkomatiitic komatiitic basalts, basalts, Stops Stops2A 2A and and 2B 2B . . 26 . . Table 2: Stratigraphic Stratigraphicsubdivision subdivisionof of part part of of the Winston Footwall Block .... 55 55 Table 3: Partial Partialwhole wholerock rockand andtrace traceelement elementgeochemistry, geochemistry,Winston Winston Lake Lake .. 59 59 LIST OF PLATES PLATES Plate 1: 1: Photomicrograph Photomicrographof of spinifex-textured, spinifex-textured, basaltic komatiite, komatiite. Stop 2A . 2211 . Plate 2: Photomicrograph Photomicrographof of spinifex-textured, spinifex-textured, basaltic komatiite, Stop 2A .. 21 21 Plate 33:: Photographofvariolitic, Photograph of variolitic,pillowed pillowedhigh-Mg high-Mgtholeiite, tholeiite. Stop Stop2B 2B . . . . . 31 31 Plate 4: Photomicrograph Photomicrographof of variolitic, variolitic,pillowed pillowed high-Mg tholeiite, Stop 2B 31 31 Plate 5: 5: Photograph of vein-related alteration, Gold Range property, Stop Stop 4 .. 45 45 Plate �Guide to to the the Schreiber SchreiberGreenstone GreenstoneAssemblage Assemblage Field Guide includes includes stop stop descriptions descriptions for: for: -- STOP STOP 1: 1: Steel Steel River River Turbidites Turbidites - STOP STOP2:2:Steel SteelRiver RiverKomatiites/Pillowed KomatiitedPillowedTholeiites Tholeiites -- STOP STOP3: 3:Terrace TerraceBay Bay Batholith Batholith - STOP STOP4: 4:Gold Gold Range Range Prospect Prospect - STOP STOP5: 5: Winston WinstonLake LakeMine Mine - Road Road Log Logfor forStops Stops11-- 55 (Marathon (Marathon Starting StartingPoint) Point) Total TotalKilometres Kilometra LandmarWieId Trip TripStop Ston Landmark/Field 0.0 Junction of of Highways Highways17 17and and626 626 Junction (Marathon (MarathonTurn-off) Turn-off) 33.9 Dead Horse Horse Creek Creek road road turn-off turn-off Dead 50.6 STOP STOP 1: 1: Steel Steel River River Turbidites Turbidites 52.6 STOP STOP2A: 2A: Steel Steel River RiverKomatiites Komatiites 53.2 STOP STOP2B: 2B:Steel Steel River Ever Pillowed PillowedTholeiites Tholeiites 58.7 Coach CoachHouse HouseMotel Motel 65.0 STOP STOP3: 3: Terrace TerraceBay BayBatholith Batholith 79.0 TouristInformation InformationCentre, Centre,Terrace TerraceBay Bay Tourist 88.5 Turn-off to to STOP STOP 4: 4: Gold Gold Range Range Prospect Prospect Turn-off 92.6 VoyageurRestaurant/Service Restaurant/ServiceStation, Station, Voyageur Schreiber Schreiber 101.7 Turn-off to to STOP STOP 5: 5: Winston WinstonLake LakeMine Mine Turn-off �INTRODUCTION INTRODUCTION This field trip highlights geology and mineral deposits deposits of the western portion of the highlights the geology Neoarchean Schreiber-Hemlo Schreiber-Hem10greenstone belt. This Thissegment, segment,termed termed the the Schreiber Schreiberlithotectonic lithotectonic assemblage, extends from assemblage7 from the western contact contact of of the the Mesoproterozoic MesoproterozoicCoidwell Coldwellalkalic alkaliccomplex, complex, west to Schreiber and north to the Big Duck Lake area (Figures 1 and 2). ItIt comprises comprises aa large large of Lake Superior and and the the Slate Slate Islands. Islands. The Trans-Canada Highway portion of the shoreline of (Highway 17) 17) provides access to the southern southern part of the area and a number of excellent roadside numberof of field field guides, guides?including includingthose those of of Pye Pye (1969), (1969)? exposures of greenstone belt rocks. AAnumber Schnieders et al. (1991) and Sabina (1991) describe describe various various aspects aspects of of the thegeneral generalgeology. geology. Other guides, guides?reports and papers papers will be referenced in describing individual individual stops stops and/or andfor areas. areas. Please note that many of the field trip stops stops located on the side of Highway 17 17 do not provide adequate parkinglpull-off parking/pull-offareas. areas.Extreme Extremecaution cautionmust mustbe beexercised exercisedwhen when stopping, stopping, parking parking and and visiting visitingthese thesesites. sites.Permission Permissionisisrequired requiredfrom fromproperty propertyowners ownerswhen when visiting visiting the the Gold Range and Winston Lake Mine properties. Please Pleasecontact contactthe theResident ResidentGeologist's Geologist'sOffice, Office? Schreiber-Hemio District? District, Thunder Bay7 Bay, for current information regarding regarding property property ownership at at Schreiber-Hem10 475-1331. 1331. (807) 475- Schreiber Assemblage 22 Sclzreiber Assemblage �W W 9w SP 8. 89' 9W 87.w B7'W 68' west Port Perf West Long Lok, Long Lok Quet ice Subprovince 49N -. ...ntOfl Slot lxi — fi- S .S - Lk —SSSS AnoL0-1- s) , Lake Superior .SSSS_J_S___2_ 87W Legend Legend Metavolcanic Metmlconic and ondmetasedimentOry metosedtmentoryassemblages ossembloges (2.73 Go) Heron Bay, Gamitogama, Greenwoter 12.73tot o2.70 2.70 Go): Hercm Boy, Gomitogorno,Cattish, Cotftsh, Greenwoter Pmteromlccover m r - Animikie AnimikieBasin, Bosin,Nipigon NipigonEinbayrnent Emboyrnent Proterozoic b r tColdweil Coldwellalkalic olkoliccomplex complex Proterozoic intrusions intrusions~Port Proterozoic ' 0 Groniticrocks rocks(large (lorgeareas oreosbetween, between,and ondsmall smollplutons plutonswithin, wtthin, Gronitic greenstone belts) belts) greenstone Shebondowon ossembloge, Loke assemblage ossembloge (-2.69 Shebondowon assemblage, Knife Knife Lake (-2.69 Go) Metosedimentory assemblages ossembloges (probably tprobobly -2.70 -2.70 Ga) Go): Mishi, Mishi, Metosedimentory Gorgontuo,Quetico Ouet~cu Gargantua, Memvolconicassemblage ossembloges Soganagoris Sogonogonsassemblage ossemblo~e Metavolcanic Metovolcanie Metovolconicand and metasedimentary mttOsedimentoq assemblages ossembloges (2.77 (2.77 toto2.70 2.70GO, GO, probably2.77 2.77tot2.75 o 2.75 Schreiber, Monttouwoage-Mrnepoyne, prababiy Ga)'Go) Schreiber, Monhtouwadge-HornePOYfle, Chapleou, Doyohessuroh-Kobinokogomi Chopleou, Doyohessaroh-Kabinakagorni Metovoicanic Metovolconic assemblage ossembloge (2.77 12.77toto2.75 2.75Ga) Go]: Hernia, nernlo, Wawa, WOWO, Burchell ~ ~ ~ ~ h ~ l l Metavolconic Metmlconic assemblage oisembloge (-2.89 Ga) GobHawk Howk / Geological Geologicalboundary bmdory v Fault and/Or shear zone; arrow Faun om/or sheor zone; orrowindico indtm sense .a sense of of direction directton 7 Top TOPdirection direction Synform, Synform, ontitorfin antiform ,r, International boundary / / htem~on o boundary l LS*fZ LSWZLake LokeSuperior-Hernia Superior-Hemlofault fOlIltzone ZOfK NLpG Northern Northern Light-Perching Light-Perchtng Gull GullLakes WeS NLPG botholithic batholithic-complex CUfnplW Tectonic T d cassemblage assemblagemap mapofofthe theWawa WawaSubprovmce, Subp~&ce, showing showingthe thegreenstone grcmsmnebelts Mtsand andtheir thatconstituent mstitumtassemblages, assmblages. selectedsuaiigraphic-facing smtigraphic-facingdata, data,major majorgranitoid gmnitmd faults. masses and faults. masses Figure 1. 1. (Williams et al. al. 1991) 1991) Figure Schreiber Assemblage Asse~nblage 33 Schreiber �Sclzreiber Assemblage 4 �_______ _________________________________________________________ _____________ 87°O0' + + + ++ + 4 49°O0 4s000' 4 49°OO 8 L ++ + + rlgUre F • + 4 •? + + + + + + + + + + + ' ++ ++ + + + + ÷ + roaman + +.4 4 + + + + + + + + + + + • 0 + + + + a + + + + + 01 + + + + +, + + +,+ + + + +1+ + + I'.. + + + + %+ + + % + + + + ++' +\.fV j..—tVV,4+ + 4jVVVVVVv + + + + + +'. + + vLak. vv v + + 4'... + ++ ++ + ++ + + + + + + + + + + + + + + + + + + +++/f''VV VV + . V + ++ + + + + + + + + +__/+ + + + vVvV Vv +++++++ + + + 4. + + + V + + vv4 ++ + + + + + VVV V + VVVVV..V + + + + + + + v+ + + + + .•.vV + + ++ + + + .+ +,-#_\ VLOk. + + + + vV1+++ ++S.( + + +(ff + + + VV74 + + + + + VV ++ + + + + + —. + VV/ + + + + + + + + Vf+ + + + + + + + + + + + + +Vv+ + + + + + + + + + vr+++++++++÷++. ++ Vl + + + + + ÷/V + VVVVVVVVV>V'+ + +/VVVVVVV + +++++++++VVVVVVVVVV,, vvc\ v'.,+ ++ ++ +/vVvVVv ++ + + + ÷\'..1vvvvvv 1'+ + ++,'..yv + + + + ++v' vs_VvV %4VVVvv V VSv' V v —————-..—'vVV' Whlteeond batholuth v v v v v v 'Ji'.k v v V V . + + + + + 4. V + + + 44 ++ çvVv V + + + vv : +vVvvvVvVvc:;cVv ++ 3 +-+ 4 + + + + + IV' VVVVVVVVV V + + + + \VVV VV VVVVVVVVVVVV + + +1+ Jvvvvvvvvvv + + + + + +fr VVv VVVVVVVVVvV 17 Lk. -vv vv v + + ÷ ++++++++ v Vvvvvvvvvvvv C re er v a + + + + 4 v Bay + + vvvvvvvv VVVV5 + +++\.v ++++ + botholith vvV V + + vvv\ v + VVVtf+t.v 4 /f// I jc .10011ffh I V + & 4S0W +++++ V' + + 4 +J1 + + + + 0 + 7v vv , .+T:rroce.&::f" VVV' V V V £' VV, V VVV Vv V 2 Coldweli. Aikalic complex V Boy 1 Coppar blond Jack fish Channel Figure 3 vvv V VSlatev Islands vvvvv Scale 10 VV V 2?km Lake Superior 87°00 LEGEND LEGEND PROTEROZOIC PROTEROZOIC SYMBOLS SYMBOLS @ Carbonatitlc-Alkalic lntrualve Rock Carbonatitic—Alkalic Intrusive Rocks Sop LI] FieldField hipTrip Stop vv vv vv vv Osier Group Group Maflc Maflc and and Felsic Felslc Volcanic Volcanic Rocks Racks Osler and associated associated conglomerate canglamerote ond and orkose arkase ARCHEAN ARCHEAN Felsic Intrusive Intrusive Rocks Rocks Felsic 5 Tonalitic Tonalitic to t oGranodloritic GranodiaritlcCnelsses Cnelases G ~ ~ I O Contact ~h n I t~a Ic t Geological EEII @ Fault Fault Highway Highway Producing Mine L!I1 Producing Mine I.1.Winston WinstonLake Lake(Zn.cu.Ag) (Zn,Cu,Ag) Maflc Maflc to to Ultramaflo Ultrarnaflc Intrusive Intrusive Rock, Rocks Pad Praduclng Mlne [II] Poet Producing Mine Migrnatlzed Supracrustai Supracrustol Rocks Rock Migmatized Metosedimentary Metasedimentary Rocks Racks of of the theQuetico QueticaSubprovlnce Subpravlnce , vvv Figure Figure 2. 2. MaRc Maflc to FelsIc Felalc Metovolcanic Metavolcanlc Rocks Rocks and andassocloted associated Metasedirnentary Rock, Rocks Metosadlmentary Regional Regional geology geology of the the Schreiber Schreiber assemblage. assemblage. Schreiber Schreiber Assemblage Assemblage 55 2. ZenIth/Zenmac Zenlth/Zenmac (Zn.Cu) (Zn,Cu) 2. 3. 3. North NorthShore, Shares(Au) (Au) 4. 4. Davis Davis Sulphur Sulphur Ore Ore (5) (S) 5. 5. Harkneas—Hoys Harkness-Hays (Au) (Au) 6. 6. Empress Empress(Au) (Au) �GENERAL GEOLOGY Definition of Terms The term tectonic assemblage assemblageas asinformally informally applied applied by by the the Ontario Ontario Geological Survey in the Ontario part of the Superior Province has been defined by Thurston (1991) as consisting of: "stratified volcanic and/or sedimentary rock units built during during aa discrete discrete interval of time in a common depositional or volcanic setting. The The rock rock share aa common common or or dominant dominant lithofacies; lithofacies; they they may may also also share share units typically share some additional attributres, such as structural, metamorphic, geochemical geochemical and geophysical features features... ... An An assemblage assemblage is is typically typically bounded bounded by by faults, faults, unconformities or or intrusions." intrusions." term greenstone greenstone belt refers to: The term "elongate or belt-like, kilometre-scale areas of supracrustal rocks within granite-greenstone granite-greenstone subprovinces, subprovinces, with tectonic or intrusive boundaries. Greenstone belts may consist of one or more assemblages. assemblages. AAsubprovince subprovince generally consists consists of of several several greenstone greenstone belts." belts. " (Thurston (Thurston 1991) 1991) Regional Geology The Schreiber lithotectonic assemblage comprises Neoarchean con~prisesthe western segment of the Neoarchean (Williams et et al. al. 1991). ItIt consists Schreiber-Hemlo greenstone belt of the Wawa Subprovince (Williams consists of of Schreiber Assemblage 66 Schreiber Assem.blage �narrow, arcuate arcuate segments segments of of supracrustal supracrustal rocks rocks that that are are bounded bounded and and enclosed enclosed by by a number of narrow, Regionalmetamorphic metamorphicgrade graderanges rangesfrom fromupper uppergreenschist greenschistfacies faciesto tomidmid- to to granitoid bodies. Regional Themajority majority of of lithologic lithologic and and structural structural upper amphibolite facies near granitoid contacts. The (1922),Harcourt Harcourt(1939), (1939), has been been gleaned gleaned from from regional regional scale scale mapping mapping by by Hopkins Hopkins(1922), information has (1939; 1942), 1942),Pye Pye (1964), (1964),Walker Walker (1967) (1967)and andCarter Carter(1988). (1988). Bartley (1939; Supracrustal SupracrustalRocks Rocks supracrustal rocks have been recognized by Carter (1988): (1988): (1) (1) tholeiitic, Three major types of supracrustal (2) calc-alkalic, mafic to felsic volcanics, and (3) (3) clastic and chemical sedimentary mafic volcanics, (2) rocks. Tholeiitic volcanic rocks comprise mainly massive to pillowed basalt, tuffs and related autoclastic breccias (STOP (STOP 2B). 2B). Basaltic Basaltickomatiites komatiiteshave haverecently recently been been recognized recognized within tholeiite-dominated (STOPS 2A, 2B). Calc-alkalic, Calc-alkalic, felsic felsic rocks are dominated by tholeiite-dominated successions (STOPS fine to coarse pyroclastic units that attain significant thicknesses in the Prairie River to Rhumly Lake (STOP5). 5).Sedimentary Sedimentaryrocks rocksconsist consistmainly mainly of of wacke wacke Lake area and in the Winston Lake area (STOP and slate of turbiditic origin and lesser, but significant oxide- and sulphide-facies banded iron formation (STOP1). 1). formation (STOP Few Few geochronologic geochronologic data data are are available available from from this this part part of of the the Wawa Wawa subprovince. subprovince. AAU-Pb U-Pbzircon zircon Schreiber Assemblage Assemblage 77 �+ dateof of2723 2723± 22Ma Mawas wasdetermined determinedby bySchandl Schandletetal. al.(1991) (1991)for forhost hostrhyolite rhyoliteat atthe theWinston Winston date + Lake Mine. Mine. AAvirtually virtuallyidentical identicalage ageof of2720 2720± 22 Ma Ma(Davis (Daviset et a!. al. 1994) 1994)was was derived derived from from Lake altered felsic felsicvolcanic volcanicrocks rocksatatthe theGeco GecoMine Mine in inthe theManitouwadge Manitouwadgegreenstone greenstone belt. belt. Monazites, Monazites, altered interpreted as as synmetamorphic, synmetamorphic,gave gaveages agesof of2677±1 267721Ma Ma and and 2675±1 267551Ma Ma at atWinston WinstonLake Lakeand and interpreted Geco, respectively respectively (ibid). (ibid). Geco, GranitoidRocks Rocks Granitoid The supracrustal supracrustalrocks rocksare areintruded intrudedby byand andbounded boundedby bytwo twomain mainsuites suitesof ofNeoarchean Neoarchean The granitoids: aa gneissic gneissictonalite tonalitesuite, suite,and and aa massive massive granite granite to to granodiorite granodiorite suite. suite. Rocks Rocksof ofthe the granitoids: gneissictonalite tonalitesuite, suite,comprising comprisingfoliated foliated to to gneissic gneissic tonalite tonalite to to granodiorite granodiorite with with minor minor gneissic supracrustalinclusions, inclusions,bound bound the the greenstone greenstonebelt belt to to the the northeast, northeast, south south of of Killala Killala Lake. Lake. Similar Similar supracrustal rocks occur occur within within Quetico Queticometasedimentary metasedimentaryrocks rocks to to the the north. north. Williams Williamseteta!. al.(1991) (199 1)have have rocks consideredthat that the the tonalitic tonaliticrocks rocks may, may, in in part, part, be be synvolcanic synvolcanic with with regard regard to to the the 2.77 2.77 to to 2.70 2.70 Ga Ga considered greenstone assemblages. assemblages. greenstone Massivegranite granitetotogranodiorite granodioriteintrusions intrusionscomprise compriseaamore morevoluminous voluminousand andperhaps perhapsmore more Massive influentialsuite suiteof of rocks rocks within within and and adjacent adjacent to to the the Schreiber Schreiber assemblage. assemblage. These Theseso-called, so-called, influential km. "internalgranitoids", granitoids",are aretypically typicallycomposite, composite,ovoid ovoidintrusions intrusionsthat thatvary varyininsize sizeup uptoto25 25km. "internal They have haverelatively relativelysharp sharpcontacts contactswith withthe thesupracrustal supracrustalrocks, rocks,characterized characterizedby byassimilated assimilated They Schreiber Assemblage Schreiber Assemblage 88 �septa,xenoliths xenolithsand and hybridization, hybridization, suggesting suggestinghigh-level high-level emplacement. emplacement. Walker Walker(1967) (1967)mapped mapped aa septa, narrow, amphibolite-facies amphibolite-facies contact contact aureole aureole around around the the Terrace Terrace Bay Bay batholith (STOP 3) 3) and and noted noted narrow, batholith (STOP that some someremnant remnant supracrustal supracrustalslivers slivershad had been been metamorphosed metamorphosed to to granulite-facies. granulite-facies. AAfoliation foliation that or gneissosity gneissosityisis commonly commonlydeveloped developedin in the the intrusion intrusion parallel parallel and and adjacent adjacent to to its its contact contact with with the the or countryrocks. rocks. country Intrusionsare arecomposite, composite,with withlithologies lithologiesranging rangingfrom fromdominantly dominantlygranite graniteand andgranodiorite, granodiorite,toto Intrusions quartzdiorite, diorite,syenite, syenite,and andquartz quartzmonzonite, monzonite,accompanied accompaniedby bytheir theirgneissic gneissicequivalents equivalentsand and quartz apliteand andpegmatite pegmatite dykes. dykes.These Theseintrusions intrusionsare areconsidered consideredtotobe besynsyn-totopost-tectonic post-tectonicand and are are aplite Hemloassemblage assemblagetotothe theeast. east. probablycorrelative correlativeininage ageand andemplacement emplacementstyle styletotothose thoseininthe theHemlo probably Plutonsin inthe theHemlo Hemloassemblage assemblagereturned returnedages agesbetween between 2678 2678 and and 2688 2688 Ma Ma (Corfu (Corfu and and Muir Muir Plutons 1989).Examples Exampleswithin withinthe theSchreiber Schreiberassemblage assemblageinclude includethe theTerrace TerraceBay, Bay, Crosman CrosmanLake Lake and and 1989). Whitesandbatholiths. batholiths. Whitesand StructuralGeology Geology Structural Despite aa marked markedlack lackof ofstratigraphic stratigraphicfacing facing determinations, determinations, recent structural structural studies studies suggest suggest Despite that there thereisislikely likelyaagreat greatdeal dealof oftectonic tectonic juxtaposition juxtaposition between between supracrustal supracrustal units in in addition addition to that ubiquitous, upright upright folding folding(Schnieders (Schnieders1987; 1987;Carter Carter 1988; 1988;Williams Williams 1989). 1989). Facing Facingreversals, reversals, ubiquitous, conflictingyounging younging directions, directions, unit unit repetition, repetition, inhomogeneous inhomogeneous deformation deformation and thickening of conflicting Schreiber Assemblage Schreiber Assemblage 99 �successions indicate that kilometre-scale folding and duplication duplication by by thrusting thrusting were were significant significant successions (Williams 1989). 1989). Schnieders Schnieders(1987) (1987)noted noted complex complexfolding folding events, events, accompanied accompanied by large-scale large-scale faulting in the Steel River area. Deformation Deformationof of original original stratigraphy stratigraphy has has resulted resulted in in aa fragmentationof of volcano-sedimentary volcano-sedimentarysuccessions successionsand and produced produced aa pseudostratigraphy. pseudostratigraphy. fragmentation Williams (1989) and and others others have have noted that, that, for for the the most most part, part, the the supracrustal supracrustal rocks rocks in in the the Schreiber assemblage assemblage display display non-penetrative non-penetrative strain strain fabrics fabrics produced by rotation, rotation, without without significant significant internal internal distortion. distortion. In Inmarked markedcontrast, contrast,discrete discretezones zones of of strong strong deformation, deformation, such such as as by dip-slip dip-slip style, style, steeply steeply plunging, plunging, mineral mineral the Jackfish-Middleton shear zone, are characterized by and stretching Phyllites and stretching lineations lineationsthat that are are superimposed superimposedon on tectonic tectonic layering layering or or schistosity. schistosity. Phyllites slates, derived from volcano-sedimentary volcano-sedimentary protolith, are locally locally carbonatized, carbonatized, sericitized sericitized and and hematitized. hematitized. clastic sedimentary sedimentary rocks rocks are are juxtaposed with with the the supracrustal supracrustal and and granitoid granitoid Quetico subprovince subprovince clastic rocks of the Wawa subprovince along its northern boundary. The The Quetico Quetico accretionary accretionary complex complex was likely contiguous 2689-2684 Ma, Ma, and and possibly possibly contiguous with the Wawa subprovince at least since 2689-2684 since 2696-2689 2696-2689 Ma (Percival 1989). 1989). AAU-Pb U-Pb zircon zirconprovenance provenance study study of of Manitouwadge Manitouwadge belt belt I wackes by Zaleski Zaleski et et al. al. (1995) (1995) placed placed aa maximum maximum age age limit limit on on deposition deposition of of 2693 2693 Ma. Ma. I A variety of diabase rocks. These diabase dyke swarms swarms intrude the granite-greenstone country rocks. These include include the Paleoproterozoic Paleoproterozoic Hearst Hearst (northwest-trending, (northwest-trending,2454 2454 Ma) Ma) and and Marathon Marathon(north-trending, (north-trending, Schreiber Assemblage Assemblage 10 Schreiber 10 �2170 Ma) Ma)swarms, swarms,and andMesoproterozoic MesoproterozoicPigeon PigeonRiver Riverand andPukaskwa Pukaskwa(north-northeast (north-northeastand and 2170 northwest-trending,respectively; respectively;1100 1100Ma) Ma)swarms swarms(Osmani (Osmani1991). 1991). northwest-trending, Economic EconomicGeology Geology Metallic mineral mineraldeposits depositswithin withinthe theSuperior SuperiorProvince Provinceof ofOntario Ontarioconsist consistof: of:(1) (1)those thoserelated relatedtoto Metallic the the tectonic tectonicsetting settingof ofrock rockassemblages, assemblages,and and(2) (2)those thoserelated relatedto toorogenic orogenicprocesses, processes, superimposedupon upon rock rock assemblages assemblages(Fyon (Fyon et et al. al. 1991). 1991).Rocks Rocksof ofthe theSchreiber Schreiberassemblage, assemblage, superimposed like those thosein inall allgranite-greenstone granite-greenstonesubprovinces, subprovinces,host hostexamples examplesof ofboth bothtypes typesof ofmineralization. mineralization. like The Thefirst firstcategory categorycomprises comprisesthose thosedeposits depositsthat thatwere wereformed formedduring duringearly earlytectonic tectonicand andmagmatic magmatic events, events,including includingsyn-volcanic, syn-volcanic,base base metal metal sulphide sulphide deposits. deposits. Volcanogenic, Volcanogenic,massive massivesuiphide sulphide (VMS),zinc-copper-silver zinc-copper-silvermineralization mineralizationoccurred occurredininthe thebimodal, bimodal,subaqueous subaqueousvolcanic volcanic (VMS), succession (STOP5). 5).The Thehost hostrocks rocksconsist consistof ofmafic maficflows flowsand and successionat at the the Winston Winston Lake Lake Mine Mine (STOP felsicpyroclastic pyroclasticrocks. rocks.Similar Similarrocks, rocks,characterized characterizedby bythe thesame samedistinctive distinctivemajor majorand andtrace trace felsic element elementchemistry chemistryand andhydrothermal hydrothermalalteration alterationmineral mineralassemblages assemblagesoccur occurininthe thePrairie PrairieRiver River area, km to to the thesoutheast southeast(Schnieders (Schniedersand and Smyk Smyk1994). 1994).Lithologic, Lithologic,metallogenetic metallogeneticand and area,45 45 km temporalsimilarities similaritiesthat thatexist existbetween betweenthe theWinston WinstonLake Lakeand andManitouwadge ManitouwadgeVMS VMS camps campsmay may temporal suggest suggestan anoriginal originalstratigraphic stratigraphicconnection. connection. Schreiber SchreiberAssemblage Assemblage 1111 �VMS deposits, deposits, oxideoxide- and and sulphide-facies sulphide-faciesbanded banded iron iron formations formationslocally locally Closely related to VMS within both both volcanic volcanic and and sedimentary sedimentarysuccessions, successions,but but have have limited limited lateral lateral and and vertical vertical occur within Magnetite,pyrrhotite pyrrhotiteand/or and/or pyrite pyrite are are intercalated with chert, wacke Study of extent. Magnetite, wacke or or pelite. pelite. Study km south southof of Schreiber, Schreiber,by by Schnieders Schnieders(1987) (1987) and and Fralick Fralick et etal. al. the Morley pyrite pyrite deposit, deposit,33 km (1989) suggested that massive sulphide precipitation resulted both from the (1989) the venting of hydrothermal hydrothermal fluids fluids and and activity activity of of deep-water, deep-water,organic organic mats. mats. Archean lode lode gold gold deposits, deposits, which which exemplify exemplifythe the second, second,epigenetic epigenetictype type of of mineralization, mineralization,are are Archean typically associated associated with late late tectonic elements elements such as regional deformation zones (Colvine et al. 1988). 1988). However, However,gold goldoccurrences occurrencesininthe theSchreiber Schreiberassemblage, assemblage,while while commonly commonly hosted hosted by by with major major deformation deformation zones. zones. They discrete, local structures, structures, have no discernable association with They to felsic intrusive intrusive rocks rocks on on aa variety variety of of scales. scales. The The are spatially, and perhaps genetically, related to majority of gold gold occurrences occurrences in in the the Schreiber Schreiberarea area lie lie at at or or near the the contact contact of of the the Terrace Terrace Bay Bay porphyry serves as as aa locus locus for for gold gold batholith (Marmont 1983), 1983), while the Big Duck Lake quartz porphyry mineralization in that area (Pye 1964; mineralization 1964; Patterson et al. 1985). The The majority majority of of occurrences occurrences are are quartz quartz vein-hosted, vein-hosted, narrow, narrow, high-grade high-grade deposits deposits which which have have collectively collectively produced produced several several STOP 4). thousand ounces ounces of gold (e.g. Gold Range prospect, STOP 4). Schreiber Assemblage Assemblage 12 Schreiber 12 -- �________ __________ LEGEND CENOZOIC RECENT AND PLEISTOCENE Sand gravel clay and boulders + + — +1..) J + + + + + + + + - + — + + + + + + + + + 1- .4- + s... +(I, + 4. + .4- + GREAT UNCONFORMITY • .4- .4- — + + + 4. + + 4- 4. + + + • + + 4. + + + 4. - PRECAMBRIAN + LATE PRECAMBRIAN + Oiabase UNCONFORMITY I + + + + + + + + + + + 4. + + 1• + — + + + + EARLY PRECAMBRIAN Grani(ic rocks: aplite, pegmatite, LJ0t + + 4. phyries; pink and grey horn blende and + biotite granite and gneiss; hybrid 4- granites. 1 4• + 4.- iNTRUSIVE CONTACT + 7///,2 Greywacke and slate; minor quartzite %7J and conglomerate; guartz-seriCile .4- ,- V/////h7////A biotite-garnet schisis and gnefsses from + sediments. .4- + + + + + + + + + 1- + + Acidic volcanics: agglomerate and tuft; porphyritic lava; guanz.seric,te.gatnet schist and gneiss; minor layers of sediments and basic volcanics. ' + + + 4_ I I Basic to intermediate olcanics: pillow lava and tuft; diabasic to dioritic lava: uinniw !IflhIIthIIIIII I ii chloritebiOtitehOrnblende garnet schists: black hcrnblende-plagioclaS garnet gneiss; chert and minor acidic and sedimentary layers. ao (IL. Field Trip Stop 'I. 0 /c 2km Il'/ ''7-'f717A Lake Superkw Bottle Point Geologyand andStop StopLocations, Locations,Jackfish Jackfisharea; area;Geology Geologyfrom fromWalker Walker (1956). (1956). Figure 3. Geology Schreiber Assemblage 13 Assemblage 13 �DESCRIPTIONS: Stops 11-5 FIELD STOP DESCRIPTIONS: -5 STOP 1: 1: Steel SteelRiver River Turbidites Turbidites STOP 2A: Steel SteelRiver River Komatiites Kornatiites STOP STOP 2B: Jackfish JackfishPillowed Pillowed Basalts Basalts STOP STOP 3: 3: Terrace TerraceBay Bay Batholith Batholith STOP 4: Gold GoldRange Range Prospect Prospect STOP 5: STOP 5: Winston WinstonLake LakeCu-Zn Cu-Zn Mine Mine Schreiber Assemblage Assemblage 14 Schreiber �STOP 1: STEEL STEELRIVER RIVER TURBIDITES TURBIDITES This roadcut exposes exposes clastic clastic sedimentary rocks within aa structured, structured, submarine submarine fan fan sequence sequence with submarine submarine volcanic volcanic rocks and metalliferous metalliferous sedimentary sedimentary rocks, rocks, including including rocks and associated locally with (1 987) and and sulphide-facies As described described by by Schnieders Schnieders (1987) suiphide-facies iron formation formation (Schnieders 1987). As Fralick and Barrett Barrett (1991), (1991), the sedimentary sedimentary succession succession here is dominated dominated by A- and and organized into into upward (southward) (southward) coarsening and thickening, AB-turbidites, organized thickening, and fining and thinning sequences. sequences. These Theseassemblages assemblageswere were thought thought to to represent represent deposition deposition on suprafan suprafan lobes and submarine channels, channels, respectively respectively (Schnieders (Schnieders 1987; 1987; Fralick Fralick and and Barrett Barrett 1991) 1991) Purdon (in progress) has has recognized recognized features features ascribable ascribable to a submarine submarine ramp environment environment in in McKellar Harbour Sequence. These These elastic clastic sedimentary sedimentary rocks, what he has termed the MeKellar dominated by sandy krn east east to to Middleton Middleton where where they they are are truncated truncatedby by the the sandy turbidites, turbidites, extend extend 16 16km Coidwell Coldwell alkalic alkalic complex. complex. Constituent Constituentturbidites turbiditestypically typicallyshow showonly only obscure obscureordering, ordering, transitional boundaries between subsequences and no evidence of channelized channelized deposition. deposition. Local transitional Local turbidites km along strike. There turbidites are are laterally continuous; continuous; some some units have been traced for over 1 km There is also a general thinning- and fining-upward trend within within this this sequence. sequence. In In this this context, context, the the Steel River turbidites may represent channelized channelized deposition on a small lobe on the larger, larger, submarine ramp (R. Purdon, personal communication, 1995). Geochemical Geochemical similarities similaritiesbetween between the Steel common Steel River rocks and and the main part of the McKellar Harbour Sequence support a common provenance and similar similar tectonic tectonic setting. setting. Schreiber Assemblage Assemblage 15 15 �Primary sedimentary sedimentary features, features, such such as as graded southerly Primary graded bedding, bedding, scours scours and and load load casts, casts, indicate indicate aa southerly younging direction. These Thesefeatures featureshave havebeen beenobscured obscuredand and somewhat somewhat transposed transposed along younging along aa 20Âto to bedding. bedding. Schnieders Schnieders(1987) (1987)has has noted noted other other features, features,such such as as foliation, oriented oriented at at about about 200 foliation, parallel and and convolute convolutelamination, lamination,cross-bedding, cross-bedding,flame flamestructures, structures,ripples, ripples, loaded loaded ripples ripples and and parallel rip-up clasts. rip-up clasts. This locality localityisis close closeto to the thewestern westernend endof ofwhat whatWilliams Williams(1989) (1989)described described as the the This Jackfish-Middleton/ McKellar McKellar Harbour Harbour shear zone. This Thisnortheast-trending northeast-trending zone lies between Jackfish-Middletonl mafic volcanic volcanicrocks rocksto to the thesouth southand andsedimentary sedimentaryrocks rocksto to the the north, north, varying varyingin inwidth widthbetween between22 mafic and 3 km. krn. The Thebiotite-in biotite-inisograd isogradand andmore morenortherly northerlygarnet-in garnet-inisograd isograd (Walker (Walker 1967) 1967)obliquely obliquely transect transect the the shear shear zone. zone. Phyllites Phyllitesderived derivedfrom frommafic maficvolcanic volcanicand andsedimentary sedimentaryrocks rocksexhibit exhibit vertical vertical stretching stretchingand and mineral mineral lineations, lineations,horizontal horizontalcrinkle crinklelineations lineationsand and flat-lying, flat-lying, calcite-filled calcite-filledextension extension fractures. fractures. Steeply Steeplyplunging, plunging,tight tightto toisoclinal isoclinalfolds foldsoccur occurwithin withinthe the wackes, metapelites. Tectonic wackes, but but fold fold limbs limbs parallel parallel aa strongly strongly developed developed slaty cleavage in the metapelites. Tectonic disruption, disruption, bed attenuation attenuationand conflicting conflicting kinematic and younging indicators characterize much of of this zone (Schnieders 1987). 1987). Williams Williams(1989) (1989) has suggested suggested that an early dip-slip style of deformation deformation was was followed followedby by dextral dextralshear shearas asevidenced evidenced by by overprinting, overprinting,Z-asymmetric Z-asymmetricfolds foldsand and sub-horizontally sub-horizontally plunging plunging slickensides. slickensides. Schnieders Schnieders(1987) (1987)has has suggested suggestedtwo two separate separate folding folding events events or or aa polyphase polyphase folding folding event eventin inthe the Steel SteelRiver River area. area. Schreiber Assemblage Assemblage 16 16 �STOP 2A: STEEL STEELRIVER RIVER KOMATIITES KOMATIITES This section sectionof of the the local localvolcanic volcanicsuccession successionhas hasbeen beeninvestigated investigatedbecause becauseof ofthe therecent recent This discovery of of aa spinifex-textured spinifex-textured flow flow unit unit within within pillowed, pillowed, tholeiitic tholeiitic basalt, basalt, similar similarto to pillowed pillowed discovery units exposed exposed 600 600 m northwest (STOP (STOP 2B). 2B). These Thesetwo twosections, sections,while whilepart part of of the the same same volcanic volcanic units package, are are remarkably remarkably different differentin interms termsof oftheir their lithologic lithologicand and eruptive eruptivecharacteristics. characteristics. package, This 70 70 m m detailed detailedsection section(Figure (Figure4) 4)along alongthe thesouth southside sideof ofthe thehighway highwaycomprises comprises aa number of This different flows/flow flows/flowunits units which which dip dip steeply steeply (60°SE) (60°SEand and young to the southeast. Subsequent Subsequent different tectonic deformation, deformation,alteration alterationand andquartz-carbonate quartz-carbonateveining veininghave haveobscured obscuredsome someof ofthe theprimary primary tectonic features featuresand and relationships. relationships. Individual Individualflow flowunits, units,separated separatedby bysharp, sharp,locally locallysheared, sheared,contacts, contacts, range range in in thickness thickness from from approximately im 1mto to perhaps perhaps 20.m. 20 m. These Theseunits unitscomprise comprisemassive, massive, locally locally pillowed, pillowed, basalt, basalt, iso1ate""isolate"-toto"crowded"-pillow "crowdedu-pillowbreccia brecciaand and massive massive to to spinifex-textured, spinifex-textured, basaltic basaltic komatiite. komatiite.Individual Individualflow flowunits unitsdisplay displaymarked markedgeochemical geochemicalvariation. variation. Perhaps komatiite. ItItisis Perhaps the the most most noteworthy noteworthy lithologic lithologic unit unit is is the the spinifex-textured, spinifex-textured, basaltic komatiite. apparently metapyroxenite(?)base, base, an anoriented, oriented,plate plate apparently aa composite compositeflow flowconsisting consistingof ofaamassive, massive,metapyroxenite(?) spinifex-textured spinifex-texturedcentral centralunit unitand andaafiner-grained, finer-grained,randomly randomlyoriented, oriented,upper upperspinifex-textured spinifex-textured portion. portion. Serpentine-rich Serpentine-richveins veinsoccur occurwithin withinthe themassive massive flow. flow. Whole-rock Whole-rockgeochemistry geochemistryshows shows aa progression progressionfrom frombasaltic basaltickornatiite komatiiteatatthe thebase baseto tohigh-magnesium, high-magnesium,tholeiitic tholeiiticbasalt basaltatatthe thetop top of of the the flow flow(Table (Table1). 1).Immediately Immediatelyabove abovethe thecontact contactwith withthe themassive massivekomatiite, komatiite,spinifex spinifex crystals crystals Schreiber Schreiber Assemblage Assemblage 17 17 �are oriented cm)crystals crystals oriented parallel parallel to to the the contact. contact. Less than a metre up from the contact, large large (58 (8 cm) and sheaf-like aggregates are oriented at right angles to the contact and and locally locally branch branch upwards upwards in Coarse-grainedspinifex spinifexgradually graduallygives givesway way to toaafiner-grained, finer-grained, more more a plumose fashion. Coarse-grained randomly oriented texture in which individual crystals are ~O.8 0 .cm 8cmlong. long. to44mm, mm, massive, non-magnetic, non-magnetic, basalt basalt flows flows are are characterized characterized by by 22to Incipiently pillowed, largely massive, light green varioles which coalesce into lobate, amoeboid patches patches or may may concentrate concentrate along irregular (synvolcanic?) stockwork fractures. Pillow Pillow forms forms are are indistinct indistinct but but are are suggested suggested by by lobate variole pods and selvage-like patterns. Selvages Selvages are are characterized characterized by by bands bands of of coalescing coalescing varioles, and/or andlor quartz quartz ±Âhyaloclastite hyaloclastite layer(s). layer(s). This unit may be related or transitional with an isolate pillow breccia, a massive flow unit with discrete, isolated isolated or detached detached pillows pillows and and pillow pillow fragments. fragments. "Crowded' "Crowded" pillow pillow breccia contains a higher proportion of discernable pillows and pillow fragments ranging in size from 10 10 to 100 100 cm. Smaller pillows are spherical to bun-shaped, while larger counterparts are are ovoid ovoid to to mattress-shaped. Many mattress-shaped. Many of of the the larger larger pillows pillows contain contain stacked, stacked, quartz-filled, "drain-away" cavities which represent successive stands of falling lava (cf. Wells Wells et et al. al. (1978). (1978). Hyaloclastite occurs in the interpillow spaces and within lenticular pods in seemingly more massive flow units. Autoclastic breccias occupy most flow contacts. textural variation variation The spinifex-textured flow shows remarkable similarities with the serial textural SchreiberAssemblage Asse,nblage 18 Schreiber �described by Pyke et al. a!. (1973) (1973) in in the the Abitibi Abitibigreenstone greenstonebelt. belt. Common subunits, in descending descending order, include: chilled, fractured and brecciated upper contact; contact; upper, upper, randomly randomly oriented oriented spinifex spinifex zone (KOM-3); lower, plate spinifex zone (KOM-1); foliated phenocryst zone (KOM-7) and a massive, ultramafic base (KOM-2,-5,-6). (KOM-2,-5,-6). Thin section and X-ray diffraction diffraction analyses analyses reveal that the constituent constituent crystals in the spinifex spinifex are optically continuous, skeletal, skeletal, branching grains of magnesio-hornblende magnesio-hornblende and chlorite (clinochiore) (clinochlore) likely the the alteration products products of of primary, primary, magensium-rich magensium-richclinopyroxene. clinopyroxene. The (Plate 1). They are likely matrix is a fine-grained fine-grained matte matte of of talc, talc, serpentine, serpentine, carbonate, carbonate, chlorite chlorite and amphibole amphibole resulting resulting from greenschist-facies metamorphism. alteration and greenschist-facies metamorphism. The massive, basal portion of the flow (samples (samples KOM-2,-5,-6), KOM-2,-5,-6), interpreted as a metapyroxenite, consists of a very fine-grained, decussate to weakly foliated (parallel to flow contact), talcose, Fe-oxides and andcalcite. calcite. Relict, equant serpentinized matrix with minor amphibole, Fe-oxides clinopyroxene(?) clinopyroxene(?) phenocrysts phenocrysts average average0.15 0.15 mm mm in in size. size. Foliated spinifex (KOM-7) occurs at the lower contact of the spinifex-bearing portion of the flow. ± calcite aggregates that have replaced It is characterized by subparallel, talc  subparallel, serpentine serpentine ++ talc mm phenocrysts. phenocrysts. Equant, blocky clinopyroxene phenocrysts phenocrysts (50.6 (0.6 xx1.0 acicular, 0.3 xx 1.0 mm 1.0mm, mm, 0.15 to 2 mm mm square) are also evident. evident. Phenocrysts and pseudomorphs are set in a averaging 0.15 finer-grained finer-grained matrix matrix of of subparallel, subparallel,0.05 0.05to to 0.07 0.0755 mm, acicular crystals and Fe-oxides. Fe-oxides. Schreiber Assemblage Assemblage 19 19 �Plate 1. Photomicrograph Photomicrograph(PPL) (PPL)of of optically opticallycontinuous, continuous,branching branching and and plumose plumose rnagnesio-hornblende and chlorite textured, magnesia-hornblende chlorite (clinochiore) (clinochlore)in in coarse, coarse, plate plate spinifexspinifex-textured, (KOM-1), STOP 2A. Field Field of of view view is is 4.0 mm. mm. basaltic komatiite (KOM-I), Plate 2. Photomicrograph Photomicrograph(PPL) (PPL)ofofupper, upper,randomly randomlyoriented orientedspinifex—textured spinifex-textured portion of flow (KOM-3), STOP 2A. Field Field of of view view isis 4.0 4.0 mm. mm. Schreiber Assemblage Assemblage 20 Schreiber �Schreiber Schreiber Assemblage Assemblage 21 21 �1 STOP 2A 2A STOP STOP 2B 2B STOP LEG: Lithologic units units Lithologic Al: A1: A2: Az: Bl: B1: B,,: B: Cl: Cj: Chilled Zone Zone (upper (upper contact) contact) Chilled S p W a zone zone (Au: (Aa: upper. upper, rendomly randomly oriented orientedzone) zone) spinhlex lower, plate plate spinllex spinifex zone) zone) (As: (Aa : Ie'wer. Foliated spinitex spinifexzone zone Foliated Massive, ultramafie ultraxnafic basal basalzone zone(unsubdivided) (unsubdiyided) Massive, bfa=si~e brisdt/basdtic komatlite Massive basalt/basaltic kornatlite , Crowded' pifiow basalt/basaltic komatilte Cze : mCrowded*. pfflow basalt/basaltic komatiite C2: Ca : hci*iently pillowed b a s a l t f i n d t i c komatilte komatUte Inciient1y pillowed basalt/basaltic Ca: bx : : Autoclastic Autocladic breccia breccia(broken (brokenpillow/flow pUow/flow breccia) breccia) bx I Figure 44 : Geological Geological sketch maps, maps, detailed detailed flow flow cross—sections cross-sections (looking (looking southwest), southwest), stops stops2A, ZA,2B. 2B. Figure : Sc1zreibe1-Assemblage 22 Schreiber Assemblage 22 �LEGEND Symbob 1-1 Flow Flow contact/Internal contact/internd subdiviaion subdivision IH m Pillow outline ixI OUwe Hyaloclastite Hyaloclasti~ 1 x 1 Drain—away Drain-away ca'vities cadties Schreiber Assemblage Assemblage 23 23 Schreiber 1 7 1Spinifex orientation orientation Spinifex • . qv T Sample Sample location location and and number KOM—l) number(e.g. (e.g. KOM-1) quartz quartz1-/— +/- calcite calcite vein/pod v8in/pod �Plate spinifex spinifex(KOM-1) (KOM-1)isischaracterized characterizedby by amphibole amphibolepseudomorphs pseudomorphsof of 0.15 0.15toto0.2 0.2 mm, mm, acicular acicular Plate crystals that that occur occur in in optically optically continuous continuous aggregates aggregates up up to to 1.0 1.0 mm nlm wide and in excess of 20 mm mm crystals long. Amphibole-replaced Amphibole-replacedcrystals crystalsare areseparated separatedby by serpentinized serpentinizedcrystals. crystals. Relict, Relict,subhedral subhedral long. pyroxene phenocrysts, phenocrysts, equant equant to to lathlike, lathlike, reach reach lengths lengths of up to 1.0 1.0 mm. The Thefine-grained fine-grainedmatrix matrix pyroxene consists consists mainly mainly of of plumose plumoseto to sheaf-like sheaf-likeserpentine, serpentine7with with subordinate subordinateepidote epidote (sausserite?). (sausserite?). The serpentinized, con~pletely serpentinized,0.05 0.05 xx 1.0 1.0mm, mm, The upper, upper, spinifex-texured spinifex-texuredflow flow(KOM-3) (KOM-3)consists consistsof ofcompletely mm) randomlyoriented orientedbooks booksof of crystals crystalsin in aa devitrified devitrifiedglass glass matrix matrix (Plate (Plate 2). 2). Larger Larger(0.3 (0.3xx44mm) randomly phenocrystscomprise compriseapproximately approximately5% 5%of ofthe therock rockand andhave havebeen beenaltered alteredtotoserpentine serpentine++epidote epidote phenocrysts ++calcite. calcite. The flow Theoverlying overlyingbasaltic basaltickornatiite kon~atiite ilow(KOM-4) (KOM-4)consists consistsof of aavery veryfine-grained, fine-grained,decussate decussate intergrowth (after intergrowthof of turbid turbid amphibole amphiboleand and epidote. epidote. Pseudomorphs Pseudon~orphs (afterpyroxene) pyroxene)are areequant equantand and blocky mm in in size. size. Fe-oxides Fe-oxidesare arenotably notablyrare. rare.Pyroxene Pyroxenephenocrysts, phenocrysts, blocky and and average average 0.1 0.1 to to 0.2 0.2 mm comprising comprisingapproximately approximately3% 3%ofofthe therock, rock7fange rangeuo uototo0.6 0.6mm mmininsize sizeand andare areinvariably invariablyaltered alteredtoto magnesian magnesianchlorite chlorite(penninite) (penninite)±&epidote epidote± serpentine. serpentine. Schreiber Assemblage 24 �FeC ÷ Fe203 +Ti02 High-Fe Tholeätic Basalt KOM-3 KOM-4 • KOM-2, KOM- 1 Basaltic Komatite A1203 AE03 Figure Figure5: 5:Jensen Jensen(1976) (1976)Cation CationPlot PlotofofSteel Stee!IRiver Rivermafic maficvolcanic volcanicrocks. rocks. Schreiber SclzreiberAssemblage Assemblage 25 25 ''Uttramafic MgO �Table Table 1.1.Geochemical GeochemicalResults, Results,Tholeiitic Tholeiiticand andKomatiitic KomatiiticBasalts, Basalts,STOPS STOPS2A 2A and and 2B 2B Sample Sample SiO2 Si02 A1203 A1203 Fe203 Fe203 MgO MgO CaO CaO Na20 Na20 K2O K20 P2O5 P205 Ti02 Ti02 MnO MnO BaO BaO Cr203 Cr2O3 SrO SrO LO1 LOl Total(%) (%) Total KOM-i 48.00 11.29 11.82 1000 9.10 1.89 0.12 0.146 0.701 0.182 0.013 0.174 0.10 2.7 96.1 KOM-2 41.08 9.42 13.25 19.53 7.03 0.10 0.01 0.106 0.545 0.215 0.006 0.350 0.001 6.7 98.3 KOM-3 48.35 11.60 12.14 8.07 11.70 1.49 0.05 0.099 0.660 0.191 0.007 0.250 0.013 3.6 98.2 KOM-4 47.40 11.07 12.66 10.84 9.28 1.72 0.06 0.084 0.656 0.206 0.007 0.219 0.008 3.8 98.0 JACK-i JACK- 1 48.71 13.95 12.34 7.17 12.35 1.13 0.24 0.065 0.932 0.203 0.011 0.085 0.009 2,6 99.8 BRS-48 BRS-48 44.77 10.43 13.37 12.04 8.67 1.96 0.01 0.16 0.65 0.26 7.40 99•741 SRG-22 SRG-22 51.70 14.40 12.00 7.04 7.81 2.86 <.10 0.90 0.21 SRG-14 SRG-14 45.70 13.00 11.10 11.80 7.74 2.18 0.24 1.12 0.18 5.00 98.062 SRG-15 SRG-15 37.50 4.40 9.15 32.00 2.05 0.07 0.05 0.03 0.29 0.15 13.0 98.582 Pyrox F'yroxb 46.27 7.16 11.45 16.04 14.08 0.92 0.64 0.38 1.47 0.16 1.26 99.83 PerjcJt Perid'' 42.26 4.23 10.19 31.24 5.05 0.49 0.34 0.10 0.63 0.41 5.27 99.46 Dunite Dunite 38.29 1.82 12.97 37.94 1.01 0.20 0.08 0.20 0.09 0.71 5.27 98.53 Schreiber Schreiber Assemblage Assemblage 26 26 97.522 �Sample Sample Descriptions: Descriptions: STOP 2A: KOM-l: KOM1:Coarse, Coarse, plate plate spinifex-textured, spinifex-textured, basaltic komatiite KOM-2: Massive, basal metapyroxenite metapyroxenite unit (basaltic (basaltic komatiite) KOM-3: Randomly oriented,fine-grained, KOM-3: oriented,fine-grained, spinifex-textured upper flow (high-Mg tholeiitic basalt) KOM-4: Overlying, Overlying, pyroxene-phyric, pyroxene-phyric, pillowed pillowed basaltic basaltic kornatiite komatiite STOP 2B: JACK-1: Variolitic Varioliticpillow, pillow,section sectionrim rimtotocore core(high-Mg (high-Mgtholeiitic tholeiiticbasalt) basalt) JACK-i: BRS-48: Ultramafic [3 km east of STOP2A]' STOP~A]~ Ultramaficintrusion, intrusion,Little LittleSteel Steel Lake Lake [3 Massive,high-Mg high-Mgtholeiitic tholeiiticbasalt, basalt,Stoughton-Roquemaure Stoughton-RoquemaureGroup, Group,Abitibi AbitibiBelt2 Belt2 SRG-22: Massive, SRG-14: Massive, Massive,basaltic basaltickornatiite, komatiite,Stoughton-Roquemaure Stoughton-RoquemaureGroup, Group,Abitibi AbitibiBelt2 Belt2 SRG-15: Pillowed, Pillowed,ultramafic ultramafickomatiite, komatiite,Stoughton-Roquemaure Stoughton-RoquemaureGroup, Group,Abitibi AbitibiBelt2 Belt2 'from Schnieders from Schnieders (1987) 2from 'from Jensen (1976) (1976) 3Average Major Element Compositions of Igneous Rocks 'Average Major Rocks (LeMaitre (LeMaitre 1976) 1976) Schreiber Assemblage 27 Schreiber Assemblage �STOP 2B: JACKFISH JACKFISHPILLO PILLOWED BASALTS WED BASALTS complete without a pillow lava stop! However, However, not not only only does doesthis this stop stop No trip would be complete exemplify well-preserved volcanic volcanic features features it also also represents represents one end of the deformationdeformationmetamorphism spectrum in the Schreiber assemblage. ItIt represents represents the most unmetamorphosed unmetamorphosed (greenschist comparison, the rocks we see see (greenschist fades), facies), undeformed supracmstal supracrustal rocks rocks in in the the area. area. By comparison, east along along the the highway highway are are progressively progressively more more deformed, deformed,metamorphosed metamorphosedand and altered. altered. to the east This exposure, first mentioned by Walker (1 967), affords an (1967), an excellent, excellent, three-dimensional three-dimensional view view of of basalt flows flows which which dip dip steeply steeply relatively undeformed, pillowed, high-magnesium tholeiitic basalt (70°SE) and young to the southeast. About (70°SE Aboutone-half one-half of ofthe the flow flowsuccession successionwithin within the the 60m 60m is pillowed; pillowed; the the remainder remainder is is relatively relatively massive massive or or shows shows some some detailed section section (Figure (Figure 4) is incipient pillow development. Where Wheretraceable, traceable,flow flowcontacts contacts are are sharp sharp and and conformable conformable with other, horizontal features such as drain-away cavities and lava lava tube tube surfaces. surfaces. Flow Flow morphology morphology thickness are and thickness are not readily readily apparent apparent because because of of the the lack lack of of reliable reliable marker units units and and the the limited limited exposure along strike. strike. Internal Internalfeatures featuresof ofthe theflows, flows,however, however, are are remarkably remarkably well-preserved well-preserved and provide insight insight into into the the nature nature of of the the lava lava and and its its eruptive eruptive environment. environment. The pillow-forms pillow-forms vary vary from from small, small,ellipsoidal, ellipsoidal,bun-shaped bun-shaped masses masses (50-100 (50-100cm) cm) to to large, large,flat, flat, in) which are interepreted as lava tubes (nomenclature mattress megapillows(2 ( 33 m) mattress megapillows (nomenclature of Dimroth et al. 1978). 1978). Pillows Pillowsare aretightly tightlypacked packedand andmolded molded to to one one another, another, with with little little massive, massive, interpillow interpillow Schreiber Assemblage Assemblage 28 28 �Thereisisconsiderable considerablesize sizevariation variationamongst amongstpillows pillows within within the the same same part part of of the the flow. flow. space. There 979). There There is is Areas with rounded, bulbous pillow forms may represent flow tops tops (Wells et et al. al. (1 (1979). some evidence evidenceof of lateral lateralbudding buddingof ofpillows pillowsininthe theform formofof"neck-and-knob'1 "neck-and-knob"development developmentand and some re-entrants of of chilled chilled pillow pillowcrust, crust,perhaps perhapsindicating indicatingtoo too rapid rapid chilling. chilling. Pillow re-entrants Pillow imbrication imbricationis. is minimal. minimal. Hyaloclastiteis is locally locally developed developed in in the the interpillow interpillow spaces. Autoclastic Autoclasticbreccias brecciasare arenotably notably Hyaloclastite absent southeast absent in in this this part part of of the the succession succession but become volumetrically significant to the southeast (STOP (STOP 2A). 2A). Interfiow Interflowsedimentary sedimentaryrocks, rocks,absent absentin inthis this section, section, occur occur within stratigraphically lower flows to the northwest. Quartz-filled Quartz-filleddrain-away drain-awaycavities cavities or or lava lava shelves shelves provide provide excellent excellent geopetal indicators. indicators. Individual Individualpillows pillowsmay maycontain containup up to to44 or or55stacked stackedcavities, cavities, which which represent represent successive successive stands stands of of falling falling lava lava (cf. (cf. Wells Wells et et al. al. 1979). 1979). Although Although small, small,2-4 2-4 mm, mm, spherical sphericalvesicles vesiclesand and amygdules amygdulesof of quartz quartzand and calcite calciteare areevident, evident,the the local flow succession is characterized characterizedby bythe thedevelopment developmentofoflime-green lime-greenvarioles. varioles.Smaller Smaller(52 (2 mm) (1 00mm) mm) varioles varioles tend tend to to develop develop near pillow selvages selvages while larger (51 mm)counterparts counterpartsoccur occur closer closer to the core core of of the the pillow. pillow. They Theytypically typicallycoalesce coalesceto toform formarcuate, arcuate,somewhat somewhatconcentric concentric bands Insome someexamples, examples, bands and and pods pods along along flow flow contacts, contacts, selvages selvages and in pillow cores (Plate 3). In they they comprise compriseover over one-half one-half of of the the pillow. pillow. Some Somevarioles variolesdisplay displayaaconcentric, concentric,macroscopic macroscopic zonation zonation between originally originally plagioclase-rich plagioclase-rich cores and more mafic, outer envelopes. Plagioclase Plagioclase crystals crystals may may project project radially radially outwards outwardsfrom fromthe the otherwise otherwisefairly fairlysmooth, smooth,spherical sphericalvariole variole margin. margin. Schreiber Assemblage Assemblage 29 29 �Plate 3. Photograph Photographof of coalescing coalescing varioles varioles in pillows, STOP 2B. Note Note hyaloclastite hyaloclastitein in interpillow interpillow spaces. Lens cm in in diameter. diameter. Lenscap capisis55 cm Plate 4. Photomicrograph Photomicrograph(PPL) (PPL)of of reticulate reticulateplagioclase plagioclase microlites microlites and and devitrified devitrified glass glass in variole (JACK-I),high-Mg high-Mg basalt, basalt, STOP STOP 2B. 2B .Note Noteeuhedral euhedralphenocryst phenocrystofofplagioclase(?), plagioclase(?), (JACK-i), pseudomorphed by fine-grained quartz and and epidote epidote (dark (dark patches patches near near core). core). Field of view is 4.0 mm. Schreiber Assemblage Assemblage 30 Schreiber �Schreiber Assemblage 31 Schreiber Assemblage 31 �Local pillows are morphologically similar similar to spherulitic spherulitic pillows pillows described described by by Dimroth Dimroth and and They described described aa rim rim to to core core succession: succession: Lichtblau (1979). They devitrified glass @asscrust-4 crust* zone zone of of albite albitespherulites spherulites—, -4 isolated isolated spherulites spherulites -4 -4 hyaloclastite -4 devitrified spherulites -4 coarse, coarse,fibrous fibrous spherulites spherulites or or dendrites dendrites -4 -4 microlitic microlitic zone zone (core). (core). coalescent spherulites section, the the varioles varioles consist consist of of aa glassy, glassy, altered altered groundmass groundmass which which hosts hosts aa polygonal polygonal In thin section, network of discrete, 0.02 to 0.04 mm wide, dendritic and plumose plagioclase microlites (Plate 4). Subparallel, branching branching microlite microlite arrays/intergrowths an-ays/intergrowths Fe-oxides occur adjacent to the microlites. Subparallel, These linear linear arrays arrays are are somewhat somewhat similar similar to to quenchmay occupy sections between larger crystals. These (1974) in Archean, hightexture, skeletal olivine chains described by Gelinas and Brooks (1974) magnesium tholeiites. The The fine, fine, fibroradial textures described by Fowler et al. (1987) (1987) are notably notably absent. absent. Conspicuous, Conspicuous, subhedral subhedral to to euhedral euhedral phenocrysts phenocrysts have have been been replaced replaced by by fine-grained fine-grained quartz. quartz.They They are typically <:1 1 mm mminindiameter diameterand andoccur occurboth bothwithin withinvarioles variolesand andininthe themore moremafic mafic groundmass. groundmass. Quartz comprises coarser, polygonal mosaic-textured cores and finer-grained margins. Hollow Hollow crystal crystal cores commonly host "islands" "islands" of epidote. Crystal Crystalhabit habitand andshape shapesuggest suggestthat that the the original and/orolivine, olivine,both both of of which whichhave havesimilar similarcross-sections cross-sectionsinin original phenocrysts phenocrysts were were plagioclase plagioclaseand/or orientations parallel to the c-axis. Quench Quench olivine olivine described described by by Gelinas Gelinas and and Brooks Brooks (1974) (1974) bears some striking similarity to the phenocrysts in question. They They described described hollow, hollow, quartz-replaced quartz-replaced olivine olivine euhedra euhedra in in aa matrix matrix of of plumose plumose and and branching branching clinopyroxene, clinopyroxene, with with intervening intervening calcic calcic Schreiber Assemblage 32 Schreiber Assemblage 32 �plagioclase and and devitrified devitrified glass. glass. These Thesequench quenchtextures textureswere wereascribed ascribedtotorapid rapidcooling cooling(not (not plagioclase necessarily supercooling) supercooling) and and are are identical identical to to those those found found in modern submarine submarine lavas. lavas. necessarily The greener greener (in (in hand hand specimen) specimen)areas areasbetween between the thevarioles variolesConsist consist of coarse, polygonal chlorite The aggregates with with accessory, accessory, blocky blocky epidote, epidote, quartz quartz and and Fe-oxides. Fe-oxides. aggregates This section section of of subaqueous subaqueousbasalt basalt flows flowswas was probably probably extruded extrudedin in fairly fairlydeep deepwater wateras assuggested suggested This low vesicularity and and small small vesicle vesicle size size and and sphericity, sphericity, by the absence of significant significant volumes volumes of by low al. 1978). 1978). The Theconformity conformityof of primary primary horizontal horizontal features features suggests suggests (cf. Dimroth et a!. pillow breccia (cf. relatively flat flat depositional depositional surfaces. surfaces. Stacked Stackedmegapillows megapillowsare areinterpreted interpreted as as successively successively relatively emplaced flow flow lobes lobes or or lava lava tubes, tubes, each each behaving behaving as as aa single cooling unit. These Thesetubes tubeswere were emplaced perhaps feeders for overlying, overlying, pillowed sections. The The lack lack of of isolated, isolated, detached detached pillows pillows may perhaps relate relate to to relatively relatively slow slow rates rates of of spreading spreading and and lava lava production. production. However, However,laboratory laboratoryexperiments experiments conducted by by Gregg Gregg and and Fink Fink (1995) (1995)showed showed that that pillows pillows become become larger larger and and flatter flatter as as effusion effusion conducted rate rate and and slope slopeincrease increaseand/or and/orcooling coolingrate ratedecreases. decreases. The origin originof of varioles varioleshas hasbeen beenrelated relatedtotoundercooling undercoolingof ofthe theliquid liquidduring duringcooling cooling(Fowler (Fowlereteta!. al. The 1987). havebeen beensuggested suggestedfor for 1987).Lava Lavaeruption eruptiontemperatures temperaturesofofbetween between13000 1300'and and1400° 1400' CChave basaltic (R.Keays, Keays,personal personal communication, communication,1994). 1994).In In basaltickomatiites komatiitesand and siliceous, siliceous,high-Mg high-Mgbasalts basalts(R. Archean Archean tholeiites, tholeiites,varioles variolesare arespherulites spherulitesproduced produced by by crystallization crystallizationwhen when nucleation nucleation is is suppressed suppresseduntil until the thephase phaseisiswell wellbelow belowits itsliquidus liquidustemperature; temperature;this thistextural textural development developmentisisdue due Schreiber Assemblage 33 Schreiber Assemblage 33 �to immiscibility. ItItisisinteresting interesting to to note note that that Fowler Fowler et et a!. al. (1987) (1987) stated that the textural development of varioles and komatiites are analogous in that both result from supersaturation brought about by supercooling. supercooling. about by Schreiber Assemblage Assemblage 34 34 �STOP 3: TERRACE TERRACEBAY BAY BATHOLITH stop is is located located near near the the northeastern northeastern contact contact of of the the Terrace Terrace Bay is in in This field stop Bay batholith, batholith, where where it it is predominantly mafic mafic metavolcanic metavolcanic rocks, rocks, similar similar to to those those at at Stops Stops2A 2A and and 2B. 2B. The The contact with predominantly along the the base base of of aa prominent, prominent, east-trending east-trending ridge ridge of of mafic mafic metavolcanic metavolcanic rocks rocks that that contact lies along 800 m m north north of of this this highway highway stop. stop. approximately 800 lies approximately 30 km km from from south south of of Schreiber Schreiber is ovoid ovoid in in plan plan view view and and extends extends for for approximately approximately 30 The batholith is to this vicinity. As Asdescribed describedby byMarmont Marmont(1984), (1984),the the bulk bulk of of the the batholith batholith consists consistsof of massive, massive, homogeneous, equigranular, medium-grained granodiorite. However, However, variations variations in in texture, texture, grain grain size, colour and composition are common, especially at and near near intrusive intrusive contacts. contacts. Largely Largely pristine and and undeformed, undeformed, the the batholith batholith may may exhibit exhibit local, local, weakly weakly developed developedmineral mineral foliations foliations and lineations near its margins. Marmont Marrnont(1984) (1984)suggested suggestedthat that the the lack lack of of a chill margin, the presence presence of of perthitic perthitic feldspar feldspar and and the the largely largely homogeneous, homogeneous,medium-grained medium-grained texture texture suggest suggestaa level. The relatively slow cooling history and a mesozonal emplacement level. The abundance abundance of assimilated country stoping was was important. important. country rock rock xenoliths xenolithsindicates indicates that that passive passive stoping A number of of polymetallic, polymetallic, auriferous auriferous quartz quartz veins, veins, including including the the Mogotherium, Mogotherium,Beaver BeaverCreek, Creek, Ferguson Ferguson (Crystal (CrystalCreek), Creek), Elgin/Siville-Ferrier ElgidSiville-Ferrier and and Mocan Mocan occurrences, occurrences,occur occur in in the the vicinity. vicinity. The largest largest of these, the Empress Empress Mine Mine (see (see Frontispiece), Frontispiece), is is located located approximately approximately 11 km km north north of this field stop, ridge. Operated stop, midway up the aforementioned aforementioned metavolcanic ridge. Operated around around the the turn turn Schreiber Assemblage Assemblage 35 35 �Base metal metal suiphides sulphides of the century, this mine reportedly produced just just over 100 ounces of of gold. gold. Base galena, chalcopyrite and sphalerite tend to characterize auriferous The Ferguson Ferguson such as galena, auriferous veins. veins. The (Ag2Te),acanthite acanthite(Ag2S), (Ag2S),native native occurrence is is somewhat somewhatunique uniquein inthat thatthe theminerals mineralshessite hessite(Ag2Te), occurrence bismuth, nuffieldite nuffieldite(CuPb2(Pb,Bi)Bi2S7) (CuPb2(Pb,Bi)Bi2S7)and andan anunidentified unidentifiedCu-Bi-Pb-sulphide Cu-Bi-Pb-sulphide have have been been discovered there (Patterson (Patterson et al. 1987; 1987; Kissin and McQuaig 1988). The The possible possible role role of of the the Terrace Bay batholith batholith in in epigenetic, epigenetic, Au-Cu-Mo Au-Cu-Mo mineralization mineralization is is discussed discussed prior prior to to the the description Stop 4. 4. description of Stop The granite granite exposed exposed at at this this location location isis grey-weathering, grey-weathering,equigranular, equigranular,medium-grained medium-grainedand and contains contains approximately approximately 25% quartz, quartz, 40% potash feldspar, 25 to 30% oligoclase-andesine and 5% hornblende or biotite biotite (Walker (Walker 1967). 1967). Minor Minorconstituents, constituents,in inorder orderof of decreasing decreasing abundance, abundance, are are and magnetite. magnetite. Molybdenite sphene, apatite, fluorite, tourmaline, muscovite, epidote and Molybdenite has has been been noted locally. locally. These glacially polished outcrops outcrops are are characterized characterized by numerous, numerous, partially digested, digested, rounded rounded to to sub-rounded, mafic xenoliths. The Thexenoliths xenolithsrange range in in size sizefrom from <1 4 to to 15 15cm, cm, averaging averaging 22 to to 55 cm. Average Averageabundance abundanceisis in in the the order order often of tenxenoliths/m2. xenoliths/m2.Xenoliths Xenolithsrange range in in composition compositionfrom from small, small, amphibole amphiboleclots clots that that presumably presumably represent represent the the refractive refractive residuum residuum left left over over from from partial partial digestion, amphibole-phyric, diorite and mafic metavolcanic fragments. Xenoliths Xenolithsare are digestion, to larger, amphibole-phyric, recessively weathered, perhaps due to the presence of biotite. These These xenoliths xenolithsrepresent represent assimilated mafic metavolcanic metavolcanic country country rocks rocks and and earlier, earlier, more more mafic mafic intrusive intrusive rocks rocks Schreiber Assemblage Assemblage 36 Schreiber �that pre-dated pre-dated granitic granitic intrusion. intrusion. Marmont Marrnont(1984) (1 984)stated statedthat thatthe theabundance abundanceof ofmafic maficenclaves enclavesisis that directly proportional proportional with with their their proximity proximity to to the the present present batholith batholith contacts contacts and its upper/roof upperlroof directly zone. zone. Hematitic Hematitic alteration alterationselvages selvageshave havedeveloped developedalong alongcross-cutting cross-cuttingfractures fracturesin inthe thegranodiorite. granodiorite. Minor, chlorite occur occur on joint surfaces. The Therock rock Minor, glassy glassy quartz quartz veins veins are are also present. Epidote Epidote±Âchlorite cut cut immediately immediatelyeast eastof of the the polished polished outcrops outcrops has has followed followed aa prominent, steeply dipping joint plane. plane. A A composite, composite,east-southeast-trending, east-southeast-trending,Proterozoic Proterozoicdiabase diabasedyke dykeintrudes intrudesthe thegranite graniteaashort short distance distanceto tothe theeast eastand andisisexposed exposedon onboth both sides sidesof of the the highway. highway. This Thisdyke dykeisis1.2 1.2rn mwide wideand and dips dipssteeply steeplynorth northto tovertically. vertically.ItItisislocally locallycharacterized characterizedby byquartz-carbonate quartz-carbonateveinlets veinletsand andclay clay alteration. alteration. Schreiber Schreiber Assemblage Assemblage 37 37 �Mineralizationin the the Schreiber Schreiber Area Area Gold Mineralization The Schreiber Schreiber area area first first gained gained notoreity notoreity in in 1851 1851when when Terrace Terrace Bay Bay became became the the site site of of the the first first The molybdenite discovery discovery in in Canada Canada(Geological (GeologicalSurvey Survey of of Canada, Canada, Report Report of of Progress, Progress, 1853-1856, 1853-1856, molybdenite Someofofthe theearliest earliestclaim claimstaking stakingon onthe thenorth northshore shoretook took place place on on aa gold gold property property south south p.40). Some Schreiber in 1872, 1872, prior to the construction of the Canadian Pacific Railway. Early gold gold of Schreiber Railway. Early discoveries bewteen bewteenthe themidmid-1 890's and 1920 1920 around around Schreiber Schreiberand and north north at at Big Big Duck DuckLake Lakewere were discoveries 1890's described by Hopkins Hopkins (1922). (1922). This Thisexploration explorationultimately ultimatelyled ledto to surface surfaceand and underground underground described development development on on a number number of small small properties, resulting in a modest, collective gold production of approximately approximately 3000 3000 ounces. ounces. The Thelargest largestproducer, producer,the theNorth North Shores ShoresMine, Mine, yielded yielded 2441 2441 ounces ounces at at an an average average grade grade of of 0.64 0.64 ounce Au per ton. Exploration Explorationand and test test milling milling have have continued continued since since mining mining activity activity lapsed lapsed in in the the 1930's. 1930's. Much Much of the the following followinginformation informationhas has been been gleaned gleaned from from aa variety variety of of unpublished unpublished reports reportsand and articles articles archived archived in in the the Resident Resident Geologist's Geologist'sFiles, Files, Schreiber-Hemlo Schreiber-HemloDistrict, District,Thunder ThunderBay. Bay. The The vast vast majority majority of of the the more more than than 25 25 gold gold occurrences occurrencesin in the the Schreiber Schreiberarea area are are hosted hosted by by discrete ± carbonate veins. Vein discrete structures, structures, usually composite, composite, quartz quartz 2 Vein orientations orientations are are generally generally subparallel subparallelto to one one another anotherand and to to fault/joint faultljointsets setsin inhost hostrocks; rocks;en enechelon echelonand andconjugate conjugatearrays arrays are common. common. Auriferous Auriferousstructures structuresare arehosted hostedby by aavariety varietyof of rock rock types, types, including including supracrustal supracrustal and and felsic felsic intrusive intrusive rocks. rocks. Veins Veinsare arecommonly commonlylocalized localizedalong along contacts contactsand and discontinuities. discontinuities. Schreiber Assemblage 38 Schreiber Assemblage 38 �Host rocks show little evidence of ductile deformation although some primary be primary features features may maybe somewhat somewhat flattened. flattened. There is a strong strong spatial spatial association association between between gold gold occurrences occurrencesand and felsic felsic intrusive intrusiverocks rocks (quartz(quartz- quartz-feldsparporphyries, porphyries, syenite syenite and and trondhjemite) trondhjemite) as as well well as as lamprophyre lamprophyre dykes. dykes. and quartz-feldspar (1984) investigated investigated the the occurrence occurrenceof of polymetallic, polymetallic, auriferous auriferous veins veins and and Cu-MoCu-MoMarmont (1984) bearing veins in and around the contact zone of the Terrace Bay batholith. batholith. Locally Locally auriferous, auriferous, sericite-chlorite-quartz-pyrite ± carbonate sericite-chlorite-quartz-pyrite carbonate ± Âtourmaline alteration is commonly commonly developed developed around around veins, but is is usually usually of of limited limited lateral lateralextent. extent. The vein-hosted nature of of the the gold gold suggests suggests that that mineralization mineralization took took place place in in aa brittle brittle shear shear setting. Dilatancy Dilatancyin insuch suchan anenvironment environmentmay may have have resulted resulted chiefly chiefly from from bulk, bulk, inhomogeneous inhomogeneous flattening, perhaps related flattening, related to compressive compressive stress stress imaprted imaprted by the the enclosing enclosing Terrace Terrace Bay Bay and and Whitesand batholiths. Zones (e.g. contacts, contacts, Zonesof ofcompetency competencycontrast contrastand and pre-existing pre-existing weakness weakness (e.g. interfiow interflow sedimentary sedimentary units, units, etc.) etc.) were were important important in in the the localization localization of of shear shear zones zones and and fractures. fractures. The close close spatial spatial association associationbetween between felsic felsic intrusive intrusive rocks, rocks, gold gold occurrences occurrencesand and hydrothermal hydrothermal loci for for fracturing. fracturing. It suggests that the alteration may reflect the fact that these rocks are loci hydrothermal activity which which accompanied accompanied gold gold deposition deposition may be related related in in part to to late-stage late-stage events within these intrusions. intrusions. Schreiber Assemblage Assemblage 39 Schreiber 39 �The two two most most important important exploration explorationcriteria criteriaappear appear to to be: be: The (1) evidence evidenceof ofhydrothermal hydrothermalfracturing fracturingand andalteration, alteration,and and (2) rocks rocksthat thatare areattributable attributabletotofelsic felsicmagmatism, magmatism,the thelate latestages stagesof of which which may may often often lead lead to to the the (Burnhamand and Ohmoto Ohmoto1980). 1980). formationof of hydrothermal hydrothermal ore ore deposits deposits(Burnham formation A number number of of volcanic volcanic and and intrusive intrusive igneous igneous rocks rocks sampled sampled by Carter Carter (1988) (1988) near Schreiber Schreiber have have alkalic, shoshonitic shoshoniticaffinities. affinities. They Theycan canbe begeochemically geochemicallyclassified classified(LeMaitre (LeMaitre1989) 1989)as as latites, latites, alkalic, mugearites -like mugearites and and biotite biotitelamprophyre lamprophyre(kersantite), (kersantite),similar similarto to those those of ofthe the Timiskaming Timiskaming-like successions successionsof of the the Shebandowan Shebandowangreenstone greenstone belt (summarized by Fyon et al. 1991). Pye Pye(1969) (1969) referred referred to to aa package packageof ofconglomerate, conglomerate,quartzite quartziteand andlimestone limestonemapped mapped by by Harcourt Harcourtand andBartley Bartley (1939) south southof ofSchreiber Schreiberas asTimiskaming. Timiskaming. Hornblende-phyric, Hornblende-phyric,syenitic syeniticrocks rocks are are spatially spatially associated associated with withmany many gold goldoccurrences occurrencesin inboth bothareas, areas,bearing bearingsimilarity similaritywith withsyenite-hosted syenite-hostedgold gold deposits deposits in in the the Matatchewan Matatchewanand and Kirkland KirklandLake Lake areas areas of of eastern eastern Ontario. Ontario. Schreiber Schreiber Assemblage Assemblage 40 40 �STOP 4: 4: GOLD GOLDRANGE RANGEPROSPECT PROSPECT STOP Goldwas wasdiscovered discoveredjust justbefore beforethe theturn turnof ofthe thecentury centuryon onaa northeast-trending northeast-trending ridge ridge of of Gold km east eastof of Schreiber. Schreiber. metavolcanicrock rocknear nearthe thecontact contactwith withthe theTerrace TerraceBay Baybatholith, batholith,44km metavolcanic Severalsubsequent subsequentdiscoveries discoveriesof ofauriferous auriferousquartz quartzveins veinsled ledtotothe thedevelopment developmentof ofthe theadjoining adjoining Several Otisse,Harkness-Hays Harkness-Haysand andGold GoldRange Rangeproperties. properties. Otisse, TheGold GoldRange Rangeprospect prospectwas wasfirst firststaked stakedinin1917 1917and andexplored exploredfor forseveral severalyears. years. In In 1922, 1922,two two The aditswere weredriven driveninto intothe thehillside hillsideby bythe theJackson JacksonDevelopment Development Co. Co. Ltd. Ltd. Newly Newlyincorporated incorporated adits Gold Range RangeMines MinesLtd. Ltd.acquired acquiredthe theproperty propertyin in1934, 1934,continued continuedunderground undergrounddevelopment developmentand and Gold investigatedthe the placer placer potential potential of of the the sand sand and and gravel gravel at at the the base base of of the Overburden investigated the hill. hill. Overburden oneextractedfrom from test test shafts shaftswas was treated treated with with aa Denver Denver concentrator. concentrator. Sampling Samplingof oftwo twoshafts shaftsatat oneextracted footintervals intervalsin in1936 1936returned returnedaverages averagesof of0.04 0.04ounce ounceAu Auper perton tonto to17 17feet feetand and0.10 0.10ounce ounceAu Au foot tramwayand andaasmall smallmill millwere wereerected erectedon onsite siteto tohandle handlehighhighper ton ton to to 22 22 feet, feet,respectively. respectively.AAtramway per grade vein vein ore. ore. Ore Orewas wascrushed, crushed,pulverized pulverizedand androasted. roasted. Gold Goldwas wasrecovered recoveredwith with grade amalgamation;tables tableswere werereportedly reportedly installed installed to to produce produce aa suiphide sulphide concentrate concentrate as as well. well. The The amalgamation; first gold gold brick brick(22 (22ounces), ounces),representing representing40% 40%of ofthe thetotal totalgold goldconcentrates concentratesprocessed processedto tothat that first time,was waspoured pouredin inmid-1936. mid-1936.Gold GoldRange RangeMines Mineswas wassubsequently subsequentlysucceeded succeededby byRolac RolacMines. Mines. time, Theproperty propertybecame becameinactive inactivearound around1941. 1941.ItIthas hasbeen beenexplored exploredby byvarious variousindividuals individualsand and The companiessince sincethen. then. companies Schreiber Assemblage Assemblage 41 41 Schreiber �Local Local Geology Geology The property property straddles straddlesthe the northern northerncontact contact(trending (trending0300) 030¡of the the Terrace Terrace Bay Bay batholith batholith with with mafic metavolcanic rocks. This This contact contact is is locally locally obscured by deep glacial drift. The mafic mafic drift. The metavolcanic rocks are are locally locally pillowed pillowed and and have have been been upgraded upgraded to amphibolite-facies amphibolite-facieswithin within the the contact metamorphic aureole of the batholith. Coarser-grained, Coarser-grained, mafic mafic units units have have been been interpreted interpreted Sulphide-and andoxide-facies oxide-faciesbanded banded iron ironformation, formation,wacke wacke and and conglomerate conglomerate are are as gabbros. Suiphideintercalated with the mafic flows. Tracing Tracingof ofone one iron iron formation formation across across the the Harkness-Hays, Harkness-Hays, Gold intercalated 1939;Resident Resident Otisse properties properties reveals reveals tight tight to to isoclinal isoclinal folds folds (Hoibrooke (Holbrooke1939; Range and Otisse Geologist's Files, Files, Schreiber-Hemlo Schreiber-HemloDistrict, District, Thunder Thunder Bay). Bay). Geologist's In the vicinity of the main workings, workings, aa series series of quartz-feldspar quartz-feldspar porphyry dykes dykes intrudes intrudes the the 20° to to 40 40°northwest. northwest. Biotite-bearing, 030" and dips 20 Biotite-bearing, brown brown mafic metavolcanic metavolcanic rocks and and strikes strikes 030° to black lamprophyre lamprophyre (kersantite?) (kersantite?) dykes dykes intrude intrude all all of of the the aforementioned aforementionedrocks rocks and and are are intimately associated with some some of of the the veins. veins. Gold mineralization mineralizationon on the the property property is is associated associated with with aa series series of of at at least least seven seven numbered, numbered, subparallel veins that strike subparallel strike north-northeast north-northeast and dip steeply steeply to the northwest northwest (Figure (Figure 6). 6). surface, only only veins veins No.'s No.'s 1I and 2 were investigated investigated Although all these veins were discovered on surface, and mined underground underground using using three three adits adits and and short short drifts. drifts. Schreiber Assemblage 42 Schreiber Assemblage 42 �/ S / S —4,- . ^-S^ 0 Sw No.3 No. 3 ad/f adit S Overbt.rden Test Holes S • No.1 adit •e- No;2 adit S Overb'sden 1 OverburdenTest TestPtts Pits / S  S aD 0 DD° 0 30m Sketchmap mapofofthe theGold GoldRange Rangeprospect prospect(from (fromHoibrooke Holbrooke1939) 1939) Figure 6. Sketch Sclzreiber Assemblage 43 Schreiber Assemblage 43 • • • • S �The veins are typically narrow (5 to 25 cm) but are remarkably persistent along strike. They may split and develop horse-tail" structures that increase the vein width. Sub-parallel microveinlets are also common. The veins are rarely composite or crack-seal textured, but do contain septa and xenoliths of wall rock. Cockscomb textures are developed in drusy quartz and calcite. Vein breccias contain fragments of other vein gangue as well as altered wall rock. Slickensides are visible along vein margins. Despite the narrow widths of the veins, hydrothermal alteration extends from the vein margins several centimetres into the wall rock. This alteration is manifested as a pale, grey to lime green zone that has a rusty weathered appearance (Plates). Marmont (1984) has identified mineralogic zonation within the alteration envelope (from host towards vein): [host] I sericite-biotite sericite-carbonate-Mg(?)-chlorite carbonate-Fe(?)-chlorite-quartz [vein] I I potassic alteration I carbonatization I silicification I Sulphides, predominantly pyrite, are ubiquitous, but are locally developed immediately adjacent to the vein itself. Altered zones are themselves commonly auriferous. Coarse, visible gold occurs within quartz, but it also occurs as discrete grains within large (s2,5 cm), euhedral pyrite crystals. The No.2 vein displays abundant pyrite euhedra where the vein is crosscut by a lamprophyre dyke. Gold-bearing tellurides, calaverite (AuTe,) and sylvanite Schreiber Assemblage 44 �((Au,Ag)Te2),have have also also been been noted. noted. Accessory Accessorysulphides sulphidesinclude includepyrite, pyrite,with withlesser lesserchalcopyrite, chalcopyrite, ((Au,Ag)Te2), pyrrhotite,sphalerite, sphalerite,molybdenite molybdeniteand andgalena. galena. Calcite, Calcite,graphite, graphite,epidote epidoteand andmagnetite magnetite are are also also pyrrhotite, present. In Inaddition, addition,Sabina Sabina(1991) (1991)noted notedgarnet, garnet,goethite goethite and basaluminite (A14S04(OH),,,~4H20) present. and basaluminite (A14SO4(OH)104H20) on the the adjacent adjacentHarkness-Hays Harkness-Haysproperty. property. on Plate 5. 5.Alteration Alterationenvelope envelopearound aroundquartz quartzvein veininingabbro, gabbro,Gold GoldRange Rangeprospect prospect(STOP (STOP4). 4). Plate 1.5cm cminindiameter. diameter. Coinisis1.5 Coin Schreiber Assemblage Assemblage 45 45 Schreiber �Sampling by Holbrooke Holbrooke (1939) (1939) of of the the No. 22 vein vein returned returned an an average average of of 0.49 0.49 ounce ounce Au Au per per ton ton Sampling Theseresults resultswere were probably probably typical typical of of the best-mineralized over 0.28 m for a length of 7.6 m. These sections of the veins. Typical Typicalgrab grabsamples samplesof ofhigh-grade high-grade material material have have commonly commonly returned returned sections between and 20 20 ounces ounces Au Au per per ton. ton. Silver Silvervalues valuesare areabout aboutone-half one-halfthat that of of the the corresponding corresponding between 55 and samples. Approximately Approximately42 42ounces ouncesof of gold gold were were eventually eventually recovered recovered during during gold assays in these samples. early mining mining operations. operations. Geology of the No. 7 Vein Shaft Area The shaft shaft exposed exposed near near the the access accessroad road was was sunk sunk to to aa depth depth of of 7.7 7.7 m m to to investigate investigatethe the No. No. 77vein. vein. This This vein, vein, striking striking040° 040Âand and dipping dipping 75° 75O northwest, returned up to 0.98 ounce Au per ton over 0.36 0.36 m; most most samples samples returned returned only only trace trace amounts amounts of gold (Hoibrooke (Holbrooke 1939). 1939). Harcourt Harcowt (1939) (1939) reported that the the vein vein was was wider and and carried gold at the shaft bottom. Visible Visiblegold goldwas was noted notednear near the the shaft shaft bottom bottom by by the the authors authors during during aa 1987 1987 property visit. Diamond Diamonddrilling drillingand andthe thestripping stripping in in the the vicinity vicinity of of the the No.7 No.7 vein vein were were carried out in 1987 1987 by Forerunner Resources Limited (now Beardmore Beardmore Resources Resources Limited). Limited). The host host rocks rocks consist consistdominantly dominantly of ofequigranular equigranulargabbro gabbrothat that has has been been intruded intrudedand and brecciated brecciated by dykes dykes of pink pink granodiorite granodiorite that extend off the main mass of ofthe the Terrace Terrace Bay Bay batholith batholithto to the the Schreiber Assemblage 46 Schreiber Assemblage 46 �east, across across the the road. road. InInthin thinsection, section,the theunaltered unalteredgabbro gabbrocontains containsplagioclase plagioclaseand and pyroxene, pyroxene, east, includinginverted inverted pigeonite. pigeonite. Where Wherealtered alteredadjacent adjacentto toquartz quartzveins, veins,the the original originalgabbroic gabbroictexture texture including has has been been replaced replaced by by aafine-grained fine-grainedmatte matteof of carbonate, carbonate,sericite, sericite,quartz, quartz,epidote epidoteand andpyrite. pyrite. Coarse grains grains of of visible visible gold gold have have been been noted noted in in this this altered alteredzone. zone. Coarse Subparallel Subparallelstringers stringersof of quartz, quartz, enveloped envelopedby by conspicuous, conspicuous,rusty, rusty, carbonate-rich carbonate-richalteration alterationhaloes, haloes, are exposed at the shaft collar. Well-developed, prominent. Dump Well-developed, orthogonal joint sets are also prominent. Dump material, material, extracted extracted during during shaft shaftexcavation excavationand and subsequent subsequentreclamation, reclamation,has has been been piled piled nearby. nearby. Vein Vein material material with with ubiquitous ubiquitousalteration alterationisisabundant abundantin inthe thedump. dump. Schreiber Assemblage Schreiber Assemblage 47 �STOP5: 5: WINSTON WINSTON LAKE LAKE Cu-Zn Cu-ZnMINE MINE STOP Explorationand andMining MiningHistory Historyof ofthe theWinston Winston Lake Lake Mine Mine Exploration Theexploration explorationhistory historyof ofthe theWinston WinstonLake LakeMine Minehas hasbeen beendescribed describedby byBalint Balintetetal. al.(1990) (1990)and and The Severinet et a!. al. (1990). (1990). The Theearliest earliestexploration explorationactivity activityisislargely largelygleaned gleanedfrom fromgovernment governmentreports reports Severin andother otherdocuments documents(Resident (ResidentGeologist's Geologist'sFiles, Files,Schreiber-Hemlo Schreiber-HemloDistrict, District,Thunder ThunderBay). Bay). and Activityin inthe thearea areadates datesback backto tothe thediscovery discoveryand and initial initial development development of of the the Zenith Zenith Mine Mine in in Activity 1879. High-grade High-grade (45% (-45%Zn), Zn),sphalerite-rich, sphalerite-rich,massive massivesuiphide sulphidewas was mined mined on onsurface, surface, 1879. hand-cobbedand andshipped shippedoverland overlandto toaarailway railway spur spurnear near Schreiber. Schreiber. Around Aroundthe theturn turnofofthe the hand-cobbed century,the theGrand GrandCalumet CalumetMining MiningCompany CompanyLtd. Ltd.mined minedand andconcentrated concentratedapproximately approximately2700 2700 century, ZenmacMetal MetalMines Mines tonsof ofore. ore.The Theproperty propertyremained remainedlargely largelydormant dormantuntil untilthe the1960's 1960'swhen whenZenmac tons Limitedbegan beganshaft shaftsinking, sinking,underground undergrounddevelopment developmentand anderected erectedsurface surfaceplant plantfacilities. facilities. Limited Productionfrom from1966 1966toto1970 1970totalled totalled164 164000 000tons tonsofofore oreatataagrade gradeofof16.5% 16.5%Zn. Zn. Production InOctober, October,1978, 1978,Corporation CorporationFalconbridge FalconbridgeCopper Copper(CFC) (CFC)carried carriedout outreconnaissance reconnaissancegeological geological In andlithogeochemical lithogeochemicalsurveys surveysaround aroundthe theZenith ZenithMine Mineininorder ordertotoassess assessthe theexploration explorationpotential potential and of this this portion portionof ofthe theBig BigDuck DuckLake Lakevolcanic volcanicassemblage, assemblage,previously previouslymapped mappedby byPye Pye(1964). (1964). of Rockspreviously previouslyinterpreted interpretedas asmetasedimentary metasedimentarywere wererecognized recognizedas ashydrothermally hydrothermallyaltered, altered, Rocks felsicmetavolcanic metavolcanicrocks. rocks.The Thelithogeochemistry lithogeochemistryofofthese thesealtered alteredrocks rockswas wasnoted notedto tobe besimilar similarto to felsic Schreiber Assemblage Assemblage 48 48 Schreiber �that of rocks at CFCs CFC'sSturgeon SturgeonLake LakeMine, Mine, primarily primarily on on the the basis of sodium sodium depletion depletion and and zinc zinc Thedelineation delineationof ofan analteration alterationzone zone 1200 1200m m west west of of the the Zenith Zenith Mine Mine prompted prompted CFC CFC enrichment. The to acquire acquire on on option option on on the the Zenith Zenith property property and and stake stake the the ground ground around around it. it. , In 1979 1979 and 1980, 1980, detailed detailed geological, geological, lithogeochemical lithogeochemicaland and geophysical geophysical (magnetometer, (magnetometer, VLF-EM, and Max-Mm 11) surveys were conducted. Although Although geophysical geophysical results results were were Max-Min II) disappointing, disappointing,geological geological and and lithogeochemical lithogeochemicalsurveys surveyssucceeded succeededin in discovering discovering zones zonesof ofcherty, cherty, bedded ash ash within within the the calc-alkaline, calc-alkaline, felsic felsic volcanic volcanic rocks rocks and and they they further further delineated delineated the the hydrothermal alteration alteration zone. AAgeological geologicalmodel modeldepicted depictedthe the Zenith Zenith deposit depositas as aa raft raft of of massive massive suiphide that had been stoped stoped off off of of aa larger, larger, as as yet undiscovered, undiscovered, felsic felsic volcanic-hosted, volcanic-hosted, sulphide sulphide sulphide deposit by a composite, composite, gabbroic gabbroic intrusion. intrusion. In 1981, 1981, eight eight diamond diamond drill drill holes holes were were completed, completed, four four of of which which tested tested the the geological geological model. model. They intersected intersected aa cherty cherty ash ash horizon horizon that that occurs occurs at at the the top top of of the the felsic felsic volcanic volcanic pile, pile, overlying overlying the alteration alteration zone, at the contact with the gabbro. Encouraging Encouragingresults results included included up up to to 0.5% 0.5% Zn Zn over 4.3 m. Subsequent Subsequentborehole boreholepulse pulse EM EM surveys surveysdetected detected aa strong, strong, edge-type edge-type anomaly anomaly down-dip of the mineralized mineralized exhalite exhalite intersection. intersection. 1.10% Cu, 19.11% In June, 1982, 1982, a follow-up follow-up drill drill hole hole intersected intersected 2.1 2.1 m m of of massive massive sulphide sulphide (@ (@ 1.10% 19.11% Zn, 22.2 g/t glt Ag Ag and and 0.73g1t 0.73glt Au) Au) at the base of the gabbro gabbro sill, sill, 300 300 m m below below surface. surface. Assemblage 49 Schreiber Assemblage 49 �Subsequent definition definition drilling and exploratory shaft sinking produced produced aa reserve reserve figure figure of of 2 675 000 t grading grading 0.94% 0.94% Cu, Cu, 17.8 17.81% 1% Zn, Zn, 25.3 25.3 glt g/t Ag Ag and and 0.85glt 0.85g/t Au Au (Severin (Severin and and Balint Balint 1984). A production decision decision was was delayed delayed as as the the price price of of zinc zinc fluctuated fluctuated and development development was was suspended suspended 1985. Activity Activitywas wasrenewed renewed by by Minnova Minnova Inc. and development ore was to surface in 1985. was hoisted hoistedto throughout 1987. 1987. Original Originalmineable mineablereserves reserves(all (allcategories, categories, including including 20% 20% dilution dilution at at zero zero on November November 1, 1, 1987 1987were 33 076 076 339 339 tonnes tonnes at at aa grade grade of of 1.00% 1.00% Cu, Cu, 15.60% 15.60% Zn, Zn, grade) reported on g/t Ag and 1.02 glt g/t Au (Severin et al. a!. 1990). The 30.87 glt The first concentrate was produced in January, In May, 1993, 1993, Minnova Minnova Inc. 1988 and the mine's official opening took place place in in July, July, 1988. In merged with aa wholly-owned wholly-owned subsidiary subsidiaryof of Metal! Metal1 Mining Corporation. Corporation. Mine reserves as of January 1, 1, 1995 1995 stood stood at 733 733 306 306 tonnes at at a grade grade of 12.05% 12.05% Zn, 0.89% 0.89% Cu, Cu, glt Ag and 1.647 1.647g/t glt Au Au (G. Doiron, 26.82 g/t Doiron, Metal! Metal1 Mining Corporation, Corporation, personal communication, communication, 1995). These Theseestimates estimatesinclude include proven, proven, possible possible and and potential ore with a 20% dilution at 0% grade. grade. Metall m level level of of the the Winston Winston Lake Lake Mine Mine in in August, August, 1993 1993in in order orderto to Metal1 began drifting drifting from from the the 615 615 m assess the Pick Lake upper zone deposit. This Thisdeposit depositwas was initially initially defined defined by by surface surface drilling drilling from the mid-1980's to 1992. 1992. The Thedeposit depositconsists consists of of two two thin, thin, but but continuous, continuous, massive massive sulphide sulphide sheets with a down-plunge length of 1400 m. The TheUpper Upper Zone Zone and and Lower Lower Zone average average approximately 2.2 and 4.0 m in thickness, respectively. Potential Potential reserves reserves stand stand (as (as of of January, January, 1995) at 1147 1 147442 442 tt (20% (20%dilution dilutionat at 0% 0% grade grade included) included) at at 1.24% 1.24% Cu, 20.05% Zn, 56.11 g/t glt Ag Assemblage 50 Schreiber Assemblage �and 0.33 glt Au. Au. Underground drilling drilling in early 1995 1995 will be used to determine determine the economic economic feasibilty of mining mining the the Pick Pick Lake Lake deposit. deposit. feasibilty Geology of of the the Winston Winston Lake Mine Geology The local local geology, geology, particularly particularlythose those aspects aspects which which are are associated associated with with volcanogenic volcanogenicmassive massive sulphide, Cu-Zn Cu-Zn mineralization, mineralization, has has been been studied studied by the aforementioned aforementioned authors, authors, as as well well as as Osterberg Osterberg (1993), (1993), Osterberg Osterberg and and Morrison Morrison (1991), (1991), Severin Severin and and Balint (1984) (1984) and and Thomas Thomas (1991). (1991). The Winston Winston Lake Lake area area lies lies within within the the northernmost northernmost portion portion of of the the Schreiber Schreiber greenstone greenstone the boundary boundary with with the the Quetico Quetico subprovince. subprovince. Local assemblage and the Wawa subprovince, near the metavolcanic, km by by 15 15km kmpackage package metavolcanic, metasedimentary metasedimentaryand and associated associated intrusive intrusive rocks rocks comprise comprise aa 44 km of rocks informally informally referred to as as the Big Duck Duck Lake Lake greenstone greenstone belt (Balint (Balint and and Severin Severin 1984). 1984). These rocks are are separated separated from from the bulk of of the Schreiber Schreiber greenstone greenstone assemblage assemblage to the south south by by granitoid rocks of the Crosman Lake batholith. Several Severalmapping mapping projects projects covered covered the Big Big Duck Duck (1909), (1915; 1921) Bartley (1 (1942). 1) and Bartley 942). Gold Gold was was Lake area, including those of Collins (1 909), Hopkins (1 9 15; 192 discovered discovered at Big Duck Duck Lake Lake in in 1906, 1906,leading leading to to the the subsequent subsequent discovery discovery and and exploration explorationof of over over twenty gold and polymetallic polymetallic occurrences for the next two decades. Activity Activity in in the the "Duck "DuckLake Lake gold field", field", as as itit was was then then termed, termed,peaked peaked in in the the 1920's 1920'sbut but has has continued continued to to the the present. present. Schreiber Assemblage Assemblage 51 51 �flanks of of this this part part of of the the Schreiber Schreiberassemblage assemblagehave have undergone undergone upper upper greenschist greenschistto to The outer flanks arnphibolite grade grade regional metamorphism, typified by garnet and hornblende, while amphibolite while rocks rocks in the quartz-chlorite-actinolite-albiteassemblages assemblagestypical typical of of greenschist greenschistfacies facies(Pye (Pye1964). 1964). core display display quartz-chlorite-actinolite-albite Pye (1964) (1964) also did a comprehensive comprehensive investigation investigation of the mineral deposits deposits of of the the area area in in the the course of his mapping. Balint and Severin Severin (1984) (1984) outlined outlined the the basic basic architecture architecture of of the the supracrustal supracrustal and and associated associated rocks rocks 7): in the vicinity the Winston Winston Lake Lake Mine Mine (Figure (Figure 7): vicinity of the (1) (1) Winston Winston Lake Lake Sequence: Sequence: metasedimentary rocks - calc-alkaline, felsic and mafic metavolcanic metavolcanic and lesser metasedimentary - predominantly lava flows flows with subordinate subordinate pyroclastic pyroclastic rocks (2) (2) Big Duck Duck Lake Big Lake Sequence: Sequence: - overlies overlies Winston Winston Lake Lake Sequence Sequence - predominantly predominantly tholeiitic tholeiitic basalt basalt flows flows - flows intruded by Big Duck Lake quartz- and quartz-feldspar quartz-feldspar porphyry sills sills series of of differentiated, - separated from Winston Lake Sequence byby aa series differentiated, tholeiitic, tholeiitic, mafic mafic to to ultrarnafic ultrarnafic sills sills As a result 1%O's, subsequent subsequentbase base metal metal result of of mapping mapping and and lithogeochemical lithogeochemicalsampling samplingin in the the 1980's, Schreiber Assemblage Assemblage 52 52 �exploration and and associated associated research research have have been been confined confined to the the Winston Winston Lake Lake Sequence, Sequence, which which exploration Winston Lake, Lake, Zenith Zenith and and Pick Pick Lake Lake deposits, deposits, as as well well as as aa number number of of surface, surface, hosts the the Winston occurrences. Metall Metal1Mining MiningCorporation Corporationconducted conducted surface surface exploration explorationand and copper and zinc occurrences. diamond drilling on their Cleaver Cleaver Lake, Lake, Ciglen, Ciglen, Gesic, Gesic, Pick Lake, Lake, Winston Lake Lake and and Zenith Zenith properties in in 1994 1994(G. (G. Doiron, Doiron,Metall Metal1Mining Mining Corporation, Corporation,personal personal communication, communication,1995). 1995). properties volcanological studies Physical volcanological studies by Osterberg Osterberg (1993) (1993) and and Osterberg Osterberg and and Morrison Morrison (1991) (1991) indicated indicated by interlayered interlayered successions successions of of that the footwall rocks to the Winston Lake Mine are dominated by deep-water volcaniclastic, sedimentary and flow units. Footwall Footwall volcanic volcanic stratigraphy stratigraphy apparently apparently developed developed as the result result of of cyclic cyclic accumulation accumulation of of volcaniclastic volcaniclastic and and volcanic volcanic rocks rocks in in aa subsiding, subsiding, subaqueous, stratigraphiccolumn columndepicting depicting the the lithologic lithologic subdivisions subdivisionsof of the the subaqueous, rift environment. environment. AAstratigraphic Winston Footwall Block (Osterberg 1993) 1993) is shown in Table 2. Volcanic Volcanic rocks rocks have have been been extensively extensively intruded intruded and and block block faulted. faulted. Tectonic Severin(1984), (1984), Tectonic deformation deformation features features in in local local rocks rocks have have been been described described by Balint Balint and and Severin (1993) Osterberg (1 993) and Williams (1989). Ductile Ductiledeformation deformation is is typically typically manifested in flattening flattening and foliation, as well as minor folds. The Thedegree degreeto to which which original originalstratigraphic stratigraphicand and contact contact relationships have been relationships been modified modified by tectonism tectonism is is still still aa matter matter of of much much debate. debate. Williams 1989)has has described described extremely extremely deformed deformed rocks rocks of of what what he he termed termed the the Big Big Duck Duck Williams (1988, (1988, 1989) Lake shear zone. In Inhis hisopinion, opinion,the theubiquity ubiquityof oftectonic tectoniclayering layering precludes precludes recognition recognitionof of the the Schreiber Assemblage Assemblage 53 53 �deformation and original lithologic relationships. Moreover, Moreover,Williams Williams (1988) (1988) interpreted interpreted state of deformation and altered altered footwall footwallrocks rocks the schistose schistose contact contact between between the the hanging hanging wall wall gabbro, gabbro, the the ore ore zone zone and 5A) asashighly highlysheared, sheared,with withslip slipdirections directionsgenerally generally down-dip down-dip of the schistosity, schistosity, (Stop5A) (Stop suggestive suggestive of of thrusting thrustingand and dip-slip dip-sliptectonics. tectonics. Schreiber Assemblage 54 Schreiber Assemblage 54 �Table 2. Stratigraphie Stratigraphicsubdivision subdivision of of part partofofthe theWinston WinstonFootwall FootwallBlock Block (from (from Osterberg Osterberg 1993) 1993) Table Winston Lake Lake Horizon Horizon (WLH) (WLH) Winston Winston Lake Lake VMS VMSDeposit Deposit(WLH-MS) (WLH-MS) Winston Mafic volcanic volcanic and and intrusive intrusivefeeder feederrocks rocks (WLH-FR) (WLH-FR) Mafic (WLH-CRT)" Mixedlaminated laminatedash ashand andexhalative exhalativesedimentary sedimentaryrocks rocks(WLHCRT)5A Mixed Maficlava lavaflows flows(WLH-MA), (WLH-MA),including includingFootwall FootwallFlow Flow(WLHFWF)sB (WLH-FWF)'" Mafic ................................................................................................... Upper Upper Clastic ClasticSuccession Succession(UCS) (UCS) Clotted ClottedRhyolite Rhyolite(CLR)5B (CLR)5B Volcaniclastic Volcaniclasticand andassociated associatedrocks rocks(SIV) (SIV) Felsic Felsictuffs tuffs(SIV-FT), (SIV-FT),Intermediate Intermediatevolcaniclastic volcaniclasticrocks rocks(SIV-VC) (SIV-VC) ................................................................................................... Middle MiddleFlows FlowsSuccession Succession(MFS) (MFS) Synvolcanic (CT)SD Synvolcanicfelsic-derived felsic-derivedvolcaniclastic volcaniclasticsedimentary sedimentaryand andtuffaceous tuffaceousrocks rocks (CT)'" Undivided Undividedmafic maficrocks rocks(MA) (MA) Middle andassociated associatedrocks rocks(MMF) (MMF) Middlemafic maficflow flowand Camp dikes (QFF)SC CampFlow Flowrhyolite rhyoliteand andassociated associatedfeeder feeder dikes (QFF)5c Ladder Ladderbasalt basaltflow flow(LF)5E (LF)^ (QFP)5F "Main Main"quartz-feldspar quartz-feldsparporphyry porphyry (QFP)" Trip Stopwhich displays this unit.) (n.b. (n.b.Superscripted Superscriptednumbers numbersdenote denotethe theField Field Trip Stop which displays this unit.) Schreiber Schreiber Assemblage Assemblage 55 55 �VVVVVVVV VVVVVVVVVVVVVV VVVVVVVVVVVVVVVVVVV VVVVVV VVVVVVVVVVVVVVVVV VVVVVVVVV V VVVVVV VV VVVVVVVVVVVVV VVVVVVVVVVVVVVVVVV VVVVVVVV V VVVVVVVVVV VV V VVVVVVVVVVVVVVVVVVVV V VVVVVVVVVV VVVVVV VVVVVVV LV V V V V V V V V V V V V V V V V V V V V VVV V V V VVVVVVV V V V VVVV VVV V V VVVVVVV VVVVVVV VVVVV VV VVV V V VVVVVVVVVVVV V VVVVVV V V V V V V V V V VVVVVVVV (VVVVVVVVVVVVVVVV VVVVV VV V VV V V V V V V V V V V V V V V V V V V V V V V V V V V V V V V V VVVVVVV 'VVVVVVVVVVVVVVVVVVV V VVVVVVVV V VVVVVVVV VVVVVVVVVVVVVVVVVVVVVVVVVVVVVVVVVV (VVVVVVVVVVVVV VVVVVVV VVVVVVVVVVVVVVV VVVVVVVVVVVVVVVVVV VVVVV VV VVVVVVvv VVVVVVVVVVVVVVVVV VVVVVVVVVVVVV VVVVVVV VVVV VVVVVVV VVVVVVVVV VV VV V VVVVVV VVVV V V V V VVVVVVVVVVVVVVVVVVVVVV IVVVVVVVVVVVVVVVVVV •VV VV V V VV V VV V V VV V V V VVVV VVV VV V VVVVV V V VVVV VVVV VVV V VVV VV V V V V 4VVVVVV VVVVVV VVVV VVVVVV VVVVVVVVV VVVVVV VVVVVVVVVVVVVVVVVVVVVVVV 'VVVVVVVVVVVVV VVVVVVV VVVVVVVVV VV VVVVVVVVVVVVVVVVVVVVVVV VVV VVVVVVVVVVVVVVVV • VVV VVVV V VV V V VVVV V VV V V VVVVVVVV VVVVVVVVVV VVVVVVVVVVVVVV VV V V V V V V VV VV VVV VVVVVV VVVVVVVVVVVVVVVVVVVVV VVVVVVVVVVVVVVVVVV+ VVVVVVVVVVVVV VVVVV VVVVVVVVVVVVVVVVVVVVVVVVVVVVVVVVVVVVVVVVVVVVV VVVVVV VVVVVVVVVVVVVVVVVVVVV VVVVVVV VVVVVVVVVVVVVVVVVVVVV VVVVVVVVVVVVVVVVVVVV 'VVVVVVVVVVVVVVVVVVVVVV VVVVV V VVV VVVVVVVVVVV VVVV VVV VVVVVVVVVVVVVVVVVVVVVVV VVVVVVVVVVVVVVVVVVVVV 1VVVVVVVVVVVVVVVVVVVVVVV 4VVVVVVVVVVVVVVVVVVVVVVVVV 'VVVVVVVVVVVVVVVVVVVVVVVVV 'V VV V VV V V V VVVVV V V V V V V VV 'VVVVVVVVVVVVVVVVVVVVVVV 'VVVVVVVVVVVVVV VVVVVVVVVVVVV VVVVV VVVVV V VVVVVVVVVVVVVVVV VVV VVVVVVVVVV V VVVVVVVVVV VVVVVVVVVVVVVVVVVVVVVVVVVV 'VV VVVVVVVVVVVVVVVVVVVVV(,VV - 'VVVVVVVVVVVVVVVVVVVVVVVV 'VVV V VVV V VVVVV VVVV V V V V V VVV VVVV V V VVV V V V VVV VVV V VV V V V VVVV4 VVV V VVVVVV V 'VVVVVVVVVVVVVVVV V VVV VVVVVVVVVVVVVVV - /VVVVVVVVVVVVVVYVVVVVVVVVVVVVVVV 'V VV V V V V V VVV V V VV VVVVV VVV VVV #VVVVVVVVVVVVFVVVVVVVV 'V V V V V V V V V V Vj V V V V V V V V V V V V V V V V V V V VVVVVVVVVV4VVVVVVVVVVVVVVVVVVV V V V V V V V V 4\V V V V V V V V V V V V V V V V V V V VVVVV VVV4.IVVV VVVVVVV VVVVVVVV + - IVVV VV V VI? V V VV V VV V V V V VV VVVVV ?VV VV V V V V V V V V V VVVV V VVV V V + 4 4. + 4' ± + 4' + + + 4 4 + 'VVVVV"' 4' + 4 + + + 4 4 + + + + + 4' VVVVVVVVVVVVVVVVV 'VVVVVVVVVVVVVV + + 4. 4- 4' VVV VV VV VVV VV V V V VV + + + + 4' VVVVVV VVV V V VVVVVV V VVVVVVVVVVVVVVVVV + + 4. 4 + 4 + 4 + + + 4' + + PICK ÷ LAKE i + + 4 + + PICK LAKE f + 4' + 4 + 4 + 4 + '4.4.44. + + + + # + + + + + - + ALTER ATIC+ t,,_Z,,t.1 + + +4 + + + 4' + + + + 4• + + + + + + + , CASt + + + + C t' 4' SALM ALTERAn0N ZONE +4'++++++++++ + 4+ t + 4+4.4 .++ + + + + ,4 4+4 +4+4+4+ +44+444 + ++ + + 4 I - 4 4 4 ÷ + + ÷ + -' ÷ + 4 4'+ + + + + + + + # 4 Km 0 FELSIC TO INTERMEDIATE VOLCANICLSTIC GRANITE DIFFERENTIATED GABBRO SLLS Iiv- + LAKE AREA WINSTON MAP GEOLOGY Fl ure 7 APHYRIC "'i' MAFIC - SchreiberAssemblage Assemblage 5656 QUARTZ FELDSPAR PHRIC FLOW - QFP FLDW/SUBVOLCAIIC FLOWS FELDSPAR PHYRIC MAFIC FLOWS ALTER ATION -':': ':c—:- INTRUSION METASEDIMENTS WACKES S ARENITES MINERALIZEQ HORIZON �Hydrothermal Alteration Hydrothermal Alteration The recognition hydrothermally altered altered rocks at Winston Winston Lake by CFC CFC geologists geologistsin in the the late late recognition of hydrothermally 1970's led to the acquisition hrther exploration ultimately acquisition of the property, prompted further exploration work and led ultimately to the discovery of the Winston Lake and other deposits. The The occurrence occurrence of cordierite cordierite and orthoamphibole (anthophyllitelgedrite)or or sillimanite sillimanitewas was ascribed ascribed to syn-volcanic, syn-volcanic, hydrothermal hydrothermal orthoamphibole (anthophyllite/gedrite) metamorphism. Osterberg metasomatism and subsequent, subsequent, isochemical amphibolite-facies metamorphism. Osterberg (1993) (1993) has noted that approximately approximately50% 50Y0of of the the footwall footwall stratigraphy stratigraphy has has been altered altered in in sub-concordant sub-concordant to cross-stratal cross-strata! zones, presumably related related to to original, lithologic lithologic permeability. permeability. Other minerals that comprise the various various alteration alterationassemblages assemblagesinclude include tremolite-actinolite, tremolite-actinolite,biotite, biotite, muscovite! muscovite/ sericite, staurolite, staurolite, chlorite, chlorite, K-feldspar K-feldspar and and quartz. quartz. Hydrothermal alteration has greatly changed the primary lithogeochemistry. Mineralogic Hydrothermal Mineralogic variation variation in in altered alteredrocks rocks isisreflected reflectedby byvariable variableenrichment enrichmentof ofMgO, MgO,Fe2O3T, Fe203T,and 1(20, K20, as well as depletion CaO and and Na20 Na20(Osterberg (Osterberg 1993; 1993;Severin Severin and and Balint B a h t 1984 1984(Figures (Figures8A,B; depletion of of CaO 8A,B;Table Table3); 3); a!. 1990). Osterberg Severin et al. Osterberg(1993) (1993) noted noted that that all all major oxides, with the exception exception of Ti02 Ti02and A12O3, showsignificant significantmobility. mobility. Component changes, while similar A1203,show similar in each each alteration alterationtype, type, sillimanite 5 generally increase biotite << sillimanite staurolite 5 generally increase in the order: order: tremolite/actinolite tremolitelactinolite5 biotite ± staurolite anthophyllite/gedrite anthophyllitelgedrite(Osterberg (Osterberg 1993). 1993). Osterberg Osterberg (1993) (1993) has has envisaged envisaged aa multi-stage, multi-stage, syn-volcanic syn-volcanic hydrothermal hydrothermal model model at at Winston Winston Schreiber Assemblage Assemblage 57 Schreiber �Lake that involves involves at least least three three distinct distinct hydrothermal hydrothermal fluids, fluids, including: including: (1) seawater-based seawater-based fluids fluids that were primarily responsible responsible for Mg-enrichment, Mg-enrichment, (2) chemically chemically evolved evolved fluids fluids that reacted with the rocks rocks to produce produce stratiform stratiform zones zones of variable Fe-aluminous assemblages, and (3) metalliferous metalliferousfluids fluids that that were were base base metal-rich metal-rich and and probably otherwise otherwise similar similarto to chemically evolved evolved fluids. fluids. Schandi and Gorton Schandl Gorton (1991) (1991) identified identified REE-rich REE-rich monazite monazite and xenotime xenotime within within chiorite-sericitechlorite-sericitebiotite biotite alteration alterationaround around the the Winston Winston Lake Lake and and other other Precambrian Precambrianmassive massive sulphide sulphidedeposits. deposits. Intimate textural the alteration textural associations associations suggested suggested that these REE-enriched phosphates and the fluid at 2677 2677 2± 1Ma iMa (U-Pb assemblage minerals co-precipitated from a common fluid (U-Pb age age of monazite, monazite, Schandl Schandl et al. al. 1991). 1991). This interpretation interpretation conflicts conflicts with the widely accepted accepted model of synvolcanic synvolcanic alteration alteration by stating stating that that alteration alteration represents represents aa late, late, post-mineralization, post-mineralization, metasomatic metasomatic overprint. overprint. A U-Pb zircon age of 2723 ±2 2 2Ma Mafor forthe thehost hostrhyolite rhyoliteat at Winston Winston Lake Lake was was published published by by Schandl et al. (1991). (1991). Schreiber Assemblage Assemblage 58 Schreiber �PartialWhole WholeRock Rockand andTrace TraceElement ElementGeochemistry, Geochemistry,Winston WinstonLake Lake Volcanic Volcanic Rocks Rocks Table 3. Partial Lithology Lithology Si02 Si02 A1203 Al203 FeOT FeOT MgO MgO CaO CaO Na20 Na20 K20 1(20 Ti02 Ti02 Cu Cu Zn Zn WLH-FWF WLH-FWF 48.7 15.25 8.49 6.94 7.89 7.89 4.06 0.75 1.01 94 35 WLFlFWF* WLH-FWF* 34.3 19.72 11.83 19.85 0.80 0.80 1.12 1.88 1.26 104 50 MMF MMF 52.1 15.49 8.49 5.01 7.96 7.96 3.71 0.48 1.34 45 10 MMF* rnF* 51.2 14.69 10.00 11.57 0.11 0.11 0.54 1.39 0.89 109 43 F-IV F-IV 72.2 10.96 3.25 1.19 2.53 2.53 5.04 0.26 0.41 36 12 FIV* F-IV* 68.1 11.35 6.04 5.92 0.53 0.53 1.13 1.79 0.36 441 125 QFPRF QFPRF 77.3 12.18 1.63 0.32 1.23 1.23 6.06 0.09 0.23 3 7 QFPRF* QFPRF* 74.9 10.32 3.63 6.19 0.62 0.62 0.47 1.13 0.27 83 17 LF LF 46.7 18.00 10.51 5.06 7.25 7.25 3.59 1.67 0.94 233 21 LF* LF* 49.6 14.35 19.29 7.65 0.34 0.34 0.52 0.19 0.82 42 76 QFP QFP 74.6 11.43 2.22 0.91 1.88 1.88 4.16 0.65 0.30 5 23 QFP* QFP* 79.9 7.86 5.60 2.64 0.06 0.06 0.06 2.03 0.27 20 58 Gabbro Gabbro 50.9 14.30 11.60 7.94 11.10 11.10 1.85 0.30 0.76 Pyroxenite Pyroxenite 41.5 6.03 15.50 24.20 5.05 5.05 0.07 0.02 0.50 Key Key to to Abbreviations: Abbreviations: WLII-FWF FootwallMafic MaficFlow Flow WLH-FWF Footwall MMF Middle MiddleMafic MaficFlow Flow F-IV F-IV Felsic-Intermediate Felsic-IntermediateVolcaniclastics Volcaniclastics QFPRF QFPRF Quartz-Felsdspar-Phyric Quartz-Felsdspar-PhyricRhyolite fiyolite Flow LF LF 'Ladder" Mafic "Ladder" Mafic Flow Flow QFP QFP Quartz-Feldspar Quartz-Feldspar Porphyry Porphyry Hydrothermally (*). Hydrothermallyaltered alteredequivalents equivalentsare aremarked marked with with an an asterisk asterisk (*). Data Data from from Severin Severinand andBalint B a h t (1984). (1984).Some Someabbreviations abbreviationsfrom fromOsterberg Osterberg(1993). (1993). Schreiber Assemblage 59 Schreiber Assemblage 59 �Geochemical Geochemical Changes Changes with Alteration "Ladder" "Ladder" Mafic Mafic Flow Flow - Legend }LF LP Figure 8A. Geochemical Geochemicalchanges changesbetween between unaltered unaltered (LF) (LF) and and altered altered (LF*) (LF*) rocks, rocks, "Ladder't "Ladder" mafic flow. Data (1984). Datafrom from Severin Severin and and Balint B a h t (1984). Schreiber Assemblage Assemblage 60 60 - �Geochemical Changes Changes with with Alteration Alteration Geochemical Quartz-Feldspar-PhyricRhyolite RhyoliteFlow Flow Quartz-Feldspar-Phyric Legend 1QffPRF QFPRF — ,—.—.—.—.—;'. t Na20 K20 Figure 8B. 8B.Geochemical Geochemicalchanges changesbetween betweenunaltered unaltered(QFPRF) (QFPRF)and andaltered altered(QFPRF*) (QFPRF*)rocks, rocks, Figure quartz-feldspar-phyric rhyolite rhyolite flow. flow. Data Datafrom fromSeverin Severinand andBalint Balint(1984). (1984). quartz-feldspar-phyric SchreiberAssemblage Assemblage 61 61 Schreiber �Suiphide Ore Massive Sulphide The ore zone at Winston Winston Lake, Lake, as as described described by Severin Severin et al. (1990) and Balint B a h t et et a!. al. (1990), varies varies in in thickness from 2m to >20 m (horizontal), averaging 7m. Two Two main, main, apparently apparently unzoned, unzoned, ore ore types exist: exist: (1) "low-grade" "low-grade" (7-14% (7-14% Zn): - massive to locally banded, fine- to medium-grained - homogeneous mix of sphalerite, sphalerite, pyrrhotite, pyrrhotite, pyrite, chalcopyrite chalcopyrite - 10-20% included fragments fragments (<1-5 (<I-5 cm) (2) "high-grade" "high-grade"(5 ( 54% Zn): (2) 54% Zn): - massive, mediummedium- to coarse-grained coarse-grained sphalerite sphalerite - locally banded with chalcopyrite chalcopyrite andlor pyrrhotite Less conmion common metallic metallic minerals minerals include include magnetite, magnetite, marcasite, marcasite, arsenopyrite, arsenopyrite,mackinawite mackinawite and and galena galena (Barr 1991). galenobismutite(PbBi2S4)and and anhydrite anhydrite (Ban199 1). Bismuthinite Bismuthinite(Bi2S3), (Bi2S3),gladite gladite(CuPbBi5S9), (CuPbBi&), galenobismutite(PbBi&,) have also been identified identified by X-Ray diffraction diffraction analysis analysis (Resident (Resident Geologist's Geologist's Files, Files, Schreiber-Hemlo Schreiber-Hemlo andtellurobismuthite tellurobismuthite(Bi2Te3) (Bi2Te3)have have also also been been District, Thunder Thunder Bay). Bay). Hessite Hessite(Ag2Te), (Ag2Te),native nativesilver silverand noted, as have the spinels spinels franklinite, franklinite, chromite chromite and and gahnite. gahnite. Schreiber Assemblage Assemblage 62 Schreiber 62 �of the the ore ore zone zone corresponds corresponds to to the the thickest thickest portion portion of of the the footwall footwall alteration alterationzone. zone. The thickest thickest part of There is no apparent zinc and copper zonation within the deposit, although although there there is is evidence evidence of of remobilization concentricallyzoned, zoned,sulphide-filled sulphide-filledcavity cavity was was discovered discovered remobilization on a small scale. scale. AAconcentrically during mining operations in 1992 chimney, akin akin to to "black 1992 and has been interpreted as a sulphide chimney, smokers" of modem consists of aa chalcopyrite-rich chalcopyrite-rich core, core, a modern oceanic hydrothermal systems. ItIt consists crystals. Sulphur sphalerite zone and an outer zone of large selenite crystals. Sulphur isotope analyses of the massive suiphide and selenite-rich values of -0.6 %o % and and ++13.1 (G. sulphide selenite-rich portions portions returned returnedo34S 634Svalues 13.1 %o, %, respectively (G. Doiron, Metal! Metal1 Mining Corporation, personal communication, 1995). Samples Samples of of massive massive suiphide sulphide anhydrite from the Geco valuesof of+0.5 +0.5 and and +10.0 +10.0,, and anhydrite Geco Mine, Mine, Manitouwadge, Manitouwadge, returned similar similar o34S 6^S values respectively (Franklin (Franklinetetal. al.1981). 1981).Most MostPrecambrian Precambrianmassive massivesuiphide sulphidedeposits depositsyield yield ore ore suiphide sulphide 0% (close values close to 0%0 (close to the "mantle" "mantle" composition). Metamorphism Metamorphism precludes reasonable interpretation of data data and isotopic isotopic disequilibria. disequilibria. metalliferous fluids fluids migrated migrated through through Osterberg (1993) proposed a metallogenetic model in which metalliferous altered rocks and were trapped under impermeable CLR cap rock. rock. Synvolcanic Synvolcanic faulting faulting allowed allowed environment, resulting resulting in the the these fluids fluids to migrate from the pressurized reservoir to the sea floor environment, repeated repeated precipitation precipitationof of massive massive ZnZn- and and Cu-sulphides. Cu-sulphides. Schreiber Assemblage Assemblage 63 Schreiber 63 �Individual Individual Stop Descriptions: Footwall Footwall Stratigraphy Stratigraphy The following that structurally and following stops stops exemplify both altered and unaltered footwall lithologies that massive sulphide suiphide deposit. deposit. These stops stratigraphically underlie the Winston Lake massive stops have been prepared and used on on numerous numerous field field trips trips and and therefore therefore their their descriptions descriptions have have been been largely largely gleaned gleaned Balint from previous workers, including including Balint B a h t et et a!. al. (1990), Severin Severin and B a h t (1984) and Severin Severin et et a!. al. (1990). (1 990). The Thestratigraphic stratigraphicand andvolcanological volcanologicalsetting setting of of the the individual individual field field stops stops has has been been described most recently and completely completely by Osterberg Osterberg (1993), (1993), whose lithologic lithologic nomenclature nomenclature (Table (Table 2) 2) will will be be descriptions. Refer Refer to toFigures Figures9A 9A and and 9B 9B for for stop stop locations. locations. adopted for these descriptions. STOP STOP 5A: 5A:Winston WinstonLake LakeHorizon Horizon/ /Hanging HangingWall WallGabbro GabbroContact Contact STOP 5B: Creek CreekCopper Copper Showing Showing STOP 5C: 5C: Altered Camp Flow Rhyolite STOP 5D: STOP 5D: Incipiently IncipientlyAltered AlteredLadder LadderFlow Flow /1Trail Trail Showing STOP STOP 5E: 5E: Altered AlteredPillowed PillowedLadder LadderFlow Flow STOP STOP 5F: 5F: "Main" "Main"Quartz-Feldspar Quartz-FeldsparPorphyry Porphyry Schreiber Assemblage 64 Schreiber Assemblage 64 �- _____ _____ _____ Figure 9A Figure 9A Winston Lake Lake Winston Detailed Surface Surface Geology Geology Detailed - 0 0 100 100 200 - 3 0 0 rn. 200 300 m. Winston Lake Deposit / / Projection 00—O 0 0 0 0 0 0 0 0 0000000000000 O000 000000000 000000000000000 0000000000000000 00000000000000000 000000000000 0000000000000°Trail°0 00 O oShowjn 0000000 0000000000 0000000 GAB B RO 0000000 00000000 META - PYROXENITE 00000000 000000000 V V VV MAFIC 000000000 FLOWS VVV 0000000000 000000 CHERTY ASH 000000 000000 FELSIC/ INTERMEDIATE 000000 VOLCANICLASTICS• 000000 000000 FELSIC TUFFS/SEDIMENTS 000000 000000 QUARTZ - FELDSPAR P1-lYRIC 000000 000000 RHYOLITE FLOW 0 00 0 0 0 000 QUARTZ - FELDSPAR 00000000 000 PORPHYRY 0000000 0000000 ALTERATION 000000 000000 '0000 5 D TOUR STOPS '000 Schreiber Assemblage 65 DO DO llII Creek Copper Showing • ,—• ,' \ / �Schreiber Assemblage 66 a 0 a 0 a 0 0 0 0 a 0 0 0 0 0 0 0 0 0 0 0 000000000 no 0000 00000 000000 00 0 0 a 0 000000 0000000 0000000 00000000 0000 000 0 0 d' 00 0 0 00 00000 00000 no 0 00 000 on 000.. 00 0000 no 0 Figure 9B Zn 30.0 gm/T 16.O0 100 %Cu Ag Au 0 500m. Winston Lake Deposit COMPOSITE SECTION LOOKING noon 0000000000 0000 0000 0000 0000 anon 0000 anon 000 000 000 000000000 000000 000000 000000 000000 0 0 0 0 0 0 0 0 ..,' 000000000 0000000.. 0000 00000 0000 0000 0 o CI 4' a 0 0 MASSIVE SULPHIDES ALTERATION PORPHYRY QUARTZ- FELDSPAR NNW 0 Io-1 a] QUARTZ- FELDSPAR PHYRIC RHYOLITE FLOW FELSIC TUFFS/SEDIMENTS FELSIC/ INTERMEDIATE VOLCAN ICLASTICS CHERTy ASH MAFIC FLOWS META- PYROXENITE GAB B RO �STOP STOP 5A: WINSTON LAKE HORIZON! HORIZON1 HANGING WALL GABBRO CONTACT This stop lies at the top of the Winston Footwall Block (WFB) where it is in contact with with gabbro of the Big Duck Sequence. Sequence. The Theuppermost uppermostpackage packageof of footwall footwall rocks, rocks, the the Winston Winston Lake Lake Horizon Horizon Succession (WLH), consists of volcanic volcanicand and volcaniclastic volcaniclastic rocks situated situated between the underlying underlying Clotted Rhyolite (WLH-CLR) (WLH-CLR) and and overlying overlying mafic flows flows and gabbro of the Big Duck Duck Sequence. Sequence. The Winston Lake massive suiphide m sulphide deposit is hosted by the WLH rocks, approximately 450 m down-dip along this contact. contact. The WLH WLHrocks rocksatatthis thissite siteare areinterepreted interepretedas asmixed mixedlaminated laminatedash ashand and exhalative exhalativesediments sedimentswhich which are thinly laminated and locally folded (WLH-CRT). They as fine-grained, fine-grained, recrystallized recrystallized They appear appear as and dark dark green. green. Their rocks which range in colour from white to creamy yellow, light and Their mineralogy is is variety of of accessory accessory minerals. minerals. Felsic dominated by quartz, plagioclase and lesser hornblende and a variety Felsic volcaniclastic/tuffaceous units predominate; minor cherty exhalites exhalites are are also also present. present. Pyrite to mafic volcaniclastic/tuffaceous Pyrite and pyrrhotite dominate, dominate, comprising comprising up to 20% of the rock locally. Near Near the the Winston Winston Lake Lake deposit, deposit, sphalerite-rich beds and massive magnetite have been noted. sphalerite-rich It has been noted noted by many many observers observersthat that this this exposure exposuredisplays displaysaa great great deal deal of of hitherto hitherto undescribed undescribed deformation, deformation, manifested manifested in in aa pervasive pervasive schistosity schistosity(locally (locally crenulated), crenulated),steeply steeplyplunging plungingmineral mineral lineations, chioritic chloritic shear planes and minor folds. ItIthas haseven evenbeen been suggested suggestedby by Williams Williams(personal (personal lineations, cornmuncation, 1988) that these these laminated laminated rocks represent a mylonitized mylonitized anorthosite anorthosite that that contains contains communcation, 1988) Schreiber Assemblage 67 Schreiber Assemblage 67 �very calcic plagioclase. There Therehave havealso alsobeen beensuggestions suggestionsof of dip-slip dip-slip movement movement and and thrusted thrusted contacts in this vicinity. vicinity. contacts STOP STOP 5B: 5B: CREEK COPPER COPPERSHOWING SHOWING CREEK This stop comprises comprises aa variety variety of of lithologic lithologic units, units, suiphide sulphide mineralization mineralization and and alteration-related alteration-related straddlesthe thecontact contactbetween between rocks rocks of of the the WLH WLH and volcaniclastic rocks of the features. ItItstraddles underlying Clotted Rhyolite (CLR). (CLR). Outcrops Outcropson onthe theeast eastside sideof of Selim SelimCreek Creek consist consist of of alternating alternating flows and thin, ashy sedimentary units. Gabbro Gabbro outcrops outcrops approximately approximately 10 10to to 15 15m m bands of mafic flows east of the creek. Volcaniclastic Volcaniclastic(CLR) (CLR)rocks rocksextend extendfrom from this this location location south south and and west west and and host host the the pyrite- and and chalcopyrite-bearing, chalcopyrite-bearing, Creek Creek suiphide sulphideshowing showing(gossan) (gossan) on on the the access access trail. trail. The mafic flows flows (WLH-MA) range in thickness thickness from from 2 to 33 m; most are between between 4 and and 10 10m m thick thick and uniform in thickness. They Theyare aretypically typically finefine- to to medium-grained, medium-grained, aphyric, aphyric, dark dark green-gray green-gray to black where fresh. Although Althoughprimary primary features features@illows, (pillows, sheet structures, hyaloclastite, autoclastic autoclastic breccias) are rare, long, long, pillow-like pillow-like structures structures have been been noted noted at at this this locality. locality. In the vicinity vicinity of the Winston Lake deposit, deposit, these these mafic mafic rocks rocks have been altered to a cordierite-anthophyllite-biotite cordierite-anthophyllite-biotite assemblage. assemblage. The CLR volcaniclastics volcaniclastics exposed exposed along along the the trail trail are are heterolithic, heterolithic, containing containing both both mafic mafic and and felsic felsic Schreiber Assemblage Assemblage 68 68 �(quartz-phyric) elongate, flattened fragments ranging in Finely laminated laminated in size from from 44 to to 100 cm. cm. Finely sections are also present. The Themajority majorityof of the the CLR CLR has has been been interpreted interpreted as as aa felsic felsic pyroclastic pyroclastic flow. flow. Incipient hydrothermal alteration alteration has has affected affected the mafic mafic component, component, smaller smaller felsic felsic fragments fragmentsand and ash ash component Relatively unaltered, unaltered, felsic felsic component to produce a biotite-cordierite-anthophyllite biotite-cordierite-anthophyllite assemblage. Relatively lenses may therefore therefore be preserved preserved in in aa dark, dark, altered altered matrix, matrix, producing producing what has has been been locally locally termed termed aa clastic protolith. protolith. "pseudo-fragmental" texture texture that that is is not not necessarily necessarily predicated upon upon aa primary primary clastic "pseudo-fragmental" STOP STOP SC: 5C: ALTERED CAMP FLOW RHYOLITE RHYOLITE Felsic rocks of the Camp Flow Flow rhyolite (QFF), thought to represent massive lava flows, outcrop on the access trail immediately immediately west of the mine road. This Thisunit unit isis laterally laterally extensive extensive (>5 (>5 km) km) but but relatively thin (50 (50 to 200 200 m). Phenocrysts Phenocrystsof ofquartz quartzand andplagioclase plagioclaserange range in in size size from from 11to to 33 mm mm quartzo-feldspathic matrix. matrix. The and are set in a fine- to medium-grained, recrystallized, quartzo-feldspathic The recognition of individual flow flow units units is is precluded precluded by by shearing, shearing, recrystallization recrystallization and and hydrothermal hydrothermal alteration. alteration. Compositional banding developed in mafic minerals (biotite, hornblende, hornblende, magnetite) magnetite) may may represent represent flow banding. Such Suchbanding bandingisisexposed exposedin inaaroadside roadsideexposure exposureacross across from from the the Cleaver Cleaver Lake Lake campsite. Unaltered QFF rocks vary vary from from tan tan to pale pale gray, gray, while while their altered altered counterparts counterparts may may be be bright bright white white (sericite-rich) or brownish (biotite-rich). With Withincreasing increasinghydrothermal hydrothermal alteration alterationthese these rocks rocks may may Schreiber Assemblage Assemblage 69 69 �contain: contain: (1) Quartz Quartz -- Muscovite Muscovite -- Biotite Biotite ++ Feldspar Feldspar (2) Quartz Cordierite -- Sillimanite Sillimanite -- Biotite Biotite ++ Staurolite Staurolite ++ Garnet Garnet Quartz -- Cordierite (3) (3) Quartz Quartz -- Cordierite Cordierite -- Anthophyllite Anthophyllite ++ Sillimanite Sillimanite ++ Staurolite Staurolite ++ Garnet Garnet Where exposed exposedalong alongthe thetrail, trail,QFF QFFrocks rocksare arevariably variablyaltered. altered.Large Large(_<2.5 (52.5 cm) cm) dark darkred red Where porphyroblasts of of garnet garnet and and smaller, smaller,honey-brown honey-brownstaurolite stauroliteporphyroblasts porphyroblasts occur occur in in the the more more porphyroblasts outcrop. Fine-grained, Fine-grained,whitish-pink whitish-pinkandalusite andalusiteporphyroblasts porphyroblastsoccur occur in in aa pervasively pervasively easterly outcrop. sericitized matrix matrix at the outcrop outcrop west along the trail. Intense Intensebiotitization biotitization characterizes characterizes altered altered core core sericitized samples samples at at the the site. site. It is notable that altered altered rocks containing containing in excess excess of 30% 30% biotite biotite (perhaps (perhaps regarded 75% Si02. SiO,. regarded as as "mafic") "mafic")still still contain containapproximately approximately75% STOP STOP5D: 5D: INCIPIENTLY INCIPIENTLYALTERED ALTERED LADDER LADDER FLOW FLOW / TRAIL TRAIL SHOWING SHOWING The Ladder Ladder Flow Flow (LF) (LF) is is aa 20 20 to to 200 200 m m thick thick series series of of mafic mafic rocks rocks consisting consisting of of thin thin sheet sheetflows, flows, thicker massive hyaloclastite. No massive flows flows and flow flow lobes, pillow lava, pillow breccia and hyaloclastite. No obvious obvious discernable discernable facies facies relationships exist. exist. Sharp Sharpcontacts contactsbetween between different different flow flow morphologies morphologies suggest suggest compound coarsecompound lava lava flows. flows. These Theselavas lavasvary varyfrom fromfine-grained, fine-grained,dark darkgrayish-green grayish-greento to mediummedium- to to coarsegrained, grained, greenish-brown, greenish-brown,altered alteredequivalents. equivalents. Schreibçr Assemblage 70 Schreiber Assemblage 70 �location, dark dark green green flows flowshost host 11 to Elongatepillows pillows At this location, to 55 mrn, mm, lathlike lathlike plagioclase plagioclase phenocrysts. phenocrysts. Elongate (feeders to lava lava lobes?) lobes?) display display local local budding budding and and re-entrant, re-entrant, hornblende-rich selvages. hornblende-rich selvages. zones usually very very rare, rare, occurs occurs as 10 to Hyaloclastite, usually as 10 to 20 20 cm cm wide, wide, 11 to to 55 m m long, long, discontinuous discontinuous zones 40 cm cm subsubbetween lobate, pillowed and massive flows. A A flow flow breccia, breccia, consisting consisting of of 20%. 10 to to 40 20%, 10 rounded to sub-angular sub-angular pillow fragments fragments occur occur at the base of the LF. Trailcopper coppershowing showingconsists consistsof ofaapyrite-, pyrite-, pyrrhotitepyrrhotite- and and chalcopyrite-bearing, chalcopyrite-bearing, felsic felsic interfiow interflow The Trail sedimentary unit (CT). ItItisisexposed exposedas as patches patches of of aa rusty-weathering, rusty-weathering, laminated, siliceous siliceous rock. 6230 ppm Cu Cu have have been been returned returned from from this this 0.15 0.15 rn m thick thick unit unit (Severin (Severinand and Balint Baht Values of up to 6230 1984). This This unit unit occurs occurs within within mafic mafic flows and between the quartz-feldsparporphyry porphyry (QFP) (QFP) the "Main" Main" quartz-feldspar Garnet occurs occurs within within the the altered altered base base of of this this unit unit and and is is and mafic flows farther south along the trail. Garnet displayed along along aa steeply steeply dipping dipping outcrop outcrop surface surface which which follows follows the the undulating undulating top top of of the the underlying underlying displayed lava flow. The Themafic maficlava lavaflows flowson on either either side side of of the the sedimentary sedimentary unit are partially altered to anthophyllite-biotite-cordierite+garnet assemblages. Hyaloclastic anthophyllite-biotite-cordierite+gamet Hyaloclastic units may be preferentially altered. ALTERED PILLOWED PILLOWED LADDER LADDER FLOW FLOW STOP SE! STOP 5E: ALTERED opportunity to view pervasively altered and This series of large large outcrops outcrops provides provides an an exceptional exceptional opportunity to view pervasively altered and 71 Schreiber Assemblage 71 �metamorphosed, undeformed, undeformed, pillowed basalt flows. East-younging, East-younging,metre-scale metre-scalepillows pillows have have metamorphosed, bladed to to sheaf-like sheaf-like recessive-weathering, biotite-altered biotite-altered selvages. selvages. Pillow cores coreshost hostcoarse coarse(55cm) (5cm) bladed anthophyllite and and blue-gray blue-gray cordierite cordierite porphyroblasts (Figure 13). Anthophyllite Anthophylliteand and cordieriite cordieriite anthophyllite have undergone undergone some some retrograde retrograde alteration alterationto to chlorite chlorite++ talc talc and pinite, respectively. Siliceous Siliceous occupy interpillow interpillow spaces. spaces. Further Furtherwest, west,garnet garnethas has pervasively pervasively(up (up to to 100% 100%garnet garnet++ material may occupy quartz) quartz) replaced primary, ovoid ovoid patches (selvages? lava tubes?) to cm) to produce coarse coarse (53.5 (3 .5 cm) porphyroblasts, porphyroblasts, armored armoredwith with biotite. biotite. STOP STOP 5F: 5F: "MAIN" "MAIN"QUARTZ-FELDSPAR QUARTZ-FELDSPARPORPHYRY PORPHYRY The "Main" "Main" QFP, QFP, confonnably conformablyoverlain overlainby by mafic mafic (LF) (LF) rocks, rocks, extends extends along strike for over 4.6 km and reaches an apparent map thickness of 11 km. ItItvaries variesin inappaearance appaearancefrom from tan tan to to pinkish-gray pinkish-gray to to gray-brown. gray-brown. Unaltered UnalteredQFP QFPisisremarkably remarkablyhomogeneous, homogeneous,massive massiveto to foliated, foliated,and and contains contains20 20 to to 50% 50% quartz quartz phenocrysts phenocrysts and and I1to to25% 25%lath-shaped, lath-shaped,feldspar feldsparcrystals. crystals. ItIthas hasbeen beeninterpreted, interpreted,ininpart, part, as as aa subaqueous, subaqueous, felsic felsic lava lava flow flow deposit. deposit. Alteration Alterationassemblages assemblagesin inthe the QFP QFPinclude: include: Quartz-Muscovite Quartz-Muscovite Quartz-Biotite-Sillimanite Quartz-Biotite-Sillimanite Cordierite-Quartz-Biotite-Sillimanite Cordierite-Quartz-Biotite-Sillimanite Cordierite-Quartz-Anthophyllite Cordierite-Quartz-Anthophyllite plus plus accessory accessorystaurolite, staurolite,garnet, garnet,spinel, spinel,magnetite, magnetite,zircon zirconand andrutile. rutile. Schreiber SchreiberAssemblage Assemblage 72 72 �REFERENCES REFERENCES Balint, F., Sim, R.C. and Morrison, Morrison, I.R. 1990. The Winston Lake massive sulphide deposit; deposit; in Mineral Deposits of Central Canada, Canadian Institute of of Mining Mining and and Metallurgy, Metallurgy, Field Field 1/6, p.63-78. Trip Guidebook Guidebook # 1/6, Barr, C. 1991. 1991. Application Application of of the the sphalerite sphalerite geobarometer geobarometer to the the Winston Winston Lake Lake massive massive sulfide sulfide unpublished B.Sc. deposit; unpublished B.Sc. thesis, thesis, Lakehead Lakehead University, University, Thunder Thunder Bay, Bay, Ontario, Ontario,34.p. 34p. Bartley, M.W. 1939. 1939. The The northwestern northwestern part part of of the the Schreiber Schreiber area; area; Ontario Ontario Department Department of of Mines, Mines, Annual Report, Report, 1938, 1938, v.47, v.47, pt.9, pt.9, p.29-40. p.29-40. -----. 1942. Duck-Aguasabon lakes area; Ontario Department Department of Mines, Mines, Annual Annual 1942. Geology of the Big Duck-Aguasabon . Report, 1940, v.49, v.49, pt.7, pt.7,p.1-11. p.1-li. Burnham, Burnham, C.W. C.W. and and Ohmoto, Ohmoto, H. H. 1980. 1980.Late-stage Late-stage processes processes of of felsic felsic magmatism; magmatism;Mining MiningGeology, Geology, p.1-11. Special Issue, no.8, p. 1-11. Carter, Carter, M.W. M.W. 1988. 1988.Geology Geology of of the the Schreiber-Terrace Schreiber-TerraceBay Bay area, area, District District of of Thunder Thunder Bay; Bay; Ontario Ontario Geological 2W7p. GeologicalSurvey, Survey,Open OpenFile FileReport Report5692, 5692,287~. Collins, W.H. 1909. 1909. Report Report on on the region region lying lying north north of of Lake Lake Superior Superior between the the Pic Pic and and Nipigon Rivers, Rivers, Ontario; Ontario;Geological Geological Survey Survey of of Canada, Canada, Publication PublicationNo.1081. No. 1081. Colvine, A.C., Fyon, A.J., A.J., Heather, Heather, K.B., Marmont, Marrnont, S., S., Smith, Smith, P.M. P.M. and and Troop, Troop, D.G. D.G. 1988. 1988. Archean lode gold deposits in Ontario; Ontario Geological Survey, Miscellaneous Paper deposits 1139, 3 9 ,l36p. 136~. Corfu, F. and Muir, T.L. T.L. 1989. 1989.The The Hemlo-Heron Hemlo-Heron Bay greenstone greenstone belt and and Hemlo Hemlo Au-Mo Au-Mo deposit, deposit, Superior Superior Province, Province, Ontario, Ontario, Canada Canada 1: 1: Sequence Sequence of igneous igneous activity activity determined determinedby by zircon zircon 83-200. U-Pb geochronology; geochronology;Chemical ChemicalGeology Geology(Isotope (IsotopeGeology GeologySection), Section),v.79, v.79,p.1 p. 183-200. Davis, D.W., Schandl, Schandl, E.S. E.S. and and Wasteneys, Wasteneys, H.A. H.A. 1994. 1994.U-Pb U-Pb dating dating of of minerals minerals in in alteration alterationhalos halos of Superior Superior Province Province massive massive sulphide sulphide deposits: deposits: syngenesis syngenesis vs. vs. metamorphism; metamorphism; Contributions Contributions to Mineralogy Mineralogy and and Petrology, Petrology, v.115, v.115, p.427-437. p.427-437. Dimroth, E. and Lichtblau, Noranda Lichtblau, A.P. 1979. 1979. Metamorphic evolution of Archean hyaloclastites, Noranda area, Quebec, Canada. Part I: Comparison of Archean and Cenozoic sea-floor metamorphism; metamorphism;Canadian CanadianJournal Journalof ofEarth EarthSciences, Sciences,v.v.16, 16,p.1 p. 1315-1340. 3 15- 1340. Y. 1978. Structure and and organization organization of of Dimroth, E., Cousineau, Cousineau, P., Leduc, M., and Sanschagrin, Y. Archean subaqueous subaqueous basalt flows, flows, Rouyn-Noranda Rouyn-Noranda area, Quebec, Canada; Canada; Canadian Canadian Journal of Earth Earth Sciences, Sciences, v.15, v. 15, p.902-918. Schreiber Assemblage 73 Schreiber Assemblage 73 �Fowler, AD., A.D.,Jensen, Jensen,L.S. L.S.and andPeloquin, Peloquin, S.A. S.A. 1987. 1987.Varioles in Archean basalts: Fowler, basalts: Products Products of of spherulitic crystallization; crystallization;Canadian Canadian Mineralogist, Mineralogist, v.25, p.275-289. p.275-289. spherulitic Fralick, P.W. P.W. and and Barrett, Barrett,T.J. T.J. 1991. 1991.Precambrian Precambrian depositional depositional systems systemsalong alongthe the southwestern southwestern Fralick, Superior craton; craton; Geological Geological Association of Canada-Mineralogical Canada-Mineralogical association association edge of the Superior of Canada-Society Canada-SocietyofofEconomic EconomicGeologists, Geologists,Joint JointAnnual AnnualMeeting, Meeting, Toronto Toronto'91, '91, Field Field of Trip Trip A3 A3 Guidebook, Guidebook, 54p. 54p. Fralick, P.W., P.W., Barrett, Barrett,T.J., T.J.,Jarvis, Jarvis, K.E., K.E.,Jarvis, Jarvis, I., I., Schnieders, Schnieders,B.R. B.R.and andVande VandeKemp, Kemp,R. R.1989. 1989. Fralick, Sulfide-faciesiron iron formation formation at at the the Archean Archean Morley Morley occurrence, occurrence, northwestern northwestern Ontario: Ontario: Sulfide-facies Contrasts Contrasts with with oceanic oceanic hydrothermal hydrothermal deposits; deposits; Canadian Canadian Mineralogist, Mineralogist,v.27, v.27, p.601-616. p.601-616. Franklin, Franklin, J.M., J.M., Lydon, Lydon, J.W. J.W. and and Sangster, Sangster, D.F. D.F. 1981. 1981.Volcanic-associated Volcanic-associated massive massive sulphide sulphide deposits; deposits; in in Seventy-fifth Seventy-fifthAnniversary Anniversary Volume, Volume, Economic Economic Geology, Geology, p. 485-627. 485-627. Fyon, J.A., J.A., Breaks, Breaks, F.W., F.W., Heather, Heather,K.B., K.B., Jackson, Jackson, S.L., S.L., Muir, Muir, T.L., T.L., Stott, Stott,G.M. G.M.and and Thurston, Thurston,P.C. P.C. 1991. 1991. 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The chemical variability of some common igenous rocks; Le Maitre, R.W. 1976. rocks; Journal Journal of Petrology, Petrology, v.17, v.17, p.589-637. p.589-637. ----- . 1989. 1989.A A classification classificationof of igneous igneous rocks rocks and and glossary glossary of of terms; terms; in in Recommendations Recommendationsof ofthe the . International Union Union of of Geological Geological sciences sciencesSubcommission Subcommission on on the the Systematics Systematicsof of Igneous Igneous International Rocks, Rocks, Blackwell Scientific Scientific Publications, Publications, Melbourne, l92p. 192p. Marmont, S. S. 1984. 1984.The The Terrace Terrace Bay Bay batholith batholith and and associated associated mineralization; mineralization;Ontario OntarioGeological Geological Marmont, Survey, 95p. 5514,95p. Survey, Open File Report 5514, Ontario Bedrock geology geology of of Ontario, Ontario, west-central west-central sheet; sheet;Ontario Ontario Ontario Geological GeologicalSurvey. 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S.A. 1993. 1993.Stratigraphy, Stratigraphy,physical physical volcanology volcanologyand andhydrothermal hydrothermalalteration alterationof ofthe the footwall footwall rocks rocks to to the the Winston WinstonLake Lakemassive massivesulfide sulfidedeposit, deposit,northwestern northwesternOntario; Ontario; unpublished unpublishedPh.D. Ph.D.thesis, thesis,University University of ofMinnesota-Duluth, Minnesota-Duluth,254 254p. p. Osterberg, Osterberg, S.A. S.A. and and Morrison, Morrison, I.R. I.R. 1991. 1991.Physical Physical volcanology volcanology of of the the footwall footwallrocks rocks at atthe the Winston Winston Lake Lake massive massive sulphide sulphidedeposit; deposit; Institute Institute on on Lake Lake Superior SuperiorGeology, Geology,Proceedings Proceedings and Abstracts p.82. Abstracts Volume, Volume, Part Part 1, 1,p.82. Patterson, Patterson, G.C., G.C., Mason, Mason, J.K. J.K. and and Schnieders, Schnieders,B.R. B.R. 1985. 1985.Thunder Thunder Bay Bay Resident ResidentGeologist Geologistarea, area, North North Central CentralRegion; Region; in in Report Report of of Activities, Activities, 1984, 1984, Regional and Resident Geologists, Geologists, Ontario Ontario Geological GeologicalSurvey, Survey, Miscellaneous Miscellaneous Paper Paper 122, 122,p.56-133. p.56- 133. Patterson, Patterson, G.C., G.C., Scott, Scott, J.F., J.F., Mason, Mason, J.K., Schnieders, B.R., MacTavish, A.D., Dutka, R.J.A., Kennedy, Kennedy, M.C., M.C., White, White, G.D. G.D. and and Hinz, Hinz, P. P. 1987. 1987.Thunder ThunderBay Bay Resident ResidentGeologist's Geologist'sarea; area;inin Report Report of of Activities, Activities,1986, 1986,Regional Regionaland andResident Resident Geologists, Geologists,Ontario OntarioGeological GeologicalSurvey, Survey, Miscellaneous MiscellaneousPaper Paper 134, 134,p.72-127. p.72-127. Percival, Percival, J.A. J.A. 1989. 1989.A A regional regionalperspective perspectiveof ofthe the Quetico Queticometasedimentary metasedimentarybelt, belt, Superior Superior Province, Canada; Canadian Journal of Earth Sciences, v.26, p.677-693. Province, Canada; Canadian Journal of Earth Sciences, v.26, p.677-693. Schreiber Assemblage Assemblage 75 75 �1964. Mineral Mineral deposits deposits of of the the Big Big Duck Duck Lake Lake area; area; Ontario Ontario Department Departmentof of Mines, Mines, Pye, E.G. 1964. 47p. Geological Report 27, 27,47p. -----. 1969. 1969. Geology Geology and and scenery, scenery, north north shore shore of of Lake Lake Superior; Superior; Ontario Ontario Department Department of of Mines, Mines, . Geological Guide Book Book 2, 2, 144p. l44p. (in progress). progress). Lithostratigraphy Lithostratigraphyand and geochemistry geochemistryof of the the McKellar McKellar Harbour Harbour area; area; Purdon, R. (in unpublished M.Sc. M.Sc. thesis, thesis, Lakehead Lakehead University, University, Thunder Thunder Bay. Bay. unpublished Naldrett, A.J. A.J. and and Eckstrand, Eckstrand,O.R. O.R. 1973. 1973.Archean Archean ultramfic ultramfic flows flows in in Munro Munro Township, Township, Pyke, D.R., Naldrett, Ontario; Geologiëal Geological Society Society of America Bulletin, v.84, p.955-978. 1991. Rocks and minerals minerals for for the collector: collector: Sudbury Sudbury to Winnipeg; Winnipeg; Geological Geological Survey Survey Sabina, A.P. 1991. of Canada,Miscellaneous Canada,MiscellaneousReport Report 44 Schandl, Schandi, E.S. and Gorton, M.P. 1991. Postore mobilization of rare rare earth earth elements elements at at Kidd Kidd Creek Creek and other Archean massive sulfide sulfide deposits; deposits; Economic Economic Geology, Geology, v.86, p.1546-1553. p. 1546-1553. Schandi, H.A. 1991. Geochronology Geochronology of of Schandl, E.S., Davis, D.W., Gorton, M.P. and Wasteneys, H.A. hydrothermal alteration around volcanic-hosted massive massive sulphide sulphide deposits deposits in in the the Superior Superior in Geoscience GeoscienceResearch ResearchGrant GrantProgram, Program,Summary Summaryof ofResearch Research1990-199 1990-1991,1, Province; in Ontario Geological Geological Survey, Survey, Miscellaneous Miscellaneous Paper Paper 156, 156, p.105-120. p. 105-120. Schnieders, B.R. 1987. 1987. The geology of sulfide-facies sulfide-facies iron formations formations and associated associated rocks in in the the lower Steel River-Little Steel Lake area, Terrace Bay, Ontario; unpublished M.Sc. thesis, Steel River-Little Steel Lake area, Terrace Ontario; unpublished M.Sc. thesis, Lakehead University, Thunder Bay, Ontario, l96p. 196p. Resident Geologist's Geologisfs District; in Report of Schnieders, B.R. and Smyk, M.C. 1994. Schreiber-Hemlo Resident Activities 1993, 1993, Resident Resident Geologists, Geologists,Ontario Ontario Geological GeologicalSurvey, Survey,Open Open File File Report Report 5892, 5892, p.80-lOS. p.80-105. Schnieders, B.R., Smyk, Smyk, M.C. and Speed, Speed, A.A. 1991. 1991. Field Field trip guidebook guidebook for for the the NipigonNipigonMarathon area; Ontario Geological Geological Survey, Survey, Open File Report 5763, 5763, 55p. 55p. of the the Winston Winston Lake Lake massive massive sulphide suiphide Severin, P.W.A. and Balint, F. 1984. The geological setting of deposit; Canadian Canadian Institute Institute of of Mining and and Metallurgy, Metallurgy, District District 44 Meeting Meeting Field Field trip, trip, l9p. October, 1984, 19p. Severin, P.W.A., Balint, Balint, F. F. and and Sim, Sim, R. R. 1990. 1990.Geological Geologicalsetting setting of of the the Winston Winston Lake Lake massive massive suiphide in Mineral Mineral deposits deposits of of the the western western Superior Superior Province, Province, Ontario, Ontario, 8th 8th sulphide deposit; deposit; in IAGOD Symposium, Symposium, Field Field Trip Trip Guidebook Guidebook #9, #9, p.58-73. p.58-73. Schreiber Assemblage Assemblage 76 Schreiber 76 �Thomas, D.A. D.A. 1991. 1991.The The application applicationof of mineralogy, mineralogy, whole whole rock rock chemistry chemistry and and mineral mineralchemistry chemistryto to Thomas, volcanogenic massive sulphide sulphide exploration exploration at the Winston Lake Zn-Cu deposit, deposit, volcanogenic massive northwestern Ontario; unpublished M.Sc. thesis, Queen's University, Kingston, Ontario, northwestern Ontario; unpublished M.Sc. thesis, Queen's University, Kingston, Ontario, 329p. Thurston, P.C. 1991. 1991. Archean Archean geology geology of of Ontario: Ontario: Introduction; Introduction;in in Geology Geology of of Ontario, Ontario, Ontario Ontario 1, p.26-57. Geological Survey, Survey, Special Special Volume 4, Part 1, Walker, J.W.R. 1956. 1956. Preliminary report report on on the geology geology of of the Jackfish-Middleton Jackfish-Middleton area; area; Ontario Ontario Department of Mines, Mines, Geological Geological Circular No.4, No.4,6p; accompanied by map, scale scale 1: 1:63 63 360. 360. 6p; accompanied -----. 1967. of the Jackfish-Middletonarea; area; Ontario Ontario Division Division of of Mines, Mines, Geological Geological Report Report 1967. Geology Geology of the Jackfish-Middleton . 50, 4lp. 50,41p. morphology of of ancient ancient and and modem modern Wells, G., Bryan, W.B. and Pearce, T.H. 1979. Comparative morphology pillow lavas; lavas; Journal Journal of of Geology, Geology, v.87, v.87, p.427-440. Williams, Williams, H.R. 1989. 1989.Geological Geologicalstudies studies in in the the Wabigoon, Wabigoon, Quetico Quetico and and Abitibi-Wawa Abitibi-Wawa subprovinces, subprovinces, Superior Superior Province Province of of Ontario, Ontario, with with emphasis emphasis on on the the structural structuraldevelopment development of the Beardmore-Geraldton belt; Ontario Ontario Geological Geological Survey, Survey, Open Open File File Report Report 5724, 5724, l89p. 189p. Williams, Williams, H.R. and Stott, Stott, G.M. 1991. 1991. Subprovince accretion in the southern Superior Province (or cross-section cross-section through through the the Wawa-Quetico-Wabigoon Wawa-Quetico-Wabigoon subprovincial subprovincialboundaries boundaries and and the the Beardmore-Geraldton Beardmore-Geraldtonbelt); belt); Geological Geological Association Association of of Canada-Mineralogical Canada-MineralogicalAssociation Association of Canada-Society Canada-Society of Economic Geologists, Joint Annual Meeting, Toronto '91, Field Trip B6 Guidebook, 26p. Williams, H.R., Stott, Stott, G.M., G.M., Heather, Heather, K.B., K.B ., Muir, Muir, T.L. T.L. and and Sage, Sage, R.P. R.P. 1991. 1991.Wawa Wawa subprovince; subprovince; in Geology of Ontario, Ontario, Ontario Ontario Geological Geological Survey, Survey, Special Special Volume 4, Part Part 1, 1, p.485-539. p.485-539. 0. 1994. 1994.Geological, Geological, geochemical geochemical and age age Zaleski, E. Peterson, V.L. and Van Breemen, 0. constraints constraints on base metal mineralization mineralization in in the Manitouwadge Manitouwadge greenstone greenstonebelt, belt, northwestern Ontario; in Current Current Research Research 1994-C, 1994-C, Geological Geological Survey Survey of of Canada, Canada, p.225p.225northwestern Ontario; in 235. 235. ----- . 1995. 1995. Geological Geological and and age age relationships relationshipsof of the margins margins of of the Manitouwadge Manitouwadge greenstone greenstonebelt belt . and the Wawa-Quetico in Current CurrentResearch Research Wawa-Quetico subprovince subprovince boundary, boundary, northwestern northwestern Ontario; Ontario; in 1995-C, Geological Geological Survey of Canada, p.35-44. Survey of Canada, p.35-44. Schreiber Assemblage 77 Schreiber Assemblage 77 �NOTES NOTES �NOTES NOTES � https://digitalcollections.lakeheadu.ca/files/original/ed5aa49809fd3764d2fca6d149c243fc.pdf 89cf4530938bfeb7fc00e2b97b962941 PDF Text Text GEOLOGY AND GOLD GOLD DEPOSITS DEPOSITS OF THE HEMLO AREA REVISED EDITION EDITION REVISED Compiled and Edited by T.L. B.R. Schnieders Schnieders and M.C. Smyk T.L. Muir, B.R. �Archean Archean Mafic Metavolcanics Granitoids Intermediate to toFeisic FelsicMetavolcanics Metavolcanics Intermediate and Related RelatedMetasediments Metasediments and Mafic Intrusions Intrusions Mafic Metasediments Metasediments Ultramafic Ultramafic Intrusions Intrusions Proterozoic Coidwell Complex (alkalic) Field to 29 29 not not Field Trip Trip Stop Stop (numbers (numbers 88 to shown 5) shown for for clarity: clarity: see see Figure Figure 5) Headframe: Headframe: Hemio Hemlo Deposit Deposit LL Lake Lake Figure14. 14. Location Locationmap map(inset) (inset) and and regional regionalgeology geology of of the the Hemlo-Heron Hemlo-HeronBay Bayarea. area. Figure STOPS 11to to 7, 7. and 30, 30,31 indicated. Other Otherstops stopsare areshown shownon onFigures Figures18 18and and19. 19. STOPS 31 are indicated. P.2701, P2702, P2738, P.2739). (Modified after OGS maps 2220, 2439, 2452, (Modified after OGS maps 2220,2439,2452, P.2701, P.2702, P.2738, P.2739). �Originally published published for the the Originally Geological Geological Association Association of of Canada Canada Mineralogical Association Canada Mineralogical Association of Canada Society of Economic Economic Geologists Geologists Joint Annual Annual Meeting, Meeting,1991 1991 Toronto, Ontario, Canada Canada Toronto, GEOLOGY AND GOLD GOLD DEPOSITS DEPOSITS OF THE HEMLO AREA REVISED REVISED EDITION EDITION Compiled and Edited Edited by by T.L. Muir 1, B.R. Schnieders Schnieders 22 and and M.C. Smyk T.L. 1, B.R. Smyk22 with contributions contributions from from A. Chong Chong 3,, P. Johnston3,, R. , D. I? Johnston R. Kusins Kusins 3, D. Mcllveen 3,, K. K. McNena McNena3and andG. G.Patterson Patterson 22 1 Ontario 1 Ontario Geological Geological Survey, 933 Ramsey Lake Road, Sudbury, Ontario Ontario P3E 6B5 2 Northern Development Developmentand and Mines, Mines, Resident ResidentGeologist's Geologist's Office, Office, 2 Ministry of Northern Schreiber-Hemlo District, 435 435 James James Street Street South, South, Thunder Thunder Bay, Bay, Ontario Ontario P7E P7E 6E3 6E3 Schreiber-Hemlo District, 3 Hemlo Gold Mines Mines Inc., Inc., Golden Golden Giant Giant Mine, Mine, P.O. P.O. Box 40, Marathon, Marathon,Ontario OntarioPOT POT 2E0 2E0 3 TORONTO 19jj GAC/AGC •M A C / A M C • SF6 SEG GACIAGC MA(/AMC Original published published with the permission permissionof V.G. VG. Milne, Original Milne, Director, Director, Ontario Ontario Geological Geological Survey Survey permission of J. Wood, Director, Revision published with the permission Director, Ontario Ontario Geological Geological Survey @ Copyright Copyright Geological GeologicalAssociation Associationof ofCanada, Canada,Toronto Toronto '91 '91 Committee Committee © �Cover Photograph: Photograph: Hemlo camp gold mines, summer summer 1989. 1989. Photograph courtesy of Ray Ray Ettinger. Ettinger. TORONTO '91 '91 FIELD TRIP COMMITTEE: COMMITTEE: TORONTO Chairman: R.M. R.M. Easton Easton Vice-Chairman: Vice-chairman: G.W. G.W. Johns Johns Guide Book Production: M.G. M.G. Easton Easton Other Assistance Provided Provided by: P. P. Hinz Hinz RECOMMENDED RECOMMENDEDCITATION: CITATION: Muir, T.L., Schnieders, Schnieders, B.R. B.R. and and Smyk, Smyk, M.C., M.C., (Compilers and and Editors), 1995, Geology and Gold Muir, T.L., Deposits of the Hemlo Area; Geological Association of Canada—Toronto'91, Hemlo Area; Geological Association of Canada-Toronto991, Hemlo Field Field Trip Trip Guidebook, 120p. 120p. Guidebook, PUBLISHED BY: PUBLISHED AND AND DISTRIBUTED DISTRIBUTED BY: Geological Association of of Canada Canada TORONTO '91 '91 Organizing Committee, do c/o Ontario Ontario Geological Geological Survey Survey Room 8056, 933 Ramsey 8056,933 Ramsey Lake Road Road Sudbury, Ontario Ontario Canada Canada P3E P3E 6B5 6B5 First edition, edition, printed printedApril April1991. 1991. Revised edition, edition, printed printedMarch March1995. 1995. Printed in Canada by Love Printing Service Ltd., Stittsville, Ontario Ontario �GEOLOGY AND GOLD GOLD DEPOSITS DEPOSITS OF THE HEMLO AREA TABLE TABLE OF OF CONTENTS CONTENTS Part 1: 1 1: Introduction Introduction ....................................................................................................................................................1 Schnieders and M.C. Smyk by TL. T.L.Muir, Muir, B.R. Schnieders Smyk Part 2: Exploration Exploration History History ....................................................................................................................................... 3 3 by B. R.. Schnieders Schnieders and C.. Smyk B.R and M. M.C Regional Geology Geology .......................................................................................................................................... 8 Part 3: Regional by TL. TL.Muir, Muir, B.R. B.R. Schnieders Schnieders and M.C. Smyk Property ...................................................................................................................................10 10 Part 4: Peekongay Property R.. Schnieders Schnieders and and M. C. Smyk Smyk by B. B.R M.C. Mineralization Types 10 Mineralization Types ................................................................................................................... 10 11 11 Main Zone Mineralization Mineralization .......................................................................................................... BayMine 11 Heron Bay Mine ............................................................................................................ 11 Bowhill Mines Bowhill Mines Trench ...................................................................................................12 12 Porphyry Porphyry Zone Zone .............................................................................................................................12 12 CZone 13 C Zone ........................................................................................................................................... 13 13 South South Zone Zone ................................................................................................................................... 13 14 14 Part 5: Hemlo Deposit Overview Overview ........................................................................................................................... by B.R. and T.L. TL. Muir B.R. Schnieders, Schnieders. M.C. Smyk and Part 6: Geology of the Golden 16 Golden Giant Mine and Golden Sceptre Orebody .................................................... 16 by R. R. Kusins, Kusins. A. A . Chong, Chong. P I? Johnston, Johnston. D. D.Mcllveen Mcllveen and and K. K.McNena McNena Introduction Introduction ..................................................................................................................................16 16 Mine Geology 16 Geology ............................................................................................................................... 16 Formation ................................................................................................19 Moose Lake Formation 19 Lower Mineralized MineralizedZone Zone (Unit (Unit 5) 5) .................................................................19 19 Footwall Footwall Schists Schists (Unit (Unit 3) 3) ...............................................................................19 19 Mafic Mafic Fragmental Fragmental (Unit (Unit 4) 4) .............................................;...............................20 Main Ore Zone (Unit (Unit 5) 5) .................................................................................20 20 Cedar Creek Formation 21 Formation ............................................................................................... 21 Intrusive Rocks Rocks ............................................................................................................. 21 21 Level Level Plan Plan Descriptions Descriptions ...............................................................................................22 22 4750 Main Main Drift ...............................................................................................22 22 4700 2W Crosscuts Crosscuts ...................................................27 4700 Sublevel SublevelPlan Plan— - OW, OW, 2W 27 Observations Observations ................................................................................................................. 29 29 Golden Sceptre Property Property ...........................................................................................................31 31 Discussion Discussion .................................................................................................................................... 32 32 Summary ...................................................................................................................................... 33 33 Part 7: Road Log for the Hemlo-Heron HemIo-Heron Bay Bay Area ............................................................................................... 34 by TL. TL. Muir Introduction 34 Introduction .................................................................................................................................. 34 Heron Heron Bay Bay Area Area Segment Segment (STOPS (STOPS 1-4) 1-4) ..................................................................................36 36 Hemlo Hemlo Area Segment Segment (STOPS (STOPS 5-31) 5-31) ....................................................................................... 43 43 Hemlo 91 Hemlo Deposit Deposit Segment: Segment: Williams Williams Property PropertyVisit Visit (STOPS (STOPS 32-35) 32-35) ....................................91 103 8: References References ................................................................................................................................................. 103 Part 8: 107 Photographs .............................................................................................................................................. 107 Part 9: Photographs �Introduction Introduction 1 THE HEMLO AREA AREA GEOLOGY AND GOLD DEPOSITS OF THE PART 1: INTRODUCTION INTRODUCTION by by TL. Muir, B.R. Schnieders Schnieders and T.L. Muir, B.R. and M.C. Smyk 35 km Marathon, Ontario, The Hemlo Hemlo gold gold deposit depositisislocated locatedroughly roughly35 kmeast eastof of the the Town Town of Marathon, Ontario,and andlies, lies, in in part, part, beneath beneaththe theTrans-Canada Trans-CanadaHighway Highway(Highway (Highway17) 17)(see (seeFigures Figures14 14and and19 19on on inside insidefront front and and back covers, respectively, and and Figure 21). 21). Estimates, Estimates, in in 1989, 1989, indicated indicated there were at at least least 80 million tonnes g/tAu Au(Harris (Harris 1989). 1989). The The deposit deposit is currently currently being million tonnes of of ore ore at at an average average grade grade of of 7.7 7.7 glt being mined by three companies: Teck-Corona Teck-CoronaOperating OperatingCorporation Corporation(David (DavidBell BellMine), Mine),Hemlo HemloGold Gold Mines (Golden Giant Mine), and Williams Williams Operating Operating Corporation Corporation (Williams mines Mines Inc. (Golden (Williams Mine). All All33 mines were 50 gold producers producers in the world world in 1992. 1992. Their Their standings were: Williams were ranked rankedin in the the top top50 standingswere: WilliamsMine, Mine, Golden Giant Mine, 19th; and David David Bell Bell Mine, Mine,49th. 49th. Collectively, Collectively, they 8th, 17th: Golden 19th; and they would would have haveplaced placed8th, accounting accounting for almost 4% of the total production production of of the the top top 50 50 gold gold producers. producers. Annual production from the 33 mines mines has has totaled totaled over over 11 million million ounces ounces for for the the last last66years years (Figure I), 1), for for aatotal total production, production, since commencing commencing operations (1989-1994) (Figure operationsin in1985, 1985, until untilthe the end end of 1994, of almost almost 9.5 9.5 million million ounces ounces (see Table Table1). 1). Production Production for the last 5 years years has has accounted accounted roughly for over one-half of Ontario's gold production production and and roughly roughly one-quarter one-quarter of of Canada's Canada's gold gold production. The total contained ore-grade gold of the deposit (mined and remaining) is about The total contained ore-grade gold of the deposit (mined and remaining) is about 20.69 million January 1, 1994. Ore reserve reserve and million ounces ouncesbased basedon on data data as as of January 1,1994. and grade grade estimates estimates(as (asof of January January 1, 1, 1995) 1995) are presented presentedininTable Table 2. 2. Table 1: 1: Hemlo Hemlo Deposit Deposit Gold Gold Production: Production:1985-1994 1985-1994 YEAR 1985 1985 1986 1986 1987 1987 1988 1988 1989 1989 1990 1990 1991 1991 1992 1992 1993 1993 1994 1994 TOTALS DAVID BELL MINE MINE 20,989 20,989 52,888 52,888 130,122 130.122 218,333 218,333 312,190 312.190 318,098 318,098 295,284 295,284 210,121 210,121 215,188 215,188 192,217 192,217 1,965,430 1,965,430 GOLDEN GIANT GIANT MINE MINE WILLIAMS WILLIAMS MINE MINE 10,369 10,369 98,155 98,155 254,545 254,545 369,300 369,300 336,700 336,700 378,400 378,400 435,300 435,300 443,438 443,438 451403 451,403 422,528 422,528 446,850 446,850 3,636,581 3,636,581 198,515 198,515 256,809 256,809 378,827 378,827 494,127 494,127 594,128 594,128 518,703 5 18,703 496,920 496,920 492,251 492,251 445,320 445,320 3,885,969 3,885,969 TOTAL TOTAL OUNCES 129,513 129,513 505,948 505,948 756,231 756,231 933,860 933,860 1,184,717 1,184,717 1,347,526 1,347526 1,257,425 1,257425 1,158,444 1,158,444 1,129,967 1,129,967 1,084,387 1,084,387 9,488,018 9,488,018 Table 2: Ore OreReserve Reserveand and Grade Grade Estimates Estimates Ore Reserves Reserves (tonnes) David David Bell BellMine Mine11 Golden Giant Golden Giant Mine Mine 22 Williams Mine Mine 3 I 4,956,219 4,956,219 10,582,000 10,582,000 30,890,000 30,890,000 Grade Grade (g/t Au) (g/t Au) 10.86 10.86 11.10 11.10 5.72 5.72 Mineable and diluted ore ore reserves, reserves, Dec. Dec.31, 31,1994; 1994;P. F?Desautels, Desautels, Chief Chief Geologist, Geologist, David David Bell BellMine, Mine,Teck-Corona Teck-Corona Operating Operatin! Corporation, ;orporation, personal personalcommunication, communication,1995. 1995. Total ore reserves reserves as as of of Dec. Dec.31, 31,1994; 1994;R. R.Kusins, Kusins,Chief ChiefGeologist, Geologist, Golden Golden Giant GiantMine, Mine,Hemlo HemloGold GoldMines MinesInc., Inc.,personal person! 2 Total ommunication,1995; 1995;includes includestonnages tonnagesofof99504 504463 463t t@@11.38 11.38g/t g/tAu Au(Golden (GoldenGiant GiantDeposit DepositNo. No.1),I)and ,and1 1077 077176 176t @ t @8.74 8.74glt communication, g/t AI Au (Quarter QuarterClaim). Claim). Total proven and reserves as as of of Dec. Dec. 31, 31,1994; 1994;J. Gray, Senior Geologist, williams WilliamsMine, Mine,Williams William and probable diluted ore reserves Senior Production Production Geologist, Operating )prating Corporation, Corporation,personal personal communication, communication,1995. 1995. �Geology Geology and Gold Deposits Deposits of the Hemlo Hemlo Area 2 The delineation of the Hemlo Hemlo deposit deposit in in the the early early 1980s 1980s spurred spurred an exploration exploration blitz blitz of of the the Schreiber-Hemlo greenstone belt. belt. Several Several years years later, although much more is known about the area, no other economic gold deposit has been found. However, However, the presence presence of of aa major major gold gold deposit within any belt carries with it the substantial possibility that additional deposits remain to deposit with the substantial possibility that be discovered. discovered. This deals mainly with the geology of the Hemlo deposit deposit vicinity, touches on vicinity, but but touches This field field trip trip guide guide deals mainlywith the geology some guide includes includes updated updated some other other interesting interestingoccurrences occurrencesas asfarwest farwestas asHeron HeronBay. The field trip guide and detailed descriptions of the Exploration Exploration History History of the Hemlo Hemlo area, area, brief brief overviews overviews of the Regional Regional Geology of the Hemlo area and the Hemlo deposit, a description of the the geology geology of of the the Golden orebody (both (both of of Hemlo Hemlo Gold Gold Mines Mines Inc.), Inc.), and a detailed Golden Giant Giant Mine Mine and and Golden Golden Sceptre Sceptre orebody Road Log for the Hemlo-Heron Bay area. area Although Hemlo-Heron Bay Althoughoriginally originallywritten writtenfor forthe theGAC-MAC-SEG GAC-MAC-SEG Toronto '91 meeting, the the guide guide has has been been updated, updated, and and serves servesas asaa 3-day 3-dayplanned plannedoverview overviewofofthe the Hemlo Hemlo deposit, deposit, or or reference referencefor for aa more more detailed, detailed, self-guided self-guidedtour. tour. We had had initially initially hoped hopedthat that contributions contributionsby bystaff stafffrom fromall all33mines minesininthe theHemlo Hemlocamp, camp,using usingaa common basis for documenting observations, would permit a preliminary 3-dimensional configuration deposit to be envisaged, particularly particularly in distributions as uration of of the deposit in terms terms of element and mineral distributions as well well as as lithologic, lithologic, structural, structural, metamorphic, metamorphic, and and alteration alteration features. This Thiswould wouldhave haveinvolved involvedaa significant significant additional additional work-load work-load for for geological geological mine mine staff, and, as such, it is is unfortunate unfortunate that that the the deposit represented here. However, a description of the However, adescription deposit component componentfrom from 22 of the mines cannot be represented central central and and westernmost westernmost part partof of the the deposit deposit is is presented, presented, in in this this field field guide, guide, by by staff at the Golden Golden Giant Mine a!. (1986), Mine (see (see Part Part 6). 6). Papers Papersby byWalford, Walford,Stephens Stephensetetal. (1986),and andWalford, Walford,Weicker, Weicker,and and Guthrie (1986) provide the most recent, detailed descriptions of the Williams Mine, as does the Guthrie (1986) Williams Mine, as paper by Burk eta!. etal. (1986) (1986) for the David David Bell Mine. Readers Readerswill will find find additional additional information information on on surface and subsurface geological features features of of the the Hemlo deposit deposit area in other subsurface geological other field field guides guides prepared prepared by by Patterson Patterson(1984), (1984), McMillan McMillanand andRobinson Robinson(1985), (1985), Harris Harris(1986a, (1986a, 1986c), 1986c), Harris Harris and and Muir (1987), and and Smyk Smyk eta!. etal.(1990). (1990). HEMLO HEMLO MINES, 1985-1994 1985-1994 1985 1985 1986 1986 1987 1987 1988 1988 1989 1989 1990 1990 1991 1991 1992 1992 1993 1993 1994 1994 Figure Figure1. 1. Hemlo Hemlo camp camp gold gold production productionfrom from 1985 1985 (initiation) (initiation)to to1994. 1994. �ExplorationHistory History Exploration 3 PART 2: 2: EXPLORATION EXPLORATIONHISTORY HISTORY PART by by B.R. B.R. Schnleders Schniedersand andM.C. M.C.Smyk Smyk Exploration dates back Explorationininthe theHemlo Hemloarea areadates backtoto1869 1869when whengold goldwas wasdiscovered discoveredby byMoses MosesPee-KongPee-KongGay reported activity there: Gaynear nearthe the present presenttown town of of Heron Heron Bay. Bell Bell (1873) reported there: pits pitsand andshafts shaftswere were reportedly reportedlysunk sunkon onauriferous auriferousquartz quartzveins veinsand andaasmall smallamount amountofofore orewas wasshipped shipped(The (TheWeekly Weekly Sentinel,Port PortArthur, Arthur,Ontario, Ontario,March March1,1,1889; 1889;McKellar McKellar1874). 1874). Sentinel, In Canadian Pacific Inthe the 1920s, 1920s, J. LeCours, a station agent agent with the Canadian Pacific Railway Railwayat at Hemlo Hemlo station, station, sank sanktest test pits pitson onaamineralized mineralizedshear shear zone zone "a "a few few hundred hundred feet north north of of the the station" station" (Bartley (Bartleyand and Page Page 1957), 1957), 6 km km southwest southwest of the the Hemlo Hemlo deposit. deposit. Reported Reportedassays assaysranged rangedfrom from0.22 0.22toto4.16 4.16 ounces gold per 1927; July ouncesgold perton ton(The (TheFort FortWilliam WilliamDaily DailyTimes TimesJournal, Journal,Fort FortWilliam, William,Ontario, Ontario,July July12, 12,1927; July 25, 1927). As on aamineralized 25,1927). Asreported reportedby byThomson Thomson(1933), (1933), atestpitwas a test pit wassunk sunkon mineralizedshear shearzone, zone,but butno no gold values were obtained. Additional work and assays for occurrences north and south of the gold values were obtained. Additional work and assays for occurrences north and south of the railway described (Canadian August12, 1927). At Ataboutthe railwaywere were also also described (Canadian Mining Mining Journal, August 12,1927). about thesame sametime, time, aagroup small quartz groupof of claims claimswas wasstaked stakedon onaasmall quartzvein veinjust justnorth northofofmile milepost post38 38(measured (measuredfrom fromWhite White River) was done (Bartley River)on on the the railway. railway. Some Somelow lowgold gold assays assays were were obtained, obtained, but but no no further further work workwas (Bartley andPage Page1957). 1957). and J.E. J.E. Thomson Thomson mapped mapped the the area areainin1930 1930and and1931 1931for for the theOntario OntarioDepartment DepartmentofofMines Mines (Thomson 1933). He recommended several Hemlo (Thomson1931, 1931,1933). He recommended severalareas, areas, including includingthe the area areanortheast northeastof of the the Hemlo station stationand andanother anotheraround aroundManitouwadge ManitouwadgeLake, Lake, for for further further exploration. exploration. In Bowhill Mines explored explored in vicinity of in the vicinity of Heron HeronBay Bay and and shipped shippedaa 500 500 lb. Ib. (227 (227 kg) kg) test test In1937, 1937, Bowhill sample sample which returned returned 0.30 0.30 ounce ounce gold gold per per ton ton and and1.53 1.53 ounces ounces silver silver per perton ton(Resident (Resident Geologist's Geologist'sFiles, Files,Ministry MinistryofofNorthern NorthernDevelopment Developmentand andMines, Mines,Thunder ThunderBay). Bay). In Inthe the early early1940s, 1940s,Zeb Zeb and and Simon Simon Moses Mosesof of Heron Heron Bay Bay noticed noticed"shiny "shinyminerals" minerals"ininthe therocks rocks on on the the north northside sideofofMoose MooseLake Lakewhile while checking checkingZeb's Zeb's father's father's (Peter (Peter Moses) Moses) trapline. They Theytold told Peter Peter Moses Moses who prospected prospected and and collected collected samples samples from from the area area in in 1944 1944(Peter (PeterMoses, Moses, prospector, prospector, Marathon, personal communication, 1990). Moses Moses discovered discovered aasiliceous, siliceous,minermineralized (Bartley alizedshear shearzone zone approximately approximatelyone-half one-halfmile mile(0.8 (0.8 km) km) north northof of mile milepost post 37 37 on the railway (Bartley and and Page Page 1957). 1957). Samples Samplesreturned returnedassays assaysupto up to0.415 0.415 ounce ounce gold gold perton per ton(Bartley (Bartleyand andPage Page1957; 1957; 1958). 1958). Peter PeterMoses Mosesapparently apparentlybrought brought the the showing showing to to the the attention attention of of Harry HarryOllmann Ollmannof of Heron Heron Bay, Bay, who in turn interested interestedDr. Dr. Jack Jack K. K. Williams Williams of Maryland. Maryland. Eleven Elevenclaims claimswere werestaked stakedinin1945: 1945: five Ollmann'sname namein inAugust, August, 1945, 1945, and and six were recorded recorded in in Williams' Williams' name name in in fivewere wererecorded recordedininOllmann's September, September, 1945 1945 (Mining (Mining Recorder's Recorder's Files, Ministry Ministry of Northern Northern Development Developmentand and Mines, Mines, Thunder Thunder Bay). Bay). The Theeleven elevenclaims claimsthey theystaked stakedand andstarted startedexploring, exploring,inin1945, 1945,became becameknown knownas asthe the Ollmann-Williams Ollmann-Williams property. Gold Goldvalues valueswere were encountered encounteredin inaa large largeshear shear zone zone and and during during the the next trenching, and and diamond diamond drilling drilling were were conducted. conducted. The next year, year, stripping, trenching, The program program of of X-Ray X-Ray diamond diamond drilling drilling was unsuccessful unsuccessful mainly mainly due to the the inefficient inefficient operation operationof of the themachine machine(Page (Page 1948), and and thus, thus, likely, likely, poor poor core corerecovery. recovery. 1948), In In the the spring spring of of 1946, 1946, consulting consultinggeologist geologistTrevor TrevorPage Pagestaked stakedaa group groupof of claims claimsadjoining adjoiningthe the Ollmann-Williams Ollmann-Williams property property on the east. These These claims, together with others others staked by associates including includingMoses MosesFisher Fisher(J.E. (J.E. Thomson's Thomson'sguide), guide),became becamepart partof of the the property propertyheld heldby byLake LakeSuperior Superior Mining (Bartleyand andPage Page1957, 1957, 1958). Samples Samples collected collectedby byPage Pageon onthe the Mining Corporation Corporation Limited Limited(Bartley newly newly staked staked ground ground assayed assayed from from trace trace to to 0.13 0.13 ounce gold per ton whereas whereas samples samples from the the Ollmann-Williams property reportedly returned up to 0.49 ounce gold per ton (Prospectus, Lake Ollmann-Williams property reportedly returned up to 0.49 ounce gold per ton (Prospectus, Lake �4 Geology Geologyand and Gold Gold Deposits Depositsof of the the Hemlo HemloArea Area Superior Superior Mining Mining Corporation Corporation Limited, Limited,1947). 1947). InIn1947, 1947, Lake Superior Superior Mining Mining Corporation Corporation Limited Limited was was formed formedand andcarried carriedout outmapping, mapping,trenching, trenching,chip chipand andchannel channelsampling, sampling,and andX-Ray X-Raydiamond diamond drilling drilling on on both both properties properties under under the direction direction of of Page. Page. Fifteen Fifteenand andthirteen thirteenX-Ray X-Raydiamond diamonddrill drill holes were drilled on the Ollmann-Williams and Lake Superior properties, respectively, on what holes drilled on the Ollmann-Williams and Lake Superior properties, respectively, on what was 947a, 1948). 1948). This drilling tested tested the the shear shear zone zone was termed termedthe theLake LakeSuperior SuperiorShear ShearZone Zone(Page (Page11947a, over over approximate approximate strike strike lengths lengthsof of600 600m m and and 500 500 m m on on the the Ollmann-Williams Ollmann-Williams and and Lake Lake Superior Superior properties, properties,respectively, respectively,and andestablished establishedthe the lateral lateralcontinuity continuityof of the the mineralized mineralizedshear shear zone zone over at at least least three three kilometres kilometreson onboth bothproperties properties(Resident (Resident Geologist's Geologist's Files, Files, Ministry Ministry of of Northern Northern Development Developmentand and Mines, Mines, Thunder ThunderBay). Bay). Page recognizedthat: that: Page (1947b) initially recognized "The "The main main mineral-bearing mineral-bearing structure structure consists consists of a quartz porphyry porphyry that that has has undergone undergone intense intense alteration alteration through through shearing, shearing, silicification silicification and and sericitization." sericitization." Page Page (1948) (1948) later later stated: stated: "The HemloFault Faultis is considered consideredto to be be the the most most important importantstructural structuralfeature featureas asititappears appears T h eHemlo to to bear bearaaclose closerelationship relationshiptotothe theLake LakeSuperior SuperiorShear ShearZone Zoneininwhich whichall allpresent presentgold gold discoveries discoveriesof ofeconomic economicinterest interesthave havebeen been found. With Withititalso alsoare are associated associatedporphyporphyries riessimilar similarto to those thoseof of the the shear shear zone. Probably Probablythe thegreatest greatestfeature featuretotodate datehas hasbeen beenthe the use use of of the the fault fault in in locating locatingthe theprojection projectionofofthe theore-bearing ore-bearingzone:' zone." Page HemloFault Faultwas was continuously continuouslytraceable traceableover overaadistance distanceofof Page(1949) (1949) suggested suggestedthat that the theHemlo 13 km. 13 km and and the the Lake Lake Superior SuperiorShear ShearZone Zone for for over over11 11 km. W.L.Greer, Resident Resident Geologist, Geologist, Department WL.Greer, Departmentofof Mines, Mines, Port Port Arthur, Arthur, Ontario Ontario noted in aa memorandum, 1949 (Resident Geologist's Files, Ministry of Northern Northern Development memorandum,dated datedJune June24, 24,1949 (Resident Geologist's Development and andMines, Mines,Thunder ThunderBay): Bay): 'Further drilling drillingand and trenching trenching should should be be done, done, particularly to to the the east east of of the the present present "Further drilling. 400feet feettotothe theeast, east,aa north-south north-southtrending trendingdiabase diabasedike dikecuts cutsacross across drilling.Here, Here,about about400 the theshearing shearingatatright rightangles. angles.ItItisispossible possiblethe thegold goldvalues valuesmay maybe bebetter betterconcentrated concentratedinin the theshear shearzone zonefor foraafew fewhundreds hundredsofoffeet feeton oneither eitherside sideofofthe thediabase." diabase." Ollmannand andWilliams' Williams'initial initialgrubstake grubstakemoney moneywas wasexhausted exhaustedduring duringthe thedrilling drillingprogram, program,and and Ollmann the thepair pairdecided decidedto topool pooltheir theireleven elevenclaims claims for for the the purpose purpose of patenting. patenting. Harry HarryOllmann Ollmanndied diedinin December 1947 1947 and the eleven eleven claims claims were were put put in in Williams' Williams' name name in intrust trustby bymutual mutualconsent consent December (Financial 1987). Other (FinancialPost, Post,August August3, 3,1987). Othergroups, groups,including includingNorthern NorthernCanada CanadaMines MinesLtd., Ltd.,had hadstaked staked presumed presumedstrike strikeextensions extensionsofofthe themineralized mineralizedzones zonesto tothe theeast eastof of the the properties properties(Page (Page1948). 1948). InIn 1948, Lake Lake Superior Superior Mining MiningCorporation CorporationLimited Limiteddrilled drilledfour fourholes holesto to the the southeast, southeast, south southof of Cedar Cedar 1948, Lake(see (seeFigure, Figure,inside insidefront frontcover) cover)on onclaims claimsstaked stakedby byZeb ZebRenshaw; Renshaw;no noassays assayswere werereported reported Lake (Resident (ResidentGeologist's Geologist'sFiles, Files,Ministry MinistryofofNorthern NorthernDevelopment Developmentand andMines, Mines,Thunder ThunderBay). Bay). Explorationon onthe theLake LakeSuperior SuperiorMining MiningCorporation Corporationproperty propertycontinued continuedinto intothe thespring springofof Exploration 1949, at at which which time time diamond diamond drilling drilling had had indicated indicated aamineralized mineralizedzone zone with with aastrike strikelength lengthofof 1949, 900 (2m) m)and andan an average averagegrade gradeof of 0.256 0.256 ounce ouncegold goldper per 900feet feet(275 (275m), m),an anaverage averagewidth widthofof6.5 6.5 feet feet(2 ton(Northern (NorthernMiner, Miner,April April21, 21,1949). Thiszone zonewas waslater laterreported reportedtotohave haveaastrike strikelength lengthof ofonly only ton 1949). This 200 m)(Northern (NorthernMiner, Miner,June June9,9,1949). 1949). 200feet feet(61 (61m) Bartleyand andPage Page(1957) (1957)noted noteddiscrepancies discrepanciesbetween betweendrill drillcore coreand anddrill drillsludge sludgeassays assaysinintwo two Bartley drill drillholes holesand andstated statedthat thatititwas wasaasignificant significantfeature: feature: 'Inone onecase, case,core coreassays assaysreturned returned0.327 0.327ounce ouncegold goldacross across8.3 8.3feet feet[2.5 [2.5m] m]while while30 30feet feet "In [9.1 m] m] of sludge returned 0.243 ounce ounce [gold [gold per per ton]. Inthe thesecond secondcase, case,core corereturned returned [9.1 sludge returned toni. In �Exploration Exploration History 5 ounce gold gold [per m], and and sludge sludge returned returned 0.594 0.315 ounce [per ton] across across 5.0 feet feet [1.5 [1.5 m], 0.594 [ounce [ouncegold gold per ton] ton] across across25 25feet feet[7.6 [7.6 m]." m]." Page (1949) related the mineralization mineralization to the observed observed structure: structure: "The 'Hemlo Break' is probably part of the Heron Bay Break which is recognized recognized as one 'Hemlo Break' is probably part Heron Breakwhich structural features associated associated with the Precambrian section of the large structural Precambriangeology geology in this section bodies with with which mineralization of the the Canadian Canadian Shield. Shield. Porphyry Porphyry bodies mineralization of of economic economic importance importance is associated associated have have been been guided guided in in their their emplacement emplacement by by this this regional regional structural pattern." Lake Superior Mining Corporation Limited had had diversified diversified their their exploration exploration program program and and discovered radioactive discovered radioactive zones zones (including (including the Herrick Herrick occurrence) occurrence) adjacent adjacent to to its its original originalproperty property (Northern Miner, June 9,1949). 9, 1949). Deeper and south of mile post 36 (Northern Deeper diamond diamond drilling drillingwas was initiated initiatedinin m), were were drilled drilled (Resident the fall of of 1949 1949 and and eventually eventually 10 10 holes, holes, totalling totalling 3761.5 3761.5 feet (1146.5 (1146.5 m), Geologist's Ministry of Northern Northern Development mineralized zone Geologist's Files, Ministry Developmentand and Mines, Thunder Bay). A mineralizedzone containing depth of with a calculated calculated width containing31 31 543 543 tons tons to to aadepth of 300 300 feet feet (91 m) with widthof of 8.8 8.8 feet feet(2.7 (2.7 m) m) and and a cut grade of 0.22 ounce ounce gold outlined (Northern 1950). Trenching cut grade gold per per ton ton was outlined (NorthernMiner, Miner,May May18, 18,1950). Trenchingof ofthe the strike extension of the mineralized zone to to the east extension of mineralized zone east near near the the Struthers Struthers railway railway station was was undertaken in position was secured secured by Lake Superior Superior Mining Corporation Corporation Limited undertaken in 1950 1950 when land position Limited (Resident Geologist's Files, Ministry Ministry of Northern Northern Development Developmentand and Mines, Mines,Thunder ThunderBay). Bay). Teck-HughesGold GoldMining MiningLimited Limitedoptioned optionedthe the Lake Lake Superior Superior property property and comIn 1951, 1951, Teck-Hughes Files, Ministry Ministry of of pleted 6 diamond drill holes totalling 2733 feet (833 m) (Mining Recorder's Recorder's Files, Northern Development and Mines, Mines, Thunder Thunder Bay) Bay) in in addition addition to the over Development and over 6000 6000 feet feet of of drilling drilling completed to that time by by Lake Lake Superior Superior Mining Corporation Limited. The Thesize sizeofofzone zoneNo. No.11 (formerly increased to 76 76653 grade of 0.27 ounce gold per ton (Northern (Northern 'A zone) was increased 653 tons tons at at aagrade (formerlythe the 'A 25, 1951). One Miner, January 25,1951). One of the holes holes missed missed what what is is now now the the main main Hemlo Hemlo ore ore zone zone by by less less than 30 m (Patterson (Patterson 1985). 1985). The The prevailing prevailingUS$35 US$35 per per ounce ounce gold price price and and the the relatively relativelylow low grade precluded further work for Teck Exploration Exploration Company for the the next next few few years. years. In 1957, 1957, Teck Company Ltd. Ltd. carried packsack diamond diamond drilling. Seven Sevenholes holestotalling totalling289 289feet feet(88 (88m) m) were were drilled drilledin in carried out out some packsack the footwall footwall mineralized mineralized zone zone ('B ('B zone') which which returned returned values values ranging ranging from from trace trace to to 0.04 0.04 ounce ounce gold per per ton ton (Resident (Resident Geologist's Geologist's Files, Files, Ministry Ministry of of Northern NorthernDevelopment Developmentand andMines, Mines,Thunder Thunder Bay). Bay). M.W. T.W. Page Pagewrote wrote aageological geological report report on the Hemlo area (Bartley M.W. Bartley and T.W. (Bartley and and Page Page for the the Canadian Canadian Pacific Railway 1957) for Railway and stated: "The section from Hemlo attention Hemlo to Struthers has received considerable prospecting attention to date, and its potential depends mainly on further exploration ...'I. Cusco Mines Mines Ltd. optioned the the ground ground from Lake Lake Superior Mining Corporation Limited Limited in in 1958 and and carried carried out out diamond drilling drilling to test the main 1958 main mineralized mineralized zone zone which which contained contained an an estimated estimated 71 000 tons averaging averaging 0.22 0.22 ounce ounce gold gold per per ton ton within withinaazone zone550 550feet feet(168 (168m) m)long, long,10 10feet feet (3 (3m) m) thick, and and 300 300 feet feet (91 (91 m) deep (Northern (Northern Miner, Miner, October October 23, 1958). 1958). The Theprogram's program'sresults resultswere were "inconclusive" "inconclusive" but but sufficient sufficient mineralization mineralizationwas encountered encountered to maintain maintain interest interest (Northern (Northern Miner, November 5, 1959). November 5, 1959). As no exploration had had recently recently been been undertaken undertaken on on the the Williams Williams property, property, aa caution caution (lien (lien by Harry Ollmann's Ollmann's brother brother to to protect protect his against title) was filed on the eleven claims, in 1955, by interest. interest. Williams Williams died died that that year year and and his his lawyers lawyers attempted in vain to clear up the partnership partnership agreement. The 1987, agreement. Thecaution cautionwas wasstricken strickenfrom fromthe theclaim claimblock blockinin1970 1970(Financial (FinancialPost, Post,August August3,3,1987, p.1-2). �6 Geology Geologyand andGold GoldDeposits Depositsofofthe theHemlo HemloArea Area The TheLake LakeSuperior Superiorproperty propertyhad hadbeen beenstaked stakedintermittently intermittentlyby byprospectors prospectorsduring duringthe the1960s. 1960s. Walter west ground in in 1961, WalterBaker, Baker,accompanied accompaniedbybyhis hisson, son,Nelson, Nelson,prospected prospected westofofthe theWilliams Williams ground 1961,on on what whatbecame becamethe the Golden GoldenSceptre Sceptreproperty. property.Several Severalgold golddiscoveries discoverieswere weremade madeon onsurface surfaceand and goldwas waspanned pannedininthe thesandy sandyloam loamoverburden overburden(Nelson (NelsonBaker, Baker, prospector, prospector,personal personalcommunicacommunicagold tion, tion,1990). 1990).These Theseoccurrences occurrenceswere wereinvestigated investigatedininthe thenext nextfew fewyears yearswith withtrenching trenchingand andX-ray X-ray drilling, drilling,ininpart partfunded fundedby byFred FredJowsey. Jowsey. Visible Visiblegold goldwas wasreported reportedininthe thedrill drillcores cores(Lefolii (Lefolii1987). 1987). Stairs StairsExploration Explorationand andMining MiningCompany CompanyLtd. Ltd.funded fundedaaprogram programof ofsoil soilsampling samplingand andprospecting prospectinginin H.Hansen Hansenand andD. D.Michano Michano(Harris (HarrisHansen, Hansen,prospector, prospector,personal personal 1964and and 1965 1965 conducted conducted by byH. 1964 communication,1990). 1990). communication, The The Lake LakeSuperior Superiorproperty propertywas wasstaked stakedby byJ.E. J.E. Halonen Halonenin in1973 1973 for for Ardel Ardel Explorations ExplorationsLtd. Ltd. who whodrilled drilledthree threeholes holestotalling totalling789.9 789.9feet feet(241 (241m) m)(Resident (ResidentGeologist's Geologist'sFiles, Files,Ministry MinistryofofNorthern Northern Development Development and and Mines, Mines, Thunder Thunder Bay). Bay). The Thedeposit deposittonnage tonnagewas wasincreased increasedtoto150 150000 000tons tons grading 1973). grading0.21 0.21ounce ouncegold goldper perton tonabove above60 60feet feet(18 (18m) m)depth depth(Northern (NorthernMiner, Miner,November November8,8,1973). Ardel Ardeldropped droppedthe theclaims claimsand andwas waslater laterfollowed followedby byCypress CypressResources ResourcesLtd. Ltd. Claims property and Claimswere werestaked stakedby byR.G. R.G. Newman Newmanin in1976 1976 west of the Williams property and investigated investigated byCopper CopperLake LakeExplorations ExplorationsLtd. Ltd.inin1977. 1977. Soil Soil and and rock rockgeochemical geochemicalsampling samplingsucceeded succeededinin by identifying zone of identifyingaazone of anomalous anomalousgold goldvalues values(up (up to to 10000 10 000ppb) ppb)roughly roughlycoincident coincidentwith withthe thecontact contact between between metasedimentary metasedimentaryand andquartz-feldspar-porphyritic quartz-feldspar-porphyriticrocks rocks(Resident (ResidentGeologist's Geologist'sFiles, Files, Ministryof ofNorthern NorthernDevelopment Developmentand andMines, Mines,Thunder ThunderBay). Bay). Ministry T.L. T.L. Muir Muir of the the Ontario OntarioGeological GeologicalSurvey Surveymapped mappedthe theHeron HeronBay Bayand andHemlo Hemloareas areasinin1977 1977 In addition to summarizing the area's exploration and1978, 1978,respectively respectively(Muir (Muir1982a, 1982a,1982b). 1982b). In addition to summarizing the area's exploration and activity activity and and economic economic potential, potential, Muir Muir reported reported an an occurrence, occurrence, presently presently referred referred to to as asthe the "Highway Hemlo "HighwayZone", Zone", in in altered altered felsic felsic metavolcanic metavolcanicrocks rocksseveral several kilometres kilometreswest west of of the themain mainHemlo deposit. deposit.This Thisoccurrence occurrenceisisprobably probablyininthe the vicinity vicinityof of the the mile mile post post 38 discovery of the 1920s. A A grab grabsample samplereturned returned0.32 0.32 ounce ouncegold goldper perton tonand and0.48 0.48 ounce ounce silver silver per per ton ton (Muir (Muir 1982b). 1982b). Claim Claim stakers stakersand andexplorationists explorationistswould wouldlater laterbase basemuch muchof of their their land land acquisition acquisitionduring duringthe the staking stakingrush rush on Muir's Muir's maps. maps. on Various Hemlo camp camp have havebeen beenoffered offered by by Various accounts accounts of of the the recent recent developments developments in in the the Hemlo Patterson Patterson(1983, (1983,1984), 1984),Knoll Knoll(1984), (1984),Hart Hart(1985a, (1985a,1985b), 1985b),Lefolii Lefolii(1987) (1987)and andBittler Bittler(1988), (1988),among among others. others. The Thefollowing followingsynopsis synopsisdraws drawsupon uponthese theseand andother othersources, sources,published publishedand andunpublished, unpublished, including includingthe the Resident ResidentGeologists Geologist'sFiles Files(Ministry (Ministryof of Northern NorthernDevelopment Developmentand andMines, Mines,Thunder Thunder Bay). Bay). Beginning Beginning in in December, December, 1979, 1979, prospectors prospectors Donald McKinnon and John Larche staked staked the the claims claims surrounding surroundingthe the 11 11 patented patented Williams Williams claims. claims. The Thetwo twomen menagreed agreedto topool pooltheir theirclaims claimsin inaa partnership partnershipand and unsuccessfully unsuccessfullytried tried to find a potential optioner. In InSeptember September 1980, 1980, an optioner finally found found in in the the form formof ofCorona CoronaResources ResourcesLtd., Ltd., aaVancouver-based Vancouver-based junior exploration exploration was finally company which later later became became International InternationalCorona CoronaResources ResourcesLimited. Limited. Following Following preliminary preliminary company linecutting linecuttingand and geophysical geophysicalsurveys surveysin inlate late1980, 1980, Corona Coronabegan began aa $600 $600 000 000 drilling drilling program, program, in in January supervision of consulting consulting geologist, David January1981, 1981, under the supervision David Bell. In InMarch, March,R. R. Hughes Hughesand and F. optioned 156 partnership's claims F. Lang optioned 156 of the partnership's claims which which lie lie to the the east east and and west of the Williams Williams and and Corona Corona properties. properties. These Theseclaims claimswere wereput putinto intothe theholding holdingofoftheir theircompanies, companies,Golden GoldenSceptre Sceptre ResourcesLtd. Ltd. and and Goliath Goliath Gold Gold Mines Mines Ltd., who subsequently relinquishedcontrolling controllinginterest interestto to Resources subsequently relinquished Noranda Exploration ExplorationCompany CompanyLtd. Ltd. Noranda In representatives of LAC Minerals Ltd. visited Corona's In May, May, 1981, 1981, representatives Corona's drill drill site site and and exchanged exchanged information pursuant to a possible joint-venture agreement. While negotiations with Williams' possible joint-venture agreement. While negotiations Williams' �Exploration History 7 7 widow in in Maryland Maryland for for the the Williams Williams property propertywere were ongoing, ongoing, diamond diamonddrilling drilling was was stepped steppedback backto to the outlined deposit. deposit. Drill section grading the east east of the outlined Drillhole hole76 76 intersected intersectedaa10.5-foot 10.5-foot (3.2 m) section grading 0.209 ounce depth ofof336.5 Hemlo ounce gold gold perton per tonata at adepth 336.5feet(102.5 feet (102.5m). m).This Thisnew, new,separate separatezone zonewas was the the main main Hemlo orebody. orebody. By ByAugust, August,120 120drill drillholes holestotalling totalling43 43000 000feet feet(13 (13106 106m) m) had had delineated delineated750 750000 000tons tonsof of rock ounce gold gold per per ton ton in in the the 'West' 'West' zone zone and and had had begun begunto to indicate indicate the much much larger rock grading grading 0.10 0.10 ounce reserves 1981). Corona reserves of of the the 'East' 'East' or or main mainzone zone (Northern (NorthernMiner, Miner, August August 13, 13,1981). Coronashares, shares,buoyed buoyedup up by the new discovery, soared from less than $2 to $34 by year-end. The Hemlo gold rush, new discovery, soared from less than $2 year-end. The Hemlo gold rush, ultimately 7000new newclaims claimswere were staked stakedin in the the area area by by the ultimatelyinvolving involving180 180 companies, companies, ensued. ensued. Over Over7000 end end of of 1982. 1982. Both Corona and LAG had been been actively actively negotiating negotiating for the the Williams property. In LAC had In July, July, Mrs. Williams accepted LAC's offer. Corona, citing a breach LAC'S offer. breach of a fiduciary agreement, agreement, sued LAC LAC for ownership of the Williams claims. Teck Teck Corporation Corporation subsequently subsequently entered entered into into aa joint joint venture venture agreement with Corona to develop what what would would become the David Corona in in December, December, 1981 to David Bell Mine, presently presently controlled controlled by by the the Teck-Corona Teck-Corona Operating Operating Corporation. Corporation. In August 1982, LAC LAG announced announced the the discovery of of the deposit deposit on on their their property, property,which whichwould would become known known as as the thePage-Williams Page-WilliamsMine. Mine. Drilling Drilling by Goliath Gold Gold Mines Mines intersected intersected the the northward-dipping northward-dippingextension extensionof of the the ore ore zone. The The Goliath Goliathpart partof of the the deposit depositbecame, became,after afteraajoint joint venture with with Noranda Noranda Exploration ExplorationCompany Company Limited, Limited, the the Golden GoldenGiant GiantMine. Mine. In January, January,1987, 1987, ownership of the Golden Golden Giant Giant Mine Mine was gained gained by Hemlo Hemlo Gold Mines Mines Inc. Inc. by by acquiring acquiring Golden Golden Sceptre Resources Resources Limited, and Goliath Goliath Gold Gold Mines Mines Limited Limited (Canadian (Canadian Mines Mines Handbook, Handbook, 1987-88, p.185). p.185).The Themajor majorshareholder Gold Mines Mines Limited Limited is shareholderof Hemlo Hemlo Gold is Noranda Noranda Inc. Inc. By Bythe the end end of 1985, all all three three mines had commenced commenced gold production. production. In March March 1986, after after several several months of testimony, testimony, the the Supreme Supreme Court Court of Ontario Ontario awarded awarded the Page-Williams Mine to to International Corona Resources Ltd. Ltd. LAC LAC appealed appealed the the decision decision to to the the Ontario conditions imposed OntarioCourt Court of of Appeal Appeal but but continued continuedto to operate operate the the mine mine under under conditions imposedby bythe thecourt. court. The Ontario Ontario Court Court of of Appeal Appeal upheld upheld the the earlier earlier decision decision in in October, October, 1987. 1987. The Supreme Supreme Court Court of Canada later granted LAG LAC the right to appeal appeal the provincial provincial court ruling. ruling. In August, 1989, 1989, the the Supreme Supreme Court Court of of Canada Canadaawarded awardedthe thePage-Williams Page-WilliamsMine, Mine,Canada's Canada's largest largestgold goldproducer, producer,to to Corona which shortened the name name to to the theWilliams Williams Mine. Mine. In July, 1982, 1982, Homestake Homestake Mining Mining Company Corona Corporation Corporation and Willams and David Company took took over Corona and thus thus acquired acquired 50% 50% interest interest in in the Willams Bell Bell Mines. The Theremaining remaining50% 50%interest interestisisstill stillheld heldby byTeck Teck Corporation. Corporation. �8 Geology and Gold Deposits of the Hemlo Hemlo Area PART 3: REGIONAL REGIONAL GEOLOGY by by TL. Schnieders and T.L. Muir, Muir, B.R. Schnieders and M.C. M.C. Smyk Smyk The geology geology of of the the Hemlo Hemloarea areahas hasbeen beenmapped mappedby byThomson Thomson(1931, (1931, 1933), 1933), Bartley Bartleyand andPage Page Mime (1967, (1967, 1968), 1968),Muir Muir(1982a, (1982a, 1982b), 1982b),and andSiragusa Siragusa (1984a, (1984a, 1984b, 1984b, 1985a, 1985b). This (1957), Milne This regional mapping inside of of front front cover) cover) shows shows that that the the Hemlo Hemlo deposit deposit occurs regional mapping (refer (refer to Figure Figure 14 14 on inside generally east-trending, east-trending,mixed mixedassemblage assemblage of Archean Archean metavolcanic metavolcanic and and metasedimenmetasedimenwithin aa generally tary granitoid bodies. bodies. These tary rocks rocks sandwiched sandwichedbetween betweenmajor major granitoid These supracrustal supracrustalrocks rocksare are part part of of what is termed the Schreiber-Hemlo Schreiber-Hemlo greenstone greenstone belt belt of of the the Wawa Wawa subprovince. subprovince. (1 982a,1982b, 1 982b,1983) 1983) tentativelysubdivided subdividedthe theHeron HeronBay-Hemlo Bay-Hemlo part part of the the greenstone greenstone Muir (1982a, tentatively belt into two groups: (1) (1) the the southern southern Playter PlayterHarbour Harbour Group, Group, comprising comprising mainly tholeiitic mafic mafic subordinate, intercalated, flows with subordinate, intercalated,intermediate intermediatetotofelsic felsictuffs tuffsand andsiltstones; siltstones;and and(2) (2) the the northern northern Heron Bay Bay Group comprising mainly dacitic dacitic and Heron comprising mainly and rhyolitic rhyolitic calc-alkalic calc-alkalic pyroclastic pyroclastic rocks rocks and and reworked equivalents, equivalents, and and tholeiitic tholeiitic basalts. basalts. AAperceived progressive decrease in grain and perceived progressive decrease in grain and fragment size, together with a general increase in the the proportion proportion of of volcaniclastic volcaniclastic and epiclastic sedimentary sedimentary units units toward toward the the east, east, was interpreted interpreted in in terms terms of a volcanic complex, centred in the Heron Bay area, that shed material material into into aa distal distal basin basin to to the the east east (Muir (Muir1982b, 1982b, 1983). 1983). Subsequent to this interpretation interpretation and and the the discovery discovery of of the the main main part part of of the the Hemlo Hemlo deposit deposit in in 1981, moredetailed detailedmapping mappingindicated indicatedthe thepresence presenceofofafelsicvolcanicpile afelsicvolcanicpileininthe thevicinity vicinityof ofHemlo Hemlo 1981, more a!. 1985). 1985). U-Pb (Brown et at. U-Pb geochronology geochronology has has since since shown shown that that the the volcanic volcanic piles pilesat atHemlo Hemloand and different in respectively, 2772 Ma and 2695 2695 Ma (Corfu (Corfu and and Muir Heron Bay are notably different in age, being, respectively, 1989a). facies model model may may not not be be appropriate. appropriate. Conse1989a). This This suggests suggests a simple proximal/distal proximalldistal facies quently, Corfu proposed that Corfu and and Muir Muir (1989b) (1989b) proposed that an an extensive extensive structural structuralbreak break(i.e., (i.e., the theHemlo Hemlofault) fault) may separate separate 2 different different assemblages assemblages of supracrustal supracrustal rocks, although they pointed out this model rocks, although they pointed out this model poses its own problems. In keeping keeping with the the above above alternative alternative model, model, Williams Williams et et aL al. (1991) (1991) have have proposed proposed aa redefinition of redefinition of the the general general construction construction of of the the supracrustal supracrustalrocks rockseast east of the Coldwell Coldwell Complex. In In their their scenario, scenario, the the Hemlo Hemlofault fault as as seen seen on on Highway Highway17 17 near the Hemlo Hemlo deposit, deposit, is is extended extendedwest, west, the Coldwell CoIdwell Complex, Complex, and southeast southeast to eastbetween the Gowan Lake and Heron Bay plutons to the southeast southeast from the the Highway Highway 17 17 location location to to the the east east end end of of the the Schreiber-Hemlo Schreiber-Hemlogreenstone greenstonebelt. belt. The extent extent and and position positionof of the the fault fault is is speculative speculativeat atthis thisstage stageand andisisnot notshown shownon onthe the map map(inside (inside front cover). The The supracrustal supracrustalrocks rocksare aresubdivided subdividedinto intothe the Heron HeronBay Bay assemblage, assemblage, south south of of the the assemblage, north north of of the the fault. fault. Muir Hemlo Fault, and the Hemlo-Black Hemlo-Black River assemblage, Muir(1988) (1988) presented presented supracrustal rocks differences and similarities between lithological and structural features of the supracrustal a!. (1991) to the north north and and south of the Hemlo Hemlo fault in the vicinity vicinity of of the the Hemlo Hemlo deposit. deposit. Pan Panetetal. (1991) maintain a geochemical uniformity uniformity throughout throughout the supracrustal supracrustal rocks, maintainthat there is ageochemical rocks, to to the the north north and and lo deposit, which, which, they south of the Hemlo Hemlo fault fault several several kilometres kilometresto to the the east eastof of the the Hem Hemlo they suggest, suggest, single tectonic tectonic environment, not notaajuxtaposition juxtaposition of ofsuspect suspectterrains. terrains. More detailed detailed field field favours a single work and additional geochronologic geochronologic results results are are required required to to resolve resolvethis this issue. issue. any case, case, recent recent detailed detailed mapping mapping in the the vicinity vicinity of the the Hemlo Hemlo deposit, deposit, and elsewhere elsewhere in the the In any Hemlo-Heron HemIo-Heron Bay part of the Schreiber-Hemlo greenstone belt, indicates that that the the interpretation interpretation and delineation delineation of incompatible with of "groups" "groups" and and simple simple facies changes changes in this belt is incompatible with the the degree degree and style of deformation deformation now now recognized recognized (e.g., (e.g., see Part Part 7). geochronology from from zircon zircon crystals crystals indicates indicates that that there there are are 3 main generations of U-Pb geochronology �Regional RegionalGeology Geology 99 granitoidplutonism plutonismin in the Hemlo-Heron Hemlo-Heron Bay area: -2719Ma, Ma,-P2688 -2688 Ma, Ma(Corfu (Corfuand and granitoid area: 2719 Ma, and and-2678 2678 Ma Muir 1989a). 1989a). The Thefollowing followingages agesare arefrom fromCorfu Corfuand andMuir Muir(1989a). (1989a).To Tothe thesouth southofofthe thebelt beltlies liesthe the Muir Pukaskwa Gneissic Complex Complex which to gneissic gneissic phases phases of of Pukaskwa which consists mostly of weakly foliated to tonalite tonalite and and granodiorite granodiorite(2688 (2688Ma) Ma) with with pegmatite pegmatiteand andaplite aplitedikes. dikes. AAmarginal marginalzone zone(2719 (2719Ma) Ma) possibly thick, exhibits possiblyup upto to 11 km km thick, exhibitsaa weak weak mylonitic mylonitic fabric fabric generally generallyoriented orientedparallel parallelto tothe thecontact contact with with the the supracrustal supracrustal rocks. rocks. Within Withinthis thispart partofofthe thegreenstone greenstone belt beltlie lie two two major major granodioritic granodioritic plutons: plutons: the theHeron HeronBay BayPluton Pluton(2688 (2688Ma) Ma)to tothe thewest, west, and andthe theCedar CedarLake LakePluton Pluton(2688 (2688Ma), Ma),with with the smaller, smaller, satellite Cedar Creek Stock To the north of the belt belt lies lies a the Stock (2684 (2684 Ma), Ma), to to the the east. east. To granitoid separated from granitoidgneiss gneisscomplex, complex,the theBlack-Pic Black-PicBatholith Batholith(Mime (Milne1968), 1968),which whichisisseparated fromthe thebelt beltby by the the crescent-shaped crescent-shapedgranodioritic granodioritictotoquartz quartzmonzonitic monzoniticGowan GowanLake LakePluton Pluton(2678 (2678Ma). Ma). The variations variations Themetamorphic metamorphicgrade rangeslocally locallyfrom fromggreenschist The grade ranges reenschist to to amphibolite amphibolite facies. The reflect reflect the the proximity proximityto to granitoid granitoidbatholiths batholithsand/or and/orthe thesuperposition superpositionofofup uptotoseveral severalepisodes episodesofof metamorphismand andhydrothermal hydrothermalalteration alteration(Kuhns (Kuhns1988; 1988;Kuhns Kuhnseta!. etal.1994; 1994;Corfu Corfuand andMuir Muir1989b; 1989b; metamorphism Pan Pan and and Fleet Fleet 1992). 1992). The The rocks rocksof of the the Hemlo Hemlodeposit deposit area area have have undergone undergone amphibolite amphibolite facies facies regional regionalmetamorphism. metamorphism. In In the the vicinity vicinity of of the the Hemlo Hemlodeposit, deposit,Muir Muirand andElliott Elliott(1987) (1987) and and Muir Muir eta!. etal. (1988) (1988)identified identifiedatat least least four four generations generations of of structures structures produced produced by at least least two deformation events: events: (1) (1)an anearly early phase F, folds folds and and possible possiblelow-angle low-anglenormal normalor or thrust thrustfaults; faults;(2) (2)aamajor, major, phaseresulting resultingininsmall-scale small-scaleF1 regional, second secondphase phase producing producingsmallsmall- to large-scale, large-scale, tight tight to to isoclinal, isoclinal, generally generally northwestnorthwest- to to regional, north-northwest-plungingF2 F2folds, folds, along along with with a penetrative penetrative axial axial planar schistosity and differentinorth-northwest-plunging differentiatedlayering layering(S2), (So),possibly with sinistral sinistral shearing shearing and mylonitization; (3) dextral dextral shear shear ated possibly associated associated with mylonitization; (3) which whichlocally locallyresulted resultedinins-c-c' s-c-c'mylonitic myloniticrocks rocksand andsmallsmall-to to medium-scale, medium-scale,generally generallynortheastnortheast-to to F3folds folds with with axial axialplanar planarschistosity schistosityand andcrenulation crenulationcleavage cleavage(S3); (S3);and and(4) (4)smallsmalleast-plunging,F3 east-plunging, scale scale F4 F4kink kink folds folds and and brittle brittle faults. faults. AAsomewhat somewhatdifferent differentstructural structuralhistory historyhas hasbeen beengiven giveninin Kuhns a!. (1994) Kuhns (1986, (1986, 1988), 1988), Kuhns Kuhns et etal. (1994) (see (seePart Part6), 6),and andMichibayashi Michibayashi(1991). (1991). The interrelationship interrelationshipofofstructural structuralelements elementsand andintrusive intrusivebodies bodiesin in the the vicinity vicinity of, of, and and within, within, The the theore orezone zoneat atHemlo Hemlosuggests suggeststhat thatintrusions intrusionssuch suchas asthe theCedar CedarLake LakePluton Plutonand andassociated(?) associated(?) dikes dikeswere werelikely likelyemplaced emplacedafter afterF1, F,, during duringthe thelate latestages stagesof, of,ororafter, after,F2, F2,but butbefore beforeF3 F3(see (seeMuir Muir 1993). The Therelationships relationshipsbetween betweenstructural structuraland andmetamorphic metamorphicelements elementswithin withinthe thedeposit depositremain remain 1993). somewhat somewhatcontroversial controversialbecause becauseof of the the complex, complex, polymetamorphic/metasomatic polymetamorphic/metasomaticcharacter characterof ofthe the ore orezone zone(e.g., (e.g., see see Parts Parts55and and6). 6). U-Pbgeochronology of titanite, rutile, and monazite (Corfu andMuir Muir1989b) 1989b)reveals revealsaanumber number U-Pbgeochronologyoftitanite, rutile, and monazite (Corfu and of interesting features. Outside of of an anill-defined ill-definedbroad broadzone zone of ofalteration alterationand andmineralization mineralization of interesting features. Outside associated associatedwith withthe theHemlo Hemlodeposit, deposit,titanite titaniteages agesrange rangefrom from00toto10 10Ma Mayounger youngerthan thanzircon zirconages, ages, averagingabout about66Ma Mayounger. younger.However, However,within withinthis thisbroad broadzone, zone,titanite titaniteages agesrange rangefrom from1313toto15 15 averaging Mayoungerthan younger thanzircon zirconages. ages.Rocks Rocksoutside outsidethe thezone zonecontain containessentially essentiallyno norutile, rutile,whereas whereasmany many Ma of ofthe therocks rockswithin withinthis thiszone zonedo docontain containrutile rutilecrystals crystals(and (andininone onecase, case,monazite) monazite)which whichare areabout about 25 crystals. This 25to to40 40 Ma Ma younger than the titanite crystals. Thissuggests suggeststhat that an an episodic episodicor or protracted protractedthermal thermal historyhas hasoccurred occurredwithin withinthis thiszone, zone,which whichlies lieswithin withinone oneofofseveral severalhigh-strain high-strainzones zones(Corfu (Corfuand and history Muir1989b; 1989b;Hugon Hugon1986). 1986).However, However,ititcan canbe beargued arguedthat that this thispossibility possibilitycan canonly onlybe betested testedififrutile rutile Muir isisalso alsopresent, present,and anddated, dated,ininrocks rocksoutside outsideofofthe thezone. zone. Allof of the the aforementioned aforementionedArchean Archeanrocks rocksare areintruded intrudedby bymuch muchyounger youngerProterozoic Proterozoicintrusive intrusive All rocksincluding includingup upto toseveral severalages agesofofdiabase diabasedikes, dikes,and andyounger youngerlamprophyre lamprophyreand andalkalic alkalicdikes dikes rocks that thatare aremost mostlikely likelytemporally temporallyassociated associatedwith withthe thealkalic alkalicCoIdwell ColdwellComplex, Complex,centred centredwest westofof Marathon.The TheColdwell ColdwellComplex Complexhas hasbeen beendated datedatat1108±1 1108±Ma Mafor for early early gabbroic gabbroic and and syenitic syenitic Marathon. phases, (Heamanand andMachado Machado1987). 1987). phases,and and-'1099 -1099 Ma Mafor forlate lategranitoid granitoidphases phases(Heaman �10 Geology and Gold Deposits Deposits of the Hemlo Area 4: PEEKONGAY PART 4: PEEKONGAY PROPERTY PROPERTY by by B.R. Schnieders and B.R. Schnieders and M.C. M. C. Smyk The Peekongay property is located located in in Plc Pic Township, Township, centred near near the the town town of of Heron HeronBay, Bay, and and extends from Lake Superior to the Pic former Heron extends Lake Superior Pic River. ItIt includes includes the the sites sites of the former Heron Bay Bay Mine Mine and and V. Stenlund. Stenlund. The property property has has the mineralized mineralized Bowhill Bowhill Mines test trench, and is currently held held by V. also been referred referred to as the Bowhill Bowhill Mines Mines property, the Stenlund Stenlund property, property, and the Lytton Lytton Minerals Minerals property. The The carbonate-quartz carbonate-quartzvein veinofofthe theHeron HeronBay BayMine Mineoutcrop outcrop(described (describedbelow; below;see see Stop Stop 11 of road log as well) represents one type of of gold mineralization that that was discovered early in the in the the late late 1860s. 1860s. Recently, Recently, additional history of sporadic exploration of the area, which began in exploration, to the the Heron Bay Bay Mine, Mine, has hasidentified identified other other gold gold occurrences occurrences exploration, the west, within 3 km of the and mineralized mineralized zones. Lytton Minerals oned the property property from Stenlund Stenlund in 1982 and and conducted conducted 3 phases phases Lytton MineralsLimited Limitedopti optioned of diamond drilling, to May May 1985, 1985, totalling approximately 40 000 feet (12 (12 192 192 m) from 53 holes holes Geologist's Files, Files, Schreiber-Hemlo Schreiber-HemloDistrict, District,Thunder ThunderBay). Bay). The The drilling drilling resulted resulted in the the (Resident Geologist's outlining of some additional gold-bearing zones, termed the "Porphyry Zone" and the "C Zone", outlining additional gold-bearingzones, termed the "Porphyry Zone" and the "C Zone", as as well as further delineating delineating the the "Main "Main Zone" Zone" and and a mineralized mineralizedzone termed the "South "South Zone". The The Main Zone Zone includes mineralization in the Heron Bay Mine and the the Bowhill Mines trench. trench. MINERALIZATION TYPES TYPES MINERALIZATION Hartwick et a!. a/, (1985) (1985) described 4 major major types of of gold gold mineralization mineralization on on the the Peekongay Peekongay property, which are summarized summarized below, from Patterson Patterson (1986): "(1) possibly stratiform stratiform unit in Ic to '(1) A A pyritic pyritic quartz-rich quartz-richmolybdenite-bearing, molybdenite-bearing, possibly in mat mafic intermediate intermediate tufts tuffs ("C" ("C" Zone). Zone). Vuggy, pyritic pyritic quartz-carbonate quartz-carbonate veins and stringers cutting a possible subvolcanic (2) Vuggy, quartz-feldspar quartz-feldspar porphyry porphyry sill sill ("Porphyry" Zone). quartz-sericite-altered, dacitic pyroclastics and, to aa lesser lesser (3) Pyritic, silicified and and quartz-sericite-altered, extent, mafic mafic to intermediate intermediatetufts tuffs (Main (MainZone, Zone, eastern eastern part part of of North NorthZone). Zone). (4) Quartz-carbonate veins and vein breccias with variable amounts of pyrite, chalcopyrite, galena, galena, sphalerite sphalerite and and tourmaline tourmaline (Bowhill (Bowhill trench, trench, 1872 1872 shaft shaft area area trench, trench, western part part of North North Zone)." Zone)." The gold mineralization mineralization and and mineralized mineralized zones zones are are further further described describedby byPatterson Patterson(1986) (1986) based on the report of Hartwick eta!. (1985). eta/, (1985). intersections over "Ore grade intersections over significant significantwidths widths(Le., (i.e., 66feet feet (2 (2 m) m) or or greater) greater) have havebeen been obtained from the "C" and and "Porphyry" "Porphyry" Zones. Zones. In contrast, contrast, the silicified and and quartzquartzsericite-altered sericite-alteredpyroclastics pyroclasticsofofwhich whichthe theMain MainZone Zoneisisthe the most mostprominent, prominent, are are characcharacterized by geochemically anomalous gold values values in the order of 100 to 200 ppb with oz/ton Au Au over 3.1 31 feet (0.91 locally high values as great great as as 0.11 0.11 ozlton (0.91 m), but no ore grade intersections have intersections have been been obtained. obtained. "Quartz-carbonate veins veins and and vein vein breccia breccia occur occur in essentially "Quartz-carbonate essentially all all lithologies lithologies and, and, although these veins at at some places places contain contain gold gold values greater greater than than 0.40 0.40 oz/ton ozlton Au, Au, they are very erratic and discontinuous. The The continuity continuity both both laterally laterallyand and vertically, vertically, of of high grade intersections intersections is is very very limited." limited." �Peekongay Property 11 11 Discontinuous and erratically distributed quartz-carbonate quartz-carbonate veins veins and and stringers stringershave havebeen been observed observed by the authors authors over over a strike strike length length of of 2 km km in the Heron Heron Bay area. The individual individual zones zones are are described described in in more more detail detail below. below. MAIN MAIN ZONE ZONE MINERALIZATION MINERALIZATION mineralization includes ill Mines The Main Main Zone mineralization includesthe theold oldHeron HeronBay BayMine Minesite, site,and andthe theold oldBowh Bowhill Mines Trench site. As summarized by Patterson (1986): Trench site. As summarized by Patterson (1986): "The zone consists of a series of sericitic units 'The units within felsic felsic metavolcanic metavolcanic rocks and trends across the the property. property. The moderately moderately foliated foliated sericite sericite schist trends at at 0600 060' across schist contains contains55 to to 10% blue blue quartz quartz eyes that that are up to to 22 mm mmin insize. size. The The quartz quartz eyes are deformed deformed parallel parallel the most strongly foliated sections, the quartz to foliation. foliation. In the quartz eyes eyes are are absent absent and and the the molybdenite. Drilling narrow quartz-rich layers (less than 2 mm) contain molybdenite. Drillingand andsurface surface exploration has defined five occurrences are exploration hasdefined five parallel parallelunits. units. AA number number of occurrences are known knownalong alongthe the zone. The The best bestintersection intersectionreported reportedwas was4.83 4.83 ounces ouncesper perton tongold goldacross across1.0 1.0 feet." feet." East of the the Peekongay Peekongay property, property, Esso Minerals Canada Limited reported results results from from aa mineralized mineralized zone on strike from the Main Main Zone, with with assays assays up up to 1300 1300 ppb ppb Au and and 280 ppm ppm Mo 0.6 m (Resident Geologist's Files, Ministry Ministry of Northern across 0.6 Northern Development Development and and Mines, Mines, Thunder Thunder Bay). Bay). Heron Heron Bay Bay Mine Mine The abandoned abandoned Heron Heron Bay Bay Mine Mine is located locatedadjacent adjacent to to the thecommunity communityofofHeron HeronBay, Bay,and andisis approximately and30 30 m m south south of of the the CP CP Railway. Railway. The exploration approximately 200 m west of Highway Highway 627, 627, and history of the old mine mine dates back to 1869 1869 with the discovery of of veins by by Moses Moses Pee-Kong-Gay Pee-Kong-Gay western one is is 16 16 m deep), and (Roland 1887). Two Two shafts (the (the eastern eastern one one is is 8 m deep and the western some open cuts were developed developed in in 1873 1873 and 1874. 1874. Ore was apparently shipped and processed processed (McKellar 1874; Strickland 1979; (McKellar 1874; Strickland 1979; Patterson Patterson1984). 1984). carbonate-quartz vein, approximately 70 m long stripped stripped A carbonate-quartz vein, up upto to 11 m m thick, is exposed exposed on an approximately outcrop, in which 2 shafts shafts are separated separated by m (see (see Road Road Log, Log, Figure Figure 16). 16). The The vein vein strikes strikes outcrop, by about 40 rn at 270° 270' to 300°, 300° dips 70°N 70° to vertical, and is hosted within a shear zone which cross-cuts the obliquely. The volcanic stratigraphy obliquely. The foliation foliation within the the metavolcanic metavolcanic rocks rocks strikes from 245° 245O to 262° and dips from 50° ions trend 262O 50' to 64°N. 64ON. Mineral Minerallineat lineations trend 250° 250' and andplunge plungefrom from 32° 32' to to38°W. 38OW. The carbonate-quartz carbonate-quartz vein contains contains abundant abundant ankerite ankerite (up (up to to 70%) 70%) and andblack blacktourmaline, tourmaline, chalcopyrite, pyrite, sphalerite, and molybdenite. molybdenite. Barite galena, chalcopyrite, Barite has has also been identified (Patterson 1986). Patterson Patterson (1984) (1984) described the vein material thus: "Samples of vein material, when slabbed, show several generations of vein development: (a) (a) barren barren white white quartz; quartz; (b) (b) carbonate-rich; carbonate-rich;(c) (c) tourmalinetourmaline- and and sulphide-bearing; sulphide-bearing; (d) banded quartz-carbonate quartz-carbonate and and barite:' barite." Gold values within within the vein vein are are erratic erratic and and sporadic. sporadic. Patterson reported aachip chip sample Gold Patterson(1984) (1984) reported returned 0.22 ounce 3.00 ounces per per ton ton Ag Ag across across 0.82 0.82 m. m. Grab samples, by the returned ounce per ton Au and 3.00 authors, of dump material assayed assayed up up to to 0.04 0.04 ounce ounce per per ton ton Au. Au. Samples authors, Samplesfrom from nearby nearby pyritic pyritic quartz-se ricite units (Resident Geologist's quartz-sericite unitsassayed assayedup upto to0.314 0.314 ounces ouncesper per ton ton Au Au over over 0.9 m (Resident Geologist'sFiles, Files, Ministry of Northern Development and Mines, Thunder Bay). Earlier workers reported that, at Ministry Northern Development and Earlier reported that, at the the �12 12 Geology and Gold Deposits Deposits of the Hemlo Hemlo Area Number 1 shaft, predominantly predominantlycopper-, copper-, zinc-, zinc-, and and lead-bearing lead-bearing minerals minerals were were found, along along with with "deposit" of gold and silver. However, However, at at aa depth depth of of 35 feet (10.87 m), a rich "deposit" of gold gold and and less less copper copper was discovered District, Thunder Bay). discovered (Resident (Resident Geologist's Geologist's Files, Files, Schreiber-Hemlo District, The host volcanic rocks consist of interbedded, fine- to coarse-grained, pyroclastic rocks of intermediate intermediate to felsic felsic composition. composition. The metavolcanic metavolcanic rocks display display intense intense shearing shearing and and alteration (bleaching) on the north side of the the vein. vein. The pyroclastic breccia is commonly matrixsupported except except for for the very section. Two supported very coarse coarse fragmental fragmental section. Two predominant predominant clast clast types types are are present: a whitish quartz-porphyritic present: quartz-porphyritic variety and a mafic, mafic, chloritic chloritic type type containing containing feldspar feldspar phenocrysts. AA sample sample of of aaquartz-porphyritic quartz-porphyritic fragment fragment within within the the altered altered zone, zone, taken taken by by the the authors, assayed assayed 102 ppb gold Ministry of Northern Northern Development Developmentand and gold (Geoscience (Geoscience Laboratories, Ministry Mines, Mines, Toronto). Toronto). Bowhill BowhillMines MinesTrench Trench The Bowhill located about town of Bowhill Mines Mines trench trenchis is within within the the Main MainZone Zone and and is is located about11km km west west of the town Heron Bay. Bay. The Heron The following following description of the trench trench is is taken taken from from an an assessment assessment file report report submitted by Hartwick Hartwick eta!. etal.(1985), (1985), for for Lytton Lytton Minerals Minerals Limited: Limited: "This trench, excavated excavated by by Bowhill Bowhill Mines Mines in in the middle middle 1930s, 1930s, is about 200 feet (60 m) long by 30 feet (9 m) m) deep deep and and 10feet feet (3 (3m) m)wide. wide. The trench trench is largely largely caved caved in in but but the pyritic quartz-sericite schist unit unit is is exposed exposed at the end end of of the the carbonate-quartz carbonate-quartz vein vein which sample of taken presumably presumably which contains containssphalerite, sphalerite,galena galenaand andpyrite; pyrite;aabulk bulksample of 500 500 Ibs, taken from this this vein vein material materialby byBowhill BowhillMines, Mines, assayed assayed0.3 0.3 oz oz Au/ton Aulton and and1.5 1.5 oz Ag/ton." Aglton." The following section section is is from from Patterson Patterson(1986): (1986): Lytton Minerals Limited Limited (Resident Geologist's Geologist's Files, "Drilling and geochemical geochemical work by Lytton Ontario Ministry Ministry of of Northern Northern Development Development and and Mines, Mines, Thunder Bay) shows the Main Main Zn, Cu. The Zone to be depleted in Na Na and enriched enriched in K, Mo, Au, Zn, The Main Main Zone Zone and and the the carbonate dyke. The carbonate carbonate vein vein are are cut cut by a lamprophyre dyke. carbonate vein vein also also contains contains black black tourmaline and molybdenite. tourmaline molybdenite. "Stripping on the main Occurrence (1100 (1100 m east of "Stripping main zone just west of the Bowhill Mines Occurrence Highway No. 627 and 200 200 m m south south of ofthe the Canadian Canadian Pacific Pacific Railway) Railway) has exposed exposed ashear a shear Highway zone evidence of progressive deformation. deformation. The zone which shows evidence Theearliest earliestphase phase was was largely largely ductile, with the the volcanic volcanic fragments fragments within a felsic felsic pyroclastic pyroclastic rock rock being being folded folded and and stretched cite schist stretched out out parallel parallel to foliation. foliation. Next Nextaaseries seriesof of discrete discretesen sericite schist zones, zones, 20-200 20-200 wide and heavily heavily carbonatized carbonatized cut cut across across the theductile ductileshear. shear. Carbonate Carbonate pods pods within within cm wide the cite schist have been deformed. deformed. Subsequently, the sen sericite Subsequently,aa mafic mafic dyke dyke 30-60 30-60 cm wide was intruded into intruded into the sericite schist. schist. The Thedyke dykecontains containsfragments fragmentsof of sericite sericite schist schistand andhas has where it crosses the the sericite sericite schist zone. zone. The final phase appears to have been folded where deformation, with been brittle deformation, with the the formation formation of of quartz-tourmaline quartz-tourmalineveins veins along along the the margin margin of the mafic mafic dyke dyke and and in in the the carbonate carbonatepods." pods." PORPHYRY ZONE following section The following section is is from from Patterson Patterson(1986): (1986): "Further "Further detailed detailed work work by by Derry, Derry, Michener, Michener, Booth Booth and and Wahl identified identified aa mylonite mylonitezone zone Bay. This unit was along the north contact contact of a porphyry porphyry intrusion intrusion 11 km west of Heron Bay. previously ~ u s l ycalled a thinly bedded bedded hematitic hematitic ash ash tuff tuff marker marker(W.N. (W.N. Pearson, Pearson, personal person;a1 previ( communication, nunication, Geological Geological Consultant, Consultant, Derry, Derry, Michener, Michener, Booth Booth and andWahi, Wahl,Toronto, Toronti3, comn 1985).I~ 1985). �Peekongay Peekongay Property Property 13 "The unit is is highly highly foliated foliated and and locally locally folded. folded. It is comprised comprised of of fine-grained, fine-grained, red red drill core the mylonite grades (hematitic) thinly (hematitic) thinly laminated laminatedchlorite chloriteand andfelsic felsiclayers. layers. In drill grades into sheared and deformed feldspar porphyry to the south." south." white quartz veins from 1 to 5 cm thick with with minor minor The porphyry apparently contains 10% white tourmaline. Diamond foot section section within within the pyrite and 3 to 5% black tourmaline. Diamond drilling intersected a 23.5 foot porphyry near porphyry near the the hanging hangingwall walland andhad hadaagrade gradeofof0.19 0.19 ounces ounces per per ton ton Au Au (Patterson (Patterson1986). 1986). C C ZONE ZONE following section The following section is is from from Patterson Patterson(1986): (1986): "The C-Zone C-Zone mineralization mineralization occurs at or or near near the the footwall footwallof ofthe thefeldspar feldsparporphyry. porphyry. Mineralization consists quartz up to 1 cm cm thick thick in in aa chlorite chlorite schist schist Mineralization consistsof of layers layersand and lenses lenses of quartz (possibly a sheared mafic metavolcanic). The quartz-rich layers contain molybdenite. The quartz-rich layers contain molybdenite. occurs as as 1 to 3 mm cubes cubes which have have been deformed and and possibly possibly Pyrite (5-10%) (5-10%) occurs rotated rotatedin in foliation. foliation. The Thezone zoneappears appearsto to cross-cut cross-cutthe the mafic maficmetavolcanic metavolcanicrocks rocksand andthe the feldspar porphyry. porphyry. Late Latequartz-carbonate quartz-carbonateveins veinscut cutthe the foliation foliationin inthe the zone. zone. Most Mostof of the the rocks north north of of the railway railway tracks consist consist of heavily carbonatized mafic mafic volcanics volcanics which have a felsic appearance. The Thebest bestdiamond diamonddrill drillintersection intersectionobtained obtainedwas was17.0 17.0feet feet of of 0.19 ounces per ton ton gold." gold:' 0.19 ounces SOUTH SOUTH ZONE ZONE The following section section isis from from Patterson Patterson(1986): (1986): sericitic zone occurs approximately approximately 100 south of the Heron "A sericitic zone similar to the main zone occurs 100 m rn south Heron Stripping and and trenching trenching has has exposed quartz-carbonate veins veins within within a Bay Mine. Mine. Stripping exposed quartz-carbonate sheared volcanic volcanic breccia. breccia. tourmaline." The veins The veins contain contain chalcopyrite, chalcopyrite, galena, galena, pyrite and and �14 Geology and and Gold Gold Deposits Deposits of of the the Hemlo Hemlo Area Area Geology PART 5: HEMLO PART 5: HEMLODEPOSIT DEPOSITOVERVIEW OVERVIEW by by B.R. Schnieders, C. Smyk L. Muir B.R. SchnIeders, M. M.C. Smyk and and T 1L. The The Hemlo Hemlo deposit deposit isis situated situatedwithin withinsupracrustal supracrustalrocks rocksininaasouthern southernbifurcated bifurcatedsegment segmentofofthe the eastern eastern part partof of the theSchreiber-Hemlo Schreiber-Hemlogreenstone greenstonebelt. belt.Page Page(1947a, (1947a,1947b, 1947b,1948, 1948,1949) 1949)was wasthe the first important structural structural feature firstgeologist geologistwho who recognized recognizedthe theHemlo HemloFault Faultas as an important feature and and identified identifiedthe the close close co-planar co-planarrelationship relationshipthe thefault faulthad hadwith with the the Lake Lake Superior Superior Shear Shear Zone. He Healso also recognized recognized that thatall allthe the gold golddiscoveries discoveriesat atthat thattime timewere werehosted hostedby bythe theLake LakeSuperior SuperiorShear ShearZone, Zone, and andstated stated that that the thezone zone had hadbeen beentraced tracedon on surface surface for for over over 12 12 kilometres. Page Pagealso alsonoted notedthat thatthe thegold gold mineralization mineralizationwas was associated associated with with felsic felsic porphyritic porphyriticbodies bodiesand andthat thatthe theemplacement emplacementof of these these porphyries Break". porphyrieswas was related related to to aa major majorstructure structurewhich which he hetermed termedthe the"Heron "HeronBay-Hemlo Bay-HemloBreak". The The Hemlo Hemlo deposit deposit largely largely lies lies at at or near the contact contact between between felsic to intermediate intermediate quartzquartzfeldspar-phyri imentary rocks. feldspar-phyricc rocks (pyroclasti (pyroclasticc and subvolcanic(?) subvolcanic(?) varieties) varieties) and andmetased metasedimentary rocks. Here, the rocks generally strike at 290° to 295° and dip between 60° and 700 to the northeast. Here, the rocks generally strike at 290' to 295' and dip between 60' and 70' to the northeast. Hugon Hugon (1984) (1984) presented evidence that the Hemlo Hemlo deposit is is contained contained within within aamajor majorductile, ductile, dextral, dextral,shear shearzone. zone. He Heinterpreted interpretedthat thatthe thedeposit depositoccupies occupiesthe themost mostintensely intenselydeformed, deformed,central central portion portionof of aalarge-scale, large-scale,wide widezone zone of of ductile, ductile, oblique obliquethrusting thrusting(Hugon (Hugon1986). 1986). The Hemlo Hemlo deposit deposit isispresently presentlyinterpreted interpretedby bythe theauthors authorsas asbeing beinglargely largelyhosted hostedwithin within The 290°-striking, 290°-strikinghighly highly strained, strained, transposed, transposed, and and juxtaposed, lithotectonic lithotectonic supracrustal supracrustalsegments, segments, which generally east-striking whichlie lieininaagenerally east-strikinggreenstone greenstonebelt. belt.The Thedeposit deposithas hasnot notbeen beendemonstrated demonstratedtotobe be stratiform or stratabound. stratiform or stratabound. Sporadically Sporadically distributed, distributed, anomalous anomalous gold goldmineralization mineralizationhas hasbeen been noted, noted,several severalkilometres kilometressoutheast southeastand andeast-southeast east-southeastof ofthe theHemlo Hemlodeposit depositon onthe theLac LacMinerals Minerals Limited, spatially associated associated with with sericitic and Limited, White White River River property, as being spatially and pyritic pyritic rocks rocks within within what whatisisinterpreted interpretedas asaabrittle-ductile brittle-ductileshear shearzone zone(Pan (Panand andFleet Fleet1988, 1988,1989, 1989,1990; 1990;Pan Pan1990). 1990). Undergroundmapping mapping and and drilling drilling have demonstrated existence of of parallel parallel mineralized mineralized Underground demonstrated the existence zones zones within within both boththe themetavolcanic metavolcanicand andmetasedimentary metasedimentaryrocks, rocks,as aswell wellas asmineralized mineralizedzones zones which which transect transectthe themetavolcanic-metasedimentary metavolcanic-metasedimentarycontact. contact. The The Hemlo Hemlodeposit depositorebodies, orebodies, collectively, collectively, extend extendfor for aastrike strikelength lengthofofabout about3.7 3.7 km, km,aadepth depthofof1.35 1.35 km, km,and andan anapproximate approximate down-plunge down-plungedistance distanceofof2.5 2.5km km(see (seeFigures Figures21 21and and22). 22). The Themain mainmineralized mineralizedzone zoneextends extendsfor foraa strike down-dip distance of strikelength lengthofofabout about2.9 2.9 km, km,and andaadown-dipdistance of2.5 2.5 km km (Harris (Harris1989). 1989).The Thethickness thicknessofofthe the main theDavid DavidBell BellMine Mine(Burk (Burketa!. etal.1986) 1986)toto50 50mrnininthe the mainmineralized mineralizedzone zoneranges rangesfrom fromabout about22mmininthe Williams WilliamsMine Mine(Walford, (Walford,Stephens Stephenseta!. etal.1986). 1986). Several mines,based basedlargely largelyon onthe thepredominant predominant Severaltypes typesof ofore oreare aredelineated delineatedinineach eachof ofthe the33mines, mineral(s) and/or textures present. Commonly, because of extensive metasomatism and mineral(s) and/or textures present. Commonly, because of extensive metasomatism anddeformadeformation, protolith(s).Alteration, Alteration,collectively, collectively,isisinin tion,the themineralized mineralizedzones zonescomprise compriserocks rocksof of equivocal equivocalprotolith(s). the theform formof ofwidely widelyvarious various degrees degrees of of microclinization, microclinization, sericitization, sericitization, biotitization, biotitization,silicification, silicification, carbonatization, albitization, albitization, pyritization, pyritization, and andtourmalinization. tourmalinization. Significant Significantamounts amountsof of barite barite of of carbonatization, equivocal equivocalorigin originare arelocally locallypresent. present.Bright Brightgreen greenvanadian vanadianmuscovite muscovite(Harris (Harris1989) 1989)isiscommonly commonly present presentin inthe thealtered alteredrocks, rocks,as asisismolybdenite. molybdenite.AtAtleast leasttwo twoages agesofofquartz quartzveins veinscan canbe befound found within within the theore orezones: zones:some someveins veinsdisplay displayconsiderable considerablefolding, folding,attenuation, attenuation,boudinage, boudinage,and and dismemberment, dismemberment,whereas whereasothers othersdisplay displayminimal minimaldeformation. deformation. In In some some cases, cases, outside outsidethe theore ore zone, zone, there thereare arenumerous numerousquartz quartzveins veinswhich whichtend tendto todisplay displayaalower lowerdegree degreeofofdeformation. deformation. Collectively,the theores oresare areenriched enrichedininAu, Au, Mo, Mo,Sb, Sb, Hg, Hg, As, As, TI, TI, V, V, and Ba. Gold Goldisiscommonly commonly Collectively, disseminated disseminatedalong alongwith withmolybdenite. molybdenite. Native Native gold gold grains grains are are mercury mercuryrich richand andoccur occuralong along �a r 9,' Hemlo Deposit Overview 15 ! quartz-feldspar and pyrite grain boundaries and fractures, as well as inclusions in, or rimmed with, several varieties of sulphide minerals including, rarely, pyrite and molybdenite (Harris 1989). Visible gold is not common overall, but does occur within quartz veins in feldspathized, molybdenite-bearing rocks, along molybdenite-green-mica-bearing fractures, in stibnite- and cinnabarbearing quartz pods, and rarely in fractures in some of the plagioclase-porphyritic dikes. Molyb- a C P rp c' r C 0 fl a a a a p p r r U' a a P U U a a p a a denite is the second most abundant sulphide, after pyrite, and occurs as fine- to very fine-grained, foliation-parallel blades, euhedral crystals, and platy masses mostly in association with silicate minerals, chiefly feldspar and quartz (Harris 1989). During the pastdecade, since the discovery of the Hemlo gold deposit as it is nowdelineated, various metallogenic models have been proposed. As summarized by Patterson (1984), Harris (1986b, 1989), Corfu and Muir (1989b), and Muir (1993), earlier workers favoured syngenetic, exhalative models in which mineralization was penecontemporaneous with volcanism (e.g., Cameron and Hattori 1985; Goldie 1985; Quartermain 1985; Valliant and Bradbrook 1986). Later workers suggested a porphyry deposit model (e.g., Kuhns 1986, 1988; Kuhns eta!. 1994; Johnston and Smyk 1992; Johnston et a!. in press), structural/hydrothermal models (e.g., Burk et al. 1986; Hugon 1986; Walford et a!. 1986), and a skarn model (e.g., Pan and Fleet 1991, 1992). It is interesting to note that the earliest observations in the Hemlo camp, made by Page (1947a, 1947b, 1948, 1949), invoked a close relationship between regional structure, local faults and shear zones, porphyries, alteration, and gold mineralization. Geochronologic evidence, coupled with field and underground observations, attest to the difficulty in clearly defining the timing of the gold mineralization relative to deformation events, the regional metamorphic event(s), and hydrothermal alteration events (Corfu and Muir 1989b). This is also evident by the variety of differing observations, some apparently in conflict, reported by Burk et at (1986), Kuhns (1986), Hugon (1986), Walford, Stephens et at (1986), Muir and Elliott (1987) and Muir (1993). Muir and Elliott (1987) suggested that apparent conflicts in observations may be a result, in part, of comparing features related to different deformation and/or alteration and/or metamorphic events. They also noted that dextral shear zones did not everywhere control the site of mineralization and that the deposit has been affected possibly by two generations of structures, including at least some of the dextral-shear-related deformation. In reviewing the various Hemlo genetic models, Harris (1989) stated that more recent research and evidence led to the recognition of features which tend not to favour the earlier syngenetic models but more stronglysupport ore deposition by hydrothermal fluids within or near a ductile shear zone. The Hemlo deposit has been ductiley deformed. Neither a temporal association between a porphyry intrusion(s) and the mineralizing event(s) nor a temporal association between the mineralizing event(s) and early ductile shearing has yet to be clearly established. In addition, disagreement exists as to whether the deposit formed prior to regional metamorphism (Kuhns 1986; Kuhns eta!. 1994), pre- orsyn-metamorphism (Burk etat 1986). or post-metamorphism (Walford, Stephens etat 1986; Pan and Fleet 1991, 1992). Muir (1993) has summarized some of the points that are consistent or inconsistent with the various depositional models proposed forthe Hemlo deposit. The complex geological history of the Hemlo area has led to some incongruous observations or interpretations which only much-needed, careful, and detailed additional studies may help to resolve. The past 15 years have resulted in a spectrum of geological observations, interpretations, and proposed models. Currently, no single genetic model adequately explains all of the complexities of the Hemlo deposit. It is possible that a combination of more than one model or the development of a new model may be required to account for the formation of the Hemlo deposit Genetic models can be useful exploration tools but must be used with caution. The Hemlo deposit was "overlooked" for over 30 years, possibly in part, because it did not fit classic genetic gold deposit models. �Geology Geologyand and Gold GoldDeposits Depositsof of the theHemlo HemloArea Area 16 I PART PART 6: GEOLOGY GEOLOGYOF OFTHE THE GOLDEN GOLDENGIANT GIANTMINE MINE AND ANDGOLDEN GOLDENSCEPTRE SCEPTREOREBODY OREBODY by by I I I I Robert Doug MCII veen and RobertKusins, Kusins,Albert AlbertChong, Chong,Paul PaulJohnston, Johnston, Doug Mcllveen andKen KenMcNena McNena 4 INTRODUCTION INTRODUCTION The The Golden GoldenGiant GiantMine Mineis is located located35 35km kmeast east of of Marathon, Marathon, Ontario Ontario(Figure (Figure2) 2)and andlies lieswithin within the the central centralpart partof of the the much muchlarger larger Hemlo Hemlo deposit. deposit. Three Threeseparate separatemining miningoperations operationshave havebeen been established established on the deposit deposit since since its its discovery discovery in in 1981. 1981. The TheGolden GoldenGiant GiantMine Minehas hasbeen beeninin production productionsince sinceApril, April,1985 1985and andhas hasproduced produced11436 436163 163ounces ouncesofofgold goldfrom from33892 892218 218tonnes tonnes mined 31, 1989. Current 1990, stand stand at at 16 16227290 minedas as of of December December31,1989. Currentreserves, reserves, as as of of December December31, 31,1990, 227 290 tonnes millioncontained containedounces ounces(178 (178662 662kg). kg). tonnesat at11.01 11.01 g/t, or 5.269 million The Hemlodeposit deposit is is situated situated within within aa "sequence" "sequence"of of moderate moderate to to locally locally high-grade high-gradeclastic clastic The Hemlo and and volcanic rocks rocks of of the the Schreiber-Hemlo Schreiber-Hemlo greenstone greenstone belt. This Thisbelt beltranges rangesfrom from88toto20 20km kminin width widthand andisispart partofofthe theeast-trending, east-trending,Schreiber-White Schreiber-WhiteRiver Riversection sectionofofthe theWawa WawaSubprovince Subprovince within 1982a,1982b). 1982b). withinthe theSuperior SuperiorProvince Provinceofofthe theCanadian CanadianShield Shield(Muir, (Muir,1982a, The are taken, taken, in part, from a field The following following descriptions and summary are field trip trip guide guide book book prepared et a!. a/, 1990). 1990). AAprevious previousfield fieldguide guidecovered covered prepared for the the 8th 8th IAGOD IAGODSymposium Symposium (Brown (Brown et additional additional features features (Brown (Brown et eta!. a/.1986). 1986). Stratigraphic Stratigraphicterminology terminologyin in Part Part66 of of this this field fieldguide guideisis used informally by Hemlo Gold Mines Inc. and Noranda Exploration Limited. used informally by Hemlo Gold Mines Inc. and Noranda Exploration Limited. MINE MINE GEOLOGY GEOLOGY The The "stratigraphy" "stratigraphy" in in the the mine mine area area as as shown shown on on the the surface surface plan plan (Figure (Figure 3), 3), has hasbeen been subdivided subdivided into into four four major major formations. From Fromsouth southto tonorth norththey theyare arethe theCache CacheLake, Lake,Rule RuleLake, Lake, Moose Lake, formations. The Lake, and Cedar Creek formations. The Moose Moose Lake Lake formation formation is is the the most mostimportant important economically mineralized zones. number of other mineralized zones. These These economicallyas asitithosts hoststhe the main main Hemlo Hemlodeposit depositand and aa number formations formations represent represent aa package package of rocks rocks approximately approximately 3 km thick within the tower lower part part of of the the Heron Heron Bay Bay group. Rocks Rocksininthe themine minearea areastrike strikeat at115° 115O and and dip 65° 65' northeast. northeast. <. Figure2. 2. Location Locationmap mapof of Hemlo. Hemlo. Figure �Geology Geology of the Golden Golden Giant Giant Mine Mine and and Golden Golden Sceptre Sceptre Orebody Orebody 17 17 The Cache Lake formation, formation, which forms the structurally lowermost unit of the the "stratigraphy", comprises comprises mafic metavolcanic metavolcanicschists and granofels. In In the deposit deposit area, this formation is is about thick. It was was used used as as aadistinct distinct marker marker during during initial initial deep deep exploration exploration drilling drilling of the deposit. deposit. 150 m thick. Drill holes holes were normally normally stopped once they reached reached this formation, formation, being being deemed deemed through through the the potentially favourable ore zones. The The formation formationtends tendsto tobe bemore morehighly highlysheared shearedand andcontains contains hematite-filled hematite-filled fractures fractures adjacent adjacent to its its contact contact with with the the overlying overlying Rule Rule Lake formation. The Rule consists of laminated laminated metasedimentary metasedimentary schists Rule Lake formation consists schists and and gneisses. The The total portion of total thickness thicknessof of this thisformation formationisisabout about150 150m m in in the mine area. The The basal basal portion of the the formation formation is dominated by gneiss, whereas whereas the the upper portion is comprised of by amphibole-feldspar-biotite amphibole-feldspar-biotite gneiss, caic-silicate-rich calc-silicate-richmetasedimentary metasedimentaryrocks rockswhich which commonly commonly contain contain kyanite, kyanite, staurolite, staurolite, and and garnet adjacent adjacent to the structurally structurally overlying overlying contact. contact. This Thisformation formationisiscomprised comprisedof ofrock rocktypes typessimilar similar to to the Cedar Cedar Creek Creek formation formation and and there there is is no no observable observable difference difference between between the the two. two. 12 Diabase 1 Gronodlorlte CEDAR CREEK FORMATION 7 6 Clastic Sedinentory Rock Upper Fraonentnl MOOSE L A K E F O R M A T I O N 5 Minei-nllzed Zone 4 Mafic F r o p e n t a l 3 Moose Lake Porphyry - RULE L A K E FORMATION 2 S u r f a c e Plan C t c Sedimentar-y Rock CACHE L A K E F O R M A T I O N FIgure Figure3. 3. Geological Geologicalcompilation compilationof of the theHemlo Hemlocamp camp(modified (modifiedafter afterKuhns Kuhns1988). 1988). �Geology and Gold Deposits of the Hemlo Hernlo Area ' 1 1 - Golden Giant Mine Section 10075 E 1 1 LEGEND P O ~ P ~ Y ~ Y hw n e t a s e d 1 men t s o r e zone footwa L L sch i s t 5 b i o t i t l c schists n a f i c fragnen t a L fw n e t a s e d i men t s FIgure Figure4. 4. Generalized Generalized cross-section cross-sectionthrough throughthe theGolden GoldenGiant Giantorebody. orebody. �Geology Geology of the Golden Golden Giant Giant Mine Mine and and Golden Golden Sceptre Sceptre Orebody Orebody 19 19 The Moose Moose Lake formation formation within within the the Golden Golden Giant Giant Mine, Mine, shown shown on on aa typical typical cross-section cross-section (Figure (Figure 4), can can be be subdivided subdivided into into four units units which, from south south to north, northl are: are: (1) Lower Mineralized MineralizedZone; Zone; (1) Lower (2) (2) Footwall Footwall Schists; Schists; (3) Mafic Mafic Fragmental; Fragmental; (4) Main Main Ore Ore Zone. Footwall Schists are interpreted interpreted to to have have been been derived derived largely largely from from the the Moose MooseLake Lake The Footwall Porphyry, which is avariably much Porphyry, a variably altered altered and anddeformed deformedquartz-feldspar quartz-feldspar porphyry porphyry that constitutes constitutes much Moose Lake formation. Thisformation formationattains attainsthicknesses thicknessesupto up to100 100mmininthe themine minearea, area, and and of the Moose formation. This up to the the west west of ofthe thedeposit deposit area. area. The formation formation pinches pinchesto to the the east east until until the the Cedar Cedar Creek Creek up to 400 m to formation structurally structurally overlies the Rule Lake formation. In Inthis this area, area, the the transition transition between between the the Cedar Creek and Rule thick silicate silicate and and oxide oxide facies facies iron iron Rule Lake Lake formations is is marked marked by an 8 m thick formation. formation. Moose Lake Formation Formation Lower Mineralized Mineralized Zone (Unit (Unlt 5) 5) The Lower Lower Mineralized Zone, Zone, normally located along the contact between betweenthe theMoose MooseLake Lakeand andRule Rule Lake Lake formations, formsaa mineralized mineralizedzone zonefrom from11to to 20 20 contact formations, forms m this zone, located located in the the lowerwestern lowerwestern partof orebody, is is commonly commonly m thick. The The thicker thicker part part of of thiszone, part ofthe theorebody, uneconomic uneconomicdue due to low low gold grades. Locally Locallythough, though, the the zone zone may may contain contain economic economicgold gold grades grades over thicknesses thicknesses of of 33 m. m. Economic Economicmineralization mineralizationwithin withinthe theLower LowerMineralized MineralizedZone Zonetends tendstotobe bemore morerestricted restrictedtotothe the lower levels levels in the the mine, mine, generally generally in in areas areas where where the the Main MainOre OreZone Zonehas hasbegun begunto topinch pinchout. out. Typical Typical ore ore thicknesses thicknessesare areininthe the22to to 55 m m range, range, with with this this zone zone representing representing2.2 2.2million milliontonnes tonnesofof the stated statedreserves. reserves.The Thepredominant predominantrock rocktypes typesare arevery verysimilar similartotothose thoseininthe theMain MainOre OreZone Zone the and include feldspathic feldspathic and and sericitic sericitic varieties varieties which which locally locally may may be bebaritic baritic andlor and/orpyritic. pyritic. Gold mineralization mineralization tends tends to to be be less less dependant dependant on rock rock type type in comparison comparison to the Main Main Ore Ore Zone. Plagioclaseporphyry porphyrysills, sills,which whichessentially essentiallybisect bisectthe theorebody orebodyalong alongits itslength, length,are arecommon common Plagiociase within the the zone zone and and locally locallymake makeeither eitherthe thehanging hangingwall wall and/or andlor footwall footwall lenses lenses uneconomic uneconomic to to Overall,sills sillsrange rangein inthickness thicknessfrom fromless lessthan than 11m mto to in in excess excessof of 10 10 m. m. mine. Overall, Footwall FootwallSchlsts Schists(UnIt (Unit3) 3) The The Footwall Footwall Schists Schists generally generally structurally structurallyoverlie overliethe theLower LowerMinerMineralized Zone, Zone, but but itit is is common common to to get get aa thin thin zone zone developed developedon on the the underlying underlyingfootwall footwallside sideof ofthe the alized Lower Mineralized Zone. Zone. This 3a)# This unit unittypically typically isiscomprised comprisedof ofQuartz QuartzEye EyeSchist Schist(Subunit (Subunit3a), FeldspathicSchist Schist (Subunit (Subunit3b), 3b), and and Biotitic BiotiticSchist Schist(Subunit (Subunit3c). 3c). ItItforms formsthe thestructural structuralfootwall footwallto to Feldspathic the the Main Main Ore Ore Zone. Zone. Footwall Schist in the mine mine area area and and is is comprised comprised of of quartzquartzSubunit 3a dominates the Footwall muscovite~feldsparschists schists with with distinctive distinctive 11to to33mm mmquartz quartzlenses lensesor or"eyes" "eyes" and, and, locally, locally, fewer fewer muscovite±feldspar plagioclaseeyes. eyes. This ThisQuartz QuartzEye EyeSchist Schistsubunit, subunit,which whichisispart partofofthe theMoose MooseLake LakePorphyry, Porphyry,may may plagioclase also contain minor tourmaline, tourmaline, anhydrite, anhydrite, green green mica mica and andpyrite. pyrite. Adjacent zones of of Adjacent to Unit Unit 55 zones 5% pyrite, pyrite, minor minor mineralization, the subunit may be weakly weakly mineralized, mineralized, containing mineralization, the subunit containing up up to 5% gltrange. range. molybdenite,and and gold goldvalues values in inthe the 11to to55g/t molybdenite, termed Feldspathic FeldspathicSchist, Schist, is is massive massive to to weakly weakly schistose schistoseand andisiscomprised comprised Subunit 3b, termed predominantly amounts of of muscovite. muscovite. Lenticular predominantly of feldspar, quartz, and lesser amounts Lenticular plagioclase plagioclase eyes are common. common. Locally, Locally,generally generallyininproximity proximityto todiabase diabaseintrusions, intrusions,this thissubunit subunitmay maybe behematized hematized are andlor potassium-rich resulting in a pink to Contacts between between this this subunit subunit and and/or to red colouration. colouration. Contacts �20 20 Geology and Gold Deposits Deposits of the Hemlo Hemlo Area either plagioclase porphyry porphyry sills may be quite quite gradational. gradational. InInthe either the Quartz Quartz Eye Eye Schist Schist and plagioclase thelower lower levels of the mine, the unit becomes more porphyritic porphyritic in appearance appearance and and itit is is often often difficult to establish discrete contacts Schist and and plagioclase plagioclase porphyry porphyry sills. sills. The contacts between the Feldspathic Schist is weakly weakly mineralized mineralized with pyrite pyrite and and molybdenite molybdenite occurring occurring within within hairline hairline subunit locally is fractures. Subunit 3c, termed Biotitic Biotitic Schist, Schist, consists consists of of aaquartz-biotite-muscovite quartz-biotite-muscovite schist schist which which generally generallylacks lacks quartz quartzor or plagioclase plagioclaseeyes. eyes. This Thissubunit, subunit,which whichisisnot notpresent presentin in the the upper upper levels levels of the levels, locally locally marking the strike extension of, or the mine, becomes becomes more more abundant in the lower levels, being proximal to, weakly FootwallSchists. Schists. This subunit subunit may may weakly mineralized mineralized zones within the the Footwall represent represent less less altered altered metasedimentary metasedimentaryrocks rocksor or aa fine-grained fine-grainedMafic Mafic Fragmental Fragmentalrock. rock. Mat Ic Fragmental Fragmental Unit Mafic Unit(Unit (Unit4) 4) The Schists The Mafic MaficFragmental FragmentalUnit Unit occurs occurs between betweenthe Footwall FootwallSchists and the structurally overlying metasedimentary rocks rocks of of the the Cedar Cedar Creek Creekformation. formation. The unit overlying metasedimentary unit comprises quartz granofels granofels and and biotite biotite schist within a comprises lenticular lenticular fragments of feldspar porphyry, quartz strongly foliated biotitic biotitic matrix. matrix. The distribution of this this unit unit shows shows an anoverall overall antipathetic antipathetic relationshipwith withthe theMain MainOre OreZone, Zone,pinching pinchingout outat atdepth depthand andto tothe theeast eastand andwest westof of the the Golden Golden relationship Giant orebody (Walford, Weicker eta!. 1986; Burk eta!. 1986). The predominant subunit is a Biotitic predominantsubunit is Biotitic Giant orebody (Walford, Weicker eta/. 1986; Burk eta/,1986). Fragmental composition of 40% biotite, 8% Fragmental (4a) having having an average composition 4O0loquartz, 24% 24Y0 biotite, 8Ol0plagioclase, plagioclase,7% 7Y0 actinolitic 7% pyrite (Kuhns, 1988). 1988). The unit actinolitic hornblende, hornblende, 3% 3OlOtremolitic tremolitic hornblende, hornblende, and 7Y0 unit locally locally contains contains economic economic grades grades of of gold gold mineralization mineralizationbut, but, in in general, general, only only contains containsanomalous anomalousgold gold values. values. Other subunits subunits within withinthe theMafic MaficFragmental FragmentalUnit Unitconsist consistof of Sericitized SericitizedFragmental Fragmental(4b) (4b)and and Other Fine-grained Sericitized Fragmental Fine-grained Fragmental (4c). The Sericitized Fragmental commonly commonly occurs occurs as as an an altered alteredzone zone between replacement of biotite with between Biotitic BiotiticFragmental Fragmentaland and ore ore units. units. It is characterized characterized by the replacement biotite with muscovite, pyrite, molybdenite molybdenite and muscovite,and and an an increase increase in in the amount of green mica, pyrite, and gold. The TheFineFinegrained Fragmental Fragmentalis generally difficult metasedimentaryrocks rocks of the grained difficult to distinguish distinguish from clastic clastic metasedimentary Cedar Cedar Creek Creek and and Rule RuleLake Lake formations. formations. Main Ore Zone (Unit (Unit 5) 5) The Main Main Ore Ore Zone comprises comprises several distinctive distinctive subunits subunits that that are are characterized Zone subunits subunits contain contain molybdenite molybdenite characterizedon onthe thebasis basisof of mineralogy. In In general, Main Main Ore Zone and tend to be be either either feldspathic or sericitic. Accordingly, Accordingly, the the two two most most common common subunits subunits are Feldspathic Feldspathic Ore Ore (5a) and Sericitic Sericitic Ore Ore (5b). (5b). 5a consists consists ofofquartz-microcline quartz-microcline granofels granofels with with10% 10Y0pyrite, pyrite,0.1% 0.lY0 fine-grained fine-grained Subunit 5a molybdenite, 3% green mica. The characteristic blue-grey The molybdenite molybdenitegives gives the rock rock its its characteristic blue-grey rnolybdenite,and and11 to 3Y0 colour. colour. Subunit 5a 5a isis commonly commonly further furthersub-divided subdivided into intohighhigh-and andlow-pyrite-barite-bearing low-pyrite-barite-bearing varieties corresponding correspondingchemically chemicallyto to lowlow-and and high-aluminum high-aluminum contents, pyrite-baritecontent content varieties contents, with with pyrite-barite increasing at the the expense expense of of microcline. microcline. Baritic-Feldspathic Ore (5d) contains contains fragments fragments of of Siliceous FeldspathicOre Oresurrounded surroundedby by aa Au-Mo-poor matrix of barite Feldspathic Au-Mo-poor granoblastic granoblastic matrix barite andlor and/or pyrite. Siliceous (5q) consists consists of of aamixture mixtureofoffine-grained fine-grainedfeldspar, feldspar, molybdenite, molybdenite, and quartz occurring occurring in in Ore (5q) massive massive layers layers 0.5 to to 55 m m thick. Pyrite occurs occurs as as very very fine-grained, fine-grained, euhedral to anhedral crystals within the ore, ore, and and as as Pyrite coarser grains grains in in the the matrix matrix of feldspathic ore that that has has undergone deformation.There Thereisisno no coarser feldspathic ore undergone brittle brittle deformation. direct correlation correlationbetween betweengold goldgrades gradesand and pyrite pyritecontent, content, although, although,iningeneral, general, as as the the pyrite pyriteand and direct barite barite contents contentsof of the the ore oreincrease, increase, the the gold goldgrades grades decrease. decrease. (vanadian muscovite) are the best best visual visual indicators indicators for for the the Molybdenite and green mica (vanadian presenceof of gold gold mineralization. mineralization.Gold Goldoccurs occursininnative nativeform formalong alongsilicate silicategrain grainboundaries boundaries(Brown (Brown presence �Geology of the Golden Giant Mine and Golden Sceptre Orebody 21 et a!. 1985) and along pyrite-gangue grain boundaries (Harris 1986b). Visible gold has been observed in most subunits but is most commonly noted in feldspar-quartz pods or biotitic shears within the ore. The feldspar-quartz pods that occur in the green-mica-molybdenite-rich subunit may contain titanite, titanite, cinnabar, cinnabar; realgar, stibnite, sphalerite, sphaleritel pyrite, pyrite, and and molybdenite. molybdenite. Cedar Creek Formation Formation (UnIt (Unit7) 7) The Cedar Creek formation consists of a diverse group of clastic metasedimentary metasedimentary rocks rocks which subunits (Kuhns 1988). The two most common subunits intersected which can can be be divided divided into into 14 14 subunits intersected L., &I.-:-A ..,a..l.:--. - . ..A. I & C-lA,.:..-b kn:-.. P-1-:I:--&C..L..-:A /-A\ --A A IA---A P--:-:L:by workings the Golden eU Giant Mine CaIc-silicate Subunit (7d)~ and Sericitic uy the LI IG mine IIIIIIG WUI KII lya at LI IG UUIUGII IIL ~ IVIII IG ~are I u G m - W I I GDUUUIIIL ~ L G \/u) I ~Altered U~ i e r aerluuG e u Subunit Subunit (7e). (7e). The CaIc-silicate Calc-silicate Subunit Subunit is is predominant predominant and and consists consists of of brown brown to to black, black, laminated laminated and banded, banded, fine-grained, fine-grained, granoblastic-textured, granoblastic-textured, foliated, quartz-biotite-feldspar schist. schist. This This schist is interbanded with medium to dark green, amphibole-feldspar-biotite granofels. The schist is interbanded medium amphibole-feldspar-biotite The unit unit may also contain contain minor minor kyanite, kyanite, garnet, garnet, and and staurolite. staurolite. There appears to be an an increase increase in in abundance abundance of of alumino-silicate alumino-silicateminerals minerals proximal proximal to the Moose Moose Lake formation. The Thecalc-silicatecalc-silicaterich predominant in the lower levels of of the the mine. mine. Some sections sections within rich bands become predominant within the the subunit subunit . . a consist of massive calc-silicate crystals, and commonly contain pyrite and pyrrhotite mineralization. The Altered Sericitic Subunit is a pyritic, quartz-muscovite-feldspar schist spatially associated isISfine clatea with w m the meMain wlam Ore ure Zone. Lone. It11 m e grained, grariea, granoblastic grarioulasuctextured, textures,light llgnlbrownish Drownlsngrey greyto 10grey, grey, laminated laminatedand and foliated, foliated, and and exhibits exhibits gradational gradationalcontacts contactswith withother otherunits unitsand andsubunits, subunits,of ofwhich whichitit may be an an altered altered or or bleached bleached equivalent. equivalent. The average composition composition of the subunit is 4G0lO 46% quartz, quartz, 26% microcline, and 4Y0 4% plagioclase piagioclase (Kuhns (Kuhns 1988). 1988). Kyanite, is locally 26Y0muscovite, muscovite,13% 13OlOpyrite, pyrite, 10% 10Y0microcline, common. contains rare grains of molybdenitel molybdenite, green common. This Thissubunit subunitisisslightly slightlyanomalous anomalousin in gold gold and and contains mica, arsenopyrite. Pods mica, and and arsenopyrite. Podsconsisting consistingofofquartz quartzor orfeldspar feldsparare arelocally locallypresent, present,and andmay maycontain contain minor minor realgar and and stibnite. stibnite. Intrusive Intrusive Rocks Rocks Intrusive Intrusive rocks found in the Hemlo Hemlo stratigraphy stratigraphy are divided divided into into four four units. units. Feldspar-porphyritic, Feldspar-porphyritic,quartz quar monzonite and monzodiorite sills, referred to:oas asUnit Unit9, 9,occur occuras as thin thin to to thick thick (0.5 (0.5 to to 30 30 m), m), nearly nearly concordant concoraamintrusions lnuuslonswithin w m nand ana structurally suucwrallybelow belowthe theMain MainOre Ore Zone, commonly in the hanging wall wall metasedimentary metasedimentary rocks. The Zone, and and less less commonly The sills sills occur occur individually individually or in swarms swarms containing containing up upto sills, and andare arecommonly commonlyfoliated. to 20 sills, foliated. Thicker Thicker sills sills (5to (5 to 30 30 m) m) generally exhibit of feldspar and in places exhibit minor minor to moderate moderate sericitization sericitization of feldspar crystals, crvstals, and places are are cut cut by by quartz+orthoclase+fluorite quartz+orthoclase+fluoriteveins. veins. A particularly Darticularlvinteresting interestinaintrusion intrusionoccurs occurs in in the the central central part Dartof of the the deposit, depositl as as observed observedon on 4600 the flexure in &elliptical ellipticalporphyry porphyryplug plugoccupies occupi~s theaxis axis;of)faaflexure ( ~ i ~ u5). r i 5Here, Here, ) . an 4600 level Ii v e l (Figure inthe the geologic geologic units. The cmthe Theplug plugplunges plungesto tothe thenorthwest northwestatatabout about60° 60' as asoutlined outlinedon thegram-metre-value gram-metre-value , ,.4:....1 tr:-, G6). @\ Thn n:.b,.:..I.....,.. . .-.-I longitudinal section transection I ~ ~G I U I U I I(Figure trlyul w). The I IIGintrusion 11 ILI U ~ I U I shows I31I U W a ~ C I general YGI I G I ~ IA-..----b:..m L I ~ I ~ G G L Ifrom from U ~ ~ footwall footwall to hanging hanging longitbu11 wall with with depth depth in in relationship relationshipto to the the Main Main Ore Ore Zone The TIi e ore wall adjacent to this pporphyry ore zone adjacent lorphyrybody body is relatively thin. ..A,.*:.... ,-A Basaltic to dacitic sills, known as Unit 10, occur throughout the mine area. They eyare arethin thin(5 (5to to 50 cm) and cut all mineralization and alteration associated with the deposit. These "mafic "maficsills", sills",as as they to .. .-> are -. - commonly --......-. ..> referred .-.-. . --to .-in...the .. .- mine ......- terminology, .-. ......-.-aJl are, -. -, on -. .average, -.-aw, composed - w m m n yof ofw35 35 ~~ tod40% 40Yo biotite, biotite, 35 35to to40% 4070hornblende, hornblende,10% 1O0hplagioclase, plagioclase,00 to to 10% 1O0l0microcline, microcline, and and00to to10% 10Y0quartz, quartz,with with minor zoisite, pyrite, pyritel magnetite, magnetite.calcite, calcite.and andtitanite titanite(Kuhns (Kuhns1988). 1988). -- �22 Geology Geology and Gold Deposits Deposits of the Hemlo Hemlo Area is a asmall, The third main intrusive intrusive unit is the the Cedar Cedar Creekstockwhich Creek Stockwhich is small, oval, granitoid granitoid intrusion intrusion located about 800 800 to to 850 850 m m north north of of the the Main Main Ore Ore Zone. This Thisintrusion intrusionisis2.5 2.5by by1.5 1.5 km km in in surface surface located about extent, and its southern margin is subconcordant The subconcordant with with the the upper metasedimentary metasedimentary schists. schists. The stock consists mainly mainly of a medium-grained, hypidiomorphic-granular hypidiomorphic-granular rock which has an average composition 35Y0 quartz, quartzl 15 15 to to 35% 35Y0plagioclase, plagioclase, 10 10 to to 25% 25Y0microcline, microcline, 10 10 to to 20% 20Y0 composition of of 25 to 35% O / O biotite, hornblende, and 1 to to ~5% biotite, with minor magnetite, titanite, and apatite. high angles. angles. Diabase dikes dikes represent Proterozoic mafic mafic intrusions intrusions which which cut cut the the strata at high These dikes, referred to as Unit 121 12, are are composed composed mostly mostly of of pyroxene pyroxene and and plagioclase. plagioclase. Typically they they exhibit exhibit gabbroic gabbroic textures textures internally internallyand andgrade grade outward outwardto to chilled chilled margins. margins. Four Fourmain maindiabase diabase dikes cut the Main Main Ore Ore Zone Zone and and range range in in thickness thickness from from 11 to to 30 30 m. m. DescrIptions Level Plan Descriptions MaIn Drift DrIft The 4750 Level drift 4750 Main drift plan (Figure 7) covers covers the the main main access access to to the the Golden Golden Giant Giant orebody adjacent adjacent the shaft area, including both the hanging wall and footwall rocks. The hanging shaft area, including both the hanging and footwall The hanging wall metasedimentary rocks in this area are composed mostly of Unit Unit 7d 7d "calc-silicates" llcalc-silicates" with with either garnetiferous garnetiferous (subunit (subunit 7a), 7a), or or characterized characterized by by garnetgarnetinterbanded metapelites that are either staurolite±kyanite/sillimanite (subunit staurolite~kyanite1sillimanite (subunit7b). 7b). 7 / Golden G i a n t Mine .. Plan 4600 Level 4a __,+_+ + + + + + + ++ ++ ++ ++ ++ + + ++ ++ ++ ++ ++ ++ ++ + + +÷ ++ ++ ++ ++ ++ + + + + • + + /+ + + + + + + + + + + + ' ++ ++ ++ i095+ + + + + + + + ++ ++ ++ ++ ++ + + ++ ++ ++ ++ + + + + + ÷ + - + + - .* + + + + + + + - + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + 3 -- + + + + + + + + ÷ ÷ + + + + + + + + + + + + ÷ + + + + + + +_ LEGEND LEGEND +_ + + + INTRUSIONS INTRUSIONS z77L/71777 27___, 275 + + + + 4+ + + + + .•+ + + + ÷ + + + + + + + - + + 9 9 Feldspar Feldspar Porphyry Porphyry CEDAR CEDAR CREEK CREEK FORMATION FORMATION 3 - 0 5 5 10 10 metres FIgure 5. Figure intrusion. intrusion. 15 15 3 Hongingwoll Clastic 7 Hangingwoll Clastic Metasediments Metasediments I ERID MINE RID MI N MOOSE LAKE MOOSE LAKE FORMATION FORMATION 5 5 4 4 3 3 Mineralized Mineralized Zone Zone Fragmentol Fragmental Unit Unit Footwall Footwoll Schist Schist Level plan plan of of part of Level of the the 4600 4600 level levelshowing showing the the elongate elongateplagioclase plagioclase porphyry porphyry �Geology of the Golden Giant Mine and Golden Sceptre Orebody 9800 5200 23 23 10220 M_© ©U Golden Giant Giant Mine Mine Longitudinal Longitudinal Projection Projection Gram—Metre Gram-Metre Values II 1 4800 4800 4400 4400 20 0 20 40 9800 10200 FIgure 6. Longitudinal Figure Longitudinal projection projection of of the the Golden GoldenGiant Giant orebody orebody showing showinggram-metre gram-metrecontours contours (Au grade by by ore ore thickness thickness in in gram-metre/tonne gram-metreltonnevalues). values). �24 Geology Geology and Gold Deposits Deposits of the Hemlo Hemlo Area Moving south, or structurally through the strata, subunit Moving south, structurally downward downward through subunit 7e 7e isisencountered encountered structurally Zone. The structurally above, and adjacent adjacent to, the Main Mineralized Mineralized Zone. The quartz-muscovite-feldspar quartz-muscovite-feldspar schist (subunit 7e) is almost everywhere found found in in this this stratigraphic stratigraphic position, position, and is thought to alteration envelope envelope surrounding surrounding the the Main Main represent the upper part of an asymmetrical, sericitic alteration 4750 MAIN DRIFT MAIN DRIFT ACCESS LEGEND LEGEN INTRUSIONS INTRUSIONS 10 10 9 9 Mafic Sill Mafic Sill Feldspar Porphyry Sill Feldspar Sill CEDAR CREEK CEDAR CREEK FORMATION FORMATION 7 Hongingwall Hangingwall Clastic Clastic Metasediments Metosediments MOOSE LAKE LAKE FORMATION FORMATION Mineralized Zone 5 Mineralized Zone 4 Fragmental 4 Fragmental Unit Unit 3 Footwoll Footwall Schist Schist 3 Figure Figure7. 7. 4750 SCALE: / I 1:250 LEVEL DATE: APRIL 1990 II Geology Geology plan plan of the 4750 main access access drift. drift. �Geology Geology of the the Golden Golden Giant Giant Mine Mine and and Golden Golden Sceptre Sceptre Orebody Orebody 25 25 Mineralized Mineralized Zone. ItItis is weakly weakly mineralized, mineralized, most most obviously obviously with pyrite, but but studies studies show that itit is is also enriched enriched in ore-related minor in most most of the ore-related minorelements elements(Ba, (Ba, Ag, Hg, Hg, As, Sb). This This unit unitalso also shows shows aa very strong, pervasive pervasive planar planar foliation, the same as seen in the very the ore ore zone, zone, indicating indicating the the sericitic alteration was developed prior to, to, or at the same same time time as, as, metamorphism and andtectonism. tectonism. Chip 4750 MAIN MAIN DRIFT DRIFT ACCESS ACCESS SYMBOLS SYMBOLS CHIP SAMPLE SAMPLE LOCATION LOCATION 17.5 ASSAY (g/t Au) ASSAY (g/t Au) [te[nn)0@<3f~^S CHIP 4750 / SCALE: 1:250 GOLDEN GIANT MINE PLAN LEVEL DATE: APRIL 1990 Figure Assay plan plan of of the the 4750 4750 main main access access drift. drift. Figure8. 8. Assay �26 26 Geology and Gold Deposits Deposits of the Hemlo Area which are are typical typical of Unit 4. These sample grades (Figure 8) show anomalous gold values which These values values are insufficient insufficient to meet minimum mining requirements requirements currently set at 2.8 2.8 glt g/t Au over 3.0 m. Moving southward southward again, again,into intothe thefootwall footwallschist, schist,subunit subunit3a 3aisisencountered. encountered. This quartzMoving muscovite-feldspar characterized by muscovite-feldsparschist schistis is the the most most common common variety variety of of Unit Unit 3, and and is characterized by lenticular lenticular plagioclase eyes, eyes, and andcommonly commonlycontains containstourmaline tourmalinecrystals. crystals. This unit is is quartz eyes and lesser plagioclase rhyolitic in chemical a/. 1986) 1986) and is is interpreted interpreted as as being being an an altered altered chemical composition (Kuhns (Kuhns et a!. porphyry intrusion interbanded with subunit intrusion which is is part part of of the the Moose Moose Lake Lake Porphyry. Porphyry. It is interbanded subunit 3b, 3b, which is microcline-rich microcline-rich and and contains contains lenticular lenticular plagioclase plagioclaseeyes. This Thisbuff buff to to pink pink rock rock is is marked marked by potassium enrichment, a decrease in muscovite, and a more massive texture. PlagioclasePlagioclaseintrusions (Unit "mafic sills" sills" (Unit (Unit 10) 10) extensively extensively cut the the footwall footwall schist schist porphyritic intrusions (Unit 9) 9) and "mafic throughout the extent of the Hemlo Hemlo deposit. Here, Here,feldspar-porphyritic, feldspar-porphyritic,quartz-monzonite quartz-monzonitesills sills 9a), and fine-grained fine-grained dacitic dacitic sills sills (subunit (subunit 10a) ba) can (subunit 9a), can be be examined. examined. - 4700 Sublevel Sublevel Plan 2WCrosscuts Crosscuts The Plan - OW, OW, 2W The4700 4700Sublevel Sublevelplan plan(Figure (Figure9) 9)covers coversthe the00West West West crosscuts crosscuts located approximately half-way down down dip dip on on the the Golden Giant part of the and 2 West deposit, just west of the the upper part part of ofthe theorebody orebodywithin within the the Quarter Quarter Claim. Claim. The ore at this this location location deposit, occurs as 2 lenses, termed hanging hanging wall ore lens and footwall ore lens, separated by a body body of subeconomic, Unit 4, quartz-mica-feldspar-amphibole quartz-mica-feldspar-amphibole schist. The hanging wall metasedimentary The hanging metasedimentary rocks are poorly exposed, as cutting into them with drift walls causes excessive dilution. The ore exposed exposed in the crosscuts crosscuts and and sill drifts drifts is is typical typical of ofthe the Golden GoldenGiant Giantorebody, orebody, with with occurrencesof of Feldspathic FeldspathicOre Ore (5a), (5a), Sericitic Ore (5b), and Baritic Ore (5d). The footwall occurrences Sericitic Ore footwall ore lens predominantly Baritic Baritic Ore, Ore, which which is is typical typical for for most mostof of the the Golden GoldenGiant Giantorebody. orebody. It contains is predominantly contains some quartz-rich material(subunits (subunits5d, 5d,5q) 5q)and andisiscut cutby by numerous numerous"mafic "maficsills" sills"(subunit (subunitbOa). 1Oa). The The quartz-rich material Unit 4 quartz-mica-feldspar-amphibole quartz-mica-feldspar-amphiboleschist schist separating separating the the 22 ore ore lenses lensesconsists consistsof, of, inin body of Unit part, avery a very representative representative example of the the Biotitic Fragmental Fragmental subunit 4a. 4a. At the contact between this body of Unit 4 and the footwall ore lens, is an occurrence occurrence of footwall footwall schist schist that that contains an unusual unusual amount amount of green green mica. mica. distinct lack of barite and is typically composed The hanging wall ore lens shows a distinct composed of more Sericitic Ore (5b) (5b) as as opposed opposed to to Feldspathic FeldspathicOre Ore (5a). (5a). The Thehanging hangingwall wall contact contactof of this this ore ore lens lens is is Sericitic Ore marked by the presence of of the Calc-silicate Caic-silicate Subunit (7d), (7d), with with the the more typical typical Altered Altered Sericitic Subunit (7e) found further within the hanging hanging wall. wall. Small-scale folding folding is observable within the footwall ore lens. lens. Tight, eastward eastward plunging plunging Small-scale observable within Z-shaped folds with axial axial planes planes parallel parallel to foliation foliation are are most most common. common. Brittle units such as as boudinaged. However, plagioclase porphyry sills and mafic dikes are boudinaged. However, there is is no no predominant predominant direction. Overall, elongation direction. Overall, the the ore ore zone zone at at this this location location shows shows moderate moderate to strong strong tectonic disruption as indicated indicated by by the the folding folding visible visible in in the the footwall footwall ore ore lens, lens, boudinage boudinage of of mafic mafic sills sills (subunit bOa),and andoffsets offsetsalong alongcross-cutting cross-cuttingfractures. fractures. The The degree degree of of tectonic tectonic disruption disruption is (subunit IOa), orebody, due, due, in in part, part, to to the the lenticular lenticular greater here as compared to the rest of the Golden Giant orebody, nature of the ore. Parts Partsofofthe theorebody orebodythat thatare arecomposed composedsolely solelyof of Unit Unit55generally generallyshow show less less tectonic disruption. disrupt ion. (Figure 10) 10) is typical of the Grade distribution within the footwall ore lens at this location (Figure deposit. The Thefootwall footwalllens lensshows showslower-than-average lower-than-average grades grades as as compared compared to to the the hanging hangingwall wall lens, due to increased increased amounts of barite and pyrite which tend to dilute the the gold gold content. content. �Geology Geology of of the the Golden Golden Giant Mine and Golden Sceptre Orebody Orebody 27 27 Observations Observations To date, date, the following observations observations have have been been made made concerning concerningthe the principal principalfeatures featuresof of the the Golden Giant orebody: Golden Giant orebody: 1. the Main Ore Ore Zone Zoneis isneither neitherdemonstrably demonstrablystratiform stratiform nor norstrata-bound. strata-bound. Non-economic 1. Overall, the Non-economic mineralization subzoneswithin withinthe the mineralizationgenerally generallyhas hasthe thesame sameform formas as the the Main Main Ore Zone. High-grade High-gradesubzones Main Main Ore Ore Zone Zone tend tend to toshow showtransecting transectingrelationships, relationships, from from footwall footwall to to hanging hangingwall, walll with with increasing increasing depth depth in in section section and and from from east east to west in plan. These These same sametransecting transectingrelationships relationships are are exhibited exhibited by by the the plagioclase plagioclaseporphyry porphyrysills, sillsl whereas whereas the the relative relativeorientation orientationof ofthe themafic maficsills sillsis is too irregular to permit a valid generalization. too irregular to permit a valid generalization. 2. icult to 2. Ore Oreisishosted hostedwithin withinaavariety varietyof oflithological lithologicalunits. units.Protoliths Protolithsare arevery veryduff difficult to determine determineas as aa result degree of metamorphism metamorphism and deformation, deformation, but thought to be represented represented by result of the high degree but are thought mudstones, as well as felsic felsic and and mafic mafic volcanic volcanic and andvolcaniclastic volcanictasticrocks. rocks. The distribution of the Mafic Mafic Fragmental Fragmental Unit shows an antipathetic relationship relationship to the distribution distribution of of the the ore. ore. 3. 3. The Thepredominant predominantstyle styleof ofmineralization mineralizationininthe theGolden GoldenGiant Giant orebody orebodyis is disseminated disseminatedgold gold and and molybdenite molybdenite within within rocks rocks containing containing the the assemblages assemblages microcline-quartz, microcline-quartz, muscovite-quartz, muscovite-quartz, biobiotite-microcline-quartz, and andrarely, rarely, calc-silicate calc-silicate minerals. minerals. AAsecondary, secondary, minor minor style style of of mineralizamineralizatite-microcline-quartz, tion tion consists consists of of gold, gold, stibnite, stibnite,and andcinnabar cinnabarwithin within deformed deformedquartz quartzpods podsand andveinlets. veinlets. 4. 4. High High gold grades grades within the the Main Main Ore Ore Zone Zone are are related related to tohigh highrelative relativeabundance abundance of of molybdenumand andvanadian vanadianmuscovite muscovite(green (greenmica). mica).Low Lowgold goldgrades gradesare arenoted notedininMain MainZone ZoneOre Ore molybdenum subunits subunits containing containingabundant abundant coarse coarse pyrite pyriteand/or andlor greater greater barite baritecontents. contents. 5. Ore-related Ore-relatedelements elementsfound spatialassociation associationwith withthe theAu Auand andMo Mo mineralization mineralizationinclude includeHg, Hg, 5. found ininspatial Ag, Zn, and and locally locally minor W, W,Tel Te,and andTI. TI.Studies Studies indicate indicate strong strong spatial correlation correlation V, Znl Agl Ba, Ba, As, Sb, V, between between Au, Aul Ag, Ag, and and Mo Mo as as the the principal principaldisseminated disseminatedore oretype, type,and andAu, Au,Hg, Hg,and andSb Sbas asaaminor, minor, quartz quartz pod pod(remobilized) (remobilized)ore oretype type(Kuhns (Kuhns1988). 1988). 6. 6. Ore Oreisishosted hostedwithin withinamphibolite amphibolitefacies faciesmetamorphic metamorphicrocks, rocksland andmineralization mineralizationpreceded precededpeak peak Thisisisindicated indicatedby bythe thepresence presenceof ofkyanite kyaniteand and sillimanite sillimanite in in the the hanging hanging wall wall metamorphism. This metasedimentary prograde metasedimentary rocks adjacent to the ore ore zone zone and and by by gold gold grains grains in in contact contact with withprograde kyanite kyanite(Kuhns (Kuhns1988). 1988). 7. 1 Alteration Alteration consists consistsof of an an interior interior potassic potassic (microcline/biotite) (microclinelbiotite) zone zone with with localized localized silicification silicification and pyritization, pyritizationl aasurrounding surroundingsericitic/phyllitic sericiticlphyllitic (muscovite±pyrite) (muscovite~yrite) zone,and andan anouter, outer, discondisconand zone, tinuousaluminosilicate aluminosilicate(kyanite) (kyanite)"halo" "halo"(Figure (Figure11). 11). Secondary Secondaryalteration alterationconsists consistsofofcalc-silicate calc-silicate tinuous (actinolite/tremolite) (actinoliteltremolite) zones in and and around around the the mineralized mineralized rocks; rocks; aa weak, weak, widely widelydistributed, distributed, fracture-controlledl sericitic sericitic alteration alteration (bleaching); (bleaching); aa secondary secondaryaluminosilicate aluminosilicate(fibrolite) (fibrolite)zone zone fracture-controlled, coincident coincident with the the kyanite kyanite zone; zone; and and local local carbonate carbonate alteration alteration associated associated with with parts partsofofthe the barren barren hanging hanging wall rocks rocks or locally locally within within biotitic biotiticsubunits subunitswithin withinthe theMain MainOre OreZone. Zone. 8. Mineralized Mineralizedzones zonesare arespatially spatiallyassociated associatedwith withaahighly highlydeformed deformedand andmineralized mineralizedquartz quartzeye eye 8. porphyry (footwall (footwall schist), schist), and and numerous numerous post-mineralization post-mineralization feldspar porphyry sills and and dikes dikes porphyry related Pluton. related to to the theCedar CedarCreek CreekStock Stockand andCedar CedarLake LakePluton. 9. At Atleast least33deformational deformationalevents eventshave havebeen beenrecognized recognizedininthe theHemlo Hemloarea area(Kuhns (Kuhns1988): 1988): 9. (i) (i) Pre-peak Pre-peak metamorphic metamorphicisoclinal isoclinal folding foldingand andfaulting. faulting. This This first first event event is is recognized recognized by by the the presence of isoclinal folds through which a penetrative metamorphic fabric has developed. presence of isoclinal folds through which a penetrative metamorphic fabric has developed. (ii) Syn-peak Syn-peak metamorphic metamorphic isoclinal isoclinal folding folding and and post-peak post-peak metamorphic metamorphic ductile-brittle ductile-brittle shearing shearing (ii) and associated associated drag drag folding. folding. The Thesecond secondfolding foldingevent eventisisindicated indicatedby bythe thepresence presenceofofisoclinal isoclinal and foldingof of the themetamorphic metamorphicfabric fabricand andrefolding refoldingof of F1 F, generation generation structures. structures. The Theore orezones zonesand and folding non-mineralized non-mineralizedcountry country rocks rocks are are strongly strongly foliated foliated and and exhibit exhibit dextral dextral mylonitic mylonitic and and cataclastic cataclastic textures texturesattributed attributedtotopost-peak post-peakmetamorphic, metamorphic,ductile-brittle ductile-brittleshearing. shearing. (iii) Late Late brittle brittle faulting. faulting. Brittle Brittledeformation deformationisisindicated indicatedby bymultiple, multiplelwell-developed, well-developed,angular angularfault fault (iii) brecciasand andclayey clayeyto to rock rock flour-rich flour-richgouge gouge zones zones which which are developed subparallel to to the the regional regional breccias developed subparallel metamorphic metamorphicfabric. fabric. �Geology and Gold Deposits of the Hemlo Hem10 Area 28 0 X-CUT q 2W X—CUT X-CUT - - -- ---- - - -- --- — 277 -ov.. 274'__L, 1W X—CUT LEGEND INTRUSIONS 10 10 99 Mafic Mafic Sill Sill Feldspar Feldspar Porphyry Porphyry Sill Sill CEDAR CEDAR CREEK CREEK FORMATION FORMATION 7 Hangingwall Hangingwall Clastic Clastic Metasediments Metasediments MOOSE MOOSE LAKE IAKEFORMATION FORMATION Mineralized Mineralized Zone Zone 44 Fragmental Fragmental Unit Unit 3 Footwall Schist 55 4700 SUBLEVEL FIgure Geology plan plan of of the the 4700 4700level. level. Figure9. 9. Geology �Geology of the Golden Golden Giant Mine and Golden Sceptre Orebody Orebody 29 0 X- U T 2W X—CUT X-CUT — 2.1 Ore Waste -- /5.7 -- Ore 18.2 17.8 12.7 12.4 0.7 14.8 6.2 1W X—CUT 8.2 1s :-33 5.8 77 I / SYMBOLS 1 LocA CHIP SAMPLE SAMPLE LOCATION GOLDEN ;OLDEN GIANT GIANMINE MINE 17.5 ASSAY (g/t Au) ASSAY (g/t Au) 1 I11 CHfP SAMPLE CHIP SAMPLE PLAN PLAN 4700 SUBLEVEL 4700 SUBLEVEL SCALE: DATE: APRIL APRIL 1990 1:250 1 ~ 2 5 0 DATE Figure 10. Figure 10. Assay plan of the 4700 level. level. �30 30 Geology Geology and Gold Deposits Deposits of the Hemlo Hemlo Area GEILDEN GOLDEN GIANT G I A N T DEPUSIT DEPOSIT A±eraion A t t e r a t i o nand andMineroiization Mineratization 10 10 AU CEDAR CEDAR CREEK FORMATION FaRMA J l U N 7c UNALTERED UNALTERED ALUMINU—SILICATES ALUMIND-SILICATES 7b 7e --- 45cxb MOOSE MaUSE LAKE LAKE FORMA TION :::::: 3 3b 3b --RULE LAKE LAKE FORMATION SERICITIC SERICITIC PDTASSIC PUTASSIC UNALTERED UNALTERED POTASSIC PUTASSIC 5a SERICITIC SERICITIC 3a POTASSIC PUTASSIC UNALTERED UNALTERED PDTASSIC PDTASSIC 3cx SERICITIC SERICITIC 5ob PDTASSIC PUTASSIC SERICITIC SERICITIC 2b,e 3a ALUMINU—SILICATES ALUMIND-SILICATES UN AL TE RE D UNALTERED Mocified Modified after a f t e rKuhns Kuhns1988, 1988, FIgure Figure11. 11. Generalized Generalizedspatial spatial relationships relationshipsof of alteration alteration and and mineralization mineralization characteristics characteristics of of the the Golden Golden Giant Giant orebody. orebody. Modified Modifiedafter afterKuhns Kuhns(1988). (1988). Qz QZ MOOSE LAKE LAKE PORPHYRY PORPHYRY MOOSE Louden Giant Ghnt Golden A Goden GoLden Sceptre Sceptre 0 granite 0 0 0 1) q u a r t z syenlte UR q u a r t z nonzonite q u a r t z monzodlorlte PG Figure Figure12. 12. Normative Normative orthoclase orthoclase (OR), (OR), piagioclase plagioclase (PG), and quartz (QZ) (QZ) plot plot for for the the Moose Moose Porphyry from the Golden Golden Giant and Golden Sceptre areas. Modified Modifiedafter afterKuhns Kuhns(1988). (1988). Lake Porphyry �S Geology of the Golden Giant Mine and Golden Sceptre Orebody 31 GOLDEN SCEPTRE PROPERTY In the summer of 1990, 1-lemlo Gold Mines Inc. began open pit mining of the North Zone of the Golden Sceptre property. Mining was carried out in conjunction with a quarrying operation that was to provide rockfill for a tailings dam expansion project. The Golden Sceptre pit/quarry is situated about 1.5 km west of the Golden Giant minesite. Numerous, weakly mineralized zones have been identified on the Golden Sceptre property. The most promising of these zones, referred to as the North Zone, is currently being mined. Approximately 180 000 tonnes at a grade of 2.6 g/t Au will be extracted from the North Zone and milled at the Golden Giant Mill. The North Zone occurs within a package of probable clastic metasedimentary and felsic metavolcaniclastic rocks. Host rock protolith determination is difficult due to deformation and alteration. North of the mineralized zone, rock types are more obviously sedimentary, consisting of metamorphosed equivalents of sandstone, pelite, and minor conglomerate. The Moose Lake Porphyry body (Golden Sceptre porphyry of Kuhns, 1988), lies about 100 m south of the Golden Sceptre pit. Kuhns (1988) recognized three textural varieties of the Moose Lake porphyry on this property, which comprise: a predominantly unaltered, minimally strained, feldspar porphyry; a weakly foliated, mica-bearing, feldspar porphyry; and a minimally altered and strained quartz porphyry. Normative quartz÷orthoclase-*.plagioclase abundances indicate a granite to granodiorite composition (Figure 12). Variation in composition is likely due to alteration (Kuhns 1988). Comparable rocks found within the Moose Lake Porphyry may be found in the Footwall Schist of the Golden Giant orebody and have been referred to as the Golden Giant porphyry (Kuhns 1988). North Zone mineralization is characterized by stockwork molybdenite-filled fractures accom- panied by feldspar and biotite alteration. The most obvious alteration occurs as fine-gralned, feldspathic selvages about molybdenite-(±green mica)bearing fractures. Biotite is commonly developed beyond the feldspathic alteration. Carbonate is pervasive throughout the entire mineralized zone. The stockwork zone has been slightly flattened parallel to the regional foliation. Feldspathic margins of fractures oriented perpendicular to foliation are wider and folded relative to contiguous linear fractures oriented parallel to foliation (Figure 13). Complex cross-cutting relationships between mineralized and unmineralized fractures and overprinting of alteration suggests multiple fracturing and mineralizing events. Visible gold is observed along the molybdenite- and green mica-bearing fractures and within the feldspathic alteration rind. There is a direct relationship between gold mineralization and the amount of molybdenite and green mica, Where molybdenite stockwork fracturing is intense, gold grades In excess of 15 g/t Au have been measured. Euhedral, black tourmaline crystals occur along fractures bearing molybdenite + green mlca±pyrlte. The tourmaline grains are randomly oriented within the fracture planes and in some cases are boudinaged. Randomly oriented tremolite and carbonate crystals within vein-like structures or discrete lenses cross-cut the feldspar rinds and molybdenite-green-mica-bearing fractures. �32 Geology and Gold Deposits Deposits of the Hemlo Hemlo Area Area Geology DISCUSSION DISCUSSION Geological relationships evident evident on on the the Golden Geological relationships Golden Sceptre Sceptre property property have been useful useful in in understanding understandingthe the Hemlo Hemlo deposit. The The similarities similaritiesand anddifferences differencesbetween betweenthe the Golden GoldenGiant Giant and and Golden Golden Sceptre Sceptre orebodies orebodiesare arediscussed discussedbelow. below. The gold grade of the Golden Sceptre orebody is much lower than than that that of the the Golden Giant orebody. orebody. In the Golden Golden Sceptre Sceptre orebody, orebody, gold mineralization is confined confined to to narrow narrow fractures fractures dispersed throughout large large volumes volumes of of barren dispersed throughout barren rock, rock, whereas whereas in the the Golden Golden Giant Giant orebody, orebody, mineralization mineralization is is contained contained in in aa zone zone of of pervasively pervasivelyand and intensely intenselyfractured, fractured,feldspathized, feldspathized,and and subsequently subsequently strained strained rocks. rocks. Intense sericitic alteration typical of of the the Golden Golden Giant Giant orebody orebody is is not not developed developed on on the the Golden Golden Sceptre property. Since Since the the competency competency of of the the host hostrocks rockshas hasnot notbeen beenreduced reducedby by sericitization, sericitization,strain strainisismuch muchlower loweron onthe theSceptre Sceptreproperty propertythan thanon onthe theGolden GoldenGiant Giantproperty. property. LEEEND rnolybdenvte green mica bo±i1e £e1dspr 10cm 0 scoe scale FIgure showing the the style style of of alteration alteration and mineralization Figure13. 13. Tracing from a photograph showing mineralization of of the the Golden Sceptre orebody. Golden Sceptre orebody. �Geology Geology of the Golden Golden Giant Giant Mine Mine and and Golden Golden Sceptre Sceptre Orebody 33 The 22 orebodies orebodies display display similar similarmineralogy. mineralogy. Both deposits show the same same relationship relationship grade and and the the abundance abundanceof ofgreen greenmica micaand andmolybdenite. molybdenite. Feldspathic Feldspathic alteration alteration is between gold grade associated with associated with gold gold mineralization mineralizationon on both bothproperties, properties,however, however, ititisisnot not as as intense intenseor or pervasive pervasive on the Golden Golden Sceptre Sceptre property. property. The Hemlo deposit is is commonly commonly described described as as aadisseminated disseminatedgold-molybdenum gold-molybdenum deposit, deposit, implying implying that gold and and molybdenite molybdenite are evenly evenly distributed distributed throughout the ore ore zone. zone. Close Close examination examinationof of ore ore at at aa hand hand sample sample scale reveals reveals that molybdenite molybdenite(and (andgold gold where whereobserved) observed)isis concentrated along along anastomosing anastomosing seams and and vein structures structures within within pervasively pervasivelyfeldspathized feldspathized that the style of mineralization mineralization of the Golden Sceptre and rock. It is becoming apparent that and Golden Giant orebodies is similar. The Golden Giant orebody represents a much more altered, and similar. The Golden Giant orebody represents a much more altered, and mineralized, equivalent of the Golden Golden Sceptre Sceptre orebody. orebody. Golden Sceptre Sceptre mineralization mineralization exhibits exhibits the same spatial relationship relationship to felsic rocks as does the Golden Giant mineralization. The occurrence of the Golden The occurrence of the GoldenGiant Giant orebody orebody at at the the interface interface between quartz-eye quartz-eye schist pelitic metasedimentary between schist (Moose (Moose Lake Lake Porphyry) Porphyry) and and politic metasedimentaryrocks rocksisisnow nowwell well established. Although Althoughthe the Golden GoldenSceptre Sceptre North NorthZone Zone orebody orebody is is not not in in direct direct contact contact with with the the isproximal proximalto toit.it. Other Other mineralized mineralized zones zones on onthe theGolden Golden Sceptre Sceptre property property Moose Lake Porphyry, itit is occur within the the Moose Moose Lake Lake Porphyry. Except Except for for differences differences in in strain, the parts parts of of the the Moose Moose Lake Porphyry at the Golden Sceptre property and in the Golden Giant Mine are very similar in appearance. appearance. There has much dispute dispute over formation and There has been been much over the origin origin of the Moose Moose Lake formation and many many different different protoliths protoliths have have been been suggested suggested to explain favoured genetic models. ItItisistempting temptingjust just to todeclare declare Whatever the the origin of the Hemlo aa rock-hosted deposit and and be be done done with with it. Whatever the Moose Moose Lake Lake Hemlo rock-hosted deposit formation, itit empirically empirically is is the locus locus of hydrothermal hydrothermal alteration and mineralization. mineralization. SUMMARY SUMMARY The Hemlo Hemlo deposit deposit has has undergone undergone a complex complex geological geological history which makes makes genetic genetic modelling of the the orebody orebody rather difficult. difficult. One points that has recognized is that the modelling Oneof of the the key key points has been recognized distribution distribution of of the the ore ore zones zones is is strongly strongly controlled controlled by by the the presence presence of of the the Mafic MaficFragmental Fragmentalunit unit and host host rocks. rocks. The which has resulted resulted in well-defined contacts between ore and The distribution distribution of of the the Mafic Fragmental unit shows an antipathetic relationship with the gold gold mineralization mineralization and and may may In suitable site site for for focussing focussing mineralization. mineralization. In have provided, or represented, an extension of aa suitable addition, addition, the the plagioclase plagioclaseporphyry porphyryintrusions intrusionscommonly commonlyfollow followthe thesame sametrends trendsas asthe the higher highergold gold grades, indicating indicating aa strong strong spatial spatial association associationand andsource sourcefor for the the mineralizing mineralizingevent. event. Hemlo Hemlo Gold Mines Mines Inc. Inc. is committed to an an ongoing, ongoing, detailed examination of the Hemlo Hemlo deposit surrounding area. This deposit and and surrounding Thiscommitment, commitment,in in the the form form of exploration exploration drilling, drilling, structural structural and and geochemical geochemical studies studies (both (both in-house in-houseand and academic), academic), three-dimensional three-dimensionalcomputer-aided computer-aidedmodelmodelof information with neighbouring operations, will help towards a better underling, and sharing of standing standing of this world-class world-class gold gold deposit. �Geology and Gold Deposits of the Hemlo Hemlo Area Geology Gold Deposits 34 PART PART 7: 7: ROAD ROAD LOG LOG FOR THE HEMLO-HERON HEMLO-HERON BAY AREA by 1L. Muir INTRODUCTION INTRODUCTION road guide in this volume incorporates incorporatesover over 30 30 stops, many many of which are are not not part part of of the the The road actual actual field field trip. trip. ItIt is is hoped hoped that that the the guide guide will will provide provide an an opportunity opportunityfor forsubsequent subsequentself-guided self-guided tours 3-day overview (*) tours by by other other geologists. geologists. Stops Stopsintended intendedfor foraa3-day overviewtrip tripare areflagged flaggedwith withan anasterisk asterisk(*) and and cover cover many many of the features features in in the the Hemlo Hemloarea, area, and andsome someof of the the features featuresininthe theHeron HeronBay Bayarea. area. The additional additional stops are intended intended to toprovide provideaamore morecomplete completepicture. picture.ItIti sismandatory mandatory to obtain obtain permissIon permission from the the appropriate mining mining and and exploration explorationcompanies companies to to examine examine outcrops outcrops that that are are not noton onthe thehighway highwayrIght-of-way. right-of-way.Such Suchstops stopsare areindicated. indicated. Over the Hemlo area area have have undergone undergone partial partialto to the last last ten ten years, many many of the exposures exposures in in the Hemlo radical radicalface-lifts, face-lifts,including includingobliteration. obliteration.Those Thoseoutcrops outcropsininthe theimmediate immediatevicinity vicinityofofthe themines mineshave have been susceptible, but been the most most susceptible, buteven even the the highway highway exposures exposures have have undergone undergoneat at least least three threephases phases of modification due to road construction. 1970s, largely due construction. The Thelatest latestand andmost most modification since the late late 1970s, extensive phase phase involved involvedthe the removal, removal,during duringthe the 1989 1989 field field season, season, of up up to 2 m of the exposures extensive back either side side of the highway for safety, safety,drainage, drainage, and andesthetic(?) esthetic(?) reasons. This back from either This resulted resultedin in the loss (e.g.,Patterson Patterson1984; 1984; loss of many many features features that that have have hitherto hithertobeen beenshown shownon onprevious previoustrips trips(e.g., Quartermain Quartermain1985). 1985). The Theoutcrop outcropdescriptions descriptionsprovided providedininthis thisguide guidehave havebeen beenupdated, updated,as asmuch much as possible, to reflect information,based basedon previous as reflect what is observable. observable. Additional Additional information, previous exposures, exposures, is provided few further configuration have providedand and so so noted. noted. AAfew further changes changesin in outcrop outcrop or road configuration haveoccurred occurredsince since the with embossed the original originalpublication publicationofofthis thisguide guideinin1991. 1991. All All Stops Stops have have had had metal metal (claim) (claim) tags tags with embossed Stop Stop numbers numbers attached attached to to the the outcrops outcrops(somewhere) (somewhere) for for cross-referencing cross-referencingwith with the thefield fieldguide. guide. The 3-day 3-day field field trip trip version version begins begins in in Heron Heron Bay Bay (Figure (Figure 14, 14, inside inside front front cover) cover) with with an an The examination of pyroclastic rocks, typical of this section of the greenstone belt, at the Peekongay examination of pyroclastic rocks, typical of this section of the greenstone belt, at the Peekongay Hemloarea. area. property, which is one one of of the the more moreinteresting interestinggold goldoccurrences occurrencesoutside outside of of the theHemlo property, be Followingthis, this, the the Northern NorthernEagle Eagleproperty, property,located locatedabout about21 21km kmwest westof ofthe theHemlo Hemlodeposit, deposit,can canbe Following examined. Here Herealteration alterationand andmineralogy mineralogyare aresimilar similarto tothat thatof ofthe the Hemlo Hemlodeposit, deposit,with withthe thenotable notable examined. exception exception that that gold gold (and (and possibly possibly molybdenite) molybdenite) is is present present only only in in low low and and erratically erraticallydistributed distributed amounts. amounts. Next, Hemlo deposit depositarea area(see (see Figure Figure 18), 18), the Homestake Homestakeproperty propertycan can Next, at at the outskirts outskirtsof of the the Hemlo be visited, in order order to to view view aa variety variety of of features features and and to to provide provide an an opportunity opportunity to to discuss discuss the the relevance to the Hemlo Hemlo deposit. Finally, Finally, aa visit visit to to the the erratically erraticallyauriferous, auriferous, low-grade low-grade Highway Highway Hemlofault fault zone, zone, which which isisnear nearand andsubparallel subparallel to to Highway Highway 17 17 for for several several Zone and and to to the the Hemlo Zone kilometres, kilometres, should shouldcomplete completeDay Day1.1. The second day of the planned field trip includes: includes: aa detailed detailed examination examination of the tectonotectonostratigraphic section section through through the the Hemlo Hemlo deposit deposit along along Highway Highway 17; 17; a visit with the the staff staff of of the the stratigraphic Williams property to see see some some exposures exposures that are are illustrative illustrative of of the the structural structuraland andalteration alteration complexitiesininthe theimmediate immediatevicinity vicinityofofthe theHemlo Hemlodeposit; andaavisit with the the Hemlo HemloGold Gold staff staff to complexities deposit; and visit with examine core and specimens from the Golden Giant Mine. The Thesection sectionalong alongHighway Highway17 17isis presentedin in an an east-to-west east-to-west direction because this allows the field trip participants start with with presented direction because participants to start the and/or altered alteredrocks rocksand andwork work towards towards an anincreasing increasingnumber number of of geological geological the least least strained strained and/or conundrums. conundrums. Two figures are repeatedly referencedin inthe the text. text. Figure Figure14 14shows shows the the regional regionalgeology geologyof of the the Two figures are repeatedly referenced Hemlo-Heron Bay area, along with some of the accompanying field stops, and is located locatedon on the the Hemlo-Heron �Road — Introduction Road Log Introduction 35 35 inside front cover. Figure Figure19 19 shows shows the the local local geology geology of of the the Hemlo Hemlo deposit, deposit, along alongwith withmost mostfield field stops, and is located on the inside back cover. and is located on the inside back cover. It will become become evident evident over the course of the tour that many particularly those many of the rocks, particularly thoseinin the Hemlo Hemlo area, area, have have undergone undergone considerable considerable deformation deformation and, and, locally, locally, alteration, alteration, which whichhave have developed developed heterogeneously. heterogeneously. ItIt is acknowledged, therefore, that these factors, coupled with the the metamorphism, render types, quite quite effects of metamorphism, render lithologic lithologic terms, terms, used used to to denote primary rock types, interpretive interpretive in in many many cases. The Theterms termsused usedin inthis thisfield field guide guide are are based based on on the the examination examination of of many many rocks rocks in in the area area and and their their applicability applicabilitymay may not not be be readily readily apparent apparent in in any any one one outcrop. outcrop. InIn many the interpretation interpretation of many cases, there is is no consensus, among geologists, of the of protolith, protolith, structural structural features, metamorphic metamorphicand/or and/oralteration alterationfeatures, features,and andrelative relativetiming timingof of the the various variousrelated relatedevents, events, features, including including in in some some cases, cases, intrusive intrusiverelationships relationships(see (seeMuir Muir1993 1993for for aa more moredetailed detaileddiscussion). discussion). Another point to note note is is that that the the present present configuration configurationof of the theunits, units,for forinstance instanceas asviewed viewed along the highway highway for this trip, represents represents a highly modified crustal section. The Therocks rockshave have undergone transposition, attenuation, undergone various various stages stages of folding, transposition, attenuation,shearing shearing(i.e., (Le., largely largelyductile), ductile),and and faulting (i.e., largely brittle). The units shown in Figure 19, for example, actually represent (Le., The units shown in Figure 19, for example, actually represent an an assemblage of lithotectonic assemblage of lithotectonic components, components, only some of of which which preserve preserve reasonably reasonably original original stratigraphic stratigraphic segments. segments. In the more more highly highly strained strained parts parts of of this this greenstone greenstonebelt, belt, the theoriginal original stratigraphy stratigraphy is is aa matter matter of of notable notable conjecture, conjecture, and and hence, hence, no no formal formal stratigraphic stratigraphic nomenclature nomenclature has has been been applied. applied. A simplified simplified interpretation interpretation of of the the structural structural history historyused usedfor for this this field field guide guide is is based based on on Muir Muir and given below. Structural and Elliott Elliott(1987) (1987) and and given Structuralmeasurements measurementsare arepresented presentedininthis thisguide guideusing usingthe the right-hand (i.e., strike given such that dip direction direction is is to to the the right). right). right-hand rule rule (i.e., S sedimentaryfeatures. features. S, S refers Sorefers referstotobedding, bedding, generally generally with primary sedimentary refersto to aa composicomposi- Sowith tional layering layering similar similar to bedding which lacks lacks sufficient sufficientcriteria criteriato to be be termed tional bedding but butwhich termed S0 with confidence. confidence. S, small scale. (F,), apparently apparentlyon onaasmall scale. These Thesefeatures featuresare areoverprinted overprintedby by Soand/or and/or S S,are arelocally locallyfolded folded(F1), an S2 So fabric which forms the axial axial planar planar cleavage cleavage to F2 F2 folds, which appear to reflect reflect aa regional regional folding folding event. event. The fabric occurs as a penetrative penetrative foliation, foliation, or a spaced spaced cleavage, and/or a differentiated differentiated Sofabric The S2 layering layering which which locally locally shows showsevidence evidenceof ofmore morethan thanone one stage stageof of development. development.The TheF2 Fgfolds foldsare are open commonly display display S-shaped open to tight (locally (locally presently presentlyisoclinal), isoclinal), and and commonly S-shaped asymmetry asymmetryin in the Hemlo deposit vicinity. The Thefolds foldsplunge plungemoderately moderatelytowards towards the northwest northwest in in the the western western part part of of the the A number number of Hemlo area, and moderately toward toward the the northeast northeast in in the the eastern eastern part part of of the the area. area. A equivocal equivocal explanations explanationsfor for this this configuration configurationcould couldbe beinvoked. invoked. S3fabric fabric above structures structures are are overprinted overprintedby by aa widely widely developed, developed, generally generallymicaceous, micaceous,S3 The above which which is is axial axial planar planar to to F3 F3 folds. The TheF3 F3folds folds have have Z-shaped Z-shaped asymmetry asymmetry and, although although locally locally S3fabric fabricranges rangesfrom from weakly weakly steeplyplunging, plunging,generally generallyplunge plungemoderately moderatelyto to the the northeast. northeast.The TheS3 steeply developed(common),to (common), topossibly possiblypredominant predominantininhigh-strain high-strainzones. zones.The Thefabric fabriclocally locallyisispresent presentas as developed be a crenulation crenulation cleavage, cleavage, particularly particularlywithin withinand andnear nearF3 Fafolds folds and and boudin boudin necks. necks. ItIt appears appears to to be associated associatedwith withaaperiod periodof ofdextral dextralshear, shear, in in which which case, case, where where the the high highstrain strainzones zonesoccur, occur, the the S3 S3 fabric system of components components corresponding fabrics ininshear fabricisisinterpreted interpretedto toconsist consistof of aasystem correspondingwith withs-c-c' s-c-c'fabrics shear S30,and andS3c. S3^. Some Someofofthe thecrenulation crenulationfabrics, fabrics,and andaccompanying accompanyingF3 F3 zones, here here denoted denoted as S33, zones, S3, S3, folds, superposed on shear fabrics, fabrics, possibly possibly as aa result result of ofprogressive progressivedeformation. deformation. IfIf folds, appear appear to to be superposed not specified, specified, the the term termS3 Sofabric fabric refers refers to to the the flattening flatteningfabric fabricof of the the developing developingshear shearsystem system(i.e., (i.e., not S38). S3s). �Geology Geology and Gold Deposits Deposits of the Hemlo Hemlo Area 36 36 Locally F4folds. folds. In In some some Locally there there are are kink kinkfolds, folds, some some in in conjugate conjugatepairs, pairs, which whichare aretermed termedF4 cases, the sense movement on the the conjugate conjugate kinks suggests an east-west directed directed shortening. sense of movement kinks suggests shortening. Only vague hint hint of ofnorth-south north-south oriented oriented pressure pressure shadows; shadows; no no north-striking north-striking Only rarely rarely is there even a vague foliation has cases, conjugate brittle fractures indicate a north-south has been been observed. observed. In other cases, directed shortening. shortening. Relatively late, layer-parallel, layer-parallel, brittle breccias, breccias, ultracataclasites, ultracataclasites, and/or andlor pseudotachylite occur in most units in the vicinity of the Hemlo deposit. deposit. These These features features rarely rarely provide dextral. However, provideany any sense sense of movement, but where determinable, the sense sense is dextral. However,because because these these features featuresappear appearrelatively relativelyfresh, fresh,and andrarely rarelydisplay displayany anyfabric, fabric, they they may maybe be considerably considerablylater later (Proterozoic?) than would be features formed by a progressive transition from ductile to brittle (Proterozoic?) to brittle dextral deformation. dextral deformation. Designations Designations for planar planar fabrics of undetermined undetermined chronology are alphabetically alphabetically subscripted subscripted (e.g., northerly direction direction except (e.g.,5a' Sa,Sb). SJ. Dips Dips are, almost everywhere, in a northerly except for for isolated isolatedcases cases of the 83 S3 crenulation crenulationfabric. fabric. HERON HERON BAY AREA SEGMENT SEGMENT Figure (inside front cover) depicts depicts the generalized generalized geology Figure 14 14 (inside geologyof of the the Hemlo-Heron Hemlo-HeronBay Baypart partof of the indicates the approximate approximate location location of the field stops. Note, indicates the greenstone greenstone belt belt and indicates Note, a "h" "*" indicates field field stops stops intended intended for for the the 3-day 3-day overview overview field field trip. Hotel iy 627 , I I I I I I I- CPR tracks CPR tracks *' £ N -/- store I 00 I 165m 40 4I 0 20 20 I 60 60 I m m scale scale approximate approximate 0 0 A @-Outcrop designation ®..___0utcroP designation :® a—atop A - s t o p number number lamprophyre quartz—carbonate Quartz-carbonate vein aystem, system, crenulated fabrics fabrics Figure Figure15. 15. Stops Stops1,2: 1,2: Simplified Simplifiedsketch sketchmap mapof of the the Heron HeronBay Bay area area stops. Outcrop Outcropat atStop Stop11is is arelapilli-tuff lapilli-tuffand and lapilli-tuff, and and pyroclastic pyroclasticbreccia breccia(see (seeFigure Figure16). 16). Outcrops Outcrops"a" "antoto"d" "d"ofofStop Stop22are lapilli-tuff, lapilli-stone. lapilli-stone. �Road Log Log — -Heron Heron Bay Bay Area Area Road 37 37 * Stop 15 &&16) Stop1: 1: PEEKONGAY PEEKONGAYPROPERTY PROPERTY(Figures (Figures14, 14,15 16) Permission property is formation on Permissionfor for access access to to the the property is required. required. InInformation on whom whom to to contact contact should should be obtained obtained from from the the Resident Resident Geologist's Geologistk Office, Office, Thunder Thunder Bay (see address address on title title page). Location: just south of the Lecours Location: 165 165 m west of Highway 627 on the gravel road just Lecours sporting goods goodsstore, store,about about80 80m msouth southof ofthe theCP CPrailway railwaytracks tracksat atthe thetown townof of Heron HeronBay. Bay. Climb Climbover overthe thehill hill at cleared off outcrop outcrop area. area. A description description of at the the north northside sideof of the the road road to a cleared of the the Peekongay Peekongayproperty property in the section section "Part 4: Peekongay Peekongayproperty" property" in in this this field field guide. guide. The Theoutcrop outcropfor for in general general is given in the Stop shafts of of the the Heron Heron Bay Bay Mine Mine (see (see "Main "Main Zone Zone Mineralization", Mineralization", Stop11(Figure (Figure16) 16)is is the the site site of of the the 22 shafts Part Part4). 4). This This outcrop outcroparea areaconsists consistsofofheterolithic, heterolithic,intermediate intermediate(to (tofelsic), felsic),quartz-feldspar-phyric, quartz-feldspar-phyric, lapilli-tuff size). Variations lapilli-tuff and pyroclastic breccia (by fragment size). Variations in in the the size size and andabundance abundance of of fragments fragments in in the the outcrop outcrop can can be be seen, particularly particularly from from north north to to south, south, but but no no bedding bedding is is clearly clearly defined. defined.Some Somefragments fragmentsare areblocks blocksup uptoto50 50cm cmlong. long.The Themajority majorityofoffragments fragmentsare aremore morefelsic felsic than than the the matrix. matrix. Some Somefragments fragmentsconsist consistmainly mainly of of chlorite chlorite and and feldspar feldspar phenocrysts. phenocrysts. The The Metavoicanic Rocks SYMBOLS — lithologic iithoiogiccontact contact —-.,_......—.—— fault/shear faultlshearzone zone small small cliff cliff shaft shaft 3 pit/open p w o p ecut n cut dump dumpmaterial material —• • . . la heterolithic breccia with some mafic clasts lb iapilli-tuff and/or massive porphyritic rocks 22 mafic(biotite—rjch) (biotite-rich) dike dike mafic 33 sericite-carbonate achiet schist serlcite—carbonate quartz-carbonate vein vein quartz—carbonate trail trail outcrop outcrop access access \ 10 m Figure Figure16. 16. Stop Stop1:1: Detailed Detailedsketch sketchmap mapof ofan anoutcrop outcropon onthe thePeekongay Peekongayproperty propertyatatthe theold old Heron Heron Bay Bay Mine. Mine.Outcrop Outcropconsists consistsofofcalc-alkalic, calc-alkalic,intermediate intermediatecomposition, composition,quartz-feldsparquartz-feldsparporphyritic, porphyritic,pyroclastic pyroclasticdeposits depositswith withlocal localcarbonatization carbonatizationand andaamineralized mineralizedquartz-carbonate quartz-carbonate vein veinsystem. system.(Geology (GeologybybyB.R. B.R.Schnieders, Schnieders,MNDM, MNDM,1990). 1990). �Geology Geology and and Gold Gold Deposits Deposits of of the the Hemlo Hemlo Area Area 38 fragments are elongated and plunge moderately to the west. west. Sericite±chlorite Sericitekchloriteare arepresent presentinin various variousamounts amountsin inthe the matrix matrixand andfragments. fragments. Two Twoto to three threeplanar planarfabrics fabricsare arepresent presentand andalthough although the the rock rock has has aa "sheared" "sheared" appearance, appearance, kinematic kinematic indicators indicators are are insufficiently insufficientlydeveloped developedto to allow allow deduction deduction of of sense sense of of movement, movementl if any. any. AAsample sampletaken takenfrom fromthis thisoutcrop outcropfor forU-Pb U-Pbzircon zircon geochronology 2 6 9 5 e Ma Ma(Corfu (Corfuand andMuir Muir1989a). 1989a). geochronologygave gavean anage ageof of 2695±2 The rocks carbonatization as quartz-carbonate veins rocks show pervasive, disseminated carbonatization as well as quartz-carbonate which planarfabrics, fabricsl Sa Saand and Sb. AAconspicuous conspicuous0.3 0.3to to22mmthick, thick'sinuous sinuous which are are deformed deformedabout about22planar carbonate quartz vein carbonate++quartz veinsystem systemcuts cutsacross acrossthe the outcrop, outcrop,striking strikingfrom from 275° 275O to to 300°, 300°oblique obliqueto to the the predominant planar fabrics in in the theoutcrop. outcrop. The vein system system locally consists consists of up up to to 70% 70% carbonate. Sulphide minerals minerals present present include include pyrite, pyrite, chalcopyrite, chalcopyrite, galena, galena, sphalerite, sphaleritel and and carbonate. molybdenite. tourmaline veinlets veinlets molybdenite. The The wall wall rocks rocks to to the the vein vein system system appear appear bleached. Quartz Quartz++tourmaline which quartz + carbonate±chlorite±tourmaline(?) which are are slightly slightly deformed deformedare are locally locallypresent, present' as as are quartz + carbonat~chloritektourmaline(?) veinlets. veinlets. Structural StructuralSummary: Summary: Overall flattening flattening of of fragments; fragments; Sa Sa 250/44 250144 Overall Subordinate Subordinate fabrics fabrics (not (not everywhere everywherefound): found): 256166 (forms (forms diamonds/lozenges diamondsllozengeswith withabove) above) Sb 256/66 5b Sc 225/45 225145 S 280187 (crenulates (crenulatesthe the above above 22 to to33 fabrics) fabrics) Sd S,, 280/87 275/23 elongation Lineations: elongation 1. 275123 Lineations: 290/35 L ,, 290135 (tourmaline) (tourmaline) mineral mineral L, crenulation L 252/30, 252130, 266/0 266107275/23 275123 crenulation Stop Stop 2: 2: HERON HERON BAY BAY PYROCLASTIC PYROCLASTICROCKS ROCKS(Figures (Figures14 14 && 15) 15) 110 m msouth south of of the the CP CP railway railway tracks tracks at the town of Location: Set Set of outcrops outcropson on Highway Highway627, 627,110 Location: Heron Bay. Bay. Heron These These outcrops outcropsare are typical typicalof of Heron HeronBay Bay pyroclastic pyroclasticrocks rocksand andconsist consistof oflapilli-tuff lapilli-tuffand andlapillilapillistone. The The rocks rocksare are caic-alkalic calc-alkalic dacite (intermediate) (intermediate) in composition, compositionl although although rhyolite rhyolite breccias breccias are heterolithic in texture and are locally locally found. Overall, Overall,the thefragments fragmentsare are subrounded subrounded to to subangular, subangularl heterolithic composition, commonly more felsic than the matrix, and quartz-feldspar phyric. Some Someof ofthe the compositionl matrixl fragments fragments are more mafic than the the matrix matrix and and include include intermediate, intermediate, feldsparfeldspar- ±quartz-phyric Quartz-phyric Thematrix matrix and mafic, mafic, aphyric aphyric rocks. rocks. Bluish quartz phenocrysts are locally common. The rocks, and consists quartz, sericite, *chlorite. The Theupper upperparts partsof ofoutcrops outcrops"b" "bl' and and"c" "c"reveal revealthat that consists of of feldspar, feldspar' quartzl sericite, ±chlorite. the degree of fragment elongation elongation is greater greater than than the the degree degreeof offlattening. flattening. Elongation lineations plunge plunge moderately moderately to to shallowly shallowly to to the the west. west. The outcrops, outcrops, particularly "b" llbll and and "c", llclll display display evidence evidence of of irregularly irregularly developed, developedl dissemidisseminated carbonatization, light-brown-weatheringl quartz-carbonate quartz-carbonate veins. veins. carbonatization, as as well well as asdeformed, deformedl light-brown-weathering, Pyrite 3 mm) are are present present in inthe thecountry country rock. rock. Within Within this zone Pyrite cubes cubes upto up to55 mm rnm across across (commonly (commonly3 of carbonatized carbonatized rocks, fragments, which which contain contain chloritekbiotite, chlorite±biotite, may have quartz quartz rocks' the more more mafic fragments, are intruded by aa foliated pyrite cubes. cubes. These outcrops outcrops are foliated (Archean?), (Archean?), carcarphenocrysts and pyrite bonatized, bonatized, biotite biotitelamprophyre lamprophyre dike. dike. The south face of of outcrop outcrop "b" "b" shows shows folded, foldedl quartz-carbonate quartz-carbonate veins veins and and schistose schistose planes planes with lineations. The with 2 and possibly possibly 3 sets of crenulation lineations. The south south end end of of outcrop outcrop "c" shows shows a planar fabric compared to the fabrics in the the fragments. fragments. There fabric in the matrix matrix that is oriented differently compared There are also a few, few, west-plunging' west-plunging, minor folds folds with with "S" asymmetry. �Road Log — Heron Bay Area 39 Structural Structural Summary: Summary: Outcrop "b": 'b": Predominant (undulating) Predominantfabric fabric —270/87 -270187 (undulating) Crenulation Crenulation lineations: lineations: 090/00±07 09010M7 L1 LLC* —088/67 L). -088167(overprints (overprints L,). consists of short, consists short, small-amplitude, small-amplitude, small-scale, small-scale, anastomosing anastomosingcrenulations. crenulations. L1 Ll L, is predominant. predominant. Outcrop "c": "cn: General flattening 240/50 flatteningof of fragments fragments 240150 Fabrics in fragments (anastomosing): predominant 258/? predominant 245/? 24519 and subordinate 25817 matrix: 268/? Fabric in matrix: 2681? Elongation lineation lineation (fragments): Elongation (fragments): Le 280/30 280130 275/75; 290/44 Minor "S" " Sfold: fold: axial plane 275175; axis 290144 Quartz-tourmaline Quartz-tourmaline veinlet veinlet 240/60 240160 THOLEIITIC PILLOWED Stop 3: Stop 3: THOLEIITIC PILLOWED FLOWS FLOWS (Figure (Figure 14) 14) Location: north on Highway Highway 627, from the the railway railway crossing crossing at Heron Heron Bay, to to an an outcrop outcrop Location: Go 4.2 km north 627 from on the west side where a power line crosses the the highway. highway. This is a minor stop and is intended to illustrate belt are are relatively relatively undeformed undeformed compared compared to illustratethat that some some segments segmentsof of this this part part of the belt to rocks rocks in in the Hemlo deposit vicinity. Discrete Discretezones zones of of significant significant strain, up up to several metres thick within pillowed flows exposed on the shoreline mafic pillowed flows for example, example, are are well exposed shoreline of Lake Lake Superior Superiorat at Pulpwood Pulpwood National Park to to the the south. south. However, Hemlo deposit, Harbour in Pukaskwa National However, in the vicinity of the Hemlo significant significant strain strain is is essentially essentiallypervasive. pervasive. Several The more more northerly northerlyones onesconsist consistof of aa "massive", "massive", Several small outcrops constitute constitute this stop. The mediummafic,tholeiitic tholeiiticflow. Oneoutcrop outcropdisplays displayswhat appearstotobe beaadike with medium- to fine-grained, fine-grained, mafic, flow. One what appears dike with highly irregular Themain mainoutcrop outcropconsists consistsof of mafic, mafic, tholeiitic tholeiiticpillows pillowsand andaa "massive" "massive" irregular orientation. orientation. The section, possibly part part of the same flow. Although the pillows pillows are somewhat flattened, they have flow. Although well-defined shapes preserved and indicate well-defined indicate that that the the top top direction direction is toward toward the the south. south. The most southerly outcrop exposes exposes aa section section that thatdisplays displayspossible possibleflow flowbanding bandingand andwhat whatappears appearsto tobe beaa southerly outcrop breccia or pillow breccia. Minor Minorquartz±carbonate quart*carbonate veins veins are arepresent, present, particularly particularlyininthe the flow top breccia main outcrop. Structural Structural Summary: Summary: S —100/75 "flattening" Sp 400175 "flattening"of of pillows pillows V 190/25 quartz-carbonate V 190125 quartz-carbonate vein vein * Stop Stop 4: 4: NORTHERN EAGLE NORTHERN EAGLE PROPERTY PROPERTY(Figures (Figures14 14&& 17) 17) Permission for access to the property is required, required. In formation on whom to contact Permission Information contact should should be Resident Geologist's page). obtained from the Resident Geologistk Office, Thunder Bay (see address on title page), Location: Return north to Highway Location: Highway 17 17 and head head 6.3 km east on Highway Highway 17 17 to the the Black Black River River bridge, the east end end of of the the bridge. bridge. (This point can be more more accurately accurately bridge, then continue continue 900 900 m m beyond the located gravel road, locatedby bynoting notingaagravel road, that thatheads headssouth southfrom fromthe the highway highwayabout about650 650m mfrom from the the bridge, bridge,then then continuing320 320 m m beyond beyond it, it, to to aa point point 30 m past the Beaver Beaver Tourist Centre Take the the diamond diamond continuing Centre sign.) Take drill road, which is on the north side of Highway 17 at at this this point, point, and follow it, essentially essentially north, north, for about 230 230 m to a power [Note: As of 1993, aanew about power line. line. [Note: newsubsidiary subsidiary powerline powerline now now crosses crosses the the highway here rendered delineation delineation of difficult. However, here and and has rendered of the the drill drill road road difficult. However,the thedrill drill road roadintersects intersectsthe theeast east side of the powerline powerline right-of-way near the the west the highway.] highway.] Cross the power line (slight jog to the across continue on essentially north, across a small creek) and and continue on the same drill road, again essentially north, to to aa small hill. Go Go �4ab end of clearing / 4ab 5bc 5ac 2a3d 411a 6 —3d,2? 4b 4ab - 4dba 4b- 0 3a 2 - 54acj 4a 5ab_t 4c - 4c(a,b)'2a 4b 2d,3c garnet 3ab 4b,3ab 3a 3a 4b,3ab 2dbc C 4 3a 6 -4b 4a,3a 14e 4aI' 2b a3a 2b 8 4b'4b 1 4e,5b \p Trench 4 m °4a 4ab 5d 2b 4a.(2b) 4d e5c 5d 4ab 5c - 4cac 4c /4ba Trench 1 x=rocks with distinctive spaced cleavage 4ba ,_2d 5a- 4b 4c 2d3c -2d A CD 3 0 -' CD CD 0 -I' Cl) 0 Cl) -C CD a a 0 G) a p) 0 0 CD CD G) 0 Geology and Gold Deposits of the Hemlo Area �Road — Heron Road Log Heron Bay Area Figure legend below) Figure17. 17. (Opposite (Oppositepage, page, legend below) Northern Eagle property. Detailed Stop 3: 3: Eagle property. Detailed sketch map of the main barite showing. showing. Upper Upper part of figure figure represents represents the west half of the the stripped area. area. Lower Lower part part represents representsthe the east east half. Point Point"A" "A" in each part of figure figure represents represents the same geographic geographic location. location. Identification Identification of alteration is minerals and alteration is based basedon on field field obserobservations and and interpretation. interpretation. (Geology by by T.L. T.L. Muir, OGS, 1990). 1990). LEGEND: STOP STOP 4 LEGEND: Mafic Metavolanics(?) ~etavolanicd?) 1 1 biotite+amphibole biotite+amphibole schist (mafic), (mafic), subgneissic subgneissic Metamudstone 2a 2a black black 2b 2b 2c 2c dark gray dark 2d 2d medium—light gray gray medium-light mediumgray, gray, sandstone medium sandstone Altered Rocks Mudstone Rocks Derived Derived from from Mudstone 3a 3a sericitekbiotite (laminated, cleaved) cleaved) sericite±biotite (laminated, 3Sb b sericite+biotite+pyrite (laminated, cleaved) cleaved) sericite±biotite+pyrite (laminated, 33c c 3d 3d feldspar+sericite+green feldspar+sericite+green mica+pyrite mica+pyrite schist feldspar+sericite schist feldspar+sericite schist Altered Rocks Rocks of of Undetermined Undetermined Protolith Protolith Schistose Schistose 4aa 4 4b 4b 4c 4c 4d 4d 4e 4e feldspathized sericitized, feldspathized sericitized, pyrite sericitized, sericitized, green green mica, mica, pyrite pyrite sericitized, silicifled sericitized, silicified sericitized, sericitized, silicified, silicified, barite barite Granular 5a 5a feldspathized+silicified+ barite feldspathized.i-silicified±barite 5b 5b 5cc 5 5 5dd feldspathized+pyrite (commonly feldspathized+pyrite (commonly in in seams)+barite seams)tbarite silicified±feldspathized+pyrite silicified* feldspathized+pyrite barite—richsilicifiedfeIdspathized±pyrite barite-richtsilicified~feldspathizedkpyrite Dikes Dikes 6 / / feldspar porphyry porphyry quartz vein quartz 41 41 over the the hill on an old grid line to a up and over m from from the the power powerline. line. clearing, about 360 m The road road and grid line are flagged flagged and and recut recut for this this trip. the Northern Northern Eagle Eagle For the most part, the property structurally overlies overlies south-dipping south-dipping mafic metavolcanic metavolcanic and and metasedimentary metasedimentary rocks. In Inthe the stripped strippedarea, area, exposures exposureshave have been overastrike been created over astrikelength lengthof ofabout about100 100 m and a width width of up to to 12 m m (Figure (Figure 17). 17). The showing showing is is now now considerably co-nsiderablyovergrown overgrown and and oxidized in parts. parts. In 1995, significant additional stripping stripping was undertaken undertaken to the north, north, adjacent to the original stripping. This adjacent stripping. This new new exposure has not been mapped by the auauthor. As presently presently exposed, exposed, the the outcrops outcrops consist of argillite, argillite, which which locally locally has has been been moderately to intensely altered and demoderately to intensely altered deformed, massive massive to laminated laminated barite barite and and sulphide minerals, minerals, sericite sericite schists, minor mafic schists, and feldspar In feldspar porphyritic porphyritic dikes. dikes. In earlier reports, these rocks collectively collectively have have interpreted to been interpreted to be be barite±sulphide-bearbariteksulphide-bearing cherts and quartzites, quartzites, as graphitic as well well as graphitic argillite, siltstone, quartz ÷+ seriargillite, siltstone, arkose, arkose, quartz sericite±carbonate±limoni schists, "massive" "massive" cite±carbonate±Iimonite barite, and barite, and quartz-feldspar quartz-feldspar porphyries porphyries (MNDM assessment assessmentfiles, files, Thunder ThunderBay; Bay;GlidGlid(MNDM don 1985). don 1985). The western western part of the the stripped stripped area area consists of black to dark dark grey grey argillite, argillite, and and white-weathering rocks, rocks, consisting consisting of feldwhite-weathering spar, quartz, quartz, sericite, sericite, and and green green mica, mica, which which interpreted to be altered altered argillite because are interpreted of the similar of similar cleavage cleavage developed developed in both both rocks and the intimate intimate spatial spatial association association between light light and dark coloured between coloured rocks. rocks. Xenoliths of the green-mica-bearing green-mica-bearing schists are present in the feldspar feldspar porphyry porphyry dikes. dikes. suggests that that the alteration This suggests alteration preceded preceded intrusion, because black black argillite is intrusion, because is locally locally present present as the host rock rock to the dikes, and and itit is considered unlikely that alteration considered unlikely alteration could could have pervasively pervasively altered altered the the dike dike (and (and xenolith) and not the immediately immediately adjacent adjacent councountry rock. The The porphyritic porphyriticdikes dikesare are similar similar to inferred to have have inindikes at Hemlo that are inferred truded at truded at 2687±3 2687± Ma Ma (Corfu (Corfu and and Muir Muir 1989a). 1989a). �42 42 Geology and Gold Deposits Deposits of the Hemlo Area If the the alteration alteration exposed property was contemporaneous contemporaneous with exposed at the Northern Northern Eagle Eagle property withthe themineralizmineralization of the Hemlo Hemlo deposit, and if the porphyry dikes at this stop are coeval with those at at the the deposit, then then aa minimum minimum age age of of mineralization mineralizationisis2687±3Ma. 2687±3Ma The majority of the remainder remainder of the exposures in the east part of of the the stripped stripped area area are are interpreted to be be highly highly altered altered rocks rocks derived derived from from an anequivocal equivocalprotolith. protolith. However, several several outcrops along the north north side and east east end endreveal revealgrey greyand anddarkgrey darkgreyargillitic argillitic metasiltstones metasiltstones which which outcrops along locally schists. An locally can can be seen to grade relatively abruptly into white to buff schists. An isoclinal isoclinalfold fold can can be be seen near the east end of the stripped stripped area. The The main mainfabric fabrichere hereis isaxial axial planar planarto to the the fold fold and and is is parallel weakly defined layering in inthe thesiltstone. siltstone. Transposition and differentiation differentiation of the layering parallel to weakly layering appears appears to have have locally locally taken taken place. place. As Assuch, such,the thelayering layeringpresent presentin inthese theseoutcrops outcropsshould shouldnot notbe be assumed to be bedding. In Inthis thisarea, area, several several discordancies discordanciesof of fabrics fabrics and and layering layering can can be be seen suggesting suggesting faulting faulting has has taken taken place. place. There trenches across exposed area. These variety of There are are 4 trenches across the width of the exposed These trenches trenchesreveal revealaavariety schists and "massive" rocks which are heavily weathered. weathered. The rocks are considerably considerably deformed and appear to have resulted, based on field identification (i.e., (i.e., no laboratory laboratory confirmation) confirmation) from from feldspathization, silicification, sericitization, and and pyritization, pyritization, which which in in places places is is reminiscent reminiscent of of alteration at alteration at the the Hemlo Hemlo deposit deposit(e.g., (e.g., Stop Stop33A) 33A) and/or and/or the the Barren BarrenSulphide SulphideZone Zone (Sucker (SuckerZone) Zone) (Stop 14). The The schists schists range range considerably considerably in in their their content content of of green green mica, mica, barite, barite, feldspar, quartz, quartz, sericite, and and pyrite. pyrite. The Thegreen greenmica micahere hereisissomewhat somewhat different different in in colour colour than than that that of of the the Hemlo Hemlo deposit and thus may contain different types or relative abundances of trace elements. The green deposit and relative abundances of trace elements. along cleavage cleavage planes. planes. Pyrite is mica at this stop is largely present in flattened lenses and along is the The barite occurs in common sulphide. The in zones zones of of various various concentrations concentrations and and isiscommonly commonly equigranular and and fine fine grained. grained. Gliddon recrystallized. Barium equigranular Gliddon (1985) interprets it to have been recrystallized. Barium occurs in trenches trenches ito barite-rich zones occurs 1 to33ininamounts amountsininexcess excessof of 20% 20% (Cavey (Cavey 1984). Some Some of the barite-rich zones variably laminated laminated parallel parallel to tothe thepredominant predominantfabric. fabric. The The origin originof ofthe thebarite bariteisiscontentious. contentious. It are variably appears here to be spatially associated associated with with shear shear zones zones (Gliddon (Gliddon 1985) 1985) and and alteration, alteration, and andlies lies within isoclinally isoclinally folded folded and tectonically tectonically disrupted disrupted argillite. results from these trenches returned returned values of of 50.005 0.005 oz Assay results ozof ofAu/short Aulshortton, ton,up upto to 32.76% 32.76% Ba in zones containing containing barite, barite, and and up up to 1000 1000 ppm As (MNDM (MNDM assessment files office, office, Thunder Thunder Bay). Gold ton have been reported reported (Northern 1983, Goldvalues valuesup upto to0.12 0.12 oz. per ton (NorthernMiner, Miner,November November23, 23,1983, p.23), but were not noted noted in the assessment assessment files. Structural Summary: Structural West end: end: Fabrics Fabrics at at 090/80, 090180,and and 077/83 077183 in argillite argillite Foliated Foliated dike oriented oriented at 265/56 265156 with internally internally deformed deformed quartz quartz veins veins Central: Central: Fabrics at 082/77 and 072/77 in in green mica mica schist schist 084171 plane of west-closing isoclinat isoclinalfold fold at at084/71 East East end: end: Layering and axial plane Fabric Fabric overprinting overprinting fold at at 095/77 095177 cleavage at Faint cleavage at 077/79 077179 �Road Road Log Log — -Introduction Introduction 43 HEMLO AREA AREA SEGMENT: SEGMENT: HIGHWAY HIGHWAY17 17 HEMLO Figure 18 18 displays the location location of of field field stops stops numbered numbered 5 to 31 inclusive. Figure Figure19 19(inside (inside Figure back back cover) cover) and and Figure Figure 20 illustrate illustrate the lithologic lithologic units units and and major major structural structural components components in in more more detail. detail.Figure Figure21 21shows showsthe the"cultural" "cultural"features featuresand andprojected projectedore orefor forthe theHemlo Hemlodeposit depositand andvicinity, vicinity, and and includes includes locations locationsfor for Stops Stops 77 through through 26. Figure Figure22 22 depicts depictsaa projected projectedlongitudinal longitudinalview viewof of the (*) Hemlodeposit deposit at at the the same same scale scale as as in in Figure Figure 21. 21. Note, Note,an an asterisk asterisk(*) the main mainore ore zone zone of of the the Hemlo indicates indicatesfield fieldstops stopsintended intendedfor forthe the3-day 3-dayoverview overviewfield fieldtrip. trip. Stop INTERIOR OF OF CEDAR CEDAR LAKE LAKEPLUTON PLUTON(Figures (Figures14 14and and18) 18) Stop5: 5: INTERIOR Location: km east east of of the the Highway Highway 614 turnoff turnoff (to Location: Highway Highway17, 17, about about 1.1 1.1 km (to Manitouwadge), Manitouwadge),ororififone one is Creek which enters iscoming comingfrom fromthe theeast, east,ititisisabout about3.7 3.7 km km west west of Wabikoba Creek enters Cedar Cedar Lake. Lake. The The stop stopisisat at the the west west end endof of aa long long roadcut roadcut on both both sides sides of the highway. The The following followingdescription descriptionisis based basedon on the the westernmost westernmost 75 75 m m of of the the roadcut roadcut on on the the north-northwest north-northwestside. side. The The majority majority of of the theCedar CedarLake LakePluton Plutonconsists consists of of very veryweakly weakly totomoderately moderatelyfoliated, foliated, medium-grained, microcline-megacrystic, microcline-megacrystic, hornblende-biotite hornblende-biotite granod granodiorite contains ubiqubiqmedium-grained, iorite that contains uitous mafic/ultramafic(?) xenoliths. This main main phase phase has has been been intruded intruded by by aanumber number of of uitous mafic/ultramafic(?) xenoliths. This subordinate,fine-grained, fine-grained,more moremafic maficphases. Themegacrystic megacrysticphase phaseatatStop Stop5 hasbeen beendated dated at at subordinate, phases. The 5 has 2688±3 2688± Ma Ma (Corfu (Corfu and and Muir Muir 1989a). 1989a). The The effects effects of of hematization hematization and and epidotization epidotization are are locally locally present, present, and and may may be be extensive. extensive. There There isissome some evidence evidence that that this this type type of of alteration alteration may maybe be associated with fault zones. associated with fault zones. Other Other exposures exposures of of this this phase, phase, such such as ason onHighway Highway614 614toto Manitouwadge, Manitouwadge,display displayaa wider wider variety varietyof of xenoliths xenolithsand anddikes, dikes, including includingaplite apliteand andpegmatite. pegmatite. Themicrocline microclinemegacrysts megacrystsrange rangefrom frommedium mediumto tocoarse coarsegrained, grained,up uptoto2.5 2.5cm cmlong, long,and and The contain contain fine-grained fine-grained crystals crystals of of hornblende, hornblende, quartz, quartz, plagioclase, plagioclase, and and possibly possibly biotite. biotite. Crude Crude zoningisisapparent apparentininsome somemegacrysts. megacrysts.The Thexenoliths xenolithsrange rangefrom fromabout about55mm mmtoto30 30cm cmlong, long,and and zoning are are most most commonly commonly about about 2 to to 44 cm cm long. long. Most Mostofofthem themappear appeartotobe befine-to fine-tomedium-grained medium-grained amphibolite, amphibolite, although although some some appear appear to to have have little littleor or no nosalic salicminerals mineralsand andare are hence hencepresently presently ultramafic. ultramafic. The The xenoliths xenoliths are are generally generally aligned aligned parallel parallel or subparallel subparallel to the the foliation foliation in in the the granodiorite,where wherethe thelatter lattercan canbe bediscerned. discerned.The Theorientation orientationofofthe thefoliation foliationisissimilar similartotothat thatof of granodiorite, S3 Soin in the the country countryrocks rocksand andisisinterpreted interpretedtotobe bemost mostlikely likelyrelated relatedtotoD3. Do. Themegacrystic megacrysticgranodiorite granodioriteatatthis thisstop stophas hasbeen beenintruded intrudedby byaafew fewintermediate intermediatedikes, dikes, The likely Archeanage, age, and and aa Proterozoic Proterozoicbiotite biotite lamprophyre lamprophyredike. dike. The TheArchean Archeandikes dikesare aresheared, sheared, likelyof ofArchean with withan anapparent apparentdextral dextralsense. sense. This Thisrelationship relationshipand andthe thepresence presenceofofan an"S3-oriented" "So-oriented"fabric fabric within postdated intrusion withinthe thepluton plutonsuggests suggeststhat thatatatleast leastsome someof ofthe the D3 Dostrain postdated intrusionand andcrystallization crystallization (i.e., (i-e,,2688 2688Ma). Ma). Structural StructuralSummary: Summary: S9 Sgranges rangesfrom from260/70 260170toto275/60; 275160; alignment alignmentofofmafic maficminerals mineralsiningranodiorite granodiorite shearedintermediate intermediatedike; dike;fabric fabricsubparallel subparalleltotodike dikemargins margins Sd Sd 302° 302' sheared dike;biotite/hornblende; biotitehornblende;back backrotated rotated Sa Sa 281° 281 inindike; Sb Sb 327° 327' inindike; dike;deflects deflectsSa Sa DD 145/70 14-5/70 lamprophyre lamprophyredike dike * Stop Stop6:6: WEST WESTCONTACT CONTACTOF OFCEDAR CEDARLAKE LAKEPLUTON PLUTON(Figures (Figures14, 14,18 23) 18 &&23) LocatIon: Location: Go Goabout about1.1 1.1km kmwest-southwest west-southwestof ofthe theHighway Highway614 614turnoff turnoff(to (toManitouwadge) Manitouwadge)on on Highway Highway17, 17,to to the the contact contactof ofthe theCedar CedarLake LakePluton Plutonnear nearthe theeast eastend endofofaalong longroadcut roadcutbeginning beginning on onthe thenorthwest northwestside sideofofthe thehighway. highway.The Thelast lasthighway highwayexposure exposure(in (inthis thisdirection) direction)ofofmicroclinemicroclinemegacrystic megacrysticgranodiorite granodioritelies liesabout about300 300mmeast-northeast east-northeastofofhere. here. �5 A A0 BAA ^</ otham A Williams Mine A e Hwy 17 Manitouwadge If / White River 0 CD 0 0 CO a. Yellow Brick Road 0 0 a a CD 0 Cl) 0-1 I CD CD 3 0 -' CD �— Hemlo Area Road Log - 45 45 The contact contact phase phase of of the the Cedar Cedar Lake LakePluton Plutonisisfinefine-totomedium-grained, medium-grained,biotite-hornblende biotite-hornblende granodiorite weak foliation within several several metres metres of the the contact. contact. This granodioritewhich whichisismassive massiveexcept exceptfor for aaweakfoliation This phase is not exposed exposed elsewhere the bush phase elsewhereon on roads roadsor or railways railwaysand and its its extent extentin in the bush is is unknown, unknown, as as is is its its relationship phase(s) (see 5). The relationshipwith with the the main main megacrystic megacrysticphase(s) (seeStop Stop5). The granodiorite granodioriteatStop at Stop66has hasbeen been 2687± Ma Ma (Corfu (Corfu and and Muir Muir 1989a). 1989a). dated at 2687±3 to 40 cm thick, thick, and some pegmatitic pegmatitic The granodiorite is intruded by many aplite dikes, up to cmthick. thick. Some of of the the dikes dikes are arecomposite composite aplitelpegmatite. aplite/pegmatite. Although dikes, up to 10 cm Althougheither eithertype type may crosscut the other, other, more often often than not, pegmatitic dikes crosscut aplite dikes. The Thedikes dikes terminate against against the the schist, ductile deformation within the contact terminate schist, although some some display display ductile deformation within contact granodiorite (Photo granodiorite (Photo 1). 1). This This may may indicate indicate that that extensions extensions of the dikes into the country rocks have been sheared off. The The dikes dikes display display aa range range in in strike strike but tend to have preferred preferred orientations orientations as as approximated approximatedbelow. below. DIke orientations: orIentations: Dike 305/52 5 m from contact 290/64, 290164,305152 260±5°, 290±5O 290±5°, 330S0 330±5° 10 m from contact contact 260±5O 65 m from contact 250±5°, 250±5O270±5° 270±5 The country within about The country rocks within about 9 m m of of the the contact contact consist consist of of crenulated crenulated mafic mafic schist schist containing containing several several aplitic aplitic and and granodioritic granodioriticdikelets dikeletsand andstringers stringerswhich which display displayrefolded refoldedfolds foldsand and are locally dismembered. dismembered. Refolded dikeletsadjacent adjacentto to granitoid granitoidbodies bodiesin in the the area area Refoldedfolds foldsin inaplitic aplitic dikelets have been noted elsewhere elsewhere (e.g., (e.g., Cedar CedarCreek CreekStock, Stock,Pukaskwa PukaskwaBatholithic BatholithicComplex). Complex). Although Although it may be inferred inferred that these refolded by F3 (which is is associated associated with the crenulation these are are F2 F, folds refolded Fy (which crenulation fabric), this poses poses problems based on the inferred timing of intrusion relative to regional regional folding folding be more more likely likely that, that, during during intrusion, intrusion, differential differential ductile movement (see Stop 11). It may be movement between Stop 11). relatively softened, contact-metamorphosed relativelysoftened, contact-metamorphosedcountry countryrocks rocksand and the the intruding intruding granitoid granitoid magma, led to marginal-restricted marginal-restricted zones zonesof of progressive progressivedeformation deformationthat thatdid didnot not produce produceanalogous analogousstructures structures farther farther away away from the plutons. plutons. To the the west west of of the the crenulated crenulated mafic schists, schists, for for about about 15 15 m, m, the the country country rocks rocks consist of of a To mixture of mafic, biotite-hornblende schist (either of sedimentary or igneous origin), pyritiferous argillitic rocks, dikeletsand and argillitic rocks, and and some some metawacke, metawacke,all all of of which which have have been been intruded intrudedby by aa few few aplitic aplitic dikelets quartz veins. veins. Within this schist, a granodioritic granodioritic dike intruded intruded by quartz quartz veins veins contains contains minor minor molybdenite, molybdenite, although although most most of this this has has been "excavated" "excavated" by by moly-thirsty moly-thirsty "geotourists". "geotourists". For approximately approximately the the next next 150 150 m, m, the the country rocks consist For consist mostly of various various sets sets of of metawackes and metasiltstones which which have been been intruded intruded by by swarms swarms of of dikes. dikes. These These sets are crudely differences in layering layering thickness, thickness, composition, composition, and and grain grain size. size. Several crudely defined defined based on differences sets consist of feldspathic metasandstones and, and, in in at at least least one onecase, case,possibly possiblyquartzite. quartzite. A few gossans occur in some of the feldspathic metawackes. There There are are several several isoclinal isoclinal folds folds which which have developed locally. have developed locally.AAfew fewof of these theseappear appearto to be be intrafolial. intrafolial. InInthe thefirst firstoutcrop outcropto tothe thewest westof of the the "Yellow Brick Road" highway sign, the S2 S2 fabric is clockwise clockwise with with respect respect to to layering, layering, as as ititisisat at Stops Stops 66 (west (west end) end) and and 77 (west (westend). end). Figure 18. strip map map of of the Highway 17 section of (opposIte page) Three-component strip Figure 18. (opposite field stops numbered area. The numbered 5 to 31 inclusive, for the Hemlo area. The uppermost uppermost strip strip represents representsthe the west third; the lowermost lowermost strip represents represents the east east third. East and west boundaries boundaries defining defining connected strips are are mutually mutually adjoining adjoining (i.e., (i.e.,no no overlap). overlap). Only the outcrops outcrops for field field stops stops described in this road log are shown. described in this road log are �LSSZ Lake Superior Shear Zone 82, Sg in granitoids Figure 20. Form-surface map of the Hemlo deposit area showing generalized traces of different generations of fabrics. (Modified after Muir and Elliott, 1987). HFZ Hemlo Fault Zone •.. High Strain Zone '— Supracrustal/Granitoid contact So, Si, and/or Sm (mylonitic) Form Surface Lines 0 0) 3 0 -' CD CD CD I 0 C') 0 C/) CD a 0. 0 0 0. (0 0 0 CD Geology and Gold Deposits of the Hernlo Area �Road Log — Hemlo Area 47 The dikes within the above-mentioned above-mentionedsets sets comprise compriseaa wide wide variety variety of foliated granitoiddikes dikes foliated granitoid mostly of weakly as well as some some mafic mafic dikes dikes that that display display boudinage. boudinage. The granitoid dikes consist mostly foliated granodiorite, granodiorite, which is is similar in grain size and composition to the marginal marginal phase of the Cedar Lake Pluton, and some some plagioclase-porphyritic plagioclase-porphyriticdikes. dikes. The The granitoid granitoid dikes dikes have have been been intruded by fine-grained, dikes. The Therelationship relationshipbetween betweenthe the granitoid granitoid fine-grained, intermediate-composition intermediate-composition dikes. dikes and the mafic dikes (Archean) is not established. established. A A small small diabase diabase dike (Proterozoic) (Proterozoic) has intruded the country rocks. Structural StructuralSummary: Summary: S1 330/66 84 m S, 330166 m from the contact contact S 318/52 mafic S predominant predominant 318152 mafic schist schist 296/57 S3 crenulation crenulation S3 296157 crenulation Ilneation LC 104126 crenulation lineation L 104/26 METASEDIMENTARY ROCKS 14,18,19 & 23) ROCKS AND GRANODIORITE GRANODIORITE SHEET (Figures (Figures 14,18,19 Stop 7: Stop 7: METASEDIMENTARY essentially a continuation continuation (for Stop 6. 6. For Location: Stop Location: Stop 7 is essentially (for another another 200 m) of the roadcut for Stop the most part, the features features described described here here are are on on the southeast southeast side of the the highway. highway. The Thestop stop begins about west of of the the "Yellow Brick Brick Road" Road" highway highway sign. sign. The about 65 m west The more more important importantfeatures featuresof of this roadcut roadcut are are at at the the east-northeast east-northeastend, end,say, say, for for the the first first 80 80 m m (see (see Figure Figure23). 23). In the northeast northeast end end of this outcrop is a thick, composite composite sheet sheet of of foliated, foliated, medium-grained, medium-grained, plagioclase-porphyritic, biotite-amphiplagioclase-porphyritic,amphibole-biotite amphibole-biotitegranodiorite, granodiorite,and and foliated, foliated, finer-grained, biotite-amphibole granodiorite, granodiorite, both bothof of which which were were intruded intrudedby by aplitic aplitic dikes dikes and and subsequently subsequentlyby by quartz quartz veins. veins. bole The granodiorite occurs occurs as as "layers" or sheets, The finer-grained finer-grained granodiorite "layers" or sheets, parallel to the the foliation. foliation. The relationship between established but circumstantial circumstantial evidence relationship between the the two two phases phases is is not not well established evidence suggests suggests that the finer-grained younger. Aplitic dikelets finer-grained phase is younger. dikelets in the country country rocks rocks are are folded folded about about the foliation. Thedikelets dikeletshave havealso alsobeen beensinistrally sinistrallyoffset offsetin in a number of places. phase foliation. The places. The porphyritic porphyritic phase has been 2687±Ma Ma(Corfu (Corfuand andMuir Muir1989a). 1989a). been dated dated at at 2687±3 Across Across the highway highway at the the structurally structurally lower lower contact contact of of this this sheet, sheet, apophyses apophyses of of the the porphyritic granodiorite porphyritic granodiorite are are folded foldedabout aboutaa less lesssteeply steeplydipping, dipping, S2-like So-likefoliation, foliation, with with attendant attendant attenuation and boudinage which has taken place in two two dimensions dimensions (features (features on on horizontal horizontal section are no longer longer visible). visible). This relationship relationship could could suggest suggestthat thatthe theintrusions intrusionspredated, predated, orwere orwere section the overall overall deformation deformation of of the S2 synchronous with, the D2 Doevent. event. However, However, the So fabric near near the the granitoid bodies Hemlo area area suggests that the intrusions intrusions post-dated post-dated most, most, ifif not not all, all, the the D2 Do granitoid bodies in in the Hemlo deformation (see deformation (see Figure Figure 20). The units of metasedimentary metasedimentary rock west of the granodioritic sheet sheet consist consist of of aa variety variety of of metawacke with minor amounts of of metasiltstone. metasiltstone. Different Differentunits units collectively collectively display displayaarange rangeof of biotite/amphibole biotitefamphibole ratios ratios from biotite biotite predominant predominant to amphibole predominant. As As exposed exposedin in the the roadcut, be crudely crudely subdivided subdivided into into several several sets, sets, based based on on roadcut, the metasedimentary metasedimentary rocks can be composition, composition, grain-size, grain-size, and and layering layering thickness thickness and and definition. definition. Metasedimentary units west of the sheet sheet (for (for about about 120 120 m), m), display display layering layering that that tends tends to to become S2 cleavage cleavageis isnot notdistinct distinctfrom fromlayering, layering,which suggests: transposition transposition of become wispy. Here, Here, the So which suggests: the intersection intersection of S, S1 and and So S2isisessentially essentiallyhorizontal. horizontal. Vertical layering has taken place; or the Vertical faces faces cleavage that that strikes strikes parallel parallel to to the the layering layering and and dips dips less less steeply steeply to to the the locally show an S2-like So-like cleavage fold axes axes are are essentially essentially horizontal horizontal here. here. Subhorizonnortheast. This Thiswould would suggest suggest that that the the F2 F2fold tally plunging visible in the the roadcut roadcut face. face. Insufficient plunging folds in some mafic dikes are visible Insufficientinformation informationis is define the character 7, to available to define characterof of the the range rangein in orientation orientationof ofF2 Fnaxes axes from from horizontal horizontalat atStop Stop7, northeast plunging northeast plunging at at Stop Stop 8, 8, to to northwest northwestplunging plungingat at Stop Stop33B. 33B. �03 Hemlo Gold Mines (Goliath Gold Property) Yellow Brick Road South Z w - Teck-Corona Hemlo Gold Mines (Golden Sceptre Property) 0 CD 2. 0 CD - a. G) 0 0.5 0 a km CD XX, - Ore /Subore /Subore Zone Zone at at Surface Surface Ore Up-dip Projection Zone to to Surface Surface Up—dip Prolection of of Ore Zone I2 00 A Shaft Shaft/Headframe /Headframe . • Main Mine Mine Buildings/Structures Buildings/Structures Main Field Field Trip TripStop Stop Mine-Related Mine-Related Road Road 0 C,) o i CD Figure21. 21. Main Main cultural cultural features features of of the theHemlo Hemlocamp, camp, and and up-dip up-dip ore ore projection projection of of the the Hemlo Hemlo FIgure Same scale 26, and 32 to 35 are shown for reference. deposit. Locations of field stop numbers 7 to deposit. Locations of field stop numbers 7 to 26, and 32 to 35 are shown for reference. Same scale (Modified after after Smyk Smyk eta!. eta/.1990). 1990). as Figure Figure 22. (Modified as -' CD �Road Log — Hemlo Area 49 49 of the the roadcut indicate that the S2 cleavage is clockwise with respect The last 50 m or so of respect to layering, relationshipas as with with the the "Jake" "Jake" unit unit(see (seeStop Stop8) 8) which whichisison on the the southwest southwestlimb limb layering, the same relationship of a southeast-closing northwest fold closure closure may may be present within southeast-closing F2 fold. fold. This suggests that a northwest the vicinity of Cedar Cedar Creek Creek where there is is essentially essentially no no exposure. exposure. Ill w w Co) 0 Iii z -l -J 'LI a > a w z I- z a z 'Li a -J 0 C, 'Li z a, -J -J z orebody projected projected onto onto aavertical vertical plane. plane. Property Longitudinal section of the Hemlo orebody Longitudinal Property boundaries projected onto the orebody plane plane before final projection. projection. Same Samescale scaleas asFigure Figure21. 21. (Modified (Modified after after Canadian CanadianMining MiningJournal, Journal, February February1990, 1990,p.28, p.28, 29). 29). Figure Figure22. �Geology and Gold Deposits of the Hemlo Area 50 Co0 • Structural Summary: Structural S0/S1 323/62 away from contact with granitoids Sn/S, 323162 granitoids 336/? S, 3361? toward west end of roadcut S2 S1/S2 granitoids 3 10/49 S,/S, 310149 near granitoids S3? 297/? alignment of amphibole S3? 297/? alignment amphibole Sg 305/? granitoid sheet Sg 305/7 in granitoid sinistral faults in aplitic aplitic dikelets dikelets in Range of sinistral in sheet: sheet: 285° 285O to to 320° 320 I ..2 '0 •00 00,_• fa 00 * Stop 8: CEDAR CREEK FOLD FOLD in in metawacke/ metawackel metasiltstone turbidites (Figures metasiltstone turbidites (Figures18, 18,19 19 & & 24) 24) 0 U — 0 Location: 650 west-southwest Location:GoGo 650mm west-southweston onHighway Highway 17 from from the the Yellow Brick Road Road (Golden (GoldenGiant Giant Mine) Mine) turnoff point at the first turnoff at at the the west west end end of Stop Stop 77 to aa point first large roadcut large roadcut east east of Cedar Cedar Creek. Creek. The set set of of exposures on the south south side side of the the highway, highway, at this roadcut, extends for about 400 m. The The starting starting point for this stop is on the south south side, side, at at aa northeastnortheastfacing rock with the facing rock face with the word word "Jake" "Jake" plastered plasteredon on itit (loathsome (loathsome as as itit is is to acknowledge acknowledgerock rock defacing defacingof of any kind, let alone outcrop painting), painting), assuming that highway maintenance personnel have not painted painted over it in an an attempt attempt to to deface deface the the defacement. defacement. This starting point is about 120 120 m east of a "0 m" m" referreference point at the west end end of this this set set of outcrops. outcrops. 50 0 .2 00 .0 o. 00 z>. C 0 00 The main features of interest lie on both sides this point and further of the highway, between this and 75 m m further along along the highway highway to the the east-northeast east-northeast (i.e., (i.e., at at about 195 m). m). In In this this part part of of the the roadcut, roadcut, aa section section through a mediummedium-to through to large-scale, large-scale, southeast-closing southeast-closing F2 fold fold is unusually well exposed exposed as as a result F, unusually well result of of original construction, despite original highway construction, despite recent recent highhighway "improvements". "improvementsn. 00 0>, •0— 0 :20 0 o * •0 E o 04 U o U 0 5 C 0 V 0 C C 0 C 0 V The outcrops along along this this part of the the highway highway show a variety show variety of of turbiditic turbiditic deposits depositscomposed composed mostly of medium mostly medium grey grey metawacke metawacke and and metametasiltstone. Light and dark grey varieties are locally siltstone. locally Ic metawackes present. Some Somecrenulated crenulatedmaf mafic metawackes are are exposed at 2 exposed 2 places, places, at at about about 55 55 m m and and 300 300 m m(see (see Figure 24) 24) and are inferred to be folded about the which is Cedar Creek fold axis axis which is located locatedat atabout about163 163 m. These Thesemafic maficmetawackes metawackes also also contain contain minor minor conglomeratic components conglomeratic componentsconsisting consistingof of wacke wacke and and sub-porphyritic granitic clasts subporphyritic clasts in a mafic matrix. LoLocally there there are are unidentified unidentifiedretrograded retrogradedporphyroporphyroparticularly just just to the west of blasts (andalusite?), particularly the eastern, mafic schist unit. A fewmicaceous micaceous eastern, schist unit. Afew gossans occur on both sides of the axial gossans occur on both sides of the axialplane. plane. It is is not clear any of the gossans not clear whether whether any gossans can be be matched across the axial matched axial plane plane as as folded foldedunits. units. FIgure 23. Stops 6,7: Simplified contact of the Cedar Figure Stops 6,7: Simplifiedsketch sketchmap map of the west contact Cedar Lake Lake Pluton Pluton (Stop (Stop 6) and adjacent metasedimentary rnetasedimentaryrocks rocks(largely (largelymetawacke) metawacke)and andgranitoid granitoidsheet sheet (Stop (Stop7). 7). �____ __ _ ______________ Road Log — Hemlo Area 51 51 The "Jake" 24) is a reference turbidite for this stop in "Jake" unit (see Figure 24) reference turbidite in terms terms of of primary primary features, m). The The "Jake" "Jake" unit unit(Photo (Photo2) 2)is features, and and isto is to be be compared comparedto to the "anti-Jake" "anti-Jake"unit unit (at (at about 193 m). is interpreted turbiditeunit unitin in the the following following context. context. The The structurally structurallylower lowerhalf half of the unit unit is fine interpreted to be aaturbidite fine grained, light weathering, and quartzo-feldspathic. quartzo-feldspathic. The Thestructurally structurallyupper upperhalf halfisiscoarser coarsergrained, grained, darker weathering, weathering, biotite- ±amphibole-bearing, and has has aa set set of of laminations defined defined by mafic ±amphibole-bearingand minerals in its uppermost uppermost part. The minerals Thedarker darkerhalf half is is considered consideredto to be bethe the upper, upper, more more silty silty part part of of the the turbidite turbidite deposit deposit which, which, through throughmetamorphic metamorphic recrystallization, recrystallization,has hasbecome becomecoarser coarsergrained grainedthan than the lower quartzofeldspathic part. lower quartzofeldspathic part. AAtraverse traversealong alongthis this section section of of the the exposure exposure to the "anti-Jake" unit (this unit is is not not likely likely the same bed bed as the "Jake" unit, but is an unmarked unmarked reference reference unit unit for comparison) reveals reveals bedding bedding deformed deformed about about the the fold fold axis, axis, with preservation of the comparison) the turbidite turbidite features northeast limb. structurally lower features in in reverse reverse on the northeast limb. That Thatis, is, the laminations laminationsare are on on the structurally lower part part which is interpreted to indicate overturned of the unit, which overturned bedding. Within the lame F2fold, fold, the thelayering layeringthickness thicknessisisgreatly greatlyexaggerated, exaggerated,pseudof pseudoflame the nose nose of of the theF2 have developed developed from incipient incipient transposition of layering, and recrystallization recrystallization is is more more structures have pronounced. AAfoliated, foliated,boudinaged, boudinaged,plagioclase-porphyritic plagioclase-porphyriticdike dike(at (atabout about170 170m) m)isisnear nearand and paraltel parallel to the axial plane. The The strike strikeof of the the foliation foliationappears appearsto to be be parallel parallelto to S2. So. An Anuncommon, uncommon, relatively medium-grained,mafic maficdike relatively fresh, medium-grained, dike which which is chemically chemically equivalent to calc-alkalicandesite calc-alkalic andesite has intruded the mafic mafic metawacke metawacke of the northeast northeast limb limb (at (at about about 296 296 m). m). Possible graded graded bedding at 405 m (end of exposure exposure on the the southeast side) suggests suggests tops are to the southwest, as bedding with with the the "anti-Jake" "anti-Jake" unit. unit. Stereonet construction of the fold indicates indicates itit is is reclined reclined with with aa northeast-trending, northeast-trending,modermodernorthwest-striking axial ately plunging plunging axis axis and a northwest-striking axial plane. plane. Structural Structural facing facing is is toward toward the the northwest. northwest. Exposures Exposures along along the highway highway to the the southwest southwest and and northeast northeast of of Cedar Cedar Creek Creek (about (about 335 335 m m from highway) suggest that anorthwest-closing a northwest-closing fold present, which would would the fold axis along the highway) fold may may be present, produce an overall S-shaped pair of folds. folds. The The axial axialplanar planar cleavage, cleavage, S2, S2, strikes at about about 310°, 310° roughly parallel parallel to the contact contact with the the Cedar Cedar Lake Lake Pluton Pluton to the northeast northeast (Stop (Stop 6), and and oriented oriented 40° clockwise relative 40' clockwise relative to to Stop Stop 13. 13. Another fabric be 53. S3. fabric is is weakly developed developed throughout throughout the folded folded strata strata and and is is interpreted interpreted to to be of strike strike span span over over 50 50°which whichsuggests suggeststhat: that: more than one deformation deformation feature Measurements of was measured; measured; or products was measured measured (e.g., S38'S3=, S3, etc.); or more more than than one one component componentof of the the D3 D3productswas (e.g., S3=, etc.); or deformation subsequent to the so-called so-called D3 D3 event (separate or progressive) progressive) has occurred. occurred. Crenulation schistosities measured measured in in the the mafic mafic schist schist (i.e., (i.e., mafic maficmetawacke) metawacke) show show aa range rangein in 26, and orientations which is is consistent consistent with with that that of of other otheroutcrops outcrops (e.g., (e.g., Stops Stops 25, 25,26, and 29). 29). Cedar Creek Cedar Creek fold axial plane axial plane // N /// 0 9 2 0 2P 400 4 60 60 m scale approximate aproximate scale / \60 \/ \r\ ,, L gossan gossan gossan I I "Jake', Jake gossan gossan / zone zone of disarray disarray / (shallow (shallow plunge plunge of of folds. folds, transposed layering) transposed \\' \ ri p—u p clasts dark wacke dark thick bedded dark wacke wacke " \ \ crenulated crenulated mafic schist; minor granule conglomerate conglomerate fl8$C 5' — —4- gossan g,ossan ,9ossan ,flossan Anti Jake /Anti Jake" ° Y I j\ poi - 0 0 2 A " 1" medium—to to coarse-grained coarse—grained medium54 wacke wacke conglomerate F conglomerate \ \\ \ ^, -- Hwy 17 Hwy 17 J.- I\ — - pgabbrol \ ° e I dark wacke feldspar Lhick feldspar porphyry porphyry I" "1w thick bedded bedded —' crenulated wacke crenulated Nmafic porphyry ' fold axis Nsmafic schist schist feldspar retrograded porphyroblasts porphyroblasts retrograded (andalusite?) (andalusite?) Figure 24. Figure 24. Stop 8: Simplified sketch map of turbiditic metawacke metawacke and siltstone units units of of the the (Fo). Cedar Creek Creek fold fold (F2). �Geology Geology and Gold Gold Deposits Deposits of the the Hemlo Hemlo Area 52 52 After completing the section section from from "Jake" "Jake" to to "anti-Jake", "anti-Jake", cross the highway highway and and walk back through this different section of the fold. The through The"beds", "beds", not not all all of of which which show show sufficient sufficient primary primary features for top indications, indications, overall overturned, as expected from features overallreveal revealthe the layering layeringto be overturned, as would be expected an uncomplicated uncomplicated fold, (see next nextparagraph). paragraph). Semi-aligned Semi-aligned rip-up clasts can fold, which which this this may may not be (see to the northeast northeast of the fold axis (see Figure 24). 24). Here, S2 fabric strikes strikes at be seen at a point to Here, the the S2 296°, (S0/S1 at 344°). A sampling of clasts indicates alignment ranges from 291° 296O, (S&, at 344O). A sampling of clasts indicates alignment ranges from 291' to to309°, 30g0, suggesting the clasts did did not not completely completely rotate rotate into into the the S2 S2 plane. Opposite a point point about about 25 25 m m east east of of aa hydro hydro pole pole (see (see Figure Figure 24), 24), is is aa zone zone of of structural structural complexity, about 5 m northeast northeast of the fold fold axis, that that has no no unequivocal unequivocal explanation, explanation, particularly particularly after of the devilish devilish structural structural inconsistencies inconsistenciesin inthe thefold. fold. Here, after recent recent blasting blasting removed some of Here, some of the the layering layering ranges ranges from from pseudoflame pseudoflame features to notable notable transposition transposition and andwispy wispy development of-differentiated oLdifferentiated layering parallel to to So. S2. What is no longer evident is is that that there there is a section folds, best defined by the section of the the units unitshere herethat thatdisplayed displayedshallow, shallow, northwest-plunging northwest-plunging folds, laminations at exposed laminations at the the overturned(?) overturned(?)top topof of one one of the beds. The The actual actual nose nose of of the main main fold, exposed on this this side side of of the the highway, highway, appears appears to be relatively relatively uncomplicated. uncomplicated. Structural side of of highway (see Figure distance StructuralSummary: Summary:southeast southeast side highway (see Figure24; 24; distancereference referencefrom fromwest west end end of of exposures) Distance Distance (m) (m) Measurement Feature S o6 so/si 306/63 50 50 306163 315/63 50 s2 315163 50 S2 308/60 163 s2 S, axial axial plane plane 308/60 163 crudely crudely fans fans from from 296° 296O to to 320° 320Âand and crudely crudelydips dipsmore moresteeply steeply(5° (5Oto to10°) lo0)on on southwest southwest limb limb 045/55 163 axis F2 axis 045155 163 332/55 210 so/Si so& 332l55 210 312/53 210 % 312l53 210 53 to 265 265 S3 overail; overall; biotite, biotite, faint faint(crudely (crudelyfanned?) fanned?)264° 264Oto to316° 316O 120 to (crudely fanned?) (crudely fanned?) 260/85 to 280/72 S3 crenulation, biotite biotite 53 and 298 S, crenulation, 260185 280172 53 298 (range is present present in in each outcrop outcrop of mafic mafic metasedimentary metasedimentaryrocks) rocks) —070/67 L crenulation 53 L, crenulation(various) (various) -070167 53 —073/63 298 -073163 298 —0871—70 porphyritic dike dike L, boudin -0871-70 ininporphyritic Lb boudin N ------.-. E2 F 2 fold fold axis axis Bell Mine Mine David Bell --\ Teck—Corona Roa \ j 82 cwS1 8 2 ccw S 1 .1... / Hwy 17 S2 ccw S1(?)—c w u^- intermediate dike dike'/ pole mafic dike (boudins) (boudins) Mixed metasediments metasediments retrograded porphyroblasts porphyroblasts (andalusite?) Metawacke Metawacke FIgure Stops 9,10 Simplified Figure 25. Stops sketch map mapof of F2-folded Fg-foldedmetawacke metawacke(Stop (Stop9) 9) and andF2-folded, F2-folded, Simplified sketch mixed metasedimentaryrocks rocks(Stop (Stop10) 10) at at the the Teck-Corona Teck-Corona Road Road turnoff. turnoff. mixed metasedimentary �Road — Hemlo Road Log Hemlo Area Area 53 53 Stop 19 & Stop 9: 9: FOLDED FOLDEDMETAWACKE METAWACKE(Figures (Figures18, 18,19 & 25) 25) Location: Corona Road Location: Northeast Northeastcorner cornerofofthe theTeck TeckCorona Roadturnoff turnoff (to (tothe the David DavidBell BellMine) Mine)on on Highway Highway 17, about370 370m mwest-southwest west-southwestof ofthe the "Jake" "Jake"unit. unit. Note: 17, about Note: this this outcrop outcrop is is now now "landscaped" "landscaped"(i.e., (i.e., largely largely covered coveredover). over). With the the exception exception of of the theeast eastend endofofthe theeasternmost easternmostoutcrop outcropat atStop Stop10, 10,this thisoutcrop outcrop represents a relatively thickset thick set of grey grey representsthe thelast lastexposure, exposure,as asone oneheads headswestward westwardon onHighway Highway17, 17,of arelatively wacke/siltstoneunits, units, which which are are interpreted interpretedto to be be turbidites. turbidites. This Thisset setofofunits unitsextends, extends,ininterms termsof of wacke/siltstone highway highway exposure, exposure, from from here herealmost almostto tothe theCedar CedarLake LakePluton, Pluton,about about1.3 1.3km kmalong alongthe thehighway. highway. The biotite±amphibole metawacke and metasiltstone. metasiltstone. Some The outcrop outcrop at Stop Stop 9 consists of biotitekamphibole Some of the the metawacke metawackeis is relatively relativelyfeldspathic. feldspathic.An AnF2 F2fold foldisispartly partlyexposed exposedand anddisplays displaysgood goodexamples examples of Socharacteristics. characteristics. of aa variety variety of of S2 The Therange rangeininthe thestrike strikeof ofS2 S2cleavage cleavageisisapproximately approximatelythe thesame sameas asthe therange rangeininstrike strikeofoflayering layeringon on the the limbs limbsof of the the fold. fold. This Thisrelationship relationshiphas hasbeen beenshown shownfor forother otherF2 F2folds foldsas aswell, well, for for example, example, the the fold fold at Stop 10° to to 12Owithin 12° within the the same same structure. structure. Locally, Stop13, 13, and and commonly commonlyresults resultsininaa local localrange rangeof of S2 S2of 10' Locally,the the S2 S2 fabric at this this stop stop has has been been deformed deformed near near the the fold fold nose, nose, possibly possiblyby byD3. D3. The developed in 9. The Thefirst, first,S2a, Sga, The S2 S2 fabric appears appears to have have developed in two stages stages in in the the locality localityof of Stop Stop9. appears appears to be be aa vein-like vein-like cleavage cleavage with with development development of of quartz quartz ++feldspar feldspar±Âamphibole amphibolewhich which isis presently presently at aa relatively relatively high high angle angle to the the axis axis of of the the fold. fold. The Thesecond, second,S2b, Sob,isis represented representedby by aa spaced, biotite and wispy compositional spaced, hairline hairlinethick thickcleavage, cleavage, and and by by biotite and wispy compositionallayering layering which which is is essentially essentially the the typical typicalaxial axialplanar planarcleavage cleavage(see (seeMuir Muirand andElliott Elliott1987 1987for for more moredetails). details). Pseudoclasts have locally locally developed developed in in some some layers layers in in the the nose nose of of the fold as Pseudoclasts have as aa result result of of compositional of the rock compositional changes changes of rock along along the the S2 S2cleavage cleavage and and transposition transposition of of the thelayering. layering. Retrograded Retrogradedporphyroblasts, porphyroblasts,possibly possiblyinitially initiallymediummedium-to tocoarse-grained coarse-grainedandalusite, andalusite,are arepresent presentat at the this stop. stop. A set of of narrow narrowquartz quartz veins veinswith withassociated associated saussuritization(?) saussuritization(?) the west west and and east ends of this of of feldspar feldspar isis locally locallypresent. present. Structural StructuralSummary: Summary: Note: Note:complexities complexitiesininthe thesouthwest southwestcorner cornerofofthe theoutcrop outcropsuggest suggestthat thatthe thefold foldmay maybe bedeformed deformedand/or andlornot notcompletely completelyintact. intact. S0/S1 S2a S2b S3 QV Southwest Northeast Southwest limb limb Northeast limb limb 297/56 286/56 297156 286156 280/61 298/61 280161 298161 286/52 292/61 286152 29 216 1 272/? 273/63 27217 273163 262/74 set of of quartz quartz veins veins associated associatedwith with"bleaching" "bleaching" 262174 set ** Stop Stop10: 10: FOLDED, FOLDED,MIXED MIXEDMETASEDIMENTARY METASEDIMENTARYROCKS ROCKS(Figures (Figures18, 18,19 19&& 25) 25) Location: Location: Southwest Southwestcorner cornerofofthe theTeck TeckCorona CoronaRoad Roadturnoff turnoffon onHighway Highway17. 17. There There are are 33 outcrops outcrops to to this thisstop. stop. Most Most of of the the exposure exposure here hereconsists consists of ofvariably variablyrusty rusty weathering, weathering, feldspathic and and biotitic, biotitic, locally locally garnet-bearing garnet-bearing metawackes with a variety variety of of many many amphibole-rich <5 cm amphibole-richinterlayers. interlayers.The Thepresent presentlayering layeringisisgenerally generallyc5 cm thick, thick, but but tectonic tectonicmodification modificationisis evident. evident. The The eastern eastern end end of of these theseexposures exposures consists consists of of light lightgrey greymetawacke metawacke with withsome some amphibole-rich amphibole-richlayers. layers. Retrograded Retrograded porphyroblasts, porphyroblasts, possibly initially initially medium-to medium-tocoarse-grained coarse-grained andalusite, andalusite,are arepresent presentwithin withinsome somelayers. layers.The Theporphyroblasts porphyroblastsare arealigned alignedwithin withinthe theS3 S3and andL3 Lw(fold (fold axis) axis) structures; structures; aarelationship relationshipwhich whichhas hasbeen beenestablished establishedelsewhere elsewhere(Muir (Muirand andElliott Elliott1987, 1987, �S Geology and Gold Deposits of the Hemlo Area 54 S Muir 1988), more than 1 km from the Hemlo deposit. This suggests that a relatively large-scale (regional?) metamorphic event was contemporaneous with the dextral shear event. Vestiges of the S2 cleavage can be seen locally. Both counterclockwise and clockwise orientations relative to layering can be seen (see Figure 25), but no fold closures are discernible. However, the presence of at least 3 folds was corroborative from previous exposures across the highway (presently "pleasingly" landscaped with grass). Some of the 2 fabric has taken the form of a spaced cleavage commonly filled with thin quartz seams. Examples of this style of cleavage are better displayed at Stop 9. A mat ic dike with backrotated boudins can be seen adjacent to an intermediate dike exhibiting no boudinage. An example of layer-parallel brecciation is present in the middle exposure and locally is discordant (at 265°) to the layering. As a matter of not-insignificant note for the "ditch-pigs" among you, a few, small outcrops in the highway ditch, within 50 m west of the westernmost outcrop of this stop, successively reveal the presence of: dark grey, amphibole-bearing metawacke; garnet + staurolite + aluminosilicate(?) porphyroblastic, schistose metasedimentary rocks; and a felsic quartz-feldspar-porphyritic sericite schist. These units structurally overlie the metaconglomerate/metawacke unit of Stop 11, but because of lack of exposure, are not well delineated within the tectono-stratigraphic section beyond this locality. Structural Summary: S S S 290/50 $dS1 S 305/53 alignment of amphibole; spaced, quartz-tilled cleavage 53 272/65 alignment of micas, locally amphibole * Stop 11: METACONGLOMERATE, METAWACKE (Figures 18 & 19) Location: About 130 m west-southwest on Highway 17 from Stop 10 to a set of outcrops on the northwest side (the main outcrop is easily visible). 5 S S The set of 3 outcrops at this stop reveal several units of metaconglomerate and metawacke that form a relatively distinctive unit up to about 70 m thick (on surface). The main, western-most outcrop consists of 2 metaconglomerate units, one with predominantly cobble- and boulder-sized clasts, the other with predominantly pebble-sized clasts, separated by a medium- to coarse- grained metawacke with an entrained zone of pebble- to cobble-sized clasts (Photo 3). Any possible grading is equivocal because, at least in part, the units are too deformed. The clasts comprise various proportions of feldspar-porphyritic rocks, biotite±amphibole schist, teldspathic rocks, and wacke. The porphyritic clasts, with plagioclase phenocrysts up to 8 mm long, are not identical to the many feldspar-porphyritic dikes in the Hemlo area which tend to have smaller and more uniformly sized phenocrysts. A small proportion of some of the coarsergrained crystals are presently K-feldspar. This feature has not been noted elsewhere in plagioclase-porphyritic dikes of this area, and some microscopic evidence suggests that this may be a product of metasomatism. These crystals appear to occur as phenocrysts in some clasts, and/or phenoclasts in the matrix. The matrix consists of biotite, quartz, and feldspars. Rare, small, quartz crystals can be found as phenoclasts in the matrix and as phenocrysts in some fragments; virtually none are seen in the feldspar-porphyritic clasts. The adjacent outcrop to the east consists of athick subunit of coarse-grained metawacke, and metaconglomerate. The third outcrop consists of several thinner subunits of granule to pebble, S 5 S S S S S S S �Road Log Road — Hemlo Area 55 55 polymictic metaconglomerateand andmedium-to medium- tocoarse-grained coarse-grainedmetawacke, metawacke,all allof of which which are are notably notably polymictic metaconglomerate the other other 22 outcrops. outcrops. In these these thinner thinner subunits subunits of of metaconglomerate, metaconglomerate, more amphibole rich than in the some of the clasts are mafic in composition; composition; felsic felsic clasts clasts are are generally either fine-grained fine-grained and homogeneous, feldspar-phyric. InInall homogeneous, or feldspar-phyric. alloutcrops outcropsat at this this stop, stop, magnetite magnetiteis islocally locallynoticeable noticeableininthe the matrix matrix and in some clasts. clasts. Some of the subunits subunits here here are are reminiscent reminiscentof of amphibole-rich amphibole-richconglomerate/wacke conglomerate/wacke units units north north of the North North Zone Zone on on the Golden Golden Sceptre Sceptre property, property, and and near near Botham Botham Lake Lake (see (see Figure Figure 18 18 for location of the there is is insufficient insufficient information information to to relate the two units, stratithe lake). lake). However, However, there units, stratigraphically or structurally. graphically structurally. The metaconglomerates metaconglomeratesand and metawackes metawackes of the the unit unit at at Stop Stop 11 11 are are moderately moderatelyto to strongly strongly deformed. On Onthe the relatively relativelyhorizontal horizontaloutcrop outcropsurface, surface, the the clasts clasts appear appear "flattened" "flattened" with with aspect aspect ratios of about about 2:1 to to 5:1 5:1 (locally (locally greater). greater). There slightly sinuous ratios There is is aaslightly sinuous shape shape to many many of the clasts as a result result of the development development of of an an anastomosing anastomosing pattern pattern in in the the matrix matrixand andthe themicaceous micaceousclasts. clasts. This D3on onD2. Do.The Theclasts clasts This pattern patternisisinterpreted interpretedtotobe bethe theresult, result,atatleast leastininpart, part,of ofthe theoverprinting overprintingofofD3 aligned slightly slightly clockwise are aligned clockwiseto to the the crude crude layering; layering; the the alignment alignmentis is interpreted interpretedto to be beparallel parallelto to S2 S2 consistent with this this unit northeast limb the large fold fold on on the the Williams Williams property property and is consistentwith unit being being on the northeast limb of the (see Figure 19). The The unit unit can can be be traced, traced, for for the the most most part, part, into into the the fold foldnose. nose. 2 fabric clockwise relative to that that at at Stop Stop 13. 13. This This represents represents part part fabricatatStop Stop11 11isis about about 200 20Âclockwise The So "swing" in in orientation orientation of of S2 So from about 305160 270165 at Stop 13 13 (see of the "swing" 305/60 at Stop 8, to about 270/65 Figure 20), and is possibly possibly a result result of of deformation deformation from the the intrusion, intrusion, or presence, presence, of the Pukaskwa Pukaskwa Figure Gneissic Complex (2719 +61-4Ma Maand and 2688± 2688±3Ma) Ma) to to the the southwest, southwest, the Cedar Lake Lake Pluton Pluton (2719 +61-4 (2687±3 east-northeast, the Stock (2684 (2687± Ma) to the east-northeast, the Cedar Cedar Creek Creekstock (2684+4/-3 +4/-3 Ma) Ma) to to the the north north(ages (agesfrom from Corfu D3 event. Corfu and and Muir Muir 1989a), 1989a), and/or andlor the the D3 A fine-grained, felsic dike dike has has intruded the boulder fine-grained, foliated, foliated, amphibole-bearing, amphibole-bearing, felsic boulder metametaconglomerate conglomerate (westernmost (westernmost outcrop), outcrop), and and is is locally locally deformed, deformed, along along with with the the clasts, clasts, into intoaa small, small, open, F3 fold. fold. The The presence presence of of amphibole amphibole in in the the matrix matrix of of the the metasedimentary metasedimentaryrocks, rocks,ininsome some clasts, the dike dike may may be beinferred inferredto toindicate indicate that thatsome sometype typeof ofalteration alteration has hasbeen beensuperposed superposed clasts, and and in the on the rocks, or, alternatively, alternatively, it reflects metamorphism of of compositionally compositionally distinct distinct metasedimenmetasedimentary rocks rocks with local local effects effects on on the dike. Structural Summary: Structural Summary: 287/53 287153 clast alignment biotite fabric S2 291/74 Sy 291174 alignment and biotite fabric flattened 282/50 flattened side of aligned clast, parallel to to fabric in that that clast 282150 Sa Sa Sac,? 3001? weak; part part of of "anastomosing" "anastomosing"system system 300/? weak; S3? axial plane S3*? 250/? axial plane of of small small F3 F3fold S38? 250/? L 065/45 Lpa 065145 axis axis of above above fold fold elongation of IL0 à 005/47 005147 elongation of clasts clasts (from (from south south side side of of highway) highway) S0/S1 SdS, * Stop 12: FELDSPATHICVOLCANICLASTIC VOLCANICLASTIC METASEDIMENTARY METASEDIMENTARY ROCKS ROCKS ("ARKOSE") 12: FELDSPATHIC (Figures 18 (Figures 18 & & 19) 19) LocatIon: 50 50 mm west-southwest onon Highway 1717 from Location:GoGo west-southwest Highway fromStop Stop11 11totoan anoutcrop outcropon on the the south south side. There are 3 3 relatively relatively small small outcrops outcrops at at this this stop. stop. somewhat similar that the This unit unit is somewhat similar to to that that of of Stop Stop 15 15 except that the layering layering is is thinner, thinner, ranging rangingfrom from cm, and and the the quartz quartz crystals (phenoclasts?) 3 to 15 cm, (phenoclasts?) are are generally generally fewer and and finer grained grained (<1 ( 4 mm). weathers rusty brown brown from oxidation oxidation of fine-grained fine-grained pyrite. The The outcrop weathers The matrix matrixis is fine-grained, fine-grained, white, and feldspathized and sericitized to and appears appears to have have been feldspathized and sericitized to some some degree. degree.Very Veryminor minorgreen green �Geology Geology and and Gold Gold Deposits Depositsof of the the Hemlo HemloArea Area 56 56 mica grab sample (Schnieders micais is present. present. AAgrab samplefrom fromthis thisoutcrop outcropreturned returnedan anassay assayvalue value of of 77 ppb ppb Au (Schnieders eta!. etal.1988). 1988). AApebble pebbleconglomeratic conglomeraticunit unitisisvisible visibleatatthe theeast eastend endof of the the easternmost easternmostoutcrop outcropand and possibly possibly is is part part of of the the unit unitseen seenat at Stop Stop11. 11. AA felsic felsic dike dike isislocally locallydiscordant discordanttotothe thelayering. layering. The The feldspathic feldspathic volcaniclastic volcaniclastic metasedimentary metasedimentaryrocks rocks of of this this stop stop have have been interpreted interpreted to be be the the equivalent equivalentof of the the unit unitat atStop Stop15, 15, folded folded about about the the large largefold foldaxis axiscentred centredon onthe theWilliams Williams property property(Kuhns (Kuhns1988). 1988). InInany anycase, case,the therocks rocksat atStop Stop12 12do do not not have have the the same same adjacent adjacentunits unitsat at both fold, the the S2 2 fabric, both locations. locations.IfIfthis thisunit unitisison onthe the northeast northeastlimb limb of of the large fold, fabric,ififpresent, present,should should be be clockwise clockwiseto to layering. layering.Fabric FabricSb Soisisininsuch suchan an orientation orientationbut butisisnot notclearly clearlyan anS2 S2fabric. fabric. ItIt is is still still possible D3. possiblethat thatthe theSb Sbfabric fabricmay maybe be related relatedto toD3. Structural StructuralSummary: Summary: 290/56 S&, 290156 S0/S1 Sa 275/63 275163 sericite sericite Sa Sb 299/? 2991? sericite sericite Sb (Figures 18,19,26 ROCKS (Figures 18,19,26 Stop13: 13: FOLDED, FOLDED, PORPHYROBLASTIC, PORPHYROBLASTIC,METASEDIMENTARY METASEDIMENTARY ROCKS * Stop & & 27) 27) west-southwest on Location: Go Go 100 100 m m west-southwest on Highway Highway17 17 to a roadcut, roadcut, on on the the north northside, side, that thatbegins begins LocatIon: The roadcut consists of almost The roadcut consists of almost with an outcrop on which there is a survey tripod and pin. with an outcrop on which there is a survey tripod and pin. continuous continuous exposure exposure for for the the next next 200 200 m, m, but but is is divided divided into into 33 stops stops for for lithological lithological(if(ifnot notlogical) logical) reasons. to aahydraulically hydraulically cleaned cleaned area. The reasons. Stop Stop13 13extends extendsfor forabout aboutthe the first first 150 150 m to The rocks rocks range range from open-folded metapelites from straight-layered straight-layeredmetapelites metapelitesand andmetawackes, metawackes,at at the the eastern eastern end, to open-folded metapelites and and metawackes, metawackes,to to sheared shearedand and tightly tightly folded folded metapelites metapelitesat atthe the western westernend. end. Figure Figure27 27shows showsaa detailed detailed sketch sketchmap mapof of the the west westhalf halfof of this thisstop. stop. The west end of Stop 13 is is "on "on strike" strike" from from the the axial axial plane plane of of the the relatively relatively large, tight, northnorthnorthwest-plunging, west-closing fold best exposed on the Williams property (see Figure 19) northwest-plunging,west-closing fold best exposed property (see Figure 19) and thus expected to display display an overall overall "M" "M" oorr U "W" configuration. Complicated thus might might be expected Wconfiguration. Complicatedfeatures featuresininthe the outcrop suggest that a simple folding event is inadequate to explain all of the features. Hugon Hugon (1986) described a progressive, ductile, dextral shear event for the Hemlo area. Muir Muirand andElliott Elliott survey tripod tripod and and marker marker / mafic dike dike (boudins) (boudins) discontinuous outcrop; outcrop; S2 S 2 ccw c c w Si S1 Outcrop Outcrop shown shown in in detail detailininFigure Figure 27 27 dike mafic dike 9 bouctins 20 10 3 m scale approximate approximate . Barren Sulphide Sulphide Zone Zone . F2 fold axis axis p Stops13, 13,14, 14, 15: 15: Simplified Simplified sketch map of folded and sheared metapelitic metapelitic rocks rocks Figure Figure26. 26. Stops (Stop 13), 13), sheared and altered rocks rocks of of the the Barren Barren Sulphide Sulphide Zone Zone (Stop (Stop 14), 14), and and feldspathic feldspathic metavolcaniclastic metavolcaniclasticrocks rocks (Stop (Stop15). 15). �Road Log — Hemlo Area 57 57 (1987) (1987) proposed that F2 F2 generation folds may may have have been been produced produced during during aa sinistral sinistralevent, event, followed F3 folds. followed by by aa dextral dextral event event which which produced producedF3 The layering is generally well defined in much of this this section section of of exposures, exposures, and andappears, appears, differencesbetween betweenbeds bedsof of siltstone, siltstone,wacke, wacke, and andthe the preprelargely, to reflect original original compositional compositional differences cursors to the amphibole-rich layers. The Theamphibole-rich amphibole-richlayers layersin in the the east east end end of the stop display cursors amphibole-rich layers. display reaction rims involving some type type of of bleaching bleaching process. process. The involving some The outcrop outcrop depicted in Figure Figure 27 27 displays displays aa zone zone in in which the the amphibole-rich amphibole-richlayers layersappear appearto to be be unaltered, unaltered,followed followedto to the thewest westby by increasingly altered altered amphibole-rich amphibole-richlayers layers which which are are completely completely bleached bleached at at the the west west end. end. increasingly The layering is presently presently enhanced enhanced by by the development of porphyroblasts asts which which occur occurin inaa variety of composition. of combinations combinations and and are arecontrolled controlledto some extent by bedding/layering lyering composition. Porphyroblasts staurolite, aninopnymie~gearite, anthophyllite/gedrite, cummingtonite, cummingtonite, sillimanite, sillimanite, Porphyroblasts identified identified are garnet, stauroli~e, I'etrograded cordierite, retrograded cordierite, retrograded kyanite(?), and and possibly possibly chloritoid, chloritoid, in aa variable retn^graded kyanite(?), variable matrix matrix (sonsisting of consisting of biotite, biotite, muscovite, muscolvite, quartz, quartz,and andfeldspar feldspar(Muir (Muir1982b; 1982b;Patterson Patterson1984; 1984;Burke BurkeetetaL at. .. . , ... orcummingtonite 1986). iyub). Anthophyllite/gedrite Antnopnyiiite/aearlteor cumminatoniteare arepresent presentininindividual individuallayers lavers(based (basedon onaalimited limited thin section sextion study) study) and and are are locally locally variably variably lineated. lineated. Staurolite tends to to be be'non-preferentially non-preferentially oriented. oriente?d.Cross-twinned Cross-twinnedcrystals crystalsare arelocally locallypresent. present.Some Somegarnet garnetporphyroblasts, porphyroblasts,in inoriented orientedthin thin sections, display open Z-shaped patterns in inclusion trails (Hugon 1986). However, S-shaped "~ - , patterns in (oriented thin section) in inclusion inclusion trails trails in in some some garnet garnet porphyroblasts porphyroblasts (oriented section have been recently recently noted, noted,from fromthe theauthor's author'sstudy, study, iningarnet-staurolite garnet-staurolitemetapelitic metapeliticrocks rocksalong aloneHighway 17, about 11 km trails, km west west of ofStop Stop27. 27. The regional regional significance of the the asymmetry asymmetry of of inclusion in( therefore, therefore, is is not notreadily readilyassessable. assessable. >--a. rn ..a. . a . - The F2 generation I I I G open U ~ G Ifolds I U I Uin 111 ~ the me west W G part ~ LL of UI ~ Stop Q ~ LI U13 1 ~ 0 are cue interpreted ~ ~ ~ ~ e r p rto LU ebe iue eu r2 ymieraiiurifolds d d sbased basedon on their style. style. The Theretrograded retrogradedcordierite cordieriteoccurs occursas their ssurfaces, aslenses, lenses,most mostvisible visibleon onweathered weatheredsurfaces, which which are are constrained constrainedto tospecific specificlayers layersand andlie lieparallel parallelto to what whatis is interpreted interpretedto tobe bethe theaxial axialplanar planar -..- a- few cleavage (i.e., there are are lenses (i.e., S2) of these these folds. folds. Locally, Locally,, mere ~ew ~urisusof uifresh, Tresn, unrecrystallized urirecrystallized cord lerite that appear boud ins and andare arenot notapparently apparently related related to to the the retrograded retrograded lenses. cordierite appear to be boudins lenses. The The metapeliticrocks rocksininthe thewestern westernpart partofofthe theoutcrop, outcrop,shown shownininFigure Figure27, 27, are are similar similar to to those those in in Stop Stop metapelitic 17 in terms of types types of of porphyroblasts porphyroblasts (garnet, (garnet, staurolite, sillimanite), folds, and the S3 S3 fabric overprint. overprint. &I,.-..- 1-.-. I----- -1 ^..--I,. easternmost 30 m m or or so so of ofStop Stop13 13display displayequivocal equivocalevidence evidencefor forthe thelimb/layering limbllayering The easternmost relationshipin interms termsof of the the large large fold fold centred centred on on the Williams This stems stemslargely largelyfrom from the the relationship Williams property. property. This significantly well-developed well-developed S3 S3 cleavage here and the lack lack of retrograded retrograded cordierite cordierite porphyroporphyrosignificantly blasts.Within Withinthe thenext next50 50mmororso, so,up upto tothe theeast eastend endof of the the outcrop outcropdepicted depictedininFigure Figure27, 27,there thereare are blasts. retrograded retrograded cordierite cordierite lenses lenses which which are are aligned aligned counter-clockwise counter-clockwise to the layering. The The relationrelationship of the retrograded in the the east part part of the outcrop indicates that retrograded porphyroblasts to layering in many of the the rocks rocks in in the the east east part part of this this pelitic peliticunit unitare, are, in in aa relative relative sense, sense, on on the the north northlimb limbof of an an many east-closingfold. fold. This Thisappears appearsto tobe becontrary contrarytotowhat whatwould wouldbe beexpected expectedififthe theaxial axialplane planeofofthe the east-closing large fold on the Williams property extended extended through the centre of a thickened, repeated repeated unit unit of large pelitic pelitic metasedimentary metasedimentaryrocks rocksin inthe the nose noseof of the thefold. fold. Further Further study is is required required to to resolve resolvethis this problem. problem. partly preserved, preserved,west-northwest-closing, west-northwest-closing, northeast-plunging northeast-plunging fold is well exposed at the A partly west westend endof of Stop Stop 13 13 (Figure (Figure 27). 27). Based Basedon onthe thestyle styleof ofthe thefold foldand andthe thedevelopment developmentofofaxial axialplanar planar is interpreted interpreted to be an F2 fold. The axial axial plane plane is slightly convex convex to the cleavage, this structure is fold. The northeast, northeast,ranging rangingfrom from 270° 270' to 275°. 275'. The Theplunge plungeof of the the fold, fold, is is similar to that that of the Cedar Cedar Creek Creek fold 8), but butis is contrary contraryto tothe theplunge plungeofofF2 F2folds folds to to the the west-northwest west-northwestof ofthis thisstop, stop,including including fold (Stop (Stop8), the the large large fold fold on on the the Williams Williams property, property, which which are are generally generally north-northwest north-northwestplunging. plunging.Generally, Generally, �D3-sheared metapelitic rocks with Figure 27. Stop 13: Geology of F2-folded, 'ocally altered, detail. (After Muir 1990). amphibole-rich layers. Inset shows central area of outcrop in more 0 (J1 p3 CD -' 0 Cl) I-. 0 Cl) CD 0 0. 0 G) 0. CO 0 0 CD Geology and Gold Deposits of the Hemlo Area �Road Log Log — -Hemlo Hemlo Area Area Road 59 59 F, fold axes plunge to Interestingly,aa minor minor fold fold in in a rootless rootless section section of of an an altered altered F3 to the northeast. Interestingly, amphibole-rich layer plunges to the northwest, northwest, next to a northeast-plunging northeast-plunging fold in in contiguous contiguous amphibole-rich layering. layering. Note Notealso alsothat thatthe theaxial axialplane planeorientation orientationofofS2, S2,at at 2700 270Âto 275°, 275O, is uncharacteristically uncharacteristically (i.e., counterclockwise) counterclockwise)than than is isthe the case case for for much much of of the the Hemlo Hemloarea, area, north north of of more west-striking west-striking (i.e., more Highway from Stop 6 to Stop Highway 17, 17, from Stop 24 24 (Figure (Figure20). 20). The disrupted, in part along The southern southernlimb limb of of the the fold fold in this outcrop is partly disrupted, along ill-defined ill-defined faults which display display apparent apparent dextral and sinistral displacements. displacements. Some which Some layers layers within within the the folded folded metasedimentary rocks rocks display display aligned aligned lenses lenses which have have been been interpreted to to be be retrograded retrograded metasedimentary cordieriteporphyroblasts. porphyroblasts.The Thelenses, lenses,which whichare arenot notreadily readilyvisible visibleon onfresh freshsurfaces, surfaces,lie lieparallel parallelto to cordierite what is interpreted to be the axial planar cleavage (i.e., S2) of the fold. Proceeding eastward, there what is interpreted to be the axial planar cleavage (i.e., of the fold. Proceeding eastward, is aa poorly poorlyexposed exposedeast-closing east-closing fold fold that that can can be bedetected detectedfrom fromchanges changesininthe theorientation orientationofof is layering and and from minor, minor, or parasitic, fold asymmetry. Recent Recentblasting blastinghas has removed removedmuch much of of the the layering previously previouslyexposed exposedparts partsof ofthis thisfold. fold. The The western westernend endof ofthe theoutcrop outcropat atStop Stop13 13is is variably variably schistose, schistose,and andaltered altered(feldspathized, (feldspathized, sericitized). Some Someofofthat thatalteration alterationincludes includespyritization, pyritization,leading leadingtotoaarusty rustyweathering weatheringsurface surface sericitized). that tends tends to to obscure obscuresome somefeatures. features. The Theschistose, schistose,altered alteredrocks rocksofofthe theBarren BarrenSulphide SulphideZone, Zone, that immediately pelitic rocks. immediatelyto tothe thewest, west, may mayhave have been been derived, derived, at at least least partly, from these politic rocks. Locally, Locally, boudins or or "rafts" "rafts" of of what what are are interpreted interpretedto to be be altered altered amphibole-rich amphibole-rich layers layers are "adrift" in in the the boudins schistose schistose matrix, matrix, attesting attesting to to the theanisotropic anisotropictectonic tectonicdisruption disruptionof oflayering. layering. The The metasedimentary metasedimentaryrocks rocks have have been been intruded intruded by by aa plagioclase-porphyritic plagioclase-porphyriticgranodioritic granodioritic dike,aaboudinaged maficdike withinternally internallydeformed deformedlayering, layering,and andaathin thindiabase diabasedike dikeininthe thewest west dike, boudinaged mafic dike with end of of Stop Stop 13. 13. The The feldspar feldspar porphyritic porphyritic dike dike uncharacteristically uncharacteristicallycontains containsgarnet garnetcrystals. crystals. This This end type typeof of porphyritic porphyriticdike dikeininthe theHemlo Hemloarea area typically typically did did not not incorporate incorporate xenoliths xenoliths of of country country rock rock duringintrusion, intrusion,so so intrusive intrusivecontamination contamination is is not not considered considered important. important. The Thequestion questionremains remains during whetherthe the dike dikeunderwent underwentalteration alterationinvolving involvingrelative relativealuminum aluminumenrichment, enrichment,in in which which case case aa whether relativetiming timing for for the the alteration alterationmay maybe beinferred inferred(i.e., (i.e., postdating postdating about about 2687 2687 Ma: Ma: see seeCorfu Corfuand and relative Muir 1989a), or or whether whether the the dike dike intruded intrudedaluminous, aluminous, altered alteredmetasedimentary metasedimentaryrocks rocksand andwas was Muir 1989a), subsequentlymetamorphosed, metamorphosed,which whichwould wouldput putaaminimum minimumage agefor foralteration alterationatatabout about2687 2687Ma. Ma.ItIt subsequently shouldnot notbe be automatically automaticallyassumed assumedthat that this this alteration alterationisis related related to to the the gold gold mineralization. mineralization.The The should aboveproblem problemisissimilar similarto tothat thatoutlined outlinedfor forthe thedikes dikesatatthe theWilliams WilliamsAAZone Zonepitpit(Stop (Stop2121B), B),and andatat above the theNorthern NorthernEagle Eagleproperty property(Stop (Stop4). 4). The superposition superpositionof ofalteration alterationand andcomplex complexdeformation deformationon onthe therocks, rocks,particularly particularlythose thoseinin The thewest westhalf halfof ofthe theoutcrop, outcrop,has hasresulted resultedininthe therecording recordingof ofaa"microcosm" "microcosm"ofofevents eventswhich whichhave have the affectedthe therocks rocksininthe theHemlo Hemloarea areaaswell. Forinstance, instance,there thereisisevidence evidencefor foraanumber of fabrics fabrics affected as well. For number of within withinthe therocks rocksofofthe thewest-northwest-closing west-northwest-closingfold fold(Figure (Figure27). 27). Deflection, Deflection,backrotation, backrotation,and and sinuous sinuous and and anastomosing anastomosing sericitic and and biotitic biotitic schistosities schistosities present present aa confusing confusing picture. picture. ItIt requisitedegree degreeof ofsimplification simplificationand andinterpretation!), interpretation!),that thatthe theF2 Fofolds, folds,with withthe the appears,(with (withaarequisite appears, axialplanar planarS2 S2cleavage, cleavage, have have been been overprinted overprinted by by aa dextral dextral shear shear event event which which has has led led to to the the axial developmentofofs-c-c' s-c-c'fabrics. fabrics.The Theorientation orientationofofthese theseshear shearfabrics fabricsrelative relativetotolayering layeringisisvariable, variable, development dependingmostly mostlyon onthe theorientation orientationof oflayering layeringwithin within the the F2 F2structures. structures. The Thegeneralized generalizedfabric fabric depending orientations orientationsand andrelationships relationshipsare arepresented presentedbelow. below. Structural StructuralSummary: Summary: S0/S1 SdS, variable variablewithin withinfolds; folds; —290° -290 away away from from detectable detectablefolds folds S2 S2variable variablewithin withinfolds; folds; generally -270167 fans fansfrom from265° 265Ototo275°; 275O; generally—270/6Z biotite, biotite,alignment alignmentofofretrograded retrogradedcordiente cordieritelenses lenses S3, S3c 292/54 292154 locally locallysinuous, sinuous,deflects deflectsS2; S2;biotite biotite S3. S3c- 318/46 318146 locally locallysinuous sinuousand andspaced, spaced,deflects deflectsS2 S2and andS3; S3.; biotite biotite �Geology Geology and and Gold Gold Deposits Deposits of of the the Hemlo Hemlo Area Area 60 60 locally S(?), locally locally backrotated by S&(?), locallyanastomosing anastomosingwith withS2; Sg; biotite biotite general generalF2 F, fold foldaxes axes Leg —320/49 -320149 isolated isolatedF2(?) F,(?) fold fold axis axis LF2 stretch and/or crenulation (?) -312100 stretch andlor crenulation (?)lineation, lineation,variable, variable,depends dependson onreference referenceschistosity, schistosity,may maybe beshallowly shallowlyeasteast-or orwestwest—312/00 L,, plunging plunging S38 S3* 2601? 260/? Lm LF2 -043149 —043/49 L * Stop Stop14: 14: BARREN BARRENSULPHIDE SULPHIDEZONE ZONE (Figures (Figures 18, 18, 19 19 & & 26) 26) Location: Location: Immediately Immediately adjacent adjacent to the the west west end end of of Stop Stop 13 13 (Figure (Figure 26) and and comprises comprises aa few few noticeably noticeably rusty rustyweathering weatheringsection sectionof ofoutcrops outcropstotalling totallingabout about30 30m malong alongthe thehighway. highway. This This rusty rusty weathering weathering Barren Barren Sulphide Sulphide Zone Zone (BSZ), (BSZ), also also known known "affectionately" "affectionately" as as the the "Sucker Zone", does not have clearly defined contacts because it appears to "grade" into the Zone", appears "grade" into the adjacent development and composition. composition. The adjacent "units" "units" in in terms terms of fabric development TheBSZ BSZappears, appears, though, though, to to be be about about 15 15 m thick here here based based on on the the most most intensely intenselyaltered alteredand andsheared shearedrocks. rocks. The BSZ BSZ consists of sericitized, feldspathized, feldspathized, and pyritized pyritized schist schist which has has an equivocal equivocal protolith(s). It is is in in ill-defined ill-defined (because (because of of exposure) exposure) contact contact with with the thealuminous, alurninous,well-layered well-layered protolith(s). metasedimentary metasedimentaryrocks rocksto to the theeast east (Stop (Stop13), 13), and and the quartz-crystal-bearing quartz-crystal-bearingfeldspathic feldspathicvolcanvolcaniclastic iclastic metasedimentary metasedimentary rocks rocks to the west (Stop (Stop 15). The The oxidation oxidationon on weathered weathered surfaces surfaces is is severe, and it is not possible to positively recognize features of the adjacent units within the BSZ, severe, and it is possible positively recognize features of the adjacent units within the BSZ, assuming these units. Towards assuming the BSZ BSZ was derived from either or both of these Towards the structurally lower "contact" "contact" there there isis what what appears appears to to be be quartz-crystal-bearing quartz-crystal-bearing rock bounded by sericitic sericitic schists. schists. Elsewhere Elsewhere in the exposures, exposures, rare rare quartz quartz crystals crystalscan can be be seen seen which which suggests suggests the the protolith protolithisisthe the feldspathic described, from diamond diamond feldspathicvolcaniclastic volcaniclasticmetasedimentary metasedimentaryrock rockof of Stop Stop15. 15. The The BSZ BSZ is is described, drill core pyrrhotitelpyrite, and and 10% 10% core specimens, specimens, as consisting consisting of of 10 10 to to 20 20 cm cmofofmassive massivepyrrhotite/pyrite, disseminated suiphides footwall units units (Quartermain (Quartermain sulphides extending 10 10 m into into the the hanging hanging wall wall and and footwall 1985). Grab Grabsamples samplesfrom fromthe thehighway highwayexposure exposurereturned returnedAu Auvalues valuesofof<0.01, ~0.01,0.02, 0.02, and and0.51 0.51 ounces ounces per per ton ton (Patterson (Patterson1986), 1986), and and 11 11 ppb ppb (Schnieders (Schnieders eta!. et a/.1988). 1988). The schist some up up to to 1 m by schist displays lozenges, lozenges, some by 0.3 0.3 m m ininplan planview, view, with with apparently apparently backrotated deflected, and anastomosing fabrics. These backrotatedfabrics fabricsas as well well as sinuous, deflected, These fabrics fabrics could, could, given their relative relationships, be representative of s-c and possibly c' fabrics of a dextral given their relative relationships, be representative of s-c and possibly c' fabrics of a dextral shear system, system, although althoughthis thisisisnot notcompletely completelyclear. clear. A relatively relatively fresh-appearing, dike occurs fresh-appearing,competent, competent,multiplely multiplelyboudinaged, boudinaged,mafic maficdike occursininthe thewest west part of the BSZ outcrop. The dike is comparable in composition to tholeiitic basalt but has elevated part outcrop. comparable in composition tholeiitic basalt elevated Ni and and Cr Cr contents contents relative relative to to most mostmafic maficdikes dikesininthe thearea areahaving havingsimilar, similar,major majorelement element compositions. compositions. Structural Structural Summary: Summary: 284/59 284159 sericite, sericite,deflects deflectsSb; Sb;also also crude crude compositional compositionallayering layering S predominant predominant(S*?) (S?) 272/66 S, (S2?) (S,?) 272166 sericite sericite S8 254158 sericite, sericite, backrotated backrotated within within lozenge lozenge Sb Sb(S38?) (Saç? 254/58 246166 folds foliation, foliation, almost almost chevron chevron style style F3 246/66 Axial plane planeof ofF3 Axial VOLCANICLASTIC METASEDIMENTARY METASEDIMENTARY ROCKS ROCKS ("ARKOSE") ("ARKOSE") * Stop Stop 15: 15: FELDSPATHIC VOLCANICLASTIC (Figures 19 & (Figures18, 18,19 & 26) 26) Location: Location: This stop, stop, immediately immediately adjacent adjacent to Stop Stop 14, 14, accounts accounts for for the the westernmost westernmost 25 25 m, m, approximately, approximately, of the section section of of exposures exposuresfor for Stops Stops 13 13 to to 15. 15. �Hemlo Area Road Log — Hemlo 61 61 The rusty weathering, layered, feldspathic, feldspathic, quartz-crystal-bearing quartz-crystal-bearing The outcrops outcrops consist consist of slightly rustyweathering, (phenoclast?, (phenoclast?, phenocryst?) phenocryst?)rocks. rocks. The Thelayering layeringis is poorly poorly to to moderately moderatelydefined definedby by grain grain size size and and mineral thick, and displays displays no other primary primary sedimensedimenmineral abundance, ranges from about 4 to 20 cm thick, tary tary features. features.The Thequartz quartzcrystals crystalsappear appearmoderately moderatelystrained strainedand andrange rangefrom from0.5 0.5toto44mm mmacross; across; most crystals are about 1 mm across. The matrix consists largely of feldspar and sericite. The matrix consists largely The rock rock has has an almost chalky white to grey appearance towards the Barren Barren Sulphide Zone (i.e., coupled with the presence presence of irregularly irregularly disseminated disseminated pyrite, (i.e,, to the east). This, coupled pyrite,small smalllenses lensesof of green mica less less than than 33 mm mm long, long, and and moderate moderate amounts amounts of of microcline microcline along along some some bedding! bedding1 cleavage cleavage planes, planes, indicates indicatesthis thisunit unithas hasundergone undergonealteration alterationsimilar similarto to that thatof of the theHemlo Hemlodeposit. deposit. rocks appear appear to "grade" "grade"into into the the Barren BarrenSulphide Sulphide Zone Zone unit unit at at the the structurally structurallyupper uppercontact. contact. The rocks The feldspathic feldspathic volcaniclastic volcaniclasticrocks rocks are are structurally structurallyunderlain, underlain, based based on on highway highway exposure, exposure, by by quartz-feldspar-porphyritic,felsic felsicmetavolcanic, metavolcanic,fragmental fragmentalrocks rockstotowhich whichthey theymay maybe berelated relatedas as quartz-feldspar-porphyritic, reworked reworked equivalents. equivalents. As mentioned for Stop interpreted the mentionedfor Stop12, 12, Kuhns Kuhns (1988) (1988) has has interpreted the unit unitexposed exposedat atStop Stop15 15to to be be the the folded equivalent equivalent of the unit unit exposed exposed at at Stop Stop 12. 12. Figure 19 19 suggests this may may be be the the case. case. However, should be noted noted that the unit unit at these locations locations is is bounded boundedby by different differentrock rocktypes typesat atits its However, it should structurally upper and lower contacts, facing directions are not not determinable, determinable, and and structural structural complexities that may require an alternative interpretation. pr complexities are present Structural Structural Summary: Summary: S0/S1 SdS, 294/58 294158 generally, generally, locally deflected to 302° 277° (possibly forms small Sgand and Sb: Oh: sericite 277 and 286° c.uu ipuoofwiy S2 uo and S3, u3aÃrespectively, iwot^3uttvwiy, but uuiindeterminable); 1 1 l U d d lllllICIUIuJ, oinati lozenges lu~utlMuO Sa sericite Sd: possiblyS3, S 302°; note similarity to to deflected SO/SI So: possibly 302O; note similarity deflected So/Sl * Stop 19 && 28) Stop16: 16: FELSIC FELSICPYROCLASTIC PYROCLASTICROCKS ROCKS(Figures (Figures18, 18,19 28) LocatIon: 50 50 m further west onon Highway 17,17,south Location:GoGo m further west Highway southside, side,totoaatailings/haulage tailingsfhaulageroad roadturnoff turnoffto to the parts:Stop Stop16A 16Alies liesto to the the southeast southeastof of the the turnoff, turnoff, and and Stop Stop16B 16B the south. south. This Thisstop stopconsists consistsofof22parts: lies lies just to the the west west of of the the turnoff. turnoff. * Stop Stop 16A: TECK-CORONA TECK-CORONATRIANGLE TRIANGLE(Figure (Figure 28) 28) Permission Permissionto to visit visitthis thisstop stopisisrequired requiredfrom fromthe theTeck-Corona Teck-CoronaOperating OperatingCorporation. Corporation. These hydraulically uartz-feldspar-porphyritic fragmental hydraulically cleaned cleanedexposures exposuresshow showfelsic, felsic, qquartz-feldspar-porphyritic fragmental rocks structurally overlying "dl,and and "b", "c", rocks (outcrop (outcrop "a") structurally overlyingfeldspathic feldspathicmetasedimentary metasedimentaryrocks rocks(outcrops (outcrops"b", "d"). The Thefragments fragmentsininthe thepyroclastic(?) pyroclastic(?)rocks rocksare arefairly fairlymonolithic monolithicand andrange rangefrom fromlapillilapilli-to tosmall small block-size, 5:1. This unit is better better represented represented block-size,and andhave have aspect aspect ratios ratiosranging rangingfrom from about about 3:1 up to 5:1. in Stop 16B. in Stop 166. The southern southern 33 exposures exposures comprise comprise well-layered, feldspathic, metavolcaniclastic(?) metavolcaniclastic(?) rocks. (%i+nrn* "k'l nnn~~itÈ+t n 4 + h i n l / l n ~I - x n r n A ~InnunA Outcrop "b" schistose rocks. The >^'UL^IUIJ u consists ^UIIOIOLO of UI thickly Llll^i\ly layered, l a y c l c u , cleaved, ^>icavcu,and ai1u locally 11%ally Thelayering layeringisis disrupted <jisrupted by by irregularly irregularly shaped, shaped, locally locally truncated truncated bodies bodlies ofof"layer-parallel" "layer-parallel" breccia, breccia, and and by by numerous highand low-angle faults accompanied by some block rotation. The metasedimentary Iiumerous highmetasedimentary low-angle accompanied soni e block rotation. .--I.- display A:--I,... -..A&.. .....AL.-~:..n..~-~-rocks zones. ILJLR~ U I ~ ~ irregular 11 I I~ GY YU I ~ Irusty I UWY weathering W G ~ LIGI I IIIY LUI I B ~ Outcrop .UULGIUIJ "c" "c" consists consists of of similar rocks rocks except that here, layers relatively relatively rich rich in in amphibole amphibole are present. Locally Locallythere thereisisaaconsistent consistentasymmetrical asymmetrical distribution distribution of of amphibole amphibole across across the the thickness thickness of of the thelayers, layers, with withmore moreabundant abundant amphibole amphibole present on the structurally structurally upper upper (i.e., (i.e., north) side. The Thehighhigh-and andlow-angle low-anglefaults faults(relative (relativeto to layering) collectively display dextral offsets. offsets. Some laye?ring)found found here here collectively display apparent apparent sinistral sinistraland and dextral Some light-coloured light-coloured pseudotachylite/u Itracataclasite, ppossibly associated with the ossibly associated the layer-parallel layer-parallel faulting, faulting, based based on on PSeudotachylitelultracataclasite, :W-..-..~m- �Geology and Gold Deposits Deposits of the Hemlo Hemlo Area 62 62 of the the outcrop. outcrop. Outcrop other exposures, is present near the southwest end of Outcrop "d" "d" shows showsaa highly highly deformed mafic dike within feldspathic metasedimentary metasedimentary rocks. of these rocks suggests that they may The white-, and locally rusty, rusty, weathering character of have undergone some degree of alteration. This bestudied studiedininmore moredetail. detail. Thisaspect aspectneeds needsto to be Structural Structural Summary: Summary: Felsic Felsic porphyritic porphyriticrocks rocks predominant, flattening(?) flattening(?) fabric fabric 286/55 S, Sp 286155 predominant, rocks Feldspathic metasedimentary rocks SO/SI 290/62 SdS, 290162 alignment of amphibole amphibole 267/? S,w minor alignment S2? 2677 Displacements along generalized subvertical sets: Displacements along displacement with the orientation displacement orientation of of aa fault) fault) * Stop Stop 16B: 16B: 305O, 340°, 340°020°, 020°050° 070°(there is no no apparent apparent consistent consistent sense sense of of 305°, 050°, 070°, FELSIC PYROCLASTIC PYROCLASTIC UNITS(Figure UNITS(Figure 28) This the best best for fordisplaying displayingthe thefragmental fragmental character character of of this this unit. unit. Here, This exposure exposureis is one of the Here, one felsic, quartz-feldspar-phyric, quartz-feldspar-phyric, fragmental fragmental rocks rocks interpreted interpreted to represent can see crudely layered, felsic, pyroclastic deposits. pyroclastic deposits. The south part of of the the outcrop outcrop consists consists of of lapilli-tuff lapilli-tuff which contains contains heterolithic heterolithic fragments. fragments. Some fragments are more mafic than the matrix, and many are not porphyritic. porphyritic. Several Severallayers layersof of lithified tuff, or volcaniclastic volcaniclastic sedimentary material, separate the lapilli-tuff lapilli-tuff from the structurally structurally The tuff tuff is similar overlying pyroclastic breccia. overlying breccia. The similar to to what what isisinterpreted interpreted to to be bevolcaniclastic volcaniclastic metasedimentary rocks north and northwest of of the the Hemlo Hemlo deposit. deposit. The pyroclastic pyroclastic breccia metasedimentary rocks to the north breccia (block and ash flow?) is almost monolithic: one one ill-defined ill-definedlayer layer is is defined defined by by an an abundance abundance of of block-size fragments. block-size fragments. Hwy 17 - o 20 20 10 30 30 m m pyroclastics scale approximate scale approximate Teck—Corona Property 11 Stop 16: Figure ure 28. 28. Stop 16: Simplified sketch map of quartz-feldspar-porphyritic fragmental rocks structurally overlying feidspathic, metasedimentary metasedimentary rocks breccias and structurally overlying layered, feldspathic, rocks with with layer-parallel layer-parallel breccias and pseudotachylite/ultracataclasite. pseudotachylite/ultracataclasite. �Road Log Log — -Hemlo Hemlo Area Area Road 63 63 Both the the fragments fragments and and matrix matrix of of the the fragmental fragmental rocks rockscontain containquartz quartzand andfeldspar feldsparphenophenoBoth crysts. are more felsic than the matrix crysts. Most Most fragments fragments are more felsic matrix which which contains contains more more biotite. biotite. The The phenocrysts phenocrystsrange rangefrom fromabout about11to to55mm mmacross. across. The The predominant predominant fabric fabric in in this thisoutcrop outcropisisthe the one one in inwhich which the thefragments fragmentsare areflattened. flattened. ItIt isis interpretedtotobe bethe theS2 S, axial axial planar planar cleavage cleavage and and is here counter-clockwise tothe thelayering. layering.This Thisisis interpreted counter-clockwise to S& relationship atStop Stop24, 24, so there may may be an contrarytotothe theS1/S2 contrary relationship at an east-closing east-closing fold nose somewhere somewhere betweenthese these stops. stops. The Thedistribution distributionofofquartz-feldspar-phyric quartz-feldspar-phyricrocks rocks(see (seeFigure Figure28) 28)supports supportsthe the between bethe the "mate" "mate" possibilityof of aa tectonically tectonicallydisrupted disruptedfold foldclosure closuresoutheast southeastofofStop Stop13, 13,which whichcould couldbe possibility to property. If the the structural structural and and lithological lithological interpretation is to the the large large fold on the Williams property. is correct, the unit unitat at Stop Stop16 16 represents representsthe the repeated repeatedunit unitwhich whichhosts hoststhe theore, ore, although althoughcomplexities complexitiesmake make the thisinterpretation interpretationequivocal. equivocal.The Theunit unitisisconsiderably considerablythicker thickerininthe thevicinity vicinityofofthis thisstop stopand andexhibits exhibits this lithological characteristics characteristicsas aswell well as as heterogeneous heterogeneous strain strain and and alteration from outcrop outcrop aavariety variety of lithological alteration from to to outcrop outcrop(e.g., (e.g., compare compareStop Stop17 17with withStop Stop16B). 16B). As reported reportedby byQuartermain Quartermain(1985) (1985)from fromthe theexamination examinationofofdiamond diamonddrill drillcore, core,part partof of this this unit unit As contains "molybdenite-bearing fragments". fragments". The ramifications containsan an "ore "ore clast", clast", with visible gold, and "molybdenite-bearing ramifications implicit in in these these interpretations interpretations highlight highlight the the necessity necessity for for explicit explicit documentation documentation of of details details implicit regarding primary features, the timing of of mineralization mineralization relative to deformation, deformation, and and the the stratistratiregarding graphic graphicand andstructural structuralfeatures featuresthus thusproduced. produced. Structural StructuralSummary: Summary: S0/S1 SdS, 295/46 295146 273/56 S2 S, 273156 alignment alignmentofofflattened flattenedfragments fragments S38(?) S3J?) 252° 252O sericite sericite S3J?) 285° 28S0 deflects deflectsS3 S3s 53C(?) 1.2 L-> (L0?) (L?)352/42 352142 also alsopossible possibleelongation elongationlineation lineation ** Stop Stop17: 17: BILITHOLOGIC BILITHOLOGICOUTCROP OUTCROP(Figures (Figures18 18&&19) 19) Location: north side, from the tailingslhaulage tailings/haulage turnoff Location: Go Go115 115m m west west on on Highway Highway17, 17, north turnoffatatStop Stop16. 16. The a structurally overlying Theoutcrop outcropconsists consistsof ofaa felsic felsic metavolcanic(?) metavolcanic(?)unit, unit, and and astructurally overlying metasedimentary metasedimentary felsicrock rockin in contact contactwith withan an approximately approximately30 30m mthick, thick, unit.The Thewest westend endof ofthe the outcrop outcropshows showsthe thefelsic unit. subalkalic subalkalic(i.e., (i.e., common) common)diabase diabasedike. dike. Felslc FelsicMetavolcanic MetavolcanicRock Rock The Thestructurally structurallylower lowerpart partof ofthis thisoutcrop outcropconsists consistsof of altered, altered, felsic, felsic, lenticular, lenticular, quartz-"eye"quartz-"eye3'bearing due totothe bearingrock. rock.On Onfresh freshsurfaces, surfaces,the thematrix matrixisispale palegreenish greenishyellow, yellow,possibly possiblydue thepresence presenceofof saussurite. saussurite.The Therock rockappears appearstotobe berecrystallized recrystallizedand andaltered. altered. 10:l (Photo (Photo4) 4) are are The lenses, lenses, which which generally generally have have aspect aspect ratios in in the the order order of of 4:1 4:1 to to10:1 The commonlypinkish pinkishand/or and/ormedium mediumto todark darkgrey greyininappearance. appearance.Some Somelenses lensesare arelighter-coloured lighter-coloured commonly thanthe thematrix. matrix.The Thepink pinkcolouration colourationextends extendsalong alongsome somecleavage cleavageplanes, planes,forms formsill-defined ill-definedand and than irregularlyshaped shapedbut butcommonly commonlylenticular lenticularzones, zones, and andforms formsrims rimsaround aroundsome someofofthe thedarkish darkish irregularly lenses(Photo (Photo4). 4). Staining Stainingindicates indicatesthe thepink pinkcolour colourisisdue, due,atatleast leastininpart, part,to topotassium potassiumfeldspar. feldspar. lenses Some colouration may may be be the the result resultofofcontact contact Some geologists geologists have have suggested suggested that the pink pink colouration metamorphismfrom fromthe thenearby nearbydiabase diabasedike. dike.The Thedark darkcolour colourininsome somelenses lensesisispossibly possiblydue duetoto metamorphism chlorite chloriteand/or and/orbiotite. biotite.The Thedarker darkercolour colourisisnot notevident evidenton on weathered weathered surfaces. surfaces. AAdeeper deeperpinkish pinkish orangealteration alterationalso alsoextends extendsalong alongrelatively relativelylate latefracture fractureplanes planesatathigh highangles anglestotothe thefabric, fabric. ItIt orange has potassicor orhematitic hematiticalteration. alteration. hasnot notbeen beendetermined determinedwhether whetherthis thisisispotassic �Geology Geology and Gold Deposits Deposits of the Hemlo Hemlo Area 64 64 The quartz 4:1 in faces 1.5:1 to 4:1 quartz "eyes" "eyes" are are variably variably flattened flattened and and range range in in aspect aspect ratios ratios from from 1.5:1 perpendicular to to dip and dip direction. The "eyes" are heterogeneously distributed and The "eyes" are heterogeneously distributed and are not surfaces. Finereadily apparent on fresh surfaces. Fine-to to medium-grained medium-grainedfeldspar phenocrysts phenocrysts are present present be throughout the matrix although although they they are are best seen in cut surfaces. There Thereare arewhat what appear appearto to be feldspar fe~ ldspar crystals (phenocrysts?, (phenocrysk?, porphyroblasts?) within the lenses. lenses. Discontinuous the predominant Discontinuous Iaminae laminae of quartz are locally present as stringers 1parallel to the . . .. . . , .. . * Several quartz-muscovite clots Quartz veins are buckled and/or dismembered. clots are are fabric. uuartz veins are DucKlea analor aismemDerea. beverai A . present. present. Although the rock is is altered and and deformed (possibly mylonitized), it is interpreted to have have been, originally, originally, aaquartz-feldspar quartz-feldspar porphyritic porphyritic fragmental (pyroclastic?) (pyroclastic?) rock particularly particularly given given that that the outcrop outcrop is on strike strike with with the the one one at at Stop Stop16B. 16B. Porphyroblastlc PorphyroblasticMetasedimentary Metasedimentary Rock Rock The structurally upper part of this outcrop presently consists of finely laminated, laminated, aluminous which are in sharp contact with with the felsic metavolcanic rock described metasedimentary rocks which above. The above. The layering, layering, defined defined by by variations variations in in mineral mineral content content and and grain grain size, size, shows shows no no primary primary sedimentarv features. amohibole-rich lavers which underdone attenuation and Relict amphibole-rich layers which have undergone attenuation and sedimentary features. - -- - r - - ..- . .- -,* -boudinage locally present. The inage are locally The layering layering presently presentlydefines defines an an east-closing, east-closing, almost almosit isoclinal, boud isoclinal, F2 F2 been overprinted overprinted and and modified modified by bythe the S3 S3foliation foliation(D, (03). fold, which subsequently has been ,). The south - I J J :A -..-I.. ÑÑ&&AK..M&AJ * . L., . I & ~L..:AI...AAA L A IA.,Af iiL;niI ~ W UI it; iciye~ ing. There There is limb OT of ims this 1IUIU fold is IIIUGI muchI Imore attenuated as :..J~J:A..&AJJ indicated by thickness of &LIthe layering. is I I U I ~ciiiei iuci~eu cis 11 I U I L . ~u ~ y~ LIthe U LI some eqi equivocal evidence for for aa west-closi~ west-closing fold to the south of this fold. A few late fractures / south of this fold. iivocal evidence 4 few late fractures ng fold to the associated with pink-orange pink-orangealteration alteration are are present. present. associateid with J -1 1.L:- -Adn ;4 . . . A I The porphyroblasts comprise staurolite, sillimanite, sillimanite,and and possibly possibly aa fourth type ~ U IIYIUUIWS ~ I G W I I ~ 13e I ygarnet, a I let, staurolite, type represented white-weathering which may be be retrograded retrograded crystals. ring mineral(s) which ssented by roughly equant, white-weathe repre Garnet fine- to to medii medium-grained, crystals which are distributed, distributed, ~m-grained,euhedral crystals let occurs as reddish brown, fineGarn &LAt.accoruiny to KJ the me composition G U I I I ~ U S I L I Uof UI I ~ the me layering. layering. Staurolite crystals are fine- to coarsecoarsein part, pan, according grained, euhedral euhedral to subhedral, dark to medium medium brown, and and locally locally have have overgrown overgrown and and preserved preserved layering. The the modified metasedimentary layering. The entrained entrained layering is straight within the crystals, crystals, suggesting static suggesting static conditions conditionsduring duringgrowth. growth. Many Manyof of these these crystals crystalshave havesubsequently subsequentlyundergone undergone a cl clockwise fold as as indicated indicated by the the re-orientation re-orientation of the layering. Fgfold layerir1Q. lockwise rotation, rotation, on on both bothlimbs limbs of of the F2 Thiss suggests the effects effects of the dextral dextral shear shear event event post-dated post-dated porphyroblast porphyroblastgrowth, growth, at at least least: in Thi in Pnrnhvrnhlactc whioh appear annoar in in long Innn section cortinn on nn the tho outcrop niitornn chnw weak tonrlonov to tn part. which tendency par-t,. Porphyroblasts ,. uk^k^Vui VÇÇ.N^Iw show Iv..aa weak ..VuI. .w be be aligned parallel aligned parallel to to the the S3 S3 fabric. -I:-- .__A 1.- ÑÑ .., I VltaflUU.u *JVw.lw.. llVII I 1V4uI Sillimanite occurs occurs as as fibrolite fibrolite and appears, on the glaciated Sillimanite appears, on glaciated surface of this outcrop, outcrop, as as The tibrolite relatively dark, wispy, splaying, aligned, aligned, sigmoidal sigmoidal ("S") ("S") clusters of crystals. wispy, splaying, crystals. The fibrolite is is commonly adjacent to, to, and locally is commonly is deformed deformed around, around, staurolite porphyroblasts, porphyroblasts, particularly where angle to to the the layering. layering. The The sigmoidal sigmoidal deflection deflection of the clusters clusters appears appears where the the latter latter are are at at a high angle represent an an s-c s-c fabric fabric relationship relationship in in aa dextral dextral shear shear zone. zone. These to be a D3 feature and may represent metasedimentary strike from metasedimentaryrocks rocksare arevery verysimilar similarto tothose thoseat atStop Stop13, 13, although althoughthey they are are not not along along strike this this outcrop. outcrop. Structural Structural Summary: Summary: Metasedimentary Rocks Metasedimentary Rocks S1 282/58 S, 282158 S3 S3 273/? 273/7 alteration) Late fracture (pink-orange (pink-orangealteration) Metavolcanic Rocks Met, S predominant (mylonitic?) 292/51 356/90± 356/90 �— Hemlo Area Road Log - 65 65 * Stop Stop 18: 18: FELDSPATHIC FELDSPATHIC METASEDIMENTARY METASEDIMENTARYROCKS ROCKS(Figures (Figures18, 18,19 29) 19 && 29) LocatIon: weston south side, to apoint a point just just before before a turnoff Location: Go Go 160 160 m west onHighway Highway17, 17, south side, from from Stop Stop17, 17, to to the north. north. This Thisunit unitisisapproximately approximatelyon onstrike strikewith withthe themetasedimentary metasedirnentaryunit unitatatStop Stop16A. 16A. This outcrop outcropis is not not nearly nearly as as illustrative illustrativeas as itit was before before the recent recent blasting. blasting. ItIt shows grey to to This shows grey light grey grey weathering, feldspathic feldspathic metasedimentary metasedimentaryrocks rocks with with some someamphibole-rich amphibole-richlayers laversand and light garnet-bearing layers. layering is likely a result of a combination comll in at ion of some minor garnet-bearing layers. The present layering of primary compositional compositional layering layering and and subsequent, subsequent, locally locally developed, tectono-metamorphic tectono-metamorphic layerprimary layerA --. ...l~&'. GUU~I~LS Atthe theeast eastend endof of the the outcrop outcroo some layers lavers disolav reoetitive. liahtldarkgrey-grade" ing. At display repetitive, light/dark -,- .~, -,-- . . a -. . - grey-graded couplets (dark part on on the north north side) side) (ci. (cf.Stop stop 16A). 16A). Some Someflattened, flattened,S-shaped S-shapedfolds folds in inquartz quartzveins veinswith with (dcirk part dismembered present. The The flattening flattening fabric fabric ranges ranges from parallel parall1el to slightly counterdismembered limbs are present. clockwise to the the layering. laverina. d o ckwise to --, - - - - - - - - - 4 - - -z - W~ Several low-angle, low-angle, counter-clockwise counter-clockwise (to (to layering), layering), dextral dextral faults faults are are present presentand andmay maybe be Several genetically breccias and and pseudotachylitelultracataclasite pseudotachylite/ultracataclasite geneticallyrelated relatedto to several severalzones zones of layer-parallel breccias that are are visible visible at at this this stop. stop. The faults are are locally locally parallel parallel to to layering layering along along strike. strike. The The pseudotachylite, which locally contains spherical to elongate elongate vesicular features (naturally (naturally at aa precarious spot at the top edge edge of of the the roadcut), roadcut), has has possibly possibly undergone ductile deformation in places. places. At At the theeast eastend endof ofthe theoutcrop outcropat atroad roadlevel, level, is is aazone zone of of breccia brecciain inwhich which blocks blocks of of metasedimentaryrocks rocksappear appearto to have have undergone undergone clockwise clockwise rotation rotationwith withinfilling infillingby bymore morefinely finely metasedimentary brecciated variety of breccias brecciatedhost hostrock. rock.This Thismay may~.represent representaavariety of the the layer-parallel layer-parallel brecciasthat thathave haveresulted resulted . from displacement. There from dextral sense displacement. There are are also also sets sets of of numerous, numerous, relatively late, brittle brittle faults faults which whichare areat ataahigh highangle angleto tolayering. layering. On bepurplish purplishgrey greyand andpale pale On the the fresh fresh roadcut roadcutface, face, the the metasedimentary metasedirnentaryrocks rocksappear appearto tobe ----:.... ~. greenisrl grey. However, nowever, the ine greenish greenisn grey grey colour coiour is spanany associatea with wiin the inesets seis of OTfractures Traciures greenish spatially associated mentioned above, above, and appears appears to be be some some type of of alteration alteration involving involving bleaching bleaching of of the the rock. rock. mentioned Locally, similarly bleached. This Locally, up up to 80% 80% of the rock rock is similarly Thisraises raisesquestions questionsabout abouthow howmuch muchofofthe the rocks, what form form of alteration alteration has taken place. Some rocks, here here and and elsewhere, elsewhere, are altered, and what Some hematiticalteration alterationisispresent, present,along alongwith with quartz quartzand andchlorite, chlorite,on on some some fractures. Other Otherfractures fractures hematitic contain epidote epidote ++ calcite±amphibole. calcite±amphiboleThe The metasedimentary metasedirnentaryrocks rocks are are intruded intruded by by aa schistose schistose contain dike, not not readily readily apparent apparent on on horizontal horizontal surfaces, surfaces, that that has has undergone undergone significant significant pinching pinching and and boud in age. boudinage. ---!-I- I I !-L LL- ---L?-t* -!-.--I ~ .LL a*-- - r r ~ - - The metasedimentary metasedirnentaryrocks rocksat atthis thisstop stopshould shouldbe be compared comparedto to those those at at Stop Stop 24, structurally The structurally underlying underlyingthe the deposit, deposit, which which some somegeologists geologiststhink think are are part partof of the thesame sameunit. unit. 1" 00 N 30 30 20 20 10 10 m m scale scale approximate approximate A Hwy 17 Hwy 17 itewac % m b i o . \ ~ wacke e k 1 layer-Darallel breccia breccia layer—parallel // / O\POI~ amyg7I eudotac hylite with ~seudotachylite with amygdules 1 deformed deformed mafic mafic dike dike zone zone of rotated rotated blocks blocks (related (related to tolayer—parallel layer-parallel breccia) breccia) Figure feldspathic metasedirnentary metasedimentary rocks Figure29. 29. Stop Stop18: 18: Simplified Simplifiedsketch sketch map map of feldspathic rocks with with breccibrecciated ated zones zones and and pseudotachylite/ultracataclasite. pseudotachylite/ultracataclasite. �66 66 Geology Geology and and Gold GoldDeposits Depositsof of the the Hemlo HemloArea Area StructuralSummary: Summary: Structural SOIS, 297/55±5 297/55± overall overall S/S1 layeringadjacent adjacenttotozone zoneofofaligned alignedblocks blocks(see (seedescription descriptionabove) above) S0/S1 SOIS, 285/? 2851? layering 303Oto to320° 32O0 (long (longaxis) axis) Alignmentof ofblocks blocks 303° Alignment Low-angle,faults faults 265/80 265180 dextral, dextral,brittle-ductile; brittle-ductile;03 D3 Low-angle, High-anglefaults faults 358/85 358185 dextral dextral High-angle sinistral;offsets offsetsaalow-angle, low-angle,03-related D3-relatedfault fault 328/90 sinistral; 328/90± 010190± 010/90 sense sensenot notdetermined determined L, (slickenside) (slickenside) -297/05± -297/05 L5 Stop19: 19: "HANGING "HANGINGWALL" WALL"METASEDIMENTARY METASEDIMENTARYROCKS ROCKS(Figures (Figures18 18&&19) 19) * Stop Location: 50 m west on on Highway 17,17, south side, Location:Go Go 50further m further west Highway south side,from fromthe thewest westend endofofStop Stop18 18(which (whichisis opposite oppositeaaturnoff turnoffto tothe thenorth). north). This Thisisisthe thefirst firstrelatively relativelylarge largeoutcrop outcropto tothe theeast eastofofthe theMain MainMineralized MineralizedZone Zone(Stop (Stop20A), 20A), and the highway. highway. The metasedimentary metasedimentary and best best represents representsthe the "hanging "hanging wall" unit unit as exposed along the rocks rocks display display indistinct, indistinct, possibly possiblytransposed transposed layers, layers, defined defined mostly mostly by by various various proportions proportionsofof feldspar, feldspar, quartz, and biotite, biotite, as as well well as assome someamphibole-rich amphibole-rich layers. layers. There There are are also also zones zones consisting associated with few veinlets associated with tourmaline tourmaline consistingof of numerous numerousamphibole-rich amphibole-richknots knotsor or lenses. AA few and and bleaching bleaching of the the country country rock rockare arepresent. present.There Thereare areseveral severallayer-parallel, layer-parallel,fine-grained fine-grained gossans gossans which which are are locally locallyill-defined. ill-defined. In In this this outcrop, outcrop, there thereare areseveral, several,weakly weakly defined, defined,angular angulardiscordancies discordanciesbetween betweensets setsofof layered rocks and between angular of cleavage cleavagewith with respect respect to to layering. layering. These angular relationships of These features may be examples of juxtaposed faulted blocks, or, possibly 3 or so ill-defined, tight, F2 features may be examples of juxtaposed faulted blocks, or, possibly 3 or so ill-defined, tight,F2 folds, folds, or or aa combination combinationof of both bothfeatures. features.F2 F2folds foldshave havebeen been observed observedin in the the hanging hanging wall rocks rocks at the the Williams Williams A A Zone Zone pit, pit, and and north northof of the the highway highway along along the the effluent/haulage effluentlhaulageroad roadbetween betweenStops Stops 19 and and 20. 20. 19 The The metasedimentary metasedimentaryrocks rocksexposed exposedat at this this stop stopshould should be be compared comparedto to those thoseat atStop Stop22 22 which footwall rocks rocksto to the the main mainpart partof of the theQuartzQuartzwhich form, form, with with respect respectto to highway highwayexposure, exposure, the the footwall Feldspar-PorphyriticComplex Complex(Stop (Stop20). 20). Feldspar-Porphyritic StructuralSummary: Summary: Structural Northpart partof of outcrop: outcrop: North (predominant) 295/60 295160 $S(predominant) South part partof of outcrop: outcrop: South Rangeof ofSO/SI SdS, layering layering 282° 282O to to 297° 297O Range Rangeof of possible possibleS2 Q,cleavage cleavage 292° 292O to to 282° 282 Range QUARTZ-FELDSPAR-PORPHYRITICCOMPLEX COMPLEXAND AND MAIN MAINMINERALIZED MINERALIZEDZONE ZONE Stop 20: 20: QUARTZ-FELDSPAR-PORPHYRIT1C * Stop (Figures 30 && 31) (Figures18, 18,19, 19,30 31) further weston low-lying outcrop Go 235 235 m m furtherwest onHighway Highway17 17from from Stop Stop19, 19, to a low-lying outcrop (Stop (Stop20A), 20A), Location: Go north northside, side, about about55 55m mwest westof of an aneffluent/haulage effluentlhaulageroad. road. * Stop Stop20A: 20A: MAIN MAINMINERALIZED MINERALIZEDZONE ZONE(Figure (Figure30) 30) This completely buried, This outcrop, outcrop, which whichused usedto to be be larger larger before before being completely buried, then then partly partlyrecovered, recovered, is property (see Figure 22). The is part part of of the the rootless, rootless, mineralized, mineralized,West West Zone of the Teck-Corona property The West 17. West Zone Zone presently presentlyisisnot noteconomical economicaltotomine, mine,ininpart partbecause becauseofofits itslocation locationbeneath beneathHighway Highway 17. �Road Log — Hemlo Area 67 67 The outcrop outcrop consists consists of of rusty rustyweathering, weathering, schistose, schistose, locatly locallylenticular, lenticular,heterogeneously heterogeneously sericitized sericitized and and pyritized pyritizedquartz-feldspar quartz-feldsparporphyritic porphyritic rock rockwhich whichdisplays displaystourmaline, tourmaline, some some relarelatively of very very fine-grained fine-grained molybdenite. molybdenite. The tively large large green green mica mica lenses, and wisps of The green green mica micain in the the Hemlo camp has been determined to be vanadian muscovite (Harris 1986b, 1989). Grab samples Hemlo camp determined muscovite (Harris 1986b, 1989). Grab samples from this outcrop outcrop returned returned values values of of 016 016 ounce ounce Au Au per per ton ton (0.05% (0.05% MoS2) M0S.J (Patterson (Patterson1984), 19841, 6.35 6.35 24.35 ppm ppm Au, Au, and and 550 550 ppm ppm Mo Mo(Schnieders (Schnieders eta/. eta!. 1988). 1988). Channel samples from this outcrop and 24.35 (J. Londry, Londry, geologist, geologist, Hemlo Hemlo Gold Gold Mines Mines Inc., lnc., assayed assayed up up to to 9.0 9.0 ppm ppmAu Au across across1.14m 1.l4m (J. by Hemlo Gold Mines Mines Inc., lnc., personal personal communication communication1994). 1994). Despite considerable considerable recent recent oxidation, oxidation, one one can can still still see see a variety Despite variety of of lenses lenses defined defined by by and porphyriticlnon-porphyritic, schistose/"massive"), schistose~lmassive~'), and differences in grain grain size, size, texture texture (e.g., (e.g., porphyritic/non-porphyritic, composition (e.g., sericite/biotite) (Photo 5). Some (e.g., sericitelbiotite) Someof of the the lenses lensesconsist consist of of quartz quartz which which may may indicate indicate that that some some quartz quartz veins veins have have been been completely completely dismembered. Considerable Considerable variation variation in in texture and between fabric-parallel, fabric-parallel, non-lens-bearing texture and grain grain size size also also can can be be seen between non-lens-bearing"zones", '2ones", some someof of which are not pyritized. There consensus as to the the protolith protolith of the the unit. unit. Some geologists interpret to be There is is no consensus Some geologists interpretthe the rock rockto be a mylonite, and others a deformed, deformed, possibly possibly mylonitized mylonitized pyroclasticlvolcaniclastic pyroclastic/volcaniclastic fragmental. fragmental. The unit appears texturally unit appears texturallysimilar similar to to sericitized sericitized"fragmental" "fragmental"rocks rocksininthe themines minesand andininthe theTeck-Corona Teck-Corona trench (Stop A). Felsic, monolithic and heterolithic, quartz-feldspar-phyric quartz-feldspar-phyric pyroclastic/volcan(Stop 21A). pyroclastic/volcaniclastic rocks rocks can can be be seen seen elsewhere in the area, (e.g., (e.g., Stop 16B, 16B, and outcrops on the Williams Because of of the internal property and Golden Sceptre property property property (Hemlo (Hemlo Gold Mines Mines Inc.)). lnc.)). Because internal complexities in this unit (particularly (particularly to to the the west-northwest), west-northwest), such as "massive" and and fragmental porphyritic rocks, Muir Muir (1985) (1985) coined the term "Quartz-Feldspar "Quartz-Feldspar Porphyritic Complex" Complex'' for the essentially contiguous essentially contiguous quartz-feldspar-phyric quartz-feldspar-phyricrocks, rocks, of of which which this this unit unit appears appears to to be be part. part. m east east of the east east end end of the the main main outcrop outcropat at Stop Stop20A, 20A,shows showsaa22m m A small outcrop, about about 77 m ium-grained, subporphyritic subporphyritic (plagioclase) granodiorite dike thick, apparently apparently unaltered, unaltered, med medium-grained, dike which has intruded has muscovite muscovite intruded the sericitized, sericitized, pyritized, pyritized, porphyritic porphyritic rocks. rocks. The dike has poikitoblasts. poikiloblasts. c- ----- -— - I lensy (fragmental?), porphyritic, (fragmental?), quartz—(feldspar)q u a r t z - ~ f e I d sporphyritic, par~-~o~~~~ ~ i tI~ quartz-(feldspar) ~ quartz—(feklspar) porphyritic, sericite sericite schist t— sericiteschist schist IJ sericite 0 plagioclase-subporphyritic granodiorite granodbrite J plagioclase—subporphyritic Figure 30. 30. Stop 20A: 20A: Detailed sketch sketch map & 22) 22) map of the West Zone Zone (See (See Figures Figures21 21 & (Teck-Corona property) as originally originally exposed exposed (Teck-Coronaproperty) along Highway 1Z Present outcrop outcrop outline outline Highway 17 differs. (Modified (Modifiedafter afterPatterson Patterson1984). 1984). 0plagioclase—subporphyriUc plagioclase-subporphyritic granodiorite granodiorite FIgure Figure31. 31. Stop Stop 20B: 20B: Detailed Detailed sketch sketch map map of part of of the the Quartz-Feldspar-Porphyritic Quartz-Feldspar-Porphyritic ComComplex, structurally structurally underlying underlying the West West Zone Zone 221, as as originally originally exposed exposed (See Figures 21 & 22), along Highway Highway 17. 1Z Present Present outcrop outcrop outline outline difdiffers. (Modified after Patterson 1984). fers. (Modified after Patterson 1984). �Geology Geology and and Gold Gold Deposits Deposits of of the the Hemlo Hemlo Area Area 68 68 Structural StructuralSummary: Summary: S (predominant) (predominant) (S*?) 2881-70 S (S?) 2881-70 (subordinate)(S35?) (S3*?) 263/? 26W? deflected deflectedby byabove aboveSS(predominant) (predominant) SS(subordinate) (subordinate) (Sw?) 29777 backrotates backrotatesSS(predominant) (predominant) 297/? SS (subordinate) (S.?) S3?(late (lateoverprint?) overprint?) 250174 250174 crenulation crenulationininF3 F3fold fold S3? Axial Axial plane planeboundary boundary 011/? O l l l ? sinistral sinistralsense sensekink kink "MASSIVE" "MASSIVE"QUARTZ-FELDSPAR QUARlZFELDSPARPORPHYRY PORPHYRY(Figure (Figure31) 31) Stop 20B: 20B: * Stop LocatIon: Go 55 m to the west of Stop 20a, north side. This Th low-lying outcrop structurally underlies the main mineralized zone, seen IininStop Stop20A, 20A, and and consists porphyry which consist! of white-weathering, felsic, foliated, green-mica-bearing, quartz-feldsparr porphyry intrllnen by nv several n r n r i..,....v r t T l r : rllKI+S. 1 lie quartz-feldspar-porphyritic q u ~ ~ ~ ~ - ~ ~ i u ~rock rock p ~ may ~ -have have p ~ ~ p i ~ y is intruded several feldspar nr-.r porphyritic dikes. The may - -. -. Telnsnar .-.--r-. -...--. been subvoicanic intrusion low. Some Some of of the the dikes dikes display display boudinage boudinagewith with intrusion or or part part of a massive massive fflow. be(?n a subvolcanic cs. The dikes are foliated with sericite&chlorite, D3-related features (Le., 83, F3) evident in the necks. The dikes are foliated with sericite±chlorite, D3, and contain non-preferentially-oriented muscovite ana conlam non-pre~erenua~~y-orlen~ea rnuscovne poikiloblasts. poikiloblasts.Small-scale, Small-scale,conjugate(?), conjugate(?),sinissinistral and dextral kinks (F4?) are present. m d dextral kinks (F4?) are present. tral i 8 8.. --"- .,w, Structural summary: Predominant fabric 286/70 Subordinate fabric anastomosing with above 275/74 304° weakly developed fabric deflects(?) above 037° Trace of sinistral kink band boundary 002° Trace of dextral kink band boundary Teck—Corona Teck-Corona trench trench 3>5 \a •.(fewer (fewer lenses) lenses) A quartz-feldspar—porphyrltiC sericite schist quartz-feldspar-porphyritic sericite schist (± (*feldspathized. feldspathized, sheared) sheared) 1a lb quartz—feldspar-porPhYritic sericite schist quartz-feldspar-porphyritic sericite schist with (k feldspathized. feldspathized, sheared) sheared) with green green mica mica (± 2a sericitized. sericitized, pyritized, pyritized, feldspathized feldspathized lensy lensy schist schist with quartz—feldspar fragmental(?) quartz-feldspar phenocrysts: fragmental(?) 2b biotitized biotitized feldspathized feldspathized lensy lensy schists schists with with quartz—feldspar quartz-feldspar phenocrysts; phenocrysts: fragmental(?) fragmental(?) 3 feldspathlzed feldspathized metasedimentary metasedimentary schist schist with with biotite biotite 5 foliated quartz dioritic dike 6 plagioclase—porphyritic granodioritic ~nodioriticdike dike abruptly transitional contact — sharp contact la 0 5 10 m lb k-Corona trench trench showing showing Figure 32. Stop 21A: Detailed sketch map of the westernmost Teck-Corona the AALone. Zone. (Geology T.L.Muir, Muir,OGS OGS1987). 1987). the non-economic, non-economic.on-strike on-strikeequivalent eaulvalentofotthe tneWilliams Witt~ams (tieotogybybyT.L. �Road Log — Hemlo Area * Stop Stop 21: 21: 32 & 33) 33) 32 & 69 69 TECK-CORONA TRENCH and and WILLIAMS WILLIAMS A 18, 19,21,22, TECK-CORONA A ZONE ZONE PIT PIT SITE (Figures 18,19,21,22, Location: m west west from from Stop Stop20B 20Bto toaashort shortturnoff turnoff to to the the north north used for access to the A Location: Go 165 m Zone exhaust turbines. * Stop 21A: TECK-CORONA TECK-CORONATRENCH TRENCH(Figure (Figure32) 32) Permission Permission to to visit visit this this site site is is required requiredfrom from Teck-Corona Teck-CoronaOperating OperatingCorporation. Corporation. Location: Enter thebush the'bush (to Location: (to the north), north), from from the the highway highway right-of-way, right-of-way, on a cut line about 25 m east of the the short short turnoff road. Follow the line/trail for about 40 m to to aa 35 35 m m long long stripped stripped "trench1' "trench" Follow Iineltrail which is is roughly roughly on strike strike with with the the Williams Williams Mine Mine A A Zone. foliated, sericitic, felsic, quartz-feldspar The southern end of the stripped zone consists of foliated, quartz-feldspar porphyry which locally contains contains green mica lenses. Structurally Structurallyoverlying overlyingthis this isisaamineralized, mineralized, rusty, highly schistose (sheared?), lensy, lensy, sericitic sericitic rock with with quartz eyes, pyrite, and sparse, very fine-grained molybdenite. fine-grained molybdenite.AAgrab grabsample samplefrom from the the mineralized mineralizedpart partof of this thistrench trenchreturned returnedaavalue value of 2.27 ppm ppm Au and and 105 105 ppm ppm Mo Mo (Schnieders (Schnieders et eta!. a/.1988). 1988). There There is is no no agreement agreement as as to to whether whether the the lenses lensesare are in in whole whole or or in in part partprimary, primary,but but this this rock rock appears to to be the the sericitized equivalent of of the structurally overlying, overlying, schistose, schistose, biotitized biotitized rock appears which contains contains heterolithic heterolithic lenses. lenses. Both Bothrocks rockshave havebeen been altered altered and and are referred referred to generally in terminology as "fragmentals", although although the term term is used used non-genetically non-genetically by some some geologists. geologists. mine terminology To the north, the rocks in the trench consist of schistose, quartz-eye-bearing, biotite biotite + sericite To the somewhat feldspathized feldspathized and and sericitized sericitized metasedischists, structurally overlain by what may be somewhat metasediplagioclase-porphyritic granodioritic granodioritic dikes and mentary rocks. The The rocks rocks have have been intruded by plagioclase-porphyritic fine-grained, "quartz dioritic" dioritic" dikes. dikes. Structural StructuralSummary: Summary: North end of stripping stripping S S, (mylonitic?) (mylonitic?) 295/57 BY57 S3? 284/70 S3?(forms lozenges with above above fabric) fabric) 28470 South defined by sericite) sericite) South end end of stripping stripping (all fabrics defined S S (predominant) (predominant) 291/64 291164 S S (subordinate) (subordinate) 281/64 281164 forms lozenges with above fabric fabric 304/57 seems to deflect deflect either (subordinate) S (subordinate) 304157 either or or both both of of the the above abovetwo two fabrics fabrics Stop 21 WILLIAMS A * Stop 21 B: WILLIAMS AZONE ZONE PIT PIT (Figures (Figures22 22 & & 33) 33) Operating Corporation. Permission to visit this site is required from Williams Williams Operating Corporation. Location: stripping where a flagged flagged shortcut Location: Return Return to just south of the south end of the stripping shortcut takes takes one westerly westerly to the A Zone pit area, or, or, return return to tothe the highway highway right-of-way right-of-way and approach approach the fencedfencedto the AZone off open pit area from from the the short short turnoff road. This stop" which which is achieved by walking This is is a "view stop1' is best best achieved by walking north along along the the outside outsideof of the the east east end end of the fenced-off area area for about 50 m to Hidden just north to aa knoll. knoll. Hidden in the bush original small bush on the way in in is what appears appears to be one of the original small pits pits created createdininthe the1940s. 1940s. The west end of the open pit shows a rusty zone which which crudely marks the uneconomic, onstrike extent extentof of the the A AZone Footwallrocks rocksto to the the ore ore zone zone are are variably variably altered altered strike Zone of the the Williams Mine. Footwall schistose, felsic, felsic, quartz-feldspar quartz-feldspar porphyry. tight to to isoclinally isoclinally and schistose, porphyry. The The hanging hangingwall rocks consist of tight folded and transposed metawacke and metasiltstone with with amphibole-rich amphibole-rich layers. layers. Staurolite Staurolite and �0 N 10 m 30 40 S 50 . 2 S Approximate outline of present day pit—' Figure 33. Stop 21 B: Generalized sketch map of detailed surface geology of the Williams A to excavation for the open pit. (Modified after mapping by T.L. Muir 1985; Muir et a!. 20 S Interpreted ill—defined Iithologic contact: observed generalized outcrop area with patch of remaining overburden . CD CD I -P 0 C,) - C,) V 0 CD 0 0. 0 0 0. CO 0 0 CD 0 0 Geology and Gold Deposits of the Hemlo Area �Road Log — -Hem Hemlo Road Log lo Area 71 71 kyanite are present present in these hanging zone up to to about about 50 m m thick thick (Walford, Stephens Stephens kyanite in these hangingwall wall rocks rocks in in aazone eta!. 1986). The biotitized/sericitized "fragmental" unit appeared, on surface, to pinch out to the eta/. 1986). The biotitizedlsericitized "fragmental" unit appeared, on surface, to pinch about midway the open open pit pit area area (Figure (Figure 33). 33). The ore, as exposed exposed on surface surface west, about midway into into what is now the (Photo 6), 6), was was interpreted interpreted to to be derived, (Photo derived, for the most most part, from from feldspathized feldspathized and pyritized 4, Figure 33). 33). At metasedimentary rocks (Unit 4, At surface, itit was up to 35 m thick and and "H" shaped shaped Weicker eta/. eta!. 1986) 1986) with tails tails to to the the east east and andwest. west. (Walford, Weicker Open pit operations, which began in August, 1985 1985 and ended July 1986, 1986, resulted in the the extraction of 3.8 million million tons tons of of rock, rock, including including0.8 0.8 million milliontons tons of of ore oregrading grading5.13 513 ppm ppm Au Au (A. (A. Guthrie, Williams Operating Corp., written communciation communciation1992). 1992). Pit dimensions are are approxapproximately 275 imately 275 m m by by 170 170 Int T? (top), 150 m by 25 m (bottom), and 70 m deep (Resident (ResidentGeologist GeologistFiles, Files, MNDM, Thunder Bay). Bay). Plagioclase-porphyritic and and quartz quartz dioritic dikes dikes appear appear to have have intruded intruded the the AAZone Zoneore ore (Photo (Corfu and Muir 1989a). Kuhns (1988) also also interpreted interpreted feldspar porphyry porphyry and and intermediintermedi(Photo 7) (Corfu ate composition composition "sills" "sills" to to have have intruded intruded the the Golden Golden Giant orebody. orebody. The The dikes dikes within within the the AA Zone Zone (and elsewhere in the Hemlo area) typically contain contain muscovite muscovitepoikiloblasts poikiloblastsand andare areanomalous anomalousinin (and elsewhere ore, then a minimum Au, Ba, Hg, and Au, and Sb. Sb. IfIf they actually intruded intruded an existing ore, minimum age age for for the the mineralization mineralization can can be be inferred inferred to to be be about about 2680 2680 Ma, Ma, based based on on U-Pb U-Pb dates dates from from Corfu Corfu and and Muir Muir likely have undergone subsequent metamorphism metamorphism which would would account (1989a). The dikes likely account for the poikiloblasts. poikiloblasts. Whether Whetheror ornot notthe the dikes dikes assimilated assimilatedmineralized mineralizedmaterial material or "absorbed" the metals during unclear. Native fractures within an essentially essentially during metamorphism metamorphismis is unclear. Native gold gold is locally locally found along fractures unaltered, plagioclase plagioclase porphyritic porphyritic dike dike that has unaltered, has intruded intruded the the David David Bell Bell Mine Mineorebody orebody(Paul (Paul Bankes, Teck Exploration Exploration Limited, Limited, personal communication, communication, 1987), suggesting that 19871, suggesting that some some remobilremobilization has occurred. LEGEND:STOP STOP 21B LEGEND: Metavolcanic? /1 Metasubvolcanlc? Metavolcanic? Metasubvolcanic? Rocks 1 a la lbb 1 felsic. variably microcline felsic, variably schistose: schistose: quartz—feldspar quartz-feldspar porphyritic. porphyritic, sericite± sericiteLmicrocline intermediate, variably variably schistose: schistose: quartz-feldspar quartz—feldsparporphyritic, porphyritic. biotite ± sericite ±microcline biotite?sericite~microcline intermediate, Fragmental? Rocks volcanic? volcaniclastic? volcaniclastic? - volcanic? Rocks — 2a 2a 2b 2b biotitized, feldspathized, biotitized, feldspathized, lensy rock sericltized, sericitized, feldspathized. feldspathized, lensy lensy rock rock (with (withgreen Qreenmica mica lenses) lenses) Metasedimentary Rocks Rocks 3a 3a wacke, feldspathic siltstone?amphibole-rich layers feldspathicarenite arenite±ksiltstone±amphibole—rich schistose wacke, feldspathic feldspathic arenite±siltstone areniteksiltstone feldspathized feldspathized to to schistose schistosemetasediments metasediments feldspathized metasediments 3d feldspathized 3d metasediments 3b 3b 3c Schists Origin (possibly metasedimentary) Schists and and Granofels Granofels of Undetermined Undetermined Origin metasedimentary) 4a sericite±biotite schist±mlnerallzation sericitekbiotite schisthnineralization 4b intensely mineralization intensely feldspathized feldspathized rocks± rocks~mineralization 4c 4c feldspathized to schistose rocks feldspathized to Dikes Dikes 5 foliated, quartz dioritic dioritic intermediate, foliated, 66 plagioclase—porphyritic Qranodiorite granodlorite plagioclase-porphyritic intrusive contact contact 7 7 diabase diabase intrusive contact contact 8 magnetlte—biotite lamprophyre lamprophyre (Proterozoic) (Proterozoic) magnetite-biotite Most ore 4a Most ore comprises comprises subunits subunits 4 a and and 4b 4b �__ ________ ________ ______ 72 72 Geology Geology and Gold Deposits Deposits of the Hemlo Hemlo Area operation, and From this open pit operation, and given given the character characterof the the rocks rocks in in the nearby nearby Teck-Corona Teck-Corona trench, one can appreciate the potentially potentially narrow narrow "windows" (Figure 22) of exploration for ore ore of this type, type, even even though though this this is a large large deposit. deposit. One bodies of One can can also also appreciate the relative quietness of the highway highway after after leaving leaving this this stop. Structural ural Summary: Summary: 292±5/64±4 292±5164 hanging hangingwall w,all S0/S1 iIlR/Ci h-nilinn ut 305/62 hanging wwe, wG ,, ,, , wall ..all S2 schistose schistose ore; ore; felsic felsic metavolcanic metavolcanicrock rock S3? 270/65±5 2701695 schistose schistose ore, ore, felsic felsic metavolcanic metavolcanicrock rock 295/60±5 295160± S3? 060/60, schistose ore F3 060160,100/43 100143 schistose ore tourmaline 307/33 307133 tourmaline mineral mineral lineation lineation Lm slickenside 107/07 107107 slickenside L3 19 & 34) * Stop 22: MAGNETITE-LAYER-BEARING MAGNETITE-LAYER-BEARINGMETAWACKE METAWACKE (Figures (Figures18, 18,19 34) Location: Location: This stop is is beside besic and opposite the A Zone pit turnoff referred to for rthe theStop Stop21 21 location. location. * Stop Stop 22A: MAGNETITE-BEARING METAWACKE AND AND PORPHYRY DIKES (Figure 34) 34) MAGNETITE-BEARING beleaguered outcrop, on the the north side, immediately immediately to the west of of the the turnoff, turnoff, is all all that that The beleaguered remains of of a larger larger predecessor. predecessor. The The rocks rocksare are mostly mostlytransposed, transposed, foliated foliated metawacke metawacke with ± amphibole-rich layers magnetite  layers (Photo 8). 8). The metawacke metawacke appears to contain contain muscovite muscovite poikiloblasts. It has been intruded by two types of plagioclase-porphyritic dikes, both of which poikiloblasts. magnetite crystals have magnetite crystals within within many manyof of the the phenocrysts phenocrystssuggesting suggestingthis thisisisaa secondary secondary(metamor(metamorphic?) phenomenon. The The structurally structurallyupper upperdike dike is is more more typical typical of of feldspar feldspar porphyry porphyrydikes dikesin inthe the Hemlo (although a wide variety of textures and grain sizes sizes exists exists among among dikes) dikes) and and contains contains Hemlo area (although numerous, medium-grained, medium-grained, plagioclase plagioclasephenocrysts. phenocrysts. The structurally lower dike, now now visible only in the the blasted blasted face, contains contains fewer, fewer, and and mediummedium- to to coarse-grained, coarse-grained, plagioclase plagioclase phenocrysts. phenocrysts. It is colloquially known as "popcorn" "popcorn" porphyry. porphyry. Structural Summary: Structural Summary: 290/62 S,, 290162 S1, S2(?) S2(?) A—Zone Pit A-Zone t magnetite layers layers no magnetite layers \ gossan go; popcorn porphyry 0 I A 10 20 30 , , I plagioclase porphyry Hwy 17 cjD lQ^ amphibole—magnetite layers layers amphibole-magnetite m scale scale approximate approximate magnetite layers layers-" feldspathizedfsericitized rocks feldspathized ± sericitized rocks :0 ..,diamond drill drill corepile pile :..iam01 core exploration shack shack foundation foundation exploration etite-amphiSimplified sketch map of transposed metawacke with magnetite-amphibole layers and localized alteration. Figure 34. Stop 22: Figure �Road Log — Hemlo Area Stop 22B: 73 METAWACKE WITH WITH MAGNETITE-AMPHIBOLE-RICH MAGNETITE-AMPHIBOLE-RICH LAYERS (Figure 34) Almost immediately south of the turnoff is is an an outcrop outcrop of of foliated foliated but but "massive"-appearing "massive"-appearing metawacke which has magnetite + + amphibole-rich amphibole-rich layers and and is is locally locally garnet garnet rich. rich. The The layering layering appears to to be transposed to some some degree. degree. Some appears Some of of the the amphibole-magnetite-rich amphibole-magnetite-rich layers layers are disrupted. There disrupted. Thereare arediscordancies discordanciesbetween between blocks blocks or or wedges wedges with with respect respect to tolayering layering and and fabrics. Some Some of of the the layering layering may may be tightly folded with "S" asymmetry. The The rock rock isis intruded intruded by by foliated, boudinaged, plagioclase-porphyritic dikes containing muscovite poikiloblasts. plagioclase-porphyritic poikiloblasts. Structural summary: Structural summary: 289/68 S1, S2(?) S2(?) St, 289168 Stop Stop 22C: 22C: \ ALTERED MAGNETITE-BEARING MAGNETITE-BEARINGMETAWACKE METAWACKE (Figure (Figure 34) 34) The northernmost northernmostoutcrop outcropof of this thispart partof ofthe thestop stoplies lies27 27m msouth southof of the thewest westend endof of Stop Stop22B 22B and consists of metawacke with poorly defined magnetite magnetite layers. A the and consists A second second outcrop outcroplies lies 8 m to the southeast and consists of variably schistose, schistose, sericitized and locally pyritized pyritized rocks rocks intruded intruded by by Several years years ago ago one one could see felsic dikes. dikes. Several see magnetite magnetite layers layers within feldspathic feldspathic whitewhiteweathering rock, magnetite-bearing metawacke which weathering rock, suggesting suggestingthe the rock rock is altered magnetite-bearing metawacke (see (see Stop 23 which the outcrops is approximately on strike from this this outcrop). outcrop). Presently the outcrops in this area area are are being being reclaimed by lichen. A two more sericitic sericitic outcrops reclaimed A trail trail to to the the southeast southeast of of here here leads to two outcrops as as well as pile of ofdrill drill core. core. This was the campsite of the the foundation to a drill core shack and an unruly pile Lake Superior Mining Mining Corporation Corporation from from the the late late1940s. 1940s. Structural Summary: Structural Summary: St 284174; S,? S1 284/74; S2? * Stop Stop 23: 23: 29417; 294/?; S3 S, 066/88 066188 crenulatiort) (weak crenulation) LOWER MINERALIZED 35 & MINERALIZEDZONE ZONE (Figures (Figures18, 18, 19, 19,35 & 36) 36) Location: GoGo 110 mm further west Location: 110 further westononHighway Highway17, 17,north northside, side, from from the the A A Zone pit pit turnoff, past a small, previously previously unexposed, unexposed, rusty rusty weathering, weathering, schistose, schistose, alteration alterationzone, zone, to to aarusty rustyweathering, weathering, hydraulically cleaned outcrop (Figure 35). The small alteration zone returned a value from a grab grab hydraulically cleaned 35). alteration returned communication, 1990). sample of 43 ppb Au (M. Smyk, MNDM, personal communication, 1990). outcrop at Stop 23 is is the the surface surface expression expression of of aazone zoneof ofmineralization mineralization that that structurally structurally The outcrop underlies the main ore body, and is ore grade at about a depth of 900 m. Surface grab underlies body, and ore grade at about a depth of 900 m. Surface grab samples samples returned values of 0.02 0.31 ounces Au Au per ton (Patterson 1986). 1986). The 0.02 and 0.31 The outcrop outcrop consists consists of of transposed wacke transposed wacke \ feldspathized and sericitized,Z. feldspathized and sericitized. silicified(?) metasediments slllcified(?) . . metasediments . feldspathized. feldspathized, sericitized \\ 1 transposed wacke transposed w a c k e (magnetite) (magnetite) wacke magnetite-bearing w a c k e \ magnetite—bearing n 9 intermediate—mafic dike dike intermediate-mafic 10 10 .- , 20 2,0 I m m scale approximate approximate granodiorite dike granodiorite V / Hwy 17 Hwy 17 / rmediate— mafic dikes intermediate-mafic uartz-feldspar rtz—feIdspar porphyry / / Approximate location location of of Figure Figure 36 36 Stop 23: Mineralized Figure 35. Figure 35. Stop 23: Simplified Simplified sketch sketch map map of the surface equivalent of the Lower Mineralized Zone quartz-feldspar porphyry, metasedimentary rocks Zone quartz-feldspar porphyry, and and the adjacent, locally altered, metasedimentary rocksstructurstructurally underlying underlying magnetite-bearing magnetite-bearingmetawacke. metawacke. �______ _____ 74 74 Geology Geology and and Gold Gold Deposits Deposits of of the the Hemlo Hemlo Area Area altered, schistose, schistose, quartz-feldspar quartz-feldspar porphyry, (structurally lower part of the outcrop), outcrop), which is is in in sharp contact contact with with intensely intenselyaltered alteredrocks rocksthat thatpossibly possiblyare arederived derivedfrom fromthe the structurally structurallyoverlying overlying sharp metawacke. metawacke. recognizable features indicative indicative of of aa volcanic volcanic origin, is is white The porphyry, which shows no recognizable consistsof of feldspar feldspar (some (some of which weathering, except exceptfor for local, local, bright bright orange, surface weathering, surface staining. ItIt consists which pyrite, tourmaline, and sparse green mica. Locally, Locally, the is microcline), quartz, and sericite, with pyrite, Baritehas hasrecently recentlybeen beennoted notedinincrosscrosstourmaline is is euhedral euhedraland and up up to several millimetres tourmaline millimetres long. Barite cutting cutting veinlets veinlets and and layer-parallel layer-parallel seams seams (B.R. (B.R. Schnieders, Schnieders, personal personalcommunication communication1994). 1994). feldspathized/sericitizedrocks rocksadjacent adjacent to to the the porphyry porphyryare areabout about40 40 cm cm thick thickand andare are The feldspathized/sericitized distinguishable largely largely because of the lack lack of quartz eyes, eyes, finer finer grain size, and and more more abundant abundant distinguishable sericite. Layering Layeringisisdefined definedby bygrain grainsize sizedifferences differencesand andvariations variationsin inthe the abundance abundanceof of sericite. sericite. sericite. Locallythere there are are fragment-like fragment-likefeldspathic feldspathiclenses lenseswhich whichmay mayhave haveresulted resultedfrom fromdisrupted disruptedlayering layering Locally "veins". There Thereare arealso alsonumerous, numerous,small, small, white white porphyroblasts porphyroblastswhich which appear appear to to be be or alteration "veins". retrograded. retrograded. The Theorigin originof of the the rock rockisisequivocal. equivocal. Tracing the contact between the the 2 rock types on on the the outcrop outcrop indicates indicates that that it is only locally straight: straight: ititappears appearstotochange changeabruptly abruptlybecause becausethe theporphyry porphyryisisnot notpresent presentatatthe thewest westend endofofthe the outcrop. Where Where the thecontact contactisisstraight straightand andparallel parallel to to the thepredominant predominant fabric, fabric, the the layering layering is is conformable. conformable.However, However,atatthe thewest westend, end,the thelayering layeringand andsome some of the the numerous numerous quartz quartz veins veinsfound found here are folded folded and and disrupted disrupted (Figure (Figure36) 36) and and possibly possibly transposed, transposed, suggesting suggesting the the contact contact has has here been left stepping. stepping. Several fine-grained, fine-grained, foliated, foliated, boudinaged, boudinaged, intermediate, intermediate, biotitebiotitebeen folded and is left bearingdikes dikes appear appearto to be be unaffected unaffectedby by this this folding, folding,suggesting suggestingthe thefolding foldingisisof ofthe theF2 F2generation. bearing generation. outcrop shows a fine-grained, fine-grained, biotite granodiorite dike with with finefine- to to The southwest end of the outcrop coarse-grained coarse-grainedmuscovite muscovitepoikiloblasts. poikiloblasts. -- - - - -- - -1 N quartz quartz veins veins sericite sericite schist schist 1 \ m scale scale approximate appioximate feldspathized and/or andlor silicified silicified rock rock Figure outcrop shown shown in Figure 35, as originally originally Figure36. 36. Stop Stop23: 23: Detailed Detailedsketch sketchmap mapof of part part of of the outcrop in Figure exposedalong alongHighway Highway17. 1Z Location Locationof of the the sketch sketch map map site, indicated in Figure Figure35, 35, is is approximate. exposed indicated in approximate. (Modified (Modifiedafter afterPatterson Patterson1984). 1984). �Road Log — Hemlo Hemlo Area 75 75 The adjacent to porphyry display display a fairly fairly abrupt abrupt "contact" "contact" with with the the The altered rocks adjacent to the porphyry structurally overlying overlying metawacke. metawacke. The The metawacke metawacke displays displays wispy wispy to ill-defined ill-defined layering which is structurally possibly transposition. Within possibly the the result result of transposition. Withinthe themetawacke metawackeare are transposed transposedlayers layers rich rich in in magnetite magnetite and amphibole. amphibole. Two Two outcrops outcrops to the the north north of of the theroadcut roadcutare arepart partofofthis thismagnetite-bearing magnetite-bearing metawacke unit, seen at at Stop Stop 22. 22. The magnetite-bearing unitl which has already been seen magnetite-bearingmetawacke metawacke is is intruded by feldspar porphyry dikes. intruded by porphyry dikes. Structural Summary: Summary:' Predominant Predominantcleavage cleavage (sericite) (sericite) Subordinate Subordinate fabric fabric (sericite) (sericite)(S3?) (S3?) S3? S3?fabric (sericite) in in boudin boudin neck neck * Stop Stop 24: 24: 280/68 280168 269/65 269165 242/78 242178 (late (lateoverprint?; overprint?;see see Stop Stop20A) 2OA) FELDSPATHIC METASEDIMENTARY ROCKS FELDSPATHIC METASEDIMENTARY ROCKS (Figures (Figures 18 18 and and 37) 37) Location: south side, roadcut with with outcrop Location: Continue Continuewest weston onHighway Highway17, 17 south sidel for for about about410 410 m to a roadcut outcropon on both both sides sides of of the the highway, highway, south of Moose Lake. The The features features of of the the unit unitat atStop Stop24 24should shouldbe be compared comparedto to those thoseat atStop Stop18, 1BI which which some some geologists geologistsinterpret interpretas asthe the same sameunit. unit. ItItshould shouldbe bekept kept in in mind mind that that the the highway highway exposures exposures do not not provide provide a continuous continuous section through the deposit "stratigraphy", and that that changes in rock types are evident %tratigraphy", and changes in evident along strike and and down down dip. dip. The The immediate hanging wall and and footwall footwall rocks rocks to to the Hemlo hanging wall Hemlo deposit are not not exposed exposed along along the the highway. highway. South SouthSide Side of of Highway Highway17 17 The The east east end end of of the the roadcut roadcutshows shows aa finefine- to to medium-grained medium-grainedplagioclase-pyroxene-phyric plagioclase-pyroxene-phyric diabase diabase dike. dike. This Thisisisthe thesame samedike dikethat thatlies liesnear near the the boundary boundarybetween betweenthe the Williams Williamsproperty propertyand and the Figure 22). 22). Country the Golden Golden Giant property (see Figure Country rocks adjacent adjacentto to the thedike dikeshow shownotable notable epidote epidote and and pink pink (hematized?) (hematized?)feldspar. feldspar. The outcrop consists consists mostly mostly of ofrelatively relativelyfeldspathic feldspathic metasedimentary metasedimentary rocks The remainder remainder of the outcrop which at the the next nextstop. stop. Compared Compared which show show some cleavage-parallel alteration that is better displayed at to which, although notably to Stop Stop 25, 2sl the the rocks rocks here here display display more more pronounced pronounced layering whichl notably tectonic tectonic in in origin, partly reflect reflect modified modified primary primary compositional originl is is interpreted interpretedto to at at least least partly compositionallayering, layeringlas as itit is is similar to tectonized rocks variations and partl by by grain size variations and the to less less tectonized rockselsewhere. elsewhere. The Thelayering layeringisisdefined, defined, in in part, abundance examples (modified?) abundanceof of amphibole amphiboleand/or andlorfeldspar. feldspar. Some Someof ofthe thelayers layersappear appearto to be be examples (modified?)of of amphibole-rich amphibole-rich layers common common in in other other metasedimentary metasedimentaryunits. units. For the most most part, part, the the S2 S2 Moose Moose Lake Lake mpostf8ParP0rPhYrYSwarm claim post gossan layer—parallel layer-parallel breccia breccia \ lamprophyre m -A " scale approximate :caI::Pr:ima: 1gossan Hwy 17 / N feldspar porphyry swarm 1 1gossan breccia diabase ,/ tite lamprophyre biotite lamprophyre tourmaline tourmaline alteration alterationand andbleaching bleaching I variety variety of oflayer—parallel layer-parallel breccias breccias 1 Figure feldspathic, Figure37. 3Z Stop Stop 24: 24: Simplified Simplified sketch sketch map map of of "footwall", "footwall", mylonitic(?), myl~nitic(?)~ feldspathicl metasedimetasedimentary mentary rocks rocksand andlayer-parallel layer-parallelbreccias. breccias. �Geology and Gold Deposits of the Hemlo Area 76 cleavage, where identifiable, is oriented counterclockwise to layering. Intrafolial folds are present near the east end of the outcrop and near the eastern gossan and may reflect an F1 folding event. There are two gossans in this outcrop which are sufficiently oxidized on surface to hinder determination of the "protolith' The western gossan, about 1 m thick, appears to be composed of metasedimentary rocks similar to the bounding layers. The eastern gossan, about 3 m thick, appears to consist of rocks with more biotite and feldspar (alteration?) than the bounding metasedimentary rocks, and has along its northern boundary a narrow (c20 cm), somewhat heterolithic, lensy unitwhich may have been a volcaniclastic/conglomeratic rock initially. Some of the lenses/fragments are feldspar phyric. This zone may be the eastern extension of the Highway Zone (Patterson 1986) (see Stop 27). A grab sample from this gossan returned a value of 0.01 ounces Au per ton (Patterson 1986). The roadcut face reveals clots of calcite + pyrite + tourmaline, quartz + pyrite, and pink/ orange feldspar + fluorite. Subhorlzontal to shallowly west-plunging slickensides are also present. The outcrop at Stop 24 displays layer-parallel breccias. Collectively, in the Hemlo deposit area, layer-parallel breccias are relatively late, given that there is rare evidence of ductile deformation in most cases and generally no overprinting fabric. The brecciation has affected all Archean rock types (except possibly diabase). Overall, in this part of the greenstone belt, the breccias occur from the mafic metavolcanic rocks near the Pukaskwa Gneissic Complex, about 2 km to the south, to the metawacke units about 3 km to the north (Golden Giant Mine tailings site). The breccias are most common and volumetrically important in relatively competent feldspathic rocks such as this outcrop. Layer- and fabric-parallel fault gouges within sericitic rocks, spatially associated with the Hemlo deposit, are likely equivalent examples of this brecciation. Light grey to black pseudotachylite, with or without internal layering, is spatially and apparently genetically associated with the breccias in the more feldspathic rocks. The sense of movement on the fault planes is generally not determinable, but locally shows a dextral component of displacement. Some of the breccias terminate abruptly along strike and become thin seams which may or may not contain pseudotachylite/ultracataclasite. The brecciation could be associated with a continuation of the dextral shearing noted in other stops, resulting from a change from predominantly ductile to predominantly brittle processes, or it could be a manifestation of Proterozoic crustal movement, or both. Examples of these breccias that show at least 3 stages of brecciation have been noted locally. There are about 4 "types" of layer-parallel breccias exposed in one part of the outcrop at Stop 24: (A) an uncommon semi-ductile type, with aligned layering in fragments and blocks at about 075° — the boundaries of the breccia are ill-defined; (B) the most common type, with angular, unoriented fragments in a matrix similar in colour to the host rock — generally has sharp boundaries to the breccia zone with one side commonly straight and the other slightly to very irregular in form — possibly affects (Le., postdates), type A; (C) tabularzone with angular, unoriented, various-sized fragments of country rock in a light-brownweathering, relatively high proportion of matrix. A thin section of this breccia shows that prehnite constitutes a significant portion of the matrix; (D) an in-situ shattering of the country rocks with a recessively weathering matrix — predominant fracturing at 342°. North Side of Highway 17 S S S S S S S S 5 5 S S 5 S The units are much the same as for outcrops on the south side. Several previously interesting features did not survive recent blasting. S S S �a a r ______ Road Log — Hemlo Area 77 Some features to note: • some amphibole-bearing layers contain small quantities of garnet; • collectively, both the slightly discordant faults and the layer-parallel breccias cut across layering structurally up and down; • a very-fine-grained, white matrix of a layer-parallel breccia body (type C?) south of the claim post (Figure 37). Locally forms up to 50% of the breccia; • a swarm of feldspar porphyry dikes occurs at the east end of the outcrop as did some epidotebearing pseudotachylitefultracataclasite (before recent blasting); • there are some sinistral and dextral kinks (F4) in the layering; • northerly striking, Proterozoic, biotite + pyroxene(?) lamprophyre dikes occur in the western third of the outcrop; one has a central "core" consisting of a 3 cm thick calcite vein. Structural Summary: SI 82? cleavage (local) 285 to 293/62±2 298/56 5? fabric (sericite) L? (intersection) 2 72/63 (muscovite elongation?) L1? (intersection) 345/53 078/49 L (slickenside) 103/08 to 283i8 * Stop 25: HEMLO FAULT ZONE (Figures 18, 19 & 38) LocatIon: Go 600 m furtherwest on Highway 17, north side, from the claim post shown in Figure 37, to a set of small outcrops on both sides of the highway, about 60 m west of the Williams Mine tailings/effluent overpass. These outcrops also show many of the same features as at Stop 26 but have suffered less from the ravages of recent blasting. This is one of several sets of outcrops that depict the Hemlo fault zone, which the highway roughly parallels for a few kilometres. The Hemlo fault zone is characterized, in this area, by strongly deformed rocks which comprise mafic, magnesian schists at or near the contact between gneissic amphibolite and gneissic feldspathic rocks. The layering in these rocks is Interpreted to be, in part, mylonitic (Photo 9). The amphibolite is part of the mafic unit of Stops 26 and 28 and has a whole rock composition comparable to high-iron tholeiltic basalt. No primary volcanic features have been observed. Multiplely deformed veinlets of quartz, feldspar, epidote, and calcite are common in the amphibolite. The gneissic feldspathic rocks are felsic in composition and locally contain phenoclasts(?) of quartz, similar to volcaniclastic metasedimentary rocks in the area. a a a a a a 0 a N gnelssic feldapathic rocks chlorite schist. © 'hand fold 1 chlorite sohist amphibolite S breeds br•ccla with epidole and hematite Hwy 17 0 'P . m scale approximate 20 5 °"e7 Williams Mine telling; overpass gnelsslc amphibolite FIgure 38. Stop 25: Simplified sketch map of lithologic units and structures of the Hemlo fault zone, including the "hand" fold. �78 78 * Stop Stop 25A: 25A: Geology Geology and and Gold Gold Deposits Deposits of of the the Hemlo Hemlo Area Area NORTH NORTHSIDE SIDEOF OFHIGHWAY HIGHWAY 17 17 (Figure (Figure38) 38) Outcrop "a" Feldspathic Feldspathiclaminated laminated rock rock showing: showing: (1) tectono-metamorphic features such such as as symmetrical, symmetrical, pale pale pink (hematite?, potassic feldspar?) (1) tectono-metamorphic features (hematite?, potassic and sericitic sericiticalteration alterationalong alongcleavage cleavageplanes planesas as well well as as bleached bleached rims rims along along planes planes defined defined by by and chlorite chlorite(similar (similarto to that thatseen seenlocally locallyat atStop Stop24); 24); (2) (2) west-closing west-closing fold fold in inlayering; layering; (3) (3) quartz quartz necks necksin in boudins boudins(traces (tracesof ofnecks neckson on surface surfaceare are080±5), 080&5),and androlls rolls(075/50) (075150) in in undulating, undulating, locally garnet-bearing layers; locally garnet-bearing layers; (4) (4) fine-grained, intermediate intermediate dike; dike; (5) of recent blasting). The (5) zone of layer-parallel, cataclastic breccia breccia (not well exposed because of The exposure exposure used used to to show show that that the the country country rocks rocks and and the the intermediate intermediate dike dike were were brecciated. brecciated. (See (See Stop Stop24 24 for for discussion discussionof oflayer-parallel layer-parallelbreccias.) breccias.) Outcrop Outcrop "b" This This outcrop outcrop displays displays the the contact contactbetween betweengneissic gneissic feldspathic feldspathic rocks rocks and andgneissic gneissicamphibolite amphibolite containing chlorite + amphibole schist. The feldspathic rocks form part of a unit that containing chlorite + amphibole The feldspathic rocks form part of a unit that structurally structurally overlies overliesthe theamphibolite amphiboliteunit unitfor foratatleast leastseveral severalkilometres. kilometres.To Tothe theeast east(e.g., (e.g., Stop Stop24), 241,the therocks rocksofof this this package package display display layering layering that that isisbetter betterdefined definedand andsomewhat somewhat resembles resembles less less tectonized tectonized feldspathic metasedimentary metasedimentary rocks. rocks. To To the thewest, west, opposite opposite"Fault" "Fault" Lake Lake (Figure (Figure 18), 18), the the correcorrefeldspathic sponding quartz-feldspar phyric spondingfeldspathic feldspathicrocks rocks(i.e., (i.e., structurally structurallyabove above the the amphibolite amphibolite unit) unit) are quartz-feldspar phyric and and contain contain lapilli-size lapilli-size lenses lenses suggesting suggesting a fragmental protolith. The Thefeldspathic feldspathicrock rockpackage package may volcaniclastic deposits maycomprise comprisemore more than than one one primary primary unit unit derived derived from pyroclastic pyroclastic and/or andlor volcaniclastic deposits that thathave havebeen beenheterogeneously heterogeneouslytransposed. transposed. In outcrop outcrop 25b, 25b, the the thinly thinlylayered layeredfeldspathic feldspathicrocks rockshave haveaatectono-metamorphic tectono-metamorphiclayering/ layering1 In cleavage cleavage which is is interpreted interpreted to be, be, in in part, part, mylonitic. mylonitic. Many Manyofofthe thecleavage cleavageplanes planeshave have an an associated associated symmetrical symmetrical alteration alteration which which itself itselfproduces producesaasmall-scale small-scaletectono-metamorphic tectono-metamorphic layering, considered consideredhere hereto to be be superposed superposedon on flattened flattenedand andtransposed transposedprimary primarylayering. layering.The The layering, layersare arelocally locallydisplay displaypinching pinchingand andboudinage, boudinage,which whichhas hasresulted resultedininapparent apparentintrafolial intrafolialfolds foldsinin layers some places. places. The Thelayers layersare arealso alsolocally locallydiscordant discordantas asaaresult resultofofslightly slightlyoblique obliquedextral dextralfaults. faults. some Isolated, Isolated, small, small, flattened flattened quartz quartzcrystals crystals(phenoclasts?) (phenoclasts?)are aresparsely sparselydistributed. distributed. Elsewhere, Elsewhere, quartz quartzoccurs occursas asflattened(?) flattened(?)thin thinseams, seams, particularly particularlywithin withinill-defined ill-definedzones. zones. The mafic maficschists schistsare arephyllonites phyllonitesand andmay mayhave havebeen been derived derived from from the theamphibolite amphiboliteunit unit The exposed andlor from from relatively relatively magnesian-rich magnesian-richdikes dikes in in the the fault fault exposedon onthe thesouth southside sideof ofthe thehighway highwayand/or zone zone(see (see Stop Stop 26). 26). As Aswith withStop Stop26, 26,deflection, deflection,backrotation, backrotation,and andcrenulation crenulationofofmore morethan thanone one fabricappears appearsto to have havedeveloped developedin in response response to ductile shearing. Irregular Irregularzones zones and and clusters clustersor or fabric podsconsisting consistingof ofcoarse-grained coarse-grainedtourmaline tourmalineand andaafine-grained fine-grainedunidentified unidentifiedwhite whitemineral mineralcan can pods locally befound. found. locallybe At Atleast leasttwo twotypes typesofofdikes dikesare arepresently presentlycontained contained within within the the schists: schists: both bothtypes typesshow show boudinage. boudinage. The Thetypes typesare: are: (1) (1) an analtered, altered,chloritized chloritizedgranitoid granitoiddike dikewhich whichhas hasundergone undergoneboudinage boudinageand andhas hasirregularly irregularly distributed distributedpink/hematitic pinklhemat iticalteration; alteration; (2) (2)aafoliated foliatedmafic maficdike dikecontaining containingnumerous numerousmafic maficxenoliths xenoliths(possibly (possiblyakin akintotothe thelamprophyre lamprophyre dike dikeof ofStop Stop29), 29),and andhaving havingaafolded foldedand andcrenulated, crenulated,internal internalfabric. fabric. Towards the the east east end end of of this this outcrop outcrop within within the the feldspathic feldspathicrock, rock, isisaa 10 10 cm thick, thick, brittle brittlefault fault Towards breccia(oriented (orientedatat345/74), 345174),which whichdisplays displaysat atleast leasttwo two stages stages of of brecciation brecciation (i.e., (i.e., breccia brecciawithin within breccia �— Hemlo Area Road Log - 79 79 breccia). breccia). The Thecountry countryrocks rockshave haveundergone undergone hematization hematization and and epidotization epidotization within within and and adjacent adjacent to this zone. The does not to exposure exposure limitations) limitations) to have affected the The breccia brecciadoes not appear appear (in part due to have affected phyllonite.However, However,with withthe theexception exceptionofofrelatively relativelylate latestrike strikeslip slipmovement movementon onearlier earlierfaults, asis is phyllonite. faults, as suggested in the Hemlo Hemlo area area by by offset offset diabase diabase dikes and subhorizontal slickensides, slickensides, the fault breccia is is considered considered to to post-date post-date ductile ductile deformation deformationbecause because of of the theundeformed, undeformedlangular, angularl fragments it contains. Outcrop Outcrop "C" "c" This is aa small small outcrop, outcrop, about about 25 25 m m west west of of outcrop outcrop 25b, 25b, which which shows shows schistose schistose and and gneissic gneissic amphibolite notably folded. folded. The amphibolite intruded intruded by by granitoid granitoid dikes, dikes, all all of which have been notably The main main fold, the "hand fold", fold", is atypical in in that that the the "fingers", "fingers", defined defined by by several several folds in in aa granitoid granitoid dike, dike, display display multiple orientations of a crenulation cleavage defined defined by by the the schists schists (Photo (Photo 10). 10). Crenulation Crenulation cleavage various orientations D3, and although it displays various orientationsin inany any cleavage in the Hemlo Hemlo area area is is ascribed ascribed to D3, one outcrop outcrop (±200 for example), example), ititgenerally generallystrikes strikes east-northeast east-northeast to to east-southeast. east-southeast. However, (X?OOfor However, in this case, the about 125O 125°from fromnorth north to to southeast. southeast. Although this the strike strike of of the the cleavage cleavage spans spans a range of about Although not fully understood, this fold fold could could be be an aberration aberration within the the fault fault zone zone because becauseof of the the overall overall orientation large-scalecrumpling crumpling of orientation of of the the layering layering and and dikes. It is possibly a result of a relatively large-scale layers adjacent to a detachment. detachment. Chevron-like Chevron-likefolding folding of of the theschistose schistoselayering, layeringl and andisolated isolated boudins of dikes attest to considerable shortening and extension in different Isolated boudins different directions. directions. Isolated "knots" of mediummedium- to coarse-grained coarse-grained tourmaline are locally present. \ Structural Summary: 280/60 (tectono-metamorphic in feldspathic 280160 (tectono-metamorphic feldspathic rock) rock) Layering Layering S 265/83 S* 265183 chlorite; chlorite;various various orientations orientations chlorite; various orientations orientations 300/85 chlorite; S*, 300185 205/78, 225/77, 240/8 247/53, S3 205178, 225177 240187 247153,297/51 297151 crenulation crenulation fabric fabric with with corresponding: corresponding: S3 242/52, 282/70, 022/43, 015/40, 043/39 crenulation lineations 282/70,022/43, 015140,043139 lineations L 242152, 281/06 slickenside 281106 slickenside lineation lineation L8 S. Stop 25B: SIDE OF HIGHWAY Stop 25B:SOUTH SOUTH SIDE OF HIGHWAY17 17(Figure (Figure38) 38) Outcrops "d" "d" and "e" "e" The gneissic amphibolite amphibolite is is considered considered to to be be derived derived from from highly highly deformed deformedmafic maficmetavolcanic metavolcanic rocks because it can be traced as part of a "wedge" of mafic mafic rocks rocks into into the the pillowed pillowed mafic mafic rocks rocks described at Stop 28. However, there are no unequivocal (let alone equivocal?) volcanic features described at Stop However, there are no unequivocal (let alone equivocal?) volcanic features at this outcrop. outcrop. The Theamphibolite amphiboliteconsists consistsofofplagioclase, plagioclaselhornblende, hornblende,and andlesser lesseramounts amounts of of biotite. biotite. The Thelayers layersare arepoorly poorlyto tomoderately moderatelydefined definedby byvariations variationsininthe the abundance abundanceof of these thesethree three constituents. Well-defined main mineral constituents. Well-definedmicaceous micaceouslayers, layers, comparable comparableto to those thosedisplayed displayedat at the the "hand fold" outcrop (25c), were present near outcrop 25e before recent blasting. outcrop (25~1, 25e before recent It is not not known known whether these layers layers are largely primary primary (e.g., (e.g., interflow interflow sediments) sediments) and/or tectonic in in origin. origin. The outcrop contains numerous veins veins consisting consistingofofeither either quartz quartz or or quartz quartz + epidote k± contains numerous feldspar. feldspar. The The veins veinshave havebeen beenbuckled, buckled,dismembered, dismemberedl and/or and/or transposed transposed depending depending on on their their orientation and time of emplacement relative to the complex tectonic history. Various Various veins veins are are folded with "S" "S'' or "Z" asymmetry: asymmetry: locally locallyrefolded refoldedfolds folds are are present. present. Two fabrics in the amphibolite, one one parallel parallel to to the the layering layering and and one one axial axial planar planar to to the the folds, folds, Closeinspection inspectionofofthe thefabrics fabricsreveals revealsaathird thirdfabric fabricwhich whichappears appearsto to can be locally discerned. Close crenulate crenulate the other other two. two. Structural Summary: Structural Layering —290±5/81 (with Layering -29M5181 (with internal internal foliated foliated biotite) biotite) Fabric —276/85 biotite Fabric -276185 biotite biotite, -260±5/85(±) S3 fabric -26W5185(*) biotite, crenulating crenulating fabric fabric �_I 03 0 5 012345 Legend:Stop 26 Legend: Stop 26 1 1 22 gneissic(mylonitic?) (mylonitic?) amphibolitic amphiboliticmafic maficmetavolcanic metavolcanic gneissic m gneissic (mylonitic?) (mylonitic?) feldspathic feldspathicvolcaniclastic volcaniclasticmetasediments metasediments gnelssic 1 3a 3a chlorite±actinolite±talc schist chlorite~actinolite~talc schistdikes? dikes? 3b 3b biotite schist schistdikes dikes biotite -outline of ofoutcrop outcrop outline 4 n - -- - - - - ! lithologiccontact contact ——-lithologic 3c 3c tourmaline ± feldspar dike/vein tourmaline±quartz ?quartztfeldspar dikelvein + —. 44 plagioclase-porphyritic dike dike plagioclase—porphyrltic 55 diabase dike dike dlabase ..ae. fault fault top edge edge of of roadcut roadcut 4 2 :zz=-:-3b 2 3b —___, 2 0 CD 2 0 0 31 cc 0. 2 C) 0 a 0 CD D 0 C,, Hwyl7 Hwy 17 C,) 0 -I, -I. i CD Detailed sketch sketch map map of of the the Hemlo Hemlofault fault zone zone and andthe thecontact contactbetween between Figure39. 39. Stop Stop 26: 26: Detailed Figure and mylonitic(?), gneissic amphibolite feldspathic, mylonitic(?), gneissic, metasedimentary rocks, feldspathic, mylonitic(?), gneissic, metasedimentary rocks, and mylonitic(?), gneissic amphibolite with withschists schistsderived derivedfrom fromsheared shearedmagnesian-rich magnesian-richdikes. dikes. (Modified (Modifiedafter afterSmart Smart1988). 1988). 5 CD �Road Log — Hemlo Area 81 81 Stop 19 &&39) Stop 26: 26: HEMLO HEMLOFAULT FAULT(Smart's (Smart'soutcrop) outcrop)(Figures (Figures18, 18,19 39) Location: Go Go about about370 370 m m to to the thewest weston onHighway Highway17, 17 north north side, side, to to aa steep, steep,77m mhigh highroadcut. roadcut. The outcrop outcrop has has been been studied studied in in detail detail(Smart (Smart1988) 1988) although although the theexposed exposedface facehas hasbeen been The considerably modified modifiedby by subsequent blasting. The The outcrop outcrop shows the contact between between gneissic considerably feldspathic' rocks rocks and and structurally structurally underlying, underlying, gneissic, amphibolitic rocks, rocks, both both of of which which are are feldspathic similar to corresponding units described for Stop 25. similar corresponding units described for Stop 25. Refer to Stop Stop 25 25 for for aa more moredetailed detailed descriptionof ofthese these22rock rocktypes. types. At AtStop Stop26, 26, a pyritiferous gossan lies lies within the feldspathic rocks description pyritiferous gossan feldspathic rocks at or near the contact with the amphibolite. amphibolite. Mafic Mafic schists schists of of distinct composition composition lie lie within the gneissic gneissic amphibolite. amphibolite. The mafic and mafic schists schists comprisechlorite±tremolite/actinolite comprise~chlorite~tremolite/actinolite andchlorite chlorite++talc±tremolite/actalettremolitelacphyllonites, all of of which which contain contain sufficient sufficient magnetite magnetite to attract attract aa hand hand magnet magnet to to some some tinolite phyllonites, degree. These Theseschists schistscommonly commonlycontain containundeformed, undeformed,med medium-grained, pyritecubes cubes(common (commonin in degree. ium-grained, pyrite similar shoreline near Heron Bay). The similar schistose schistose rocks rocks as as far far away away as the Lake Superior shoreline The schists schists are interpreted interpreted to to have havebeen beenderived derivedlargely largelyfrom fromlineated/foliated, lineatedlfoliated, finefine- to tomedium-grained medium-grained actinolite-rich actinolite-rich dikes, dikes, as as can can be be seen seen 1.0 1.0 km to the west on the north side of of the highway highway at the contact between between amphibolite amphibolite and feldspathic rocks. These These dikes dikes are highly highly deformed within the contact picriticbasalt basalt(based (basedon on Irvine lrvine and and Baragar Baragar fault aacomposition fault zone. They Theyhave compositioncomparable comparableto to picritic .komatiitic .....have .Dasait .. ,. . . .. .. - ... . 1971) basalt (based contain considerably I Y A 1 or Komatlmc pzsea on on Jensen Jensen 1976) i.---. w q and contain considerablymore moreMgO, M ~ ONi, Ni, , and andCr cr than chioritic schists than the the tholelitic tholeiiticbasalts basaltsand andamphibolite amphibolite(see (see Muir Muir 1982b). 1982b). Locally, Locally, some of the chloritic schists which which have have aa somewhat somewhat different different colour, colour, appear appear to have have been been derived derived from from the thegneissic aneissic amphibolite. amp >--A. The by: mafic I ne gneissic gnelsslc feldspathic tetaspatnlc rocks rows have nave been intruded by: maficdikes dikes which which may may have have been been isoclinally folded and are now biotite schists; and numerous plagioclase-porphyritic dikes that isoclinally folded and are biotite schists; and numerous plagioclase-porphyritic dikes thatare are slightly boudinage. Some porphyritic dikes display slightlydiscordant discordantto tothe the gneissosity gneissosityand and display display boudinage. Some of of the porphyriticdikes poikilofracture and and cleavage cleavage controlled controlled hematization, hematization, and and some some show show subhedral subhedral muscovite muscovite poikilofracture blasts. AAfine-grained, fine-grained,feldspathic, feldspathic,dike-like dike-likebody, body, containing containing crystals crystals and and clumps clumps of of crystals crystals of of blasts. mediumto very coarse-grained tourmaline, occurs within chlorite + actinolite schist. Coarse+ Coarsemedium- very coarse-grained grained grained tourmaline tourmaline also also occurs occurs as as clusters clusters or or pods pods in in the schists. schists. The phyllonites phylloniteshave haveaavariety varietyof of fabrics, fabrics, within within and andbetween betweenlozenges, lozenges,that thatdisplay displaydeflected deflecteld The 1; n,,w,,eA\ L.-+nLwn+-4..A A ..., A-nn..l-+..A C-t..-:-... k:-L. --.. -----A - A tu - result ---.. n (IS., WI VGUJ, backrotated, uawuuiawu, and a11ucrenulated WGIIUI~LGU Ifabrics ~ J I I G S WIIIGII are tr~~erpreteu ue aa resuil of OTD3 u3 (i.e., curved), which are interpreted to be deformation deformation (see (see also Muir Muir and Elliott 1987). 1987). Many Many of of the the fabrics fabrics appear appear to to be be consistent consistent with with ductile that thev they disdavs-c-c'-like display s-c-c'-like confiaurations. configurations. However, ductiledextral dextralshear shear(see b e eHugon Huaon1986) 19861in that However,the the :-A fi A- L- IA -f following points should be made: (1) The temporal and geometric relationships of fabrics are locally complex and equivocal, with with some overprinting by another set of crenulation fabrics, possibly due to progressive flattening/ ling1 shearing. (2)Extension kxtension by ~yboudinage, Douainage,shortening snortenmgby Dyfolding, tolamg,and andundulations undulationsininthe thelayers layersand anddikes, dikes,has has (2) occurredinin33 dimensions, dimensions,resulting resultingininhighly highlyvariable variableorientations orientationsof oflozenges, lozenges,fabrics, fabrics,and andminor minor occurred fold fold axes. axes. D2event event produced produced regional regionalfolds, folds, with with "S" "S" (3) The The structural structuralhistory historyof ofthis thisarea areasuggests suggeststhat thatthe theD2 (3) asymmetry, asymmetry, that thatmay mayhave haveresulted resultedfrom fromaacomponent componentofofsinistral sinistralshear. shear. alnnfl this t r--.-.-. t ~ c t ~ discontinuity disrmntin~~itv ~ r A .... .-..J should c Therefore. a s- i m,-. ~-lhistory e.historvof movement Therefore, simple structural not - - - - ,a -. ,of- .movement . .-along .= this -...- zone --. .- of -. s-.. -.---. whould not be assumed. assumed. AAdiabase diabasedike dikehas hasintruded intrudedall allrock rocktypes typesatatthe theeast eastend endofofthis thisoutcrop. outcrop. be ~~ �Geology Geology and Gold Deposits Deposits of the Hemlo Hemlo Area 82 82 Structural Structural Summary: Summary: structures, overall, are are quite quite variable within within the the outcrop; "typical" "typical" orientations (most measured structures, orientations are are listed listedbelow) below) Layering -'263/63 Lm —312/42 D S, —265/60 —259/60 S3 —283/59 —243/64 L3 '-053/37 S —290/17 * Stop Stop 27: 22 gneissic gneissic mineral lineation of hornblende and locally tourmaline orientation of porphyritic porphyritic dikes orientation dikes chlorite chlorite chlorite (deflects Ssc) chlorite (deflects53c) crenulates above crenulates above planar planar fabrics fabrics (later (later overprint?) overprint?) crenulation crenulation lineation lineation possible possible stretch stretch lineation lineation HIGHWAY ZONE ZONE (Figures (Figures 18 18 & 40) Proceed 1.3 17,north northside, side, to to aa point point 175 m m to to the west of the Location: Proceed 1.3 km west on Highway 17 Highway sign indicating indicating "Cigar "Cigar Lake". Lake". The highway sign is incorrect, but there is no Highway sign highway sign no widely the lake lying immediately immediately to to the the south south of of the the highway highwayat atthis this location. location. This accepted name for the This term "Fault" reference in the assessment guide uses uses the term "Fault" Lake Lake because becauseof of a similar earlier reference in the assessment records records because it is geologically geologically appropriate. appropriate. (Officially and because (Officiallyrecognized recognizednames namesfor forother otherlakes lakesininthe thearea area named Lake (also (alsooccasionally occasionally applied applied to to "Fault" "Fault" Lake) Lake) already already exist.) exist.) At Stop named Cigar Cigar Lake Lake and Rule Lake 27, aa hydraulically hydraulically cleaned cleaned outcrop outcrop extends extends up up the the hill, hill, to to the north, north, within the 27 the cleared clearedhighway highway right-of-way. right-of-way. This This exposure exposure is is particularly particularlyuseful usefulfor for at at least leasttwo two reasons. reasons. ItItisisone oneof of the the best bestexposures exposuresof of what is locally locally known as the Highway Zone, and it demonstrates some of the structural complexknown Highway demonstrates the structural complex- that complicate complicate stratigraphic stratigraphic reconstruction reconstruction and and interpretation. interpretation. The Highway Highway Zone is is ities that essentially a deformed, and possibly possibly altered, erratically quartz-feldsparerratically auriferous auriferous unit unit of felsic, quartz-feldsparphyric, phyric, fragmental fragmentalrocks rockswhich whichare areinterpreted interpretedtotobe bevolcanic volcanicininorigin. origin.ItItisistraceable traceablefor forabout about22km km but its character along strike does change from from place place to to place. The The style style of of deformation deformationin inthe the outcrop, including discordancies in andlor fabrics, illustrates illustrates that that folding, folding, including numerous discordancies in the layering layering and/or ductile and brittle faulting have ductile shearing, shearing, and have produced, produced, on this mesoscopic mesoscopic scale, scale, aa tectonotectonostratigraphic primary, stratigraphic stratigraphic section. section. Detailed stratigraphic section section rather rather than a preserved, primary, Detailedmapping, mapping, overall, suggests this style of deformation deformation is is represented represented on a much larger scale as well. The southern half of the outcrop consists of: of: aa zone of slightly rusty weathering, schistose, garnetiferous, metasedimentary rocks rocks which which display display thinly garnetiferous, biotite-quartz-feldspar-bearing biotite-quartz-feldspar-baring metasedimentary laminated, tectono-metamorphically modified modified primary primary layering; and a zone of feldspathic metasedimentary rocks which which display display highly highly cleaved, cleaved, more more widely widely spaced, spaced,tectono-metamorphic tectono-metamorphic layering. The Thelayering, layering, which which may may be be mylonitic, mylonitic, at at least least in part, reveals reveals sharp, tight, and and in some cases cases rootless, S-shaped S-shaped folds with later, locally locally developed, Z-shaped folds. The central part of of this this outcrop outcrop consists consists of what what appear appear to be be wedges wedges or or lozenges lozenges of fragmental units units which are juxtaposed juxtaposed and apparently interleaved interleaved with medium fragmental medium to to coarse-grained coarse-grained wacke. The Thefragmental fragmentalrocks rockscan canbe besubdivided, subdivided,at atleast leastlocally, locally, on on the the basis basis of of type, type, size, size, and and abundance of the fragments. The structurally lowest fragmental unit is pyritiferous, rusty abundance the fragments. lowest fragmental unit pyritiferous, rusty weathering, quartz-feldspar phyric, and relatively monolithic, although a variety of fragments is weathering, present overall (Photo 11). Some Some of the the fragments fragments have been converted converted into into 22 or or more more smaller smaller lenses by the development of of aa sericitic sericitic cleavage through through them. them. Some lenses consist entirely of completely dismembered. dismembered. The quartz which may indicate that some quartz veins have been completely structurally distinctive for its chloritickbiotiticfragments, chloritic±biotitic fragments, many display 2 many of which display2 structurallyuppermost uppermostunit unit is distinctive or more "tails". "tails' Grab ounces per ton Grabsamples samplesfrom fromthe thepyritiferous pyritiferousunit unitreturned returnedAu Auvalues valuesof of <0.01 <0.01 ounces ppb (M. (M. Smyk, Smyk, MNDM, MNDM, personal personal communication, communication, 1990). 19861, and 164 ppb (Patterson 1986), �Road Log Log — -Hemlo Hemlo Area Area Road 83 83 At the the north northend endofofthe theoutcrop, outcrop,the thefragmental fragmentalunits unitspresently presentlylielieadjacent adjacenttotolayered, layered, At feldspathic, volcaniclastic volcaniclasticmetasedimentary metasedimentaryrocks rockswhich whichdisplay displayvestiges vestigesofofF2, Fg,S-shaped S-shapedfolds folds feldspathic, F3, Z-shaped folds. Relatively small lenses of a tectonically overprinted by narrow, planar zones of overprinted by narrow, planar zones of F3, Z-shaped folds. Relatively small lenses of atectonically disrupted unit unit of of schistose, schistose, garnetiferous garnetiferousmetawacke, metawacke, illustrate illustrate the the disruption disruption of of layering layering in in the the disrupted northern third of the outcrop (e.g.. Unit 1 e in Figure 40). northern third of the outcrop (e.g., Unit 1 e in Figure 40). Although aa few few straight straight quartz quartz veins veins are arepresent presentininthe theoutcrop, outcrop,most mostsecondary secondaryquartz quartz Although occurs as knots or deformed veins. The deformed veins range from continuous and buckled, to occurs as knots or deformed veins. The deformed veins range from continuous and buckled, to highly dismembered. Brittle faults, which overprint the ductile deformation fabrics, are mostly highly dismembered. Brittle faults, which overprint the ductile deformation fabrics, are mostly byapparent apparentsense senseof ofdisplacement. displacement. dextralby dextral The country countryrocks rocksare areintruded intrudedby byfoliated, foliated,medium mediumgrey, grey,fine-grained fine-graineddikes, dikes, one one of of which which The Archean diabase dike which has locally shows tightly folded internal layering, and by a late shows tightly folded internal layering, and by a late Archean diabase dike which has locally intrudedparallel parallelto to the thelayering. layering. intruded Pyritiferous, schistose, schistose, high-strain high-strainzones zones are are exposed exposed in in 22 other other places places to to the the west west of of this this Pyritiferous, They may be the equivalent of the Highway Zone but each has somewhat different outcrop. outcrop. They may be the equivalent of the Highway Zone but each has somewhat different lithologiccharacteristics. One gossan,inin rockcut about350 350mmtotothe thewest westof ofStop Stop27 an lithologic characteristics. One gossan, a arock cut about 27, returned returned an assay value of 337 ppb Au, and the other gossan, near a turnoff to the north (shown on Fiaure 18), assay value of 337 ppb Au, and the other gossan, near a turnoff to the north (shown on Figure * - -18), allout700 DM, 700mmwest westof Stop stop27, 27 returned returnedan anassay assayvalue valueofof22ppm ppmAu Auand and66ppm ppmAg Ag(M. (M.Smyk, smyk,MN MNDM, about communication,1990). 1990).Previous Previousassay assayresults, results,from fromthe thelatter lattergossan, 0.32 ounces ounce;sAu Pisrsonalcommunication, Au personal gossan, ofof0.32 ar tnn 2nd ft AQ nl mr^nc*A n n n r tnn ivvGI xfnrn rannr+a/Â¥ hi, k h i i r /ift00l^\ .-+-Aif-li .A- È -A n 4 n n 4 PL. .", ,and w.-ru ounces uunwuQ cuul i cby UY ~ Muir IVIU~I (1982b), IIWLU,, a1 IUvalues V ~ I U C Sof UI<0.01, <-U.UI,0.01, U.U I, and and per ton 0.43 Ag per ton were reported and 0.04 ounces ouncesAu Au per per ton ton were were reported reportedby byPatterson Patterson(1986). (1986). This Thisgossan gossanisisinincontact, contact,on onthe the north north 0.04 side, with a locally highly strained and hematized, plagioclase-porphyritic felsic body that has side, with a locally highly strained and hematized, plagioclase-porphyritic felsic body that has been intruded by less deformed, essentially foliation-parallel, plagioclase-porphyritic felsic dikes. been intruded by less deformed, essentially foliation-parallel, plagioclase-porphyritic felsic dikes. of ui lu>ci StructuralSummary: Summary: Structural Feldspathicmetasedimentary metasedimentaryrocks rocks(south (southpart partofofstop): stop): Feldspathic Myloniticlayering layering 270/64 270164 Mylonitic PossibleS2 Syfabric fabric 279/74 279174 Possible PossibleS3 S3fabric fabric 253/74 253174 Possible Metasedimentaryschists: schists: Metasedimentary Mylonitic layering 275-290160 Mylonitic layering 275-290/60 Sericitic,quartz-feldspar-phyric quartz-feldspar-phyricfragmental fragmentalrock: rock: Sericitic, Crudelayering layering(S0/S1?) (SdS,?) 2700 270 Crude S2fabric fabric (alignment (alignmentof of fragments) fragments) 283° 283O S2 Sericitic fabric 252i5O Sericitic fabric 252±5° Volcaniclasticmetasedimentary metasedimentaryrocks rocks(north (northpart): part): Volcaniclastic SdS, layering layering 270/61 270161 SO/SI S2cleavage cleavage(axial (axialplanar planarto toS-folds) S-folds) S2 280167 in feldspathic schist 280/67 in feldspathic schist 295167 in inadjacent adjacentfeldspathic feldspathicwacke wacke 295/67 S3fabric fabric 255/61 255161 in in feldspathic feldspathicschist schist S3 245Oto to255° 255O Axialplanar planar(to (toF3 F3Z-folds) 2-folds)S3 S3 245° Axial 230° 310° 340 Dextral brittle-ductile faults Dextral brittle-ductile faults 230°, 310°, 340° �Geology Geologyand andGold GoldDeposits Depositsofofthe theHemlo HemloArea Area 84 84 amphibole + garnet ± quartz layer opposite page) Stop Flgure40. 40. (legend (legend on oppositepge) Stop27: 2 2 Detailed Detailedsketch sketchmap mapof of the the Highway HighwayZone: Zone: Figure folded folded and and faulted, faulted,auriferous, auriferous, felsic, felsic,quartz-feldspar-phyric quartz-feldspar-phyric pyrociastic pyroclastic rocks rockssandwiched sandwichedbebetween T.L.Muir, Muir,OGS, OGS, 1990). 1990). tween variably variably strained strainedmetasedimentary metasedimentaryrocks. rocks. (Geology (Geologyby byT.L. �Hemlo Area Road RoadLog Log — - Hemlo Stop 28: * Stop 85 TURNOFF MAFIC HEMLO TURNOFF MAFIC PILLOWS PILLOWS(Figures (Figures18 18&& 41) 41) west on Highway 17, north side, side, for for 2.6 2.6 km to an unmarked Location: Continue west 17 north unmarked gravel road road turnoff, to the westbound passing passing lane (this the south, south, at at the the west west end end of a awestbound (this road road leads leads to the old old site of Hemlo). Hemlo). The outcrops outcrops at at this this stop stop display display pillowed pillowedand and non-pillowed, non-pillowed, high-iron high-irontholeiitic tholeiiticbasalt basaltflows. flows. They are part of a large, tectonic(?) "wedge" of mafic rocks that are 250 m thick here and thin to the They are part alarge, tectonic(?) "wedge" of mafic rocks that are 250 m thick here and thin tothe than 50 50 m. m. The stratigraphic stratigraphic relationship east to less than relationshipof of this this "wedge" "wedge"to toaathick thickpillowed pillowedunit, unit,lying lying LEGEND: STOP STOP 27 27 Volcaniclastic Volcaniclastic Metasediments Metasediments la feldspathic wacke: wacke: highly strained, strained, mylonitic(?), mylonitlc(?), transposed, cleaved lb garnet-biotite-feldspar garnet—biotite—feldsparwackelsiltstone: wacke/siltstone: mylonitic(?), transposed, transposed, laminated laminated highly strained, mylonitic(?), ic garnetiferous garnetiferous wacke, transposed transposed 1d feldspathic siltstone: siltstone: with preserved preservedS0S, S& layering generally with 1e metawacke: garnet—feldspar—biotjte garnet-feldspar-biotite schist schist if feldspathic, feldspathic, feldspathized(?) feldspathized(?) arenite Quartz-Feldspar-Porphyritic, Felsic Units Ouartz—Feldspar—Porphyritic, Felsic Pyroclastic Pyroclastic Units 2a 2a tuff(?) crystal tuff(?) 2b 2b relatively monolithic relatively monolithiclapilli—tuff, lapilli-tuff, lapilli—stone, lapilli-stone, tuft: tuft pyritiferous, altered(?) pyritiferous, sericitic, sericitic, altered(?) 2c 2c heterolithic lapilli-tuff, lapilli—stone: !a.pilliistone: heterolithic lapilli—tuff, with chloritic and and sericitic lenses lenses Dikes Dikes 3 fine—gralned, intermediate intermediate fine-grained, Intrusive Contact Contact 4 diabase outline of of outcrop with outline with internal internal patch patch of of overburden overburden lithologic contact: contactmay mayalso alsobe betectonic tectonicdiscontinuity discontinuii layering layering - —- — apparent tectonic discontinuity discontinuity — predominant cleavage predominant cleavage bounded zone zone of F3 bounded F3 'Zn—shaped 'Ze-shaped folds quartz veins, veinlets veinlets �86 86 Geologyand and Gold Gold Deposits Depositsof of the the Hemlo HemloArea Area Geology to the thenorth northand andwest-northwest west-northwestat atBotham BothamLake Lake(and (andextending extendingintact intactto tothe theColdwell Coldwellalkalic alkalic to complexl 27 km to the west)] is unclear. The exposures at this stop allow one to view the vestiges of complex, 27 km to the west), is unclear. The exposures at this stop allow one to view the vestiges of some primary features which, beyond about 1750 m to the east, are no longer preserved] even some primary features which, beyond about 1750 m to the east, are no longer preserved, even though the the mafic mafic unit unit can canbe betraced tracedfor forwell wellover over10 10km kmfurther. further. The The unit unit appears appears to to be be though geometricallyand andgeographically geographicallycontrolled, controlled,for forthe themost mostpart, part,by bythe theHemlo Hemlofault fault zone. zone. geometrically i Opposite the the turnoff, turnoff, on onthe thenorth northside sideofofthe thehighway, highway]are aregarnetiferous garnetiferousand andnon-garnetifnon-garnetifOpposite erous, moderatelystrained basalt pillows with aspect ratios of at least 511. The strike of ill-defined ill-defined erous, moderately strained basalt pillows with aspect ratios of at least 5:1. The strike of unitsis is about about 2700, 270°slightly Fine- to garnet, present presentin in both both units slightly oblique oblique to to the the highway. highway. Fineto coarse-grained coarse-grained garnet, the selvages and pillow cores] is most abundant here. Overall, garnet is heterogeneously the selvages and pillow cores, is most abundant here. Overall, garnet is heterogeneously distributedthroughout throughoutthe theremainder remainderofofthe theoutcrop outcropto tothe thewest westwhere wherethere thereare arenon-pillowed non-pillowed(Le., (i.e., distributed massive) units units as as well. well. Prior Priorto torecent recentblasting, blasting,features featuresreminiscent reminiscentof of highly highlystrained strainedflow flow top top massive) breccias, and and possibly possibly interfiow interflowsediments, sediments]were were present. present. breccias, Varioliticpillows pillowsare arepresent presenton onthe thesouth southside sideof ofthe thehighway highwayto tothe thewest westof of the the turnoff. turnoff.To Tothe the Variolitic east of of the the turnoff turnoff (not (notshown shown on on Figure Figure40), 401, on on the the south south side side of of the the highway, highway, there are variolitic variolitic east there are and non-variolitic non-varioliticpillowed units. At Atleast least2,25 2,25 cm cmthick, thick]interflow interflowunits unitsof of rusty-weathering, rusty-weathering]pyritic, pyritic] and pillowed units. mediumto very dark grey metasiltstone are present at about 95 m and 155 m from the turnoff. medium- to very dark grey metasiltstone are present at about 95 m and 155 m from the turnoff. The flows flowshave havebeen been intruded intrudedby by at at least least three types of of foliated, fabric-paralleldikes: dikes: The three different different types foliated, fabric-parallel plagioclase-porphyritic; schistose mafic; and fine-grained intermediate. A recently intermediate] intermediate, plagioclase-porphyritic; schistose mafic; and fine-grained intermediate. A recently revealedcarbonatitic/alkalic carbonatiticlalkalicdike, dike,oriented orientedatat355/77, 355177 occurs occurs at at the the first first(heading (headingeast) east)oxidized, oxidized, revealed interflow, metasiltstone unit. The dike appears to be associated with fracturinglfaulting and some interflow, metasiltstone unit. The dike appears to be associated with fracturing/faulting and some form of alkalic(?) alteration. form of alkalic(?) alteration. StructuralSummary: Summary: Structural Predominant andflattening flatteningfabric fabric 266/70 266170 Predominant and Subordinate,locally locallypresent presentfabric fabric 276/72 276172 Subordinate, Stop29: 29: HOMESTAKE HOMESTAKEPROPERTY PROPERTYF3 F3Z-SHAPED 2-SHAPED FOLD FOLD(Figures (Figures18 18&&42) 42) ** Stop Permissionfor foraccess accessto tothe theproperty propertyisisrequired. required. InInformation onwhom whomto tocontact contactshould shouldbe be Permission formation on obtained from the Resident Geologistb Office, Thunder Bay (see address on title page). obtained from the Resident Geologist's Office, Thunder Bay (see address on title page). Lecours Tp Tp Lecours 1 Bomby Bomby Tp Tp gossan pillowed flow flow pillowed variety of dikes garnetiferous garnetiferous pillowed flow flow pillowed P0 le N A / .massiven flow massive flow - 00 20 20 40 40 - - garnetiferous gmassivemflow variolitic variolitic pillowed pillowed flow flow Microwave Tower Tower 60 60 m m Hemlo s c a l e approximate approximate scale Figure41. 41. Stop Stop28: 28: Simplified Simplifiedsketch sketchmap mapof of varieties varietiesof of pillowed pillowedand and"massive" "massive"mafic maficflows flows FIgure which are locally garnetiferous or variolitic. which are locally garnetiferous or variolitic. �Road Road Log Log — - Hemlo Hemlo Area 87 lb lb la brittle ¶ 2b LEGEND: STOP STOP 29 LEGEND. 024 0 Intermediate Intermediate Metavolcanics Metavolcanics(CaIc—alkalic) (Calc-alkalic) llaa massive flow llb b pillowed flow flow Ic lapilli—tuff or or volcaniclastic volcaniclastic l c lapilli-tuff conglomerate 2 6 6 8 81 4 10 0 m m 2c lc Volcaniclastic/Epiclastic VolcaniclasticlEpiclastic Metasediments Metasediments feldspathic arenite (altered wacke?) wacke?) 2a 2a feldspathic 2b 2 b thinly layered, light gray and buff wacke layered, sparse sparse 2c thickly layered, 2dd 2 granule—pebble clasts granule-pebble clasts fine—grained, gray wacke, siltstone: brittle breccia very thinly layered to thickly laminated 2e gray wacke: wacke: thinly layered layered 2c 2d 2d Dikes Dikes 3a fine—grained,gray, gray, intermediate, fine-grained, 3b 3b with sparse sparse biotite biotite phenocrysts phenocrysts fine—grained,gray grayt o to pink pink (hematitic). (hematitic), fine-grained, m fine—grained, mafic: mafic: fine-grained, moderately foliated foliated tto moderately o very very schistose schistose 2dd 2 intermediate (alkalic?) (alkalic?) rn version" of versio;' m "net-veined above two dike above two d ~ k etypes 2dd 2 2d mafic, mafic to mafic, biotite biotite lamprophyre± lamprophyretmafic to ultramaf Ic xenoliths: xenoliths: very very schistose ultramafic I 1? I? types feldspathized rock with with disseminated disseminated pyrite pyrite ...... ... ... feldspathized —maybe bemore moreintensely intenselyaltered altered equivalent equivalent of 2a -may 2a 2d 2d - ------ lithological contact: contack observed observed lithologicsl contact: Interpreted lithological interpreted trace of layering -.Z trace of layering T S -- —- — -. --- / -..- approximate boundary of highly strained pillows 2e fault (horizontal (horizontal component component of of movement movement shown ifIf observed) shown outline of of outcrop with outline with internal internal patch patch overburden remaining remaining of overburden {( J1 3 2e boundary of highly strained pillows -- approximate zones of weakly defined zones dismembered quartz quartz veins dismembered 2d 2e t. J 2d 2d 2d unusually large, Z-shaped, fold with with high-alumina high-alumina basalt Figure Stop29: 29: Geology Geologyof an unusually Z-shaped, F3 F3fold basalt FIgure 42. Stop F2-folded metasedimentary metasedimentary rocks, gabbro dikes, and pillows, F2-folded rocks, numerous numerousArchean Archean lamprophyre lamprophyre and and gabbro local, minor "Hemlo style1'(?) style"(?) alteration 1990). local, minor "Hemlo alteration(Homestake (Homestakeproperty). property).(Geology (GeologybybyT.L. T.L.Muir, Muir,OGS, OGS, 1990). �88 88 Geology Geology and and Gold Gold Deposits Deposits of of the the Hemlo Hemlo Area Area Location: south side, Location: Continue Continuefor for525 525mmwest weston onHighway Highway17, 17 south side, from from the the Hemlo Hemloturnoff, turnoff,to to aa 44 m m high roadcut. roadcut. Climb Climbthe theoutcrop outcroptotothe thehydraulically hydraulicallycleared clearedarea areawhich whichextends extendsfor forabout about70 70 m m high south from from the the roadcut. roadcut. This This stripping stripping was was undertaken undertaken by by Esso Esso Minerals Minerals Limited Limited prior prior to to acquisitionof of the the proerty propertybybyHomestake HomestakeExplorations ExplorationsLimited. Limited.Exposed Exposedhere hereisisone oneof of the the largest largest acquisition F3 generation, Z-shaped folds presently presently observed observed in in the Hemlo Hemlo area. The TheF3 F3fold fold has has resulted resulted in in F3 generation, Z-shaped rotation rotationof of the thelayering layeringfrom fromabout about285° 285' to to330°. 330'. The The north northend endof of the the outcrop outcrop consists consists of of pillowed pillowed flows. The The pillows pillowsare are feldspar feldspar phyric phyricand and are presently presently alkalic alkalic in in composition. composition. Locally, Locallylamygdaloidal/vesicular amygdaloidal1vesiculartextures textures can can be be seen. seen. The The are pillows pillows contain contain finefine- to to medium-grained medium-grained hornblende crystals. The Theselvages selvages are are relatively relativelythick, thick, biotiterich, richland andlocally locallypyritiferous. pyritiferous.The Thepillows pillowsare arefound foundnowhere nowhereelse elseininthe thearea area(except (exceptfor for the the biotite adjacent suggestions that adjacent roadcut roadcutabout about 70 70 m m to the west). This This has has led led to suggestions that these these rocks rocks represent represent altered altered tholeiitic tholeiiticpillows pillows(MNDM (MNDMassessment assessment files, files,Thunder ThunderBay). Bay). However, However! the the significant significant (cf.Stop Stop28), andthe the differencesbetween betweenthe thetwo two"types" "types"ofofpillows, pillows,ininterms termsofofselvages selvagesand andcores cores(cf. differences 28), and presenceof of small, smalll feldspar feldspar phenocrysts, phenocrysts, suggests suggests the the pillowed pillowedunit unitat at Stop Stop29 29was was not nottholeiitic tholeiitic presence originally. originally. Chemically, Chemically, the the pillows pillowsare are relatively relativelysodic sodic(from (fromspilitization?) spilitization?)and andmore moreakin akinto tohigh high alumina basalt. alumina basalt. The pillowed pillowed unit unit displays displays an an abrupt abrupt change, change, towards towards the the south, south, from fromslightly slightlydeformed deformed The pillows to moderately and highly strained equivalents, within the northern part of the fold. pillows to moderately and highly strained equivalents, within the northern part of the fold. ItItisis not not clear D3folding foldingor orwhether whetheraazone zoneofofheteroheteroclear whether whether the the considerable considerable strain strain isisaaresult resultof of the theD3 geneous, strained pillows pillows pass into (relationship (relationship geneous$high highstrain strainformed formedprior prior to to the the F3 F3 fold. The highly highlystrained unclear) unclear)aa volcanic volcanic breccia brecciaor or volcaniclastic volcaniclasticunit. unit.The Thefragments fragmentsininthis thisunit unitare arevariably variablystrained, strainedl feldspar phyric, and appear to be similar in composition to the pillows (pillow breccia?). feldspar phyricl and appear to be similar in composition to the pillows (pillow breccia?). metasedimenAdjacent to to this thisfragmental fragmentalunit unitare are"units" "units"of oflight lightgreygrey-to towhite-weathering white-weatheringmetasedimenAdjacent tary taryrocks rocksand andmedium mediumgrey grey metasedimentary metasedimentaryrocks. rocks. Although Althoughthe thetwo two"units" "units"overall overallare aredistinct distinct from from one one another, another, detailed examination shows that some of the colour colour differences differences are are locally locally independentof oflayering. layering.This Thissuggests suggeststhat thatat atleast leastsome some of of the feldspathic characterof ofthe the lighter lighter independent feldspathic character weatheringunit unitmay maybe bedue dueto tofeldspathization, feldspathizati~n~ typeofofalteration alterationcommon commonininthe theHemlo Hemlodeposit. deposit. weathering aatype Locally tol the thecontact contactbetween betweenthe thefragmental fragmentalunit unitand andthe the feldspathic feldspathic Locallyat, at, and andslightly slightlydiscordant discordantto, metasedimentaryrocks rocksisisaableached, bleachedlrusty rustyweathering, weatheringltabular tabularzone zonethat thatappears appearstotohave havebeen been metasedimentary (F3)and and is is very very similar similar in in appearance appearance to to some some of the alteration in the the Hemlo Hemlodeposit depositarea. area. AA folded(F3) folded alteration in grabsample sample from fromthis thiszone zonereturned returnedan anassay assayvalue valueofof103 103ppb ppbAu Auand and100 100ppm ppmMo Mo(M. (M.Smyk, Smykl grab MNDM, MNDM,personal personalcommunication, communication,1990). 1990). The remainder remainder of of the theoutcrop outcropconsists consistspredominantly predominantly of of varieties varieties of of variably variablydeformed deformed The metawacke garnetkmagnetite octaoctametawacke and metasiltstone metasiltstone locally locally containing containing sparse sparse garnet±magnetite hedrakretrograded,yellowish yellowish porphyroblasts porphyroblastswhich which were were possibly possibly staurolite. staurolite.InInthe thesouth southhalf halfofof hedra±retrograded, theoutcrop, outcrop,preserved preservedF2 F2folds foldswith withS-asymmetry S-asymmetrycan canbe beseen seenamongst amongstF3, F3,locally locallychevron-like, chevron-likel the Z-shaped In one one case, casel an anindividual individuallayer layerdisplays displaysaaF2, F2,S-shaped S-shapedfold foldadjacent adjacenttotoaaF3, F3, Z-shapedfolds. folds. In Z-shaped Z-shapedfold. fold. Strainwas washeterogeneous heterogeneousas asindicated indicatedby bythe thelayering layeringwhich whichranges rangesfrom fromwell welldefined definedand and Strain continuous, continuousl to to wispy wispyand anddiscontinuous, discontinuous,suggestive suggestiveofoftransposition. transposition. Transposition Transposition isisalso also suggested suggestedby bythe theconsiderable considerable disruption disruptionand anddismemberment dismemberment of of quartz quartz veins veins and anddikes dikesconconstrained strainedto tocrudely crudelydefined definedzones zoneswhich whichare aresubparallel subparallelto tolayering layering(see (seeFigure Figure42). 42). Severalfoliated foliateddikes dikeshave haveintruded intrudedthe themetavolcanic metavolcanicand andmetasedimentary metasedimentaryrocks rocksand andall allof of Several them dike, and themhave havebeen beenaffected affectedby bythe theF3 F3folding. AA relatively relativelythick thickdikes andseveral severalnarrower narrowersubsidiary subsidiary dikes*of of Archean, Archeanl mafic, maficl biotite biotitelamprophyre lamprophyre show show diverse diverse textures textures and, andl to to aalesser lesserextent, extent, dikes, �Road Log Log — -Hem Hemlo Road lo Area mineralogy. mineralogy. They They locally locally contain contain mafic mafic to to ultramafic ultramaficxenoliths xenoliths which which are are locally locallyconcentrated concentratedinin zones. The The matrix matrix of of these these dikes dikes is is similar similar to that that of of intrusion intrusion breccia breccia (diatreme) (diatreme) bodies bodies on on the Golden Sceptre and Williams properties. properties. Conflicting Golden Sceptre Conflictingrelationships relationshipsare are present, present, but but itit appears that these dikes have been been followed by numerous, numerous, thin, gabbroic dikes which have have behaved more competently during subsequent deformation. deformation. competently gabbroic dikes locally locally display display considerable The gabbroic considerable variation variation in in response responseto to strain strain (e.g., (e.g.,buckling buckling boudins), depending depending on on orientation orientation relative to shortening or and regularly spaced, backrotated boudins), dike extension. AA locally locally developed developedbrecciation brecciation involving involving fragmentation fragmentation of of the main main lamprophyre dike and adjacent metawacke, chloritic matrix, and adjacent metawacke,and andhaving havingaachloritic matrix,can canbe beseen seenin in the the north northpart partof of the the outcrop. outcrop. The matrix is foliated. Relatively late, sinistral and dextral, brittle brittle faults faults have have produced producedminor minoroffsets offsetsof of layering. layering. Some earlier(?) ductile sinistral indicated by hooked disrupted dikes. sinistral sense movement is indicated hooked tails on disrupted Structural Structural Summary: Summary: S0/S1 from 285' 285° (local (local strike) strike) to SdS, from to 340° 340Â(on (on short shortlimb limbof of large largeF3 F3fold) fold) —305° S2 fabric fabric S, -305' fabric S3 fabric ranges from strike of 230° 230' to 280°, 280°and dip of 85°N 85ON to 85°S 85's (rarely (rarely 65°S) 65's) depending depending on on position positionwithin withinF3 F3fold fold 068/72, 105/47 various 068172, 105147 F3 axis: axis: various L crenulation: 096/62, 110/34, 265/60 & crenulation: various various 096162, 110134, 265160 080/20 L, boudinage 080120 Lb boudinage Zones of transposition 285° to 290 290° 285O Backrotated Backrotated boudins boudins of mafic mafic dike: dike: 285° 285' (within (within layering layering that that strikes strikes at at 295°) 295') General trend of late breccias 225° and breccias 225' and 3550 355' Late 3 15°,330° 330°, 345' 345° Late dextral dextral faults faults 315O, Late 180°, 210° 210°, 225' 225° Late sinistral sinistral faults faults 180° Stop 30: Stop CONTACT OF HERON (Figures 18 HERON BAY PLUTON (Figures 18 and 43) furtherwest on north side, roadcut opposite Location: Proceed Proceed1.5 1.5 km furtherwest onHighway Highway17, 17, north side, to to aa 7 m high roadcut opposite an area cleared cleared of of trees trees on on the the south south side. side. This outcrop outcrop shows: whichappears appearstotorepresent representthe themarginal marginalrock rockof ofthe theHeron Heron (A) plagioclase-porphyriticgranodiorite plagioclase-porphyritic granodiorite which similar in in many many ways waysto to some someof ofthe theplagioclase-porphyritic plagioclase-porphyritic dikes dikes found in the the Bay Pluton and is similar supracrustal rocks in the area. area. The aplitelpegmatite dikes and The granodiorite granodiorite is is intruded intruded by pink aplite/pegmatite white quartz veins; N A I Metasediments Metasedirnents Metasedirnents - 1 Granodiorite 0 o 10 io 20 20 30 30 m rn H w y 17 I scale s c a l e approximate approximate lamprophyre larnprophyre I I 89 89 FIgure 43. Figure Pluton. Pluton. Stop Stop 30: Simplified sketch geology at Simplified sketch map map of the geology at the the east east contact contactof of the the Heron HeronBay Bay �90 90 Geology Geology and Gold Deposits Deposits of the Hemlo Hemlo Area (B) deformed deformed (e.g., biotite-hornblende-bearing metawacke (e.g.,folds, boudins), boudins), medium medium to to dark dark grey, biotite-hornblende-bearing metawacke which which locally locally contains containsgarnet garnet(east (eastside side of of diabase diabase dike); dike); veins, in in the the metawacke, metawacke, which display display boudinage boudinage (sub-horizontal (sub-horizontal (C) quartz-feldspar-muscovite quartz-feldspar-muscovite veins, necks). The The top top surface surfaceof of the the outcrop outcrop used used to show that necks). that boudinage boudinage had occurred occurred in the the horizontal horizontal and vertical vertical planes; planes; (D) a mediummedium- to fine-grained, piagioclase-porphyritic plagioclase-porphyriticdiabase diabase dike; dike; Proterozoic, massive, massive, pyroxene(?)-magnetite pyroxene(?)-magnetitelamprophyre lamprophyre dike dike likely likely associated associatedwith withLake Lake (E) a Proterozoic, Superior rift ing. Superior rifting. Stop Stop31: 31: HERON HERON BAY BAY PLUTON PLUTON(Figure (Figure18) 18) Location: km from from Stop30, Stop 30, to to aa roadcut roadcut (both sides) about Location: Continue Continueeast easton on Highway Highway17 17for for 1.3 1.3 krn about 180 m west west of of the the "Rouse "Rouse Lake" highway sign. sign. The correct correct name name of of the the lake lake is is Rous Rous Lake. Lake. The The outcrop outcrop is is opposite opposite aa large largeclump clumpof of trees treesbetween betweenthe thehighway highwayand andthe thelake. lake. These These outcrops outcrops are are typical typical of of the the inner inner part part of of the the Heron Heron Bay Bay Pluton, Pluton, as as exposed exposed along along the the highway, although although different different phases, microcline-megacrystic, are within the phases, such as microcline-megacrystic, are present presentfurther furtherwithin the pluton. granodiorite is is intruded pluton. At this this roadcut, roadcut, massive massive biotite-hornbiende biotite-hornblende granodiorite intruded by aplite aplite and and pegmatitic dikes. The xenoliths. An Thegranodiorite granodiorite locally locally contains contains sparse mafic xenoliths. An extremely extremely faint faint fabric 300' to to330°. 330'. fabric appears appears to to strike strikefrom from300° The dikes 050°, and 070 070°and anddip dipsteeply steeplyto tothe thesoutheast. southeast. The The latter latter dikes commonly commonlystrike strike at at 030°, 030°050° two orientations few quartz-rich quartz-rich veins veins which which cut cut the dikes are oriented oriented orientations tend tend to to be predominant. AA few at 260-280/40 260-280140 and display a fabric which is possibly mylonitic. mylonitic. Samples within the Samples for for U-Pb U-Pb geochronology, geochronology, taken here here and farther within the pluton, pluton, gave gave a combined combined age age of 2688±5 2688± Ma Ma for the the granodiorite granodiorite(Corfu (Corfuand andMuir Muir1989a). 1989a). END END OF OFHIGHWAY HIGHWAY 17 17 ROAD ROADTRIP TRIP Note: Note: Those Thosechoosing choosingto todo dothe theentire entirefield fieldtrip tripfrom fromeast east to to west west should should proceed proceed to to Stop Stop 4, about 31) on to apoint a point on on the the north north side, about about13.2 13.2 km km to to the the west west (of (of Stop Stop31) on Highway Highway17, 17,to about 900 900m m east east of the Black Black River River bridge. bridge. �Stop Stop Descriptions Descriptions— -Hemlo HemloDeposit: Deposit:Williams Williams Property Property 91 91 HEMLO DEPOSIT SEGMENT: WILLIAMS PROPERTY PROPERTY VISIT HEMLO SEGMENT: WILLIAMS This part of the trip will be be supervised supervised by by Williams Williams Operating Operating Corporation Corporation staff. Hard Thispart Hardhats hats and and safety be worn wornby by everybody everybodywhile whileon onthe theproperty. property. safety glasses glasses must mustbe This This is is an an instrumental instrumental part part of of the the Hemlo Hemlotrip tripbecause because of of the theexposures exposuresavailable available on on the the property. property. However, However, at at the the time time of of writing writing and andup up to to the the time time of of the the field field trip, no no guarantees guarantees can can be made made as to which exposures exposureswill will be be "available". "availableJ'.In Incase case some some of the the exposures exposuresare are "unavailable", "unavailableJ', brief descriptions of detailed sketch sketch maps brief descriptions of the the potential potentialstops stops are are presented presentedhere, here, with examples examples of detailed showingthesalient thesalientfeatures. features.Because Becausethe thegeological geologicalhistory historyisiscomplex, complex,aasummary whatwill willbe be showing summary ofofwhat presented detailed presentation presentation of the development development of the interpretapresentedis is given given for each stop, not a detailed interpretation. tion. Matters Mattersofofcontention contentioncan canbest bestbe bedebated debatedon on the spot. Previous Previousfield field guides guides covering covering similar and eta!. al. (1985) (1985) and and and additional additional aspects aspects of of the the mine mine and andproperty property were were presented presented in in Valliant Valliant et Walford, Walford, Weicker, Weicker, and and Guthrie Guthrie(1986). (1986). [Note: Stop 33A outcrop has all all but but vanished; vanished; Stop Stop 35 35 outcrop outcrophas has been been destroyed.] destroyed.] Stop Stop 32: 32: "BACK "BACK40s" 40s"OUTCROPS OUTCROPS(Figures (Figures18 18&& 44) 44) LocatIon: Location: The The Back Back40s 40s outcrops outcrops lie lie about about 450 450 m m northeast northeastof of the the Heritage Heritageoutcrops outcrops(Stop (Stop33). 33). They They have have miraculously miraculouslyavoided avoidedburial burialfor forsome some time time now. now. The Theoutcrops outcropshave havebeen beenchosen chosen(aside (aside from from the the fact fact that that they they are arethe the only onlyones onesleft leftin in this this area), area), because becausethey they show showaa number numberof of features features that that epitomize epitomizethe thestructural structuralhistory historyofofthe thearea, area,and andthey they are are relatively relativelyfar faraway away from from the the ore ore zone with with its itsattendant attendanthigh highstrain strainand and substantial substantial alteration. alteration. The The southernmost southernmostand andlargest largestof ofthis thisset setof of exposures exposuresconsists consistsof ofaavariety varietyof ofmetasedimenmetasedimentary tary rocks rocks derived derivedfrom fromvolcaniclastic(?) volcaniclastic(?) feldspathic feldspathic arenite, arenite, wacke, wacke, siltstone, siltstone, and andpossibly possibly conglomerate. conglomerate. There There are are also alsonumerous numerousamphibole-rich amphibole-richlayers. layers. The The northernmost northernmostoutcrop outcrop consists consistsof of turbiditic turbiditicwackes, wackes,some somecontaining containingrip-up rip-upclasts. clasts. These These exposures exposures lie lie on on the the northeast northeastlimb limbof ofaatight, tight,large-amplitude, large-amplitude,northwest-closing, northwest-closing, north-northwest-plunging north-northwest-plunging fold, centred centred on on the the Williams Williams property property (Figure (Figure 19). 19). The TheS2 S2cleavage, cleavage, which whichisisprominent prominentin in this this outcrop, outcrop, is is thus thus oriented oriented clockwise clockwisewith with respect respectto to the the layering. layering.Several Several layers, suggest that the units layers, including one comparable comparable to volcaniclastic volcaniclastic conglomerate, conglomerate, suggest units are are overturned overturned at at this this location, location,assuming assumingnormal normalgrading. grading. Structural Structural features featuresthat thatare areimportant importantare areas asfollows: follows: F1 Fl sheath fold fold or interference interferencefold fold F1 conglomeratic(?) rocks Fl isoclines isoclines in an unusual, unusual, layer-parallel layer-parallel zone of conglomeratic(?) rocks F2 F2 S-shaped, parasitic parasitic folds folds with with north-northwest north-northwestplunges plunges S2 within some layers, layers, and andSo 2 fabric S2 stripey cleavage developed within fabricand andclast clast alignment alignment in in others others F3 F3 related related folds folds in in boudin boudinnecks necks S3 fabric occurs: boudin necks crenulation cleavage; S3 fabric occurs: in in F3 F3folds and and boudin necks as as a crenulation cleavage;ininsericitic sericiticlayers; layers;and andas as pressure pressureshadows shadows around aroundgarnet garnet porphyroblasts. porphyroblasts. Two structural discontinuity Two zones of structural discontinuityoccur occurininthe theBack Back40s 40s outcrops, outcrops,one one at at the the south southend endof of the 12),the theother othernear nearthe the north northend endof of the northernmost northernmostexposure. exposure. thesouthernmost southernmostexposure exposure(Photo (Photo12), The The southern southernzone zonehas hasbeen beeninterpreted interpretedto tobe befolded foldedabout aboutthe theF2 F2axis axis and and thus thus predates predatesthat thatfold fold generation. generation. Its Itsorigin originisisnot notwell wellunderstood understoodbecause becauseititdisplays displaysfeatures, features,some someof of which which can canbe be interpreted (e.g., soft soft sediment sediment slump slump structures), and others in in aa tectonic tectonic interpreted in in aa primary primary sense sense (e.g., sense sense(e.g., (e.g.,low-angle-to-layering low-angle-to-layeringfaulting faulting or or thrust thrust faulting). faulting). Both Bothprocesses processesmay mayhave haveoccurred. occurred. The The northern northern zone zone isisassociated associatedwith withvarieties varietiesofofmetasiltstone metasiltstoneand andamphibole-rich amphibole-richlayers layers displaying discordant layering, disrupted folds, layer-parallel breccias and sinistral faults. The displaying discordant layering, disrupted folds, layer-parallel The �______ Geology and Gold Deposits of the Hemlo Area 92 92 2D 2D 2B— 2C 0 0 10 5 5 15 metres metres Detailed sketch sketch map map of of the Back Figure Figure 44. 44. (legend on opposite opposite page) page) Stop 32: 32: Detailed Back 40s property), showing showing aa variety variety of of lithologic lithologic units units and and structures structures that that reflect the outcrop (Williams property), to D-,. D3. Legend and scale same as as for for Figures 45 45 and and 46. 46. (After Dl to (AfterMuir Muir1986). 1986). events of D1 �Descriptions — -Hemlo Hemlo Deposit: Deposit: Williams Property Property Stop Descriptions 93 93 strike, across across what appears appears to be a folded contact, contact, into into thick-layered, thick-layered,rip-uprip-upzone passes, along strike, clast-bearing metawackes metawackeswhich which do do not not seem to (SeeMuir Muir and and clast-bearing to show show similar similar deformation deformation features. features. (See more details.) Elliott (1987) for more lithologic Fine-to medium-grained garnet garnet porphyroblasts are are common common within within many of the lithologic the southern southern 30 m m of ofexposures, exposures,including includingthe theamphibole-rich amphibole-rich layers. layers. The occurrence occurrence here units of the here of garnet in amphibole-rich amphibole-rich layers, which elsewhere is uncommon, may may be be aa result result of of alteration alteration prior to metamorphism. metamorphism. Outcrops Outcrops in in the the central central part part of ofthe theoutcrop outcroparea areacontain containgarnet garnet and and staurolite porphyroblasts. two generations. generations. The earlier(?) generation generation is staurolite porphyroblasts. The Thelatter latterappear appear to to be of two aligned parallel to the S2 S2 fabric, and and is is partly partly retrograded retrograded to to staurolite, staurolite, quartz, quartz, feldspar, feldspar, and and muscovite. The Thelater latergeneration generationtends tendsto tobe besubhedral subhedral and and non-retrograded. non-retrograded. alteration, at at least least on on aa more more local localscale, scale, involves involvesan an incipient incipientto to wellwellAnother example of alteration, developed, stripey, development of "lenses", "lenses", along the S2 S2 stripey, differentiated layering, and locally aa development cleavage in silty and arenaceous layers. layers. Here, mineralogical composition of the Here, the textural and mineralogical non-primary layers and lenses so produced, presently resembles resembles the range of compositions compositions among silty and arenaceous arenaceous layers. Hence, interpreted feldspathic Hence,some some or or all all of the interpreted feldspathicarenite arenitemay may actually alteration of wacke and possibly possibly siltstone. siltstone. This actually be be a result of alteration This underscores underscoresthe thedifficulty difficultyinin distinguishing between originally feldspathic feldspathic rocks and feldspathized feldspathized rocks, rocks, particularly if the the latter were initially feldspathic. Two gabbro dikes dikes intrude the the central part of these these exposures. One Two gabbro One dike dike isislayer-parallel layer-parallel and and displays boudinage with with quartz fillings in the the necks. necks. The The other other dike dike is is slightly slightly discordant discordant and, and, although otherwise otherwise similar similar in in appearance appearance and and composition, composition, displays displays back-rotated back-rotatedboudins boudinswith with quartz + + tourmaline neck fillings and locally associated bleaching of the country rocks. rocks. In the southern slightly discordant gabbro southern part part of of the the main main outcrop, there there is is a slightlydiscordant gabbro dikelet dikelet which which isis somewhat somewhat similar to the adjacent amphibole-rich layers. adjacent amphibole-rich layers. LEGEND LEGEND STOPS 32,33 32, 33 Symbols Symbols PROTEROZOIC PROTEROZOIC Lamprophyre: Lamprophyre: biotite, pyroxene pyroxene 6 ARCHEAN ARCHEAN Quartz, Quartz, veins veins and and pods: pods: kyanitetpyrite c7 Outcrop outline: 4 Outcrop outline: 1986 mapping 1986 mapping •2 Outcrop outline: L.Outcrop outline: 1985 1985 mapping mapping .A'> ±tourmalinetmuscoviteichloritet itourmalinetmuscoviteichlorite~ Alteration Alteration Feldspathized: Feldspathized: locally identifiable !dentifiable as epiclastic epiclastic and and volcaniclastic metasediments metasedlments Pyritized: locally identifiable Feldspathized and Pyritized: identifiable as as and volcaniclastic volcan,clastic metasediments metasedimnts epiclastic and Feldspathized Feldspathizedand and Biotitized: Biotitized: locally locally identifiable identifiableas as epiclastic epiclastic and and volcaniclastic volcaniclasticmetasediments metasediments Intrusions Intrusions Felsic dike: feldspar, quartz, sericite sericite biotite, feldspar Intermediate dike: biotite, Mat icdike, dike,gabbro: gabbro: xenoliths shown Mafic shown where significant significant :I'.-:.-.. -— .' ? Outline of of specific features in altered zone ::--I zone see pa em (see pattern) locally . bedding destroyed, very fine bedding destroyed, very finegrained: grained: locally with molybdenite wlth molybdenite oo highly highlyschistose, schistose,fissile fissileon onoutcrop outcropsurface surface 0 Metasediments1 ~etasediments' Caic—silicate Calc-silicate IEIJJI 2C a 2* lB is Siltatone Siltstone Wacke Wacke Arenite: Arenite: largely volcaniclastic volcaniclastic largely volcaniclastuc Conglomerate, granule and pebble: largely volcaniclastic Metaporphyries Metaporphyries Felsic, sericitic, porphyry: flow?, sericitic, quartz—feldspar quartz-feldspar porphyry: flow?, hypabyssal hypabyssalintrusion? intrusion? Felsic, aericitic, porphyritic pyroclastic sericitic, quartz—feldspar quartz-feldspar porphyritic pyroclastic rock rock Outline of pervasively altered delineable Outline of delineable units units of conglomerate limonite covered _— Limits of pervasive alteration / alteration u 's Fault: sense senseshown shown where where determined determined ,-' -" FoldFold axis: trace of unexposed axial axis: trace of unexposed axialplane plane -'- - Bedding Beddingtop topdirections: directions: upright facing, facing, overturned overturned fabric trends @ Local Local bedding or fabric trends 555 nferred extension Inferred extension of of units unitswith withdistinctive distinctivesimilar similar features IT Till: cemented cemented D D Dirt: overburden overburden B B Boulder: erratic erratic c Clast: composite Clast: composite �94 Geology Geology and Gold Deposits Deposits of the Hemlo Hemlo Area Structural StructuralSummary: Summary: South South part part of of stripped strippedoutcrops outcrops S0/S1 290/75 general orientation in SOBl 290175 general orientation in outcrop outcrop S0/S1 292/63 north north limb limbof of aa F1 S& 292l63 Fl isocline isocline S0/S1 288/60 south SdSl 288160 Fl isocline isocline south limb limb of of same same F1 312-316/82 range overprinting above range of of S2 S2 overprinting above F1 Fl isocline isocline s2 312-316182 S3 275/73 commonly sericitic sencitic s3 27973 252/63 pressure porphyroblasts: (possibly 252163 pressure shadows about garnet porphyroblasts: (possibly aa later later development development of S3(?)) S3(?)) 32 1/67 isocline isoclinefold fold axis axis LF1 LFI 321167 290/47 one foldlinterferencefold fold one hinge hinge of sheath sheath foldfinterference Lm 290147 311/77 parasitic parasiticF2 F2fold fold axis axis LF2 LF~ 311177 L \ North North part part of stripped stripped outcrops outcrops 289/72 tops to to south(?): south(?): grading gradingand and distribution distributionof of amphibole amphibole SO/SI SdS1 289172 s2 s3 S3 * Stop Stop 33: 33: 301/83 301183 260/73 260173 HERITAGE HERITAGE OUTCROPS (Figures 18,45 18,45 && 46) 46) These These exposures exposuresare areconsiderably considerablyworse worsefor forwear wearthan thanaafew few years years ago. ago. The Theurge urgefor forparking parking lots "clearly" illustrated lots to reproduce reproduceand and grow grow is is "clearly" illustratedhere. here.Many Manyofofthe thefeatures featuresininthe theeast eastoutcrop outcropare are no longer visible, relative to Figure 45. no longer relative to Figure 45. Stop Stop 33A: 33A: HERITAGE HERITAGE EAST EAST OUTCROP OUTCROP (Figure (Figure45) 45) Location: Location: About 40 m to the west of the security building. The considered the the mineralized, mineralized, The Heritage HeritageEast Eastexposure exposureused usedto to show show part part of of what might might be considered 6 Zone Zone (Figure (Figure 22; Photo Photo 13), 131, although although itit may may not notbe be equivalent of Williams Mine B updip equivalent of the Williams connected connectedto to it. it. In some aspects, this mineralized mineralizedsection is similar similar to the the A A Zone section, section, based based section is on (F2?),footwall, sericitized sericitizedand and microclinized, microclinized,quartzquartzon surface surface exposures. exposures. The Theinternally internallyfolded folded(F2?), feldspar m thickzone thick zone of of considerably considerably folded, folded, transposed, feldspar porphyry porphyryisisstructurally structurallyoverlain overlainby byan an 18 18 rn and and altered, altered, metavolcaniclastic metavolcaniclasticdeposits depositsof ofwacke wacke and and granule granule and and pebble pebble conglomerate. conglomerate. The alteration alteration is is interpreted interpreted to to include includefeldspathization feldspathization (microclinization), (microclinization), sericitization, sericitization, pyritization, and and possibly possibly local local silicification, silicification, with withanomalous anomalousgold gold and and locally locallyvisible, visible, very very finefinepyritization, grained molybdenite. molybdenite.Numerous, Numerous,deformed deformedquartz quartzveins veinslie lieininaacentral centralzone zoneof of feldspathized feldspathizedand and grained biotitizedvolcaniclastic volcaniclasticmetasedimentary metasedimentaryrocks, rocks, which which are are structurally structurally overlain overlain by by feldspathized, biotitized feldspathized, sericitized, and and pyritized pyritized metasedimentary metasedimentary rocks. The The zone zone of of altered altered rocks rocks is is in in sharp, faulted sericitized, contact with the the hanging hanging wall wall volcaniclastic volcaniclastic metasedimentary metasedimentary rocks which are are locally locally partly partly alteredand and isoclinally isoclinallyfolded. folded.Initially, Initially,the theexposure exposureshowed showed44folds, folds,with with alternating alternatingeast eastand andwest west altered closures closures (the (the folds folds must mustnow nowbe be examined examinedat at Stop Stop 33B). 33B). The hanging hanging wall rocks to the the zone zone of of alteration alteration and andmineralization mineralization were were intruded intruded by by aa xenolith-rich (net-veined?) (net-veined?) gabbroic gabbroic dike, and and subsequently subsequently by a swarm of granitoid dikes. The The xenolith-rich quartz-feldspar porphyritic porphyriticfootwall footwall unit unit was was intruded intruded by by dikes of intermediate intermediate composition. composition. quartz-feldspar Structural StructuralSummary: Summary: S 293/74 Sl 29374 % s3~' S38? S? sac? Sac,? S3.? Lm Lm L0 La 287/75 287175 265/70 26W70 275/63 27963 320/76 320176 323/55 32355 348/51 348151 volcaniclastic volcaniclastic metasediments metasediments stripey stripeycleavage cleavage altered alteredrock rockininmineralized mineralizedzone zone altered alteredrock rockininmineralized mineralizedzone zone altered alteredrock rockininmineralized mineralizedzone zone tourmaline tourmalinelineation lineation elongation elongationof of clasts clasts in in volcaniclastic volcaniclastic conglomerate conglomerate �a e r ___ - Stop Descriptions — Hemlo Deposit: Williams Property I-c 047776 Im 0 081/34 077-128/50 291)80 Vq 090±5° F3 95 crenulation (sericite) lineation retrograded feldspar('?) porphyroblasts told axes feldspar porphyry dike (from swarm) generalized quartz vein orientation (steep dipping) Fo)ded, Transposed Section consists of about 31% dikes a a p a a a a a a U a a a a a a a 0 a a a a fr a '4 2C Dextraly sheared, Folded, Transposed, Altered / I 0 5 10 15 metres 'U FIgure 45. Stop 33A: Detailed sketch map of the Heritage East outcrop (Williams property), showing highly transposed and altered/mineralized, metavolcaniclastic/meta-epiclastic rocks (possibly equivalent to the Williams Mine B Zone) between footwall quartz-feldspar porphyry, and hanging wall metavolcaniclastic/meta-epiclastic rocks. Legend and scale same as for Figures 44 and 46. (After Muir 1986). �Bedding Bedding Folded (possibly 2 folds), Transposed, Disrupted Section consists of about 37% dikes 0 2C Bedding Transposed 2D 2D20Q 2C 2C 20 , ', 25 Incipiently Altered Altered 5 10 10 15 15 -\ ' 4 0 0 (0 a C) 0 a. ci CD 00 1 CD metres metres V 0 0) 0-I, :7 CD the Heritage Heritage West outcrop (Williams property), Figure Figure46. 46. Stop 33B: 33B: Detailed sketch map of the disrupted and metavolcaniclastic/meta-epiclastic showing disrupted and tightly tightly F2-folded, F,-folded, mixed, mixed, hanging wall metavolcaniclastic/meta-epiclastic rocks, as well as a swarm of granitoid dikes. Legend Legendand and scale scale same same as as for for Figures Figures 44 44 and and 45. 45. (After (After Muir Muir 1986). 1986). �Stop Stop Descriptions Descriptions— -Hemlo Hemlo Deposit: Deposit: Williams Williams Property Property 97 97 Stop Stop 33B: 33B: HERITAGE HERITAGE WEST OUTCROP OUTCROP (Figure (Figure 46) 46) Location: Location: About 50 m to the west-northwest of the Heritage Heritage East East outcrop. This outcrop outcrop shows shows the the hanging hanging wall metasedimentary metasedimentaryrocks rocks which which are are composed composedof of folded folded This metavolcaniclastic wacke, pebble conglomerate, and siltstone, with numerous numerous amphibole-rich amphibole-rich layers. staurolite bearing. The layers. Some Somelayers layers within within the the northernmost northernmostfold fold are garnet and/or staurolite The rocks rocks aswarmof of granitoid granitoiddikes dikes(the (thesame same swarm swarmno no longer longervisible in the Heritage Heritage have been been intruded intrudedby by aswarm have visible in East outcrop). The The granitoid granitoiddikes dikespostdate postdateF2 F2folding folding and and display display muscovite muscovitepoikiloblasts. poikiloblasts. ~hree,'ti~ht, F2-generationfolds folds are are well exposed These folds folds are are associated associated Three, tight, F2-generation exposed in this outcrop. These with cleavagewith with local local attendant attendant transposition transposition and disruption So cleavage and disruption with aa well-developed, well-developed, axial axialplanar, planar, S2 of layering, particularly in in the noses noses of the folds where horsetail structures are locally locally developed developed (Photo in response to the strain, (Photo 14). 14). The The variations variations of layers layers of different different composition, composition, in response to strain, is is particularly particularly interesting. interesting. Locally, in the the nose of the the northernmost northernmost fold, staurolite occurs within within grey grey weathering weathering rock. rock. This rock represents represents the remnant remnant part of the metasedimentary metasedimentary unit unit that that has has been been unaffected unaffected by alteration planes. Interpretation Interpretationisis alteration (bleaching) (bleaching) along along multiple, multiple, fairly fairly closely closely spaced spaced S2 cleavage planes. equivocal equivocal regarding regarding the timing timing of the formation formation of of the the staurolite staurolite crystals crystals relative relativeto to the thedevelopdevelopment ment of cleavage/alteration. cleavagelalteration. Dextral displacement subparallel subparallel to the the limbs limbs isisdemonstrable. demonstrable. Smaller-scale, sinistral sinistral displacement of the layering is also present. Some of the conglomeratic units show asymmetric displacement present. conglomeratic distribution of about the fold axes of lenses lenses within layers layers which reverses reverses about axes and and is is interpreted interpreted to to represent representgrading grading of of clasts. clasts. IfIfthe the grading gradingwas was normal, normal, the the northeast northeastlimbs limbsare are overturned overturnedwhich whichisis consistent with evidence, albeit equivocal, for the large, F2 fold (see Stop 32), 32),and implies implies a equivocal, for structural structural facing facing to to the the east-southeast. east-southeast. However, However,this this isisnot not consistent consistentwith withthe theF2 F2fold fold at at Stop Stop 8. A zone of incipient incipient alteration alteration is present present in the the south south end endof ofthis thisexposure. exposure. Quartz Quartz +tourmaline + tourmaline Azone alteration, alteration,and andquartz quartz++muscovite muscovite++kyanite kyaniteknots knotsare arepresent presenthere herebut butalso also occur occurlocally locallyininother other parts parts of of the the Heritage Heritageoutcrops. outcrops. A north-northeast-striking, north-northeast-striking, Proterozoic, Proterozoic, bifurcating, bifurcating, biotite biotite ++pyroxene pyroxene lamprophyre lamprophyre dike is is present present in in parts parts of of recessively recessivelyweathering weathering fractures fractures in in the the east east part part of of the the outcrop. outcrop. Structural StructuralSummary: Summary: S 293/66 SI 293166 to to 303/73 303173 279/73 279173 to to282/81 282181 287/78 % 287178 257/66 S3 s3 257166 F2 316/62 FZ 316162 vq 090±5° vq 090±S north northlimb, limb,E-closing E-closingF2 Fafold fold south south limb, limb,E-closing E-closingF2 F, fold fold generalized generalizeddue due to to variations variationsthroughout throughoutoutcrop outcrop generalized generalized quartz quartz vein vein orientation orientation (steeply (steeply dipping) dipping) * Stop EASTCCZONE ZONEOUTCROP OUTCROP(Figures (Figures18 18&&47) 47) Stop 34: 34: EAST Location: Location: About About 400 400 m m west west of of the the Heritage Heritageoutcrops. outcrops. This feldspathized (microclinized (microclinized and albitized?), albitized?), sericitized, This outcrop outcrop consists consists of variably feldspathized sericitized, and and silicified silicified quartz-feldspar-porphyritic quartz-feldspar-porphyriticrocks rockswhich whichhave havebeen been localty locally pyritized pyritized and and mineralized mineralized with gold gold and locally locally visible, visible, very very fine-grained fine-grained molybdenite. molybdenite. Figure Figure47 47depicts depictsthe thevisually visuallyapproxiapproximated distribution of the various types of alteration and mineralization. The quartz-feldspardistribution of the various types of alteration and mineralization. The quartz-feldsparporphyritic porphyriticrocks rockshave haveno nounequivocal unequivocalmajor majorprimary primaryfeatures featurespreserved, preserved,such suchas asunit unitlayering. layering. �______ Geology Geology and and Gold Gold Deposits Deposits of of the the Hemlo Hemlo Area Area 98 — 0 ' -'- ', e —— - '\\ \\ \\ Iy 'I__ alt t - --- - 4 4, '4 \\ 4 £ OV bo \. \__---_--• D Mo .. e sea - D — \ 0 0 -- - 0 bo 10 0 15 metres Detailed sketch sketch map map of of part part of of the the C C Zone, Zone, (legend on on opposite oppositepage) page) Stop Stop 34: 34: Detailed Figure Figure47. 47. (legend east property), showing showing variably variably altered altered and andmineralized mineralizedquartz-feldspar-porphyritic quartz-feldspar-porphyritic east end (Williams property), rocks (lapilli-tuff?) (iapilii-tuff?) intruded by several several dikes dikes of of various various compositions. compositions. (After (After Muir Muir 1988). 1988). �______ _____ Stop Descriptions Descriptions — -Hemlo Hemlo Deposit: Deposit: Williams Property Property LEGEND: STOP STOP 34 LEGEND: / Quartz veins INTRUSIVE C CONTACT INTRUSIVE ONTACT Dikes I Biotite—plagioclase—porphyritiC, biotite biotite diorite Biotite-plagioclase-porphyritic, diorite (sheared) e INTRUSIVE CONTACT aa Biotite gabbro (sheared) (sheared) b b Biotite quartz diorite Biotite diorite c Feldspar porphyry porphyry d d Quartz-feldspar porphyry Quartz-feldspar porphyry INTRUSIVE CONTACT Country Rock Country r\ Sericitic, porphyry S e r ~ c ~ tquartz—feldspar quartz-feldspar ~c, porphyry r— ] Feldspathized, biotitized, quartz—feldspar Feldspathlzed, blotltized, quartz-feldspar porphyry porphyry [J Feldspathized quartz—feldspar Feldspathlzed quartz-feldsparporphyry porphyry 1-1 Quartz—feldspar porphyry with with irregularly Quartz-feldspar porphyry ~rregularlyshaped shaped chlorite—sericite lenses, layers chlor~te-seric~telenses, Pyritized quartz—feldspar porphyry with m j Pyritized quartz-feldspar porphyry with irregularly shaped ~rregularly shaped chlorite—sericite chlorite-sericite lenses, lenses, layers layers [ ] Intensely feldspathized rockrock withwith py—Mo—Au(?) Intensely feldspathized py-Mo-Ad?) mineralization m~neralization m j Zone Zone of notable pyritization, pyritization, Au(?) Ad?) rock (dike—like) (dike-like) Intensely silicified rock - -- — - Intensely - - # - - - Quartz stringers, veinlets veinlets *' Quartz veins Quartz veins r\ [ -- ] pink (tiematitic) pink (hematitic)alteration alteration conspicuous fracturelshear, fracture/shear, conspicuous with wlth or or without without alteration alteration -.-- alteration vein" along alteration %einW alongfracture fracture '2 \ \\ i\ --* D D area of of fragment—bearing fragment-bearing rocks closely spaced fracture sets closely spaced fracture sets ,highly schistose zones highly schistose zones dirt d ~rt 99 9 9 However, many many parts parts of of the outcrop However, outcrop display display numerous lapilli-sized lenses considered considered to be be possible pyroclasts pyroclasts (Figure possible (Figure 47; Photo 15). Many of the small of small lapilli-size lapilli-size fragments fragments are are barely barely discernible because of the the alteration. There There is is also a section of the outcrop outcrop reminiscent reminiscent of a coarse fragmental unit. unit. This exposure is on on from, and about about 400 400 m to the east of, a strike from, porphyritic rock quartz-feldspar porphyritic rock dated dated at at 2772 2772 (Corfu and Ma (Corfu and Muir Muir 1989a). 1989a). There There are several several dikes in this this outcrop outcrop which collectively have a variety variety of of composicompositions and textures. The The dikes dikes strike strike parallel parallel to the main 275' to to 280°, 280° main fabric, which which is is at at about about 275° and are also also foliated. foliated. Some of the dikes display Some dikes display muscovite poikiloblasts. poikiloblasts. AA few muscovite few of of the the dikes dikesare are with a hematitic hematitic alteration spatially associated with which, which, in at at least least one one case, case, appears appears to to have have affected the dike and thus postdates it. Two Two of the dikes consist consist of of quartz-feldspar quartz-feldspar porphyry porphyry roughly on and are roughly on strike strike from, from, and and about about400 400m m of, aaquartz-feldspar quartz-feldspar porphyritic porphyritic dike to the east of, dike that was dated at either 2684 Ma Ma or 2695 Ma (geochronological (geochronological problems not not resolvable; resolvable; Corfu and Muir Muir 1989a). 1989a). Note that the more more felsic dikes, dikes, in particular, to have infelsic particular, appear appear to intruded the the altered, truded altered, pyritized, pyritized, and and minermineralized(?) country rocks. rocks. It is not clear whether the dikes could could have have undergone undergone the same same alalteration history teration history as the country rocks, rocks, but reacted to itit differently differently because because of of chemical chemical and and rheological properties. The The same same problem problem has been 13and and21. 21. been addressed addressedfor for Stops Stops13 A few few of of the thedikes dikeshave haveundergone undergone boudinage. F3 boudinage. F3folds folds with with axial axial planar planarS3 S3 crecrenulation cleavage occupy many of the the necks. necks. The The more mafic dikes display display the effects effects of of ductile, dextral ductile, dextral shear. shear. quartz is abundant in the exNon-primary quartz posure whole. It occurs occurs as: dike-like dike-like zones posure as aa whole. of silicification; irregularly shaped silicification; irregularly shapedzones zones assoassociated with intense intense feldspathization feldspathization and very fine-grained fine-grained molybdenite; molybdenite; zones zones of of numerous, numerous, thin stringers stringers parallel to the main main fabric (Photo 16); local local areas areas of of brecciated brecciated country country rock rock with with a quartz quartz matrix matrix (Photo (Photo 16); 16); and and two two or or more more generations of quartz veins, generations of veins, some some of of which which show considerable shortening shortening due due to to buckling. buckling. �Geology Geology and Gold Deposits Deposits of the Hemlo Hemlo Area 100 100 northwest-striking set set of ofnorthwest-striking northwest-striking veinA northwest-striking setof of dextral dextralsense sense faults faults is is present presentas as is is a set veinlike alteration alteration zones. involved intense, intense, fracture-controlled fracture-controlled feldspathizzones. These Theseveins veins appear appear to have involved feldspathization, possibly albitization (i.e., which overprinted overprintedthe thesericitization. sericitization. In irregularly (Le., not microcline)which defined, specific zones, north-striking set defined, but but specific zones, there there is is an almost north-striking set of closely spaced fractures. There There are also relatively relatively late late northeast-striking, northeast-striking,sinistral sinistraland anddextral dextralfaults. faults. Structural Structural Summary: Summary: various fabrics - sericite sericite sericite sericite sericite (locally sericite (locally within withinAV AV 320°) 320') sericite; crenulation sericite; crenulation fabric fabric sericite sericite crenulation fold axis —074/51 074151 alteration 320' vein-like alteration 262°, 27g0, 279°, 292°, 262O, 292O,320° relatively early fracture sets (with without displacement) early fracture (with or without displacement) 260°, 311/70 260°311/70 relatively late late fracture fracture set (with (with or without without displacement) displacement) 004/77 210/61 004177 210161 relatively S8 2700 S3? S3? 282° 282' 290/70 290170 264/82 264182 258/80 258180 sa sSbb Sd % sS33 F3 F3 AV CE CE CL CL 270 , within mafic Fabrics within mafic dike: dike: s3~ 3c s3~ s3e Sac- S3S LS 1.8 Vq vq b L9 chlorite chlorite chlorite chlorite chlorite chlorite slickenside 102/10 1OZlO slickenside orientation (steeply dipping) dipping) 000°, 000°020°, 020°060°, 060°090° O W 0 generalized quartz vein orientation glacial striation 236° 236O glacial striation 273/70 27W70 284/69 284169 308/75 308175 Stop 35: Stop 35: WEST WESTCCZONE ZONEOUTCROP OUTCROP(Figures (Figures18 18 and 48) Location: About 200 m Location: m west-northwest of the the East East C C Zone Zone outcrop. outcrop. quartz-feldspar-phyric, This outcrop outcrop consists consists of of metamorphosed metamorphosed and notably notably altered: altered: quartz-feldspar-phyric, heterolithic fragmental rocks, many of which have the characteristics of lapilli-tuff, lapilli-stone, and heterolithicfragmental rocks, many which the characteristics tuff (Photo 17); volcaniclastic(?) granule granule and and pebble pebbleconglomerate; conglomerate;and andwacke. wacke. A few of the 17); volcaniclastic(?) the contacts are well welldefined, defined,sharp, sharp, and andfolded. folded. Some contacts between between subunits subunits of lapilli-stone lapilli-stoneand lapilli-tuff are of the quartz-feldspar-phyric quartz-feldspar-phyric rocks rocks may may be be intrusive intrusive (subvolcanic?) (subvolcanic?) porphyry. Remnant layering layering in in the the country rocks Remnant rocks (Photo (Photo 18), 181, where identifiable, identifiable, commonly commonly strikes northeast displays S-shaped northeast and and displays S-shaped asymmetric folds. The The predominant predominantfabric, fabric, which which is is considered considered to be S2, is is clockwise clockwise to to the the layering. layering. This indicates indicates that there there is is either either another another fold fold axis axis south south of the major northwest-closing fold centred on the Williams property (Figure 19), or that tectonic Williams (Figure 19), that tectonic crust have have resulted resulted in in this this configuration. configuration. There are also juxtaposition of segments of the upper crust displacements of layering, numerous displacements layering, up to a few metres apparent magnitude, along the predomipredomifabric, which which has resulted resulted in aa very very blocky blocky configuration configuration of rock rock types types in places. places. There are a nant fabric, few north-northwest north-northwestand and west-northwest-striking, west-northwest-striking,dextral dextral faults faults and and east-northeast-striking, east-northeast-striking,sinissinistral faults. faults. Stop 35: Figure (opposite page) Stop Figure 48. 48. (opposite 35: Detailed Detailed sketch map of part part of the the C C Zone, Zone, west west end end (Williams property), property), showing showing variably variably altered, altered, folded, folded, faulted, faulted, and discordant blocks of (Williams of metametapyroclastic rocks and rocks intruded intruded by several dikes of and metavolcaniclastic/metasedimentary metavolcaniclastic/metasedimentary rocks various compositions. compositions. Vein-like shear-controlled alteration/mineralization alteration/mineralization overprints Vein-like and and fault- or shear-controlled earlier pervasive alteration/mineralization. alteration/mineralization. (After (AfterMuir Muir1989). 1989). �Stop Stop Descriptions Descriptions — -Hemlo Hemlo Deposit: Deposit:Williams Williams Property Property Overburden Overburden DIKES, DIKES,VEINS VEINS Diabase Diabase INTRUSIVE INTRUSIVECONTACT CONTACT Quartz Quartzveins, veins, stringers, sthgers, knots knots 11111111 llIlllll Biotite Biotitegabbro gabbro PIaocIase Ptadoclaseporphyry m y r y b\\F Granodiorite Granodiorite INTRUSIVE INTRUSIVECONTACT CONTACT Fragmental Fragmentalrocks rocks (pyrocIastic (pyroclastic,volcaniclastic) vdcaniclastic) aa coarse coarse bb medium mediumtotofine fine Granule Granule to to pebble pebbleconglomerate conglomerate Wacke Wacke 101 SYMBOLS SYMBOLS ALTERATION ALTERATION (vein-like) (vein-like) ...... Feldspathization Feldspathization(and/or (andlorsilicification?) silicification?) -* Sicification, Siliiification,molybdenite molybdenite Feldspathization, Feldspathization,pyrite pyrite(±(tAu?) Au?) — Iron carbonate Iron carbonate FAULTS FAULTS (ductile (ductile and/or andlwbrittle) brittle) .-& . - Senseof ofdisplacement &splacementknown known Sense Planarschistose schistosezones zones—sense -sense unknown unknown Planar BEDDING BEDDING - Internal Internalbedding bedding Unit contact contact Unit �102 102 Geology and Gold Deposits Deposits of the Hemlo Area Pervasive alteration is in the the form form of offeldspathization feldspathization and andbiotitization. biotitization. Some Some of the layering to be selectively feldspathized. Vein-like alteration alteration is is in the form of appears to feldspathized. Vein-like of feldspathization feldspathization (albitization?), carbonatization, pyritization, and silicification. Molybdenite Molybdeniteisislocally locallyassociated associated feldspathization±silicification. The with the vein-like feldspathization~silicification. The "veins" "veins" are are collectively collectively oriented oriented with with prepreferred strikes of about 250°, 290°. which which have been been locally locally dextrally dextrally offset. offset. Sizeable 250°270°, 270°and 290° Sizeable quartz veins are uncommon but but there there are are numerous numerousquartz quartz knots. knots. A few of these knots show of the the country country rock with with associated development of coarse-grained coarse-grained adjacent, incipient bleaching of muscovite in dilational zones. Gold distribution but muscovite Goldmineralization mineralizationisissporadic sporadicin in grade grade and and distribution but is is most associated with molybdenite this outcrop. outcrop. About 100 m east-northeast east-northeast commonly associated molybdeniteand/or andlor pyrite in this was aa small small exposure exposure containing containing sugary sugary textured barite, pyrite, and of the West C Zone outcrop was and possibly molybdenite. molybdenite. Three types of dikes, which are presently presently foliated, foliated, have have intruded intruded the the country countryrocks rocksand andare are parallel or subparallel to the predominant fabric. An unfoliated Archean diabase dike crosscuts parallel subparallel to the predominant fabric. unfoliated Archean diabase crosscuts all the rock types on the west side of the exposure. Structural Summary: Structural Summary: 250/72 S0/S1 sds~ 250172 parallel to to long dimension of 260/77 S2 s2 260177 parallel long dimension of fragments fragments (horizontal (horizontal surface) surface) 050°, axial planar folds S3 s3 050°080° 080' axial planar to to F3 F3 folds 270/55, 290/73 vein-like alteration; alteration; most AV Avf 270155, 290173 vein-like most are are feldspar feldspar rich rich 260/75, 280/75, 300/74 vein-like alteration; alteration; some some are are carbonate carbonate rich rich AV AVC 260175, 280175,300174 vein-like 265°-290° planar o C 265'-290 planar schistose schistose zones (with (with or or without withoutapparent apparentdisplacement); displacement); some are associated associated with pyrite molybdenite ± silicification? silicification? pyrite ± Au?, some with molybdenite elongation lineation 328/58 b 3281% elongation lineation of fragments I.e rare, relatively 070° '4 070 relatively long long quartz quartz vein vein orientation orientation Vq * * �103 I03 References References 8: REFERENCES PART 8: REFERENCES Bartley, 1957AAgeological geological report report on on the the Hemlo Hemlo area, area,Thunder Thunder Bay Bay District; District; unpublished unpublished Bartley, M.W M.W. and andPage, Pagel T.W. 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Hemlo-a Hemlo-a golden golden difference; difference; Thunder Thunder Bay Bay Field FieldNaturalists' Naturalists'Newsletter, Newsletter,v.39, v.39, no.4, no.4, November, November,1985, 1985,p.2-6. p.2-6. Patterson, files, SchreiberPatterson,G.C. G.C. 1986. 1986. Report Report on on the the Lytton LyttonMinerals MineralsLimited Limitedproperty, property,Resident ResidentGeologist's Geologist'sfiles, SchreiberHemlo Hemlo District, District,Thunder ThunderBay, Bay,6p. 6p. Quartermain, Quartermain,R. R.1985. 1985.Road Roadguide guideto tothe thegeology geologyofofthe theTeck-Corona Teck-CoronaMine MineatatHemlo, Hemlo,Ontario; Ontario;ininGold Goldand and copper-zinc copper-zinc metallogeny rnetallogeny within withinmetamorphosed metamorphosedgreenstone greenstoneterrain, terrain,Hemlo-ManitouwadgeHemlo-ManitouwadgeWinston WinstonLake, Lake, Ontario, Ontario, Canada, Canada, joint publication publication of of Geological Geological Association Association of of Canada Canadaand andCanaCanadian dian Institute InstituteofofMining Miningand andMetallurgy, Metallurgy,p.39-46. p.39-46. Roland, Roland, W. W. 1887 Algoma west: Its Itsscenery sceneryand andindustrial industrialresources; resources;Warwick Warwickand andSons, Sons,Toronto, Toronto, Ontario. Ontario. Siragusa, geology, White White Lake Lake area, area, western western part, part, District of Thunder Siragusa, G.M. 1984a. 1984a. Precambrian geology, Thunder Bay; Bay; Ontario OntarioGeological GeologicalSurvey, Survey,Preliminary PreliminaryMap MapP2701, P.2701,scale scale1:15 1:15840. 840. Siragusa, Siragusa,G.M. G.M. 1984b. 1984b.Precambrian Precambriangeology, geology,White WhiteLake Lakearea, area, eastern easternpart, part,District Districtof of Thunder ThunderBay; Bay;Ontario Ontario Geological 1:15840. 840. GeologicalSurvey, Survey,Preliminary PreliminaryMap MapP.2702, P.2702,scale scale1:15 Siragusa, Siragusa, G.M. G.M. 1985a. 1985a. Precambrian Precambriangeology, geology, White White Lake Lake area, Animons Lake Lake section, section, District Districtof of Thunder Thunder Bay; 1:15 840. 840. Bay; Ontario Ontario Geological GeologicalSurvey, Survey,Preliminary PreliminaryMap MapP2739, P.2739,scale scale1:15 Siragusa, 1985b. Precambrian Precambrian geology, White Lake area, Theresa Lake section, District of Thunder Thunder Siragusa, G.M. G.M. 1985b. Bay; Bay; Ontario Ontario Geological GeologicalSurvey, Survey,Preliminary PreliminaryMap MapP2738, P.2738,scale scale1:15 1:15 840. 840. Schnieders, Schnieders, B.R., B.R., Smyk, Smyk, M.C. M.C. and andWhite, White,G.D. G.D.1988; 1988;ininReport ReportofofActivities Activities1987 1987Resident ResidentGeologists, Geologists, Ontario Paper 138, p.135-159. OntarioGeological GeologicalSurvey, Survey,Miscellaneous Miscellaneous Paper 138, p.135-159. Smart, lithologicalstudy studyalong alongthe theHemlo Hemlofault; fault;unpublished unpublishedBSc BScthesis, thesis,Queen's Queen'sUniversity, University, Smart, PP.1988. 1988.AAlithological Kingston, Kingston,Ontario, Ontario,43p. 43p. Smyk, Smyk,M.C., M.C., Schnieders, Schnieders,B.R. B.R.and andMuir, Muir,T.L. T.L. 1990. 1990. Field Fieldtrip trip guide guideto to the the Hemlo Hemloarea; area;ininMineral Mineraldeposits depositsinin thewestern westernSuperior SuperiorProvince, Province,Field Fieldtrip trip99guidebook, guidebook,8th 8thIAGOD IAGODSymposium, Symposium,Ottawa, Ottawa,August, August, the 1990; 1990;p.26-38. p.26-38. Strickland, Strickland,H.M. H.M. 1979. 1979. Silver Silver under under the sea: sea: The Thestory storyofofthe theSilver SilverIslet IsletMine Minenear nearThunder ThunderBay, Bay,Ontario, Ontario, Canada; Canada;Highway HighwayBook BookShop, Shop,Cobalt, Cobalt,Ontario. Ontario. Thomson, Thomson,J.E. J.E.1931. 1931. Geology Geologyof of the the Heron HeronBay Bay area, area, District Districtof of Thunder ThunderBay; Bay; Ontario OntarioDepartment Departmentof ofMines, Mines, Annual AnnualReport, Report,v.40, v.40,pt.2, pt.2,p.21-39. p.21-39. Thomson, Thomson, J.E. J.E. 1933. 1933. Geology Geology of of the the Heron HeronBay-White Bay-White Lake Lake Area, Area, District District of ofThunder ThunderBay; Bay;Ontario Ontario Department DepartmentofofMines, Mines,Annual AnnualReport, Report,v.41, v.41, pt.6, pt.6,p.34-52. p.34-52. Valliant, Valliant, R.I., R.I., Guthrie, Guthrie, A., A., Bradbrook, Bradbrook, C., C., Motzok, Motzok, A., A., Mcllveen, Mcllveen,D., D., Kent, Kent,J., J., MacMillan, MacMillan,G., G.,Skrecky, Skrecky, G., G., Wingfield,T. T. and andSheehan, Sheehan,D.G. D.G. 1985. 1985.Field Fieldguide guide to to geological geologicalsetting settingofofLac LacMinerals MineralsLtd. Ltd.pyritic pyritic Wingfield, gold gold orebodies, orebodies, Hemlo HemloOntario; Ontario;ininGold Goldand andcopper-zinc copper-zincmetallogeny metallogenywithin withinmetamorphosed metamorphosed greenstone terrain, terrain, Hemlo-Manitouwadge-Winston Hemlo-Manitouwadge-Winston Lake, Lake, Ontario, Ontario, Canada, Canada, joint joint publication publicationofof greenstone Geological GeologicalAssociation AssociationofofCanada Canadaand andCanadian CanadianInstitute InstituteofofMining Miningand andMetallurgy, Metallurgy,p.47-57 p.47-57 Valliant, Valliant,R.I. R.I. and andBradbrook, Bradbrook,C.J. C.J.1986. 1986.Relationship Relationshipbetween betweenstratigraphy, stratigraphy,faults faultsand andgold golddeposits, deposits,PagePageWilliams Mine, Mine, Hemlo, Hemlo, Ontario, Ontario, Canada; Canada; ininProceedings ProceedingsofofGold Gold'86, '86,Toronto, Toronto,Ontario, Ontario,1986, 1986, Williams p.355-361. p.355-361. Walford, of the Zone, Page-Williams P., Stephens, Stephens,J., J.,Skrecky, Skrecky,G. G.and andBarnett, Barnett,R. R.1986. 1986.The Thegeology geologyof the"A' %'Zone, Page-WilliamsMine, Mine, Walford,P., Hemlo,Ontario, Ontario,Canada; Canada;ininProceedings ProceedingsofofGold Gold'86, '86,Toronto, Toronto,Ontario, Ontario,1986, 1986,p.362-378. p.362-378. Hemlo, Walford, Walford, P.C., PC., Weicker, R. R. and Guthrie, Guthrie, R. R. 1986. 1986. The Page-Williams Page-Williams property; property; in inThe The Hemlo Hemlogold golddeposits, deposits, Ontario; Ontario;Field FieldTrip Trip4: 4: Guidebook, Guidebook,Geological GeologicalAssociation AssociationofofCanada-Mineralogical Canada-MineralogicalAssociation Associationofof Canada-CanadianGeophysical GeophysicalUnion, Union,joint jointannual annualmeeting, meeting,May May1986, 1986,Ottawa, Ottawa,Ontario, Ontario,p.53-62. p.53-62. Canada-Canadian Williams, Subprovince; inThe geology Williams,H.R., H.R.,Heather, Heather,K.B., K.B.,Muir, Muir,T.L., T.L., Sage, Sage,RP. R.P.and andStott, Stott,G.S. G.S.1991. 1991. Wawa Subprovince; inThegeology of ofOntario, Ontario,Ontario OntarioGeological GeologicalSurvey, Survey,Special SpecialVolume Volume4,4,Part Part1,1,p.485-539. p.485-539. �107 PART PART 9: PHOTOGRAPHS PHOTOGRAPHS Photo 19,23). 23). Highly strained (mylonitized) aplite dike within virtually Photo1:1: STOP 6 (Figures 18, 19, unstrained biotite biotite granodiorite. Aplite Aplitelocally locallydisplays displaysribbon ribbonquartz. quartz. Fabric Fabricisislikely likelyS3. S3. unstrained Photo 19,21,24). Turbidite Photo2: 2: STOP STOP88 (Figures (Figures18, 18,19,21,24). Turbidite(top (topand andbottom bottomoutlined outlinedininpart partby bywhite whitelines lines at at left) left) consisting consisting of of aafeldspathic feldspathic arenite arenitebottom bottompart part(lower (lowerpart partofofphoto), photo),aafeldspathic feldspathicwacke wacke middle middle part, part, and and aa laminated laminated (not (not clearly clearly visible visible ininthis thisphoto) photo)uppermost uppermostpart. part. View View toward toward northeast. northeast. �108 Geology and Gold Deposits of the Hemlo Area (Figures 18, 18, 19, 19,21). 21). Moderately strained conglomerate in Photo 3: STOP 11 (Figures in two two well-defined well-defined Photo 3: units units (left and and right right sides sides of of photo) photo) and and one one ill-defined ill-defined unit unit (near (near centre) centre) entrained entrained within within feldspathic wacke (centre). Main structuralfeatures are indicated. Scale card outlined at centre is Main structural features are indicated. Scale card outlined at 9 cm long. View View toward toward northwest. northwest. �, Photographs 109 109 Photo 4: STOP 17 (Figures 18, 19, 21). Variably altered, highly strained, quartz-(feldspar)Ph )ar)phyric fragmental from stained OT potassium poiassium feldspar, relaspar, as evident eviaent Trom stainea slab sIaD face, race, ~ragmeniairock. rocK. Distribution uisiriDuiion of appears to have been partly controlled by the presence of fragments fragments and and cleavage cleavage planes. planes. C = deformed clast. QE deformed clast. QE == quartz quartz eye. eye. MM= =microcline-rich microcline-richzone. zone. P = = pyrite-rich pyrite-rich zone. zone. Some Some concentrations concentrations of of potassium potassium feldspar feldspar are are oval oval and enigmatic enigmatic (E). (E). �110 Geology and Gold Deposits of the Hemlo Hemlo Area STOP 20A (Figures (Figures 18, 18, 19, 19, 21, 21, 30). 30). Highly strained, feldspathized and and Photo 5: 5: (above) (above) STOP sericitized are indicated. sericitized fragmental fragmentalrockfrom rock fromthe theMain Mainmineralized mineralizedzone. Main Main structural structural features featuresare indicated. This rock may be the feldspathized equivalent of of a biotite-predominant conglomerate or biotite fragmental unit, spatially Hemlodeposit deposit(see (seeMuir Muir1993). 1993). spatially associated associatedwith with the theHemlo (Figures 18,19,21,33). 18, 19, 21, 33).General General view view of of the the western western Photo 6: (opposite page, top) STOP 21BB(Figures Photo (opposIte page, half of the A Zone as seen seen before before open open pit pit mining. mining. View toward west. west. Generalized Generalized Zone orebody, orebody, as from left to to right: A — footwall, footwall, partly partly microclinized, descriptions of major units in the photo are, from quartz-plagioclase porphyry; — feldspathized metasedimentary metasedimentary quartz-plagioclase porphyry; B B— -plagioclase-phyric plagioclase-phyric dike; C — structurally lower, sericitized, and pyritized lower, rusty-weathering, rusty-weathering, microclinized, sericitized, pyritized rocks rocks rocks; D (ore), likely derived from metasedimentary E— -variably variably feldspathized feldspathized and andschistose schistose (ore), metasedimentary rocks; E wackes; F feldspathized, sericitized, sericitized, pyritized schists F— -structurally structurally upper, upper, rusty-weathering, rusty-weathering, feldspathized, schists (ore), derived derived from metasedimentary rocks; G — hanging wall, mixed wacke, siltstone, metasedimentary rocks; G - hanging wacke, siltstone, and amphibole-rich layers amphibole-rich layers (Figures 18, 18, 19, 19,21, 21,33). 33). View of main part part of of Photo 7: (opposite (opposite page, page, bottom) bottom) STOP 21 BB(Figures orebody showing showing aa dioritic dioritic dike swarm that that intruded a mineralized pseudobreccia pseudobreccia(ore). (ore). The orebody (PBX) is enhanced enhanced by differential weathering of of highly altered and pseudobreccia (PBX) and tectonized tectonized rocks. The lenses consist mostly of feldspathized rockand the matrix is largely granularpyrite largely granular pyrite with rocks. The lenses consist mostly of feldspathized rockand atbottom some biotite. Dikes Dikesare are partly partly indicated indicated by by dashed lines at bottom of photo. Scale Scale card card outlined at centre left left is is 9 cm long. View View toward toward east. east. à �Photographs Photographs 111 �112 112 Geology Geology and and Gold Gold Deposits Deposits of of the the Hemlo Hemlo Area Area (Figures 18,19,21,34). 18, 19,21,34). Subtle folding and transposition transposition (enhanced Photo8: STOP STOP 22A (Figures Subtle folding (enhancedby by acidacidPhoto etched, sawn hand specimen surface) in layered, layered, magnetite-rich, magnetite-rich, feldspathic feldspathic wacke, wacke, located located between the Main Main mineralized mineralizedzone, and and the the Lower Lower mineralized mineralizedzone. zone. �Photographs 113 113 I I I I Photo 9: STOP 25A (Figures 18, 19, 21, 38). Gneissic feldspathic metasedimentary/ rocks Pht rocks displaying spaced cleavage. Quartz disp1cty11 lY tectonometamorphic LGUUI IUI I I G L ~I IUI I [JI IILlayering IC~YGI11 19and ctl IU layer-parallel 1ctp1-pct1 ~~IIG apct~eu I LIGC~VC~YG. UUC~I LL gash ydbl I infilling indicated (Qz). North Northtoward toward top top of of photo. photo. �Geology and Gold Deposits of the Hemlo Area folded mafic schist, STOP 25A (Figures (Figures 18, 18, 19, 19, 21, 21, 38). 38). Polyclinally Polyclinally folded schist, gneissic gneissic Photo 10: 10: STOP amphibolite, and and subporphyritic subporphyritic granitic granitic dikes dikes within within the Hemlo amphibolite, Hemlo fault fault zone. zone. S3 crenulation cleavage collectively as indicated indicated by by dashed dashed lines. lines. Folding Folding may may collectively fans fans over over a range of about 125°, 125O, as with attendant attendant crumpling crumpling or folding of units and have resulted from a detachment along a plane with fabrics. Hammer North toward toward top of photo. existing fabrics. Hammer is 40 cm long. North �Photographs 115 115 Photo 11: STOP 27 (Figures 18, 40). Moderateiy to strongly deformed possibly altered, felsic, Pho slsic, quartz-plagioclase-phyric lapillistone. Most fragments are similar in composition and texture. A , e . A quat.- r.-a .--.--- -I - - - - -r - - - few lenses are composed composed of quartz quartz (Qz) (Qz) and and may may represent represent accidental, accidental, fragmented fragmented quartz quartz or or tectonically dismembered quartz quartz veins. North Northtoward towardtop topof ofphoto. photo. J -9 �Geology and Gold Deposits of the Hemlo Area 116 116 Photo 12: (above) STOP 32 (Figures 18, 19, 21, 44). Back 40s outcrop, south half. Zone of PI tectonic disruption, by lines LCII canI be teuiui iiti UULIII ICU v long-dashed lui uc traced 11aucu around aiuui IU large-scale la1UG-ouaic fold IUIU on un - uiai - - uuiiui -,-- - I. outlined - - -- u -, - iu-uaai - - - icu - - mica Williams and is is aa Dl D1or or Do D0feature. feature. Main Main structural structural features features 2are W i l kims property (Figure 19), and ire indicated. Gabbroic View toward toward west. west. Gabkxoic dikelet outlined by short-dashed lines. View d 3 4 ---- - n - I-----:A.R c ~ n onn n ~ r ' : - . . ~ -4 -n 4 n n 4 A C \ I I--:L--STOP 33A irlyuies (Figures 18, 19,, L21,45). Heritage easi east uutcrop, outcrop, south south i ur oort 10, w I , 43). neiiiciye Photo (opposite page, A&-\ top) Photo 13: 10: \uppusiie iup; o half. Outcrop Outcrop almost almost entirely covered covered over now. now. View to east-southeast. Squiggly Squiggly lines lines represent faults. Width Widthof of visible visible outcrop outcropisis about about 15 15 m. Generalized Generalized descriptions descriptionsofofnotable notablesegments segmentsininthe the photo are, from right to to left: left: A A -footwall, — footwall, partly partly microclinized microclinized and andsericitized, sericitized, quartz-plagioclase quartz-plagioclase porphyritic displaying fraaments: fragments;BB—variably metasedimentary rocks; porohvritic rock, rock. locally locallv -variably feldspathized metasedimentarv .disolavina C -— transposed, microclinized and possibly silicified metasedimen1structurally lower gossan of transposed, metasedime!ntary contents; D — zone similar similarto exceptwith rocks, locally locally with with molybdenite molybdeniteand and ore-grade ore-grade gold gold contents; D -zone to C except wiith tan/ rocks, b - : -. E E A $ f n l A / t f t ' - i + h I - ~ n / "//-*-AIr\r)\ i n n r 4 l-\!n+!+!-~nArn-l^(t more- uudi quartz veins; central zone of teldspathized and rocks LL v e i n s L-— LEI I L I ~ LUI I ic ui icluauaii IILGU I(sodic?) Q U U I ~i :ai iu Ubiotitized I~LILILGU iuuno with vviii I numerous I iuiiiciuUS mOie -- deformed quartz veins; F-zone F— zone of of variably variablyand andrelatively relativelyweaklyfeldspathized weaklyfeldspathized metasedimentary metasedimentary def ormed quartzveins; rocks; —structurally upper weathering, feldspathized, feldspathized, metasedimentary rocks; upper gossan of rusty weathering, ks; G -structurally roc I1 ..-..:-I-!.. --A --A k:-&:&:--A--b--~A:-~-b-w., B.--I.— hanging...wall, variablyanu and--l-b:.,-l.. relativelyI--lessC-lA---bk:--A feldspathized and metasedimentary rocks H -iianging wail, vanauiy ~eiaiivt!iy lea^ ie iuq~aini~a e1 uIU ubiotitized ~ u i m ~ ie i~ u e i a ~ e u ~iiai i i i ye IUL>I\S> ~ m B a - - ~a,!+hr^ia^^r-tnrn n m + v < - t l "rnnn . -I--- - ? - I----:-- - , . ....au west ...,".outcrop. ~~tcrop. STOP w33B (Figures 18, 19, 21, ,46). Heritage w,a-a page, Photo 14: m-r. t(opposite wppwen puy-, bottom) w of tiaht tight FF2 fold fold disolavina displaying"horsetail" "horsetail"structure structure and andtransoosed transposed laverina. layering. Darker Darker layers lavers are Nose of 6- wubbummm, m - v \n v w 0 - 9 8 u, 4, amphibole rich. Main structural features are indicated. Dismembered quartz vein outlined by ar dashed lines. d< �I -I. -L Cl, V 0 0 (0 -' Photographs �118 Geology and Gold Deposits of the Hemlo Hemlo Area 19, 21, 21,47). 47). C C Zone Zone east east outcrop. outcrop. Pervasively Photo 15: Pervasively feldspathized Photo 15: STOP 34 (Figures 18, 18, 19, quartz-plagioclase-phyric Arrows indicate some of the quartz-plagioclase-phyric rock rock (tuff/lapitli-tuff?). (tuffllapilli-tuff?). Arrows the many, many, variably variably discernible fragments. Lens green muscovite muscovite indicated indicated (Gm). (Gm). Scale Scale in centimetres. centimetres. North discernible fragments. Lens of green North toward top of photo. photo. �I I I I Photographs Photographs 119 ENTIMETRES Photo16: 16: STOP STOP 34 34 (Figures (Figures 18, 18, 19, 19,21,47). Feldspathizedand and possibly possibly Photo 21, 47). C Zone Zone east east outcrop. outcrop. Feldspathized partlysilicified silicifiedquartz-plagioclase-phyric quartz-plagioclase-phyricrock rockwith with numerous numerous quartz quartz stringers stringers (OS) (QS) and and breccia breccia partly (QBX) consisting of angular country rock fragments within Northtoward toward top top of of (QBX) within aa quartz quartz matrix. matrix. North photo. photo. �120 120 Geology and Gold Deposits of the Hemlo Area 35 (Figures 18, 19, 19,21, 21,48). 48). C C Zone Zone west west outcrop. outcrop. Variably feldspathized Photo 17: Photo 17: STOP 35 feldspathized and and biotitized, quartz-plagioclase-phyrictuff-breccia. tuff-breccia. Strain Strainisismoderate moderatebut butlower lower half half of biotitized, heterolithic, heterolithic,quartz-plagioclase-phyric near-dip-face plane plane thereby thereby masking the the degree degree of offlattening. flattening. View toward south. Scale photo is a near-dip-face Scale card is 9 cm long. 35 (Figures (Figures 18, 18, 19, 19,21, 21,48). 48). C C Zone Zonewest westoutcrop. outcrop. Folded feldspathic wacke Photo Photo 18: 18: STOP 35 (outlined quartz-plagioclase-phyric lapilli-tuff lapilli-tuff(top (topand andbottom). bottom). (outlined by dashed lines) separates units of quartz-plagioclase-phyric Clasts are aligned parallel to to So. S2. All All units units are arefeldspathized feldspathized to tosome somedegree. degree. North towards right of of photo. Hammer 40 cm cm long. long. Hammer(beside (besidescale scale card) card) isis40 �Mafic Metavolcanics 1 1 Metavolcanics 7 Metaconglomerate 7 Metaconglomerate 2 Mixed MixedMafic—Felsic Mafic-Felsic Gneissic Gneissic Rocks Rocks 8 8 Metawacke Metawacke with with Magnetite Magnetite Layers Layers 3 3 Felslc FelsicQuartz—Feldspar Quartz-Feldspar Metaporphyry Metaporphyry and Metapyroclastics Metapyroclastics and 4 Intermediate Intermediate to to Mafic, Mafic, coarse Metavolcaniclastics Metavolcaniclastics 5 Intermediate, medium to coarse coarse Intermediate, medium to MetavolcafliClastics ~etavolcaniclasti~~ 9 9 Metawacke/turbidite Metawackelturbidite 10 10 Metasiltstone/Pelite MetasiltstonelPelite 11 Meta-arkose 1 1 Meta—arkose -"n. • A a - Lithotectonic Contact Lithotectonic Contact Fold Axis Fault/shear Faultlshear Field Stop Field Stop (Numbered) (Numbered) Headframe Headframe 12 Granodiorite 12 Granodiorite / Diabase Diabase 6 Feldspathic Feldsoathic Metavolcaniclastics Metavolcaniclastics Figure 19. Simplified geological Figure 19. Simplified geologicalmap mapof ofthe the Hemlo Hemlodeposit depositarea, area,covering coveringSTOPS STOPS77to to26, 26, and and32 32 to 35. Units Unitsshown shownrepresent representlitho-tectonic litho-tectonicunits: units:that thatis,is,each eachunit unitdepicts depictsaavariety varietyofofsimilar similarrock rock be simple to complex complex internal internal structures which, which, in some some cases, cases, appear appear to be types displaying simple independentof of the the adjacent adjacentunits. units.(Geology (GeologybybyT.L. T.L.Muir, Muir,1985-1990). 1985-1990). independent � https://digitalcollections.lakeheadu.ca/files/original/ea1eccc25b4d3d1f273041ef65d84b32.pdf d2761042fa5199cca6962ebf6395a06d PDF Text Text Kim berlite, Base Metal and and Gold Gold Exploration Kimberlite, Exploration Using Overburden, Overburden, Wawa WawaArea Using Institute Instituteon onLake LakeSuperior SuperiorGeology Geology 41st 1995 41st Annual AnnualMeeting, Meeting,May May13-18, 13-18,1995 Marathon, Marathon, Ontario Ontario Proceedings ProceedingsVolume Volume 41: 41: Part Part2e 2e Field Field Trip TripGuidebook Guidebook �Kimberlite, Base Metal and Gold Exploration Using Overburden, Overburden, Wawa Wawa Area by Tom F. Morris Morris Sedimentary Sedimentary Geoscience Geoscience and and Geochemistry GeochemistrySection Section Ontario OntarioGeological GeologicalSurvey Survey Ministry Ministry of of Northern Northern Development Development and and Mines Mines 7th Floor, 933 7th Floor, 933 Ramsey Lake Road Sudbuiy, Sudbury, ON ON P3E P3E 6B5 6B5 Frontispiece: 1500(after (afterAgricola Agricola1556, 1556,p.323, p.323, Frontispiece:Sluicing Sluicingoperation operationcirca circa1500 reproduced Mining Journal, Journal, February, reproduced from the the cover of Canadian Mining February,1975) 1975) �I TABLE OF CONTENTS BACKGROUND INFORMATION Introduction History of Quaternary Geology Mapping, Wawa Area Wawa Quaternary Geology Project Michipicoten River- Wawa Quaternary Geology Project Physiography Topography Drainage Basin Characteristics Climate and Vegetation Regional Geology Bedrock Geology Quaternary Geology Time Frame Ice Advance Ice Flow Indicators Material Subglacial Till Ice Retreat Bedrock Features Materials and Related Landform Flow Till and Related Landform Glaciofluvial Materials and Landform Glaciolacustrine Materials and Landform Flow Till, Glaciofluvial and Glaciolacustrine Materials as Media for Drift Prospecting Recent Deposits Eolian Deposits Colluviurn Older Alluvium Modern Alluvium Eolian Deposits, Colluvium, Older Alluvium and Modern Alluvium as Media for Drift Prospecting. Overburden Sampling Methodologies Sampling Design Material Sampling 1 1 1 4 5 5 5 5 6 6 9 9 10 10 10 10 11 11 11 11 12 12 .14 .14 14 14 14 14 15 15 15 16 Field Trip Introduction Site * 1: Introductory Overview Site DrivetoSite*2 2: Pothole, Mafic Volcanic Rock, Lamprophyre Dyke Drive to Site * 3 Site * 3: Lodgement Till Section Site 4$ Soil Weathering Subglacial Till as a Media for Drift Prospecting. DrivetoSitejt4 Site 4$ 4: Proglacial Outwash Section... DrivetoSitelt5 17 18 18 19 19 20 20 23 28 28 28 �Table of Contents (Continued) Field Trip (Continued) Site ft 5: Moraine and Ice-Contact Stratified Drift Drive to Site ft 6 Site * 6: Minong Delta Drive to Site U 7 Site ft 7:kame and Kettle (Dead Ice) Topography Drive to Site ft 7A Site ft 7A: Modern Alluvium, Ice Margin Deposit Sampling Modern Alluvium Restrictions of Stream Sediment Sampling. Drive to Site U S Site U 8: Mink Lake Glaciofluvial Fan, Striae and "P" Forms Drive to Site U 9 Site * 9: Older Alluvium Section.. Drive to Site ft 10 Site ft 10: Glaciolacustrine Section. 30 32 32 33 33 33 34 34 36 36 38 39 40 41 41 Drive to Site ft 11 Site U 11: Steephills Falls Moraine. Drive to Site ft 12 Site ft 12: Summary Site 43 43 44 44 ACflOWLEDGENTS 45 REFERENCES 45 List of Figures Figure 1: Location Figure 2: Wawa and Michipicoten River- Wawa Quaternary Geology Project Locations Figure 3: Regional Bedrock Geology Map Figure 4: Wawa Area Geology Map Figure 5: Distribution of Glaciofluvial Meitwater Channels Figure 6: Lodgement Till Section Figure 7: Location of Till Sampling Transects Figure 8: Mall Lake Dispersal: small local target Figure 9: Wawa Lake Dispersal: larger, regional target Figure 10: Black Trout Lake Dispersal: topography shadow Figure 11: Proglacial Outwash Section Figure 12: Ice Contact Stratified Drift Section Figure 13: Scott Lake Moraine Section Figure 14: Sampling Modern Alluvium Within Drainage Basins Figure 15: Glaciolacustrine Section 2 3 7 8 13 21 24 25 26 27 29 31 35 37 42 APPENDICES Appendix A: Route Maps Appendix B; Site and Material Observation Sheets MAPS; QUATERNARY GEOLOGY MAPS (Back Pocket) .49 .54 �KIMBERLITE, KIMBERLITE , BASE BASE METAL AND GOLD GOLD EXPLORATION EXPLORATION USING USING OVERBURDEN, OVERBURDEN, WAWA WAWA AREA Background Backcrround Information Information Introduction Introduction Wawa Wawa is is located located 220 220 km km north north of of Sault Sault Ste. Ste. Marie, Marie, Ontario, Ontario, east east of of Lake Lake Superior Superior (Figure (Figure1). 1). Wawa, Wawa, accessed accessed by Highway Highway 17, 17, Highway Highway 101 Michipicoten greenstone greenstone 101 or scheduled scheduled air service, service, sits sits on the Michipicoten belt which (Gledhill which has been been mined for for iron iron and and gold gold since since 1866 1866 (Gledhill 1927). 1927) History of Quaternary Geology Mapping, Wawa Area Surf icial materials materials of of the the Wawa Wawa area area were were first delineated at a Surficial a regional A more more detailed detailed regional scale by by Boissoneau Boissoneau (1966, (1966, 1968). 1968) . engineering and terrain geology geology map map was compiled by Gartner and engineering and McQuay provide a McQuay (1979). (1979). The The purpose purpose of of this this map map was was to to provide a guide guide for for engineering engineering and and resource resource planning planning functions. functions. Frey Frey (1987) (1987) defined defined and outwash systems systems and and glacial glacial and described described several several glacial glacial outwash landforms. landforms. Recently, Recently, the the On.tario Ontario Geological Geological Survey Survey (OGS) (OGS) initiated initiated 22 Quaternary Quaternary geology geology projects. projects. The The first first project project involved involved 22 summer summer field seasons seasons in in 1990 1990 and and 1991. 1991. The second second project project involved involved aa field field visit visit in in the the fall fall of of 1993 1993 and and aa summer summer field field season seasonin in 1994. 1994. WAWA WAWA QUATERNARY QUATERNARY GEOLOGY GEOLOGY PROJECT PROJECT The The area area mapped mapped and and sampled sampled during the the summers summers of 1990 1990 and and 1991 1991 includes includes the the 1:50 1:50 000, 000, NTS NTS 42 42 C/2 ~ / Hawk 2 Hawk Junction Junction map map sheet sheet (84°30'W (840301W and and 48O15'N), 48°15'N), the the northern northern half and 85°00'W; 850001W;48°00'N 480001Nand half of of the the 1:50 1:50000, 000, NTS C/l Manitowik Manitowik Lake Lake map map sheet sheet and and the the southern southern half half of of the the NTS 42 42 c/i 1:50 1:50 000, 000, NTS NTS 42 42 C/8 C/8 Franz Franz map map sheet sheet (84°00'W (840001Wand and 84°30'W; 840301W;48°07'30"N 48O07'30I1N and and 48°22'30"N; 48O22'30I1N;Figure Figure 2). 2). This This area area was was chosen chosen in in order order to to cover cover as much of the Michipicoten greenstone belt as possible in 2 field as much of the Michipicoten greenstone belt as possible in 2 field seasons. seasons. The The purpose purpose of of the the first first OGS OGS Quaternary Quaternary geology geology project project was was to: to:a) a) compliment OGS bedrock mapping and related projects focused over over the Michipicoten greenstone the Michipicoten greenstone belt belt (Sage (Sage1994); 1994); b) b) define define the the types, types, distribution, distribution, physical and geochemical geochemical properties of of overburden overburden materials; c) define define the the Quaternary Quaternary history history of of the the region; region;and and d) d) materials; c) apply apply this this knowledge knowledge towards towards exploration, exploration, environmental environmental and and land land use use applications. applications. Quaternary geology mapping and and an an overburden overburden materials program were were initiated materials sampling sampling program initiated to meet these these goals goals (Morris (Morris 1990, 1990, 1991, 1991, 1992a, 1992a, 1992b) 1992b). 1 �ONTARIO ONTARIO Thunder Thunder Study Bay Area LAKE SUPERIOR 11mm ins Timmins . 'mLcwawa /Sault ',Ste •Marie Sudbury Sudbury  U.S.A. 'LZ '1 200 0 U.S.A. km Figure 1: 1: Study Study area area location location Figure 2 �PI;J 85JO i 7?2200 C. 5:: '1 CD . tJ HO igJ ¼DCD CD '10 (D(D CD mci Itj'< H H- 0 LQrt I-. I P1 '1 H• U. (DQ 00 C)(D rtO POSSIBLE SITES, ALLUVIAL DIAMOND ALLUVIAL DIAMOND c) mo H TOWNS CD '1(l) 1 O 1h(D WATER BODIES WATER BODIES H '0 RAILROADS P. HP) ::i PP @ § ci 64OO .. C. /-o ,.,.,... ;. .:; '.' .,....,,,. : ;,; C. �MICHIPICOTEN RIVERRIVER- WAWA QUATERNARY QUATERNARY GEOLOGY PROJECT PROJECT MICHIPICOTEN Two Two diamonds, diamonds, and possibly possibly aa third, recovered from the the third, were were recovered Michipicoten River-Wawa area area (Figure 2) by C. C. Clement Clement (local Michipicoten River-Wawa (Figure 2). (local prospector) during prospector) during the the summer summer of of 1991. 1991. The exact exact location location of of the the discovery discovery site site could could not not be be positively positively identified. identified. It is thought, thought, It is however, the diamonds however, that that the collected from either either older older diamonds were were collected alluvium (sand (sand and gravel) in a point bar of the Dead River, near alluvium gravel) in the Michipicoten River and/or modern alluvium alluvium (sand (sand and and gravel) gravel) associated This discovery discovery was OGS associated with with Wawa Wawa Creek. Creek. This was reported reported to to the the OGS the fall in the fall of of 1993. 1993. Two of the the 3 diamonds loaned to to the OGS and then forwarded to Two diamonds were loaned forwarded to the Royal the Royal Ontario Ontario Museum, Museum, Department of Mineralogy, Mineralogy, for for Department of confirmation. stones were were identified identified as as industrial industrial grade grade confirmation. The stones diamonds diamonds with with carat carat weights weights of of 1.05 1.05 and and 1.13. 1.13. focused sampling program was A focused sampling program was subsequently subsequently initiated initiated by by the the OGS OGS in in September of of 1993, 1993, in order order to to establish establish authenticity authenticity of the the diamond Ten, 25 kg samples samples were collected collected from reported from the reported diamond find. find. Ten, 5 modern modern alluvium alluvium samples samples from from Wawa Wawa Creek Creek and and 55 discovery sites: 5 older alluvium samples from a a point point bar bar associated associated with with the Dead Dead River. Kimberlite indicator sampling indicator minerals recovered recovered from from this this sampling River. Kimberlite program verified that the 2 2 industrial industrial grade diamonds could have been been recovered recovered from from the the Dead Dead River River site site (Morris (Morriset et al. al. 1994). 1994). follow-up to these preliminary preliminary discoveries, discoveries, the undertook As a follow-up the OGS undertook a program in Michipicoten River-Wawa River-Wawa area a regional regional sampling sampling program in the the Michipicoten area in in The area 2). area from from the the first first OGS OGS the summer of of 1994 1994 (Figure (Figure 2). Quaternary Quaternary mapping mapping project project was was included. included. In In addition, the mapping mapping addition, the and sampling sampling of of Quaternary Quaternary materials materials was was extended extended to to include include the the northern scale N/15 Michipicoten Michipicoten Harbour Harbour NTS northern third third of of the the 1:50 000 000 scale map sheet (84°O0'W (840001Wand and 85°00'W; 850001W;47°07'30"N 47'07' 30"Nand and 48°00'N) 480001N) map sheet . The area area was was considered considered optimal optimal for for kimberlite kimberlite exploration exploration as: as: a) a) The it includes the the area where where 22 industrial grade diamonds and it includes industrial grade diamonds and associated bedrock and overburden overburden b) bedrock associated heavy heavy minerals minerals were were recovered; recovered; b) geology is is well understood (Morris (Morris 1990, 1990, 1991, 1991, 1992a, 1992a, 1992b; 1992b; Sage geology 1994); and C) c) the the area includes includes the the northern northern contact contact of of the the 1994); and Kapuskasing structural structural zone, zone, a bedrock bedrock zone zone thought thought to be aa favourable host favourable host for for kimberlite. kimberlite. This provide regional regional information 1) provide information on on the the This study's purpose purpose was was to: to: 1) types and distribution of kimberlite heavy mineral indicators types distribution of kimberlite heavy mineral indicators(KIM) (KIM) found within overburden overburden in in the the Michipicoten Michipicoten River-Wawa River-Wawaarea. area. In In addition visible gold grains were also also identified addition to to the the KIM's, KIM'S, visible gold grains identified in in characterize the way the heavy 2) heavy mineral mineral assemblage; assemblage; 2) characterize the way heavy heavy fluvial systems minerals are are transported transported through through modern fluvial systems by minerals evaluating variations variations in gold grains grains with with evaluating in concentration concentration and and wear wear on on gold distance from from a known source; 3) distance known point point source; determine the the types, types, 3) physical and geochemical distribution, physical geochemical properties properties of of overburden overburden 4 �materials within the the Michipicoten Michipicoten River River valley valley area; area; and and 4) materials 4) determine the Quaternary history of the Michipicoten River valley determine area. area. Phys iography Physiography TOPOGRAPHY TOPOGRAPHY Topography of the area is described as moderate to undulating by by Boissoneau (1966, Boissoneau (1966, 1968) 1968) and moderately moderately to severely severely rugged rugged by by landscape can can be be flat, flat, Gartner and and McQuay McQuay (1979). (1979) Locally this landscape although relief in in some some areas areas achieves achieves 198 198 m. m. although relief . DRAINAGE BASIN DRAINAGE BASIN CHARACTERISTICS CHARACTERISTICS The study study area is is located located south south of of the the Great Great Lakes-Hudson Lakes-Hudson Bay regional regional drainage drainage divide divide and and all all water water within within the the study study area area flows flows south south to to the the Lake Lake Superior Superior basin. basin. Three major drainage drainage basins basins cross the cross the study study area. area. These These include, include, from from west west to to east: east : the the Dore', Dore1, and Michipicoten Michipicoten rivers rivers Magpie and (the Michipicoten Michipicoten being being the (the the The largest). The orientation orientation of many of of the the major major rivers rivers and and lakes lakes largest) within drainage drainage basins basins is controlled by bedrock bedrock structural structural features features within is controlled Emily Bay, Bay, Dog Lake and such as deformation deformation zones zones (e.g. Emily and McKewen McKewen Lake (Heather and Buck Buck 1988). Lake deformation deformation zones) zones) (Heather 1988). . Water flow in the Water the upper upper reaches reaches of each of of the the major major drainage drainage basins is relatively basins relatively slow slow due due to to low low stream stream gradients. gradients. As aa result, alluvium is is poorly poorly sorted sorted in in their their northern northern (upstream) (upstream) reaches. In addition, drainage drainage within within the Magpie and Michipicoten Michipicoten reaches. In addition, rivers is rivers is now largely largely controlled controlled by hydro hydro electric electric dams. dams. CLIMATE CLIMATE AND VEGETATION VEGETATION In the Wawa area, area, Lake Lake Superior Superior has aa moderating moderating effect effect on on the the climate in climate in a belt 60 60 to to 91 91 km inland inland from from the the Lake Lake Superior Superior shore. shore. Cooler, summer Cooler, more moist shoreline shoreline conditions conditions prevail during the summer months which result in in more more frequent frequent cloud cloud or or fog fog cover. cover. This This reduces local local evaporation reduces evaporation rates rates and and slightly slightly modifies modifies temperature temperature and precipitation. precipitation. July July has the the warmest warmest monthly monthly mean mean temperature temperature and (15.6' C) while January has the the coldest coldest (-14. lo C). C) The yearly yearly (15.6° C) (-14.1° C. The The temperature average based on on the the monthly mean is is 2.0° 2.0' C. wettest month is is September September (113.8 (113.8 mm) while the the driest driest month month is is monthly precipitation February (55.9 mm). mm) . The The monthly precipitation average average is is 78.8 78.8 mm. mm. February (55.9 . The area east east of of Wawa Wawa (towards (towards Chapleau) Chapleau) is is classified classified as aa subarctic continental subarctic continental climate. climate. July has the the warmest monthly mean temperature (17.0° The temperature (17.0' C) while January January has has the the coldest coldest (-16° (-16' C). C) The yearly temperatureaverage averagebased basedon onthe themonthly monthlymean meanis is1.3° 1.3' C. C. The yearly temperature The month is wettest month is September September (116.9 (116.9 mm) mm) while the the driest driest month month is is mrn). The monthly precipitation average based on on the the March (48.9 (48.9 mm). yearly precipitation total yearly precipitation is is 75.1 75.1 mm. mm. . 5 �In In the the Wawa area area the the St. St. Lawrence Lawrence vegetation vegetation assemblage assemblage is is present present largely largely due due to to the the moderating moderating effect effect of of the the local local climate climate by by Lake Lake Superior This vegetation assemblage is at Superior (Rupert (Rupert 1979). 1979) at it's it's . northern northern limit in in the the Wawa Wawa area area and and includes includes maples, maples, white white and and yellow birch, red red and and white white pine, pine, jackpine, jackpine, hemlock, hemlock, cedar cedar and and spruce. spruce. AA low low crown crown density density and and thick thick development development of of underbrush underbrush are characteristic characteristic of the the assemblage assemblage in in the the Wawa Wawa area. area. East East towards Chapleau, Chapleau, the vegetation is is dominated dominated by by conifers, conifers, more more typical typical of of Boreal Boreal forest. forest. Regional Geology Bedrock Bedrock Geology Geology The The Michipicoten Michipicoten River-Wawa River-Wawaarea area lies lies within within the the Wawa Wawa subprovince subprovince of the the Superior Superior Province Province of of the the Canadian Canadian Shield. Shield. The The study study area area straddles much of of the the Michipicoten Michipicoten greenstone greenstone belt. belt. This This belt belt extends inland 150 km, km, to to the the northeast, northeast, from from the the Lake Lake Superior Superior shore with 38 km. km. This greenstone greenstone belt belt with an average average width of of 38 This consists consists largely largely of of supracrustal supracrustal rocks rocks of of Archean Archean age. age. Younger Younger Archean Archean granitic granitic rocks rocks surround surround the the greenstone greenstone belt belt (Figure (Figure3). 3). The The Kapuskasing Kapuskasing structural structuralzone zone extends extends east east from from the the shore shore of of Lake Lake Superior northeast through Superior and and then then northeast through Kapuskasing Kapuskasing into into the the Hudson Hudson Bay Bay Lowland Lowland (Figure (Figure 3). 3). The The northern northern margin of of this this zone zone is is traced traced through through Wawa, Wawa, Hawk, Hawk, Manitowik Manitowik and and Dog Dog lakes. lakes. This This structure structure is is significant significant as as it it consists consists of of fractured fractured crustal crustal material material that that may may host Structures kimberlite rock rock (Boland (Boland and and Ellis Ellis 1989). host kimberlite 1989). Structures associated associated with with this this zone zone include include northeast northeast striking striking Proterozoic Proterozoic lamprophyre 1994). lamprophyre dykes dykes formed formed by by alkalic alkalic magma magma emplacement emplacement (Sage (Sage1994). The The Precambrian Precambrian geology geology of of the the area, area, and and related related studies, studies, are are summarized There are (1994) are 44 major major sedimentary sedimentary and and summarized by Sage Sage (1994). metavolcanic metavolcanic rock rock types types recognized recognized within within the the Michipicoten Michipicoten greenstone 1) intermediate intermediate to to mafic mafic metavolcanic metavolcanic greenstone belt. belt. These These are: are: 1) rocks; 2) intermediate intermediate to to felsic felsic volcanic volcanic rocks; rocks; 3) 3) clastic clastic rocks; 2) metasedimentary 4) chemical chemical metasedimentary metasedimentary rocks rocks metasedimentary rocks; rocks; and and 4) (Figure 4) . (Figure4). . Intermediate Intermediate to to mafic mafic metavolcanic metavolcanic rock rock is is exposed exposed throughout throughout most most of of the the greenstone greenstone belt. belt. The The intermediate intermediate to to felsic felsic metavolcanic metavolcanic rocks rocks are are less less widespread widespread and and are are restricted restricted to to belts belts and and blocks blocks scattered scattered across across the the greenstone greenstone belt. belt. The The intermediate intermediate to to mafic mafic and major, and and aa and felsic felsic metavolcanic metavolcanic rocks rocks were were deposited deposited during during 22 major, third third minor, minor, volcanic volcanic cycles. cycles. The The materials materials derived derived from from the the 22 major major volcanic volcanic cycles cycles range range in in composition composition from from tholeiitic tholeiitic basalt basalt to Materials 1986) Materials to calc-alkalic calc-alkalic felsic felsic volcanics volcanics (Thurston (Thurston 1986). derived derived from from the the third third minor minor volcanic volcanic cycle cycle represent represent basaltic basaltic to to . peridotitic peridotitic komatiite komatiite volcanism volcanism followed followed by by calc-alkalic calc-alkalicfelsic felsic volcanism 1991). volcanism (Sage (Sageand and Heather Heather 1991). 6 �H'1 CD Li.' t. ¼01Q • a-; : •' : . ' . . •.. . • ,Qu;coSu8povi.jc'. 4...4 •: '• : S • + + 4- • .. .- '. : . p.' I-i CD '1 0 C) (Q CD 0 0 H- Hi CD '-1 0 C') p.' (Q CD p.' pi Metavolcanic and Metasedirnentary Rocks Metovolcanic and Metasedimentary Rocks Massive to Foliated Felsic Plutonic Rocks Massive to Foliated Felsic Plutonic Rocks Tonolitc-Granodiorite Gneisses Tonolite—Granodjorjte Gneisses Towns CD p.' Ct CD Towns Paragneiss and Migmotic Rocks Poragneiss and Migmotic Rocks Huronian Group Rocks Huronian Group Rocks Coldwell Complex Coidwell Complex Ice Flow Direction Ice Direction (1 Flow Oldest Flow, 2 Youngest Flow) - (1 Oldest Flów 2 Youngest Flow) �U H- H- CD CD 0 Ci) Ii rt CD CD '1 CD rt 0 C) H H- 'ti a H- CD rt 0 0 (.Q 'QCD CDPJ cl)'l Cl) 0C) 'lCD CD 'I (Q Figure 4: Precambrian geology of the Michipicoten greenstone belt (from Sage 1994) �Metasedimentary rocks are more common in the western part of the the study study area area than than they they are are in in the the east. east. They They were were deposited deposited within within aa marine marine alluvial alluvial fan fan depositional depositional environment environment and and were were subsequently shallow braided stream stream environment environment (Neale subsequently buried buried by a shallow (Neale 1981; The metasedimentary rocks rocks Consist consist of of either either 1981; Thomas Thomas 1984). 1984) The conglomerate, conglomerateI wacke, wacke, and and siltstone siltstone or or argillite aFgillite (Sage (Sage and and Heather Heather . 1991) 1991). Iron chemical metasedimentary metasedimentary rock found Iron formation formation is is the dominant chemical rock found within belt and and is most most Commonly commonly found found in the the within the greenstone greenstone belt southwestern, central and northeastern parts of the the study study area. area. southwestern, The The iron iron formation formation consists consists of of 55 facies facies which which include, includelfrom from base base to to surface: b) pyrite pyrite (sulphide (sulphide surface: a) a) siderite siderite (carbonate (carbonate facies); facies); b) c) chert-magnetite chert-magnetitewacke wacke (oxide (oxidefacies); facies);and and d) d) argilliteargillitefacies); c) facies); pyrite-graphite. pyrite-graphite. Occasionally, Occasionallyl calcite calcite substitutes substitutes for for siderite siderite and 1991). The and represents represents the the fifth fifth facies facies (Sage (Sageand and Heather Heather 1991). The origin origin of of the the iron iron formation formation is is summarized summarized by by Sage Sage and and Heather Heather (1991). (1991). Intermediate mafic intrusions peridotite to quartz Intermediate to to mafic intrusions consisting consisting of of peridotite to quartz diorite diorite occur predominantly predominantly within within the the central central part part of of the the greenstone They belt. They vary vary in in age age and and are are finefine- to to coarsecoarsegreenstone belt. grained. grained. Several Several stocks stocks are are scattered scattered across across the the greenstone greenstone belt. belt. These These stocks trondhjemite to to granodiorite granodiorite to to stocks range range in in composition composition from from trondhjemite granite. granite. All All are are younger younger than than the the surrounding surrounding supracrustal supracrustal rocks rocks and and may may have have been been emplaced emplaced at at the the same same time time as as the the granitoid granitoid rocks rocks external external to to the the greenstone greenstone belt. belt. Surrounding Surrounding the the supracrustal supracrustal rocks rocks are are felsic felsic intrusive intrusive rocks rocks that that range tonalite and and trondhjemite trondhjemite to to granite granite (Sage (Sageand and Heather Heather range from from tonalite External 1991). 1991). External granitoid granitoid rocks rocks on on the the south south side side of of the the greenstone greenstone belt belt are are older older than than the the external external granitoid granitoid rocks rocks on on the the north north side. side. Quaternary Quaternary Geology Geology TIME FRNE Overburden Overburden materials materials throughout throughout the the Michipicoten Michipicoten River-Wawa River-Wawa area area were were deposited deposited during during the the last lastglaciation. glaciation. The The Wawa Wawa area area has has likely Wisconsin which which likely been been covered covered by by glacial glacial ice ice since since the the Early Wisconsin occurred 000 years yearsago. ago. Bedrock Bedrock features, featuresI materials materials and and occurred about about 115 115 000 landforms landforms associated associated with with this this advance advance include: include: a) a) ice ice flow flow indicators whalebacks, indicators (straie, (straiel grooves, grooves whalebacks chattermarks); b) b) chattermarks); enhancement enhancement of of bedrock bedrock structure structure (structure (structureparallel parallel to to ice ice flow flow is is enhanced, flowis enhancedl structure structure perpendicular perpendicular to ice flow is not); not); and and c) c) thin thin till till over over bedrock bedrock (subglacial (subglacialtill). till) . 9 �100 years A radiocarbon radiocarbon date date of of 9210 9210 ±k 100 (GSC 1851) 1851) from from aa basal basal years BP (GSC organic sediment in Alfies sediment in Alfies Lake (south Wawa) provides provides a a minimum minimum (south of Wawa) date of deglaciation of ofthe the Wawa Wawa area area (Saarnisto (Saarnisto1974). 1974). Howeverl However, Mothersill (1988) (1988) argued that radiocarbon radiocarbon dating of material from with old old within the Lake within the Lake Superior Superior basin is potentially potentially contaminated contaminated with carbon. Using Using palaeomagnetic palaeomagnetic dating, datinglMothersill Mothersill concluded concluded that that the the Lake Lake Superior Superior basin basin had had been been deglaciated deglaciated by by 8200 8200 years years BP. BP. This This is is compiled by Mahanic and Teller Teller (1985). (1985). in agreement with data compiled Mahanic and The types and distribution distribution of Quaternary Quaternary materials materials and and features features are are The types summarized in Quaternary Geology Geology maps, mapsl back back pocket. pocket. summarized in the Quaternary ICE ADVANCE ADVANCE ICE Ice Flow Flow Indicators Ice Indicators Striations, Striationsl glacial glacial grooves grooves , chattermarks chattermarks and ice moulded bedrock and ice bedrock knobs knobs are preserved preserved on on smooth, smoothl unweathered bedrock bedrock surfaces. surfaces. , Striations Striations are the most common common glacial glacial erosion erosion feature feature and and are are found found throughout throughout the the study study area. area. The orientation of these these glacial erosion features varies between 165° to 263O 263° with with a 1 65' to a mean mean of of 214°. 214O. Most of the the striae striae variation variation is is due due to to deflection deflection of of regional regional flow flow by by bedrock bedrock highlands. highlands. Cross-cutting straie Cross-cutting straie have have been been observed observed in in only only 44 places. places. In In all all cases, the location casesI location of these these sites sites are are within within major major west west trending trending bedrock controlled bedrock controlled valleys. valleys. At the the 44 sites sites straie straie formed formed by the the regional ice flow flow (mean (mean of of 214°) 214O) are cross-cut by aa younger younger set set of of regional ice cross-cut by striae (mean The younger 266'). younger set set of of striae striae are are orientated orientated striae (meanof of 266°). parallel to the parallel the orientation orientation of of the the bedrock bedrock controlled controlled valleys valleys within which within which they they were were observed. observed. The older set striae represents represents flow flow that was was largely largely unaffected unaffected The older set of striae younger set of straie straie represents by bedrock bedrock topography. topography. The younger represents flow flow controlled by bedrock bedrock topographyI topography, commonly in westerly controlled commonly in the the westerly orientated valleys. This occurred occurred due thinning during orientated valleys. This due to ice sheet thinning latter stages stages of of glaciation. glaciation. the latter Material Material Till Subglacial S ubglacial T i l l discontinuous till till was was deposited deposited over over the the area area by ice A thin, thinl discontinuous ice associated associated with with the the last last glaciation. glaciation. This till was derived from the debris base of it advanced. the debris rich rich base of the the ice ice as as it advanced. This This interpretation of the subglacial origin origin of of the the till till is is based based upon upon interpretation the subglacial morphology, structural characteristics morphologyl characteristics and and pebble pebble composition. composition. tillls thickness thickness varies varies from from non-existent non-existentover over bedrock bedrock highs highs This till's This to 1.0 to 1.5 m thick in bedrock lows. outcrops are are 1.0 to 1.5 m thick in bedrock lows. Bedrock outcrops commonly associated this unit unit and and the material commonly associated with with this material can be be 10 �described as aa thin, thinl discontinuous discontinuous veneer. veneer. described as The unweathered exposures exposures of this this till till are are usually usually structureless structureless and massive. and massive. Occasionally faint shear shear were observed observed in in sections sections located up-ice up-ice of of bedrock bedrock ridges. ridges. When When dry, dryl the the material is is very located detailed discussion discussion regarding regarding subglacial subglacial till till as as aa hard. A more more detailed hard. A media for for drift drift prospecting prospecting is is contained contained in in the the notes notes for for Site Site media "Field Tript1 Trip" section. # 3, 3, l1Fie1d section. # RETREAT ICE RETREAT Bedrock Features Features The with ice ice retreat retreat in in the the Wawa The 2 bedrock bedrock features features associated associated with Wawa area area forms. are the the potholes potholes and and 1lP1l forms. Both features features are formed formed by sediment Potholes are glacial meitwater meltwater under under high high pressure. pressure. Potholes are sediment rich rich glacial not widely widely recognized not recognized throughout throughout the the Wawa Wawa area. area. They They are are circular circular features that can extend 1 to 3 m below the the rock rock surface surface and and are are formed by the circular circular rotation rotation of boulders boulders within within swirling swirling water water under high pressure pressure at the the base base of of the the ice. ice. The boulders are are dentistls drill, drill, whereby whereby the the boulders boulders literally literally analogous to aa dentist's drill drill into into the the rock. rock. Grinders, Grindersl as as these these boulders are are called, called, can can sometimes be found sometimes found in in the the bottom bottom of of the the hole. hole. llPtl the Magpie and the the Wawa Wawa "P" forms forms were were observed only within the Magpie valley valley and Lake Lake basin. basin. Characteristic Characteristic "P" llPtl forms include include furrows, furrowsI comma comma form form forms and 1989, Kor Kor et et al. al. 1991). 1991) Although and sicheiwannen sichelwannen (Sharp (Sharp and and Shaw Shaw 1989, Although . "P" forms are commonly l1Pl1 commonly restricted restricted to to valley valley floors, floorsI they were were observed on sides 65 65 mm above above the the Magpie Magpie River. River. They are are on valley sides aligned oblique to to valley valley orientation orientation suggesting suggesting that that glacial glacial aligned meitwater flow did meltwater did not not necessarily necessarily follow follow bedrock bedrock controlled controlled depressions. Straie exist exist within "P" forms suggesting suggesting that that glacial depressions. Straie l1Ptt forms ice was let let back back down down onto onto the the bedrock bedrock surface surface after after glacial glacial meltwater was meltwater was expelled. expelled. Materials and and Related Related Landforms Landforms The landform indicate The distribution distribution of materials and related landform that indicate that the ice margin retreated to the the north in in the the western western part part of of the the of region and to to the the northeast northeast in in the the eastern eastern part. part. The bulk of overburden materials were deposited deposited within within bedrock bedrock controlled controlled overburden materials valleys where valleys where glacial glacial meitwater meltwater was was concentrated. concentrated. Flow Till T i l l and Related R e l a t e d Landforms Landforms A second second type type of of till till was was deposited deposited during during ice ice recession. recession. This This (>I m) m) than than the the subglacial subglacial till. till. It is is commonly comonly till is is thicker thicker (>1 associated moraines, or or is found in isolated associated with west trending morainesl isolated patches commonly located at the headwaters of outwash systems or around Bedrock around the the periphery periphery of of former former glacial glacial lake lake basins. basins. Bedrock outcrops are rarely rarely associated associated with with this this till till type. type. 11 �The material material comprising comprising this this till till type was derived derived from from the the subglacial subglacial (base), (base), englacial englacial (middle) (middle) or or supraglacial supraglacial (surface) (surface) positions wflowsw. Because Because of of the the positions of of the the glacier glacier and and deposited deposited as as "flows". flow-like flow-likestructure structure associated associated with with these these tills tills , they they are are commonly commonly referred referred to to as as flow flow tills. tills. , Glaciofluvial Materials Glaciofluvial M a t e r i a l s and Landform subdivided into into 22 units: units: ice-contact ice-contact Glaciofluvial deposits are subdivided stratified drift and and glaciofluvial glaciofluvial outwash. outwash. The The sides sides of of iceicecontact contact stratified drift drift deposits are are commonly commonly steep due due to to deposition deposition of of the the sediments sediments against against ice ice walls. walls. Deposits Deposits consist consist of of a a wide wide variety variety of of materials materials ranging ranging from from sandy sandy silt silt to to boulders. boulders. Related Related landform landform consist consist of of eskers eskers and and moraines. moraines. Glaciofluvial outwash deposits deposits commonly commonly have gentle gentle slopes slopes as as Glaciofluvial outwash outwash outwash was was deposited deposited in in front front of of but but proximal proximal to to the the ice ice margin. margin. Kettles associated with glacial ice Kettles are are associated with several several outwash outwash deposits deposits as as glacial ice blocks blocks buried buried by by outwash outwash melted. melted. Materials Materials comprising comprising the the outwash outwash range range from from sand sand to to coarse coarse boulders. boulders. Within area glacial glacial meltwater meltwater flowed Within the the western western part part of of the the area flowed freely freely downslope from from the the ice ice margin margin toward toward the the Lake Lake Superior Superior basin. basin. Associated with this this free-flow free-flow of of water water there there are are several several well well defined within the bedrock controlled defined meltwater meltwater channels channels situated situated within controlled valleys 5) valleys (Figure (Figure5). . In In the the eastern eastern part part of of the the area, area, glacial glacial meitwater meltwater was was commonly commonly trapped in in glacial glacial lakes lakes which which formed formed between between bedrock bedrock controlled controlled topographic topographic highs highs and and the the ice ice margin. margin. Meltwater Meltwater flow flow from from these these lakes occurred occurred either either through through channels channels which which opened opened between between the the lake margin or lake and and ice ice margin or topographic topographic lows lows situated situated around around the the rim rim of of the the ice-controlled ice-controlledlake lake basin. basin. Smaller Smaller glaciofluvial glaciofluvial deposits deposits are are associated associated with with bedrock bedrock depressions glacier, melted melted depressions where where blocks blocks of of ice, ice, detached detached from from the the glacier, in-situ. Where meltwater in-situ. meltwater was dispersed dispersed onto open open space space from from concentrated channel flow flow leading leading from from this this wasting wasting ice, ice,small, small, fan-shaped fan-shaped bodies bodies of of aggregate aggregate were were deposited. deposited. Glaciolacustrine Materials and Landform Glaciolacustrine M a t e r i a l s and. Landform Glaciolacustrine materials consist consist of of fineGlaciolacustrine materials fine- and and coarse-grained coarse-grained sediments. sediments. The The fine-grained fine-grained sediments sediments consist consist of of horizontally horizontally bedded bedded couplets couplets of varved silt silt and and clay clay deposited deposited within within deep deep (quiet) (quiet) water. water. They They are are exposed exposed at at surface surface along along the the shores shores of of Dinginan Bay on on Manitowik Manitowik Lake Lake and and Localsh Bay on Dingman Bay on Dog Dog Lake. Lake. They They were deltaic section section associated associated with were also also observed observed at at the the base base of of a deltaic with the the Magpie Magpie River. River. Coarse-grained material occurs Coarse-grained material occurs where where the the western, western, free-flowing free-flowing glaciofluvial glaciofluvial systems systems empty empty into into the the Lake Lake Superior Superior basin basin and and 12 �N UI 000IacS F E In Ia F In N C C F g I) 0 " OcLc,cS C NW Figure Figure 5: 5: Distribution Distribution of of glaciofluvial glaciofluvial meitwater meltwater channels channels 13 �in shallow glacial lakes formed between the ice ice margin and and the the eastern these lakes lakes coarse-grained coarse-grained sediments eastern bedrock bedrock highlands. highlands. In In these sediments formed deltas and and sheet sheet sand sand deposits. deposits. Where rivers rivers have have cut cut through deltaic deposits, in response to to lake lake level level lowering lowering in in the the through deltaic deposits, in response Lake Superior Superior basin, basin, magnificent terraces terraces have have developed developed in in the the Dore', Dore1, Magpie and and Michipicoten Michipicoten river river valleys. valleys. More detailed detailed discussion of of the the lake lake level level history history in in the the Lake Lake Superior Superior basin basin is is discussion contained contained in in the the description description at at Site Site ## 8. 8. Flow Till, Materials a ass Media T i l l , Glaciofluvial G l a c i o f l u v i a l and Glaciolacustrine G l a c i o l a c u s t r i n e Materials for D r i f t Prospecting f o r Drift These media for drift These materials materials are are not not desirable desirable overburden overburden media for local local drift prospecting prospecting since since they: 1) 1) are are not widespread throughout the the Wawa area; 2) commonly commonly do do not not give give aa local local signature signature of of the the bedrock bedrock as as area; 2) material is is aa blend blend of of both both regional regional and and local local materials materials derived derived from the the basal, basal, englacial englacial and supraglacial supraglacial positions positions of of the the icesheet; icesheet; and 3) 3) undergo undergo several several depositional depositional processes processes that that may may either either concentrate concentrate or or dilute dilute the the indicator indicator signatures. signatures. Glaciofluvial materials materials found found in in eskers eskers and glaciolacustrine glaciolacustrine deposits to gain aa quick, deposits are used used successfully successfully to quick, inexpensive inexpensive regional Craigie 1993). 1993). regional indicator indicator signature signature (Baker (Baker 1985; 1985; Craigie RECENT RECENT DEPOSITS DEPOSITS Eolian Eolian Deposits Deposits Eolian deposits deposits consist consist of of yellow, yellow, fine fine to to medium-grained medium-grained sand. sand. These These deposits deposits are are not not widespread widespread and and are are commonly commonly located located on on the the down-wind down-wind side side of of glacial glacial lake lake and and glaciofluvial glaciofluvial deposits deposits such such as as the the broad outwash outwash plain plain east east of of Goudreau. Goudreau. A A very very thin thin cover cover of of eolian eolian material material exists exists on on the the Steephills Steephills Falls Falls Dam, Dam, Magpie Magpie River. River. Colluvium Colluvium Colluvium Colluvium consists consists of of light light brown brown to to brown, brown, coarse sand sand and and boulders. Well boulders. Well developed developed colluvium colluvium aprons aprons are are most most commonly commonly associated associated with with terrace terrace scarps scarps within within the the Magpie Magpie River River valley. valley. Older Older Alluvium Alluvium Older Older alluvium alluvium consists consists of of pale pale brown, brown, fine fine to to coarse coarse sand. sand. Older Older alluvium alluvium is is restricted restricted to to the the lower lower reaches reaches of of the the Dore', Dore', Magpie Magpie and Wawa region, and Michipicoten Michipicoten rivers. rivers. In In the the Wawa region, alluvium alluvium consists consists of of material material derived derived from from the the erosion erosion of of higher higher elevation elevation glaciolacustrine glaciolacustrine deltas deltas within within these these valleys valleys as as lake lake level level dropped dropped within the Lake Superior basin. within the Lake Superior basin. Modern Modern Alluvium Alluvium Modern minor quantities Modern alluvium alluvium consists consists primarily primarily of of sand sand and and minor quantities of of organic rich sand and gravel. Thick deposits of alluvium organic rich sand and gravel. Thick deposits of alluvium (>1 (>1m) m) 14 �commonly associated associated with rivers or or streams streams flowing flowing are commonly with those rivers through glaciofluvial glaciofluvial or or glaciolacustrine glaciolacustrine deposits deposits where where there there is is through a ready ready supply supply of erodable erodable material. material. Where a Where stream stream or or river river flow flow is is over bedrock bedrock dominated dominated terrain terrain alluvial alluvial sand sand is is scarce, scarce, found found usually as small pockets within sediment traps (behind (behind or under boulders, steps in in the the stream stream bed, bed, or or inside inside curves curves of of streams). streams). boulders, steps Colluvium, Older Older Alluvium Alluvium and and Modern Modern Alluvium Alluvium as as Eolian Deposits, Eolian Deposits, Colluvium, Media for for Drift Drift Exploration Exploration Media Eolian deposits, colluvium and older alluvium are not recommended Eolian deposits, colluvium recommended as for local for the the same same reasons given for for as media for local drift exploration exploration for reasons given flow tills, tills, glaciofluvial glaciofluvial and glaciolacustrine glaciolacustrine deposits. deposits. In In addition, addition, they have all undergone undergone at least least one one more more cycle cycle of of transportation and deposition deposition which which will will likely likely further further erosion, transportation complicate tracing tracing of of any any indicator indicator signature signature back back to to the the source source or or complicate target. target. modern alluvium alluvium is is regionally regionally prevasive prevasive and thought to to As modern and is thought represent aa signature signature of of a a whole it is is commonly represent whole drainage drainage basin basin it commonly used used as a means for for gaining fast, regional signature as gaining a fast, signature for either gold or kimberlite kimberlite exploration exploration (Gonzaga (Gonzaga et et al. al. 1994; 1994; Marshall Marshall 1986; 1986; Maurice 1988, 1988, 1991; Morris et et al. al. 1994; Seely and and Senden Senden 1994; 1994; Sutherland Sutherland 1982, 1982, 1993; 1993; Wolf Wolf et et al. al. 1975). 1975) Commonly, samples samples are are taken at the mouths mouths of drainage drainage basins basins to provide provide a a regional regional heavy heavy taken mineral signature signature for for that that drainage drainage basin. basin. The The merits of such such aa sampling program are 7a. sampling are discussed discussed in in the the write-up write-up for for Site Site *# 7a. . Overburden Samolincr Methodolocries Overburden Samlin Methodologies Sampling Sampling Design Commonly overburden overburden materials are are sampled sampled at at 22 different different scales; scales; regional and and local. local. Regional scale scale sampling sampling in in Ontario Ontario involves involves the collection collection of samples samples from from glaciofluvial glaciofluvial deposits deposits such such as as eskers and outwash, outwash, glaciolacustrine glaciolacustrine deposits, deposits, modern modern alluvium alluvium and eskers lacustrine deposits. This type of sampling lacustrine deposits. This type of sampling program program allows allows evaluation evaluation of aa large large area area relatively relatively quickly quickly and and inexpensively. inexpensively. The density at scale varies depending depending on the commodity commodity The sample sample density at this this scale of material material being collected being sought, distribution distribution of collected and being sought, exploration exploration cost. cost. Local scale sampling usually done done once an anomaly has been sampling is usually identified from the identified the regional regional scale scale sampling. sampling. Individuals have have sampled from from a variety soil sampled variety of of materials materials and and from from different different soil horizons. The exploration horizons. exploration limitations limitations of these these materials materials are are discussed In Samplingwand and at at all all "Field "Field Trip" Tripw stops. stops. In discussed in in "Material "MaterialSampling" the Wawa area subglacial subglacial till is is probably probably the the best best material material to to sample due to it's relatively relatively simple simple depositional depositional history and and aa to it's local heavy mineral and geochemical signature. Sample collection local heavy mineral and geochemical signature. Sample collection sites are based on on an an artificial artificial grid grid placed placed over over the the anomaly. anomaly. Grid Grid spacings spacings are are commonly commonly 30 30 to to 300 300 mm apart apart (Craigie (Craigie1991). 1991). 15 �Material Sampling Consistently overburden material material in overburden Consistently sampling samplincr the same same overburden in an overburden - the sampling program is critical critical when it it comes comes to to interpreting interpreting the the geochemical geochemical and/or and/or heavy heavy mineral mineral data. data. Often, Often, individuals individuals collect collect material exists at aa prescribed prescribed sample sample point point without without whatever material taking the time time to to evaluate evaluate the the site site or or material material being being sampled. sampled. different depositional depositional histories histories of the the materials materials and and the the The different different ways ways and and rates rates at at which which certain certain materials materials weather weather give give different different different geochemical, geochemical, and possibly, possibly, different different heavy mineral mineral signatures. signatures. For For example, example, sulphide minerals near surface surface minerals in a near oxidizing oxidizing environment environment weather weather quickly. quickly. Because of of this, this, it is is essential essential to take take the the time time to to make make some some basic sample sample site site and and material material observations. observations. This can can be be done done quickly and and accurately by providing the sampler sampler with with a a checklist of quickly accurately by providing the checklist of observations. These observations. These observations, observations, if if done done correctly, correctly, may be be invaluable invaluable during during data data interpretation. interpretation. Appendix B consists site observation observation sheets sheets and aa list list of of consists of of 22 site related term Although there term definitions. definitions. there is always always room room for for improvement, prove useful useful in improvement, these these observation observation sheets sheets prove in providing an outline for for some some of of the the fundamental fundamental observations observations that that should should be be made made at at either either aa till till or or sand sand and and gravel gravel sample sample site site (Appendix (AppendixB, B, p. p. 55) 55) or or aa modern modern alluvium alluvium sample sample site site (Appendix (AppendixB, B, p. p. 57). 57). humus geochemical geochemical sampling gm of of organic organic rich rich For humus sampling at at least 20 gm material material is is required. required. Ensure Ensure that that the the sample sample consists consists primarily primarily of of organics, removing removing as as much much of of the the mineral mineral material material as as possible. possible. organics, For "B" I1BI1and and "C" I1CI1horizon horizon geochemical geochemical sampling sampling (-63 ( - 6 3 micron micron or or finer) finer) For of 200 gm of of material material is is required. required. of aa subglacial subglacial till, till, only only 200 Preferably, horizon Preferably, the the unoxidized unoxidized "C" llC1l horizon should should be be collected, collected, however, however, this this horizon horizon may may not not always always be available available or or practical to to get deep is is required. required. A get at at as as soil soil pit pit or or section section at at least least 11 mm deep subsample 50 or or more more pebbles pebbles is is worth worth collecting collecting as as the the pebbles pebbles subsample of of 50 willgive will giveyou youan anexcellent excellentsignature signatureof of the the local local bedrock. bedrock. For For the the "B" I1BI1or or "C" I1CI1horizon heavy heavy mineral mineral sampling, sampling, material should should be be passed cm2 steel steel mesh mesh sieve. sieve. AA sample sample of of at at least least 10 10 passed through through aa 11 cm2 kg kg of of the the -10 -10 mesh mesh (-2 (-2mm) mm) fraction fraction should should be be collected. collected. The materials collected The types types and and quantities quantities of of materials collected can can be streamlined streamlined for for specific specific indicators. indicators. However, However, when when possible possible and and feasible, feasible, collect kg sample collect samples samples of of humus, humus, "B" 10 kg sample I1Bl1and and "C" I1CI1horizons, horizons, aa bulk bulk 10 of "C" llCI1horizon horizon material material and and pebbles pebbles at at each each sample sample site. site. Since Since much much in in the the way way of of financial financial resources resources is is invested invested in in placing a crew in in aa field field area, area, as as wide wide aa variety variety of of material material should should be be sampled sampled as as possible possible while while the the crew crew is is at at the the sampling sampling site. site. Sampling of modern modern alluvium alluvium or or other other sand sand and and gravel gravel deposits deposits is is commonly commonly done to to obtain obtain aa heavy heavy mineral mineral concentrate concentrate (specific (specific 16 �. gravity gravity >3.3). >3.3) Material Material should shouldbe be passed passed through throughaa11cm2 cm2 steel steel mesh mesh sieve sieve so so that that 10 10 kg kg of the the "finer" "finerwmaterial material is is collected. collected. Pebbles Pebbles from the the coarser coarser fraction fraction should should also also be be sampled. sampled. If resources resources permit, "finern material can can be further further processed in in permit, the the 10 10 kg kg of "finer" field through through the use use of of finer finer meshed meshed sieves sieves and and shaking shaking the field tables. tables. This This will will reduce reduce the the cost cost of of shipping shipping materials materials from from the the field, field, but will will potentially potentially increase increase the the field field time time and and hence hence expense expense of of field field programs. programs. Field Field Trip Trio Introduction Introduction The The Wawa Wawa region region was was initially initially settled settled in in 1725, 1725, with with the the establishment establishment of of aa fur fur trading trading post post at at the the mouth mouth of of the the Michipicoten gold rush accompanied Michipicoten River. River. In In the the late late 1890's 1890's aa gold rush was accompanied by the the establishment establishment of of the the Wawa Wawa townsite. townsite. Attention, Attention, however, however, quickly ore discovery, discovery, the development of quickly focused focused on on an an iron iron ore the future future development of which which became became the the town's town's main main industry. industry. Between Between 1900 1900 and and 1922, 1922, iron iron was was mined mined from from an an open open pit pit at at the the Helen Helen Iron Iron Range Range and and gold gold from from deposits deposits around around Wawa. Wawa. Mining Mining ceased ceased until until the when in mining of siderite siderite for began from the 1930's when in 1938, 1938, mining for iron iron began from the the Helen Iron Iron Range. Range. Operations continue continue to to the present. present. Gold Gold prospecting prospecting flourished flourished during during the the 1930's 1930's but but decreased decreased during during World World War Recently 11. Recently aa renewed renewed interest interest has developed developed for for the the War II. exploration exploration and and mining mining of of gold gold (Sage (Sage and and Heather Heather 1991). 1991). In In 1978, 1978, the the OGS OGS initiated initiated aa systematic systematic bedrock bedrock geology geology mapping mapping program program of of the the Wawa Wawa area area which which was was completed completed in in 1988. 1988. During During the the summers 1991, a regional regional Quaternary Quaternary mapping mapping program program was was summers of of 1990 1990 and 1991, completed mapping and provide provide Quaternary completed to to compliment compliment the the bedrock mapping geology mineral exploration, geology information information for for mineral exploration, environmental environmental and and land land use use applications. applications. With With the the announcement announcement of of he he alluvial alluvial diamond diamond discovery discovery in in the the Michipicoten Michipicoten River River area area in in the the fall fall of of 1993, 1993, the the OGS OGS extended extended it's it's mapping mapping and and overburden overburden sampling sampling program program to to the the Michipicoten Michipicoten River River valley. valley. From From these these Quaternary Quaternary mapping mapping projects projects an an understanding understanding of of overburden overburden types, types, their their distribution, distribution,and and physical physical and and geochemical geochemical properties guidebook and properties has has been been established. established. The The purpose purpose of of this this guidebook and related related field field trip trip is is to review review what what these local local overburden overburden materials effectively for mineral materials are are and and how how they they can can be used most effectively for mineral exploration. exploration. 17 �#I: Introductory Introductory Overview Overview Site Site Site *1; Appendix Appendix A: Algoma Algoma Ore Ore Division, Division, Helen Helen Mine Mine This first first stop stop overlooks overlooks abandoned abandoned open open pit pit workings workings on on the the Helen This Helen Iron Range from which a hematite-goethite hematite-goethite gossan gossan above siderite Iron Range from which above the the siderite and suiphide sulphide facies facies iron formation formation was was removed. removed. Extractive Extractive operations operations between 1900 1900 and and 1918 1918 produced produced an an estimated estimated 2,780,236 2,780,236 tons tons of of ore. ore. Operations Operations did did not not resume resume until until 1939 1939 when when open open pit pit mining mining of of the the unweathered unweathered siderite siderite began. began. Underground Underground mining mining of of siderite siderite began began in in 1949 1949 and and continues continues to to the the present. present. An estimated estimated 83,711,391 tons of siderite 83,711,391 tons siderite have been been produced produced up up until until 1986; 1986; reserves as of of 1984 1984 were were estimated estimated at at 58,246,000 58,246,000 tons tons (Sage (Sage and and Heather Heather 1991). 1991). On On aa clear clear day, day, this this site site provides provides aa spectacular spectacular overview overview of of the the Wawa area. The Wawa townsite, Citadel Gold Mines and the Wawa area. The townsite, the Lake Lake Superior basin can can be be seen seen to to the the southwest. southwest. Directly Directly south south is is Wawa Lake Lake which which occupies occupies a a linear linear bedrock controlled controlled valley 1 1 km km wide by by 88 km km long, long, and and 20-35 20-35mm deep. deep. During During deglaciation, deglaciation, this this valley was connected to higher lake levels within the Lake Superior valley was connected to higher lake levels within the Lake Superior basin. basin. The west end end of of this this basin basin closed closed as as aa barrier barrier bar, bar, on on which which Wawa Wawa is is built, built, formed formed during during regression regression of of lake lake levels. levels. At the the east east end end of of the the lake, lake, one one can can see see where where water water was forced forced through narrow bedrock bedrock controlled through aa narrow controlled constriction constriction to to form form aa delta delta in in Glacial Glacial Lake Lake Minong. Minong. To To the the north north is is aa spectacular spectacular view view of of the the defoliated defoliated zone zone where the the impressive impressive terraces terraces of the the Magpie River can be seen. can be seen. At summary of the the area's area's cultural cultural and and economic economic history, history, At this this site site aa summary vegetation, vegetation, climate, climate, bedrock bedrock and and Quaternary Quaternary geology geology in in addition addition to to the the physiography physiography will will be be reviewed. reviewed. Much Much of of this this information information is is provided guidebook. "Background Information" information^ section section of of this this guidebook. provided in in the the "Background Drive Drive to to Site Site #2. #2. As As we we pass pass through through Wawa the the road road rises rises onto onto aa pronounced, pronounced, raised raised The eastern part of Wawa is built entirely on sand surface. surface. The eastern part of Wawa is built entirely on sand and and minor minor gravels gravels of of aa barrier barrier beach beach bar bar that that sealed sealed the the southwest southwest end end of the the Wawa Wawa Lake Lake basin basin during during the the middle-Minong middle-Minong Lake Lake stage. stage. The The barrier beach was was modified modified by by aa combination combination of of shoreline shoreline wave wave cutting and fluvial terrace development of the Magpie River. cutting and fluvial terrace development of the Magpie River. The The western half terrace/beach half of of the the town occupies occupies aa prominent prominent terrace/beach surface. surface. There There is is an an arcuate arcuate escarpment escarpment edge edge that that limits limits urban urban development. Three steep escarpments are traceable across development. Three steep escarpments are traceable across town. town. 18 �Site *2: #2: Pothole. Pothole, Mat Mafic Lamwrowhvre Dike. Dike. Site ic and and Volcanic Volcanic Rock and Lamprophyre Appendix A: South South side side of of Highway Highway 101, 101, about about 10 10 km km east east of of Wawa. Wawa. Appendix This pothole, maf mafic volcanic rock lamprophyre This site site features features aa pothole, ic volcanic rock and and a a lamprophyre dyke. dyke. At At this this location location the the ice ice margin margin retreated retreated north-northeast north-northeast and and east east from from around around this this bedrock bedrock high. high. Debris-charged Debris-charged meltwater meltwater from this this wasting ice ice created created aa delta delta at at the the Glacial Glacial Lake Lake Minong Minong from level level within within the the Lake Lake Superior Superior basin. basin. Remnants Remnants of of this this delta delta are are visible visible below; below; aa site site we we will will visit visit later. later. At this this site, site, meltwater meltwater was was forced forced through through this this narrow narrow opening opening in in the bedrock under great hydrostatic pressure. demonstrated the bedrock under great hydrostatic pressure. This This is is demonstrated by by the the formation formation of of aa scour scour pool pool and and pothole. pothole. As As water water was was forced forced up and through this narrow bedrock up and through this narrow bedrock constriction, constriction, it it scoured scoured the the ground low side side of of the the constriction, constriction, leaving leaving what ground on on the the upf upflow what is is now now Ghost Ghost Lake. Lake. Within this this constriction, constriction, the the circular circular rotation rotation of of water rotated rotated "grinders" "grindersn that that literally literally drilled aa hole hole into into the the bedrock bedrock surface. surface. As ice ice continued continued to to waste waste eastward eastward from from this this site, site, this this meltwater meltwater channel channel was was abandoned abandoned and and flow flow was was directed directed south through the Firesand Creek Creek meltwater meltwater channel, channel, to to the the east east the Firesand . (Figure (Figure5). 5) There There are are excellent excellent exposures exposures of pillowed mafic volcanic bedrock and and aa lamprophyre lamprophyre dyke. dyke. The The dyke dyke has has an an elevated elevated radiation radiation level. level. There which likely There are are several several of of these these dykes dykes which likely radiate radiate outwards outwards from from aa carbonatite mineralogy carbonatite to to the the south. south. Little Little is is known known about about the the mineralogy of these these dykes dykes and and their their possible possible association association to to kimberlite. kimberlite. Drive Drive to to Site Site #3 #3 As As we we proceed proceed east, east, the the landscape landscape opens opens up up and and becomes becomes flat. flat. This This feature feature is is aa glaciofluvial glaciofluvial outwash outwash plain, plain, with with glacial glacial drainage drainage south Firesand Creek Creek meltwater meltwater channel channel to to the the south through through the the Firesand Michipicoten Michipicoten River River valley valley (Figure (Figure5). 5). Highway Highway 101 101 crosses crosses several several terraces downcutting of the outwash outwash surface surface terraces which which are are the the result result of downcutting of the by rivers rivers as as the the base base (lake) (lake) level level in in the the Lake Lake Superior Superior basin basin dropped. dropped. During it's it's eastward eastward retreat retreat across across this this valley, valley, the the glacier glacier likely likely stopped stopped several several times. times. Thebest The best evidence evidence for for this this is aa moraine moraine composed composed of of ice-contact ice-contact stratified stratified drift drift which which is is orientated perpendicular to the the valley valley axis. axis. The The highway highway cuts cuts through examine the materials of this moraine moraine through this this feature: feature: we we will examine the materials of this at 5. at Site ##5. At the the turnoff turnoff to to Hawk Hawk Junction, Junction, note note the the depression depression on on the the west side side of of Highway Highway 547. 547. This This circular circular depression depression is is aa kettle kettle which which formed when an ice block, after being detached from the main formed when an ice block, after being detached from the main ice ice body, These outwash and andsubsequently subsequentlymelted. melted. These body, was was buried buried by by outwash circular depressions, depressions, when filled filled with with water, water, look similar similar to to circular circular lakes lakes associated associated with with kimberlite. kimberlite. The The ice ice sitting sitting in in this this valley Firesand valley continued continued to to force force water water west west and and south south through through the the Firesand Creek meltwater channel water south Creek meltwater channel but but now now also also forced forced water south through through the the 19 �Grant Lake Lake meltwater channel (Figure (Figure 5). 5). meltwater channel In In route route to the town town of of Hawk Hawk Junction Junction Highway Highway 547 547 has been built on fine sand associated the distal distal edges edges of of aa glaciofluvial glaciofluvial fan. fan. associated with with the To the north north the the road road crosses crosses several several cycles cycles of of finefine- and and coarsecoarseTo the grained grained sand. sand. Each of these these cycles cycles represents represents proximal (coarse (coarse sand, boulders) and distal (fine sand) fans sand, boulders) and distal (fine sand) facies facies of glaciofluvial glaciofluvial fans associated stillstands of the the ice ice margin margin during during northward northward associated with stillstands retreat McVeigh Creek Creek valley. valley. retreat up up the the McVeigh Site #3: #3: Lodgement Till Section Section Appendix Appendix A: West of of Hawk Hawk Junction Junction this site site aa section section through through lodgement lodgement till is is examined examined and At this discussed discussed (Figure (Figure6). 6). The site is located located on on the the up-ice up-ice side side of of aa site is prominent bedrock Here, a prominent bedrock high. high. Here, relatively thick thick lodgement lodgement a relatively (subglacial) till has (subglacial) has been been deposited. deposited. The section consists consists of of aa black black (10 (10YR YR2/1 2/1rn), m), 10 cm cm thick thick humus humus The section layer containing abundant abundant decomposed decomposed roots roots and and leaf leaf matter. matter. The The I1Ael1horizon horizon lower contact is is wavy wavy and and clear. clear. The underlying "Ae" consists of consists of 13 13 cm cm of of light light grey grey silt silt (10 (10YR YR 7/2 7/2 m) m). This This material material appears The lower appears massive when when wet wet but but platy platy and and loose loose when when dry. dry. The lower contact is contact is wavy wavy and and diffuse. diffuse. The I1Bl1horizon horizon consists consists of of 25 25 cm cm of of The "B" reddish brown (10 (10 YR 4/4 4/4 m), m) , thick thick sandy sandy silt. silt. This is This material is massive and and slightly slightly compact. compact. Subangular clasts, up cm in in up to 9 cm diameter, diameter, are are common. common. The The lower lower contact contact is is wavy wavy and and diffuse. diffuse. The The I1Cl1 brown (10 (10 YR YR 4/4m), 4/4m), >> 50 "C" horizon horizon consists consists of dark dark yellowish yellowish brown 50 cm thick, sand. material is very very fissile, fissile, platy and and thick, silty sand. This material compact. to subangular subangular clasts clasts are are abundant. abundant. compact. Angular Angular to . In general, general, clast abundance abundance within within subglacial subglacial till till ranges ranges from from rare rare In with clasts to common, common, with clasts usually usually concentrated concentrated near the the bedrock bedrock contact. Till Till pebble lithology lithology determinations determinations indicate contact. indicate that that clasts clasts collected from collected from this this till till facies facies tend tend to to have have local local origin. origin. Pebbles Pebbles subglacial till collected from subglacial collected over over the the greenstone greenstone belt belt consisted consisted of granitic clasts clasts and 69.2% 69.21 clasts of 29.81 29.8% granitic the clasts derived derived from the supracrustal supracrustal rocks. rocks. Pebbles Pebbles from from till till collected collected over over the the granitic granitic terrane consisted consisted of granite clasts clasts and 30% clasts clasts derived derived from from terrane of 701 70% granite greenstone belt. the greenstone belt. SOIL SOIL WEATHERING Soil horizons are produced produced due due to to the the weathering weathering of of overburden overburden translocation of of weathered materials subsequent translocation weathered products products materials and subsequent through the through the soil soil profile. profile. This commonly commonly leads leads to to the the development development "B" and "C" of humus, "Aw, l1BI1 l1Cl1horizons. horizons. humus, "A", Soil profile profile studies studies have have demonstrated demonstrated geochemical geochemical differences differences between the oxidized "B" horizon (Coker between the oxidized I1Bl1horizon and unoxidized "C" l1CI1horizon (Coker and DiLabio DiLabio 1989; 1989; Shilts Shuts and and Kettles Kettles 1990; 1990; Law Law et et al. al. 1991). 1991). 20 �___ 1.0- Humus - Humus - "A" Horizon Horizon "B" W" Horizon Honzon iii ii. :. x z • 0 ... . . "C" C" Horizon Horizon 217/ç 148' 0— CL '••••• Si .. Ss Civ I GRftJN GRAIN SIZE SIZE CL Clay Clay Si SI Ss Cry Grv Sdt Silt Sand Sand Gravel Gravel 0- a Vvç bedding Mvy, bedding Humus Humus EIJ Fabric Fab(iC Figure 6: Lodgement till till section. See See text text for for description. description. 21 �Commonly, Commonly, the chalcophile chalcophile elements elements such such as as copper, copper, lead, lead, zinc, zinc, cobalt and nickel are leached out of the horizon the "B" I1Bv1 horizon due due to to the the breakdown of of the host host suiphide sulphide mineral. mineral. Chromium is as Chromium is not as susceptible to leaching-out I1BI1horizon horizon as as it it is is commonly commonly leaching-out of the "B" hosted hosted in in more more resistant resistant chromite. chromite. A horizon A relationship relationship exists exists between between the the clay clay percentage percentage of of aa soil soil horizon and and the the metallic metallic element element abundance abundance within within that that horizon. horizon. Clay Clay has has a high high element element adsorption adsorption capacity capacity due due to to the the large large clay clay mineral mineral a surface surface area and and related related charge. charge. and Kettles Kettles Shilts and (1990) (1990) demonstrated ( ~ 2 micron) micron) yields yields demonstrated that that the the clay clay fraction fraction (<2 significantly higher higher metallic metallic element element values values than than the the silt silt and and clay significantly clay size micron) fraction (~63 micron) fraction of of the the same same sample. sample. This This is is due due to to the the size (<63 dilution dilution of the the metal metal rich rich clay clay fraction fraction by by the the metal metal poor poor silt silt fraction. fraction. The clay clay mineral mineral distribution distribution with depth in in soil soil profiles profiles is is largely largely dependant dependant upon upon the the local local leaching leaching conditions conditions and and depth depth of of the soil soil profile. profile. Leaching conditions can be broken broken down down into into extensive, extensive, moderate and negligible negligible categories categories with with the the extensive extensive and negligible leaching and negligible leaching conditions conditions producing producing uniform uniform grain grain size size and and geochemistry geochemistry throughout throughout the the profile. profile. Intermediate leaching leaching Intermediate conditions provide variable variable grain grain size size and and geochemistry geochemistry through through conditions can can provide the (Birkland1974). 1974). the soil soil profile profile (Birkland Most of of the the till till deposits deposits in in the the Wawa Wawa area area are are thin thin and and consist consist largely horizon. largely of of aa "B" IIBI1 horizon. The The degree degree of of leaching leaching is is assumed assumed to to be be intermediate intermediate to to extensive extensive given given the the climatic climatic conditions conditions and and vegetation vegetation type. type. The The geochemistry geochemistry of of some some composite composite soil soil profiles profiles from from the the Wawa Wawa area area indicate arsenic and antimony are concentrated concentrated in indicate that that lead, lead, zinc, zinc, arsenic in the the humus humus layer layer relative relative to to the the other other soil soil horizons. horizons. This This may may be be due to to anthropogenic anthropogenic reasons reasons and and may may not not be be due due to to a a local local bedrock due bedrock source horizon llB1l horizon geochemistry geochemistry does does not not indicate indicate source as the the related related "B" any any anomalous anomalous geochemical geochemical values. values. The platy structure horizon has has the the typical typical platy structure and and light light colour colour of of The "A" "ANhorizon an horizon llAell horizon (Agriculture (AgricultureCanada Canada 1977). 1977) The an "Ae" The "Ae" I1Ael1 horizon of of the the horizon Wawa area area is is characteristically characteristically depleted depleted of of metallic metallic elements elements as as Wawa . clay from horizon. I1BI1 horizon. from this this horizon horizon has has been been eluviated eluviated into into the the "B" he "B" I1BI1horizon horizon commonly commonly has has aa sharp sharp upper upper contact contact with with the the "Ae" I1Ael1 The horizon. The horizon. The "B" IIBI1horizon is is typically typically enriched enriched with with element element illuviated horizon. illuviated from from the the "Ae" I1AeI1 horizon. The The occurrence occurrence of of aa "C" I1CI1horizon horizon in in the the subglacial subglacial till till is is rare. rare. Where horizon Where observed, observed, the the "B-C" llB-C1l horizon contact contact is diffuse diffuse with with no no accumulation The geochemistry accumulation of of clay clay at at the the contact. contact. geochemistry data data indicates indicates that an an enrichment enrichment of of metallic metallic elements elements within within the the "C" I1CI1 horizon horizon does does not not occur. occur. 22 �SUBGLACIAL TILL TILL AS AS A A MEDIA MEDIA FOR FOR DRIFT DRIFT PROSPECTING PROSPECTING SUBGLLCIAL from aa mineral mineral deposit deposit has has properties properties that that make make it it Till derived from unique from from surrounding surrounding tills. tills. unique properties properties could could These unique include specific specific clast clast types types or geochemical geochemical or heavy heavy mineral mineral signatures. signatures. The The unique unique property property is is referred referred to to as as the the indicator. indicator. bedrock from from which which these these unique unique properties properties were were derived derived is is The bedrock called called the the target. target. The indicator indicator is is usually concentrated concentrated at or or the target target (the (the head) head) and and decreases decreases exponentially exponentially down down ice ice near the (the tail; 1989, Peltoniemi Peltoniemi 1985, 1985,Szabo Szabo et et al. al. (the tail; Kazycki Kazycki and and Shilts Shuts 1989, . 1975, 1975, Shilts Shilts 1976) 1976) Recognition of variables variables which which control control material material dispersal dispersal were were defined defined during during the the first first OGS OGS Quaternary Quaternary project project in in the the Wawa Wawa area. area. This done through through examining examining the regional and local distribution distribution This was was done the regional of of clasts clasts within within till. till. On regional scale, control the relative On a a regional scale, the the rate rate of of ice ice flow flow will control the relative distance pass over distance of of material material transport. transport. Faster Faster flowing flowing ice ice will pass over a surface surface many many more more times times relative relative to to slower slower moving moving ice ice and and therefore therefore incorporate incorporate and and disperse disperse more more target target material. material. Studies Studies have demonstrated demonstrated that that ice ice streams streams within within ice ice sheets sheets transport transport materials materials farther farther than than the the surrounding surrounding ice ice (Dyke (Dykeand and Morris Morris 1989). 1989). One the more more important important observations observations made One of of the made from from the the regional regional clast clast data data was was that that ice ice flow flow over over the the Wawa Wawa area area was was relatively relatively uniform. uniform. This This is is reflected reflected in in the the relative relative uniform uniform concentration concentration and and dispersal dispersal distance distance of of clasts clasts from from related related bedrock bedrock types. types. This This is is not f of not to to imply imply that that the the broad broad dispersal dispersal of of material material on onto toor orofoff of different different bedrock bedrock terranes terranes is is everywhere everywhere equal. equal. There There are are local local factors which can can control control local local distance distance of of transport; transport; bedrock bedrock topography topography being being one one of of prime prime importance. importance. Some Some of of the the more more important important controls controls of of mineral mineral dispersal dispersal were were determined from from several several semi-regional semi-regional studies studies in in the the Wawa Wawa area. area. These These semi-regional semi-regionalstudies studies involved involved collection collection of of till till samples samples in in a a down down ice ice direction direction from from aa chosen chosen target. target. Indicators Indicators within within the the till were clasts till were clasts which which had had been been eroded eroded from from the the target. target. Although Although several studies are presented presented here here (Figure (Figure studies were completed completed only only 33 are 7). 7) Some Some of of the the more important important controls controls recognized recognized are: are: a) a) target target size size (Figures 8, 9); 9); b) b) topography topography (Figure (Figure 10); 10); c) c) relative relative hardness hardness of of (Figures 8, materials materials (Figure (Figure9); 9); and and d) d) relative relative rate rate of of ice ice flow. flow. The The semisemiregional regional studies studies indicate indicate that that distance distance of of transport transport was was consistently less less than than 88 km km and and commonly commonly less less than than 55 km. km. Source Source areas, perpendicular to areas, or or targets, targets, for for these these studies studies had had width width perpendicular to ice ice flow km or or greater. greater. flow of of 44 km 23 �H Cu H 0< rt (DLQ 0 rr (Drt (/)1—' (D• tiw (Drt CD '1w 1I1 CDrt rI) d CD I-i '<HH CD -o 0 irt H woo :j:i H Q F- (t PJ(DPJ rtNQ CD(D0 ci t CD II I-I. Ph Figure 7: Location of till sampling tranSeCtS. Although several were done, only 3 are presented here. See text for details. C in O 4 6 8 10 kilometers flow Pilot project Transect line. Orientation of line in direction of ice Felsic instrusive terrane Supercrustol terrane 2 �(rse u) NOUYA3 I 8 I .2 1 0 wc >t 0CLL ø 0 0 0 co 0 O 0 0 sseio % Figure Figure 8: 8: Mall Mall Lake Lake dispersal dispersal (small, (smallIlocal local target). target). Ice flow flow has has Ice dispersed dispersed granitic granitic clasts clasts southwest southwest of of granitic granitic terrane terrane over over the the greenstone greenstone belt. belt. The The percentage percentage of of granitic granitic clasts clasts decreases decreases exponentially, exponentiallyIas as expected, expected, until until the the ice ice crossed crossed aa small small granitic granitic stock. stock. The The percentage percentage of of granitic granitic clasts clasts increases increases at at this this point point then thendisappears disappears to within4 4km kmdownice downiceof of the the stock. stock. to O0%within 25 �(Ts i) NOLLVA31 . 1-e '- 8 I' r C-) C) C 0 >±f ocu-0 I DM1 I sseio % Figure Figure9:9: Wawa Wawa Lake Lake dispersal dispersal (larger, (larger! regional regional target). target). Granitic Granitic clasts clasts were were dispersed dispersed southwest southwestonto ontothe the greenstone greenstonebelt belt through f of through the the Wawa Wawa Lake Lakebasin basinofoff of aa granitic granitic terrane. terrane. This This granitic granitic terrane terraneis isaa large large target target with with flow flow into into aa basin. addition! the theindicator, indicator,granitic graniticclasts, clasts! is is basin. In In addition, relatively relativelyharder harder than thanmaterial material making-up making-upthe the greenstone greenstone belt. of belt. These These factors factorsallow allowfor foraalonger longerdistance distanceof transport, transport,10 10km. kmlthan thanmost mostother othersites. sites. 26 �(rse ii) NOUYA313 88 ,- - 'Eli 8 I .2 — 0 c E oE DII 0 0 0 (0 s1sIo % Figure Figure 10: 10: Black Black Trout Trout Lake Lake dispersal dispersal (topographic (topographicshadow). shadow). The The ice dispersed granitic clasts southwest off ice dispersed granitic clasts southwest off the the granite granite terrane topographically terrane onto onto the the greenstone greenstone belt in a topographically One sample rough area. collected on on the the down down ice ice rough area. One sample was collected side of a bedrock high, a site protected from site from the the side of a bedrock high, deposition deposition of of material material from from the the granitic granitic terrane. terrane. 27 �Drive Drive to to Site Site #4. #4. Air DaleI Dale, a sea We head back along Highway 547 to the turnoff to Air plane plane base that that caters caters largely largely to to sport sport fishermen fishermen during during the the summer. summer. Proglacial Outwash Site #4: Proqlacial Outwash Section Section Appendix A: Southeast Junction Appendix Southeast of Hawk Junction This This site site is is typical typical of of aa proglacial proglacial outwash outwash deposit deposit (Figure (Figure11). 11). The section section exists exists as as material material from from this this site site was was used used for for local local road construction. glacier was close proximity proximity to site road construction. The The glacier was in in close to this this site during deposition deposition of of the the material. material. This is indicated indicated by the the coarseness of of the the sediments sediments in in the the lower lower part part of the coarseness the section section indicating a high high energy, energyl ice ice proximal proximal depositional depositional environment. environment. The associated associated glacial meitwater meltwater spilled through the the Hawk Hawk Lake Lake basin meltwater channel Firesand Creek Creek meltwater channel and and south south into into the the basin into into the the Firesand Grant Grant Lake Lake meitwater meltwater channel channel (Figure (Figure5). 5). The The upper upper part part of of the the section, sectionl Unit Unit 11 (Figure (Figure11), 11)1consists consists of of 1.9 1.9 m pale brown brown (10 m of pale (10 YR YR 6/3 6/3 m) m) cobbly, cobblyl coarse coarse sand. sand. The The material is material is massive and and slightly slightly cemented cemented with with calcium calcium carbonate. carbonate. The lower lower contact is marked marked by a a 15 15 cm cm layer layer of of finely finely planar, planarl laminated laminated underlying unit, coarse coarse sand sand (Unit (Unit2). 2). The The underlying unitl Unit Unit 3, consists consists of of 3.5 3.5 m Faint, planar bedding 6 1 3 m) m) cobbly cobbly sand. sand. FaintI m of of pale pale brown brown (10 (10 YR YR 6/3 is best observed observed after after aa rain rain storm storm event. event. The beds dip dip gently gently west, westl parallel parallel to to Hawk Hawk Lake. Lake. Clasts Clasts are are subangular subangular to to subrounded subrounded and the the lower lower contact The lower lower unitl unit, Unit Unit 4, 4, consists consists and contact is is diffuse. diffuse. The pale brown of >13.7 >13.7 m of pale brown (10 (10 YR YR 6/3 613 m) m) boulder-rich boulder-rich gravel gravel with with aa The material coarse sand sand matrix. matrix. material is massive massive and loose loose with with subangular subangular to to subrounded subrounded boulders. boulders. material at this site The material site would be useful useful for for aa regional regional heavy heavy mineral is not not an ideal ideal media media for mineral or or pebble pebble sample. sample. It It is for local local drift drift sampling depositlsrestricted restricted distribution distribution and and more more sampling due to to the the deposit's regional regional material material composition. composition. This site, sitel and the the finefine- grained grained material we crossed crossed upon upon entering Hawk Junction, Junctionl demonstrate the variability materials associated associated with glaciofluvial glaciofluvial variability in in textures textures of materials outwash. With distance outwash. distance from from the the ice ice margin, marginl material material generally generally sorted becomes better and heavy mineral becomes better sorted and heavy mineral signatures more signatures more concentrated. concentrated. Drive to to Site Site #5 #5 Road conditions gravel track west that that Road conditions permitting, permittingl we we will will follow follow aa gravel track west skirts skirts the the outwash outwash plain plain to to the the south south and and the the south south shore shore of of Hawk Hawk Lake. Lake. 28 �____ . 19.25 S •s S. 5 S Unit II . • • . S • • . 17.35 17.20 . . ... ...- .•: . • . • Unit Unit 22 ...- ....-..- •\ •\\ .\\ •:•: I= w I Unit 3 Unit 3 •;::•;•::•; 2940 2624. ::.: 2460 13.7- . .. Unit 4 i * . . . CL Si Ss Grv GRAIN SIZE SIZE GRAIN CL CL Si Si ss Ss Grv Grv Clay Clay Sift Silt Sand Sand ?c m!/ Gravel Gravel bed bed Course dirty Course dirty outwash outwash Planarsand Planar sand beds beds I Paleocurrent Gravel Gravel Figure Figure 11: Proglacial outwash outwash section. section. See text for detailed description description and and discussion. discussion. 29 �#5: Moraine and Ice-Contact Ice-Contact Stratified Stratified Drift Drift Site #5: Appendix Appendix A: Southwest Southwest end end of of Hawk Hawk Lake Lake At At this we will this site will examine ice-contact stratified site we examine ice-contact stratified drift drift This is is the the associated with a a recessional recessional moraine (Figure (Figure 12). 12) same moraine moraine that that we we crossed Sites #2 and #3 while crossed between Sites #2 #3 while travelling travelling east east on on Highway Highway 101. 101. The ice ice sheet sheet existed existed in in aa state state of equilibrium equilibrium long enough enough to to deposit deposit the the morainic morainic material. material. Occasional flows of of diamicton diamicton (flow (flowtill) till) extended extended out out from from the the ice ice Occasional flows margin. The meitwater meltwater associated associated with this ice margin flowed margin. with ice margin flowed Firesand Creek Creek meltwater meltwater channel channel westward south into into the the Firesand westward then south (Figure 5) (Figure 5). . . section consists upper unitI unit, Unit lI 1, of reddish reddish The section consists of of 10 10 cm cm of an upper 413 m) m) cobbly cobbly sand. sand. The unit is is massive massive and and the the brown (5 YR 4/3 cobbles cobbles are are well well rounded, roundedIsome some flat. flat. The The lower lower contact contact is and is wavy and sharp. 514rn), m) I sharp. Unit Unit 22 consists consists of of 21 21 cm cm of of yellowish yellowishbrown brown(10 (10 YRYR5/4 very very fine fine sandy sandy silt. silt. The The material is masSive, massive, compact compact and and shows shows material is no reaction reaction with with HC1. HCl. Common Common clast types are of of rounded rounded granite granite and mafic mafic volcanic volcanic rock. rock. The lower lower contact contact is is smooth smooth and and wavy. wavy. is composed composed of 1.6 1.6 m m of of dark dark greyish greyish brown brown (10 (10 YR YR 4/3 413 m), m)I Unit 3 is coarse coarse sand. sand. The upper few few centimetres centimetres are massive with a few few large, largeI subangular subangular granite granite clasts. clasts. The The massive structure structure grades grades to to planar bedded sand, sandI with the layers accentuated by darker heavy mineral mineral bands. bands. The lower contact contact is is sharp. sharp. The lower Unit 4 4 consists consists of 3.61 3.61 m m of of light light yellowish yellowish brown brown (10 (10 YR YR 6/4 6 1 4 m) m) sand. sand. The upper 83 cm cm is is coarse coarse sand sand with with planar planar beds beds and and some some fine downwards to to sand sand which which comprises comprises most most of of the the ripples which fine The lower lower part of the the unit consists consists of of 1.44 1.44 m m of of m) unit (2.17 (2.I7 m). cycles cycles of of finer finer and and coarser coarser sand sand with with low low and and high high angled angled ripples, ripplesI some some with with foreset foreset bedding. bedding. The lower lower contact contact is is clear clear and and wavy. wavy. Unit 5 consists consists of greyish brown brown (10 4/2 m) coarse coarse Unit of 12 12 cm cm of dark greyish (10 YR 412 pebbly sand. pebbly sand. The The material material is is massive massive and and loose. loose. The are The pebbles pebbles are subangular subangular to to subrounded subrounded and and consist consist mainly mainly of of granitic granitic rock. rock. The The lower lower contact contact is is clear clear and and wavy. wavy. . consists of 38 38cm Unit 6 6 consists cmof of greyish greyish brown brown (10 (10YR YR 5/2 5/2 m) m) silty silty sand. sand. The material material is massive, compact The is massiveI compact and and reacts reacts strongly strongly with with HC1. HCl. The The lower contact is is wavy wavy and and clear. clear. Unit 7 7 consists consists of of of >5 m of brown (10 greyish brown (10 YR YR 5/2 512 m) coarse, coarseI pebbly pebbly sand. sand. The is The material is and loose. loose. There are abundant abundant subangular subangular to to subrounded subrounded massive and clasts. clasts. This lengthy lengthy section section description description emphasises emphasises the the stratification stratification of of materials associated with this type of deposit. The lower part of materials associated with this type of deposit. The lower part of the section (Units demonstrate the the very very close close proximity proximity of the section (Units 66 and 7) demonstrate of the site to the ice margin. Unit 66 represents f the site to the ice margin. Unit represents aa debris debrisflow flowofoff the margin, whereas the ice ice marginI whereas the the very very coarse coarse Unit Unit 77 represents represents aa highhighenvironment typical energy glaciofluvial typical of of an glaciofluvial environment an ice ice proximal proximal The upper units location. location. upper units represent represent either either an an ice ice marginal, marginalI 30 �31 for text See description. section. drift stratified contact Ice 12: Figure bedding Way, Paleocurrent bedding Planar 2W liii Colluvium outwash dirty Coarse, bed Gravel Gravel Sand Grv Silt Clay Si CL SIZE GRAIN 0 7 Unit 1 2 6 Unit 5 Unit 3 (I, 2350 Ui 0 z 271° 4 Ui 295° 4 Unit 5 6 229° 3 Unit 7 2 Unit 8 1 Unit Ss �perhaps fluctuating fluctuating setting, setting! or or aa braided braided stream stream environment. environment. The material associated associated with with this this site site is is not not regarded regarded as as aa prime prime sampling media f or local drift prospecting studies. sampling media for local drift prospecting studies. The The materials materials are derived derived from from both both local local and and distal distal sources. sources. In In addition, addition, the the distribution of material is distribution not widespreadI making it of this this material is not widespread, it difficult to to maintain maintain sample sample continuity. continuity. In In terms terms of of aggregate aggregate potentialI the materials are not not ideal ideal for for roadbed roadbed use use due due to to their potential, the materials are their example of how poor this this material is is for for fine-grained nature. An example fine-grained nature. roadbed construction construction is is demonstrated demonstrated by by the the poor poor road road which which we roadbed we just just travelled travelled over. over. Drive D r i v e to to Site S i t e #6 #6 Just east Site #5 the road takes takes a sharp sharp bend bend across across the the channel channel Just east of of Site where meltwater flowed from the Hawk Lake basin into the Brummer Lake into the Lake basin basin before before exiting exiting into the Firesand Firesand Creek Creek meitwater meltwater channel. As we we continue continue east, east! the enters onto a a broad broad channel. the road enters glaciofluvial outwash associated with the the Firesand Firesand Creek Creek glaciofluvial outwash plain associated meltwater meltwater channel. channel. Site Minon Delta S i t e ##6: 6 : Minonu Delta Appendix Appendix A: North North side side of Highway Highway 101, loll 10 10 km IUII east of Wawa The road which we have turned onto (Loonskin (Loonskin Lake Road) follows a series series of of sites sites which which demonstrate demonstrate features features associated associated with meltwater channels. channels. This site site is is at the the terminus terminus of a meltwater meitwater channel. HereI flowing from from ice ice situated situated in in the the Scott Scott channel. Here, meltwater flowing basinI empties into into Glacial Lake Lake Minong Minong (308 (308 mm asi). asl) The Lake basin, The materials you you see see here here are are associated associated with with aa delta delta which formed in in materials which formed this this lake lake about about 9200 9200 years years ago. ago. . There are There are several several excellent excellent sections sectionsthrough throughthe thelower lowerpart. part of of this this delta. delta. Material associated with the the upper upper part of of this this delta delta is is obscured by colluvium. It does does not not appear, appearI however, however! that the the by colluvium. topset beds of aa classic classic Gilbert-style Gilbert-styledelta delta exists exists at at this this site. site. topset beds of The lower lower part of of the the delta delta consists consists of of steeply steeply dipping dipping foreset foreset beds composed composed of poorly poorly sorted, sorted! subrounded subrounded to to subangular subangular cobbly cobbly gravel and and coarse coarse sand. sand. The bedding has has aa strong strong paleocurrent paleocurrent weakly to moderately cemented direction directionofof222266°. '. The The clasts clasts are are weakly to moderately cemented by by and, to a lesser lesser extent, extentI iron iron oxides, oxidesI primarily primarily limonite. limonite. calcite and! The origin The origin for for the the carbonate carbonate cement cement is is not not well well understood. understood. There There are 2 potential sources: are 2 sources: 1) 1) from abundant abundant syngeneic syngeneic carbonate carbonate alteration alteration (primarily (primarily ankerite) ankerite) of the the local local early early Precambrian Precambrian or; 2) from clasts originating from bedrock! or; clasts originating from the the metavolcanic bedrock, 2) Paleozoic carbonates of the Hudson Bay Lowland, Lowland! found found within within the the material. material. 32 �This This deposit deposit is is of of limited limited value value for for local local drift drift prospecting. prospecting. The The clast signature is a a blend blend of of both both local local and and heavy mineral and clast distal distal sources. sources. In addition, additionl the regional regional distribution of this this material material is is restricted restricted to to bedrock bedrock controlled valleys. valleys. The The aggregate aggregate from from this this pit pit has has been been used used for for road road bed bed construction. construction. Drive Drive to to Site Site #7 #7 We proceed proceed along Loonskin Lake Road as it it skirts skirts the the meltwater meltwater channel associated with the Minong Delta. the Minong Delta. Loonskin Lake Lake Road Road provides mined from was mined from the the provides access access to to the the Eleanor Eleanor Iron Iron Range Range which which was Sir Sir James James Dunn Dunn open open pit pit from from 1958 1958 to to 1967 1967 and and produced produced 1,646,000 116461000 tons tons of of siderite. siderite. Reserves Reserves below below the the pit pit floor floor are are estimated estimated at at 1,250,000 112501000tons tons of of siderite siderite (Sage (Sage and and Heather Heather 1991). 1991). The The Eleanor Eleanor Iron Range is at the eastern extension Iron Range is extension of the Helen Iron Iron Range and occurs in in aa wedge-shaped block bounded bounded on on the the west west and and the the east east by occurs wedge-shaped block Wawaof the the Mildred Mildred Lake Lake Fault Fault and and on on the the south south by by the the Wawabranches of Hawk-Manitowik Hawk-Manitowik lakes lakes fault. fault. Once pit, the passes over Once we we pass pass the the Sir Sir James James Dunn Dunn open open pitl the road road passes over the the surface flat! open open surface of of the meltwater meltwater channel channel represented represented by by flat, stretches stretches of of ground ground covered covered by by sand sand and and gravel. gravel. Site #7: and Kettle Xett].e(Dead (DeadIce) Ice)ToQoqraQhy ToPoraDhv # 7 : Xa.me Kame and A an excellent excellent example A brief brief stop stop is is made here here to to view an example of of kame kame and and kettle kettle topography. topography. Here, Herel aa block block of of glacial glacial ice ice became became detached detached from from the the active active ice ice margin and and was was subsequently subsequently buried by buried by glaciofluvial glaciofluvial deposits. deposits. Upon Upon melting, melting! depressions depressions and and conical conical hills hills composed composed of of sand sand and and gravel gravel formed. formed. Material associated associated with with this this deposit deposit is is derived derived from from both both local local and distal The distal sources. sources. The associated associated heavy heavy mineral mineral and and clast clast signature signature would be useful useful for for obtaining obtaining aa regional regional heavy heavy mineral mineral signature. signature. The The aggregate aggregate is is excellent excellent for for roadbed roadbed use. use. Drive Drive to to Site Site #7A Loonskin The Loonskin Lake Lake Road Road eventually eventually splits. splits. The west west branch, branch! now now blocked, blockedl leads to the the Lucy Lucy Pit Pit developed developed within the the Lucy Lucy Iron Iron Range. eastern extension Range. The The Lucy Lucy Iron Iron Range Range is is the the eastern extension of of the the Eleanor Eleanor Iron separated from the Eleanor Eleanor Iron Range by roughly roughly Iron Range. Range. It It is separated from the Iron Range 3500 m m of of left-lateral left-lateralfaulting. faulting. Mining operations operations were were short short lived lived and and ceased ceased in in 1970 1970 after after 33 years years of of operation. operation. The The operation operation produced 110731000tons tons of of siderite siderite and and reserves reserves are are estimated estimated at at produced 1,073,000 1,300,000 tons of siderite (Sage and Heather 1991). 113001000tons of siderite (Sage and Heather 1991). We We proceed proceed north north along along the the north north branch branch of of Loonskin Loonskin Lake Lake Road Road as as it it begins to drop in elevation. begins to drop in elevation. The The road road splits splits again again just just south south of of Scott lakel this this is is Site Site #7a. #7a. Scott lake, 33 �Site #7A: #7A: Modern Alluvium. Alluvium, Ice Ice Margin Maruin Deposit Deoosit site provides provides an an excellent excellent opportunity opportunity to to emphasize emphasize the the This site complexity complexity of of glaciofluvial glaciofluvial systems systems and associated associated meltwater meltwater channels. channels. As As noted, noted, the the road road falls falls in in elevation elevation from from the the Lucy Lucy Pit Pit turnoff to to this this site. site. For glacial meltwater to feed feed into into the the Loonskin Lake meltwater channel and the Minong Delta, Delta, Site Site ## 6, 6, drainage through Loonskin Lake have been been drainage through the the Loonskin Lake channel channel had had to have blocked. blocked. This This required required the the presence presence of of an an ice ice margin margin at at this thissite. site. However, margin receded, opening occurred However, as as the the ice ice margin receded, an an opening occurred between between the the ice ice margin margin and and the the bedrock bedrock controlled controlled high high ground. ground. This caused This caused abandonment of the the Loonskin Loonskin Lake Lake meitwater meltwater channel channel and and the the the abandonment establishment of glacial meltwater the Magpie Magpie River River establishment of glacial meltwater flow into the meltwater meltwater channel channel (Figure (Figure5). 5) . The Loonskin Lake Lake Road exposes exposes material material The section section on on the the east east side side of Loonskin associated associated with with this this moraine moraine (Figure (Figure13). 13). Although Although in in contact contact with with the margin, the the ice ice margin, the sand sand and and gravel gravel deposited deposited is is remarkably remarkably clean. clean. Unit yellowish brown consists of of 2.7 2.7 m m of of dark dark yellowish brown (10 (10 YR YR 4/3 4/3 m) m) sand sand Unit 11 consists (Figure material is massive and (Figure13). 13). The The material is massive and loose loose and and the the clasts clasts are are rounded. Unit 2 consists of 1.2 m layer of boulders that angle rounded. 2 consists of 1.2 m layer of boulders that angle upward through consists of of >5 m of of dark dark through the the section. section. Unit 33 consists yellowish brown brown (10 YR 4/3 4/3 m) m) cobbly sand sand containing containing abundant abundant angular angular clasts clasts and and boulders. boulders. As at at Site Site #7, #7, materials materials associated associated with with this this deposit deposit are are derived derived As from from local local and and distal distal sources. sources. Limestone Limestone clasts clasts from from the the Hudson Hudson Bay Bay Lowland, Lowland, for for example, example, have have been been found found here. here. Therefore Therefore the the heavy mineral mineral and and clast clast component component of of this this deposit deposit would would be be useful useful heavy for obtaining obtaining aa regional regional signature. signature. The The sand sand and and gravel gravel would would be be for an an excellent excellent source source for for road road bed. bed. SAMPLING SAMPLING MODERN ALLUVIUM A A small, small, unnamed unnamed stream stream flows flows north north into into Scott Scott Lake Lake at at this this site. site. As is heavily As this this stream stream flows flows through through glaciofluvial outwash it is charged with sediment sediment allowing allowing for for aa modern modern alluvium alluvium sampling sampling demonstration. The sample demonstration. sample site site consists consists of of aa well well developed developed diagonal modern alluvium diagonal bar. bar. Site Site observations observations are are made made using using the the modern alluvium site site sampling sampling observation observation sheet sheet (Appendix (AppendixB, B, p.57). p.57). Material Material is collected collected from beneath beneath the bar surface surface and and passed passed through a 1 cm2 steel mesh sieve. When enough material (10 kg) has has through a 1 cm2 steel mesh sieve. When enough material (10kg) passed passed through through the the sieve, sieve, excess excess water water is is drained drained from from the the sample sample and and poured poured into into aa sturdy, sturdy, well well labelled labelled plastic plastic bag. bag. The The bag bag is is placed placed in in aa haversack haversack and and the the weight weight is is roughly roughly checked checked by by scale. scale. A "baggywand and A piece piece of of paper paper with with the the sample sample number number is is placed placed in in aa "baggy" inserted inserted in in with with the the sample sample before before the the bag bag is is sealed. sealed. 34 �13. 12 • Unit II • 11 307' • 273-4. Unit2 Unit 2 243' 10 10 9 8 7 /L 6 Unit3 Unit 3 /L 5 4 3 30' /i 0 165' /L 2 /L 0 Si Ss Grv GRJN StZE CL CL CL Si ss Ss Grv Gw Figure Figure Clay Clay Silt Sand Sand Gravel Gravel [] Sand and gravel Sandandgravel BOUfS BOUHWS 13: Scott Lake Lake moraine moraine section. section. description description and and discussion. discussion. [] Cobbly C o wSand sand J% l pa~men Paleocurrent t See See text text for for detailed detailed 35 �Approximately 50 to 100 clasts Approximately 50 clasts are subsampled subsampled from the the coarse coarse material material retained retained on on the the screen. screen. In In additionl a subsample subsample of of the the addition, a finer finer grained grained material material (<1 (elcm2) cm2) is is panned and observations observations of of the the heavy mineral mineral fraction fraction are are made. made. material is also also The panned material stored in in a labelled labelled "baggy" vvbaggyll and put put in in with with the the clast clast sample sample bag bag stored and for future reference. reference. Any associated with for future samples associated Any interesting interesting rock rock samples the the site site are are also also collected collected and and labelled. labelled. The minerals and are derived derived The heavy heavy minerals and clasts clasts collected collected from from this this site site are from both the bedrock and from both the bedrock and overburden overburden through through which which this this stream stream has has passed. When interpreting passed. interpreting the data data from from this this sample, sampleI it it is is essential essential to to catalogue catalogue what what bedrock bedrock types types and and overburden overburden materials materials exist exist within within the the catchment catchment area area of of the the stream. stream. This This information information will provide a guide as to whether the stream sediment sediment signature will provide a guide as to whether the stream signature is is local. local. Any indicators indicators from from this this stream stream may may very very well well have have come come from from a great distance distance away away given given that that they they may may have have been been derived derived from large glaciofluvial glaciofluvial deposit deposit present present in in the the immediate immediate area. area. from a large RESTRICTIONS SEDIJ!4ENT SAMPLING SAMPLING RESTRICTIONS OF OF STREAM STREAM SEDIMENT Stream Stream sediment sediment sampling sampling in in the the Wawa Wawa area area has has demonstrated demonstrated that that aa sample collected at the mouth of aa drainage drainage basin basin gives gives aa heavy heavy mineral signature of the overburden (and to a lesser extent signature the overburden (and to a lesser extent the the bedrock) over which the over the stream stream flows between the sample sample site and the significant sediment standing body of water the first first significant sediment trap trap (i.e. (i.e. a standing such Therefore, as a to maximize such as a lake). lake). Thereforel to maximize the the area area being being "fingerprinted", it is advisable I1fingerprintedvv, it advisable to choose choose aa sample sample site site that that maximizes maximizes the the length length of of stream stream between between a a lake lake and and the the sample sample site site . (Figure (Figure 14). 14) It It is is also also critical critical to to recognize recognize the the orientation orientation of of the the drainage drainage basin being being sampled sampled relative relative to to ice ice flow. flow. The The heavy heavy mineral mineral signature modern alluvium alluvium sample reflect a deposit deposit farther farther signature of of a a modern sample may reflect up up the the drainage drainage basin basin or or beyond. beyond. Glacial Glacial erosion erosion of of such such aa target target may may result result in in related related heavy heavy minerals minerals being being transported transported and and deposited within the the area area of of the the stream stream segment segment that that the the sample sample site site represents. represents. If the the drainage drainage basin basin being being sampled sampled is is not not aligned aligned in in the the direction direction of of ice ice flow, flow, aa danger danger exists exists in in that that the the heavy mineral signature signature of that that drainage drainage basin basin may may represent represent aa target target located located up-ice up-ice but but in in the the neighbouring neighbouring (or (orfarther farther removed) removed) drainage drainage basin basin (Figure (Figure14). 14). Such Such a a problem problem was was recognized recognized in in aa sampling sampling program program in in Brazil Brazil (Gonzaga (Gonzaga et et al. al. 1994). 1994). Drive Drive to to Site S i t e #8 #8 We We will will backtrack backtrack south south down down Loonskin Loonskin Lake Lake Road Road to to the the Sir Sir James James Dunn Dunn Pit. Pit. Here Here we we will will follow follow an an abandoned abandoned rail rail bed bed north north to to the the defoliated defoliated zone zone of of the the Magpie Magpie River River drainage drainage basin. basin. The The railbed railbed initially cuts through bedrock terrane as as it it skirts skirts around around Lena Lena Lake Lake before before veering veering sharply sharply west west towards towards the the Magpie Magpie River River valley. valley. Just Just after after the the sharp sharp turn turn west, westl the the ground ground opens opens up up into into a a 36 �lndicator Dispersal Dispersal Examples of of Kimberlite Kimberlite Indicator within within Fluvial FluvialDrainage Drainage Basins Basins A t'o14 ¼ —KimberIite Pipe Kimberlite Indicator Mm erals Drainage Basin B Kimberlite Kirnberlite Indicator Indicator Minera Minerals \ Kirnberlite Drainage Basin I I I& 4?? A Kimberlite Indicator Minerals Drainage Basin 2 Lake Figure associated with modern alluvium Figure 14: 14: Problems Problems associated with sampling sampling modern alluvium within within drainage demonstrates llA1l demonstrates the the ideal ideal drainage basins. basins. Part Part "A" orientation I1Bf1 orientation of of drainage drainage basin basin to to ice ice flow. flow. Part Part "B" demonstrates problems associated associated with drainage drainage basin basin demonstrates problems orientation orientation perpendicular perpendicularto toice ice flow flow and and the the effects effects of of a a lake lake on on heavy heavy mineral mineral dispersal. dispersal. See See text text for for details. details. 37 �remarkable landscape, landscapeI reminiscent of the midwest midwest prairies prairies or or reminiscent of central arctic central arctic desert. desert. The glaciofluvial deposit which has been The road road passes over over a broad glaciofluvial fed number of meltwater meltwater channels fed by a number channels issuing issuing from from the the more more rugged, rugged! bedrock controlled controlled landscape landscape to to the the north north (Figure (Figure5). 5). As As the the road road bedrock swings south, pass onto swings southl we pass onto the the surface surface of of aa delta delta which which formed formed in in glacial Lake Lake Minong. Minong. surface elevation elevation of delta is is The surface of this delta equivalent to eqyivalent to the the surface surface elevation elevation of of the the delta delta at at Site Site #6. #6. As we we continue south south on on this this road, roadl we we will will descend descend over over several several terrace terrace surfaces which which formed surfaces formed as as the river river cut cut through through the the delta delta in in response to to lower lower lake lake levels levels in in the the Lake Lake Superior Superior basin. basin. *8: Mink Lake Glaciofluvia]. Fan, Straie Straie and and NU Forms Site #8: Glaciofluvial Fan, Forms This This site site overlooks overlooks the the basin basin that that contains contains Mink Mink Lake. Lake. Around Around the the shores of Mink Mink Lake Lake are These are shores are several several conical conical hills. hills. These are kames deposited in in association association with dead dead ice. ice. interpreted to be kames North, basin, is a smaller basin North! and immediately immediately in front of the basinI rimmed with rimmed with sand. sand. These These features features demonstrate demonstrate aa process process which which has has occurred throughout throughout the the topographically topographically higher higher areas. areas. Blocks Blocks of of ice ice became detached detached as as the the ice ice sheet sheet wasted wasted back. back. Over Over time time these these sediment-rich blocks of ice sediment-rich blocks ice melted melted in in place place leaving leaving kame kame deposits deposits such as In as those those which rim rim Mink Mink Lake. Lake. In addition, addition! meltwater meltwater associated with the blocks drained from from the basin basin associated the wasting of these blocks often leaving often leaving small small fans fans composed composed of of coarse coarse sand. sand. The heavy minerals and and clasts clasts associated associated with with these these deposits deposits are are derived from and distal distal sources sources and therefore therefore give give a regional regional derived from local local and signature. signature. They are not useful useful for for local local studies studies because because of of the the distal component of the material and their erratic and restricted distribution. distribution. Beyond the the small small fan fan there there is is aa spectacular spectacular view view to to the the northwest northwest of the the Magpie Magpie River River terraces terraces and and glaciofluvial glaciofluvial sandur sandur surface surface to to the northeast. The delta surfaces the northeast. The terrace terrace surfaces surfaces grade grade to to former former delta surfaces composed composed of material material transported transported to the Lake Lake Superior Superior basin basin by by meltwater meltwater channels. channels. Lake levels post date the last last retreat retreat of glacial glacial ice ice from from the the water plain in the Lake area. area. The highest continuous continuous water Lake Superior Superior basin associated with Minong which which existed within the basin basin is is associated with Lake Lake Minong existed within the basin PointI Sault Sault Ste. Ste. at about 9500 years years EP. BP. A drift drift sill sill at at Nadoway Nadoway Point, about 9500 Marie area, area! was cut through in in 5 5 or or 66 steps steps reflecting reflecting temporary lake lakes are referred lake levels levels in in the the Lake Lake Superior Superior basin. basin. These lakes to post-Minong (Dorion-I-IV) levels and terminated terminated with the to as the post-Minong (Dorion-I-IV)levels lowest, lowest! Houghton Houghton level level prior prior to to the the isostatic isostatic rebound rebound of of an an outlet outlet North Bay. at North Bay. The The terrace terrace surfaces surfaces viewed viewed from from this this site site are are all all related related to to the the above above chronology. chronology. 38 �Below the the Houghton Houghton level level there there were were aa series series of of additional additional lakes lakes Below which formed formed at at subsequently subsequently lower lower levels levels within the Lake Superior which within the Superior basin. Evidence basin. Evidence of of these these lower lower levels, levelsI which which include include the the Nipissing! Algoma! Sault and sub-Sault, sub-Sault! are all preserved within Nipissing, Algoma, lower reaches reaches of of the the Magpie Magpie and and Michipicoten Michipicoten river river valleys. valleys. the lower The The coarse coarse material material on on the the terrace terrace surfaces surfaces northeast northeast of of this this site site does does not not extend extend much much farther farther southwest. southwest. This This coarse coarse material material was was deposited by a progradation deposited by progradation of sandur sandur south south onto onto the the terrace terrace surfaces surfaces as as water water levels levels dropped dropped in in the the Lake Lake Superior Superior basin. basin. This This coarse material is overlies up to 33 m of finer finer thick and overlies coarse material is only only 11 m thick grained glaciolacustrine glaciolacustrine material material associated associated with with the the bulk bulk of of the the grained delta delta deposit. deposit. Once ice ice receded receded from from the the area area this this supply supply of of coarse material was coarse material was no no longer longer available. available. Site Site #10 #10 will will demonstrate demonstrate this this relationship relationship of of coarsecoarse- and and fine-grained fine-grainedmaterials. materials. North North of of the Mink Lake Lake basin basin is is an an exposed exposed surface surface of of highly highly polished polished and and striated rock which has also also been been incised incised by by glacial glacial meltwater meltwater forming forming ttfl I1Pl1forms. forms. Measuring when using overburden Measuring striae striae orientation orientation is is essential essential when overburden as as an an exploration exploration medium. medium. Obviously Obviously it is is necessary necessary to to know know the the direction direction from from which which materials materials were were derived. derived. At this this site site striae striae are are aligned aligned southwest southwestat at235°. 235'. The actual actual direction direction of of ice ice flow flow is is The determined determined by looking looking at at the the morphology of small small scratch scratch marks on on the bedrock surface. wall, the the the bedrock surface. On On the the up-ice up-ice side side of of the the fracture fracture wall! wall been plucked plucked by ice wall is is steep steep as as it it had had been ice freezing freezing onto onto the the rock rock surface, surface! thereby thereby pulling pulling the the rock rock away. away. As As ice ice continued continued to to flow flow over over the the fracture, fracture! the the down down ice ice wall wall was was smoothed smoothed by by abrasion. abrasion. Much Much controversy controversy exists exists regarding regarding the the formation formationof of "P" l1Pwforms. forms. Some Some argue argue that that they they are are the the result result of of strictly strictly glacial glacial erosion erosion while while others others argue argue they they are are caused caused by by glacial glacial meltwater meltwater flow flow under under high high pressure forms pressure between between the the rock rock surface surface and and ice ice base. base. These P" llP1l forms were were likely likely caused caused by by aa combination combination of of both both glacial glacial ice ice and and glacial glacial meltwater. forms llP1l forms indicates indicates meltwater. The The presence presence of of straie straie within within the the "P" that down onto the rock rock surface surface once once meltwater meltwater had that ice ice was let back down had been evacuated evacuated from from the the base base of of the the ice. ice. The The orientation orientation and and location of the I1Pl1 forms indicates that meitwater meltwater under high high the "P" hydrostatic pressure pressure did not not have have to to follow follow bedrock bedrock controlled controlled channels. The channels. The water water formed formed channels channels within within the base base of of the the glacier, glacier! ignoring ignoring the the configuration configuration of of the the bedrock bedrock topography. topography. Drive Drive to to Site S i t e #9 #9 • We backtrack backtrack northeast northeast along the Magpie River River road road to to Site Site #9, #9! crossing over the coarse surface of at least 2 terraces. crossing over the coarse surface of at least 2 terraces. 39 �#9: Older Alluvium Section Section Site *9: Appendix Appendix A: Magpie Magpie River River Road This site site is is optional optional given given the the time timeand andnunther number of of participants participants willing to willing clamber down down 33 coarse terrace terrace colluvium. to claniber 33 m of of coarse colluvium. Remember, in in this this case, case, that that what goes goes down down must must come come back back up up to to the the trucks. trucks. This site site is is situated situated on on the the south south bank bank of of the the Magpie Magpie River River just just upstream from where the sharp northwest jog upstream from where the river river takes takes a sharp jog around a bedrock outcrop. bedrock outcrop. The The section section is is through through a small small terrace composed of older older alluvium alluvium which which exists exists north north of of and and away away from from the the base base of of the 33 m of coarse terrace colluvium. coarse terrace colluvium. The The origin origin of of the the material material within this derived directly directly from sheet but within this terrace terrace is is not derived from the the ice ice sheet consists of reworked material derived from from the the higher higher elevation elevation deltas. This terrace terrace surface is graded to aa lower lower lake lake level level deltas. within the Superior basin basin after after glaciers glaciers had receded receded from within the Lake Lake Superior from the immediate area. immediate area. The bulk of of the the section section consists consists of of light light brown brown fine fine sand, sand, about about 1.5 m thick. thick. The material consists of couplets about 10 to 20 cm thick comprised comprised of thick of light light brown brown sand sand with with foreset foreset beds, beds, capped capped by by 55 cm of darker darker brown brown silt. silt. Paleocurrent measured from from the the fine— finegrained grained sand sand indicates indicates that that the the direction direction of of flow flow was was upstream! upstream! The couplets couplets of sand sand and and silt silt suggest suggest that that the the river river flow flow was was cyclic. cyclic. Cyclicity is is likely likely related related to to seasonal seasonal changes changes in in flow. flow. During the reduced During the summer summer months sand sand was deposited and during the reduced flow winter months the flow of the winter the deposition deposition of of the the finer finer grained grained silt silt took place. took place. Obviously, the silt would have to to settle settle through through aa standing body upstream flow direction is standing body of of water. water. The The upstream flow direction is confusing confusing until the site site is is put into into context context with the the bedrock bedrock obstruction obstruction downstream. downstream. This This site site was likely likely a whirlpool at one point in in time as as river river flow flow was was deflected deflected upstream upstream off off of of the the bedrock bedrock obstacle. obstacle. modern analogue analogue to occurs just downstream downstream from A modern to this this process occurs from this this site. site. The heavy minerals minerals and and clasts clasts associated associated with with this this alluvium alluvium deposit deposit The heavy would provide a regional regional signature as the materials are derived from both local local and and regional regional sources. sources. As aa local local indicator indicator this this material is is aa very very poor poor media media to to use. use. Not only only is is the the material material blended distally derived blended with with both both locally locally and and distally derived material, material, but but it it has has several cycles cycles of transportation and gone through through several of erosion, erosion, transportation gone deposition, deposition, making making it it impossible impossible to to trace trace an an indicator indicator back back to to it's In material is restricted source. In addition, addition, the material restricted to the lower lower source. reaches of the area's major rivers, rivers, making it it impossible impossible to to use use this material as as aa regional regional sampling sampling media. media. 40 �Drive Drive to to Site Site #10. #lo. We backtrack along Magpie River We continue continue to to backtrack along the the Magpie River Road Road until until the the road road branches just below a glaciofluvial escarpment. branches just below a glaciofluvial escarpment. Fine Fine sand sand winnowed winnowed from the coarse coarse aggregate aggregate by by prevailing prevailing northeast northeast winds winds blowing blowing off fromthe off Lake Superior is trapped trapped on on the the southwest southwest side side of of this this bedrock bedrock the road road bed bed is is made made of of eolian eolian sand, sand, it may not not be be As the possible to to get get to to Site Site #10 #10 if if the the road road is is wet. wet. possible high. high. Site #10: #lo: Glaciolacustrine Glaciolacustrine Section Section Appendix A: Magpie Magpie River River Road Appendix The The section section at at this this site site shows shows the the complete complete suite suite of of materials materials associated his is is one one of the the few few associated with with the the terraces terraces (Figure (Figure15). 15). This sites sites where where the the terrace terrace escarpment escarpment is is not not obscured obscured by by boulders. boulders. In In simple simple terms, terms, the the section section consists consists of of 33 main main units. units. The The upper upper unit, unit, Unit Unit 1, 1, consists consists of of 11 mm of of brown brown to to dark dark brown brown (10 (10YR YR 4/3 4/3 m) m) coarse coarse sand sand and and boulders. boulders. The The material material is is massive massive and and loose. loose. The The boulders and clasts clasts consist consist of of aa wide wide variety variety of of lithologies lithologies of of varying sizes sizes and and degrees degrees of of roundness. roundness. The lower lower contact contact is is abrupt abrupt and and smooth. smooth. Unit Unit 22 makes makes up up the the bulk bulk of of the the terrace. terrace. The The description description here here is is an an extremely extremely simplified simplified description description of of the the associated associated material material structures Essentially, structures and and textures. textures. Essentially, Unit Unit 22 consists consists of of alternating m) coarse coarse sand, sand, brown brown (10 (10 alternating beds beds of of pale pale brown brown (10 (10YR YR 4/3 4/3 m) YR YR 4/3 4/3 m) m) sand sand and and light light grey grey (2.5 (2.5 YR YR m) m) fine fine sand. sand. Thicknesses Thicknesses of of each each sandy sandy bed varies varies between between 22 mm and and 30 30 cm. cm. Related Related structures structures include include massive massive to to planar planar beds beds in in the the course course sand, sand, planar planar beds beds to to trough trough cross-bedding cross-bedding in in the the sand sand and and trough trough cross-bedded, cross-bedded,planar planar and and massive massive beds beds in in the the fine fine sand. sand. The The vertical vertical distribution distribution of of sand sand textures textures represent represent fining fining upward upward cycles. cycles. The The lower lower contact contact associated associated with with the the coarse coarse sand sand is is often often smooth smooth and and clear. clear. The The lower lower contacts contacts associated with the other other sand sand textures textures are are more more gradual gradual or or diffuse. diffuse. Unit 3, the the lowermost lowermost unit, unit, consists consists of of horizontally bedded bedded Unit 3, couplets couplets of of varved varved silt silt and and clay. clay. There There are are at at least least 25 25 couplets couplets each about about 25 25 cm cm thick. thick. The lowest lowest couplet couplet drapes drapes the the bedrock bedrock The surface. surface. This This section section represents represents the the progradation progradation of material (Units (Units 11 and over material deposited in deeper water (Unit 3) Clearly, 2) Clearly, 2) over material deposited in deeper water (Unit 3) this section indicates that the bulk of material that makes this section indicates that the bulk of material that makes up up the the is fine-grained and has limited use as an aggregate terraces terraces is fine-grained and limited as an aggregate resource. resource. Samples Samples of of the the heavy heavy minerals minerals and and clasts clasts of of this this deposit deposit would be useful These would be useful to define define aa regional regional signature. signature. These same' same * materials for local local prospecting prospecting due due to: to: the the materials would would not not be be as as useful useful for local and distal distal sources sources for for the the materials; materials; and and the the restricted restricted distribution distributionof of these these deposits deposits to to the the mouths mouths of of major major rivers rivers around around . . 41 �Unit II Unit Gravel Gravelbed bed Wavy, planar planarbed bed 278° Trough Trough cross cross bed bed /203° Planar Planarbed bed Foreset Foresetbed bed \1500 Massive Massive bed bed Diffuse Diffusebed bed 1195° Rounded Roundedclasts clasts '\145° 260° Unit 2 Unit2 220° 277 CL Si Ss Grv Paleocurrent Paleocurrent Clay Clay Silt Silt Sand Sand Gravel Gravel Ui (I) 228° 230° . /'220° 25 Couplets Unit 33 Unit 0 CL CL Si Si Ss Grv Gw GRAIN GRAIN SIZE SIZE Figure Figure 15: Glaciolacustrine Glaciolacustrine section. section. discussion. discussion. See See text for description and 42 �the the Lake Lake Superior Superior basin. basin. Drive to Site Site *11 #11 again backtrack backtrack to the the Magpie Magpie River Road and and continue continue north We again toward across glaciofluvial glaciofluvial outwash #ll. The The road road continues continues across toward Site Site #11. associated with aa remarkable remarkable glaciofluvial glaciofluvial fan, fanl east east of of the the road. road. associated with Parallel to to the the railroad railroad is is an an elongated elongated lake. lake. This is is aa scour scour #2. Note the lag lag of of pool similar to the the one one discussed discussed at Site Site #2. boulders on the the downf downflow low side side of of the the lake lake which which where where literally outwash surface surface by by water water under under blasted out of the the glaciofluvial glaciofluvial outwash tremendous hydrostatic hydrostatic pressure. pressure. tremendous Site *11: #11: Steephills Stee~hillsFalls Falls Moraine Moraine Appendix Appendix A: Magpie Magpie River River Road This site site provides an example of a recessional recessional moraine moraine composed of This materials materials more more typically typically described described in in the the literature. literature. The The moraine represents state of equilibrium equilibrium between between ablation ablation and and accumulation accumulation represents aa state of ice within the ice within the ice ice sheet's sheetlsglacial glacial budget. budget. However! this state state However, this was short-lived short-lived since since the the moraines moraines are are relatively relatively of equilibrium was small sections through small and and not not laterally laterally extensive. extensive. There are no sections this moraine moraine although although the this the moraine moraine is is likely likely composed composed of of flow flow tills. tills. This assumption assumption is made from from observations observations of sections sections through through recessional moraine moraine elsewhere recessional elsewhere in in the the area. area. Clast abundance abundance ranges ranges from from rare rare to to common common with with clasts clasts sometimes sometimes concentrated within flow concentrated flow structure. structure. Pebble type assemblages assemblages Pebble determined moraine deposited deposited over over greenstone greenstone and and determined from from flow flow tills tills in in moraine granitic granitic terranes terranes were were compared. compared. Pebble Pebble assemblages assemblages within flow flow till associated with moraine till associated with moraine deposited deposited on the the greenstone greenstone belt belt consisted of granitic clasts clasts and and 67.8% 67.8% clasts clasts of 31.6% granitic of greenstone greenstone consisted of 31.6's Pebble assemblages within flow till of belt origin. origin. Pebble assemblages within of moraine moraine deposited granitic terrane 34.91 clasts clasts of greenstone greenstone deposited on on granitic terrane consist consist of of 34.9% belt origin origin and and 61.5% granitic granitic clasts clasts. These belt These pebble pebble type type assemblages differ little from from the the pebble assemblages differ little pebble type assemblages type assemblages associated with subglacial subglacial till till collected collected from from over over granitic granitic and and greenstone greenstone belt belt terrane. terrane. . The average average concentration concentration of Paleozoic Paleozoic clasts clasts within lodgement lodgement and The However, flow tills tills differs differs little. little. However, Paleozoic within Paleozoic clasts within subglacial till till have aa more regional! homogeneous homogeneous distribution distribution subglacial more regional, throughout the region whereas Paleozoic Paleozoic clasts clasts tend to have a more more throughout the region distribution within moraines; moraines; more more concentrated concentrated within within erratic distribution certain moraines moraines over certain over others. others. The geochemical, heavy mineral The geochemicall mineral and and clast clast composition composition of of the the morainal material morainal material at at this this site may be be useful useful as a regional as a regional as the moraine is signature as is composed composed of of materials materials derived derived from from local and reason! the the moraine moraine would would not not local and distal distal sources. sources. For For this this reason, be be useful useful as as aa local local sampling sampling media. media. 43 �Drive D r i v e to t o Site S i t e #12 #12 The The trip trip continues continues towards towards the the Steephills Steephills Falls Falls Dam. Dam. West West of of the the dam, daml the the road road crosses crosses several several valleys valleys filled filled with with glaciofluvial glaciofluvial materials. materials. These These are are former former meitwater meltwater channels channels that that fed fed into into the the Magpie southlHighway Highway 17 Magpie River River valley valley (Figure (Figure5). 5). Proceeding Proceeding south, 17 drops drops below below the the Lake Lake Minong Minong level level north north of of Wawa Wawa and and again, againl the the road road crosses over several terrace surfaces. crosses over several terrace surfaces. Site S i t e #12: Summary Summarv Site Site Appendix Appendix A: A: Visitors Visitors centre, centreIWawa Wawa This This last last stop stop provides provides an an excellent excellent view view over over the the lower lower reaches reaches of of the the Magpie Magpie River River valley. valley. Several of the the terraces terraces thatrim thatrim the the valley valley walls walls provide provide aa perspective perspective of of how how high high former former lake lake levels levels were were within within the the Lake Lake Superior Superior basin. basin. visitors centre centre is is The visitors situated m) situated on on the the lowest lowest Glacial Glacial Lake Lake Minong Minong terrace terrace surface surface(294 (294m). . It It is is sincerely sincerely hoped hoped that that this this guidebook guidebook and and related related field field trip trip provided provided an an appreciation appreciation regarding regarding the the use use and and limitations limitations of of overburden overburden in in mineral mineral exploration. exploration. When When done done correctly, correctly, drift drift prospecting prospecting can can be be an an effective effectivetool tool to to aid aid mineral mineral exploration. exploration. Sunixnary of Sites: Sites: Summary of 1) 1) Bedrock Bedrock surface surface features features associated associated with with glacial glacial advance advance and and ice ice margin #I and and 8). 8). Discussion Discussion margin retreat retreat were were reviewed reviewed (Sites (Sites#1 included included the the importance importance of of ice ice flow flow indicators indicators in in establishing establishing ice ice flow flow direction, directionl essential essential for for determining determining material material source. source. 2) 2) The The need need to to understand understand local local Quaternary Quaternary history history was discussed discussed (all sites) local ice ice flow flow patterns patterns across across an an area area (all sites) to determine determine local and and to to determine determine ice ice margin margin retreat retreat patterns patterns and and associated associated meltwater meltwater flow. flow. This This aids aids in in interpreting interpreting the the results results of of any any glaciofluvial glaciofluvial (Sites (Sites#2, #21 4, 4, 8), 81, glaciolacustrine glaciolacustrine(Sites (Sites#6, #GI 8, o1 10) or or modern modern alluvium alluvium (Site (Site #7, #71 7a) 7a) samples samples taken. taken. 10) 3) The The use use of of subglacial subglacial till till (Site (Site *3) #3) as as the the important important medium 3) for for local local drift drift prospecting prospecting was was highlighted. highlighted. The The physical physical characteristics characteristicsand and pedogenic pedogenic processes processes that that affect affect geochemical geochemical signatures signatures and and style style of of material material sampling sampling were were reviewed. reviewed. 4) 4) Glacially Glacially derived derived materials materials and and related related landforms landforms that that provide provide aa more more regional regional signature signature for for drift drift prospecting prospecting were were discussed. discussed. These These included included proglacial proglacial outwash outwash (Site (Site#4), #4) ice ice contact contact stratified stratified drift drift (Site (Site *5), #5), glaciofluvial glaciofluvial outwash outwash (Sites (Sites#7, #7# 7a, 7a1 8), 8)1 recessional recessional moraine moraine (Site (Site #11) #ll) and and glaciolacustrine glaciolacustrine 10). The The discussion discussion considered considered the the value value deposits (Sites (Sites#6, #GI10). deposits and and limitations limitations of of these these materials materials as as drift drift prospecting prospecting media. media. 44 �5) The materials materials and arms that that have have undergone undergone several several 5) The and related related landf landforms cycles cycles of of erosion, erosionl transportation transportation and and deposition deposition were were investigated. investigated. These These include include modern modern alluvium alluvium (Site (Site #7, #7, 7a), 7a)! older alluvium (Site #9) #9) and and glaciolacustrine deposits (Site (Site#6, #GI older alluvium (Site glaciolacustrine deposits 10). The The value value and and limitations limitations of of using using these these materials materials as as 10). sampling media media for for drift drift prospecting prospecting were were also also reviewed. reviewed. sampling ACKNOWLEDGEMENTS The or allowing allowing The author author thanks thanks Rudy Rudy Hoffman Hoffmanand and Algoma AlgomaOre OreDivision Divisionffor property property access. access. This This trip trip would not not have have been been possible possible without without their cooperation. Ed Freyls Frey's comments comments regarding regarding Quaternary Quaternary studies studies their cooperation. within the the Wawa Wawa area area was was appreciated. appreciated. Ron Ron Sage Sage (OGS) (OGS) provided provided direction regarding regarding the bedrock component component of this this field field trip. trip. Catherine Catherine Farrow and Cam Cam Baker Baker (OGS) (OGS) reviewed the the manuscript. manuscript. 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BSc. Thesis, Thesis, McMaster McMaster University, University, Hamilton, Hamilton, Ontario, Ontario,54p. 54p. Peltoniemi Peltoniemi H. H. 1985. 1985. Till Till lithology lithology and and glacial glacial transport transport in inKuhmo, Kuhmo, eastern eastern Finland; Finland; Boreas, Boreas, v.14, v.14, p.67-74. p.67-74. Rupert Rupert R.J. R.J. 1979. 1979. Geology Geology of of McMurray McMurray Township Township and and parts parts of of surrounding surrounding townships, townships, District District of of Algoma; Algoma; Ontario Ontario Geological Geological Survey, Survey, Open Open File File Report Report 5283, 5283,170p. 170p. Saarnisto Saarnisto M. M. 1974. 1974. The The deglacial deglacial history history of of the the Lake Lake Superior Superior region region and and its its climatic climatic implications; implications; Quaternary Quaternary Research, Research, v.4, v.4, p.316-339. p.316-339. 47 �I Sage R.P. 1994. Geology of the Michipicoten greenstone belt; Ontario Geological Survey, Open File Report 5888, 592p. Sage R.P. mineral Canada, Toronto and Heather K.?. 1991. The structure, stratigraphy and deposits of the Wawa area; Geological Association of Society of Economic Geologists, Joint Annual Meeting, '91, Field Trip AG, Guidebook, 118p. Seely J.B. and Senden T.J. 1994. Alluvial gold in Kalimantan, Indonesia: a colloidal origin?; Journal of Geochemical Exploration, v.50, p.457-478. Sharp D.R. and Shaw J. 1989. Erosion of bedrock by subglacial meltwater, Cantley, Quebec; Geological Society of America Bulletin, v.101, p.1010-1020. Shuts W.W. 1976. Glacial till and mineral exploration; in Glacial Till, Royal Society of Canada, Special Publication 12, p.205-224. Shilts W.W. and Kettles I.M. 1990. Geochemical/mineralogical profiles through fresh and weathered till; in Handbook of Indicator Tracing, A.A. Balkema, Rotterdam, p.187-216. Sutherland D.G. 1982. The transport and sorting of diamonds by fluvial and marine processes; Economic Geology and the Bulletin of the Society of Economic Geologists, v.77, no.7, p.1613-1620. Sutherland D.G. 1993. The diamond deposits of the Mandala basin, SE Guinea, West Africa; Transactions of the Royal Society of Edinburgh; Earth Sciences, v.84, p.137-149. Szabo N.L., Govett G.J.S. and Latjai E.Z. 1975. Dispersion trends of elements and indicator pebbles in glacial till around Mt. Pleasant, New Brunswick, Canada; Canadian Journal of Earth Sciences, v.12, p.1534-1556. Thomas D.A. 1984. Stratigraphy, Lithology, Petrography and Depositional Environments of the Dore' Sediments Proximal to the Lucy Iron Range, Wawa, Ontario; Unpublished BSc. Thesis, Carleton University, Ottawa, Ontario, 37p. Thurston P.c. 1986. Volcanic cyclicity in mineral exploration: the caldera cycle and zoned magma chambers; in Volcanology and Mineral Deposits, Ontario Geological Survey Miscellaneous Paper 129, p.104-123. Wolfe W.J., Lee H.A. and Hicks W.D. 1975. Heavy mineral indicators in alluvial and esker gravels of the Moose River Basin, James Bay Lowland, District of Cochrane; Ministry of Natural Resources Geoscience Report 126, 60p. 48 �APPENDIX APPENDIX A A ROUTE ROUTE MAPS Appendix Appendix Appendix A A consists consists of: of: Regional Regional plan plan of site site locations, locations, Appendix A-i A-1 : Portion Portion of NTS Sheet Sheet 42 42 C/2 C/2 (Hawk (Hawk Junction), illustrating illustrating location location of of site site Junction), numbers 6, 7, 7, 7A, 7A, 8, 8, 9, 9, 10, 10, ii 11and numbers 1, 1, 2, 2, 6, and route; route; Appendix Appendix A-2. A-2. : Portion Portion of of NTS NTS sheet sheet 42 42 C/2 C/2 (Hawk (HawkJunction) Junction) illustrating illustratinglocation locationof of site sitenumbers numbers3, 3,4, 4, 5 5 and and route, route, Appendix Appendix A-3. A-3. : Portions Portions of of NTS NTS sheets sheets 42 42 C/2 C/2 (Hawk (Hawk Junction) (Michipicoten Junction) and and 41 41 N/15 ~/15 (Michipicoten Harbour) illustrating illustrating location location of of site site Harbour) nuniber 12 and and route; route; Appendix Appendix A-4. number 12 A-4. 49 �0 I-i. (D Appendix A - 1 N. C. •7S N. C. C. RAILROADS ROADS VATER BODIES TDWNS SIt• Numb•r 723325 N. C. 7?tOO . C. I § �'___i V - V\ —H - L \Site#l - I Appendix Appendix A-2 A-2 51 �Appendix Appendix A-3 A-3 52 52 �Appendix A-4 53 �APPENDIX APPENDIX B B SITE SITE AND AND MATERIAL MATERIAL OBSERVATION OBSERVATION SHEETS SHEETS Appendix Appendix consists consists of: of: Till Till observation observation forms, forms, p.55 p.55 : Modern Modern alluvium alluvium observation observation forms, forms, p.57 p.57 : Field Field note note definitions, definitions, p.58 p.58 (modified (modified from from Agriculture Agriculture Canada Canada (1977) (1977) 54 �Air Photo: Photo: Air U.T.M. U.T.M. Ref.: Ref.: Stop Stop Number: Number: Sample Sample Number(s): Number(s): -- Comment: Comment: Site Site Description Description A) A ) Genetic Genetic Material: Material: B) B) Surface Surface Expression: Expression: apron/ apron/ blanket! blanket/ fan/ fan/ hummocky/ hummock$/ inclined/ inclined/ • level/ level! rolling/ rolling! ridged/ ridged! steep/ steep! terraced/ terraced! undulating/ undulating/ veneer! veneer/ location: location: C) C) Slope: Slope: InclinationInclination- AspectAspect- D) D) Drainage: Drainage: Well Well drained! drained/ Moderately Moderately well well drained/ drained/ Poorly Poorly drained drained E) E) Vegetation: Vegetation: TypeType- Coniferous! Coniferous/ Deciduous/ Deciduous/ Mixed/ Mixed/ Scrub! Scrub/ Grass! Grass/ Bog! Bog/ Other: Other: State: State- Virgin! Virgin/ Logged! Logged/ Fired! Fired/ Stress: Stress: F) F) Material Material Thickness: Thickness: Class Class 1/ I/lÀ! 1A/2/ 2/ 3/ 3 / Other: Other: Material Material Description Description Horizon: Horizon: AA BB C A) A ) Colour: Colour: Munsell Munsell Code: Code: B) B) Texture Texture Sand: Sand: Coarse! Coarse/ Medium! Medium/ Fine Fine Silt: Silt: Sandy! Sandy/ Silt! Silt/ Clayey Clayey Clay: Clay: Silty! Silty/ ClayClay- Organic Organic C) C ) Structure Structure Type: Type: Structureless! Structureless/Block! Block/ Plate! Plate/ Prism! Prism/ Flow Flow Other: Other: Kind: Kind: Massive! Massive/ Blocky, Blocky, << blocky! blocky/ Platy/ Platy/ Prismatic, Prismatic,Columnar Columnar Flow: Flow: Size: Size: D) D) Consistency Consistency WetWet- Nonsticky/ Nonsticky/ Slightly Slightly ' Sticky! Sticky/ Sticky Sticky MoistMoist- Loose! Loose/ Friable! Friable/ Firm Firm DryLoose! Soft! Dry- Loose/ Soft/Kard Hard E) E) Plasticity Plasticity —Nonplastic/ -Nonplastic/Slightly Slightly Plastic! Plastic/Plastic Plastic 55 �Material Material Description Description (Cont) (Cont) Horizon: Horizon: A B C F) Cementation Cementation (Yes/ (Yes/ No) No) - Weak! Weak/ Strong! Strong/ Indurated Indurated C) G) Clasts Clasts Rare/ Few! Few/ -Abundance; Rare! Common! Common/ Abundant -- Size; Size; -- Shape; Shape; Rounded! Rounded/ Subrounded Subrounded Angular/ Angular/ Subangular Subangular -Striated (Yes/ No); No); -Striated (Yes! -Type; -Type; Plutonic/ Plutonic/ SupraSupracrustal/ Marine Marine H) Lower Lower Horizon Horizon Boundary Boundary Diffuse/ -Distinctiveness; Diffuse! Gradual! Gradual/ Clear Clear - Form; Form; Smooth! Smooth/ Wavy! Wavy/ Irreg. Irreg. I) I) Unit Unit Thickness: Thickness: COMMENTS/ COMMENTS/ DIAGRAM(S) DIAGRAM(S) 56 �__ _________ MODERN ALLUVIUM ALLUVIUM OBSERVATION OBSERVATION FORM FORM General General Aerial Aerial Photo: Photo: U.T.H. U.T.M. Reference: Reference: #: Stop #: Stop Sample SampleNuiriber(s): Nurnber(s) : Site Site Description Description A) Material: Material: A) B) B) Surface Surface Expression: Expression: apron! apron/ blanket! blanket/ fan! fan/ hunimocky! hummocky/ inclined! inclined/ level! level/ rolling! rolling/ ridged! ridged/ steep! steep/ terraced! terraced/ undulating! undulating/ veneer veneer AspectAspect - C) Slope: Slope: InclinationInclinationC) D) D) Drainage: Drainage: Strong! Strong/ Moderate! Moderate/ Weak! Weak/ Ephemeral Ephemeral E) E) Vegetation: Vegetation: TypeType- Coniferous! Coniferous/ Deciduous! ~eciduous/Mixed! Mixed/ Grass! Grass/ Bog! Bog/ Other; Other; StateVirgin! Logged! State- Virgin/ Logged/ Fired! Fired/ Stress: Stress: Material Material Description Description Munsell Mimsell Code: Code: A) Colour: Colour: A) B) Fine/ Other: Other: B) Texture: Texture: SandSand- Coarse! Coarse/ Medium! Medium/ Fine! C) C) Structure: Structure: Structureless! ~tructureless/Current Current and and Wave Wave Ripples! Ripples/ Cross Cross Bedding! Flaser and and ~edding/Climbing Ripple Lamination! Lamination/ Flaser Lenticular Bedding! Graded Bedding! Rhythmites/ Flow! LenticularBeddinq/ Graded~edding/ Rhythmites/ Flow/ Undetermined Undetermined D) D) Form: Bar Form: Bar ROW Foan Pattern Longitudinal: Transverse: [) i\_"'' Pton 1) " Growth Pattern Transverse Longitudin( J ..—. ' /'' -' Pot Diagonot: E) Clasts: Clasts: E) \ — Abundance; Abundance; Rare! Rare/Few! Few/Common/ Common/ Abundant Abundant Size Size Range; Range; Shape; Subrounded/ Angular Shape; Rounded! Rounded/ Subrounded/ Angular Striated; Striated; Yes! Yes/ No No Types; Types; 57 �FIELD DEFINITIONS FIELD NOTE NOTE DEFINITIONS Stop Number: HJxx/91 Stop Number: HJxx/91 HJRefers : HJRefers to sheet. to project project NTS NTS map sheet. xxRefers : xxRefers to Sample numbers numbers run to sample sample number. number. Sample run consecutively from consecutively from 1-n. 1-n. /91- Refers Refers to : /91to the the project project year. year. U.T.M. Reference: Reference: This This fixes fixes the the ground ground sample sample point point to to a a location location U.T.M. on on the the NTS NTS topographic topographic map map (identified (identified in in the the stop number). stop number). Aerial Photograph: Photograph: This This number number is is the the aerial aerial photograph Aerial photograph number which which relates relates to to the the sample sample collection collection site. site. Sample Sample Number: 91FxxLBA 91FxxLBA : 9191- Refers Refers to to the the project project year. year. : F F -- Refers Refers to the the NTS NTS map map sheet. sheet. xx- Refers Refers to : xxto the the sample sample number. number. Sample Sample numbers run numbers run consecutively from from 1-n. 1-n. Each sample sample has has it's consecutively own number. own number. L -- Refers Refers to material : L type; i.e. i.e. till, till, material type; glaciolacustrine, outwash, lacuatrine lacuatrine etc. etc. glaciolacustrine, outwash, B -- Refers Refers to fraction : B fraction sampled. sampled. B B refers refers to to bulk, bulk, C refers refers to to clasts clasts only. only. : AA- Refers to to soil soil horizon horizon sampled; sampled; H, HI A, A, B, B, C. C. Genetic Material: This mapping unit and landform landform type Genetic Material: This describes describes the the mapping unit and type from from which the the sample sample is is being being taken. taken. Surface Surface Expression: Expression: Refers Refers to to the the lay lay of of the the land. land. - Apron: Apron: - A relatively relatively gentle gentle slope slope at the the foot foot of a steeper steeper slope, slope, and formed formed from from the the materials materials of of the the steeper steeper slope. slope. Blanket: A mantle of unconsolidated materials thick enough enough to - Blanket: - mask minor irregularities irregularities in in the the underlying underlying unit unit but but which still still conforms conforms to the general underlying topography. topography. -- Fan: Fan: A A fan-shaped fan-shapedform form that that can can be be likened likened to to the the segment segment of of aa cone, and possessing possessing a perceptable perceptable gradient cone, gradient from from the the apex apex to the the toe. toe. Huinmocky: A very complex -- Hummocky: complex sequence sequence of slopes slopes extending from from somewhat rounded rounded depressions depressions or or kettles kettles of of various various size to size to irregular irregular to to conical conical knolls knolls or or knobs. knobs. There There is a general lack of concordance between knolls is general lack concordance between knolls or or depressions. Slopes and350• 35'. depressions. Slopes are are generally generallybetween between55and 58 �- - - - - - Inclined: Inclined: A A sloping, sloping, unidirectional unidirectional surface surface with a a generally generally constant broken by marked marked irregularities. constant slope slope not broken irregularities. Slopes Slopes are are between between 11 and and 35°. 35'. The form form of inclined inclined slopes slopes is is not related related to to the the mode mode of of origin origin of of the the underlying material. underlying material. Level: unidirectional surface surface with flat, or or gently sloping, sloping, unidirectional Level: A flat, a generally generally constrant slope slope not broken by marked elevations elevations and and depressions. depressions. Slopes Slopes are are generally generally<10. <lo. Rolling: Rolling: A very regular regular sequence sequence of moderate slopes slopes extending from rounded, from rounded, sometimes sometimes confined, confined, concave concave depressions depressions broad, rounded wave-like to broad, rounded convexities convexities producing producing aa wave-like pattern Slope length pattern of of moderate moderate relief. relief. Slope length is is often often or greater greater and and gradients gradients are are <5 c5 %. %. 0.5 km 0.5 km or Ridged: Ridged: A A long, long, narrow narrow elevation elevation of of the the surface, surface, usually sharp usually sharp crested, with crested, with steep steep sides. sides. The ridges may The ridges may be be parallel, parallel, sub-parallel or sub-parallel or intersecting. intersecting. Steep: Erosional unconsolidated and Steep: Erosional slopes, slopes, >35°, >35O, on both unconsolidated and consolidated materials. The form consolidated materials. The form of of a a steep steep erosional erosional slope is not not related related to to the the slope on unconsolidated unconsolidated materials materials is origin of the underlying material. initial mode of origin the underlying material. Terraced: Scarp Scarp face face and and the the horizontal horizontal or or gently gently inclined inclined Terraced: surface surface (tread) (tread) above above it. it. Undulating: Undulating: A very very regular regular sequence sequence of of gentle gentle slopes slopes that that extend from from rounded, rounded, sometimes sometimes confined confined concavities concavities extend to broad rounded rounded convexities convexities producing producing wave-like wave-like pattern of low local relief. Slope length pattern of low local relief. Slope length is is km and dominant c1 km dominant gradient gradient of of slopes slopes generally <1 from 2-5 2-5 %.. - Veneer: Veneer: Unconsolidated unconsolidated materials too too thin thin to mask the minor irregularities irregularities of of veneer will range veneer will range and and will will pocesses pocesses genesis. genesis. the the underlying underlying unit unit surface. surface. A between 10 cm and 1 m between 10 cm and 1 m in in thickness thickness no no form form typical typical of of the the material's material's Slope: Describes Describes the the slope slope inclination inclination and and aspect. aspect. Drainage: Drainage: Describes Describes the the slopes slopes ability ability to to drain. drain. Well drained: - Well drained: Water is removed from the soil readily downward - - - into or laterally as into underlying underlying previous previous material material or laterally as subsurface subsurface flow. flow. Soils Soils have have aa low low to to intermediate water water moisture intermediate moisture storage storage capacity. capacity. somewhat slowly Moderatley well drained: Water is is removed somewhat slowly in in relation relation to to supply. supply. Excess water is is Excess water removed removed somewhat somewhat slowly slowly due due to to low low perviousness, perviousness, shallow shallow water water table, table, lack lack of gradient or or some some combination combination of these. Soils have intermediate intermediate to of these. Soils to water storage high water storage capacities. capacities. 59 �- Poorly Poorly drained: drained: Water Water is is removed removed so so slowly slowly in in relation relation to to supply that the supply the soil soil remains remains wet for for aa comparitively large comparitively large part of of the the time time the the soil soil •is not frozen. frozen. Excess is not Excess water water is is evident evident in in the the soil for a a large large part part of of the the time. time. soil for Refers to to the the type type of of vegetation cover, cover, coverage coverage and Vegetation: Refers vegetation vegetation state. state. - Type: Type: ConiferousConiferous- More More than than 80 80 1% coniferous coniferous cover. cover. - Deciduous- More 80 1 % deciduous deciduous cover. cover. DeciduousMore than than 80 MixedMixed- Mix of coniferous coniferous and deciduous deciduous cover cover with one or the c80 1% of of the the cover. cover. the other other <80 c50 1 % canopy, canopy, mixture of open grass or bushland Scrub- <50 Scruband tree. and tree. Grass- >50 >50 1% grass grass cover. cover. GrassBog>50 1% wetland. wetland. Bog- >50 - State: No evidence evidence of of recent recent cutting cutting or or forest forest fire. fire. Virgin- No State: VirginForest is Forest is mature. mature. Loggedrecent logging logging activity. activity. Forest Logged- Evidence of recent Forest area area mature mature cover cover largely largely logged. logged. Fired- Evidence Forest area area mature FiredEvidence of of recent recent fire. fire. Forest cover largely cover largely burned. burned. StressStress- Evidence that vegetation vegetation is stressed by by envirtonment; i.e. envirtonment; i.e. drought, drought, insects insects etc. etc. Material unconsolidated Material Thickness: Thickness: Refers Refers to to the the thickness thickness of unconsolidated material material over over the the bedrock bedrock surface. surface. Virtually bare - Class bare bedrock. bedrock. Maybe Maybe thin thin drift drift within within Class 1: Virtually - undulations of undulations of the the bedrock bedrock surface. surface. Thin drift drift (<1 over bedrock. bedrock. Does - Class (el m) over Does not not obscure obscure the the Class 1A: Thin - bedrock bedrock topography. topography. 2: Pockets of drift within within bedrock bedrock depressions >1 >1 m m -- Class Class 2: thick. c1 m m of of drift. drift. thick. Bedrock crests crests are are covered covered by by <1 -- Class Class 3: Bedrock surface surface expression expression obscured by by unconsolidated unconsolidated material >1 mm thick. thick. material >1 Colour: Refers Refers to to the the colour colour of of aa sp[ecific sp[ecific unit unit based based on on the the Munsell Munsell Soil Soil Colour Colour Chart. Chart. representative grain size of a particular Texture: Refers to the representative unit. unit. - Coarse Coarse Sand: 25 1 % or more very corase corase or or coarse coarse sand, sand, and and <501 ~50% - any any other other one one grade grade of of sand. sand. very coarse Sand: 25 1 - Sand: % or or more very coarse or or coarse coarse sand sand and and medium medium sand, sand, - and c50 1% fine fine or or very very fine fine sand. sand. and <50 - Fine Fine Sand: Sand: 50 1% or or more more of of fine fine sand, sand, or or <25 c25 1% very very coarse, coarse, - - Sandy Sandy - Silt: Silt: - coarse coarse or or medium medium sand. sand. silt, and and <50 c50 1% sand. sand. Silt: Contains Contains >50 >50 1% silt, Contains at Contains at least least 80 80 1% silt silt and and <2 c2 1% clay. clay. 60 �- Clayey Clayey Silt: Silt: Contains Contains >50 >50 % silt, silt, and and <50 c50 1% clay. clay. - Silty Silty Clay: Clay: >501 >SO% clay clay and and <501 ~50% silt. silt. - Clay: Clay: Contains Contains at at least least 40 1% clay, clay, <45 c45 1% sand sand and and <40 c40 1% silt. silt. - Organic: Organic: Contains Contains at at least least 30 30 6% organic organic material. material. - Structure: Structure: Refers Refers to to the the physical physical characteristics characteristics of of the the unit. unit. - Type: Type: StructurelessStructureless- Simply Simply no no structure. structure. - BlocklikeBlocklike- Have Have distinct distinct blocklike blocklike shape shape consisting consisting of of 44 or or more more sides. sides. PlatelikePlatelike- Ped(s) Ped(s) are are arranged arranged horizontally horizontally to to give give aa platelike platelike structure. structure. PrismlikePrismlike-Peds Peds are are longer longer than than wide wide giving giving aa columnar columnar or or peaked peaked shape, shape, the the peak peak towards towards the the top top of of the the ped. ped. FlowFlow- There There is is the the presence presence of of flow flow structure; structure; flow flow cones, cones, stringers, stringers, injections, injections, rip-ups, rip-ups,flames, flames, balls, pillows, dish, planar, crossbedding, balls, pillows, dish, planar, crossbedding, trough trough crossbeds, laser, graded. crossbeds, ripples, ripples,fflaser, graded. - Kind: Kind: MassiveMassive- Refers Refers to to structureless structureless type, type, and indicates indicates homogeneous homogeneous arrangement arrangement of of materials. materials. Angulartype, where where there Angular- Refers Refers to to the the bloc]clike blocklike type, there are are just sides to to the the ped. ped. just 44 sides SubangularSubangular-Refers Refers to to the the blocklike blocklike type, type, where where there there are are 5 or or more more sides. sides. •PlatyRefers to to the the platelike platelike type, type, where the Platy- Refers the peds peds are are arranged arranged horizontally. horizontally. PrismaticPrismatic- Refers Refers to to the the prismlike prismlike type, type, where where the the peds peds are are rounded rounded or or angled angled at at the the surface. surface. ColumnarColumnar- Refers Refers to to the the prismlike prismlike type, type, where where the the peds peds are are longer longer than than wide wide and and do do not not have have a a rounded rounded or or angled angled surface. surface. FlowFlow- Indicate Indicate the the flow flow regime regime based based on on the the flow flow structure structure type. type. Consistency: cohesion and and adhesion adhesion Consistency: Refers Refers to to the the degree degree and and kind kind of of cohesion or or to to the the resistance resistance of of the the soil soil to to deformation deformation or or rupture. rupture. -- Wet: Wet: NonstickyNonsticky- After After release release of of pressure, pressure, practically practically no no soil soil material material adheres adheres to to thumb thumb and and finger. finger. Slightly Slightly stickysticky- After After pressure pressure is is applied, applied, the the soil soil material material adheres adheres strongly strongly to to both both the the thumb f one thumb and and forefinger, forefinger,but but comes comesofoff one or other rather rather cleanly. cleanly. The or the the other The soil soil is is not appreciably stretched when the digits not appreciably stretchedwhenthe digits are are separated. separated. StickySticky- After After pressure pressure is is applied, applied, the the soil soil material material adheres thumb and forefinger forefinger adheres strongly strongly to to both both the the thumb and and tends tends to to stretch stretch somewhat somewhat and and pulls pulls apart apart rather than pulling free from either digit. rather than pulling free from either digit. -- Moist: Moist: LooseLoose- Noncoherent Noncoherent soil soil material material 61 �- Friable- The soil soil material crushes crushes easily easily under under gentle gentle Friableto moderate pressure between betweenthe thethumb thumbarid and to moderate pressure forefinger forefinger and and coheres coheres when when pressed pressed together. together. FirmThe soil soil material material crushes crushes under under moderate moderate pressure pressure Firm- The or greater, greater, but resistance resistance is is distinctly distinctly or noticeable. noticeable. Dry: LooseLoose- Noncoherent soil material material Dry: Noncoherent soil Soft- The The soil soil material is is weakly weakly resistant resistant to to pressure pressure Softand easily easily broken broken between between the the thumb thumb and and forefinger. forefinger. and Hardis moderately resistant or or greater Hard- The The soil soil material material is moderately resistant greater to pressure, it can can be broken in in the the hands hands with with pressure, it moderate to moderate to some some degree degree of of difficulty. difficulty. Plasticity: Plasticity: Is Is the the property property of of changing changing shape shape continuously continuously under under the influence influence of an applied applied stress and of retaining retaining the the of an stress and the new shape new shape after after removal removal of of the the stress. stress. - Nonplastic: Nonplastic: A A roll roll 44 cm cm long long and and 44 mm mm thick thick cannot cannot be be formed. formed. Slightly plastic: - Slightly A roll roll 44 cm cm long plastic: A long and 2 mm mm thick thick can be be formed formed - but will will not not support support its its own own weight. weight. - Plastic: Plastic: A roll roll 4 4 cm long and 2 mm mm thick thick can be be formed formed and will will - support support it's it's own own weight. weight. Cementation: soil is cemented cemented and the Cementation: Refers Refers to to whether whether or or not the the soil degree degree to to which which the the unit unit is is cemented. cemented. Clasts: Describes the relative abundance abundance of each type, type, shape Clasts: Describes the type, type, relative and size and size of of clasts. clasts. Rare- <5 - Abundance: Abundance: Raree5 1% Common- 15Common15- 20 1% FewFew- 10 10 1% Abundant- >20 >20 '% Abundant-- Size: Size: State common and and largest largest size. size. State common Shape: Rounded, Rounded, subrounded, -- Shape: subrounded, subangular, subangular, angular. angular. Striated: Yes -- Striated: Yes or or no no Type: As detailed sample -- Type: detailed pebble counts counts are usually done per sample site, it is site, is only necessary necessary to to describe describe the the clasts clasts generally generally as as granitic, granitic, volcanic, volcanic, metamorphosed metamorphosed or or sedimentary. sedimentary. - Lower Lower Horizon Horizon Boundary: Boundary: Describes Describes the characteristics characteristics of the units units lower lower contact. contact. - Distinctiveness: Distinctiveness: DiffuseDiffuse- Vertical change >15 cm - - Gradual- Vertical Vertical change Gradualchange within within 55 to to 15 15 cm. cm. to 55 cm. cm. Clear- Vertical Vertical change change within within 22 to Cleare2 cm. cm. AbruptVertical change change <2 Abrupt- Vertical Form: Smooth- Nearly Form: SmoothNearly aa plane. plane. Wavy- Pockets WavyPockets wider wider than than deep. deep. IrregularIrregular- Pockets Pockets wider wider than than deep. deep. Unit Thickness: Thickness: State State thickness thickness of of each each horizon. horizon. 62 � Dublin Core The Dublin Core metadata element set is common to all Omeka records, including items, files, and collections. For more information see, http://dublincore.org/documents/dces/. Title A name given to the resource Institute on Lake Superior Geology Dublin Core The Dublin Core metadata element set is common to all Omeka records, including items, files, and collections. For more information see, http://dublincore.org/documents/dces/. Title A name given to the resource Institute on Lake Superior Geology: Proceedings, 1995 Description An account of the resource Institute on Lake Superior Geology. Marathon, Ontario. May 13-18, 1995. Creator An entity primarily responsible for making the resource Institute on Lake Superior Geology Date A point or period of time associated with an event in the lifecycle of the resource 1995 Format The file format, physical medium, or dimensions of the resource PDF Language A language of the resource English https://digitalcollections.lakeheadu.ca/files/original/454203bdafbcf2bc7c5abe3f8b5cf5b5.pdf 2f835a3f7d8f969acd904f670359f1da PDF Text Text 42' Annual INSTITUTE ON LAKE LAKE SUPERIOR GEOLOGY CABLE, WISCONSIN WISCONSIN CABLE, 19,1996 MAY 15 --19, 1996 '''''I ,,I1I/ 1II / I 1%/ 'I ' I..I I ,' ,' '. '''''I,,,,,, - ..-' % .' % % % I/I/I/I 1I/II 'I I I I I / I / / I PROCEEDINGS VOLUME VOLUME 42 1--PROGRAM PART 1 PROGRAMAND ANDABSTRACTS ABSTRACTS �42ND ANNUAL ANNUAL MEETING MEETING 42ND INSTITUTE ON LAKE SUPERIOR GEOLOGY GEOLOGY Volume 42 consists consists of: Program and and Abstracts Abstracts Part 1: Program Part Suffide Deposits Deposits of of Northern Northern Part 2: Volcanogemc Volcanogenic Massive Sulfide Wisconsin: Wisconsin: A Commemorative Volume Field Trip Guidebook Part 3: Field 1. Glacial geology of western Wisconsin 1. Glacial 2. Geology Monodine: Geology of of the Montreal River Monocline: through 25 km of the crust A traverse through 4. Early Early to to Middle Middle Proterozoic Proterozoic geology of the Lake Namekagon region 5. Lake Lake Namekagon and Penokee Gap areas, west Gogebic Range, Wisconsin Reference to material in this volume should should follow follow the example below. Darrah, K. S., 5., Holm, Darrah, K. Hoim, D. K., Dahl, Dahi, P. P. 5., S.,and and Lux, Lux, D. D. R., R.,1996, 1996,Petrographic Petrographicand and thermobarometric thermobarometric metamorphosed Little Formation, central central Minnesota, Minnesota, with with implications implications for for Little Falls Formation, analysis of the metamorphosed Early Proterozoic tectonism [abstract]; Institute on Lake Superior Geology Proceedings, 42nd Annual Meeting, v. 42, part part 1, I, p. 1010 -11. 11. Annual Meeting,Cable, Cable,WI, WI,1996; 1996; v. Published Published and and distributed distributedby bythe theInstitute Instituteon onLake Lake Superior Superior Geology Mark Jirsa, Secretary-Treasurer Minnesota Geological Survey 2642 University University Avenue 2642 St. MN 55114-1057 55114-1057 USA St. Paul, MN ISSN 1042-9964 1042-9964 �INSTITUTE ON LAKE SUPERIOR GEOLOGY 42ND ANNUAL MEETING MAY 15 - 19, 1996 CABLE, WISCONSIN CABLE, SPONSORED BY: SPONSORED BY: U. S. S. GEOLOGICAL GEOLOGICAL SURVEY SURVEY AND UNIVERSITY OF WISCONSIN WISCONSIN - OSHKOSH UNIVERSITY OF PROCEEDINGS PROCEEDING S VOLUME 42 1----PROGRAM PART 1 PROGRAMAND AND ABSTRACTS ABSTRACTS EDITORS: LAURELG. G. WOODRUFF, WOODRUFF, U. U. S. GEOLOGICAL SURvEY,ST. ST.PAUL, PAUL,MN MN GEOLOCICAL SURVEY, LAUREL SUZANNE W. NICHOLSON, NICHOLSON, U. U. S.S.GEOLOGICAL GEOLOGICAL SURVEY, SURVEY,RESTON, RESTON,VA VA �CONTENTS Part 1 Program and Abstracts Institutes onLake Lake Superior SuperiorGeology Geology to to 1996 1996 Institutes on onLake Lake Superior Superior Geology Geology Constitution of the the Institute Instituteon Constitution of i ii Institute on on Lake Lake Superior Superior Geology Geology By-Laws of the Institute iii .iii and Field Field Trip Trip Guidebooks Guidebooks Index of Proceedings Proceedings Volumes Volumes and .iv iv Award Guidelines Guidelinesfor for Sam Sam Goldich Goldich Medal Medal Award ix Board of Directors x Local Local Committees xX Student Paper Committee xi Session Chairs xi Goldich Medal Committee xi 1996 1996 Goldich Goldich Medal Recipient xii Past Goldich Goldich Medalists xii Banquet Speaker xii 1996 1996 Goldich Goldich Medal Recipient Citation xiii Student Travel Award xv Chair of of the 41st Annual Institute Report of the Chair xvi Calendar of Events and Program xxi Abstracts 11 �ON LAKE LAKE SUPERIOR GEOLOGY INSTITUTES ON GEOLOGY INSTITUTE DATE INSTITUTENUMBER NUMBER DATE 11 1955 1956 1956 1957 1958 1959 1959 1960 1960 1961 1961 1962 1963 1963 1964 1965 1966 1966 1967 1968 1969 1969 1970 1971 1972 2 3 4 55 6 77 8 99 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 1973 '---1973 1974 L-1975 L--l975 L—1976 1...---1976 1977 L— L-- ~ c_ — 1978 1978 1979 1980 1980 L-1981 t.<1981 1982 1983 — 1983 <.--1.984 -1984 1985 1985 L __ t—1986 v--1986 t 1987 1987 \.--1988 1988 1989 1989 1990 1990 1991 1991 1992 1992 1993 1994 1994 1995 1995 1996 PLACE Minneapolis, Minnesota Houghton, Michigan East Lansing, Michigan Duluth, Minnesota Minneapolis, Minnesota Madison, Wisconsin Port Arthur, Ontario Houghton, Michigan Michigan Duluth, Minnesota Ishpeming, Michigan St. St. Paul, Paul, Minnesota Ste. Marie, Marie, Michigan Sault Ste. East Lansing, Michigan Superior, Wisconsin Oshkosh, Wisconsin Thunder Bay, Thunder Bay, Ontario Duluth, Minnesota Houghton, Michigan Madison, Wisconsin Ste. Marie, Marie, Ontario Ontario Sault Ste. Marquette, Michigan St. Paul, Minnesota St. Thunder Bay, Thunder Bay, Ontario Milwaukee, Wisconsin Duluth, Minnesota Eau Claire, Wisconsin East Lansing, Michigan International Falls, Minnesota Houghton, Michigan Michigan Wausau, Wisconsin Kenora, Ontario Wisconsin Rapids, Wisconsin Wawa, Ontario Marquette, Michigan Duluth, Minnesota Thunder Thunder Bay, Bay, Ontario Eau Claire, Wisconsin Hurley, Wisconsin Eveleth, Minnesota Houghton, Michigan Marathon, Ontario Cable, Wisconsin CHAIRMAN CE. Dutton C.E. Dutton A.K. Sneigrove AK. Snelgrove B.T. Sandefur B.T. Sandefur RW. Marsden G.M. G.M. Schwartz Schwartz & & C. C. Craddock Craddock E.N. Cameron E.N. Cameron E.G. Pye A.K. Sneigrove AK. Snelgrove H. Lepp A.T. Broderick AT. P.K. P.K. Sims Sims & & R.K. R.K.Hogberg Hogberg R.W. White RW. White W.J. Hinze Hinze W.J. A.B. A.B. Dickas LaBerge G.L. laBerge & E. Mercy M.W. Bartley & D.M. D.M. Davidson J. J. Kalliokoski M.E. Ostrom M.E.Ostrom P.E. Giblin J.D. Hughes Hughes J.D. M. Walton M.M. Kehlenbeck Kehienbeck G. Mursky D.M. Davidson D.M. Davidson P.E. Meyers W.C. Cambray W.C Cambray D.L. D.L. Southwick Southwick T.}. Bornhorst T.J. G.L G.L. LaBerge laBerge C.E. Blackburn CE. J.K. Greenberg J.K. Greenberg E.D. Frey Frey & & R.P. R.P. Sage E.D. }.S.Klasner 1. S. Kiasner J.C. J.C Green M.M. Kehienbeck M.M. Keh1enbeck P.E. Meyers P.E. A.B. Dickas AB. D.L. Southwick D.L. Southwick T.J. Bornhorst Bornhorst T.J. M.C. M.e. Smyk L.G. Woodruff L.G. Woodruff �__________ CONSTITUTION OFTHE THE INSTITUTE INSTITUTE ON ON LAKE LAKE SUPERIOR GEOLOGY GEOLOGY CONSTITUTION OF Article I Name ~ on Lake Lake Superior Geology'. Geology". The name of the organization shall be the "Institute 'Institute on Article II Objecti yes Objectives The objectives of this organization organization are: A. To A. Toprovide provideaameans meanswhereby wherebygeologists geologists in in the the Great Great Lakes Lakes region may exchange exchange ideas and and scientific scientific data. B. To promote better understanding Lake Superior Superior region. region. understanding of of the the geology of the Lake C. To plan and conduct conduct geological geological field trips. Article III Status ~ No part of shall insure insure to to the the benefit of any member or of the the income income of the organization organization shall individual. In In the theevent eventof of dissolution dissolution the assets of of the the organization organization shall shall be be distributed distributed organization). to (some tax free organization). (To avoid avoid Federal taxes, the the organization organization should should be not (To Federal and and State State income income taxes, not only only "scientific" butalso also "non-profit".) "non-profit".) "scientific" or or "educational, 'educational, but 290.Q1, subd. subd. 44 Minn. Stat. Anno. Anno. 290.01, Minn. Stat. Stat. Anno. Anno.290.05(9) 290.05(9) 1954 RevenueCode Codes.501(c)(3) s.501(c)(3) 1954 Internal Internal Revenue IV Article [V Membership of the the organization shall consist of the The membership of the board. board.of ofdirectors; directors. Any geologist interested shall be permitted to attend and participate in and vote at the the annual annual meetings. meetings. Article V Meetings The organization shall year, preferably preferably during during the the month of April. April. The shall meet once aa year, The place place and exact exact date date of of each meeting will be designated by the board of directors. Article VI VI Directors The board of of directors directors shall shall consist consist of the Chairman, Chairman, Secretary-Treasurer, Secretary-Treasurer, and the last last three past Chairmen; but ifif the board should should at any time of fewer than five three Chairmen; but the board time consist consist of fewer than five or inability inability of of any any of of the the above above persons persons to to serve as as persons, by reason of unwillingness unwillingness or directors, the the vacancies vacancies on the board may be filled filled by the annual meeting meeting so so as as to to bring bring the membership of of the the board up up to to five five members. Artide VII Article VII Officers The officers of this this organization shall be a Chairman Chairman and Secretary-Treasurer. A. The A. TheChairman Chairmanshall shallbe beelected elected each each year year by by the board of directors, who shall give due consideration to to the the wishes wishes of of any any group group that that may may be be promoting promoting the the next next annual annual consideration meeting. His will terminate terminate at at the close close of of the the ann.ual annual meeting. His term term of of office office as Chairman Chairman will meeting over which he presides or when his his successor successor shall have been been appointed. appointed. He will then serve for a period of three years as a member of the board board of of directors. directors. B. The The Secretary-Treasurer Secretary-Treasurershall shallbe beelected electedatatthe theannual annual meeting. meeting. His His term term of of office office be two years or until his his successor successor shall shall have have been beenappointed. appointed. shall be 11 ii �Article VIII VIII Amendments of those those persons persons who who are are personally This constitution may may be be amended amended by by a majority vote of present the organization. organization. present at, at, participating participating in, in, and and voting voting at at any annual meeting of the BY-LAWS I. Duties of the Officers Qfficers and Directors Directors duty of of the the Annual Annual Chairman Chairman to: to: A. It shall be the duty 1. Preside 1. Presideat atthe the annual annual meeting. meeting. 2. Appoint 2. Appointall allcommittees committees needed needed for for the the organization of the annual meeting. 3. Assume Assumecomplete completeresponsibility responsibility for for the the organization and financing financing of the annual meeting over over which which he he presides. presides. meeting B. It shall be the duty duty of of the the Secretary-Treasurer Secretary-Treasurer to: to: 1. Keep 1. Keep accurate accurateattendance attendancerecords recordsof ofall all annual annual meetings. meetings. 2. Keep and correspondence between, the board 2. Keep accurate accurate records records of of all all meetings meetings of, and of directors. 3. Hold Holdall allfunds fundsthat thatmay mayaccrue accrueas as profits profits from from annual meetings meetings or or field field trips trips and and to and operation operation of of future to make make these these funds funds available available for for the organization organization and meetings as required. to plan locations locations of of annual annual meetings meetings and C. It shall be the duty of the board of directors to to advise on the organization and financing of all meetings. the organization and financing of all II. and Expenses Expenses Duties and 1. 2. III. There shall be no regular membership dues. Registration for the the annual annual meetings shall be be determined determined by by the the Chainnan Chairman in Registration fees fees for meetings shall consultation with the board of directors. directors. ItIt is is strongly strongly recommended recommended that these be kept at a minimum to encourage attendance of of graduate graduate students. students. Rules of Order The rules contained in in Robert's Robert's Rules Rules of Order shall govern this this organization organization in in all all cases cases to which they are applicable. IV. Amendments These by-laws may be amended by those persons persons who are personally by a majority majority vote of those present at, participating present participating in, and voting voting at at any any annual annual meeting meeting of of the the organization; organization; with the the constitution constitution as as presently provided that that such such modifications modifications shall shall not conflict conflict with presently adopted adopted or or subsequently subsequently amended. 111 iii �AND FIELD FIELDTRIP TRIP GUIDEBOOKS GUIDEBOOKS INDEX OF PROCEEDINGS VOLUMES VOLUMES AND OF THE INSTITUTE ON LAKE SUPERIOR GEOLOGY GEOLOGY 1955-1996 Compiled by Mark MarkJirsa, Jirsa, Secretary-Treasurer, Secretary-Treasurer,LLSG ILSG Compiled by ** Denotes abstracts volumes and and guidebooks guidebooks which which can can be ordered ordered from from the the Secretary-Treasurer. Secretary-Treasurer. 2642 University UniversityAvenue, Avenue,St. St.Paul, Pau"MN, MN,55114-1057, 55114-1057,Phone: Phone:(612)-627-4539, (612)-627-4539,fax: fax:612-627-4778, 612-627-4778, jirsaOO1@maroon.tc.umn.edu e-mail: jirsa001@maroon.tc.umn.edu as author, author, editor, editor, chairperson, chairperson, and and sponsoring sponsoring organization A complete list containing such information as maintained by erson Spence, archivist at byMs. Ms.Theresa TheresaSand Sanderson at the the J. Robert Van Pelt Library, Michigan is maintained Photocopiesof ofback backvolumes volumes can can be be Technological University, University, Houghton, Houghton,MI MI49931 49931 (906-487-2505). (906-487-2505). Photocopies ordered from copy rate. rate. Some guidebooks guidebooks were published ordered from Ms. Ms. Sanderson Sanderson Spence at the prevailing copy separately by and Wisconsin Wisconsin Geological Geologicaland and Natural History separately by the theMinnesota MinnesotaGeological Geological Survey Survey (MGS), (MGS), and History Survey (WGNHS), as indicated indicated below; below; however, most are no longer available. (Each italicized item is aa separate bound document) LOCATION 1 1955 MINNEAPOLIS, MINNESOTA Program Abstracts(contains (contains no no record record of of field field trips) Program and Abstracts HOUGHTON, MICHIGAN 2 1956 Program and Abstracts Geological GeologicalExploration Exploration(inferred (inferred to tobe beaa field field guide) guide) 3 1957 EAST EAST LANSING, MICHIGAN Program and Abstracts 4 1958 DULUTH, MINNESOTA Program and Abstracts Abstracts 55 1959 MINNEAPOLIS, MINNESOTA Program and Abstracts 6 1960 MADISON, WISCONSIN Program and Abstracts 7 PORT ARTHUR, ONTARIO 1961 Program ted label reads reads 6th annual meeting) Program and and Abstracts Abstracts(misprin (misprinted 8 1962 HOUGHTON, MICHIGAN Program and Abstracts 9 1963 DULUTH, MINNESOTA Program and Abstracts Itinerary: Stratigraphy Stratigraphyofofthe theBiwabik Biwabik Iron Iron Formation Formation Field Itinerary: 10 1964 ISHPEMING, MICHIGAN Program and Abstracts Abstracts Field Trip: Marquette iron-mining iron-mining district district and and Republic Republic trough 11 1965 ST. PAUL, PAUL, MINNESOTA Program and Abstracts Gaud granite district, central Minnesota Field Trip Guide to the St. Cloud VOL. YEAR YOL, YEAR 12 1966 SAULT STE. MARIE, ONTARIO Program and and Abstracts Abstractsincludes includesfield field guides to: Regional geology geologyof ofthe theSault SaultSte. Ste. Marie Marie area area 1. Regional 2. 2. Geology Geology and and mineral mineral deposits deposits of of the the Manitouwadge Manitouwadge Lake Lake area, Ontario 3. The River area, area, Ontario Ontario 3. The relationship relationship of of mineralization mineralization to to the Precambrian stratigraphy, Blind River 4. Sudbury Sudbury nickel nickel irruptive irruptive tour, tour, Ontario Ontario 4. iv �13 14 15 16 17 17 18 19 1967 EAST LANSING, MICHIGAN Program and Abstracts . Field Trip: Grenville Province of of southeastern Ontario, Bancroft-Madoc Bancroft-Madoc area area 1968 SUPERIOR, WISCONSIN Technical Sessions and Abstracts Guide for Field Field Trip Trip in the Duluth Minnesota Guidefor Duluth Complex Complex near Ely, Ely, Minnesota 1969 OSHKOSH, WISCONSIN Technical Sessions Sessions and and Abstracts Technical Guidebook: Central Wisconsin Wisconsin volcanic volcanic belt belt Guidebook: 1970 THUNDER BAY, ONTARIO THUNDER BAY, Technical Sessions, Abstracts and and Field Field Guides Field trips: A. Proterozoic formations formations in in the the Thunder ThunderBay Bay area A. Proterozoic B. Sturgeon River metavolcanic-metasedimentary formations in the Beardmore-Geraldton area B. Sturgeon C. The The Port PortCoidwell Coldwell alkalic alkalic complex complex D. Geology D. Geology of of the the Atikokan Atikokan area area (title (title not not exact) exact) 1971 DULUTH, MINNESOTA Technical Sessions, Sessions, Abstracts and Field Field Guides Field trips: A. A. North NorthShore ShoreVolcanic Volcanic Group Group B. Precambrian Precambrian rocks rocks of of northwestern northwestern Cook Cook County County as as exposed along the Gunflint Trail B. C. Mesabi C. Mesabi Range Range magnetite magnetite taconite taconite D. D. Geology Geology of of the the Vermilion Vennilion metavolcanic-metasedimentary metavolcanic-metasedimentary belt, northeastern Minnesota 1972 HOUGHTON, MICHIGAN Part Part I.1. Technical Technical Sessions-Agenda Sessions-Agenda and Abstracts (describes (describes trips A-D) Field Trips: A. Penokean A. PenokeanOrogeny Orogenyin inthe thecentral centraland andwestern westernGogebic Gogebic region, region, Wisconsin Wisconsin and Michigan Michigan B. B. Guide to to Penokean deformation style and regional metamorphism at the western Marquette Marquette Range, Michigan 1973 WISCONSIN MADISON, WISCONSIN Technical Program and and Abstracts* Abstracts" Field Trip: Field Trip: Guidebook Guidebook to the geology and and mineral deposits of the the central central part of Jackson Jackson County County and and part of Clark County, Wisconsin (WGNHS) part of Clark County, Wisconsin (WGNHS) Field Trip:Guidebook Guidebook to to the the Precambrian Precambrian geology geology of ofnortheastern northeastern and north-central Field Trip: north-eentral Wisconsin Field Trip:Guidebook Guidebook to the upper upper Mississippi Field Trip: Mississippi Valley Valley base-metal district district (WGNHS (WGNHS Information Information circular No. 16) circular No. 16) of Current Research inin the theLake Lake Superior Superior Region Region Bibliography of Current Research 20 SAULT STE. MARIE, MARIE, ONTARIO 1974 Field Trip 1: 1: Middle Keweenawan Keweenawan rocks rocks of of the the Batchawaria-Mamainse Batchawana-Mamainse Point area FieldTrip Trip2:2: unknown Field Field Trip 3: 3: Precambrian igneous rocks rocks of the north shore of Lake Lake Huron Huron region Field Trip 4: Stratigraphy and and sedimentation sedimentation of of the Huronian Huronian Supergroup Supergroup Field Trip5:5: The Michipicoten greenstone belt Field Trip Bibliography of Current Current Research Region (First (First Supplement) Supplement) Research in the the Lake Lake Superior Region 21 1975 MARQUETFE, MARQUETTE, MICHIGAN Proceedings Includes the following field trip guides and and aa supplement supplementby by Burton Burton Boyum Boyum containing containing aa color color map of the Marquette Marquette Mineral Mineral District: District 1. Glacial 1. Glacial geology (trip canceled, no guidebook) 2. Greenstone 2. 3. The The Jacobsville Jacobsville Sandstone: Sandstone: Evidence Evidence for a Lower-Middle Keweenawan age 4. Marquette Marquette Iron Iron Range Range 5. and 6. 6. The TheEmpire EmpireMine Mineand andMill, Mill,Palmer, Palmer, Michigan Michigan vV �22 23 24 25 26 27 28 29 1976 ST. PAUL, PAUL, MINNESOTA Proceedings Includes abstracts abstracts and and guide guidetotoField Field Trip Trip BB (no formal formal guidebook guidebook printed) Field Trip A: Minnesota Minnesota River River Valley Valley field conference (no printed) Field Trip B: B: Engineering Engineering and and Pleistocene Pleistocene geology in the Twin Cities area 1977 THUNDER BAY, BAY, ONTARIO THUNDER Proceedings Field Field Trip Trip AA Geology of the Coldwell alkaline Complex Field Trip Proterozoic rocks rocks of of the the Thunder Thunder Bay Bay area, northwestern northwestern Ontario Ontario("Proterozoic ("ProterozoicTrip") Trip") Field Trip BB Proterozoic Field TripCC Archean metallogeny and stratigraphy Field Trip stratigraphyof ofthe theSouth South Sturgeon SturgeonLake Lake area area ("Mattabi ("Mattabi Trip") Trip") MILWAUKEE, WISCONSIN 1978 MILWAUKEE, Abstracts and and Proceedings Proceedings Abstracts Field Trip II Southwestern Field Trip Trip Guide Guide Book Book Number Number 1) Field Trip Southwestern Wisconsin Wisconsin zinc-lead zinc-lead district district(WGNI-IS (WGNHS Field FieldTrip TripIIII Mineral Mineral extraction extractionand and processing processingequipment equipment manufacturers manufacturers in the Greater Milwaukee Field area (no guidebook) FieldTrip TripIII III Precambrian rhyolite and Field and granite graniteinliers inliersin insouth-central south-eentralWisconsin Wisconsin(WGNI-IS (WGNHS Field Field Trip Guide Book Book Number 2) 1979 DULUTH, MINNESOTA TechnicalSessions Sessionsand andAbstracts AbstractsJoint Joint meeting meeting with with North-Central Technifal North-eentral Section SectionGSA. GSA. Field Trip Guidebooks: some some were were published publishedseparately separatelyas as MGS MGS Guidebook Guidebook Series referenced below, the remainder are apparently apparently unavailable. unavailable. AAtotal total of of eight eight trips trips were were listed listed in in GSA GSA proceedings: 1. Middle 1. Middle Precambrian Precambrian volcanic volcanic and plutonic plutonic rocks rocks of northern northern Wisconsin 2. Stratigraphy, Stratigraphy,structure structureand andmineral mineralresources resourcesofofeast-central east-eentralMinnesota Minnesota(MGS (MGS Field Field Trip no.9) 9) Guidebook Series Series no. 3. Quaternary 3. Quaternarygeology geology of of the Duluth area 4. Geology 4. Geology of of the the Mesabi Mesabi Iron Range 5. Geologic Geologic history history and and engineering engineeringgeology geology of of the the western Lake-Superior Lake-Superior region 6. Cambrian 6. Cambrian and and Ordovician Ordovician stratigraphy stratigraphy and and paleontology paleontology of southeastern Minnesota 7. Keweenawan Keweenawan(Upper (UpperPrecambrian) Precambrian)North NorthShore ShoreVolcanic VolcanicGroup, Group,Minnesota Minnesota(MGS (MGS Field Field Trip Trip Guidebook no. 11) Guidebook no. 11) 8. Archean District, northeastern northeastern 8. Archean volcanism volcanism and and sedimentation sedimentation of of the the western western Vermilion District, Minnesota Guidebook Series (MGS Guidebook Series no. 10) 10) Minnesota (MGS 1980 EAU EAU CLAIRE, CLAIRE, WISCONSIN WISCONSIN Proceedings and Abstracts Trip 1 I Precambrian Field Trip Precambrian geology geology of of the Chippewa Chippewa Valley, Valley, Wisconsin Field Trip 22 Precambrian Precambriantectonic tectonichistory historyofofthe theBlack BlackRiver River Valley Valley the Wausau Wausau and Stettin syenite plutons, Field Trip 3 Petrology, geochemistry, and contact relations of the Central Wisconsin Field Trip44 Precambrian geology and tectonics of Marathon County, Wisconsin Field Trip EAST LANSING, LANSING, MICHIGAN 1981 EAST Abstracts and Proceedings Proceedings Field Field Excursion ExcursionGuide GuideThe TheHuronian Huronian rocks rocks between between Sault Sault Ste. Ste. Marie Marieand and Thessalon, Thessalon, District of Algoma, Ontario 1982 INTERNATIONAL INTERNATIONAL FALLS, FALLS, MINNESOTA Proceedings: Abstracts Abstracts and and Field FieldTrips Trips(in (inone one volume) volume) Proceedings: Field Trip I Mineral Mineral deposits depositsof ofthe the Fort Fort Frances-Mine Frances-Mine Centre area, Ontario Field Trip II Archean Archean geology geology of of the the International International Falls-Kabetogama Falls-Kabetogama area, Minnesota 1983 HOUGHTON, MICHIGAN VolumeI:I: Abstracts Abstracts and Field Trip -- Ropes gold mine and its Volume its geological setting Volume VolumeII:II: Field Field guide guide to the geology of the Keweenaw Peninsula Vl vi �30 1984 WAUSAU, WISCONSIN Abstracts Field Trip I1 Guide to Proterozoic rocks rocks in in northeastern northeastern Wisconsin to the the geology geology of the Early Proterozoic Field Trip 22 Early Proterozoic tectonostratigraphic terranes terranes of of the the southern southern Lake Lake Superior Superior region region Field Trip33 The Field Trip The Wausau Wausau Syenite Syenite Complex 31 1985 KENORA, KEN ORA, ONTARIO Abstracts Field Trip Guidebook Guidebook 1. The Cameron 1. Cameron Lake Lake Deposit 2. Geologic Geologic setting settingand andstyle styleof ofgold gold mineralization mineralizationininthe theLake Lake of of the the Woods Woods area area 3. Geological River subprovincial subprovincial Geological relationships relationships in in the the vicinity vicinity of the Wabigoon-Winnipeg Wabigoon-Winnipeg River interface in the Kenora area 4. A A volcanic volcanic facies facies interpretation interpretationof ofthe the Berry Berry River River Formation 5. Granitoid Granitoid related related mineralization mineralization in in the the Dryden area 32 1986 WISCONSIN RAPIDS, RAPIDS, WISCONSIN Abstracts* Abstracts· Field Field Trip Trip[I The Wolf and Baraboo Baraboo interval interval (published (published as Field Field Trip Trip Guide Book Wolf River Batholith and Number Number 12, 12, Wisconsin Geological and Natural History History Survey) Survey) Field TripIIII Penokean Field Trip Penokean deformation deformationand andmetamorphism metamorphisminincentral central Wisconsin: Wisconsin: volcanic volcanic rocks and gneisses (published as un-numbered un-numberedField Field Trip Trip Guide Guide Book Book of the Wisconsin Geological and and Natural History Geological History Survey) Survey) ia ~ (compiler note: new newreference referencedesignations designationswere wereadopted adoptedtotoconform conformto to ISSN ISSN standards standardsin in1987) 1987) WAWA, ONTARIO ONTARIO 33 1987 WAWA, Part Part 1: 1: *• Abstracts Part 2: and gold mineralization Part 2: *• Geology of the Wawa area and Part Part 3: 3: *"" Geology and stratigraphy stratigraphyof of the the Michipicoten Michipicoten Iron-Formation Iron-Formation Part Part 4: 4: *"" Geology of the Hemlo Deposit Part Part 5: 5: *"" The Kapuskasing Uplift: Uplift: Archean Archean greenstones and granulites 34 MARQUEITE, MICHIGAN 1988 MARQUETTE, Part 1: Part 1: *"" Abstracts 2: Field Part 2: Field Trip Guidebook 1. An the Marquette 1. An introduction introductionto to Archean Archean geology geology and precious precious metal mineralization of the Greenstone Belt, Greenstone Belt, Michigan 2. Marquette Marquettemineral mineraldistrict districtofofMichigan, Michigan, mining mining history history and and geology geology partof of the the Penokean Penokean orogen illustrating Early Proterozoic 3. A A structural structuraltraverse traverseacross acrossaa part overthrusting in overthrusting in northern northern Michigan Michigan 35 DULUTH, MINNESOTA 1989 1: Abstracts Part 1: 2: Field Trip Guidebook Part 2: 1. North Shore Shore rhyolites, rhyolites, Minnesota Minnesota 1. North 2. Penokean PenokeanStructural StructuralTerranes Terranesin ineast-central east-eentralMinnesota Minnesota 3. Mellen Mellen Complex, Complex, Wisconsin Wisconsin Archean gold gold occurrences occurrences and and their their structural structural settings settings (Virginia (Virginia Hom) 4. Archean Horn) 36 1990 THUNDER BAY, ONTARIO THUNDER BAY, Part 1: Abstracts Part 2: Field Trip Guidebook 1. Mafic intrusions, 1. intrusions, PGE PGE mineralization, mineralization, and and granitoid granitoidrocks rocks of of Lac Lac des Illes Illes area Geology of of the the Shebandowan Shebandowan and andQuetico Quetico Archean Archean subprovinces subprovinces 2. Geology 3. Granitoid-related Granitoid-relatedmineral mineraldeposits depositsin inthe the western westernLake Lake Superior region 4. Base 4. Base metal mineralization mineralization in in the the Shebandowan Shebandowan Greenstone Greenstone Belt Belt vii VB �CLAIRE, WISCONSIN WISCONSIN 1991 EAU CLAIRE, Part Part 1: 1: *"" Abstracts Part 2: 2: *"" Field Trip Guidebook 1. 1. Mountain Mountain Shear Shear Zone Zone --- a post Penokean discrete ductile ductile deformation deformation zone Features and andsignificance significance of of the the Precambrian-Cambrian Precambrian-<:ambrian contact in western 2. Features western Wisconsin 3. Proterozoic Proterozoicvolcanogenic volcanogenic massive massivesulfide sulfidedeposits depositsof ofNW NW Wisconsin Wisconsin 38 1992 HURLEY, HURLEY, WISCONSIN WISCONSIN Part 1: 1: *"" Program and Abstracts Abstracts Part Part 2: 2: *"" Field Trip Guidebook 1. Archean Archean and andEarly EarlyProterozoic Proterozoicgeology geologyof ofthe the Gogebic Gogebic District District 2. Evolution 2. Evolution of of the Keweenawan sedimentary sequence 3. Geology Geology of of the the Keweenawan Supergroup Supergroup at at Porcupine Mountains 4. Geology late Archean Archean paleosuture paleosuture Geologyof of the theGreat GreatLakes Lakes Tectonic Tectonic Zone-Marquette area -- a late 39 1993 EVELETH, EVELETH, MINNESOTA MINNESOTA Part Part 1: 1: *"" Program and Abstracts Abstracts Part Part 2: 2: *"" Field Trip Guidebook: 1. Geology Geology and and taconite taconite mines mines of of the the Mesabi Mesabi range 2. DNR Core Library Library (Biwabik Iron 2. DNR Iron Formation, Formation, Partridge Partridge River Riverand and South South Kawishiwi Kawishiwi intrusions, intrusions, Regolith in Rotasonic cores-northern Minnesota) 3. Geology Geologyof of Archean Archean greenstone-granite greenstone-graniteterrane: terrane:Cook-Side Cook-Side Lake Lake area area Duluth Complex Complex at Duluth Duluth 4. Duluth 40 1994 HOUGHTON, MICHIGAN Part 1: 1: *"" Program and Abstracts Part Part 2: 2: *"" Self-guided geological field field trip to the Keweenaw Peninsula, Michigan (available from Dr. T.]. Bornhorst, 402 Emerald EmeraldStreet, Street,Houghton, Houghton,MI MI49931-1413 49931-1413(906-482-5507)) (906-482-5507» T.J. Bomhorst, 402 Part 3: Volcanic Volcanic geology geology of of eastern easternIsle IsleRoyale, Royale, Michigan Michigan Part Part 4: 4: *"" Michigan kimberlites and diamond diamond exploration exploration techniques techniques Part Part 5: 5: *"" Lessons from mining mining case case histories: West West Menominee Range, Michigan Michigan 41 1995 MARATHON, ONTARIO 1995 Part 1.* 1. "" Program Program and Abstracts Abstracts Part 2: Field Field Trip Trip Guidebooks Guidebooks (some (some may may also also be acquired from Ontario Geological Survey, Ministry 002,435 of Northern Northern Development Developmentand andMines, Mines,Field FieldServices Services Section, Section, Suite Suite B B 002, 435 South James Street, Thunder ThunderBay, Bay, Ontario OntarioCanada, Canada,P7E P7E6E3, 6E3,Phone: Phone:807-475-1331) 807-475-1331) 2a.* 2a. "" Alkalic Alkalic rocks rocks of the Midcontinent Midcontinent Rift Rift 2b.* 2b."" Geology and base metal deposits of the Manitouwadge Greenstone Greenstone Belt Belt 2c. Schreiber Greenstone Greenstone assemblage assemblage and and itit gold gold and and base metal mineralization 2e. *"" Geology of the Schreiber 2d. 2d. Geology Geologyand andgold golddeposits depositsof of the the Hemlo HernIo area 2e.* overburden, Wawa 2e. "" Kimberlite, base metal, and gold exploration using overburden, Wawa area area CABLE, WISCONSIN 1996 42 1996 CABLE, WISCONSIN Part 1: 1: Program Program and and Abstracts Abstracts 2: Volcanogenic Volcanogenic Massive Massive Sulfide Deposits Part 2: Deposits of of Northern Northern Wisconsin: Wisconsin: A Commemorative Volume (published (published in in conjunction conjunction with with Field Field Trip Trip 3 to the Flambeau Flambeau Mine) Mine) Part 3: 3: Field Field Trip Guidebook 1. Glacial 1. Glacial geology geology of western western Wisconsin Wisconsin 2. Geology Geology of of the the Montreal Montreal River River Monocline: Monocline: A A traverse traverse through through25 25 km km of of crust crust 4. Early Early to to Middle Middle Proterozoic Proterozoic geology geology of of the the Lake Lake Namekagon region Lake Namekagon Namekagonand andPenokee PenokeeGap Gaparea, area,west westGogebic Gogebic Range, Range, Wisconsin 5. Lake Future Meeting Meeting Locations: Locations: 1997 SUDBURY, ONTARIO ONTARIO 43 1997 1998 KENORA, 44 1998 KEN ORA, ONTARIO 37 37 vu' viii �AWARD GUIDELINES SAM GOLDICH G0LDIcH MEDAL SAM MEDAL Preamble Lake Superior Geology was born bom on or around 1955, 1955, as The Institute on Lake as documented documented by by the fact fact that the meeting was was held held in in 1981. 1981. The The Institutes Institutes are are exemplary exemplary in in their their continuing continuingobjectives objectives of of 27th 27th annual meeting encouraging the with those those aspects aspects of of geology geology that that are are related related geographically to Lake Superior; of encouraging dealing with subjects and sponsoring sponsoring field field trips which will will bring together geologists geologists from discussion of subjects from academia, academia, government government surveys, surveys,and andindustry; industry;and andof ofmaintaining maintainingan an exceedingly exceedingly informal but highly effective mode of operation. During the the course course of of its its existence existence the membership membership of of the the Institute Institute (that (that is, is, those those geologists geologists who who indicate indicate by attending) attending) has has become become aware aware of the fact fact that certain of their an interest interest in In the the objectives objectives of of the the I.L.S.G. I.L.S.G. by colleagues contributions to to the improvement of colleagues have made particularly particularly noteworthy and meritorious meritorious contributions understanding of"Lake "Lake Superior" Superior" geology and its mineral deposits. understanding of The exemplary award award was wasmade madeby byI.L.S.G. I.L.S.G. to to Sam Sam Goldich Goldich in 1979 1979 for to the the for his his many contributions to geology of the region extending extending over over about about 50 50 years. Award Guidelines 1) 1) Directors to to aa geologist whose name The medal shall shall be be awarded awardedannually annuallyby bythe theI.L.S.G. I.L.S.G. Board of Directors with aa substantial substantial interest interest in, in, or or aa major major contribution contribution to, to, the the geology geology of of the the Lake Lake is associated with Superior region. region. 2) Directors, LL.S.G. appointment The Board of Directors, LL.S.G.shall shallappoint appointthe theNominating NominatingCon::unittee. Conmittee. The initial appointment will be of three one for three members, members, one to to serve serve for for three three years, years, one for two, and one one for for one one year, year, the the member with with the the briefest briefest incumbency incumbency to to be be chairman. After After the the first first year yearthe theBoard Boardof ofDirectors Directors shall appoint who will will serve serve for forthree three years. years. In the third appoint at at each each spring spring meeting meeting one new member member who year this this member member shall shall be be the the chairman. chairman. The The Committee Committee membership membership should should reflect reflect the the main main fields fields of interest and geographic geographicdistribuhon distributionofofI.L.S.G. LL.S.G. membership. membership. interest and 3) By Committee shall shall make make its its recommendation to the By November 1, I, the Goldich Medal Nominating Committee the Chairman of Chairman of the the Board Board of of Directors Directors who who will will then then inform inform the the Board Board of of the nominee. nominee. 4) the Committee, will inform the medalist The Board of Directors normally will accept the nominee of the medalist immediately, and and will will have have one one medal medal engraved engraved appropriately for for presentation presentation at at the the next next meeting meeting of the Institute. 5) It is recommended that that the the Institute Institute set set aside annually from whatever sources, such funds as will be required to support supportthe thecontinuing continuingcosts costs of of this this award. required to April 4, 1981 1981 April 4, J. Kalliokoski, Kalliokoski, Chairman Bill Cannon Bill Cannon Fred Kehlenbeck G.B. Morey Greg Mursky ix IX �BOARD OF DIRECTORS 1996 Laurel G. Woodruff, Chair U. S. Geological Survey, St. Paul, Minnesota Minnesota 1995 Mark C. Smyk Ontario Ontario Geological Geological Survey, Thunder Thunder Bay, Bay, Ontario 1994 Theodore J. Bornhorst Michigan Technological University, University, Houghton, Houghton, Michigan 1993 David L. Southwick Minnesota Geological Survey, St. St. Paul, Minnesota Permanent Secretary-Treasurer Permanent Secretary-Treasurer Mark Mark Jirsa Minnesota Geological Survey 2642 University Ave. 2642 University MN55114-1 55114-1057 St. Paul, Paul, MN 057 LOCAL COMMITTEES GENERAL CHAIR Laurel G. Woodruff U. S. Geological Survey, St. Paul, Minnesota PROGRAM COMMITTEE Laurel G. Woodruff, U. S. S. Geological Geological Survey, Survey, St. St. Paul, Paul, Minnesota Suzanne W. W. Nicholson S. Geological Geological Survey, Reston, Virginia U. S. FIELD TRIP COMMITTEE Gene Gene L. L. LaBerge LaBerge University of University of Wisconsin-Oshkosh, Wisconsin-oshkosh, Oshkosh, Wisconsin William William F. F. Cannon U. S. S. Geological Survey, Survey, Reston, Virginia SECRETARY-TREAS URER SECRETARY-TREASURER Sally LaBerge LaBerge University of University of Wisconsin-Oshkosh, Wisconsin-Gshkosh, Oshkosh, Oshkosh, Wisconsin Wisconsin x �STUDENT PAPER PAPER COMMITTEE COMMITrEE Jirsa Mark Jitsa Minnesota Geological Minnesota Geological Survey, Survey, St. St. Paul, Paul, Minnesota Minnesota Suzanne Nicholson U. S. S. Geological Geological Survey, Reston, Virginia SESSION CHAIRS Glen Adams Consulting Consulting Geologist, Geologist, Rhinelander, Rhinelander, Wisconsin Wisconsin Terry Boerboom Minnesota Geological Survey, St. Paul, Minnesota Sidney Hemming Lamont-Doherty Earth Earth Observatory, Observatory, Palisades, Palisades, New York York Mark Jirsa Minnesota Geological Geological Survey, Survey, St. Paul, Minnesota Minnesota Suzanne Nicholson U. S. S. Geological Geological Survey, Reston, Virginia Edward Ripley Indiana University, University, Bloomington, Bloomington, Indiana Ron Sage Ontario Geological Survey, Sudbury, Ontario Ontario Ontario Klaus Schulz S. Geological Geological Survey, Reston, Virginia U. S. Mark Smyk Ontario Geological Ontario Geological Survey, Survey, Field Field Services Services Section, Thunder Bay, Bay, Ontario Ontario 1995-96 GOLDICH 1995-96 GOLDIeH MEDAL MEDAL COMMITrEE COMMITTEE Penelope Morton (1996) (1996) University of Minnesota-Duluth, Duluth, Minnesota Ken Card Ca.rd (1997) (1997) Ontario Geological Ontario Geological Survey Survey (retired), (retired), Kanata, Ontario Ontario Dan England England (1998) (1998) Eveleth Fee Office, Incorporated, Eveleth, Minnesota xi �1996 GOLDICH GOLDICH MEDAL MEDAL RECIPIENT RECIPIENT David L. 1. Southwick Minnesota Geological Survey University of Minnesota St. Paul, Paul, Minnesota St. MEDALISTS PAST GOLDICH MEDALISTS 1979 1979 1980 1980 1981 1982 1982 1983 1983 1984 1985 1986 1986 1987 1988 1989 1990 1991 1992 1993 1994 1995 Samuel S. Goldich not awarded awarded Carl E. Dutton, Dutton, Jr. Jr. Ralph W. Marsden Burton Boyum W. Ojakangas Ojakangas Richard W. Paul K. K. Sims C. G. B. Morey Henry H. Halls Walter S. Whit Walter Jorma Kalliokoski Kenneth C. Card William J. Hinze William F. F. Cannon Donald W. Davis Cedric Iverson Gene LaBerge LaBerge 1996 BANQUET SPEAKER SPEAKER 1996 BANQUET Steven Kesler Department of Department of Geological Geological Sciences University of Michigan Ann Arbor, Michigan Sustainable Mineral Development Development -- Fact or Fiction? xii Xl! �CITATION David S.S. Goldich Goldich Medal Medal Recipient David L. L. Southwick, Southwick, 1996 19965.5. It is my pleasure pleasure to to introduce introduce to to you you this this evening, evening, David David L. L. Southwick, Southwick, 17th 17th recipient for for 1996 1996 of the Institute's Institute's S.S. 5.s. Goldich medal. recipient When Laurel asked me me to to make make these she prefaced When Laurel Woodruff Woodruff asked these remarks remarks she prefaced her request by noting noting that that II had had worked worked with with Dave Dave on on several several projects and that II had had been been the Institute Institute for for many many years. years. Dave Dave and and II have have worked worked together together for many years around the been fortunate fortunate to to have have him him as as a professional colleague However, and I have been colleague and and friend. friend. However, having been around aroundthe theInstitute Institutefor for aa long long time time is is nothing nothing more more than than aa matter matterof ofluck, luck, and II now find myself writing memorials for friends who were not so lucky. Believe now find myself writing memorials friends l~cky. Believe me, this occasion occasion is is much much more more enjoyable. enjoyable. So who is Dave Dave Southwick? He He was was born bornin inRochester, Rochester, Minnesota Minnesota in in 1936 1936 and graduated from School in in 1954. 1954. He He wanted wanted to be a draftsman, graduated from Rochester Rochester Senior Senior High School but his his parents parents prevailed prevailed and and he hegraduated graduatedfrom fromCarleton Carleton College College in in Northfield, Northfield, there he he went on to graduate Minnesota with aa degree degree in in geology geology in 1958. 1958. From there graduate school school where he he studied studied under under Aaron Aaron Waters. Waters. His at the Johns Hopkins University University where His Ph.D. Ph.D. dissertation to do do with with ultramafic ultramafic rocks rocks in the Cascades Cascades of He dissertation had had to of Washington. Washington. He wondered about about ophiolites ophiolites long long before before it was was fashionable fashionable to do so. so. After graduate school, his professional professional career career with with the the U.S. U.s. Geological Geological Survey, school, Dave Dave started his Survey, Eastern States States Branch, Branch, in 1962. 1962. He He returned returned to to Minnesota Minnesota in in January, January, 1968 1968 having a joint joint appointment in the appointment the Department Department of of Geology Geology and and Geophysics Geophysics at the the University University of of Minnesota Minnesota and andthe theDepartment DepartmentofofGeology GeologyatatMacalester MacalesterCollege College in inSt. St. Paul, Paul, Minnesota. Minnesota. He moved as aa Professor Professor of of Geology. Geology. During that moved to to Macalester Macalester full-time full-time in in 1971 1971 as that time, time, Survey. He summers for for the the Minnesota Minnesota Geological Geological Survey. He began began full-time full-time work work Dave worked summers with with the the Survey Survey as asaaSenior SeniorScientist Scientist in in 1977, 1977, and has been Director of the Survey since 1993 and and Professor of Geology in the Department Department of of Geology Geology and and Geophysics Geophysics since since 1993 1994. So much for vital 1994. vital statistics. statistics. It goes without without saying saying that that receiving receiving the the S.S. S5. Goldich Goldich medal considerable medal is a considerable honor. Unfortunately, Unfortunately, II do not not know know what what criteria criteria were were used used by bythe theSelection Selection Committee when they chose to honor Dave. In fact I do not even know who sits on the they chose Dave. In I Selection Committee. Therefore, will look look toto the the medal medal itself itselffor forguidance. guidance. On the Selection Committee. Therefore, II will reverse side itit reads reads "presented "presentedfor for outstanding outstandingcontributions contributionsto tothe thegeology geologyof of the the Lake Lake What does does that that tell tell us? Superior region." What "geology" refers The word "geology" refers to to aa science science and and profession profession dedicated dedicated to to the the study of of the the Earth. Earth. Obviously Obviouslythe thescience science and andprofession profession is is practiced practiced by by geologists. geologists. the history of who study study the the history history of of the the earth earth like like to to call themselves earth These days some people who scientists rather than than geologists. geologists. II distinguish distinguish the the two two groups by by the the fact that geologists geologic maps. Looking over over the the list list of of previous previous medal medal recipients, recipients, many were make geologic maps. Looking first mappers. Dave first and foremost foremost geologic geologic mappers. Dave has has produced produced aa variety variety of of very very good good xiii �geologic Surveys. By geologic maps while with both both the the U.S. U.s. and Minnesota Minnesota Geological Geological Surveys. By that that criterion Dave Dave is is aa worthy worthy recipient recipientof of the the medal. medal. The word word "contributions" "contributions" on the medal medal refers—again refers-again in my view—to view-to any "body work" which has advanced geologic knowledge in in the the region. region. Again it seems seems to me me of work" geologic knowledge that any number for their their "bodies "bodies of ofwork" work" that number of of the the previous previous recipients recipients were honored for have included included research, research, teaching, teaching, and and above above all all professionalism. professionalism. Dave Dave has made made professional contributions in in the the areas areas of of both both research research and and teaching. teaching. His professional contributions His extensive extensive topics and and is is frequently frequently cited. cited. More importantly, bibliography covers a wide variety of topics however, there are any however, any number number of of younger younger geologists geologists in the the profession profession who who have have received basic basic training under Dave's tutelage. tutelage. Many received Many of you are in this room! room! The The fact fact that.you are here here makes makes him himaaworthy worthyrecipient recipientof of the the medal. medal. that you are significance of "outstanding" is The significance of the the word "outstanding" is somewhat subjective subjective and a little on. A is warranted. warranted. The more difficult to get aa handle on. A little little history is The medal medal is is named named in in honor of S.S. S.s. Goldich. Goldich. Many of you are are probably probably too too young young to to remember remember Sam. Sam. I have the pleasure of knowing him 40 years. years. Most him for nearly 40 Most of you have heard war stories stories about him and and many many probably probably are are true. true. After Aftermy my first first year year in in graduate graduate school school II decided that my family family had forgotten forgotten to to tell tellme methat thatmy myreal realname namewas was"Morey 'Moreyyou youstupid stupid_." _." In truth truth Sam was a wonderful man, but he could be be tough tough at at times. times. He was very much like the Drill Instructor we see on TV ads for for the the U.s. U.S.Marine MarineCorps. Corps. Sam Sam was was tough like TV ads because he he wanted wanted you you "to "to be be the the best best that that you you can can be." be." He He wanted wanted his his people to because people to excel—topush push the the envelope-at envelope—atwhatever whateverthey theydid. did. He wanted his people to excel-to to make make aa to be outstanding—to outstanding-to make a difference. difference--he wanted them to difference. Dave has excelled and has His structural and has pushed pushed the the envelope. envelope. His structural studies studies on the the Penokean Penokean orogen orogen represented aa scientific scientific revolution of sorts. sorts. His ideas have changed the way many of us for me me about about iron-formation. iron-formation. Thus think about the the rocks--and rocks--and especially especially for Thus by by Sam's Sam's geologists whose whose body body of of work work has has made made aa difference. difference. All of creed, Dave is one of those geologists him. II know us are better geologists because of him. know Sam is pleased and that makes makes Dave Dave a worthy recipient recipient of of the the medal. to present present to you the 17th worthy medal. Therefore, Therefore, I am pleased pleased to 17th s.s. Goldich metal, David David L. L. Southwick. recipient of the the S.S. G.B. Morey G.B. Minnesota Geological Survey University of Minnesota St. Paul.. Minnesota Minnesota 55114 55114 xiv �TRAVEL AWARD AWARD STUDENT TRAVEL I.L.S.G.Student StudentTravel Travel Award Award to support support The 1986 1986 Board of Directors established the I.L.S.G. student student participation participationatatthe theannual annualmeeting meeting of of the the Institute. The The awards awards will will be be made made from a special fund set up up for this purpose. This This award award is intended intended to to help help defray defray some of the direct travel travel costs costs to to the the Institute Institute and and includes includes a waiver waiver of of registration registration fees, fees, but but excludes expenses for meals, lodging, and field field trip trip registration. registration. The number number of of awards awards and value value are are determined determinedby bythe theannual annualChairman Chairmanin inconsultation consultationwith withthe theSecretarySecretaryTreasurer and and will will be be announced announced at at the the annual banquet. The following general general criteria criteria will be considered by the annual Chairman, who who is is responsible for for the the selection: selection: 1) 1) The The applicants applicants must musthave have active active resident (undergraduate or graduate) student status student statusatatthe thetime time of of the the annual meeting meeting of the Institute, certified by the department department head. head. 2) Studentswho whoare arethe thesenior seniorauthor authoron oneither either an an oral oral or or poster poster paper paper will will be be 2) Students given favored consideration. consideration. 3) It is desirable for two or more students students to to jointly request travel travel assistance. assistance. 4) In 4) Ingeneral, general,priority prioritywill willbe be given given to to those in the Institute region who are farthest away. away. 5) Each 5) Eachtravel travelaward awardrequest requestshall shallbe be made made in in writing, writing, to to the annual annual Chairman, Chairman, with with an an explanation explanation of of need, possible author status or other significant details. Successful applicants will receive their awards at the time of registration for the Meeting. xv �41ST ANNUAL INSTITUTE ON LAKE SUPERIOR SUPERIOR GEOLOGY MARATHON, ONTARIO The 41st Annual Institute The Institute on onLake Lake Superior SuperiorGeology Geology was was held heldMay May13-18, 13-18, 1995, 1995, in in Marathon, Ontario. The Marathon, The meeting meeting was was organized organized by by staff staff of of the the Ontario OntarioGeological Geological Survey, Services Section, Chairman, Mark Mark Smyk, Smyk, was was Survey, Field Services Section,based based in in Thunder Thunder Bay. Bay. Chairman, assisted in the the organization organization of of the the Technical Technical Sessions Sessions by former chairman, Manfred Kehienbeck of Lakehead University. Kehlenbeck The Proceedings of the the 41st 41st ILSG ILSG was Proceedings of was published published in six parts: Part 1: Program Programand andAbstracts Abstracts (edited (editedby by Mark Mark Smyk Smyk and and Manfred Manfred Kehienbeck) Kehlenbeck) Part 2: 2: Field Field Trip Guidebooks 2a: Alkalic Alkalic rocks rocks of the Midcontinent Midcontinent rift (Ron Sage and David Part 2a: Watkinson) Part 2b: of the the Manitouwadge Manitouwadge 2b: Geology, Geology, structure and age relationships of greenstone belt and the Wawa-Quetico Wawa-Quetico subprovince subprovince boundary boundary (Eva Zaleski, Virginia VirginiaPeterson, Peterson,Hugh Hugh Lockwood Lockwood and and Otto van (Eva Zaleski, Breeman) Part 2c: Schreiber greenstone greenstone assemblage assemblage and its gold and 2c: Geology Geology of the Schreiber base metal mineralization mineralization (Mark (Mark Smyk and Bernie Bernie Schnieders) Part 2d: Geology Geology and and gold gold deposits deposits of of the the Hemlo Hernlo area area (Tom (Torn Muir, Muir, Bernie Bernie Schnieders and Mark Smyk) and Mark Smyk) Part 2e: metal and gold exploration exploration using overburden, 2e: Kimberlite, Kimberlite, base metal Wawa area (Tom Morris) (Torn were run both as pre- and post-meeting All trips, with the the exception exception of Wawa, were post-meeting events in in order to to accommodate accommodate large large subscription subscription levels levels and and travel travel schedules. schedules. The The Hemlo Hemlo trips trips order spurred spurred the the revision revisionand andre-publication re-publication of of aa guidebook guidebook first first published published jointly jointly by by the the Geological Association of of Canada, Canada, the Mineralogical Associationof of Canada Canada and and the Mineralogical Association Geological Association the Society of Economic Geologists Geologists in in 1991. 1991. The The successful successful running running of of the the meeting and the associated field field trips trips gave valuable insight insight in in the the planning associated gave some some valuable planning of a field field trip trip associated with with the the International International Geological Geological Correlation Program in August. Logistical Logistical in May May were were put put to to use use when when Ron Ron Sage Sage and II led led the the IGCP IGCP delegates delegates lessons learned in through alkalic rocks rocks of larger trip looking looking at through the alkalic of the the Marathon Marathon area area as as part part of of aa larger the Midcontinent rift. intrusive rocks associated with the intrusive rocks There 145 paid registrants at the the 41st 41st ILSG. ILSG. The The nine nine field field trips trips attracted attracted163 163 There were 145 participants, some of whom were not able to attend the technical sessions. participants, some of whom were not able the technical banquet was was attended attendedby by approximately approximately 135 135 delegates. The The Goldich Goldich Medal, Medal, The annual banquet contributions to to the the understanding understandingof of Lake Lake Superior Superior geology, geology, exemplifying outstanding outstanding contributions The award was awarded awarded to toGene GeneLaBerge LaBerge of of the the University University of of Wisconsin, Wisconsin, Oshkosh. The was presented by by Tim Tim Flood Flood of St. St. Norbert College. College. The banquet speaker was was Peter Lightfoot Geological Survey, the relationship relationship Lightfoot (Ontario Geological Survey, Sudbury) Sudbury) who who addressed the between mantle plumes, plumes, flood flood basalts and mineralization. xvi XVI �PaperAward Awardrecipients recipientswere wereGeoff Geoff Shore (University of Western Ontario) The Student Student Paper spoke about aboutalkaline alkaline gabbroic gabbroic rocks rocks of of the the Coidwell Coldwell alkalic alkalic complex, complex, and and Kim Kim who spoke Darrah (Kent State University) University) who of the the who presented presented information information on on the application of aluminum-in-hornblende barometer. Five students were given travel awards totaling barometer. Five $500. The Board of Directors of the Institute on Lake Superior Superior Geology Geology met in Marathon on on attendance were wereMark MarkSmyk Smyk (1995 (1995 meeting chair), Ted Bornhorst Bornhorst (1994 (1994 May 15, 1995. 1995. In attendance and associate associate secretary-treasurer), secretary-treasurer), Jim Jim Miller Miller (proxy for David David Southwick, Southwick, 1993 1993 chair and (secretary-treasurer). Guests Guests included included Laurel Laurel Woodruff Woodruff (chair (chair for for chair) chair) and Mark Jirsa (secretary-treasurer). 1996 Cable, Wisconsin), Wisconsin), Gene Gene LaBerge LaBerge (alternate 1996 meeting), 1996 meeting meeting in Cable, (alternate chair for 1996 Sally LaBerge, Wilf Sally LaBerge, Wilf Meyer Meyer and and Ron Sage Sage (co-chairs (co-chairs for for 1997 1997 meeting meeting in Sudbury, Ontario). The Board of Directors: 1. Accepted 1. AcceptedReport Reportof ofChairman, Chairman,40th 40thILSG ILSG meeting 2. ApprovedCable, Cable,Wisconsin, Wisconsin,as ashost hostfor for 42nd 42nd ILSG ILSG (1996) (1996) with 2. Approved with Laurel Woodruff as Chair; Gene LaBerge LaBerge agreed agreed to to assist assist Laurel Laurel and and take take over Chair duties, if need be. 3. Approved ApprovedSudbury, Sudbury,Ontario, Ontario,asashost hostfor for43rd 43rdILSG ILSG (1997). (1997). Wilf Wilf Meyer Meyer suggested suggested 3. topical sessions field trips trips that highlight highlight correlations correlations and and contrasts contrasts between sessions and field the Huronian Huronian and and the theequivalent equivalentstrata stratain inWisconsin, Wisconsin, Michigan, Michigan, and Minnesota. Minnesota. He further suggested that a session session devoted devoted to to environmental environmental remediation remediation would would appropriate, and be appropriate, and the the Board Board agreed. 4. Accepted ILSG ILSG Financial Financial Report (Mark Jirsa Jirsa and and Ted Bornhorst) 5. Approved 5. ApprovedGene GeneLaBerge LaBergeas asrecipient recipientof of1995 1995 Goldich Medal 6. 6. Approved ApprovedDan DanEngland Englandasasnew newGoldich GoldichMedal Medal Committee Committee member member (replacing (replacing Glen Glen Adams) 7. Approved 7. Approvedmotion motiontotoallow allowsecretary-treasurers secretary-treasurers to to set setreduced reducedprices priceson onback backILSG ILSG volumes to to reduce reduce inventory inventory and and make make volumes volumes affordable affordable before their shelf shelf life is exceeded. The The motion motion also also allows the secretary-treasurers some lee-way to set those prices to accommodate regional considerations and costs. 8. Approvedaamotion motiontotodonate donate$1.00 $1.00 from from each each meeting registrant to the the Michigan Michigan 8. Approved efforts. Technological Technological Institute Institute Library Library to to assist assist in in their their research research and archiving efforts. They only known known full full set set of of ILSG ILSG volumes the They maintain the only volumes dating dating back to the in 1955. 1955. Donations Donations ($100-$150) ($100-$150) will inception in Institute's inception will be be made made following following the 1996 1996 meeting meeting and every year thereafter. 9. Approvedaamotion motiontotoallow allowdonation donationofofselected selectedback backvolumes volumesof ofILSG ILSG Proceedings 9. Approved their collection collection the Minnesota Minnesota Geological Geological Survey Survey (MGS) (MGS) Library to the Library to to rebuild their after theft. xvii �10. Approved 10. Approvedloan loanof ofVan VanHise Riseand andLeith Leithmonograph monograph(1911) (1911) to a secure section section of MGS MGS Library for safe-keeping. The monograph was was donated donatedto tothe theILSG. Il.SG. The monograph and Suggestions Suggestions to to Chairpersons." Chairpersons." Ted 11. Discussed "Requirements "Requirements and Ted Bornhorst Bornhorst is is constructing with time and passed constructing a manuscript manuscript that can be modified modified with passed from from chairperson to chairperson. chairperson. It It would would detail detail what must be done by the chair and meeting that that runs runs in in the the black. black. The suggest tips for how to operate a smooth smooth meeting board agreed agreed that that would would be be very very helpful. helpful. It will eventually eventually reside with the the secretary-treasurer who will have responsibility to see see that that itit isis passed passed onto the responsibility to incoming Chair. 12. OTHER 12. OTHER BUSINESS BUSINESS a. Motion a. Motion approved approvedtotoprohibit prohibitthe theuse useof ofcameras cameras in in both both oral oral and and poster postersessions, sessions, unless the photographer has of individual individual authors. tmless has the permission of b. Motion b. Motion approved approvedto torequire requirepeer peerreview review of of abstracts. abstracts. The The local local chairpersons chairpersons must establish review committee committee (size (size and composition composition at at their their discretion). discretion). establish aa review Implicit in the the review review process process is is the the right right of of the the committee committee to to refuse refuse acceptance. acceptance. Authors of of rejected rejected abstracts can make changes changes and re-submit, if they can do so within the within the time time limit limit established establishedfor for receipt receipt of of abstracts. abstracts. c. Ted Bornhorst suggested that that the Board into desktop Ted Bornhorst suggested Board look look into desktop publishing of peerpeerreviewed, expanded abstracts and short papers. This This would allow allow authors who might not normally publish in established journals to semi-formally publish their not normally publish in established journals research. The The idea idea was was tabled tabled for for future future discussion. discussion. d. AAsuggestion newsletter that that would be suggestionwas wasmade madeby byTed TedBornhorst Bornhorstto to create create an ILSG ILSG newsletter published early published early in in the the calendar calendar year. year. ItItwould wouldserve serve to to publicize publicize upcoming upcomingILSG ILSG meetings and and other meetings other events, events, as as well well as as highlight highlight exploration exploration and research research activities. The approved. Ted activities. The concept concept was generally generally approved. Ted will prepare aa mock-up mock-up in the following months with a student assistant. assistant. Board Board members will continue to and track track the the progress progress of of the venture. discuss and e. Board 1995. Boardagreed agreedtotohave havea aformal formalmeeting meetingatatthe theIGCP IGCPConference, Conference,August August25-27, 25-27,1995. Budgeting for the 41st was designed designed to to keep keep registration registration costs costs at at aa minimum in 41st ILSG ILSG was order to to help help attract attractpotential potential delegates delegates to to Marathon Marathon despite despite prohibitively prohibitively long long travel travel distances. Fees were largely largely set set on on a cost-recovery basis. Many Many of of the the duties cost-recovery basis. duties and Fees were services which could normally services normally be contracted contracted out to to other other agencies agencies (e.g., (e.g., university university OGS staff staffininorder order to to reduce reduce costs. costs. Field trip extension services) were taken care of by OGS guidebooks guidebooks were also sold at at just just above above cost cost to to attendees. attendees. Since Since the the meeting, the guidebooks guidebooks have have been beenreprinted reprintedseveral severaltime; time;sales sales in in Thunder ThunderBay Bay continue continue to to be be brisk, brisk, especially during during field field season. The financial analysis The final final financial analysis appears appears to indicate that the 41st ILSG ILSG managed managed to to turn turn a Thisis, is,ininitself, itself, especially especially rewarding, rewarding, considering our 'user-friendly' 'user-friendly' modest profit. This pricing practices, unforeseen unforeseen print-run print-run problems problems and and losses losses in inCanada-US Canada-US exchange exchange xviii XVlll �is to to be be commended for his role in rates. Mark MarkO'Brien, O'Brien, local local Secretary-Treasurer, Secretary-Treasurer, is commended for in keeping us keeping us on onan aneven evenfinancial financial keel. keel. I have received many favourable favourable comments and kudos on the the organization organization of of the the 41st 41st flSG. Despite typical) north north many'arms-length' 'arms-length'logistical logistical problems, uncooperative (but typical) ILSG. Despitemany shore weather and and minor minor glitches, glitches, itit proved proved to to be be aa very very successful successful meeting. meeting. I must again thank all all the the people people in in Thunder Thunder Bay Bay and Marathon who helped helped to pull itit off. off. Special thanks must also go out to all the field field trip trip leaders for for their their perseverance. perseverance. Cliff Cliff Special Shaw graciously filled in on the Shaw graciously filled the alkalic alkalic rocks rocks trip for for Dave Dave Watkinson, Watkinson, who was was unfortunately ill. Former chairmen, Ron Sage, Ted Bornhorst, Manfred Kehienbeck unfortunately ill. Former chairmen, Ron Sage, Ted Bornhorst, Kehlenbeck and Ed Frey Ed Frey provided provided invaluable invaluable organizational organizational advice. advice. Lastly, II would would like like to to to Marathon and who continue to acknowledge all those who made made the the effort to come come to to support the support theInstitute Instituteon onLake LakeSuperior Superior Geology. Geology. Mark Smyk MarkSmyk Chairman,41st 41stILSG ILSG Chairman, Thunder Thunder Bay, Bay, Ontario xix �PROGRAM �OF EVENTS EVENTSAND AND PROGRAM PROGRAM CALENDAR OF WEDNESDAY, MAY WEDNESDA Y, MA Y 15 8:00 AM AM - 6:00 PM FIELD FIELDTRIPS TRIPS 11 AN]) AND 22 1. GLACIAL GLACIALGEOLOGY GEOLOGY OF WESTERN WISCONSIN Leader: Mark Mark D. D. Johnson (Gustavus Adoiphus Adolphus College) College) 2. GEOLOGY GEOLOGYOF OFTHE THE MONTREAL MONTREAL RIVER RIVER MONOCLINE: TRAVERSE THROUGH 25 KM OF THE A TRAVERSE 25 KM THE CRUST Leader: William WilliamF. F. Cannon Cannon(U. (U. S. S. Geological Survey) 5:00 PM PM - 8:00 PM REGISlRATION REGISTRATION 7:00 PM PM ICEBREAKER AND POSTER POSTERSESSION SESSION(Cash (Cash Bar) Bar) PM - 10:00 PM ICEBREAKER AND 9:00 PM) (Authors present at posters 7:30 PM (Authors present at posters 7:30 PM - THURSDAY, THURSDA Y, MAY 16 NOTE: ThCHNKAL SESSIONS ARE IlW NOTE: TECHNICAL SESSIONS AREIN INTHE THENAMEKAGON NAMEKAGONROOM, ROOM,TELEMARK TELEMARK LODGE ...* STUDENT STUDENT PRESENTAnON PRESENTATION 8:00 8:00 AM AM REGISTRATION REGISlRATION CONTINUES CONTINUES TECHNICAL TECHNICAL SESSION I SESSION CHAIRS: CHAIRS: KLAUS AND GLEN GLEN ADAMS ADAMS SESSION KLAUS SCHULZ AND — 8:55 8:55 AM AM OPENING - 42ND ANNUAL ANNUAL INSTITUTE INSTITUTE ON LAKE SUPERIOR GEOLOGY L. G. G. Woodruff, Woodruff, General Chair L. 9:00 AM KEYNOTE ADDRESS Miller, J. D., Jr., and Vervoort, Vervoort, J.J. D. D. The Latent Magmatic Maginatic Stage Stage of ofthe theMidcontinent MidcontinentRift: Rft: A Period of Magmatic Magmatic The Crust Underplating and and Melting Melting of of the the Lower Crust — 9:30 AM Bornhorst, T. Bornhorst, T. J., and Dolan, Dolan, M. M. T. T. An Electronic Electronic Component Component of of the Institute Institute on on Lake Lake Superior Geology L 9:50 AM AM 10:00 10:00 AM AM PRESENTATION OF PROPOSED PROPOSEDCHANGES CHANGESTO TOTHE THE1.I.L.S.G. L.S.G. CONSTITUTION COFFEE BREAK AND POSTER SESSION xxi XXi �10:20 AM 10:20 AM Ames, D. E., Jonasson, Jonasson, 1.I. R, R.,Parrish, Parrish, RR R., R., Watkinson, Watkinson, D. H., and and Gibson, Gibson, H. H. L. L. Regional HydrotherrnJ1l'Massive Hydrothermal Massive Sulphide Suiphide Producing System and U/Pb U/Pb Hydrothermal Titanite Age ping FOrrnJ1tion, Formation, Sudbury Age Constraints, Ona Onaping Structure, Ontario 10:40 AM 10:40 AM Ripley, E. Ripley, E. M. Pet rogenetic Relationships between A pat ite-B earingand andApatite-Deficient Apatite-Deflcient Iron Petrogenetic Apatite-Bearing Oxide-Rich Intrusions Intrusions and and Massive Massive Sulfide SulfideMineralization Mineralizationinin the the Duluth Duluth Oxide-Rich Complex, Complex, MN 11:00 AM 11:00 AM "'Peterson, D. D. M. M. *peterson, Targeting Targeting Footwall Footwall Copper-PGE Copper-PGE Deposits Deposits in the the Duluth DuluthComplex ComplexBased Based on on Sudbury Mining Mining Camp Camp Analogs Analogs 11:20 AM 11:20 AM Saini-Eidukat, B., Rudashevsky, N. N. S., 5., and Polozov, Polozov, A. A. G. G. Saini-Eidukat, B., Occurrence of Hibbingite Hibbingite in in the the Duluth Complex, Complex, Minnesota, Minnesota, and in the Noril'sk Complex Iron Ore Deposit, Russia Complex and Korshunovskoe Korshunovskoe Iron ,-11:40 AM 12:00 PM 12:00 PM Mudrey, M. G., G., Jr., Jr., Brown, Brown, B. B. A., Freiberg, P. G., and and Simo, Simo, J. J. A. A. Mudrey, M. Mineralization in the Fox River Valley, Mississippi Valley-Type Valley-Type Mineralization Valley, Eastern Wisconsin LUNCH BREAK BREAK TECHNICAL SESSION SESSION II II TECHNICAL SESSION ED RIPLEY RIPLEY AND SMYK SESSION CHAIRS: CHAIRS: ED AND MARK SMYK \-/ 2:00 PM Boerboom, Boerboom, T. T. J. J. Southward Extension the Penokean PenokeanTerrane Terrane through through Steams Stearns County, Central Extension of the Minnesota 2:20 2:20 PM PM "'Darrah, *Darrah, K. 5., S., Holm, Hoim, D. D. K., K., Dahl, Dahi, P. P. 5., S.,and and Lux, Lux, D. D. R. it Petrographic Pet rographic and Thermobarometric Analysis of the Metamorphosed Little Falls Formation, Central Minnesota, Minnesota, with with Implications Implications for Early Early Proterozoic Proterozoic Tectonism ."j/ 2:40PM 2:40 PM Hoim, D. Holm, D. K., K., Dahi., Dahl., P. S., 5., and Lux, Lux, D. D. R. R Was Lithospheric Lithospheric Delamination Delamination an an Important Process in the Evolution Was Evolution of of Early Proterozoic Collisional Orogens? '( / 3:00 PM PM BREAK AND AND POSTER POSTER SESSION SESSION COFFEE BREAK 3:20 3:20 PM PM Schmidt, S. Th., and Stern, Stern, W. W. Clay Minerals of of the North Shore Shore Volcanic Volcanic Group and and Possible Possible Relationship Relationship to to Copper Precipitation during Alteration xxii XXll �'I 3:40 PM PM *BeMcer A., A., and and Karhu, *Bekker, Karhu, J. J. A. Study of ofCarbon Isotope Ratios Carbon Isotope Ratios in in Carbonates Carbonates of of the the Early Early Proterozoic Proterozoic Snowy Snowy Pass Supergroup, WY WY and and Its Its Application Application for Correlation with with the the Chocolay Chocolay ian Supergroup, Supergroup, ON ON Group, MI and the Huron Huronian 4:00 PM 4:00PM Larsen, C. Late Holocene Lake Lake Superior -- Isostatic and Climactic Climactic Lake-Level Lake-Level Change 4:20 PM Uchytil, S. S. J., Steffensen, C. K., Jarvie, D. M., Dickas, A. A. B., B., Uchytil, Mudrey, M. and Mudrey, M. G., G., Jr. Jr. Outcrop and and Subsurface Subsurface Core Core Analysis and Relationship Relationship to to Regional Regional Hydrocarbon Pros pectivenessof ofthe theMiddle MiddleProterozoic ProterozoicNonesuch Nonesuch Formation in Prospectiveness in Northern Wisconsin and Michigan Wisconsin I. — — PM MIXER 6:30 PM - 7:30 PM MIXER - CASH BAR v PM ANNUAL 7:30 PM - 9:30 PM ANNUALBANQUET BANQUET&&AWARDS AWARDSPRESENTATION PRESENTATION Announcement Announcement of of the the 43rd Annual Annual Meeting Meeting location. location. 1996Goldich GoldichAward Award presentation presentation to Dr. Dr. David Southwick, 1996 by Dr. Dr. G. G. B. B. Morey. Minnesota Geological Survey, by Banquet speaker: Dr. Dr. Stephen Stephen E. E. Kesler, University of Michigan, Michigan: Ann Arbor, Michigan: — SUSTAiNABLE MINERALDEVELOPMENT DEVELOPMENT-OR FICTION? FICTION? SUSTAINABLE MINERAL -- FACT OR FRIDAY, FRIDAY, MAY 17 8:30 8:30 AM AM REGISTRATION CONTINUES TECHNICAL SESSION SESSION III III TECHNICAL SESSION CHAIRS: SIDNEY HEMMING AND SIDNEY HEMMING ANDTERRY TERRY BOERBOOM BOERBOOM V 9:00 AM 9:00AM Chandler, V. W. Chandler, V. The West-Central West-Central Minnesota Minnesota Earthquake EarthquakeofJune of June5,5,1993: 1993:An AnOpportunity Opportunity to The Re-examine Seismicity Seismicity near near the the Morris Fault 9:20 9:20 AM AM S. M., M., and Kiasner, *Wilson, S. Klasner, J.J. S. A Structural Structuraland andKinematic Kinematic Analysis Analysis of of the McCaslin Formation near near McCaslin McCaslin Mountain, Wisconsin Wisconsin 9:40 AM AM 9:40 Westjohn, D. Westjohn, D. B. B. Regional Finite Strain Strain Patterns in Proterozoic Slates and and Quartzites: Regional Finite Proterozoic Slates Implications for for Heterogeneous Heterogeneous Strain Strain Related Related to to Flexural Flexural Slip Slip Folding in the Marquette Synclinorium 10:00 AM 10:00 AM COFFEE BREAK BREAK AND AND POSTER POSTER SESSION xxiii �10:30 AM AM *Adamson, K. F. Petrology, Stratigraphy, Stratigraphy, and andSedimentation Sedimentationof ofthe the Middle Middle Proterozoic Proterozoic Bayfield Bayfield Group of Northwestern Wisconsin Wisconsin 10:50 AM 10:50 AM Ojakangas, R W. Ojakangas, R. Tidalites of Early Proterozoic Age in the Western Lake Lake Superior Region: Region: Minnesota, Wisconsin Wisconsin and and Michigan Michigan 11:10 AM AM Ojakangas, G. W. Ojakangas, Cyclic Tidal Tidal Laminations Laminations in in the the Early Early Proterozoic ProterozoicPokegama PokegamaFormation: Formation: Digital Digital Cyclic Image Analysis and Computer Modeling Modeling 11:30 AM AM LUNCH BREAK clIE NOTE: ALL POSTERS MUSTBE BEREMOVED REMOVED LUNCH BREAK NOTE: ALL POSTERS MUST TECHNICAL TECHNICAL SESSION SESSION IV JIRSA AND AND RON SAGE SESSION CHAIRS: MARK JIRSA 1 \ 1:30 PM Hemming, S. S. R., R, McLennan, S. S. M., Hemming, M., and and Hanson, G. N. Geochemical GeochemicalSource SourceCharacteristics Characteristicsand and Diagenetic Diagenetic Trends Trends of the the Virginia Formation, Mesabi Iron Range, Range, Minnesota 1:50 PM Medaris, Jr., Fournelle, J. Medaris, L. L. G., G., Jr., Dott, R. R H., Jr., J. H., Johnson, C. C M., M., Schott, R. C, C., and Baumgartner, Baumgartner,L. L. P. P. Age and and Geological the Baraboo Baraboo Quartzite Quartzite Geological Significance of the 2:10 PM PM Jirsa, M. A. of a Timiskaming-Like Timiskaming-Like Sequence Sequenceininthe theSouthern Southern Wawa Wawa Subprovince, Genesis ofa Northeastern Minnesota 2:30 PM PM Smyk, M. M. C Kingston, D. D. M. C. and Kingston, Basaltic Komatiites Associated Rocks: Rocks: Implications Implications on on the the Nature Nature of Komatiites and Associated Volcanism Part of of the Schreiber-Hemlo Schreiber-Hemlo Greenstone Volcanism in Part Greenstone Belt, Belt, Northwestern Northwestern Ontario 2:50 PM PM PRESENTATION OF STUDENT PAPER AWARDS PRESENTAnON 3:00 PM PM CLOSING C LOSING REMARKS REMARKS 3:10 PM PM COFFEE BREAK 3:30 PM Gene LaBerge Discussion of for the Flambeau Flambeau Mine Mine Field Field Trip of Logistical Details for Minerals of of the Flambeau (no abstract) abstract) Flambeau Mine Mine (no 4:00 PM PM SESSION ENDS xxiv XXIV �SATURDAY, MAY 18 7:00 AM AM - 6:00 PM PM FIELDTRIP3 FIELD TRIP 3 3. TOUR TOUROp OFFLAMBEALI FLAMBEAUCOPPER-GOLD COPPER-GOLD MINE Leaders: Gene GeneL. L. LaBerge LaBerge (University of Wisconsin-oshkosh) Wisconsin-Oshkosh) and Staff Geologists, Flambeau Mine SUNDAY, MAY 19 8:00 AM AM - 5:00 PM FIELD TRIPS TRIPS 4 AND 5 PM FIELD 4. EARLY EARLYTO TOMIDDLE MIDDLEPROTEROZOIC PROTEROZOICGEOLOGY GEOLOGY OF OF THE THE LAKE LAKE NAMEKAGON REGION Leaders: William William F. F. Cannon, Laurel G. Woodruff, and Suzanne W. Nicholson Nicholson (U. (D. S. Geological Survey) LAKENAMEKAGON NAMEKAGONAND ANDPENOKEE PENOKEE GAP GAP AREAS, AREAS, 5. LAKE WEST GOGEBIC RANGE, RANGE, WISCONSiN WISCONSIN Leaders: John John S. S. Kiasner Klasner (Western Illinois University) and LaBerge (University (University of Wisconsin-oshkosh) Wisconsin-Oshkosh) Gene L. L. LaBerge POSTER SESSION SUZANNE NICHOLSON SESSION CHAIR: PM WEDNESDAY, WEDNESDAY, MAY MAY 15, 15, TO TO NOON NOON FRIDAY, FRIDAY, MAY 17 17 7:30 PM Cannon, W. W. F., F., and andKress, Kress, T. T. H. H. Cannon, New Minnesota, Wisconsin, Nw Digital Digital Geologic Geologic Map of ofMinnesota, Wisconsin, and Upper Michigan (no abstract) (no Cannon, W. F., F., Nicholson, Nicholson,S. S. W., W., Woodruff, Woodruff, L. L. G., Hedgman, C. A., A., and and Schulz, Schulz,K. K. J. J. Cannon, W. Hedgman, C. Geologic Map Map of the the Ontonagon Ontonagon and part of the Wakefield Wakefield30' 30' xx 60' 60' Quadrangles, Michigan Geologic (no (no abstract) Gere, M. M. A., A., Jr. Michigan Mineral Mineral Lease Lease Exploration Exploration Data Inventory Johnson, Johnson, A. A. M., M., and andGere, Gere,M. M. A., A., Jr. Jr. IdentifyingGeologic Geologic and and Other OtherPotential Potential Resources Resources from Abandoned Underground Identfying from Michigan's Michigan's Abandoned Mine inventory Inventory Kalliokoski, J.J. Kalliokoski, Bay, Michigan ", Keweenaw An Ancient AncientLandslide Landslideatat"Red "RedRocks Rocks", Kweenaw Bay, ./' Kucks, R P., P., and andHorton, Horton,R. R J.J. Aeromagnetic Aeromagnetic Map Map of ofLake Lake Superior xxv �Morey, G. G. B., B., and and Cleland, Cleland,J.J. M. M. Morey, Preliminary Sedimentologic and Petrologic Analysis of the Early Proterozoic Mahnomen Preliminary Sedim.entologic (North Range Range Group) Group) East-Central East-Central Minnesota Minnesota Formation (North *Naiman, Z., *Naiman, Z., Wirth, Wirth,K. K. R., R, Morey, Morey,G. G. B., B., and and Miller, Miller, J.J. D. D. Metamorphism Chengwatana Volcanic from Osseo Metamorphism of ofChengwatana Volcanic Group Group near near Taylors Taylors Falls Falls and and-from Osseo Core *Neilson, K. Stendahl, R, Kropf, E., and J. P. Stendahi, R., and Craddock, Craddock, J. A Continuum ContinuumofofStress-Strain Stress-StrainFields Fields(2.0-1.0 (2.0-1.0 Ga) Ga) along along the the Northern Northern Margin Marginofofthe theKeweenaw Keweenaw Province, Ontario, Canada Province, R P., Morris, T. F., Crabtree, D., Murray, C. C. A., Bennett, G., Hailstone, M., Sage, R. Hailstone, M., Nicholson, T., T., Painosi, Painosi,S., S., and andJosey, Josey, S. S. Nicholson, Exploration in in Wawa Ultramafic Dike Dike with Mantle Xenoliths: Xenoliths: Implications Implications to Diamond Exploration Wawa Spector, A., and and Lawler, Lawler, T. T. L. Northeastern Minnesota Minnesota Duluth DuluthComplex Complex Mineral Potential Swenor, Swenor, W. W. T. T. Update on on the the Geological Geological Core Core and and Sample Sample Repository Repository Wattrus, Wattrus, N. N. J., J., Anderson, Anderson,K., K., Sharkey, Sharkey,J., J., and and Holcombe, Holcombe, T. T. Bathymetric Map Map of ofLake Lake Superior A New Bathymetric Wirth, Wirth, K. K. R., R., Naiman, Naiman,Z., Z.,Vervoort, Vervoort,J.J. D., D.,Miller, Miller, J.J. D., D., and and Morey, Morey,G. G. B. B. Chengwatana Volcanic Geochemistry of ofChengwatana Volcanic Group near.Taylors near Taylors Falls Falls and and from from Osseo Osseo Core Core xxvi �ABSTRACTS �PETROLOGY, STRATIGRAPHY, PETROLOGY. STRATIGRAPHY, AND AND SEDIMENTATION SEDIMENTATiON OF OF THE MIDDLE PROTEROZOIC BAYFIELD GROUP GROUP OF OF NORTHWESTERN NORTHWESTERN WISCONSIN. WISCONSIN. PROTEROZOIC BAYFIELD Minnesota, Duluth, ADAMSON, Kent Kent F., F., Department of Geology, University of Minnesota, 10 University Drive, Drive, Duluth, Duluth, MN MN 55812, 55812,kadamson@d.umn.edu kadamson@d.umn.edu Petrographic and Petrographic and field field evidence evidence suggest suggest that that the the Bayfield Bayfield Group Group units, units, the the lithofeldspathic Orienta Formation Formation and and the the lithofeldspathic Iithofeldspathic Chequamegon Chequamegon Formation, Formation, Iithofeldspathic Orienta are the same unit Formation. Previous unit beneath beneath the quartzose quartzose Devils Island Island Formation. Previous stratigraphic thefollowing following order, order, from from the the bottom bottom up: up: stratigraphic studies studies place place the the three threeunits unitsininthe Orienta, Devils Myers, 1971). 1971). The Devils Island Island and and Chequamegon Chequamegon (Thwaites, (Thwaites, 1912; 1912; Myers, The contact contact between the Devils Devils Island Island Formation Formation and and Chequamegon Chequamegon Formation Formation is not not present present on on Devils Island Island as as previous previous studies studies suggest. suggest. This Thisstratigraphy stratigraphywould would better better match match the the correlative units units some some tens tens of ofmiles miles to to the the west west in in east-central east-central Minnesota, Minnesota, the the probable correlative lithofeldspathic Fond du Lac Formation and the overlying quartzose Hinckley lithofeldspathic Fond du Lac Formation and the Sandstone. The Orienta Orienta and and Chequamegon Chequamegon Formations Formations both both appear to have been been formed formed by by fluvial processes processes while while the the Devils Devils Island Island Formation Formation is is more more indicative of a shallow standing body body of of water water (Ojakangas (Ojakangas & & Morey, Morey, 1982; 1982; Morey Morey & Ojakangas, Ojakangas, 1982). Supporting evidence includes includes aa northeasterly northeasterly paleocurrent paleocurrent direction trend for both the Orienta and Chequamegon Formations. The The Devils Devils Island Island Formation Formation has has aa less less prominent northeasterly paleocurrent paleocurrent trend along with many many divergent divergent paleocurrent paleocurrent directions. Preliminary petrographic data data from the Devils Devils Island Island Formation show that nearly 100% of the primary primary framework framework grains are are quartz. quartz. The primary framework grains of the Orienta Formation Formation are are 45 45 to to 65% 65% quartz, quartz, 35 35 to to 50% 50% feldspar, feldspar, and and 00 to to 10% 10% rock rock fragments (volcanic and granitic). The to the the TheChequamegon Chequamegon Formation is very similar to quartz, 30 30 to to 50% 50% feldspar, feldspar, and and 55 Orienta Formation, generally generally consisting consisting of of 45 to 65% quartz, to 10% rock rock fragments. fragments. References Morey, G. Morey, G. B., B., and R. W. Ojakangas, Ojakangas, 1982 1982, Keweenawan Keweenawan sedimentary sedimentary rocks of eastern Minnesota and northwestern Wisconsin, in Wold R. W. J. Hinze, eds., R. J. J. and W. basin: GSA GSA Memoir Memoir 156, 156, p. p. 135-146. 135-146. Geology and tectonics of the Lake Superior basin: Myers, W. D., 1971, The sedimentology and tectonic significance of the Bayfield Myers, 1971, sedimentology significance the Bayfield Group (upper Keweenawan?) Wisconsin and Minnesota: Minnesota: Unpublished Unpublished Ph.D. Ph.D. of Wisconsin, Madison, Madison, Wisconsin, 269 p. University of dissertation, University Ojakangas, R. R. W., W., and and G. G. B. B. Morey, Morey, 1982, 1982, Keweenawan Keweenawan sedimentary sedimentary rocks rocks of of the the Lake Lake R. J. and W. J. Hinze, eds., Geology and summary, ininWold WoldR. J. and W. J. Hinze, eds., Geology and Superior region: aasummary, tectonics of the Lake Lake Superior basin: GSA GSAMemoir Memoir 156, 156, p. p. 157-164. 157-164. T., 1912, 1912, Sandstones Sandstones of the Wisconsin Thwaites, F. 1., Wisconsin coast coast of of Lake Lake Superior: Superior: Wisconsin and Natural Natural History History Bulletin Bulletin 25, 25, 117p. 117p. Geological and 1 1 �REGIONAL HYDROTHERMAL MASSIVE REGIONAL HYDROTHERMAL MASSIVE SULPHIDE SULPHIDE PRODUCING SYSTEM AND PRODUCING SYSTEM AND U/PB U/PB HYDROTHERMAL TITANITE TITANITE AGE AGE CONSTRAINTS, CONSTRAINTS, ONAPING HYDROTHERMAL ONAPING FORMATION, FORMATION, SUDBURY SUDBURY STRUCTURE, ONTARIO. D.E.*, Ames , D.E. Jonasson, I.R., I.R., Parrish, Ames, *, Jonasson, Parrish, R.R. R.R. Geological Geological Survey Survey of of Canada, Canada, 601 Booth Street, Ottawa, Ontario, K1A 0E8; Centre, Department of Earth KIA OE8; Watkinson, Watkinson, D.H. D.H. Ottawa-Carleton Ottawa-Carleton Geoscience Geoscience Centre, Department of Earth Sciences, Sciences, Carleton Carleton University, H.L.. Geology Geology Department, Department, Laurentian Laurentian University, University, Sudbury, Sudbury, University, Ottawa, Ottawa, Ontario, Ontario, K1S KIS 5B6; 5B6; Gibson, H.L, Ontario, P3E 2C6. The objectives objectives of Fonnation, Sudbury Structure of the the present study study in the Onaping Formation, Structure are are to to detennine: determine: 1) the stratigraphic and and structural stratigraphic structural controls controls on on alteration, alteration, 2)2)the thespatial spatialdistribution, distribution,mineralogy, mineralogy,mineral-chemical mineral-chemical characteristics, timing, and and origin originof ofalteration alterationtypes typesand, and,3)3)the therelationship relationshipbetween betweenregional regional scale scalehydrothermal hydrothennal alteration alteration with with intra-Onaping intra-Onaping base base metal metal occurrences occurrences and to to the the overlying overlying Zn-Cu-Pb Zn-Cu-Pb Errington Errington and and Vermilion Vennilion massive sulphide deposits. deposits. Research Research isis based based on on 1:2000 1:2000scale scale mapping mapping carried carried Out out during three field field seasons, of of ten transects up up to to 66 km of the the structural structural transects k:m width width across across the theOnaping Onaping Formation, Fonnation, distributed distributed around around the the circumference circumference of basin. The Paleoproterozoic Onaping Formation Fonnation forms fonns the the base base of of the the Whitewater Whitewater Group, Group, Sudbury Sudbury Structure Structure and and is footwall sequence sequence to the the 8.7 8.7 Mt MtErrington Erringtonand andVermilion VennilionVMS VMSdeposits. deposits. Comprehensive Comprehensive field field evidence evidence is the footwall indicates that that this fall and flow, indicates this 1400m 1400m thick thick fragmental fragmental succession succession isis hydrothermally hydrothermally altered altered pyroclastic-like pyroclastic-like fall flow, debris-flow deposits hydroclastic breccia (Ames and and Gibson, Gibson, 1995). 1995). Syndepositional Syndepositional radial and minor minor debris-flow deposits and and hydroclastic breccia (Ames radial and faults partially control emplacement emplacement of the lower part of the the Onaping Onaping Formation Fonnation and are conduits conduits for for concentric faults metasomatic fluids. fluids. Evidence Evidence for for aa regional regionalsubseafloor subseafloorhydrothermal hydrothennal system system includes includes vertically vertically stacked, stacked, alkali metasomatic "basin-wide" semiconfonnable alteration from base base to to top, silicification, albitization, basin-wide' semiconformable alteration zones zones consisting consisting of, of, from chioritization, and celsian. chloritization, carbonatization carbonatization and feldspathization. feldspathization. The latter latter includes includes microcline, rnicrocline, hyalophane hyalophane and celsian. The syndepositional basal zone zone of of silicification silicification consists consists of of an an earlier phase of K-feldspar by albite albite and and syndepositional basal K-feldspar overprinted overprinted by quartz quartz with with minor minor epidote. epidote. These These events events are are also also mimicked mimicked ininthe theoverlying, overlying, locally locally discordant, discordant, zones zones of of syndepositional albitization. Chlorite syndepositional albitization. Chlorite although although dominant dominant in in the the Contact Contact units units isis present present throughout throughout the the Onaping Onaping Formation and deposits deposits and and the the basal silicification Fonnation as pycnochlorite-ripidolite except near base base -metal occurrences occurrences and silicification zone where more Mg-rich associated with withpyrrhotitepyrrhotiteMg-rich varieties varieties are present. present. A A late late stage stageofofhigh highFe-ripidolite Fe-ripidolite isisassociated chalcopyrite-siderite the base-metal chalcopyrite-siderite inin the base-metal deposits deposits and occurrences. occurrences. Proximal Proximal alteration alteration to to base base metal metal deposits deposits includes, muscovite, hyalophane, carbon, ankerite, ankerite, dolomite dolomite and late siderite. siderite. Regional Regional includes, barian barian muscovite, hyalophane, celsian, celsian, quartz, quartz, carbon, and late carbonatization, consists of of calcite, calcite, and and is pervasive in the carbonatization, consists the upper upper 1I km k:m except except around around base base metal metal showings showings and and local zones of lower temperature temperature siicification. silicification. The Theupper upperzone zoneofoffeldspathizaiion feldspathization contains contains low-temperature local zones low-temperature kfeldspar with minor minor albite albite which which isisoverprinted overprintedby bycelsian, celsian,reflecting reflectinglow-temperature low-temperature seawater-rock seawater-rock reactions in the shallow subseafloor. Amphibole veins with with albitized haloes represent one of the youngest hydrothermal events events in in the the Onaping Onaping Amphibole veins youngest hydrothennal Formation: Fonnation; they they crosscut igneous -textured intrusions intrusions cogenetic cogenetic with with the the fragmental fragmental andesitic andesitic Onaping Onaping Formation. Fonnation. Conventional of hydrothermal Conventional U/Pb U/Pb geochronology geochronology of hydrothennal titanite titanite within within the themetasomatized metasomatized haloes haloes of the amphibole amphibole veins yields yields an an age circa 1850 veins 1850 Ma. Ma. One One of ofthe theworld's world'smost mostextensive extensivehydrothermal hydrothermalcirculation circulationsystems systemsdeveloped developed in the the Onaping Onaping breccias breccias due due to to heat heatloss lossfrom from the the1850 1850Ma MaSudbury SudburyIntrusive IntrusiveComplex Complex and and coeval coeval sublayer sublayerrocks. rocks. was new U/Pb U/Pb titanite titanite age age on onlate-stage late-stagehydrothermal hydrothennal alteration proves the complex complex Sudbury Sudbury event event was This new proves that the complete within within error error of of geochronological geochronological dating. dating. volcanic The mechanisms of brecciation and emplacement of the Onaping Formation are similar to some volcanic deposits deposits however, however, itit is not not aatypical, typical,volcanic volcaniccauldron cauldronsequence sequence ororfallback fallbackbreccia. breccia. The TheOnaping OnapingFormation Fonnation represents a dominantly deposited impact impact melt melt based based on on the the epsilon epsilon Nd Nd crustal crustal signature dominantly subaqueously subaqueously deposited signature between between -lack of of phenocrysts phenocrysts in in explosive explosive ash ash flow-like flow-like deposits suggesting suggesting little crustal residence time, the the 7.6 to -10.3, the lack presence presence of abundant abundant shock shock metamorphic metamorphie features features including including shocked shocked zircons zircons and and cuspare, cuspate, plaley platey and and blocky blocky microvesicular microvesicular shard morphologies. morphologies. Emplacement of the the SIC SIC and and sublayer sublayer provided provided the the heat heatrequired requiredto. to initiate initiate 1.4 km k:m thick fragmental sequence and led to the development of a short-lived hydrothermal hydrothennal fluid circulation in the 1.4 system the overlying replacement deposits depositshosted hosted inin carbonate carbonate sinter sinter mounds. mounds. The The system that produced produced the overlying Zn-Cu-Pb Zn-Cu-Pb replacement 22 �exceptional preservation preservationof of the the fragmental strata and one exceptional fragmental strata one of ofthe theworld's world'smost mostextensive extensivesemi-conformable semi-conformable involved in generating Paleoproterozoic alteration systems, permits detailed investigation of processes processes involved Paleoproterozoic massive suiphide deposits, deposits, the the role in large and the sulphide role of of hydrothermal hydrothermal processes processes in large scale scale meteorite meteorite impact impact structures structures and the emplacement mechanisms for large large impact impact crater-ifil crater-fill deposits. deposits. HL. 1995: Controls geological setting regional hydrothermal hydrothermal alteration within within Ames, D.E. and Gibson, H.L. Controls on and geological setting of of regional Errington and and Vermilion Vermilion base base metal metal deposits, deposits, Sudbury Sudbury Structure, Ontario; footwall to the Errington the Onaping Formation, footwall in Current Research 1995-E; 1995-E; Geological Survey of of Canada, Canada, 161-173. 161-173. 3 �STUDY OF CARBON ISOTOPE RATIOS RATIOS IN CARBONATES OF THE EARLY PROTEROZOIC PROTEROZOIC· SNOWY PASS SUPERGROUP, WY WY AND AND ITS ITS APPLICATION APPLICATIONFOR FORCORRELATION CORRELATIONWITH WITh THE CHOCOLAY GROUP, MI MI AND AND THE THE HURONIAN HURONIAN SUPERGROUP, SUPERGROUP, ON. ON. BEKKER, Andrey, Andrey, Department Department of ofGeology, Geology, University of Minnesota, Duluth, Duluth, MN, MN, Bekkergeo1.uchicago.edu and A., Geological Geological Survey Survey of of Finland, Finland, 55812, Bekker@geol.uchicago.edu andKARHU, KARHU,Juha JuhaA., FIN-02 150 Espoo, Finland, Juha.Karhugsf.fi. FIN-02I50 Juha.Karhu@gsf.fi. Carbon has a relatively to the the mixing mixing time time of of sea sea water, water, thus thus making making marine marine waters waters relatively long long residence time in the oceans relative to nearly homogenous in respect As such, such, carbon carbon isotope isotope ratio ratio changes changes can can be be used used for for respect to to carbon carbon isotope isotope composition. composition. As stratigraphic correlations between basins. In In addition, addition, carbonates are are usually usually considered considered to to between carbonate carbonate units deposited in open basins. retain their diagenetic and and even even in in metamorphic metamorphicalterations. alterations. In this their original original carbon carbon isotope isotope signatures signatures nearly unchanged in diagenetic study, analyses of Schist, and the Nash Fork Formation were of carbon carbon isotope isotope ratios ratios from from the Vagner Vagner Formation, the Lookout Schist, carried carried out. We Wecompare compareour ourresults resultswith withavailable availabledata datafrom from the the Huronian Huronian and and Marquette Marquette Range Range Supergroups, Supergroups, and other other sequences worldwide ofdeposition, deposition, and and to to draw draw aa correlation correlation between between these thesesequences. sequences. worldwide to to put put some some constraints constraints on on the the time time of Our results results also also have haveimplication implicationfor for understanding understanding of ofthe the carbon carbon cycle cycle in Early Proterozoic time. consists of of the the Deep Deep Lake Lake(DLG) (DLG)and andthe the Libby LibbyCreek Creek (LCG) (LCG) Groups. Groups. The The The Snowy Pass Supergroup, Wyoming, Wyoming, consists DLG and the lower lower LCG LCG were were deposited deposited between between 2.45 2.45 and and 2.1 2.1 Ga Ga (Premo (Premo and and Van Van Schmus, Schmus, 1989) 1989) and and are areoverlain overlainby bythe the cycles with tillites at the base and allochthonous upper LCG. The Theupper upperDLG DLG and and the the lower lower LCG LCG exhibit three-large scale cycles sandstones Fm., Vagner Vagner Fm.~Rock Fm.-3Rock Knoll Knoll Fm., Fm., Headquarters Fm.—*Heart Fm.and and Fm.~Cascade Fm., Fm.~Heart Fm. sandstones above above (Campbell (CampbellLake LakeFm.—+Cascade Medicine Peak Quartzite). Limestones glacial retreat; they exhibit fme Limestonesof ofthe theVagner Vagner Formation Formation were were deposited deposited following following glacial of the the lower lower LCG locally locally includes interlayering with with siltstone. The TheLookout Lookout Schist Schist of laminations and interlayering includes thin thin layers of brown brown impure impure TheNash NashFork ForkFormation Formation isisaathick thick(>2 (>2 km) km) sequence sequence of of siliceous siliceous cross-bedded dolomites dolomite. dolomite. The dolomites with flat-pebble conglomerates, pseudomorphs after gypsum, gypsum, and and stromatolite stromatolite bioherms, biohenns, enclosed enclosedby byblack blackphyllites phylliteswith withgraphite graphiteand andpyrite, pynte, indicating a reducing environment. To of deposition deposition were were suggested suggested for for this this unit unit To that thatend, end, intertidal intertidal and andsubtidal subtidal environments environments of the grade grade increases increases to to the the lower lower (Houston and Karlstrom, 1992). 1992). Greenschist Greenschistmetamorphic metamorphic facies facies dominate dominate in all units, units, but the amphibolite facies to the NE, NE. the Vagner Fm. were were analyzed analyzed for forcarbon carbonand andoxygen oxygenisotope isotoperatios. ratios.Each Eachsample sample exhibits exhibits aa Fourteen samples from from the Vagner Fm. negative carbon isotope -2. l96. Data of 6'3C= 8 1l C= -2.1960. Data comparison comparison with with the the correlative correlative Bruce Bruce Member Memberof ofthe the isotope values values with with an an average average of Espanola Formation, (Huronian by Veizer Veizer et a!. a!. (1992) reveals reveals a strong strong resemblance resemblance (Fig. (Fig. 1), 1),which which (Huronian Supergroup) Supergroup) reported reported by -l8.7%o, PDB) we follow the supports their correlation. 8180values values(average (averagefor forthe theVagner Vagner Fm.: Fm.: 8 180 == -18.7960, correlation. Regarding Regarding the the low low 8O of Veizer et a!. a!. (1992) (1992) that that the the lower lower values values may may be be due due to to meteoric meteoric water water flux. flux. suggestion of IJ 6O == -19.05960, -19.05%o, PDB. The8"C Only one one sample sample was was analyzed analyzed from from the the Lookout LookoutSchist; Schist;ititshowed showed8"C 5'C == 2.7960, 2.7%o, 8'"0 PDB. The C is is Only intermediate between 8"Cvalues valuesmeasured measuredfrom fromthe theunderlying underlying Vagner Vagner Formation Formation and the the high high values values of of the the overlying overlying between the the low low '3C Nash Fork Fm. These indicateaasignificant significantpositive positive shift shift in in the the isotopic isotopic composition of the marine carbonates. Thesedata dataseem seemtotoindicate Four samples were the Nash Nash Fork Fork Formation. Formation. All except one one exhibit high positive carbon isotope isotope were analyzed analyzed from from the 8 1J C= 5%o, 5960, highest: ratios (average: (average: S'3C highest:8"C= 3"C= 8.23960). 8.23%o).These Thesecarbon carbonisotope isotoperatios ratiosresemble resemblevalues valuesof ofthe theKona KonaDolomite Dolomite(Fig. (Fig. I), Fennoscandian carbonates, and other carbonates of about about the the same same age age worldwide worldwide(see (seeKarhu, Karhu, 1993). 1993). Based on Sm-Nd and UPb dating of sequences in which this excursion occurs occurs in in Fennoscandia, Fennoscandia, itit isis bracketed bracketed between between 2.21 2.21 and and 2.06 2.06 Ga. Ga. Correlation Correlation Formation with wIth these these better better geochemically geochemicallystudied studiedand anddated datedunits unitson onthe thebasis basisof of of the Kona Dolomite and the Nash Fork Formation carbon isotope ratios suggests a similar time of deposition. should be be noted, however, that one sample from from the Nash Fork deposition. ItIt should "low" carbon carbon isotope isotope ratio in comparison comparison with both the Kona Kona Dolomite Dolomite and the Formation has a "loW' with the the general general trend. trend. In addition, both values than than the the 2.2 2.2 -- 2.1 Ga Fennoscandian carbonates (6"C (O"C= 10 ± 3%o; 3960; Karhu, Nash Fork Formation have somewhat lower values 1993). (1993) correlated correlated the the DLG DLG and the the lower lower LCG LCG with the the Huroman Huronian Supergroup, Supergroup, and and the the upper upperLCG LCG Roscoe and Card (1993) stratigraphic, sedimentological, sedimento logical,and andage agesimilarities. similarities. Our data support with the Marquette Marquette Range Range Supergroup Supergroup on the bases of stratigraphic, ofchemostratigraphy chemostratigraphy as aa tool tool in in the the correlation correlation of ofEarly Early Proterozoic Proterozoic their correlation and and demonstrate demonstrate the the applicability applicabilityof carbonates from different basins. Our data confirm the aforementioned aforementionedcarbon carbonisotope isotopeexcursion. excursion. This This carbon isotope isotope confmn the worldwide character of the matter, leading leading to to increased increased atmospheric atmosphericoxygen oxygenlevel. level. This increase in of burial of of organic organic matter, excursion indicates a high rate of oxygen level level was was suggested between 2.2-1.9 2.2-1.9 Ga Ga based based on on independent independent geological geologicaldata data(Holland (Hollandand andBeukes, Beukes, 1990). 1990). Iron oxygen formations formations were were deposited deposited after after the the deposition depositionof ofthe the"C-enriched 'C-enriched carbonates carbonates in in MI, MI, WY, WY,and andFennoscandia. Fennoscandia. This This indicates excursion, while while dissolved dissolved iron iron was was transported transported and and precipitated precipitated in in the shallow that deep oceans remained anoxic even after the excursion, shelf areas. The Thehigh highpositive positiveexcursion excursioninincarbon carbonisotope isotope ratio ratio might might be be correlated correlated with rifting, formation formation of of anoxic basins and sedimentation rate rate and and many manyother otherfactors. factors. More detailed work is necessary carbonate platforms, high biomass fertility, fertility, high sedimentation before a working model can be developed. developed. 4 �Fig.1. Fig.1. Scatter Scatter diagram diagram of of d180 d180 vs. vs. d13C dl3C for studied Early Proterozoic carbonates. Data for the Kona Dolomite Dolom ite from from Feng Feng (1986) (1986) and and for the Member from from Veizer Veizer et et al. al. (1992). (1992). Bruce Member IIil •Vagnec .VagrerFm. Fm. Nash Fork l1li Nash ForkFm. Fm. Loo1ScFst A LookotJ Sellst Kor Dolomite X Kora DolomiteFm. Fm. Brte Member. • Bru::e Member. . 8.2 x X 7.2 X X I i*'\ :l.~ X x X • X x xX III X X 6.2 ::.xX 5.2 X 4.2 iii o x Q. U ..,(.) 3.2 ... 2.2 'C 1.2 1.2 l1li I -21 •• -20 •• • ••• -19 I I -18 -17 , -. I I •.- -16 .15 -15 I -14 -13 • •• •• •.sS •• I.. ":.# • I • • •• •• • ••• I I -12 -11 .2 I -10 -9 -8 -7 -0.8 -1.8 -28 -2.8 d180 References Precambrian marine marine sulfate and chert: chert: Unpub. Unpub. M.S. thesis, Feng, J., 1986, 1986, Sulfur Sulfurand andoxygen oxygen isotope isotope geochemistry geochemistry of Precambrian Illinois University. University. Northern illinois H. D. D. and andBeukes, Beukes,N. N.J., J.,1990, 1990.AApaleoweatheting paleoweatheringprofile profilefrom fromGriqualand GriqualandWest, West,South SouthAfrica: Africa: evidence evidencefor foraa Holland, H. rise in inatmospheric atmosphericoxygen oxygen between between 2.2 and 1.9 1.9 b.y.b.p.: b.y.b.p.: Am. J. Sci., 290A, p. 1-34. 1-34. dramatic rise R. S. S. and andKarlstrom, Karlstrom,K. K.E., E.,1992, 1992,Geological Geologicalmap mapof ofPrecambrian Precambrian metasedimentaty metasedimentary rocks rocks of ofthe the Medicine MedicineBow Bow Houston, R. Mountains, Albany Albany and andCarbon CarbonCounties, Counties,Wyoming: Wyoming: U. U. S. S. Geological Geological Survey Survey Miscellaneous Miscellaneous Investigations InvestigationsMap MapI-1Mountains, 2280, scale 1:50,000. 1:50,000. Karhu, J. A., 1993, 1993, Paleoproterozoic Paleoproterozoic evolution evolution of of the carbon isotope ratios of sedimentary carbonates in the Fennoscandian Shield: Geological ofFinland Finland Bulletin Bulletin371, 371, 8'7p. 87p. Geological Survey Survey of W. R. R. and and Van VanSchinus, Schnms,W. W.R., R.,1989, 1989,Zircon Zircongeochronology geochronology of Precambrian·rocks in southeastern southeasternWyoming Wyoming and and Premo, W. Precambrianrocks in northern Geology of of the theSouthern SouthernRocky RockyMountains, Mountains,(Eds.) (Eds.)Grambling, Grambling,J.J.A., A., and and northern Colorado: Colorado: In Proterozoic Geology Tewksbury, Geological Society of America Special Paper 235, pp. 13-48. 13-48. Tewksbuxy, M. and and Card, Card,K. K.D., D.,1993, 1993,The Thereappearance reapPearanceofofthe theHuronian HuronianininWyoming: Wyoming: rifting rifting and and drifting drifting of ofancient ancient Roscoe, S. M. continents: Canadian J. Earth EarthSci. Sci. 30, 30, pp. pp. 2475-2480. 2475-2480. Canadian J. Veizer, J., Clayton, Clayton, R. R. N., N., and andHinton, Hinton,R. R. W., W.,1992, 1992,Geochemistiy Geochemistry of ofPrecambrian Precambrian carbonates: carbonates: IV. IV. Early Early Paleoproterozoic Paleoproterozoic vol. 56, 56, pp. pp. 875-885. 875-885. (2.25± 0.25 0.25 Ga) Ga) seawater seawater:Geochimica GeochimicaetetCosmochimica CosmochimicaActa, Acta, vol. (2.25± 5 �SOUTHWARD EXTENSION SOUTHWARD EXTENSION OF OF THE THE PENOKEAN PENOKEAN TERRANE TERRANE THROUGH THROUGH STEARNS STEARNS COUNTY, CENTRAL CENTRAL MINNESOTA MINNESOTA BOERBOOM, Terrence J., I., Minnesota MinnesotaGeological Geological Survey, Survey, St. St. Paul, Paul, Minn., Minn., 55114-1057. 55114-1057. E-mail Boerb00l@maroon.tc.umn.edu BoerbOOI@maroon.tc.umn.edu ofthe thePrecambrian Precambrian bedrock bedrockgeology geology of ofStearns StearnsCounty County Recent remapping remapping by by the the Minnesota MinnesotaGeological Geological Survey1 Surveyl of has identified identified aa previously previously unrecognized unrecognized southwestern southwestern extension extension of of the the Penokean Orogen (Fig. 1). 1). Prior Priorto tothis this study, most of of Stearns Stearns County County was was considered.to considered.to be be underlain underlain by by Archean Archean high-grade granitoid gneisses, with the exception of county. Although of some some Penokean Penokean intrusions intrusions in in the the southeastern southeastern part of the county. Although the the northwestern northwestern part part of of the county isis still still interpreted interpreted to to be beArchean Archean gneiss, gneiss, itit is is now now recognized recognized that that Early Proterozoic Proterozoic rocks, which Formation, as as well well as as many many intrusions intrusions of of include supracrustal rocks of the Mule Mille Lacs Group and Little Falls Formation, varied size and and composition, composition, are are predominant. predominant In Inaddition, addition, thrust thrust and and strikestrike- or dip-slip faults are an important aspect of glacial drift drift and and patches patchesof of of the geology in this region. Because Becausemost most of of Stearns Stearns County County is covered by glacial Cretaceous rocks, structural and and lithologic lithologic rocks, drill-hole drill-hole and and geophysical geophysical data data were utilized utilized extensively to infer the structural attributes of of the the bedrock. bedrock. The revised revised geology geology can can be be subdivided subdivided into into the the following following six six broad lithologic units, listed from oldest to youngest: (1) (I)Archean Archeangranitoid granitoidgneisses; gneisses; (2) (2)the theArchean Archeanor orEarly EarlyProterozoic, Proterozoic, grarnilite-grade granulite-grade Sartell Gneiss (broadly grouped with with the Hiiman HillmanMigmatite Migmatiteoutside outside of ofStearns Stearns County); County); (3) (3) the theEarly Early Proterozoic Proterozoic Mille Mille Lacs Lacs Group; (4) Formation; (5) (4) the the Early Early Proterozoic Proterozoic Little Little Falls Formation; (5) Animikie strata of the Long Prairie and (6) (6) Group; Prairie basin; basin; and Early Proterozoic Proterozoic intrusions intrusions that thatintrude intrude most most of ofthe the above. above. Archean granitoid granitoid gneiss gneiss at at the the northwest northwest corner corner of of the the county is is foliated and variably lineated along a epidote. The minerals northeast trend and locally pervasively altered to epidote. The Sartell Sartell Gneiss Gneiss contains the metamorphic minerals orthopyroxene, garnet, gamet, sillimanite, sillimanite, and and local local hercynite hercynite and and corundum, corundum, and and includes includes some some granitoid gneiss. between older Archean Archean The Mule Mille Lacs Lacs Group Group underlies underlies the the southwest southwest corner corner of of the county in a block wedged between basement rocks. rocks. This Thisgroup groupofofrocks rocksisisconjectured conjecturedto toconsist consistof ofmetamorphosed metamorphosed volcanic volcanic and and sedimentary rocks of iron-formation. Thrust Thrustfaults faults are are indicated indicated by by geophysical geophysical data to occur both within and marginal and thin beds of marginal to the Mille Lacs Group. to Group. The Little Falls Falls Formation Formation contains contains aa sillimanite-garnet-staurolite sillimanite-gamet-staurolite assemblage that typifies this unit to the north. The north. Thewestern westernedge edgeof ofthe theLittle LittleFalls FallsFormation Formationhas hasbeen beenthrust thrustover over the the Mille Mille Lacs Lacs Group. Group. The Long Prairie Prairie basin basin forms forms an an outlier outlier of of Animikie Animikie strata strata that that correlates correlates with, but but is is physically physically separated from, the Virginia Formation from, Formation to to the the northwest. northwest. The Thestrata strataare areonly onlyweakly weakly deformed deformed relative relative to to other other Early Early Proterozoic is strongest strongest along along its its southeastern southeastern edge, where it is has been Proterozoic supracrustal supracrustal rocks, rocks, but but deformation deformation is overthrust by older older rocks rocks of of the the Penokean Penokean Orogen. Orogen. The intrusive intrusive rocks rocks range range widely widely in in size size and and composition composition from from small small ultramafic ultramafic plugs, plugs, irregularly irregularly shaped shaped mafic charnockitic chamockitic bodies, bodies, large large plutons plutons of ofgabbroic gabbroic to to granitoid granitoid rocks, rocks, to to thin thin cross-cutting cross-cutting dikes dikes of of diabase diabase and and orall allof ofthese these intrusions intrusions are are inferred inferred to to be be latelate- to post-kinematic with porphyritic granite. Most Mostor with regard regard to to the the the southeast southeast part part of of Penokean orogeny. They Theyoccur occurnot notonly only as as discrete discrete bodies bodies in in the the supracrustal supracrustal rocks but, in the the county, as as aa continuous continuous plutonic plutonic terrane terrane of ofdominantly dominantly granitoid granitoid bodies bodies that include the Richmond Granite, Reformatory granodiorite. granodiorite. Earlier workers workers established established Early Early Rockville Granite, St. Cloud (Red) Granite, and the Reformatory Proterozoic ages for these granitoid rocks and diabase dikes, dikes, but but modern modern geochronologic geochronologic data dataare arelacking. lacking. These These plutonic rocks at a scale of 1:2400 rocks are are so so well well exposed exposed in in this this part part of of the the county county that that local local remapping on airphotos airphotos at was possible. been recognized recognized from fromgeophysical geophysicaldata. data. The The wedge wedgeof ofMille Mile Lacs Several gross structural attributes have been is bounded bounded on on its its northwest northwest side side by by aa steep steep northwest northwest dipping dipping fault fault interpreted interpreted to to be be an Archean Archean Group strata is orogeny. On bounded by by aa brittle brittle tear tear structure reactivated during the Penokean orogeny. On its its southwest southwest side the wedge is bounded fault that has juxtaposed the the Penokean Penokean strata against older Archean rocks over some 50 km length and produced a terminate against against this this major offset of the Penokean margin. Although Although supracrustal supracrustal rocks rocks of of the Penokean Orogen terminate fault, evidence suggests that the across but but may may be be affected affected by by it. it. The fault, the Penokean Penokean Rockville Granite extends across The fault north-striking, southeasthas has also acted as a locus of emplacement for other smaller Penokean Penokean plutons. plutons. Other north-striking, southeastdipping thrust faults have have imbricated imbricated the the Mille Mille Lacs Group strata; they they also also occur occurbeneath beneath the the overriding overriding Little Little Falls Formation. These Thesesoutheast-dipping southeast-dippingthrust thrustfaults faultsare areconsistent consistentwith with previously previouslymapped mapped faults faults in in Penokean Penokean Archean ofthe the thrusts thrusts within within the the Penokean Orogen near the Archean strata to the north. The Theeast-curving east-curvingmorphology morphology of block to the northwest northwest imply imply that thatthe the latter lattermay may have have acted acted as as an an buttress buttress that that deflected deflected deformation. deformation. County are are the the recognition recognition The most important important findings fmdings of of the the newly newly interpreted interpreted bedrock geology of Stearns County terrane extend extend considerably considerably farther farther that the Mille Lacs Group Group and Little Little Falls Formation within the Penokean Penokean terrane south than previously recognized, recognized, that that aa tear tear faulthas fault hassubstantially substantiallyoffset offset the the Penokean Penokean margin margin and and juxtaposed juxtaposed the the Penokean terrane terrane against against older older Archean Archean rocks, rocks, and and that that thrust thrust faults faults have have played played a significant significant role in the structural evolution of recognized of this area. The Thesize, size,distribution, distribution, and and abundance abundance of ofPenokean Penokean intrusive intrusive rocks are also better recognized and understood. 'This 1This interpretation interpretation was was completed completedasaspart partofofthe theStearns Steamscounty countygeologic geologicatlas atlas(Minnesota (MinnesotaGeological Geological Survey, Survey, County County Atlas Series Atlas Atlas C-b, C-10,Part PartA), A),which whichincludes includesdata database, base,bedrock bedrockgeology, geology,surficial surficialgeology, geology,Quaternary Quaternarystratigraphy, stratigraphy, depth to bedrock, bedrock, bedrock bedrock topography, topography, and and mineral mineral resources resources plates. plates. depth �.. ._ ..95O .. ... .' ... ... .-. -, .,.--.. -.. -.. "",J,~""'~"'" ... ..' .— .. —. ... — ... ... —, —. —, —. -.. -.. - .— — "~~"""""",, 4 -.. -.' -. - - -. -.' -' - " A- " -" -'"-'" -' -"-' . -' -"--fl - #-c•-" -. -, -.fl — -.. - ... .-. — — -k-• — -' . — -.' ..' -'fi — -'fi — -. ..' -.fl -. .— -. -. -'fi -fi -. .0.0.0 .0..' fl .0 -. -. -. .— —. .0.0 .0.0 .0 .0 .0 .0 .0.0.0.0.0. .0 .0 .0.0.0.0' .0.0 .0 .0.0 .0 0.0.0.0.0.0• .0.0.0.0.0 _0 -' .0.0'.0 .0.0.0.0.0..0 .0 .0 .0.0.. .0 — .0 .0.0.0.0' .0 .0 .0 .0 .0.0 .0 .0..' .0 .0 .0.0 .0 .0 .0.0.0 .0 .0 .0 .0 .0 f fi , A / Location of Stearns County Partial funding funding for the Steams Steams Partial for the ' '-// ij7 /// ',,, ,';' -1 ii S's..' '1'.(" //(1''-l'••' " ,5,s -l—I-l-l-I—I County At/as Atlas was was approved approved by by the the Minnesota Legislature Legislature (M.L. (M.L. 91, Minnesota 91. Ch. Ch. 254, 254, Art. Art. 1, I, Sec. Sec. 14, 14, Subd. Subd. 4[F], 93, Ch. Ch. 172, 172. Sec. Sec. 4[FJ, and and M.L. M.L. 93, 14, II[gJ) as recommended 14, Subd. Subd. 1119]) by the Legislative Legislative Commission Commission on Minnesota Resources Resources from from the Minnesota the Minnesota Environment and Natural Resources Trust Trust Fund. Fund. 5/., - I - I1.<i:k5., .,, ,,. ., , : III'LJ III,. _ 5 5 miles miles EXPLANATION EARLY PROTEROZOIC ROCKS to ultramafic plutons; includes ~ Mafic to peridotite, gabbronorite. gabbrononte, & gabbro. peridotite. Falls Formation 1-) Little (staurolite schist). Gabbro, norite, nonte, chamockite;includes [.. :. . . :. .j Gabbro, Mule Lacs Lacs Group. Group, undivided. ~ Mille '. '. charnockitic affinities. affinities. granites with charnockitic c:=J Granitoid plutons, undivided Granitoid plutons. undivided -, . Richmond Granite ~ Rockville Granite Rockville D Reformatory Granodiorite Granodiorite çcq Long Prairie ~ Long Prairiebasin basin(Animikie (Animikie LJ Basin, argillite and graywacke). ~ Basin. argillite and graywacke). Strike-slip or dip-slip fault. ~ Miscellaneous metamorphosed ~ volcanic and sedimentary rocks. rocks. t+:+:+j St. Cloud (Red) (Red) Granite Granite ~~j~j Little Falls F0f!"ation (staurolite schist). Thrust fault. ARCHEAN ROCKS ~ Sartell Gneiss Gneiss and and Hillrnan Hillman ~ Migmatite (may be Early Proterozoic). f ......1 Granite-greenstone terrane. terrane. o Lithologic contact. contact. High-grade gneiss terrane. Figure 1. Simplified Figure Simplified pre-Cretaceous pre-Cretaceous geologic geologic map map of of central Minnesota. Stearns Minnesota. Stearns County is is outlined. outlined. 7 �AN ELECTRONIC COMPONENT OF THE INSTITUTE ON LAKE SUPERIOR AN COMPONENT OF INSTITUTE ON GEOLOGY BORNHORST, Theodore Theodore J., and DOLAN, Michael, T. Department Department of of Geological Geological Engineering and Sciences, Sciences, Michigan Michigan Technological Technological University, University, Houghton, tjbornho@mtu.edu, mtdolan@mtu.edu. Houghton, MI 49931; tjbornho@mtu.edu, is becoming an increasingly increasingly important important part part of daily The information superhighway superhighway is becoming.an Electronic communication communication can, can h~lp help the the Institute on Lake Superior Superior professional activities. Electronic Geology better serve itit constituents, Geology constituents, perhaps perhaps attract attract new professionals professionals to participate in the organization, make the the JILSG n...SG better Lakes region. region. organization, and make better known known beyond beyond the the bounds bounds of the Great Lakes The Board of Directors of the Institute on Lake Superior Geology has authorized the creation Institute Geology has authorized the creation of an ILSG home page. page. 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The considerable The URL URL will will be be considerable information information by by early early September, September, 1996. 1996. The http://www.geo.mtu.edu/great_lakeslilsgl http://www .geo.mtu.edu/greaClakes/ilsg/ in many many areas areas of of professional professional interest. interest. Participants in these lists lists Discussion exist in Discussion groups now exist comments toto other other members membersofofthe thelist. list. Members the list make comments Members of the can ask questions questions of or make will receive email email through throughthe thelist listserver. server. A Lake Superior Geology list will be will automatically automatically receive Geology list maintained by the the senior author author through through Michigan MichiganTech. Tech. The Board of Directors of the maintained by Institute on Lake Superior Superior Geology Geology encouraged creation creation of this list. For more information on the Lake Superior Geology Geology discussion list, email the list list server server at at Michigan Michigan Tech: Tech: For information on the the list: list: Send Send mail mail to: to: majordomo@mtu.edu Subject: Subject: (enter no subject) Body of message: message: info Isg-l lsg-l To subscribe: subscribe: Send mail mail to: Send to: majordomo@mtu.edu Subject: (enter no subject) Subject: Body of message: message: subscribe subscribelsg-1 lsg-l 8 �THE WEST-CENTRAL OF JUNE JUNE 5, 1993: WEST-CENTRAL MINNESOTA MINNESOTA EARTHQUAKE EARTHQUAKE OF 1993: AN AN OPPORTUNITY OPPORTUNITY TO RE-EXAMINE RE-EXAMINE SEISMICITY NEAR NEAR THE MORRIS MORRIS FAULT CHANDLER, VAL VAL W., W.,Minnesota Minnesota Geological Geological Survey, Survey, 2642 University University Ave., Ave., St. St. Paul, Minn., 55114-1057 1) provides provides an an opportunity opportunity 1993, west-central west-central Minnesota Minnesota earthquake earthquake (mbLg=4. (mbLg=4.1) The June 5, 1993, Minnesota seismicity seismicity and and its its possible possible relationship relationship to to reactivated basement basement to re-investigate Minnesota structures. The The earthquake earthquakeoccurred occurred within within 25 25 kilometers kilometers of of the the much larger July 7, 1975, 1975, which has has been been attributed attributed to to the the Morris west-central Minnesota earthquake (mbLg=4.6), (mbLg=4.6), which fault, a northeast-striking crustal fault, crustal discontinuity discontinuity separating separating two two distinct distinct Archean Archean terranes. terranes. Intensity data data from Intensity from the the 1993 1993 earthquake earthquake confirm confirm the the position position of the the instrumentally instrumentally determined epicenter epicenter and and reveal reveal a felt area of of about about 69,500 69,500 square square kilometers, kilometers, with a determined of V. V. Some Somelocal localperturbations perturbations in in the the isoseisms isoseisms correlate correlate with with features features maximum intensity of in the Precambrian bedrock, bedrock, implying implying that that seismic seismic energy may be focused significantly by crustal structure. Focal Focal depth depthestimates estimates based based on on intensity intensity data data imply imply that that the 1993 1993 focal depth is similar to that that of of the the 1975 1975 earthquake, earthquake, which which has has been been independently estimated estimated to to be 7.5 kilometers. The Morris fault has been generally thought to be the major seismogenic feature in the region, but neither the 1993 1993 hypocenter inferred by by this this study study nor nor the the 1975 1975 hypocenter hypocenter agree the fault fault as as revealed revealed by seismic-reflection seismic-reflection data agree with the subsurface trace of the data and and magnetic modeling. Alternative Alternativesources sourcesfor forthe the1975 1975and and1993 1993earthquakes earthquakesinclude includewest— westare interpreted to consist consist chiefly chiefly of of mafic mafic northwest-striking sub-vertical structures that are Someof ofthese thesefractures fractures are are associated associated with with minor minor faulting—as faulting-as dikes and related fractures. Some small offsets offsets in in the the Morris Morris fault—and fault-and possible possible disruption disruption of Cretaceous Cretaceous evidenced by small strata. Neither the Morris Morris fault fault nor nor the the west-northwest west-northwest structures structures agree with with aa loosely loosely constrained focal mechanism for the 1975 1975 earthquake, but the west-northwest west-northwest structures structures are are to be be reactivated reactivated by by the the east-northeast east-northeast regional regional compression compression that that has has favorably oriented to been averaged for for the the eastern eastern United United States. States. This indicates that that minor minor basement basement structures, structures, such such as mafic mafic dikes dikes and and This study indicates associated fractures, may a largely may play playa largely unappreciated unappreciatod role role in in seismicity seismicity of of mid-continental mid-continental regions. Such regions. Suchstructures structuresmay maynot notbe beevident evidentin inmany many existing existing geological geological and and geophysical geophysical data sets. This study study was Minnesota through through the the State Special Special This was supported by the the University University of Minnesota ofthe the Minnesota Legislature. Appropriation Appropriation of 9 �Petrographic and Petrographic and thermobarometric thermobarometricanalysis analysisof ofthe the metamorphosed metamorphosed Little Little Falls Falls Formation, central Minnesota, Minnesota, with with implications for Early Proterozoic Proterozoic tectonism tectonism DARRAH, KS., K.S., HOLM, HOLM, D.K., D.K., DAHL, DAHL, P.S., P.S., Dept. Dept of of Geology, Kent State University, Kent OH 44242; and LUX, D.R., Dept. of of Geological Sciences, University of of Maine, Orono, ME 04469. Recent advances in in thermobarometry thermobarometry have have significantly significantly increased increased our our Understanding Understanding of regional metamorphism metamorphism in in ancient ancient orogenic orogenic belts, belts, allowing allowing important important constraints constraints to to be be made made on on their tectono-thermal evolution. However, their tectono-thermal evolution. However, there have been been few few quantitative quantitative studies studies of the the pressure and temperature of rocks rocks metamorphosed metamorphosed during the Early Proterozoic (1870 temperature evolution evolution of -1820 Ma) Penokean Penokean orogeny orogeny in Minnesota. Minnesota. One One previous previous study study in in east-central east-central Minnesota Minnesota suggests that that Early Early Proterozoic Proterozoic sedimentary sedimentary rocks rocks metamorphosed metamorphosed during during the the Penokean Penokean orogeny orogeny reached temperatures of 450-600°C and minimum pressures of 5-6 kbar (Hoim and Selverstone, Selverstone, temperatures of 450-600°C and minimum pressures of 5-6 kbar (Holm and 1990). Formation (LFF), (LFF), located located within within the the internal internal zone zone of of The Early Proterozoic Little Falls Formation orogenic belt, belt, isis aa biotite-quartz-plagioclase-muscovite biotite-quartz-plagioclase-muscovite schist schist whose whose protolith protolith was was the Penokean orogenic graywacke sequence sequence with with carbonate carbonate concretions. Metamorphic Metamorphic'grade gradeincreases increasesfrom from a shale and graywacke garnet grade in the north to staurolite grade in the south. south. One One drill drill core core sample sample and and one outcrop outcrop sample both from from within within the the staurolite staurolite zone zone contain contain synkinematic synkinematic garnets and post-kinematic post-kinematic Thegarnets garnetsare areabout about1-2 1-2mm mm in in diameter diameterand and are are characterized characterized by by quartz-inclusionquartz-inclusionstaurolite. The rich cores and of crystal crystal and inclusion-free inclusion-free rims, rims, indicating indicating that that there there may may have have been been two two episodes episodes of Thesegarnets garnetsoccur occurboth both within within the the matrix matrix and and as as inclusions inclusions within the staurolite. staurolite. The The growth. These the main main fabric fabric of of the the unit. unit. Petrographic staurolite occurs as 1-2 1-2 cm em porphyroblasts that cross cut the the foliation foliation preserved preserved within within the the staurolite staurolite (as (as quartz quartz and and garnet garnet inclusions) inclusions) is is work shows that the Overall, the the petrographic petrographic features of the LFF are similar to parallel to the foliation in the matrix. matrix. Overall, to that described for Early Early Proterozoic Proterozoic metasedimentary metasedimentary rocks located over 150 150 km to the the northeast northeast (Hoim and Selverstone, 1990). (Holm Detailed microprobe microprobe analyses analyseswere wereperformed performedon onboth bothsamples samplesofofthe theLFF. LFF. Garnet Garnet Detailed interiors exhibit uniform with an overall almandine. interiors uniform compositional compositional patterns patterns with overall composition composition of almandine. and spessartine spessartine Closer to the rims, the the almandine almandine and pyrope content increases and the grossular and prograde garnet garnet growth. growth. These content decreases, decreases, a trend that suggests prograde These compositional compositional changes changes appear to correspond correspond with the the transition transition from from inclusion-rich inclusion-rich core an inclusion-free inclusion-free rim. appear core to an However, the textural change within the garnets is abrupt whereas the compositional change is gradational. The LFF contains contains appropriate appropriate mineral mineral assemblages assemblages on on which which geothermobarometry geothermobarometry can can be be performed. Weapplied appliedthe thegarnet-biotite garnet-biotite thermometer thermometer (Ferry (Ferry and and Spear, Spear, 1978; 1978; Hodges Hodges and and performed. We Spear, 1982) 1982) and and the the garnet-plagioclase-biotite-muscovite garnet-plagioclase-biotite-muscovite barometer (Ghent and Stout Stout 1981; 1981; Hodges and and Crowley, to the LFF Hodges Crowley, 1985) 1985) to LFF samples samples in order order to to determine determine the the pressure pressure and and temperature conditions during during garnet garnet growth. growth. Core of 450-500°C 450-500°C temperature conditions Core analyses analyses gave gave temperatures temperatures of Sinceonly onlyquartz quartzoccurs occurs as asinclusions inclusions within within the the garnets garnets we we used used and pressures of 5-6 kbar. Since in order to estimate the pressures of matrix plagioclase, biotite, and muscovite muscovite compositions compositions in pressures of garnet core growth. Rim Rimanalyses analysesyield yieldhigher highertemperatures temperaturesofofapproximately approximately500-550°C 500-5500C and and The isobaric similar pressures of 5-6 5-6 kbar. kbar. The isobaric garnet growth we infer infer presumes presumes that that matrix matrix similar pressures plagioclase did not change in composition during garnet garnet growth. growth. These composition during These results results concur concur with with plagioclase did previous work done of the the orogenic orogenic belt belt (Hohn (Holm and and Selverstone, Selverstone, 1990). 1990). done in in other other areas areas of We interpret interpret the the inclusion-rich inclusion-rich core of of the the garnets garnets to to represent represent syntectonic syntectonic mineral mineral growth oflate late garnet garnet rim rim and andstaurolite staurolite growth during during the Penokean Penokean orogeny. orogeny. However However the the timing timing of growth is uncertain. ItItisispossible just after after the the possiblethat thatboth boththe thegarnet garnetrims rimsand and the thestaurolite staurolite grew grew just formation of the foliation within the rock. rock. In Inthis thisscenario, scenario, the the 'peak' 'peak' metamorphic metamorphic conditions conditions formation would associated with with conductive conductive relaxation relaxation after after crustal crustal thickening thickening during during the the orogeny orogeny would be associated Alternatively the the garnet garnet rim rim and late staurolite (Holm 1988). Alternatively staurolite growth growth could could have have (Holm and and others, 1988). 10 �occurred much later, perhaps perhaps as as aathermal thermalresponse responsetotothe the—1770-1760 -1770-1760 Ma Ma post-tectonic post-tectonic occurred much magmatism in in the region. then the the 'peak' 'peak' metamorphism metamorphism would yield yield pressure pressure and and magmatism region. If so, then temperature conditions well after the Penokean Penokean orogeny. orogeny. In In this this second scenario, the the discordance discordance between 'peak' metamorphic pressures pressures (5-6 (5-6 kb) and the emplacement pressures determined determined for the post-tectonic plutons (3.0-4.5 kbar, Holm, 1995) 1995) would the post-tectonic piutons (3.0-4.5 kbar, Darrah' Darrah and and Hoim, would require rapid uplift concomitant with plutonism. 9Ar hornblende 40Arf3 two 40Arf39Ar hornblendecooling coolingdates datesmay mayallow allowusustoto distinguish distinguish between between the two scenarios presented above. above. Country Countryrock rockhornblende hornblendedates datesolder olderthan than—1770 -1770 Ma would indicate temperatures Three temperatures below below 500°C 500°C prior to to pluton pluton intrusion, intrusion, thus thus ruling ruling out out the the second second scenario. scenario. Three from widely scattered scattered samples samples of of both both Archean Archean rocks rocks and and metamorphosed metamorphosed hornblende separates from Early to the east of the LFF all yield yield dates dates approximately coeval or slightly Early Proterozoic Proterozoic rocks rocks to concordant with with the the uniform uniform 1750-1760 younger than the age of the plutons, and approximately concordant 1750-1760 Ma 40Ar(39Ar Thus, although although somewhat somewhat preliminary preliminary 40Ar/39Arbiotite biotitedates datesof ofHolm Hoimand andLux Lux (1996). (1996). Thus, (more (more hornblende hornbiende dates dates are currently currently being being processed), processed), the the data data at at present present may may suggest suggest a major major period of rapid rapid unroofing unroofmg of of this this portion portion of of the the Penokean Penokean orogenic orogenic belt during aa pulse pulse of ofpostpostThe new new results results presented presented here are consistent consistent with occurrence of tectonic tectonic plutonism. plutonism. The with the the occurrence of a of orogenic collapse of the Penokean orogeny proposed episode of orogeny (Holm (Hoim and and Lux, Lux, 1996; Schneider 1996). and others, 1996). References Darrah, K.S., and Holm, D.K., O.K., 1995, 1995, Application of the Aluminum-in-hornblende barometer on Early Proterozoic, post-Penokean post-Penokean plutons, Lake Superior Superior plutons, central central Minnesota: Minnesota: Institute on Lake Geology Abstracts, v. 41, p. 7-8. Ferry J.M., J.M., and Spear, F.S., 1978, calibration of of the the partitioning partitioning of Fe and Mg Ferry 1978, Experimental Experimental calibration between biotite Contributions to Mineralogy Mineralogy and Petrology, Petrology, v. 66, p. 113113between biotite and and garnet: garnet: Contributions 117. Ghent, E.D., E.D., and Stout, M.Z., 1981, of plagioclase-biotiteGhent, 1981, Geobarometry Geobarometry and and geothermoetry of assemblages: Contributions garnet-muscovite assemblages: Contributions to Mineralogy and Petrology, v. 76, p. 9297. Hodges, 1985, Error estimations estimations and empirical geothermobarometry geothennobarometry Hodges, K.V., and Crowley, P.D., 1985, for pelitic systems: American American Mineralogist, Mineralogist, v. 70, p. 702-709. Hodges, K.V., and Spear, F. F. 1982, 1982, Geothermometry, Geothermometry, geobarometry geobarometry and and the the A12SiO5 Al2SiOs triple point at Mt Mt. Moosilauke, New Hammpshire, American Mineralogist, Mineralogist, V. V. 67, 67, p. p. 1118-1134. Holm, DX., D.K., Hoist, Holst, TB., T.B.,and andEffis, Ellis,M.A., M.A,1988, 1988,Oblique Oblique subduction, subduction, footwall footwall deformation, deformation, and Hoim, imbrication: A model for the Penokean orogeny in east-central east-central Minnesota: Geological imbrication: Minnesota: Geological v. 100, p. 1811-1818. Society of America Bulletin, v. Holm, D.K., and Selverstone, J., 1990, 1990, Rapid groth and strain rates inferred inferred from from synkinematic synkinematic Hoim, Geology, v. 18, 18, p. 166-169. garnets, Penokean orogeny, Minnesota: Minnesota: Geology, Hoim, Holm, D.K., and Lux, D.R., D.R., 1996, 1996, Core Core complex model proposed for gneiss gneiss dome dome development development during collapse of the Paleoproterozoic Penokean orogen, Minnesota: during collapse the Paleoproterozoic Penokean orogen, Minnesota: Geology Geology (in (in press). Schneider, D., Holm, D.K., and Lux, D., 1996, 1996, On the origin of of Early Proterozoic Proterozoic gneiss gneiss domes domes and metamorphic nodes, northern northern Michigan: Michigan: Canadian and metamorphic nodes, Canadian Journal Journal of of Earth Earth Sciences Sciences (in (in press). 11 �MICHIGAN MINERAL MINERAL LEASE EXPLORATION DATA INVENTORY MICHIGAN INVENTORY Milton A. Gere, Jr. Real Estate DMsion, Division, Michigan Department Department of of Natural Natural Resources Resources Marquette, MI MI49855 49855 Upon Upon termination of a metallic or or nonmetallic nonmetallic mineral mineral lease lease on on State State of of Michigan Michigan owned owned minerals minerals land, land, exploration data, data, geological records and and samples, samples, including including drill drill cores cores and and cuttings, cuttings, from the work exploration performed are performed are submitted submitted to to the the State State to to become become part part of ofthe the public public record. record. Periodically, exploration on private land leases is also donated to the State. information collected by companies during dUring work on Records are on on file file for exploration exploration and and mining mining activity activity for for numerous numerous mineral mineral commodities. commodities. Past Records are Past leases leases involved efforts to locate locate and/or and/or mine mine copper, copper, diamonds, diamonds, gold, iron, iron, limestone limestone and and dolomite, dolomite, uranium uraniumand and and base base metals. metals. associated precious and The exploration information is is now inventoried on a computer database which allows access by county name, town and and range, range, company company name name or orState State lease leasenumber, number,etc. etc. The The inquiry indicates if geological or name, town geophysical geophysical work work was was performed, performed, ifif any any drilling was was done, done, what what type type and and any any drill drill log log confidential status. It also lists if any drill core, were submitted submitted and additional core, cuttings cuttings or other samples or assays were information. inventory is is kept kept in in hard hard copy copy files files which may may be be reviewed reviewed on on an an appointment appointment Information listed in the inventory basis. Geologic Geologic and and geophysical geophysical data on file may prove to be an important lead to the future basis. understanding of Michigan's Michigan's geologic geologic and and mineral mineral resources. resources. Commodities Commodities located located in in the past may now understanding of be economic to produce. Also, Also, the the lack lackof ofknown known specific specificresources resources in in an an area area may maysuggest suggest that that expenditure expenditure of new exploration exploration dollars dollars would would be be better betterused usedininanother anotherMichigan Michiganlocation. location. Additionally, Additionally, determined for a parcel other companies are interested in leasing so terminated lease status may be determined their exploration activities activities can can take place. place. The quantity quantity and and quality quality of of the the information informationon onfile filevaries variesdrastically drasticallyfrom fromlease leasetotolease. lease. The The type typeof of lease, or or contract, contract, the the years years that that the the lease lease was was in in effect, effect, the the amount amount of of work work done done on on the the property property and and lease, the lessee lessee all all playa play a part part in in determining determining what what eventually is submitted to be the public consciousness consciousness of the be placed into open-file status. placed The leasing of State owned minerals is a function long managed by the Minerals Lease Management Section, Real Estate Division of of the Michigan Michigan Department Department of of Natural Natural Resources Resources (MDNR). (MDNR). For For many many years the the collection of exploration data and samples at the termination of of the leases leases was handled by the However, during during the the split split of of functions functions of of the the MDNR, MDNR, Michigan Geological Geological Survey Division (GSD). (GSD). However, Quality October 1, 1995, the GSD was placed placed into the new Michigan Michigan Department of Environmental Quality (DEQ). During geologic, metallic and (DEQ). During this this process process the limited general geologic, and nonmetallic mineral resources and groundwater resource resource related related functions, functions, and and staff, staff, of the GSD were were transferred transferred to the Real Estate Division Division (RED) (RED) of the DNR. RED geologic staff and functions are located in Lansing, Escanaba, and Marquette. Through the above changes, records from terminated State mineral leases changes, the geologic records leases now now reside reside in files of the RED/MDNR. samples submitted submitted at at lease leasetermination terminationare. are. RED/MDNR. Any Any geological geological drill core or other samples in the the GSD/DEQ's GSD/DEQ's Geological Geological Core Core and and Sample Sample Repository Repositoryfor for public public use. use. Both the Mineral then placed placed in Lease Lease Data Data Inventory Inventory and and the the Repository Repository are are located located in in the the Marquette, Marquette, MI Ml locations of the DNR and the DEQ. information about about the the Mineral Mineral Lease Lease Data Data Inventory, Inventory, call call Milt Milt Gere, Gere, RED/DNR, RED/DNR, or or for for information information For information about the Repository, Repository, call Bill Swenor, Swenor, GSD/DEQ. Both Both can can be reached via phone phone at at 906/228-6561. 906/228-6561. 12 �GEOCHEMICAL SOURCE TRENDS OF THE SOURCE CHARACTERISTICS CHARACTERlSTICS AND DIAGENETIC TRENDS FORMATION, MESABI MESABI IRON IRON RANGE, RANGE, MINNESOTA MINNESOTA VIRGINIA FORMATION, Hemrriing, Lamont-Doherty Earth S. R. Hemming, Earth Observatory, Observatory, Rt. Rt. 9W, Palisades, NY 10964, ng@lamont.ldeo.columbia.edu; S. M. McLennan,and and G. 0. N. Hanson, hemming@lamont.ldeo.columbia.edu; S. M. Mclennan, hem Department of Earth and Space Sciences, SUNY, Stony Brook, NY 11974 Understanding of the Animikie Animikie Basin is integral to understanding the regional tectonic Understanding the the evolution evolution of (heat Lakes Proterozoic. The Animikie Basin Basin contains contains aa framework in the Great Lakes area area during during the Early Proterozoic. number of of approximately approximately correlated correlated shale to turbidite sequences that fonn form the youngest wlit unit within the Animikie Aniniikie Group. Group. In Inthe the Mesabi Mesabi Iron Iron Range Range of of northern Minnesota, Minnesota, the Virginia Virginia Fonnation Formation is is of shales and is is relatively relatively undeformed. undefonned. The geochemistry of of sedimentary composed dominantly of powerful information rocks provides powerfiul informationconcerning concerningbasin basinevolution. evolution. However, However, there there are are aa number number of of complexly interactive parameters that control the composition of The ideal ideal of sedimentary sedimentary rocks. rocks. The ofelements elements that could could be used to quantify the original composition of the characteristics characteristics of the ultimate ultimate igneous inunobility in igneous source are relative immobility in most most natural natural fluids fluids and and different different enough enough behavior behavior during during igneous differentiation as to be sensitive to source source composition. composition. Although Although no element is completely igneous immune well known immune from chemical attack, it is well known that that the the rare earth elements elements and and Th Th and and Sc are well isotopes provide valuable constraints on on the characterizing source source compositions compositions and and Nd isotopes suited for characterizing of the sources. Compared Compared to to post-Archean post-Archean Australian average antiquity of average shale shale (PAAS), (PAAS), shales shales of of the Early Proterozoic Proterozoic Virginia Virginia Formation Formation have have light light rare earth earth element element enriched patterns and high of rare earth elements, elements, low low m/Sc thlScratios ratiosthat thatare arecorrelated correlatedto toTh Thabundances abundancesand andhigh high abundances of LaiTh ratios. The La!Th TheSm-Nd Sm-Ndisotope isotopecomposition composition of ofVirginia Virginia samples indicates a source that was earth element element depleted depleted reservoir, and and the the trace trace element element long-tenn light light rare rare earth recently derived from aa long-term character best fit fit aa young young character indicates indicates itit was was aa continental continental source. These Thesegeochemical geochemical data best as the the dominant dominant source source for for the Virginia Formation. differentiated arc as Elements are variably susceptible attack by by surface suthce waters waters and and thus thus well well susceptible to chemical chemical attack understood trends in chemical composition are arecreated createdduring duringweathering. weathering. Published Published reports reports have have chemical composition showed that major major element variations predicted by thennodynamic thermodynamic calculations calculations are are generally generally consistent with trends in weathering weathering profiles. proffles.In Incontrast, contrast, many diagenetic diagenetic reactions reactions may may create create an an approximately reverse trend trend from from weathering. weathering. Accordingly, approximately reverse Accordingly, estimates of weathering intensity rocks will will tend tend to to be be minimum minimum estimates. estimates. Major of sedimentary sedimentary rocks Major based on chemical compositions of elements elements in elements and alkali and alkaline earth trace elements in the the Virginia Virginia Fonnation Formation are are strongly are substantially substantially divergent divergent from igneous contents are correlated and are igneous differentiation differentiationtrends. trends. Ca contents extremely low, mostly less than 11 wt. %. %. Thus the sediments' compositions are almost almost totally totally controlled by aqueous alteration alteration during during sedimentary sedimentary processes. Two Twomain mainlines linesof ofevidence evidence suggest the measured measured compositional compositional trends are largely products of of diagenetic/metamorpbic diagenetic/metamorphic reactions. First Firstof ofall, all,aaSHRJMP SHRIMPU-Pb U-Pbzircon zircon age age from from an an ash ash layer layer near the base base of of the Virginia Formation constrains the time time of of deposition depositiontotobe beabout about1.85 1.85Ga. Ga. However, However, aa Rb-Sr isochron isochron from from (Petennan, 1966, 1966, the Virginia Formation is is very very well well correlated and yields a 1.6 Ga age estimate (Peterman, GSA Bulletin), consistent consistent with with a time time of of pervasive resetting of of the Rb-Sr system in in the region. ternary (CIA, (CIA, chemical chemical index index of of alteration) alteration) the the samples samples lie lie Secondly, on a A1203-Na20+CaO-K20 Al20 3-Na20+CaO-K20 ternary along a mixing mole % albite. Illite and mixing line line between between illite and albite, ranging from about 50 to 80 mole albite are commonly commonly formed fonned during burial diagenesis. diagenesis. The strong strong correlation between K K20 Na20 2 0 / Na20 Rb/Sr isis likely likely aa product productof ofvarious variousmixtures mixturesof ofthese thesediageneticlmetamorphic diagenetic/metamorphic minerals, minerals, and and· and Rb/Sr thus the 1.6 1.6 Ga Ga Rb-Sr Rb-Srage ageapproximately approximately dates dates the the time time of of their formation. fonnation. 13 �WAS LITHOSPHERIC LITHOSPHERIC DELAMINATION AN IMPORTANT IMPORTANT PROCESS PROCESS IN IN THE THE WAS DELAMINATION AN EARLY PROTEROZOIC PROTEROZOIC COLLISIONAL OROGENS? EVOLUTION OF EARLY HOLM, D.K., DAHL, P.S., Dept Dept. of Geology. Geology, Kent State University. University, Kent, 44242 HOLM, DAHL. P.S., Kent, OH 44242 (216-672-4094; (216-672-4094; dholm@kentvm.kent.edu) dholm@kentvm.kent.edu)and and LUX, LUX, D.R., D.R., Dept. Dept. of Geological Geological Sciences, Sciences, University of Maine, Orono, ME 04469. Mantle lithospheric lithospheric delamination delaminationhas has been been proposed proposed as as a ubiquitous Mantle ubiquitous process process in collision zones to the point that it may require a paradigm shift in our understanding Phanerozoic coffision of how collisional evolve. The collisional orogens orogens evolve. The process process of ofrapid rapid mechanical mechanical thinning thinning of of the the mantle mantle orogenic belt ("delamination") has fundamental implications for both the lithosphere beneath an orogenic chemical and structural evolution of of continents (Nelson, 1991, 1992). Although Althoughgeophysical geophysical data data from relatively young orogens orogens seem to to support support the the delamination hypothesis, hypothesis. these these data data (i.e., (Le.• deep deep seismic profiling) profiling) seem limited (at best) for assessing very ancient ancient orogens. orogens. seismic assessing delamination delamination in very importance in in Precambrian Precambrian orogenic belts must rely, rely. unfortunately, unfortunately. on on less less Evaluation of its importance Evaluation direct evidence. Two Twoconsequences consequences of ofmantle mantle lithospheric lithospheric delamination delamination are rapid isostatic uplift of the overlying overthickened crust (orogenic collapse) and heating of the lower crust resulting magmas (Turner (Turner and and others. others, 1992). 1992). Investigations in generation generation of post-tectonic post-tectonic magmas Investigations of of the the postpostplutonism may therefore be a means to collisional uplift history and its relation to post-tectonic plutonism assessing the delamination hypothesis in the Precambrian. Precambrian. We We summarize summarize below below evidence evidence from from two which may may be at least two Early Proterozoic orogens orogens in the the North North American American midcontinent midcontinent which least consistent with (though not exclusively indicative of) the delamination hypothesis. Southern Trans-Hudson Trans-Hudson orogen. orogen. In In the thesouthern southern Black Black Hills Hills of ofSouth SouthDakota, Dakota,medium medium pressure rocks metamorphosed during an Early Proterozoic collisional orogeny where uplifted at least 8-10 km km before before being being intruded intruded by by the thepost-tectonic post-tectonic Harney Harney Peak PeakGranite Graniteatat—1700 -1700 Ma. Abundant thennobarometric thermobarometric data indicate that the granite was emplaced at midcrustal depths depths (12(12km) and thermochronologic Ma period period of 14 km) thennochronologic data data suggest suggest emplacement emplacement was was followed followed by byaa—200 -200 Ma stability tectonic quiescence quiescence with with little little uplift. uplift. Isotopic Isotopic and trace-element data from the the stability and tectonic granite (Nabelek (Nabelek and and others, b) indicate indicate that that at least the interior portions of the pluton granite others. 1992a, 1992a, b) were derived melting of biotite in were derived from high-extent high-extent vapor-absent vapor-absent melting in deep-seated deep-seated Archean/Early ArcheanlEarly rocks. The Proterozoic metasedimentary rocks. The generation generation of of the the granite granite has has commonly commonly been been attributed attributed to thennal relaxation relaxation of to thermal of the the overthickened overthickened crust crust following following collision. collision. However, However. heat-flow heat-flow modeling results results suggest suggest that that thermal was probably modeling thennal relaxation relaxation was probably not a viable viable mechanism mechanism for achieving the the >850°C temperatures achieving temperatures (Vielzeuf and Holloway, Holloway. 1988) 1988) necessary necessary to to produce produce We speculate speculate that that generation generation of of the the Harney Harney Peak voluminous voluminous crustal crustal melts melts in in the the Black Black Hills. Hills. We Granite magma and the crustal uplift which preceded preceded it may have been the result of thinning of the mantle lithosphere the mantle lithosphere (delamination) (delamination) beneath beneaththe the southern southernBlack BlackHills. Hills. This scenario seems supported the whole whole of of the the Black Black Hills, Hills. the the Harney Harney Peak Peak Granite Granite is is spatially spatially supported by the fact that, in the associated with with the deepest exposed exposed Early Early Proterozoic Proterozoic country country rock. rock. Because associated Because uplift uplift preceded preceded midcrustal granite emplacement, we emphasize emphasize that that this this spatial spatial association association is not related to in emplacement, we situ melting of the deepest-exposed portions of the orogen. orogen. Rather, Rather, preferential preferential intrusion intrusion into the the is exactly exactly what what would be expected if if both uplift uplift and and melt melt generation generation were deepest exposed rocks is the result of of the the delamination delamination process. process. Recent Recentage ageconstraints constraintssuggest suggestsyncollisional syncollisional regional regional -1740-1750 Ma the at —1740-1750 metamorphism at Masuggesting suggesting aa time-lag time-lag of of 30-50 30-50 Ma between collision and the proposed delamination. Penokean orogen. orogen. In Lake Superior Superior region region Early Early Proterozoic Proterozoic post-Penokean post-Penokean granites granites In the Lake Holm and and Lux Lux (1996) (1996) suggested intruded into rapidly uplifting crust beginning around around 1770 Ma. Ma. Holin represent deep deep crustal crustal melts melts related related to to an an episode episode of of orogenic orogenic collapse collapse perhaps perhaps that the granites represent triggered lithospheric delamination. delamination. Abundant Abundant post-Penokean post-Penokean NE-striking NE-striking basaltic triggered by by mantle lithospheric dikes intruded synchronously with with dikes (in both central Minnesota and Wisconsin) which were likely intruded 14 �or just after the the granites granites are are evidence evidence for for aa significant significant mantle mantle thermal thermal input input into into the the base base of of the the (Van Wyck, Wyck, 1995). 1995). The Thespatial spatialand andtemporal temporalrelation relationcif of rapid uplift, melting of the lower crust (Van and basaltic basaltic dike dike intrusion intrusion isisconsistent consistentwith withan anepisode episodeofofmantle mantlelithospheric lithospheric·'thinning. thinning. crust and Alternatively, somewhat younger younger (-.1730 (-1730 Ma) Ma) deformational deformational and and Alternatively, recent recent evidence evidence for for aa somewhat metamorphic event suggests metamorphic event suggests the the post-Penokean post-Penokean reheating reheating event event responsible responsible for for magma magma generation might be related to distant subduction to the south (Van Wyck, 1995). Conduding remarks. The summaries presented above suggest that for the southern Black Concluding Hills crustal thinning thinning preceded preceded granite granite emplacement emplacement whereas whereas for the Penokean orogeny igneous intrusion occurred occurred during during tectonic We suggest suggest that that this this difference difference in in the the relation relation intrusion tectonic thinning. thinning. We between plutonism and uplift between the two orogenic belts may be more apparent than real by simply being being an an artifact artifact of the the level level of exposure available for for us us to to investigate. investigate. That is, the simply exposure available Penokean orogenic during the theproposed proposedcollapse collapse episode episodewhereas whereas orogenic belt belt exposes exposes midcrustal midcrustal depths depths during midcrustal depths after after the the period period of of post-collisional post-eollisional uplift. uplift. the Black Hills exposes midcrustal Nelson (1991) has suggested that the delamination process may actually involve both the mantle portion of of the the lithosphere lithosphere and and portions portions of of the the lower lower crust, crust, making making itit perhaps perhaps aa critical critical step step in both the chemical and structural evolution of continental continental lithosphere. lithosphere. Nelson's proposed view of craton evolution relies heavily on uniformitarian principles by invoking processes observed in active or young orogenic belts to have occurred throughout throughout the the Earth's Earth's history. history. Detailed studies of the the exposed exposed mid-and mid-and lower lower crustal crustal roots roots of of Precambrian Precambrian orogenic orogenic belts belts will will provide provide one one important test of of Nelson's unified view of of craton evolution. References ReCerences Holm, D.K., O.K., and Lux, D.R., 1996, 1996, Core complex complex model model proposed proposed for gneiss gneiss dome development development of the the Paleoproterozoic Penokean orogen, Minnesota: Geology (in press). during collapse of Nabelek, P.1, C., and and Haeussler, G.T., 1992a, isotope evidence evidence for for the p.r, Russ-Nabelek, Russ-Nabelek, C., Haeussler, G.T., 1992a, Stable isotope petrogenesis and fluid evolution evolution in the the Proterozoic Proterozoic Harney Hamey Peak Peak leucogranite, leucogranite, Black Black petrogenesis Geochimica et et Cosmochimica Cosmochimica Acta, v. 56, p. 403-417. Hills, South Dakota: Geochimica Nabelek, p.r., Russ-Nabelek, Denison, J., 1992b, 1992b, The The generation generation and and crystallization crystallization Nabelek, P.1., Russ-Nabelek, C., C., and and Denison, conditions of of the Proterozoic Harney Hamey Peak leucogranite, Black Hills, South Dakota, USA: Petrologic and geochemical constraints: Contributions geochemical constraints: Contributions to to Mineralogy Mineralogy and Petrology, v. llO,p.p.173-191. 110, 173-191. Nelson, Nelson, K.D., K.D., 1991, 1991, A unified unified view view of of craton craton evolution evolution motivated motivated by by recent recent deep deep seismic seismic results: Geophysical reflection and refraction results: Geophysical Journal Journal International, v. 105, p. 25-35. Nelson, K.D., K.D., 1992, 1992, Are Are crustal crustal thickness thickness variations variations in in old old mountain mountain belts belts like like the theAppalachians Appalachians delamination? Geology, Geology, v. 20, p. 498-502. a consequence of lithospheric delamination? S., Sandiford, Sandiford, M., M., and and Foden, Foden, J., 1., 1992, 1992, Some Some geodynamic geodynamic and and compositional compositional constraints constraints Turner, S., on "postorogenic" magmatism: magmatism: Geology, v. 20, 20, p. p. 931-934. 931-934. Geology, v. ofeclogites, eclogites, N., 1995, 1995, Oxygen Oxygen and and carbon carbon isotopic isotopic constraints constraints on on the the development development of Van Wyck, N., Holsnoy, Norway Norway and and Major Holsnoy, Major and and trace trace element, element, common common Pb, Sm-Nd, Sm-Nd, and and zircon zircon geochronology constraints constraintson on petrogenesis petrogenesis and and tectonic tectonic setting setting of pre-and geochronology pre-and early early Proterozoic rocks in Wisconsin: Ph.D. dissertation, dissertation, University University of of Wisconsin-Madison. Wisconsin: Ph.D. Vielzeuf, D., and Holloway, deterniination of the fluid-absent melting melting Holloway, J.R., 1.R., 1988, 1988, Experimental determination relations Contributions to to Mineralogy Mineralogy and and Petrology, v. 98, p. 257relations in the pelitic system: system: Contributions 276. 15 �______ GENESIS OF OF A A TIMISKAMING-LIKE SEQUENCE SEQUENCE IN THE SOUTHERN WAWA SUBPROVINCE, SUBPROVINCE, NORTHEASTERN MINNESOTA J1RSA,Mark Mark A., A., Minnesota Minnesota Geological Geological Survey, Survey, 2642 2642University University Avenue, Avenue, St. Paul, Minn., JIRSA, Minn., 55114-1057;e-mail: e-mail: jirsa001@maroon.tc.urrin.edu 55114-1057; jirsa001@maroon.tc.umn.edu unusual conglomeratic conglomeratic sequence sandwiched between two An unusual two units of Archean Archean graywacke graywacke in in the the Virginia (Fig. 1) 1) has has been been recognized recognized since the the 1960s 1960s as attributes of of the theclassic classic Virginia Hom Horn (Fig. as having attributes Timiskaming in the Kirkland Kirkland Lake area, area, Ontario. Ontario. Since Since that time, considerable attention has been been given to such sequences sequences throughout the the Superior Superior Province, Province, and many are now now well well documented. documented. focus on the Timiskaming was fueled in part by the association of these these sequences sequences with major The focus gold camps. strata were were deposited deposited in structurally camps. Most Most Timiskaming-like Timiskaming-like strata structurally controlled controlled basins basins inferred be the product during early of the inferred to. to be product of of localized localized extension extension during early regional regional transpression transpression of the greenstone sequences pull-apart basins) basins) prior prior to metamorphism greenstone sequences (i.e., (i.e., pull-apart metamorphism which accompanied accompanied D2 Because they they are are the the youngest youngestof of Archean Archean supracrustal supracrustalrocks, rocks, the the Timiskaming-like Timiskaming-like deformation. Because sequences are unique temporal sequences temporal pins in the structural and stratigraphic stratigraphic evolution of the Superior Province. 92°37'30' 92°30'00· 92"22'30' 92°15'00. 17°3T30 , .. '" ..' ," .. ' .. '" .. ' .. " .. " .. ' .. ' ..' ..' ..' ..' ..' ...' ...' ..' ..' .. ' ..' ..' ..' .. ' . . ' .... ' ..' .. ' .. ' ..' ..' .. ' .. ' .. ' ..' ..' ..' 47°37'30" .. "'"" " " " " " " , , , , , , , , , , , , .. , , , , , , , , .. .. .. .. .. " " '" . .. .. ................................................... . PROTEROZOIC EARLY PROTEROZOIC . Virginia Formation Formation 1,*;Jii~.1 Virginia """""""""""""" " """"", '" " ' "..".." " . " " ' . ' " ' ' ' ' ' ' ' ' ' ' ' ' ' ' ' ' " ' " " " " " " " " " " " '" 1'''''''''''''''''' .. .. ", , , , , , , '" ".. , , , , ,.., ,. . .. " " " , , ,", , , , '" .. , , , , , , , , , , , , .. .. . . . . . " '" " . .." .. .." . " .. " " " " , .. " " " " .. , .. " " " " , "" .. " """ "" "" " "" .. .......... , .. " , .. " " " .. " "...... , ...... " " ...... "" " ,.. ." "," .. " , .. " "" .. ," .. " " " ...." " " , .. .. " , ," , ." , "" " ...." , , " ", " , W~~,,>< +)-,I;l£t'jti(~ .~~ Biwabik Iron Iron Formation Formation D Pokegaina Formation Pokegama LATE ARCHEAN ARCHEAN ' 1:-, :-, :-, I Giants Range batholith • Timiskaming-like (TLS) sequence (TLS) ~~~~~~ Graywacke and slate [IllIll] fflffl Metavolcanic rocks The term "Virginia "Virginia Hom" Horn' refers to Figure 1-- Simplified geologic geologic map of the Virginia Horn Hom area. area. The the hook or or horn-shaped hom-shaped distribution distribution of of Early Early Proterozoic Proterozoic Biwabik Biwabik Iron vicinity Iron Formation Formation in in the vicinity The iron-formation onlaps of Virginia, Minnesota, surrounding it. The onlaps of Virginia, Minnesota,and and isis applied applied to to the area surrounding Archean bedrock, which is is likely the southernmost exposures of the Wawa subprovince. The Timiskaming-like Timiskaming-like sequence sequence (TLS) (US) in the Virginia Virginia Hom Horn lies lieswithin within an an east-trending, east-trending, broadly broadly synclinal succession rocks. It succession of graywacke graywacke and and slate underlain by mafic to intermediate volcanic rocks. forms a northeast-trending northeast-trending structural structuralwedge wedgeat atleast least 55 km km long long and and aa maximum maximum of of 11 km thick. thick. The The TLS TLS isis homoclinal, homoclinal, steeply steeply dipping, dipping, and and consistently consistently south south facing. facing. Early Proterozoic strata conceal "'Ml"westem part of the TLS, TLS, and and the the sequence sequenceisisterminated terminatedon onthe theeast eastby byaafault. fault. Although Although the the boundaries boundaries of of the the US TLSare arerarely rarelyexposed, exposed,aacomposite compositesection sectioncan can be be inferred inferred in in aa few few areas areas from from aa combination The sequence sequence is combination of of drill drill core core and and outcrops. outcrops. The is divided divided into into several several units units that vary in character along strike. The The basal basal unit unit isis sandstone sands.tone and andpebbly pebblyconglomerate, conglomerate, which which thickness and character absent to to 30 30 m thick, and coarsens up-section. composed of of detritus detritus derived, derived from varies from absent up-section. ItIt isis composed greenstone, and distinctive distinctive quartz phenocrysts phenocrysts eroded from the quartz-feldspar quartz-feldspar porphyry porphyry older greenstone, is a fault intruded the thegreenstone. greenstone. The The basal basal contact contact is fault in in most most places; places; but butlocally locally is that intruded atop aa variety variety of of older rocks. rocks. A A thin thin and and discontinuous discontinuous volcanic volcanic unit unit containing containing unconformable atop 16 �flows and and hypabyssal hypabyssal sills sillsofofa adistinctive, distinctive,caic-aLkalic, calc-alkalic, hornblende hornblende trachyandesite trachyandesite porphyry flows (HAP) isis present present locally above the the basal the volcanic unit is (HAP) locally above basal unit. Where Where the volcanic unit is absent, absent, laterally laterally equivalent strata are anit can be seen in in outcrop, outcrop, it are dominated dominated by by HAP HAP clasts. clasts. Where Where the the volcanic volcanic unit grades into flowtop flowtop breccia, breccia, agglomerate, agglomerate, and conglomerate conglomerate made up almost almost entirely entirely of of clasts clasts of of HAP. This This conglomeratic conglomeratic unit unitmakes makesup upthe thebulk bulkofofthe theTLS TLS sequence sequence and and is is composed composed of of poorly poorly sorted, clast-supported, clast-supported, and vaguely graded beds. Clasts more sorted, Clasts within within the the conglomerate conglomerate become become more diverse and bedding, grading, and and sorting diverse in texture texture and and composition composition up-section, up-section, and bedding, grading, sorting are better better developed. This stratigraphic sequence records a progression from gentle subsidence of aa sediment-starved Clasts in the basin, followed followed by volcanism, volcanism, basin collapse, collapse, and in-filling in-filling with coarse detritus. Clasts the conglomeratic unit were conglomeratic unit were initially initially derived derived largely largely from from intrabasinal intrabasinal volcanic volcanic rocks, rocks, but progressively more extrabasinal extrabasinal material material was was supplied supplied as as the the basin's basin's watershed watershed expanded. expanded. The progressively more The absence implies that that much much of the deposition was absence of demonstrably lacustrine or fan-delta fan-delta deposits deposits implies subaerial. The Thegreat greatthickness thicknessof ofcoarse, coarse, poorly poorly sorted sorted conglomerate conglomerate indicates indicates deposition within within subaerial. alluvial local bedded and and cross-bedded cross-bedded sandier units probably have a fluvial fluvial origin. origin. alluvial fans, fans, and local Lateral continuity of of individual in part because individual units units is difficult difficult to establish, establish, in because of abrupt facies facies Lateral continuity changes along along strike, strike, which which are are inferred inferred to to be the changes the result result of of deposition deposition in the the many many sub-basins sub-basins pull-apart settings. common in pull-apart settings. Earlier Earlier workers in the the Archean Archean of of the the Virginia Virginia Horn Horn attempted attempted to to link link deposition deposition of of the the TLS TLS with that by inferring with that of of the theenclosing enclosing graywacke-slate graywacke-slate sequence sequence by inferring that the the TLS TLS represented represented proximal turbidite channel deposits, while the graywacke and slate slate units units were deposited as distal proximal graywacke and which utilized utilized outcrop and aa series Remapping, which series of of cores cores drilled drilled by by exploration exploration turbiditic fans. fans. Remapping, companies along the basal contact contact of of the the sequence sequence (which (which were not available available earlier), demonstrates that they do not not represent represent aa depositional depositional continuum continuumfor for the the following following reasons: reasons: Structural data indicate sequence isis twice twice folded, folded, and and in fact 1. Structural indicate that that the the graywacke-slate graywacke-slate sequence fact much of the graywacke strata was was overturned overturned during during DI, Di, prior to deposition of the the TLS. US. much graywacke strata deposition of Locally Locally recumbent, recumbent, east-trending east-trending F1 FI folds folds are are cut cut at at an an acute acute angle angle by by the the basal basal unconformity and and faults faults which which bound bound the theTimiskaming-like Timiskaming-like sequence. 2. Quartz-feldspar porphyry intruded the greenstones, but not not the the TLS, US, and greenstones, but and in in fact fact provided provided detritus to to the the TLS. TLS. 3. Flows, and detrital detrital hornblende hornblende Flows, intrusions, intrusions,and andclasts clastsofofHAP HAP are are unique uniquetoto the theTLS US,, and derived from from HAP HAP is is common common in in conglomerate conglomerate matrices matrices and associated associated sandstone units. homblende does Detrital hornblende does not notoccur occurin in the thegraywacke-slate graywacke-slate sequence. sequence. 4. Hornblende-phyric Hornblende-phyric dikes, dikes, texturally texturally similar similar to to and inferred to be be feeders feeders of of HAP HAP flows, flows, cut all all rock rock types. types. 5. A sharp contrast contrast in in depositional depositional style style occurs occurs between between the the resedimented resedimented facies facies graywackegraywackeand the thevolcanic volcanicand andalluvial alluvialfan-fluvial fan-fluvialfacies faciesdeposits depositsofofthe theTLS. TLS. slate sequence, and The TLS TLS contains contains all all the the characteristics of pull-apart pull-apart basin basin deposition, deposition, including including structural structural and and The characteristics of unconformable boundaries, lateral facies facies changes, changes, thick thick and and variable variable alluvial alluvial sediments, sediments, unconformable boundaries, abrupt lateral and the the association association of unique volcanism. volcanism. Although Althoughother otherconglomeratic conglomeratic units units in in Minnesota Minnesota may be candidates candidates for aa similar similar designation designation (Seine (Seine Group in in the the Rainy Rainy Lake Lake area area and and Okishkemucie Okishkemucie conglomerate in the the Knife Knife Lake Lake Group), Group), none none has the unique combination of Timiskaming Timiskaming attributes attributes present in this present this sequence. sequence. Support for mapping in the Support for mapping in the Virginia Virginia Horn Horn isis being being provided provided by by the the State State Legislature Legislature and and is is administered by administered by the the Minerals Minerals Coordinating Coordinating Committee. Committee. 17 �Identifying Geologic Geologic and and Other Other Potential Resources From Michigan's Abandoned Underground Mine Inventory Allan M. M. Johnson(1) Johnson(1) and and Milton Milton A. A. Gere, Gere, Jr.(2) Allan Introduction.AAtwo-year two-yearcontract contractto toinventory, inventory, document document and and map map abandoned abandoned underground mines mines Introduction. in the the State StateofofMichigan Michigan was wasawarded awardedtotoMichigan Michigan,Technological rechnological University University (MTU) in (MTU) by by the Geological Survey Division (GSD) of ofthe the Michigan Michigan Department Department of ofNatural Resources (M1)NR) (MDNR) in in Natural Resources late summer summer of of1995. 1995. The project is is now now being being overseen overseen by the Real Real Estate Estate Division Division (RED) (RED) following structure of ofthe the MDNR. following recent changes in the structure is needed preserve aa data data base base on on the location of The inventory inventory is needed to permanently permanently preserve location and condition condition of underground mine openings openings and identifYand andrank rankany anyunsafe unsafeconditions conditionsfound found during during the the field field and to identii investigation phase phase ofthe of theproject. project. These data will willhelp helpplanners plannerstoto avoid avoid undermined undermined areas for future investigation future development will call call attention to the the conditions conditions needing corrective action to protect protect public public development and will safety. Similar 1970's for the Similar work work on on abandoned abandoned iron iron ore ore mines minesinin Iron Iron County Countywas was done done in in the the 1970's for the GSD-MDNR problems ofmine of minesubsidence subsidenceand andacid aciddrainage drainagewere were addressed addressed (Johnson and GSD-MDNR in which problems An inventory inventory of of mines mines was This research research Frantti, 1978). An was also alsodone done(MacDonald (MacDonaldand andJohnson, Johnson, 1984). 1984). This been useful useful for for planning planningpurposes purposesand andininpreserving preservingaarecord record of of the the mines which otherwise might has been might lost with with the the passage passageof have been lost oftime, time, and andalso also in in documenting documenting first-hand first-hand knowledge knowledge from from aging aging miners, 15'0 years becomes a relic of the past. miners, as underground mining activity of the last last 150 Goals.. The project project requires requires a computerized mine mine map Goals. The map data base compatible with MIRIS (Michigan System), the the State's State's Geographical GeographicalInformation Information System. System. This This will will preserve mine Resource Information System), map data data and andwill willultimately ultimately make make ititavailable available electronically electronically to the the public. public. The three three major major map of the project project are: are: requirements of 1. To provide provide accurate accurate information on the location and and extent of of underground openings for each of 1. To of the more more than than 500 500 abandoned abandoned and andclosed closedunderground underground mines mines in in Michigan. Michigan. Selected mine mine map map software. information will be digitized digitized and stored in a computerized data base using AutoCAD software. 2. To provide information and county-by-countybasis. basis. and maps maps for for each eachofthe of the underground underground mines on a county-by-county This will willinclude includemine minename, name,location, location,years yearsofofoperation, operation,production productionrecords, records, mine mine ownership, ownership, mine mine operator, number number of of shafts shafts and and other other openings openings to the the surface, surface, subsidence subsidence pits pits if if present, and other data obtainable obtainable from from records records and and mine mine maps. maps. Also Also included included will will be be assessments assessments of the relevant data condition of of shafts and other other surface surface features features at at each eachmine mine based based upon upon field field observations. observations. 3. identify and and rank rank: potential potential problems problems atat abandoned abandoned mines mines in in terms terms of ofpublic public safety safety from from open open 3. To identify shafts, caving around shafts, deterioration of shafts, of shaft seals or caps, subsided areas, and other unsafe 18 �conditions. Assistance mmmg company company personnel, other Assistance of of mining personnel, county county mine mine inspectors inspectors and and other knowledgeable individuals will be important in the field field inspection inspection phase phase of of this this project. Opportunities and and Attributes. Attributes. It is is recognized recognized that abandoned abandoned mines mines do possess possess esoteric esoteric many old mines have historical significance which, remnants attributes. For Forexample, example, many attributes. which, if enhanced by remnants ofold of old mine minebuildings buildingsand andartifacts, artifacts,may maybe beof ofvalue valuefor fortourism. tourism. A A good good example example is is the the Keweenaw Keweenaw National Historic Park. On-going research research has has identified identified aa number number of of Michigan Michigan underground underground mines mines as as sites sites of active active bat hibernation during during winter winter months months (Millie (Millie Hill Hill Mine in in Iron Iron Mountain). Mountain). The International Bat Conservancy, seeking to preserve preserve these these mines, mines, reports that large large numbers numbers of of bats bats migrate migrate from from surrounding states and and Canadian Canadian provinces to hibernate there. there.. Flooded mines mines represent representaapotential potentialresource resourceof ofhuge hugevolumes volumesofwater of water suitable suitable for for industry (Norrie Mine, Mine, Ironwood) Ironwood) and, and, inin some somecases, cases,high highquality qualitypotable potablewater water(Champion (ChampionMine, Mine,Painesdale). Painesdale). Flooded mine pools are also geothermal energy suitable suitable for extraction ofreadily readily available geothermal also aa source source of using heat pump technology technology (Osceola (Osceola Mine, Mine, Calumet). Calumet). Formerly discarded mine mine wastes, waste rock and mill tailings, are becoming recognized as mill tailings, as valuable valuable Formerly raw materials materials for for industry. inJustry. Examples Examples include include using using these these wastes wastes as as aggregate aggregate (iron and copper districts) ice and in districts) and snow snow traction traction (Keweenaw (Keweenaw Peninsula) Peninsula) and and potentially potentially as as raw raw materials materials in manufacturing such such products productsas asfloor floorand andceiling ceiling tiles, tiles, thermal thermal insulation, insulation, building and construction manthcturing materials products. Tailings of speciality speciality products. Tailings from from the the Republic Republic Mine are being being used for for materials and a variety of Corporation in in Alpena. Alpena. portland cement manufacture at Lafarge Corporation References Johnson, AM and and Frantti, Frantti, GE, GE, 1978, 1978, Study Study ofMine of MineSubsidence Subsidenceand andAcid AcidWater Water Drainage Drainage in the Iron Iron Johnson, River Valley, Valley, Iron Iron County, County, Michigan, Michigan,prepared preparedfor forGSD-MDNR, GSD-MDNR,Lansing, Lansing,MI MI by by Institute Institute ofMineral of Mineral Research, Michigan Michigan Technological Technological University, University, 220 p. p. MacDonald, U and MacDonald, U and Johnson, Johnson, AM AM,1984, 1984,AADirectory Directoryof ofIron IronMines Mines ininIron IronCounty, County, Michigan, Michigan, Report prepared Report prepared for for GSD-MDNR, GSD-MDNR, Lansing, Lansing, MI by by Institute Institute of ofMineral Mineral Research, Research, Michigan Michigan p. Technological University, University, Houghton, MI, 294 p. (1) Director, Director, Mineral Mineral Technology Technology Research Research Group, Group, Department Departmentof ofMining Mining Engineering, Engineering, Michigan Michigan Technological University, 49931 and and Project Project Principal Principal Investigator. Investigator. University, Houghton, MI, Ml, 49931 (2) Geologist, Geologist, Real Real Estate Estate Division, Division, Michigan Michigan Department Department of Natural Natural Resources, Resources, Marquette, Marquette, MI, MI, 49855 and Project Officer. Officer. 19 �AN ANCIENT LANDSLIDE AT AT "RED "RED ROCKS", ROCKS", KEWEENAW KEWEENAW BAY, BAY, MICHIGAN MICHIGAN Jorma Kalliokoski, Kalliokoski, Professor Professor Emeritus, Emeritus, Michigan Technological University, University, Houghton, Houghton, MI MI 49931 49931 At the south end of of Keweenaw Keweenaw Bay Bay is is an an outlier outlier of Jacobsville Jacobsville At Sandstone, red along the highway and purplish Sandstone, purplish grey along along the the lake lake shore where the batton botton 1—3 1-3 m m of the the section section is is exposed, exposed, and and rests rests Michigaimiie on Michigamme Michigamme slate slate (Fig.l). (Fig. 1). There Therethe thesub—horizontal sub-horizontal Michigamme surface exhibits parallel parallel striations, striations, leading leading Murry Nurry (1955) (195) to surface exhibits to period of of glaciation. glaciation. Conversely, Conversely, on propose a a pre--Jacobsville pre-Jacobsville period on the the basis of bedding slips in in the the sandstone, sandstone, and evidence evidence for for aa non-glacial paleoclimate, paleoclimate, I I suggested that the striations striations were were produced by basal pebbles as the the entire entire sandstone mass mass slid slid northerly (Kalliokoski, (Kalliokoski,1982). northerly 1982). Additional detailed mapping mapping last last summer summer revealed revealed aa clayey clayey fault, fault, traceable for about 15 15 m m along the the slate/sandstone slate/sandstone contact contact traceable (Fig.1) At Sta.43 Sta.43 aa strand strand of of this this shear shear rises rises obliquely obliquely (dip (dip 1~ 1° (Fig.l) At SW) through a SW) a 40 cm cm sandstone bed, bed, and and merges merges into into the the base base of of the overlying conglomerate. the conglomerate. The The orientation orientation of of the fault fault indicates that that the indicates the upper block mcved moved northeast. northeast. About 20 20 mm southwest is a a larger larger one one along which which sedimentary sedimentary southwest of this fault is beds have moved up up along along aa low—angle low-angle ramp ramp fault fault (strike (strike N35 N35 W, W, 30°SW: Fig.1, dip 3ifSW: Fig.1, Sta.23; Sta.23j Fig.2). Fig.2). The The orientation orientation of of this this fault fault also denotes northeast movement. movement. Moreover, Moreover, features features in in Fig.2 Fig.2 indicate indicate that that the footwall footwall conglomerate first moved along a a bedding fault, fault, and at this this locality, locality, up up an an inclined inclined fault fault (a (a stage beyond that illustrated illustrated at Sta.43). Sta.43). When When movement movement of of this this conglomerate had slowed or ceased, ceased, the the poximal poximal part part of of the the conglomerate bed bed over—rode over-rode the the previously previously ramped ramped one. one. Below the (Fig.2j Sta.43) are parallel striations striations on on the fault fault (Fig.2; Sta.43) there are 2 faint ones at Michigamme slate slate surface: surface: 12 at at 54°-234° 5~-234°, the Michigamme , and 2 90~270c. The prevalent direction is is the same as for the fault fault 90-2'7O° movement vectors, vectors, and suggests suggests strongly strongly that that the the striations striations and and movement faults formed within the faults the same same dynamic dynamic system. system. . The south of of the the Bishop The elevation of Michigamme Michigamme slate outcrops outcrops south Earaga statue statue and along the lake Baraga lake shore shore suggest suggest that that the the 'sub-Jacobsville surface surface slopes slopes about about 6° ~ northerly. 'sub—Jacobsville The indicates that that the the sandstone sandstone outlier outlier slid slid The above above evidence indicates northeast along along bedding bedding faults, faults, one one along along the the smooth smoothMichigamine Michigamme slate surface and others along higher slate higher bedding bedding surfaces. surfaces. Where Where aa the mass stopped moving, more distal distal portion of the moving, stresses within the portions of of beds beds to to override override the system caused the more proximal portions the in landslides the distal distal ones, ones, as as is characteristic in landslides and and along along zones of imbricate imbricate thusting. thusting. 20 20 �Mass Mass movement movement of the sandstone in post—Glacial post-Glacial of the sandstone probably occurred in time. This may the sub-vertical, time. may be the cause cause for for the sub-vertical, north dipping exposure, not fractures in in the highway exposure, not seen anywhere else in in Jacobsville Sandstone outcrops, outcrops, and for for the more irregular irregular jointing in in the the lowermost lowermost beds. beds. The purplish color in in the the basal basal sandstone may be aa product product of of groundwater flow above the the Impermeable impermeable Michigamme Michigamme basement. basement. References Kalliokoski, J., J., 1982, Jacobsvllle Jacobsville Sandstone, Sandstone, in in Wold, Wold, J. J. R., R., and Hinze, Hinze, W W. E., E., eds., eds., Geology Geology and and tectonics tectonics of of the the Lake Lake Superior Basin: Basin: Geological G~ological Society Society of of America America Memoir Memoir 156, 156, 147—155. p. 147-155. p. Murry, 1955, Late Murry, R. R. C. C. ,,1955, Late Keweenawan Keweenawan or or Early Cambrian glaciation in Upper Michigan: in Michigan: Geological Society of of America America Bulletin, Bulletin, v. 66, p. p. 341-344. 341—344. .- .••.. ~""""""""""~""""""'" 15 . D ... . . . 35 a Michlgamme Michigamme slate • F--H Jss Jssconglomerate conglomerate JacobsvilleSs overburden . Ii 2 meters meter~ 3, Figure 1. Vertical shore outcrop; Figure 1. Vertical outcrop; azimuth of of profile profile 55°. 55°. Jacobsville Sandstone is is in in fault contact <Wavy (Wavy line) line) with with Michigamme slate, and and rests on striated slate at Sta.43. Sta.43. At At Sta. Sta. 43 43 and 23 are inclined inclined thrust faults, faults, indicating indicating that that higher higher strata have have moved moved NE. HE. slate, overburden V JV 'I V -. • b C . • meters 21 Figure 2. 2. Detail Detail at at Sta.23; Sta.23; b, sandst, , c, sandst., sandst. Lower sandst. inclined congl. slid on its inclined congl. its inclined base and up an inclined fault surface. fault surface. Later Later the the sandst. and and congl. congl. of the sandst. upper plate plate were thrust into upper into place. a, a, corigl. congl.,, indurated indurated �Aeromagnetic Map of Lake Superior by P. Kucks· and Robert Robert J. J. Horton Horton· Robert P. Kucks and ** U.S. Geological Survey, Survey, Box Box 25046, 25046, MS MS 964, 964, Denver Denver Federal Federal Center, Center, Denver, Denver, CO., 80225. CO., 80225. Introduction An aeromagnetic map of the Lake Superior Superior" region (figure (figure 1) 1) was compiled as part of the Great Lakes International Multidisciplinary Program on Crustal Crustal as set was was compiled from digitized Evolution (GLIMPCE). (GLIMPCE). The magnetic anomaly data set and digital data data acquired acquired from from aa diverse diverse group group of of magnetic magnetic surveys. surveys. This abstract describes the procedures used to reduce and and merge the individual aeroinagnetic surveys surveys to to make make the the Lake Lake Superior Superior aeromagnetic map. aeromagnetic map. Surveys Aeromagnetic Surveys The aeromagnetic aeromagnetic surveys surveys were were flown flown with with flight-line flight—line spacings spacings ranging ranging The surveys surveys were were flown mode from 0.25 0.25 mi mi (0.4 (0.4 3cm) kID) to to 33 mi mi (4.8 (4.8kin). kID). The flown in draped mode (constant (constant elevation above terrain or water) water) at at elevations elevations ranging ranging from from 300 300 ft ft (91.44 to 1000 1000 ft Figure 22 shows shows the the location location of of the the surveys (91.44 in) m) to ft (304.8 (304.8 in). m). Figure compiled to make the Lake Lake Superior Superior aeromagnetic aeromagnetic map. map. Reduction Data Reduction Data set J, 3, for the UP (Upper Data (Upper Peninsula Peninsula Michigan), was was only only available available as as hand—contoured Digital data data were were created created by by digitizing digitizing hand-contoured magnetic magnetic maps. maps. Digital 1:24,000 and 1:62,500 1:62,500 magnetic magnetic maps. maps. For For maps maps with with 0.5 0.5 mi mi (0.8 (0.8kin) km) flight line line spacings, spacings, data were generated by digitizing the intersections of contour lines lines In with flight flight lines. lines. In the case where individual individual surveys surveys were were flown flown at at 0.25 0.25 mi mi (0.4 km), 3cm),every every other other line line was was digitized digitized due due to to the the time time allotted for the (0.4 Part of project and the expected anomaly resolution of the final final product. product. Part survey 3 J was flown flown with flight line line spacings of 1.0 and 3.0 mile (1.6 (1.6 and 4.8 kin). For greater control, kID). control, these more widely spaced data were digitized both at contour intersections along the flight at inflection points of at flight lines and at contours between flight flight lines. lines. Gridding For magnetic the seven sets that up J, 3, the magnetic surveys surveys B, E, F, F, G, G, B, H, and and the seven sets that make make up the total—intensity total-intensity data data were were projected projected to tothe theLambert Lambert conic conic conformal conformal projection projection (standard 42.5°N (standard parallels parallelsofof 42.5ONand and48.5°N 48.5ON and and central central meridian meridian of of88.5°W) 88.5OW) then then gridded gridded at 0.4 km km using using aa computer program program (Webring, (Webring, 1981) 1981) at an interval of 0.4 Surveys A, A, B, B, C, based on on minimum minimum curvature curvature (Briggs, (Briggs, 1974). 1974). Surveys C, D, D, and II were were and were reprojected and and regridded regridded to to the the above above acquired in grid form and projection and and grid grid interval interval specifications. specifications. The digital surveys surveys (A, (A, B, B, C, C, H) H) at aa 0.25 flown at 0.25 mile mile (0.4 (0.4kin) kID) spacing spacing were gridded at at aa finer finer interval interval of of 0.2 0.2 km (0.125 0.4 km and then regridded to 0.4 (0.125 mile) mile) to to honor honor the the data data more more closely closely and km (0.25 mile) and BB were were used used to (0.25 mile) for for the the final final merge. merge. Surveys A A and to minimize minimize edge edge effects along 83GW longitude, and and therefore therefore were were not not used used in their entirety. effects 830W longitude, entirety. Reference Field Field Removal Removal The geomagnetic reference fields calculated for the date and location location of the individual individual surveys surveys were subtracted subtracted from from the the total—intensity total-intensity grids grids to to produce the the residual residual total—intensity total-intensity grids. grids. The particular geomagnetic geomagnetic reference field field removed removed depended depended on on the the year year in in which aa given given survey survey was was flown flown International Geomagnetic Geomagnetic Reference Reference Field Field and consisted of the definitive International (sweeney, (Sweeney, 1990) 1990) or or in in the the case case of of the the Minnesota Minnesota Survey Survey C, C, the the American American World World Chart (AWC) (AWC) Regional Regional reference reference field field (Peddie, (peddie, 1976). 1976·). consisted of the definitive Merging Merqjii data sets, magnetic field values of of each survey grid were were Before merging data sets, magnetic field values adjusted by aa constant amount amount using survey D D as an absolute datum, datum, to to minimize Theoriginal original observation surfaces of discontinuities at merge boundaries. boundaries. The observation surfaces of the at merge been maintained maintainedwhich whichmay may alsoaccount accountforforslight slight discrepancies discrepancies at data have have been also at merge boundaries. 22 22 �two grid grid Data set J J was created created from from seven seven separate grids by removing two the gap using using the the cells from the edges of each and assigning assigning values across across the one—dimensional splining and others others one-dimensional splining techniques described by Bhattacharyya and merged by by (1979). The major surveys surveys denoted on the index map were then merged one and and two two grid grid cells cells respectively, respectively, from from the borders of survey E and removing one the remaining remaining sets. sets. The resultant grids grids were were combined combined leaving leaving data data gaps gaps gaps were then assigned data values within the final final composite composite grid. grid. These gaps using the computer computer program program MEGAPLUG MEGAPLUG (Phillips (Phillips and and others, others, 1993), 1993), by the same minimum curvature curvature technique technique used used by by Briggs Briggs (1974) (1974) and Webring (1981) (1981) when gridding. Data were then then removed removed from from areas areas where where no no reasonably reasonably compatible compatible Some margin surveys exists (white (white areas areas in in the the southwest southwest part part of of figure figure 1). 1). Some areas along along latitude latitude 46°N 46~ contain data created by the process, process, but due due to to their minimal impact, impact, they they have have been been retained. retained. of 0.4 0.4 km km (0.25 mi) and and The final final compiled data set has a a grid spacing of (0.25 mi) is projected using aa Lambert conformal parallels of of conformal conic conic projection (standard (standard parallels 42.5°N and 48.5°N, central meridian of 42.5~ and 48.5~, central of 88.5°W, S8.5OW, and base latitude latitude of of 46°). 46°). The of Interior, EROS gridded magnetic data are are available available from from the U.S. u.S. Department of Interior, EROS Data 1990), or or from NOAA (Hittelman Data Center Center (I(ucks, (Kucks, 1990), (Hittelman and and others, others, 1992). 1992). The above grid using the the color aeromagnetic map (figure (figure 1) 1) was produced from the above program GDRELIEF (unpublished (unpublished USGS USGS program, program, information information available from from the author). References Ehattacharyya, Bhattacharyya, B.K., B.K., Sweeney, Sweeney, R.E., R.E., and and Godson, Godson, R.H., R.H., 1979, 1979, Integration of times with with varying varying elevation elevation and and aeromagnetic data acquired at different different times line spacing: spacing: Geophysics, v.44, v.44, no. no. 4, 4, pp. pp. 742—757. 742-757. Briggs, I.C., 1974, 1974, Machine Machine contouring contouring using using minimum minimum curvature: curvature: Geophysics, Geophysics, Briggs, I.C., V.39, no. no. 1, 1, p.39-48. p.39—48. Hittelman, Buhmann, R.W., R.W., Racey, Racey, S.D., S.D., and and Chandler, Chandler, V.W., V.W., 1992, 1992, Hittelman, A.M., Buhmann, Minnesota Region Region CD-ROM, CD-ROM, Aeromagnetics Aeromagnetics Earth Earth System System Data, Data, DOS DOS Release, Release, September 1992: 1992: U.S. U.S. Department Department of of Commerce, Commerce, National National Oceanic Oceanic and and Atmospheric Administration, Administration, National National Geophysical Geophysical Data Data Center, Center, Boulder, Boulder, CO. 80303 CO. 80303 Kucks, Kucks, R.P., R.P., 1990, 1990, Description Description of of magnetic magnetic tape tape containing containing Lake Lake Superior Superior region magnetic anomaly data, data, United States and Canada: Canada: U.S. U.S. Department Department of Interior, EROS EROS Data Data Center, Center, Mundt Mundt Federal Federal Building, Building, Sioux Sioux Falls, Falls, South Dakota, 57198. 57198. [phone: [phone: 605-594—6976] 605-594-6976] Peddie, N.W., N.W., and and Fabiano, Fabiano, E.B., E.B., 1976, 1976, Model Model of the the Geomagnetic Field for for Peddie, 1975: Journal of 1975: of Geophysical Research, Research, V. V. 81, 81, pp. pp. 2539—2542. 2539-2542. Phillips, J.D. Duval, Duval, J.S., J.S., and and Ambroziak, Ambroziak, R.A., R.A., 1993, 1993, National geophysical Phillips, J.D. data grids-—gamma—ray, grids--gamma-ray, gravity, gravity, magnetic, magnetic, and topographic data for the States: U.S. U.S. Geological Survey Digital Data Series conterminous United States: DDS-9, DDS—9, 11 CD—ROM CD-ROM disk. disk. [includes [includes potential-field potential-field software software version version 2.1] 2.1] Sweeney, R.E., R.E., 1990, 1990, IGRFGRID, IGRFGRID, AA program program for for creation creation of of aa total total magnetic Sweeney, field (International (International Geomagnetic Reference Field) Field) grid representing the Earth's main magnetic field: field: U.S. U.S. Geological Survey Open-File Report Report 9045a, 37 45a, 37 p. p. Webring, M.W., M.W., 1981, 1981, MINC: MINC: AA griddirig gridding program based based on on minimum minimum curvature: curvature: U.S. U.S. Geological Survey Survey Open—file Open-file Report Report 81—1224, 81-1224, 41 41 p. p. 23 23 �AEROMAGNETIC AEROMAGNETIC SURVEY SURVEY REFERENCES REFERENCES Survey A A Bracken, Bracken, R.E., R.E., and Godson, Godson, R.H., R.H., 1987, 1987, Aeromagnetic Aeromagnetic map map of 0 x 2° International. Falls Falls 110 Quadrangle, Minnesota and International x 20 Quadrangle, and U.S. U.S. Geological Geological Survey Survey Open—File Open-File Report Report 87—620, 87-620, scale scale the Ontario: Ontario: 1:250,000. 1:250,000. B B Bracken, R.E., and and Godson, Godson, R.H., LH., 1988, Bracken, R.E., 1988, Aeromagnetic Aeromagnetic map map of of the the northwestern part part of of the the Ribbing Hibbing 10 10 xx 20 20 Quadrangle, Quadrangle, Minnesota: Minnesota: U.S. U.S. Geological Geological Survey Survey Open—File Open-File Report Report 88—0008, 88-0008, scale scale 1:62,500. 1:62,500. C. C Chandler, V.W., V.W., 1983, 1983, Aeromagnetic map map of of Minnesota: Minnesota: Total magnetic magnetic Chandler, intensity anomaly, anomaly, Cook and Lake Lake Counties: Counties: Minnesota Geological Geological Survey Map A—I, A-I, 22 sheets, sheets, scale scale 1:250,000. 1:250,000. C C Chandler, V.W., V.W., 1983, 1983, Aeromagnetic map map of of Minnesota: Minnesota: Total magnetic magnetic Chandler, intensity anomaly, St. County: Minnesota Geological Survey Survey St. Louis County: Map A—2, A-2, 22 sheets, sheets, scale scale 1:250,000. 1:250,000. C C Chandler, V.W., 1983, 1983, Aeromagnetic map map of of Minnesota: Minnesota: Total magnetic magnetic Chandler, V.W., intensity and Pine Pine Counties: Counties: Minnesota intensity anomaly, anomaly, Carlton Canton and Survey Map Map A—3, A-3, 22 sheets, sheets, scale scale 1:250,000. 1:250,000. Geological Survey C C Chandler, V.W., 1983, 1983, Aeromagnetic map map of of Minnesota: Minnesota: Total magnetic Chandler, V.W., intensity anomaly, anomaly, east—central east-central region: region: Minnesota Geological Geological Survey Map A—4, A-4, 2 sheets, sheets, scale scale 1,250,000. 1,250,000. D D Geological Survey of Canada, Geological Canada, 1977, 1977, Magnetic Magnetic anomaly anomaly map map of of Canada: Canada: Geological Geological Survey of of Canada Map 1255A, 1255A, scale scale 1:5,000,000. 1:5,000,000. E E Geological Canada, 1988, 1988, Aeromagnetic Aeromagnetic survey survey of of Lake Lake Geological Survey of Canada, Superior, data. Superior, unpublished data. F F U.S. Geological Survey, Survey, 1979, 1979, Aeromagnetic Aeromagnetic map map of of Sault Sault Sainte Sainte Marie Marie U.S. and vicinity, Michigan: Michigan: U.S. Survey Open—File Open-File Report Report U.S. Geological Survey 79—833, scale 1:250,000. 79-833, 1:250,000. C G U.S. Survey, 1980, 1980, Aeromagnetic Aeromagnetic map map of of the the Manistique Manistique Lakes Lakes U.S. Geological Survey, area, U.S. Geological Survey area, Michigan: U.S. Survey Open—File Open-File Report Report 80—830, 80-830, 44 sheets, scale scale 1:62,500. 1:62,500. H H u.S. Geological Survey, Survey, 1988, 1988, Aeromagnetic Aeromagnetic survey of of Northwestern Northwestern U.S. Wisconsin, data. Wisconsin, unpublished data. I I Wisconsin Geological Geological and Natural Natural History Survey, Survey, 1983, 1983, Aeromagnetic Aeromagnetic map map of northern Wisconsin: of Wisconsin: Wisconsin Geological Geological and and Natural Natural History History 83-4,scale 1:250,000. Survey Map 83—4, scale 1:250,000. JJ Zietz, and Kirby, Aeromagnetic map map of of the northern Zietz, I., I., and Kirby, J.R., J.R., 1971, 1971, Aeromagnetic the northern peninsula, Michigan and and part part of of northern northern Wisconsin: Wisconsin: Geophysical peninsula, Investigations GP-750, scale 1:250,000. 1:250,000. Investigations Map Map GP—750, 24 �490 490 •5•sS..•••.• .5. f...•s... , w. . . . . . . S • • • S • • *.f*.SS.S.S.S.S..S. A S•.lr• . . . . 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VV5-5 46° __ -_,_, S •___ 930 93° 840 LINE SPACING 1I1E SPACING fW4~ ,?::~:~~, .5 PIlLEOR OR LESS LESS • 5MILE E3 f:::~1-1.2 1-1.2lilIES ftlLES m 2 MILES 'ULES ~ :33 MILES 'ULES ~ MILES OR 6 'ULES OR GREATER GREATER Lake Superior Aeromagnetic Survey Index Figure 2. Index map map showing showing the the location Figure 2. Index location of of individual individual surveys, surveys, flight line spacing, spacing, year(s) year(s) flown, flown, flight flight altitude in thousands thousands of altitude in of feet feet above above ground ground (.SAG (.sAG = 500 feet above ground), and data feet above ground), and data format (D format (0 = = digital). digital). �This page intentionally left blank �Glimp c e/Lake Sl.-lperior Superior Magnetics Glimpce-/Lake -92° —p2° -90° —90° -88° —88° 5fJ0 50° -86° —86° -84° —84° 500 50° 1000.0 900.0 800.0 490 49° I l ' ,. 48° I '., .i:.¥.• ,~.~~~ ;r.,,-",·,~.iii-:.t:~ 470 47° 14. , "_ .~~. :. ' . -.' ",,_ j -- - .' ;~. ~ ~. ~~ ~<~=~. . --- ;.'- ~ ...... JJ11"f3.."• ~: ~~,5;·;·>,.~ "/~___ ,. ~ .'.'1:. ,~~~~~~".:~~ '~',,",:,:~-:~.~.- I 490 49° . -4 I 48° '" '"~ .~~.'--a I . . . ~.T_ _ _ _ "" 46° 47° 47° 46° -92° -88 0 -90° o 0 -86 0 ca1e scale 100 II 200 kilometers I _ L L _ Li . L J I I I I I I I I I I I I I I I I - . J U i F4gure F~gufe 1. 10 I Kucks and and Horton KllCks Honon -84 0 I 700.0 600;0 1600;0 500.0 400.0 300.0 200.0 i10o.0 100.0 i :o.o i 0.0 —100.0 100 . 0 ! -200.0 !200.0 i -300.0 —300.0 -400.0 —400.0 -500.0 —500.0 —600M ~I ~ -600.0 -70.0.0 —700.0 ~800.0 —800.0 -900.0 —900.0 1- �This page intentionally left blank �LATE LATE HOLOCENE LAKE LAKE SUPERIOR SUPERIOR -- ISOSTATIC AND CLIMATIC CLIMATIC LAKELAKEE., U. S. S. Geological Geological Survey, Reston, Reston, VA VA LEVEL LARSEN, Curtis E., LEVEL CHANGE. CHANGE. LARSEN, 22092 Beach-ridge complexes complexes along along the the south shore of Lake Superior record Beach-ridge record a composite from 5,000 5,000 B.P. B.P.toto the the present that composite history history of lake-level lake-level change change from that includes includes the effects effects of past past climatic climatic episodes episodes superimposed superimposed on on differential differential pattern of of isostatic isostatic uplift plays plays aa dominant dominant role role basin. The The pattern isostatic uplift of the basin. reconstructing past past lake-level lake-level changes changes from from coastal landforms. in reconstructing For Lake Superior, uplift uplift increases with distance distance northeastward from from For Lake Superior, increases with Duluth, Minnesota, Ontario. Isobases Minnesota, to to Michipicoten, Michipicoten, Ontario. Isobases of equal movement trend trend northwest to to southeast southeast across across the basin. The The outlet outlet to to the the basin basin at at Sault Sault Ste. Ste. from northwest Marie is rising at an apparent apparent constant constant rate rate of of 0.27 0.27 meter per century relative relative to to Duluth. Michipicoten, rising at at about about 0.5 0.5 meter per century relative relative to to Michipicoten, Ontario, Ontario, isis rising Duluth. The throughthe theoutlet outletchannel, channel, however, however, controls controls the the mean mean The flow flow rate rate through level of of the the lake. level lake. For For modern modern Lake Lake Superior, Superior, the outlet is rising more rapidly U. S. shore of the lake. mean level level than the U. lake. Such differential movement raises the mean at Duluth meter per per century. century. Along Duluth and and submerges submerges that that area area at at aa rate rate of of 0.27 0.27 meter Along the the Canadian shore, shore, uplift exceeds that at at the Canadian exceeds that the outlet so that the the mean mean level level falls falls relative to the outlet. This pattern of of submergence submergence of the southern shore shore and and relative This pattern emergence of the northern shore is is a relatively recent event linked to the uplift of the St. Mary's Rivers rapids rapids above above the the surface surface of of Lake Lake Huron Huronatatabout about2,100 2,100 B.P. B.P. Between 5,000 5,000and and 2,100 2,100years yearsago, ago, Lake LakeSuperior Superiorwas was part part of the Between the Algoma phases of the upper Great Lakes. Nipissing and Algoma Lakes. A confluent lake linked linked the three basins at Sault Sault Ste. Ste. Marie. Marie. The The mean mean level level of of the the lake lake was was controlled controlled basins at mainly by the outlet to Lake Huron at Port Huron, Michigan. Michigan. Coastal landforms from Nipissing and and Algoma Algoma phases phases are are common common to to all all three three lake lake basins. basins. from the Nipissing These landforms landforms have have been been uplifted to the controlling outlet at Port These uplifted relative relative to controlling outlet Port Huron and Huron and correlate correlate directly directly between between Lake Lake Huron Huron and and Lake Lake Superior Superior near near Sault Sault Ste. Following the the separation separation of of Lake Lake Superior lakes at Ste. Marie. Marie. Following Superior from from the the lower lower lakes of lake-level lake-level change change developed. developed. Beach-ridge 2,100 B.P., 2,100 B.P., aa different different record of complexes near Sault Ste. Marie Marie and along the Canadian Canadian shore shore of of Lake Lake Superior Superior Lake Huron Huron have have been been raised raised above above the the control control of of their their controlling controlling outlets; outlets; and Lake preserve aa subaerial subaeriallake-level lake-level record recordfrom from5,000 5,000 B.P. B.P. to present. these complexes preserve 2,100 B.P. After 2,100 B.P.Lake LakeSuperior Superiorhas hasits itsown ownunique unique lake-level lake-levelrecord. record. Uplift of the St. Mary's River relative to Duluth has caused aa progressive progressive submergence submergence of of the the St. coast as the outlet outlet has has risen. risen. 29 �Near Duluth and and the the Apostle Apostle Islands, Islands, much much of of the the coastal Near Duluth geomorphological record At least least 5.8 5.8 m m of of submergence submergence has has geomorphological record isis submerged. submerged. At occurred at Duluth Duluth and andabout about4.4 4.4 m m at atthe theApostle Apostle Islands Islands since since uplift upliftof of the the St. St. Mary's rapids B.P. The Nipissing rapids became became the the sole sole control control of of Lake Lake Superior Superior 2,100 2/100 B.P. level of the confluent Great Lakes is indicated by by a raised coastal beach and Lakes that is dune dune complex complex at at an an elevation elevation about about13 13 m m above above the the surface surface of Lake Superior near near Sault Ste. Ste. Marie Marie isis preserved as an apparent Sault preserved as apparent inner inner barrier barrier island island system system preserved in in marshes marshes atatBark Bark Bay Bay and and Big Big Bay Bay State preserved State Park, Park, Wisconsin, Wisconsin, and and most noticeably as an inner noticeably as inner bar bar system system bordering bordering Duluth Duluth harbor harbor at at Superior, Superior, Wisconsin, these bays bays and and the outer Wisconsin. Prominent Prominent beaches beaches at the lakeward edges of these barrier island island at at Duluth Duluthrepresent representthe theprobable probableposition positionofofthe theAlgoma Algomabeach beach(Ca. (ca. 3,500 B.P.). B.P.). This This landform landform has has continued to build vertically as the mean level of 3/500 Lake Superior has risen. studies of of beachbeachLake Superior risen. The The record record is is complex, complex, but detailed studies ridge complexes complexes and and marshes marshes (such (such as as Bark Bark Bay) Bay) indicate steadily rising rising water water levels in this part part of of Lake Lake Superior controlled controlled by uplift uplift of of the the outlet outlet at at Sault Sault Ste. Ste. Marie. by drowned drowned in Marie. Recent Recent submergence submergence is also evidenced evidenced by in situ situ trees near Ashland, Wisconsin, and in in Duluth Duluth harbor. harbor. Our studies suggest Wisconsin, and suggest that that the the rate rate of of uplift at Sault Ste. Ste. Marie has remained constant constant for for at at least least the the past past4,000 4,000 years. years. The long-term prognosis for western Lake Superior Superior is is aa continued rise in mean mean lake level, level, upon upon which which may may be be superimposed superimposed both both higher higher and and lower lower lake lake level level lake episodes episodes related related to to climate climate changes. changes. The range of past in Lake Superior is past climate-related climate-related fluctuations fluctuations in Lake Superior is also The significant. From significant. From an an historical historical perspective, perspective, the range range of of Lake Lake Superior levels levels from 1860 1860 to 1.2 m to present present is 1.2 m or or ca. ca. ±±0.6 0.6mmabout aboutthe themean. mean. The earliest historical accounts from from the 1830's suggest a range of 2.4 accounts 1830's and 40's 40's suggest 2.4 m (± (± 1.2 1.2 m) m) prior to to Our most most recent recent research results from from submerged submerged construction of the Soo locks. locks. Our spit at at Ashland, Ashland, deposits at atBay Bay Mills, Mills, Michigan, and the active Long Island spit spit deposits Wisconsin, indicate 1.5 m lower than than present presentabout aboutAD AD1400 1400 indicate that that lake lake levels levels were were 1.5 m higher higher during the early during the the 'Medieval 'Medieval Warm Phase' and about 11 - 1.2 m 1700's. The range of premodern lake level appears to to have 1700's. level appears have been on order of of double the range of of modern modern levels. levels. 30 �AGE AND GEOLOGICAL SIGNIFICANCE OF OF THE BARABOO BARABOO QUARTZITE QUARTZITE MEDARIS, L.G., Jr., DOTT, RH., R.H.,Jr.; JI.;FOHRNTELLE, FOURNELLE, JH., J.H., JOHNSON, JOHNSON, C.M., SCHOTT, RC., R.C.,and andBAUMGARTNER., BAUMGARTNER, L.P., L.P., Department Department of ofGeology Geology & &Geophysics, Geophysics, University ofWisconsin-Madison, of Wisconsin-Madison, Madison, Madison, WI, WI, 53706 University Post-Penokean mature red quartzites in the southern Lake Superior region (Baraboo, Barron, and Sioux Sioux Quartzites) Quartzites) provide provide important important evidence evidence on on Proterozoic Proterozoic cratonic cratonic evolution. evolution. The Baraboo Quartzite has been re-examined to resolve resolve the the question question of ofits its age, age, identify identify its its mineralogy, mineralogy, determine conditions determine conditions of weathering weathering in in the the source rocks and subsequent metamorphism, metamorphism, and and regime in which the mature red quartzites were formed. formed. evaluate the mid-Proterozoic tectonic regime Age ofthe of the Baraboo Baraboo Quartzite: Quartzite: the the Baraboo BarabooQuartzite Quartziteisisunconformable unconformable on on rhyolite rhyolite (Daiziel (Dalziel & Dott, 1970; 1970; Dott, 1983), 1983), but but was was previously previously thought to be be intruded intruded by the Baxter Hollow & granite (Gates, 1942). Both Bothrhyolite rhyoliteand and granite granite were were interpreted interpreted to to be be correlative correlative with with 1760 1760 Ma Ma (Gates, 1942). rhyolite and granite elsewhere in Wisconsin, Wisconsin, and this this interpretation has been confirmed by U-Pb U-Pb of 1754±44 l754±44 Ma Ma for for rhyolite rhyolite from from the the north north limb limb of ofthe the Baraboo Baraboo syncline syncline and and 1752±15 l752±15 zircon ages of Thus, aa geological geological paradox paradox arises: arises: how Ma for the Baxter Hollow granite (Van (Van Wyck, Wyck, 1995). 1995). Thus, could a mature quartz feldspar, be closely associated in space quartz arenite, arenite, which which is is virtually virtually devoid of offeldspar, and time with granite-rhyolite magmatism? magmatism? The quartzite-granite contact has been re-examined in Baxter Hollow, and in cores from eight drill drill holes holes that that penetrated the quartzite-granite contact, which were obtained obtained by the U.S. Army Corps of of Engineers in in 1959. 1959. There There isis no no evidence evidence in in the the field, field, or in any of of the drill cores, that quartzite was intruded by granite. Shearing Shearinghas hasdeveloped developednear nearthe thecontact, contact,especially especiallyin in granite, which has been transformed locally to illite-quartz illite-quartz semi-schist. semi-schist. Among the drill drill holes holes that that penetrated the quartzite-granite contact, material Among material from the contact interval was was recovered recovered only only in in Hole Hole No. No. 613, 613, where where there there is is aa two-foot two-foot thick, reddish-purple zone interval fine-grained hematite, hematite, quartz, illite, and kaolinite, kaolinite, which which appears appears to to be a regolith, between of fine-grained illite, and overlying Pebbles in in the quartzite quartzite consist consist mostly mostly overlying pebbly pebbly quartzite quartzite and and underlying, underlying, ahered altered granite. granite. Pebbles of quartz, quartz, although although a few few pebbles pebbles of of red, red, altered altered rhyolite rhyoliteoccur. occur. We conclude that the Baraboo Quartzite is unconformable on the Baxter Hollow granite, and and that that shearing shearing was was localized localized along along the contact between these two two competent competent rock rocktypes typesduring during later later folding. folding. The two-foot interval interval between quartzite and and granite granite may represent a paleosol, which was derived from weathering of ofthe underlying granite and and modified modified by subsequent subsequent shearing shearing and and the underlying metamorphism, In addition, addition, metamorphism,,and·a anda chemical chemical investigation investigation isis in inprogress progress to to test test this hypothesis. hypothesis. In detrital zircons, some of of which are euhedral, have been separated from the quartzite quartzite and and are are being being analyzed any were derived derived from 1760 1760 granite-rhyolite granite-rhyolite sources. sources. analyzed to to test whether any Mineralogy: Minera1o: sheet sheetsilicates silicatesininthe theBaraboo BarabooQuartzite Quartziteare aredominated dominatedby bypyrophyffite, pyrophyllite, A14Si5O20(OH)4,and andkaolinite, kaolinite, Al A14Si4O10(OH)8, whichoccUr occurinterstitially interstitially in in quartzite quartzite and in Al4Sig0ZO(OH)4' in 4Si40lQ(OH)g, which K15A14[Si65A115O20](OH)4, and and occurs interstitially pyrophyllite-rich layers. K-mica K-micaisisilhite, illite, - K1.5Al4[Si6.5Al1.50zoJ(OH)4' in alteration product product of offeldspar feldspar in in granite. granite. in quartzite, in the regolith(?) in Hole 613, and as the alteration Diaspore, a-AlO(OH), a-A1O(OH), was discovered in in quartzite quartzite in in Holes Holes 613 613 and and 6l4A, 6l4A, where where itit is is associated associated Diaspore, with pyrophyllite, Thepresence presenceof ofsuch suchaluminous aluminous minerals minerals in the Baraboo pyrophyllite, kaolinite, kaolinite, and and illite. jute, The Quartzite indicates derivation from from maturely maturely weathered weathered soil, soil, such such as aslaterite, laterite,and andsignifies signifies aa mid-Proterozoic episode ofintense intense chemical chemical weathering weathering and and leaching leaching of ofalkalies. alkalies. episode of 31 �common assemblage, assemblage, Metamorphism: the common quartz+pyrophyllite+kaolinrte±illite,linritsthe quartz±pyrophyffite+kaolinite+illite, limits the H20 temperature of metamorphism to less than 280°C at an of less ~ 280~ tillite v assumed P(~O) P(H20) of of 500 bars. bars. However, assumed However, kaolinite kaolinite occurs as micron-scale interlayers in pyrophyllite, pyrophyllite, and and if kaolinite isis aa retrograde retrograde mineral, ifkaolinite mineral, rather than temperatures could could have have been been as as high high as as prograde, temperatures 3 50°C,which which isis the the stability linrit limit ofpyrophyllite. of pyrophyllite. 350°C, in the the Baraboo Quartzite is always separated Diaspore in from quartz by pyrophyffite, pyrophyllite, and may represent relict grains, which were derived from a lateritic detrital grains, source, and which were protected by by surrounding Qtz ern And Cm pyrophyffite from complete complete reaction reaction with quartz pyrophyllite from during metamorphism. metamorphism Geological Significance of ofthe the Baraboo Baraboo Interval: Interval: the the Baraboo Baraboo interval interval was was defined defined by Dott (1983) as as aa sequence sequence of ofsedimentation, sedimentation, deformation, deformation, and andmetamorphism metamorphismin in the the time time span span of of1450 1450 to 1750 region. Deposition 1750 Ma in the southern Lake Superior region. Deposition of of the Baraboo, Barron, and Sioux quartzites was was thought to have occurred after 1750 quartzites 1750 Ma, but prior to 1650 1650 Ma, Ma, which which was a time of Rb-Sr isotopic re-setting in Wisconsin Wisconsin and and perhaps perhaps folding folding of of the the Baraboo Baraboo Quartzite Quartzite (Van (Van Schmus, 1980). 1980). Now that the post-1760 post-1760 Ma Ma age age of ofthe theBaraboo BarabooQuartzite Quartzitehas hasbeen beenfirmly firmly established, established, based based on the new evidence from drill core 613, the deposition deposition of ofred, red, mature, mature, fluvial fluvial quartz quartz arenites, arenites, which are regionally regionally extensive extensive and and up up to to 2,000 2,000 meters thick, thick, can be viewed viewed as as the result result of cratonic cooling and subsidence, following following the cessation of of 1760 Ma granite-rhyolite magniatism. magmatism The time of the Baraboo Quartzite of folding and metamorphism of ofthe Quartzite is is still still unclear; it could could have have been at 1650 1650 Ma, Ma, but but recently recently obtained obtained isotopic isotopic evidence evidence indicates indicates the the existence existence of ofaametamorphic metamorphic event at at -1720 —1720Ma Maininthe thesouthern southernLake LakeSuperior Superiorregion region(Van (VanWyck, Wyck,1995). 1995). Thus, Thus, the event Baraboo-Barron-Sioux triad triad could could have have been deposited in either of ofthe 1760-1720 Ma, Baraboo-Barron-Sioux the intervals, 1760-1720 or 1720-1650 Ma. Ma. In either case, ample time, on the order of 40 or 70 Ma, would In either case, ample time, on the order of 40 or 70 Ma, would have have been been available available for for development development of mature mature quartz sandstones, especially in in response to lateritic aluminous minerals weathering, as indicated by aluniinous minerals in in the the Baraboo Quartzite. The Baraboo interval is a valid and useflul useful concept conceptfor for interpreting interpreting the the mid-Proterozoic mid-Proterozoic evolution of of the the Lake Lake Superior Superior region, region, but but itit applies applies only onlytotopost-1760 post-1760 Ma Ma quartzites. quartzites. Treating all evolution Proterozoic quartzites quartzites in in Wisconsin Wisconsin as correlative leads to serious misinterpretations of of the Baraboo Quartzite, in in particular, and and of ofthe Proterozoic Proterozoic evolution evolution of ofthe the Lake Lake Superior Superiorregion, region, in in generaL general. REFERENCES CiTED REFERENCES CITED Dalziel, I.W.D. and Dott,R.R, RJ{, Jr. (1970) Wis. Wis. Geol Nat. Hist. DalzieL LW.D. and Dott, Rist. Sun'. Surv. Inf Inf Circ. Circ. 14, 14, 164 164 p. p. Dott, RH., 1. R.H.,Jr. Jr.(1983) (1983)GeoL Geol.Soc. Soc.Amer. Amer.Memoir Memoir160, 160,129-14 129-141. Amer. Mineral., Mineral., v. 27, Gates, R.M. (1942) Amer. 27, 699-711. 699-711. Schmus, W.R. Soc. Amer. Amer. Special Special Paper 18, Van Sckmus, W.R. (1980) Geol. Soc. 18, 159-168. 159-168. Van Wyck, Wyck, N. N. (1995) Ph.D. thesis, UW-Madison, OW-Madison, 280 p. p. <28O 32 �THE LATENT MAGMATIC STAGE OF THE MIDCONTINENT MIDCONTINENT RIFT: A PERIOD OF MELTING OF THE LOWER CRUST MAGMATIC UNDERPLATING AND AND MELTING MILLER: J.D., Jr., Minnesota Minnesota Geological Geological Survey, Survey, 2642 2642 University University Ave., Ave., St. St. Paul, Paul, MN MN 55112 55112 MILLER, (mi1le066@maroon.tc.umn.edu) andVERVOORT, VERVOORT,J.D., J.D.,Dept. Dept.ofofGeosciences, Geosciences,University University of of (mille066@maroon.tc.umn.edu) and Arizona, Tuscon, Tuscon, AZ AZ85721 85721(vervoort@geo.arizona.edu) (vervoort@ geo.arizona.edu) Field studies, seismic and and gravity gravity data, data, U-Pb U-Pb zircon zircon dating, dating, and and geochemical geochemical studies studies of of intrusive rock rock suites suites around around the the Lake Lake Superior Superior basin basin show show that that the the Midcontinent Midcontinent rift rift volcanic and intrusive Most (MCR) evolved in several distinct magmatic stages stages between between 1109 1109 and and 1086 1086 Ma Ma (1-4). (1-4). Most recently, a period of of substantially reduced reduced volcanism volcanism and and aa shift to to more more intermediate intermediate to to felsic felsic has been been identified identified between between 1107 1107 and and 1100 1100 Ma—an Ma-an interval interval we we refer refer to to as as magma compositions has 1). Overall, Overall, MCR MCRmagmatism magmatism resulted resulted from from an an anomalously anomalously hot the latent magmatic stage stage (Fig. (Fig. 1). mantle plume emplaced at at the the base base of of the the lithosphere lithosphere at at about about 1109 1109 Ma Ma (5). (5). The most obvious magmatism is is the the large large volume volume (over (over 22 million million km3) km 3) of mostly basaltic volcanic aspect of this magmatism rock that accumulated in of up up to 20 20 km km (1). (1). Less Lessobvious,. obvious, in the the central central rift rift graben graben to to thicknesses thicknesses of but equally significant is is aa comparable comparable volume volume of of mafic mafic magma magma that that intruded intruded and and underplated underplated the the (6,7). We crust beneath the Lake Superior region (6,7). We present present evidence evidence here here that that suggests suggests a not aa causal causal relationship relationship between between the the latent latent magmatic magmatic stage, stage, magmatic magmatic contemporaneous ifif not underplating, and lower lower crustal melting. melting. The first hint of of aa latent latent magmatic magmatic stage stage was was recognition recognition of of aa hiatus hiatus in in mafic mafic intrusive intrusive activity activity 1107 Ma and 1099 Ma (8). More recent recent U-Pb U-Pb dating dating of of the the in the Duluth Complex between 1107 (8). More Group (9) (9) and and the the Powder Powder Mill Mill Group Group (10) (10) has has revealed revealed aa decrease decrease in in North Shore Volcanic Group Volcanic rocks rocks occuring occuring within within and and adjacent adjacent to both both volcanic activity over this same period. Volcanic these low production intervals intervals are are mixed mixed rhyolite, rhyolite, andesite, andesite, and and evolved basalt (4, (4, 11). 11). Insufficient dating has has been been conducted conducted to to determine determine if if aa similar similar decrease decrease in in basaltic basaltic volcanism volcanism is is However, itit is is noteworthy noteworthy that that the the present in the Osler and Mamainse Point volcanics volcanics suites. suites. However, and. central 12), yields an Agate Point rhyolite, which separates the upper and, centralsuite suiteof of Osler OslerGroup.( Group.(l2), l105±2 Ma (9). At Mamainse Mamainse Point, Point, abundant abundant felsic flows and intrusions have been age age of 1105±2 (9). At mapped below the 420-rn-thick, 420-m-thick, polymict Great Conglomerate (13), which presumably signifies volcanic activity. activity. Further Further evidence evidence that that felsic volcanism predominated a prolonged hiatus of volcanic during an overall diminution of volcanic activity comes from the preponderance of rhyolite clasts in the Copper Harbor Conglomerate and their age of 1104±2 1104±2 Ma (14). We propose that the latent magmatic stage represents a period of reduced extension coupled underplating and and melting melting of of the the lower lower crust. crust. If the rate and intensity of with extensive magmatic underplating extension in the MCR was largely controlled by external stresses imparted by contemporaneous Grenvillian tectonism (15), then then ponding of magmas at the crust-mantle interface was likely a passive response to decreased tensile (or perhaps compressive) stresses in the lithosphere. However, to the extent that lithospheric thinning and extension was driven by the bouyancy and thermal energy of the mantle mantle plume (16), then perhaps magma underplating actually caused diminished extension of of the the crust crust by by delam.inating delaminating and structurally decoupling it from the lithospheric mantle. In In either eithercase, case, underplating underplating was was probably probably instigated instigated by the heating and of the earliest mantle-derived magmas coupled anatexis of the lower crust caused by the passage of The creation creation of of felsic felsic melts melts and and an increasingly ductile with heating from the rising plume. The lower crust would have created density density and and rheologic barriers to impede the passage of mafic melts and promote their ponding (17). Once magma chambers would have Once initiated, initiated, mafic mafic magma continued to expand as as additional additional rising mantle mantle melts melts became trapped and triggered more more At the the peak peak of of the the latent latent stage, stage, the lower crust may have widespread melting of the lower crust. crust. At magmas. Although Although the the resumption resumption of volcanic activity at been largely impermeable to mafic magmas. about 1102-1100 Ma (earlier near the axis of the rift) may have been externally triggered by of the the crust, crust, itit seems seems also also possible possible that that density cleansing of the lower crust increased extension of caused by the upward migration of low density felsic melts and perhaps thinning of the ductile lower crust concomitant with magma underplating may have played important roles in allowing basaltic magmas to emerge from deep crustal magma chambers. 33 �The formation fonnation of of large large magma magma chambers chambers in in the the lower lower crust crust helps helps explain explain many of of the the lithologic, and geochemical characteristics characteristics that that are are generally generally common to all volcanic suites formed during the latent fonned latent magmatic magmatic stage stage as as well well as as magmatism magmatism leading leading up to and following itit (Fig. 1). Some Some of ofthe the more more cogent cogent features features are: are: (Fig. • Felsic magmatism—The magmatism-The bulk bulk and and isotopic isotopic composition composition of of rhyolite rhyolite flows flows and and their their greater greater abundance relative to to flows flows of of intermediate intennediate composition composition indicates indicates that that many many if if not not most most were were generated from partial melting melting of of crustal crustal sources sources rather rather than than as as differentiates differentiates of of mafic mafic magmas magmas (18, 19). The The greater greaterconcentration concentration of offelsic felsic lavas lavas in in stratigraphic stratigraphic intervals intervals straddling straddling the the latent latent stage (Fig. 1) 1) is consistent with with itit being being aa period period of of lower lower crustal melting melting coupled coupled with with diminished diminished basaltic volcanism. volcanism. However, basaltic However, the the moderately moderately negative ENd(1100) Nd(1100) (--4) (—-4)ofoffelsic felsiclavas lavas in in the the lower part of the NSVG (Fig. 1) 1) is is difficult difficult to to explain explain by by melting melting of of Archean Archean lower lower crust, crust, which which should should have £Nd(1 100) = -12 to -17 (18,19). (18,19). Although have cNd(lIOO) Although this this may may indicate indicate mixing mixing of of Keweenawan Keweenawan felsic differentiates with Archean crustal melts melts (19), (19), an an intriguing intriguing alternative alternative explanation is is that that the the lower crust (ENd(1100) -12). The crust isis composed composedofofEarly EarlyProterozoic Proterozoicrocks rocks (cNd(lloo) ==-4 to -12). The persistence persistence of well into into the middle of felsic volcanism volcanismwith withvaried variedENd(1100) ENd( 11 00) well of main main stage stagemagmatism magmatism(—1096 (-1096 Ma) Ma) ofof thethe high cNd(1 may reflect reflect melting meltingof ofthe thebase baseofofthe thevolcanic volcanicpile pileproducing producingsome some high CNd( 100) 1100) (18) or levels with low £Nd(1 100). melting of of progressively progressivelyhigher higher(Archean) (Archean)crustal crustal levels with low ENd(1100). • Evolved basalt and and intermediate intennediate lavas—Basalt lavas-Basalt in in all all stratigraphic stratigraphic intervals intervals straddling straddling the the latent latent general indicator of the differentiated stage displays a broad, but overall low low range range of of mg# mg# - aa general composition of mafic magmas (Fig. 1). Moreover, Moreover, intermediate intennediate lava lava compositions compositions that that were probably generated by differentiation of of mafic mafic magmas magmas (e.g., (e.g., basaltic andesite, andesite, andesite andesite and and icelandite) are highly concentrated within within these these same same intervals intervals in in the the Powder Mill Mill Group Group (4) (4) and and Thisconcentration concentration of ofevolved evolved lava lava compositions compositions is is consistent consistent North Shore Volcanic Group (11). This with prolonged crustal staging of mantle-derived mantle-derived magmas magmas leading leading to to greater greater degrees degrees of of differentiation during this period. period. The The broad broad and and commonly commonly erratic erratic range range of of compositions erupted prior prior to to and and following following the the latent latent stage stage (e.g., (e.g., 21) 21) suggests suggests that that multiple, multiple, open-system open-system staging chambers existed throughout the lower lower crust. • Contaminated basalt—Trace basalt-Trace element (e.g. (e.g. ThIYb) and Nd isotope geochemistry of basalts (Fig. 1) suggest that crustal contamination was most prevalent in the period leading up to the latent 1) magmatic stage. The The greatest greatestpotential potential for for interaction interaction between between mantle mantle melts melts and continental crust would be expected to occur during the inital inital development of of lower crustal magma chambers. Once chambers. Once established, established, crystallization crystallizationand andcontinued continued inflation inflation of of such chambers would have insulated them from further contamination and and diluted the initial contamination. • Plagioclase crystal mush—Leucocratic mush-Leucocratic intrusions of of the Mellen Complex formed fonned at 1102 1102 Ma Ma (10), the anorthositic series of of the Duluth Duluth Complex at at 1099 1099 Ma (9), and the widespread lava flows flows (p. (p, Fig. Fig. 1) I) indicate indicate that that plagioclase-enriched plagioclase-enriched basaltic basaltic occurrence of plagioclase-phyric lava the upper upper crust crust between between 1108 1108 and and 1096 1096 Ma. Ma. Such magmas were commonly emplaced into the plagioclase crystal mushes were were likely likely generated in lower crustal magma chambers where high high flotation of plagioclase plagioclase (20). (20). An pressures would have promoted the flotation An implied consequence of this flotation is the fonnation formation of of anorthositic anorthositic roof roof zones zonesininthese thesedeep deepchambers. chambers. Such roof-zone flotation material was the likely source of of anorthosite anorthosite inclusions inclusions found found in in the Beaver Bay Complex. The interpretation of of the latent latent magmatic magmatic stage stage as as a period period of of extensive magmatic magmatic underplating and crustal melting melting carries significant significant implications implications for the geodynamic and magmatic evolution of the MCR which need need to to be be more more fully fully explored. explored. Whether Whether underplating was the cause or effect of of reduced crustal extension and and the development of of the latent latent magmatic magmatic drives continental continental rifting. rifting. Future stage hinges on the larger question of what drives Future petrologic studies at evaluating the the extent to to which which open-system open-system crystallization differentiation of of should be directed at mantle-derived magmas under high high pressures pressures (7-10 (7-10 Kb) Kb) can account for the compositional range range of MCR lavas and at more precisely determining determining the the sources sources of of felsic felsic magmas. magmas. In addition, more high precision U-Pb ages ages are are necessary necessary to to verify verify the the existence and duration of of the the latent latent all sequences and and to to better establish correlation between Mamainse Mamainse Point Point magmatic stage in all lavas and volcanic sequences sequences in in the the western western Lake Lake Superior Superior region. 34 �References (1) Cannon, 1992, (1).Cannon, 1992, Tectonophys T~ctonophys 213, p.41; p. 41; (2) (2) Shirey Shirey et et a!., aI., 1994, 1994, GCA GCA 58, 58, p. aI., 1995, 1995, MGS MGS p. 4475; (3) Miller et al., Guidebook et al., aI., in in review, review, CJES; CJES; (5) (5) Hutchinson Hutchinson et et al., a!., 1990, 1990, JGR JGR 95, 95, p. 10869; 10869; (6) Behrendt et GUidebook 20; 20; (4) (4) Nicholson Nicholson et al., aI., 1990, 1990, Tectonophys Tectonophys 173, 173, p. 1991, GRL 18, p. p. 625; & Miller, 1993, 1993, JGR 98, p. p. 617; (7) Trehu Trëhu et aI., at., 1991, ORL 18, 625; (8) Paces & 13997; 9; (10) (10) Zartman Zartman et et al., aI., in in review, review, CJES; CJES; (11) (11) Green, Green, 1972, 1972,Geol Geol of ofMN: 13997; (9) (9) DaVIS Davis et aI., al., 1995, 41st ILSG, p. p.9; MN: Cent. Vol., Vol., p. p. 294; 294; (12) (12) Lightfoot Lightfoot et et al., aI., 1991, 1991, JGeol JGeol 99, 99, p. 739; (13) Annels, 1973, 1973, GSC Paper 72-10; (14) Davis Davis & Paces, 1990, 1990, EPSL EPSL 97, 97, p. p. 54; 54; (15) (15) Cannon Cannon & &Hinze, Hinze, 1992, 1992, Tectonphys Tectonphys 213, 213, p. Campbell & Griffiths, 1990, 1990, p. 49; (16) CampbeLl EPSL 99, p. 66; 66; (17) (17) Huppert Huppert & & Sparks, Sparks, 1988, 1988, JPet JPet 29, 29, p. p. 599; 599; (18) (18) Nicholson Nicholson & & Shirey, Shirey, 1990, JGR JGR 95, 95, p. p. 10851; (19) Vervoort Ver~oort & & Green, Green, in in review, review, CJES; CJES; (20) (20) Miller Miller & & Weiblen, Weibien, 1990, 1990, JPet JPet 31, 31, p. 295; (21) Brannon, 1984, 1984, WashU WashU PhD 1988, MTU PhD thesis; (23) (23) Nicholson, Nicholson, 1992, 1992,.USGS Bull 1970-B. 1970·B. PhD theSIS; thesis; (22) Paces, 1988, USGS Bull TECTONOMAGMATIC GEOLOGIC, GEOCHRONOLOGIC AND AND INTERPRET INTERPRETATION GEOCHEMICAL DATABASE DATAB Magmatic Chrono- lLithostrati a h Basalt Chemostrati a h Eruption Crust~l Magma Magma EXlenslOn Stage P Inlr. NSVG PLlPM OGflR MPF ENd (1100) m8# Rate Rate Sources Staging 'J!1IYb 1092 ~-+t:r"""'---:--+-~--I-;;"="T--+---+-";;-~ Late \ .\ Gp7 /~ lrhyolite\ \ 1094 V 1096 r sv ~ --- 1098 : / :I :/ / ~1102 / / / I: Ii /~ ~'-'!~bvl \/ Volcanism (LC) , \ \ Volcanism I I I I r \ Early EP+LM (Laue) / Ii I If I V basalt I I \ \ 1104 . Latent EP UCIKL / ), a) a.> 1108 / ~ "' I I I I I 1 I : 1100 1106 \ . :. ~ !PL EP EP+LM j M H L M H FIGURE1.I.Correlation Correlationofofunits, units,summary summaryofoflithologic lithologicand andchemical chemicalcharacteristics, characteristics, and and interpretations interpretations of of the FlGu1 tectonomagmatic evolution during during magmatic magmatic stages stages of ofthe theMidcontinent Midcontinentrift. rift. Intervals Intervals of of Normal and Reversed magnetic magnetic tectonomagmatic evolution polarity indicated (P). Relative Relativeabundances abundances of ofbasaltic basaltic and and felsic felsic volcanics volcanics schematically schematically portrayed portrayed and and genera! general locations locations of plagioclase porphyritic flows flows (p) (p) noted noted for for the the major major volcanic volcanic suites—NSVG-North suites-NSVG-North Shore Shore Volcanic Volcanic Group( Group( 11); 11); PLIPMPLlPM- Portage Lake Volcanics Volcanics and and Powder Powder Mill Mill Group Group (4); (4); OG/IROGIIR- Osler Osler Volcanic Volcanic Group Group and and PL PL on on Isle Isle Royale Royale(12); (12); MPF- Mamainse Point Formation(2,13). Subdivisions Subdivisions of ofvolcanic volcanic suites suites are are NSVG: NSVG: IGP/uGP, IGP/uGP, HL, HL, NSV-n, NSV-n, SLBlower/upper Grand Portage lavas, Hoviand Hovland !avas, lavas, NSVG-normal NSVG-normal polarity, polarity, and and Schroeder-Lutsen Schroeder-Lutsen basalts basalts of (11); PM: ISCluSC, 1KC/uKClKC/uKC· lower/upper ISC/uSC, lower/upper Seimens Seimens Creek Creek lavas lavas and and lower /upper Kallander Creek volcanics volcarncs of (4); (4); OG: OG: lower, central and upper suites of (12); MPF: Groups 1-7 1-7 of(2).; of (2).; CHC-Copper CHC-Copper Harbor Harbor Conglomerate; Conglomerate; CCGC- Great Great Conglomerate. Conglomerate. Intrusive rock units are LS- Logan Sills, CC- Coldwell Complex, Complex, NLSNLS- Nathan's Layered Series, MC- Mellen Complex, Average U-Pb V-Pb ages ages for for various various volcanic volcanic and and intrusive intrusive rocks rocks indicated indicated DC- Duluth Complex, BBC- Beaver Bay Complex. Average ENd(I'OOl data from MPF (2), filled (felsic) by filled (felsic) and and open open (mafic) (mafic)circles; circles;data datafrom from (8), (8), (9), (9), (10), (10), and and sources sources listed listedtherein. therein. EN1OI PLIPM (4), NSVG rhyolite (19), NSVG basalt (21). mg# PL/PM mg#(=(=MgO/(MgO+FeO)* MgO/(MgO+FeO)*100) 100) of of common range displayed by 22,23). ThIYb data data from from MPF MPF (2), (2), PM (4), OG (12), NSV-n (21), PL (22, 23). basalt in all volcanic suites (2,4,11,12,21, 22, 23). ThJYb 23). Relative from thicknesses thicknesses of volcanic Relative eruption eruption and and extension extension rates rates (Low, Medium, High) interpreted from volcanic suite suite relative relative to to Magmasources sourcesfor forbasaltic basalticcomposition: composition: EPEP- enriched enriched plume, plume, LMLM- lithospheric lithospheric mantle, mantle, DMDMperiod of eruption. Magma in parentheses: parentheses: LCLC(3)). Magma Magma sources sources for for felsic felsic compositions compositions in depleted asthenospheric mantle (modified from (2) and (3)). lower crust, UC UC -- upper crust, KL - Keweenawan lavas. Interpretations of relative volumes of magma staging in the lower crust (LC) and upper crust (UC) (VC) denoted by by relative relative widths widths of of curves. curves. �PRELIMINARY PETROLOGIC ANALYSIS ANALYSIS OF OF THE THE EARLY EARLY PRELIMINARY SEDIMENTOLOGIC SEDIMENTOLOGIC AND PETROLOGIC PROTEROZOIC MAHNOMEN MAHNOMEN .FORMATION RANGE GROUP) GROUP) EASTEASTPROTEROZOIC FORMATION (NORTH (NORTH RANGE CENTRAL MINNESOTA CENTRAL MOREY, G.B., G.B., and CLELAND, MOREY, CLELAND, J.M., Minnesota Geological Survey, 2642 2642 University Ave., Ave., St. Paul, Paul, Minn. Minn.55114-1057 55114-1057 The term North Range Range Group Group was was proposed proposedby bySouthwick Southwick et etal, al. (1988) (1988) for Early Proterozoic Proterozoic The strata sandwiched sandwiched between between the the underlying underlying Mule Mille Lacs Lacs Group and overlying Animikie Group on Cuyuna range. range. As Asdescribed describedby bySchmidt Schmidt (1963), (1963), the group consists consists of a lower lower the North Cuyuna siltstone-shale sequence-the sequence—the Mahnomen Mahnomen Formation; Formation; an an intermediate intermediate and dominantly Fe Fe + Mnunit-the Trommald Formation, Formation, and aa upper uppergraywacke-shale graywacke-shale sequence—the sequence-the Rabbit Rabbit Lake Lake rich unit—the Formation. Much Much of of the the Trornmald Trommald Formation Formation contains contains evidence evidence of hydrothermal or or fumarolic fumarolic processes; little is known To clarify processes; little known however, however, about about the the enclosing enclosing epiclastic epiclastic strata. strata. To clarify the sedimentary history history of of the the Mahnomen Mahnomen Formation, Formation, we we have have re-examined re-examined more more than than 320 320 m m of of continuous core first described described by by Grout Grout and and Wolff Wolff (1955) (1955) from from four four sites sites across across the range. However, our work must has estimated However, our must be be considered considered preliminary, preliminary, for for Schmidt Schmidt has estimated that the the Mahnomen isis at Mahnomen at least least 600 600 m m thick. thick. as 90 90 percent of of the the Mahnomen Mahnomen core core consists of laminated to very thin-bedded thin-bedded As much as claystone, shale, and and siltstone. siltstone. Claystone-now clay-size sericite sericite ±. ± claystone, mudstone mudstone or shale, Claystone—now mainly clay-size chlorite—contains <5 <5 modal modal percent, percent, silt-size silt-sizequartz. quartz. Mudstone contains contains from from ~25 25 percent chlorite-contains percentsiltsiltsize size quartz scattered more or less less randomly randomly through the the matrix, matrix, whereas whereas in shale shale similar amounts of quartz quartz define define aa fissile fissile layering. layering. Siltstone Siltstonecontains contains 25-80 25-80 modal modal percent percent silt, silt, plus plus some fine some fine sand-size sand-size quartz quartz ± trace trace amounts amounts of of chert chert or or iron-formation. iron-formation. Some Some beds beds are are calcareous 20 modal modal percent percent calcite, calcite, whereas whereas others others contain contain >50 >50 modal modal percent, percent, calcareous with with 20 The fine-grained rocks define constituting limestone of of several several varieties. varieties. The fine-grained rocks define upward-fining constituting limestone sequences 5-20 5-20 mm thick, thick, where where siltstone siltstone predominates predominatesinin the the lower lower parts parts and and claystone and sequences claystone and is straight straight and and regular mudstone or shale predominate predominate in upper parts. parts. Bedding Bedding is regular but mudstone in the upper interrupted in and other evidence in places places by by synsedimentary synsedimentary faults, faults, overturned overturned folds, folds, and evidence of slumping. are graded, graded, and are topped by slumping. Many Many siltstone siltstone beds beds have have scoured scoured lower lower surfaces, surfaces, are by climbing-ripple laminae. Compaction climbing-ripple laminae. Compaction features features such as flame flame structures and load load casts(?) casts(?) are common. Contrary to to earlier earlier published published descriptions, descriptions, sandstone sandstone is is aa rare rare component component comprising comprising no no more than the described cores. cores. It occurs in generally structureless to vaguely graded than 55 percent of the and layered they are are interspersed interspersed throughout throughout the the cores. cores. Most layered beds beds 2-3 2-3 cm to 1 meter thick; thick; they Most fine- to medium-grained, medium-grained, quartzose quartzose or or lithic lithic wackes wackes having having>15 beds are fine>15 modal percent matrix (mainly (mainly chlorite ± sericite). sericite). Other constituents (Fig. (Fig. A) include 2-29 2-29 modal percent percent cement cement (possibly (possibly ankerite ankerite ± hematite) hematite) and and 52-94 52-94 modal modal percent percent framework framework grains. grains. Quartz (50-92 (50-92 percent), dominates dominates the theframework frameworkgrains grains(Fig. (Fig. B), B), especially in coarser modal percent), coarser grained samples, followed fragments of of metasedimentary metasedimentary origin origin (9-43 (9-43 modal percent) and feldspar, feldspar, followed by by rock fragments modal percent) (5-15 modal mainly plagioclase (5-15 modal percent). percent). These modal abundances are misleading, however, for there is considerable textural evidence evidence that that much much of of the the matrix matrix has has been been formed by the there considerable textural formed by breakdown breakdown of of unstable metasedimentary metasedimentary rock rock fragments. Nonetheless, Nonetheless, the the Mahnomen is is clearly a second-cycle second-cycle sequence sequencederived derivedfrom froman anolder oldermetasedimentary metasedimentaryprovenance-most provenance-most likely the the underlying Mule Lacs Group, a possible provenance also suggested by quartz types that point Mille possible provenance also suggested by to a "low rank metamorphic metamorphicsource" source" (Fig. (Fig. C). C). 'low rank Major, minor, minor, and trace-element (Fig. D) D) are are similar similar to to those those of of an average Major, trace-element compositions compositions (Fig. shale, where plagioclase and, consequently, sodium are generally lacking and where potassium potassium is associated associated with sericite. sericite. REE REE compositions compositions (Fig. (Fig. E) cratonic is E) are are broadly broadly consistent consistent with with a cratonic source, HREE and are· marked marked by by flat flat Ce Ce anomalies anomalies and and mostly mostly source, show show slight depletion in HREE and are positive Eu anomalies. anomalies. However, However, aa few few samples samples have have low low REE REE totals totals and negative negative Eu Eu positive Eu Beds of of volcanogenic material as thick anomalies; they may contain a volcanogenic component. Beds 36 �cm, are are mainly ash-fall ash-fall tuff. tuff. They have been recognized and as 10 em, and described described from from elsewhere elsewhere on on the range range by byMeicher Melcheretetal. al.(1996). (1996). The The North Range Range Group Group has has been been folded folded at at least least twice twice and and metamorphosed metamorphosed to to the the greenschist facies. As such it is is part part of of the the Penokean Penokean fold-and-thrust fold-and-thrust belt. Hemming et et al. al. greenschist facies. As belt. Hemming in the the Mahnomen Mahnomen were were derived derived from from an an (1993) used (1993) used Sm-Nd Sm-Nd techniques techniques to to show show that detritus in provenance. Morey Morey and and Southwick Southwick (1995) (1995) used information to Archean provenance. used that information to suggest suggest that the Mahnomen was was deposited deposited on on an an evolving evolving continental continental margin margin early early in in thetectonic the tectonic history history of of the the Penokean orogen. orogen. However, second-cyde sand, sand, such such aa suggestion suggestion Penokean However, because because the Mahnomen is a second-cycle orogen. may no longer be applicable to the tectonic evolution of the Penokean orogen. 100 100 Fiamework Framewor1( greene grains ! A D. •0. 10 10 If J 10.1 10.1 en • • 0.u ntHlEui1 ThY Ybt.u 0.01 Rb BaTh U U NbTal( M,Th LaC.SrNdI"SmZrHfEun ThY Vb Lu • • PolycrystalNne PoIyerystaJ!ne quartz Cement -/ / Matrix Matrtx ra,* rn.twIOrpC Low Lowl1lnk~ au.,tz Quartz 6.1' I ••• • . .e • / / ••• :\ •.'' / / I.Idde and UIlC* • rank~ / / •• / / / / / Plutonic • • . • quartz 10g. E. S 10 S N-3 IC WCSI ~ Uthc wucice 1 Week.(manix (matrix> 15%) Wed. > 15%) Si Fe4dspar Feldspar 5/ I 51 5.1 00 N13. N-13· S.f 5/ — SI RocX'IWgi".tta tVu4ut. Rod< (1nctudInQ thart) chert) 37 1 0.1 0. N<l Sm Eu Th LICI4dSrnEUTh L. C. Yb Lu Vb �IN THE FOX FOX RWER RIVERVALLEY, VALLEY, MISSISSIPPI VALLEY-TYPE MINERALIZATION [N EASTERN WISCONSIN M1JDREY, MUDREY, M.G. ,, Jr. Ir. and BROWN, B.A., Wisconsin Geological and Natural History 100, Survey, WI 53705-5 53705-5100, Survey, 3817 Mineral Point Road, Madison, WI mgmudrey@facstaff.wisc.edu, babrown l@facstaff.wisc.edu; FREIBERG, FREIBERG, mgmudreyfacstaff. wisc. edu, and babrownl@facstaff.wisc.edu; PG., and P.G., and SIMO, SIMa, J.A., lA., Department Department of ofGeology Geology and and Geophysics, Geophysics, 1215 1215 W. Dayton St., Madison, Madison, WI WI53706-1692, 53706-1692,simo@geology.wisc.edu simogeology.wisc.edu St., Regional NURE (National Uranium Resource Evaluation Program) Program) geochemical geochemical data data suggest suggest that anomalous concentrations concentrations of ofarsenic arsenic and and other other mineral mineral exploration exploration path-finder path-finder elements elements are are of Green Green Bay, Wisconsin Wisconsin where the Sinnipee, Sinnipee, Ancell present in the area southwest of Ancell and Prairie du Chien Groups are the uppermost bedrock units. units. InInaddition, addition,fluorine fluorine levels levels in in groundwater groundwater have long been known to be be high high in the Fox River valley between Green Bay and Appleton, where fluorite and other other Mississippi Mississippi Valley-type minerals in well minerals are are reported to be present in cuttings from the Sinnipee Sinnipee Group. Areas of elevated values values occupy occupy northwestern Outagamie county and of significantly significantly elevated adjacent areas. areas. AAclearly clearly defined defined nickel nickel province that spatially corresponds to the arsenic polymetallic (As, Co, Mo, Mo, Ni, Ni, Th, Th, V) V) hydrogeocheniical hydrogeochemical province province exists exists province suggest that aa polymetallic in eastern Wisconsin Wisconsin and and may may relate relate to to documented documented faults faults (Mudrey (Mudrey and and Bradbury, Bradbury, 1992). 1992). The The geology differs from the better documented documented five-element five-element (Ni-Co-As-Ag-Bi) veins (Kissin, (Kissin, 1993) being carbonate hosted rather by being rather than than shale shale or or volcanic volcanic hosted, hosted, but bUf are are similar similar in in essential essential mineralogy and elements. elements. Economic concentrations of ofMississippi Mississippi Valley-type mineralization have not been found in Wisconsin Wisconsin outside of Grant, Iowa, and and Lafayette Lafayette Counties, Counties, but but geologic geologic logs logs of of16 16 mineral mineral in eastern eastern Wisconsin Wisconsin contain reports of ofminor minor 600 water water wells wells in exploration holes and more than 600 mineralization. In addition, more than 100 occurrences of sulfide mineral have been reported mineralization. In addition, more than 100 occurrences of sulfide mineral have been reported from outcrops and and quarries quarries throughout throughout southern southern and and eastern eastern Wisconsin Wisconsin (Brown and and Maass, 1992). AAfairly fairlycontinuous continuoushorizon horizonofofsulfide sulfidemineralization mineralizationhas hasbeen beenobserved observedininquarries quarries and and drill cores from Kenosha to Green Bay. Bay. Mineralization Mineralizationwithin within this this horizon horizon infills infills intergranular drill m below below the the base base of ofthe the middle-Ordovician middle-Ordovician Platteville and moldic porosity from 2 m above to 66 m Formation, cross-cutting the cross-cutting bedding bedding and and strata strata of ofvarying varying lithologies lithologies that immediately immediately underlie underlie the and Freiberg, Freiberg, in in press).] press).] Platteville Formation (Simo, Freiberg, and References: Brown, B.A., and Maass, R.S., 1992, 1992, AAreconnaissance reconnaissancesurvey surveyof ofwells wells in in eastern eastern Wisconsin Wisconsin for indications of of Mississippi Valley type mineralization: Wisconsin Geological and and Natural Natural History History p. Survey Open-file Report WOFR WOFR 1992-3, 1992-3,31 3 1 p. Brown, B.A., and possible source source and Maass, Maass, R.S., R.S., 1994, 1994, Mississippi Mississippi Valley-type Valley-type mineralization: mineralization: A possible 38 �of heavy metal anomalies in the Paleozoic carbonate carbonate aquifers aquifers of ofWisconsin Wisconsin (abs.): (abs.): American American Water Resources Association Wisconsin Wisconsin Section Section Meeting, Meeting, 18th (Wisconsin (Wisconsin DeUs), Dells), paper 37. Kissin, S.A., 1993, Five-element Five-element (Ni-Co-As-Ag-Bi) (Ni-Co-As-Ag-Bi) Veins:· Veins: in in P.A. P.A. Sheahan Sheahan and andM.E. ME. Cherry, Kissin, S.A., v. 6, 6, p. Ore Deposit Models, Volume II, Geoscience Canada Reprint Series, Series, v. p. 87-98. Mudrey, M.G., Jr., and Bradbury, K.R., 1992, NIJRE hydrogeochemical Mudrey, 1992, Evaluation Evaluation of ofNURE hydrogeochemical data for use in Wisconsin Wisconsin groundwater studies: Wisconsin Geological and and Natural History Survey Openfile Report WOFR 93-2, 61 file 61 p., p., 1 computer computer diskette. Mudrey, M.G., Jr., Bradbury, Mudrey, M.G., Bradbury, K.R., K.R., and and Kammerer, Kammerer, P., P., 1992, 1992, Progress Progress towards towards rapid rapid retrieval retrieval of of Wisconsin's NURE dataset (abs.): American Water Resources hydrogeochemical data from Wisconsin's Association Wisconsin Wisconsin Section Section Meeting, Meeting, 16th 16th (La (La Crosse), Crosse), paper paper 26. 26. Simo, in press, press, Geologic Geologic constraints constraints on on arsenic arsenic in in Simo, lA., J.A., Freiberg, P.G., and Feiberg, K.S., in groundwater with with applications applications to to groundwater groundwatermodeling: modeling: University University of ofWisconsin Wisconsin Water groundwater Resources Center. 39 �______________________________________ Group Near Taylors Taylors Falls Falls and and From Metamorphism of of Chengwatana Volcanic Volcanic Group Osseo Core NAIMAN, Zachary and WIRTH, WIRTH,Karl Karl R., R., Geology Geology Department, Department, Macalester Macalester College, St. Paul, Minnesota 55105, 55105, znaiman@maca1str.edu znaiman@macalstr.edu and G.B. and wirth@macalstr.edu; wirth@macalstr.edu; and and MOREY, G.B. and MILLER, James, D., D., Minnesota Minnesota Geological Geological Survey, Survey, 2642 University University Ave., Ave., St. MILLER, James, St. Paul, Paul, Minnesota 55114, 55114, moreyO0 morey001@maroon.tc.umn.edu 1 @ maroon.tc.umn.eduand andmille066@maroon.tc.umn.edu mille066@maroon.tc.umn.edu The southernmost exposed flows flows from from the the 1100 1100 Ma Ma Midcontinent Midcontinent rift rift of of North North America America comprise comprise the Chengwatana Volcanic Group, aa sequence sequence of more Volcanic Group, more than seventy mafic flows exposed in in the the Taylors Falls-Interstate State Park region (>2800 meters Taylors meters thick) thick) on on the the Minnesota-Wisconsin Minnesota-Wisconsin borborder. A A core at at Osseo Osseo (63 (63 km SW of the exposures) sampled 980 meters of more than fifty der. fifty flows flows of Chengwatana Chengwatana basalt basalt 230 230 meters below the surface. Flows Flows in both sequences are typically interlayered with sedimentary of the the North North sedimentary breccia. breccia. Stratigraphic Stratigraphic correlation correlation with other volcanic volcanic sequences sequences of Shore region of of the the rift rift are are complicated complicated by by faulting. faulting. Volcanic (plagioVolcanic flows flows from from both both regions regions have have similar similar primary primary igneous mineral assemblages (p!agioFe-Ti oxides) and and display aa variety of igneous textures (ophitic, (ophitic, sub-ophitic, sub-ophitic, clase + clinopyroxene clinopyroxene ++ Fe-Ti ophimottled, intergranular, textures indicate indicate a ophimottled, intergranular,intersertal, intersertal,plagioclase plagioclasephyric, phyric,and andseriate). senate). The The textures sequence of plag -> cpx -> oxides typical crystallization sequence Single flows flows comtypical of of tholeiitic tholeiitic basalt. basalt. Single ophitic texture texture isis more monly exhibit more than one texture; ophitic more common common in in flow flow interiors interiors where where the the cpx presumably presumably had sufficient sufficient time time to to crystallize crystallize during during slow slow cooling cooling whereas whereas intersertal intersertal and and textures are more common at at flow flow tops tops where where more more rapid rapid cooling cooling prevented prevented the the forforophimottled textures Osseoflows flows have have aa higher higher proportion proportion of ofophitic ophitic texture texture and and on on averavermation of large cpx crystals. Osseo age are coarser coarser grained grained than than Taylors Taylors Falls Falls flows. flows. The metamorphic environment of the Chengwatana volcanics volcanics is is best modelled by the CaOMgO-A1203-Fe203-Si02-H20-C02 (CMAFSH-CO (CMAFSH-C02) basaltic system determined by by Liou Liou et et al. al. ) basaltic system detennined MgO-AI203-FeZ03-SiOTHZO-COZ z (1985) and Cho and Liou (1987). The (1985) and Cho and Liou (1987). equilibrium metamorphic mineral assemFigure 11 pumpellyite - actinolite blage of the top top 670 670 meters meters of of the the Osseo Osseo facies core consists of of calcite ++ epidote ++ chlocWoOsseo -- upper flows • rite + quartz + albite rite albite + + oxides oxides ± ± white white .~ Osseo Osseo - lower flows ,L:.....J Taylors Falls Towardthe the bottom bottomof ofthe the drill drill core, core, mica. Toward the occurrence occurrence of calcite is is limited limited to to the prehnite - pumpellyite veins and amygdules amygdules whereas whereas actinolite actinolite facies becomes prominent in the the groundmass. groundmass. t These assemblages, defined by the reac- ~ greenschist tioncal+chl+qtz=ep+act+H20+ tion cal + chI + qtz = ep + act + H20 + Q: facies C02, COz, are are consistent consistent with with the the transition transition from calcite-chloritefacies calcite-chlorite facies to greenschist greenschist calcite- I ÷ facies (Fig. (Fig. 1). 1). The entire section section at The entire chlorite /ShiftoffieldbounShift of field boun;f daries as a function Taylors Falls displays the mineral assemJ>of Xco2 Xc02 blage: blage: actinolite actinolite + epidote + chlorite chlorite + Shift of invariant quartz ++ albite ++ oxides oxides ± ± white white mica. mica. ShftofI.nanant points with The stability region of the calciteincreasing Fe+ increasing Fe33 chlorite facies in PIT is constrained constrained chloritefacies prr space is Temperature by amounts of CO2 CO 2 and by the amounts and Fe+ Fet33 in the E 40 �________________________________________ 0.8 , . . - - - - - - - - - - - - - - - - . , Chengwatana Volcanic Volcanic Group Figure 2 Actinolite Analyses system (Fig. (Fig. 1). Currently Currently there there are are no no geothermometers which which can can be applied to geothermometers this system. system. However, this However, the the Na-content Na-content of o0 Osseo Core the M4-site (NaM4) of actinolite in the pres06 CJ 0.6 Tailors Falls •I Taylors Falls ence of chlorite, chlorite, epidote, epidote, and and quartz quartz is aa ence 'til ~ useful geobarometer (Brown, 1977). 1977). SEMSEMusefulgeobarometer(Brown, ~ 5 kb analyses of actinolite in the Osseo core analyses of actinolite in the Osseo core EDS ....Q contain less NaM4 than actinolite from the C 0.4 CJ Taylors Falls region Taylors Falls region suggesting suggesting that the the = Q 4kb Osseo flows Osseo flows were were metamorphosed metamorphosed at at <.I eo: slightly lower pressure (Fig. 2). Z 0.2 The temperature temperature conditions during during kb metamorphism of the Chengwatana flows 2 kb o Taylors Falls Falls are are constrained constrained by the presat Taylors ence of actinolite ence actinolite and epidote (Fig. (Fig. 1), 1), by 00.0 0 the absence of co-existing prehnite and absence co-existing prehnite and the 0.0 0.2 0.4 0.6 0.8 pumpellyite, and by the lack of hornblende Al content of tetrahedral site coexisting with epidote, chlorite, actinolite, Epidote,rather ratherthan thanclinozoisite, clinozoisite, isis present present in in the the Chengwatana Chengwatana flows flows due due to to the the highhighand quartz. Epidote, iron protolith. At Ata apressure pressureof of2.5 ::::::2.S kbar,thetheequilibrium equilibriummineral mineralassemblages assemblages iron content content of of the th protolith. kbar, of 325 325 -- 37SoC. indicate metamorphic temperatures temperatures of 375°C. Assuming a peak metamorphic temperature of 350°C and burial depth of 7.5 3S0°C 7.S km, km, the the metamorphic metamorphic data data from from the the Chengwatana Chengwatana flows flows imply imply aa geothermal gradient of approximately this portion geothermal approximately 45-50°C/km 4S-S0°C/km within this pbrtion of the the midcontinent midcontinent rift. rift. results have have have determined elsewhere elsewhere in in the the midcontinent midcontinent rift rift and and in in the the Kenya Kenya Rift Rift of Similar results have determined east Africa. facies in in the the Osseo core, the ubiquitous presThe change from calcite-chlorite to greenschist greenschistfacies greenschistfacies ininthe ence of greenschistfacies the Taylors Taylors Falls Falls exposures, exposures, and and the the lower NaM4 content of of actinolite sampled by by the the Osseo Osseo drill drill core core were in the Osseo core imply imply that the the Chengwatana Chengwatana flows flows sampled were not Taylors Falls. Falls. IfIf the buried as deeply as the flows exposed at Taylors the flow flow sequences sequences in in these these two two regions regions are part of the same volcanic plateau-segment plateau-segment of of the the midcontinent midcontinent rift, rift, and and ifif the the these these regions regions are are not separated with large offsets, the the flows flows sampled sampled in in the the Osseo Osseo core core might might be not separated by structures structures with large offsets, of the the Taylors Taylors Falls Falls region. region, stratigraphically younger than than those those of - - References Cited Brown, E.H., 1977, to pressure of metamorphism: metamorphism: Journal of Petrol1977, The crossite content of Ca-amphibole as a guide to ogy, v. 18, 18, P. p. 53-72. Cho, M. and Liou, J. G., 1897, to greenschist greenschist facies facies transition transition in in the the Karmutsen Karmutsen metabasites, metabasites, 1897, Prehnite-pumpellyite Prehnite-pumpellyite to Cho, Vancouver Island, B.C.: B.C.: Journal Journal of ofPetrology, Petrology, v.v. 28 28 p. 417-443 Green, lC., 1983, 1983, Geologic Geologic and and geochemical geochemical evidence for for the the nawre nature and and development development of of the the Middle Middle Proterozoic Proterozoic Green, J.C., 94, p.p.413-437. 413-437. (Keweenawan) Midcontinent Rift Rift of North North America: America:Tectonophysics, Tectonophysics,v.v.94, of volcanic volcanic and and volcaniclastic volcaniclastic rocksrocksLiou, J.G., Maruyama, S., S., and and Cho, Cho, M., M., 1987, 1987. Very Very low-grade low-grade metamorphism metamorphism of and mineral mineral facies: facies: in in Frey, M., ed., Low Temperature mineral assemblages and Temperature Metamorphism, Metamorphism, Glasgow, Blackie, p.59-113. p. 59-113. G. R., R., Brew, D.A., and Ford, A.B., 1995, Low-grade, M1 M 1 metamorphism of of the Douglas Douglas Island Island Volcanics, Volcanics, Himmelberg, G. western metamorphic H.W., editors, Low-Grade Low-Grade MetamorP. and Day, H. W., editors, metamorphic belt belt near near Juneau, Juneau. Alaska: Alaska: in in Schiffman, Schiffman, P. of Mafic Rocks, Rocks, Geological Geological Society Society of ofAmerica America Special Special Paper Paper296, 296, p. 51-66. phism of 41 �A CONTINUUM OF STRESS-STRAIN STRESS-STRAIN FIELDS FIELDS (2.0-1.0 (2.0-1.0 Ga) CONTINUUM OF Ga) ALONG THE MARGIN OF OF THE THE KEWEENAW KEWEENAW PROVINCE, NORTHERN MARGIN PROVINCE, ONTARIO, CANADA NEILSON, NEILSON, Kim, STENDAHL, STENDAHL, Rebekah, KROPF, KROPF, Elizabeth and and CRADDOCK, CRADDOCK, John P., Geology Dept., Macalester College, St. Paul, MN 55105, 55105, Craddock@Macalstr.edu evolution of of the the Keweenaw Keweenaw rift rift (1.1 (1.1 Ga) Ga) is well constrained for for much much The The structural evolution of the exposed southern arm, arm, and and involved involved early early extensional extensional faulting faulting and and magmatic magmatic activity, followed by by closure closure of of the the rift rift along along the the same same boundary boundary faults faults by thrust activity, followed (e.g., Douglas Douglas and andKeweenaw-Lake Keweenaw-LakeOwen Owenthrusts) thrusts)at at -1.06 Ga (Bornhorst et et motion (e.g., -—1.06 al., 1987; Cannon, 1994). 1994).This Thisstructural structural scenario scenario isis complimented complimented by studies of 1987; Cannon, of the the mechanical preserved in in calcites calcites (amygdules, (amygdules, veins, veins, cements, cements, mechanical twinning strains preserved clastic dikes, dikes, and overlying overlying Paleozoic Paleozoic limestones) region cements in clastic cements limestones) throughout the region rift, followed followed by which record syn-rifting subhorizontal subhorizontal shortening parallel to the rift, rift-normal subhorizontal closure of the rift rift (Craddock (Craddock rift-normal subhorizontal shortening shortening related related to to thrust closure et al., in press). The other portions of the Keweenaw rift-triple junction are press). The other portions of the Keweenaw rift-triple unexposed (gravity, (gravity, magnetic anomaly) beneath the Michigan Michigan basin or poorly poorly constrained north of Lake Superior. of Lake Superior. In this study study we we have have characterized characterized the the structural structural relations relations of of calcite calcite twinning twinning patterns to to the the "failed "failed third arm" arm" portion of the rift system between the Kapuskasing suture, the the Coidwell Coldwell alkali alkali complex complex and the the Nipigon Nipigon Embayment Embayment over the the interval interval -2.0-1.0 Ga. regional —2.0-1.0 Ga.Our Ourresults results(Table, (Table,Figs. Figs.1-3) 1-3)suggest suggestthat thatthe the orientation orientation of the regional compressive stress (or shortening strain) strain) field was subhorizontal and N-S field was N-S prior to to compressive stress rifting, subhorizontal and rift-parallel rifting, rift-parallel during rifting, and subhorizontal subhorizontal and and riftriftnormal as the rift rift closed closed by thrusting. Sample 11 2 3 4 55 6 7 8 9 10 11 12 13 13 14 15 16 16 17 18 18 19 20 21 22 23 24 25 26 e1(%) el(%) pI) e1(tr el(tr && p1) -7.7 -3.5 -5.5 -2.1 -4.5 -5.9 -9.8 -3.4 -3.3 -0.2 -0.8 -0.7 -2.4 -1.6 -1.2 -6.7 -1.9 -0,4 -0.4 -0.2 -0.2 -0.2 -0.6 -2.9 -4.9 -0.4 -0.4 -4.9 340°,0° 0° 340°, 170°, 8° 8° 170°, 5° 5° 16°, 5° 5° 164°, 0° 0° 50°, 0° 41 0, 0° 41°, 52°, 0° 55°, 0° 20,0 20, 0 3550, 20° 355°, 76°, 76°, 8° 56°, 56°, 17° 150°, 0° 150°, 171°, 0° 171°,0° 162°, 0° 0° 165°, 0° 0° 165°, 170°, 00 0° 170°, 0° 0° 0° 168°, 0° 270°, 5° 270°, 160°,7° 253°, 00 0° 170°, 5° 5° 355°, 12° 12° 300°, 7° 7° NEVs (%) (%) 16 a 0a 0 21 12 30 28 37 0 47 28 5 0 26 30 14 13 33 0 8 7 100 100 0 20 30 16 42 -Age (Ga) Calcite e —Age (Ga) Calcite type Dikemarginvein Dike margin vein Dike Margin vein Dike Sibley Limestone Sibley Limestone Limestone Basalt amygdule amygdule Basalt Basalt amygdule amygdule Basalt Basalt amygdule Basalt amygdule Basalt amygdule amygdule Basalt Vein Vein Vein Carbonatite Vein Vein Vein Vein-amygdu.le Vein-amygdwe Veth-amygdule Vein-amygdwe Vein Vein Vein Carbonatite Vein Vein Vein Lamprophyre 2.0 2.0 1.54 1.54 1.54 —2.0 -2.0 1.1 1.1 1.1 1.1 -1.1 —1.1 —1.1 -1.1 -1.1 —1.1 -1.1 —1.1 <1.06 <1.06 <1.06 <1.06 <1.06 <1.06 <1.06 <1.06 -1.1 —1.1 <1.06 <1.06 <1.06 <1.06 �Kenora-Kabetogama and Sibley Group (2.0-1.5 Ga) Gal Group (2.0-1.5 Figures 1-3: 1-3: Regional Regional summary summary calcite twinning data plots of calcite (see (see Table) Table) for for time time increments between—2.0-1.0 -2.0-1.0 Ga. between Ga. Solid, Solid, bold lines are are calcite calcite shortening shortening lines strain axes, with sample number number (see Table). Table). RegionaF compressive (see Regional compressive strain (E) (E) stress(cr) stress(o) or shortening shortening strain fields are inferred from these data fields are for each each time period. Lake for Lake Superior is used as a reference, is reference, with no attempt being made to include plate or fault fault boundaries boundaries that that plate or active during during the were active billion years years of of Earth Earth history billion involved. \ Wiscon5in Portage Lake Volcanics-Osler Group (1.1 Gal Ontario Late Keweenawan Keweenawan (<1.06 «1.06 Ga) Gal o "o_ColdweU~ .), .. Ontario Complex ~24 References Bornhorst, P.J., P.J., Paces, N.K., 1987, Paces, J.B., J.B.,Grant, Grant, N.K., N.K.,Obradovich, Obradovich, J.D., J.D.,and and Huber, Huber, N.K., 1987,Age Ageof ofnative native copper copper mineralization, mineralization, Peninsula,Michigan: Michigan:Economic EconomicGeology, Geology, v. Keweenaw Peninsula, v. 83, 83, p. 619-625. Cannon, W.F., W.F., 1994, 1994, Closing of the Midcontinent Midcontinent rift: rift: aa far-field far-field effect effect of Grenvillian Grenvilliancompression: compression:Geology Geology22, 22,p.p.153153Cannon, 38. A., McGovern, McGovern, M., M., Kropf, Kropf, E.P., E.P., Moshoian, Donnelly, K., K., in press, Post-extension Craddock, J.P., J.P., Pearson, A., Craddock, Moshoian, A., A., and and Donnelly, shortening strainspreserved preservedinincalcites calcitesofofthe theKeweeriawan Keweenawanrift: rift:Geological GeologicalSociety Society of of America America shortening strains Special Paper Paper 312. 312. 43 �CYCLIC TIDAL LAMINATIONS IN THE EARLY PROTEROZOIC POKEGAMA EARLY PROTEROZOIC FORMATION: DIGITAL IMAGE ANALYSIS AND COMPUTER MODELING OJAKANGAS, W., Department of of Geology, Geology, University University of of OJAKANGAS, Gregory W., Minnesota, 10 University University Dr., Dr., Duluth, Duluth, MN MN 55812, 55812, Minnesota, 10 gojakang@d.umn.edu Evidence of the diurnal inequality inequality operating operating in in Early Early Proterozoic Proterozoic time is apparently recorded in in aa sequence sequence of of alternating alternating thicker thicker time is and thinner clastic silt laminae laminae identified identified in in the the lower lower member member of Formation of of northern northern Minnesota. Minnesota. The sequence sequence of of of the Pokegama Formation apparently semidiurnal semidiurnal laxninae laminae is lens-shaped is present present in aa silty lens-shaped the argillaceous member, member, interpreted interpreted to to be be aa small small arm arm of of bed of the aa tidal the shore shore of of the the transgressive transgressive sea sea that that tidal channel system on the occupied the ancient Animikie Animikie basin. basin. The sequence consists of of approximately 60 60 thin (0.1 (0.1 -- 1mm) silty laminae which tend to to in thickness, thickness, separated separated by by thin thin mica-rich mica-rich layers layers that that alternate in exhibit a similar tendency. a tendency. Such thick-thin thick-thin patterns are are expected to be generated by sediment transport transport in in semidiurnal semidiurnal tidal environments, environments, due to the alternating magnitudes of tidal of successive tidal velocity peaks in in such such environments environments (i.e., (i.e., due to the tidal inequality). to inequality). Thus, they may be used to to support Thus, they tidal environments of of deposition deposition (cf. (cf. de de Boer Boer et et al., al., proposed tidal 1989), here strongly strongly supports supports the the 1989), and the sequence described here conclusion of Ojakangas (1983) (1983) that that the the Pokegama Pokegama Formation is is of tidal origin. that the the depositional depositional site site was tidal origin. It also suggests that probably non-equatorial in in the the Early Early Proterozoic. Proterozoic. Hand specimens specimens of the rhythmic sequence described above and other specimens sequence described above and other specimens from the the lower lower member member of of the the formation formation displaying periodicities from slabbed, coated with oil oil to to enhance enhance detail, detail, and and have been slabbed, photographed. The resulting images were then then digitized and are currently under analysis using using image-processing image-processing techniques. techniques. In order to better understand the the potential for for extraction the ancient lunar lunar orbit orbit from from rhythmic rhythmic tidal tidal of information on the sedimentary sequences such as the one described here, here, a computer model has been created (Ojakangas model (Ojakangas et et al.,1995) al.,1995) which which generates generates synthetic tidal tidal rhythinites rhythmites from from first first principles, principles, given arbitrary the earth and and moon, moon, and and the latitude and orbital elements of the longitude of a a hypothetical location location on on the the earth. earth. Assuming in the the open open ocean, ocean, tidal tidal currents currents are are equilibrium tide heights in generated in a hypothetical tidal tidal channel channel linking linking the the ocean ocean to to aa tidal basin. The current in in the the channel, channel, driven driven by the the difference in water surface elevation elevation between between the the basin basin and and the the open ocean, uniform turbulent turbulent flow flow according ocean, is computed assuming uniform (cf. Dingman,1984), Dingman, 1984) , and and this this flow flow is is assumed to Chezy's equation (cf. transport capacity capacity as described by Yang to carry sediment at peak transport and Stall (1976). (1976). Both mud and and silt, silt, transported transported in in suspension, suspension, are deposited when the current speed speed drops drops below below respective respective 44 44 �critical values. values. The vertical vertical eddy diffusion diffusion time time is is assumed assumed critical short relative to the the tidal tidal cycle, cycle, so so deposition is is w "instantaneous". ninstantaneous synthetic • The program successfully produces synthetic that closely closely resemble resemble those those of of known known rhythmite sequences that rhythmites, such as those of the Late Proterozoic Elatina rhythmites, Formation described by Williams (1991), (1991) ~ Because the the tides tides are are analytically generated, generated, the the significance significance of peaks in in the the power power spectrum of the synthetic rhythmites rhythmites can be understood. understood. The The conditions under which predetermined lunar lunar orbital parameters can can be retrieved from from the the corresponding corresponding synthetic synthetic rhythmites rhythmites are are under investigation with this this model, model, as is is the probable appearance and spectral content of very ancient rhythmites, rhyt~ites, as as yet undiscovered. undiscovered. With this this model as a tool, tool, lamina sequences sequences Formation including including the the one one described described above are from the Pokegazna Pokegama Formation under analysis for for possible clues to to the the ancient lunar lunar orbit. orbit. References; Reerencep: de Boer, Boer, P.L., P.L., Oost, Oost, A.P., A.P., and Visser, M.J., M.J., 1989, 1989, The diurnal inequality of a parameter for for recognizing tidal of the tide as as a influences. J. J. Sed. Sed. Petrology, Petrology, V. V. 59, 59, p. p. 912-921. 912-921. Dingman, Dingman, SS.L., 1984, Fluvial Hydrology, L., 1984, Hydrology, W. W. H. H. Freeman and Company, p. 112-113. Company, 112-113. Ojakangas, Ojakangas, G.W., G.W., Tan, Tan, H., H., and and Sickler, Sickler, B., B., 1995, 1995, TidaL TidaL rhytbmites rhythmites and the ancient lunar lunar orbit: orbit: Improved Improved understanding through through aa synthetic model (abs): (abs): Bull. Bull. Am. Am. Astron. Astron. Soc., Soc., Proceedings proceedings of the 27th Annual meeting of the the Division for for Planetary Planetary Sciences, p. p. 57. 57. Ojakangas, R.W., Ojakangas, R.W., 1983, 1983, Tidal deposits in the early Proterozoic Proterozoic basin of the Lake Superior region region -- The Palms and the the Pokegarna Formations: Evidence Evidence for for subtidal-shelf subtidal-sheif deposition Pokegama Formations: of Superior-type Superior-type banded banded iron-formation: iron-formation: in in Medaris, Medaris, L.G. L.G. Jr., ed., Jr., ed., Early Proterozoic Proterozoic Geology of the Lake Superior Region: Geological Society Society of of America America Memoir Memoir 160, 160, p. p. 49-66. 49-66. Williams, G.E., 1991, 1991, Upper Upper Proterozoic Proterozoic tidal tidal rhytbmites, rhythmites, South South Williams, G.E., Australia: Australia: Sedimentary Sedimentary features, features, deposition, deposition, and and implications for the the earth's earth's paleorotation: paleorotation: in in Smith, Smith, D.G., D.G., Reison, Zaitlin, B.A., B.A., and R.A. R.A. Rabmani, Rahmani, eds., eds., Clastic Reison, G.E., G.E., Zaitlin, Tidal Sedimentology: Sedimentology: Canadian Society of Petroleum Geologists Memoir Memoir 16, 16, p. p. 161-178. 161-178. Yang, C.T. C.T. and Stall, Stall, J.B., J.B., 1976, 1976, Applicability Applicability of of unit unit stream stream Yang, equation, American American Society Society of of Civil Engineers Engineers power equation, Proceedings, Proceedings, Journal of the the Hydraulics Division, Division, V. V. 102 102 (HY(HY. 5), 5), 559—568. p. 559-568. 45 45 �TIDALITES OF EARLY PROTEROZOIC AGE AGE IN IN THE THE WESTERN WESTERN LAKE LAKE SUPERIOR SUPERIOR REGION: REGION: MINNESOTA, WISCONSIN AND MICHIGAN OJAKANGAS, RICHARD Geology, University of OJAKANGAS, RICHARD W., W., Department Department of of Geology, Minnesota, Duluth, MN 55812, 55812, rojakang@d.umn.edu rojakang@d.umn.edu Minnesota, Duluth, The Palms of the Gogebic The Palms Formation Formation of Gogebic Range Range of Michigan Michigan and and the the lithologically correlative correlative Pokegama PokegamaFormation Formationofof the the Mesabi lithologically Mesabi Range Range of Minnesota, deposited upon upon Archean Archean basement basement and and both both underlying underlying Minnesota, both both deposited major iron-formations, major iron-formations, are terrigenous clastic clastic units interpreted to be are terrigenous tidal deposits of aa tidal deposits formed formed on on the the east-west-trending east-west-trending shoreline shoreline of northward-transgressing Early Early Proterozoic Proterozoic sea (Ojakangas, northward-transgressing (Ojakangas, 1983). 1983). The above four four formations formations were were either either deposited depositedon on aa stable stable shelf shelf prior above prior to the the the peripheral peripheral bulge bulge development of foreland basin, basin, or were were deposited deposited on the development of aa foreland of aa foreland foreland basin basin developing developing to north of aa major major fold fold and and thrust thrust belt belt of to the the north caused by by the caused the collision collision of of the the Wisconsin Wisconsin Magmatic Magmatic Terrane Terrane with with the the In either either model, model, itit can can be be assumed assumed that that the the terrigenous terrigenous continent. In clastics and the the iron-formations iron-formations form form continuous, continuous, but but diachronous, diachronous, clastics and sheetlike deposits deposits across across the sheetlike the basin. basin. The well-exposed 150 m m thick has a minor The well-exposed 150 thick Palms Palms Formation Formation has minor basal basal largely comprised comprised of of three conglomerate, but is largely conglomerate, three major major gradational gradational facies facies which are which are as as follows: follows: 1. A thin-bedded thin-bedded argillaceous argillaceous facies facies (lower (lower member), 2. 2. AA dominant dominantargillite-siltstone-sandstone argillite-siltstone-sandstone facies facies (middle (middle member) thin-bedded intercalated intercalated lithologies sandstone facies facies member) of of thin-bedded lithologies and and 3. 3. aa sandstone (upper member) of thick (upper member) of thick beds beds of of parallel parallel and andplanar planarcross-stratified cross-stratified The sandstones. The middle middle member member includes includes lenticular, lenticular, wavy, wavy, flaser flaser and and parallel bedding A total parallel bedding and and minor minor mudcracks. mudcracks. A total of of 250 250 paleocurrent paleocurrent measurements, mostly including sole sole marks, marks, measurements, mostly cross-bedding cross-bedding but but including asymmetrical ripples, trough axes, axes, yields yields an an overall overall bimodal-bipolar bimodal-bipolar asymmetrical ripples, and and trough distribution. The modes are are roughly roughly parallel parallel to The modes to the the inferred inferred shoreline. shoreline. The poorly Formation,as as thick thick as as 50 The poorly exposed exposed Pokegama Pokegama Formation, 50 m, m, contains contains the same the same sequence sequence of sedimentary sedimentary facies facies as as does does the the Palms. Palms. A few few dozen dozen scattered paleocurrent indicators polymodal paleocurrent paleocurrent plot, plot, but scattered paleocurrent indicators form form aa polymodal detailed work work on on one one long long roadcut roadcut yielded yielded 57 57paleocurrent paleocurrent indicators, indicators, detailed mostly paralleling paralleling the presumed shoreline an embayment, embayment, but but with with oneonemostly the presumed shoreline of of an fifth of of them them normal normal to to the the shoreline. shoreline. By the By the application application of Walther's Walther's Law, Law, the the lateral lateral relationships relationships can can be be 46 �interpreted. The conglomerate facies locally present present on on the the lowlowThe conglomerate facies was was locally lying peneplaned surface transgression of the sea. sea. The The argillite argillite lying peneplaned surface prior prior to to transgression of the facies facies was was the the most most proximal proximal marine marine facies facies (i.e., upper tidal flat)' upper tidal flat) resting upon conglomerate or basement upon conglomerate or basement Archean Archean rocks. rocks. Seaward the upper upper tidal tidal Seaward of of the flat was was the the middle middle tidal flat (argillite-siltstone-sandstone and (argillite-siltstone-sandstone facies) fades) and still further further seaward seaward was the lower lower tidal tidal flat or subtidal environment environment was the or subtidal (sandstone facies). (sandstone facies). As As the sandstone sandstone fades facies is is gradational gradational with with the the overlying iron-formation, overlying iron-formation, this places the the site site of the formation formation of of iron this places of the minerals on the shelf, shelf, seaward seaward of of the theterrigenous terrigenous clastics. clastics. minerals on the Ignoring basal conglomerates, conglomerates, which which likely likely have have aanOn-tidal non-tidal Ignoring the the basal origin, the Palms and the Pokegama are coarsening-upward sequences origin, the Palms and the Pokegama are coarsening-upward sequences which are which are interpreted products of aamarine marine transgression. transgression. Such interpreted as as products Such aa model has been described by Reineck (1972) and Yeo and Risk (1981). model has been described Reineck (1972) and Yeo and Risk (1981). Dutch tidal Dutch tidal flats flats provide provide aamodern modern analogy analogy (De (DeJong,1977). Jong,1977). Consistent with with aa tidal Consistent tidal environment environment is the the textural textural and and mineralogic mineralogic maturity the sands sands (Swett (Swett et al., a!., 1971; 1971; Balazs Balazs and and Klein, Klein, 1972). 1972). maturity of of the Rounding best in in the the sandstone sandstone facies facies where where the the energy energy was was Rounding and and sorting sorting is is best first-cycle quartz quartz sand sand eroded highest. However, However, first-cycle eroded off off of of the the vegetationvegetationfree, weathered and and wind-swept wind-swept adjacent adjacent peneplain peneplain may may have have already already been been free, weathered we 11- rou nded. well-rounded. REFERENCES Balazs, Klein, G. G. deV., deV., 1972, 1972,Roundness-mineralogical Roundness-mineralogical relations relations Balazs, R. R. J., and and Klein, v. 42, 42, p. p. 425-433. 425-433. of some some intertidal intertidal sands: sands: Jour. Jour. of Sed. Sed. Pet., Pet., v. DeJong, Sedimentary Geo!., Geol., v. 18, p. Dejong, J.D., 1977, Dutch Dutch tidal flats: flats: Sedimentary v. 18, p. 13-23. 13-23. J.D., 1977, Ojakangas, the early early Proterozoic Proterozoic basin basin of the the Ojakangas, R.W., R.W., 1983, 1983, Tidal Tidal deposits deposits in in the Lake Superior region--The region--The Palms Palms and and the the Pokegama Pokegama Formations: Formations: Lake Superior Evidence subtidal-shelf deposition deposition of of Superior-type Superior-type banded banded ironironEvidence for for subtidal-sheif Medaris, L.G. L.G. Jr., Jr., ed., formation: in Medaris, formation: ed., Early Early Proterozoic Proterozoic Geology Geology of of the the Geol. Soc. Lake Region: Geol. Soc. of America America Memoir Memoir 160, 160, p. p. 49-66. 49-66. Lake Superior Region: and Hamblin, Hamblin, W.K., eds., eds., Reineck, Rigby, J.K., J.K., and Reineck, H.E., H.E., 1972, 1972, Tidal Tidal flats: flats: in Rigby, Recognition of of Ancient Ancient Sedimentary Sedimentary Environments, Environments, Soc. Soc. of of Econ. Econ. Recognition 146-159. Paleont. and Mineralogists Mineralogists Special Special Publication Publication 16, 16, p. Paleont. and p. 146-159. Swett, Keene, Keene, Klein, deV., and and Smit, Smit, D.E., D.E., 1971, 1971, AA Cambrian Cambrian tidal tidal sand sand Swett, Klein, G. G. deV., An ancientancientbody--the Eriboll Sandstone Sandstone of of Northwest Northwest Scotland: Scotland: An body--the Eriboll recent analog: Journal Journal of Geology, Geology, v. 79, 79, p. p. 400-415. 400-415. recent analog: R.K. and and Risk, Risk, M.J., M.J., 1981, 1981, The Thesedimentology, sedimentology, stratigraphy stratigraphy abd abd Yeo, R.K. Yeo, intertidal deposits deposits in in the preservation the Minas Minas Basin Basin System, System, Bay Bay preservation of intertidal v. 51, 51, p. p. 245-260. 245-260. of Fundy: Fundy: Jour. Sed. Pet., Pet., v. Jour. of Sed. 47 �Targeting Footwall Copper-PGE Deposits in the Duluth Duluth Complex Complex Based Based on Sudbury Sudbury Mining Mining Camp Camp Analogs Analogs Dean M. M. Peterson, Peterson, University University of of Minnesota -- Duluth Dean workers have have studied studiedthe thegenesis genesisof ofthe the footwall footwall Cu-PGE Cu-PGE mineralization in Numerous workers the Sudbury Mining Camp. Camp. The TheCu-PGE Cu-PGE deposits deposits are are characterized characterized by by massive massive chalcopyrite veins, pods, and stringers halos. The stringers with with little little (if (if any) alteration halos. The deposits deposits are are spatially spatially hundredsof of meters meters into into the the footwall footwall associated with contact Ni-Cu ore deposits and extend hundreds Veingrades gradesofof30% 30% Cu, Cu, 3% 3% Ni, and 0.30 0.30 oz/st precious metals metals rocks beneath these deposits. Vein oz/st precious (Au, Ag, Ag, Pt, Pt, Pd) Pd) are are typical. typical. The most fundamental geologic process process associated associated with the Sudbury Mining Mining Camp Camp is is the the migration migration of of the the ore ore metals metals from from the the footwall deposits of the Sudbury Naldrettetetal. al.(1982) (1982) suggested that that Sudbury Igneous Complex into the footwall environment. Naldrett the fractional fractional crystallization crystallization of the sulfide liquid responsible for for the the the ores are attributable to the formation of the contact Ni-Cu Ni-Cu deposits. deposits. The The footwall footwall ores are believed to have formed by migration of the the fractionated, fractionated, copper-rich copper-rich residual liquid away from from the early crystallizing crystallizing monosuiphide into and along along footwall footwall structural structural zones. zones. Subsequent monosulphide solid solution (mss), into geological studies have refined this this early ore ore deposit deposit model. model. The targeting of mineralization beneath the Duluth Complex must first be based on the fundamental geologic geologic process process (migration (migration of of fractionated metals metals into into the the footwall) footwall) associated associated fundamental The diagnostic diagnostic criterion criterion that that indicates indicates copper migration is the spatial with deposit formation. The variation of Cu-Ni Cu-Ni grades and the lowering of the the Cu/Ni Cu/Ni ratio ratio in the the source rock. rock. An approach is being being developed developed to generate Cu-PGE exploration target areas in is in the the footwall footwall rocks rocks beneath Determination of of copper copper depletion depletion in in mineralized mineralized basal basal troctolites troctolites of of the the Duluth Complex. Determination Duluth Complex is the first step in the generation generation of of footwall exploration targets. The likelihood footwall Cu-PGE Cu-PGEmineralization mineralization beneath beneath the the Duluth Complex is is being being modeled modeled from from of footwall visualizing visualizing the the three-dimensional three-dimensional distribution of of Cu-Ni Cu-Ni in inthe the Duluth Diluth Complex. Complex. The The distribution of Cu-Ni in the Duluth Complex has been determined from a comprehensive compilation of hole chemistry database (Cu, of all all available availabledrill drillhole holechemistry. chemistry. To To date, date, the the drill drillhole S. Au, Au, Ag, Ag, Pt, Pt, Pd, Rh, Ir, as, Os, V, V, Cr, Cr, and and Co) Co) includes 61,560 assays (249,629 (249,629individual individual 61,560 assays Ni, 5, analyses) analyses) from from 1435 1435drill drill holes holes (Table (Table2). 2).Individual Individual analyses analyses are are located located in in three-dimensions three-dimensions (UTM east, east, UlM UTMnorth, north, elevation/ elevation/feet (UlM feet above above basal basal contact) contact) from collar information information and and basal basal 95% of of all drill hole assays are currently in the database. contact piercing points. Approximately Approximately95% Total assays assays for for the the areas in the Duluth Complex included in this study Total study are are given given in in Table Table 1. 1. The drill hole chemistry has been used to create weighted average (over 50 to 100ff used to create weighted average (over 50 to 100ft zones) gridded gridded image image maps of of Cu-Ni grades, Cu-equivalent, Cu-equivalent, and Cu/Ni zones) Cu/Niratios ratiosfor for individual individual deposit areas. The The maps maps reflect reflect the the distribution distribution of of the the ore-metals ore-metals in relation to the basal contact the Duluth Complex. Complex. Eight Eight zones have been used to to define define the distribution distribution of of ore-metals in of the the basal 500ff of the the ten ten main main Cu-Ni Cu-Ni deposits of the Duluth Complex. 500ft of Complex. The Thezones zonesinclude include0-50', a-50', 50-100', 50-100', 100-150',150-200',200-250',250-300',300-400' 100-150', 150-200', 200-250', 250-300', 300-400'and and400-500' 400-500'above abovethe thebasal basalcontact. contact. The of high high Cu-Ni Cu-Ni grades grades and and low low Cu/Ni Cu/Ni ratios for individual zones has been correlation of determined by merging the Cu-Ni grade and Cu/Ni Cu/Niratio ratiodata datasets. sets. An An example example of of a composite composite copper migration migrationin in the the basal basal 500' 500' of the Spruce Road Deposit is image depicting modeled copper Posted within withinthe theimage image are are dots dots representing representinglocations locations of of drill drill hole hole presented in Figure 1. Posted the Duluth Duluth Complex, Complex, in in the the underlying underlyingGiants Giants Range Range Granite. Granite. A A strong strong assay samples, beneath the >1% hole assays assays with with>1 % Cu (suffide (sulfide veins ranging to to correlation exists between footwall drill hole 7.9%Cu) Cu)and and the the modeled modeled copper copper migration migration in in the the overlying overlying Duluth Duluth Complex. Complex. Based on 7.9% preliminary data, this new method appears to to be be a good mineral exploration targeting method that could be used to to predict predict favorable favorable areas areas for for hosting hosting footwall footwall deposits. deposits. 48 �sSpruce pru ceRa adD epas it Road Deposit ,+ 4_,____J ,- + + + + +__+~ + + +"t + + + + ,(25 + , ; Granite 1- + 4- 4- + + ÷ 1- + + Modeled Copper Copper Migration' Migration Modeled in the Basal Basal 500 500' ofofthe the in Duluth Complex Complex + + :::÷:÷:÷:÷ + + + T High .- HiKh 19 + 1- + + I.• -1- • •- Low Coer Assays Copper Assay'sBeneath Beneath the the buluth Duluth Complex Complex in In the the I Footwall Giants Range Range Granite . I: 26 30 Granite Granite - Duluth Compiel Complex Basal Basal ContactDips Contact Dips to to theSE at25 IheSEat2S' Duluth Complex — •->l%Cu • - > 1% Cu C!! = 694) I - <1%Cu < 1% Cu I • Figure 1. Correlation of of modeled modeled copper coppermigration migrationin in the the basal basal 500 500' of of the the Duluth DuluthComplex Complex and and 1. Correlation known mineralization mineralization in in the the footwall footwall Giants Giants Range Range Granite, Spruce Road Deposit. Table 1. Total Total deposit deposit assays/ assays' Deposit analyses for for individual individual element Table 2. 2. # of analyses Element # Element Spruce Road Sprnce Road 9282 9281 Copper 61,159 Palladium 5,897 Maturi 3246 Nickel 60,300 Rhodium 1,881 Birch lake 958 Sulfur 37,120 Iridium 203 Dunka Pit 4223 Cu/Ni 60,266 Osmium 202 102 Serpentine 2000 Gold 5,109 Vanadium 1,770 1,770 30069 Silver 4,223 Chromium 2,799 Dunka Road Road 2607 Platinum 5,598 Cobalt 3,202 Wetlegs 1248 Babbitt Wyman Creek Waterhen # # 922 1813 Bibliography Naldrett, A.J., A.J./ Innes, D.G., Sowa, hines, D.G., Sowa, J.J. And And Gorton, Gorton, M., M., 1982/ 1982,Compositional Compositionalvariation variation within within and between 5 Sudbury ore deposits; Economic Geology, v. 77/ p. 1519-1534. between 5 Sudbury ore deposits; Economic Geology, v. 77, p. 1519-1534. 49 �PETROGENETIC RELATIONSHIPS BETWEEN BETWEEN APATITE-BEARING APATITE-BEARING AND AND APATITE-DEFICIENT APATITE-DEFICIENT IRON IRON PETROGENETIC RELATIONSHIPS OXIDE-RiCH OXIDE-RICH INTRUSIONS INTRUSIONS AND AND MASSIVE SULFIDE MINERALIZATION IN THE DULUTH DULUTH COMPLEX, COMPLEX, MN. RIPLEY, RlPLEY, Edward M., Department of Geological IN Geological Sciences, Sciences, Indiana University, University, Bloomington, [N 47405 Within the Duluth Complex oxide-rich, mafic to ultramafic ultramafic·intrusions by Severson intrusions (referred to as OUI by and and Hauck, Hauck, 1990), occur as as cross-cutting cross-cutting bodies bodies and and semi-conformable semi-conformable lenses. lenses. These bodies are rich in both ilmenite and titanomagnetite, and and have have been been the subject of of recent investigations investigations by Jill Pasteris Pasteris and and students at Washington University, University, and and Penny Penny Morton Morton at at the the University University of ofMinnesota, Minnesota,Duluth. Duluth. Although Although these oxide-rich bodies occur throughout the Complex there are some differences between those located located of the Complex and those in in the central and northern sections that have only in the southern portion of recently been recognized. The The best best studied studied OUl OUI in in the the central central and and northern northern portion of of the Complex are characterized by by low apatite content. In Incontrast, contrast,many manyof ofthe theOUT OUI in the southern portion of of the Complex, in particular the Boulder Lake Lake area area (Severson, (Severson, 1995), 1995), are are marked markedby byabundant abundantapatite. apatite. In at least a few areas true nelsonites (ilmenite-apatite rocks) rocks) have have been been found. found. These types of apatite-oxide occurrences are similar to cross-cutting bodies bodies that are frequently found found associated with massif-type massif-type anorthosites (e.g. Marcy, Grenville Province, Province, Rogaland Rogaland Complex). Complex). Accessory minerals in the nelsonites spinel, and sulfides. include biotite, zircon, Zn-rich spine!, Massive sulfide mineralization at at the the Babbitt Babbitt deposit is is also cross-cutting in in form, form, and and is is composed of essentially the same mineralogy as the apatite-oxide rocks, but obviously in different of mineralogy but in different proportions. Euhedral Euhedral apatite apatite (locally (locally up up to to 5%) 5%) occurs occurs disseminated disseminated in in the massive sulfides, along with spinel, baddeleyite, biotite, Zn-rich hercynitic spine!, baddeleyite, ilmenite, ilmenite, and and other other oxides. oxides. We have previously proposed of a volatile-rich, immiscible imm iscible that the massive mineralization mineralization at at Babbitt Babbitt resulted resulted from from the the emplacement emplacement of sulfide liquid. The Thesame same elements elements may may be be partitioned partitioned into into an an immiscible immiscible Fe-Ti-P-rich oxide liquid, liquid, and an origin similar to that of the massive sulfides is proposed. Sulfur is proposed. Sulfur isotopic isotopic values of of the netsonites nelsonites (34%o) 4%o), and suggest that 4%0) are distinctly different different from from those thoseof ofthe themassive massivesulfides sulfidesatatBabbitt Babbitt(10-1 (10-14%0), sulfur contamination of of the the nelsonites nelsonites has has not not occurred. The distinctly lower lower Cl Cl and and REE REE contents of of the apatite from nelsonite and related rocks (Fig. 1) I) suggests that they either either crystallized crystallized from from aa magma magma that that had had previously previously separated a ClCI- and and REE-rich REE-rich fluid, or that had experienced prior crystallization crystallization of aa CICl- and and REE-compatible REE-compatible mineral. mineral. Both mechanisms are are consistent consistentwith with the the premise premisethat thatthe theapatite-rich apatite-richOUT OUI are genetically genetically associated associated with with highly evolved, residual melts. For Forexample, example, Severson Severson (1995) (1995) has has described layered oxide-rich gabbros in in the the Boulder Lake Lake area area where where apatite apatite isis aa cumulus cumulus mineral. mineral. Just to the south in in the the Duluth Duluth Layered Layered Series, Miller (1995) has also also described described five-phase five-phase cumulates cumulates where whereapatite apatiteisisaaprimocryst primocrystmineral. mineral. In In Series, contrast, apatite apatite is is never never aa cumulus cumulus phase phase in in the the Partridge Partridge River River (PRI) (PRl) and South South Kawishiwi Kawishiwi (SKI) Apatite in in the massive sulfide mineralization at Babbitt Intrusions in the central portion portion of the the Complex. Complex. Apatite in troctolites of of the PRI PRl (Fig. 1) 1) are characterized by by and that which occurs as an interstitial mineral in higher Cl CI and REE values relative relative to to apatite apatite in in the the apatite-rich apatite-richOUT. OUI. The The 01_fl OUI in in the the central portion of of the > 45 vs. Fo Fa < 45 in in apatite-rich apatite-rich OUI), OUI), and and the Complex are not as as chemically evolved evolved (e.g. (e.g. olivine olivine Fo Fo> <45 appear to be related to interstitial melts melts of of the the FRI PRl and SKI. In Inboth bothtypes typesof ofOUT OUI the paucity of of feldspar liquid component suggests that fractionation either through buoyant mineral accumulation or liquid immiscibility is an important genetic factor. 50 �References Jr., 1995, 1995,Emplacement Emplacementand and open-system open-system crystallization crystallization of ofthe the Duluth Duluth Complex Complex at at Duluth, Duluth, Miller, J. D., Jr, Minnesota (Abs.): Proceedings of IGCP Conference, Duluth, MN, 1995, P. 127-128. ofIGCP 1995, p. 127-128. Severson, M. J., and Hauck, Hauck, S. S. A., A., 1990, 1990, Geology, Geology, geochemistry, and stratigraphy stratigraphy of ofaa portion portion of ofthe the NRRITechnical TechnicalReport ReportNRRIJGMIN-TR-89NRRIlGMIN-TR-89-11, Partridge River Intrusion: NRRI 11, 236 p. Severson, M. J., 1995, 1995, Geology Geology of of the the southern southern portion portion of of the the Duluth Duluth Complex: Complex: NRRI NRRI Technical Technical Report Report NRRI/GMIN-TR-95-26, N RRIJG MIN-TR-95-26, in in press. press. F F + + Duluth Complex Complex Apatite OH Cl CI 1.2 1 Duluth Duluth Complex Apatite 0~ l UJ w w UJ a:: •*U.. • • 0.8 0.6 •* 0.4 , 0.2 0 0 0 ...--, . •* 1 • •* *• • * •. • U 0.5 U U. •• • • • • • • U Troctolite • . • Sulfide Suffide U U Nelsonite U 1I *• 1.5 2 CI wt.% Cwt% Figure 1. 1. Compositional Compositional variations variations between between apatite apatite from from apatite-rich OUI (here nelsonite), massive sulfide mineralization at Babbitt, and and Fe-Ti-P-rich gabbroic to troctolitic tfoctolitic rocks of of the Partridge Partridge River River Intrusion. 51 �ULTRAMAFIC DIKE WITH MANTLE TO MANTLE XENOLITHS: XENOLITHS: IMPLICATIONS TO DIAMOND EXPLORATION DIAMOND EXPLORATION IN IN WAWA WAWA Sage. R P.1, P.l, Morris, Morris, T. T. F.1, F.1, Crabtree, D.2, 0. 2, Murray, C. A.1, A.l, Bennett, G.1, G.l, Hailstone, Hailstone, M.l, Pianosi,S.f, 5.1,and andJosey, Josey,S1. 51. M.1,Nicholson, Nicholson, T.3, i., Pianosi, 1 Ontario Geological Survey, 1 Ontario 933 P3E 6B5 6B5 933 Ramsey Ramsey Lake Lake Road, Road, Sudbury, Sudbury, ON P3E 2 Ontario Geosciences Centre, 933 2 933 Ramsey ON P3E P3E6B5 6B5 Ramsey Lake Lake Road, Road, Sudbury, Sudbury, ON 33Prospector, Prospector, Wawa, ON The Ontario Geological Survey completed completed 10 10 years years of of bedrock bedrock mapping mapping in the Geological Survey Wawa of R. R. Sage. Sage. When Wawa area area in 1988 1988 under under the supervision supervision of When the the Survey Survey undertook O±tario for for ~amond diamond in undertook aa project project to to examine examine kimberlite occurrences in ontario 1993, R. R.Sage Sagerevisited revisitedthe theWawa Wawaarea area to toexamine examineultramafic ultramaficdikes dikes that that displayed displayed 1993, kimberlitic At the the time time of of this this visit visit Mr. Mr. Seymour Seymour Sears, Sears, Consulting Consulting kimberlitic features. features. At the attention attention of of the the OGS OGS that that Mr. Mr. "Mickey" "Mickey" Clement had Geologist, Geologist, brought to the found what appeared appeared to to be be diamonds diamonds in the area. The The stones stones were confirmed confirmed to be diamond which promptly promptly launched the diamond by by the the Royal Royal Ontario Museum in in 1993 1993 which OGS under the OGS into a sampling program for for kimberlite indicator minerals (K[Ms) (KIMs) under T. Morris. Morris. The alluvium sampling found abundant abundant KIMs KIMs just south south direction of T. prompting prospecting of Wawa prompting prospecting activity activity in the region. In InAugust August1995 1995 Mr. Mr. Terry Nicholson, Prospector, Prospector, Wawa, Wawa, encountered encountered subcrop subcrop of of what what appeared appeared to be aa Nicholson, lamprophyre dike with 1.0 m m wide wide lamprophyre with mantle-derived mantle-derived xenoliths xenoliths approximately approximately 1.0 trending 245 245 degrees, dipping 74 74 south in August 1995. 1995. Preliminary analysis of and some some of of the the xenoliths xenoliths has identified identified minerals the mineralogy of the dike and comparable to those found found in in kimberlite. kimberlite. Thin section, analysis and and geochemical geochemicalstudy study of of this this dike dike are in section, microprobe microprobe analysis progress within within the the OGS. OGS. 52 �OCCURRENCE OF HIBBINGITE HIBBINGITE IN IN THE THE DULUTH DULUTH COMPLEX, COMPLEX, MINNESOTA, MINNESOTA, AND AND IN NORn..'SK COMPLEX COMPLEX AND AND KORSHUNOVSKOE KORSHUNOVSKOE IRON ORE DEPOSIT, DEPOSIT, IN THE NORIL'SK RUSSIA Department of of Geosciences, Geosciences, North North Dakota Dakota State State University, University, SAINI-EIDUKAT, Bernhardt, Department Fargo, ND, 58 105-5517 USA (sainieid@badlands.nodak.edu). RUDASHEVSKY, NO, 58105-5517 USA RUDASHEVSKY, 21 Line Line 8A, 8A, St. St. Petersburg, Petersburg, 199026 199026 Nikolai S., Mechanobr Technical Corporation, 21 Russia. G., Institute Institute of of Geochemistry, Geochemistry, SB SB RAS, RAS, P.O. P.O. Box Box 4019, 4019, Russia. POLOZOV, Alexander G., 664033 Irkutsk, Russia (poloz@igc.irkutsk.su) Hibbingite, y-Fe2(OHhCl, ?-Fe2(OH)3C1,first firstidentified identifiedas as an an unnamed unnamed iron iron hydroxy hydroxy chloride chloride in the the Deep Copper Zone of the Sudbury Complex (Springer, (Springer, 1989), 1989), was was characterized characterized and and named named based based on on drill core samples from the Duluth Complex (Dahlberg, (Dahlberg, 1987, 1987, Dahlberg Dahlberg and and Saini-Eidukat, Saini-Eidukat, 1991; 1991; Saini-Eidukat and others, 1994). is also also found found associated associated 1994). Our Our investigations investigations show show that that hibbingite hibbingite is with platinum-group minerals in in the the Noril'sk Noril'sk Complex Complex and and with with the the Korshunovskoe Korshunovskoe iron iron ores ores of of the southern Siberian platform. as aa platfonn. Hibbingite Hibbingite has has also also been been documented documented by by Buchwald Buchwald (1995) (1995) as terrestrial weathering product of Antarctic Antarctic meteorites meteorites and and of of ancient ancient iron iron archeological archeological artifacts. artifacts. product of Hibbingite found in ofthe the Duluth Duluth in samples from from the the Noril'sk Noril'sk Complex Complex differs differs from from that that of Complex in containing significant significant kempite kempite (Mn2(OH)3C1) (Mn2(OHhCl) component; in some cases it contains mol. % % Mn. The grains, which are up to 0.6 mm in diameter, are associated over 50 mol. associa.ted with with the the platinum-group minerals froodite, froodite, cabriite, cabriite, urvantsevite urvantsevite and and with with native native silver silver in in massive massive pentlandite—cubanite—chalcopyrite pentlandite-cubanite-chalcopyrite ore. ore deposit, Hibbingite was also recognized in drill core from the Korshunovskoe iron ore km to to the the NNE NNE of of Irkut.sk Irkutsk city in the southern Siberian platform platform located approximately 500 km (Polozov and others, 1995). fine-grained 1995). The sample in which it was found is composed of fine-grained magnetite ore associated with halite. Late pyrrhotite, calcite and chlorite crystals occur occur in in numerous cavities; pyrrhotite may contain inclusions of of halite. Hibbingite, hematite hematite and and silver grains are are found in cavities in halite; the reddish-brown hibbingite grains usually grains usually occur occur as as encrustations in the cavities. The The size size of ofhibbingite hibbingite and and hematite hematitegrains grainsisisup uptoto100 100I.tm. ~m. The grains from the the Korshunovskoe Korshunovskoe deposit deposit were were analyzed analyzed in in spring spring 1992, 1992, immediately immediately after after polished section preparation, and again in winter 1995-1996. 1995-1996. The re-analysis established that that chlorine content of the grains decreased to approximately 6 wt.% with time the cWorine wt. % concomitant with with a small increase in iron. This agrees with re-analyses of Duluth Complex hibbingite and with the Fe8(O,OH) 16CL<2, hibbingiteis isakagendite, akageneite, Feg(O,OH) 16Ck2, for for which which Cl Cl hypothesis that that aa breakdown breakdownproduct productofofhibbingite 1991). is probably an essential component (Post and Buchwald, 1991). 53 �References Cited: c.B., 1995, 1995, Hibbingite Hibbingite (-Fe2C1(OH)3C1), (~Fe2Cl(OHhCl), aa chlorine-rich chlorine-rich corrosion corrosion Buchwald, V.F,, V.F., and Koch, C.B., product in meteorites and ancient iron objects [abstr.j: [abstr.]: Meteoritics, Meteoritics, v.v. 30, 30, p.p. 493. 493. Dahlberg, E.H., E.H., 1987, Drill core evaluation for platinum group mineral mineral potential of the basal basal Dahlberg, platinum group 39 p. 255,39 p. zone zone of the the Duluth Duluth Complex: Complex: Minnesota Minnesota Department Department of Natural Natural Resources, Resources, 255, Dahlberg, Dahlberg, E.H., E.H., and and Saini-Eidukat, Saini-Eidukat, B., B., 1991, 1991, A chlorine-bearing chlorine-bearing phase phase in in drill drill core core of serpentinized troctolitic rocks rocks of of the the Duluth Duluth Complex, Complex, Minnesota: Minnesota: Canadian CanadianMineralogist, Mineralogist,v.v. 29, p. 29, p. 239-244. AG., Vorontsov, A.E., AE., and Amirzhanov, A.A., A.A, 1995, The latest process Polozov, A.G., process of mineragenesis in iron ore deposits of of the Angara-Ilim Angara- Him type, type, Siberian Siberian Platform Platform [abstr.]: [abstr.]: ill Petrology and Metallogeny of Volcanic and and Intrusive Intrusive Rocks Rocks of of the the Midcontinent Midcontinent Rift Rift System, System, Proceedings, IGCP IOCP Project 336 International Field Field Conference and and Symposium, Symposium, Duluth, Duluth, MN, MN, p.151. p. 151. Post, I.E., J.E., and Buchwald, V.F., 1991, Post, 1991, Crystal structure refinement refinement of of akagenéite: akageneite: American American Mineralogist, v. 76, p. 272-277. H., 1994, 1994, Hibbingite, Hibbingite, 'y-Fe2(OH)3C1, y-Fe2(OH)3Cl, a new mineral Saini-Eidukat, B., Kucha, Kucha, H., H., and and Keppler, Keppler, H., of Fe-bearing Fe-bearing from the Duluth Complex, Minnesota, with implications for the the oxidation oxidation of from American Mineralogist, Mineralogist, v. v. 79, 79, p. p. 555-561. 555-561. compounds compounds and and the transport of metals: metals: American Springer, uncommon minerals minerals in the the Strathcona Strathcona Deep Deep Springer, G., G., 1989, Chlorine-bearing and other uncommon zone, Sudbury Sudbury District, Disthct, Ontario: Ontario: Canadian p. 311-313. 311-313. copper zone, Canadian Mineralogist, Mineralogist, v. 27, p. 54 �Clay minerals Clay minerals of the the North North Shore Shore Volcanic Volcanic Group Group and and possible possible relationship to copper copper precipitation precipitation during alteration alteration relationship SCHMIDT, Susanne Th & STERN, Willem, Mineralogisch-Petrographisches Institut, Bemoullistr. 30, CH 4056 Basel, Switzerland; email: SchmidtS@ubaclu.unibas.ch Bernoullistr. chalcopyrite, covellite, Several occurrences of native copper with chalcopyrite, Several small occurrences covellite, and and galena are known Precambrian North North Shore Whole rock values for known in the Precambrian Shore Volcanic Volcanic Group, Group,Minnesota. Minnesota. Whole rock values for flow units units (massive (massive flow flow interiors) range range copper in altered (flow (flow tops tops and bottoms) bottoms) and less altered flow between Due to the between 11 11 and 241 241 ppm, ppm, and and Zn Zn values values between between 49 49 and and 167 167 ppm. ppm. Due the general general of the the series from a continental to an aborted rifting geochemical evolution of rifling environment there is a general increase in in the the lava lava flow flow interiors interiors from stratigraphically stratigraphically lower lower to to in the the primary primary Cu Cu content content in higher flows (Basaltic Volcanism Project, 1982; Schmidt, Schmidt, 1990). 1990). Superimposed Superimposed on on this this trend trend are are secondary trends. In Inlower lowermetamorphic metamorphic grade grade flows, flows, the the massive massive flow interiors (dark square square in in Fig. la) la) show show in in general general higher higher copper copper values values than the flow flow tops tops and and bottoms. bottoms. This This trend trend isis Fig. of the the series series where where the the flows flows show show alteration alteration assemblages assemblages typical typical of of reversed at the the bottom bottom of reversed beginning greensehist greenschist facies (prehnite-pumpellyite-chlorite (prehnite-pumpellyite-ehlorite or epidote-chlorite epidote-chiorite assemblages). assemblages). Here, Here, the altered flow flow tops tops and and bottoms bottoms and and the the transitions transitions zones show higher Cu values values than than the the massive flow interiors. At Atall allstratigraphic stratigraphiclevels, levels, the the highest highest copper copper values values are are observed observed in in the the transition transition zone zone to the the massive massive flow flow interior, interior, i. e. the the near near top top or or near near bottom bottom areas areas with with clay clay minerals ± ± quartz quartz -- prehnite ± pumpellyite ± albite assemblages. is only in the highest grade flow A similar trend is observed for zinc. zinc. ItIt is flow where the massive flow interior shows lower values values than than the the other other flow flowunits units(Fig. (Fig.Ib). ib). Again flow Again the transition zones to the massive flow interior interior (near (near bottom bottom and and near near top) top) display display the the highest highest values. values. minerals show a great variety in chemical composition as well as In these metabasites clay minerals in structural type. Various Varioustypes types have have been been identified identified based based on on electron electron microprobe microprobe analysis, analysis. Xray diffraction and deconvolution analysis. Smectites Smectites and and mixed mixed layer layer phyllosilicates phyllosilicates are are common in the flow tops higher levels levels of of lower lower metamorphic metamorphicgrade. grade. Chiorites in tops of of strat.igraphically stratigraphically higher Chlorites and more common common in in flow flow tops tops of of the the stratigraphically stratigraphically lower lower part part or or higher higher grade grade corrensite are more Smectites as as well well as as metamorphic (Schmidt, 1993 1993 and metamorphic units units (Schmidt, and Schmidt Schmidt & & Robinson, Robinson, submitted). submitted). Smectites mixed-layer minerals identified in massive flow stratigraphically minerals have also been identified in the massive flow interior of stratigraphically lower or higher grade flows. 55 �Clay minerals have been been isolated isolated from from the the different different morphological morphological units and have have been been by XRF.. XRF. They They show show varying varying contents contents of of copper copper and and'zinc. zInc. In addition, selenium has analyzed by In addition, been detected in in smectite. Smectitic relationship of clay This suggests a close relationship clay minerals minerals to to copper copper mineralization. mineralization. Smectitic phases dominant in low grade grade metamorphic metamorphic rock will not be stable under beginning beginning greenschist greenschist conditions. They They will willbreak breakdown down and and the the copper copper will will be bereleased. released. Chlorite Chlorite ± prehnite prehnite ± ± conditions. stable and and copper will will be be locally enriched in these these pumpellyite ± ± albite ±± quartz assemblages wifi will be stable assemblages. Basaltic Volcanism Study Project Project (1981) (1981) Basaltic Basaltic Volcanism Volcanism on the !.he Terrestrial Planets, Planets. Pergamon Pergamon Press, Press. New York, p. York. 1289 1289 p. metamorphism in in the the North North Shore Shore Volcanic Volcanic Group. Group, Schmidt, S. Th. (1990) Alteration under conditions of burial metamorphism Minnesota -- Mineralogical and geochemical zonation. Heidelberger Geowissenschaftlicbe Abhandlungen. Geowissenschaftliche Abbandlungen, Band 41, 41. 3O9p. 309p. Group. Schmidt, S. Th. (1993) Regional and local patterns of low-grade metamorphism in the North Shore Volcanic Group, Minnesota, USA. 401-414. of Metamorphic Metamorphic Geology, Geology. 11, 11.401-414. USA. Journal Journal of Schmidt, S. Th. & Robinson, Schmidt. Robinson. D. D. (submitted) Metamorphic grade and porosity/permeability controls on mafic in aa regional regional metamorphic metamorphic zeolite to greenschist facies transition of ofthe the North North distributions in phyllosilicate disthbutions fades transilion Shore Volcanic Group, Group. Minnesota. GROUP, WHOLEWHOLE ROCK VOLCANIC GROUP, NORTH SHORE SHORE VOLCANIC ::. top of sequence zeolitezones zeolite zones <:l!.. D: • o~ ~ III 0 0 ~ Ll. beginning beginnin,g green8chl8t greenechist zones bottom of sequence 8o AVO '" <> ~ 0 • o0 25 26 50 <:> "'-0 00 00 • • • • 00 00 ~ <D aDa tV0 o Ll. 0o 6 0 o • • ~ 0 A ~ 0 0 cl>o 0 • <> near bottom •• massive massive flow flow o near top 6 flow top 0'" Av:v; :• :. <> 10 ooo~ '11 6 'V 0 6 00 ~ 0 'V flow Fwrn bottom ROCK 'V ~o 0 to.o oU0 o~. 0 0 o ~ • 0 75 100 175 200 100 125 125 150 150 175 200 2252500 Cu (ppm) (ppm) 20 40 0 60 {:;,. <> 'V 140 160 80 100 120 140 160 180 Zn (ppm) (ppm) Cu content content (Fig. (Fig. 1a la ) and and Zn Zn content content(Fig. (Fig.1b) ib) in in basaltic basaltic lava lava flows Cu 56 0 <> �BASALTIC KOMATIITES AND ASSOCIATED ROCKS: ROCKS: IMPLICATIONS IMPLICATIONS ON ON THE THE NATURE OF VOLCANISM IN PART OF THE SCHREIBER-HEMLO GREENSTONE BELT, NORTHWESTERN ONTARIO BELT, SMYK, Survey, Ministry of NQrthern SMYK, M.C., M.C., Ontario Geological Survey, Development and Mines, Mines1 Suite B002, Development B002, 435 S. S. James St, Thunder Bay, St, Bay, Ontario, Ontario, P7E P7E 6E3, 6E3, and and KINGSTON, KINGSTON, D.M., Surface Science Western, Western, University of D.M., Western Ontario, Ontario, London, London, Ontario, Ontario, N6A N6A 5B7 5B7 Well-preserved, basaltic basaltic komatiltes komatiites have have recently recently been been discovered discovered Well-preserved, succession of of subaqeuous subaqeuous basalts basalts and andinterf interflow within aa succession low sedimentary rocks of the the Neoarchean Schreiber-Hemlo Schreiber-Hemlo greenstone greenstone belt. Two, sections consist consist of of pillowed pillowed to to massive, massive, Two, detailed sections high-Mg tholeiitic basalt and basaltic komatiite. komatiite. Individual flow sub-units, sub-units, varying in thickness m, are flow thickness from 1 to 20 20 m, "Crowded' and and/or conformably conformably stacked. stacked. "Crowded" intercalated and/or (- 10% 10% pillows) pillows) flows flows and and autoclastic autoclastic incipiently pillowed (— breccias comprise the the bulk bulk of of the the succession. succession. Pillows pillows range from from small small ((~ 30 30 cm), cm), bun-shaped bun-shaped forms forms to to large, large, mattress-shaped mattress-shaped (>3 m). m). Broken pillow breccia and hyaloclastite megapillows (>3 occur between flow flow units and in in interpillow interpillow spaces. spaces. These These extrusive rocks are characteristically variolitic; variolitic; varioles varioles tend tend to coalesce in pillow cores, to cores, along selvages selvages and and along along flow flow contacts. A A 99 m m thick, thick, composite, composite, basaltic basaltic komatiite komatiite flow flow has has been been identified in in the the upper upper section. section. It It consists of of aa massive, massive, ultrarnaf Ic base base (MgO ~ 20%) ultramafic 20%) followed upwards by three, three, spinifexspinifextextured flow flow units: units: (i) foliated; (ii) (ii) coarse (~8 cm), cm), lower, foliated; coarse (8 (I) lower, plate; plate; and (iii) (iii) upper, upper, randomly randomly oriented. oriented. The The MgO MgO contents contents of of flow units range range from from 8% 8% to to 11%. 11%. Primary minerals have have these flow been replaced and pseudomorphed by metamorphic mineral assemblages consisting consisting of of tremolite-actinolite, tremolite-actinolite, serpentine, serpentine, calcite, quartz and Magneslan hornblende has replaced calcite, and chlorite. chlorite. Magnesian primary clinopyroxene clinopyroxene that that originally originally comprised comprised the the spinifex spinifex megacrysts and In addition addition to to these characteristic and phenocrysts. phenocrYsts. In petrographic features, features, the major element chemistry is is consistent consistent with known known basaltic basaltic komatiites. komatiites. Thin section petrography has revealed revealed polygonal dendrite networks, skeletal / hollow-cored phenocrysts led networks, skeletal/hollow-cored phenocrysts and and devitrif devitrified glass. textures, together together with with the the various various spirilfex spinifex glass. These textures, textures and tremendous variole development, development, suggest suggest rapid rapid textures The chilling/quenching and chilling/quenching and undercooling undercooling of of these these basaltic basaltic lavas. lavas. the pillowed and brecciated brecciated low vesicularity and disposition of the flow units units suggest suggest deep deep water extrusion, flow extrusion, on relatively flat flat Successive flow lobe depositional surfaces. surfaces. lobe or lava tube emplacement, with fluctuating fluctuating lava lava levels, levels, is is supported supported by by emplacement, stacking and and the the presence presence of of stacked stacked lava lava shelves shelves megapillow stacking pillows. The progression from from (mega)pillow-dominated (mega)pillow-dominated within pillows. flows section, to incipiently pillowed and flows in in the the lower section, brecciated units in in the the upper, upper, komatiitic section section may indicate indicate waning from from high high to to lower lower effusion effusion rates. rates. 57 �NORTHEASTERN MINNESOTA MOR!rDASTElUf MIMHESarA DULUTH COMPLEX MINERAL IlIHERAL POTENTIAL Allan Allan Spector, Allan Allan Spector Spector, Spector and and Associates Associates Ltd., Ltd., Toronto, Canada, M5N 1S7 157 Toronto, Canada, 24 Strathallan Boulevard, Boulevard, 24 Strathallan T.L. Lawler, of Natural T.L. Lawler, Minnesota Department Department .of Natural Resources, Resources, Division Division of of Minerals, Minerals, 1525 Third Ave. E., Hibbing, Hibbing, Z1 MN 55746 55746 Ave. B., of northeastern northeastern Minnesota Minnesota show show older older assemblages assemblages of of late late Archean Archean Geologic maps of and early early Proterozoic Proterozoic rocks truncated by crescent shaped shaped intrusive intrusive unit unit rocks truncated by aa crescent approx~ately 1.1 billion billion years years old. old. The igneous rocks welled in a rift of the approximately 1.1 welled up in earths crust which runs northeasterly from Nebraska, through Iowa earths and up the the Iowa and eastern side side of of Minnesota. Minnesota. It then curves curves out out into intoLake Lake Superior Superior and and runs It then southerly into Michigan. The is aa major major continental continental feature feature which which is well into Michigan. Therift rift is is well defined by gravity and defined by gravity and aeromagnetic surveys. surveys. Extrusive Extrusive volcanic rocks to rocks related related to these intrusivee these intrusives are are found found in the the north north shore shore volcanics, volcanica, widespread widespread volcanic volcanic assemblages in the western western part assemblages part of of the Opper Upper Peninsula Peninsula of Michigan Michigan and some some flows flows in Wisconsin. In in northern Wisconsin. In Minnesota the the intrusive intrusive rocks rocks are are known as the Duluth Complex. form a belt extending north from Complex. These rocks form from Duluth Duluth to to Hoyt Hoyt Lakes Lakes then running northeasterly, northeasterly, then running then east east to to Lake Lake Superior, Superior, not not far far south south of the Canadian They underlie underlie an area with considerable border. They of about aDout 20,000 considerable area of 20,000 square miles with outcrop, or or covered bya athin thin layer layer of of glacial outcrop, covered by glacial deposits. deposits. The rocks rocks of The of the theDuluth DuluthComplex complex form a a patchwork patchwork of intrusions.Some Some of of layered layered intrusions. the minerals contain contain iron iron and and are are quite quite dense, dense, therefore therefore they they display display distinct distinct responses on gravity and magnetic surveys. surveys. Similar intrusive rocks in; in; Montana (the Stillwater Stillwater Complex), complex), Africa (the (the Buahveld Bushveld Complex), Complex), Ontario (the (the Sudbury Sudbury Igneous Igneous Complex), complex), and and Russia Russia (the (the Noril'ak—Talnakh Noril' sk-Talnakh Intrusion) Intrusion) host host economic economic deposits of copper—nickel, and some deposits copper-nickel, platinum platinum group group minerals, minerals, and some gold. gold. Massive Massive copper—nickel sulfide p.g.m. are are commonly cozon1y found copper-nickel sulfide deposits deposits with with minor p.g.m. found near near the the base base with intruded intruded rocks rocks or or as as dike dike like of the intrusive at or or near the contact contact with like intrusive body, at bodies intruded intruded into into the footwall footwall rock. rock. In In addition addition platinum platinum group group minerals, and and chromium horizons chromium horizons are are found found in in reefs, conmonly commonly well above aDove the intrusive intrusive contact. contact. bearing sulfide In the mid 1960a of dark 1960s outcrops outcrops and and boulders boulders of dark igneou. igneous rocks rocks bearing sulfide copper—nickel minerals were recognized along the the footwall footwall contact contact of of the the Duluth Duluth copper-nickel Complex in the northeast complex northeast trending trending section section of the the contact contact zone. zone. Exploration Exploration of of this area located mineral deposits deposit. which contained marginal economic mineralization estimated est~ted to be 4.4 billion tons with a a copper copper content content of of 0.66% 0.66\ copper to nickel ratio and a copper ratio of of 3.3:1 3.3:1 (Liaterud (Listerud and and Meineke). Meineke). of the of the Inferred the footwall footwall of the Duluth Duluth Complex Complex based based on Inf erred geological geological maps naps of geophysical interpretations, interpretations, were prepared by Dr. Dr. Allan spector Spector and Associates Associates under contract display lithology, under DNR. The The maps maps display lithology, structure, depth to contract to to the the DNR. magnetic basement basement and and mineral potential modeled from geophysical magnetic geophysical characteristics. characteristics. data (shown mineral potential areas are are character:ized characterized by The mineral by gravity gravity and and magnetic data on profiles) which indicates the intrusive. extend to to the the west west of of the the mapped mapped on profiles) which indicates the intrusives extend contact as sills, contact sills, or features not not explained explained by by outcrop outcrop or or drilling. Some of of the MPAS correlate with geochemical Alminas (Alminas and northern KPAs geochemical anomalies anomaliesmapped mapped by Alminas Dahlberg). Dahlberg) • structure, depth drilling. Alminas, Henry V. and Dahlberg, B. B. Henk, Henk, 1994, 1994, Platinum, Platinum, palladium, palladium, and and gold gold and Dahlberg, of the the Duluth distribution distribution in B—Horizon B-Horizon soils soils on on the the northwestern northwestern part part of Complex, Complex, Minnesota: Minnesota: Mimi. Minn. Dept. Dept. of Natural Natural Resources, Resources, Div. Div. of of Minerals, Minerals, Report 308, 308, Hibbing, Bibbing, Minn., Minn., p. p. 15. 15. Listerud, Listerud, W.B. portion of the the W.H.and andMeineke, Meineke,D.G., D.G.,1980, 1980,Mineral Mineralresources resourcesofof aa portion Duluth Complex and adjacent rocks in Louis and and Lake Lake Counties, Counties, in St. St. Louis northeastern Minnesota: Mimi. Minn. Dept. of Natural Resources, Div. of Minerals, Minerals, Report 93, 93, Hibbing, Hibbing, Mimi., Minn., p. p. 49, 49, illustrations illustrations 47, 47, tables tables 3. 3. Spector, Allan, 1995, 1995, Report Report on on aeromagnetic aeromagnetic data data interpretation interpretation western western Duluth Duluth Complex: Prepared Prepared for for the the Minn. Minn. Dept. of of Natural Natural Resources, Resources, Div. of Complex: Minerals, Proj. Minerals, Proj. 308, 308, p. 15, figs. 24. p. 15, figs. 24. 58 �UPDATE ON ON THE THE GEOLOGICAL CORE AND SAMPLE REPOSITORY REPOSITORY William T. T. Swenor Geological Survey Division, Department Of Environmental Quality Marquette, Michigan Marquette, The The Geological Geological Survey Survey Division Division (GSD) (GSD) of the the Michigan Michigan Department Department of Environmental Environmental Quality Quality (DEQ) (DEQ) drill maintains maintains the the Geological Geological Core Coreand andSample SampleRepository RepositoryatatMarquette, Marquette,Michigan. Michigan. The The collection collection of of dnll core, core, cuttings, cuttings, and and other other samples samples are are from from 63 63 counties counties in in Michigan, Michigan, including including 14 14 of the 15 counties from the the Upper Upper Peninsula. Peninsula. The The purpose purpose of of this this collection collectionisisto to act act as as aa "rock" rock" library library and and make make the the stored stored researchers and industry for geological study study and and to to promote promote mineral mineral and and samples available to individual researchers fuel exploration and fuel and development in Michigan. As January 1, 1996, there holes containing As of January 1, 1996, there are are 771 771 drill drill holes containing 251,000 251,000 feet feet of of actual actual core, core, mostly mostly from from the the Upper Peninsula. Peninsula. Another holes have have abbreviated abbreviated core core representing representing 124,000 124,000 feet. feet. Also, an Another 365 365 holes Also, an additional 202 holes have cuttings cuttings that that represent represent 54,000 54,000 feet. feet. In addition to the exploration exploration drill holes, holes, additional In addition the repository repository is storing oil and and gas cores cores and cuttings from throughout throughout the the State. State. Since January, January, 1994, 1994, selected selected cuttings cuttings from from all all new new oil oil and and gas gaswells wellsdrilled drilled inin Michigan Michigan have have been beensent sentto tothe the repository. repository. The 317 317 wells wells have have cuttings cuttings that that represent representover over538,000 538,000feet. feet. An An additional additional 9,100 9,100 feet of oil and and gas core is is also in storage. The most was the the early The most significant significant recent recent addition addition was early release release of confidentiality confidentiality of of the the deepest deepest all-cored all-cored mineral March, 1995. 1995. AMOCO AMOCO Production Production Company Company released released the confidentiality on core, mineral well well in in March, the confidentiality on the the core, wells logs logs and and file file data data for their St. Amour #1-29 and wells and #1-29R test wells. The 1-29R 1-29R is is aa 7,238 7,238 foot foot hole hole drilled in in late late 1987 1987 to to learn leam more more about about the the Mid-continent Mid-continent Rift. Rift. It was was located located southeast southeast of that was drilled Munising, near near Wetmore, Wetmore, inin Alger Alger County County in in the the Upper The hole hole went went through through 110 110 feet feet of Munising, Upper Peninsula. Peninsula. The glacial drift and entered bedrock bedrock ininthe the Paleozoic Paleozoicaged agedAutrain AutrainFormation FormationofofOrdovician Ordoviciantime. time. The The hole hole glacial and entered ended in Precambrian Precambrian aged aged Portage Portage Lake Lake Volcanics Volcanics of of Keweenawan Keweenawan time. This This core core should should be be of of ended interest to to geologists geologists from from academia, the oil and gas and the mineral exploration interest exploration industry. industry. The GSD's metallic mine includes thousands mine and and data data collection collection isis also also stored storedatatthe the repository. repository. This includes thousands of of surface and maps from from early to more recent mines from the and underground underground maps the western westem one-half one-half of of the the Upper Upper Peninsula. Reports Reports and and other other miscellaneous miscellaneous information information isis also also available available from from this same area. area. This collection helps helps in in the the understanding understandingof ofthe the geology geology and and mineral mineral resource resourcepotential potential of of the the State, State, as as well well collection as being being an an aid aid to to public safety and land use planning. as planning. ItIt is a record record of potential potential mine mine subsidence subsidence areas areas of the State State which should be avoided when when construction is planned. planned. The repository occupies occupies two two separate separate buildings. buildings. The first building building is is 4,000 square feet with electricity and and examination room. room. The a heated heated examination The second second building building contains contains 3,200 3,200 square square feet of of storage storage space space and and is is adjacent to to the main building. Retrieval, replacement, replacement, splitting, splitting, and and slabbing slabbing of material material is provided by adjacent building. Retrieval, Limited sampling sampling of material is allowed cores and and other other samples samples is is possible possible on on aa staff. Limited allowed and and borrowing borrowing cores case-by-case basis. case-by-case basis. Currently, no user user fees. fees. The is open open by by appointment, appointment, Monday Monday The facility is Currently, there there are no through Friday, Friday, 8:00 8:00 a.m. a.m. to 4:30 p.m. Also, a complete complete inventory inventory of of the the Core Core and and Sample Sample Repository Repository isis appointment or at at thethe Upper available. For an aøpointment available. For or more moreinformation, information,call callBill BillSwenor, Swenor.Geological GeologicalTechnician, Technician, Uer Peninsula Peninsula Field Headquarters in in Marquette at 906- 228-6561. 228-6561. The GSD GSD also also maintains maintains oil oil and and gas gas well well cuttings cuttings from from over over 10,000 10,000 wells wells drilled drilled prior prior to to 1994 1994 and and over over The 45,000 drillers logs logs and thousands of geophysical geophysical logs. logs. Contact Contact the the Petroleum Petroleum Geology Geology and andProduction Production water well well logs Unit in Lansing Lansing for more more information information at at 517-334-6930. 517-334-693.0. For Statewide Statewide water logs and and microfilm microfilm records, contact contact Lisa Lisa Farhat Farhatinin the the Administrative AdministrativeSupport SupportUnit Unitatat517-334-6936. 517-334-6936. Copies Copies of of all all Upper Upper records, Peninsula water well well records records and and well well cuttings cuttings from from over over 600 Peninsula water 600 selected selected wells wells are are stored stored at at the the DNR DNR Escanaba Office. Call Escanaba Office. Call Frank Frank Chenier Chenier at at 906-786-2351 906-786-2351 for for more more information. information. 59 �OUTCROP AND SUBSURFACE CORE ANALYSIS AND RELATIONSHIP OUTCROP AND RELATIONSHIP TO REGIONAL HYDROCARBON INNORTHERN NORTHERNWISCONSIN WISCONSIN PROSPECTIVENESS OF THE MIDDLE MIDDLE PROTEROZOIC PROTEROZOIC NONESUCH NONESUCH FORMATION FORMATION IN AND MICHIGAN MICHIGAN S. J. J. Uchytil Uchytil and and C. C. K. K. Steffensen. Steffensen,Vastar Vstar Resources, S. Resources. Inc. Inc. Houston, Houston. TX 0. M. D. M. Jarvie, Jarvie. Humble Geochemical Services, Services. Humble, Humble, TX TX A. B. B. Dickas, A. Dickas. University Wisconsin-Superior, Wisconsin-Superior. Superior, Superior. WI WI M. G. 0. Mudrey, WI M. Mudrey. Jr., Jr.. Wisconsin Geological Geological and and Natural Natural History History Survey, Survey, Madison, Madison, WI The Middle Proterozoic Nonesuch Formation, Formation. often often described described as as aa hydrocarbon hydrocarbon generating generating source source rock, rock. partially partially infill sequence sequence of composes the sedimentary rock infill of the the Midcontinent Midcontinent Rift Rift System System in in northern northern Wisconsin Wisconsin and and Michigan. Michigan. Nonesuch Formation, Formation. acting acting as as both both aa hydrocarbon hydrocarbon source source and and reservoir reservoir unit, unit. is is The exploration potential of the Nonesuch supported the VVhite White Pine Pine. Ml, MI. and numerous geochemical geochemical studies studies that that demonstrate demonstrate supported by oil seeps in the Pine Mine. Mine, White White Pine, derived from from the the Nonesuch Nonesuch Formation. Formation. that the oil inri the White Pine Mine is derived Outcrop, subsurface core samples. samples, and an oil sample from the White Pine an Outcrop, Pine Mine were collected, collected. along an approximate 150 150mile miletransect transectfrom fromnorthwest northwestWI WInortheast northeastto tothe the Keweenaw KeweenawPeninsula Peninsulaof ofMI, Ml, and and analyzed analyzed for fortheir their approximate organic organic geochemical characteristics charactenstics (Figure I). In addition. addition, the rate rate of kerogen kerogen decomposition was measured on on a Nonesuch Formation Formation shale shale core core sample. sample. The exposure is is required required to to convert convert Nonesuch The kinetic kinetic results results suggests suggests a high thermal thermal exposure Nonesuch Formation Formation kerogen kerogen into hydrocarbons, in the the Nonesuch hydrocarbons. and and the the Nonesuch Nonesuch Formation Formation is a poor to fair source source rock rock in areas quality hydrocarbon hydrocarbon source source rock. rock. areas examined examined and and presumably never was a high quality While we do not discount the possibility ofMidcontinent Midcontinent Rift Rift hydrocarbon hydrocarbon accumulations accumulations in in the the study study area, area. possibility of successful hydrocarbon exploration, in the the northern northern Midcontinent Midcontinent Rift Rift for for major major successful exploration. targeting targeting the the Nonesuch Nonesuch Formation Formation in million barrels barrels of of oil oil equivalent) is unlikely. 10 million unlikely. reserves (over 10 Outside the Nonesuch Formation outcrop area, area. the the hydrocarbon hydrocarbon prospectiveness prospeetiveness is is less less well known. known. However, However.with with St. Amour #I-29R release release of of the the former former proprietary proprietary Amoco St. #l-29R core (Alger County, County, MI), Ml), the known deposition of Nonesuch-type stratigraphy is extended Nonesuch-type extended eastward eastward to tothe thelongitude longitudeofofMunising. Munising.Here Here182 182 ftft of of brown, brown. gray, gray, and and black black fine-grained typical Copper Harbor Conglomerate Conglomerate rocks. rocks. fine-grarned clastics, clastics. enveloped enveloped in in 46 and and 50 50 ftft basalt basalt flows, flows. underBe underlie typical This diversion from the Oronto Group type-section type-section sequence sequence suggests suggests an an eariier earlier initiation rnitiation of of Nonesuch-style Nonesuch-style deposition in in the the eastern eastern Lake Superior Basin. Basin. Consideration deposition Consideration of of multiple multiple time penods periods of Nonesuch-type NoneSUch-type deposition during the extension phase of Midcontinent Midcontinent Rift Rift development development would would indicate indicate the the hydrocarbon hydrocarbon potential potential of of the the Middle Middle U. S. is yet to be fully evaluated. Proterozoic Proterozoic of the the midcontinent U. Bibliography Bibliography AlIen, 0. J., the J.. Hinze, Hinze. W. J., J.. Dickas, Dickas. A. B., B.. and and Mudrey, M. 0. G. Jr., Jr.. in in press, press. Integrated Integrated geophysical modeling of the Allen. D. North American American Midcontinent Rift System: new interpretation for western Lake Superior, North Superior. northwestern Wisconsin, Wisconsin, w.. Dickas, Dickas. A. B. B. and Green J. C. (eds), (eds). Middle Proterozoic to Cambrian and and eastern eastern Minnesota: Minnesota: in Ojakangas. Ojakangas, R. W.. rifting, central North America, ofAmerica, America.Special SpecialPaper Paper312. 312. rifting, America. Geological Geological Society Societyof Elmore. R. R. 0., Elmore. D.. Milavec. Milavec. S. S. W., W .. Imbus, Imbus.S. S.W. W.and andEngel, Engel.M. M.H.. H..1989, 1989. The The Precambrian Precambrian Nonesuch Nonesuch Formation Formationof ofthe the North American Midcontinent rift, lacustrine deposition: North American rift. sedimentology and organic geochemical aspects of lacustnne Precambrian 43.p.p.191-213. 191-213. Precambrian Research, Research,v.v.43, Hieshima, G. G. B.. 8., Zaback, potential of Precambrian Precambrian Nonesuch Nonesuch Formation, Formation, Hieshima. Zaback. 0. D. A., A.. and and Pratt, Pratt. L. L. M., M.. 1989, 1989. Petroleum potential Mid-Continent Rift Rift System (abstract). (abstract), Bulletin American Association of Petroleum Geologists, Geologists. v. 73, 73. p. 363. Hieshima, 0. Sulfur/carbon ratios ratios and and extractable organic matter of the Middle Proterozoic G. B. B. and and Pratt, Pratt. L.L. M., M.,1991, 1991. Sulfur/carbon Proterozoic Nonesuch Formation. Formation, North American Midcontinent v. 54, 54, p. p. 65-79. 65-79. Nonesuch Midcontinent Rift: Rift: Precambrian Precambrian Research, Research. V. 60 �Imbus. S. S. W. W., Engel. The origin. ongin. distribution distnbution and hydrocarbon Imbus. Engel. M. M. H. H.. Elmore, Elmore. R. R. D., D.. and and Zumberge. Zumberge. J.J. E., E.. 1988, 1988. The generation potential of organic-rich facies generation facies in in the the Nonesuch Nonesuch Formation, Formation. central central North North Amencan Amencan Rift Rift System: System: aa regional study: Geochemistry v. 3, p. regional study: Organic. Organic Geochemistry, v. 13, p. 207-219. 207-219. Imbus. S. S. W., W. Engel, Imbus. Engel, M. M. H.. H.. and and Elmore, Elmore, R. R. 0., D.,1990, 1990, Organic Organic geochemistry geochemistry and and sedimentology sedimentology of of Middle Middle Proterozoic ProterozoIc Nonesuch Formation-hydrocarbon Formation—hydrocarbon source source rock rock assessment assessmentof ofaa lacustrine acustnne sift sift deposit deposit: in in Katz. Katz. B. B. J. J. (ed), (ed), Lacustnne Lacustrine Nonesuch basin exploration case studies and basin and modem modem analogs: analogs: American American Association Association of of Petroleum Petroleum Geologists Geologists Memoir Memoir 50, 50, p. p. 197-208. Kelly, W.C. W.C. and and G.K. GK. Nishioka, and the the role role of hydrocarbons hydrocarbons on on copper copper Kelly, Nishioka. 1985, 1985, Precambrian Precambrian oil inclusions in late veins and mineralization at at White White Pine, Pine, Michigan: Michigan: Geology, G.e!agy, v. 13, 13. p. 334-337, 334-337, 1985. 1985. mineralization Pratt. Pratt, L. L. M.. M., Summons, Summons, R. R. E., E.. and Hieshima, Hieshima. G. G. B., B., 991, 1991, Sterane Sterane and and trrterpane trtterpane biomarkers biomarkers in in the the Precambrian Precambrian Acta. v. v. 55,55. p. p. 911-916. 911-916. Nonesuch Formation, Formation, North North American AmericanMidcontinent MidcontinentRift: Rift:Geochemica GeochemicaetetCosmochemica Cosmochemica Acta. Price, K. K. L.: L Huntoon. the Price. Huntoon.J.J.E.. E..and andMcDowell, McDowell,S.S.D., D.,996, 1996,Thermal Thermalhistory historyofof the1.1 1.1 Ga Ga Nonesuch Nonesuch Formation, Formation. North North American Mid-Continent Rift, Rift, White White Pine, Pine. Michigan: Michigan: American American Association of of Petroleum Petroleum Geologists Bulletin, Bulletin, v. v. 80, 80. p. p. 1-15. 1-15. Price. S. D., 993, 1993, Illite/smectite Illite/smectite geotherinometry geothermometry of ofthe the Proterozoic Proterozoic Oronto Oronto Group, Group, Midcontinent Midcontinent Price, K. K. L. L, and and McDowell, McDowell, S. 41, 41.p.p.134.147. 134-147. Rift System: Clays Claysand andClay ClayMinerals, Minerals,v. v. Uchytil, S. S. J., J., Jarvie. 0. Uchytil, D. M., M., and and Steffensen, Steffensen, C. C. K., K.. in in press, press. Hydrocarbon Hydrocarbon prospectiveness prospectiveness of of the the Middle Middle Proterozoic ProterozoIc Nonesuch Formation Formation in northern Wisconsin and Michigan: Wisconsin Geological and Natural History Survey. Nonesuch Survey. ..a_........, WISCONSIN i-"'=".- _ ..-.. 'ACQIa1OI.U - 1--'- _1Dl ~ "",,"1UClI ~~:=... _itA IT.~ ~ "'lIlA . . . .AIDl N i ~ _u.- - vou:.uc ee.~ - 15 MI o FRda Fonft8l1on • NonnuctI Form8l1on m:m ~ Fm. HwDor ~ PortaGe LaIaI Vol. GrOUIl Figure I.I. GeologiC Geologic and and location map of the southern region. Circles of the the southem Lake Superior region. Circles identify identify cored cored sites sites (1-6) (1-6) of Nonesuch Formation Formation by by the Bear Creek Mining Company. Company. Squares Nonesuch Squares identify identify outcrop outcrop sections sections (7-20) (7-20) where where Nonesuch Map redrawn redrawn from from Elmore Elmore and others, 989, 1989, and and Allen Allen and andothers, others, inin Nonesuch Formation Formation samples were collected. collected. Map press. 61 �New Bathymetric Map of Lake Superior A New Nigel 1. Wattrus, Large Large Lakes Lakes Observatory-University Observatory-University of of Minnesota; Minnesota; Ken Keri Anderson, Anderson, University University of i. Wattrus, John Sharkey, Sharkey, Large LargeLakes LakesObservatory-University Observatory-Universityof ofMinnesota; Minnesota; and andTroy TroyHolcombe, Holcombe, Minnesota; John National Geophysical Data Center Center -- NOAA, Boulder, Boulder, Colorado. INTRODUCTION The Large Lakes Observatory is producing The producing a new new bathymetric bathymetric map map of Lake Superior using data collected by the the National Ocean Survey (formerly the U.S. Coast and Geodetic Survey) and archived by archived at at the the National National Geophysical Boulder. Colorado. This data is is supplemented with with data digitized from from earlier earlier Geophysical Data Center in Boulder, bathymetric charts to to create create maps maps that that show show detail detail never never before before attained. attained. this project project is focused focused on western western third Lake Superior, Superior. from The initial phase phase of this The initial third of Lake from Duluth Duluth up up to to the international border near Isle Royale. Subsequent phases of this project will address the central and and eastern eastern portions of the lake. lake. DATA ANALYSIS After the the data are received and remove bad data points. After received they they are carefully carefully checked checked to to identify identify and remove bad points. Maps are created using using the the GMT GMT software software system system (Wessel (Wessel and Smith, Smith. 1991) 1991) for for gridding gridding and and contouring. contouring. The The data data are to aa 3-minute 3-minute grid. grid. Figure Figure 1I shows shows an an example example of ofthe themaps maps produced. produced. This This example example shows shows the the are fit to bathymetry of of the the lake lake at its extent near near Duluth. Duluth, Minnesota. Minnesota.The The map map isis contoured contoured at at 5 m bathymetry its westernmost westernmost extent intervals. The new new map map reveals reveals details details not not previously previously seen seen in in earlier bathymetric bathymetric maps of the lake. The steep slope of of the North Shore of Minnesota exhibits irregular ridges ridges and and channels channels that that probably probably correlate correlate with with dikes dikes and and fracturing of of the contour maps. maps, the the GMT can also fracturing the basalt basalt exposed exposed on the the shoreline. shoreline. Besides Besides contour GMT package package can produce produce a variety variety of other other displays displays of of the the data. data. Figure Figure 22 illustrates illustrates an an example example of of the the shaded shaded relief relief maps maps that that GMT GMT can produce. produce. This type type of of display display can can enhance enhance low low relief relief structures structures which which are not not readily readily observed in the contour displays. In In this this particular particular example, the lake lake floor near near the the Wisconsin Wisconsin south south shore shore is shown by a tight is shown illuminated illuminated by light source source located located at 120 120 degrees degrees to the the lake. lake. The lake lake floor floor exhibits exhibits aa well well developed network of of low low amplitude amplitude ridges ridges and and furrows furrows that that trend trend approximately approximately NE-SW. NE-SW. These These features features are probably related to the glacial history of the Lake Superior region. region. CONCLUSION The GMT software system is being used to create a new new bathymetric map for Lake Superior. The new new map reveals details not not previously seen in in earlier earlier maps maps of of the the lake. lake. Subtle Subtle features features on on the the lake lake floor floor can can be be reveals details previously seen enhanced using the tools available in GMT. REFERENCES Wessel, P. and Smith, W.H.F., W.H.F.• 1991, 1991. Free software helps map and display data, EOS Trans. AGU, 72, pM!. p441. 62 �0 0 268° 30' 268 268 268° 00' J I I I rwo Harbo Harbor iTwo 47" 47° 00' 0 ~---+------+--- 47° 00' 47 -4 r ',' 0 268° 30' 268° 268 00' I, Bathymethc Bathymetric map map of ofwestern western Lake LakeSuperior Superiorbetween between Duluth Duluth and and Two Two Harbors. Harbors. (5m (5m contours) Figure 1. 0 268° 10' 268 0 268° 20 268 20' 0 268° 268 20' 268° 10' 268 0 Figure 2. 2, Shaded Shaded relief map the Wisconsin Wisconsin south shore. shore. Source of illumination illumination located 120 120 map of the lake floor near the degrees from the map. map. 63 �REGIONAL FINITE STRAIN PATTERNS IN PROTEROZOIC SLATES AND QUARTZITES: IMPLICATIONS FOR HETEROGENEOUS STRAIN RELATED QUARTZITES: TO FLEXURAL SLIP FOLDING IN THE MARQUETTE SYNCLINORIUN SYNCLINORIUM WESTJOHN, D.B., U.S. U.S. Geological Survey, Survey, 6520 6520 WESTJOHN, D.B., MI 48911 Mercantile Way Suite suite 5, 5, Lansing, Lansing, MI are part of Proterozoic rocks in the Marquette synclinorium are metasediments that extends extends from aa sequence of deformed metasediments northern Michigan (Marquette (Marquette Range Supergroup; Supergroup; MRSG) MRSG) to (Animikie Group). Group). Slates in the MRSG near Minnesota (Animikie Marquette, Michigan, Marquette, Michigan, contain reduction reduction spots, spots, sandstone dikes, and deformed dikes, deformed veins. veins. Quartzites contain conglomerates, ellipsoidal ellipsoidal spots, spots, deformed deformed veins, veins, deformed conglomerates, and grain grain aggregates. aggregates. These strain rutile needles, and experienced weak to indicators are present present in in rocks rocks that. that experienced to' substantial substantial distortions, distortions, and they were used to to characterize regional finite finite strain strain patterns. patterns. Quartzites in open folds folds show no indication of being Strains in quartzites can be strained. strains be discerned discerned where where fold 60 degrees, degrees, and the the largest fold limbs dip greater than 60 strain ratios were observed observed in in steep steep and and overturned overturned limbs. limbs. heterogeneous, and the the deformation Strains in quartzite are heterogeneous, style ranges from from slight slight constriction constriction to to slight slight flattening; flattening; strain ratios are are less less than than 1.3. 1.3. Argillites experienced experienced early early compactional strain and slight distortions related to the development of open flexures. strains in early early stages stages of of Strains must have developed in folding, because veins are buckled or stretched folding, stretched even even in in weakly deformed deformed argillites. argillites. Strains are heterogeneous, particularly along contacts between units that have large Angular shear strain estimates ductility contrasts. contrasts. AngUlar These indicate extensions locally locally exceed exceed 200 200 percent. percent. strains are localized in slate beds, and are not in beds, and are not representative for the MRSG at the regional regional scale. scale. strain Strain ratios for slates are approximately twice twice those those observed for quartzites in closed and overturned folds. in and overturned folds. The orientation of the principal strain axes in fold fold limbs to fold geometry (except near show aa consistent relation to fold geometry (except near major shear zones); zones); the XY plane is is approximately parallel to (maximum to the axiai axial trend of the Marquette Marquette trough, trough, and and X (maximum stretch) stretch) is is subvertical. subvertical. Major structural features features in in the MRSG appear to have inherited from from the the Archean Archean basement. basement. Fold geometry is is been inherited tectonics involving consistent with basement-controlled tectonics translations along faults faults and shear zones zones in in the the Archean Archean blocks. Regional strain patterns and and orientations orientations of of penetrative fabric fabric support aa heterogeneous heterogeneous strain model model that includes folding folding related related to to flexural flexural slip. slip. 64 �A STRUCTURAL AND KINEMATIC ANALYSIS OF THE McCASLIN FORMATION NEAR McCASLIN MOUNTAIN, WISCONSIN WISCONSIN FORMAnON of Geology, WILSON, Susan Susan M., M., and John S., WILSON, and KLASNER, KLASNER, John S., Department Department of Geology, Western Western Illinois Illinois University, University, Macomb Macomb Illinois Illinois 61455. ABSTRACT Located along the north edge of the Wolf Wolf River River batholith in northeastern Wisconsin is the McCaslin McCaslin Formation. Formation. The The formation formation is one of several Precambrian quartzite bodies that lie within the Penokean orogen orogen and and may may be be Penokean Penokean in age the Penokean (LaBerge, Klasner Klasner and and Myers, Myers, 1991). As the dominant foci of Mancuso Mancuso (1960) (1960) and and Olson (1982) were the the lithology and provenance of the McCaslin, our field study Olson (1982) were the lithology and provenance of the McCaslin, Qur field study addressed its structure and kinematics. Detailed structural mapping mapping was was carried on within a four-section area of the McCaslin near McCaslin Mountain. Kinematic analysis involved the identification of sense-of-movement indicators indicators in the field and of sense-of-movement the laboratory, as well as as Fry Fry (1979) (1979) analysis. analysis. the laboratory, as well Our studies Our studies showed showed the the following: following: The McCaslin 1) The McCaslin is mostly aa thick-bedded thick-bedded orthoquartzite orthoquartzite with with a conglomeratic conglomeratic unit unit at its base. generally weak absent except except along along two two newly newly discovered discovered zones zones of of 2) Foliation is generally weak or or absent intense shearing. 3) Great-circle pi plots to bedding indicate the area is folded gently toward the northeast. which diverge diverge toward toward 4) Within exposed as as two 4) Within the the study study area area the the quartzite quartzite is exposed two limbs limbs which toward' the south. overturned toward the northeast; the southern limb is stratigraphically overturned shear zone indicate 5) Fry analyses of the quartzite and c-s fabrics within the thrusting toward thrusting toward the the south in the main shear shear zone. zone. the main area of Based on on these in the area Based these findings findings we we conclude conclude that, that, iIi of study, study, the the McCaslin McCaslin We also Formation is part of a south-verging fold-thrust belt. We also suggest that the Baraboo and of the McCaslin is a part of the family of quartzite quartzite bodies that include the Baraboo and which were Waterloo, which were thrust southward southward during during convergent convergent Penokean Penokean tectonism. tectonism. This suggests that the McCaslin is pre-Penokean and significantly older than previous interpretations. interpretations. REFERENCES Fry, N., 1979, Random point distributions Fry, N., 1979, Random point distributions and and strain strain measurements measurements Tectonophysics, v. 60, p. 89-105. 89-105. 60, P. in In rocks: LaBerge, G. G. L., New observations on the J. S., and Meyers, Meyers, P. P. E., 1991, 1991, New observations on the age age and and LaBerge, L., Kiasner, Klasner, J. S., and structure of Proterozoic in Contributions structure Proterozoic quartzites quartzites in Wisconsin: Wisconsin: in Contributions to the Precambrian M. H. H. Precambriangeology geologyofofthe theLake LakeSuperior Superiorregion, region,P.P.K.K. Sims Sims and and L. L. M. Carter Geological Survey 1904-B, pp. Carter (eds.): (eds.): U. U. S. Geological Survey Bull. Bull. 1904-B, pp. B1-B18. Bl-Bl8. Mancuso, 3. structure of the the McCaslin McCaslin district, district, Wisconsin: Wisconsin: Mancuso, J. J., 1960, 1960, Stratigraphy Stratigraphy and and structure Unpublished Ph. thesis, Michigan Michigan State State University, University, 101 p. Unpublished Ph. D thesis, p. M., 1982, 1982, The The sedimentation sedimentation and and petrology petrology of of the theLower LowerProterozoic Proterozoic McCaslin McCaslin Olson, J. M., Formation, Formation, northeastern northeastern Wisconsin: Wisconsin: Unpublished Unpublished M. M. S. thesis, University of Minnesota, 106 Minnesota, 106 p. p. 65 �______________________________ _________ Volcanic Group Geochemistry of Chengwatana Volcanic Group Near Taylors Taylors Falls Falls and From Osseo Core WIRTH, Karl WIRTH, Karl R., R., and and NAIMAN, NAIMAN, Zachary, Zachary, Geology Geology Department, Department, Macalester Macalester College, College, St. St. Paul, Paul, MN 55105,wirth@macalstr.edu 55105,wirth@macalstr.edu and and znaiman@macalstr.edu; znaiman@macalstr.edu;VERVOORT, VERVOORT, Jeff D., D., Department of Geosciences, Geosciences, University of Arizona, Arizona, Tucson, Tucson, AZ AZ 85721, 85721, vervoort@geo.aiizona.edu; andMILLER, MILLER, James, James, D., D., and and MOREY, G.B., vervoort@geo.arizona.edu; and G.B., Minnesota Minnesota Geological Survey, Geological Survey, 2642 2642 University University Ave., Ave., St. Paul, Paul, Minnesota Minnesota 55114, 55114, rnille066@maroon.tc.umn.edu and andmorey00 moreyOOI@maroon.tc.umn.edu. mil1e066@maroon.tc.umn.edu 1 @ maroon.tc.umn.edu, the composition composition and character of volcanism volcanism in the Keweenawan Keweenawan (1100 (11 00 Ma) Previous studies of the Midcontinent Rift have primarily focused on the well-exposed flow Midcontinerit flow sequences in the the Lake Superior Superior region. This This study study presents presents geochemical data of flows flows from from the the more more poorly poorly exposed exposed Chengwatana Chengwatana Volcanic Group Group of the Taylors Taylors Falls Falls region region and sampled by drill core (Osseo, Minnesota). Minnesota). Volcanic A 3000 meter thick Section of the Chengwatana Fe+2 ++Fe3 Fe+3 ++Ti Ti section the Chengwatana F' Fe2 Fi19ure gure 11 . " volcanic Group is volcamc IS exposed in ill the the Taylors Falls - St. region. This This section section isis composed composed pripriCroix Falls region. ro Taytors Falls marily of of mafic volcanic flows flows with with minor interfiow interflow Osseo Core sedimentary rock. The basalt basalt flows flows are are high-Fe high-Fe sedimentary rock. The tholelites tholeiites (Figure (Figure 1) 1) with plagioclase plagioclase phenocrysts phenocrysts and and clinopyroxene. Much Much of of the the ophitic to sub-ophitic clinopyroxene. basalt is olivine-nonnative olivine-normative or weakly quartz-nonnaquartz-normative, but olivine is not present in thin section. AbunAbunchlorite, epidote, epidote, and and actinolite actinolite inindant secondary chlorite, dicate that the group was metamorphosed that the group was metamorphosed to to Komatiite greenschist facies. facies. These These basalts basalts are are characterized characterized Mg#'s (0.58-0.37) (0.58-0.37) and and Ni Ni contents contents (185-36 (185-36 by low Mg#'s ppm) which indicate indicate that that the the flows flows have have undergone undergone Mg AI fractionation. Flows Flows near near the top of the Al significant fractionation. exposed section have lower Mg#, Ni, Cr, Cr, and and higher higher Ti0 Ti022 and and PP205 indicate that the the younger 20 S and indicate flows fractionated. Incompatible Incompatible element element abundances abundances are inversely correlated with flows are are the most fractionated. on most most variation variation plots plots can can be be grouped grouped into into highhigh- and and low trace element element groups groups (e.g. (e.g. Mg#; samples on Ti, P, Zr). The P, Zr). The basalts basalts are are enriched enriched in in the the light light rare rare o30 r=:---:-------;::===~ 00 Taylors Taylors Falls Falls Figure earth elements and Th (Figures 22 & 3), 3), but are variFigure 22 Osseo Core Core \ • Osseo relative to Ce Ce and and Th Th ably depleted in Ta and Nb relative (Figure 4). Initial Initial143NdJ1"4Nd 143Nd/ l44 Nd compositions (1100 (Figure Ma) of 1099 20 fof the the group group range range from from0.51122 0.51122 toto0.5 0.51099 (initial ENd =+0.1 0.1 to ENd = to 4.5), -4.5),but butten tenof oftwelve twelve samples samples s: have that fall have Nd isotopic isotopic compositions compositions that fall within within a . • narrow range 0 range (initial (initial ENd ENd==-1.6 1.6 to to -2.5); 2.5); flows with • •.. • 10 f-• (+0.1) and lowest lowest (4.5) (-4.5)initial initialENd ENd valval10 the highest (0. 1) and ues ues have isotopic isotopic compositions compositions that are are inversely inversely correlated with trace element abundances and ratios (e.g. (e.g. La/Yb, LaIYb, Th/La, ThlLa, ThJTa). Thffa). The The combined combined major major and trace element and Nd isotopic data suggest that °0.3 0.4 0.7 0.5 0.6 0.7 0.8 Mg# the flows at Taylors Falls originated originated by variable variable fracfrac- I a o1 -. . -. 66 �________ 4..------------------, o tional crystallization crystallization and crustal crustal contamination contamination of asthenospheric interacted with with enriched enriched asthenospheric melts melts that interacted Figure Fi gure33 o o o r~O-T-aYI-OI;-F-all-S 0 Taylors Falls -~I lithospheric mantle. U • Osseo Osseo Core Core I o 33 o More than 900 meters of of mafic volcanic flows flows q,O o were were sampled by a drill sampled by drill core core near near Osseo. Osseo. Petroo graphic features features and and major majorelement elementcompositions compositionsofof . 2 graphic o o these flows are similar to the flows from from the the Taylors .c 6'0 EoFalls are generally generally more more primiprimiFalls region except they are • ~ tive (Si02 (Si0 2 == 44-50 44-50 wt. wt. %; %; Mg# Mg# == 0.72-0.42; 0.72-0.42; Ni Ni = tive • = — 0-. 200-70 Most of ofthe the Osseo Osseo flows flows would would be be 200-70 ppm). ppm). Most • low-Ti0 2 flows flows near near Taylors Falls, grouped with the low-Ti02 OL----.....JL....---.....J ---' however some Osseo flows flows have have very very high P205 P 20 5 however some Osseo 0 200 200 300 o 100 300 (>0.39 wt. wt. %). Several Several fractionation fractionation cycles cycles can can be be Zr (ppm) Zr(ppm) recognized in the sequence and there is an an overall overall recognized trend toward more evolved of the the Osseo core similar similar to to the the trend seen in in the the evolved flows flows in in the the upper upper part part of ofOsseo Osseo and and Taylors Taylors Falls Falls flows flows plot plot Chengwatana section exposed near near Taylors Falls. Analyses Analyses of NbIY versus versus Zr/Ti02 ZrfTi02 and and Ti-Zr-Y Ti-Zr-Y and are are most most similar similar to to regions on diagrams diagrams of Nb/Y in identical regions Osseo flows flows exhibit exhibit lower lower trace trace element element abundances abundances transitional basalts and continental tholeiites. Osseo (e.g. REE, Zr, Y) and ratios (e.g. CelYb, major element element Ce/Yb, Th/La) ThJLa) consistent consistent with their more primitive major compositions On diagrams diagrams involving involving elements that are sensitive compositions (Figures (Figures 2,3 2,3 && 4). 4). On sensitive indicators indicators of crustal and mantle mantle components components (e.g. (e.g. Mg# Mg# versus versus NbINb*, NblNb*, Th-Nb/16-Hf/3; Th-Nb/16-Hf/3; Ce/Th CefTh versus versus ThfNb) ThlNb) Osseo flows are displaced displaced toward toward more more mantle mantle compositions compositions relative relative to to the the Taylors Taylors Falls Falls flows flows & 4). These features features indicate indicate that that the the melts melts sampled sampled in the Osseo core underwent less (Figures 3 & 4). These interaction with continental crust or subcontinental lithosphere than those those near near Taylors Taylors Falls. Falls. If the the Osseo flows are stratigraphically higher, higher, as suggested by their generally lower pressure metamormetamorvolphic mineral compositions (Naiman et al., this vol0.5 0.5 t 00 TJylors TaylorsFafls Falls I Figure 4 ume), then the Chengwatana Chengwatana flows might might record record aa C,Lr rust C Osseo Core Core 1• Osseo decrease in aa 'crustal' componentas asmagmatism magmatism proprocrustal component 04 0.4 ofthe the Furthermore,the theChengwatana Chengwatanaflows flows of gressed. Furthermore, Osseo core appear to contain Osseo core contain a greater greater 'depleted 'depleted 0.3 component (Figure 4). Similar Similar trends trends have have ~ 0.3 mantle' component oO~ been recognized in other Keweenawan basaltic flow ~ 02 in the the Lake Superior Superior region region (Shirey (Shirey et et al., al., Eo- 0.2 sequences in 05' • ••• 1994; Nicholson Nicholson et al., al., 1995). 1995). This may suggest that 1994; O~.'. 0.1 magmas in the later stages of of rifling rifting were were produced _N41 ORB _N-MORB Primit~ ~ : ... Primitive • •UI'• •U.• • Mantle Mantle • by melting a greater proportion of of depleted asthenosphere and that these melts underwent less contami00 80 20 40 80 60 nation during their passage through the lithosphere. Ce/Th Ce / Th - I ..—- .. ._.... ...'"• _• .,..'1 . o• • References Cited S.w., Shirey, S.B., Schulz, K.J., K.J., Berg, Berg, J.H., Kiewin, Klewin, K.W., K.W., and Green, J.C., J.e., 1995: 1995: Proceedings, Proceedings, InternaInternaNicholson, S.W., tional Project 336, 336, Meeting Meeting on on the the Petrology Petrology and and Metallogeny Metallogeny of ofVolcanic Volcanic and and IntruIntrutional Geological Correlation Project sive Rocks of of the Midcontinent Midcontinent Rift Rift System, Duluth, Duluth, Minnesota, Minnesota, 141-142. 141-142. Shirey, Klewin, K.W., K.w., Berg, Berg, J.H., J.H., Carlson, Carlson, R.W., R.W., 1994: 1994: Geochimica et Cosmochim. Acta, Shirey, S.B., SB., Kiewin, Acta, 58, 4,475-4,490. 67 � https://digitalcollections.lakeheadu.ca/files/original/de64836c611ae9690c258daa7805c96f.pdf a6f2b99ac876d5c8d466f886d58f029c PDF Text Text Volcanogenic Massive Sulfide Deposits of Northern Wisconsin: A Commemorative Volume Edited by Gene L. LaBerge Institute on Lake Superior Geology Proceedings Volume 42, Part 2 �Front Cover Aerial photo of the Flambeau mine and vicinity looking north. Flambeau Mining Company photo. © T-BO Stiios Back Cover Photo of a 4.0 cm tall twinned orthorhombic chalcocite crystal recovered from a cavity in the supergene ore. The purple patina is produced by a thin coating of bornite on the chalcocite. From the collection of F. John Barlow. Photo by Malcolm Hjerstedd, Munroc Studios, Neenah, WI. �Proceedings Volume 42, Part 2 FIRST PRINTING—MAY 1996 Publisher Institute on Lake Superior Geology Distributor Theodore J. Bornhorst do Department of Geological Engineering, Geology, and Geophysics Michigan Technological University 1400 Townsend Drive Houghton, Michigan 49931-1 295 ISSN 1042-9964 Reference to Volume 42, Part 2 should follow the example below: LaBerge, G. L., Ed., 1996, Volcanogenic massive sulfide deposits of northern Wisconsin: A commemorative volume: Institute on Lake Superior Geology Proceedings, 42nd Annual Meeting, Cable, WI, v. 42, part 2, 179 p. �Proceedings Volume 42, Part 2 Institute on Lake Superior Geology Volcanogenic massive sulfide deposits of northern Wisconsin: A commemorative volume Edited by: Gene L. LaBerge Department of Geology University of Wisconsin Oshkosh, Oshkosh, WI 54901 Published for 42nd Annual Meeting Institute on Lake Superior Geology Cable, Wisconsin May 15-19, 1996 ISSN 1042-9964 �PREFACE The mineral industry has played an important role in deciphering the local and regional geology of the Lake Superior region by gathering basic geologic information to assist in the exploration for and development of mineral resources. More than a century ago the discovery of the great iron ore resources in the Lake Superior region led to numerous studies by mining companies, government surveys, and academic institutions, providing a wealth of information on the geology of the iron-bearing districts, as well as the sedimentary sequences and the contained ore deposits. The copper deposits of northern Michigan provided the impetus for similar detailed and regional studies yielding a basis for understanding these important resources. Although research on the genesis of the mineral deposits and the regional geology is on-going, we continue to utilize much of the basic data provided by mining companies. However, relatively little information was compiled on the area of northern Wisconsin now known as the Wisconsin magmatic terranes. In the 1960s, a new concept of sulfide ore deposition related to volcanic activity — volcanogenic massive sulfide deposits — led to widespread exploration activity by numerous companies for this type of deposit in the Lake Superior region. Along with new concepts of ore deposition came new technology to aid in the search for mineral deposits. Aeromagnetic and airborne electromagnetic (EM) surveys became standard procedures, and, along with ground magnetics, EM and gravity surveys, these geophysical techniques have greatly modified both detailed and regional exploration. Drill core data provided by exploration companies has provided the "ground truth" to permit broad-scale correlation of rock units within the region. Much of these data have been made available to government surveys to permit at least a "first pass" at deciphering the bedrock geology of the "Wisconsin magmatic terranes," which are very poorly exposed because of the thick cover of glacial deposits. Although our present understanding of the geology of northern Wisconsin is an outgrowth of the efforts of many scientists, I believe it is important that we recognize the central role that the mineral industry has played. Therefore, I feel it is appropriate that all of the chapters in this volume except one were written by geologists in the mineral industry, for some of these authors represent some of the corporations and individuals who have been at the forefront of generating some of the basic data. I am confident that the data and interpretations contained in these papers will be helpful in promoting an understanding of massive sulfide deposits as well as further refining the regional geology of the Wisconsin magmatic terranes. �11 ACKNOWLEDGEMENTS This volume was conceived by Edwarde May, who thought a volume on volcanogenic massive sulfide deposits in Wisconsin would be appropriate in conjunction with the field trip to the Flambeau Mine. We all owe Ed a vote of thanks for initiating the project. Each of the authors took time from their schedule to prepare descriptions of the various deposits. I would like to acknowledge, with thanks, their efforts. I extend my thanks to Suzanne Nicholson of the U.S.G.S. who reviewed all of the manuscripts. A very special thanks to Mary Fahley, in the Geology Department at UW-Oshkosh, who undertook the task of getting all the manuscripts on one computer and formatting the volume. I really couldn't have done it without her. Proceeds from the sale of this volume will be used by the Institute on Lake Superior Geology to help fund student travel to future Institute meetings. The following organizations and individuals have made financial contributions to help defray the cost of publication of the volume, and in so doing, have contributed to future generations of student participants at Institute meetings. Thanks to each contributor. List of Contributors Flambeau Mining Company Kennecott Exploration Company Ames Construction, Inc. BHP Minerals International, Inc. Crandon Mining Company Boart-Longyear Cooper Engineering DeWitt, Ross & Stevens, S.C. Foth and Van Dyke David Hoffman Peter J. Hoffman Midwest Drilling Minnesota Exploration Association North Central Mineral Ventures, Inc. (in memory of F. H. Eisenbrey) T. D. Drilling, Inc. Wood Communications Group Ayres Associates F. John Barlow Edwarde R. May Casey Jones, Burminco Glen W. Adams Russell C. Babcock Jack V. Everett Gene L. LaBerge Paul G. Schmidt �111 DEDICATION Edward H. Eisenbrey 1926 - 1985 "Ned" Eisenbrey, to whom, along with his co-worker Jack Phillips, this volume and meeting are dedicated, can truly be said to be one of the "fathers" of the study and exploration for volcanogenic massive sulfide mineral deposits in Wisconsin. Those of us who had the good fortune to work with Ned in the Precambrian shield of the Upper Midwest and elsewhere, recognize that he had a unique talent as an ore finder, a geologist, and a teacher. In the last ten years of his life, during my close association with him as a co-worker and friend, I marveled at his uncanny, often apparently intuitive knack for sizing up a mass of geophysical data, mix it with an apparent minimum of hard geologic ground truth and to come up with targets that, in a remarkable number of cases, were not graphite, not "formational," not just pyrite, but were mineralized prospects and potential base and precious metal deposits. During his tenure in Wisconsin and Bear Creek (Kennecott) he was responsible for the initiation of drilling at the site of the current Flambeau Mine. He also recognized and proposed �iv drilling at the Thornapple site (now fittingly named the Eisenbrey prospect). Subsequently, in his year with the North Central Mineral Venture and in his capacity as a senior geologist with Earnest K. Lehmann & Associates, he recognized the mineralization of the Reef deposit and was instrumental in, among others, the discovery of the Ritchie Creek prospect and the Horseshoe deposit which was discovered on the day of his untimely death. His insight was also important in our later discovery of the Bend deposit in Taylor County. Ned was born in 1926 and grew up in Cleveland, Ohio. He attended the Staunton Military Academy in Virginia. During World War II, he enlisted in the U.S. Navy at age 17 and served in the South Pacific. He graduated in geology from Case Western in 1950 and obtained a MS from the University of Toronto in 1952. During his college summers, he worked as a surveyor on the Quebec, Nova Scotia and Labrador Railroad then being built to develop the Labrador iron mines. On graduation, he joined the American Metal Company and worked on massive sulfide deposits in New Brunswick. Later, he transferred to various other locals including Virginia, Colorado, Wyoming, and Arizona. Following the merger of American Metals and Climax to form AMAX in 1958, he was a consultant and mine operator in Arizona. In 1959, he joined Bear Creek, working first on the exploration of the porphyry copper deposit at Safford, Arizona, and later as an assistant to Paul Bailey, the President of Bear Creek. In 1963 he joined the Rocky Mountain regional office of Bear Creek and in 1967 moved to the upper midwest. Leaving Bear Creek in 1971, he first managed the North Central Mineral Venture for Superior Oil, and then joined Ernest K. Lehmann & Associates in 1975. He worked with ELA until his death in 1985. He and Elizabeth (Liz) Eisenbrey were married in 1955. They have two children, Mary and Fred. With Liz's help and the support of his family, he was able to maintain an active and full life in spite of a severe diabetic condition, which hampered him during almost all of his adult life. His interests outside of geology were strongly focused on his desire to share his knowledge and his abilities as a teacher. In this capacity, he was active in the Boy Scouts and in his church. In the later years of his life, he had a keen interest in introducing earth science teachers to geology and ore deposits. He participated in a program for this purpose at the University of Wisconsin-Platteville. Teaching came naturally to him. This skill, coupled with his acute knowledge of economic geology generally and volcanogenic massive sulfides in particular, was a gift from which all his associates benefitted. We are still indebted to him for his knowledge, his skill in applying that knowledge and his sharing it with us. Ernest K. Lehmann August, 1995 Memorial to John S. Phillips 1928 - 1987 On March 20, 1987, Jack Phillips was killed in a plane crash as he was returning from work at Andacollo, Chile, to his home in Santiago, ending an outstanding career in minerals exploration. Jack grew up on a ranch 30 miles south of Cripple Creek, Colorado, and his interest in geology may have been stirred by visits to this old mining camp. He graduated from the Colorado School of Mines in 1949, and began his professional career at the New Jersey Zinc Company mine in �V Gilman, Colorado. This was interrupted by a two-year hitch with the U.S. Army in Germany, where he met his caring and supportive wife, Danielle, a French interpreter with the Army. On returning to the U.S., he earned his M.S. degree at Syracuse, and his Ph.D. at Harvard, studying under Hugh McKinstry. Jack joined Cominco in 1960, exploring the Jerome District in Arizona, applying the volcançgenic model recently developed at Bathurst, New Brunswick. In 1965, he was hired by Kennecott to manage a drilling project near Marquette, Michigan, testing the Kona Dolomite for rhodesian-type copper deposits. At the same time, Jack was characteristically looking for other exploration possibilities, and, influenced by his Jerome experience, recognized the area west of Ladysmith, Wisconsin, as having potential for hosting volcanogenic massive sulfide deposits. Before his transfer to another assignment, Jack's enthusiasm and persistence led to Kennecott's approval of an INPUT survey, which resulted in the discovery of the Flambeau deposit in 1968. Jack continued to work for Kennecott for a number of years, mostly in the Western U.S., but including foreign assignments as well. He joined Chevron in 1978, was instrumental in bringing it into the Stillwater platinum operation, and later headed its copper exploration in Chile. Jack is remembered by those of us privileged to have known him, for his keen interest in all types of ore deposits, his enthusiastic approach to exploration, and his enjoyment in exchanging thoughts with fellow geologists. Ray E. Gilbert Englewood, Colorado �vi TABLE OF CONTENTS PREFACE ACKNOWLEDGEMENTS DEDICATION INTRODUCTION HISTORY OF EXPLORATION FOR VOLCANOGENIC MASSIVE SULFIDES by Russell C. Babcock IN WISCONSIN 1 GENERAL CHARACTERISTICS AND GEOLOGIC SETFING OF THE WISCONSIN by Gene L. LaBerge MAGMATIC TERRANES 17 A GEOLOGIC FRAMEWORK FOR EARLY PROTEROZOIC VOLCANOGENIC MASSIVE SULFIDE DEPOSITS IN WISCONSIN: AN EXPLORATION MODEL by Theodore A. DeMatties 31 AN OVERVIEW OF THE FLAMBEAU SUPERGENE ENRICHED MASSIVE SULFIDE DEPOSIT GEOLOGY AND MINERALOGY, RUSK COUNTY, WISCONSIN by Edwarde R. May and Stephen R. Dinkowitz 67 CASE STUDY OF ENVIRONMENTAL REQUIREMENTS FOR THE PERMITFING, OPERATION, AND RECLAMATION OF A METALLIC MINERAL MINE IN by Jana E. Murphy and Richard T. Dachel WISCONSIN-FLAMBEAU MINE EISENBREY: A STRUCTURALLY COMPLEX PROTEROZOIC COPPER-ZINC MASSIVE SULFIDE DEPOSIT, RUSK COUNTY, WISCONSIN by Edwarde R. May GEOLOGICAL SUMMARY - CRANDON DEPOSIT by A. J. Erickson and R. COt .... 95 107 129 THE BEND DEPOSIT: AN EARLY PROTEROZOIC COPPER-GOLD by Theodore A. DeMatties and William F. Rowell VMS DEPOSIT. 143 GEOLOGY OF THE LYNNE BASE-METAL DEPOSIT, NORTH-CENTRAL by Glen W. Adams WISCONSIN, U.S.A. 161 �1 HISTORY OF EXPLORATION FOR VOLCANOGENIC MASSIVE SULFIDES IN WISCONSIN Russell C. Babcock Chief Geologist (Retired) Kennecott Exploration Company Salt Lake City, Utah INTRODUCTION Exploration for massive sulfide deposits in Wisconsin was driven by the observation that whereas numerous base metal deposits and mines were present in the Superior Craton north of Lake Superior, none were known in rocks suspected to be of the same age south of the lake. It was assumed that the reason for this was not a lack of deposits but rather the presence of extensive glacial cover south of the lake. Therefore, exploration in Wisconsin focused on techniques that would lead to the discovery of blind deposits beneath this glacial cover. Such was the reasoning of Kennecott geologists who began the first phase of the modern era of base metal exploration and mining in Wisconsin in the early 1950's. Kennecott pursued its exploration program in Wisconsin without competition intermittently for almost two decades before announcing the discovery of the Flambeau Deposit in 1970. With this announcement dozens of competitors joined Kennecott in Wisconsin, opening a second phase of this exploration history, one of competitive and relatively unencumbered activity. This phase ended and the third phase began when Exxon announced the discovery of the huge Crandon Deposit in 1976. Within a year after this announcement the political climate changed dramatically in Wisconsin. The third phase of exploration in Wisconsin became one of difficult regulation, permitting, and taxation, made even less palatable by a sustained period of very low base metal prices. In 1993 Kennecott finally brought the Flambeau Deposit into production, and in 1995 Exxon and Rio Algom joined in an attempt to bring the Crandon Deposit on stream. Perhaps a fourth, productive phase will soon be added to this history. PHASE ONE: THE KENNECOTF YEARS Early Kennecott Exploration Kennecott established an exploration program on the Duluth Gabbro in 1951 following the discovery of copper-nickel mineralization along the Kawishiwi River in Minnesota. A few years later an office was set up in Mellen, Wisconsin, to test some copper-nickel occurrences in the Mellen Gabbro. The geologist in charge of this office, George Moerlein, began looking for massive sulfide deposits in Wisconsin in 1954, and although he found a number of iron sulfide occurrences, none contained more than trace amounts of base metal sulfides. Moerlein compiled the references to sulfides in the literature and visited the offices of the government geologists who were involved in mapping in Wisconsin and Upper Michigan. Carl Dutton, a U.S.G.S. geologist working with the Wisconsin Geological and Natural History Survey, showed Moerlein a copper-stained rock reported to have come from a hand-dug well at a schoolhouse south of Ladysmith. Moerlein could find little at the schoolhouse site other than a �2 small amount of felsic schist with some weak copper staining but with little evidence of having contained much sulfides. Kennecott flew extensive airborne electromagnetic surveys over their copper-nickel properties in Minnesota and the Mellen, Wisconsin, area in 1954. Several surveys of several lines each were also flown over sulfide occurrences in Wisconsin that were felt to have some potential for base metals. One of these surveys was flown over the schoolhouse south of Ladysmith. None gave Kennecott much encouragement and no anomalous response was seen at the schoolhouse. On the basis of this survey Kennecott assumed that the glacial overburden in western Wisconsin was probably too thick for effective use of airborne electromagnetics. In spite of this lack of encouragement, Kennecott continued to feel strongly that base metal massive sulfide deposits could be hidden under the glacial overburden in Wisconsin. Through the last half of the 1950's Dr. W. F. Read, Professor of Geology at Lawrence College in Appleton, spent a good part of his summers prospecting in northern Wisconsin for Kennecott. Using glacial till sampling (pebble counts), abundant stone fences in some areas, and mapping every outcrop he could find, Bill Read added significantly to Kennecott's understanding of the bedrock geology of Wisconsin. He found almost no base metals but mapped several areas of pyritic felsic schist. The author worked with Read for two of these summers, visiting the schoolhouse site for the first time in 1956, but like most young geologists of the time, had no understanding of what was to become the volcanogenic massive sulfide model. Moerlein recognized the potential for Rhodesian-type copper deposits in the Kona Dolomite near Marquette, Michigan, just prior to the closure of Kennecott's Wisconsin office in 1962. In 1965 Jack Phillips was hired by Kennecott to pursue this target and establish an office in the Upper Peninsula. In 1966 Phillips visited the Wisconsin Geological and Natural History Survey and U. S. Geological Survey in Madison to see if other prospects could be generated in Michigan and Wisconsin. There he "rediscovered" the copper-stained sample of felsic schist from the well at the schoolhouse south of Ladysmith, reportedly still on Carl Dutton's desk. Dutton told Phillips of showing the rock to Moerlein and some of the work Kennecott had done in Wisconsin. Fortunately for Kennecott, Phillips had spent his previous several years working on volcanogenic massive sulfide deposit exploration and was fully aware of the new model for these types of deposits developed in Canada in the early 1960's. He knew that the discovery of the major base metal deposits at Bathurst, New Brunswick, and Kidd Creek, Ontario, were the direct result of applying this new model to exploration in Canada. He recognised in the schoolhouse rock the slightly pyritic, felsic volcanic material common to the new volcanogenic massive sulfide model. When he visited the schoolhouse site a few weeks later he recognized and became very excited about the potential for finding another Kidd Creek deposit in Wisconsin. Schoolhouse became a pivotal prospect for Kennecott in Wisconsin. A review of the Kennecott files led to Read's and Moerlein's work, which in turn led Phillips to quickly recognize the presence of several pyritic felsic volcanic piles elsewhere in north-central Wisconsin. The records in Madison and some mapping indicated sulfides to the west of Ladysmith near Weyerhaeuser and at Blue Hill. Magnetic surveys run with dip needles along widespaced lines in the early 1900's by the Wisconsin Geologic and Natural History Survey indicated areas of possible "greenstone" bedrock. It was clear that a major exploration effort was justified. Phillips' experience in volcanogenic massive sulfide exploration exposed him to the newly developed INPUT system, the time-domain airborne electromagnetic system of Barringer Research. �3 This system had significantly greater resolution and depth of penetration than the system used by Kennecott in the 1950's. The success of the volcanogenic model and the INPUT system in Canada, and the confidence and enthusiasm of Phillips in and for the potential of the felsic volcanic terrain he saw in Rusk County, was sufficient for Kennecott to plan a significant program in 1967. With this new model and new technology they would try one more time to find a massive sulfide deposit under glacial cover south of Lake Superior. Flambeau Discovery Flying began in May, 1967, on a survey located just west of Ladysmith (Figure 1). The first line indicated a strong, six-channel conductor that was to become the Flambeau Deposit; the second line to the west picked up only a weak conductor. On the strength of the first line conductor, and the strong recommendation of the Geoterrex geophysicist, Don Wagg, two additional lines were flown to the east of line one, and confinned the presence of a very strong but short responsive body at shallow depth. Other anomalies were found, many of which were long and although strong, probably represented formational conductors. Wagg was convinced that the first line anomaly, called F-22, was the best and should be drilled first. It was not the first anomaly drilled, however, for reasons of land availability rather than priority. The apparent success of Kennecott's first airborne survey encouraged them to plan a second survey east of their initial one. At the same time crews were mobilized to conduct ground follow-up surveys on the better anomalies as land agreements were signed. Electromagnetic, magnetic and gravity surveys were completed at anomaly F-22 and all were strongly indicative of a sizeable massive sulfide deposit. There were no nearby outcrops which would give any clue as to the geology of the anomaly, but one outcrop of andesitic volcanics one mile to the south suggested that the right environment was present. Based on the geophysical signature Kennecott geophysicist Carl Schwenk was absolutely certain he was seeing a classic volcanogenic massive sulfide deposit. On November 6, 1968, Kennecott's first hole, drilled under the direction of Helmut Sichermann, intersected tens of feet of chalcocite mineralization hosted by pyritic metavolcanic rocks. The next few holes established F-22 as the first volcanogenic massive sulfide copper-zinc deposit to be found in the Superior Craton south of Lake Superior. The presence of thick chalcocite mineralization was a complete surprise to Kennecott, and the fact that it clearly represented Precambrian enrichment prior to the deposition of the basal Cambrian sandstone was even more intriguing. Thornapple Discovery Detailed geologic mapping and prospecting began in the Ladysmith area in 1966 and was accelerated as soon as it was apparent that the airborne survey had turned up a sizeable number of anomalies. This work identified several occurrences of felsic volcanic rocks in and around Rusk County, the pattern of which determined the lay-out of Kennecott's first airborne survey. One outcrop in particular, found by geologist Bill Spence under a railroad bridge over the Thornapple River, contained weakly mineralized iron formation. When Kennecott's third airborne survey was flown in 1969 it covered this Thornapple area, and a modest anomaly was found, but it was coincident with a local power line, railroad, and bridge, and was attributed to "culture". Responsibility for the Wisconsin project was handed over to E. H. "Ned" Eisenbrey, one of Kennecott's senior geologists, in early 1967. He was as enthusiastic about the Ladysmith area as �4 RUSK COUNTY DEPOSIT c \ BLUE HILLS \ * \WEYE RHAE U S ER RUSK COUNTY I .1 1967 INPUT SURVEY 0 Ladysmith * Proterozoic Outcrop with Sulfides Madison 0 0 2 4 6 8 10 Miles Figure 1. WITH KENNECOTT'S FIRST AIRBORNE ELECTROMAGNETIC SURVEY THE LOCATION OF MASSIVE SULFIDE DEDPOSITS AND CHIEF OUTCROPS, RUSK COUNTY, WISCONSIN �5 Phillips had been before him. He supervised the initial flying and encouraged Wagg to fly the extra lines on the F-22 anomaly. He also managed the detailed geological and geophysical work and drilling that followed. He had made a large commitment to the success of the project. As a sign of this commitment he was not about to let the Thornapple anomaly, coincident with mineralized iron formation, go untested. He and geologist Bob Stuart completed three holes in the Thornapple area before overcoming the objections of the geophysicists and securing some ground surveys. They completed a ground magnetic survey which produced a good anomaly west of the wealdy mineralized outcrop and ran one gravity line which also was anomalous. In 1970 the fourth hole at Thornapple intersected thick sulfides with intervals of copper and zinc mineralization. Kennecott had made their second volcanogenic massive sulfide discovery in Wisconsin. Momentum built in the Kennecott program and new airborne surveys continued to produce new anomalies. Broad areas were flown with aeromagnetics to locate favorable volcanics, and smaller areas were flown with INPUT (Figure 2). Land was acquired and ground surveys completed farther to the north and east. Like the anomalies near Ladysmith, most were related to formational sulfides or graphite, while others consisted of only sulfides. Some anomalies were on land that could not be acquired at the time, and were deferred for later follow-up. Surveys in the Schoolhouse area produced only weak airborne anomalies, indicating that little conductive material was present. Perhaps the 1955 survey was testing bedrock after all, but no conductors were present. Had Kennecott covered the area to the north of Schoolhouse, Flambeau might have been found thirteen years earlier. Newcomers Join the Search Kennecott announced the discovery of the Flambeau Deposit in 1970. Several companies already knew or learned then that Kennecott had discovered something new and exciting in Wisconsin, and recognized an enviromnent favorable for volcanogenic massive sulfides. Duval, Exxon, Noranda, U.S. Steel and several other companies joined the search and were flying or planning surveys by 1972. But while others were moving in, Kennecott was moving out. Late in 1971 Kennecott's exploration program suffered heavy and universal budget cuts which essentially ended the Wisconsin program. Drilling continued on the F-22 anomaly, now called the Flambeau Deposit, and at Thornapple, but all exploration in Wisconsin had ceased by the end of 1972. At this time Kennecott had flown less than half of the favorable terrane, as it was then known. In 1966 the author pointed out to an enthusiastic Jack Phillips on his first visit to the Schoolhouse prospect that the most difficult job was not to convince Kennecott that they should fly an airborne geophysical survey over part of Rusk County, but that they should continue to fly airborne surveys in Wisconsin until they found "the big one." In spite of their success, in 1972 Kennecott was leaving with the job undone. PHASE TWO: EXPANDED EXPLORATION Kennecott continued to drill both the Flambeau and Thornapple deposits over the next few years, defining reserves at Flambeau that would be developed for production in 1993, but outlining only a small, structurally complex resource at Thornapple. Detailed descriptions of these deposits will be the subject of separate articles in this volume by May and Dinkowitz (Flambeau) and May (Thornapple, now the Eisenbrey Deposit). In 1969 the job of drilling out the Flambeau Deposit was assigned to Ed May, who became and remains Kennecott's key geologist and project champion. Drilling under May's direction defined the precious metal gossan, chalcocite enrichment zone, and the underlying, classic copper-zinc �6 Kennecott Aeromagnetic Surveys DEPOSITS F Eisenbrey Flombeau B Bend E Ritchie Creek T Tomahawk P Pelican River R I Lynne C Cranclon Figure 2. KENNECOTT PRE—CRANDON AIRBORNE ELETROMAGNETIC AND MAGNETIC SURVEYS (in order flown, 1967—1971) �7 volcanogenic massive sulfide deposit. He persisted in producing excellent geologic records at a time when the outlook for the project was uncertain, a contribution which would pay off for Kennecott in the 1990's. Exxon Program Exxon was the second major company to begin a volcanogenic massive sulfide program in Wisconsin. Jim Mancuso of Exxon's Houston office became aware of Kennecott's intense drilling activity at Ladysmith in 1969 and recognized the marks of a new discovery. In 1970 he assigned Mel Erskine the task of organizing and implementing an exploration program. Erskine completed a wide-spaced airborne magnetic survey over a large area east and northeast from Ladysmith and identified several potentially favorable terrains for airborne electromagnetic surveys. Exxon also began to map and prospect the geology of northern Wisconsin in great detail, and by this means added several other target areas to their list. Paul Schmidt became Exxon's District Manager in early 1971 and took over responsibility for the Wisconsin program, and Jerry Dolence was transferred in as Project Geologist. Eleven airborne electromagnetic surveys were flown in 1971 and 1972, including one in the Tomahawk area (Figure 3). Results were equivocal and there was talk of pulling Out of Wisconsin. After all, Flambeau had already been found and was small. However, follow-up of the Tomahawk survey in 1973 led to the discovery of the small Hawk deposit which, although not commercially viable, gave Exxon sufficient encouragement to undertake additional airborne surveys, including a huge airborne magnetic survey of most of northern Wisconsin. This was used successfully to identify volcanic bedrock areas favorable for testing with electromagnetic surveys. Field geology and prospecting was expanded. This second surge of activity included a survey eastward from the Tomahawk area where a completely covered greenstone belt was inferred based on the interpretation of magnetic survey results. Airborne Magnetic Survey 1970 Airborne Magnetic Survey Miles 0 DEPOSITS F Eisenbrey Flambeau B Bend E Rjchje Creek I Tomahawk R P I Pelican River Lynne C Crandon Figure 3. Exxon Pre-Crandon airborne electromagnetic and magnetic surveys (1 = 1970, 2=1972, 3=1973, 4=post-Crandon) 50 �8 After four years and little more than a technical success to show for their efforts, Exxon decided to terminate exploration in Wisconsin in 1975. Schmidt was given sufficient funds to drill four more anomalies before wrapping up the program. One of these was a mile-long, six-channel anomaly at Skunk Lake detected in the 1974 survey east of Tomahawk. Although the anomaly was rated only as "fair" because it lacked a magnetic response, Schmidt decided it deserved a test (Schmidt, 1991). The first drill hole in this anomaly in July, 1975, discovered clearly ore-grade base metal sulfides. By July, 1976, when the details of the new Crandon Deposit were released to the public, it was apparent to the industry and the public that Exxon had found "the big one." Noranda Program Noranda was the third major player in Wisconsin. Geologic reconnaissance work began in 1968 and in 1970 Bob Miller heard Gene LaBerge talk about the rhyolites at Wausau while attending a meeting of the Institute on Lake Superior Geology, visited the area, and liked what he saw. Miller started a program right away under the direction of District Geologist Lawrence Machesky (Mudrey, et a!., 1991). Frank Condon also came down from Canada as project geologist. Several airborne electromagnetic surveys were completed in the early 1970's, including a large survey in Forest and Oneida Counties flown in 1973 (Figure 4). A large number of good-looking anomalies turned up on this survey, many of which were on County land. An agreement was reached with Consolidated Paper Company to explore their large holdings in northern Wisconsin, which gave the Noranda program a good start. A strong anomaly on the Pelican River was acquired and drilled, and Noranda had its first discovery. The Pelican River Deposit turned out to be small and of only modest grade, but it stimulated one of the longest, most continuous exploration efforts by any company in Wisconsin. Don Cross was brought in from Canadian operations in 1975 because of his volcanogenic massive sulfide experience. Figure 4. Noranda pre-Crandon airborne electromagnetic surveys (1= 1971, 2= 1973, 3-post 1974) �9 Like Exxon, Noranda completed considerable geological mapping and prospecting to supplement their airborne work, and compiled the available data. Noranda had the perceived advantage of their experience in the Noranda District in Quebec, a classic volcanogenic massive sulfide district. Miller recognized that the outcrops around Monico were what they were looking for in Wisconsin, and their work in the Pelican River area started from there and expanded outward. Every company had their own idea of what constituted favorable terrane for prospecting in Wisconsin, based on their interpretation of poorly exposed bedrock and differing views of the detailed volcanogenic massive sulfide model. Noranda was attracted to the large area of pyritic felsic volcanics around Monico. Their airborne surveys were located on the basis of geology, magnetic patterns, assumptions regarding land availability, previous exploration by competitors, and the limits of budgets. There was no sure way of knowing what areas had been flown by the competition, and there was often an overlap of competing surveys. After the announcement by Exxon of the Crandon discovery, Noranda realized that one of their surveys stopped just short of Skunk Lake. In looking over the tapes of the survey it became clear that the survey plane had made its turn over Crandon and had actually picked up a strong, six channel anomaly. Such data picked up outside the survey area is often discounted or not reported, and in this case escaped Noranda's consideration. In addition, so many responses turn up in the course of an ordinary electromagnetic survey that is unlikely that all will be checked. Coming back to these old surveys with new ideas and new models is standard procedure, and eventually paid off for Noranda at Lynne. U. S. Steel Program By 1974 both Noranda and Exxon realized that their chief competitor in the greater Monico area was U. S. Steel. U. S. Steel had been exploring in Wisconsin since the early 1950's, admittedly for iron. The U. S. Steel program was conceived by Ralph Marsden, who felt that perhaps they could find an iron deposit of higher than taconite grade in the older, more highly metamorphosed rocks south of the Gogebic Range. The field work was being directed by Cedric Iverson and consisted of relatively crude magnetic surveys, but also detailed geologic mapping and pebble counts on three-mile centers all across northern Wisconsin. Iverson used large numbers of student geologists, including at least one current authority on the geology of northern Wisconsin, Gene LaBerge. When U. S. Steel learned of the discovery of the Flambeau Deposit, Iverson was asked why he had not found it, a question many exploration managers would be asked as subsequent discoveries were announced. This was enough to stimulate the conversion of Iverson's program from iron to base metals, and by 1970 U. S. Steel was flying airborne surveys in Chippewa County. They based their priorities on their knowledge of Precambrian bedrock, pebble count results, and some semiquantitative geochemical results from soil samples taken at pebble count stations. Their program moved to Taylor, Wood, and Portage Counties, and there was no shortage of anomalies (Figure 5). U. S. Steel flew some large aeromagnetic surveys, but mostly in the search for iron formation north of the Niagara Fault. Drilling results were not encouraging, however, and the U. S. Steel crew referred to themselves as the "Pyrrhotite Kings" of Wisconsin. Of course they would drill only those anomalies with a magnetic response, a consequence of their understanding of the volcanogenic model. The U. S. Steel airborne program had moved into the area south of Monico and Crandon by 1974, again with a number of airborne anomalies but no base metals. They were gravitating to the Monico area for the same reasons that Noranda and Exxon favored the area, the abundance of sulfide-bearing felsic schist. There must have been considerable overlap of surveys, if not out and out competition for land. �10 DEPOSITS E F Eisenbrey Flambeau B Bend R Rjchje Creek T Tomahawk P Pelican River L Lynne C Crandon Figure 5. U.S. Steel pre-Crandon airborne electromagnetic surveys (in order flown, 1970-1975) When it became apparent to U. S. Steel that Exxon had a discovery at Crandon they took a look at their data for the area. Like Noranda, U. S. Steel had flown two lines over the Crandon Deposit which picked up the anomaly. One they attributed to culture and the other to topography. Part of the problem was that the airborne system that U. S. Steel was using was not as sensitive as that used by Exxon. U. S. Steel looked at their pebble count and geochemical data, too, and found that a gravel pit near Crandon had more sulfide-bearing felsic volcanic pebbles than anywhere else in the state. Hindsight is wonderful; the more difficult task is converting hindsight into foresight and carrying on. Not many succeed. Kennecott, Noranda, and U. S. Steel had all missed their chance to find "the big one." Iverson kept at it for a couple years after Crandon, but eventually U. S. Steel retired from the Wisconsin scene empty-handed. He observed that all the base metal deposits and occurrences were located along a fairly narrow east-west line from Crandon to Flambeau, with only iron sulfides on either side. It remains to be seen whether or not this "Highway Eight Lineament" has any geological merit, or whether it is merely an artifact of the exploration model of the day. Other Companies The Duval Corporation learned of Kennecott's activity at Flambeau and quickly initiated a field program in 1970, flying an area in Marinette County in 1971. This program under the direction of A. L. Barker was designed to explore an area with some favorable volcanics but little outcrop well east of Ladysmith, in an area where large blocks of County and some State land might be available �11 for leasing (Mudrey, et a!., 1991). A small, low-grade sulfide iron fonnation-type deposit was found in early 1972 after ground testing and drilling eight anomalies. Although no further discoveries were made by Duval, their technical success tended to expand the efforts of other companies into eastern Wisconsin. As many as a dozen other companies came into Wisconsin in the early 1970's; some of these are listed on Table 1. More surveys were flown, offices opened and closed, and anomalies drilled, but only small deposits or shows were found. In later years much of the data generated by these companies became available to others through joint ventures and farm-out agreements, and provided a foundation for intermittent exploration and the discovery of a few additional small deposits in the 1980's. But no more large deposits were found. TABLE 1 Companies Exploring in Wisconsin 1969 to 1976 Exxon Kennecott AMAX Superior Oil Cominco Universal Oil Products New Jersey Zinc Texasguif ACNC (INCO) Cleveland Cliffs Noranda U. S. Steel Anaconda Homestake ASARCO Phelps Dodge Cerro de Pasco Calumet & Hecla National Lead Kimberly Clark Midwest Oil General Crude Oil The political climate in Wisconsin prior to 1976 was beginning to show signs of the problems which would erupt within a year. The State recognized at the time of the Flambeau announcement that it did not have sufficient regulatory and statutory control to handle a developing base metal industry. Kennecott worked with the State to develop a set of permitting rules and reclamation regulations which, although modified, form the basis for the current legal framework. Kennecott also began to work with the legislature to develop a reasonable tax regime. Unfortunately by 1976 many of the issues surrounding mine development and taxation were moving toward discord, rather than agreement. PHASE THREE: THE PROBLEM YEARS The discovery of the Crandon Deposit was the beginning of the third phase of base metal massive sulfide exploration in Wisconsin. Exxon accelerated its program and others came into the state, or rebuilt their earlier programs. Unfortunately, the excitement of the exploration community was soon severely dampened by political events in Madison. Efforts to regulate and tax, or even stop, base metal mining were accelerated. What was perhaps a local issue involving Kennecott and the residents of Rusk County suddenly took on a new perspective. Acrimonious debate began on a new level over both economic and environmental issues. In 1976 Kennecott was denied a local zoning permit to develop its Flambeau deposit. The following year the Wisconsin Legislature enacted an untenably high tax on base metal mining. The years between 1976 and 1991, when Kennecott finally received approval for the Flambeau mine, became a roller coaster ride of off-again, on-again exploration involving intermittent political negotiations at local and state levels, compounded by historically low metal prices. �12 Kennecott Returns Kennecott attempted to resurrect the Flambeau project several times, but concern for the political climate in Wisconsin, severe financial problems brought on by depressed copper prices, opportunities in gold elsewhere, and new ownership, all impacted the project and kept it on the shelf. In 1986, Larry Mercando was assigned to the project and moved to Ladysmith, and by the late 1980's had developed a strong commitment from Kennecott management to obtain permits for an open pit, direct shipping operation. This coincided with an upturn in copper prices, the purchase of Kennecott by RTZ, and a new government attitude in Madison which was more supportive of mining. Although some of the negative concerns of the earlier years remained to be overcome, Mercando's five-year effort brought reason to the front and in January, 1991, Kennecott received the necessary state and local permits and started construction. ln May, 1993, after a brief delay for a final environmental review, based on the discovery of an unusual, wayward clam in the nearby Flambeau River, the mine was in production. Exxon Leaves Geological and engineering work progressed smoothly at Crandon following the initial drilling. Ed May was hired to manage the development drilling and produce resource and reserve estimates, and his experience at Flambeau was put to good use. By 1980 most of the technical work was in hand and it remained for the engineers and managers to develop a mine plan and get it permitted. Exxon began to encounter the same kind of political problems at Crandon that Kennecott ran into at Flambeau. Development of a reasonable mine plan was frustrated by the passage of the punitive tax law in 1977 and a series of unresolved revenue and environmental issues. These uncertainties complicated the permitting process. Although a revised tax law took effect in 1981, other issues such as local zoning were still obstacles to obtaining a permit. The political climate in Wisconsin was decidedly unfriendly. On top of this, metal prices were as low as they had been in decades. It was not a good time to try to promote a base metal mine in Wisconsin to management. Before permitting efforts could be carried forward, a decision was made by Exxon in 1986 to get out of the minerals exploration business and to divest itself of its mineral properties. Over the next several years several companies entertained the possibility of developing Crandon in joint venture with Exxon, but again a combination of poor metal prices and concern over the political risks in Wisconsin prevailed. In 1994 Exxon and Rio Algom announced a joint effort to permit and operate a scaled-down underground zinc mine at Crandon, subject to a positive feasibility report and acquisition of the necessary permits. This effort is currently in full swing and appears to be headed toward success. Governor Thompson has repeatedly supported responsible mining, and it appears that the overall political climate has changed for the better. Noranda Persists The years following the Crandon announcement were difficult ones for Noranda, as well. Carl Schwenk took over management of the program and continued to explore the greater Monico area with encouragement but no real success. Glen Adams joined the program from Exxon. In 1978 Wisconsin passed into law the Geologic Information Act which required all subsurface exploration data, whether from government or private land, to be made a part of the public record. You can imagine the concern this caused in the exploration community, given the number of companies involved and the intensity of competition. Noranda took up the cause of the industry and filed suit �13 against the state in 1979 to overturn this law. To demonstrate the seriousness of their concern for this law and the punitive tax burden, Noranda closed their Wisconsin office in 1978, although they maintained their land holdings and continued on a reduced basis to test their better targets. In anticipation of success in overturning the Geologic Information Act, Noranda reopened their Rhinelander office in 1981, and renewed their exploration efforts. They still liked, but could not acquire, the Oneida County land. Several more good grade but small size discoveries would come along, but nothing approaching economic scale. Although Noranda was frustrated by the fact that good anomalies on Oneida County land could not be acquired, they maintained their interest in them and worked with the County to develop a leasing policy. When it was announced in 1989 that there would be a lease sale, Noranda had a good idea of what land was favorable. They won the bid for land in Lynne Township and drilled their second significant discovery in January of 1990. The Lynne Deposit is a tribute to the persistence of Noranda, their faith in the volcanogenic massive sulfide model, and the importance of appreciating and using old data. New Companies Join The Search Competition continued at a high level after 1976, in spite of the adverse political environment and low metal prices. In addition to the standard base metal companies with their "go-it-alone" approach, a proliferation of joint ventures were formed. Leading the way was Ernie Lehmann who established several ventures with oil companies such as Chevron, Getty, Superior and General Crude. Ernie had been a consultant for several of these companies prior to Crandon, but became an equity partner in these new ventures. Ned Eisenbrey joined Ernie after Kennecott pulled out in the early 1970's, and Ernie attributes much of the success of these joint ventures to Ned's ability to sort out which anomalies were sulfides and which were graphite. From 1980 to 1984 these ventures added Ritchie Creek, Bend, Horseshoe, and Jump River to the list of discoveries in Wisconsin. These are small deposits, at this point, but continue to be of interest and may some day, like any of the other numerous small deposits, lead to bigger things. Opportunities still exist for those who persist. A list of some of the companies who entered the fray following the Crandon announcement are shown in Table 2. This list is probably not complete, but will illustrate the scale of interest and competition that existed, and essentially continues today. TABLE 2 Companies entering Wisconsin After Crandon AMOCO Chevron Kerr McGee Falconbridge Inspiration Newmont St. Joe Rayrock Getty Dennison B.I.A. (Mole Lake) BHP Cyprus Sharp Resources �14 PHASE FOUR: THE PRODUCTIVE YEARS Entry into the next phase of the history of massive sulfide exploration in Wisconsin is almost upon us, or may have already started. Two operating base metal mines in northern Wisconsin confirm Kennecott's original thesis of the 1950's: there is no reason why major deposits should not occur under glacial cover on the Superior Craton south of Lake Superior. Exploration now has been conducted for forty years based on this premise, by a large number of companies. North of Lake Superior new discoveries are still being made after a much longer period of exploration, using more sophisticated technology and models. There is no reason why the same persistence and approach will not be brought into Wisconsin. Many of the anomalies found in earlier electromagnetic surveys remain untested, for reasons of land inaccessibility, weaker response, or unavailability of the proprietary data. Some areas with potential may have been missed, deep targets under small, nearsurface occurrences may be developed, and clearer understanding of the bedrock geology may generate a more favorable interpretation of potential for parts of northern Wisconsin. Whatever the case, the fact that two major deposits have been found and were brought into, or are headed for, production will certainly stimulate a resurgence in exploration. Let us all hope that this fourth phase of massive sulfide exploration in Wisconsin is the smoothest, longest, and most successful. Acknowledgements A history is never complete because all the people who form it are generally not always represented in the telling of it, nor are the memories of those polled always reliable. In the case of the early volcanogenic massive sulfide exploration in Wisconsin a few of the players are still around and have given advice on this presentation of some of the history involved. Much of the Kennecott story was compiled as part of a paper authored by Michael Mudrey of the Wisconsin Geological and Natural History Survey in 1991 in which this author participated. Other comments on Kennecott's experience were solicited from Larry Mercando and Ed May. Events in Exxon's history were discussed with Paul Schmidt and Ed May. Noranda's experiences were reviewed with Bob Miller, Michael Donnelly, Carl Schwenk, and Glenn Adams. The activities of U. S. Steel were recounted by Cedric Iverson and Thon Ginn. Ted DeMatties and Ernie Lehman offered comments on the more recent exploration history in Wisconsin. All contributed to the list of players on Tables 1 and 2. Ed May and Jay Hammitt reviewed this paper and provided very constructive comment and encouragement. Exploration history is complicated by the fact that programs and discoveries are team efforts. Geologists, geophysicists, and managers at several levels all become intricately involved in the planning and implementation of any one program. All deserve a share of the credit, and the blame, as things go right and wrong. Explorationists understand that it is often external factors that force decisions that make or break a program. It is a tribute to explorationists that they persist in their optimism and enthusiasm, often for decades, in spite of the variety of obstacles they encounter. The successful but unfinished search for volcanogenic massive sulfide deposits in Wisconsin is a prime example of how talent and persistence combine to win the day, to the benefit of us all. �15 References Cited DeMatties, T. M., 1994, "Early Proterozoic Volcanogenic Massive Sulfide Deposits in Wisconsin: An Overview," Economic Geology, vol. 89, P. 1122. Mudrey, M. G., Jr., Evans, T. J., Babcock, R. C., Jr., Cummings, M. L., Jr., Eisenbrey, E. H., LaBerge, G. L., 1991, Hollister, V. F., ed., "Case Histories of Mineral Discoveries, Volume 3, Porphyry Copper, Molybdenum, and Gold Deposits, Volcanogenic Deposits (Massive Sulfides), and Deposits in Layered Rock": Society for Mining, Metallurgy, and Exploration, Inc., p. 117. Schmidt, P. G., "Discovery Case History of the Crandon Massive Sulfide Deposit, Forest County, Wisconsin, j Hollister, V. F., ed., "Case Histories of Mineral Discoveries; Volume 3, Porphyry Copper, Molybdenum, and Gold Deposits, Volcanogenic Deposits (Massive Sulfides), and Deposits in Layered Rock": Society for Mining, Metallurgy, and Exploration, Inc., P. 99. �16 �17 GENERAL CHARACTERISTICS AND GEOLOGIC SETTING OF THE WISCONSIN MAGMATIC TERRANES by Gene L. LaBerge Geology Department UW-Oshkosh Oshkosh, WI ABSTRACT The Wisconsin magmatic terranes (referred to by workers in the mineral industry as the "Ladysmith-Rhinelander volcanic belt") constitute a major addition to the Lake Superior region that formed during Early Proterozoic convergent tectoucs. Radiometric dating indicates that the volcanic and plutonic rocks were generated between 1,890 and 1,830 million years ago. Continuing geological, geochemical, and geophysical studies have allowed refinements on earlier interpretations of the general character and tectonic setting of the terranes. Available information indicates that a variety of different geological environments, including an oceanic island arc, back arc basins, and a continental volcanic arc, and perhaps other environments are represented within the area commonly referred to as the Wisconsin Magmatic terranes. Recognition of the existence of the magmatic terranes in the 1960's led to extensive exploration for volcanogenic massive sulfide deposits in Wisconsin. Geophysical surveys identified dozens of exploration targets that were subsequently drilled. These data have added greatly to the database on the volcanic belt, an area that is generally very poorly exposed because of the thick cover of glacial deposits. Three areas within the magmatic terranes contain sufficient outcrop to permit traditional geologic mapping: the Pembine area in northeastern Wisconsin, the Monico area in the central part of the belt, and the Marathon County area on the southern margin of the belt. Studies in these areas suggest that each area represents a different environment. The Pembine area contains remnants of a dismembered ophiolite and an oceanic island arc. The Monico area contains an older sequence of gneissic rock overlain by a bimodal suite of basalts and rhyolites that may represent a back-arc, or perhaps an intra-arc rift environment. This postulated rift may represent the "Highway-8" lineament, along which most of the major sulfide deposits formed. The Marathon County area contains several sequences of volcanic and plutonic rocks that appear to have a more complex origin. Some volcanic rocks belong to a basalt-andesite-rhyolite sequence that appears to be arc-related. A sequence of caldera-related rocks in the Wausau area unconformably overlies an older volcanic sequence, and appears to be a post-tectonic feature. These various environments may host rather different types of mineral deposits. INTRODUCTION In the past several decades great strides have been made in understanding the geologic evolution of the Lake Superior region. One of the major developments has been the recognition of a major belt of Early Proterozoic volcanic and plutonic rocks, named the Wisconsin Magmatic Terranes, that extends across northern Wisconsin from near Pembine, Wisconsin, westward approximately 200 miles to near Weyerhaeuser, Wisconsin (Figure 1). However, rocks correlated with the magmatic terranes are present in eastern Minnesota and northern Iowa, and the terranes extend eastward under Lake Michigan (probably to the Grenville Front). The belt is overlain by �18 930 890 880 DULUTH HINGE LINE FOR KEWEENA WAN TILTING CONTINENTAL MARGIN ASSEMBLAGE 450 44 100 MILES 150 KILOMETERS Figure 1. Generalized tectonic map of the southern part of the Lake Superior region (modified from Sims, 1992). �19 Paleozoic rocks to the east and west, and most of the belt is covered with a thick mantle of glacial deposits, with the result that much of the belt is not exposed. The northern boundary of the belt is the Niagara Fault zone (Greenberg and Brown, 1983), which separates the volcanic and plutonic rocks from the dominantly Early Proterozoic sedimentary rocks of the Marquette Range Supergroup that were deposited on the margin of the Archean Superior Craton. The southern margin of the volcanic and plutonic belt is near Stevens Point, in central Wisconsin, where Archean rocks are again present (Morey and others, 1982). Thus, the belt is about 100 miles wide. The Middle Proterozoic Wolf River Batholith cuts out a major portion of the volcanic and plutonic belt in northeastern Wisconsin. Because of the cover of glacial deposits, elucidation of the major features of the volcanic and plutonic belt has been a long-term process with major input from the mineral industry. The early compilation of geologic data by Dutton and Bradley (1970) demonstrated that outcrop density necessary for mapping was present in only a few areas: the Pembine area in the east, the Monico area about 80 miles to the west, and the Wausau area in the south. The Wausau area was mapped in 1969-1975 (LaBerge and Myers, 1983); the Pembine area was the subject of several graduate theses, and was mapped by Sims and Schulz (1993); the Monico area was also the subject of several graduate theses (Schriver, 1973; Venditti, 1973; Bowden, 1978), and was mapped by LaBerge, John Franidin, and John Klasner in 1990-199 1 (LaBerge and Kiasner, in review). However, it remained for the regional aeromagnetic survey by Karl (Zietz, Karl, and Ostrom, 1978) to provide a basis for extrapolation of data from one area to another. Detailed aeromagnetic and EM surveys and drill core data from various mining companies have provided much of the lithologic information currently available for unexposed portions of the Wisconsin magmatic terranes. The general distribution of major units within the volcanic belt was shown on the regional geologic map of Morey and others (1982). Recent lithologic, geochemical, geochronologic, and structural data permitted Sims (1992) to refine the bedrock geology of the belt. General Features of the Wisconsin Magmatic Terranes The Wisconsin magmatic terranes consist of an extensive suite of volcanic, plutonic, and associated sedimentary rocks that formed in the Early Proterozoic Penokean Orogen of the Lake Superior region. The rocks were produced during a complex convergent tectonic regime that existed from about 1,890 m.y. to 1,830 m.y. ago along the southern margin of the Archean Superior craton. A number of massive sulfides and other mineral deposits were produced during the Penokean igneous activity and tectonism. Convergent tectonics culminated with accretion of an island arc (or arcs) to the Superior Craton as well as collision of an Archean "microcontinent" of unknown dimensions with the accreted island arc. Outcrops and drill core data indicate that the most widespread rocks are massive and pillowed basalts, with localized areas of andesitic to rhyolitic volcanic rocks and associated sedimentary rocks, mainly graywackes (Figure 2). Areas of metasedimentary rocks may represent a variety of environments. Graphite is abundant in some sedimentary sequences, but is largely lacking in others. In the Pembine area the older rocks in the volcanic succession are tholeiitic basalt and basaltic andesite with associated gabbro sills (Sims and others, 1989) that comprise the Quinnesec Formation. The discovery of sheeted dikes, serpentinites, and plagio-rhyolite within the Quinnesec Formation suggests that these rocks are a dismembered ophiolite (Schulz, 1987). The tholeiites are overlain by a sequence of caic-alkaline rocks (the McAllister and Pemene volcanics, Jenkins, 1973) ranging in �20 VOLCANIC ISLAND Figure 2. Idealized east-west cross-section of the Wisconsin magmatic terranes, showing felsic volcanic centers alternating with sedimentary basins. composition from andesite to rhyolite, whose composition falls within the fields of subduction-related magmatic suites and are geochemically similar to volcanic suites from oceanic island arcs (Sims and others, 1989). Both subaerial rhyolites (volcaniclastic rocks) and subaqueous (hyaloclastite) rhyolites are present in the Pemene Formation, indicating at least periodic emergence in the area. Volcanic rocks in the Monico area comprise a bi-modal sequence of high-Al basalts and lowSi02 andesites interbedded with felsic volcanic rocks of dacite to rhyolite composition (Sims and others, 1989). The mafic rocks are massive to pillowed with pillow breccia (Figure 3) relatively common. Pillows tend to be highly vesicular. Felsic volcanic rocks are massive porphyritic flows and lithic tuffs (subaqueous?) along with some probable subaerial welded tuffs (Figure 4) (LaBerge and Klasner, in review). The bimodal volcanic sequence has generally undergone only greenschist grade metamorphism, and presumably overlies amphibolite grade rocks exposed north of Highway 8 (Figure 5). A large quartz porphyry (the Neptune Lake porphyry) is intrusive into the amphibolitegrade rocks, and may have resulted in widespread chloritization, epidotization, and quartz-feldspar veining of the overlying volcanic succession near the Pelican River deposit (Figure 6). Several massive sulfide deposits, the Pelican River, Duckblind, and Wolf, occur within the volcanic sequence, and may have formed from the fluids that gave rise to the hydrothermal alteration. The volcanic rocks are compositionally similar to the bimodal calc-alkaline rocks that host Kuroko-type massive deposits elsewhere (Sims and others, 1989) and may represent a back-arc basin. However, according to K. J. Schulz (personal communication, 1995) the composition of the Monico volcanic suite appears to be unique within the Wisconsin magmatic terranes. He suggests that the volcanic rocks in the Monico area may be a remnant of an intra-arc rift that split the Pembine-Wausau Terrane, and may be the setting of the massive sulfide deposits. This postulated intra-arc rift may account for the so-called "Highway 8 lineament" formed by the known distribution of massive sulfide deposits within the terrane. In central Wisconsin, the basaltic rocks in Marathon County are tholeiitic with compositions that are very similar to basalts of the Quinnesec Formation (Sims and others, 1989). Several large gabbroic bodies and several serpentinites are also associated with the basaltic rocks in Marathon County (LaBerge and Myers, 1983) (Figure 7). The tholeiitic sequence in Marathon County is overlain by calc-alkaline andesite to rhyolite rocks (LaBerge and Myers, 1984) that contains abundant, vaguely bedded, waterlaid tuffs and breccias and some welded (subaerial) tuffs and flows. Thus, �21 Figure 3. Photo of basaltic debris flow southwest of Monico. Wisk broom in upper right-hand portion of photo provides a scale. Figure 4. Photomicrograph of somewhat deformed felsic tuff southwest of Monico. Note the deformed quartz phenocryst near the center of the photo. Horizontal dimension of photo is 6 mm. �Xfv / — — -- Xmv——— / / / x mY // / — -,- - - - Xfv MILES - — ,. PELICAN 2 LAKE Xg — / Xmv — MON1CO / - -- Xmv XAgn Xqp —— — —P xA<j Xfv — N. — N XA9n - N N IN OS Xfv; -, XAmg " XAgn Figure 5. Geologic map of the Monico area. (From LaBerge and Kiasner, in review.) Xg Xqp .—-. - -- -.- Xfv , Xmv XAgn Xfv -- xfv X rn V —._ Facing direction of pillows XAgn—t.neissic rocks XPng-Metagabbro Early Proterozoic or Archean Xmv—Mafic metavolcanics Xfv-Felsic mtavolcanics Xmd—Metadi abase Xqp-Quartz porphyry Early Proterozoic Xg— Pink to red granite Yd— Diabase — Xfv -- - -- -- 8 —— — - -—--'- Xqp — 6 Yd Xmv'Xrn/'xrnv Middle Proterozoic LEGEND —— Xmv PELICAN DEPOSIT /Xfv —.- / ,)(Agn // , , , -— -. XAgn / / , /, / / / �23 Figure 6. Photo of highly altered basalt from west of the Pelican River deposit. Knife is four inches long. there are similarities between the rocks in central Wisconsin and the Pembine area. However, the calc-alkaline rocks in the Wausau area are chemically distinct from those in the Pembine area (Schulz, 1984; Sims and others, 1989). It is possible that the Marathon County area may have developed at least in part on an older basement, perhaps similar to the Archean rocks in central Wisconsin. This interpretation is supported by the presence of numerous Early Proterozoic intrusions into Archean basement rocks, and sillimanite-bearing quartzite xenolith in the 1,500 m.y. Wausau Pluton. The quartzite is interpreted to have been buried beneath the 1,850 m.y. volcanic rocks and subsequently carried up to its present level in the syenite pluton (LaBerge and Myers, 1984). Sims and others (1989) also suggest that volcanics in the Marshfield terrane were deposited on Archean basement. The Wausau area in central Wisconsin contains at least two distinctly different types of rhyolitic rocks. An older group of rhyolitic rocks is composed mainly of somewhat recrystallized and deformed subaqueous lithic tuffs and breccias, such as those exposed along County Hwy. J about five miles east of Wausau, and along County Hwy. A about five miles west of Wausau. They typically have a steeply dipping northeast trending foliation, with prominently flattened clasts. They are commonly interbedded with pillowed basalts, andesites, and graywackes, as shown in eastern and west-central Marathon County (fv and vs on Figure 7) (LaBerge and Myers, 1983). Locally the felsic volcanics show bleaching from hydrothermal alteration associated with significant pyritization. The younger rhyolites are subaerial welded pyroclastic flows, flow breccias, and possible rheoignimbrites along with associated volcanic sandstones and conglomerates. These rocks are �1 2 a Ninemile Granite Wolf River Batholith Diorite-Quartz Diorite Gneiss. Migmatite and Amphibolite Anorthosite Mafic Volcanics Quartz Monzonite Quartz Syeoite ARCHEAN Intermediate Volcanica Felsic Volcanics Volcanogenic Sediments IJltramatic Rocks Granite Metagabbro Mylonitic Rocks Quartzite LOWER PROTEROZOIC Syenite Nepheline Syenite MIDDLE PROTEROZOIC deposits Paleozoic and Quaternary (From LaBerge and Myers, 1983) Figure 7. Geologic map of Marathon County. The "Reef deposit" is located north of Ringle in the eastern part of the map. a WISCONSIN GEOlOGICAL AND NATURAL HISTORY SURVEY MARATHON COUNTY, WIS. OF GEOLOGY EXPLANATION �25 gently-dipping, essentially non-foliated with excellently preserved primary volcanic textures and structures. In short, they appear to be unconformable on the "older" volcanic units. Weidman (1907) named the conglomeratic units the "Marshall Hill Conglomerate", and suggested that it is unconformable on surrounding volcanic rocks. These lithologies are well exposed within the city of Wausau and in the Brokaw area south of the red granite pluton. A number of presumably normal faults offset various rhyolite lithologies within the 3M quarry at Brokaw. These offsets juxtapose lithologies unfavorable for quarrying against favorable horizons and present problems in the quarry operations. The various rhyolites consist of welded tuffs, rheoignimbrites, laharic deposits, massive flows, volcanic sandstones, and massive porphyritic rhyolite. The rhyolite flows, tuffs, and lahars may be part of a caldera complex and the massive rhyolite may represent part of a resurgent dome. In Sections 12 and 13, T.29N., R.7E and Section 8, T.29N., R.8E, just north of Wausau, a northeast-trending block of pillow basalts is in fault contact with gently-dipping rhyolite lithologies on both its north and south margins. The fault-bounded block of pillow basalts may represent an uplifted block of the older volcanic rocks on which the caldera-related rocks were deposited. The rocks interpreted as pre-caldera phases consist of basalts, andesites, and rhyolites, and typically have a well-developed steeply dipping northeast-trending foliation. In contrast, the calderarelated rhyolites are gently dipping, and are mainly non-foliated. This suggests that the proposed caMera rhyolites are unconformable on the foliated rocks and may be post-tectonic. The red granite north of Wausau truncates the several rhyolite lithologies, and may post-date the postulated caldera. In summary, the three areas with relatively good exposure appear to represent rather different environments within the volcanic belt: the Pembine area may be a remnant of an oceanic island arc; rocks in the Monico area may represent an intra-arc rift or back-arc basin; and the Marathon County area is a complex area formed during the general convergent tectonics that produced the Wisconsin volcanic belt. Areas of Economic Interest The Wisconsin magmatic terranes are the host for a number of mineralized areas, mostly volcanogenic massive sulfide deposits. Although numerous areas containing some mineralization have been identified, only a handful are large enough to be of economic interest. The richer deposits include the Flambeau deposit (in production) (May, 1977, 1996), the Crandon deposit (actively working on permitting) (Schmidt and May), the Bend deposit (continued exploration) (DeMatties, 1996), the Eisenbrey (Thornapple) deposit (continued exploration) (May, 1996), and the Lynne deposit (presently inactive) (Adams, 1996). These deposits are the subject of separate chapters in this guidebook. Some smaller deposits (the Pelican River, Duckblind, and Wolf) also occur as was noted earlier in this chapter. Because these major deposits are covered in separate chapters within this volume, they will not be described here. Deposits other than massive sulfides may also be present in the Wisconsin magmatic terranes. Examples of two other types of deposits, an epigenetic gold deposit and mineralization associated with a postulated caldera setting are discussed here. The Reef gold deposit, in eastern Marathon County, has been examined by a number of mining companies since the mid-1970s. Mineralization in the area was first recognized during regional geologic mapping in 1970 (LaBerge and Myers, 1972). At least 80 core holes have been drilled in the area in an effort to characterize the mineralization. �26 The main rock types in the area of the Reef deposit are steeply dipping mafic volcanic rocks, gabbros, and serpentines with a chemistry suggesting that they have ophiolitic affinities (K. J. Schulz, personal communication, 1995). A swarm of granophyric to porphyritic felsic dikes or sills cut the mafic rocks in the mineralized area (Kennedy and Harding, 1990). The mineralized area is one of intense deformation near the Eau Claire River shear zone and lies just west of the western margin of the Wolf River Batholith. A thick sequence of metasediments and felsic volcanics, in which massive sulfides consisting mainly of pyrrhotite have been drilled, occur just west of the gold mineralized area. Mineralization at the Reef consists of pyrrhotite, chalcopyrite and gold in silicified shear zones and quartz veins that cut the mafic volcanic rocks and gabbros. According to Kennedy and Harding (1990), the northeast-trending, northwest-dipping quartz-sulfide veins and zones of sulfideveinlets host gold, copper, silver, and tellurium mineralization in the area of interest. They state that the mineralization is closely associated with the felsic dikes and sills and that the intrusions and vein system are hosted by a granofels unit (a distinctive, biotite-rich, foliated to mylonitic rock derived chiefly from gabbro). Visible gold in quartz-goethite blocks, widely distributed at the surface, is probably the result of weathering of gold-bearing veins (Kennedy and Harding, 1990). Seven distinct zones of mineralization containing 454,600 tons grading 0.262 opt gold and approximately 0.28% copper have been identified, and the deposit is open at depth. The transgressive nature of the mineralization (in sheared gabbroic rocks) and the apparent relationship to felsic intrusions, indicates that the Reef deposit is epigenetic, and thus is distinctly different from the volcanogenic massive sulfide deposits elsewhere in the magmatic terrane. Deformation resulted in the development of numerous shear zones and mylonitic rocks similar to those illustrated in Figures 8 and 9 from the Monico area. Epigenetic gold mineralization in sheared rocks of the Reef deposit suggests that other mylonitic zones may also have potential for gold mineralization. Possible mineralization associated with the caldera-type rhyolites include the following features in the Wausau area. (1) Waste rock at an abandoned small shaft along the fault contact between pillow basalts and rhyolite along Troy Avenue in northeastern Wausau contained abundant sphalerite, some galena in a breccia zone cemented by quartz, and carbonate. (2) Numerous jasper veins and patches occur within the rhyolitic rocks in the Brokaw area. These veins appear to be jasperoid alterations of the volcanics and associated sediments and locally contain pyrite. In 1978 roadcuts for a new subdivision north of County Hwy. W on -the east side of the Wisconsin River at Brokaw exposed tuffs with rounded and angular clasts to 5 cm in a finer volcanic matrix interbedded with conglomerate to the north. The conglomerate contains clasts up to 12" in diameter. Most clasts are rhyolite, but quartzite and granite boulders are also present. The matrix of the conglomerate is mainly volcanic sandstone, with local jasperoid cement in the coarser conglomerate. Extensive epidotization of units is also common. (3) Disseminated sulfide (pyrite and chalcopyrite) in the rhyolites exposed in the railroad cuts in Gilbert Park and at the former hospital in northeastern Wausau. Tectonic Setting The general tectonic setting in which the Wisconsin magmatic terranes formed has been discussed in the literature since the mid-1970s. There is now a general consensus that the Penokean orogen formed in a complex convergent tectonic environment. Lack of subduction-related volcanic �27 U Figure 8. Photo of sheared basaltic rocks with abundant quartz veins. This lithology is transitional between massive basalt and the banded mylonite shown in Figure 9. From west of the Pelican River southwest of Monico. Figure 9. Photo of outcrop of banded mylonite that cuts basaltic rocks southwest of Monico. Hammer provides a scale. �28 rocks north of the Niagara Fault zone (the exposed margin of the Superior craton) clearly indicates that subduction was away from the craton margin. Ophiolitic rocks with associated calc-alkaline rocks in the Pembine area suggest the development of an oceanic island arc between 1,890 and 1,860 m.y. ago that docked against the Superior craton about 1,860 m.y. ago along the Niagara Fault zone (Sims and others, 1989). Schulz (1984) suggests that the arc was "evolved," or "mature," based on its chemistry. The tectonic history of the southern margin of the volcanic belt is much more equivocal. Some models suggest northward subduction, away from the Archean "microcontinent" that borders the Marshfield terrane on the south (Cannon and others, 1991) whereas others suggest a southward subduction beneath the Archean microcontinent (LaBerge, 1986). The author favors a model with south-directed subduction, but recognizes that northward subduction beneath the just-accreted island arc probably also occurred. Subduction may have been Jth north-dipping and south-dipping before final closure of the "Penokean Sea" about 1,840 m.y. ago. References Cited Adams, G. W., 1996, Geology of the Lynne Base-Metal deposit, north-central Wisconsin, U.S.A. iii Volcanogenic Massive Sulfide Deposits of Northern Wisconsin: A Commemorative Volume, G. L. LaBerge (ed.), Institute on Lake Superior Geology, v. 42, part 2. Bowden, D. R., 1978, Volcanic rocks of the Pelican River massive sulfide deposit, Rhinelander, Wisconsin: A study of walirock alteration: Unpublished M.S. Thesis, Michigan Technological University, 62 p. Cannon, W. F., Lee, M. W., Hinze, W. J., Schulz, K. J., and Green, A. G., 1991, Deep crustal structure of the Precambrian basement beneath northern Lake Michigan, mid continent, North America: Geology, v. 19, p. 207-210. DeMatties, T. A., 1994, Early Proterozoic volcanogenic massive sulfide deposits in Wisconsin: An overview: Economic Geology, v. 89, p. 1122-1151. DeMatties, T. A., 1996, A geologic framework for Early Proterozoic volcanogenic massive sulfide deposits in Wisconsin: An exploration model: iii Volcanogenic Massive Sulfide Deposits of Northern Wisconsin: A Commemorative Volume: G. L. LaBerge (ed.), Institute on Lake Superior Geology, v. 42, part 2. Duuon, C. E., and Bradley, R. E., 1970, Lithologic, geophysical, and mineral commodity maps of Precambrian rocks in Wisconsin: U.S. Geological Survey Miscellaneous Geologic Investigations Map 1-631, scale 1:500,000, with accompanying report, 15 p. Greenberg, J. K., and Brown, B. E., 1983, Lower Proterozoic volcanic rocks and their setting in the southern Lake Superior district: In Early Proterozoic geology of the Great Lakes region. Edited by L. G. Medaris, Jr., Geological Society of America, Memoir 160, p. 67-84. Jenkins, R. A., 1973, The Geology of Beecher and Pemene Townships, Marinette County, Wisconsin (Abstract), Institute on Lake Superior Geology, 19th, Madison, Wis., p. 15-16. Kennedy, L., Harding, T., 1990 �29 LaBerge, G. L., 1986, The Proterozoic geology of the Lake Superior region: j LaBerge, G. L., Attig, J. W., and Mode, W. N., Guidebook 50th Annual Tn-State Geological Field Conference, Wausau, Wisconsin, p. 1-29. LaBerge, G. L., and Kiasner, J. S., (in review), Geology and tectonic significance of Early Proterozoic rocks in the Monico area, Wisconsin: U.S. Geological Survey Bulletin. LaBerge, G. L., and Myers, P. E., 1972, 1971 progress report on mapping of Precambrian geology of Marathon County: Open file report, Wisconsin Geological and Natural History Survey. LaBerge, G. L., and Myers, P. E., 1983, Precambrian Geology of Marathon County Wisconsin: Wisconsin Geological and Natural History Survey, Info. Circular 45. LaBerge, G. L., and Myers, P. E., 1984, Two Early Proterozoic successions and their tectonic significance: Geological Society of America Bulletin, v. 95, p. 246-253. May, E. R., 1977, Flambeau: A Precambrian Supergene Enriched Massive Sulfide Deposit: Geoscience Wisconsin, v. 1, p. 1-26. May, E. R., and Dinkowitz, S. R., 1996, An Overview of the Flambeau Supergene Enriched Massive Sulfide Deposit: Geology and Mineralogy, Rusk County, Wisconsin: jj Volcanogenic Massive Sulfide Deposits of Northern Wisconsin: A Commemorative Volume: G. L. LaBerge (ed.), Institute on Lake Superior Geology, v. 42, part 2. Morey, G. B., Sims, P. K., Mudrey, M. G., and Southwick, D. L., 1982, Geologic Map of the Lake Superior region, Minnesota, Wisconsin, and northern Michigan: Minnesota Geological Survey State Map Series S-13. Schniver, G. H., 1973, Petrochemistry of Precambrian greenstones and granodiorites in southeastern Oneida County, Wisconsin: Unpublished M.S. Thesis, University of Wisconsin-Milwaukee, 83 p. Schulz, K. J., 1984, Early Proterozoic Penokean igneous rocks of the Lake Superior region: Geochemistry and tectonic implications: Abstract, 30th Annual Institute on Lake Superior Geology,Wausau, Wisconsin, p. 55-56. Sims, P. K., 1992, Geological Map of Precambrian rocks, Southern Lake Superior region, Wisconsin and northern Michigan: U.S. Geological Survey Miscellaneous Investigations Series Map I2 185. Sims, P. K., Van Schmus, W. R., Schulz, K. J., and Peterman, Z. E., 1989, Tectono-stratigraphic evolution of the Early Proterozoic Wisconsin magmatic terranes of the Penokean orogen: Canadian Journal of Earth Sciences, v. 25, p. 2145-2158. Venditti, A. R., 1973, Petrochemistry of Precambrian rocks in southeastern Oneida County, Wisconsin: unpublished M. S. Thesis, University of Wisconsin-Milwaukee, 93 p. Weidman, S., 1907, The Geology of North Central Wisconsin: Wisconsin Geological and Natural History Survey, Bulletin 16, 697 p. �30 Zietz, I., Karl, I. H., and Ostrom, M. E., 1978, Preliminary aeromagnetic map covering most of the exposed Precambrian terrane in Wisconsin: U.S. Geological Survey Miscellaneous Field Study MF-888, scale 1:250,000. �31 A GEOLOGIC FRAMEWORK FOR EARLY PROTEROZOIC VOLCANOGENIC MASSIVE SULFIDE DEPOSITS IN WISCONSIN: AN EXPLORATION MODEL by Theodore A. DeMatties Geological Consultant 10-353rd Ave. NW Cambridge, Minnesota 55008 ABSTRACT The Early Proterozoic greenstone belt of northern Wisconsin possesses some of the best volcanogenic (volcanic-hosted) massive sulfide (VMS) potential in North America. A 100-million-ton resource of base- and precious-metal-bearing mineralization, distributed in 13 or more deposits and occurrences and clustered in three districts, has been identified in the belt. Host rocks for the VMS mineralization are part of the 144 mile long, east-west trending Ladysmith-Rhinelander metavolcanic complex, which consists of various greenschists, amphibolites, cherty iron-formations, and sericite to quartz-sericite schists. These 1880-1860 Ma old metamorphic rocks are concealed beneath Pleistocene glacial cover. Development of the Flambeau mine, initiation of mine permitting for the Lynne deposit, and reactivation of the Crandon Project indicate the belt will receive a higher level of activity than in the past. Geologic and geophysical data compiled since the late 1960s define three depositional environments, each containing volcanogenic massive sulfide (VMS) mineralization in the 1880 to 1860 Ma Ladysmith-Rhinelander metavolcanic complex: (1) a main volcanic-arc sequence, the structural core of the complex; (2) laterally equivalent and/or younger(?) back-arc-basin volcanicvolcaniclastic succession that includes a series of mafic volcanic piles; and (3) major felsic volcanic centers in the back-arc basin and along the flanks of the main volcanic arc. VMS mineralization in all three depositional environments includes: (1) syngenetic and epigenetic strata-bound to stratiform massive sulfide mineralization and epigenetic strata-bound stringer sulfide mineralization within, along the flanks of, or near the top of the felsic volcanic centers; (2) syngenetic strata-bound to stratiform massive-sulfide mineralization associated with cherty magnetic iron-formation within the main volcanic-arc sequence; and (3) epigenetic stringer sulfide mineralization and syngenetic stratiform massive sulfide mineralization associated with mafic volcanic piles developed within the back-arc basin. Identified VMS deposits and occurrences are classified by metal content into three groups (Cu, Zn-Cu, Zn-Pb-Cu). Each group exhibits various styles of mineralization which include sheets, mounds, stacked lenses, and replacements. Potentially economic deposits are associated with felsic volcanic centers and sulfide-bearing meta-argillite formations that are favorable stratigraphic units deposited before, during, or after the ore-forming event(s). Stratigraphic correlations supported by lead isotope data suggest most VMS deposits in the greenschist succession formed in a narrow time interval. �32 INTRODUCTION Four potentially economic volcanogenic (volcanic-hosted) massive sulfide (VMS) deposits have been discovered in northern Wisconsin since the 1960s. Only one, Kennecott's Flambeau, is currently being developed; the Crandon deposit, with an identified resource in excess of 70 million tons, is being permitted for development by the Rio Algom-Exxon joint venture. The Lynne deposit, discovered in 1990 by Noranda, is temporarily on hold because of environmental concerns, but the Bend deposit, discovered in 1986, continues to be evaluated by Canadian junior companies Sharpe Energy and Resources and Freewest. The Precambrian of northern Wisconsin has some of the best VMS potential in North America. About 400 prospects drill-tested since the mid-1960s has resulted in discovery of four potentially viable deposits, approximately one for each 100 prospects tested. This very high success ratio has been offset by a strict state permitting process that is believed to be responsible for the slow pace of mine development in northern Wisconsin. A general geologic framework for volcanogenic massive sulfide mineralization was proposed for the western end of the belt (DeMatties, 1989). This paper is an expansion of that communication and summarizes important geologic features which characterize volcanogenic massive sulfide mineralization identified in the belt thus far. The proposed geologic framework can be utilized as both a genetic and empirical model for future exploration in the belt. However, as with all models, change is inevitable. Regional Geologic Framework of VMS Deposits in Wisconsin Regional metamorphism that developed during intense isoclinal folding has overprinted the original volcanic and sedimentary rock units in the Precambrian terranes of northern Wisconsin. This metamorphic overprinting varied in intensity, ranging from upper amphibolite facies (relict textures are totally or partially obscured and foliation, in this case schistosity, is intense) to lower greenschist facies (relict textures are well preserved and foliation development is weak). Knowledge of these metamorphic rock units and their distribution is derived mainly from geophysical patterns, drillhole data, and few bedrock outcrops. The present paper emphasizes the character of the rocks, their structural and stratigraphic setting, and interpretations of the original lithology and depositional environment before metamorphism and structural dislocation modified the original patterns. Major Geologic Terranes The VMS deposits in northern Wisconsin lie within the Early Proterozoic Penokean fold belt of the Southern Structural Province of the Precambrian Shield (Fig. 1). In Wisconsin the fold belt is divided (Greenberg and Brown, 1983; Sims et al., 1989) into two major terranes (Fig. 2). The first is the northern Penokean terrane (NP'!'), distinguished in part by a thick platformal turbidite sequence of clastic and chemical sedimentary rocks (Sims's continental margin assemblage) interbedded with subordinate tholeiitic metavolcanic rocks (bimodal suite of basalt-rhyolite). The NPT contains major oxide-facies iron-formations and some rare granitic intrusions. This supracrustal assemblage was deposited on an Archean basement and correlates stratigraphically with the Marquette Range Supergroup in Michigan. �33 La Roni Belt 200 MI Uchi 200 KM Huronian — Supergroup North Range & MUle Lacs Group . • .\ Wisconsin Magmatic Terranes (Penokean Volcanic Belt) Marquette Range S u perg roup Figure 1. Geologic provinces of the Canadian Shield, including Early Proterozoic supracrustal sequences of the Penokean Fold Belt and major greenstone belts of the Canadian Shield, including the Penokean Volcanic Belt of Wisconsin (modified from Franklin and Thorpe, 1982). �Marquette Range Supergroup Northern Penokean Terrane (NPT) CONTINENTAL-MARGIN ASSEMBLAGE Gneiss (2 800 Ma) Metavolcanic and granitoid rocks (1,835-1,890 Ma) MARSHFIELD SUBTERRANE Metavolcanic and granitoid rocks (Ladysmith—Rhinelander & Wausau Volcanic Complexes; 1,760-1,880 Ma) PEMBINE- WA USA U SUBTERRANE Penokean Volcanic Belt (PVB) WISCONSIN MAGMATIC TERRANES Anorogenic igneous rocks (1,470-1,510 Ma) A Athens shear EP Eau Pleine shear (suture) JR Jump River shear M Mountain shear D Dunbar dome Shear zone Thrust fault Figure 2. Geologic map of northern Wisconsin showing major terranes (modified from Sims, 1989). A High-angle fault and greenstone (2,600-3,550 Ma) >\' (1,820-2,100 Ma) and gneiss, granite, + Middle Proterozoic (Keweenawan) maf Ic igneous and sedimentary rocks of Midcontinent rift system (1,000-1,200 Ma) Sedimentary rocks (Paleozoic) Explanation _______ �35 The second major terrane, south of the NV!', the Penokean volcanic belt (PVB) or Wisconsin magmatic terrane, is characterized by a volcanic island-arc-basin assemblage containing abundant calcalkaline metavolcanic units (basalt, andesite, and rhyolite) and lesser amounts of deep- and shallowwater metasedimentary rocks. It lacks major oxide-facies iron-formation but contains abundant tonalite-granite intrusions. Radiometric dating by Sims et al. (1989) has established an Early Proterozoic age ranging from 1889 to 1835 Ma. They further divide this southern terrane into two volcanic-arc subterranes, the Pembine-Wausau (P-W) and the Marshfield, on the basis of lithology and structure (LaBerge and Myers, 1984). The more northern of the two, the Pembine-Wausau subterrane, was deposited during the interval 1860 to 1889 Ma and is dominated by calc-alkaline metabasalt-andesite-rhyolite with oceanic affinities and localized bimodal high-A1203 metabasalt-rhyolite suites. In the vicinity of Wausau, a younger, more restricted calc-alkaline metavolcanic succession with abundant rhyolite (LaBerge and Myers's greenschist succession) was deposited at approximately 1835 to 1845 Ma on the older succession, which is considered to be 1860 to 1889 Ma in age and is part of LaBerge and Myers's amphibolite succession. Granitoid plutons dated at 1870 to 1760 Ma, ranging from gabbro and diorite through quartz monzonite and granite, intruded the volcanic succession (Sims et a!., 1989; LaBerge and Myers, 1983). The southern subterrane, the Marshfield, is believed to represent remnants of an 1860 Ma volcanic succession that stratigraphically overlies Archean basement (Sims et al., 1989). The NPT, P-W, and Marshfield terranes and subterranes are separated from one another by two major paleosuture zones -- the Niagara Fault Zone and the Eau Plaine Shear Zone (Fig. 2) -- that are believed to represent Proterozoic subduction zones (Sims et a!., 1989). The more prominent Niagara Fault Zone is as much as six miles wide and is defined by a broadly arcuate system of ductile shears. At the exposed east end, Schulz (Sims et a!., 1989) has recognized dismembered subductionzone-type ophiolites along the fault structure, which was active from 1900 to 1830 Ma, during the Penokean orogeny. This major orogenic event also resulted in intense regional-scale folding, regional metamorphism, and emplacement of major granitic plutons. Most past and present base-and precious-metals exploration activity has been in the PembineWausau arc sequence. Wausau volcanic complex From regional gravity and magnetic data, and limited lithologic, geochemical, and structural data, at least two volcanic complexes can be defined in the Pembine-Wausau subterrane (Fig. 3). One in the Wausau area has been intruded by the Middle Proterozoic (1469±28 Ma) Wolf River Batholith and the Wausau syenite-granite plutonic series. The unintruded portion of the Wausau volcanic complex has been intensely explored since the 1960s because of its thin glacial cover and relatively abundant outcrop. The Wausau volcanic complex as mapped by LaBerge and Myers (1983), consists of an older (Archean? and lower Proterozoic- 1880-1860 Ma?) amphibolite facies sequence (quartz-feldspar gneisses and amphibolites-metabasalts) unconformably overlain stratigraphically by younger (18451835 Ma) greenschist facies, cal-alkaline mafic to felsic volcanic rock suite. The volcanic rocks were syntectonically intruded by numerous calc-alkaline epizonal plutons. The complex is characterized by a number of large, nearly vertical, cataclastic fault-shear zones which form the boundaries between greenschist and amphibolite facies sequences. �37 Several well-developed, sulfide-bearing, felsic volcanic host sequences or centers (greenschist facies succession) mapped in the complex are interpreted by LaBerge and Myers (1983) as representing in part a subaerial depositional environment. Such an environment would not be conducive for development of VMS systems and may be one reason why no significant VMS occurrences have been discovered in this complex. Rather the complex appears to be a more favorable host to gold mineralization; a number of lode gold (quartz veins) occurrences and a small (454,600 tons @ 0.262 opt Au), structurally controlled gold deposit (Reef) are known. Ladysmith-Rhinelander volcanic complex The northern portion of the P-W subterrane is occupied by the Ladysmith-Rhinelander complex, referred to informally as the Ladysmith-Rhinelander Greenstone Belt (Fig. 3). Its areal extent is at least 144 miles long and 30 to 50 miles wide, striking easterly across northern Wisconsin and into the Upper Peninsula of Michigan. Sequences of metavolcanic-volcanoclastic and associated metasedimentary rocks that have been metamorphosed to varying degrees dominate the complex. Three basic rock packages have been defined and will be discussed later in detail. The complex is covered by glacial deposits up to 200 feet thick, and bedrock outcrops are relatively rare. Unlike the Wausau Complex, the Ladysmith-Rhinelander Complex contains a number of VMS occurrences and deposits, including the potentially economic Crandon, Flambeau, Lynne, and Bend deposits. The original contact relationship between the Wausau and the Ladysmith-Rhinelander complexes is not known, but they are now in juxtaposition, their contact marked by major faults, shear zones, and granitic intrusives (Fig. 3). GEOLOGIC SETIING OF VMS MINERALIZATION IN ThE LADYSMITH-RIIINELANDER VOLCANIC COMPLEX An extensive geophysical database and abundant drillhole information compiled since the late 1960s by exploration companies and the state geologic survey has allowed mapping of broad, regional rock units that represent basic volcanic fades changes within the complex (Table 1, Fig. 3, 4a, anl 4b). Interpretations of rock units, contact relationships, and fault structures are based on magnetic and gravity patterns. Because of the thick, widespread glacial overburden, information from outcrops is limited. Three basic rock packages are defined. Each has distinctive rock types and structural setting. Further, each package contains VMS mineralization that is thought to be correlative based on stratigraphic and radiometric evidence. Main Volcanic Arc Sequence (Pinv) This sequence is characterized by the presence of magnetic and nonmagnetic amphibolite or amphibolitic schist and, to a lesser degree, quartzo-feldspathic schists. Regional metamorphic grade is high, generally reaching amphibolite rank, and as a result few relict primary textures are present. Thin, interbedded oxide-facies iron-formations (Algoma type) are quite common in the sequence and can be traced in some cases for thousands of feet. Several serpentinized ultramafic intrusions are present. �(Pfv) Felsic Center (Pvs) Basin Arc Back - (Pmv) facies iron-formation (Algoma type) ; serpentinized metasediments) - Altered felsic volcanic sequence (daciterhyodacite to rhvolitic flows, metatuffs, lapilli tuffs, cherty metatuffs, and associated chemicalvolcaniclastic (Pmvf) - Tuffaceous metasediments (metagraywackes, reworked metatuffs, chemical metasedlments) and lesser graphiteand/or sulfide-bearing meta-argillite (Pms), porphyritic and/or amygdaloidal metahasalt to meta-andesite flows (calc-alkaline and tholeiitic affinity) and subvolcanic intrusi'Jes (Ply) - Intermediate to mafic metavolcanic flows, interbedded metatuffs, tuff breccias, tuffaceous metasediments oxide - Same Same Steeply dipping, isoclinally folded to to locally gently dipping volcanic sections; northeasterly fold axes that plunge easterly are common (F-l) , more open coaxal folding locally (F-2( almandine - almandine - (amphibolite fades) - muscovite assemblages cordier ite - (lower greenschist facies( to andalusite- muscovite -albite-quartz Chlorite -epidote - fades) assemblages. muscovite -albite- quartz (middle greenschist (lower greenschist facies) to biotite- -quartz centers developed in the Ladysmith, Bend, Ritchie Creek, Lynne, Pelican Lake areas; larger felsic sequence in Ladysmith area repeated; repetition result of volcanic cycles or folding (amphibolite) succession. Major Mainly greenschist orogeny - LaBerge et al (1986) suggested that these rnetasediments may have been deposited in a number of basins formed by fault grabens during the late Penokean epidote muscovite -albite Chlorite - assemblages (lower greenschist fades) Greenschist succession, possibly a younger volcanic sequence or shallower part of Partially volcanic arc, envelops core (Pmv) Chlorite -epidotemuscovite -albite -quartz facies) assemblages (amphibolite hornblende - Aniphibolite succession, forms structural core of complex; possibly an older volcanic sequence or deeper part of volcanic arc. Dominantly kyanitesillimanite -staurolite- Steeply dipping, isoclinally folded volcanic section; WMW-NE fold axes common (F-l), and tight coaxial folding (F-2) common. Aniphibolite or Main Volcanic Arc amphibolitic schist and lesser quartzo-micaceous to quartzo-feldspathic schists; little or no relict textures preserved; interpreted as mafic metavolcanic flows, interflow tuffs and sediments, Comments Metamorphic Grade Structure Dominant Lithology Mineralization - mineralization at or near stratigraphic top of or deeper within Pfv, or along the flanks of the center; e.g., Flambeau, Bend, Crandon, and Lynne deposits. Zn- Pb-Cu-Ag) - Depositional environment Syngenetic number 1 strata-bound and stratiform massive sulfide (Cu-Au or mineralization at or near stratigraphic top of Pmvf. E.g., Kivela Zone (Ritchie Creek), Horse Shoe, Spirit prospects. (Zn-Pb-Cu-Au) Depositional environment Epigenetic number 3 stringer sulfides (Cu-Au) and syngenetic strata-bound, stratiform massive sulfide deposit. (Zn-Cu) associated with cherty magnetic iron-formation; e.g., Eisenbrey (Thornapple) (pyrrhotite -pynite) Depositional environment Syngenetic, number 2 stratiform, dominantly massive sultides VMS General Description of Regional Volcanic Facies in the Ladysmith-Rhinelander Volcanic Complex. Sequence Table 1. �a metadiorite and rnletasyenite Pmv — mafic to ultramafic volcanicintrusive complex; includes metavolcsnic flows, interflow tufts and sediments, and cherfy iron formation (if) Main Volcanic Arc Sequence CLEAR CREEK Ply — dominantly intermediate to mafic mefavolcanic flows and interbedded metetufts and tuffaceous metasediments Pmv Pmvf — dominantly intermediate to mafic metavolcanic flows and subvolcanic intlusives Pvs — dominantly tuffaceous metesediments; includes metagraywacke, bedded or reworked metatuffs, and associafed chemical metasediments Back-Arc Basin Sequence Pmv\ Pmv Pms — graphific, sulfide-bearing melaargillite formations Pm intrusives, syenodiorite -.. Metagabbro, altered ultramafic Lower Proterozoic Metavoicanic and Related Rocks -' [, Metagranite, quartz metadiorite, Pfv — dominantly intermediate to felsic mdtavOlcanic tuffa/lapilli metatuffs (lithic/ crystal) and flows, cherty metatuffs, and associated chemical mefasediments (metachert) Felsic Center(s) 0 A 0 \\ 5km DEPOSIT (Zn, P4Ag) 5 miles Reverse and normal magnetized mafic dikes (Keweenawan age) Deposit with defined reserves Prospect Shear zone —— Projected or inferred fault Contact, based on airborne magnetic data Figure 4a. General geologic map of the western portion of the Ladysmith-Rhinelander Volcanic Complex (after DeMatties, 1990). a- Lower Proterozoic Barron Quartzite Units locally covering basement metavolcanic units not shown :'': Undifferentiated Cambrian sandstone formations; thin (<50 It) sandstone Lower Proterozoic (?) Intrusive Rock Units £ Sedimentary Rock Units —— o 0, 0 0 U a C A �B 5km I I 5miles Pms__ Figure 4b. General geologic map of the east-central portion of the Ladysmith-Rhinelander Volcanic Complex. 0 I I LANG LADE — Crandon Unit Pfv (Zn, Pb, Cu, Ag, Au) CRANDON DEPOSIT (Zn, Pb, Cu, Ag, Au) MOLE LAKE PROSPECT (Zn, Cu) -RABBIT & DUCK BLIND WOLF RIVER PROSPECT �41 The sequence, which was deposited between 1880 and 1860 Ma (Sims et cii., 1989), is assigned to the amphibolite succession. Its magnetite-rich mafic composition produces a geophysical expression of strong magnetic anomalies with steep gradients and distinct gravity highs. This mappable unit forms the core of the complex and is interpreted as representing dominantly mafic flows and interfiow tuffs and sediments generated in a central to proximal submarine volcanic facies and referred to in this paper as depositional environment #2. Structurally the sequence has been complicated by steeply dipping isoclinal folding (F-i) and a pronounced second(?) refolding (F-2). This deformation has produced a fold pattern of tight, steeply plunging antiform and synform structures within the unit. VMS mineralization is known to occur in this environment. Eisenbrey (Thornapple), the only significant deposit discovered thus far, probably represents the style of mineralization that can be expected in this sequence, i.e., tightly folded, steeply plunging, syngenetic stratiform massive sulfide mineralization (stacked lenses) associated with thin cherty magnetic iron-formation. Partially enveloping the core sequence is a steeply dipping, isoclinally folded unit (Piv) dominated by intermediate to mafic, porphyritic and nonporphyritic metavolcanic flows and lesser chloritic schists, phyllites, and semi-schists. The unit is interpreted to be a sequence of volcanic flows with interbedded metatuffs, tuff-breccias, and tuffaceous sediments. Because regional metamorphism is lower grade and relict textures are discernible, this unit is assigned to the greenschist succession. A proximal subaqueous volcanic environment is indicated by the rock protoliths, insofar as it is known. Back-Arc Basin Sequence (Pvs) The back-arc basin is characterized by a steeply dipping, isoclinally folded, sequence of dominantly feldspathic, quartzo-micaceous, and chlorite schists-semischists and metachert believed to be originally tuffaceous metasediments. Rock protoliths include interbedded metagraywackes and argillites, reworked pyroclastic rocks, and chemical sediments including locally oxide-sulfide facies iron formation. Lesser intermediate to mafic metavolcanic flows are also present in the sequence. The sequence is geophysically expressed as weak to neutral magnetic anomalies and weak, broad gradient gravity anomalies. Structurally, this unit flanks the main volcanic arc and is interpreted as representing a distal subaqueous marginal volcanic basin facies. Regional metamorphism is generally lower rank than in the main volcanic-arc sequence (Pmv) and therefore the sequence can be assigned to the greenschist succession. Locally, amphibolite grade contact metamorphism resulting from thermal effects is achieved near intrusions. The metavolcanic flow units (Pmvf) within the basin facies tend to concentrate in distinct piles that can be mapped as moderately high magnetic anomalies. Drilling indicates that these units are usually porphyritic and/or amygdaloidal metabasalts to meta-andesites and associated tuffaceous and chemical metasediments. These volcanic piles are referred to below as depositional environment #3 and are associated with epigenetic stringer sulfide mineralization and syngenetic stratiform massive sulfide mineralization. Examples include the Kivela zone at the Ritchie Creek prospect, the Spirit occurrence and the Horse Shoe deposit. An important series of units within the basin facies and also the Piv unit of the main volcanic arc facies are the meta-argillite formations (Pms) which are described later in detail. These units are �42 characterized by their distinct linear electromagnetic anomaly patterns, which allows them to be used as mappable marker horizons. These key formations are intimately associated with all the potentially economic VMS deposits. Felsic Centers (Pfv) The felsic centers have been defined by drilling and identified in some outcrops, particularly toward the east end of the complex; but their magnetic expression is neutral and cannot be readily distinguished from metasediments or granitic intrusives in covered areas. Thus the exact areal extent of most of the centers is poorly known. Extensive drilling indicates that the centers are steeply to moderately dipping sequences dominated by strongly to weakly metamorphosed and sheared quartz±feldspar-sericite-chlorite schistssemischists (commonly crystal and/or fragment-bearing) and metacherts. Protolithologies include altered dacitic to rhyolitic metavolcanic flows, pyroclastic rocks, and associated chemicalvolcaniclastic metasediments. Mafic to felsic subvolcanic intrusions, feeders for the volcanic units, may be quite abundant. In several centers such as those hosting the Flambeau and Lynne deposits, large intrusions which may or may not be related to the volcanic activity have either disrupted or cut out significant portions of the felsic sequences. At Lynne, post-intrusive activity is so extensive that the host volcanic section occupies an embayment of a large tonalite pluton. Lesser interbedded mafic metavolcanic suites are almost always present in the felsic centers, resulting in a bimodal sequence. The sequences are interpreted as proximal subaqueous felsic volcanic pile facies and designated depositional environment #1. This environment hosts massive syngenetic stratiform and epigenetic strata-bound massive to stringer sulfide mineralization which occurs within (e.g. Flambeau, Bend, and Crandon), along the flanks of (e.g. Lynne), or near the stratigraphic top (e.g. Ritchie Creek main zone) of felsic volcanic centers. Host rock units are generally hundreds of feet thick, range in composition from quartzsericite schist (felsic tuffs, e.g. Flambeau and Bend) to chioritic schist (argillite, e.g. Crandon), and may contain abundant chemical sediments (chert and carbonate-rich exhalites) which can overlie the syngenetic stratiform mineralization (e.g. Flambeau and Bend), or are interbedded with it (e.g. Crandon). Although the locus of VMS mineralization within a center commonly occurs at breaks or changes in volcanic activity, there is not yet enough information to link mineralization to specific volcanic cycles within the centers. Hydrothermal alteration associated with VMS mineralization in the centers includes sericitization, silicification, and to a lesser extent, chloritization. Limited immobile trace element studies (Lavery, 1985, and DeMatties and Rowell, 1991), indicate that widespread intense silicification (silica enrichment) may be responsible for many of the dacitic to rhyolitic compositions found in some of the centers. At least seven major centers are known in the complex, four of which host the four potentially economic deposits. Other deposits or occurrences hosted by this environment include Pelican River, Catwillow, Wolf River, Spirit, Hawk(?), School House, and Clear Creek. The known centers are assigned to the greenschist succession and are located within the back-arc basin or along the flanks of the main volcanic arc. �43 DISTRIBUTION AND CLASSIFICATION OF MASSIVE SULFIDE MINERALIZATION To date about 100-million-short-ton resource (80 million short tons of potentially economic reserves) of base- and precious-metal massive sulfide mineralization, in 13 or more deposits or occurrences, has been discovered in the Ladysmith-Rhinelander Volcanic Complex (DeMatties, 1989; DeMatties and Mudrey, 1991) (Fig. 5 and Table 2). (All tonnages herein are in short tons.) The world-class Crandon deposit accounts for approximately 72 percent of this total. The remaining tonnage is distributed among 12 or more occurrences and deposits whose average size is approximately 2.5 million short tons. Only four deposits are believed to be potentially viable economically; the largest is Crandon, containing an identified resource of 72.5 million tons. Next are Lynne, with a resource of 7.5 to 8 million tons (a mining reserve of 6.7 million tons), and Flambeau, with a resource of 6 to 7 million tons (a mining reserve of 1.9 million tons). The fourth is the Bend deposit, which contains a reserve base of 3.7 million tons. Further exploration on other deposits could expand their size and define potential mineable reserves. The obvious gap in size between these deposits is dramatized in Figure 5. This lopsided distribution may be a function of exploration having been focused on a particular deposit or area. Table 3 compares the known Wisconsin tonnage distribution with other VMS provinces and belts. Assuming the tonnage distribution for Wisconsin VMS deposits will define a natural geometric progression similar to those in other greenstone belts, and given the large size of the complex (approximately 5700 square miles) as well as the Penokean Volcanic Belt (approximately 19,000 square miles), additional deposits with mineable reserves in the 10- to 60-million-ton range are likely to exist. Current knowledge suggests that the known VMS deposits and occurrences are concentrated into three clusters or districts within the Ladysmith-Rhinelander Volcanic Complex (Fig. 6). The spatial distribution of the three districts appears to be linear, trending in an east-west direction (the socalled Highway 8 trend), with deposits separated by 20 to 30 miles. However, a more complicated arrangement of individual deposits and occurrences is evident within each district. Massive sulfide deposits and occurrences may be classified by ratios of principal metals into groups of copper deposits, zinc-copper deposits, and zinc-lead-copper deposits. Because of its simplicity, Solomon's classification scheme, as modified by Huston and Large (Large, 1992), has been used in classifying Australian VMS deposits and has been adopted in this paper (Large, 1992). This classification is based upon principal metal ratios (Cu/Pb/Zn), and by use of a copper ratio (100 Cu/Cu+Zn) and a zinc ratio (100 Zn/Zn+Pb). Under this scheme, the Wisconsin deposits can be categorized (Fig. 6) into the following groups: 1. Cu deposits: Cu ratio > 60, Zn ratio > 60; e.g., Flambeau, Bend, Ritchie Creek (Main Zone). 2. Zn-Cu deposits: Cu ratio < 60, Zn ratio > 90; e.g., Crandon, Thornapple, Pelican River, Catwillow, and Hawk. (1) The terms "resource", "reserve", "reserve base", "indicated", and "inferred" are used herein as defined in USGS Circular 831, 1980. �0.1 II I 10 I I I 100 II III Medium to iarge (10-60 million st) deposit(s) World-class remaining to be VMS deposit d iscovered* which might be discovered 'C 11111111 1o ':3 0 l- iI Millions of short tons (st) 1 11111 Tonnage classification: ++ Geologic Reserve Base (drill indicated & inferred) + Identified Resource (drill indicated and/or inferred) (* The Duval deposit (10 million st) in Marinette County is considered a sulfide facies iron formation and not a typical VMS deposit in the belt.) deposit with mineable reserves ® Potentially economic VMS ICb 40' 0 0 1< CD5 CCD o (D E. C C) Figure 5. Current (1992) tonnage distribution of known VMS deposits and occurrences in the Wisconsin Penokean Volcanic Belt. 1 5 10 50 100-:: )c �- Prospect 2.9 1.5 Prospect Prospect Catwillow Hawk Prospect N + - 1% Cu 2.76% Zn 5.31% Pb 100 Cu/Cu+Zn 100 Zn/Zn+Pb 1991 prices @ § Calculated from average grade of deposit Geologic reserve base Average grade of deposit 0.9 ? ** * (Main Zone) BLM preference right lease Ritchie Creek in 1993 Application made for Bend Flambeau Under development6 to 7 operating mine 0.74 Prospect Horse Shoe Cu Type 7.5 to Mine permitting on hold Lynne Zn-Pb-Cu Type 2.2 Prospect 3 Pelican (Thornapple) Eisenbrey 72.5 Total Resource Identified (million st) - 3.7 (1990) 0.045 opt Au (1989) - 5.33 opt Ag 2.11 (1.49 (4.1 (1972) 10.5 1.9 2.45 (1990)! -- 6.7 (1992) 0.64 -- trace trace 0.9 1.65 - - approx 0,5k 8 -- 1.5 0.8 present -- 0.48 -- - Pb (%) 1.0 1.5 (1.04 (%) Cu -- -- (1979) 67.4 Drill' indicated Reserved (million st) 0.37 0.010 present 0.3) 0.88)* 0.10 2.1 0085 1.05 0.10 006 245 2.45 3.77 13.78 6.54 6.07 5.06 1.77 0.023 2.96 0.45 2.7 2.8 4.13 Grade' present L00 trace Copper- equivalent 0.02 0.51 trace l,25)* )opt) Ag present trace trace 0.035 (opt) Au 1.60 535 870 2.7 2.60 4.50 34 556 (%) Zn Tonnages and Grades Reported for Wisconsin VMS Deposits 0.5 million Tons or More in Size. Mine permitting in progress Status Total-resource Crandon Zn-Cu Type Deposit Table 2 85 100" SO.5 31.4 6.9 22.9 36.6 18.2 29.4 15.8" Cu Ratio 100 100" 100** 85.5 ,, 84.1 100 100 100 100 92.05** Zn Ratio �38.5% Southern Province Penokean Volcanic Belt (Proterozoic) Kuroko Provence (Miocene) (Paleozoic) Tasman Geosycline (Proterozoic) Central Volcanic Belt 80.0% 33.0% 92.9% 59.0% Churchill Province Fun Flon, Lynn Lake, LaRonge Belts (Proterozoic) *Includes reserves and/or identified resources •*Includas total number of deposits Australia Arizona 33.0% Slave Province Hackett River, Elu Inlet, Black River, Cameron River, Besulleu River Belts (Archean) 42.0% Su,erior Province Abitjbi, Wawa, Wabigoon Belts (Archean) (0.1-1.1) 0.1-1.0 1.8% 57.1% 5.7% 54.0% 34.0% 58.7% 43.0% 1-10 (1.1-10.1) 7.7% Ruttan (40.7 ml) Flon (57.5 mt) 1.6% (30 mt) Motoyama (15 ml) Matsutnine (16.0 ml) Hellyer (19.4 tnt) 7.1% Rosebery United Verde (72.7 mt) 1.4% Crandon (65.8 ml) Elm Fox Lake (13.2 mt) 7% Izok Lake (13.4 mt) 8.3% Mattaganni Lake (19.6 mt) Louvicour t (24 mt) 13.8% 10-100 (10.1-101.1) st) 1.0 tnt (1.1 st) less than (3.0 st) 2.7 mt (1.1 st) less than 1.0 St (2.5 2.3 tnt 1.60 tnt st) (1.80 )3.1 at) 2.8 ml 1.65 mt (1.83 st) Median Size 126 42 70 13 44 12 72 Number of Deposits Data from Franklin and Thorpe, 1982, Large, 1990, and Lindberg, 1989. 0% 2.4% Mt. Lyell (119.9 mt)** 0% 0% 0% 0% (140.95 mt) Kidd Creek 1.4% 100* (101.1.) Arizona, Australia, and Japan Militons of Metric Tonnes Short Tons)* ComparisOn of Tonnage Distribution of VMS Deposits in Canadian Shield (including Wisconsin) (as percentage of deposits in each size range) - Canadian Shield Table 3. �0 I' N type ZnPb-Cu Shoe A Horse / Zn Thornapple Hawk Pelican River Catwi Plow Zn-Cu type Ritchie Creek (Main Zone) IFlambeau I type Cu Figure 6. Weight proportions of base metals in Wisconsin VMS deposits (after LaBerge, 1992). Pb CR = 100 Cu Cu + Zn ZR = 100 Zn Zn + Pb 0 Cu type • Zn-Cu type A Zn-Pb-Cu type Explanation IBend I Cu �48 3. Zn-Pb-Cu deposits: Cu ratio < 60, Zn ratio = 60 to 90; e.g., Lynne, Horse Shoe. The general mineralogy of each deposit type is given in Table 4. An analysis of these data shows that, in general, the largest Cu deposits (Flambeau and Bend) occur in the Ladysmith district, at the west end of the complex. Zn-Cu and Zn-Pb-Cu deposits become much more prevalent in the Somo and Crandon districts. Along with this change in basemetal ratios, both gold and silver content change from the Ladysmith district (high gold, low silver) to the eastern Somo and Crandon districts (high silver, low gold) (Fig. 7). These changes in metal ratios and content between districts give rise to a broad regional zoning pattern with generally copper- and gold-rich deposits (Cu type) toward the west, in the Ladysmith district, and zinc-rich (Zn-Cu type) deposits toward the east, in the Crandon district. Telescoping or overlapping of deposit types (Cu, Zn-Cu, and Zn-Pb-Cu) occurs in the centrally located Somo district. These zoning patterns may be more apparent than real, and may be a function of exploration and discovery. However, if they are real, the variable metal ratios may indicate a progressive or systematic change in hydrothermal fluid chemistry (i.e., temperature, f02, pH, salinity), and discharge site conditions (i.e., original composition and permeability of stratigraphic footwall unit(s), and seawater depth). The average tonnages and grades of the three deposit types are listed in Table 5 and compared with other VMS districts in the world. Although the number of Wisconsin deposits is limited, the table does suggest that the Cu deposits are above average in copper grade and gold content when compared to other Cu deposits in the table. The Wisconsin Zn-Cu and Zn-Pb-Cu deposits as a whole contain relatively average base- and precious-metal grades, but generally lowerthan-average tonnages if Crandon is excluded. Styles of Wisconsin VMS Mineralization At least seven styles of VMS mineralization have been recognized in the P-W subterrane. These include the following: Layered Sheet Thus far only the Flambeau deposit (Cu type) is known to exhibit this style within depositional environment #1. It is characterized by an extensive copper rich sheet of stratiform, syngenetic, layered massive sulfide with minor zinc-pyrite lenses and gold-bearing chert in the stratigraphic hanging wall. No well-developed epigenetic alteration pipe or stringer sulfide zone is present. However, a widespread laterally extensive sericite-disseminated pyrite alteration halo is developed mainly in the stratigraphic footwall rock units but also extending into the hanging wall as well (Figs. 8a and 8b). Sulfide deposition for this style may be related to poorly focused, lower temperature (<300 degrees C) hydrothermal fluid flow (Large, 1990). �Sphalerite, pyrrhotite, galena, pyrite, chalcopyrite Zn—Pb—Cu (± tetrahedrite, polybasite, native silver, pyrargyrite electrum, native gold) arsenopyrite, tetrahedrite— tennantite (± marcasite, electrum, covellite, chalcocite) Pyrite, pyrrhotite, sphalerite, chalcopyrite (± galena, magnetite) Zn—Cu chalcocite, bornite tennantite, gold tellurides, lead telluride, electrum, native gold, arsenopyrite, sphalerite (± galena, magnetite, pyrrhotite) Pyrite, chalcopyrite, tetrahedrite — Cu Type Minor Minerals Lynne Crandon Ritchie Creek Kennedy et al., 1991 Lambe & Rowe, 1987 May, 1977 DeMatties & Rowell, 1991 DeMatties, l99O Fl ambe au B end References Examples Summary of the typical ore-related opaque minerals in Cu, Zn—Cu, and Zn—Pb-Cu VMS deposits in Wisconsin. Major Minerals Table 4. VMS in Wisconsin �0 2 I 6 I 8 I I 10 I Lynne A 12 0 0 Cu type S Zn-Cu type Explanation (Cu + Pb + Zn) % 4 I .s. A 0 0 2 0Bend I 6 I Catwillow 8 I Flambeau , , o /// Shoe ,1 A I 10 I ' A Horse S Crandon (Cu + Pb + Zn) % 4 / A Zn-Pb-Cu type 0 0.2 0.4 0.6 0.8 1.0 1.2 1.4 1.6 1.8 2.0 2.2 Lynne Figure 7. Variation in Au and Ag content with base-metal content for the Cu, Zn-Cu, and Zn-Pb-Cu VMS deposits in Wisconsin. I o Ritchie Creek Catwillow 0.02 .s. Horse Shoe Flambeau Crandon5 0 Bend 0.04 0 0.06 0 c 0.08 0.10 0.12 2.4 2.6 12 �Number of Deposits (%) Cu tonnage 5 2 Zn-Cu Zn-Pb-Cu 1 Zn-Pb-Cu 20 0.6 17 1 Zn—Cu Zn-Pb-Cu 17 0 0.0 0.2 2.0 1.2 1.6 1.0 10 Zn-Pb-Cu 10 0.5 4.7 6.9 11.8 1.6 1.1 4.7 1.7 11 Zn-Pb-Cu [Cu! (Cu+Zn) 1100 3. average Ag Au 0.01 0.02 0.02 0.01 0.04 0.09 0.04 0.01 0.06 0.02 0.05 0.0 0.0 3.5 Million Short Tons Zn 100 Ratio 13.6 3.6 3.7 8.4 9.1 13.9 20.9 5.7 3.5 15.7 2.2 17.3 5.9 3.7 82 100 87 72 93 85 86 98 100 71 88 98 100 84.8 2.4 100 (Crandon not included) 0.03 0.09 (opt) Au ani g grades. 2.81 1.71 0.15 3.39 1.77 0.23 0.06 0.06 1.8 6.2 1.1 0.26 1.75 0.48 0.43 (opt) 4. Close clusters or unit orebodies of Kuroka deposits are grouped as single deposits. Data for all deposits other than Wisconsin are from Large, 1992. [Zn/(Zn+Pb)JlOO 2. 1. Number of deposits for wtiicfl data are available to calculate 1 0.0 3.8 1.3 2 Zn-Cu 3 2 0.0 0.2 1.1 4 (Tertiary) 1.0 3 0.0 0.2 1.3 Cu Tuff Belt4 4 Zn-Cu Jananese Green 16 Cu 14 7 0.0 19 0.5 2.2 1.9 Australian Deposits (Archean-Paleozoic) 7 Cu 5.5 1 1.4 10.0 2.7 Norwegian Caledonides (Paleozoic) Zn-Pb-Cu 34 0.1 3.7 1.5 6 2 0.0 1.3 7.0 1.6 2 0.8 0.5 3.8 1.2 2 Note1 1.8 trace (%) Pb 0.5 (%) Zn and grade data of Wisconsin and other VMS deposits. 2.6 Bathurst Camp (Paleozoic) 36 Zn-Cu Canadian 7 Cu Canadian Archean Deposits 3 Cu Wisconsin Deposits (Proterozoic) Deposit Type Table 5 — Comparison of mean VMS in Wisconsin 2 27 26 84 8 19 85 45 43 79 9 21 28 69 19.2 26.8 88.5 Cu Ratio �NW 250 Cholcopyrite CJ)5 na ted cosson U- VAt. u ES SE I Enrichment Supergene Base of Au Figure 8b. Schematic cross-section showing zonation patterns - Flambeau (after May, 1977). C,) EE 00 >, U) > U) :0 CU) U) 0) (Cove lute) Bornite 00 O C .C U) Chalcocite Oxide (I'- .10-20 Leached Sandston GociaI Overburden J30 600 j B ________Saprolite _________ �53 Bedded sheet plus strata-bound stringer zone This style of mineralization is similar to the layered sheet, except a well defined copper-rich strata-bound epigenetic stringer zone is present and extends the full length stratigraphically below a main massive zinc-lead horizon. This style of VMS mineralization commonly forms between volcanic cycles in sedimentary host units such as argillites and is characteristically developed by giant (>55 million st) VMS deposits such as Crandon (Zn-Cu type), which is hosted in depositional environment #1. Sulfide deposition may be related to hot (>300 degrees) poorly focused hydrothermal fluids moving through a permeable footwall rock package (Large, 1990). At Crandon the stratigraphic footwall consists of a series of breccia (debris flow) lobes (Fig. 9). This style is also represented in depositional environment #3 by the high-grade Horse Shoe (Zn-Pb-Cu type) deposit which exhibits a semiconformable stringer zone. Stacked lenses Most identified Wisconsin VMS deposits assume this style, in which massive sulfide lenses develop at several stratigraphic levels and are connected by zones of fragment-bearing semimassive sulfides, stringer mineralization, or intense alteration with disseminated sulfides. Metal zonation and/or upward base-precious metal refining from the lowermost lens to the upper lens is common. Depositional environment #1 (greenschist succession) frequently hosts this style of mineralization as exemplified by Bend (Cu type) (Fig. 10), Pelican River (Fig. 11), Hawk, Wolf River(?) and Catwillow (all Zn-Cu types). Only the Eisenbrey (Thornapple) deposit and possibly one other occurrence (the Fence prospect) are known to exhibit this style of mineralization in depositional environment #2 (amphibolite succession). Massive sulfide mound This style is not common in the P-W subterrane; only the Kivela zone (Zn-Cu type in depositional environment #3) at the Ritchie Creek prospect has been reported to exhibit this classic style. It is characterized by a mound-shape, syngenetic massive-semimassive sulfide accumulation which is stratigraphically underlain by a crosscutting epigenetic stringer sulfide-chiorite-sericite alteration zone. Vertical metal zonation from a copper±zinc±lead rich stringer zone to a zinc±lead±copper rich massive-semimassive zone is evident (Fig. 12). The footwall sericite-pyrite (pyrrhotite) alteration halo is generally limited in aerial extent. This style develops when hydrothermal fluids are well focussed along a syn-volcanic structure and through a relatively impermeable footwall sequence such as the mafic flows present at the Kivela zone (Large, 1990). Sulfide mound replacement Generally a thick mound-shaped, epigenetic sulfide accumulation which forms as a result of successive, subsurface replacements of previously deposited exhalite (commonly carbonate and/or chert rich). Vertical metal zonation pattern from a copper-rich base to a zinc-lead-silver top is strong. The Lynne deposit (Zn-Pb-Cu type) in depositional environment #1 is reported to exhibit this style of mineralization (Fig. 13). The replacement mound style may develop from hot (>350 degrees C) well focussed hydrothermal fluids (Large, 1990). �Footwall •1 0 0 S — -200rn o 400 I 200 meter, 800 tee, lopilli luff coarse tuft - S 0 0 C GaciaI Overburden orgillite Breccia lobes Il & Ill Stringer sulfide mineralization Massive sulfide mineralization Carbonaceous-pyrilic argitite and tuft Crandon Unit: Explanation Crondon Unit Hangingwall fluffs cherl and debris flows) Slraligraphic Top I0 S S Figure 9a. Geologic cross-section 94360E - Crandon (after Lambe and Rowe, 1987). uoo I — 0 See L,,et 0 4, 0 0 S (tufts and volcanic breccios) — 200m — 400' A I •1 0 S 0 n. 4, 0 0 S 0 o — -ZOOm 400 200 meter, coo feci argillite .t C S S GIocaI Overburden Breccta lobes I, II & Ill Stringer sulfide mineralization Massive sulfide mineralizalion Carbonaceous-pyrilic argillite and tuft Crandon Unit: Explanation Crandon Unit Hangingwall (tutts,chert and debris flows) Strotigraphic Top 4, C S S Figure 9b. Geologic cross-section 94400E - Crandon (after Lanibe and Rowe, 1987). tOO — 0 Sec Level (tufts and volcanic breccios) Footwoll — 200,, — 400m B ______ �— 05cc — 200' — 400' — 600' — 800' in feet ElenOliOn Level Southwest Looking West — Regional fuL n -4 9 I 8$ F H 1 N Mineralized sequence: Hanging-wa)) andesite: mat ic metavolcanic flows with associated melatuff a and tu)faceous metasediments Quartz diorite Breccialed rock Explanation 9 I 6S (XI unit) OuOrtZ Crystal lelsic luff Gold mineral izoliOn (tuck—unde, gold zone) stringer sulfide ove, print sulfide ,nineroli lotion with (bedded ond massive) Figure 11. Geologic cross-section 110 +OOE - Pelican River (after Bowden, 1978). Footwall andesile: mafic melavolcanic flows, flow breccia, inlerflow metatuffs and tuffsceous metasediments Hydrothermal alteration Multiple massive to semimassive sulfide lenses 0 Top .1. Fragment - beorinA semimossive II' f','tO 9' en,,- J-s A°, Fit4d n j'°bO Ott Slrotigrophic S Andesilic to felsic cherty metatuffs and tullaceous melasediments -1000 —500' .e4 DFPTH IFT) Moss,ne sulfide ninerOljzolion Es plan of ion Footwall sequence bedded tuffs Precambrian regolith Glacial Overburden NW Figure 10. Geologic cross-section 49235E - Bend (after DeMatties and Rowell, 1991). Looking Slroligrophic Top complex felsic flow/ fragmental Hanging-wall sequence' — l000• — 1200' SE — 400 �56 Line 12E, looking northwest DEPTH, IN FT 0 Granitic intrusive Intermediate to mafic amygdaloidal metavotcanic flows i. ft mineralization Laminated cherty metatuff Felsic metatuff Intense chlorite + sericite alteration (altered mvf) Semimassive (30%-50%) fragment-bearing pyrrhotite (± pyrite + chalcopyrite + sphalerite) lens + Cu 300 Stockwork-stringer mineralization mvf Q) a) \\ 900 Stratigraphic top mvf Ct 1200 0 100 FT Figure 12. Geologic cross-sectionLine 12E - Kivela Zone of the Ritchie Creek Prospect. �M OH + Marble Tonalite + + + Tonal te + ± + + + Looking west + + VOS + Talc Figure 13. Geologic cross-section Line I000E - Lynne (after Kennedy et al.. 1991) Volcaniclastic unit Skarn Massive P0, Mt H. ] Talc + + Semi-massive to massive sulfide 2 'j Rhyolite ] vcs__ IIIIIJIIII + BPM Talc. ??':0; ___jChert 100FT ELE\'. IN FT 1000 1200 1400 1600 �58 Replacement This style is similar to the mound replacement but represents only a partial replacement of previously deposited exhalite. The Ritchie Creek main zone (Cu type) in depositional environment #1 isa good example (Fig. 14). Stockwork/disseminated Broad zones of stockwork pyrite±chalcopyrite with associated sericite alteration characterize this style. These horizons could represent failed VMS systems or possibly contain central zones of massive pyrite-chalcopyrite mineralization. Minor copper±zinc lenses may be present at the stratigraphic top of the system. Good examples of this style in depositional environment #1 are found at the School House and Clear Creek (Cu type) prospects. This style may develop from hot and dense hydrothermal fluids which move laterally through permeable volcanic units below the sea floor (Large, 1990). MASSIVE SULFIDE MINERALIZATION ASSOCIATED WITh META-ARGILLITE FORMATIONS (PMS) The meta-argillite formations (Fig. 4a and 4b) are important stratigraphic sub-units within the greenschist succession of the P-W subterrane and may be related in both time and space to the economic VMS deposits. These important lithologic units are expressed geophysically as long formational airborne electromagnetic (AEM) conductors, both with and without direct magnetic response. As previously mentioned, the source of the AEM conductors is usually graphite, and/or pyrrhotite-pyrite, hosted by black to greenish-gray, weakly to strongly schistose, chlorite-rich metaargillites and associated tuffaceous metasediments (metagraywackes). Individual units are generally less than 100 feet thick and may exhibit well-developed internal lamination or bedding. These units contain only geochemically anomalous base-metal-bearing pyrrhotite and/or pyrite mineralization with varying amounts of associated graphite or, in some cases, carbon. The sulfide-tographite ratio varies widely from conductor to conductor; the argillites are thought by some workers to be sulfide-facies iron-formations. Textural evidence (Finlow-Bates, 1980) suggests that significant amounts of sulfide mineralization in these units is hydrothermal in origin rather than diagenetic. Drillhole data from many of these strataform AEM conductors indicate that the sulfide mineralization can mimic, at least in part, typical VMS systems that have both syngenetic and epigenetic components. In some systems, graphite is not present and the massive pyrrhotite beds (with and without fine sphalerite intergrowths) may be tens of feet thick. These massive pyrrhotite beds contain fragments (usually altered meta-argillite clasts) and have a stratigraphic footwall underlying alteration zone consisting mostly of sericite, chlorite, and/or quartz (silicification), some with crosscutting pyrrhotite stringers containing fine chalcopyrite and sphalerite intergrowths. There may be more extensive stringer zones of network-textured pyrrhotite and sometimes chalcopyrite. The texture is formed by anastomosing veinlets hosted by altered meta-argillite. Cyclic repetition of one or both components of the sulfide mineralization within a given section is common in the more well-developed systems, possibly reflecting multiple hydrothermal �59 A A' 100 ft Scale: lOOm Explanation Mineralized horizon: Massive (>50%) to semi-massive (3050%) sulfide mineralization :::: Sulfide-bearing hydrothermal alteration (altered exhalite?) • Limit of stockwork sulfide halo (<30% sulf ides) Intermediate to mafic subvolcanic intrusive Gold assay zone Figure 14. Geologic cross-section A-A' - Ritchie Creek Main Zone (after DeMatties, 1990). ft - felsic to mafic tuff-lapilli tuff (quartz-biotite-feldspar to biotite-feldspar-amphibole-quartz schist). mf - altered and mineralized felsic tuff yritic quartz-sericite schist). mt - mafic to intermediate tuffs and tuffaceous sediments (feldspar-biotite-amphibole-quartz schistsemischist). �60 pulses. Metamorphic overprinting and/or shearing may have locally remobilized the sulfides, but relict primary features are still recognizable in many formations. Interbedded cryptocrystalline laminated chert, displaying the typical interlocking-quartz-grain texture (serrated grain boundaries) in thin section, or cherty tuffaceous sediments are almost always associated with the sulfide mineralization. Because the meta-argillite units are structurally incompetent, shear zones are easily developed within them, resulting in the brittle deformation (brecciation and fragmentation) of the chert units. Meta-argillite is believed to be deposited as fine-grained epiclastic sediments, possibly in smaller isolated sedimentary basins, generally within the back-arc-basin sequence, under reducing conditions and during periods of volcanic quiescence. Although clusters or groups of these metaargillite formations are found in the P-W subterrane, they are concentrated in the back-arc-basin sequence and commonly along the flanks of the main volcanic arc (Piv) of the Ladysmith-Rhinelander Volcanic Complex. No formations have been recognized in the central portion of the main volcanicarc sequence (amphibolite succession). Argillite formations have also been mapped in the Marshfield subterrane, but their spatial distribution is not clearly understood. All of the VMS districts defined to date are generally within a mile or less of major argillite formations. This spatial relationship was recognized early by explorationists in Wisconsin. Although to date this sulfide mineralization has been generally found to be only geochemically anomalous or to contain low grades of copper and zinc, its presence in meta-argillite formations has metallogenic significance in terms of a possible indicator of potentially economic VMS mineralization. Discussion Aside from a close spatial relationship to VMS mineralization, certain mineralized metaargillites may be genetically related to VMS ore-forming events. In other words, the barren or wealdy metal-bearing sulfide mineralization might have formed before, during, or after major ore deposition, reflecting either the beginning of the event, or deposition itself, or the last stages of the hydrothermal event in the VMS system. In terms of a modern analog, it might be considered "black smoker debris." Current geologic data indicate that all four potentially economic and many of the subeconomic or under-explored deposits contain these units in their "local" stratigraphic section (Fig. 4a and 4b). As has been described, the Massive Sulfide Zone of the Crandon deposit is within one of these units (Crandon Unit). Finlow-Bates (1980) discussed the possibility that the formation of graphitic argillite (carbonaceous sediments) was the result of ore deposition which set up anoxygenic conditions, a type of ground preparation in which reducing conditions allow the preservation of carbon (whose source is uncertain). The model assumes that the ore-fluid chemistry was in a reduced state, which it likely was during the Precambrian. This might explain the close spatial (genetic?) relationship of the Pms formations with the major deposits discovered thus far. If this empirical-genetic model is valid, the stratigraphic implications are obvious: Pms formations associated with VMS deposits would represent gross time-marker horizons which mark ore-forming events and could be used in regional correlations. This concept of "favorable horizon" is a characteristic of other VMS districts, in the Canadian shield and elsewhere in the world. �61 Figures 3, 4a, and 4b show formations in the P-W subterrane and the western and east-central parts of the Ladysmith-Rhinelander Volcanic Complex. A number of major formational groups can be seen. However, the geology is complicated and has been made even more so by isoclinal folding and faulting. Detailed correlations of individual formations are impossible at our current level of knowledge. Using the general geologic framework which has been established for the cOmplex, it is possible to grossly correlate the formational clusters on the basis of structural and stratigraphic position relative to the central core of the main volcanic-arc complex. At least two "sets" or groups can be defined in the western portion of the Complex: Pms I, structurally along the flanks of (probably stratigraphically above) the core, and Pms II, in the back-arc basin. A tentative interpretation of the composite stratigraphy in this area is presented in Figure 15. Under this stratigraphic arrangement, the Eisenbrey (Thornapple) deposit would occupy the lowest position within the amphibolite succession. The first major ore-related argillite formational group (Pms I) in the greenschist succession occurs stratigraphically above the Flambeau deposit, but possibly below the Lynne deposit. However, because stratigraphic interpretation has been further complicated in the Lynne area by more complex faulting, folding, and igneous intrusion, the Lynne deposit may actually be closer stratigraphically to the meta-argillite formational group than the composite section indicates, or possibly laterally equivalent to Flambeau. The Bend deposit occupies the highest stratigraphic position and appears to be associated with the second major ore-related argillite formational group (Pms II) in the back-arc basin. This concept can be extended to the eastern part of the belt where one prominent formational group (Pms I) can be seen linking together the Pelican River, Wolf River, and Catwillow deposits (Fig. 3 and 4b). The Crandon Unit is associated with the formational group south of the deposit, which may be the lateral equivalent of the ore horizon(?) and, using this scheme, would be considered to be associated with the Pms II formational group. Because of complex regional isoclinal folding, the true spatial and stratigraphic separation between the two productive formational groups may be much less; they may even be the same unit in different volcanic facies. Nonetheless, gross correlations suggest that most of the ore deposits in the greenschist succession were formed in a fairly narrow stratigraphic interval and are nearly coeval in their time of deposition. The narrow stratigraphic interval and the correlation of Pms formational groups to link the VMS deposits in time are partially supported by lead isotope data. Afifi et al. (1984) established a lead model age of approximately 1.8 to 1.9 Ga for Flambeau, Pelican River, Hawk, and Crandon. A strong linear trend is defined by the lead isotope data, suggesting that the deposits are nearly coeval in their formation (Fig. 16). More recent lead isotope work by Thorpe (written communication, 1992) on the Ritchie Creek, Spirit, Horse Shoe, and Lynne deposits indicates that they also plot along this trend, further supporting this contention. Thorpe's lead model age for the VMS mineralization is approximately 1.86 Ga. As previously mentioned no meta-argillite formational groups have yet been identified in the amphibole succession of the main volcanic-arc facies. However, thin but laterally extensive oxidefacies iron-formations are known and, as described for Eisenbrey (Thornapple), may represent a similar type of favorable horizon for VMS mineralization. There are no lead isotope data for the Eisenbrey deposit; therefore, it is not known whether it plots on the linear trend defined by Thorpe. If it does plot on the trend line and is coeval with the �62 Cambrian Mt. Simon Fm. (sandstone) Barron Quartzite a pre-Cambrian regolith Pvs 0 Pms Pmvf a Pfv Greenschist Succession - - (j)) / Bend Deposit (Cu, Au) PmsIl o Nm o oa o 0° o 1 - Pvs Ci) Pvs (chemical sediments) Pfv Lynne Deposit Ag (Zn, Pb, Ag) > Pvs W Ci C> PmsI Zn Cu-Au (Cu, Au) Pfv Unconformity, fault, and/or gradational contact?? (0 If 0 > E-' E ('3 0 . • Flambeau Deposit <.Pjv G) — Ci) I Pmvf I— Li .E Q > -' Thornapple Arnphibolite Succession xxxxxxxxxxxxxxxxx — Deposit (Cu,Zn) Cu /xxxxIf Unconformity Archean (>2500 MA) Basement: granitic gneiss, migmatite, amphibolite Figure 15. Schematic composite stratigraphic section, west-central portion of the Ladysmith-Rhinelander Volcanic Complex. �63 15.5 15.4 207/ 204 15.3 15.2 15.1 15.2 15.4 15.6 15.8 16.0 206/204 Figure 16. Lead isotope data for VMS deposits in the Wisconsin Penokean Volcanic Belt (after Thorpe, et a!.). greenschist succession deposits, then the oxide-facies iron-formations could possibly represent lateral equivalents of the ore-related Pms units. Conclusions 1. Two volcanic complexes can be recognized in the Early Proterozoic Penokean volcanic belt (Wisconsin magmatic terrane) on the basis of lithology, structure, and age relationships. These include the Wausau Complex, host to at least one structurally controlled gold deposit, and the larger Ladysmith-Rhinelander metavolcanic complex, which contains at least 13 volcanogenic massive sulfide deposits and occurrences, clustered in three districts. 2. Volcanogenic massive sulfide mineralization occurs in at least three distinct geologic depositional environments. The four potentially economic deposits occur in environment #1, which is the felsic volcanic center facies. 3. The identified volcanogenic massive sulfide deposits and occurrences can be classified on the basis of metal content and divided into three groups (Cu, Zn-Cu, Zn-Pb-Cu). Each group exhibits various styles of mineralization. �64 4. The meta-argillite association in the Ladysmith-Rhinelander metavolcanic complex may have significant exploration importance, i.e., certain formations or formational groups at the right stratigraphic level could theoretically lead to potentially economic VMS mineralization particularly in areas where they are associated with felsic centers (depositional environment #1). Two key formations are known and others may be present in the Ladysmith-Rhinelander metavolcanic complex and Marshfield subterrane. 5. The Wausau volcanic complex is known to contain only a few meta-argillite formations. That lack, indicating no major breaks in volcanism, and felsic centers which may be mostly subaerial and younger (1835-1845 Ma) than the main ore-forming event (1860 Ma) might explain the poor rate of discovery of significant massive sulfide deposits in this area. Acknowledgments The author is grateful to Ernest K. Lehmann and Associates Inc. for permission to release data for this paper. Also to Economic Geology for allowing publication of portions the original manuscript for this memorial volume. A final thanks to the late Ned Eisenbrey for his major contribution to the ideas expressed here. His exploration effort on behalf of Kennecott in the 1960s coupled with earlier work compiled by the late Jack Phillips, led to the discovery of the Flambeau and Thornapple deposits (now appropriately named the Eisenbrey deposit) and paved the way for later explorers to enter the Wisconsin greenstone belt. On a personal note, Ned was my mentor at E. K. Lehmann and Associates for many years. He helped shape my exploration philosophy, and it is with gratitude and friendship I contribute to this commemorative volume. References Cited Afifi, A., Doe, B. R., Sims, P. K., and Delevaux, M. H., 1984, U-Th-Pb isotope chronology of sulfide ores and rocks in the Early Proterozoic metavolcanic belt of northern Wisconsin: Economic Geology, v. 79, p. 338-353. Bowden, D. R., 1978, Volcanic rocks of the Pelican River massive sulfide deposit, Rhinelander, Wisconsin: a study in wallrock alteration: Unpublished MS Thesis, Houghton, Michigan Technological University, 62 p. DeMatties, T. A., 1989, A proposed geologic framework for massive sulfide deposits in the Wisconsin Penokean volcanic belt: Economic Geology, v. 84, p. 946-952. 1990, The Ritchie Creek Main Zone: a Lower Proterozoic copper-gold volcanogenic massive sulfide deposit in northern Wisconsin: Economic Geology, v. 85, p. 1908-1916. DeMatties, T. A., and Mudrey, M. G., Jr., 1991, Geologic setting of the Early Proterozoic base- and precious-metal-rich metavolcanic belt of Wisconsin: 37th Annual Institute on Lake Superior Geology, Eau Claire, Wisconsin, 1991, Proceedings, p. 29-33. �65 DeMatties, T. A., and Rowell, W. F., 1991, Bend, a Lower Proterozoic, copper- and gold-enriched volcanogenic massive-sulfide deposit in Taylor County, Wisconsin: 37th Annual Institute on Lake Superior Geology, Eau Claire, Wisconsin, 1991, Proceedings, p. 34-40. Finlow-Bates, T., 1980, The chemical and physical controls on the genesis of submarine exhalative orebodies and their implications for formulating exploration concepts, a review: Geologisches Jahrbuch, Ser. D, no. 40, p. 131-168. Franidin, J. M., and Thorpe, R. I., 1982, Comparative metallogeny of the Superior, Slave and Churchill provinces in Hutchinson, R. W., Spence, C. D., and Franklin, J. M., Precambrian sulfide deposits (H. S. Robinson Memorial Volume): Geological Association of Canada Special Paper 25, p. 3-90. Greenberg, J. K., and Brown, B. A., 1983, Lower Proterozoic volcanic rocks and their setting in the Southern Lake Superior district: Wisconsin Geological and Natural History Survey Miscellaneous Paper 83-4, 18 p. Kennedy, L. P., Harding, T. A., Schaff, J. H., and Zielinski, A. M., 1991, The Lynne massive sulfide deposit, Oneida County, Wisconsin: 37th Annual Institute on Lake Superior Geology, Eau Claire, Wisconsin, 1991, Proceedings, p. 63. LaBerge, G. L. and Myers, P. E., 1983, Precambrian geology of Marathon County, Wisconsin: Geological and Natural History Survey Information Circular, No. 45, 88 p. LaBerge, G. L. and Myers, P. E., 1984, Two Early Proterozoic successions in central Wisconsin and their tectonic significance: Geologic Society of America Bulletin, v. 95, p. 246-253. Lambe, R. N., and Rowe, R. G., 1987, Volcanic history, mineralization, and alteration of the Crandon massive sulfide deposit, Wisconsin: Economic Geology, v. 82, p. 1204-1238. Large, R. R., 1990, Tonnage-grade data for VMS deposits in Ore deposit studies and exploration models: Center for Ore Deposit and Exploration Studies, University of Tasmania, Master of Economic Geology Work Manual, v. 1, section 4, parts 1, 2, and 3. 1992, Australian volcanic-hosted massive sulfide deposits: Economic Geology, v. 87, p. 471-510. Lavery, N. G., 1985, Quantifying chemical changes in hydrothermally altered volcanic sequences silica enrichment as a guide to the Crandon massive sulfide deposit: Journal of Geochemical Exploration, v. 24, p. 1-27. May, E. R., 1977, Flambeau - a Precambrian supergene enriched massive sulfide deposit: Geoscience Wisconsin, v. 1, p. 1-26. Sims, P. K., Van Schmus, W. R., Schulz, K. J., and Peterman, Z. E., 1989, Tectono-stratigraphic evolution of the Early Proterozoic Wisconsin magmatic terranes of the Penokean Orogen: Canadian Journal of Earth Sciences, v. 26, p. 2145, 2158. �66 �67 AN OVERVIEW OF THE FLAMBEAU SUPERGENE ENRICHED MASSIVE SULFIDE DEPOSIT: GEOLOGY AND MINERALOGY, RUSK COUNTY, WISCONSIN Edwarde R. May Consulting Mining Geologist and Stephen R. Dinkowitz, Geologist Flambeau Mining Company INTRODUCTION The discovery of the Flambeau orebody coincided with the signing of the National Environmental Policy Act (NEPA) in 1968. As a consequence, both the development of this supergene enriched massive sulfide deposit and implementation of NEPA went through intense public debate. At the same time basic industrial segments of the economy such as mining, steel, and auto manufacturing were restructuring to compete in an emerging global economy. Neither Kennecott Copper Corporation (Kennecott), the mining industry, nor governmental regulatory agencies fully appreciated the consequences of NEPA when development drilling of the Flambeau orebody was completed in 1971. Kennecott was aware, however, of the deteriorating copper market. Therefore Kennecott's Flambeau development policy was to secure the mining permits, then make a decision whether or not to develop the project. The project was discontinued in 1977 after receipt of an approved Environmental Impact Statement (EIS) but before issuance of the mining permits, due to depressed metal prices and unfavorable economics. A lean, restructured base metal mining industry reemerged by the mid-1980's, one ready to meet mine development challenges within the context of a strong national and state environmental awareness. Kennecott reopened the Flambeau project and, shortly thereafter, entered into discussions with local city, township, and county officials and citizens. Once their concerns had been identified, a Local Agreement was drafted and signed that alleviated their concerns and allowed permit hearings to proceed under a more cooperative and constructive spirit. This bold and innovative approach has since been incorporated in Wisconsin's metallic mineral regulations. The Flambeau Mine has been in successful production for the past three years. It has been successful economically, environmentally, socially and politically. Considerable up-front planning, public dialogue, and company commitment resulted in dire environmental predictions not coming true, for example, the water treatment plant out performs even its most enthusiastic design predictions. Geologically, this mine has presented the industry with unusual mineral assemblages as well as an example of high grade ores which have not been mined in North America since the turn of the century. Enriched Canadian Shield massive sulfide orebodies are rare; moreover, the size and grade of the Flambeau orebody is unusual. Sampling and mining of the overlying gold-rich gossan was a technical challenge rarely experienced by North American mining geologists. The opening of the Flambeau orebody thus became a dual challenge of extracting gossan while simultaneously mining 10% Cu ore. Each of these ores required a different sampling and mining approach. This was accomplished without environmental incident during start-up of the mine through one of Wisconsin's �68 wettest summers. There was no offsite discharge of waters from the 182 acre site except through the approved water treatment discharge line. The following paper is intended to give an overview of the geology and gossan/sulfide mineralogy. It is limited to observed megascopic-macroscopic data, supported only by minor microscopic and geochemical work conducted in the early 1970's. HISTORY Kennecott discovered the Flambeau deposit in November 1968, following a long history of exploration in the upper Midwest, when their first diamond drill hole, drilled to test a geophysical conductor, intersected 47.7 feet averaging 9.25% Cu and 0.049 opt Au. During the 1950's George Moerlein noted that Precambrian volcanic rocks, similar to those known to host massive sulfide deposits in the Canadian Shield of Quebec, Ontario, and Manitoba occurred in Wisconsin (Babcock, 1996). Of particular note was the recording of a well dug about 9 miles south of Ladysmith in 1915 that yielded a specimen of volcaniclastic rock with copper oxide mineralization. Amazingly, this specimen is still on file in Madison eighty years later. A small airborne electromagnetic (EM) geophysical survey was flown over the nearby Schoolhouse Prospect in 1955 with negative results (Figure 1). In 1966 Jack Philips continued the pioneering work of Moerlein with the discovery of additional "favorable looking" volcaniclastic rocks west and northwest of Ladysmith. A large airborne geophysical survey flight block including the Schoolhouse Prospect in the southeast corner, some weakly pyritized outcrops between Weyerhaeuser and Bruce, and outcrops of similar rock northwest of Bruce, was flown in May 1967. The east boundary of the aerial survey was coincident with the Flambeau River as it flows south past the future Flambeau mine site. A favorable response was noted and brought to Ned Eisenbrey's attention. He approved the addition of two short flight lines between the river and State Highway 27. These three lines delineated what was later to be the Flambeau deposit, thus initiating the rebirth of Wisconsin's base metal mining industry after an absence of nearly 25 years when the lead-zinc mines in the southwest corner of the state were closed (Schweuk 1977). Delineation drilling at the Flambeau deposit was accomplished from 1969 to 1971. An Environmental Impact Report was compiled during 1974 and infill drilling on the west end of the deposit was completed. The EIS was approved by the Wisconsin Department of Natural Resources in early 1976; however, the mining permit application hearing was canceled after Rusk County turned down the Company's zoning request. In 1986, the Flambeau project was reopened and another round of infill and confirmation drilling completed on the east end of the deposit. The scope of the project was changed to mine only the supergene enriched mineralization as direct shipping ore, thus eliminating on-site milling and disposal of tailings as originally proposed in the 1970's. In addition, the smaller open pit was to be backfilled and not flooded as proposed for the larger pit designed in 1976. Economic considerations precluded underground mining; consequently, the planned open pit development was restricted to a depth of 225 feet, which is the base of the deepest secondary enrichment zone. A second EIS was submitted in 1990 to mine 1.8 million tons averaging 10.92% Cu and 0.088 opt Au. Hearings were held in 1990 and permits and approvals to commence construction were issued in January of 1991. Flambeau Mining Company, a wholly owned subsidiary of Kennecott Minerals, commenced construction in July 1991, only to be stopped by an injunction filed �PROTEROZOIC OUTCROP HAND DUG WELL #" 0 LEGEND Figure 1 Location of Massive Sulfide Deposits and Chief Outcrops. Rusk County, Wisconsin EISENBREY DEPOSIT SCALE 1"6.5 MILES �70 shortly thereafter. The injunction was based on the Endangered Species Act and the suspected presence of purple warty-backed clams and unusual dragon flies. Subsequent studies showed that the proposed operation would not endanger the species in question. Construction recommenced early in 1992 and ore production began in May 1993. All told, 24.5 years had elapsed from discovery to production, although active time spent on the project was 16 years (1968 to 1977 and 1986 to 1993). LOCATION AND CULTURAL SETFING The Flambeau orebody is located in northwestern Wisconsin approximately 150 miles northeast of Minneapolis-St. Paul and 220 miles northwest of the state capital at Madison (Figure 1). The town of Ladysmith, immediately north of the 2700 acre project site, is a picturesque rural-retail community of 3,900 and the Rusk County seat. Ladysmith lies at the junction of north-south and east-west highway and railroad systems. The orebody may be conveniently reached by traveling south 1.5 miles on State Highway 27 from its junction with U.S. Highway 8, then west 0.2 mile on a paved private road. Rusk County and the project site are characterized by low, gently rolling sub-parallel ridges striking generally in an east-to-northeast direction. Greatest relief is normally found along the outside bends of the major rivers, although banks greater than 45 feet are uncommon. The Flambeau River cuts diagonally across the county from the northeast corner, meandering through Ladysmith, across the project site and over the west end of the deposit before turning south to its confluence with the Chippewa River. Weather conditions are typically continental with temperature extremes ranging from a recorded high of 108°F to a low of -40°F. Precipitation averages 32 inches per year. Annual snowfall averages 43 inches, typically covering the ground from late November to the beginning of April. GENERAL GEOLOGY OF NORTHERN WISCONSIN At least 13 volcanogenic massive sulfide deposits have been discovered within Early Proterozoic greenstone rocks of northern Wisconsin (DeMatties, 1994). The Ladysmith-Rhinelander metavolcanic belt, which strikes across the state for a distance of 150 miles, is the host rock for this mineralization. These 1.86 to 1.88 billion year old rocks consist of mafic metavolcanics, gabbroic sills, lesser amounts of felsic metavolcanics, and some cherty iron formations. The LadysmithRhinelander metavolcanic belt clearly shows on regional airborne gravity and magnetic reconnaissance maps of northern Wisconsin as an anomalous linear feature. North of the Ladysmith-Rhinelander belt are rocks that form a thick platformal turbidite sequence of clastic and chemical metasedimentary rocks including major iron formations. The Niagara Fault separates the Northern Penokean Terrane of continental margin assemblages from the Pembine-Wausau Subterrane that contains the Ladysmith Rhinelander belt of rocks (Figure 2). The paper written by G. LaBerge in this volume shows the location of these subterranes. South of the Ladysmith-Rhinelander belt are rocks of the Wausau and Marshfield Complexes. The Eau Pleine shear separates the Marshfield Subterrane from the Pembine-Wausau Subterrane (LaBerge, 1996). The Marshfield Subterrane is characterized by Archean gneisses and 1.86 billion year old metavolcanic rocks and granitoids. The Wausau Volcanic Complex consists of 1.88 billion year old amphibolite facies rocks unconformably overlain by 1.84 billion year old intermediate to felsic metavolcanics. Intruding the Wausau volcanic complex are anorogenic igneous rocks, 1.47 to �I FLAMBEAU MINE CRANDON DEVELOPMENT EISENBREY DEPOSIT 0 10 20 SCALE 40 MILES 1"40 Figure 2 Generalized Geology of Northern Wisconsin (Modified after Morey, Sims, Cannon, Mudrey, Southwich, 1982) �72 1.51 billion year old, the largest of which is the Wolf River Batholith. DeMatties and LaBerge more fully discuss these subterranes and the Wausau Volcanic Complex in this volume. Paleozoic sediments onlap the southern portions of the Southern Superior Province of the Precambrian Canadian Shield. MINE SITE GEOLOGY Geological data for the Flambeau orebody initially came from airborne geophysical data, 63,220 feet of diamond drill core, one outcrop and a subcrop. Interpretation of the airborne EM and magnetic data provided exploration geologists with the regional rock fabric as well as possible areas of "greenstone" rock and plutons. Most of the geology and mineralogical descriptions for the remainder of the paper are from observations made during mining of the open pit. Data from core holes in the deeper and less altered rock have been extrapolated to supplement descriptions of the upper and more altered rocks. Subcrop is approximately 1,100 feet in elevation with planned pit bottom elevations of 880 to 94.0 feet. Identification of rock units while core logging was difficult due to intense alteration, The dominant regional metamorphic alteration suites particularly in the supergene enriched zone. of minerals were first identified in drill core, and subsequent petrographic work provided clues to rock genesis and identification of rock units. An angular unconformity between steeply dipping, saprolitic altered intermediate volcaniclastic rocks and Upper Cambrian Mount Simon Sandstone crops out approximately one mile south of the mine on the banks of Meadowbrook Creek. A subcrop of Precambrian rock was discovered in 1988 during very low waters in the Flambeau River west along strike of the orebody. This rock consisted of small and large fragments of quartz-sericite schist and rusty metachert containing small amounts of malachite. The Flambeau orebody is interpreted to be overturned to the southeast; however, stratigraphic nomenclature will be used throughout this paper. Structural hangingwall rocks in the mine on the north side of the orebody are actually the stratigraphic footwall. Since 1993 detailed open pit mapping has occurred to the scale of 1 inch to 20 feet. This mapping has confirmed the earlier derived geological model and added some structural complications not recognized during core examination. The rock classifications (Table 1) were developed by Jeff Hulen for Kennecott in 1970, and in general hold true today. A water-lain tuff in the footwall of the ore horizon and felsic tuff altered to sericite-clay beds in the hangingwall sequence have been added to this classification since mining began. PLEISTOCENE Several ages of Pleistocene glaciation covered the area and deposited unconsolidated, poorly sorted materials that range in thickness from 12 feet to 30 feet. Most deposits are typical outwash with materials ranging from silt to boulders up to four feet in diameter. These poorly sorted outwash deposits are more interbedded with silty bess away from the Flambeau River. A two to three foot thick bess deposit covered the interbedded outwash deposits over the eastern half of the deposit. Iron and manganese staining is prevalent in the lowermost parts of the outwash and is interpreted to be of �TABLE 1 CLASSIFICATION OF FLAMBEAU MINE ROCK TYPES RUSK COUNTY, WISCONSIN Rock Name Genetic Name Quartz-eye schist andalusite-biotite schists, Sericite-clay schist Dacite quartz crystal tuff and Rhyolitic quartz crystal lapilli tuff Dacitic flows and tuff Dacitic and andesite tuffs and lapilli tuffs Felsic tuff Quartz-sericite schist Metachert Massive sulfides Feldspar-clay schist Rhyolitic tuffs and lapilli tuff Chert Massive Sulfides Felsic tuff Actonolite Schist Hangingwall Chlorite, spessartite and Ore horizon Footwall Actinolite and chlorite phyllite Actinolite and andalusite-biotite schist Quartz-eye schist Andesitic tuff Dacitic-andesitic lapilli tuff Rhyolitic-dacitic quartz crystal tuff recent origin, unrelated to the underlying sulfide orebody. A relatively well sorted, heavily ironstained, rounded, pebble to cobble outwash overlies the sandstone and is clearly older than the overlying purplish silt-rich outwash, indicating at least two ages of Pleistocene glacial deposition at the mine site. The last glacial period almost completely eroded the underlying Cambrian sandstone outlier. Glaciation has removed the sandstone, approximately 450 feet along strike, on the west and east ends of the orebody. In addition, several large blocks of sandstone were removed down to bedrock north of the pit perimeter (Figure 3). A Pleistocene to Recent stream meandered across the west end of the orebody in a southwesterly direction and a waterfall was created where the stream flowed over the footwall metachert. Water-worn chert boulders were clearly evident as well as near total removal of gossan over a 200 foot strike length. The stream gravels are still visible on the south wall of the open pit. Pleistocene glaciation has played a small structural role in the host rock geology. A small thrust fault is visible in the west pit wall. It has been interpreted that glacial forces from the north squeezed Out a highly incompetent, 10 foot thick clay-sericite bed. The glacier then moved more competent footwall volcanic rock south to cover the truncated and incompetent tuffaceous unit. CAMBRIAN SANDSTONE A thin, narrow, near flat-lying outlier of Upper Cambrian sandstone overlies most of the Flambeau deposit. The presence of this outlier was of enormous economic significance in that areas of poorly cemented gossan and supergene enriched sulfides were protected from erosion. The sandstone has been identified as the Mount Simon Formation. It is a light yellow to tan, very poorly cemented, medium to coarse grained sandstone with numerous light green-gray shale partings. The sandstone is characterized by rounded to subrounded, frosted, medium sized quartz grains. A thin �HIi �75 basal conglomerate is present and consists of rounded to subrounded white quartz particles up to 2.5 inches in diameter. Sandstone has been deposited in depressions and collapsed structures at the top of the gossan and in depressions between the more resistant and enclosing metachert units. No evidence was seen to suggest that these structures were post-Cambrian. The base of the sandstone has been examined for evidence of gossan mineralization incorporated within the basal conglomerate and appears to contain no fragments of Precambrian bedrock other than quartz pebbles. PRECAMBRIAN GEOLOGY STRATIGRAPHIC FOOTWALL The footwall rocks (stratigraphic footwall) on the north side of the deposit consist of three main units: metadacite, quartz-eye tuff, and andalusite-biotite schist (Figure 4). A more detailed description of the composition of these units has been reported previously by this author (May, 1977a). A comparison of Flambeau dacite and rhyolite tuffs with average whole-rock chemistry for such lithologies is shown on Table 2. Certain oxides such as Si02, A1203, and Fe203 are generally close to average. Metasomatic alteration, associated with mineralization, probably explains the large increase in FeO, and MgO and general decreases in CaO, Na20 and K20. TABLE 2 A COMPARISON OF FLAMBEAU WHOLE-ROCK ANALYSES WITH WORLD AVERAGE DACITE AND RHYOLITE COMPOSITIONS Nt. % Si02 Al203 Fe203 FeO MgO CaO Na20 K20 Flambeau Worldm Flambeau Deviation Norld (1) Flambeau Deviation Rhyolitic Deviation Avg. Dacitic from Avg. Rhyolitic from Qtz. Crystal From Dacite Lapilli Tuff World Av. Rhyolite Lapilli Tuff World Av. Lapilli Tuff (2) World Avg 63.58 63.12 -0.46 73.66 73.28 -0.38 73.07 -0.59 16.67 2.24 3.00 2.12 5.53 3.98 1.40 16.78 2.25 6.45 8.13 0.73 0.54 2.00 0.11 0.01 3.45 6.01 -4.80 -3.44 0.6 13.45 1.25 0.75 0.32 1.13 2.99 5.35 14.47 1.86 2.23 3.42 0.91 0.64 3.19 1.02 0.61 1.48 3.10 -0.22 -2.35 -2.16 13.46 0.01 1.01 -0.24 2.05 5.29 -0.63 2.80 5.61 0.50 1.88 1.67 -1.11 -3.68 (1) Average dacite and calc-alkali rhyolite from Nockolds (1954) (2) Analyses by Kennecott Exploration Services, Salt Lake City, Utah Ouartz Eve Schist. The northern-most unit of the footwall stratigraphy generally consists of a very well foliated quartz eye schist that has been interpreted as a quartz crystal ignimbrite of intermediate composition. This unit is distinctive due to the presence of "bluish quartz eyes" that vary in size from 1 mm to 10 mm. Under the microscope these eyes are actually aggregates of quartz grains. Some show relict euhedral outlines, but most commonly they are polygonal-shaped grains. A triple-point junction was a commonly observed feature suggesting metamorphic recrystallization. The �PIT PERIMETER- Figure 4 Geological Plan Map 1050 Level, Flambeau Mine Rusk County, Wisconsin 0 1" =200' SCALE100 i FEET 200 SURFACE ELEVATION 1120' BIOTITE—FELDSPAR (lUFF) QUARTZ—SERICITE (RHYOLITE TUI MASSIVE SULFIDES "A" LENS "B" & "C" SULFIDE HORIZONS METADACITE (FLOWS, TUrFS) ANDALUSITE—BIOTITE (SEDIMENTS) QUARTZ—EYE (TUrF) PRECAMBRIAN PROTEROZOIC MOUNT SIMON SANDSTONE CAMBRIAN [II] GLACIAL TILL PLEISTOCENE LEGEND �77 quartz eye schist also contains numerous but difficult to recognize lithic fragments of similar composition. These fragments have been greatly elongated parallel to schistocity, as have all fragments associated with the Flambeau orebody. Chief alteration minerals are chlorite, sericite, and clay, with chlorite being the dominant mineral. Whole rock chemistry taken from samples below the supergene alteration zone indicates the quartz eye schist to be dacite tuff to rhyolite lapilli tuff in composition. Metadacite. A major lithologic change occurs at the hangingwall or south of the quartz eye schist. A complex suite of greenish-purple metadacitic rock was deposited that probably reflects intermediate flows and associated tuftheds. Pillow structures have been sought but not found, but there is evidence of volcanic bombs. The metadacite flows produced a more massive, poorly foliated rock that has been altered from an actinolite schist below the supergene alteration zone to chloriteclay-sericite. Surrounding and on the flanks of the metadacite are chlorite schists that are well foliated consisting of chiorite-clay-sericite. These chlorite schists are either fine-grained, chilled borders of flows, or dacite tuffs. Contacts between rock units in the pit are generally sharp in contrast to that reported previously from examination of core samples (May, 1977b). The metadacite unit forms a major rock unit in the north wall from sections 401 to 420 in contrast to minor flows found in the south wall. Andalusite-Biotite Schist. Partially enclosing the metadacite is another distinctive unit known as the andalusite-biotite schist. This unit extends along the entire north side of the orebody, as does the quartz eye schist. The andalusite-biotite schist contains up to 10 to 15% laths of andalusite, some of which exceed 2 inches in length. Andalusite is scattered irregularly throughout the rock and is best displayed on foliation planes. Coarse biotite occurs as distinctively cross-cutting porphyroblasts; however, it also occurs within foliation-bounded "beds" and is more common than andalusite. The andalusite-biotite porphyroblasts range in length from 0.2 mm to 3 mm and from 5 to 25% in volume. Whereas the quartz eye schist and metadacite contain 1 to 2% pyrite, the andalusite-biotite schist contains 2 to 15% pyrite. Andalusite and biotite porphyroblasts decrease in volume eastward in the open pit, with a corresponding increase in chlorite and sericite. The andalusite-biotite schist is in contact with the northern boundary of the ore horizon and occupies the stratigraphic footwall position. In many other volcanogenic massive sulfide deposits, the stratigraphic footwall contains the stringer or feeder zone. However, no strong evidence for the presence of a discrete feeder zone or alteration pipe in these rocks has yet been identified at Flambeau. What is observed in the andalusite-biotite schist is a gradual southward increase up the footwall stratigraphic column of sericite, sulfide and chert mineralization over a stratigraphic thickness of 100 feet towards the orebody. Fragments, less than 1 inch thick, of both chert and quartz-sericite with pyrite and/or chalcopyrite increase toward the ore horizon. The quartz-sericite and chert fragments are better mineralized than the matrix, containing 5 to 7% pyrite with less that 2% chalcopyrite. The contact between the quartz-sericite and other rocks of the ore horizon is, therefore, gradational over 5 to 15 feet and difficult to identify in the pit. Geochemically, the ore horizon is readily identifiable due to the sharp increase in gold values (Table 3). Two beds of sericite-clay and spessartite garnet occur in the footwall north of the orebody, identified as a 5 to 15- foot wide fissile sericite-clay bed that was probably a felsic tuff. One of these sericite-clay beds has been used recently as a marker horizon. Alteration has totally destroyed original mineralogy leaving a greasy mixture of highly foliated sericite-clay. This bed can be traced from the west wall to the east end of the pit where it is covered by the main haulage ramp. �78 TABLE 3 BUILD-UP IN GOLD VALUES iN HOLE 13, TOWARDS ORE HORIZON FLAMBEAU MINE, RUSK COUNTY, WISCONSIN Geology Hangingwall Ore Horizon Footage (it) Ondalusite -- 21 5-220 Biotite Schist Quartz-Sencite Schist Massive Sulfides 220-225 225-230 230-232 232-237 237-242 242-247 247-252 Copper (%Cu) 0.189 0.226 0.531 1.544 11.154 6.286 11.762 11.559 Gold (opt Au) Trace 0.005 0.050 0.080 0.030 0.090 0.210 0.120 A second marker bed consisting of spessartite-chiorite has been recognized in the footwall on the east end of the orebody in core samples taken beneath the pit. Metadacite flows have interrupted this bed to the west. The unit is recognized at depth by the presence of 20 to 25% chlorite and 2% lightorange to pink dodecahedral spessartite porphyroblasts. This unit has not yet been recognized in the pit. ORE HORIZON Ouartz-Sericite Schist. The quartz-sericite schist of the ore horizon is interpreted to have originally been a rhyolite tuff based upon thin section studies. Interbedded within the tuff and in close association are metacherts and massive sulfide mineralization. Metacherts are interbedded with, and flank much of the enriched ore, with the thicker silica-rich beds in the stratigraphic footwall on the north side of the deposit. The quartz-sericite schist has been explored and traced a strike length that exceeds 12,000 feet. True thickness varies from approximately 20 feet to as much as 180 feet. The average thickness is 105 feet, where it hosts the orebody. Along strike away from the orebody, the well foliated unit is recognized by an increase in sericite and pyrite but less quartz and chalcopyrite. The unit was traceable geophysically by using induced polarization (IP) which responded positively to the ho?izon's 5 to 15% pyrite content. Along strike, away from the massive sulfides, are also narrow zones containing cherty fragments with up to 1 or 2% chalcopyrite and/or sphalerite. In the pit, the quartz-sericite schist is a light gray, very well foliated rock containing up to 60% quartz, up to 50% sericite, and averages 15% pyrite. There are minor amounts of chlorite, andalusite, and biotite present, particularly towards the outer edges of the unit or along strike, where a greater proportion of mafic tuff and volcanic debris appears to have been deposited. Lapilli Tuffs. Lapilli tuffs on the stratigraphic hangingwall side of the orebody are intercalated with tuffs and exhalitive deposits of the ore horizon. In general, the lensoidal-shaped felsic fragments make up from 5 to 10% of the unit although certain beds consist predominately of fragments. The ore horizon is, nevertheless, dominated by sediments and sulfides deposited under quiescent conditions with occasional outbursts of high energy as evidenced by internal lapilli units. The size of the siliceous fragments are generally less than one inch with an occasional fragment to 2 or 3 inches. Most fragments consist of sugary-textured quartz with varying amounts of sericite, �79 pyrite, and chalcopyrite that have been enriched to chalcocite and/or bornite. Metachert fragments up to 3 to 4 inches long and one-half inch thick have been observed in the ore horizon. Fine Grained Tuff. A well-bedded, light milky tan colored siltstone or very fine grained water-lain tuff occurs at the stratigraphic top of the ore horizon. Sulfide mineralization which averages 15% in the quartz-sericite schist decreases to 2 to 4% in this horizon. An occasional fine-grained, highly elongated sulfide fragment has been noted. Near the hangingwall of the quartz-sericite schist, and the argillized sericite schists on the east end, are erratic gold-mineralized zones. These gold-rich zones occur within fine grained massive to semimassive pyrite zones and are associated with porcelaneous-type clays. Arsenopyrite and minor galena is preferentially found in this area of the ore horizon and in the footwall or north side of the fine grained tuff. The fine grained tuff has been included within the ore horizon since this unit generally represents a water-lain sequence of materials in a quiescent depositional environment, and contains greater compositional and genetic affinities to the other units of the ore horizon than with the hangingwall rocks south of the ore horizon. A pronounced change occurs in rock deposition stratigraphically above the fine grained tuff with the return of volcaniclastic materials similar to those in the footwall rock. STRATIGRAPIIIC HANGINGWALL The geology of the hangingwall is less well known since core holes and the Flambeau pit extend for only a short distance into these poorly mineralized rocks; still, a pronounced lithologic change is evident. In general, the rock units are thinner and consist of interbedded chlorite-phyllites, quartz eye schist, metadacite and biotite-feldspar schist. These lithologies represent deposition of intermediate to mafic volcaniclastic and flow rock. Further to the south, away from the deposit, the hangingwall becomes mostly quartz eye schist. One of the deep exploration drill holes intersected a foliated mafic rock with repetitive narrow one to 2 inch zones of chlorite-epidote. These were inferred to be pillow lava structures in a mafic "dacitic" rock. Excellent pillows have, subsequently, been mapped in the hangingwall at the east end of the open pit. STRUCTURE The Flambeau orebody has been interpreted to occur on the limb of a large isoclinal fold which is indicated by the fact that cleavage is parallel to the bedding. Slickensides have been noted on foliation planes indicating dynamic metamorphism during the Penokean Orogeny. The chief rock fabric is the N45 °E striking foliation that dips 690 to 760 to the northwest, parallel to lithologic units. Cross-cutting faults have been noted in the massive sulfides but cannot be traced with any degree of certainty into the host volcaniclastic rocks. Numerous, small cross-cutting displacements, with 2 to 5 foot offsets, in the footwall chert and massive sulfides on the north contact of the orebody have been disclosed by pit mapping. These displacements could represent minor graben and horst development in the original ocean floor. The presence of these fault blocks indicates to the authors that the Flambeau orebody has not been highly folded and sheared as suggested by some geologists. These structures are shown on Figure 5. r �FOLIATiON BIOTITE—FELDSPAR (lUFF) QUftTZ—SERlC[TE (RI-IYOLITE lUFF) MASSWE SULFIDES ANDALUSITE—BIOTITE (SEDIMENTS) METACHERT — FAULT r:i PRECAMBRIAN PROTEROZOIC GLACIAL TILL PLEISTOCENE LEGEND Rusk County, Wisconsin Figure 5 Geology of 1070 Bench, Flainbeau Mine A LENS 0 SCALE1 1"20 10 20 _ // FEET (.n 0 1 D I z D I- I- N (Il D �81 The largest recognized cross-cutting fault occurs near mine Section 408 where the east side of the stratigraphic footwall of the orebody has been offset 30 feet to the south. The fault strikes N85°W, and dips 65° to 85° NE. This right lateral offset relationship holds true along the strike length of the orebody where other smaller offsets have been mapped. Although these cross-cutting structures appear to be a part of the northwest fabric identified by Sims and others (1989) for the Precambrian in northern Wisconsin, none of the northwest faults at Flambeau can be traced southward into the hangingwall. Cross-cutting faults can be traced for short distances of less than 50 feet north into the footwall where they rapidly deteriorate into weak joint surfaces. It is therefore suggested that these faults are penecontemporaneous with the mineralizing events and not more deep-seated structures associated with the later Penokean Orogeny. The east end of the orebody may have been subjected to post-ore faulting, with the end of the orebody rotated clockwise to the south. There is evidence of a fault offset at the very east end of the orebody with the east side dropped down an unknown distance. Deep drilling into the down-dropped block gave negative results. The rock in the Flambeau open pit is intensely fractured by several series of joint sets. There are two predominant flat joint sets, one striking approximately N65°W and dipping 15° to 25°N, the second striking N75°W and dipping 30° to 40°N. There are also three principal groups of high angle joints striking: 1) N40°E dipping 65° to 85°S; 2) N85°W, dipping 65° to 85°N; and 3) N70°E dipping 65° to 85°N. ALTERATION The Flambeau orebody has been subjected to intense alteration associated with primary sulfide mineralization, regional metamorphism during the Penokean Orogeny, and by significant near-surface supergene alteration of the silicate rocks leading to enrichment of the massive sulfides. The combined effect of these three processes is that original mineralogy is obscured and in some cases totally changed. No systematic study of the alteration zones has been undertaken; therefore, the account given here is preliminary. Mineralogy of the rocks stratigraphically below the ore zone suggest a complex history of hydrothermal alteration. Abundant andalusite in the footwall rocks indicates that the primary volcanic rocks have been significantly enriched in alumina. This may have been accomplished by hydrothermal leaching by acidic fluids which removed K, Na, and Ca from the felsic and intermediate volcanic rocks (Table 2). FeO and Mg were added with iron-rich chlorite probably accounting for most of these increases. The altered rocks were presumably rich in kaolinite, which was prograded to andalusite during regional metamorphism to upper greenschist facies. The decrease in andalusite at the east end of the orebody suggests less hydrothermal alteration of the primary volcanic rocks. This hydrothermal alteration was presumably associated with massive sulfide deposition. It must be emphasized, however, that no well-defined alteration "pipe" or stringer ore found in other massive sulfide deposits has been identified in rocks associated with the Flambeau orebody. The two beds of spessartite-chlorite in the stratigraphic footwall indicate significant manganese enrichment in those horizons. Origin of the manganese-rich horizons is problematical. They may be the result of seawater-sediment interaction, and may not be related to hydrothermal alteration associated with the massive sulfide deposition. �82 Regional metamorphism produced an upper greenschist or lower amphibolite facies suite of minerals with predominately biotite, andalusite and some cordierite. Supergene alteration, while low temperature and low pressure, profoundly altered the first two mineralogical events. The alteration effects on the sulfide mineralogy will be discussed further in the subsection entitled Supergene Enrichment. Supergene alteration produced acidic conditions that totally bleached the host rocks for a horizontal distance of 100 feet into the footwall and 50 feet horizontally south into the hangingwall volcaniclastics. The ferromagnesian minerals have been almost completely altered to clay (montmorillonite) and sericite or chlorite-sericite further away from the orebody. As described further under the subsection entitled "Gossan," large volumes of supergene activated silica were mobilized and recemented to form-s hard, dense silica breccia. On the margins of the highly bleached zone is the leached and oxidized zone where the chloritized ferromagnesium minerals plus small amount of sulfides (1 to 2%) have been oxidized. Overlying the bleached and weathered leached zones is a thick saprolite layer. This layer varies from about 5 feet to over 30 feet of intensely clay-altered volcaniclastic rock. X-ray diffraction has identified the chief minerals to be montmorillonite, micron-sized silica and in some areas pyrite. OREBODY SHAPE In general, the Flambeau orebody is a steeply dipping, near tabular massive sulfide lens. It averages 45 to 50 feet in thickness reaching a maximum thickness of about 70 feet on section 407. The strike length is 2,400 feet and is parallel to foliation. The orebody subcrops at the 1 100-foot elevation and bifurcates below the 1070-foot elevation, suggesting it is actually the roots of a much larger and eroded mineral system. The main part of the orebody is referred to as the "A" lens. The "B" lens, located south of the "A" lens, averages 10 feet in thickness. It is joined to the "A" lens at section 4.06 and diverges south/westward into the hangingwall, so that on section 400 it is about 100 feet south of the "A" lens. The "C" mineralized horizon occurs 50 feet north of the "A" lens in the footwall and probably represents an early mineralizing event in an emerging mineral-rich system. The "C" horizon is less than 10 feet thick discontinuous, deficient in gold values, and poorly mineralized with chalcopyrite. Contrary to previous reports (May, 1977) the hangingwall and footwall contacts are sharp and clearly defined where seen in the open pit. MINERALOGY The supergene mineralogy, paragenesis, and crystallography probably ranks Flambeau as unique among massive sulfide deposits in the Canadian Shield. Although other enriched massive sulfides have been found in the Shield, none have been as well preserved, with an extensively supergene enriched copper zone capped by a gold-enriched gossan. PRIMARY MINERALIZATION Primary mineralization occurs 130 to 185 feet below the subcrop and supergene enriched mineralization. Pyrite (60%) is the chief mineral with lesser amounts of chalcopyrite (12%) and sphalerite (2.5%). Gold, silver, galena, and pyrrhotite occur in minor quantities. The above minerals occur in various proportions and combinations as massive, semimassive, and disseminated �83 sulfide mineralization. Based on drill-core observations, the author has defined massive sulfide to contain greater than 50 weight percent sulfides, semimassive to contain between 20 and 50 weight percent sulfides, and disseminated to contain less than 20 weight percent sulfides. Although the above definitions may conflict with previous work on other deposits, they best suit conditions found in the Flambeau deposit. Massive sulfide dominates the upper part of the steeply dipping and overturned deposit to 600 feet beneath the subcrop. However, the east central portion of the sulfide deposit contains semimassive mineralization. Semimassive mineralization increases with depth from a strike length of 500 feet in subcrop to 2,400 feet at 600 feet beneath the surface. A disseminated sulfide halo which averages 215 feet in width and contains 7% pyrite encloses the massive-semimassive mineralization. The halo extends along strike for at least 5000 feet in either direction and downdip for an unknown distance. Therefore, massive-semimassive sulfide mineralization gradually decreases with depth and rapidly decreases horizontally away from the deposit. The massive sulfide mineralization displays well developed mineral zoning across the deposit. The stratigraphic footwall or northern part of the ore zone tends to be chalcopyrite-rich with sphalerite noticeably more abundant toward the hangingwall. Most of the hangingwall satellitic lenses are sphalerite-rich. Based on stratigraphic-mineral zoning work conducted in the Noranda District (Gilmour, 1965), where copper favors the stratigraphic footwall, it is believed that the Flambeau deposit is overturned. The semimassive sulfide mineralization is weakly zoned with pyrite the dominant sulfide. It forms narrow, sub-concordant, massive to semimassive layers interbedded with wealdy mineralized and chloritized quartz-sericite schist and metachert. Chalcopyrite is coarser grained than that found in the massive sulfide mineralization, occurring as large irregular masses up to 50mm in diameter. It also occurs as interstitial fillings around the 1mm to 3mm pyrite grains. Small amounts of sphalerite (less than 1%) are scattered throughout the zone as grains, as narrow bands up to 6mm in width, and as occasional irregular clots less than 7mm in diameter. Gangue minerals in both the massive and semimassive zones are quartz (metachert), sericite, and lesser amounts of chlorite and andalusite. The grain size and distribution of the gangue minerals is highly variable: they may occur as small, irregular particles 2mm to 5mm; across, as patchy inclusions 40mm to 50mm; across, or as narrow, concordant, ellipsoidal lenses or fragments. COSSAN A total of 115,000 tons of gossan with an average grade of 0.6 opt Au have been mined from the top of the massive sulfide orebody. Three types of gossan have been recognized during core examination and mining, which, in general, grade from chert gossan in the west end of the pit, to argillic gossan, then to ankeritic gossan in the far east end. Chert Gossan. Chert gossan was dominant in the west half of the open pit and has been further sub-divided into the cherty breccia, the purple-red, and the sandy gossan (Figure 6). A cherty breccia zone overlaid a purple-red gossan from Section 401 to 413. A sandy gossan occurred on the hangingwall between Sections 404 and 408. All three zones consisted of subrounded to angular cherty and possibly secondary quartz fragments. Iron oxide coated the silica-rich particles and fragments in varying amounts. Fine-grained gold was present in all three zones. Hematite was the chief iron oxide followed by goethite with lesser amounts of jarosite. �NW SE 03 BR IAN SANOSTO NE CHERIY BRECCIA ±0.1—0.6 opt Au SAPROLITE 20PURPLE— RED ±1.0 opt Au 3—5' —FOOTWALL CHERT UPPER ZONE CI-IALCOCITE 15—80' II MIDDLE ZONE CHALCOCITE—BORNITE —FOOTWALL MIDDLE ZONE 35—125' GOLD HORIZON BORNITE—CHALCOPYRITE ORE HORIZON - - - LOWER ZONE CHALCOPYRITE—BORNITE CHALCOCITE 10—80' / 10 SCALE 0 20 FEET 1" =20' LOOKING NORTHEAST Figure 6 // // Supergene Vertical Zoning — Generalized Section West End, Flambeau Mine Rusk County, Wisconsin �85 i) Cherty Breccia. The cherty breccia or silica-rich gossan was not a true breccia, although it did contain abundant fragments of partially decomposed chert. The stratigraphic footwall chert on the north side in many places collapsed on top of this zone during volume reduction as the massive sulfides were being oxidized. These collapsed chert fragments (<2 inches) and blocks (<2 feet) capped much of the gossan. A gradual disintegration occurred from the footwall massive, hard chert towards the hangingwall where the chert became sandy in texture. A large amount of secondary silica has remained high up in the gossan, which could have been derived by solution of small amounts of cherty inclusions found around sulfide grains in the protore. Botryoidal and stalagmitic silica has been observed in the west wall gossan. The cherty breccia must have been in constant flux as the underlying massive sulfides were being leached, enriched, and then oxidized with the gossan collapsing on top. Eventually a stage of semi-equilibrium was reached where the cherty breccia was recemented into a hard, dense, light gray, poorly to nonfoliated silica-rich rock. This rock consisted of 2 mm to silt-size subrounded to angular quartz particles. Very small amounts of iron oxide, and traces of native copper, and gold make up the remainder of the rock. Quartz content ranges from 88 to 96 volume % of the rock. The cherty breccia thickness ranges from 6 to 12 feet and has a sharp contact with the underlying purple-red gossan. ii) Purple-Red. The purple-red gossan was named because of its distinct coloration resulting from a high hematite content. This zone was unconsolidated, subrounded to angular quartz grains in a matrix of hematite, goethite, and jarosite. Hematite occurs as botryoidal coatings up to 1 cm in diameter or as earthy masses. Small amounts of kaolinite have been noted. The purple-red zone ranges in thickness from 6 to 12 feet. iii) Sandy-Gossan. A sandy gossan zone formed in the stratigraphic hangingwall adjacent to the cherty breccia and purple-red zones over a thickness of 20 feet and a strike length of about 500 feet. Contacts with the adjacent two zones was gradational over a foot or two, and less gradational with the hanging wall volcaniclastics to the south. This zone had a distinct salmon pink to purple-red color, was unconsolidated and consisted of fine-grained, subrounded quartz grains with varying amounts of iron oxide and less clay particles. It was a well-sorted, iron stained quartz sand with high gold content. Fragments and blocks of sandstone several inches to a foot in size were noted as deep as 13 feet into the sandy gossan. These blocks have been tentatively identified as Late Precambrian sandstone incorporated within a water reworked section of the gossan. Gold content was in places at least two to four times higher than that in the purple-red zone. Gold in all three zones of the chert gossan occurred as less than 20 micron-sized grains with only small amounts of silver. Silver in the gossan does not occur as electrum. In the cherty breccia zone, gold contained 2 to 4% silver, whereas gold in the purple-red contained less than 0.5% silver. The purple-red zone however, generally hosted about three to four times more gold than the overlying cherty breccia. Argillic Gossan. The argillic zone formed over the orebody from Section 413 to 418. Petrographic examination of this zone has shown it to be dominated by quartz with smaller amounts of hematite, goethite, jarosite, chlorite, montmorillonite, illite, rutile, chalcopyrite, and the alunitejarosite family of minerals. This gossan was yellow-brown in color, highly foliated, broken, and contained a moderately developed zone of purple-red gossan along the base. The purple-red gossan corresponded well to underlying internal massive sulfide zones within a predominantly semimassive portion of the orebody. Free-silica values were significantly lower in both the argillic �86 and ankeritic gossans than in the chert gossan. The argillic gossan was about 40 feet wide and 15-20 feet thick. Ankeritic Gossan. Gossan in the east end was characterized by a high ankerite and very low silica content. At least 35 vertical feet of ankerite gossan have been mined with small zones going to greater depths along contacts or strong joints. This zone was a dark purple-brown poorly to well cemented, massive textured gossan. Ankerite was well developed with cleavage planes and crystal faces. up to 0.5 inch developed. It also contained quartz grains with hematite, iron oxides, native gold and lesser amounts of chalcopyrite. Silver values, in the inunediate underlying enriched copper zone, are up to ten times higher than in the rest of the orebody. The reason for this phenomenon is still uncertain, but is suspected to be linked to the ankerite mineralization. OXIDE ZONE An oxide zone was present beneath much of the gossan and had a thickness of two to five feet. This zone consisted of cuprite, goethite, and malachite, with lesser amounts of azurite, chalcopyrite, and native silver. The oxide zone contained up to 20% copper oxides. Malachite occurs as earthy coatings or occasionally as botryoidal fillings. Azurite occurred as earthy fillings and occasional small crystals. Copper oxides have been found on faults and fractures 60 feet or deeper below the subcrop. At the top of the oxide zone, horizontal manganese "pipes" up to two to three inches in diameter were observed. These tubes, now filled with sand, appear to have once transported large volumes of groundwater along the top of the enriched massive sulfide orebody. The gossan and oxide zones wrap around the sides of the sulfide orebody. The oxide zone descended about five to ten feet, whereas the gossan zone with minor azurite and malachite draped 20 to 30 feet down the flanks of the orebody in more porous areas. The top of the black supergene enriched sulfides below the gossan and oxide zones was remarkably smooth, and sloped gently at the edges towards the enclosing volcanic host rocks. Vertical relief rarely exceeded two to four feet with slope angles of one to two degrees. SUPERGENE ENRICHMENT Supergene enrichment affected the primary massive, semimassive, and disseminated sulfide halo zones. The extent and degree of enrichment depended upon original base metal mineralogy, rock permeability, foliation planes, structure, and a fluctuating groundwater table. The well developed schistosity planes in the wealdy mineralized volcaniclastic host rock directed mineral-rich, acidic waters to depth. Medium grained, subhedral to granular, and weakly foliated massive sulfides had a higher permeability than the clay-rich host rock permitting the supergene enrichment processes to extend to greater depths. The west end of the orebody has been enriched locally to 185 feet below the subcrop, and the east end to 140 feet, as shown on Figure 7. Enrichment has been restricted to 80 to 100 feet below the subcrop in the central part of the deposit. Enrichment in the volcaniclastic host rock was generally several tens of feet shallower and of much lower grade due to its lower permeability. The more felsic and extensively pyritized stratigraphic footwall volcaniclastic rock have been preferentially enriched relative to the more basic, less pyritic, and chlorite-rich hangingwall rocks south of the orebody. Individual grains of primary sulfides in the disseminated sulfide halo have been partially or completely replaced with chalcocite and/or bornite. These secondary minerals form solid replacement minerals, microrimmings on the protore surfaces, or as sooty coatings. Sphalerite and galena were preferentially replaced relative to chalcopyrite and even less reactive pyrite. Consequentially, zinc �QUARTZ—SERICITE SCHIST BIOTITE—FELDSPAR SCHIST CHERTY GOSSAN PURPLE—RED GOSSAN ANDALUSITE—BIOTITE SCHIST, SERICITE—CLAY MASSIVE SULFIDES PRECAMBRIAN PROTEROZOIC MOUNT SIMON SANDSTONE CAMBRIAN MEGACHERT [] GLACIAL TILL PLEISTOCENE LEGEND Section 406 1=50 i 50 FEET Rusk County, Wisconsin LOOKING NORTHWEST 0 SCALE25 Figure 7 Geological Cross Section 406 & 418, Flambeau Mine Section 418 11 B LENS �88 values are generally less than 0.05% and lead is rarely detectable in the enriched ore. It is suspected that some of the high grade sooty chalcocite zones were formed in areas of high primary sphalerite. The supergene enriched mineralization is zoned vertically. The Upper zone is chalcocite dominant, the Middle zone is bornite-chalcocite dominated, and the Lower zone is a mixture of chalcopyrite-bornite-chalcocite. The formation of these zones is determined by original base metal content, fracturing, and faulting that directed supergene enriched fluids to depth within the orebody. Some of the structural features that helped determine this pattern of enrichment are shown on Figure 8. Supergene sulfides in the Upper and Middle zones were developed at the expense of all of the primary base metal minerals and much of the pyrite. The contact between the two zones is gradational. Chalcocite occurs as irregular steely masses, microrimmings, sooty films, sandy zones and fracture fillings. Some of the best copper grades were found in sandy-chalcocite areas located close to and parallel with the orebody contacts. The Upper and Middle zones of the west end of the deposit are of approximate equal vertical thickness of about 75 feet. In the Middle zone, bornite occurs as massive replacements or as numerous reticulating veinlets replacing chalcopyrite. As this replacement became more complete the veinlets coalesced to form irregular bornite masses and "veins". The replacement process continued with bornite being replaced by chalcocite. At each successive enrichment stage, additional pyrite was consumed so that at the end of the replacement process significant amounts of pyrite had been replaced. The supergene paragenesis, described in the next subsection, is based on relationships observed in the supergene enriched zone. Botryoidal secondary chalcopyrite is common in the Lower zone as well as in the Middle zone. Chalcopyrite botryoids have been observed ranging from less than a millimeter in thickness to over five millimeters. Most of the thicker botryoids show fluctuating deposition with bornite. Micron-size tetragonal chalcopynte crystals have been frequently noted, particularly on bornite. Bornite has not shown any crystal habits. On the other hand, chalcocite occurs in a variety of spectacular crystals both twinned and untwinned. These crystals are generally coated by blue to purple iridescent or gold colored chalcopyrite and more rarely bornite. To form an enriched orebody the size of Flambeau would require weathering, taking mineralization into solution, and reprecipitation of a deposit on the order of 6 to 10 million tons. Therefore, the enrichment must predate deposition of the overlying Cambrian sandstone, because the volume of rock between the sandstone and the enriched zone could not have produced the enriched ore present. PARAGENESIS The paragenesis of the Flambeau orebody has been subdivided into three stages as shown on Figure 9. These stages are: 1) primary deposition of the host rocks and mineralization, 2) regional metamorphism, and 3) secondary enrichment and weathering. Stage 1 consists of three main stages of base metal and silica deposition commencing with the early "C" horizon. The second stage resulted in the formation of the "A" horizon with at three exhalative silica pulses. Pulse one formed the thicker footwall chert, pulse two was ongoing weak intermittent deposition of silica within the orebody, and pulse three formed the hangingwall chert south of the orebody. Base metal mineralization during stage two is dominated by copper with a few areas of zinc. The third stage is dominated by zinc, gold, �L 400 LEGEND INTERPRETED FAULTS PRIMARY SULFIDES 410 MINE SECTION LOOKING NORTHWEST Figure 8 Longitudinal Section of Supergene Mineralogical Zoning, Flambeau Mine Rusk County, Wisconsin BORNITE—CHALCOCITE CHALCOCITE, LOWER ZONE BORNITE—CHALCOCITE, MIDDLE ZONE CHALCOCITE—BORNITE, MIDDLE ZONE CHALCOCITE—DOMINANT, UPPER ZONE GOSSAN PRECAMBRIAN PROTEROZOIC MOUNT SIMON SANDSTONE CAMBRIAN GLACIAL TILL PLEISTOCENE SW 420 0 75' 150' 5 300' 424 300' 600' • 150 75. 37.5' 0 NE �90 and decreasing amounts of copper extending out into the hangingwall (i.e., the "B" lens), giving a zoning profile of copper changing to zinc upward in the original stratigraphy. Regional metamorphism is characterized by the formation of upper green schist to lower amphibolite facies minerals. Diagnostic minerals are andalusite, spessertite garnet and biotite. Quartz "sweats" are common with many showing boudinage structures. Schistose textures and foliation developed during this stage. Chalcopyrite, and other sulfides, were remobilized to form coalescing irregular blebs, while pyrite recrystallized to form medium grained subhedral grains. These sulfides along with minor gold are associated with localized quartz "sweats" on the flanks of the orebody. The enrichment stage resulted in the formation of a suite of secondary minerals, probably during late Precambrian time. Simplistically this stage produced significantly enriched copper values in the upper part on the deposit through the removal of iron and reprecipitation of copper from higher levels in the weathering zone. The enrichment shows the classic mineral zonation, with the conversion of primary pyrite to secondary chalcopyrite in deeper levels of the deposit, overlain by a bornite-nch zone, developed by enrichment of the chalcopyrite. Chalcopyrite is commonly found in three forms: botryoidal, rosettes of platy chalcopyrite; and shiny brassy platy open-fracture fillings. Finally, chalcocite developed by removal of iron from the bornite, probably at the paleo-water table. Native copper, cuprite, azurite and malachite developed in the oxidized zone above the paleo-water table. However, this simple pattern was complicated by local variations in porosity, permeability and mineralogy in the ore. For example, irregular masses of primary pyrite and chalcopyrite are found within the secondary chalcocite. Possible fault zones allowed oxidation and enrichment to extend much deeper in the orebody. The result is a very irregular mixture of minerals within the ore. The mineralogy is also complicated by major changes in the level of the water table that occurred subsequent to the main enrichment. The present water table is much closer to the surface than the paleo-water table during supergene enrichment, as shown by the presence of secondary oxide minerals below the present water table. In addition to massive material, much chalcocite occurs as "sooty" and granular, or sandy-textured material that may have formed by replacement of the granular pynte produced by metamorphism or by replacement of massive beds of sphalerite. Enrichment also produced numerous cavities within the ore, in which late-stage minerals developed. Some cavities contain well-formed chalcocite crystals in a variety of crystal forms to nearly three inches long. These chalcocite crystals typically have a blue, purple, or brassy yellow patina produced by a thin surface coating of bornite and/or chalcopynte. The surface coating probably formed when the rising water table placed the chalcocite crystals in the stability field of bornite and chalcopyrite. Chalcocite crystals occur as psuedohexagonal plates up to two inches in diameter, stacked psuedohexagonal columns or barrels up to 0.75 inch long by 0.25 inch wide, twinned orthorhombic crystals, up to 2.5 inches in length by 0.75 inch in width, and curvilinear "scimitar-like" forms up to 0.5 inch long. A picture of a twinned orthorhombic chalcocite crystal appears in this memorial volume. �EARLY LATE PRIMARY METAMORPHISM SECONDARY 1.76 BY upper greenechist to lower amphibolito late Pro-Cambrian -? early Cambrian Cu-Au-Ag-Zn VMS DEPOSITED IN BACK-ARC BASINAL SETTING PYRITE CHALCOPYR lIE SPHALERITE GALENA EXHALATIVE SILICA QUARTZ ARSENOPYRITE DURING OROGENY, SULPHIDES RECRYSTALLIZED, LOCAL PRECIOUS METAL MOBILIZATION, QUARTZ INJECTION, LOCALIZED FOLDING. POSSIBLE EXTENSIONAL SMEARING FROM REGIONAL FOLDING SUPERGENE ENRICHMENT OF COPPER SULPHIDES, ASSOCIATED WITH GOSSAN GENESIS ON OVER-TURNED, SUB-VERTICAL DEPOSIT DIT FLUCTUATING WATER TABLE OXIDING AND VERY ACIDIC Zn mobized out of system —— '7 Pb mobtzed out of system —— AN DALU SITE CHLORITE (ALTERED DACITIC) BIOTITE SERICITE (ALTERED RHYOLITIC) GARNET GOLD SILVER CHALCOCITE BORN ITE CHALCOPYR lIE ANKERITE-SIDERITE HEMATITE ? CALCITE ?IN PRIMARY EXOTICS AZURITE MALACHITE CU PR lIE DIGENITE CHALCOCITE PSEUDOMORPH AFTER GALENA BORNITE PSEUDOMORPH AFTER BOTRYOIDAL CHALCOPYRITE CHALCOCITE CRYSTALS NATIVE COPPER BORNITE 'BULLETS & BOTRYOIDS AFTER CHALCOPYRITE (WITH INTERNAL CHALCOPYRITE LAYERS) HORIZON PYRITE CHALCOPYRITE SPHALERITE GALE NA GOLD SILVER CHERT QUARTZ Figure 9 "C', . PRIMARY "A" - -I — --— —1- _- -_ — "B" pt— --— A w GENERALIZED PARAGENESIS OF THE FLAMBEAU OREBODY �92 Occasionally some bizarre relationships or textures occur, for example, the exquisite "scimitar-like" chalcocite crystals that occurred high up in the orebody (1070 level). In contrast, twinned orthorhombic chalcocite crystals were collected from a 3x3x 10-foot vug on the 1010 level. Other cavities contain botryoidal growths of bornite, chalcopyrite or chalcocite, or may contain encrustations of carbonate minerals (mainly ankerite, dolomite and siderite). Some carbonate crystals have tiny rosettes of chalcopynte on which are specks of lead oxide scattered on crystal faces. Agaul, the chalcopyrite may have formed after the water table rose. The gold-rich gossan evidently formed by residual concentration of gold as erosion slowly lowered the paleosurface as supergene sulfide enrichment was in progress. Coarse crystalline pyrite with scalehedrons of arsenopyrite have been collected near the stratigraphic hangingwall. Quartz pods are associated with this mineralization, as are native gold, bornite, and chalcocite. This gold is very fine grained and is possibly a supergene product. Similar gold has been observed within, but close to, the orebody's contacts. This gold is intimately associated with quartz that contains bornite, minor chalcocite, and lesser chalcocite psuedomorphs after galena and is interpreted to be related to remobilization processes during regional metamorphism, later acted upon by supergene processes. CONCLUSIONS The Flambeau orebody is a well preserved supergene enriched massive sulfide deposit capped by a gold-enriched silica-iron oxide gossan. A small, thin, poorly indurated Cambrian sandstone outlier capped the gossan and supergene enriched mineralization and helped protect them from significant glacial erosion. The dominant chalcocite-bornite enriched mineralization was formed to depths up to 185 feet below the subcrop. Copper values in excess of 20% have been mined, particularly in areas of massive steely-gray chalcocite, and zones of sooty chalcocite that probably replaced massive sphalerite. A total of 1.71 million tons grading 10.3% Cu, 0.116 opt Au, and 1.837 opt Ag will be mined from 1993 to 1997. Three products are shipped via rail from the open pit. Gossan ore and direct smelting shipping ore greater than 14% Cu are railed to Noranda's Home Smelter at Rouyn-Noranda, Quebec, Canada. Mill ore grading 6 to 10% Cu is railed to the Kidd Creek Mill located at Timmins, Ontario, Canada where it is concentrated then redirected to the smelter. While modest in size, the Flambeau orebody will be remembered for its classical supergene mineral zoning, high copper and gold grades, and exquisite twinned chalcocite crystals. The importance of the pioneering environmental safeguards implemented at Flambeau match the economic contributions made by both private and public institutions (May, 1977) Successful mining of the orebody beside the Flambeau River and City of Ladysmith, while enhancing and maintaining surface and groundwater quality respectively, is in itself a milestone for the American base metal mining industry (Murphy, 1996). �93 Acknowledgments The authors wish to thank Tom Myatt, General Manager of Flambeau Mining Company, for allowing this paper to be written and for supporting and hosting the 1996 Institute on Lake Superior Geology field trip. A considerable amount of assistance was provided by Jay Hammitt, Russ Babcock, Gene LaBerge, and Ray Yost, all of whom polished the manuscripts with almost too much enthusiasm but whose insights and efforts were greatly appreciated by the authors. A special thanks to Tammy Fredrickson who repeatedly deciphered our geological scribblings and prepared the manuscript for this volume. References Cited Babcock, R, 1996, History of Exploration for Volcanogenic Massive Sulfides in Wisconsin: Institute on Lake Superior Geology, 42nd Institute, 1996 Field Trip Volume. DeMatties, Theodore A., 1994, Early Proterozoic Volcanogenic Massive Sulfide Deposits in Wisconsin: An Overview: Economic Geology, v. 89, p. 1122-115 1. Gilmour, P., 1965, The Origin of the Massive Sulfide Mineralization in the Noranda District, Northwestern Quebec: Geologic Association of Canada, v. 16, p. 63-82. LaBerge, G. L., 1996, General Characteristics and Geologic Setting of the Wisconsin Magmatic Terranes: Institute on take Superior Geology, 42nd Institute, 1996 Field trip volume. May, E. R., 1977a, Flambeau - A Precambrian Supergene Enriched Massive Sulfide Deposit: Geoscience Wisconsin, v. 1, p. 1-26. May, E. R., 197Th, Case study of Environmental impact - Flambeau Project: Mining Congress Journal, v. 63, p. 39-46. Morey, G. B., Sims, P. K., Mudrey, M. G., and Southwick, D. L., 1982, Geologic Map of the Lake Superior region, Minnesota, Wisconsin, and northern Michigan: Minnesota Geological Survey State May Series S-13. Murphy, J., Dachel, R., 1996, Case Study of Environmental Requirements for the Permitting Operation, and Reclamation of a Metallic Mineral Mine in Wisconsin - Flambeau Mine: Institute on Lake Superior Geology, 42nd Institute, 1996 Field Trip volume. Schwenk, C. G., 1977, Discovery of the Flambeau Deposit, Rusk County Wisconsin Geophysical Case History: Geoscience Wisconsin, v. 1, p. 27-42. - A �94 �95 CASE STUDY OF ENVIRONMENTAL REQUIREMENTS FOR THE PERMITFING, OPERATION, AND RECLAMATION OF A METALLIC MINERAL MINE IN WISCONSIN FLAMBEAU MINE by JANA E. MURPHY Supervisor of Environmental Affairs, Flambeau Mining Company and RICHARD T. DACHEL Environmental Chemist, Flambeau Mining Company INTRODUCTION The Flambeau Mining Company (Flambeau), a subsidiary of Kennecott Minerals Company, owns and operates an open pit copper mine located just south of Ladysmith, Wisconsin. The 181 acre mine site is bounded on the west by the Flambeau River, on the east by State Highway 27, and to the north by the City of Ladysmith. While Flambeau owns the majority of the surrounding properties as a buffer, there are private properties and homes within 100 feet of the perimeter of the mine site. The surrounding natural and anthropogenic features made the permitting of the Flambeau Mine especially unique. A representation of the unique features within and surrounding the project area are listed below: • • • • • • • Flambeau River located 140 feet from west edge of pit; Intermittent streams requiring relocation and re-establishment; Wetlands requiring mitigation; State highway within 1000 feet of facilities; Private landowners within 100 feet of the perimeter of the mine site; The center of the City of Ladysmith is located 1.6 miles north of mine site; Relatively shallow groundwater table within 20 feet of surface. FLAMBEAU PERMITS Another unique aspect of Flambeau is that it is currently the only operating metallic mineral mine in the State of Wisconsin. The Flambeau Mine is also the only metallic mineral mine to receive permits under Wisconsin's current mining laws. Flambeau received its eleven permits following: 1) extensive baseline monitoring; 2) data compilation and review; 3) identification of potential environmental impacts; 4) facility design to minimize impacts; 5) submittal of permit applications and management plans; 6) Wisconsin Department of Natural Resources (WDNR) review; 7) public comment; and 8) a contested case hearing. Typically, four to five years (or longer) is required to complete the aforementioned process prior to the granting of permits allowing the operation of a mining facility. The WDNR granted eleven permits to Flambeau during January 1991. Flambeau's permits are listed below: • • • • Mine Permit Wisconsin Pollutant Discharge Elimination System (WPDES) Permit Air Pollution Control Permit Groundwater Withdrawal Permit �96 • • • Permit for a One-Time Disposal Facility Water Regulatory Permits (five individual permits) Approval for the Wastewater Treatment Facility In addition, numerous management plans, studies and models were submitted to the WDNR which detailed the measures to be taken to protect the environment. These management pians were incorporated by reference into Flambeau's permits. STUDIES AND MODELS Waste Rock Characterization Several studies were performed and models developed prior to the final design of the Flambeau site facilities. One of the primary considerations was characterization of the various waste rock products. Characterization of waste rock determines: 1) the best practices for temporary stockpiling; 2) methods of water treatment prior to discharge to the Flambeau River; 3) preferred methods of backfilling the open pit; and 4) prediction of groundwater quality down gradient from the backfilled pit. Waste rock characterization studies included both static and kinetic geochemical tests performed in a laboratory on samples which had been collected during core drilling of the orebody and surrounding waste rock. The static tests included bulk chemical analyses for all potential mine waste and acid production and neutralization tests on the waste rock composites. The kinetic tests included wet-dry leaching tests which simulated the conditions under which the waste rock would be temporarily stored. The wet-dry leaching tests were followed by saturated leaching tests which simulated conditions within the backfilled pit. The results of the wet-dry leaching tests determined that waste rock containing less than two percent sulfur had a very low acid-producing potential. The low sulfur waste rock can be temporarily stockpiled without an underlying liner system since there is minimal potential impact to groundwater quality. Likewise, the waste rock containing high sulfur (>2%) is required to be temporarily stored on a high density polyethylene liner (HDPE) and leachate collection system since these materials have the potential to produce acidic leachate. Flambeau chose to add an additional factor of protection by restricting the waste rock placed in the unlined stockpile to that containing less than one percent sulfur. Waste rock containing less than one percent sulfur is referred to as Type I material. Type II material is that waste rock containing one percent or greater sulfur content. Water Treatment Methods The waste characterization also determined the appropriate treatment methods for water contacting each waste rock type. Water which contacts the Type II waste rock must be treated through Flambeau's onsite Wastewater Treatment Plant (WWTP). The types of water treated are groundwater, storm water and snow melt runoff that discharge into the open pit and leachate from the Type II stockpile. The WWTP operation is discussed in detail in a following section. The Type II stockpile was anticipated to generate acidic leachate shortly after stockpiling was initiated. Following two years of stockpiling, the Type II stockpile has recently begun to generate a lower pH leachate of approximately 6 standard units (s.u.). This pH is still significantly higher than the leachate studies predicted. These studies resulted in a model predicting the leachate to have a pH of 2.95 - 4.10 s.u. Water contacting Type I wasterock requires minimal treatment. This treatment includes two settling �97 ponds designed to contain in excess of a 25-year storm event. Intermittent discharges from the settling ponds were anticipated during spring, summer, and fall; however, the storm water runoff has infiltrated into the open pit rather than requiring discharge. Pit Backfill The laboratory testing of the two types of waste rock helped determine the most appropriate methods of backfihling the pit. The waste rock will be returned to the pit in the following order, bottom to top: 1) Type II waste rock; 2) Type I waste rock; 3) saprolite; 4) sandstone; 5) till; and finally 6) topsoil. Each material type is segregated as mined from the pit to allow for a sequential backfill. The saturated leaching tests indicated the potential for leachate to contain substances from the Type II waste rock. Four parameters (copper, iron, manganese and sulfate) were predicted to be found in measurable concentrations in the groundwater emanating from the Type II waste rock in the reclaimed pit. Further testing showed that the addition of lime significantly reduced the concentration of some substances within the leachate. As a result, lime will be backfilled with the Type II waste rock at the rate of 2.5 pounds lime for each ton waste rock. The impact of these four parameters is minimal to the Flambeau River. Based upon a mean river flow of 1, 855 cubic feet per second and predicted groundwater flow into the river from the waste rock zone of 0.0045 cubic feet per second, the incremental increase in river concentrations would be: • • • • Copper - 0.000000034 mg/l Manganese - 0.0000013 mg/i Iron - 0.00000078 mg/l Sulfate - 0.0033 mg/i. The predicted increase in river concentrations will be below analytical detection limits. It is evident that there will be minimal, actually undetectable, impact upon the Flambeau River associated with materials backfilled within the pit. Groundwater Drawdown Model Another study performed is the model of the predicted groundwater drawdown contour and potential impacts upon private wells. Five private wells are known to be located within the maximum extent of drawdown which has been modelled to extend 2750 feet from the edge of the mine pit. Four of the wells will not be significantly impacted, while the fifth well could be impacted by a predicted eight foot drop in water elevation. The potential effects upon the five wells are considered within the Local Agreement that Flambeau signed with the local government entities. If wells are impacted by mining activities, Flambeau will provide water or replace the wells. To date, water supply to local wells has not been significantly impacted and property owners are convinced that the palatability of their water supply has improved. OPERATION PHASE The studies and models previously mentioned provided Flambeau the knowledge to use modern technology and a pro-active environmental commitment in the construction of an environmentally safe facility. Flambeau has constructed and is operating a facility that is a model of modern mining technology, engineering and science, providing superior environmental protection. Environmental safeguards include the treatment of all contact water, suppression of dust, erosion �98 control, on-site spill prevention programs and an extensive monitoring program that ensures that the environmental safeguards work as they were designed and approved by the WDNR. Wastewater Treatment Plant The WWTP is a key component of Flambeau's protection of groundwater and surface water in its commitment to conducting environmentally responsible mining. Sources of contact water include mine seepage, precipitation into the open pit and storm water run-off from the lined Type II stockpile and the lined crusher/loader areas. The WWTP design allows for pH neutralization and metal removal in a three-stage process consisting of lime treatment, sulfide precipitation and multi-media filtration (Figure 1). The WWTP design capacity of 800 gpm is more than adequate to handle normal conditions. The open pit acts as an ultimate sump during extreme storm events. Mine seepage and precipitation require an average pumping rate of approximately 225 gpm throughout the year. The WWTP incorporates scientific treatment processes with advanced computer technology through its control system, a General Electric LM 90-70 Series Programmable Logic Controller. Flambeau's WWTP operators, certified by the state use knowledge, experience and the control system to ensure optimum treatment and compliance with stringent effluent limitations. Flambeau began operation of the WWTP on March 15, 1993 and to date over 340 millions gallons of high quality effluent has been discharged into the Flambeau River. FLAMBEAU MINING COMPANY WASTEWATER TREATMENT PROCESS PaYUER PRECJPT*TI rL1RA1Y TRELT() AT(R Figure 1. Flambeau's Wastewater Treatment Plant Schematic �99 Flambeau's WPDES permit was issued during January 1991 and defines the limitations under which the WWTP must operate. The WPDES permit contains categorical and water quality-based chemical specific limitations. The Wisconsin Administrative Code in NR809.541 places a copper action limit of 1300 ugh as compared to Flambeau's WPDES permit limit of 50 ugh for copper. A representation of the stringent limitations and Flambeau's effluent long-term average concentrations are listed in Table 1. WWTP effluent has fully complied with all WPDES permit categorical and water quality-based chemical specific limitations during some extreme operational periods that included a 100-year flood event on September 15, 1994. Table 1. SUMMARY OF FLAMBEAU'S WPDES PERMIT LIMITATIONS AND EFFLUENT LONG-TERM AVERAGE CONCENTRATIONS. Cadmium Chromium Copper Lead Silver Zinc Daily Maximum Limit (ugh) 79.8 5400 50 590 6.6 300 Weekly Average Limit (ugh!) 7.1 980 — — 140 Effluent Long-Term Average (ug/l) 0.02 <10 8.9 0.35 0.09 11 Flambeau has an on-site laboratory with a 4100 atomic absorption graphite furnace that provides the resources to monitor the WWTP and make minor treatment adjustments to optimize its efficiency. Flambeau's on-site laboratory also allows WWTP effluent to be tested prior to discharge to the Flambeau River ensuring full compliance with chemical specific limitations. An internal limit of 25 ug/l for copper, equal to one-half the permit limitation, has been established by Flambeau to be used as a guideline for discharge criteria. If the on-site laboratory results are not less than one-half the permit limit, the WWTP effluent is discharged to the runoff pond and retreated through the WWTP until it meets this criteria. Flambeau monitors the WWTP process a minimum of every two hours to ensure that the proper adjustments are made for optimum treatment. Whole effluent toxicity (WET) testing is also required by the WPDES permit. Flambeau's effluent is subject to chronic WET testing using Ceriodaphnia dubia (C. dubia), a water flea, and Pimepliales promelas (P. promelas), fathead minnow, as test species. Flambeau's chronic WET is based upon reproduction (C. dubia) and weight gain (P. promelas). Acute WET testing is also required using C. dubia and P. promelas as test species and is based upon mortality within 100 percent effluent. Acute toxicity tests have shown only one of the two test species, C. dubia, to be sensitive in undiluted effluent. Two acute toxicity tests using C. dubia as the test species resulted in a mortality rate greater than 50 percent which represents a positive acute toxicity. These two positive acute toxicity tests occurred within a twelve month period requiring Flambeau to complete a toxicity reduction evaluation (TRE) as prescribed by Flambeau's WPDES permit. �100 Flambeau conducted a TRE during the period December 1993 through January 1995. Trace-metal copper within Flambeau's WWTP effluent was determined to acutely effect the test species C. dubia at concentrations that were substantially below Flambeau's permit limitation of 50 ug/L copper. Research toxicity testing was performed to evaluate the relationship that hardness and organic compounds have upon acute toxicity in Flambeau's effluent. The addition of an organic chelating agent into Flambeau's effluent was found to provide effective and consistent reduction of acute toxicity. Citric acid was selected to provide the citrate ion which greatly reduced copper bioavailability within the effluent. Following approval from the WDNR, Flambeau implemented the use of citric acid within its treatment process reducing trace-metal copper toxicity to C. dubia. In October 1995 Flambeau presented its TRE as a case study at the 68th annual Water Environment Federation Conference held in Miami Beach, Florida. Stockpile Monitoring The Type I stockpile is equipped with a collection lysimeter used to determine the characteristics of the exfiltrate. The lysimeter is sampled on a quarterly basis for a variety of parameters. Type I exfiltrate analyses to date have shown pH values in the range of 5.9-6.8 s.u. which are comparable to shallow well samples as was predicted in the waste rock characterization studies. The Type II stockpile is lined with an HDPE liner and a collection system made up of polyvinyl chloride leachate lines. All runoff and exfiltrate is contained within the system and gravity flows into the surge pond. This contact water is then treated through the WWTP as previously discussed. The integrity of the Type II system is confirmed through annual inspections. The series of pipes between the Type II stockpile and the surge pond are camera inspected. The leachate line system below the stockpile responsible for the collection of the leachate is also assessed. Flambeau River Monitoring The Flambeau River is monitored through an extensive program that further ensures the discharged effluent does not impact the quality of the river. Figure 2 shows the locations of all the Flambeau River sample points. The monitoring program began as part of the environmental studies supporting the initial permitting process. River samples were collected from sample points located upstream from the mine area as well as downstream. The collection of background water quality data was conducted once a month from October 1987 through September 1988. As required by Flambeau's mining permit, Flambeau again commenced conducting similar surface water quality monitoring on a quarterly basis. This surface water quality monitoring consists of samples being collected at SW-i (upstream from the mine area) and samples being collected at SW-2 (downstream from the mine site within the mixing zone of the WWTP effluent). Over 20 water quality analyses are conducted on each collected sample. The Flambeau River monitoring program to date, has shown no significant difference in the upstream samples as compared to the downstream samples. Flambeau's environmental monitoring of the Flambeau River includes sampling river sediment. Flambeau River sediment analysis began in 1988 with the collection of sediment samples to establish a point of reference for background concentrations of selected chemical parameters. This list of chemical parameters include arsenic, beryllium, cadmium, chromium, mercury and nickel. Sediment sampling has been conducted throughout the operation phase of the mine on an annual basis. �F—i 'ZD M—l S—i c SW—i AIR MONITOR SITE SAMPLING LOCATIONS FOR MACRO— INVERTEBRATES SAMPLING LOCATIONS FOR SEDIMENTS SAMPLING LOCATIONS FOR SAMPLING LOCATIONS FOR SURFACE WATER SAMPLES Figure 2 Flambeau River Monitor Locations and Air Monitor Locations. PORT ARTHUR 0 .5 ScaIe 1.0 Miles �102 Collection of walleye on the Flambeau River is an annual monitoring event conducted by Flambeau. During the low flow period of the year various sizes of fish are collected at an upstream site (Ladysmith Flowage) and at a downstream site (rhornapple Flowage). Fillets with skin left on are tested for total mercury. The livers of fish collected at each sample site are composited and analyzed for an extensive list of parameters. Fish surveys were initiated during the Fall 1987. Flambeau has started conducting fish surveys annually again in 1991 with no significant differences in metal content of fish tissue sampled downstream of mine compared to upstream of the mine. Crayfish are collected annually from the Flambeau River at three sampling locations for metal analyses. Whole bodies are used for analysis and the results represent a composite for all crayfish collected per site. Flambeau has conducted crayfish surveys annually starting in 1991 with no significant differences in metal content of fish tissues sampled downstream of mine compared to upstream of the mine. Groundwater Monitoring Flambeau regularly monitors groundwater quality to ensure that the environmental protection measures work as they were designed. Collection of groundwater data began in the 1970s as baseline groundwater quality and groundwater flows were evaluated. The collection of groundwater data has continued through the construction phase and into the operational phase. Groundwater elevations are determined weekly at numerous wells strategically located around the perimeter of the open pit. The collection of this data allows for the interpretation of the groundwater drawdown in the area surrounding the open pit. Figure 3 shows the locations of the groundwater monitoring wells. The data collected indicates the groundwater drawdown is similar to that predicted in the groundwater drawdown model previously discussed. Groundwater quality data is collected quarterly at eleven different monitoring wells strategically placed up gradient and down gradient from the open pit. Groundwater samples are evaluated based on twelve different parameters, which are copper, manganese, pH, conductivity, hardness, sulfate iron, alkalinity, total dissolved solids, color, odor and turbidity. Quarterly groundwater monitoring has indicated no adverse impact upon the area groundwater supply during mining. An extensive, long-term groundwater monitoring program will continue after the completion of the operational and reclamation phase of mining. The monitoring program will include a dynamic monitoring schedule for monitoring wells up gradient and down gradient of the reclaimed open pit. Two monitoring well nests will be established inside the backfilled pit following the completion of the reclamation construction activities. Each well nest will consist of two wells which will be sampled similarly to the previously established monitoring wells. Wetland Monitoring Water level gauges were placed in five separate wetlands outside the parameter of the mine site, but within one mile of the perimeter fence. Figure 3 shows the locations of the wetland staff gauges which are recorded monthly. If staff gauge readings as well as visual inspections of wetlands indicate a need for wetland mitigation, Flambeau will mitigate the wetlands by the addition of water. The monthly staff gauge readings will continue until the pit is backfilled. The data will then be compared to preconstruction levels and recent precipitation history for the region resulting in an established long-term and maintenance monitoring schedule. �0 MW—100SP MONITORING WELL LOCATION WETLAND STAFF GAUGE MW— 1002 MW—i 002G o ——— 0 SCALE500 DWT-2 Jansen Rod = = = = = = = = MW—100SP MW—1005 MW—1005S Figure 3 Groundwater Monitoring Well Locations and Wetland Staff Gauges Ancillary Facilites Low Sulfur Waste Rock Stockplie FEET 1000 I �104 Ambient Air Monitoring Particulate matter in the ambient air generated by mine operations is suppressed by the use of WWTP effluent and monitored by four high-volume air samplers. Figure 2 shows the four sampling site locations. The four sampling site locations were based on USEPA siting criteria and are calibrated on a quarterly basis. The instruments are audited at least on an annual basis by the WDNR. Each monitor operates for 24 consecutive hours starting at midnight. During the preproduction phase each monitor operated once every three days. During the mining phase, each monitor was operated once every other day. Since Flambeau had not exceeded its Total Suspended Particulates (FSP) secondary standard of 150 ug/m3 following one year of mining, the sampling schedule was reduced to once every six days. Each filter from the TSP monitors is retained with a portion of each filter being composited for a three month period. These composites are analyzed for arsenic, chromium, nickel, beryllium, cadmium and mercury. Analyses of the filter composites have resulted in very low to non-detectable cOncentrations of these metals. Asbestiform monitoring is another component of Flambeau's air quality monitoring program. Asbestiform monitoring was conducted monthly from May through September during the years 1993 through 1995. Asbestiform monitoring during the first three years of active mining indicated that no asbestiform fibers were generated from the mining operations. As a result, Flambeau is no longer required to monitor for asbestiform fibers. Meteorological data is obtained from Flambeau's Meteorological Station located south of the mine site. The meteorological station continuously collects information on the precipitation, temperature and wind speeds and wind direction. This information is submitted with the air monitoring data to the WDNR. RECLAMATION AND LONG-TERM CARE The reclamation of the mine site includes backfilling the open pit and returning the site to a topography which approximates the original contours. Following establishment of final contours, reclamation includes wetland construction, topsoil, vegetative stabilization, tree planting, and longterm care and maintenance. Wetlands Construction Prior to site construction, wetland delineation had identified 8.3 acres of low to medium quality wetlands which would be disturbed. The disturbed wetlands are required to be replaced. The hydric soils from the disturbed wetlands were stockpiled to be used during wetland construction. During Fall 1991, Flambeau constructed a one-acre wetland referred to as the aquascape in the northeast corner of the property. The aquascape varies from a sedge meadow to open water which allows for a range of wetland species as does the hydric soil stockpile. The aquascape not only serves to replace one acre of disturbed wetland area, but also provides information to be used for the construction of the remaining wetland area. The aquascape has been assessed on an annual basis since 1992. The aquascape has become a stable wetland area which supports a diversity of wetland species. The aquascape was originally established with both plants and seeds. Over the past four years species diversification has dramatically increased. Several species which had been seeded remained dormant and have become �105 evident in only the last year. The 1995 assessment has shown an increase in diversification by seven species compared to the previous year. Topsoil Stabilization Approximately 220,000 cubic yards of stockpiled topsoil were placed between the east end of the mine and Highway 27 and will be replaced on the mine site following backfihling and contouring. The topsoil will be stabilized with a vegetative cover consisting of native prairie grasses and wild flowers with a nurse crop of oats. Additional erosion control features including straw bales, silt fence, and mulch will be utilized. The species of wild flowers and grasses to be used during final reclamation has not been definitively determined at this time. The species of wild flowers and grasses will be selected based upon studies performed on the prairie seed test plots. Prairie seed test plots were established on the mine site during 1993. The test plots are located on the mine site north of the Type I stockpile and south of the open pit. A total of 196 test quadrants were defined which consider the following test variables: 1) type of fertilizer; 2) type of mulch; 3) mowing; and 4) type of seed mix. The annual assessments show the progression from exotic species to desirable native species. The information gathered from the prairie seed test plot annual assessments will be utilized to select the best methods for establishment of native species for stabilization. Tree Planting During 1991 the WDNR and Flambeau selected trees from the mine site to be transplanted to a temporary nursery located north of the Type I stockpile. The tree selection was primarily based upon the WDNR approved tree species and appropriate tree size. Trees which would grow too large before transplanting would have a low survival rate when replaced to the mine site, and were therefore not selected for placement in the temporary nursery. Additionally, Flambeau has planted nursery stock tree seedlings into the temporary nursery during 1993 and 1995. The tree seedlings have provided information on survival rates of specific species. Also, the management of the seedlings has established procedures which will be implemented during the planting of approximately 14,000 seedlings at the time of final reclamation. Long-Term Care and Maintenance Flambeau will be responsible for the reclaimed mine site in perpetuity with a minimum long-term care and maintenance period of 40 years. Long-term care will initiate when final site grading and revegetation have been completed. Long-term care and maintenance will include inspections of the site, maintenance of land forms, vegetation and monitoring devices, and monitoring groundwater, surface water, vegetation and terrestrial ecology. The long-term care period monitoring plan is shown in Table 2. �106 Table 2. SUMMARY OF FLAMBEAU' LONG-TERM CARE PERIOD MONITORING PLAN. Event Site Inspections Year 1-4 5-40 Groundwater Monitoring Perimeter Wells Backfilled Pit Wells 1-40 2-4 5-7 8-40 Frequency Semi-annual Annual Quarterly Quarterly Annually Every 5 years Sediment, Crayfish & Fish 1-2 Annually River Water Quality 1-2 Annually Wetland Surface Flows 1-10 Spring, Summer, Fall Vegetation Assessment 1-6 Annually Terrestrial Ecology 1-4 Annually Every 5 years 5-40 CONCLUSION Flambeau's commitment to environmental protection goes beyond permit compliance. Respect for the environment is a personal commitment for every employee at the Flambeau Mine. This continued commitment is evident with the successful operation of this environmentally responsible mine. Flambeau's use of modern technology and personal creativity provides the environmental protection criteria which may serve as a benchmark for the mining industry. �107 EISENBREY: A STRUCTURALLY COMPLEX PROTEROZOIC COPPER-ZINC MASSIVE SULFIDE DEPOSIT, RUSK COUNTY, WISCONSIN by Edwarde R. May Consulting Mining Geologist Littleton, Colorado INTRODUCTION The discovery of the Flambeau copper-gold massive sulfide deposit in late 1968 (May and Dinkowitz, 1996) rapidly expanded Kennecott's search for satellite deposits. The search was immediately conducted along strike of the Flambeau discovery and soon expanded to cover all airborne electromagnetic (EM) anomalies within the Glen Flora airborne survey selected for review and ground follow up (Babcock, 1996). Ned Eisenbrey recalled a rusty, wealdy mineralized iron formation outcrop located by Bill Spence in 1967 along the bank of the Thornapple River about 7 miles northwest of Flambeau. A weak airborne EM conductor detected in the area of the outcrop was not encouraging since a farm and railroad bridge were located on either side of the strike extension of the outcrop to which the anomaly was attributed. Eisenbrey, nevertheless decided to drill the weakly copper-zinc-silver anomalous exposure in 1970 over the doubts and objections of most of his colleagues. The first drill hole encountered a 14.6-foot interval within an iron formation that averaged 477 ppm Cu, 2400 ppm Zn, and 422 ppm Pb. The second hole was collared 350 feet to the west and resulted in the discovery of the Thornapple deposit. This hole intersected 5.9 feet true width of massive sulfides that averaged 0.44% Cu, 1.36% Zn, 0.02 opt Au, and 0.29 opt Ag. The Thornapple deposit was, therefore, a geological discovery; ground geophysics were conducted over the deposit after its discovery. Ground magnetics were run in 1970 and 1971 to trace pyrrhotite and iron formation mineralization, and one line of gravity was conducted at the same time over the thickest portion of the deposit. A development team took over the project in 1971 after Ned and Bob Stuart had completed ten holes, six of which intersected mineralization. Unlike Flambeau, no significant supergene mineralization was encountered. The project was shelved in 1974 due to falling copper prices; however, land was purchased by Kennecott to cover the deposit and any potential strike extension. A total of 40 holes had been drilled by 1974 to an average depth of about 500 feet below surface. A complex, isoclinally folded, eastward plunging, thin multi-lensed deposit was partially defined consisting of zoned bodies of pyrrhotite-chalcopyrite and pyrite-sphalerite mineralization. The resource was estimated to be 1.6 million tons of 1.3% Cu, 0.06% Zn, 0.007 opt Au, and 0.20 opt Ag, and 700,000 tons averaging 0.35% Cu, 4.10% Zn, 0.02 opt Au, and 0.4 opt Ag. While initial results were disappointing, the deposit was not thoroughly drilled and was open to depth. The Thornapple deposit was renamed Eisenbrey in 1994 to honor the significant contributions made by Ned Eisenbrey to Wisconsin economic geology. In the same year, Flambeau Mining Company, a wholly owned subsidiary of Kennecott Minerals, decided to test the deposit to depth. A gravity survey was conducted to verify that the deposit was indeed plunging steeply to the east. To everyone's astonishment, a large anomaly was recognized that could not be explained by the shallow, thin sulfide intercepts cored by previous drilling campaigns. Eight holes drilled in 1994-1995 confirmed the presence of a large, near vertically dipping and plunging, complexly folded deposit. Resource estimates to depths in excess of 3000 feet indicate the presence of 50,000,000 to possibly �108 100,000,000 tons of low-grade copper-zinc mineralization in which copper and gold values are erratic and zinc values consistently low. LOCATION The Eisenbrey deposit is easily reached via paved roads commencing at the intersection of Highways 8 and 27 in Ladysmith. Drive north on Highway 27 four miles to the junction with County Road A. Proceed west on County A for a distance of two miles then north 'on Bass Lake Road for 1.75 miles to the 514.5-acre project site which is east of the Flambeau township road (Figure 1). The Thornapple River bisects the west one third of the site and is entrenched 50 feet within glacial outwash. The Wisconsin Central Railroad also cuts across the site and river in a southeasterly direction. The project site is essentially flat, has an elevation of about 1160 feet, and is covered east of the river by highland mixed deciduous forest. West of the river the site is covered by old meadows and woods. GENERAL GEOLOGY OF NORTHERN WISCONSIN At least 13 volcanogenic massive sulfide deposits have been discovered within Early Proterozoic greenstone rocks of northern Wisconsin (DeMatties, 1994). The Ladysmith-Rhinelander metavolcanic belt within the Pembine-Wausau Subterrane, which strikes across the state for a distance of 150 miles, is the host rock for this mineralization. These 1.86 to 1.88 billion year old rocks consist of mafic metavolcanics, gabbroic sills, lesser amounts of felsic metavolcanics, and some cherty iron formations. The Ladysmith-Rhinelander metavolcanic belt clearly shows on regional airborne gravity and magnetic reconnaissance maps of northern Wisconsin as an anomalous linear feature. North of the Ladysmith-Rhinelander belt are rocks that form a thick platformal turbidite sequence of clastic and chemical metasedimentary rocks including major iron formations. The Niagara Fault separates the Northern Penokean Terrane of continental margin assemblages from the Pembine-Wausau Subterrane (Figure 2). The paper by G. LaBerge in this volume shows the location of these subterranes. South of the Ladysmith-Rhinelander belt are rocks of the Wausau and Marshfield Complexes. The Eau Pleine Shear separates the Marshfield Subterrane from the Pembine-Wausau Subterrane (LaBerge, 1996). The Marshfield Subterrane is characterized by Archean gneisses and 1.86 billion year old metavolcanic rocks and granitoids. The Wausau Volcanic Complex consists of 1.88 billion year old amphibolite facies rocks unconformably overlain by 1.84 billion year old intermediate to felsic metavolcanics. Intruding the Wausau volcanic complex are anorogenic igneous rocks, 1.47 to 1.51 billion year old, the largest of which is the Wolf River Batholith. DeMatties and LaBerge more fully discuss these subterranes and the Wausau Volcanic Complex in this volume. Paleozoic sediments onlap the southern portions of the Southern Superior Province of the Precambrian Canadian Shield. SITE GEOLOGY Glacial outwash covers the entire site to a vertical depth of about 50 to 60 feet into which the Thornapple River has entrenched itself to expose Precambrian bedrock. Outcroppings of Precambrian metasedimentary, metavolcaniclastic, and igneous rocks occur on either side of the Wisconsin Central Railroad bridge (Figure 3). �0 S. HAND DUG WELL PROTEROZOIC OUTCROP LEGEND "V Figure 1 Location of Massive Sulfide Deposits and Chief Outcrops. Rusk County, Wisconsin EISENBREY DEPOSIT SCALE I 1 6.5 MILES HA WK IN S �0 MINNESOTA LEGEND PALEOZOIC [-€J CAMBRIAN SANDSTONE FLAMBEAU MINE CRANDON DEVELOPMENT SCALE20 0 10 1"4O EISENBREY DEPOSIT Figure 2 Generalized Geology of Northern Wisconsin (Modified after Morey, Sims, Cannon, Mudrey, Southwich, 1982) 40 MILES �IRON FORMATION EAST LENS MAFIC TUFFS SILICIFIED INTERMEDIATE TUFFS INTERMEDIATE TUFFS LIII MASSIVE SULFIDES LI1 PRECAMBRIAN PROTEROZOIC DIABASE KEWEENAWAN LEGEND .1 Rusk County, Wisconsin Figure 3 Thornapple River Outcrops, Eisenbrey Prospect. GEOCHEMLCAL SAMPLE AND SAMPLE NUMSER — FAULT -> OUTCROP INFERRED GEOLOGIC CONTACT — GEOLOGIC CONTACT 0 1" =50' SCALE25 50 FEET �112 Upstream of the bridge a distance of about 0.25 mile is an outcrop of a Keweenawan diabase dike. Downstream and immediately east of the bridge are outcroppings of another dike that cuts across intermediate tuffs and graywackes. These highly regionally-metamorphosed and silicified rocks contain thin units of mafic tuffs that show very tight isoclinal folding with a near vertical plunge. West of the bridge is a mafic tuff (amphibolite schist) that contains a rusty and broken iron formation. The upstream iron formation is in a fold nose and the formation does not strike beneath the river. Instead it is interpreted to be folded back upon itself to reemerge further downstream (field observations by P. Lindberg, Aug. 1995). The second outcropping of iron formation strikes west across the river and is interpreted to be the ore horizon for the Eisenbrey deposit. Volcaniclastic and graywacke rocks of intermediate composition occur between the mafic tuff and pyroxenite downstream. The pyroxenite is interpreted to be part of a gabbro sill with a chilled margin in sharp contact with the host sediments. The sill occupies the center of syncline that hosts the Eisenbrey deposit. Four zones within the outcrop were sampled and geochemically analyzed. It was these geochemical results and rock exposures upon which the Eisenbrey drilling was founded. The geochemical results are shown in Table 1. TABLE 1 GEOCHEMICAL RESULTS FROM THE EISENBREY OUTCROPS EISENBREY DEPOSIT, RUSK COUNTY, WISCONSIN Sample Number 1 2 3 4 Copper % Cu 0.03 0.03 0.04 0.06 Zinc % Zn 0.03 0.05 0.17 0.20 Gold opt Au trace 0.003 0.010 0.002 Silver opt Ag trace 0.1 0.3 0.1 GEOPHYSICAL SURVEYS The Eisenbrey project site was flown for Kennecott in 1969 as part of the Glen Flora airborne survey, and a weak EM anomaly was recorded west of the Wisconsin Central railroad bridge. A ground check, however, found a power line and railroad bridge coincidental with the EM conductor; therefore, it was discounted as culture. A large magnetic response was also recorded with the EM conductor, but this anomaly was attributed to the bridge. Ned Eisenbrey was not convinced the response was entirely the result of culture and was determined to drill the outcrop even though the iron formation did not fit the "Noranda" model being used by the company while exploring Wisconsin. No ground geophysical work was done until after base-metal anomalous massive pyrite and pyrrhotite mineralization had been drilled. Ground geophysics conducted after the discovery consisted of magnetic and gravity surveys. The gravity survey, however, consisted only of one north-south line run over the nose of the fold that contained most of the Eisenbrey mineralization. Ground magnetics were also run on north-south lines spaced from 50 to 200 feet apart with the closer spaced lines over mineralization. Readings were taken on 50 or 100 foot intervals over an area that eventually covered approximately five square �113 miles and surrounded the deposit. This survey was useful in helping decipher bedrock structure and in locating suspected iron formations and one thin pyrrhotite lens. A complex magnetic anomaly shown in (Figure 4) was observed over an east-west strike length of 1750 feet by 700 feet north-south. Drilling confirms that the large east-west elliptical response of up to 8000 gammas on the west end is coincident with the pyrrhotite-chalcopyrite fold nose of the Eisenbrey deposit. An iron formation occurs to the southeast and accounts for a northeast striking response that peaks at 12000 gammas. Near the center of the anomaly is an unexplained northwest striking response peaking at 4800 gammas. A ground gravity survey recommended by Paul Schmidt was conducted in 1994 before commencement of deep drilling (Figure 5). The purpose of the survey was to confirm that the interpreted steeply east plunging deposit was true. This survey did indeed suggest a very steeply dipping and plunging deposit, but the size and magnitude of the anomaly was much larger than expected and could not be explained by sulfides encountered in the previous shallow drilling. GENERAL GEOLOGY The Eisenbrey deposit is hosted within a thick pile of interbedded intermediated tuffs, lapilli tuffs and graywackes which have been regionally metamorphosed and folded. These Proterozoic volcaniclastic and sedimentary rocks form the platform into which younger mineralized and altered rocks were deposited. On the flanks of the massive sulfide mineralization are magnetite iron formations with weak base metal mineralization. Closer to the suspected center of "ore"/sulfide deposition the host rock is interpreted to be a dirty chert and volcanic rock altered to anthophyllite, cordierite, and magnetite with associated mafic tuffs. Minor rhyolite flows have been recognized, but do not appear to play a significant role in the formation or hosting of sulfide mineralization. A gabbro sill was emplaced after the mineralizing events and before folding. A series of Keweenawan diabase dikes were intruded after the Penokean Orogeny to cut across the property in a northeasterly direction. Approximately 60 feet of Pleistocene glacial outwash covers the project site except where the Thornapple River has exposed Proterozoic and Keweenawan aged rocks east of the deposit. GEOLOGY OF THE EISENBREY DEPOSIT Introduction. A brief geological description is presented below and is based upon core examinations, outcrop and some petrographic work conducted by Mary Jø Sweany in the 1970s. In general the rock descriptions commence with what are believed to be the oldest rock units through to Pleistocene Till. Intermediate Dacitic Tuff and Graywacke. The most abundant rock types within the footwall, upon which massive sulfide mineralization was later deposited, consist of dacite tuffs, lapilli tuffs, and graywackes (Figure 6). Petrographic analyses of core samples repeatedly suggested the presence of graywacke. Graywacke, if present, is intercalated with thick sequences of dacitic lapilli tuffs all of which have been highly recrystallized by regional metamorphism. In general, these tuffaceous and sedimentary rocks have been metamorphosed to a finegrained, sugary to granular mixture of plagioclase, biotite, amphibole, and minor amounts of garnet and quartz. Relict bedding is observed under the microscope and in the Thornapple outcrop where �Figure 4 1" = 300' i FEET 300 Eisenbrey Prospect. Rusk County, Wisconsin Magnetic Anomalies, 0 SCALE150 -—--1000--- GAMMAS LEGEND �Eisenbrey Prospect, Rusk County, Wisconsin Gravity Anomaly, Figure 5 LEGEND I �STRATIGRAPHIC TOP ANTICLINE SYNC LINE LAPILLI TUFFS, MAFIC TUFFS. INTERMEDIATE TUFFS, MASSIVE—SEMIMASSIVE SULFIDES IRON FORMATION PYROX EN lIE PRECAMBRIAN PROTEROZOIC LII1 KEWEENAWAN LEGEND Figure 6 Geology Plan Map 900—foot Elevation, Eisenbrey Prospect. Rusk County, Wisconsin WEST LENS 0 1=200' SCALE100 i FEET 200 �117 thin (1 to 2 inches) mafic ash beds have been isoclinally folded. Table 2 shows a strong similarity between Eisenbrey dacite tuffs and world wide average rhyolites (Nockolds, 1954). TABLE 2 A WHOLE ROCK ANALYTICAL COMPARISON BETWEEN EISENBREY DACITE TUFF AND RHYOLITE WITH WORLDWIDE AVERAGE RUSK COUNTY, WISCONSIN Oxide Mineralization Si02 A12O3 Fe203 and FeO MgO CaO Na20 1(20 Partial Totals Eisenbrey World'Mde Dacite luff Dacite Average 67.2 14.0 6.63 2.84 2.60 3.76 63.58 16.67 5.24 2.12 5.53 3.98 1.67 1.40 98.52 98.70 Eisenbrey Rhyolite 70.4 14.5 4.54 1.62. 2.34 2.38 2.84 98.60 Wotidwide Rhyolite Average 73.66 13.45 2.00 0.32 1.13 2.99 5.35 98.90 Dacite Lanilli tuffs. Lapilli tuffs are interbedded with intermediate composition tuffs and graywackes stratigraphically beneath the Eisenbrey deposit. Stratigraphic thicknesses range from a few feet up to 75 feet. Felsic to intermediate lapilli fragments are generally well preserved although collapsed and elongated due to regional deformation. The lapilli tuff fragments consist of biotite, plagioclase, quartz, and amphibole within a matrix of biotite and amphibole. Lapilli fragments range in size from less than 0.5 inch to over 4 inches in length by 0.2 to 0.5 inches in width. Intense deformation has elongated the fragments so that they now plunge nearly vertically. Occasional fragments contain 1 to 6% disseminated pyrrhotite, pyrite, chalcopyrite, and magnetite grains. The average mineral composition for the Eisenbrey dacite tuffs was obtained from 13 petrographic thin sections of core as shown on Table 3. These minerals consist of fine to coarse grains which have been metamorphosed into growths of subrounded to subangular grains. Minerals such as epidote and sericite are present in some examined rock thin sections. Opaque minerals consist of varying proportions of hornblende, garnet, sphene, and interstial clay generally kaolinite. Intrusion of the gabbro sill and strong regional metamorphism have severely baked the host rock and "sweated" quartz into the matrix of the dacite tuffs. The tuffs were misinterpreted by this author and previous geologists during the 1970's as a rhyolite dome. Major oxide geochemistry needs to be conducted to quantitatively determine original rock composition. Anthophyllite-Magnetite Ore Horizon. An anthophyllite-rich horizon is intimately associated with sulfide mineralization and is on strike of the iron formation outcrop (Figure 7). It is a distinctive rock consisting of sheaf-like bundles of radiating needles of anthophyllite within a fine grained, sugary, granular matrix of quartz, magnetite, antigorite, and cordierite. The anthophyllite rock could possibly represent the altered footwall rock containing the stockwork zone. The Eisenbrey deposit has undergone penetrative deformation so that the mineralization has been stretched into a vertically plunging pencil-shaped deposit. The underlying stockwork and footwall alteration zone appears to have been transposed to a position that is now in lateral conformity with the stretched sulfide body similar to that seen at Flin Flon and Snow Lake, �118 TABLE 3 MINERAL COMPOSITION PERCENTAGES OF VARIOUS EISENBREY ROCKS RUSK COUNTY, WISCONSIN Mineral Name Quartz Cordierite Plagioclase Anthophyllite Chlorite Antigorite Epidote Sericite Muscovite Carbonate Homblende Garnet Sphene Andalusite Clay Magnetite Opagues Totals Dacite Tuff 46 Anthophyllite Altered Rock Mafic 30 24 12 Tuff 10 16 19 7 10 6 12 1.5 10 1 3 1.5 8 3 2.5 48 7 2 2.5 5.5 6 2.5 99.5 2.5 100 3 99 Manitoba (Lydon, 1984). Lydon also reported major additions of magnesium and iron to the alteration pipe and surrounding rock at Fun Flon and Snow Lake as suggested by the presence of a cordierite-anthophyllite assemblage. The anthophyllite-magnetite rock at Eisenbrey is found on either side of the northwest fold nose, partially shown in Figure 6 (Section 5500E) and Figure 7 (Section 5850E) and is similar to observations reported by Lydon (1984). This strongly suggests the Eisenbrey deposit has been isoclinally folded with stratigraphic footwall occurring on either side on the northwest fold nose. Table 4 shows the mineralogy on either side of the fold nose based upon rock thin section studies. TABLE 4 ANTHOPHYLLITE-MAGNETITE ROCK MINERALOGY ON EITHER OF THE NORTHWEST FOLD NOSE, EISENBREY DEPOSIT, RUSK COUNTY, WISCONSIN Mineralogy Quartz Chlorite Sericite Anthophyllite Cordiente Andalusite Antigonte Magnetite Pyrrhotite Pynte Total North of Fold Nose South of Fold Nose % 35 7 3 15 30 2 0 6 % 25 6 0 25 20 0 20 2 I 100 100 �IJIIII • L 1000 ,j,:'/,,i ',/' IIii I I / / ,T—22 II1/ I ,1 ii / I / I II I 500 1 I 1—18 4c6 8/3 ' I / hj /1' /1/ / / / '14' /' I'/ I 1 / - I,, __L___ Ii/,"—/4c II / II! II ,/ 11/ I I ,'/ I III I 3/8k r I I I Ij' III I /jI''I 4 III II II I ti, 'Ix 4c!! I / j / 'II —500 / ' I/S / / / / I I I ii (// II I 1 I I I I I j / I I I ! I I INTERMEDIATE TUFFS LAPILLI TUFF L1 RHYOLITE—RI-IYOIJTE I, I QUARTZ—SERICITE SCI-IIST l I' ' I /4 II / I SYNCLINE P I 'I I 'I \T II 1318/f / 'III Ii 6a ii I I I I I ALTERED ROCK — l/i II I ANTHOPHYLLITE—MAGNETITE 8 II I I I MASSIVE SULFIDES 4 !j I II I I I I PRECAMBRAIN PROTEROZOIC I '8/"'III I I TILL jI I, I I / I I I PLEISTOCENE 3/I / I II I I I I KEWEENAWAN [] DIABASE DIKE & SILL I I 1 LEGEND //II I I iii", ii II I I III, I/Il I/Il I,,! III jI I I I HII II I! I IJ /1 I I j I ,i, I, I, II I II 8/4,I I /1/Il —1000 I I I '4c HI'6',' II 4 I / /// III Ill /111, / // // / / I I I '5; 6a1_JLIf 1/ i, I I JT—4 / I, I H, (6//I I /j3 / 1//3d' 54, —.4—— 51T, 4 11 i7',, I 40 I I , '18 —1500 I / z QI 0 0! I 0 'I h/ ii' 'ii z 3,',! I II ' 4 6a E—45 0 0 Figure 7 Geological Cross Section 5850E, Eisenbrey Prospect. Rusk County, Wisconsin 300 FEET 1" =300' Iz 1/ 150 SCALE i z 0 0 0 U, �120 Another distinguishing mineral is magnetite that occurs as euhedral grains up to 0.2 inch octahedrons. Magnetite content ranges from one to 15% and generally occurs within a granular mixture of quartz, cordierite, plagioclase, minor garnet, and an unknown clove-brown silicate mineral, possibly grunerite. Immediately west of the south syncline the mineral content and texture of the ore horizon changes dramatically. The matrix is massive chlorite containing 8 to 15% magnetite as octahedral crystals up to 0.25 inch in diameter. Light gray patches or poikiloblasts of quartz, cordierite, plagioclase, and smaller magnetite crystals also occur within the chlorite matrix. These irregular intergrowths make up approximately 35% of the rock volume. Sulfide mineralization is generally low and makes up less than 2 to 5% of the rock volume. It is possible that this chlorite-magnetite horizon could represent the center of a feeder pipe that supplied mineralization to the Eisenbrey depositional basin. Metachert. A few thin impure metachert horizons have been recognized in the core. Generally the metachert is closely associated with or incorporated within the above anthophyllitemagnetite horizon. The metachert has a distinctive sugary texture made up of recrystallized quartz and impurities consisting of minor amounts of plagioclase and ferromagnesian minerals. Occasionally, very fine bedding, characteristic of chert horizons reported at other deposits, has been observed in the Eisenbrey core. Magnetite and sulfide minerals are uncommon and generally average less than 5% of the rock volume. Rhyolite. A rhyolite dome had been interpreted by previous geologists to have been intruded in the footwall beneath the east end of the 4eposit and outcrops east of the railroad bridge. Petrographic studies have indicated, however, that the rhyolite is a hard, dense almost baked dacite tuff or greywacke. Quartz content usually ranges from about 45 to 55% and averages 46%, as shown on Table 3. A few thin rhyolite flows have been recognized and are distinguished by being extremely hard, and composed of a fine-grained to aphanitic groundmass with occasional (5%) phenocrysts of feldspar. A partial whole rock chemical analyses of a couple of rhyolite flows are averaged and included in Table 2. Mafic Tuffs. Mafic tuffs are intimately associated with massive sulfide mineralization as thin beds flanking or within the sulfides. Table 3 shows that the mafic tuffs are rich in amphibole and chlorite. The rock is usually fine-grained, and well-foliated with indistinct lapilli fragments, and occurs as thin beds less than 20-feet thick. Thin beds of predominantly ferromagnesian minerals are intercalated with much thicker beds of massive sulfides. One sample taken within the northwest fold nose was petrographically examined and found to contain chlorite (5%), anhydrite (15%), gypsum (20%), serpentine (possibly antigorite after olivine) (10%), dolomite (10 to 15%), calcite (3 to 5%), magnetite (15 to 20%), and pyrite (15%). The amount of gypsum and anhydrite varies considerably throughout the rock. Likewise serpentine is irregularly distributed. Talc has also been detected by X-ray defraction. Iron Formation. The term iron formation is used at Eisenbrey to describe a rock rich in magnetite with accessory epidote, garnet and amphibole (actinolite). Thin sections were prepared on a core sample collected east on strike of the iron formation outcrop in drill hole 9. The rock consisted of quartz (25%), chlorite (10%), actinolite (20%), garnet (5-10%), epidote (10%), carbonate (5%), magnetite (20%), and pyrite (2%). �121 Magnetite is concentrated into thin one to two-inch thick black bands consisting of 30 to 70% magnetite. Actinolite with epidote and garnet enclose the magnetite-rich beds, whereas chlorite occurs as veinlets and disseminated grains throughout the host rock. Light gray to white beds of nearly pure quartz could represent recrystallized chert. Iron formations have been interpreted to strike for over two miles into a series of isoclinal folds, with associated minor amounts of sulfide mineralization, along the eastern-most strike extension. Much of the Eisenbrey magnetic anomaly, particularly on the south side, is due to iron formation. It is unclear whether the iron formation in the area is one horizon that has been folded and faulted, or whether more than one unit of iron formation is present. Ouartz-Sericite Schist. A number of thin, less than 20-foot thick, quartz-sericite schist beds or alteration zones have been intersected during the 1994-1995 deep drilling program. The schists are light gray, highly foliated and in close association with sulfide mineralization located in the south syncline. Sulfide content is low within the schists, averaging about 10 to 15%. Quartz-sericite schist is the dominant lithology of the ore horizon at the Flambeau orebody, but this rock type or alteration zone is uncommon at Eisenbrey. Gabbro. A sill or multiple sills of gabbro occur within the hangingwall of the axial portion of the steeply plunging Eisenbrey syncline axis. It consists of a medium-to coarse-grained recrystallized mixture of feldspar (35%), hornblende (35 to 40%), epidote (10%), and chlorite (5 to 10%). A chilled margin is present having a true thickness of 3 to 5 feet. Closer to the surface, the gabbro has been largely altered to chlorite (up to 60 to 65% of the rock volume). Intrusion of the gabbro greatly elevated the temperature of the enclosing volcaniclastic and sedimentary rocks. This could account for the wide variety of amphibolite facies minerals seen in the deposit and its host rocks. Diabase Dikes. Keweenawan diabase dikes and sills are fresh, medium-grained, holocrystalline, intergranular, non-porphyritic rock having a typical diabasic texture. The rock consists of plagioclase (35%), interstitial chlorite (25%), biotite (3-5%), muscovite (5%), hornblende (1-2%), augite (10%), olivine (10%), serpentine (2-3%), carbonate (5%), and ilmenite (3%). An 80-foot thick dike striking N 60°E and dipping 650 NW intersects the Eisenbrey deposit as shown on Figure 6. The dike splits on the east end of the West lens and also forms a sill in the footwall of the West lens (Figure 7). Pleistocene Till. Approximately 60 feet of unconsolidated glacial outwash materials blanket the Eisenbrey deposit and surrounding area, except where removed by the downward and westward migrating Thornapple River. STRUCTURE The structure of the Eisenbrey deposit is complex based upon outcrop observations, and interpretation of geophysical and drill core data. The current geometry of the deposit is interpreted to be the result of isoclinal folding with possible fault offsets. This interpretation is supported by the following observations: �122 i) a one-to two-inch thick mafic tuff bed found in the outcrop east of the railroad bridge has been tightly isoclinally folded and has a near-vertical axial plunge; and, ii) in the same outcrop elliptically shaped rod structures that also have a vertical plunge, and S planes that show a very steep plunge to the east. The iron formation also shows evidence of isoclinal folding as described above in subsection on Site Geology. In addition, mineral zoning briefly described in the Mineralogy subsection suggests the presence of folding due to repetition of zones within drill holes. Therefore, the deposit is interpreted to strike west from the outcrop through the East massive sulfide lens (Figure 6). A north to northwest striking fault is believed to have offset the gabbro and mineralized horizon. Further evidence for significant faulting comes from hole 4 which contains a large gouge zone where rock foliation is rotated on either side of the structure. This fault is coincident with the northwest striking magnetic response; however, offsetting relationships, if present, are unclear. ALTERATION The Eisenbrey deposit has been subjected to multi-phased hydrothermal and metamorphic processes. To date, no stringer zone or alteration pipe has been definitively recognized. It is interpreted that there is a thermal metamorphic aureole caused by intrusion of a gabbro sill superimposed upon Penokean regional upper greenschist metamorphism. As a result, some unusual mineral assemblages are present, such as chiorite-tremolite-forsterite and pyroxene-garnet-quartz. Regional metamorphism has produced a suite of silicate minerals that include actinolite, albite, garnet, andalusite, anthophyllite, chlorite, cordierite, quartz and sericite-muscovite. The relative abundance of pyrrhotite is interpreted to be a product of localized thermal metamorphism. The host rocks have not been altered by supergene processes although small patches of supergene enrichment have been cored at the top of the deposit. FORM OF THE DEPOSIT The geometry of the Eisenbrey deposit is shown in plan in Figure 6; the deposit occurs as pinched and remobilized massive sulfide enlargements at fold noses within impure chert, anthophyllite, and iron formation host rocks. The isolated East lens has probable structural complications at depth whereas the west lens is a complex arrangement of two synclines open to the east with an intervening very tightly folded anticline. The south syncline is a convoluted, accordion type fold over a north-south direction of almost 200 feet. The ore horizon continues west of the east lens, through a pyrite-sphalerite lens and into a tight syncline referred to as the northwest fold. The south limb of this syncline strikes east into a very tight anticline whose south limb returns west one half the distance of the north limb to enter into a complex and convoluted syncline known as the south fold. The fold nose within massive sulfide mineralization is approximately 170 feet north-south. The south limb may either continue south into an iron formation (Lindberg) or continue east to be intruded by the gabbro (May). In cross section 5850 East, the massive sulfide lenses extend for at least 2500 feet below surface as near-vertical plunging rods, as shown on Figure 7. The length of the deposit, including the east and west lenses, is 3300 feet prior to folding. Isoclinal folding has compressed the once tabular deposit into an area 400 north-south by 1000 east-west. �123 MINERALOGY Base metal mineralization occurs within both pyrrhotite and pyrite matrices. Pyrrhotite is found within and on the south side of the anticline and on the west end of the south syncline nose, and minor pyrrhotite occurs on the south side of the northwest syncline. Chalcopyrite is generally associated with pyrrhotite, whereas pyrite hosts most of the sphalerite and gold mineralization. The Northwest syncline is predominantly pyrite, as well as the north side of the anticline and south side of the South syncline. In shallow drilling the pyrrhotite occurs as massive, amorphous lenses containing irregular grains and layers of chalcopyrite. Chalcopyrite also occurs as finely disseminated grains within the matrix. Most of the copper values, however, are within the larger chalcopyrite patches, many of which halo single or clusters of pyrite cubes. Chalcopyrite can also occur as conformable blebs, some of which are irregular in shape and cross cut pyrrhotite laminations. The pyrrhotitechalcopyrite zone is restricted to the nose of the south fold and has been intersected at depth. Figures 8 and 9 show the general distribution of copper and zinc, respectively, on the 900-foot level. Pyrite occurs as subeuhedral to anhedral grains with interstitial sphalerite and minor chalcopyrite. Chalcopyrite is found as microscopic grains within sphalerite or as small irregular lenses interbedded with pyrite. Typical sphalerite-pyrite layering, common to many massive sulfide deposits, is present, but not well developed. At depth and along strike of the south fold nose the pyrrhotite-chalcopyrite and pyritesphalerite mineral zoning becomes less distinct. Instead, pyrrhotite and pyrite are intermixed within a ragged almost shredded texture of wispy pyrrhotite patches within medium- to fine-grained subhederal pyrite. Wisps of pyrrhotite vary in size from a fraction of an inch to one to two inches. Some areas consist of large masses of amorphous pyrite with essentially no base metal mineralization, whereas some other zones contain thick sequences of cherty chalcopyrite. A distinctive mineral zone contains abundant chalcopyrite-pyrite fragments within a pyrrhotite matrix. The relatively small grain size at Eisenbrey is surprising, as one would have expected coarser grained sulfides due to amphibolite grade regional and contact metamorphism. Near the surface there are thin interbeds of metadolomite present within the massive sulfide in the nose of the sulfide-rich anticline. The beds are about one to two feet thick consisting of 80% dolomite, 10% veined chlorite, 5% magnetite, 3 to 4 % pyrite, and 1% epidote. The relationships between the above mineral zones and structure of the deposit are not clear. Identification of a copper-rich "hot spot" within this very large structurally and mineralogically complex system is proving to be difficult. CONCLUSIONS AND COMPARISONS The Eisenbrey deposit is a typical massive sulfide deposit in that it is hosted within a thick sequence of volcaniclastic lapilli tuff, tuff and graywackes, and capped by a gabbro sill or intrusive. It is an unusual Wisconsin massive sulfide deposit because it is very large, structurally complicated, contains unusual silicate minerals and sulfide textures, and is associated with an iron formation. Bedded magnetite occurs on the flanks of the sulfide system and as disseminated grains or blebs adjacent to or within the deposit. �ANTIC LINE SYNCLINE DRILL HOLE <—0.25 0.25—0.49 0.50—0.99 1.00—1.49 1.50—1.99 >2.00 % Cu LECEND Rusk County, Wisconsin Figure 8 Distribution of Copper Grades, 900ft. Elevation, Eisenbrey Prospect. 0 1" =100' SCALE50 FEET 100 �ANTICLINE SYNCLINE DRILL HOLE <0.50 0.50—0.99 1.00—1.99 2.00—2.99 3.00—3.99 >4.00 % Zn LEGEND Rusk County, Wisconsin Figure 9 Distribution of Zinc Grades, 900ft. Elevation, Eisenbrey Prospect. 0 i FEET 100 —'I 1" = 100' SCALE50 �126 In detail the structure, mineralogy, texture, and metal grades of the Flambeau and Eisenbrey deposits are very dissimilar. A comparison between the similarities and differences are listed on Table 5. ACKNOWLEDGMENTS The author wishes to thank Tom Myatt, general manager, Flambeau Mining Company for allowing this paper to be written. Considerable advise and suggestions were provided by Russ Babcock, Stephen Dinkowitz, Jay Hammitt, Paul Schmidt, Paul Lindberg and Gene LaBerge and to Tammy Fredrickson who somehow managed to put all the comments together. Finally this paper is dedicated in memory of Ned Eisenbrey whose foresight and persistence resulted in the discovery of an interesting and significant metal resource. References Cited Babcock, R., 1996, History of Exploration for Volcanogenic Massive Sulfides in Wisconsin: Institute on Lake Superior Geology, 42nd Institute, 1996 Field Trip Volume. DeMatties, Theodore A., 1994, Early Proterozoic Volcanogenic Massive Sulfide Deposits in Wisconsin: An Overview: Economic Geology, v. 89, p1122-1151. LaBerge, G. L., 1996, General Characteristics and Geologic Setting of the Wisconsin Magmatic Terranes: Institute on Lake Superior Geology, 42nd Institute, 1996, Field trip volume. Lydon, J. W., 1984, Ore Deposit Models-8. Volcanogenic Massive Sulfide Deposit Part 1: A Descriptive Model: Geoscience Canada, V.11, N.4. May, E. R., and Dinkowitz, S. R., 1996, An Overview of the Flambeau Supergene Enriched Massive Sulfide Deposit - Geology and Mineralogy, Rusk County, Wisconsin: Institute on Lake Superior Geology, 42nd Institute, 1996 Field Trip Volume. Nockolds, S. R., 1954, Average Chemical Compositions of Some Igneous Rocks: Bulletin Geol. Soc. Am. 65, pp. 1007-1032. �Preservation of Depositional Features Dikes Foliation Strike and Dip Faulting Folding 8. Structural Sefting Outcroppings Overburden Weakly mineralized iron formation, volcaniclastics, and pyroxenites on Thomapple River bank. None recognized but presence suspected Slightly eroded; looking at the top of a very large system. 60 feet of Pleistocene Till. Iron formation with bedded magnetite or disseminated magnetite with anthophyllite. Impure cherts Intermediate dacite tuffs and lapilli tuffs capped by gabbro sill. IEisenbrey Deposit Structurally complex - tight isoclinal folding. Strong evidence of significant faulting with foliation dip changes on either side of gouge. Moderately Foliated E-W, dipping very steeply north or vertical with near vertical plunge. None Thick diabase dikes and sills occuping probable NE regional tension cracks. Pillows, volcanic bombs, lapillis,graben Lapillis well preserved and highly rodded. and horst features, and facies changes well preserved. Structurally simple-on limb of large isoclinal fold. Strong evidence of prenecontemp oraneous localized stuctures; little evidence of post depositional faults Strongly Foliated N45° E, 75U NW; probably overturned. Intermediate dacite tuffs altered to andalusite-biotite Schist with pillow lavas in stratigraphic hangingwall. None recognized; could be eroded Probably deeply eroded; looking at roots of a much lager system. 0 to 20 feet of Cambrian sandstone and 12 to 30 feet Pleistocene Till. Subcrop of weakly mineralized metachert and quartz-sericite schist under east side of Flambeau River. Host Rocks Atteration Pipe Precambnan Erosion Quartz-Sericite Schist or rhyolite tuff. Metacherts common Flambeau Orebody Ore Horizon A._Depositional Environment TABLE 5 COMPARISON BETWEEN THE FLAMBEAU AND EISENBREY DEPOSITS RUSK COUNTY, WISCONSIN �Supergene Protore Size E. Economic Geology Sphalerite Chalcopyrite Chief Sulfide texture D. Massive Sulfide Textures Gold Cap Precious Metals Gossan Supergene Enrichment Magnetite Sulfide Halo Protore Metamorphic Grade C. Mineralogy I Eisenbrey Deposit 2400 feet long, 45 feet thick 900 feet below subcrop. Approximately 6 million tons total resource. Insufficient size to support a mill. 3% Cu, 2% Zn. Economical. 1 .8 million tons at 10% Cu, 0.1 optAu. Insufficient tonnage. Approximately 1500 feet long, upto 200 feet thick and open below 3000 feet. Plus 50 million ton resource. Sufficient size but low grade. 1% Cu, 2.5% Zn. Poorly bedded. Massive pyrite and pyrrhotite with Well bedded with remobilized large pyrite cubes in pyrrhotite rimmed with chalcopyrite In semi massive protore. Occasslonal sulfide or cherty fragment. chalcopyrite. Whispy pyrrhotite and magnetite. Numerous magnetite and cherty/volcanic fragments. Remobilized and recrystallized around pyrite In massive beds to ragged patches in cubes, disseminated in pyrrhotite, or finely semimassive protore disseminated in sphalerite. lnterstial grains with pyrite, weakly bedded. Well bedded - massive beds Amphibolite grade. Upper greenschist to lower amphibolite. Pyrite with sphalerite and pyrrhotite Pyrite with chalcopyrite, minor with chalcopyrite. sphalerite and trace pyrrhotite. Halo restricted to anthophyllite magnetite Disseminated pyrite with chert rock package. Thickness complicated by folding up to 300 feet wide. Several percent magnetite in some massive Trace to few percent of magnetite in sulfides, host rock, and along strike in ironmafic rocks. None associated formation. with ore. Minor enrichment within 25 feet of subcrop. Extensive enrichment 80 to 185 feet beneath subcrop. Well preserved gold, silica, iron oxide, Minor gossan with iron oxides and minor precious metals. and ankerite gossan. Low precious metal content with gold associated High gold content associated with with sphalerite. chalcopyrite. Precious metal cap on top of massive None recognized. sulfides. Flambeau Orebody �129 GEOLOGICAL SUMMARY - CRANDON DEPOSIT By A. J. Erickson, Jr. Exxon Coal & Minerals Co., Houston, TX and R. COté Rio Algom Exploration Inc., Val d'or, Quebec, Canada INTRODUCTION Crandon Mining Company, a Wisconsin general partnership of subsidiaries of Exxon Coal and Minerals Company (Houston, Texas) and Rio Algom Limited (Toronto, Ontario, Canada) is in the process of seeking the required local, state, and federal agreements, approvals, and permits to mine the Crandon volcanogenic zinc-copper sulfide deposit. The deposit, located in Forest County, Wisconsin, is approximately 5 miles south of the town of Crandon, and 2 road miles east of State Highway 55, on Little Sand Lake Road. The deposit was discovered in 1975 by an Exxon Coal and Minerals predecessor company, Exxon Minerals Company (Schmidt et a!., 1978; May and Schmidt, 1982; Lambe and Rowe, 1987; and Schmidt, 1991). As described by Schmidt (1991), Exxon had been active in the Lake Superior region since the late 1960's and initiated work in northern Wisconsin in 1970 with reconnaissance mapping and airborne electromagnetic surveying (INPUT). A number of targets were identified and drilled. Additional (INPUT and other) airborne surveys were flown in 1974 over areas interpreted to contain favorable felsic volcanics. This work lead to the identification of other anomalies and further land acquisition, including the Skunk Lake target. Follow-up ground geophysical work was carried out in the spring of 1975 which confirmed the presence of a bedrock conductor. Drilling of the target was initiated in June 1975 and discovery was made with the first hole. The deposit was subsequently renamed the Crandon Deposit after the nearby town of Crandon. The target was the 25th prospect drilled by Exxon over a 5 year period of exploration (1970-1975) in Wisconsin after an expenditure of approximately $2.5 million. Since discovery, a total 340,000 feet of drilling of various types and diameters has been completed in 272 holes in and about the deposit. All interpretive work is based on this drilling as the nearest outcrops are several miles from the deposit. REGIONAL GEOLOGY The deposit is hosted by early Proterozoic rock of the Precambrian Southern Province of the Canadian Shield in the east-west trending Rhinelander-Ladysmith Greenstone Belt (Schmidt et al. 1978; May and Schmidt 1982). The belt is between 30 and 50 miles wide (N-S) and approximately 200 miles long (E-W) extending from the towns of Ladysmith in the west to Pembine in the east. (Sims, 1984, refers to the area as the Ladysmith-Pembine volcanic belt). The northern portion of the belt consists of mafic metavolcanic rocks, basalts, locally pillowed, basaltic andesites, flows, tuffs, some gabbroic rocks, and associated granites, tonalites, and granite gneiss. More felsic to mafic pillowed flows, dacitic to rhyolitic tuffs, porphyries and dikes are present in the southern portion of the belt (Sims, 1992). �130 The Rhinelander-Ladysmith greenstone belt forms the most northern portion of the Wisconsin Magmatic Terranes in the Penokean fold belt, south of the Niagara Fault as shown on Figure 1 (Hoffman, 1989; Sims et a!., 1989; Sims, 1992; and DeMatties, 1994). The magmatic terranes are complex, poorly exposed, and have been divided into three "subterranes" identified from north to south as, the Ladysmith-Pembine Belt, the Chippewa-Wausau Belt, and the Marshfield-Stevens Point Belt (Sims, 1984). More recently, Sims et a!. (1989), and Sims (1992), combined the two northern "subterranes" into the Pembine-Wausau Terrane. The southern belt has been renamed the Marshfield Terrane. The juxtaposed terranes and contained sulfide deposits, as shown in Figure 1, are interpreted to be the result of plate tectonic processes during the early Proterozoic. These terranes are believed to be the renmants of volcanic arc - continent and volcanic arc - volcanic arc subduction and plate collision zones. This accretion of the plates was initially at a juncture now referred to as the Niagara Fault Zone with subsequent accretion of a second plate along the Eau Pleine Shear Zone. This deformation and accretion occurred during the Penokean Orogeny, dated at approximately 1860 to 1840 Ma (Van Schmus, 1975; Schulz, 1984; Hoffman, 1989; Sims et a!., 1989; Sims, 1990; Kiasner et al., 1991). The recent summary by LaBerge (1994), provides a simplified discussion of these complex Proterozoic plate tectonic relationships, and the Lake Superior regional geology. GENERAL DEPOSIT GEOLOGY The following details are largely summarized from the descriptions of Schmidt et al. (1978), May and Schmidt (1982), Rowe and Hite (1984), and Lambe and Row (1987). Their work is supplemented by more recent work by the authors. Specific citations from all individual items are commonly not included in this summary and the reader is encouraged to consult the references for further details. The Crandon deposit is a "typical" volcanic hosted sulfide deposit as described in reviews by Solomon (1976), Franldin et a!. (1981), or Lydon (1988), of the "primitive" zinc-copper rich type using Hutchinson's (1980) classification. The deposit consists of two major styles of mineralization 1) a syngenetic, commonly laminated, zinc-bearing, pyrite-rich, sulfide zone which is partially underkuin by 2) an epigenetic, cross cutting zone of copper-bearing, quartz-pyrite-chalcopyrite stringer mineralization in altered volcanic rocks stratigraphically beneath the zinc mineralization. Early published reserve estimates (Schmidt et al., 1978; May and Schmidt, 1982; Rowe and Hite, 1984; and Lambe and Rowe, 1987) have generally included both the zinc and copper mineralization of the primary sulfide facies. The referenced tonnage is in the 55 to 65 million ton range with corresponding grades reported for this material as slightly over 1% copper, 5% zinc, and only minor amounts of lead, silver, and gold. The reserve estimate for the conformable syngenetic zinc mineralization alone is estimated as 30 million tons containing 9.4% zinc and 0.4% copper (Anon, 1994). At the property scale, the deposit is conformably contained in a sequence of mafic, intermediate, and felsic volcanic rocks. Pyroclastic units are dominant but numerous intercalated flows have been noted within the volcanic sequence. Chert, argillites, bedded sulfides, and volcaniclastic sandstone intercalations probably indicate periods of quiescence during formation of �______ / I 47. 46 45. EAU PLEINE ZONE — .) 0 Possible limit rhyolite-granite 0 44• terrana S. 0 I MINNESO1>1 IOWA Baraboo Synciine o -..----—- Waterloo 0 43 4 MA 1)ISOIV WISCONSIN 9T PROTEROZOIC Middle Proterozoic (Keweenawan) mafic igneous & sedimentary rocks of Midcontinent rift system (- 1,100 Ma) island-arc metavoicanic & granitoid rocks in EIBllHff Pembine-Wausau terrane (1834-1,880 Ma includes post-tectonic granttic rocks (1.760 Ma) island-arc metavoicanic & granitold rocks (1,835-1,890 Ma) Anorogenic granites. syenite, & anorthosite (1470 -1525 Ma) L._.... 2128148 Baraboo, Barron, Waterloo quartzites (age uncertain) (<1750 Ma?) Central Wisconsin myoiites & granite rocks (—1760 Ma) —.. High-angie fault WISCONSIN MAGMATIC TERRANES Sedimentary rocks of Paieozolc age CONTINENTAL MARGIN ASSEMBLAGE . Marquette Range Supergroup (1 .820-2,100 Ma) ARCH EAN Basement gneiss, granite, & greenstone IttF (2600 - 3550 Ma) I Thrust fault - Possible suture Sulfide Deposits 75 MILES 0 I I I TECTONIC MAP SOUTHERN LAKE SUPERIOR REGION Modified after Sims, 1992 Figure 1 �132 the volcanic pile. Syn-and post-volcanic, commonly mafic but occasionally felsic, intrusive dikes and sills constitute a small portion of the sequence. The host volcaniclastic assemblage along with the contained sulfide deposit strike generally east-west (N85°W) and dip steeply (7O09O0) north. Relict depositional features, internal mineral zonation within the sulfide mineralization, and gross sulfide zone relationships consistently indicate a normal, north facing volcanic sequence. A small portion of the deposit on the extreme west end is steeply overturned to the south. Rowe and Lambe (1986), have informally divided the volcanic package into a lower Hemlock Creek Group, which contains the Crandon deposit, and an upper Swamp Creek Group. Figure 2 is their reconstructed stratigraphic column and is included to provide a general summary of the lithologies and stratigraphic relationships. Detailed description of the units, discussions of the stratigraphic relationships, and interpretations of the genesis of the units are included in the above reference. Discussions here will be limited to the deposit features in the Crandon Unit with its conformable zinc mineralization, and to the stringer copper mineralization within the underlying Sand Lake Formation. SULFIDE DEPOSITS As indicated, the two major mineralization types of the Crandon deposit include 1) conformable, locally laminated, syngenetic, zinc-rich pyritic sulfide lenses and 2) cross cutting, epigenetic copper-bearing stringer sulfides commonly beneath the zinc deposit. Fine grained felsic and intermediate pyritic ash and lapilli tuffs, cherts, laminated pyritic cherts, and black thinly laminated pyritic argillite are locally interbedded with the conformable sulfide mineralization. Overprinting of stringer copper zone mineralization on the zinc mineralization is occasionally seen near the base of the zinc-rich sulfide zones. Crandon zinc mineralization consists of three or locally four sub-parallel stacked lenses of sulfide (COté et al., 1994), which are locally interbedded with tuffs and argillites. The lenses, occur either as unique horizons separated by epiclastic or pyroclastic lithologies containing lesser amounts of total sulfides, as shown on section A - A', Figure 4, or as stacked sulfide horizons with common boundaries, as shown in portk)ns of section B - B'. The sulfide bands contain sphalerite as continuous or discontinuous laminae and patches in laminated to more massive pyrite. Laminae or seams of chalcopyrite or galena are present but less common and are often cross-cutting due at least in part to late remobilization. The mineralization was cyclically deposited by pulses of sulfide-rich emanations in a restricted basin characterized by a shallow western half and a deeper central portion. At the eastern extremity of the deposit the sulfides thin and pinch out in the shallow end of the basin. Relationships are well illustrated on the mine level plan, Figure 3, at a depth of approximately 665 feet below surface and on cross sections A - A', B - B', and C - C' (Figure 4). Figure 5 provides an east-west longitudinal projection, showing the distribution of the zinc mineralization at a >3% zinc cutoff. The cyclicity of mineralization is shown in simplified form in the three sections as interpreted from internal stratigraphy and assay data analysis. This cyclicity has been clearly documented in recent logging and analysis of core from the latest drilling program and re-analysis of earlier drilled core. Thesethree main stratigraphically stacked sulfide lenses are laterally very continuous and can be traced in the majority of holes. The correlation diagram D - D' on Figure 6 highlights the internal sulfide stratigraphy and relative zinc and copper values as they relate to the specific sulfide facies �____ ___ __________ L dg DuCK LAKE GABBRO (dg) GENERALLY 25 M IN WIDTH t'4 TRUSIVES U L: UNALTEREOANDUNFRACTURED U: UNDIFFERENTIATED. GENERALLY ALTERED DIKES OF WHICH SOME COULD BE SMALL FLOWS LLJLLJ (3 U - FOREST UNIT (fi) A SEQUENCE OF EPICLASTIC ARGILL5CEOUS CONGLOMERATE AND SANDSTONE CONSISTING OF GRANITE CLASTS AND VOLCANIC CLASTS LOCAL FLOWS AND TUFF, ft I I I :<Lf) ' J 7 PINE UNIT (pn) A BASINAL SEQUENCE CF CHERTY TUFF. CHEAT AND SILICIFIED lUFF BECOMES MORE SERICITIC. PYRITIC, AND ARGILLITIC TO THE WEST. u-J (.f) 7 LINCOLN UNIT (In) PORPHYRITIC RHYOLITIC FLOWS WITH NTERBEDDED TUFF. CHEAT AND ARGILLITE. $ SKUNK LAKE UNIT (sk) A BASINAL SEQUENCE OF SLUMPED AND L CONTORTED CHEAT AND ARGILLACEOUS TUFF LAMINAE. SOFT SEDI MENT FEATURES ABUNDANT. LOCAL INTERBEDOED CHEAT OR TUFF, AND LOCALLY UP TO 10% SULFIDES. RICE LAKE UNIT (rc) A SERIES OF VOLACANIC DEBRIS FLOWS AND rc EUTAXITIC ASH FLOWS. rcm BLUEBIRD SUBUNIT (rcb1) BLOCKY TO TABULAR CHLORITIC FRAGMENTS. (LOCALLY EXHIBITING ATTENUATION). MATRIX PREDOMI- NANTLY FELSIC: (rcb2) CHLORITIC FRAOMENTS MODERATLEY ATTENUATED. POSSIBLY WEAKLY WELDED. cb2 CARRIDGE SUBUNIT (rcc) DOMINANTLY WELDED ASH FLOWS ALTHOUGH DEGREE OF WELDING VARIABLE. INTERBEDDED TUFF U COMMON. -J CHEPTY TUFF. LOCAL REWORKED TUFF. No SULFIDES. MILLSTREAM SUBUNIT (rcm) : i< OAK LAKE UNIT (Ok) A BASINAL SEQUENCE CONSISTING DOMI- ok F I NANTLY OF CHERTY TUFF AND SERICITIC TUFF CONTAINING I TO 5% STRATABOUND PYRITE. LOCAL INTERBEDOED CHEAT OR CHLORITE SERICITETUFF MOLE LAKE UNIT (ml) A FINE TUFF CONTAINING ONLY MINOR ml p I BASINAL ENVIRONMENT. USUALLY COARSE PYROCLASTICS. THE EAST HALF OF THE FORMATION IS A FINE CHLORITIC TUFF. THE WEST HALF ISA SILTY. HOMOGENEOUS, SERICITE ml CHLORITE REWORKOED TUFF. CONTAINING 0 TO 4% PYRITE. INTER- I LU BEDDED CHEAT IS COMMON IN THE WEST HALF. PROSPECT SUBUNIT (mip) FELSIC DEBRIS FLOWS. GENERALLY 4 TO U 15MM FELSIC DEBRIS IN A FINE CHLORSTIC MATRIX. EAGLE SUBUNIT (mle) A VOLCANIC SANDSTONE CONTAINING 80% ROUNDED QUARTZ SAND IN A SERICITE-CHLORITE MATRIX U 0 cr J I CRANDON UNIT (Cr) A BASINAL SEQUENCE CONSISTING OF STRATABOUND MASSIVE SULFIDE (GREATER THAN 50% TOTAL SULFIDE), PYRITIC ARGILLITE AND PYRITIC TUFF LOCAL THIN CHERT BEDS. LU SAND LAKE UNIT (Sd) FINE DRAINED TUFF WITH MINOR DEBRIS FLOWS, CHERTY TUFF AND FLOWS. GRADES WITH DEPTH INTO COARSER REWORKED TUFF AND FINE LAPILLI TUFF. TOWNSHIP SUBUNIT (sdt) A SERIES OF VOLCANIC BRECCIAS CONSISTING OF ANGULAR. POORLY SORTED HETEROLITHIC OR MONOLITHIC FRAGMENTS. MATRICS STRONGLY SILITIC sdt1 A TRANSITIONAL BRECCIA AT THE TOP OF THE SAND LAKE UNIT. CONSISTING OF FRAGMENTS OF TUFF,AAGILLITE. CHERT AND MASSIVE SULFIDE. sdt2 VOLCANIC BRECCIA CONSISTING OF HETEROLITHIC FRAGMENTS EXHIBITING MANY STAGES OF SILICIFICATION. sdt3 VOLCANIC BRECCIA CONSISTING OP MONOLITHIC FRAG- MENTS. FRAGMENTS GENERALLY WEAKLY SILICIFIED. NASHVILLE UNIT (nh) PORPHYRITIC BASALTIC FLOWS. LOCAL THIN TUFF BEDS CRANDON DEPOSIT - RECONSTRUCTED STRATIGRAPHIC COLUMN LAMBE & ROWE (1987) Figure 2 �I I 7 0 I 9 I I 12 -- 11 13 14 I 1 I 16 274000 £ 274400 C MODEL_LEVEL 13 270000 MINE PLAN ELEV. 1025 GEOZONE OUTLINES Crandon Mining Company 0 274400 — 6 C RA2RI 201 ==-I 5 274000 IA -— 13 20 I I 0 21 22 23 24 25 I 275200 I I N 0 I 276000 I I I I £ I 276400 275600 £ — C I I I £ I 'I I I £ 277620 C I I III Z77 E/// Zo C I C 276404 B --# B' 71 --- 64 65 66 67 CA 69 70 - I 270400 0 59 60 61 62 6 I 274000 MINE RA LI ZATI ON ZINC 4849 50 51 52 57 54 55 56 57 277200 2 43 44 45 46 4 I 276400 C RI C A' 72 73 II C I Figure 3 I I I 81 82 83 84 C RAN DON 80 FORMATION I I _ I 279600 4 75 76 7? 70 7 I 279200 CRANDON DEPOSIT — CRANDON DEPOSIT MINERALIZATION ON THE PROPOSED 665 LEVEL 275204 MIDDLE MINEROLIZED GEOZONE 2021 OJ LO/ER M1NRALIZED GEOZONE 2023 Z UPPER MINERALIZED GEOZONE 0011 0 I —_- MINE LEVEL 665 LECENI?: I £ 6 27 28 29 30 3 32 33 34 35 36 37 38 39 40 275600 COPPER MINERALIZATIO ZONE 19 £ 240000 �2f28215 C N - S SECTION C-C' 2,276,793 E LOOKING WEST CH 0 400 800 1200 FT. N - S SECTION B-B' 2,278,565 E LOOKING WEST (0 0 0 c'J z Figure 4 N - S SECTION A-A' 2,279,008 E LOOKING WEST CRANDON DEPOSIT - SIMPLIFIED GEOLOGIC CROSS SECTIONS �Limit Copper Stringer Zone 200 et [Z) 400 9)0 IAJEJRCI9 IF II RC/r IA I E Jr .RC 1119 1119196 12/2195 11115195 Area of prolonged hydrothermal activity & thick sulfide accumulation MINERALIZATION ZINC & COPPER Longitudinal Projection Looking North 1200 -800 — N 0 8 0 C- Ui I 0 ((9 9)0) 9— (20 W0 9- z 00z IN U) ———--—-9— C CO Limit Copper Stringer Zone I' B — 0 A >3% Zn 'Crandon Zinc Zone - 0 0 0 2F28213 k/ .1-- Figure 5 CRANDON DEPOSIT - EAST-WEST LONGITUDINAL PROJECTION SHOWING LIMITS OF MINERALIZATION U - -k 0-z 0 CRANDON MINING COMPANY -400 — West — - a Level OO 20 o— A' �137 depicted by drill holes 137, 159, and 265. Individual lenses generally consist of an upper, zinc-rich, bedded to laminated pyrite-sphalerite (±galena) facies which grades stratigraphically downward into a commonly zinc-lean, poorly bedded pyritic fades. These primary textural variations and associated metal zoning are essentially repeated from one sulfide lens to the next, analogous to that described at the Mobrun deposit in the Noranda camp (La Rocque et a!., 1993). Typically, the lower facies consists of fme-grained colloform or spheroidal pyrite with lesser granular (in part, recrystallized) medium grained pyrite with fine interstitial sphalerite and/or fine "lacy" interstitial chalcopyrite. This lower facies may also locally include an appreciable amount (20-40%) of fine botryoidal silica gangue thought to represent a primary exhalative gel or sinter. Individual lenses generally average from 40 to 55 feet in true thickness and taper to thin horizons at the margin of the basin. Where sulfide lenses are in direct contact, the true thickness of the sulfide package may exceed 100 feet. Stringer copper zone mineralization occurs stratigraphically beneath the zinc mineralization. It consists of multiple stages of quartz, quartz-pyrite, quart.z-pyrite-chalcopyrite, locally quartz-pyritechalcopyrite-sphalerite, and thin pyrite veinlets. Age relationships are complex. Barren milky white quartz veinlets clearly predate the mixed quartz sulfide veinlets, whereas most thin barren pyrite veinlets post-date the quartz sulfide veinlets. This network of veinlets is localized as a semiconformable envelope in the Sand Lake Formation "breccias" immediately below the Crandon Unit with its contained zinc mineralization as described by Lambe and Rowe (1987). Although described as mono and heterolithologic volcanic breccias, it should be noted that some of the breccia-like textures are clearly alteration features. SULFIDE MINERALOGY Sulfide mineralogy is simple in both the conformable sulfide zinc zone and the footwall copper stringer zone. Pyrite is clearly the dominant sulfide in the zinc zone and may range up to nearly 100% at the base of individual sulfide lenses and in the less prevalent sub-seafloor replacement pyrite immediately beneath some of the zones of zinc mineralization. Sphalerite is the zinc sulfide. There are lesser amounts of chalcopyrite, galena, tetrahedrite, and rare pyrrhotite and arsenopyrite are present in both the zinc and copper zones. Marcasite and enargite have been reported. Near surface, a typical iron oxide, silica-rich gossan is present due to pre-Cambrian weathering of the sulfide mineralization. The gossan generally extends less than 100 feet below the subcrop, and is commonly only a few tens of feet thick. Very locally it extends in excess of 400 feet below the subcrop along particular lithologic horizons, or contacts within and along the margin of the Crandon Unit. A limited amount of supergene sulfide mineralization, chalcocite, covellite and rare bornite, is present beneath the gossan as well. Minor amounts of copper oxides have been noted. The supergene enriched zone is small, in part due to the proportionally low amount of copper in the primary mineralization and in part due to its removal through weathering and erosion since perhaps the middle Paleozoic. In this respect the Crandon deposit contrasts with the Flambeau deposit in western Wisconsin (May 1977). At Flambeau, the primary mineralization is generally more copper rich and the secondarily enriched ore zone was largely preserved from weathering, erosion, and Pleistocene glaciation by the presence of the Cambrian cover rock. ALTERATION Synvolcanic hydrothermal alteration at Crandon is most strongly and extensively developed within the Crandon Unit and the immediate stratigraphic footwall (Sand Lake Formation) unit south of the zinc mineralization. However, alteration features are complex and commonly overlap. Footwall �Pv ItIcf a-a a R. C., A.J.E. Jr., J.T.S Il b I- k'Y1 I'" "'1 /11/ / / \\\\ \ \\\\ /\I/Il \\\\/ I//I \ \\\\\ \ \ \ \ \ \ \ \ \ \\ \ 159 __— a N IA —R D Sand Lake Breccias Lower poorly bedded granular, colliform, pyrite. Sphalerite lean Upper laminated sphalerite rich sulfide Pyritic argillite 'a a ET i; UL çT' aa,O Diorite — I I_— mafic lapilli tuffs. Mole Lake: Intermediate to HANGING WALL - a -a - - a - I' II Ill EARLY LATE C - - a - - a Q - - I 0 I 25 a FEET I 50 - o0 a 0— O - I 100 2F28526 I 75 / / / II \\\ / / / / / / / / / / / I // / I I / /\\ I//I pyritized footwall polymitc felsic/ intermediate "breccias". COPPER r ZINC - // / / / \ \ \\\ \ \ /\\\I//I \ \\\\ \ \\\/ \ \\\\ I/I/I / ,,, FOOTWALL Sand Lake: Strongly silicified & - SULFIDE CYCLES C -o 265 \ \\ / / I 7/ \\ \ \ \ / / 7/I III / / I \ \\ \ \ \ \\ \/ \\\\ \ \\\ / / / // / / / \ \\ \ \ \\ \ \ \ \\ \ \\\ \\\ \ \ \\\\\\ Relative histograms at different scales Figure 6 a a. fl 17 — —= - D' 137 SECTION D ________ _____________ _______ __________ SELECTED ORE ZONE SULFIDE CORRELATION DIAGRAM �139 alteration is dominated by partial to pervasive silicification, whereas lesser chioritization, sericitization, and carbonatization (mostly dolomite) are also present. Intense pyritization in zones varying in thickness from 25 to 200 feet immediately below the conformable zinc zone accompany this alteration. Limited information on the footwall stringer mineralization and the fact that erosion has left only a portion of the original deposit make it difficult to fully define a classic feeder pipe beneath the tabular zinc mineralization, as described by Lydon (1988). A zone of prolonged hydrothermal activity is inferred due to thick alteration and mineralization located approximately middistance between cross sections B-B' and C-C' (See Figure 5). Here an important thickness of massive and semi-massive sulfides exhibits an abundance of textural features that are interpreted to be the result of sub-seafloor replacement. Intense black chlorite alteration within the footwall Sand Lake Formation is well developed at this locality. The "tabular appearing" footwall silicate alteration assemblage illustrated on the level plans by Lambe and Rowe (1987) suggest more intense chloritic alteration beneath the western half of the deposit, whereas to the east sericitic alteration is more abundant. Within the Crandon Unit, some of the "pyritic argillite" in fact represents strongly metasomatized zones of magnesium-chlorite alteration within the laminated, pyrite bearing, fine epiclastic sediment. In other areas, however, the "pyritic argillite" represents pyrite-rich zones of intense black, magnesium-iron-chlorite alteration as is typically found in footwall stringer zones in volcanic-hosted sulfide deposits. This later hydrothermal alteration is both cross-cutting and locally conformable to bedding. Most commonly, it is associated with epigenetic, stringer copper mineralization and localized as multistage quartz-sulfide, or sulfide veinlets in a complex semiconformable zone of quartz-sulfide brecciation in the footwall beneath the zinc mineralization. STRUCTURE AND METAMORPHIC ATFRIBUTES The Penokean Orogeny produced a generally steep dipping attitude in the volcano-sedimentary assemblage hosting and surrounding the Crandon deposit. Bedrock units in the area of the deposit have been metamorphosed to the lower greenschist facies. The structural deformation is generally weak to moderate such that delicate primary volcanic and sedimentary textures are preserved at various localities. The resulting overprint of principal structural fabric includes a regional east-west trending subvertical dipping schistosity and the local development of longitudinal east-west shears. The pervasive planar structure or S1 schistosity, as noted in core, is presumed axial planar to the regional fold features and is generally sub-parallel to the bedding attitudes except where small scale parasitic folding is developed. Local zones of more pronounced to strong shearing are less frequent and preferentially developed as bedding parallel features and along major lithological contacts. Major faults have not been recognized at Crandon as shown on level plans (Figure 3) and cross-sections (Figure 4). These figures illustrate the undisturbed lateral continuity of the hanging wall contact of the deposit indicating minimal structural complications as might otherwise be indicated by marked thickening, thinning or offset due to significant folding and/or faulting. This lack of significant structural offset has been substantiated in five separate drilling programs since 1980. All holes intersected stratigraphy as anticipated, thus indicating no important structural effects. �140 CONCLUSIONS The lithological and mineralogical features of the Crandon Deposit described above are typical of many submarine volcanogenic sulfide deposits emplaced at and directly below the sea floor. Internal sulfide stratigraphy, as indicated by mappable sulfide facies, document the presence of at least three major stacked lenses, i.e., pulses of pyrite-sphalerite mineralization. Long lived, both focused and diffuse discharge of metal-bearing hydrothermal fluids are indicated. These solutions percolated upward through the Sand Lake submarine volcanics to precipitate their contents at and below the Proterozoic sea floor. The resulting concentration of the conformable pyritic, zinc-rich sulfides, uninterrupted by major structural dislocation, and the underlying discordant, copper-rich stringer mineralization is the largest known volcanic-hosted zinc copper deposit in the Rhinelander-Ladysmith Greenstone Belt. Acknowledgment We would like to take this opportunity to thank T. E. Warren, Rio Algom Exploration Inc., and G. Westra, Exxon Coal and Minerals Company, for constructive comments and Crandon Mining Company, Exxon Coal and Minerals Company and Rio Algom Exploration Inc.,for permission to publish this paper. Secretarial support by L. Gonzales and drafting by J. L. Shaw, Exxon Coal and Minerals Company, is greatly appreciated. References Cited Anon, 1994, Annual Report, Rio Algom Limited. Cot, R., Erickson, A. J., Jr., Donahue, S. V., Thresher, J. E. Jr., and Anderson, P. F., October 1994, Bedrock Hydrogeology of the Crandon Project Site: Foth & Van Dyke Memorandum, 19 p. DeMatties, T. A., 1994, Early Proterozoic Volcanographic Massive Sulfide Deposits in Wisconsin: An overview: Economic Geology, v. 89, p. 1123-1 151. Franidin, J. M., Lydon, J. W., and Sangster, D. F., 1981, Volcanic-associated massive sulfide deposits: Economic Geology, 75th Anniversary Volume, p. 485-627. Hoffman, P. F., 1989, Precambrian geology and tectonic, history of North America: in Bally, A. W., and Palmer, A. R., eds., The Geology of North America-An Overview; G.S.A., The Geology of North America, v. A, p. 447-512. Kiasner, J. S., Ojakangas, R. W., Schulz, K. J., and LaBerge, G. L., 1991, Nature and Style of deformation in the foreland of early Proterozoic Penokean Orogen, Northern Michigan: USGS Bull 1904-K, p. K1-K22. Lambe, R. N., and Rowe, R. G., 1987, Volcanic history, mineralization, and alteration of the Crandon Massive Sulfide Deposit, Wisconsin: Econ. Geol. v. 82, p. 1204-1238. LaBerge, G. L., 1994, Geology of the Lake Superior Region: Geoscience Press, Phoenix, AZ, 309p. �141 LaRocque, A. C. L., Hodgson, C. J., and La Fleur, P. J., 1993, Gold distribution in the Mobrun volcanic-associated massive sulfide deposit, Noranda, Quebec: A Preliminary Evaluation of the Role of Metamorphic Remobilization: Economic Geology, v. 88, p. 1443-1459. Lydon, J. W., 1988, Volcanogenic massive sulfide deposits Part 1: A descriptive model: Part 2: Genetic models: in Roberts, R. G., and Sheahan, P. A., eds., Ore Deposit Models, Geoscience Canada Reprint Series 3, Geol. Assn. Canada, Memorial University, St. Johns. Nfld. p. 145-181. May, E. R., 1976, Flambeau - A Precambrian Supergene Enriched Massive Sulfide Deposit: SME preprint 76-1-55, 35p. May, E. R., and Schmidt, P. G., 1982, The discovery, geology, and mineralogy of the Crandon Precambrian massive sulfide deposit, Wisconsin: in Hutchinson, R. W., Spence, C. D., and Franklin, J. M., eds., Precambrian Sulfide Deposits, H.S. Robinson Memorial Volume, Special Paper 25, Geol. Assn. of Canada, p. 448-480. Rowe, R. G., and Hite, R. G., 1984, Applied geology: The foundation for mine design at Exxon Minerals Company's Crandon Deposit: in Erickson, A. J., Jr., ed., Applied Mining Geology, SME, Denver, p. 9-26. Schmidt, P. G., 1991, Discovery case history of the Crandon Massive Sulfide Deposit, Forest County, Wisconsin: in V. F. Hollister, ed., Porphyry Copper, Molybdenum, and Gold Deposits, Volcanogenic Deposits (Massive Sulfides) and Deposits in Layered Rock, SME Case Histories of Mineral Discoveries, v. 3, p. 99-102. Schmidt, P. G., Dolence, J. D., Lluria, M. R., and Parsons III, (3., 1978, Geologists block out Exxon's big find of Zn-Cu at Crandon: Engineering and Mining Journal, v. 179, p. 61-66. Sims, P. K., 1984, Metallogeny of Archean and Proterozoic Terrains in the Great Lakes Region - A Brief Overview: in Bush, A. L., ed., Contributions to Mineral Resources Research, 1984, USGS Bull. 1694, p. 57-71. Sims, P. K., (compiler), 1990, Geologic map of Precambrian rocks of Iron Mountain and Escanaba 10 x 2° Quadrangles, Northeastern Wisconsin and Northwestern Michigan: USGS Miscellaneous Investigation Series, Map 1-2056. Sims, P. K., (compiler) 1992, Geologic map of Precambrian rocks, southern Lake Superior Region, Wisconsin and Northern Michigan: USGS Miscellaneous Investigation Series, MAP 1-2 185, 2 sheets. Sims, P. K., Van Schmus, W. R., Schulz, K. J., and Peterman, Z. E., 1989, Tectono-stratigraphic evolution of the Early Proterozoic Wisconsin magmatic terrains of the Penokean Orogen: Can. J. Earth Sci. v. 26, p. 2145-2158. Solomon, M., 1976, "Volcanic" massive sulfide deposits and their host rocks - a review and explanation: in Wolf, K. H., ed., Handbook of Stratabound and Stratiform Ore Deposits, Elsevier, Amsterdam, v. 2, p. 21-50. Van Schmus, W. R., 1976, Early and Middle Proterozoic history of the Great Lakes area, North America: Phil. Tran. R. Soc. Lond. A. 280, p. 605-628. �142 �143 THE BEND DEPOSIT: AN EARLY PROTEROZOIC COPPER-GOLD VMS DEPOSIT by Theodore A. DeMatties and William F. Rowell Geological Consultants INTRODUCTION Exploration conducted between 1985 and 1994 by the former Jump River Joint Venture, and more recently Sharpe Energy and Resources, has identified a potentially economic copper-gold volcanogenic massive sulfide deposit in the Chequamegon National Forest of north-central Wisconsin. The deposit, known as Bend, is located in Taylor County, approximately 19 miles north-northwest of Medford, the county seat (Fig. 1). Mineral rights controlling the known deposit and its extensions are currently held under a BLM Preference Right Lease Application, BLM prospecting permits, and private leases by a joint venture consisting of Sharpe Energy and Resources, Freewest Resources and Cyprus-Amax. Originally discovered as a single high-priority, six-channel electromagnetic (INPUT) anomaly in 1978, the property was not available to the former Jump River Joint Venture for acquisition until 1985. Drilling began in 1986 on the blind (100-120' of glacial overburden) electromagnetic target and since that time a total of 38 diamond driliholes (approximately 47,000 feet of drilling) have indicated a resource of 3.9 million short tons grading 1.87% copper, 0.09 opt gold, and 0.39 opt silver. LOCAL AND REGIONAL GEOLOGY The Bend deposit is one in a cluster of at least three volcanogenic massive sulfide (VMS) deposits which occur within the Ladysmith district (Fig. 2). Other significant deposits in this district include Flambeau (Cu-Au), which is currently being mined, and Eisenbrey (Thornapple) (Zn-Cu) where exploration has recently (1995) been conducted; previously explored VMS showings also occur at the Schoolhouse (Cu), and Clear Creek (Cu) prospects. This district, as well as two others which have been identified, is located in the LadysmithRhinelander volcanic complex. The complex lies in the Early Proterozoic Penokean volcanic belt (or Wisconsin magmatic terrane), which is a major component of the Southern Structural Province of the Canadian Shield. The Bend deposit is hosted by a felsic center located structurally along the southern margin of a major volcanic arc and within a back-arc basin facies. Locally, the center is associated with, and occurs along the flanks of, a mafic pile succession (Fig.3). The host rock section is up to 2000 feet thick and consists of steeply dipping (upright), interbedded, schistose, rhyolitic to rhyodacitic, bedded metatuffs (sericite schist) and quartz-crystal metatuffs (quartz-sericite schist-semischist, Fig.7A) that are overlain (stratigraphic hangingwall) by an andesitic to rhyolitic (dominantly dacitic-rhyodacititc) metavolcanic flow-fragmental sequence and associated fine tuffs or metasediments (Fig. 4 and Table 1). �130N T31 132 N T33 N P3W Substation 01 2345 miles P1W Figure 1. Bend project location map, Taylor County, Wisconsin. j P2W Power transmission line uss..wgbs,. P4W z, a-. North PIE U R2E Fig.1 R3E �Anorogenic igneous rocks (1,4701,510 Ma) Alkali-feldspar granite (=1835 Ma) Xv Gneiss and schist (2,800- 3,000 Ma); includes tonalite (1,890 Ma) Volcanic rocks in the Marshfield subterrane Wausau Volcanic Complex Ladysmith-Rhinelander Volcanic Complex Back arc basin sequence (greenschist succession) Main volcanic arc sequence (amphibolite succession) Volcanic and lesser sedimentary rocks (1,840-1,880 Ma): Gneiss and granitoid rocks (1 835-1,865 Ma) •j—. 1 - Tonatite-granodiorite-granite (1,760-1870 Ma) -,- + + + .- + + + + ÷ + + + + + + + Wolf River + Batholith + + + Xs Shear VMS Shear-zoneoccurrence hosted gold deposit A Thrust x — High-angle --- Potential economic VMS deposit Foliation — Gneiss (2,700-3,550 Ma) Marquette Range Supergroup (=1,850-2,100 Ma) CONTINENTAL-MARGIN ASSEMBLAGE + + , + + VMS deposit + + ÷ + + ________ II AEM formational group and type Figure 2. Geological map of northern Wisconsin showing major volcanic complexes, and distribution of VMS deposits and occurrences (modified Sims, 1989). + IH Middle Proterozoic (Keweenawan) mafic igneous and sedimentary rocks of the Midcontinent rift system (1,0001,200 Ma) rocks Paleozoic sedimentary WISCONSIN MAGMATIC TERRANES (PENOKEAN VOLCANIC BELT) _______ �if I Main Volcanic Arc Sequence Piv — dominantly intermediate to malic metavolcanic flows and interbedded metatufts and tuffaceous metasediments intnisive complex; includes melavolcanic flows, interfiow tuffs and sediments, and cherty iron formation (if) F' ' \N Pmv — mafic to ultramafic volcanicI I I Back-Arc Basin Sequence intwsives, syenodiorite Pms — graphilic, sulfide-bearing metaargillite formations \ Pmvf — dominantly intermediate to mafic metavolcanic flows and subvolcanic infrusives Pvs — dominantly tuffaceous mela--1 sediments; includes metagraywacke, bedded or reworked melatuffs, and associated chemical metasediments I Pvs • I.. .1 Metagabbro, altered ultramafic Lower Proterozoic Metavolcanic and Related Rocks Lower Proterozolc (?) Intrusive Rock Units . j Metagrariite, quartz metadiorite, -' ' metadiorite and metasyenite I ::I Lower Proterozoic Barron Quartzite Sedimentary Rock Units Undifferentiated Cambrian sandstone formations; thin (<50 ft) sandstone units locally covering basement metavolcanic units not shown — PPE PROSPECT ,,y BEND DEPOSIT (Cu,Au) DeMatties, 1994). 0 0 Deposit with defined reserves A 4 /92 Z z LYNNE DEPOSIT (Zn, Pb,Ag) 5km Smiles Reverse and normal magnetized mafic dikes (Keweenawan age) Prospect Shear zone a Figure 3. General geologic map of the western portion of the Ladysmith-Rhinelander metavolcanic complex (after CH - - _ -< magnetic data Contact, based on airborne —— Projected or inferred fault — — __ ___ Pfv — dominantly intermediate to felsic mdtavolcanic tuffs/lapilli metatuffs (lifhicl cryslal) and flows, cherty metatuffs, and associated chemical mefasediments (metachert) Felsic Center(s) v4I1 C) 0 N 0 (0 0 3 C) _____ �I 500 FEET Figure 4. �Tab'e 1 DESCRIPTION OF LITHOLOGIC UNITS VOLCANIC UNITS HANGING-WALL SEQUENCE (FEISIC FLOW-FRAGMENTAL COMPLEX) fl/ I D L I V7 INTERMEDIATE TO MAFIC FLCMSLVR ] INTERMEDIATE TO FELSIC FLOWS (dacite to rhyo(andesite to basaltic andesite) Dark greenish dacite) Greenish gray, gray, fine— to medium— fine— to medium—grained, thin—to thick bedded, grained, massive, commonly porphyritic (feldspar and fractured and healed ferrornagnesian mineral (quartz and carbonate), porphyritic (feldspar phenocrysts) and nonporphyritic inetavolcanic flows and flow breccias. Interflow tuffs and sediments and interbedded siliceous and metavolcanic flows occur locally. IV11T i- phenocrysts) metavolcanic flows and/or subvolcanic intrusives. FELSIC FLOWS (rhyolite) Light gray to pinkish— white, fine— to medium— grained, massive, fractured and healed, very hard, commonly porphyritic (blue quartz eyes and feldspar phenocrysts), siliceous rnetavolcanic flows, sub— volcanic intrusives, and flow breccias; localized well-developed banding?. flow Locally, weakly mineralized and altered. INTERBEDDED FLCYS AND INTERFLOW PYROCLASTIC BEES Dominantly thin, intermediate to felsic metavolcanic flows (Vp) , flow breccias, and carbonath-rich lnterflow metatuffs and lapilli metatuffs. LT INTERMEDIATE TO FELSIC LAPILLI TUFFS Greenish gray, medium- to coarse— grained, thin- to thick-bedded, carbonate-rich coarse metatuffs, lapilli metatuffs, and tuff breccias. Normal graded bedding is common. LLI INTERMEDIATE TO FELSIC FINE AND COARSE TUFFS Light to dark greenish gray, fine- to medium—grained, thinly bedded to laminated metatuffs and associated tuffaceous meta— Black meta—argillite laminations sediments. locally. Intercalated thin inter- mediate to felsic metavolcanic flows (VD) locally. I Cs TUFFACEOUS SEDIMENTS Dark gray to CT black, fine—grained, laminated, commonly graphitic, chlorite—rich meta—argillite. Commonly sulfide— bearing. Chert laminations common. CHERTY TUFF Fine-grained, finely laminated cherty and hematitic inetatuff. Chert component greater Thin massive-sulfide than 50%. beds may be present. MINERALIZED SEQUENCE ALTERED AND MINERALIZED QUARTZ-CRYSTAL FELSIC TUFF Medium to light gray, fine- to inedium-grained, poorly bedded, well-foliated (schistose) , crystal-bearing (blue quartz eyes) quartz-sericite schist. Well—developed tuffaceous texture is preserved. Widespread stockwork sulfide mineralization is characteristic, consisting of up to 30% (commonly l%-lO%) pyrite ± chalcopyrite as disseminations, cross-cutting veinlets, and conformable bands. This unit hosts copper- and gold— bearing massive to semimassive and stringer mineralization. 1xT1_31 ALTERED AND MINERALIZED CRYSTAL FELSIC TUFFS Medium to light gray, fine- to poorly to well—bedded, weakly to well—foliated (schistose), crystal—bearing (quartz and feldspar crystals), locally fragmental qnartz—sericite (ifeldapar) schists and semi—schists. Widesprad disseminated sulfides (pyrite ± chalcopyrite) and conformable massive to semitnassive sulfide bands. Crystal tuff units are separated by thin argillite (CS) and felsic tuff (GT) beds. Unit XT medium-grained, hosts copper-bearing fragmental massive sulfide and stringer sulfide mineraliztion FOOTWALL SEQUENCE GT7 BEDDED FELSIC TUFF Gray to greenish gray, fine—grained, thinly to thickly laminated, well—foliated (schistose) sericite schist. disseminated pyrite, up to 5%. [F 9203001 CE11O3 GEO Commonly contains INTERMEDIATE TO MAFIC FLOWS AND INTERFLOW SEDIMENTS (andesite) Dark greenish gray, fine- to medium-grained, locally laminated, foliated (schistose) chlorite Carbonate alteration common. schist. �— MPFIC FLOW(S) (basalt) Dark greenish gray, aphanitic to fine—grained, nonfoliated, fractured and healed, nonporphyritic (massive) metavolcanic flows and/or subvolcanic intrusives VM INTRUSIVE UNITS 1 +] SUBVOLCANIC INTRUSIVE Dark gray, medium—grained, equigranular, massive, fractured [± intermediate to mafic dike or sill. +1 and healed, SULFIDE MINERALIZATION MASSIVE SULFIDE MINERALIZATION Fine- to very fine—grained, poorly to well-bedded, locally fragment—bearing (less than 20% XT fragments) , massive (greater than 50%, up to 90%) granular pyrite with varying amounts of fine chalcopyrite and tetrahedrite-tennantite intergrowths. Gangue minerals include quartz + sericite ± chlorite. SEMIMASSIVE SULFIDE MINERALIZATION 30% to 50% pyrite. SULFIDE MINERALIZATION Medium- to coarse-sized, sithrounded to subangular, coimnonly silicified XT fragments (greater than or equal to 20%) FRAGMENT-BEARING supported in a fine-grained matrix of semimassive pyrite (30%-5O%) ± chalco— pyrite. --- FRAGMENTAL SULFIDE MINERALIZATION Medium- to coarse-sized, subrounded to (py) fragments (greater than or equal to 30%) supported in a fine matrix of quartz and sericite. subangular sulfide /JJ STRINGER SULFIDE MINERALIZATION Fine—grained cross—cutting pyrite (1O%-3O%) ± / chalcopyrite or wispy chalcopyrite veinlets and blebs; commonly overprints massive sulfide and fragment-bearing sulfide mineralization. HYDROTHERMAL ALTERATION alteration and weak to Includes weak to strong fine—grained black wispy chlorite intense silicification. DL — upper lens LL — lower lens Level GEOLOGIC SYMBOLS contact N observed projected in drillhole or infeed contact strike + dip of relict bedding strike of vertically dipping bedding strike of foliation (sistosity) strike fault, dashed where projected Plans of vertically dipping foliation (sjstosjty) relict bedding attitude foliation attitude (schistosity) flow breccia unless otherwise designated shear zone TOP direction of stratigraphic top Abbreviations py-pyrite, po-pyrrhotite, cp-cbalcopyrite, sp—sphalerite, tet—tetrahedrite DDH significant sulfide mineralization base- and precious-metal—bearing Ore grade Cu Ore grade Au sulfide mineralization �150 The felsic sequence remains open along strike to the west of the deposit, but is cut off to the east by an extensive rhyolitic dome-flow complex of unknown dimensions. In general, the felsic complex is relatively unaltered, although localized hydrothermal alteration has produced zones of moderate to intense silicification, sericitization and chioritization. Disseminated pyrite often occurs within sericitized zones, whereas stringer-like chalcopyrite is associated with black chlorite alteration. Geophysically mappable meta-argillite formational units closely parallel or are interbedded with the felsic tuffs and the deposit. These units locally contain anomalous copper mineralization and are an important ore equivalent marker horizon that extends several miles along strike in both directions. Regionally the felsic center may be isoclinally folded, though there is no evidence of folding in the immediate deposit area. Metamorphic grade of the succession is lower greenschist; a weak to moderately strong foliation (schistosity) has developed parallel to relict bedding in the tuffaceous units; however, many relict volcanic and sedimentary features have been preserved. GEOCHEMISTRY To classify the geochemical affinity of the volcanic succession, major and trace element compositions were determined for 58 core samples taken from 12 driliholes that intersect the deposit. Twenty-two samples were from the host quartz-sericite schist (mineralized quartz-crystal felsic metatuff, designated the XT unit), 26 samples were of relatively unaltered volcanic rocks from the hangingwall sequence and 4 samples were from the felsic dome-flow complex. FeO* Alk MgO Figure 5. AFM diagram for hangingwall and felsic dome. Squares = hangingwall volcanics; Crosses = felsic dome samples. �151 Because the hangingwall and felsic dome rocks are generally not hydrothermally altered and have undergone only lower greenschist facies regional metamorphism, they can be classified based on major element composition. On an AFM diagram (Fig. 5) most samples plot within or near the calc-alkali field. Limited data on Si02 and alkali content suggests that the hangingwall sequence includes a fully differentiated rock suite ranging from basaltic-andesite to rhyolite (Fig. 6). Samples from the felsic dome complex plot primarily in the rhyolite field. To ascertain the primary geochemical affinity of the hydrothermally altered quartz-sericite schist it is necessary to use immobile element ratios. TiC)2 and Zr are generally considered to remain immobile in rocks that have been subjected to low-grade metamorphism and/or hydrothermal alteration (Pearce and Cann, 1973). If these elements have remained immobile during alteration, they should define a regression line that trends toward the origin in binary plot. The precursor composition of the altered rock can be determined by the intersection of the trend of the plot with the fractionation trend developed by less altered rocks of the sequence. On a TiC)2 vs. Zr plot (Fig. 7), rocks from the hangingwall and felsic dome define a normal differentiation trend of decreasing Ti02 with increasing Zr. In contrast, quartz-sericite schist samples plot along a linear trend toward the origin which is consistent with relative immobility during hydrothermal alteration. The regression line for the quartz-sericite schist intersects the felsic end of the fractionation trend indicating rhyolite/rhyodacite as the precursor rock type. Immobile element plots also provide an indication of the nature and extent of mass changes due to hydrothermal alteration. Mass loss due to solution increases the relative concentration of immobile elements, whereas mass addition, such as during silicification, has the opposite effect. Samples that have undergone mass addition will plot between the fractionation trend and the origin, whereas those with mass loss will plot above the fractionation trend. On the Ti02 vs. Zr plot, most quartz-sericite schist samples are located between the fractionation trend and the origin indicating mass dilution. Visually, it is apparent that dilution is probably related to silicification and, to a lesser extent, the addition of sulfides. Evidence of a net silica increase can be demonstrated graphically on a plot of Zr vs. Si02 (Fig. 8). For the hangingwall and felsic dome rocks a positive linear trend consistent with normal fractionation is apparent. In contrast, the trend of decreasing Zr with increasing Si02 evident for the quartz-sericite schist samples indicates dilution due to silicification. In Figure 9 it is apparent that, in addition to silicification, the quartz-sericite schist has undergone K-enrichment and Na-depletion during hydrothermal alteration. Changes in the alkali composition would have been produced during sericitization of the quartz crystal tuff precursor. Silicification must have occurred after changes in the alkali composition because sericitization produces a net quartz loss. MINERALIZATION Massive-Semimassive Sulfide Mineralization Drilling completed thus far indicates that the bulk of the deposit consists of two steeply dipping, stacked, proximal massive (50%-90%) and semimassive (30%) sulfide lenses developed at �152 16 14 12 0 10 + 8 0 z Cl, 6 4 2 0 35 40 50 45 60 55 65 70 75 SiO 2 Figure 6. Volcanics from the hangingwall and felsic dome complex classified on the basis of alkali and silica content (after Lebas et al., 1986). Symbols same as Figure 5. 1.0 0.8 Basaltic Andesite LiLI L1 0.6 0 Li I— Li 0.4 LII Li Li Li LI >EILIX Li 0.2 Li fl Li Li Rhyolite 0.0 0 50 100 150 200 Zr Figure 7. Ti02 vs. Zr plot for quartz-sericite schist, hangingwall volcanics and felsic dome complex. Hangingwall and felsic dome samples (squares) define a normal differentiation trend of decreasing Zr with increasing Ti02. In contrast, quartz-sericite schist samples (X) plot along a trend toward the origin. �153 90 I x 'XXrXD 80 70 El El El ElEl x El El 60 50 — 0 40 50 0 I I 100 150 200 Zr Figure 8. Plot of Zr vs. Si02 vs. Zr for quartz-sericite schist, hangingwall volcanics and felsic dome. Hangingwall and felsic dome samples (squares) plot along a normal differentiation trend, while for quartzsericite schist samples (X) Zr is diluted due to silicification. X 0 El / El x Hydrothermal 0 Alteration 4 X x x >:< x x X El 2 x x 1 I o 0.0 I 0.2 I 0.6 0.4 0.8 K 0/Na Q+K 0 2 2 2 Figure 9. Plot of Na2+K20 vs. K20/Na20+K20 for quartz-sericite schist, hangingwall volcanics and felsic dome. Quartz-sericite schist samples (X) and Na depleted and K enriched relative to the sodic hangingwall and felsic dome samples (squares). �154 or near the stratigraphic top of an altered quartz-crystal felsic tuff (XT) unit. True thicknesses of the lenses range from 5 to 40 feet. The lower lens is thickest near the center of the deposit but interfingers with quartz-crystal tuff (Xl') downdip and along strike; the upper lens is more continuous along dip and strike (Fig. 10 and 11). Both lenses extend to subcrop and are overlain by 100-120 feet of Chippewa end moraine. Other stratigraphically lower massive sulfide lenses are known, particularly along the eastern flank of the deposit, but have not been well defined by drilling. Each lens contains medium to very fine grained, granular (locally recrystallized), pyrite with varying amounts of interstitial chalcopyrite ± tetrahedrite-tennanite ± arsenopyrite ± bornite ± chalcocite and ± gold tellurides. Gangue minerals include quartz, carbonate (calcite), and sericite. Petrographic analysis indicates that chalcopyrite and bornite also occur as exsolutions within pyrite grains. The presence of tetrahedrite-tennanite, arsenopyrite, and gold tellurides explains the unusual geochemistry of the mineralization, which includes anomalous concentrations of arsenic, antimony, bismuth, and tellurium. Individual beds within the lenses may be fragment-bearing (altered and unaltered quartzcrystal tuft); the stratigraphically lower lens is massive or exhibits vague bedding, whereas the upper lens is generally well bedded and laminated (Fig. 12B). Sedimentary features, such as graded bedding, have been observed in drill core. The pyritic lenses are connected by a fragment-bearing semimassive sulfide zone (a debris apron) that has been overprinted by poorly developed epigenetic copper and gold stockwork-stringer mineralization (Fig. 10 and 11). The semimassive sulfide zone is characterized by a fine pyrite matrix which supports subrounded to angular, silicified quartz-sericite schist clasts that, in general, range from 2 to 10 cm in diameter. The zone thickens where the two lenses converge up dip toward the center of the relict sulfide mound. Isopach data suggests that the original mound developed within and along the flanks of a paleotopographic high formed by a thickening of the quartz-crystal tuff unit. The double plunge (east and west) of the upper massive sulfide lens may be a primary feature produced by paleotopographic control of sulfide deposition. Near the subcrop both lenses exhibit evidence of shallow oxidation and supergene enrichment. A thin ( 5') replacement zone containing secondary chalcocite and bornite after primary sulfides is known from drilling. Stockwork-stringer sulfide mineralization Stockwork-stringer mineralization consists of fine cross-cutting chalcopyrite and/or pyrite ± chalcopyrite ± gold tellurides (calaverite, petzite, and krennerite) anastomosing veinlets-veins (Fig. 12C). In addition to overprinting the semimassive sulfide zone, wispy chalcopyrite stringers locally cross-cut bedded massive sulfide (Fig. 12D). The stockwork-stringer mineralization may be accompanied by weak to strong silicification and generally weak, wispy chlorite alteration. Both lenses are enveloped by a pyritic stockwork sulfide halo ( 30% sulfides) which extends an undetermined distance along strike. The halo, which is associated with widespread pervasive sericitization, consists of pyrite disseminations, discontinuous bands or laminations and veinlets that are cross-cutting and parallel to foliation and bedding. Stockwork-stringer mineralization developed stratigraphically below the major lenses grades both vertically and laterally into the halo. �a C • 0 / . a* 0 • 200 C 0 I 1 • • 0 • FEET C C 0• • 3 200 o * 0 . C C C CL A C . L • o C — C. V0 - . a C . 0 Figure 10. Geologic cross-section 49505E. 0 . . 0 0 a. .__, C C 0 ° C: ,..::. . •. —'.--- a • GT GT SAPR0LTE XT LOOKING WEST �________ . °•c •0 LOOKING WEST C .0 0. o .Q .0 o '. •.•• .,.,,• . •o .•0. .00 •0 '. . .c' •.'• Q0 • •C pD0 ,o Q• . Q. , .0 GLACIAL -. I VD L GT 4 20 GT JO Fig. H �157 Copper-Gold Distribution The deposit, classified as copper-type VMS mineralization (DeMatties 1994), contains only minor amounts of zinc and, therefore, has not developed any zonation of base metals. However, the deposit does exhibit distinct copper-gold zoning patterns, i.e. development of copper-rich massive sulfide lenses accompanied by several prominent parallel gold zones. In the massive sulfide mineralization hypogene copper grades exhibit a significant increase stratigraphically upward from the lower to upper lens. The well-bedded stratigraphically upper lens contains the highest copper grades in the deposit. This copper distribution may have resulted from hypogene enrichment by stratigraphically upward migration or "refining" during multiple copper-gold hydrothermal pulses within the developing sulfide mound. The highest gold values in the system occur stratigraphically below each lens as semiconformable ore-grade ( 0.1 opt) gold assay zones (designated as the "tuckunder" and lower gold zones). These zones, which developed in the enveloping stockwork-sulfide halo, appear to be stratigraphically controlled and have continuity along strike and down dip. Locally, structures cross-cutting the halo host auriferous quartz-carbonate veins containing gold-silver tellurides that assay in the multiple ounce-per-ton range. The frequency of cross-cutting gold-silver mineralized structures is unknown at this time. Widespread gold values 0.01 opt have been found throughout the stockwork sulfide halo. Higher values can form poorly developed stratiform assay zones of limited down dip or lateral extent. POTENTIAL ORE RESERVES A potential copper ore reserve (copper zone) is contained in the two stacked lenses, semimassve sulfide zone, and associated stringer mineralization. The zone contains accessory amounts of gold and silver reported as gold and silver telluride minerals. Where the lenses coalesce, the copper zone may total 70 feet in thickness. Overall dimensions of the zone include a strike length ranging from 1100 feet at the subcrop to 1800 feet at depth and a thickness which varies from 10 to 70 feet; it has been tested to a depth of 2000 feet. A 1994 estimate calculated a drill indicated resource of 3.3 million tons grading 2.05% copper, 0.07 opt gold and 0.41 opt silver (estimate includes "tuckunder" gold zone). A high-grade core in the center of the copper zone contains 1.42 million tons grading 3.11% copper, 0.07 opt gold and 0.41 opt silver. The copper zone remains open down dip and down plunge to the west; it appears to terminate against the domal complex along its eastern margin. In addition to the copper zone, ore potential exists in the adjoining lower gold assay zone, which is characterized by pyritic gold mineralization with minor copper and silver values. Though poorly defined, it is estimated (1994) to contain a resource of 602,850 tons grading 0.885% copper, 0.21 opt gold, and 0.26 opt silver. The zone remains open in all directions. EXPLORATION POTENTIAL In addition to expanding the identified resource down dip and down plunge, there is good potential for discovery of additional VMS deposits along strike to the east where the ore-equivalent horizon has been located. The horizon is represented by a section of laminated to thin bedded hematitic cherty tuffs (tetsusekiei), meta-argillites (commonly graphitic or sulfide-bearing) and �Figure 12 Polished drill core samples from the Bend deposit. 158 A B Altered felsic quartz-crystal metatuff (quartzsericite schist) host rock, productive XT unit. Note flattened and elongated blue (dark gray in photo quartz eyes which characterize this unit. A. Bedded and laminated massive sulfide from the upper lens of the copper zone. Relict bedding features are well preserved. Large host host rock fragment (quartz-sericite schist) is draped by bedding. Darker laminae are B. tetrahedrite-tennantite. C C. Pyritic stringer mineralization cross cutting quartz-crystal tuff. D D. Fine chalcopyrite stringer mineralization (light gray) overprinting massive pyritic sulfide, copper zone. F E E. Laminated cherty hematitic metatuff (tetsusekiei) that stratigraphically overlies the deposit along its eastern flank. The light laminae are the tuffaceous (sericite-rich) component whereas the darker laminae represent the exhalative (quartz-hematite) component. F. Mineralized argillite. Note fine discontinuous pyrite-chalcopyrite laminations (light gray). 0 1 2 3inches �159 copper-bearing massive sulfide beds (Figs. 12E and 12F). Although the horizon is interrupted by the felsic dome, geophysical surveys suggest it reappears again on the northeastern margin of the complex and extends along strike for nearly 5000 feet. Several isolated electromagnetic anomalies have been identified along the trend of the horizon. These targets remain untested. Acknowledgments The author would like to acknowledge Sharpe Energy and Resources for permission to release these data. Also thanks are extended to Mark Burdick who prepared the illustrations. References Cited DeMatties, T. A., 1994, Early Proterozoic massive sulfide deposits in Wisconsin: an overview: Economic Geology, v.89, p. 1122-1151. LeBas, M. J., LeMaitre, R. W., Streckeisen, A., and Zanettin, B., 1986, A Chemical Classification of Volcanic Rocks Based on Total Alkali Silica Diagram: Journal of Petrology, v. 27, p. 745750. Pearce, J. A. and Cann, J. R., 1973, Tectonic Setting of Basic Volcanic Rocks Determined Using Trace Element Analyses: Earth and Planetary Science Letters, v. 1, p. 290-300. Sims, P. K., Van Schmus, W. R., Schulz, K. J., and Peterman, Z. E., 1989, Tectonic-stratigraphic evolution of the early Proterozoic Wisconsin magmatic terranes of the Penokean Orogen: Canadian Journal of Earth Sciences, v.26. p 2145-2158. �160 �161 GEOLOGY OF THE LYNNE BASE-METAL DEPOSIT, NORTH-CENTRAL WISCONSIN, U.S.A. by Glen W. Adams Geological Consultant Rhinelander, Wisconsin ABSTRACT The Lynne polymetallic deposit was discovered in early 1990 by Noranda Exploration Inc., in north-central Wisconsin, U.S.A. The deposit is the most recent base-metal discovery in the Early Proterozoic, Rhinelander-Ladysmith greenstone belt and has a reported open-pit reserve of 5.61 million tons grading 9.27% Zn, 0.47% Cu, 1.71% Pb, 2.38 opt Ag, and 0.021 opt Au. Mine permitting procedures have been suspended and the future of the deposit is uncertain. The Lynne deposit consists of four stacked, strataform massive to semi-massive sphalerite-rich bodies hosted within a predominantly felsic sequence of subaqueous volcanic and volcaniclastic rocks, volcanic—derived wackes and tuffs, and chemical sediments. Unusually abundant amounts of carbonate rocks are directly associated with the sulfide ore. The Lynne stratigraphy is underlain by an intrusive tonalite body that locally disrupts and intrudes the lowest sulfide unit. No definitive stringer zone or alteration pipe has been identified; however, a broad alteration assemblage, similar to other volcanogenic massive sulfide deposits, envelopes the immediate host rocks. Skarn-style mineralization is associated with carbonate rocks along the flanks of the sulfide bodies. Metal zoning compatible with volcanogenic massive sulfide deposits is present. Although the Lynne deposit has characteristics of both volcanogenic massive sulfide and skarn-type deposits, a volcanogenic model is preferred. INTRODUCTION The Lynne polymetallic deposit is located in Lynne Township approximately 25 miles west-northwest of Rhinelander in north-central Wisconsin (Figure 1). The deposit site is approximately nine miles north of State Highway 8 and the small town of Tripoli. All-weather paved and gravel roads access the project area and the Wisconsin Central Railway has a siding at Tripoli. The Lynne deposit occurs on Oneida County surface and mineral lands that are under lease to Noranda Minerals Wisconsin Corp. (Figure 2). Subsequent to the discovery of the deposit in January, 1990, 138 drill holes were drilled to delineate the Lynne massive sulfide body and conduct stratigraphic tests in the immediate deposit area. In January, 1992, a Notice of Intent To Collect Data and Proposed Scope of Study was filed with the Wisconsin DNR as Noranda's initial step in the involved Wisconsin mine permitting process. The deposit is intimately associated with an area of wetlands that would be disturbed by mining. On October 23, 1993, Noranda suspended all permitting activity, citing uncertainties surrounding DNR wetlands and lake-bed designation issues and metal prices. All surface disturbances related to the exploration and initial permitting procedures were reclaimed as of January, 1996 and the future of the deposit is uncertain. All Noranda's county mineral leases on the Lynne deposit remain in good standing. �1Lake, \) 5TL 0 7VQ ,c ';( c__in \O , Lke-' UPineL I S I( Fk!( L 1u e 3 ? N2 - !ueL } I Tomahè4k 4H A( 3%/cs Jkainao \C!ear ( Flo ' Sa tI -. _- -J t- kó z.L1I 2("— 1r\ I c o pA fn -i -Wi3jw - .iThree-*zaes Sugar Camp ethurst \'J Bear LateU ch / stL I F!owa -McNau t n —f —--Ste//a L -.' \, s8\.\ Jf,' (1 9( __c NE cagen RhineIander'7 L Scale \\ \r onico •I5fl, ci 10 miles 10 3Ci -- 'r-2 Jennhigs0 15 kilometers /A /T WISCONSIN Piaure 1 Location Map Lynne Base—Metal Deposit Oneida County, Wisconsin �_____ i: ,/ ti 0 2000 0 60 4000 feet Private land Private land purchased by Noranda Figure 2 Noranda Mineral Lands Lynne Base-Metal Deposit Oneida County, Wisconsin 1200 meters �164 REGIONAL GEOLOGY The Lynne deposit is located in the central part of the Rhinelander-Ladysmith greenstone belt, a belt of Proterozoic, volcanic and sedimentary rocks within the Southern Province of the Canadian Shield. The Rhinelander-Ladysmith greenstone belt (Figure 3), is the informal designation for the northern part of the Pembine-Wausau terrane of Sims et a!. (1989). It is approximately 50 miles wide and extends roughly 150 miles in an east-west direction across northern Wisconsin and the central Upper Peninsula of Michigan. Rocks within the greenstone belt range in age from 1,860 Ma to 1,889 Ma (Sims eta!., 1989), and have been affected by the Penokeon Orogeny, resulting in locally intense folding, major faulting, thermal metamorphism, and granitic plutonism. Widespread Pleistocene glacial deposits mantle much of the greenstone terrane resulting in minimal outcrop exposure. On the west the greenstone belt is overlain by Late Proterozoic quartzite and Paleozoic sandstones, while on the east there is an onlap of Early Paleozoic sandstone and carbonate rocks. Indepth reviews .f the Rhinelander-Ladysmith Greenstone belt are presented in this volume by DeMatties and by LaBerge. Mineral exploration over the past 30 years, dominated by airborne geophysical surveys, has identified over two dozen significant base-metal massive sulfide occurrences scattered throughout the Rhinelander-Ladysmith greenstone belt (Figure 4). The Flambeau mine, currently in production, and three other potentially economic occurrences, the Crandon, Bend, and Lynne deposits, all occur within the Rhinelander-Ladysmith greenstone belt. Geologic knowledge of the Lynne deposit area is very limited due to poor outcrop exposure. Regional airborne E.M. and magnetic data and scattered drill hole information suggest that the general geology of the Lynne area consists predominantly of mafic to intermediate volcanic rocks with at least one felsic eruptive and intrusive event, represented by the lithologies in the immediate Lynne deposit area. The felsic volcanic-related rocks associated with the Lynne deposit predominate over mafic to intermediate rocks by a significant amount. The increase of felsic volcanic rocks in the Lynne deposit area is common to other significant base-metal occurrences in northern Wisconsin and elsewhere (DeMatties, 1994). LYNNE DEPOSIT DISCOVERY HISTORY The Lynne deposit is the most recent major base-metal discovery in Wisconsin. However, at least two exploration companies were aware of the Lynne airborne E.M. anomalies up to 14 years before its discovery. Exxon Minerals identified isolated anomalies over what is now the Lynne deposit from an airborne E.M. survey flown in the mid 1970's. Because the mineral rights covering the anomalies were owned by Oneida County, and unattainable at that time, no serious interest was given to the target. Kerr McGee conducted an airborne E.M. survey over the area in the early to mid-1980's following up on anomalous lake sediment samples taken about two miles southeast of the deposit. They too had detected the Lynne E.M. response; however, Oneida County lands were still not available for mineral leasing. Not until Oneida County made their mineral lands available for lease through competitive sealed bid in 1989, did the lands hosting the Lynne deposit become attainable. Unfortunately, by this time neither Exxon Minerals nor Kerr McGee were still actively exploring in Wisconsin. Noranda Exploration remained active in the state on the belief that Wisconsin's greenstone belts hosted additional base-metal deposits. Noranda's staff was experienced in Wisconsin exploration and knew of the Lynne airborne E.M. anomalies. Noranda's perseverance paid off when, in May �Figure r 3 Schematic Geology Rhinelander-Ladysmith Greenstone Be North—Central Wisco Paleozojc sediments Flamb — a foIith :__I::!-: - A • Massive sulfide occurrence __:: 50 miles Scale �4 I 0 20 Scale p 40 60 miles Massive Sulfide Occurrences North-Central Wisconsin Figure N A �167 1989, they were the successful bidder on four sections of Oneida County mineral lands in Lynne Township. Initial ground geophysical surveys conducted by contractor Rodney Ikola and Associates, and later by Noranda staff, revealed a moderate to strong E.M. anomaly with an associated strong out-ofphase E.M. component (Figure 5), which was initially attributed to an overburden response. Gravity data indicated a relatively low, but anomalous, gravity response of about 0.8 milligals. On January 6, 1990, after two failed attempts to penetrate 56 feet of glacial overburden, the Lynne massive sulfide deposit was intersected in the first of two initial drill holes (Adams, 1990). Discovery hole W90-1 intersected 128 feet of zinc-rich massive sulfides followed by a second hole, drilled 150 feet to the north of the first hole, which stayed in relatively massive sulfides for over 375 feet (Fable 1). It was now understood that the large out-of-phase E.M. response was caused by widespread, relatively poorly conductive, massive sphalerite mineralization. The massive orebody corresponds with the main strong in-phase E.M. anomaly of Figure 5. The narrow in-phase E.M. anomaly southeast of the orebody is not related to sulfide mineralization. On June 19, 1990, Noranda publicly announced the discovery of the Lynne deposit. After 18 years of exploration, the drilling of several promising massive sulfide occurrences, and the expenditure of several millions of dollars in Wisconsin, Noranda appeared to have a massive sulfide deposit with commercial potential. Reported reserves of 5.61 million tons grading 9.27% Zn, 0.47% Cu, 1.71% Pb, 2.38 opt Ag, and 0.021 opt Au (American Mines Handbook, 1995), are considered recoverable by open pit methods. In 1990, Noranda flew a detailed airborne E.M. survey over the Lynne deposit and surrounding region defining additional attractive targets. To date no other discoveries have been made, although the exploration potential is favorable. In early 1993, Noranda Exploration Inc. closed its Wisconsin exploration office sighting a general unfavorable mineral exploration and development climate in the state. GEOLOGY AND MORPHOLOGY OF THE LYNNE DEPOSIT The area hosting the Lynne deposit is covered by 40 to 75 feet of unconsolidated glacial till. Lithologies, alteration and structure of the orebody and its host rocks are derived from drill hole information and detailed ground and airborne geophysical data. The only known outcrop within several miles of the deposit is an area of moderately foliated granitic rock occurring in, and adjacent to, the Willow River about 4000 feet northeast of the orebody. There is evidence of an oxidized cap on the ore deposit. The Lynne ore body consists of four strataform, massive to semi-massive, stacked, polymetalhic, sulfide bodies with an aggregate thickness of approximately 325 feet in the central part of the ore zone. The sulfide bodies exhibit abrupt thickening and coalescing in the core of the ore zone with ore dissipating relatively quickly on the flanks. Sphalerite is the predominant sulfide mineral followed in abundance by pyrrhotite, pyrite, galena, and chalcopyrite. Gold occurs in the lower sulfide body and in association with skarn mineralization on the flanks of the deposit along with magnetite. Silver mineralization occurs in the central to upper part of the ore body. Metal zoning occurs as a relative enrichment of copper toward the base of individual sulfide units. Metal zoning also occurs as a progression of relative copper and iron enrichment toward the base of the composite sulfide deposit, grading upward into strong zinc mineralization followed by concentrations of lead and silver in the upper parts of the ore zone. The sulfide-bearing zone has a strike length of approximately 1300 feet and both the ore deposit and its host rocks strike in a general east-southeast �168 Table 1 Assay Results From Drill Holes W90-l & W90-2 Lynne Base-Metal Deposit Oneida County, Wisconsin Composite Zones from Drill Hole W90-1 From (Ft) To (Ft) Width (Ft) Zn Cu % Pb Ag Au % % opt opt 135.50 150.70 15.20 34.78 0.38 3.64 0.608 0.010 150.70 168.20 17.50 5.02 0.83 0.36 0.293 0.012 168.20 197.20 29.00 34.44 0.88 3.13 1.104 0.006 205.40 263.50 58.10 22.17 0.58 3.83 1.435 0.014 135.50 263.50 128.00 22.71 0.64 2.95 1.039 0.011 Ag opt Au opt Composite Zones from Drill Hole W90-2 To (Ft) Width (Ft) Zn Cu % % Pb % 55.00 66.60 11.60 18.59 0.05 8.47 8.558 0.016 102.60 242.30 139.70 6.41 0.17 2.82 10.746 0.014 250.90 320.60 69.70 21.64 0.54 2.82 1.257 0.012 320.60 350.20 29.60 2.79 0.12 0.77 0.901 0.012 372.20 405.50 33.30 4.71 0.16 0.29 0.498 0.009 405.50 439.00 33.50 11.20 0.74 0.76 0.844 0.018 55.00 439.00 384.00 8.45 0.26 2.09 4.736 0.012 From (Ft) �Max-Mm 0 S 5 0 0 EXPLANATION 100 1.00 Sc 01. 800 eel I 200 meters Out a) Phase In Phase {HLEM response widths) HLEM Ground Geophysical Data Lynne Base-Metal Deposit Oneida County, Wisconsin Figure t5 N ( �170 direction dipping northeasterly at about 40 degrees. Graded beds within the host rocks indicate that the stratigraphy is upright with tops to the northeast. The zinc-rich sulfide bodies lie within a subaqueous, volcaniclastic, sedimentary and carbonate-rich sequence of rocks. Drill hole data from host rocks indicate a general coarsening of pyroclastic material to the north, or down-dip, suggesting a more proximal location to a possible volcanic eruptive source in that direction. The lowest sulfide-rich horizon of the deposit is underlain, and locally disrupted and cut off, by an intrusive tonalite body. The deposit and its host rocks show no major structural complexities. East to southeast striking, vertical to sub-vertical, fracture zones exhibit minor movement in stratigraphy within and down-dip from the ore zones, and according to Kennedy (1992), postdate the tonalite. The fracture zones are commonly filled with rhyodacite dikes and less often with basaltic dikes. A shallow depression or trough occurs in the upper surface of the tonal ite beneath the thickest, central part of the ore deposit. There has been some speculation that the fracture zones may have some relationship to this trough-like feature, and that the fracture zones, and possibly the depression in the tonalite, are genetically related to the deposition of sulfide mineralization (Adams, 1991). Both structural features may represent remnants of a down-dropped, or graben-like, feature that helped to localize ore deposition. The entire lithologic package, although variably altered and locally affected by contact metamorphism and skarnification, is metamorphosed to greensehist metamorphic rank. Evidence of retrograde alteration of higher temperature minerals to lower temperature minerals is widespread. Chlorite and talc-bearing alteration assemblages occur in the lower parts of the Lynne stratigraphy; however, no distinct stringer zone or alteration pipe is evident. A pervasive alteration assemblage does occur in the enveloping host rocks. Because of the unusual combination of base-metal and alteration assemblages, and the host rock lithologies, the Lynne deposit exhibits characteristics common to both volcanogenic massive sulfide and carbonate-related skarn, deposits. Sulfide Mineralization The massive and semi-massive strataform lenses of the Lynne ore deposit are divided into four separate zones or units based on physical, or discrete compositional, differences (Adams, 1990; Adams, 1991). The sulfide lenses are designated as units A through D with A being the lower-most, and progressing stratigraphically upward to units B, C, and D (Figures 6 and 7). Unit A Sulfide Unit A exhibits the greatest lateral extent of all the zones and reaches up to 60 feet in thickness, although it is locally disrupted and intruded by the foot-wall tonalite. The zone is a pyritic, massive sphalerite body enriched in chalcopyrite and pyrrhotite relative to the other zones. Over 50 percent of the copper and over 30 percent of the gold content of the ore deposit occurs in cherty, chloritic, pyrrhotitic massive to semi-massive sulfide portions of this unit (Kennedy, 1992). Partially enveloping the unit is a talc-rich assemblage containing disseminated to massive sulfides with Mgchlorite, phiogopite and lesser tourmaline, serpentine, cummingtonite, and galena (Kennedy et a!., 1991). Also present locally within the alteration envelope is stringer-like and disseminated sphalerite and pyrrhotite. An extensive barren zone of this alteration assemblage, with laminated cherts containing disseminated pyrrhotite, pyrite and minor magnetite lanünae, continues up to 300 feet along strike and down-dip from Unit A. �6 Sulfide Units (Section 10,000 E.) Lynne Base-Metal Deposit Oneida County, Wisconsin Figure Looking West �7 Composite Assay Results from Sulfide Unit (Section 10,000 E.) Lynne Base—Metal Deposit Oneida County, Wisconsin Ficrure Looking West )16 088 �— 173 Unit B Narrow intervals of carbonate rock, with local skarn-type mineralization, separate units B and A. Sulfide mineralization in Unit B differs strongly from Unit A in that it occurs in association with lenticular masses of chemical sedimentary rocks including calcareous and siliceous fades. Disseminated sphalerite and pyrite is ubiquitous to the carbonate host rocks, and massive to semimassive sphalerite, with lesser galena and subordinate chalcopyrite, forms lenses up to 50 feet thick. The composite thickness of Unit B reaches approximately 150 feet in the central part of the ore body. Unit B contains over 50 percent of the total deposit tonnage and almost 60 percent of the total zinc content of the deposit (Kennedy, 1992). Thin beds of carbonate-rich volcaniclastic and sedimentary rocks within the unit are pervasively replaced by caic-silicate minerals. Sphalerite, and to a lesser extent pyrrhotite and pyrite, are disseminated throughout the carbonate host rocks. The carbonate rocks are relatively planar bedded near the base of the unit becoming increasingly disrupted toward the top. Carbonate beds tend to be finer grained and well bedded off the flanks of Unit B. Unit C Narrow beds of barren volcaniclastic wackes or tuffs and a rhyolitic sill separate units B and C. Unit C is approximately 160 feet thick and consists predominantly of contorted, folded, or disrupted calcareous chemical sediments that can be divided into two zones. The lower calcareous zone is about 50 feet thick and consists of marble with massive to semi-massive sphalerite and galena. The upper 110 feet of the unit is calcareous, but within the upper 50 feet it becomes extremely siliceous containing cherty layers and diopside-rich cherts. Sulfide mineralization in the upper part of Unit C consists of disseminated to semi-massive sphalerite, pyrite and galena. A large proportion of the deposit's silver content occurs in the upper siliceous part of Unit C in the form of native silver, tetrahedrite, and argentiferous galena. Here, silver content averages over 100 ounces per ton for several tens of feet. As with Unit B, this unit shows a relative abundance of chalcopyrite toward the base of the sulfide assemblages. An envelope of diopside-garnet-pyrrhotite-magnetite skarn mineralization occurs on the south side of the lower part of Unit C and on the upper part of Unit C in association with rhyolite sills (Kennedy, 1992). Unit D Unit D, the uppermost sulfide unit, is a massive to semi-massive zone of sphalerite with accessory galena and appreciable chalcopyrite in siliceous, cherty, chemical sediments. This unit is truncated by the bedrock surface and grades rapidly down-dip into barren volcaniclastic sediments. The unit is separated from the underlying unit C by a 50-foot thick, rhyolitic sill. Host Rocks The rocks hosting the Lynne deposit (Figure 8), have had little in-depth investigation with the exception of work done by Kennedy (1992), who, in conjunction with Noranda's predevelopment staff, studied the immediate host-rocks and their alteration assemblages as part of the deposit delineation drilling program. Much of the following information on the host rocks is drawn heavily from Kennedy (1992), and the findings of the predevelopment staff. Kennedy (1992) has divided the Lynne deposit host rocks into five units consisting of, in ascending order, the Lower Rhyolite, the ore-bearing Lynne Horizon, the Upper Rhyolite, the Upper YCS and the Hanging Wall Unit. Subsequent to the deposition of this felsic volcanic-rich sequence, the rocks were intruded by a probable subvolcanic tonalite body that partially ingested and disrupted the lower surface of sulfide Unit A. �174 Lower Rhyolite The Lower Rhyolite consists of massive to poorly sorted, rhyolitic lapilli to ash tuff containing abundant pumice fragments and locally poorly graded beds of fine ash tuff. Dark green to black chioritic material is common as veinlets and irregular masses. Kennedy (1992) interprets this lithologic package as a sequence of subaqueous debris flows. Angular and shattered coarser felsic lapihi fragments suggest possible local autobrecciation of rhyolitic flow rocks. The Lower Rhyolite interfingers with the stratigraphicahly higher Lynne Horizon north of the orebody but is absent from the immediate vicinity of the orebody either due to non-deposition or incorporation into the intruding tonalite. Rhyolitic tuffs with distinctive angular lapilli clasts occur north of the orebody and approximately one mile south of the orebody, suggesting that this unit may be relatively widespread. Lvnne Horizon The Lynne Horizon hosts the Lynne ore deposit and consists of a sequence of predominantly volcaniclastic, detrital, and chemical sedimentary rocks with lesser interlayered intermediate to felsic volcanic flow rocks and minor rhyohitic crystal tuffs. The horizon is up to 320 feet thick and extends over one-half mile east of the ore deposit. The volcaniclastic rocks consist of greywackes and laminated siltstones of volcaniclastic or reworked volcanic material interbedded with and grading into crystal to crystal-hithic tuffs. Carbonate-rich sediments, characteristic to this horizon, and lesser laminated cherts occur over 1300 feet away from the orebody and increase in abundance and thickness toward the orebody where they exceed 200 feet thick in the center of the ore deposit (Kennedy, 1992). The bulk of the carbonate rocks are directly associated with the massive to disseminated parts of the sulfide ore zones where they are partially or mostly replaced by sulfide minerals. Some partial replacement continues for a considerable distance away from the main orebody to the north and east where it is often associated with an envelope of potassic and magnesium alteration. On the flanks of the Lynne Horizon the carbonates are often well bedded, while less sulfide-rich carbonate zones within and between the main ore zones are commonly laminated though often disrupted and contorted. The carbonate rocks form sharp contacts with overlying volcaniclastic horizons. Descriptions by Kennedy et al. (1991), Kennedy (1992), and Kennedy and Donnelly (1992), suggest that the carbonate assemblages at Lynne show considerable compositional variations. Dolomitic rocks are the most abundant, and directly associated with base-metal mineralization, while limestones are associated with barren or poorly developed sulfide mineralization on the eastern and western flanks of the deposit. The tendency of more Mg-carbonate toward the central part of the orebody, combined with Mg-silicate alteration assemblages in the immediate host rocks, could denote Mg-metasomatism related to carbonate build-up and ore formation. Since the initial drill holes into the ore body, it has been speculated that the buildup of carbonate material is directly associated with ore deposition (Adams, 1990). The carbonate rocks are relatively restricted to a north-northeasttrending basinal feature (Kennedy, 1992), which coincides with the thickest part of the sulfide ore body, suggesting a direct relationship between the ore body and a carbonate build-up. Upper Rhyolite The Upper Rhyolite unit consists of rhyolite crystal and crystal lithic, lapilhi tuffs and massive rhyohite with minor interlayers of dacite and andesite, and thin basal horizons of greywacke and chert. The unit is over 300 feet thick north of the orebody and thins southward where it becomes interlayered with the ore stratigraphy. Rhyohitic sills that intrude the ore body are similar to massive rhyolites in the Upper Rhyolite. Epidote-rich skarn is associated with some of the rhyolitic sills on �175 the west edge of the ore body, suggesting a possible correlation between the intrusion of narrow rhyolite sills of the Upper Rhyolite and the formation of skarn mineralization. The Upper VCS Unit The Upper VCS Unit consists of volcanic-derived greywacke and laminated siltstone with increasing amounts of andesite as the horizon is traced northward. The updip southerly projection of the horizon is represented by the narrow, upper-most, silicious sulfide Unit D. In the immediate vicinity of the orebody, the Upper VCS Unit is less than 100 feet thick but thickens to over 200 feet to the north and west. Iron sulfides commonly occur in this unit as fracture fillings within 100 feet of the orebody, and form sulfide-rich laminae associated with magnetite in siltstones. Chlorite, epidote and minor actinolite alteration minerals are common. Hanging Wall Unit The Hanging Wall Unit is a mixture of felsic to mafic tuffs, heterolithic wackes and agglomerates, or conglomerates. Characteristic to this unit are clast-supported agglomerates containing beige to pink lapilli-sized rhyolitic clasts. The wackes contain lapilli-sized rhyolitic to andesitic clasts and plagioclase and quartz crystals in a mafic groundmass. Interpretations by the Noranda pre-development team suggest that the unit may be a series of debris flows that appear to dissipate to the north and are therefore derived from a southerly source area. Tonalite The tonalite underlies the Lynne ore and host-rock stratigraphy. It has an irregular upper contact that dips at a shallow angle to the northeast. The tonalite intrudes and disrupts the lower part of sulfide Unit A, displacing and enclosing parts of the unit. Flexures in the overlying stratigraphy appear to be associated with a northeast-striking trough in the tonalite surface. The intrusive is often porphyritic with quartz ovoids and euhedral, zoned plagioclase crystals in a fine-grained, commonly graphic, matrix (Kennedy and Donnelly, 1992). Within 50 feet of the contact, the tonalite is characterized by a granophyric texture. Low temperature alteration is common in the tonalite, but is strongest in association with local fracturing or faulting. Within 35 feet of the tonalite, local recrystallization of adjacent volcanic and volcaniclastic rocks occurs and a hornfels texture is sometimes present (Kennedy and Donnelly, 1992). The magnetic response associated with the known area of tonal ite grades into a relatively constant regional magnetic low south of the deposit that is interpreted as a large granitic body. Alteration There does not appear to be a distinct alteration pipe, or stringer zone, beneath or adjacent to the Lynne deposit as is common to other volcanogenic massive sulfide deposits (Franklin et a!., 1975; Franklin et a!. 1981). It is possible that the subvolcanic tonalite body has engulfed and destroyed any pre-existing alteration stringer zone. There is, however, an alteration mineral assemblage associated with the lower Lynne ore stratigraphy and the stratigraphically higher encompassing host rocks. Talc-rich zones up to 25 feet thick occur beneath and grade into the lower massive sulfide Unit A, and talc-rich zones up to 15 feet thick separate zinc-rich ore from skarn and marble units along the northern flank of the orebody (Kennedy, 1992). Local stringer-like veins and disseminations of sphalerite and pyrrhotite occur within Mg-chlorite and muscovite-rich talcose rocks associated with the lower parts of sulfide Unit A (Adams, 1990; Kennedy, 1992). Observations by the Noranda predevelopment team (personal communication), reveal a Mg- and K-rich secondary mineral assemblage extending laterally up to 1300 feet down-dip, and over 2000 feet east, in the footwall rocks of the orebody, and within several hundred feet of the orebody, feldspar in tuffs of the �176 Upper Rhyolite and the Upper VCS Unit are altered to muscovite and chlorite. These criteria support a broad alteration assemblage similar to semiconformable alteration zones found in conjunction with several world-wide volcanogenic massive sulfide occurrences described by Franldin et al. (1981). Tonalite in contact with the orebody, on the other hand, appears to be little altered, suggesting a postalteration intrusive event. Skarn Mineralization The abundant caic-silicate mineral assemblage associated with the Lynne deposit is uncommon to volcanic-related massive sulfide deposits. It is apparent that the skarn-style of mineralization is directly related to the anomalous amount of carbonate rock associated with the orebody. The most intensive skarn mineralization is associated with the extensive replacement of carbonate along the updip flanks or projected edges of the orebody (Figure 8). Here pyrrhotite and magnetite are also locally abundant, especially along the southern edges of the orebody. Quartz-diopside skarn assemblages are characteristic of the upper parts of the deposit and epidote skarn occurs in conjunction with intrusive rhyolitic sills within the orebody (Kennedy, 1992). Skarn mineralization is seldom associated with base-metal ore, but the highest ore-grade gold concentrations have a direct skarn relationship (Adams, 1991; Kennedy, 1992). No other known massive sulfide occurrence in the Rhinelander-Ladysmith greenstone belt is associated with such abundant carbonate material. DeMatties (1990) describes possible carbonate-rich exhalites at the Ritchie Creek occurrence, and significant dolomitic units make up part of the Crandon deposit stratigraphy (Lambe and Rowe, 1987). Franklin et a!. (1975) refer to a dolomitic host rock package for the Mattabi deposit in the Sturgeon Lake camp of northwestern Ontario. The significant skarn assemblage associated with the Lynne deposit makes this one of the most unique base-metal deposits of the Rhinelander-Ladysmith greenstone belt. Proposed Genetic Model for the Lynne Deposit Although the Lynne deposit has characteristics of both volcanogenic massive sulfide and skarn-related deposits, it is believed that the supporting evidence is sufficient to suggest a volcanogenic origin for deposit. A sulfide depositional scenario is proposed whereby a graben-like depression, perhaps developed in conjunction with a caldera collapse feature, forms on the flank of a felsic volcanic complex centered to the northeast of the present-day Lynne deposit. The association of the near-vertical fracture zones in the Lynne stratigraphy, and the trough-like depression in the tonalite surface, with the rapid thickening of the core of the ore deposit, may represent remnant features of the postulated graben. Within the confines of the down-dropped block of felsic volcanic rocks, and using bounding growth faults as conduits, volcanic vents may have began an effusive build-up of carbonate-rich chemical sediments. Either syndepositionally, or closely following the carbonate build-up, solutions rich in zinc, with subordinate lead, silver, copper and gold, replaced much of the central portion of the carbonate mound. At least four episodes of metal infusion prevailed over the deposition of volcaniclastic and chemical sedimentary material within the graben complex. As the sulfide deposition evolved, the relatively abundant copper and iron dropped out of solution, both at the onset of each sulfide event, and throughout the entire sulfide depositional period, and was supplanted by zinc with progressively increasing amounts of lead and then silver. Coincident with the evolution of metal-bearing solutions was the progression from carbonate-rich toward silicarich chemical sedimentary facies. The confines of the proposed graben feature may account for the stacked layering of chemical sedimentation and sulfide deposition. �j • 0 • t + co — carbonate oh — chert. (Qz) Gt Massive Po, Mt + T 0. 509 0' + Tonal t e Semi—massive to Massive Sulfide Disseminated sulfide + + 0 — talcose sk — Tr, Di, + + 10 304 0 Talc BPM 0 9''0BpMo •O•O•O•O•Q/.O 0 O0Q 1.0. IR1 (After Kennedy, 1992) Rhyolite 794 0 1.0. Tonal ite Marble Ml 666.0' + 553.0' 1.0. + Chert Volcaniclastic unit Gt+Di ± Tr Skarn + Looking West CH ___ Figure 8 ft. Host Rock Geology (Section 10,000 E.) Lynne Base—Metal Deposit Oneida County, Wisconsin MS 100 Scale _1lp 0 .i!O _L0° �178 Associated with a resurgence of volcanic activity, the sulfide-bearing stratigraphy was covered with a sequence of felsic to intermediate, volcanic flow, pyroclastic, and epiclastic rocks, and intruded by rhyolitic sills. At the same relative time, or subsequent to this point in the volcanic history of the area, a subvolcanic, tonalitic mass intruded the base of the graben feature and its metalrich sequence of volcanics and chemical sediments. During its intrusion, the tonalite could have engulfed an alteration pipe associated with the graben-bounding fracture system leaving only the more widespread wallrock alteration assemblage. Associated either with the intrusion of the tonalite, the intrusion of higher level rhyolitic sills, or a combination of both, a skarn-style alteration assemblage developed in the flanks of the carbonate mound in which sulfide mineralization was less pronounced. Pyrrhotite, magnetite and gold mineralization was produced or remobilized in association with this event. Later movement reactivated the bounding faults and subsequent bimodal intrusive activity filled some of the fault zones with dikes. It is of course unknown if additional massive sulfide bodies were deposited in this graben feature prior to, or following, the formation of the current Lynne sulfide units, their possible existence being either destroyed by the intruding tonalite or erosion. Since the geological environment favored the deposition of the Lynne deposit, it is likely, as substantiated by base-metal camps throughout the world, that additional massive sulfide deposits formed in conjunction with the Lynne felsic build-up of the prolific Rhinelander-Ladysmith greenstone belt. Summary The Lynne base-metal deposit consists of a series of four strataform, massive to semi-massive, sphalerite-rich sulfide bodies containing accessory galena, silver, copper, and gold. The deposit is hosted by a dominantly felsic volcaniclastic and sedimentary sequence of rocks with a significant amount of carbonate-rich chemical sediments. The immediate ore-bearing stratigraphy is overlain by felsic to intermediate volcanic flow, pyroclastic, and epiclastic rocks. An intrusive tonalite underlies the Lynne stratigraphy disrupting and intruding the lower-most sulfide unit. No definitive alteration or feeder pipe is evident; however, an alteration assemblage common to volcanogenic massive sulfide deposits world-wide, is present in the deposit's immediate host rocks. Metal zoning is suggested by relative copper enrichment toward the base of individual sulfide units. Deposit-wide metal zoning occurs as a relative enrichment in copper and iron in the lower sulfide units, an upward increase in zinc, and the development of galena concentrations and strong silver enrichment in the upper parts of the deposit. There is a corresponding evolution from carbonate-rich rocks lower in the sequence to more siliceous chemical sediments higher in the host rock stratigraphy. Skarn-type mineralization is characteristic to the carbonate-rich host rocks, especially along the up-dip flanks of the deposit and locally associated with intrusive rhyolitic sills. The highest concentrations of gold, and an increase in pyrrhotite and magnetite mineralization, are associated with the skarn-type assemblage. Characteristics common to volcanogenic massive sulfide and skarn-related deposits occur within the Lynne deposit lithologic sequence. Data suggest that the main sulfide mineralizing events were related to a volcanogenic-related, carbonate-generating, hydrothermal system. Skarn development in carbonate rocks within the main sulfide orebody and its lateral equivalents may be related to the intrusion of the subvolcanic tonalite, the rhyolite sills, or a combination of both events. �179 Acknowledgements The author strongly acknowledges the contributions of the Lynne predevelopment team of L. Kennedy, T. (Harding) Kennedy, J. Schaff, A. Zielinski and T. Suszek for their contributions to the author's knowledge through reviews, reports and conversations during the delineation of the Lynne deposit. Special recognition is due Larry Kennedy, author of the Noranda summary report, from which much of the descriptive text regarding alteration assemblages and host rock lithologies was taken. The management of Noranda Exploration Inc. is also acknowledged for their philosophy of exploration persistence and their confidence in the Superior District staff. I also thank Noranda Exploration Inc. for permission to publish this paper. References Cited Adams, Glen W., 1990, Lynne Base-Metal Discovery, North-Central Wisconsin: New Discoveries in North America Session, Northwest Mining Association 96th Annual Meeting, Spokane, Washington, transcript, 18 p. Adams, Glen W., 1991, Lynne Base-Metal Discovery: The Minnesota Prospector, Vol.!, No. 5, p. 2-7. AMERICAN MINES HANDBOOK, 1995, Noranda Exploration Inc., Company Profiles, Southam Magazine and Information Group publishers, p.167. DeMatties, T. A., 1990, The Ritchie Creek Main Zone: A Lower Proterozoic Copper-Gold Volcanogenic Massive Sulfide Deposit in Northern Wisconsin: Economic Geology, Vol. 85, p. 1908-1916. DeMatties, T. A., 1994, Early Proterozoic Volcanogenic Massive Sulfide Deposits in Wisconsin: An Overview: Economic Geology, Vol. 89, p. 1122-1151. Franklin, J. M., Lydon, J. W. and Sangster, D. F., 1981, Volcanic-Associated Massive Sulfide Deposits: ECONOMIC GEOLOGY 75th ANNIVERSARY VOLUME, p. 485-627. Franldin, J. M., Kasarda, J., and Paulsen, K. H., 1975, Petrology and Chemistry of the Alteration Zone of the Mattabi Massive Sulfide Deposit: Economic Geology, Vol. 79, p. 63-79. Kennedy, L. P., Harding, T. A., Schaff, J. H., and Zielinski, A. M., 1991, The Lynne Massive Sulfide Deposit, Oneida County, Wisconsin: Annual Institute on Lake Superior Geology, 37th, Eau Claire, Wisconsin, 1991, p. 63 Kennedy, L. P., 1992, Lynne Project Summary Geologic and Geotechnical Report: unpublished report, Noranda Exploration, Inc., Rhinelander, Wisconsin, 29 p. Kennedy, L. P., and Donnelly, M. E., 1992, Geology of the Lynne Zn-Pb-Cu-Ag Deposit, a Proterozoic Massive Sulfide, Oneida County, Wisconsin: unpublished report, Noranda Exploration Inc., Rhinelander, Wisconsin, 3 p. Lambe, R. N., and Rowe, R. G., 1987, Volcanic History, Mineralization, and Alteration of the Crandon Massive Sulfide Deposit, Wisconsin: Economic Geology, Vol. 82, p. 1204-1238. Sims, P. K., Van Schmus, W. R., Schulz, K. J., and Peterman, Z. E., 1989, Tectono-Stratigraphic Evolution of the Early Proterozoic Wisconsin Magmatic Terranes of the Penokean Orogen: Canadian Journal of Earth Sciences, Vol. 26, p 2145-2 158. �� https://digitalcollections.lakeheadu.ca/files/original/71b0c827f509c536d2918ec571adc342.pdf 68c03aa4e70493a5c919ae04e3a00d7c PDF Text Text I P ANNUAL P r INSTITUTE ON LAKE SUPERIOR GEOLOGY P CABLE, WISCONSIN WISCONSIN CABLE, P - MAY 19, 1996 M A Y 15 15- 19,1996 H - [1 ' ''-F,,, '- - '- \_ '- '- ' ',-,-''' '''-Fe,,',,, '-F',',', •' # / ''''-F-F/-F-F H P 'I, -F,,, ''''' '' -F ) 1 1. Glacial geology of western Wisconsin 2. Archean --Middle Middle Proterozoic Proterozoic transact transect Nainekagon region 4. Geology Geology of the Lake h7amekagon 5. Structure Structureof of the the western western Gogebic Gogebk Range I) PT P PROCEEDINGS VOLUME 42 PART 3- FIELD TRIP GUIDEBOOK P �I I I I I INSTITUTE ON LAKE SUPERIOR GEOLOGY 42NDANNUAL A N N U A L MEETING 42ND MEETING - M A Y 15 19,1996 MAY 15-19, 1996 CABLE, WISCONSIN CABLE, WISCONSIN SPONSORED BY: SPONSORED BY: U. S. GEOLOGICALSURVEY U. S. GEOLOGICAL SURVEY AND AND UNIVERSITY OF WISCONSIN OSHKOSH UNIVERSITY OF WISCONSIN - OSHICOSH - 1 I I I I I I I I I I PROCEEDINGS VOLUME 42 PART 3-- FIELD TRIP GUIDEBOOK EDITORS: SUZANNE W. NICHOLSON, U. S. GEOLOGICAL SURVEY, RESTON, VA SUzANNE W. NICHOLSON, U. S. GEOLOGICAL SURVEY, RESTON, VA LAUREL G . WOODRUFF, U.S. GEOLOGICAL SURVEY, ST. PAUL, MN LAUREL G. WOODRUFF, U. S. GEOLOGICAL SURVEY, ST. PAUL, MN �GLACIAL GEOLOGY OF OFWESTERN WESTERNWISCONSIN WISCONSIN FIELD TRIP #1: GLACIAL LEADER: MARK MARK D. JOHNSON LEADER: Department of Geology Gustavus Adolphus Adolphus College 56082 St. Peter, Minnesota 56082 FIELD TRIP #2: #2: GEOLOGY RIVER MONOCLINE: MONOCLINE: FIELD GEOLOGY OF OF THE MONTREAL RIVER TRAVERSETHROUGH THROUGH 25 25 KM OF THE CRUST A TRAVERSE LEADER: WILLIAM F. F. CANNON LEADER: U. S. Geological Geological Survey Survey National Center MS-954 National CenterMS-954 Reston, Virginia 22092 22092 FIELD FIELD TRIP TRIP #4: #4: EARLY EARLYTO TOMIDDLE MIDDLEPROTEROZOIC PROTEROZOICGEOLOGY GEOLOGY OF OF THE LAKE NAMEKAGON NAMEKAGON REGION LEADERS: F. CANNON!, CANNON1, LAIJRELG. LEADERS: WILLIAM WILLIAM F. LAURELG.WOODRUFF2, WOOD RUFF^, SUZANNE W. NICHOLSON1 AND SUZANNE NICHOLS ON^ 1U. 1 U. S. Geological Survey National Center MS-954 National Center MS-954 Reston, Virginia 22092 22092 2U. S. Geological Survey 2 U. Survey Woodale Drive 2280 Woodale Paul, Minnesota 55112 55112 St. Paul, FIELD TRIP TRIP #5: #5: LAKE LAKENAMEKAGON NAMEKAGONAND ANDPENOKEE PENOKEEGAP GAPAREAS, AREAS, WEST WEST GOGEBIC RANGE, WISCONSIN LEADERS: GENE L. LABERGE2 LEADERS: JOHNS. JOHN S.KLASNER1 KLASNER~AND AND GENE LABERGE~ 1 1 Department of Geology Western Western Illinois University minois 61455 Macomb, Illinois 61455 2 Geology 2 Department of Geology University of University of Wisconsin Wisconsin - Oshkosh Oshkosh, Wisconsin Oshkosh, Wisconsin 54901 54901 - L �I I 11 U TABLE OF CONTENTS I I FIELD TRIP #1: GLACIAL GEOLOGY OF WESTERN WISCONSIN M. D. Johnson I OVERVIEW OF THE BEDROCK GEOLOGY OF THE CABLE-BURLEY AREA, WISCONSIN W. F. Cannon and S. W. Nicholson I I I I I I I I I I 3 FIELD TRIP #2: GEOLOGY OF THE MONTREAL RIVER MONOCUNIE: A TRAVERSE THROUGH 25 KM OF THE CRUST W. F. Cannon 35 49 FIELD TRIP #4: EARLY TO MIDDLE PROTEROZOIC GEOLOGY OF THE LAKE NAMEKAGON REGION W. F. Cannon, L. G. Woodruff, and S. W. Nicholson 67 FIELD TRIP #5: LAKE NAMEKAGON AND PENOKEE GAP AREAS, WEST GOGEBIC RANGE, WISCONSIN J. S. Kiasner and G. L. LaBerge 83 �fl I I I I I I I 1 I I I 1 I I I GUIDE FIELDTRIP TRIP##11 GUIDEFOR FIELD GLACIAL GEOLOGY OF WESTERN WISCONSIN �I I I I I I I I HELD TRIP TRIP #I #1 HELD GLACIAL GEOLOGY OF OF WESTERN WESTERNWISCONSIN WISCONSIN by Mark D. Johnson of Geology, Geology, Gustavus Gustavus Adolphus Adolphus College Department of St. Peter, Peter, Minnesota Minnesota 56082 56082 I. Introduction I. The purpose purpose of of this this ILSG fieldtrip trip isis to to get of the the The ILSG field get aa general general overview overview of history of the Pleistocene features of of northwest landforms, sediments, and geologic geologic history Pleistocene features Wisconsin. To that end, the field trip has been designed to show exposures exposures and and Wisconsin. outcrops that reveal the different types of of deposits deposits and and landforms landforms throughout throughout the outcrops different types region. Though will hand hand out and refer to a publication region. Though not not bound bound in in this this booklet, booklet, I will of Wisconsin" Wisconsin"by byClayton Claytonand and others others (1991). (1991). Figures Figures 1 1 through through 5 called "Glaciation of are the figures figures from from the the"Glaciation "Glaciation of of Wisconsin" Wisconsin" brochure; the figures figures included included within this report start start with with Figure Figure 6. Certainly, one of of the goals goals of of aa regional regionalunderstanding understanding of of glacial glacialdeposits deposits isis to to able to to predict, variationsthat that in in part part be able predict, or at at least least expect, expect, surface-material surface-material variations be determine the character with the landscape determine the character of of human interaction interaction with landscape (groundwater (groundwater resources, geologic engineering character Additionally, glacial resources, character of of sediment, etc.). etc.). Additionally, the primary primary record record for forthe the study study of of the the nature nature and and sediments and landforms provide the of former ice ice sheets. sheets. Studies of of these these features, features, along alongwith with the the use use of of modern modern history of environments as as analogs, analogs, provide provide aa foundation upon which glacial environments foundation upon which one can can glacial reconstruct glacial history. II. Ice Ice lobes, lobes, phases, stratigraphy, and brief glacial history of western Wisconsin Wisconsin 11. Wisconsin was was glaciated glaciated several several times times during during the Pleistocene, Northwestern Wisconsin Pleistocene, but theNorthwestern topography associated primarily primarily with with advances advances of of topography and and surficial surficial sediment are associated the Superior Lobe Lobe and Grantsburg Grantsburg Sublobe Sublobe (an offshoot of the Des Des Moines Moines Lobe) Lobe) during during the the last lastpart partofofthe theWisconsinan WisconsinanGlaciation Glaciation(Fig. (Fig.1-4). 1-4). The earliest earliest known known glacial glacial advance advancewas wasduring during the the Reeve Reeve Phase Phase ofof the the Des Des The Lobe, which which occurred probably probably over over 730,000 730,000years yearsago agoand and deposited deposited gray, Moines Lobe, Moines loam till This material material is is deeply buried till of of the thePierce PierceFormation Formation(Fig. (Fig.1-3, 1-3, 1-5). 1-5). This occur in in throughout the region region and and occurs occurs only in patches; patches; some surface exposures occur southern St. St. Croix Croix County County and and Pierce PierceCounty. County. The The till till is deeply weathered, weathered, even southern I 1 �AOKA JSANT) .— KANABEC _\ - _____ N I / &; WASHBURN ri* — 0' I BURNETT POLK / r( / 1/ 7 H 71 H c OO DUNNI CHIPPEWA sI.$y UCR.8( \LiN*t/ 'CHAGO % ) PINE La nia&net S pItt tiers at the Ctrenqtrettrrk Kee P—f s3t. Croft dw..I — lithe tovOieiett — -- — —— 0 • A o 1490 160 0 —I N LIce o.wi.6, eec.*esh.d tIt 5 I 101cr,. .ead — a90 of — &ecstor LIte locebon rd S.vIt(on 01 9SSS 91-f LIce US — -y otcp ci gius, Lake us Tied. ((Sec N — at? — — .Iatp of ØecII Lake Of.St.9 — 'of, 0tcti S gIt La. OailtbU5 o pci • o o 009_t -- H.yP-r $ w w— as, N H Red C — — —Isrun -It --— — — in.. — — - br — — S-lu, d.eN.S Gwist*so &lcO. kInd liar. II Sboc •INIt Sel of HeIs.cr ,d t.SwMt (1971) •ctn ol giec '-si us — sVn ci bted red tad brael S.asd — .ethn.nl �Figure Portion of of northwestern Wisconsin Wisconsin and and adjoining Minnesota Minnesota showing showing features associated associated with with the mostFigure 1-6.-1-6.- Portion recent induded to recent glacial glacial events. Spot elevations are included toshow showthat thatelevations elevationsincrease increasefrom fromcentral centralBurnett BurnettCounty Countyto tothe theSt. St. Croix ice margin. Based on their relative position, the Centuria, Luck, Fox Creek, and McKinley ice margins are correlated Croix Based on their relative position, the Centuria, Luck, Fox Creek, and McKinley are correlated with with the theTiger Tiger Cat Cat ice ice margin margin of Clayton (1984). (1984). Tiger Cat and Hayward Haywardice ice margins marginsfrom fromClayton Clayton(1984) (1984) and Attig and and others others(1985). (1985). Emerald, Emerald, St. St. Croix, Croix, Early Early Chippewa, Chippewa, and andLate LateChippewa Chippewaice icemargins marginsfrom fromJohnson Johnson(1986). (1986).Pine PineCity Cityice ice margin in Minnesota from Cooper (1935) and Hobbs and Goebel (1982). Location of glacial Lake Grantsburg and glacial margin in Minnesota from Cooper (1935) and Hobbs and Goebel(1982). Grantsburg and glacial Lake Lake Lind varved clay day in Minnesota Minnesota from Chris Hemstad and and myself myself (unpublished (unpublished data) data)and andGary GaryMeyer Meyer (personal (personal communication). Only tunnel channels in Wisconsin are shown. Extent of the glacial Lake Grantsburg in Minnesota is in in communication). Only tunnel channels in Wisconsin are shown. Extent of the glacial part location of Camp Sunrise. LL == townsite townsite of of Lind, Wisconsin. Till Till part from fromCooper Cooper (1935). (1935). CS CS (in (in eastern eastern Minnesota) Minnesota) == location fabric measurements in Minnesota from Chernicoff (1983). fabric measurements in Minnesota from Chernicoff (1983). �where overlain overlain by younger younger material. material. The Pierce Pierce till till is overlain in places by reddish-brown, sandy loam till The reddish-brown, sandy till and and outwash of which was was deposited deposited during the Baldwin outwash of the the River River Falls Falls Formation, Formation, which Baldwin of the Chippewa Chippewa Lobe probably over Phase of the Superior Superior Lobe and the Dallas Phase of over 130,000 years ago ago (Fig. (Fig.1-3, 1-3,1-5). 1-5).This Thismaterial materialisisweathered, weathered, as as shown shown by clay-mineral 130,000 years alterations and magnetite magnetite weathering weathering(Johnson, (Johnson, 1986) 1986) and thick soil soil profiles profiles (Baker (Baker interpret this this weathering weathering to have have likely likely occurred occurred during during the the and others, others, 1983). 1983). I interpret Sangamon Interglacial Interglacial interval. interval. Lobe and and Chippewa Chippewa advances advancesthat that occurred occurred during during the last part The Superior Lobe of the Wisconsinan Glaciation began began with with the Emerald Phase and early of Wisconsinan Glaciation Emerald Phase early Chippewa Chippewa 1-6). Deposits from from these these phases phases occur occur at at the surface underneath underneath the the Phase (Fig. 1-1, 1-6). gently rolling gently rolling topography topography of the the southern southern Barren Barren County, County, southeastern southeastern Polk Polk County, and and central central St. St. Croix Croix County. County. Part-way through through the thelate lateWisconsinan Wisconsinan Glaciation, Glaciation, the the Superior Superior Lobe Lobe changed changed behavior and and began different suite suite of of landforms landforms and sediment sediment types. types. behavior began to form form aa different These are associated positions in western These associated with more than 10 10 former former ice-margin ice-margin positions Wisconsin (Fig. (Fig. 1-6, 1-6, 1-7), 1-7),beginning beginningwith withthe theSt. St.Croix CroixPhase. Phase. During these events, Wisconsin events, the Superior and Chippewa left behind behind reddish-brown reddish-brown sandy sandy loam loam till and Chippewa Lobes Lobes left outwash of the the Copper Copper Falls Falls Formation, Formation, as well as as striations, striations, grooves, grooves, outwash outwash plains, outwash outwash fans, fans, tunnel tunnelchannels, channels,eskers, eskers, hummocks, hummocks, ice-walled-lake ice-walled-lake plains, plains, ice-dammed-lake plains, plains, end moraines, and the Spooner Spooner Hills of of northeastern northeastern Polk Polk Burnett County, County, and and central central Washburn Washburn County. County. The Superior County, southeastern Burnett Lobe ice-margin positions (Fig. 1-6) can can be be traced traced for for several several kilometers laterally and represent ice-margin stillstands, ice-margin advances, or sedimentologic events that imprint the the location location of of the the ice ice margin margin (for (for example, example, the tunnel-valley/outwash-fan tunnel-valley/outwash-fan pairs clearly indicate the position of the ice margin but do do not not require require an anice-margin ice-margin stilistand or readvance). stillstand readvance). As the Superior Superior Lobe Lobe retreated, glacial glacial Lake Lind formed in in the the preglacial preglacialSt. St. Croix River valley valley (Fig. 1-7A) 1-7A)and and lasted lasted about about 1000 1000years yearsbased basedon on the the number number of of varved silt silt and and clay clay couplets coupletsfound foundin inlake lakesediment sediment(Sunrise (Sunrise Member Member of of the the Copper Copper Falls Formation). Formation). 1-7D), The Grantsburg GrantsburgSublobe, Sublobe,an anoffshoot offshootof of the theDes DesMoines MoinesLobe Lobe(Fig. (Fig.1-7C, 1-7C,1-7D), advanced during during the the Pine Pine City City Phase Phase across a fluvial plain that developed on on top top of of glacial Lake Lind Lind sediments sediments(Fig. (Fig.1-7B). 1-7B). The Grantsburg Sublobe deposited gray, gray, loam till of the Trade Trade River River Formation and left behind end end moraines, moraines, till till plains, plains, iceicemarginal channels, Lake Grantsburg Grantsburg was channels, and and ice-dammed-lake ice-dammed-lake plains. plains. Glacial Glacial Lake 6 �-1 ___ ___ ___ ___ ___ ___ ___ ___ ___ ___ drainage basin at this time. 7E—Clacial Lake Duluth drained through the study area along the St. Croix River. to advance to the Pine City margin and glacial Lake Grantsburg expanded. The Superior Lobe may have still been in the area. 71)—The Grantsburg Sublobe continued St. Croix River valley in the Taylor's Falls Crantsburg. The initial outlet of glacial Lake Grantsburg would have formed the modern St. Croix River, and formed glacial Lake Late Wisconsinan ice-margin positions of the Superior Lobe. 7B—Clacial Lake Lind filled in with sand deposited in prograding deltas and fluvial plains. 7C—.The Grantsburg Sublobe advanced across the sand plain, dammed the Superior Lobe at this time is shown by the heaviest line; the medium lines mark former events. 7A--Clacial Lake Lind formed In the lowland of the former St. Croix River. The area showing selected Late Wisconsinan Figure 1-7.—Five sketch maps of the field-trip I �dammed in front front of of the the advancing advancingice ice and and lasted lastedapproximately approximately100 100 years, years, based on the number of varved varved silt silt and and clay clay couplets couplets of the the Falun Falun Member Member of the Trade Trade River River Formation (see The location location of of the the lake's (see varve varve localities localities in inFig. Fig.1-6). 1-6). The lake's outlet outlet is is unknown. Numerous drainage events Numerous events from from ice-dammed ice-dammed Lake Lake Superior Superior (glacial (glacial Lake Lake Duluth, Fig. caused the the St. St. Croix Croix River Rivertoto incise incise its its valley valley and and created the Duluth, Fig. 1-7E) 1-7E) caused famous famous potholes potholes in the the basalt basalt around aroundSt. St.Croix Croix Falls. Falls. An interruption in these these drainage events events allowed drainage allowed aa large sand surface surface to develop develop in in northwestern northwestern Polk Polk County and in Burnett Burnett County. Dunes Duneslater laterdeveloped developed on on this thissurface. surface. IlL Ages of late Wisconsinan 111. Wisconsinan glacial events The date of the of northwestern Wisconsin the late late Wisconsinan Wisconsinan glacial events of Wisconsin is uncertain. AAradiocarbon radiocarbondate dateofof20,500 20,500years yearsB.P. B.P.± i400 400(1-5443) (1-5443)(Wright, (Wright,1972; 1972; Wright and others, organic matter matter in lake others, 1973) 1973) was obtained obtained from disseminated disseminated organic lake This lake lake is behind the sediments at Wolf Wolf Creek Creek in in central central Minnesota. Minnesota. This the St. St. Croix Croix until the ice ice margin had retreated 60 moraine and would not not have have been been ice-free ice-free until 60 km krn from the maximum maximum limit, limit, possibly post-dating the St. St. Croix Croix Phase maximum maximum by by hundreds of years. years. However, However,there thereisisaapossibility possibility of of contamination contamination of the sediment sediment by old Clayton and Moran by old carbon, carbon, and and the the date date may may not notbe bereliable. reliable. Clayton Moran(1982), (1982), Mickelson and others (1986)suggest suggestaa somewhat somewhat younger date others (1983), (1983), and Johnson (1986) for the years B.P. B.P. Their chronologies the St. St. Croix Croix Phase, Phase, approximately approximately18,000 18,000 to 15,000 15,000 years chronologies are based on on dates dates from from wood wood in in other other regions, regions, where where there there is is less less chance chance of of contamination. However, However, little little wood wood is associated associated with the deposits of the St. St. Croix Phase. The TheEmerald EmeraldPhase Phase(the (thepre-St. pre-St.Croix CroixPhase, Phase,Late-Wisconsinan Late-Wisconsinan advance advance in in western in press) to have western Wisconsin) Wisconsin) is considered by Johnson Johnson (1986; (1986; in have occurred occurred around 20,000 around 20,000 to to25,000 25,000 B.P. B.P. of the phases that occurred after the St. Croix Croix Phase Phase are are unclear unclear with with The dates of B.P. (Clayton, (Clayton, the exception of the Marquette Marquette Advance, Advance, which is dated dated around around9,900 9,900 B.P. 1984). 1984). IV. Landforms Landforms of western western Wisconsin Wisconsin The landscape created during overall retreat of of the Superior Lobe Lobe in western Wisconsin Wisconsin consists consists predominantly predominantly of hummock hummock tracts, tracts, ice-walled-lake ice-walled-lake plains, plains, of collapsed outwash, and and rolling to streamlined till pitted-outwash plains, regions of collapsed outwash, uplands. Tunnel Tunnelvalleys, valleys,eskers, eskers, and and the the Spooner Spooner Hills are also present. Pleistocene Pleistocene deposits are generally 30 30 to to 45 45 m m thick thick (up to 85 m m in places). places). Precambrian Precambrian basalt 8 �I r crops out out as in the the western and northern crops as striated striated and and grooved grooved knobs knobs in western and northern parts parts of of Polk Polk County, Barron Barron quartzite quartzite in in eastern Barron County, and and Cambrian Cambrian sandstones sandstones in in County, Barron County, southern Barron County. County. Drainage meltwater during retreat was generally generally to to the the Drainage of of meltwater south during duringdeglaciation deglaciation(see (seearrows, arrows,Fig. Fig. 1-6). 1-6). In the following section, section, II discuss discuss the the major majorlandform landform types types in in the the region, region, and In describe what each landform landform type type signifies. signifies. Moraines.--There are very few moraines, in the classic sense, in western Wisconsin. ---There The best-developed are along the Pine City Phase margin of of the Grantsburg Grantsburg Sublobe, Sublobe, but only in in places places (Fig. (Fig. 1-6). Few Few morainic morainic ridges occur at Superior Lobe ice-margin positions. The positions. The term term 'morainic 'morainic ridge' is is used used for for relatively narrow features deposited They contain contain little little hummocky hummocky topography, topography, and and are are at the at the margin margin of of the the ice. ice. They composed ofof various various types types ofof till till and and ice-contact ice-contactsand sandand andgravel. gravel. Much Much of of the the composed length of of the "St. Croix moraine" is not characterized by by morainic morainic ridges, ridges, but but consist consist of hummock tracts, outwash plains, and glacial thrust systems. of Hummocks and hummock tracts (Stop usethe the term term 'hummock' 'hummock' to to mean mean aa (Stop 1-3).--I 1-31.--1 use Hummocks occurring in in groups, groups, and associated hill or knob, irregular to circular to oval in plan, occurring This term term is with irregular to to circular circular to to oval oval hollows, hollows, depressions, depressions, or wetlands. wetlands. This regardless ofof the the type type of of sediment sediment composing composingthe thehummock. hummock. A A variety variety of of used regardless used has been applied to this type of landform in glaciated regions, terms regions, including including deaddeadice moraine, hummocky ice hummocky moraine, stagnation moraine, moraine, collapsed collapsed outwash, kame, 'hummock tract' to describe a distinct region region of and kame complex. I use the term 'hummock hummocks (in (in the the same same way way that that the the term group of hummocks term 'drumlin 'drumlin field' field' describes describes aa group of drumlins). hummocks within within the the field-trip field-triparea area are are 55 to to 20 20 m m high high and 25 25 to Individual hummocks Individual 400 m m in in diameter diameter with with a mean mean height height of of 10 10mmand andwidth width of of 130 130m. m. Hummocks Hummocks are are 400 irregularly spaced with respect to each other but show a frequency of of one hummock hummocks/km2. Hummock meters. There per 250 to 500 meters. There are are 15 15 to to 40 40 hummocks/km2. Hummock slope ranges from 2 to 14 degrees. degrees. 1-8)lie lieininaazone zoneparallel paralleltotoand and up up to 20 20 k km Hummock tracts (Fig. 1-8) m behind the St. Croix Croix and other Superior positions; hummocks hummocks are are absent along St. Superior Lobe ice-margin positions; The hummock hummock tracts tracts do certain lengths of of former former ice-margin ice-margin positions positions(Fig. (Fig.1-8). 1-8). The not form a continuous band but are are separated separated from each other by outwash plains, regions of tunnel valleys, valleys, and and rolling, rolling, upland upland till regions of collapsed-outwash, collapsed-outwash, tunnel till surfaces. surfaces. tracts in the form upland upland areas areas that have Hummock tracts the field-trip field-trip area area commonly commonly form have Hummock above above adjacent adjacent outwash outwash surfaces. surfaces. Outwash surfaces surfaces that lie adjacent to elevations the hummock hummock tracts are graded graded to to nearby nearby ice-margin ice-margin positions a few few kilometers kilometers 9 �, -i--' I 7 '.:.j:-._-- :3 — C .J2!k rTT pitted n CroixL.......J outwtsh Darn • ce-walled. lake plain hummocky ice-margin posi outwash o hummock tract 0 noii-humn,odcy suriace compos.d of till striation channel margin — cour bour Sb. 1 Figure part of Rgure 1-8.—A 1-8.-A part of western western Wisconsin Wisconsin showing the field-trip field-trip area area (black (black in in inset) inset) and and geomorphic geornorphicfeatures. features.Areas Areas left blank on the map map include includepredominantly predominantly rolling rolling to to dendritically-drained dendriticallydrained surfaces surfaces underlain by till (with a few few basalt basalt knobs knobs in in the the western western and northwestern northwestern parts parts of of the the study studyarea). area). NR=city NR=dty of New New Richmond, Richmond, SCF=city SCF=aty of St. Croix Croix Falls, Falls, TL=city TLscity of of Turtle Turtle Lake, Lake, C=Centuria ice-margin position, C-Centuria ice-margin position,BL=Balsam BL=Balsam lake lake ice-margin ice-marginposition, position,R=Range R=Rangeice-margin ice-margin position, PC=Pine City ice-margin position, position, P C = P i City ice-marginposition, SC=late SC=late St. Croix Croix ice-margin ice-margin position, position, GS=Grantsburg GS=GrantsburgSublobe. Sublobe. Dashed Dashed line line in in inset is is trace trace of the Superior Superior thbe Lobeice-margin ice-margin limit limit where where covered coveredduring duringthe thePine PineCity City Phase Phase of of the theGrantsburg GrantsburgSublobe; Sublobe; arrows arrowsin inset inset show general direction. general ice-flow ice-flow direction. 10 �I I I I I I I I I further up up ice further ice to to the the north north or orwest. west.In Inseveral severallocations, locations, the the outwash outwash plains plainslocated located between hummock tracts are collapsed into tunnel valleys valleys that that had been filled with thick, stagnant thick, stagnant ice. ice. In In part, part, the the tunnel tunnel valleys valleys may may have have controlled controlled the the location location of of outwash plains plains by by localizing localizing meltwater drainage in supraglacial troughs that that formed formed as ice flowed into the quiescent quiescent tunnels. Additionally, Additionally, tunnel-valley tunnel-valley formation formation may have affected location of of hummock tracts and and development development of of hummocks hummocks by by locally locally removing basal and and englacial englacial debris debris from from overlying overlying glacial ice as the tunnel tunnel formed. formed. The origin origin of of hummocks has has been been interpreted interpreted in in many many different ways. I have found at at least least twelve twelvedifferent differentmodels: models: 1- supraglacial 1supraglacial reworking reworking and and redistribution redistribution of of debris debris released released supraglacially supraglacially from from stagnant ice Clayton, 1967; 1967;Clayton Clayton and and Moran, 1974; stagnant ice (Boulton, (Boulton, 1967, 1967, 1972; 1972; Clayton, 1974; Paul, 1983). 1983). 2- slumping 2slumpingof ofsupraglacial supraglacialdebris debrisinto intocrevasses crevasses(Tanner, (Tanner,1914); 1914); 3- squeezing of of subglacial debris into basal crevasses or hollows under stagnant stagnantice ice (Hoppe, 1952; (Hoppe, 1952;Stalker, Stalker,1960). 1960). 4- molding of of basal till under active ice ice as as a transition form form between between drumlins and Rogen moraine moraine (Aario, (Aario,1977). 1977). deposition of s- patchy 5patchy deposition of lodgement lodgementtill till under underactive activeice ice(Menzies, (Menzies,1982); 1982); 6- melting 6melting of of simple simple or or stacked stacked layers layers of of debris-rich debris-rich ice ice producing producing melt-out melt-out till till hummocks (MOller, (Moller,1987). 1987). hummocks 7- deformation by rising diapirs of 7deformation of supraglacial supraglacial and englacial englacial debris by of clean clean ice ice (Minell, (Minell,1979). 1979). 8- rising diapirs 8diapirsof of subglacial subglacialdebris debris(Zelcs, (Zelcs,1993). 1993). 9- patchy 9patchy formation formation of of ground ground ice icebeneath beneathstagnant, stagnant,cold-based cold-based glaciers glaciers(Aario, (Aario, 1992). 1992). 10-melting of of debris-rich, stagnant ice ice containing containing extensive karst tunnels tunnels(Kemmis (Kemmis and others, and others,1994). 1994). 11-partial 11-partial erosion erosion of of till till plains plains by by subglacial subglacialmeltwater meltwater(Rains (Rainsand andothers, others,1993). 1993). 12-Extrusion of of proglacial sediment by glacier-forced glacier-forced groundwater groundwater flow (Boulton (Boulton and Caban, 1995). Caban, 1995). The hummocks in the the field-trip area are considered to have The hummocks in field-trip area considered to have formed formed as as stagnant-ice features features (#'s (#Is 11and and 6) 6)because because of of their their close close association association with with ice-walledice-walledformed from from the melting of stagnant, lake plains. plains. The hummocks formed stagnant, debris-rich debris-rich ice. ice. The The resulting topography formed as a result result of of collapse collapse and differential differential settling as the melting, the melting, buried, buried, debris-rich debris-rich ice ice lowered lowered the the overlying overlying supraglacial supraglacial debris. debris. Numerous show the the presence of faults, faults, folds, folds, and and steeply Numerous exposures exposures show presence of steeply tilted beds 11 I �a within within the the hummocks. hummocks. These Thesefeatures featuresare arebest best explained explained as as being being caused caused by collapse collapse due to to the the melting melting of of buried, buried, stagnant stagnant ice. ice. However, much of of the till in the hummocks is interpreted to be melt-out melt-out till. The interpretation of melt-out till in many of the hummocks is based primarily on the the strong strong pebble pebble fabric fabric parallel parallel to to regional regional ice ice flow flow (Fig. (Fig. 1-9). 1-9). I interpret the the diamicton with strong fabric as likely being melt-out melt-out till till (rather than lodgement fill till or deforming-bed (1) The The diamicton diamicton contains faults and deforming-bed sediment) sediment)for for three three reasons. reasons. (1) subtle The thin subtle stratification stratification that have have been been related related in in the the literature literature to to melt-out melt-out fill. till. The sand sand lenses lenses present present in in the thediamicton diamicton at at the the St. St. Croix Croix Falls dump and and speedway speedway sites sites are Möller uses these are similar similar totolenses lensesdescribed describedinindiamicton diamictonbybyMOller Moller(1987). (1987). Moller lenses as In over half half of of the samples as arguing arguing for for aamelt-out melt-out origin. origin. (2) In samples with with ice-flowice-flowparallel parallel fabric, fabric, the fabric fabric is stronger stronger than than those those reported reported for for lodgement lodgementfill. till. (3) Meltout and stagnant ice ice is is indicated out till till requires requires stagnant stagnant ice ice for for formation, formation, and indicated by the the hummocks till does does occur occur in in some some exposures, exposures,but but itit is not as hummocks themselves. themselves. Flow Flow till as common as the till Flow till till has has poor poor fabric development till II interpret interpret as as melt-out melt-out till. till. Flow and is fluvialsediment. sediment. is interbedded interbedded with withfluvial In terms hummockshave have been been used used to imply terms of of glaciologic glaciologic implications, implications, hummocks imply surging surging conditions conditions leaving leaving large large hummock hummock tracts tracts (Wright, (Wright, 1980; 1980; Johnson Johnson and and Savina, 1987) or that the 1987) or the hummocks hummocks indicate indicate extensive extensive freezing-on freezing-on of material material under under non-temperate non-temperateglaciers glaciers(Boulton, (Boulton,1972; 1972; Paul, Paul, 1983; 1983; Moller, Moller, 1987; 1987; Sollid and and Sørbel, Attig and others, 1990)and and therefore therefore indicate indicate cold Serbel, 1988; 1988; Attig others, 1989; 1989; Mooers, Mooers, 1990) conditions. conditions. The The ice-walled-lake ice-walled-lake plains and melt-out-till melt-out-till hummocks of of western Wisconsin Wisconsin represent the the coarse-grained coarse-grained end of of aa continuum continuum with with the the stagnant stagnant ice ice landscape landscape developed developed in in clayey clayey till till that thatwas wasdescribed describedininNorth NorthDakota Dakotaby byClayton Clayton(1967). (1967). In general, I suggest that sandier debris tends tends to to yield yield aa greater proportion proportion of of sandier glacial glacial debris melt-out till in glacial debris debris tends tends to produce in hummocks, hummocks, and more more clay-rich clay-rich glacial produce a greater greater proportion proportion of of flow flow till till and anddebris-flow debris-flow sediment sediment in in hummocks. hummocks. Ice-walled-lake plains in the I c e - w a l l e ~plains l a i n (Stop s(Stov 1-4).--There 1-4).--There are over 40 ice-walled-lake ice-walled-lake plains field-trip of them occur in hummock tracts, suggesting field-trip area area (Fig. (Fig. 1-8), 1-8), and nearly all of suggesting that that their their origin origin isisrelated related to tothe theorigin originof of the thehummocks. hummocks. Ice-walled-lake Ice-walled-lake plains plains form form initially initially as as supraglacial supraglacial lakes lakes on on stagnant, stagnant, debris-rich debris-rich ice. The lake water melts through through the thethin thinice, ice, and andsediment sedimentisisdeposited depositedin inthe thelake lakefrom fromadjacent adjacent debris-rich debris-rich ice. ice. Upon Uponmelting meltingof of stagnant stagnantice, ice, the the sediment sediment left behind forms a smooth, smooth, dishshaped shaped plateau plateauin inthe themidst midstof of aahummock hummocktract. tract. Ice-walled-lake plains in in the field-trip area range in Ice-walled-lake plains in size size from from 11toto13 13km2, km2, 12 �DIAMICTON FABRIC Figure Figure 1-9.--Map 1-9.-Map of of the study study area area showing showingrose rose diagrams diagrams of of fabric fabricin indiamicton. diamicton. Lake ice-margin position); stippled Balsam positions (B = ice-margin Hachured lines = ice-margin positions (B = Balsam Lake ice-margin position); stippled Hachured lines = Fabric measurements north. locations; arrows = site tracts; circles = hummock tracts; circles = site locations; arrows = north. Fabric measurements areas==hummock areas consist consistof of 25 25pebbles pebblesexcept exceptsite site44(75 (75pebbles pebbles combined combined from from three three places places in in the the places in each outcrop); sites 9, outcrop); outcrop);sites sites55aztd and66(50 (50 pebbles pebbles combined combimedfrom fromtwo two places in each outcrop); sites8,8,9, dipping stratification 11,and and 12 12(50 (50pebbles). pebbles). Diamicton at site site 4 contains contains steeply steeply dipping stratification 10,11, 10, showing showingthat thatfabric fabrichas hasbeen beenrotated. rotated.Rotation Rotation of of stratification stratificationto to 00 0Ârotates rotates dominant dominant fabricmode modetotoN70°W. W W . fabric 13 �plains commonly commonly have have aa rim with a typical typical size size around around 22 km2. km2. Ice-walled-lake Ice-walled-lake plains around their their margin that stands around margin that stands 3 to 10 10 m m above above the the center center of of the the lake lake plain. plain. Stream- and wave-sorted sand and and gravel gravel occur occur along the margins margins of of the the ice-walled ice-walled lakes. In Inplaces, places, the the rim rim sediment sediment is is interbedded interbedded with with till till that flowed flowed from from adjacent adjacent ice into the Coarse sediment sediment isis restricted restricted to to the the margins of the lake. lake. Coarse of the lake lake plain; plain; much of of the are underlain by silt, silt, with with as much the interior interior portions portions are underlain by as much much as as 20 20 m m underlying the the larger larger plains. plains. The sediment in the plains was deposited after active the ice-walled-lake ice-walled-lake plains active ice ice left left the area. plains cross known area. This is known known because because some some ice-walled-lake ice-walled-lake plains known iceicemargin positions, signifying that the ice that walled the lake came from two separate two separate advances. advances. Tunnelelvalleys and 1-8),--Tmel 1-SE--Tunnel valleys (Stom1-1. 1-1,1-2. 1-2,1-6.and valleys are are river river valleysand andeskers eskers(Stops valleys believed to have been carved valleys carved by subglacial subglacial streams streams that that became became incised incised into into the glacier bed. These These valleys valleys were were first first described in Denmark and later recognized in northern northern Germany. Germany. Numerous Numeroussubglacial subglacial river river channels channels associated associated with late late Wisconsinan Glaciation Glaciation in in the Upper Midwest have been described Wisconsinan described by by Mickelson Mickelson and Attig and others asbeing beingformed formed by by rapid rapid or catastrophic and others others (1983) (1983) and others (1989) (1989) as catastrophic drainage. these authors authors have have proposed proposed the term drainage. Therefore, Therefore, these term tunnel tunnel channel channel for for these features, suggesting that their formation occurred under bank-full conditions. conditions. Tunnel valleys are aa common common landform landform in western western Wisconsin, Wisconsin, the greatest greatest number is ice margin. margin. Half is associated associated with the the St. St. Croix Phase ice Half of of the the tunnel tunnelvalleys valleys in western westernWisconsin Wisconsincontain containeskers eskers(Fig. (Fig.1-6). 1-6). In western Wisconsin, link together tunnel valley valley segments segments Wisconsin, it is possible to link into a network 40 km. km. However, network with with some some valley valley systems as long as 40 However, breaks breaks in in the the sequences, development development of of outwash outwash plains plains of of different different ages graded to tunnel-valley sequences, different parts of of the the same same tunnel-valley tunnel-valley sequence, sequence, and the the presence presence of of the the bestbestdeveloped tunnel valleys suggest that the developed valleys next to to former former ice-margin ice-margin positions, positions, suggest the tunnel valleys valleys in in western western Wisconsin Wisconsin were formed as relatively short segments segments near near former ice-margin positions during during overall overall retreat. retreat. About half About half of the the tunnel tunnel valleys valleys in inwestern westernWisconsin Wisconsin also also contain contain central central eskers. The Theassociation association of of eskers eskers within within the the tunnel tunnel channels channels indicates indicates two two levels levels of of discharge during subglacial subglacial drainage. A A large large discharge discharge is shown by the large large size size of the tunnel channel channel as as well well as as the the fact fact that that itit isis an anerosional erosionalfeature. feature. It is suggested that the that the tunnel tunnel channel channel represents represents an an initial, initial, short-lived short-lived burst burst of of subglacial subglacial meltwater, perhaps under hydraulic head built up behind meltwater, behind aa frozen frozen margin margin (Wright, (Wright, 1973; Attig and and others, 1989). 1989). As discharge abates, the subglacial meltwater pathway 1973; Attig pathway 14 �isismaintained maintainedatataasmaller smallersize. size. This This smaller smaller tube tube later later becomes becomes filled filled with with stream stream sediment sedimentand andbecomes becomesan anesker eskerupon uponmelting meltingofofthe thesurrounding surroundingice. ice. Eskers Eskers that that do do not notoccur occur inintunnel tunnelchannels channels are are also alsopresent present ininwestern western Wisconsin. Wisconsin. The Thelargest largestoccurs occursin innorthwest northwestPolk Polk County County and and has hasits itsterminus terminusatatthe the lies. The elevation of this esker apex of the large outwash fan upon which Frederic apex of the large outwash fan upon which Frederic lies. The elevation of this esker rises feet at at its terminus, 1080 feet feet near near West West Sweden Sweden to to 1200 1200 feet terminus, indicating indicating that that rises from from1080 the thesediment sedimentin inthis thisesker eskerwas wasdeposited deposited as as water water flowed flowed up up regional regional slope. slope. Other Other prominent eskers include one, locally referred to as "The Hogsback," at the St. Croix prominent eskers include one, locally referred to as "The Hogsback," at the St. Croix County Countyline, line,and andone onerevealed revealedininaalarge largecollapse collapsepit pit 33km km north northof of Centuria. Centuria. Outwash Outwash plains plains (Stops (Stovs1-1 1-1and and1-2L--Outwash 1-21.~0utwashplains plains cover cover much much of of western western Wisconsin Wisconsin and and constitute constituteone oneof of the themost mostcommon commonlandforms landformsremaining remainingfrom fromthe the Wisconsinan 1-6). These These plains plains were were built built by by meltwater meltwaterstreams streams WisconsinanGlaciation Glaciation(Fig. (Fig.1-6). emanating emanatingfrom fromthe themelting meltingSuperior SuperiorLobe. Lobe. Outwash Outwash plains plainsare areclearly clearlyassociated associated with with former former ice-margin ice-margin positions, positions, and and the margins are are interpreted interpreted in part by the position positionof of former former Superior Superior Lobe Lobe ice margins by the the sharp sharp northern northern and andwestern westernup-slope up-slopelimits limits of of the the outwash outwash plains plains (Fig. (Fig. 1-5). 1-5). Near Near former former ice-margin the slope ice-margin positions, positions, the slope of of the the outwash outwash plains plains is is relatively relatively steep steep ranging ranging from as high high as as 8.5 8.5 m/km. m/km. InInmore from 2.0 2.0 to 4.0 4.0 mIlan, m/km, but but may may be be locally locally as moredistal distal positions, 1.0m/km. m/km. positions, the the slope slopeisis around around1.0 A A significant significant amount if not most of of the outwash in the the outwash outwash plains plains was was derived derived from from tunnels tunnels underneath underneath the theSuperior Superior Lobe Lobe discharging discharging meitwater meltwater and and plain has has aa fan sediment. sediment. In In several several places places in in the the county, county, the the outwash outwash plain fan shape shape at at former with the the mouths of former ice-margin ice-margin positions whose apex is coincident coincident with of a tunnel tunnel valley valley or or an anesker. esker. ItIt isis clear clear in in these these cases cases that that the the tunnel tunnel system system underneath underneath the the ice, ice, now indicated indicated by the the tunnel tunnel valleys valleys and eskers, was the source for the sediment that outwashplain. plain. that composes composes the the outwash Spooner Hills (Stop SpoonerHills Hillsrefer referto to aa line line of of hills of (Stov 1-1O).--The 1-I@.-The Spooner of high relief relief These hills are distinct from any other that 1-7). These hills are distinct from any other that contain containunlithified unlithifiedsediment sediment(Fig. (Fig.1-7). landform landform in the the field field trip trip area areaand andrepresent represent aalandform landform type typenot notcommonly commonly described described in inglaciated glaciatedregions. regions. I refer refer to to these these hills hills as as the the Spooner Spooner Hills Hills after after the the village of the band of village of of Spooner, Spooner, Wisconsin, Wisconsin, which lies in the center of of hills. hills. The The Spooner Spooner Hills range in area area from 11 to 55 km2 km2 and exhibit relief relief as high as 60 but a number 60 m. The TheSpooner SpoonerHills Hills are areroughly roughly equidimensional, equidimensional, but number of of them them are are elongate elongate to to the the southeast southeast parallel parallel to tothe thedirection directionof of regional regional ice ice flow, flow, suggesting suggesting that that they they may mayhave havebeen beensomewhat somewhatstreamlined. streamlined.Hill-top Hill-top elevations elevations in in the the Spooner Spooner Hills Hills generally generally increase increase from from the the northwest northwesttotothe thesoutheast southeast(Fig. (Fig.1-7). 1-7). 15 1 �Based on on this information, the following hypothesisisis offered offered as as an Based information, the following hypothesis explanation Because the the hills hills contain a explanation for the the formation formation of of the theSpooner Spooner Hills. Hills. Because of sediment types representing a variety of depositional environments, and variety of because because the sediment may may predate the most most recent glaciation, glaciation, itit is likely likely that the the Spooner Hills are lines of of evidence evidence suggest suggest that the are erosional erosional features. features. Several Several lines the erosion occurred subglacially. subglacially. The The Spooner Spooner Hills are commonly commonly covered with the the till of till of the the most most recent recent glaciation glaciation and are are somewhat somewhat streamlined streamlined in aa direction direction parallel to the the regional regionalice-flow ice-flow direction direction of of the the most most recent recentglaciation. glaciation. In addition, the orientation of the the band band of of the the Spooner Spooner Hills Hills parallels parallels the the St. St. Croix Croix ice ice margin margin valleys form a branching suggesting that they are suggesting are related. related. The inter-hill valleys branching network network that, in some some places, places, connects up with with prominent prominenttunnel tunnelvalleys. valleys. It is suggested suggested that these valleys by subglacial meltwater and and the these valleys were excavated excavated by subglacial meltwater the tunnel tunnel valleys valleys represent the outlets for meitwater meltwater and sediment. However, However, this this connection connection cannot be shown The water water and be shown convincingly convincingly along the the entire entire Spooner Spooner Hills Hills chain. chain. The and sediment was released sediment was released at the the glacier glacier margin margin and and the the sediment sediment was was deposited deposited proglacially in large outwash fans and outwash proglacially outwash plains. In this scenario, scenario, the Spooner Hills would have formed formed when the the ice ice was at at the the St. St. Croix Croix ice margin or the the Tiger Tiger Cat-McKinley ice margin margin(Fig. (Fig.1-6). 1-6). in the Midwest similar to Two published descriptions of landforms elsewhere in the Spooner Spooner Hills support the the suggestion suggestion that that subglacial subglacial meltwater meltwater erosion erosion may may Clayton (1986) (1986)describes describestill till ridges ridges in in Portage have created have created them. them. Clayton Portage County, County, Wisconsin, that that have have similar similar characteristics characteristicstotothe theSpooner SpoonerHills. Hills. He He suggests that Wisconsin, they In the they may may have have been been cut cutby bysubglacial subglacialmeltwater. meltwater. In the Puget Puget Lowland, Lowland, Washington, hills hills occur occur that that have have a size and shape Washington, shape similar similar to to the the Spooner Spooner Hills Hills (Booth and and Hallet, Hallet, 1993). 1993). The hills hills in in the the Puget Lowland Lowland occur occur among among channels that (Booth have been interpreted interpretedas ascut cutby by subglacial subglacialmeltwater. meltwater. V. fill discussed discussed on this V. Types of till this field field trip. trip. The of the glacial The interpretation interpretation of glacial landscape landscape requires requires that the the sediment sediment composing landforms be interpreted as as well. well. The The following following list list describes describes the the basic basic of lodgement till, till, melt-out melt-out till, till, flow flow till, till, and and deforming bed sediment. characteristics of sediment. All of of these sediment types may poorly sorted, pebbly), but All may look look similar similar (massive, poorly subtle differences allow interpretation interpretation in in some some places. places. Lodgement till.--Lodgement till till is is deposited deposited by by plastering of of glacial glacial debris from the JnfiOL-till.-Lodgement sliding base base of sliding of aa moving moving glacier glacier by pressure pressure melting melting and/or and/or other othermechanical mechanical processes (Dreimanis, (Dreimanis,1989), 1989), and and is is characterized characterizedby: by: 16 �I Laterally and and vertically vertically consistent consiste orientation of fabric elements, structures, and surface marks on on clasts. clasts. a.. parallel parallel striae striae on on lodged lodged clasts dusts b.. parallel parallel a-axes a-axes of pebbles c.. sediment smudges, thrust shear planes, and fissility showing shear thrust structures, str 2. 2. Comminution producing producing bi-modal grain-size with terminal modes in silt silt size. size. 3. Materials of local derivation nearer the base of the till. till. 4. Overconsolidated. Overconsolidated. of end moraines. 5. 5. Occurs in ground moraine, moraine, flutes, drumlins, proximal sides of Melt-out till.-t&- Melt-out till is deposited by a slow release of of glacial debris from ice that is and is characterized by: is not not sliding slidingor ordeforming deforminginternally internally(Dreimanis, (Dreimanis,1989), 1989), and 1. 1. Debris banding from ice preserved but with gradational contacts and flattening flattening of of structures. structures. Melt-out Melt-out till may may be be massive. massive. 2. 2. Clasts of unlithified material may be present. flow, but but may may be be transverse. transverse. Dip Dip of of pebbles pebbles is is upup3. Clasts aligned parallel to glacier glacier flow, 1. 1. Laterally I I I but lessened ice ice but lessened by by loss loss of of ice. ice. I I I I I i I I i 4. Grain-size may be coarser than lodgement till, till, and grain-size distribution may be more variable. variable. Striated clasts present, but 5. 5. Striated but faceted faceted clasts clasts are rare. 6. Draping Draping of of layers layersover over clasts clasts as as interstitial interstitialice ice is is lost. lost. 7. 7. Winnowing of fine particles and redeposition, perhaps as coats around around clasts. clasts. Sorted sediment sediment deposited deposited in 8. Lenses and veins veins of of sorted sorted sediment sediment cased cased in in till. till. Sorted englacial tubes. tubes. englacial 9. Normal consolidation. consolidation. 10. Associated with stagnant stagnant ice ice landforms. Flow till.--Flow till.--Flow tills tills (broadly (broadly speaking) speaking)may mayderive derivefrom fromany any glacial glacialdebris debris upon upon its Flow release from glacier ice or from a freshly glacier ice freshly deposited till, in direct direct association association with glacier ice. The The redeposition redeposition isis accomplished accomplished by gravitational gravitational slope process, mainly by gravity gravity flow, flow, or or by by squeeze squeeze flow, flow, and and ititmay maytake takeplace placeice-marginally, ice-marginally, supraglacially, or subglacially, 1989), subglacially, and and subaerially subaerially or or subaquatically subaquatically(Dreimanis, (Dreimanis,1989), and and is is characterized characterized by: by: Lithology (color, (color, grain-size, grain-size, mineralogy) mineralogy)inherited inheritedfrom fromparent parent ice ice (so (some sorting 1. 1. Lithology during flow). flow). 2. Common stratification and and interbedding with water-sorted sediments. 2. Depending on grain size sorting, grading grading (inverse or or normal) normal) 3. Depending 3. siz and water er content, sorting, may occur. occur. 17 17 �4. Fabric Fabric determined determined by (local slopes) slopes)and and stresses stresses are are low, low, producing producing 4. by local local stresses stresses (local random to to strong strong fabric fabric with with maxima maxima parallel parallel to transverse transverse stress stress orientation orientation (not (not ice flow). flow). 5. 5. Normally consolidated. consolidated. Deforming bed sediment.--Deforming bed sediment sediment forms forms under under aa sliding, -Deforming bed sliding, wetwetbased glacier. The is transmitted to the bed, causing based The glacier's glacier's basal basal shear stress is causing bed deformation. The thickness thickness ofof this this deforming layer is is hotly deformation. The deforming layer hotly debated debated among among glaciologists and and glacial geologists: is it centimeters glaciologists geologists: is centimeters or meters? meters? Deforming bed sediment ostensibly ostensibly has has the as lodgement sediment the same same characteristics characteristics as lodgement till, till, although although some some suggest that that deforming deforming bed bed sediment sediment has has a weak pebble authors (i.e., Hart, 1994) 1994) suggest pebble fabric. .. VI. Contrasts in glacial landforms landforms VI. One of of themes of this field field trip trip is to point out and discuss themes of discuss the variations variations in morphology of glacial deposits in the the terminus terminus region region of of the the Superior SuperiorLobe. Lobe. Emerald Phase Few hummocks Few collapse depressions No tunnel valleys valleys or eskers eskers No mappable outwash outwash plains plains Integrated, dendritic dendritic drainage drainage No drumlins(?) drumlins(?) St. Croix Phase and and- later phases 1 Many hummocks and ice-walled-lake ice-walled-lake plains plains behind multiple multiple ice-margin ice-margin positions positions Many collapse depressions Many tunnel valleys, some with with eskers, eskers, as well as as the the Spooner Spooner Hills Hills Extensive outwash plains plains Deranged drainage drainage Thrust (?) Thrust features features (?) No drumlins The landforms left behind during the the Emerald Emerald Phase of the Superior Superior Lobe Lobe are distinct from those formed during the St. Croix Croix and and later later phases. phases. Features Features formed formed by by widespread stagnant widespread stagnant ice ice (hummocks (hummocks and and ice-walled-lake ice-walled-lake plains) and extensive extensive discharge eskers, and outwash discharge of of subglacial subglacial meltwater meltwater (tunnel (tunnel valleys, valleys, eskers, outwash plains) plains) dominate left by by the the St. Croix Phase, Phase,but but are are absent absent or or rare rare in the dominate the landscape landscape left St. Croix landscape landscape left by the the Emerald Emerald Phase. Phase. I interpret interpret these phases to to have have occurred occurred during the the last last part partofofthe theWisconsinan Wisconsinan Glaciation Glaciation and that the the difference difference in in the the landform landform suites suites is is due due to to aachange changein incharacter character of of the the Superior Superior Lobe at the the beginning of the St. Superior Lobe changed from a cold, cold, nonSt. Croix Croix Phase. Phase. I suggest that the Superior 18 �[ "1 fl glacier during during the Emerald Phase, to to aa less less cold, cold, surging surging glacier glacier during during the surging glacier Emerald Phase, St. Croix Phase. The landforms of above), the the thin thin to patchy cover of of the Emerald Phase (listed above), of till deposited the till deposited during during the the Emerald Emerald Phase, Phase, and and the the presence presence of of well-developed well-developed permafrost features suggest suggest that that climate dimate during the Emerald Emerald Phase was colder than during the the St. St. Croix Croix Phase. Phase. The Theabsence absence of of tunnel tunnel valleys valleys indicates indicates less less subglacial subglacial meltwater present present during prevented meltwater during this this phase, phase, perhaps perhaps because because cold cold conditions conditions prevented meltwater from from draining draining through through the the glacier to the Meltwater formed meltwater glacier to the bed. bed. Meltwater formed flowed, for for the the most most part, part, over over dean clean ice ice and and had had a low predominantly supraglacially flowed, sediment load. Ice Iceflowed flowedinto intopre-Emerald-Phase pre-Emerald-Phase river valleys, which later became collapse depressions depressions when when warming warming allowed allowedburied buried ice iceto tomelt. melt. Following retreat retreat of of collapse the ice margin, conditions helped helped to to allow allow rapid rapid development of a the margin, permafrost permafrost conditions development of In part, part, the dendritic drainage drainage network much surface surface till till was was eroded. eroded. In dendritic network and likely much drainage network may have drainage have been been inherited inherited from from the the pre-Emerald-Phase pre-Emerald-Phase surface because it would not have been deeply buried by Poskin till. till. (Though (Though II suggest suggest that that because cold conditions, conditions, they they may may also also imply imply that that the Emerald Emerald Phase these features indicate cold did not last last long.) long.) During the St. subglacial drainage drainage of of the Superior During St. Croix Phase, large-scale large-scale subglacial Lobe began began and and formed formed tunnel tunnel valleys valleys and and eskers. eskers. As mentioned earlier, much much of of Lobe mentioned earlier, the meltwater stream sediment in in the outwash plains of western Wisconsin can be be Wisconsin can Additionally,the theSpooner SpoonerHills Hillsare arethought thought to to be be traced to tunnel-valley tunnel-valley mouths. mouths. Additionally, the result of erosion by subglacial meltwater. The meltwater subglacial meltwater. The increase in subglacial meltwater features is accompanied by the presence of of widespread stagnant stagnant ice ice features. features. suggestthat thatthe the Superior SuperiorLobe Lobesurged surged during during the the Johnson and Savina (1987) (1987) suggest St. Croix Croix and and later phases, and Clayton suggest that that many lobes of of Clayton and others others (1985) (1985) suggest Increased subglacial subglacial discharge discharge of of meltwater meltwater is the Laurentide Ice Ice Sheet Sheet surged. surged. Increased associated with surging (Kamb and others, 1985), and surging surging can leave large 1985), and large associated with (Kamb and Clapperton amounts of stagnant ice ice that that melts melts to toform formhummocks hummocks (Wright, (Wright, 1980). 1980). Clapperton (1975)suggests suggeststhat that large large amounts amounts of of debris debris are are frozen frozen on on to to the base of of the glacier (1975) surging. AA thick, layer in in aa mass mass of of stagnant stagnant ice ice would would during surging. thick, basal, basal, debris-rich debris-rich layer Surging isis aa periodic produce high-relief like those in Polk produce high-relief hummocks hummocks like Polk County. County. Surging behavior of of glaciers glaciers and and the size and geometry of the the tunnel valleys indicate that that behavior geometry of valleys indicate they operated only for a short time, and that they were not all operating at the same time (Attig and other, other, 1989; 1989; Patterson, personal communication). On the other On other hand, hand, the the hummocks hummocks may may simply simply indicate indicate cold cold conditions conditions rather than surging. Many are produced produced by by nonnonrather Many authors authors suggest suggest that hummocks hummocks are 19 �temperate glaciers temperate glaciers (glaciers (glaciers with with ice ice colder colder than than0°C) O°C(Boulton, (Boulton,1972; 1972; Paul, Paul, 1983; 1983; Mäller, 1987; Sollid and and Sørbel, Attig and Moller, 1987; Sollid Sorbel, 1988; 1988; Attig and others, others,1989; 1989;Mooers, Mooers, 1990). 1990). These These the process process of of meltwater meltwater generation generation where where the the bed bed is at 0°C authors describe, describe the P C and the subsequent freezing-on of of debris at the base of the glacier glacier as the the meltwater meltwatermoves moves subglacially towards towards the margin and ertcounters ice colder colder than than 0%. 0°C. This This process process subglacially encounters ice produces aa thick, zone. The produces thick, basal, basal, debris-rich debris-rich zone. The margin margin of of the the cold cold glacier glacier stagnates stagnates during melting and the melting of the debris-rich ice produces hummoclcy during melting and the melting of the debris-rich ice produces hummocky topography. Evidence of permafrost permafrost in in western suggests that that the topography. Evidence of western Wisconsin Wisconsin suggests the hummocks may may simply indicate a non-temperate glacier, and and not necessarily hummocks simply indicate non-temperate glacier, necessarily aa surging glacier. surging glacier. It is not the water water that cut not clear clear in in western western Wisconsin Wisconsin ifif the cut the the tunnel tunnel valleys valleys was melted from from the the bed or or from from the the surface surface of the the glacier. glacier. Wright Wright(1973) (1973) states that that tunnel valleys valleys formed under under the theSuperior SuperiorLobe Lobe because because subglacial subglacial meitwater meltwater was was held by aa frozen frozen margin margin of of the the glacier. glacier. Mooers Mooers(1989) (1989) argues that the Superior Superior Lobe Lobe was temperate and that that the the tunnel tunnel valleys valleys indicate indicate meltwater from the surface surface of of Gustavsonand andBoothroyd Boothroyd(1987) (1987) document document aa the glacier reaching the glacier glacier bed. Gustavson surficial source for subglacial tneltwater meltwater on on the the temperate temperateMalaspina MalaspinaGlacier, Glacier,Alaska. Alaska. The presence of ice-wedge casts behind behind the St. Croix limit in The presence of ice-wedge casts Croix Phase ice-margin ice-margin limit Wisconsin suggests suggests that that the ice surface would would have been well below below 00C and that 0OC and Wisconsin little surface meltwater would make it to to the the glacier glacier bed. However, cold conditions conditions were present when no no or few were present during the the Emerald Emerald Phase Phase when few tunnel tunnel valleys valleys were were formed. I suggest that that the the climate climate supported supported permafrost permafrost conditions conditions during both both the the Emerald and St. St. Croix Croix Phases, Phases, but was was gradually gradually getting gettingwarmer. warmer.Ice-wedge Ice-wedgecasts casts outside the Emerald outside Emerald Phase Phase ice-margin ice-margin limit are are numerous numerous and and well-developed well-developed (Johnson, 1986),whereas whereas those those behind behind the St. Croix Phase ice-margin limit limit are are few few (Johnson, 1986), During the St. Croix and less less well well developed. developed. During Croix Phase, even though though permafrost permafrost conditions were present, present, surface surface meltwater began to find pathways pathwaysto tothe theglacier glacierbed. bed. of increased water at the bed caused the lobe to surge, tunnel The presence of tunnel valleys valleys to to form, and left widespread widespread stagnant stagnantice. ice. VII. Bibliographic information VII. Bibliographic information on on the the glacial glacial geology geology of western western Wisconsin Wisconsin foraa north-south north-south band of The St. Croix moraine was named by Berkey Berkey (1897) (1897) for of occurring immediately immediately east east of of the town hummocks occurring town of of St. St.Croix Croix Falls, Falls, Wisconsin. Wisconsin. However, the the first comprehensive mapping and and description description of of the St. However, comprehensive mapping St. Croix Croix moraine and associated associated deposits deposits was was that that of ofStrong Strong(1880) (1880) and and T.C. T.C. Chamberlin Chamberlin 20 �•• I I fl I I I (1883). (1932)transferred transferredthe thename nametotoapply applyto to the the hummocky hummocky deposits deposits that that (1883). Leverett (1932) marked the Wright and Ruhe marked the edge edge of of the theSuperior Superior Lobe Lobe in in western western Wisconsin. Wisconsin. Wright (1965) called called the the event event that made these features the the St. St. Croix Phase. Along the St. Croix Phase Phase deposits deposits in Wisconsin, Wisconsin, aa number number of of geologists have have Along made several somewhat dissimilar interpretations ofof the the position position and and nature of the dissimilar interpretations St. Croix Croix ice-margin ice-margin position position(Chamberlin, (Chamberlin, 1905, 1905, 1910; 1910; Leverett, 1932; 1932; Mathieson, 1940; Black, Black, 1959; 1959;Berg, Berg, 1960; 1960;Wright, Wright,1972; 1972;Wright Wrightand and others, 1973; Johnson, 1986; 1973; Johnson, 1986; Johnson and Refinementsinin the the stratigraphy have Johnson and Savina, Savina,1987; 1987;Mooers, Mooers,1989). 1989). Refinements been made by by Baker Baker and andothers others(1983), (1983),Mickelson Mickelson and andothers others(1984), (1984),Johnson Johnson(1986; (1986; in press), The history history of press), and and Attig Attig and andothers others(1988). (1988). The of the glacier-dammed glacier-dammed lakes lakes (glacial Lake Lind and glacial glaaal Lake Grantsburg) occupying the St. Croix, Clam, and Yellow River drainage basins has has been been discussed discussed by by several severalworkers workers(Berkey, (Berkey,1905; 1905; Hansell, 1930; Johnson, 1992, 1994; Addis Addis 1930; Burkhead, Burkhead, 1931; 1931; Butz, Butz, 1931; 1931; Cooper, 1935; Johnson, and glacial period and others, 1996). A A regional regional understanding of of the details of of the last glacial has has been enhanced enhanced by by large-scale large-scale geologic geologic mapping of of Pleistocene Pleistocene deposits in the the Lake Superior Barron 1985), Barren Superior region region (Clayton, (Clayton, 1984), 1984), the Twin Cities region (Meyer, 1985), County, Hennepin County, County, Minnesota Minnesota (Meyer (Meyer and County, Wisconsin Wisconsin (Johnson, 1986), 1986), Hennepin Hobbs, 1989), Dakota County, County, Minnesota Minnesota (Hobbs (Hobbs and others, 1990), 1989), Dakota 1990), Washington Ramsey County, Minnesota (Patterson, County, Minnesota (Meyer (Meyer and and others, others, 1990), 1990), Ramsey 1992), and and Polk County, County, Wisconsin (Johnson, in press). VIII. References References cited Aario, R. ,1977, ,1977,Classification Classificationand andterminology terminologyofofmorainic morainiclandforms landformsininFinland: Finland: Boreas, Boreas, v. v. 6, 6, p. 87100. 100. 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Baker, Baker, R.W., R.W., Diehl, J.F., Simpson, T.W., T.W., Zelazny, Zeiazny, L.W., L.W., and Beske-Diehl, Beske-Diehl, S., S., 1983, 1983, Pre-Wisconsin Pre-Wisconsin glacial stratigraphy, chronology, paleomagnetics of west-central west-central Wisconsin: Wisconsin: Geological Geological Society of America America Bulletin, Bulletin, v. v. 94, 94, p. p. 1442-1449. 1442-1449. Berg, T.E., Wisconsin Berg, T.E., 1960, 1960,Differentiation Differentiationofofthe the St. St.Croix Croixand and Emerald Emerald moraines, moraines, in in west-central west-central Wisconsin [abstract]: Institute Instituteon onLake LakeSuperior SuperiorGeology, Geology, 6th Annual Annual Meeting, Meeting, Madison, Madison, Wisconsin, Wisconsin, p. 14. p. 14. Berkey, Geology of of the St. Croix Dalles: Dalles: American Berkey, C.P., 1897, Geology American Geologist, Geologist, v. v. 20, 20, p. 345-383. p. 345-383. 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J.T.,and and Attig, Attig, J.W., J.W.,1985, 1985,Surging Surgingofofthe thesouthwestern southwesternpart part of of the Laurentide Clayton, Lee, Teller, J.T., Laurentide Ice Ice 14, p. Sheet: Boreas, Boreas,V. v. 14, p. 235-241. 235-241. Clayton, Lee, Clayton, Lee, Attig, 1W., J.W., Mickelson, Mickelson, D.M., D.M., and Johnson, Johnson, M.D., M.D., 1991, 1991, Glaciation Glaciation of of Wisconsin: Wisconsin: Wisconsin Geological and Natural History Survey Educational Series 36, 4 Natural History Survey Educational Series 36,4p. p. 1935,The Thehistory history of of the the upper Mississippi River in late Wisconsin and Cooper, W.S., W.S., 1935, and postglacial postglacial time: time: Minnesota Geological 116 p. 26,116 p. Minnesota GeologicalSurvey SurveyBulletin Bulletin26, Dowdeswell, J.A., J.A., and and Sharp, M.J., 1986,Characterization Characterizationofofpebble pebble fabrics fabrics in in modem modern terrestrial terrestrial Dowdeswell, M.J., 1986, sediments: Sedimentology, glacigenic sediments: Sedirnentology,v.v.33, 33,p.p.699-710. 699-710. Tills:their their genetic genetic terminology terminology and and classification, in in Goldthwait, R.P., Dreimanis, Alexis, Alexis, 1989, 1989, Tills: R.P., and and C.L., (eds.), Genetic classification classificationof of glacigenic glacigenicdeposits: deposits: Balkema, Rotterdam, Rotterdam, p. 17-83. Matsch, C.L., 17-83. J.C., 1987, 1987,AAdepositional depositionalmodel modelfor foroutwash, outwash, sediment sediment sources, and Gustavson, T.C., T.C., and Boothroyd, J.C., hydrologic characteristics, Malaspina Glacier, Alaska: a modem analog characteristics, Malaspina Glacier, Alaska: modem analog of of the the southeastern southeastern margin margin of of the the Laurentide LaurentideIce IceSheet: Sheet:Geological GeologicalSociety Society of of America America Bulletin, Bulletin, v. v. 99, 99, p. 187-200. 187-200. J.M., 1930, 1930,Glacial Glacialgeology geologyofofananarea areaininthe thenorthwestern northwesterncomer cornerof ofWisconsin: Wisconsin: unpublished Hansell, J.M., Ph.D. thesis, University 90 p. p. Universityof of Wisconsin-Madison, Wisconsin-Madison,90 1994,Till Tillfabric fabricassociated associatedwith with deformable deformablebeds: beds: Earth Surface Processes and Landforms, Landforms, Hart, J.K., 1994, v. 19, 19, p. p. 15-32. 15-32. 22 �g I Helgesen, J.O., and and Lindholm, Helgesen, J.O., Lindholm,G.F., G.F., 1977, 1977, Geology and water-supply water-supply potential of the Anoka Anoka sand-plain sand-plain • • V aquifer, Minnesota: Minnesota Department Department of of Natural NaturalResources, Resources, Division Division of Waters, Waters, Technical Minnesota: Minnesota Number 6, 17 p. Paper Number 6,17 Hobbs, H.C., Aronow, Saul, Saul, and and Patterson, PatterSon, Cl., C.J.,1990, 1990,Surficial Surficialgeology, geology, Plate Plate 3, 3, in in Balaban, Balaban, N.H., N.H., and and H.C., Paper Hobbs, H.C., (4s.). Geologic Minnesota Geological Geological Survey H.C., (eds.), Geologic Atlas Atlas Dakota Dakota County, County, Minnesota: Minnesota: Minnesota Series, Atlas AtlasC-4, 04, scale County Atlas Series, scale 1:100,000. 1:100,000. H.C., and and Goebel, Goebel, J.E., J.E., 1982, 1982, Geologic Geologic map geology, Minnesota Minnesota Hobbs, H.C., map of of Minnesota, Quaternary geology, Geological Survey Survey State StateMap MapSeries SeriesS-i, S-1,1:500,000. 1500,000. G., 1952, 1952, Hummocky moraine interior of of Norrbotten: Norrbotten: Hoppe, G., moraine regions regions with special reference to the interior Annaler, ,v.v.34, 34,p.p.1-72. 1-72. Geografiska Annaler Johnson, M.D., 1986,Pleistocene PleistoceneGeology GeologyofofBarron BarronCounty: County:Wisconsin WisconsinGeological Geologicaland andNatural Natural History Johnson, M.D., 1986, Survey, Information 42 p. InformationCircular Circular55, 55,42 Johnson, M.D., M.D., 1992, 1992, Glacial in western western GlacialLake LakeLind: Lind: aa long-lived long-lived precursor to Glacial Lake Grantsburg in Wisconsin Society of of America Abstracts with Wisconsin and Eastern Eastern Minnesota Minnesota [abstract]: [abstract]: Geological Geological Society with v.24, p24. Programs, v. 24, p.24. Evidence for for aa short-lived short-lived Glacial Glacial Lake LakeGrantsburg Grantsburg [abstract]: [abstract]: Geological Johnson, M.D., M.D., 1994, 1994, Evidence Geological Society Society of America Abstracts Abstracts with of with Programs, Programs, v. v.26, 26, p. p. 22. 22. Johnson, M.D., ofPolk Polk County: County: Wisconsin Geological and and Natural History Johnson, M.D., in press, Pleistocene Geology of History Survey, Bulletin Bulletin 92. 92. 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Tanner, Tanner, V., V., 1915, 1915, Studier Studier ofver ofver kvartarsystemet kvartarsystemeti iFennoskandias Fennoskandiasnordiga nordigadelar. delar.111. 111.Oni Omlandisens landisens rorelser rorelser och och afsmaltning afsmaltningii Finska F i k a Lappland och angrãnsande a n g m d e trakter: Bulletin Bulletinde deIalaCommission Commission geologique 815 p.p. 38,815 geologiquede deFinlande, Fiande,v.v.38, Walder, Geometry of of former subglacial water water channels and 1979, Geometry and cavities: cavities: Walder, J.S., J.S., and Hallet, Hallet, Bernard., Bernard., 1979, Journal JournalofofGlaciology, Glaciology,v.v.23, 23,p.p.335-346. 335-346. 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E., E., Jr., Jr., 1980, 1980, Surge Surge moraines moraines of the the Klutlan Klutlan Glacier, Glacier, Yukon Yukon Territory, Territory, Canada and and application 14,p.p.2-17. 2-17. applicationto tothe theLate LateGlacial Glacialof of Minnesota: Minnesota: Quaternary QuaternaryResearch, Research,v.v.14, Wright, of Minnesota Minnesota and Iowa, Wright, H.E., H.E., Jr., Jr., and and Ruhe, Ruhe,R.V., R.V., 1965, 1965, Glaciation of Iowa, in in Wright, Wright,H.E., H.E., Jr., Jr.,and and Frey, Frey, D.G., D.G., (eds.), The Quaternary of the United States: Princeton, Princeton,Princeton PrincetonUniversity UniversityPress, Press,p.p. 29-4 1. 29-41. Wright, Wright, H.E., H.E., Jr., Jr., Matsch, Matsch, CL., C.L., and andCushing, Cushing,E.J., E.J., 1973, 1973, The Superior and and Des Des Moines Moines Lobes, Lobes, in in Black, Black, R.F., R.F., Goldthwait, Goldthwait, R.P., R.P., and and Wiliman, Willman, G.P., G.P., (eds.), (eds.), The The Wisconsinan Wisconsinan Stage: Geological GeologicalSociety Societyof of America AmericaMemoir Memoir136, 136,p.p.153-188. 153-188. Zelcs, Glaciotectonic landforms landforms of of divergent divergent type glaciodepressional lowlands Zelcs, V., V., 1993, Glaciotectonic lowlands (dissertation (dissertation work work synthesis): synthesis):University UniversityofofLatvia, Latvia,Riga, Riga,Latvia, Latvia,105 105p. p. I I I I I 24 �I I IX. trip sites. I X. Field trip Mileage Mileage from from Cable Cab to Stop 1-1: 60 miles . I U I I I I I I I I I . . . Stop and Stop Stop 1-1 1-1and Stop1-2 1-2 St S t.Croix Croix Phase outwash outwash plain, plain, distal distal site site and and St. St. Croix Croix Phase outwash fan, proximal, ice-marginal ice-marginal site site Quadrangle: Haugen Haugen Quadrangle, Quadrangle,Wisconsin, Wisconsin, 7.5 7.5 minute minute series, series,sec. sec. 18, 18, T. T. 36 36 N., N., R. R. 11 W., sec. 13, T. T. 36 36 N., N., R R. 12 12W. 1 1W., W. Significance: These These stops stops show the character of sediment deposited by braided, character of braided, outwash streams, both immediately immediately next to a former former ice-margin position, as well as further away. away. Description: Lobe outwash outwash is probably the most common sediment Description: Superior Lobe sediment facies facies western and consists consists primarily primarily ofof sand, sand, slightly slightly gravelly gravelly sand, sand, and western Wisconsin Wisconsin and gravelly sand, with much much of of the the gravel gravel in in the thepebble pebblefraction. fraction. Stream sediment deposited within within 11km km of of former formerice-margin ice-margin positions positions is is commonly commonly much much coarser coarser and contains cobbly boulders. This This coarser coarser facies facies of of Copper Copper cobbly gravel with occasional boulders. Falls stream sediment is crudely horizontally horizontallybedded bedded and and is is more more poorly poorly sorted than stream sediment deposited in more distal positions. positions. Further Further away away from from former former iceicemargin positions, positions, the the stream stream sediment sediment is is dominated dominated by by sand in horizontal horizontal and and cross-bedded cross-bedded layers. layers. Gravel Gravel in the outwash, outwash, as as well well as as Superior Superior Lobe Lobe till, is composed primarily of of basalt, gabbro, granite, gneiss, rhyolite, rhyolite, and and sandstone. This This assemblage assemblage is typical typical of sediment sediment derived derived from from the theLake Lake Superior Superior basin. basin. proximal site is located on an outwash The proximal outwash fan fan associated associated with the the tunnel tunnel valley in which which Bear Bear Lake Lake lies. lies. It is suggested that all the outwash in this this outwash outwash plain emanated from from the the tunnel-valley tunnel-valley mouth at at Haugen. Haugen. Questions: Are rapid deposition? deposition? What Arethere thereany anyfeatures features present present here that suggest rapid would a catastrophic catastrophic deposit deposit look look like? like? Mileage from from Stop Stop1-2 1-2to to Stop Stop 1-3: 1-3:15 15 miles miles Stop 1-3 1-3 Stop Barron County hummock Barren hummock sites sites Quadrangle: Lower LowerVermillion VermillionLake LakeQuadrangle, Quadrangle,Wisconsin, Wisconsin, 7.5-minute 7.5-minute Series, Series, T. 36 N., R. R.13 13W. Significance: (1) Discussion of of the the occurrence of of melt-out till in hummocks (1)Discussion hummocks and and(2) (2) contrast between the landforms of the Emerald and St. Croix Phases. 1 25 �Description: Uniform Uniformdiamicton diamictonisisexposed exposed in infive fivehummocks hummocks in in northwestern northwestern Barron County exposures are are Barren County (sites (sites8, 8,9,9,10, 10,12, 12,13, 13,Figs. Figs. 1-8, 1-8,1-9). 1-9). In all cases, the exposures small and only pebble fabric fabric at these sites is strong only uniform uniform till till isis revealed. revealed. The pebble strong (Si=0.72, (1979) for melt(Si=O.72 0.80, 0.80, 0.74,0.72,0.85) 0.74, 0.72, 0.85)and andsimilar similartotothose thosereported reported by by Lawson (1979) out till till and and by byDowdeswell Dowdeswell and andSharp Sharp(1986) (1986) for melt-out melt-out till till and and undeformed undeformed lodgement till. Additionally,the the major major mode mode in in each each fabric fabric isis parallel parallel to the till. Additionally, the regional ice-flow direction as as determined determined by by local local striations striations and and the orientation of ice-flow direction of the nearby nearby ice-margin ice-margin position position (Fig. (Fig. 1-9). At At site site 12 12 (Fig. (Fig. 1-8), aa drill revealed 20 20 drill hole revealed m of of diamicton diamicton with with uniform uniform grain grain size size and anduniform uniform relative relativemagnetic magnetic beneath the base of of the surface surface exposure. exposure. Though these sites susceptibility beneath sites were were not not well-enough exposed to to investigate other structures well-enough exposed investigate other structures and contacts, contacts, the the strongly strongly oriented oriented pebble fabric parallel parallel to the the regional regional ice-flow ice-flow direction direction indicates indicates the diamicton is likely likely melt-out melt-out till. till. As discussed As discussed in the the text, text, features features formed formed by by widespread widespread stagnant stagnant ice ice (hummocks and ice-walled-lake plains) and extensive (hummocks and ice-walled-lake plains) extensive discharge discharge of of subglacial subglacial meitwater (tunnel valleys, valleys, eskers, eskers, and and outwash outwash plains) plains) dominant dominant the landscape left meltwater by the St. in the the landscape landscape left left by by the theEmerald Emerald St. Croix Phase, but are absent or rare rare in Phase. I have interpreted this Phase. this change change to represent a change change in ice dynamics, from a non-surging glacier cold, non-surging glacier to aa less-cold, surging glacier. See See text text for for discussion. discussion. Questions: Is it possible possible for for supraglacial supraglacial melt-out melt-out till to to survive survive collapse? collapse? Is it merely chance that till fabrics fabrics in hummocks are strong and parallel parallel to to regional regional iceiceflow direction? Do Do the thechanges changesseen seen from from the the Emerald Emerald to to St. Croix Phases represent changes in erosion erosion (and thus age)? changes in ice ice dynamics? dynamics? or merely merely differences differences in age)? Is it possible for supraglacial meltwater to ppenetrate through the thickness ckness of the the glacier glacier if if permafrost conditions conditions are are present? present? Mileage 16 miles from Stop Stop1-3 1-3 to Stop Stop 14: 14.16 Mileage from Stop 1-4 Stop 1-4 McKinley McKinley ice-walled-lake ice-walled-lake plain plain Quadrangle: McKinley, T.36 36N., N., R. R. 14 14W. W. Quadrangle: McKinley,Wisconsin, Wisconsin,7.5 7.5minute minuteseries, series,sec. sec.31, 31,T. Significance: One Significance: Oneof of the thelargest largestice-walled-lake ice-walled-lake plains in in western western Wisconsin. Wisconsin. km2 and is is one one of of the the Description: The TheMcKinley McKinley ice-walled-lake ice-walled-lake plain is about about 77 km2 largest ice-walled-lake plains in western western Wisconsin Wisconsin (Fig. 1-8). About About 40 40 ice-walledice-walledlake plains occur in the the terminus terminus region region of of the the Superior Superior Lobe Lobe in in western western Wisconsin, Wisconsin, and another another 20 20 to to 30 30 occur occur in in the the continuation continuation of of these these deposits deposits in in Minnesota. Minnesota. Nearly of them occur in hummocky hummocky tracts, Nearly all of tracts, suggesting suggesting that that their their origin is related 26 �I I I I I I I I I I I the origin plains in in the the study study area to the to origin of of the the hummocks. hummocks. Ice-walled-lake Ice-walled-lake plains area range range in in size size from 1 to 13 km2, with a typical size around 2 km2. Ice-walled-lake plains from 1 to 13 km2, with a typical size around 2 km2. Ice-walled-lake plains commonly have a rim around their their margin margin that stands stands 33 to to 10 10 m m above above the the center center of of the the lake lake plain. plain. StreamStream-and andwave-sorted wave-sorted sand sand and and gravel gravel occur occur along along the the margins margins of of the lakes. In In places, places, the the rim rim sediment sediment is is interbedded interbedded with with till till that that flowed flowed the ice-walled ice-walled lakes. from adjacent ice ice into the lake. Coarse Coarse sediment sediment is restricted to the margins margins of the the lake plain; much lake plain; much of of the the interior interior portions portions are are underlain underlain by by silt. silt. Drill Drill holes holes at at Stop Stop 55 encountered encountered 20 20 m m of of silt siltoverlying overlyingSuperior SuperiorLobe Lobe till. till. The ice-walled-lake plains plains occur at elevations similar to those of the surrounding hummocks. The rim ridges occur at elevations similar to those of the surrounding hummocks. The rim ridges of the ice-walled-lake ice-walled-lake plains are approximately the same elevation or slightly slightly lower lower than the the tops topsof of hummocks hummocksadjacent adjacent to to the the lake lakeplain. plain. Ice-walled-lake described elsewhere may may occur in hummock tracts, Ice-walled-lake sediment described tracts, but within apparently ice ice was was thin thin enough enough that that the open within the the Southeastern Southeastern Sector, Sector, apparently water was able able to to melt melt entirely entirely through through the the stagnant stagnantice, ice, leaving leaving nicely nicely preserved preserved ice-walled-lake plains. plains. Questions: What is the relationship relationship of of permafrost permafrost to to the the ice-walled-lake ice-walled-lake plains? plains? Do Do the ice-walled-lake plains indicate indicate that that the the hummocks must be the ice-walled-lake plains hummocks must be stagnant stagnant ice ice What was the source of sediment for the ice-walled-lake plains? What do features? features? source ice-walled-lake plains? What do they indicate about sediment sediment distribution distribution in in the the ice? ice? Mileage (optional): 10 Mileage from from Stop Stop1-4 1-4to Stop Stop 1-5 1-5(optional): 10 miles miles Mileage Mileage from from Stop Stop1-4 1-4to Stop Stop 1-6: 1-6:16 16 miles miles 1-5 (optional) (optional) Stop 1-5 Turtle Turtle Lake ice-walled-lake plain delta Quadrangle: 7.5 minute minuteseries, series,sec. sec.6,6,T. T. 33 33N., N.,R. R. 14 14W. W. Quadrangle: Clayton, Clayton, Wisconsin, Wisconsin, 7.5 Significance: An Anexposure exposureof of aadelta deltathat thatprograded progradedinto intothe theTurtle TurtleLake Lakeice-walledice-walledSignificance: lake lake plain. 1-5to to Stop Stop 1-6: 1-6:23 23 miles Mileage from from Stop Stop1-5 Stop 1-6 Stop 1-6 Eskedahl tunnel valley and esker esker Big Round Lake, Wisconsin, 7.5 minute series, sec. sec. 28, 28, T. 36 N., R. R. 16 16 Quadrangle: Big Wisconsin, 7.5 w. Significance: Significance: A good example of of a tunnel valley with an an esker esker Description: The TheEskedahi Eskedahltunnel tunnelvalley valley and andesker eskerisis25 25 km km long long and and 0.5 0.5 to to 0.8 0.8 km krn relief of of the from the the bottom bottom ofof one one of of the lakes wide. The The relief the valley valley from lakes to to the the 27 �surrounding plain is is about about 25 25 m; the top top of of the the esker esker is is almost almost everywhere everywhere several several meters below below the top of the surrounding surrounding plain. plain. Many tunnel valleys end in an outwash fan, but the Many valleys end the Eskedahi Eskedahl tunnel tunnel valley valley with no no apparent apparent outwash outwash fan. fan. Tunnel Tunnel valleys valleys and esker ends in in Big Big Round Lake Lake with deeply buried buried by by outwash outwash tend tend to lose their straight shape and that later become become deeply and collapse into bulbous, elongate collapse elongate lakes, like Bone Bone Lake Lake or Big Big Round Lake. Lake. Very coarse outwash outwash occurs occurs at the head of Creek outwash outwash plain, plain, and it is coarse of the Fox Creek is likely likely that the tunnel tunnel valley valley fed fed the the Fox Fox Creek Creek outwash outwash plain. plain. of road cuts occur in the esker here and little is revealed about Only a couple of about of predominantly predominantly sand. the internal composition of of this esker. One outcrop consists of Questions: Does Doesthe thegeometry geometryof of the the tunnel tunnel valley valley and and esker esker indicate indicate the levels of of discharge? Or marking 'the meandering tunnel with the esker marking discharge? Or is is the the valley valley cut cut by a meandering last' position of of the tunnel? What last' What was was the the sources sources of of water? water? Does Does this this geometry geometry require a frozen frozen toe? toe? Mileage 1-6to to Stop Stop1-7: 1-7: 13 13miles miles Mileage from from Stop Stop1-6 Stop 1-7 1-7 Stop Erickson striations striations and and grooves grooves 7.5 minute minute series, SW1/4 SW1/4 sec. Quadrangle: Milltown, Wisconsin, Wisconsin, 7.5 sec. 11, 11,T. T.36 36 N., R. 18 18 W. w. Significance: Striations and Nye channels cut into basalt that Significance: that indicate indicate two two ice-flow ice-flow directions and and two twodifferent differentglacier-bed glacier-bed conditions. conditions. Description: Description: At Atthis thissite, site,broad, broad,shallow shallowgrooves grooves are are present present that that are are oriented oriented NENESW. These SW. These are are cut cutby byyounger youngerstriations striationsthat thatshow showice-flow ice-flowtotothe theSE SE(Fig. (Fig.1-10). 1-10). of basalt basalt in this area show a similar pattern, with the grooves, Numerous outcrops of grooves, interpreted to be interpreted be Nye Nye channels, channels, consistently consistently showing showing ice-flow ice-flow to the the SW. SW. The The and are likely cut by grooves resemble those described by Walder and and Mallet Hallet (1979) and subglacial meltwater. The striations within the grooves were cut by ice ice flowing flowing into into the grooves. grooves. We postulate postulate that the We the grooves grooves form during surges surges when when the the Superior Superior Lobe Lobe exhibited plug flow flow and and flowed flowed directly directly to to the the SW. SW. The Theexcess excess amount amountof of subglacial subglacial water present during during surging surging would have have cut cut the grooves. grooves. When surging stopped, a normal ice ice profile profile developed developed and and ice flowed flowed laterally laterally towards towards the the margins (to the normal SE). SE). Questions: Can Questions: Canice iceform formthese these grooves grooves or is water necessary? necessary? Is it possible possible that the grooves are are pre-Late-Wisconsinan? pre-Late-Wisconsinan? 28 �I LI Figure Figure1-10.-1-10.- Striations Striations and and grooves groovesin in Folk Polk County. County. Double Double arrows arrows== grooves; grooves; single single arrows striations. A: A: Orientation Orientation of grooves and striations showing showing ice ice flow flow to to the the arrows== striations. southwest places, southwestInInmost most places,cross-cutting aoss-cuttingrelationships relationshipswere wereapparent apparentand andalways alwaysshow show striations shown in B. 3. Striations inthis thisorientation orientation to be older than those shown Striationsat at striationsand andgrooves groovesin X are striations and crag-and-tail striations atop Eagle Peak and Observation Rock in X are striations and aag-and-tail striations atop Eagle and Observation Rock in Interstate C:Striations Striations Prominentsoutheast southeaststriations striationswith withsome somegrooves. erooves.C: InterstateState StatePark. Park. B:B:Prominent showing easterly flow and Pine City and Centuria ice-margin positions. The group showing easterly flow and Pine City and Centuria ice-margin positions. The groupat atZZ are are interpreted interpreted to tohave havebeen been cut cut by by the the Superior Superior Lobe Lobe but later than striations striations at the the same explanation. The group at Y was interpreted by same site site shown shown in in B. B. See See text for explanation. by Chamberlin Chamberlin(1905) (1905)to to have have been been formed formed by by the the Grantsburg GrantsburgSublobe. Sublobe. 29 �Mileage Mileage from from Stop Stop1-7 1-7to to Stop Stop 1-8: 1-8: 99 miles miles Stop 1-8 Stop 1-8 Frederic esker and fan fan Quadrangle: Quadrangle:Frederic, Frederic,Wisconsin, Wisconsin,7.5 7.5minute minuteseries, series,sec. sec.21, 21,T. T.37 37 N., N., R. R. 17 17 W. Significance: AAprominent prominentesker eskerfeeding feedingan anice-marginal ice-marginaloutwash outwashfan. fan. Description: This Thispit pitcontains containsaacomplicated complicatedsedimentology sedimentology with large variations in grain size. Collapse Collapse features, antiform bedding, and possible possible injection injection features are are present. present. Questions: IfIfthis thisesker eskerisissurrounded surroundedby bycollapse collapsehummocks, hummocks, how how is is the the esker esker form form preserved? IsIs ititpossible possible that that the the antiform antiform bedding is primary? What does does this this esker esker indicate about the nature nature of of the the Superior Superior Lobe? Lobe? What What do doeskers eskersmean? mean? Mileage Mileage from from Stop Stop1-8 1-8to to Stop Stop 1-9: 1-9: 20 20 miles Stop 1-9 Stop 1-9 Searles varve site Quadrangle: Hertel, Quadrangle: Hertel,Wisconsin, Wisconsin,7.5 7.5minute minuteseries, series,SW1/4 SW1/4NE1/4 NE1/4sec sec15, 15,T. T.38 38 N., N., R. R. 15 W. W. Significance: Proglacial Proglaciallake lakesediments sedimentsand and melting-out melting-out of of stagnant stagnantice ice Description: Description: This Thissandpit sandpitcontains containsaared, red,sandy sandySuperior SuperiorLobe Lobe till till that that is is overlain overlain by a coarsening coarsening upward upward sequence sequenceof of varved varved lake lakesediment. sediment. This This sequence sequence is is overlain overlainby by fluvial pebbly pebbly sand sand that is part of of an an outwash outwash plain plain that that grades grades to to the theHertel Herteliceicemargin position 3 km to the north. north. The Superior Lobe Lobe till, till, occurring occurringatatthe thebase baseofofthe thepit pit and and in a large knob in in the center of Lobe till fillfurther furthersouth. south. It is interpreted of the pit, is finer than Superior Lobe interpreted to to represent represent till deposited deposited during during aa readvance readvance of of the the Superior Superior Lobe Lobe during during overall overall retreat at at which which time time the theproglacial proglacial lake lake sediment sediment was was incorporated incorporated into into the theice. ice. Several outcrops of finer Superior Lobe till occur occur throughout the region region (triangles (triangles in in Fig. 1-6) and and suggest that this till may be associated associated with with an ice advance that reached the northernmost northernmost part part of of Polk Polk County. County. As ice retreated from an unnamed unnamed ice ice margin margin 3 km km to to the the south south(Fig. (Fig.1-6), 1-6), aa proglacial lake fronted the The pit pit contains a wonderful coarsening upward the ice. ice. The sequence of varved lake lake sediment. sediment. It is not not clear clear if this this lake lake sediment sediment belongs belongs to to glacial Lake Lake Lind, glacial glacial Lake Lake Grantsburg, or some other ice-marginal lake. If If it is glacial is glacial Lake Lake Grantsburg, Grantsburg, the the sediment sediment contains contains no no sediment sediment derived derived from the glacial the Grantsburg GrantsburgSublobe. Sublobe. 30 �I The 47 winter winter clay clay layers layers 22 to 10 The The varved section contains contains 47 10 mm mm thick. thick. The I I I I I I I I summer layers cm thick, thick, to to layers thicken thicken and and coarsen coarsen upward, upward, from from silty silty layers layers less less than than 11 cm fine-sand, ripple-bedded layers up to 40 crn cm thick. thick. The The varved section section is overlain by horizontally laminated sand sand with with laminations laminations of of segregated segregated heavy heavy minerals minerals(beach (beach fluvial sand. sand. turn overlain overlain by pebbly sand, interpreted to to be be fluvial sand?), which is in turn grades to to the theHertel HerteliceiceThe fluvial sand underlies an outwash plain that grades margin position that roughly 50 position (Fig. (Fig.1-6). 1-6). This This means means that 50 years passed from from the the uncovering of of this spot to the the filling filling in of the lake by sand derived derived from from the the nearby nearby Superior m/yr. Superior Lobe. This This suggests suggests an an ice ice retreat rate of 80 m/yr. The lake sediment is draped over the till knob, knob, but but faults and steeply dipping beds show that aa large large part partof of the therelationship relationship isis due duetotocollapse, collapse,presumably presumably by by melting of buried buried ice. ice. An angular unconformity unconformity in the varve varve sequence sequence indicates indicates progressively while while the the lake lake was was in in existence. existence. The cranberry that collapse occurred progressively bogs to the the south south of of the the pit pitoccur occur in inaalarger largercollapse collapse pit pit that thatindicates indicatesmelting melting of of buried buried ice ice continued continued after after the the lake lakewas wasfilled filled in. in. A possible ice-wedge cast was found at at this this site site in in 1990 1990 in the fluvial fluvial gravel. gravel. Questions: What of buried buried ice? There Whatisisthe therole roleof of lakes lakes in in hastening hastening the melting of There is a lot of detail is detail in in this this pit, pit, what whatelse elsecan can we we learn learn from from this thissequence? sequence? Mileage from Mileage from Stop Stop1-9 1-9 to to Stop Stop1-10: 1-10: 10 10 miles 1-10 Stop Stop 1-10 Spooner Hills The Spooner The Hills Quadrangle: Quadrangle:Timberland, Timberland,Wisconsin, Wisconsin,7.5 7.5minute minuteseries, series,sec. sec.4,4,T,T.37 37N., N., R. R.14 14W. W. Significance: Significance: A stop in the midst midst of of the the Spooner Spooner Hills, suggested to have been cut by by subglacial meltwater. Description: As discussed in the text, the Spooner Hills is aa name given to this band Description: of hills hills that lie position. Some lie 15 15 to to 25 25 km km behind behind the the St. St. Croix Croix Phase Phase ice-margin position. Some key observations observations include: include: -- the the hills have have an an area areafrom from11to toS5km2, krn2, -- relief as high high as as 60 60 m, m, -- aa number of them are are elongate to the southeast parallel to the direction direction of regional flow, regional ice flow, -- hill-top elevations generally increase increase from from the the northwest northwest to the the southeast, southeast, - inter-hill inter-hill valleys tend to align with tunnel-valleys in places, -- the the hills are composed of a variety variety of unlithified unlithified materials. materials. The hypothesis isis offered offered as as an explanation for the formation The following following hypothesis explanation for formation of of the the - 31 I �S the hills hills contain contain a variety variety of of sediment types representing Spooner Spooner Hills. Hills. Because Because the representing aa variety of depositional depositional environments, environments, and because because the sediment may predate predate the the most recent glaciation, most glaciation, it is likely likely that that the the Spooner Spooner Hills Hills are are erosional erosional features. features. Several lines lines of Several of evidence evidence suggest suggest that the the erosion erosion occurred occurred subglacially. subglacially. The Spooner Hills are commonly covered covered with with the the till till of of the most recent glaciation and are somewhat somewhat streamlined streamlined in in aa direction direction parallel parallel to to the the regional regional ice-flow ice-flow direction direction of of the most recent of the band of the recent glaciation. glaciation. In addition, the orientation of the Spooner Spooner Hills parallels the St. Croix Croix ice ice margin margin suggesting suggestingthat that they they are are related. related. The The interinter- hill valleys that, in some up with hill valleys form a branching branching network network that, some places, places, connects connects up with prominent tunnel valleys. prominent valleys. It is suggested suggested that these these valleys valleys were were excavated excavated by by subglacial meltwater meltwater and the tunnel valleys represent the outlets for meltwater and and sediment. However, sediment. However, this connection connection cannot cannot be shown shown convincingly convincingly along along the the entire Spooner Hills water and sediment Hills chain. chain. The The water sediment was released at the the glacier glacier margin and the in large outwash fans and and margin the sediment sediment was was deposited deposited proglacially proglacially in outwash plains. In In this this scenario, scenario, the Spooner Spooner Hills would have formed formed when when the theice ice was at at the the St. St. Croix Croix ice ice margin marginor orthe theTiger TigerCat-McKinley Cat-McKinley ice margin margin (Fig. (Fig. 1-6). 1-6). We suggest that this type of landform may be more common than presently We recognized in in glacial glacial landscapes. landscapes. Questions: Questions: What Whatare arethe thecritical criticalquestions questionsto toask askto toascertain ascertainthe the origin origin of of these these hills? What of water water needed needed to cut these hills? What is is the the source source of of the the tremendous tremendous amount of these hills? What Whatare areother otherpossible possiblemechanisms mechanisms for for their their origin? origin? miles Mileage to Cable: 45 Mileage from fromStop Stop1-10 1-10 to 45 miles 32 �S I I I I I I I I I I I I OVERVIEW OF THE BEDROCK BEDROCK GEOLOGY GEOLOGY OVERVIEW - AREA, OF - HURLEY OF THE THE CABLE CABLE HURLEY AREA,WISCONSIN WISCONSIN �OVERVIEWOF OF THE ThE BEDROCK OVERVIEW BEDROCK GEOLOGY GEOLOGY OF ThE CABLE-HURLEY AREA, WISCONSIN THE CABLE-HURLEY AREA, by by W.F. Cannon and SW. Nicholson Nicholson W.F. Cannon and S.W. U. S. Geological Geological Survey, Reston, VA 22092 MS 954, Reston, Survey,MS I I I I I I I I I I I I I The area encompassing Field Field Trips Trips 2,4, 2,4, and and 55 is is underlain underlain by by bedrock bedrock ranging ranging in Proterozoic. Rocks of age from Late Archean to Middle Proterozoic. Rocks record three principal cycles cycles of deposition and deformation: volcanism and and sedimentation sedimentation in in Late deposition deformation: 1) submarine submarine volcanism Late Archean time, time, followed by major and granite 2) Archean followed by major deformation deformation and granite emplacement; emplacement; 2) Proterozoic time, time, followed followedby by weak weak to to epicontinental marine sedimentation in Early Early Proterozoic moderate faulting basaltic moderate faulting and and folding folding during duringthe the Penokean Penokean Orogeny; and 3) 3) extension, basaltic volcanism and related intrusions, and continental sedimentation sedimentation in in the Midcontinent volcanism Rift System System in in Middle Middle Proterozoic Proterozoic time, time, followed followedby byinversion inversionand and thrust thrust faulting. Rift Figure 11 shows of the the region, and Figure Figure shows the general general geology geology of region, and Figure 2 2 indicates indicates the approximate location trips 2,4, 2,4, and 5. approximate location of stops for trips GEOLOGY OF ARCHEAN ARCHEAN ROCKS ROCKS GY OF Volcanic and sedimentary rocks of late late Archean Archeanage ageare areexposed exposed in in aa westwardwestwardocks of tapering wedge Mellen, Wisconsin, Wisconsin,forming formingthe thebasement basement directly directly tapering wedge from from Huxley Hurley to near Mellen, rocks. The Thevolcanic volcanicrocks rocksgrade gradesouthward southwardand and westward westward beneath Early Proterozoic rocks. into gneiss and migmatite in a border zone of the Puritan Puritan Batholith, Batholith, a large granitic intrusion emplaced and others, 1977). West of of Mellen, volcanic volcanic intrusion emplaced at atabout about2750 2750 Ma (Sims and rocks are unknown and Early rocks rest rest directly directly on on gneiss and granite. rocks Early Proterozoic rocks Archean rocks are not a focus of the field trips but will be seen at one stop on Trip 2 (Stop 2-10). Details of Archean geology are imperfectly known because of very sparse exposures. sures. The The most most complete complete exposures are in the areas underlain underlain by volcanic rocks of basalt, basalt, andesite, andesite, and and between Hurley Hurley and and Upson. Upson. These Thesevolcanic volcanic rocks rocks consist mostly of 2-10)isisthe themost mostcommon commonrock rocktype type directly directly beneath beneath the rhyolite; dacite breccia (Stop 2-10) Middle Proterozoic Proterozoic rocks between Huxley Hurley and Upson (Greathead, (Greathead, 1975). The The volcanic rocks form form aa section at least and are overturned so that they face rocks section at least 66 km km thick, thick, and overturned so face northwestward and southeastward. northwestward and dip dip steeply steeply to moderately southeastward. 35 35 �CEOLOGY PROTEROZOIC ROCKS GEOLOGY OF OF EARLY EARLY PROTEROZOIC ROCKS Early Proterozoic rocks include strata of of the Marquette Range Supergroup Supergroup along along the Gogebic Iron hon Range. Range. These Theserocks rocks are arethe the focus focus of of Field Trip 5, and will also be seen on parts and 4. 4. The Thecontinuity continuityof of Early Early Proterozoic strata across the area is parts of of Trips Trips 2 and broken by the Mineral Lake intrusion, which truncates the sequence from near Mineral Lake westward westward to tothe theMarengo MarengoRiver, River,aadistance distanceof of about about10 10km. km. Area east of Lake intrusion: of Mineral M i n m East of of Mineral Lake, the Early Early Proterozoic Proterozoic sequence displays the Range stratigraphy stratigraphy with a basal the classical classical Gogebic Gogebic Range basal argilliteargillitequartzite unit by banded iron-formation unit (Palms (PalmsFormation) Formation) overlain overlain successively successively by iron-formation (Ironwood Iron-formation) and aa shale-graywacke shale-graywacke turbidite turbidite unit unit(Tyler (TylerFormation). Formation). From about about Ballou Creek westward westward a thin, possibly discontinuous, discontinuous, unit unit of of dolomite and chert breccia chert breccia of of the the Bad Bad River River Dolomite Dolomite lies between between the Palms Palms Formation Formation and and underlying Archean underlying Archeanbasement basement rocks. rocks. The Early section is is 2-3 2-3 km km thick and The Early Proterozoic Proterozoic section and records records sedimentation sedimentation successively on on aa stable stable craton, craton,passive passivemargin, margin,and andcompressional compressionalforeland. foreland. The oldest strata, represented by by the the Bad Bad River River Dolomite, Dolomite, were deposited deposited unconformably unconformably on on Archean rocks, The Bad Bad River River is a cherty rocks, apparently in aa stable stablecratonic cratonic setting. setting. The cherty dolomite, commonly metamorphosed metamorphosed to to tremolitic tremolitic marble. marble. It It also also includes includes aa distinctive distinctive breccia (Stops 2-9 2-9 and and 2-10) 2-10) that that constitutes constitutes most most of of the unit from chert brecaa from near near the. the Bad Bad River eastward eastward for about 10 km to near Ballou Creek. The River Ballou Creek. The breccia breccia appears to be be aa variably reworked residuum residuum of of chert chert nodules and and beds beds left left by solution solution of the dolomite dolomite during the the weathering weathering interval, interval, prior prior to to deposition deposition of of the the unconformably unconformably overlying overlying Formation. Palms Formation. The principal principal iron-bearing iron-bearing sequence sequence is the the Menominee Group, Group, consisting consisting of of the the and Ironwood bonwood Iron-formation. Palms Formation and Iron-formation We interpret the Menominee Group to have been deposited depositedon onaasouth-facing south-facing passive passive margin. margin. The ThePalms PalmsFormation Formation(Stops (Stops2-9 2-9 and 2-10) consists consists of of banded banded argillite argillite near near the the base, base, and and grades upward into into thickthickbedded quartzite near the unconformably on on Archean Archean rocks rocks and the Bad Bad the top. top. It lies unconformably River Dolomite. Dolomite. At its upper contact the Palms grades grades upward upward over a meter or two into Iron-formation. The Ironwood bonwood contains ferruginous beds of the Ironwood Iron-formation. contains numerous numerous lithologic types of iron-formation. East Eastof of Upson, Upson,Wisconsin, Wisconsin, itit consists consists of five laterally laterally continuous members that are alternating units of thin, even-bedded, carbonate ironformation and and thick, thick, wavy-bedded, wavy-bedded, hematitic hematiticiron-formation iron-formation(Hotchkiss, (Hotchkiss,1919; 1919; Huber, 1959). West of Upson Upson (Stops 5-B),these theselithologies lithologiesare arealso alsopresent, present, but but laterally (Stops 2-8 and 5-B), 36 �46° 46° 45 LAKE SUPERIOR 46° 00 46° 451 90° 00! 900 00! Figure 1: Geologic map of part of northern Wisconsin and Michigan showing region of field trips 2, 4, and 5. 91° 30 •S • • S S S SS S •• . . . S SS • • 91030 �L :: z, 3 : Chengwatana Kallander Creek Volcanics conglomerate - w ffl 3 3 3 Olivine gabbro and serpentinite Anorthosite and gabbro Granophyre Granite andesite and basalt Kallander Creek Volcanics 3 ffl2. 0 3- " 5 / SQ Siemens Creek Volcanics :a g 5' Copper Harbor Conglomerate rhyol ito Â¥ (A. xg 3 Nonesuch Formation s3 3-7; < = S ?= S Q n g,; % y s ss s 0- 3 conglomerate facies 3 -a r. 50 3 a ~ 3 sa $ s ¤g w 5 $? Freda Sandstone n8 > 5 m s s0 g0 u 77 m 0) 2 g m ^ Freda Sandstone 2s: a 77 Kallander Creek Volcanics 77 < m 6 Orienta Sandstone Lri:tJH 0- 0- w Portage Lake Volcanics w 0 0- Devils Island Sandstone w andesite and basalt " g^ 0 =s 0< 0" m Chequamegon Sandstone 3 Porcupine Volcanics 3. s 0 w 3 Jacobsville Sandstone 51 Middle Proterozoic g< Porcupine Volcanics rhyolite w Cambrian sandstone 2. 53" " 3 $6 à I 8 -B8- w 5 w 3. 0 3. n' Cu 3- EXPLANATION 2g 8 8 3. 8 ^ 01 Gneiss Early Archean Metavolcanic Rocks Gneiss and Amphibolite Puritan Quartz Monzonite Late Archean Bad River Dolomite and Palms Formation lronwood Iron-formation Blair Creek Formation Tyler Formation Metasedimentary and metavolcanic rocks Metadiabase Early Proterozoic �h I I I I I I p I I continuous members membersare are more more difficult difficulttoto define, define, in in part part because continuous because of of primary primary sedimentary changes, induced by by deformation and changes, but also also because of complications complications induced metamorphism. metamorphism. The Tyler Formation (Stops 2-7 2-7 and and 5-B) 5-B)overlies overliesthe the Ironwood Ironwood and is aa thick thick succession of succession of graywacke and slate deposited in a foreland basin during accretion accretion of of island Ma. We believe that the basal contact with island arc arc terranes terranes to to the the south southat atabout about1850 1850 Ma. the Ironwood Iron-formation unconformity, although the Iron-formation is most likely a low-angle unconformity, nature natureof of the the contact contact has has been been aa point point of of controversy controversy for many years. rocks are are essentially essentially unmetamorphosed unmetamorphosed east east of of Upson, Upson, but Early Proterozoic rocks metamorphic grade is progressively metamorphic progressively higher towards the the west west where whereassemblages assemblages including abundant abundant grunerite. grunerite. Near include garnet and aa variety variety of amphiboles, including Near the the contact with the Mineral Lake intrusion, assemblages include fayalite, orthopyroxene, and garnet in in iron-formation. iron-formation. The The metamorphism metamorphism was static and caused by Middle Middle Proterozoic thermal thermal events. events. Early Proterozoic Proterozoic rocks rocks dip steeply to vertical Early vertical nearly everywhere everywhere along along the the Gogebic Iron Iron Range. Range. This attitude attitude results Froterozoic deformation, deformation, results mostly from Middle Proterozoic discussed below, below, but we have have distinguished distinguished aa component component of relatively relatively strong Early Early Proterozoic deformation deformation as as well. well. The deformation is is part of the Proterozoic The Early Early Proterozoic Proterozoic deformation the Penokean of island island arcs arcs with with the southern southern edge Penokean orogeny, orogeny, caused caused by by collision collision of of a series of edge of the Superior and others, 1989). 1989). The area lies north north of 1850 Ma (Sims and Superior craton craton at atabout about1850 the suture and the suture andspans spansthe thetransition transitionfrom fromaa foreland foreland fold and and thrust thrust belt belt to to the the essentially essentially undeformed craton. undefonned craton. From Hurley to Upson, Penokean deformation is is nearly nearly nonexistent. nonexistent. A Penokean deformation A weak weak Formation but no folds slaty cleavage is developed locally in the Tyler Formation folds are are known. known. Westward deformation intensifies and is expressed both by Westward from Upson, compressional deformation thrust faults faults and and folds folds(Stops (Stops 2-10 2-10 and 5-8). 5-B). On OnMt. Mt. Whittlesey, Whittlesey, the Ironwood Ironwood IronIronformation is structurally thickened both by by folding folding and and repetition by by thrust faults. formation thickened both faults. Farther west, near Mineral nearly isoclinal isoclinalfolds foldswere were developed. developed. These Mineral Lake, large, nearly These folds originally were upright but but now now are are recumbent recumbent as as aa result result of of Middle MiddleProterozoic Proterozoic tilting. tilting. Ballou Creek Creekwestward westward there there appears appears to to be be aa detachment detachment fault at or From about Ballou so that that Early Proterozoic very near the the base base of of the theEarly EarlyProterozoic Proterozoicsection section (Stop (Stop 2-10) so Archean rocks rocksduring duringPenokean Penokeandeformation. deformation. The amount rocks were decoupled from Archean of structural shortening shortening in in the the Early Early Proterozoic Proterozoic strata is unmatched in in the the Archean Archean basement. �C — 1 25 I C 9'fl'ft'—k CCLJ J00.Io.,.o.,, r 0!.lI,M!. 20 I 5 F '41 (I LH/ J4_ckALI Jj Jf]}\ 17 0 I r- — — IS ; <'ii— 10 ________ — 20 i2-1 - -10 I — 0 0 f—1 • F-! 5 — — F—i 0 — 5 - — locations. detailed more for guides individual See 5. and 4, 2, trips field for stops of locations approximate the showing quadrangle 10x2° Ironwood the of Part 2. Figure - 5 �Area Area west west of of Mineral Mineral Lake I.ake intrusion: intrusion: West of of the Mineral Mineral Lake Lake intrusion, intrusion, Early Early Proterozoic strata are River to to the the north Proterozoic strata are present present from from the the Marengo Marengo River north side side of of Lake Lake Namekagon. Namekagon. These Thesestrata stratashare sharemany manysimilarities similaritieswith with their equivalents equivalents to to the the east east but but also alsodisplay displaysome someimportant importantdifferences. differences. The The Early Proterozoic succession includes an approximately approximately 300-rn 300-m thick section of of Bad Bad River River Dolomite, Dolomite, exposed exposed near near the the Marengo Marengo River River south south of of Grand Grand View, View, marble with with abundant lenses and beds of Wisconsin. Wisconsin. It It is is typically typically a gray gray dolomitic marble chert, partly replaced unconformably on on Archean Archean rocks. rocks. This is replaced by tremolite, tremolite, and lies unconformably the Group rocks rocks preserved preserved on on the the Gogebic GogebicIron Iron Range. Range. The the thickest thickest section section of Chocolay Group overlying laminated overlying Palms Palms Formation Formation is is much like that known to the east, consisting consisting of laminated argillite argillite near the the base and and thick-bedded quartzite quartzite near the top. The Ironwood lacks wavy-bedded wavy-bedded hematitic IronwoodIron-formation Iron-formation (Stops (Stops 4-1 and 5-A) lacks hematitic iron-formation iron-formationthat thatare arecommon commonto to the the east. east. However, However, it does does contain contain units units of laminated laminated cherty cherty magnetite magnetite iron-formation. iron-formation. The Ironwood grades laterally to the west into into nonnoncherty silicate iron-formation, magnetic and non-magnetic argillite, and black pyritic cherty silicate iron-formation, black pyritic shale. shale.Large Largesills sillsof ofmetadiabase metadiabase(Stops (Stops4-1 4-1and and5-B) 5-B) also occur in the iron-formation, iron-formation,in in contrast abundant. contrast to to areas areas farther farther east east where where mafic intrusions are much less abundant. Two unusual each as much as 20 m thick, are unusual breccia breccia units units(Stops (Stops4-1 4-1 and and 5-B), 5-B), each are exposed exposed in in the the iron-formation iron-formation near Atkins Lake. They have not been described prior to 1995 (Feher (Feher and and Flood, Flood, 1995). 1995). The The breccias breccias consist consistofofangular angular to to subrounded subrounded clasts as much sedimentary rocks in a matrix matrix of of dark dark much as as11m m across across composed composed of banded siliceous sedimentary gray-green clearly igneous and has a basaltic composition gray-green massive massive rock. rock. The matrix is clearly but but whether whetherthe theunits unitsare areextrusive extrusiveor or intrusive intrusive is uncertain. In In either either case, case, the presence of these indicates that igneous occurred very close deposition these breccias indicates igneous activity activity occurred dose in time to deposition of the the iron-formation iron-formationin in the the western westernpart partof of the theGogebic Gogebic hon IronRange. Range. The situation situation is similar to that observed in the eastern part part of of the the Gogebic Gogebic Iron Range in Michigan, Complexisis interlayered interlayered with with the Michigan, where the Emperor Emperor Volcanic Volcanic Complex bonwood hon-formation. Ironwood Iron-formation.Apparently Apparentlyquiescent, quiescent,platform-like platform-like conditions, expressed in the lateral of the Menominee Menominee Group Group in the central part of lateral continuity continuity of of lithologic units of the Gogebic Range, change into more volcanically-active volcanically-activeenvironments environments to to both both the the east and and west. west. Lateral Lateralchange changefrom fromcherty chertyiron-formation iron-formation common in the central part of the range, to non-cherty and ferruginous argillite in the west, also non-cherty silicate silicate iron-formation and suggests that diluted the chemically precipitated precipitated suggests proximity to to aa clastic clastic sediment source that components of the iron-formation. in the Ironwood, bonwood, iron-formation. The The increased detrital component in volcanism,atatboth boththe the east east and and west west end of of the range, along with contemporaneous volcanism, may indicate transition of extension and and rift-basin rift-basin development development that that marked transition to to a region of 39 �continental breakup continental breakupatatthe theoutset outsetof of the thePenokean Penokeanorogenic orogeniccycle. cycle. The Tyler Tyler Formation Formation isis unknown unknown west west of of the the Mineral Mineral Lake Lake intrusion intrusion but is The probably present, beneath low, low, swampy swampy country country north north of of the the Ironwood present, at at least locally, beneath outcrop belt. Magnetic traverses traverses across across these these areas areas show show extremely flat profiles outcrop belt. Magnetic profiles characteristic of the Tyler elsewhere. characteristic The western western termination termination of of strata strata of of the the Gogebic GogebicIron hon Range Rangeisis in in the the area area The between Lake Lake Namekagon Namekagon and and Cable, Cable, where where the the Atkins Atkins Lake Lake fault, fault, a Middle between Middle Proterozoic structure structure discussed discussed below, below, cuts cuts down down section section and and truncates Proterozoic truncates Early Early volcanicrocks. rocks. Outcrops are extremely Proterozoic strata against Middle Proterozoic Proterozoic volcanic sparse in that area, but the using magnetic magnetic data. the fault fault trace can be located using GEOLOGY OF MIDDLE MIDDLE PROTEROZOIC ROCKS GY OF ..,. Middle Proterozoic of continental continental volcanic rocks Middle Proterozoicrocks rocks consist consist of a thick sequence of overlain by red fluvial rocks and and lesser lesserlacustrine lacustrinedeposits, deposits, that that together together make up overlain fluvial clastic rocks the Keweenawan Supergroup. All All are are related related to the Midcontinent Rift Rift System System that that rift was was tectonically tectonicallyinverted inverted shortly shortly after it formed. developed at Ma. The rift developed at about about1100 1100 Ma. area, the the inversion inversion resulted resulted in in southward-directed southward-directed thrusting thrusting and and In the Hurley-Cable area, northward tilting northward tilting of of aa crustal-scale crustal-scale block, so that the Middle Proterozoic rocks now lie River monocline monocline (Cannon (Cannon in a northward-dipping northward-dippingmonoclinal monoclinal sequence, sequence, the Montreal River monocline provide provide aa complete complete history history of of the the rift rift and others, 1993b). 1993b). The rocks in the monocline including extension post-rift thermal thermal subsidence subsidence and and including extension and continental continental volcanism, volcanism, post-rift sedimentation, and sedimentation, and later later inversion inversion resulting from regional compression. Extension and volcavolcanism: The lower part of of the Keweenawan Keweenawan Supergroup Supergroup is composed of volcanic volcanic and and lesser sedimentary rocks rocks that that formed formed during during the the extensional phase phase of of of the rift and accumulated of as much as 12 krn km in in this this area, area, but but were as accumulated to a thickness thickness of km thick along the rift axis axis to to the the north. north. The much as 20 krn The lowest lowest unit unit is is the the Bessemer Bessemer Quartzite (Stop chieflygray grayto to white, white, thin-bedded thin-bedded quartzite, quartzite, mostly of of lacustrine Quartzite (Stop 2-6), 2-6), chiefly (akangas and Morey, made up up mostly mostly origin (Ojakangas and Morey,1982). 1982).AAmassive massivebasal basal conglomerate conglomerate is made of clasts of of Early Early Proterozoic and and Archean rocks rocks typical typicalof of those thoseexposed exposed south south of of the the of Bessemeroutcrop outcropbelt. belt. The TheBessemer Bessemerappears appearstotohave haveformed formedininaabroad broad basin basin that that Bessemer of extension contained a shallow lake. This This basin is apparently the first manifestation of related to the Midcontinent rift, and formed immediately prior to the initiation of related Midcontinent rift, immediately prior flood-basalt volcanism, which which was was soon soon to to dominate dominate the the region. region. continental flood-basalt The oldest volcanic sequence sequence is is the the 1.3-km 1.3-km thick Siemens Creek Volcanics (Stops 40 �I 4-3, volcanic rocks rockshave havenot notbeen beendated dated in in this area, but are 4-3, and and 4-7). 4-7). These These volcanic are probably equivalent equivalent to to the theOsler Osier Volcanics Volcanics on the north shore shore of Lake Superior where eruption 1985). We have made an eruption began at at about about 1109 1109 Ma (Davis (Davis and Sutcliffe, Sutcliffe, 1985). an informal into a thin, discontinuous discontinuous lower informal subdivision subdivision of of the the Siemens Siemens Creek Creek Volcanics Volcanics into lower unit unit and aa much much thicker thicker upper upper unit. unit. Flows Flows in the lower lower unit unit (Stop (Stop2-6) 2-6) are are geographically cinopyroxene phenocrysts, aa rarity geographically restricted basalts that have small clinopyroxene rarity in in Keweenawan Keweenawan volcanic rocks, and we recognize recognize a distinctive distinctive chemical composition composition(low (low Al203, MgO, and and steep steepREE REE patterns), patterns), indicating that that the theflows flowsreflect reflect Al2O3, high Cr, Cr, Ni, Ni, MgO, partial partial melts from a deep, enriched mantle source with little or no fractionation prior to eruption. eruption.The Theupper upperpart partofofthe theSiemens SiemensCreek CreekVolcanics Volcanics(Stops (Stops4-3 4-3 and and 4-7) 4-7) comprises comprises widespread flood more evolved evolved composition, composition, ranging from from basalt to to flood basalts basalts of of aa more andesite. indicates aa larger larger degree of of partial melting andesite. Their chemical composition indicates melting of of aa mantle source, during ponding within source, modified by fractional fractional crystallization during within or or at atthe the base base of of the lithosphere lithosphere prior to to eruption. eruption. The Thebasal basal1-3 1-3flows flowsof of the theSiemens SiemensCreek Creek Volcanics, erupted erupted into Quartzite was being deposited, into the the lake lake into into which the Bessemer Quartzite deposited, typically typically are are pillow basalt basalt and and pillow pillow breccia. brecaa. The The Bessemer Bessemer was unconsolidated unconsolidated at at the the time of eruption, and can be be found in places and Bessemer-like Bessemer-like sediments can places as as interfiow interflow accumulations above the lowermost lowermost flow. All remaining overlying flows appear appear to to be be subaerial subaerial based based on onlack lack of of pillow pillow structures. structures. The Kallander km thick) overlie the Siemens Kallander Creek Creek Volcanics Volcanics (1.2-4.5 (1.2-4.5 km Siemens Creek Creek Volcanics and consists of of a much higher proportion proportion of andesite andesite and and rhyolite rhyolite flows flows than than are are present present in in the theSiemens Siemens Creek. Creek. We Werecognize recognize two two informal informal units units in in the theKallander Kallander Creek Creek Volcanics. A A lower lower unit, unit, about abouthalf half of of the total stratigraphic stratigraphicthickness, thickness, is mostly andesite and and basalt basalt (Stop (Stop 4-6), 4-6), and appears to record continuation of of the widespread continental continental flood basalt eruption eruptionpresent presentin inthe theSiemens SiemensCreek Creek Volcanics, Volcanics, whereas the upper part part isismore morelocalized localized and andmost mostprobably probably represents represents aa central central volcano volcano near near Mellen. Mellen. The The upper upperpart partofofthe thesection sectioncontains containsabundant abundantrhyolite rhyolite and andconglomerate conglomerate (Stops 2-4 2-4 and 4-8) 4-8) in in addition to basalt, andesite, and other rocks rocks of intermediate intermediate composition 2-5). The composition (Stop 2-5). The lower unit is is very very similar similar to to the the lower lowerSiemens Siemens Creek Creek basalts basalts (small (small degree partial melts melts erupted from from deep deep in in the the mantle). mantle).However, However, our our analyses show that the analyses show the basalts basalts in in the the lower lower Kallander Kallander Creek Creek are are more more strongly strongly fractionated fractionated (high (high Ti02 and FeO, FeO, low MgO), and lack clinopyroxene as aa phenocryst phenocryst phase. AArhyolite rhyolitenear nearthe thetop topofofthe thelower lowerunit unitwas waserupted eruptedabout about1107 1107Ma Ma(Davis (Davisand and others, others,1995). 1995). In abundant In contrast contrast to to the the lower lower unit, the the upper upper Kallander Kallander Creek unit contains abundant rhyolite and and conglomerate conglomerate in addition addition to to basalt and andesite. Chemical Chemicalcompositions compositionsof of 2-6, 2-6, I I I I I I I I I fl I I 41 i �mafic and and intermediate rocks indicate that parent magmas were generated from largemafic fractional crystallization crystallization degree partial melts of of a mantle source, and that substantial fractional took place place within or near the base of of the crust. crust. Rhyolites took Rhyolites were generated, at least in of crustal crustal material. material. A A rhyolite rhyolitethat thatforms formsthe theuppermost uppermost unit unit of of part, by partial melting of (Stop 2-4) 2-4)was waserupted eruptedat at about about 1099 1099Ma Ma(Zartman (Zartmanand and the Kallander Creek Volcanics Volcanics (Stop others, 1995). and 4-5), 4-5),an an intrusive intrusive suite suite of of gabbroic 1995). The The Mellen Mellen Complex Complex (Stops (Stops 4-4 4-4 and Volcanics and and rocks, granophyre, and granite, granite, was emplaced into the Kallander Creek Volcanics older units at and probably probably represents represents aa at about about 1102 1102 Ma (Cannon and others, 1993a) 1993a) and shallow magma reservoir that fed eruptions eruptions from from the the central central volcano. formation of the central The area near Mellen remained a topographic high after formation volcano and and no further volcanic rockswere weredeposited. deposited. To To both both the east and west, volcano volcanic rocks additional flood basalt volcanism deposited a great thickness of of volcanic volcanic rocks, rocks, mostly mostly additional confined to the central graben of of the the rift. rift. These rocks are are represented represented by the These volcanic rocks Portage Lake Volcanics to the east and and the the Chengwatana ChengwatanaVolcanics Volcanics(Stops (Stops4-9 4-9and and 4-10) 4-10) to the west. The eachdominated dominatedby bybasalt basaltwith with The two two units units are are quite quite similar similar chemically, chemically, each lesser intermediate intermediate and felsic felsic rocks. rocks. In each, the the basalts basalts can canbe bedivided divided into into two two major major groups based on on whether whether the the Ti02 Ti02 content content is is greater greater or less less than than 2.5 2.5 wt % % (Nicholson The low-Ti02 low-Ti02basalts basaltsare arethe the most most abundant abundant and and represent 1990). The represent and Shirey, Shirey, 1990). widespread flood basalt volcanism: they they are are typically typicallyophitic ophiticin intexture texture and and commonly commonly than the high-Ti02 basalts. basalts. The Thehigh-Ti02 high-Ti02basalts basaltsform formthinner thinner and and form thicker flows than and commonly are are interlayered interlayered with with more more intermediate intermediate and felsic more localized flows, and rocks in in the section. continued for for rocks section. The The main main phase phase of of rift rift extension extension and volcanism volcanism continued about 55 m.y., until until about about1094 1094Ma Ma (Davis (Davisand andPaces, Paces, 1990). 1990). about The youngest youngest volcanic volcanicrocks rocksininthe thearea area are are basalt basalt and and andesite andesite flows flows of of the the The Porcupine Volcanics (Stop 2-3) 2-3)that thatmake makeup up aa central centralvolcanic volcaniccomplex complexcentered centeredto tothe the Porcupine of the Hurley-Cable Hurley-Cable area, area, near near the the Porcupine PorcupineMountains Mountainsin inMichigan. Michigan. Outcrops Outcrops of of east of in the the Hurley-Cable Hurley-Cable area area comprise comprisebasalt basalt and and andesite flows the Porcupine Volcanics Volcanics in and interflow conglomerate conglomerate and and sandstone. sandstone.AArhyolite rhyolitenear nearthe thetop top ofof the the unit unit was was erupted at erupted atabout about1094 1094Ma Ma (Zartman (Zartmanand andothers, others,1995). 1995). Thermal subsidence and sedimentation: Following eruption of of the the Portage Lake Lake and and Following eruption Chengwatana Volcanics, of the Porcupine Chengwatana Volcanics, and coincident with development of Porcupine Volcanics, changed. Earlier extension-driven subsidence subsidence and and related volcanism the tectonic regime changed. rapidlywaned waned and and further subsidence was was replaced by a regime in which extension rapidly The thermally thermally caused by by cooling cooling and and contraction contraction ofof the the hot hot root root zone zone of of the the rift. rift. The caused subsiding basin basin was was generally generally centered centeredover overthe the previous previousrift riftbasin basin but but was was much much subsiding 42 �I p broader. fluvialrocks rocksand andlesser lesserlake lakedeposits. deposits. As broader. This This basin was filled with red clastic fluvial much of sedimentary sedimentary rocks accumulated accumulated in in the the deepest deepest part part of of the the basin. basin. much as 7 km of The oldest sediments, sediments, comprising the Copper Copper Harbor Harbor Conglomerate Conglomerate(Stop (Stop2-2) 2-2) and perhaps perhaps the theoverlying overlyinglake lakebeds beds of of the theNonesuch NonesuchFormation Formation (stop (stop2-2), 2-2), were deposited in aa basin rift basin basin and and the basin transitional transitional between between the earlier extensional extensional rift successor thermally subsiding subsiding basin. A Aregional regional topographic topographic high high centered centered near near Mellen Mellen affected the distribution distribution and of nearby nearby sedimentary sedimentary units. units. The and lithology of The Copper Copper Harbor Harbor Conglomerate Conglomerate and and Nonesuch Nonesuch Formation Formation both pinch out against this highland so that the overlying Freda Sandstone locally lies lies unconformably unconformably on on volcanic volcanic and and Sandstone (Stop (Stop 2-1) locally intrusive intrusiverocks. rocks. The TheFreda FredaSandstone Sandstonenear near Mellen Mellen is atypically conglomeratic, reflecting proximity proximity of of the the nearby nearbyhighland highlandthat thatserved servedasasaasource sourceof of coarse coarseclastic clastic debris. debris. P U Rift Toward Rift inversion: inve& Towardthe theclose close of of the the thermal thermal subsidence phase and and coincident coincident with late late phases of of sedimentation, sedimentation, a period period of of regional regional compression compression began, that caused caused inversion inversion of of the the rift structure. structure.In Inthe theCable-Hurley Cable-Hurley area, area, compression compression resulted resultedin in aa series series of major listric thrust faults along which previously previously deeply deeply buried buried parts of the rift were thrust southward southward and and the the upper upper plates plates of of the the faults faults were were tilted tilted northward. northward. This thrusting in the the present present distribution distribution and structural thrustingevent eventisis the the major major controlling controlling factor in attitude attitudeof of the therocks rocksof of the the region. region. The principal fault in the area fault and its western extension, area is the Marenisco fault the the Atkins Atkins Lake fault. From From east east to to west west across across the area, the Marenisco fault gradually rises rises in in the the stratigraphic stratigraphicsection. section. In Inthe theeast, east,the the fault fault trace trace is is about about 10 10 km south south of the contact so so that that a large thickness thickness of of Archean Archean rocks rocks and and the Early Proterozoic-Archean contact Early entire entire Early Early Proterozoic Proterozoic and and Middle Middle Proterozoic Proterozoic section is in the upper plate plate above above the the structure was fault. The The importance importance of of the the Marenisco Marenisco fault as a Middle Proterozoic structure was not not fault. recognized until Rb-Srbiotite biotiteages agesdemonstrated demonstratedthat that the the upper upper plate had until 1992, 1992, when Rb-Sr been and others, 1993b). In the eastern been uplifted uplifted and andcooled cooled at at about about1060 1060 Ma (Cannon and part of of the upper plate has resulted in of the the area, area, thrusting and northward northward rotation of exposure exposureof of aa cross cross section section of nearly vertically dipping strata strata about about 20 20 km km thick as as well as basement rocks. rocks. This structure, the Montreal as about about 10 10 km of underlying Archean basement Montreal River 3/4 of of the the crust crust as as itit existed just after rifting and is the River monodine, monocline, exposes exposes about about 3/4 focus focusof of Field Field Trip Trip2.2. To rises to higher higher structural levels in To the west, west, the the Marenisco Marenisco fault gradually rises Archean Archean rocks rocks until, until, along alongthe the Marengo Marengo River, River, it cuts upward upward across acrossEarly Early Proterozoic Proterozoic strata. strata. From Fromthere therewestward, westward,the thefault faulthas hasthrust thrustMiddle MiddleProterozoic Proterozoicvolcanic volcanic rocks rocks southward rocks. The southward over over Early Early Proterozoic Proterozoic and Archean rocks. The fault fault is is traced traced mostly mostly by by 43 �aeromagnetic aeromagnetic data, data, but but extensive extensive exposures exposures of of intensely intensely sheared sheared and and rnylon.itized mylonitized rocks can been seen seen along along the the valley valley of of the the Marengo MarengoRiver River south south of of Grand GrandView, View, Wisconsin. Wisconsin. A second important important fault is the Lake Owen fault. Southwestward Southwestwardfrom fromCable, Cable, this fault separates separatesMiddle Middle Proterozoic Proterozoic volcanic volcanic rocks rocks of the the Chengwatana ChengwatanaVolcanics Volcanics from Archean Archean rocks. rocks. Northeastward the fault fault passes passes up section in the Northeastward from Cable Cable the footwall, so that footwall, that the theChengwatana ChengwatanaVolcanics Volcanics are are juxtaposed juxtaposed against against successively successively younger rocks. northeast of of Mellen, Mellen, the the fault fault passes younger rocks. Eventually, Eventually, northeast passes into the the Freda Freda Sandstone, where Sandstone, where its its expression expression is obscure and it appears to die out. Iceweenaw fault, fault, aa major major reverse reversefault fault to to the the east east of of the the area, area, also dies out out The Keweenaw within the within the volcanic volcanicsection section northeast northeastof of Mellen. Mellen. REFERENCES REFERENCES - Cannon, W.F., Cannon, W.F., Nicholson, Nicholson,SW., S.W., Zartman, Zartman,R.E., R.E., and andDavis, Davis,12W., D.W., 1993a, 1993a, The The Kallander KaUanderCreek CreekVolcanics Volcanics - aa remnant of a Keweenawan central volcano centered near Mellen, Wisconsin [abstract]: Institute on remnant of a Keweenawan central volcano centered near Mellen, Lake Superior Geology, Abstracts, v. 39, p. 20-21. Superior Geology, Abstracts, v. 39, p. 20-21. Cannon, WE., Crustal-scalethrusting thrusting and and origin Cannon, W.F., Peterman, Peterman,Z.E., Z.E., and and Sims, Sims, P.K., P.K.,1993b, 1993b, Crustal-scale origin of of the the Montreal Montreal River monocline -- aa 35 km-thick km-thick cross cross section sectionofofthe theMidcontinent Midcontinentrift riftin innorthern northern Wisconsin Wisconsin and and Michigan: Tectonics, v. 12, p. 728-744. Michigan: Tectonics, v. 12, p. 728-744. Davis, D.W., J.W., 1990, 1990,Time Timeresolution resolutionofofgeologic geologicevents eventson onthe theKeweenaw KeweenawPeninsula Peninsula and and D.W., and Paces, J.W., implications for development of the Midcontinent rift system: Earth and Planetary Science Letters, implications development of the Midcontinent rift system: Earth and Planetary Science Letters, v. 97, p. 54-64. Davis, D.W., D.W., and Sutcliffe, R.H., Ri-I., 1985, 1985,U-Pb U-Pbages agesfrom fromthe theNipigon Nipigonplate plate and and northern Lake Lake Superior: Superior: Geological Society Society of America America Bulletin, Bulletin,v. v. 96, 96, p. 1572-1579. 1572-1579. D.W., Green, J.3.and and Manson, Manson, M., M., 1995, 1995,Geochronology Geochronologyofofthe the1.1 1.1Ga GaNorth NorthAmerican American midcontinent midcontinent Davis, D.W., [abstract]: Institute rift [abstract]: Instituteon onLake LakeSuperior SuperiorGeology, Geology,Abstracts, Abstracts, v, v, 41, 41, p. p. 9-10. and Flood, T., 1995, Vesiclesand andbreccia brecciadue due to to injection injection of ofmafic maficmagma magma into partially partially lithified Feher, L., and 1995, Vesicles lithified sediments of the early NW Wisconsin sediments early Proterozoic Proterozoic Ironwood Iron-formation, Iron-formation, western western Gogebic Range, NW [abstract]: Institute Instituteon onLake LakeSuperior SuperiorGeology, Geology, Abstracts Abstracts,, v. 41, p. 13-15. 13-15. Greathead, The geology geology and and petrochemistry petrochemistry of of the the greenstone greenstone belt south of Hurley Greathead, C., C., 1975, 1975, The Hurley and and Upson, Upson, Iron County, County,Wisconsin: Wisconsin: Milwaukee, Milwaukee, Wisc., Wise., University of of Wisconsin-Milwaukee, Wisconsin-Milwaukee, unpublished unpublishedM.S. M.S. Thesis, 191p. Thesis, 191 Hotchkiss, W.O., 1919, Geology Geologyofofthe theGogebic GogebicRange Rangeand andits itsrelation relation to to recent recent mining developments: developments: W.O., 1919, Engineering Engineeringand andMining MiningJournal, Journal,v.v.108, 108,p.443-452,501-507,537-541,577-582. p. 443-452,501-507,537-541,577-582. Huber, N.K., aspects of the origin origin of the the Ironwooci Iron-formation of Huber, N.K., 1959, 1959, Some aspects Ironwood Iron-formation of Michigan Michiganand andWisconsin: Wisconsin: Economic Economic Geology, Geology, v. v. 54, 54, p. 82-118. 82-118. Nicholson, S.W. S.W. and and Shirey, S.B., 5.8., 1990, 1990, Evidence Evidencefor foraaPrecambrian Precambrianmantle mantle plume: plume: A A Sr, Sr, Nd, and Pb Pb isotopic study Rift System System in in the the Lake Lake Superior Superior region: region: Journal Journal of of Geophysical Geophysical study of of the theMidcontinent MidcontinentRift Research, v. 95, P. p. 10851-10868. 10851-10868. Research, v.95, qakangas, R.W., Keweenawanpre-volcanic pre-volcanicquartz quartzsandstones sandstones and and related rocks Ojakangas, R.W., and andMorey, Morey,G.B., G.B., 1982, 1982, Keweenawan Rj., and and tectonics of of the Lake Superior region, in in Wold, R.J., and Hinze, H i ,W.J., W.J., (eds.), Geology and of the Lake Superior Superior 156,p.p.85-96. 85-96. SuperiorBasin: Basin: Geological GeologicalSociety Societyof of America AmericaMemoir Memoir156, P.K., Peterman, Peterman, Z.E., Z.E., and and Prinz, W.C., 1977,Geology Geologyand and Rb-Sr Rb-Srage ageofofthe thePrecambrian Precambrian W W Puritan Sims, P.K., W.C., 1977, Quartz 5, p. p. 185185QuartzMonzonite, Monzonite,northern northernMichigan: Michigan:Journal JournalofofResearch Researchofofthe theU.S. U.S. Geological GeologicalSurvey, Survey,v.v.5, 192. 192. 44 �I I I I I I I I I I I I I I I I I I I Sims, and Peterman, Z.E., Tectono-stratigraphic evolution Sims, P.K., P.K., Van Van Schmus, Schmus,W.R., W.R., Schulz, Schulz, K.J., K.J., and Pete-, Z.E.,1989, 1989,Tectono-stratigraphic evolutionof of the the Early EarlyProterozoic ProterozoicWisconsin Wisconsin magmatic magmatic terranes terranes of of the the Penokean Penokean orogen: orogen:Canadian CanadianJournal Journal of of Earth EarthSciences, Sciences,v.v.26, 26,p.p.2145-2153. 2145-2158. Zartman, Zartman,R.E., R.E., Cannon, Cannon,W.F., W.F., and andNicholson, Nicholson,S.W., S.W.,1995, 1995,U-Th-Pb U-Th-Pb ages agesof of some someKeweenawan Keweenawanrocks rocksfrom from western western Lake LakeSuperior, Superior,northwestern northwesternWisconsin, Wisconsin,and andeast-central east-centralMinnesota Minnesota[abstract]: [abstract]:Proceedings Proceedings of of International InternationalField FieldConference Conferenceand and Symposium Symposiumof ofInternational InternationalGeologic Geologic Correlation CorrelationProgram Program Project 336, Duluth, Duluth,Minn., Minn.,p.p.217-218. 217-218. Project336, 45 45 �. I U I I I I I I I I 1 I I I I I I I I FOR FIELD TRIP TRIP ##22 GUIDE GUIDE FOR FIELD OF RIVER GEOLOGY OFTHE THE MONTREAL MONTREAL RIVERMONOCLINE: MONOCLINE: GEOLOGY A THROUGH ATRAVERSE TRAVERSE THROUGH25 25KM KMOF OFTHE THE CRUST CRUST �I I I I I I U I fl FIELD TRIP TRIP #2 GEOLOGY RIVER MONOCLINE: MONOCLINE: GEOLOGY OF THE MONTREAL RIVER A ThROUGH 25 A TRAVERSE THROUGH 25 KM OF OF THE CRUST by by W.F. Cannon Cannon U. U. S. Geological Geological Survey, Survey,MS MS954, 954, Reston, Reston,VA VA 22092 22092 South border, aa remarkable remarkable cross cross South of Lake Superior, near the Wisconsin-Michigan border, section of the crust. This section displays displays what what had had been been the the upper upper 35 35 km of This section exposed as a sequence of nearly vertically dipping and north-facing volcanic volcanic and and sedimentary units of of Early Early and and Middle MiddleProterozoic Proterozoic age age and and underlying underlying Archean Archean rocks rocks (Figures (Figures 2-1 and 22). 2). This Thisstructure, structure,named namedthe theMontreal MontrealRiver Rivermonocline monocline by by Cannon Cannonand andothers others(1993), (1993), resulted resulted from from southward-directed southward-directed thrusting on a northward-dipping northward-dipping listric listric thrust of of crustal crustalscale, scale, the the Marenisco Marenisco fault. fault. The Theage ageof of thrusting thrustingisisknown knowntotobe beabout about1040-1060 1040-1060 Ma, rocks that that were were upthrust upthrust and Ma, the the date dateof of reset reset biotite biotite Rb-Sr Rb-Sr ages in Archean rocks andcooled cooled on on the the upper upperplate plateabove abovethe the fault fault(Cannon (Cannon and others, 1993). 1993). The trip begins at the mouth of vertically vertically dipping Freda mouth of the the Montreal Montreal River River where extensive exposures of Sandstone, Sandstone, the the youngest youngest unit unitexposed exposed in in the themonocline, monocline, form form bluffs bluffs along along the the Lake Lake Superior southward for for about about 25 25 km through through Superior shore. shore. The The traverse traverse progresses progresses southward successively older and and steeply successively older steeply dipping dipping to vertical vertical strata strata of of the theKeweenawan Keweenawan Supergroup, Supergroup,the theEarly EarlyProterozoic ProterozoicMarquette Marquette Range Range Supergroup, Supergroup, and and into intoLate Late Archean Archean metavolcanic metavolcanicrocks. rocks. STOP 2-1. Freda FredaSandstone Sandstoneatatthe themouth mouthofofthe theMontreal MontrealRiver River(Fig. (Fig.2-3) 2-3) STOP2-1. The The Freda Freda Sandstone Sandstoneisisthe theyoungest youngestunit unitexposed exposedin inthe theMontreal MontrealRiver River monocline monoclinebut but probably probably was was overlain overlain originally originally by as as much much as as aafew fewkilometers kilometers of of continental continental sandstones sandstones deposited deposited late late in the the history history of of the the rift. rift. The exposures seen seen here, here, representing representingthe the middle middleto toupper upperparts partsof of the theFreda, Freda, may may have have been been buried buried by by as as much much as as 3-5 3-5 km under under younger younger parts parts of ofthe theFreda Freda and andyounger youngersediments sedimentsof of the theBayfield Bayfield Group. Group. The Thesandstone sandstoneisiswell wellexposed exposedininhigh highcontinuous continuousbluffs bluffs along along the the Lake Lake Superior Superiorshoreline. shoreline. ItItisismostly mostlyaawell well bedded bedded and andcommonly commonly crossbedded crossbeddedfeldspathic feldspathic sandstone. sandstone. Dips Dips are areessentially essentiallyvertical. vertical. Volcanic Volcanic rock major rock fragments fragments are aa major constituent,indicating indicating that thatrift-derived rift-derived volcanic volcanic rocks rocks composed much of the the source source constituent, area. Muscovite Muscoviteisisalso alsoaacommon common detrital detrital mineral mineral in many layers indicating that a area. basementterrane terranewas wasalso alsoexposed exposedthat thatcontributed contributedaasubstantial substantialpart partof of the the detritus. detritus. basement 49 �00 Cii 0) NW Moho Archean White's Ridge mylield Group Bayfield Peninsula / MONTREAL MONTREAL RIVER RIVER Ml MONOCLINE S. S. shore shore of of Lake LakeSuperior Superior Moho I Archean Keweenawan Keweenawan I bio~~te ages diabase dikes S1 Figure the southern southernlimb limb of of the theMidcontinent Midcontinent rift rift showing regional structural structural context context of of the the Montreal Montreal River River monocline. monocline. The The Figure2-1. 2-1. Schematic Schematiccross cross section section ooff the showing the the regional section extends approximately from the Bayfield Peninsula to Mercer, Wisc., a distance of roughly 100 km. To the NW a prominent basement high, White's section extends approximately from the Bayfield Peninsula to Mercer,Wise., a distance of roughly 100 fan. To the NW a prominent basement high. White's Ridge, muchofofthe theKeweenawan Keweenawanvolcanic volcanicsection sectionand andremained remainedaapositive positivetopographic topographicfeature featureuntil untilthe theclose closeofofthe theextensional exiensional Ridge,limited limitedthe thedepositional depositionalextent extentofofmuch phase phase of of the the rift. rift.AsAsmore morewidespread widespreadthermal Ihennalsusiderice susidencesupplanted supplantedextension, extension,the theridge ridgewas wasburied buriedbeneath beneath the the Oronto Orontoand and Bayfied BayfiiGroups, Groups,which whichremain remain nearly nearly flatJying. flauying. Southeastward Southeastwardfrom fromWhite's White'sRidge Ridgetotothe thepresent present outcrop outcropbelt belt ofofthe thevolcanics, volcanics,the thevolcanic volcanicsection sectionbecomes becomes progressively progressively thicker. thicker. This This geometry part of thai the the deepest deepest part of the therift riftininthis thisarea areamay mayactually actuallyhave havebeen beentotothe thesouth southofofthe thepreserved preservedvolcanic volcanicrocks, rocks,ininananarea areasince sinceuplifted upliftedand and geometrysuggests suggests that deeply eroded. The Thepresent present steeply steeply northward-dipping northward-dippingattitude altitudeof ofthe therocks rocksininthe theMontreal MontrealRiver Rivermonocline monoclineisisbelieved believedtotobebethe theresult resultofofcrustal-scale crustal-scaleramping ramping deeply eroded. on to have have thrust thrust rift rift units and Archean on the the Marenisco Marenisco fault. fault. The TheMarenisco Mareniiofault faultisisinterpreted interpretedtotopenetrate penetrate the the entire entire crust crust and to units and and their their Early Early Proterozoic Proterozoic and Archean basement southward. The listric geomerty of the fault surface caused the upper plate to tilt northward, after which erosion has exposed the present crustal-scale basement southward. The listric geomerty of the fault surface caused the upper plate to tilt northward, after which erosion has exposed the present crustal-scale by the southerly dip dip of of originally and by by Middle Middle cross The involvement involvementof of Archean Archean rocks rocks in in the the monoclinal monoclinal structure structure is is shown shown by the southerly originallyvertical verticaldiabase diabase dikes dikes and cross section. section. The of biotite, was located Rb-Sr blocking temperature of uplift and cooling. 270°C isotherm, the which mark time The Proterozoic Rb-Sr ages of biotite, Proterozoic Rb-Sr ages of biotite, which mart lime of uplift and cooling. The 27WC isotherm, the Rb-Sr blocking temperature of biotite, was located by by of biodte determining determiningRb-Sr Rb-Sr closure closureages ages of biotitein in Archean Archean rocks. rocks. Rocks Rocks north north of of the the isothenn isotherm(originally (originallyabove abovethe theisotherm) isotherm)remained remainedcooler coolerthan than 270°C 27WCthroughout throughout ages reflecting reflecting Early Early Proterozoic and Keweenawan and retained retained ages Prot&ic and Archean Archean thermal thermal conditions. conditions. Rocks Rocksbetween between the theisotherm isothennand andthe the Marenisco Mareniscofault faultwere were Keweenawanburial burial and from about Ma and date the the time time of of heated heated above above 270°C 27WCby by Keweenawan Keweenawan burial burialand and Rb-Sr Rb-Sr biotite biotite ages ages were were reseL reset In In this this area area biotite bi& ages ages range range from about 1040-1060 1040-1060 Ma and date fault South uplift, andcooling coolmgcaused causedby bythrusting thrustingalong along the the Marenisco Marenisco fault Soothofofthe thefault, fault.Middle MiddleProterozoic Proterozoicburial burialwas was not notdeep deepand and biotite b i t eages agesagain again uplift,erosion, erosion,and reflect EarlyThoterozoic Proterozoicthermal thermalcvents. events. reflect Early �(ii 1 I 15 2 2' 2KM Figure 2-2. Cross section of the Montreal River monocline showing the location of field trip Figure 2-2.indicates Cross section of the Montrealburial Riverdepth along top estimated maximum duringshowing development of Midcontinent ri stops. Scale monocline the location of field trip along indicates estimated uplift top of the monocline. Agesmaximum of dated burial Middledepth Proterozoic units are shown in Ma.rift and prior to during igneous development of Midcontinent uplift of the monocline. Ages of dated Middle Proterozoic igneous units are shown in Ma. I 10 I— �/ 7T A721 / . / L - I. L -— '\ ' Freda Sandstone. I N 4 \\\ 1 15 — : \\ 1 n__ 11 I :- - - / I .1 II / — \; ___L___j_ // 7* 2 - H -\ ,- f 24 4 -ci 5CcPe t--- - x S lsaxUnI cOD - tC !I\X 4fl 0 ) MILE ? FEE! e._ I KILOMEtER Figure Bay Figure2-3. 2-3.Pans Partsofofthe theOronto Oronto Bayand andLittle LittleGirls GirlsPoint Point771/2' 112'quadrangles quadrangles showing 1 , 2, 2,and and3.3. showingthe thegeneral generalgeology geologyand andlocation locationof offield fieldtrip tripstops stops 1, 52 I �F' I I I I I 1 I I I I I r of numerous nearly An interesting secondary structural element is the presence of flatlying or very gently north-dipping faults. These These faults faults invariably invariably have only only aa few few centimeters to about a meter of of offset in which the upper plate plate has has moved moved relatively relatively north, as expressed by by drag on bedding and in some places by kinked, kinked, rather rather than places by broken, beds. Such along the the Montreal Montreal River. River. In Suchsmall small faults faults are are common in exposures along they cut clasts clasts that can be identified on opposite the Copper Harbor Harbor Conglomerate, Conglomerate, they displacements. The agee and cause of these small sides of the fault giving precise displ small faults faults are unknown. unknown. STOP 2-2. 2-2. Middle Middle part partof of Oronto OrontoGroup Groupalong alongParker ParkerCreek Creek(Fig. (Fig.2-3) 2-3) The top of the Copper Harbor Conglomerate, the Nonesuch Formation, and the lower part of of the the Freda Freda Sandstone Sandstonecan can be be seen seen along along the the incised inased bed bed of of Parker Parker Creek. Creek. of the the Nonesuch and adjacent The Parker Creek section is the most complete exposure of adjacent units in the Lake Superior region. region. Beds 75°N to to vertical. vertical. Detailed stratigraphy stratigraphy Beds dip from 75oN of of the Parker Parker Creek Creek section section was was described described by by Suszek Suszek (1991) (1991) on whose work the the following generalized description descriptionisisbased. based. The The upper upper part of the following generalized the Copper Copper Harbor Harbor Conglomerate of massive to to crudely crudelybedded bedded clast-supported clast-supported conglomerate with Conglomerate consists consists of of basalt and rhyolite cross-bedded, pebbly sandstone interbeds. Clasts Clasts consist consist mostly of with lesser granite granite and and gabbro, gabbro, all all probably probably derived derived from from slightly slightly older older Keweenawan Keweenawan jasper, quartzite, and chert clasts are are aa minor minor component component rocks. Banded iron-formation, jasper, rocks. but are but are widespread, widespread,indicating indicatingthat thatpre-Keweenawan pre-Keweenawanbasement basementwas wasalso alsoexposed. exposed. The Nonesuch Formation is about 130 m m thick thick and and comprises of of mostly mostly gray to pale brown siltstone, siltstone, sandstone, sandstone, and and minor minor shale, shale. It is generally thinly bedded to to laminated, but thicker thicker massive beds also occur. Small-scale Small-scale trough crossbedding crossbedding is is an an overall overall coarsening-upward coarsening-upward trend trend to to the the formation, formation, although although many common. There is individual units rocks of units display displayfining-upward fining-upward textures. textures. The fine-grained fine-grained rocks of the the Nonesuch Formation of the the Copper Copper Harbor. Harbor. A Formation lie on coarse conglomerate of A transitional transitional bed, one meter meter thick, thick, contains contains reddish-brown, trough-crossbedded sandstone at the base and grades grades upward upwardinto intogray-brown gray-brown calcareous calcareous siltstone. The The upper upper contact contact of the Nonesuch with the Freda Sandstone is gradational over about 20 m, in which gray siltstone and shale are interbedded interbedded with reddish-brown, reddish-brown, medium medium to to coarse sandstone. sandstone. Additional exposures exposures of the upper part of of the Copper Harbor Harbor Conglomerate Conglomerate can can be seen seen in in low low roadcuts roadcutsalong alongHighway Highway122 122ininthe theNW NW1/4 1/4ofofSec. Sec.30, 30,T. T.47 47N., N.,R. R. 11E. E. b I I 53 �I I I 0 1000 ----0 — — -l I1 1000 2000 5 5 3000 00 4 I MILE 5000 6000 -— 7000 FEET , 1 KIL0METCR KILOMETER 1 Figure Figure2-4. 2-4. Parts Parts of of the the Little LittleGirls Girls Point Point and and Iron Iron Belt Belt 7 1/2' 112'quadrangles quadrangles showing and 5. 5. showing the the general general geology geology and location of field trip trip stops stops 44and 54 I I I I I �— STOP STOP 2-3. Top Topof of Porcupine PorcupineVolcanics VolcanicsatatSaxon SaxonFalls Falls(Fig. (Fig.2-3) 2-3) Basalt flows flows and and interflow interfiow conglomerate conglomerateand andsandstone sandstoneofofthe theuppermost uppermost part part of of the River below below the dam at Saxon the Porcupine PorcupineVolcanics Volcanics are exposed along the Montreal River Saxon Falls flowage. The uppermost uppermost exposed unit is thin-bedded red sandstone and siltstone, which which is is underlain underlainby byaamassive massivebasalt basaltflow flow about about100 100 m m thick. This This flow is underlain by about interbedded conglomerate and sandstone. The about 30 30 m of interbedded The lowest lowest exposed exposed unit unit is is another partly brecciated brecciatedtop. top. About the upper half another basalt flow with an amygdular, partly half meter breccia, and and the the upper upper three meters are meter of of the the flow flow shows shows typical rubbly flow-top breccia, coarsely coarsely amygdular. amygdular.The Themost mostabundant abundantamygdule-filling amygdule-filling mineral is thomsonite, which occurs radiating blades blades in in the the larger larger amygdules. amygdules. The predominance predominance occurs in masses of coarse radiating of this this low low temperature temperature zeolite zeolite indicates indicates that rocks at this level of burial were only I weakly weakly heated heatedbefore beforeuplift. uplift. I STOP STOP2-4. 2-4. Rhyolite Rhyoliteatattop topofofICallander KallanderCreek CreekVolcanics Volcanics(Fig. (Fig.2-4) 2-4) I I I I I I I I The uppermost uppermostunit unitof ofthe theKallander KallanderCreek Creek Volcanics Volcanics is a thick, mostly massive, quartzrhyolite. We quartz- and and plagioclase-phyric plagioclase-phyric rhyolite. We informally designate this unit the Sheep Sheep Farm Farm rhyolite rhyolite and and this this stop stopisis our ourinformal informal type type locality. locality. The The reason reason for for the the name name isis obvious. obvious. The The unit unit is is at at least least 300 300 m thick and appears to be the product product of of aa single single eruptive eruptiveevent. event.ItItcan canbe betraced tracedfrom fromthis this locality locality westward for about about 30 30 km to Copper Copper Falls Falls State State Park near near Mellen, Mellen, where it is the the resistant resistant rock rock that that holds holds up upBrownstone Brownstone Falls Falls on on the theTyler Tyler Forks Forks River. River. At At that thatlocality, locality, we we have have located located by field measurement measurement the the horizon horizonof of the theprincipal principalmagnetic magnetic reversal reversal recorded recorded in in the theKeweenawan Keweenawansection. section. The The reversal reversal lies lies aa few fewflows flows beneath the rhyolite. The The rhyolite rhyolite has has been been dated dated atat1099 1099 Ma Ma (Zartman (Zartman and and others, others, 1995), 1995), so the age age of of the the magnetic magnetic reversal reversal must must also also be be approximately approximately 1099 1099Ma. Ma. At At this this stop, stop, the the exposures reveal the basal part of of the the flow, flow, which These blocks blocks which contains contains numerous numerous blocks blocks of rhyolite up to about about 20 20 cm across. These have haveaaslightly slightlydifferent differenttexture textureand andphenocryst phenocrystcontent contentthan thanthe thehost hostrhyolite. rhyolite. STOP STOP2-5. 2-5. Dacite DaateininKallander KallanderCreek CreekVolcanics Volcanics(Fig. (Fig.2-4) 2-4) The abundant rocks The upper uppermember memberof ofthe theKallander KallanderCreek Creek Volcanics Volcanics contains abundant rocks of of intermediate intermediatecomposition compositionin in addition additionto to basalt and rhyolite. We We have have proposed proposed that thatthe the upper upper part partof of the theKallander KallanderCreek CreekVolcanics Volcanics represents the partly eroded eroded remains remainsof of aa broad broad central centralvolcano, volcano, and and that thatthe theMellen Mellen Complex Complex is the crystallized remnants of aa magma magma chamber chamber that thatwas wasintruded intrudedinto intothe thevolcanic volcanic edifice edifice late in its eruptive eruptive history history (Cannon (Cannon and others, others, 1993). 1993). At At this this locality our data show that the rock knob in the gravelpit pitisisa afine-grained fine-grainedreddish-brown reddish-brown dacite (Si02=64-66wt%; wt%;Ti02=1.26 Ti02=1.26wt%; wt%; gravel dacite (SiO2=64-66 �I I I I I I I - -- - -- --3 7 I 0 U 1000 C I :000 2WX 5 3000 2000 - - ? . + - - , 0 0 4000 4000 -, 5000 5000 6000 60CC , 1 MILE 7000FEET I MILE 7000 FEET I KILOMETER I KILOMETER Figure 2-5. Part of the Saxon 7 112' quadrangle showing the general Figure 2-5.and Part of the Saxon geology location of field7trip stop 6. 1/2' quadrangle showing the general geology and location of field trip stop 6. 56 �I STOP STOP 2-3. Top Topof of Porcupine PorcupineVolcanics VolcanicsatatSaxon SaxonFalls Falls(Fig. (Fig.2-3) 2-3) Basalt flows and and interflow interfiow conglomerate conglomerate and and sandstone sandstone of of the the uppermost uppermost part Basalt flows part of of the Porcupine Volcanics are exposed along the Montreal River below the dam at Saxon the Porcupine Volcanics are exposed along the Montreal River below the dam at Saxon Falls flowage. The Falls flowage. The uppermost uppermost exposed exposed unit unit is is thin-bedded thin-bedded red red sandstone sandstoneand andsiltstone, siltstone, which underlain which is is underlain underlainby by aamassive massivebasalt basalt flow flow about about 100 100 m m thicic. thick. This This flow flow is is underlain by about mof about 30 30 m of interbedded interbeddedconglomerate conglomerate and sandstone. The The lowest lowest exposed exposed unit unit is is another basalt basalt flow flow with with an an amygdular, amygdular, partly partly brecciated brecciatedtop. top. About About the the upper upper half another half meter of the flow shows breccia, and and the upper three shows typical rubbly flow-top breccia, three meters meters are are coarsely amygdular. amygdular. The Themost mostabundant abundantamygdule-filling amygdule-fillingmineral mineral is is thomsonite, thornsonite,which which occurs in masses of of coarse coarse radiating radiatingblades bladesin inthe thelarger largeramygdules. amygdules. The predominance predominance of this of this low low temperature temperature zeolite zeolite indicates indicates that that rocks rocks at at this this level level of of burial burial were were only only weakly heated heated before before uplift. uplift. I STOP Rhyolite at attop topof ofKallander KallanderCreek CreekVolcanics Volcanics(Fig. (Fig.2-4) 2-4) STOP 2-4. Rhyolite I The uppermost uppermostunit unitof of the theKallander KallanderCreek CreekVolcanics Volcanics is aa thick, thick, mostly mostly massive, massive, rhyolite. We this unit quartz- and plagioclase-phyric rhyolite. We informally designate 'this unit the the Sheep Sheep I I I I I I I -. Farm rhyolite and this stop is our informal type locality. locality. The reason for the name is Farm The unit unit is at least m thick thick and and appears appears to to be be the the product product of obvious. The 300 m of a single single obvious. least 300 eruptive 30 km km to to Copper Copper eruptive event. event.ItIt can can be be traced traced from from this this locality locality westward for for about about 30 Falls State Park near Mellen, where where itit is is the resistant rock rock that holds up up Brownstone Brownstone River. At that Falls on the Tyler Forks River. that locality, locality, we have located by field measurement the horizon of the the principal principal magnetic magnetic reversal reversal recorded recorded in in the the Keweenawan Keweenawansection. section. beneath the the rhyolite. rhyolite. The rhyolite has been The reversal lies a few flows beneath been dated datedatat1099 1099 Ma (Zartman so the the age age of of the magnetic reversal must also be Ma (Zartrnan and others, others, 1995), 1995), so magnetic reversal Ma. At this stop, the exposures reveal the basal part approximately 1099 approximately 1099 Ma. part of of the the flow, flow, of rhyolite rhyolite up to about 20 cm across. These which contains numerous blocks of These blocks blocks have a slightly different texture and phenocryst content than the host rhyolite. STOP 2-5. Dacite Dacite in in Kallander KallanderCreek CreekVolcanics Volcanics(Fig. (Fig.2-4) 2-4) The upper upper member Volcanicscontains contains abundant abundant rocks of of The member of of the the Kallander Kallander Creek Volcanics intermediate composition basalt and and rhyolite. rhyolite. We have proposed proposed that the intermediate composition in addition to basalt represents the the partly partly eroded eroded remains of a upper part of of the the Kallander Kallander Creek Volcanics Volcanics represents broad central central volcano, volcano, and and that that the the Mellen Mellen Complex is the crystallized remnants of aa eruptive history magma chamber that was intruded intruded into into the the volcanic volcanic edifice late in its eruptive (Cannon and others, 1993). our data show that the rock 1993). At this locality locality our rock knob in in the the gravel pit pit isisaafine-grained fine-grainedreddish-brown reddish-browndacite dacite(SiO2=64-66 (Si02=64-66wt%; wt%;Ti02=1.26 TiO2=1.26wt%; wt%; 55 I �I I I I I $1 n I I I CeN/YbN=4.5) thatcontains containssmall smallplagioclase plagioclasephenocrysts. phenocrysts.The The rock rock has has a strong CeN/Yt>N=4.5)that primary and weathers weathers primary foliation, perhaps indicating that it is the basal zone of a flow, and into into platy platy fragments fragments parallel parallel to to the the nearly nearly vertical vertical foliation. foliation. Small Smalloutcrops outcropsnearby nearby show aa coarser, coarser, more more massive massive dacite. dacite. The Thedacite daciteisisoverlain overlainby bya abasalt basalt(Si02=50.24 (Si02=50.24 wt%; wt%; Ti02=3.78 Ti02=3.78wt%; wt%;CeNIYbrc_3.7) CeN/Yt>N=3.7)that is exposed in low outcrops along the power line north north of the the gravel gravel pit. pit. STOP 2-6. 2-6. Upson Upson Lake area--Siemens Bessemer Quartzite, Quartzite, and area--Siemens Creek Volcanics, Bessemer and Tyler Tyler Formation Formation (Fig. (Fig. 2-5) 2-5) of the Keweenawan section is is exposed exposed in contact with the At this locality the base o ft he Keweenawan underlying Tyler Formation. At underlying At the the top top of of the the prominent prominent bluff north north of of Upson Upson Lake Lake the Volcanicsare areexposed. exposed. They are pillowed lowermost basalt flows of the Siemens Creek Volcanics pillowed and brecciated brecciated as a result result of of eruption eruption into into aashallow shallow lake lake in inwhich whichthe theBessemer Bessemer Quartzite had been deposited. deposited. The Theflows flowshave haveaadistinctive distinctivechemical chemical composition composition marked by low (8-12wt%), wt%),and andhigh highCr, Cr,Ni, Ni,and andMgO. MgO. In In addition, rare earth low A1203 &03(8-12 earth element (REE) patterns patterns are and heavy heavy REEs REPs have have low element are quite quitesteep steep(CeN/YbN (CeN/YbN = about 15) and abundances. These indicate that that the the magmas magmas formed by a small abundances. These chemical characteristics indicate degree of partial melting of a deep, enriched mantle source (postulated to be a mantle plume), and that the plume), the magma magma erupted erupted directly directly to to the the surface surface without without undergoing undergoing significant crystallization and fractionation. fractionation. Flows Flows of of this this chemical chemical character character can can be recogi-uzed in the field by the phenocrysts of of clinopyroxene. clinopyroxene. These recognized the presence presence of small phenoaysts clinopyroxene-phyric flows flows have have been traced from near Bessemer, Michigan, to just just Bessemer, Michigan, west of this locality. They They apparently apparently represent represent aa unique unique magma magma composition compositionthat thatwas was erupted erupted only at the very outset outset of volcanism. volcanism. Identical Identical flows have been recognized at the base of the Minnesota, both both at at Ely's Ely's Peak Peak and at Pigeon the North North Shore Shore Volcanics Volcanics in Minnesota, Point Point and and Grand GrandPortage Portage(Green, (Green,1977). 1977). An interflow sedimentary bed is exposed between the first and second second flows. flows. The sediments are, in part, an algal laminite and and are are now now substantially metamorphosed metamorphosed so that that original original calcareous calcareous layers layers are are aa fine-grained fine-grained mat mat of of wollastonite. wollastonite. The The metamorphism was metamorphism was caused, caused, at at least least in in part, part, by by emplacement emplacementof the Potato Potato River Gabbro about 11km up-section. about up-section. Creek Volcanics Volcanicsare areunderlain underlain by by the the Bessemer Bessemer Quartzite, Quartzite, the oldest The Siemens Creek oldest unit in the Keweenawan Supergroup. Scattered of white white to to gray laminated Scattered exposures of quartzite are on the quartzite the slope slope below below the the basalt basalt exposures. exposures. Passing down-section, the Bessemer contains basal basal beds of coarse Bessemer contains coarse conglomerate conglomerate composed largely largely of of Early Early �•r -t ) i\ a-m / N V -: - $eiForma_yf vi; I — - -o •1475 !r •L 0 - • / Forts - - - °° F -4 Mlt€ 0 :OO 2O 3O o0 wo 7000 FEET KILOMETER Partof of the the Mt. Mt. Whittlesey Whittlesey 7 1/2' ~Figure i ~ u 2-6. r e Pan 112' quadrangle quadrangle showing the general geology geologyand andlocation locationof of field field trip trip stop stop 7. 7 general 58 N �I I Proterozoic metasedimentary metasedimentary clasts, Small garnet Proterozoic clasts, including including iron-formation. iron-formation. Small garnet porphyroblasts are common in the matrix. porphyroblasts are common in the matrix. A small small exposure exposure near near the base of the slope A slope shows an angular angular unconformity unconformity between basal conglomerate conglomerate of of the Bessemer Bessemer and thin-bedded argillite argillite of of the the Tyler Tyler Formation. Formation. This This is is the the only only exposure exposure known known to to us uswhere wherethe theunconformable unconformable relationship and the relationship between between the the Keweenawan Keweenawan Supergroup Supergroup and the Marquette Marquette Range Range Supergroup Supergroupcan can be be seen. seen. H STOP Tyler Formation Formation(Fig. (Fig.2-6) 2-6) STOP 2-7. Tyler I I This roadcut This roadcut exposes typical thin-bedded graywacke and argillite of the Early Early Proterozoic Tyler Formation. Although Althoughdips dipsare arenearly nearlyvertical, vertical, the the lack lack of of penetrative penetrative fabric indicates little fabric indicates little structural structuraleffect effect of the Penokean Penokean orogeny orogeny on on the the Tyler Tyler in in this thisarea. area. The highest grade common throughout the grade metamorphic metamorphic mineral is biotite, biotite, which is common matrix. a I I I I I I I I I a 1 STOP STOP 2-8. Ironwood Ironwoodhon-formation Iron-formationon onMt. Mt.Whittlesey Whittlesey(Fig. (Fig.2-7) 2-7) - The prominent held up by The prominent ridge of of Mt. Whittlesey Whittlesey isis held by the the Ironwood Ironwood IronIronformation. An Anunusually unusuallygreat greatthickness thickness of of iron-formation iron-formation is present here owing owing to to structural repetition structural repetition by thrust thrust faults faults and and folds folds produced during during the the Penokean Penokean orogeny. orogeny. shows our recent interpretation interpretation of Whittlesey area that of the the geology geology of the Mt. Whitdesey Figure 2-7 shows will be seen at Stops 2-9, and and 2-10. 2-10 Mt. easternmost extent will Stops 2-8, 2-8,2-9, Mt. Whittlesey lies at the easternmost extent of of Proterozoic)foreland forelandfold foldand andthrust thrust belt. belt. At the Penokean (Early Proterozoic) At Mt. Mt. Whittlesey, Whittlesey, a thrusts repeats series of thrusts series repeatsthe the Early Early Proterozoic Proterozoic section, having detached it from from Archean rocks along a basal decollement. The The thrusts thrusts all all rise rise in in the the section section to to the the east east along along aa series of of lateral ramps. ramps. Northward Northwardtilting tiltingof of the theregion region in inMiddle Middle Proterozoic Proterozoic time time results in the current results current map map pattern pattern that thatprovides provides an anunusual unusualcross-sectional cross-sectional view of the thrust complex. To To understand understand the thePenokean Penokean structural structural geometry geometry the map pattern pattern should be viewed as a longitudinal longitudinal cross cross section along the original trend of of the thrust thrust belt, so that the the upper upperplates platesof of originally originally nearly nearly flat-lying flat-lying faults would have have moved moved northward away from the viewer. Because Because of later tilting, these original thrusts thrusts now now mimic the geometry of of normal faults-that faults--that is, is, the the upper upper plates plates appear to have moved down to the north. The Theramps rampsthat thatrise risetotothe theeast eastare arelateral lateralramps rampsalong alongwhich which the the plates have have undergone undergone transcurrent transcurrent movement movement rather rather than thanoverthrust overthrustmovement. movement. Displacement along along the basal decollement diminishes eastward eastward as splays from the Displacement decollement diminishes the rise in the section. East decollement successively rise 2-10 the the Early Early Proterozoic Proterozoic decollement Eastof of Stop Stop2-10 section unconformably on section lies unconforrnably on Archean Archean rocks. �2 5/; ) U U — J (4\6(' itou — $ROMHfR 1 FEH /000 1 —- 6(X))) -_- 5000 afl I —: -- -a =——1 4(U) ) rrT _r 0 F X) I — I0 172 5 - -- I_i I 0 I Ft= : iLiT\ç ES?.. '-: o2:j '1;-c - 10. and 9, 8, stops trip field of location and geology general showing quadrangles 1/2' 7 MeIlen and Whittlesey Mt. the of Part 2-7. Figure , V$1? Y — (-) ' tvyt1 00J C' 1! ;iHI!t �S At Stop 2-8 2-8 excellent excellentexposures exposuresofofthe the Ironwood bonwood Iron-formation hon-formation occur At occur on on the the north face of of the ridge near the summit, and along a railroad grade near the Berkshire mine ruins. At Atthe theformer formerlocality, locality, aa large large area area was was cleaned cleaned of overburden overburdenin in the the 1920s 1920s in anticipation of open pit mining. mining. Only near the base base of of Only a small pit was developed near glacially polished, polished, exposure cleared area; the remainder remainder provides provides an an excellent, excellent, glacially exposure in which many At the many details details of of sedimentary sedimentary features features are are extraordinarily extraordinarily well well displayed. displayed. At mine ruins ruins an abandoned railroad grade provides a continuous cross section Berkshire mine of several several hundred hundredmeters metersof of section section and and aa tight tight fold fold is exposed in the cut. The iron-formation contains several several lithologic lithologic variations. The classic fivemember internal member internalstratigraphy stratigraphydefined definedtotothe theeast east(Hotchldss, (Hotchkiss,1919; 1919; Huber, Huber, 1959) 1959) consists of alternating alternatingmembers members of of even-bedded, even-bedded,carbonate carbonate iron-formation iron-formation (slaty (slaty iron-formation) iron-formation) irregularly-bedded hematitic jasper. jasper. This stratigraphy stratigraphy becomes more more complex complex and and and irregularly-bedded and irregular westward westward along alongthe the iron ironrange; range; we we have have not not been been able to apply apply itit west west of of Mt. has many lithologic Whittlesey. The iron-formation exposed here characteristically characteristically has Whittlesey. of variations on a small scale so that individual exposures may show a complete range of lithologies interbedded lithologies interbeddedon onaascale scale of meters or less. 2-9. Palms STOP 2-9. Palms Formation Formationand andBad Bad River River Dolomite Dolomite at at Eagles Eagles Peak Peak (Fig. ( ~ i ~2-7) .2-7) At the southwest prominent bluff, Eagles Peak, is is held held up up southwestend endof of Mt. Mt. Whittlesey a prominent by laminated At the laminated argillite argillite typical of the the lower lower part part of of the thePalms PalmsFormation. Formation. At westerost tiptip of the bluff thethe unconformable -westernmost of the bluff unconformablecontact contactbetween between the the Palms Palms and and underlying Bad Dolomite is is well well exposed. exposed. The Palms Palms can can be be seen seen to to be be draped draped underlying Bad River Dolomite which also has has a weathered into shallow depressions along the top of the Bad Bad River, River, which contact. The rusty color appears to be into rusty and rusty zone zone for for about about half a meter below the contact. caused by recent recent oxidation oxidationof small small amounts amounts of pyrite pyrite along along the the contact. contact. The breccia composed composed of of angular to The Bad River Dolomite at this locality is a chert breccia subrounded fragments subrounded fragmentsof of gray graychert chertcemented cemented mostly mostly by aa second second generation generationof of chert. chert. fill interstices interstices between between breccia breccia fragments, Locally, well-rounded well-rounded quartz quark grains grains partly partly fill Locally, matrix. At and magnetite magnetite is locally abundant as euhedral grains in the matrix. At other other localities localities nearby, magnetite of prospect magnetite was sufficiently abundant to have promoted the sinking of shafts in the early days days of of iron iron exploration. exploration. These These are are present present generally generally immediately immediately below the contact contact with with the the Palms Palms Formation. Formation. This This distinctive distinctive chert chert breccia breccia has been Locallyitit is is underlain underlain by by traced as aa mappable mappable unit unit for for about about12 12km km along along strike. strike. Locally marble River Dolomite Dolomite in inthis thisregion. region. We marble and and tremolitic tremolitic marble marble more more typical typical of the Bad River believe that the the breccia is a residual deposit, formed by solution of an originally thick section of of cherty dolomite during the weathering interval prior to to Palms Palms deposition. deposition. P 61 �The residue of insoluble chert was variably reworked into its present character and cemented by secondary silica. Magnetite Magnetite was apparently introduced introduced hydrothermally sometime sometime after after deposition depositionof of the the Palms PalmsFormation. Formation. STOP 2-10. 2-10. Contact of Early Proterozoic strata and Archean Archean metavolcanic rocks on the the southeast 2-7) southeastflank flankof of Mt. Mt.Whittlesey Whittlesey(Fig. (Fig.2-7) Low outcrops outcrops near near the the base base of a prominent ridge supported by the Low prominent ridge the Palms Palms Formation reveal the basal contact Proterozoic strata strata with with underlying contact of Early Proterozoic underlying dacite breccia of The breccia breccia has has a penetrative structural fabric, breccia of Late Archean Archean age. age. The fabric, best best expressed by the expressed the prominent prominent elongation elongation of of clasts. clasts. Long Long axes axes plunge plunge moderately moderately southward, southward, but but must musthave haveplunged plungedmoderately moderatelyto to steeply steeply northward northwardprior priortototilting tiltingof of the rocks into the monoclinal structure. structure. The Thebasal basalEarly Early Proterozoic Proterozoicunit unitisischert chertbreccia breccia of the Bad River Dolomite, Dolomite, the the same same unit unit seen seen at at stop stop 2-9. 2-9. Along Along the the contact contact the the upper meter or two two of of the the dacite dacitebreccia breccia is strongly sheared parallel to the contact, and the the overprinted by by this this secondary secondary fabric. fabric. Shearing Archean fabric typically is completely overprinted Shearing is weak to absent absent in in the the chert chertbreccia. breccia. To our knowledge these outcrops are the only ones in the western part of of the the Gogebic Range Range where where a basal detachment between the Early Proterozoic strata and Gogebic and observed. We Archean basement rocks can be directly observed. We believe believe the Early Early Proterozoic flatlying basal contact during the Penokean strata were thrust thrust northward northwardalong alongaanearly nearly flatlying orogeny. Because River monocline, monocline,the thepresent present apparent apparent Because of of later later tilting tilting of the Montreal River This fault fault can be traced displacement reflects a down-to-the-north down-to-the-north normal normal fault. fault. This traced westward, and westward, andabout about11km km to to the the west west of of these these exposures exposures it passes up-section up-section so so that that the the Bad River-Palms-Ironwood River-Palms-Ironwood sequence sequenceofofthe theupper upper plate plate is juxtaposed juxtaposed over Ironwood Bad Iron-formation in in the lower plate, plate, producing producing the the unusually Iron-formation unusually wide outctrop belt of of Whittlesey. Just east of of this stop the basal thrust Ironwood along higher parts of Mt. Whittlesey. appears appears to to pass pass upward upwardinto intothe theEarly EarlyProterozoic Proterozoic strata. strata. Exposures Exposuresnear nearBallou Ballou Creek Creek show that that the thebase baseofofthe theEarly EarlyProterozoic Proterozoicrocks rocks lies liesunconformably unconformably on onArchean Archean without an volcanic rocks without an intervening intervening shear shearzone. zone. The Archean Archean rocks rocks seen seen at at Stop Stop 2-10 2-10are arethe the structurally structurally lowest lowest parts parts of of the The monocline that the master that are are seen seen on on the the field field trip. trip. But But the the trace trace of the the Mareriisco Marenisco fault, the thrust that lies about about 88 km km to to the the south. south. Thus, thrust that formed formedthe theMontreal MontrealRiver River Monodline, Monocline, lies Thus, all of the stratigraphic seenon on the the trip, trip,plus plusan. an additional additional88 km km stratigraphicsection section to to the the north north that thatisisseen of Archean rocks to the south, form the upper of upper plate plate of of the the Marenisco Marenisco fault, a coherent structural unit structural unit that that was was uplifted uplifted and andtilted tilted late late in in the the Middle Middle Proterozoic history of the region. region. 62 I �— I I I I I I REFERENCES REFERENCES Cannon, Crustal-scale thrusting thrusting and Cannon,W.F., W.F., Peterman, Peterman,Z.E., Z.E., and andSims, Sims,P.K., P.K., 1993, 1993, Crustal-scale and origin originof of the theMontreal Montreal 35-km-thick cross section of the Midcontinent rift in northern Michigan River monocline a and River monocline - a 35-km-thick cross section of the Midcontinent rift in northern Michiganand Wisconsin: Wisconsin:Tectonics, Tectonics,v.v.12, 12,p.p.728-744. 728-744. Green, Green,J.C., J.C., 1977, 1977, Keweenawan Keweenawanplateau plateauvolcanism volcanismininthe theLake LakeSuperior Superiorregion, region,ininBaragar, Baragar,W. W.R.R.A., A.,and and others, (eds.), Volcanic regimes in Canada: Geological Association of Canada Special Paper 16, p. 407others, (eds.), Volcanic regimes in Canada: Geological Association of Canada Special Paper 16, p.407422. 422. Hotchkiss, Hotchkiss,W.O., W.O., 1919, 1919, Geology Geology of of the the Gogebic Gogebic Range Range and and its its relation relationtotorecent recentmining miningdevelopments: developments: Engineering Journal, v. v. 108, p. p. 443452, 501-507, 537-541, 577-582. Engineeringand andMining Mining Journal, 108, 44342,501-507,537-541,577-582. Huber, Huber,N.K., N.K., 1959, 1959, Some Some aspects aspectsof of the the origin originof of the the Ironwood IronwoodIron-formation Iron-formationofofMichigan Michiganand andWisconsin: Wisconsin: Economic p. 82-118. EconomicGeology, Geology,v.54, v. 54,p.82-118. Suzek, 1991, Suzek,T.J., T.J., 1991, Petrology and and sedimentation sedimentation of of the theMiddle MiddleProterozoic Proterozoic(Keweenawan) (Keweenawan)Nonesuch Nonesuch Formation, Formation,western westernLake LakeSuperior Superiorregion, region,Midcontinent Midcontinentrift rift system: system: Duluth, Duluth,Minn., Minn.,University Universityofof Minnesota, 198p.p. Minnesota,Duluth, Duluth,unpublished unpublishedM.S. MS.thesis, thesis,198 Zartman, 1995, U-Th-Pb U-Th-Pb ages ages of of some some Keweenawan Keweenawanrocks rocksfrom from Zartrnan,R.E., R.E.,Cannon, Cannon,W.F., W.F.,and andNicholson, Nicholson,S.W., S.W.,1995, western Lake Superior, northwest Wisconsin and east-central Minnesota [abstracti: Proceeding western Lake Superior, northwest Wisconsin and east-central Minnesota [abstract]: Proceedingofof International International Field FieldConference Conferenceand andSymposium, Symposium,International InternationalGeologic Geologic Correlation CorrelationProgram ProgramProject Project 336, 336, Duluth, Duluth,Minn., Minn.,p.p.217-218. 217-218. I I I I I I I I I I 63 �r I I I I I I I I I I I I I I I I I I I FIELDTRIP TRIP##44 GUIDE GUIDEFOR FOR FIELD PROTEROZOIC GEOLOGY OF EARLY EARLYTO TOMIDDLE MIDDLE PROTEROZOIC GEOLOGY OF THE REGION THE LAKE LAKENAMEKAGON NAMEKAGON REGION �I FIELD TRIP TRIP #4 I I I EARLY TO TO MIDDLE PROTEROZOIC GEOLOGY OF EARLY THE LAKE NAMEKAGON REGION GION by W. Cannonl, L. W. F. cannon1, L. G. G.Woodruff2, Woodruff2, and andS. S. W. W. Nicholson1 Nicholson1 Geological Survey Survey U. S. Geological 1Eastern Mineral Resources, eastern Mineral Resources,Reston, Reston,VA VA22092 22092 2Central Central Mineral Mineral Resources, Resources, St. St. Paul, Paul, MN MN55112 55112 This field trip offers offers new new interpretations interpretations of the structure, structure, geochemistry, geochemistry, and ana stratigraphy of the based on recent studies by the U. S. S. the Lake Lake Namekagon Namekagon region region based the U. Geological Survey. The Geological Survey. The trip trip will will emphasize emphasize the rocks of of the Powder Powder Mill Mill Group 1 I I I I I I n (Siemens Creek and Chengwatana Chengwatana Volcanics (Siemens Creek Volcanics Volcanics and Kallander Kallander Creek Volcanics) and Volcanics of the 'of the Keweenawan KeweenawanSupergroup, Supergroup,and andthe thecogenetic cogenetic Mellen Mellen intrusive intrusive complex, all rocks related Ga Midcontinent Midcontinent rift. rift. Stratigraphic and geochronologic data data from the the 1.1Ga related to the 1.1 different suggest a complicated differentrock rock units units of of the the Midcontinent Midcontinent rift in this region suggest complicated history of of volcanic eruption eruption and andmagma magma emplacement. emplacement. Early Earlyextrusive extrusivevolcanics, volcanics, flood flood basalts of the the Siemens Siemens Creek Creek Volcanics Volcanics and perhaps perhaps the thelower lowerKallander Kallander Creek CreekVolcanics, Volcanics, erupted subsiding basin basin throughout erupted from a number of of different different centers in a generally subsiding the the western western Lake Lake Superior Superior region. region. Development Development of of aa large largeshield shieldvolcano volcano complex, complex, possibly possibly centered centerednear nearthe thepresent presentlocation locationof of Mellen, Mellen, Wisconsin, was accompanied accompanied by intrusion shield. This produced the intrusion of multiple multiple magma magma chambers chambers in the volcanic shield. the Mellen Mellen intrusive complex complex and eruption eruption of of volcanic volcanic equivalents, the upper Kallander Kallander Creek Volcariics Volcanics (Cannon (Cannon and and others, others, 1993). 1993). With With aa decline decline in in shield shield volcano volcano activity, activity, floodfloodbasalt eruption eruptionfrom fromwithin withinthe thecentral centralgraben grabenof of the the rift rift became became dominant, dominant, forming forming aa thick series series of basalt flows, flows, the Chengwatana Chengwatana Volcanics. Volcanics. Sedimentary rocks deposited during glacio-fluvial during the thepost-extensional post-extensionalphase phaseof of the therift riftare arecovered coveredby byPleistocene Pleistocene glacio-fluvial and and lake lake deposits depositsand and are arenot not exposed exposed in in this this area. Post-rift Post-rift reverse reverse faulting faulting along the Lake Owen fault fault and andMarenisco-Atkins Marenisco-Atkins Lake fault during during late late Keweenawan Keweenawan time time rotated vertical in in some some areas. areas. As a rotated all all units units to to the the northwest, northwest, tilting tilting them to nearly vertical result, result, aa south-to-north south-to-north traverse traverse through through the the rift rift lithologies lithologies in the the area area north north of of Lake Lake Namekagon from older older to younger, younger, and and of of Namekagon provides provides aa cross cross section both through time, from crustal crustaldepth, depth,from fromrelatively relativelydeep deepto toshallow. shallow. The The first first stop stop will will be be in inan anEarly EarlyProterozoic Proterozoic sequence sequence of of iron iron and andsilica-rich silica-rich argillites argillitesof of the the bonwood Ironwoodhon-formation Iron-formationand andaametadiabase metadiabasesill. sill. This Thisstop stopis is notable notable for spectacular exposure exposure of of unusual unusual igneous igneous breccia breccia units units (Figs. (Figs. 4-1 4-1 and and 4-2). 4-2). All aa spectacular I i 67 �1'- KJIOMHFR 7 I 5000 40(W) r_3-__—_-i-z:==-- &)1X) 0 3000 0 2000 - 5 - I€0 _td L: 0 I 10® _______ - - 5. and 4, 3, 2, 1, stops trip field of locations and geology general showing quadrangle 1/2' 7 View Grand the of Part 4-1. Figure FEET ________ -: 144 -î I — — �I subsequent stops will will examine examine rocks rocks of of the the Middle Middle Proterozoic Proterozoic Midcontinent Midcontinent rift, rift, subsequent including 4-4, and includingthe theMellen Mellenintrusive intrusivecomplex complex(Stops (Stops4-2, 4-2,4-4, and4-5: 4-5:Fig. Fig. 4-1) 4-1)and and volcanic volcanic 4-6, rocks of the the Powder PowderMill MillGroup Group(Stops (Stops4-3, 4-3, 4-6,4-7, 4-7,and and 4-8: 4-8:Figs. Figs. 4-1 4-1and and 4-3) 4-3)and and rocks Chengwatana and ChengwatanaVolcanics Volcanics(Stops (Stops4-9 4-9 and4-10: 4-10:Figs. Figs.4-3 4-3and and4-4)). 4-4)). - STOP 1. Early Early Proterozoic Proterozoicdebris debrisflow flowand andmetadiabase metadiabase(Figs. (Figs.4-1 4-1and and4-2). 4-2). The topographic topographic highland highland extending extendingnortheastward northeastwardfrom fromForest ForestService ServiceRoad Road 379 numerous 379 hasThe numerousexposures exposuresof of bonwood Ironwoodhon-formation Iron-formationand andmetadliabase metadiabasesills sillstypical typical of the westernmost Range. Near the westernrnost extent extent of of the the Gogebic Gogebic Iron Range. the junction junction with with Forest Forest Service Road 201, just east of of Atkins Lake, Lake, two two unusual unusual breccia breccia units are 201,just are also also exposed. exposed. The breccia units contain angular to to subrounded subrounded clasts, clasts, up up to to 11 m in breccia units contain angular in length, length, of of metamorphosed, metamorphosed, banded banded siliceous siliceous sedimentary sedimentary rocks in a matrix matrix of of dark dark gray-green gray-green massive rock. Clasts Clastsmainly mainlyare aresiliceous siliceousargillite, argillite, aa very veryfew fewof of which whichare aremagnetic. magnetic. Most are are tabular tabular with with angular angularcorners, corners,but butsome someclasts clasts are are bent bent or orfolded, folded,suggesting suggesting that they Clastsconsist consist of of they were were not not fully fully lithified lithified when when incorporated incorporated in the matrix. Clasts alternating alternating layers layers of of recrystallized recrystallized quartz, quartz,fine-grained fine-grained chlorite, chlorite, biotite biotite or oractinolite, actinolite, garnet, garnet, and andgenerally generallyminor minoramounts amountsof ofmagnetite magnetite(Feher (Feherand andFlood, Flood, 1995). 1995). The The matrix matrix is aa fine-grained fine-grainedmafic mafic rock, rock, composed of fine- to medium-grained amphibole, amphibole, garnet, garnet, plagioclase, and magnetite, magnetite, with conspicuous conspicuous amygdules amygdules in in places. places. Metamorphic Metamorphic recrystallization has destroyed destroyed much much of the primary texture, texture, although although relict plagioclase phenocrysts phenocrysts are present present locally. locally. Preliminary geochemical geochemical data indicate indicate aa tholeiitic tholeiitic composition for the matrix Between the breccia units is is aa matrix (Feher (Feher and Flood, Flood, 1995). Between massive metadiabase 50 itt m thick. thick. The The top top of of the the sill sill is is chilled against againstthe thebase base metadiabasesill sill about about50 of the upper breccia breccia unit. The Thebase base of of the the sill sill is is separated separated from from the top top of of the the lower lower breccia unit by by aathin thinselvage selvageofofmagnetic magneticiron-formation. iron-formation. The breccia breccia units and interlayered km along along strike, but likely extend farther farther into into interlayeredsill sill can can be be traced traced for for about about11 km areas areas with with poor poor exposure, exposure. units may may be be extrusive extrusive basalt flows or ash ash that that incorporated incorporatedclasts clasts The breccia units The perfectly during eruption. eruption. Features suggestive of of an extrusive extrusive origin origin include: include: 1) perfectly concordant contacts sediments and concordant contacts between breccias and thinly laminated sediments and aa lack lack of any observed 2)strong strong lithologic lithologic contrast contrast between between the the breccias breccias observed cross-cutting cross-cuttingrelationships; relationships; 2) and undoubtedly undoubtedly intrusive intrusive metadiabase metadiabase exposed exposed in the the same same outcrop; outcrop; 3) 3)common common amygdular amygdular textures textures in in the the breccias breccias that are are absent absent in nearby nearby metadiabase; metadiabase; and and 4) 4)rare rare areas areas of rubbly rubbly matrix matrix that that resemble resemble pyroclastic pyroclastic textures. Alternatively Alternativelythe thebreccias brecaas may may be be related relatedto tothe themauic mafic sill, which could could have have been been emplaced sediments. Evidence consistent emplaced at at aa shallow shallow level into wet, semiconsolidated sediments. 69 �r — MAFIC MAlRCt El BRECCIA Br '9 BRECCIA IN IN AA MAFIC MATRIX Md Br —— — META DIABASE ——— c 50i Mg —— META GABBRO 0 ——— Mg / fl ci E a GIF —— — WAVY-BANDED WAVY-BANDED GRANULAR IRON FORMAT10 FORMATION GRANULAR ® FJELDSTOPS @ FIELDSTOPS GIP —— LAMINATED SILICATE SIUCATE LAMINATED IRONFORMATION FORMATION IRON — GIF 45 -" 5 — 0 0 0 OUTCROP 0 OUTCROPAREAS AREAS X mn 10 50 IXMm STRIKE AND AND DIP DIP STRIKE OF BEDDING OFBEDDING 'F # GEOLOGIC CONTACT CONTACT GEOLOGIC Fig. 4-2. area sshowing outcrops and and geologic geologic 4-2. Detailed map of the Atkins Lake area Fig. h o w i n g outcrops among iron-formation, iron-formation,bbreccia diabase and and gabbro. relationships among relationships r e c c i a uunits, n i t s , diabase gabbro. Unpublished map Unpublished mapprepared preparedby byKiasner Klasnerand andLaBerge. LaBerge. I I I I I I I I I I I 70 I I I I �with with an an intrusive intrusiveorigin originincludes: includes:1)1)occurrence occurrenceof of aa breccia breccia zone zone both both above above and and below below the metadiabase metadiabasesill sill (although (althoughthe thelower lowerzone zoneisis separated separatedfrom fromthe thesill sillby by aa thin thinseam seamof of iron-formation); War (initially lithified) lithified) and iron-formation);and and2) 2)incorporation incorporationinto intothe thebreccias brecciasof of tab tabular bent bent (initially (initiallyunlithified) unlithified)blocks blocks of of the the same same composition. composition. Neither Neither of of the the above above interpretations interpretationsseems seems to to explain explain all all observed observed relationships, relationships, and the the origin origin of of the the breccia breccia units thus thus remains enigmatic. An An especially especially problematic feature feature is that that nearly nearly all all of of the the clasts clasts are are exotic exotic and are not composed of immediately surrounding surroundingiron-formation, iron-formation, but but most mostclosely closely resemble resemble banded argillite argillite of of the the lower lower part part of of the the underlying underlyingPalms PalmsFormation. Formation. j STOP 2: 2: Granite Graniteof of the theMellen Mellenintrusive intrusivecomplex complex(Fig. (Fig.4-1). 4-1). The The metadiabase and iron-formation seen in Stop 4-1 are intruded by by several several dikes probably probably are offshoots offshoots of of a small granite body small granitic dikes. dikes. These These dikes in the open woods south of exposed in several outcrops east of Atkins Lake, Lake, in of Forest Forest exposed Service Road Road 379. 379. The granite is pink and and white, white, with with aa mediummedium-to tocoarse-grained coarse-grained minerals are potassium equigranular to porphyritic porphyritic texture. texture. Principal Principal minerals potassium feldspar, feldspar, plagioclase, biotite, and and quartz. The plagioclase, The granite granite intrudes intrudesEarly Early Proterozoic Proterozoic metasediments metasediments equigranularbiotite, of the Ironwood of metamorphic effects effects and and shearing shearing within within of Ironwood Iron-formation; Iron-formation; the lack of the granite suggests it is in age. age. The is Middle Middle Proterozoic Proterozoic in The granite granite is is very very similar similar in in appearance to appearance to the thewell-known well-knownMellen Mellen granite, granite, aaphase phaseof of the theMellen Mellen intrusive intrusivecomplex, complex, which is locally exposed over a large area more than 20 km to the northeast northeast of of this this locality. locality. intrusive complex is made up In addition addition to to this this small small granite granite body, body, the the Mellen Mellen intrusive of two large, intrusion and of large, layered layered gabbroic gabbroic bodies, the Potato River intrusion and the theMineral MineralLake Lake intrusion (Stop intrusion (Stop 44), 44), and andseveral severalrelated relatedigneous igneousbodies bodies including including the the Mellen Mellen granite, granite, the peridotitic Rearing peridotitic Rearing Pond Pond intrusion, intrusion,and andaaseries seriesof of gabbro gabbro and and granophyre granophyresills sills(Stop (Stop445). A Agranophyre granophyreofofthe theMineral MineralLake Lakeintrusion intrusionhas hasa aU-Pb U-Pbzircon zirconage ageofof1102.0 1102.0±Â2.8 2.8 Ma Ma and brecciates gabbro gabbro (Zartman and others, others, 1995). 1995). The Mellen granite, which intrudes and (Zartman of the Mineral Lake intrusion, has an an indistinguishable indistinguishableU-Pb U-Pb zircon age (within (withinerror) error)of ± 1.4 Ma Ma (Zartman (Zartman and 1100.9 andothers, others,1995). 1995). 1100.9 pyroxene hornfels 3. Siemens STOP 3. Siemens Creek Creek Volcanics Volcanics ---pyroxene homfels and and granophyre granophyre(Fig. (Fig.4-1). 4-1). Volcanics,the thelowermost lowermost unit unit of of the the Powder Powder Mill Group, is The Siemens Creek Volcanics, Wisconsin. It consists consists of a the oldest volcanic unit in the Midcontinent rift in northern Wisconsin. sequence erupted as as relatively relatively thin thin flows. flows. The TheMarenisco-Atkins Marenisco-AtkinsLake Lake sequence of flood basalts erupted fault bounds the the Keweenawan Keweenawan rocks rocks in this area area with with Keweenawan Keweenawan rocks thrust I 71 �I I I I p I I I I I I I I I extension of the larger intrusion extension intrusion to to the the east. east. The Therock rockconsists consistsof of mediummedium-to to coarsecoarsegrained grained plagioclase, plagioclase, pyroxene, and and magnetite, although although minerals minerals in in the the gabbro gabbro typically typically are altered. Because Because pyroxene pyroxene and and magnetite magnetite are are more more resistant resistant than thanplagioclase plagioclase to to weathering, a hackley hackley surface has developed on the outcrop, outcrop, with with knobs knobs of of mafic mafic minerals minerals prominent. prominent. STOP GranophyreofofLong LongMile MileLookout Lookout(Fig. (Fig.4-1). 4-1). STOP 5. Granophyre upper part The upper part of of the theMineral MineralLake Lake intrusion intrusion becomes becomes increasingly Fe-rich with the development development of ferrogabbro and granophyre. Seifert Seifert and and others others(1992) (1992) determined that intrusions associated anorthosite formed from that felsic intrusions associated with with the the Mineral Lake gabbroic anorthosite evolved mantle magmas that intruded along along older, mafic intrusive bodies and early with further crystal fractionation occurring occurringin in place. place. The granophyre granophyre at volcanics, with at this this stop stop is is an an offshoot offshoot from the upper upper part partof of the theMineral Mineral Lake Lake intrusion, intrusion, one one of of several several thin thin granophyric granophyric sills that interfinger with gabbroic sills in the western part part of of the theMellen Mellen intrusive complex. Granophyre exposed exposed in in the small hill of complex. Granophyre of Long Long Mile Mile Lookout Lookout typically typically is pink, pink, finefine- to to medium-grained, medium-grained, and contains contains small small phenocrysts phenocrysts of of plagioclase in aa graphic-textured of potassium feldspar and quartz. The plagioclase graphic-textured matrix matrix of potassium feldspar quartz. The granophyre typically weathers weathers brick red granophyre red because because of the presence presence of hematite. hematite. Basalt and andbrecciated brecuatedflow flowtop, top,lower lowerKallander KallanderCreek CreekVolcanics Volcanics(Fig. (Fig.4-3). 4-3). STOP 6. Basalt The Volcanics consists consistsofof aa sequence sequence of of basalt, basalt, andesite, and The Kallander Creek Volcanics of flood basalts, similar to the rhyolite. The Thelower lowerKallander KallanderCreek CreekVolcanics Volcanics consists of Siemens Creek Creek Volcanics, Volcanics,but but the the upper upper Kallander Creek may may be an Siemens Kallander Creek an extrusive extrusive equivalent equivalentto to the the Mellen Mellen intrusive intrusivecomplex. complex. AAwedge wedgeof of the theKallander KallanderCreek CreekVolcanics, Volcanics, striking and dipping dipping to the northwest, striking northeast-southwest northeast-southwest and northwest, occurs occurs between the Marinesco-Atkins Lake Lake fault to to the south, the Lake Lake Owen Owen fault fault to to the the north, north, and the Marinesco-Atkins Mineral Lake intrusion intrusion to the the east. Largely Largelyunaltered unalteredvolcanics volcanicsof of the the Kallander KallanderCreek Creek can can be traced into into thin thin bands bandsof of metavolcanic metavolcanic rocks within the the Mineral Lake Lake intrusion, intrusion, caught up between thin thin sills sills of of gabbro gabbro and and granophyre, granophyre, attesting attesting to to aacomplicated complicated history eruption and and magma history of of volcanic eruption magma emplacement. emplacement. At this stop stop aabasalt basaltflow flownear nearthe thebase baseofofthe theKallander KallanderCreek CreekVolcanics Volcanics isis exposed, including a thick flow top-breccia. top-breccia. The basalt varies from massive to sparsely exposed, including sparsely amygdular, and and isis metamorphosed metamorphosedto toan anassemblage assemblageof of hornblende-epidote-biotitehornblende-epidote-biotitechiorite-plagioclase. breccia consists consists of of angular fragments of highly chlorite-plagioclase. The flow-top breccia highly fragmentsare are mostly mostly aa few few centimeters centimeters in in diameter diameter but amygdular basalt. Breccia Breccia fragments range Arnygdulesmainly mainly comprise quartz and epidote epidote with with minor range up up to to about about 11meter. Amygdules �I i-—-, — /&aHanai Vo - iI - y- -' o / - - 45' C- - - — -9-4r /J '-t v ptvnt/Crflk - I I —v --0 DavisLake xna2- — ç - — —— - Th — ans' ---\ f i: ste T 'N - C— ---1- - -- rt-_ - 2 - - - iemertsCreel(Votcanics 'LakeLizzie ci l 0 - "—HvM€sO-- - I 2 3 4 5 6 7 FEET 5 o KILOMETER 7 - Figure 4-3. Part Part of of the the Grand Grand View View 7 1/2' Figure 112' quadrangle quadrangle showing showing general general geology 8, and and 9. geology and and the the locations locations of of field field trip trip stops 6, 7, 8, u �I I I I I I I I I I I I I I I I I K-feldspar K-feldsparand and very verysparse sparsesulfide sulfideminerals. minerals.Locally, Locally,vesicles vesicles are are exceptionally large, as and some are incompletely filled filled with with secondary secondary minerals, minerals, leaving leaving open open much as 10 cm, and spaces. spaces. The matrix of the the flow flow top top breccia breccia is is aa very very fine-grained fine-grained clastic clastic rock, rock, now now metamorphosed metamorphosedto to chert-like chert-like material, material, although although clastic clastic textures are readily seen seen in thin thin secti on. Locally the matrix is finely laminated parallel to the orientation section. orientation of the the flow, flow, even though the the matrix matrix isis only only thin thinseams seamsdeposited deposited between between the the clast-supported clast-supported breccia. In In places places (best (bestseen seen in other outcrops) outcrops) the laminations laminations are highly contorted. contorted. We interpret this silty silty matrix to be wind-blown dust that rapidly rapidly settled settled onto onto basalt flows while they were still molten and moving, becoming incorporated incorporated into open spaces in flow top breccias. the sudden sudden eruption of breccias. Under Under some some climatic climatic conditions the of flood basalt basalt may have have generated generated intense wind wind and and dust dust storms, storms, which which quickly quickly deposited deposited aa layer layer of of dust dust over over the the erupting eruptingflow flow. A thin basalt dike cuts cuts the the basalt basalt flow flow near the northeast end end of of the the outcrop. outcrop. Field measurements of Field of magnetic magnetic polarity indicate that the basalt basalt flow flow isisreversely reversely elsewhere. The polarized, consistent with results results for for the the Kallander Kallander Creek Creek Volcanics Volcanics elsewhere. The dike has normal polarity, and possibly was emplaced during during the later eruption of the normally polarized normally polarizedChengwatana ChengwatanaVolcanics. Volcanics. STOP (Fig. Picritein inthe theSiemens SiemensCreek CreekVolcanics Volca~cs (Fig.4-3). 4-3). STOP 7: Picrite This stop is out out of of stratigraphic stratigraphic sequence, sequence, but the the significance significance of the outcrops outcrops makes it notable. The Thesmall smalloutcrop outaopjust just off off County County Road Road D, D, east east of of Lake Lake Knotting, Knotting, shows shows basalt basalt flows flowswithin withinthe thelowest lowestexposed exposedunit unitof of the theSiemens SiemensCreek CreekVolcanics Volcanics in in the the region. Immediately Immediatelytotothe thesouth, south,Keweenawan Keweenawanintrusive intrusiverocks rocks separate separatethe theflows flowsfrom from from this outcrop is the Marenisco-Atkins Lake fault. A A sample sample of these flows collected from 16.9 wt %; 0.72) and to date picritic (MgO picritic (MgO = 1 6.9 wt %; Mg# = = 0.72) date represents represents the the only only Keweenawan Keweenawan picrite identified on the south south shore shore of of western western Lake Lake Superior. Typically Typically the the lower lower member member of of the theSiemens SiemensCreek Creek Formation Formationhas hassubstantially substantiallylower lowerAl203 A1203(8(8to to<13 c13wt wt%) %) than any other Keweenawan elementpatterns patterns((Ce/Ybg and steeper rare earth element ce~/Yb =~ 15) than basalts. This well-documented picrites Thispicrite picriteisis different differentin in composition composition from the welldocumented picrites in the ICeweenawan section section at at Mamainse Point in eastern Keweenawan eastern Lake Lake Superior Superior (Berg (Berg and and Klewin, Klewin, Chemical modelling modelling suggests suggests that that the picritic composition sampled at this 1988). 1988). Chemical this outcrop represents an uncontaminated small-degree partial melt of the mantle plume outaop represents an uncontaminated small-degree mantle plume postulated to have postulated have produced produced the thevoluminous voluminous magmatism magmatism associated associated with the the Midcontinent rift. c Midcontinent rift. 75 75 �a STOP 8. STOP 8. Conglomerate and and rhyolite rhyolite of of the the Kallander Kallander Creek Creek Volcanics Volcanics at 'Davis 'Davis Hill' Hill' (Fig. (Fig.4-3). 4-3). The middle portion portion of of the theKallander Kallander Creek Creek Volcanics Volcanics in the the Lake Lake Namekagon Namekagon area mainly comprised comprised conglomerate conglomerate and rhyolite with subordinate subordinate amounts amountsof of basalt. basalt. Exposures at this stop of the the unit. unit. From stop illustrate illustrate the the lithologic variations of From Forest Forest Service 213, walk walk northward northward over the prominent Road 213, prominent bill hill (informally (informally known as as Davis Davis Hill Hill in older reports) immediately north of the road. The The best best exposures exposures of conglomerate are of the hill hill and along the the north slope. slope. Outcrops high on the western slope of Outcrops are are poorly poorly sorted and and crudely crudelybedded beddedvolcanogenic volcanogenic conglomerate conglomerate containing containing minor sandstone sandstone interbeds. Clasts Clastsof of cobble cobble to to boulder size are mostly rounded to subrounded subroundedrhyolite, rhyolite, and lesser basalt and and andesite. andesite. Some Someclasts clastsconsist consist of of basalt basalt containing containing large large pink pink phenocrysts of common in in Kallander Kallander Creek Creek flows, flows, but but phenocrysts of plagioclase; plagioclase; this lithology is fairly common is very rare elsewhere is elsewhere in in the theKeweenawan Keweenawan section. section. It appears, therefore, therefore, that the the conglomerate formed through conglomerate through erosion erosion of of the slightly older lower part part of of the the Kallander Kallander Volcanics. About Creek Volcanics. Creek About aa kilometer to the east, this same conglomerate unit is cut by a tongue Ma (Zartrnan (Zartman and tongue of of the the Mineral MineralLake Lake gabbro gabbrothat thatwas wasemplaced emplacedatat1102.0 1102.0±k 2.8 Ma and others, 1995), which which places places aa minimum minimum age age on on deposition deposition of ofthe the conglomerate. conglomerate. Cement Cement others, in the conglomerate of epidote and quartz, quartz, suggesting conglomerateis is mostly a mixture of suggesting that that relatively relatively high-temperature fluids high-temperature fluids permeated permeated this this part part of of the the section. section. AAlittle little copper copperstaining stainingcan can be seen rarely, but we have not identified any primary copper minerals. Continue walking northward for a few hundred meters to a prominent bedrock Continue exposed a rhyolite unit unit about 20 m thick. The knob. Along the south knob. southface face of this knob is exposed The rhyolite is purplish, phyric, and and mostly mostly massive. massive. In a few places near the purplish, plagioclase plagioclase phyric, base of the hill, faint outlines outlines of flattened pumiceous fragments fragments can be seen, seen, indicating indicating that the the rhyolite rhyolite probably probably is is aa welded welded tuff. tuff. The Theremainder remainderof of the theknob knobcontains containsgood good exposures of typical conglomerate. exposures conglomerate. From the the top of view to to the the north north can can be be seen. seen. The From of the knob a panoramic panoramic view The prominent prominent east-west east-westridge ridgeabout aboutaakilometer kilometerdistant distantisisunderlain underlainby byophitic ophiticbasalt basaltflows flows of the Chengwatana whichwill willbe beexamined examinedatatthe the next next stop. stop. The of Chengwatana Volcan.ics, Volcanics, which The Lake Lake Owen fault lies just south south of of the the ridge ridge and andhas hasthrust thrustthe theChengwatana ChengwatanaVolcanics Volcanics southward over southward overthe theKallander KallanderCreek CreekVolcanics. Volcanics. 9. Amygdaloidal STOP 9. Amygdaloidalophitic ophiticbasalt basaltflow flowin inChengwatana ChengwatanaVolcanics Volcanics(Fig. (Fig.4-3). 4-3). The Chengwatana Chengwatana Volcanics Volcanics records the main stage stage of flood-basalt volcanism of Basalts erupted erupted as a thick the Midcontinent thick series series of of Midcontinent rift rift in innorthern northernWisconsin. Wisconsin. Basalts subaerial flows into a subsiding central central graben. graben. Reverse Reverse faulting during a regional regional 76 I j I I fl p Ii �I I I I I I I I I I I I I I I I N. N 7 I - \\.. 1r MILE Figure 4-4. Parts of the Drumrnond and Upper Eau Claire Lake 7 112' Figure 4-4. Parts quadrangles showing geology and the location of field trip stop 10. of thegeneral Drummonä Upper Eau Claire Lake 7 1/2' quadrangles showing general geologyand and the location of field trip stop 10. 77 �compressional event inverted the the graben, graben, forming forming the the St. St. Croix horst, which which contains contains compressional Syncline. On Onthe thenorth northlimb limbof of the thehorst, horst,the theChengwatana ChengwatanaVolcanics Volcanicsare are the Ashland Syncline. along the the Douglas Douglas fault faultover over sediments sediments of of the the yourtger younger Bayfield Bayfield Group, while thrust along the southern southernlimb limbthe theLake Lake Owen Owen fault faultthrusts thrustsyounger youngerChengwatana ChengwatanaVolcanics Volcanics along the over over older olderKallander KallanderCreek CreekVolcanics. Volcanics. this stop stop flows flows of the upper upper Chengwatana Chengwatana Volcanics Volcanics are exposed along along aa steep steep At this The Lake Lake Owen Owen fault, fault, probably at the the base base of of the the bluff, bluff, cuts cuts up up south-facing bluff. bluff. The section so that the are not exposed here. The the lower lower Chengwatana Chengwatana Volcanics Volcanics are Theflows flowsare are Severalamygdular amygdular thick, monotonous ophitic basalts, typical typical of of this this part part of of the unit. Several variety of of secondary secondaryminerals, minerals, are well well exposed. exposed. Amygdules Amygdulescomprise comprise aa variety flow tops are including including quartz quartz and and epidote. epidote. STOP 10. 10. Ophitic near the top of of the Chengwatana Ophitic basalt and interfiow interflow conglomerate near Chengwatana Volcanics (Fig. 4-4). 44). These exposures upper flows, exposures show what what is is certainly certainly one of of the upper flows, and and may may be be the the uppermost flow, flow, of of the theChengwatana ChengwatanaVolcanics Volcanics and and an aninterfiow interflowconglomerate. conglomerate. Immediately north north of of the the road road are arelow lowoutcrops outcropsof of coarse coarse volcanogenic volcanogenic conglomerate and interbedded 30' to the the north. north. The conglomerate conglomerate is is interbedded sandstone sandstone that dip 20 20 -- 30° composed principally of of rhyolite rhyolite clasts. clasts. Cement Cement in the conglomerate conglomerate and sandstone sandstone varies from from calcite to epidote plus quartz, indicating that even in in this this stratigraphically stratigraphically high part part of of the thevolcanic volcanic section, section, relatively high-temperature alteration alteration has produced produced quartz-epidote quartz-epidoteassemblages. assemblages. Immediately to the north of of the the conglomerate conglomerate outcrops, along a low ridge, is is exposed of many many flows flows in in the the upper upper part of exposed coarse-grained ophitic ophitic basalt. This This is typical of of the Chengwatana predominate. Rocks ChengwatanaVolcanics Volcanics where where thick ophitic flows predominate. Rocksof of aasimilar similar type are m farther north. Whether are exposed exposed in in aa series series of of low outcrops for about 100 m Whether these outcrops are the same flows is is unknown. unknown. Magnetic same flow or additional flows Magnetic maps maps suggest suggest that that the thecontact contactwith with the theoverlying overlying Copper Copper Harbor Harbor Conglomerate Conglomeratelies lies just north north of of these outcrops, and that that the the featureless featureless sand plain to the north is underlain by the Copper Copper Harbor. Harbor . 78 �I I REFERENCES REFERENCES I I I I I I I I I I I I I I I I I Berg, J. H., H., and Klewin, High-MgOlavas lavas from from the the Keweenawan Keweenawan midcontinent midcontinent rift near Berg, 1. Klewin, K. K. W., 1988, 1988, High-MgO 16,p.p.1003-1006. 1003-1006. Mamainse Point, Point, Ontario: Ontario:Geology, Geology,v.v.16, Cannon, W. W. F., F., Nicholson, Nicholson, S. S. W., W., Zartman, Zartman, R. R. E., E., and and Peterman, Peterman, Z. Z. E., E., 1993, 1993, The The Kallander KallanderCreek Creek Volcanics -- a remnant of a Keweenawan Keweenawan central central volcano centered near Mellen, Mellen, Wisconsin [abstract]: Institute 39,p.p.20-21. 20-21. Instituteon onLake LakeSuperior SuperiorGeology GeologyAbstracts, Abstracts,v.v.39, Feher, Vesiclesand andbreccia brecciadue dueto to injection injectionofofmafic maficmagma magmainto into partially partially lithified Feher, L. and Flood, T., 1995, 1995, Vesicles sediments of the NWWisconsin Wisconsin sediments the early early Proterozoic Proterozoic Ironwood IronwoodIron-formation, Iron-formation,western westernGogebic GogebicRange, Range,NW [abstract]: Institute 41,p.p.13-15. 13-15. [abstract]: Instituteon onLake LakeSuperior SuperiorGeology GeologyAbstracts Abstractsv.v.41, M.W., 1954, 1954,Petrogenesis Petrogenesisof ofaa gabbro-granophyre gabbro-granophyre complex in northern Leighton, M.W., northern Wisconsin: Wisconsin:Geological Geological Society of America America Bulletin, Bulletin,v.v.65, 65,p. p.401-442. 401-442. Olmsted, J. Petrology of of the Mineral Lake intrusion, northwestern Origin of J. F., F., 1969, 1969, Petrology northwesternWisconsin, Wisconsin, in in Origin anorthosite and related rocks, Isachsen, Y. W. (ed.), New York State Museum and Science anorthosite and related rocks, Isachsen, Y. W. (4.). New York State Museum and ScienceService Service pp. 149-161. Memoir 18, pp. 149-161. Seifert, E., Peterman, Peterman, Z. E., and Thieben, F., 1992, 1992,Possible Possiblecrustal crustal contamination contamination of Midcontinent Seifert, K. E., E.,and Thieben, S. E., MidcontinentRift Rift igneous rocks: examples from the Mineral Lake intrusions, Wisconsin: Canadian examples from the Mineral Wisconsin: Canadian Journal Journal of Earth Sciences, v. 29, p. 1140-1153. p. 1140-1153. Sciences, Zartnian, RE., Cannon, U-Th-Pbages agesof ofsome someKeweenawan Keweenawan rocks from Zartman, R.E.,Cannon,W.F., W.F., and andNicholson, Nicholson,S.W., S.W.,1995, 1995, U-Th-Pb western Lake Superior, northwestern Wisconsin, and east-central Minnesota western Lake Superior, northwestern Wisconsin, and east-central Minnesota [abstracfl: [abstract]: Proceedings Proceedings of International Field Conference and Symposium of International Geologic of International Field Conference and Symposium of International Geologic Correlation Correlation Program Program Project 336, Duluth, Duluth, MN, MN,p.p.217-218. 217-218. Project �-- I I I I I I I I I I I I I I I I I I UIDEFOR FOR FIELD FIELDTRIP GUIDE TRIP # #55 LAKENAMEKAGON NAMEKAGON ANDPENOKEE PENOKEEGAP GAPAREAS, AREAS, LAKE AND WEST GOGEBIC RANGE, WISCONSIN �HELD TRIP FIELD TRIP #5 LAKE NAMEKAGON NAMEKAGON AND PENOKEE PENOKEE GAP GAP AREAS, AREAS, WEST GOGEBIC GOGEBIC RANGE, RANGE, WISCONSIN WISCONSIN by John S. Kiasner, Klasner, Department Department of of Geology, Geology, One University University Circle, Circle, Western Illinois Illinois University, Macomb, Illinois 61455, and Gene L. LaBerge, Department of Geology, 61455, LaBerge, Geology, Macomb, Oshkosh, Oshkosh, Oshkosh, Wisconsin Wisconsin54901 54901 University of Wisconsin Wisconsin -- Oshkosh, INTRODUCTION INTRODUCTION This field guide This guide focuses focuses on on two two regions regions of of the theWestern WesternGogebic GogebicRange: Range: Atkins Lake in the Lake Lake Naniekagon Namekagon area and and Penokee Penokee Gap near near Mellen, Mellen, Wisconsin Wisconsin Gogebic Range Range is is approximately approximately 120 120 kilometers kilometers long long and (Overview Fig. Fig. 1). 1). The Gogebic consists mainly mainly of consists of aa northwest-dipping northwest-dipping sequence sequence of of Early Early Proterozoic Proterozoic ironironrocks and and detrital sediments sandwiched between formation, interbedded volcanic volcanic rocks Archean basement rocks rocks on on the southeast Archean crystalline crystalline basement southeast and and Middle MiddleProterozoic Proterozoic (Keweenawan) volcanicand and sedimentary sedimentary strata strata of of the Midcontinent (Keweenawan) volcanic Midcontinent Rift on the the northwest. northwest. of the Gogebic Range Range that that lies west of of Mineral Lake Lake provides the The section of westernmost exposures exposures of of Early rocks of of the Marquette westernmost Early Proterozoic Proterozoic rocks Marquette Range Range Supergroup (Cannon and and Gair, Gair, 1970). 1970). Unlike Unlike the eastern eastern end end of of the theGogebic Gogebic Range Range where the Sunday Sunday Lake Lake Quartzite Quartzite underlies underlies the the dolomite, dolomite, the the Bad Bad River River Dolomite Dolomite at the western end end of of the the range rangerests restsdirectly directly on onArchean Archean gneisses gneisses and and volcanic volcanic rocks. rocks. In the Atkins Atkins Lake Lake area, the dolomite dolomite is aa 300 300 m thick gray dolomitic dolomitic marble with abundant lenses and beds dolomite thins thins towards towards the the east and isis beds of of chert. chert. The The dolomite Creek (east (east of discontinuously exposed. exposed. Near Near Ballou Ballou Creek of Mellen) Mellen) it is mostly mostly aa variegated chert breccia cemented by by chert chert and and (or) quartz, locally variegated breccia cemented locally with lenses of of dolomite near the base. This Thislithology lithology is interpreted as a residuum residuum of of chert chert nodules nodules dolomite and beds formed formed as as the the dolomite dolomite was dissolved during the weathering interval prior to deposition deposition of of the theunconformably unconformablyoverlying overlying Palms Palms Formation. Formation. Locally, magnetite and and hematite hematite concentrations concentrationsare arepresent present at at the top of Locally, magnetite of the the shafts were were sunk sunk on some of these magnetite-rich chert chert breccia. breccia. Exploration shafts magnetite-rich zones Penokee Gap and on the near the eastern eastern flank flank of of Mt. Mt. Whittlesey Whittlesey during during early early near Penokee Gap and exploration for for iron iron ores ores near near the turn of exploration of the the century. century. The occurrence of these these in conglomerate conglomerateatat the the top of the magnetite concentrations concentrations in the Bad Bad River River Dolomite Dolomite magnetite suggests that they are are paleo-placer paleo-placer deposits produced by streams streams flowing flowing on on the the prepre- I 83 �Palms erosion surface. Alternatively, Alternatively, they they may be of of hydrothermal hydrothermal or or metamorphic metamorphic origin. origin. The Palms Formation, which is is well well exposed exposed at at Penokee Penokee Gap Gap and at Atkins Formation, which Atkins Lake in the Lake area, is the basal unit of the Lake Namekagon area, the Menominee Menominee Group and unconformably overlies of a thinly bedded overlies the theBad Bad River River Dolomite. Dolomite. It is comprised of argillaceous lower unit unit and a thickly relatively pure, pure, quartzite quartzite upper unit. argillaceous lower thickly bedded, relatively unit. Ojakangas (1983) similarly similarly described described the the Palms Palms elsewhere elsewhere on on the Gogebic Range and suggested that the the Palms Palms Formation Formation was deposited in a tidal-flat environment in a transgressing transgressing sea. sea. Near Penokee grades across across 1 1 to to 2 m Penokee Gap, the uppermost Palms Formation Formation grades into the Here, the the base base of the overlying overlyingIronwood IronwoodIron-formation. Iron-formation. Here, of the Ironwood Ironwood has thin (3 Elsewhere aa one one meter meter thick thick zone of stromatolitic (3m) m) conglomerate conglomerate zone. zone. Elsewhere stromatolitic jasper occurs Detailed mapping mapping and and drill core occurs at at the the base base of ofthe theiron-formation. iron-formation. Detailed core analysis analysis by by U.S. U.S.Steel Steel geologists geologists in in the the late late1950's, 1950's, based based on onwork workof ofHotchlciss Hotchkiss(1919), (1919), subdivided the eastward from from Penokee Penokee Gap Gap into five the Ironwood Ironwood Iron-formation Iron-formation eastward five units. that alternating alternating units units of granular, units. Although Although our mapping indicates indicates that granular, wavy bedded and are present present west west of of Penokee Gap, it also and laminated laminated iron-formation iron-formation are Penokee Gap, also indicates that, except for the first west of of the gap, the first few few hills of iron-formation iron-formation west the five-fold division of of U. U. S. S. Steel Steeldoes doesnot notextend extendwestward. westward. In the the Lake Lake Namekagon Namekagon area the the Ironwood Ironwood hon-formation Iron-formation contains contains interbedded interbedded units of of granular, granular, wavywavy- bedded bedded and and laminated laminated cherty chertymagnetic magnetic iron-formation, iron-formation, similar similar to to exposures exposures elsewhere elsewhere along along the the Gogebic Gogebic Range. Range. The The iron-formation, iron-formation, however, is interbedded interbedded with with and andgrades gradeslaterally laterallyinto intomagnetic magneticand andnon-magnetic non-magnetic argillite, argillite, as as well well as asmafic mafic igneous rocks appear appear to be large sills of metadiabase igneous rocks. rocks. These igneous igneous rocks metadiabase with textures textures suggesting suggesting emplacement emplacement into into semi-consolidated semi-consolidated sediments (or (or basalt basalt flows flows interbedded just north of in the the Trapper Trapper Lake area, just of interbedded with with the the sediments). sediments). Drill Drill cores cores in Lake Lake Namekagon, Namekagon, intersected intersected granular granular and and laminated laminated magnetic magnetic iron-formation iron-formation with thin thin interbeds interbeds of of argillite, argillite, and and at atleast least 60 60 m m of of black black pyritic pyritic argillite, argillite, several several metadiabase Thus, the metadiabase sills, sills, and several several thin dikes dikes of of granite granite and and pyroxenite. pyroxenite. Thus, bonwood Ironwoodhon-formation Iron-formationgrades gradeswestward westward into intoaadeeper deeperwater, water,anoxic, anoxic, detritus-rich detritus-rich environment This is in environment with with penecontemporaneous penecontemporaneous igneous igneous activity. activity. This in marked marked contrast contrast to to the thecentral centralpart partof ofthe theGogebic GogebicRange, Range, where detrital detrital rocks rocks are are essentially essentially lacking lacking in in the the iron-formation, iron-formation, and andigneous igneousrocks rocksare arescarce. scarce. Recent work on the the east eastend end(LaBerge (LaBerge and and Ojakangas, Ojakangas, 1992; 1992; Anderson and Klasner, Klasner and and LaBerge, LaBerge, 1994A; 1994A; Klasner Kiasner et al., Klasner, 1993; 1993; LaBerge and Klasner, 1994; Klasner in press) press) and andininthe thecentral centralpart partand andwest westend end(Kiasner (Klasnerand andLaBerge, LaBerge,1994B; 1994B;LaBerge LaBerge 84 �• I I I I I I I I I I et a!., of the the Gogebic GogebicRange Rangeshows showsthat, that,inincontrast contrastto tothe the central central part, part, strata on al., 1995) of either end of of the the range range thicken thicken abruptly, abruptly, are are structurally structurally more more complex, complex, and contain contain volcanic strata interbedded with Ironwood hon-formation. Iron-formation. On Onthe theEastern EasternGogebic Gogebic Range abrupt lateral changes in stratigraphy Range stratigraphy and structure within within the the Ironwood Ironwood and interbedded rocks are are interpreted Iron-formation and interbedded volcanic volcanic rocks interpreted to indicate indicate the the development of grabens development of grabens in in an anextensional extensional tectonic tectonic environment environment (Klasner (Klasner and and on the the western western end of the LaBerge, 1994A; LaBerge and Kiasner, Klasner,1994). 1994). Likewise, Likewise, on range, deposition deposition of of detrital detrital sediments sediments(mainly (mainly argillites) argillites) and andcontemporaneous contemporaneous igneous activity also suggest a more tectonically active environment. environment. We igneous activity tectonically active We suggest suggest that these stratigraphic stratigraphic and structural structural relationships relationships indicate the development of of rift basins at both both ends ends of of the theGogebic Gogebic Range Range in aa divergent divergent tectonic tectonic regime regime during during deposition of platform platform sediments, sediments, including including iron-formation. iron-formation. The Tyler Formation overlies the Ironwood Iron-formation, and at at Penokee Penokee bedded black slate and Gap consists consists of about about 800 800 m of cyclically cyclically bedded and siltstone. siltstone.We We believe believe that the that the Tyler Tyler isis unconformable unconformable on the the Ironwood, Ironwood, as as isis the thestratigraphically stratigraphically equivalent Copps Formation in the Eastern Gogebic GogebicRange. Range. This This is is supported supported by an equivalent an outcrop of conglomeratic, sandy graywacke graywackethat that lies lies near near the the base outcrop conglomeratic, sandy base of the the Tyler Tyler Formation about 600 west of of Penokee Penokee Gap Gap along along the the north north slope of of the ridge of 600 m west of Tyler along the the contact iron-formation. Other Other remnants remnants of Tyler exposed exposed along contact with the the underlying underlying iron formation formation at Penokee Penokee Gap are are intensely intensely sheared sheared and and consist consist primarily of fine-grained quartz in an an anastomosing anastomosing matrix of opaque opaque carbonaceous carbonaceous material. In near the contact with the Inan anexposure exposureabout about22 km krn west west of of Penokee Penokee Gap, near Ironwood Iron-formation, the Tyler Tyler is is aa black, black, carbonaceous carbonaceous slate. slate. In thin thin section section the carbonaceous slate is quartz-rich with aa strongly strongly foliated foliated biotitic biotitic matrix matrix in in which which superimposed concentrically-zoned cordierite porphyroblasts porphyroblasts give give it a spotty superimposed concentrically-zoned cordierite spotty appearance. The Thecordierite cordieriteporphyroblasts porphyroblasts are arehexagonal hexagonal in in cross crosssection, section, about about 22 mm in length and 11mm mm wide wide and and display display remnants remnants of of aligned aligned mica mica flakes in their cores. cores. Farther north, north, in in a rock Farther rock cut cut along along the the railroad railroad tracks tracks that extend extend though though Penokee consistsbeds beds of of slate slate and and siltstone that show Penokee Gap, the Tyler Tyler Formation Formation consists show subtle grading from quartz-rich silt at the base base to to more more clay-rich clay-richunits unitsat at the the top. top. The The slate is carbonaceous with aligned flakes of of biotite, biotite, sericite sericite and and chlorite, chlorite, and and it also slate Although contains porphyroblasts activity was contains porphyroblasts of cordierite. cordierite. Although igneous igneous activity was depositionon on both both ends of the contemporaneous with iron-formation iron-formation deposition the Gogebic Gogebic Range, we we found no Early igneous rocks rocks within within or cutting the overlying Range, Early Proterozoic igneous overlying Tyler Formation Formation that that lies along most most of of the the Gogebic GogebicRange. Range. We We interpret the lack Tyler lack of 85 �igneous rocks within the gap between igneous rocks within the Tyler Tyler to to indicate indicate aa significant significant gap between deposition deposition of of the Ironwood the Ironwood and and Tyler Tyler Formations. Formations. In addition to to cordierite cordierite within within the the Tyler, Tyler, there are are numerous numerous other otherminerals minerals that indicate strata near that indicate that that the theEarly EarlyProterozoic Proterozoic strata near Penokee Penokee Gap Gap were were metamorphosed. Foliation metamorphosed. Foliation within the Tyler Tyler and and Palms Palms Formations, Formations, expressed expressed by by aligned aligned mica mica and and chlorite, chlorite, along along with with other other deformational deformational features features in in the the Early Early Proterozoic strata, indicate that that there Proterozoic strata, indicate there was was aaregional regional deformational deformational and and metamorphic event event in in the Penokee Gap region. region. Other porphyroblasts in the Early metamorphic Penokee Gap Proterozoic strata, strata, along with the cordierite, of a Proterozoic cordierite, however, however, suggest the occurrence of later metamorphic include garnet garnet within within the iron-formation later metamorphic event. event. These These include iron-formation and skeletal garnets in the the Tyler Tyler near near its its contact contact with with the theiron-formation, iron-formation,non-aligned non-aligned chlorite locallywithin within the the Palms Palms that that overprint chlorite porphyroblasts porphyroblasts locally overprint the the regional regional foliation, and possibly the euhedral euhedral magnetite magnetite crystals along the contact between the the Palms and Although the the origin of Palms and Bad Bad River River Formation. Formation. Although of these these metamorphic metamorphic minerals has not been studied in detail, the fact that some of of them overprint the minerals has regional deformational fabric clearly clearly indicates indicates that that they they postdate it. regional deformational fabric it. The most most obvious possibility possibility is that they they were were caused caused by by thermal thermal metamorphism metamorphism associated associated Lake Gabbro Gabbrothat thatlies liesabout about22 km km to to the the north of with intrusion of of the Mineral Mineral Lake Penokee Gap, Gap, but but further study of Penokee of metamorphism metamorphism in this region is needed needed to to fully fully confirm this. this. NOTE: Field stops at both the Atkins Lake Lake and and Penokee Gap Gap involve involve walking walking NOTE: Penokee Gap. Cap. Also, over steep, hilly terrane, especially at Penokee Also, a walk of of approximately approximately four miles is involved in in the the Penokee Penokee Cap Gap part of of this field field trip. trip. PART A: LAKE LAKE NAMEKACON NAMEKAGONAREA AREA(ATKINS (ATKINSLAKE) LAKE) Numerous exposures exposures of of the Ironwood and the Numerous Ironwood Iron-formation Iron-formation and the Palms Palms Formation are present in in aa 4,000 4,000 m long northeast-trending zone from Atkins Lake Lake units are are truncated to the the Marengo Marengo River, River, where where the Early Early Proterozoic Proterozoic units truncated by the the Marenisco-Atkins Lake fault The Palms Palms Formation Formation consists consists of of an an upper Marenisco-Atkins fault (Fig. (Fig.5-1). 5-1). The massive quartzite member and aa lower massive lower argillaceous argillaceous quartzite member, member, similar similar to to Range. (Note: exposures elsewhere on the Gogebic Gogebic Range. (Note: Due to time time limitations, limitations, we we will will The Ironwood Ironnot visit visit exposures exposures of of the the Palms Palms Formation Formation on this this trip). trip). The Ironformation consists of magnetic wavy-bedded and laminated laminated cherty cherty iron-formation iron-formation and argillite, argillite, some some of which is also also magnetic. Mafic Mafic sills sills or flows flows lie lie in in contact contact with with the of field field stops in this area, the iron-formation. iron-formation. Unusual Unusual breccia breccia units, the focus of area, are are associated with one one of of the the sills. sills. 86 H H �i_ '0% rsIIIn _j_. 0 2I) 5 L 3000 ——— 0 40% 5000 - -- — 70% FEET -i_: :-JnT] 6000 - MILE I +--: I—--4 I I 0 I f:j T-==-_=___ - KIt OMFTLR Figure 5-1. Part of the Grand View 7 1/2' quadrangle showing general geology and location of field trip stop A. 10% irCfleEiI jTV. Lt — :n—-i —- - I a— �The The breccia units contain contain angular angular to to sub-rounded sub-rounded clasts, clasts, up up to toseveral severalmeters meters in in length, length,of of banded bandedsiliceous siliceoussedimentary sedimentaryrocks rocks in in aa matrix matrix of of fine-grained, fine-grained,massive massive igneous igneous rock. rock. The Theigneous igneousrock rock isislocally locally fine-grained fine-grained near the margins margins where the the breccia breccia occurs but coarse-grained coarse-grained in the interior of of the igneous body, where it ranges ranges from from fine-grained fine-grained diabase diabase to tomedium-grained medium-grained gabbro gabbro (Feher (Feherand andFlood, Flood,1995). 1995). However, However, the the mineralogy mineralogy and, and, to tosome someextent, extent, the the textures textures have havebeen beenmodified modifiedby by Middle Clasts within the the breccia breccia are are Middle Proterozoic Proterozoic(Keweenawan) (Keweenawan)metamorphism. metamorphism. Clasts mainly mainly siliceous siliceous argillite: a few are magnetic. magnetic. Most Most clasts ciasts are are long, long, tabular tabular bodies. bodies. Bent or folded folded clasts clasts are are not not uncommon, uncommon, suggesting suggesting that the the sediments sediments were wereonly only semi-lithified semi-lithified when incorporated in the the breccia. breccia. The Theargillite argilliteconsists consistsof of alternating alternating layers layers of of recrystallized recrystallized quartz, quartz, fine-grained fine-grained chlorite, biotite or actinolite, garnet, and variable variable amounts amountsof of magnetite magnetite(Feher (Feher and and Flood, Flood, 1995). 1995). The The matrix matrix is is aa fine-grained fine-grained mafic rock with conspicuous conspicuous vesicles around some clasts. The Thematrix matrixisiscomposed composed of medium-grained medium-grained amphiboles amphiboles and plagioclase plagioclase laths, laths, probably probably aa relict relict ophitic ophitic phenocrysts are present texture texture (Feher (Feher and andFlood, Flood,1995). 1995). Plagioclase Plagioclase phenocrysts present locally. locally. Preliminary data indicates Preliminary geochemical geochemical data indicates a tholeiitic tholeiitic composition composition for the the matrix matrix (Feher (Feher and andFlood, Flood,1995). 1995). The origin of the the breccia breccia is problematic. problematic. The The breccia is a not not aa debris debrisflow flow because the matrix matrix is is igneous igneous and and not not fragmental: fragmental: the clasts appear to have have been been incorporated incorporated into into aamagma. magma. The Thepresence presenceof of angular, angular,and andin inplaces placesdeformed, deformed,blocks blocks of country country rock rock within within aamagma magma argues arguesfor forintrusion intrusioninto intosemi-consolidated semi-consolidated sediments at aa shallow shallow depth. depth. The Thepresence presence of of breccia breccia at both the upper upper and andlower lower margins of the igneous body argues for a common origin for both breccia units, margins of the igneous body argues for a common origin for both breccia units, most most likely the intrusion intrusion of of aa sill sill into into wet, wet, unconsolidated unconsolidated sediments, forming, perhaps, a peperite-like peperite-like body. body. Alternatively, the breccia may represent an extrusive breccia and mafic rocks may extrusive basaltic basaltic flow of the sediments flow that that incorporated incorporated blocks blocks of sediments over over which which it flowed, flowed, with with subsequent concordant concordant intrusion of aa mafic mafic sill separating the basalt basalt flow flow into into two two for this this origin origin are: are: 1) 1) perfectly perfectly concordant contacts contacts with with parts. Features arguing for parts. thinly laminated at several and the lack laminated sediments sediments exposed exposed at several outcrops, outcrops, and lack of of any any observed cross-cutting 2) marked marked lithologic lithologic contrast contrast between between the the cross-cutting contacts; contacts; and 2) breccia breccia and undoubtedly undoubtedly intrusive intrusivesills sillsofofcoarse-grained, coarse-grained,massive, massive,inclusion-free inclusion-free metadiabase within within the thesame sameoutcrops. outcrops. Regardless of whether whether the breccias breccias are are the the result result of Regardless of of an extrusive extrusive or or aa very very shallow intrusive igneous igneous event, event, they they indicate indicate that that igneous igneous activity activity was wasoccurring occurring contemporaneously with iron-formation iron-formationdeposition depositionininthe the western western part part of contemporaneously with of the the 88 �I Gogebic Range. The Gogebic Range. The situation situation is is similar similar to that of of the the eastern eastern part part of of the the Cogebic Gogebic I Range Complex isis interlayered interlayered with with the Ironwood Range where the Emperor Emperor Volcanic Volcanic Complex Ironwood Iron-formation Iron-formation (LaBerge and Kiasner, Klasner, 1994). 1994). In both areas areas platformal platformal sediments, sediments, including the the Bad the Palms Palms Quartzite, Quartzite, and and the Sunday including Bad River River Dolomite, Dolomite, the Sunday Lake Lake Quartzite in in the east, are rocks in in the the central Quartzite are similar similar to equivalent equivalent rocks central part of of the the I I Gogebic Range. Range. Igneous becomes a significant significant feature feature during the Gogebic Igneous activity, activity, however, becomes of deposition of the on both ends of time of the Ironwood Ironwood Iron-formation Iron-formation on of the the Gogebic Gogebic Range. Whereas Whereas igneous igneous activity activityininthe the central centralpart part ofof the the range range is limited to Range. (R. G. G. Schmidt, Schmidt, personal personal communication, communication, 1995), 1995), deposition of aa few few minor minor ash ashbeds beds(R. igneous deposits on igneous on either either end endof of the theGogebic Gogebic Range Range indicate indicate aa far far more morevolcanically volcanically active environment in in these these regions. regions. I I j I I I I I I I HELD STOPS ATKINS LAKE FIELD STOPS(see (seeFigure Figure5-2) 5-2) Our mapping mappingof of the thesill silland andbreccia breccia units unitsnear nearAtkins AtkinsLake Lake(Fig. (Fig.5-3) 5-3)reveals reveals aa body with breccia units up to 20 m thick along both the upper 70 m thick igneous body breccia units upper and lower margins. margins. STOP SA-1. STOP 5A-1. This outcrop consists of layered magnetic, magnetic, greenish, greenish, actinolitic actinolitic iron-formation with metadiabase, iron-formation metadiabase, and aa breccia breccia zone with with clasts clasts of of iron-formation iron-formation Bedding orientations orientations atat this this outcrop are in aa fine-grained fine-grained metadiabase metadiabase matrix. matrix. Bedding of bedding bedding elsewhere elsewhere in in the the area area indicating consistent consistent with orientations of indicating that the and not not aa raft raft of of iron-formation iron-formation entrapped in in the the igneous igneous rock. rock. outcrop is in place and Walk northeast about 60 m to the top top of of aa hill. hill. STOP 5A-2. 5A-2. At Atthis thislocation, location, large large thin thin slabs slabs of argillite argillite lie in aa matrix matrix of of locally vesicular metadiabase. locally metadiabase. The The slabs have various various orientations: orientations: some some are are contorted and folded, and one is contorted is rolled rolled into into aa ball ball with with aacentral central layered layered portion portion surrounded by Slabs zone of of smaller smaller clasts clasts in aa metadiabase metadiabase matrix. matrix. Slabs surrounded by aa concentric concentric zone range range from a meter or more more in in length length down down to to aa centimeter centimeter or or less. less. Walk east along the crest of the hill about 90 m to a north-northwest-trending north-northwest-trending of the hill toward the valley. valley. When in the valley valley follow follow the edge of the south-southwest south-southwest for about about 60 60 m. m. STOP 5A-3. Strongly Strongly magnetic, STOP 5A-3. magnetic, wavy-bedded, wavy-bedded, cherty cherty iron-formation. iron-formation. Lenticular chert chert beds beds are up to 15 Lenticular 15 cm thick. This This bedding bedding style styleisis typical typical of of wavywavybedded bedded iron-formation iron-formationfarther farthereast eastalong alongthe theGogebic GogebicRange. Range. Walk north-northeast along edge of of hill about about 25 25 m. m. 89 �S a Br BRECCIA INA MARC MATRIX Md Br META DIABASE ———— —— METAGABBRO ———— Mg ci / 60/ OW 0-- GIF -9 LAMINATED SILICATE IRON FORMATION D WAVY-BANDED GRANULAR IRON FORMATION OlE UF —— E -9— -9 © 45 STRIKE AND DIP Ø) OF BEDDING 0 OUTCROP AREAS 0 0 10 20 X mflt 60 GEOLOGIC CONTACT 1OO$. Fig. Fig.5-2. 5-2. Detailed Detailedmap mapof ofthe theAtkins Atkins Lake Lake area area showing showing outcrops outcropsand andgeologic geologic relationships units, diabase relationships among among iron-formation, iron-formation, breccia breccia units, diabase and and gabbro. gabbro. Unpublished Unpublishedmap mapprepared preparedbybyKiasner Klasnerand andLaBerge. LaBerge. 90 �I I I I I I I t I I I STOP 5A-4. non-magnetic chert-argillite chert-argillite or or argillaceous iron5A-4. Thin-bedded, non-magnetic formation. Some boudinaged. The formation. Some cherty cherty layers appear boudinaged. The argillite argillite unit unit is is about about 50 50 m m thick and grades grades into into aa more more argillaceous argillaceous unit with less cherty layers to the the north. north. Walk northeast about about 55 55 m. STOP (UFon onFig. Fig. 5-2) 5-2)is is STOP 5A-5. 5A-5. The top top of the the argillaceous argillaceousiron-formation iron-formationlayer layer(LIP in sharp sharp contact contact with with the the overlying overlying breccia breccia unit, unit, in which which argillite argillite clasts clasts are are surrounded by by aa metabasalt metabasalt matrix. matrix. Clasts in the breccia breccia tend to to become become larger larger higher in the section section (northward (northward from the contact). Remnants Remnants of what appears appears to to be be a thin slab slab of of iron-formation iron-formation lie lie along along the the top top of of the thebreccia breccia unit unit (Br (Br on onFig. Fig. 5-2) 5-2) at at stops 55 and both stops and 6. 6. m. Walk east-southeast east-southeast about about 10 10m. STOP SA-6. Observe the the southeast southeast continuation continuation ofof the the thin slab of 5A-6. Observe of ironironSTOP formation that lies along formation along the the contact contact between between the breccia breccia on the southwest southwest and and massive metagabbro on the the northeast. northeast. Walk northeast northeast about about 50 50 m. m. STOP 5A-7. 5A-7. Massive metadiabase/metagabbro. STOP Walk northwest northwest about about 35 35 m. m. Breccia. Clasts Clasts of of mainly STOP 5A-8. 5A-8. Breccia. mainly argillite in aa vesicular vesicular metabasalt metabasalt matrix. matrix. Argillite clasts are contorted. contorted. PART B: PENOKEE GAP Penokee Penokee Gap lies lies about about3.2 3.2 km km southeast southeastof of Mellen, Mellen, Wisconsin. Wisconsin. It is a water water formed by by the Bad gap in the the Gogebic Gogebic Range Range formed Bad River River as it cuts cuts across across the the Range. Range. by a 1.6 km km walk walk south south along the railroad tracks that Easiest access to Penokee Gap is by that follow the Bad Bad River. River. The Penokee Gap area itself itself and the area just west of the gap gap (Fig. (Fig. 5-3) provide abundant data on on local local stratigraphy stratigraphy and and structure structureof of the theGogebic GogebicRange. Range. It is is important to note, however, that the entire region important however, that region was tilted tilted steeply steeply northward northward the closing tectonisni so so that all during the closing phase phase of of Middle Middle Proterozoic Proterozoic tectonism all Early Early Proterozoic and Archean structural structural orientations orientations are not original original orientations. orientations. Strata at Penokee Gap consist of Archean gneiss overlain by Early Strata Early Proterozoic Proterozoic Bad River River Dolomite, Dolomite, Palms Palms Formation Formationwith with aa thin-bedded, thin-bedded, intensely intensely sheared lower Bad unit and and aamassive massivequartzitic quartziticupper upperunit, unit,Ironwood Ironwoodhon-formation Iron-formationand andcyclicallycyclicallybedded Tyler Tyler Formation, Formation, mainly mainly consisting consisting ofof slates slates and and siltstones. A thin Middle Middle Proterozoic (Keweenawan) (Keweenawan)diabase diabase dike dike intrudes intrudes the Tyler Proterozoic Tyler Formation. Formation. More More 91 �I - TABLE11: Summary of of structural structural components and our interpretation TABLE : Summary interpretation of of the thetectonic tectonic evolution at Penokee Penokee Gap. Gap. EVENT E YmI STRUCTURAL ELEMENTS Archean gneissic foliation SA- Archean foliation - OA-- Late Archean tectonism Discrete, narrow shear zones ss Ss -- Discrete, parallel to to gneissic gneissic foliation. foliation. 0o -- Divergent tectonism associated Do with rifting rifting of of Archean Archean continent. continent. Formation of passive passive continental continental margin. So So - Flat-lying Flat-lying beds unconformably unconformably Oi-- Convergent Convergent tectonism causing thin-skinned, north-verging north-verging folding folding and thrusting. thrusting. Regional Regionalgreenschistgreenschistgrade metamorphism. metamorphism. F1 -- Folds in 5o F1 So with Li Ll fold fold axes. axes. Ji - deposited on passive continental continental margin in the Penokee Penokee Gap Gap area. area. -- Continued Continued north-verging thinthin- - Axial planar foliation. Si Sl - Axial foliation. of boudins. boudins. LB LB -- Long axes of S; -- Spaced Spaced fracture fracture foIiation. foliation. F2 F; -- Kink folds folds primarily primarilyininS1 Sl with with L2 L2 fold fold axes. axes. skinned deformation deformationcoaxial coaxial with Di. Dl. L>M -- Middle Middle Proterozoic Proterozoic rifting rifting of the continental crust and and associated associated deposition of sediments and and igneous igneous activity. activity. Formation of of the Midcontinent Midcontinent Rift. Rift. Intrusion of Mineral Lake Gabbro Gabbro and, possibly, thermal metamorphism metamorphism to form porphyroblasts at at Penokee Penokee Gap. Gap. DK- Northward Northward lilting DKtilting of Archean Tilting resulted in formation formation of of a northwest-dipping northwest-dipping monoclinal monoclinal sequence of of Early and Middle Middle Proterozoic strata strata and formation formation of of north-northwest-striking, near vertical faults, including the formation joints and fractures. formation of Sic SKjoints fractures. and Early Early Proterozoic Proterozoic crust listric thrusts thrusts during along listric compressional phase of the Middle Middle Proterozoic Proterozoic Midcontinent Rift. Rift. 92 �I I I a I I I • p information information on the Early Early Proterozoic Proterozoic stratigraphy stratigraphy at Penokee Penokee Gap Gap is is covered coveredabove above in the introduction. discussions below below summarize the structural structural introduction. Table Table 1 and the discussions observed in in the Penokee Penokee Gap Gap area area and and our interpretation and stratigraphic features observed of the tectonic tectonic events that formed formed them. them. Archean deformation (DA) resulted in in the the formation of of the now near(DA)resulted nearLate Archean vertical, easterly-striking easterly-striking gneissic gneissic foliation foliation (SA (SAon Fig. 5-3) and parallel shear shear zones zones (Ss, not shown structural fabric fabric isis not not present present in any of the (Ss, shown on onFig. Fig.5-3). 5-3). This This structural the overlying Early Proterozoic Proterozoic strata that were were unconformably unconformably deposited on on it. it. The The time of of formation of the shear zones time formation of zones is not known: known: the shears may have formed formed during the subsequent convergent convergent phase of of Early Early Proterozoic Proterozoic tectonism, but they they have a different orientation than than structural structural features features in in the the Early Early Proterozoic Proterozoic strata. strata. Initial rifting of the Archean Do was accompanied accompanied by by unconformable unconformable Initial Archean crust Do on Archean Archean gneisses. gneisses. The rift event was deposition of Early Early Proterozoic Proterozoic strata (So) (SJ) on followed by convergent convergent tectonism. tectonism. At Penokee Penokee Gap, two phases phases (Di (Dl and andD2) D2)of of recognized in the Early Early Proterozoic Proterozoicrocks. rocks. Dl Di involved thindeformation have been recognized thinskinned, north-verging north-verging overthrusting overthrusting that detached Early Proterozoic strata from skinned, from the underlying underlying Archean Archean crust, folded it, and and formed formed multiple multiple bedding-parallel bedding-parallel shear shear zones within the the Early Early Proterozoic strata. Along Along the the Gogebic Gogebic Range, west of Upson, Wisconsin, numerous numerous upward-ramping (Cannon, personal Wisconsin, upward-ramping thrust thrust faults (Cannon, personal Kiasner and LaBerge, detach Early Early Proterozoic strata communication, 1994; 1994; Klasner LaBerge, 1994B) 1994B) detach strata deformation isis abundant from the underlying Archean basement. basement. Evidence Evidence for D1 Dl deformation the iron-formation, iron-formation, folds folds (F1) (Fl) in in Early Proterozoic Proterozoic strata near near Penokee Penokee Gap. Gap. In the bedding define gently gently northwest-plunging northwest-plunging fold see Figs. 5-3, 5-4A and bedding (So) (SJ) define fold axes axes (Li (Ll -- see 5-3,5-4A 45). 4B). AAfield fieldsketch sketchofofaarecumbent recumbentfold foldininiron-formation iron-formation isis shown shownin inFigure Figure5-5. 5-5. Similarly, northwest - plunging folds folds occur occur in in the Tyler Similarly, Tyler east of the Penokee Penokee Gap fault as shown by the 5-4C). Penetrative (Fig. 5-4C). the best best great great circle circle fit of poles to bedding (Fig. axial planar foliation foliation (Si) (Sl)to to the the F1 Fl folds in the Tyler Formation tends tends to to be be flat-lying flat-lying 5-4D). In the the iron-formation iron-formation Si Sl foliation foliation occurs as aa fracture fracture cleavage cleavage (see (see Fig. Fig. (Fig. 5-4D). 5-5). Prominent Prominent shear shear zones zones with with penetrative penetrative Sl S foliation 5-5). foliation occur occur at the base of of the Palms and top top of of the the Ironwood Ironwood hon-formation Iron-formation along along the the contact contact between the the Tyler Tyler and Ironwood strata (Fig. (Fig. 5-3). 5-3). Near Near its its lower lower contact, contact, the Palms is thinly-bedded and units units that that contain containfine-grained fine-grained quartz quartz in in aa sericite sericite matrix matrix are are intercalated intercalated with with finer grained, sericite-rich layerswith with ultra-fine ultra-finequartz quartzgrains. grains. Both the quartz-rich sericite-rich layers layers are foliated foliated and constitute constitute a broad zone of shearing and sericite-rich layers shearing within within the basal Palms: layers with ultra Palms: however, however, the the more more strongly-foliated, strongly-foliated, sericite-rich layers fine quartz are Si shear fine are more moreintensely intenselysheared. sheared. The The Sl shear foliation foliation generally generally dips dips - - • 1 1 �Penokee Gap )1. ? Sct BLOCK III Et Et 25 Et I p I Et 5- TO t Fa u ft 20 40 600 meters 100 2 00 feet Sect is Ss 16 BLOCK ll4 $ct 72 K A S_ 75 A , Middle Middle Proterozoic Proterozoic Keweenewan diabase dike El Early Early Proterozoic Proterozoic WlerFormation Formalon Tyler 1 1 Ironwood IronIronwood Ironformation Palms Formation Palms Formation Bad River DolomiBad River Dolomite Archean Archean G"dss Onelss ' Section comer, dashed Section corner, 11&on dashed 11H-- lines t section lines jS- Railroad Railroad tracks tracks Large exploration pit 4 Large exploration pit \ Fault Faulttrace trace Shearzom Sheer zone Thrust fault, Wangle* fault, triangles 44 Thrust on upthrown block on upthrown block Orientation of joint or \ Orientation of joint or f'=CtumplÇn — fracture planes (S^ 0 1 . II t (5K) Orientation of vertical joint Orientation vertical joint or fractureof planes or fracture planes Geologic contact Geologic contact 'j Strlkeand dlp of bddlng (SJ Strike and dip of bedding C) Strikeand dl of Eari 'V StrIke and dipfoiiation of Early ~roterozoic Proterozoic foliation (S.) SWke and dip of Archean Strike and(Sdip foliation ) of Archeen -C foliation L.1 K ' Strike Of vertical Archean Strike of vertical foliation (sA) Archeen foliation Plunge of first generation Plunge of (LJ first generation '^,fold fold axis axis (L) Plunge of Èçco generation '^,fold axis (L} Plunge of second generation fold axis (U d Fig.5-3: 5-3: Geologic sketch map of Penokee Gap area. Blocks I, II, and III represent Fig. Geologic sketch map of Penokee Gap area. Blocks I, U, and UI represent segments of the Gogebic range near Penokee Gap that are delineated by northwestsegments of the Gogebic range near Penokee Gap that by northwesttrending faults. Capital letters indicate general location of are datadelineated for stereoplots in Fig. 5-4. trending faults. Capital letters indicate general location of data for stereoplots in Fig. 5-4. 94 �I I I I I I I I r I I I I I I i northwest and strikes and constitutes constitutes the the zone along which strikes northeast northeast (Fig. (Fig. 5-4E), 5-4E), and which Early Proterozoic Proterozoic strata are Early are detached detached from from Archean Archean basement. basement. Likewise, a shear shear along the contact contact between the bonwood Ironwood and andTyler Tyler Formations Formations constitutes constitutes another another zone of of detachment of the from underlying underlying Ironwood honwood Iron-formation. hon-formation. We zone detachment of the Tyler Tyler from We consider that both both formation formation of of the the shear shear zones, zones, with withaccompanying accompanyingfoliation, foliation, and and of the Tyler and older strata, with folding of with accompanying accompanying axial planar foliation, were the same (Dl). That is, they they were were formed formed part of the same fold-thrust fold-thrust event event (D1). contemporaneously, and and we we therefore therefore label label both both the the shear foliation and the contemporaneously, the axial axial planar foliation foliation as as Sl. D2 deformation was characterized by continued continued north-verging thrusting thrusting that D2 characterized by resulted in further along the the Sl S shear resulted further deformation deformation along shear zones zones in inpre-Tyler pre-Tyler Early Early Proterozoic strata. Proterozoic strata. Within the lower lower Palms, Palms, prominent F2 kink folds in Si Sl shear shear foliation plunge plunge gently 5-4F) and and are prime foliation gently northwest northwest (Fig. (Fig. 5-4F) prime examples examples of of D2 D; deformation. Although Although F2 kink folds folds are are not not present present in in the Tyler, Si foliation Tyler, Si foliation in deformation. F; kink compared to to the generally northwest these strata tends tends to tobe beflat-lying flat-lying (Fig. (Fig. 5-4D) 5-4D) compared dipping Sl Sj foliation in pre-Tyler strata (Fig. (Fig.5-4E), 5-4E),and andSlS is is folded about a nearly dipping pre-Tyler strata northwest-trending fold fold axis axis that thatisisroughly roughlycoaxial coaxialwith withF2 F; fold foldaxes axes(Fig. (Fig.5-4F) 5-4F) in the sheared D2 sheared Palms Palms Formation. Formation. Thus, we think that that the the Tyler Tyler was was also alsoaffected affected by by D2 deformation. Sense of of structural vergence in the lower Palms shear zone is shown shown in in Fig. Fig. 556A, B 6A, B and C; C. Northward Northwardstructural structural vergence vergence along along a small, small, south-dipping south-dipping thrust Fig. 5-6A) 5-6A)in inwhich whichthe thehanging hangingwall wallmoves movestoward towardthe the north north as as shown by fault (see Fig. 5-6B)and andby by the the sigmoidal sigmoidal curvature curvature and offset a telescoped tabular layer (Fig. 5-6B) offset of of beds across across the the thrust thrustfault fault(Fig. (Fig.5-6C). 5-6C). Sense of of structural vergence Sense vergence in the Tyler Tyler Formation Formation at Penokee Penokee Gap is also also toward the north where where vertical vertical to overturned overturned graded beds of of siltstone siltstone and and slate slate stratigraphically face northward (even (evenafter after post-Early post-Early Proterozoic Proterozoic (Keweenawan) (Keweenawan) rotation is removed). Although rotation Although such such sense sense of folding and rotation of bedding is not proof of the northward northward sense of of rotation in Tyler strata proof of overall structural vergence, vergence, the agrees with kinematic indicators agrees indicators in the older older strata, strata, suggesting suggesting that that D1 Dl and and D2 D; represent represent a continuum continuum of of northerly-directed northerly-directed overthrusting overthrusting associated associated with the the convergent phase phase of of Early Early Proterozoic Proterozoic tectonism tectonism in the the Penokee Penokee Gap Gap area. area. Evidence for for the formation Evidence formation of of the the Middle MiddleProterozoic Proterozoic Midcontinent Midcontinent Rift Rift in Table Table 1) 1) lies lies mainly mainly north north of of the the Gogebic Gogebic Range. Range. Nevertheless, this (labeled DM DM in event affected Early Proterozoic Proterozoic and and Archean Archean strata at Penokee Gap. For example, example, the final the final phase phase of of tectonic tectonic evolution evolution of of the the Midcontinent Midcontinent Rift Rift involved involved aa �S 96 �S I I I I I I I I I I I I I Fig. 5-4: 5-4: Lower hemisphere, equal area stereo plots of of structural features observed in Fig. the Penokee Gap area. Stereoplots and according the Stereoplotsare arekeyed keyed to toFig. Fig. 5-3 5-3 by capital letters and according shown on observations. to blocks shown on Fig. 5-3. N N == number of observations. A. Poles to bedding primarily from iron-formation in blocks II bedding(So), (So), primarily Il and and ifi. in. Best fit great circle defines defines an 14O,N85°W. ~85¡W great an F2 F2 fold with an an axis that that plunges plunges14°, B. Orientation of Lz axes of of folds folds in in bedding bedding (So), (So),primarily primarily from from iron-formation, iron-formation, B. Orientation Soliddots dotsare arefield fieldmeasurements, measurements, best best fit fit orientation orientation (open in blocks blocks II J.I and and 111. in. Solid (open defines aa fold circle) defines fold axis axis that that plunges plunges17°, 17¡ N82°W. N82¡W C Poles primarily from from the the Tyler TylerFormation. Formation Best-fit C. Polesto tobedding bedding(So) (So) in block I,I, primarily Best-fit great that plunges great circle circle defines definesan anF1 Fi fold fold axis that plunges15°, 15O,N64°W. N64"W. D. Poles to Sl Si foliation foliation in in the the Tyler Formation. 8est-fit Best-fitgreat greatcircle circledefines definesan anF2 F; fold axis 04O,S62°E. S62OE. axis that that plunges plunges04°, IL Poles to to Sl S shear E. Poles shear foliation foliationin in the the lower lower Palms Palms Formation Formationof of block II. II. orientation F2 that plunges plunges 22°, Best-fit great circle defines the orientation Fa fold that 22O, N77°W. N77¡W F. Orientation Orientation of Si shear foliation in the lower of L2 L2 kink folds in Sl lower Palms, Palms, block block U. II. Solid Solia measurements, best-fit fold axis axis that that dots are field measurements, dots best-fit orientation orientation (open (open circle) defines aa fold plunges 31°, plunges 31°N75°W. N7W. �a —la/V Im •1 Im field sketch Fig. Fig.5-5: 5-5: Field Field sketch sketch of of recumbent recumbent fold fold in in Ironwood Ironwood Iron-Formation Iron-Formation just west of Penokee PenokeeGap. Gap. So ==bedding. bedding. S1 Si==axial axialplanar planarfracture fracturefoliation. foliation. ' 98 �99 photograph. in bed offset and folded Sigmoidally C. photograph. in layer Telescoped B. layering. shortened and fault thrust of sketch Hand A. fault thrust north) the toward wall (hanging north-verging small, a showing Formation Palms in zone shear Si within from photograph and Sketch 5-6: Fig. I I I I I I I I I I I I I I I * �compressional stage (Dic (DK on Table Table 1) that affected affected Early Proterozoic and Archean Archean strata at Penokee Gap. Gap. During OK deformation, deformation, rigid blocks of Keweenawan Keweenawan and During 0K Early strata, along Early Proterozoic Proterozoic strata, along with underlying underlying Archean Archean gneiss gneiss were tilted tilted northward along along north-dipping north-dipping listric listric thrust faults faults (Cannon (Cannon and others, 1993). 1993). This This northward northward tilting tilting created created the the north-dipping north-dipping monoclinal monoclinal sequence sequence of of Early Early Proterozoic strata that that characterize characterize most most of of the theGogebic Gogebic Range Range today. today. In addition, our mapping at Range to to the west of the gap at Fenokee Penokee Gap Gap and and along along the the Gogebic Gogebic Range gap indicates that the rotated blocks are divided into discrete segments (blocks I, II and ifi the rotated blocks are divided into discrete segments (blocks in on Fig. Fig. 5-3) 5-3) that are are bounded bounded by bysteeply-dipping, steeply-dipping,north-northwest-striking north-northwest-striking fault. fault. Besides the stratigraphic stratigraphic offsets across the the inferred inferred faults, numerous steeply-dipping, steeply-dipping, northwest-striking joints or closely northwest-striking joints closely spaced spaced fractures fractures (Sic) (SK)are are also also considered considered structural structural expressions expressions of of this thisphase phaseof of deformation deformation(Fig. (Fig. 5-3). 5-3). The Penokee Gap fault fault is perhaps the the most most prominent prominent of of these these faults, faults, and and itit created created aazone zoneof of weakness weakness along which the Bad River ultimately ultimately flowed flowed forming forming the the Penokee Penokee water water gap gap in the Gogebic Range. Steeply northwest-plunging northwest-plungingfolds folds adjacent adjacent to to these these faults are Range. Steeply are observed in outcrops of the Tyler Tyler and were were most most likely likely formed by drag drag along along the the faults. faults. Formation Formation of of the Midcontinent Rift Rift may may have have also also resulted in metamorphism of of Early Early Proterozoic Proterozoic strata. strata. As noted above, above, geologic geologic evolution of the Gogebic Range near Penokee Gap involved Gogebic Range involved at least two two metamorphic metamorphic events. events. The Dl The first first was was a adynamic, dynamic,low-grade• low-grade event event that thataccompanied accompanied regional regional D1 deformation. deformation. It is characterized characterized by formation of platy minerals minerals of of sericite, sericite, biotite, biotite, The second second metamorphic metamorphic event event was most and chlorite chlorite that lie lie along along Si SI foliation. foliation. The most likely related to to intrusion intrusionof of the theMiddle MiddleProterozoic ProterozoicMineral Mineral Lake Lake Gabbro, Gabbro, which whichlies lies about 1.6 km north This event event is is characterized by a suite of north of of Penokee Penokee Gap. Gap. This characterized by of metamorphic minerals including metamorphic minerals including cordierite, cordierite, garnet, garnet, chlorite, chlorite, magnetite, magnetite, and and deformational fabric and, thus, Dldeformational amphibole, some of of which clearly dearly overprint the D1 however, has has not not been been studied studied in in detail in this area and postdate postdate it. it. Metamorphism, however, is worthy of further further study. study. PENOKEE CAP PENOKEE GAPFIELD FIELDSTOPS STOPS(see (seeFig. Fig.5-7) 5-7) south from Walk south from County County Road Road GG GG at Foster Junction along railroad tracks tracks for for 1cmtotothe thefirst firstlarge largerock rockcut cut (Stop (Stop11on onFig. Fig.5-7). 5-7).Although Although most most field field stops about 1.3 1.3 krn will be be in stratigraphic order from oldest oldest to youngest, youngest, the the first first stop will will be in the will Tyler Formation, Formation, the the youngest youngest Early Early Proterozoic Proterozoicunit unit encountered encountered on on the walk Tyler southward southward along along the the railroad railroad tracks tracks to to the the older older strata. strata. 100 �I I I I I I I I I I I I I I I I map of the Penokee Gap area showing showing location location of field stops. stops. Geologic field map Fig. Fig.5-7: 5-7: Geologic 101 �Ti r STOP SB-i. Tyler Tyler Formation Formationand and Keweenawan Keweenawandiabase diabasedike: dike: SW SW 1/4, 1/4, NE NE 1/4, STOP 5B-1. SW 1/4, 1/4, 511, Sll, T44N, T44N, R3W R3W The Tyler Formation isis exposed exposed for for roughly roughly 100 100m m in in a rock cut along Tyler Formation along the the railroad railroad tracks and and consists consists of of multiple multiple beds beds of of black black carbonaceous carbonaceous slate and and siltstone, subtly subtly graded graded with stratigraphic tops tops toward toward the north. The TheTyler Tyler strata strata consist of of mostly silt-sized quartz grains in aa carbonaceous carbonaceous matrix of biotite, chlorite Small (—1 cm-diameter)cordierite cordieriteporphyroblasts porphyroblasts are are dispersed and sericite. sericite. Small (-1 cm-diameter) throughout the siltstone/slate. siltstone/slate. in the the Tyler Tyler at at the the northernmost northernmost end end of of the rock cut (east side of (So) in Bedding (So) the railroad railroad tracks) tracks) is overturned overturned toward toward the the north, north, but, but, progressing progressing southward, southward, most bedding dips dips steeply steeply northwest northwest and and strikes strikes northeast as shown shown in in Fig. Fig. 5-4C. 5-4C. Si Sl foliation lies at a large angle to bedding, is generally low-dipping to to flat-lying, and and is is that plunges plunges gently gently to to the the southeast as shown by the (1-2) that folded around aa fold fold axis axis (L2) great great circle circle on onFig. Fig.5-4D. 5-4D. zones of steeply-dipping, Isolated zones steeply-dipping, north-northwesterly-trending north-northwesterly-trending fracture fracture cleavage with steeply plunging folds (possibly drag drag folds) are found in cleavage with in outcrops outcrops especially along along the west side of especially of the the railroad railroad tracks. tracks. These, These, and other northwestnorthwesttrending joints joints and fracture fracture zones in the region, region, are considered part of of aa family family of of north-northwest faults in the the Penokee Penokee Gap area that divide divide the the Gogebic Gogebic Range Range into individual II, Fig. 5-3). 5-3). They They are are interpreted as Middle 1, and III on Fig. individual segments segments (blocks (blocks I, 1 of formation of of the - -- Proterozoic Proterozoic SK structures formed during the final closing phase of Midcontinent Rift. Midcontinent Rift. A 33 rn-wide diabase dike dike is is exposed exposed at the north m-wide undeformed Keweenawan Keweenawan diabase north end of the rock rock cut on on the the west west side sideof of the the railroad railroad tracks. tracks. Walk further south along the railroad tracks to to the first rock rock cut on the east Walk further railroad tracks east side side of the tracks, tracks, just past past the the second second bridge. bridge. STOP 5B-2. 5 5 2 . Archean Archean gneiss: gneiss: SE SE1/4, 1/4,NW NW1/4, 1/4,514, S14,T44N, TUN, R3W R3W Amphibolitic to granitoid granitoid gneiss. gneiss. The Archean Archean gneiss forms the basement basement The westupon which westupon which overlying overlying Early Early Proterozoic Proterozoic strata were were deposited. deposited. The northwesterly-striking gneissic foliation foliation dips dips steeply steeply south. Parallel shear northwesterly-striking gneissic shear zones zones wide occur occur in in the the gneiss. gneiss. Although the strike of the gneissic and several centimeters wide shear shear foliations foliations is roughly roughly parallel to the the strike strike of of Early Early Proterozoic Proterozoic structural structural features, there are no no structures structures in in the the overlying overlying Early Early Proterozoic Proterozoic strata that that have have similar dips. Other Otherthan thanpostdating postdatingthe thegneissic gneissicfoliation, foliation, the the age age of of shear shear formation formation is not known. known. The Theshears shearsmay maybe beEarly EarlyProterozoic Proterozoic in inage. age. Examine outcrops outcrops along both banks of Bad River, just just beneath railroad bridge. bridge. 102 j �I STOP STOP 5B-3. 5B-3. Bad Bad River Dolomite: NE NE 1/4, 1/4,SE SE 1/4, 1/4,NW NW1/4, 1/4,S14, S14,T44N, T44N, R3W R3W Exposures on the south side with side of of the the Bad Bad River are tan-colored tan-colored dolomite with chert Bedding is is oriented oriented N80'W, N80°W,45"N. 45°N.Note Note that that the dolomite chert lenses lenses and and layers. layers. Bedding rests directly on Archean gneiss. On directly on Archean gneiss. On the the eastern eastern end of of the the Range, Range, the the Sunday Sunday Quartzite occurs occurs between the the Archean Archean basement basement and and the theBad Bad River River Dolomite. Dolomite. Quartzite At Dolomite isis about about 20 20m m thick. thick. The basal portion At this this locality locality the the Bad Bad River Dolomite is is mainly mainly dolomite dolomite that that has hasvague vaguecross-bedding cross-bedding and andpossible possiblestromatolites stromatolites suggestive of of shallow water water deposition. deposition. The The upper part part of of the the Bad Bad River River Dolomite Dolomite (on the north side breccia. This side of of the the river) river) is a variegated chert and chert breccia. This lithology is is typical typical of exposures exposures for for about about 15 15 km krn in the western part of of the the Gogebic Gogebic Range. We We interpret interpret the the cherty chertyupper upperportion portionof of the theBad Bad River River Dolomite Dolomite to represent a residual concentration concentration of of chert layers and nodules nodules formed formed by solution solution of of dolomite dolomite during during erosion erosion that that preceded precededdeposition depositionof ofthe theoverlying overlyingPalms PalmsFormation. Formation. We of the cherty portion of the We will will examine examine another exposure of the Bad Bad River River Dolomite about about 515 m to the west at a later stop. stop. Walk north north from from the the railroad railroad bridge to to the first large outcrop on the the west west side side Walk of of the the tracks. tracks. STOP STOP 5B-4. 5B-4. Palms Palms Formation: Formation: SE SE 1/4, 1/4,NW NW 1/4, 1/4,NW NW1/4, 1/4,S14, S14,T44N, T44N, R3W R3W Alternating Alternating beds beds (So) (So) of silty silty to to finer-grained, finer-grained, more argillaceous strata are present present here. here. Thicker-bedded, Thicker-bedded, more more psammitic psamrnitic (silty) strata on the south end grade grade strata on the north end of into finer-grained, finer-grained, more mica-rich mica-rich strata of the the outcrop, outcrop, indicating indicating into that that stratigraph.ic stratigraphic facing is to the north. Both Both the the silty silty layers layers and and mica-rich mica-rich layers layers are are penetratively foliated, but the the argillaceous argillaceous layers have less quartz as well well as as finerfinerpenetratively grained (Si)isis grained quartz quartzininan anintensely-foliated intensely-foliatedsericite sericitematrix. matrix. Penetrative Penetrative foliation foliation (Si) generally parallel to to bedding. There are also F; generally oriented oriented N75°E, N75'E, 60°NW, 60°NWparallel also numerous numerousF2 kink kink folds folds in in Si Slfoliation foliationwith withL2 L; axes axesthat thatplunge plungeabout about16°, 16',N87°W. N8TW. These These penetratively-foliated strata are are considered consideredpart part ofof aa Di penetratively-foliated strata Dl shear shear zone zone that that was was subsequently kink folds. folds. We subsequently deformed deformed by by aaD2 D; deformational deformational event to form the F2 F; kink will will take take aa closer closer look look at at the the style style of of deformation deformation in this shear zone to the west at at Stops and7.7. Stops66and Walk Walk west west from from the the railroad railroad bridge bridge for for approximately approximately 515 515 m to to aa large largetalus talus slope hill. Climb slope along along the the steep steep south south flank flank of an easterly trending hill. Climb the the talus talus slope slope to to two twoexploration explorationpits pitsnear nearthe thetop topofofthe thesteep steepslope. slope. Note: Note: This Thiswalk walkisisstrenuous, strenuous,through through thick thick brush brush and and along along steep steep hillsides hillsides with with loose loose rocks rocksthat thatmay mayroll rolldown downthe thehillside hillsideififdisturbed. disturbed.BE BECAREFUL! CAREFUL! r 103 �STOP 50-5. 5B-5. Bad NW1/4, 1/4,NW NW1/4, 1/4,514, S14,T44N, T44N,R3W R3W BadRiver River Dolomite: Dolomite: SE SE 1/4, 1/4,NW The between the the Bad Dolomite and and the the Palms Bad River River Dolomite Palms Formation Formation is is The contact contact between exposed in in two pits at this exposed two exploration exploration pits pits at at this thislocality. locality. Other Other exploration exploration pits this stratigraphic horizon are are present present on on the stratigraphic horizon the eastern eastern flank flank of of Mt. Mt.Whittlesey, Whittlesey, approximately 9 km to the east. of magnetite magnetite are are localized Concentrations of localized in approximately 9 km to the east. Concentrations conglomeratic zonesatat the the top top of conglomeratic zones of the the cherty cherty breccia breccia portion portion of of the the Bad Bad River River Dolomite. The that surrounds angular and rounded Dolomite. The magnetite is in a sandy matrix matrix that chert fragments fragments up up to do not chert to at at least least 70 70 cm cm long. long. Magnetite-rich Magnetite-rich zones zones do not extend extend up up into the the magnetite into the overlying overlying Palms PalmsFormation. Formation. Therefore Therefore the magnetite concentrations concentrations appear to to be be pre-Palms. pre-Palms. Along Alongstrike strikefrom fromthe themagnetite magnetiteoccurrence, occurrence, the the Bad Bad River River Dolomite consists of of a spectacular breccia breccia with with some some rounded rounded and angular angular blocks blocks of of chert in tic matrix. in aa reddish reddishhemati hematitic matrix. The of magnetite in conglomeratic rocks at at an The local local concentrations concentrations of magnetite in conglomeratic rocks an unconformity argue for for a paleo-placer unconformity argue paleo-placer origin origin along along aa braided braided stream stream course. course. However, much of of the magnetite However, much magnetite is euhedral, showing no indication indication of rounding rounding that might be The euhedral magnetite may indicate be expected expected in in aa placer placer deposit. deposit. The indicate that these that these are are hydrothermal hydrothermal deposits, deposits, but but no nohydrothermal hydrothermal bleaching bleaching of of surrounding rocks is evident, evident, nor are are any any hydrothermal hydrothermal gangue gangue minerals, minerals, such such as as quartz crystals, the euhedral crystals, present. present. Alternatively, Alternatively, the euhedral magnetite magnetite crystals crystals may be be metamorphic in origin. origin. Clearly, Clearly, the origin of these peculiar magnetite magnetite occurrences occurrences is is problematic. A and report report that problematic. A mining mining company company has analyzed analyzed these conglomerates conglomerates and there are no no precious precious metals metals in in them. them. Walk north-northeast about 80 m to the crest and north flank Walk flank of of the the hill. hill. STOPS 5B-6 5B-6and and 5B5B-7.7. Sheared, Sheared, thin-bedded thin-bedded Palms Palms Formation: Formation: SE 1/4, NW 1/4, NW NW 1/4, 1/4,S14, S14,T44N, T44N,R3W. R3W. The purpose purpose of of these The these two stops stops is to to illustrate illustrate our our interpretation interpretation of the the kinematics of of deformation deformation in a D1 shear zone. zone. Lithology kinematics Dl shear Lithology at this stop stop is is similar similar to to that at at Stop Stop 44 where where layers layers of of silty silty Palms Palms are are intercalated intercalated with with finer-grained finer-grained micamicarich layers, both of which numerous small small which have have penetrative penetrative Si S1 foliation. foliation. At Stop 6 numerous boudins are formed formed in in thin thin quartz-rich quartz-rich layers layers that have have orientations orientations close to the the orientation of Si Also, several several F; F2 kink kink folds folds with L2 orientation Sl foliation foliation planes. planes. Also, L; fold axes axes deform the at this this stop. stop. At the S1 S1 shear fabric at At Stop Stop 7, about 70 m northwest of the area of Stop 6, there is is aa small, small, south-dipping south-dipping D1 Dl thrust thrust fault fault (Fig. (Fig. 5-6A) 5-6A) with telescoped telescoped layers (Fig. and a sigmoidal layers (Fig. 5-6B) and sigmoidaldrag dragfold foldwith withoffset offsetbeds beds(Fig. (Fig.5-GC). 5-6C). Si foliation, foliation, the the boudinaged boudinaged quartz layers and The three structural structuralelements: elements: Sl the small thrust fault fault provide provide information information to interpret the kinematics kinematics of of the shear shear 104 �I I I I N fl !+ [1 Fig. Fig. 5-8: 5-8: Lower Lower hemisphere, hemisphere, equal equal angle angle stereoplot stereoplot showing the orientations orientations of ofS1 foliation foliation(great (greatcircle), circle),orientation orientationof of the the long long axes axes of of boudins boudins(LB), (LB), orientation orientationof of the the axis (XI, and andorientation orientationof ofthe theaxis axis of of shortening shortening (Z) in in the the sheared shearedPalms Palms axisof ofstretching stretching(X), - (Z) Formation FormationatatStops Stops5B-6 5B-6and and5B-7. 5B-7.See Seetext textfor fordiscussion. discussion. 105 �j zone. structures. Penetrative zone. They are all considered to be D1 Dl structures. Penetrative Si SI foliation foliation formed as a result result of of simple simple shear shear along along an aninferred, inferred,now now steeply steeply north-dipping north-dipping to to vertical vertical shear Sense of of movement shear zone zone that that dips dipsmore moresteeply steeplythan thanSi SIfoliation. foliation. Sense movement in the the shear couple couple must have have been been down down to to the the north north to toform formSi Slfoliation. foliation. The general orientation of Si, SI, based based on on field field measurements, measurements, is shown by the the great great circle circle on the stereographic stereographic plot plot in inFig. Fig.5-8. 5-8. The boudins formed by stretching perpendicular to their axeslie lieroughly roughlyin inthe theST Siplane plane and and plunge about about 45° 45' toward their long longaxes axes(LB). (LB).LBaxes the northwest. in the shear zone can be northwest. The Theorientation orientationof of the theaxis axis of of stretching stretching (X) (X) in be estimated from the orientation of the boudins. The (X) orientation of the long axes of Thestretch stretchaxis axis(X) also lies in the the Si SI plane plane at atright rightangles anglesto tothe thelong longaxes axesof of the theboudins boudinsLB, LB, as shown on on Fig. Fig. 5-8. That That isis the therocks rocks in in the the shear shear zone zone were were stretched stretched along along an an axis axis (X) (X) that plunges plunges toward towardthe thenortheast northeastasasshown shownon onFig. Fig.5-8. 5-8. Finally, the small small thrust thrust formed formedinin aa region region where where Sl S foliation Finally, the foliation did did not develop. (Zon onFig. Fig.5-8). 5-8). develop. The Thethrust thrustlies liesparallel paralleltotothe theaxis axisofofmaximum maximumshortening shortening(Z That That is, is, itit developed developedat atright rightangles anglesto toSi S1foliation foliationas as shown shownon onFig. Fig.5-8. 5-8. Essentially, Essentially, the where Sl Si foliation the small small thrust thrust accommodated accommodated shortening in rocks rocks where foliation could not develop develop because because of of their theircomposition composition(see (seethe thephotograph, photograph,Fig. Fig.5-6). 5-6). The absence absence of similar similar structures structures in in the the underlying underlying Archean Archean basement basement requires requires that that Early Early Proterozoic Proterozoic strata must must be be detached detached from from them. them. Thus, we we interpret interpret the the intensely intensely foliated foliated strata strata in in the the lower lower part part of of the thePalms PalmsFormation Formation to to represent represent aa ductile ductile shear shear zone zone that that detached detached the the Early Early Proterozoic Proterozoic from from the the underlying underlyingArchean Archeangneiss. gneiss. Walk Walk north, north, across across aa narrow narrow valley valley for about 70 70 m to the next steep steep hill. hill. STOP STOP 5B-8. 5B-8.Uppermost UppermostPalms Palms Formation: Formation: SE SE 1/4, NW NW 1/4, 1/4, NW NW 1/4, 1/4,S14, S14, T44N, R3W. T44N, R3W. This This stop stop illustrates illustrates the the massive, massive, thickly bedded quartzite typical of the upper upper part bedded unit and the part of of the thePalms. Palms. Both Both this massively massively bedded the lower lower thin-bedded thin-bedded argillaceous argillaceous units units continue continue westward at at least least to to the the Atkins Atkins Lake Lake area, where outcrop outcrop dies diesout. out. The The Palms Palms Formation Formation generally generally strikes strikes N80°W N80'W and dips dips 65°NE 65'NE in this this area, area, shows shows cross-bedding, cross-bedding, and is aa clean clean orthoquartzite. orthoquartzite. Westward Westward from from Penokee Penokee Gap Gap the the quartzite quartziteisisaaprominent prominentridge-former ridge-formerwith withnumerous, numerous,excellent excellent exposures. exposures. Because of the exceedingly steep slopes slopes and loose rocks rocks it is dangerous for Because of for aa large large group group to toclimb climb to tothe thetop topofofthe thebluff blufftotoview viewthe thequartzite-iron-formation quartzite-iron-formation contact. contact. Walk Walk north north up up the therelatively relatively gentle gentle slope slope just just west of the the quartzite quartzite bluff bluff for for 106 fl I �L a about about 30 m. m. n fl-I I I I I I STOP 1/4, NW 1/4, STOP 5B-9. 5B-9. Ironwood Iron-formation: Iron-formation: NW NW 1/4, 1/4, S14, S14, T44N, T44N, R3W. R3W. The Ironwood Iron-formation overlies the the Palms The Iron-formation conformably conformably overlies Palms Formation Formation from which it grades through aa transition transition of of several beds of granular iron-formation iron-formation in the upper upper Palms. Palms. Locally, Locally,the thebase base of of the the Ironwood Ironwood has has aa thin thin (3 (3m) m) conglomerate conglomerate thick zone of of stromatolitic stromatolitic jasper jasper occurs occurs at at the base of the zone, elsewhere, locally a thick iron-formation. The eastward from Gap was The Ironwood Ironwood Iron-formation Iron-formation eastward from Penokee Penokee Gap was subdivided subdivided into five into five units units based based on onbedding beddingstyle styleand andmineralogy mineralogy(Hotchkiss, (Hotchkiss,1919). 1919). Our mapping west of of Penokee Penokee Gap shows that that the the iron-formation iron-formation consists consists of alternating alternating units of of granular, granular, wavy-bedded wavy-bedded iron-formation iron-formation and and laminated laminated iron-formation. iron-formation. However, except except in the first few west of of Penokee Gap, Gap, the However, few hills hills of iron-formation iron-formation west five-fold field field division of of Hotchkiss Hotchkiss and and U. U. S. S. Steel Steeldoes doesnot not extend extend westward westward along five-fold the Gogebic Gogebic Range. Range. basal 75 75 m m of of the the iron-formation iron-formationisismainly mainlyaagranular, granular, wavy wavy bedded bedded unit The basal with irregular lenticular layers that branch lenticular chert beds separated by magnetite-rich magnetite-rich layers unit may represent the and recombine recombine around the the cherty cherty lenses. lenses. This This unit the Plymouth Plymouth member of this wavy-bedded wavy-bedded unit unit is about 30 of Hotchkiss Hotchkiss(1919). (1919). Overlying Overlying this 30 m m of of mainly laminated, magnetic magnetic iron-formation with scattered intraformational breccia breccia units. This lithology may represent units. represent the the Norrie Norrie and andPence Pencemembers membersofofHotchlciss Hotchkiss (1919). The The uppermost exposures (1919). exposures are laminated, laminated, weakly weakly to to non-magnetic non-magnetic ironironformation. Some Some layers layers contain contain rounded rounded elongate elongate chert chert concretions concretions in aa somewhat somewhat matrix, possible representing the Anvill argillaceous matrix, Anvil1 member member of of Hotchkiss Hotchkiss(1919). (1919). Near the northernmost Near northernmost exposures exposures of the the Ironwood Ironwood Iron-formation, Iron-formation, the recumbent 5-5) mentioned mentioned above above isis present, present, and and the contact with with the Tyler Formation fold (Fig. 5-5) of the hill hill supported by by the iron-formation. iron-formation. There are no lies along the north flank of exposures of the Tyler Tyler in in this this region, region, however. however. END OF OF FIELD FIELD STOPS STOPS Walk east-southeast for for about 820 820 m m to to railroad railroad tracks along the Bad Walk Bad River, River, and then then about about 22 km km north northon onrailroad railroadtracks trackstotovehicles. vehicles. ACKNOWLEDGMENTS I We are grateful to the their help: Suzanne the following following persons persons for their SuzanneNicholson Nicholson for reviewing for reviewing the manuscript manuscript and and preparing preparing itit for forfinal finalpublication; publication; William William Cannon Cannon for reviewing reviewing the the manuscript; manuscript; Don Don Harrison, Harrison, of of Western Western Illinois Illinois 107 I �University, preparation of stereoplots; stereoplots; and Susan Susan Wilson, Wilson, also also of of Western Western University, for for preparation Illinois University, University, for computer drafting of the Illinois the figures. figures. Both and Both the reviews and field guide. guide. technical assistance aided considerably in preparation of this field REFERENCES REFERENCES Anderson, Mitchell, Mitchell, and Klasner, Klasner, John S., 1993, 1993, Geologic Geologicevidence evidencefor forthin-skinned thin-skinned deformation deformation in the Eastern Gogebic Gogebic Range Range [abstract]: [abstract]: Abstracts Programs, North-Central North-Central Section Section of the Eastern Abstracts with with Programs, of the Geological Society paper no. Geological Society of America, America, v. 25, 25, n. 3, paper no. 028211, 028211, p. 2. p. 2. J. E., E., 1970, 1970, A revision middle Precambrian Precambrian Cannon, W. F., and Gair, Gair, J. revision of of stratigraphic nomenclature of middle rocks in northern northern Michigan: Michigan: Geological GeologicalSociety Societyof of America America Bulletin, Bulletin, v. 81, p. 2843 2843 -- 2846. 2846. Z. E., E., and and Sims, Sims, P. K., K., 1993, origin of of the the Montreal Montreal Cannon, W. F., Peterman, Peterman, Z. Cannon, W. 1993,Crustal-scale Crustal-scalethrusting thrusting and and origin River rnonocline -- aa 35 kilometer-thick Northern River monocline -kilometer-thickcross cross section sectionofof the the Midcontinent Midcontinent Rift Rift in Northern Michigan: Tectonics, Tectonics,v.v.12, 12,p. p. 728 728 -- 744. Feher, L., Flood, T. P., 1995, 1995, Vesicles partially L., and Flood, Vesiclesand and breccia brecciadue due to injection injection of of mafic mafic magma magma into partially lithified sediments sediments of of Early Early Proterozoic, Proterozoic, Ironwood Iron-formation, western Gogebic Gogebic Range, N. W. Wisconsin [abstract]: [abstract]: 41st 41st Annual AnnualInstitute Instituteon onLake Lake Superior SuperiorGeology, Geology, Marathon Marathon Ontario, Ontario, v. 41, part Wisconsin 1., p. p. 13 13-- 15. 15. I., Hotchkiss, W. W. O., 0., 1919, Gogebic Range Rangeand and its its relation relation to to recent mining developments: ~otchkiss, 1919, Geology of the Gogebic developments: Journal, v. 108, p.p.443 507,537-- 541, and and 577 577-582. 452,501 - 507,537 - 582. Engineering and Mining Mining Journal, 443 --452,501Klasner, J. S., LaBerge, G. S., and and LaBerge, G. L., L., 1994A, 1994A,Structural StructuralEvolution Evolutionofofthe theEastern Eastern Gogebic GogebicRange, Range, Northern Northern Michigan [abstract]: 40th Annual Institute on Lake Superior Geology, Houghton, Michigan, v. 40, 40, [abstractj: on Lake Superior Houghton, Michigan, v. part 1, p. 23-24. 1, p. 23 - 24. and LaBerge, LaBerge, G. L., L., 19948, 1994B, Structural geology of the the Gogebic Gogebic Range, Range, Penokean Penokean Orogen, Orogen, Klasner, J. S. and Northern Michigan Michigan and and Wisconsin Wisconsin [abstract]: [abstract]: Abstracts with Programs, North-Central North-Central Section Section of of the Geological GeologicalSociety Society of of America, America, v. v. 26, 26, no. 5, paper paper 12069, 12069, p. 23. the p. 23. Klasner, J. S., LaBerge, the Eastern EasternGogebic GogebicRange, Range, Kiasner, LaBerge, G. G. L., L., and and Cannon, W. F., F., in press, Geologic Map of the Northern Northern Michigan: Michigan: U. U.S.S.Geological Geological Survey Survey Miscellaneous Miscellaneous Investigations Map. LaBerge, G. L., L., Cannon, Cannon, W. W. F., F., and and Klasner, J.J. S., S., 1995, 1995,New Newobservations observationson onthe the geology geology of of the the Western Gogebic Iron Range [abstract]: 41st 41st Annual Annual Institute Institute on on Lake Superior Superior Geology, Geology, Marathon, Marathon, Ontario, Gogeb'ic v.41, v. 41, part part1,1,p.p.33-34. 33-34. LaBerge, C. L., and Klasner, LaBerge, G. L., Klasner, J.J. S., 1994, 1994, Tectonic Early Proterozoic Proterozoic Tectonic implications implications of of the Early lithostratigraphy on on the theEastern EasternGogebic Gogebic Range, Range, Northern Northern Michigan Michigan [abstract]: [abstract]: 40th Annual Annual Institute Instituteon on Lake LakeSuperior SuperiorGeology, Geology,Houghton, Houghton,Michigan, Michigan,v. v.40, 40, part part 1,1, p. 27 27 -- 28. 28. W., 1992, 1992, Archean Gogebic LaBerge, LaBerge, G. G. L. L. and and Ojakangas, R. W., Archean and and Early Early Proterozoic Geology Geology of of the Gogebic District, Northern Michigan and Wisconsin: District, Northern Wisconsin: 38th 38th Annual Annual Institute Instituteon onLake LakeSuperior SuperiorGeology, Geology, Hurley, Wisconsin, v. v.38, 38, part part 2, 2, p. p. 11-40. - 40. Hurley, Ojakangas, W., 1983, 1983, Tidal Tidal deposits deposits in in the the Early Early Proterozoic Proterozoic basin of the the Lake Lake Superior Superior region region -- the the qakangas, R.R.W., Palms and Pokegama Formations: Formations: Evidence Evidence of sub-tidal deposition of the Superior-type banded in Maderis, Maderis, L. L. G., G., (ed), (ed.), Early Early Proterozoic Proterozoic Geology Geology of the the Great GreatLakes LakesRegion: Region: iron formation, formation, in Geological Society 56. Geological Society of America America Memoir Memoir 160, 160, p. 49 -- 56. 108 � Dublin Core The Dublin Core metadata element set is common to all Omeka records, including items, files, and collections. For more information see, http://dublincore.org/documents/dces/. Title A name given to the resource Institute on Lake Superior Geology Dublin Core The Dublin Core metadata element set is common to all Omeka records, including items, files, and collections. For more information see, http://dublincore.org/documents/dces/. Title A name given to the resource Institute on Lake Superior Geology: Proceedings, 1996 Description An account of the resource Institute on Lake Superior Geology. Cable, Wisconsin. May 15-19, 1996. Creator An entity primarily responsible for making the resource Institute on Lake Superior Geology Date A point or period of time associated with an event in the lifecycle of the resource 1996 Format The file format, physical medium, or dimensions of the resource PDF Language A language of the resource English https://digitalcollections.lakeheadu.ca/files/original/3993ef81ee739d90f8703b1f07d9f6f0.pdf 08b32baa603f79ec4677898139749c26 PDF Text Text 43rd 43rd Annual INSTITUTE ON ON INSTITUTE LAKE SUPERIOR GEOLOGY GEOLOGY LAKE Sudbury, Ontario Ontario May 66-11, 1997 - 11,1997 and Proceedings Volume: Volume: Program Program and Abstracts Abstracts Volume 43, Part 11 Volume 43, Part �Institute on Lake Superior Geology 43rd 43rd Annual Annual Meeting Meeting May61997 May 6 -11, 11,1997 Sudbury, Ontario, Ontario, Canada Canada Sponsored Sponsoredby: by: Ministry Ministry of Northern Northern Development Development and and Mines Mines Ontario Geological Geological Survey Survey Resident Geologist's Geologists Office, Office,Sudbury Sudbury Proceedings Proceedings Volume Volume 43 43 Part I1--- Program Programand and Abstracts Abstracts Editors: Editors: Ron Ron Sage, Ontario Ontario Geological GeologicalSurvey Survey Wilf Geologists Office Wilf Meyer, Meyer, Resident Resident Geologist's Office �Contents Contents Patti Part I Program and Abstracts Institutes Institutes on on Lake LakeSuperior Superior Geology Geology to to 1997 1997..................................................i Constitution of the Constitution the (nstitute Institute on Lake Superior Geology..................................iiii ... iii By-Laws of the Institute Institute on on Lake Lake Superior Superior Geology Geology.......................................111 Proceedings Volumes and Field Trip Guidebooks Guidebooks ...........................iv Index of Proceedings Award Guidelines Guidelines for for Sam Sam Goldich Goldich Medal Medal.......................:.............................ix XI Board of Directors Directors.......................................................................................... xi Committees .......................................................................................... xi Local Committees xi .. Xii1 Student Paper Paper Committee Committee............................................................................ xi Session Session Chairs Chairs...................................... .. ...................................................... xii XII ; .. XII Goldich Goldich Medal Medal Committee Committee....................................................;.......................xii ... xiii Goldich Medal 1997 Goldich Medal Recipient Recipient.....................................................................xi11 xiii Goldich Medalists Past Goldich Medalists................................................................................ xm 0.. Banquet Speaker Speaker......................................................................................... ... Xlii xi11 1997 Goldich Medal 1997 Goldich Medal Recipient Recipient Citation Citation........................................................xv .. ... Report of the Chair Chair of the 42nd Annual Institute institute....:...................................xviii xvm Student Student Travel Travel Award Award.................................................................................xvii xvii xxi Calendar of Calendar of Events Events and and Program Program.................................................................xxi 1 Abstracts Abstracts.. ....................................................................................................... 1 �Institutes Institutes on Lake Lake Superior Geology Institute Institute Number Number 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 Date Date 1955 1956 1957 1958 1959 1960 1961 1962 1963 1964 1965 1966 1967 1968 1969 1970 1971 1972 1973 1974 1975 1976 1977 1978 1979 1980 1981 1982 1983 1984 1985 1986 1987 1988 1989 1990 1991 1992 1993 1994 1995 1996 1997 Place Place Minneapolis, Minneapolis, Minnesota Minnesota Houghton, Houghton, Michigan Michigan East East Lansing, Lansing, Michigan Michigan Duluth, Minnesota Duluth. Minnesota Minneapolis. Minnesota Minneapolis, Minnesota Madison, Wisconsin Wsconsin Port Arthur, Ontario Port Ontario Houghton, Houghton,Michigan Michigan Duluth, Duluth, Minnesota Minnesota lshpeming, Michigan Ishperning, Michigan Paul, Minnesota St. Paul, Minnesota Sault Sault Ste. Ste. Marie, Marie, Michigan Michigan East East Lansing, Lansing, Michigan Michigan Superior, Wisconsin Superior, Wisconsin Oshkosh, Oshkosh, Wisconsin Wisconsin Thunder Bay, Thunder Bay, Ontario Duluth, Duluth, Minnesota Minnesota Houghton, Michigan Houghton, Michigan Madison, Wisconsin Sault Sault Ste. Ste. Made, Marie, Ontario Ontario Marquette, Michigan Marquette, Michigan St. Paul, Paul, Minnesota Minnesota Thunder Bay, Thunder Bay, Ontario Ontario Milwaukee, Milwaukee,Wisconsin Wisconsin Duluth, Duluth, Minnesota Minnesota Eau Eau Claire, Claire, Wisconsin Wisconsin East East Lansing, Lansing, Michigan Michigan International InternationalFalls, Falls,Michigan Michigan Houghton, Michigan Houghton, Michigan Wausau, Wisconsin Wsconsin Kenora, Ontario Kenora, Ontario Wisconsin Rapids, Wsconsin Wisconsin Wisconsin Wawa, Ontario Ontario Marquette, Marquette,Michigan Michigan Duluth, Minnesota Duluth, Minnesota Thunder Bay, Thunder Bay, Ontario Ontario Eau Eau Claire, Claire, Wisconsin Wisconsin Hurley, Hurley, Wisconsin Wsconsin Eveleth, Eveleth, Minnesota Minnesota Houghton, Houghton, Michigan Michigan Marathon, Ontario Ontario Cable, Cable,Wisconsin Wisconsin Sudbury, Ontario Ontario Chairman Chairman C.E. Dutton Dutton C.E. A.K. Snelgrove Sneigrove A.K. B.T. Sandefur Sandefur R.W. Marsden Marsden G.M. C. Craddock G.M. Schwartz & C. E.N. Cameron E.N. Cameron E.G. Pye E.G. Pye AX. A.K. Snelgrove Snelgrove Lepp H. Lepp A.T. A.T. Broderick Broderick P1<. Sirns Sims & & R.K. R.K. Hogberg Hogberg P.K. R.W. White White W.J. W.J. Hinze Hinze AR. A B. Dickas Dickas LaBerge G.L. LaBerge & E. E. Mercy Mercy Bartley & M.W. Bartley D.M. Davidson Davidson J.. Kalliokoski J Kalliokoski M.E. Ostrom Ottrorn M.E. P.E. Giblin Giblin J.D. J.D. Hughes Hughes M. Walton Walton M.M. M.M. Kehlenbeck Kehlenbeck G. Mursky Mursky D.M. Davidson Davidson P.E. P.E. Meyers Meyers W.C. W.C. Cambray Carnbray D.L. Southwick Southwick T.J. Bornhorst Bornhorst T.J. G.L. LaBerge LaBerge G.L. C.E. C.E. Blackburn Blackburn J.K. J.K. Greenberg Greenberg E.D. E.D. Frey & R.P. R.P. Sage LS. Klasner J.S. Klasner J.C. Green Green M.M. Kehlenbeck Kehlenbeck M.M. Meyers P.E. Meyers A.B. Dickas Dickas A.B. D.L. D.L. Southwick Southwick T.J. Bornhorst T.J. Bornhorst M.C. Srnyk Smyk M.C. L.G. Woodruff L.G. R.P. Sage Meyer R.P. Sage & W. Meyer �______________ Constitution of the Institute on on Lake Lake Superior Superior Geology Geology Constitutjon Article!I Article Name &gy+ Geology'. The name on Lake The nameof of the theorganization organizationshall shallbe bethe the"Institute "InsMute on Lake Superior Geologr. Article II Artidell Obieclives Objectives thii organization organization are: The objectives objectivesof of this A. To Toprovide provideaameans meanswhereby wherebygeologists geologistsin in the Great Great Lakes Lakes region region may may exchange exchangeideas ideasand and scientific data. scientitic B. To To promote promotebetter betterunderstanding understandingof ofthe the geology geology of of the the Lake Lake Superior Superiorregion. region. C. To trips. Toplan planand andconduct conductgeological geologicalfield fieldtrips. Article Ill Article Ill Status No to the the benefil benefit of of any any member member or No part pafi of the income income of of the the organization organization shall insure to or individual. in&idual. In dissolution the assets of the organization shall shall be distiibuted distributed to In the event event of diiltAion (some free organization). organuation). (some tax free ifo avoid should be be not only only "saen~c'~or "scientific" or (To avoidFederal Federaland andState Stateincome incometaxes, taxes, the organization should "educational", but "educational", but also also "non-profit".) "non-proiit".) Minn. Stat. Anno. Anno. 290.91, 290.91, SUM. subd. 4 Mnn. Minn. Stat. Anno. 290.05(9) 290.05(9) 1954 Internal 1954 InternalRevenue RevenueCode Codes.501 s.501(c)(3) (c)(3) Article IV Article IV Membership Membership The the Board of of Directors. Any The membership membershipof of the the organization organuation shall shall consist con& of the Anygeologist geologist interested thai! be to vote at at the the annual annual meetings. interested shall bepermitted perm~ed to attend attend and and participate participate in and vote meetings. Article V ArticleV Meetinas Meetings The organization shall meet once a year, year, preferably preferablyduring duringthe themonth monthof ofApril. April. The The place place and and organizationshall the Board Board of Directors. Directors. will be be designated designated by the exact date of each each meeting meetingwill Article VI A WeW Directors Directors Chairperson, Secretary-Treasurer, Secretary-Treasurer, and and the last three The Board Board of Directors Directors shall shall consist cons.& of the Chairpemon, past Chairpersons; Chairpersons; but time consist of of fewer than than five board should should at any time five persons, persons, by by past but ifif the board reason of unwillingness the above above persons persons to to serve serve as as directors, directors, the vacancies reason unwillingnessor or inability inabilii of any of the on so as as to to bring bring the the membership membership of the board on the board board may may be be filled filled by by the annual annual meeting so board up up to five fwe members. members. Article Article Vii Wl Officers The officers and Secretaiy-Treasurer. Secretary-Treasurer. thii organization organization shall be a Chairperson and The officers of of this beelected electedeach eachyear yearby by the the Board Board of of Directors, Directors, who who shall shall give g ~ due due e A. The TheChairperson Chairpetsonshall shallbe consideration the wishes of any group that may be promoting promoting the next annual meeting. consideration to the nexl annual meeting. His/her will terminate terminate at at the the close close of of the the annual annual meeting meeting over H i e r term of office office as Chairperson Chairperson will which successor shall shall have have been been appointed. appointed. He/she which he/she helshe presides presides or when the successor Helshewill will then then serve serve for for aa period periodof of three three years years as as aa member memberof of the the Board Boardof ofDirectors. Directors. B. The be TheSecretary-Treasurer Secretary-Treasurershall shallbe beelected elected at the annual meeting. The The term termof of office office shall shallbe two years or until the successor shall have been appointed. two years or until the successor shall have been appointed. Article Wl Vii Article Amendments Amendmenls This majority voteof ofthose thosepeffions personswho who are are personally personally present present This constitution constitution may be amended by a majotityvote participating in, and at, participating and voting at any annual annual meeting meeting of of the organization. organization. �By-Law By-LawII Duties Duties of the Officers Officers and and Directors Directors A. ItItshall shallbe bethe theduty duly of of the the Annual Annual Chairman Chairmanto: 1. 1. Preside Presideat atthe the annual annualmeeting. meeting. Aqpointall allcommittees w m m ~ e eneeded needed s forthe theorganization organizationof the annual annual meeting. meeting. 2. Appoint for 3. Assume the annual meeting meeting Assumecomplete completeresponsibility responsibiliifor for the the organization organization and financing of the over overwhich which he/she helshepresides. presides. B. B. ItIt shall shall be be the the duty duty of of the the Secretary-Treasurer Secretaw-Treasurerto: to: 1. Keep Keepaccurate accurateattendance attendancerecords recordsof ofall allannual annualmeetings meetings 2. 2. Keep Keepaccurate accuraterecords recordsof ofall allmeetings meetingsof, of, and andcorrespondence wrrespondencebetween, between, the the Board Board of of Directors. Directors. 3. Hold Holdall allfunds fundsthat thatmay mayaccrue accrueas asprofits protitsfrom *om annual annualmeetings meetingsor or field field hips tripsand and to to make make asrequired. required. these funds funds available available for forthe organizationand and operation operation of of future Mure meetings meetingsas these the organization C. annual meetings C. ItIt shall shall be be the the duty duty of of the Board Board of of Directors Directorsto plan plan locations locations of annual meetingsand and to to advise adhe on on the the organization organizationand andfinancing financingof ofall allmeetings. meetings. By-Law By-LawIII1 Duties Dutiesand andExpenses menses 1. There I. Thereshall shallbe beno noregular regularmembership membershipdues. dues. 2. 2.Registration Registrationfees feesfor forthe theannual annualmeetings meetingsshall shallbe bedetermined determinedby bythe theChairperson Chairpersoninin consultation consultationwith with the the Board Boardof of Directors. Directors. ItIt is is strongly recommended that these thesebe bekept keptto toaa recommended that minimum minimumto to encourage encourageattendance attendanceof ofgraduate graduatestudents. students. By-Law Rulesof of Order Order By-LawIllIll Rules The thisorganization organizationininall allcases casesininwhich which The rules mlescontained containedin in Roberts RobeesRules RulesofofOrder Ordershall shallgovem governthis they they are are applicable. applicable. By-Law IV Amendments Amendments By-Law IV These by-lawsmay maybe beamended amendedby by aa majority majorityvote vote of of those those persons persons who are are personally personallypresent present Theseby-laws at, at, participating paftiapatingin, in, and andvoting voting at at any any annual annualmeeting meetingof ofthe theorganization; organuation;provided providedthat thatsuch such modifications modificationsshall shallnot notconflict conflictwtih wtihthe theconstitution constitutionas aspresently preseniyadopted adoptedor orsubsequently subswuentlv amended. amended. Ill iii �Index of Proceedings Volumes and Field Field Trip Guidebooks Guidebooks of the Institute on Lake Superior Geology the Institute on Lake Superior Geology 1955 1955 -- 1997 1997 compiled by Compiled byMark MarkJissa, Jim, Secretary-Treasurer, Secretary-Treasurer, ILSO ILSG *Denotes abstracts volumes and guidebooks which can be ordered from from the the Secretary-Treasurer. Secretary-Treasurer. .Denotes abstracts and guidebooks UniversityAvenue, Avenue,SStt Paul, Paul, MN, MN,55114-1057, 55114-1057,Phone: Phone:6124274539, 612-627-4539,fax: fax:6124274778. 612-6274778, e-mail: 2642 Un~esity jirsaOOl@?maroon.tc.umn.edu jirsa001@maroon.tc.umn.edu complete list A complete liicontaining containingsuch such information informationas as author, author, editor, ed*or, chairperson, chairpemn, and andsponsoring sponsoringorganization organizationisis maintained Van Pelt maintained by Ms. Theresa Sanderson Sandeson Spence, archMst a r c h i d at at the J. Robert Robert Van PeltUbrary, Library, Michigan Michigan Technological Ml 49931 (906487-2505). (906-487-2505). Photocopies Photocopiesof of back backvolumes volumescan canbe beordered ordered Technolcgical University, Unwersity, Houghton, MI from Sanderson Spence some guidebooks were publiihed published separately separately by the the from Ms. Sanderson Spence at at the prevailing prevailingcopy rate. Some Mnnesota Survey MinnesotaGeological GeologicalSurvey Survey(MGS), (MGS), and and Wisconsin Wsconsin Geological Geolcgical and Natural Natural History Hiiory S u ~ e (WGNHS), y as indicated indicated below, below; however, however, most most are are no no longer longeravailable. available. (Each is a separate separate bound bound document) (Each italicized italicizeditem item is documenq Volume Location . Volume Year Location .--. . -- -.. 1 1955 Minneapolis, Minnesota 1955 Minnesota Program Program andAbsfracts andAbstracts (contains (contains no no record record of of field fieldtrips) trips) 2 1956 Houghton, Michigan 1956 Houghton, Michigan Program Abstracts Program and andAbstracts Geological GeologicalExploration ExplorationOnferred (inferred to to be be aa field field guide) guide) 3 1957 1957 East Lansing, Michigan Michigan Program and Abstracts h g r a m andAbshds 4 1958 Duluth, Minnesota 1958 Minnesota Program and and Abstracts Pfvgram 5 1959 Minneapolis, 1959 Minneapolii, Minnesota Minnesota Program and P -m andAbstracts Abstmcts 6 1960 Wisconsin 1960 Madison, W ~consin Program and Program andAbstracts AbsWs 7 1961 Port Arthur, Ontario Ontario 1961 Program and and Abstracts label reads reads 6th Program Abstracts (misprinted (misprinted label 6fh annual annualmeeting) 8 41962 962 Houghton, Michigan Michigan Program and and Abstracts Program Abstracts 9 1963 Duluth, 1963 Duluth, Minnesota Minnesota Program and Abstracts Program andAbstracts Field lfinera!y: Itineraty: Stratigraphy Strafigraphy of the Biwabik Iron m Fonnation Field of the Bwabik lmn ation 1964 10 Michigan 1964 lshpeming, Michigan Program andAbstracts Ptvgram andAbstrads Field Trip: Marquette imn-mining iron-mining d district and Republic Republic h trough Field Trip: Maque~e W and igh 11 1965 St. Paul, Minnesota 1965 Minnesota Program and and Abstracts Program Abstracts Field Trip Trip Guide Guidetto the St. St Cloud granite Idistrict Field o fhe Cloudgranite $&, central centralMinnesota Minnesota 12 1966 Sault Ste. Marie, Ontario Ontario 1966 Sauk Program and and Abstracts guides to: Program Abstractsincludes includesfield field guides to: 1. Regional Regional geology geology of I. of the Sault Sault Ste. Marie area 2. Geology Geologyand andmineral mtneraldeposits depositsof ofthe the Manitouwadge Manitouwadge Lake Lake area, Ontario 3. The Therelationship relationshipof ofmineralization mineralizationto to the the Precambrian Precambrianstratigraphy, stratigraphy, Blind River Rier area, Ontario 4. Sudbury Sudburynickel nickelirruptive irmptive tour, tour, Ontario Ontario 13 1967 3967 East Lansing, Michigan Michigan iv �Program tracts Programand andAbs Abstracts Field Field Trip: Trip: Grenville Grenville Province Province of of southeastern southeasternOntario, Bancroft-Madoc Bancrofl-Madoc area area Volume Location Volume Year Location 14 1968 Superior, Wisconsin Wisconsin 14 1968 Superior, Technical Sessions and and Abstracts Abstracts Technical Guide for Field complex F ~ e lTrip Trip d in in the fhe Duluth DU U IUI wm@x near nearEly, EM, Minnesota Minnesota Guide Wisconsin 15 1969 15 1969 Oshkosh, Wisconsin Technical Abstracts Technical Sessions Sessions and and Abstracts Wsconsin volcanic volcanic belt belt Guidebook: Central Central Wisconsin 16 1970 Thunder 16 1970 ThunderBay, Bay,Ontario Ontario Technical Sessions, Abstracts Abstracts and andField FieldGuides Guides Field Technical Sessions, Field Trips: A. A Proterozoic Proterozoicformations formations in in the the Thunder ThunderBay Bayarea area Sturgeon Riier River metavolcanic-metasedimentary metavolcanic-metasedimentary formations in the the Beardmore-Geraldton Beardmore-Geraldton area area B. Sturgeon C. The Port Coldwell alkalic alkalic.complex Port Coldwell complex Geology of the Atikokan area area (title not D. Geology not exact) Duluth, Minnesota 17 1971 17 1971 Minnesota Technical Sessions, Sessions, Abstracts Abstracts and and Field Field Guides Guides Field Technical FieldTrips: Trips: Group A. North Shore Volcanic Group B. Precambrian Precambrian rocks Cook County exposed along the the Gunflint Gunflint Trail Trail rocks of northwestern northwestern Cook County as e x w e d along C. Mesabi Mesabi Range Range magnetite magnelite taconite taconite 0. metavolcanic-metasedimentarybelt, belt, northeastern northeasternMinnesota Minnesota D. Geology Geologyof of the the Vermilion Vermilion metavolcanic-metasedimentary Houghton, 18 1972 18 1972 Houghton, Michigan Michigan Part L Technical Technical Sessions -Agenda - Agenda and and Abstracts (desmies (describes trips A-D) Partl. hips A-D) Field Trips: Field Trips. A. Penokean and PenokeanOrogeny Orogenyin in the the central centraland andwestern westernGogebic Gogebicregion, region,Wisconsin W~consin andMichigan Michigan B. Guide to to Penokean deformation deformation style style and and regional metamorphiim metamorphism at the the westem western Maquette Marquette Range, Michigan Michigan Madison, Wisconsin 19 19 1973 Abstracts* and Abstracts* Technical Program Program and Technical Field Trip: to the the geology geology and and mineral mineral deposits deposits of of the the central central part part of of Jackson Jacksoli County and part Field Trip: Guidebook to County and part County,Wisconsin W w n s i n (WGNHS) of Clark County, Field Trip: to the the Precambrian Precambrian geology geology of northeastern and and north-central north-central W Wisconsin Field Trip: Guidebook to mnsin Field Trip: to the the upper upper Miissippi MississippiValley Valleybase-metal base-metald'itrict district(WGNHS (WGNHSInformation Informationcircular circular No. No. Field Trip: Guidebook to 16) 16) Bibliography Lake Superior Superior Region Region ~ ! b l i o ~ r of of a Current ~Cutrent h ~ Research Researchin inThe tbe Lake Sault Ste. Marie, Ontario 20 1974 1974 SauR Marie, Ontario Field Middle I: Middle Keweenawan Keweenawan rocks rocks of of the the Batchawana-Mamainse Batchawana-MamainsePoint Pointarea area FieldTrip Trip 1: Field 2: unknown unknown FieldTrip Trip 2: Field Trip 3 3:: Precambrian Precambrian igneous rocks of the north shore of Lake Huron region Field Field Trip sedimentation of 4: Stratigraphy Stratigraphy and sedimentation of the Huronian Huronian Supergroup Supergroup Field Trip 4: Field Trip 5 5: belt. : The The Michipicoten Michipkoten greenstone belt Field Bibliography of Research in in fhe the Lake Lake Superior Superior Region Region (First Supplement) (first Supplement.) Bibliography of Current Cutrent Research Marquette, Michigan 21 1975 21 1975 Michigan Proceedings Proceedings Includes the following following field trip trip guides guides and and aa supplement supplement by Burton Burton Boyum Boyum containing containing aa mlour colour map map of the the Includes Marquette Marquette Mineral Mineral District District 1.. Glacial geology geology (trip cancelled, cancelled, no I Glacial no guidebook) guidebook) 2. Greenstone Greenstone 3. The The Jacobsville Jacobville Sandstone: Sandstone: Evidence Evfdencefor for aa Lower-Middle Lower-Miidle Keweenawan Keweenawanage age 4. Marquette Marquette Iron Iron Range Range 5 and and 6. The The Empire EmpireMine Mine and and Mill, Palmer, Palmer, Michigan Michiian Minnesota 22 1976 22 1976 St. Paul, Minnesota - V �Location Volume Year Location Proceedings Proceedngs Includes abstracts abstracts and Includes and guide guide to Field Field Trip B Field Trip A: A: Minnesota R River Valley field conference conference (no formal formal guidebook Field i ~ eValley r field guidebookprinted) printed) Field Trip B: Engineering Engineering and and Pleistocene Pleistocenegeology geologyin inthe the Twin TwinCities Ciies area area Thunder 1977 Thunder Bay, Bay, Ontario Ontario Proceedings Proceedings Field Trip Geology of the Coldwell alkaline Complex Trip A Geology Field Field Trip Trip B Proterozoic Proterozoicrocks rocks of of the the Thunder Thunder Bay Bay area, area, northwestern northwestern Ontario Ontario ("Proterozoic Trip") Trip") Field Field Trip South Sturgeon Trip C C Archean Archean metatlogeny rnetallogenyand and stratigraphy stratigraphy of of the South Sturgeon Lake Lake area area ("Mattabi ("Mattabi Trip") Trip? Field Wisconsin 1978 24 1978 Milwaukee, Wisconsin Abstracts Abstracts and andProceedings Procee&ngs Field zinc-lead district Trip IISouthwestern Southwestern Wisconsin Wiconsin zinelead d i i c t (WGNHS Field Field Trip Guide Guide Book Book Number Number1) I) FieldTrip Reid processing equipment manufacturers manufacturers in FieldTrip TripPI1Mineral Mineral extraction extraction and pro-hg in the Greater Greater Milwaukee Milwaukeearea area (no guidebook) guidebook) Field FieldTrip Trip lii IllPrecambrian Precambrianrhyolite rhyoMeand andgranite graniteinliers inliersin in south-central south-central Wisconsin Wiconsin (WHNHS (WHNHSField FieldTrip TripGuide Guide Book Number Number 2) Duluth, 25 1979 25 1979 Duluth, Minnesota Minnesota Technical Sessions Sessions and and Abstracts Abstracts Joint meeting meeting with North-Central Section Section GSA Technical Field Trip Trip Guidebooks: Guidebooks: some were published separately as MGS Guidebook referenced below, the the some were publiihed separately Guidebook Series referenced remainder are apparently unavailable. A in GSA GSA proceedings: proceedings: remainder A total total of of eight eight trips were listed in Precambrian volcanic and plutonic rocks 1. Middle Precambrian rocks of northern northern Wisconsin 2. Stratigraphy, Stratigraphy, structure structure and and mineral mineral resources resources of of east-central east-central Minnesota Mmnesota (MGS (MGS Field FieldTrip Trip Guidebook Guidebook series no. 9) no. 9) 3. Quaternav Quaternary geology geology of the Duluth Duluth area area Geology of the Mesabi 4. Geology Mesabi Iron Range Geologic history western Lake Lake Superior region 5. Geologic hiiory and engineering engineering geology of the western 6. Cambrian Cambrian and paleontology of southeastern Minnesota Minnesota and Ordovician Ordoviaan stratigraphy and paleontologyof (tipper Precambrian) v1GS Field 7. Keweenawan (Upper PrecambM) North NorthShore Shore Volcanic Volcanic Group, Minnesota (MGS Field Trip Tfip no 11) Guidebook no. 11) 8. Archean Archean volcanism volcanism and sedimentation of the w&em western Vermiliin Vermilion D District, northeastern Minnesota 8. and sedimentation k k t , northeastarn Mhnesota (MGS Guidebook Series Guidebook Series no. 10) 10) Eau Claire, Wisconsin Wisconsin 1980 1980 26 Proceedings Abstracts Proceedingsand andAbshcts Field Trip II Precambrian Precambriangeology geologyof ofthe the Chippewa Chippewa Valley, Wisconsin. Wsconsin Field Trip Field Trip 22 Precambrian Precambriantectonic tectonic history hiitow of the Black Black River Riier Valley Field Trip Field Field Trip Trip 33 Petrology, Petrology, geochemistly, geochemisby, and and contact contactrelations relations of of the the Wausau Wausau and andStettin Stettinsyenite syenite plutons, plutons, Central Wisconsin Central Wisconsin Reid Trip Trip44 Precambrian Precambriangeology geologyand andtectonics tectonicsof ofMarathon MarathonCounty, County, Wisconsin W~consin Field 1981 27 1981 East Lansing, Michigan Michigan Abstracts Abstracts and andProceedings Pmeedngs Field Excursion Guide Thessalon, District Algoma, D i i c t of Ngoma, FieldExcursion Guide The TheHuronian Huronianrocks rocksbetween betweenSault Sault Ste. Marie and Thesalon, Ontario Ontario 1982 28 International Falls; 1982 International Fans, Minnesota Minnesota Proceedings: Field Trips TripsQn (in one volume) h m d i n g s : Abstracts Abshcfs and andField Field Trip II Mineral Mineral deposits of the Fort Fott Frances-Mine FrancesMine Centre Centre area, Ontario Ontario Archean geology of the International International Falls-Kabetogama area, Minnesota III Archean Field Trip 1 29 1983 1983 Houghton, Michigan Volume I I::Abstracts Ropes gold mine geological setting Abstractsand andField FieldTrip Trip— Ropes mine and and its its geological setting Volume Volufne II: 11: Field guide to the the geology geology of of the the Keweenaw KeweenawPeninsula Peninsula 30 1984 Wausau, Wisconsin Wisconsin 1984 Wausau, Abstracts Abstracts 23 23 - vi �Volume Location Volume Year Location I Guide Guide to ofof thethe Early Proterozoic rocksrocks in northeastern Wisconsin Field Trip Trip 1 tothe thegeology geology Early Proterozoic in northeastern Wisconsin Field Field Trip tectonostratigraphic terraines of theof southern Superior region Trip22Early EarlyProterozoic Proterozoic tectonostratigraphic terraines the southern Lake Lake Superior region Field Field Trip Field Trip 3 3 The Wausau Wausau Syenite Complex 1985 31 31 1985 Kenora, Ontario Absfracts Abstracts Field Trip Field Trip Guidebook Guidebook The Cameron Cameron Lake 1. The Lake Deposit Deposit 2. Geologic the Lake Lake of of the the Woods Woods area Geologic setting setting and and style of gold mineralization in the 3. Geological Geologicalrelationships relationshipsin in the the vicinity of the Wabigoon-Winnipeg River River subprovincial subprovincialinterface interfaceininthe the Kenora Kenora area area 4. A volcanic volcanic fades 4. fades interpretation interpretationof of the the Berry BerryRiver River Formation Formation Granitoid related 5. Granitoid relatedmineralization mineralizationin in the Dryden Dryden area area 32 1986 32 1986 Wisconsin Rapids, Wisconsin Abs tracts AbsfnactsField Trip! The Field Trip I TheWolf WolfRiver RiverBatholith Batholithand andBaraboo Baraboointerval interval (published (published as as Field Field Trip Trip Guide Guide Book Book Number Number 12, 1 2,WGNHS) Il Penokean Penokean deformation and metamorphism metamorphism in central Wisconsin: volcanic volcanic rocks Field Trip Trip I1 rocks and and gneisses gneisses un-numbered Field Trip Guide Book Book of of the the WGNHS) WGNHS) (published as un-numbered . were adopted adopted to to conform conform to to ISSN standards standards in 1987) (compiler note: new new reference reference designations were 33 1987 Wawa, Ontario 1987 Ontario Pan' 1 1: Abstracts : 'Abstracts Part Part 2: *Geology Part2: "Geology of of the the Wawa Wawa area area and and gold gold mineralization mineralization Pail 3: 3: Geology 'Geology and andstratigraphy stratigraphyof ofthe theMichipicoten Michipicoteniron-Formation Iron-Formation Part *Glogy ofofthe Part 44: : 'Geology theHemlo HemloDeposit Deposit PantS: 5: TThe h eKapuskasing KapuskasingUplift UpliftArctiean Archeangreenstones greenstones and and granulites Part 1988 1988 Marquette, Michigan Michigan Pail I: Abstracts Parti: 'Abstracts Pant2:Field FieldTrip TripGuidebook Guidebook Part 1. An introduction introduction to to Archean Archean geology geology and and precious precious metal metal mineralization mineralization of of the the Marquette Marquette Greenstone Belt, Michigan Michigan 2. Marquette geology Marquette mineral mineraldistrict district of of Michigan, Michigan, mining mining history history and geology A structural traverse across aa part part of ofthe the Penokean Penokean orogen orogenillustrating illustrating Early Early Proterozoic Proterozoic overthrusting overthrusting in in 3. Astructural northern Michigan northern Michigan Duluth, 1989 1989 Duluth, Minnesota Minnesota Part : Abstracts Abstracts Part I:1 Part : Field Guidebook Pan' 22: Field Trin Dip Guidebook North Shore 1. ~o-rth Shore rhyolites, rhyolites, Minnesota Minnesota 2. Penokean PenokeanStructural StructuralTerranes Terranesinineast-central east-centralMinnesota Minnesota Mellen Complex. 3. Mellen Complex, Wisconsin Wisconsin 4. Archean Archean gold goldoccurrences occurrencesand andtheir their structural structuralsettings settings(Virginia (Virginia Horn) Horn) Thunder 1990 1990 Thunder Bay, Bay, Ontario Part I: tAbstracts Abstracts Part2 Part 2:Field FieldTrip TripGuidebook Guidebook and granitoid granitoid rocks rocks of of Lac des lies lies area 1. Mafic intrusions, PGE mineralization, and area 2. Geology Geology of of the the Shebandowan Shebandowan and and Quetico QueticoArchean Archean subprovinces subprovinces Granitoid-related mineral Lake Superior Superior region 3. Granitoid-related mineral deposits deposits in the western Lake region 4. Base Base metal metalmineralization mineralizationin in the the Shebandowan ShebandowanGreenstone GreenstoneBelt Belt 1991 Eau Wisconsin 1991 Eau Claire, Wisconsin Part *Abstracts Part I:1:*Abstracts Part Part 2: 2: *Fieid 'Field Trip Trip Guidebook Guidebook Mountain Shear post Penokean Penokean discrete discrete ductile ductile deformation deformation zone 1. Mountain Shear Zone Zone — - a a post zone 2. Features Featuresand and significance of of the the Precambrian-Cambrian Precambrian-Cambriancontact contactin in western westernWisconsin Wsconsin 3. Proterozoic Wisconsin Proterozoic volcanogenic volcanogenic massive massive sulfide sulfide deposits of NW NW Wisconsin - 34 35 36 37 . VII vii �Location Year Volume Year Location Volume Hurley, 38 1992 Hurley, Wisconsin Wisconsin 1992 38 Pad 1:*Program "Program and andAbstracts Abstracts Part1: Part 2:'Field Trip TripGuidebook Guidebook Pad2:Field 1. Archean and andEarly EarlyProterozoic Proterozoicgeology geology of of the the Gogebic GogebicDistrict District 1. Archean 2. Evolution Evolutionof ofthe the Keweenawan Keweenawansedimentary sedimentarysequence sequence 2. 3. 3. Geology Geologyof ofthe theKeweenawan KeweenawanSupergroup Supergroupat atPorcupine PorcupineMountains Mountains 4. late Archean paleosuture paleosuture 4. Geology Geologyof of the the Great GreatLakes LakesTectonic Tectonic Zone - Marquette area - a late Eveleth, 1993 39 1993 Eveleth, Minnesota Minnesota 39 Part 1: 1:'Program andAbstracts Abstracts Pan' Program and Part2: 2: Field 'Field Trip TripGuidebook Guidebook Pad 1. 1. Geology Geologyand andtaconite taconitemines minesof ofthe theMesabi Mesabirange range 2. 2. DNR DNRCore CoreUbrary LibraryBiwabik 'B'wabikIron IronFormation. Formation,Partridge PartridgeRiver Riverand andSouth SouthKawishiwi Kawishiiintrusions, intrusions,Regolith Regolithinin northernMinnesota) Minnesota) Rotasoniccores cores--northern Rotasonic 3. 3. Geology Geologyof ofArchean Archeangreenstone-granite greenstone-granite terrane: terrane: Cook-Side Cook-SideLake Lakearea area 4. Duluth DuluthComplex Complexat atDuluth Duluth Houghton, 40 1994 Houghton, Michigan Michigan 40 1994 Pad *Program and Part1: 1:"Program andAbstracts Abstracts Pad 2: *Self..guided geological Keweenaw Peninsula, Michigan (available from Part2:'Self-guided geological field trip to the Keweenaw from Dr. Dr. T.J. T.J. Bornhorst, 402 Emerald Street, Street,Houghton, Houghton,MI Ml 49931-1413 49931-1413 (906482-5507)) (906482-5507)) Part3: 3: Volcanic Volcanicgeology geologyof ofeastern easternIsle kle Royale, Royale, Michigan Michigan Pad Pad 4: Michigan "Michigankimberlites kimbetiiesand anddiamond diamondexploration explorationtechniques techniques Part4: Pad Part5: 5: Lessons 'Lessons from frommining miningcase casehistories: histories:West WestMenominee MenomineeRange, Range,Michigan Michigan Marathon, 1995 41 1995 Marathon, Ontario Ontario 41 Pad Part1: 1:*Program 'Program and andAbstracts Abstracts Pad Part2: 2: Field FieldTrip TripGuidebooks Guidebooks(some (some may mayalso also be beacquired acquiredfrom fromOntario OntarioGeological GeologicalSurvey, Survey,Ministry Ministryof of Northern 435 South NorthernDevelopment Developmentand andMines, Mines, Suite Suite 8002, B002.435 SouthJames JamesStreet, Street,Thunder ThunderBay, Bay,Ontario, Ontario, Canada Canada P7E P7E6E3 6E3 (807475-1331)). (807-475-1331)). 2a. Alkalic *Alkalicrocks rocksofofthe theMidconlinent MidcontinentRift Rift 2a. 2b. 2b.'Geology and andbase basemetal metaldeposits deposits of of the the Manitouwadge Manitouwadge Greenstone Greenstone belt belt 2c. 2c. Geology 'Geology ofofthe theSchreiber SchreiberGreenstone Greenstoneassemblage assemblageand andits itsgold goldand andbase basemetal metalmineralization mineralization 2 d Geology Geologyand and gold gold deposits deposits of of the Hemlo Hemloarea area 2d. 2e. 'Kimberlite, area *Kimberliie,base basemetal, metal,and andgold goldexploration exploration using using overburden, Wawa area Cable, Wisconsin 1996 42 1996 Cable, Wisconsin 42 Part1: 1:Program Programand andAbstracts Abstracts Pad Pad Part2: 2: Volcanogenic Volcanogenic Massive Massive Sullide Sulfide Deposits Deposits of Northern NorthernWisconsin: Wsconsin: A Commemorative CommemorativeVolume Volume (published (publishedin in conjunction conjunctionwith with Field Field Trip Trip 33 to to the the Flambeau FlambeauMine) Mine) Pad Part3: 3: Field FieldTrip Trip Guidebook Guidebook 1. Glacial Glacialgeology geologyof ofwestern westernWisconsin Wisconsin 1. 2. 2. Geology Geologyofofthe theMontreal MontrealRiver RiverMonocline: Monocline: A A traverse traverse through through 25 km km of of crust crust 4. 4. Early EarlytotoMiddle MiddleProterozoic Proterozoicgeology geologyof of the the Lake Lake Namekagon Namekagonregion region 5. Lake LakeNamekagon Namekagonand andPenokee PenokeeGap Gaparea, area, west west Gogebic Gogebic Range, Range, Wisconsin Wsconsin Sudbury, Ontario 43 1997 Ontario 43 1997 Pad 1: Program Parti: Programand andAbstracts Abstracts Pad2 Huronian Supergroup The Huronian Supergroupbetween betweenSault SaultSte. Ste.Marie Marieand andElliot ElliotLake Lake Part 2:The Pad 3: New Part3: NewDevelopments DevelopmentsininGrenville GrenvilleFront FrontGeology, Geology, Sudbury Sudbury Area, Ontario Ontario Pad 4: The TheSudbury SudburyStructure Structurewith with Emphasis Emphasis on on the the Whitewater Whitewater Group Group Part4: Pad 5: Magmatic Part5: MagmaticOre OreDeposits Depositsof ofthe the Sudbury Sudbury Igneous Igneous Complex Complex Part 6: 6: Alkalic Alkalicrocks rocksof ofthe theSudbury Sudbury Region Region Pad Pad Part?:7: Regreening Regreeningof of Sudbury Sudbury - Future Meeting Meeting Locations: Future 44 1998 ? 44 1998 ? 1999 45 1999 ? 45 VIII viii �Award Guidelines Award Guidelines Sam Goldich Sam Goldich Medal Medal Preamble Preamble The documented by by the the fact fact that that the 27th 27th The Institute Institute on on Lake Lake Superior Superior Geology Geology was born in or around 1955, as documented with those those aspects aspectsof of annual meeting meeting was was held held in in 1981. 1981. The TheInstitute's Institute's continuing continuing objectives objectives are are to to deal dealwith geology geology that that are are related relatedgeographically geographicallyto to Lake Lake Superior, to encourage encouragethe the discussion discussionof of subjects subjectsand and sponsoring sponsoring field field tips tripswhich whichwill willbring bringtogether togethergeologists geologistsfrom fromacademia, academia,government governmentsulveys, surveys,and andindustry, industry, and and to maintain maintain an an informal informalbut buteffective effective mode mode of of operation. During itsexistence existencethe the membership membershipof of the the Institute Institute(that (thatis, is, those those geologists geologistswho whoindicate indicatean an During the the course courseof ofits interest attending) has hasbecome become aware awarethat interest in the objectives objectives of the ILSG by attending) that certain certainof of their theircolleagues colleagueshave have made to the the understanding understanding of made particularly particularlynoteworthy noteworthyand and meritorious meritoriouscontributions to of Lake Lake Superior Superior geology geology and mineral mineral deposits. deposits. The was made to Sam Sam Goldich in in 1979 for for his many contributions contributions to the geology of of the the The first award award was made by by the the ILSG to region extending over some 50 years. region extending over some 50 years. Guidelines Award Guidelines The medal medal shall of Directors Directors to to a geologist geologist whose name 1) The shall be be awarded awarded annually annually by by the ILSG Board of name is substantial interest in, and and contribution contribution to, to, the the geology geology of the Lake associated with a substantial Lake Superior Superiorregion. region. 2) The the Nominating Nominating Committee. Committee. The The Board Board of of Directors Directorsshall shall appoint the The initial initial appointment appointment shall shall be be of three members, years, and and one for for one year. The member with the the members, one oneto to serve serve for for three three years, one for two years, memberwith briefest incumbency shall year, the the Board shall shall appoint briefest incumbency shall be be chairman. chairman. After the first year, appoint at at each each spring spring meeting meeting one new member member who will serve for three three years. years. In the third third year year this this member member shall shall be the the chairman. chairman. The The Committee membership membershipshould shouldreflect reflect main fields of interest geographic dbon ofofILSG thethe main fields of interest andand geographic distribution ILSG membership. membership. 3) By Committee shall shall make By November, November, the the Goldich GoldichMedal Medal Nominating Nominating Committee make its its recommendation recommendationto tothe theChairman Chairman of the Board Board of Directors inform the the Board of of the the nominee. Directorswho will then inform 4) The TheBoard Boardnormally normallywill willaccept acceptthe thenominee nomineeof of the the Committee, Committee, will will inform informthe the medallist medallistimmediately, immediately,and and will have meeting of the Institute. have the medal medalengraved engravedappropriately appropriately for presentation presentation at the next meeting recommended that set aside aside annually annuallyfrom from whatever whatever sources, sources, such such funds as will will be 5) that the the Institute Institute set 5) It is recommended required to support support the cosk of this award. required the continuing continuing costs Nomination Nomination Procedures Procedures 1) Nominations shall be taken at any any time lime by bythe theGoldich GoldichMedal MedalCommittee. Committee. Committee members members may themselves November 1. themselves nominate nominate candidates. The The deadline deadline for nominations nominations is November 1. supported by by appropriate appropriatedocumentation documentation such such as letters of 2) Nominations Nominations must must be be in in writing and supported recommendation, recommendation,lists listsof ofpublications, publications,c.v.'s, c.v.'s, and and evidence evidence on on contributions contributionsto to Lake LakeSuperior Superiorgeology geologyand andto to the Institute. Institute. 3) Nominations attendees but are open to anyone Nominations are are not notrestricted restrictedto to Institute Institute attendees anyone who who has hasworked workedon onand and contributed contributed to Lake LakeSuperior Superiorgeology. geology. ix �Selection Guidelines Selection Guidelines Nominees are Lake Superior 1) Nominees are to to be beevaluated evaluated on on the basis basis of their contributions to Lake Superiorgeology geology(sensu (sensulato) lato) including: importance of relevant a) importance relevantpublications publications b) promotion of natural natural resources promotion of of discovery discovery and utilization of natural history and environment c) contilbutions contributionsto to understanding understanding of the natural environmentof ofthe theregion region d) generation generation of new new ideas and concepts the training training and and education education of of geoscientists geoscientists and and the the public. public. e) contributions contributions to the - as demonstrated demonstrated by 2) Nominees Nomineesare are to to be beevaluated evaluatedon on their contributions contributionsto the Institute as by attendance attendance at at Institute meetings, presentation and service service on on Institute boards, committees, committees, and and field field Institute meetings, presentation of talks and posters, and trips. 3) The remain flexible The relative relativeweights weightsgiven given to each of the foregoing criteria must remain flexibleand andat atthe thediscretion discretionof of the the Committee members. Committee members. 4) There There are are several severalpoints pointsto to be be considered considered by the selection committee: balance of of medal medal recipients recipients from each a) an attempt attempt should should be be made made to maintain aa balance each of of the the three three estates, industry, academia, and and govemment. government. b) it must must be geoscientists are areat ataadisadvantage disadvantagein inthat that much much of their work is Is not not be noted noted that industry geoscientists published. published. one the the United UnitedStates, States,the theother otherCanada. Canada. This This is undoubtedly undoubtedly one of the the 5) Lake Lake Superior Superior has has two sides, one great strengths strengths and should should be be nurtured nurtured by equitable equitable recognition recognition of excellence excellence in Institutes' great in both both countries. x �Board Board of Directors Directors 1997 1997 Ronald Co-chainnan Ronald P. P. Sage, Co-chairman Wilt ned Meyer, Co-chairman Co-chairman Wilfried Ontario Ontario Geological GeologicalSurvey, Survey, Sudbury, Ontario Ontario 1996 1996 LaurelG.Woodruff Laurel G. Woodruff U.S. Geological Geological Survey, St. Paul, Paul, Minnesota Minnesota U.S. Survey, St. 1995 1995 Mark C. C. Smyk Ontario Geological Ontario GeologicalSurvey, Survey, Thunder Thunder Bay, Bay, Ontario Ontario 1994 1994 Theodore J. Bomhonst Bornhorst Michigan Technological Michigan TechnologicalUniversity, University, Houghton, Michigan Michigan Permanent Secretary-Treasurer Mark Jirsa Jirsa Mark Minnesota Geological Minnesota GeologicalSurvey Survey 2642 University 2642 UniversityAvenue Avenue St Paul, MN55114-1057 55114-1057 St. Paul.MN Committees Local Committees General Chair Ronald P. Sage Ronald Ontario Geological Geological Survey, Ontario Survey, Sudbury, Ontario Ontario Wilt ned Meyer Wilfried Geologists Program, Resident Geologist's Program,Sudbury, Sudbury, Ontario Ontario Program 'Committee Committee Program Ronald Ronald P. P. Sage Sage Geological Survey, Ontario Geological Survey, Sudbury, Sudbury, Ontario Wilfnied Meyer Wilfried Meyer Geologists Program, Resident Geologist's Program, Sudbury, Sudbury, Ontario Ontario Tracy Livingstone Resident Geologists Program, Resident Geologist's Program,Sudbury, Sudbury, Ontario Ontario Field Field Trip Trip Committee Committee P. Sagi Ronald P . Sage Geological Survey, Ontario Geological Survey, Sudbury, Sudbury, Ontario Ontario Wilfnied Wilfried Meyer Meyer Geologists Program, Resident Geologist's Program, Sudbury, Sudbury, Ontario Ontario Livingstone Tracy Livingstone Resident GeolgoisCs Geolgoist's Program, Resident Program, Sudbury, Sudbury, Ontario Ontario Secretary-Treasurer Secretary-Treasurer Tracy Livingstone Geologists Program, Resident Geologist's Program, Sudbury, Sudbury, Ontario xi �Student Paper Paper Committee Committee Kalliokoski Jorna Kalliokoski Technological University Professor Emeritus, Michigan Technological University Jim Miller Miller Senior Geologist, Geological Survey Geologist, Minnesota Minnesota Geological Darrell Long Long Department of Earth Earth Sciences, Sciences, Laurentian Laurentian University Session Chairs Chairs LaBerge Gene LaBerge of Wisconsin Wisconsin Oshkosh, Oshkosh, Oshkosh, Oshkosh, Wisconsin Wisconsin and and U. U.S. S. Geological GeologicalSurvey Survey University of Terrence Boerboom Boerboom Minnesota St. Paul, Paul, Minnesota Minnesota Minnesota Geological GeologicalSurvey, Survey, St. Mark Mark Smyk Ontario Ontario Geological GeologicalSurvey, Survey, Thunder ThunderBay, Bay, Ontario Ontario Jirsa Mark Jirsa Minnesota St. Paul, Paul, Minnesota Minnesota Minnesota Geological GeologicalSurvey, Survey, St. Gordon Gordon Medaris, Medaris, Jr. of Wisconsin-Madison, Wisconsin-Madison, Madison, Wisconsin Wisconsin University of Frank Luther Luther of Wisconsin-Whitewater, Wisconsin-Whitewater, Whiiewater, Whitewater, Wisconsin Wisconsin University of Theodore Bornhorst Michigan Michigan Technological TechnologicalUniversity, University, Houghton, Houghton,Michigan Michigan Phil Thurston Phil Thurston Ontario Ontario Geological GeologicalSurvey, Survey, Sudbury, Sudbury, Ontario Ontario 1996-97 Goldich Medal 1996-97 Medal Committee Committee Ken Card Ken Card (1997) (1997) Consulting (formerly Geological Consulting Geologist, Kanata, Ontario (formerly Geological Survey Survey of of Canada) England (1998) (1998) Dan England Eveleth Fee Office, Incorporated, Eveleth Incorporated,Eveleth, Eveleth, Minnesota Minnesota 999) (1999) John Klasner Klasner(1 Macomb, Illinois Western Illinois Illinois University, Macomb, Illinois XII xii �1997 GOLDICH MEDAL MEDAL RECIPIENT RECIPIENT RONALD P. SAGE, SAGE, ONTARIO ONTARIO GEOLOGICAL GEOLOGICAL SURVEY SURVEY Past Goldich Goldich Medalists Medalists Samuel Samuel S. Goldich Goldlch not not awarded awarded Carl E. Dutton, Dutton, Jr. Jr. Carl E. Ralph Ralph W. Marsden Marsden Burton Burton Boyum Boyum Richard Richard W. Ojakangas Ojakangas Paul Paul K. Sims Sims G.B. G. 6.Morey Morey Henry Halls Henry H. Halls Walter S. Whit Whit Jorma Kalliokoski Kalliokoski Kenneth Kenneth C. C . Card Card William William J. J. Hinze Hinze William F. Cannon Cannon William F. Donald W. Davis Davis Donald W. Cedric Cedric Iverson Iverson Gene LaBerge LaBerge Southwick David L. Southwick 1979 1980 1981 1982 1983 1984 1985 1986 1987 1988 1989 1990 1991 1992 1993 1994 1995 1996 1997 Banquet Speaker Dr. Peter Lightfoot Lightfoot Inco Limited Limited Ontario Copper Cliff, Ontario Origin Origin of the Sudbury Sudbury Structure Structure and its its Mineral Mineral Wealth Wealth XIII xiii �Banquet Banquet Speaker Dr. D r.Peter Peter Lightfoot Lightfoot Inca Inco Limited Limited his BScdegree degreein inGeology Geologyfrom fromWorcester WorcesterCollege, Collee, Oxford, in Peter received h is BSc Oxford, England Englandin in 1980 1980 and and his MSc in Geology under the supervision of of A.J. A.J. NaldretI Naldrett from from the the University Universityof ofToronto Torontoin in1982. 1982. He returned returned to England England received his PhD in Geochemistry from from the Open University, Milton Keynes, Keynes, England England under under the supervision and received supervision C.J. Hawkesworth. .J.Hawkesworth. of C During the period 1985 through through 1987, 1987, Peter Peterwas was aa Post-doctoral Postdoctoralfellow fellowat atthe theUniversity Universityof ofToronto, Toronto,Canada Canada During the periodof of 1985 conducting diabase in in the Temagami Temagami and andNew NewLiskeard Uskeardarea areaof ofOntario. Ontario. conductingresearch researchon onthe the Nipissing Nipissing diabase joined the Ontario Geological Geological Survey Survey and became became Supervisor, Mineral MineralSciences SciencesSubsection, Subsection, In 1987 Peter joined Geoscience played aa major major role in in the the design design of of the the Ontario Ontario Geological Geological Survey Survey Geoscience Laboratories Laboratories until 1990. Peter played Geoscience Geosaence Laboratories Laboratoriesat at the the Willet Willet Green GreenMiller MillerCentre Centrein inSudbury. Sudbury. From conducted research research into into mafic mafic to to ultramafic ultramafic rocks rocks for for the the Ontario Geological Geological From 1992 1992 unth until 1996 Peter conducted Survey. During During his research has included included projects his career, his his research projects on the petrogenesis petrogenesis of of the the Nipissing Nipissingdiabase, Keweenawan Keweenawan flood flood basalt basalt sequences, sequences, Siberian Siberian Trap Trap lavas, lavas, Noril'sk-Tainakh Noril'sk-Tainakh intrusions intrusionsand andDeccan DeccanTraps. Traps.The The development rocks of mafic and ultramafic development of of suiphide sulphide accumulations accumulations in rocks ultramafic composition compositionhas has been been one one of of his his prime prime interests. interests. In at the the Ontario Ontario Geological Qeological Survey to to become become Senior 1996 Peter Peter resigned resigned his his position at Senior Geologist with Inco Inco In 1996 Limited in Sudbury, Ontario. Peter continues continues to to work work in in mafic mafic to ultramafic ultramafic rocks rocks and and their their associated associated sulphide sulphide Limited mineralization. One gabbro-hosted, Cu-Ni-Co hiscurrent currentinterests interestsis isthe the Voisey% Voise/s Bay, gabbro-hosted, C u - N i i deposit depositin in minerariuation. Oneof ofhis Newfoundland, Canada. Newfoundland, Peter resides with wife wife Nancy, Nancy,who whosupervises supervisescancer cancer research research projects projects at Laurentian Laurentian Peter resides in Sudbury, Ontario with Hospital, and Hospital, and daughter daughterMeagan. Meagan.- xiv . �CITATION CITATION Sage, 1997 1997 S.S. 5.5. Goldich Ronald Parker Sage, Goldich Medal Medal Recipient Recipient Ladies and Gentlemen: Gentlemen: Ladies my pleasure pleasure tonight to introduce to you Ronald Ronald Parker It is my Parker Sage, the the 1997 1997recipient recipientof ofthe theS. S. S. S. Goldich GoldichMedal. Medal. is the 43rd 43rd annual on Lake Lake Superior Superior Geology, and the 18th annual meeting meeting of of the Institute on 18th time the medal medal is is This is awarded. being awarded. IImet met Sam Goldich only once, and that that happened happened many manyyears yearsago agoat ataaconference conference on on iron ironformations. formations. From Sam Goldich became clear to me that he was was one one of of the the giants giants of of Lake Superior Superior geology. In Inaaheated heated the discussions it became debate the moderétor to challenge challenge Sam Sam Goldich this point"? point"? There There were were no no debate moderatorasked asked "Does "Does anyone wish to Goldich on on this years citation. citation,Glen GlenMorey Moreycompared comparedSam SamGoldich Goldichtotothe the"Drill "DrillInstructor Instructorwe wesee seeon onTV Wads ads for takers. In last years U.S. Marine Corps", tough, tough, expecting his people the U.S. people to perform perform at at their their best, yet yet aa wonderful wonderfulman. man. Before IIrecite recite to you the the many manyaccomplishments accomplishmentswhy why Ron Ronthe the scientist scientistis is the the worthy worthy 1997 1997 recipient recipient of the S. ~ efore Goldich medal, let S. Goldich let me me tell tell you you about Ron Ron the person. Ron was born the city where where he also also spent his childhood and his childhood and youth. Ron born in in 1938 1938 in in Pontiac, Michigan, the married Carol been happily In 1974, he married Carol Ann Raebiger from Philadelphia, and they have been happily married married for 23 23 years. honeymoon to to the the sunny sunny beaches and warm waters on some exotic While many many young couples couples travel for their honeymoon tropical tropical island, island. Ron Ron and and Carol Carol chose chose an anexotic exoticisland islandof of another anotherkind, kind, they theytravelled travelledto toIceland, Iceland,where wherethere there are Ron and and Carol have three three teenage children, Douglas, are glaciers, volcanic volcanic rocks, rocks, and no no tourists. Ron Douglas, Victoria, and and Alexandra. graduated in 1960 with with aa BSc BScdegree degreein ingeological geological engineering engineering from from Michigan Michigan Technological Technological Ron first graduated University Houghton. While While at at MTU, of his free free time lime wllec collecting MTU. Ron Ron spent spent moSt most of Univecsitv in Houahton. ting rocks rocksand and minerals mineralsin in the the copper and eaming him the the nickname nickname "Rocky". "Rocky". He Hewas wasaastudent ffirilSpiroff, Spiroff, the the "Mad "Mad copper and iron iron mining mining districts, earning studentof ofKiril remember, Ron holds his Alma Mater Russian", whom many many of you will remember. Mater in high hiiih esteem, his his son Douglas Douglas is L ~to1~ - -Scientific ~~.. enrolled there year 0study siuay oaenunc now enrolled there in in a premedicine premedicine program, and anddaughter daughterVictoria Victoriawill willfollow follownext nexi year and Technical technical Communications. Communications. .A..2~..-<--.<c. the early 1960s, 1960s,Ron Ronworked workedfor forthree threeyears yearsas asExploitation ExploitationEngineer Engineerfor forthe the Shell Shell Oil Oil Company Company in west west In the included well sitting, well well logging, well well workovers, and Texas. His duties included and other other production productionrelated relatedactivities. activities. graduated with aa Master's Master'sdegree degreein inGeology Geologyfrom fromthe the Colorado Colorado School School of Mines. It Itwas In 1966, Ron graduated was here here that to alkalic alkalic rocks, rocks, h his studytopic topicand andthesis thesisbeing being"Geology "Geologyand andMineralogy Mineralogyof ofthe theCripple cripple is study he was first exposed to Creek Teller County, County, Colorado". Colorado". This led to toemployment withAnaconda AnacondaAmerican AmericanBrass BrassLtd Ltdto to Creek Syenite Stock, Teller employmentwith investigate the Port Port Coldwell CoIdwell alkalic alkalic complex complex near near Marathon, Ontario. investigate Cu-Ni-PGE minerals in the During summer of During the summer of 1967, 1967, Ron Ron searched searched for basemetals basemetalsininthe theEly ElyGreenstone GreenstoneBelt BeltininMinnesota Minnesotafor forBear Bear Creek Mining. It was was in in that that year yearthat thathe hefirst first met met two two other other greats greats of of Lake Superior Superior geology, Ned Ned Eisenbrey Einbrey Creek and Gene Gene Laberge. Laberge. Ron again worked for Anaconda American American Brass Ltd, Ltd. this this time time north north of of Lake Superior in the the Schreiber Schreiber In 1969, Ron greenstone greenstone belt, belt, searching searching for for gold gold and and basemetals. fall of 1969, Geological Survey, Survey, his In the fall 1969, Ron Ron joined the Ontario Geological his professional professionalhome hometo to this this day. day. Ron's Ron's work for for the the OGS OGS has hastaken takenhim himto to many manyparts partsof of the the province, province, but but never never very very far far and andnever neververy verylong longfrom fromLake Lake Superior. helicopter reconnaissance reconnaissance in in Northern Ontario, then Superior. He He spent spent the first four years on aa helicopter thenmapped mappedthe the Slate worked on on aa multiyear multiyear program program to to study alkalic alkalic rocks rocks north Slate Islands Islands in in Lake Lake Superior, and next worked north of Port CoIdwell the Trans Trans Superior Superior Tectonic Tectonic Zone Zone and along along the Kapuskasing Coldwell along along the the northern northern extension extension of the Kapuskasing Structural greenstone belt. StructuralZone. Zone. In In1978, 1978,Ron Ronwas was assigned assigned to the Michipicoten Michipicoten greenstone belt.Here Herehe hespent spent10 10years years xv �mapping supracrustal rocks over approximately approximately 540 square miles, with emphasis on the the gold gold and mapping Archean supracrustal base metal potential. In 1993, Ron Ron was was assigned assignedto to aa province provincewide wideprogram program of of kimberliie kimberlite occurrences occurrences to to base metal stimulate diamond diamond exploration. Some Some of stimulate of this work was was again again in in the Michipicoten Michipicotenarea, area, where where diamond diamondindicator indicator minerals are common. minerals Despite his busy busy professional professional schedule, schedule, Ron was was able to complete complete his Despite hisPhD PhDdegree degreein in1986 1986for foraathesis thesis submitted to Carleton Catleton University in in Ottawa. Ottawa.The The topic: topic: "Aikalic submitted "Alkalic Rock Rock Complexes Complexesand andCarbonatites Carbonatitesof of Northem Northern Ontailo, and Ontario, and their their Economic EconomicPotential". Potential". xvi �Student Student Travel Travel Award Award The Travel Award to support support student The 1986 1986 Board Board of of Directors Directors established established the LL.S.G. I.L.S.G. Student Travel student participation participation at annual meeting Institute. The awards will be made from a special special fund fund set set up up for this purpose. This This the annual meeting of the Institute. award intended to help defray defray some some of of the the direct direct travel travel costs to to the the Institute and and includes a waiver waiver of of is intended award is The number numberof ofawards awards registration fees, fees, but but excludes excludesexpenses expensesfor formeals, meals,lodging, lodging,and andfield fieldtrip tip registration. registration. The and Chairman in Secretary-Treasurer and andwill willbe be and value value are are determined determined by by the annual annual Chairman in consultation consultation with the Secretary-Treasurer announced announced at at the the annual annualbanquet. banquet. The responsiblefor forthe theselection: selection: The following followinggeneral generalcriteria criteriawill will be be considered considered by by the the annual annual Chairman, Chairman,who who isisresponsible 1) resident (undergraduate (undergraduate or graduate) student student status 1) The applicants applicants must must have active resident status at at the time of of the annual annual meeting meetingof of the the Institute, Institute, certified by by the department departmenthead. head. 2) Students paper will be given Students who who are are the senior author on either an oral or poster poster paper given favoured favoured consideration. consideration. is desirable or more more students students to jointly requesttravel travelassistance. assistance. 3) ItIt is desirable for two or jointly request 4) In farthest away. In general, general, priority priority will be be given to those in the Institute region who are farthest away. 5) Each travel award writing, to to the the annual Chairman, Chairman, with with an Each travel award request request shall be made in writing, an explanation explanation of need, need, possible possible author author status status or or other other significant significantdetails. details. Successful Successful applicants applicantswill will receive receive their their awards awards at at the the time time of of registration registrationfor forthe theMeeting. Meeting. xvii xvii �Institute on Lake Lake Superior Superior Geology Geology 42nd Annual Institute Cable, Wisconsin Wisconsin - The Geology was 1996, at the Telemark Telemark Lodge The 42nd 42nd Annual Annual Institute Instituteon on Lake Lake Superior Geology was held held May May 15 15 - 19, 19,1996, Lodge in in Cable, Wisconsin. The (Chair, Laurel Laurel Woodruff, Reid U. S. Geological Geological Survey Survey (Chair, Field Themeeting meetingwas was organized organizedby by the U. Trip Oshkosh (Field - Oshkosh Trip Coordinators, Coordinators, William William Cannon Cannon and and Suzanne SuzanneNicholson), Nicholson),and andthe theUniversity Universityof of Wisconsin Wsconsin — Trip Secretary/Treasurer, Sally Trip Coordinator, Coordinator, Gene Gene LaBerge, Secretary~Treasurer, Sally LaBerge). The published inS The Proceedings Proceedings of of the 42nd 42nd ILSG ILSG were published in 3 parts: parts: Part Laurel woodruff Woodruff and Programand andAbstracts Abstracts (edited (edited by Laurel and Suzanne Suzanne Nicholson) Nicholson) Part I:1: Program Part of Northern Northern Wisconsin: Wisconsin: A Commemorative 11: Volcanogenic Volcanogenic Massive Massive Sulfide Deposits of CommemorativeVolume Volume (edited (edited by by Part II: Gene Gene L. L. LaBerge) LaBerge) Part Ill: Field Suzanne Nicholson Nicholson and Laurel Woodruff) FieldTrip TripGuidebook Guidebook(edited (edited by Suzanne Laurel Woodmfl) Part 111: Part 1: Glacial GlacialGeology Geologyof of Western Western Wisconsin Wisconsin (Mark (Mark 0. 0.Johnson) Johnson) Part 1: Part 2:: Overview Cable-Hurley Area, Wsconsin Wisconsin (William (William F F.. Cannon and and Part 2 Overviewof of the Bedrock Geology of the Cable-Hurley Suzanne Suzanne W. Nicholson) Nicholson) Part Traverse through through 25 25 km of the Crust Part 3: Geology Geologyof ofthe theMontreal MontrealRiver River Monocline Monocline— AA Traverse Crust (William (William F. F. Cannon) Cannon) Part Namekagon Region Part 4: Early Earlyto to Middle Middle Proterozoic Proterozoic Geology of the Lake Namekagon Region (William (William F. Cannon, Laurel Laurel G. G. Woodruff Woodruff and and Suzanne Suzanne W. Nicholson) Nicholson) Part LakeNamekagon Namekagonand and Penokee Penokee Gap Gap Areas, Areas. West West Gogebic Gogebic Range, Range, Wisconsin Wisconsin (John S. Klasner Klasner and and Part 5: Lake Gene L. LaBerge) LaBerge) - The the The commemorative commemorativemassive massivesulfide sulfide volume, volume, originally originallyconceived conceivedby byEdwarde EdwardeMay, May, consulting consultinggeologist geologistat atthe Flambeau and John John S. Phillips, early pioneers pioneers in In (he the exploration exploration FlambeauMine, Mine, and and dedicated to Edward H. Eisenbrey and and study sulfide deposits in In Wsconsin, Wisconsin, was was published published in conjunction conjunction with with aa post-meeting post-meetingfield fieldtrip trip and study of of massive massive sulfide to Wisconsin. The to the the Flambeau Flambeaugold-copper gold-copper mine mine in in Ladysmith, Ladysmith, Wsconsin. Thevolume volumecontains containsnine ninechapters: chapters: History for volcanogenic volcanogenic sulfides sulfides (Russell (Russell C. C. Babcock) History of exploration for L.LaBérge) LaBerge) Generalcharacteristics characteristics and and geologic geologic setting terrains(Gene (Gene L. General sethng of the Wsconsin Wisconsin magmatic magmatic terrains A A geologic geologic framework framework for for Early EarlyProterozoic Proterozoic volcanogenic volcanogenicmassive massivesulfide sulfidedeposits deposits in in Wisconsin Wsconsin (Theodore (Theodore A. DeMatties) DeMatties) An overview of of the the Flambeau Flambeau supergene supergene enriched enriched massive massivesulfide sulfidedeposit deposit Geology Geologyand andmineralogy, mineralogy.Rusk Rusk County, County, Wisconsin Wsconsin (Edwarde R. May May and and Stephen Stephen R. R. Dinkowitz) Dinkowitz) Case study of environmental environmental requirements for the permithng, permitting, operation, and reclamation of aa metallic metallicmine mine Case reclamation of in Flambeau Mine Mine (Jana (Jana E. E. Murphy Murphy and Richard Richard T. Dachel) in Wisconsin Wisconsin — Flambeau Oachel) Eisenbrey: AA structurally structurallycomplex complexProterozoic Proterozoiccopper-zinc copper-zincmassive massivesulfide sulfidedeposit, deposit. Rusk RuskCounty, County, Wisconsin Wsconsin(Edwarde (Edwarde R. R. May) May) Geological Crandon deposit (A. (A. J. Erickson GeologicalSummary Summary— Crandon Ericksonand and R. R. Cote) Cote) The AnEarly EarlyProterozoic Proterozoiccopper-gold coppergoldVMS VMSdeposit deposit(Theodore (TheodoreA. A. DeMatties DeMattiesand andWilliam WilliamF. F. The Bend Benddeposit depositAn Rowell) Rowell) Geology base-metal deposit, north-central north-central Wisconsin, A Adams) Geology of of the the Lynne Lynne base-metal Wsconsin, U.S.A. U S A . (Glen (Glen A. - - Gene the volume. volume. Most Gene LaBerge LaBerge undertook undertook the formidable task of organizing the Mostof of the the printing printing costs costs for the volume individuals and and corporations. corporations. Proceeds volumewere weregenerously generously donated donated by a number of individuals Proceedsfrom from the the sale sale of of the the volume volumewill willbe beused usedto to promote promotestudent studentparticipation participation in in future future ILSG ILSGmeetings. meetings. Motel 148people peopleregistered registeredfor forthe themeeting meetingininCable. Cable.Field Fieldtrips tripsassociated associatedwith withthe themeeting meetingwere wererobust, robust, A totalofof148 with 177 paid participants, including 11 for the glacial geology of northern Wisconsin, 43 on the Archeanwith 177 paid participants, glacial geology of northern 43 on the ArcheanMiddle MiddleProterozoic Proterozoictransect transect trip, 18 18 looking at the Early Early Proterozoic Proterozoicin in the Lake Lake Namekagon Namekagonregion, region,and and17 17on on the the trip trip to to the the Penokee Penokee Gap. The The tip triptotothe theFlambeau FlambeauMine Minewas wasone oneofofthe thelast lastofficial officialtrips tripsto tothe themine mineprior priorto to the 88 participants. participants. Many Manylogistical logisticaldetails detailsfor forthe thetrip tripwere were the start start of of planned plannedshut shut down down phase, and and had had 88 generously generouslysupported supportedby by Kennecott Kennecotl Copper Copper and and the Flambeau FlambeauMining Mining Company. Company. XVIII �annual banquet The annual banquetwas was attended attended by by 111 111 diners. The TheGoldich GoldichMedal Medalwas was awarded awardedto toDavid DavidSouthwick Southwickof ofthe the Geological Survey in in recognition recognition for for his his outstanding outstandingcontributions contributionsto togeology geology in inthe the Lake Lake Superior Superior Minnesota Geological Geological Survey, Survey, presented presentedthe the award. award. To region. Glen GlenMorey, Morey, also also from from the the Minnesota Geological To correct correct an an oversight during during the the annual meeting of of the the ILSG Board Board of of Directors, Directors,the the term term of of the the Secretaryrnreasurer Secretary/Treasurer v1ark (Mark E. approved by a belated, but unanimous The banquet banquetaddress addresswas wasgiven givenby byDr. Dr. Stephen StephenE. Jirsa) was approved unanimous act. The Kesler of the the University University of Michigan, presenting Kesler presenting aawell-received well-received lecture lecture titled, titled, Sustainable Sustainable Mineral Mineral Development Development — Fact Fact or or Fiction. Fiction. - Student Paper Paper Awards Awards were were given given to to Kimberly Kimberly Darrah Darrah(Kent (Kent State State University) University) for for her hertalk talkon onPetro Pefrographicand Student graphic and the srmoba rometic analysis the metamorphosedLittle LittleFalls FallsFormation, Formation,Central CentralMinnesota, Minnesota, with with implications implications thermobarometic analysis ofofthe metamorphosed for Early Early Proterozoic Proterozoic tectonism; tectonism; Susan Wilson Wilson (Western Illinois University) University)for for her her talk, talk, AA stmcfural structural and kinematic kinematic analysis analysis of of the McCaslin McCaslln Formation Formationnear nearMcCaslin Mccaslln Mountain, Mountain, Wisconsin, Wisconsin, and Zachary Zachary Naiman (Macalester Chengwatana Volcanic Group (Macalester College) College) for for his his poster, Metamorphism of Chengwatana Group near nearTaylors Taylors Falls Fateand and Osseo core. Five Fivestudent studenttravel travelawards awards totalling totalling$400 $400 were were presented presentedto to Zachary ZacharyNaiman, Naiman,Kim KimNeilsón, Neilson, from Osseo Andrey Bekker, Andrey Bekker, Susan Susan Wilson, Wilson, and andKimberly KimberlyDarrah. Darrah. The Board Lake Superior Geology Geology met met in in Cable Cable on May 16,1996. 16, 1996. Members Members of The Board of of Directors Directorsof of the the Institute Institute on Lake were: Laurel the Board Board in attendance were: LaurelWoodruff Woodruff (Chair), (Chair), Mark Jirsa (Secretary/Treasurer), Ted Ted Bomhorst, Bomhorst, David Southwick, and and Mark Mark Smyk. Smyk. Invited guests guestsincluded: included: Ken Card, Ron Sage, Wilf Meyer, Charles Blackburn, Blackbum, Gene Gene LaBerge LaBergeand and Sally Sally LaBerge. Actions Actions taken taken were: were: 1. Accepted Smyk), which which included included the the minutes of of the the last last Acceptedthe the Report Reportof ofChairman, Chairman, 41st 41st ILSG ILSG meeting (Mark Smyk), meeting Board meeting. 2. Approved Approved an anoffer offerby bythe the Ontario Ontario Geological GeologicalSurvey Survey to host host the 43rd Annual Institute on on Lake Lake Superior Superior Annual Institute Geology in Sudbury, Ontario. Ron Sage Sage and and Wilf Wilt Meyer Meyerwill willact actas asco-chairs co-chairs for for the the meeting. Geology 3. Approved host for the 44th 3. ApprovedKenora, Kenora,Ontario, Ontario, and and the the Ontario Ontario Geological GeologicalSurvey as host 44th ILSG ILSG in in 1998, 1998, with Charles Blackbum Charles Blackbumas as Chair. Chair. 4.. Accepted 4 AcceptedILSG ILSGFinancial FinancialReport Reportfrom fromthe theSecretary/Treasurer SecretarytTreasurerMark MarkJima. Jirsa. 5. Approved ApprovedDavid DavidSouthwick Southwickas as recipient recipient of of 1996 1996 Goldich Goldich Medal. 6 Approved Morton). 6. ApprovedJohn JohnKlasner Klasneras asnew newGoldich Goldich Medal Medal Committee member (replacing Penny Morton). 7. Discussed Discussedthe thefuture futureof ofthe theILSG ILSGNewsletter Newsletterand and the the establishment establishment of of aa home homepage pagefor forthe theILSG. ILSG.Results Results from from the the members memberspoll pollin inthe the llrst firstnewsletter newsletterwere were presented. presented. The The Board Board approved approvedthe thecontinuation continuationof ofthe the newsletterat at the the rate rate of of one/annum onelannumwith with Ted Ted Bomhorst Bomhorstcarrying carryingthe theinitiative initiativefor for both bothactivities. activities. newsletter 8. Discussed Discussedthe the distribution distributionand and continued continued sale of back back issues of ILSG Field Trip Guidebooks, Guidebooks, which are being being handled handledby by Mark Mark Jirsa Jirsa as as Secretary/Treasurer. Secretary/Treasurer. 9. Discussed the commemorative commemorative volume volume on -the 9. Discussedthe the recent recentpublication publicationof of Proceedings Proceedings Volume Volume 42, Part Part 22 — Wisconsin massive sulfides. The The Board agreed agreed to to send send aa letter letter of of thanks thanks to to all all the the contributors contributors who donated Wisconsin money for the publication of of the the volume. volume. Proceeds Proceedsfrom fromthe thesale salewill willbe beused usedfor forthe theencouragement encouragementof of student participation ILSG, and and will will be be kept kept separate separatefrom from the the general general working working fund. With participation in the ILSG, Withthe theBoard's Board's approval and sale sale of the the volume. volume. approval Ted Ted Borrihorst Bornhorstwill will promote promote the advertising and The Board Board approved voted on by the the participant the 10. The approved changes changes to the constitution constitution of the ILSG voted participantmembers membersof ofthe 11.80 duringthe themorning momingTechnical TechnicalSession Sessionon onMay May16, 1996. These These changes changes included included wording changes to to ILSG during 16,1996. make for the theterm term for for the the Secretaryfheasurer, Secretary/Treasurer, which was make the the constitution constitution gender gender neutral, and an extension for actually carried carried out at the annual actually annual banquet. banquet. To establish aa list list of of members members for for the ILSG, ILSG. the the Board agreed to to longcomprehensive mailing mailing list which includes (those participants participants with longcreate a comprehensive includes both both permanent permanent members members (those standing interest in Lake Superior geology) geology) and and aa list listof ofmembers members who who have have attended attended ILSG meetings in in the the past. The TheBoard Boardassigned assigned Laurel LaurelWoodruifto Woodruff tocomplete completethis thismembership membershipmailing mailinglist, list,which whichwill willthen thenbe be be assessed assessedat at this thistime. passed from Chair Chair to Chair for successive meetings. Membership dues dues will will not not be meetings. Membership 11. In a discussion discussion of requirements requirements and suggestions suggestions to ILSG Chairs, Chairs, itit was was determined determined that that the the Chair Chair needs needs 11, freedom to to act act independently independentlywithin reasonable intuitive the freedom intuitiveguidelines guidelinesthat that follow follow general general historical precedents. by Ken Ken Card Card on the standardization of the the selection selectionpolicy policyfor forthe the Board discussed discussedaa presentation presentationby 12. The Board standardization of Goldich Goldich Medal Medal award. The Thematter matterwas wastabled tabledfor forfuture futurereview. review. Board agreed agreed that that the Student Paper Committee independentlywithin 13. The Board Committee needs the the freedom freedom to act independently reasonable historical precedents. reasonableintuitive intuitive guidelines guidelines and and need need not not be be constrained constrained by historical precedents. xix xix �was done doneto tokeep keepcosts costswithin withinreasonable reasonablelimits, limits,and andnot notlose losemoney. money. This This was was Budgeting for the 42nd ILSG ILSG was successful, in excess excessof of $6000. $6000. However, However, as as much muchas as the the Chair successful, as as the the meeting meetingmade made an an approximate profit in would would like like to to claim claimcredit creditfor forthis, this, aa substantial substantial portion portion of this sum was a a result resultof of support supportfrom fromthe theElambeau Flambeau Mining Company Company for the Flambeau field trip. tip. InInaddition, withmany manyof ofthe thepublishing publishingcosts costsfor forthe the Flambeau Mine field addition,with Proceedings underwrittenby by the numerous numerous contributions contributionsfrom from individuals individualsand andcompanies companiesall allhsture future ProceedingsVolume Volume22underwritten sales will will directly student participation sales directlypràfit profitthe theInstitute's Institute'sstudent participationfund. fund. II enjoyed enjoyed my on Lake Lake Superior Superior Geology, Geology, and the opportunity my tenure tenure as as Chair Chair of of the the Institute on opportunity to interact interact with people associated organization. There are a number of people number of people involved involved with with the meeting meeting who were people associated with the organization. essential to its its overall overall success general well-being. well-being. I I thank thank Gene Gene and success and and the Chair's general and Sally SallyLaBerge, LaBerge,who who essential and guided guided me whom it would would have have been been nearly nearlyimpossible, impossible, and and coaxed and methrough through the the experience experience and without whom willingto todo do everything everythingIIasked askedher hertotodo, do,and andititwas wasalot. aId. Bill Bill Cannon Cannon Suzanne Nicholson Nicholson who was more than willing originally ILSG and then generously generously deferred originally conceived conceived of ofthe the USGS USGSsponsoring sponsoring an ILSG deferredthe the duties dutiesof ofChair Chairto to me, me, rather TedBornhorst Bomhorstand andMark MarkSmyk Smykwillingly willinglygave gaveadvice, advice, rather than than taking takingon onthe theglory gloryfor for himself, himself, former former Chairs ChainTed and and SecretaiyiTreasurer SecretaryrnreasurerMark MarkJirsa Jirsa covered covered all all the money money questions for me. Laurel Woodruff Laurel Woodruff Chairman, 42nd Chairman, 42nd ILSG ILSG Cable, Wisconsin Wswnsin xx �PROGRAM PROGRAM �Calendar Calendar of of Events Eventsand and Program Program Tuesday 1997 6,1997 TuesdayMay May6, - 8:00 8:00 a.m. a.m. - 7:00 7:00 p.m. p.m. Field FieldTrip Trip11 Field FieldTrip Trip 11--The TheHuronian HuronianSupergroup Supergroupbetween betweenSauft SaultSte. Ste. Marie Marieand andElliot ElliotLake Lake (day 1) (day 1) Leaders: Ken Ken Card Card(Geological (GeologicalSurvey Surveyof ofCanada, Canada,retired) retired) Leaders: Gerry Gerry Bennett Bennett (Resident (ResidentGeologist, Geologist, Sault Sault Ste. Ste. Marie, Marie, Ontario OntarioGeological Geological Survey) Survey) Wednesday, 1997 Wednesday, May May7, 7,1997 8:00 a.m. a.m. --6:30 p.m. Field 1,2, 3, 3,4 8:00 6:30 p.m. Field trips 1,2, 4 Field FieldTrip Trip 11-- The TheHuronian HuronianSupergroup Supergroup(day (day2) 2) Leaders: as as above above Leaders: Field New Developments Field Trip Trip 22 -New DevelopmentsininGrenville GrenvitleFront FrontGeology, Geology, Sudbury SudburyArea, Area, Ontario Ontario Leader Tony Tony Davidson Davidson(Geological (GeologicalSurvey Surveyof ofCanada) Canada) Leader: - FieldTrip Trip 33 The TheSudbuty SudburyStructure Structurewith withemphasis emphasison onthe the Whitewater WhitewaterGroup Group Field Leader Stu Stu Gibbons Gibbons(Falconbridge (FalconbridgeLimited) Limited) Leader 4 -Magmatic MagmaticOre OreDeposits Depositsof ofthe theSudbuiy SudburyIgneous IgneousComplex Complex FieldTrip Trip 4Field Leader: Steve Steve Prevec Prevec (Laurentian (LaurentianUniversity) University) Leader: Mike Mike Cosec Cosec (Resident (Resident Geologist's Geologist's Program, Program, Ontario Ontario Geological Geological Survey) Survey) 9:30 p.m. p.m. Registration, Registration,Poster Poster Set-up Set-up 7:30 p.m. p.m. -- 9:30 7:30 Alphonse Raymond Building, Alphonse Raymond Building, Laurentian Laurentian University UniversityCampus Campus , - 10:00 p.m. Icebreaker, Icebreaker, Cash Cash Bar Bar 7:30 p.m. - 10:00 Alphonse Alphonse Raymond Raymond Building, Building, Laurentian LaurentianUniversity University Campus Campus Thursday, 1997 Thursday, May May8, 8,1997 NOTE: NOTE: Technical TechnicalSessions Sessionsare arein inthe the auditorium, auditorium,Alphonse AlphonseRaymond RaymondBuilding, Building, Laurentian Laurentian University Campus Campus odi xxii �a.m. -- 4:30 4:30 p.m. p.m. Registration continues 8:00 a.m. Technical Session Technical Session11 Session Session Chairs: Gene GeneLaBerge LaBergeand and Terrence TerrenceBoerboom Boerboom 8:30a.m. Andy Andy Fyon Fyon Precambrian Geoscience Section, Ontario Senior Manager, Precambrian Ontario Geological Geological Survey 43rd Annual Annual Institute Institute on Lake Lake Superior Superior Geology Geology Opening Remarks - 43rd 8:40 Don Rousell Rousell Mineralization History The Tectonic, Magmatic Magmatic and Mineralization History of of the the Sudbury Sudbury Structure Structure 9:40 T. F. Morris Morris Results of modern alluvium alluvium sampling for kimberlite kimberlite indicator indicator minerals, Wawa-Kinniwabi Lake Lake Region Region and and the the implication implicationfor for kimberlite kimberliteexploration, exploration, Northeastern Northeastern Ontario Ontario 10:00 Coffee Break and Poster Session Session Limited Exploration Exploration Sponsored by Falconbridge Limited 10:20 Shawn M. M. Carlson and Glen W. Adams Adams. ultramafic lamprophyric WI The diamondiferous six-pak ultramafic lamprophyricdiatreme, Kenosha, Wl 10:40 Dean Dean M. Peterson Peterson GIS for Archean Archean gold gold exploration: exploration: using GIs applications for usingCanadian Canadianmining miningcamp camp GIS exploration in GIs queries to target gold exploration in Minnesota Minnesota 11:00 Ken Keri Anderson and Nigel Nigel Wattrus Wattrus Western Lake Superior A seismic stratigraphic study of Western 11:29 C. M. Mancuso, Mancuso,D. 0. K. K Hoim, KA Holm, U A.Foland Folandand andF. F. A. A. Hubacher Hubacher resultsof ofArIAr k/k mineral mineraldating datingfrom fromthe thePeavy Peavynode nodearea area of of northern Initial results northeastern Wisconsin Wisconsin Michigan and Dunbar dome area of northeastern 11:40 D. K. K Holmand Holm andD. D. H. H. Henderson Henderson of Early Proterozoic Proterozoic post-Penokean (1800-1600 Ma) Space-time patterns of metamorphism and and cooling cooling in in the the southern southern Lake Superior region region 12:00 p.m. Lunch Break Lunch Break XXIII �Technical Technical Session Session 22 MarkSmyk Smyk and and Mark Mark Jirsa Jirsa Session Chairs: Mark 2:00 2:OO L LaBerge LaBerae Gene L. The Early Early ~rotirozoic Implications of drill Proterozoic break-up of of the the Superior SuperiorCraton: Craton: Implications core and and geophysical geophysical data data south south of of the the Gogebic Gogebic range, range, northern northernWisconsin Wisconsin core 2:20 T. Arcuri Arcuri and and E. E. M. Ripley Ripley Interactionbetween between a Virginia Formation xenolith and mafic mafic magma magma at the Interaction Virginia Formation xenolith and Babbitt Babbitt Cu, Ni Ni deposit deposit Duluth Duluthcomplex, complex, MN MN 2:40 Edward R. Fridk Frick Edward M. Ripley, David David 0. D. Lambert Lambert and and Louise LouiseR. Re-Os, Sm-Nd Sm-Nd and and Pb Pb isotopic isotopicconstraints constraintson onmantle mantleand andcrustal crustal contributionsto to magmatic magmatic sulphide sulphide mineralization mineralizationin in the the Duluth Duluthcomplex complex contributions 3:00 Coffee Coffee Break Break and and Poster PosterSession Session Sponsored by Ministry of Northern Sponsored by Ministry of NorthernDevelopment Development&& Mines Mines 3:20 John John Siriunas Siriunas and and John John Wiebe Wiebe Overview Overview of the the Gregor Goldfields Goldfields Corp. Corp. Marathon Marathon (Wire (Wire Lake) Lake)Gold Gold Property Property in in the the Hemlo Hemlo Area of of central central Ontario, Ontario, Canada Canada 3:40 3:40 Tom Tom Muir Muir The The Hemlo HemloGold GoldDeposit: Deposit: It may be gold but its not black and white 4:00 4:OO Steve Steve Jackson Jackson Patterns of structure structure and and metamorphism metamorphism in in the Hemlo Hemlo greenstone greenstonebelt belt Patterns 6:30 --7:30 Mixer -- cash cash bar bar 7:30 Mixer Cavern, Science Cavern, ScienceNorth North 7:30 --9:30 9:30 Annual AnnualBanquet Banquetand andAwards AwardsPresentation Presentation Announcement of of the the 44th 44th Annual Annual Meeting Meeting location location Announcement 1997 1997 Goldith GoldichAward Award presentation presentationto to Ronald RonaldP. P. Sage Sage Banquet speaker speaker:Dr. Dr.Peter PeterLightfoot, Lightfoot,Inco IncoLimited, Limited,Copper CopperCliff) Cliff, Banquet Ontario: Oiigin Stwdure and Origin of of the Sudbury Structure and its its mineral mineralwealth wealth Friday, Friday, May May 9, 9,1997 1997 Technical Technical Session Session33 Session Gordon SessionChairs: Chairs: Gordon Medaris, Medaris, Jr. and and Frank Frank Luther Luther 8:30 8:30a.m. a.m. Registration Registrationcontinues continues xxiv �9:00 George Hudak George Hudak and and Ron Ron Morton Morton The evolution associated with the Sturgeon evolution of the hydrothermal hydrothermal systems associated Sturgeon Lake Lake Caldera Caldera complex, complex, northwestern northwestern Ontario Ontario 9:20 Jon Jon Devaney Devaney Stratigraphy, tectonics and mineralization of the Sioux Sioux Lookout Lookout orogenic orogenic belt, Western Wabigoon Wabigoon Subprovince Subprovince 9:40 Gerry Gerry Bennett Bennett The Huronian from the The Huronian--from thebottom bottomUp up 10:25 Coffee Coffee Break Break and and Poster Poster Session Session Sponsored Sponsored by by Laurentian Laurentian University University 10:45 Steve Jackson Steve Jackson Structural and metamorphic contraints contraints on on the the tectonic tectonic history of the Structural the Sault Ste. Marie Marie - Espanola area Southern Province in the - 11:05 Robert G. Tipping and Douglas Douglas Allen Hydrogeology of saline- and boron-bearing ground waters in in the North North Shore volcanic group - Minnesota Minnesota 11:25 Douglas Allen, W. E. Jr., and R. G. Tipping Tipping E. Seyfried, Jr., Douglas Allen, Boron, bromide and chloride in groundwaters and and rocks of the north north shore of incursion into the mid-continent Lake Superior - evidence for a seawater incursion mid-continent rift rift - 11:45 Richard W. Ojakangas Richard Ojakangas within the the Marquette Range Range Supergroup Supergroup (Michigan) Correlative sequences within and the Huronian Supergroup (Ontario): Glaciogenics, Huronian (Ontario): Glaciogenics, paleosols paleosolsand and orthoquartzites orthoquartzites 12:05 Woodard Hank Woodard The The Mckenzie McKenzieLake LakeAntiform Antiform and and the the Kawa Kawa Bay Bay Synform, Quetico Quetico Provincial Provincial Ontario Park, Ontario 12:30 p.m. Lunch 12:30 p.m. Lunch break break (remove posters) Technical Technical Session Session 44 Session Chair: Ted TedBomhorst Bornhorstand and Phil PhilThurston Thurston 2:00 2 :OO E. Zaleski, 0. 0.van van Breemen Breemenand and V. L. Peterson Peterson Age constraints on plutonism, metamorphism and deformation constraints on plutonism, metamorphism and deformationacross acrossthe the Manitouwadge Greenstone Wawa-Quetico Subprovince Subprovince boundary near the Manitouwadge Greenstone belt, northwestern northwestern Ontario Ontario xxv XXV �2:20 L. G. Medaris, Jr., L. P. Baumgartner, R. R. H. H. Dott Dott and and K. K. McSweeney McSweeney Sub-Baraboo Paleosol, Paleosol, Wisconsin: Wisconsin: geochemical evidence for The Sub-Baraboo Proterozoic weathering Proterozoic weathering and and metasomatism metasomatism 2:40 Keith Winterhalder Keith The greening The greening of Sudbury 3:05 Coffee Break Break 3:25 Masood Siddiqui Siddiqui and and Mark Mark Smyk Smyk Gerard Doiron, Masood investigations of the Pick Lake deposit, Winston Winston Lake Preliminary investigations Lake Mine, Mine, Ontario: AA remobilized massive suiphide orebody remobilized massive sulphide orebody 3:45 Theodore Bomhorst Bomhorst and Laurel Woodruff Woodruff copper precipitation precipitation by fluid-mixing, fluid-mixing, Keweenaw Peninsula, Michigan Michigan Native copper 4:05 Frank Frank R. Luther Luther The petrology of greenspar greenspar: aa Proterozoic Proterozoic porphyritic porphyriticdiabase diabase dike; dike; Pither Pifher and Irwin Irwin townships, Lake Lake Nipigon Nipigon Oistrict, District, Ontario Ontario 4:25 Presentation Presentationof of Student Student Paper Paper Awards Awards 4:30 Closing Remarks Closing Remarks Saturday, May Saturday, May 10, 1997 1997 p.m. Field Field trips 3, 4, 5, 6 6 8:00 a.m. -- 7:00 p.m. Field on the the Whitewater Group Field Trip 33 -- The The Sudbury Sudbury Structure with emphasis on Leader: Stu StuGibbons Gibbons(Falconbridge (FalconbridgeLimited) Limited) - Field Trip of the Sudbury Igneous Igneous Complex Field Trip 44 Magn7atio Magmatic Ore Ore Deposits of Complex Leader Leader Steve StevePrevec Prevec(Laurentian (LaurentianUniversity) University) Mike Cosec (Resident Geologist's Program, Ontario Ontario Geological Geological Survey) Mike Survey) - Field 5 Alkafic Alkalicrocks rocksof ofthe theSudbury Sudbury Region Region(day (day 1) 1) Field Trip Trip 5Leader: Ron RonSage Sage(Ontario (OntarioGeological GeologicalSurvey) Survey) Field 6--Regreening Regreeningof Sudbury Field Trip 6 Leaders: Keith KeithWinterhalder Winterhalder(Laurentian (LaurentianUniversity) University) John John Gunn Gunn (Laurentian (Laurentian University) University) XWi �Sunday, May May11, 1997 11,1997 8:00a.m. a.m. -- 7:00 7:00p.m. p.m. Field FieldTrip Trip55 8:00 Field Trip Trip 55 -AIkalic Alkalicrocks rocksof ofthe theSudbury SudburyRegion Region(day (day 2) 2) Field Leader Leader: Ron Ron Sage Sage (Ontario (Ontario Geological GeologicalSurvey) Survey) a Poster Poster Session Session Wednesday, Wednesday, May May 7, 1997 1997 (set-up begins begins at 7:30 p.m.) -Friday, May 9, 1997 (tear-down at 1997 (teardown at 12:00 12:OO p.m.) p.m.) Dave Dave DahI Dahl Minnesota Minnesota Department Department of of Natural NaturalResources Resources Gravity for Recognizing Recognizing Crustal Fabric Fabric and Gravity Aspect as a Tool for and Structure at Minnesota Minnesota Jon Devaney Devaney Ontario Ontario Geological Geological Survey Survey Stratigraphy, Stratigraphy, tectonics tectonics and and mineralization mineralizationof of the the Sioux SiouxLookout Lookoutorogenic orogenicbelt, belt, Western Western Wabigoon WabigoonSubprovince Subprovince Mike Mike Easton Easton Ontario Ontario Geological Geological Survey Survey S. James James R. S. Department Department of Geology, Geology, Laurentian Laurentian University University Revisiting Revisitingthe the disappearance disappearanceof of the the Huronian Huronianin inthe theSudbury-Crerar Sudbury-Crerararea: area: insight from the geochemistry of amphibolites and paragneisses paragneisses D. KK.HoIm Holm 0. Department Department of of Geology, Geology, Kent Kent State State University University D. R. Lux aR.Lux Department Geological Sciences, University University of of Maine Maine Department of Geological Results Results of Ar/Ar ArIAr dating of dikes in in central central Minnesota Minnesotaand andthe the Minnesota MinnesotaRiver River Valley Valley Tom Lawler Lawler and and Darold DaroldRiihiluoma Riihiluoma Tom Department of Natural Division of Minerals, Natural Resources, Division Minerals, State State of of Minnesota Minnesota Mineral greenstone belt using boulder boulder tracing, Ely-Bigfork Mineral potential potential study of aa greenstone area, Minnesota Minnesota xxV �F. Morris Morris T. F. Ontario Geological GeologicalSurvey Survey Ontario Results Results of of modern modern alluvium sampling for kimberlite kimberlite indicator indicatorminerals, minerals, Wawa-Kinniwabi Lake and the implication Lake Region Region and implicationfor for kimberlite kimberliteexploration, exploration, Northeastern NortheasternOntario Ontario Tom Muir Muir Tom Ontario Geological GeologicalSurvey Survey Ontario The area: aa surface The Hemlo Hernlo gold deposit area: surface perspective perspective Zachary Zachary Naiman Naimanand andKarl KarlR. R. Wirth Wirth Geology Department, Macalester Geology Department, MacalesterCollege College Petrogenesis volcanics, Minnesota Minnesota and Wisconsin Wisconsin Petrogenesis of Chegwatana volcanics, John John M. M. Siriunas Siriunas and and Neil Neil Willoughby Willoughby NR8J Resource ResourceAssociates Associates Limited Limited NR&J Copper mineralization in Eastern Eastern Sault Ste. Marie Copper and precious-metal mineralization Marie Mining Mining Division Division with focus on the Jentina Property, Property, Albanel Albanel and andNicholas Nicholastownships, townships, District Algorna District of of Algoma T.E. Wahl, Wahl, J.D. J.D. Miller MillerJr., Jr.,M.A. M.A.Jirsa, Jirsa, T.J. T.J. Boerboom, Boerboorn, V.W. Chandler, Chandler, A.C. A.C. Runkel Runkel • Minnesota Minnesota Geological Geological Survey Survey D. Dahl D.DahL Minnesota Resources, Division Division of Minerals Minerals Minnesota Department of Natural Resources, Severson M.J. Severson M.J. Natural Natural Resources Resources Research Research Institute, Institute, University Universityof of Minnesota Minnesota Geologic system (GeMS): (GeMS): A digital approach Geologic mapping system approach to bedrock bedrock geologic mapping mapping xxvii �ABSTRACTS ABSTRACTS xxix �groundwaters and Boron, bromide and chloride in groundwaters and rocks rocks of of the North North Shore Shore of of Lake Lake Superior, evidence for a seawater incursion into the Mid-Continent Rift E. Seyfried SeyfriedJr., Jr.,Dept. DeptofofGeology Geologyand andGeophysics, Geophysics,University University Douglas E. Allen and W. K of Minnesota, Robert C. E-mail: alle0167@maroon.tc.umn.edu, alle0167@maroon.tc.unm.edu, Robert G. Minnesota, Minneapolis, MN. E-mail: Tipping, Tipping,Minnesota Minnesota Geological Geological Survey, St S tPaul, Paul,MN. MN. geochemically distinctive distinctive groundwater groundwatertypes types have have been recognized in the Two geochemically the North Group (NSVG) (NSVG) rocks rocks of of the North Shore of Lake North Shore Shore Volcanic Volcanic Group Lake Superior, Superior, Northeast Minnesota. Minnesota. The The chemistry chemistry of of these these groundwaters groundwatersmay may contain contain evidence evidence of of aa Northeast incursion into the Mid-Continent Rift. seawater incursion Mid-Continent Rift. The most widespread widespread groundwater type is characterized by high pH and and boron boron concentrations, which reach reach values valuesof of 1 10.26 and 5.4 5.4 ppm, ppm, respectively. respectively. The Minnesota 0.26 and Minnesota concentrations, which imit, for boron in drinking water is 0 .6 ppm (STS Department of of Health, Health, Health Risk Risk L Limit, 0.6 Consultants Report, 1995), 1995), so so the the genesis genesis and distribution distribution of of these these waters waters is of some Consultants Report, some as being of of interest interestgeochemically. geochemically. The second groundwater type is a concern, as well as dissolved chloride chloride concentration concentrationnearly nearly twice twice that that of ofseawater, seawater, Ca-Cl brine, which has a dissolved and has a conspicuously conspicuously high Br/Cl ratio ratio (0.0089). (0.0089). Mineral-fluid equilibria equilibria calculations calculations reveal Mineral-fluid reveal that that the thehigh highp1-I pH groundwaters plot vithin the quartz-kaolinite-Iaumontite-calcite stability field (fig. 1). within the quartz-kaolinite-laumontite-calcite stability field (fig. 1). This assemblage of minerals is is ubiquitous ubiquitous in in the the North North Shore Shore basalts basalts (Schmidt, (Schmidt, 1993). 1993). As evidenced minerals evidenced by assemblage fixes fixes pC02 pCO2 at relatively low values I, the laumontite-bearing laumontite-bearing assemblage values (log (log figure 1, pCO2-5.2 atat25°C), pC02=-5.2 2S°C)which whichhelps helpstotoaccount accountfor forthe therelatively relativelyhigh highpH pH groundwaters groundwaters in in the NSVG rocks. 11 Preliminary boron boron isotope isotope data data for for the North North Shore groundwaters poundwaters reveal 8B Preliminary reveal SB11 I1 Typical SB values ranging from +21(Ca-Cl brine) to to +45.5. Typical 6B values for crystalline rock brines and and sedimentary sedimentary sources sources are arewell wellbelow below +20 (Barth, and non-marine brines (Barth, 1993). 1993). Rocks Rocks 11 =+39.5), formed and brines derived formed in marine marine environments environments and derived from seawater seawater (SB (5B =+39.5), II however, can have however, have SB' 5B greater than +50 Thus, interaction of NSVG (Barth, 1993). 1993). Thus, +50 (Barth, rocks with could have have with seawater derived derived fluids during late stage and post rifting events could resulted in uptake of seawater derived boron during basalt weathering and hydrothermal alteration. Indeed, Indeed, NSVG NSVG rocks rocks are are variably variably enriched in boron and have concentrations concentrations as high as 33 ppm (interflow Subsequent interaction of the (interfiow sedimentary sedimentary unit). unit). Subsequent the boron-rich boron-rich alteration minerals with high pH groundwater groundwater would enhance enhance mineral dissolution, dissolution, and and help to account for the high boron-bearing gmundwaters. groundwaters. A positive linear linear correlation correlation exists exists between between dissolved dissolved bromide bromide and chloride chloride concentrations in the groundwaters (fig. (fig. 2). 2). A positive correlation between mutually mutually conservative elements such as bromide bromide and chloride chloride suggests suggests a common common source source for for these these elements. This anendendThiscan canbe beexplained explained by bythe themixing mixingand andaccompanying accompanying dilution dilution of of an member brine. brine. There There isisaanegative negativecorrelation correlationbetween between boron boron and and chloride, chloride,however, however, which is consistent with a model involving boron uptake from seawater, seawater, decoupling decoupling the the controls controls on dissolved boron from from those those of of dissolved dissolved chloride chloride and and bromide. bromide. �- Boron Boron concentrations concentrations and and isotopic isotopic composition compositionof of NSVG NSVG groundwaters, groundwaters,as aswell well as the the bromide bromide and and chloride chloride data, da@ suggest suggest aa model model involving involving seawater seawater evaporation evaporation and and as subsequent subsequentrock rockalteration. alteration. ItItisisnot notunreasonable unreasonablethat thatsuch suchaaseawater seawaterincursion incmionresulted resulted in inthe thecharacteristic characteristicmarine marineboron boronisotopic isotopicimprint imprinton onthe therocks rocksand andresidual residualbrines brinesof ofthe the rift ofofthese riftInteraction Interaction thesealtered alteredrocks rocksand andbrines brineswith withmodern modem groundwater groundwatersystems syaemsresult result ininthe thedistinctive ditinctivenature natureof ofthe theNorth NorthShore Shoregroundwaters. groundwaters. Figure Figure1 I 20 Figure Figure22 18 // 2 16 14 10 'C t12 6 E a a 108 6 Ca-Cl brine 6 0 C 4 0 2 pg 0 0 0 -6 -5 -4 log aSiO2(aq) -3 -2 0 200 400 600 000 '000 1200 Cl (ppm) References References Barth, Barth,S., S.,1993, 1993,Boron BoronIsotope Isotope Variations Variations in Nature: Nature: a Synthesis. Geol GeolRundsch Rumkch v.82 v.82 p.640-652. p.640-652. Schmidt, PatternsofofLow-grade Low-gradeMetamorphism Metamorphismininthe the 1993,Regional Regionaland andLocal Patterns Schmidt,S.Th., S-Th.,1993, North N o dShore ShoreVolcanic VolcanicGroup, Group,Minnesota, Mimeso@USA. USA.Journ. JournMetamorphic MetamorphicGeoL Geol.v.11 v.11 p.401-414. p.401-414. STS STSConsultants ConsultantsReport Report (1995) (1995) Evaluation Evaluation of of boron boron impacted impacted wells. wells. To ToLTV LTVSteel Steel Mining Company. Mining Company. 2 1400 �A SEISMIC STFWTIGRAPHIC STRATIGRAPHIC STUDY OF WESTERN LAKE LAKE SUPERIOR SUPERIOR ANDERSON, Ken A., and WATTRUS, Nigel Ken A., and WATRUS, Nigel J., Large Large Lakes Lakes Observatory Observatory and and Department of of Geology, Geology, University of of Minnesota, Minnesota, Duluth, Duluth, MN MN 55812, Depahnent and nwattrus@d.umn.edu nwatt~s@d.umn.edu knebe@d.umn.edu and profiles were collected Approximately 1000 I000 km of high high resolution resolution seismic profiles collected in in the the third of Lake Superior during three cruises in the summer of Of 1996. 1996. The western third The study study from Grand Portage, Minnesota area extends from Duluth, Minnesota to a line running tlom Minnesota to Houghton, Michigan. The The data data were were acquired acquiredwith with an an ORE ORE Geopulse Geopulse system system and and for later later processing processing with with the the Seismic UNIX software software system (Cohen digitally recorded for Stockwell, 1996). Post enhancement and Stockwell, Post acquisition acquisition processing processing of the data permits the enhancement of subtle features not visible visible in paper paper sections. sections. The The profiles profiles are are being being studied studied to to identify identify describe seismic seismic reflectors reflectorswithin withinthe thewestern westernbasin basinof ofLake LakeSuperior. Superior. The and describe interpreted profiles are are then then correlated correlated with with several several cores cores collected collected during previous mterpreted cruises In in th~s this part crulses parl of the lake. lake. are commonly commonly obsewed observedthroughout throughoutthe thebasin. basin. Each Four reflectors are Each has has a features in a representative representative distinct acoustic signature and can be correlated with features 1)) Scholz (1985). (1985). The first section (Figure I of Lake Superior sediments described by Schok strong and and continuous continuous and and is is associated associatedwith withthe thelake lakefloor. floor. The second reflector is strong strong, wavy wavy character characterwith withdiscernible discernibleinternal intemal reflections. reflections. This reflector has aa strong, discontinuous reflector is correlated correlated with with the the varved varved clay clay horizons. horizons. The third reflector reflector discontinuous acoustic acoustic character which which is correlative with with the the till horizon has a strong, discontinuous described by Scholz (1985). The Thefourth fourthreflector reflectorisisaastrong, strong,hard hardreflector. reflector. It's irregular surface and the presence of scattered channels throughout associate it with bedrock. bedrock. cover for for Western Western Lake Lake Superior Superior generated generatedfrom from this this data data: A map of sediment cover of the the basin basin where where sediment sedimentfocusing focusing is isoccurring. occurring. Acoustic Acoustic refle&we* reflectivity shows regions of (in conjunction with with data from from coring) coring) is used to to produce a distribution distribution map of sediment sediment type in the basin. This This information informationwill will further further our our understanding understanding of circulation circulation dynamics to improve sampling strategies for future within the western basin and will help to investigations sediment binding investigations of sediment binding contaminants. contaminants. 3 �Idealized Stratigraphic Stratigraphic Section Section of Idealized Lake Superior Sediments Sediments Lake Thickness (cm) {cm) Brown Brown clayey clayey sediment sediment Gray Clay Clay 10-350 15-400 Gray Gray Varves Vawes 257-900 Varves Red Varves Red 91-300 Red Clay Red Clay 100-3000 Brown Sand Brown Sand (After Scholz, 1985) Tilt Till Figure 1 References References cited cited J.K. and CWP/SU: Seismic Unix Cohen, J.K. and Stockwell, Jr. J. W., 1996, CWPJSU: Unix Release Release29: aa free free package for seismic research and processing, Center for Wave Phenomena, package Phenomena, Colorado Colorado School Schoolof of Mines. Mines. Scholz, C.A., and sedimentation sedimentation rates rates in the the western western arm of of C.A., 1985, 1985, Sediment distribution and Lake geochronology, Lake Superior Superiorusing using3.5 3.5 kHz kHzseismic seismicreflection reflectionprofiles profilesand and210Pb 210Pbgeochronology, M.S. thesis, thesis, 129 129pages. pages. 4 �INTERACTION AAVIRGINIA FORMATION XENOLLTR I N T E R A ~BETWEEN BEWEEN ON VIRGINIA FORMATION XENOLITH AND MARC MAGMA AT THE THE BABBITT -NI AND MARC MAGMA AT BABBJTF aCu-NI DEPOSIT, DULUTH COMPLEX, MN. DEPOSIT, DULUTH COMPLEX, MN. Arcuri, kcuri, T., T., and andRipley, Ripley, B. E. M., M., Department Department of Geological Geological Sciences, Sciences, Indiana IndianaUniversity, University, Bloomington, IN47405 47405 Bloomingtou,IN ., Previous Previouswork workon on the the Duluth Duluth Complex, Complex, MN, has shown shown the importance importanceof of the the interaction interaction between betweenVirginia VirginiaFormation Formationxenoliths xenolithsand andtholeiitic tholeiiticmagmas magmas in inthe theformation formationof ofsulfide sulfidemineralization. minerdimtion. In In this thisstudy studythe theeffects effectsof ofaasingle singlexenolith xenolithon onthe thesurrounding sumundiugigneous igneousrocks rocks were were examined examined from fromdrill &ill core factor coreininorder ordertotoassess: assess:I)1)ififininsitu situintroduction introductionofofsedimentary sedimenkuysulfur sulfurwas wasan animportant impo-t factorininthe the formation formationof ofthe themassive massivesulfide sulfidelayer layeratatthe thetop topof ofthe thexenolith, xenolith,2) 2)ifif aa flow flowpath pathof ofaapartial partialmelt meltderived derived from the xenolith can be determined from major element gradients, 3) if sulfur and oxygenisotopic isotopic from the xenolith can be determined from major element gradients, 3) if sulfur andoxygen gradientswere werepreserved preservedatatthe thexenolith xenolithcontacts, contacts,and andififso soto tomodel modeltheir theirorigins originsusing usingmass massbalance balanceand and gradients diffusion diffusioncalculations. calculations. Sulfur m yfrom fmrn12.4 12.4toto Sulfurisotopic isotopicvalues valuesof ofdisseminated disseminatedand andlenticular lenticularpyrrhotite pymhotitein inthe thexenolith xenolithvary 17.47~with prima^^ layer to layer differences in the the protolith pmtolith(Fig. (Fig. 1). 1). 17.4%o with the the variation variation thought to reflect primary differences in The Themassive massivesulfide d d eatatthe theupper uppercontact contactofofthe thexenolith xenolithisischaracterized c h a m m i dbyby6M5 6% values valnesof of 12.0 12.0 to l2.4%. 12.4%. In Inthe theigneous ignwusrock rockabove abovethe themassive massivesulfide, suEde,6M5 6% values valuesrange range from fmrn 10.7 10.7to to 111.5%0. The.sevalues valuesare are 1.5%. These strongly stronglysuggestive suggestiveof ofaasedimentary sedimentaqsource sourcefor forthe thesulfur sulfurin in the thesulfide sulfideminerals; minerals;taken takentogether togetherwith withthe the pyrrhotite-rich nature of the sulfide the 6'S values are also consistent with an in situ origin of the pymhotite-rich nature of the sulfide 6% values are also consistent with an in sim origin of the massive massivemineralization mineralizationat atthe the xenolith xenolith border. Andrews Andrewsand andRipley Kpley (1989) (1989) detected detectedaanegative negative correlation correlationbetween betweenwhole wholerock rockSScontent contentand andFe/Mg F&g ratios ratiosof of orthopyroxene orthopyroxeneand andbiotite biotiteininVirginia Virginia Formation Formationfootwall footwallrocks. rocks. This Thisrelationship relationshipwas wasattributed attributedto tosulfur sulfurfixation fixationininthe thecountry countryrocks rocksand andthe the sulfurization of Fe-bearing silicates. The opposite relationship was observed in the xenolith from sulfurization of Fe-bearing silicates. The opposite relationship was observed in the xenolith fromcore core BBl-127, 1-127, suggesting or process suggestingthat that sulfurization sulfurizatiouof of Fe-bearing Fe-bearingsilicates silicateswas wasnot notaamaj major process and and that thatFe/Mg F a g ratios betweenoriginal ariasedimentary sedimentary ratiosof ofminerals mineralsininthe thexenolith xenolithreflect reflectdifferences differencesininbulk bulkcomposition compositionbetween layers. 6S values layers. The 6% valuesof of the theigneous ignwus rocks rocksbelow below the the xenolith xenolith are are very very different differentfrom fmrnthose thosein inthe the igneous rocksabove abovethe thexenolith, xenolith,and andrange rangefrom fmrn-2.8 -2.8toto5.2%o. 52%. ignwusrocks Oxygen Oxygenisotopic isotopicvalues valuesalso alsoshow showvery verydifferent differenttrends hcnds above aboveand and below belowthe thexenolith xenolith(Fig. (Fig.1). 1). 6'o values of of thethe xenolith vary from 9.89.8 to to 1111.77m, .7%o, with 6'*0 values xenolith vary from withthe thelowest lowestvalue d u e near near the theupper upper contact. alsO 6% values values of 6.2%0 6.2% over valnesof ofthe theoverlying overlyingigneous igneousmaterial material gradually ddecrease e c m e to nnormal o d values over a 30 30 foot foot interval. gradient muchsharper sharper8O 6l80 gradientisisfound foundatatthe thelower lowercontact, contact,with with8180 P O values values of of 5.8 to 6.3% interval.AAmuch found foundininthe theigneous igneousrocks rockswithin withina adistance distanceofofless lessthan than1.5 1.5feet. fet. Major Majorelement elementanalysis analysisofofthe thexenolith xenolithindicate indicatethat thatitithas hasundergone undergoneextensive extensivepartial partialmelting, melting, with K-and andNa-bearing Na-bearingcomponent. component.Unmetamorphosed UnmetamorphosedVirginia VirginiaFormation Formation withthe theloss lossofofaaSi-rich, Si-rich,Ktypically wt. % % Si02, Si02,whereas whereas xenoliths contain from from 45 to 50. However, However, typicallycontains containsbetween between55 55and and65 65wt. gradients in Si02 content in the igneous rocks above the xenolith that might track the movement gradients in Si02content in the igneous rocks above the xenolith that might track the movementofofaa partial detected. The partialmelt meltand andalso alsoexplain explainthe the8180 6"O gradient w e n t are are not deected. Theabsence absenceof ofSi02 Si02gradients gradientsmay maybe be related magmadue duetoto relatedto: to:1)1)relatively relativelyrapid rapidmelt meltextraction extmctionand andmovement movementinto intothe thesurrounding surroundingmagma buoyancy, buoyancy,2)2)homogenization homogenizationininthe themagma magmadue dueto toconvection, convection, 3) 3) destruction destructioncaused causedby bythermal thermal perturbations resulting from later magma pulses. Modeling of SiC)2 transport into the surrounding melt perturbations resulting from later magma pdses. ModeIing of S O 2transpo~into the surroundingmelt via viadiffusion diffusionalone aloneindicates indicatesthat thatan aninitial initialSi02 Si02gradient w e n tcould couldbe behomogenized homogenizedwithin withinaamaximum rnaximumtime time ofof10,000 interpret thethe also proffle at the toptop of of thethe xenolith as being duedue to retrograde 18C).. 10.000years. years.We We interpret 6180 profile at the xenolith as being to retrograde l80exchange exchange(i.e. (i.e.developed developedafter afterthe theextraction extractionofofaagranitic graniticmelt meltfrom fromthe thexenolith xenolithand andhomogenization homogenizationofof the enclosing magma). Diffusion modeling indicates that a retrograde oxygen isotopic the enclosing magma). Diffusion modeling indicates that a retrograde oxygen isotopicexchange exchangeprofile profile could -3 x lO 10.'cm2/sec. cm21sec. couldbe beestablished establishedininasaslittle littleasas100 100toto500 500years, years,assuming assumingan anoxygen oxygendiffusivity diffusivityofof—3 The Thevery verydifferent differentisotopic isotopicprofiles profilesdeveloped developedatatthe theupper upperand andlower lowercontacts contactsofofthe thexenolith xenolith correlate correlatewith withdistinct distinctdifferences differencesbetween betweencomposition compositionand and mineralogy mineralogy of the the igneous igneous rocks. rock. The Theupper upper unit Ti02 and Si02 contents, and Fe/Mg ratio relative to the unit below the xenolith unitisismarked markedby by.higher higher TiO, and SiO, contents, and F&z ratio relative to the unit below the xenolith (Fig. ananevolved to gabbronorite is the (Fig.2). 2).This Thisunit unitisis evol<ednorite norite-to gabbronoritethat thatis themost mostfrequently frequentlymineralized mineralidrock rocktype type ininthe thePartridge PartridgeRiver Riverintrusion. intrusion,InIncontrast contrastthe thelower lowerigneous igneousunit unitisisaamore moreprimitive primitivetroctolite hctolitewith with only oxygen and onlysparse sparsesulfide s&de mineralization. mineralization.The Thewell welldeveloped developed-oxygen andsulfur sulfurisotopic isitopicprofiles profilesininthe the 55 �gabbronorite are are indicative indicative of the preservation of at gabbronorite of aa primary primaryxenolith-magma xenolith-magmainterface. interface. Isotopic values at the lower contact interface. Geochemical data suggest that the troctolitic contact are are indicative indicative of a secondary interface. magma was was aa later laterpulse pulsethat thatmay may have have intruded intruded after sulfur and oxygen isotopic equilibrationwith with mafic magma isotopic equilibration liquids had been been established establishedin in the the xenolith. Alternatively Alternativelythe the troctolitic tmctolitic magma magma may have have delaminated delaminated aa liquidshad portion of the the Virginia VirginiaFormation Formation that that formed f o n d the base t h i i e s s of portion base of of aa magma magmachamber. chamber. Because of the thinness the troctolitic troctoliticmagma magmasheet sheetisotopic isotopicgradients gradients did not develop due to rapid m liig. the cooling. REFERENCE: REFERENCE: Andrews, hdrews, M. M. and andRipley, Ripley,E. E. M., M., 1989, 1989,Mass Mass transfer and sulfur fixation in the contact contact aureole aureoleof ofthe the Duluth Duluth Complex, Complex, Dunk DunkaRoad RoadCu-Ni Cu-Nideposit, deposit,Minnesota: Minnesota: Can. Can. Mineralogist, Mimraiogist,v. v. 27, 27, p. 293-310. 293-3 10. &'S Depth 6% and and8180 ti1*0vs vs Depth 6180 (%) 6% (%) 22 44 66 88 I2 12 10 10 14 14 \Tirzinia Formation Tioctolite_____ -5 0 5 10 20 15 6S (%) Figure Figure1.1. 6180 6"Oand andoMS 6=S values valuesthrough throughaaVirginia Virginia Formation Formation xenolith and igneous igneous rocks rocksof of the thePartridge ParhidgeRiver River Intrusion, drillcore coreB1-127. Bl-127. Inmsion,drill SIC)2 SiO, vs vs Depth Depth(ft.) (ft.) FeO FeOand andMgO MgOvs vs Depth Depth wL% wL% 30 3 0 35 35 40 40 45 45 50 SO 55 55 Ti02 Ti02vsvsDepth Depth wt.% *% wL% wL% 0 10 20 30 40 50 0 2 4 6 8 10 Figure Figwe2.2.Variations Variationsininchemical chemicalcompositions compositionsthrough throughxenolith xenolithand andsurrounding surroundingigneous igneousrocks, rocks,Babbitt Bahbinarea, area,drill drill coreBl-127. wreB1-127. 66 �THE HURONIPJT UP THE HURONIAN -- FROM FROM THE THE BOTTOM BOTTOM —- UP G. G. Bennett, Bennett, Ontario Ontario Geological Geological Survey Survey The The HuronianSupergroup Huronian supergroupis is aa sequence sequence of of Early Early Proterozoic Proterozoic sedimentary sedimentary and minor volcanic rocks, up up to to 12 12 000 000 mm thick, thick,which unconfo±mably upon which lies lies unconfonnably minor volcanic Archean Huronian belt extends Archean rocks rocks of of the the Superior Superior Province. The Huronian extends eastward, eastward, about 450 tan km along the north north shore shore of of Lake Lake Huron Huron and and into into Quebec. The The age for about Huronian Supergroup is constrained by by the the ages ages of of basal basal volcanic volcanic rocks of the Huronian rocks (2.45 Ga) Ga) and Nipissing (2.45 Nipissing intrusions intrusions (2.2 (2.2 Ga). Ga). The Huronian HuronianSupergroup Supergroup subdivided, ascending order,into intothe the Elliot Elliot The is is subdivided, ininascending order, Lake, the Lake, the the Quirke and the the Cobalt Lake, the Hough Hough Lake, Quirke Lake Lake and CobaltGroups. Groups. The The Elliot Elliot Lake Lake Group Group contains contains the theonly onlyvolcanic volcanicrocks rocksand and important importanturanium uranium deposits. deposits. The abundanceofofdetrital detrital pyrite Matinenda The abundance pyrite and and uraninite uraninitein inthe the MatinendaFormation, Formation, and and the general lower, three Huronian the general lack lack of ofhematite hematitein inrocks rocksof o fthe the lower-three Huroniangroups, groups, points to points toaareducing reducingatmosphere atmosphere during during early earlyHuronian Huronian sedimentation. sedimentation. The The appearance of hematite hematite in in the marksthe the accumulation accumulation ooff free free appearance of theCobalt Cobalt Group Group marks oxygen in the Earth's atmosphere(Roscoe, 1968).Studies studies of oxygen in the Earth's atmosphere(Roscoe, 1968). of Huronian Huronian paleosols paleosols have also also provided valuable insight into into the the evolution evolution of of the the Earth's Earth's have atmosphere (References atmosphere (References in in Bennett Bennett et et al.l9Sl). al-1991). The 1-Juronian volcanicrocks, rocks,the theEast EastBull BullLake Lake Suite(EBLS) Suite(EBLS) of of layered layered mafic The Huronian volcanic mafic intrusions, intrusions, and and the the dikes dikes of of the the Matatchewan—Hearst Matatchewan-Hearst swarm swarm are are an an essentially essentially coeval(circa 2.45 Ga) igneous suite (Peck et al., al., 1995; 1995; Heaman, Heaman, 1997) (Peck et 1997) emplaced near The distribution distribution of EELS near the the base base of of the the Huronian Supergroup. The EBLS intrusions intrusions may form The northern northern group includes form two two approximately approximately linear arrays. The includes the the Agnew Lake A second Agnew Lake and and the the East East Bull Bull Lake Lake intrusions. intrusions. A second group group of of EELS EBLS intrusions west end end of of the the SudburyIgneous Sudbury Igneous Complex, intrusions extends extends from from near the west Complex, in in aa southwest direction, along the the base bise of of the the Huronian Huronian Supergroup. Supergroup. These These two two southwest groups magma chambers chambers emplaced emplaced under under two groups of of EELS EBLS intrusions intrusions represent magma two rift rift segments which joined joined just Sudbury Complex. segments which justwest westof ofthe thepresent present SudburyIgneous Igneous Complex. The proposed proposednorthern northern rift rift segment, The segment, which which contained contained the the Livingstone LivingstoneCreek Creek Formation andthe thevolcanic volcanicrocks rocksof of the the Thessalon Thessalon Formation Formationofofthe the Sault Sault Ste. Formation and Ste. Marie— ElliotLake Lakearea, area,has hasbeen beendeeply deeplyeroded, eroded,with withdeeper deepererosion erosion (i.e. (i.e. Marie- Elliot greater uplift) in The southern southern rift rift segment, segment, which which contains contains greater uplift) in the east. The volcanic much intercalated intercalated sandstone volcanic rock rock with with pillow pillow structures and much sandstone and and wacke wacke (Card, 1978) was was probably probably at a a much much lower lower topographic topographic level level during (Card, 1978) during erosion erosion of of the northern northern rift volcanic sequences sequences may may correspond correspond to the rift segment. These volcanic the "seaward dipping reflectors" margins. "seaward dipping reflectors" of of modern continental continental margins. Following was Following rifting, rifting,there there wascontinued continuederosion erosionand and an an eventual eventualsubsidence subsidence as as indicated and uraniferous uraniferous conglomerates conglomerates of indicated by the the deposition deposition of the arenites and of the Matinenda Formation. Formation. The Theturbidites turbidites of Formation which which overlie overlie the ~atinenda ofthe theMcKim McKim Formation - -- - the along aa foundering the Matinenda Matinenda Formation, Formation, suggest suaaest marine marine encroachment encroachment alona founderina continental margin. continental margin. It isissuggested Huronian It suggestedhere herethat thata a Huronian continental continentalflood floodbasalt basaltprovince provincemay may oncehave haveexisted existednorth northofofthe thepresent presentHuronian Huronian belt. so,at at least least the once belt. IfIfso, the southern portion of CFBP, must must have have been been eroded eroded prior to southern of this proposed CFBP, to the the deposition of the since the the latter latter has has a a mainly mainly granitic deposition the Matinenda Formation, since provinance. The sub—Matinenda disconformity (Bennett (Bennett et et al., al., 1991) marks this provinance. The sub-Matinenda disconformity potentially long potentially long erosion erosion interval. interval. Heaman(1997) mantle plume plume related, large large igneous Heaman(1997) provides provides evidence for a mantle igneous province at intrusive rocks rocks noted noted above. The 2 . 4 5 Ga Ga which includes includes the intrusive The model model province at 2.45 for the described here, here, although although arrived arrived at for the Elliot ElliotLake LakeGroup Group described atindependently, independently, supports of the supports many many of theconclusions conclusionsofofHeaman(l997). Heaman(1997). 7 �Following Following rifting rifting and and early early Huronian Huronian magmatic magmatic events, events, post—volcanic post-volcanic Huronian Huronian sediments were were deposited, deposited, either either along along aa passive passive continental continental margin, margin, or or (less (less sediments likely) within a continually sinking, sinking, intracratonic intracratonic basin. basin. Thecyclic Thecyclic likely) withina sedimentation groups above above the Elliot Elliot Lake Lake Group sedimentation of of each each of of the the three Huronian groups Group are and retreat retreat of of Huronian Huronian ice ice are generally generally believed to to record the advance and sheets.Each cycle cycle begins begins with with aa mainly mainly diamictite diamictite sequence(glacia1 sequence (glacial advance),• sheets: Each advance), overlain or carbonate carbonate (glacial overlain by by aa marine marine sequence sequence of of mudstones, siltstone or (glacial loading by a relatively thick thick arenite arenite loading and and marine marine transgression), transgression), followed followed by sequence . The sequence (interglacial (interglacialoutwash) outwash). The presence presence of of drop—stones drop-stones in in some some laminated units units of of all all three three groups supports the glaciogenic laminated glaciogenic model model by indicating the the presence presence of of floating floating ice ice (Roscoe, (Roscoe,1968). 1968). indicating The was variably variably deformed deformedand andfaulted faulted during during several The entire entireHuronian Huronian sequence sequence was several deformational of Nipissing deformational events, events,some some of ofwhich which preceded preceded the theemplacement emplacement of Nipissing sills 2.2 sillsatat 2.2Ga Ga(Card, (Card,1978). 1978). - - References References Bennett, Bennett, G., J.A. 1991. The The Huronian Euronian Supergroup Supergroup G., Dressler, Dressier, B.C. B.O. and Robertson, J .A. 1991. and and Associated Associated Intrusive Intrusive Rocks. Rocks. in in Geology Geology of Ontario Geological Geological of Ontario. Ontario. Ontario Survey, Survey, Special SpecialVolume Volume 4, 4, p. p. Card, Card, 633—641. 633-641. K.D. of the the Sudbury-Manitoulin Sudbury-Manitoulinarea, area,districts districts ofofSudbury Sudbury K.D. 1978. 1978. Geology Geology of and and Manitoulin; Manitoulin; Ontario Ontario Geological Geological Survey, Survey, Report Report 166, 166, 238p. 238p. Heaman, Heaman, L. L. M. M. 1997. 1997. Global Global mafic mafic magmatism magmatism at at 2.45 2.45 Ga: Ga: Remnants Remnants of of an an ancient ancient large large igneous igneous province?; province?; Geology, Geology, Vol. Vol. 25, 25, no. no. 4, 4, p. 299—302. 299-302. Peck, Peck, D.C., D.C., James, James, R.S., R.S., chubb, Chubb, P.T., P.T., Prevec, Prevec, S.A. S.A. and andICeays, Keays, R.R. R.R. 1995. 1995. Geology, Geology, Metallogeny Metallogeny and and Petrogenesis Petrogenesis of of the the East East Bull Bull Lake Lake Intrusion, Intrusion, Ontario; Ontario; Ontario Ontario Geological Geological Survey, Survey, Open Open File File Report Report 5929, 5929, ll7p. 117p. Roscoe, uraniferous conglomerates; Geological Geological Roscoe, S.M. S.M. 1969. 1969. Huronian Huronian rocks rocks and and uraniferous Survey Survey of of Canada, Canada, Paper Paper68—40, 68-40, 2OSp. 205p. - 8 �NATIVE NATIVE COPPER COPPER PRECIPITATION PRECIPITATION BY BYFLUID-MIXING, FLUID-MIXING, KEWEENAW KEWEENAW PENINSULA, PENINSULA, MICHIGAN MICHIGAN BORNHORST, Departmentof of Geological GeologicalEngineering Engineeringand andSciences, Sciences,Michigan Michigan BORNHORST,Theodore TheodoreI.J. Department Technological University, Houghton, MI 49931, tjbomho@mtu.edu; and Technological Houghton, MI 49931. tibornho@mtu.edu: and WOODRUFF, U.S. Geological Survey, WOODRUFF, Laurel G., G., U. s.Geological survey,St. St. Paul, Paul, MN MN 55112. 55112. woodruff@usgs.gov. woodruff@usgs.gov. Large billion kg kg of of refmed refined copper copperextracted) extracted)are arehosted hostedby bybrecciated brecciated Largenative nativecopper copperdeposits deposits(about (about 55 billion and andamygdaloidal amygdaloidaltops topsof of basalt basalt lava lava flows flows and and interfiow interflow conglomerates conglomeratesin inthe the1.1 1.1Ga GaMid-continent Mid-continent rift riftsystem systemalong alongthe theKeweenaw Keweenaw Peninsula, Michigan. AAsuite suiteof ofsecondary secondaryminerals mineralsparagenetically paragenetically associated associatedwith withthe thedeposition depositionof of native native copper copper includes includescalcite, calcite, epidote, epidote,quartz, quartz, and andprehnite, prehnite, in in addition numberof of other other low low temperature temperature minerals. Most Mostgenetic geneticmodels modelsfor forthe thenative nativecopper copper additionto toaanumber deposits from rocks deeper deeperwithin withinthe therift rift(e.g., (e.g.,White, White,1968; 1968;Bornhorst, Bomhors 1997). depositsderive deriveore ore fluids fluids fromrocks 1997). Mechanisms Mechanismsfor forprecipitation precipitationare aremore moreproblematic; problematic;proposed proposedmechanisms mechanismsinclude includecooling, cooling,fluidfluidrock rockinteraction interactionvia viametamorphic metamorphic reactions and fluid mixing. Cooling Coolingalone alonecannot cannotaccount accountfor fornative native copper complexedas asCu* Of (copper (1° (copper chloride), chloride), but precipitated as CuO copperprecipitation precipitationas as copper is likely complexed (native (nativecopper). copper).High Highwater/rock waterlrockratios ratiosininthe theore orezones zoneslimit limitthe theeffectiveness effectivenessof of fluid-rock fluid-rock interaction bodies. Wells interactionin inaccounting accountingfor for the the total mass of native copper found concentrated in ore bodies. Wells (1925) (1925)first firstsuggested suggestedmixing mixingof of dilute dilutewaters waters with with ore-bearing ore-bearingfluids fluidsas asaa mechanism mechanismfor fornative native copper 60years yearslater, later,Richards Richardsand andSpooner Spooner(1986) (1986) copperprecipitation precipitationbased basedon onchemical chemicalprinciples. principles. Some Some60 revived revivedthe theidea, idea,and, and,based basedon onfluid fluid inclusion inclusion studies, studies, suggested suggestedthe the mixing mixingof oflow-temperature, low-temperature,lowlowsalinity native copper copper precipitation. precipitation. Based salinityfluids fluidswith with ore-fluids ore-fluids as as a mechanism for native Based on on these these publications publicationsand andon onaareinterpretation reinterpretationof of stable stableisotope isotopedata dataof of Livnat Livnat(1983), (1983). Bomhorst Bornhorst(1992) (1992) proposed that"mixing "mixingofofore orefluids fluidswith withresident resident reduced reducedsemi-stratified semi-stratifiedfluids fluidsmay mayhave havebeen beenan an proposedthat important importantmechanism mechanismfor forprecipitation precipitation of native copper." Oxidized Oxidizedmeteoric meteoricwaters watersseem seemto tobe be eliminated eliminatedasasaapossible possibleend-member end-memberfluid fluidas asprecipitation precipitationof ofnative nativecopper copperrequires requiresreduction reductionofofthe the ore-fluid. ore-fluid. In Inorder ordertototest testthe thehypothesis hypothesis of fluid-mixing, fluid-mixing, aa suite suiteof of calcite calcitesamples sampleswas was collected collected for for12 12 km deposit. Samples kmalong alongthe thestrike strikeof ofthe theKearsarge Kearsarge deposit, the largest basalt-hosted basalt-hosted deposit. Sampleswere were from from mine range of drillcore. core. Calcites Calcitesfrom fromthe theKearsarge Kearsargedeposit deposithave haveaarange of6"O 8"0 from from20.1 20.1toto minerock rockpiles pilesand anddrill 11.3 %O and and8'3C 5° from from-1.7 -1.7 to to -3.1 -3.1 %, %o, based based on on 39 39analyses analyses from fromthis thisstudy studyand and16 16from fromLivnat Livnat 11.3 % (1983). (1983). The Thetemperature temperatureofofcalcite calcite(and (andaccompanying accompanyingnative nativecopper) copper)deposition depositionisisconstrained constrainedby by the minerals,alsO S"0 values values for for coexisting coexisting mineral mineral pairs pairs suggest suggestan anaverage average theassemblage assemblageofofgangue gangueminerals; temperature of about 215°C (Livnat, 1983). (215°q,calculated calculated 6O inin At this this temperature temperature (215¡C) 8"0_ temperature of about 215C (Livnat, 1983). At equilibrium +11.5%o %O (59 (59% %between between3.8 3.8and and5.8 5.8%o) %o) and andcalculated calculated equilibriumwith withcalcite calciteranges rangesfrom from+3.5 +3.5toto+11.5 rçrangesfmm-4to-l%o(71%between4.75and...3%0). 8°C ranges from -4 to -1 %o (71 % between -1.75 and -3 %). ForthesefluidsçandpHis For these fluids f,,, and p H is predicted to be an unimportant source of variation to account for Vc. predicted unimportant source of variation to account for 8 " To To~explain explain ~ the thedata databy byaa uniform assumed8'08O of of +5.0 % %O requires a temperature variation uniform ore ore fluid fluid with assumed +5.O requires a temDerature variationofof130 130toto260°C; 260¡Caa similar carbon in similartemperature temperature range range is is required required for an an assumed assumed uniform unifo&carbon inthe thefluid. fluid. The Thegangue gangue mineral mineralassemblage assemblageisisrather rathersimilar similarthroughout throughoutthe thedeposit depositand anddoes doesnot notsupport supportsuch suchaalarge largerange rangeinin temperature. lack of of correlation contlation between between8"'0._ 8"O and cannot Inaddition, addition, the lack and6'3C< 8'3~.,.,, cannotbebeexplained explainedby by temperature. In temperature data may maybe beinterpreted interpretedby bychanging changingtemperature temperatureand and However, the the data temperaturevariation variationalone. alone. However, mixing mixing of oftwo twoorormore morefluids. fluids. This This model model can can also alsoexplain explain the thewide widespread spreadininW'O 8"Ofor forquartz quartzasas reported Livnat(1983). (1983).The Theend-member end-memberore orefluid fluid(represented (representedby bymost mostofofthe thedata) data)has hasaa 8"0,,,,, reportedby byLivnat 9 �13cm ( - 8 " ~of~of ) about+5+5and and-2-2%c, %o, respectively respectively and is consistent with and '3C (—6'3C) about with derivation from the riftbewell welldefined, defined, but but has has 6"omand 60CQ S^Cm of of greater greater filling basalt Theother otherfluid fluidcannot cannotbe basalt section. section. The than + +11 11and andless lessthan than -3.5 -3.5 %4 %o,respectively. respectively. This fluid is interpreted as as water water resident resident at at the site of ore deposition. deposition. The Thedata datapresented presentedhere heresupport support the the hypothesis hypothesis that fluid-mixing fluid-mixing played a role role in in precipitation precipitation of native copper wpper in in the theKeweewan KeweewanPeninsula. Peninsula. Additional Additional studies studies are are in progress to further further test the the fluid-mixing fluid-mixinghypothesis. hypothesis. References References Bomhorst,Li, TJ.,1992, 1992, overview theKeweenaw KeweenawPeninsula Peninsulanative nativecopper copperdisthct, district,Michigan: Michigan: Bomhorst AnAn overview ofofthe Society GuidebookSeries, Series,v. v. 13, 13,p. p. 33-62. 33-62. Societyof of Economic EconomicGeologists GeologistsGuidebook Bomhorst, Bornhorst, TJ., TJ.,1997, 1997,Tectonic Tectoniccontext contextof ofnative nativecopper copperdeposits deposits of the North American American Midcontinent Special Paper 312, MidcontinentRift Rift System: System: Geological Geological Society Society of America Special 312, p. 127-136. 127-136. Livnat, 1983,Metamorphism Metamorphismand and copper coppermineralization mineralization of the Portage Portage Lake Lake Lava Lava Series, Series, Livnat, A., 1983, northern northern Michigan Michigan (Ph.D. (Ph.D.dissertation): dissertation): Ann Arbor, University of Michigan, 292p. 292p. Richards, J.P., and Spooner, high temperature, temperature, Spooner, E.T.C., E.T.C., 1986, 1986,Native Native copper copper deposition by mixing of high high cool dilute dilute groundwaters, groundwaters, high salinity salinity fluids fluids of possible possible magmatic association with cool Keweenaw Peninsula, Michigan: Geological Society of America Abstracts with Pmgrams, Keweenaw Peninsula, Geological Programs, v. v. 18, 18, p.730. p. 730. Wells, ltC., R.C,1925, 1925,Chemistiy Chemistryofofdeposition depositionofofnative nativecopper copperfrom fromascending ascendingsolutions: solutions:U.S. U.S. Geological Survey Bulletin 778.71~. 778, 'lip. Geological Survey 1968,The Thenative-copper native-copper deposits deposits of northern Michigan, in Ridge, J.D., J.D., ed., ed., Ore Ore White, W.S., 1968, White, deposits of of the the United United States States 1933-1967 1933-1967 (the (the Graton Sales volume): American Institute Institute of deposits Mining, Mining, Metallurgical Metallurgicaland andPetroleum PetroleumEngineering, Engineering,New New York, York, p. 303-325. 10 �THE DIAMONDIFEROUS SIX-PAK SIX-PAK ULTRAMAFIC ULTRAMAFIC LAMPROPHYRE LAMPROPHYRE DIATREME, KENOSHA, WISCONSIN, U.S.A. CARLSON, CARLSON, S. M., Ashton Mining Mining of of Canada Canada Inc., Vancouver, B.C., Canada Canada ADAMS, U. G. W., The The Doe Doe Run Company, Viburnum, MO, USA (former Chief Geologist Geologist for for Crystal Crystal Exploration Inc.) Diamond Diamond exploration exploration in in the the midwestern midwestern United States States began began with the the discovery Lake Ellen Ellen discovery of the Lake kimberlite kimberlite in in 1971. 1971. Early Early exploration exploration focused focused on on the the Upper Upper Peninsula Peninsula of of Michigan, Michigan, resulting resulting in in the the discovery of over over 20 20 kimberlite kimberlite bodies bodies in Iron, Iron, Dickinson Dickinson and and Menominee Menominee counties. counties. These These post-Ordovician post-Ordovician intrusives intrusivesrange range in fromnarrow narrow dikes dikes to to diatremes diatremes in in excess of 20 20 acres. acres. Diamonds are present present in in many of of the the Michigan Michigan in size size from kimberlites, but but to to date date no no economic economicdeposits depositshave havebeen been identified. identified. Further Furtherregional regional exploration explorationidentified identified concentrations concentrations of fresh fresh "kimberlitic" in glacial glacial "kimberiitic" indicator indicatorminerals mineralsin tilts tills in in southeastern southeasternWisconsin, Wisconsin, where at least least six six historic historic diamond diamond finds finds occurred, occurred, including including the the 21.5 21.5 carat carat "Theresa" major diamond diamond exploration exploration companies companies have have been active in "Theresa" stone. stone. Although Although several major in southeastern southeastern Wisconsin, the Six-Pak Six-Pak diatreme, diatreme, discovered by the Crystal Exploration-Ashton Exploration-Ashton Mining Joint Venture, Venture, is is the the only only pipe pipe ever everreported reportedininthis thisregion. region. Exploration Inc. carried out sporadic exploration Crystal Exploration exploration in in southeast southeast Wisconsin Wisconsin from from the the mid mid 1980's, and in in joint joint venture venture with with Ashton Ashton Mining Mining of Canada Canada Inc. Inc. from from 1992 1992 through through 1995. 1995. Target Target identification identification concentrated on kimberlitic kimberlitic indicator indicator mineral mineral anomalies and data data from from public publicairborne airbornemagnetic magneticsurveys. surveys. In In early 1994, 1994, Crystal Crystal Exploration Exploration acquired a little-known little-known airborne magnetic survey which had been been flown flownand and later donated to Case by a major oil company conducting base metal Case Western Western Reserve University University by metal exploration. exploration. From the new data, three "kintherlite-style" magnetic targets were recognized and ground checked. Two data, three "kimberlite-style" targets were recognized and ground checked. Twotargets targets were eliminated as cultural responses. eliminated as cultural responses. During During the spring and early summer summer of 1994, 1994,land landacquisition acquisition and and detailed ground magnetic surveys were completed completed on on the the third third target target and and in late August of 1994, 1994, the the Six-Pak Six-Pak diatreme intersectedininthe thefirst first of of eight eightexploration explorationdrill drill holes. diatreme was was intersected The The Six-Pak Six-Pak diatreme diatreme is is approximately 50 acres in size and is located within the the outskirts outskirtsof ofKenosha, Kenosha, Wisconsin. Reverse Reversecirculation circulationwith with selective selective core drilling was used to test the target. Between Betweenone oneand andseven, seven, one-ton samples of cuttings were recovered from each each hole. hole. A recovered from Aconcentrate concentrate was was generated generated from fromeach eachsample, sample, and and splits splitswere were submitted submittedto to Ashton Ashton Mining's Mining's laboratory laboratory facility facility in in Perth, Perth, Australia for for caustic causticfusion fusionprocessing. processing. The The remainder remainder of of this this"mini-bulk" "mini-bulk"sample sample was was processed processed through through Ashton's Ashton's one-tonne-per-hour one-tonne-per-hour dense densemedia media separation separationplant plant in inCrystal CrystalFalls, Falls,Michigan. Michigan. The upper upper portions portions of of the the diatreme diatreme are are complex, complex, containing containing sequences of fossiliferous fossiliferous dolostone dolostone and and red, bedded breccias at at depth. depth. The to80 80feet feetinintl1ickness thickness bedded arenites arenites which which grade grade into ultramafic breccias The arenites arenites range range up up to and minerals. They may represent andcontain containsparse sparsevolcaniclastic volcaniclastic fragments and indicator minerals. represent true true crater-facies crater-faciesrocks rocks or, after diatreme diatreme emplacement emplacement or, along alongwith withthe theminor minorcarbonate carbonaterocks, rocks,they they may may have formed formed long after Beneath rocks, the Six-Pak diatreme consists of fairly uniform uniform ultramafic ultramafic breccias breccias Beneath these these sedimentary sedimentary rocks, composed composedprimarily primarilyof ofserpentine, serpentine,calcite, calcite, mica, and various opaques; fresh olivine is is not not present, present, and and melilite meliliteor or pseudomorphs after melilite have not been recognized. Angular sedimentary xenoliths are common, ranging up pseudomorphs after melilite have not been Angular sedimentary xenoliths are common, ranging up to to five five feet feet across. across. Basement Basementxenoliths xenolithsare areextremely extremelyrare. rare. "Autolithic" "Autolithic" fragments fragmentsare arepresent presentininmany manysamples, samples, but but they they are aredifficult difficultto to characterize, characterize,making facies determinations determinations uncertain. Much Muchof ofthe the"diatreme" "diatreme"appears appearstoto be be hypabyssal hypabyssalin incharacter. character. many similarities similaritiesbetween between this this Classificationof of the the Six-Pak Six-Pak diatreme diatreme is not straightforward, as there are many Classification body body and and other other rock rocktypes typessuch suchasaskiinberlites kimberlites and andlamproites. lamproites. However, However, groundmass groundmass mica and and spinet spinel compositional trends are are inconsistent inconsistent with with both both kimberlites kimberlites and andtamproites. lamproites. The Six-Pak Six-Pak diatreme diatreme is is best best classified (Rock, 1991) 1991) or or a "melnoite" classified as an an ultramafic ultramafic larnprophyre lamprophyre (Rock, "melnoite" using using terminology terminology recommended recommended by Mitchell Mitchell(1994). (1994). ii �recovered from from processed processed concentrates concentrates include includethe thetypical typical"kimberlitic" "kimberlitic" indicator indicator Heavy mineral species recovered Cr-pyrope, low-Cr pyrope, pyrope, Cr-diopside, Cr-diopside, picroilmenite, picroilmenite,Cr-spinel Cr-spine!and andzircon. zircon. Apatite, rutile, minerals Cr-pyrope, mtile, amphibole, amphibole, barite and and celestite present, along along with with a variety of sulphide pyrite, galena and sulphide minerals minerals including pyrite, barite celestite are also present, millerite. The through red, red, and and exhibit exhibitlate-stage late-stage etching etching thought thought TheCr-pyrope Cr-pyrope garnet garnetsrange rangeinincolor colorfrom frompurple purplethrough to be These garnets garnet are are quite quite common common in in the the heavy heavy mineral mineral be produced produced by byinteractions interactions with with groundwater. groundwater. These concentrates, and contain up to to 6.5 6.5 wt% Cr203; Cr203; they are believed to be derived from garnet-bearing garnet-bearing peridotites. No subcalcic 10" varieties have been identified. subcalcic"G "G10" identified. Orange low-Cr pyrope is also common common in in Six-Pak Six-Pak concentrates, concentrates, often strongly strongly etched etched and and skeletal skeletalinin appearance with with deep deep corrosion corrosion sculpture sculptureand andinternal internaldecomposition decompositionchannels. channels. The The average average MgO MgO content content of of appearance these grains is 19.1 wt%, wt%, and andthe therange rangeisisbetween between13.9 13.9wt% wt%and and20.6 20.6wt%. wt%.Both BothCr203 Cr203 and and Ti02 Ti02 are are typically than 1.0 wt%. Most Most of of these these garnet garnetsare areprobably probablyderived derivedfrom from the the Cr-poor Cr-poor megacryst megacryst suite, although the less than lower MgO values found in in some somegrains grainssuggest suggestthat thatminor minoreclogitic eclogiticand andgranulitic granuliticgarnets garnet may may also also be bepresent present Cr-diopside is rare, appearing as as emerald-green emerald-green anhedral anhedralfragments. fragments. The diopsides are typically diopsides are typically coated coated with orange-white reaction products products and exhibit exhibit classic classic"cockscomb" "cockscomb" resorption resorptionmorphologies. morphologies. Green Green orange-white reaction amphibole is common, common, and and whereas whereas some some of of these these grains may be crustal, crustal, most are are probably probably derived derived from from amphibole modally-metasomatizedmantle mantlerocks. rocks. These These amphiboles amphibolescontain containup uptoto3.0 3.0wt% wt%Cr203 Cr203 and some are found as modally-metasomatized with purple purpleCr-pyrope Cr-pyropegarnets. garnet. mineral pairs with Picrojlmenjte Six-Pak concentrates. concentrates. It occurs occurs as asanhedral anhedral Picroilmenite is one of the most abundant minerals in the Six-Pak fragments with leucoxene reaction reactioncoatings coatingsand andcontains containsbetween between3.7 3.7wt% wt%and and9.8 9.8wt% wt%MgO. MgO. These These low low MgO MgO values, coupled coupled with with extremely extremely low low Cr203 Cr203 (<0.2 wt%) evidence that that the Six-Pak wt%) are supplementary supplementary evidence Six-Pak is is an an values, ultramafic lamprophyre, lamprophyre, not an archetypal kimberlite. kimberlite. spinels are are present present in in the the heavy heavy mineral mineralconcentrates. concentrates. Some are reasonably Cr-rich, with up to Various spinels wl% Cr203 Cr203 plus A12O3. Other spinels include magnetite and titanomagnetite. 58 wt% plus appreciable appreciable MgO and A1203. Coarse honey-yellow honey-yellowto to orange-brown orange-brownzircon zirconcrystals crystalsare arequite quitecommon. common. These grains are typically subhedral, and and are are mantled mantledby by fine-grained fine-grainedreaction reactionproducts, products,possibly possiblybaddeleyite. baddeleyite. A A date of anhedral, rarely subhedral, from these these zircons zirconsusing usingU/Pb U/Pbtechniques techniques(Ashton (AshtonMilling, Mining unpublished unpublished date). data). This 686 MY has been obtained from This Silurian carbonates; however, however, the age may may represent representaa is an unrealistic emplacement age as the diatreme intruded Silurian significant metasomatic significant metasomatic event event in in the the underlying underlyingmantle. mantle. Importantly,the the Six-Pak numeroussmall small diamonds diamonds have have been Importantly, Six-Pak lamprophyre lamprophyre isis diamondiferous; diamondiferous; numerous been recovered through caustic caustic fusion fusion techniques. techniques. Most Most diamonds diamonds are sharp-edged sharp-edged octahedra or macles, macles, some some showing intricate surficial surficial patterns including growth plates and trigons. trigons. Six-Pak does not not contain containeconomic economic of the large historic drift diamonds. diamonds. concentrations of diamonds, diamonds, and is unlikely to be the source ofthe The discovery of of the Six-Pak diatreme is is very very significant, significant, as as itit is the the first first recorded recorded mantle-sourced mantle-sourced Six-Pak diatreme diatreme to be be identified identified in in the thesoutheastern southeasternWisconsin Wisconsin region. region. The diatreme diatreme is also an enigma enigma as itit raises raises numerous questions regarding the the existence of of other other pipes pipes in in the the area and their economic economic potential. Do the Do the large large Wisconsin "drift" "drift" diamonds diamondshave haveaalocal localsource, source,ororare arethey theyindeed indeedderived derivedfrom fromrocks rocksfar farto to the the north north in Wisconsin Canada? Canada? authors wish to to thank Ashton AshtonMining MiningofofCanada CanadaInc. Inc.and and Crystal CrystalExploration ExplorationInc. Inc.for forpermission permission to topublish publish this this The authors givento toDr. Dr. Daniel DanielJ.I Schulze data. Additional Additionalappreciation appreciationLv is given Schufee at at the the University University of Toronto, Erindale College and and Mrs. Anne Anne Hall Hall of Winspear Resources ResourcesLtd. Ltdfor for critical critical reviews, reviewv,and andto to Dr. Dr. Ron Ron Sage of the Ontario Mrs. OntarioGeologjcal Geological for general general assistance. Survey for assistance. RH. (1994): 137-146. MITCHELL, RH. (1994): The TheLamprophyre Lamprophyrefacies. fades. MineraL Mineral.Petrology Petrology 51, 51,137-146. N.M.S. (1991): (1991): Lainprophyres. ROCK, N.M.S. Lamprophyres. Blackie Blackie& & Son, Son, Edinburgh. 12 �as aa Tool Toolfor forRecognizing RecognizingCrustal CrustalFabric Fabricand andStructure Structure Gravity Aspect as at Minnesota at 55746 D. A. Dahl, DahI, Minnesota Dept. Dept. of of Natural Natural Resources, Resources, Minerals Minerals Division, Division, Hibbing, Hibbing, Mn Mn 55746 Gravity aspect, the facing direction of Gravity gravity gradient, gradient, is is apparently apparently a sensitive sensitiveindicator indicatorof of of gravity crustal fabric, one that can can aid aid in in the therecognition, recognition,unmixing unmixingand andmapping mappingofof individual individual components of composite components composite gravity gravity signatures. signatures. Reported as a compass bearing (0-360). (0-360), aspect aspect records records the the direction direction normal normal to to the the strike of gradient. In the case of a potential field like gravity, aspect depicts the bearing bearing direction direction of of aa gradient In the case of a potential field like gravity, aspect depicts vector that is the components of gravity the sum sum of all all of the horizontal components gravity features featuresthat that affect affectaasite. site. Displayed in HSV (hue-saturation-value) color space, where hue (aspect) is valued in the (aspect) valued in the range range 0-360, gravity fabrics based on hue, and overlap of gravity gravity fabrics 0-360, fabrics can be recognized based fabrics can can be be recognized as vector-like color summing summing of of component component hues. hues. Conveniently, Conveniently, HSV color color space space also provides a means of comparing gravity aspect (hue) to Bouguer intensity, slope, slope, or or curvature (each plotted as gray scale value, with or without shadowing). curvature (1st and 2nd horizontal At MnDNR, terrain analysis tools such as slope and curvature horizontal derivatives) routinely used used to tocheck checkdata datasets setsfor foridiosyncrasies idiosyncrasies and and artifacts artifacts before before they are derivatives) axe are routinely included in a GIs-based GIS-based information system. system. Slope Slope and and curvature curvature provide provide an an excellent excellent means means of of caused by by inconsistencies inconsistenciesin indata datahandling handlingand andreduction. reduction. In the recognizing edge artifacts caused the case case Minnesota gravity of the Minnesota gravity data data set set (55,900 (55,900 points, Chandler and Schaap, 1991), 1991). terrain analysis analysis maps, and also to generate related maps of was used to generate slope slope and curvature haps, of aspect, aspect, profile curvature, curvature, and and planform planformcurvature. curvature. The aspect aspect pattern for for the Minnesota gravity data set is particularly interesting, interesting, because because itit reinforces structure in the Lake Superior reinforces several several interpretations of pre-existing structure Superior region region and and provides a basis for additional discussion discussion about about the the geologic geologic history history of of the the crust. crust. Readily Readily apparent apparent are are the the following: following: 1) 1) Overlapping Overlapping gravity gravity fabrics fabrics can be recognized. As As good good examples, examples,at at least least two two ancestral ancestral fabrics can be recognized beneath beneath the the Bayfield Bayfield basin basin of the the mid-continent rift system. gravity fabrics system. The Duluth Complex The gravity gravity aspect aspect pattern of the footwall of the ~ uluth Complex can also also be be reliably reliably traced tracedto to 30-40 30-40 km tan inside inside the the western westernmargin margin of of the the complex. complex. 2) Gravity Gravity aspect aspectcan can be be used used as an effective means of delineating the axes of gravity lows and highs. Elongate the statewide statewidepattern. pattern. Domal or bowl-like aspect gravity highs. Elongate "hinges" dominate the patterns patterns are, are, for for the the most part, part, restricted to individual intrusive intrusive features. features. 3) A A pervasive pervasivenorth-northwest north-northwest striking striking gravity fabric is parallel to the magnetic expression expression of 13 �similarly trending regional dike swarms. The The fabric fabrichas has aa much much broader broader "wavelength" "wavelength"than than the the of depth, and a general general lack spacing of the dikes. Curvature Curvatureprofile profile maxima, as a rough indicator of of magnetic that this this broader broader fabric fabric may may be be more more deeply deeply rooted than the magnetic expression expressionsuggest. suggest that the higher amplitude, amplitude, more more easily easily recognized recognized gravity gravity fabric fabric of the the east-northeast east-northeasttrending trending greenstone-granite-gneiss greenstone-granite-gneissterranes terranes that that overprint overprint it. it. 4) Pm-rift Pre-riftgravity gravityfabric fabricisisonly onlypartly partly obliterated obliterated by the the mid-continent mid-continent rift rift system system in in Minnesota. Minnesota. edge of of the the Penokean Penokean orogen orogen area in 5) A prominent gravity 5) gravity fabric parallels the northern edge completely interupts the north-south north-south aspect aspect pattern pattern that that can can be be traced on either Minnesota, but completely interuption. The side of the interuption, ThePenokean Penokean area, area,in in general, general, expresses expresses aa complex complex interplay interplay of of fabrics. fabrics. begseveral severalquestions. questions. What What is the geologic The patterns of gravity aspect in Minnesota beg significance significance of axial "hinges"? "hinges"? What What is is the the significance significance of the north-northwest trending fabric, and at what depth within or below the the crust crust does does that thatfabric fabricexist? exist? Can aspect be applied applied in interpretation interpretation of magnetic data? data? Will Will additional additionalgravity gravity data data increase increasethe the signal-to-noise signal-to-noiseratio ratioin in features can can be beresolved? resolved? Can algorithms be applied, in the aspect pattern so that more subtle features conjunction with aspect, to separate component fabrics? conjunction aspect, to separate component fabrics? References References Chandler, Anomaly Map Map of Minnesota, V.W., and and Schaap, Schaap, B.D., B.D., 1991, 1991,Bouguer Gravity Anomaly Chandler, V.W., Minnesota Minnesota Geological GeologicalSurvey, Survey,State StateMap Map Series Series Map Map S-16, S-16, 1:500,000. 1:500,000. 14 �STRATIGRAPHY, TECTONICS TECTONICS AND AND MINERALIZATION MINERALIZATION OF OF THE THE SIOUX LOOKOUT STRATIGRAPHY, OROGENIC BELT, BELT, WESTERI WESTERNWABIGOON WABIGOON SOBPROVINCE SUBPROVINCE Devaney, J.R., Ontario Ontario Geological Geological Survey, Lake Rd., Rd., Devaney, Survey, 933 933 Ramsey Ramsey Lake Sudbury, P3E 6B5, Canada Canada Sudbury, Ontario Ontario P3E Tectono-stratigraphic analysis of of the metamorphosed and variably Tectono-stratigraphic analysis deformed Archean Archean supracrustal supracrustal rocks rocks of of the the Sioux Lookout deformed Lookout Belt Belt (western Wabigoon Subprovince) Subprovince) suggests suggests the accumulation accumulation of (western Wabigoon of lower, lower, older, subaqueous basalt 2), 1, 2 ) , capped by by older, subaqueous basalt successions successions (Stages (Stages 1, sequences of more felsic volcaniclastic rocks (Stages 4), with sequences volcaniclastic rocks (Stages 3, 4), minor lavas lavas and and porphyries porphyries (at or small volcanic volcanic centres), centres), or near small overlain by by upper sedimentary rocks rocks (Stage 4), such as turbidite (Stage 4), deposits, by synchronous synchronous intermediate-felsic intermediate-felsic deposits, which which were were influenced influenced by volcanism (interbedded tuffs, volcanic pebble conglomerate, volcanism (interbedded tuffs, volcanic pebble conglomerate, magnetite iron formation). Minor magnetite iron formation). Minor volcanogenic sulphide volcanogenic sulphide mineralization sub-exhalite hydrothermal alteration are mineralization and and sub-exhalite hydrothermal alteration are rocks. A A relatively small small (3 km tan uncommon in the the volcaniclastic volcaniclastic rocks. thick) andesitic stratovolcano stratovolcano succession succession and thick) andesitic and its its comagmatic comagmatic subvolcanic subvolcanic intrusion intrusion (Stage (Stage 3, but undated) undated) are are well well preserved, preserved, but no no epithermal epithermal mineralization and only insignificant insignificant amounts mineralization and amounts of of porphyry copper-type copper-typemineralization mineralization have have been been found. foundNorthwest-southeast compression compression segmented the original original basin basin Northwest-southeast (arc on basalt, basalt:, buriedand andflanked flankedby byyounger younger volcanic volcanic (arc volcanics volcanics on buried detritus) thrust slices slices that detritus)into intoan animbricate imbricate stack stack of of numerous numerous thrust that generally 5, a a forelandforelandgenerally dip and young young to to the the southeast southeast (Stage (Stage 5, vergent fold-and-thrust fold-and- thrust belt). Fluvial polymict polymict conglomerates vergent belt). Pluvial conglomerates accumulated narrow, linear linear (strike-parallel), intra-orogenic accumulated in in a a narrow, (strike-parallel), intra-orogenic "molasse" basin basin and and were were overthrust overthrust by by oldervolcanic older volcanic rocks rocks forming forming nmolasse" the bases of thrust slices (relative ages confirmed by published Uthe bases thrust slices (relative ages confinned published UPb zircon dates). A large volume of basaltic strata zircon dates). large volume of basaltic strata (Northern (Northern Volcanic Belt) Volcanic Belt) was overturned overturned adjacent to to the the microcontinental microcontinental Winnipeg River River Subprovince Subprovince foreland; the overturning overturning was was likely likely Laramideproduced by by large-scale large-scalefaulting faulting (hypotheses (hypotheses include: include: aa Laramidetype uplift, uplift, or flower flower structures structures in cross-sectional cross-sectional views of of strike-slip to major faults strike-slip to oblique-slip oblique-slipfaults). faults). The The major faults appear appear to to be be sinistral strike-slip some of which strike-slip faults faults (Stage (Stage 6), which may may be be 6), reactivated thrust reactivated thrust faults faults (i.e., (i.e., Stage Stage 66 superimposed superimposed on on Stage Stage 5). 5). along some some of of these these major major faults. Late Granitoid plutons intruded along stage sinistral-sense a pullpullsinistral-sense motions motions produced produced features features such such as a apart Patara Fin.), Fm.), releasing releasing bend bend plutons, plutons, and apart basin basin (20 (20kin-long km-long Patara Quartz veins appear tension gashes. gashes. Quartz appear to be be thicker thicker and more more abundant, and contain near the major major deformation deformation zones zones abundant, contain more gold, near (thrust and/or and/or strike-slip faults). faults). At At a (thrust a regional regional scale, scale, gold gold occurrences appear to to be be located located along along lineaxuents lineaments which occurrences appear which resemble Riedel shear Riedel shear fracture fracture systems. systems. 15 �This left blank This page page left blank intentionally. intentionally. 16 �PRELIMINARY INVESTIGATIONS OF THE PICK LAKE DEPOSIT, WINSTON REMOBILIZEDMASSIVE MASSIVESULPHIDE SULPHIDEOREBODY OREBODY LAKE MINE, ONTARIO: ONTARIO: AAREMOBJLIZEI) LAKE DOIRON, Gerard, and SIDDIQUI, Masood, Imnet Inmet Mining Corporation, Winston Lake ON, POT POT 2SO; C., Resident Resident Division, P.O. Bag Bag 2, Schreiber, Schreiber, ON, Division, 2S0; and SMYK, Mark C., Geologist Northwest, Ontario Ontario Geological Geological Survey, Ministry of Northern Northern GeologistProgram Program- Northwest, Ministry of Development 435 S. James St., Thunder Bay, ON, Development and Mines, Suite Suite B002, B002,435 ON, P7E 6S7. P7E 6S7. - The The Winston Winston Lake Lake mine mine is is situated situated in in lower lower amphibolite-facies, amphibolite-facies,cale-alkalic calc-alkalicrocks rocksof ofthe the Neoarchean Schreiber-F{emlo greenstonebelt. belt. It comprises Schreiber-Hemlo greenstone comprises several volcanogenic volcanogenic massive massive suiphide sulphide (VMS), (VMS), zinc-copper zinc-copper deposits: deposits: Deposit Deposit Ore Ore (all (all categories) categories) (million (million tonnes) tomes) Winston Winston Lake Lake Zn Zn (%) (%) Metal Metal Grades Grades Cu Cu(%) (%) Ag Ag (g/t) (gft) Dilution4 Dilution* Au Au (gft) (glt) (%I (%) 3.1 3.1 15.90 15.90 1.00 1.00 30.3 30.3 1.02 1.02 20 20 Upper+Middle Upper + Middle 0.26 0.26 11.21 11.21 0.77 0.77 31.5 31.5 0.65 0.65 30 30 Lower Lower 1.2 1.2 15.90 15.90 0.86 0.86 38.0 38.0 0.46 0.46 25 25 Pick Pick Lake: Lake: (4 (* n.b. n.b. Possible Possible category category of of Pick Pick Lake Lake is is non-diluted) nondiluted) The The Pick Pick Lake Lake deposits deposits occur occur within within strongly strongly foliated, foliated,felsic felsicto to intermediate intermediatevolcaniclastic volcaniclasticrocks, rocks, approximately southwestof ofthe theWinston Winston Lake Lake deposit, deposit, and and 1 I km 1.31cm km southwest km lower lower in in the thefootwall footwall approximately 1.3 stratigraphic stratigraphic succession. succession. The Thedeposits deposits are are thin, thin, but but continuous, continuous, massive massive suiphide sulphide sheets sheetswith with aa down-plunge down-plungelength length of approximately 1000 1000 m. The TheUpper Upperand andLower Lower zones zones average average approximitely approximately2.0 2.0 and and 4.0 4.0 m m in thickness, respectively. Massive Massivesuiphide sulphide ore, ore, in in sharp sharp contact contact with to 400 400 m. m. ItIt forms formsaa dyke-like dyke-like with its its host host rocks, has a strike strike length which varies from 100 m to body body which which locally locallycrosscuts crosscutsboth bothfoliation foliationand andgranitic graniticdykes. dykes. Despite metal grades grades and and mineralogy mineralogy (sphalerite, (sphalerite, pyrrhotite, pyrrhotite, pyrite, pyrite,chalcopyrite), chalcopyrite), Despite similar similarmetal suiphide are markedly markedly different different. Finersulphidetextures textures in in the the Winston Lake and Pick Lake deposits are Finergrainecl ubiquitous development grained Pick Lake ore is characterized by the ubiquitous developmentof of durchbewegung durchbewegungtexture, texture, in the massive massive sulphide. Xenoliths, inwhich which brecciated wall-rock xenoliths comprise 10 to 15 % of the Xenoliths, generally ranging in size from <1 mm to 10 cm, are typically: (1) sub-rounded grains of quartz typically: (1) quartz±Â generally ranging in size from 4 rnm feldspar, chlorite, amphibole; feldspar, sericite; sericite;(2) (2) tabular tabular crystals crystals or aggregates aggregates of of biotite biotite ±Â±chlorite amphibole; or or(3) (3) subsubrounded rounded granitic granitic dyke dyke fragments. They Theymay may be be kinked, kinked, folded folded and/or andlor aligned aligned parallel parallel to to one one another and with suiphide banding. Large (>lm) ratted host rock xenoliths are also apparent. another sulphide banding. (>lm) rafted host rock xenoliths are also apparent. 17 �Piercement cusps and and injection injection structures are developed where massive sulphide sulphide has migrated migrated Piercement cusps into folded folded and and boudinaged boudiiaged host host rocks. The nature nature and and scope scopeof of these secondary textures at Pick Lake are characteristic of large-scale large-scale The characteristic of sulphide replacementand andannealing. annealing. The flowage sulphide remobilization, subsequent replacement flowage of massive sulphide, arising arising from from substantial substantial competency contrasts between competent silicate silicate xenoliths xenoliths and and incompetent incompetentsulphides sulphides during during deformation (Marshall and Gilligan 1989), 1989), has resulted resulted in in widespread widespread durchbewegt durchbewegt ore. The Thehigh high degree degree of of remobilization remobiiization at Pick Pick Lake Lake may may be be the the result result of Lake granite granite (averaging (averaging40 40 m) m) and and the the development development of of of the deposit's deposit's proximity proximity to the Winston Lake high fluids in in the the contact contact aureole. aureole. Crosscutting high strain strainzones zones and and hydrothermal flmds Crosscutting relationships relationships demonstrate suiphide deposition depositionpostdated postdatedthe theintrusion intrusion of of granitic demonstratethat that remobilized r e m o b i l i i sulphide granitic dykes, dykes, perhaps presumedprimary primaryVMS VMSdeposition deposition(ca. (ca. 2720 2720 Ma). Ma). The 35 million million years after the presumed The perhaps 35 location, suiphide deposit(s), from which location, size size and and characteristics characteristics of the primary sulphide which the the enigmatic enigmatic Pick Lake ore was derived, are as yet unknown. Pick Lake ore was derived, are as References: References: Marshall, piercement cusps Marshall, B. B. and and Gilligan, Gillipn, L.B. L.B. 1989. 1989. Durchbewegung structure, piercement cusps and and piercement suiphide deposits: Formation and interpretation. piercement veins veins in massive sulphide interpretation. Economic 11-2319. EconomicGeology, Geology,v.84, v.84, p.23 p.2311-23 19. 18 �THE HURONIAN IN THE SUDEURY-CRERAR AREA: REVISITING THE THE DISAPPEAffANCE DISAPPEARANCEOF THE SUDBURY-CRERAR AREA: THE GEOCHEMISTRY GEOCHEMISTRY OF AMPHIROLITES AMPHIBOLITES AND AND PARAGNEISSES INSIGHT FROM THE EASTON, RM., Rise!.,Precambrian PrecambrianGeoscience GeoscienceSection, Section,Ontario Ontario Geological Geological Survey, Survey, 933 933 Ramsey Lake Road, Road, Sudbury, Sudbury.Ontario Ontario P3E P3E 6B5, 6B5,eastonm@ndm.gov.on.ca and andLIMES, JAMES,R.S., R.S., Department Departmentof of Geology, Geology, Laurentian LakeRoad, Road,Sudbury, Sudbuiy, Ontario Ontario P3E 2C6 LaurentianUniversity, University, Ramsey Lake The Huronian Supergroup The presence presence of of high high grade grade metamorphic equivalents of Huronian Supergroup(Sgp.) (Sgp.) and and Nipissing Nipissing Suite Suite (GFTZ) in in Ontario has been long debated. A 5 km krn wide wide zone zone south south rocks in the Grenville Grenville Front Tectonic Zone (GFTZ) the Grenville Grenville Front in the Sudbury-Conision-Crerar of die Sudbury-Coniston-Orerar area provides provides an an opportunity opportunity to to test testthis thissuggestion suggestion geochemically. variety of of amphibolites, amphibolites, quartettes quartzites and muscovite±kyanite-bearin muscovite±kyanite-bearing In addition addition to containing a variety geochemically.In metapelites, the area and covered covered by by aa database database of of some some 155 metapelites, area is well mapped and 155 chemical analyses, including 80 major element element analyses analysesby by Kwak (1967), (1967). Pearson (1959) (1959) and and LaTour LaTour(1979), (1979). as aswell wellas as75 75newly newlyacquired acquired major and unpublished). RoughIy Roughly 80 (Easton,unpublished). 80 of these these analyses analyses are are of of amphibolites, amphibolites, and trace trace element element analyses analyses (Easton, with with another another60 60representing representingparagneisses. paragneisses. Amphibolites: Two types are are recognized recognized in in the the field: migrnadtic rnigmatiticamphibolites, amphibolites, typically typically Amphibolites: Twomain mainamphibolite ainphibolitetypes garnet-bearing, and diabasic textured, textured, typically typically clinopyroxene-b&ng, clinopyroxene-bearing, amphibolites. gamet-bearing, and non-miginatitic, non-mipatitic, locally diabasic Geochemic ally, all all datasets datasetsshow show33similar similargroups groupsof ofamphibolites amphibolites (Rg. (Fig. la); Ia); from most to to least least abundant, abundant, Geochemically, these are: (1) tholeiite group group corresponding corresponding to the migmatitic amphibolites. (2) a (1)aa tightly clustered high-Fe tholeiite magnesium-rich group with with Mg#70-78, Mg#70-78,Mg0=7.7-13.1%. MgO=7.7-13.l%, and Ca0=10.8-14.5%. CaO=l0.8-14.5%. Pods Podsof of orthopyroxene orthopyroxene homblendites in homblendites in the the area area may be related to this group, and (3) a high-Mg tl]oleiite tholeiite group, with Mg#=54-59, Mg#=54-59, MgO=7-9%, Both groups groups 22 and 3 show relict relict differentiation differentiationtrends trends within within individual individual Mg0=7-9%. and CaO=9.6-1ft5%. Ca03.6-10.5%.Both bodies (Fig. (Pig. Ia). la).In In the thefield, field.group goup 33 corresponds corresponds to diabasic-textured diabasic-texturedrocks rocks previously previouslyinterpreted interpretedas as Nipissing diabase; and chemically, itit lies lies in in die theHeld fieldof ofNipissing Nipissing diabase diabase chill chill margins. margins. In In die the field, group group 22 amphibolites locally show diabasic textures, but more typically are black; thinly layered rocks, with associated amphibolites locally show but more typically are black, thinly layered rocks,with gabbroic anorthosite. Chemically, group 2 corresponds corresponds to gabbrowrite gahbronorite cumulate cumulate rocks gabbroic rocks of of the the Nipissing Nipissingsuite. Group chemical similarities similarities with plutons of the Huronian Huronian magmafic magnialic suite suite Group 2 or or 3 amphibolites amphibolitesshow no clear chemical group 22 and 3 amphibolites amphibolites are (e.g. River River Valley Valley anorthosite). Consequently, group are interpreted interpreted as as equivalents equivalents of of the the 2.2 Ga Nipissing suite. Group I amphibolites plot in the field of Archean and Huronian metavolcanic rocks. Nipissing 1 amphibolites the field of Archean and Huronian metavolcanic rocks. In suiterocks rockswith withMg#=54-59 Mg#=54-59predominate, predominate,whereas, whereas,in inthe theGFIZ, GFrZ, to the Southern Southern Province, Nipissing suite interlayered gabbroic gabbmic anorthosite. anorthosite. One Oneexplanation explanationisis that that those with high Mg# (>70) (>70) are most common, as is interlayered the GFTZ, we see the mid-crustal magma chambers chambers of the Nipissing suite, postulated by various in die mid-cmstal "auxiliary" magma anorthositic cumulate cumulate rocks. so,this this leads leadsto tospeculation speculation workers, which would be dominated by mafic and anorthositic rocks. IfIf so, migmatization of the country countiy rocks may may be be related related to to wall wall rock-magma rock-magma chamber interaction. It is still that migmatizatiou unclear if these these magma magma chambers chambers are are hosted in Archean or or Paleoproterozoic Palwproterozoicrocks. rocks. Paragneisses: Kyanite-bearing chemical groups groups (Fig. (Fig. lb). ib). Most are intennediate are intermediate Paragneisses: Kyanite-bearing gneisses gneisses fall into two chemical composition micaceous micaceous gneisses gneisseswith withSi0~57-64%. SiO=57-64%,&03=19.9-26.855, AIO,=19.9-26.8%, Ti02=I.2-1.8%, Fe103t=4.5-8% Ti02=1.2-1.8%. P%03'=4.5-8% and and CIA=73-83. rocksare aremost mostlikely likelyof ofsedimentary sedimentaryderivation. derivation.Gamet-biotite Garnetbiotite gneisses CIA=73-83. Chemically, these rocks spatially associated contents (13spatially associatedwith withthe thekyanite kyanitegneisses gneisseshave havesimilar similarchemistry, chemistry,apart apart11Dm fromlower lowerA12O3 A@, contents contents (Fig. (Fig. lb). lb). The second second group group of of kyanite kyanitegneisses gneisses isis characterized characterizedby by 18%) and higher MgO and CaO contents high FfriO,' Fe103' contents (10-1255). (10-12%), varied varied Al,O, Al203content content(12-30%), (12-30%),and and high high CT, Cr, Ni, Ni, V V and and Ti Ti contents. contents. The The origin unclear, although although derivation derivation from from altered altered metavolcanic metavolcanic rocks is possible on on origin of these these kyathte kyanite gneisses is unclear, the trace and and REE REE abundances. abundances. the basis basis of of field fieldrelationships relationshipsand and trace garnet-biotite gneisses gneisses have havetrace traceelement element signatures signatures similar similar to to those those of of intercalated intemalated garnet garnet Many of the gamet-biotite intermediatetotofelsic felsicvolcanic volcanicrocks rocksor orvolcaniclastic volcaniclasticsediments. sediments.Some Someof of amphibolites, and could represent intermediate the garnet-biotite gamet-biotite gneisses have pronounced pronouncedpositive positiveCe Ceanomalies anomalies(Hg. (Fig. lc), lc), suggesting exposure to an oxidizing environment. weathering profiles, profiles, and and itit isispossible possiblesome someof ofthe the oxidizing environment. Similar Similar anomalies are common in weathering garnet-biotite gneisses represent a weathering profile developed on older metavolcanic rocks. No rare earth gamet-biotite gneisses represent developed older metavolcanic rocks. NOrare earth element element studies studieshave havebeen been conducted conducted on on any Huronian weathering weathering profiles, profiles, so soitit isisunknown unknownififHumnian Huronian 19 �regoliths possess similar similar cerium anomalies. Both the lcyanite and garnet-biotite garnet-biotite gneisses gneisses are associated with quartzose quart-zosegneisses gneisses(SiOy>74%), (Si02>74%), kyanite and quartzites, which locally show relict transposed bedding, and rare conglomerate conglomeratehorizons. Typically, Typically,quartzites quartzites have higher FGO," Fe203tand andTi02 Ti02contents contentsthan thando doany anyof ofthe theHuronian Huronianquartzitic quariziticor orconglomeratic conglomeraticunits units(Fig. (Fig. Ib), Ib), derivation of the metasedimentary metasedimentaiy gneisses gneisses from however, derivation from volcanic-derived volcanicderived sediments sediments such such as as those thosein inthe the Mm. and Stobie gneiss and associated quartzite quartzite Elsie Mtn. Stobie formations formations is not precluded. In In one one instance, instance, aa Icyanite kyanite gneiss present in in the the Pecors Pecors and McKim McKim formations (Fig. (Fig. Id). show REE patterns similar to those present Based on field relationships and geochemistry, it is most likely likely that that the the paragneisses paragneisses and and associated associated garnet theSudbury-Crerar Sudbury-Crerararea areaare arederived derivedfrom fromboth both an an Archean Archean metasedimentaiymetasedimentaryamphibolites in in the the GFTZ 0HZ ininthe succession and high grade grade equivalents equivalents of of the the Paleoproterozoic Paleopmtemzoic Elliot Elliot Lake Lake Group. Group. metavolcanic succession Feo* + TiC2 a) a 0 high-Mg# hioh-Mgf ençhibolites mnphlbolites u a modorate-Mg# moderate-Mflffaniphiboiftes amphibdtes • Nipissirq Nipissingdiabase dabase  o garnet 0 garnetampfllbolites amphbolites xx Opx-homblendites Opx-homblend'rtes 20  Slobb. E M Mtn.. CoppÈrO Fma. 0 0 A1203 A1203 (wt %) MgO 1000 1000 c) GARNET-BIOTITE GNE!S5€S 100 100 10 10 I .1 1 La Ce Pr Nd Sm Eu Gd Tb Dy Ho Er Tm Yb Lu La Ce Pr Nd Sni Eu Gd Tb Dy Ho Er Tm Yb Lu Figure 1: and paragneisses paragneisses from from the the Sudbury-Crerar Sudbury-Crerar area. area. 1: Geochemical Geochemical characteristics characteristics of of amphibolites and Data Kwa/c(1967). (1967),Pearson Pearson (1959). (1959), LaTour LaTour (1979) (1979)and and Easton Easton (unpublished). (unpublished). A) Jensen Jensen plot Data from Kwak showing three main groups of amphibolites. amphibolites.Arrows Arrowsindicate indicatedifferentl&ion differentiationtrends trendsin inindividual individualbodies. bodies. B B)) showing Plot of total iron forStreet StreetTwp. Twp.paragneisses paragneissesand and1owerHuronian lower HuronianSgp. Sgp.units. units. C) C) Chondrite Chondrite iron versus versus A1203 A120,for normalized REEplot REE plot of gt-bi gt-bi gneissesfrom gneisses from Street SweetTwp. Twp.showing showing+ve +vecerium ceriumanomalies. anomalies. D) Chondrite Chondrite normalized REE REE plot plot of of Huronian tiuronian Sgp. units and metasedimentary metasedimentary rocks south of the the Grenville Grenville Front. Front. 20 �Space-lime patterns of Space-time patterns of Early Early Proterozoic Proterozoic post-Penokean post-Penokean (1800-1600 (1800-1600 Ma) metamorphism metamorphism and cooling iin Superior region n the southern Lake Superior DX. and Holm, D.K. andHenderson, Henderson, D.H., D.H., Dept. of Geology, Kent State State University, Kent, OH OH 44242 Introduction. The Precambrian terrane of of the southern Precambrian terrane southern Lake Superior region has has experienced experienced a protracted Proterozoic Proterozoic history history from accretion/colllsion accretion/collisionduring during the the Early Early Proterozoic ProterozoicPenokean Penokean orogeny omgeny to to rifling at 1100 Ma. Ma. Recognition Recognitionand and characterization characterization of of post-orogenic post-orogenic metamorphism, metamorphism, aborted cratonic rifting cooling, and thermal resetting is essential for understanding the evolution evolution from active active accretion/collision accretionlcollision et al., al., 1984, Geology). Geology). In to development of a stable craton (Rogers et In this thisregard, regard,considerable considerableadvances advances the excellent excellent overview overview of of Precambrian Precambrian metamorphism metamorphism by by Geiger Geigerand andGuldotti Guidotti have been made since since the Wisconsin v.v. 13). 13). We summarize differences in In the nature and extent summarize here important differences (1989, Geoscience Wisconsin Early Proterozoic post-Penokean thermal histories between olfferent different portions mst-Penokean (1800-1600 Ma) lhermal mrttons of the the of Eariy exposed exposed orogenic orogenic belt belt (I.e. (i.e. central Minnesota, Mhesota, northern northern Wisconsin, and and northern northern Michigan) Michigan) and and speculate speculate that some that some of of these thesedifferences differences may may reflect reflect Initial initial differences differencesIn in the the metamorphic metamorphicgrade grade(namely (namely.pressure) pressure) . attained attained during during the the Penokean Penokean Otugeny. Orogeny. - Central Minnesota. fades In increasesfrom from subgreenschist submeenschist fades in Central Minnesota.Penokean-age Penokean-aeemetamorphism metamomhismin inMinnesota Minnesotaincreases the north to ainphibolite near the amphibolite facies in the south southnear the first first appearance appearance of Penokean-age ~enokean^ageplutonic rocks (Morey, 1978, 78-10). New 1978, GSC Paper 78-10). New thermochronologic thcrmochronologic and thermobarometric thcrmobaromecric data from rocks of the internal zone of the the Penokean Penokean orogen in central central Minnesota ~innesotaindicate indicatethat that the the Early EarlyProterozoic Proterozoicsediments sediments initially during the Penokean Penokean Orogeny Orogeny (1870-1820 (1870-1820 Ma) Ma) and and again again during during an an were metamorphosed twice - initially at 1770-1760 Ma (Holm (Iloim and Lux, Darrah et et a!., al., episode of post-orogenic magmatism magmatism at Lux, 1996, 1996,Geology; Geology;Darrah 1996, ILSG). ILSG). Thermobarometric a]., 1981, 1981, GSAA; GSAA; Holm Holm and and Selverstone, Selverstone, 1990, 1990, Thermobarometric results (Labotka et al., kbar paleopressures pa!eopressures for both metamorphic Darrah et etal., al., 1996) 1996)indicate indicate—6 -6 kbar metamorphic events events suggesting suggesting Geology; Dauah little crustal uplift during during the theintervening interveningperiod. period. The The 66 kbar bar pressure pressureestimates estimatesfor for the the 1770-1760 1770-1760 Ma staurolite grade nildcrustal (13-15 km) emplacement emplacement depths of the the poststaurolite grade metamorphism in Minnesota, the midcrustal plutons, and the complete lack of of any Penokean-age hornblende AdAr Ar/Ar dates dates from from the the area area tectonic plutons, complete. lack Penokean-age hornblende (Darrah et al., 1996) 1996) argues against a simply contact contact related metamorphism metamorphism adjacent adjacent to mid-or mid-or shallow shallow crustal plutons. Instead, In tee the thickest portion portion of of the the orogenic orogenle crustal Instead, increased increased heat-flux heat-flux at the base of the crust in belt (the Internal zone) was was responsible responsible for for both both partial partial melting melting of of the lower crust and belt internal zone) and regional regional to staurolite staurolite grade gradeof ofthe themiddle middlecrust crust. The midcrustal mldcrustal rocks underwent underwent rapid rapid exhumation exhumation metamorphism to shortly after intrusion and metamorphism and may have even been exposed exposed before before 1700-1650 1700-1650Ma Ma (based (based on the the probable probable age age of the the Sioux Sioux Quartzite Quartzite in southwest southwest Minnesota, Chandler Chandler and and Morey, Morey, 1992, 1992, USGS USGS Bulletin 1904-N). 1904-N). The The1770-1760 1770-1760Ma Ma metamorphism, metamorphism,intrusion, intrusion, and and rapid rapid exhumation exhumationof ofthe theinternal internal zone of the Penokean orogen probably represents orogenic collapse and was the last major 'event' to have affected this region aside from the final formation of the McGrath gneiss dome dome around around 1700 1700Ma Ma (HoIm (Holm and Lux, 1996). 1996). Northern Early NorthernWisconsin Wisconsinand andnorthern northernMichigan. Michigan.Uniform Uniform EarlyProterozoic Proterozoicmetamorphic metamorphicpressures pressures from the internal in central Minnesota are greater than the typical 2-4 kbar paleopressure estimates for internal zone in throughoutmost most of of Wisconsin (Geiger (Geiger and Guldotti, Penokean metamorphism metamorphism throughout Guidotti, 1989). 1989). In contrast contrast metamorphic üodal patterns patterns in northern metamorphic nodal northern Michigan Michigan are are superposed superposed on onlow-grade low-grade greenschist greenschist metamorphism. metamorphism. The The origin origin of of the the prominent prominent nodal nodal metamorphic metamorphic patterns has been one one of of the the most most Interesting questions questions in in geologic geologicresearch researchofofthe thearea. area. Pressure differences among the nodes (4 kb at interesting Peavy, 2 kb at at Republic and 7 kb at Watersmeet) probably reflect initial differences differences in in crustal crustal thickness Orogeny (Attoh (Attoh and Klasner, 1989, Tectonics) TectonIcs) although for at least the attained during the Penokean Omgeny Watersmeet area, the uplift uplift and and doming doming of of the theisograds isogradsoccurred occurredsignificantly significantlylater later(at (at—1755 -1755 Ma; et al., aL, 1996, 1996,CJES). dES). Emilio Emilioetetal. al.(1996, (1996,Eos) Eos)have haverecently recentlysuggested suggestedthat thatthe themapped mapped nodal nodal Schneider et pattern at Peavy pattern Peavy isis actually actually aasimplification simplification of ofaamore morecomplex complexpolyphase polyphasemetamorphic metamorphichistory history characterized by possibly three three discrete metamorphic events. characterized The extent Mametamorphism metamorphism within withinthe the Penokean Penokean orogen in Wisconsin is just extent and and nature nature of of —1760 -1760 Ma unraveled. Van VanWyclc Wyck (1995, (1995, UW-Madison UW-Madison Ph.D.) Ph.D.) illustrated aa thermal thermal disturbance disturbance beginning to be unraveled. adjacent to Mapluton plutoninincentral centralWisconsin Wisconsin and and Romano Romano et et al. a]. (1997, (1997, GSAA) obtained obtained evidence to an an —1760 -1760 Ma evidence adjacent for partial thermal resetting interpreted to to be be related related to to -1760 -1760 Ma magmatism magmatism in in west-central west-central Wisconsin. 21 �However, these disturbances disturbances appear to be aa more more localized contact-related phenomenon phenomenonbecause becauseseveral several localities in Wisconsin (and upper datesthat that reflect reflect cooling from upper Michigan) Michigan) yield hornblende Ax/Ax ArIAr dates Schneider et et al., al,, 1996; Romano Romano et al., al., 1997; (i.e., 1800-1850 1800-1850 Ma; Sdmeider 1997; Mancuso Penokean-age metamorphism (i.e., with the the -1760 -1760 Ma granites In et al., al., 1997, 1997, ILSG). ILSG). This Thisinterpretation interpretation is also consistent consistent with in northwest northwest Wisconsin depths than similar Wisconsin having having been been emplaced emplacedatatsomewhat somewhatshallower shallower(9-11 (9-111cm) km) depths similar age agegranites granitesInin Minnesota (Anderson central Minnesota (Andersonet et al., al., 1980, 1980,CMP). The timing timing of unroofing unroofing of the the post-tectonic post-tectonic granites in northern Wisconsin is poorly poorly constrained constrainedbut but probably occurred fairly shortly after intrusion. In In northwest northwest Wisconsin, Wisconsin, an an area area little littleaffected affected by by later later reheating and deformational biotite cooling cooling dates dates (both (both RbISr Rb/Sr and ArIAr) Ar/Ar) are 1700-1730 defonnational events, biotite 1700-1730 Ma Ma (Peterman see spectrum spectrumbelow). below). Also, the 1760 (Petennan and Sims, 1988, Tectonics; see 1760 Ma Radisson Radisson granite granite in this area is Is overlain by the which, if If correlatable the Sioux Sioux Quartzlte Quartzite the undeforined undefonned Barron Quartzlte Quartzite which, cordatable with the (Chandler (Chandler and and Morey, Morey, 1992) 1992)might might indicate indicate exposure exposure by about about 1700 1700Ma. Ma. Precambrian rocks in Wisconsin Michigan were were also affected by younger Precambrian rocks Wisconsin and northern northern Michigan younger Early Early Pmterozoic at -1720 -1720 Ma Tlieseinclude includepossible possible contact contact metamorphism metamorphism at Ma In Innorthern northern Michigan Michigan Proterozoic events. These al., 1996). 1996), a cryptic cryptIc 1720 Ma node (Schneider (Schneideret a al., which may have created the Republic metamorphic metamorphic node metamorphic event in In Wisconsin (Van Wyck, Wyck, 1995) 1995) and and the the w widespread but little little understood 1630 Ma idespread but low-grade event which affected reeks rocks thmughout throughout much of Wisconsin and perhaps portions of of northern northern Michigan. Michigan. The Theabsence absenceof ofthese theseyounger younger overprinting overprinting events in in areas areas such suchasascentral centralMinnesota, Minnesota, northwest Wisconsin and portions of northern Michigan (i.e., (i.e., Watersmeet) Watersmeet) allow allow us us to learn learn much about the earliest and extremely metamorphic4ilutonic event event at at 1770-1760 1770-1760 Ma. extremely important important post-Penokean metaIII~rphidplIIt~ni~ Implications. Implications.Based Basedon onthe theabove aboveoverview, overview,ititappears appearsthat thatthe thenature natureand andextent extent of of post-Penokean post-Penokean Early Early Proterozoic metamorphism and cooling is distinctly different within different parts parts of of the theorogenic orogenicbelt. belt. areas where where the the We note that the the 1770-1760 1770-1760Ma post-tectonic post-tectonic plutons have deeper emplacement depths in areas paleopressure estimates are greater (i.e., (i.e., central Minnesota compared to northern Penokean paleopressure northern Wisconsin). Wisconsin). This suggests that little Ma but that little unroofing unroofing of of the the Penokean Penokean orogenic orogenic belt occurred prior prior to to —1770 -1770 Ma (and variable) variable) amounts amountsof of unroofing unroofingoccurred occurredrapidly rapidlythereafter thereafter(-10 (-10 tan km of of unroofing unroofing in In significant (and northern Wisconsin same time 1760 Ma and 1700 Ma but 15-20 km during the same time span span for for central central Wisconsin between 1760 Minnesota). We that the thedifferences differences may reflect initial differences iInn the amount amount of of crustal crustal Minnesota). Wespeculate speculatethat orogen. Post-orogenic metamorphism thickening attained across the Early Proterozoic orogen. metamorphism appears to have have grade) perhaps perhaps because because crustal thickening been more pervasive pervasive in central central Minnesota (reaching staurolite grade) thanin in the the island island arc arc terrane terrene of Wisconsin Wisconsin (Geiger and and Guidottl, Guidotti, 1989). 1989). was greater greater there there than of the complete Early Proterozoic Proterozoic unroofing unroofinghistory historyof of the the Penokean orogenic oregenic belt Is Knowledge of is critically dependent dependent on the age of the quartzites quaitzites mentioned mentioned above. above, If they they are are indeed indeed Early Early Proterozoic Proterozoicin in paleomagnetic data, thta, by ages of detrital zircons age (as seems to be suggested by palmmagnetic zircons in other other quartzites quartzitesof of the the region, Ma) then these quartzites region, and by the fact fact that that some some were were probably probably deformed at 1630 Ma) quartzites may represent of continental continental crust crust in in the the Lake Lake Superior region region after after a protracted history of represent stabilization of tectonic instability which lasted hundreds of millions of of years years (Greenberg (Greenberg and and Brown, 1983, 1983, J. Geology). the sudden sudden and and rapid rapid collapse collapse of the overthickened overthickened Penokean orogen orogen together together with withthermal thermal It appears appears that the re-equilibration of the lithosphere the Early Early Proterozoic Proterozoic re-equilibration lithosphere was a critical step in crustal stabilization during the etal., (ill). al., 1984; 1984; Nelson, 1991, GJI). (Rogers et 2000, Powell Kyanite Locality AGE' Northwest Wisconsin Ma: 1500- 1000— 0 1 Biotite — . . Tg = 1668±12 Ma Tp = 1696±13 Ma U • U %39Ar % 39 Ar I I U — 100 100 Complete citation of references will be available at at the the presentation presentation and andupon uponrequest request (dholm@kent.edu). (dholm@kent.edu). Complete citation 22 �Ar/Ar dating of dikes dikes in incentral central Minnesota Minnesota and and the the Minnesota River Valley Results of ArIAr D.K., Dept 44242 (dhoIm@kent.edu); HOLM, D.K., Dept.of ofGeology, Geology,Kent Kent State State University, Kent, OH 44242 (dholm@kent.edu); and LUX, D.R., D.R. Department of Geological Sciences, University of Maine, Orono, Orono, ME ME 04469 04469 Ma) magmatic magmatic suites suites of of central Minnesota Late- and and post-tectonic post-tectonic (1820-1770 (1820-1770 Ma) Minnesota are are crosscut crosscut by by mafic dikes east-west. Much of the dikes that that generally generally trend northeast-southwest northeast-southwest totoeast-west the region region affected affected by by the the Penokean orogeny, Minnesota, Wisconsin, Wisconsin, and the upper peninsula orogeny. including including central Minnesota, peninsula of of Michigan, Michigan, isis crosscut CJES; Chandler, Chandler, 1993, 1993,in in USGS USGS Prof. Prof. crosscut by similar similarlate latenortheast-trending northeast-trending mafic dikes (King, 1990, CJES; Paper 1556). 1556). Some Someofofthese thesedikes dikesare arecertainly certainly related related to to 1100 1100Ma Ma mid-continent mid-continentrift riftmagmatism magmatism(Green (Green 34). However, et al, 1987, 1987, In in GAC Spec Spec Paper 34). However, some are also significantly older and appear related to the -1770-1760 Ma mafic dikes dikes that that crosscut crosscut -1770 -1770 Ma InWisconsin. Wisconsin, northeast-oriented northeast-oriented mafic Ma magmatic magmatic suite. In plutons fades at 13W-MadIson Wyck,1995; 1995; UW-MadisonPh.D. Ph-D. plutons were weremetamorphosed metamoqhosedto to amphibolite amphibollte fades at-1720 -1720Ma Ma(Van (VanWyck, thesis). InInaddition, addition,Inincentral centralMinnesota MinnesotaPb PbIsotope isotopedata datafrom fromthe themafic maficdikes dikesare areconsistent consistentwith witha a—1800 -1800 thatthe thedikes dikesmay may have haveintruded intrudedonly onlyshortly shortlyafter afteremplacement emplacementofofthe the—1770-1760 -1770-1760 Ma age age suggesting suggestingthat Ma magmatic suite aL, 1987, 1987.Prec. Prec.Res.). Ret). Mafic Maficdikes dikesof of Early Early Proterozoic Proterozoicage agehave havealso alsobeen been suite (Horan et al.. reported (Hanson and Himmclberc. Hiinmelberg, 1967, rcoorted from from the the Minnesota Minnesota River River Valley Vallcv Manson 1967. GSAB). GSAB1. We (MRV-5A, MRV-3C, MRV-3C, &d and MRV-3) of andesite dated three three whole-rock whole-rock samples sampl&(MR~-5,4, kdesite dikes dikes from from the the We dated Granite AdArIncremental incremental Granite Fails Falls area, area,Minnesota MinnesotaRiver River Valley Valley (Himmelberg, (Himmelberg, 1968, 1968, MGS MGS Pub.) using usingthe theAr/Ar heating technique. No ATloss loss Noplateau plateau dates dates were were obtained. Rather, Rather,all allthree threespectra spectradisplay displaysignificant significantAr profiles and Ma)are aretherefore thereforemeaningless. meaningless. The The oldest increments for the and their total gas dates (1429-1551 Ma) three samples (1567 Ma, K-Armineral mineral Ma, 1685 1685 Ma, and 1723 1723 Ma) Ma) are are somewhat somewhat younger younger than than the theK-Ar (hornblende 1690-1930 Ma obtained on andesite dikes near Granite GraniteFalls Fallsby by Hanson Hanson (hornblende and and biotite) biotite) dates dates of 1690-1930 and Himrnelberg (1967). Because AI loss indicated by the spectra, spectra, the the oldest oldest increments increments we Himmelberg (1967). Because of the Ar minimumdates datesfor forintrusion intrusionofofthe thedikes. dikes. This is consistent consistent with the fact obtained should be considered minimum that at Ma -pluton (granite of section at least least one oneandesite andesitedike dikein inthis this area areaisisintruded intrudedby by an an—1850 -1850 Ma section 28; Goldich Goldich etetaL, al., 1970, 1970,GSAB). GSAB). We dated northeast trending basalt dikes dikes which cross-cut twowhole whole rock samples of noflheast cross-cut 1770 1770 Ma We dated two granites -2-95 and date(MN MN-2-95 andMN-37A), MN-37At. the the granites near near St. St. Cloud. Cloud Although AIthonehneither neithersample samoledisplayed dimlavedaaplateau nlateaudate spectra are total gas dates &bstantially substantially younger younger (1150-1200 &ma are considerably considerably less less disturbed and the btal (1150-1200Ma) ~ athan than ) River Valley. Valley. Feldspar separated from aa quartz-feldspar those obtained from the Minnesota Minnesota River quartz-feldspar porphyry yielded aa distinct distinctsaddle-shaped saddle-shapedspectra spectraindicative indicativeofofexcess excessargon argot In this case the dike in the same area yielded age minimum of 1456 wouldrepresent representaamaximum maximumage agefor forintrusion Intrusionof of the thedike. dike. Our 1456 Ma for this spectra would Ar/Ar whole-rock whole-rock basalt dates from the the St. St Cloud area are significantly younger than the three three whole-rock &/AT basalt K-Ar dates dates of of 1280 1280Ma, Ma, 1460 1460 Ma, and 1570 Ma obtained from this area by Hanson Hanson (1968, (1968, MGS MGS Rept. mv. isotope data Inv. 8). 8). Those Thosedates dateshave havecommonly commonly been interpreted as partially reset dates and the Pb isotope of Horan al. (1987) (1987) seem seem to to support support that interpretation. interpretation. However, However, we we interpret interpretour ourresults results from from the the Horan et et al. mafic dikes dikes (MN-2-95 indicating that that some some of of the northeast-oriented dikes in the St. MN-37A) as indicating St. (MN-2-95 and MN-37A) Cloud area are are Keweenawan in age. We We note note that the the morphology morphology of the the dike dike spectra spectrafrom from the the two two areas areas aredramatically dramatically different and this probably reflects a difference differenceIn in their theirintrusion intrusionages ages (MRV and CM) are post-Intrusion histories. and post-intrusion Our interpretation outside of the Our interpretation that that Keweenawan Keweenawan dikes were intruded outside the main mainrift rifttrough troughIn incentral central given the the evidence evidence for for Keweenawan dike dike swarms in northern Minnesota does not seem unreasonable unreasonable given Michigan (Baraga-Marquette) and in in central central Wisconsin Wisconsin (Green (Green et et al., al., 1987; 1987;KIng, King, 1990). 1990). Indeed, Indeed, (Baraga-Marquette) and position and and similarity similarity of of strike strike that that the the central central Wisconsin Wisconsin dike Chandler (1993) inferred on the basis of position swarm may correlate northeast -striking -strikingdike dikeswarm swarminincentral centraland andsouthwestern southwesternMinnesota. Minnesota. We correlate with the northeast conclude that conclude that there there are areprobably probably two two northeast-oriented dike populations in central central Minnesota: Minnesota: an an older older probably intruded intruded very very shortly shortly after after intrusion intrusion of the 1770 Early Proterozoic population that probably 1770Ma Ma postpostwith Keweenawan Keweenawan rift rift magmatism. tectonic granites granites and and aa younger younger population associated with dike swarms swarmsthroughout throughoutthe theLake LakeSuperior Superior region region may may cause cause at least Intrusion of Keweenawan Keweenawan dike locallzed of the older Early and localized thermal thermal overprinting overprinting and and complications complications of and Middle MiddleProterozoic Proterozoicregional regional thermal patterns. Schneider In Schneideretetal. al.(1996, (1996, CJES) CJES) reported Keweenawan disturbances of Ar/Ar MAT spectra in northern Michigan and Romano Ar/Ar biotite date from Romano et al. (1997, GSAA) obtained a Keweenawan AdAr west-central Wisconsin Wisconsinpossibly possiblyrelated relatedtotodike dikeresetting. resetting.The Thelocus locusof of <1.2 dates 4 2 Ga Ga Rb/Sr RhISr biotite biotite dates mapped in attributed to uplift in northeast northeastWisconsin Wisconsin (the (the Goodman Goodman Swell) has been attributed uplift associated associatedwith withloading loading 23 �__= Keweenawan rift rift trough trough (Peteman (Peterman and and Sims, Sims, 1988, 1988,Tecto~cs). Tectonics). We suggest lhat that Keweenawan along the Kewee~wan Keweenawan dikes and depth, if p pervasive enough, may provide provide an an alternative explanation explanation (see (see and associated associated plutons at depth, a s i v e enough, also also Coaldey Coakley and and Wang, 1992, lW2, Eos). bs). 2000: AGE Ma. %- U 1685 C Whole rock 1 ioooj, 1600 AGE: 1723 • '"' 1500 - 100 K-feldspar K-feldspar = Tg=1638±l2Ma Tg=1638*12 Ma —No -No Plateau Plateau ,m 100 MN-2-95 1000 - 1458 • Whole Whole rock rock Tg=1551±11 Tg=1551H 1 Ma Ma MN-4-95-FSP 0 16O0 Ma: 100 MN-37A - I 100- 1100 Whole rock Tg=1190±9Ma Whole rock Tg=1164±12 Ma Wv 0 0 2000, MRV-3 Whole rock Tg=1429±11 Tg=l&gkll Ma Ma S DUU 10 Ma: 15W MRV-3C 1150. TQ=1496±11 Ma 1000 ISO? = = 1500- AGE 1700• M RV-5A %39Ar - 10oowo %39Ar 100 , n r - swarms in the the Lake Superior Superior region region (after (afterChandler, Chandler,19G3). 1993). CM is central central Minnesota, Dike swarms MRV is is Minnesota Minnesota River Valley, Riled MRV Valley, KK is Kenora-Kabetogama Kenora-Kabetogamadike dikeswarm, swarm,M Mis isMarquette. Marquette. Filled circles are are Keweenawan region of Rb/Sr circles Keweenawan biotite biotite dates and and large large ellipse ellipse encloses encloses region RblSr biotite biotite dates dates (Goodman (Goodman Swell Swell of Peterman Peterman and Sims, 1988). 24 �The Evolution of the Hydrothermal Hydrothermal Systems Systems Associated Associatd with the Sturgeon Lake Caldera CalderaComplex, Complex, Northwestern Ontario George Hudak and Ronald Ronald L. L. Morton Morton George J. Hudak Research Lab, Duluth, Duluth, Duluth, h b , Geology Department, Depaament, University University of of Minnesota Minnesota-- Duluth, Economic Volcanology Research Minnesota, USA USA 55812 55812 The Archean Sturgeon Lake Caldera Complex (SLCC, (SLCC; Morton Mortonet et al., al., 1990) is is located within the Wabigoon volcan~sedimentaq volcano-sedimentarygreenstone greenstonebelt beltappruximately approximately200 200Km Kmnorthwest northwestof of Thunder Thunder Bay, Wabigoon Ontario. The Complex Complex is host host toto66known knownmassive massivesulfide sulfideorebodies orebodiesand andnumerous numeroussubeconomic subeconomic massive dsulfide lenses. Combined, these orebodies orebodies pproduced ore grading gradiig d e lenses. Combined, these r o d u d nearly 18.4 million tons of ore massive 8.5% 'Z Zn, Cu, 0.91% 0.91% Pb, and 3.73 ounces per ton Ag between 8.5% n, 1.06% Cu, W e e n 1971 1971 and 1991. 1991. Based on detailed mapping, core core relo.&g, relogging,petrographic petrographicinvestigations, investigations,and andevaluation evaluationof of whole rock and trace element analyses, the the caldera caldera wmplex complex has has been been divided into three rock element lithogeochemical lithogeochemical analyses, into three distinct volcanic volcanic sequences sequences (Hudak, (Hudak, 1996). 1996). The Pre-Caldera F're-Caldera Sequence Sequence (PCS) (PCS) represents a large, large, dominantly subaerial shield-type basalt volcano with with localized fields fields of of subaerial to shallow shallow subaqueous subaqueous basaltic tuff tuff and and cinder cone deposits 1988). The Early basaltic deposits (Groves (Groves et al., al.. 1988). Early Caldera Caldera Sequence Sequence (ECS) (ECS) represents the the onset onset of of explosive explosivefelsic felsicvolcanism volcanismand andthe thefonnation formationofofthe the major majorcaldera caldera structure. structure. The represents ECS comprises laterally very thick thick (up to 900 ECS laterally extensive extensive (up to 16 16 km km along along strike) strike) and locally locally very 9Cil m) m) mesobreccia and megabreccia deposits interlayered with and overlain by a series of shallow subaqueous mesobreccia and megabrecc~a overlain series of shallow subaqueous (<1000 m deep) quartz-phyric pyroclastic flow deposits deposits (up to 1200 i m thick) which which host host the F-Group and (<lo00 n thick) Mauabi massive sulfide orebodies. orebodies. The the change in volcanic Mattabi The Late Late Caldera Caldera Sequence (LCS) (LCS) represents the dominantly explosive explosive to to passive passiveeruptions. eruptions. The stratigraphic section in the LCS LCS progresses prupsses style from dominantly feldspar-phyric pyroclastic pyroclastic flow deposits deposits (which host the Sturgeon Lake, Lyon Lake, M e , Creek Creek from quartz ± feldspar-phyric orebodies) through through subaqueous andesite andesite and and kdacite Zone and Sub-Creek Zone o~bodies) i t e lava flows and and domes d o m s to to chemical sediments which include iron the formation of thick sequences of volcaniclastic sediments and chemical fonnation. Age rocks (Davis (Davis et et al., aL, 1985), 1985). as well well as as trace trace formation. Age dates datesof ofthe thecaldera-associated caldera-associated volcanic volcanic rocks element suggest that the element evidence evidence (Campbell (Campbell et et a!., al., 1981), 1981), suggest the Beidleman Beidleman Bay Bay Intrusive IntmsiveComplex Complex (trondjhemite to quartz diorite) was the subvolcanic magma chamber for the emptive eruptive material. (trondjhemite The style evolved during during the the development developmentof of the the SLCC. SLCC. Two style of of hydrothermal hydrothermal alteration alteration also evolved Two alteration suites suites have have been been identified: identified: a) a) an assemblage distinct hydrothermal hydrothermal alteration assemblage associated with massive sulfide mineralization mineralization early in the development of the SLCC, SLCC; and b) an assemblage assemblage associated associated with with iron iron formation which which formed formed during during the the later stages of the formation the SLCC. SLCC. Detailed Detailed mapping indicates that that both both alteration localized "pipe-like'' alteration suites suites illustrate semi-confonnable semianformable geometry geometry with with localized geometry near near "pipe-like" geometry synvolcanic fault zones. synvolcanic The massive sulfide associated alteration suite contains the following mineral fol1owing m i n e d assemblages: assemblages: a) aluminum pyrophyllite, sericite); sericite); b) b) aluminum silicate ++ chioritoid 2 pyrophyIlite, aluminum silicate chIoritoid aluminum silicate (andalusite/kyanite (andalusitdkyanite ± (andalusite/kyanite ± Fe-rich chlorite, pyrophyllite, pyrophyllite, sericite); sericite); c) c) sericite 2 ± pyrophyllite; (andalusitekyanite ++ chloritoid chloritoid 2 pyrophyllite; d) d) chioritoid + chlorite/Fe-rich &natq carbonate; e) e) Fe-rich Fe-rich chlorite 2 ± Fe/Mg-carbonate; + Fe-rich chloriteFe-rich Fehlg-carbonate; and 1) f) localized localii chloritoid zones of secondary secondary feldspar feldspar ++ Mg-rich chlorite. The The iron iron formation formation associated alteration alteration suite suite contains contains the the following following mineral assemblages: assemblages: a) a) FeFerich chlorite + magnetite + grunerite; b) chloritoid + chlorite ++ garnet + + Fe-rich carbonate carbonate ±2 pnerite; + Fe-rich chlorite ±2 FeFe+ Fe-carbonate rich carbonate; and c) Fe-chlorite + Fe-carbonate 2 sericite. ± sericite. There appears to be a change change in in the the style style of of alteration alteration in in the the caldera calderacomplex complex from from early, early, high high systems to to later, later, lower temperatum temperature Fe-formation temperature base-metal sulfide producing hydrothermal system Fe-formation * 25 �hydrothermal systems. systems. The change in alteration style appears to be temporally associated with producing hydrothermal pyroclastic to passive volcanism. the change from pyroclastic may be Archean Archean examples examples of "High "High The Cu-Zn Cu-231 orebodies orebcdies associated associated with with the the SLCC SLCC may massive sulfide sulfide deposits deposits as as described described by by Sillitoe Sillitoe (19951, (1995), Sillitoe. Sillitoe et al., aL, (1996), (1996), Sulfidation" volcanogenic massive et al. a!. (1997). (1997). The inpart, p ~ , and Gamo et The massive massive sulfide sulfideassociated associatedalteration alterationassemblages assemblagesmay may have haveformed, formed, in by reactions between originally glass-rich volcaniclastic rocks and pulses pulses of of metal-rich, metal-rich, magmatic magmatic fluids fluids which were were transported transported from from the the top top of of the Beidleman Bay intrusion which Beidleman Bay intrusion to the seafloor seafloor in in synvolcanic synvolcanic Mineralization appears to have structures structures during the early early stages stages of of caldera calderadevelopment. development. Mineralization appears have occurred occurred directly beneath beneath the the seafloor by of the strata. by sulfide sulfide replacement replacement of strata. The iron iron formation formation alteration alteration directly assemblages resulted from metasomatism by hydrothermal fluids composed of evolved assemblages evolved seawater seawaterwhich which occurred at at increasingly lower temperatures temperatures as as the Beidleman Bay intrusion occurred increasingly lower Beideman Bay intrusion continued continued to cool cool and and rnagmatic volatiles were less magmatic less abundant. abundant. References Campbell, I. H., Franklin, J. M., M., Gorton, M. M. P., P., Hart, Hart, T. R R., S.D. ., and Scott, S. D. (1981): (1981): The Therole roleof of subsubvolcanic 2248-2253. volcanic sills sills in in the the generation generation of of massive massivesulfide sulfidedeposits. deposits.Economic EconomicGeology Geology76, 76,2248-2253. Davis, D. W., Krogh, T. E., E., Hinzer, J., 1..and Nakamura, Nakamura, E. E. (1985): (1985): Zircon Zircon dating datingof of polycyclic polycyclicvolcanism volcanism at Sturgeon Lake and implications for base metal metal mineralization. mineralization. Economic Geology 80, 194219421952. 1952. . . Charlou, J.-L., J.-L., Auzende, J.-M., J.-M., Ishibashi, J., Shitashima, Gamo, T., Okamura, K., K.,Chadou, Shitashimq K., K., Chiba, Chiba, H.,and H.,and the the Shipboard Scientific Scientific Party of the MannsRux ManusFlux Cruise (1997): (1997): Acidic and sulfate-rich hydrothermal Shipboard hydrothermal basin, Papua Papua New Guinea. Guinea. Geobgy Geology 25 25(2), fluids from the Manus back-arc basin, (2). 139-142. 139-142. Groves, D. A, A., Morton, R. L., L., and Franklin, J. J. M. M. (1988): (1988): Physical Physical volcanology of of the the footwall m rocks near ks near massive sulfide sulfide deposit, deposit,Sturgeon SturgeonLake, Lake,Ontario. Ontario.Canadian CanadianJJournal of &ah Earth Science Science o u m l of the Mattabi massive 25, 280-291. 25,280-29 I. and hydrothermal hydrothermal alteration alteration associated associated with late caldera Hudak, G. J. (1996): The physical volcanology and volcanic rocks and volcanogenic massive sulfide deposits in volcanic and volcaniclastic volcaniclastic rocks volcanogenic massive in the the Sturgeon Sturgeon Lakee region of northwestern Ontario. Unpublished Ph. D. dissertation, M dissertation, University Universityof of Minnesota, Minnesota, Minneapolis, MN, 463 pages. Minneapolis, L., 0. J., S., and Franklin, I. J. M. (1990): Physical volcanology volcanology and h hydroMorton, R. L .,Hudak, G. 1.. Walker, Walker, 1. I. S., y b thermal alteration of the Sturgeon Lake Caldera Complex. Complex. In In Mineral Deposits of the Western Western Superior Province, Ontario, Geological Suwey Survey of Canada Open Open File File 2164,7494. 2164,74-94. Superior R. H. H. (1995): (1995): The influence of of magmatic magmatic hydrothermal hydrothermal models models on on exploration exploration strategies strategies for for Sillitoe, R. volcano-plutonicarcs: arcs:In In Mamas. Magmas.Fluids. Fluids,and and Ore Ore Deposits Deposits (Thompson, (Thompson,J.J. F. F. H. H. ed), ed),MAC volcano-plutonic Short Course Short Course Volume Volume 23, 23.5511-525. 11-525. .,Hannington, Hannington,M. D., and Thompson, J. F. H. sulfidation deposits deposits in in the Sillitoe., Sillitoe, R. R. H H., H. (1996): (1996): High sulfidation environment. Economic Geobgy Geology 91,204-212. 91, 204-212. volcanogenic massive sulfide environment. 26 �Patterns of structure structure and and metamorphism metamorphismin i nthe the1-lemlo Hemlo greenstone greenstone belt. belt. S.L. Jackson, Ontario Geological Survey, (705 670 jacksos@gov.on.ca) S.L. Jackson, Ontario Geological Survey, (70s5997; mo 5997; ja&so~@gov.~n.ea) Hemlo greenstone belt rocks generally possess possess a welt-developed well-developed (strong) (strong) penetrative planar penetrative planar fabric that is variably defined by combinations of mineral mineral shape foliation, metamorphic metamorphiciayering, layering. In In foliation, shape layering, and compositional compositional layering. map view the traiectories trajectories of this fabric are curvilinear and aenerallv generally strike maD " internal plutons. Within the subparallel to bounding biunding granitoid masses and larger internal stretch, mineral, and crenulation crenulation lineations lineations are plane of the strong fabric, stretch, common. Stretch Stretch and and mineral mineral lineations tend to be subparallel in a given area; crenulation crenulation lineations lineations may may or may not be subparallel to the stretch and and mineral mineral orientation although there is a lineations. lJneations Lineationshave have notable notable variation variation in orientation general granitoid general westward westward component to their plunges. Internal and external granitoid bodies development. Marginal phases of the bodies show show variable variable degrees of fabric development. Pukaskwa fabrics near the the granitePukaskwa and Black Black Pic batholiths exhibit strong fabrics greenstone belt well-developed fabric greenstone belt contact. The Dotted Doned Lake pluton has aa well-developed near its its margin margin that decreases decreases in in intensity intensity toward toward its its interior. interior. In contrast, the Heron appears to be weaklv weakly to to non-foliated. non-foliated. The The Cedar Lake Pluton Pluton Heron Bay Bav Pluton Pluton amears has weak'to weak to moderate developed at its margin and and aa weak weak foliation foliation in its moder&e fabric developei interior. interior. The variable orientation of the strong fabric within the the greenstone greenstone belt folding. At results, in part, from post-fabric folding. At Mussy Mussy Lake Lake the the granite-greenstone granite-greenstone boundary strong fabric are are sub~arallel subparalleland andfolded. folded. A well-develo~ed well-developed boundarv and strona crenulation fabric and iiss axial crenulathn cleavage cleavagi deforms deforms the earlier margin-parallel margin-parallel strong fabricand axial trace. Similarly, the the Heron Bay Pluton is is interpreted interpreted as planar to the fold axial trace. folded greenstone belt. &It. Again, folded along along with with an an earlier-formed earlier-formed strong fabric in the greenstone this this folding folding is is associated associated with a crenulation cleavage in the greenstone belt belt rocks. The TheGowan GowanLake Lake Pluton Pluton roughly roughly follows the contact between the granitegreenstone the pluton pluton greenstone belt belt which which is is concave concave to to the the northeast. northeast. It is unclear unclear if the configuration curved boundary boundary of the configuration resulted resulted from emplacement into an already cuwed greenstone folding. observations Observations by G.P. G.P. Beakhouse Beakhouse greenstone belt, belt, or from subsequent folding. (OGS) of magmatic magmatic flow flow foliations foliations in in the pluton pluton that that parallel parallelthe the granitegranitegreenstone supporl the interpretation interpretation of post-folding post-foldingemplacement. emplacement. greenstone boundary boundary support Metamorphic Metamorphic grade grade increases increases both both from west to east east and and as as one one approaches external and internal granitoid bodies. bodies. In metabasites, metabasites, the the increase approaches in metamorphic metamorphic grade is is reflected reflected by a decrease in in chlorite chlorite content content with with an an increase in hornblende content, content, the the appearance appearance of of garnet garnet andlor and/or cummingtonite cummingtonite increase and, at the highest the appearance appearance of ofclinopyroxene. clinopyroxene. In highest grades, the In metapelites, mineral assemblages progress from from west west to to east east from from garnet-chlorite garnet-chlorite to to staurolite .mineral to garnet-biotite-sillimanite assemblages exhibit a garnet-biotite-sillimanite assemblages. Calcareous assemblages transition from quartz-iron in the the west west to to quartz-calcitequartz-calcitetransition quartz-iron carbonate+/-chlorite in amphibole epidote-garnet+/-clinopyroxene, hornblende hornblende amphibole assemblages assemblages to epidote-garnet÷/-clinopyroxene, assemblages in assemblages in the the east. east. In In general, the the strong strong fabric in in the greenstone belt belt is is defined defined by by peak peak metamorphic deformed by metamor~hicmineral mineral assemblages. assemblaaes. This fabric is deformed bv the the later later crenulation internal plutons and crenulatibn cleavage that is is associated asskated with folding of internaiplutons andthe the boundary. The general westward component component of of plunge to granite-greenstone boundary. ~ 27 2~~ �and increase increase in in metamorphic grade from west west to to east east suggests linear elements and that deeper erosional levels levels of of the the greenstone greenstone belt belt are are exposed exposed in inthe the east. east. At deformation model is envisaged for the greenstone present a general two-stage deformation greenstone well-defined belt. An early, high-temperature, high-strain stage generated the well-defined foliation foliation that that is is parallel parallel to unit contacts and the granite-greenstone granite-greenstone boundary. There appears appears to be a paucity of map-scale folds related related to this deformation; T.L. Muir (OGS) has observed observed folds with strong axial planar fabric near however, T.L. deposit. A the Hemlo gold deposit. A low-temperature, low-temperature, regional, regional, compressive compressive deformation deformation stage followed and resulted resulted in folding of: the earlier-formed, high-strain high-strain fabric; internal plutons; and, and, the the granite-greenstone granite-greenstone boundary. boundary. This This later later deformation deformation internal stage, which may consist of more than than one generation of folding and faulting, is interpreted to be the main contributor to the current geometry of the graniteinterpreted greenstone belt. greenstone Pubhshed geochronology geochronology allows allows a a general general time frame to be Published be assigned assignedto to stages. The early high-temperature high-temperature deformation the deformation deformation sages. deformation occurred occur6d 2.695 Ga (aae (age of of metavolcanic rocks involved in the deformation) and between 2.695 H & ; Bay and Cedar Lake plutons). The younger lowlow- ' 2.688 Ga Ga (age of Heron temperature deformation occurred between 2.688 Ga (age of Heron Bay temperature deformation occurred between Ga (age of Heron Bay Pluton) Pluton) of Gowan Cowan Lake and, speculatively, 2.678 Ga (age of Lake Pluton). Pluton). At aa subprovince subprovince scale scale greenstone belt is similar to the Manitouwadge the general aeneral history historv of the Hemlo oreenstone Manitouwadae greenstone conjectural, the high grade metamorphism gre&stone belt. AAlthough I ~ ~ Oconje&ral, U ~ ~ the metamorphism and early ea& with comparable "D2" "D2' events rnav be correlative with events (Zaleski (Zaleski et et al. al. 1995) 1995) deformation may recorded Manitouwadge greenstone The late folding may correlate recorded in the ~ anitouwad~ greenstone e belt. The with formation "03" (Zaleski formation of the "D3 (Zalesk et et al. al. 1995) 1995)Manitouwadge Manitouwadgesynform. synforrn. REFERENCES REFERENCES Corfu Chem. Geol. Gaol. ,,79,201-233. 79, 201-233. Corh and Muir Mulr (1989) Chern. T.L Ont.GeoI.Surv. Report 289. 1.LMuir, Muir.1997, 1997.OnI.Geo1.S~~. ReDorl289. Zateski ei at al., at., 1.995. 1995,IISG LSG Field Field?ri; Trip Guidebook Guidebook Zaleski 28 �constraints on the tectonic history Structural and Metamorphic Metamorphic constraints historyof of the the Southern Southern Ste. Marie Marie - Espanola Province in i n the the SauD Sault Ste. Espanola area. area. Ontario Geological Survey, Sudbury Ontario (705 670-5997; S.L. Jackson, Jackson, Ontario Geological Survey, Sudbury Ontario (705 670-5997;Jacksos@gov.on.ca) Jacksos@gov.on.ca) - exhibit aa beauilinalv beguilingly sim~le simple concave to the north Southern Province rocks exhibit attributed to structural grain. Regional Regional structures structures are are commonly comrnonlyattributed to compression compressionduring during PenOkean Orogeny; however, structural, intrusive, and metamorphic relationships Penokean Oroaenv: however, structural, intrusive, and metamor~hicrelationships permit other interpretations. North of tthe h; Murray Murray Fault Fault rocks rocks of of low lowmetamorphic metamorphic grade grade are deformed about generally upright folds folds and reverse/thrust faults. faults. The folds affect Nipissing Gabbro and 2.22 Ga Nipissing and the 1.85 Ga Sudbury Sudbury complex complex and and are are commonly commonly weakly to to moderately moderately developed, developed, steeply steeply dipping, dipping, axial axial planar associated with weakly cleavage. Confusion Confusionabout aboutthe theage age of of folding foldingarises arisesbecause becausemany manygabbro gabbrodykes dykes structures parallel parallel to the axial trace trace of some regional folds which may indicate occupy structures deformation deformation prior to, or synchronous synchronous with, gabbro gabbro emplacement. Scenarios Scenariosthat that account account relationships include: 1) gabbro dykes and sills that were emplaced emplaced into for observed relationships structurally prepared faults/fractures); 2) crustal prepared sites (fold hinges and axial planar faultslfractures); crustal cover accompanied or or flexure resulting in fracturing and faulting of the basement and cover followed by emplacement of gabbro dykes and sills (subsequent compression resulted (subsequent compression resulted intrusive events may be confused confused as as aa single single in folding); and and 3) two or more mafic intrusive event (one represented by pre-folding 2.22 2.22 Ga gabbro sills and one by post-folding post-folding gabbro dykes). the Murray Fault there there is evidence evidence for at least deformationalevents events South of the least 33 deformational pre-Nipissing faulting and large-scale folding related related to syn-depositional syn-depositional including: 1) pre-Nipissing and/or post-depositional post-depositional unconsolidated deformation deformation of of strata; strata;2) 2)"Dl" "Dl" layer-parallel layer-parallel andlor structural pre to to syn peak structural elements reflecting high extensional strain that formed pre metamorphism; and 3) 3) "D2" "02" regional regionalfolds folds and andfaults faults parallel parallelstructures structures north north of the metamorphism; and fault that that deform metamorphic isograds isograds and and are associated associated with a crenulation Murray fault cleavage. Both D2structures structuressouth southof ofthe theMurray MurrayFault Fault affect affect Nipissing Nipissing D land and02 cleavage. Both Dl that D2 02 structures 1.75 Ga Ga gabbro; however, field observations indicate that structures post-date post-date the the 1.75 Cutler Batholith. Batholith. The origin involving staurolite and origin of high-grade high-grade metamorphic assemblages involving the Murray Fault is a perplexing biotite in the McKim McKim Formation south of the perplexing aspect aspect of of tectonics. High previously attributed attributed to Southern Province tectonics. High grade grade metamorphism metamorphism was previously crustal thickening during Although this this could explain the crustal thickening during the Penokean Orogeny. Although mesoscopic 01 structural oriented at a low angle to bedding, the lack structural elements oriented lack of mesoscopic Dl regional structural evidence for the required thickening during Dl and the observation regional structural for the required thickening during Dl and that metamorphism predates regional regional folding folding do do not support this this interpretation. Furthermore, geobarometry indicates relatively relatively low-pressure (2-3kbar; kbar; 6-10 6-10km) km) low-pressure (2-3 metamorphism at a crustal thickness thickness close close to, to, or less than, the estimated estimated thickness thickness of clastic prism prism which would also seem to preclude preclude metamorphism metamorphism related related to the Huronian Huronian clastic crustal thickening. Crustal Crustal extension and increased increased mantle mantle heat heat flow flow might might better better layer-parallel foliation, lack of structural evidence for significant explain the near layer-parallel significant crustal thickening, and andthe thelow-pressure low-pressuremetamorphism. metamorphism. - 0 . 29 �in general, extension of the Superior craton and deposition In deposition of the the Huronian Huronian 2.22 Ga, the age of Supergroup is thought to have occurred between 2.45 Ga and 2.22 and Nipissing gabbro, respectively. lower Huronian volcanic rocks and respectively. However, there is is aa well-established angular well-established angular unconformity unconformity between the 2.45 Ga volcanic rocks rocks and and units are reported overlying formations and no volcanic units reported from within strata strata above the unconformity. Conseauentlv. Consequently, crustal extension and resultant deposition deposition of units unconformitv. units above this mafic this unconformity unconformitymay may have have shortly shortly preceded preceded2.22 2.22 Ga GaNipissing ~i~issin; maficmagmatism. magmatism. Deep parts of the basin basin may have been subjected subjected to elevated elevatedheat heat flow flow during during Dll structural extension resulting in D structuralelements elements and and high-temperature, high-temperature, low-pressure low-Pressure inferred to to shortly shortly follow follow Nipissing Nipissing magmatism. magmatism. Post metamorphism inferred Post metamorphic metamorphic regional .75 Ga generated generated the regional folds and regional compression compression at -1 -1.75 and associated associated axial axial planar cleavage /I crenulation cleavage. cleavage. The The above above interpretation interpretationinvokes invokessubstantial substantial pre- and post-Penokean tectonic tectonic events, events, but does not require deformation or metamorphic metamorphic events in the 1.85-1.82 1.85-1.82 Ga Ga interval. interval. 30 �The The Early Proterozoic break-up of the Superior Superior Craton: Implications Implications of drill core core and and geophysical data south of the Gogebic range, northern Wisconsin. Gene L LaBerge, Gene L. LaBerge,Geology GeologyDepartment, Department, University University of of Wisconsin Wisconsin Oshkosh, Oshkosh, WI WI 54901 and U. S. Geological Geological Survey. Exploration drill cores cores and and geophysical geophysical data data reveal reveal several several nearly continuous continuous belts of Early Exploration thin Proterozoic rocks that extend extend northeasterly northeasterlv from from Proterozoic metasedirnentary metasedimentm and metavolcanic metavolcanic rocks Butternut, the south end of Lake Gogebic, Michigan. The Butternut, Wisconsin to thesouth Thebelts, belts, shown shownby by Menominee Sims (1992) as Blair Creek Formation and as undifferentiated Chocolay and Menominee Group granitoid rocks. rocks. The Group rocks, are separated by expanses of gneissic granitoid Thedistinct distinct geophysical on the the belts belts suggests suggeststhat thatthey theyare arefault ftult bounded. bounded. The boundaries on The - - aeromagnuic and provide information on the nature nature and and aeromagnedc and electromagnetic electromagneticgeophysical geophysical data provide distribution distribution of rock units encountered encountered in the the drill cores. cores. Some cores contain intercepts of up to 100 meters doloinitic mathle, 100 m eters of dolomitic ma~ble,some some of of which which Some inteabeddedbiodte biotiteschist schist Other bunOther cores cores contain contain granular and laminated ironcontains inteabedded massive quartrite, quartzite, which, in turn, grades grades formation that grades abruptly downward into massive into into more more thinly thinlv bedded quaitzite a d t e and and then then into intointerbedded intabeddedquartzite auartziteand and biotite biotiteschist. schist. Iron-formation is commonly interbedded breccias and hn-formationis ~ornmo&~ intobedded with basaltic basaltic pillow lavas, lavas, pillow breccias and hyaloclastite units. Some Somecores corescontain contain granular granularjasper and and hematite hematiteiron-formation iron-formation rocks. Several interbedded with basaltic rocks. Several cores cores intersected intersected zones of strongly foliated foliated gneiss. Some granitoid gneiss. Someof the the cores cores contain contain breccias breccias composed composed of tabular tabular clasts clasts of ironironformation, formation, quartzite, dolomite, or mixtures of these lithologies in a matrix of graphitic bioitite schist. Several Several of of these these breccia zones may be be present in a given core. Lithologies encountered in in the the cores cores are are similar similar to to rode rock units units exposed exposed to to the the northeast northeast in in the the Uthologies (LaBerge and Klasner, 1994). 1994). The The granitoid granitoid gneiss gneissmay may eastern Gogebic range in Michigan (LaBerge baseman, similar be slivers of Archean basement, similarto tothe thePresque PresqueIsle Islegranite graniteexposed exposed near nearMarenisco, Mareiusco, the Bad River Dolomite exposed exposed east eastof of Michigan. The Thedolomite dolomiteis is comparable comparableto the similarin in all all respects respects to to the the Palms Palms Formation Formation Wakefield, Michigan. The Thequartzite quartziteisissimilar of the length length of of the the Gogebic Gogebic range. range. The iron-formation with exposed throughout much of Theiron-formation with rocks is is very very similar similarto tothe theIronwood JronwoodIron-Formation hon-Formation and and interbedded interbedded interbedded volcanic rocks Marenisco, Michigan. The Emperor Volcanic Complex north of Marenisw, The geophysical geophysical data data indicate indicateaa and the the eastern eastern Gogebic Gogebicrange. range. Therefore, it near-continuity of units within these belts and likely that the units are correlative from the Gogebic Gogehic southward as suggested by appears Likely Allen and Barrett (1915) (1915) and and Dutton Dutton (1983). (1983). The volcanic rocks are largely restrictedto to units containing iron-formation, consistent with The volcanic stratigraphic eastern and western ends aids of stradgraphic relations on the &stern of the theCiogebic Gogebic range, (LaBerge (LaBergeand and others, the observations also supports smmorts the observations of Allen Alien and Barrett (1915, (1915. p.90o.90others. 1995). This This study studv also intertiedded with iron-formation are are widely distributed 91) that volcanic vol&c rocks hterbedded distributed in &I several several rocks south of of the the Gogebic Gogebicrange. range. Thus, belts of rocks Thus, volcanism volcanism contemporaneous with ironformation deposition is present present on the eastern and western ends of the Gogebic range and formation Gogebic rangeand iron-formation units along along the the length lengthof of the therange rangeto to the the south. south. The The widespread with iron-formation widespread occurrence (logebic range occurrence of volcanic rocks south of the Gogebic range indicates indicates aa broad distribution distributionof of volcanism southward toward the proposed margin of the Superior Craton. The sediments The breccia units are interpreted as depositional breccias, where shallow-water sediments (dolomite, quartzite, quartzite, and and iron-formation) slumped into deeper, deeper, stagnant basins basins in in which which carbonaceous, mud was was accumulating. accumulating. These These stagnant carbonam&, pyritic mud stagnant basins basks are interpreted to be restricted, fäult-bowrded fault-bounded basins into which miodic shallow-water sediments sediments periodic slumuine slumping of shallow-water occurred along along fault fault scarps. scarps. 31 �Collectively, formal environment environment at least 60-100 Collectively, the thedata data suggest suggest that 1) 1)aa plat platformal 60-100 km km wide wide extended range, on which dolomite dolomite and quartzite extended southward southward from from the present Gogebic range, quartzite of Marquette Ciange Supergroupaccumulated; accumulated; 2) volcanism commenced commenced during during ironironGange Supergroup the Marqueite formation demsition. deposition, mobablv probably associated with rifting rifling and the formation of fault-bounded fault-bounded formation basins. Volcanism the overlying ocean stagnant bas&. ~ol&sm may &ay have have contributed contributediron iron and and silica silica to theoverlying ocean water, which as iron-formation; iron-formation; 3) 3) breccias containing clasts breccias containing dasts of which was was then precipitated as that rifting rifling and the shallow-water sediments within carbonaceous sediments suggests that formation occuned along along the the margin marginof ofthe the Superior SuperiorCraton. Craton. In this formation of stagnant basins occurred inteipretation rocks in the several "ranges" to the south are prepminterpretationthe the Gogebic Gogebic range and the rocks coffision, and not related to foreland basin basin evolution. evolution. Available collision, Availableevidence evidenceindicates indicatesthat that the the overliethe theiron-formation. iron-formation. These Tyler and Copps Copps Formations unconformably overlie These formations formations are interpreted collisional tectonics, tectonics, and be foreland foreland basin basiin deposits related to wllisional and to to be be are interpreted to to be significantly younger significantly younger than the the iron-formation. Referfences Cited. Referfences Cited. Allen A lien ,,R.C., R.C., and Barrett, LP., 1915, 1915, Contributions Contributionsto tothe thePro-Cambrian Pre-Cambrian geology of Michigan and Wisconsin: Michigan Geological and Biological Biological Survey, Survey, northern Michigan Publication Publication 18, 18,Geology Geology Series Series15, 15, pp pp 65-139 65-139 Lithology and and geologic geologic setting settingof of Lower Lower Proterozoic Proterozoic iron-formation in Dutton, C. E., 1983, Lithology parts of northern Wisconsin: U.S. 15p. U.S. Geological Geological Survey, Survey, Open-File Open-File Report 8484- ,, iSp. LaBerge, G. L., Cannon, Cannon, W. F., and Klasner, J. S., 1995, 1995,New New observations observations on on the the range (Abstract): (Abstract): 41st 41st Annual Annual Institute Institute on on Lake Lake geology of the the western Gogebic iron range Superior Superior Geology, Geology, Marathon, Marathon, Ontario, vol. 41, 41, part part 1,1,p. p. 33-34. 33-34. L and LaBerge, G. L andKiasner, Klasner,I.J. S., S., 1994, 1994, Tectonic Tectonic implications implicationsof the the Early Early Proterozoic Proterozoic lithostratigraphy on the range, northern Michigan (Abstract): 40th Whostratigraphy the eastern eastern Gogebic range, 40th Annual Annual Houghton, Michigan, Michigan,vol. vol. 40, 40, part part 1, 1, p. p. 27-28. Institute on Lake Superior Geology, Houghton, P.K., 1992, Sims, P.K., 1992,Geologic Geologic map of Precambrian rocks, southern southern Lake LakeSuperior Superiorregion, region, Investigations Wisconsin Wisconsin and and northern northern Michigan: Michigan: U.S. U.S. Geological Geological Survey Survey ,,Miscellaneous Investigations Series, Map 185. Series, Map1-2 1-21 85. 32 �Mineral Potential Study of a Greenstone Greenstone Belt Area, Minnesota Using Boulder Boulder Tracing, Tracing, Ely—Bigfork Ely-Bigfork Area, Minnesota Tom Lawler and Darold Darold Riihiluoma Riihiluoma of Natural Natural Resources, Resources, Division of State of Minnesota, Department of Minerals, Ave. E. 55746-1461 Minerals, 1525 1525 Third Ave. E. Hibbing, MN 55746—1461 Internet: lawler@dnr.state.mn us Internet: torn. tom.lawler@dnr.state.mn.us • Abstract Minnesota is an area of complex The Ely—Bigfork Ely-Bigfork area of northern Minnesota Archean bedrock geology. geology. Bedrock lithologies, structure, lithologies, structure, alteration, mineral occurrences and exploration exploration geochemistry alteration, mineral occurrences geochemistry indicate there thereshould should be be undiscovered undiscovered valuable valuable metallic metallic mineral mineral indicate deposits. sample site deposits. The The poster displays sample site locations locations and and anomalous anomalous results metal potential. The results which which indicate indicate gold or base metal The granite granite greenstone similar to those those hosting hosting economic greenstone belt (Morey, (Morey, 1996) is similar economic mineral deposits mineral deposits in in the the Archean of of Canada Canada and and Scandinavia. Scandinavia. - objective of this to provide provide a a reconnaissance reconnaissance study The objective this project is to of mineral mineral potential potential for for a a sixty—one sixty-one township township area area in in northern northern St. St. Louis County, southeastern Koochiching Koochiching County County and County, southeastern and northeastern northeastern Itasca achieved by by mapping mapping alteration alteration and analysis Itasca County. This This is achieved of mineralized rock samples found in glacial glacial drift drift deposits deposits from from pits. Anomalous gold values ranged 144 sites, mostly mostly gravel pits. ranged to to Base metal metal values values 3,598 ppb, with arsenic values up to 1,900 ppm. Base include zinc to 2,899 2,899 ppm, lead to to 248 248 ppm, copper to to 14,944 ppm and lead ppm, barium to to 1,980 1,980 ppm. ppm. Partial Partial analytical analytical results are ppm, also barium presented table with with anomalous anomalous areas areas designated designated as as Mineral Mineral presented in aa table Potential Areas (MPAs). The map map presents presents site number, number, designation Potential (MPAs). The as gold or or volcanogenic volcanogenic massive massive sulfide model, and and MPA MPA number. number. Samples of analyzed rock are displayed for many sites. The sites. The table table Mineral Potential Areas From Analysis displays selected Potential From displays selected analysis analysis used to to model model mineral mineral potential. potential. The location The location of of the the source source of mineralized samples samples is is indicated indicated by: by: 1. Development of mineralized—altered boulder 1. Development of mineralized-altered boulder dispersal dispersal trains. trains. 2. 2. amount of the sample The amount of mineralized rock at the sample site site which which decreases decreases denudation. 3. 3. Hand Hand lens classification classification with distal distal dispersion dispersion and denudation. lithologies contributing pebbles to a randomly selected sample of lithologies of 100 100 pebbles pebbles from from each each site site which which are are compared compared with with mapped mapped bedrock lithology bedrock lithology (Morey (Morey 1996). 1996). MPAs MPAs 1, 1, 2, 7, 7, 8 and 17 17 are are in in an an area mapped by Mooers, et al. al. (1996) as scoured scoured bedrock uplands uplands or (1996) as Lobe deposits. By all the the criteria criteria the the northern northern sites sites of MPA Rainy Lobe MPA5 7 and 17 are near the 1 and 2, and all of MPAs the bedrock bedrock source source of mineralized these MPAs, MPA5, Mooers, et mineralized rock. rock. West West 0of these et al. map additional additional dispersion by 3, 4, 5, 9, Kooochichinq Lobe. Lobe. 14PAs MPAs 3, dispersion by the the Kooochiching 9, 10, 10, 11, 11, 12, 12, 13, 14 and 15 their source 15 are are reasonably close to their source by by most most of of the the criteria. some distance distance from criteria. MPA MPA 6, 6, 88 and and 16 16 might be some from their their source. source. 33 �Morey, G.8., G.B., Compiler, Compiler,1996, 1996,Geologic GeologicMap Map of ofMinnesota, Minnesota, Minnesota Morey, Minnesota Geological Surveyl Digital Version Geological Survey, Digital Version H.D., et etal., al., 1996, 199G1Geomorphology Geomorphology of of the the Basswood Basswood Lake, Mooers, H.D., Mooers, Lake, Crane Lake, Little Fork, Ely, Vermilion Lake and Bigfork Crane Lake, Little Fork, Ely, Vermilion Lake and Bigfork 1: 1,000,000quadrangles quadranglesand and the the development developmentof of the the Land Land Type 1:1,000,000 Type Association layer of the Ecological Classification System, Association layer of the Ecological Classification System, MinnesotaDepartment Departmentof ofNatural Natural Resources Resources—-Division of Forestry Forestry Minnesota Division of MINERAL POTENTIAL AREAS I I P318 STUDY AREA • VMS BASE METAL CC:) MINERAL POTENTiAL AREA • GOLD SITES WITH NO MINERAL POTENTIAL SCALE 1:1mom SCALE 1:1.000,000 34 34 A �THE THE PETROLOGY PETROLOGYOF OFGREENSPAR: GREENSPAR: A A PROTEROZOIC PROTEROZOICPORPHYRITIC PORPHYRITICDIABASE DIABASEDIKE; DIKE; PIFHER NIPIGON DISTRICT, DISTRICT, ONTARIO PIFHER AND IRWIN IRWIN TOWNSHIPS, LAKE NIPIGON ONTARIO by Whitewater, Wl WI 53190 by Frank Frank A. R. Luther, Luther, Geology, UW-Whitewater, Whitewater, 53190 This This approximately approximately50 50 m mwide wide porphyritic porphyritic diabase diabase dike, dike, outcropping outcroppingininwestern western Irwin and Pifher Townships in the Lake Nipigon district, is locally known as greenspar. Irwin and Pifher Townships in the Lake Nipigon district, is locally known as greenspar. The The dike dike has has aa characteristic characteristic greenish greenish mottled appearance in outcrop as a result result of sausseritized sausseritized plagioclase plagioclaseglomerophenocrysts glomerophenocrysts in in aa diabase diabasegroundmass. groundmass. The The dike dike strikes strikes due due north northand anddips dipsvertically. vertically. ItIt is is located located approximately 15 15 km km east east of Lake Lake Nipigon Nipigon and and 5-20 5-20 km km north northof ofHwy Hwy11. 11. Mackasey off-set by by east-west east-westfaulting faulting Mackasey (1975) mapped mapped the dike as segments segments off-set and and suggests suggests that that only onlyone onedike dikewas was originally originallyintruded. intruded. Kresz Kresz and and Zayachivsky Zayachiiky (1989) observed chill borders borders on dike apophyses and stated that the the dike dike has has been been obsewed chill seen seen some some50 9km kmsouth southof of Irwin IrwinTownship. Township. Both Both reports reports stated stated that that the the glomerophenocrysts distribution; Mackasey reported glomerophenocrysts are erratic in distribution; ~ac-kasey reported aa segregation segregation of the the glomerophenocrysts glomerophenocrystsinto into bands bandsat at one one location. location. Alteration Alteration of of the the country muntryrock rockwas was not not reported reported by by these these workers workers nor nor was was itit seen seen by by the the author. author. The (1975) determined determinedthat that The greenspar greenspar dike dike isis of of Proterozoic Proterozoicage. age. Mackasey Mackasey (1975) this this dike dike is is cut cut by by the the large large middle middle or or late late Proterozoic Proterozoic (Keweenawan?) (Keweenawan?) sill in in Irwin Irwin Township. Township. There There are are no no radiometric radiometric dates dates on on this this rock rock or or associated associatedrocks. rocks. A A whole whole rock r w k chemical chemicalanalysis analysis of of the the greenspar greenspar isispresented presentedininTable Table1.1. The The texture textureand andmineralogy mineralogyof of this this rock rock were were studied studied by by petrographic petrographic and and electron electron microprobe microprobeanalysis. analysis. The The rock rockconsists consistsof of 20% euhedral, 20% glomerophenocryst g l o m e r o p h e n ~plagioclase: plagioclase: t euhedral, 1-5 1-5cm, cm,with withremnant remnantplagioclase plagioclase cores (an), the bulk of these crystals are altered to a very fine-grained cores (an83),the bulk of these crystals are altered to a very fine-grained mixture mixtureof of albite, albite,epidote, epidote,sericite, sericite,and andzeolite(?). zeolite(?). 45% (an) totorim 45% groundmass groundmassplagioclase: plagioclase: normally normally zoned core (ans) rim(an61), (an6,), subhedral subhedral laths, 0.5-1.O mm, mm, cores coresare are rarely rarelyaltered alteredto to aafine-grained fine-grainedmixture mixtureofof laths, 0.1-0.3 0.1-0.3 xx 0.5-1.0 sericite sericiteand andepidote. epidote. 30% Mg, minterstitial , interstitialtotosubhedral, subhedral,0.2-0.3 0.2-0.3 mm. mm. zonalcore coreMg70 Mg7,3to rim M 30% augite: augite:zoned 4% 4% opaques: opaques:euhedral euhedralmagnetite, magnetite,ilmenite, ilmenite,and andpyrite, pyrite,0.1-0.3 0.1-0.3mm. mm. <1% quartz: interstitial grains 0.1-0.3 mm. 4 % quartz: interstitial grains 0.1-0.3 mm. The haveremnant remnantcores coresofofanm an composition compositionwhile while the the The glomerophenocrysts glomerophemcrysts have bulk bulk of these these large large crystals crystals are are altered altered to aa mixture mixture of albite, epidote, sericite, sericite, and and zeolite(?). zeolite(?). The The glomerophenocrysts glomerophenocrystsare are interpreted interpretedas as phenocrysts phenocrystsbecause becauseof of their their euhedral form. No broken crystals, xenocrysts of other composition or mineralogy, euhedral form. No broken crystals, xenocrysts other composition or mineralogy, or or xenoliths xenolithswere wereobserved. obsewed. The The glomerophenocrysts, glomerophenocrysts, being being highly highly calcic, were were easily easily sausseritized during during sub-solidus sub-solidus events. The Thenormally-zoned normally-zonedplagioclase plagioclaseof of the the sausseritized wasnot notas assusceptible susceptibletotoalteration; alteration; groundmass with an average composition groundmass composition of of aanMwas some somecrystals crystals show show minor minor alteration alteration of of the the more more calciccores. calcic cores. Clinopyroxene Clinopyroxeneininthe the 35 �grouridmass in rims; there there is groundmass is is zoned zonedfrom fromMg70 MgTO in the the core core to to Mg40 MgdOin the rims; is minor minor alteration of of the clinopyroxene clinopyroxene to to actinolite actinolite and and zeolite(?). zeolite(?). Euhedral Euhedral Mn-bearing Mn-bearing ilmenite (sometimes skeletal or intergrown with with Ti Ti hematite?), magnetite, and pyrite pyrite groundmass. Olivine are present throughout the groundmass. Olivine was was not not observed. observed. It is The length is interesting interesting to speculate on the age age and and origin origin of the the greenspar. greenspar. The length of 15 vertical dip, uniform strike, and 15 (perhaps up to 65) km, minimal variation in width, vertical apparent over-all compositional homogeneity point point to to a deep-seated source and a long period of cooling at considerable depth to crystallize the exceptionally large large glomerophenocrysts. glomerophenocrysts. Following this period of quiescence, the magma magma was was intruded intruded into cooler Archean country rocks where the remaining remaining melt melt cooled cooled rapidly rapidly enough enough to to form zoned plagioclase and clinopyroxene. The glomerophenocrysts were zoned plagioclase and dinopyroxene. glomerophenocrysts were deuterically altered soon after emplacement while the groundmass plagioclase, less less minerals were less calcic in composition, and other groundmass minerals less affected. With mineralogical similar.@ similarity to to middle or late late Proterozoic Proterozoic respect to the time of intrusion, the mineralogical (Keweenawan?) diabases is (weak) evidence evidence that that this this rock may be an early early phase phase of Keweenawan Keweenawan activity. Logically, a lone dike in this location, given the characteristics characteristics enumerated above, with no compositional similarity to lamprophyre lamprophyre or kimber!ite, kimberlite, could easily be an early phase of Keweenawan Keweenawan magmatic magmatic activity. activity. Alternatively, Alternatively, the the east-west strike-slip offsets noted by Mackasey are not consistent with mostly mostly dip-slip dip-slip preKeweenawan faults resulting resulting from rifting. rifting. This faulting could indicate indicate a preKeweenawan origin of the greenspar. greenspar. Table of the greenspar. greenspar. (XRAL 1. A bulk chemical analysis of (XRAL Laboratories) LaMratories) Table 1. Si02 Si02 Al203 A 10 CaO CaO MgO MCJo Na20 NazO 1<20 K20 FeOt FeOt MnO MnO 1102 Ti02 P205 Pa5 Cr203 cr2m LOl LO1 TOTAL 48.9 13.2 13.2 11.0 11.0 6.02 1.94 0.28 14.2 0.21 0.21 1.33 0.15 <.01 c.01 Rb Sr V Zr Nb Ba 2 ppm 209 22 105 11 137 0.85 98.1 98.1 REFERENCES REFERENCES D.U. and Zayachiisky, Zayachivsky, B., Kresz, D.U. B., 1989, Precambrian Precambrian geology, Barbara, Meader Meader and and Townships; Ontario Geological Geological Survey, Survey, rpt rpt 270 270 with with maps 2536-2537, 2536-2537, 91 p. Pifher Townships; W.0., 1975, Dorothea, Sandra, and and Irwin Irwin Townships, Townships, District Districtof of Mackasey, W.O., 1975, Geology Geology of Dorothea, of Mines, r rpt Thunder Bay; Ontario Division of pt 122 with map 2294, 83 p. 36 �Initial results of ArlAr Ar/Ar mineral dating from the Peavy Peavy node nodearea area of ofnorthern northern Michigan and and Dunbar dome Dunbar dome area areaof of northeastern northeastern Wisconsin. Wisconsin MANCUSO, C.M. Cit. HOLM, OH MANCUSO, HOLWD.K., D.K.Dept k p t .of(Jeology, of Geology,Kent KentState StateUniversity, U ~ v e r s i t yKent, Kent, , OH 44242 (dholm@kentedu); (dholm@kent.edu); FOLAND, FOLAND, K.A., KA,and and HUBACHER, m A C H E R , F.A., FA, Dept. of of Geological Geological Sciences, The The Ohio Ohio State State University, University, Columbus, Columbus, OH OH 43210. 43210. The origin has The origin of gneiss gneiss domes domes and and metamorphic nodes exposed within the Penokean Penokean orogenic orogenicbelt belt has perhaps areas of of geologic geologic research research in in the the Lake Superior pexhaps been one of the most important and controversial areas region. have re$zion. Although Althouzhthe thenodal nodaJisograd isomadpatterns patlemsappear a o mgrossly mossl~similar similar In in map mm view, view. they they may mav actually actuall~ have very different tim&, times, and and may may evin even be the product veiy different diffmnt origins, 6rigjm. may hhave a k formed f o b & at dffere2 pbduit of polyphase po~bhase metamorphism. For For Instance, htance, Emiio Emilioetetal. al. (1996) (1996) on on the basis basis of textural relationships suggested that the node In in northern northern Michigan may be the result of three threediscrete disaetemetamorphic me$amotphieevents. events. metatnorphic node Peavy metamorphic Peavy node Winnet. (Winnet, 1981) ArIAr thermochronologlc t h e n n o c h r o ~ ~ l results o ~ c within tthe he Peaw 1981) are are suggestive su~~estive In addition Initial initial Ar/Ar post-orogenlc reheating episdes. episodes. Finally, numerous R Rb/Sr and mica d&s dates from within ~ I and'KlAr S ~ K/Ar &ca frogwitAin of several post-omgenic south) of the Peavy node also suggest a protracted history history of post-omgenic post-orogenic uplift uplift and outside (mainly south) andor reheating Petennan et al., aL, 1985). 1985). We (Aldrich et el al., al., 1965; 1965; Peterman We report here the the results results of of new new Ar/Ar ArlAr and/or reheating (Aldrich mineral mineral dates dates which whichfurther furtherelucidates elucidatesthe thethermal thermalhistory hisloryof ofthis thisarea. area dated one Result of hornblende hornblendedating. dating.We We dated onehornblende hornblendeseparate separate(96-MI-4) (96-MI-4) from froman anaxnphibolite amphiblite schist collected from the south kmwest westofofFoster FosterCity, City,MI). MI). lThis 3 i s sample sample yielded south side side of the the Feich Felch Trough (—7 (-7 km an excellent plateau date of 1799±6 total gas date of 1797 1799% Ma (and concordant concordant total 1797Ma). Ma). This date is comparable to the oldest post-Penokean K/Ar hornblende hornblendedate date from fromthis this area area obtained obtained by Aldrich et al. post-Penokean WAr a1. (1965) and is interpreted below interpreted to to represent represent the thetime timeofofinitial i ~ t i acooling cooling l below—500°C -51N° after after Penokean-age Penokean-age regional metamorphism. We Wenote notethat thatprevious previous hornblende hornblende Ar/Ar AdAr total gas dates d a m and and K/Ar WArdates datesobtained obtained Ma) and may well to the the west are are substantially substantially younger youngex (predominantly (predominantly 1730-1500 Ma) well represent representlocalized locaked thermal recognized 1630 thermal overprinting oveaprinting effects effects possibly possibly associated associated with the the.long recopizd 1630Ma Ma metamorphic m W o r p h i cevent went or or of the the Middle MiddleProterozoic Protozoic Wolf WolfRiver RiverBatholith. Batholith. even iintrusion n w o n of Result of muscovite muscovitedating. dating. Muscovite Muscovitefrom froman anArchean Archeanmuscovite-biotite m m v i m i o t i t e schist collected mUected at Foster l%stec City (94-MI-i) plateau date date of of 167335 1673±6 Ma oover the last last (94-M-1) showed showedsome somepossible possible recoil effects but yielded a plateau w the released. Coarse (96-MI-5) located located in in the the north ecentral part 50% of the gas released. Coam muscovite m m v i t e from a pegmatite (96-MI-5) n W part plateau date date of of 1653*4 1653±4Ma. Ma. nThese the oldest oldest mica mica dates dates of the Felch Trough gave an excellent plateau e s e dates are the aL, ArtAr or K/Ar WAr methods (see Aldrich et d .,1965 1965 and Winnet, Winnet, 1981). 1981). obtained from the area by either the Ar/Ar comparable to to the 1610-1680 Ma RbtSr Rb/Sr and and ArIAr Ar/Ar biotite biotite dates dates obtained obtained from from the the They are roughly comparable 1610-1680 Ma et al., aL, 1996) and may indicate the wan Schmus Sciunw and Woolsey, 1975; 1975: Schneider et Republic area to the north (Van regional time of initial i ~ t i aslow slow l regional cooling coolingthrough throughmica micaclosure closuretemperatures temperatures(—350-300°C) (-350-31N°C long after the Penokean Orogeny. Alternatively, Penokean Alternatively,these thesedates dates may may represent nearly complete complete thermal resetting resetting associated associated with the 1630 morphologyof of the the spectra spectrado do not not seem to support this 1630 Ma low-grade event although the morphology interpretation. Result of of biotite biotite dating. dating. We Wedated date4two twobiotite biotiteseparates separatesfrom from rock rock samples samples collected collected in in northeast northeast Wisconsin south southof of the the Niagara NiagaraFault Fault AAsample WI sampleof of aaPenokean Penokean pluton pluton collected collected near near Aniberg, Amberg, W I Wisconsin (southeast of of the the Dunbar Dunbar dome) dome) yielded yieldedaaplateau plateauage ageofof1456H 1456±4Ma. Ma. RblSr Rb/Sr biotite dates from (southeast fiom this locality younger (1350-1390 locality and and from fiom several severalsurrounding mounding localities lcalities are are substantially substantially youngex (1350-1390 Ma, Ma, Peterman Pemmanetetal., al., 1985). The meAr/Ar ArlArbiotite biotitedate dateisisnearly n w l y concordant concordant with with the intrusion age age of of the theWolf WolfRiver Riverbatholith batholith (exposed -25 -25 km to to the the southwest). southwest). The m enearest nearest exposed exposed portions portions of the the batholith batholith contain contain miarolitic miarolitic (exposed cavities composition which which suggests suggests cavities and a late late differentiate differentiate of of itit (the (theBelongia Belongia Granite) Granite) has has aacomposition Anderson and and Cullers, 1978). emplacement at shallow shallow crustal crustal levels levels (<4 (<4 1cm, km, Anderson 1978). Considering that the batholith extends for a considerable subsurface distance beyond beyond iB its map new view exposure exposure (Allen baU101ith extmds (Nlcn and and Hinze, Him, 1992), we suesxt suggest that the 1456 1992). we 1456 Ma Ma biotite biotite date date represents renresents thermal resetting resettine of shallow sliallowcrustal crustal rocks rocks intruded by th<-wolf the Wolf River intruhh R v a Batholith. km north north of of (WI-7) collected collected within the Dunbar Dunbar dome dome (—8 (-8 Ian Biotite from a biotite augen augen gneiss (WI-i) WI) yielded yielded aa near-plateau near-plateaudate dateof of 1128B 1128±3Ma Ma(and (andtotal totalgas gasdate dateofof 1116 1116Ma). Ma). This hDunbar, n b a r , WI) 'IXs date is nearly (Peterman et etal., al., 1985) 1985)and and nearly concordant concordant with with previous pxeviow Rb/Sr RbtSr biotite biotite dates obtained from this locality (FWexman - 37 �_____ ___________________ _________ from localities to the west (i.e., (i.e., the locus 01<1.2 of 4.2 Ga GaRb/Sr RblSrbiotitc biotitedates datescalled called the theGoodman Goodman Swell Swell by by from Peterman Peteand Sims, 1988). 1988). Our Ourdate daceisisconsistent consistentwith withthe theinterpretation intametationthat thatthis thisarea areacooled cooledduring durinz uplift be related to to loading loading along along the the Keweenawan Keweenawanrift riftbut but may mayalso alsoalternatively ~ltematively bcexplained, explained,perhaps, perhaps, by bi uplift related resetting igneousactivity. activity. m t t i n g due due to to subsurface subsurfaceKeweenawan Kcweenawanigneous References References Aldrich, LT., L.T., Davis, Davis,G.L, G.L.,and andJames, James,Hi., H.L.,1965, 1965, Ages mineralsfrom frommetamorphic metamorphicand andigneous igneous Aldrich, Ages ofof minerals rocks Petrology, 6: 445-472. 445472. rocks near near Iron Iron Mountain, Michigan: Journal of Pelrology, Allen, D.J., D.J., and and Hinze, Him,W.J., W.1,. 1992, 1992,Wisconsin Wisconsin gravity gravityminimum: minimum:Solution Solutionof ofaageologic geologicand andgeophysical geophysical Alien, puzzle evolution: Geology, p W e and and implications implications for for cratonic cratonic evolutiozx Geology, 20: :515-518 515-518 Anderson,J.L., J.L., and and Cullers, R.L., RL.,1978, 1978,Geochemistry Geochemistryand andevolution evolutionof ofthe theWolf WolfRiver RiverJ3athollth, Batholith, aa late late Anderson, Precambrian rapakvi massif in northern Wisconsin, Wisconsin, U.S.A.: U.S.A.: Precambrian PrecambrianResearch, Research,2 7:287-324 287-324 Ejnilio, IstC., MC., Johnson, Johnson, EL., EL., Matty, Mat& D., D., 1996, lW6,AACritique Critiqueof ofNodal Nodal Isograd Isograd Patterns P m in in the theUpper U p Emillo, Peninsula of Michigan: Michigait FLIS, as, 77: S285 Peninsula of SZ85 Petermnan, Z.E.,and andSim, Sims,P.K. P.K.,1988, 1988,lXe TheGooduma Goodman.% Swell: lithosphericflexure flexurecaused causedby bycrustal austal Peteman, 2.E.. WE AAJithospheric loading rift s system: Tectonics, 2 7:1077-1090. loading along the the Midcontinent rift ystem:Teuonics. 1077-10!90. Peterman, Z.E., Sims, P.K., P.K., Zartman, Zariman, RE., RE., and Schultz, K.J., Petem~an, ZE., KJ- 1985, 1985,Middle MiddleProterozoic F'mtemzoic uplift uplift events wen@in the Dunbar Dunbar Dome Dome of northeastern northeastan Wisconsin, Wimnsin, USA: USA: Contributions Contributionsto Mineralogy Mineralogy and Pemlogy, the Petrology, 91: 138150. 138-150. Schneider,D., D., HoIm, Holm, D., D., and and Lux, D., D., 1996, 1996,On Onthe theorigin originof ofEarly W l yProterozoic Proterozoicgneiss gneissdomes domesand and Schneider, metamorphic nodes, northern Michigan: Canadian Ekrth Science, 33: 1053-1063 1053-1063 metamorphic Canadian Journal of Earth Van Schmus, Schmus, W.R., W.R., and Woolsey, L.L., 1975,Rb/Sr RblSrgeochronology geochrono1ogyofofthe theRepublic Republicarea, area,Marquette Marquette Van Li., 1975, county, EarthSciences, Sciences,12: 1 21723-1733. 1723-1733. county,Michigan: Michigau: Canadian Canadian Journal Journal of of Earth Winnett, T.L., 1981, Middle Precambrian (PreCambrian thenualhistoiy historyofofnorthern n o d e mMichigan: Michigan: Winnett, tL, 1981, Middle PreCambrian (PreCambrian X)X)thermal Master's StateUniversity. U~versity. Master'sthesis, thesis,Ohio OhioState 94Mk1 iso- 1650- - Age Ma Ma .° 0 Muscovite Muscovite 1625 Tp=1673±6 Ma Age Ma Ma Tg=1640 Ma I I I 20 2 0 40 4 0 660 0 880 o l100W 00 : o0 9&M15 = 1150 - o-•_ 1100 4060 40 40 , 00 20 2 0 440 0 6 600 96-MM I, 4 1700 Ma 00 a.— — Homblencte Hornblende Tp=1799±6Ma T p l 7 9 W Ma 1Tg=1,7971'4a 20 20 40 40 60 60 %3OAr 38 80 80 100 iC Riotite Biotite Tp=1128+3Ma Tp=1128*3 Ma Tg-1116 a Tgflll6Ma %39Ar 1800 80 80 - %39Ar 1900 60 60 WI-7 - Age Ma 20 2 0 4 0 6 0 880o l100W P3 20 -— 1125 Biotite Biotite Tp=1456±4Ma Tp=1456*4 Ma 1Tg=lp7My Tg=1437 M Muscovite Muscovite Tp=1653*4 Ma Ma Tp=1653±4 Tg=1647 Ma Tg=1647 Ma I I I 00 WI-4 p 100 100 80 100 �THE SUIB-BARABOO PALEOSOL,WISCONSIN: WISCONSIN: GEOCHEMICAL GEOCHEMICAL EVIDENCE EVIDENCE FOR SUB-BARABOO PALEOSOL, PROTEROZOIC WEATHERING AND AN]) METASOMATISM METASOMATISM RH., Jr., Jr., Dept. Dept. of ofGeology Geology & & MEDARIS, L.G., MEDAKIS, L.G.,Jr., Jr.,BAUMGARTNJB, BAUMGARTNER,L.P. L.P.and andDO'IT, DOfl, 1CR, Geophysics; McSWEENEY, K, K,Soil SoilScience; Science;all allatatUniversity Universityof ofWisconsin-Madison, Wisconsin-Madis04 Geophysics; Madison, WI, 53706 53706 Precambrianpaleosols paleosolsprovide provideimportant importantdata data for for the the interpretation interpretation of ofpaleoclimates Precambrian paleoclimates and paleoatmospheres, but the chemical compositions of such ancient soils have paleoatmospheres, but the chemical compositions of such ancient soils havecommonly wmmonlybeen been modified by subsequent subsequent &genesis diagenesis or orm metamoiphisni. etamorph A A paleosol pdwsol has has recently recently been been discovered discoveredat at modified by the Chanite (Medaris (Medark et etaL, the base of the post-1760 Ma Baraboo Baraboo Quartzite Quartziteon onBaxter BaxterHollow HollowGranite al., 1996; have been obtained 1996%1996b), 1996b),and andchemical chemicalanalyses analyses have obtained to evaluate evaluate the conditions conditions of of weathering and possiile possible effects effects of of metasomatism metasomatisim The The geochemical geochemicalprofile profle of the sub-Baraboo sub-Baraboo paleosol palwsol is is consistent -withweathering weatheringunder wider conditions conditions of of mtense intense leaching, leaching, but but appreciable appreciable potassium potassium was condent with added added to saprolite saprolite and and the the associated associated pedogenic pedogeniczone m eduring duringlater latermetamorphism. metamorph f the sub-B sub-Barabm paleosol:the thequartzite-granite quaxtzite-ganite contact contactin inBaxter BaxterHollow Hollowisis Description ooft/ic araboo paleosol: not exposed in outcrop, but the the contact contact was was penetrated penetratedby by eight eight holes that that were were drilled drilled by the the U.S. Army Corps of Engineers in in 1959. Material the contact Materialfrom fiomthe contact zone zone was was recovered recoveredonly only in in drill from Hole No. 613, in which overlying pebbly quartzite d d core &om quartzite is separated separated from fromunderlying underlying granitic by aa 2.5 2.5 foot-thick, foot-thick, reddkh-pqle reddish-purple pedogenic gsa~ticsaprolite by pedoge~czone, consisting consisting of flne-grained he-grained hematite, quartz, quartz, and illite (kkaolinite). (±kaolinite). The The pedogenic pedogenic zone zone shows shows features features that are are commonly commonly associated with physical reorganization reorganization (e.g., (e.g., repeated repeated wetting wetting and drying) d q h g ) of of weathered weatheredrock rockin m soil-forming environments, which include: 1) aggregates of clay-size and larger grains with small soil-fonning w%ich include: aggegates of larger gains with wall intra-aggregate network of mtra-aggregate voids, 2) 2)a network of large largeinterconnected mtercomectedvertical, vertical, horizontal horizontaland andoblique obliquevoids voids separating the the aggregates, 3) discrete accumulations of claythy- and along andsilt-size silt-& materials matalong some some %changoK2O % dwge %charwK20 void walls and large grain edges, and 4) 4) stress stress orientation orientation .00 a -40 a a 0 SD2 , o a a 80 20 -$0 -40 0 40 -20 40 0.I 0.' within witbin some some clay-size clay-& accumulations. accumulations. 0.1 p p (iranitic texture is Granitic texture is preserved presewed in saprolite, saprolite, but but biotite biotite 3 .p p is largely largely replaced replacedby byhematite, hematite,and andfeldspar feldsparisiscompletely: completely I, replaced by illite; the the first feldspar in granite granite is is located located 2 P —30 feethelow belowthe thequamite. quartzite. We We presume presume that the -30 feet 10 I:10 10 intensity and fiequency frequency of processes processes driving intensiv driving physical physical aa G G reorganization reorganization of of the the soil-saprolite soil-saproliteprofile profile diminished dbbi&ed = ' G G Inn with IW surfice. with increasing maeasing depth below the land surfice. 1~ ha^ Na20 NaZO ~ CaOc ~ o %%change Geochemistry: XRF been obtained Geochemis~: XRF analyses analyseshave been obtained for for -125 %m.75change -25 -125 75 -25 42s -75 -25 00 25 25 -125 -75 .23 00 25 25 0.1 0.I major major and and selected selectedtrace traceelements elementsin mtwenty twentysamples. samples. p Data Data for for four four oxides oxidesare areplotted plotted in mthe theadjacent adjacentfigure figurein m p terms terms of% of %change changewith withrespect respect to to the the average averageof oftwo two , unweathered unweathered granite granite samples samples closest to saprolite, saprolite, and and normalized which is is assumed to be normalized to to A1203, %03,which be immobile immobile during duriag weathering. Some Somefeatures featuresof ofthe thepaleosol paleosol I38 10 ! chemical chemicalprofile profile resemble resemble those those of of modem mod& soils soilswhich which * are such as :: are produced produced by by intense intense chemical chemical leaching, such as aa 100 P = Pedogenic Zone P = Pedogenic Zone decrease in Si02 and severe depletion in CaO and Na20, deciease sio2 severe depletion C ~ O and N%O, S s== Saprolie sapr01te due quartz and release of Ca and Na fiom from G= due to solution solution of quartz = tJnvathered u-ath~ed Granite ~rmite Ki@.: . I ' • I8 2* 8 1 iG 1 43rd ILSG, 1997, p. 1 39 �plagioclaseduring during replacement by kaolinite. However, However, Ca Caand andNa Nadepletion depletionshould shouldbe be plagioclase accompanied by K depletion due to the exception exception of ofthe the accompanied to weathering of K K feldspar, but with Mth the uppermost the paleosol, is 30-40% 30-40% higher in m the paleowl, compared comparedto to average average granite. m e . We We uppermostsample, sample, 1(20 &O is believe believe that thatall a l l feldspar in the paleosol was altered altered during during weathering weatheringand andthat thatKKleaching leaching occuned, occurred,but butthat thatKKwas wasreintroduced reintroducedduring duringlater latermetamorphism metamoqhismby byfluid fluidflow flowalong alongthe the sub-Baraboounconformity. Note Notethat that detrital detritalfeldspar feldspar is israre rarein inquartzite, quartzite,and andinterlayered, interlayered,highly highly sub-Baraboo aluminous ofpyrophyffite+kaolinite+quartz, aluminous metapelites, consisting of pyrophyllite+kaolinite+q~are areimpoverished impoverishedininK, &Na, Na, and andCa. Ca. Similar Sjmilarchemical chemicalfeatures featureshave havebeen beendescribed descniedfrom fiomsub-Huronian sub-Huronianpaleosols paleowls on ongranite graniteat at Pronto, Ontario (Gay & Grandstag 1980), and Vile Marie, Quebec (Rainbird Pronto, Ontario (Gay & GrandstaK 1980), and ViUe Marie, Quebec (Rahbiid et et al, aL,1990), 19901,and and interpreted interpretedas asthe theresult re& ofK-metasomatism of K-metasomatismdating duringdiagenesis &genesis or orlow-grade low-grademetamorphism metamorphism of of pre-existing preexistingweathering weathe@ profiles. profiIes. The Therelative relative effects effectsof ofweathering weathering and and metasomatism m e t a s o m a h on onpaleosols paleowlscan canbe beevaluated evaluatedby byusing using aaplot (A),CaO+N%O CaO+N;O (CN), (CN), and q0 1(20 6). (K). A plotof ofmolar molar A1203 @03(A), A theoretical theoreticalweathering weathering trend trend for for Baxter BaxterHollow HollowGranite Granitewas wascalcuated calcuatedfrom fiomthe the AA CIPW CPWnorm normof ofaverage averagegranite graniteand and release releaserate rate constants Young, 1984). constantsfor forfeldspars feldspars(Nesbitt (Nesbitt& &Young, 1984). The the weathering Therelative relativepositions positionsof ofthe weatheringtrend trendand and analyses of sub-Baraboo paleosol indicate an analyses of sub-Ba~aboopaleosol indicate an addition additionof—1O of -10 mol% mol% 1(20 &O during duringmetasomatism, metasomatisq 5 which is comparable to the -44 mol% which is comparable to the -14 mol%estimated estimatedfor forC.) 070 the theVille V i eMarie Mariepaleosol paleowl(Fedo (FedoetetaL, aL,1995). 1995). The Thechemical chemicalindex indexof ofalteration alteration(CIA), (CIA),which whichisis defined defined as as A120J(A1203+CaO+N;0+}0), %OJ(@03+CaO+NQ+&O), can canbe be determined determinedfor forpre-metasomatized premetasomatizedpaleosol palms01by by Kcp extending extendinglines q0apex apexthrough throughthe the h e sfrom fiomthe the1(20 paleosol CN KK paleosolanalyses, analyses,to tointersect mtersectthe theweathering weatheringtrend, trend, CN yielding values ofSl-83. Such values are yielding of 81-83, Such values are significantly the effects signi6cantly higher higher than than those those obtained, obtained, ififthe effectsof ofK-metasoniatism K-metasomatismare areneglected. neglected. Conclusions: aawell-developed Conclus~om: well-developedweathering weatheringprofile profilewas wasestablished establishedon onthe theBaxter BaxterHollow Hollow Granite Graniteprior priorto todeposition depositionof ofthe theBaraboo BarabooQuartzite. Quamite. During Duringlater latermetamorphism metamoqhismand andfolding foldingof of thequartzite, quartzite,significant significantamounts amountsof ofKKwere wereadded addedtotothe thepaleosol paleowlby byfluids fluidschanneled channeledalong alongthe the the sub-B araboo unconformity. sub-Bamboo unwnfonnity. An Aninvestigation mvestigationof offluid &id inclusions mchwiom is is underway underway to todetermine determinethe the characteristics other characteristicsof ofthe themetasomatizing metasomatizing fluids. The Thetime timeof ofweathering weatheringremains remainsunknown, &OWJI, otherthan than being younger than 1760 Ma. An apparent Rb-Sr isochron being younger than 1760 Ma. An apparent Rb-Sr hcbronage ageofthe of thepaleosol paleowlisis1360±50 1360250Ma, Ma, raising raisingthe theintriguing mtriguingpossiblilty possiblilty that that K-metasomatism, K-metasomatism, metamorphism metamorphism,and andfolding foldingmight mighthave have been River events beenrelated relatedtotoWolf WolfRiver events(--1400-1500 (-1400-1500 Ma). Ma). REFERENCES REJBRENCESCITED CrnD Fedo, 92 1-924. Fedo,C.M. C.M.etetaLaL(1995) (1995)Geology, Geology,v.v.23, 23,921-924. Gay 349-373. Gay&&Grandstaff(1980) GrandstaE(1980)Precamb. Precamb.Res., Res.,v.v.12, 12,349-373. Medaris, aL(1996a) (1996a)42nd 42ndInst. Inst.Lake M eSuperior SuperiorGeoL, Ged,v.v.42, 42,31-32. Medaris,L.G., L.G.,Jr. Jr.etetaL 3 1-32. Medaris, L.G., Jr. et al (1996b) GeoL Soc. Amer. Absts. with Progs., Medark, L.G., Jr. et aL (1996b) GeoL SOC.h e r . Absts. with hogs.,v.v.28, 28,A-376. A-376. Nesbitt, Young, G.M. Nesbitt,11W. HW.&&Young G.M(1984) (1984)Geochini. G e o c hCosmochim. C o s m o c h Acta, Acta,v.v.48, 48,1523-1534 1523-1534 Rainbird v.v.98, 801-822. Rainbirdet et al. aL (1990) (1990) Jour. (led, (301, 98,801-822. . 43rdILSG, LSG,1997, 1997,p.p.22 43rd 40 �RESULTS OF MODERN A ALLUVIUM SAMPLING FOR KINIBERLITE L L U W M SAMPLING KIMBEJCLKTE INDJCATOR INDICATOR MINERALS, LAKEREGION, REGION, AND ANDTEIE THE JMPLICATION IMPLICATION FOR MINEMLS, WAWA-KTh4NIWABI WAWA-KINNIWABI LAKE FOR NORTHEASTERN ONTARIO. KIMBERLITE EXPLORATION, EXPLORATION, NORTEEASTERN ONTARTO. T.F. Morris, Ontario Survey, 933 933 Ramsey Ramsey Lake Lake Road, Road, Sudbury, Sudbury, Ontario, Ontario Geological Geological Survey, Ontario, Canada. P3E P3E 6115. 6B5. Quaternary till sampling samplingover overthe the Mlchipicoten Michipicoten greenstone greenstone belt, north and northeast Quaternary mapping and till northeast of Waw* Wawa, were i~tiated initiated in in 1990 1990 and and completed completed in in 1991. Following Following the discovery discovew of of diamonds in - the modem huvium alluvium by byaaprospector prospector in in 1993; 1993,the the Ontario Ontario Geological Survey conduAed conducted a modem modern alluvium sampling samplingprogram programin in 1994. 1994. The The area area sampled sampled included included the the region regionoriginally originally mapped in in 1990 1990 and 1991. At Atthe thesame sametime, time, Quaternary Quatemavmapping, mapping,modem modernalluvium alluviumsampling samplingand andtill till sampling were completed in the the Michipicoten Michipicoten River valley, south south of of Wawa. Wawa. the release release of of data data in in 1994, 1994, aa small smalldiamond diamondrelated related staking stakingrush rushoccurred. occurred. The The Following the distribution of kimberlite indicator indicatorminerals mineralssuggested suggested aa relationship relationship to to a northeast structural structural collected over over only aa part part of this structure during the the 1994 trend. As Asmodem modem alluvium alluvium was collected survey, the Ontario Ontario Geological Survey initiated a second second modem modemalluvium alluviumand andtill till sampling sampling Lake area, area, east east of of Wawa, in 1996. program in the Kirmiwabi Kinniwabi Lake 1996. indicator minerals mineralsrecovered recoveredinclude: include: 1) 1) chrome chrome pyrope pyrope garnetq.2) garnets; 2) chromite; 3) Kimberlite indicator magnesium-rich ilmenites chrome pyrope magnesium-rich ilmenitesand andchrome chromediopsides. diopsides.To Todate, date,aatotal totalofof 77 'GlO" "010" chrome chrome pyrope garnets, 60 60 "(39" "G9" chrome pyope garnets, 3 high chrome chrome chromites, 217 217 low low chrome chrome chromites, 292 ilmenitesand and3318 chromediopsides diopsideshave havebeen beenrecovered. recovered. The distribution 292 magnesium-rich magnesium-rich ilmenites 18 chrome and relative concentration of these these heavy minerals minerals clearly clearly illustrates illustrates aa correlation correlation with with northeastnortheasttrending regional fiiults fiults associated associated with withthe theKapuskasing Kapuskasing Stmctural StructuralZone. Zone. In In particular, a number trendiig regional of sample sites along the the fault controlled controlled Shikwamkwa River valley and and the the Shikwamkwa Lake Lake basin yielded yielded significant significantnumbers numbersand andtypes types of of kimberlite kimberlite indicator indicator minerals. minerals. These Theseminerals mineralsare are similar to to recovered recovered in in the the Trout Trout Creek Creek drainage drainage system, system, located along strike to the southwest, southwest, Dalton, situated situated along along strike striketo tothe the northeast. northeast. This and at Dalton, This may may suggest suggest that faults faults within the Kapuskasing Structural Zone, kom from Wawa Wawa to to the James Bay Lowland, could represent represent promising kimberlite kimberlite exploration exploration targets. targets. 41 �This page pageleft left blank blank intentionally. intentionally. This 42 �TIlE HEMILO GOLDDEPOSIT: DEPOSIT: IT MAY BE GOLD BUT IT'S NOT THE HEMLO GOLD NOT BLACK AND WHITE WHITE Ontario Geological Survey, Sudbury, Ontario, Ontario, P3E P3E 6B5. 6B.5. Muir, Tom L., Ontario Over 15 years have passed since the the "discove@' "discovery"of of the Hemlo gold deposit. A Aplethora plethoraof ofideas ideas as to its origin has has emaged. emerged. The diversity of interpretations, all drawing upon some type of The of interpretations, type of hydrothermal alteration system, reflects the complex geological history history of of the area, area, including including the the deposit. The interpretations regarding the deposit must be Theimplications implications for observations observations and interpretations integrated with an overall assessment of of events. events. The The establishment establishment of of fundamental hndamental relationships is paramount paramount to to developing an an appropriate appropriate depositional model and among geological events is ultimately a reliable exploration strategy. strategy. The deposit deposit currently currently lies within one of several high strain zones, largely at or or near near the the hanginghangingS-shaped, E2 F2fold. fold. The km amplitude, s-shaped, The ore ore overall overall transgresses transgresses wall side of the south south limb limb of of a 2.5 Ian units. In Inthe thewestern western part partof ofthe thedeposit, deposit, ore oreoccurs occurslargely largelyas as several several east-striking, east-striking, low-grade low-grade within massive massive (subvolcanic) (subvolcanic)and andfbgmental, fragmental,felsic, felsic,quartz-plagioclase-phyric quartz-plagioclase-phyricrocks. rocks. In In the the zones within central and eastern parts it occurs occurs mostly as 11 to 2 large, tabular, east-southeast-striking, east-southeast-striking,higher higher grade zones grade zones within within highly highly feldspathized feldspathized rocks. rocks. fundamental relationships relationships ffom from this thiswork work are are that that mineralization and alteration: 1) currently currently The hndamental are largely structurally 3) predate predate felsic to stmcturally controlled; 2) post-date regional-scale regional-scale (D2) (DJ folding; 3) intrusions (plutons (plutons and and dikes); dikes);4) 4)predate, predate, or or are are synchronous with, with, the development intermediate intmsions D2 high-strain zones; 5) 1)3ductile ductile and and brittle-ductile brittle-ductile flattening, which 5) predate predate regional scale D3 of D2 superposed dextral resulted in superposed dextral shear shear constrained constmined to to zones zonesof ofexisting existinghigh high strain strainand/or and/orfissile fissile rocks; rock, and 6) 6 ) predate predate regional regional metamorphism. By By inference, s e r e n e , the the mesoscopic mesoscopicand and microscopic microscopic features represent modiied modified primary primaryfeatures features and andthe the current current setting of of features which we presently observe mpresent the deposit does not accurately reflect the the original originaldeposit deposit characteristics. characteristics. The role of superposed superposed alteration and remobilization deposit-related metals is considered to have remobiiiition of deposit-related have been been generally generally underrated. The Therearrangement rearrangement of of primary primary characteristics impedes impedesaa simple simple reconstruction reconstruction of of the the mineralization/alteration events. mineralizatiodalteration events. Syngenetic and skarn models do not Syngenetic not account accountsufficiently sufficientlyfor for the the observed observedfield fieldrelationships. relationships. However, simple porphyry and shear-zone-hosted shear-zone-hosted models, models, as as presented, have notable shortcomings. Problems the deposit deposit to the origin of the quartzProblems revolve revolve around the relationship of the plagioclase-phyric rocks, rocks, the identification of of superposed alteratiodmineralization alteration/mineralization events, the role of of stmctural structural control and the present distribution initial role distribution of of various various mineral mineral phases phases (e.g., (e.g., muscovite, microcline). microcline). Most of the ambiguity arises from enigmatic relationships resulting Most of the ambiguity arises f?om enigmatic relationships resulting from fiom history of of superposed superposedevents. events. Nevertheless, Nevertheless, the H Hemlo the complex history e d o deposit does not appear to fit a single deposit model. model. Rather from an unexposed porphyry(?) porphyry(?) single classic deposit Rather itit may may be linked to fluids, fkom magma, which were channeled by by existing structural structural weaknesses weaknessesduring duringactive activetectonism. tectonism. 43 �This This page page l left e f t blank blank intentionally. intentionally. 44 �PETROGENESIS PETROGENESISOF OFCIIENGWATANA CHENGWATANA VOLCANICS, MINNESOTA MINNESOTA AND AND WISCONSIN WISCONSIN KarlR., R.,Geology GeologyDepartment, Department, Macalester Macalester College, St. Paul, NAIMAN, Zachary J., WJIRTH, WIRTH, Karl Paul, MN 55105, znaiman@macalester.edu, wirth@macalester.edu znairnan@macalester.edu,wirth@macalester.edu The Chengwatana Chengwatana Volcanics (CV), (CV), aa >3000 >3000 meter meter unit unit of of high high iron iron and and aluminum tholeiitic basalt interflow sediments, 2.0 with interflow sediments,were were erupted erupted south south of the presumed Penokean Penokeansuture suturezone zone(the (thesite siteof of 2.0 Ga southward dipping subduction) and are the southernmost exposed lavas of the 1.1 Ga Midcontinent Ga southward dipping subduction) the southernmostexposed Ga Midcontinent rift (MCR), studying magmatic magmaticprocesses processesalong alongthe the rift rift axis. axis. CV (MCR), making them ideal for studying CV flows flows contain An), clinopyroxene contain primary primary plagioclase plagioclase(—60% (-60% modal An,.), clinopyroxene(—30% (-30% modal modalWo35En45Fs), W o E n 4 F s ) ,and and Fe-Ti oxides modal). The The geochemistry geochemistryof of the the CV CV is is similar similar to to basalts from other eruptive (-8% modal). oxides (—8% centers MCR; the flows are characterized characterized by by low low magnesium magnesium (Mg#= (Mg# = 0.58-0.37), and can centers along along the theMCR; be divided divided into low-Ti02 groups, Volcanics (PLV). into high- and low-TiO, groups, resembling resemblingthe the Portage PortageLake LakeVolcanics (PLV). The TheCV CV are enriched in incompatible elements (TTE) (ITE) similar are enriched incompatibletrace elements similarto toPLV PLV basalts basalts as as well well as as basalts basalts from from the the Powder Mill Group of the Mamainse Point Formation (MPF), but exGroup (PMG), and group 6 flows of hibit more pronounced Nb and and Ta Ta anomalies. anomalies. ITE are negatively correlated with Mg# and are pronounced Nb positively positively correlated correlatedwith withTi02. TiO. Isotopic Isotopiccompositions compositions(ENd (Gfrom from 4fl V.11 to 4.5) -4.5)are arepositively positively correcorreabundances and and ratios ratios (eg. (eg.Y, Y, lated with the Nb anomalies and are negatively correlated with ITE abundances of fractional crystallization (e.g., (e.g., Mg#). Mg#). Petrographic La/Sm), Ti02 LdSm), T i 0 ,, and indices of fractional crystallization Petrographic observations observations coupled with geochemical CV were were derived derived from from an enriched enriched mantle source, coupled geochemical trends suggest that the CV similar and assimilated assimilated continental continental crust while fractional fractional crystallization similar to some some other MCR rocks, and crystallization occurred in in cmstal crustalmagma magma chambers. chambers. occurred Geochemical constraints on the petrogenetic petrogenetic processes processes involved Geochemicalmodeling modeling provides constraints involved in in CV CV genesis and evolution. Mass-balance Mass-balance models' models1demonstrate demonstratethat that the the major major element element trends trendsexhibited exhibited by by the CV CV flows flows can can be be accounted accounted for by 5-50% crystallization of varying varying proportions proportions of of olivine olivine(0(06%), clinopyroxene(0-15%), (0-15%),magnetite magnetite(0-5%), (0-5%),and and ilmenite ilmenite (0-5%). (0-5%). Al6%), plagioclase (5-20%), (5-20%), clinopyroxene though section, geophysical though no no olivine olivineis is observed observed in thin section, geophysicalstudies studiesof of the theMCR2 MCR2suggest suggest the the presence presence crust which which might mightbe bemafic maficcumulates. cumulates. Representative of high-velocity layers in the lower crust Representative models illustrated in in Figure Figure 1.1. are illustrated ClosedClosed- (Rayleigh) (Rayleigh)and andopen-system open-system(RFC)3 (RFC)3fractional fractional 3 crystallization crystallizationmodels models(using (usingmineral mineral proportions proportions predicted predicted by the mass-balance mass-balance equations equations and and from from petrographic petrographic analysis) successfully successfullymodel model the the enrichment enrichment of of some some trace trace analysis) elements (e.g., but fail fail to to model model highly $ elements (e.g., Zr, Zr, Hf, Y; Y;Fig. 2a), but incompatible trace elements and ratios (e.g., La/Sm, incompatible trace elements and ratios (e.g., LaISm, ZrlZr/X' 22 Nb; Nb;Fig. 2b,c). 0 fr< 5.1%0l Models of combined combined fractional crystallization and asfractional crystallization 11.9%plag 81%melt Fig. I similation similation have been used to account for the geochemical variation in basalts from various pans of the MCR. Simple variation basalts parts of the MCR Simple i1 0.4 0.5 0.6 03I 0.4 0.6 mixing models models between between CV CV and and average average Archean granumixing lite do do not not accurately accurately predict predict trace trace element element compositions compositions of CV flows, flows, but but Nd Nd isotopic isotopic compositions constrain the amount of cmstal crustal component in the CV to Combined assimilation assimilation and and fractional fractional crystallicrystallito <30%. <30%. Combined crustal compositions compositions zation (AFC) model? models4with with 15% 15%and and 30% crustal assimilation assimilation of a variety of crustal ; . 0 " 45 �250 I • I I I Alt (rO.I5) 200 - N 150 — Alt ( r03O) ;RFc(.cycles) F=0.95 S Fig. 2a AFC (-0.30) a 3 • •• • 85 (ID = 095 1P=0.95 41015 Ct — ,. A(r0.I5. 0.8 0.7 'Rayltith 20 XI RFC (# cycles) G cycles) 4 2 .0 iS .1 •• .. • z N 10 - •• . • •*• • .1 • .1 . 0 I I 20 I II I $ is RFC(# RFâ C cycles) Net) 5 25 2s Fig.2b Fig. 2b (lower, upper, upper, and and bulk bulk crust; ernst; granulite; shale) suc(lower, cessfully predict N4 E N and and most trace element element abunabundances of of enriched enriched CV CVflows flows (Fig. (Fig. 2a,b). 2a,b). AFC modpredict the the low Nb (high Zr/Nb, Fig. Fig. 2c). 2c). els do not predict The low Nb concentrations can be explained by by (1) assimilation of a crustal components with assimilation of with exextremely low concentrations concentrations of of Nb Nb relative to ITE, (2) (2) derived from from lithospheric lithospheric mantle melts derived mantle that that was was varivariin Nb Nbrelative relative to to other other ITE, ITE, or (3) melts melts ably depleted in asthenospheric mantle which which had incomincomderived from asthenospheric patible elements, elements, but butlittle littleNb, Nb, added added during during chemichemical interaction with lithospheric lithospheric mantle.5 Lithoscal pheric mantle could could have have become become enriched in incompatible elements elements (relative (relative to to Nb) Nb) by metasomatism metasomatism related to Penokean Penokean subduction. subduction. An An enriched enrichedmanUel mantle1 lithospheric mantle source source for for MCR rocks has lithospheric mantle has been been proposed for volcanics volcanics from from the early stages stages of riftrifting, including flows from from the the MPF MPFand andthe thePMG.678 PMG.6"x A modified mantle source has also modified lithospheric mantle also been proposed for the Portage Lake Volcanics.9'° volcanic^?^^^ Geochemicalmodels modelsindicate indicate that that a variety of Geochemical petrogenetic processes, processes, including including derivation derivation from mulpmgenetic mantle sources, sources, crustal crustal assimilation, and fractiple mantle tional crystallization, crystallization,operated operated to to produce the trace tional element and isotopic isotopic variations variations exhibited exhibitedby bythe theCV. CV. Fig.2c Fig. 2c II 40 30 40 Y (ppm) y(PP~) I I 0 50 50 0.95 -2 References References F = 0.35 (1) Bryan, Finger, L.W., Chayes, F., Bryan,W.B., W.B.,Finger, L.W.,and andChayes, F., 1969, 1969, Science 926-927. (2) Allen, D.J., Science 163, 163.926-927. (2)Allen. D.J.. Braile, Braile. L.W., L.W.. Hint, WJ., Mariano, J., Hinze. WJ..and &d~ariano, J.,1995, 1995,Continental continentiRifts: ~ifts: Evolution, Structure, Tectonics, 375-407. (3) O'Hara, Evolution, Structure,Tectonics, M.J., 1977, 503-507. (4) M.J., 1977, Nature, 266, 266,503-507. (4)DePaolo, DePaolo,D.J., D.J., 1981, Earth Earth Planet. Planet. Sci. Len., 53, 189-202. Lett., 53, 189-202. (5) (5) . -4 4 -6 -6 AFC(d.15) F = 02% AFC(r.3) AX (d.3) t 0 55 Fig. Fig. 3 1 10 10 Patchet, 1993, Patchet, P.J., RJ., Lehnert, M.R., M.R., and Sieber, Sieber, G., 0., 1993, Th Th ( PmP ~ Journal of Petrology, Petrology, 35, 35, 1095-1125. 1095-1125. (6) Shirey, Shirey, Steven B, Klewin, Kenneth Kenneth W., W., Berg, Jonathan H., H., W., 1994, Geochimica et et Cosmochimica CosmochitnicaActa, Acta,58,4475-44906. 58, 4475-44906. (7) Klewin, and Carison, Carbon, Richard W., Klewin, K.W., K.W., and and Berg, Berg, J.H., 1991, Journal of Geophysical Geophysical Research, 96,457-474. 96,457-474. (8) J.H., (8)Miller, Miller,J.D., J.D., and and Vervoort, J.D.. J.D., 1996, 1996,Institute Instituteon onLake Lake Superior Geology, 33-35. (9) GeochimicaetetCosmochimica CosmochimicaActa, Acta,53,2023-2035. 53, 2023-2035. (tO) Superior (9) Paces, J.B., J.B., and Bell, K., 1989, Geochimica (10) Nicholson, S.W., S.W., and Shirey, S.B., S.B., 1990, 1990, Journal of Geophysical Research, 95, 10,851-10,868. 10,851-10.868. 46 �CORRELATIVE SEQUENCES SEQUENCESWITHIN WItHIN THE MARQUETtE (MICHIGAN)AND AND THE THE MARQUETTERANGE RANGE SUPERGROUP SUPERGROUP (MICHIGAN) I-IURONIAN SUPERGROUP (ONTARIO): GLAaOGENICS, PALEOSOLS, AND ORTHOQUARTZ1ES HURONIAN SUPERGROUP (ONTARIO): GLAdOGENICS, PALEOSOLS, AND ORTHOQUARTZFTES - Ojakangas, Richard W W., Geology, University Universityof of Minnesota - Duluth Duluth ,. Department Department of Geology, Duluth, Minnesota 55812 55812 In the the Early of the Upper Peninsula subvertical Early Proterozoic ProterozoicMarquette MarquetteRange Range Supergroup Supergroup of Peninsula ooff Michigan, Michigan, subvertical diamictite and dropstone-beadng units that unconformably overlie Archean basement (the and dropstone-bearing units that unconformably overlie Archean basement (theFern FernCreek Creek Formation of the Iron Mountain area and the Enchantment Lake Formation of the Marquette Trough) Formation of the Iron Mountain area Lake Formation of Marquette Trough) have have been considered glaaogenic glaciogenic and and correlative correlative(Pettijohn, (Pettijohn, 1943; 1943; Gair, Gair, 1981; 1981; Ojakangas, Ojakangas, 1984). 1984). Orthoquartzite units which overlie these two units (the Sturgeon Quartzite and the Mesnard Orthoquartzite units which overlie these two units (the Sturgeon Quartzite and the MesnardQuartzite, Quartzite, respectively) also be be correlative correlative(e.g., (e.g., Morey, Morey,1972; 1972; Young, Young, 1983). 1983). respectively) have have long long been been assumed assumed tto o also Mother basal Archean basement on the the northern Another basalconglomeratic conglomeraticunit unitunconformably unconformably overlying overiying Archean northern CreekFormation) Formation)has hasbeen beeninterpreted Interpretedinindifferent different ways. ways. A edge of the the Marquette MarquetteTrough Trough (the (the Reany Reany Creek glacial origin origin has hasbeen beenclaimed daimedby byPuffett Puffett (1 (1960), Gair(1 (1981) Ojakangas(1(1984), but Mattson 960), Gair 981) and Ojakangas 984). but Mattson and glacial Cambray(1 (1983) without the Cambray 983) a,ued arguedfor fora amass-flow mass-flowmechanism mechanism of deposition without the lnwAvement involvement of of glaciers. glaciers. age was was proposed proposedby bySmall Smalland andBomhorst Bomhorst(1988). (1988).Sims Sims(1991) (1991) Interpreted Interpreted the A possible Archean age the Reany Creek Creekas as an an Archean Archean strike-slip strike-slip basin basinfill fill along along aa major major fault. fault. Reany The Reany Creek, Creek,which whichtops topssouth, south,isisshown shownonongeologic geologicmaps mapsas asbeing beingininfault fault contact contact with both MchigammeSlate Slate(Formation) (Formation)and andwith withsheared shearedrhyolite rhyolitetuff tuff of both the the overlying overiyingEarly Early Proterozoic Proterozoic Mchigamme the Archean Mona Schist. However, recent field work has verified an observation by Puffett (1974, Archean Schist. However, recent field work has verified an observation by Puffett (1974, p. 23) that a quartzite mapped Creekmight mightsomeday somedaybe beproven provent to belong tto that a quartzite mappedas asuppermost uppermostReany Reany Creek o belong oa I contend that this unnamed quartzite is a remnant of a faulted-out overlying different formation. that unnamed quartzite is a remnant of a faulted-out formation. quartzite unit unitthat thatisiscorrelative correlativewith withthe theSturgeon Sturgeonand andMesnard MesnardQuartzites. Quartzites. Creek Formation Formationisisoverlain overlainbybythe theSturgeon SturgeonQuartzite. Quartzite.AA two-meter two-meter thickness of The Fern Creek of just beneath the Sturgeon Quartzite and it it was. suggested by Trow was suggested sericite schist is is exposed exposed locally just Sturgeon Quartzite (1948) that ititrepresents Creek. A similar sericite schist is Interbedded (1948) representsaazone zone of ofweathered weathered Fern Creek. similar seriate interbedded with quartzite in the uppermost Enchantment Lake Formation near the contact with the overlying Mesnard quartzite in the uppermost Enchantment Lake near the contact with the overlyingMesnard Quartzlte. Similarly, In the upper Reany Creek, sheared sericite schist is Is present present beneath beneath the Quartzite. Similarly, In the upper Reany Creek, sheared seridte schist the unnamed unnamed quartzite units and quartzite unit unitmentioned mentionedabove. above. The Theseticite seriate schists schists between between the three glaclogenic gladogenic units and the the overlying quartzites are herein interpreted tto (i.e., e., paleosol paleosd or reworked reworked paleosol) paleosol) overiying o be be metaregolith metaregdith (I. units. The overlying oveilying quartzites quartzites are areinterpreted interpreted tto products of formed upon the glaciogenic gladogenic units. o be products of the the cover of of glaciogenic glaciogenicmaterial material (i(i.e., the paleosol) that erosion and reworking of a deeply weathered weathered cover .e., the thatwas was The tripartite tripartite sequence present on the the Early EarlyProterozoic Proterozoic land land surface. surface. The sequence of glaciogenic glactogenic rock, paleosol, paleosol, and quartzite thus interpreted interpreted as erosional remnants of quartzite ininthree threeareas areasof ofthe theUpper UpperPeninsula Peninsula of Michigan Michigan isis thus what was and likely likely continuous continuoussequence. sequence.This Thissimilarity similarityin in lithology, lithology, stratigraphy, stratigraphy, was once aa widespread widespread and and interpreted evidence that that the as strong strong circumstantial evidence the three threesequences sequences are are interpreted history historyisisherein herein cited cited as indeed correlative. correlative. The Huronian Supergroup Supergroup200 200 km tto the east o the east in in Ontario Ontario contains contains three threeglaciogenic glaciogenicunits—the units-the Ramsay Lake,the the Bruce, Bruce, and andthe the Gowganda GowgandaFormations Formations(e.g., (e.g.,Young, Young,1981a, 19813,1981b). 1981 b). The The uppermost, uppermost, Ramsay Lake, been units(e.g., (e.g.,Puffett, Puffett, 1969; 1969; Young, Young,1970, 1970, 1983; 1983; the Goanda, Gowganda,has has beencon-elated correlated with with the the Michigan Michigan units Ojakangas, 1988). Description Formation that that oveilies Ojakangas, 1988). Descriptionof ofan aninterpreted interpretedpaleosol paleosol within the the 10.-rain Lorrain Formation overlies the the Is in In preparation preparation by Mamio,and and R.R.Ojakangas; Ojakangas;this thispaleosol paleosol is Is being being Interpreted by K. K. Card, Card, .1. J. Manno, Interpreted Gowganda is as con-elative with those in (1983) correlative with in Michigan. Michigan. Young Young (1 983) emphasIzed emphasized that thatthe theMichigan Michigansequences sequences of of glaciogenic rock, quartzite, and (e.g., Kona Kona Dolomite) Dolomite) can can be be correlated correlated with glaaogenic and overlying dolomite (e.g., with the the Ontario Lonain, and and Gordon GordonLake LakeFormations. Formations. Recent RecentCCIsotope Isotope studies studies have Ontario sequence sequence of of Gowganda, Gowganda, Lonain, also been used as evidence Sdence for forcon-elation correlationof ofcarbonate carbonateunits unitsin inthe thedescribed describedsequences sequencesas as well well as as correlation with with Early Early Proterozoic Proterozoiccarbonate carbonate units 'oming (Bekker (Bekkeret et alal., 1996). Correlation correlation units in in Wyoming ., 1996). Correlation with with was proposed proposed earlier earlier (Marmo (Mamlo and similar Early Proterozoic Proterozoicsequences sequences in in Finland Finland and Russia Russia was andOjakangas, Ojakangas, 1984; 1984; Ojakangas, Ojakangas, 1985, 1985, 1988) 1988)and andthe thepossible possibleexistence existence of of an an Early Early Proterozoic Proterozoic supercontinent supercontinenthas has proposed (Ojakangas et al., been proposed (Ojakangas et at., 1991). The correlation Supergroupwith withthe thelower lowerpart part of of the correlation of of the the upper upper part part of of the the Huronian Huronian Supergroup the Marquette Range Supergroup Supergroupisissteadily steadilybeing beingstrengthened strengthenedininspite spiteofofthe the lack lackof of radiometric radiometric dates dates in in Marquette the the Marquette MarquetteRange RangeSupergroup. Supergroup. 47 �______ ______ ______ REFERENCES REFERENCES Bekker, A, A., Karhu, Karhu,J.,J.,and andBennett. Bennett,G.G., 1996, Lomagundi Lomagundievent eventin in North NorthAmerica: America: Application for , 1996, Bekker, stratigraphic correlation correlation (ethsj: (Abs,): Geological Geological Society Society of ofAmerica America Program Program and and Abstracts, Abstracts, Denver, CO. CO. Gair, 1981, Lower Proterozoic glacial glacial deposits deposits of of northern Michigan, Michigan,U.S.A.. U.S.A.:jaHambrey, jHambrey, M.J. Gair, J.1. . E.,E.,1981, MJ. and Harland, Hariand, W.B., W.B., (eds.), (eds.), Earth's Earth's PrePre- Pleistocene PleistoceneGlacial Glaaal Record, Record, Cambridge Cambridge University University Press, p. Press, p. 803-806. Marmo, J.S., Ojakangas, 1984, 1 984, Lower Lower Proterozoic Proterozoic glaaogenic glaciogenic deposits, deposits, eastern Marmo, J. S., and Ojakangas, eastern Finland: Finland: GeologicalSociety Societyof of America AmericaBulletin Bulletinv.v.95, 95, p. p. 1055-1062. Geological Cambray,FF. W., 1983, The The Reany ReanyCreek CreekFormation: Formation:aa mass-flow mass-flow deposit deposit of R. and Cambray, . W ., 1983, Mattson, S. S. R. possible post-Menominee post-Menominee age age (Abs.): (Abs.): Proceedings Proceedingsand andAbstracts, Abstracts,29th 29th Institute Institute on onLake Lake Superior Geology, Houghton, MI, Ml, p. p. 27. Geology, Hwghton, Morey, geologic setting: setting: jg Morey, 6. G 8., B., 1972, 1972,Middle MiddlePrecambrian: Precambrian: General General geologic inSims, Sirns, P.K. P.K. and andMorey, Morey, G.B. GB. (eds.), Geology Survey, p p.. 199-217. (eds.). Gedogy of Minnesota: Minnesota: AA Centennial Centennial Volume. Volume. Minnesota MinnesotaGeological Geological Survey, Ojakangas, R R. W., 1984, Basal Ojakangas, . W ., 1984, Basal Lower Lower Proterozoic Proterozoic glaciogenic glaaogenic formations, formations, Marquette MarquetteRange Range Supeigroup, Upper tipper Peninsula, Michigan(Abs.): (Abs.): Proceedings Proceedingsand andAbstracts, Abstracts, 30th 30th Annual Supergroup, Peninsula, Michigan Institute on WI, p. 43. 43. Institute onLake LakeSuperior SuperiorGeology, Gedogy, Wausau, Wausau, Wl , p. for Early Early Proterozoic Proterozoicglaaation: glaciation: the the dropstone unitdiarnictite unit-diamictite association: -1985, 1985, Evidence Evidence for association: Geological Survey Surveyof of Finland, Finland,Bulletin Bulletin331, 331, p. p. 51-72. 51-72. Geological __1 Glaciation: An An uncommon "mega-event" -1 988,988, Glaciation: uncommon "mega-event"asasaakey keytot ointracontinental intracontinentaland andintercontinental intercontinental correlation of Early basin fill, fill, North American and Baltic Baltic cratons: cratons: in in Kleinspehn, Kleinspehn, Early Proterozoic basin American and K.L. and Paola, C., (eds.), (eds.), New 1-444. New Perspectives Perspectives in in Basin Basin Analysis, Analysis, Springer-Verlag, Springer-Verlag, p. 43 431-444. K.L. Paola, C., Ojakangas, R.W., 1 991, Early Early Proterozoic Proterozoicglaciogenic glaciogenicdeposits: deposits: A R.W., Heiskanen, K.l., K.I., and and Marmo, Marmo, J.S., J.S., 1991, connection?j Ojakangas, North America-Baltic America-Baltic connection?& Ojakangas,R. R. W., W., (ed.), (ed.), Precambrian Precambrian Geology of the the Shield and and the the Eastern Southern Canadian Shield Eastern Baltic Baltic Shield, Shield, Minnesota Minnesota Geological Survey Survey Circular 34, 34, p. p. 83-91. Information Circular Pettijohn, F. F. J., J., 1943, 1943,Basal BasalHuronian Huronian conglomerates conglomerates of MenoMnee Menomineeand and Calumet Calumet districts, districts, MIchigan: Michigan: Pettijohn, Journal of of Geology, 51, p. Geology, v.v. 51, p. 387-397. Puffett, W. W. P., P., 1969, 1969,The TheReany ReanyCreek Creek Formation, Formation, Marquette MarquetteCounty, County, Michigan: Michigan: U.S. U.S. Geological Survey Survey Bulletin 1274-F, 1274-1, 25 p. Bulletin 1 974, Geology of of the Negaunee Quadrangle, Marquette Marquette County, Michigan: , 1974, Negaunee Quadrangle, Michigan: U.S. U.S. Geological Geological Professional Paper Paper788, 788, 53 p. Survey Professional Sims, P.K., for Archean Sirns, P. K., 1991, Great Great Lakes Lakes Tectonic Tectonic Zone Zone in in Marquette Marquettearea, area, Michigan—Implications Michigan-Implications for U.S. Geological GeologicalSurvey SurveyBulletin Bulletin 1904-E, 1 904-E, 17 17 p. tectonics in in North-Central North-Central United United States: U.S. 1 988 The The Reany Reany Creek Creek Formation, Formation, Northern Northern Marquette Marquette County, Small, JJ.R., and Bomhorst, 1. J., 1988 County, T. J., Small, .R., and Michigan:Archean ArcheanororProterozoic? Proterozoic?(Abs.) (Abs.):: Proceedings Proceedingsand andAbstracts, Abstracts,34th 34th Annual Annual Institute Michigan: on Lake Lake Superior Superior Geology, Geology, Marquette, Marquette, Ml, MI, p. p. 104105. 104-105. Trow, J.W., J.W., 1948, The The Sturgeon Sturgeon Quartzite of of the theMenominee Menominee district, district, Michigan: Michigan: Unpublished UnpublishedPh.D. Ph.D. Thesis, Thesis, University of of Chicago. Chicago. Young, G. 6. M., M., 1970, 1970, An An extensive extensive early early Proterozoic Proterozoic glaciation glaaation in in North NorthAmerica?: America?: Palaeogeography, Palaeogeography, Young, Palaeoclimatology, p. 85-101. 85-1 01. Palaeodirnatology, Palaeoecology, Palaeoecology, v. v. 7, p. 1981 a, The The early early Proterozoic ProterozoicGowganda GowgandaFormation, Formation,Ontario, Ontario,Canada: Canada:inj Hambrey, , 1981a, Hambrey, MJ., MJ., and and Hartand, W. B. (eds.), Record, Cambridge CambridgeUniversity University Press, Press, p. p. Harland, W . B. (eds.), Earths Earths Pre-Pleistocene Pre-Pleistocene Glacial Glaaal Record. 807-812. 807-81 2. 1981 b,b, Diarnictites Diamictites of of the Lake and and B Bruce Formations,north north shore shore -, 1981 the early eariy Proterozoic Proterozoic Ramsay Ramsay Lake N C ~Formations, in Hambrey, M.J. M.J. and and Hariand, Hailand, W W.B., (eds.), Earth's of Lake Lake Huron, Huron, Ontario, Ontario, Canada: Canada: in .B., (eds.), Earth's PrePreGlacial Record, Record,Cambridge CambridgeUniversity UniversityPress, Press,p.p. 790-794. 790-794. Pleistocene Glacial 1983, Tectono-sedimentary of Early Early Proterozoic rocks of the the northern northern Tectono-sedimentary history of Medaris,LL.G., Jr.(ed.), (ed.), Early EarlyProterozoic ProterozoicGedogy Geologyof of the the Great Lakes in Medaris, Great Lakes region: jn .G., Jr. Region, GeologicalSociety Societyof of America America Memoir Memoir 160, 160, p. p. 15-34. Region, Geological 15-34. 48 �Applications for for Archean Archean Gold Gold Exploration: Exploration: Using Using Canadian Canadian Mining Mining Camp Camp GIS Queries to GIS Applications Target Gold Exploration in Minnesota DEAN M. PETERSON Research Lab, Lab, Geology GeologyDepartment, Department, University of of Minnesota Minnesota - Duluth, Duluth, Economic Volcanology Research Duluth, Minnesota, Minnesota. USA USA 55812 55812 is to to discover discover ore ore mineralization mineralization before before funding is The objective objective of mineral exploration is in the the exploration exploration team. team.Exploration Exploration tends tends to to use use the exhausted or management loses confidence in simplest, cheapest, and lowest risk criteria, criteria, methods, methods, and and ore ore deposit deposit models models available. available. However, However, as as and deposits deposits become becomemore moredifficult difficultto todiscover, discover,exploration exploration risks risks increase, increase, and and the the mining camps mature and to mineral mineral exploration exploration increases. increases. In In this this case, case, the the exploration exploration amount of data potentially applicable to enhanced exploration methods and ore deposit models, that incorporate geologist must use enhanced incorporateadditional additional data, to continue to discover new ore deposits. data, continue to discover new ore explorationgeologist. geologist.This This Today, vast quantities of geological information are available to the exploration information includes field notes and measurements, geological maps, drill hole data, data, geochemical geochemicaldata, data, geophysical survey data, remote sensing data, data, and and geologic geologic literature. literature.Geologists Geologists must must integrate integrate vast vast quantities of data covering large areas in order to determine the best criteria for effective mineral quantities data covering in order to determine the best criteria for effective exploration. exploration. Currently, Currently, the the best best method to integrate integrate large data sets sets is to store store all all geologic geologicinformation informationinto into a Geographic overlays of (- <10km2), <10km2),simple light-table overlays GeographicInformation Information System System(GIS). (GIs). For small small areas areas (-. geological, geological, geochemical, geochemical, and geophysical data may be appropriate for interpretation. interpretation. However, However, small small analog data compilations typically do not answer the larger questions dealing with the fundamental compilations dealing with the fundamental controls types of of ore ore deposits. deposits. For Archean mesothennal mesothermal controls on the the formation and spatial location of specific types gold deposits, fundamental mineral exploration questions include: Which greenstone greenstone belt should should be be explored? explored? in the the greenstone greenstone belt beltshould shouldexploration explorationbe beconcentrated? concentrated? Where in What are are the best best criteria criteriafor for target target selection selection in inthe theconcentrated concentratedexploration exploration area? area? Geologic GIS format for the Hemlo, Timmins, Geologic compilations compilationshave been converted into GIs Timmins, and and Kirkland Lake Cadillac-Bousquet-Malarctic Lake gold camps of Ontario. An additional GIS data set from the Cadillac-Bouquet-Malarctic completion. The TheGIS GISdata dataincludes includesgeology, geology,1" ,l 2ndand gold camp in Quebec is near completion. and3r4 3"' order order shear shear zones zones (Figure (Figure 1), I), faults, faults, alteration, alteration, gold mines, gold occurrences, ore zones, and quartz-gold veins. veins. These TheseGIS GIs data 015 data set covering covering 6000 of northeastern Minnesota. The data sets sets are are being compared to a similar GIS 6000km2 km2of goal of the study of northeastern northeastern Minnesota Minnesota that that have have geological geological features features similar to to study is to highlight areas of present within those present within the the gold gold camps camps of of Canada. Canada. A series exploration models have series of Archean Archean mesothermal gold deposit exploration have been been developed developedfrom from 015 data data sets. sets. The The models models are are based based on on unique unique queries queries and spatial analyzes of the Canadian gold camp GIS analyzes that define define the the location location of of the the major major gold gold deposits deposits in analyzes of structural structural and lithological attributes that these < 1% 1% of the total area area of the the analog analogmining mining these mining mining camps. One One set of unique queries that defines < camps but hosts > > 90% 90% of all all gold mined is given below (Figure (Figure 2). 2). 2 1) Select Select compressional compressionaljog jogsegments segmentsofofI"1 Order Order shear shear zones zones(Figure (Figure lIa) a) Create aa 6-kilometer Order shear 22)) Create 6-kilometerbuffer around the selected F" Is Order 3) Intersect all 3) all data datalayers layerswith withthe the 1" I" Order Ordershear shearzone zone buffer 4) buffer, select select2"' 2" Order Riedel Riedel PP shears shears (Figure lb,c) Ib.c) 4 ) Within the buffer, 5) Order shears shears 5) Create Createaa 200-meter 200-meterbuffer buffer around around the the selected 2"" 2ndOrder 6) P-shear buffer 6)Intersect all all data datalayers layerswith withthe the 2"" 2"' Order P-shear 49 �Within the GIS environment, the outcome of these queries would would be a new subset of geological aspects of the original data data that incorporates all aspects data into a much smaller area. The geologist must now structural, lithological, geochemical, alteration data to target exploration use detailed structural, geochemical, geophysical, and alteration exploration programs in in these high potential areas. The Hollinger-McIntyre Hollinger-Mclntyre and Dome mines of the Timrnins Timmins camp; programs Kirkland lake lake gold the Ken Addison, Upper Canada, and the Kirkland Lake Main Main Break Break mines nines of the Kirkland camp; and and all all of of the the Hemlo gold gold mines are are defined defined by by the the simple queries queries listed listed above. above. Similar Similar queries are being applied to the Minnesota GIS to outline areas with high potential for hosting large Archean Archean gold deposits. deposits. 1st I Order Shear Zone Segment Classification " Order S h e a r Zone Classification Compressional Jog Compressional / A Extensional Jog Jog 7 A 2'"Order 2 '" Order Shear Shear Zones Zones (Riedel Shear Shear Arrays) (Riedel Arrays) CIS CIS Classification of of 2'td 2"i Order Shear Zones Zones zOrder Shears. Figure Figure 1. 1. A) Classification Classification of of 1" l order ordershear shearzone zonesegments segments B) 2nd ordershear shear zone zoneclassification classification based based on Riedel shear shear arrays 2* order arrays 2ndorder order shear shear zone zone classification classification C) GIS methodology for 2°' —R (8.6) —R'(2.3) P(98.6)— FIgure Figure 2. 2. Coffelation of mined gold and and 2" Correlation 2* order ordershear shearzone zoneclassification classification for for the the Timmins, Timmins, Kirkland Lake and Hemlo Gold Camps. Values in millions of ounces of gold. Values ounces of gold. 50 50 �RE—os,SM-ND, SM-ND, AND ANDPB PB ISOTOPIC ISOTOPICCONSTRAINTS CONSTRAINTSON ONMANTLE MANTLEAND AND CRUSTAL CoNTlunuTroNs TO RE-OS, CRUSTAL CONTRIBUTIONS MAGMATIC SULFIDE DULUTH COMPLEX. MAGMATIC SULPIDEMINERALIZATION MINERALIZATION IN THE DULUTH COMPLEX. Edward Ripley, Department Department of Geological Geological Sciences, Sciences, Indiana Indiana University, University, Bloomington, Bloomington, Edward M. Ripley, 47405; David IN 47405; David D. Lambert and Louise Louise R. Frick, Victorian Institute Institute of Earth Earth and and Departmentof ofEarth EarthSciences, Sciences,Monash MonashUniversity, Universy, Clayton, Planetary Sciences, Department Clayton, VIC 3168, 3168, Australia Australia Previous Previous petrologic petrologic and and stable stable isotopic isotopic studies studies of of sulfide sulfide mineralization mineralization in in the the Duluth Duluth Complex Complex have have led led to to the the premise premise that that sulfide sulfide genesis genesis is is strongly strongly linked to the the interaction interaction between between mantle-derived country rocks rocks in in aa rift riftzone zoneenvironment. environment. In order to mantlederived magmas and sedimentary country more fully evaluate evaluate the nature nature of this interaction, and to gain an insight insight into the possible possible importance of externally-derived externally-derived metals in the ore-forming ore-forming process, Pb, Sm-Nd, and and Re-Os Re-0s isotopic studies of the Babbitt Cu-Ni deposit were initiated. Rock-types Rock-types examined examined include include lowlowtroctolite that show evidence for contamination, disseminated sulfide troctolite show very little petrologic evidence disseminated contact with country sulfide-bearing troctolitic troctolitic to gabbroic rocks that occur occur close to the basal contact country metasedimentary xenoliths, and and massive massive sulfide. sulfide. Pb isotopic values of rocks and contain metasedimentary of whole whole rocks, plagioclase mineral separates, and massive sulfides show only subtle differences, differences, and are are contamination of a mantle-derived melt with a Proterozoic Proterozoiccrustal crustal compatible with 3 to 5% contamination cNd (1.1 (1.1 Ga) values of the troctolite and gabbro samples are chondritic, and only contaminant. Nd sulfides show strong the massive sulfides strong evidence for contamination based on Sm-Nd isotopic isotopic values. values. Massive be more more sensitive sensitiveindicators indicatorsof contamination contamination in in the the Sm-Nd Sm-Nd system system Massive sulfides sulfides tend tend to to be (apatite) because of late-stage late-stage incorporation incorporationof of aa light lightrare rareearth earthelement-rich element-richfluid fluidinto intoa aCa-PCI)4 Ca-PO4 (apatite) component ofthe theimmiscible immisciblesulfide sulfideliquid. liquid.Yes y (1.1 component of (1.1 Ga) values are also strongly anomalous, anomalous, and range from -500 to to1300 1300in indisseminated disseminatedsulfide-bearing sulfide-bearing troctolites troctolites and and massive massive sulfides. sulfides. contamination by Proterozoic sedimentary These values are also sedimentary also consistent consistent with from 3 to 5% contamination rocks. Elemental 30 to 60% 60% of the the Pb Pb Elementaland andisotopic isotopicmass massbalance balance calculations calculations suggest suggest that from 30 and 0 Oss in the sulfide mineralization have been been derived derived from from external external sources. sources. A corollary corollary is that other metals may also be in part derived from external sources, which would aid in explaining explaining the the mineralization. Selective compositional diversity of the sulfide mineralization. Selective assimilation of country country rocks by mantle-derived mantle-derived magmas may occur in crustal staging chambers, during ascent to shallower levels, or in situ as a result of devolatilization reactions and partial melting. 51 �T h i s page page left blank intentionally. intentionally. This left blank 52 �The Tectonic, MineralizationHistory Historyof ofthe the Sudbury Sudbury Structure Structure Tectonic, Magmatic and Mineralization Don H. Rousell Rousell and and Harold Harold H. H. Gibson, Gibson, Department Department of of Earth EarthSciences, Sciences,Laurentian LaurentianUniversity, University, Don H. Sudbwy, Ontario Ontario P3E Sudbury, P3E 2C6 The Sudbury Structure major components: components: 1) Structure consists of three major 1) the Sudbury Sudbury Basin; Basin, 2) the Sudbury Igneous Igneous Complex (SIC) which surrounds surrounds the basin as an elliptical collar; collar; and, and, 3) an outer zone of shatter-coned shatter-coned and and brecciated footwall rocks. The area has gained fame as a result of the SIC and the Ni-Cu-PGE ores ores which it hosts, as as well as the proposed proposed meteorite meteoriteimpact impactorigin origin for for the structure structure(Sudbury (Sudbury Event). Event). However, However, the thearea areahas hasundergone undergoneseveral severalsignificant significantArcheanArcheanProterozoic tectonic, magmatic and mineralization events which have been largely overshadowed Proterozoic tectonic, magmatic and mineralization been overshadowed by the Sudbury Sudbury Event. Event. extension and closure, namely a The Sudbury Sudbury area was was shaped shaped by two Wilson cycles of crustal extension Paleoproterozoic cycle and and aa Mesoproterozoic Mesoproterozoic cycle. cycle. The Sudbury Structure was apparently the the Paleoproterozoic site of a triple junction or Thefirst firstcycle, cycle, from from2500 2500tot o1700 1700Ma,, Ma, or hot-spot hot-spot during duringthese thesecycles. cycles.The included the following events: doming (uplift of Levack Levack gneiss complex); complex); NW-SE extension extension Ni-Cu-POE, (Matachewan dikes); N-S to NW-SE rifling rifting (faults, mafic intrusions, sedimentation, N-Cu-PGE, U); diabase,Ni-Cu-PGE, Ni-Cu-POE, Ag, Ag, Co); Co); and, NW-SE closure U ); NW-SE extension extension (Nipissing diabase, closure (Penokean Zn-Cu-Pb). Orogeny, 1900-1700 1900-1700 Ma) with imposed meteorite impact (1850 Ma; Ni-CU-POE, Ni-Cu-PGE, Zn-Cu-Pb). NThe second cycle, from 1700 1700 to 1000 1000 Ma, included: N-S extension (alkali metasomatism, Au); NS extension (homblende Murray fault set); NNE-SSW (hornblende diabase diabase dikes along Murray NNE-SSW extension extension(olivine (olivine diabase dikes); NE-SW extension (Fecunis Lake Lake fault fault set); set); and, and, NW-SE NW-SE closure closure (Grenville Orogeny). Orogeny). The extensive and rich mineralization which which is is characteristic characteristic of of the the Sudbury Structure, Structure,isis related related magmatism. Although Although the the Ni-Cu-PGE Ni-Cu-POE and ZnZnto endogenic endogenic and impact-triggered extension and magmatism. Cu-Pb ore are are located located within within an an impact structure, their age age and tectonic tectonic setting settingisis similar similar to to NiNiCu-POE the world. Geochemical arguments have been Cu-PGE and Zn-Cu-Pb deposits deposits elsewhere elsewhere in the presented which ascribe the origin of of the the SIC SIC and and its its ores ores to to aa melt melt sheet sheet or or to to contaminated mantle-derived magma. The melt sheet origin origin divorces divorces the the SIC and and its its ores ores from their geologic setting setting and pre-impact history, whereas the SIC and its ores are are consistent consistent with with evolutionary, evolutionary, global metallogenic events. Meteorite Meteorite impact impact is is interpreted interpreted as as aa triggering triggering event which focussed ore4orming processes long-lived ore-forming processesatatSudbury. Sudbury.IfIfviewed viewedin inthis thismanner, manner, layered layeredmaflc maficintrusions intrusions immediate host host rocks, rocks,both botholder olderand andyounger youngerthan thanthe the SIC, SIC, warrant warrant farther further and their immediate examination to assess assess their potential for for hosting hosting Ni-Cu-POE Ni-Cu-PGE ores. ores. 53 �This page page left blank intentionally. This left blank 54 �OVERVIEW OF OVEROF THE THE GREGOR GmGOR GOLDFIELDS GOLDFIELDS CORP. COW. MARATHON (WIRE LAKE) GOLD PROPERTY IN THE LAKE) GOLD PROPERTY IN THE HEMLO HEMLO AREA AREA OF OFCENTRAL CENTFLU ONTARIO, CANADA ONTAFUO, John M. Resource Associates Limited and John M. Siriunas, Siriunas,P.Eng., P.Eng,, NR&J NR&J Resource Associates Limited John John Wiebe, Wiebe, President, President, Gregor Gregor Goldfields Goldfields Corp. Corp. Gregor GoldfleldsCorp. Corp.(Gregor) (Gregor)has hasbeen been carrying carrying out out exploration work on Gregor Goldfields portions of of its its 4,000 ha Marathon-area property since since the the ground was first Marathon-area property ground was fist portions that staked in in 1983, 1983,during during the the rush" "rusP thatfollowed followedthe the1981 1981discovery discoveryof ofeconomic economic gold mineralization at ilemlo. There is no record of exploration work gold minerahation at Hemlo. is no rword of eqloration work being being to o that that time. time. Gold Gold mineralization mineralization was was carried out on the Gregor Gregor property prior t first located located on the property property in in1985 1985and andsubsequent subsequentprograms progrms of of diamond diamond drilling have have encountered encountered at at least four zones or areas drilling areas of of mineralization. mineralization. The property area area is is underlain underlainpredominantly predominantlyby bymafic malicvolcanic volcanic rocks; the auriferous auriferous mineralization is associated with zones of intense alteration that occur mineralization associated with zones of intense that occur within within these volcanic rocks. Much Much of of the detailed detailed exploration exploration work, work, especially especially the the volcanic rocks. drilling,has has been beencarried carried out outin in the the central central area of the property in the diamond drilling, vicinity of of Wire vicinity Wire Lake. Lake. The The best bestdiamond-drill diamond-drillintersection intersection of of gold-bearing gold-bearing mineralizationtto date is 7.39 o date 7.39 g Au/t Adt over ovw 3.04 3.04 m while while grab grab samples samples from fiom minerakation surface have returned up to 26.743 gAult. surface returned up ta 26.743 g Auk 55 �This left blank intentionally. This page page left blank intentionally. 56 �PRECIOUS-METAL MINERALIZATION IN COPPER AND PRECIOUS-METAL IN EASTERN SAULT STE. MARIE M A R E MINING MINING D1VISION DMSION WITH THE JENTINA JENTINA STE. WITH FOCUS FOCUS ON THE PROPERTY, ALBANEL AND AND NICHOLAS PROPERTY, ALBANEL NICHOLAS TOWNSHIPS, TOWNSHIPS, DISTRICT DISTRICT OF OF ALGOMA ALGOMA M. Siriunas, Siriunas,P.Eng. P.Eng. and andNeil Neil0.0. Willoughby,NR&J NR&J ResourceAssociates Associates John M. Willoughby, Resource Limited Limited Copper mineralization O n e o , though first &st Copper mineralizationin in the the Huronian Supergroup of of central Ontario, 1846, has importance discovered aatt Bruce Mines in 184S, has histofidly historically been overshadowed in importance deposits of of the copper-nickel copper-nickel deposits of by the ofthe the Sudbury Sudiburyarea, area, the the palmplacer paleoplacer uranium uranium deposits Elliot Elliot Lake Lake and andthe thesilver-arsenide silver-anenidevein veindeposits depositsof of the theCobalt-Gowganda Cobalt-Gowgandaregion. region. Previous have postulated postulated a variety F'revim investigations investigations have variety of origins origins for for the copper copper mineralization present within the the Huronian. H u r o n h . The Theemerging emergingconsensus consensusinineconomic economic geology in general general is that that regional-fault patterns and regional-fault patterns andzones mnesof ofdeformation deformationhave haveplayed played geology in aa major inthe theformation formationof of metallic-mineral metallic-mineraldeposits, deposits,irregardless irregardlessofofgeologic geologicera, era, majorrole rolein and that thatthe therecognition recognitionof of geological geological stactwe can lead leadto to the thediscovery discovery and structure and and alteration alteration can of signi6cant significant economic economicdeposits. deposits.The Thefact factthat that most most researchers researchers consider the the HuronianHuronianM e a n interaction interaction to to be beone oneofofcontinental continentalco]lision-subduction collision-subduction zone zone mechanics mechanics Archean invokes as invokes epithermal epithermal (Cordilleran-type) (Cordilleran-type) and mesothermal mesothermal (Archean-style) (Amhean-style) models models as being being applicable applicable to the the Huronian Huronian Basin. Basin. The Flack Lake Fault is is aa reverse reverse thrust thrust fault faultof of regional regional extent extent that thatisislocated locatedalong along The the the northern northernboundary boundaryof of the the Huronian Hmnian volcano-sedimentary volcano-sedimentary basin. bash. This Thisfault fault was was most most likely likely an an active active normal normal fault during during the the Archean Archean and and was wasre-activated re-activated during during the the Penokean Indications are are that that the thecurvilinear, curdinear,locally l d yeast-west east-westtrending, trending, Penokean Orogeny. Orogeny. Indications Hack Rack Lake Lake Fault FaultSystem Systemhas hasproduced produced considerable considerable ductile ductile shearing shearing and and brittle brittle deformation within within the the nearby nearby host rocks across the HuronianBasin. Basin. deformation the northern northern Huronian Major Major deposits deposits of of structurally-controlled structurally-mntmlled copper copper and and precious-metal precious-metal mineralization mineralization within Proterozoic Proterozoic terranes world in in such suchsettings settings as as within terranes can be found elsewhere in in the world northern northern Australia Australiaand andFennoscandia. Femoscandia. Within the the Huronian HuronianBasin Basinofofcentral centralOntario, Ontdo, the occurrencesare are associated associated with with the the Murray Murray Fault, themost most well-known well-known occurrences Fault, which which parallels pad& and and lies lies to to the the south south of of the Flack Lake Fault. Copper Ccpper mineralization mineralization in in this thisregion region has has been (43,000 tt Cu) Cu) and and the Pater been exploited exploited at at Bruce Bruce Mines (43,000 Pater Mine M h e(36,000 (36,000 ttCu, Cu,140 140kg kg Au, 4,300 of ckpper copper ocmrrenm occurrencesare are known known to to be present present along 4,300 kg kg Ag). A number of alongthe the northern northernmargin marginof of the the Basin Basin in in the the vicinity vicinity of the Flack Rack Lake Lake Fault; Fault; the theBi-Ore Bi-Ore Mine Mine at Cobre Lake produced 700 t Cu during its brief period of production (1948-49). at Cobre Lake produced 700 t Cu during its brief period of production (194849). 57 �The Jentina Property Property of AJ. AJ. Roy Roy of of Sudbury, Sudbury, Ontario, Ontario, is located located in Albanel Albanel and Nicholas Townships straddling the Flack Lake Fault. Several copper and Nicholas Townships straddling the Black Several copper and preciouspreciousmetal showings on the Jentina Property areindicated indicated to be be associated associated with with east-west east-west showings on PruperQ are striking striking shear shear and andfault faultzones zones associated associated with the the main main system systemof of faulting. faulting. The TheNo. No. 11 zone on the the Jentina Jenthia Property, mapping, iiss thought to have Pmperty, as as determined determined from surface mapping, have a strike The h. Thezone zonecomprises comprises quartz-carbonate quartz-carbonate veining veining with with strike length length of of about about11km. extensive albitization, silicification and chloritization chloritization of ofthe the host host Espanola Espanola Formation; silicification and Formation; massive mineralizationisislocally locallypresent. present. The The No. m k v e sulphide (chalcopyrite-bomite) (chalcopyrite-bornite) mineralization No. 22 zone zone is about about 1½ 1%km h in inlength. length. This 'l'his zone zoneincludes includes quartz quartz veining, veining, breccias breccias and and stockworks. Considerable chloritization ebloritizationand and sili&cation silicificationoccur occurwide while albitization albitization is stdcworks. Considerable is limitet limited Scattered h t k r e d pods pods ofofmassive massive chalcopyrite chalcopyrite occur occur within within this this zone zone which which transgresses several lithologies. On the Canamiska section of the claim bloclç a 3 transgresses several Iithologies Canamiska section the claim block, a 3kmIanlong and conductive conductive geophysical geophysicalanomaly anomalyhas has been been drill-tested drill-tested for only long soil geochemical and 75 m of of its its strike strikelength. length. Intersections Intersections of of up up to to1.44% 1.44% Cu Cu over over 19.5' 19.5' (5.9 (5.9 m) m) were were encountered during thatdrill drillprogram pmgram in in1965. 1965. during that Regional studies wwithin NTSSheet Sheet41J 41J have have demonstrated demonstratedthat that the available Regional studies ithin NTS available lake lake sediment geochemistry especiallymagnetics, magnetics, can can be used as as geochemistxy and airborne airborne geophysics, geophysics, especially effective tools toolsto tomap mapgeological geologicalstructures structuresand andbe beused usedtto locateother other areas, areas, similar o locate M a r to to the Jentina, Jentina, that thataxe are favourable favourable targets targets for mineral mineral exploration in the region. 58 �GEOIJXIICMAWINGSYSThM TO BEDROCK G E O L O G I C M A P P (CeM: N G ~A(DIGITAL A ~ : D AH1ROACH I ~ K ~ O GEOLOGIC A ~ MA ~ WNG B D WAHL, T.E., MILLER, J.D., J.D., JR., JIRSA, M.A., M.A., BOERBOOM, BOERBOOM, T.J., T.J., CHANDLER, V.W., WAHL, A.C., Minn. Mimi. Geological Suwev. Survey, 2642 2642 University University Ave., Ave., St. St. Paul. Paul, Mi~nn., Mimi., 55114: 55114; RUNKEL, A.C., D:, Mimi. Mii.Dept. of ~a-&d i i k l s , P.O. Box Box 567, 567, ~ ibbin~, DAHL, D., Natural ~esoukxs, Resources, Div. of M Minerals, Hibbing, Minn., 557M. and SEVERSON, MJ., Natural Natural Resources Eksources Research Institute, Institute. Univ. of Mint, 55746; Minn., 3051 3051 Miller Miller Trunk Tmnk Hwy., Hwy., Duluth, Duluth, Minn., 55811. 55811. Computers geophysical data Computers have have long long been bcen used nsed by geologists geologists to visualize remotely sensed gwphysical data and and manipulate point-source data. data. Increasingly in recent years, Geographic manipulate and image numerical point-source Information System System (GIS) (GIs) software software has been used to produce geologic maps and to archive archive the the raw data however, to make use of the data on on which which the the maps maps are arebased. based. Little has been done, however, exceptional data-management capabilities 015 for evaluating exceptional capabilities of GIs evaluating and sorting sorting geologic, geologic, structural, structural, geochemical, and geophysical creating a geologic map. geochemical, geophysical data, data, activities that must be done before creating the Miinesota Minnesota Geological Survey and other other agencies have developed developed Over the past several several years, the (Geologic Mapping GIS that consists of a graphical graphical user GeMS (Geologic MappingSystem), System), an Arc/Info-based Adhfo-based GIs user interface, image/grid base layers and data structures for storing and manipulating geologic interface,imagdgrid stmctures for storing and manipulating geologic field the capability capability for forgenerating generatingmaps. maps. The The utility utility of of GeMS GeMS as as itit has has been been and analytical data, and the current mapping in the notthwestem northwestern part part of of the the Duluth Duluth Complex Complex will will be be demonstrated applied to current at the the poster poster session. session. ' GeMS GeMS has has three three major major goals: goals: 1. use by by both both the the geologist geologist and and the the potential potential user. user. GeMS I. To make a system easy to use GeMS has has aa menu-driven, menudriven, point-and-click point-anddick interface for data entry, retrieval, manipulation, and imaging. This This reduces the time needed to learn how to use GIs GIS software and and allows allows geologists geologists to to focus on using GIS GIs as an aid in in making making geologic geologic interpretations. intetpretations. the subjective subjective nature nature of of most most 2. To Todevelop developaa flexible flexibledata-base data-base structure that accommodates the nonuniformity of nomenclahm, nomenclature, and and the the unique unique mapping mapping styles styles of of individual individual field data, the nonunifonnity geologists, retrieval and and sorting of of that that diverse and geologists, while while permitting permitting the straightforward straightforwad rettieval descriptive information. descriptive information. 3. To allow rendering prior prior data data bases bases To allowfor forexpansion expansionand and upgrading upgrading of the system without rendering obsolete. GeMS GeMSmay mayalways alwaysremain remainaawork-in-progress, work-in-progress, as as new new users users identify identify modifications modificationsto to describe aa particular particular geologic geologic terrane. tenane. better suit their style style of mapping or to better describe of five five gened general functions functions (Fig. (Fig. 1): 1): (1) The basic structure smcture of GeMS consists of (1) selection selection of of the the area, base maps, maps, and and overlays overlays[SETUP]; [SETUP];(2) (2)addition additionand andmodification modificationofof basic mapping area, geologic data (3) manipulation manipulation of of the the data using geologic data [OUTCROP, SAMPLES, and STRUCTURE]; (3) sorting, statistical, [TOOLS]; geologic interpretation interpretation [GFDLOGYI, [GEOLOGY], and (5) sortiug, statistical, and imaging ixnagiig tools W LS]; (4) gwlogic pLOTJ.This Thisbasic basicstructure structureisis outlined outlined in in the the startup stamp menu of GeMS. &MS. map plotting [PLOT]. Choices of the mapping area, base maps, maps, and transparent transparent overlays overlays for for all all other other GeMS Choices operations are made through the SETUP function. function. The operations The standard standard base for for detailed detailed bedrock bedrock Minnesota is the theUSGS USGS 1:24,00O-scale 1:24,000-scale(7.5') (7.5 topographic geologic mapping in Mimesotais topographic quadrangle quadranglemap, map, digital-raster-graphicand anddigital-elevation-model digital-elevation-modelformats. formats. Low-altitude which is available in digital-raster-graphic Low-altitude orthophotoquads and geophysical anomaly images images (aeromagnetic (aeromagnetic and and gravity) gravity) are are also also available. available. orthophotoquads outcrop patte.rns, patterns, sample sample lwations, locations, structure structure symbols, symbols, and and other Transparent overlays can include outcmp point- and line-source line-sowce data. Basic Basic field field and and analytical analyticaldata data are are entered e n t e d in three threegeologic geologic data data layers—OUTCROP, layers-OljTCROP, SAMPLES, STRUCTURE. Data constructed to tobe bemenudriven, menu-driven,whereby wherebythe the user user SAMF' LFS, and STRUCTURE. Jhta layers are constructed appropriate term termfor foraaparticular particularattribute. attribute. The outcrop-data selects from a look-up table the most appmpnate outcmpdata layer records the physical outcrop. Attributes physical characteristics of an outcmp. Attributes of three beerock rock types typesper per outcrop outcmp may be eentered tables, which which have have been been customized to pennit permit custom^ to n t e d through one of four menu-driven tables, description of intrusive-igneous, sedimentary, and and metamorphic metamorphic rocks. rocks. The description intrusive.-igneous, volcanic, sedimentaq, The sample sample 59 R ~ ~ �___________ _____________HArea _______ _____________ ______ __________ layer records the physical sample and the types of analyses conducted conducted on layer records physical state state of the sample on itit (e.g., (e.g., petrographic, petrogmphic, microprobe, microprobe, geochemical geochemical (whole-rock, (whole-rmk, isotopic, isotopic, and assay), assay), geophysical geophysicalproperties, properties, gemhronologic). These Thesedata dataare arestored storedin inassociated associated files filesand and are are indexed indexed to to aa unique unique sample sample geochronologic). identifier. The structure layer records the type of linear or planar feature and its orientation; its orientation; The structure layer records the type of linear or planar feature standard symbols type. A are assigned to each type. A fourth fourth data data layer layer containing conthimg drill-hole drill-hole infonnation information symbols are soon,and andfield fieldphotographs photographs may may constitute wnstitute aa fifth layer layer at a later later date. will be added soon, The TOOLS TOOLS function functionprovides provides subroutines subroutines for for sorting, sorting, numerical numerical manipulation, manipulation,and andimaging imaging The data from from the the three three geologic geologic data layers and related This function is is still still being beimg of data related data data tables. tables. This develop&, but butwill willinclude includeoptions optionslike likecolor colorcoding ccdimgof of outcrops outcropsby by specified specifiedattributes, attributes,and andthe the developed, calculation calculation and andplotting plottingof ofthe thevalues values of of geochemical geochemicalparameters parameters (e.g., (e.g., Fo Fo in in olivine, olivine,tracetraceelement elementratios, ratios, normative normativeabundances). abundances). The The GEOLOGY GEOLOGYlayer layerprovides provides for for the the creation creation and and description description of map map units units (polygons), (polygons),unit unit contacts contacts (polygon (polygonedges), edges), and and linear linear features features like like faults faults (lines). (lines). Lastly, to Lastly, the the PLOT PLOT function function permits permits layout layout and scaling scaling of printed p ~ t e maps d to include includeany any combination basematerial, material,raw raw or or processed processed data, data, and and geologic geologic interpretations. interpretations. combinationof of base The GeMSoffers offersan an increasingly increasingly useful useful tool tool for for the thecollection wllwtionand and Thecontinuing continuingevolution evolutionof ofGeMS manipulation manipulationof of geologic geologicinformation, information, map map production, production, and, and, most most importantly, imporfantly,interpretation interpretationof of bedrock geology. GeMS can be used from the beginning of a mapping project to the final map bdrock geology. GeMS can be used from the beginning of a mapping project to the final map creation with future future aquisitions aquisitions of of data. data. In creation and and allows allows for for straightforward straightforward upgrades with In addition, addition, users users have have easy easy access, access,in in aa geographic geographic context, context, to to all all the the original original information on which aa map map interpretation interpretation isisbased. based. GeMS H Backgroüi i j Jimage sample topography orlliophoto aeromag structure geology Joverlay(s) $PCWJ 9FEb14' SAMPLES (points) Jbiite j—JAdd J I I one frkgrounci data jsample description petrography probe phricalpropethes isotope assay geochrunology related data tables I—I v.ljole rock --ABl STRUCTURE STRUCTURE (points) F-* I OUTCROP lygons) I I!*°Y eIeJ I one background data twcture typj Jorientadj 9dily j I—kd 1bround data utcrop description elete )—jäean }-_oone ne f Jiled rock type(s) descriptions klteon J Intrusive Igneous Volcanic I Volcanic JsuildH I—J snta,y lidefomlation Metamoiphic TOOLS GEOLOGY ete F—F1ean1-—Pone Modify dd map unit descriptions jLOT I pir-l IQUIT edges F— contact relationships v t 1 " 8 jes —(ault&dikedescdptions faun & dike d m p t i o n s Figure Figure 1.1. Conceptual Conceptualframework frameworkfor forGeMS GeMS 60 Build I �HYDROGEOLOGY OF SALINE- AND AND BORON-BEARING BORON-BEARiNGGROUND GROUNDW WATERS INTHE ThE HYDROGEOLOGY AERS l h ' NORTH SHORE SHOREVOLCAMC VOLCANICGROUP, GROUP, MINNESOTA MINNESOTA TIPPING, TIPPING, Robert Robert G., G., Mimi. Miin. Geol. G a l . Survey, Survey, 2642 2642 University University Ave., St. St. Paul, Paul, Minn., 55114; 55114;and and Geol. Univ. of of Minn., Minn., 310 310 F~llsbury Pillsbury Dr. Dr SE, ALLEN, Douglas, Dept. of G a l . and Geophysics, Univ. SE, Minneapolis, Minn., 55455. Mimeapolis, Public levels of boron boron in ground water. Public concern concem grew grew in in late late 1994 1994 along the North Shore over high levels water, The The LTV LTV Mining Mining Company, which owns a large coal burning operation near the town of Schroeder, from the the plants plant's fly ash piles or initiated a study study to to determine determine whether boron in ground water was from from natural natud sources. sources. The Theresulting resultingreport(6) report(6)shows showsthat thatboron boron isis at at levels levels above abovethe therecommended mommended allowable limit of 300 North Shore Shore and and concluded concluded that that it is allowable 300 ppb in ground water all along the Nor&h saliie, coming from natural sources. In Inaddition, addition,the the LTV LTV study study sampled sampled two two wells wells that that were were highly highly saline, chloride concentrations concentrations greater than 40,000 ppm. The raisedtwo two questions questionsabout about with chloride The LTV LTV report report raised composition of ground water along the North North Shore: Shore: 1—What the composition 1-What is is the geologic geologic source sourceof of the the boron? Thisstudy studyuses uses chemical chemicaland and boron? and 2—What 2-What is is the the distribution and origin of the dsaline i n e water? This isotopic information on on the the shape shape and and evolution evolution of the isotopic analysis analysis of ground water, combined wmbined with new infomntion Portage resides under under the the lake, lake, at least in Portage Lake Lake volcanic volcanic basin(1,5) to propose that the saline water resides sedimentary unit located strat&aphicaIly stratigraphically at at the the base base ofthe of the (A0 m) interfiow interflow sedimenm part within withii a thick thick (>40 youngest Group (NSVG). (NSVG). Mien, youngest basalts of the the middle middle Proterozoic North Shore Volcanic Group Allen,D.E., D.E., eteta!. al. (this vol.) describe describe a possible model for the dissolution of boron boron in in ground ground water water and and offer offer evidence evidence basin. The for the presence presence of marine waters in the rift basin. Thepreliminary preliminary data data suggest suggest that that boron boron and and the the occurrence of saline occurrence salinewaters waters along along the the North Shore Shore are are genetically genetically related. are fractures fractures within within the thebasalts basalts of of the the NSVG. NSVG. Typical The primary source source of water for wells are Typical yields for per minute minute..Wells for these wells are 2-4 gallons per Wellsfmished finished in in the the interfiow interflow sedimentary sedimentaryrocks rocks generally of these these strata. strata. Interfiow generally have have higher higher yields due to the greater permeability of Interflowsedimentary sedimentary units are the the 70-rn-thick 70-m-thick unit unit units typically are are no more than a few meters thick(3). Notable Notable exceptions exceptionsare 40-rn-thickpolymict polymictconglomerate conglomerate partially partially Good Harbor Harbor Bay and an approximately 40-m-thick exposed at Good Little Marais MarS (Fig. 1). exposed near Little (Fig. 1). composed of of mediummedium- to to -grained coarse-grained sandstone sandstone grading grading into into The Good Harbor Hahor Bay unit is wmposed interbedded finewell-sorted sand sand and and shale shale beds beds;the theunit unit becomes becomes increasingly increasingly f m e to medium-grained well-sorted interbedded 10-15 degrees degreesto to shaly nnear e x the top. The Thebeds bedsin inthe the interfiow interflow rocks rocks and and the the overlying overlying basalts b d t s dip dip 10-15 the south-southeast Little Marais, Marais, like like the the Good Good Harbor south-southeast(Fig. (Fig. 1). 1). The The polymict conglomerate near Little Bay interfiow overlying Schroeder-Lutsen Schroeder-Lutsen basalts. basalts. The intefflow unit, unit, is is structurally conformable with the overlying The LTV study study demonstrated demonstrated that that the the water water from from wells wells finished finished in in both both sedimentary sedimentaryunits units contain containboron. boron. In addition, two wells sampled near near Little LittleMarais Maraisas aspart partof ofthe theLTV LW study had chloride 1eveLs levels greater than 40,000 40,OW ppm. These Thesesites siteswere were chosen chosen for foradditional additional water water and rock rock sampling sampling because because reasonable conceptual conceptual model model could could be be constructed constructed to to sampled from outcrop, and a monable the units could be sampled demonstrate the demonstrate the path path of of ground-water ground-water flow flow to to the wells. Marais and and Good Goad Harbor H&r Bay units units have not previously been correlated, correlated, Although the the Little Little Marais similar stratigraphic uncommon thickness imply these units units were their similar skitigraphic position position and uncommon imply that these were deposited depositedat at the same same time. Furthermore, Furthermore,the thelocation locationof of these theseunits units relative relativeto to the the shape shape of of the the Portage Porfage Lake Lake volcanic basin, as proposed by Mien, energy deposition D.J., et et aL(1), al.(l), fits fits a model of high energy depositionalong alongthe the volcanic Allen, D.J., cusp deposition farther farther from from the the basids basin's edge edge (Good (Good cusp of the basin (Little (Little Marais) and lower energy deposition Harbor basalts supports supports this Harbor Bay). AAbroad broadseismic seismicreflector reflectorat at the the base baseof of the the Schroeder-Laitsen Schder-Lutsen basalts depositional depositional model(l). model(1). From Fromaahydrostratigraphic hydrostratigraphicperspective, perspective, correlation of the two units provides for a laterally laterally extensive, extensive, porous porous aquifer aquifer extending extending along along the shore shore and and beneath beneath the the lake. lake. between dissolved dissolved bromide bromide and andchloride chloride concentrations concentrations in in A positive linear linear correlation exists between al.; this this vol.). vol.). the sampled sampled ground ground waters waters from from Little Little Marais Marais and Good Harbor Harbor Bay (Allen, (Allen, D.E., et et al.; results dilute waters waters moving movingdownslope dowuslopetoward toward the the lake lake The ~ s u l t fit s the conceptual model of fresh, dilute sites, saline saline ground ground water waterat ator ornezu near lake lake level. level. At mixing with, in the case of the Little Marais sites, At Harbor saline water was was sampled, sampled, the the similar similarbromide-to-chloride bromide-to-chlorideratio ratio may may be be Good H a b r Bay, where no salime result of meteoric waters moving through through sedimentary sedimentary units, units, which whichonce oncewere weresaturated saturated with with the mult compositionallysimilar similartotothe thewater wateratatLittle LittleMarais. Marts. Boron saline water that was compositionally Boron concentrations concentrations above at both both sites. sites. Boron was 600 ppb ppb were were found found in the majority of wells sampled at was also also found found in in above 600 61 �samples samples from from the the Good Good Harbor HarborBay Bay interfiow interflow unit, with with concentrations concentrationsgreater greaterthan than 30 30ppm ppm in in shaly shdy members. members. AApH pHmechanism mechanismfor forthe thedissolution dissolutionof of boron boron in in ground ground water waterfrom fromthese these shaly shaly members members is vol.). Based is presented presented in in Allen, Allen, D.E., D.E., et et at. al. (this vol.). Based on on their their preliminary preliminary boron boron isotopic isotopic results, results, the the boron beof ofmarine marineorigin. origin, boron in in the theGood GoodHarbor HarborBay Bayinterfiow interflow sedimentary sedimentaryrocks rocks isisthought thoughtto tobe implying implyingthe theporous porousinterflow interflowsedimentary sedimentaryunits units at at Little LittleMarais Marais and and Good GoodHarbor HarborBay Bay were were inundated inundated with with sea seawater waterat atsome sometime timeduring during the the development developmentof of the the rift rift basin. basin. Thepresence presenceof ofseawater seawaterisisunnecessary umece.ssary to account for saline s a h e waters in the rift. Hardie(2) Hardie(2) The demonstrates canproduce produce demonstrateshow howhydrothermal hydrothermalconvection convectionand andweathering w e a t h e ~reactions greactionsin in aa closed closedbasin basincan cakium-chloridebrines brinesfrom fromaawide widerange rangeof of source sourcewaters waters similar similarto to those thosesampled samuledin inthis thisstudy. studv. calcium-chloride i& utility utilityin in settings seniigs However,the the heavy heavy boron boron isotopic isotopicsignature signature of of the the waters waters analyzed analyzed highlights highlightsits However, like likethe therift, rift,where wheresedimentary sedimentaryevidence evidencefor formarine marineenvironments environmenbisisinconclusive. inconclusive. This thither work. This study studysuggests suggestsseveral seve& possibilities possibiiities for further work. The Theproposed proposedcorrelation comelationof ofthe theLittle Little Marais beinvestigated. investigated. Marais polymict polymictconglomerate conglomerateand andthe theGood Good Harbor Harbor Bay Bay interfiow interflow unit unit needs needsto tobe Detailed areanear near Good Good Harbor HarborBay(9) Bay@)has has revealed revealedaamore more.complex complex Detailedmapping mappingof ofthe theCascade CascadeRiver Riverarea stratigraphy stratigraphythan thandescribed describedin inthis this study. study. Although Althoughnot notas asconcentrated, concentrated,the thesaline salinewater waterisis chemically chemicallysimilar similartotothe thecalcium-chloride calcium-chIoridebrines brinesin inMichigan Michigancopper coppermines(4; mines(* see seealso also sfs. rifs.totoLane h e therein) 8).; these be therein)fluid FIuidmovement movementwithin withinthe thebasin basinisiscurrently cumntlybeing beiigmodeled(7, modeled(7,8).; thesemodels modelscould couldbe modified modifiedto toincorporate incovoratenew newinformation informationon on the the shape shapeof of the the rift rift and and the the possibility possibilityfor foraalaterally latedly continuous continuousporous porousunit unitatatthe thebase baseof ofthe theSchroeder-Lutsen Sctuoeder-htsenbasalts. basah. References: etal., 1997. MS. v.290, References:(1) (1)Allen, Allen,DJ., D.J. .etd.. 1997,GSA GSASpec. SF. Paper P a p312; 3 1 2 (2) (2) Hardie, Hadie. 1990, AN, v. 290,p.p. 43-106; 4 3 - I N (3)Jirsa, (3) Jirsa.1984, 1984, -~ MGS 30,20 p.; p.; (4) (4)Kelly Kellyet eta!., aI.. 1986, 1986, AJS, v. 286, p.281-308; p. 281-30%(5) (5)Miller. Miller. & &Chandler, 1997, GSA Spec. Spec Paper3l2, Papr312,p.p. MGS RI Rl30.20 v.286, Chandler, 1997, 73-96;(6) (6)STS STSConsultants, Consultants,I995, 1995.Eva!. Eval.ofofBoron BomnImpacted ImpactedWells; Wells;report repntotoLTV LTVSteel SteelMining MiningCo.; (7)(7)Swenson Swemon&& 73-96; Person,1995, 1995,IGCP 336,Duluth, Duluth.Minn., Minn.,p.p.187-188; 187-18%(8) (8)Woodruff Woodruffetetal., al..1995, 1995,IGCP IGCP336, 336,Duluth, Duluth,Minn., Mim.,p.p. 213-214; 213-21k(9) (9) Person, IGCP 336, Green, Green.1996, 1996.Geology Geologyon onDisplay. Display,Minn. Minn.DNR, D M ,69 69p.; p.;(10) (10)Green, Green,1982, 1982.Two TwoHarbors H h sSheet, Sheet,1:250,000, 1 : 2 5 0 , MGS. ~MGS. , a,; R6W , 95W R4W , + R3W • R2W , RIW R2W + Good Harbor Bay + e p * SamPled Wella Fauft Attitude of 15 Uttle Marais —r 26 volcanic rocks Attitude of Igneous layering /'Road 0 5 kilometers NORTh SHORE VOLCANIC GROUP Sd,roeder-Lutsen basafts red sandstone NSVG, undifferentiated H BEAVER BAY COMPLEX Marc and intermediate intrusions Felsicinfrusions Levaux porphyry • Feriodiorite River Figure I. Generalized geology of the Noflh 5hore of Lake Superior, Little Mania to Good Harbor Bay. Minnesou, and locations of sampled wells. Modified from Green ([0), and Figure 5 from Miller and Chandler (5) �The Greening of of Sudbury Keith Winterhalder Winterhalder Sudbury lies lies at the southern southern edge edge of of the Precambrian Precambrian Shield, Shield, in aa vegetation vegetation zone zone transitional between the boreal forest to to the north and the boreal coniferous co~ferous forest the deciduous deciduous to the the south. south.Prior Priortotothe theadvent advent of of the the miNng mining and smelting industry 1883, forest to industry in in1883, the area was characterized by extensive extensivestands standsofofred red pine pine and and white white pine. pine. One the characterized by One hundred years years of of logging, logging,fire, fire,soil soilerosion erosionand andenhanced enhancedfrost frost action, action,as as well well as hundred fumigationand and copper, copper, ~nickel iron particulate particulate fallout from from the sulphur dioxide fumigation c k e and land iron region's three smelt-, smelters, severely severelydamaged damaged the the Sudbury Sudbury landscape, landscape, giving giving rise rise to region's three 10,000 barrenland land forming forming concentric concentriczones zonesaround around the three smelters. 1 0,000 hahaofofbarren smelters. The The of the the barren barren zone zone are are stmngly strongly aadified, acidified, with with pH pH values values ranging fiom from 2.2 2.2 to to 4.4, 4.4, soils of and both Cu and and Ni Ni levels levels in in the the soils soils of of the the barren barren zone zone are are greatly greatly elevated, elevated, from several severalhundred hundred to to several severalthousand thousand&g. pg/g. As varying from As well well as as solubilizing solubilizing the Cu and Ni Ni that that has hasaccumulated accumulated in in the the soil soilfrom fromatmospheric atmospheric fallout, fallout, the the acidity acidity of of Sudbury soil releases aluminum ions ions from from aluminosilicate aluminosilicateminerals minerals such such as as days, releases aluminum clays, stunted, relict relict individuals individuals of of woody contributing to to the the soil's soil's phytotoxicity. phytotoxicity. A few stunted, woody plants such such as as red red maple, maple,red redoak oakand andaspen aspencan canbe befound found on on the otherwise barren slopes, which have have aa stony stony covering coveringthat thatresulted resulted from from the the combiied combined action of frostslopes, which frostthe barrens barrens is a heaving and erosion erosion on on the the glacial glacial till-derived till-derived soil. soil. Surrounding Sumounding the 36,000hectare hectarezone zone of of stunted, stunted, semi-barren semi-barren woodland, woodland, characterized characterized by patches of 36,000 of bare soil between the relict, relict, coppiced coppiced white white birch, birch, red red maple maple and red oak. In the the past past 25 25 years, years, some some areas of previously previously barren soil have been been colonized colonized by by species suchas astdted tuftedhair hairgrass, grass,tickle ticklegrass grassand anddwarf dwarfbirch, birch,asasaaresult result of of the speaes such evolution of of metal-tolerant metal-tolerant ecotypes. ecotypes. Furthermore, Furthermore, since sincethe the closure closure of of the Coniston CoNston smelter in 1 1972, thereappears appearstotohave have been been some some natural natural amelioration amelioration of of pH pH and 972, there smelter in metal levels levels in in that that vicinity, vicinity, and less plant such such as as white white birch birch and metal less metal-tolerant metal-tolerant plant wavy hairgrass hairgrass have begun to to colonize colonize the the area. area. The announcement by Inco Inco Ltd. Ltd. in in 1969 of its intention to construct 1%9 of intention to construct a 381 381 m The announcement by smokestack stimulated stimulatedthe theOntario OntarioDepartment DepartmentofofhLands andForests Forestsand and Laurentian smokestack n d s and University to iinitiate program. The frees University ~ t i a t ea joint experimental free-planting tree-planting program. trees planted planted barrens showed total mortality, mortality,but butititwas wasfound foundthat that the the soil could be on the barrens showed almost total detoxified suf£icientl sufficientlytoto initiate initiate colonization colonizationby bythe the surface-application surface-applicationof of p ground und detoxified limestone. Small-scaleexperiments experimentsinitiated initiatedinin1974 1974showed showedthat thatthe the surface surface of of the limestone. Small-scale 63 �stone-covered soil could be be detoxified by the stone-covered soil could detoxified by the manual manual application application of of ground ground limestone, and and that that seeds limestone, seeds were were trapped trapped by the the stony stony mulch, mulch, and andgerminated germinated successfully.The Theopen open structure structureofof the the resulting resulting grassy grassy sward was successfully. was beneficial beneficial for for colonization by native native plants plants with with wind-blown wind-blown seeds, seeds, since since itit offered offered numerous colonization by openings and microhabitats microhabitats for volunteer seedlings. In 1975 1975 and and 1977, 1977, small groups groups of elementary school pupils successfuUy successfullyestablished establishedgrass grass on on small small patches patches of of barren of land near near their their schools, schools, using using this this approach. approach. job-creation funds to the Regional Regional Municipality Municipalityofof Sudbury Sudbury appfied applied for In 1978, 1978, the for job-creation to employ one hundred and students to carry out and seventy-four seventy-four post-secondary post-secondaq students out largelargerevegetation employing employingthe the same same technique. technique.The Theprogram program reached reached its its peak peak in scale revegetation 1983, when when 1,277 1,277 unemployed unemployedpersons persons were were employed 1983, employed on combined combined federal, federal, provincial, m municipal industry funding. funding. So ha of of land land 3,500 ha provinaal, u ~ c i p a and land industry So far, far, approximately approximately 3,500 have been been greened greened in in this this way. way. More Inco has employed have More recently, recently, Inco employed aa commercial commercial crop-dusting company to apply limestone, limestone, fertilizer fertilizer and and seeds from the air.. aopdusting Spontaneous colonizationof ofthe thegrassed grassedland landby by larger larger woody woody plants plants is is so Spontaneous colonization so far far confined to birch, birch, poplar poplar and willows, willows, because confined because conifer seed source iiss scarce and the . seed bed conditions are poor. poor, More More than than 2.5 2.5 million million native native trees, trees, mostly mostly Jack Jack pine, red pine and and white white pine pine which which were were the the dominant dominant species species of the the pre-disturbance pre-disturbance landscape, have have been been planted planted since since1978 1978ininsmall smallinformal informalgroups, groups, which which break break up landscape, of the winter landscape, landscape, and and form form aa seed seed source source for for future future spread. the monotony of Plant communities communities that results from the revegetation revegetation procedure contains contains planted trees, trees, the seed rain, components derived from from the the seed seed mixture, mixture, planted rain, and any any metal-tolerant plants already on site. site.ItItisisassumed assumedthat that the the landscape will will ultimately ultimately metal-tolerant plants resemble the the original original pine pine forest, forest, but but concern concern exists existsas as to to how quickly resemble quickly the the typical typical understory species species will will move movein. in. The The usefulness usefulnessofofintroducing introducingplugs plugs of of soil soil that understory contain desirable understory understory species, species,aa seed seed bank, contain desirable bank, and and soil soilmicroorganisms microorganisms isis currently under investigation, and is meeting investigation, and meeting with with some some success. success. Another Another current current area of of interest interest isis the the use use of of liming liming and and revegetation on a watershed area revegetation on watershed basis, basis, thus thus dual problems of barren land and and acidified acidified lakes. lakes. solving the dual problems of the minimal the Sudbury Unique features Sudbury program program include include the minimal amelioration amelioration Unique features of of the approach, in which recolonizationplays playsa acritical criticalrole, role,and and the strong approach, in which natural natural recolonization strong manual component component and and resulting resultingjob-creation job-aeation benefits. benefits. 64 �THE MCKENZIE MCKENZIELAKE LAKEANTIFORM ANTIFORM AND THE KAWA BAY SYNFORM, PROVINCIAL THE SYNFORM, QUETICO PROVINCIAL PARK, PARK, ONTARIO ONTARIO WOODARD, H., Department of of Geology, Geology, Beloit Beloit College, College, Beloit, WOODARD, Henry H., Beloit, 53511and andPARHAM, PARHAM,Peter, Peter, P.O. P.O. Box 59510 Wis. 53511 Box 1647, Havre, Mont. Mont. 59510 The Mckenzie McKenzieLake Lake antiform antiform occurs occurs in in the the northeastern northeastern part part of Quetico QueticoProvincial ProvincialPark. Park. ItIt The was formed formedby bylate-stage late-stagetranspression, which of the the was which produced ductile deformation deformation of Quetico-Wawa subprovince subprovince boundary. The The fold fold measures measures at at least least 18 18 km km along alongits itsaxial axial Quetico-Wawa strike outcropwidth. width. The strike and and is is about about 55 km in maximum outcrop The crest crest of of the the fold fold defines definesthe the subprovincejunction junctionand andarches arches through through a distance of about 16 km; its hinge, which which does subprovince not correspond correspondto tothe thecrest, crest, is is very sharp. Both Bothlimbs limbsdip dip steeply steeplynorthwest, northwest,and andthe the not underlying very tight. tight, severelv severely stretched stretched and and dismembered. dismembered,. but underlyingKawa KawaBay Bay synform svnform is vew but still still traceable in outcrop and on Fig.1). Although traceablein outcropand on aerial aerial photographs (see Fig.l). Although the the plunge plungeof ofthe the Mckenzie McKenzieLake Lakestructure structureisisto to the the northeast, northeast, the degree of plunge plunge is is not not easily easilymeasured. measured. Lineation Lineationon on slickensided slickensidedsurfaces surfaces plunges plunges gently gently southwest southwest on on the the related relatedSide SideLake Lake zone zone of of backthrusting, backthrusting,and andthis thissuggests suggeststhat that the the folds folds plunge plungesteeply steeplynortheast. northeast.The TheSide Side Lake the antiform as a southwest-trending southwest-trending Lake shear zone zone emanates emanates from the crest of the backthrust of shear. shear. About backthrustwhich whichexhibits exhibitsleft-lateral left-lateral sense of About 28 28 km kmto to the thesouthwest, southwest, the the Side undeformed Lac La Croix Croix leucogranite leucogranite which Side Lake Lake shear shear zone zone cuts cuts a portion portion of the undeformed which is is dated datedat at 2,662 2,662 + 55Ma Ma(Woodard (Woodardand and others, 1995). This This age age is is approximately approximately30 30my my younger Ma)of of the theWawa Wawa subprovince, subprovince,and and15 15my my youngerthan thanthe thefolded foldedtonalite tonalitesills sills(2694 (2694 + 11Ma) younger younger than thanthe thefolded foldedquartz quartz monzonite sills (2678 + 6 Ma) in adjacent portions portionsof of the the Quetico synform is Quetico subprovince. subprovince. The Thesouthwest southwesthinge hingearea area of the underlying underlying Kawa Kawa Bay Bay synform is cut age for for this this granite should should allow cut by byaa stock-like stock-likebody bodyof of undeformed undeformed granite, and an age determination junction was wasfolded. folded. The determination of of the the time the junction The southwest southwest hinge hinge and and trough trough area area of fold axes, which of the theKawa KawaBay Bay synform synform is is broken broken into into aa mega-breccia, and major fold which were were developed developedin inWawa Wawasubprovince subprovincerocks rocksduring duringan an earlier earlier phase phase of the the juxtaposition, juxtaposition, are are secondarily are randomly randomly oriented. oriented. This secondarilyfolded foldedinto intomany many open open folds whose axes are This secondary accomplished by secondarydeformation deformationappears appears to to have have been been accomplished by aa process processwe we call call "backshoving" synform is "backshoving"where where the the trough trougharea area of of the the Kawa Kawa Bay synform is squeezed squeezedbackward backward (toward overriding-mass of the [toward the the southwest) southwest)under under the the northeastward northeastwardoverridina-mass the Mckenzie McKenzieLake Lake antiform (see Fig. 1). + + Figure 1 - - - Lake 9 4 15V '4 7 Km I Relationship of Side Lake Shear Zone to the Development of the Mckenzie Lake Antiform. 65 �This left blank intentionally. This page page left blank intentionally. 66 �AGE CONSTRAINTS CONSTRAINTS ON ON PLUTONISM, PLUTONISM, METAMORPHISM AND DEFORMATION DEFOWATION ACROSS THE SUEPROVINCE BOUNDARY NEAR THE THE WAWA-QUETICO WAWA-QUETICO SUBPROVINCE THE MANITOUWADGE GREENSTONE GFtEENSTONE BELT, NORTHWESTERN NORTHWESTERN ONTARIO ONTARIO Zaleski, E., and van of Canada (GSC), Ottawa, Zaleski, E., van Breemen, Breemen, 0., O., Geological Geologid Survey of Ottawa, ON ON K1A V.L., Department DepartmentofofGeosciences, Geosciences,Western Western Carolina CarolinaUniversity, University, KIA 0E8; OE8; and and Peterson, Peterson,V.L., Cullowhee, Cdowhee, NC NC 28723, 28723,U.S.A. U.S.A. The and the metasedimentary-migmatitic metasedimentary-migmatiticQuetico Quetico The volcano-plutonic volcano-plutonic Wawa subprovince subprovince and subprovince subprovincerepresent represent first &st order ordersubdivisions subdivisions of the Superior Superior Province; Province; yet yet our ourwork workalong along the Wawa-Quetico boundary and in the Manitouwadge greenstone belt (MOB) shows that the Wawa-Quetico boundary and the Manitouwadgegreenstone belt (MGB) that most of the structural history is is common commonto to both both terranes, terranes, and that structural and and metamorphic metamorphic history Quetico greywackes are correlative with greywackes in the MOB. The Quetiw greywackes are correlative with greywackes in the MGB. The Manitouwadge Mmitouwadge greenstone belt (MOB) (MGB) is is aahighly highly deformed deformed remnant of of supracrustal supracrustalrocks rockscomprising comprising a mafic-to-felsic volcanic succession successionofofcca. 2720Ma, Ma, the felsic component of which mafic-to-felsic volcaaic a. 2720 which isis intercalated intercalatedwith withiron ironformation formationand andassociated associatedmassive massivesulphide sulphidedeposits. deposits.AAsynvolcanic synvolcanic tronclhjemite was both both a magma volcanismand and aa heat source trondhjemite was magma reservoir reservoir for felsic felsic volcanism source for for mineralizing mineralizing hydrothermal hydrothermal activity. activity. U-Pb U-Pbages ages of of detritai detritalzircons zirconsfrom fromgreywackes greywackes in in the the MOB, immediatelytotothe the north, north, constrain the MGB, and in the the southern southern Quetico Quetico subprovince immediately depositional packagesto to younger youngerthan than ca. ca. 2690 2690 Ma Ma and and support support depositional ages of both sedimentary packages their correlation. correlation. The TheEverest EverestLake Lakepluton plutonintrudes intrudesthe theQuetico Queticogreywackes greywackes along along the the subprovince boundary. The age age of of the the Everest Everest Lake Lake pluton pluton constrains constrains the theminimum minimum subprovince boundary. depositional age of of the Quetico greywackestotoolder olderthan than ca. ca. 2680 2680 Ma. Ma. The Thenew new ages ages depositional age Quetiw greywa&es from the work in in the northern the southern southem Quetico, Quetiw, in in combination wmbiiation with previous work northern Quetico Quetico (Davis et a!., 1990), show that Quetico sediments were deposited over at least ca. 10 at 1-t ca. 10m.y. m.y. al., 19901, that Quetico sediments and and are are consistent consistentwith with southward southward younging, younging, a test test proposed proposed by by Percival P e r c i d and andWilliams Williams (1989) (1989) for their their accretionary accretionaryprism prism model model of of the the Quetico Queticosubprovince. subprovince. Regional Regional metamorphic grade increases increases northward, from from upper upper amphibolite amphibolitefacies facies without without migmatization migmatization in the the southern southern MOB, MGB, to to granulite granulite facies facie north north of of the theWawaWawaQuetico migmatizationininthe the southern southern Quetico Quetico and and northem northern Quetiw boundary, with extensive extensive migmatization Wawa subprovinces. Regional structural evolution can be modelled by aa four-phase four-phase sese Wawa subprovinces. quence of ductile deformation. In the MOB, D2 tectonic fabrics are defined by high grade quence ductile deformation. In the MGB, D2 tectonic fabrics are d&ed by high grade metamorphicminerals mineralsand andfolded foldedby by the theD3 D3Manitouwadge Manitouwadge synform, synform, with with relatively relativelyminor &nor metamorphic development of D3 fabrics, suggesting suggestingthat that peak metamorphic conditions were attained attained development of during Inthe theQuetico Queticosubprovince, subprovince,migmatitic migmatitic segregations segregationsvary vary from from during D2 D2 deformation. deformation. In in situ situmelts meltsdeveloped developed in in pelitic pelitic beds, beds, to to discordant discordant foliated foliated and and folded folded pegmatitic pegmatitic and and in tonalitic dikes, variations that are consistent with protracted migmatization contempotonalitic dikes, that are consistent with protracted migmatization contemporaneous raneous with withprogressive progressiveD2-D3 D2-D3 (and (andpossibly possibly D4) D4) deformation. deformation. Two the region region by U-Pb U-Pb Two major major syntectonic syntectonicplutonic plutonic events events have been documented in the dating dating of of igneous igneous zircon. zircon. Firstly, Firstly, hornblende-biotite hornblende-biotite diorite comprising the oldest phase phase of of the the Black Black Pic Pic batholith, batholith,and andthe theLoken h k e nLake Lake K-feldspar K-feldspar megacrystic granodiorite, are are both both ca. ca.2687 2687 Ma. Ma. These Theseplutons plutonswere were emplaced emplaced before or during D2 deformation, deformation, based on ontheir theirstrong strongD2 D2fabrics fabricswhich whichare arefolded folded by by the theD3 D3Manitouwadge Manitouwadgesynform. synform.Secondly, Secondly, 67 �ca. 2677—2680 Maplutonic plutonicrocks, rocks,including includingthe the Nama Nama Creek K-feldspar megacrystic 2677-2680 Ma megacrysticgragranodiorite, Banana monzodiorite, monzodiorite, and Everest Everest Lake Lake monzodiorite, monzodiorite, were were emplaced emplaced late during D2 or prior to to D3 D3 deformation. deformation. The TheEverest EverestLake Lakemonzodiorite monwdioriteintrudes intrudesQuetico Quetico greywackes and and is is veined veined by by anatectic anatectic segregations, hence hence constraining migmatization to greywackes to 2680Ma. Ma. In In the the MGB7 MOB, aa tonalite tonalite dike which which cuts cuts the the strong strong D2 fabric in the Loafter Ca. ca. 2680 ken Lake pluton, pluton, but also has a late-D2 foliation, constrains late D2 to to Ca.ca. 2675—2680 but also has a late-D2 foliation, constrains late D2 2675-2680 Ma. Ma. intrusive rocks, including foliated foliated to nearly massive aplites, Additional younger intmsive aplites, granites, granites, pegmatites pegmatite8 and and lamprophyres, lamprophyres, have not been dated. dated. The distribution distribution of U-Pb titanite titanite ages ages defines defines aa crude m d e gradient gradient ranging ranging from from ca. ca. 2686—2688 Masouth southofofthe theMGB, MOB,where wheretitanite titaniteages agesoverlap overlap with with the ages of igneous 2686-2688 Ma Maininthe thenorthern northernMGB, MOB, to to ca. Ca.2640 2640Ma Ma in in the the Everest Lake ca. 2650—2655 2650-2655 Ma zircons, to ca. pluton in in the theQuetico Queticosubprovince. subprovince. While While our our titanite titaaitegeochronology geochronology is still still in in progress, progress, preliminary indications are are that the prelimixiary indications the ages agea date dateregional regionalcooling cooling through through Ca. ca. 600°C, 6OO0C, the closure temperature of of the U-Pb system in titanite closure temperature titanite (Heaman (Heaman and andParrish, Parrish,1991). 1991). In In our work thus far, deviations from from the the northerly northerly younging 'ounging pattern are permissive of an pattern are permissive interpretation in terms of of D3 D3 or or D4 D4 deformation deformation of the the 600°C 6OO0Ccooling cooling surface in the southern MOB Ma. Structural southem MGB after ca. 2655 Ma. Structural relationships relationships and isotopic isotopic dating dating suggest suggest a prolonged migmatization event in the the Quetico Queticosubprovince, subprovince,possibly possibly commencing commencing during during or soon after the the emplacement emplacement of the Everest Lake pluton (ca. 2680 Ma), and continuing until foliated granitic granitic dike interpreted interpreted as until ca. ca. 2642 2642 Ma, the age of monazite from aa foliated a injected injected leucosome of local derivation. References References Davis, D.W., Pezzutto, F.,and and Ojakangas, Ojalcmgas, R.W., R.W., 1990: 1990: The age age and andprovenance provenance of of Davis7 D.W.? Pezzutto, F., metasedirnentary rocks in the rnetasedimentary the Quetico Quetico subprovince, subprovince, Ontario, Ontario,from fromsingle singlezircon zircon analyses: analyses: implications Archean sedimentation sedimentation and and tectonics tectonics in in the the Superior Province; Earth Earth and implications for Archean Planetary Science Planetary ScienceLetters Letters99, 99,195—205. 195-205. Heaman, L.M., and R.,1991: 1991:U-Pb U-Pbgeochronology geochronologyof of accessory accessory minerals; minerals;in in AppliAppliHeaman, and Parrish, Parrish,IL, cations of R.adiogenic Isotope Systems Systems to to Problems Problems in Geology, Short Short Course cations Radiogenic Isotope Course Handbook, Handbook, Mineralogical Association 59—102. 1g7 59-102. Mineralogical Association of of Canada, Canada,v.v.19, Percival, J.A., and and Williams, Williams, H.R., H.R., 1989: 1989: The late late Archean Archean Quetico Queticoaccretionary accretionarycomplex, complex7 Superior Province, Superior Province,Canada; Canada;Geology GeoIogy17, 17,23—25. 2S25. 68 � https://digitalcollections.lakeheadu.ca/files/original/3e6ca9983eab16833ef2eda88f3a6c48.pdf 4b6d21870aa8d2e4765dc27ef5fa0dbd PDF Text Text THE HIJRONIAN HURONIAN SUPERGROUP SUPERGROUP THE BETWEEN SAULT SAULT STE. STE. MARIE MARIE BETWEEN LAKE AND ELLIOT ELLIOT LAKE THE EARLY PROTEROZOIC EVIDENCE FOR THE PROTEROZOIC ATMOSPHERE, CLIMATE CLIMATEAND AND TECTONICS TECTONICS ATMOSPHERE, by by G. Card and G. Bennett, K. D. Card and K. Tomlinson K. Y. Y. Tomlinson (2-21G.) \\\\\\ NlpIulng Diabase Cobb,o. dlabae. gatr Bar River Fm. .\ \ Quarla areMe. sto*o.. manc, n,ud,tone. ttone. Gordon Lake Fm. '''''1 U,d. ne $UVJStOn. —' ' \ n m. \ \ \ \ \ \ \ '. '---c- Y9 \ Quartz areiPt QuaI12 pebu. cOngantot• Mire.. iuba*o.. ML.tone, rltdaie II Gowgida Fm. Mccse.eltstcrs Diarrictile. pdymbtlc ccnglom.rat. ,/ .-.-.-. —'—V - Seipeci Fm. / Esprola Fm. Biuco Fm. ''''I '' ,-. \ Msdua Fm. Suba¼o... waa. 0c. Diartlttt .anthtone &treta.., a.kre. . •g p a . ::-_1rs!T;rst p t_._c____t_ c'rc—r _j Pecon Fm. t.maton.. attton. McKlm Fm h*jthtont ttaw ¾i - '\\\\\\ \ \ \ \ \ \ \ 1- 'fr Matln.nda Fm '- Iheudon Fm tscwI +4 — A—. .jba&re. jath-p.bbIe conorner& $o. Mcc — p Ita r. pe ce. thffigsta* creek Ftt —- +++ 4, + + INSTITUTE INSTITUTE ON LAKE SUPERIOR SUPERIOR GEOLOGY GEOLOGY 43 rd 11, 1997 rdANNUAL ANNUAL MEETING, MEETING,MAY MAY6,6,11,1997 SUDBURY, ONTARIO ONTARIO Field Trip part 22 Trip Guidebook, Guidebook,Volume Volume 43, part �RKUNI1 gYENI MIDDLE PROTEROZOIC Grenville Orogeny Grenville Midcontinent Rift Rift System ICeeweenawan volcanics, volcanics, sediments sediments Keeweenawan Dyke emplacement Sudbury Sudhury swarm - Anorogenic magmatism magmatism 1000-1200 Cu 1000-1200 Cu 1100 1100 1238 1238 Croker Island Island complex, Complex, Manitoulin Manitoulin Island Island intrusions intrusions 1450-1500 1450-1500 Chief Lake, Cutler Cutler batholiths batholiths 1700-1750 1700-1750 EARLY PROTEROZO$C Felsic plutonism Felsic plutonism Deformation and metamorphism Deformation metamorphism (late (latePenokean) Penokean) Sudbury Sudbuw Event Event Sudbury Sudbury Igneous Igneouscomplex Complex Whitewater Group Group Whitewater 1850 Ni, Ni, CU, 1850 Cu, PGE, Zfl PGE, Zn Pb Pb Deformation and metamorphism Deformation metamorphism (early Penokean) (early Penokean) Dykeemplacement, emplacement,rifting rifting Dyke (ocean opening?) (ocean opening?) Kenora-Kabetogama, Kenora-Kabetogama, Marathon swarms swam Mafic magtnatism Uafic magmatism Nipissing diabase diabase Nipissing -2150 2219 Ni, Mi, Cu, Cu, 2219 POE, ffiE, Ag, Ag, Co. Cu, Cu, CO, Au Deformation Deformation (Blezardian Orogeny) (Blezardian Orogeny) Oxyatmoversion Oxyatmoversion Upper Nuronian Kuronim Supergroup Superyroup Upper Si Si Sedimentation, Sedimentation, mafic mafic Huronian Supergroup Lower Kuronian Supergroup U V magmatism Matchewan dykes,mafic-felsic mafic-felsic volca m, Matchewan dykes, volca2450-2496 2450-2496Ni, Ni, Cu, gabbro-anorthosite gabbm-anorthosite intrustions intrustions - POE PGE Creighton, Creighton, Murray Murray granites granites N ARC A5uiEAM Late deformation Late deformation Late plutonism Late plutonism Au Algwan granites Algoman granites Early Early deformation deformation and and plutonism plutonism Levack Complextonalite tonalite gniess Levack Complex gniess Vocanism and sedimentation sedimentation —2650 -2650 U -2680 -2680 Abitibi Suhprovince Cu, Zn,Fe Subprovince greenstone greenstone belt belt 2735-2700 2735-2700Cu. Zn,Fe Table 1. Precambrian Precambrian rock units units and tectonic tectonic and and metallogenic metallogenic events events in in the the Lake Huron Region Region (After Card Jackson. 1995) 1995) CAfter Card and Jackson, �THE HURONIAN SUPERGROUP SUPERGROUP BETWEEN SAULT STE. MARIE BETWEEN AND ELLIOT ELLIOT LAKE L m EARLY PROTEROZOIC PROTEROZOIC EVIDENCE FOR THE E&Y AND TECTONICS TECTONICS ATMOSPHERE, CLIMATE AND by D. Card Card and G. Bennett, K. D. K. Y. Y. Tomlinson Tomlinson INSTITUTE ON LAKE SUPERIOR GEOLOGY rd ANNUAL MEETING, 43 rd MEETING,MAY MAY 6, 6 ,11, l l , 1997 ONTARIO SUDBURY, ONTARIO 43, part part 2 Field Trip Guidebook, Guidebook, Volume 43, �CONTENTS CONTENTS page Page Introduction Introduction. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .11 . The The Elliot Elliot Lake Lake Group Group . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .44 The The Livingstone Livingstone Creek Creek Formation Formation......................44 Early Early Huronian Huronian Intrusive IntrusiveRocks Rocks . . . . . . . . . . . . . . . . . . . . . . .66 Huronian Huronian Volcanic Volcanic Rocks Rocks of of the the Sudhury Sudbury Area Area . . . . . . . . . .77 The The Huronian Huronian Volcanic Volcanic Rocks Rocksof ofthe theSault SaultSte. Ste . Marie-Elliot Marie-ElliotLake Lake area area . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .99 Sedimentary Sedimentary Rocks Rocks Associated Associatedwith withthe the Thessalon 14 Thessalon Formation Formation. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .14 The The Matinenda Matinenda Formation Formation. . . . . . . . . . . . . . . . . . . . . . . . . . . . .15 15 The TheF4cKim McKim Formation Formation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18 18 Stratigraphic StratigraphicRelationships Relationshipswithin withinthe the Elliot Elliot Lake Lake Group Group of of the theSault SaultSte. Ste .MarieMarieElliot Lake Area Elliot Lake Area . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19 19 Hough Hough Lake LakeGroup Group . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20 20 Ramsay 20 RamsayLake LakeFormation Formation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20 Pecors PecorsFormation Formation .................................... 21 21 Mississagi MississagiFormation Formation. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .2].21 Quirke QuirkeLake LakeGroup Group . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2222 Bruce 22 BruceFormation Formation ..................................... 22 Espanola EspanolaFormation Formation..................................2323 Serpent SerpentFormation Formation...................................2424 Cobalt CobaltGroup Group . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. ..2424 . �GowgandaFormation. Formation. .... . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .24 24 Gowganda LorrainFormation Formation. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 26 26 Lorrain Gordon Lake Lake Formation Formation. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 27 27 Gordon Bar River River Formation Formation................................. 28 28 Bar Nipissing Intrusions Intrusions. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Nipissing 28 Huronian Paleosols Paleosols . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Huronian 29 Regional Regional Tectonic Tectonic Patterns Patternsand and Metamorphism Metamorphism . . . . . . . 35 Tectonic Models Models for for the the Huronian Huronian Basin Basin . . . . . . . . . . . . Tectonic 40 Road Log Log -.Day Day 11 .................................. Road 42 Road Log Log -- Day Day 22 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Road 56 �List List of of Figures Figures Figure 1. The The distribution distribution of of rocks rocks of of the the Huronian Huronian Figure 1. Supergroup Supergroup . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22 Figure Figure 2. 2. Huronian Huronian stratigraphy, stratigraphy,Sault Sault Ste. Ste. Marie-ElliotLakearea Marie-ElliotLakearea.................................... 33 Figure Figure 3. 3. The The cyclicity cyclicity of of Huronian Huronian Sedimentation Sedimentation......55 Figure Figure 4. Stratigraphic Stratigraphic relationships relationships in in the the Elliot Elliot Lake Lake Group Group -. Sault Sault Ste. Ste. MarieMarie- Elliot Elliot Lake Lake area area.. . . . . . . . 55 Figure Figure 5. 5. Paleocurrent Paleocurrent roses roses for for the the Mississagi Mississagi and and Matinenda Matinenda formations formations................................ 8 Figure Figure 6. 6. The The distribution distribution of of the the Thessalon Thessalon Formation 10 Formation and and Livingstone Livingstone Creek Creek Formation Formation . . . . . . . . . . . . . . 10 Figure Figure 7. 7. Distribution Distribution of of Huronian Huronian volcanic volcanic rocks rocks . . . . .10 10 Figure Figure 8. 8. schematic Schematic stratigraphy stratigraphy of of the the Thessalon Thessalon Formation Formation . . . . . . . . . . . . . . . . . . . . . 11 Figure Figure 9. 9. Discrimination Discrimination diagrams diagrams for for volcanic rocks of the Thessalon Formation volcanic rocks of the Thessalon Formation. . . . . . . . . . . . . . 12 12 Figure Figure 10. 10. Pebble Pebble size size vs. vs. pyrite pyrite grains grains size size Matinenda Matinenda Formation, Formation, Elliot Elliot Lake Lake . . . . . . . . . . . . . . . . . . . . . . . 16 16 Figure Figure 11. 11. Concentration Concentration rations rations relative relative to to A1203 A1203 in in the the Pronto Pronto Paleosol Paleosol................................. 31 31 Figure Figure 12. 12. Concentration Concentration ratios ratios of of components components in in the the Denison Denison paleosol paleosol . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 31 31 Figure Figure 13. 13. Concentration Concentration ratios ratios in in Sub-Matinenda Sub-MatinendaFm. Fm., Sub-Lorrain Sub-Lorrain Fm. Fm. and and sub-Matinenda sub-Matinenda Formation Formation paleosols paleosols .............................................. 32 32 Figure Figure 14. 14. Geological Geological cross-section cross-sectionof of the the Blind 34 Blind River River and and Sudbury-Maintoulin Sudbury-Maintoulinareas areas . . . . . . . . . . . . . . .34 Figure Figure 15. 15. Metamosphism Metamosphism of of the the Huronian Huronian Supergroup Supergroup .....37 37 �Figure Figure 16. 16 . The distribution distribution of of rocks rocks of of the the Huronian Huronian 43 Supergroup.. Sault Ste Ste.. Marie-Elliot Marie-Elliot Lake Lake area area . . . . . . . . . 43 Supergroup Thessalon area Figure 17. 17. Geology of the Thessalon area .............. 46 46 Figure 18. 18 . Plan Plan and section section of of the the Geology Geology of of the the Pronto Pronto Mine Mine area area . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .54 54 19.. Geology of the Elliot Lake 58 Figure 19 Lake area area . . . . . . . . . . . . 58 Precambrian rock units units and tectonic Table 1. Table 1 . Precambrian tectonic cover and metallogenic events events in in the the Lake Lake Huron Huron region. region. ..back back cover �ELLIOT LAKE THE BETWEENSAULT SAULTSSTE. THE HURCNIAN HURONIAN SUPERGROUP SUPERGROUP BETWEEN T E . MARIE MARIE AND ELLIOT LAKE Introduction Introduction The Huronian Earth's most studied The Huronian Supergroup Supergroup is is one one of the Earth's studied sequences of sequences of rocks. rocks. Since Since the turn of the century the results results of of hundreds of Huronian rocks have been published in hundreds of studies studies of Huronian in scientific journals and government publications. These studies scientific journals publications. studies Earth's have led geoscientists geoscientists to present evidence for the Earth's of free oxygen in earliest glacial glacial periods, the development of in the atmosphere paleoplacer atmosphere of of the the early early Earth, Earth, the deposition of paleoplacer deposits tectonic activity deposits of of uranium, uranium, and evidence evidence for for plate tectonic activity during the during the Proterozoic. Proterozoic. Much of the evidence presented is is based based on rock rock exposures exposures which which will will be be visited visited during during this this field field trip. trip. Paleoproterozoic The Huronian Huronian Supergroup Supergroup is a sequence of Paleoproterozoic sedimentary and unconformably upon sedimentary and minor volcanic rocks lying unconformably Archean rocks Archean rocks of of the the Superior Superior Province Province of of the the Canadian Canadian Shield. Shield. The Superior, along The Huronian Huronian belt belt extends extends eastward eastward from Lake Superior, along the the north shore of Lake Huron to Sudbury and then northward to the north shore of Lake Huron Sudbury northward to the Noranda area Noranda area of of Quebec, Quebec, aa distance distance of of about about 450 450 km km (270 (270miles) miles) (Figure 1). The Huronian Huronian Supergroup attains it greatest thickness thickness (Figure (40,000 feet) feet) southwest southwest of of Sudbury. Sudbury. The of 12,000 12,000 metres metres (40,000 The sequence sequence thins basal units, thinning thins northward northward due due to to the wedging out of basal thinning of clastic units, and erosion within the sequence (Roscoe, of clastic units, and erosion within the sequence (Roscoe,1969; 1969; Frarey and 1970). Frarey and Roscoe, Roscoe, 1970). The The 2219 2219 Ma Ma radiometric radiometric age age of the Nipissing intrusions intrusions places an an upper Supergroup, while while the upper limit limit on on the the age age of the the Huronian Supergroup, the is probably close to the date Copper Copper Cliff Cliff Ryolite Ryolite (2450 (2450Ma) Ma) probably to the date of of initial initial Huronian Huronian deposition deposition in in the the Sudhury Sudbury area. area. The Huronian Huronian Supergroup Supergroup consists of four groups, which in in ascending stratigraphic Elliot Lake Lake Group, Group, Hough ascending stratigraphic order are: The Elliot Lake 2,3). Lake Group, Group, Quirke Quirke Lake Lake Group Group and and Cobalt Cobalt Group Group (Figures (Figures 2,3) Formations of the with the exception of the Formations the three upper groups, with Serpent Formation, continuity, and and display display a Serpent Formation, show show stratigraphic continuity, remarkable cyclicity of lithological units; beginning with remarkable cyclicity of lithological matrix-supported conglomerate(diamictite), conglomerate(diamictite), followed followed by by mudstone, mudstone, matrix-supported siltstone or or limestone by coarse, coarse, cross-bedded cross-bedded siltstone limestone and capped by sandstone. sandstone. Many Many paleocurrent paleocurrent studies studies have have shown shown paleocurrent paleocurrent flowed being the predominant predominant flowed south south to to southeast, southeast, with southeast being direction(Figure 5) . direction (Figure 5). 1 �Whitewater Group __..'' Internal tonal boundary Provincial boundary Murray Foul, System Grenville Front Tectonic Zone Figure 1. The distribution of rocks of the Huronian Supergroup Poleo,oic rocks Huronion Supergroup Sudiry Igneous Complex Keweeriowan rocks Grertville Province Superior Province �______ __________ (2.21 Ga) Ga) (2.21 Nipissing Gabbro. diabase. gronophyre NipissingDiabcise Diabase Gobbro, diobase, gronophyre - NNNNNN NNNNNN Quartz arenfte, orenite,subarkose suborkose Bar B~~ River ~i~~~Fm. F ~ .Quartz minor minor mudstone, mudstone,siltstone. siltstone. -,-N__N N N N N N N NNN\ NNNN 4''' Slltstone, mudslone mudstone Slitstone, Gordon chert, sandstone GordonLake LakeFm. Ft-f~. chert, sandstone NN'NNN'\N\N \NNNNNNNNNNNN 'N --N N N N N N N NNNN\NNNN Lorrain Fm. Fm. NNN NN N N N N NN N N NN N N N N NN N N N N NNNN \N N N N N N N N NNNNNNNNNNNNN N N N' NNIX N N N N N - 0-C> - C' - Gowganda Arkose. slltslone Gowganda Fm.Fm. Arkose,slltstone Diamlctite, polymictic conglomerate conglomerate Diamictite, polymictic Unconformity Unconformity -.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.. N NN N N N N NN N N N NN NNNNNN NNN N N N N N NNNN NNN NN N N N N N / / / / / / / / / / / / / / / /1A -c--V-CC Cc z_ SerpentFm. Fm. Serpent Subarkose. wacke Subarkose, wacke Espanola ppanola Fm. F ~ Dolostone hfostone slltstone. wooke sinstone. , wwke limestone limestone Bruce BruceFm. Fm. 0) C) x S Ca 0 -3 ¡ -' Diamictite. Diomictite. sandstone sandstone siltstone siitstone 'Do0 (U ;. 0 a 6 - Nj N NNN N N NNNNNNN Mississagi MississagiFm. Fm. N N N NN NNNN NNN N NN N NN N NNNNN NNN NNNNNNNN NNNN NNN N NNNNNNN NNNN NNN NNNNNNNNNNNN Pecors P ~ C OFm. Fm. ~S Subarkose. Suborkose,arkose orkose quartz-pebble quartz-pebble conglomerate conglomerate N 'Vc-VN--N-- McKim McKimFm Fm NN NNNNNNNNNNNNC NN NNNNNNNNNNNNNNNNN NN NNNNNNNNNNN NN N N NN NNNNNNNNNNNNN 'N \NNNNNNNNNNNN N N NN NNNNNNNNNNNNN 1' Mudstone, siltstone Mudstone.siltstone Disconformity Thessalon Fm. Arkose. subarkose quartz-pebble conglomerate Molt volcorks Livingstone Creek Fm. Areh4o, + + 8oqrtetd. + + 1 Dkconfo,,,,* DcOnfo,Th#)I Minor qtz. peb. cong. Disconformity 1 Layered gabbro, onorthosite + a0 a. ¡ -J 2 - 3 t (:5 i 0 0 0 x - Mudstone, Mudstone.siltstone siltstone wacke Mafinenda Fm a- 0) a, S x 6a) 00 Ramsay RamsayLake LakeFm. Fm.Diomictite Dfomictite .-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-. --:> : +j 0—0 00 00 Mudstone. Mudstone.siftstone siftstone NNNNNNNNNNNNNN -NN NNNNNNNNNN \NNNN NNNNNNN N 5 -3 ¡ no - 2 .: .: if:0: -o• :-. a a 0a ° a a 0 C> 'C> , C> C> Quartz arenne, arenlte, quartzquartzpebble conglomerate congbmerate pebble Arkose. subarkose Arkose. subarkose °- a) S 2o w Mefavolcanics, metasedirnents, gronitic rocks Figure Figure 2. 2. Huronian Huronian Stratigraphy Sault Ste. Ste. Marie-Elliot Marie-Elliot Lake Lake area area Stratigraphy -- Sault 3 �The The Elliot Elliot Lake Lake Group Group The Huronian groups groups The Elliot Elliot Lake Lake Group Group differs differs from the overlying Huronian in internal stratigraphy stratigraphy is is generally generally discontinuous discontinuous in that: that: (flits (1)its internal does not not show show the the diamictite-mudstonediamictite-mudstoneand less less extensive; extensive; (2)it does sandstone sequence; the only only important important uranium uranium sandstone sequence; (3)it (3)it contains the deposits; deposits; (4)and (4)and the the only only volcanic volcanic rocks rocks in in the the entire entire supergroup. supergroup. The Livingstone The Livinastone Creek Creek Formation Formation polymictic conglomerates The polymictic conglomerates and and sandstones sandstones of of the the Livingstone Livingstone Formation (Frarey, the lowermost lowermost Huronian Huronian Creek Formation (Frarey, 1967) form the formation. It formation. It is is the the only only Huronian Huronian formation formation known known to to precede precede some of the the Huronian Huronian igneous igneous activity. activity. The Livingstone in) The Livingstone Creek Creek Formation Formationis is at at least least1200 1200feet feet(400 (400 m) thick thick in in the the Sault Sault Ste. Ste. Marie Marie area area and and between between 300 300 feet feet (100 (100 m) m) Thessalon area. and 1000 in) and 1000 feet feet(300 (300 m) thick thick in the Thessalon area. The sandstone and The formation formation has has been correlated with grey sandstone conglomerate near Lake in Township (Bennett, conglomerate near Crazy Crazy Lake in Nicholas Township (Bennett,1978; 1978; member occurs Bottrill, 1971) A remnant of the conglomerate conglomerate member occurs as as Bottrill, 1971). A far far east east as as Pecors Pecors Lake Lake on on the the south south limb limb of the the Quirke Quirke Lake Lake (Figures 4, Syncline (Jensen, Livingstone Creek Syncline (Jensen,1990) 1990) (Figures 4, 6,). 6,). The Livingstone Creek Formation has Formation has not not been been recognized recognized east of the Quirke Quirke Lake Lake - Syncline. Syncline. of two two distinctive distinctive rock The Livingstone Livingstone Creek Creek Formation consists of types: an medium-grained arkose, arkose, subarkose subarkose and an upper upper finefine- to medium-grained subwacke; subwacke; and and aa lower lower clast-supported clast-supported polymictic conglomerate conglomerate with with cobble cobble to to boulder-sized boulder-sized megaclasts. megaclasts. The sandstone sandstone member of Formation may of the the Livingstone Livingstone Creek Formation may be be distinguished by the the uniform uniform grain distinguished from from other other Huronian sandstones by size Mudstone and and pebbly pebbly size (fine(fine- to to medium-sand) medium-sand) of the former. Mudstone units units (even (even isolated isolated pebbles) pebbles) are are lacking lacking within within the the sandstone sandstone member of Another characteristic member of the the Livingstone Livingstone Creek Creek Formation. Formation. Another characteristic feature of the sandstone units is the presence of carbonate feature of the sandstone units is of carbonate along along the foresets foresets of of the the commonly commonly well-developed well-developed trough trough cross-beds. cross-beds. Planar Planar cross-beds cross-bedsare are rare. rare. 4 �___ ______ ____ _____ ___ COBALT GROUP GROUP COBALT Bor River River Formation Formation Bar GordonLake LakeFormation Formation Gordon Lorrain Formation Formation Lorroin GowgandaFormation Formation Gowganda W I R K E LAKE LAKE GROUP GROUP QUIRKE m JW -.-----a MSn eefl -V •CRIO r0LW -----6 — I ———— I CI M"em,-& of 01 a ~ Mudstone. satafone. cothonote (Esponola Elm) MARINE 0 LCi1 E3 C Mississagi Mississagi Formation Formation Pecors Formation Formation Pecors Lake Formation Formation Ramsay Lake 0 0 S LakeGroup Group Elliot Lak. i)tarnlclfle. mudstone, sfltstone h k w e , m"d,~.'i"%,me clad suppotted conglomerate cm-dcmb-,,,e GLACIAL GLACIAL I____ lu II>- V (Melornoaphac grade mainly < m Mg ,wS b &W sst-gIreeoacbbt ~ " w ~lode,) l l ~ k , ~ Disconformity V 3 3 ~ FLU VIAL FLUVIAL 4 HOUGH LAKE LAKE GROUP GROUP HOUGH igure Figure Mose, m- soborkoso. m m - , qoodz q"om orenlte '"mu. quartz-pebble q w * conglomerate . ~ ~ m _____ Iii; rH!>. ki MalnRock RockTypos Types Mum -&" Ir 0 Serpent Formation Formation Serpent Espanola Espanola Formation Formation Bruce Formation Formation Bruce I I" / 'i Volcanic racks, morthe ond fluvial depoefta. Poleopbceruroruwnaeposns . The The cyclicity of of Huronian Huronian sedimention . LEGEND LEGEND HoughLakeGroup nough Lake Group fflIhHI MATINENDA MATINENDAFM FM m-. @I quatlz-peliue wa**-k.m=mte congianwate -- ri .... ..... - -, k - +1 + -P .-, tJ ThjJ.py —. —- —. N SAULT SAULT STE. STE. MARIE MARIE AREA AREA -. Uncønfonnhlyorthsconfonnity Paleosol on LMngstone Cr. Fm and basaltic dike (Ibessalon Fm.) -. -. 1., u.m. / —. L w " ! ~ ~ ~ , e ARCHE.AN BASEMENT G(arHtcgreenstone Quanz—pe4bIecongIooiemte loon C THESSALON FM. Dasal.sndeslerliyolileflows -at. -*e ,h"dde k basaJldce .,*e LNINGSTGNECREEK CREEKFM. FM, LMNGSTONE mey a*sxbrkme PolylilIclic conglomerate :LL -. ThESSALON THESSMONAREA AREA EIAUGHT0N-OrTER HAIJGHTONQTTERTWPS W S (DUNN'S (WNWS VALLEY V&Lâ‚ AREA) AREA) CRAZY C W LAXE LbKEAREA AREA NiCHOLAS NICHOUSTWP. W. -. -. -. , auoT LAKE 'ELLIM ME AREA AREA Stratigraphic relationships in the Elliot Elliot Lake Group — Figure 4. 4 . Stratigraphic Figure Sault Marie Elliot Elliot Lake Lake area. area. Sault Ste. Marie 5 5 e �Clast-supported, polpictic polymictic conglomerate is a a prominent prominent rock type Clast-supported, in the lower lower sections sections of of the the Livingstone Livingstone Creek Creek Formation. Formation. CobbleCobbleto boulder-sized clasts to boulder-sized clasts of of grey grey granitic granitic rocks rocks and and minor minor mafic mafic plutonic and metamorphic rock clasts clasts are set in a sparse matrix of coarse, of Huronian Huronian coarse, grey arkose arkose or arkosic grit. No clasts of recognized. Thin units units of of cross-bedded, cross-bedded, grey volcanic rocks were recognized. arkose are locally locally interbedded interbedded with with the the conglomerate conglomerate (Frarey, (Frarey, 1977, al., 1991). 1977, Bennett et al., 1991). The The grey grey granitic granitic mega-clasts mega-clasts of of the the conglomerate member is in contrast with with the predominantly predominantly reddish conglomerate hues hues of of the the underlying underlying Archean Archean basement basement rocks. rocks. This This colour colour difference of ferric iron in difference appears to be due to the reduction of the feldspars conglomerate, and feldspars of the red granitic clasts in the conglomerate, not a a result result of of differing differing provenance. provenance. This This conclusion conclusion is is supported supported by the the observation observation that that granitic granitic rocks rocks in in aa "paleosol "paleosol zone" few tens tens of of metres metres below below the the base base of of the the zonet9a few few metres to to aa few Livingstone Creek Livingstone Creek Formation Formation commonly commonly display display a a grey grey colour colour as as well. well. The The clast clast size, size, local local source source and and low low stratigraphic stratigraphic position position of of Livingstone Creek conglomerates the Livingstone conglomerates are are consistent consistent with with deposition mediumdeposition on on an an alluvial alluvial fan. fan. The The uniform, uniform, finefine- to to mediumgrained sand of the trough cross-bedded sandstone member sand of the trough cross-bedded sandstone member suggests suggests a different, different, although although probably probably related related depositional depositional environment environment than than that of the the conglomerate. conglomerate. The The sandstone sandstone member member may may represent represent a fault bounded bounded valley valley deposition by median streams flowing in a with scarps scarps covered by alluvial alluvial fans fans (Bennett (Bennett et et al., al., 1991). 1991). The The well sorted nature of the sandstone suggests an aeolian component sorted nature of the sandstone suggests an aeolian component (Meyer,W., W., 1983) 1983). or even aeolian aeolian deposition deposition (Meyer, Early Earlv Huronian Huronian Intrusive Intrusive Rocks Rocks Several petrographically petrographically distinctive, Several distinctive, mafic to to ultramafic ultramafic intrusive bodies intrusive bodies have been recognised recognised between the the eastern eastern end end of of the Sudbury Igneous Complex and the nose of the Quirke Lake Sudbury Igneous Complex and the nose the Quirke Lake Syncline. The intrusions Syncline. intrusions are are characterized characterized by the the presence presence of of anorthositic phases and locally well developed, primary rhythmic anorthositic phases and locally well developed, primary rhythmic layering of alternating layering alternating anorthositic anorthositic and and gabbroic gabbroic layers. layers. Segregations, Segregations, dikes dikes and and sheet-like sheet-like bodies bodies of of granophyre granophyre are are locally present (Card and Palonen, 1976; Peck et al., 1995). locally (Card and Palonen, 1976; Peck et al., 1995). Major intrusions Lntrusions of gabbro-anorthosite gabbro-anorthosite are are found found at at Agnew Agnew Lake Lake and Palonen, Palonen, 1976) and at East Bull Bull Lake Lake (Born (Born and and James, James, (Card and (1991) report report two 1978; 1978; Kamineni Kamineni et et al., al., 1984). 1984). Bennett, Bennett, et et al. a1.(1991) two 6 �additional additional bodies bodies between between Blind Blind River River and and Thessalon. Thessalon. All All gabbrogabbroanorthosite bodies bodies found found to to date date have have been been emplaced emplaced in in the the anorthosite Archean Archean basement basement at, at, or or just just below below the the Archean-Huronian Archean-Huronianboundary. boundary. Krogh (1984)reported reporteda aU-Pb U-Pbage age2491+5.5 2491 Ma al.(l984) Ma for for zircons zircons Krogh et et al. from the the gabbro-anorthosite gabbro-anorthosite intrusion from intrusion at at Agnew Agnew Lake Lake and and 2480+10-5 2480'° for for the the East East Bull Bull Lake Lake gabbro-anorthosite gabbro-anorthosite body. body. The The similarity similarity of of these these ages ages to to the the 245O2510Ma 2450+25.10 Ma (U-Pb (U-Pbzircon) zircon) age age of of rhyolite rhyolite of of the Huronian Huronian Copper Copper Cliff Cliff Formation Formation(Krogh (Kroghet et al., al.,1984) 1984) the indicates that that these these gabbro-anorthosite gabbro-anorthosite intrusions intrusions form form part part of of indicates the early Huronian volcanic events (Card, 1978a) the early Huronian volcanic events (Card, 1978a). The The north north to to northwest northwest trending trending Matachewan-Hearst Matachewan-Hearst dike dike swarm swarm is is the the second second largest largest dike dike swarm swarm of of the the Canadian Canadian Shield. Shield. The The 2.45 2.45 Ga Ga age age of of the the swarm swarm (Heaman, (Heaman,1988)is 1988)is essentially essentially the the same same as as that that of of the East Bull Lake Suite and the Huronian volcanic rocks of the the East Bull Lake Suite and the Huronian volcanic rocks of the Copper Copper Cliff Cliff Formation. Formation. Krogh report a U-Pb U-Pb age age of al. (1996) (1996) report of 2.48 2.48 Ga Ga for for the the Murray Murray Krogh et et al. Granite; Granite; one one of of several several granitic granitic intrusions intrusions cutting cutting the the lower lower part of the Huronian Supergroup near Sudbury. It is possible part of the Huronian Supergroup near Sudbury. It is possible that that these felsic volcanic volcanic these intrusions intrusions are are magma magma chambers chambers for for Huronian Huronian felsic rocks rocks in in the theSudbury Sudburyarea. area. Huronian Huronian Volcanic Volcanic Rocks Rocks of of the the Sudbury SudburyArea Area The The Huronian Huronian bimodal bimodal volcanic volcanic sequence sequence in in the the Sudbury Sudbury area area has has been been subdivided subdivided in in the the predominately predominately mafic mafic Elsie Elsie Mountain Mountain (1000 (1000mm thick) thick) and and Stobie StobieFormations Formations(1500 (1500mmthick) thick), and and the the felsic felsic Copper Cliff Formation (760 m thick) by (Card 1978a) Copper Cliff Formation (760 m thick) by (Card 1978a) (Figure (Figure7). 7). Krogh zircon) Krogh et et al.(1984) al. (1984)obtained obtained an an age ageof of24502510Ma 2450+25.10 Ma(U-Pb (U-Pb zircon) age age for for rhyolite rhyolite of of the the Huronian Huronian Copper Copper Cliff Cliff Formation; Formation; the the only only Huronian Huroniansupracrustal supracrustalrock rock for for which which there there is is an an absolute absolute age. age. The The volcanic volcanic rocks rocks of of the the Sudbury Sudburyarea area show show evidence evidenceof of submarine submarine eruption from fault controlled vents along the edge of eruption from fault controlled vents along the edge of aa depositional depositionalbasin basin into into which which arkosic arkosic sandstones sandstoneswere were being being transported Archean granitic granitic terrain terrain to to the the north, north, while while transported from from the the Archean turbidites turbiditeswere were deposited deposited from from sediment sediment from from both both the the volcanic volcanic 1978a). The The and rejuvenated rejuvenated basement basement marginal marginal to to the the basin basin (Card, (Card,1978a). and volcanic rocks of the Sudbury area differ in terms of internal volcanic rocks of the Sudbury area differ in terms of internal stratigraphy, stratigraphy,overall overall thickness thickness and and depositional depositional environment environment from from the the Huronian Huronianvolcanic volcanic rocks rocks in in the the Sault Sault Ste. Ste. Marie-Elliot Marie-ElliotLake Lake , area. area. 7 �00 Figure 5. Paleocurrent roses for the Mississagi and Matinenda fonnations. �The The Huronian Huronian Volcanic Volcanic Rocks Rocks of of the the Sault Sault Ste. Ste. Marie-Elliot Marie-Elliot Lake Lake area a Volcanic Volcanic rocks rocks overlying overlying the the Livingstone Livingstone Creek Creek Formation Formation were were named the the Thessalon Thessalon Formation Formation of of the the Elliot Elliot Lake Lake Group Group by by named Frarey(l967). Frarey(l967). Jolly(1987) Jolly(l987) concluded concluded the the Thessalon Thessalon Formation Formation is is aa continental continental flood flood basalt basalt sequence sequence associated associated with with continental continental rifting. Bennett Bennett et et al. al.(1991) volcanic rifting. (1991) proposed proposed that that the Huronian Huronian volcanic rocks of of the the Quirke Quirke Lake Lake Syncline Syncline should should also also be correlated correlated with with rocks the the Thessalon Thessalon Formation. Formation. Attempts Attempts to to obtain obtain an an absolute absolute age age determination determination from from rocks rocks of of the the Thessalon Thessalon Formation Formation have have so so far far been been unsuccessful. unsuccessful. However However the spatial spatial association association of of the the East East Bull Bull Lake Lake intrusions intrusions with with the the the Huronian of the the Quirke Quirke Lake Lake Syncline Syncline suggest suggest Huronian volcanic volcanic rocks rocks of Huronian Huronian volcanism volcanism in in that that area area occurred occurred about about the the same same time time as as the emplacement emplacement of of the the East East Bull Bull Lake intrusions intrusions (2480 (2480 Ma). Ma). Given Given the the the potential potential error error for for the the relevant relevant age age dates dates (Krogh (Kroghet et al., al., 1984), the age of the Thessalon Formation may not differ 19841, the age of the Thessalon Formation not differ significantly from from that that of of the the Copper Copper Cliff Cliff Formation Formation of of the the significantly Sudbury Sudbury area area (2450 (2450Ma). Ma) . The The maximum maximum thickness thickness of of the the Thessalon Thessalon Formation Formation in in the the Sault Sault Ste. Marie Marie area area is is approximately approximately 650 650 m m (2100 (2100 feet) feet) and and 820 820 mm Ste. (2700 (2700 feet) feet) (Frarey, (Frarey,1977) 1977). Diamond Diamond drilling drilling has has indicated indicated at at least least 670 670 mm (2200 (2200 ft) ft) of of Thessalon Thessalon volcanics volcanics under under Lake Lake Huron Huron south south of of the the town town of of Thessalon. Thessalon. The The Thessalon Thessalon Formation Formation may may be be as much much as as 1080 1080 mm (3500 (3500 feet) feet) thick thick at at Bass Bass Lake Lake in in Aberdeen Aberdeen as Township. Township. . Tomlinson(l996), Tomlinson(l996), who who studied studied the the geochemistry geochemistry of of the the Huronian Huronian volcanic volcanic rocks rocks between between Sault Sault Ste. Ste. Marie Marie and and Thessalon, Thessalon, concluded concluded that that the the lavas lavas of of the the Thessalon Thessalon Formation Formation are are divisible divisible into into 77 distinct distinct units units based based on on mapping, mapping, petrography petrography and and major major and and trace trace element units were were grouped grouped into into 8). The The 77 units element geochemistry geochemistry (Figure (Figure 8). two two "lava "lava series". series".The The upper upper lava lava series series (units (units66 and and 7, 7, of of Tomlinson, Tomlinson, 1996) 1996) is is equivalent equivalent to to the the upper upper tholeiitic tholeiitic basalt basalt sequence of Bennett et al. sequence of Bennett et al. (1991) (1991). The The lower lower lava lava series series (units (units 1-5, 1-5, of of Tomlinson, Tomlinson, 1996), 1996), consists consists mainly mainly of of basaltic basaltic andesite andesite with with subordinate, subordinate, local local rhyolite, rhyolite, mugearite, mugearite, andesite andesite and and high high magnesium magnesium basalt basalt flows; flows; and and corresponds corresponds to to the the "diverse "diverse member" member'' . of (1991). of Bennett Bennettetetal. al.(1991). 9 �___ 5 LEGEND PH Mesa-Proterazoic and Phanerozalc racks (Mngsfone Creek Fm. Sandstone. polymlctic conglomerate (tras, outcrop dabs. Upper Huronian rocks East Bull Lake Suite Goobro, onorthotite Thessalon Formation Sasolt. Ifli] Archean racks andesite. (waite etc •__s (Ftom outcrap and dre hale data) Quartz pebble conglemerote at baseotmessatonflows. (locaty rodioocttve) r' + / I -4.j/ c._r\7_ Se. a.......'4 + — —s 7 + + + + + + + + + + + + + + + ÷ + + + (Con, a hot. dot ,4' 4, NON — rocte (from Dtt4ltng =_) No mr÷+ —U— + + No I+aonla, thorn Fault J tO U Hi,oS, ÷ ± > .1*' -'sr -c + /e—' EtotL&o+++++J Murray Fault ——S——— —. Lake Huron Figure Figure 66 . . The Distribution of Thessalon Formation Formation The Creek Formation Formation. and Livingstone Creek 47°N orn7N km / ult St LAKE 46 it HURON Sudbury Structure Lillilill Poleozoic racks Huronion Supergroup Grenvitle Province Metasedimentary rocks - Metavolconic rocks Metovolconic rocks Exposed in in outcrop Exposed outcrop ~ m m Diamond-drill n d - d r r l indicated l 4ndtcote-d 7 ? Distribution D k ~ n a u ~ i ounknown unknown n Superior Province superior Province \ Quirke Ouifke Loke Loke Syncline Synclor ,' Fault Faulr Figure 7. 7. Distribution Distributionof ofHuronian Huronianvolcanic volcanic rocks. rocks. 10 �- unit f$* t t4 Livingstone Creek Fm 500m — unit 1 Bass Lake Figure 8. Schematic stratigraphy of the Thessalon Formation. Livingstone Creek Fm Radioactive \ Basalt to andesite cycles Rhyolite —.. Basalt —_- Thessalon unit I Urn 650 to 820m From Tomlinson (1996) Livirigstone Creek Fm unit 7 B as a 1200m Upper Island Lake �20 20 I basalts A - Within plate basalts 10 * 1 B - Island Island arc arc basalts basalts 0- Mid-ocean ridge basalts Z'/Y 5 0 I 1000 10 Zr Tc2 TO, 0 island arc basalts 0.5- i 200 200 IOU 100 40 40 300 300 400 400 Zr FeO* FeO* Nb * 2 A WPA ALAII WPT AII,C E 51 -56%SE02 - 56% 30, MOPS: S N MOPS: D VAB C,D y Zr/4 - Spreading Centre I -Spreading 1 Centre Island Island Orogeni 2 -- Orogenic 3 -- Ocean Ocean Ridge and Floor 4--Ocean 4 OceanIsland Island Continental 5 --Continental MgO Unit 1=0 Unit2=° Unit3=a Unit4='< Unit5 Unit6=° Umt7=x WPA = = within plaEetholeiite, tholeiite,E-MORB=enriched E-MORBenriched type mid-ocean within plate alkali basalt, basalt, WPT—within WPT=within plate mid-ocean ridge ridge basalt, basalt, N-MORB=normal N-MORB=nonnal mid-ocean mid-oceanridge ridgebasalt, basalt,VAB—volcanic VAB=volcanic arc arc basalt. basalt. Formation Figure 9. 9. Discrimination Discrimination diagrams diagrams for volcanic rocks of the Thessalon Formation (from Tomlinson, Tomlinson, 1996). 1996). 12 203 �Bennett et (1991) proposed proposed that that the the upper, upper, basaltic basaltic flows Bennett et al. al.(1991) flows of of probably represent the Thessalon Thessalon Formation (upper (upper lava lava series) series) probably represent part of of aa continental diverse continental flood basalt sequence, sequence, while the diverse member (lower (lower lava lava series) series) appears appears to to have erupted erupted from from central central member vents. The The Ruronian Huronian volcanic volcanic rocks rocks of the Quirke Lake Syncline Syncline Quirke Lake display lithological display lithological and geochemical similarities similarities to to the the lower lower lava lava series series of the Thessalon Formation Formation west of the the Quirke Quirke Lake Lake Syncline (G. (G. Bennett, Bennett, unpublished unpublished data). data). Syncline The The upper, upper, tholeiitic tholeiitic basalt flows flows of the Thessalon Thessalon Formation Formation (upper of Tomlinson, Tomlinson, 1996) are almost almost uniformly (upper lava series of uniformly greenish-grey finemedium-grained tholeiitic greenish-grey fine- to medium-grained tholeiitic metabasalt. metabasalt. The The essential minerals essential minerals are are albite, albite, actinolite, actinolite, chlorite, chlorite, clinozoisite, epidote and Fe-Ti Fe-Ti oxides. Primary clinozoisite, Primary clinopyroxene clinopyroxene is is present present in in only only aa few few samples samples of of basalt from from the the Sault Sault Ste. Ste. Marie Marie generally area. The andesitic rocks of the lower lava series are generally darker coloured and commonly contain stilpnomelane and biotite darker coloured and commonly contain stilpnomelane and biotite with with green green pleochroism (Fe3 (Fe+3rich?) rich?) in in addition addition to to albite albite and and actinolite actinolite (Bennett (Bennett et et al. al. 1991) 1991). Tomlinson(1996) the reports the Tomlinson(1996) reports presence of in some some flows. flows. Quartz is is a a minor component component presence of tremolite tremolite in metamorphic of basaltic and andesitic types. In In most areas the metamorphic grade of the Thessalon Formation flows grade flows is lower greenschist . fades. facies . Amygdules of quartz and Amygdules of epidote, epidote, chlorite, chlorite, calcite, calcite, quartz stilpnomelane, stilpnomelane, in in complex complex zonal zonal arrangements, arrangements, are are common. common. Flattened chlorite-filled amygdules a centimetre or Flattened chlorite-filled amygdules centimetre or less less across across Thessalon are a distinctive feature of most mafic flows of the Thessalon Formation. structures are rare but in most Formation. Pillow structures but were were observed observed in areas. areas. Scoriaceous Scoriaceous flow-tops flow-tops and and cross-cutting cross-cutting breccias breccias are are commonly filled filled with a fine-grained fine-grained mixture of quartz and grey grey to to commonly quartz and red secondary albite. red secondary albite. Tomlinson(1996) Tomlinson (1996)states: states: "The data indicate that that the lavas lavas are comparable comparable to "The field and geochemical data to modern day andesites but that their their source modern day continental continental basalt and andesites source was was similar 9 shows shows the the lavas lavas plotted plotted similar to to that that of of island island arc arc basalt. basalt. Figure Figure 9 variety of comparable to on a variety of discrimination discrimination diagrams where they are most comparable to modern Their arc-basalt modern within-plate within-platebasalt. basalt. Their arc-basalt geochemical geochemical characteristics characteristics result from upper mantle mantle that had been result from their derivation from an upper metasomatically enriched during subduction Kenoran orogeny. metasomatically subduction in in the Kenoran orogeny. Units Units within the generated from within the sequence sequence were generated from different pulses of of magma, magma, each each region of the relatively relatively homogenous of which which stemmed stemmed from from a different region homogenous Huronian mantle. lavas require generation generation from Huronian mantle. Only the unit 2 lavas from part of of 13 �the mantle with with slightly slightly different characteristics similar to to the characteristics to a source source similar that that required required to to generate generate island island arc arc basalt basalt 1D16 ID16 (a (a primitive basalt used used primitive basalt by (1996)inmaking making calculations) calculations). Different Different degrees degrees of of partial partial by Tomlinson Tomlinson (1996)in melting of of this this source source that that contains contains garnet in the residue (at less less than than melting residue (at 29.8% partial partial melting) are are responsible responsible for the REE characteristics of 29.8% characteristics of each generation of the the lower each unit. unit. In In the generation lower lava lava series, series, different different batches batches of or lesser of magma magma underwent underwent crustal crustal contamination contamination to a greater or lesser extent extent within within the the lower lower or or upper upper crust crust (or (or both) both) prior prior to to eruption. eruption. The The upper upper lavas lavas series series rocks rocks are are not not contaminated. contaminated. In In all all but the the unit unit 22 lavas lavas crystal fractionation fractionation occurred occurred both early, as magma to shallower shallower crystal magma ascended ascended to depths, depths, and and later, later, in in shallow shallow level level sills sills or or magma magma chambers. chambers. Early Early fractional Mg, Ni and Cr fractional crystallisation crystallisation was responsible responsible for the low Mg, Cr values values in in most most units, units, while while later later stage stage crystal fractionation fractionation was was responsible responsible for for the the major major element element and compatible compatible element trends trends within within single (Tomlinson, 1996). plots"(Tomlinson, single units, units, as as shown shown on on bi-element bi-elementplots" 1996). . On On the the geochemistry geochemistry and and tectonic setting setting of the Thessalon Thessalon volcanic volcanic rocks rocks Tomlinson Tomlinson (1996) (1996)states: states: "various "various lines lines of of evidence evidence from from the the Elliot Elliot Lake Lake Group Group as as aa whole whole can can be be used used to to characterize characterize the the Ruronian Huronian rifting rifting event. event. Active Active rifting rifting involves involves deep deep mantle mantle upwelling upwelling or or plume plume magmatism magmatism which which splits splits the the continental passive rifting continental crust; crust; whereas whereas passive rifting involves involves mantle diapirism diapirism and and adiabatic adiabatic upwelling upwelling induced induced by by differential differential stresses stresses and and stretching stretching in in the the lithosphere lithosphere (Wilson, (Wilson,1989) 1989). The The geochemical geochemical evidence Formation indicates that the evidence from from the the Thessalon Thessalon Volcanic Formation the source upper mantle mantle rather rather than a deep source of of the the lavas lavas was metasomatised upper deep mantle mantle or or plume plume component. component. Structural Structural subsidence subsidence patterns patterns in in the the Archean basement basement (Zolnai (Zolnai et et al., al., 1984) 1984) are thought to be responsible responsible Archean for for lithospheric lithospheric stretching, stretching, in-turn in-turn causing causing mantle mantle upwelling, upwelling, episodic episodic partial partial melting melting and and volcanism. volcanism. This This is is supported supported by by the the presence 400 metres of of Huronian Huronian syn-depositional faults faults in in up up to to 400 presence of of syn-depositional sedimentary sedimentary rocks rocks below below the the volcanics. volcanics. G. G. Bennett Bennett (personal (personal communication,1996) 1996) has has also also described described syndepositional syndepositional features features(at (at22 communication, locations sault Ste. Marie) Marie) where where sedimentary sedimentary locations near near Elliot Elliot Lake and Sault rocks ill fractures fractures in rocks of of the the Livingstone Livingstone creek Creek Formation Formationinf infill in the the underlying underlying Archean Archean basement. basement. These These features features indicate indicate that that initially initially volcanism volcanism was was aa consequence consequenceof ofrifting. rifting. In In active active rifts rifts just just one one uplift uplift and and melting melting event event occurs occurs as as aa plume plume impacts impacts the the lithosphere, lithosphere, but but in in passive passive rifts rifts uplift uplift and and melting melting are are episodic episodic (Williamson (Williamson and and Keen., . Multiple Keen.,1995) 1995). Multiple erosional erosional surfaces surfaces within within the the Elliot Elliot Lake Lake Group occurred. Based Group indicate indicate that that numerous numerous episodes episodes of uplift occurred. Based on on these these lines lines of of evidence evidence the the Huronian Huronian rifting rifting event event can can best best be be characterised characterised as as aa typical typical passive passive rifting riftingevent" event" (Tomlinson, (Tomlinson, . 1996) 1996). Sedimentary Sedimentarv Rocks Rocks Associated Associated with with the the Thessalon Thessalon Formation Formation In In the the Sault Sault Ste. Ste. Marie Marie area, area, thin thin units units (<10 (<I0m) m) of of radioactive radioactive and and pyritic, pyritic, quartz-pebble quartz-pebble conglomerate, conglomerate, with directly directly overlying overlying arkose arkose and and arkosic arkosic grit grit are are found found just just above above lowermost lowermost flows flows of of 14 �the the Thessalon Thessalon Formation. Formation. In In the the Thessalon Thessalon area area and and in in the the Quirke Quirke Lake Lake Syncline, Syncline, similar similar units units of quartz-pebble quartz-pebble conglomerate conglomerate and and arkose are found directly below the mafic volcanic rocks where arkose are found directly the volcanic rocks where they they lie lie upon upon the the Livingstone Livingstone Creek Creek Formation, Formation, or or upon upon the the Archean Archean basement, basement, where where the the former former is is not not present present (Hay, (Hay,1963; 1963; Bennett Bennett et et al., al., 1978; 1978; Meyer, Meyer, 1983). 1983). Bennett et et al. al.(1991) of these these Bennett (1991) proposed proposed that that the wide distribution distribution of units units (Figures (Figures4, 4, 6) 6) indicate indicate the the presence presence of of aa disconformity disconformity at at the base of the Thessalon Formation throughout the Sault Ste. the base of the Thessalon Formation throughout the Sault Ste. Marie-Elliot Marie-Elliot Lake Lake area area. The The Matinenda Matinenda Formation Formation The The Matinenda Matinenda Formation Formation of of the the Elliot Elliot Lake Lake Group Group (Roscoe, (Roscoe,1957) 1957) is is aa sequence sequence of of arenites arenites and and intercalated intercalated quartz-pebble quartz-pebble conglomerates which host the once important conglomerates which host the once important uranium uranium deposits deposits of of the the Elliot Elliot Lake Lake area area (Figure (Figure2) 2 ) . The The Matinenda Matinenda Formation Formation is is up up to to 180 180 mm (600 (600 feet) feet) in in the the Elliot Elliot Lake Lake area area (Robertson, (Robertson,1981) 19811, where volcanic rocks rocks and and Archean Archean basement. where it it lies lieson on1-luronian Huronian volcanic basement. In In the the Thessalon Thessalon and and Sault Sault Ste. Ste. Marie Marie areas areas the the Matinenda Matinenda Formation Formation consists predominantly predominantly of of fine fine to to medium medium grained grained subarkose subarkose and and is is consists probably probably less less than than 50 50 m(150 m (150ft) ft)thick thick(Bennett (Bennettet etal., al.,1978 1978). ). In In the the Sudbury Sudbury area area clastic clastic units units correlated correlated with with the the Matinenda Matinenda Formation Formation are are as as much much as as 600 600 mm (200 (200ft) ft) thick thick but but they they thin thin rapidly rapidly eastward eastward where where they they are are intercalated intercalated with with the the mainly mainly metavolcanic rocks of the Stobie Formation and the mudstones metavolcanic rocks of the Stobie Formation and the mudstones of of the the McKim McKim Formation Formation (Card, (Card,1978a). 1978a). . The The most most abundant abundant rock rock type type of of the the Matinenda Matinenda Formation Formation in in the the Elliot Elliot Lake Lake area area is is generally generally described described as as mediummedium- to to coarsecoarsegrained subarkoses, arkoses and grits consisting of poorly grained subarkoses, arkoses and grits consisting of poorly sorted sorted quartz quartz and and feldspar feldspar grains grains set set in in aa matrix matrix of of sericite sericite and and comminuted sodic feldspar feldsparis is comminuted fragments. fragments. The The ratio ratio of of K-spar K-sparto to sodic about about 8:1. 8:l. Minor Minor constituents constituents are are pyrite, pyrite, calcite, calcite, chlorite, chlorite, zircon zircon and and rarely, rarely, leucoxene leucoxene coated coated iron iron oxides oxides and and monazite monazite Variable (Robertson, 1968) (Robertson, 1968). Variable amounts amounts of of sericite sericite produce produce what what has has variously variously been been described described as as aa green, green, apple apple green green or or greenishgreenishyellow yellow colour. colour. Well Well sorted sorted quartz-pebble quartz-pebbleconglomerate conglomeratebeds, beds, containing containing well well rounded rounded pebbles pebbles and and cobbles cobbles of of quartz quartz and and chert, chert, and and pebbly pebbly subarkose subarkose units units are are scattered scattered throughout throughout the the coarse coarse subarkose units of the Matinenda Formation, but are more subarkose units of the Matinenda Formation, but are more common common near near the thebase. base. (Robertson, (Robertson,1968; 1968; Pienaar, Pienaar,1963). 1963). . Trough cross-bedding,scour scour and and fill fill structures structures are are common common in in Trough cross-bedding, 15 �Cl-) N U) 0.6 12 2.4 14 I 21 I 35 _I 42 I Pebble size (mm) 28 I S S S S 49 56 From Theis, 1976 S S Figure 10. Pebble size vs. pyrite grains size. Matinenda Formation, Elliot Lake. 7 I S S .... . S Correlation Coefficient = 0.93 . 63 . . �arkosic arkosic units units (Robertson, (Robertson,1968; 1968; Roscoe, Roscoe,1969) 1969). Paleocurrent Paleocurrent studies studies by by McDowell(1957) McDowell(1957) and and Long(1977) Long(1977) have have established established aa northwest northwest source source area area for for the the sediments sediments of the the Matinenda Matinenda Formation 5). Fralick Fralick and Miall(1989) suggest the the Formation (Figure (Figure5). Miall(l989) suggest Matinenda Matinenda Formation Formation was was deposited deposited from from shallow shallow braided braided streams streams flowing underwent tilting flowing down down aa south south dipping dipping paleoslope which underwent tilting to the southeast during deposition. Kimberly (1980) to the southeast during deposition. Kimberly (1980) reported reported that that the uraniferous uraniferous conglomerates conglomerates contained contained almost almost no no magnetitemagnetitethe ilmenite ilmenite and and had had very very high high potash/soda ratios. ratios. These These are are also also features features of of Huronian Huronian paleosols, paleosols, and and suggest suggest the the sediment sediment of of the the Matinenda Formation Formation was was formed formed by by the the intense intense weathering weathering of of aa Matinenda granitic source terrain as proposed by Roscoe(1969) granitic source terrain as proposed by Roscoe(1969). . Two Two southeast southeast trending trending ore ore zones zones were were recognized recognized since since the the early early days days of of uranium uranium mining mining in in the the Elliot Elliot Lake Lake camp. camp. The The Nordic Nordic zone, zone, east (1.6 Im) km) wide wide and and east of of the the City City of of Elliot Elliot Lake Lake is is about about 11 mile (1.6 3.6 3.6 miles miles (5.6 (5.6 km) km) long. long. The The Quirke Quirke Zone, Zone, in in the the Quirke Quirke Lake Lake area, is is about about two two miles miles (3.2 (3.2 km) km) wide wide and and six six miles miles (9(9km) km) long. long. area, Paleotopographic Paleotopographic features features of of the the basement basement are are thought thought to to have have had had aa determining determining influence influence on on the the position position and and orientation orientation of of the the zones. 0.1 % tJ3O3) % U,0.) conglomerate conglomerate occurs occurs as as zones. Ore Ore grade grade(circa (circa 0.1 persistent lenses lenses with with individual individual units units up up to to 15 15 feet feet (4.5 (4.5m) m) persistent thick. thick. The The uraniferous uraniferous quartz-pebble quartz-pebble conglomerates conglomerates are are commonly commonly well well developed developed at at the the base base of of the the Matinenda Matinenda Formation Formation but but also also occur occur within within the the arkose arkose up up to to 150 150 feet feet (45 (45 m) m) above above the the base base (Roscoe, (Roscoe,1968) 1968) . The The quartz-pebble quartz-pebbleconglomerate conglomerate consists consists mainly mainly of of well-rounded well-rounded pale-grey pale-grey to to dark-grey dark-grey quartz quartz and and chert chert pebbles pebbles set set in in aa matrix matrix of of pyrite pyrite with with some some quartz/feldspar quartz/feldspar grit grit and and sericite. sericite. Pyrite Pyrite usually usually forms forms about about 15% 15% of of minable minable units. units. Radioactive Radioactive minerals minerals include uraninite, brannerite, uranothorite (Roscoe, 1968) include uraninite, brannerite, uranothorite (Roscoe, 1968). Monazite Monazite and and zircon zirconare are characteristic characteristic heavy heavy minerals. minerals. The The sedimentological sedimentological and and mineralogical mineralogical features features of of the the uranium uranium bearing bearing zones zones of of the the Elliot Elliot Lake Lake camp camp are are now now generally generally believed believed to support a modified paleoplacer origin of the ores as outlined to support a modified paleoplacer origin the ores as outlined by supportingthe paleoplacer by Roscoe(1969). Roscoe(1969). Convincing evidence supportingthe paleoplacer hypothesis hypothesis was was provided provided by by Theis(l979) Theis(1979) who who demonstrated demonstrated that that aa direct direct relationship relationship exists exists between between the the size size of of quartz quartz pebbles pebbles and and pyrite pyrite grains grains (Figure (Figure10), 101, and and the the concentration concentration of of many many other other 17 �components accumulation of components of of the the ore ore zones. zones. Prior to the accumulation significant atmosphere, southeastward southeastward significant free free oxygen in the Earth's atmosphere, flowing pyrite and and uraniferous uraniferous minerals minerals flowing streams streams carried quartz, pyrite released by the extensive weathering of the Archean granitic released the of the Archean terrain, and terrain, and deposited deposited them them as as southeast southeast trending trending units units determined determined by by basement basement topography. topography. The McKim Formation Formation uppermost formation formation of of the Elliot Lake The McKim Formation Formation is the uppermost turbidite sequence It is mainly a turbidite sequence of generally generally dark dark grey, grey, subarkosic wackes, subarkosic wackes, mudstones, mudstones, subarkoses, subarkoses, lithwacke lithwacke and and litharenite which River area litharenite which extends extends from from the Blind River area to to the the Grenville Front. Grenville Front. Graded Graded beds, beds, parallel parallel laminations, laminations, ripple ripple marks, marks, ripple-drift cross-laminations and Bouma cycles, indicative ripple-drift cross-laminations Bouma cycles, indicative of of deposition by currents are are reported reported deposition by submarine submarine turbidity currents (Parvianen, (Parvianen, 1971; 1971; Card Card et et al., al.,1977). 1977). Group. Group. Robertson(1968) thickness of of 0-380 0-380 feet feet (0-100 (0-100 m) for the the Robertson(1968) gives gives aa thickness m) for McKim Formation of the the Quirke Quirke Lake Lake syncline. syncline. It Formation on on the south limb of It Formation is is missing on on the the north limb. limb. The McKim Formation is thickest thickest in in the Sudbury Sudbury area, area, where where it it is is up to to 2400 2400 metres metres (8000 (8000 feet) feet) thick. thick. The an important important influence The Murray Murray Fault Fault appears to have exerted an influence deposition of the McKim McKim sediments. sediments. North North of of the the Murray Murray on the deposition metres in Fault the the McKim McKim rarely rarely exceeds exceeds a few few hundred metres in thickness, thickness, whereas south of the fault the thickness of the McKim Formation south of of the McKim Card(1978a) noted noted that that the the change change from is at least 2400 2400 metres. Card(1978a) laminated siltstone laminated siltstone in in the west to more wacke in in the the east east indicated proximal facies, indicated aa change change from from more distal to proximal facies, in in turn turn suggesting more suggesting more tectonic tectonic activity activity and possibly a source source for for the the McKim sediments in the east. Fralick and Miall(l989)concluded sediments in the and Miall(1989)concluded the McKim that the McKim Formation Formation of the Elliot Lake area represents represents aa marine transgression transgression which which gradually gradually drowned drowned the the Matinenda Matinenda fluvial plain. fluvial plain. 18 �Straticrraohic Relationships Relationships within within the the Elliot Lake Lake Group Group of of the the Stratigraphic Sault Sault Ste. Ste. Marie-Elliot Marie-Elliot Lake Lake Area The stratigraphic stratigraphic relationship relationship between between the the Matinenda Matinenda Formation Formation The and the the Livingstone Livingstone Creek Creek Formation Formation is is revealed revealed on on aa rock rock face face and near near the the southern southern Boundary Boundary of of Otter Otter Township Township about about 30 30 km km (18 (18 miles) miles) north north of of the the town town of of Thessalon. Thessalon. At At this this location location pyritic pyritic quartz-pebble quartz-pebble conglomerate conglomerate of of the the Matinenda Matinenda Formation Formation (Chandler, (Chandler, 1976) 1976) directly directly overlies overlies an an apple-green apple-green paleosol paleosol on on grey, grey, finefinegrained sandstone of the Livingstone Creek Formation. About grained sandstone of the Livingstone Creek Formation. About 600 600 metres metres (380 (380 feet) feet) northwest northwest of of the the above above occurrence occurrence arkose arkose and and quartz-pebble quartz-pebble conglomerate conglomerate of of the the Matinenda Matinenda Formation Formation disconformably disconformably overlies overlies aa steeply steeply dipping, dipping, east-striking, east-striking, mafic mafic dike, dike, the the upper upper few few metres metres of of which which are are sericite-Jeucoxene sericite-leucoxene paleosol paleosol (Figures (Figures4, 4, 6). The The dike dike intrudes intrudes grey grey sandstone sandstone and and apple-green apple-green paleosol paleosol of of the the Livingstone Livingstone Creek Creek Formation Formation (Bennett (Bennett et al, al, 1991; 1991; Sutton Sutton and and Maynard, Maynard, 1992). 1992). Less Less than than 22 km km south south of of et the the above above location location Chandler(l976) Chandler(1976) identified identified aa fault-bounded fault-bounded block block of of Thessalon Thessalon Formation Formation volcanic volcanic rocks rocks with with aa minimum minimum thickness of approximately 500 m. thickness of approximately 500 m. The The above above observations observations show show clearly clearly and and unequivocally unequivocally that that there there was was aa period period of of volcanic volcanic activity, activity, as as well well as as aa significant significant period period of of erosion, erosion, separating separating the the Matinenda Matinenda Formation Formation and and the the Livingstone paleosols are are well well known known upon upon Livingstone Creek Creek Formation. Formation. Since Since paleosols Huronian Huronian flows flows in in the the Elliot Elliot Lake Lake area, area, the the sub-Matinenda sub-Matinenda unconformity extended to the Quirke Lake Syncline. unconformity extended to the Quirke Lake Syncline. In In addition, addition, the the above above observations observations imply imply that: that: 1. 1. The The mafic mafic dike dike referred referred to to above above was a a feeder feeder for for Thessalon Thessalon flows, flows, since since the the Thessalon Thessalon Formation Formation is is the the only only known known igneous igneous activity activity at at this this stratigraphic stratigraphicposition. position. 2. 2 . The The Thessalon Thessalon Formation Formation may may once once have have extended extended beyond beyond the the limit limit suggested suggested from from its its present present outcrop outcrop distribution. distribution. This This is is to to be exacted on consideration of Macdougall's(l988) statement be exacted on consideration of Macdougall's(1988) statement "Since 'Since many many CFB CFB provinces provinces have have been been uplifted uplifted and and occur occur as as elevated elevated plateaus, plateaus, dissection dissection and and removal removal is is rapid". rapid". He He notes notes as as well that the general scarcity of pre-Cretaceous Continental well that the general scarcity of pre-Cretaceous Continental flood flood basalt basalt provinces provinces is is probably probably due due to to their their erosion. erosion. 19 �Hough Lake Lake Group Group The Hough Lake Group (Robertson, (Robertson, et al., Hough Lake al., 1969; Roscoe, Roscoe, 1969) is groups which which display display the the cyclic cyclic the lowest lowest of of the the three three 1-luronian Huronian groups deposition deposition of of diamictite diamictite followed followed by by aa mudstone, mudstone, siltstone, siltstone, turbidite by aa cross-bedded cross-bedded turbidite or or carbonate carbonate sequence, sequence, and and overlairx overlain by arenite unit. represent a arenite unit. Each cycle is generally thought to represent sequence sequence of of glaciogenic glaciogenic -- marine marine -- fluvial fluvial and/or and/or shallow shallow marine marine deposition deposition (Figure (Figure3). 3) . Ramsay Ramsav Lake Lake Formation Formation The Ramsay formation of the Hough Ramsay Lake Lake Formation Formation is the lowermost formation Lake conglomerate units Lake Group Group and and is is the the oldest of three such conglomerate units which Quirke Lake Lake and Cobalt which define define the the base base of Hough Lake, Quirke Groups (Figures 2,3) 2,3). Groups (Roscoe, (Roscoe,1969; 1969; Piennar, Piennar,1963) 1963) (Figures The The Ramsay Ramsay Lake Lake Formation Formation is is aa widespread, widespread, relatively relatively thin thin unit unit which is which is up up to to 41 41 mm thick thick in in the the Dunns Dunns Valley Valley area area (Chandler, (Chandler, 1973) 1973). In In the Elliot Lake area the thickness of the the Ramsay Ramsay Lake Lake Formation is Formation is from from 00 to to just just over over 30 30 m. m. (Diamond logs (Diamond drill logs Assessment files, Sault Ste. Marie Resident Geologist's Assessment files, Sault Ste. Marie Resident Geologist's Office) Office). The Ramsay 70 to to 170 170 m thick thick in in the the The Ramsay Lake Lake Formation Formation is is from from 70 Sudbury-Manitoulin Sudbury-Manitoulinarea area (Card (Card1978a) 1978a). . Matrix Matrix supported supported polymictic polymictic conglomerate conglomerate (diarnictite) (diamictite) is the the most most abundant rock Lake Formation, Formation, especially especially near abundant rock type type in in the Ramsay Lake the base. of the formation formation usually usually the base. The lowermost few metres of reflects reflects the the underlying underlying rock rock type type (Robertson, (Robertson, 1968; 1968; Parviainen, Parviainen, 1973) Minor amounts of mudstone, wacke and arenite are 1973). Minor mudstone, wacke and arenite are locally locally present. present. . Subrounded to Subrounded to well well rounded rounded pebbles and cobbles cobbles of of grey grey granitic granitic rocks and angular of very very dark dark green green to black rocks angular to rounded clasts of volcanic rocks generally form less than 30 percent volcanic rocks generally form less than 30 percent of of the the total total volume of volume of the the diamictite. diamictite. The The dark dark matrix matrix consists consists of of quartz, quartz, feldspars, chlorite, muscovite-sericite-illite and and pyrite pyrite feldspars, chlorite, muscovite-sericite-illite (Parviainen, (Parviainen,1973). 1973). Although flow origin, origin, most Although some some writers writers have have argued for a debris flow 20 �writers writers now now accept accept the the Ramsay Ramsay Lake Lake Formation Formation as as having having aa significant significant glaciogenic glaciogenic component component (Roscoe, (Roscoe,1969; 1969; Robertson, Robertson, 1976). 1976). Fralick Fralick and and Maill(1989) Maill(l989) identified identified an an ice ice proximal proximal association association of of pebbly pebbly sandstone sandstone and and diamictite; diamictite; subaqueous subaqueous gravity gravity flows flows and and ice ice rain-out rain-out deposits; deposits; and and ice-proximal, ice-proximal, fluvial fluvial outwash outwash deposits. deposits. Pecors Pecors Formation Formation The Ramsay Lake Lake Formation Formation is is conformably conformably overlain overlain by by aa sequence sequence The Ramsay of of generally generally dark, dark, bedded bedded and and laminated laminated wackes, wackes, mudstone, mudstone, siltstones 1969). siltstones and and sandstones sandstones of of the the Pecors Pecors Formation Formation (Roscoe, (Roscoe,1969) The The Pecors Pecors Formation Formation is is 30 30 mm thick thick at at Quirke Quirke Lake Lake (Robertson, (Robertson, 1968) but is as much as 900 m thick south of the Murray 1968) but is as much as 900 m thick south of the Murray Fault Fault in in the Sudbury area area (Card, (Card,1978a) 1978a). It It was was not not identified identified in in the the the Sudbury area area between between Thessalon Thessalon and and Sault Sault Ste. Ste. Marie Marie (Frarey, (Frarey,1977). 1977). Ripple Ripple marks, marks, graded graded bedding, bedding, cross-laminations cross-laminationsparallel parallel laminations, clastic dikes dikes and and laminations, ball ball and and pillow pillow structures, structures, clastic slumpage slumpage features features have have been been reported reported in in the the formation. formation.The The basal basal part part of of the the formation formation is is commonly commonlylaminated laminated resembling resemblingvarves varves and, and, in in places, places, has has dropstones dropstones (Robertson, (Robertson,1968; 1968;Parviainen, Parviainen, 1973) 1973). Partial Partial Bouma Bouma sequences sequences are are common common (Card, (Card,1968; 1968;Robertson, Robertson, 1976) 1976). The The Pecors Pecors Formation Formation is is the the result result of of transgressive transgressive units units formed in deep water by turbidity currents (Card, l978a) formed in deep water by turbidity currents (Card, 1978a). The The presence presence of of drop drop stones stones is is evidence evidence of of aa cold cold paleoclimate, paleoclimate, and and provides provides supporting supporting evidence evidence for for the the glaciogenic glaciogenic origin origin of of the the underlying Ramsay Lake LakeFormation. Formation. underlying Ramsay . . . Mississagi Mississacri Formation Formation The The Mississagi Mississagi Formation Formation is is aa thick thick sequence sequence of of predominantly predominantly grey, grey, arenitic arenitic rocks rocks extending extending throughout throughout most most of of the the length lengthof of the outcrop belt. Within synclinethe the the Iluronian Huronian outcrop Within the the Quirke Quirke Lake Lake syncline Mississagi Formation is from 344 to 704 m thick. South of the Mississagi Formation is from 344 to 704 m thick. South of the Murray Murray Fault Fault the the formation formation is is notably notably thicker, thicker, being being more more than than 3000 3000 mm in in the the Sudbury Sudbury area area (Card, (Card,l978a; 1978a;Long, Long,1978). 1978). By By far far the the dominant dominant rock rock type type in in the the Mississagi Mississagi Formation Formation is is moderately moderately well well sorted, sorted,medium medium to to coarse coarse grained grained subarkose subarkose and and arkose. arkose.Small Smallto to medium quartz/chert pebble conglomerate is a minor component of medium quartz/chert pebble conglomerate is a minor component of the the formation, formation, but but is is more more common common in in the the western western and and northeastern northeastern parts foresets parts of of the the Huronian Huronian belt. belt. Fine-grained Fine-grainedpyrite pyrite along alongforesets 21 �commonly results results in in rusty rusty staining stainingof of outcrops. outcrops. Greenish, Greenish, thin, thin, commonly sericitic units units form form relatively relatively thin thin planar bedded units units between between sericitic cross-bedded sandstones. sandstones. Palonen Palonen (1971) (1971) provided provided evidence evidence cross-bedded supporting aa marine marine origin origin for for the the Mississagi Mississagi Formation; Formation; however, however, supporting Long (1978) (1978) argued argued that that the the abundance abundance of of mud-grade mud-grade matrix matrix in in the the Long immature paleocurrent immature arenites, arenites, and and the the predominance of unimodal paleocurrent arenites argued 5), and and the the lack lack of quartz arenites argued directions (Figure (Figure5) directions against against aa marine marine environment environment for for the the Mississagi Formation. Formation. He He concluded deposited from concluded that that the the Mississagi Mississagi Formation Formation was deposited from braided streams with low to intermediate sinuousity and braided streams with low to intermediate sinuousity and high high width to to depth depth ratios. ratios. width , Bedding Bedding units units are are commonly commonly about about aa metre thick but range range from from aa few cross-stratification few centimetres centimetres to to over over four four metres. Trough cross-stratification and ripple cross-stratification are common sedimentary and ripple cross-stratification are common sedimentary structures structures (Long, 1978). Individual Individual cross-stratified (Long, 1978). cross-stratified beds may so so show show grain grain size size gradation gradation (McDowell, (McDowell,1957) 1957). Long Long (1978) (1978) measured over over 2500 2500 cross-stratified cross-stratified units in in the the Two major stream systems Mississagi 5)5). . Mississagi Formation Formation(Figure (Figure Two systems were were recognized: a stream stream system system flowing flowing southeast to easterly from from the stream system the Sault Sault Ste. Ste. Marie Marie area area joined joined aastream system flowing flowing southwestward a southward flowing southwestward from from the Cobalt Cobalt Plain Plain to form a flowing system system southwest southwest of of the the Sudbury Sudbury area. area. These These observations observations suggest suggest that Complex was that the the area area now now occupied occupied by by the the Sudbury Sudbury Igneous Igneous Complex was elevated elevated during during the the period period of of Mississagi Mississagi deposition. deposition. Quirke Quirke Lake Lake Group Group Bruce Bruce Formation Formation The The Bruce Bruce Formation Formation extends extends from from the the Bruce Mines area to about about 70 70 km northeast northeast of of Sudbury. Sudbury. It It consists consists mainly of matrix supported supported km and and minor minor clast clast supported supported conglomerate. conglomerate. Pebbly Pebbly wacke, wacke, arkose, arkose, wacke reports wacke and and siltstone siltstone are are locally locally present. Robertson(1968) reports the the Bruce Bruce Formation Formation is is from from 79 7 9 mm (260 (260 feet) feet) to to 12 12 mm (40 (40 feet) feet) thick in the Elliot Lake area. It is 26 m (85 feet) to 37 thick in the Elliot Lake area. It is 26 m (85 feet) to 37 mm (120 (120 feet) feet) thick thick under under the the greater greater part part of of the the Quirke Quirke Lake Lake Syncline. Syncline. Pebble angular to subrounded clasts clasts generally generally Pebble to boulder sized, sized, angular 22 �consist of granitic rocks, consist of pale-grey pale-grey to whitish granitic rocks, Archean Archean supracrustal rocks supracrustal rocks and fine grained mafic clasts. clasts. The The upper upper parts parts of the 5% carbonate carbonate (Robertson, (Robertson, the formation formation may may contain contain up up to to 5% 1968) . 1968) Bruce Formation generally interpreted The Bruce Formation is is generally interpreted as as a a tillite tillite with with minor beds and lenses of glacially derived sandstone. Dropstones beds and lenses glacially derived sandstone. Dropstones been observed have been observed in in laminated laminated units units (Robertson, (Robertson,1964, 1964,1971). 1971). Casshyap (1969) Casshyap (1969) concluded the formation formation was deposited deposited from from terrestrial wet-base (1981) terrestrial wet-baseglaciers. glaciers. However HoweverSimms Simmsetetal. al.(1981) proposed that proposed that the the Bruce Bruce Formation Formation is is an an accumulation accumulation of of debris debris faulting, a sudden flows released as a result of normal faulting, sudden increase increase in paleoslope and in paleoslope and aa sudden sudden increase 'increasein in water water depth. depth. EsDanolp Formation Espanola Formation The Espanola widespread carbonate The Espanola Formation Formation is is the only widespread carbonate unit unit of of Huronian Supergroup. the Huronian Supergroup. It is present from from the the Sault Sault Ste. Ste. Marie area to to the the Maple Mountain Mountain area area about about 70 70 km km northeast northeast of of Sudbury.. Sudbury., Its widespread widespread distribution distinctive lithology Its distribution and distinctive lithology make it it the the most most useful useful stratigraphic stratigraphicmarker markerunit unitofofthe the1-luronian Huronian Supergroup. Supergroup. In the Elliot Lake area the Espanola Espanola Formation Formation can be subdivided can subdivided three parts: into three parts: a a lower lower limestone limestone member member (the (the Bruce Bruce Limestone) Limestone), a middle Greywacke) middle siltstone, siltstone, wake, wake, arenite arenite member member (the (the Espanola Espanola Greywacke) and an and an upper upper dolomitic dolomitic limestone limestone member member (the (theEspanola Espanola Limestone) Limestone) latter generally generally contains 4% total (Robertson, (Robertson,1968). 1968). The latter contains 33 -- 4% total iron which gives iron which gives a distinctly brownish colour colour to to weathered generally thinly bedded to surfaces. surfaces. All 3 members are generally to The threefold subdivision is not so well developed laminated. laminated. subdivision Contacts between between members members south of the Murray Fault (Young, (Young, 1982). Contacts tend to to be be gradational. gradational. Intraformational breccias, mud mud cracks, ripple ripple marks, marks, flame Intraformational flame structures and ball-and-pillow structures are common sedimentary structures and ball-and-pillow structures are common sedimentary features. (1980) described described stromatolites stromatolites in features. Hofmann Hofmann et et al. al. (1980) in the the Espanola Espanola Formation Formation at at Quirke Lake. Lake. These These features features suggest suggest deposition in a quiet shallow water environment with deposition in a quiet shallow environment with carbonate carbonate deposition deposition being being interrupted interrupted by by influx influx of of fine-grained fine-grainedsediment. sediment. Young (1973) proposed that the relatively sharp change from Young (1973) proposed relatively sharp change from the the diamictites diamictites of of the the Bruce Formation Formation suggests suggests warm climatic climatic However, the conditions conditions following following aa glacial glacial advance. advance. However, the recognition recognition 23 �of carbonate carbonate deposition deposition at high latitudes latitudes (Williams, (Williams, 1975) 1975) and and association of the association of detrital detrital uranium uranium with with intense intense chemical chemical weathering uncertainty to attempts weathering (Maynard (Maynard et al, 1991) 1991) adds uncertainty attempts to to model Huronian Huronian paleoclimate paleoclimate (Bennett (Bennett et et al, al, 1991) 1991). Serpent Formation Serpent Formation The Serpent Huronian The Serpent Formation Formation is found throughout much of the Huronian belt; however, however, it it is is locally removed by erosion during a period Gowganda of tectonic tectonic activity activity preceding deposition of the Gowganda Formation Formation of of the the Cobalt Cobalt Group. Group. Reported Reported thickness thickness estimates estimates of of the Serpent Serpent Formation Formation range range from from 150 150 up up to to 1500 1500 mm (Bennett (Bennett et et Robertson(l968) states states that nowhere nowhere in al., 1991). al., 1991). Robertson(1968) in the the Blind Blind River-Elliot Lake area is there any evidence that the total River-Elliot Lake area is there any evidence that the total thickness of thickness of the the Serpent Serpent Formation Formation has has been been preserved. preserved. The The Serpent Serpent Formation Formation is is mainly mainly fine fine to to medium-grained, medium-grained, quartz quartz arenite and arenite and arkose. arkose. Conglomeratic Conglomeratic units units have have been been noted, noted, especially especially near near the the base of the the Formation. Formation. Carbonate Carbonate is is aa significant significant component component near near the the base base of of the the formation formation in in the the Planar cross-bedding, cross-bedding, Elliot Lake area area (Robertson, (Robertson,1968) 1968). Planar Elliot Lake festoon festoon cross-bedding, cross-bedding, rip—up rip-up clasts, clasts, fine-laminations fine-laminations and and mud mud cracks have been Long(1976) proposed proposed that that the the Serpent Serpent cracks been reported. reported. Long(1976) Formation was was deposited distal braided stream Formation deposited in in a distal stream environment environment with calcareous calcareous units units representing representing aa sabkha sabkha environment. environment. presence of of very very large cross-beds cross-beds and Young(1982) noted that the presence bi-modal size a bi-modal size distribution distribution suggest suggest eolian eolian processes processes may may have have been been active active at at least least locally. locally. . Cobalt Cobalt Group Group Gowganda Formation Gowaanda Formation Gowganda Formation The Gowganda Formation is is a a complex complex sequence sequence of of conglomerates, conglomerates, sandstones, mudstones which sandstones, siltstones siltstones and mudstones which comprise comprise the the lowermost lowermost formation of the Cobalt Group. Its thickness is about 1070 formation the Its thickness is about 1070 mm in in Sault Ste. the Sault Ste. Marie area, area, from from 970 970 to to 1150 1150 m around around Whitefish Whitefish Falls, on the Huron, and from Falls, the North Shore Shore of Lake Huron, from 950 950 to to 2700 2700 mm near Sudbury. near Sudbury. Near Near Dunlop Dunlop Lake, Lake, in in the the Elliot Elliot Lake Lake area, area, the the 24 �Gowganda Gowganda Formation Formation is is about about 600 600 mm thick. thick. Matrix-supported Matrix-supported conglomerates conglomerates are are common, common, especially especially in in the the lower lower parts parts of of the the formation. formation. However, However, these these are are commonly commonly intercalated intercalated with with clast-supported clast-supported conglomerates, conglomerates, sandstone, sandstone, and and wacke wacke units. units. Laminated Laminated mudstones mudstones and and siltstone siltstone are are especially especially prominent prominent in in the the upper upper parts parts of of the the Gowganda Gowganda Formation. Formation. Many Many occurrences of of ice-rafted ice-rafted drop-stones drop-stones have have been been reported reported in in occurrences units. Individual Individual units units are are laminated mudstone/siltstone units. laminated generally generally relatively relatively thin thin and and discontinuous discontinuous making making subdivision subdivision of of the the Gowganda Gowganda formation formation difficult difficult except except in in well-exposed well-exposedareas. areas. Most Most granitic granitic clasts clasts of of Gowganda Gowganda conglomerates conglomerates have have aa distinctly distinctly pinkish pinkish or or reddish reddish hue, hue, in in comparison comparison to to the the grey grey granitic granitic clasts clasts in the matrix supported conglomerates of the stratigraphically in the matrix supported conglomerates the stratigraphically lower Ramsay Lake Lake and and Bruce Bruce Formations. Formations. Also, Also, pink pink and and red red hued hued lower Ramsay sandstones sandstones first first make make their their appearance appearance in in the the Gowganda Gowganda Formation. Formation. Roscoe(1969) Roscoe(1969) pointed pointed out out the the appearance appearance of of red red colouration colouration(i.e. (i.e. ferric ferric iron) iron) just just above above the the basal basal units units of of the the Gowganda Gowganda Formation, and argued that it represents the appearance Formation, and argued that it represents the appearance of of free free oxygen oxygen in in the the Earth's Earth's atmosphere, atmosphere, and and aa change change from from the the previously previously reducing reducing atmospheric atmospheric conditions conditions that that allowed allowed the the accumulation accumulation of of readily readily oxidized oxidized minerals minerals such such as as pyrite pyrite and and uraninite fluvial environment. environment. uraninite in in aa fluvial The depositional depositional environment environment of of the the diamictites diamictites in in the the Gowganda Gowganda The Formation Formation have have been been the the subject subject of of discussion discussion since sinceColeman(1905) Coleman(1905) proposed proposed aa glacial glacial origin origin for for the the matrix matrix supported supportedconglomerates. conglomerates. Many Many later later writers writers including including Ovenshine(1965), Ovenshine(1965),Cassyhap(1969), Cassyhap(1969). Lindsay(1971), Young Young and and Nesbitt(1985), Nesbitt(1985), and and others, others, have have also also Lindsay(1971), supported glaciolacustrine origin origin supported aa glacial, glacial, glacial-marine glacial-marine or or glaciolacustrine for for the the Gowganda Gowganda Formation. Formation. Card(1968) Card(1968) concluded concluded that, that, although although glaciation glaciation may may have have supplied supplied coarse detritus to the basin initially, debris flows and coarse detritus to the basin initially, debris flows and turbidity turbidity currents, currents, released released by by vertical vertical tectonic tectonic movement, movement, may may better better explain explain the the thickness thickness variations, variations, rock rock associations associations and and distribution Manitoulin area. area. distribution he he observed observed it it the the Sudbury Sudbury Manitoulin Roscoe(1969) Roscoe(1969) also also emphasized emphasized that that glaciation glaciation is is only only one one of of several processes responsible for the deposition of Gowganda several processes responsible for the deposition of Gowganda sediments. sediments. 25 �Lorrain Lorrain Formation Formation The The Lorrain Lorrain Formation Formation is is generally generally well well exposed exposed throughout throughout most most of the the Huronian Huronian belt, belt, where it commonly forms a background to some of the some the most scenic scenic views in in northern northern Ontario. Ontario. It It is is overwhelmingly overwhelmingly an an arenitic arenitic sequence, sequence, with with local local siltstone siltstone units units formation is up to present in in lower lower parts of the section. The formation 2500 2500 m thick thick near near Sault Sault Ste. Ste. Marie Marie and and in in the the LaCloche LaCloche Syncline, Syncline, southwest southwest of of Sudbury. Sudbury. It It is is up to to 2300 2300 m m thick thick in in the the Cobalt Cobalt Embayment.. Embayment In general, the In general, the lower lower part of the the Lorrain Lorrain Formation Formation is is dominated dominated by by pink, pink, arkosic arkosic sandstones, sandstones, the the middle middle by by hematite-rich hematite-rich subarkose and subarkose and quartz-arenite, quartz-arenite, and the the upper upper portion portion by by pale pale grey grey white mature, distinctive jasper-pebble jasper-pebble to white mature, quartz-arenite. quartz-arenite. A distinctive conglomerate conglomerate found found in in the the Sault Sault Ste. Ste. Marie Marie area area is is aa popular popular decorative decorative stone, stone, known known locally locally as as "pudding "pudding stone". stone". The The presence presence of of aluminous aluminous minerals is is a a characteristic characteristic feature feature of of the the upper, upper, piartz-arenites quartz-arenites of the Lorrain Lorrain Formation. Formation. Diaspore Diaspore and and kaolinite are kaolinite are common common in in the quartz-arenite quartz-arenite of of the the Sault Sault Ste. Ste. of Elliot Elliot Lake Lake (Wood, 1973) 1973) whilekyanite, whilekyanite, Marie area area and north of andalusite andalusite and and kaolinite kaolinite are are present present as as metamorphosed metamorphosed equivalents equivalents in the the LaCloche LaCloche Lake-Killarney Lake-Killarney area area (Card, (Card, l978a). 1978a). Young(1973) Young(1973) and Wood(l973) and Wood(1973) interpret interpret the the presence of of diaspore diaspore and and kaolinite kaolinite as the as the result result of of post-depositional post-depositional in-situ in-situ alteration alteration of of feldspar feldspar under hot under hot and and humid humid climatic climatic conditions. conditions. presence of The presence of abundant detrital hematite hematite in in the the Lorrain Lorrain Formation and Formation and the the occurrence occurrence of thorium-rich, thorium-rich, monazite-bearing, monazite-bearing, quartz-pebble quartz-pebble conglomerate conglomerate north north of of Elliot Elliot Lake Lake has has been been interpreted by Frarey Roscoe(l970) as interpreted Frarey and Roscoe(1970) as indicating indicating an an oxidizing oxidizing environment. environment. Planar Planar and and trough trough cross-bedding cross-bedding are are common, common, as as are are ripple ripple marks marks and other other primary primary depositional depositional structures. structures. There There is is no no consensus consensus as to to the the depositional depositional environment environment of the the Lorrain Lorrain Formation. Formation. Most Most of the sedimentary structures of the Lorrain Formation can be the sedimentary structures Lorrain Formation can be 26 �found found in in either either shallow shallow marine marine or or fluvial fluvial environments. environments. Wood(1973), Wood(1973) , Young(l973) Young(1973) and and Frarey(l977) Frarey (1977)favoured favoured aa fluviatile fluviatile model while while Pettijohn(1970) Pettijohn(l970) supported supported a a marine environment for for model the Lorrain Formation. Formation. Card(1976b) Card(1976b) proposed that that the the Lorrain Lorrain the Lorrain Formation Formation represents represents near-shore near-shore coastal coastal shelf shelf deposition deposition during during episodic marine transgression and regression. episodic marine transgression and regression. Gordon Gordon Lake Lake Formation Formation The The Gordon Gordon Lake Lake Formation Formation displays displays aa gradational gradational contact contact with with the the underlying underlying Lorrain Lorrain Formation. Formation. It It is is made made up up predominantly predominantly of of variegated variegated mudstone, mudstone, siltstone, siltstone,chert chert and and minor minor fine-grained fine-grained sandstone. sandstone. Robertson(1986) Robertson(1986) subdivided subdivided the the Gordon Gordon Lake Lake Formation Formation of of the the Flack Flack Lake Lake area area into into aa lower lower member member of of reddish reddish arenite, arenite, siltstone, siltstone, and and chert chert with with anhydrite anhydrite and and gypsum gypsum nodules, nodules, aa middle middle member member of of green green siltstone siltstone and and mudstone, mudstone, and and an an upper upper reddish reddish mudstone, mudstone, siltstone siltstone and and chert. chert. Abundant Abundant sedimentary sedimentary features features include include small-scale small-scalecross-bedding, cross-bedding,ripple ripple marks marks and and desiccation desiccation cracks. cracks. Some Some of of the the features features of of the the Gordon Gordon Lake Lake Formation Formation are are unique unique for for the Supergroup. Wood(1973) Wood(l973) noted noted the the abundance abundance of of the 1-Juronian Huronian Supergroup. feldspar feldspar in in the the formation, formation, aa marked marked contrast contrast to to rocks rocks of of the the immediately Lorrain Formation. Formation. He He also also described described immediately underlying underlying Lorrain hematite 0 . 0 2 to to 0.05 0.05 hematite ooliths ooliths and and the the abundance abundance of of grains grains in in the the 0.02 mm mm range, range, aa relatively relatively uncommon uncommon grain grain size size in in sedimentary sedimentary rocks. rocks. Since Since this this size size is is found found in bess loessdeposits, deposits, Wood(1973) Wood(1973) proposed proposed that that the the quartz quartz silt silt of of the the Gordon Gordon Lake Lake Formation Formation was was formed formed by by glacial glacial action action and and carried carried by by the the wind wind and and deposited deposited in in aa tidal tidal flat flat environment. environment. Jackson(1994) Jackson(1994) identified identified nodules nodules and and layers layers of of dolostone dolostone in in siltstone siltstone and and chert chert of of the the Gordon Gordon Lake Lake Formation Formation in in the the Aberdeen Aberdeen area, (1989) reported area, east east of of Sault SaultSte. Ste.Marie. Marie.Bennett Bennettetetal. al.(1989) reported aa unit unit of of dobostone dolostone in in Fenwick Fenwick Township, Township, near near Sault Sault Ste. Ste. Marie Marie and and proposed proposed aa correlation correlation with with the the Gordon Gordon Lake Lake Formation Formation in in the the Bruce Bruce Mines Mines area area and and to to the the Kona Kona Formation Formation of of the the Marquette Marquette Range Range Supergroup. Supergroup. 27 �Bar River Formation Formation The Bar River the uppermost formation formation of the the The River Formation Formation is is the 1-luronian Supergroup. It is characterized by quartz-arenite Huronian Supergroup. It is characterized by quartz-arenite with with siltstone. It is approximately approximately 300 minor ferruginous ferruginous arenite and siltstone. 300 m m thick thick in in the the Flack Flack Lake Lake area, area, north north of Elliot Lake. Wright and and Rust(l985) deposited Rust(1985) concluded concluded that the the Ear Bar River Formation was deposited in in a a tidal tidal environment. environment. Nipissing Nipissing Intrusions Intrusions Dikes, Dikes, sills, sills, and and cone cone sheets sheets of of gabbro, gabbro, diabase diabase and and granophyre, granophyre, Nipissing diabase" are the most commonly referred to as commonly referred to as " Nipissing diabase" are the most widespread igneous widespread igneous rocks rocks within within the the Huronian Huronian Supergroup. Supergroup. Baddeleyite from the Gowganda Gowganda area have Baddeleyite from Nipissing gabbro sills in the been dated at 2219 Ma U-Pb; u-pb; the minimum, minimum, age age for for the the Huronian Huronian Supergroup Card(1985) Supergroup (Corfu (Corfu and and Andrews, Andrews, 1986). 1986). Buchan Buchan and and Card(l985) report that paleomagnetic data suggest at least two report data suggest least two periods periods of of Nipissing Nipissing intrusive intrusive activity. activity. Olivine-bearing Olivine-bearing hypersthene hypersthene gabbro, gabbro, gabbro, gabbro, feldspathic feldspathic pyroxenite, pyroxenite, two-pyroxene two-pyroxene quartz quartz gabbro, gabbro, hornblende hornblende gabbro, gabbro, granophyric granophyre have been been identified in qranophyric qabbro gabbro and qranophyre bodies are Nipissing Nipissing intrusions. intrusions. Many of the the Nipissing bodies are characterized wide, overlain overlain by characterized by chilled margins 50 cm to 55 mm wide, 10-20 10-20 m of quartz quartz gabbro, gabbro, then then 100-500 100-500 m of hypersthene-poor hypersthene-poor gabbro-norite and vari-textured van-textured diabase gabbro-norite diabase (Lightfoot (Lightfoot and and Naldredt, Naldredt 1996) 1996) Nipissing Nipissing intrusions intrusions are are widely widely and and evenly evenly distributed distributed throughout throughout Huronian belt but, the Huronian but, with few few exceptions, exceptions, are not not recognized recognized intrusions may be within the Archean terrain. terrain. Individual intrusions be up up to to within the Archean several hundred metres thick several thick and and extend over an area area of of several several hundred hundred square square kilometres. kilometres. The form and orientation of Nipissing intrusions indicate intrusions indicate that their their emplacement may be controlled controlled by by older faults, folds and competency of the enclosing rocks (Card older faults, folds enclosing rocks (Card and and Pattison, Pattison, 1973) 1973). 28 �Lightfoot Lightfoot and and Naldredt(1996) Naldredt(1996) discuss discuss the the geochemical geochemical characteristics characteristics of of the the Nipissihg Nipissing magmas magmas and and the the potential potential for for platinum platinum group group metal metal deposits. deposits. They They conclude conclude that that the the Nipissing Nipissing magmas magmas were were emplaced emplaced into into the the Huronian Huronian sedimentary sedimentary sequence sequence over over a a period period of of less less than than 10 10 million million years. years. Parental Parental magmas magmas of of remarkably remarkably uniform uniform composition composition underwent underwent in-situ in-situ contamination contamination and and differentiation differentiation within within the the intrusions intrusions (Lightfoot (Lightfoot and and Naldredt, Naldredt, 1996) 1996) . AA spatial spatial association association between between Nipissing Nipissing intrusions intrusions and and both both magmatic magmatic and and vein-type vein-typemineralization mineralization has has long long been been recognized. recognized. Card Card and and Pattison(l973) Pattison(1973) noted noted also also that that there there is is aa variation variation in in style style and and type type of of mineralization mineralization associated with with Nipissing Nipissing intrusions intrusions from from the the Cobalt Cobalt area area in in the the east east to to the the Sault Sault Ste. Ste. Marie Marie area area in in the the west. west. Huronian Huronian Paleosols Paleosols and and Evidence Evidence for for the the Accumulation Accumulation of of Oxygen Oxygen in in the Huronian Atmosphere the Huronian Atmosphere It It has has long long been been recognized recognized that that the the study study of of Huronian Huronian paleosols paleosols (ancient (ancient soil soil profiles) profiles) could could provide provide information information pertaining pertaining to to the the development development the the Earth's Earth's atmosphere atmosphere and and climate climate during during the the Proterozoic. Since iron is much less soluble in the ferric Proterozoic. Since iron is much less soluble in the ferric state state than than when when in in the the ferrous ferrous state, state, the the behavior behavior of of iron iron in in paleosols paleosols should should provide provide some some indication indication of of the the oxygen oxygen partial partial pressure pressure of of the the environment. environment. Many Many of of the the best best descriptions descriptions of of Precambrian Precambrian paleosols paleosols have have been been from from those those associated associated with with Huronian Huronian unconformities unconformities (Gall, (Gall,1992) 1992). Grandstaff (1986) identified 8 features features of of paleosols, paleosols, most most al.(1986) Grandstaff et et al. of which can been observed in Huronian paleosols. These features of which can been observed in Huronian paleosols. These features are: are : 1. 1. Stratiform Stratiform 2. 2 . Relatively Relativelythin thin(<20 ( < 2 0 m) m) 3. Transitional lower boundary-sharp 3. Transitional lower boundary-sharp upper upper boundary boundary 4. 4. Colour Colour variations variations 5. 5 . Destruction Destruction of of primary primary rock rock textures textures accompanied accompanied by by the the development development of of soil soil textures textures 6. 6. Destruction Destruction of of primary primary minerals minerals with with formation formation of of clay clay 29 �minerals minerals or or metamorphic metamorphic equivalents equivalents 7. Dikes material from from overlying sediment washed down down 7. Dikes of material into desiccation cracks in in the the soil soil into desiccation cracks 8. Rip-up Rip-up clasts clasts of of overlying overlying sediments sediments Well preserved preserved paleosols paleosols below below the the Matinenda Formation Formation in in the the Well Elliot Lake area area have have been been described described by by many many workers workers (Roscoe, (Roscoe, Elliot Lake 1957a, 1969, 1969, 1973, 1973, 1981; 1981; Pienaar, Pienaar, 1963; Robertson, 1964; Frarey Frarey l957a, Robertson, 1964; and Roscoe, Roscoe, 1970; 1970; Freyer, Freyer, 1977; 1977; Gay Gay and and Grandstaff, Grandstaff, 1980; 1980; and Kimberly et et al, al, 1984; 1984; G-Farrow G-Farrow and Mossman, 1988; 1988; Prasad Prasad and and Kimberly Roscoe, Roscoe, 1991, 1991, Sutton Sutton and and Maynard, Maynard, 1991, 1991, 1993) 1993). Bennett et et al. al.(1991) Bennett (1991) have have proposed proposed that that there there are are three three disconformities disconformities or or unconformaties unconformaties within within the the Elliot Elliot Lake Lake Group Group which have have potential potential for for paleosol paleosol development (Figure (Figure 2). 2). These These which are in descending stratigraphic order: 1)the sub-Matinenda are in descending stratigraphic sub-Matinenda disconformity; disconformity, and 2)the sub-Thessalon sub-Thessalon Formation Formation disconformity, and disconformity; 2)the sub-Livingstone sub-Livingstone Creek Creek Formation Formation unconformity. unconformity. The The sub-Livingstone sub-Livingstone Creek Creek Formation Formation unconformity unconformity is is the the basal basal unconformity Supergroup and and is is the the only only entirely unconformityof of the the1-luronian Huronian Supergroup entirely sub-iluronian unconformity (Figure sub-Huronian unconformity (Figure2) 2). This This unconformity unconformity is is exposed metres of exposed in in the the Thessalon Thessalon area, area, where the upper few few metres of the the Archean Archean granitic granitic rocks rocks can can be be seen seen to to progress progress from from angular, angular, slightly grit and fine-grained slightly rotated rotated blocks, blocks, separated separated by grey grit fine-grained sandstone, boulders with with a higher sandstone, upward, upward, to to more rounded boulders proportion clastic material material (Collins, (Collins,1925) 1925). This This zone zone proportion of of finer finer clastic may be termed termed aa "paleo-regolith", "paleo-regolith",since since there is little little or or no no obvious development of the yellow, sericitic paleosol commonly commonly obvious development of the yellow, found found in in the the younger, younger, sub-Matinenda sub-Matinendapaleosols. paleosols. . . Prasad paleosols in the same Prasad and and Roscoe(1996) described two paleosols same drill drill core Denison Mine Mine at at Elliot Lake. A paleosol was was found found core from from the the Denison above Huronian volcanic rocks and another, less well developed above Huronian volcanic rocks and another, less developed paleosol, paleosol, was was found found upon upon Archean Archean tonalite tonalite below below aa short short section section of of quartz-pebble quartz-pebble conglomerate conglomerate and and grit grit (Prasad, (Prasad, personal personal communication, communication, 1997) 1997) below below the the 99 m thick volcanic unit (Figure (Figure 13). 13). The paleosols have The best best developed, developed, and and most most studied, studied, Huronian paleosols have been Formation. On On mafic been found found directly directly below below the the Matinenda Formation. mafic rocks, the sub-Matinenda paleosols can generally be recognized rocks, the sub-Matinenda paleosols can recognized by by the the presence presence of of an an upper, upper, distinctly distinctly apple-green apple-green to to yellowish, yellowish, 30 �0 0.5 5.5 0.03 0.01 0.03 3 II 10 Concentration Ratio Concentration Ratio Figure Figure 11. Concentration ratios relative relative to to A1203 A1203 of of components components paleosol. of the Pronto paleosol 0 0.3 0.6 3 a. a, C 4.5 6 8.5 8.5 - 1 0.5 10.5 LOSS I I I llllll 0.03 0.01 I I I 1 0.03 lllll A"*G 1 <wm. "-G&+ 1 I Ill 3 10 Concentration ConcentrationRatio Ratio Figure 12 12 Figure Concentration ratios of components . Concentration components of Denison Denison . paleosol paleosol relative relative to to A1203. A1203. 31 �CD H' 0 (0 0 8 -o 0 CD F--' 9 Di ID a a 0 0 3 a -U 0 m J S S -. HDi '-I 0 CD L1 r 7 0 C 9C (/, 0 CD breccia Forrnaflon Paleosd Heqnalitc N N N zone III! 0 9 II +>+..+++JN 8 F-) gronite Marie 'Idle Transition C)- Di S hPJ I I 0' 0CD N) 6 U, ID Di H 30 7 C 0 (0 CD S J 0 0 F Poleosol 0 upward weathered Increasingly - Tonailte ________ Coglornerate t:ijaF:,? a, ?lt)/49 '_ F>-' F-' Di 0) —— — 0, CD 0 I p F I I I S . 7 0 Ca 0 C CD CD 0 -U :, ——.1 0 L - 0 3 0 Co 0 F-'- çt Di Fl -n a a D 0 CD J a — Di F-I C C CD Co C) (paieoscj) WgiIIite I pcileosot rich sericile CNoriie. I upward weathered Metabadt-increastngFy LL 0 C) U) CD I-' C tO H- �sericitic zone grades downward, downward, over a few sericitic zone which grades few centimetres centimetres to to several metres, to an underlying, underlying, black, black, fine-grained, several fine-grained, chloritechloriterich eluvial eluvial zone zone up up to to several several metres metres thick. thick. Abundant Abundant pseudomorphs of titanium pseudomorphs titanium oxides oxides after after ilmenite ilmenite are are a a feature feature of of paleosols clast of of sericitic sericitic paleosols on on mafic mafic igneous igneous rocks. rocks. Rip-up Rip-up clast paleosol paleosol (the (the "argillite "argillite scraps" scraps'' of of mine mine geologists) geologists) are are commonly commonly found overlying Matinenda Matinenda found in in the the lower lower few few metres of the overlying Formation. Prasad and Roscoe(l996) Roscoe(1996) report significant Formation. significant amounts amounts of of carbonate carbonate and and pyrite pyrite in in sub-Matinenda sub-Matinenda paleosols paleosols in in the the Elliot Elliot Lake Lake area. area. The uppermost uppermost sections sections of sub-Matinenda sub-Matinenda Formation Formation paleosols paleosols on on Archean granitic rocks and arkosic sedimentary rocks, are Archean granitic rocks and arkosic sedimentary rocks, are generally apple-green yellowish rock composed generally apple-green to yellowish composed mainly of quartz quartz and sericite(Robertson, (1980); Sutton Sutton sericite(Robertson,1963; 1963; Gay Gay and and Grandstaff Grandstaff(l980); and and Maynard(l992). Where the texture texture of the protolith is is well replaced, the preserved, preserved, but but the the original original mineralogy mineralogy is is replaced, the paleosol paleosol may be (Rainbird et et al, al, 1990). 1990). The chloritechloritebe termed termed aa saprolith saprolith (Rainbird eluvial zone of paleosols on granitic rocks rocks is generally rich eluvial lacking or lacking or relatively relatively thin. thin. Sub-Matinenda Sub-Matinenda paleosols commonly commonly show show the pronounced loss loss of soda soda found 11) . Lime, found in in most most paleosols paleosols(Figure (Figure 11). Lime, and magnesia are are also also depleted, generally a large depleted, but there is generally large increase increase in in potash In content (Figure 12) (Gay (Gay and Grandstaff, Grandstaff, 1990) 1990). In most cases, cases, content (Figure12) iron iron and and manganese manganese are are depleted depleted in in upper upper parts parts of of the the paleosol. paleosol. weathering in This This is is held held to to provide provide good good evidence evidence of of weathering in aa reducing environment. However, Gay and Grandstaff (1980) reducing environment. However, Gay and Grandstaff(l980) noted an an upward increase upward increase in in total iron iron in in paleosol from from the the Pronto Pronto Mine 11). They concluded concluded this this upward increase increase in in iron iron area (Figure11) area (Figure . They content indicated the presence of free content free oxygen in in the early Huronian atmosphere although Huronian although at approximately 1% 1% of the present level (Gay and Grandstaff, 1980). They suggested suggested that the loss loss of of (Gay Grandstaff, iron iron shown shown in in most Huronian Huronian paleosols paleosols could could be be due due to to local local reducing environments. Some writers have concluded that the reducing increase in sericite) in Huronian paleosols is largely increase in potash (as (as sericite) largely due which may mask the due to to diagenetic diagenetic and metamorphic processes which the environmental and hydrologic conditions operative during paleosol environmental conditions operative during paleosol development (1980); G-Farrow G-Farrow and Grandstaff(l980); and development (Gay (Gayand and Grandstaff Mossman(1988) Mossman (1988). . geochemistry of Sub-Lorrain Sub-Lorrain Formation The mineralogy and geochemistry Formation paleosols have been described by Rainbird et al. (1990) and paleosols have been described by Rainbird et a1.(1990) 33 �84W 82W N 1 .5 Th / r — Elliot Lake tJ •1 -46N 46N Channel B 0 $ 60km AfterZolnaj Zolnaietetal. d.(1984) (1984) After Legend [1111 Paleozc rocks Thrust fault, teeth indicate Mesoproterozoic rocks (Grenv,lle Province) Normal fault, spat indicates bangi wall downthrown side [III] Cobalt Group rocks Fault (observed, assirned) Pre - Cobalt Group rocks fl Pee—Cobalt Grow rocks derived from Archean basement rocks Archean basement rocks (Swerior Province) Anticline, syncline Manitoulin Isto-id Discontiroity -' Grenville Front Tectonic Zone (traceable on surface, traceable in subsurface) Location of cross sections ELF FLF Flock FlockLake LokeFault Foul1 ALF Agnew Lake Fouls MF Murray Fault MFS MFS SS MGB MGE EF M w r qFault Foul1 System Murray System Sudbury Structure McGrqa6ay b y McGregor Unwmei fault fwlt 22km kmnorth nonhofof Unnamed Espanola E ~ 0 " 0 1Fault 0 Fa"!? Figure Figure14. 14: Geological Geological cross-section cross-section of of the the Blind Blind River River and andSudbury-Maintou!in Sudbury-Maintoulinareas. areas 34 �Sutton and and Maynard(1991). Maynard(l991). In In contrast contrast to to the the older, older, sub-Matinenda sub-Matinenda Sutton paleosols, Sub—Lorrain Sub-Lorrain paleosols paleosols commonly commonly show show an an enrichment enrichment of of paleosols, Fe3 without a significant Fei3at at the the expense expense of of Fe2 Fe+2without significant loss loss of of total total iron iron (Figure (Figure13) 13). Hematite Hematite is is a a common common mineral mineral in in the the upper upper parts parts of of sub-Lorrain sub-Lorrain paleosols, paleosols, in in contrast contrast to to the the presence presence of of pyrite pyrite in sub-.Matinenda sub-Matinenda paleosols. sub-Lorrain in paleosols. In In this this respect respect the sub-Lorrain paleosols paleosols resemble resemble many many post-Huronian post-Huronian paleosols paleosols and and are are consistent with weathering in an oxidizing atmosphere consistent with weathering in an oxidizing atmosphere (Prasad (Prasadand and Roscoe, 1990), Rainbird et et al., al.,1990). Roscoe, 1996; 1996;Rainbird . Since Since pyrite pyrite and and uraninite uraninite are are unstable unstable under under oxidizing oxidizing conditions, the the abundance abundance of of detrital detrital pyrite pyrite and and uraninite uraninite in in the the conditions, paleoplacer uranium uranium ore ore zones zones in in the the Matinenda Matinenda Formation Formation provide provide paleoplacer good good evidence evidence for for an an oxygen oxygen deficient deficient atmosphere atmosphere during during weathering, weathering, transport transport and and deposition deposition of of early early Huronian Huronian sediments. sediments. In clastic In marked marked contrast contrast to to the the common common red beds of of younger younger clastic sequences, sandstones sandstones (and (andmost most granitic granitic clasts clastsin inconglomerates) conglomerates) sequences, below below the the Cobalt Cobalt Group Group are are almost almost all all drab drab coloured coloured in in spite spite of of the the abundance abundance of of red red and and pink pink granitic granitic rocks rocks in in the the continental continental source (1970)noted noted source area area (Roscoe (Roscoe1969, 1969,1973). 1973). Frarey Frarey and and Roscoe Roscoe (1970) the the above above and and proposed proposed that that the the drab drab colour colour of of lower lower Huronian Huronian clastic clastic rocks rocks is is due due to to the the lack lack of of free free oxygen oxygen in in the the atmosphere atmosphere during I-iuronian during the theperiod periodofofdeposition depositionofoflower lower Huronian rocks. rocks. Red Red hued, hued, hematite hematite bearing bearing rocks, rocks, which which Roscoe(1969) Roscoe(l969) proposed proposed mark mark the the presence presence of of an an oxidizing oxidizing atmosphere, atmosphere, make make an an appearance appearance with with the the Gowganda Gowganda Formation Formation of of the the Cobalt Cobalt Group, Group, and and are are important important in in parts parts of of the the Lorrain Lorrain and Gordon Gordon Lake Lake Formations Formations of of that that group. group. What What may may be be the the first first true true red-beds red-beds are are found found in in the the purple Lorrain Formation Formation near near Sault Sault Ste. Ste. purple siltstone siltstone member member of of the the Lorrain Marie Marie (Frarey, (Frarey,1977). 1977). Regional Regional Tectonic Tectonic Patterns Patterns and and Metamorphism Metamorphism Major Major structures structures of of the the Huronian Huronian belt belt follow follow two two main main trends: trends: l)west-northwest 1)west-northwest trending trending folds folds and and faults faults of of the the Sault SaultSte. Ste. Marie-Elliot 2)east to to northeast northeast striking striking folds folds Marie-Elliot Lake Lake area; area; and and 2)east and and faults faults of of the the Sudbury-Manitoulin Sudbury-Manitoulinarea area (Figure (Figure14) 14). These These two two structural structural orientations orientations are are associated associated with with differing differing fold fold styles, metamorphic grade and metamorphic fabric. Changes styles, metamorphic yrade and metamorphic fabric. Changes are are . 35 �notable across across the the east-west east-west faults faults of the Murray fault most notable Murray fault system. system. This This fault fault zone zone (Figure (Figure14) 14) is is the most significant significant structural structural feature feature of of the the Huronian Huronian belt. belt. Since Since many many formations formations significant increase increase in in thickness thickness south south of of the the fault, fault,it it show aa significant show is generally generally interpreted interpreted as as an an inverted inverted growth growth fault. fault. (i.e. (i.e. an an is early listric listric normal normal fault, fault, active active during during sedimention, sedimention,which, which, early during aa later later compressive compressive regime, regime, was converted to a thrust thrust or or during converted to reverse reverse fault fault (Card, (Card,l978a; 1978a; Jackson Jackson (1997) (1997). The subjected to The rocks rocks of of the the Huronian Huronian Supergroup have been subjected to several deformational deformational events. This is particularly south several particularly evident evident south of of the the Murray Murray Fault Fault zone. zone. In In the Whitefish Falls Falls area area (south (south of of the Murray Fault) Young and Nesbitt(l985) conclude that some the Murray Fault) Young and Nesbitt(1985) conclude that some large-scale large-scale folding folding is is related related to to syn-depositional syn-depositional and/or and/or postpostdepositional sediment. Early depositional deformation deformation of of unconsolidated sediment. Early syndepositional syndepositional deformation deformation is is also also indicated indicated by by an an important important unconformity unconformity below below the the Gowganda Gowganda Formation Formation of of the the Cobalt Cobalt Group; Group; and the presence of ragged, slumped contacts and large slump and the presence of ragged, slumped contacts large slump blocks 1978a; Young, Young, 1983) 1983). blocks along along major major faults faults (Card, (Card,1978a; Convincing Convincing evidence evidence of of at at least least one one important important pre-Nipissing pre-Nipissing(2.2 (2.2 Ga) deformational deformational event, event, assigned assigned to to the the Blezardian Blezardian Ga) Orogeny(Stockwe11, 1982), 1982), is is provided by the observation that Orogeny(Stockwell, observation that Nipissing area transect Nipissing bodies bodies in in the the Sudbury-Whitefish Sudbury-Whitefish Falls area transact axial Jackson (1997) axial surfaces surfaces of of major major folds folds (Card, (Card, 1978a). Jackson (1997) did did not observe observe such such relationships relationships in in the areas north of the the Murray Murray not Fault. However, However, Jackson Jackson (1997) (1997) points out, noted by by Fault. out, as earlier earlier noted Robertson (1964), that the tendency of Nipissing dikes to occupy dikes to occupy Robertson (1964), that the Chiblow Anticline, Anticline, structures parallel parallel to to the the axial axial plane plane of of the the Chiblow structures suggests pre-Nipissing pre-Nipissing folding. folding. Jackson Jackson (l997)also (1997)also noted noted evidence evidence suggests of pre-Nipissing pre-Nipissing faults faults north north of of the the Murray Murray Fault Fault zone. zone. of Following intrusions but prior prior to Following emplacement emplacement of of the the Nipissing intrusions to the the emplacement emplacement of of the the Sudbury Sudbury Igneous Igneous Complex Complex (SIC) (SIC) there there was was further further deformation deformation and and regional regional metamorphism. metamorphism. Rb-Sr Rb-Sr isotope isotope studies studies on on Huronian Huronian metasediments metasediments indicate indicate that that prograde prograde metamorphism metamorphism occurred occurred at at about about 1.90-1.85 1.90-1.85 Ga Ga (Fairbairn (Fairbairnet et al., al., 1969) Jackson(1995) state state that this this event event is is probably probably 1969). Card Card and and Jackson(1995) correlative correlative with with the the Penokean Penokean Orogeny Orogeny of of Michigan-Minnesota Michigan-Minnesota (Simms (Simms et et al., al., 1989). 1989). . After After the the emplacement emplacement of of the the SIC SIC and and the the deposition deposition of of the the Whitewater deformation and Whitewater Group, Group, there there is is evidence evidence of further further deformation and 36 �64W BrW Legend 4&N fl LI -- &gresd,ist fades —— Apgroximote meianorphic diogenetic and epigenelic zones — Low to middle reenscthsi fades cfilorite aid biotite zones Middle to tçper greerchSi tomes garnet aid ctiloriioid zones focies basidory Grenvulle Front Tectonic Boundary of Nuronion Supergroup aid Sutury — Struc tire Ariwhibohte tac'es stourolite zone Prnvinciol boundary rid/s Hornblende— horniels focus Cobalt FeIs.c nirustorts 40 0 N 80 km N 4rN 1' Superior Province - ,,tt 9'? —a Figure 15. 15. Metamorphism Metamorphism of of the Huronian Huronian Supergroup Supergroup(From (From Card, Card, 1978b) 19780) 37 �low-grade low-grade metamorphism, metamorphism, followed followed by by intrusion intrusion of of granite granite plutons plutons at about about 1.75 1.75 and and 1.5 1.5 GaGa. The The post-SIC post-SIC deformation deformation and retrograde retrograde at metamorphism metamorphism was was found found mainly mainly south south of of the the Murray Murray Fault, Fault, especially in in the the area area between between the the SIC SIC and and the the Grenville Grenville Front. Front. especially Shanks and and Schwerdtner(1991) Schwerdtner(1991) report report that that this this deformation deformation is is Shanks characterized by south-dipping south-dipping thrust faults faults or deformation zones zones characterized with northeast-trending northeast-trending foliation foliation and and southeast-plunging southeast-plunging with lineation. affecting lineation. The The last last recognized recognized deformational feature affecting Huronian rocks rocks is is the the movement movement along along faults faults which which post-date post-date the the Huronian diabase dikes dikes of of the the 1.25 1.25 Ga Ga Sudbury Sudbury swarm swarm (Card (Card and and Jackson, Jackson, diabase 1995). 1995) Recent Recent work work on on magnetic magnetic fabrics, fabrics, strain strain patterns, patterns, and and microstructures microstructures in in granitoid granitoid rocks rocks of of the the Creighton Creighton and Murray plutons Riller(1996) have have plutons and and their their Huronian Huronian host host rocks rocks by by Riller(1996) provided provided aa wealth wealth of of new new information information on on the the pre-2.2 pre-2.2 Ga Ga "Blezardian Orogeny" (Stockwell, Blezardian Orogeny" (Stockwell, 1982). 1982). Riller Riller concluded concluded that that major folding folding and and amphibolite amphibolite facies facies regional regional metamorphism in in the the Sudbury Creighton and Sudbury area area was coeval coeval with the the emplacement of the Creighton Murray Murray Plutons, Plutons, which which were were dated dated at at 2.3 2.3 Ga Ga by by Frarey Frarey et et al(1982) al(1982) (1984) and more recently at 2477 9 Ma by and Krogh et al. and more recently at 2477*'9 Ma by Krogh Krogh and Krogh et al. . Large-scale Archean et al. al. (1996) (1996). Large-scale dome-and-basin dome-and-basin structures structures in in Archean et basement and and Huronian Huronian cover cover rocks rocks represent represent major major north-vergent north-vergent nappes. nappes. The The Sudbury Sudbury Structure, Structure, aa deformed deformed relic relic of of an an astrobleme, astrobleme, is Archean is superimposed superimposed on on a a major major antiformal antiformal dome dome cored cored by by Archean granulite and granitoid rocks and flanked by overturned 1-luronian granulite and granitoid rocks and flanked by overturned Huronian strata strata on on the the south south and and several several remnant remnant rim rim synclines synclines of of Iluronian Huronian rocks on on the the north north (Riller, (Riller,1996). 1996). rocks In In the Sault Sault Ste. Ste. Marie-Elliot Marie-Elliot Lake Lake area area fault fault and and fold fold structures trend in general west-northwest to northwest. structures trend in general west-northwest to northwest. Folds Folds are are generally generally upright, upright, open open concentric concentric structures structures with with gentle, gentle, variably variably plunging plunging hinges hinges (Figure (Figure 14). 14). There There is is only only aa weak weak development development of of minor minor tectonic tectonic structures. structures. The The metamorphic metamorphic grade grade 1978b). The major major structural structural features features of of is subgreenschist subgreenschist(Card, (Card, is l978b) . The the Elliot Lake area include a gently south-dipping homocline the Elliot Lake area include a gently south-dipping homocline south south of the the Flack Flack Lake Lake Fault, Fault, the the open open fold fold of of the the Quirke Quirke Lake Lake Syncline Syncline and and the the Chiblow Chiblow Anticlinè Anticline between between the the Quirke Quirke Lake Lake Syncline Syncline and and the the Murray Murray Fault. Fault. Jackson Jackson (1997) (1997) found found no no evidence evidence of detachment detachment at at or or near near the the basement-cover basement-cover interface interface in in the the Elliot growthElliot Lake Lake area. area. He He also also proposed proposed that that the the "inverted "inverted growthfault" (1984) to fault" model model as as applied applied by by Zolnai Zolnaiet et al. al.(1984) to structuralstructuralstratigraphic stratigraphic relationships relationships in in the the Huronian Huronian may, may, in in some some cases cases at at 38 �least, be interpreted interpreted as thrust faults faults with flats flats following following least, depositional boundaries, boundaries, and and ramps ramps that that cut cut up up through through the the depositional stratigraphic stratigraphic section. section. Given Given the the data data available, available, neither neither model model could could be rejected rejected for for major major northwest northwest trending trending faults faults in in the the Sault Sault Ste. Ste. Marie Marie area. area. (Jackson, (Jackson, in in press). press). Jackson Jackson (1997) (1997) points points out out that that the the curvature curvature of of the the Flack Flack Lake Lake Fault Fault is is in in the the opposite opposite direction direction to to that that expected expected if if it it is is aa thrust thrust fault fault as as proposed (1984). Zolnaiet etal. al.(1984). In the the Sault Sault Ste. Ste. Marie Marie area area proposed by by Zolnai In the the presence presence of of trust trust faults, faults, as as suggested suggested by by out-of-sequence out-of-sequence units, has has been been confirmed, confirmed, in in at at least least one one location, location, by by diamond diamond units, Ste. Marie Marie Resident Resident Geologist's Geologist's drilling (Assessment (Assessment files, files, Sault Sault Ste. drilling Office). South-southwest South-southwest dipping dipping foliation, foliation, and and south-southwest south-southwest Office). plunging foliation foliation may may reflect reflect north-northwest north-northwest thrusting plunging thrusting (Jackson, (Jackson,1994) 1994) . The The Murray Murray fault fault zone zone separates separates the the moderately moderately deformed, deformed, low low metamorphic metamorphic grade grade rocks rocks to to the the north north from from the the multiply-deformed, multiply-deformed, higher higher grade grade rocks rocks of of the the Sudhury-Manitoulin Sudbury-Manitoulinarea area to to the the south. south. The The Sudbury-Manitoulin Sudbury-Manitoulin area area is is characterized characterized by by open open to to subisoclinal, flattened flattened buckle buckle folds folds with with upright upright to to northward northward subisoclinal, overturned axial axial surfaces. surfaces. Elongate Elongate domes domes and and basins basins are are formed formed overturned by by reversals reversals in in plunge. plunge. Penetrative Penetrative axial axial place place cleavage cleavage and and steeply rodding or or mineral mineral lineation lineation are are well well developed. developed. steeply plunging plunging rodding More More than than one one age age of of major major and and minor minor structures structures can can be be discerned discerned south south of of the the Murray Murray Fault Fault (Card (Cardand and Jackson, Jackson, 1995) 1995). Metamorphism Metamorphism south south of of the the Murray Murray fault fault ranges ranges from from low low greenschist fades (Card, (Card, l978b). 1978b). Rocks Rocks of of greenschist to to low low amphibolite amphibolite facies higher higher metamorphic metamorphic grade grade occur occur in in two two zones zones or or nodes, nodes, one one along along the the Murray Murray Fault Fault zone zone and and another another northwest northwest of of the the Grenville Grenville Front. Front. Both Both zones zones coincide coincide with with major major anticlinoria, anticlinoria, although although in in detail, detail, metamorphic metamorphic isograds isograds transect transect fold fold axes axes (Card (Card and and Jackson, Jackson, 1995). 1995). Higher Higher grade grade metamorphic metamorphic nodes nodes do do not not coincide coincide with with the the few few granitic granitic intrusions intrusions which which intrude intrude the the Huronian Huronian rocks rocks south south of of the the Murray Murray fault. fault. The The 1.850-1.900 1.850-1.900 Ga Ga age age of of metamorphism metamorphism is is much much younger younger than than the the Creighton-Murray Creighton-Murray granite granite (2.45 (2.45 Ga) Ga) and and older older than than the the 1.700-1.750 1.700-1.750Ga Ga of of the the Chief Chief Lake Lake and and Cutler Cutler granites. granites. Jackson Jackson (1997) (1997) considers considers the the origin origin of of the the high-grade high-grade staurolitestaurolitebiotite biotite assemblages assemblages of of the the McKim McKim Formation Formation in in the the hanging hanging wall wall of of the the Murray Murray Fault Fault as as one one of of the the most most enigmatic enigmatic aspects aspects of of the the tectonic tectonic history history of of the the Southern Southern Province. Province. He He concludes concludes that that 39 �geobarometry metamorphism (2geobarometry indicates indicates a a relatively relatively low low pressure metamorphism (233 kbar) kbar) at at high high temperature temperature. These These conditions conditions differ differ significantly from from the the 6-7 6-7 kbar kbar pressures pressures estimated estimated for for the the significantly Penokean metamorphism in in Minnesota as determined by Holm and Penokean Balm and Silverstone(1990). Silverstone(1990). He He concluded concluded that that the the high-temperature high-temperature metamorphism was at or below pressure corresponding metamorphism was at or below pressure corresponding to to the the thickness thickness of of the the Huronian Huronian rock rock column, column, thereby thereby precluding precluding crustal crustal thickening thickening as as the the origin origin of of the the metamorphism. metamorphism. Jackson Jackson (1997) (1997) concluded areas of concluded that that a a high high heat flow flow regime developed in in areas of crustal crustal extension extension and and related related mantle mantle upwelling. upwelling. Such Such aa model model is is Card's(1964) view that the high-grade compatible with compatible with Card's(1964) view that the high-grade metamorphism metamorphism may may be be the the result result of of rapid, rapid, focused focused heat heat flow. flow. Tectonic Huronian Basin Basin Tectonic Models Models for for the the Development Development of the Huronian There for the early There have have been been various tectonic tectonic models proposed for early development basin. Many Many development and and later laterdeformation deformationofofthe the1-luronian Huronian basin. reconstructions reconstructions are are essentially essentially modifications modifications of of the the model model put put forth Holden(1966)which whichstated statedthat thatthe theJ-Iuronian Huronian forth by by Dietz Dietz and and Holden(1966) Supergroup represents a rift and passive margin sequence Supergroup represents a rift and passive margin sequence that that was was compressed, compressed, partly tectonically tectonically buried and metamorphosed during during aa collision collision with with the the Superior Superior craton craton and and another another mass mass which Zolnai et et al. al. (1984), (1984), Bennett Bennett which overrode overrode its its southern southern edge. edge. Zolnai et et al. al. (1991) (1991) accept the essential aspects of the Dietz Dietz and and Holden Holden (1966) (1966) model. They They propose that rifting rifting and continental continental breakup breakup was was coeval coeval with with Huronian Huronian volcanism volcanism (2.45 (2.45 Ga) Ga) and and that that the the much much later later deformation deformation was was equivalent equivalent to to the the Penokean Penokean Orogeny Orogeny (1.860-1.835 (1.860-1.835Ga) Ga). This This model model does does not not attempt attempt to to account account for for the the multiple multiple deformation deformation events events affecting affecting Huronian Huronian rocks rocks and and the the origin of the Nipissing magmatic event. origin of the Nipissing magmatic event. . Young Huronian Supergroup Young (1982) (1982) proposed proposed that the the Huronian Supergroup was deposited deposited in in an an aulocogen, aulocogen, an an easterly easterly trending trending fault fault bounded bounded trough trough which which opened opened towards towards an an ocean ocean in in the the area area now now occupied occupied by by the the Grenville Grenville Province. concluded that that the the Huronian Huronian Province. Sims Sims et et al. al. (1980, (1980, 1981) concluded Supergroup, Animikie rocks rocks Supergroup, the the Marquette Marquette Range Range Supergroup Supergroup and and Animikie were were deposited deposited as as intracontinental, intracontinental, fault fault controlled controlled basins basins developed along a major, late Archean structure, the Great Lakes developed along a major, late Archean structure, the Great Lakes Tectonic Tectonic Zone. Zone. More More recently, recently, Roscoe Roscoe and and Card Card (1992), (19921,noting noting the the close close stratigraphic stratigraphic correlation correlation between between the the Early Early Proterozoic Proterozoic sequences sequences 40 �of Supergroup, proposed of the the Wyoming Wyomingcraton cratonand andthe theI-iuronian Huronian Supergroup, proposed that that the the Superior Superior and and Wyoming Wyoming cratons cratons are are rifted rifted portions portions of of what what was was once once aa single single continental continental land land mass. mass. They They suggest suggest the the direction direction of of the the Matachewan-Hearst Matachewan-Hearst dike dike swarm swarm (2.45 (2.45 Ga) Ga) indicates indicates an an easteastwest west tensional tensional regime regime which which resulted resulted in in aa Huronian Huronian basin basin elongated elongated in in aa north-south north-south direction. direction. On On this this larger larger craton craton the the Huronian sediment was deposited in a southward deepening Huronian sediment was deposited in a southward deepening intracratonic intracratonic basin. basin. Roscoe Roscoe and and Card Card (1992) (1992) propose propose that that it it was was during during the the Nipissing Nipissing igneous igneous event event (2.2 (2.2 Ga) Ga) that that successful successful rifting rifting of of the the Superior Superior Province Province took took place place with with the the eventual eventual drifting drifting of of part part of of the the missing portion portion to to its its present present location location as as the the Wyoming Wyoming craton. craton. They attribute attribute pre-Nipissing pre-Nipissing folding folding to to the the Blezardian Blezardian Orogeny Orogeny of Stockwell Stockwell (1982) (1982) and and the the later later more more important deformation deformation to to be coeval coeval with the Penokean Penokean Orogeny Orogeny of of important Michigan, 1992). Michigan, Wisconsin Wisconsin and and Minnesota Minnesota (Roscoe (Roscoeand and Card, Card,1992). Jackson Jackson (1997) (1997) supports supports the the model model of of Roscoe Roscoe and and Card Card (1992) (1992) since since the the high high heat heat flow, flow, which he he considers considers necessary necessary to to give give the the observed observed features features of of the the high-grade high-grade metamorphic metamorphic rocks, rocks, would would be be aa necessary necessary effect effect of of mantle mantle upwelling upwelling during during continental continentalbreak-up. break-up. He He also also interprets interprets some some of of the the early early high-strain high-strain deformation deformation as as being being consistent consistent with with aa Nipissing Nipissing age age break-up break-up of of the the Superior Superior craton. craton. 41 �ROAD ROAD LOG LOG -- HURONIAN SUPERGROUP SUPERGROUP BETWEEN BETWEEN SAULT SAULT STE. S T E . MARIE AND AND ELLIOT E L L I O T LAKE LAKE INTRODUCTION INTRODUCTION Some Some of of the the outcrops outcrops briefly briefly described described below below will will not not form form aa part part of of the the present present ILSG ILSG field field trip. trip. They They are are included included to to allow allow those those interested interested to to visit visit them them if if travelling travelling in in the the area area at at some some future future date. date. UTN UTM coordinates coordinates have have been been provided provided for for some some locations locations for for those on a map, map, or those who who may may wish wish to to plot the locations locations on or who who may may have have aa GPS GPS device. device. The The accuracy accuracy is is about aboutSO 50m. m. ROAD LOG ... DAY 1 Proceed Proceed east east along along Highway Highway 17 17 from from Sault Sault Ste. Ste. Marie. Marie. The The road road log log starts starts at at the the intersection intersection of of Highway Highway 638 638 and and Highway Highway 17 17 East East in in the the Town Town of of Echo Echo Bay Bay 0.0 638 at 0.0 km km -- 0.0 0.0 miles miles -- Highway Highway.638 at Echo Echo Bay Bay -- continue continue east east on on Highway Highway 17. 17. 44 km km -- 2.5 2.5 miles miles -- Start Start of of divided divided highway highway 7.9 7.9 km km -- 4.9 4.9 miles miles -- At At sign sign for for Calabogie Calabogie Road Road (UTH (UTM 1616- 55 144 144 004 Sub-Jacobsville 004 N, N, 725 725 322 322E). E). Sub-Jacobsvilleunconformity unconformity Outcrop Outcrop on on west west side side of of Highway Highway 17. 17. The The most most southerly southerly outcrop outcrop is is white white and and grey grey quartzite quartzite (quartz (quartzarenite) arenite) of of the the white white orthoquartzite (Frarey,1977) 1977) of of the the Lorrain LorrainFormation Formationis is orthoquartzitemember member (Frarey, overlain overlain by by aa basal basal sharpstone sharpstone conglomerate conglomerate of of the the Keweenawan Keweenawan Jacobsville Formation. The conglomerate conglomerate is is comprised comprised of of angular angular Jacobsville Formation. The clasts Lorrain quartzite quartzite up up to to 60 60 cm cm across across in in aa red red siltstone siltstone clasts of of Lorrain matrix. matrix. The The contact contact is is irregular. irregular. No No stratification stratificationwas was observed. observed. 20.0 20.0 km km -- 12.7 12.7 miles. miles. Highway Highway to to St. St. Joseph Joseph Island. Island. Continue Continue east east on on Highway Highway 17. 17. 42 �a U) 4 + / + -I- + 4 + + -t- + + -p-"- + I + + + 'I- + ++ + + 7 + ± ¼, + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + +_.i- + + + + + + + .p• + + + + + + + 4 + + + + + + r + + + 4+ ++ -' 4 — . _+ + + + + + + + + + + + + + + + + + + + + + ++ +-F+ + + + + + + + + + + + + (' + + + + + + + +_-'{+ + + + + + area. + + + IL,j: 4 + + Archean rocks — + + + + + + + + +•'+ +/+ + + + + + + + + + #+ + + + + + + + + + + + + + + +)+ 50km + +'tf- -k •'_+ + + + + + ,* + + + 4 + + + + + + + + + + + + + + + +%, + +_•.+ + + + + + + + + + *.+ + + + + + 4- + East Bull Lake Suite (Gabbro-Anormosite) ,_+ Murray Fault + Elliot Lake, -lough Lake and Quirke Lake Grouos Huronlan Supergroup Cobalt Group + ++1+ -+ + +.+ ' + .+-'+ ++ + - +,I' + + See Flr7rjrer 16,17 & 181cr remair-ng stops eIdtripatop Faults Cutler Granite + LEGEND + Paleazolc and Keweenawan racks .AKE HURON + + + —.— T1IIIfl Thessalon ,+ '1- + —'+ + + + + + + + + —______ +—c+ + + +#.. + + + + + Figure 16. The distribution of rocks of the Huronian Supergroup. Sault Ste. Marie-Elliot Lake + t t North '-1:, �25.0 25.0 km km -- 15.5 15.5 miles miles STOP Lorrain Formation Formation 1: Lower Lower red red quartzite member of the Lorrain STOP 1: (Frarey, (Frarey,1977) 1977). (Refer (Refer to to Figure Figure 16) 16). . - On On the the north north side side of of Highway 17 steeply dipping beds of the the lower lower member well preserved preserved member of of the the Lorrain Lorrain Formation Formation reveal well oscillation oscillation ripples ripples on on aa large large south south facing facing surface. surface. red red Note: Note: the the differing differing ripple ripple directions directions and and local local interference interference ripples. This This impressive impressive outcrop outcrop is known locally "Ripple ripples. locally as the "Ripple Rock". Rockw. Main Street Street in in the the town town of of Desbarats Desbarats (pronounced (pronounced"Debarah" "Debarah" 1 Main 26.8 26.8 km km -- 16.6 16.6 miles miles STOP STOP 2: 2: Purple Purple siltstone siltstone member member of of the the Lorrain Lorrain Formation. Formation. Dark Dark red red to to purple purple siltstone siltstone and and sandstone sandstone constitute constitute true true redredbeds 1977) in in the the Huronian. Huronian. These These hematite-rich hematite-rich rocks rocks beds (Frarey, (Frarey,1977) display the the reduction reduction along along fractures fractures typical typical of of red red beds, beds, and and aa display good good indicator indicator of of deposition deposition in in an an oxidizing oxidizing environment. environment. The The bedding 140 and and dipping dipping bedding is is faint, faint, but but locally locally distinct, distinct, striking striking 140° 10° 1O0 south. south. 27.7 27.7 km km -- 17.2 17.2 miles miles Lake Lake Huron Huron Drive Drive in in the the town town of of Desbarats Desbarats 28.0 28.0 km km -- 17.4 17.4 miles. miles. STOP STOP 3: 3: Basal Basal Arkose Arkose Member Member of of Lorrain Lorrain Formation. Formation. UTM UTM Zone Zone 17. 17 275461N, 275461N, 5l36234E. 5136234E. Large Large outcrops outcrops of of pink, pink, medium—grained medium-grained , rather rather massive massive arkose arkose beds beds with with hematite-rich hematite-richspots spots about about one one centimetre centimetre across. across. Pale Pale laminations in outcrop on south side of the road indicate shallow laminations in outcrop on south side of the road indicate shallow dips loowest. west. The The unit unit is is about about 1700 1700 feet feet thick thick in in dips of of about about10° this this area area (Frarey, (Frarey,1977). 1977). , 40.5 km -- 25.0 25.0 miles miles copper copper bearing bearing quartz quartz vein vein in in town town of of Bruce Bruce 40.5 km Mines. Mines. In 17, in in the the town town of of In aa rock-cut rock-cut on on the the north north side side of of Highway Highway 17, 44 �Bruce Bruce Mines, Mines, is is aa 33 metre metre wide wide quartz quartz vein vein in in Nipissing Nipissing diabase. diabase. The The vein vein contains contains small small amounts amounts of of chalcopyrite, chalcopyrite,chalcocite, chalcocite, bornite bornite and and malachite. malachite. It It is is one one of of the the few few remaining remaining remnants remnants of of the the copper copper mineralization mineralization that that once once made this this town town known known throughout throughout the the mining mining world. world. Mining Mining began began here here in in 1846 1846 and and continued continued to to 1875, 1875, making making Bruce Bruce Mines Mines the the first first mining mining town town in in Canada. Please do do not not take take samples samples from from this t h i s outcrop. outcrop. Canada. Please About 75 metres metres north north of of this this outcrop outcrop there there is is aa reconstruction reconstruction About 75 of of aa copper copper mining mining operation operation of of that that period period built built on on one one of of the the original mine workings, known as the "Simpson Shaft". original mine workings, known as the "Simpson Shaftn. During During the the summer summer months months the the Simpson Simpson Shaft Shaft site site is is open open as as aa tourism tourism operation. operation. 42.6 42.6 km km -- 26.5 26.5 miles miles Entrance Entrance to to the the quarry quarry of of Ontario Ontario Trap Trap Rock Rock (R.W. (R.W. Tomlinson Tomlinson Limited). Limited)'.The The quarrying quarrying of of trap trap rock rock (Nipissing (Nipissing diabase) diabase) at at Bruce Bruce Mines predecessor near near the the lake lake operated operated Mines resumed resumedin in1990. 1990. AA predecessor during during the the First First World World War. War. 45.1 45.1 26.0 28.0 Highway 17-5 Highway 17 17 17-5 129 129 846N, 846N, 289 289 Sl2E, 512E, Low Low outcrops outcrops of of Mississagi Mississagi Formation. Formation. Waltonen Waltonen Road Road at at 45.4 45.4 km km or or 28.2 28.2 miles miles at at east east end end of of outcrop. outcrop. Medium-sand Medium-sand to to grit-sized, grit-sized,grey1 grey, subarkose subarkose with with thin thin quartzquartzpebble pebble beds beds and and prominent prominent planar planar cross-bedding cross-bedding are are well well exposed exposed along along the the north north side side of of the the highway. highway. Rusty Rusty staining staining on on the the outcrop detrital(?) pyrite pyrite along along the the foreset foresetbeds. beds. outcrop reflects reflects minor minor detrital(?) Black Black chert chert pebbles pebbles in in pebbly pebbly beds, beds, minor minor pyrite pyrite and and metre metre scale scale bedding bedding are are common commonfeatures featuresof of the the Mississagi Mississaqi Formation. Formation. Roscoe, Roscoe, (1969) (1969) concluded concluded that that the the drab drab colour colour and and presence presence of of detrital detrital pyrite pyrite in in Huronian Huronian sandstones sandstones and and conglomerates conglomerates is is evidence evidence of of the the reducing reducing nature nature of of the the early early Huronian Huronian atmosphere. atmosphere. 60.6 60.6 km km -- 37.6 37.6 miles miles Intersection Intersection of of Highway Highway 17 17 and and Highway Highway129. 129 UTM Zone 17 303590E, 17-5126450N UTM Zone 17 - 303590E, 17-5126450N STOP STOP 4: 4: Thessalon ThessalonFormation Formationtholeiitic tholeiiticbasalt. basalt. Refer Refer to toFigure Figure17. 17. Dark Dark green, green, fine fine to to medium medium grained grained basalt basalt is is exposed exposed on on the the east east 45 �+ ± + + + + -I + -l + ÷ -I + + -l + + -I ÷ -I -4 4 4 at— -1 + 2"/j5S 4jçr74Cv Thessalon -l Lake Huron IL EGEND EGEND Thessalon lhessalonFm Fm Basalt, andesite. rhyolite rflyolite Basait. andesite. Nipissing Nipissing Gabbro. Gobbro.diabase. diabase,granophyre granophyre A MississadFm. Fm. Mississagi Subarkose,pebble pebbk conglomerate conglomerate Subarkose, 3 AAA AAA High magnesium basalt High magnesium basalt felsic pyroclastic rocks fetsfc flows, flows, pyroclostic rocks Frn MdinendaFm Malinendo Subarkose. arkose %barkose.ark- Arkose, quartz-pebble conglomerate conglomerate Arkose, quartz-pebbk (localty pyriticand and radioactive) radioacWe) (iocalty pyritic quartz-pebble quartz-pebble conglomerate conglomerate Iivlngstone Cr.Fm. Fm. livingstoneCr. Anticlinal ax // X Nkose. conglomerate Arkose, polymictic conglomerate Synclinal axis Archeon Afchean Plutonic and and gneissic gneissicgranite graniterocks, rocks, rnigmatite migmatite N 25 00 Bedding attitude attitude Fault Fault * / 1 I * + 22 d km krn I I Field trip stop - Figure 17. Figure 17. Geology of of the the Thessalon Thessalon Area Area 46 �north of the intersection intersection with Highway side of Highway 129 just north 17. Thessalon 17. This tholeiitic tholeiitic basalt forms the top of the Thessalon Formation Formation in in the Thessalon area and is typical of the thicker thicker tholeiitic tholeiitic sequences sequences which which make make up up the the upper upper parts parts of of the the Aberdeen Township Township Thessalon Formation in the Sault Ste. Marie and Aberdeen The rocks areas. The rocks consist consist of albite, albite, chlorite, chlorite, epidote, epidote, clinozoisite, leucoxene minor quartz clinozoisite, leucoxene and minor quartz and and oxides. oxides. The The metabasalt contains amygdules albite, quartz, quartz, epidote, epidote, calcite s of albite, contains amygdule calcite and chlorite. relatively small, monomineralic monoimineralic chlorite slatively small, chlorite chlorite. The .. The . r< . buttons") .. , are amygdules amygdules ("chlorite ("cniorite buttons"; are characteristic cnaracteristic of of the the mafic mafic volcanics Ste. Marie and and volcanics of the Thessalon Formation between1 Sault Ste. Elliot Lake. Elliot Lake. 7 7 Glacial striae and cnaci-er chatter marxs marks are we± well aeveloped developed on the the striae ana outcrop surface. outcrop surface. Proceed north 129. Reset Reset odometre odometre to to 00 00 at at Proceed north on on Highway Hi< Intersection of Higl Highway 17 andd Highway Highway 129. 129. Intersection 1.0 miles km -- 0.62 0.62 miles 1.0 km STOP 5: Outcrop of Matinenda Formation Formation on east side of Highway 129. 129. This pink to greenish grey, grey, subarkose which This fine-grained, fine-grained, pale pink directly Thessalon area directly overlies the Thessalon Formation in the Thessalon has been correlated with with the Matinenda Matinenda Formation of of the Elliot al., 1991). Faint outlines of trough Lake Group (Bennett (Bennett et al., cross-bedding, visible on the upper cross-bedding, upper surface surface of of the the outcrop, outcrop, indicate paleocurrent directions directions from the northwest. northwest. The The greenish greenish (sericitic) units and and the the trough trough cross-beds cross-beds are typical of the (sericitic) units the Matinenda Formation, but the fine grain size is not. At Thessalon Formation, At Thessalon Point about 4 contain 4 km southwest of this location these rocks contain thin quartz pebble conglomerate thin quartz conglomerate units, units, but but the the pyrite pyrite and and radioactivity, radioactivity, characteristic characteristic of of the the Matinenda Matinenda Formation Formation of of the the Elliot Lake Lake area, area, are are lacking. lacking. village of Warncliffe 23.0 km -- 14.9 14.9 miles The village 23.0 km north end 29.1 km km -- 18.4 end of of Appleby Appleby Lake. Lake 18.4 miles north 47 �30.3 3 0 . 3 km km -- 19.4 19.4 miles miles UTM UTM 17, 17, 5 144 748N, 320 320 904E 904E STOP 6: 6: Laminated Laminated siltstone siltstone of the Gowganda Formation Formation on on scarp scarp STOP west west of of Highway Highway 129. 129. (Refer (Refer to to Figure Figure 16.) 16.) Proceed Proceed up up steep steep slope slope to to scarp scarp located located aa few few tens tens of of metres metres into into the bush. bush. the Vertical Vertical joint joint faces faces in in laminated laminated siltstones-mudstone siltstones-mudstoneof of the the Gowganda Formation Formation form form an an impressive impressive cliff just just west of of Highway Highway Gowganda 129. The The bedding bedding comprises comprises regular regular and and remarkably remarkably continuous continuous 129. mudstone-siltstone couplets from 0.5 to 2 cm thick. mudstone-siltstone couplets from 0.5 to 2 cm thick. The The grey grey siltstone siltstone unit unit at at the the base base of of each each couplet couplet grades grades up up to to aa darker darker mudstone mudstone which which is is in in sharp sharp contact contact with with the the siltstone siltstone base base of of the the resembles varves vanes of overlying overlying couplet. couplet. The sequence closely resembles of Pleistocene few pink, pink, discontinuous, discontinuous,fine, fine, Pleistocene glacial glacial lakes. lakes. AA few sandstone sandstone beds beds are are also also present. present. Widely boulder-sized Widely scattered scattered through through the sequence are pebble to boulder-sized Archean granitic granitic rocks. rocks. In In the the "drop stones", stones", predominantly predominantly of Archean "drop absence absence of of volcanic volcanic activity activity within within the the Gowganda Gowganda Formation, Formation, the the only plausible source of the drop stones is the presence of only plausible source of the drop stones is the presence of floating floating ice ice which which released released its its rock rock load load during during melting. melting. This This outcrop, outcrop, and and many many others others of of aa less less spectacular spectacular nature, nature, provide provide some some of of the the best evidence evidence for for aa cool cool climate climate during during Gowganda Gowganda time. time. interpret the the laminated unit unit as a varved Church and and Young, Young, (1972) interpret Church sequence. They They also note the presence of small small sedimentary sedimentary sequence. clasts, lithologically similar to the enclosing rocks. clasts, litholoqically similar to the enclosing rocks. They They interpret interpret the the clasts clasts of sedimentary sedimentary rocks rocks as as having having been been derived derived from upper surface from the the ablation ablation of sediment sediment on on the upper surface of of the the glacier. glacier. reported pyritic, pyritic, carbonaceous carbonaceous inclusions inclusions and and Jackson, (1971) reported Jackson, "fossil fossil gas gas bubbles", bubbles", which which he he considered considered to to be be biogenic biogenic origin, origin, associated associated with with drop-stones drop-stones at at this this location. location. 30.9 km km -- 19.5 19.5 miles. miles. Intersection Intersection with with Highway Highway 554. 554. Return Return to to 30.9 Thessalon along Thessalon along Highway Highway 129. 129. Intersection of Highway 17 and 30.9 km km -- 19.5 miles. Intersection and Highway Highway 19.5 miles. 30.9 129 at at Thessalon. Thessalon. Reset Reset odometer odometer to to 0.0. 0.0. 48 �2.6 miles. 2.6 km km -- 1.6 1.6 miles. 17- 126567N. 126567N. Green Lane. Lane. Cross Cross UTM 306085E, 306085E, 17railway tracks (with (with care) and immediately immediately turn left then then south south railway tracks to short short section section of of unpaved unpaved road road between between private private properties. properties. Outcrops of Thessalon Formation felsic metavolcanics lie at the Outcrops end end of of the the road. road. STOP 7: Rhyolite Rhyolite of of the the Thessalon Thessalon Formation. Formation. (Refer STOP 7: (Refer to Figure Figure 17) . 17) Volcanics are Volcanics are fine fine grained, grained, grey to to pink and maroon rhyolite rhyolite (Table consisting of a fine (Table 2) consisting fine grained grained mosaic mosaic of of albite, albite, K-feldspar, and K-feldspar, and quartz quartz with minor minor green green pleochroic pleochroic biotite. biotite. Amygdules Arnygdules are are filled filled with with quartz, quartz, biotite biotite and and stilpnomelane. stilpnomelane. Collapsed iron staining Collapsed vesicules are also present. Local iron staining and darker chloritic darker chloritic areas areas indicate indicate the the presence presence of of iron iron sulfides. sulfides. 5.9 km 3.6 miles. miles. km -- 3.6 At Pine Pine Ridge Ridge Road Road Reset odometre odometre to to 000 000 Intersection of 17 and and Pine Pine Ridge Ridge Road. Road. Intersection of Highway Highway 17 (south) onto Pine (south) Pine Ridge Ridge Road. Road. 2.9 1.8 miles. miles. 2.9 km km -- 1.8 property. property. At Lake Lake Huron. Huron. Turn right Turn right Causeway to Causeway to private private NOTE: In residents there will be NOTE: In consideration consideration of the privacy of residents no road road log log for for the the next next four four stops. stops. STOP STOP 8: 8: Sub-Livingstone Sub-Livingstone Creek Creek Formation Formation regolith. regolith. NOTE: NOTE: High High water water levels levels on on Lake Lake Huron may prevent access to part of this this area. area. Supergroup is exposed near The granitic granitic basement to the Huronian Supergroup the predominantly the shore shore of of Lake Lake Huron. Huron. The granitic rocks rocks are predominantly red to red to grey grey coloured coloured with with zones zones of of mafic mafic xenoliths. xenoliths. sub-Livingstone Creek This will be a brief stop to examine sub-Livingstone Formation regolith Archean granitic granitic rocks. rocks. This This Formation regolith on on the the lowermost lowermost Archean sub-Livingstone Creek sub-Livingstone Creek Formation Formation unconformity unconformity is is the the lowermost lowermost unconformity A saprolitic paleosol is is unconformity in in the the Huronian Supergroup. A not as sub-Matinenda as well developed developed as at the well studied sub-Matinenda 49 �paleosol of paleosol of the the Elliot Elliot Lake Lake area. area. On fine-grained On a a 22 by S5 m outcrop at the waters edge, grey, fine-grained arkosic sandstone sandstone surrounds arkosic surrounds sub-rounded sub-rounded blocks blocks of grey to reddish reddish granitic basement. granitic basement. The The granitic blocks appear appear to to be in in place or place or only slightly slightly dislocated. dislocated. only tens of of metres metres further east, east, very very On shoreline shoreline outcrops a few tens fine-grained steeply dipping, silicious fine-grained steeply dipping, silicious veins veins may may also also be be related related Locally, sandstone to the the pre-Livingstone pre-Livingstone Creek Creek weathering. weathering. Locally, sandstone filled seams (fissure or crack filling) appear to dip filled seams (fissure filling) appear to dip steeply steeply to to the east, east, i.e. i.e. about about perpendicular perpendicular to to the the paleosurface. paleosurface. the Return to Return to the the driveway. driveway. STOP 9: STOP 9: Base of the Livingstone Livingstone Creek Creek Formation. Formation. About 3 3 m m of of fine-sand fine-sand to to grit-sized, grit-sized, grey grey sandstone sandstone of of the the Livingstone Livingstone Creek Creek Formation Formation is is exposed exposed in in outcrops outcrops along along the the short short ascent ascent to to the the driveway. driveway. Although Although neither neither the the contact, contact, nor nor a complete Archean basement complete transition transition zone zone between the Archean basement granite granite and 1-juronian Supergroupare areexposed, exposed,these these sandstones sandstones are are only only a and Huronian Supergroup few few metres (stratigraphically) (stratigraphically) above the Livingstone Livingstone Creek Creek Formation—Archean unconformity. Formation-Archean unconformity. At the section, the Livingstone Creek the base base of of the the short exposed section, sandstone sandstone is is massive and has a few few scattered scattered (matrix (matrix supported), supported), well-rounded well-rounded to to sub-rounded sub-rounded granitic granitic cobbles cobbles and and boulders. boulders. The The diffuse edges and embayments of of some some clasts clasts suggests suggests that that they they diffuse have have undergone undergone little little transportation transportation and and may may be be core core stones stones of of weathered granitic blocks, weathered granitic blocks. Widely distributed distributed rusty rusty areas areas up to to 4 4 cm cm across across indicate indicate the presence of sulfide sulfide concentrations concentrations (nodules?). The basal basal portion portion of this section section may may be be paleosol or paleosol or material derived from paleosol. The material from adjacent adjacent paleosol. The upper upper part part of of the the exposed sandstone The exposed sandstone section section shows shows trough trough cross-bedding. cross-bedding. The recessive weathering pattern indicates indicates that carbonate recessive carbonate is is prominent along foreset beds. beds. prominent along the the foreset STOP STOP 10: 10: member of of the Livingstone Livingstone Creek Formation Conglomerate member Formation A A low low outcrop outcrop adjacent adjacent to to the the driveway driveway on on private private property. property. 50 The The �rocks are are clast.-supported clast-supported polymictic commonly rocks polymictic conglomerate conglomerate which which commonly forms the the lowermost lowermost member member of of the the Livingstone Livingstone Creek Creek Formation. Formation. forms The boulder-sized clasts The conglomerate conglomerate is is made made up of cobble cobble and boulder-sized clasts to white-weathering white-weathering massive, and of pale-grey pale-grey to massive, porphyritic porphyritic and gneissic granitic rocks rocks with with some some foliated foliated amphibolite amphiboliteand andmat mafic gneissic granitic ic plutonic plutonic rocks. rocks. There There are a few few thin beds of intercalated coarse intercalated coarse arkose. arkose. No No clasts clasts of of Huronian Huronian volcanic rocks rocks have have been been identified identified in the the Livingstone Livingstone Creek Creek Formation. Formation. The polymictic polymictic clast clast population, population, sorting sorting and size size indicate indicate The deposition in in aa high high energy energy environment environment such such as as an an alluvial alluvial fan. fan. deposition Although the the grey grey colour colour is is dominant dominant in in these these conglomerates, conglomerates, the the Although pink to basement rocks, rocks, is is to red red colour, colour, common common in in the the Archean basement scarce scarce or or lacking lacking in in the the conglomerate conglomerate clasts. clasts. This This colour colour difference between between the the clasts clasts and and the the source source granites granites may may be be due due difference preto reduction reduction of of ferric ferric iron iron in in the the feldspar feldspar lattice lattice during during preto Huronian Huronian weathering weathering or or diagenesis. diagenesis. STOP STOP 11: 11: Base Base of of the the Thessalon Thessalon Formation Formation -- Sedimentary Sedimentary rocks rocks of of the the Thessalon Thessalon Formation. Formation. Fine Fine to to medium medium sand-sized, sand-sized, cross-bedded cross-bedded dark-grey dark-grey sandstone sandstone marks marks the top top of of the the Livingstone Livingstone Creek Creek Formation Formation is is this this area. area. The The the grey grey colour, colour, recessive recessive weathering weathering along along the the foreset foreset beds, beds, and and the the restricted range range of of clast clast size, size, is is characteristic characteristic of of the the restricted sandstone member member of of the the Livingstone Livingstone Creek Creek Formation. Formation. sandstone Near Near the the water water line line on on the the west west side side of of the the outcrop, outcrop, aa thin thin unit unit (a few cm cm thick) of radioactive, radioactive, quartz-pebble quartz-pebble and and cobble a few cobble conglomerate, 040' and and dipping 45"west, lies on on the the conglomerate, striking striking O4O 45west, lies upper upper surface surface of of the the grey grey sandstone sandstone of the Livingstone Livingstone Creek Creek Formation. The The conglomerate conglomerate consists consists predominantly of pale-grey pale-grey Formation. predominantly of and dark-grey pebbles and dark-grey to to black, black, well-rounded well-rounded quartz pebbles and cobbles cobbles up bed is, in turn, turn, overlain 10 cm cm across. across. The conglomerate bed overlain up to to 10 by by aa unit unit of of massive massive to to cross-bedded, cross-bedded, grey grey grit grit and and arkose arkose which which forms forms the the basal basal unit unit of of the the Thessalon Thessalon Formation Formation in in the the area. area. displacement of of the the quartz quartz pebble pebbleconglotherate conglomerate Note: the the 55 mm displacement Note: along along aa steeply steeply dipping dipping dextral, dextral, northwest northwest striking striking fault. fault. Diamond Huron in Diamond drilling drilling done done from from the the ice ice of Lake Huron in the the 1970's 1970's indicates indicates that that the the volcanic rocks rocks which form the the bulk of of the the Thessalon are at at Thessalon Formation Formation directly directly overlie overlie the the grit grit unit unit but are 51 �this this location location covered covered by by the the lake lake waters. waters Measurement gamma ray Measurement of of gamma gamma radiation radiation made with a McPhar TV1A gamma ray spectrometer are spectrometer are given given below: below: Livingstone Tl=2,000; T2=60; T2=60; T3=30 T3=30 Livingstone Creek Creek sandstone: sandstone: Tl=2,000; Quartz Pebble Quartz Pebble Conglomerate Conglomerate (Thessalon (ThessalonFormation) Formation) T2=700; T3=6O T2=700; T3=60 T2=U+Th; Th. where Tl=K÷U-i-Th; Tl=K+U+Th; T2=U+Th; T3 == Th. where : : T1=20,000; Tl=20,000; measurements in measurements in counts/mm counts/min Earlier radioactive Earlier writers writers have have (reasonably) (reasonably) concluded that the radioactive conglomerate conglomerate is is aa unit unit of of the the underlying underlying Livingstone Livingstone Creek Creek concluded that the Formation. However, Formation. However, Bennett Bennett et et al. al. (1991) concluded the radioactive stratigraphically radioactive conglomerate conglomerate at this locality is stratigraphically equivalent and significantly significantly equivalent to to the the Thessalon volcanic rocks and younger than younger than the the Livingstone Livingstone Creek Creek Formation. Formation. Some Some of of the the evidence evidence for for this this conclusion conclusion is is as as follows: follows: 1. Radioactive conglomerates occur within within the the volcanic volcanic flows near 1. Radioactive the base of the Thessalon Formation in the Sault of the Thessalon Formation in Sault Ste. Ste. Marie Marie area area (Hay, 1963) 1963) and the Aberdeen Aberdeen Lake (Hay, Lake area area (Bennett, (Bennett,1982) 1982). 2. At At a few few localities localities in in the Quirke Lake Syncline Syncline radioactive radioactive conglomerate below the Thessalon Thessalon conglomerate and and arkose are found directly below Formation Formation flows flows upon upon the the Archean Archean basement where where the the Livingstone Livingstone Creek Formation Creek Formation is is not not present. present. 3. No quartz-pebble 3. quartz-pebble conglomerate conglomerate has has been identified identified anywhere anywhere within within the the Livingstone Livingstone Creek Creek Formation. Formation. 4. 4. The The resistate resistate nature nature of of the the minerals minerals in in the the conglomerate conglomerate suggests extensive area and suggests extensive weathering of the source source area and the the presence presence of a disconformable relationship with the underlying unit. disconformable relationship with the underlying unit. Proceed Proceed from from west west end end of of causeway causeway northward northward along along Pine Pine Ridge Ridge Road. Road. STOP 12: Archean Granitic Basement Rocks Rocks STOP 12: Saprolith Saprolith on on Archean gneiss, up to Blocks of pale-weathering pale-weathering granitic granitic gneiss, to 11 m across, across, are are separated by separated by brownish-weathering brownish-weathering arkosic sandstone sandstone filled filled cracks, cracks, 52 �which which appear appear to to be be products products of of the the paleoweathering paleoweathering of of the the gneiss. gneiss. The The grain grain size size of of quartz quartz in in the the inter-block inter-block sandstone sandstone is is consistent consistent with with derivation derivation from from weathering weathering of of the the surrounding surrounding granite. In places the prominent gneissosity in the granite. In places the prominent gneissosity in the granitic granitic rocks rocks shows shows that that no no rotation rotation of of the the blocks blocks has has taken taken place place during during the the development development of of the the sandstone sandstone units. units. The The sandstone sandstone units units are are up wide, and and in in places places include include numerous numerous sub-angular sub-angular to to up to to 22 mm wide, sub-rounded sub-roundedblocks blocks of of granitic graniticgneiss. gneiss. The The very very thin thin arkosic arkosic units units appear appear to to be be no no more more than than altered altered seams seams in in the the granitic granitic basement. basement. At At the the west west end end of of the the outcrop outcrop the the sandstone sandstone units units are are fined fined grained, grained, grey grey and and resemble resemble the the sandstones sandstones of of the the overlying overlying Livingstone Livingstone Creek Creek Formation. Formation. Proceed Proceed north north on on Pine Pine Ridge Ridge Road Road to toHighway Highway17. 17. then then proceed proceed east east on on Highway Highway17. 17. Reset odometer odometer Reset Reset Reset odometre. odometre. 13.5 13.5 km km Melwell Melwell Road Road 14.1 14.1 km km Chalcopyrite Chalcopyrite bearing bearing quartz quartz carbonate carbonate vein vein cut cut pebbly pebbly siltstone siltstone of of the the Gowganda Gowganda Formation Formation on on the the south south side side of of Highway Highway 17. 17. The The vein vein and and mineral mineral assemblage assemblage (quartz-carbonate-pyrite(quartz-carbonate-pyritechalcopyrite-hematite) chalcopyrite-hematite) is is typical typical of of many many in in such such occurrences occurrences between between Sault Sault Ste. Ste. Marie Marie and and Sudbury. Sudbury. 47.6 47.6 km km Downtown Downtown Blind Blind River River(at (atTim TimHorton's). Horton's). 66.7 66.7 km km Pronto Pronto Road Road Turn Turn north north onto onto the the Pronto Pronto road road and and continue continue until until prevented prevented by by aa gravel gravel barrier barrier from from proceeding proceeding further. further. Continue Continue on on foot foot past past the the barrier barrier to to the the west west end end of of aa beaver beaver pond pond just just north north of of the the road. Proceed along along aa trail trail across acrossthe the west west outlet outletof ofthe thepond, pond, road. Proceed then then around around the the north north end end of of the the pond pond and and up up aa steep steephill. hill. Turn Turn left (to the north) on a gravel road at the top of the hill. left (to the north) on a gravel road at the top of the hill. Continue Continue to to an an area area of of outcrop outcrop and and gravel gravel fill fill which which marks marks the the former stope of of the the Pronto Pronto mine. mine. If If not not accompanied accompanied by by aa former open open stope guide, guide, please please do do not not attempt attempt to to access access this this site site without without aa compass compass as as well well as as suitable suitablefootwear footwearand andclothing. clothing. NOTE: NOTE: During During the the field field trip trip we we hope hope to to arrange arrange for for access access from from the the normally normallyrestricted restrictedmine mineproperty. property. 53 �(13) '7',' 7,,,, +—+-- -:—:-:::÷:÷ 7,',, 7,,,, .7/,, '7,, ''/, 7,' ''7 '77, ::÷::t:*::t.. LEGEND HIJRON1AN + 4 + + + + * + + * ++ + + >/ formations above the Motinenda 7, 7 7 / + * + + , + + + +4 +,+ 4+, + + + + + [V71 Matinendo, conglomerate + + +4 + 4-4 + + Poieosol + 4 + + + ++4 +-*+ ++ ++ + ARCHEAN + +++++ + + + + ftfterRobrtsorj(197O) fl Gronitic rocks + y;ç' y Pond"\ / —. c-:: :v- 1/ 12 / —'- Pond c_f /''///' '''','''' •'''C t%_ _*++,+e,,,,, -70- z,zz,,,,,z / / //'/'/ —4- /7/ ,, ,,,,,,,,,/,-,, /7/7/7/7/7/7/, /17/7/7/7' / ,,,,,,,,,,,,,, /4 ,,• • -0. ,f',/ ,+,-////////7//,+/1/ /7/ + 7 +-..2yc 7/fly /7/77/7/7/7 ,,,,,,,,,'''''' -,r,,,,,,,,,,,,,,,,,,,,,,,,,,,, ////////f7////////////7///////// /71/7/'//'// ,,,,,, ,,,,,,, / /77/7/. C t.+ +V V - VVV, VVVVVVVV 0/'''' /' /''/'''/'' /7+,,,,,, VVVVVVVVVV,VV, ,,,,, 7,,,,,,, 7'//'// 7,7,7,,,,,, VVVVVVV VVVVVV VVV /7/7/7/' -C '',,,,, 0 /////,/////7.///// / / VVVVVV VVVVVVVVVVVVV 7,, +1-''// /7/' ,,,,,,,,,,,, c+,,, , 0_,,//,,4.__j", /7/7/7/77 , - + '+ V VVVVVVVVV VVVVVVVV'VVVVV VVVVVV VVVVV VVVVVVVVVVVVV VVVVVVVVVVVVVVVVVVVVVVVVVVZ '-VVVVVVVVVVVVVVVVVVV""""-4 VV VVV VVVV VV V V V V VV VVVV V ,,,, /77177+V-V0" / 4\iV' - //VVVVVVVVV 77vV'VVVØ4 VV4Sk1i.& VVVVVV VVVVVVVV'+ VVVVVVVVVVVVVVVV VVVVVVVVVV VVVVVVVVVV V/ JVVVV VVVVV V VVVVV — VVVVVVVVVVVVVVVVVVV +r'+' V1 VVVV V V V V V V V V V V V V V V V .VVVVVVVV'' . t V V,VW V V V V V V V V V V V V V V V V V'VVVV V V V V V V V V V V V V V V V VVV'V V V_-—' / VVVVVVVV'+ VVVV I VVVVVVVVVVVVVV.+M - V - VVVVVVVVVVVV V V V V V VVVVVV V V V V VV'L+_-+ - '1 HURONIAN Formations above the Matinenda -.- Hi Matinenda Formatloin Pat~F.xmat#m a fl Gronilic rocks Gron8ltc rocks Fautt Fault c<^ Bedding attitude Bedding attitude 0Paler Formation ARCHEAN ARCHEAN SYMBOLS SYMBOLS — '13' ,_ ----4 13 Fieldtrip stop Fieldtnp slop -d I Projection ore body Projection ofdoriginal original ore body , 1 krn 1 km ? . Figure Plan and section of of thethe Geology ofof the Figure18.18. Plan and section Geology thePronto ProntoMine Minearea. area. 54 �STOP STOP 13: 13: Pronto Pronto Mine Mine (past (pastproducer) producer) -- This This property property is is currently currently undergoing restoration restoration to to a a condition condition as as closely closely as as undergoing possible possible to to it's it's original original state. state. (Refer (Refer to to Figure Figure 18). 18). This This is is one one of of the the few few locations locations where where exposures exposures of of uraniferous uraniferous quartz quartz pebble pebble conglomerate conglomerate of of the the Matinenda Matinenda Formation Formation can can be be found found on on surface surface in in the the Elliot Elliot Lake-Blind Lake-BlindRiver River area. area. In In the the depression depression south south of of the the road road are are exposed exposed rusty-weathering rusty-weathering outcrops outcrops of of radioactive, radioactive, pyritic, pyritic, quartz-pebble quartz-pebble conglomerate conglomerate of of the the Matinenda Matinenda Formation Formation which which mark mark the the base base of of the the ore ore bed bed of of the the Pronto Pronto Mine. Mine. The The conglomerate conglomerate lies lies directly directly upon upon yellowish, yellowish, sericitic Archean granitic granitic baAement. basement. sericitic paleosol paleosol developed developed on on Archean Proceeding Proceeding in in aa general general northerly northerly direction direction some some features features of of the the original granitic rocks, displayed as dikes and irregular bodies original granitic rocks, displayed as dikes and irregular bodies of of aplite aplite and and pegmatite, pegmatite, can can be be recognized recognized in in the the paleosol paleosol (saprolith). southward sloping sloping outcrop outcrop the the (saprolith). Continuing Continuing up the the southward yellowish yellowish colour colour of of the the paleosol paleosol can can be be seen seen to to take take on on aa pinkish pinkish and Archean granitic granitic rocks rocksof of the the area. area. and reddish reddish hue hue normal normal to to the the Archean Continuing north and west to near the highest point on the Continuing north and west to near the highest point on the outcrop outcrop one one can can discern discern the the faint faint outline outline of of core-stones core-stonesin in the the granitic rocks. granitic rocks. Return Return to to Highway Highway 17. 17. Continue Continue east east along along Highway Highway 17 17 to to Highway Highway 108 108 to to Elliot Elliot Lake. Lake. Continue Continue eastward eastward for for aa few few hundred hundred metres metres past to low low outcrops outcrops in in an an open open area area just just south south of of 108 to past Highway Highway 108 Highway 17. Highway 17. STOP STOP 14: 14: McKim McKim Formation Formation —- Staurolite Staurolite schist. schist. Low Low outcrops outcrops aa few few tens tens of of metres metres south southof of Highway Highway17. 17. (Refer (Referto to Figure Figure16) 16). This This outcrop, outcrop, which which lies lies aa few few hundred hundred metres metres south south of of the the Murray Murray Fault Fault Zone, Zone, displays displays the the higher higher metamorphic metamorphic grade grade and and deformation deformation common commonto torocks rockssouth southof of the thefault. fault. At At this this location location argillaceous argillaceous units units of of the the McKim McKim Formation Formation contain contain pale pale prismatic prismatic crystals crystals of of staurolite staurolite which whichhave have undergone undergone retrograde retrograde metamorphism metamorphism to to sericite-quartz sericite-quartzaggregates. aggregates. AA few few pseudomorphs pseudomorphs show show the the characteristic characteristic cruciform cruciform twinning twinning of of staurolite. staurolite. The The enhanced enhanced growth growth of of staurolite staurolite crystals crystals in in the the originally originally more more 55 �argillaceous argillaceous upper upper portions portions of of the the beds beds has has resulted resulted in in graded bedding" graded bedding" in in aa few few places. places. "reverse "reverse Return Return to to the the intersection intersection of Highway Highway 17 17 and Highway 108. Proceed Proceed north north along along Highway Highway 108 108 to to the the Town Town of of Elliot Elliot Lake. Lake. ROAD LOG ... DAY 2 Day Day 22 of of the the field field trip trip begins begins in in the City of Elliot Lake at the intersection 108 and and Hillside Hillside Drive DriveNorth. North. (Refer (Refer to to intersection of of Highway Highway 108 Figure Figure 18). 18) . Turn Turn west west onto onto Hillside Hillside Drive Drive North. North. Continue Continue west west on on Hillside Hillside Drive Drive North North for for about about 11 km km to to Spine Spine Road. Road. Turn Turn west west onto onto Spine Spine Road Road 1.9 1.9 km km Spine Spine Road Road at at Lawrence Lawrence Ave Ave (End (Endof of Spine Spine Road). Road). UTM UTM 370525E, 17-5137802N 370525E. 17-5137802N STOP 15: 15: Radioactive Radioactive quartz-pebble quartz-pebble conglomerate conglomerate of of the the Matinenda Matinenda Formation. Formation. The The low low outcrops outcrops on on the the north north side side of of Spine Spine Road Road are are grey, grey, buff buff and dark-grey dark-grey arkose arkose and and radioactive, radioactive, pyritic, pyritic, quartz-pebble quartz-pebble conglomerate conglomerate of of the the Matinenda Matinenda Formation. Formation. Pebble Pebble units units are are about about 20-30 cm thick and dip about 10 degrees to the north. 20-30 cm thick and dip about 10 degrees to the north. Pebbles in Pebbles in this 1-2 cm cm across across and and are are generally generally much much this outcrop outcrop are are about about 1-2 smaller smaller than than the the pebbles pebbles in in the the ore ore zones zones of of the the Elliot Elliot Lake Lake mines. LeCheminant, (1984) (1984) report radioactive mines. Ruzicka Ruzicka and and LeCheminant, report the radioactive conglomerate conglomerate contains contains : "rare-earth-elements-bearing uranothorite (7) large 'rare-earth-elements-bearing uranothorite(?), large zircons, ?), zircons, aa Ti-U-Si-Fe Ti-U-Si-Fephase phase (brannerite (brannerite7), chalcopyrite chalcopyrite and and chromite. chromite. The The distribution distribution of of radioactive radioactive minerals minerals in in the the conglomerate conglomerate displays displays layering thus indicating layering thus indicating aa detrital detrital origin origin of of these these grains" grains " , The The dark-grey dark-grey areas areas in in the the radioactive radioactive beds beds are are due due to to the the presence known in presence of of minor minor amounts amounts radioactive radioactive carbon carbon generally known in 56 �_______ LEGEND For figure 18 POST-HURONIAN MAFIC INTRUSIVE ROCKS Ramsay Lake Formation NIPISSING DIABASE [Li "1 Conglomerate Dabase, gabbm, melagabbm, INTRUSIVE CONTACT ELLIOT LAKE GROUP McKirn Formation HURONIAN SUPEROROUP COBALT GROUP Sttston., argIIIIts,wecks Bar River Formation MatInanda Formation Ouartz arentle p.— pn. p., a. O,bnL..ty'. tJ x-1 Subaricosa, adios., conglomerate, Gordon Lake FormatIon uranhini-beer%ng conglomerate SlIlatone, argilItte, subail<ose DISCONFORMITY Lorraln Formation Thessalon FormatIon (5) Ouarft erenlte, subarkose, eikose, conglomerate, thorium-bearing conglomerate Basalt, andaste, mInor mugeadte-hawallte, rtiyollte, metabasalt, and Intercalated sedImentary rocka Gowganda FormatIon Conglomerate, argllilte, wacke, subarkoes, sittetone DISCONFORMITY? HIATUS HIATUS LMngetone Creek Formation QUIRK LAKE GROUP Mlcose, polymicec conglornerata Serpent Formation UNCONFORMITY Subaricose, conglomerate ARCHEAN Espanola FormatIon (3) LImestone, dolomIte, calcareous alltetone Plutonic granldc rooks, gnelsees, Bruce Formation (3) FeIslo to motto metavolcanlc rooks, metasedimentary rocks Cong?omerata HOUOHLAXEGROUP UOUGH IAKE QROUP Mlssissagl Formation Mls~i~s Fomallon e~l Subalcose, añcoes, $%behem, ahme,conglomerate mngbmemle Peoors PemmFormation Fomatlon(4) (4) flglItits alllstone r Shaft-fornior uranium mine Fault @ Field Field trip tripstop stop so_ w eeO5& sad L•IM'(lflsI --wmm �c4(4c :o'o.go.0 ç ',,".", v a 0 0 0 0 00 00C0 :o:c:00o: 0 d. 00 0 0 2°°° 99090909 ° 0cc' (4\ I, 0 Figure 19. Geology of the Elliot Lake area. 00 00000000'0 000 0000000000000000oo ):o:o:c,o:o:o,c:c:o:o:o:o:o:o:o:oo*o*o* 0,o,c. ,c.oo, .o,o:6:o:c:o, o:o:o:oo:c,o,c:o:oo:o:oo:o oCc0c\0c0o r—tc. ,, 7))*e ;::zz:k fl0 OtQ 09 Lake U - 0 (1.CÔ 0j0 g° sr-- 00000000 ' Quince * ——— 6 — $,* — — —— a 000 2 r!d1:1T :00 000000t a e Lake Hake �the thucoliteT but also referred the Elliot Elliot Lake Lake area area as as "thucolite" referred to to as as aa hydrocarbon hydrocarbon kerogen. kerogen. Ruzicka Ruzicka and and LeCheminant, LeCheminant, (1983) that (1983) note note that several several generations generations of carbon carbon occur in the conglomerates conglomerates of of the the Matinenda generation occurs occurs as Matinenda Formation. Formation. The earliest generation as layers layers concordant with the bedding or a component of the matrix matrix and and appears to appears to have have been been deposited deposited in in areas areas of of quiescent quiescent sedimentation during the last phase phase of an upward fining sedimentation fining sedimentary cycle. Later generations generations are probably probably remobilized remobilized sedimentary phases of phases of the the first first generation generation of of carbon. carbon. The carbonaceous carbonaceous matter matter in in the the Elliot Elliot Lake Lake ores ores is is comparable comparable in in occurrence occurrence and and composition hydrocarbon in the Witswatersrand Witswatersrand gold composition to to similar similar hydrocarbon gold reefs; interestingly LeCheminant(l984) report report reefs; interestingly Ruzicka and LeCheminant(l984) elevated gold 2000 ppb) ppb) in in the the Elliot Elliot Lake Lake elevated gold content content (1000 (1000 -- 2000 carbonaceous matter. carbonaceous matter. The radioactive radioactive carbon carbon at this this site site is is although the gold content is is not reported to be auriferous, although available. available. A drill drill hole hole was was drilled drilled about 30 30 m south south of this this location location by by Rio Rio Algom Mines Mines Limited Limited in in 1955. The logs logs of this this hole hole indicate indicate that that radioactive beds exposed here are about 35 metres above the radioactive above the the basement of Archean granitic granitic rocks. rocks. Diamond Diamond drilling drilling has has basement of Archean indicated that indicated that there there are are no no ore-grade ore-grade units units in in this this area. area. Grab returned up to Grab samples samples collected by G. Bennett in 1982 1982 returned to .80 .80 lbs/ton tJ308 and 0.78 0.78 lbs/Ton lbs/Ton Th02. Th02. AA continuous continuous chip chip sample lbs/ton U308 and returned lbs/ton U308 U308 and and 0.53 0.53 lbs/ton lbs/ton Th02. Th02. returned 0.31 0.31 lbs/ton Return Return to to Highway Highway 108 108 and proceed north on Highway 108 108 to to Milliken Milliken Road Road (about (about 1.5 1.5 km km north north of of Hillside Hillside Drive Drive North). North). Reset odometer odometer at at Milliken Milliken Road. Road. miles 1.0 0.63 miles 1.0 km km -- 0.63 Mississagi Formation, STOP 16: 16: Subarkose Subarkose of the the Mississagi Formation, Rough Hough Lake Lake Group. Group. Grey subarkose Formation displays wellwellsubarkose of the Mississagi Formation developed developed trough trough cross-bedding cross-bedding in bedding units about a metre thick. thick. Paleocurrents Paleocurrents are from the west. The rusty iron-staining iron-staining on pyrite content on the face face of of the outcrops reflects the minor pyrite content beds. The grey grey which commonly commonly is is deposited along the foreset beds. colour presence of apparently apparently colour of these these sandstones, sandstones, and the presence detrital pyrite, pyrite, is held to indicate very very low partial partial pressure of detrital 59 �free free oxygen oxygen of of the the atmosphere atmosphere in in this this time. time 1.4 km km -- 0.9 0 . 9 miles miles 1.4 17: Nipissing Nipissing Diabase/Gabbro, DiabaselGabbro, altered altered Mississagi Mississagi Formation, Formation, STOP 17: STOP Bruce Bruce Formation. Formation. AA sill-like sill-likebody body of of Nipissing Nipissing gabbro/diabase gabbro/diabase is is exposed exposed on on the the east side side of of Highway Highway 108. 108. Rhythmic, Rhythmic, compositional compositional layering layering is is east visible on on the the vertical vertical face face of of the the exposure. exposure. Near Near the the north north end end visible of of the the Nipissing Nipissing sheet sheet the the present present erosion erosion surface surfacedisplays displays evidence evidence of of water water erosion erosion presumably presumably as as aa result result of of melting melting of of adjacent adjacent Pleistocene Pleistocene glacial glacial ice. ice. North North of of gabbro gabbro sill, sill, the the upper upper portion portion of of the the Mississagi Mississagi Formation Formation is is exposed exposed along along the the east side side of of the the highway. highway. The The sandstones sandstones here here have have been been east subjected subjected to to metasomatism, metasomatism, presumably presumably related related to to the the adjacent adjacent Nipissing metasomatic effect Nipissing intrusion. intrusion. The The metasomatic effect is is visible visible as as the the distinctly distinctly pinkish pinkish hue hue of of the the sandstone, sandstone, which which is is probably probably due due to to The dark-green dark-greento to black black chlorite chlorite the development development of of albite. albite. The the deposited deposited along along thin thin fractures fractures may may also also reflect reflect metasomatic metasomatic alteration by by fluids fluids circulated circulated by by the the hot hot diabase. diabase. alteration Continue Continue northward northward on on foot foot for for aa few few tens tens of of metres. metres. Here Here the the Mississagi Mississagi Formation Formation is is overlain overlain by diamictite diamictite of of the the Bruce Bruce Formation Formation at at the the base base of of the the Quirke Quirke Lake Lake Group. Group. The The dispersed dispersed megaclasts megaclasts of of the the Bruce Bruce Formation Formation are are predominantly predominantly grey grey granitic granitic rocks rocks with with smaller smaller mafic mafic clasts clasts of of what what appear appear to to be, be, at at least least in in The abundant matrix of the part, part, Huronian Huronian volcanic volcanic rocks. rocks. The abundant matrix of the conglomerate conglomerate is is dark-grey dark-grey to to black. black. Sand-sized Sand-sized quartz quartz grains grains have have a a glassy, glassy, black black appearance, appearance, aa reflection reflection of of the the chlorite chlorite content content There is no evidence of significant disconformity of the the matrix. matrix. There is no evidence of significant disconformity of at the the base base of of the the Bruce Bruce Formation. Formation. at Proceed Proceed by by vehicle vehicle to to near near the the top top of of the the hill. hill. 1.8 km km -- 1.4 1.4 miles. miles. 1.8 STOP 18: 18: STOP Espanola Espanola Formation Formation and and Nipissing Nipissing diabase diabase sills. sills. The The base base of of the the Espanola Espanola Formation Formation is is aa green green laminated laminated unit unit about overlain by laminated about aa metre metre or or so so thick. This is overlain laminated silty silty limestones limestones of of the the Bruce Bruce Limestone Limestone member, member, Espanola Espanola Formation. Formation. At At this this location location the the proximity proximity of of Nipissing Nipissing intrusions intrusions has has led led to to 60 �the development skarn with grossularite garnet, idocrase development of a skarn garnet, idocrase (vesuvianite) (vesuvianite), diopside, diopside, and wollastonite. The The latter latter can can be be and wollastonite. found, found, just just below below the the north-dipping north-dipping diabase diabase sill sill near near the the north north end of the the exposure. exposure. Wollastonite Wollastonite occurs occurs as as sub-parallel sub-parallel groups groups of of pale-grey pale-grey to to white white prismatic prismatic crystals crystals about about one one mm mm wide. wide. The The pink (KFCa4[Si8020]8H20) (KFCa4[Si802,,l8H20) an an pink coating coatingon onjoint jointsurface surfaceisisapophyllite apophyllite uncommon mineral, mineral, sometimes sometimes found found in in amygdules amygdules in in basalts, basalts, but but is is uncommon also associated with cab-silicates. Young(l99l) states that the also with calc-silicates. Young(l991) states that the small small scale scale thrust thrust faults faults and and folds folds displayed displayed in in the the limestone limestone on on the the west side side of of the the highway highway are are probably the result of slumping slumping during during early early tectonic tectonic activity. activity. , ferruginous dolostone-bearing dolostone-bearing member of the the Espanola Espanola The upper, upper, ferruginous The Formation present at Formation and and the the overlying overlying Serpent Serpent Formation Formation are are not present at They have have probably probably been been removed removed during during a a period period of of this this location. location. They pre-Gowganda pre-Gowganda erosion. erosion. The The basal basal units units of of the the Gowganda Gowganda Formation Formation are are visible visible on on the the west west side side of of the the highway. highway. 2.0-2.5 1.3-1.6 miles miles Gowganda Gowganda Formation Formation diamictite. diamictite. km -- 1.3-1.6 2.0-2.5km Massive Massive diamictite diamictite of of the the Gowganda Gowganda Formation. Formation. Megaclasts Megaclasts of of pink pink granite, granite, grey grey granite granite and and granitic granitic gneiss gneiss and and mafic rocks rocks are are widely distributed in a dark green matrix. widely distributed in a dark green matrix. Most Most geologists geologists now now consider consider at at least least some some of of the the diamictites diamictites in in the the Gowganda Gowganda Formation Formation to to be be tillites, tillites, although although a a debris-flow debris-flow origin, origin, either either glaciogenic glaciogenic or or as as sub-marine sub-marinedebris debris flows flows is is also also reasonable. reasonable. Roscoe, Roscoe,.(1969) (1969) places of free free oxygen oxygen in in the the places the appearance appearance of atmosphere ("oxyatmoversion") ("oxyatmoversion")as as coinciding coinciding with the the appearance appearance atmosphere of of the the reddish reddish hue hue of of hematite hematite just just above above the the base base of of the the Gowganda Formation. Gowganda Formation. 3.8 3.8 km. km. -- STOP STOP 19: 19: 2.4 2.4 miles. miles Stratified Stratified Gowganda Gowganda Formation. Formation. Park Park just just south south of of the the rock-cut rock-cut on on east east side side of of the the highway. highway. This This is is an an impressive impressive exposure exposure through through aa stratified stratified sequence sequence of of diamictites diamictites and and sandstones sandstones of of the the Gowganda Gowganda Formation. Formation. The The base base of of the the sequence sequence at at the the extreme extreme southern southern end end of of the the exposure exposure on on the the west side of Highway 108 consists of massive diamictite overlain west side of Highway 108 consists of diamictite overlain 61 �by a thin thin unit of of laminated laminated mudstone mudstone siltstone siltstone with with drop drop stones. stones. About 11 m of stratified Gowganda overlies the siltstone. m stratified Gowganda overlies the siltstone. Diamictite, Diamictite, sandstone, sandstone, pebbly sandstone and clast clast supported polymictic conglomerate conglomerate are are present. present. Some Some conglomerate conglomerate units units polymictic display normal normal and and reverse reverse grading grading suggestive suggestive of of debris debris flows. flows. display The The rocks rocks displayed displayed here here may may be be interpreted interpreted to to represent represent aa depositional environment environment proximal proximal to to aa retreating retreating glacial glacial margin. margin. depositional Note: the predominance of red and pink granitic clasts, Note: clasts, is is in in marked contrast contrast to to the the pale grey grey clasts clasts of of the the Bruce Bruce and and Livingstone Creek Livingstone Creek Formations Formations seen seen earlier. earlier. 4.7 km. 2.9 miles. Pink sandstones 4.7 km. -- 2.9 sandstones and diamictite diamictite of of the the Gowganda Formation. Gowganda Formation. 6.7 km 4.2 miles. Diamictite 6.7 km -- 4.2 Diamictite with with large large boulder, boulder, Gowganda Gowganda Formation. Formation. Pink and red arkose arkose with pebbly and bouldery bouldery mudstone mudstone Relatively (diamictite). Relatively massive bed of pink arkose arkose with with (diamictite).. scattered pebbles and a boulder of red granite on on the the west west side side of the the highway. highway. The The continuity continuity of of strata strata is is broken broken by by faulting, faulting, channelling and deformed arkose bodies in grey pebble siltstone siltstone (near south end (near south end of of rock-cut) rock-cut). 8.2 8.2 km. km. 11.4 - 5.1 5.1 miles Stanrock Stanrock Road Road Denison Mine east. Denison Mine Road Road -- Turn Turn east. Reset odometre odometre to to 000 km km 3.6 km. 3.6 km. Serpent Formation STOP Gowganda Formation Formation -- Serpent Formation disconformity disconformity STOP 20: Gowganda 376l02E, 5150299N 376102E, 1717partially removed The Serpent Formation Formation has been partially removed during during aa period period pre-Gowganda erosion in the southwestern of pre-Gowganda southwestern part of of the the Quirke Quirke Lake Syncline and the Blind River Sault Ste. Marie area. Lake Syncline and the Blind River Sault Ste. Marie area. At this this location, south side of the road, road, well-sorted well-sorted sandstone location, on the south sandstone of of Formation is overlain by polymictic conglomerate the Serpent Formation conglomerate of of contact is the the Gowganda Gowganda Formation. Formation. The contact is sharp sharp but but irregular. irregular. disconformity at this Evidence of a sub-Gowganda sub-Gowganda disconformity this location location is is given by the given the presence presence of pebble and and cobbles cobbles of the the Serpent Serpent 62 �Formation Formation near near the the base base of of the the Gowganda Gowganda Formation. Formation. Return Odometre, turn Return to to Highway Highway 108 108 Reset Odometre, turn north north 000 000 0.5 km km -- 0.5 0.5 miles. miles. Disseminated Disseminated carbonate carbonate in in sandstone sandstone of the the Serpent Formation Serpent Formation on on east east side side of of Highway Highway 108. 108. 0.8 miles. Outcrop Limestone Member 1.4 km km -- 0.8 Outcrop of of Espanola Espanola Limestone Member of of the the Espanola Formation Formation with ripple is exposed on on the east side side Espanola ripple marks is of Highway Highway 108. 108. The carbonate carbonate units units of of the the Espanola Espanola Limestone Limestone are actually actually ferruginous ferruginous dolomite dolomite containing containing approximately approximately 3% 3% total total iron. iron. 1.6 1.6 km km -- 1.0 1.0 miles. miles. Road to to Quirke Quirke Lake Lake and and former former Panel Panel Mine. Mine. Turn onto Turn onto Panel Panel Mine Mine road. road. Reset Reset odometre odometre to to 000 000 1.3 km miles 1.3 km -- 0.8 0.8 miles STOP 21: STOP 21: Espanola Espanola Member Member of of the the Espanola Espanola Formation. Formation. Rock-cut Rock-cut in in ferruginous ferruginous dolomite dolomite and and siltstone siltstone of of the the Espanola Espanola Limestone The Espanola Limestone Member Member of of the the Espanola Espanola Formation. Formation. The Espanola Limestone Limestone Member Member is is the the uppermost uppermost member member of of the the thee thee members members of of the the Espanola Espanola Formation Formation recognized recognized in in the the Elliot Elliot Lake Lake area. area. It It is is characterized by intercalated characterized intercalated siltstone siltstone and and reddish-weathering, reddish-weathering, ferruginous ferruginous dolostone dolostone beds containing containing 3-4% 3-4% FeO. FeO. Intraformational Intraformational breccia, breccia, ripple ripple marks, marks, small small scale scale cross-bedding, cross-bedding,and and various various present. Near soft sediment features features are present. Near the the east east end end of of the the outcrop a grey, complex clastic dike crosses the stratification stratification outcrop grey, complex at a a high high angle. angle. 4.1 km 2.5 miles miles. 4.1 km -- 2.5 STOP STOP 22: 22: Ramsay Lake Formation Formation overlain overlain by by Pecors Pecors Formation. Formation. Diamictites of the Ramsay Lake Formation contain contain cobbles of grey Diamictites granitic rocks, granitic rocks, mafic clasts clasts of of Huronian Huronian volcanic volcanic rocks rocks and and Archean dark-grey to Archean felsic felsic volcanic clasts clasts in in an an abundant dark-grey to black sandy matrix. The Ramsay Lake Formation is overlain by dark Lake Formation is overlain by dark sandy matrix. laminated mudstone of laminated siltstone siltstone and and mudstone of the the Pecors Pecors Formation. Formation. The The 63 �latter latter contains contains aa few few drop-stones. drop-stones. Note: Note: the the Matinenda Matinenda Formation Group, expected Formation of the Elliot Lake Group, expected between the the basement basement and Ramsay Lake Lake Formation, Formation, is is truncated truncated by by the the Ramsay Ramsay Lake Lake and the the Ramsay Formation Formation in in this this area. area. The The Matinenda Matinenda Formation Formation does does occur occur in in the the mine mine workings workings down-dip down-dip from from this this location. location. Continue Continue east east to to the the end end of of the the Panel Panel Mine Mine road. road. This This is is the the rehabilitated rehabilitated area area of of the the former former Panel Panel Mine. Mine. There There is is little little evidence mill complex complex that was on evidence of of the the uranium uranium mine mine and. and mill on this this site site until until 1993. 1993. Return Return to to Highway Highway 108. 108. Continue Continue north north on on Highway Highway 108. 108 Tailings Tailings dam dam of of the the Quirke Quirke Mine Mine is is visible visible west west of of the the Highway. Highway. Highway Highway 108 108 ends ends and and Highway Highway 639 639 begins. begins. Reset Reset odometre. odometre. 0.8 0.8 km km -- 0.5 0.5 miles. miles. Diamictite Diamictite of of the the Bruce Bruce Formation Formation is is exposed exposed west west of of the the Highway. Highway. 1.5 0 . 9 miles. miles. Outcrops Outcrops of of Mississagi Mississagi Formation Formation are are exposed exposed 1.5 km km -- 0.9 along along Highway Highway 639. 6 3 9 . Note Note the the yellowish yellowish colour colour characteristic characteristic of of the the Mississagi Mississagi Formation Formation where it lies directly on on the the Archean Archean granitic granitic basement basement (Robertson, (Robertson,1968) 1968) . 2.2 2.2 km km -- 1.4 1.4 miles miles STOP STOP 23: 23: Huronian Huronian volcanic volcanic rocks rocks of of the the Thessalon Thessalon Formation Formation (Dollyberry (DollyberryVolcanics) Volcanics) . Road Road leading leading west west from from Highway Highway 639 639 leads leads to to the the Quirke Quirke Mine Mine tailings tailings dams. dams. Park Park near the the gate gate and and walk a a short short distance distance along along the road to a snowmobile bridge over the stream from the the road to a snowmobile bridge over the stream from the tailings tailings dam. dam. Follow Follow the the trail trail from from the the bridge bridge to to outcrops outcrops of of mafic (Dollyberry mafic volcanics volcanics of of the the Thessalon Thessalon Formation Formation (Dollyberry Volcanics)near Vo1canics)near the the crest crest of of aa low low hill. Chemical Chemical analyses analyses of of the the Huronian Huronian volcanics volcanics in in this this area area indicate indicate the the volcanic volcanic rocks rocks include include transitional transitional alkalic alkalic types, types, hawaiite hawaiite and and mugearite. mugearite. The The unconformity unconformity between between the the Archean granitic granitic basement basement rocks rocks and and Huronian Huronian volcanic volcanic is is visible visible in in this this area. area. There There is is no no visible visible paleosol paleosol at at this this location. location. Near Near the the trail trail aa thin, thin, quartz-pebble quartz-pebble 64 �conglomerate unit of angular conglomerate angular to to subrounded, subrounded, quartz-clasts, quartz-clasts, overlies overlies the the granitic granitic rocks rocks at at the the base base of of the the volcanic volcanic unit. unit. Walking eastward from-this from this point scattered, scattered, isolated, isolated, pebblepebble- and and cobble-sized cobble-sized clasts of quartz can be found found along along the the unconformity. A similar unconformity. similar quartz-pebble quartz-pebble conglomerate conglomerate occurs occurs at at the the base where they Archean base of of the the Huronian volcanic rocks rocks where they overlie overlie Archean mafic mafic volcanic volcanic rocks rocks in the haulage drift of the Stanleigh Stanleigh Mine on on the the south south limb limb of the Quirke Lake Syncline. Syncline. A few few kilometres kilometres west of this this location, location, occurrences of this this conglomerate conglomerate unit unit contain clasts, and are contain more rounded quartz clasts, are commonly commonly overlain overlain by by a thin thin arkosic arkosic unit. unit. Quartz-pebble Quartz-pebble conglomerate, conglomerate, which which locally locally contains significant pyrite pyrite as well as uranium, uranium, occurs occurs sporadically base of the Huronian Huronian volcanic sequence sporadically at the base sequence of the the Quirke Syncline and and westward westward to to the the Sault Sault Ste. Ste. Marie Marie area. area. Quirke Lake Lake Syncline The The conglomerate conglomerate at this location is is correlated correlated with with the the radioactive, 11. radioactive, quartz-pebble quartz-pebble conglomerate conglomerate of of Stop Stop 11. Return to Return to Vehicle and and continue continue north north on on Highway Highway 639. 639. Archean Archean granitic granitic rocks rocks cut cut by by diabase diabase outcrops outcrops along along the the highway. highway. 8.8 km 8.8 km 5.5 miles 5.5 miles STOP 24: STOP 24: Archean pillowed (Refer to Figure pillowed metavolcanics. metavolcanics. (Refer Figure 16). 16). Archean well-developed pillow Archean mafic metavolcanics displaying displaying well-developed pillow structures are exposed on on a north north sloping outcrop outcrop on the east structures side deformed, but facing side of of highway. highway. Pillows Pillows are deformed, facing directions directions can can easily easily be determined. Small amygdules are concentrated near the upper surface upper surface of of many many pillows. pillows. Lake fault occupies a valley near this 9.4 5.8 miles. Flack Lake 9.4 km km -- 5.8 point. point. 9.9 km 6.1 miles. miles. Outcrops Outcrops of of 9.9 km -- 6.1 the the Bar Bar River River Formation. Formation. 10.5 miles. 6.5 miles. 10.5 km km -- 6.5 hematite-stained sandstone hematite-stained sandstone of Entrance Entrance to to Mississagi Mississagi Provincial Provincial Park. Park. 10.8 10.8 km km -- 6.7 6.7 miles. Pale grey sandstone sandstone of of the the Formation with Formation with herringbone herringbone cross cross bedding. bedding. 11.4 11.4 km km -- 7.2 7 . 2 miles. Christman Christman Lake Lake 65 Bar River River �STOP STOP 25: 25: Bar Bar River River Formation Formation Sandstones Sandstones of of the the Bar Bar River River Formation Formation display display ripple ripple marks, marks, mud cracks cracks and and sinuous sinuous structures structures which which have have been been described described as as possible possible worm worm casts. casts. Comparison Comparison with with desiccation desiccation structures structures in in the the Gordon Gordon Lake Lake Formation Formationled ledYoung, Young, (1969) (1969) to to suggest suggest that that these these features features are are the the result result of of the the transportation transportation of of consolidated consolidated desication fracture fillings. desication fracture fillings. 15.3 15.3 km km -- 9.5 9.5 miles. miles. STOP STOP 26: 26: Gordon Gordon Lake Lake Formation Formation Laminated, Laminated, maroon maroon buff buff siltstone siltstone and and chert chert with with reduction reduction spots spots in in the the upper upper part part of of the the Gordon Gordon Lake Lake Formation. Formation. This This is is another another red-bed occurrence within the Cobalt Group. red-bed occurrence within the Cobalt Group. 16.6 10.3 miles miles 16.6 km km -- 10.3 StoD Stop 27: 27: Gordon Gordon Lake Lake Formation. Formation. Siltstones Siltstones and and sandstones sandstones of of the the Gordon Gordon Lake Lake Formation Formation display display ripple ripple marks, marks, desiccation desiccation cracks, cracks, cross cross bedding bedding and and aa late late cleavage. cleavage. Note: Note: the the presence presence of of pyrite pyrite in in contrast contrast to to the the generally generally hematitic hematitic nature nature of of the the Gordon Gordon Lake Lake Formation Formation near near the the top of the formation. top of the formation. 19.7 12.2 miles. miles. View View of of the the Boland Boland River River valley. valley. 19.7 km km -- 12.2 21.0 21.0 km km -- 13.0 13.0 miles miles STOP STOP 28: 28: Lorrain LorrainFormation Formation White White to to pale pale pink pink quartz quartz arenite arenite of of the the upper upper portion portion of of the the Lorrain Lorrain Formation Formation is is exposed exposed on on the the east east side side of of the the highway. highway. 22.8 22.8 17.8 17.8 miles. miles. Junction Junction with with Little Little White White River River road road (Highway (Highway 546.) 546.) End End of of field fieldtrip. trip. 66 �REFERENCES REFERENCES Bennett, Bennett, G. G. 1978. 1978. Huronian Huronian volcanism, volcanism, districts districts of of Algoma Algoma and and Sudhury; in Summary Summary of of Field Field Work, Work, 1978; 1978; Ontario Ontario Geological Geological Sudbury; in Survey, Survey, Miscellaneous MiscellaneousPaper Paper82, 82,p.105-111. p.105-111. Bennett, Bennett, G. G. 1982. 1982. 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Long, D.G.F. 1976. 1976. stratigraphy Stratigraphyand andsedimentology sedimentologyofofthe the1-luronian Huronian (Lower Aphebian) Aphebian) Mississagi Mississagi and Serpent Serpent Formations; Formations; unpublished unpublished (Lower PhD thesis, thesis, University University of of Western Western Ontario, Ontario, London, London, Ontario, Ontario, 291 291 p. P. Long, Long, D.G.F. D.G.F. 1978. 1978. Depositional Depositional environments environments of of aa thick thick Proterozoic Proterozoic sandstone, sandstone, the the (Huronian) (Huronian) Mississagi Mississagi Formation Formation of of Ontario, Canada; v.15, Ontario, Canada; Canadian Canadian Journal Journal of of Earth Earth Sciences, Sciences, v.15, p.190-2O6. p.190-206. McConnell, R.G. McConnell, R.G. 1927. 1927. Sault Sault Ste. Ste. Marie Marie area, area, District District of of Algoma; Algoma; Ontario Ontario Department Department of of Mines, Mines, v.35, v.35, pt.2, pt.2, p.1-52. p.1-52. McDowell, petrology of of the Mississagi McDowell, J.P. J.P. 1957. 1957. The The sedimentary petrology quartzite in quartzite in the the Blind Blind River River area; area; Ontario Ontario Department Department of of Mines, Mines, Geological Circular 6, 3lp. Geological Circular 6, 31p. Discussion following Meyer, W. Meyer, W. 1981. 1981. Discussion following papers papers by by Drs. Drs. Robertson, Robertson, Ruzicka, Ruzicka, Roscoe Roscoe and and Little; Little; in in Genesis Genesis of UraniumUranium- and and GoldGoldBearing United States States Geological Geological Bearing Quartz-Pebble Quartz-Pebble Conglomerates; United Survey, Professional Paper 1161-A-RB, p.XlO-X14. Survey, Professional Paper 1161-A-BB,p.Xl0-X14. Meyer, W. gold; an an investigation investigation of of quartzquartzW. 1983. 1983. Lower Lower1-luronian Huronian gold; Meyer, conglomerates between Sault Ste. Ste. Marie Marie and and Elliot Elliot Lake; in clast conglomerates in Summary of Summary of Field Field Work, Work, 1983; 1983; Ontario Ontario Geological Geological Survey, Survey, Miscellaneous Paper 116, p.259-262. Miscellaneous Paper 116, p.259-262. Miall, A.D. 1985. Miall, 1985. Sedimentology Sedimentology of of an an early early Proterozoic Proterozoic continential continential margin margin under under glacial glacial influence: influence: the the Gowganda Gowganda Formation (Huronian), Formation (Huronian), Elliot Elliot Lake Lake area, area, Ontario, Ontario, Canada; Canada; Sedimentology, v.32, v.32, no.6,p.763-788. no.6,p.763-788. Sedimentology, Palonen, P.A. 1973. of the the Mississagi Nississagi Formation Formation Palonen, 1973. Paleogeography of lower Huronian cyclicity; cyclicity; in in Huronian Huronian Stratigraphy Stratigraphy and and lower Sedimentation, Geological Geological Association Association of of Canada, Canada, Special Special Paper Sedimentation, 12, p.157-168. 12, p.157-168. Parvialnen, E.A.U. 1973. sedimentology of of the the Huronian Huronian Ramsay Ramsay 1973. The sedimentoloqy Parviainen, Lake and of Lake Lake Huron; Huron; unpublished Lake and Bruce Bruce formations, formations, north shore of 72 �PhD thesis, thesis, University university of of Western Western Ontario, Ontario, London, PhD London, Ontario. Ontario. Peck, Peck, D.C., D.C., James, James, R.S., R.S.,and and Chubb, Chubb,P.T. P.T. , Previc, Previc, S.A. S.A. and and Keays, Keays, R.R. R.R. 1995. 1995. Geology, Geology, metallogeny metallogeny and and petrogenesis petrogenesis of of the the East East Bull Bull Lake Lake Intrusion, Intrusion, Ontario; Ontario; Ontario Ontario Geological Geological Survey, Survey, Open File File Report Report 5923, 5923, ll7p. 117p. Open , Pettijohn, in Pettijohn, F.J. F.J. 1970. 1970. The The Canadian Canadian Shield: Shield: a a status status report; report; in Symposium Symposium on on Basins Basins and and Geosynclines Geosynclines of of the the Canadian Canadian Shield, Shield, Geological Geological Survey Survey of of Canada, Canada, Paper Paper 70-40, 70-40,p.329-355. p.329-355. Pienaar, petrography and Pienaar, P.J. P.J. 1963. 1963. Stratigraphy, Stratigraphy,.petrography and genesis genesis of of the the Elliot Elliot Group, Group, Blind Blind River, River, Ontario, Ontario, including including the the uraniferous uraniferous conglomerates; conglomerates; Geological Geological Survey Survey of of Canada, Canada, Bulletin Bulletin 83, 83, 140p. 140p. Prasad, altered zones Prasad, N. N. and and Roscoe, Roscoe, S.M. 1991. 1991. profiles Profiles of altered zones at ca 2.45 2.45 Ga Ga unconformaties unconformaties beneath beneath iluronian Huronian strata, strata, Elliot Elliot Lake Lake Ontatio: Ontatio: evidence evidence for for early early Aphebian Aphebian weathering weathering under under anoxic anoxic conditions; in Current Current Research Research Part Part C, C, Geological Geological Survey Survey of of conditions; in Canada Canada paper paper 9l-lC, 91-lC,p. p. 43-54. 43-54. Prasad, Prasad, N-, N., and and Roscoe, Roscoe, S. S. M. M. 1996. 1996. Evidence for for anoxic anoxic to to oxic oxic atmospheric atmospheric change change during during 2.45-2.22 2.45-2.22Ga Ga from from lower lower and and upper upper subsubHuronian paleosols, Canada; Catena 27, Huronian paleosols, Canada; Catena 27, p. p. 105-121. 105-121. Pretorius, Pretorius, D.A. D.A. 1981. 1981. Gold Gold and and uranium uranium in in quartz-pebble quartz-pebble conglomerates; Economic conglomerates; Economic Geology, Geology, 75th 75th Anniversary Anniversary Volume, Volume, p.117p.117138. 138. R.H., R.H., Nesbit, Nesbit, H.W. H.W. and and Donaldson, Donaldson, J.A. J.A. 1990. 1990. Formation Formation and comparison with a and diagenesis diagenesis of sub-Huronian sub-Huronian saprolith: saprolith: comparison modern modern weathering weathering profile; profile; Journal Journal of of Geology, Geology, 98, 98, p. p. 801-822. 801-822. Rainbird, Rainbird, Rice, Rice, R.J. R.J. 1991. 1991. Regional Regional sedimentology sedimentology and and paleoplacer paleoplacer gold gold potential Supergroup, in potential of of the the Lorrain Lorrain Formation, Formation, Huronian Huronian Supergroup, in the the Cobalt Cobalt plain; plain; Ontario Ontario Geological Geological Survey, Survey, Open Open File File Report Report 5761. 5761. Riller, affecting the Riller, U.P.l996. U.P.1996. Tectonometamorphic Tectonometamorphic episodes affecting the southern Sudbury Basin.and Basin.and their significance significance for footwall of the Sudbury for southern footwall the the origin origin of of the the Sudhury Sudbury Igneous Igneous Complex, Complex, Central Central Ontario, Ontario, Canada; Canada; unpublished unpublished Ph.D. Ph.D. thesis, thesis, University University of of Toronto, Toronto, 135 135 p. p. Robertson, Ontario Robertson, J.A. J.A. 1961. 1961. Geology Geology of townships townships 143 and 144; 144; Ontario 73 �Department Department of of Mines, Mines, Geological Geological Report Report 4, 4, EGp. 66p. Robertson, Robertson,J.A. J.A.1962. 1962. Geology Geoloqy of of Townships Townships 137 137 and and 138; 138; Ontario Ontario Department 94p. :. Department of of Mines, Mines, Geological Geological Report Report 10, 10,94p. Robertson, Robertson, J.A. J.A. 1968. 1968. Geology Geoloqy of of Township Township 149 149 and and Township Township 150, 150, District District of of Algoma; Algoma; Ontario Ontario Department Department of of Nines, Mines, Geological Geological Report Report 57, 57, l62p. 162p. Robertson, Robertson, J.A. J.A. 1970. 1970. Geology Geology of of the the Spragge Spraqge area, area, District District of of Algoma; Algoma; Ontario Ontario Department Department of of Mines, Mines, Geological Geological Report Report Number Number 76, 76, lO9p. 109p. Robertson, Robertson, J.A. J.A. 1976. 1976. The The Blind Blind River River uranium uranium deposits; deposits;the the ores ores and Miscellaneous Paper and their their setting, setting, Ontario Ontario Division Division of of Mines, Mines, Miscellaneous Paper 65, 65, 45p. 45p. Robertson, Robertson, JA., J A ,Frarey, Frarey,M.J. M.J.and andCard, Card,K.D. K.D. 196gb. 1969b.The TheFederalFederalProvincial Provincial Committee Committee on on Huronian Huronian Stratigraphy: Stratigraphy: Progress Progress Report; Report; Canadian v.6,p.335-336. p.335-336. Canadian Journal Journal of of Earth Earth Sciences, Sciences,v.6, Roscoe, Roscoe, S.M. S.M. 1969. 1969. Huronian Huronian rocks rocks and and uraniferous uraniferous conglomerates; conglomerates; Geological Survey of Canada, Paper 68-40, 2O5p. Geological Survey of Canada, Paper 68-40, 205p. Roscoe, Roscoe,S.M. S.M.1981. 1981. Temporal Temporal and and other other factors factors affecting affecting deposition in Genesis Genesis of of UraniumUraniumdeposition of of uraniferous uraniferous conglomerates; conglomerates;in and and Gold-Bearing Gold-BearingPrecambrian Precambrian Quartz-Pebble Quartz-Pebble Conglomerates; Conglomerates; United United States States Geological Geological Survey, Survey,Professional Professional Paper Paper 116l-A-BB, 1161-A-BB,p.W1-W7. p.Wl-W7. Roscoe, Roscoe, S.M. S.M. and and Card, Card, K.D., K.D., 1992. 1992. Early Early Proterozoic Proterozoic tectonics tectonics and and metallogeny metallogeny of of the the Lake Lake Huron Huron region region of of the the Canadian CanadianShield; Shield; Precambrian V. 58, 58, 9. 9. 99-119. 99-119. PrecambrianResearch, Research,V. Ruzicka, Ruzicka, V. V. and and LeCheminant, LeCheminant, G.M. G.M. 1984. 1984. Uranium Uranium deposit deposit research research 1983; 1983; in in Geological GeologicalSurvey Surveyof of Canada Canadapaper paper 84-lA, 84-1A,p. p. 39-44. 39-44. Shanks, Shanks,W.S. W.S. and and Schwerdtner, Schwerdtner, W.M. W.M. 1991. 1991. Structural Structuralanalysis analysisof of the central and southwestern Sudbury Structure, Southern the central and southwestern Sudbury Structure, Southern Province, Province,Canadian Canadian Shield; Shield; Canadian Canadian Journal Journal of of Earth Earth Sciences, Sciences, vol. V O ~ 28, .28,p. p.411-430. 411-430. Sims. Sims. P.K., P.K., Card, Card,K.D. K.D. and and Lumbers, Lumbers, S.B. S.B. 1981. 1981. Evolution Evolution of of early early Proterozoic in Proterozoic Proterozoic Proterozoic basins basins of of the the Great Great Lakes Lakes Region; Region; in 74 �Basins of of Canada, Canada, Geological Geological Survey Survey of of Canada, Canada, paper paper 81-10, 81-10,p. p. Basins 379-397. 379-397. Sutton, Sutton, S.J. S.J. and and Maynard, Maynard, J.B. J.B. 1992. 1992. Multiple Multiple alteration alteration events events in sub-Huronianregolith regolith at at Lauzon Lauzon Bay, Bay, in the the history history of of aa sub-Huronian Ontario, Canada; Canada; Canadian Canadian Journal Journal of of Earth Earth Sciences, Sciences, vol. vol. 29, 29, p. p. Ontario, 432-445. 432-445. Sutton, Sutton, S.J. S.J. and and Maynard, Maynard, J.B. J.B. 1993. 1993. Sediment Sediment and and basalt basalt hosted hosted regoliths regoliths in in the the Huronian Huronian supergroup: supergroup: role role of of parent parent lithology lithology in in middle middle Precambrian Precambrian weathering weathering profiles; profiles; Canadian Canadian Journal Journal of of Earth Earth Sciences, Sciences, vol. vol. 30, 30,p. p. 60-76. 60-76. Theis, Theis, N.J. N.J. 1979. 1979. Uranium-bearing Uranium-bearing and and associated associated minerals minerals and and their their geochemical geochemical and and sedimentological sedimentological context, context, Elliot Elliot Lake, Lake, Ontario; Ontario; Geological Geological Survey Survey of of Canada, Canada, Bulletin Bulletin 304, 304, 50p. 50p. Tomlinson, Tomlinson, K.Y. K.Y. The The geochemistry geochemistry and and tectonic tectonic setting setting of of early early Precambrian Precambrian greenstone greenstone belts, belts, Northern Northern Ontario, Ontario, Canada; Canada; unpublished Ph.D. Thesis, Thesis, University University of of Portsmouth, Portsmouth,278p. 278p. unpublished Ph.D. Williamson, Williamson, M. M. and and Keen, Keen, C.E. C.E. 1995. 1995. How How active active are are passive passive margins? Modern analogues of magmatism in rifts; the margins? Modern analogues of in rifts; the Canadian Canadian vol. 33, 33, p. p. 943-944. 943-944. Mineralogist, vol. Mineralogist, Wright, D.J. and and Rust, Rust, P.R. B.R. 1985. 1985. Preliminary Preliminary report report on on the the Wright, D.J. stratigraphy stratigraphy and and sedimentology sedimentology of the Bar River Formation; Formation; in in Geoscience Research Grant Program, Summary of Research 1994-1995, Geoscience Research Grant Program, Summary of Research 1994-1995, Ontario Ontario Geological Geological Survey, Survey, Miscellaneous Miscellaneous Paper, Paper, 127, 127, p. p. 119-123. 119-123. Young, glaciation in Young, G.M. G.M. An An extensive extensive early early Proterozoic Proterozoic glaciation in North North America?; America?; Palaeogeography, Palaeogeoqraphy,Palaeoclimatology, Palaeoclimatology, Palaeoecology, Palaeoecology,vo. vo p. 85-101. 85-101. 7, p. 7, Young, Young, G.M. G.M. 1982. 1982. Field Field excursion excursion guide guide book; book; excursion excursion 13B: 13B: Depositional environments and tectonic setting of the early Depositional environments and tectonic setting the early Proterozoic International Association Association of Proterozoic Huronian Huronian Supergrciup; Supergroup; International of Sedimentologists, Eleventh International Congress on Sedimentologists, Eleventh International Congress Sedimentology, Sedimentology, McMaster McMaster University, University, Hamilton, Hamilton, Ontario, Ontario, Canada. Canada. Young, G.M. 1983. 1983. Tectono-sedimentary Tectono-sedimentary history history of early early Young, G.M. Proterozoic northern Great Lakes; Lakes; in Early Proterozoic rocks rocks of the the northern 75 �Proterozoic Geology of the Great Great Lakes Lakes Region, Region, Geological Geological Society Proterozoic of America America Memoir, Memoir, v.160, v.160, p.15-32. p.15-32. Young, I-J.W. 1985. G.M. and andNesbitt, Nesbitt, H.W. 1985. Young, G.M. The The Gowganda Gowganda Formation Formation in in the southern southern part part of of the the Huronian Huronian outcrop outcrop belt, belt, Ontario, Ontario, Canada; Canada; Precambrian Precambrian Research, Research, v.29, v.29, p.265-3O1. p.265-301. Zolnai, A.I., A.I., Price, 11. 1984. Regional 1984. Regional Zolnai, Price, R.A. R.A. and and Helmstaedt, Helmstaedt, H. cross-section of cross-section of the the Southern Southern Province Province adjacent adjacent to to Lake Lake Huron, Huron, Ontario: implications Ontario: implications for for the the tectonic tectonic significance significance of of the the Murray fault fault zone; zone; Canadian Canadian Journal Journal of of Earth Earth Sciences, Sciences, v.21, v.21, p.447-456. p.447-456. 76 � https://digitalcollections.lakeheadu.ca/files/original/2d6c621da28d3b6ef1ab078bea8bc378.pdf 03bc1a08726e8b70887f134fc605f576 PDF Text Text NEW INFORMATION ON THE THE GRENVILLE GRENVILLE FRONT FRONT NEAR NEAR SUDBURY SUDBURY BY A. 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INSTITUTE INSTITUTE ON ON LAKE LAKE SUPERIOR SUPERIOR GEOLOGY GEOLOGY 43rd MEETING, MAY 66- 11, 1997 43rd ANNUAL MEETING, 11,1997 SUDBURY, ONTARIO ONTARIO - Field Trip Part 33 TripGuidebook, Guidebook, Volume Volume 43, Part �Frontispiece: Line Linedrawing drawingfrom frompart partof ofGLIMPCE GLIMPCE Seismic Seismic reflection reflectionLine LineJ, J, W W to to EEline line crossing crossing the the Grenville GrenvilleFront Frontin inGeorgian GeorgianBay Bay(from (fromGreen Greenet etat, al, 1988, Geology, v. 16, p. 790, Figure 2) 1988, Geology, 16, p. 790, Figure 2) �NEW DEVELOPMENTS DEVELOPMENTS IN IN NEW GRENVILLE GRENVILLE FRONT GEOLOGY, GEOLOGY, SUDBURY AREA, ONTARIO SUDBURY AREA, ONTARIO A. Davidson Davidson Geological Survey of Canada, Canada, 601 601 Booth Street, Street, Ottawa, Ontario Ontario K1A KIA0E8 OE8 Geological Survey of of Canada Canada contribution contribution no. no.1997031 1997031 �NEW DEVELOPMENTS DEVELOPMENTS IN IN NEW GRENVILLE GRENVILLE FRONT GEOLOGY, GEOLOGY, SUDBURY SUDBURY AREA, AREA, ONTARIO ONTARIO A. A. Davidson Davidson Geological Geological Survey Survey of of Canada, Canada,601 601Booth Booth Street, Street, Ottawa, KIA0E8 OE8 Ottawa,Ontario OntarioK1A Geological Geological Survey Survey of of Canada Canadacontribution contributionno. no.1997031 1997031 �. ... IllI l l LIST LISTOF OFCONTENTS CONTENTS Southern Province . Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Introduction 11 Southern Province . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22 GrenvilleProvince Province . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 55 Grenville TheGrenville GrenvilleFront Front . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 66 The Sudbury dyke swarm . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 99 Sudbury dyke swarm Fieldtrip tripsummary summary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1313 Field Roadlog logand andstop stopdescriptions descriptions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .1515 Road Mississagi sandstone, Stop 1 Mississagi sandstone.Nipissing Nipissinggabbro gabbroand andSudbury Sudburydiabase diabase . . . . . . 1515 Stop 1 Stop22 Slaty Slatyargillite, argillite. Pecors PecorsFormation, Formation. and and"trap "trapdyke" dyke" . . . . . . . . . . . . 1616 Stop Stop33Conglomerate, Conglomerate.Ramsey RamseyLake LakeFormation Formation . . . . . . . . . . . . . . . . . 17 17 Stop 18 Stop44 The TheGrenville GrenvilleFront, Front.Highway Highway69 69 . . . . . . . . . . . . . . . . . . . . . 18 Stop Metasedimentary rocks in the Grenville Province Stop 5 Metasedimentary rocks in the Grenville Province . . . . . . . . . . . 20 20 Stop 5 21 . Stop66 Truncation Truncationof of the theGrenville GrenvilleFront Frontmylonite mylonitezone zoneatatAlice AliceLake Lake . . . 21 Stop . . . Stop77 Comparison ComparisonofofSouthern Southernand andCrenville GrenvilleProvince Provincerocks rocks Stop 24 on onopposite oppositesides sidesof ofthe theWanapitei Wanapiteifault fault . . . . . . . . . . . . . . . . 24 Stop88 Grenville Grenville Front Front relationships relationships near near the theStinson Stinsonhydroelectric hydroelectricdam dam . . 25 25 Stop Stop Stop99 Metamorphosed MetamorphosedSudbury Sudburydiabase diabasedyke dykesegments segments inmetasedimentary metasedimentarygneiss gneiss . . . . . . . . . . . . . . . . . . . . . . . 27 27 in Comments problemsof of correlation correlation and andhistory historyof ofthe theGrenville GrenvilleFront Front problems Comments —. References References . . . . . . 2929 .......................................... 33 33 LIST LISTOF OFILLUSTRATIONS ILLUSTRATIONS Figure1.1. Figure Figure2.2. Figure Figure3.3. Figure Figure4.4. Figure Figure5.5. Figure Figure6.6. Figure Figure7.7. Figure Figure8.8. Figure Generalizedgeology geology of of the the Sudbury Sudburyregion region . . . . . . . . . . . . . . . 33 Generalized The The Sudbury Sudbury dyke dyke swann, swarm. Southern Southernand andGrenville Grenvilleprovinces provinces . . . . . 10 10 Geology of of the the Grenville Grenville Front Front southeast southeastof of Sudbury Sudbury . . . . . . . . . 14 14 Geology 19 Detailed Detailedgeology, geology. the the Grenville GrenvilleFront Frontat atStop Stop4, 4. Highway Highway69 69 . . . . . . 19 22 . The The Grenville Grenville Front Front between between Highway Highway 69 69 and andConiston Coniston . . . . . . . 22 Fault interpretations interpretations in in the theConiston Coniston area area . . . . . . . . . . . . . . . . 23 23 Fault 26 . . . . . . . . . . . . . . . The Grenville Grenville Front Front at at Stop Stop 7, 7. near near Stinson Stinson 26 The Metadiabase Metadiabase dyke dyke remnants; remnants; relics relics of the the Sudbury Sudburyswarm swarm . . . . . . . 28 28 . . Table1.1. Table Huronian HuronianSupergroup Supergroupstratigraphic stratigraphic succession succession in the the Sudbury Sudbury area area . . . . . . 22 �NEW DEVELOPMENTS IN GRENVILLE DEVELOPMENTS IN GRENVILLE FRONT GEOLOGY, SUDBURY SUDBURY AREA, AREA, ONTARIO GEOLOGY. INTRODUCTION INTRODUCTION The Grenville orogen, formed formed during during the the latter part The Grenville orogen, part of ofmid-Proterozoic mid-Proterozoic time, time, Scandinaviato toTexas Texasand andbeyond. beyond. The Grenville Crenville Province is that part extends from Scandinavia of the orogen which is exposed exposed in in the the southeastern southeastern Canadian Canadian Shield. Shield. Its Its northwest northwest boundary with older Shield provinces is known as the Crenville Front, boundary Shield provinces is known as Grenville Front, and is aa major lineamentmarked markedby by faults faults and and mylonite mylonite zones zones inclined inclined to to the major tectonic tectonic lineament southeast. southeast. It is a stnictural structural front in the sense that it truncates the structural trends the older older provinces provincestotothe thenorthwest. northwest: It is aa metamorphic that characterize characterize the metamorphic front in the sense that that high-grade high-grade metamorphic metamorphic rocks characterize characterize the the marginal marginal Crenville Grenville metamorphic grade grade varies varies along along the the footwall of of the front, dependorogen, whereas metamorphic ing on the level exposed exposed in in the different provinces that abut it. the exhumed exhumed crustal level different provinces The high-grade high-grade metamorphism metamorphismin in the the immediate immediate hangingwall hangingwall is not everywhere The everywhere Grenvillian in in age; age; itit attests attests to to uplift uplift in Grenvillian time of the Grenvillian the Crenville Grenville orogen orogen relative to the the adjacent adjacent Shield Shield provinces. provinces. The Grenville Front is is well well exposed exposed in the Grenville Front the vicinity vicinity of of Sudbury, Sudbury, Ontario, Ontario, 1). It has been the the subject subject footwall (Fig. (Fig. 1). where the the Southern Southern Province Province constitutes constitutes its its footwall of attention—and controversy—forseveral several decades, decades, and and shadows of attention-and in retrospect, controversy-for former attempts some of of the the more enigmatic features of of this structure former attempts to explain explain some enigmatic features Crenvillian terrane terrane that that forms its hangingwall are still evident and the the complicated complicated Grenvillian in recently recently compiled compiled maps maps(e.g. (e.g.Card Cardand andLumbers Lumbers1977; 1977;Dressier Dressier1984). 1984). It must be admitted that the Southern Provinceisis known known in in much much more more detail, detail, and is admitted Southern Province is thus thus better understood, than the better understood, than the adjacent adjacent Crenville, Grenville, despite despite recent recent advances advances in in interpreting the interpreting thelatter latter(Davidson (Davidson1986a, 1986a,1995; 1995;Easton Easton1992). 1992). This is not to say that there is consensus on the interpretation of the geologic history of there consensus on interpretation of geologic history of the Southern Southern Province—there are several severaltopics topicsofofdispute dispute outstanding, outstanding, and reinterpretations Province-there are reinterpretations to to of many of be made (e.g.Davidson Davidsoneteta!. 01. 1992; 1992; Card Card 1992). 1992). Resolution of of these these will will made (e.g. have have a direct direct bearing bearing on how how the the rocks rocks in in the theadjacent adjacentCrenvilie Grenville Province Province are are viewed. Before outlining outlining the the historical development of of ideas Before historical development ideas concerning concerning the the Crenville Front Front in in the the area area southeast southeast east east of of Sudbury, Sudbury, it is Grenville is advantageous advantageous to be be presently known known about about the local geology. geology. Brief familiar with what is presently Brief summaries of of the geology geology of of the the Southern Southern and Grenville our current knowledge of Grenville provinces in this area are are therefore presented below. below. �Southern SouthernProvince Province The Southern Province in in Ontario, Ontario, which which isis characterized above all all by wellThe Southern Province characterized above wellpreserved supracrustal strata of of the Huronian Supergroup, Supergroup, early early Proterozoic Proterozoic in age (<2.5>2.22Ga), Ga),can canbe bedivided divided into into two parts: i), (<2.5>2.22 1),aa northeastern northeastern region, region, the Cobalt Embayment, in in which which these these strata strata are little deformed and barely Embayment, barely metamorphosed, metamorphosed, and ii), ii), aa southwestern southwestern belt of steeply folded and variably variably metamorphosed metamorphosed strata (though with a less-deformed northern fringe). fringe). The Huronian Supergroup, less-deformed northern Supergroup, at at least least km thick within the fold belt, lies unconformably on Archean cratonic cratonic rocks. It is 12 krn divided into four four groups, groups, each each group consisting consisting of of at least least three three formations formations (see (see Table 1). The groups generally have immature dastic (gladogenic in part) sedimenhave immature clastic (glaaogenic Table 1). shaly to to silty silty rocks rocks in in the the middle, middle, and sandstone at the top, tary rocks at the base, shaly top, defining upward-maturing cycles with with each cycle cycle reaching reaching greater greater maturity maturity than the preceding one. InInplaces, places,notably notablynear nearSudbury, Sudbury,both bothmafic mafic(Elsie (Elsie Mountain, Mountain, Stobie Stobie formations) and felsic volcanic rocks rocks occur occur at at the base of felsic (Copper Cliff) volcanic of the the Elliot Elliot Lake Group; the mafic flows may may be related to to coeval coeval diabase diabase dykes dykes (Matachewan (Matachewan swarm) and anorthositic complexes that that intrude the adjacent anorthositic gabbro complexes adjacent basement, and the Copper Cliff Cliff rhyolite to granites (Murray, (Murray, Creighton, Skead) which occur only of note within the the volcanic volcanic formations. formations. Other Other features features of note are are the the restriction restriction of of Huronian Supergroup stratigraphic succession succession in in the Sudbury Table 1. Table 1 . Huronian Supergroup stratigraphic Sudbury area area Thickness, m Cobalt Group Group Bar River Bar Gordon Lake Lorrain Gowganda Gowganda Quirke Lake Group Serpent Serpent Espanola Espanola Bruce Bruce Hough Lake Lake Group Group Mississagi Mississagi Pecors Ramsey Lake Lake Elliot Lake Group McKim Matinenda Copper Cliff Copper Stobie Stobie Elsie Mountain orthoquartzite, orthoquartzite, minor iron iron formation formation siltstone, minor argillite, argillite, sandstone arkose, and ortho- quartzite quartzite arkose, feldspathic and polymictic conglomerate, argillite >1220 1060-1280 1500-2400 180-1200 feldspathic quartzite quartzite calcareous siltstone, limestone, dolomite dolomite polymictic conglomerate conglomerate 180-1500 150-550 60-460 cross-bedded feldspathic feldspathic arenite arenite shale, siltstone, wacke wacke polymictic conglomerate conglomerate 760-3000 60-600 60-180 laminated shale, siltstone, wacke wacke conglomerate, wacke, wacke, feldspathic feldspathic arenite arenite conglomerate, felsic flow flow and pyroclastic roclcs pyroclastic rocks flows, intercalated wacke pillowed mafic flows, wacke pillowed mafic flows flows 1500-1800 180-300 730 1500 1000 Abstracted Abstractedfrom fromCard Cardcietal. al.(1977), (19771, Frarey Frarey (1985) (1985) and and Bennett Bennetteteta!. al.(1991). (1991). �- Grenville GrendeProvince Province =1.75 -1.75 Ga plutonic plutonicrocks rocks I.''' IF I'''# # / Paleozoic Paleozoic - =1.45 1.GGa Ga metaplutonic metaplutonicrocks rocks 1.45 1.45 Ga plutonic p l u t o ~rocks crocks B88 1.85 1.85 Ga Ga Sudbury Sudburycomplex complex 1Whitewater WhitewaterGroup Group Murray, Murray, Creighton Creightongranites granites Huronian HuronianSupergroup Supergroup m- 1111111 L 3 LI =2.45 =2& Ga Ga gabbro, gabbro, anorthosite anorthosite Archean Archeanrocks, rocks, undivided undivided =1.7 = 1.7Ga Ga metaplutonic metaplutonicrocks rocks a F ...m.. nfl.. Undated Undatedmetaplutonic metaplutonicrocks rocks Wanapitei Wampiteimafic maficcomplex complex Metagabbro, Metagabbm, anorthosite anorthosite ''IllIllI Gneissic undivided Gneissic rocks, mcks, undivided Front 4 Grenville GrendeFmnt mylonite mylonitezone zone geology ofof the the Sudhury Figure Figure 1.1 . Generalized Generalized geology Sudbury region. region. Plutonic Plutonic units units Killarney; Islands; K mentioned in the the text text are: are: CC -- Cutler; Cutler; CI C1 -- Croker Croker - Killarney; mentioned in B --Bell k k e ; FE -- Eden Eden Lake; lnke; CL -- Chief Chief Lake; W -- Wanapitei. Wanapitei. B Bell Lake; �carbonate rocks rocks to the middle of the Quirke Quirke Lake Lake Group (Espanola (Espanola Formation), and the immense immense thicknesses thicknesses of Cobalt Group Group of extremely extremely pure pure orthoquartzite orthoquartzite in in the Cobalt (upper Lorrajn Lorrain and Bar Bar River fiver formations). Where Where basement-cover basement-cover relationships relationships are are preserved in the Cobalt Embayment, Embayment, it is evident in places that younger younger cycles cycles well presewed successively overlap onto tothe thebasement basement(Bennett (Bennetteteta!. al.1991). 1991). overlap northward northward on Voluminous masses masses of of Nipissing gabbro (formerly Voluminous (formerly called Sudbury Sudbury gabbro, gabbro, now commonly referred Nipissing diabase) formations of of the now commonly referred to to as Nipissing diabase) intrude intrude all formations Huronian Supergroup and has and its itsadjacent adjacentArchean Archean basement. basement. Nipissing gabbro has Ga W-Pb (U-Pbbaddeleyite baddeleyite age age 2219 2219 Ma; Ma; Corfu Corfu and Andrews been dated dated at at—2.22 -2.22 Ga Andrews 1986; 1986; 1993). Although Although folded folded with with its its Huronian Huronian host in the Southern Noble and Lightfoot 1993). Southern Province fold fold belt, belt, there there is is some some evidence evidence that that its its intrusion intrusion postdated postdated an earlier Province earlier (Blezardian orogeny orogenyof of Stockwell Stockwell1982). 1982). stage of folding folding (Blezardian Major, upright, upright, east-west east-westfolds foldsinin the the fold fold belt belt are generally attributed Major, attributed to Penokean orogeny, dated in 1239 and and 1.83 1.83 in its its type type area area(northern (northernMichigan) Michigan) between between1.89 Ga (Bickford a!.1986). 1986). Metamorphic Metamorphicculminations culminationswithin withinthe thefold fold belt, belt, in in part Ga (Bickford etetal. associated with intrusion intrusion of of sanitoid granitoid rocks, rocks, isis of of low low pressure pressure type type and and appears to associated with overprint an earlier, overprint earlier, regional, regional, low-grade low-grade dynamothermal dynamothermal metamorphism metamorphism (Card (Card rocks with with ages in the Penokean range have yet to 19780). to be be identified; identified; 1978a). Plutonic rocks determinations for Cutler (titanite) (titanite) and Eden Eden Lake Lake plutons plutons recent U-Pb U-Pb age determinations for the Cutler Ma (Davidson (Davidson et et al. a!. 1992; 1992;Sullivan Sullivan and and Davidson Davidson (monazite), for example, example, are are—1750 -1750 Ma 1993) 1). 1993) Pig. (Fig. 1). Although not a player in the the Grenville Grenville Front story, a world-renowned feature feature of 01.1984). 1984). of this area area is is the theSudbury SudburyIgneous IgneousComplex, Complex,dated datedatat1849 1849Ma Ma(Krogh (Kroghetetal. Now widely accepted as the product of a massive impact (though not without vocifwithout vociferous detractors; to which which breccias brecciasand and shatter shatter cones cones in in its et a!. al. 1984), 1984), to detractors; see Pye et country rocks rocks are are attributed, attributed, thii this feature feature serves serves to to constrain constrain the the age age of of part part of of the deformation affecting affecting the the Southern deformation Southern Province Province fold belt. belt. The The south south half half of the the Sudbury structure, including including the the sedimentary sedimentary Whitewater Whitewater Group which which itit encloses, encloses, 1978a), displaying northerly, thrust-sense thrust-sense deformed (Card (Card l978a), is metamorphosed and deformed displacement on faults and ductile deformation zones (Shanks and Schwerdtner displacement on ductile deformation (Shanks Schwerdtner 1991). 1991). A belt belt of of elongate elongate granitoid granitoid plutons plutons (Killarney (Killarney batholithic batholithic complex complex of Lumbers the Lumbers 1975) 1975)intrudes intrudes folded folded Huronian Huronian Supergroup Supergroup strata strata adjacent adjacent to to the Grenville Front Front from from near near Sudbury Sudbury to to the coast Grenville coast of Georgian Georgian Bay, Bay, where where the Killarney granite granite and associated, predominantly felsic volcanic volcanic and and hypabyssal rocks Killaney dated atat—1740 -1740 Ma have been dated Ma (U-Pb (U-Pbzircon; zircon;van vanBreemen Breemenand and Davidson Davidson 1988). 1988). A for a phase of the similar age was obtained by Krogh Krogh and and Davis Davis (1970) (1970) for the Chief Chief Lake Lake batholith nearer to Sudbury, but aa new batholith new U-Pb U-Pb analysis analysis of of zircon zircon from from coarse, coarse, pink pink granite of this this unit unitsuggests suggestsan anage ageofof—1465 -1465 Ma (Davidson and and van vanBreemen Breemen1994). 1994). This much younger age is comparable to those reported earlier for the Bell This much younger comparable those earlier for the Bell Lake Lake Ma; van van Breemen Breemen and and Davidson 19881, 1988), and and for the granite farther southwest (1471 (1471 Ma; Croker Island Islandcomplex complexwest westofofKillarney Killarney(—1465 (-1465 Ma; Van Schmus %hmus 1965). 1965). All these rocks are cleanly cut by southeast-trending, vertical dykes of fresh (Uolivine diabase to the the Sudbury Sudburyswarm, swarm,now nowreliably reliablydated datedatat -1235 Ma Ma (Udiabase belonging to —1235 Pb, baddeleyite; Krogh Dudàs eet a!. 1994). 1994). The The importance importance of these Krogh et ef a!. nl. 1987; 1987; Dud& f 01. these dykes dykes is elaborated later in this text. A younger set of east-trending dykes of quartz-bearing A younger set of east-trending dykes of quartz-bearing �5 diabase, diabase, belonging to to the the Grenville Grenville swarm swarm and anddated datedatat595 595Ma Ma(Kamo (Kamoeteta!. al.1995), 19951, 600 the Southern Southem Province Province through the the Grenville Grenville Province Province for for at atleast least600 extends from the km. km. Grenville Province Geological maps of of the the Grenville Provinceadjacent adjacenttotothe the front front in the Sudbury Geological maps Grenville Province Sudbury region (Lumbers Frarey 1985; 1985;Card Card and and Lumbers 1977) portray this terrane 197'7) portray terrane (Lumbers 1975; 1975; Frarey primarily as a 'sea 'sea of of gneisses', gneisses', a large large proportion proportion of which is interpreted interpreted to to be be sedimentary in in origin. origin. The gneisses gneisses include undoubted metasediments metasediments such as as quartzite, gneissand and marble, marble, but but many many are rather calc-silicate gneiss quartzite, pelitic gneiss, and rare calc-silicate ordinary quartzofeldspathic protoliths are uncertain. These quarkofeldspathic rocks whose specific speafic protoliths uncertain. These gneisses are interlayered with with mafic maflc gneiss gneiss and and metagabbro metagabbro near near the the front southeast of Sudbury, and with with anorthositic anorthositic gneiss farther northeast; northeast; they are are interspersed interspersed with irregular and and commonly commonly sinuous units units of of foliated foliated or or gneissic gneissic granitoid, granitoid,particparticularly Bay. A ularly toward Georgian Georgian Bay, A few few small small plutons plutons have have more more equant equant outlines. outlines. Notable among these these is an Notable among an oval oval body body of of mafic mafic rock, rock, the theWanapitei Wanapiteicomplex complex (Lumbers 1975;Rouse11 Rouselland andTrevisiol Trevisiol1988), 1988),situated situatedclose closetoto the the front east of (Lumbers 1975; of Sudbury, which more more information informationisisgiven givenbelow. below. Also Also present present in this area Sudbury, about which of pegmatite, pegmatite, as well well as numerous small pegmatite are several large masses of pegmatite dykes dykes and lenses, and small bodies of mafic rock mapped as 'cataclastic metadiabase' small bodies of mafic rock mapped as 'cataclastic metadiabase' (Lumbers 1975). 1975). The The latter latter are are now now confidently correlated correlated with with Sudbury Sudbury diabase on the grounds outlined below. grounds outlined below. itIt isis easy easytotoassume assumethat thatthe themetasedimentary metasedimentary gneisses gneisses and and interlayered interlayered metagabbro were derived derived from metagabbro were from the Huronian Supergroup Supergroup and and Nipissing Nipissing gabbro gabbro respectively, but ifif this is the case, of stratigraphic stratigraphic order permitting case, all semblance of respectively, but direct correlation with the well-known Huronian succession has been been obscured or well-known Huronian succession has destroyed destroyed during deformation deformation and and high-grade high-grade metamorphism. metamorphism. Northeast Northeast of of Sudbury, metasedimentary biotite biotite schist schist and gneiss gneiss (Red (Red Cedar Cedar Lake Lake formation), formation), formerly interpreted as aa coarse clastic facies of of Huronian sediment sediment by by Lumbers Lumbers coarse clastic (1978), are now now considered considered to to be be Archean, Archean, probably representing reworked wacke (1978), are wade and siltstone siltstone of of the the Pontiac Pontiac Group Group of of the the adjacent adjacent Superior Superior Province; Province; Archean Archean ages ages are preserved units in this p r e s e ~ e din metagranitoid metagranitoid units this area. area. On the the other other hand, hand, some some metasedimentary rocks in in the marginal metasedimentary rocks marginal Crenville Grenville Province Province south of of Sudbury, Sudbury, extending extending to to the the north north shore shoreof of Georgian Georgian Bay, Bay, have Nd-model Nd model ages ages (2.32 (22.32Ga, Ga,Dicldn Dickin and McNutt 2.12 Ga, McNutt 1989; 1989; 22.12 Ga, P.O F.O Dudas, Dud&s,pers. pers. comm., comm., 1991) 1991) which are are too tooyoung young (unless disturbance of of Nd systematics systematics isis admitted) admitted) for for them them to to be be correlated with the Huronian Supergroup, whose sediments sediments have have Archean Archean provenance provenance and Nd model model ages; for example, Nd isotopic analyses of sedimentary rocks from the Lorrain ages; example, isotopic analyses of sedimentary the Lorrain Formation northeast of Sudbury (Lightfoot and Naldrett Naldrett 1989) 1989) yield depleted depleted mantle mantle 2.85 Ga. Ga. model ages agesof of 2.85 model In the same U-Pb zircon zircon ages ages provide provide reason to correlate same region, region, however, however, U-Pb correlate metamorphosed granitoid rocks rocks with those in the the Southern Southern Province, Province, both 1.74 1.74 and 1.47 Ga Ga age age groups being being represented represented (Davidson (Davidsoneta!. el al.1992; 1992; van van Breemen Breemeneta!. et al.1986; 1986; van Breemen pers. comm. 1993). 1993). van Breemen Breemen and and Davidson Davidson (1988) (1988) suggested suggested corcorrockswith withthe the—1.75-Ga -1.75-Ga graniterelation of the the Killarney Killamey granite granite and and allied alliedvolcanic volcanicrocks �rhyolite association of the the Central Central Plains Plains orogen orogen in the association of the mid-continent mid-continent (Sims (Sims and itselfpart part of of the the larger larger Yavapai/Mazatzal Yavapai/Mazatzal province exposed farther Peterman 1986), 19861, itself 19%). They also noted that the the 1.47-Ca 1.47-Ga age of the Bell Bell Lake granite west (Hoffman 1988). lies within the lies the range range of of the the older olderofoftwo twoso-called so-calledanorogenic anorogenicgranite-rhyolite granite-rhyolite a!. 1986). provinces et al. 1986). In the the adjacent adjacent provinces in the the buried buriedmid-continent mid-continent (Bickford (Bickford et Grenville Rovince, Province, the the supracrustal supracrustal rocks rocks which which originally originally hosted hosted the the older of of the two granite suites and which appear to be younger than the Huronian Supergroup, the Huronian Supergroup, for this event has have presumably presumablyundergone undergone—1.7-Ga -1.7-Ga orogeny. orogeny. Evidence Evidence for has been been recognized in in the Key Harbour area of the Georgian recognized Key Harbour Georgian Bay Bay coast, where the oldest oldest associated with with deformed granite dated migmatitic gneisses are assoaated dated at at1685 1685Ma (Corrigan 1990). In addition, it now appears that this 1990). this part part of of the theGrenville Grenvilleorogen orogen also also underunder-1.47-Ga plutonwent widespread widespread metamorphism metamorphism and anddeformation deformationshortly shortlyafter afterthe the—1.47-Ca ism. Monazite al. 1994) 1994) and titanite Monazitein inhigh-grade high-grade metasedimentary metasedimentary gneiss gneiss (Dudas (Dud& et a!. in 1.74-Ga et a!. al. 1993), 1993), both the front, front, 1.74Ga metagranitoid rocks (Haggart (Haggart et both within within 10 km of the leucosomes farther farther into the Crenville and zircon zircon in in orthopyroxene-bearing orthopyroxene-bearing leucosomes Grenville orogen orogen (Ketchum 1994), all record record ages ef a!. al. 19941, agesofof—1.45 -1.45 Ga. Ga. (Ketchurnet orogeny in in this this comer corner of of the the province province appears appears to be restricted to Grenvillian orogeny deformation and metamorphism metamorphism late in the age-range age-range ofof1.3-—1.0 51.3--1.0 Ga Gaaccorded accordedtoto and presumthe broader 'Crenvillian 'Grenvillian orogenic orogenic cycle' (Moore and Thompson 1980), and ably associated with tectonic burial accompanied by deep-seated, deep-seated, large-scale thrust imbrication directed directed toward toward the the front, followed followed shortly shortly thereafter thereafter by by rapid rapid uplift and imbrication and a!. 1993; Culshaw exhumati on accompanied by by extensional tectonics (Haggart (Haggart et al. Culshaw et ef a!. al. exhumation 1994). related to tothe theonset onsetof ofGrenviUian Grenvillian 1994). There are no supracrustal rocks that can be related orogeny, and no plutonic rocks marking its culmination. culmination. A A growing growingdatabase databaseof of UUorogeny, rocks marking and titanite from this region Pb ages for zircon, zircon, monazite monazite and region suggests suggests that that tectonic tectonic activity was Ma(thii (thisseems seems aa relatively short short was restricted restricted totobetween between—1040 -1040 and —980 -980 Ma period in terms, but but nevertheless nevertheless is is equivalent equivalent to to the whole whole of the the in Precambrian Precambrian terms, Tertiary!). Much earlier Ma; van van Breemen Tertiary!). Much earlier ductile ductile deformation deformation (—1160 (-1160 Ma; Breemen and Davidson 1986) was associated associated with with emplacement emplacement of of the Parry Sound 1986) was Sound granulite granulite allochthon kmfrom from the the front, front, but so so far far there there isis allochthon in the the interior interiorof of the theprovince, province,—100 -100 km no geochronological evidence evidence for forany any event event of of this this age age closer doser to to the the front. front, The Grenville GrenvilleFront From Georgian Bay Bay to Coniston, Coniston, the Grenville Front is marked marked byby a zone of of faults faults inclined generally generallyatatmoderate moderate angle angle to to the the southeast, southeast, that cut all but and mylonites, inclined dykes, the the Grenville Grenvilleswarm. swarm. It has been well documented documented that the youngest diabase dykes, dykes disrupted by by faults and dykes of of the the Sudbury Sudbury swarm, swarm, although although disrupted and not not traceable traceable individually zones, do cut earlier, front-parallel fabrics within faultindividually across across mylonite zones, within faultbounded bounded panels panels(Henderson (Henderson1967; 1967; Brooks Brooks 1976; 1976; Frarey 1985; Bethune and Davidson Davidson 1988). A means means is is thus thus available available to to distinguish distinguishprepre-and andpost-1235-Ma post-1235-Ma structures. structures. 1988). First, some lingering lingering misunderstandings misunderstandings about about the Grenville Front are First, however, however, some the historical historical development development of of interpretation interpretation of of thii this major best assessed by following following the structure. structure. Long before the the Shield Shield was was divided into structural h n g before structural provinces provinces (Gill (Gill1948), 1948), the boundary between the Southern Southern and and Grenville Grenville Provinces was recognized recognized by Collins Collins �(1916, 1925) as as the locus of major (1916, 1925) major change, change, where where well-preserved, well-preserved, broadly-folded broadly-folded Huronian Huronian sedimentary sedimentary rocks rocks and Nipissing Nipissing gabbro gabbro intrusions, intrusions, at at relatively relatively low low metamorphic metamorphic grade, give give way way southeastward to to aa complex complexterrane terrane of of high-grade high-grade gneissic gneissic rocks. rocks. Mapping Mapping across across this boundary in in the the late late 1920s 1920s led to the idea that that granitization on aa huge huge scale scale was was responsible responsible for for the the"disappearance "disappearance of of the the granitization Huronian" (Quirke (Quirke and and Collins Collins 1930). 1930). This Thii hypothesis hypothesis was was championed championed particularly particularly Huronian" by Quirke Quirke(1927, (1927, 1940), 1940), although hotly hotly disputed disputedby byothers others(e.g. (e.g.Jones Jones1930); 1930);tracts tractsof of by metasedimentary gneiss gneiss as far as 40 40 km from the the boundary boundary were werecorrelated correlatedwith with metasedimentary speafic Huronian Huronianformations formations(Quirke (Quirke1930). 1930). specific in Inthe thearea areadirectly directly southeast southeastof of Sudbury, Sudbury, the theboundary boundarybetween betweenthe theSouthern Southern and Grenville Grenville provinces provinces was interpreted as as aa metamorphic metamorphic transition iransition by by Phemister Phemister and (1961; Grant et et al. a!. 1962) 1962)where whereHuronian Huronian sedimentary sedimentary rocks and Nipissing (1961; Grant Nipissing gabbro gabbro were were abruptly abruptly metamorphosed metamorphosed and granitized g r a n i i k d to to make makethe thegneissic gneissicand andmigmatitic migmatitic rocks rocks of of the the Grenville Grenville Province. Province. Kwak Kwak(1968) (1968) and and La La Tour Tour(1981) (1981) documented documented an an Daiziel et a!. (1969) abnormally high metamorphic gradient across this transition. abnormally metamorphic across this transition. Dalziel et al. (1969) recognized was an an important factor in this transition, and that recognized that mylonitization mylonitization was metamorphism preceded preceded the the earliest earliest recorded recorded folds. folds. They They expressed expressed some some doubt doubt metamorphism about about the the equivalence equivalence of of rocks rocks on opposing sides of the front, front, but but did didnot notinvoke invoke large-scale displacement to to explain explain the the possibility large-scale displacement possibility that different different rocks rocks had had been been juxtaposed juxtaposed or or that that metamorphic metamorphic isograds had been been 'telescoped'. 'telescoped'. Without Withoutthe thebenefit benefit of modern Dalziel (1974, (1974, p. 1577) 1577) contended that the the modern geochronology, geochronology, Brocoum Brocoum and Dalziel rocks of the including the the Sudbury Structure, and those the Southern Southern Province, Province, including those in in the the "... all all underwent underwent the thesame samemajor majordefordeforpart of of the theGrenville GrenvilleProvince Province"... adjacent part mational event after the intrusion intrusion of the the Nipissing Nipissing diabases diabases (2.15 (2.15 b.y. b.y. ago) and the Nickel Irruptive Irruptive (2.0 (2.0 b.y. ago) and prior prior to to the theintrusion inirusionofofthe thenorthwest-southeast— northwest-southeasttrending olMne olivinediabase diabasedyke dykeswarm swarm(1.46 (1.46b.y. b.y. ago) ago)...", ...",which, which, they they stated, stated, cuts a.16the the trending gneisses in the northwestern Province. This Thii major major event event was was attributed attributed northwestern Grenville Grenville Province. to a wider age-range (2.0—1.6 to the the Penokean Penokeanorogeny, orogeny,which whichwas wasatatthat thattime timeaccorded accorded a wider age-range (2.0-1.6 (1976)pointed pointed out out that the today. However, However, Brooks Brooks (1976) the same same olivine olivine Ga) than itit isis today. diabase swarm) are are deformed deformed and andmetamorphosed metamorphosed farther farther diabase dykes dykes (Sudbury (Sudbury swarm) southwest he did not dispute southwest along the front, although although he dispute the the fact fact that that they theyalso alsocut cut earlier deformation deformation fabrics fabrics in granitoid granitoid rocks rocks adjacent adjacent to to the the front. front. earlier Phemister recognizedthe theGrenville GrenvilleFront Frontinin this this area area to have Phemister (1961) (1961) recognized have two two distinct distinct manifestations, manifestations, a metamorphic transition southwest southwest of of Coniston, Coniston, and and aadisdkcrete cit., p. 61): "One of the features that makes this Crete fault to the east. He Hestated stated(op. (op. 61): "One the features that makes this region of special is that here the Wanapitei fault is seen special interest is seen to to cut cut across across the the "front" of of metamorphiim metamorphismleaving leavingno nodoubt doubt therefore therefore that that it marks a younger event the structural structural history history of of the region.... region.... Thus Thus ... ...the the boundary boundary in inthe thewestern westernsection section in the Dalziel et a!. is aa metamorphic "front" while in the eastern part it is a fault." (1969, metamorphic "front" while in it is a fault." Dalziel ei al.(1969, 211) described described the the Wanapitei Wanapitei fault fault as aa brittle brittle fracture, fracture, being being aa later latereffect effectwhich which p. 211) . The obscures"... ... the the fundamental fundamental tectonic character of front ...". The westward westward conconof the front obscures " tinuation tinuation of of the the Wanapitei Wanapitei fault in in the the Southern Southern Province Province aligns aligns with with the thewellwellknown Murray fault, passing south of of Sudbury and extending extending for at at least least aa further further to the the west west(Fig. (Fig.1). 1). 150 km to An alternative interpretation alternative interpretation was advanced advanced by by Lumbers Lumbers(1975), (1975), who who comcombined the of the front as a single the two two different different segments of single feature feature referred to to as as the the �'Grenville Front Boundary Boundary Fault'. Fault'. His map shows the Murray Murray fault fault as asremaining remaining within the Southern Province instead of being continuous with the Wanapitei Southern Province of Wanapitei fault interpretation has has been been reproduced 6, A). A). This This interpretation reproduced on subsouth of of Coniston Coniston (Fig. (Fig. 6, sequent geological compilations compilations (Card (Card and and Lumbers Lumbers1977; 1977; Dressler Dressier1984). 1984). Reaffirming the faulted nature of the Grenville Front mylonite zone east in the Coniston of the Grenville mylonite the Coniston Davidson (1992) (1992) argued post-Grenvillian normal displacement on the the area, Davidson argued that post-Grenvillian normal displacement Wanapitei fault (i.e. side down) down) best best explains explains the the abrupt opposition (i.e. Grenville Grenville side opposition of of Wanapitei high-grade high-grade gneisses gneisses and andlittle-affected little-affected Southern SouthernProvince Province rocks. rocks. Zone' is is commonly commonly used in conjunction The term 'Grenville 'Grenville Front Tectonic Tectonic Zone' conjunction First coined by Lumbers with the northwest northwest margin margin of ofthe theGrenville Grenville Province. Province. First Lumbers (1971a), itit was defined defined as as aa zone zoneof of northeast-trending northeast-trending cataclastic cataclastic foliation foliation with with (1971a), manifested mainly mainly in the gneissic attendant southeast-plunging southeast-plunging lineation manifested gneissic rocks rocks of of Province, but but also also including includingaa narrow narrow strip strip in the adjacent the Grenville Province, adjacent Superior of the 'Grenville and Southern Southern provinces, provinces, northwest northwest of 'Grenville Front Boundary Boundary Fault', Fault', in in occur. The which similarly oriented structures occur. The northwest boundary boundary of of the theGrenville Grenville Province, however, however, was was placed placed at at the boundary Province, boundary fault. fault. Wynne-Edwards (1972) Wynne-Edwards (1972) defined the the tectonic zone aa little confiningitit to to southeast of the defined tectonic zone little differently, differently, confining southeast of Grenville Front, Front, while while recognizing that front-related deformation is present Grenville recognizing that front-related deformation present northwest of the front in the ForelandZone'. Zone'. The southeast margin of of northwest of the 'Grenville 'Grenville Foreland the Grenville Front Tectonic Zone was not defined rigorously by either author. Tectonic Zone was not defined rigorously either author. Subsequently, Rivers et a!. (1989)used usedthe the term term 'Parautochthonous Belt' to describe al. (1989) describe the marginal part of the Grenville orogen containing reworked rocks the marginal of the Grenville orogen containing reworked rocks of of the the adjacent, older older Shield provinces, and and not not coincident adjacent, Shield provinces, coincident with the the Grenville Grenville Front Front Tectonic Zone. To confusion,neither neitherofofthese these two two terms terms is is used used in Tectonic Zone. To avoid avoid possible possible confusion, this guide. guide. Application of of modern kinematic kinematic analysis to fabrics in in the themylonitic myloniticrocks rocks along the Grenville along Grenville Front between between the coast of Georgian Georgian Bay Bay and Sudbury Sudbury conconsistently yields evidence for thrust-sense displacement toward toward the northwest (Pryer (Fryer thrust-sense displacement 1988). The position of this c; Davidson and Bethune Bethune 1988). 1985, 1993; Davidson Davidson1986b, 1986b,C; segment of of the front, however, Frarey and however, has been a matter of of some some contention. contention. Frarey Cannon (1969; Frarey 1985) 1985)placed placedthe thefront frontalong along the the northwest northwest contacts of the (1969; Frarey the and Bell Lakegranites, granites,on on the thebasis basisthat that these these contacts contacts are are faulted faulted in many Bell Lake Killarney and places and cut across fold trends in the Huronian rocks. rocks. The places The northeast northeast extension extension of of was shown shown to pass into the southern part this 'front', 'front', however, however, was part of of the theChief Chief Lake Lake In their Card and Lumbers granite. In their regional regional compilation, compilation, Card Lumbers (1977) (1977) placed placed the the 'Grenville Front Front Boundary Boundary Fault' Faultton onthe thesoutheast southeastside sideofofthese these granites. granites. Davidson Davidson (1986b)favoured favoured the the latter latter position, position, modified modified to to a somewhat more (1986b) more southeasterly southeasterly position near Georgian it coincided with a major Georgian Bay, Bay, because because it coincided with major zone zone of of mylonitizmylonitization across which the most pronounced change change in in structural style and orientation orientation Farther northeast, northeast, this this zone zone also also coincides coincides with with an abrupt increase occurs. occurs. Farther increase in in metamorphic grade; in in addition, metamorphic grade; addition, it marks marks the the southeast southeast limit limit of ofcontinuously continuously traceable Sudbury dykes dykes (Bethune (Bethune 1993) 1993)and andisisthus thus identifiable identifiable as as a feature traceable Sudbury feature of Grenvillian age. that a distinction must be made It has has now now become become clear clear that distinction must made between between the respective northwestern limits limits of of the the pre-Sudbury pre-Sudbury dyke dyke deformation that postdated respective the —1.47-Ga granitesand and post-Sudbury post-Sudbury dyke deformation. deformation. If the Grenville Grenville Front Front is is -1.47-Ga granites �taken as the northwest northwest limit of penetrative deformation and metamorphism related to Grenvillian Sudbury dykes dykesbecomes becomes Grenyillian orogeny, then the state of preservation of the Sudbury a crucial factor in locating locating the front. front. The youngest pre-Sudbury dyke dyke structures structures northwest of this limit northwest of limit are are unlikely unlikely to to represent represent an an early early phase phase of ofGrenvillian Grenvillian orogeny because the the Sudbury dyke swarm, swarm, which which cuts them, them, was was presumably presumably orogeny because Sudbury dyke emplaced into stable stable continental continental crust. crust. It seems more likely that aa distinctly distinctly earlier earlier Ga,recorded recordedon onboth bothsides sides of of the the Grenville Front as orogenic event at at —1.45 -1.45 Ga, as defined defined above, was was responsible responsiblefor forthe theyoungest youngeststructures structurescut cutby bythe theSudbury Sudburydykes. dykes. At above, present, present, no counterpart counterpart of of this this event event has has been been recognized recognized elsewhere elsewhere outside outside the the Grenville Province; coeval coevaligneous igneousactivity activityinin the the buried mid-continent Grenville Province; mid-continent to the the a!. Windley southwest is a al. 1986; 1986; 1989). Based on is regarded regarded as as'anorogenic' 'anorogenic' (Bickford (Bickford et 1989). less comprehensive geochronology than is is available available today, today,Stockwell Stockwell(1982, (1982, p. p. 68) 68) proposed that the ill-defined 'Killarriean orogeny', to which he ascribed a terminal terminal that the ill-defined Killarnean orogeny', to which age of of —1.5 Ga,has hasitsitstype typeregion regionwithin withinthe theGrenville GrenvilleProvince. Province This -1.5 Ga, This now now seems seems prophetic in the prophetic in the light light of of the themore morerecent recent identification identification of of widespread, widespread, prepreGrenvillian plutonism within the the adjacent adjacent Grenville Grenville orogen. orogen. Stockwell, however, (-1.74 and and had no no knowledge knowledgeof of the thetwo twodistinctly distinctlydifferent differentages agesofofgranitic graniticrocks rocks(—1.74 —1.47 Ca)that thatisisconsistently consistentlyemerging emergingfrom fromgeochronological geochronologicalstudies studies in in this area; -1.47 Ga) area; the concept of of 'Killarnean orogeny' now now seems seems inappropriate inappropriate in that the 'Killarnean orogeny' the time-span time-span assigned to it embraces embraces both age groups. groups. The ages and events in the and expression expression of of post-Penokean, post-Penokean, pre-Grenvillian pre-Grenvillian events the Southern Province are are poorly poorly documented. documented. For example, the age of Southern Province of deformation deformation and metamorphism of of the southern southern part part of of the Sudbury Structure, Structure, and how far the effects of of this this event extend extend into the neighbouring Huronian rocks, are not not known. known. It is quite possible possible that the the rocks rocks in in the the Grenville Grenville Front Front region region were were affected affected by by two two post-Penokean events before before emplacement of the the 1235-Ma 1235-Ma Sudbury Sudburydyke dykeswarm swarm—related to the of major orogens farther farther southeast that have events related the development development of major orogens been largely overprinted and obscured by later Grenvillian orogeny in the the interior interior of of Province. Displaced the Grenville Province. Displaced and telescoped remnants of these orogens, whose tectonic fronts appear appear to to coincide coincide so so closely closely with with the the Grenville GrenvilleFront Front(Bethune (Bethune1993), 19931, may may explain explain the the abundant abundant evidence evidence for for pre-Grenvillian pre-Grenvillian deformation deformation and and metamorphism within this part part of of the theGrenville Grenvilleorogen. orogen. referenceshave have been been made made to the Sudbury Throughout the foregoing, several references Sudbury diabase dyke swarm, implying usefulness as as a time-marker for discerning diabase implying its usefulness discerning the effects of of Crenvillian effects Grenvillian orogeny orogeny in this this poly-orogenic poly-orogenic terrane. Therefore Therefore a more more detailed account of of this this swarm swarm and its recognition within the Crenville detailed recognition within Grenville orogen is given below. below. The Theextent extent of of the the Sudbury Sudbury swarm swarm in in the the Southern SouthernProvince Province southwest southwest of of Sudbury and and the the known known distribution distribution of of equivalent equivalent metadiabase metadiabase dykes dykes and and remnants in 2. in the the Grenville Grenville Province Province are shown shown in in Figure Figure 2. Sudbmy dyke Sudbury dyke swami swarm Lumbers (1975)mapped mappedtwo two types types of of diabase diabase dykes dykes in the Lumbers (1975) the Southern Southern Province Province of Sudbury, Sudbury, which which he he referred referred to to simply simplyas as 'olivine 'divine diabase' and southeast of and 'diabase', 'diabase', and which are part of what what are are now now known known as the the Sudbury Sudbury and and Grenville Grenville swarms swarms olivine diabase dikes respectively (Fahrig (Fahrigand and West West1986). 1986). He He stated stated that the "... "... olivine dikes respectively �The Sudbury Sudburydyke dyke swarm swarm in inthe theSouthern SouthernProvince Provincesouthwest southwestofof Sudbury, Sudbury, Figure2.2. The Figure dykes in the Grenville and anddistribution distributionofofmetamorphosed metamorphosedand anddeformed deformedSudbury Sudbury dykes in the Grenville Province(solid (solidlines linesand anddots). dots). East-west East-westdashed dashedlines linesare areGrenville Grtimilledykes. dykes. Province areconfined confinedtotothe theSouthern SouthernProvince Provinceportion portionof of the thearea areaand andare arepart partofofa aregional regional are northwest-trending northwest-trending swarm swarm that that intrudes intrudesrocks rocksof ofboth boththe theSouthern Southernand andSuperior Superior Provinces Provinces but but which which does does not notextend extendacross acrossthe theGrenville GrenvilleFront FrontTectonic TectonicZone Zoneinin (op.cit., cit.,p.p.109). 109). Although Although he he mapped mappedoccurrences occurrencesof of theGrenville GrenvilleProvince." Province."(op. the metadiabase' in metadiabase metadiabase in inthe theadjacent adjacentGrenville GrenvilleProvince Province(termed (termed'cataclastic 'cataclastic metadiabase' in his map map legend), legend), he he did did not notequate equatethese thesewith withthe the Sudbury Sudbury dykes. dykes. Farther Farther his (1977) also documented two different types of diabase southwest,Palmer Palmer aeta!. al. (1977) two different types of diabasein inthe the southwest, Southern SouthernProvince Province south southofofLake LakePanache, Panache,but butFrarey Frarey(1985), (1985). while whileacknowledging acknowledging the the distinction, distinction, included included both types types in in the thesame samemap mapunit. unit.Frarey, Frarey, however, however, did did recognize recognize that that "Olivine "Olivine diabase diabase dykes dykes of of the the "Sudbury "Sudbury swarm", swarm", so sonumerous numerous in inthe the Province Southern Province, continue east-southeastward into the Grenville Southern Province, continue east-southeastward into the Grenville Province atat (op.cit., cit., p.p. 47). 47). His Hismap mapshows shows leastas asfar faras asTyson TysonLake Lake and andpossibly possiblymuch muchfarther." farther."(i. least several severaldyke dykesegments segmentswith withvarious variousorientations orientationsininthe theGrenville GrenvilleProvince; Province; some someof of Grenvillian "...curved curved traces, traces, suggesting suggesting late late folding folding that that isispresumably presumably Grenvillian thesehave have"... these .."(op. (op. cit., cit., p. 48), and he he recognized recognized the the'cataclastic' 'cataclastic' nature nature of of the thediabase diabasein inthin thin the Grenville section. At At the theeastern eastern edge edge of of his hismap maparea, area,some some18 18km km into into the Grenville section. Province, he mapped one dyke whose eastward continuation in Province, one dyke whose eastward continuation in the theBurwash Burwashmap map 'cataclastic metadiabase'. Farther areawas wasclassified classifiedby byLumbers Lumbers(1975) (1975)as as 'cataclastic metadiabase'. Farthereast eastnear near area within a ductile gneiss Key Harbour, 'cataclastic metadiabase' occurs as isolated pods Key Harbour, 'catadastic metadiabase' occurs as isolated pods within a ductile gneiss medium(Davidson (Davidsonand andBethune Bethune1988). 1988). medium �It is clear clear that geologic geologic units foreland of an units which which are are undisturbed undisturbed in in the foreland orogen, orogenic front front may may be be used to constrain the tectonic history history of of the adjacent orogen, provided they can can be be recognized recognized within it. it. With respect to the Grenville Front, the Sudbury dykes Southern Province and are are Sudbury dykes in in the Southern Province foreland forelandare are such such aa unit, and particularly important for for the the following following reasons: reasons: 1) they they are are oriented oriented orthogonally orthogonally to the front; front; 2) the theacross-strike across-strikewidth widthofofthe theswarm swarmisisatatleast least200 2001cm; km; 3) many many dykes dykes are are thicker thicker than than 30 30 m, some some being more than than 100 100 in; m; 4) individual individual dykes dykesare arecontinuous continuousfor formany manytens tensof of kilometres; kilometres; 5) the the diabase diabase has has aa distinctive, distinctive, evolved evolved chemistry chemistry (undersaturated, enriched in iron, alkalis and high high field field strength strength elements); elements); 6) the known (—1235 theage ageof ofthe theswann swarmisis known (-1235 Ma). Ma). The first first four four attributes attributes make make it reasonable reasonable to to expect expect them them to to be be found within the the Grenvile Province provided provided that the Grenville the Grenville Grenville Front is not not aa post-1235-Ma post-1235-Ma suture juxtaposing exotic crust crust against against the the Superior and Southern Province craton, or that that juxtaposing exotic there has been lateral displacement displacement along the front. been no no large largescale, scale, post-1235-Ma post-1235-Ma lateral front. Their distinctive distinctive chemistry chemistryshould should allow allow them them to to be be recognized Their recognized within the GrenGrenville Province, Province,provided provideditithas hasnot notbeen beenunduly unduly disturbed disturbed during during metamorphism. metamorphism. If If ville be traced traced into the front and recognized beyond beyond it, it, their known age would they can be make them them an invaluable make invaluable time marker for distinguishing distinguishing pre- and and post-emplacepost-emplacement structures. structures. Mapping along the the Grenville Front has has failed failed to trace individual Mapping along Grenville Front individual Sudbury Sudbury dykes from the Southern into the Grenville Province. Correlation of Sudbury the Southern into the Grenville Province. Correlation of Sudbury diabase and inetadiabase metadiabase must therefore therefore rely rely on on comparative comparativewhole-rock whole-rock chemistry chemistry and isotopic age. The characteristic chemistry of Sudbury diabase, documented by The characteristic by (1965),Merz Merz(1976) (1976)and andCondie Condieetetal. a!.(1987), (1987),and andunlike unlikethat that of of any any other other Fahrig et al. (1965), diabase dyke swarm in the Shield, has been corroborated by major and trace trace element element analyses of of 40 40 samples samples between between Sudbury Sudbury and and Georgian Georgian Bay, Bay,ranging ranging up up to 45 km km analyses northwest of the Grenville Front. A northwest of Grenville Front. A similar similar number number of of analyses analyses of of metadiabase metadiabase samples from the the Tyson Tyson Lake Lakearea, area,up up to to 16 km km from samples from from the front, front, and and smaller smaller numbers from both Key Harbour, —40 km from the front, and closer to the front both Key Harbour, -40 km from the front, and front east east of Sudbury, all have identical identical chemical chemicalsignatures signaturesto tofresh fresh Sudbury Sudbury diabase. diabase. These of Sudbury, results are summarized and reported reported fully in Bethune (1993). summarized in in Bethune Bethune (1989) (1989) and (1993). The U-Pb age of of 1238±4 Maobtained obtained by by Krogh Krogh eet a!. (1984) (1984)on onbaddeleyite baddeleyite in Sudbury U-Pb 1238±Ma t al. Sudbury diabase from from Espanola, Espanola,65 65km kmwest westofofSudbury Sudburyand and40 40km from the front, has been diabase km from corroborated by U-Pb U-Pb baddeleyite baddeleyite ages ages determined determined for for three three other other Sudbury dykes corroborated by northwest of the front (1994),who who also also obtained obtained similar similar ages for ef a!. al. (19941, northwest of front by by Dudãs Dudas et metadiabase in the the Grenville Grenville Province. Province. The The average average age age for for the the three dykes in the metadiabase in Southern Province, at at locations 30, 16 and 33 km from the Southern Province, locations 30, the front, front, isis1234±7 12349 Ma. Ma. Baddeleyite was separated from metadiabase at locations 2,3 2, 3 and 12 km southeast Baddeleyite was southeast of of the front at Tyson Lake, and 5 km from the front at Wahnapitae, east of Sudbury. Tyson Lake, at Wahnapitae, east of Sudbury. Ma), but all U-Pb analyses The average age for metadiabase metadiabase is slightly slightly older older (1243 (1243 Ma), analyses lie lie on a discordia whose upper intercept is 1233±4 Ma. In addition, metamorphic zircon intercept is 1233±Ma. metamorphic zircon obtained from two two of of the themetadiabase metadiabasesamples samplesgave gaveages agesofof—1000 -1000 Ma, agreeing agreeing well well with a Nd-Sm metamorphic mineral mineral isochron isochron age age obtained obtained from from the sample 12 12 km from the the front. front. In from In summary, summary, there is little reason to doubt that diabase dykes of the �Sudbury swarm are represented in the the Crenville Grenville Province Province by metadiabase metadiabase preserved preserved as folded dyke segments the area area that that segmentsand and isolated isolatedpods. pods. It is the only rock unit in the records solely the effects of younger Grenvillian deformation and and metamorphism, metamorphism, both adjacenttoto the the front both in the the Southern Southern Province Province adjacent front and within within the the Crenville Grenville orogen. Approaching the front from from the northwest, the dykes dykes are are offset offset by by subsidiary subsidiary faults faults near which which they they may may show show internal internal cataclasis cataclasis and and low-grade low-grade alteration alteration (chlorite, epidote, epidote, fibrous (chlorite, fibrous amphibole amphibole and sericitized sericitized plagioclase). plagioclase). In the the Lake Lake Panache area they swing to a more easterly trend where they cross the Bell Lake Panache area they swing to where they cross the Bell Lake granite granite and turn turn abruptly abruptly northeast northeast at the the main main Crenville Grenville Front Front mylonite mylonite zone zone (Frarey 1985; 1985; Bethune and Davidson Davidson1988; 1988;Bethune Bethune1989, 1989,1993). 1993). Although several several large metadiabase dykes are are present present immediately immediatelyto to the the southeast, large metadiabase dykes southeast, there there is no no match in in the pattern of of dyke sparing spacing on on opposing opposing sides of of this zone. zone. In obvious match In the the Chief Sudbury dykes dykes immediately immediately northwest northwest of of the mylonite Chief Lake Lake complex, complex, Sudbury mylonite zone zone follow irregular courses within fault-bounded fault-bounded panels panels(Davidson (Davidsonand andKetchum Ketchum1993). 1993). Farther northeast, northeast, dykes dykes can can be be traced traced directly directly to to the front, but have have no no potential potential counterparts counterparts in in the theGrenville Grenville hangingwall. hangingwall. In all all of of these these localities, localities, an important important and consistent consistent observation observation is that that Sudbury dykes within fault-bounded panels adjacent to the front frontfault-bounded panels front cut cut across across frontfabrics in in their host rocks; shear-sense indicators, particularly parallel mylonitic fabrics particularly in in the Chief Lake complex, imply penetrative penetrative northwest-directed thrust complex, imply thrust displacement. displacement. mylonitization is is strongly strongly developed Since this pre-1235-Ma pre-1235-Ma mylonitization developed in inthe the1.46-Ma-granitic 1.46-Ma-granitic rocks, deformation deformation must must have have been been active active along along the the Grenville Grenville Front Front in in the interval rocks, is possible between granite emplacement and dyke intrusion. It between granite emplacement and dyke intrusion. possible that this this metamorphism within within the adjacent -1.45-Ga metamorphism adjacent Grenville Grenville deformation is related to to the the—1.45-Ga orogen. Whatever Whatever the the age age of of deformation, deformation, the dykes' dykes' host host rocks rocks are are likely likely to to have have cooled suitable for for ductile ductile deformation deformation to those cooled from conditions conditions suitable those cool cool and and stable stable enough for emplacement of of a typical continental mafic dyke swarm. swarm. In the the Tyson Tyson Lake Lake area close to Georgian Georgian Bay, Bay, Sudbury metadiabase metadiabase dykes dykes display a remarkable progressive progressive change change in in structural structural style and metamorphism over over several kilometres kilometres as as they they are are traced into several into the the Grenville Grenville Province Province (Bethune (Bethune and Davidson 1988; 1988; Bethune Bethune 1989, 1989, 1993). 1993). Conditions of of metamorphism derived derived from from garnet-pyroxene assemblages within 6 km of of the the front frontare areestimated estimatedatat—6.5 -6.5 kbar and and 690°C, increasing southeastward to —7.7 kbar and a similar temperature at a distance 690°Cincreasing southeastward to -7.7 kbar and a similar temperature at of 16 from the front atatdepth) of 16 km krn (perhaps (perhaps 12 12 km km orthogonally. orthogonally. from depth)(Bethune (Bethune1993). 1993). similar change change is is evident evident in in metadiabase dykes southeast of of the Closer to Sudbury, a similar Chief Lake Lake granite granite complex, complex,where wherethe thefront frontisisalso alsomarked marked by by mylonites mylonites in in aa zone zone at at Chief In the Wahnapitae Wahnapitae area, however, however, contrasting contrasting with the least aa kilometre kilometre thick. thick. In situation recorded situation recorded farther southwest, southwest, Sudbury dykes in the the Crenville GrenvilleProvince Province as as little as 400 m from the front are represented by misoriented and dismembered little 400 front are represented by misoriented and dismembered metadiabase dyke dyke segments, in places arcuate, whose metadiabase segments, in whose sides sides commonly commonly preserve preserve chilled contacts cutting cutting across acrossgneissic gneissicfoliation foliationinintheir their host host rocks, rocks, but but whose ends chilled mobilized by by ductile ductile flow. flow. Dyke are truncated by gneiss mobilized Dyke segments segments are are cut cut by by coarse coarse pegmatite, near which which the the diabase diabase is is hydrated hydrated to coarse biotite biotite amphibolite. amphibolite. Where Where not hydrated, hydrated, itit contains contains metamorphic metamorphic garnet, garnet, clinoproxene clinoproxene and and orthopyroxene orthopyroxene with typical coronitic structure around former olivine and Fe-Ti with typical coronitic structure around former and Fe-Ti oxide oxide grains. grains. �13 Coronitic metadiabase metadiabase commonly commonly contains twisted laths of of relict relict plagioclase plagioclase whose whose Coronitic cores cores are are densely densely clouded clouded with with spinel spinel dust. dust. Farther Farther southwest, southwest, similar similar structural structural and metamorphic metamorphic features features are not attained attained until until at atleast least15 15km km southeast southeast of of the the front front and (Bethune 1993). 1993). A A remarkable remarkable variation on the the theme theme of of Sudbury Sudburydyke dykepreservation preservation (Bethune in the the Crenville Grenville Province Province is is offered offered by by the theoccurrence occurrence ofofnon-deformed non-deformed yet yet in thoroughly metamorphosed metamorphosed dykes in the theWanapitei Wanapitei mafic maficcomplex, complex, mentioned mentioned thoroughly previously, for which more detailed detailed information informationisisgiven given atat the the end of previously, for which more of this this guidebook. guidebook. Field trip trip summary summary Field This This field trip trip is is designed designed to to allow allowevaluation evaluationof of both bothaspects aspectsof ofthe theGrenville Grenville Front including the the truncation truncation of of the mylonite Front discussed discussed above, above, including mylonite zone zone by by the the Murray-Wanapitei fault, and to demonstrate Murray-Wanapitei fault, demonstrate the the dilemma dilemma concerning concerningcorrelation correlation of of metasedimentary metasedimentary gneiss in the Grenville Grenville Province Province with the the Huronian HuronianSupergroup. Supergroup. The geology in in the field trip area are 3, on on The main elements of the geology are illustrated illustrated in inFigure Figure3, which the the first first seven seven stops stops are areidentified. identified. In In the the morning, morning, the the first first three three stops stopswill will which examine rocks in the Southern Southern Province near the the Grenville Grenville Front, but but unaffected unaffected by by Grenvillian tectonism.Next Nextwill willcome comeaa stop stop to to look Grenvillian tectonism. look at the the highly highly deformed deformed equivalents footwall of of the theGrenville GrenvilleFront Front equivalents of some of these these rocks in the the immediate immediate footwall on Highway by a short traverse Highway 69, followed followed by traverse across across the the highly highly deformed deformed contact contact between quartzite and and Chief Chief Lake Lake granite granite lying structurally beneath between Mississagi Mississagi quartzite beneath mylonite and ultramylonite that are typical of the Grenville Front south of of Sudbury. This will be followed by stops on pelitic politic gneiss, quartzite and and mafic mafic rock rock near near the the southeastern southeastern edge edge of of the theGrenville GrenvilleFront Frontmylonite mylonitezone. zone. In be examined examinedwhere where In the the afternoon, afternoon, the the Grenville Grenville Front Front mylonite mylonite zone will will be itit isis truncated truncated by bythe theMurray-Wanapitei Murray-Wanapitei fault fault south southof of Coniston, Coniston,just justeast eastofofAlice Alice Lake. This will be followed by a traverse across the Grenville Front near the Stinson traverse across the Grenville Front near the Stinson This will be followed hydroelectric hydroelectric plant during during which which aa tectonic tectonicslice slice of of possible possible Archean Archean basement basement will will be seen, south of which metasedimentary rocks derived in part from conglomerate seen, south of which metasedimentary in part from conglomerate contrast strongly with the Mississagi Formationon onthe the north north side side of of the front. The Mississagi Formation The last stop visits spectacular outcrops of kyanite gneiss showing evidence for extreme stop visits spectacular kyanite gneiss evidence for extreme ductility ductility and and enclosing enclosing segments segments of highly highly metamorphosed metamorphosedSudbury Sudburydliabase diabasedykes. dykes. The road log induded in the following section is intended for those who for those who wish wish included in the following section run the the field field trip trip on on their their own. own. It It gives cumulative cumulative distances distances in inkilometres kilometres to run between each stop in the left hand column, and a cumulative cumulative log for the whole whole trip trip - this guidebook guidebook should should be sure to the right right hand hand column. column. Persons following following this to in the obtain obtain permission permission from owners of private land land for for stops stops22 to to66inclusive. inclusive. �/ /,&nis gnei in GreniIle Provthce (SE of GFMZ and Wanapitei fault) Southern Province: yI% antldine syncline Sudburydiaba ft Daisy L granodiorite Nipiing gabbro Miissagi Formation (fadng dired ion indite Pecors Formation Ramy L Formation Mokirn Formation A. Figure 3. A. Geology of the Grenville Front southeast of Sudbury; GFMZ is the Grenville Front mylonite zone. Locations of stojv 1 —7 are indicated by circled numbers. B. Regional setting; triangles in Lake Nipissing are alkaline corn plexes associated with Neoproterozoic rifting. Box shows area of A. �ROAD LOG AND STOP STOP DESCRIPTIONS DESCRIPTIONS km rum. cum.km km 0.0 0.0 0.0 Proceed southfrom from Sudbury Sudbury to to the Proceed south the intersection intersection oof f Paris and and Regent streets (Four Regent streets (Four Corners), Corners), and set set odometer odometer to zero. zero. Turn Turn 3.4 3.4 10.2 10.2 10.2 10.2 left (east) on Regent Regent Street Street (old (old Highway Highway 69). 69). Take the ramp ramp just just after and go go east Take the after the the underpass, underpass, and east on the the Sudbury bypass Outcrops along along the roadside 17E). Outcrops roadside for bypass (Highway (Highway 17E). the next 33 km krn are areNipissing Nipissinggabbro, gabbro, and and beyond beyond this, this, Mississagi Mississagi sandstone which dips dips steeply sandstone which steeply south south and isis overturned. overturned. right shoulder shoulder at at aadark darkoutcrop outcropofofmassive massiverock. rock. Stop on on the right Stop 1. Mississagi sandstone, Nipissing Nipissing gabbro gabbroand and Sudbury Sudbuiy diabase This stop lies within the Southern Province 900 900 m m northwest northwest of of the Murray fault, This 3 km km west-southwest west-southwest ofof where where this this fault truncates the Crenville truncates Grenville Front Front mylonite mylonite zone; from the the Grenville GrenvilleFront. Front. Here a southeast-trending, zone; it is only two kilornetres kilometres from vertical, 65-m-thick 65-rn-thickolivine olivine diabase diabase dyke dyke of of the 1235-Ma Sudbury swarm swarm cuts vertical, 1235-Ma Sudbury cuts across across Formation (south (south side of the road) the contact between sandstone of the Mississagi Mississagi Formation road) and Nipissing metagabbro (north side). The of the The sandstone sandstone exposed here is typical of quartz-rich and lighter in colour upper part part of of the the Mississagi, Mississagi, being somewhat more quartz-rich colour than in the lower lower part of of the the formation. formation. Cross-bedding Cross-bedding in the the sandstone sandstone indicates indicates we are on the southeast limb of that the steeply dipping beds face face north-northwest; north-northwest; we syncline, illustrated illustrated in Figure 3). The the Coniston syncline, The Nipissing metagabbro metagabbro is is massive massive secondary green green amphibole, amphibole, epidote epidote and chlorite. but metamorphosed, containing secondary chlorite. This assemblageisis typical typical of of Nipissing Nipissing gabbro gabbro throughout throughout the This metamorphic metamorphic assemblage Southern Province Provinceand anddoes doesnot not appear appear to to be be aa function of proximity to the Southern function of proximity to Grenville Front, Front, aa conclusion corroborated by by the the fact Grenville conclusion corroborated fact that the the pre-Grenvillian pre-Grenvillian Sudbury diabase cuts itit is is not not metamorphosed. metamorphosed. diabase which cuts The Sudbury Sudbury olivine olivine diabase diabase exposed exposed at at this this stop illustrates the pristine The pristine of cataclased adjacent to to the Grenville Grenville Front, Front, which which we we will will see see at protolith of cataclased diabase adjacent Stop 8, and of equivalent equivalent coronitic metadiabase in the Grenville Province, to be seen seen 9. The all but but exposed exposed on on the the south side at Stop 9. The Sudbury Sudbury dyke's northeast contact is all of the road, and of and must must have have been been excavated excavated during during road road construction, construction, as as blocks blocks its chilled chilled contact contact with with Miissagi Mississagisandstone sandstonecan canbe befound found at at the the roadside. containing its Close to this contact the diabase is fine grained grained and contains xenocrysts of of plagioclase plagiodase which in turn turninclude includeearlier-crystallized earlier-crystallizedolivine olivinecrystals crystals— - a common feature near which the margins of Sudbury dykes. dykes. In Inthin thinsection, section, there there is is no no evidence evidence whatsoever whatsoever for for reaction between between these these two two minerals minerals at at this this location location (it is principally metamorphic reaction this reaction which gives gives rise rise to the garnet reaction which garnet and and secondary secondary pyroxenes pyroxenes present in metamorphosed olivine olivine diabase). diabase). In the same same dyke on the southeast southeast side of of the the Murray fault and closer closer to to the the Grenville Grenville front, front, however, however, the plagioclase plagioclase xenocrysts xenocrysts become clouded with with fine fine epidote, epidote, and rims become clouded rims of of fine fine actinolite actinolite appear appear between between olivine and plagioclase. plagioclase. This This particular particular dyke dyke cannot cannot be traced across across the the Grenville Grenville �Front fault, Front fault, but where where Sudbury Sudbury dykes have have been been identified identified in in the the immediate immediate hangingwall of of the front, of front, olivine olivine in plagioclase plagioclase xenocrysts has reaction coronas of pale orthopyroxene with outer rims of pargasite-spinel symplectite, and Fe-Ti oxide orthopyroxene outer rims of pargasite-spinel symplectite, and Fe-Ti oxide grains are surrounded vicinity of the surrounded by by Ti-biotite Ti-biotite and and garnet garnetsymplectite. syrnplectite. In the vicinity Grenville Front 50 50 km km to to the southwest, Sudbury dykes cut across across and are are chilled chilled Grenville Front against a pre-existing mylonitic mylonitic fabric fabricthat that isis developed developed in in granitoid granitoid rocks rocks as young as 1470 Ma Ma (Bethune 1989; 1989;Davidson Davidson and and Ketchum 1993), pointing to the existence 1993), pointing existence of some kind of of pre-Crenvillian pre-Grenvillian tectonic front roughly coincident with the the Grenville Grenville In this regard it is pertinent that, sensu stricto. stricto. In that, in in the the hangingwall hangingwall within a Front sensu few kilometres of al. of the front, front, metamorphic metamorphic monazite monazite in in pelitic politic gneiss gneiss (Dudas (Dudasetet al. 1994) and and zircon from pegmatitic 1994) pegmatitic leucosomes leucosomes(Krogh (Krogh1994) 1994) record recordan anage ageofof—1445 -1445 Ma. Ma. km 0.0 5.8 5.8 65 6.5 cum.k,n CUM.^ 93 9.3 19.5 19.5 9.7 19.9 10.2 16.0 16.7 Turn around around and and return to tothe theinterchange. interchange. Take thefirst first exit exit ramp ramp to the Take the the right. right. light, turn At At the the traffic light, turn left left on on Highway Highway 69, 69, and and proceed proceed through the the next through next traffic traffic light. light. Turn right right at at the theintersection intersection with with Poitvin Poitvin Road Road and and follow follow itit round round to the the left. left. Park on the before rejoining rejoining Highway Highway 69. 69. Park the shoulder shoulder just before 2. Slaty argillite, argihite, Pecors Formation, Formation, and and "trap "hap dyke" Stop 2. Stop This stop stop and the This the next next illustrate illustrate rock types of of the the two two formations, formations, Pecors and Ramsey Lake, Lake, that that precede precede the the Mississagi Mississagi in in the Huronian stratigraphic Ramsey stratigraphic succession. succession. Both are well exposed in the City of Sudbury along the north shore and west of Both are well exposed in the City of Sudbury along the north shore Ramsey Lake, Lake,where wherethey theylie lienorth northofof the the Creighton Creighton fault fault (Fig. (Fig.3). 3). Here, Here, most of of the Ramsey low-lying area around Richard and MacFarlane lakes lakes is is devoid of of outcrop, although it is shown shown as as underlain underlain by by Mississagi Mississagi Formation on the most most recent recent compilation compilation of 1984)and andon on the the regional regional map map that preceded Sudbury geology (DressIer (Dressier 1984) preceded itit (Lumbers (Lumbers and Card 1977). The surrounding hills are underlain underlain by by Mississagi Mississagi sandstone or Card1977). in aa few fewplaces places Nipissing diabase, but sparse exposures at the the base base of of these these hills, and and in in the valley, valley, are of of sedimentary sedimentary rocks rocks that are are not not typical typical of of the theMississagi Mississagi Formation. This This was was recognized long ago by Collins (1936) who assigned recognized long by Collins (1936) assigned conglomerate that that crops crops out out along along the north side conglomerate side of of Richard Richard Lake Lake to to the the Ramsey Ramsey Lake Formation, which will be seen at the next stop. stop. At this stop, outcrop on the bill hill to the south south is is well-bedded well-bedded sandstone of the Mississagi Formation,but butatat the the base base of of the the slope slope a few metres of of grey argililte Mississagi Formation, argillite are exposed. Similar Similar exposures occur along the south side side of the the Richard Lake valley to the east. South Southof of MacFarlane MacFarlane Lake, Lake, to the southwest, southwest, argillaceous rocks in the same stratigraphic position beneath the stratigraphic the Mississagi Mississagi are represented represented by by fine finemicaceous micaceous schist schist of altered altered staurolite staurolite and andalusite; this higher grade of with small porphyroblasts of of metamorphism is is apparently associated associated with with a number of metamorphism of nearby nearby small small intrusions intrusions �17 of granodiorite and granite dated at Ma. Low Lowoutcrops outcropsaround around the east end of of at —1745 -1745 Ma. MacFarlane Lake Lakeexpose exposerocks rocksthat that are are stratigraphically stratigraphically lower lower than the argillaceous MacFarlane argillaceous rocks immediately immediately beneath beneath the the Mississagi MississagiFormation. Formation. These These are are of of fine fine wacke wacke and rocks siltstone which which have have aa greensish greensish hue hue and lack siltstone lack the the thin, thin, rusty-weathering, rusty-weathering, shaly shaly so typical typical of of the the Mississagi. Mississagi. What What is more, more, they preserve graded bedding interbeds so and and elements elements of of Bouma Bouma cycle cycle sedimentation, sedimentation, suggesting suggesting aa depositional environment altogether different different from from that that which produced environment altogether produced the the cross-bedded cross-bedded Mississagi sandstone. Taken sub-Mississagi sedimentary rocks match Mississagi sandstone. Taken together, these these sub-Mississagi of the Pecors Pecors Formation Formationin in its its type type area area and, given their stratigraphic those of stratigraphic position, position, should be assigned to to this this formation. formation. At this stop, an added feature feature is is the the presence presence of a fine-grained, fine-grained, greenish grey, diabase. Several altered diabase. Several narrow dykes of this this swarm, swarm, known as as "trap "trap dykes", dykes", trend trend east-west in this area. They They have not been dated, dated, but but are are known knownto tocut cut"offset "offset dykes" dykes" of the 1850-Ma Sudbury Intrusive Intrusive Complex, Complex,and and to to be cut by the the 1235-Ma 1235-Ma Sudbury of 1850-Ma Sudbury swarm. These Thesedykes dykesare arenot, not, therefore, therefore, related related to toNipissing Nipissinggabbro. gabbro. cum. km km cum. km get into into the right lane. left on on Highway Highway 69,; 69,;immediately immediately get lane. 19.9 Turn left 19.9 20.2 2 0.2 Turn right. right. At sharp 20.5 2 0.5 At sharp left-hand left-hand bend, bend, go go straight straight into into parking parking area area by by Walk Richard Lake Lake Homecare Hoinecare Building Building Centre Centre and and park. Richard park. Walk 0.0 0 .0 0.3 03 0.6 0.6 ahead throughgate, gate,and andgo go to to outcrop outcrop on on hill hill to to the left ahead through left of of the the buildings. buildings. Ramsey Lake Lake formation formation Stop 3. Polymictic conglomerate, Ramsey At this stop, stop, grey, grey, ill-sorted ill-sorted wacke supports sparse sparse pebbles pebbles and and cobbles, cobbles, some some of of granitoid rock; rock; aa few few are are of of boulder-size. boulder-size. Look granitoid Look for small, bluish grains of quartz, quartz, which typify much much of of the the Ramsey RamseyLake Lakeconglomerate conglomerateininits itstype typearea. area. Bedding dips southward, but but is poorly southward, poorly developed developed and facing facing direction direction cannot cannot be determined. determined. and quartz wacke are exposed exposed in a few places closest dosest to to the the Argillite and to Richard Richard Lake Lake to east, and are are similar similar to to the therocks rocks at atthe theeast eastend endofofMaciFarlane MacFarlane Lake, Lake, assigned assigned above above Pecors — Mississagi to the Mississagi from the Pecors Pecors Formation. Formation. The Thesuccession successionRamsey RamseyLake Lake—- Pecors north to to south south across across the the valley valley is is in in accord accord with with aahomoclinal homoclinal succession, succession, although although it is possible that faults and folds are concealed beneath the valley floor. of low hills hills along along the north shore of Richard The line of Richard Lake, all underlain by conglomerate, separatedfrom fromthe thehigher higherridge ridgeto to the the north north by by a strip in conglomerate, isisseparated in which which which conceals concealsthe theMurray Murrayfault. fault. The ridge is underlain by there is no outcrop, and which sandstone which faces north, north, being the same subvertical strata of of Mississagi Mississagi sandstone same limb limb of of facing on on opposite opposite side of the 1. Sedimentary Sedimentary facing the the Coniston syncline syncline as at Stop Stop 1. Murray fault fault is thus thefault fault occupies occupieswhat what may may be be a breached Murray thus "back-to-back"; "back-to-back"; the breached anticline, and and has has a net north-side-down north-side-down displacement. displacement. To the west, anticline, west, however, however, the Murray fault fault truncates fault, west Murray truncates aa north-trending north-trending fault, west of of which which the the Mississagi Mississagi Formation occupies occupies the the south south side side of of the fault and is Formation is also also north-facing. north-facing. �km cum.km km cum.km 0.0 20.5 20.5 0.3 20.8 03 20.8 2.1 2.1 22.6 33 23.8 3.3 Turn around around and and go go back back to to Highway Highway 69. 69. Turn left on Highway Turn left Highway 69. 69. Roadcuts here expose steeply inclined Mississagi Mississagi Formation. Formation. here expose steeply inclined the right Just after after the end end of of the the roadcut roadcut on on the the right, right, park park on on the at swampy swampy valley. valley. Please note that that this thisisisaavery verybusy busy highway highway with w i t h fast-moving traffic; traffic; travelling south south must must merge mergeinto into one one lane lane aatt this ttwo w o lanes of vehicles travelling this point after extreme caution; point after coming coming round round aa blind blind corner. comer. Exercise Exercise extreme keep an eye eye on on traffic traffic and and other other participants, participants, and do not step back onto keep an onto the roadway roadway when when taking taking photographs. photographs. 4. The Stop 4. The Grenville GrenvilleFront Frontat atHighway Highway69 69 Figure 4 gives some some details details of of the the geology geologyat at this thislocation. location. Looking to the the west west from from Highway 69 69 at this stop, Highway stop, mylonite mylonite and ultramylonite ultramylonite marking the Grenviile Grenville Front Front are well exposed along the south side of the broad swamp; swamp; mylonitic mylonitic foliation foliation dips dips thesoutheast southeastand and contains contains numerous numerous shear-sense shear-sense indicators of northwest-—35° 3 5 O totothe northwestdirected thrust displacement. passes through through the low point in the displacement. The front passes the skyline skyline to the left of of the island in the swamp. swamp. The The island island and the high high part part of of the the hill hill behind it are underlain by coarse granite of the Chief Lake complex, continuous are underlain by coarse granite of the Chief Lake complex, continuous in in krn to the the southwest southwest where where aa U-Pb U-Pb zircon zircon age ageof of1465 1465Ma Ma outcrop with aa locality locality 77 km was recently determined determined (Davidson (Davidson et et a!. al. 1992). 1992). Mississagi sandstone is is in in contact contact with the granite on with on the the right right (north) (north) flank flank of of this this hill. hill. The contact dips dips steeply steeply south-side-up sense, sense, but but the displacement is south and is is the the locus locus of of shearing with south-side-up Mississagi Formation north north probably not great, as dykes dykes of granite are present in the Mississagi of The ridge ridge to the right of the contact. contact. The right of of the the swamp swamp is is Nipissing Nipissing gabbro, gabbro, and and Mississagi Formation is exposed sporadically along the lower lower slope. slope. Walk north on the Walk the west west side side of of Highway Highway 69 69 to examine examine aa small, small, duplex-like duplex-like structure in Mississagi exposed in in the the roadcut structure Mississagi sandstone sandstone exposed roadcut beneath beneath Nipissing Nipissing metagabbro. Metamorphic is greenschist greenschist facies; fades; the metagabbro contains contains metagabbro. Metamorphicgrade grade here here is the assemblage assemblagealbite-chlorite-epidote-actinolite. albite-chlorite-epidote-actinolite. Cross the the highway highway when when traffic trafficpermits permitsand and walk walk back back to to the nearest point Cross where the ditch can be crossed to have have access accessto to outcrop outcrop on on the the south side of where of the the of the highway. The the Chief Chief Lake swamp east of The first first outcrop is deformed granite of the complex. Continue along the edge of of the the swamp swamp to to the the higher, higher, bare bare outcrop beyond; complex. beyond; Mississagisandstone sandstoneand and the the granite, granite, both intensely deformed, the contact between Mississagi deformed, finely laminated laminated nature of is exposed exposed here. here. Note the the extremely extremely finely of the theMississagi Mississagi quartzite, locally thrown into small small box boxfolds. folds. These rocks rocks are quartz mylonite; is it possible that that the laminae represent extremelyattenuated attenuatedbedding? bedding? The possible represent extremely The overlying overlying Chief Lake Lake granite granite is is strongly strongly foliated foliated with with aa consistent consistentsoutheasterly southeasterly dip dip of 3 35° and a 5' and Chief pronounced dip-parallel lineation. lineation. It has undergone principally brittle deformation, deformation, but with with ductile ductile flattening flattening of of its its quartz quartz content. content. Thin sections show show cataclasis cataclasis of feldspar quartz with highly feldspar and thin, thin, sinuous sinuous laminae laminae of finely finely polycrystalline polycrystalline quartz highly �19 A p4 S p. 44 4 / 4 / 1' 200m Sketch map of the the geology geology at the the GrenvÜle Grenville Front, Highway Highway 69. 69. The arrow arrow Figure 4. Sketch shows the location of the small duplex in the Mississagi Formation immediately shows the location of the small duplex in the Mississagi Formation immediately line indicates indicates the the traverse traverse described described in in the second of the the front. front. The The black black line second part north of of this stop. stop. of neoblasts of of chlorite, chlorite, pale pale green Fine interstitial interstitial neoblasts green biotite, biotite, orientation. Fine preferred orientation. epidote, microcline and albite attest to low-grade metamorphism overprinting epidote, microcline and albite attest to low-grade metamorphism overprinting deformation features. The exposed on on this this ridge ridge are considered to be in in the the deformation features. The rocks rocks exposed immediate footwall of what Lumbers (1975) referred to as the "Crenville Front "Grenville immediate footwall of Lumbers (1975) referred to as boundary boundary fault" fault" Cross the wooded valley to the south. The The next next ridge ridge of of outcrop outcrop exposes exposes dark dark mylonite that do not appear to have mylonite and ultramylonite ultramylonite that have been been derived derived from from Chief Chief Lake complex complex rocks. rocks. The mylonitic rocks rocks exposed exposedbetween betweenhere here and and the driveway driveway to to the south south are are mainly mainly derived derived from frommafic mafic and andsemi-pelitic semi-pelitic precursors. precursors. Large Large 'porphyroblasts of garnet occur locally in the latter, but despite their euhedral 'porphyroblasts' of garnet occur locally in the latter, euhedral shape, thin sections show that they are porphyrodasts porphyroclasts with late late rim rim overgrowths. overgrowths. Oriented X-Z thin sections also show a pronounced, oblique subgrain orientation in X-Z also show a pronounced, oblique subgrain quartz lamellae, to the northwest. lamellae, indicating indicating thrust-sense displacement to northwest. On the driveway, go west west to Highway 69 and examine examine the the On reaching reaching the driveway, go Highway 69 mylonitized pegmatite for for kinematic kinematicindicators indicatorsininthe thefirst firstroadcut roadcut to to the south on mylonitfzed pegmatite on the east east side side of the the highway. highway. �km km cum.km cum.km 23.8 Continue south south on Highway 23.8 Continue Highway 69. 69. 0.7 24.5 Turn right right on on Gladu Gladu Road. Road. 1.1 24.9 Stop on on the right by 1.1 24.9 Stop by open open grassy grassy area. area. Follow across open open Follow track across area to fairways to outcrop to golf golf course; course; cross cross path path between between fairways outcrop in in area open wooded area. open wooded area. 0.0 0.0 Stop 5.5. Metasedimentary Metasedimentaryrocks rocks in in the Grenville Stop Grenville Province Province margin correlatives Huronian Supergroup? correlatives of the Huronian Supergroup? - — The first outcrops are fine-grained, fine-grained, highly deformed deformed and and grain-comminuted grain-comminutedmafic mafic rock, probably probably ultimately ultimatelyderived derived from from gabbro. gabbro. Beyond rock, Beyond this is a unit of feldspathic feldspathic which shows some quartz metasandstone metasandstone which some remarkably remarkably convolute convolute fold patterns, patterns, followed by by outcrops of muscovite is present present in in this rock, but is followed muscovite schist. schist. Kyanite Kyanite is is colourlessand andhard hard to to identify. identify. Garnet is pale pale and easier easier to to spot. spot. Staurolite colourless Staurolite is also present as small grains. grains. The The metamorphic metamorphic grade grade recorded recorded by the pelitic schist at this outcrop, m on on the ground from outcrop, a mere 900 900 m from the the northwest northwest margin margin of of the the Grenville Grenville Front mylonite zone and perhaps only 500 m perpendicularly, is clearly Front mylonite zone and perhaps 500 perpendicularly, clearly much much facies) than than that in the higher (middle amphibolite facies) the Southern Southern Province Province immediately immediately across the the front. front. A of the the Pecors Pecors across A comparable comparable parent rock would be the shaly part of Formation (seen (seen at at Stop 2), 21, which which itself itself has hasdeveloped developed andalusite-staurolite andalusite-staurolite Formation assemblagesin in nearby nearby parts parts of of the the Southern Province. Province. The assemblages The presence of kyanite at at this locality indicates aa distinctly distinctly higher higher pressure pressure than than that that recorded this locality indicates recorded by the the andalusite-bearing knotted knotted schists in the the the thePecors Pecors Formation. Formation. In fact this schist records a complex kyanite and and staurolite staurolite are partly complex metamorphic metamorphic history. history. Early Early kyanite replaced by phengitic mica mica and margarite, and spongy garnet cores cores have secondary secondary overgrowths containing staurolite inclusions. P-T estimate estimate on the the younger younger overgrowths inclusions. A P-T assemblage, obtained obtained by by D.M. D.M. Carmichael, Carmichael, Queen's Queen's University, University, isis 77 kbar at 670°C, assemblage, S670°C "... the evidence of of earlier and "... the garnet garnet core core inclusion inclusion assemblage assemblage ... ... gives gives evidence earlier equilibration at about 4 kbar." 1991). As documented by La kbar." (Davidson (Davidson et a!. at. 1991). La Tour Tour equilibration (1981),the theapparent apparentgradient gradientacross acrossthe thefront frontisis too too steep steep to to be be anything (19811, anything but tectonically telescoped, telescoped, particularly particularly if if the paleoisotherms paleoisotherms are are inclined. inclined. At a locality 1994), approximately 2 km locality 1.2 1.2 km to to the the southeast southeast(Davidson (Davidson 1994), km from Front and and well beyond from the Grenville Grenville Front beyond the the zone zone of of intense intenseinylonitization mylonitization defining the front in this area, area, metasedimentary metasedimentary rocks rocks include include pelitic gneiss, quartzquartzgneiss, and and a thin, discontinuous gneiss. These rich feldspathic gneiss, discontinuous layer layer of calc-silicate calc-silicate gneiss. These are interlayered with thick are interlayered with thick units of of coarse coarse garnet garnet amphibolite amphibolite and gedritegedritehornblende gneiss of uncertain Association of of both both kyanite and uncertain origin. origin. Association and sillimanite sillimanite were reported reported to occur in this with K-feldspar K-feldspar were this area area by by Kwak Kwak (1968), (1968), although the prevalent assemblage assemblage iii in pelitic gneiss gneiss here here isisquartz-plagioclase-biotite-muscovitequartz-plagioclase-biotite-muscovitegarnet-kyanite-sillimanite; stauroliteisisabsent. absent. A garnet-kyanite-sillimanite; staurolite A P-T P-T estimate estimate obtained obtained by byD.M. D.M. Carmichael is —8 kbarat at 710° 71 0°C(Davidson (Davidsonetetal.a!.1991). 1991).The Theisograd isogradmarking marking the the first -8 kbar appearance of of sillimanite sillimanite (which (which here here texturally texturally overprints overprints kyanite), kyanite), trends trends northnorthwest toward the Wanapitei northwest toward Wanapitei fault segment segment of the the Grenville Grenville Front Front between between �21 Coniston Coniston and and Wahnapitae Wahnapitae village village(Stop (Stop7). 7). A feature of o f the the pelitic pelitic gneiss gneiss in i n this this vicinity is ( u p to to II) 10 vicinity is the occurrence occurrence within within itit of of quartz quartz pods pods with coarse blue kyanite (up cm) and minor garnet. km km cum.km cum. km 0.0 Return to Gladu 0.0 24.9 Return Gladu Road Road and Highway Highway 69, and and retrace retrace route route back back 6.9 31.8 18.5 43.4 24.1 49.0 26.5 50.4 27.6 51.5 toward Sudbury. toward Sudbury. At turn left At traffic traffic light light just just before before overpass, overpass, turn left onto onto ramp ramp for for Sudbury bypass Beyond Stop Stop 1, 1, note 17E). Beyond Sudbury bypass (Highway (Highway 17E). note that that bedding in the bedding the Mississagi Mississagi Formation Formation changes changes dip dip direction direction from from northwest northwest to south as as one onecrosses crosses the theConiston Coniston syncline. syncline. The big big roadcuts on the roadcuts on the hills hills after after the the long long left-hand left-hand curve curve The expose spectacular spectacular examples expose examples of of shatter-cones shatter-cones related related to the the impact that that caused impact caused the Sudbury structure. Take right lane lane at at traffic 17., Take right traffic light light and and go go east east on on Highway Highway 17., two defunct of Coniston passing by passing by the town of Coniston with its its two defunct The barren barren blackened rocksininthis this area area are are the smokestacks. smokestacks. The blackened rocks the èevere erosion, of vegetation result of vegetation kül, kill, subsequent severe erosion, and staining by fumes fumes from from this this former former smelter. smelter. staining by Turn right on the road to Turn to the Coniston hydroelectric road, crossing generating station. Keep on main generating station. Keep on main gravel gravel road, crossing railway. railway. Gate at entrance entrance to to ICI ICI explosives explosives plant. plant. Obtain permission permission to drive through drive through the the fenced fenced compound. compound. along the the south south side of End End of of the the road; road; park. park. Walk Walk along of the the valley valley to the the powerline. powerline. Stop 6. Truncation Truncationof of the theGrenville GrenvilleFront Frontmylonite mylonitezone zoneat at Alice Lake Two major faults faults ooff the the Murray Murray fault system in the T w o major the Southern Southern Province Province (Card 1978b), theCreighton Creightonfault faultand andthe the Murray Murray fault fault itself, converge convergeeastward eastward and and meet 1978b), the East-northeast ooff this this juncture, juncture, a narrow valley in just north 5). East-northeast in just northof o fAlice Alice Lake Lake (Fig. (Fig.5). with the Murray Murray fault fault marks marks the the Grenville Crenville Front. Front. North of line with o f this valley valley are wellpreserved sandstonestrata strata and and Nipissing preserved Mississagi Mississagi sandstone Nipissing gabbro at low l o w metamorphic metamorphic grade, and south of gneiss ooff the the Grenville Crenville Province. Province. The o f it, high-grade migmatitic gneiss covered interval interval between between the the two two conceals conceals the the Wanapitei Wanapitei fault, fault, and and iiss as little little as as covered 25 m m wide wide in places places between between Alice Alice Lake Lakeand and the village village ooff Wahnapitae Wahnapitae 66 km km to to the 25 There is is nno evidence tto suggest that the Murray northeast. There o field field evidence o suggest Murray and and Wanapitei Wanapitei faults are not one and the the same, same, contrary contrary to t o published published maps maps of o fthis thisarea area(Lumbers (Lumbers 1975; Dressier1984); 1984);the thetwo twointerpretations interpretations are are illustrated in 1975; Dressier i n Figure Figure 6. 6. The southeast-dipping zone ooff mylonitization which marks marks the Grenville The southeast-dipping zone mylonitization which Grenville Front ttoo the southwest Front southwest converges converges with the the Murray-Wanapitei Murray-Wanapitei fault fault at at Alice Alice Lake. Lake. �22 Figure 55 The The juncture juncture between between the the Grenville Grenville Front Frontmylonite mylonitezone zone and and the theMurrayMurrayFigure Wanapitei Wanapitei fault south southofofConiston. Coniston. Four Four elements elements of of the theCrenvile GrenvilleFront Frontmylonite mylonitezone zone also alsoconverge convergeatatthis thisjuncture; juncture; fromnorthwest northwesttotosoutheast southeastthese theseare: are: from 1) highly highly attenuated attenuatedHuronian Huronianmetasedimentary metasedimentary rocks, rocks, mainly mainlyMississagi Mississagi 1) Formation Nipissingmetagabbro, metagabbro,and andprotomylonitic protomylonitic Formation like like that thatseen seenatatStop Stop1,1,Nipissing �23 granitoid rocks rocksofofboth boththe theDaisy DaisyLake Lake (7-1.75 Ga) Ga)and andChief ChiefLake Lake(—1.46 (-1.46 Ga) Ga) granitoid (?—1.75 plutonic units; units; 2) migmatitic migmatiticgranitoid granitoidorthogneiss orthogneiss of unknown unknown affinity; affinity; 3) metasedimerttary metasedimentarygneiss gneiss and and schist, schist, induding includingmicaceous micaceouskyanite-bearing kyanite-bearingschists schists 3) like that that seen seen at atStop Stop5; 5; 4) Migmatitic with mafic layers layers and and pods. 4) Migmatitic quartzofeldspathic quartzofeldspathic gneiss with pods. of these elements is separated separated by by aa relatively narrow narrow (a few metres), southeastEach of dipping zone zone of of mylonite mylonite and ultramylonite carrying thrust-sense indicators. These These intense mylonite zones, themselves included within within the overall intense themselves included overall Grenville Grenville Front Front mylonite from their their truncation Murraymylonite zone, zone, diverge diverge southwestward southwestward from truncation by by the theMurrayWanapitei fault the Grenville Crenville Front itself fault (La (LaTour Tour1981). 1981). Conventionally, Conventionally, the itself is is designated as the themylonite mylonitemarking marking the the southeastern southeasternlimit limit of of recognizable recognizableSouthern Southern designated as Province rocks rocks (Grenville (Grenville Front boundary boundary fault faultof of Lumbers Lumbers1975). 1975). interpretations in in the Coniston Coniston area. area. Figure 6. 6. Fault interpretations A, after afterLumbers Lumbers (1975); (1975); B, B, modified modified after DressIer Dressier (1984). (1984). �24 this stop, stop, the the granitoid granitoid rocks rocks of of the the Daisy Daisy Lake and Chief Chief Lake Lake plutons At this exposed west of Alice Lake, Lake, have have been been cut out by the Murray-Wanapitei fault, so that only the Mississagi Mississagi and Nipissing Nipissing units, both both of of which which have have suffered suffered extreme extreme tectonic flattening, represent represent element I1(above). (above). The The migmatitic migmatitic granitoid granitoid of of tectonic flattening, element 22 is also missing, although itit may may be be represented in the pink mylonite missing, although represented in mylonite element structurally above 1. structurally above element element 1. After examining the outcrops close to Alice Alice Lake, Lake,climb climbthe thehill hill to to the the east east to gneiss of of element element 4, 4, noting noting shear see the nature of of the the heterogeneous heterogeneous migmatitic migmatitic gneiss sense in in the underlying mylonite, sense mylonite, and the ductile ductile style of deformation, deformation, including sheath folds, folds, in in the gneiss above. above. Thin sheath Thin units units of of pelitic politic gneiss gneiss are are present present locally locally within this unit. between the migmatitic quartzowithin unit. There There is some some resemblance resemblance between quartzofeldspathic gneiss seen seen here and migmatitic granitoid granitoid at Stop 8, several several kilometres to the northeast, but there there is is no no continuity continuityin inoutcrop. outcrop. 0.0 1.8 1.8 51.5 51.5 53,3 533 Return through compound. compound. Park on the the right right just justbeyond beyond the therailway railway crossing. crossing. Stop 7. Comparison on opposite opposite Comparison of Southern Southern and and Grenville Grenville Province rocks on Coniston hydroelectric hydroelectric dam dam sides of the Wanapitei fault near the Coniston This outcrop outcrop shows shows similar similarfeatures featurestotothose thoseininelement element44atatthe the last last stop, stop, and This includes narrow narrow mylonite mylonite zones zones that diverge includes diverge southwestward southwestward from the the MurrayMurrayWanapitei fault line. state of of the Wanapitei line. The The remarkably remarkably well-preserved well-preserved state the Mississagi Mississagi sandstone north of sandstone north of the fault fault can can be be examined examined on the hillside north of of the the valley, valley, where cross-bedding cross-bedding shows shows that that the succession facesnorthwest, northwest, away away from from the where succession faces Wanapitei fault. fault. To the southeast, the dark high ground ground on on the the other other side side of of the theWartapitei Wanapitei River and the Coniston plant is is underlain Coniston hydroelectric hydroelectric plant underlain by predominantly mafic mafic River and rocks of of the the Wanapitei Wanapitei complex. complex. There There is is not not time timeon onthis this trip trip to to visit this 3 x 8 k km m rocks body of of rock, whose northern contact Field work has body contact is only only 500 500 m from here. here. Field shown that this complex is not not an in situ but in fact shown that complex is situ intrusion intrusion but fact aa huge huge tectonic tectonic 1992). remnant wrapped by by aa carapace carapaceof of ductile ductilegneiss gneiss (Davidson (Davidson and andKetchum Ketchum1992). This topic topic is elaborated in the notes This notes that that follow follow the the stop stop descriptions. descriptions. Suffice it to gneiss with with garnet garnet and and both both kyanite kyanite and sillimanite say that metasedimentary gneiss sillimanite lies within the valley north of the thefact factthat that this this is less than half the Wanapitei Wanapitei complex; complex; the a kilometre from the low-grade Mississagi Formation Formationexposed exposedat at this this stop attests to to an enormous fault/Grenville Front Front at this this enormous net displacement displacement along the Wanapitei Wanapitei fault/Grenville locale. locale. �25 1.8 53.3 55.1 4.4 57.7 10.7 11.8 64.0 13.2 66.5 0.0 14.0 65.1 67.3 Continue Continue back back to Highway Highway 17. 17. Highway 17, 17, turn right. Highway right. Bridge Bridge over over the the Wanapitei Wanapitei River. River. The The highway highway crosses crosses the the Wanapitei fault and Wanapitei fault and enters enters the the Grenville Grenville Province Province at this point. Railway crossing. Turn keeptoto the the left left at at all Turn left left on on road road to to Stinson Stinson Hydro; Hydro; keep all turnings. At At the the bottom bottom of of the the hill hill after afterpassing passing under undersecond secondpowerline, powerline, take a track to the left, just before the entrance to the take a track the left, just before entrance the parking parking area by the plant (alternatively, park and area the hydroelectric hydroelectric plant (alternatively, park and walk walk along the track). along track). Park and walk the weir over the End End of of track. track. Park walk ahead, ahead, crossing crossing the the Follow instructions under Stop 8, below. river. river. Follow instructions Stop 8, below. 8. Grenville Front relationships relationships near the Stinson Stinson hydroelectric Stop 8. hydroelectricdam; dam; Mississagi Formation, Formation, ultramylonite and cataclasite, metasediMississagi and an mentary gneiss and schist including metaconglomerate, metaconglomerate, and (?)migmatitic migmatitic granite granite slice slicesouth southof ofthe the Grenville Grenville Front Archean (?I This stop requires a walk of about 2 km (Fig. 7) 7) and and will will illustrate illustrate the the abrupt abrupt changes T his stop changes of structural style and metamorphic grade associated associated with with this this part part of the Crenville Grenville Front, here marked marked by by the eastward continuation of the the Wanapitei Wanapitei fault. fault. From Front, here continuation of From the the end of the track track which which leads west from from the the lower lower road to to the the Stinson Stinsonhydroelectric hydroelectric plant, cross the weir over the Wanapitei Wanapitei River River and and follow followthe the track track until until it meets an improved gravel road, where grey sandstone sandstone beds of the the Mississagi Mississagi Formation are are Bedding dips dips steeply steeply northeast, northeast, and exposed on the north side 7). Bedding well exposed side (a (a in inFig. Fig. 7). cross beds indicate that it also faces in that direction, away from the Grenville Grenville Front. Beddingstrikes strikessoutheast southeastatatan an angle angle to to the Bedding the trend trend of of the theWanapitei Wanapitei fault. fault. Metamorphic grade is is clearly clearly low, low, and and there is no evidence of of folding or foliation Metamorphic grade foliation parallel to the nearby fault. fault. weir, but before crossing crossing it, it,go goto tothe theoutcrop outcrop on on the the north bank Return to the weir, (b). Here bedding in the the Mississagi Mississagi Formation Formation has of of the the weir weir (b). of the river east of with the Wanapitei fault, which which lies lies aa short distance to swung toward parallelism parallelism with Wanapitei fault, the south. The Therocks rocksdisplay displayaafoliation foliationand andseveral severalsmall-scale small-scale folds. folds. Cross the weir, walk back back along along the the track, track, and and take take a side-track weir, walk side-track that leads Beforereaching reachingthe thecleared clearedstrip, strip, cut cut to to the left south to to the the powerline powerlineclearing. clearing. Before through open bush toward toward rising rising ground ground below below the the powerline powerline (c). (c). All the outcrop outcrop here is brittle-ductile mylonite mylonite and ultramylonite that has aa grey, grey, closely-fractured closely-fractured surface. Foliation Foliation is is sub-vertical. At Ataalow, low,west-facing west-facing vertical outcrop outcrop face face on on the the side of the hill, small-scale kinematic kinematic indicators indicatorscan canbe beseen seenwith with the the naked eye and and hand-lens that show south-side-up south-side-up sense sense oof displacement This f displacement. This sense sense is is corroborcorroborhand-lens that ated in in oriented oriented thin thin section section by by aaspectacular spectacularC-and-S C-and-S fabric fabric formed formed by by oblique oblique subgrains in in thin quartz layers, by rotated porphyroclasts, and by by back back rotation rotation of of porphyroclasts, and �26 fl.wwwn,wr,wwrrrw,wrr ++++++++++++++++++++++ - - - +++++++++++++++++++ fin +++++++++++++++ U. - '• 'Stinson a a a a Ufl•_ S + .p*-+ + n-+.s+ + + + +! + ++ + + + + + +* + + + + :..... • * * a- -S - S S S S • tt# • S S S SSSqSSS•SS t.-l.a. / S •_S S S SSSS— []] 2 I::: I S ' — 2- .5-S • S S • 500 in 9 Ir.iza4 Sudbury Sudbury diabase diabase t.af #5 — - metasedimentary schist, metasedimentary schist, rnetaconglomerate : rnetacongiornerate mylonite ultramylonite, cataclas!te I''1 granitoid_.— ,'' Iti,',j migmatiticCgranitoid Nipissing Nipissing gabbro g&bm mixed metasedimentary %hl; mixg m amphiblite e t a ~ d i m e m ~, amphibolite schist, Mississagi Fm Mississagi Fm plagioclase gneiss garnet-hornblende plag~cclase Figure 7. Geological relationships Front near Figure 7. Geological relationships at the Grenvifle Grenville Front near the the Stinson Stinson hydroelectric hydr~decfricgenerating station. station. broken feldspar grains ("collapsed dominoes"). The The zone of of ultramylonite is parti("collapsed dominoes"). cularly thick at this locality because itit is where cularly thick locality because where two two mylonite mylonite strands sfrands converge converge westward. To To the the east, east, the the northern northern strand strand separates separates mylonitized mylonitized quartz sandstone granitoid rocks rocks to to the the south; south; the southern to the north north from from migmatitic migmatitic granitoid southen strand &anitoid unit from metasedimentary schist and gneiss to the south. separates this granitoid Walk south south through through the narrow uncut strip that separates the Walk the two two powerlines powerlines to the outcrop outaop near the base base of of the hill (d). (dl. Dark Darkmetasedimentary metasedimentaryrocks rocks here here are are well layered and contain contain biotite and garnet; garnet; some some are are derived derivedfrom fromconglomerate, conglomerate, although the evidence for this is not particularly convincing at this outcrop. outcrop. Walk back to to the the northern northern powerline powerline and and follow follow the the higher higher ground ground to the Walk back (e). Outcrop which shows a structural trend, Outaop on on this this hill is migmatitic mipatitic granitoid which east (el. given primarily by the orientation of of leucosome, leucosome, that that strikes strikes northwest northwest at a marked angle to the curves into parallelism the mylonite mylonite strands. strands. This foliation foliation curves parallelism with both both mylonite strands that enclose the granitoid lens, having an overall Z-sense. mylonite strands enclose the granitoid lens, having overall Z-sense. The The lineation within within these these rocks rocks is clearly not aa typical steep northwesterly-plunging northwesterly-plunging lineation typical Grenvillian orientation. Neither the the age age of of the granitoid nor of GrenviIIian orientation. Neither granitoid protolith protolith nor of its its migmatization is is known, known, but but both both may be older than the mipatization the metasedimentary metasedimentaryrocks rocks to to the south, given that the latter latter are are not not migmatitic. migmatitic. In addition, the granitoid and its are locally locally cut cut by by thin thin dykes dykes of of metamorphosed metamorphosed mafic rock rock which are not leucosome are �27 found in found in the the metasedimentary metasedimentary rocks. rocks. It is possible that the granitoid granitoid lens lens is is aa slice slice of Archean crust, but this remains to be tested by U-Pb dating. of the the powerline powerline clearing, clearing, Follow side of Follow the the high high ground ground eastward eastward on on the north side and where the ground ground begins north toward toward the the and where begins to to slope slope away away to to the east, go north River. On On reaching a steep, narrow gully (f), (0,go down-slope to the the right. right. Wanapitei River. Here a narrow Here narrow zone zone of of intensely intensely cataclased cataclased rock derived derived from from the the migmatitic migmatitic granitoid is exposed on the south south side side of of the gully. Cross Crossthe thegully, gully, which which conceals conceals the Crenville boundary fault; fault; on on the north side is an anoutcrop outcropof of mylonitized mylonitized Grenville Front boundary side is quartz This is is cut by a dyke 4. This dyke of of Sudbury Sudbury quartz sandstone sandstone not not unlike unlike that seen seen at at Stop Stop 4. diabase that is replete with with cataclastic cataclasticfractures fracturesand andshears. shears. It it is hard to tell whether or not the the dyke dyke actually actually cuts the mylonitic foliation in the deformed sandstone; the impression that this this is the case may be explained as the result explained alternatively alternatively as result of of impression that competency contrastduring during deformation. deformation. This dyke cannot be traced on the competency contrast the south south (Crenville) side side of of the the gully; gully; continuous outcrop of (Grenville) of migmatitic granitoid along along the the powerline crosses crosses the the strike strikeprojection projectionofofthis thisdyke. dyke. Neither Neither can the dyke be traced to the northwest; northwest; itit is, is, however, offset from outcrop of similarly cataclased Sudbury diabase at the south just below the dam, which south shore of the Wanapitei River River just which lines dyke can can be traced traced northwest northwest for for 10 10 km up with with aa thick thick dyke dyke on the north side; this dyke (Dressler,1984). 1984).AAmere mere 500 500mm northwest northwest of of the the river, river, this toward Falconbridge Falconbridge (Dressier, undisturbed as that that seen seen at at Stop Stop1. 1. diabase is as fresh and undisturbed powerline and and go go east east to to the road, then follow the road south Return to the powerline south to to powerline (g). (g). Up-slope Upslope to the left, on the north north side side of of the the the edge of the second second powerline powerline clearing, is an outcrop of in which pebbles are well clearing, is of metaconglomerate metaconglomerate in well preserved. strand lies lies farther farther up up the hill to the north, preserved. The The southern southern mylonite mylonite strand north, and has been traced northeastward for two kilometres kilometres along along the the south slope of the high northeastward for ground, everywhere markingthe thecontact contactbetween betweenthe thegranitoid granitoid unit unit and and the ground, everywhere marking metaconglomerate-bearing metasedimentary rocks. metamnglomerate-bearing 0.0 2.2 2.2 4.8 67.3 69.5 69.5 72.1 72.1 Turn round round and and return to to Highway Highway 17. 17. Highway 17, turn right. right. After lookfor for the the Norvic After the the railway railway crossing, crossing, look Norvic Motel Motel on on the the left, cross cross the the highway highwayand and park park just just beyond the motel lefi, beyond the motel (at an Walk south south to inoperativerestaurant restaurantaat the time inoperative f fhe time of of writing). writing). Walk to the west of the motel, and take a track into the woods until aa the woods the west of the motel, and take a track Go to to the top low appears to the l m ridge ridge of of outcrop outcrop appears the left. l q t . Go top of of this this outcrop. outcrop. Stop 9. Metamorphosed Sudbury diabase dyke segments segments in metasedimenmetasedintenStop tary gneiss showing extreme ductility ductility Having seen a fresh, fresh, undeformed undeformed Sudbury dyke at at Stop Stop 1, 1,and and cataclased cataclasedSudbury Sudbury diabase to see the the form that Sudbury Sudbury dykes diabase at the last stop, it is instructive to dykes assume assume in in the highly ductile medium of metasedimentary gneiss that is the common country ductile of the common country of the the front front in in this this area. area. At rock southeast of At this this stop stop (Fig. (Fig. 8), 81, two parallel, northeast- �28 oriented dyke?) are are oriented segments segments of relatively relatively thick thick dykes dykes (perhaps (perhaps parts parts of of the same same dyke?) enclosed enclosed in in kyanite-bearing kyanite-bearinggneiss. gneiss. They They terminate terminate to to the the northeast northeast with rounded ends wrapped wrapped by by gneiss. gneiss. Along Along their however, they cut cut across across gneissic gneissic their sides, however, foliation in their host rocks; this is best observed at the southeast contact of the the foliation in their rocks; this best observed contact of northern of the two segments. segments. Note Note the the prolific prolific growth of garnet porphyroblasts in the dykes dykes near near their their contacts. contacts. of Sudbury Sudbuy metadiabase metadiabase dyke dyke Figure 8. 8. Detail of remnants in in metasedimentary mefasedimentary sclzist schist and gneiss, 1200 m south south of of the the Wanapitei Wanapitei fault. fault. gneiss, No more detached segments of Sudbury metadiabase have been found along along strike to the northeast, mafic rocks rocks exposed exposed there there are strike northeast, despite despite plentiful plentiful outcrop; outcrop; mafic amphibolite derived from The southern southern segment from metagabbro. metagabbro. The segment can be be followed followed southwestward before itit disappears disappears beneath beneath cover; cover; itit reappears as aa southwestward for for nearly nearly 300 m before area beyond beyondthe thecovered coveredinterval. interval. in detached pod in the well-exposed well-exposed area In the the central central where it is 27 m wide, wide, the the outcrop surface of of the least part of this dyke segment, where altered metadiabase shows the speckled texture typical typical of altered metadiabase shows speckled texture of Sudbury metadiabase. metadiabase. Whole rock rock analysis analysis of of this rock rock confirms its chemical chemical affinity affinity with with the Sudbury Whole confirms its Sudbury swarm. In remnant, 5.5 km from the Inaddition, addition,metadiabase metadiabase from from another another tectonic tectonic remnant, front south of the relics of of primary baddeieyite front the village village of of Wahnapitae, Wahnapitae, contains contains relics baddeleyite Ma; six sixfractions fractionsofofmetamorphic metamorphic zircon zircon from coronas 1243 Ma; coronas which gave a U-Pb age of 1243 around baddeleyite 1026to to988 988 baddeleyite in in the the same same rock gave 207Pb/2Pb 207PbPPbages agesranging rangingfrom fiom1026 from a late, late, undeformed pegmatite that cuts Ma (Dud& et uI. al. 1994). 1994). Zircon Zircon from undeformed pegmatite cuts this this (Dudas et enclave gave gavean anage ageofof97= 97 Ma Ma(A. (A.Davidson Davidsonand and0.0.van vanBreemen, Breemen,unpublished). unpublished). enclave narrow wooded wooded draw draw flanking flanking the the north north side side of of the the central part of Cross the narrow of in the the open open area area beyond. beyond. Here, homogenized' this dyke and go to outcrop in 'homogenized' kyanite kyanite gneiss encloses twisted twisted fragments of of mafic mafic rock, rock, representing representing either either a small dyke dyke or or �29 pieces This outcrop the extremely extremely ductile ductile pieces tom torn from from aa larger one. one. This outcrop bears testament to the behaviour kyanite gneiss gneiss aa mere mere 1200 1200 m south-southeast south-southeast of of the the Wanapitei Wanapitei behaviour of of the kyanite fault fault. Return to to the the highway highway and and totoSudbury. Sudbury. (If (If time time permits, permits, an extra extra stop stop will be be made made totosee seethe thesuccession successionkyanite kyaniteschist-quartzite-calcareous schist-quartzite-calcareous will gneiss in the of aa fold fold just just north north of of the fhehighway highway nearby.) nearby.) the core core of - COMMENTS - PROBLEMS PROBLEMS OF CORRELATION AND AND HISTORY OF THE GRENVILLE FRONT Metasedimentary schist and and gneiss immediately southeast of of the Grenville Metasedimentary schist immediately southeast Grenville Front Front boundary fault rocks of fault in in this this region region bear no no strong strong resemblance resemblance to the sedimentary sedimentary rocks the Huronian which here Huronian Supergroup Supergroup in the the adjacent adjacent Southern Southern Province, Province, which here are represented by the the Mississagi Mississagi Formation characterized by a monotonous monotonous succession succession of cross-bedded cross-bedded feldspathic feldspathicsandstone sandstonebeds bedstotalling totallingasasmuch muchasas33km kmthick. thick. In the of Grenville Province, Province, the the metasedimentary metasedimentary rocks rocks display display an an alternation of contrasting Grenville contrasting rock types types in in units only ten to a few hundred metres thick, thick, and although one may rock appeal to thinning thinning during duringductile ductiledeformation, deformation, the the successions successions themselves do not not satisfactorily match any any parts of satisfactorily match of the the well-documented well-documented Huronian Huronian succession succession (see (see If, for example, the metaconglomerate and kyanite kyanite schist schist present in this Table 1). 1). If, metaconglomerate and thii area are are equated equated with, with, say, say,the theRamsey Ramsey Lake Lake (Stop (Stop 2, conglomerate) and Pecors Pecors (Stop (Stop 3, slaty argillite) formations, which lie stratigraphically below the Mississagi, Mississagi, then garnet-hornblende-quartz-plagioclase gneiss, gneiss, their association association with with well-layered well-layered garnet-hornblende-quartz-plagioclase presumably derived derived from from calcareous calcareous sedimentary rock, cannot be explained explained in in stratistratigraphic terms, as the only calcareous unit of consequence in the Huronian only calcareous of consequence in Huronian sucsucgraphic terms, cession k is the Espanola Formation Formation (composed (composed of of calcareous calcareoussiltstone siltstone and and wacke with cession limestone at at its base and dolomite limestone dolomite at its its top), top), which which lies lies above above the Mississagi Mississagi and Bruce formations; formations;this thiscorrelation correlationproblem problemisiscompounded compoundedby bythe the fact factthat that aa thin but Bruce persistent quartzite quartzite unit unit lies between persistent between the kyanite kyanite schist and and the thecalcareous calcareous gneiss. Equating metasedimentary gneiss. Equating the the metaconglomerate metaconglomerate with conglomerate higher succession, either either the the Bruce Bruce or or Gowganda Cowganda formations, is equally in the Huronian succession, equally since both both these formations formations are are overlain overlain by by thick thick quartz-rich quartz-rich sandstone problematic since formations respectively) respectively)that thatare arenot not present present in in this units (the Serpent and Lorrain formations part of the the Grenville Grenville Province. Province, One is left with with four four alternatives, alternatives, namely: namely: 1) the metasedimentary rocks rocks are are facies equivalents of conjecture formerly formerly favoured by of Huronian Huronianformations formations—- aa conjecture Lumbers (1975, 1978);2)2)they theyrepresent representsedimentary sedimentaryrocks rocksofof formations formations higher higher in (1975, 1978); the Huronian Table 11)) than than are curHuronian succession succession(i.e. (i.e. above above the the Bar Bar River Formation; Table 3) they they represent represent a younger rently preserved in the the Southern Southern Province; Province; 3) younger succession succession that may on the may have have been been deposited deposited unconformably unconformably on the Huronian Huronian Supergroup Supergroup (perhaps equivalent in age to the the Marquette Marquette Supergroup in the the Southern Southern Province Province of northern Michigan?); 4) they are are an an entirely entirelydifferent differentsuccession successiontectonically tectonically of Michigan?); 4) juxtaposed the Southern Southern Province. Province. The jury jury is still out on this juxtaposed at some time against the this - �matter, but, as stated matter, but, stated earlier, earlier, an inkling inkling that the the metasedimentary metasedimentary rocks rocks are not correlative comes from isotope studies studies which which correlative with with the Huronian Supergroup comes from Nd isotope show provided Nd isotope systematics show that, provided systematics have have not not been been disturbed disturbed during the metarocks, the metapolyphase structural and metamorphic history history imposed imposed on these rocks, sedimentary Grenville Province have Nd depleted depleted sedimentary rocks rocks in in the the Crenville Provincenear near the the front front have mantle model ages younger on this this basis basis younger than than those those of of the the Huronian Huronian Supergroup. Supergroup. IfIf on would probably have favoured, juxtaposition juxtaposition would the last alternative alternative given above is favoured, occurred before before -1750 —1750Ma, Ma, theage ageofofplutonic plutonicrocks rocksfound foundon onboth both sides sides of of the occurred the Grenville Front. Is this part of the front front therefore therefore coincident coinadent with aa pre-Grenvillian pre-Grenvillian Grenville suture? Penokean in in age? age? Note suture?—- perhaps Penokean Note that that Dickin Dickin and andMcNutt McNutf (1989) (1989) placed a Penokean suture much farther south within the the Crenville Grenville orogen. orogen. Two other rock Two other rock units northwest northwest of the the front front have have potential potential counterparts counterparts within within the marginal marginal part part of of the theCrenville GrenvilleProvince. Province. One of the the characteristic characteristic geologic units units in in the Southern Province,and and also also in in the neighbouring part of the geologic Southern Province, the Superior Province, Province, is is the the Nipissing Nipissing gabbro, gabbro, occurring occurring as large, sill-like intrusions. as large, sill-like intrusions. Amphibolitebodies bodiesofof similar similar size, size, derived derived from Amphibolite from gabbro, gabbro, occur occur within within the the metasedimentary rocks rocks in the Grenville metasedimentary Grenville Front zone. zone. Another characteristic characteristic unit, found near the base of the Huronian Supergroup in the Sudbury found Sudbury region region and and also also (-2.45 Ga) Gal adjacent to the front front 50 50 km km to to the thenortheast, northeast,forms formsaanumber numberofofolder older(—2.45 intrusions of gabbro and anorthosite. of similar composition, now mainly infmsions anorthosite. Rocks Rocks of mainly metamorphosed hornblende gneiss gneiss but but locally retaining relict metamorphosed to plagioclase-rich plagioclase-rich hornblende igneous texture where where not not strained, occur occur within the adjacent part of igneous of the the Crenville Grenville Province, ifIf itit isis considered Province. considered that these two two units units are are correlative correlative across across the the front front (and (and it does seem likely that the older suite suite is is correlative, correlative, as as itit can can be be traced traceddirectly directlyacross across the front at then it becomes at River River Valley), Valley), then becomes difficult to accept accept that that the theassociated assoaated If they are metasedimentary rocks rocks in in the Grenville are not Huronian Huronian equivalents. equivalents. If Huronian, then then all all that that can be said said is that during Huronian, can be during their their tectonic tectonic history history they they have been so severely sliced sliced up up and stacked together out of sequence that all semblance sequence that all semblance of Huronian Huronian stratigraphic stratigraphic order order has has been been obliterated. obliterated. With regard to the With regard the potential potential severity of tectonic tectonic 'rearrangement', 'rearrangement', two other units within the Grenville Frontzone zonemust mustbe beconsidered. considered. The The first is the narrow Grenville Front wedge of migmatitic granitoid granitoid examined examined at at Stop 8, 8, and other, smaller slivers slivers of the tucked in with metasedimentary rock and amphibolite same rock that occur tucked amphibolite toward toward Wahnapitae. The of protolith is not not known, known, but it is possible that it Wahnapitae. The age o f the granite protolith is Archean, Archean, and if so, so, that that itit represents represents basement basement to to the the Huronian Huronian Supergroup Supergroup brought up in in tectonic tectonic slices slices at the the front. front. Its migmatitic nature nature isischaracteristic; characteristic; similar is not not present similar leucosome leucosome is present in in orthogneiss orthogneiss derived derived from from post-Huronian post-Huronian granitoid rocks Chief Lake Lakegranite) granite)adjacent adjacent to to the the front front south of (e.8. Chief of Sudbury. Sudbury. granitoid rocks (e.g. The second is the fascinating fascinating Wanapitei mafic complex, mentioned mentioned at at Stop Stop7, 7, which time has not allowed allowed to be examined examined on on this this trip trip(see (seeDavidson Davidson1994 1994for for field field guidance). This This 33 xx 8-km body is composed in part part of of layered, layered, differentiated differentiated gabbro, gabbro, metamorphosed but but not deformed, deformed, and in part of of an an incredible incredible jumble jumble of of equant to to mafic rocks rocksin inaa matrix matrix of of variably variably ductile ductile material material derived from distorted blocks of mafic and an invading invading swarm swarm of of ggranite dykes. Where the dykes cut unr a ~ t edykes. both the gabbro and deformed gabbro, they are straight-walled and composite, with abundant abundant evidence evidence of gabbroic gabbroicand andgranitic graniticmagma. magma. The The granite granite from one of these dykes for comingling of �31 has a U-Pb U-Pb zircon age of 1747 1747 Ma Breemen, unpublished), Ma (Davidson (Davidson and and van Breemen, unpublished), the (1992)on (although itit is is same age as as that that obtained obtained by by Prevec Prevec (1992) on zircon from metagabbro (although possible that the zircon from All of these rocks are cut from the the gabbro gabbro is is metamorphic). metamorphic). All by straight, north-trending, north-trending, vertical dykes of of coronitic coronitic olivine metadiabase metadiabase (just (just like that in the the core core of the dyke remnant seen at at Stop Stop 9), whose chemistry is identical to diabase. In In addition, addition, the dykes dykes retain retain chilled chilled margins, margins, close to which may Sudbury diabase. be found xenocrysts and and small, found large large plagioclase plagioclase xenocrysts small, angular xenoliths xenoliths of quartz quartz 1). The outer part of do Sudbury Sudbury dykes in the Southern Province (Stop I). of sandstone, as do the Wanapitei complex, wellexposed exposedalong alongits its north north and west complex, well west sides, sides, isis entirely entirely tectonic, formed of ductile, recrystallized gneiss whose foliation tectonic, foliation wraps wraps the thecomplex. complex. in the the undeformed undeformed gabbro gabbro is is truncated truncated at this contact, and neither Primary layering in - in fact, the granite granite nor nor olivine olivine metadiabase metadiabase dykes dykes penetrate penetrate the theductile ductilecarapace carapace— large boudins of metadiabase are incorporated within the ductile rim, and metadiabase are incorporated within and occur occur as as segments in in the more distal country disconnected and disoriented segments country rocks. If the coronitic metadiabase metadiabase dykes dykes within within the Wanapitei complex are indeed If Sudbury dykes, then then itit follows that the incorporation of the as a Sudbury dykes, follows that incorporation of the complex complex as 'megaboudin' within within a ductile ductile medium, medium, was was an effect of Grenvillian Crenvillian orogeny. orogeny. The 'megaboudin' effect of fact that the the northern northerncontact contact of of the the Wanapitei Wanapiteicomplex, complex, in in contact contact with withsillimanitesillianitebearing gneiss, lies less than 500 500 m from from outcrops outcropsof ofgreenschist-facies greenschiit-fades Mississagi Mississagi Formation with preserved sedimentary structures facing away from the front front (Stop (Stop remarkably steep steep gradient gradient in in metamorphic grade and 7) belies a remarkably and style style of of deformation deformation across this part of across of the the Grenville Grenville Front. Front. It seems clear clear that that the the Grenville Grenville Front Front boundary fault, particularly particularly where coincident with the Wanapitei Wanapitei fault, exhibiting exhibiting brittle deformation, manifestation of of considerable considerable uplift uplift along along part part of deformation, is the latest manifestation margin, probably probably post-dating introduction the Grenville orogenic margin, introduction of of pegmatite pegmatite at at980 980 Ma, Ma, and perhaps related related to rebound of of the the Grenville Grenville orogen orogen induced by by southeastsoutheastdirected extensional extensional unloading of the the tectonically tectonically thickened thickened Grenville Grenville interior. interior. A word remains to be said about about possible possible renewed renewed displacement, displacement, of of normal normal of the sense (south-side-down) along the Wanapitei-Murray Wanapitei-Murray fault, fault. The truncation of 61, moderately southeast-dipping Grenville Front mylonite mylonite zone zone at atAlice Alice Lake Lake (Stop (Stop 6), metamorphic isograds isograds to the southeast, by and of the the parallel parallel Grenvillian Grenvillian metamorphic by the the subsubvertical fault isis hard hard to with uplift of vertical Wanapitei Wanapitei fault to reconcile reconcile geometrically geometrically with of the the Grenville side alone, unless unless the the preexistent pre-existent Murray-Wanapitei Murray-Wanapitei fault fault acted acted as a ramp 4) was was deflected deflected against which moderately-indined, moderately-inclined, thrust-sense thrust-sense displacement displacement(Stop (Stop 4) the Wanapitei-Murray Wanapitei-Murray fault fault may may have been reactivated vertically. vertically. Alternatively, Alternatively, the reactivated during during post-Crenvillian post-Grenvillian rifting associated with late Neoproterozoic Neoproterozoic development development of rift system, system,centered centeredfar fartotothe the east east and and related related to opening of of the the St. Lawrence Lawrence rift In this regard, some 50 50 krn km east of Sudbury the lapetus Ocean. Iapetus Ocean. In regard, some the Wanapitei Wanapitei fault curves from its position Front boundary boundary fault into the curves position as the Grenville Grenville Front the Grenville Grenville Province, cuffing across acrossthrust thrustfaults faults and and mylonite mylonite that that mark the Province, cutting the continuation continuation of of the Crenville Grenville Front Front to the northeast; northeast; it projects eastward toward toward south-side-down south-side-down faults that that mark mark the the northern northern edge edge of of the theOttawa Ottawagraben graben(Lumbers (Lumbers1971b) 1971b)in in which which Lake Nipissing Nipissing lies, lies, and and with with which are associated Lake associated several alkalic alkalic and and carbonatite carbonatite complexes dated complexes datedatat—585 -585 Ma. Ma. dearly In conclusion, (sensu late) lato) in the Sudbury region clearly conclusion, the Grenville Grenville Front Front (sensu albeitsporadic, sporadic,that that lasted lasted for for aa lot longer than the duration has a history of activity, activity, albeit duration �32 of the the Crenvillian Grenvillianorogeny orogeny itself. itself. It may have been the the locus locus of of juxtaposition juxtaposition of of of crust (based on differences differences between between the the Huronian Supergroup different blocks of Supergroup in in the Southern Grenville) Southern Province Province and the the metasedimentary metasedimentary rocks in the the adjacent adjacent Crenville) Ma. It was active before being being sealed sealed by by igneous igneous rocks rocks at at—1740 -1740 Ma. active following followingemplaceemplacement of granite plutoris at —1470 Ma, but quiescent at the time of intrusion of of the the granite plutons at -1470 Ma, but quiescent at the time of continental Ma. 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In I n Radiogenic Radiogenic the southern southern Superior Superior and and western western Grenville Grenville provinces, provinces, Ontario. Geological Survey of of Canada, Canada, Paper Paper92-2, 92-2, age and andisotopic isotopicstudies: studies: report report 6. 6. Geological age pp.97—106. 97-106. pp. L.L. 1985. 1985. Preliminary Preliminary report report on onthe theGrenville GrenvilleFront FrontTectonic TectonicZone, Zone, Carlyle Carlyle Fryer,L.L. Pryer, Township, Ontario. In Current research, part A. Geological Survey of Canada research, Geological Survey of Canada Township, Paper85-lA, 85-1A,pp. pp. 478-482. Paper 478—482. Pryer, major crustal thrust thrust zone: zone: the Fryer, L.L. L.L. 1993. 1993. Microstructures Microstructures in feldspars from a major the Grenville Geology, GrenvilleFront, Front, Ontario, Ontario, Canada. Canada.Journal JournalofofStructural Structural Geology,15:21—36. 15: 21-36. Pye, P.E., editors. editors. 1984. 1984. 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Moore, Moore, A. Davidson Davidson and A.J. A.J. Baer. Baer. Geological Geological Association of Canada, Special Paper 31, 31, 191-207. pp. pp. 191—207. Van Schmus, W.R. W.R. 1965. 1965. The geochronology geochronology of of the theBlind BlindRiver River—- Bruce Mines Mines area, ofof Geology, 73:73: 755—780. area, Ontario, Ontario,Canada. Canada.Journal Journal Geology, 755-780. Windley, B.F. Anorogenic magmatism magmatism and and the Grenvillian B.F. 1989. 1989. Anorogenic Grenvillian orogeny. orogeny. Canadian Journal of Earth Sciences, 26: 479—489. Canadian Journal of Earth Sciences, 26: 479-489. 1972. The Grenville Province. Province. In In Variations Wynne-Edwards, H.R. H.R. 1972. Variations in tectonic tectonic styles in Canada. Edited by R.A. Price and R.J.W. Douglas. Geological Geological in Canada. Edited by R.A. Price and R.J.W. Douglas. Association 11,11, pp.pp. 263—334. 263-334. Associationof of Canada, Canada,Special SpecialPaper Paper � https://digitalcollections.lakeheadu.ca/files/original/0b1e124eba531637fe45b2fc2ebef497.pdf 40b8bec228577a177ab4473d7cc44f96 PDF Text Text THE THESUBBURY SUDBURYSTRUCTURE STRUCTURE WITH ONTHE THE WITHEMPHASIS EMPHASISON WHITE WATER GROUP WHITEWATER GROUP BY BY S.F. F. M. M.GIBBINS GIBBINS S. INSTITUTE INSTITUTEON ON LAKE LAKE SUPERIOR SUPERIORGEOLOGY GEOLOGY 43rd 43rdANNUAL ANNUAL MEETING, MEETING, MAY MAY6-11,1997 6 - 11,1997 SUDBURY, ONTARIO ONTARIO SUDBURY, Field Field Trip TripGuidebook, Guidebook,Volume Volume 43, 43, Part Part44 �2 The The Sudhury Sudbury Structure Structure with Emphasis Emphasis on on the the Whitewater Group Group by S.F.M. Gibbins Gibbins Falconbridge FalconbridgeLimited Limited Kidd Kidd Creek CreekDivision DivisionGeology Geology P.O. Bag2002 2002 P.O. Bag Timmins, Ontario Ontario P4N P4N 7K1 7K1 Frontispiece: Frontispiece: Schematic diagram diagram illustrating illustratingthe thestyle style of of development and hyaloclastite emplacement of intrusive hydroclastic breccias and hyaloclastite deposits of the Sandcherry Sandcherry member Formation member of the Onaping Formation (modified from Smith Smith and and Batiza Batiza1989, 1989, Hanson Hanson 1991, 1991, and and Gibson, Gibson, unpublished) unpublished) �3 ACKNOWLEDGMENTS ACKNOWLEDGMENTS This possible without without the the support of Falconbridge This field field trip trip guidebook would not have been possible Limited, Harold Gibson of Laurentian University and Ron Sage Sage of of the the Ontario Ontario Geological Geological Survey. Survey. INTRODUCTION INTRODUCTION The The Sudbury Sudbury Structure Structureis is located located in in south-central south-centralOntario Ontarioat atthe thepresent presentboundary boundarybetween between metavolcanic and and metasedimentary metasedimentary rocks, and granitic granitic the Archean Superior Superior Province Province (,gneissic, (gneissic, metavolcanic intrusions) metasedimentary rocks), and intrusions) and the Proterozoic Southern Province (metavolcanic and metasedimentaq lies approximately approximately 10 of the the Grenville Grenville Province Province(high (high grade gradegneisses) gneisses)(Figure (Figure1). 1). 10km north-west of a!. 1984) Sudbury Structure Structure is known world-wide for for its its NiNiThe 1.85 Ga Ga old (Krogh et al. Cu-POE Cu-PGE ore ore deposits and its debated origin: endogenic endogenicvolcanic volcanicexplosion explosionversus versus meteorite meteorite impact. Two Twocarbonate carbonatehosted hosted Zn-Cu-Pb-Au-Ag Zn-Cu-Pb-Au-Ag massive massive sulphide sulphide deposits deposits also occur in the interior of the Sudbury Structure, located located at atthe thetop top of ofthe the Onaping OnapingFormation Formation of of the the Whitewater Whitewater Group. Group. The Sudbury Sudbury Structure Structure is defined by three components: 1) the Sudbury Sudbury Igneous Complex footwall rocks rocks (both (both Superior Superior and and Southern Structural Provinces) (SIC), 2) surrounding brecciated footwall that SudburyBasin, Basin, comprising comprising rocks rocks of of that extend extend some some 80 80 km away from the Complex, and 3) the Sudbury the Whitewater Group, found in the the interior interior of of the the Complex Complex (Figures (Figures 1and and 2). 2). The The Sudbury Sudbury Igneous Complex, which which has has aa noritic noritic base base and granophyric top, occurs occurs at at the the base base of of the the the surrounding surrounding brecciated brecciatedfootwall footwallrocks. rocks. The The Whitewater Whitewater Group and overlies the Group, Sudbury Basin, comprises, within the Sudbury comprises, from base base to to top, top, initially initiallyglass-rich glass-rich Group, found found only only within breccias of breccias of the the Onaping OnapingFormation, Formation, carbonates carbonatesand anda.rgillites argillites of of the the Vermilion Vermilion and and Onwatin Onwatin Formations, Formations, and and arkosic arkosic sandstones (waekes) (wackes) of the Chelmsford Formation. Formation. The The SIC SIC has has been been dated at 1850 1850Ma Ma (Krogh (Krogh et et al. al. 1984) 1984)and andisisinterpreted interpretedto tohave havebeen beenemplaced emplacedshortly shortlyafter afteror or during 984c). In during the deposition of the Onaping Formation (Rousell I1984~). Inplan, plan,the theSIC SICisiselliptical ellipticalin in shape by 27 km in in size. size. In that the the In section, section, seismic seismic reflection shows that shape and approximately 60 km by north margin (North Range) of the the Sudbury Sudbury Structure consists of, shallowly dipping dipping strata strata of of and layered layered rocks rocksof ofthe the SIC SIC and and footwall footwallgneisses gneisses.. In Incontrast, contrast,the thesouth south sediments, breccias and margin (South Range) is dominated by a series of moderately south dipping reflectors interpreted thrust fliults to be thrust faults or or shear shear zones zones on on which which considerable considerablenorth-west-south-east north-west-south-east shortening shorteningof ofthe the Sudbury et al. 1992). Sudbury Structure Structure has occurred (Milkereit et 1992). The Thepresent presentshape shapeof ofthe theSudbury Sudbury Structure, Structure, as as delineated delineated by the SIC, is due to the combination combination of structural structuralshortening shortening and and subsequent erosion. The The Sudbury Sudbury Structure, Structure,in in plan, plan, isis interpreted interpreted to to have have been originally more circular, circular, with with dimensions dimensions in in the 150 150 -- 200 200 km range (Grieve (Grieve et al. 1991). 1991). Schwerdther (1991) attributed the present elliptical shape Shanks and Schwerdtner shape of the Sudbuiy Sudbury Structure to be the result of north-westerly directed thrusting thrusting related to the Penokean Orogeny, Structure This wasresponsible responsiblefor for several several low-angle low-angle dated at 1750 1750 Ma (Rousell l984c). 1984~). Thisthrusting thrustingevent eventwas flults that reverse faults that cut cutacross acrossthe the SIC SICand androcks rocks of of the the Whitewater Whitewater Group, Group,from from the the south-west south-west to to the south-east. Deformation has also resulted in the formation of isoclinal folds and a slaty Deformation has also resulted in formation cleavage within the Onwatin Formation, open, concentric folds cleavage open, uprighf uprightconcentric folds in in the the Chelmsford Chelmsford 984c). The Formation, and locally overturned rocks in the South Range (Rousell 11984~). The effects of structural deformation are confined primarily primarilyto to rocks rocks of ofthe the South South Range Range and andthe thecentral centralpart part of of structural the Sudbury Sudbury Basin. Rocks Rocksinin the the North North Range Range are are metamorphosed metamorphosed to greenschist greenschist facies, those in South Range are metamorphosed to to lower amphibolite facies facies (Dressier 1984a; the South 1984a; Shanks Shanks and Schwerdtner Schwerdtner1991). 1991). Structure has been attributed The origin of the Sudbury Structure attributed to to volcanism volcanism or or meteorite meteorite impact of aa meteorite meteoriteimpact impactorigin originspecify speci shock (see below for authors). authors). Advocates Advocates of shockfeatures features and and breeciation associated with the Sudbury Structure, the extreme crustal contamination of brecciation Sudbury Structure, the extreme crustal contamination of the the SIC, SIC, glasses and and rapid rapid deposition of of the the Onaping Onaping Formation, Formation, and and the the original original circular circular shape heterolithic glasses �SUDBURy STRUCTURE CHELM$Fo Fm E2:ONWA11N Fm : EZi ONAPft4Q Fm SUDHURY IGNEOUS COMPLEX — - -:-:-:-:r_ - : : :--:- :T::E7 : + + + -c::z' *:- +f i-:.-t:';;:'. ..ERNGTON -- ..'..- - + + + + + •+ ± + + + + 4* FIGURE 1 0 (modified after Gibbins 1994) t + + /4 +! i + + + + 4 L Km I 10 4 + I—T_ i / -- -. + + + + + + + + + + + + + + + + 4 + + + + + __±___+ + + + + + + + + i÷ + —tç ÷ + • + + + +1+ * + * + + -+ + +/+ + + + + + * + + #7+ 4 + + -f + + + 4 +7-f + + + + + �__ 5 NOMENCLATURE NOMENCLATURE THISPAPER PAPER THIS PREVIOUS FREVIO(S CHELMSFORD FORMATION CHELMSFORD FORMATION 0 0 - - - .4 44 MIOOLEIJIITS 0z I— • 44 D6WLJNG MEMBER :±• : & 64: bc6 RitIITS - - C z 0 IL I C', z a- o-o-o-o-o-o- MEMBER C INTR1SION÷:.+.;.. z 0 x Lu Ill UPPER ZONE -J _1 r0! GRANQPf4'y C- z a 0 0 u C C-) N- RIGHT) (SEERIGHT) (SEE MIDDLE ZOWE-QU GAB p 3 0 0 wIll z 2 010 >>- cr LOWERZONE FELSIC NORITE 3 m 0 -5 cn Co XXXxx,ç4 I'tAFIC NORITE: 2 3 I0 00 (SEERIGHT) RIGHT) (SEE ll. C Q Lu UJ I— IIC < 0 u C-) u LU I l l a: 0' m m Figure Figure2:2: StratigraphicSection Section of ofthe Sudbury Structure (modifiedGrieve et al. 1991) Stratigraphic the Sudbuiy Stmctum (modified Grieve et al. 1991) �6 of the Sudbury for aa meteorite meteorite impact. impact. Proponents of a volcanic origin argue Sudbury Structure Structure as evidence for that features features such such as as Sudhury SudburyBreccia Breccia dykes dykes cutting cutting across acrossother other Sudbury SudburyBreccia Brecciadykes, dykes, composite composite fragments ("breccia within breccia") and igneous activity activity within within the Onaping Onaping Formation, Formation, and events/structures that predate and various various regional regional endogenic eventslstructures predate and and post-date post-datethe the"Sudbury "SudburyEvent" Event" are evidence that the Sudbuiy Structure is the result of prolonged endogenic processes, are Sudbury Structure is the result of prolonged endogenic processes, unexplainable unexplainable by aa one one time event such as a meteorite meteorite impact. impact. An extensive amount of literature exists on the geology and evolution of the Sudbwy Sudbury Structure, compilationcontained containedwithin withinPye Pyeetetal. ai.(1984). (1984). The withthe the most recent comprehensive compilation The Structure, with Onaping Errington and Vermilion Vennilion deposits, has been described Onaping Fonnation, Formation, the the footwail footwall rocks to the Enington product of: of: 1) volcanism volcanism (Bell (Bell 1893; Coleman Coleman 1905; Burrows and and interpreted to be the product Rickaby 1930; Williams 1957; 1957; Stevenson Stevenson 1961% 1961a, 1961b, 1972, 1990; Muir 1981, 1930; Thomson 1957; Williams 1981, 1984, 1986; 1986; discussion by Muir in Muir and Peredery 1984); 1984); 2) meteorite impact (French 1968; 1968; Dence 1972; Peredeiy Peredery 1972a, 1972a, 1972b; 1972b; discussion discussion by Peredery Peredery in Muir Muir and and Peredery Peredery 1984; 1984; Peredery Peredery and Morrison a!. 1987; Brockmeyer Brockmeyerand andDeutsch Deutsch 1989; 1989; Stoffler Stoffleret eta!. Monism 1984; 1984; DressIer Dressler et al. al. 1989; 1989; eta!. Brockmeyer 1992; 1992; Krogh Kroghet eta!. Grieve et al. 1991; 1991; Avennanu Avennann 1992; Avennann and Brockmeyer al. 1996, Deutsch et a!. (Thomson 1969; Muir 1982, al. 1995); 1995);or or 3) 3) impact-induced impact-induced volcanism (Thomson 1982, 1983; 1983;Dietz Dietz 1964; 1964; Gibbins 1994). Gibbii 1994). Additional Additional research researchhas has been been directed directed towards towards specific specificfeatures featureswithin within the the Onaping Onaping Fonnation, including (Peredery 1972% I 972a, 1972b; I 972b; Paakki Paakki 1990; Formation, including intrusive rocks (Peredery 1990; McKinley 1992), 1992), mineralization (Chubb 1990; 1990; Drake 1992), 1992), geochemistry geochemistry(Ding (Dmgand andSchwarcz Schwarcz1983; 1983;Schandl Schandleteta!. al. geochemistry, stratigraphy stratigraphy and mechanisms of emplacement 1986; McKinley 1992), geology, geochemistry, 1995and andAmesetal. Abriefsummaryofthe 1994)andalteration(AmesetaL Ames et al. 1996). 1996). A brief summary of the (Gibbins 1994) and alteration (Ames et al. 1995 (Gibbins Onaping Formation is presented presented by by Dressler Dressier et et aI. al. (1991) (199!) in an overview of the Sudbury in an Sudbury Structure. Structure. ford formations formations are are contained within Detailed descriptions of the Onwatin and Chelms Chelmsford contained within Coleman (1905), Burrows and Rickaby (1930), Martin (1957), Thomson Thomson (1957), (1957),Williams Williams (1957), (1957), Sadler Rousell (1972, !984a), Sadler (1958), Cantin (1971), Cantin and Walker (1972), Rousell(1972, 1984a),Beales Beales and and Lozej Lozej (1975), Arengi (1977), and Vezina Vezina (1992). (1992). Mineralization Whitewater Group has been Mineralization in the Whitewater discussed by Burrows and Rickaby (1930), (!930), Martin (1957), Desborough Desborougb and Larson Larson (1970), Card Card and Hutchinson Hutebinson (1972), Arengi (1977), Rousell(1983, Rousell (1983, 1984b), 1984b), Davies Davies et et al. al. (1990), (1990), Whitehead Whitehead et et a!. (1994) and and Gray Gray (1995). The al. (1990), and Paakki (1992), Gibbins (1994) Thestructural structuralgeology geologyof ofthe the by Martin Martin (1957), Rouse11 Rousell (1984c), Whitewater Group has been addressed by (1984c), Cowan Cowan and and Scbwerdtner (1991), and Milkereit et al. (1992). Schwerdtner (1990), Shanks and Schwerdtner (1991), SUDBURY STRUCTURE STRUCTURE of; in ascending ascending stratigraphic stratigraphic order, brecciated breceiated footwall footwal! rocks, The Sudbury Sudbury Structure Structureis composed of, the Sudbury Igneous Complex, and the Whitewater Group. Sudbury Igneous Complex, Whitewater Group. Brecciated FootwaH Brecciated Footwall Rocks Breccias in the footwall are are divided dividedinto intotwo twotypes: types: Sudbury Sudbury Breceia Breccia and Footwall Breccia Breccia. Their al.1991). 1991). Theirorigin originisisaasubject subjectof ofconsiderable considerabledebate debate(Dressier (Dressleret eta!. Sudbury Breccia bodies (pseudotachyiites) occur within all footwall Sudbury bodies(pseudotachy1ites) footwall rocks rocks that that predate predatethe the event,and andextend extendas asfar fir as as 80 km km away away from the the SIC, but are most Sudbury Structure-forming event, abundant in a 10 zonethat that surrounds surroundsthe theSIC SIC (Dressler (Dressier 1984a). The 10 km wide zone The breccias breccia form form subsubvertical irregular from a few millimetres to to zones 0.5 by 11 11 km km in in vertical irregular dyke-like dyke-like bodies ranging in size from size (Dressier 984a). The matrix of of Sudbury Breccia Breceia is is gray gray or or black and consists of of (Dressler 11984a). wealdy recrystallized recrystailized rock rock (Dressler (Dressier 1984a). Large microscopic, weakly Largefragments, fragments,predominantly predominantly of of the the ones are are more more angular angular (Dressler (Dressier et al. a!. 1991). 1991). Igneous Igneoustextures, textures, host rock, are are rounded, rounded, the smaller ones amygduies, and flow banding are not uncommon. Contacts with surrounding amygdules, surrounding host host rocks rocks are aresharp. sharp. Sudbury Sudbuiy Breccia Sudbury Breccia Breccia dykes cutting across other Sudbury Breccia dykes, and fragments fragments of of Sudbury Sudbury Sudbury Breccia have havebeen beenobserved observed(Dressler (DressIeretetal. al.1991). 1991). The The Sudbury Breccia udbu~ Breccia Breccia within S �7 by sudden, explosive brittle brittle failure leading leading to to a violent milling and and is interpreted to have formed by crushing 984a). crushing process process that that involved involved little little or or no no melting melting (DressIer (Dressler 11984a). The as "late granite granite breccia" and "leucocratic "leucocratic breccia" The Footwall Breccia, also described as (Langford 1960; Pattison 1979; Muir Muir 1981, 1960; Souch et al. 1969; Greenman 1970; Paitison 1981, 1983; 1983; DressIer Dressler 1984a; Lakomy 1986, 1989), bodies up up to to 150 m thick, parallel to the contact 1989), occurs as sheet-like bodies contact with the base of of the SIC, SIC, and and hosts hosts much of of the the Ni - Cu ore in the North Range (Dressier (Dressler et al. al. 1991). Contacts Contactswith withthe theoverlying overlying SIC SIC are are sharp, sharp, whereas whereas contacts contactswith with the the underlying underlyingfootwall footwall rocks are gradational (Pattison 1979). The The matrix matrix of of the Footwall Breccia is light coloured with granoblastic granoblasticand and granophyric granophyric textures. Fragments Fragmentsof ofvariable variablesize sizeand andlithology lithologyare arederived derivedfrom from (Dressier et et al. al. 1991). Dressier Dressler et et al. al. (1991) (1991) inteipreted interpreted the the Footwall Footwall Breccia to the local footwall (Dressler shock-metamorphosedrocks, rocks, similar similarto to Sudbury Sudbury Breccia, Breccia, that formed be a mass of crushed and shock-metamorphosed or meteorite meteoritecrater, crater, before before the the deposition deposition of of the the along the walls of the original endogenic-volcanic or lower Onaping Formation and the intrusion of the Sudbury Igneous Complex. Complex. - Sudbury Igneous Sudburv Imeous Complex Complex The into Sublayer Sublayer (Contact (Contact Sublayer The Sudbury Sudbury Igneous Complex (SIC) is subdivided into Sublayer and Offset Offset Sublayer) Sublayer) and and the Main Mass (norites, (norites, quartz quartz gabbros, gabbros, and and granophyres) granophyres)(Pye (Pye et et al. al. 1984). 1984). In plan view, the SIC is elliptical in in shape shape with with aa long long axis axis of of 60 60 km km and and aa short axis of 27 km. et al. al. 1992), to one cross-section, shows the threeSeismic reflection data (Milkereit et 1992), albeit limited to of at least the the north north half half of of the the Sudbury Sudbury Igneous Igneous Complex Complexto to be be similar similar to to aa dimensional shape of sheet-like sill, rather than a fiumel-shaped funnel-shaped intrusion as previously suggested by, amongst amongst others, others, Wilson (1956); (1956); Naldrett Naldrett and and Kullerud Kullerud (1976). (1976). The Sublayer, a fineto medium-grained mafic to to intermediate rock (quartz diorite The Sublayer, fine- to diorite -(Contact Sublayer) Sub!ayer) and as dykes in norite) occurring at the base of the Sudbuiy Sudbury Igneous Complex (Contact surrounding country rocks (Offset Sublayer), the surrounding Sublayer), is host to to much much of of the the Ni Ni -- Cu sulphide ores of (DressIer et et al. al. 1991). The the Sudbury Structure (Dressler The Contact Contact Sublayer Sublayer and Offset Sublayer Sublayerhave have described in detail detail by by Naldrett Naldrett et et al. al. (1984) and by Grant and Bite been described Bite (1984), (1984), respectively. respectively. Dressier that at at least some of of the the Sublayer Sublayer post-dates post-dates the Main Dressler et al. al. (1991) (1991) provided provided evidence that Mass of of the the SIC. SIC. The SudbuvIgneous Igneous Complex Complex is is subdivided subdivided into into aa Lower, Lower, Middle Middleand and The Main Main Mass Mass of of the the Sudburv an Upper zone (Pye et al. 1984; 1984; DressIer Dressler 1984b). 1984b). The Thelower lower zone zone consists consistsof ofmafic maficand and felsic felsic consists of of quartz quartz gabbro, gabbro, and and the the Upper Upper Zone Zone of of granophyres. granophyres. The The norites, the Middle Zone consists contacts between these major phases are gradational (DressIer et a!. 1991). The granophyres contacts major phases are gradational (Dressier et al. 1991). The granophyres of of the the by Peredery Peredery and and Naldrett Naldrett (1975) into an early plagioclase-rich plagioclase-rich Upper Zone have been divided by phase phase. The phase and and aa contemporaneous contemporaneous to slightly later "normal" phase. The SIC SICdoes doesnot not exhibit exhibitfine-scale fine-scale to other large, mafic mafic igneous complexes complexes such suchas as the the Bushveld Bushveld Complex. The The layering common to abnormally rich rocks of the Sudbuiy SudburyIgneous Igneous Complex Complex are are also also unique unique in being abnormally rich in in normative normative SiO2 SiO; and K20. This to suggest Thisobservation observationled led Irvine Irvine (1975) (1975) and and Naldrctt Naldrett and Macdonald (1980) to suggest that the Sudbury strongly contaminated by silica-rich silica-rich country country SudburyIgneous Igneous Complex Complex represented a magma strongly rocks. rocks. Naldrett and Rewins the published published literature literature on the the Main Hewins (1984) summarized much of the Mass Mass of of the the Sudbury SudburyIgneous IgneousComplex, Complex, and and stated stated that that three three main main models models have have been been proposed proposed for for (Dressier et et al. al. 1987). 1987). These the Igneous Complex (Dressler Theseare: are: 1) 1)the the Complex Complex is is aa folded folded differentiated differentiated sill; 2) both the norite and granophyre intruded intruded separately separately as as ring ring dikes, dikes, and and 3) 3) the the Complex Complex is is aa flinnel cataclastic fracturing fracturing of three models require an initial cataclastic of the earth's funnel shaped intrusion. These These three crust crust with the formation of a crater into which a basic magma, rising from depth (possibly from a reactivated Nipissing magma chamber), chamber), intruded intruded and andformed formedthe theSIC. SIC. The Main Mass Mass of of the the Sudbury Sudbury Igneous Igneous Complex has also also been interpreted to be the clast-free component of a melt sheet, impact (Faggart (Faggart et eta!. al. 1985, 1985, Brockmeyer Brockmeyer 1990; 1990; Grieve Grieve et et al. al. 1991). 1991). formed in situ by meteorite impact �8 The upper contact of the SIC Onaping Formation has has been been described described as SIC with the overlying Onaping both gradational gradational and sharp intrusive contact relationships (Dressier et al. at. 1991). exhibiting both 1991). Whitewater Group stratigraphic order, a The Proterozoic Whitewater Group consists of, in ascending stratigraphic conformable conformable sequence sequence of initially glass-rich breccias and melts of the Onaping Onaping Formation, Formation, carbonates and gray argillites of the Vennilion Formation, carbonaceous argillites and siltstones siitstonesof of carbonates the Vermilion Formation, carbonaceous argillites and Onwatin Formation, and and wackes wackes of of the the Cbelmsford Chelmsford Formation. Formation. the Onwatin Onaping Formation Onapine Formation Onaping Formation is the lowermost formation of the Proterozoic Proterozoic Whitewater Whitewater Group. Group. The Onaping The formation consists of a 1400 m thick succession of initially glass-rich breccias and igneousThe consists 1400 m succession breccias ignwustextured rocks within the Sudbury Basin (53 by by 17 km). km). Rocks Rocks of of the Onaping Onaping Formation are are underlain by intrusive granophyres of the Upper Zone of of the the Sudbury Igneous Complex and and are overtain by carbonates and argillaceous conformably overlain argillaceous rocks rocks of of the the Vermilion Vermilion and and Onwatin Onwatin Formations. The TheOnaping OnapingFormation Formation isis the the stratigraphic stratigraphicfootwall footwall to the carbonate-hosted Vermilion and Emngton Errington Zn-Cu-Pb-Au-Ag Zn-Cu-Pb-Au-Ag deposits that that are are found in the the south-west quadrant of the Sudbury Onaping Formation has been Sudbury Basin (Figure 1). Coeval Coevalwith with the the Sudbury Sudbury Event, Event, the Onaping interpreted interpreted as as aa meteor metwr impact impact faliback fallback breccia breccia or oraavolcanic volcanicdeposit. deposit. The Onaping Formation consists of 33 major major units'that unitsthat are are discontinuous discontinuous around around the from the the base base upward, upward, they they are are the the Basal Basal Intrusion, Intrusion,the the Sandcheny Sandcherry Member and Sudbury Basin; from the Dowling member member [Gibbins (Gibbins 1994). These Theseare are different different subdivisions subdivisions than than described described by other other workers. Figure Figure22illustrates illustratescorrelative correlativenomenclature nomenclatureused used in in this this paper paperand andmost mostrecent recentprevious previous workers. Previous Peredery 1984; 1984; Grieve Grieve et al. 1991; 1991;Avermann Avermann 1992; 1992; Previous workers, workers, such such as as Muir Muirand and Peredery Avermann and Brockmeyer Brockxneyer1992, 1992,subdivided subdividedfragmental fragmentalrocks rocksof the Onaping Onaping Formation Formation into into aa of the lower Gray Member, an upper Black Member, and a middle Green member, member, distinguished, distinguished, as as their by colour. colour. The and fluidal-texfured fluidal-textured rocks rocks of of names suggest, by The same same authors authors subdivided the igneous- and Formation into into Basal Basal member memberand andMelt MeltBodies. Bodies. Table Table 1 I summarizes the Onaping Formation summarizes the stratigraphic subdivision nomenclature and stratigraphic subdivision used by previous workers. workers. Stratigraphic subdivision breccias by by Gibbins (Jibbins (1994) using a Stratigraphic subdivision of the Onaping Formation breccias non-genetic, detailed detailedmapping mappingapproach approachbased basedon onFisher's Fisher's classification of fragmental systematic, non-genetic, rocks (Fisher (Fisher 1966), 1966), in conjunction with standard bedrock mapping criteria and detailed morphological examination of of 'glass' fragments, fragments, showed showed that that carbonaceous carbonaceousmaterial materialwithin within the the matrix of the breccias is not time stratigraphic stratigraphic and is, therefore, not a viable criterion for matrix for the the stratigraphic subdivision of the the Onaping Onaping Formation. Formation. Gibbins stratigraphic Gibbins(1994) (1994)noted notedaapronounced pronounced stratigraphic percentage, size and and type type of of fragments fragments (Figure (Figure 3), 3), the stratigraphicdifference in the percentage, the morphology morphology forthe thevarious various depositional depositionalunits unitsthat that were were of glass shards, and in the mechanisms of emplacement for delineated. Based Based on on these these differences Gibbins Gibbins (1994) (1994) proposed proposedaa revised revied stratigraphic stratigraphicclassification scheme for the Onaping Formation that thatisisnot notbased basedon oncolour colour(i.e. (i.e.carbon carboncontent) content)(Figure (Figure4). 4). area, the Onaping Formation is aa 1400 m thick succession of devitrified In the Dowling area, glass-rich breccias and hypabyssal intrusions that dips gently at 25" 25° towards towards the interior of the the Sudbury Sudbury Igneous Complex. According Sudbury Basin and strikes parallel to the contact with the Sudbury According to Gibbins (1994), the succession consists of (1) a coarse, shard-rich, shard-rich, matrix-poor, lower lower member, that that is subdivided into into Fluidal Fluidal Fragment-rich Fragment-rich and Shard-rich Sandcherry member, Shard-rich units, units,(2) (2)aa finer, shard-poor, matrix-rich upper upper Dowling Dowling member, that that is is subdivided subdivided into into Lower, Lower, Middle Middle and and referred to to as as sheet-like sheet-like and and pipe-like pipe-likebodies bodiesof of Basal Upper Units, and (3) coeval intrusions, referred Intrusion and Aphanitic dykes dykes (Figures (Figures 44 and and 5). 5). The the Sandcherry Sandcheny and The contact between the �PRESENT PRESENT PAPER PAPER PAST PAST STUDiES STUDIES GIBB1NS GIBB1NS (1997) (1997) AVERMANN AVERMANN && BROCKMEYER BROCKMEYER (1992) (1992) MUIR & MUIR & PEREDERY PEREDERY (1984) (1984) MUIR MUIR (1983, (1983, 1981) 1981) BURROW & & BURROW STEVENSON THOMSON THOMSON(1957) (1957) RICKABY RICKABY COLEMAN COLEMAN (1972a, 11972b) (1 11972b) (1961, 1972) 1972) WILLIAMS (1957) (1957) (1930) (1905) (1930) (1905) Dowling Cowling Member Member Upper Upper and and Middle Middle Units Units Upper Upper Black Black Member Member Black Black Member Member Black Black Member Member black black Onaping Onaping Lower Lower Black Black Member Member Green Green Member Member Lower Lower Units Units Sandtherry Sandcherry PEREDERY PEREDERY gray gray Onaping Onaping Gray Gray Member Member Gray Gray Member Member Green Green Member Member Melt Melt Body Body Melt MeltBody Body Grey Grey Member Member melt melt rock rock melt mett body body Basal Basal Member Member Basal Member basal basal Basal Member Member Sasal black black tuft tuff Basal Basal Intrusion Intrusion Pipe-like Pipe-like Bodies Bodies Sheet-like Sheet-like Bodies Bodies Table Table 1: 1: breccia breccia - Nomenclature - Present Present and and Past Past (after (afterMuir Muirand andPeredery Peredery1984) 1984) andesitetuft, tuff, andesite tuff-breccia tuff-breccia volcanic volcanic luff, tuff, flow flow breccia breccia grey grey tuff tuff lapilli-tuff, lapilli-tuff, glowing glowing avalanche avalanche deposits deposits pepper-andpepper-andsalt salt micromicropegmatite pegmatite (chilled) (chilled) andesite andesitewith with rhyolite rhyolite fragments fragments lavas lavas quartzite quartzite breccia breccia (tectonic) (tectonic) rhyolite, rhyolite, rhyolite rhyolite breccia breccia rhyolite, rhyolite, Member Member Shard-rich & Shard-rich & Fluidal Fluidal Fragment-rich Fragment-rich Units Units BELL BELL (1893) (1893) pyroclastic pyroclastic sediments sediments siliceous siliceous volcanic volcanic breccia breccia part of part (unspecified) (unspecified) Trout Lake Lake Trout Conglomerate Conglomerate (with igneous(withigneouslooking looking matrix) matrix) Trout Lake Lake quartzite Troul quartzite agglomerate Conglomerate Conglomerate conglomerate conglomerate agglomerate '0 �To SANDCHERRY SANDCHERRY MEMBER MEMBER D 60 E E VITRIC FRAGMENTS FRAGMENTS VITRIC LITHIC FRAGMENTS FRAGMENTS LITHIC 50 A DOWLING DOWLING MEMBER MEMBER (I) zId I— 4° C) IL 30 LI- 0 Id C) zLi P 20 15 0 10 Li a- 5 — 0 SMFL SMFL SMSR SMSR SMSRC SMSRC I DMLCT DMLCT DML DML DMM DMM I DMU DMU UNITS DEPOSITIONAL UNITS Figure3:3: Figure Average percentage ofjunvenile and basement lithic fragments gitater than 1 mm in size in the fragmental units of the Onaping Formation (SMFL= Fluidal Fragment-rich units of Sandcheny Member, SMSR = Shard-rich units of Sandcheny Member, SMSR = Conductive Shard-rich units of Sandcheny Member, DMLCT = Lower Contact Unit of fowling member, DML = Lower units of Dowling Member, DMM = Middle units of fowling Member, DMU = Upper units ofDowling Member. (after (Jibbins 1994) �11 Dowling members change in the percentage of matrix, matrix, morphology and and members marks marks aa rapid rapid stratigraphic stratigraphic change size of shards, percentage of lithic fragments, and depositional depositional character character of of units. units. shards, percentage The description of of the the Onaping Formation is based on work presented The following detailed description by Gibbins Gibbins (1994). (1994). Sandcherry Member Sandcheny The Sandcherry average of 250 Sandcheny member (an average 250 m m thick) thick) is is distributed distributedalong alongthe the base baseof ofthe the Onaping Fragment and Shard-rich Onaping Formation Formation and is subdivided into Fluidal Fragment Shard-rich Units Units (Figure (Figure5). 5). Sandcheny mm in in size), size), that that are are Sandchenymember member rocks contain at least least 60% 60% fragments fragments (>1 (>1 mm predominantly altered "andesitic" "andesitic" glass glass shards with approximately 5% 5% lithic, lithic, basement fragments fragments (Figure (Figure 4). Glass Glassshards shardswithin withinthe theSandcherry Sandchenymember memberare areweakly weakly vesiculated vesiculated (<15% (<15% vesicles) vesicles) and of two predominant types: (1) equant, blocky shards (average (average <1 xx 11cm cmin in size), size),characteristic characteristic of Shard-rich Shard-rich Units and (2) tabular tabular to to ribbony, ribbony, flow flowbanded banded(fluidal), (fluidal),lapilli-sized lapilli-sizedshards, shards, characteristic characteristicof of Fluidal Fluidal Fragment Fragment Units. Units. Sandcherry member units, as defined by mapping, are massive, extremely extremely poorly bedded, laterally discontinuous (<3 km), kin), irregular-shaped breccia breccia deposits deposits that that range rangein in thickness thickness from from 50 50 or to 350 m. Contacts Contactsbetween between units are characteristically characteristically gradational, may be conformable or represent aa facies-like ficies-like change. The discordant, and commonly represent The Sandcherry Sandcherry member member encompasses encompasses units. Where both carbon-poor and carbon-bearing units. Where carbon-bearing, carbon-bearing, the the matrix matrix of ofthe the units units isis conductive. conductive. Fluidal Fragment Units Units (SMFLa, (SMFLa, SMFLb ,SMFLc, SMFLtr) SMFLtr) -- 2a, 2b, 2c, 3 Fluidal Fragment Units comprise four distinct and7) 7)based basedon onthe the distinct map units (Figures (Figures66and percentage percentage and size of fragments that characteristically characteristicallycontain contain aa prevalence prevalence (50 (50- 90%) of tabular to ribbony, flow flow banded shards, lapilli, blocks and bombs bombs (fluidal (fluidal fragments) fragments) of of aphanitic aphanitic 'andesite', 'andesite', aa relatively relativelyminor minor amount of white, equant, blocky shards (0.5 - 1.0 1.0 cm in size), and an extremely low percentage percentageof offine fineash-sized ash-sizedmatrix matrixmaterial. material. The matrix ground mass consists consists primarily of increasingly diminutiveshards shardsof ofthe thesame sameflow flowbanded bandedaphanitic aphanitic'andesite'. 'andesite'. The increasingly diminutive The 10% lithic fragments fragments units may also contain up to 5% 5% dark dark green green chlorite-actinolite chlorite-actinolite fragments, 2 - 10% and blocks, and 3% composite fragments fragmentsof ofother other Sandcherry Sandcherry member memberunits. units. Fluidal Fragment Units are are massive, massive, non-bedded, non-bedded,dense, dense,coarse, coarse,fluidal fluidalfragment-rich fragment-richbreccias. breccias. The four units lapilli-tuff and transitional) (autobreccia, lapillistone, lapilli-tuff, transitional) are are differentiated based on clast size size and percentage percentage and represent a continuous sequence from coarse, semi-massive, flow-banded, 'andesite' autobreccia material of of similar composition. composition. The transitional unit autobrecciathrough to tuff-sized material (SMFLtr) is is a hybrid unit contlining containing fluidal fluidal fragments fragments as as well well as as equant, equant, blocky blocky shards shards that that are are characteristic below. The characteristic of the Shard-rich Units, described below. The transitional transitionalunit unit isis included included within this subgroup subgroup due due to to the the abundance abundanceof of fluidal fluidal fragments. fragments. spatially associated associated with Aphanitic dykes and Fluidal Fragment Units are commonly spatially grouped together represent "Fluidal Breccia bodies of Basal Intrusion and when grouped Breccia Complexes". Complexes", Fluidal Breccia Breccia Complexes typically are several hundred metres to kilometres in size, and are the strata strata of the the Sandcherry member member (sometimes (sometimes"stacked"), 'stacked'), but but are aremore more found throughout the towards the the base. base. Fluidal Fluidal Fragment Fragment Units are are conformable conformable with other fragmental units common towards tuffs), but also intrude discordantly discordantly through (including carbon-bearing tuffs), through them. - - - Shard-rich Units Units (SMSRa, (SMSRa, SMSRb, SMSRc, S 4c,5 SMSRc, SMSRC) SMSRC) -- 4a, 4b, 4c, The Shard-rich that are aredistinctive distinctivefrom fromthe theFluidal Fluidal Shard-richUnits consist of four mappable mappable units units that (Figures 66 and and 7). 7). Characteristic Characteristicof ofthe the Shard-rich Shard-richUnits Units isisthe the prevalence prevalence of of 40 40 Fragment Units (Figures - �12 85%, moderately moderately well sorted, white to pinkish-white, equant, blocky shards, shards, (<1 ( 4 xx 11cm cmininsize) size) 85%, within a fine fine ash-sized microcrystalline light Where carbonaceous carbonaceousmaterial materialoccurs occurs within light green greenmatrix. matrix. Where within the matrix of the Shard-rich Units, Units,the thematrix matrixisisdark darkgray grayto to black black and and conductive. conductive. The Shard-rich units also <10% also contain up to 15% 15% cored bombs, 4 0 % fluidal fluidal fragments, fragments, 1-5% 1-5%accretionary accretionary lapilli, <5% fragments of other Sandcherry <5% lithic lithic fragments, and up to 5% 5% composite fragments Sandcheny member units. The The Shard-rich Shard-rich Units Units are are distinguishable distinguishable from the Fluidal Fragment Units by the occurrence occurrence of of moderately moderately well sorted sorted blocky white shards shards within aa fine finematrix, matrix. were mapped mapped as lapillistones, lapilli-tuffs lapilli-tuft's or or tuffs, tiffs, Non-carbonaceous Shard-rich Units were the size size and and percentage percentageof offragments. fragments. Carbonaceous depending on the Carbonaceous (black (black matrix), matrix), predominantly predominantly Shardrich Units mapped as as SMSRC SMSRC (Unit (Unit 5). 5). Except conductive Shard-rich Units were mapped Except for for the the occurrence of carbon throughout throughout the matrix, this unit is lithologically the carbon the same same as as the the other Shard-rich units. Contacts carbonaceous and andnon-carbonaceous non-carbonaceousShard-rich Shard-richUnits Unitsare aregradational. gradational. The Contacts between carbonaceous Shard-rich Shard-rich Units Units are arethick, thick,confonnable, conformable,laterally laterallycontinuous continuous(several (several1cm) km) sheet-like sheet-like depositional depositional units packed, originally originallyglass-rich glass-richbreccias. breccias. The units of of massive, massive, non-bedded, densely packed, The units units may may locally locally The units units are are situated situatedthroughout throughoutthe the strata strata have a bomb- and block-rich-base, block-rich-base, and/or and/or aa finer finertop. top. The of to pinch and and swell along along strike. Shard-rich of the the Sandcherry Sandchenymember and appear locally to Shard-richUnits Units overlie, underlie, are grade laterally are intruded intruded by, and grade laterally into into Fluidal Fluidal Fragment FragmentUnits Units of ofthe theSandcherry Sandcheny member. Generally, Sandcheny member. Generally, the the Shard-rich Shard-rich Units mark the top of the Sandcheny member. Interpretation Interpretation Shards passive Shardscharacteristic characteristicof of the Fluidal Fragment Units formed by relatively passive fragmentation processes (auto-brecciation) caused caused by by the the interaction interaction of of melt melt with with surrounding surrounding fragmentation water and/or and/or "wet" "wet" (water-rich) breccias. Emplacement Emplacementand and deposition deposition of of the the Fluidal FluidalFragment Fragment Units varied from repeated shallow level intrusion and auto-brecciation to explosive explosive eruptions eruptions characterized by submarine and and subaerial subaerial fountaining fountainingand andspattering. spattering. Passive fragmentation appears to appears to have have been been widespread widespread along the base of the Sandcherry Sandchenymember, member, where where Fluidal Fluidal Fragment Units Units occur occur as as "crusts" "crusts" to to underlying bodies of Basal Intrusion, and also also higher up Fragment section Basal Intrusion intruded wet section where where Aphanitic Aphanitic dykes and pipe-like bodies of Basal wet breccias breccias and and auto-brecciated. auto-brecciated. The TheFluidal FluidalFragment FragmentUnits Unitswere were emplaced emplaced contemporaneously contemporaneouslywith with the the ShardShardrich Units of member as as both discordant, brecciated brecciated intrusive bodies and of the Sandcherry Sandcherry member confonnable conformableinterbedded interbedded units. Contacts Contactsbetween between these these two two Units, Units, where where gradational, gradational,are are represented by LMFLtr, LMFLtr, a transitional transitional unit. Emplacement Emplacementof ofFluidal FluidalFragment FragmentUnits Unitscontinued continued during the Dowling Dowling member. member. In duringand and after afterthe the deposition deposition of the Lower Units of the In conjunction conjunction with the Basal Basal Intrusion Intrusionand and Aphanitic Aphanitic Dykes, Dykes, the Fluidal Fragment Units record a complex history of continued continuedmultiple multiple intrusion, auto-brecciation, and and explosion explosion and and may may spatially spatiallyrepresent represent"vent" "vent" areas areas within within the the Onaping Onaping Formation. The Theemplacement emplacementand and deposition deposition of of Fluidal Fluidal Fragment FragmentUnits Units are are interpreted interpretedto tobe besimilar similarto to the theemplacement emplacement of (1) (1) peperites peperites described describedby by Hanson Hansonand andWilson Wilson (1993), (2) intrusive intrusivehydroclastic hydroclastic breccias breccias described by Hanson (1991), and/or and/or(3) (3)vent-fäeies vent-facies (1993), (2) deposits summits, described described by by Smith and and Batiza (1989) deposits of of hyaloclastic hyaloclastic eruptions on seamount summits, (Figures (Figures 8, 8, 9, 9, and and10). 10). The The Shard-rich Shard-rich Units Units of of the the Sandcherry Sandcheny member are are interpreted interpretedto to have haveformed formedfrom fromthe the same Units. The same melt that formed the Fluidal Fragment Units. The Shard-rich Shard-richUnits Units are arethe theresult resultof ofmore more explosive explosiveinteraction interactionand and eruption eruption of of large large volumes of predominantly juvenile material comprising comprising mostly equant, blocky shards and fine ash-sized material. The Shard-rich Units were deposited mostly equant,blocky shards The Shard-rich Units were deposited throughout throughout the the Sandcheny Sandchenymember member strata strataand and are arethe the explosive explosiveproducts products of ofthe therepeated repeated emplacement melt into into its its own ownbreccia brecciapile. pile. The emplacement and brecciation of melt The occurrence occurrenceof of accretionary accretionary lapilli lapilli indicate indicatethat that eruption eruptioncolumns columns associated associated with the deposition deposition of of the the Shard-rich Shard-richUnits Unitswere, were, in in part, part, subaerial. subaerial.The Theshard-rich shard-richUnits Unitswere weredeposited depositedrapidly rapidlyas asvoluminous, voluminous,essentially essentiallynonnonbedded, particle concentration), subaqueous subaqueous "pyroclastic" bedded, dense dense (high particle "pyroclastic" falls falls of ofslurry-like slurry-like hyaloclastic contemporaneouslydown downslope slopeas asmass massflows. flows. The hyaloclastic flows flows that likely sloughed contemporaneously �1994) GibbS (after Stnicture Sudbury Formation, Onaping the of units map of subdivision and column Stratigraphic -1 '3 ONAPING FORMATION -i<i 4: Figure �ONAPING FORMATION if. SUDBURY IGNEOUS COMPLEX GRANOPHYRE WHITEWATER GROUP CHELMSFORD FORMATION I ONWATIN FORMATION I ONAPING FORMATION DOWLING MEMBER I SANDCHERRY MEMBER SHARD-RICH UNITS FLUIDAL FRAGMENT UNITS 0 INTRUSIONS APHANITIC DYKES BASAL INTRUSION a �LEGEND LEGEND [] 15 MiDDLE MIDDLE PROTEROZOIC PROTEROZOIC Diahose tYykas (1245—1460 t/— 130 Ma) EARLY EARLY PROTEROZOIC PROTEROZOIC SUDB%JRY IGNEOUS COMPLEX (1849.6 +3.4/-3.0 Ma) ORMOPI-IYRE WHITEWATER GROUP CHELMSFORI) FORMAtiON M<oslc to lithic aricosic sandstones (wockes), minor mudstones ONWA11N ORMA1iON Black carbonaceous argllfites. minor ttones ONAPING FORMA11ON INTRUSIONS — iiwmc DYXES (commonly flow bonded, xenoflth—poor) aASAL INIRUSION (medkan to fine—grainS. ccmrnon3' xenslth—ttcsi) — Shoot—like bodies Bib - Border phase with 0rortopl'rn Sic - Pipe-4Ike bodies I 2 OM—DOWUNG MEMBER (lenficulor to plots—Se shads, >60% mabtx) UPPER UNITS (reworked, block carbonaceous matrix) OIhUc — Conductive fine bitt. CX kiplTh—zed fmgmecits (noted In drill hole only) DMUb - fine bitt, <3% cpU—ted fragments DMUo — Redded tuft. lnterbsds of UMUb and UMMc MIDDLE UNITS (<3% block-sized fmgrnenth, carbonaceous matrix) DUMo - topifilatone UMMb - Loplol-tuff DMMc — tuft LOWER UNITS (Matrix Is locally non—carbanooeous >3% block—sIzed fragments) DMb - Loplifistone/ruff BrecS OMLI, - Lopilli-tuff [El [J DMLo — Tuft DMt.CT — Cant Unit — Tuff/Lcpltil-b.sft, eutoxitic bxtur., fine motstc <10% fragments >2cnt and bombtiict base SMSANDCHERRY MEMBER W [J [J (<40% matrIx) SHARD—RICH UNITS (equant. blocky shards) tuft, grades 100* to lapifhitne ad tiff. block carbonaceous matrix SMSRC - onductive C (locally non—conductive), <3% accredonary kipilil SMSfa — Lopifiletone, nan—carbonaceous matrIx SMSRb — LoplIll—tuff. non—carbonaceous matrix SMc — luff, non—carbonaceous mattc 5 FLUIDAL FRAOMtNT UNITS (fiuldal. ribbon-like, flow bonded fragments common, ror* and locally block carbonaceous matctc) SMFIk - Thff/Tu <t%. .rt>flctn in te. equant blocky shards also SMRA — Mt.ct,reccla, 'C20% matrix, block— and bomb—rich StIFLb — Lopilistone SMELo - La$U-tiff U NDEAND UNITS (lower units, significant matrix recsystallizatlan and pervasive sftklfIoatlon) SM— — Tuft—brecalo - tn_one SM--- - Lopilli—tuiff case letters (a. b. e) In unit codes do not necessarily denote time etrotigraphic order. Figure figure6:6: Detailed Detailed legend legend and and stratigraphic d g a p h i c subdivision s u H ~ s i o nof the theOnaping OnapingFonnation FormationofThe oftheSudbury Suhy Structure GibbS 1994) Structure(after (&er Gibbii 1994) �I j I Q'a 1 ClassXcation scheme and terns used in the detaiIed legend and stratigraphic subdivision of the Cnapin~Formation of the Sudbuv S t n ~ c h ~(Figure re 6) ( a b Gibbiis 1994). LapiHi 64—2mm Ash <2mm (Modified after Fisher 1966) Blocks and Bombs >64mm 6 4 3 2 1 pre—existing sulphides sulphide fragment — fragmentary mineralization derived fran, fluldal fragments — aftered Juvenile fragments that display contorted flow banding block — fragment >B4mm ejected in a solid condition bomb — glassy fragment >64mm ejected in a molten state matrix — fragments <1mm in size shards — lapilil—sized or smaller, aftered glass fragments NON—GENETIC TERMS TO DESCRIBE FRAGMENTAL ROCKS CSSIFICATION TERMS USED HEREIN ARE �17 hyaloclastic debris was likely deposited deposited quenched quenchedor or wol, cool, as as there there is is no evidence evidence of of welding. welding. Fire hyaloclastic fountaining, fragmentation of fountaining, ejection of bombs, and explosive explosive fragmentation of ash-, ash-, lapillilapilli-and andblock-sized block-sid and composite) composite)were wereongoing ongoingprocesses processesdurini during deposition. deposition. Emplacement material (juvenile, fiivenile, lithic and hyaloclastie flows on seamount of the Shard-rich Units is interpreted to be similar to hyaloclastic seamount summits, and Batiza Batiza (1989) (1989) (Figure (Figure 8). 8). The described by Smith and The source sourceof of the the Shard-rich Shard-richUnits Units isis interpreted interpreted to be the same Fragment Units. Units. Eruption the he same vent sites as for the Fluidal Fragment Eruptionand andemplacement emplacement of both t Shard-rich and Fluidal Fragment Units occurred contemporanwusly; contemporaneously; the two Units reprSent U ~ t likely s represent different merent vent ticies faciesof ofthe thesame sameeruptive eruptiveprocess p m s that that varied variedin ineffusion e6sionrates ratesand andexplosivity explosivitywith with time. Unit U NLMFLtr ~ LMFLtrlikely likelyisis the the product product of of both both the the eruption emption mechanisms mechanisms characteristic characteristic of the Fluidal Fluidal Fragment Fragment and and Shard-rich Shard-richUnits. Units. The Sandcherry due to to fragmentxtion fragmentation and emption eruption pprocesses Sandcheny member was eemplaced m p l d due r m s e s that involved both passive and explosive interaction of water water with melt, melt, that that was wasrepeatedly repeatedlyemplaced emplaced into its own breccia pile. pile. IfIf there was aa meteorite meteorite impact, "failback" "fallback" is is not represented represented by the there was Sandcherry Intrusion (i.e. Sandcheny member, but is possibly represented by some components of the Basal Intmsion lithic lithic xenoliths). xenoliths). Dowling Member Member member comprises comprisesthe theupper upper 75% 75% (1000 m) of the Onaping Ouaping Formation, and The Dowling member consists of at least wnsists least 10 10 glass-rich, glass-rich, weakly bedded, fragmental units that that are are grouped grouped into into Lower, Lower, Middle, and Upper Units (Figures 5, 6 and 7). 7). Units Unitsofofthe theDowling Dowlingmember memberdefine defineuniform, unifom laterally continuous deposits tthat hat characteristically 60% fine fine ash-sized characteristically consist of more than 60% material material (matrix) (matrix) and and are are essentially essentially carbonaceous, carbonamus, with the the exception exception of of the the lower lower Contact Contact Unit Unit (DMLCT -- U Unit i t 6) 6) (DMLCT member rocks rocks contain contain less lessthan than40% 40% fragments fragments (>l (>1 nun mm in size) that that are Dowling member predominantly glass shards with approximately 15% predominantly altered "andesitic" glass 15%lithic fragments fragments (Figure 4). Glass Glass shards shards of of the the Dowling Dowling member, compared to shards of the Sandeherry Sandcherrymember, are are smaller, smaller, contain fewer, torn4ooking, fewer, but larger larger vesicles, display less flow banding and have a more wispy, torn-looking, lenticular lenticular to plate-like shape. Dowling Dowling member member depositional depositiod units are are of of considerable considerablestrike strikelength length (2 to more than 10 km),are uniform in thickness (25 -- 300 300 in), m), and conformable to 10 kin), and display display conformable lower contacts. contacts. Sedimentary unconformable erosional lower Sedimentarystructures stmcturesare areevident evidenttowards towardsthe thetop topof ofthe the Dowling member. Member Lower Units of the Dowling Member Dowling member member wmprises comprises four four distinct distinct map map units, including the the This subgroup of the Dowliig Lower "chioritic shard horizon'' horizon" or h w e r Contact Contact Unit Unit (DMLCT (DMLCT - Unit 6), previously known as the "chloritic member". The "Green memkr". TheLower LowerUnits Units are aredistinguishable distinguishablefrom &om Sandeherry Sandcherrymember memberunits units essentially essentially by aa greater greater percentage percentage of ash-sized a s h - s d matrix and different shard morphology, and from Middle Units of the Dowling member by by the the presence presenceof ofblock-sized block-sizedfragments fragmentsof ofcountry countryrock rock and and 'andesite' 'andesite' comprise aa reverse ggraded package (increasingly coarser coarser bombs. Collectively, Collectively, the the Lower Units wmprise d e d package crudely channellized ehannellized units, units. Individual depositional units units up section) section) of thick, thick, non-bedded, cmdely are normally graded) TheLower LowerUnits Units have have an an average average true thickness of 200 m, graded)..The in, but range than 55 in than 300 m. The locally from less than m to more than TheLower Lower Units Units were were mapped mapped as as tuffs, tuffs, lapillilapilliand aa considembly considerably coarser lapillistone tuft' breccia. breccia. ttufTs, u s , and lapillistone to tuff - - Unit (DMLCT) (DMLCT) -66 Contact Unit - green The most distinguishing feature feature of of D DMLCT the predominance predominance of 20 20 - 45% m C T unit is the 45% p n to chloritic shards (less than than 55 mm mm in insize) size)within withinaavery veryfine finematrix. matrix. The matrix is dark green ehloritic normally a pale bluish green, but may be dark gray to black due due to to fine fine carbonaceous carbonamus material, material, �Figure 8: A BY./; — //jz>'>,> — rn K//'. :'>' — 7. Schematic model for the development of intrusive hydroclastite breccias (Hanson 1991) S EM ENT SE DIM EN -_ WATER /7.;'C., — — - oc �cJ• Figure 9: • %— RHYOLITE PEPERITE --__ 1993) - PEPERITE Schematic model for the development of peperites (Hanson and Wilson FEEDER CONDUITS' - - o:. 'I REDEPOSITED _____ _ - WATER WET SEDIMENTS _ 'C �20 e. non explosive formation of splinter shards zone of explosive mixing of magma and sea water: fluidal and blocky shards produced density flow entrains vent -.J. 5 metres Schematicdiagram diagramillustrating illustratingstyle styleofoferuption eruptionenvisioned envisioned to produce the Schematic to produce the hyaloclastitedeposits depositson onseamount seamountsummits summits(Smith (Smith and Batiza 1989) hyaloclastite and Batiza 1989) Figure 10 10: Figure �21 which usually occurs the unit. unit. The which occurs towards the top of the The DMLCT Unit contains some (<15%) ( 4 5 % ) blocky shards characteristic of the the Sandcherry Sandcherry member, member, but butthe the majority majority are are finer, finer, angular angular shards similar similar to those characteristic glass glass splinters splinters and and plate-like shards. The Theunit unit commonly commonly displays displays a eutaxitic-like eutaxitic-liketexture texture (incipient (incipient welding), defined by the alignment of of plate-like plate-likelenticular Icnticularshards. shards. Locally, flow flow features features are arevisible visible around the margins of blocks blocks and and bombs. bombs. The unit also contains 5% fluidal 5% fluidal lapilli, 5% 5% bombs, The <5% fragments,and and<3% <3% composite fragments of Sandcherry member <5% lithic lithic fragments, composite fragments of Sandcheny member units, units, This unit outcrops outcropsasasdiswntinuous discontinuous lenses to several kilometres in at length at the contact lenses up toup several kilometres in length the contact between the Sandcherry and Dowling Dowlingmembers. members. The lower contact contact of of the the DMLCT DMLCT Unit is bombs, 0.5 --22 m commonly marked by an an increase increase in percentage percentage (5 -- 45%) of blocks and bombs, m in in size, size, units. Where with respect to underlying units. Where a block- and bomb-rich base is not observed, the contact contact is gradational over decrease upwards gradational over a distance distance of of 33 to to S5 m and is indicated by a decrease upwards (in (in section) section) in in shard shard in shard shard morphology. morphology. The upper contact contact of of the the DMLCT DMLCT size and percentage, as well as a change in Unit, though not typically observed, is sharp and marked by an increase (up section) section) in in lapilli-sized lapilli-sized fragments and and an an absence absence of of eutaxitic-like eutaxitic-liketextures. textures. The Contact Unit may extend around the where the the unit unit was was deposited deposited above water. basin but the "welded texture" may only be developed where compacted (not deposited Elsewhere, the Contact Contact Unit Unit is is not not welded or compacted deposited hot) and and looks looks like like other other units that that were deposited deposited below belowwater water (subaqueous (subaqueous deposition). deposition). In Dowling member units In other other words, words, = subaerial deposition and non-welded = subaerial deposition = subaqueous subaqueous deposition. Welding Welding is is aa good good welding = paleoenvironment indicator. indicator. The The DMLCT DMLCTUnit Unit isis the the first first stratigraphic stratigraphicoccurrence occurrencecontaining containingdepositional depositionalfeatures features characteristic underlying units units of the Sandcheny Sandcherry member, characteristic of of the the Dowling Dowling member.. Compared to underlying the DMLCT DMLCTUnit Unit shows shows an an increase increase in percentage percentage of composite fragments, lithic litbic fragments, fragments, bombs, and having aa block- and bomb- rich base and cored cored bombs bombs (both (both simple and complex), locally having that clearly clearly separates separates this this unit unit from from underlying underlying Shard-rich Units of the Sandcheriy Sandchenymember. member. Lower Units ((DMLa, 7a, 7b, 7c D M 4 DMLb, DMLc) -- 7% 7c Differentiated by size and percentages percentages of of similar similar fragments fragments types, types, these three three units, lapillistone to tuff breccia, lapilli tuff, and tuff, represent represent a discontinuous, discontinuous, crudely crudely interlayered interlayered sheet that comprises the the bulk bulk volume volumeof ofthe theLower LowerUnits. Units. Contacts between the the various various units are typically indistinct, but can be sharp. Lower Lower contacts contacts are locally channelized. Tuff Tuff (DMLc), (DMLc), where where preserved, preserved, is is commonly commonly the the lowest of the three units and usually usually directly directlyoverlies overliesthe the DMLCT Unit (Unit DMLCT (Unit 6). 6). Lapillistone (DMLa) is normally found near the the top top of of the the Lapillistonetototuff tuffbreccia breccia(DMILa) with lapilli-tuff lapilli-tuff(DMLb). (DMLb). Individually, Individually, the the units units are are crudely, crudely, but but normally nonnally sequence, intercalated with graded. Together, sequence. The Together,the thethree threeunits units define define a reversely graded sequence. The units units are aredistinguished distinguished from the underlying DMLCT DMLCT unit by by aa coarser coarser appearance appearance and and the the absence absence of of eutaxitic eutaxitic textures textures in in the matrix. Overlying Overlyingunits units are arebetter better sorted, sorted, and and lack lack coarse coarse lapilli lapilli and and block sized fragments. fragments. The units normally have a dark gray to black carbonaceous carbonaceous fine fine ash-sized ash-sized matrix, matrix, which which represents more than 60% of the rock. rock. The units also contain 15 25% wispy, lentieular to The units also 15 25% lenticular cuspate cuspate shards, shards, 55 - 95% flow flow banded, tabular and fluidal fluidal lapilli lapilliof ofaphanitic aphanitic 'andesite', 'andesite', 3 -- 40% of aphanitic, aphanitic, poorly poorlyvesicular vesicular'andesite' 'andesite', 5 - 10% bombs, cored bombs and blocks of lithic fragments fragments 10% lithic Sandcherry and Dowling member and blocks, and up to 10% 10%composite composite fragments of underlying Sandcheny units. Rare Rarediscontinuous diswntinuouslenses lensesof offine finetuff tuffare arelocally locallyinterbedded interbedded with with the the coarser coarserunits. units. Bedding or layering layering is is not not evident evident at the outcrop outcrop scale. scale. - - - 8a, Sb, 8c 8c Middle Units (DMMa, DMMb, DMMe) DMMc) -- Sa, The memberconsist consistof ofsimilar, similar, thick thickdepositional depositional units units of of The Middle Units of the Dowling member and lapillistone. lapillistone. The tuff, lapilui-tuff lapilli-tuff and The three map units that comprise comprise the Middle Units are are different different only in the percentage percentage of of lapilli-sized, lapilli-sized,dark, dark,chloritic chloriticshards shardsand andlithic lithicfragments. fragments. The The units units m inin true true represent the majority majority (>60%) (>60%) of of the the Dowling Dowling member, and collectively collectively average average 600 600 m �22 gradational. thickness. Contacts with underlying DML Units and overlying DMU Units are mostly gradational. the field from underlying underlying DML DML Units by the absence of blockMiddle Units are distinguished in the and bombs. bombs. Overlying sized lithic fragments and Overlying DMU DMU Units are are finer finer grained and more distinctly bedded. bedded. contain more than than 65% matrix, mostly dark gray to black due to presence of DMM Units wntain carbonaceous 35% wispy, lenticular to cuspate shards, 11 -carbonaceous material. The Theunits units also alsocontain wntain 15 15-- 35% 5% equant, flow banded 'andesite' fine lapilli-sized fragments, <7% lithic fragments (<4 (<4 cm in 5% banded fine 8% shiny, dark, rounded size) and and 2 -- 8% rounded quartz quartz grains, grains, <1-2 mm mm in in size. size. Shards size) Shards in DMM Units display similar DML Units. Some similar features to shards shards contained in underlying DML Some shards shards appear appearto tobe be coated or surrounded by fine ash-sized material material and carbonaceous material. Composite Compositeblocks blocks and and irregular clumps irregular clumps of of coarser coarser and and finer finer underlying underlying breccia breccia units units are arecontained containedin in DMM DMMUnits. Units. Upper Units of the Dowling Member This subgroup This subgroup of the Dowling member marks the top top of the Onaping Onaping Formation Formation and and isis divided into into three three map map units. units. In stratigraphic order DMU Units comprise a basal bedded In stratigraphic order DMU Units wmprise a basal bedded tufT tuff Unit 9a), a fine tuff (DMUb -- Unit Unit 9b), 9b), and and an an upper upperconductive, conductive,fine finetufT tuff (DMUe (DMUc -- Unit (DMUa - Unit 10). Overall, Overall,DMU DMUUnits Units comprise comprise aa normally normally graded graded sequence sequence that has an average average true thickness of 170 m. DMU Units are much finer than underlying units (Figure 4), and display 170 m. DMU Units are much finer than underlying units (Figure 4), and displayfeatures features suggestive of reworking suggestive reworking and and re-deposition. redeposition. - Bedded Tuff Tuff-- (DMUa) (DMUa) -- 9a This tufT(DMUa) (DMUa) occurs occurs at at the the transitional transitional contact zone between DMM and DMU This bedded tuff DMU Units and contains alternating alternating beds of material characteristic of both. DMUa DMUaisisdistinguished distinguishedfrom from underlying DMM Units by the first stratigraphic stratigraphicoccurrence occurrenceof oflaterally laterallycontinuous, continuous,shard-poor, shard-poor, fine ash-sized interbeds intercalated with the relatively coarse tuffs tufTsand and lapilli-tuffs lapilli-tuffsthat that are are characteristic characteristic of of DMM DMM Units. Units. DMUa consists consists of alternating alternating coarse coarse beds beds of of Dowling Dowling member member Middle Units and and fine beds of Dowling member member Upper Upper Units. Units. Individual beds vary considerably in thickness, but but generally average cm thick. The Theaverage averagethickness thickness of of DMUb DMUb beds beds increases upwards. DMUb DMUbbeds beds average55 to to 50 50 cm consist of fine ash-sized ash-sized fragments fragments of ofjuvenile juvenile and lithic material; fragments greater than 2 mm are uncommon. Normal beds isis absent absentto toweakly weaklydeveloped; developed; contacts contacts unwmmon. Normal grading gradingwithin within individual individual beds between beds are sharp, with uncommon soft sediment slump features and small, channel-like structures. structures. - TufT-- (DMUb) Fine Tuff (DMUb) - 9b Contacts Contacts are are conformable conformable and and gradational, gradational,marked marked by by an anabsence absenceof ofthe theDMM DMMUnit-like Unit-like comnon in (Unit9a) 9a) and and by by aa generally coarser appearance appearance and interbeds common in the theunderlying underlying DMT.Ja DMUa (Unit and lack of conductivity, compared compared to to the the overlying overlyingDMUc DMUc (Unit (Unit 10). 10). DMUb is is well sorted sorted with material finer finer than than 1 mmm insize. size. Much of the fine ash ash material material is is subsubm in greater than 95% of the material rounded lithic lithie fragments and and rounded rounded (abraded) (abraded) shards. shards. Rare, Rare, larger largeraltered altered glass glass shards shardsmay mayalso also occur. DMUb DMUbisislocally locallyinter-layered inter-layered with with beds beds of of angular angularto torounded rounded argillaceous argillaceous and cherty cherty fragments, less than 2 cm in size. Individual Individual beds are are commonly commonly less than 40 cm thick, and may contain up to 80% fragments. Many 80% of these dark gray to black fine sedimentary fragments. Many of of the the fragments fragments wntain give give the impression of of being rip-up elasts. clasts. �23 - - Conductive ConductiveFine Fine TufT Tuff - (DMUc) (DMUc) - 10 10 tuft' (DMUc) (DMUc)was was described described by by Paakki Paakki (1992) (1992) as "Conductive This conductive fine tuff 'andesite' tuft". tuff". Conductivity Conductivityisisattributed attributedto tothe the presence presence of of fine carbonaceous material. Lower Lower underlying DMUa DMUa and and DMUb DMUb are are marked marked by by aa gradational gradational fining finingand andthe theonset onsetof of contacts with underlying associated with with aa stratigraphic stratigraphic increase increase in in carbonaceous carbonaceous material. material. The conductivity, associated The upper upper contact contact with overlying sediments and and carbonates carbonates of the Vermilion Formation is sharp sharp and and conformable. conformable. from the the similar similar looking looking Onwatin Onwatin Formation Fonnation by the absence of fine DMUc is visually distinguished from laminations and siltstone laminations siltstone interbeds. interbeds. The The upper 55 to 10 10m m of DMUc DMUc is is black, black, fine, fine, poorly poorly bedded bedded to to massive, massive, and and strongly strongly conductive. Towards Towardsthe thebase baseof ofDMUc DMUcconductivity conductivitydecreases decreasesand andwispy wispylenses lensesof oflighter lighterand and slightly coarser, dark gray apparent. gray tuff tuff become apparent. Interpretation The The morphology morphology and internal internal characteristics characteristicsof ofshards shardswithin withinthe theDowling Dowlingmember memberindicate indicate that vesiculation (volatile (volatile exsolution) played a role, though though aa minor minor one, one, in in the the predominantly predominantly hydroelastic hydroclastic fragmentation fragmentation and eruption of the Dowling member. The The Dowling Dowling member member Lower Lower Contact Unit represents a deposit formed by by fragmentation processes that changed from the Contact relatively passive to moderate explosive generation of Fluidal Fragment Fragment Units (proximal, (proximal, intrusive/extrusiveauto-breccia deposits) and co-genetic Shard-rich Units (more widespread intrusive/extrusive hyaloclastic activity and and basin-wide deposition deposition of of voluminous voluminous falls, hvaloclastic deposits) to more explosive activity falls. flows and subsequent mass mass flows. Consistent and consistent with the greater explosivity expiosivity is a fine grain size &d minor (10%) in the the lithic lithicfrwment fragment content of depositionai units. The Sandcheny (10%)enrichment in content of depositional units. The Sandchem member/Dowling member contact is suggestive of an evolving hydroclastic hydroclastic eruption that that was was initially initially relatively passive, passive, but but with with time timebecame becamemore moreexplosive. explosive. The Contact Unit (the DMLCT DMLCT Unit) is interpreted interpreted to have been deposited relatively hot, possibly in aa subaerial to shallow subaqueous environment, subaerial to shallow subaqueous environment,and andisisincipiently incipientlywelded welded (where (where deposited subaerially). The TheDMLCT DMLCTUnit Unitisisthe theproduct productofofthe theexplosive explosiveintroduction introductionof ofnew newmelt melt at at surface. surface. The majority of the Dowling member units units are interpreted interpreted to have have been deposited deposited subaqueously as a prolonged, explosively erupted erupted series series of of "pyroclastic" falls, flows and subaquwusly subsequent debris or mass flows. Nearly in the the Nearlycontemporaneous contemporaneousslumping slumpingand and sloughing sloughingresulted resulted in transportation transportation and re-deposition redeposition of tuffaceous material down slope in the form of pyro-turbidite mass flows (Figure 111). 1). Cored, Cored, aerodynamic aerodynamicbombs bombs indicate indicate that that eruption eruptioncolumns columns and debris-like mass were, in part, subaerial subaerialand and associated associated with lava lava fountaining fountaining during during the the deposition of the Lower Units. Lower LowerUnits Unitswere weredeposited deposited on on fairly fairly irregular irregularpaleo-topography paleo-topographyas aspoorly poorlysorted, sorted, ehannellized sheets of significant thickness. In contrast, the Middle Units arc interpreted channellizcd of significant thickness. contrast, the Middle Units are interpreted to to have have been deposited as a series 10 m) "pulses" series of frequent, frequent, thin (1 - 10 "pulses" of generally better sorted, sorted, finer finer (block(block- and bomb-poor), possibly possibly graded graded material; material; there there isis no noevidence evidence of of significant significantsedimentary sedimentary re-working. Deposition was rapid and mass slumping destroyed primary depositional Deposition was rapid and mass slumping destroyed primary depositionalfeatures. features. The "pulses" are are typical typical of of hydroclastic hydroclastic explosions explosions where water water intermittently has access access to to melt. Deposition of the laterally continuous and uniform Middle Middle Units of of the the Dowling Dowling member marks marks aa change to a more tectonically stable stable depositional depositional environment, compared to that that of of the the Lower LowerUnits Units member. The of the Dowling member. The Upper Upper Units Units represent represent the final final deposition of fine ejecta and subsequent subsequent sedimentary sedimentary reworking. reworking. - Basal Intrusion Intrusion subdivided into intothree threeseparate separatemap mapunits. units. These are (I) The Basal Intrusion is subdivided (1) Sheet-like Sheet-like bodies (BIa), which occur occur as discontinuous sheets or or sills, up to 300 m thick, at the base base of of the the �24 Sandcheny bodies (BIG), (Bk), which occur Sandcherry member, (2) Pipe-like bodies occur as as irregularirregular-to toovoid-shaped ovoid-shapedintrusive intrusive masses Sandcheny and fragmental units of the Sandcherry and Dowling members (pipe-like bodies are masses within fragmental commonly commonly exposed in clusters, clusters, and range in size from less than 2 xx 22 in in to over 50 x 100 100 m), and and (3) Border phase with Granophyre (Bib), (BIb), which which represents represents aa transitional transitional contact zone up to 65 m thick between sheet-like bodies bodies of of Basal Basal Intrusion Intrusionand andGranophyre. Granophyre. The The border border phase phase was was not not Granophyre and fragmental units units of of the the Sandcheny Sandcheny member are in direct contact. contact. noted where Granophyre (Ma) -- 1Ia Sheet-like (Ha) l a and and Pipe-like Pipe-like Bodies (BIc) (BIc) -- lie 1l c 1 pipe-like bodies bodies of ofBasal Basal Intrusion Intrusion are are igneous-textured phases of the same Sheet-like and pipe-like same unit, and and are aredifferent differentonly only in in their their morphology morphology and stratigraphic stratigraphiclevel level of of exposure. exposure.The Themost most distinguishing 85% (ave. 35%) xenoliths of a variety of distinguishingfeature feature of of the the Basal Basal Intrusion Intrusion isis S5 - 85% leucocratic basement rock types (quartzites, granitoids). leucocratic rock types (quartzites, granitoids). Xenoliths Xenoliths are are randomly randomlyoriented, oriented, subangular to rounded, sub-equant,.and .sub-equant,and range in size from from <5 <5 mm to to 30 m, but average average 30 30 - 40 subangular cm. rounded. The cm. Locally, Locally,xenoliths xenolithsare arewell well sorted sorted and well rounded. The xenoliths xenoliths decrease decrease in size and are better higher in in strata. strata. Pristine better sorted sorted in in bodies of Basal Intrusion exposed higher Pristineto tocorroded corroded(melted) (melted) textures bleaching, recrystallization, recrystallization, assimilation textures are are common, common, with with xenoliths xenoliths showing minor bleaching, assimilation andior andlor partial partialmelting, melting, the the last lastof ofwhich which isis demonstrated demonstratedby by embayments, embayments,rounded rounded margins, margins, cavities, other fragments. fragments. This cavities, apophyses, apophyses, and and annealed margins with other This "melting" "melting" indicates indicatesmelting melting and assimilation at "depth" and then transportation to surface and this is farther evidence of assimilation at and transportation surface and this is farther evidence of the the Onaping melts being emplaced from below and not as fall Onaping fall back. back. The The matrix matrix isis medium medium greenish-gray, greenish-gray, fmefine- to medium-grained, and has a massive, salt-andsalt-andtexture. Fine pepper texture. Fineprisms prismsofofamphibole amphiboleare aretypically typically visible visible in in the the coarser-grained coarser-grainedbodies. bodies. Generally, there is a decrease decrease in in matrix matrix grain grain size size in intrusive intrusive bodies exposed exposed higher higher in in stratigraphy. 10% quartz-, chlorite-, and/or stratigraphy. Pipe-like Pipe-likebodies bodies higher higher in strata strata also contain 5 - 10% andlor sulphide-fillcd mm in size. sulphide-filled amygdules, amygdules, that that range range from from 22 - 55 rnm Contacts sharp, vertical Contacts with all all but the Fluidal Fragment Units are intrusive, sharp, vertical to to horizontal horizontal surfaces. The and usually obvious obvious on outcrop surfaces. Thelarge largesheet-like sheet-like bodies bodies display display chilled, chilled, fine-grained fine-grained generally have a thin thinchilled smaller pipe-like bodies generally chilled to aphanitic, aphanitic, xenolith-poor margins. The Thesmaller margin. Contacts with the Eluidal Fragment Units are gradational, marked by an aphanitic, Contacts with the Fluidal Fragment brecciated brecciated and and xenolith-poor margin. Where Wherethese these brecciated brecciated contact contact margins margins are arerelatively relatively large large they have have been beenmapped mappedas asAutobreccia Autobreccia(SMFLa). (SMFLa). Contact relationships suggest or extensive they emplacement emplacement of Basal Intrusion Intrusion is is contemporaneous with, pre-date predate and and post-date postdate the the emplacement emplacement of the fragmental fragmental units. Locally, Locally,where wherethe the Basal BasalIntrusion Intrusionintrudes intrudescarbon carbonbearing bearingfragmental fragmental rocks, aa 22 to to 15 15m m contact contactzone zone of of carbon-poor carbon-poor tuffs tuffs surrounds surrounds the the intrusive intrusive body. body. The The Basal Basal Intrusion Intrusionisis envisioned envisioned to represent represent an xenolith-bearing xenolith-bearing melt that that intruded intruded the the fragmental fragmental rocks of the Onaping Formation. Bodies Bodies of of Basal Basal Intrusion Intrusionwere were emplaced emplaced before, before, the Sandcherry. Sandcherry.and Dowling members. members. During during, and shortly shortly after, the deposition of the and Dowling During intrusion intrusion most of of the the fragmental fragmental units were unconsolidated and, at least least locally, locally, bodies bodies of of the the Basal Basal Intrusion for the the Fluidal Fluidal Fragment Fragment Units Units (SMFL), (SMFL), in similar Intrusion are interpreted to be the melt source for fashion fashion to to peperites. peperites. Xenoliths with@ within the Basal Intrusion are interpreted to be remnants remnants of of basement basement rocks. rocks. The variety of xenolith xenolith rock types indicates mixing of basement fragments before and during their asSimilation into, or or transportation transportation by, by, the the Basal Basal Intrusion. Intrusion. Locally, assimilation into, Locally, xenoliths were rounded and sorted according according to size sizç before or during emplacement. emplaeement. Because of the high percentage of xeholiths and relative small size of the intrusions, partial melting of the xenoliths is interpreted to xenoliths have have occurred occurred before before incorporation incorporation into into the intrusive intrusive bodies that transported transportedthem them to totheir theirpresent present site. Other Otherxenoliths xenolithsare arefresh freshand andunmelted, unmelted, suggesting variation in melt temperatures or, more likely, in the timing of incorporation. The The cataclastic cataclastic event event that that formed the Sudbury SudburyStructure Structureisis interpreted to have have formed the xënoliths, x'enoliths, that are presently found within the Basal Basal Intrusion, Intrusion,by by - - - - �25 A BEGINNING OF ERUPTION Schematicdiagram diagramof ofinferred inferred submarine eruption Schematic submarine eruption 1964) (Fiske and Matsuda (Fiske and Matsuda 1964) Figure11: 11: Figure �26 basement rocks. rocks. The brecciation of the basement The"melted" "melted" appearance appearanceof ofsome somexenoliths xenoliths may may be be evidence of impact melting: melting. Border Border Phase Phase of of the the Basal Basal Intrusion Intrusion (BIb) (Bib) -- 11lb BIb (iranophyre and bodies of the Basal Bib represents represents a gradational contact contact zone between Granophyre Intrusion. BIb Bibhas hasfeatures featuresof ofboth both these these units, units, in in varying varying percentages. The Thecontacts contactsbetween between the the bodies of of Basal Basal Intrusion (BIa) border phase of the Basal Intrusion (BIb) (Bib) and both the sheet-like bodies and and Granophyre Granophyre are are gradational gradational over over 11-- 55 m. Close Closeto tothe theGranophyre, Granophyre,the the matrix matrix of of BIb Bib isis similar Thesole soledifference differencebetween betweenthe thetwo twobeing being the the presence presenceof of55 -- 10% 10% similar to Granophyre. Granophyre. The xenoliths. xenoliths. Near Nearthe thecentre centreof ofBib, Bib,the thematrix matrixisisincreasingly increasinglyfine-grained, fine-grained,but butcommonly commonlydisplays displays aggregates of coarser coarser andlor Rareamphibole amphibole needles are visible. Lithic Lithic aggregates and/or finer crystals within within it. Rare xenoliths account account for for 15 15- 65% 65% of the rock, and and commonly commonly have a mafic mafic reaction reaction rim rim that that extends extends22 -- 77 mm into the surrounding matrix. Close Closeto toBIn, BIa,the thematrix matrixisisfine-grained fine-grainedand and homogeneous, homogeneous, and and except except for forrare rarelong longneedles needles of ofamphibole, amphibole,isisindistinguishable indistinguishablefrom fromElla. BIa. Bib bodies of of lower border phase/contact phaselcontact zone of the sheet-like bodies Bib is is interpreted interpreted to to be the lower Basal Intrusion and Granophyre. No No sharp sharpintrusive intrusivecontact contact between between Granophyre Granophyre and Bib Basal BIb has been noted. BIb Bibmay mayrepresent representaazone zoneofofmixing mixingbetween betweentwo twonearly nearlycontemporaneous contemporaneousmelts. melts. The Basal Basal Intrusion has been described described as a conglomerate (Coleman 1905), a rhyolite (Thompson 1957; 1957; Williams 1957), 1957), aa tectonic tectonic quartzite quartzite breccia (Stevenson 1972), 1972), aa breccia (Thompson 1972b), and part of of an an impact impact melt melt system system also also meteorite fall-back breccia (Peredery 1972a, 1972b), Stevenson (196 (1961a) that comprising the Sudhury Sudbury Igneous Complex (Brockmeyer (Brockmeyer 1990). Stevenson la) proposed that the matrix matrix was wasoriginally originallyaa highly highly pulverized pulverized mixture mixture of of country countryrock rock fragments, fragments,subsequently subsequently the Alternatively, the the matrix matrixhas hasbeen been recrystallized by the intrusion of the the upper upper phases of the SIC. Alternatively, 1989; interpreted to have been initially igneous-textured and intrusive (Brockmeyer and Deutsch 1989; Paakki Paakki 1990). 1990). - - Aphanitc Aphanitc Dykes (APHDYK) (APHDYK) - 12 12 Aphanitic Aphanitic dykes (APHDYK) are narrow, to irregular-shaped, irregular-shaped, intrusive intrusive aphanitic aphanitic 'andesite' dykes that are are xenolith xenolith poor, commonly commonly display regular regular to to contorted contorted flow flow banding, banding, and and are are similar similar appearanceand and composition composition to to fluidal fluidal fragments fragmentsand and bombs bombs within within the the fragmental fragmentalunits units of ofthe the in appearance Sandchenyand and Dowling Dowling members. APHDYK APHDYK occurs occursspatially spatiallyassociated associated with the margins of Sandcheny sheet-like bodies of Basal Intrusion, as narrow, narrow, or or lens-shaped lens-shaped intrusions intrusionswithin within the the Sandcherry Sandcherry member, and and uncommonly as small, thin dykes within the Lower, Middle, and Upper Units of of the the Contactsbetween between APHDYK APHDYK and and the the fragmental fi-agmental units units may may be be locally locally knifeDowling member. Contacts sharp, sharp, intrusive, intrusive, and and normally steeply steeply dipping. Elsewhere, Elsewhere,these these contacts contacts tend tend to to be be highly highly irregular and and brecciated, brecciated, with with numerous numerous apophyses apophysesextending extending outwards outwardsfrom fromthe themain main body body in in irregular lobe-shaped structures, of structures, surrounded surrounded by hyaloclastite, hyaloclastite, in similar fashion to the emplacement of peperites. Contacts Contactsof ofAPHDYK APHDYK with with bodies bodies of of Basal Basal Intrusion Intrusion are are gradational gradational over 10 10 cm and are towards the the Basal Basal Intrusion. Intrusion, The are characterized characterized by a coarsening of grain size towards The margins of APHDYK are typically strongly flow flow banded bandedparallel parallelto tocontacts. contacts. Conehoidal Conchoidal fractures and sharp flinty flinty to to cherty-like cherty-like broken edges are are characteristic characteristicof ofthe theunit. unit. APHDYK APHDYK contains contains less than 5% 5% subrounded subrounded quartz-rich lithic fragments (1 - 10 10cm cm in in size), up to 10 pyrrhotite and chalcopyrite. Spherulitic 10 % % quartz/chlorite-filled quartz/chlorite-filled amygdules, and 1% 1% pyn-hotite Spherulitic texturesare arealso alsolocally locally common. common. Higher Higherininstratigraphy stratigraphythe theunit unitisismore morevesicular vesicularand andspherulitic. spherulitic. textures APFIDYK similar in appearance appearance to bombs APHDYK is similar bombs and and fluidal fluidal fragments fragmentswithin within the the fragmental fragmental units. units. Aphanitic Aphanitic dykes are are interpreted interpreted to to be be the the less less contaminated, contaminated, lithic-poor, lithic-poor, more more rapidly rapidly crystallized crystallized equivalents (end members) of the Basal Intrusion. Intrusion. Aphanitic Aphaniticdykes dykesand andpipe-like pipe-like bodies of Basal Intrusion may represent different different phases of the same intrusion. Aphanitic Aphanitic dykes dykes - �27 hypabyssal intrusions of of non-brecciated non-brecciatedmelt meltof of 'andesite' 'andesite' are interpreted to represent small hypabyssal composition that intruded the fragmental rocks of the Onaping during and shortly after their deposition. The Theoccurrence occurrenceofofAphanitic AphaniticDykes Dykesmay may defme define "vents" and structures structures that that controlled emplacement of the Onaping breccias, fluid migration, alteration, alteration, and mineraliziation. Locally, APHOYK APHDYK represents represents sites sites where where massive massive 'andesite' 'andesite' locally locallyintruded intrudedand andflowed, flowed, tongue-like, tongue-like, into into unconsolidated, unconsolidated, wet piles of glass-rich fragmental rock, interacted with water and passively passively to explosively fragmented. Aphanitic Aphaniticdykes dykes represent represent feeders, feeders, at at least leastlocally, locally,for forthe thefragmental fragmentalunits units of the lower Onaping Formation. The The dykes dykes show show many features features similar similar to "peperites" described and Wilson Wilson (1993) (1993) (Figure (Figure9) 9) and and "intrusive "intrusivehydroclastic hydroclasticbreccias" breccias"described describedby by by Hanson and Hanson (1991) (1991) (Figure (Figure 8). 8). Aphanitic Aphaniticdykes dykesare arelikely likely representative representative of the original melt from which the fragmental fragmental rocks rocks of of the the Onaping Onaping Formation Formationwere werederived. derived Carbon Carbon Contact Contact Carbonaceous Carbonaceous material material occurs occurs locally locally within the Sandcherry Sandcherry member and is pervasive through much of the overlying Dowling Dowling member. member. The contact The wntact between between carbon-poor carbon-poor and and carboncarbontransects lithological contacts contacts and is gradational bearing fragmental rocks transects gradational over over 55 to to 20 m. Where Where carbonaceous material occurs within the the Sandcherry member member Shard-rich Shard'rich Units, the rocks are conductive. The wnductive. TheDowling Dowling member, member, though significantly significantly more carbonaceous carbonaceous than than the the Sandcherry Sandcherry conductive (due to to high high amorphous amorphous carbon carbon contents) only in in its its upper upper 50 m, directly member, is wnductive the Vermilion Vermilion Formation. Formation. Conductivity within the the Shard-rich Shard-rich Units Units of ofthe the Sandcherry Sandeheny beneath the to high high amorphous amorphous carbon contents, member, however, is not attributed solely to Carbonaceous Sandcheny rocks support support subaqueous Sandcherry and and Dowling member fragmental rocks deposition for both members. Carbonaceous Carbonaceousmaterial materialmust musthave havebeen beenrelatively relativelyabundant abundantwithin within the water of both both the the Sandcherry Sandcheny and water column and on the depositional floor during the emplacement of Dowling Dowliig members. This This suggests suggeststhe the early early incorporation incorporation of of carbonaceous carbonaceous material, locally at least, Onaping Formation. Formation. least, during during deposition deposition of of the the Onaping The The carbon carbon contact wntact isis interpreted interpreted to to mark mark either either (1) (1) the the boundary boundary between between oxic oxic and and anoxic anoxic depositional environments, or (2) an alteration front, or contact, wntact, between lower rocks (carbon-poor) (carbon-poor) and upper rocks material has has been preserved. preserved. All of the Sandcheny rocks in which the carbonaceous material Sandcherry member depositional units units may may have havebeen beeninitially initiallycarbonaceous. carbonaceous Deep Deep circulation circulation of of fluids, presumably marine water, driven by the heat of the Basal Basal Intrusion Intrusion and SIC, SIC, may may have have been been responsible responsible for the removal of the carbonaceous carbonaceous material material out outof ofmuch much of ofthe theSandcherry Sandcherrymember. member. Later cooling of the SIC may have subsequently caused the "drawing down" and and redistribution of carbonaceous material. carbonaceous material. Perederv (1972a, 1972b), Peredery and Momson Morrison (1984), Avermann (1992), (1992), and Peredery (1972a, Avcrmann Avermann and Brockmeyer (1992) proposed that the carbonaceous carbonaceous material material within the fragmental fragmental material, derived from surrounding surrounding pelagic sediments, that that was washed into units is is fine fine organic organic material, the crater fallout material. material. Alternatively, crater and and redeposited redeposited along with reworked meteorite fallout Alternatively, that the source of of the the carbon carbon is is the the result result of of aa mass mass killing of of Whitehead et al. (1990) proposed that organisms subsequently settled through the water organisms within the Basin Basin - the dead organisms subsequently water column column and were incorporated incorporated into into the the initially initially glassy glassy breccias brecciasbeing being deposited depositedon on the the crater craterfloor. floor. - Alteration The Onaping Formation displays pronounced stratigraphic stratigraphic lithogeochemical variation, variation, upwards in wt.% wt.% Si02, TiO2, Ti02, Al203, Na20, K20 K10 and illustrated by progressive apparent losses upwards A1203, NazO, MgO, and progressive progressiveapparent apparentgains gainsupwards upwardsininwt.% wt.%COz, CO2.CaO, CaO,FeiOs, Fe203, MnO, C, and S (Table (Table MgO, MnO, Cm, 13, 14, 14, and and 15). 15). The The base base of of the Sandcheriy Sandchenymember shows a marked apparent 2, Figures 12, 12, 13, Si02. Variations increase in SiO;. Variationsin in composition, composition, except for the occurrence of particulate organic (C), are carbon (Cm), areattributed attributedlargely largelytotoalteration. alteration.All Allfragmental fragmentalunits unitsofofthe theSandeherrv Sandcherrymember member �28 of aa similar andesitic andesitic composition composition(Gibbins (Gibbins 1994). 1994). Aphanitic are interpreted to have initially been of Aphanitic dykes best represent the precursor precursor composition wmposition of the glass-rich breccias. breccias. lithogeochemicalstratigraphic stratigraphic variation variation (zonation) (zonation) Glass composition wmposition heterogeneity and lithogeochemical the Onaping Formation Formation isisattributed attributed largely largely to to various various types types displayed by the fragmental rocks of the of alteration. alteration. These Theseconsist wnsistofof(1) (I)aabasal basalsilicification, silicification,(2) (2)an anoverlying, overlying,lower lowersemiconformable semiconformable + orthoclase) feldspar (albite + orthoclase) alteration alteration (similar (similar to spilitization), (3) an an overlying, overlying, upper upper semiconformable calcium carbonate alteration that increases in intensity upwards, toward the the semiconfonnable that in intensity upwards, toward contact temperature, (semiconformable?) (semiconfonnable?) wntact with the the overlying overlying Vermilion Formation, and (4) a low temperature, potassie alteration, potassic alteration, at at the the top top of of the the Onaping Onaping Formation. Sulphide Sulphide Showings Showings Base metal suiphide sulphide occurrences occurrences within Onaping Formation area are are predominantly predominantly fragmental fragmentalin in nature natureand, and,in indecreasing decreasingorder order of of mineral mineral abundance, abundance,consist consistof ofpyrrhotite, pyrrhotite, chalcopyrite and pyrite. Stringer-like sphalerite, chalcopyrite Stringer-likevein vein mineralization has been observed. All All sulphide occurrences are nickel-poor. In Instratigraphic stratigraphicorder, order,suiphide sulphideshowings showingsoccur occur at atfour fourmain main sulphide "horizons". These Units of of the the Sandcherry Sandcherry member; member; (2) (2) at at the the Theseare: are:(1) (1)ininthe thesilicifled silicified Undefined Undefined Units carbon member, and and (4) 100 carbon contact; wntact; (3) (3) within coarse Lower Units of the Dowling member, 100 - 200 200 m above above the carbonate the Dowling Dowlingmember. member. Mineralization also occurs carbonate contact contact within within the Middle Units of the occurs adjacent to pipe-like pipe-like bodies bodies of of Basal Basal Intrusion Intrusionand andinincalcite calciteveins veinsassociated associatedwith withfaults. thults. Most Most of of the sulphides occur occur as as fine fine disseminations disseminationsand replacement of glass shards, shards, but but some someof ofthe the mineralization may be the result of of brecciation and reworking of older intra-Onaping Formation Formation sulphide sulphide occurrences. occurrences. - Concluding Concluding Remarks Remarks The Sandcherry Sandcherryand and Dowling Dowlmg members constitute constitute a sequence sequence of initially glass-rich fragmental rocks (breccias) composition. The (breccia) of intermediate composition. The two members, distinguished from fragments consist each other by percentage, size, size, and and morphology of glass fragments consist of numerous numerous distinct distinct depositional units that show show an an overall overall fining upwards along with an increase, first, first, in in fine fine carbonaceous material followed by byan anupwards upwardsincrease increaseinincalcium calciumcarbonate. carbonate. Both Both carbon carbon and and carbonaceous lithological contacts. contacts. The carbonate boundaries transcend (overprint) lithological The upper upper 170 170m m of of the the Onaping Onaping Formation, Formation, compared compared to to the the rest rest of of the the sequence. sequence, isis characterized characterized by by aa pronounced pronounced decrease decreasein in grain size, greater internal stratification, and stronger evidence of sedimentary reworking. grain size, greater internal stratification, and stronger evidence of sedimentary reworking. In terms of the Onaping Formation, terms of of the the interpretation interpretation of of mechanisms of emplacement of the origin or source of the melt is inconsequential. The assumption is made, simply, that the emplacement and deposition of the breccias of the Onaping Formation was preceded and initiated lithicclast-bearing clast-bearingmelt melt of ofan anintermediate intermediate by the emplacement of a high level, "shocked" lithic composition. This wmposition. Thismelt melt may may represent represent (1) (1) aa meteorite meteorite impact melt sheet, (2) a melt generated by intracrustal ("impact-induced anatexis", anatexis", Lowman Lowman 1993), or intracmstal bulk melting beneath an impact crater ("impact-induced magma. The (3) a hypabyssal intrusion of contaminated magma. The occurrence occurrence of of shock shock features features within within lithic lithic fragments glass-rich of fragments and and zircons zircons (both (bothof of basement basement origin) origin) within within the glass-rich of the the Onaping Onaping Formation Formation melt for the breccias was at least partially produced by a meteorite impact. The suggests the source melt AphaSic dykes Basal Intrusion and, particularly, Aphanitic dykesare areinterpreted interpretedto to represent represent the the remnants remnants of of the melt source source for for the the fragmental fragmental rocks. rocks. The morphology of glass glass fragments fragments within within the Onaping Onaping Formation indicates that the the fragmental fragmental rocks (breccias) formed by the rapid cooling and fragmentation of melt upon interaction rocks (breccias) formed by the rapid cooling and fragmentation of interaction with with fragmentation and water. "Magmatic" "Magmatic"degassing degassing(vesiculation) (vesiculation)played played only a minor role in clast fragmentation of the the Onaping Onaping Formation. Formation. Deposition of the the Onaping Onaping Formation Formation is is emplacement of Deposition and emplacement of passive to explosive was continiously fed from the result of prolonged passive explosive fragmentation of melt, which was below, upon interaction with water. Deposition Depositionand andemplacement emplacementinvolved involved repeated repeated brecciation, brecciation, �29 ejection, re-deposition of of earlier earlier deposited, deposited, altered, altered, and and lithified lithified breccias breccias. Deposition ejection, and redeposition Deposition of of the the Onaping Formation occurred over a prolonged period of time, too long of a period to accommodate accommodate 'simple" meteorite impact fallback failback models. "Secondary" "simple" "Secondary"and and renewed renewed eruptive eruptive processes processes must must have occurred occurred during during emplacement emplacementand and deposition. deposition. Assuming Assuming a meteorite impact, fàllback fallback breccias were either (1) (1) deposited beneath the Sandcherry member and subsequently "eliminated" !feljinatedII or assimilated Sandcherry assimilated by the underlying underlying Basal Basal Intrusion Intrusion and SIC, or by the emplacement of the Sandcherry member, or (2) were never actually deposited emplacement Sandcherry within the crater enter defined defined by by the the Sudbury SudburyBasin. Basin. The upper contact wntact of of the the Onaping Onaping Formation Formation with the overlying argillites of the Onwatin Formation gradational and Formation has been described as gradational and conformable conformable (Muir (Muir and and Peredery Peredery 1984; 1984;Rousell Rousell 11984a; 984a;Avermann Avennann 1992; Avermann Avennann and and Brockmeyer Brockrneyer1992) 1992)to to geochemically geochemicallyand and lithologically lithologically sharp al. 1990; Paakki 1992, Gibbins 1994, Grey Grey 1995). The sharp (Whitehead et al. The upper upper 40 40 metres metres of of fine-grained, rich rich in inorganic organiccarbon, carbon,and andas as stated stated by by Martin Martin (1957) can the Onaping Formation is fine-grained, be difficult difficult to distinguish visually from from the the pelagic pelagic sediments sediments of the Onwatin Onwatin Formation. Formation. Vermilion Formation The (Martin 1957, 1994),previously previously known known as as the the The Vermilion Formation (Martin 1957,Stoness Stoness 1994), of the the Onwatin Formation (Rousell 11982a), 982a), is is situated situated at the contact wntact between Vermilion member of the Onaping and Onwatin Formations. Stoness Stoness(1994) (1994)upgraded upgraded the the member member to to formation formation status status and distinct geological geological character. character. The because of its Basin-wide occurrence and TheVermilion VermilionFormation Formation hosts the Vermilion and Emngton Errington Zn-Cu-Pb-Au-Ag Zn-Cu-Pb-Au-Ag Deposits, located in the south-west quadrant quadrant of the Sudbury Formation rocks, rocks, 1 to to 30 Sudbury Basin. While Whilediamond diamond drilling drilling has intersected Vermilion Formation m thick, elsewhere in the the North North and South Ranges, the continuity of the formation is unknown (Arengi 1977; Gibbins et eta!. al.1992). 1992).InInthe thevicinity vicinityofofthe thedeposits depositsthe theVermilion Vermilion Formation Formation has has an an average average thickness of 43 m (Martin (Martin 1957; 1957;Rousell Rousell 1982a). 1982a). The Vermilion Formation comprises fine- to coarse-grained, warse-grained, commonly commonly pyritiferous pyritiferous and and base-metal-bearing carbonate; cherty carbonate, carbonate, chert chert breecia, breccia, interbedded interbedded flne-grained fine-grained gray coarse grained granular granular to pisolitic argillite, and fine- to coarse pisolitic carbonate. carbonate. Rapid lateral lateral lithological lithological variation within the Vermilion Vermilion Formation Formation in in the the vicinity vicinityof ofthe thedeposits depositsisiscommon. common. The Vermilion Formation has been described as a syngenetic stratabound deposit (mainly recrystallized, altered by Card Card and Hutchinson Hutchinson (1972), a sedimentary-exhalitive deposit deposit (Rousell micritic limestone) by 1984b; Davies et al. 1990; 1990;Whitehead Whitehead et et a!. al. 1990; 1990;Paalcki Paakki 1992), 1992), and and an an epigenetie epigeneticvein vein deposit deposit turbiditic argillite argillite (Martin 1957). Most Mostrecently, recently,the theVermilion Vermilion Formation has been subdivided into turbiditic and carbonate exhalite exhalite sinter sinter deposits deposits(Gray (Gray 1995). The The exhalites exhalites deposits (Stoness 1994) and comprise Carbonate member of the 50 m Formation;. The comprise the Lower Carbonate m thick Vermilion Formation;. Themiddle middle member is the Grey Argillite member and consists of fine-grained grey turbidites that have Grey Argillite wnsists of turbidites that have basinbasincarbonate wide continuity; and the Upper Carbonate member is a thin hydrothermal concretionary carbonate (Gray (Gray 1995). 1995). Onwatin Formation Formation The Onwatin Formation (Coleman 1905; Burrows and and Rickaby 1930; Martin 1957; 1957; Thomson 1957; Lozej 1975; 1975;Rousell Rousell 1984a) 1984a)consists wnsistsof oflaminated laminated 1957; Sadler Sadler 1958; 1958;Beales Beales and and Lozej carbonaceous carbonates and wackes. carbonaceous and pyritic pyritic argillites argillites and siltstones, siltstones, with minor fine-grained carbonates wackes The Sudbuiy Basin, but The Onwatin Onwatin Formation is poorly exposed in the Sudbury but where where present, present, aa well well developed slatey slatey cleavage cleavagepredominates predominates(Paakki (Paakki1992). 1992). Carbonate concretions, though though rare, rare, are developed also evident. The Theformation, formation,based based on drill hole data and stratigraphic stratigraphic reconstruction reconstruction (Gibbins et al. 1992), thickness of of 600 600 m. m. The al. 1992), is interpreted to have an original thickness The formation has been �DOVVLING DOWLING MEMBER MEMBER FLU IDAL FLUIDAL ILLITE ILLITE MIDDLE UNITS MIDDLE UNITS BASAL BASAL ONW DMUc DMLJbDMUa DML)aDMMb,a DMMb,aDMMc DMMc DMLa DMLb DMLc DMLC1 SMSRC SMSRSMFLtr SMEL1FMU DMLb DMLc DMLCT DMUc DMUb DMLa SMSRC SMSR SMFL ONW SO2 SiO, wt% wL% wt.% wt.% 55.97 55.97 52.32 57.50 wt.% v,t.% 59.00 60.36 wt.% wt,% wt% wt.% 60.76 61.33 51.00 61.22 TIC2 DO2 0.63 0.63 0.44 0.44 0.40 0.43 0.48 0.49 A1203 A1203 14.33 14.33 8.77 8.77 8.64 9.62 10.61 10,77 0.59 6.27 1.17 1.84 5,23 0.14 0.14 10.24 3.87 0.14 2.10 4.00 9.02 0.54 0.40 2.22 3.70 0.15 1.89 4.13 9.26 0,39 0.01 0.01 CDI 0.01 6.99 2.34 6.11 5.81 4.38 2.04 1.84 Na20 Na20. 0.90 0.90 0.42 0.42 GaO CaO P205 P205 0.78 0.78 0.12 0.12 4.04 4.04 0.16 0.16 1<20 K20 3.62 3.64 3.32 3.32 1,23 2.00 MgO MgO Fe203 Fe20, MnO MnO Cr203 Cr2Os 2.32 2.32 3.83 3.83 3.66 8.09 8.09 12.75 12.75 11.10 0.23 0.23 0.58 0.58 0.59 3.95 Lol LO1 Clot Ca Corg C,,, 002 C02 S S 8.93 8.93 0.01 0.01 9.39 9.39 3.19 3.19 6.11 6.11 0.65 0.65 4.26 4.28 1.01 o.eg 0.99 0.18 0.49 6.81 6.81 6.49 6.48 0.37 0.37 1.25 1.25 4.46 0.72 3.92 0,43 2.94 0.28 0.94 0.48 0.01 0.01 INTRUSIONS INTRUSIONS APHAN. BASAL APHANBASAL INTRUSION INTRUSION SHARD-RICH SHARD-RICH FRAGMENT DFRAGMENT SAN ITIC SANDITIC BORDER GRANOBORDER GRANOLOWER UNITS LOWER UNITS UNITS UNITS UNITS CHERRY DYKES PIPES UNITS CHERRY DYKES PIPES SHEETS SHEETS PHASE PHASE PHYRE PHYRE ARGARO- UPPER UPPER UNITS UNITS ., sc SIC ONAPING ONAPING FORMATION FORMATION SANDCHERRY_MEMBER SANDCHERRY MEMBER wt% SM-- APHOYK APHDYK Blo EIc Bla Ela BIb Bib SICG SlOG 0,55 0.55 wt.% 61.62 0.56 0.66 0.56 wt.% $3.12 0,57 0.48 0.58 0.57 0.49 0.45 0,78 11.88 11.88 11,91 12.07 11.98 12,37 12.71 12.82 I1.61 12,94 13.21 12.62 13.12 12.31 4.21 5.07 3,54 0.15 4.41 4.78 3,44 0,14 3,94 3,68 4.00 4.00 4,04 3,45 0.14 3.03 2.21 1.70 223 1.55 0.11 0.13 0.11 0.12 1.61 1.58 2.41 1,87 2.31 3,77 3.82 6.97 0.16 0.02 3.64 0.15 2.39 3.37 3,04 1.59 0.18 2,76 1,35 0.86 6.21 6.53 3.29 5,99 5.66 4.04 5,79 0.18 0.15 0.13 0.13 0,09 0,41 0.02 0.02 0.02 0.02 0.01 0.04 1.47 1,50 1.63 1.63 1.38 1,20 0.07 1.36 0,08 0.04 0.05 0.56 62.04 0,55 wt.% 63,00 3.56 3.69 0.15 2.04 3.79 3.70 3,98 4.08 0.15 0.15 4.38 3.85 0.15 2.32 2.25 1.64 2.21 1.31 421 4.33 4.28 4,36 4,12 8.26 0.26 0.02 2.67 0.69 8.60 8,79 0.26 0.27 0.23 0.02 0.02 0.02 6.04 0.20 0.02 4.07 7,43 0,19 2.03 2.15 1.51 0.80 0,19 0.36 0.50 0.79 0.26 0.33 o.4i 62.88 3.75 0.15 1.84 3.79 7.08 0.17 0.02 1.46 wt.% 66.13 wt.% 63.44 0.09 2.15 0.41 0,02 1.32 0,08 0.14 0,06 0.37 0,03 0.03 0,04 0.03 0.03 0.10 0.31 0.13 0.05 0.32 0.03 0.38 0,17 0,10 0.13 0.23 0.09 0.16 0.11 0.35 0.02 wt% wt,% wt,% wt% 65.01 66.40 68.61 69.08 ppm ppm ppm ppm ppm ppm ppm ppm ppm ppm ppm ppm ppm ppm ppm ppm ppm ppm ppm ppm Cu 63 54 165 12 24 34 31 33 25 33 28 23 16 33 24 19 30 157 124 89 82 74 64 50 49 52 42 49 45 56 44 50 25 9 II 12 8 9 8 7 9 9 7 14 8 14 12 9 10 Ni 70 44 47 60 59 53 62 59 46 51 4 807 861 773 772 860 46 54 60 120 180 142 111 80 108 238 1198 121 138 Zr 132 97 126 552 66 138 849 Sr 404 50 85 413 149 804 52 49 674 68 215 18 626 60 457 52 710 59 782 61 Ba Rb 22 68 856 119 II 50 Pb 82 8 22 48 11 Zn 35 56 133 16 13 14 124 124 205 205 131 115 130 129 130 62 818 80 99 126 'I 22 14 12 Il 13 12 10 12 15 Nb 18 23 16 19 14 15 10 15 14 63 597 58 74 139 15 14 202 202 38 38 27 27 45 45 213 213 468 468 Ii 11 64 64 111 111 Its 115 Pts. Pts. 61 847 77 91 135 81 111 138 16 Table 2: Avetage Table2 Averagelithogeochemical lithogeochemicalcomposdion compositionofofOnaping OnapingFormation Formationunits units (after (afterGibbins Gibh'ms 1994) 1994) 52 59 SI 61 135 121 161 132 138 145 140 400 210 ¶21 121 146 217 13 14 12 14 11 11 12 23 12 13 13 12 12 I? 10 16 57 57 86 86 54 54 51 51 18 18 79 79 15 15 83 99 0 �or U 8 I I 2. �I n I I 32 ! I —0 QJ h___ H 9____ Uafl__ 2r___ fl! III!HI4HHJ HHHHHL4H} 1HHHHHEI Ø2VUI8&, tB1RP1 £ . 0 Figure Figure13:13: 0 0) 0 0 Q 0 a C a - In Lithogeochemical Lithogeochemicalstratigraphic stratigraphiccolumn column- Average - Averagecompositions compositions(major (majoroxides#2 oxides#2+ +Corg, Core,C02, C02, S,S,Zn) Zn)and andthicknesses thicknessesofofunits (afterGibbins Gibbiis1994). 1994) units (after �-'3 Figure14: 14: Figure - Lithogeochemical stratigaphic i i Average AvcrageC02/CaO CO2tCaO molar ratio and thicknesses o f LithogeochemicaJ stratigraphic w column molar ratio and thicknesses of units(after (afterGibbins Gibbims1994). 1994). units �AL2D3/TlflE 4ff I Q.BQyATIN I 0 I I I ISIDE/T102 500 J DHUb I I I INA2D/TIIJ2J I 2500 DMLJQ 300 it' II I I —t 600 DMMc I I x ' DMLb DML 900 I DNLCT 'SMSRC SMSR 1200 ciri +v r SPIFL ySM--- JfG 1500 I meters i j ' I K2IJ/T102 200 I I — — — — ZR/TIIJ2 MGEI/T102 I I I 200 ii — I I C I 200 I y - - I I I I 500 IJI — —-1 I liii- (I i J E a �35 structurally particularlyininthe theSouth SouthRange. Range.Whitehead Whiteheadetetal. at (1990), Paakki (1992), structurallythickened, thickened, particularly Stoness Gray (1995) showed Stoness (1994), Gibbins (1994) and Gray showed the Onwatin Onwatin Formation Formation (and Vermilion Formation) distinct from from the the underlying underlying Onaping Formation Formation) to to be chemically chemically and lithologically distinct to be be (Table 2). The Theupper uppercontact contactisis gradational gradational with with the Chelinsford Chelmsford Formation and is considered to at the the base base of of the the first first thick thick wacke wacke bed. The The pelagic rocks of the Onwatin Formation were deposited in a restricted restricted basin basin with with (Rousell 1984a). 1 984a). They Theygrade grade upwards upwards into into the the coarser sediments of of the the anoxic bottom conditions (Rousell Cbehnsford Formation, indicating a transition to a higher energy depositionai Chelmsford depositional environment et al. at 1991). (Dressier et 1991). Chehns ford Formation Chelmsford Formation The and Rickaby Rickaby 1930; Williams 1957; The Chelmsford Formation (Burrows and 1957; Cantin Cantin 1971; 1971; Cantin and 1972; Vezina 1992) and Walker 1972; 1972; Rousell Rousell1972; 1992) is the uppermost formation formation of of the the Wbitewater Group and has a preserved thickness similar similar to to that that of the underlying Onwatin Whitewater Formation, approximately approximately 600 m. The TheChelmsford ChelmsfordFormation Formation isis aa turbidite turbiditesuccession successionof ofmassive massive wackes, siltstones, siltstones,and andcarbonaceous carbonaceous mudstones. mudstones. Sedimentary to normally graded lithic wackes, Sedimentary structures structures carbonate concretions, rip-up clasts, clasts, U-shaped U-shaped channels, channels, climbing climbing ripples ripples and and crossinclude carbonate concretions,rip-up laminations,and andload loadstructures. structures. Paleocurrent bedding, convolute laminations, Paleocurrent studies studies indicate indicate that that the the predominant was to to the the south-west, south-west,parallel parallel to to the the long long axis axis of of the the Sudbury Basin predominant flow direction was (Cantin and and Walker Walker 1972; 1972;Rousell Rousell 1972). 1972). Errington and Emneton and Vermilion Deposits Deposits are are Paleoproterozoic carbonate-hosted carbonate-hosted Zn-Cu-PbThe Errington Emngton and Vermilion Deposits Zn-Cu-PbThe Au-Ag massive suiphide sulphide deposits located locatedin inthe thesoutheast southeastcomer cornerof ofthe the Sudbury Sudbury Basin. Basin. The deposits occur the Vermilion Formation. Formation. The occur at at the the top of Onaping Formation and partially within the The Errington toimes grading grading 4.21% Emngton deposit deposit contains contains an undiluted mineral inventory of 6.27 M tonnes 4.21% Zn, Zn, g/tonne Au Au and and 62.06 62.06gltonne g/tonneAg Ag(Severin (Severinand andGates Gates 1981). 1981). The 1.22% Cu, 1.09% 1.09% Pb, 0.86 gkome proven-probable-possible mineral mineral inventory of 2.44 m Vermilion deposit contains an undiluted, proven-probable-possible tonnes grading 5.11% Zn, 1.49% tomes 1.49% Cu, 1.37% 1.37% Pb, 1.10 1.10gltonne gltome Au and and 66.17 66.17g/tonne gltomeAg Ag (Severin (Severin the mid mid to to late late 1920's and and Gates 1981). 1981). The Thetwo twodeposits, deposits, 88 km apart, apart, were discovered in the later poor later developed developed for for production. Attempts Attemptsto toexploit exploitthe thedeposits depositswere wereunsuccessThl unsuccessful due due to topoor metal recoveries, lowmetal lowmetalprices prices and and overall overall marginal marginal grades. grades. Gray (1995) (1995) described the the deposits deposits to to be hosted by the Vermilion Formation within a CaMg carbonate complex that that grades grades laterally laterally into into Mn-Fe-rich Mn-Fe-rich carbonates carbonates (up to carbonate exhalite exhalite sinter vent complex wt% MnO and and 33 33 wt% wt%Fe203). Fe203). The TheVermilion Vermilion Deposit Depositisis underlain underlain by lower discordant 9.5 wt% chlorite zone and an upper discordant silicification silicificationand andstratiform stratiform Ca-Mg Ca-Mg carbonate carbonate stockwork zone. Gray Gray(1995) (1995)proposed proposedthe thedeposits deposits fbnned formedin in aa sub-seafloor sub-seafloorenvironment environmentby by the theinitial initiallow low temperature pyrite-sphalerite infilling of of carbonate porosity within sinters followed by later temperature later higher temperature chalcopyrite-rich mineralization that that replaced earlier pyrite pyrite and temperature and sphalerite sphaleriteand and secondary hydrothermaldissolution dissolutionleaching leachingof ofthe thecarbonates. carbonates. The carbonate secondary porosity from hydrothermal carbonate sinter host host is is attributed attributedto tosub-seafloor sub-seafloorboiling boiling and and carbonate carbonateprecipitation precipitationby byventing ventinginto intoan analkaline, alkaline, that enabled the sinter mounds to grow. grow. anoxic basin and and by successive successive replacement events that Carbonates were preserved from dissolution dissolutionby bythe theemplacement emplacementof ofturbidites. turbidites. The hydrothermal Carbonates underlying Sudbury system responsible responsible for for the Vermilion Deposit was long-lived, the underlying SudburyIgneous Igneous Complex, or precursor to drive and sustain convection cells precursor melt melt provided the thermal energy to within within the the Onaping OnapingFormation Formation (Gray (Gray1995). 1995). �36 LOCATION AND DESCRIPTION DESCRIPTION OF OF GEOLOGICAL GEOLOGICAL TOUR STOPS Tour Tour stops stops are are indicated on Figures 16 --22. 22. STOP 11 STOP SUDBURY BRECCIA An easily accessible outcrop of Sudbury Breccia is located on Highway 144, 144, 3.2 3.2 km km north north of the junction junction of Highway 144 tumofi). 144 and Regional Road 8 (Levack turnoff). The Sudbuiy Sudbury Basin is surrounded by a zone of Sudbury Breccia about 50 km wide. The wide. The to rocks rocks outside outsidethe theSudbury SudburyIgneous IgneousComplex. Complex. Fragments Fragments in the the breccia brecciation is limited to of the the same same material materialas asthe thewall wallrocks rocksand andare arerounded roundedtotovarying varyingdegrees. degrees. The generally consist of comminuted wall wallrock rockmaterial material that that has has been recrystallized matrix of the breccia consists of finely comminuted to to aa coherent coherentmass. mass. STOP 2 STOP FELSIC FELSIC NORITE This stop junction of Highway Highway 144 144 and Regional Road Road 88 stop is located located 1.4 1.4 km north of the junction (Levack turnoff), near the Elk's Elk's Club Club Road. Road. Felsic norite is the main member member of ofthe the Sudbury Sudbury Igneous Igneous Complex Complexon onthe theNorth North Range. Range. ItIt hypidiomorphic granular granular rock consisting consisting of is approximately 450 m thick and is a coarse grained hypidiomorphic plagioclase, hypersthene and augite (ration 2: 2:1), biotite, interstitial granophyre, granophyre, quartz, and l), biotite, and minor minor pyrite, apatite apatiteand and ilmenite. ilmenite. No Nolayering layeringisisevident, evident, but but the the mineralogy mineralogy changes changes gradually gradually producing producing "cryptic layering". layering". STOP STOP 33 QUARTZ GABBRO AND GRANOPHYRE QUARTZGABBROANDGRANOPHYRE Stop Stop 33 consists consists of of rock outcroppings outcroppings on either side of Regional Road 8 at the junction of of Highway 144. 144. Quartz Quartzgabbro gabbrocan canbe beseen seenin in the the road cuts cuts to to the the north north and and south south of of the the road; road, the the granophyre is thither further to to the the southwest. southwest. Complex consists consists of of granophyre, granophyre, which is pink The upper member of the Sudbury Igneous Complex plagioclase. in colour and comprises about three parts micrographic intergrowth to one part plagioclase. Quartz, biotite, biotite, amphibole, amphibole, chlorite chlorite and opaques opaques are are also alsopresent. present. granophyre, occurs occurs aa thin thin member member known knownas asquartz quartz gabbro gabbro (or transition zone), Below the granophyre, which is is more more mafic mafic than the the granophyre granophyre and and consists consists principally principally of of plagioclase, plagioclase,cimopyroxene, clinopyroxene, amphibole and intercumulus micrographic intergrowth and quartz. STOP 4 STOP CONTACT BETWEEN GRANOPHYRE AND BASAL INTRUSION, AND THE THE BASE BASE OF OF THE THE SANDCHERRY APHANITIC DYKES, AND MEMBER Stop 44 is between Granophyre Granophyre and and the the Basal Basal Intrusion Stop is a walking tour over the contact zone between glass-rich breccias and over a variety of exposures exposures of Basal Intrusion, Aphanitic Dykes, and glass-rich breccias at atthe the member of ofthe theOnaping OnapingFormation. Formation. Access Access to to the the area area is gained from aa base of the Sandcherry member private dirt private dirt road road (Gravel (Gravel Lake LakeRoad), Road), which which extends extends south south of of Falconbridge FalconbridgeLimited' Limited'ss main mainaccess access road to Strathcona Mine, approximately 4.8 km past the main gate entrance. Permission to main gate entrance. Permission to use use Strathcona Mine, approximately from Falconbridge Falconbridge Limited, Limited, as as the the area area is on mine the road and to view the outcrops is required from property. Turn Turnright rightoff offthe themine mine access access road on to Gravel Lake Road, which parallels the eastern eastern the shore shore of of the the lake lake until until aa yellow shore of a nearby lake, and continue south along the yellow road road gate gateisis �+ + + + + + FIGURE + S UD B U ONAPING Fm ONWA11N Fm + + + + + + ++ + .+ I +. + + + + -p + + + + + + + + GEOLOGICAL + + + + + -t + + + + + + + + + TOUR STOPS + 16 (modified after Glbbins 1994) * + + CHELMSFORD Fm c;:: COMPLEX fj• EE: EI OUTCROP STOPS + + - .4. - RINGTON 4 0 LCI Km 10 + + + + + + + + + + + + + • + + + + 1- + + + + ÷ + + + • + + + + + + * + + + + + + + + + + + + + I + -f .- / -e Y /4 + 1+ _*_— + + + + + +1+ + +7+ +7+ + +7+ + + ft + + + + + * ++ + + + + + + * • + + —4 �Figure 17 TOUR STOPS SUDBURY BASIN 'H:) - ix Bowling Area A WHITEWATER GROUP EH CHELMSFORD Fin C.. S, ONWATIN Fm fji:J ONAPING SUDBURY fi33 IGNEOUS COMPLEX GEOLOGICAL TOUR STOPS 1 0 00 �ONAPING FORMATION TOUR STOPS SUDBURY IGNEOUS COMPLEX WHITEWATER GROUP CHELMSFORD FORMATION ONWATIN FORMATION DOWLING MEMBER SANDCHERRY MEMBER APHANITIC DYKES BASAL INTRUSION \0 �40 ( reached (= 2 kin). reached km). The Thewalking walking tour tour begins 200 south of the gate by leaving the gravel road and following a stream eastwards for 600 m to to reach reach exposures exposures of of granophyre granophyre along along the the north north shore shore of of a small Figure small lake. The Thewalking walkingtour tour route routeisis marked marked in detail from this point onwards on Map A, Figure 19. 19. following exposures exposures will willbe beseen: seen: granophyre, granophyre, xenolith-bearing During the tour the following xenolith-bearing granophyre, both coarse grained xenolith-rich basal intrusion and fine-grained, well sorted, coarse basal Dykes and and various various 'glass'-rich 'glass' -rich units units of of the the xenolith-poor basal intrusion, flow banded Aphanitic Dykes Sandcherry tour offers offers one of of the the best exposures of Sandcheny member. Although Although a bit of a hike, the walking tour the base base of of the the Onaping Onaping Formation and of flow banded Aphanitic Dykes. The Thewalking walkingtour tourbegins begins and ends at the same same spot. spot. STOP 5 STOP FLUIDAL FRAGMENT-RICH FRAGMENT-RICH AND SHARD-RICH SHARD-RICH BRECCIAS BRECCIAS OF OFTHE THE SANDCHERRY MEMBER. MEMBER. THE CONTACT BETWEEN BETWEEN THE THE SANDCHERRY MEMBER MEMBER AND ANDLOWER LOWERUNITS UNITSOF OF THE THE DOWLING AND PIPE-LIKE MEMBER. AND MEMBER, PIPE-LIKE BODIES OF THE THE BASAL INTRUSION that extends extends eastward eastward from fromGravel GravelLake Lake Road, Road, 200 200 m south of aa Stop 5 is a walking tour that gravel pit, which is approximately 1.5 km further along Gravel Lake Road from 1.5 krn from the the yellow yellow gate gate described in the previous previous stop. After a walk of 200 m eastward from Gravel Lake Lake Road, aa small small ridge of rock is reached which marks the the beginning beginningof ofaageological geologicaltraverse traverseover over (1) (I) Fluidal Fragment-rich and Shard-rich units of of the the Sandcherry Sandcheny member, (2) a rare rare well exposed contact (running (running along along the the top of of aa steep, steep, large large ridge) between the Sandcherry Sandcherry and and Dowling Dowling members, members, with with both sharp (3) pipe-like bodies bodies of of the the sharp and and gradational gradational characteristics characteristics over its 400 400 m length, and (3) Basal Intrusion. in detail detail on onMap MapB, B,Figure Figure20. 20. The Intrusion. The Thewalking walking tour is marked in The Lower Lower Contact Unit of the Dowling member member ("chlorite ("chlorite shard shard horizon") horizon")and andthe thecarbon carbon boundary boundary are also well the southern flank flankof ofthe theridge. ridge. Alteration (silicification (silicification and albitization) exposed locally along the albitization)of the 'glass' shards shardsatatthe thetop topof ofthe theSandcheny Sandcherrymember memberisis well well featured featured within within the the vicinity vicinity of the near the the western westernend endof ofthe theridge ridgeof ofoutcrop. outcrop. From pipe-like bodies of Basal Intrusion, near From this this area, area, return to Gravel Gravel Lake Lake road by walking 150 150 m due west through through the the bush. STOP 66 STOP MIDDLE AND AND UPPER UPPER UNITS UNITS OF OF THE THE DOWLING DOWLING MEMBER MEMBER Gravel Lake Lake Road Road at at the junction junction with Morgan Road. Stop 6 is located at the south end of Gravel south of of Stop Stop 55 in inGravel GravelLake LakeRoad, Road, Stop Stop 66 must must be reached Unfortunately due to a wash-out south from the south. To 144, by by the the same same route taken in, and travel travel south, south, Toget getthere, there, return return to to Hwy. Hwy. 144, through the town of Dowling and and turn turn left left onto onto Morgan Morgan Lake Lake Road, Road,just just before the bridge on Hwy. 144 that crosses Vermilion River Rivernear near Larchwood. Larchwood. Stop crosses over the Vermilion Stop 6, 6, at at the the junction junction between between Gravel Gravel 144. Lake Road and Morgan Morgan Road is approximately approximately 3.5 km north of Hwy. 144. Stop on Map Map C, C, Figure Figure 21. 21. Representative Stop 66 is shown in detail on Representative units of of the the Middle and well exposed exposed at at this this stop, including Upper Units of of the the Dowling member are well including rarely rarely exposed exposed characteristic features bedding within withinthe theUpper UpperUnits. Units. The characteristic features of of reworking and bedding The stop stop provides providesaa good good example of the unaltered and undeformed undefonried equivalents equivalents of of the the immediate immediate footwall footwall rocks rocks to to the at the top top of the Onaping Formation Errington and Vermilion deposits located at Formation along along the the southern southern margin of the Sudbury Sudbury Basin. Basin. STOP 7 STOP CARBON BOUNDARYWITHIN WITHINSHARD-RICH SHARD-RICH UNITS OF THE CARBON BOUNDARY AND AN AN INTRUSIVE INTRUSIVE F1,UIDAL FLUIDAL BRECCIA SANDCHERRY MEMBER AND COMPLEX Offset road that Located near Sandcherrv Sandcherry Creek, Stop Stop 77 is accessed via Nickel Offset that extends extends The Nickel Nickel Offset Offset Road Road is located 5.75 km krn northwards from Morgan Road (Montpellier Road). The �- -geologic I contact - . -geologic contact gradational + -fault 4 o ,* 1 II lithie blasts I traverse route I a �42 Figure 20: Figure 20: Detailed geology geoloey of of Stop Stop55 (after (after Gibbins 1994). 1994) �43 Figure 22!: 1: Detailed geology of Stop Stop 66 (after (after(Jibbins Gibbii 1994). 1994) �44 LEGEND l l l l l t t l ~ r s eroute --- , EeOlogical contact .......carbon boundary fault ---road o blocks --- - Figure22: 22: Figure Detailedgeology geologyofofStop Stop7 7(alter (after Gibbiis 1994). Detailed Gibbins 1994). �45 Morgan Road. Road. Drive 5.5 km north on Nickel Offset Road east of Stop 6, further along Morgan Road until until the the second of two bridges that cross Sandcheriy Sandcheny Creek is reached. Park Park the the vehicle vehicle before before crossing crossingthe the 2nd bridge and walk 500 m further up Nickel Offset Offset Road Road to to aajunction junction with with aa second, second, but butless less Map D, D, Figure Figure 22. 22. Though a bit of as indicated on Map of bush bush crashing crashingand and climbing climbing traveled dirt road, as idal Fragment Fragment Units and Pipe-like is involved (50 (50 m), Stop 7 provides an excellent exposure of Flu Fluidal Pipe-like bodies of Basal Intrusion Intrusion (Fluidal (Fluidal Breccia Complexes) Complexes) intruding intruding into the Lower Contact ContactUnit Unit of ofthe the Dowling member. Only exposure of the carbon Only350 350m m to to the south south is a representative representative exposure carbon boundaiy/contact Within units of of the the Sandcheny Sandcheny member. within Shard-rich units boundarylcontact STOP 8 STOP CHELMSFORD FORMATION FORMATION Easily accessible road cuts of the Chelmsford Formation Formationare are to to be be found found on on both both sides sides of of 144and and Gordon Gordon the Gordon Lake road approximately 3.5 km south of the junction between Hwy. 144 Lake Road. The TheGordon GordonLake Lake Road Road turn off from Hwy. 144 is located 200 m south of the bridge near Larchwood. Larchwood. The that crosses over the Vennilion Vermilion River near The Chelmsford Chelmsford Formation Formation is is the the youngest youngest the Whitewater Whitewater Group Group and and occupies occupiesthe thecentral centralportion portionof ofthe theSudbury SudburyBasin. Basin. The The member of the Formation consists consists of of turbidites, turbidites, with partial to to complete complete Bouma sequences, sequences, which mark mark aa change change in the the pattern of sedimentation within within the the Basin Basin (the (theunderlying underlyingOnwatin Onwatin Formation Formation is a series of mudstones). Rusty are carbonaceous and pyritic siltstones and mudstones). Rusty weathering weathering concretions concretions and lenses are and represent concentrations concentrationsof offerruginous ferruginouscarbonate. carbonate. At this locality, a partial common and partial Bouma Bouma and dewatering dewatering structures structures also also present. sequence is present with cross bedding and STOP 9 STOP ONWATIN FORMATION FORMATION Stop 9 is located on Vennilion Vermilion Lake Road, 11 km east of the junction between between Vermilion Lake Road and Gordan Gordan Lake Lake Road. At Atthis thislocality, locality, in in the the hangingwall hangingwall to to the the Errington Errington and and Vermilion deposits and in the mid-zone mid-zone area area between betweenthe thetwo twodeposits, deposits,the the carbonaceous carbonaceous Onwatin Formation contains s. contains elevated elevated amounts amounts of of pvrite p*te and and rare rarepyritic pyriticcarbonate carbonateconcretion concretions. STOP 10 STOP 10 VERMILION FORMATION VERMILION FORMATION Stop of Gordon Gordon Lake Lake road, road, approximately approximately 75 m south of the Stop 10 10 is is located on the south side of Vermilion River. River. Varved-looking, cm thick thickbands bands of of carbonate carbonate and grey grey argillite bridge over Vermilion Varved-looking, 1-2 cm representative of the non-carbonaceous Vermilion Vermilion Formation, Formation, and and host host to to the Emngton Errington and representative Vermilion can be be seen seen at at this this rare rareexposure. exposure. Vermilion deposits, deposits, can STOP 11 11 STOP LOBATE PEPERITELIKE PEPERITE-LIKE INTRUSIVE BODIES OF OF SPHERULITIC SPHERULITIC WITHIN UPPER UNITS OF THE DOWLING APHANITIC DYKES WITHIN DOWLING MEMBER MEMBER west side side of ofGordon GordonLake Lakeroad, road,approximately approximately 200 200 m m south south of of Stop 11 11 is located on the west the Vennilion km southwest southwest of the Gordon Gordon Lake Lake road road bridge bridge over over Vermilion Mine Mine road road turn turn og off,which whichisis221cm spherulitic devitrified devitrifled as these these strongly strongly altered (silicifled) (silicified) and spherulitic the Vermilion River. Exposures Exposures such such as lobes of aphanitic 'andesite' are level of of the the Onaping Onaping Formation. Formation. They areextremely extremely rare at this level They have not been related to the mineralization at the Vermilion Vermilion or or Errington Errington deposit, deposit, but they may define structures structures that that also alsocontrolled controlled the the location location of the deposit. STOP 12 STOP 12 VERMILION FORMATION FORMATION of the the Errington Errington #1 #1 shaft, shaft, 700 m east east of of the the Stobie Stobie Stop 12 12 is located within the vicinity of Dam on Vermilion River. Though Thoughreclamation reclamationactivities activitieshave have been been recent recent in in the the area, area,trenches trenches �46 showing showing folding of the Vermilion Formation, weak mineralization and strong strong carbonate carbonate alteration alteration can still be observed. The folding is representative of the structure pattern in the deposit area The folding the structure area. STOP 13 STOP13 DISCOVERY SITE SITE Stop east side side of Highway 144, 144, 1.9 1.9 km krn north north Godfrey Godfrey Drive, Drive, or or 4.4 4.4 Stop 13 13 is is located located on the east km Nickel Mine Mine Road. Road. Look for a small paved area with an Heritage Foundation krn north of the Big Nickel historical plaque and an American Society of Metals commemorative plaque plaque marking marking the the site. site. Be Be careffil! Train hea'y. Train traffic traffic on on the railway can be heavy. careful! Though Nickel was first reported in in 1856 near near the the Creighton CreightonMine Minesite siteby byA. A.Murray Murray of of the Geological Survey was not not until 1883, 1883,during during the the construction constructionof of the the Canadian Canadian Survey of Canada, Canada, itit was Pacific Railway, that Pacific that aa railway railway rock-cut rock-cut near nearthe the site siteexposed exposed nickel-copper mineralization, which was was subsequently subsequently developed as the Murray Mine ore body. The Theoriginal originaldiscovery discoveryoutcrop outcropwas was located close to the rim of the present Murray Murray Mine Mine open open pit pit and and remained remained intact intact until untilthe themidmid1970's, when the highway and railway were relocated to to permit permit mining mining of of the the ore. ore. The TheClarabelle Clarabelle No. 22 Open Open Pit Pit and and headftame headframeof of the the inactive inactive Murray Murray Mine Mine are are visible, visible, across acrossthe thehighway. highway. the paved paved area, area, toward toward the the railway railwaytracks tracks is is aa rust-covered rust-covered outcrop outcrop of of Thirty meters from the weakly mineralized Sublayer of the Sudbury Igneous Complex and host for the nickel-copper ore Sudbury for the nickel-copper ore minerals (pyrrhotite, pentlandite, and and chalcopyrite). chalcopyrite). The outcrop is the eastern continuation of the mined-out ore ore body. body. On Onthe theeast eastside sideof ofthe the railway railway track, track, quartz-rich norite is exposed. exposed This This isis the basal unit of the Complex on the the South Range. Range. The The quartz-rich quartz-rich norite differs differs from the homogeneous and and the the quartz quartz has has a Sublayer, in that it contains contains few ore minerals or inclusions, it is homogeneous distinct blue tint. The TheSublayer Sublayerdips dipsnorthward northward at atabout about60° 60"beneath beneath the the norite. norite. STOP STOP14 14 SHATTER CONES Stop 14 14 is located on Ramsey Lake Road, on the south side in a rock cut about about 200m 200m long, long, 1.4 km east of Paris Street. Street. The fracture structures Theshatter shattercones, cones, feathery-looking feathery-looking conical striated fracture structures in the host quartzite quartzite and greywackes of the Mississagi Formation of the Huronian Supergroup, Supergroup, are are illuminatedby bythe thelate lateafternoon afternoonlight. light. The site on Ramsey Lake best observed when obliquely illuminated Road is one of the best and most easily accessible. There Thereare arenumerous numerousshatter shattercones conesininthese these exposures, exposures, most being 20 to 30 cm in size. Please Pleasedo donot not break breaksamples samplesfrom fromthis thissite. site. First noted in the early 1960's by Dr. Robert Robert Dietz, the shatter cones, which were traveling through through the the rock, rock, occur occur in in all all rocks rocks outside of the the produced by strong shockwave(s) traveling Sudbury Sudbury Basin, Basin, but but not not within, within, and and have havebeen been attributed attributedto tothe theSudbuzy SudburyEvent Eventwhich whichformed formedthe the Sudbury asevidence evidenceof ofaameteorite meteoriteimpact. impact. Sudbury Structure. Structure.The Theshatter shattercones conesare arewidely widelyaccepted acceptedas �47 REFERENCES REFERENCES Ames, D.E., Jonasson, I.R., Parish, Parish, R., R., Watlcinson, Dii. and Gibson, Ames, D.E., Jonasson, I.R., Watkinson, D.H. Gibson, H.L. 1996. 1996. Regional Regional hydrothermal massive sulphide suiphide producing producing system system and and UPb U/Pb hydrothermal hydrothennal titanite age constraints, hydrothermal constraints, 42ndAnual Anual Meeting Meeting of of the Institute Institute of of Lake Lake Superior Superior Onaping Formtion, Sudbury Structure. Structure. In: 42nd Geology, Program Program with with Abtracts. Abtracts. Cable Geology, Cable Wisconsin, p. 2-3. Ames, D.E. and Gibson, H.L. 1995. 1995. Controls Controls on, and geological setting of, regional hydrothermal alteration within within the the Onaping Formation footwall footwallto to the the Errington Onaping Formation Errington and Vermilion Vermilion base metal metal alteration Sudbuiy Sturcture, 995-F. Geological deposits, Sudbury Sturcture, Ontario. InInCurrent CurrentResearch Research11995-E. Geological Survey Survey of of Canada, Canada, 161-173. 161-173. evolutionofof the the Sudbury Arengi, Arengi, J.T. J.T. 1977. Sedimentary Sedimentary evolution Sudbury Basin; Basin; unpublished unpublished MSc. MSc. thesis, thesis, of Toronto, Toronto, Toronto, Ontario, l41p. University of 141p. Avermann, Avennann, M. 1992. 1992. Die Diegenese genese der derallochthonen, allochthonen, polymikten polymikten breccien der Onaping Onaping Formation, Formation, Sudbury Struktur, PhD. thesis, Sudbury Struktur, Ontario, Ontario, Kanada; Kana&, unpublished unpublished PhD. thesis, Munster Munster University, University, Munster, Munster, Germany, I 70p. Germany, 170p. Avermann, M. and and Brockmeyer, R 1992. of the Sudbury Avermann, M. Brockmeyer, P. 1992. The Onaping Onaping Formation Formation of Sudbury Structure, Structure, Canada: breccias; Tectonophysics, Tectonophysics, v. v. 216, 216, p. p. 227-234. Canada: An example of allochthonous impact breccias; Beales, F.W. and Lozej, G.P. 1975. 1975. Sudbury Sudbury Basin Basin sediments sediments and the meteoritic impact theory of origin for the Sudbury Sudbury Structure; Structure; Canadian Canadian Journal Journal of Earth Earth Sciences, Sciences, v.12, p.629-635. p.629-635. Bell, R. 1893. Survey of Canada, Annual Report, 1893. On On the theSudbury Sudburymining mining district; district; Geological Geological Survey Report, Bell, v.5, pt. Pt.!, 1890-91, v.5, 1, Report F, 54p. Dcutsch, A. 1989. The origin of the the breccias breccias in the the lower Onaping Formation, Brockmeyer, P. and Deutsch, evidence from petrographic observations and Sr-Nd isotope data; Sudbury Sudbury Structure Structure (Canada) (Canada) - evidence data; in in Abstracts, 20th -114. p. 113-1 14 ~bstra&, 20th conference, conference, Lunar Lunar and and Planetary PlanetarySciences, sciences,p.113 - und Isotopenuntersuchungen Isotopenuntersuchungenan an der der OnapingBrockmeyer, P. P. 1990. 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Was the the Sudbury Sudbury Basin Basin circular circular during deposition deposition of Cantin, Chelmsford Formation?; Formation?; in in New New Developments Developmentsinin Sudbury Sudbury Geology, Geology, Geological Geological Association Association of of Chelmsford Canada, Special Special Paper, Paper, no.10, no. 10, p.93-101. Card, K.D. and Hutchinson, R.W. 1972. 1972. The The Sudbury Sudbury Structure: Structure:its itsregional regional geological geologicalsetting; setting; in in New Developments in Sudbury Geology, Geological Geological Association Association of of Canada, Canada, Special Paper No.10, Paper No. 10, p.67-68. p.67-68. �48 Chubb, P.T.A. 1990. Chubb, P.T.A. 1990. Mineralization and petrology of the Ryan Showing, Black Member, Onaping Ottawa, Ontario, Ontario,Sóp. 56p. Formation, Sudbury, Sudbury, Ontario; Ontario; unpublished BSc. thesis, Carleton Carleton University, University, Ottawa, Coleman, A.P. A.P. 1905. 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PREVEC PREVEC INSTITUTh INSTITUTEON ONLAKE LAKESUPERIOR SUPERIORGEOLOGY GEOLOGY 43rd 43rdANNUAL ANNUALMEETING, MEETING,MAY MAY66- 11, 11,1997 1997 SUDBURY, SUDBURY,ONTARIO ONTARIO - Field TripGuidebook, Guidebook,Volume Volume43: 43:Part Part55 FieldTrip �THE MAGMATIC ORE DEPOSITS OF THE SUDBURY IGNEOUS COMPLEX COMPLEX INSTITUTE ON LAKE SUPERIOR GEOLOGY 43rd ANNUAL ANNUAL MEETING, MEETING, MAY MAY6-11, 6-11,1997 43rd 1997 SUDBURY, ONTARIO ONTARIO Field Trip Trip Co-leaders Co-leaders S.A. Prevec Prevec (Laurentian (Laurentian University, University, Sudbury) Sudbury) M. Cosec Cosec (Resident (Resident Geologist's Geologist's Office, Office, Sudbury) Sudbury) Conference Co-chairs Co-chairs R.P. Sage Sage (Ontario (Ontario Geological Geological Survey, Survey, Sudbury) Sudbury) Meyer (Resident (Resident Geologist's Geologist's Office, Office, Sudbury) Sudbury) W. Meyer �ILSG '97 '97 Field Trip TripGuidebook Guidebook Magmatic Magmatic Ore OreDeposits Deposits of of the Sudbury Sudbury Igneous Igneous Complex Complex S.A. Prevec Prevec of Earth EarthSciences Sciences Laurentian hurentianUniversity Universi@ Sudbuzy, Ontario Su&ury, Ontario CANADA P3E2C6 CANADA P3E 2C6 Dept. Dept. Introduction Introduction Objectives Objectives of of this this excursion excursion Acknowledgements Acknowledgements Geological Sudbury Geological Introduction Introduction to Sudbury Introduction Introduction to to the the mineralized mineralized environments environments Sublayer Sublayer Footwall Footwall Offsets Offsets Sudbury Sudbury Breccia Breccia Mineralization Mineralization T r i ~Part Part : II -- Whistle Whistle Mine Mine sField e l d Trip: Stop 1: Introduction to Whistle Whistle Mine Mine Stop Stop Stop 2: 2: Main Main Mass Mass norites nontes Stop 3: Sublayer Subhyer Stop 4: Inclusion Inclusion Sublayer Sublayer Stop 4: Stop Stop 5: 5: Footwall Footwall Footwall Breccia Breccia II-- Strathcona Trin: Part II Strathcwa Footwall Stop Stop 1: 1: Sublayer Sublayer (breccia) (breccia) Stop Stop 2: 2: Footwall Footwall Breccia Breccia Mineralized Sudbury Sudbury Breccia 3: Mineralized Breccia Stop 3: Stop Field Field Trip: a Frontispiece: Idealized sketch of aa mining mining operation that appeared on some some stationery stationery of the former Ontario Department of Mines, circa 1972. the former Ontario Department of Mines, circa 1972. Frontispiece: �Introduction Introduction 1883 Since the initial discovery of copper sulphide ores in the Sudbury area in 1883 during construction of the trans-Canadian railway, and the subsequent discovery of high nickel contents in these ores, Sudbury has remained the single largest source of in the world. For nickel in For the the first first half of this century, Sudbury produced this has has dropped to less than 20% 20% approximately 80% of the world's nickel, although this of Ni-deposits Ni-depositselsewhere elsewherein inthe theworld. world. In in recent decades with the development of addition to nickel, Sudbury also produces significant quantities of both copper and lesser amounts amounts of gold, gold, silver, silver, cobalt, cobalt, the platinum group elements (PGE), plus lesser selenium, selenium tellurium and sulphur. This This and andfurther furtherhistorical historicalinformation information isis summarized by Giblin (1984). (1984). In addition to its anomalously high abundances of base- and precious-metals, precious-metals, Sudbury is also distinguished by its somewhat unique distribution distribution of silicate silicate and and or at at least controversial controversial models for sulphide components, and the resultant enigmatic or its origin. ItIthas haslong longbeen been recognized recognized that that aa discrete, discrete, igneous-textured igneous-textured noritic noritic phase phase pockets along the interface interface between the of the complex occurs in discontinuous pockets Sudhury (SIC) and and the the footwall. footwall. This is known as the Contact Sudbury Igneous Complex (SIC) Contact Sublayer- and is characterized by the presence of a high proportion of inclusions of Sublayer~and various types (including relatively ultramafic ones), bits of assimilated footwall, and residence of the majority of the nickel most significantly, represents the residence nickel sulphides. sulphides. Offshoots of less nmfic mafic material which extend out from this interface into the footwall, or which may be emplaced into linear zones in the footwall footwall running running parallel to the SIC-footwall contact contact are are known known as as Offset OffsetDykes. Dykes. The ore mineralization in Sudbury is largely associated associated with these three thee environments, environments,as as �summarized by Morrison Momson et et al. al. (1994): (1994): 1. contact-~pe contact-type deposits depositsthat thatoccur occurat at or or near near the basal contact contact of of the the Sudbury Sudbury Igneous Igneous Complex Complex (SIC) (SIC)with with Proterozoic and and Archean basement of SIC SIC material material that extend many 2. offset dykes of kilometres into infothe th.e basement basement foorwall-tvpe deposits deposits that that occur occur as sheet-like veins 3. footwa~&ype within brecciated brecciated basement up to 2 and vein stockworks within outside the the SIC SIC ana7or and/or basement basement contact contact km outside The emplacement emplacement of the SIC SIC was a catastrophic catastrophic event, involving extensive fracturing and brecciation of the host rocks, including the appearance appearance of of shockshock- Ramsey Lake Road, west induced features such as shattercones (well-preserved on Ramey building)and andplanar planarlamellae lamellaein inquartz quartzgrains. grains. In of the Ontario Geological Survey building) the footwall footwall this fracturing fracturing has not only provided potential conduits for the introduction of magmas (such as the Offset Dykes) and heated fluids introduction fluids (which (which may may carry suiphides, sul<hdes, as as may may the the magmas), but also a distinctive pseudotachylitic-textured pseudotachyfitic-texmed rock known known as as Sudbury Sudbury Breccia, Breccia, which which has also provided a conduit conduit for later later migration migration of sulphides sulphides and and other other material. material. 2 �Objectives Objectives of this this excursion excursion This excursion will provide access to some of the best aboveground aboveground examples examples of of the the in the the Contact Contact Sublayer Sublayer (at (at Whistle Whistle pit), pit), and in the environments of mineralization in associated with footwall, associated with Sudbury Sudbury Breccia emplacement (at the Barnet Barnet showing). showing). one-half day dayexcursions. excursions. Part The trip has been arranged as two onehalf Part 11 involves involves a trip to Limited property property located located at at the northeast corner the Whistle mine, an active Inco Limited comer of the SIC. SIC. This Thisisisan anexcellent excellentexample exampleof of the the Contact Contact Sublayer-type Sublayer-typemineralization, mineralization, and displays the the transition transition from from the Main Mass to the Sublayer Sublayer to the footwall footwall environments extremely well. The Thetransition transition of of mineralization styles styles is is also alsovery very evident through this this sequence. Part will take take place place at the Part 2 of this excursion will northwest of the SIC, Levack. Here SIC, near the town of kvack. Here we we will will observe observethe thetransition, transition, breccia to to mineralized mineralized footwall footwall breccia to a bit more discontinuously, discontinuously, from Sublayer breccia mineralized Sudbury Sudbury Breccia within the footwall, courtesy of Falconbridge FalconbridgeLimited. Limited. Acknowledgements Acknowled~ements Acknowledgements Acknowledgements are are due due first fist and foremost to both Inco Limited and Falconbridge Limited, collaboration this excursion L~mited,without whose cooperation and collaboration - would not be possible. Both Boththese thesecompanies companies have provided access to their properties, logistical properties, logistical advice advice and assistance, assistance, and scientific support support and and expertise. expertise. Specific acknowledgements are due to Andy Bite and Bill Dyck (Inco) and John Fedorowich and Mike Mike Sweeny Sweeny (Falconbridge) for their assistance in preparing preparing this guidebook and and supporting supporting the the pre-excursion fieldwork involved. 3 �Introduction to Sudhury Geological Introduction Sudbury The "Sudbury "Sudbury Structure' Structure"refers refers to tothe theentire entirepackage package of of igneous-textured, igneous-textured, metamorphic rocks which which are aregenetically geneticallyinter-related inter-related or were mtamorphic and sedimentary rocks shaped by the the geological geological episode which produced this complex. These include the Sudbury Sudbury Igneous Igneous Complex Complex (SIC) (SIC) itself, the Onaping Formation (the later later subaqueous sedimentaq package package which overlies it), and the complex complex marginal marginal subaqueous sedimentary assemblage textured material materialbetween between the the main main body body of of assemblage of igneous and metamorphic textured the SIC and the the footwall, footwall, which which is the area area of of interest interest in terms of of mineralization mineralization and and indeed of many many other other aspects aspectsof of this this complex complex structure. structure. The SIC occurs occurs at at the the southern southern boundary boundary of of the Superior superior Province, Province, in in the the granitegraniteAbitibi Subprovince. Subprovince. The greenstone terrains of the late Archean Abitibi The Abitibi Abitibi has has been been overlain in this area by a thick pile of volcanogenic and sedimentary rocks known known as as the Huronian between 2480 Huronian Supergroup Supergroup (of the Southern Province), F'rovince), sometime between 2480and and 2220 Ma. The TheSIC SICwas wasemplaced emplacedat at 1850 1850Ma Ma into into these two basement basement types, such such that the "north tonalitic, "north range" range" of of the the SIC SIC is hosted by by granodioritic granodioritic to tonalitic, heterogeneous high grade gneisses and granitoids of of the the kLevack heterogeneous v a c k Gneiss Complex and Abitibi granitoids, granitoids, and and in the "south range" by more mafic, less evolved evolved low low % grade metavolcanics, metavolcanics, metasediments metasediments and granitoids of the Huronian. upper sequence sequence known known as the Main Mass, The SIC itself may be subdivided into an upper downward through consisting of an an upper granophyric granophyric sequence which grades downward through aa quartz gabbroic gabbronoritic gabbroictransition transition zone zone into into an an igneous, cumulate-textured cumulate-textured gabbronoritic rock known as "Felsic "Felsic Norite". The The sequence sequence from fiom Granophyre down through the Felsic Norite can (i.e., can be be broadly broadly viewed viewed in terms of a differentiation differentiation sequence sequence (i.e., 4 �becoming more evolved with increasing height in in the the sequence), sequence), although evidence for geochemical discontinuities and other apparent inconsistencies suggest that simple differentiation differentiation represents represents an an oversimplified oversimplifiedmodel. model. At the base of the Felsic Norite, at the contact contact with the the country country rock (footwall), (footwall), the relationships relationships become become more complex. complex. The SIC SIC is is geographically geographically described describedin in terms terms of of its its three three ""sides", North, sides", into the North, (ca. 2710 2710 to to TheNorth NorthRange Rangeisishosted hostedby byLate LateArchean Archean(cci. South and East Ranges. The granitic and heterogeneous heterogeneous gneissic gneissic rocks of the southernmost southernmost Abitibi Abitibi 2665 Ma) granitic Subprovince Province. The Subprovince of the Superior Province. The gneissic gneissic footwall suite which borders much of the North Range Range is is called called the the Levack Levack Gneiss Complex Complex (a "typical" "typical" section section of which is well-displayed along the Highway 144 just north of Windy 144 roadcut just TheSouth SouthRange Rangefootwall footwallconsists consistsmainly mainly of of volcanics and sediments sediments of of the the Lake). The Supergroupof of the the Early Early Proterozoic ProterozoicSouthern SouthernProvince Province(cci. (ca. 2480 2480 to 2200 2200 Huronian Supergroup Ma). These Theseinclude includebasaltic basalticand andrhyolitic rhyoliticvolcanics volcanics and and intercalated intercalated sediments, sediments, overlain by glacially-deposited glacially-deposited sedimentary sedimentary sequences sequences in a rift rift environment, environment,and and intruded by gabbroic gabbroic to leucogabbroic dykes and intmded and sills sills of of various variousages. ages. The South Range Range has been been much much more more extensively extensively metamorphosed than has the North Range, Range, - probably probably as as aa result resultof ofboth bothPenokean Penokean(cci. (ca. 1950 1950to 1850 1850 Ma) and and later later Grenvillian Grenvillian (ca. 1100 1100 to 950 Ma) activity. The TheEast East Range Range reflects reflects some some characteristics of both (cci. environments. In Ingeneral, general,preservation preservation of of igneous igneous textures and compositions compositions is much better in in the the North North Range Rangerocks rocks than thanelsewhere. elsewhere. 5 �Introduction Introduction to to the the mineralized mineralized environments environments The mineralized environments margins of of the the SIC Main Mass environments occurring along the margins Mass can be broadly therefore of of magmatic-origin) magmatic-origin) broadly subdivided subdividedinto into igneous-textured igneous-textured (i.e., therefore Figure 1, and and the metamorphicContact Sublayer Sublayer and Offset dykes, as shown in Figure footwall rocks recently, the igneoustextured footwall rocks which which host host them. them. Until relatively recently, igneousSublayer matrix ("lTSM't) textured Sublayer ("ITSM") and the more felsic equivalents in the Offset Offset ("QD"), had had been been grouped grouped together together as as Contact Contact dykes, referred to as quartz diorite ("QD"), petrography (e.g., 1984). Evidence Evidencefrom frompetrography (e.g., Pattison, Pattison, Sublayer (e.g., Naldrett et al., 1984). 1979), incompatible trace aL, in press), press), and and trace element element geochemistry (e.g., Lightfoot et aL., radiogenic isotope aL, 1997) suggests that the matrices of isotope geochemistry (Prevec et al., different magmas. magmas. Thus, the Offsets Offsetsand andthe theSublayer Sublayerrepresent represent distinctly distinctly different Thus, although although theft inclusion populations populations and and emplacement emplacement styles styles suggests suggests a close the similarity of their genetic relationship, relationship, they will be treated here as separate separate entities. entities. An additional subunit of the Main Mass gabbronorites known known as as "Mafic Norite" has Norite (which (which comprises comprises the the bulk of the been identified, occurring below the Felsic Norite Main Mass). Mafic MaficNorite Noriteisisparticularly particularly evident evident in locations where Sublayer and/or Offsets occur below the Main Mass. This andlor This relationship is depicted depicted in Figure Figure . petrologic grounds; 2. Mafic MaficNorite Noriteisisdistinguished distinguishedfrom fromFelsic Felsic Norite Norite on petrologic grounds; geochemicaHy the the two norites reflect a gradationally upwards upwards evolving sequence. geochemically sequence. be provided in the Specific distinctions between these two Main Mass subunits will be descriptions for for stops stopsin in the the Whistle WhistleMine Mine pit. pit. 6 �Sublayer The most recent recent formal formal publication dealing specifically with this subunit subunit of the SIC SIC (Naldrett et al., 1984) 1984)used the the term term "Contact "Contact Sublayer" Sublayer" to define define that that part part of of the the Sublayer adjacent to the Main Mass of the complex complex and not that included in (Offset) (Offset) dykes. However, However,its itsusage usageeven evenin in that that article article was was ambiguous, ambiguous, and and more more recent recent prominent distinction distinction between between study, as mentioned previously, has indicated a more prominent Contact Sublayer and Offset Dyke magmas. magmas. Therefore, Therefore, our our working working terminology terminology will henceforth refer merely merely to to "Sublayer" "Sublayer" and and "Offset" "Offset"rocks. rocks. The Offsets will be discussed in more more detail detail in in the the next next subsection. subsection. The discontinuous discontinuous marginal embayments known collectively as the Sublayer, Sublayer, as as characterized by by Pattison (19791, (1979), contain the the bulk bulk of of the the Ni-Cu-PGE ores. originally characterized This unit is characterized characterized by an an igneous-textured igneous-textured noritic matrix mamx hosting disseminated disseminated to massive sulphides and a relatively relatively large large proportion proportionof ofinclusions. inclusions. The inclusion populations may be divided into two groups; those obviously derived from the adjacent footwall, and more enigmatic mafic mafic to ultramafic ultramafic inclusions, inclusions, the the latter latter of of which appear to be spatially associated associated with sulphide occurrences (e.g., (e.g., Souch Souch and Podolsky, 1969). 1969), Sublayer Sublayerinclusion inclusiontypes types include includesmall-scale small-scalefelsic/anorthositic felsic/anorthositic . blebs (generally (generally cm-scale) cm-scale) which which are are most most abimdant abundant in, but not unique unique to, to, the the cm-scale inclusions of fine-grained, often porphyritic, hornfels-textured Sublayer, cm-scale material ("anhedral ("anhedral porphyries"), and cm- to metre-scale metre-scale inclusions inclusions of of ultramaflc ultramafic material. Although Althoughthese theseinclusion inclusionpopulations populations comprise comprise a significant significant proportion proportion of of the Sublayer (up to 25%), 25%), they are not at all well-represented well-represented in the surrounding surrounding basement. basement. 7 �Footwall Footwall The term term "footwall" "footwall" is used as a general general term to denote basement rocks underlying has been variably km surrounding surrounding the SIC has the SIC. The Thefootwall footwallwithin within about about 11 km thermally recrystallized by the contact aureole therma1Iy aureole of the SIC, producing concentric concentric epidote-albitecontact metamorphic zones from from pyroxene- to hornblendehomblende- to epidote-albite- hornfels, in order of increasing distance distance from from the thecontact. contact. It has been o observed b s e ~ e dthat mineralization in the footwall is largely associated the mineralization associated with the the most most proximal, proximal, highest temperature, temperature, pyroxene hornfels aureole aureole (Coats (Coats and Snajdr, Snajdr, 1984). 1984). In addition to the thermal aureole, fractured, both aureole, the footwall is extensively extensively fractured, both radially and concentrically around the SIC. SIC. These These fractures fractures provide conduits for the noritic magma magma bodies bodies known known as as Offset Offset Dykes injection of relatively homogeneous noritic and of distinctive shock-induced pseudotachylitic-textured rocks known as Sudbury Sudbury Breccias, Breccias, both both of of which which represent represent environments environments for hosting significant significant Cu-rich mineralization. In Inaddition addition to to the the Sudbury Sudbury Breccias, Breccias, additional additional breccia-type breccia-type environments which may host mineralization include rifootwall breccia", "late environments r'footwallbreccia", granite breccia" and Sublayer (breccia; (breccia; see see pg. pg. 21). 21). The The latter latter two reflect reflect terminology used mainly by Falconbridge Limited, Limited, and and will willbe be discussed discussed further in the text for Part Part IIIIof of this this excursion. excursion. Offsets fxfsets Offset Dykes are intrusive, igneous- to metamorphic-textured bodies occurring as elongate dykes into the footwall, 10to to 15 15km kminto footwall, occasionally occasionally dykes which which may extend extend 10 Offset in in the theNorth NorthRange). Range). These dykes upwards of 25 km (in the case of the Foy Offset occur both radiating outwards from the contact with with the base base of the SIC and also 8 �out in in the the footwall, footwall, as as in in Hess Hess and Falconbridge aligned parallel to the contact, lying out Townships. The Thesilicate silicatemineralogy mineralogy of the Offset Dykes is dominated by Pattison, plagioclase, orthogranophyre (e.g., Pattison, plagioclase, ortho- and and clinopyroxenes, clinopyroxenes, quartz and ganophyre 1979). As As the thedyke dykeextends extends further further into the footwall, this assemblage is replaced by its metamorphic equivalent, whereby the pyroxenes pyroxenes in particular particular are replaced by quartz, feldspar feldspar and and gsanophyre granophyre are recrystallized. amphibole and then biotite, and quartz, Sudbury Breccias Sudburv Breccia the SIC, where their Sudbury Breccias also occur in a wide zone surrounding the alignment, as with the Offsets, is a function of of the the local local fault fault geometries. geometries. They Theyhave have been identified identified as far as 80 80 km distance away from Sudbury (both near Lake Agnew Lake Lake to to the the west). west). They Temagami to the northeast and Agnew They consist consist of of aa very very within which whichblocks blocksof ofcountry countryrock rockare areentrained. entrained. The clast fine-grained matrix within xenocrystic grains grains to to outcrop outcrop size blocks, where size may vary enormously, from xenocrystic the rotation of regional fabrics (foliations, lineations, lineations, etc.) etc.) allow these blocks to be identified as breccia clasts. The The matrix matrix of of Sudbury Sudbury Breccia is texturally comparable consist to a low-viscosity low-viscosity liquid in terms of its fluid dynamics, although it appears to consist of the the local local country country rock, rock, displaying displaying sharp sharp contacts contacts with of the pulverized equivalent of - it but with with no no thermal thermal contact contactaureole. aureole. Mineralization Mineralization The vast majority of the ores at Sudbury are incorporated into an assemblage assemblage dominated by pyrrhotite, pentlandite, pentlandite, chalcopyrite chalcopyriteand andpyrite. pyrite. Variation in the relative proportions of these minerals within aa given given deposit deposit are atmbutable attributable to the effects of fractionation solid solution solution (Mss), (Mss), such that fractionation of a monosulphide solid 9 �fractionated liquids enriched in Ni, Cu, Pt, Pd and Au are differentiated from Fe, Co, Co, FUI, Rh, Ru, Ru, Ir Jr and and 0Oss (Naldrett, 1984). residual cumulate sulphides enriched in Fe, 1984). Differences in Cu. Ni and PGE tenor between different deposits may be attributed attributed to progressive depletion depletion of of these these elements elements from from a given batch of magma by segregation segregation of successive successive batches batches of of sulphide. sulphide. While most of the Ni is is concentrated concentrated into into pentlandite, exsolved exsolved at at low-temperatures low-temperatures (2000 250°C) from pyrrhotite, pyrrhotite pyrrhotite itself itself may may also also retain retain up up to to 1.2 wt% Ni. (200' to 250°C Cu is largely concentrated concentratedin in chalcopyrite, chalcopy&e, with lesser amounts amounts occurring occurring in in cubanite cubanite PGE are largely concentrated in the platinum-group platinum-group minerals minerals (PGM) (CuFe2S3). PGE (PtAs2). A michenerite (PdBiTe), (PdBiTe), moncheite moncheite (PtTe2) (PtTeJ and sperrylite (Pas*). A relatively relatively at Sudbury Sudbury is is provided by complete list of the metalliferous minerals occurring at Naldrett (1984). (1984). Typical Typicalaverage averagegrades grades of of these these elements elements in 100% 100% sulphide sulphide are a R as as al. follows, based on on values values given given in Naklrett Naldrett (1984), Cochrane (1984), Binney et aL (1994) (I 994) and Naldrett Naldrett et etaL ul.(1994). (I 994). Ni Cu Co Pt Pd Au (wt%) (wt%) (wt%) (ppb) (ppb) (ppb) Sublayer— S ublap 3.8 2.2 0.19 1391 1798 583 0.58 6.8 Offset 4.0 3.6 0.17 2130 3170 868 0.90 5.3 F. Breccia 4.5 2.3 0.16 756 802 122 0.51 25 S. S, Breccia 4.9 3.8 0.12 1042 1026 105 0.78 93 Cu zones 1.6 30.1 0.06 1753 2994 85 18.8 897 Unit Unit CuJNI (Pt+Pd)/ (Ru+Jr+Os) These values are are based based on on arbitrarily arbitrarily chosen data from available literature, and are intended as a very general guide to relative relative abundances. abundances. Sublayer deposits deposits are are thought to to have have CdNi CuiNiranging rangingbetween between0.1 0.1and and0.5 0.5(Morrison (Morrisonetetal.,' at, generally thought 10 10 �1994), than presented presented here. here. The 19941, which is lower than The concentrations concentrations of PGE PGE and and Au Au in between deposits, deposits, so "average" particular may vary by orders of magnitude between be treated treated with with caution. caution. The CdNi Cu/Ni ratio ratio of of the the SIC deposits as a abundances should be whole is considered to be around 1.0, 1.0, where where Sublayer deposits deposits have have Cu/Ni<l, Cu/Nici, 1, and the Offset Dyke and Sudbury Breccia (or Footwall deposits) deposits) have have Cu/Ni> Cu/Ni>l, copper and Cu>>Ni. deep copper and stringer stringer zones zones have have Cu>>Ni. 11 �Trip: Part Part I -- Whistle Field Trio: Whistle Mine The following three page page description description of the environment and history of the Whistle Whistle Mine was written written by by Inco Inco Ltd. Ltd. for for geological geological visitors to the mine site. site. It is here reproduced for courtesy of ofInco kco Limited as of January, 1997, for this field trip guide courtesy 1997, with minor updating updating courtesy courtesyof of A. A. Bite Bite (Inco (Inco Ltd.). Ltd.). WHISTLE MINE Whistle Mine Mine is located locatedin in the the extreme extreme north-east corner comer of the Sudbury SudburyBasin, Basin, of the the town town of of Capreol Capreol in in concession concession IV approximately twelve kilometres north-east of of Norman Township. Township. orebody lies lies within within the the Whistle Whistle embayrnent embayment which plunges to the west southsouthThe orebody west at about forty degrees. The Theore oreoutcropped outcropped in the form of a large hill facing to the south and is reasonably continuous to to aa depth depth of of about aboutfive fivehundred hundredfeet. feet. The ore is of two two primary primary varieties, varieties, the the most most abundant abundant type being disseminated disseminated inclusion inclusion norite in which the blebs in in aa noritic noritic matrix. matrix. Also Also within within the' sulphide sulphide exists as distinct blebs % the norite are are large large inclusions inclusions of of greenstone, amphibolite and a variety of ultramafics ultramafics (generally dark coloured rocks). The The second second most common type of ore is inclusion suiphide. ItItisischaracterized characterizedby by large large rock inclusions (as described above) above) massive sulphide. in aa matrix matrix of of massive massive sulphide. sulphide. The orebody itself itself is is overlain by a thick "floating" in layer of medium-grained, medium-grained, light light grey barren main mass felsic norite. 12 �The footwall of the Sudbury Igneous Complex (SIC) comprises partly barren However, the the true footwall footwall to the ore ore body body is is sublayer andlor inclusion basic basic norite. norite. However, a pink granite breccia breccia which is well exposed exposed on on the the north north wall wall of of the thepit. pit. The ore is made up predominantly of copper plus nickel with minor amounts of cobalt and precious metals. The The copper/nickel copperlnickelratio ratio is is approximately approximately 0.3:1 0.3:l while the pyrrhotite/nickel 23.5: 1. pyrrhotitelnickel ratio ratio is is 23.5:1. There are no major offsetting structures transecting the ore zone; however, strong strong localized joints joints are encountered and many are quite rusty in appearance, indicating significant historic historic water water movement. movement. This may be due in part to the fact that the area had previously been developed as a mine near the turn of the century. 4.5 million tons of rock and 2.7 million tons of ore have been mined To date, some 4.5 from the pit. January 15, 15,1991 1991 13 �WHISTLE WHISTLE MINE MINE HISTORY and and STATUS STATUS 12 lan km north of Capreol -LOT #6, concession concession #5 #5 -- Norman Township Township -- 12 1897 -- Isaac 1897 Isaac Whistle discovers the property 1900 - A mining patent is issued issued 1900 1903 -- Property ownership is transferred from Dominion Nickel Copper Company Company 1903 to British American Nickel Nickel Company. Company. 1910 - Exploration begins in the form 1910 form of diamond drilling and drifting drifting along along ore ore veins accessible accessible through an an adit. adit. 1912 - Whistle is abandoned in favour of the Murray prospect. 1912 1912 -- 1929 The property 1929 -- The property stagnates stagnates 1912 1929 -- The The property reverts to INCO INCO through through the the merger. merger. 1928 -- 1988 1988 -- The ore body is delineated by several series of diamond diamond 1928 programs. drilling programs. 1988 -- INCO INCO develops an open pit in January, 1988 1988 contractually contractually mined by 1988 MacIsaac MacIsaacMining Miningand and Tunnelling. Tunnelling. 1991 3,285,000 1991 -- Pit production ceases and the mine is placed on standby after 3,285,000 tons of ore are extracted along with nearly 4,868,000 tons of waste. Approximately 1.3 million tons tons of of ore remain remain to be be extracted from from the open pit. Additional Additionalmineral mineral below below the the pit could become mineable mineable if economic economic conditions become favourable. conditions favourable. in the footwall of the pit locates aa small 1993 1993 -- Exploration Exploration diamond drilling in small occurrence of high grade copper with substantial substantial precious precious metals metals between levels. -1500 and 2000 levels. 1995. to be be ready for submission by 1995. -- Closure Closure plans are being formulated to 1994 -- Exploration Exploration diamond drilling continues continues to reopen reopen Whistle. Whistle. The 1994 -- In November plans are established to The mining mining contract contract 1994 is let to Carman Construction Construction with the intention to mine approximately 1.3 1.3 million tons to the 12th 12th bench. bench. expansion which which will will access access an additional 1.0 1995 -- Plans are finalized for an expansion 1995 1.0 million tons of of ore ore and and development developmentbegins. begins. Mining will now go to cut million tons #14. -- The The mine closure plan is completed and submitted. 14 �Canmet initiates to characterize a living growing wastewaste - Canmet initiatesaaproject projecttotoattempt attempt to characterize a living growing pile. -- A rare earth earth magnet magnet is purchased to facilitate ore cobbing in an an attempt attempt to to rock" and enhance the remove significant volumes of "floatable rock the mine mine feed feed grade. grade. Mining 1996 for the the fall fullyear yearatataarate rateofof2500 2500tons tonsper perday. day. The is planned for 1996 place and and about about 70% 70% of the ore is being magnetic separation circuit is in place treated. treated. 1997 mine until until September September of this year Reserves indicate that we will be able to mine 1997 -- Reserves day. This at a rate of 2500 tons per day. This will take the pit to a depth of 14 14 benches. benches. Summary (as of June 1, 1, 1996): 1996): Total rock removed to date -Total ore shipped -shipped to date date 6.11 6.1 1 million tons tons 4.80 million tons tons 15 �At the Whistle Whistle mine, mine, the the geology geology exposed exposed in the pit includes both both felsic felsic and and mafic mafic Main Mass norites norites at at the the southwest, southwest,the the Sublayer Sublayer in its various forms, and finally corner. The The trip trip will traverse traverse these these units units in this the footwall contact at the northeast comer. order, in theory, theory, depending depending on on pit logistics, as depicted depicted in in Figure Figure 2. 2. Stop 1: Stop 1: Introduction Introduction to to Whistle Whistle Mine This stop is technically technically not a geological stop, as it will not involve involve looking looking closely closely at at the rocks, but will will provide provide aa geological geological and historical overview of the the mine, mine, courtesy of Inco courtesy Inco Limited, Limited, much of which has been provided in the previous previous text, for for your convenience. Stop 2: Stop 2: Main Main Mass Mass norites norites (south (south ramp) and the the contact contact between between them. them. The This stop includes the two Main Mass norites and The felsic norite is distinguished from the mafic norite on the basis not only of colour modal mineralogical change), but also by inclusion content content index (and therefore therefore aa modal and sulphide content. The Thefelsic felsicnorite norite isis aa two-pyroxene-plagioclase-granophyre two-pyroxene-plagioclase-granophyre massive and and homogeneous. homogeneous. Towards the base, the rock, which is relatively massive clinopyroxeneincreases increases from from roughly equal (about (about 20% 20% and and proportion of ortho- to dinopyroxene \ orthopyroxene-dominant. The 15% of the rock, respectively), to orthopyroxene-dominant. The mafic mafic norite norite dinopyroxene at all, and consists underlying it does not contain clinopyroxene consists of approximately approximately 35-45 modal% orthopyroxene, which becomes progressively more poikiliticpoikilitictextured with depth. The Theporportion porpordon of quartz and granophyric-textured quartzofeldspathic quartzofeldspathicmaterial also decreases decreases from about 10% 10% in the felsic norite to norite. The The mafic mafic norite contains contains cm-sized cm-sized less than 2 or 33 modal% in the mafic norite. felsic clasts thought to to represent anorthositic melt droplets, which have have subsequently subsequently 16 �been recrystallized and hornfelsed. Inclusions Inclusions of dark, fine-grained fine-grained massive massive "gabbro-hornfels" comprise the the other other main main inclusion inclusionpopulation populationhere. here. Minor Minor (2 (2 wt%) disseminated suiphides sulphides appear appear in the mafic norite, consisting consisting of pyrrhotite. pyrrhotite. Stop Stop 3: 3: Sublayer: Sublayer:upper upper contact contact At this stop the contact between the base of the mafic norite and the uppermost uppermost Sublayer is observed. The Thecontact contactisis irregular, irregular, and and is represented by by aa decrease decreasein in grain size, significant decrease in the abundance of coarse-grained feldspar, and an increase in suiphide sulphide content. The The mafic mafic norite here is characterized by the presence presence of coarse-grained interstitial biotite, as well. The Sublayer here here may may be broadly described as opx-rich Sub lover,and andconsists, consists,atatthe thetop, top,of of a medium-grained rock Sublayer, containing about about 40% 40% plagioclase plagioclaseplus plustwo twopyroxenes pyroxenes(ortho~clino). (ortho>>cino). Granophyre but decreases decreases with with depth depthand anddisappears. disappears. Suiphide is also present again, but Sulphide consists of pyrrhotite, grading about about 250 250 ppb ppb Ni, Ni, plus five to ten percent disseminated pyrrhotite, associated pentlandite. associated Stop Stop 4: 4: Inclusion Inclusion Sublayer Sublayer This "stop" "stop" is a sequence sequence of stops stops as we we move move progressively progressively into the more more mineralized Sublayer down down towards towards the the footwall footwallrocks. rocks. The Sublayer can be discriminated discriminated petrographically into a variety variety of of sub-groups, sub-groups, including includingolivine-opxolivine-opx- rich Sublayer, porphyritic opx-Sublayer and variations thereon, as distinguished distinguished variant at atthe thetop topof ofthe theSublayer Sublayer.. The from the opx-rich variant The presence of porphyritic- textured pyroxene distinguishes Sublayer rocks from mafic norite, which is characterized by poikilitic textured textured pyroxene. pyroxene. As the footwall contact is the Sublayer Sublayer referred referred to to as as inclusion basic approached, a relatively thin subunit of the 17 �no rite is is present, present, characterized characterized by by aa "salt "saltand andpepper" pepper"texture. texture. This is a somewhat norite leucocratic variant one time time to to be be more leucocratiic variant of of the the Sublayer, Sublayer, and and has has been thought at one representative of a possible parental composition for the Sublayer (e.g., Morrison et aL, 1994). 1994). The Theinclusion inclusionbasic basicnorite norite may may also also reflect reflect differentiation differentiation of of Sublayer Sublayer al., extends outwards from the Whistle rock into the "root" of the Offset Dyke which extends Sublayer to the northeast (forming the the Whistle Whistle and and Parkin Parkin Offsets). Offsets). The The application application of terminology such as inclusion basic norite and quartz diorite to Offset Offset rocks rocks this point. point. Many becomes somewhat subjective at this Many workers apply apply the term term "quartz "quartz diorite" to Offsets Offsets in the South South Range Range only. Sulphide textures vary through through the the Sublayer Sublayer from fromthe the interstitial interstitial pyrrhotite pyrrhotite observed observed at the top top to to progressively progressively more more interconnected, interconnected, higher sulphide sulphide content content equivalents equivalents the inclusion inclusionbasic basicnorite). norite). These include towards the core of the Sublayer (above the suiphide, ragged-textured sulphide, gabbro-peridotite disseminated (blebby) sulphide, (GPIS) and inclusion massive-sulphide. The The inclusions inclusions in in inclusion suiphide sulphide (GPIS) inclusion massive sulphide tend to consist of locally derived footwall material, whereas those in gabbro-peridotite gabbro-peridotite inclusion sulphide are thought to represent material. This potentially more exotic material. This interpretation interpretation depends depends on on knowing knowing the the source source inclusions, which whichisisunclear. unclear. Alternatives include &ore ultramafic ultrarnafic inclusions, of these more (i.e., cumulates), cumulates), a pre-existing Proterozoic Proterozoic maficmaficderivation from the Main Mass (i.e., ultramafic body, Archean footwall, or or picritic picritic mantle. mantle. The source ultrarnafic source of of these these inclusions therefore has further potential implications regarding the origins of the metals and the sulphur. sulphur. 18 �Stop 5: 5: Footwall Footwall The footwall footwall exposed exposed along along the north side of the pit consists of granitic granitic material of Complex, cut cut by bymafic maficdykes dykeslocally. locally. [Note [Note that that the cliffface cl(ffface in the Levack Gneiss Complex, in pit at the footwall footwall in particular particular is relatively unstable, due to the extensive the pit particular awareness and caution should be fracturing in in this this brecciated brecciated rock, rock, so particular Blocksofoffootwall footwallrock rockare arepresent presentwithin within the the exercised at all all times times in in this area.] area.]Blocks adjacent inclusion adjacent inclusion basic basic Sublayer, Sublayer, and and may contain Cu-enriched Cu-enriched suiphides sulphides may also be observed, particularly dominated by chalcopyrite. Pyrite-rich Pyrite-rich sulphide may associated with the and footwall footwall granite granite breccias. associated the more more "granitized" "granitized Sublayer and mineralization, can can also be observed "gash-type"copper mineralization, observed Sudbury Breccia, hosting "gash-type" breccias. The presence of well-defined Sudbury amongst and below the footwall breccias. Sudbury Breccia Breccia can can be be used used to to imply imply that that the host footwall rock is (probably) (probably) insitu, insitu, and and is is not, itself, a breccia breccia block. block. LUNCH -- Onanin Onaoins Falls Falls LUNCH 19 �Field Trip: Part Part H I1 -- Stratheona Strathcona Footwall Breccia In contrast to the Sublayer-hosted, pyrrhotite-dominated ores at Whistle mine, the along the the northwest northwest margin margin of of the the SIC SIC are are dominantly dominantly footwafl-hosted, footwall-hosted, deposits along (1984), Thefollowing followingtable, table,modified modified from from Coats Coats and and Snajdr Snajdr(1984), copper-rich deposits. The summarizes activity in this 10 10km km wide wide belt. belt. summarizes the mining activity Deposit Ownership Ownership Depth (fret) (feet) Production Production Hardy Falconbridge Falconbridge 1427 1427 1954 to 1978 1978 1954 Boundary Boundary Falconbridge 952 1961 to 1973 1973 Onaping Onaping Falconbridge Falconbridge 5348 5348 1961 to 1982 1982 McCreedy West Inco 1600 1600 1973 1973 to present Craig Craig Falconbridge Falconhridge Levack Levack Inco Inco 3915 3915 1913 1913 to present Fecunis Fecunis Falconbridge 3993 3993 1957 to 1977 1977 North Falconbridge Falconbridge 4430 4430 1964 1964 to present McCreedy East McCreedy Inco Inco Fraser Falconbridge Falconbridge 5250 5250 1981 to present Strathcona Strathcona Falconbridge Falconbridge 3205 3205 1968 to present Colemar Coleman- Inco Inco 2278 2278 1970 to 1982 1982 Lower Coleman Coleman Inco Inco Longvack Falconbridge Falconbridge open pit 1956 to to 1961 1961 1956 Longvack South South Falconbridge Falconbridge 1289 1289 1968 1968 to 1977 1977 Big Levack Inco Inco developed not developed developed not developed developed not developed not developed developed of sulphides in in the the area in 1888, production of Ni-Cu Following initial discovery of ores began in 1913, 1913, and production and reserves for the deposits in this area exceed 20 �200 million tons. A A summary summary of the so-called "North Range deposits" located located in from whom whom the the Levack Township is provided by Coats and Snajdr (1984), from following information has been derived. derived. corresponding mafic The Sublayer, Sublayer, as as characterized characterized previously, along with its corresponding noritic protrusion from poorly developed at the surface from the Main Mass, is relatively poorly surface in this area, although well-developed well-developed in in the the subsurface. subsurface. No Offset Offset Dyke Dyke projects projects outwards outwards into into the the footwall, although offset rocks hosted by Archean granitoids do occur parallel Hess and and Harty Harty parallel to to the the footwall footwall contact about 15 15 km to the north in Hess I). The Townships (Fig. 1). Thefootwall footwall in Levack LevackTwp. Twp. consists consists of of aa heterogeneous heterogeneous Gneiss Complex), Complex), in its type high-grade Archean gneiss complex (the Levack Gneiss location (or near enough). This Thiscomplex complex includes includes a mixture mixture of granitic, granitic, tonalitic, tonalitic, mafic and occasionally occasionally ultramafic rocks which have seen granulite granulite grade grade metamorphism metamorphism(and subsequently retrogressed to amphibolite facies, for the most part). The 2.5kin kmout outfrom fromthe the Thecomplex complexisisexposed exposedatatsurface surfaceto toaa width width of of about about2.5 SIC, beyond which more heterogeneous, greenschist-grade granitoids occur. The stops stops on on this this section section of of the the excursion will pass from basal Sublayer Sublayer into - Footwall Breccia Breccia and and then into the footwall proper, where mineralization is associated associated with with aa Sudbury SudburyBreccia Breccia zone. zone. Stop (garbage dump Stop 1: 1:Sublayer Sublaye~(garbage dump outcrop) outcrop) The Sublayer between the the base base of the Main Mass Sublayer here here is inclusion-rich Sublayer between and the footwall proper. ItItisisbroadly broadly equivalent equivalent to undifferentiated inclusion Sublayer between the inclusion basic basic norite described described the opx-rich Sublayer and the inclusion 21 �previously. This This rock rock type typemay may be be considered considered a breccia, given that a large have been been derived derived fiom fromthe the Main Main Mass Mass above it (as proportion of the inclusions may have Falconbridge, as opposed to the Inco perspective which which treats treats the the it is interpreted by Falconbridge, exotic). As footwall increases, increases, inclusions as largely potentially exotic). As the the proportion proportion of of footwall this becomes analogous to the footwall footwall breccias brecciasobsewed observedat atWhistle. Whistle. Inclusions gneiss, iron-rich iron-rich pyroxenite, and a identifiable here include fragments of footwall gneiss, variety of mafic inclusions in a variably crystalline crystalline felsic felsic matrix. matrix. The The granitic granitic footwall proper is evident evident in the the cliff cliff face, about 100 100 m to the north. Stop 2: Stop 2: Footwall Footwall Breccia Breccia (Strathcona (Strathcona cliff cliff face, water tower) mines, (at (at the the lefthandmost lefthandmost extreme extreme of of In front of the Strathcona and Coleman mines, Figure 3, but not shown), the contact between Sublayer breccia breccia and footwall breccia is well displayed. The Thetwo two breccias breccias represent represent a transition from a norite-dominated inclusion-rich breccia into aa granitoid-dominated granitoid-dominated environment with mafic mafic inclusions. inclusions. the water water tower, tower, access access permitting), permitting), late-granite late-granite Further up on top of the hill (under the breccia is is evident. evident. This Thiscontains containsfewer fewermafic mafic inclusions inclusions in a much more granitic matrix and is characterized characterized by by aa stockwork stockworkof of relatively relatively fine finefractures fracturesinfihled infilled with with granitic material. Mineralization this stop occurs at the base of the cliff in Mineralization evident at this \ the footwall breccia, consisting consisting of blebby pyrrhotite plus pentlandite, with chalcopyrite present locally. locally. Stop Sudburv Stop 3: 3: Mineralized M M Brecciai i(Barnet (Bametshowing) showing) This location, shown example' of footwall footwall shown in Figures 33 and 4, is an excellent example (Sudbury Breccia)-hosted mineralization, and has been summarily described by Morrison and Sweeny (1994). ItItisislocated locatedapproximately approximately 400 m into the footwall 22 �extension of the from the SIC contact, and is interpreted to be the up-plunge extension Strathcona Copper Copper Zone, characterized characterized by high-Cu, low-PGE contents contents in in the ores. ores. Limited (since (since 1979), and and the outcrops This showing is the property of Falconbridge Limited were stripped in 1987 1987 and 1989 1989 for subsequent subsequent detailed mapping and sampling. The footwall here consists of Levack Gneiss Complex gneisses and migmatites, cut by plagioclase-phyric ("Matachewan-type") ("Matachewan-type") mafic dykes, with later Sudbury Breccia units. Sudbury Sudbury Breccia pseudotachylite occurs as small cutting both of these units. veinlets at the south end of the outcrop and as a large east-west east-west trending trending dyke dyke at at the the of the mineralization mineralizationisishosted. hosted. Thin veinlets of north end, where the bulk of extensively epidotized epidotized and and hematized, hematized, cross-cut cross-cut pegmatitic feldspathic material, extensively footwall, dykes and breccias, and are also associated associated with Cu-mineralization. Cu-mineralization. This showing is located within the hornblende-hornfels homblende-homfels aureole induced in the footwall footwall by the intrusion of the SIC (as mentioned earlier). Both Both mineralization mineralizationand and alteration alteration are very strongly fractured andlor footwall and/or structurally structurally controlled in the footwall environment. environment. Mineralization is dominated by by chalcopyrite, and occurs as disseminated sulphide, h4ineralization stockworks of of veinlets. veinlets. The veins and stockworks as discrete veins, or as fine stockworks evident evident within the Sudbury Breccia body represent the best-mineralized section, where the the distribution distribution of veins and stringers stringers is controlled controlled by two two main main orientations orientations of fracture sets. The TheSudbmy SudburyBreccia Brecciaisismore more prone prone to to extension extension than than is is the the footwall, providing more zones of weakness and therefore a relatively relitively high high suiphidesulphidereservoir potential. This the Thisextensional extensionalfracture-fill fracture-filloccurrence occurrence is is equivalent equivalent to to the 23 �deep-Cu deposits, deposits, but does not display the wide mineralized zones required to produce the more massive, higher-grade ores present present at at depth. depth. 24 �References Binney, W.P., R.Y.,Sweeny, J.M. W.P., Poulin, R.Y., J.M. and Halladay, Halladay, S.H. S.H. (1994) The Lindsley Ni-CuPGE deposit Sudbury -- Noril'sk deposit and and its its geological geological setting In Proceedings of the Sudbury Norifsk Symposium (editedbyby P.C. Lightfoot Naldrett). Ontario Geological Survey, Symposium (edited P.C. Lightfoot andand A.J. A.J. Naldrett). Ontario Geological Survey, Special Special Volume 5, p. p. 91-103. 91-103. Coats, C.J.A. and and Snajdr, Snajdr, P. P. (1984) (1984) Ore Ore deposits deposits of the North Range, Onaping-Levack area, Structure (edited (edited by by E.G. E.G. Pye, Pye, Sudbury In The geology and ore deposits of the Sudbury Structure A.J. Naldrett P.E. Giblin). Giblin). Ontario Ontario Geological Geological Survey, Special Special Volume Volume 1, 1, p. 327-346. 327-346. A.J. Naldrett and and P.E. (1984) Ore Ore deposits deposits of of the Copper Cliff Cochrane, L.B. (1984) Cliff Offset OffsetIn In The The geology geology and and ore ore deposits deposits of of A.J. Naldrett and P.E. Giblin). the Sudbury Structure Structure (edited (edited by E.G. Pye, A.J. Giblin). Ontario Ontario Geological Geological Survey, Survey, Special Special Volume 1, p. 347-359. Giblin, P.E. P.E. (1984) development, of of geological geological studies studies and Gibh, (1984) History History of exploration and development, development and ore ore deposits of the Sudbury development of geological geological concepts In The geology and Sudbury Structure Giblin). Ontario Ontario Geological Survey, Structure(edited (editedby by E.G. E.G. Pye, Pye, A.J. A.J. Naldrett Naldrettand andP.13. P.E. Giblin). Special Volume 1, 1, p. 3-23. 3-23. Lightfoot, R.R., Moore, M. and Pekeski, D. (in press, K., Keays, R.R., Lightfoot, P.C., P.C., Doherty, Doherty,W., W., Farrell, Farrell, K., Mass, Sublayer, Offsets, Offsets, and and inclusions from from the Sudbury 1997) Geochemistry of the Main Mas, Igneous Igneous Complex, Complex, Ontario. Ontario. Ontario OntarioGeological GeologicalSurvey SurveyOpen Open File File Report. Report. White, T.L. T.L. (1994) (1994)Footwall Footwall mineralization mineralization of the the Sudhury Sudbury Morrison, G.G., Jago, Jago,B.C. B.C. and andWhite, Igneous Igneous Complex Complex In In Proceedings Proceediigs of of the the Sudbury Sudbury - Norifsk Noril'sk Symposium (edited (edited by P.C. Lightfoot Li&tfoot and and A.J. A.J. Naldrett). Naldrett). Ontario Ontario Geological Geological Survey, Special Volume 5, p. 57-64. 57-64. Morrison, surface tour. tour. CIM (1994) Sudbury ore environments surface CIM Geological Geological Morrison, G. and and Sweeny, Sweeny, M. (1994) Society, trip guidebook, guidebook, 35 pp. Society, Fourth Fourth Annual Annual Field Field Conference, Conierence, field field trip pp. Naldrett, In The The geology geology and and Naldrett, A.J. A.J. (1984) (1984)Mineralogy Mineralogyand and composition composition of the Sudbury Sudbury ores h ore deposits deposits of of the the Sudbury Sudbury Structure Structure (edited (edited by E.G. Pye, A.J. Naldrett Naldrett and and P.E. P.E. Giblin). Giblin). p. 309-325. Ontario Geological Geological Survey, Survey, Special Special Volume 1, p. Naldrett, R.,Asif, Asif, M. M. and and Li Li C. (1994) (1994) Compositional Compositional variation varjiition in the Sudbury Sudbury Naldrett, A.J., A.J., Pessaran, Pessaran,R., of footwall copper-PGE copper-PGE bodies In Proceedings of the ores and prediction of the proximity of 25 �Sudbury Noril'sk Symposium (edited Sudbury -- Norilsk Ontario (edited by by P.C. P.C. Lightfoot Lightfoot and AJ. A.J. Naldrett). Ontario Geological Survey, 143. Geological Survey, Special Special VolumeS, Volume 5,p.p. 133133-143. E.F. (1979) (1979)The TheSudbury SudburySublayer. Sublayer.Canadian Canadian Mineralogist, Mineralogist,v. v. 17, 17, p. Pattison, E.F. Pattison, p. 257-274. 257-274. S.A., Keays, Keays, R.R. R.R. and and Lightfoot, Lightfoot,P.C. P.C. (1997) (1997)Genesis Genesisof ofinclusions inclusionsin in the themineralized mineralized Prevec, S.A., Contact Sublayer,Sudbury Sudbury Igneous Igneous Complex: Sm-Nd Sm-Nd isotopic, isotopic, geochemical geochemicaland and Contact Sublayer, In Geological Geological Association of Canada/Mineralogical petrographic evidence evidence In petrographic Canada/Mineralogical Association of Canada Program Canada Program with Abstracts, Abstracts, v. v. 22. 22. Podolsky, T. T. and and geological geological staff of Inco Limited (1969) The sulphide ores at Souch, B.E., Podoisky, Souch, Sudbury: their particular relation to a distinctive inclusion-bearing facies facies of of the Nickel 4, p. 252-261. Irruptive. Economic Geology, Monograph 4, Recommended references: references: 1. 1. The geology and ore deposits of the Sudbury Structure Structure (edited by by E.G. E.G. Pye, A.J. A.J. Naldrett and P.E. Giblin). Giblin). Ontario Geological Geological Survey, Special Volume 1, 1984. 1984. 2. Proceedings (edited by by P.C. P.C. Lightfoot and and A.J. A.J. Proceedings of the the Sudbury Sudbury - Noril'sk Symposium (edited Naldrett). Ontario 1994. Ontario Geological Geological Survey, Survey, Special Special Volume 5, 1994. 3. Sudbury tour (prepared (prepared by by Gordon Gordon Morrison and Inco Sudbury ore environments surface tour geological staff and Mike Mike Sweeny Sweeny and andFalconbridge Falconbridgegeological geologicalstaff). stam. CIM geological CIM Geological Geological Society, Fourth field trip trip guidebook, guidebook, 35 pp., 1994. Society, Fourth Annual Field Conference, field 1994. 26 �____ 15km W4E Part I Whistle Mine (Figure 2) Whistle Offset Strathcona Fraser s.._Rigure 3) Levack West Mine -. C) Mine — a) -c Offset :- A I Frood-Stobie Offset '7 ..:.. e... r") SIC Main Mass ......................... ...^.$^$ ................. .................... ...... ...... .,:......... :..,.: :....:,: :,:...: ....... ....... .....:.: SIC Main Mass Sublayer norite 0 Sublayer noritediorite Offset quartz Offset quartz diorite Faults Faults A , Sample locations Sample locations Figure1:1: Map Mapof of the the Sudbury SudburyIgneous IgneousComplex Complex(SIC) (SIC)showing showing Sublayer and Offset Figure locations, plus plus excursion excursion stop stop areas areas (modified (modifiedfrom from Lightfoot Lightfoot et Sublayer at., 1997).and Offset locations, et at., 1997). �+++++++ aa — — a a a - aaa a -" a + + + aa LSJ J a a a L L 111ff Ii L Li. ill 11;::: EEJ Leucocrafic noifte alhopyoxene-dch rinite Olvinenorite Tvo pyroxerfe noilte ILfl MDflcNoilte Felsic t'blte Mjln Mass — — Fojit SuW&y &-eccla SCm 0 QJ Qnlzcio,ffe Cet Altered math> UItranc4lc indthlon Fresh macaria IndIcn - +++ ++- < bdIcn mczslvo sulpilde Sudbury Igneous Complex + °° X A ++++ IndLtct Gniltojd rockB Leucocrafic brecda Anof1hc6Ite4roctcMte,tho Dczo hckaris aid ratls ftpilte Gceybmdedgnes FoofclI and indusions +±++++++ +++ c ++ NJ,Cu=60 aa çaa ++++++++ + + + + ++++++ aaaaaaaaa a a aaaaaaaI aaa aI a++++ +++ a a a a a a a a a a a aa a a + + Y+ + — ,Ifr-a a a a +1 aaaaa a aaaaa aaaaaaaa + + ++ u= O.oolf + in Offtef 1- Figure 2: Geology of the Whistle pit, from Lightfoot et al. (1997). Approximate positions of stops are indicated by circled numbers. - a a a aaa aaaaa a a ++++++ ++++ ++++ ++++ +++++++++-ftlfiu=55+ L. ++-EI-++/ct++++y+++ +++ Mapped:1993-94 ++ ++++ +++++++++ + ++++ L -L +++++++++ + + cu<o.1 ++++++ ++++++++++.+++C?) SCHEMA11CANAToM WiSThEEMR'yMENff �___ ___ Strathcona-Longvack area area Strathcona-Longvack GeologicalPlan Plah map map Geological V/ ] Footwall SIC Levack Oneiss Sublayer Diabase IT'1 Fe/sic Norite as r&..a.i SudbuoiBreccia Grid 7' / / // // // // II! / //////// V -'] FootwallBrecc/a 200m //////////////// ////// / / / / / // / / / / / / / / / / ?/// •.••+. /// //////..,..+•• N / Barnet Showing '1 : /// ////// / / ///// /// / aa:asas ////// Aa A . A * . . . . . . . . . . . . . . . £ Asaaasaaaaasaaaaaaaaaaasa ALAS LA Lsaasaasaaaaaassasaaaasaa LLsLaasaaaaaAssaaaLAsLaAsaAa as a a La aLa a aLa Laa s a aa a AL A a AL as a a a a £ Aaaassaaasaaa ALL Laaaaaaaa A Lsssas A La £ As ALL a a LA Las £5 A Las £LLLLAALLSaL AL La AL Las Las LLLALSLLSaL545 Figure 3: Strathcona to Longvack area geolo9ical map, showing mine locations and location of stripped outcrops of the Barnet showing (modified after Morrison and Sweeny, 1994). �Barnet Barnet Showing Showinq Trench Map Sulphides (cpy) (cpy) Suiphides maficlultramafic inclusions inclusions mafic/ultramafic (including plag-phyric plag-phyricdykes) dykes) (including Sudbury Breccia Breccia Sudbury fr,,, I,,,,,, m j Tonalitic gneiss (Levack) gneiss (Levack) d*<*<:v*;;<;;;, 40m 40 m Figure 4: Outcrop Outcropmap mapof of Barnet Barnetshowing, showing, displaying displaying mineralized mineralized Sudbury Sudbury Figure Breccia in in Archean Archean footwall, footwall, modified modified after after Morrison Morrison and and Sweeny Sweeny(1994). (1994). Breccia � https://digitalcollections.lakeheadu.ca/files/original/4afc55d14de13fcdcaa0443badf9ba58.pdf ed2258139e0613bbe04baa280822e4ed PDF Text Text ALKALIC ROCKS ROCKS OF OF THE THESUDBURY SUDBURY REGION REGION BY R. P. P. SAGE SAGE INSTITUTE ON SUPERIOR GEOLOGY INSTITUTE ON LAKE LAKE SUPERIOR GEOLOGY 43rd ANNUAL MEETING, MEETING, MAY 43rd MAY 66 -11, -11, 1997 1997 SUDBURY, ONTARIO ONTARIO Field Trip Part 66 Trip Guidebook, Guidebook, Volume 43: Part �Alkalic Rocks of the Sudhury Sudbury Region Region by R. R. P. P. Sage Sage Precambrian PrecambrianSection Section Ontario OntarioGeological Geological Survey Survey Ministry Ministry of of Northern NorthernDevelopment Development and and Mines Mines 7th 7th floor floor 933 Ramsey Lake Road Road Sudbury, Sudbury, Ontario Ontario P3E 6B5 P3E 6B5 of aa Carbonatite Carbonatite Frontispiece: Frontispiece: Idealized Cross Section of Intrusion(modified Intrusion(modifiedfrom fromSage, Sage,1991) 1991) �ACKNOWLEDGEMENTS ACKNOWLEDGEMENTS This This field field trip trip guidebook guidebook would would not not have have been been possible possible without without the the assistance assistance of of Wilf Wilf Meyer, Meyer, Resident Resident Geologist, Geologist, and and Mike Mike Cosec, Cosec, Staff Staff Geologist, Geologist, Ontario Ontario Geological Geological Survey, Survey, Sudbury, Sudbury, Ontario. Ontario. Excluding Excluding the the Spanish Spanish River River Carbonatite, Carbonatite, author had no prior exposure manifestations the author exposure to the the many manifestations of of alkaline alkaline magmatism magmatism in in the the region. region. �1 INTRODUCTION INTRODUCTION magmatism within the Sudbury region Alkaline magmatism region manifests itself in many forms forms and in in differing differing structural structural settings(Figures 1 1 and 22). Alkaline magmatism magmatism occurs from settings(Figures ) . Alkaline the middle Proterozoic Proterozoic to to Middle Cambrian Cambrian and and expresses expresses discrete plutons and as metasomatic events itself as discrete as metasomatic events with with no no clearly recognizable recognizable magmatic magmatic phase. phase. The The various various alkaline alkaline features features are are widely widely spaced; spaced; therefore, therefore, all all will will not not be be seen seen on the field field trip. trip. Due Due to to the the wide wide spacing spacing of of the the accessible accessible sites, two sites, two days days will will be be spent spent examining examining the the alkaline alkaline rocks. rocks. alkaline rocks Day one will be spent spent examining alkaline rocks in in the the immediate area immediate area of of Sudbury Sudbury and and will will include include the the Spanish Spanish River River Carbonatite, Carbonatite, Nemag Lake fenites fenites and the French French river river nepheline-cancrinite pegmatites. The Spanish nepheline-cancrinite Spanish River River Carbonatite occurs the Sudbury Carbonatite occurs in in Archean rocks northwest of the Complex(SIC), the Nemag Nemag Lake fenites fenites occur in Igneous Complex(SIC), Supergroup at the deformed rocks rocks of the Huronian Huronian Supergroup the western western end Great Lakes of the Great Lakes Tectonic Zone southwest of Sudbury Sudbury and the French River River alkalic pegmatites occur occur in in a syenite syenite intrusion intrusion within within the the Grenville Grenville structural structural province. province. On On the the day, two second day, two alkaline alkaline intrusions of lower lower to to middle Cambrian age Cambrian age will will be be examined examined in in the the Lake Lake Nipissing Nipissing area area and and a a visit to to the the Scadding Scadding mine is is planned to to examine examine the the effects metasomatism. The effects of regional regional sodium sodium metasomatism. The visit visit to to the the Lake Lake Nipissing Nipissing area area will will require require boat boat transport. transport. �2 * • Mesozoic kimberlite (120-1507 Ma) Mesozoic kimberlrte (120-150? Ma) Mesozoic (90 125 Mat Mesozoic (90-125 Ma) £ Paleozoic (275-570 Ma) Paleazoic (275-570 Ma) • Prolerozcuc (570 2500 ~ a ) Proterozajc (570-2500 Ma) • Archean (2500 Ma) Archean (2500 Ma) K K * * * @ Cr~ptoexplosionstructures Cryptoexpiosron Structures Fault Zone Phanerczojc and Precambrian boundary Sporosimute timri of rate Precambrian supracrustar racks Parts ol St. Lawrence Graben System affec1ed by Phanerozoic faulting and recent earthquakes Midconrinenm Rrfm System Unknown age Unknown age Figure 1: Regional distribution of alkalic rock-carbonatite Figure 1: Regional distribution of western complexes in eastern Ontario and Figure alkalic Quebec. rock- carbonatite complexes in eastern ( 1 9 7 8 ) and western Sage ( 1 9 9 Quebec. 1) . modified from Lumbers Ontario Figure modified from Lumbers(l978) and Sage(lg9l). �G.ology 505111.5 PRQVINCE SUPERIOR PROVINCE - - North.,0 All.',. Map. 2197 •nd 2393 PROVINCE - sodium metasornatism) Crater; - - . - - - - - Figure 2: Distribution of alkali0 rock-carbonatite complexes in the Sudbury region. Modified from Sage(l99l) Brent 3 Callander Bay Alkalic Rock Complex; 4 (2- Manitou Island Alkalic Rock Complex; 5 Burritt Island Alkalic Rock Complex; 6 Iron Island Alkali0 Rock Complex; 7 Carbonatite; S Spanish River Carbonatite; 45 NemagLavergne iKusk Lake Fenites; 46 Allen Lake Carbonatite; 52 and Sullivan Island Carbonatite complex; A French River (Rotter Pluto0j Alkalic Rock Complex and B Scadding mine area of rem OntarIo O.plrtm.n t or Ml COBALT EMBAYMENT GREENSTONE BELTS NEOARCHEAN SUDBLJRy IGNEOUS COMPLEX DOMINANTLY METASEDIMENTS PALEOPROTEROZOIC DOMINANTLY METASEDIMENTS GRANITIC ROCKS M E SO PR 01 EROZO IC All *9•• CARBONATITE AND RELATED ROCKS LEGEND �4 SITES SITES TO TO BE BE VISITED VISITED DAY DAY 11 1. ISLAND COMPLEX 1. MANITOIJ MANITOU ISLAND COMPLEX 2. 2. CALLANDER BAY BAY COMPLEX COMPLEX 3. 3 .SCADDING SCADDINGMINE MINE DAY DAY 22 4. 4 . SPANISH SPANISHRIVER RIVERCARBONATITE CARBONATITE 5. 5 .NEMAG NEMAG LAKE LAKE AND AND KUSK KUSK LANE LANE FENITES FENITES 6. 6.FRENCH FRENCHRIVER RIVERALKALIC ALKALICROCKS ROCKS �FIGURES FIGURES Figure Figure 1: 1: Regional Regional distribution distributionof ofalkalic alkalicrocJc—carbonatite rock-carbonatite complexes complexes in in eastern eastern Ontario Ontario and and western western Quebec. Quebec. Figure Figure modified modified from from Lumbers(1978) Lumbers (1978)and and Sage(l991). Sage (1991). Figure Figure 2: 2: Distribution Distribution of of alkalic alkalic rock-carbonatite rock-carbonatitecomplexes complexes in in the the Sudbury Sudbury region. region. Modified Modified from from Sage(l99l). Sage(1991). (2 (2 -- Brent Brent Crater; Crater; 33 -- Callander Callander Bay Bay Alkalic Alkalic Rock Rock Complex; Complex; 44 -- Manitou Manitou Island Island Alkalic Alkalic Rock Rock Complex; Complex; 55 -- Burritt Burritt Island Island Alkalic Alkalic Rock Rock Complex; Complex; 66 -- Iron Iron Island Island Alkalic Rock Rock Complex; Complex; 77 -- Lavergne Lavergne Carbonatite; Carbonatite; 88 -- Spanish Spanish River River Carbonatite; Carbonatite; 45 45 Nemag Nemag and and Kusk Kusk Lake Lake Fenites; Fenites; 46 46 -- Allen Allen Lake Lake Carbonatite; Carbonatite; 52 52 -Sullivan Sullivan Island Island Carbonatite Carbonatite complex; complex; AA -- French French River River[Rutter [Rutter Pluton] Plutonl Alkalic Alkalic Rock Rock Complex Complex and and BB -- Scadding Scadding mine mine area area of of sodium sodium metasomatism) metasomatism) Figure Figure 3: 3: Geology Geology of of the the Manitou Island Island Complex(from Complex(from Lumbers, Lumbers, 1971, 1971,p. p. 82) 82). Figure 4: Aeromagnetic Aeromagnetic map map of of the the Manitou Manitou Island Island Figure 4: complex(from complex(from ODM-GSC ODM-GSC1965c) 1965c) Figure Figure 5: 5: Geology Geology of of the the Callander Callander Bay Bay Complex(from Cornplex(fromLumbers, Lumbers, 1971, 1971, p.84). p.84). Figure 6: 6: Aeromagnetic Aeromagnetic map map of of the the Callander Callander Bay Bay Complex(from Complex(from Figure ODM-GSC ODM-GSCl965a,b). l966a,b) . Figure Figure 7: 7: Topographic Topographic and and road road map map for for the the Callander Callander Bay Bay area(from topographic topographic maps maps obtained obtained from from the the Resident Resident area(from Geologist's Office, Office, Ontario Ontario Geological Geological Survey, Survey,Sudbury) Sudbury) Geologist's Figure 8: 8: Geological Geological sketch sketch map map of of the the Scadding Scadding Gold Gold Figure Mine (modified after Mine (modified after Harper, Harper, 1983) 1983) . Figure Figure 9: 9: Topographic Topographic and and road road map map for for the the Scadding Scadding Gold Gold Mine area(from area(from topographic topographic maps maps obtained obtained from from the the Resident Resident Mine Geologist's Geologist's Office, Office,Ontario Ontario Geological Geological Survey, Survey,Sudbury). Sudbury). Figure Figure 10: 10: Aeromagnetic Aerornagnetic map map of of the the Spanish Spanish River River Carbonatite(from Carbonatite(from ODM-GSC ODM-GSCl965d). 1965d). �7 DAY DAY 11 MIDDLE MIDDLE TO TO EARLY EARLY CAMBRIAN CAMBRIAN ALKALIC ALKALIC INTRUSIONS, INTRUSIONS, LAKE LAKE NIPISSING NIPISSING AREA AREA Introduction Introduction Within Within the the Lake Lake Nipissing Nipissing area area there there are are 77 alkalic alkalic rock rock intrusions intrusions into into the the gneissic gneissic rocks rocks of of the the Grenville Grenville Subprovince Subprovince of of the the Canadian Canadian Shield Shield or or areas areas of of extensive extensive alkalic alkalic metasomatism(Sage, metasomatism(Sage, 1991) 1991). These These are are Brent Brent Crater, Crater, Callander Callander Bay, Bay, Manitou Manitou Island, Island, Burritt Burritt Island, Island,Iron IronIsland, Island, Lavergne Lavergne and and Allen Allen Lake. Lake. These These alkalic alkalic rock rock complexes complexes occur occur where where the the Ottawa-Bonnechere Ottawa-BonnechereGraben Graben splits splits into into an an east-west east-west trending trending deformation deformation zone zone and and the the northwest northwest trending trending Lake Lake Timiskaming The Ottawa-Bonnechere Ottawa-Bonnechere Timiskaming Structural Structural Zone(LTSZ) Zone(LTSZ) . The Graben Graben system system is is aa branch branch of of the the St. St. Lawrence Lawrence valley valley system system which which Kumarapeli Kumarapeli and and Saull(l966) Saull(1966) compare compare to to the the East East African African rift rift valley valley system. system. Existing Existing isotopic isotopic dating dating of of the the alkalic alkalic rocks rocks of of the the Lake Lake Nipissing Nipissing area area indicates indicates that that these these alkalic alkalic intrusions intrusions were were emplaced emplaced during during the the middle middle to to early early Cambrian. Cambrian. Lying Lying to to the the east east of of this this east-west east-weststriking striking cluster cluster of of intrusions intrusions is is the the Proterozoic Proterozoic Sullivan Sullivan Island Island Carbonatite Carbonatite intruded intruded into into the the Ottawa-Bonnechere Ottawa-Bonnechere Graben(Luinbers et al., al., 1990). The GrabentLumbers et The Ottawa-Bonnechere Ottawa-BonnechereGraben Graben system system was was most most likely likely in in existence existence during during the the Proterozoic Proterozoic and and has has been been periodically periodically reactivated reactivated throughout throughout geologic geologic history(Sage, history(Sage,1996) 1996). The The St. St. Lawrence Lawrence rift rift system system and and its its many many branches branches are are seismically seismically active active to to this this day(Adams day(Adams and and Basham, Basham, 1986; 1986; Bent, Bent, 1992, 1992,1996) 1996). . . Table 1: Summary Summary of of Alkalic Alkalic Rock Rock geochronological geochronologicaldata data for for Table 1: the the Lake Lake Nipissing Nipissing area area Intrusion Intrusion Age (MA) Age(MA) Method Method Reference Reference Manitou Manitou Island1 1sland1 560 570 560 568 566 +- 38 576 +- 45 K-Ar K-Ar K-Ar K-Ar K-Ar K-Ar K-Ar K-Ar K-Ar K-Ar K-Ar K-Ar 558 ÷ 14 K-Ar K-Ar K-Ar K -Ar K-Ar K-Ar 1 1 2 3 4 4 Caliander Callander Bay2 ~a~~ 568 575 5 3 3 �8 576 ÷- 3 Pb-Pb 6,4 Brent Crater Crater 40 576 576 ++ - 40 K-Ar KAr 7 7 Footnotes Footnotes ages cited 4 are the same same as as references references 1. The ages cited by reference reference 4 1 and 2 using using different different decay decay constants. constants. 2. Except for for the the 575 575 Ma Ma age age on on nepheline nepheline syenite syenite the the cited cited isotopic ages ages are are on on lamprophyre lamprophyre dikes dikes interpreted interpreted to to be be isotopic related to to the the Callander Callander Bay Complex Complex References References 1. 2. 3. 3. 4. 5. 6. 7. Gittins et Gittins et al., al., 1967 1967 Lowden et Lowden et al., al., 1963 1963 Currie, 1976 Currie, 1976 Symons and Symons and Chiasson, Chiasson, 1991 1991 Ferguson and Ferguson and Currie, Currie, 1972 1972 Kamo et et al., al., 1989 1989 Shafiqullah et Shafiqullah et al., al., 1968 1968 The only only regional regional mapping mapping in in which which most of of the the intrusions intrusions were were examined examined was was by by Lumbers(1971). Lumbers(1971). Currie(l976) Currie(1976) prepared prepared aa brief description description of of each each of of the the occurrences occurrences in in an an abstract abstract format format but has has restricted restricted most of of his his field field investigations investigations to the Callander Callander Bay Bay complex. complex. Extensive sampling sampling for for paleomagnetic studies Symons, paleomagnetic studieshas has been beencompleted completedbybyID. D . Symons, University of University of Windsor, Windsor, on on the the Callander Callander Bay, Bay, Manitou Manitou Island Island and Iron Iron Island Island Complexes, Complexes, however however only only the the work work on on the the Callander Callander Bay Bay complex complex has has been been completed(Symons completed(Symons and and Chiasson, Chiasson, 1991) 1991). STOP STOP 1: 1: Manitou Manitou Island Island Complex Complex I I I The The Manitou Manitou Island Island complex complex lies lies in in the the east east central central portion portion Lake Nipissing of Lake Nipissing and and is is only only accessible accessible by by boat. boat. Road Log Log Proceed 112.9 km east east along along highway highway 17 17 measured measured from from the the intersection of highway intersection highway 17 17 and and the the by-pass by-pass south south of of Sudbury. Sudbury I 1 At intersection intersection with with highway highway 17B 17B in in North North Bay Bay turn turn right. right. I Go (Note: If Go 4.1 4.1 km km to to Memorial Memorial Street Street and and turn turnright. right.(Note: If you you turn turn left left you you will will be be on on Murray Murray Street) Street) �Go Go 0.6 0.6 km krn to to parking parking lot lot at at boat boat landing. landing. Travel Travel time time by by boat boat to to Newman Newman Island Island is is approximately approximately45 45 minutes minutes and and distance distanceis isapproximately approximately1010kin km or or 66 miles. miles. Geology: Geoloqv: The The Manitou Manitou Island Island Complex Complex is is outlined outlined by by aa circular islands consisting consisting of of fenitic fenitic circular distribution distribution of of 55 islands rocks. rocks. The The actual actual intrusion intrusion located located central central to to the the islands islands is is unexposed. unexposed. The The site site to to be be visited visited is is located located on on Newman Newman Island Island where where exploration exploration for for uraniferous uraniferous pyrochlore pyrochlore took took place place in in the the late late l9SOs. 1950s. Most Most of of these these islands islands are are now now included included in in the the Manitou Manitou Islands Islands Provincial Provincial Park Park even even though though the the mineral mineral rights rights are are retained retained by by the the mining mining company. company. Lumbers(197l) Lumbers(1971) describes describes the the fenite fenite aureole aureole as as consisting consisting of of an an outer outer zone zone of of quartz quartz fenite fenite approximately approximately 400 400 feet feet wide wide and and an an inner inner aureole aureole of of aegirine-potassic aegirine-potassicfeldspar feldsparfenite feniteas as much much as as 1,500 1,500 feet feet wide. wide. These These fenites fenites have have been been derived derived from from Grenville Grenville granitic granitic gneisses. gneisses. The The central central portion portion of of the the complex complex is is poorly poorly known known from from scattered scattered diamond diamond drill drill holes. holes. Lumbers(l97l) Lumbers(1971) states states that that the the west west central central portion portion of of the the complex complex consists consists of of massive massive coarse-grained coarse-grainedto to pegmatitic pegmatitic pyroxene-rich pyroxene-richrocks rocks younger younger than than the the enclosing enclosing fenites. fenites. The The carbonatite carbonatite occurs occurs as as fine fine to to coarse coarse grained grained dike-like dike-like intrusions intrusions into into the the fenites fenites and and consists consists of of aegirine, aegirine,sodic sodic amphibole, amphibole, biotite, biotite, magnetite, magnetite, apatite apatite and and locally locally pyrochlore pyrochlore and and pyrite pyrite in in addition additionto to carbonate. carbonate. On On the the west west side side of of Little Little Manitou Manitou Island, Island,located locatednorthwest northwest of of Newman Newman Island, Island, fossiliferous fossiliferouslower lower Ordovician Ordovician limestone limestone is is exposed exposed on on the the shoreline. shoreline. Attempts Attempts to to make make cement cement from from this this material material were were made made in in the the early early days days of of settlement settlement in in the the region. region. Figure Figure 33 presents presents the the geology geology of of the the Manitou Manitou Island Island Complex(Lumbers, illustrates the the airborne airborne Complex(Lumbers,1971) 1971) and and Figure Figure 44 illustrates magnetic magnetic response response of of the the intrusion(ODM-GSC, intrusion(0DM-GSC,l965a,b). 1965a,b). The The complex complex is is approximately approximately 22 miles miles long long and and 1.7 1.7 miles miles wide(Lumbers, wide (Lumbers,1971) 1971) . Economic Economic Geology: Geoloqv: Upon Upon discovery discovery of of pyrochlore pyrochlore and and uraniferous uraniferous pyrochiore pyrochloreon onNewman Newman Island Islandin inthe theearly early1950's, 19501s, testing verticalshaft shaft442 442 testing of of the the discovery discovery took took place. place. AA vertical feet feet deep deep was was sunk sunk on on Newman Newman Island Island and and 2,500 2,500feet feetof of lateral lateral drifting drifting completed(Lumbers, completed(Lumbers, 1971). 1971). This This work work outlined U303 and and 0.69% O.69 outlined 2,962,000 2,962,000tons tons averaging averaging 0.04fl 0.041% U3O8 Nb205 Nb205 all all 200 200 feet feet below below lake lakebottom(Lumbers, bottom(Lumbers,1971) 1971). The The . �10 0 0r;ft.covered areas; no subsurface data available. @ Mddle Ordovhian sedimentary rocks, . a Umi.3n PYrochlore-bearing rocks. Mahly altered feldspathic rocks. C and alkalic Mafic ~ Wsyenite Pyroxenrte. Aegirfne-potassic feldspar fe Wining minor carbonatite in a a Quart.?fenite. Geological boundary, (defined. assumed). Fautt. lsomagnetic lines. Shaft. Scale in feet !m 0 , 2 y O.D.M. €4 Figute Figure 3: 3: Geology Geology of of the the Manitou Manitou Island Island Complex(from Complex(from Lumbers, 1971, p. 82) Lumbers, 1971, p. 8 2 ) . �I I I I t - A— -k 1 1mIle mile Figure Figure4: 4: Aeromagnetic Aeromagneticmap mapof ofthe theManitou ManitouIsland Island ODM-GSC1965c) 1965~) complex~£ro complex(from ODM-GSC �12 pyrochlore mineralization mineralization occurs occurs with with fenitic Eenitic rocks rocks and and pyrochiore carbonatite. carbonatite. Newman Newman Island: Island: On On the the inner inner or or north north side side of of Newman Newman island island brecciated, brecciated, red, red, syenitic syenitic fenite fenite is is exposed exposed along along the the lakeshore. veined and lakeshore. At the the shaft, shaft, blocks of fenite Eenite veined and cemented cemented with with white white carbonate carbonate can can be observed. observed. Along Along the the shoreline shoreline an an occasional, occasional, narrow, narrow, yellow-brown, yellow-brown,fine-grafted fine-grained carbonate carbonate dike dike can can be be observed observed cutting cutting the the fenite fenite and and white white carbonate. carbonate. Towards Towards the the east east end end of of the the island island and and to to the the south south side side gneissic gneissic textures textures are are well preserved preserved and and the the rocks rocks take take on on the the appearance appearance of of Grenville Grenville gneisses. gneisses. The The general general gneissic gneissic trend trend is is 260 260 degrees degrees with with aa steep steep north north dip. dip. Locally Locally these these gneisses gneisses may may appear appear brecciated brecciated and and are are irregular white white carbonatite carbonatite dikes dikes and and on on occasion occasion by cut by irregular younger, younger, very very narrow, narrow, fine-grafted, fine-grained,brown brown carbonatite carbonatite dikes. dikes. Return Return to to the the boat boat landing. landing. STOP Bay Complex Complex STOP 2: 2: Callander Callander Bay The The Callander Callander Bay Bay Complex Complex lies lies at at the the eastern eastern end end of of Lake Lake Nipissing Nipissing and and most most of of the the complex complex lies lies beneath beneath the the water water of of Callander Callander Bay. Bay. Road Road Log Log to highway highway 17 17 and and zero zero the the odometer odometer Return to Return Proceed Proceed eastward 7.8 km km to to where where highway highway 11 11 splits splits from from eastward 7.8 highway highway 17. 17. Take Take highway highway 11 11 to to the the town town of of Callander. Callander. At 13.2 13.2 km km take take the the exit exit to to the the town town of of Callander. Callander. The The road road goes qoes right right and and then then jogs jogs left. left. km turn turn left left on on Pinewood Pinewood Drive Drive and and go go south south towards towards 13.7 km At 13.7 Callander(4 Callander ( 4 km). km). At the highway highway splits. Take highway 94 At 17.2 17.2 1cm km the 94 to to the the left left and and continue continue south. south. At 19.1 19.1 km k m Landsdowne Landsdome St. St. intersects intersects the the highway. highway �Zero the odometer Zero odometer at at Landsdowne Landsdowne St. St. and and continue continue on. on. km Main Main St. St. intersects intersects the the highway. highway. Park Park at at the the side side At 1.65 1.65 km of the the road road for for Stop Stop 2A. 2A. Geology: Geoloqy: As As with with the the Manitou Manitou Island Island Complex, Complex, the the Callander Callander Bay Complex Complex is is poorly poorly exposed exposed and and largely largely lies lies beneath beneath the the waters of Lake Lake Nipissing. Most exposures are of fenite fenite border border rocks rocks with with only only aa limited limited number number of of exposures exposures of nepheline nepheline syenite syenite towards towards the the centre centre of of the the complex. complex. Nearly all of the the exposures exposures of of nepheline nepheline syenite syenite are are on on private private property property and and not not easy easy to to access. access. Lumbers(l971) Lumbers(l971) interpreted interpreted the the Callander Callander Bay Bay complex complex to to be be approximately approximately 2.25 2.25 miles miles in in diameter diameter and and to to consist consist of of cone cone sheets of (Figures 5, sheets of fenite fenite and and nepheline nephelinesyenite syenite(Figures 5, 6) 6). Lumbers(1971) Lumbers(l971) predicts the the centre centre of the the intrusion intrusion may consist of carbonate-rich consist carbonate-richrocks rocks and and alkalic alkalic mafic mafic rocks. rocks. Lamprophyre, basaltic Lamprophyre, basaltic and and phonolitic phonolitic dikes dikes cut cut across across rocks rocks of the the fenite fenite zone zone and and these these are are in in turn turn cut cut by by barite barite and and calcite veIns calcite veins(Lurnbers,l971) (Lumbers,1971) . Currie(l976) Currie (1976) has has also also interpreted interpreted the the Callander Callander Bay Bay Complex Complex to to consist consist of of cone cone sheets sheets of of fenite fenite and and alkalic alkalic rocks rocks enclosed enclosed in in aa crescentic crescentic zone of nepheline zone nepheline syenite. syenite. The The fenitic fenitic rocks rocks were were observed observed by Currie(l976) Currie(l976) to to be be cut cut by by dikes dikes of of carbonatite, carbonatite, lamprophyre, trachyte lamprophyre, trachyte and and nepheline nepheline syenite. syenite. The The alkalic alkalic dikes dikes intruding intruding the the fenitic fenitic rocks rocks are are considered considered coeval coeval with with Callander Bay the Callander Bay complex complex and and have have been been the the most most intensely intensely studied studied rock rock group group within within the the complex. complex. . The fenitic fenitic rocks rocks are are derived derived from from Grenville Grenville gneissic gneissic rocks rocks adamellite(granitic) composition composition and and form form aa zone zone up up to to of adamellite(granitic) 1000 1000 m wide wide along along the the eastern eastern margin margin of of the the complex complex where where are well they are well exposed(Currie exposed(Currie and and Ferguson, Ferguson, 1971, 1971, 1972). 1972). Currie and Ferguson(1971) Currie F'erguson(l971) subdivide subdivide this this metasomatic metasomatic halo halo enclosing the enclosing the Callander Callander Bay Bay Complex Complex into into inner, inner, middle middle and and outer zones. outer zones. The The inner inner zone zone is is characterized characterized by by aa loss loss of of gneissosity, igneous igneous textures and miarolitic cavities cavities and the outer outer zone zone is is characterized characterized by by regional regional gneissosity, gneissosity, reddening of the the rock, rock, hematized fractures fractures and rare brecciation(Currie and Ferguson, Ferguson, 1971). 1971). The The middle zone is is brecciation(Currie and middle zone transitional between transitional between the the outer outer and and inner inner zones. zones. The The alkalic alkalic dikes were studied studied by Ferguson Ferguson and Currie(l971) and interpreted by them interpreted them to to have have formed formed by by liquid liquid immiscibility. immiscibility. the basis basis of of the the studies studies on on the the dikes dikes the the Callander Callander Bay Bay On the ,complex has has been been interpreted interpreted to to result result from from aa carbonated, carbonated, mantle-derived, magma(Fergus0n and and Currie, Currie, mantle-derived,nephelinitic nephelinitic magma(Ferguson 1971, 1972) 1971, 1972). The The fenitic fenitic rocks rocks were derived derived by fluids fluids emanating from from the the fractionating fractionating nephelinitic nephelinitic magma magma which which . �Figure 5: Geology of the Callander Bay Complex(from Lumbers, 1971, p.84). 4:- �ODMGSC1965ab) Figure 6: Aeromagnetic map of the Caflander Bay Complex(from 1 mile �16 underwent underwent liquid liquid immiscibility immiscibility in in its its late late stages stages giving giving rise rise to to aa carbonate carbonate magma(Ferguson magma(Ferguson and and Currie, Currie, 1971, 1971,1972; 1972; Cullers Cullers and and Medaris, Medaris, 1977). 1977). Since Since the the Callander Callander Bay Bay Complex Complex is is of of middle middle to to lower lower Cambrian Cambrian age age and and untilted, untilted, it it has has been been the the subject subject of of recent recent studies paleomagnetism(Chiasson, 1989; 1989; Symons Symons and and studies in in paleomagnetism(Chiasson, Chiasson, Chiasson, 1991) 1991). Economic Economic Geology: Geolocrv: The The Callander Callander Bay Bay Complex Complex has has undergone undergone prospecting prospecting and and some some diamond diamond drilling. drilling. While While anomalous anomalous niobium niobium values values have have been been encountered encountered nothing nothing of of potential potential economic economic interest interest has has been been identified identified to to date. date. STOP STOP 2A: 2A: Stop Stop 2A 2A is is located located within within the the inner inner to to middle middle fenite fenite zone(Figure zone(Figure7) 7). Numerous Numerous alkalic alkalic dikes dikes cut cut the the fenites the ont h e east east side side fenites and and can can be be observed observed in in the the road road cut cut on of highway. One of the the.highway. One should should observe observe the the diverse diverse rock rock textures textures within within the the fenites fenites and and the the variety variety of of dike dike rocks rocks available available to to study. study. . STOP STOP 2B: 2B: Continue Continue south south from from Stop Stop 2A 2A for for 2.3 2.3 km. km. AA scenic scenic lookout lookout occurs occurs on on the the right right hand hand side side of of the the road road and and provides provides aa good good parking parking spot. spot. Opposite Opposite the the lookout lookout is is an an outcrop outcrop of of granitic granitic gneiss gneiss intruded intruded by by biotite biotite porphyry porphyry mm and and the the lamprophyre. The The biotite biotite phenocrysts phenocrysts are are up up to to 44 mm lamprophyre. dike dike trends trends 010 010 degrees degrees and and dips dips approximately approximately 45 45 degrees degrees east. east. The The dike dike may may be be up up to to 55 metres metres in in width width and and is is one one of of the the widest widest dikes dikes observed observed in in the the road road cuts. cuts. The The outcrop outcrop shows shows many many sample sample sites sites and and it it is is obvious obvious that that it it has has served served as as aa source source of of material material for for aa number number of of studies studies on on dike dike rocks rocks in in the the area. area. Continue Continue south south along along the the east east side side of of the the highway highway for for approximately approximately 760 760 feet feet and and aa small small point point outcrop outcrop of of nepheline nepheline syenite syenite can can be be found. found. Contact Contact relations relations are are not not exposed exposed but but this this is is likely likely one one of of the the nepheline nepheline syenite syenite cones cones sheets sheets of of Lumbers(1971). Lumbers (1971). STOP STOP 2C: 2C: Return Return to to the the junction junction of of Main Main Street Street and and highway highway 94 (Stop 2A) 2A) and and turn left onto Main Street 94(Stop Street towards towards the the town town of km and and on on the theright rightside(east) side(east) of Callander. Callander. Proceed Proceed for for 1.8 1.8 km of of Main Main street street an an outcrop outcrop of of medium medium to to coarse coarsegrained, grained, massive, massive, equigranular equigranular nepheline nepheline syenite syenite can can be be found. found. This This is is one one of of the the very very few few outcrops outcrops of of this this rock rock type type that that is is currently currently accessible accessible to to sampling. sampling. To To avoid avoid problems problems with with flying flying rock rock chips chips since since this this is is aa highly highly travelled travelled street street II would would strongly strongly recommend recommend collecting collectingthe thesamples samplesyou youwish, wish, �N CD CD C Hi 0Q H o Ofl C) 1-"-'- HI MI Figure 7: Topographic and road map for the Callander Bay area(from topographic maps obtained from the Resident Geologist's Office, Ontario Geological Survey, Sudbury) !( \ di e - - \ 1"'tH ('- - -. - -f ''L- ) I ,WH(iN - _\ ?'Y ,i, C) rtc LIa' V Fr - I / 7 / I - -; 'Q r L —-'t' --,-- :- — \7: y, —JTh' —--'' / tH2-1 >' vtca4>'..7— ,J çX4''" H /1 �18 and and we will transport transport them them to to another another site site for for trimming trimming and and selection. selection. A thin thin section section prepared prepared from from aa sample sample collected collected of of this this coarse grained grained inequigranular inequigranular seriate senate outcrop displayed aa coarse allotriomorphic texture allotriomorphic texture with lobate lobate to to serrate serrate grain grain boundaries. boundaries. The The potassium potassium feldspar feldspar is is aa string string perthite perthite that that sometimes displays sometimes displays Carlsbad twining. The The nepheline nepheline is is fresh fresh . with sericite with sericite alteration alteration along along grain grain boundaries boundaries and and cleavage cleavage planes. ic mineral mineral is is aa dark dark greenish greenish brown brown amphibole planes. The The mat mafic amphibole appears interstitial that appears interstitial to the feldspar feldspar and and nepheline. One One possible grain possible grain of of clinopyroxene clinopyroxene was was noted noted that that was was mantled mantled with amphibole. amphibole. Biotite, Biotite, sphene, sphene, apatite apatite and and chlorite chlorite are are present as as accessory accessory or or alteration alteration phases. The The rock rock is is visually visually estimated estimated to to consist consist of of 10 10 to to 15% 15% amphibole, amphibole, 45 45 to to potassium feldspar 55% potassium feldspar and and 35 35 to to 45% 45% nepheline. nepheline. Return to Return to Sudbury Sudbury ALKALIC ROCKS OF THE ALKALIC ROCKS THE IMMEDIATE IMMEDIATESUDBURY SUDBURY REGION REGION Within the the immediate area of of Sudbury Sudburythere there are are three Within immediate area three distinct alkaline events which are not likely distinct alkaline likely coeval. coeval. The The events events are are represented represented by by the the Spanish Spanish River River carbonatite, carbonatite, regional regional sodium sodium metasomatism metasomatism and and the the development development of of the the Nemag Lake Lake and and Kusk Kusk Lake Lake fenites. fenites. The The age age relationships relationships of of these three three events events remains remains speculative speculative since since only only one one feature feature has been been accurately accurately dated, dated, one one has has been been dated dated in in aa general fashion fashion and and no no attempt attempt to to age age the the third third has has been been undertaken. undertaken. The The existing existing isotopic isotopic studies studies suggest suggest these these alkalic alkalic rocks rocks are are of of middle middle Proterozoic Proterozoic age. age. STOP STOP 3: Scadding Scadding Mine NOTE: THIS THIS SITE SITE WILL WILL LIKELY LIKELY BE BE VISITED VISITED ON ON THE THE RETURN RETURN TRIP TRIP FROM BAY FROM NORTH NORTH BAY Road log log from from the the intersection intersection of highway highway 17 17 and and the the by-pass by-pass around Sudbury Sudbury near near the the town town of of Coniston. Coniston. from the the bypass along along highway highway 17 17 to to Proceed 19.7 km east from Kukagami t(north). Kukagami Road. Road. Turn Turnlet left (north). �11 16.8 north along along the the Kukagami Kukagami Road Road there there is is aa skid skid road road 16.8 km km north or or overgrown overgrown road road to to the the left(west) left(west) . Turn left left and go 0.6 0.6 km km to the Scadding Scadding Mine Site Geology: Sodium Geoloqy: Sodium metasomatism metasomatism is is common common within within the the Sudbury region region but has has been been poorly poorly documented documented and and has has been been the the subject of only subject only one one serious serious attempt attempt to to interpret interpret the the phenomenon. Sodium phenomenon. Sodium metasomatism metasomatism is is characterized characterized by by the the development development of of albite albite feldspar feldspar which which imparts imparts aa tan, tan, pink, pink, buff, grey, buff, grey, white white to to yellow yellow color color to to the the rocks. rocks. Occurrences Occurrences of sodium sodium metasomatism metasomatism are are found found as as far far east east as as Cobalt Cobalt and and as as far far west west as as Bruce Bruce mines, mines, aa distance distance of of approximately approximately 400 400 km(Meyer, 1995) km(Meyer, 1995). Occurrences of of sodium sodium metasomatism metasomatism are are perhaps best developed developed between Espanola Espanola and the area immediately immediately east east of of Lake Lake Wanapitei(Meyer, Wanapitei(Meyer, 1995). 1995).Meyer(1995) Meyer(1995) reports reports that that the the sodium sodium metasomatism metasomatism affects affects the the Proterozoic Proterozoic rocks more than rocks than the the Archean rocks. rocks. The effects of sodium metasomatism metasomatism varies varies from from incipient incipient to to nearly nearly 100 100 percent albite replacement albite replacement with sodium sodium contents of some some altered rocks approaching approaching 11.0% Na20 indicating rocks 11.0% Na2O indicating a rock of nearly pure pure albite albite composition. composition. Meyer(1995) Meyer(1995) describes describes the the effects effects of of sodium sodiummetasomatistu metasomatism as as occurring in occurring in vein-like vein-like or or dike-like dike-like features features up up to to several several kilometres kilometres in in length length associated associated with with faults faults or or fractures fractures and and as irregular irregular shaped shaped masses. masses. The The extensively extensively altered altered rock rock can can easily easily be mistaken mistaken for for chert chert due due to to the the development development of of aa conchodial conchodial fracture fracture and and very fine-grained fine-grainednature nature and and can can be be missed in in outcrop outcrop if if color contrast color contrast is is absent(Meyer, absent(Meyer, 1995). 1995). The The tan tan to to pink pink color color of sodium metasomatism(a1bitization)blends blends into into or or with with the the sodium metasomatism(albitization) normal normal colors colors of of arkoses arkoses and and granites. granites. Within the Within the Sudbury Sudbury region region breccias breccias are are of of common common occurrence. occurrence. With respect respect to to sodium sodium metasomatism metasomatism three three breccia breccia types types have have been recognized recognized by by Meyer(1995) Meyer(1995). These are 1) 1) in-situ in-situ These are brecciation brecciation of of metasomatically metasomatically altered altered rock, rock, 2) 2) metasomatic metasomatic alteration of alteration of aa pre-existing pre-existing breccia breccia and and 3) 3) breccias breccias that that contain contain fragments fragments of of altered altered rock rock mixed mixed with with fragments fragments of of other other rock rock types. types. . When is associated associated with with other other alteration When sodium sodium metasornatism metasomatism is alteration events it is is always always the the earliest, earliest, followed followed by by carbonate, carbonate, quartz, quartz, chlorite chlorite and and possibly possibly the the introduction introduction of of Fe, Fe, As, As, Cu Cu Schandl et suiphides and sulphides and gold(Meyer, goldtMeyer, 1995) 1995). Schandl et al., al., (1994) (1994) have have completed the only detailed study on the sodium sodium metasomatism within the the region. region. Two Two generations generations of of hydrothermal hydrothermal REE . I �20 minerals were minerals were identified identified in in albitized albitized Huronian Huronian sediments. sediments. The minerals found The minerals found were were monazite, monazite, bastnasite, bastnasite, synchysite synchysite and and gadolinite. An An U-Pb U-Pb isotopic isotopic age age of of 1700 1700 ÷+ - 22 Ma Ma was was gadolinite. obtained on obtained on hydrothermal hydrothermal monazite monazite and and on on hydrothermal hydrothermal rutile(Schandl rutile (Schandl et et al., al., 1994). 1994) . The very high high light light REE enrichment enrichment within within the the albitized albitized rocks rocks prompted prompted Schandl Schandl at et al., al., (1994) the (1994) to to propose propose that the sodium-rich sodium-rich fluids fluids were derived from from a carbonatitic carbonatitic or or alkali intrusion approximately alkali intrusion at depth. depth. The The isotopic isotopic age is approximately Ma younger younger than 150 Ma than the the formation formation of of the the Sudbury Sudbury Igneous Igneous Complex(SIC) that Complex(S1C) that was was emplaced emplaced at at approximately approximately 1850 1850 Ma(Krogh Ma(Krogh at et al., al., 1984; 1984; 1996). 1996). Geoloqy Mapping Napping of the mineral occurrences east of Economic Geoloqv Lake Wanapitei by by Gates(l991) Gates(1991) has has shown shown most most mineral mineral occurrences in occurrences in the area display associated sodium metasomatism. Gates(1991) metasomatism. Gates(1991) proposed that that the the sodium sodium metasomatism has which upon metasomatism has developed developed a hard brittle rock which upon fracturing produced channelways fracturing channelways for for the the introduction introduction of of chlorite, gold chlorite, gold and and sulphide sulphide minerals. minerals. Scadding Mine(go1d) Mine(gold) is The Scadding is one of of two small mines in in the the region that display display associated associated sodium sodium metasomatism, region metasomatism, the other being the Norstar gold-copper Scadding Mine other gold-copper mine. The Scadding extracted gold from extracted from four four chlorite zones zones containing pyrite arsenopyrite within within the the Serpent Serpent Formation Formation arkose arkose near near and arsenopyrite the contact contact with with Espanola Espanola Formation Formation limestones(Gates, limestones(Gates, 1991). 1991). The The chlorite chlorite zones zones are are within within carbonate-rich, carbonate-rich, argillaceous argillaceous siltstones near the base of the Serpent Formation. The zones zones are described as as breccias(Gates, breccias(Gates, 1991) 1991) and the east-west east-west 100-300 metres in zone had an approximate dimension of 100-300 length and 30-50 30-50 metres in in width. width. The other other zones zones were much length smaller(Meyer, smaller(Meyer, 1996, 1996, Resident Geologist, Geologist, Sudbury, Sudbury, personal communication) communication). At the the site site of of the the Scadding Scadding mine, mine, samples samples of the the metasomatized Serpent Formation Formation are are abundant abundant and and large large metasomatized Serpent blocks of altered altered rock rock display display reddish-brown reddish-brown weathering weathering carbonate rhombs carbonate rhombs up up to to 11 cm cm or or more. more. The The carbonate carbonate alteration alteration post dates dates the the albitization. Samples Samples of sulphidesulphidebearing chlorite chlorite rock rock that formed formed the the gold ore can can also also be collected at at the the site. site. At At the the Scadding Scadding Mine Mine site, site, collected Gates(1991) reported total total rock rock analysis analysis of of 8.40 and and 8.15% 8.15% Gates(1991) reported Na20 (1994) reported reported values values of 7.68 Na20 and and Schandl Schandl et et al. al.(1994) 7.68 and and 7.65% 7.65% Na20 from from albitized albitized rocks. rocks. One of of the Scadding Scadding mine samples(SC-5) was isotopic dating dating of of the sodium samples(SC-5) was used used in in ti-Pb U-Pb isotopic sodium metasomatism(Schandl et metasomatism(Schand1 et al., al., 1994). 1994). �The The Scadding Scadding Mine Mine operated operated from from Septeniber September 1987 to February February 1988 milled ore July 1990. 1990. Estimated Estimated production production is is 1988 and milled ore until until July 11,000 11,000 ounces ounces from from ore ore grading grading 0.159 0.159 ounces ounces per per ton(Canadian ton(Canadian 347). Mines Handbook, Handbook, 1990-1991, 1990-1991,p. p. 347) Figure Figure 88 presents presents the the geology geology as as reported reported by by Harper(l983) Harper(1983) and Figure Figure 9 9 presents presents the the local local road road and geographic geographic features. features. �2 LEGEND LEGEND 0Upper Quartz;te Upper Quartzite a Upper Upper Chlorite. Chtorite Internediate quartz;te quartzite Intermediate Lower quartzite quartzite Lower 1Lower chlorite LI Lower Chkwite Linestone Linestone Bruce Fornoton Fornation Bruce 3 Diabase Diabase Fi~ure 8:Geotogcat Geologicat sketch nap of' o f the the Figure 8: sketch nap Scaddng ScaddingGotd GotdM;ne(nod;F;ecl Minehodif ied from from Harper, H a r p e r ,1983) 1983) �————— — — a a — — Figure 9: Topographj and road map for the Mine area (from tOpograph Scadding Gold Geologist's Office, Ontariomaps obtained from the Resident Geologi Sii,ny. �24 DAY DAY TWO TWO The second second day day of of investigating investigating alkali alkali rocks rocks of of the the Sudbury Sudbury region region will be be spent spent examining examining genetically genetically and and structurally structurally unrelated unrelated occurrences occurrences northwest, northwest, southwest southwest and and south south of of Sudbury. Sudbury. Stop Stop 4: 4: Spanish Spanish River River Carbonatite Carbonatite The The Spanish Spanish River River Carbonatite Carbonatite occurs occurs northwest northwest of of Sudbury Sudbury and west west of of Lievack. Levack. The log to to the the intrusion intrusion is is and The road log measured t to (Figure measured from fromthe theturn turnofoff to Levack Levack on on highway highway144 144(Figure 10) Proceed km to to Cartier. Cartier. Proceed north north along along highway highway 144 144 for for 16.4 16.4 km Turn t(south) along along a a road from the centre Turn let left(south) centre of of Cartier Cartier and and go km towards towards the the Fox Fox Lake Lake Lodge Lod3e where where road road splits. splits. go 10.2 10.2 km Take Take right right fork fork to to Macaulay Macaulay Lake(Fox Lake(Fox Lake) Lake) and and continue continue to to 24.0 There is is aa short short dirt dirt road to the extreme extreme northeast 24.0 kin. km. There northeast corner corner of of Macaulay Macaulay Lake Lake at at this this point. point. Continue km and and turn turn right right on on an an unmarked unmarked skid skid road road Continue to to 24.2 24.2 km through through former former cut cut over over area. area. At km road road splits, splits, take take right right fork. fork. At 26.1 26.1 km At 26.2 km aa skid skid trail 26.2 km trail to to the the left left leads leads to to several several trenches trenches recently recently dug dug into into carbonatite carbonatite regolith. regolith. Continue Continue to to 26.4 26.4 km km where where weathered weathered carbonatite carbonatite outcrops outcrops on on the the left(west) left(west) side side of of the the road. road. I I I If If one one continues continues along along this this skid skid road road to to 27.2 27.2 km km one one comes comes to to aa popular popular local local campsite campsite on on the the elbow elbow of of the the Spanish Spanish River. River. Return Return to to the the fork fork in in the the road road at at 26.1 26.1 km km and and take take the the right right fork (you are are now now on on the the return trip fork(you trip traveling traveling south) south). �___ 21 I I N in + I I Figure 10: 10: Aeromagnetic map map of of the the Spanish Spanish River River Figure ODM-GSC1965d). 1965d). Carbonatite(fr0m ODM-GSC Carbonatite(from I I �At 0.4 0.4 km k m aa skid skid road road on on the the east east side side of of the the road road leads leads to to several recent several recent trenches trenches in in carbonatite carbonatite regolith regolith at at the the top top of the the hill. hill. Geology: Geolocw: The The Spanish Spanish River River Carbonatite Carbonatite lies lies within within the the Abitibi Abitibi Subprovince Subprovince of of the the Superior Superior Structural Structural Province Province and and is one one of of 66 known known middle middle Proterozoic Proterozoic carbonatites carbonatites within within the the Province of Ontario(Sage, Ontario(Sage, 1987; 1987; Sage Sage and and Watkinson, Watkinson, 1991) 1991). Province of On On the the basis basis of of isomagnetic isomagnetic contours contours the the carbonatite carbonatite is is elongated in in a a direction direction east of north, north, however however the the lack lack of of outcrop, brecciation outcrop, brecciation and and fenitization fenitization make the the positioning of of the the contacts contacts difficult(Sage, difficult (Sage,1987) 1987)(Figure (Figure 11). 11) . The The carbonatite carbonatite has has been been emplaced emplaced into into Archean Archean granitic granitic rocks rocks of of quartz quartz monzonitic monzonitic composition composition and and the the process process of of fenitization has fenitization has desilicated these these rocks rocks close close to to the the carbonatite intrusion carbonatite intrusion creating creating syenitic syenitic compositions. compositions. The The carbonatite carbonatite occurs occurs within within aa regional regional trend trend of of Proterozoic Proterozoic outliers outliers suggesting suggesting some some regional regional structural structural control control along along the northern northern margin margin of of the the Sudbury Sudbury Igneous Igneous Complex Complex that that is is not well 1987) (Figure . Isotopic Isotopic studies not well defined(Sage, defined(Sage, 1987) (Figure12) 12). studies by Bell and and Blenkinsop(l980), Blenkinsop(1980), using using the the Rb-Sr m - S r system, system, obtained obtained an age age of of 1838 1838 ÷+ - 95 95 Ma which, which, due to the large large calculated calculated error, brackets error, brackets the the U-Pb U-Pb isotopic isotopic age age of 1850 1850 ++ - 11 Ma Ma obtained obtained on on the the Sudbury Sudbury Igneous Igneous Complex Complex by Krogh Krogh et et al. (1984). The The Spanish Spanish River River Carbonatite Carbonatite and the al.(l984). the Sudbury Sudbury Igneous Igneous Complex Complex could could be coeval coeval within within the the present present limits limits of of isotopic isotopic age age dating. dating. Within the Within the past past year, year, deep deep trenches trenches have have been been dug dug into into the the weathered(rego1it.h) surface surface of of the the carbonatite carbonatite making making it it one one weathered(regolith) of the the best best if if not not the the best best exposed exposed carbonatite carbonatite in in Ontario. Ontario. This will be This be aa very very short short lived lived feature feature since since the the regolith regolith will collapse collapse and and the the trenches trenches will will quickly quickly fill fill returning returning it to its its former former mysterious mysterious presence. presence. Over Over the the years, years, this this intrusion intrusion has has been been largely largely represented represented by the the single single weathered outcrop outcrop along along the the access access road road to to the the Elbow Elbow on on the the weathered Spanish River. Spanish River. The The one one other other outcrop outcrop area area was was exposed exposed by by the the trenches Manville Company Company Ltd., Ltd., but which which in in recent recent trenches of Johns Johns Manville years became years became filled, filled, overgrown overgrown and and essentially essentially nonexistent. nonexistent. The The present present trenching trenching has has re-exposed re-exposed this this earlier earlier area area of of weathered outcrop weathered outcrop and and removed removed all all traces traces of of the the earlier earlier work. work. Samples of of carbonatite carbonatite and and related related rocks rocks can can be be collected collected Samples from from the the regolith regolith for for study. study. In In general general terms terms the the rock rock types types recognized are recognized are syenite, syenite, sovite, sovite, silicocarbonatite, silicocarbonatite,ijolite, ijolite, pyroxenite and pyroxenite and biotitite(glimmerite). biotitite(g1immerite). The The syenitic syenitic rocks rocks are are likely the product of likely of extreme extreme fenitization fenitization of of granitic granitic wall wall rocks and the rocks the biotitites biotitites are are likely likely derived from from the the pyroxenites. The pyroxenites. The relationship relationship of of the the pyroxenites pyroxenites to to the the carbonatite is carbonatite is uncertain uncertain and the the ijolite ijolite is is likely likely an an early early �_______ 21 I I I . . . .. ..... •:•:cc•i Suc1bury Sudbury Igneous Igneous Complex Complex wA E;'i;rozoic V/////A Proterozoic V/////A Rocks I=] LEGEND LEGEND i I Grenviue E;irsille Rocks k.N\'N'J 4rchecn Archean Greenstone Greenstone BeLt Belt I I 1 Archean Granitoids I Granitoids I 1 Figure 11' RegionaL geotog;col River Carbonatite Figure 11s Regional geological s e tsetting t i n g o of f tthe h e Spanish Spanish River Carbonatite (compiledfrom from Ontario Ontario Geological (compiled Geological Survey SurveyCompilation Compilation Map Map 2543) 2543) �Figure 12: Topographic and road map for the area of the Spanish River Carbonatite(taken from topographic map 41 I/NW) 1 km + N j N) �29 phase of the carbonatite carbonatite intrusion. intrusion. The The silicocarbonatite silicocarbonatite likely has several several origins; origins; ie: ie: sovite sovite with with high high accessory accessory mineral content content and and as as aa carbonate-rich carbonate-richalteration alteration product product of xenolithic xenolithic fragments fragments from from several several sources. sources. Economic Geoloqv: Geology: The River Carbonatite The Spanish Spanish River Carbonatite has been prospected prospected over over the the years years for for asbestos, asbestos, niobium, niobium, vermiculite vermiculite and phosphate. The The present present efforts efforts are are directed directed towards towards vermiculite vermiculite of of which which examples examples can can be seen seen in in some some of the the trenches. trenches. Stop 5: Lake Fenites Stop 5: Nernag Nemag Lake Fenites The The Nemag Nemaq and and Kusk Kusk Lake Lake Fenites Fenites lie lie within within the the boundaries boundaries of of cannot be accessed accessed Whitefish Lake Lake Indian Indian Reserve Reserve 66 and cannot without permission of the the residents. residents. We will be visiting only only the the Nemag Nemag Lake Lake occurrence. occurrence. The road road log log starts starts at at the the intersection intersection of of Highway Highway 55 55 and and Regional Road 24. 24. From From the stop stop light at the intersection intersection Regional Road 24 Regional 24 goes goes north north across across the the CPR CPR railroad railroad tracks tracks into into Lively Lively and and south south of of the the intersection intersection the the road road is is known known Black Lake as Black Lake road. road. 3 . 6 km km west along along highway 55 towards towards Naughton Naughton to the turn Go 3.6 Whitefish Lake off to the the Whitefish Lake First First Nations Nations settlement. settlement. This This will be a left left turn turn going going south(see southfseeFigure Figure 13) 13). At 0.6 Whitefish 0.6 km km is is the the Administration Administration building for for the the Whitefish Nations on Lake First Nations on the the left left side side of of the the road. road. 3.0 km km there there is is a a culvert culvert on on the road between Fly Fly Lake At 3.0 and and Whitefish Whitefish Lake. Lake. Whitefish Lake Lake can can be be seen seen on on the the left hand hand side At 5.1 5.1 kin km Whitefish side of the road road and and at at 7.1 7.1 km, km, opposite opposite Makada Makada Lake, Lake, aa logging logging road splits splits from from the the main main road road and and goes goes west. west. Turn Turn right right onto this this logging logging road. road. Continue on the rough rough logging road till where a skid trail leads leads north from the right on the skid trail and continue to may wish to to park the the vehicle at the the top top reach 12.9 km you reach logging road. Turn 14.15 km where you of of the the hill and and �30 11 mIle mile Figure Figure N N 4 + 13: 13: Topographic Topographic and road road map map for for the the area area around around the the Nemag (taken from Nemag Lake Lakefenites fenites(taken from topographic topographic map map 41 41 1/6). 1/6). �31 continue on on foot. foot. The The road road will will be be swinging swinging almost almost due due west west continue as you you continue continue north north from from the the parking parking site. site. as At At approximately approximately 850 850 metres metres from from the the parking parking site site one one must must walk 90 90 to to 100 100 metres metres south south into into the the bush bush and and up up to to the the top top of a ridge ridge of of outcrop outcrop consisting consisting of Nemag Lake Lake Fenite. Fenite. If If you you reach reach Nemag Nemag Lake Lake you you have have gone gone too too far. far. NOTE: NOTE: If If the the roads roads are are muddy muddy the the site site may may be be inaccessible. inaccessible. A four four wheel wheel drive drive vehicle vehicle is is recommended. recommended. Geoloqy: Geoloqv: One One of of the the best, best, if if not not the the best, best, example example of of fenitization fenitization occurs occurs within within Proterozoic Proterozoic feldspathic feldspathic quartzite quartzite Mississagi Formation Formation southwest southwest of of Sudbury. Sudbury. The The fenite fenite of. the the Mississagi of occurs occurs in in an an explosive explosive breccia breccia and and represents represents extensive extensive replacement replacement of of the the Mississagi Mississagi Formation Formation by by aegirine, aegirine, riebeckite, riebeckite, albite, albite, potassium potassium feldspar feldspar and and rutile(Siemiatkowska rutile(Siemiatkowska and and Martin, Martin, 1975; 1975; Figure Figure 14) 14). The The brecciation brecciation and and fenitization fenitization are are part part of of the the same same event event and and represent alteration alteration by sodium-rich sodium-rich fluids fluids under under subsolidus subsolidus represent conditions conditions perhaps perhaps derived derived from from a magma of essexite essexite or or ijolite ijolite composition(Siemiatkowska composition(Siemiatkowska and and Martin, Martin, 1975) 1975). Siemiatkowska and and Martin(1975) Martin(l.975) subdivide subdivide the the brecciation brecciation and Siemiatkowska fenitization fenitization in in great great detail detail into into seven seven stages. stages. For For the the details details of of this this subdivision subdivision the the reader reader should should refer refer to to Siemiatkowska Martin(1975). The The fenitizing fenitizing fluid fluid was was Siemiatkowska and and Martin(1975). poor poor in in 002 C02 and and potassium potassium appears appears to to be be significant significant only only in in the late late stages stages of of the the fenitization fenitization process. process. The The Nemag Nemag and and the Kusk Kusk Lake Lake fenites fenites are are dominantly dominantly aa process process of of desilication desilication accompanied by by extensive extensive additions additions of of iron iron and and accompanied sodium(Siemiatkowska and and Martin, Martin, 1975). 1975). Siemiatkowska Siemiatkowska and and sodium(Siemiatkowska Martin(1975) report report aa K-Ar K-Ar isotopic isotopic age age of of 1196 1196 ÷+ - 11 11 Ma Ma on on Martin(1975) biotite biotite obtained obtained from from the the fenite. fenite. This This age age would would place place the the fenitization fenitization event event within within Grenville Grenville time time or or development development of of the the mid mid continent continent rift. rift. . The discovery discovery of of the the Nemag Nemag and and Kusk Kusk Lake Lake fenites fenites was was made made The during during regional regional mapping mapping of of the the Ontario Ontario Geological Geological Survey Survey and and they they occur occur on on opposite opposite sides sides but but near near the the northeast northeast trending trending Kusk Fault(Card et et al, al, 1975). 1975). The The region region contains contains Kusk Lake Lake Fault(Card numerous numerous faults. faults. The The northeast northeast trending trending faults faults display display aa tendency to to swing swing to to more more east-west east-west strikes strikes in in the the western western tendency portion portion of of the the map map area area perhaps perhaps parallel parallel to to the the trend trend of of the the regional (Card et et al., al., 1975). Northwest Northwest trending regional Murray Murray Fault Fault(Card trending faults are are also also common common in in the the area area and and they they are are oriented oriented faults approximately orthogonal orthogonal to to the the Grenville Grenville Deformation DeformationZone. Zone. approximately In In Figure Figure 1, 1, aa very very broad regional regional interpretation interpretation by by Lumbers(1978), Lumbers(1979), the the Nemag Nemag and and Kusk Kusk Lake Lake Fenites Fenites would would occur occur �_______ 32 LEGEND FENITIZATION ZONE (STAGE I STAGE 3,2) 3.21 LATE DIABASE DIKES (SUDBLFRY SWARP.I)b r— Olivine diabase dikes 71 Albite veins AIRicbeclsite—aegis-ine veins thermal L_i LATE ,"LkFIC LATE ,WIG DIKES DIKES 1:tv i Metagabbro Xetegabbro dikes dikes Riebeckite veins rl:T4 Granulated, L1113 L'ia)J Sphalerite—bearing ankerite vein Breccia replaced by riebeckite and aegirine in aegirine matrix (Nemag Lake) Albite—aegirinc area Breccia partly replaced by by riebeckite riebeckice sod and ragnetite snagmecite cut c n t by by albite albite veins veins Breccia e c c i a partly p a r t l y replaced r e p l a c e d by aegirine aegirine and riebeckite r i e b e c k ~ t ecut c u t by by albite a l b i t e veins wins STAGE 4 Breccia partly replaced by riebeckite and/or aegirine in aegirine matrix (Nemag Lake) Breccia partly replaced by rieberkite, aegirine and K—feldspar in aegirine, riebeckite matrix (Kusk Lake) deforred quart zitc5 [TiTT Metagabbro5 ^ctaeabbnoa MISSISSAGI FORMATION Feldspathic quartzito comonly displaying incipient fenitization Lake) Lake 1 STAGE S 5' -STAGE Rutile vein Brecciated NIPISSING GABBRO GABBRO INTRUSION INTRUSION NIPISSINC Breccia B r e c c i a replaced r e p l a c e d by byK—feldspar K - f e l d s p a r and and aegirine i n in i n aegirine a e g i t - i n e matrix m t r i x (Kusk (Kusk NiAJOR BRECCIATION AND FENITIZATION W O R B-iECCIATIOH FEMTIZATION ZONE ZONE shock zone DEFOR'tajION ZONE ( STAGE 1) CAR BONATEb FENITIZATION FENITIZATION AND AND BRECCIATION BRECCIATIOK (STAGE ( S T A G E 1,6) 7.61 I a Occurs only at Nemag Lake b. Occurs only at Frisk lake SYMBOLS SYMBOLS LIIJ Area of obedrock Area f bedrockoutcrop outcrop Bedding, B e d d i n g , top t o p unknown unknown ,= E, Bedding, ~ e d d i n g ,top t o p from f r o m cross—bedding cross-bedding Foliation Folia~~o" - Geological G e o ~ o g i c a l boundary, b o u n d a ~ ~assumed assumed , Boundary of o f outer i u c e r fenitization fenlt~zation zone, zone. assured essumd Figure 14: 14:Geology Geology of ofthe theNernag Nemaq Lake Lake Fenites(modif Fenites(modified from Figure led from Siemiatkowska and Martin, 1975; Card et al., 1975). Siemiatkowska and Martin, 1975; Card et al., 1975). �3: at the the intersection intersection of of the the eastern eastern extension extension of of the the Great Great Tectonic Zone Lakes Tectonic Zone and and the the Grenville Grenville Deformation Deformation Zone. Zone. Siemiatkowska enites may may Siemiatkowska and and Martin(1975) Martin(l.975) suggest suggest that that the the if Eenites in some some way by related to the Murray fault system system which would would follow follow the the trend trend of of the the Great Great Lakes Lakes Tectonic Tectonic Zone. Zone. At the the Nemag Lake Lake Fenite Fenite site, site, fragments fragments up to to a a metre in in maximum maximum dimension dimension can can be be observed observed concentrically concentrically mantled mantled with aegirine aegirine and riebeckite. Late Late stage stage pegmatitic pegmatitic albite albite with riebeckite riebeckite and and aegirine aegirine are are present present as as well well as as late late stage stage breccia breccia veins. veins. Economic Geology: Geolow: The The fenites Eenites are are geochemically geochemically anomalous anomalous in in niobium niobium but under under existing existing conditions conditions they they are are not not likely likely to be of of economic economic interest. interest. One One small small occurrence occurrence of of sphalerite sphalerite has has been been reported(Meyer, reported(Meyer, 1996, 1996, Residept Resident Geologist, Geologist, Sudbury, Sudbury, personal communication) personal communication) Stop 6: French French River River Alkalic Alkalic Rocks Rocks Stop 6: The French French River River Alkalic rocks rocks occur occur within the the Grenville Grenville Structural Province Structural Province on private property. Permission Permission to to access the the site site should be obtained obtained from from the property owner before entering. before entering. The The road road log log starts starts at at the the intersection intersection of of the the Sudbury Sudbury bybypass and pass and highway highway 69 69 south south of of Sudbury. Sudbury. Drive south to Bigwood Bigwood and turn Drive south on on highway highway 69 69 for for 59.9 59.9 1cm km to turn right right on on to to Hartly Hartly Bay Bay Road(see Road(see Figure Figure 15). 15). Continue Continue along along the the Hartly Hartly Bay Bay Road Road until until aa distance distance of of 65.2 65.2 km is reached reached and turn turn left towards towards a camp camp on on the the French French River. This This is is aa private private road. road. 6 6 . 6 kin krn aa dump to the the a final final distance distance of of 66.6 At a dump appears appears just to east of the road. Park at this dump site site and examine examine the exposed syenite syenite outcrops outcrops in in the the eastern eastern portion portion of of the the cleared area. cleared area. Geology: Geoloqy: The The alkalic rocks rocks have been described described by The alkalic Hewitt(1960; Figure 16) 16) and and Lumbers(l975) Lumbers(1975). The Hewitt(l960; Figure alkalic syenites were subdivided syenites subdivided into into the the French French River River nepheline nepheline syenite, syenite, French French River River alkaline alkaline syenite syenite and and Rutter Rutter nepheline nepheline syenite by by Hewitt Hewitt (1960); syenite (1960); however, however, Lumbers(1975) Lumbers(1975) refers to . �34 N — a 1 mIle Figure 15: 15: Topographic Topographic and and road road map map Figure French River a l k a l i c s y e n i t e s taken French River alkalic syenites taken 1/2) 1/2) + of the t h e area a r e a around around the the of from topographic map 41 from topographic map 41 �I Figure 16: Simplified ge0l09ic s k e t c h nap o f t h e R u t t e r Figure 16 SirnptiP;ed alkalic syenite intrusion(nodified f r o mRutter Hewitt, geoLogic sketch nap of the atkalic 1960, syeni-te p. 167) intrus:on(nod;f;ed from Hewitt, 1960, p. 167) �36 all all the the alkali alkali syenites syenites in in this this pluton pluton as as the the Rutter Rutter Pluton. Pluton. The The alkaline alkaline syenites syenites occur occur in in an an elongated elongated body body of of approximately approximately seven seven miles miles length length with with its its long long axis axis just just west west of of north. north. The The maximum maximum width width is is approximately approximately one one mile(Hewitt, mile(Hewitt, 1960; 1960; Lumbers, Lumbers, 1975). 1975). The The syenites syenites are are dominantly dominantly leucocratic, leucocratic,medium-grained, medium-grained, gneissic (Lumbers, gneissic with with streaks streaksand andlenses lensesofofmafic maficminerals minerals(Lumbers, 1975) pink leucocratic leucocratic phase phase is is the the latest latest in in the the 1975). AA pink sequence. sequence. The The mineralogy mineralogy of of the the syenites syenites is is albite, albite, nepheline, nepheline, potassium potassium feldspar feldspar and and biotite biotite with with accessory accessory hastingsite, hastingsite, aegirine-augite, aegirine-augite,magnetite, magnetite, sphene, sphene,zircon, zircon, apatite, apatite, graphite, graphite, corundum, corundum, carbonate, carbonate, sodalite sodalite and and cancrinite(Lumbers, cancrinite(Lumbers,1975). 1975). Hewitt(1960) Hewitt(1960) proposed proposed that that aa regional regional potassium potassium metasomatic metasomatic event event has has occurred; occurred;however, however, Lunibers(1975) reported that that he he found no evidence Lumbers(1975) reported evidence for for this this event rarely exposed exposed contacts contacts were were sharp sharp and and event and and that that rarely display display no no evidence evidence for for aa potassium potassium metasomatism. metasomatism. Hewitt(1960) reports that that aa lead lead alpha alpha decay decay age age of of 975 975 Ma Ma Hewitt(1960) reports was was obtained obtained on on zircons zircons from from this this body. body. This This method method of of age age dating dating is is no no longer longer in in use use and and additional additional geochronological geochronological study study is is warranted. warranted. . The The syenites syenites at at the the site site display display aa strong strong fabric fabric that that strike strike west west of of north north and and dip dip east. east. Within Within these these syenites syenites are are very very coarse-grained coarse-grainedalkali alkali peymatites pegmatites containing containing potassium potassium feldspar, feldspar, nepheline, nepheline, cancrinite, cancrinite, sodalite, sodalite, aegirine aeqirine and and magnetite. magnetite. The The pegmatites pegmatites display display aa well well developed developed pinch pinch and and swell swell structure structure along along strike strike with with the the gneissosity, gneissosity,however however the the coarse-grained coarse-grainedminerals minerals in in the the pegmatites pegmatites do do not not appear appear deformed deformed or or fractured. fractured. Samples Samples of of graphite-bearing graphite-bearingsyenite syenite have have been been found found at at the the site site and and molybdenite molybdenite flakes flakes over over 11 cm cm in in diameter diameter are are occasionally occasionally found. found. Pockets Pockets of of weathered weathered very very coarse-grained coarse-grainedbiotite biotite are are exposed exposed at at several several locations locations within within the the stripped strippedarea. area. Corundum Corundum is is present present at at the the community community dump dump site site north north of of the the road road leading leading to to this this stop, stop, however however it it is is not not abundant abundant and and no no plans plans have have been been made made to tovisit visit the thelocation. location. �BIBLIOGRAPHY BIBLIOGRAPHY Adams, '3. and Basham, Basham, p., Adams, J. and P., 1986. Seismicity and and 1986. The Seismicity Seismotectonics of Seismotectonics of Canada Canada East of the the Cordillera; Cordillera; Geoscience Geoscience Canada, v. 16, p. Canada, v. 16, p. 3-16. 3-16. 1980. Ages and Initial and Blenkinsop, Blenkinsop,'3., J., 1980. 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Society of of America America Bulletin, Bulletin, v. v. 86, 86,p. �41 Syrnons, D.T.A. D.T.A. and and Chiasson, Chiasson, AA.D., 1991. Paleoma9netism Paleomagnetism of Symons, . D . , 1991. Callander Complex the Callander Complex and and Cambrian Cambrian apparent polar wander path for for North North America; America; Canadian Canadian Journal Journal of of Earth Earth Sciences, Sciences, v. 28, pp. . 3355363. 55-363. � https://digitalcollections.lakeheadu.ca/files/original/4a485eaf390ab9a722b362ed4d66ab3d.pdf 16c0001f51f6fb6b73bc94a0d28369f4 PDF Text Text I I I I I I I I I I I I I I I I I I I THE GREENING THE GREENING OF OF SUBBURY SUDBURY BY K. WINTERHALDER LAKE SUPERIOR GEOLOGY GEOLOGY INSTITUTE ON LAKE ANNUALMEETING, MEETING,MAY MAY66-11,1997 43rd ANNUAL - 11,1997 SUDBUIRY,ONTARIO ONTARIO SUDBURY, Trip Guidebook, 43, Part Part 7 Field Trip Guidebook, Volume 43, �I I 1 THE GREENING OF OF SUDBURY SUDBURY I I May 10,1997 10, 1997 Leader: Leader: Prof. Keith Winterhalder Department of Biology Biology Laurentian Lawentian University University I 1 I I I I I I I I I I I Institute Institute on Lake Superior Superior Geology Geology Sudbury, Sudbury, 1997 1997 �Institute on on Lake Lake Superior Superior Geology Geology Greening of of Sudbury Field 1997 Greening Field Trip, May May 10, 10, 1997 I Winterhalder Keith Winterhalder (Ipe w e hundred years years of of logging, logging, fire, addification acidification by sulphur sulphur dioxide, dioxide, particulate metal metal deposition, enhancedfrost frost action action and and erosion particulate deposition, enhanced erosion have have created 10,000 hectares of of barren land and 36,000 10,000 hectares 36,000 hectares of stunted, stunted, I I I I I I I I I I I open birch woodland woodland around around the the Sudbury Sudbury copper copper and nickel smelters. smelters. It was found found that the which have have been addifled was the steep, steep, stony barren barren slopes, slopes, which acidified and can be be detoxified by aluminum, can and contaminated contaminatedwith with copper, copper, nickel and alu.minum, the manual manual application application of of pulverized pulverized doloniitic dolomitic limestone. limestone. Revegetation Revegetation began on an operational scale in 1978, and approximately 3,500 hectares operational hectares soil have have been been detoxified deiadfled by of surface soil by manual manual application application of of limestone, limestone, by and revegented revegetated using using aa grass/legume grass/legurne seed mixture. mixture. Rapid invasion invasion by birch, poplar occurred spontaneously, and the birch, poplar and willow willow seedlings seedlings occurred spontaneously, and woody deciduous dedduous cover coverhas has been been enriched enriched by by the planting resulting woody planting of than 2.5 2.5 million tree seedlings, seedlings, the majority of them native native pines. pines. more than species in in blocks blocksofoftheir their own ownssoil arebeing beingintroduced introduced at at an oil are Understory species experimental level, level,to to facilitate facilitateand and accelerate accelerate the the establishment establishment of of an experimental appropriate herb and shrub stratum, microflora and microfauna. Unique herb and shrub stratum, microflora and microfauna. Unique its community-based format, the features of of this features this program program include include its community-based format, manual approach approach employed, employed,and andthe the use use of aa minimal predominantly manual minimal colonization by amelioration approach that relies heavily on spontaneous s species and other natural dynamic processes. native other natural dynamic p addition to to the degraded natural landscape, landscape, deposits of materials materials that that In addition discarded after the ore is are discarded is separated separated by by milling milling flotation, flotation, known known as tailings, cover cover more more than than 2,000 hectares. hectares. Experimental Experimental reveg revegetation began on the tailings in in the the 1950s in in response response to to a dust problem, and the Inco Inco Ltd. Ltd. tailings which all all non-active non-active tailings tailingsareas areas are in various has has reached the point at which stages of of revegetation. The revegetation process includes includes liming liming and stages revegetation. The revegetation process seeding with a grass-legume mixture, use of a cereal rye nnurse fertilizing, fertilizing, with a grass-legume mixture, use of a cereal rye crop, and ultimately plantingofof trees, trees, many many of of which crop, and ultimately planting which are are grown gr underground underground at atthe the4600' 4600' level. level. Tower,3.5 3.5 fccn km northeast # 11- McKim Street Transmission Stop Transmission Tower, Stop # of the Copper Copper Cliff Cliff smelter previously barren barren area was grassed 1981 by the the Regional Regional Land This previously grassed in 1981 Program, and planted with red and jack pine in Reclamation Program, and planted with red jack in 1983. 1983. Also this area area were were smaller smaller numbers numbers of white spruce, white ash, planted in this maple, silver silver maple, maple,white whitecedar cedarand andred redoak. oak.As Asyou youwalk walkuup the sugar maple, volunteer trembling trembling and and large-tooth bill, you will hill, will also see volunteer large-tooth aspen, white birch will see see the the city city of ofSudbury Sudbury to Se cherry.From From the top, you will birch and and pin pin cherry. �-2- east and south-east, 20 hectares hectares of of grassed grassed barrens barrens to to the the west, west, and and a an. south-east, 20 untreated area across across the the railway railwaytracks trackstotothe the north north that that has been untreated area beex colonized by by aa metal tolerant strain of dwarf or bog- birch (Betula colonized (Betula -pumila var. glandulifera). u I Stop # 22 -- Barren Stop # Barren site II On On the way 18 U m lI I II i II II II II II I I I Copper Cliff Cliff smelter. smelter. east of Clarabelle, elle, 2 km northeastt of the to this site, we shall see a slag disposal disposal area, area, and and the process of grinding of railway grinding slag slag for construction construction of railway beds beds (coarse (coarse slag) slag) and and driveways driveways (fine (fineslag slag mixed mixed with with sand, sand,known knownasas'TDrypack"). "Drypack"). You willsee seeaamosaic mosaicofofland landthat thatisistotally totallybarren, barren,and and in in the the early u will early stages stages of revegetation, includingbare bare rock rock outcrops, outcrops, soil soil pockets pockets and stony revegetation, including stony slopes, with large white white pine stumps lopes, with stumps indicating indicating the the original originalvegetation. vegetation. The rare,, coppiced of red red maple maple and and red oak, coppiced and stunted individuals individuals of oak, which pre-date and are often predate denudation, denudation, arise arise from from large large stools, stools, and often surrounded by a litter litter of of earlier, earlier, much much larger larger stems. stems. The soil soil is is highly highly acidic, between 3.5 3.5 and 4.5, 4.5, and plant-available copper, nickel acidic, with a pH between and aluminum can each exceed ppm. Some Someofof this this land land has has been exceed 100 ppm. aluminum can aerially Ltd. in in 1990 and and 1991, and is aerially limed, fertilized and seeded seeded by by Inco Ltd. 1991, and is grass-covered. grass-covered. The sole colonizer colonizerof ofthe theuntreated untreated land is (tufted is Deschampsia Descbampsia caespitosa (tufted hairgrass), hah-grass),which which has has been beenshown shownby byCox Cox& & Hutchinson Hutchinson (New (NewPhytologist Phytologist 84: 631-647:1980) to have evolved tolerance. AA few 631-647:1980) to evolved multiple-metal multiple-metal tolerance. few individuals sca bra(tickle (ticklegrass), grass),also alsoa ametal-tolerant metal-tolerant ecotype individuals of Agrostis scabra (Archambault Botany 73:766-775), 73:766-775), (Archambault & Winterhalder, Canadian Journal of Botany have havealso alsobegun begunto tocolonize. colonize. As As we leave the area, area, aa site site opposite opposite aa school school building will be pointed out. OUT. This techniquewas wastried tried out out at the This is where where the manual manual technique the "semi"semioperational" pupils, on on one one acre of operational" level in 1975 by elementary elementary school school pupils, land beside their school. school.ItItwas wasthe the success successofof this this trial trial that encouraged encouraged the MunicipalityofofSudbury Sudburyto to apply apply for for job-creation job-creation funds funds to the Regional Regional Municipality establish establish its its ongoing ongoing land land reclamation reclamation program. program. Stop : # 33 -- Inco Inco Ltd. tailings, Copper opperCliff. Cliff. Your guide: will will be Bob Bob Stanzel Stanzel of Inco's Inco's Environmental Environmental Control Control . is my my hope hope that thatyou youwill will be be shown shown the the spigotting spigottingprocess, process, Department. ItIt is �I and the end product at stages in vegetation establishment, and stages at the the 'C-I)" "C-Darea, area, the results initiated over over 30 30 year which shows shows the results of of revegetation revegetation initiated year ago, ago, the originally originally seeded seeded grasses grasses and and legumes, iincluding n c l m the legumes, some spontaneous spontaneous colonizers, and planted pines. colonizers, and planted I I You willalso alsosee seeattempts attemptsto todivers@ diversifythe thepine pineplantations plantations by by intbducing introducing You plots or plugs of plant and their native soil from undisturbed forest. plots of plant from undisturbed forest. I I Lake,44 km km south south of of the Copper # 4 -- South shore of Kelly Stop Kelly Lake7 Copper Stop # Cliff smelter. Cliff smelter. I I Our W W walk k ~ ibegins n a ninmana area t h that a t was w hlimed, & f ~fertilized e d a n and d ~seeded e d e in d 1982, i1982, n red and jack jack pine in 1984. The The grasses grasses are are a mixture of of and planted with red tufted hairgrass and tickle grass with seeded species. The metal-tolerant metal-tolerant hairgmss and tickle seeded species. The seeded legumes Alsike clover and birdsfoot trefoil are also seeded legumes Alsike clover and birdsfoot trefoil are also present. present Colonists include include white white birch, birch, trembling trembling aspen, balsam poplar, fireweed, Colonists fireweed, well as as acid-tolerant sheep pearly everlasting, yarrow and hawkweed, hawkweed7as well sheep sorreL Relict red maple and red oak are common. We eventually emerge sorrel. Relict red maple and red We emerge Note that that here, here, at a greater untreated area.. area. Note greater distance distance from the into an untreated smelter than than Site 2, there is is an an almost almost complete complete cover of metal-tolerant metal-tolerant tufted relictred red maple maple and and red red oak. Some t ufted hairgrass, hairgms, with occasional relict Some white were also planted in this area in 1984, and one of them pines were also planted in this area in 1984, and one them has has survived and and grown grown on on the the untreated soil, survived soil, but exhibits &bits necrotic needle tips. I I I I I I I I I l I I You can of the lake, lake, with with aa clear line marking see the north shore of marking the point at at which liming stopped. stopped. return by from the smelter, We return by way way of of aa south-facing south-facing slope, slope, facing away from smelter? on there is on which there is aa relict relict community community of large red oaks. - Stop ## 55 - South of southeast Stop South of southeast bypass, bypass? north of of Richard Richard Lake, Lake, approximately midway midway between between the the Copper approximatdy Copper Cliff Cliff and and Coniston Coniston smelters. shall walk transition") We shall walk through through aa typical typicalsemi-barren semi-barren ("birch ("birch transition") community, with with birch7 birch, red red maple and red oak, some of which may have have lost some stems stems to to the combined of drought drought and gypsy lost some combined effects efFects of gypsy moth defoliation. The The larger larger red red pines pines are are native native here, here, but but some some planting planting of of tree tree seedlings (pine and and spruce) has has also occurred. occurred. ItIt is is not not necessary necessary to lime s e d b g s (pine lime before planting planting trees trees in the the soil before the semi-barren semi-barren zone. zone. The understory understory hair grass consist of tufted hak grass and and two two spedes speciesof of blueberry, blueberry, with withmosses mosses �1 I I i I I I I I I I I I I I I I I I (Poh.lia urn)and and lichens7 lichens, and and Labrador Labrador tea tea in (PohZia and Po/ytrich Polytnkhum) damp damp sites. sites. Returning of the gully, where the the soil is deeper, Labrador tea isis Returning by way of gully, where more and the Ere-tolerant fire-tolerant clubmoss known known as as ground cedar more common, and cedar can can be be seen. seen. Stop ## 66 -- north of Highway 17E, 44 km km northwest northwest of the Highway 17E7 the Coniston Coniston smelter. smelter. We by walking up the overgrown road that irt road that was was We shall shall begin begin by walking up overgrown ddirt constructed by the land reclamation reclamation crew crewin in 1979 for for the transportation of ground limestone. limestone.InIn1979? 1979,the thearea areato to the the west west of of the road, partly partly sheltered sheltered from from the the Coniston Coniston fumes, fumes?supported birch birch transition transitionwoodland, woodland, but but the the area area to the the east of the road was barren barren except except for for aa few few scattered scattered relict birches and maples. The upper section of the road crosses birches maples. The upper section of crosses the the revegetated revegetated area areaobliquely obliquelyon onits itsway way to to the thetop topof ofthe thehill. hill.Young Young birches birches predominate, relict white white birch, birch, red red maple and red predominate, with occasional occasional relict red oak. oak. Larger shrubs shrubs include include beaked beaked hazel hazel and andwillows, willows?with the the N-fixing N-fixing shrub shrub sweet fern and blueberries in the understory with hair moss sweet fern and blueberries in the understory with hair moss (Polytrichwn). (Polytri&m). At At some points along the trail trail we shall still see some of the the originally seeded seeded species species such as birdsfoot trefoil, clover and tall trefoil7Alsike Msike clover tall fescue. Note the small plantation of European fescue. Note small experimental experimental plantation European larch. The The main native herbaceous colonists are pearly everlasting, rough and main herbaceous colonists are pearly everlasting, rough and Canada and yairow, Canada goldenrod, goldenrod, fireweed firewed and yarrow, accompanied accompanied by weedy weedy non-native as the theyellow yellowand andorange orangehawkweed. hawkweed. Woody Woody nm-native species species such as colonists include pin pin cherry and colonists include and staghorn staghom sumac. sumac. Native Native woody woody plants plants such as bush honeysuckle and trailing arbutus have been seen here, such honeysuckle and trailing arbutus have here, but but we them. Near Near the treated/untreated treateWuntreated junction junction is aa we may may not not encounter encounter them. healthy red pine healthy red pine that that has has become become rooted rooted in in untreated untreated soil. soil. This This isis probably probably because the the active active physical physical weathering of rock in in this this microsite microsite has has created createdaarooting rootingenvironment environmentthat thatisisnot notmetal-toxic. metal-toxic. Emerging stopped, we see that hill7where liming stopped? that birch bircn isis Emerging at at the the top topof of the the hill, actively colonizingthis this site, site, which whichhas has been been relatively unaffected actively colonizing unaffected by by smelter in 1972. In In the the last last 20 years? years, the average average soil soil smelter fallout since closure in pH risen from from around around 35 3.5totoaround around4.5. 4.5.You Youwill will also also see see pH in in this area has risen relict relict coppiced birch, and red redmaple mapleundergoing undergoingregressive regressivedieback. dieback. The The metal-tolerant metal-tolerant grass grass is is tickle tickle grass. This hilltop may be too isolated isolated from from the the moist moist valley valley to have have been beencolonized colonized by bymetal-tolerant metal-tolerant tufted tufted hairgrass. commonare are the the moss PohZia, Pohlia, and and blueberry blueberry bushes Also common bushes which which hairgrass. Also may be relicts. relicts. Note the the signs signs of frost frost activity activity visible in in the the soil. soil. may be Looking acrossthe the highway? highway,you youwill willsee seem anarea areathat that was was limed limed but not not Looking across seeded. know that that this use of an seeded. We We know of limestone limestone as a "trigger "trigger factor" factor" is an effective regreening, but effectivemethod of regreening but the theRegional Regional authorities authoritieslike like the the �I I I1 I 1 I I1 II iI II I I I bright bright green grass in the spring. 1979, the revegetation crew ran out of spring, In in 1979, seed, demonstration site. seed, providing a useful demonstration site. On the way down, we we shall shall see see aa small small experimental plantation of white v e pine. White pine, pine, once the the dominant dominant tree tree species species in in this this area, area, is is extremely extremely again under under current current atmospheric atmospheric SO2-sensitive, but can can survive survive again 9)2-sensitive, conditions. conditions. En En route to to Stop Stop #7: #7: On the left hand side turnoff, you side of the bus, just prior to to the the Coniston Coniston turnoff, you will will see 11acre of of sloping slopingland landthat that was wastreated treated by elementary elementary school school students students in in 1975. 1975. Stop Stop #7 -- just east of of Coniston Coniston smelter smelter - I I I 1 I I I After passing passing a small industrial complex, you will will see untreated ban-en complex, you barren land on your we drive onto the your right. right. As As we the net net slag-surfaced slag-surfaced area, area, you you wifi will see aa good good transition between two-year and and three-year-old three-year-oldgrassing. grassing. We We shall area so shall take a walk on the grassed area so that that you you can cansee seethe thecolonization colonization process, rocess, mostly mostly by poplar and andwillow willow seedlings. seedlings. The second-year second-year area area seems to have probablydue duetto the right woody colonization, colonization, probably o the right have more more woody combination when the the seeds were shed. Much of the on of weather, wind etc. when the limed ground has been colonized by by the moss Fanaria hygrometrica.. moss F m ' a hygromemka.. Note how grass grows grows better at at the thesoil-rock soil-rock interface. interface. Pine Pine seedlings seedlings have already been en planted planted here. here. Stop ## 88 -- north of Highway Highway 17E, 17E, 1.5 1.S km km northeast northeast o of the Coniston ston smelter. smelter. This area a was was treated treated in 1978, no 1978, and and the theseed seedmixture mixture contained contained no legumes.. Nevertheless, Nevertheless,trefoil trefoiland and clover cloverhave have colonized colonizedfrom from aa nearby Inco Redand and white whitepine pinewere wereplanted planted here in o seeded site. Red in1983. 1983.We We shall shall examine an experiment experiment in which typical understory species species have been transplanted in blocks so-called blocks of of their th& own ownsoil soil(the (the so-called"nucleation" "nucleation" approach). successfulwere werethe thewoody woodyground groundcover cover bearberry bearbeny ch). Especially Especially successful and the nitrogen-fixing shrub soapberry soapberry (or (or buffalo berry). Note nitrogen-fixing shrub buffalo berry). Note that many other ther species species were w e introduced introduced with with the the woody woody plants, plants, wild wild strawberry and and starry starryfalse falseSolomon's Solomon'sseal sealbeing beingespecially especiallyconspicuous. conspicuous. The later nonnally limestone soils, soils,and and its its success here is success here is normally favours favours limestone probably the used.Some Sometree treespecies, species, the result result of of the thelimestone limestonetreatment treatmentused. such uch as & balsam balsam fir and and white white spruce, spruce, have have also also been been acddentally acad&aUy introduced troducedin inthe thesoil soilblocks. blml-- �I I I I I 1 I I I I I I I I I I I I Stop #9- smelter. Coniston Hydro road, 2 km east of the Coniston From point, it is possible to see land treated in 1978, 1981, From this vantage van 1987, 1993 and 1994, as well well as as untreated untreated land and 1994, respectively, respectively7as and land land aerially-limed by Inco in 1995 and 1996 in the distance. Note that the aerially-limed Inco 1995 1996 the distance. Note the untreated barren, while that to to the the east east is is untreatedland landcloser closerto to the thesmelter smelteris is still still barren7 undergoing rapid colonization white birch. birch. Plantings Plantings of of pines, black colonization by white locust and red oak can also be seen here. Some of the red and jack pine seen o. was propagated propagated underground u n d ~ r o u nby dbyInc Inco. seen here here was IfIf we we drive drive further further down down the the Hydro Hydro road, road, we we can get a close-up view of barren withbirches birchesbeginning beginningtotocolonize. colonize. barrenterrain, terrain,with Stop 10 -- north north Stop (or (or drive-by) drive-by) ## 10 km km east of of the theConiston Coniston smelter. smelter. and south of Highway 17E, 3.5 Following grassinginin1978, 1978,container container and bare-root stock of red and Jack Following grassing pine were planted here, here7plantation-style, plantation-style, in 1979. 1979. Later planting in in this this area natural-looking style. If If we we stop at this area were in aa more more informal, informal. natural-look in^ stvle. this site, site, we shall have the opportunity to look at ano&er-understory another unders tory transplanting trm trial using soil blocks. trial wing soil Stop Stop # # 11 11 -smelter. Coniston-Garson road, 4 4 km k m north north of of the theConiston Coniston Prior to initiation of manual liming of hillsides, this sandy valley bottom was limed, fertilized and seeded with Canada Canada bluegrass bluegrass in in1974. 1974.Some Some areas showed rapid, diverse colonization, while while others others remained remained bare. bare. The The latter areas were probably short of organic matter and and phosphorus phosphorus(see (see experimental plot). The nitrogen-fixing shrub called called sweet sweet fern fern is is spreading rapidly. Interesting herbaceous species now found found at s now at this thissite site include rattlesnake ferns, lathes' tresses orchids and a small small blue blue early early s and violet (Viola adunca). olet ( Viola admca). Thee red red and andJack Jack pine pine plantations plantations at at this this site sitewere wereestablished establishedfollowing followin grassing 1976, using using paper-pot container container stock. stock. Seedlings Seedlings planted in in rassing in 1976, neighbouring eighbouringungrassed ungrassedareas areasshowed showed almost almost total total mortality. mortality. �I I En route to Stop Stop # 12 12 -- north of Garson Garson I I I I I I I I I I I I I I I Here you you will will see see extensive extensive tracts tracts of blueberries, Here bluebemies, with scattered scattered pines. pines. Tree planting planting here here has has been been kept to Tree to the thenhinimuni, minimum, to to conserve conserve the the blueberry stands. stands. Past the airport airport turnoff, turnoff, on on the the Falconbridge Falconbridge road, you will d l see see extensive extensive grassing and and pine grassing pine planting planting carried carried out by byFalconbridge Falconbridge Ltd. Ltd. in collaboration collaboration with the the Region. Region. Stop (roiling (rolling stop?) ## 12 - south of Falconbridge Falconbridge Here see very very early early revegetation revegetation work work carried carried out by Tom Tom Uoyd Lloyd Here we shall see Falconbridge Ltd. Ltd.Carolina Carolinapoplars poplarswere wereplanted plantedin in large large pits filled filled with of Falconbridge black loam, loam, in in plantation plantation fashion. fashion.This Thisisisaa very very different approach from from what we would take today. Stop (rolling stop?) stop?) ## 13 community Stop (rolling 13 - Falconbridge Falconbridge communiv We Park, which is a a park We shall shall drive drive past pastCentennial Centennial Park, which is park built built on on first tailings Falconbridge's first tailings deposit. deposit. We We shall shall also also view view Fakonbridge's Falconbridge's "conservation area",aabarren barren peatland peatland that that has been restored to a cattail uconservation area", cattail marsh by flooding it with alkaline mine waste water and sewage sludge. flooding and sewage sludge. This currently being upon by slag, and This is currently being encroached encroached upon by granulated granulated slag, negotiations are underway between the Environmental Environmental and Smelter Smelter negotiations are underway between officials alternative dumping dumping site. officials to find an alternative En route, re-entering re-entering Sudhury Sudbury by by the theKingsway Kingsway As we enter enter Sudbury, you will will notice notice that the the semi-barren semi-barren woodland woodland has has As we grassy understory. Only occasionaJly occasionallyare are woodland woodland sites sites grassed grassed in this a grassy this way. way, �-8PARTIAL CHECK OF VASCULAR VASCULAR PLANT PLANT SPECIES SPECIES PARTIAL CHECK LIST LIST OF FOUND ON BARREN AND REVEGETATED m G E T A T E D SITES SITES BARREN AND CB CR P R S T * COLONIZING SPECIES CommIN'G sF'Ecm (BARRENS) (BARRENS) COLONIZING (REVJXETATED) COIDNIZING SPECIES (REVEGFFATED) PLANTED (NURSERY STOCK) PLANTED (NURSERY STOCK) RELICT RELICT SPECIES SPECIES SEEDED SPECIES SEEDED SPECIES SUSPECTED SEED SEED CONTAMINANT CONTAMINANF TRANSPLANTED TRANSPLANTEDSPECIES SPECIFS PART "WILDFLOWER" MIXTURE MIXTURE PART OF OF "WIU)FLOWER" Mosses and lichens lichens Ceratodon Cmtodon purpureus Funaria Funaria hygroinetrica hygromemica Pohlia nutans nutans Polytrichwn Poljtachum commune commune Ciadonia cI. d&omBs deformis CIa&n.ia cf. Stereocaulon paschale cf. paschaie Stereocaulon ci. Ferns and and fern-allies fern-allies Bolrychium Botrychium multifidum multifidurn Dennstaedtia Dennstaedtia punctiloba punctiloba Equisetum &uisetum arvense arvense Ophioglossum turn Ophioglossumvulga vulgatum Conifers conifers Cedar, easternwhite eastern white Cedar, Larch, European WOF larch, Japanese Japanese Pine, Jack Larch,Jack Pine, Mugo Mugo red Pine, red Pine, Pine, Pine,white white Spruce, Spruce, black black Spruce, white white Spruce, J=a I I I CR CR CB, CR GB GB 03 CR R 03 CR Thuja Thujaoccidenta.lis wadentab Larix decidua decidua larix leptolepis Larix leptolepis Pin us banksiana banksia.na l?inus Pinusmugho Pinus mugho Pin resinosa l?inus resinosa Pin us strobus Pinus su-obus Picea mañana Rcea m arha Picea Rcea glauca glauca p P P P P P P P P �I I I I I I I I I I I I I I I I I I Grasses Grasses Bluegrass, Canada Canada Bluegrass, Bluegrass, Kentucky Fescue, creeping red Fescue, tall Fescue, tall Hairgrass, wavy wavy Hairgrass, Hairgrass, tufted tufted Orchard Orchard grass grass Qpack QW& grass grass Redtop Redtop Tickle Tickle grass grass Timothy Timothy Poa compressa SS compressa Poa pratensis S Festuca rubr.a mbra SS Festuca m arundinacea dinaca S Deschainpsia Lkschampsia flexuosa KR Descharnpsia Lkschampsiacaespitosa caespitosaCB, CB,CR CR Dactylis glomerata glornerata CR CR(SC?) (SC?) Agropyron CR Agropyron repens repens Agrostis gigan tea 5, S, CR a Agmstis gigantea Agrostis CB, Agmstis scabra scabra a,CR a Phleum tense S Phleum pra pratense Other Ot31erMonocotvledons Monocotvledons False Solomon's-seal, Solomon's-seal, starry starry Lady's tresses, tresses, nodding Lady's Lady's tresses, tresses, slender slender Sedge Sedge Sedge Sedge Sedge, Sedge, wool Smilacina stellata AT stellata Spiranthes CR (moist (moist sand) Spirauthes cernua c a m sand) Spiranthes CR (moist (moist sand) sand) gradis Spirauthesgradilis Carexhoughtoniana Grexhoughtoniana CR CX Juncus brevicaudatus Jmcus brevicaudatus CB(wet) CB(wet) Scirpus cyperinus CB (wet) Herbaceous Herbaceous Dicotyledons Dicotyledons Alfalfa Alfalfa Alsike clover clover Alyssum, Alyssum, yellow Bindweed Black-eyed Susan Susan Bristly sarsaparilla sarsaparifia Cornflower cornflower Cow Cow vetch vetch Dam&s rocket Dame's rocket [)evil's Devil's paintbrush Fireweed Flax Flax Foxglove Foxglove Grass-leafed goldenrod Grass-leafed Grass-leafed stitchwort Grass-leafed Hawk's beard Heal-all Horseweed Iceland WPPY Icehd poppy Moth mullein mullein Medicago offlcinalis officit~ah Trifoliuni hybridwn TMolium hybndum Alyssum tile * Alyssum saxa saxatile* Polygonum Polygon urn &ode cilinode hirta Rudbeckia h irta** Aralia hispida Amlia hispida Can ta urea cyan us * G?Ll&Ureacyanus* Vicia cracca Hcia mcca CR CR 5, S, CR CR S 5 CB, CR 5, 1', T CRa CR CR s, 5s CR CR Hesperis matronalis **5S Heqmis matronalis Hieraciwn aurantiacwn fieraciumamtiacum Epiobiwn Epilobiutn angustifolium angustifolium Linurn pet-anne h u m p e r e m e ** Digitalis ppurpurea q m ** Solidago granilnffolia &lidago gmnhifofia Stellaria graininea S t W a graminea Crepis -pis tectorwn tectortun Prwiella h e l l a vulgaris vulgaris Conyza canadensis canaciensis Conyza Papavernudicaule Papaver nudicade ** Verbascwn blattaria Verbascum b1am.a CR CR CR CR SS S CR CR CR CR CR CR A AT T CR CR S5 CR * CR* �I I I I ' I I I I -10Muflein Mullein Northern Nodern willow-herb willow-her1 Oxeye daisy Oxeye daisy Pearly Pearly everlasting everlasting Philadelphia Philadelphia fleabane fleabane Red clover clover Rock Rock harlequin harlequin Rough cinquefoil cinquefoil Rough goldenrod goldenrod Scentless Scentless mayweed mayweed Sheep Sheep sorrel sorrel Sulphur Sulphur cinquefoil cinquefoil Tickseed Tickseed White bedstraw bedstraw White White sweet-clover sweet-clover Wild strawberry strawbeny Yarrow Ymow Yellow hawkweed hawkweed Verbascum CR Verbascum thapsus thapsus QZ Epilobiwn ulosum CR Epilobiumgland glanddosum QZ Chrysanthemum leucanthemwn CLuysanthemumleucanthemum Anaphalis Anaphalis margaritacea margm-tacea CR a Erigeron philadeiphicus CR Erigmn philadelphim CR Trifoliani tense CR TMoliumpra vratense at Coiydslis sempervirens CR a corydalis iempelvirens Potentiila norvegica CR CR Potentilla norvegica Solidago rugosa CR solidago mgosa CR Anthemis SI SI A n t h e - s cotula cotda Rumex acetosella CR acetosella CR Potentiila recta T, Potentilla recta T, CR a Coreopsis lanceolam lanceolata ** S s Galium mollugo moliugo CR Galium CR MeiLlotus a/ba Melilotus alba CR CR QZ Fragaria Fmgm-avirginiana vir&iana Achillea mulefoliuni AchiUea mill&olium Hieracium florentinum Hkracium florentillum 1, T,CR Populus balsamifera balsamifera Salix pyrifolia salixpyf%olia Arctostaphylos uva-ursi uva-ursi Robinia pseudo-acacia pseudo-acacia Prunus virgilliana l?runusvirginiana Vaccinium angustifolium Vacciniumangustifolium Vaccinium niyrtilloides Vacciniummyrtilloides II, CR a s CR, CR,S CR CR Woody woodv Dicotyledoms Dicotyledom Balsam poplar poplar Balsam willow I I I I I I I I Bearberry Black locust locust Choke cherry cherry Common blueberry blueberry Downy-leaf blueberry Downy-leaf blueberry Dwarf birch Large-toothed Largetoothed aspen Pin cherry F'in cherry Pussy Pussy willow willow Red elderberry elderberry maple Red maple Red Red Oak oak Silver Silver maple maple Slender Slender willow willow Soap or buffalo berry Sugar Sugar maple maple Sweet fern sweet fern Trembling aspen aspen White White Ash Ash White white birch birch Witherod Betula Betula pumula pumila Populus grmdidentata grandidentata Prunus l?runus pensylvanica peusylvanica Salixhumulis Salixhumilis Sam bucus ppubens Sambucus uhs Acer rubrum rubrum Quercus borealis Querm borealis Acer urn Acer saccharin saccharinum SaThcgracilis gradilis salix Shepherdia Shepherdia canadensis canadensis Acer sacsacdiarum Comptonia peregrina peregrina Populus tremuloides tiemuloides Fraxinus americana Fmxinus ameficana Betula papyrifera papyrifera Viburnum Viburnumcassinoides casinoides R,a CR CR T T P P R, CR? CR? R, CR R R R,a CB, a,CR CR CR R, R, CR? CR? CR CR CR CR R R R PP CR CR T T pP a CR CR CR P P R, R, CR CR R R �3 (ti)- 2 mIllionth free (Nickel Cenn Welcome Cean) cm - millionth vee (Tiny Pn Caphx) rtt14MJt__44_th Tree 't- a S km GREENING MAP: MAP A ,. � Dublin Core The Dublin Core metadata element set is common to all Omeka records, including items, files, and collections. For more information see, http://dublincore.org/documents/dces/. Title A name given to the resource Institute on Lake Superior Geology Dublin Core The Dublin Core metadata element set is common to all Omeka records, including items, files, and collections. For more information see, http://dublincore.org/documents/dces/. Title A name given to the resource Institute on Lake Superior Geology: Proceedings, 1997 Description An account of the resource Institute on Lake Superior Geology. Sudbury, Ontario. May 6-11, 1997. Creator An entity primarily responsible for making the resource Institute on Lake Superior Geology Date A point or period of time associated with an event in the lifecycle of the resource 1997 Format The file format, physical medium, or dimensions of the resource PDF Language A language of the resource English https://digitalcollections.lakeheadu.ca/files/original/d31e5e66626ffb77a8d6cff650edfda2.pdf f889347321a92c3ecf21c0564230434d PDF Text Text Program and and Abstracts 94th ANNUAL MEETING Minneapolis, Minnesota May 1998 May 6-10, 6-10,1998 Organized by MINNESOTA MINNESOTA GEOLOGICAL GEOLOGICAL SURVEY UNIVERSITY OF MINNESOTA UNIVERSITY MINNESOTA �44th Annual Meeting INSTITUTE ON LAKE LAKE SUPERIOR SUPERIOR GEOLOGY GEOLOGY INSTITUTE parts: Volume 44 contains the following parts: Part Part 1: Program Program and and Abstracts Part 2: Field Part 2: Field Trip Trip Guidebook Guidebook i—Early 1-Early Proterozoic Proterozoicintrusive intrusive rocks of east-central Minnesota 2—Geology 2-Geology of the southeastern southeastern portion of the Midcontinent Midcontinent Rift Rift System, eastern Minnesota and western Wisconsin 3—Glacial 3-Glacial exotica exotica of the Twin Cities Cities area 4—Stratigraphy and hydrogeology 4ÑStratigraph hydrogeology of Paleozoic rocks of southeastern southeastern Minnesota 5—Minnesota 5-Minnesota River River Valley and vicinity, vicinity, southwestern southwestern Minnesota Minnesota Reference to the material in Reference in this volume volume should should follow follow the example example below: below: P.K., Neymark, L.A., Sims, P.K., L.A., Peterman, Z.E., Z.E., and and Kotov, Kotov, A.B., 1998, 1998, Nd isotope isotope evidence evidence for for Middle Middle and and Early Early Archean Archean crust crust in in the the Wawa Wawa subprovince subprovinceof of the the Superior SuperiorProvince, Province, U.S.A., [abstract]: Institute on Lake Superior logy Proceedings, Proceedings, 44th Michigan, U.S.A., Superior Geology MN, 1998; v. v. 44, 44, Part Part 1, 1,p. p. .: Annual Meeting, Minneapolis, MN, Volume Volume 44 is is published by the Institute on Lake Superior Geology and distributed by the Institute Institute Secretary-Treasurer: Secretary-Treasurer: Mark Mark Jima Jirsa (term (term 1994-2000) 1994-2000) Minnesota Minnesota Geological Geological Survey Survey 2642 University Avenue MN USA 55114-1057 St. Paul, MN 55114-1057 (612)-627-4780 (6 12)-627-4780 email: jirsa001@tc.umn.edu jirsa001 @tc.umn.edu http://www.geo.mtu.edu/great_lakes/ilsgl ILSG website http://www.geo.mtu.eddgreat_lakes/ilsg/ ISSN 1042-9964 1042-9964 �INSTITUTE ON LA SUPERIOR GEOLOGY 4th Annual Annual Meeting Meeting 44th May 6-10, 1998 Minneapolis, Minnesota Sponsored Sponsored by: by: Minnesota MinnesotaGeological GeologicalSurvey Survey University University of Minnesota Minnesota PROCEEDINGS PROCEEDINGS Volume 44 44 Part Program and Part 11-Program and Abstracts �CONTENTS CONTENTS Proceedings Volume Volume 44 44 Proceedings Part1—Program 1-Program and andAbstracts Abstracts Part Instituteson onLake LakeSuperior SuperiorGeology, Geology,1955-1998 1955-1998 ...............................................iviv Institutes Constitution Constitution of of the theInstitute Instituteon onLake LakeSuperior SuperiorGeology Geology..........................................vv .. vu By-Laws By-Lawsofofthe theInstitute Instituteon onLake LakeSuperior SuperiorGeology Geology.. .........................................vii ... GoldichMedal MedalGuidelines Guidelines ........................................................................ viii vm Goldich PastGoldich GoldichMedalists Medalists. ............................................................................. x.x Past x GoldichMedal MedalCommittee Committee ...........................................................................x Goldich xi Citationfor for1998 1998Goldich GoldichMedal MedalRecipient Recipient.. .....................................................xi Citation .. ... Student Student Paper Paper Awards Awards ............................................................................. xiii xm ... StudentPaper PaperCommittee Committee ......................................................................... xiii xm Student StudentTravel TravelAwards Awards.. ........................................................................... xii xu Student Boardof ofDirectors Directors ................................................................................. xiv xiv Board LocalPlanning PlanningCommittee Committee.. ......................................................................xiv xiv Local SessionChairs Chairs ...................................................................................... xv xv Session BanquetSpeaker Speaker.. .................................................................................. xv xv Banquet xvi Reportof ofthe theChair Chairofofthe the43rd 43rdAnnual AnnualInstitute InstituteMeeting Meeting.. ...................................xvi Report ... Program.. .......................................................................................... xviii xvm Program Abstractsfor forSpecial SpecialSession: Session: Abstracts 1 Geolo~ical Overviewof ofthe theLake Lake Superior SuperiorRegion Region ..........................................1 Geolo2ical Overview Card,Ken Ken D. D. Card, Archean Archean geology geology of of the the Great Great Lakes Lakes region region of of North NorthAmerica America ................................33 Ojakangas,Richard RichardW. W. Ojakangas, Generalized GeneralizedEarly EarlyProterozoic Proterozoichistory, history,Lake LakeSuperior Superiorregion region ................................ .55 Cannon,William WilliamF. F. Cannon, Understanding Understandingthe theMiddle MiddleProterozoic Proterozoichistory history of of the theLake LakeSuperior Superiorregion: region: What's What's new? new? What's What'snext? next?. ...............................................................19 19 Runkel, Anthony Anthony C. C. Runkel, Paleozoic Paleozoicrocks rocksin inthe thenorthern northernpart part of of the thecentral centralmidcontinent midcontinentof of North North America America Patterson, Carrie CarrieJ.J. Patterson, Models Models for for interpreting interpreting the the Quaternary Quaternary history of the the Lake Lake Superior Superior region region L. Southwick, David David L. Southwick, 25 .........25 .................33 33 37 ...................................... .37 39 Abstracts for forGeneral GeneralTechnical TechnicalSessions Sessions ...................................................... .39 Abstracts What's What'snext nextfor forgeology geologyin inthe theLake LakeSuperior Superiorarea9 area? Ill �INSTITUTES ON INSTITUTES ON LAKE LAKE SUPERIOR SUPERIORGEOLOGY, GEOLOGY,1955-1998 1955-1998 # DATE DATE PLACE PLACE C HAIRS CHAIRS 1 1955 2 1956 3 1957 4 1958 5 6 1959 1960 7 1961 8 10 1962 1963 1964 11 1965 12 13 14 1966 15 16 1969 1970 17 1971 18 1972 9 1967 1968 19 1973 20 1974 21 1975 22 23 24 25 26 27 28 29 30 1976 1977 1978 1979 31 1985 32 33 34 35 36 37 38 39 40 1986 1987 1988 41 42 43 44 1980 1981 1982 1983 1984 1989 1990 1991 1992 1993 1994 1995 1996 1997 1998 Minneapolis, Minnesota Minneapolis, Houghton, Michigan East Lansing, Lansing, Michigan Duluth, Duluth, Minnesota Minnesota Minneapolis, Minneapolis, Minnesota Madison, Wisconsin Port Arthur, Ontario Ontario Houghton, Houghton, Michigan Duluth, Duluth, Minnesota Ishpeming, Ishpeming, Michigan Michigan St. Paul, Minnesota Sault Ste. Marie, Michigan Michigan East Lansing, Michigan Superior, Wisconsin Superior, Oshkosh, Wisconsin Thunder Thunder Bay, Bay, Ontario Ontario Duluth, Duluth, Minnesota Houghton, Houghton, Michigan Madison, Wisconsin Sault Ste. Marie, Ontario Ontario Marquette, Marquette, Michigan Michigan St. Paul, Minnesota Thunder Thunder Bay, Ontario Ontario Milwaukee, Wisconsin Duluth, Duluth, Minnesota Minnesota Eau Claire, Claire, Wisconsin Wisconsin East Lansing, Lansing, Michigan International Falls, Minnesota International Houghton, Michigan Michigan Wausau, Wausau, Wisconsin Wisconsin Kenora, Ontario Wisconsin Rapids, Wisconsin Wisconsin Wawa, Ontario Ontario Marquette, Marquette, Michigan Michigan Duluth, Minnesota Thunder Bay, Ontario Eau Claire, Wisconsin Hurley, Wisconsin Eveleth, Minnesota Houghton, Michigan Marathon, Ontario Ontario Cable, Wisconsin Sudbury, Ontario Minneapolis, Minneapolis, Minnesota C.E. Dutton C.E. A.K. Sneigrove A.K. Snelgrove Sandefur B.T. Sandefur R.W. Marsden Marsden G.M. Schwartz & C. Craddock E.N. Cameron Cameron E.G. Pye Pye A.K. Sneigrove Snelgrove H. H- Lepp L~PP A.T. Broderick Broderick P.K. Sims & R.K. R.K. Hogberg Hogberg R.W. White White WJ. W.J. Hinze Hinze A.B. Dickas Dickas G.L. LaBerge LaBerge Bartley & E. Mercy M.W. Bartley D.M. Davidson J. Kalliokoski Kalliokoski M.E. Ostrom Ostrom P.E. Giblin Giblin J.D. Hughes Hughes M. Walton Walton Kehlenbeck M.M. Kehienbeck G. Mursky D.M. Davidson P.E. Myers Myers W.C. Cambray Cambray D.L. Southwick Southwick T.J. Bornhorst G.L. LaBerge LaBerge C.E. Blackburn Blackburn J.K. Greenberg Greenberg E.D. & R.P. Sage Sage E.D. Frey & J. S. S. Klasner Klasner J.C. Green Green M.M. Kehlenbeck M.M. P.E. Myers A.B. Dickas D.L. Southwick D.L. Southwick T.J. Bornhorst M.C. Smyk M.C. L.G. Woodruff R.P. Sage, W. Meyer R.P. J.D. Miller, M.A. Jirsa J.D. iv �_________(some CONSTITUTION OF THE INSTITUTE ON LAKE SUPERIOR GEOLOGY Board—May 8, 1997) (Last amended by the Board-May 8,1997) Article Article II Name The name of the organization organization shall be the "Institute "Institute on Lake Superior Superior Geology". Geology". Article II II Objectives Objectives are: The objectives objectives of this this organization organization are: A. To Toprovide provideaameans meanswhereby whereby geologists geologists in in the the Great Great Lakes Lakes region region may may exchange exchange ideas ideas and and scientific scientificdata. data. Topromote promotebetter betterunderstanding understandingof of the the geology geology of of the the Lake Lake Superior Superior B. To region. region. C. To Toplan planand andconduct conductgeological geologicalfield field trips. trips. Article III ifi Status Status to the the benefit benefit of any No part of the income of the organization shall insure to member or individual. In the event of dissolution, the assets of the organization organization shall be distributed distributed to free organization). organization). (some tax free To avoid Federal and State income taxes, the organization should be not only "scientific" "scientific" or or "educational, "educational,but also also "non-profit". "non-profit". Minn. Stat. Anno. 290.01, subd. 4 Minn. Stat. Anno. 290.05(9) Mim. 1954 Internal Revenue Code Code s.501(c)(3) s.501(c)(3) Article IV Article Membership Membership The membership of the organization organization shall shall consist consist of persons who have have registered for an annual meeting within the past three years, and those who approved by the indicate interest in being a member according to guidelines approved Board of Directors. Directors. Article V Meetings organization shall meet once a year, preferably preferably during during the the month month of The organization April. The Theplace placeand andexact exactdate date of of each each meeting will be designated designated by the Board of Directors. Directors. Article VI Directors The Board of Directors shall consist of the Chair, Secretary-Treasurer, and the last three past Chairs; but if the board should at any time consist of fewer than five persons, by reason of unwillingness or inability of any of the above persons to serve serve as directors, directors, the vacancies vacancies on the board may be be filled filled by the Chair Chair so so as to bring the membership membership of the board board to to five five members. members. V �Article Article VII Officers Officers The The officers officers of of this this organization organizationshall shallbe be aa Chair Chairand and Secretary-Treasurer. Secretary-Treasurer. A. A. The TheChair Chairshall shallbe beelected electedeach eachyear year by by the the Board Board of Directors, Directors, who shall give due consideration consideration to the wishes of any group that may be promoting promoting the next annual meeting. His/her Hisher term of office office as Chair will terminate he/she presides, or terminate at at the close close of the annual meeting over which helshe hisher successor shall have been Helshe will then serve serve when his/her been appointed. appointed. He/she for as aa member member of the the Board Board of Directors. Directors. for aa period period of of three three years as B. The the annual annual meeting. meeting. Hisher His/her TheSecretary-Treasurer Secretary-Treasurer shall shall be elected at the term term of of office office shall shall be be four four years, years, or or until his/her hislher successor successor shall shall have have been been appointed. appointed. Article Article Vifi VIXI Amendments Amendments This vote of of the the membership membership of This constitution constitution may be amended by a majority vote the the organization. organization. vi �BY-LAWS BY-LAWS OF THE INSTITUTE INSTITUTE ON ON LAKE LAKE SUPERIOR SUPERIOR GEOLOGY GEOLOGY I. Duties Dutiesof of the the Officers Officers and and Directors A. ItItshall shallbe bethe theduty dutyof ofthe theAnnual AnnualChairman Chairmanto: to: 1. Preside Preside at at the the annual annual meeting. meeting. 1. Appointall allcommittees committeesneeded neededfor forthe theorganization organizationof of the the annual annualmeeting. meeting. 2. Appoint 3. Assume Assumecomplete completeresponsibility responsibility for for the organization and financing of the annual meeting over over which he/she helshe presides. B. ItItshall shallbe bethe theduty dutyof of the theSecretary-Treasurer Secretary-Treasurerto: 1. Keep Keepaccurate accurateattendance attendancerecords recordsof of all allannual annualmeetings. meetings. 2. Keep Keepaccurate accuraterecords recordsof of all all meetings meetings of, of, and and correspondence correspondence between, the Board of Directors. Directors. 3. Hold Holdall allfunds fundsthat that may may accrue accrue as as profits profits from from annual annual meetings meetings or or field trips for the the organization organization and and operation operation of of and to make these funds available for future meetings as required. C. ItItshall shallbe bethe theduty dutyof of the the Board Board of of Directors Directors to to plan locations locations of annual meetings and and to to advise advise on on the the organization organizationand and fmancing financingof of all all meetings. meetings. II. 11. Duties Dutiesand and Exoenses Expenses A. There Thereshall shallbe beno noregular regular membership membership dues. dues. B. Registration Registrationfees feesfor forthe the annual annual meetings meetings shall shall be determined by the Chair in The registration fees can include consultation with the Board of Directors. Directors. The expenses to cover cover operations operations outside of the annual meeting as determined by expenses the Board of Directors. ItIt isis strongly strongly recommended recommended that registration fees be kept at a minimum minimum to encourage encourage attendance attendance of graduate graduate students. students. ifi. Rules In. Rules of of Order Order The The rules rules contained contained in in Robert's Robert's Rules Rules of of Order Order shall shall govern govern this this organization organizationin in all all are applicable. applicable. cases to which they are IV. Amendments Amendments These These by-laws may be be amended amended by a majority vote of the membership of the organization; organization; provided that such modifications shall not conflict conifict with the constitution presently adopted adopted or or subsequently subsequently amended. amended. constitution as presently vu vii �GOLDICH MEDAL GUIDELINES GOLDICH MEDAL GUIDELINES (Adopted by the Board of Directors, 1981; 1981;amended 1997) 1997) Preamble Institute on Lake Superior Geology was born in 1955, as as documented documented by by the the fact fact that that The Institute the 27th annual meeting was held in 1981. The The Institute's Institute's continuing continuing objectives are to deal are related geographically to Lake Superior; Superior; to encourage encourage with those aspects aspects of geology that are discussion of subjects subjects and and sponsoring sponsoring field trips that will bring together geologists from the discussion academia, government government surveys, surveys, and industiy; industry; and and to maintain an informal informal but highly effective mode mode of operation. operation. During the course course of its existence, existence, the membership of the Institute (that (that is, those geologists geologists by attending) attending) has has become become aware aware of of who indicate an interest in the objectives of the ILSG by noteworthy and and meritorious meritorious the fact that certain of their colleagues have made particularly noteworthy contributions to the understanding understanding of Lake Lake Superior Superior geology and mineral mineral deposits. deposits. The first award was made by ILSG to Sam Goldich in 1979 for his many contributions to years. Subsequent the geology of the region extending over about 50 years. Subsequentmedalists medalists and and this this year's recipient recipient are are listed listed in in the the table table below. below. Award Guidelines Guidelines 1) The Themedal medal shall shallbe be awarded awardedannually annually by by the the ILSG ILSG Board Board of of Directors Directors to to aa geologist geologist with aa substantial substantial interest interestin, in,and and contribution contribution to, to, the thegeology geologyof of whose name is associated with the Lake Superior Superiorregion. Medal Committee. Committee. The initial 2) The TheBoard Boardof of Directors Directors shall shall appoint the Goldich Medal appointment will be of three members, one to serve for three years, one for two years, and appointment one for one year. The Themember memberwith withthe thebriefest briefestincumbency incumbencyshall shallbe be chair chair of of the the Nominating Committee. After Afterthe thefirst firstyear, year,the the Board Board of of Directors Directors shall shall appoint appoint at at each each years. In hisfher third third year year this this spring meeting one new member who will serve for three years. In his/her member shall be the chair. The TheCommittee Committeemembership membership should should reflect the main fields of interest and geographic interest geographic distribution distribution of ILSG ILSG membership. membership. November , the Goldich Medal Committee shall make its recommendation of November, 3) By By the the end of to the the Chair Chair of of the the Board Board of of Directors, Directors,who who will will then then inform inform the the Board Board of of the the nominee. nominee. 4) The TheBoard BoardofofDirectors Directorsnormally normallywill willaccept acceptthe thenominee nominee of of the the Committee, Committee, will will inform inform the the medalist medalist immediately, immediately, and and will will have have one one medal medal engraved engraved appropriately appropriately for for presentation presentation at the next meeting of the Institute. 5) ItItisisrecommended recommendedthat thatthe theInstitute Instituteset set aside aside annually annually from whatever sources, such funds as will be required to support support the continuing continuing costs of this award. Nominating Procedures Nominatin~ 1) Nominations Nominations shall shallbe be taken taken at at any time by the Goldich Medal Committee. Committee Committee members may themselves nominate candidates. The The deadline deadline for for nominations nominations is November 1. 1. 2) Nominations Nominationsmust mustbe beininwriting writingand andsupported supportedby by appropriate appropriatedocumentation documentationsuch such as as letters letters of recommendation, recommendation, lists of publications, curriculum vita's, and evidence of contributions contributions to Lake Lake Superior Superior geology geology and and to to the the Institute. vifi �Nominationsare arenot notrestricted restrictedto toInstitute Instituteattendees, attendees,but but are arc open open to anyone anyone who has has 3) Nominations worked on and contributed contributed to the understanding understanding of Lake Superior Superior geology. Selection Selection Guidelines Guidelines 1) Nominees Nominees are are to to be be evaluated evaluated on on the the basis of their contributions to Lake Superior geology (sensu lato) including: a) importance importanceof ofrelevant relevant publications; publications; b) promotion promotionof ofdiscovery discoveryand andutilization utilization of of natural natural resources; c) contributions contributionsto tounderstanding understandingof of the the natural natural history and environment environment of the region; region; d) generation generationof of new new ideas ideas and and concepts; concepts; and e) contributions contributionsto tothe thetraining training and and education education of geoscientists geoscientists and the public. Nomineesare aretotobe beevaluated evaluatedon ontheir their contributions contributionsto the Institute as demonstrated by 2) Nominees attendance at Institute meetings, meetings, presentation service on Institute Institute presentation of talks and posters, and service boards, boards, committees, committees, and andfield fieldtrips. trips. 3) The Therelative relativeweights weightsgiven givento to each each of of the the foregoing foregoing criteria criteria must remain flexible and at the the discretion discretion of of the the Committee Committeemembers. members. 4) There Thereare areseveral severalpoints pointsto tobe beconsidered consideredby by the theGoldich Goldich Medal Medal Committee: Committee: a) An Anattempt attemptshould shouldbe be made made to to maintain maintain a balance of medal recipients from each of the three three estates—industry, estates-industry, academia, academia, and and government. government. that much much of b) ItItmust mustbe benoted notedthat that industry industry geoscientists geoscientists are arc at a disadvantage in that their work in not not published. published. U.S., and the the other Canada. Canada. This 5) 5) Lake Lake Superior Superior has two sides, one the U.S., This is is undoubtedly undoubtedly Institute's great strengths and should be nurtured by by equitable equitable recognition recognition of one of the Institute's excellence excellence in in both both countries. countries. ix �GOLDICH MEDALISTS 1979 Samuel SamuelS. S. Goldich Goldich not awarded 1980 not 1989 Jorma Jorrna Kalliokoski Kalliokoski 1981 Dutton, Jr. 1981 Carl E. Dutton, 1990 Kenneth Kenneth C. Card 1982 Ralph RalphW. W. Marsden Marsden 1991 William William Hinze 1983 Burton Burton Boyum Boyum F. Cannon 1992 William William F. 1984 Richard RichardW. W. Ojakangas Ojakangas W. Davis 1993 Donald DonaldW. 1985 Paul PaulK. K. Sims Sims 1994 Cedric Cedric Iverson 1986 G.B. G.B. Morey Morey LaBerge 1995 Gene GeneLaBerge H. Halls Halls 1987 Hemy HenryH. L. Southwick Southwick 1996 David DavidL. 1988 Walter WalterS. S. White White 1997 Ronald Ronald P. P. Sage Sage 1998 1998 Zell Peterman Peterman GOLDICH MEDAL GOLDICH MEDAL COMMITTEE—1997-1998 COMMITTEE-1997-1998 (Committee membership membership through the meeting year shown) shown) Dan England England (1998) (1998) Eveleth Fee Office, Office, Eveleth, Minnesota John Kiasner Klasner (1999) (1999) Western Illinois University, University, Macomb, Macomb, Illinois Mark Mark Smyk Smyk (2000) (2000) Ontario Ontario Geological Geological Survey, Survey, Thunder Thunder Bay x �CITATION CITATION Zell Zell E. E. Peterman Peterman 1998 Goldich Medal Medal Recipient Recipient my personal personal pleasure pleasure to to introduce introduce Zell E. Peterman, this years Goldich medalist. Zell Zell It's my deserves this this highest highest honor honor of the Institute Institute on Lake Superior Superior Geology because of his richly deserves many outstanding outstandingcontributions contributions to to Precambrian Precambrian geology geology and and geochronology geochronology of of the the Lake Lake Superior Superiorregion. region. Zell received received aa Geologic GeologicEngineering Engineeringdegree degreefrom fromthe the Colorado ColoradoSchool Schoolof of Mines, Mines,aamasters masters Zell Geology from from the the University University of Minnesota, Minnesota, Minneapolis, and a Ph.D. in Geology Ph.D. in Geology in 1962 from the University of Alberta. At AtMinnesota, Minnesota,Zell Zellwas wasaastudent studentof of Sam SamGoldich. Goldich. 1962 Zell has 1994Ñwit the theGeologic Geologic has spent spent all all of ofhis hiscareer—except career-except for forthe theyears yearssince since1994—with Division Division of of the the U.S. U.S. Geological Geological Survey, Survey, and it was in this capacity that he carried out most of of his his geochronologic geochronologicresearch researchthat thatwe weacknowledge acknowledgetoday. today. Over aa period period of of several several years, years, working working with with field field geologists, geologists, Zell Zell has has been been mainly mainly responsible for for the the isotopic isotopictime time framework framework for for the the pre-Keweenawan pre-Keweenawan that that we we accept accepttoday. today. responsible A A major majorcontribution contributionwas wasaastudy studyof ofArchean Archeanrocks rocksacross acrossthe theGreat GreatLakes Lakestectonic tectoniczone zoneinin the the Marenisco-Watersmeet Marenisco-Watersmeet area in Michigan. This Thisstudy study established established that that gneisses gneisses in in the the Minnesota Minnesota River RiverValley Valley subprovince subprovinceare are as asold oldas as3,550 3,550 Ma Ma and and flanking flankingmetavolcanicmetavolcanicmetasedimentaryrocks rocksininthe theWawa Wawasubprovince subprovince(to (tothe thenorth) north)are arein inthe therange range2.6-2.8 2.6-2.8 Ga. Ga. metasedimentary This Thispattern pattern has hasproved proved to tobe becharacteristic characteristicof of Michigan-Wisconsin. Michigan-Wisconsin. In 1980's,in in an aninnovative innovativestudy study utilizing utilizing Rb-Sr Rb-Sr ages of biotite, Zell outlined the In the the late late 1980's, uplift uplift history history of of the theGoodwin GoodwinSwell Swellininnortheastern northeasternWisconsin—a Wisconsin-a lithospheric lithosphericflexure flexure caused by by crustal crustal loading loading along along the Midcontinent Rift System. This This isis the the sort sort of of thing thing that caused has been been characteristic characteristic of Zell. More Morethan than most most people, people, he he has has the the ability ability to use use various has geochronologic geochronologictechniques techniquesto tosolve solveproblems problemsmost mostof ofus usmortals mortalsdon't don'tknow knoweven evenexist. exist. Since Since 1994, 1994,Zell Zell has has been been involved involved in in DOE's DOE'SYucca Yucca Mountain Mountain Project, and some of the the successful successfultechniques techniquesused usedto tosolve solveprojects projectsjust just blow blowyour yourmind. mind. II should duties and and skills. skills. From should mention mention Zell's Zell's administrative administrative duties From 1971 1971to to 1976, 1976,he hewas was branch branch chief chief of of the theUSGS's USGS's Branch Branchof ofIsotope IsotopeGeology, Geology, aatime timewhen whenthe theIsotope IsotopeBranch Branch was Since 1994, 1994, he he has has assembled assembled an an isotope isotope hydrology hydrology team team under under the the was flourishing. flourishing. Since Yucca Yucca Mountain Mountain Project Project that that isisdoing doingmany many marvelous marvelousthings, things, particularly particularly using using Rb-Sr Rb-Sr tracers. tracers. P.K. Sims Sims P.K. xi �STUDENT TRAVEL AWARDS STUDENT AWARDS The 1986 Awards to support 1986 Board Board of of Directors Directors established established the ILSG Student Travel Awards the annual annual meeting meeting of ofthe theInstitute. Institute. The awards will will be be made made from from aa student participation at the fund set up for this purpose. purpose. These special fond These awards are intended to help defray some of the direct travel costs of attending Institute Institute meetings, meetings, and include a waiver of registration fees, fees, but exclude exclude expenses expenses for for meals, lodging, and field trip registration. The The number number of of awards awards and value are determined determined by the annual annual Chair Chair in consultation consultation with the Secretary-Treasurer. Secretary-Treasurer. Recipients Recipients will will be be announced announced at at the the annual annualbanquet. banquet. The following following general general criteria will be considered by the annual Chair, who is responsible for the selection: selection: 1) The The applicants applicantsmust must have have active active resident (undergraduate or graduate) student status at the the time time of of the the annual annual meeting meeting of of the the Institute, Institute, certified certified by the department department head. 2) Students Studentswho whoare arcthe thesenior seniorauthor authoron on either either an an oral oral or or poster paper will be given favored consideration. consideration. 3) ItItisisdesirable desirablefor fortwo twoor ormore morestudents studentsto to jointly request request travel assistance. assistance. 4) In Ingeneral, general,priority prioritywill willbe begiven givento tothose thosein in the the Institute Institute region region who are are farthest farthest away from the meeting location. 5) award request request shall shall be made in writing to the annual Chair, and should 5) Each travel award explain need, student student and and author author status, status, and and other other significant significant details. details. Successful applicants Successful applicants will will receive receive their their awards awards at at the time time of registration registration for for the meeting. meeting. xli �STUDENT STUDENTPAPER AWARDS AWARDS Each year, the Institute selects the best of the student presentations and honors presenters with a monetary award. award. Funding with Funding for for the the award award isis generated generated from from registrations registrations of the the annual meeting. meeting. The TheStudent StudentPaper PaperCommittee Committeeisisappointed appointedby by the the annual annual meeting meeting Chair Chairin in annual such a manner as to to represent represent aa broad broad range range of of professional professional and and geologic geologic expertise. expertise. Criteria for for best best student student paper—last paper-last modified modified by the the Board Board in in 1997—follow: 1997-follow: Criteria 1) The Thecontribution contributionmust mustbe bedemonstrably demonstrablythe thework work of of the the student. student. 2) The Thestudent studentmust mustpresent presentthe thecontribution contributionin-person. in-person. to grant, grant, and and whether whether or or 3) The TheStudent StudentPaper Paper Committee Committee shall shall decide how many awards to not to give give separate separateawards awards for for poster poster vs. vs. oral oral presentations. presentations. 4) In Incases casesof ofmultiple multiplestudent studentauthors, authors,the the award award will be made to the senior author, or the award award will will be be shared shared equally equally by by all all authors authors of of the the contribution. contribution. amount of the awards 5) The The total amount awards is left left to the discretion discretion of the meeting Chair Chair and and 5) Secretary-Treasurer, but in the the amount amount of of about about $300 $300US. US. Secretary-Treasurer, but typically typically is is in 6) 6 ) The TheSecretary-Treasurer Secretary-Treasurermaintains, maintains,and andwill willsupply supply to to the the Committee, Committee,aa form form for for the the numerical ranking of presentations. This by Student Paper Paper This form form was created and modified by Committees an effort effort to to reduce reduce the the difficulties difficultiesthat that may may arise arisefrom from Committeesover over several severalyears years in in an background. The selection by raters of diverse background. The use of the form is not required, but is left to the discretion of the Committee. discretion the Committee. 7) The Thenames namesofofaward awardrecipients recipientsshall shallbe beincluded includedas aspart part of of the the annual annual Chair's Chair's report reportthat that appears appears in in the the next next volume volume of of the the Institute. Institute. 1998 1998 STUDENT STUDENT PAPER COMMITTEE COMMITTEE Nancy Nelson—Committee Nelson-Committee Chair Chair North Shore Shore Technical Technical Communications Randy Van Schmus Schmus University University of Kansas Kansas Peter Whelan Whelan University University of Minnesota—Morris Minnesota-Morris ll �1998 BOARD OF DIRECTORS BOARD OF DIRECTORS (Board membership membership through the close of the meeting year shown) shown) James Co-chair (2001) (200 1) James D. Miller, Jr., Co-chair Mark A. A. Jirsa, Jirsa, Co-chair Co-chair and and Institute InstituteSecretary-Treasurer Secretary-Treasurer (2000) (2000) Minnesota Minnesota Geological Geological Survey Survey Ronald P. Sage Sage (2000) (2000) Ronald P. Ontario Ontario Geological Geological Survey—Sudbury, Survey-Sudbury, Ontario Ontario Laurel G. G. Woodruff Woodruff (1999) (1999) U.S. Geological Geological Survey—Mounds Survey-Mounds View, View, Minnesota Minnesota Mark Mark C. C. Smyk Smyk (1998) (1998) Ontario Ontario Geological Geological Survey—Thunder Survey-Thunder Bay, Bay, Ontario Ontario 1998 1998 LOCAL LOCAL PLANNING PLANNING COMMITTEE COMMITTEE James D. D. Miller, Miller, Jr.—Co-chair Jr.-Co-chair Mark MarkA. A. Jirsa—Co-chair Jirsa-Co-chair and andmeeting meeting Treasurer Treasurer Terrence TerrenceJ.J.Boerboom—Field Boerboom-Field Trip TripCoordinator Coordinator Lori LoriDay—Meeting Day-Meeting Coordinator Coordinator Assistance Assistanceto to the thelocal localCommittee Committeewas wasprovided providedby by the thefollowing followingindividuals individualsfrom fromthe the Minnesota MinnesotaGeological GeologicalSurvey: Survey: David David L. L. Southwick Southwick Director Directorof of host host organization organization G.B. G.B. Morey Morey Manuscript Manuscriptreview review Alan Alan Knaeble Knaeble Field Field and and meeting meeting preparation preparation Barb Lusardi Lusardi Manuscript Manuscriptpreparation preparation xiv �1998 SESSION SESSION CHAIRS CHAIRS (In (In order of appearance) appearance) P.K. P.K. Sims Sims U.S. Geological Geological Survey—Denver Survey-Denver G.B. G.B. Morey Morey Minnesota Geological Minnesota Geological Survey Survey Lundy Jim Lundy Minnesota Minnesota Pollution Pollution Control Control Agency Agency Laurel Woodruff Woodruff U.S. Geological GeologicalSurvey—Mounds Survey-Mounds View View Johnson Rod Johnson Bitterroot Resources Resources Ltd. Mark Smyk Smyk Ontario Geological Geological Survey—Thunder Survey-Thunder Bay John Green Green University University of Minnesota—Duluth Minnesota-Duluth Paul Weiblen Weiblen University University of Minnesota—Twin Minnesota-Twin Cities Cities 1998 BANQUET BANQUET SPEAKER Bevan French Smithsonian Institution Smithsonian "When the thesky skyfalls: falls: Large Large meteorite impacts impacts and and 'When of earth earth and other worlds" the history of worlds" xv �43rd ANNUAL INSTITUTE 43rd ANNUAL INSTITUTE ON ON LAKE LAKE SUPERIOR SUPERIOR GEOLOGY GEOLOGY MEETING SUDBURY, SUDBURY, ONTARIO The 43rd annual meeting of the the Institute Institute on on Lake Lake Superior Superior Geology Geology was held on on the the Laurentian University University in Sudbury, Sudbury, Ontario from May 6, through May 11, 11, 1997. 1997. campus of Laurentian The meeting was organized organized by the Precambrian Section and the Resident Geologists Office of the Ontario Ontario Geological Geological Survey. Ron Ron Sage, Sage,Precambrian Precambrian Section, Section, and Wilf Wilf Meyer, Meyer, co-chaired the the event. event. Mrs. Resident Geologist, Sudbury, co-chaired Mrs. Tracy Tracy Livingstone, Livingstone, Resident Resident Geologist's Office, helped organize and coordinate all all activities activitiesrelating relatingto tothe the meeting. meeting. All the guidebooks and individual abstracts were reviewed by W. Meyer, R.P. Sage, and T. Livingstone. The Proceedings Proceedings of of the the 43rd 43rd ILSG ILSGwere were published publishedin in 77 parts: parts: Part 1: Part 1: Program ProgramandAbstracts and Abstracts(edited (editedby byRon RonSage Sageand and Wilf Wilf Meyer); Parti: TheHuronian HuronianSupergroup Supergroupbetween betweenSault Sault Ste. Ste. Marie and and Elliot Lake: Evidence Part2: The for the the Early Proterozoic atmosphere, atmosphere, climate, and tectonics (G. (G. Bennett, K.D. Card, and K.Y. Tomlinson); K.D. Tomlinson); Part Part 3: 3:New Newinformation informationon onthe the Grenville Grenville Front Front near nearSudbury Sudbury (A. (A.Davidson); Davidson); Part Group (S.F.M. Part 4: 4: The TheSudbury SudburyStructure, Structure, with with emphasis emphasis on the Whitewater Group Gibbins); Gibbins); Part 5: Part 5:Magmatic Magmaticore oredeposits depositsofofthe theSudbury Sudbury Igneous Complex (S.A. (S.A. Prevec); Part 6: Part 6: Alkalic Alkalicrocks rocksof of the the Sudbury region (R.P. (R.P. Sage); and Part 7: Part 7:The Thegreening greeningof of Sudbury Sudbury (K. (K.Winterhalder). Winterhalder). A total of 101 101 people registered registered for the meeting in Sudbury and most of the field trips were well attended. There Therewere were13 13paid paid participants participantsfor for the the Huronian Supergroup Supergroup field trip, 22 for the Grenville Grenville Front, 15 15 for for the the Sudbury Sudbury Structure, 36 for the Magmatic ore deposits, deposits, 6 the greening greening of of Sudbury Sudburyfield fieldtrip. trip. Access to local mining for the Alkalic rocks, and 3 for the sites was granted granted by by INCO INCO Limited Limited and and Falconbridge Falconbridge Limited. Limited. Coffee breaks were supported by Laurentian University, University, Falconbridge, Falconbridge, and Ministry of of Northern Northern supported by Laurentian and the the Ministry Development and Development and Mines. Mines. The annual banquet banquet was attended attended by 83 83 diners and held in the Cavern of Science Science North on Ramsey Lake. The TheGoldich GoldichMedal Medal was was awarded awarded to to Ron Ron Sage Sage of of the the Ontario Ontario Geological Geological Survey geology in in the the Lake Superior Superior region. region. The Survey for his contributions contributions to geology The award award was was presented by by Wilf presented Wilf Meyer, Meyer, Resident Resident Geologist, Geologist, Sudbury, Sudbury, Ministry Ministry of of Northern Northern Development and Mines. The Thebanquet banquet address address was was given given by by Dr. Dr. Peter Peter Lightfoot, Lightfoot, INCO INCO talkwas was"Origin "Originof ofthe theSudbury SudburyStructure Structureand andits itsmineral mineral wealth". wealth". Limited. The Thetitle titleof ofthe thetalk The best Student Student Paper Paper Award, Award, consisting consisting of $270 $270 (Can), (Can), was won by Craig Craig Mancuso Mancuso for for his paper "Initial "Initial results of Ar/Ar ArIAr mineral dating from the Peevy node area of northern Michigan and Dunbar dome area of northeastern Wisconsin". Zachary Zachary Naiman Naiman won won $150 $150 for his poster "Petrogenesis of Chengwatana volcanics, volcanics,Minnesota Minnesotaand andWisconsin". Wisconsin". Three student travel awards of $150 $150 each each were were granted granted to to Terry Terry Arcuri, Arcuri, Zachary Zachary Naiman, Naiman, and and Dean Peterson. The Board Board of Directors Directors of of the the Institute Institute on on Lake Lake Superior SuperiorGeology Geology met met in in Sudbury Sudbury on on May May 8, 1997. Members Membersof of the the Board Board in in attendance attendancewere were Mark Mark Smyk, Smyk, Jim Miller (representing (representing Laurel Woodruff), Mark Jirsa (Secretary-Treasurer), Ted Ted Bornhorst, Bornhorst, Ron Ron Sage, Sage, and and Wilf Wilf Meyer. Invited LaBerge. Actions Actions taken were: Invitedguests guestswere were Tracy Tracy Livingstone Livingstone and Gene LaBerge. xvi �1) Accepted Acceptedthe thereport report of of the the Chair, Chair,42nd 42nd ILSG, ILSG, Laurel Laurel Woodruff, including the minutes of the last board meeting. the 1998 meeting. meeting. Jim 2) Approved Approvedan anoffer offerby by the the Minnesota Minnesota Geological Survey to host the Jim the meeting. meeting. The offer by Charles Blackburn to to chair chair Miller and Mark Jirsa will co-chair the the meeting meeting in Kenora Kenora in 1998 1998had to be withdrawn due due to circumstances circumstances beyond beyond his his control. The The1998 1998meeting meetingwill willbe be held held in in Minneapolis, Minneapolis,Minnesota Minnesota on on May 6-10. 6-10. 3) Approved Approvedthe the1996-1997 1996-1997financial financialreport reportpresented presentedby by Mark MarkJirsa. Jirsa. 4) Approved ApprovedRon RonSage Sageas asthe theGoldich GoldichMedal Medal winner winner for for 1997. 1997. 5) Goldich Medal guidelines guidelines prepared by Ken Card. 5) Approved the Goldich 6) Approved Approvedthe thereplacement replacementof of Ken Ken Card Card by Mark Mark Smyk Smyk on the Goldich Medal Committee. Committee. 7) Discussed Discussedthe theILSG ILSGnewsletter newsletter and and web site. The Thenewsletter newsletterhas has been been well well received received and and will be continued. We Wemay mayeliminate eliminatethe the annual annual publication of the Constitution Constitution and place (http://www.geo.mtu.edu/great_lakes/ilsg). The web a general preamble on the web site (http://www.geo.mtu.edu/great-lakeslilsg). site includes information information about about the organization organization and its constitution, constitution, award guidelines, guidelines, publications by the list of publications the Institute Institute and and Goldich Goldich Medal Medal recipients. recipients. 8) Approved Approvedthe themembership membershipguidelines guidelinesfor forthe the ILSG ILSG prepared prepared by Mark Mark Jirsa Jirsa and and Ted Ted in an an effort effort to reduce its size and lower mailing Bornhorst. Mailing Mailinglist listwill will be be revised revised in costs. 9) Discussed was tabled tabledfor forfurther furtherreview. review. A Discussed the the Eisenbrey Eisenbrey Fund and action on this fund was committee consisting committee consisting of Gene LaBerge, Mark Jirsa, and Mark Smyk was formed to study and make make recommendations recommendationson on how how the the monies monies in in the the Eisenbrey Eisenbrey Fund Fund are are to to be be used. Interest Interestearned earnedfrom fromthis thisfund fundmay maybe beused usedto to support supportstudent studenttravel travel to to the the annual annual Institute meeting, and corporations and individuals may may donate donate to to the the fund. fund. Criteria to Institute receive funding receive funding from from the the Eisenbrey Eisenbrey Fund Fund need need to to be be established. established. 10) Discussed Discussed the the ILSG ILSG mailing mailing list. list. Mark MarkJirsa Jirsaisisto tobe be in in charge charge of of the the list. list. 11) Discussed DiscussedUS-Canada US-Canada currency currency exchange. exchange. ItItwas wasagreed agreedthat that prices prices for for Canadian Canadian meetings should should always always list list aa US currency currency price price because many US US participants participants have have difficulty difficulty obtaining obtaining Canadian Canadian funds. funds. Budgeting for the 43rd ISLG was done with an attempt to keep cost down and and not not lose lose money. This Thiswas wassuccessful, successful, in in part, part, due due to to logistical logistical support support provided by the Ontario Ontario Geological Geological Survey. Survey. We enjoyed serving as Co-chairs of the 43rd Institute on Lake Superior Geology meeting. Organizing the meeting was a challenge, Organizing challenge, as the the Ontario Ontario Geological Geological Survey was going going through a difficult period of reorganization, reorganization, and two of the three individuals planning the height of of the the planning planningprocess. process. A special thanks meeting received surplusing notices at the height is due to Wilf Meyer Meyer and and Tracy Tracy Livingstone Livingstone for for staying staying with with the the planning planning and and organization organization of the meeting while their lives were were being being upset upset due due to to reorganization. reorganization. Without Without their their efforts, the meeting meeting could could not not have have been been organized. organized. Ronald P. Sage Wilf Meyer Co-chairs, 43rd ILSG Sudbury, Sudbury, Ontario Ontario xvii �PROGRAM �CALENDAR OF EVENTS EVENTS AND PROGRAM CALENDAR AND PROGRAM WEDNESDAY. MAY 6 0730-0800 0730-0800 0800-1800 0800- 1800 REGISTRATIONIPRE-REGISTRATTONPACKET PACKET PICK-UP PICK-UP REGISTRATIONIPRE-REGISTRATION -Function Area Holiday Inn Pre Pre-Function PRE-MEETING FIELD TRIPS TRIPS Pre-Function Area Depart from: Holiday Inn Pre-Function EARLY PROTEROZOIC PROTEROZOIC INTRUSIVE INTRUSIVE ROCKS ROCKS OF OF EAST-CENTRAL EAST-CENTRAL 11)) EARLY MINNESOTA MINNESOTA Leaders: Terry Boerboom, J i m , and Daniel Daniel Hoim Holm Boerboom, Mark Mark Jima, 2) 2 ) GEOLOGY GEOLOGY OF OF THE THE SOUTHEASTERN SOUTHEASTERNPORTION PORTION OF OF THE THE MINNESOTA AND MIDCONTINENT RJFF RIFT SYSTEM, SYSTEM, EASTERN MINNESOTA AND WESTERN WISCONSIN Leaders: Karl Wirth, Bill Cordua, Bill Kean, Mike Middleton, and Zach Naiman Naiman GLACIAL EXOTICA 3) GLACIAL EXOTICA OF OF THE THE TWIN TWIN CITIES CITIES AREA AREA Leaders: Howard Hobbs, A1 Al Knaeble, and Gary Meyer 1600-2200 REGISTRATION/PRE-REGISTRATION PACKET REGISTRATIONPRE-REGISTRATION PACKET PICK-UP PICK-UP PUBLICATIONS FOR SALE PUBLICATIONS Pre-Function Area Holiday Inn Pre-Function 1700-2200 POSTER SET-UP Pre-Function Area Holiday Inn Pre-Function 1800-2200 WELCOMING WELCOMING RECEPTION/POSTER RECEPTIONPOSTER SESSION SESSION Free Beer and Hors d'oeuvres; Cash Bar /Aragon Ballroom Holiday Inn Pre-Function Area /Aragon Ballroom A-B xd XXI �THURSDAY, MAY 7 0730-1630 0730-1630 REGISTRATIONIPRE-REGISTRATIONPACKET PICK-UP PICK-UP REGISTRATION/PRE-REGISTRATION PUBLICATIONS PUBLICATIONS FOR SALE SALE Holiday Inn Pre-Function Area 0730-0820 0730-0820 COFFEE COFFEE AND TEA TEA Pre-Function Area Holiday Inn Pre-Function SESSION I: 1: GEOLOGICAL SESSION GEOLOGICALOVERVIEW OVERVIEW OF OFTHE THELAKE LAKE SUPERIOR SUPERIOR REGION REGION Aragon Ballroom D-E-F Session Session Chairs: Chairs: P.K. Sims Sims (U.S. (U.S. Geological Geological Survey) Survey) G.B. Morey (Minnesota (Minnesota Geological Geological Survey) Survey) 0820-0830 0820-0830 WELCOME (Jim Miller—Meeting WELCOME Miller-Meeting Co-chair, Minnesota Geological Survey) Survey) 0830-0900 0830-0900 Card,Ken KenD. D.(Card (Cardand andAssociates AssociatesGeosearch) Geosearch) Card, America Archean geology of the Great Lakes region of North America 0900-0930 0900-0930 Ojakangas, Ojakangas,Richard RichardW. W.(University (UniversityofofMinnesota—Duluth) Minnesota-Duluth) Generalized Generalized Early Proterozoic history, Lake Superior region 0930-1000 Cannon, Cannon, William William F. F.(U.S. (U.S.Geological Geological Survey) Survey) Understanding the Middle Middle Proterozoic Proterozoic history of the the Lake Lake Superior Superiorregion: region: What's new? What's What's next? next? Pre-Function Area) AND POSTER POSTER SESSION SESSION (Holiday (Holiday Inn Pre-Function Area) 1000-1030 COFFEE COFFEEBREAK BREAK AND 1030-1100 1030-1 100 Runkel, Anthony Runkel, AnthonyC. C.(Minnesota (MinnesotaGeological Geological Survey) Survey) Paleozoic rocks in the northern part of the central midcontinent midcontinent of North Paleozoic America 1100-1130 1100-1 130 Patterson, Carrie Patterson, CarrieJ.J.(Minnesota (MinnesotaGeological Geological Survey) Survey) Models for interpreting the Quaternary Quatemary history of the Lake Superior region. 11130-1200 130-1200 Southwick, David L. (Minnesota (MinnesotaGeological GeologicalSurvey) Survey) What's next for geology in the Lake Superior Superior area? 1200-1400: LUNCH LUNCH BREAK ILSG BOARD MEETING (Grill (Grill Room Restaurant, Holiday Inn) Inn) POSTERS (Holiday -Function Area) Area) POSTERS (HolidayInn Inn Pre Pre-Function xdi �SESSION II SESSION I1 Aragon Ballroom D-E-F D-E-F Session Chairs: Session Jim Lundy (Minnesota (Minnesota Pollution Control Control Agency) Agency) Laurel Woodruff Woodruff (U.S. Geological Geological Survey) Survey) 1400-1420 1400-1420 Pfannkuch, H.0, H.O, and Paulson, Pfannkuch, Paulson, Richard A. A. assessments of groundwater Improved geologic geologic sensitivity sensitivity and vulnerability assessments groundwater pollution potential potential through fuzzy logic logic pollution through application application of fuzzy 1420-1440 1420-1440 Campion, Moira Ground water recharge, recharge, discharge discharge and and residence residence time time in Rice Rice County, County, Minnesota: Implications Implications for land use planning 1440-1500 1440-1500 Cannon, Cannon, W.F., W.F., Kolker, Alan, and and Westjohn, Westjohn, D.B. D.B. water in southeastern Michigan Michigan The geological source of arsenic in ground water -Function Area) AND POSTER POSTER SESSION SESSION (Holiday (Holiday Inn Pre Pre-Function 1500-1520 COFFEE COFFEEBREAK BREAK AND 1520-1540 1520-1540 Fralick, P.W., Fralick, P.W., and and Kissin, Kissin, S.A. S.A. The age and provenance of the Gunflint Gunflint lapilli tuff 1540-1600 1540-1600 Medaris, L.G., L.G., Jr., and Medaris, and Fournelle, Fournelle, J.H. J.H. Svanbergite Significance for diagenetic diagenetic processes Svanbergite in the Bamboo Baraboo Quartzite: Significance and phosphorus phosphorus flux flux in Precambrian Precambrian oceans oceans 1600-1620 1600-1620 Medaris, L.G., L.G., Jr., Brown, Medaris, Brown, P.B., P.B., and and Bunge, Bunge, R.J. R.J. PostT 1.76low-grade low-grademetamorphism metamorphismof ofthe theBaraboo Bamboo Quartzite Quartzite Post-1.76 1620-1640 1620-1640 Mudrey, M.G., M.G., Jr. Mudrey, aeromagnetic data for regional geology Use of high-resolution aeromagnetic investigations, investigations, southeastern southeastern Wisconsin Wisconsin (Where's (Where's the the kimberlite!) 1830-1900 1830-1 900 MJXER(Holiday Inn Pre-Function Pre-Function Area) MSXER(Ho1iday Area) Cash Bar 1900-2200 1900-2200 ANNUAL BANQUET BANQUET AND AND AWARDS AWARDS PRESENTATION PRESENTATION Aragon Ballroom D-E-F D-E-F • Announcement Announcement of 45th Annual Meeting Meeting location location • 1996 1996 Goldich Goldich Award Award presentation to Zell Peterman Peterman • Banquet speaker: Bevan French, French,Smithsonian SmithsonianInstitution Institution falls: Large meteorite impacts "When the sky sky/alls: impacts and the history of Earth and other other worlds" worlds" xll �FRIDAY, MAY 8 0730-1200 07301200 REGISTRATION/PRE-REGISTRATION PACKET PICK-UP REGISTRATION/PRE-REGISTRATION PICK-UP PUBLICATIONS FOR SALE (coffee (coffeeand and tea tea 0730-0800) 0730-0800) Holiday -Function Area Holiday Inn Inn Pre Pre-Function SESSION 111 III SESSION Aragon Ballroom D-E-F Session Session Chairs: Chairs: 0820-0840 0840-0900 0900-0920 0920-0940 0940-1000 Rod Johnson (Bitterroot (Bitterroot Resources Ltd.) Mark Smyk Smyk (Ontario (Ontario Geological Survey) Survey) Jirsa, Mark MarkA., A., Boerboom, Boerboom, Terrence Terrence J., and Chandler, Chandler, Val Val W. W. ursa, J., and Geologic setting of subeconomic in the Virginia Horn, subeconomic gold deposits in Minnesota: A horn of plenty or a or hornswoggle? hornswoggle? northeastern Chandler, Val W., W., Jirsa, Mark A., Chandler, Val A., and and Lively, Lively, Richard L. Gravity and magnetic studies studies in the Virginia Virginia Horn area, area, northeastern northeastern Minnesota Saini-Eidukat, Bernhardt, and Saini-Eidukat, and Bernatchez, Bernatchez, Raymond Raymond Herontrack silver-zinc-copper Preliminary ore mineralogy of the Herontrack occurrence, occurrence, Lumby Lake area, Ontario, Canada *Salo, *Salo, R.W., R.W., and and Kissin, Kissin, S.A. S.A. Kremzar Alteration and metamorphism metamorphism in an Archean lode gold deposit, deposit, Kremzar mine, Goudreau-Lochalsh gold camp, Ontario Ontario Hudak, George George J., J., Morton, Ron L., L., and Franklin, James M. Hudak, Morton, Ron M. to the Archean The recognition of a lava dome complex and its relationship to Sturgeon Sturgeon Lake caldera, caldera, northwestern northwestern Ontario Ontario 1000-1020 1000-1020 COFFEE COFFEEBREAK/FINAL BREAKfFINALPOSTER POSTER SESSION SESSION Pre-Function Area Holiday Inn Pre-Function 1020-1040 Sims, P.K., Neymark, L.A., and Peterman, Sims, P.K., Neymark, L.A., Peterman, Z.E. Z.E. Nd isotope isotope evidence evidence for Middle and Early Archean crust in the Wawa Subprovince Subprovince of the Superior Superior Province, Michigan, USA 1040-1100 Schulz, Klaus J., and Schulz, Klaus and Ayuso, Ayuso, Robert Robert A. A. Crustal Crustal recycling recycling in the evolution evolution of the Penokean Orogen: Isotopic Isotopic evidence evidence for for Archean Archean contributions contributions to crustal crustal growth growth in the the PembinePembineWausau terrane, northern northern Wisconsin Wisconsin Wausau terrane, 1100-1 120 Hoim, Daniel K., K., Schneider, David, and and Coath, Chris Holm, Daniel Schneider, David, Chris D. D. Age Age and and deformation deformation of Early Proterozoic Proterozoic quartzites quartzites in the southern southern Lake Lake Superior region: Implications Implications for extent of foreland deformation deformation during Superior during fmal final assembly of Laurentia *Czeck, Dyanna Dyanna M., M., and and Hudleston, Peter J. *Czeck, Hudleston, Peter Evidence for for aa modified modified Kinematic fabrics near Mine Centre, Ontario: Evidence transpression model Corfu, Corfu, F., and and Easton, Easton, R.M. R.M. 1140-1200 Extension of the Huronian magmatic magmatic suite suite inside the Grenville Grenville Province: New zircon U-Pb evidence from the Grenville Front Front Tectonic Tectonic Zone Zone in Street Township, Sudbury region, Ontario Ontario 1200-1400 LUNCH LUNCHBREAK BREAK(posters (postersto tobe beremoved; removed;publication publicationsales sales end) end) 1120-1 140 xxiv XXIv �SESSION IV SESSIONIV Aragon Aragon Ballroom Ballroom D-E-F D-E-F Session Session Chairs: Chairs: 1400-1420 (University of Minnesota—Duluth) John C. Green (University Minnesota-Duluth) ~ e i b l e (University n(university of Minnesota—Twin ~innesota- win Cities) Cities) Paul W. Weiblen Nicholson, Suzanne W., W., and Woodruff, Nicholson, Suzanne Woodruff, Laurel Laurel G. G. The Powder Powder Mill Mill Group Group revisited: revisited: Basal volcanic rocks of the Midcontinent The Midcontinent Rift Rift System System on on the the south south shore shore of Lake Lake Superior Superior 1420-1440 *Najman, Zachary J., J., and Wirth, Karl R. *Naiman, Zachary R. Composition Compositionand and source(s) source(s)of of Midcontinent MidcontinentRift Rift lavas lavas (Chengwatana (Chengwatana Volcanics) Volcanics) near near Clam Clam Falls, Falls, Wisconsin Wisconsin 1440-1500 *Vislova, *Vislova, Tatiana Tatiana The The relevance relevanceof of the the geology geology of of the the mid-ocean mid-ocean ridges ridgesand andophiolites ophiolitesto tothe the understanding understanding of layered layered intrusions in the Midcontinent Rift: Part Part I.I. Geometry; Geometry;Part Part II. 11.Internal Internal structure structureand and petrology petrology 1500-1520 *Maki, *Maki, John C., C., and and Bornhorst, Bornhorst, Theodore Theodore J. J. New New field field observations observations of the Clarksburg Volcanics, Upper Peninsula of Michigan Michigan 1520-1540 re-Function Area) 1520- 1540 COFFEE COFFEEBREAK(Holiday BREAK(Ho1idayInn InnPPre-Function Area) 1540-1600 Tikoff, Tikoff, Basil, Bauer, Bauer, Bob, Bob, Vigneresse, Vigneresse, Jean-Louis, Jean-Louis, and and Haggeman, Nick Nick A A gravity, gravity, magnetic, magnetic, and and structural structuralstudy study of of the the Wakemup Wakemup Bay Bay Tonalite, Tonalite, Minnesota Minnesota 1600-1620 Myers, Myers, Paul Paul E. E. Xenolithologies Xenolithologiesas asindicators indicatorsof of intrusion intrusionmechanisms mechanisms in in the theWausau Wausau Syenite SyeniteComplex, Complex,Wisconsin Wisconsin 1620-1640 BEST BEST STUDENT STUDENTPAPER PAPER AWARDS AWARDS CLOSING CLOSING 1905 BASEBALL: (HHH Metrodome) BASEBALL: TWINS TWINS vs. YANKEES (HHHMetrodome) xxv XXV �SATURDAY. SATURDAY. MAY MAY 9 0800-1800 0800-1 800 POST-MEETING FIELD TRIPS TRIPS Depart from: Holiday -Function Area Depart Holiday Inn Inn Pre Pre-Function 4) STRATIGRAPHY STRATIGRAPHY AND HYDROGEOLOGY OF PALEOZOIC ROCKS OF SOUTHEASTERN MINNESOTA Leaders: Tony Tony Runkel Runkel and and Bob Bob Tipping Tipping MINNESOTA RIVER VALLEY AND VICINITY, SOUTHWESTERN 5) MINNESOTA MINNESOTA MINNESOTA Leaders: Dave Dave Southwick Southwick and and Carrie Carrie Patterson Patterson SUNDAY, MAY MAY 10 SUNDAY, 10 0800-1800 08001800 FIELD TRIP TRIP 5, 5, DAY 2 FIELD Returns Returns to to Holiday Inn Inn Metrodome Metrodome xxvi �PRESENTATIONS POSTER PRESENTATIONS 1700 hrs. Wednesday, May May 66 through through 1400 1400 hrs. hrs. Friday, Friday, May 8 *Abbott, Kathleen *Abbott, Kathleen M., M., Thole, Thole,Jeffrey JeffreyT., T., and and Wirth, Wirth, Karl R. Petrography and and geochemistry of Midcontinent Rift rhyolite (Chengwatana Petrography (Chengwatana Volcanics) Volcanics) near near Clam Clam Falls, Falls, Wisconsin Bernatchez, Raymond Bernatchez, Raymond A. A. detailed geological geological description description of the new high grade grade silver-base silver-base A preliminary detailed metal discovery discovery in the the Lumby Lake Lake metavolcanic metavolcanic belt northeast of Atikokan, metal Ontario, Ontario, Canada Canada Boerboom, Terry, Terry, and Oberhelman, Boerboom, Oberhelman, Matt Dimension Dimension stone stone products products of Minnesota Chandler, V.W., V.W., Jirsa, M.A., Morey, Morey, G.B., G.B., and Lawler, Lawler, T. T. Chandler, Jirsa, M.A., Mineral potential assesment assesment of northern St. Louis County, southeastern Koochiching Koochiching County, County, and northeastern northeastern Itasca County, Minnesota Cannon, W.F., W.F., Laberge, Laberge, G.L., G.L., Klasner, Kiasner, J.S., J.S., and Schulz, Cannon, Schulz, K.J. K.J. Reinterpretation of the Penokean continental margin in part Reinterpretation part of of northern northern Wisconsin Wisconsin and Michigan Michigan Cannon, W.F., Cannon, W.F., McRae, McRae, M.E., M.E., and and Nicholson, Nicholson, S.W. S.W. Geographic information information system system on the geology and and copper copper deposits deposits of the the Geographic Keweenaw Keweenaw Peninsula Peninsula Daniels, D. L., Daniels, D. L., Snyder, Snyder, S. S. L., L., Nicholson, Nicholson, S. W., W., and and Cannon, Cannon, W.F. W.F. New aeromagnetic aeromagneticsurveys surveys in m Wisconsin Wisconsin by the the U.S. Geological Geological Survey Survey *Deangelis,M.T., M.T., Peck, Peck, W.H., W.H., and and Valley, *Deangelis, Valley, J.W. J.W. Polymetamorphism of skarns Polymetamorphism skarns related to the Morin Anorthosite Complex, Grenville Province, Quebec Quebec *Gramstad, Sally *Gramstad, Sally D. D. Minnesota River Valley Pre-Wisconsinan gray till in the Mankato area of the Minnesota Han, Han, T.M. T.M. A mineralographic mineralographic study of magnetite in the Biwabik Iron lion Formation, Mesabi Range, Minnesota Minnesota *Hensel, Erin, *Joslin, *Hensel, Erin, *Joslin, Rick, Rick, and Lehrmann, Lehrmann, Dan Dan Facies Ironwood Iron lion Facies and and depositional depositional environments environments of the Early Proterozoic Ironwood Formation, Formation, Mt. Whittlesey, Whittlesey, Wisconsin Wisconsin Kjerland, Kjerland, Dean Dean W., W., and Kjerland, Kjerland, Marc Marc Effects Effects of of electric-pulse electric-pulsedisaggregation disaggregation on on microfossil-bearing microfossil-bearing argillaceous argillaceous limestone of the Middle Ordovician limestone Ordovician Decorah Decorah Shale Shale xxvii �*Loofboro, Jeff, and Holm, *Loofboro, Jeff, Holm, Daniel Daniel Results of modeling Proterozoic thermal histories: Evaluating the the possible possible effects effects of of Wolf River River Batholith Batholith reheating reheating on on thermochronologic therrnochronologic data data from from northern northern Wisconsin Wisconsin Luther, Frank R. Luther, R. An Archean subaqueous subaqueous heterolithic debris flow, Irwin, Pifher, and Meader Townships, Lake Townships, Lake Nipigon Nipigon region, region, Ontario Ontario McRae, M.E., M.E., Cannon, Cannon, W.F., W.F., and and Woodruff, Woodruff, L.G. L.G. McRae, Post-glacial shorelines shorelines of Isle Isle Royale Royale -- Where are are they now? now? McSwiggen, Peter L. McSwiggen, Peter L. Electron microprobe Electron microprobe study of the Pt-Pd and related mineralization in the Minnamax/Babbitt Cu-Ni deposit MinnamaxIBabbitt *peterson, Dean Dean M., M., and Morton, *Peterson, Morton, Ronald Ronald L. GIS-based GIs-based mineral potential potential analysis analysis for lode-gold and massive sulfide sulfide deposits deposits in an Archean terrane terrane of northern Minnesota *Rausch, Deborah E., E., and and Wattrus, Nigel *Rausch, Deborah Nigel J. Seismic Seismic evidence evidence of pre-Nickerson Quaternary sediments in western Lake Superior *Schaper, D., *Suess, W., *Katzer, *Katzer, L., L., and Kean, *Schaper, D., *Suess, W., Kean, W. W. Additional paleomagnetic results for a 1500 Wisconsin 1500 Ma mafic dike at Waterloo, Wisconsin Schmidt, Susanne Susanne Th., Th., and Seifert, Schmidt, Seifert, Karl Karl Metamorphism, hydrothermal Metamorphism, hydrothermal alteration, and lateritic weathering of drilled MRS volcanic rocks in Iowa Schulz, Klaus Klaus J., J., and Schulz, and Ayuso, Ayuso, Robert Robert A. A. Crustal Crustal recycling in the evolution of the Penokean Orogen: isotopic isotopic evidence evidence for for Archean contributions contributions to crustal growth in the Pembine-Wausau terrane, northern Wisconsin *Soofi, M.A., M.A., and King, *Soofi, King, S.D. S.D. A thin viscous viscous sheet sheet approach approach to investigate investigate the post-rift post-rift evolution evolution of the the Midcontinent Rift System Grenville Orogeny Midcontinent System under the influence of Grenville *Thomas, C., C., Kean, Kean, W., W., and and Luther, F. *Thomas, F. Paleomagnetic studies Pither and Paleomagnetic studies of a Proterozoic Proterozoic porphyritic diabase dike, Pifher and Irwin Townships, Lake Townships, Lake Nipigon district, district, Ontario Wirth, Karl R., Wirth, R., and and Gehrels, Gehrels, George George E. E. Precise U-Pb zircon ages of Midcontinent Rift rhyolite (Chengwatana Volcanics), Clam Clam Falls, Falls, WI xxviii �ABSTRACTS SPECIAL SESSION: SPECIAL SESSION: Geological Geological Overview Overview of the Lake Superior Region The The 1998 1998ILSG ILSG planning planning committee committeeasked asked six six leading leading geologists geologists for for aa summary summary of of their their special specialsubfields subfieldsof of Lake Lake Superior geology, geology, including including what's new and what's next. The following following is is their their response. response. 1 �ARCHEAN ARCHEAN GEOLOGY OF THE THE GREAT GREAT LAKES LAKES REGION REGION OF NORTH NORTH AMERICA AMERICA CARD, CARD, K.D., Card Card and and Associates' Associates' Geosearch, Geosearch,Kanata, Kanata, ON, ON, K2K K2K 1M1, 1M1,email email culau2ag3@aol.com cu 1au2ag3@aol.com Archean Archean rocks rocks of of the the southern southern Canadian Canadian Shield Shield in in the the Great Great Lakes Lakes region form form the the world's world's largest km.) Archean craton, the Superior Province. These These ancient ancientrocks rocks largest (2 (2 million million sq. sq. km.) were were formed formed during during several several major major cycles cycles of volcanism, volcanism, sedimentation, sedimentation, plutonism, and and tectonism—mainly Archean(2.5-2.8 (2.5-2.8 Ga), Ga), but but also alsoin in the the Middle Middle(2.8-3.4 (2.8-3.4 Ga) Ga) tectonism-mainly in in the the Lake LakeArchean and and Early Archean (>3.4 (>3.4 Ga). Superior SuperiorProvince Province consists consists of northern and southern highgrade grade gneiss gneiss subprovinces subprovincesand and aa broad broad central central region region of of alternating alternatinggranite-greenstone granite-greenstoneand and sedimentary sedimentary belts belts (Figure (Figure X). Some Someof ofthe thehigh-grade high-grade rocks rocksrepresent represent exposures exposuresof of lower lower crust crust of of Superior SuperiorProvince Provinceuplifted uplifted in in the the Early Early Proterozoic; Proterozoic;others, others, notably notably the the Minnesota Minnesota River Archean crust. crust. The The volcanic and related River Valley Valley gneisses, gneisses, are exotic blocks of Early Archean plutonic plutonic rocks rocks are are similar similar to to those those of modern modem island island and and continental continental arcs formed formed along along convergent oceans. Middle convergent margins. The Themetasedimentaiy metasedimentary belts may mark Archean oceans. Middle Archean Archean rocks, rocks, including includingplutonic plutonicgneisses gneissesapproximately approximately3.0 3.0 Ga Gaold oldare areoverlain overlain unconformably unconformablyby by ca ca 2.8 2.8 Ga Ga platformal platformalsequences sequencesincluding includingquartzite, quartzite,quartz quartzpebble pebble conglomerate Incontrast, contrast,the theLate LateArchean Archean volcanic volcanicand and conglomerateand and komatiitic komatiitic volcanic rocks. In sedimentary sedimentarysequences sequencesare aremainly mainlyjuvenile, juvenile, derived deriveddirectly directlyfrom fromthe themantle mantleor orfrom fromcrustal crustal sources sourcesless less than than 200 200million millionyears yearsolder, older,and anddo donot nothave havestratigraphic stratigraphicbases; bases;many many greenstone greenstonebelts belts may may be beallochthonous. allochthonous. Superior SuperiorProvince Provinceisisrich rich in in minerals mineralsincluding includingcopper, copper,zinc, zinc,and andnickel nickelmassive massivesulfide sulfide and and lode lode gold gold deposits. deposits. Most Mostofofthe themineral mineraldeposits depositsoccur occurin in the the granite-greenstone granite-greenstonebelts belts where 100million million years years or orless less by by processes processesrelated relatedto tothe the where they they were were formed formedin in aa period period of of 100 major the Archean. Archean. These major volcanism, volcanism, plutonism, plutonism, and tectonism that marked the end of the These processes processes also alsoled ledto to the the formation formationof of aa large, large, stable stable craton craton called Kenorland. Kenorland Kenorland may supercontinent~oneof the ffirst i r t of Earth's supercontinents. ItIt was was may have have been been part part of aa supercontinent—one broken broken up upin inthe theEarly EarlyProterozoic, Proterozoic,parts parts of of itit migrating migrating westward westward to to Wyoming, Wyoming, and and other other parts parts going goingback backto tothe theold oldcountry countryto toform formthe theBaltic BalticShield. Shield. Archean Earthwas was significantly significantlydifferent different from modern modem Earth in many ways. The The ArcheanEarth Archean Archeanatmosphere, atmosphere,for forexample, example, lacked lacked free free oxygen oxygen and and was rich in ammonia, ammonia, carbon carbon dioxide, dioxide,and and methane. methane.Meteorite Meteoriteimpacts impactswere weremuch muchmore morefrequent, frequent,and anduntil untilabout about4.0 4.0Ga Ga probably Earthhistory history isiscalled calledthe the probably kept kept the the crust crust well-stirred. well-stirred. This Thisearly earlyperiod periodof ofEarth Hadean, Hadean, probably probably with with justification. Heat Heatflow flowwas wasalso alsohigher, higher,resulting resulting in in aa thicker thicker mantle Archean, the the rocks, rocks, mineral mineral mantle and and aa volcanically volcanically active active crust. crust. However, However,by bythe theLate LateArchean, deposits, are remarkably remarkably similar similarto to those those of of deposits,and andstructures structuresbeing being formed formedand and preserved preserved are modern modemaccretionary accretionaryorogens, orogens,notably notably those those around around the the Pacific Pacific Rim. Although Althoughcurrently currently the ArcheanSuperior SuperiorProvince Provincewas wasformed formedby by the subject subjectof ofdebate, debate,ititwould wouldappear appearthat thatthe theArchean subduction-driven subduction-drivenorogenic orogenicprocesses processessimilar similarininmost mostrespects respectstotothose thoseoperating operatingtoday. today. Additional Additional Reviews: Reviews: Card, Card,K.D., K.D.,AAreview reviewofofthe theSuperior SuperiorProvince Provinceofofthe theCanadian CanadianShield, Shield,aaproduct productofofArchean Archeanaccretion: accretion: Precambrian 48,p.p.99-156. 99-156. PrecambrianResearch, Research,v.v.48, Hamilton, Hamilton,W.B., W.B.,Evolution Evolution of of Archean Archeanmantle mantle and and crust, crust,p. p. 597-614 597-614in in Reed, Reed,J.C. J.C.Jr., Jr.,Ball, Ball,T.T., T.T.,Farmer, Farmer, G.L., G.L.,and andHamilton, Hamilton,W.B., W.B.,1993, 1993,AA broader broader view, view, in in Reed, Reed,J.C.Jr., J.C.Jr.,Bickford, Bickford,M.E., M.E.,Houston, Houston,R.S., R.S., Link, Link,P.K., P.K.,Ranking, Ranking,D.W., D.W.,Sims, Sims,P.K., P.K., and andVan VanSchmus, Schmus,W.R., W.R., eds., eds.,Precambrian: Precambrian:Conterminous Conterminous U.S, U.S, Geological GeologicalSociety SocietyofofAmerica, America,The TheGeology Geologyof of North North America, America,v.v.C-2, C-2,p.597-636. p.597-636. 3 �Figure Figurex. x. Subprovinces Subprovincesof of the the Superior Superior Province Province 4 �GENERALIZED GENERALIZED EARLY EARLY PROTEROZOIC PROTEROZOIC HISTORY, HISTORY, LAKE LAKE SUPERIOR SUPERIOR REGION REGION Department RichardW., W , Departmentof ofGeology, Geologyf Ojakangas, 0j akangas , Richard University Duluth, MN MN55812 55812 Minnesota-Duluthf Duluthf UniversityofofMinnesota-Duluth, rojakang@d*m*edu rojakang@d.umn.edu INTRODUCTION INTRODUCTION Over the the'last last century, centuryf countless countless geologists ueolouists have have worked worked to to Over decipher ~r&eroGoic geological geological history history of of decipher the the fascinating fascinating Early Early Proterozoic to this region. region* Unfortunately, Unfortunatelyf it it is is impossible impossible in in aa short s h o review review ~ to this acknowledge all all the the important important works, worksf but but each each cited cited reference reference acknowledge contains aa bibliography. bibliography* Two Two compendiums compendiums are are especially especially valuable valuable contains and and include include more more than than 500 500 and and 700 700 Precambrian Precambrian references, referencesf respectively respectively (Sims (Simset et al, alf1993; 1993; Sims Situs and and Carter, Carterf1996). 1996). As As in in any any limited limited review, reviewf the the bias bias of of the the reviewer reviewer will will be be present. present* The The integration history* integration of of plate plate tectonic tectonic theory theory permeates permeates this this history. HURONIAN HURONIAN After the the supercontinent supercontinent of of Kenorland Kenorland was was assembled assembled about about 2.7 2.7 Ga Ga After (Card, (Cardf 1990; 1990; Williams Williams et et al, alf 1991) 1991) during during the the Algoman Algoman (Keewatin) (Keewatin) orogeny, erosionf and and sedimentation sedimentation orogenyf aa long long period period of of weathering, weatheringf erosion, occurred on on this this stable stableand and thick thick crustal crustalplatform. platform* The The oldest oldest occurred sedimentary sequence, sequencef the the Huronian Huronian Supergroup, Supergroupf was deposited deposited sedimentary between 2-45Ga Ga and and 2.2 2.2 Ga, Gaf mainly mainly north north of of Lake Lake Huron. Huron* As between 2.45 As thick thick as km and and thinning thinning northward, northwardf this this is is aa sequence sequence quite quite unlike unlike 12 km as 12 in that "uncommon" glacial deposits, Archean sequences sequences in thatititcontains contains ffuncommon'fglacial depositsf Archean quartzose paleosolsf carbonates, carbonatesf and and abundant arkosic to to quartzose paleosols, sandstones. from sandstones* An An upper upper part part of of this this supergroup supergroup is is aa sequence, sequencef from the the bottom bottom up, upf of of glaciogenic glaciogenic rocks, rocksf paleosol, paleosolf quartz quartz sandstone, sandstonef and (evaporites). AA similar similar and carbonate carbonate rocks rocks with with sabkha sabkha minerals minerals (evaporites). sequence sequence is is present present as as erosional erosional remnants remnants in in the the Upper Upper Peninsula Peninsula Group, Marquette Marquette Range of Michigan, Michiganf 200 200 km km to to the the west west (Chocolay (Chocolay Groupf Range of An even even more more complete complete similar similar sequence sequence is is found found in in Supergroup)* An Supergroup). southeastern southeastern Wyoming, Wyomingf the the Snowy Snowy Pass Pass Supergroup. Supergroup* The The glacial glacial units units of of these these three three sequences sequences were were first first interpreted interpreted by by Young Young (1970) (1970)as as remnants remnants of of aa major major continental continental glaciation, glaciationf and and additional additional work work (e.g., ( e - g O fOjakangas, Ojakangasf 1984, 1984f 1985, l98Sf 1988) 1988) further further strengthens strengthens this this idea. idea* As an an interesting interesting aside, asidef Williams Williams and and Schmidt Schmidt (1997) (1997)stated stated that that paleomagnetic paleomagnetic data data indicate indicate that that this this Huronian Huronian glaciation glaciation occurred occurred 4-110 of of the the equator. equator* Further E'urther evidence evidence of the the correlation correlation within 4-11° within of these these three three sequences sequences was was provided provided by by Bekker Bekker and and Karhu Karhu (1996) (1996) and and Bekker Bekker (1998), (1998)fwho who found found similar similar high high values values of of 13C_enrichment 13C-enrichment and 'BO—depletion 180-depletion in in carbonate carbonate units. units* and Supercontinent Supercontinent Kenorland Kenorland began began to to undergo undergo extension extension at at 2.45 2.45 Ga, Gat as as indicated indicated by by mafic mafic igneous igneous rock rock units units at at the the base of of the the Huronian Huronian Supergroup Supergroup (e.g., ( e * g O Heaman, fHeamant 1997; 1997; Cheney, Cheneyf 1998; 1998; Balls, Hallsf 1998). 1998). Actual Actual breakup breakup occurred occurred at at 2.2 2.2 to to 2.1 2.1 Ga Ga with with emplacement emplacement of of Nipissing Nipissing diabase diabase sills sills and and major major dike dike swarms s w a m (Roscoe (Roscoe and and Card, Cardf 1993). 1993)- The The Kenora-Kabetogama Kenora-Kabetogama mafic mafic dikes dikes (2145 (2145 +1+/- 45 45 Ma) Ma) in in northern northern Minnesota 1983) that that show show up up so so well well on on Minnesota (Southwick (Southwickand and Day, Dayf 1983) aeromagnetic aeromagnetic maps maps (Chandler, (Chandlerf1991; 1991; Chandler Chandler et et al, alf 1984) 1984) appear appear to to be products products of of this this final final extensional extensional event. event* The The breakup breakup of of 5 �Kenorland has has an an even even broader broader intercontinental intercontinental significance; significance; aa Kenorland similar similar sedimentary sedimentary sequence sequence with with similar similar igneous igneous activity activity is is also also present in in Finland Finlandand and adjacent adjacentRussia Russia (Marmo (Mannoand and Ojakangas, Ojakangasf present 1984)fand and correlation correlation seems seems likely likely (e.g., (e.gOfOjakangas, Ojakangasf1984, 1984f1988; 1988; 1984), Ojakangasfet et al, alf1991). 1991). In In summary, summaryf Kenorland, Kenorland# which which formed formed in in Ojakangas, Archean, apparently apparentlybroke broke up up in inthe theEarly Early Proterozoic, Proterozoicf the Late Late Archean, the with with the the Wyoming Wyoming craton craton heading heading west west and and the the Svecofennian Svecofennian craton craton east* heading east. heading CORRELATION CORRELATION Correlation Correlation of of Early Early Proterozoic Proterozoic rock rock units units of of Michigan Michigan and and Ontario has has long long been been aaproblem. problem* Glacial Glacial units units have have been been used used as as Ontario marker marker units units (e.g., ( e - g oYoung, fYoungf1983; 1983; Ojakangas, Ojakangasf1988); 1988);on on this thisbasis, basisf the the lower lower portion portion of of the the Marquette Marquette Range Range Supergroup Supergroup (the (the Chocolay Chocolay Group) Group) is is correlated correlated with with the the upper upper part part of of the the Huronian Huronian Supergroup, Supergroupfincluding includingthe theGowganda Gowganda Formation Formationand and overlying overlyingunits. units. Correlation Correlation within within the the Lake Lake Superior Superior region region itself itself has has also also long long been been controversial controversial(Morey (Moreyand and Van Van Schmus, Schmusf1988; 1988;Morey, Moreyf1996). 1996). Correlationshave have long longbeen been made made on on lithostratigraphic lithostratigraphicgrounds; grounds; Correlations for for example, example! it it had had been been assumed assumed that that the the various various iron-formations iron-formations of the the Lake Lake Superior Superior region region were were correlative, correlativef but but this this is is now now of questioned* Correlations Correlations are are complicated complicated by by deformation deformation (both (both questioned. thin-and thick-skinned thick-skinned tectonics) tectonics)and and the thelack lackofofexposures exposures thin-and approaches, suchas C— because of extensive extensive glacial glacialcover. cover* New New approachesf such-as Cbecause isotopic studies studies of of carbonate carbonate units, unitsfhave have been been interpreted interpreted as as isotopic evidence evidence that that not not all all of of the the carbonate carbonate units units are are correlative, correlativef as as Unless 1998). long assumed assumed (Bekker (Bekkerand andKarhu, Karhuf1996; 1996; Bekker, Bekkerf1998). Unless the the long C-ratios have have been been affected affected by by diagenesis/metamorphism, diagenesis/metmrphismf they C-ratios they indicate indicate that that the the Kona Kona Dolomite Dolomite may may be be younger younger than than the the Bad Bad River River Dolomite Dolomite (WI (WIand and MI), MI)! the the Saunders Saunders Formation Formation (MI), (MI)fthe the Randville Randville Dolomite (MN) units units that that have have all all been been (WI)#and and the the Rabbit Rabbit Lake Lake (MN) Dolomite (WI), "correlative "correlative units". unitsw*An An excellent excellent summary summary of of the the sedimentation sedimentation and and correlation correlation of of the the continental continental margin margin assemblage assemblage is is by by Morey Morey (1996). (1996). IRON-FORMATION IRON-FORMATION Naturally Naturally enriched enriched iron iron ores ores of of the the Lake Lake Superior Superior region region made made the the U.S.A. U-S.A. an an industrial industrial giant, giantf but but only only two two of of the the many many ranges, rangesf the the are still still producing iron ore Mesabi and and the the Marquette, Marquettef are producing iron ore (taconite (taconite Mesabi Superior-type" siliceous known known pellets). "Lake "Lake Superior-typew siliceousiron-formation iron-formationisis pellets). world-wide, world-widef and and similar similar units unitshave havebeen been described described from from other other continents* For For nearly nearly aa century, centuryf geologists geologists had had thought thought they they continents. inrecent recent years years it it has were all allabout about2.0 2.0 Ga Ga old. old. However, Howeverf in has been been were deposition* In In suggested that that there there was was more more than than one one period period of of deposition. suggested Minnesotaf there thereappear appear to tobe bethree threeages agesranging rangingfrom from about about 2.2 2.2 Ga Ga Minnesota, to1 1.9 to •9 Ga Ga (Southwick (Southwickand and Morey, Moreyf 1991; 1991; Morey Morey and and Southwick, Southwickf1995); 1995); the oldest oldest two two are are laminated laminated and and fine-grained fine-grained (deposited (deposited below below the wave—base basin^?)^ in in contrast contrast to to the the younger younger wave-base in in extensional extensional basins?), Biwabik Biwabik Iron-formation Iron-formation that that contains contains sand-sized sand-sized grains grains of of chert chert and iron iron minerals, mineralsf is is cross-bedded, cross-beddedf and and contains contains two two stromatolite stromatolite and horizons shelf* In In horizons indicative indicativeof of deposition deposition on on aa shallow shallow shelf. Michigan-Wisconsinf there theremay may be be two two major major periods periods of of deposition deposition Michigan-Wisconsin, (e.g., Ojakangas, (e*go fOjakangas!1994; 1994;Morey, Moreyf1996). 1996)-The The older older Negaunee Negaunee IronIron- 6 �formation of of the t h eMarquette Marquette district d i s t r i c tappears appearstot ohave havebeen beendeposited deposited formation w a t e r s of i ndeeper deeper waters ofa adown-faulted down-faulted graben graben (with (with the t h e addition a d d i t i o n of of in t e r r i g e n o u s material material by by turbidity t u r b i d i t y currents c u r r e n t s from from the t h e south s o u t h side side as as terrigenous noted by by LaRue, LaRuef 1981), 1981)! whereas whereas the t h e Ironwood Ironwood Iron-formation Iron-formation of of the the noted Gogebic range range (Schmidt, (Schmidtf 1980) 1980) and and the t h e Bijiki B i j i k i Iron-formation Iron-formation member member Gogebic of the t h e Michigamme Michigamme Formation Formation appear appear to t ohave have been been deposited d e p o s i t e don on aa of stable marine marine shelf. s h e l f - Interesting I n t e r e s t i n g spirally s p i r a l l y coiled, coiled! megascopic megascopic stable e u k a r y o t i c algae a l g a e have have been been found found in i n the t h e Negaunee Negaunee (Han (Han and and eukaryotic Runnegar, 1992). 1992)Runnegar, The The Biwabik Biwabik Iron-formation Iron-formation (as (asthick t h i c k as as 225 225 m) m) on on the t h e Mesabi M e s a b i range range (Morey, t h e Gogebic Gogebic range range (Morey! 1992) 1992) and and the t h e Ironwood Ironwood Iron-formation Iron-formation on on the appear to t o have have aa common common origin; o r i g i n ; part p a r t of of the t h e evidence evidence is i s found found in in appear t h e underlying underlyingPokeama Pokegamaand andPalms Palms formations formationswhich which have have been been the i n t e r p r e t e dasashaving havingformed formed in i na atidal t i d aenvironment l environment(Ojakangas, (Ojakangas! interpreted 1996)- These These studies s t u d i e s indicate i n d i c a t e that t h a t the the G o W., W O f1996). 1983; Ojakangas, Ojakangas! G. 1983; marine tidally—influenced tidally-influenced iron-formations were were deposited deposited on on aa marine iron-formations shelf, s h e l f ! seaward seaward of of the t h e land-derived land-derived sand sand and and muds muds of of the t h e Pokegama Pokegama Palms formations. formations- Lougheed Lougheed (1983) (1983) also a l s o proposed proposed aa tidal tidal and Palms and environment, environment! with w i t h siderite-rich s i d e r i t e - r i c h limestone limestone the t h e primary primary preprediagenetic type- Deposition Deposition appears appears to t o have have been been related related to t o aa d i a g e n e t i c rock rock type. major marine marine transgression t r a n s g r e s s i o n (Simonson ( S h o n s o nand and Hassler, Hassler! 1996). 1996). major There There are are two two oft-cited o f t - c i t e d sources sources for f o r the t h e iron i r o n and and the t h e silica—silica-hydrothermal hydrothermal activity a c t i v i t yassociated a s s o c i a t e dwith withvolcanism volcanismiii ih the t h e basin basin ( e - g e, t Carrigan Carrigan and and Cameron, Cameron! 1991; 1991; Isley, I s l e y f 11995) 9 9 5 ) and and weathering weathering of of t h e Archean Archean craton c r a t o n ( e m g, oLepp, tLepp, 1987). 1987)- The The Ironwood Ironwood Iron-formation Iron-formation the on the t h e Gogebic Gogebic is i s interbedded interbedded with with volcanics volcanics (Klasner (Klasner et et al, alf on 1998)! the t h e Gunf G u n flint l i n t Iron-formation (once continuous with w i t h the the 1998), Iron-formation (once Biwabik Biwabik Iron-formation Iron-formation prior p r i o r to t o intrusion i n t r u s i o n of of the t h e 1.1 1.1 Ga G a Duluth Duluth Complex) i s aa prominent prominent ashy ashy bed bed in in Complex) contains c o n t a i n s tuff t u f f beds, beds, and and there t h e r e is t h e Biwabik. Biwabik- Hoffman Hoffman (1987) (1987) tied t i e d the t h e iron-formations iron-formations of of the t h e Lake Lake the and 00 isotopes i s o t o p e s of of the the t o foredeep foredeepvolcanism. volcanism- CC and S u p e r i o r region r e g i o n to Superior hydrothermal source source for f o r the t h e Fe+2 Fe+2 and and the the G u n f l i n t indicate i n d i c a t e aa hydrothermal Gunf silica! with w i t h siderite siderite being being the t h e primary primary iron i r o n mineral mineral in i n aa silica, basinward facies f a c i e s (Winter (Winter and and Knauth, Knauth! 1992). 1 9 9 2 ) - The The lower lower part p a r t of of basinward the beds t h e overlying o v e r l y i n g Virginia V i r g i n i a Formation Formation contains c o n t a i n s numerous numerous ash a s h beds (Lucente and and Morey, Morey! 1983). 1983)- Thus Thus there t h e r e is i s aa growing growing body body of of (Lucente of the evidence w a s the t h e main main source source of t h e iron iron evidence indicating i n d i c a t i n g that t h a t volcanism volcanism was silica! but b u t continental c o n t i n e n t a l weathering weathering may may indeed indeed have have been been and silica, and Drevet! 1974). 1974). Biota Biota have have long long been been touted touted a n o t h e r source source (e.g., ( e - g o ,Drever, another as as important important in i n the t h e precipitation p r e c i p i t a t i o n of of the t h e iron i r o n minerals (e.g., ( e - g O fLa La Berge! 1967; 1967; Lougheed, Lougheed! 1983; 1983; LaBerge LaBerge et e t al, a l f 1987). 1987)Berge, lint When When was w a s the t h e Biwabik Biwabik Iron-formation, Iron-formationf the t h e largest l a r g e s t and and probably probably the the P a r t of of the the youngest youngest iron-formation iron-formation in i n the t h e region, region! deposited? deposited? Part evidence comes from from the t h e less-metamorphosed less-metamorphosed and and correlative correlative evidence comes Gunf Iron-formation tthat G u n flint l i n t Iron-formation h a t iis s on sstrike t r i k e with and was once once continuous continuous with w i t h the t h e Biwabik. Biwabik. Faure Faure and and Kovach Kovach (1969) (1969) reported r e p o r t e d aa whole-rock whole-rock Rb-Sr Rb-Sr isochron isochron age age of of 1.64 1-64 +1+/- 0.2 0.2 Ga G a for f o r the the AA Sm-Nd isochron aageon Sm-Nd isochron ge-on deposition lint. ordiagenesis d i a g e n e s i sofofthe t h eGunf Gunflintd e p o s i t i o n or argillites was determined at a t 2.08 2-08 +1+/- 0.25 0.25 Ga Ga a r g i l l i t e s in i n the t h e Gunf G u n flint l i n t was (Stille whole-rock isochron o of ( S t i l l e and Clauer, Clauer! 1986). 1986)- A Sm-Nd Sm-Nd whole-rock f 2100 +1+/52 52 Ma M a was w a s reported r e p o r t e d for f o r "slaty" 88slatywportions p o r t i o n s of of the t h e Biwabik, Biwabik! but b u t this this 7 �probablya amixing mixingage ageofof Archeanand andProterozoic Proterozoic components isisprobably Archean components (Gerlach et et al, alf 1988). 1988). Quartz Quartz veins veins in in the the underlying underlying Pokegama Pokegama (Gerlach +/- 25 25 Ma Ma (Hemming (Hemminget et al, alf1990). 1990). Probably Probably most most were dated dated at at 1930 1930 +1were +/- 22 Ma Ma on on indicative of of the the age age is is aa new new U-Pb U-Pb date date of of 1876 1876 +1indicative euhedral lint euhedral zircons zirconsfrom fromaareworked reworkedtuff tuffbed bedininthe thelower lowerGunf Gunflint (Fralick and and Kissen,1998). Kissenf1998)*This This date date has has major major tectonic tectonic (Fralick implications, implicationsffor for it it indicates indicates that that these these two two iron-formations iron-formations were were deposited deposited on on the the peripheral peripheral foreland foreland bulge bulge of of the the Animikie AnMkie foreland basin, basinfrather rather than than on on the the continental continental margin margin prior prior to tothe the foreland development of of the the foreland foreland basin. basin. In development In this this scenario scenario of of aa northward-migrating northward-migrating foreland foreland basin, basinfthe the terrigenous terrigenous clastic clastic Palms Palms Formation Gogebic range rangeof of Formation and and the the Ironwood Ironwood Iron-formation Iron-formation on on the the Gogebic Wisconsin-Michigan Wisconsin-Michigan may may be be continuous continuous with with but but older older (i.e., (i.eOf diachronous) diachronous) than than the the more more northerly northerly (by (by100 100 km) km) terrigenous terrigenous clastic Pokegama Pokegama Formation Formation and and the the Biwabik Biwabfi Iron-formation Iron-formation on on the the clastic Mesabi range range of of Minnesota Minnesota (Ojakangas, (Ojakangasf1994). 1994). Mesabi PENOKEAN OROGEN OROGEN PENOKEAN of aa big big supercontinent, supercontinentf The Archean Archean ended ended with with the the formation formation of The Kenorland, Kenorlandf the the product product of of the the amalgamation amalgamation of of volcanic arcs arcs and and granitic granitic intrusive intrusivebodies, bodies! and and history history repeats repeats itself. itself* The The Penokean Penokean (Hudsonian) (Hudsonian)orogeny orogeny occurred occurred on on the the southern southern edge edge of of the the Superior Superior craton, cratonIextending extending over over aa distance distance of of 1100 1100 km km from from the the Grenville ONf westward westward to to the the area area just just west west Grenville Front Front near near Sudbury, Sudburyf ON, of of Lake Lake Superior, Superior! deforming deforming the the sedimentary sedimentary units units deposited deposited on on the the passive passive continental continental margin margin when when volcanic volcanic arcs arcs (the (the Wisconsin Wisconsin magmatic terranes) terranes) and and microcontinents microcontinents (that (that included included Archean Archean magmatic rocks) collided collided from from the the south south with with northward-directed northward-directed thrusting rocks) thrusting over over aa southward-dipping southward-dipping subduction subduction zone zone (e.g., (e.gOfMorey Morey and and Southwickf 1995; 1995; Sims, S h I1996). 1996). Southwick, The The Penokean Penokean has has long long been been an an enigma enigma for for it it seems seems to to have have been been long-lived, Ma to to 1770 1770 Maf Ma, with withthe long-lived! lasting lasting from from at least 1982 Ma the earliest earliest Proterozoic Proterozoic sedimentary sedimentary units units in in Minnesota Minnesota deposited deposited Southwickf1995). 1995). Volcanic Volcanic rocks rocks of of the the about 2200 2200 Ma Ma (Morey (Moreyand and Southwick, about orogen range range in in age age from from 1880-1840 1880-1840 Ma, MaI plutonic plutonic rocks rocks from from 19801980orogen 1770 1770 Ma, Maf and and deformation deformation from from 1982-1770 1982-1770 Ma Ma (e.g., (e.gOfSouthwick Southwick and and Moreyf 1991; 1991; Sims S h s et et al, alf1993). 1993). Volcanogenic Volcanogenic massive massive sulfide sulfide Morey, deposits CutZn, ZnIand and Pb, Pbf about about 1860-1840 1860-1840 Ma, Maf deposits and and occurrences occurrences of of Cu, are are abundant abundant based based on on extensive extensive exploration exploration drilling drilling of of geophysical geophysical anomalies; anomalies; more more than than 13 13 bodies have been identified identified (DeMatties, (Flambeau) has has been been mined mined to to ( M a t t i e s f 1994), 1994)f although although only only one one (Flambeau) date. Post-Penokean Post-Penokean rhyolites rhyolites and and granites granites occur occur in in Wisconsin Wisconsin date. ( S d et al, alf 1989) 1989) and and post-orogenic post-orogenic metamorphism metamorphism and and coeval coeval (Sims plutons plutons in in east-central east-central Minnesota Minnesota have have been dated at 1770-1760 1770-1760 Ma with with rapid rapid cooling cooling at at 1760-1750 1760-1750 Ma Ma (Holm (Holmet et al, alf 1998). 1998). Two !lWo deformations Formation have deformations in in the the southern southern portion portion of the the Thomson Formation been described, describedfwith with F1 Flisoclinal isoclinal recumbent recumbent folds folds and and F2 F2 upright upright been folds (Holstf1982, 1982f 1984). 1984)folds that that refolded refolded the the earlier earlier folds folds (Holst, Excellent Excellent interpretations interpretations of of Penokean Penokean deformation deformation can can be be found, found, S h e.gOf in in Holst Holst (1991), (1991)fKlasner Klasner et et al a1 (1991), (1991)fKiasner Klasner and and Simse.g., (1993), (1993)f Gregg Gregg (1993), (1993)! and and Sims S h and and Carter Carter (1996). (1996). 8 �By removing removing the t h e 60 60km-wide kxu-wide Middle Middle Proterozoic Midcontinent Rift Rift Proterozoic Midcontinent By System from from aa regional r e g i o n a l geological geological map, map, thereby thereby bringing b r i n g i n g Minnesota Minnesota system and Wisconsin-Michigan Wisconsin-Michigan into i n t o juxtaposition, juxtaposition, the t h e fold-and-thrust fold-and-thrust and belts of of the t h e two two areas areas become become one one continuous continuous zone. zone- Southwick Southwick and and belts Morey (1991) (1991) correlated c o r r e l a t e d the t h e Niagara ( W I ) and and Niagara fault f a u l t zone/suture zone/suture (WI) Morey t h e Malmo Malmo ddiscontinuity i s c o n t i n u i t y(MN). (MN). Similarly, S i m i l a r l y , the t h e various v a r i o u s turbiditeturbiditethe shale s h a l e units u n i t s (Thomson, (Thomson, Rove, Rove, Virginia, Virginia, Tyler, Tyler, Copps, Copps, and and Michigamme Michigamme onecontiguous contiguousuunit become one n i t ffilling i l l i n gthe t h eAnimikie Animikie Formations) then t h e n become Formations) Basin- This, This, however, however, does does not n o t imply imply that t h a t all a l l of of these t h e s e formations formations Basin. are the t h e same same age, age, for was migrating migrating northward northward during during f o r the t h e basin basinwas are d e p o s i t i o n of of these t h e s e units; u n i t s ; some some sediment sediment deposited in i n the t h e earlier earlier deposition s t a g e s of of basin b a s i n development development was was likely l i k e l y cannibalized cannibalized and and stages redepositedredeposited. asa anorthward-migrating northward-migrating The Animikie Animikie bbasin a s i n has been iinterpreted n t e r p r e t e d as The has been f r o n t of of (on (on the t h e north n o r t h side) s i d e ) of of f o r e l a n d basin b a s i n that t h a t developed developed in foreland in front of tthe t h e fold-and-thrust fold-and-thrust belt beltdue dueto t othe t h eweighting weighting down down of h e crust crust by by the t h i sfolded foldedand andthrusted t h r u s t e mountain d mountainrange rangethat t h a then t t h e nbecame became aamajor major this s o u r c e of of sediment sediment for f o r the t h e basin basin (e.g., ( e - g oHoffman, , Hoffman, 1987; 1987; Southwick Southwick source e t al, al, et 1988; Barovich Barovich et e t al, a l , 1989; 1989; Southwick Southwick and and Morey, Morey, 1991; 1991; 1988; Ojakangas, 1994; 1994; Morey Morey and and Southwick, Southwick, 1995). 1995)Ojakangas, N d isotope isotope data data determined determined by by Barovich Barovich et e t al a1 (1989) (1989) indicate i n d i c a t e that that Nd sampleshad hadananArchean Archeanprovenance provenancet ototthe some Michigainme Michigamme samples h e north n o r t h and and some some had had an a n Early E a r l y Proterozoic Proterozoic provenance provenance to t o the t h e south. southsome P a l e m u r r e n t data data for f o rthe t h Michigamme e Michigamme and h e Tyler n d i c a t e aa andt the Tyler iindicate Paleocurrent northward transport t r a n s p o r t of of sediment sediment from from the t h e south south side side of of the the northward southward transport t r a n s p o r t of of sediment sediment from from the the Animikie Basin Basin and and aa southward Animikie n o r t h side side of of the t h e basin b a s i n as as summarized summarized in i n Ojakangas Ojakangas (1994). north (1994). Hemming Hedng e t al a1 (1995), (19951, on on gochemical geochemicaland and isotopic i s o t o p i c evidence, evidence, described d e s c r i b e d the the et provenance of of the t h e Virginia V i r g i n i a Formation Formation as as aa young young differentiated differentiated provenance v o l c a n i c arc arc to t o the t h e south south of of the t h e basin. basinvolcanic The magmatic terranes t e r r a n e s were were located l o c a t e d just j u s t to t o the t h e south s o u t h of of The Wisconsin Wisconsin magmatic t h e fold-and-thrust fold-and-thrust belt. belt- The The Pembine-Wausau Pembine-Wausau terrane t e r r a n e is is comprised comprised the of older older (1889-1860 (1889-1860 Ma) M a ) magmatic magmatic rocks rocks that t h a t formed formed in i n an a n island island of arc and/or and/or back-arc back-arc basins b a s i n s above above aa south—dipping south-dipping subduction subduction zone zone arc magmatic rocks rocks ( t h e Niagara Niagara fault f a u l t zone zone or o r suture) s u t u r e ) and and younger younger magmatic (the (1845-1835 Ma) M a ) that t h a t formed formed above above aa north-dipping north-dipping subduction subduction zone, zone, (1845-1835 t h e Eau Eau Pleine P l e i n e shear s h e a r zone zone (Sims ( S h et e t al, a l , 1989, 1989, 1993). 1993)- Deep Deep seismic seismic the p r o f i l i n g indicates i n d i c a t e s that t h a t both both the t h e Niagara Niagara fault f a u l t and and the t h e Eau Eau Pleine Pleine profiling shear e t al, a l , 1991). 1991)- An ~n s h e a r zone zone may may penetrate p e n e t r a t e the t h e entire e n t i r e crust c r u s t (Cannon (Cannon et o p h i o l i t e sequence sequence in i n the t h e Quinnesec Quinnesec Formation Formation of of northeastern northeastern ophiolite Wisconsin basinWisconsin (Schulz, (Schulz, 1987) 1987) indicates i n d i c a t e s the t h e closure c l o s u r e of of an an ocean ocean basin. In I n the t h e southerly s o u t h e r l y Marshfield Marshfield terrane, t e r r a n e , 1860 1860 Ma M a rocks rocks were were deposited deposited on Archean Archean crust crust and and amalgamation amalgamation of of the t h e two two terranes t e r r a n e s along along the the on Eau Eau Pleine P l e i n e suture s u t u r e occurred occurred at a t about about 1840 1840Ma M a (Sims ( S h et e t al, a l , 1993). 1993)Three episodes episodes of of post-orogenic post-orogenic magmatism m a g m a t i s m followed, followed, dated dated at a t 1835 1835 Three Ma, M a , 1760 1760 Ma, ~ aand and , the t h e 1469+/1469+/- 28 28 Ma Ma Wolf Wolf River M v e r batholith b a t h o l i t h (Sims ( S h et et al, a l , 1989). 1989)- Nd N d isotopic i s o t o p i c data data of of Barovich Barovich et e t al a1 (1989) (1989) indicated i n d i c a t e d the the major growth growth of of new new crust crust from fromthe t h e mantle. mantlemajor The Penokean Penokean (Hudsonian) (Hudsonian) Orogen Orogen was was part p a r t of of the t h e reassembly reassembly The (Hoffman, new supercontinent supercontinent that t h a t Williams W i l l i a m s et et al a1 (1991) (1991) (Hoffman, 1988) 1988) of of aa new 9 �This supercontinent supercontinent also a l s o included included the the dubbed Hudsonland. Hudsonland. This dubbed (as did d i d the t h e Archean Archean supercontinent supercontinent of of Fennoscandian Shield S h i e l d (as Fennoscandian Kenorland). i s comparable comparable Kenorland). The The Svecokarelian Svecokarelian orogeny orogeny of of that t h a t shield s h i e l d is t o the t h e Penokean Penokean Orogen Orogen in i n many many aspects. aspects. to Q U A R T ZITES ITES QUARTZ The Penokean Penokean Orogen Orogen and and adjacent a d j a c e n t rock rock units u n i t s continued to t o be be The weathered weathered (Southwick (Southwick and and Mossler, Mossier, 1984) 1984) and and eroded for f o r about 100 100 Ma following the mountain-building culmination at about 1850 (?) M a following t h e mountain-building culmination a t about 1850 ( ? ) M a . Several S e v e r a l quartzite q u a r t z i t e units u n i t s were w e r e deposited deposited to t o the t h e south south of of the the Ma. orogen, orogen, including i n c l u d i n g the t h e Sioux Sioux Quartzite Q u a r t z i t e of of Minnesota, Minnesota, South South Dakota, Dakota, Weber, and Iowa Iowa (e.g., , Morey, Morey, 1984; 1984; Ojakangas and W e b e r , 1984; 1984; Southwick Southwick and e t al, a l , 1986) 1986) and and the t h e Baraboo Baraboo (Dott, (Dott, 1983), 1983), Barron Barron (Rozacky, (Rozacky, 1987), 1987), et Flambeau (Campbell, (Campbell, 1986), 1986), and and McCaslin McCaslin (Olson, (Olson, 1984) 1984) Quartzites Quartzites Flambeau of problem of Wisconsin. Wisconsin. Their Their ages ages and and correlation c o r r e l a t i o n have long been a problem e t al., a l e , 1991; 1991; Chandler Chandler and and Morey, Morey, (e.g., Brown, 1986; 1986; LaBerge LaBerge et (e.g., 1992; 1992; Ojakangas, Ojakangas, 1993), 1993), especially e s p e c i a l l y because because the t h e Baraboo, Baraboo, Flambeau, Flambeau, and and McCaslin McCaslin are are deformed deformed whereas whereas the t h e Sioux Sioux and and the t h e Barron Barron are are relatively r e l a t i v e l y horizontal. h o r i z o n t a l . These These "Baraboo "Baraboo Interval" I n t e r v a l w quartzites q u a r t z i t e s pose pose the t h e "Proterozoic "Proterozoic red r e d quartzite q u a r t z i t e enigma" enigmawof of Dott Dott (1983). (1983). Dott Dott (1983) (1983) e t al a1 (1993) (1993) suggested suggested that t h a t aa plate p l a t e suture s u t u r e exists exists and Van Van Schmus Schmus et and beneath the t h e Paleozoic Paleozoic cover cover to t o the t h e south, south, and tthat beneath h a t a southerly southerly t e r r a n e collided c o l l i d e d with with the t h e then-passive then-passive margin of h e continent continent terrane of tthe s o u t h e r l y dipping dipping subduction subduction zone. zone. Chandler over aa southerly Chandler and and Morey Morey over (1992) interpreted (1992) i n t e r p r e t e d paleomagnetic paleomagnetic data d a t a to t o indicate i n d i c a t e that t h a t there t h e r e are are two ages ages of of quartzite q u a r t z i t e bodies, bodies, one one late l a t e Penokean Penokean and and the t h e other other two post-1760 Ma. M a . Recent Recent U-Pb detrital d e t r i t a l zircon z i r c o n ages of 1730—1710 1730-1710 Ma M a for for post-1760 t h e Baraboo Baraboo and and the t h e McCaslin McCaslin and and Pb/Pb Pb/Pb ages on d e t r i t a l zircons z i r c o n s of the detrital 1730-1850 for f o r the t h e Sioux, Sioux, 1745—1880 1745-1880 for f o rthe t h eFlainbeau, Flambeau, and and 1750—1880 1750-1880 1730—1850 et al, a l , 1998) 1998) and and similar similar ages ages for for (Schneider et f o r the t h e Barron Barron (Schneider for d e t r i t a l zircons z i r c o n s in i n the t h e Baraboo Baraboo and and McCaslin McCaslin quartzites q u a r t z i t e s (Van detrital (Van Wyck, Wyck, 1995; Dott D o t t et e t al, a l , 1997) 1997) can can be be interpreted i n t e r p r e t e d to t o indicate i n d i c a t e that t h a t these these 1995; "Baraboo Interval" I n t e r v a l f fquartzites q u a r t z i t e s may may be be correlative. c o r r e l a t i v e . Holm "Baraboo H o l m et et al a1 (1997) have have located l o c a t e d aa 1630 1630 Ma M a thermal thermal front f r o n t in i n northwest northwest Wisconsin Wisconsin (1997) based on on cooling c o o l i n g ages ages in i n Ar/Ar A r / A r dates d a t e s on on mica; mica; this t h i s front f r o n t coincides coincides based with the t h e deformational deformationalboundary boundary between between tthe h e Barron Barron and the the with . Flambeau Flambeau. If I f one one assumes assumes tthat h a t the t h e quartzites q u a r t z i t e s are areerosional e r o s i o n a l remnants remnants of of aa l a r g e r sheet s h e e t of of quartz q u a r t z sand sand locally l o c a l l y >1500 >I500 m m thick t h i c k and deposited deposited larger on on the t h e continental c o n t i n e n t a l margin, margin, aa tremendously tremendously large l a r g e and and deeply deeply weathered must be be assumed. assumed. even weathered quartz-bearing quartz-bearing source source terrane t e r r a n e must Even without without the t h e assumption assumption of of aa single s i n g l e large l a r g e basin, basin, the t h e volume of quartz q u a r t z is i s enormous. enormous. Wheras Wheras aa fluvial f l u v i a l origin o r i g i n is i s most likely l i k e l y for for most most of of the t h e quartzites q u a r t z i t e s (e.g., (e.g., Southwick Southwick et e t al, a l , 1986), 1986), aa marine marine origin o r i g i n for f o r the t h e upper upper Sioux Sioux (Ojakangas (Ojakangas and and Weber, Weber, 1984) 1984) and and for for Baraboo (Dott, ( D o t t , 1983) 1983) has has been been proposed. proposed. p a r t of of the t h e Baraboo part REFEREHCES REFERENCES Patchett, P. P. J., J., Peterman, Petennan, Z. Z. E., E., and and Sims, Sims, P. P. K., K., 1989, 1989, Nd Nd Patchett, isotopes and and the the origin origin of of 1.9-1.7 1.9-1.7 Ga Ga Penokean Penokean continental continental crust crust of of the the Lake Lake isotopes Superior region: region: Geological Geological Society Society of of america America Bulletin, Bulletin, v. v. 101, Superior 101, p. p. 333—338. 333-338. Barovich,K. 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W., W., 1996, 1996, Was Was the the deposition deposition of of large large Precambrian iron—formations Journal of of Precambrian iron-formations linked linked to to major major marine marine transgressions? transgressi.ons? Journal Geology, v. V. 104, 104, p. p. 665—676. 665-676. Sims, P. K., K., and and Carter, Carter, L. L. K. M. H., H., (eds.), (eds.), 1996, 1996, Archean Archean and and Proterozoic Proterozoic 1993: Geology of the the Lake Lake Superior Superior region, region, U.S.A., U.S.A., 1993: U.S. U.S. Geological Geological Survey Survey Professional Paper Professional Paper 1556, 1556, 115 115 p. p. 15 �P.K. (ed.) region and TraneTranaSims, P.K. (ed.) and fifteen fifteen others, 1993, The Lake Superior region Hudson H u d ~ o norogen: in in Reed, 3. J. C. C. Jr. Jr. and and six six others others (eds.), (eds.), Precambrian: Conterminous v. C—2, conterminous U.S., U.s.8 The The Geology Geology of of North America v. C-2, Geological Society Society of of Project series, pp. America Decade Decade of of North North American American Geology Geology Project . 11—120. 11-120. P. K., Schulz, K. 3., E., Petrography Schulz, K. J.8 DeWitt, DeWitt8 E ., and Brasaemle, BB., ., 1993, Petrography of Early magmatic and geochemistry geochemistry of Early Proterozoic Proterozoic granitoid rocks rocks in Wisconsin magmatic terranes of terranes of Penokean Penokean Orogen, Orogen, northern northern Wisconsin: Wisconsin: U.S. U.S. Geological Survey Survey Bulletin 1904-J8 31 31 p. p. Bulletin 1904—3, Sims, Sims, P. K., Schulz, K. K. J 3., Peterman, Z. Sims, w. R., R., ., and Peterman# Z. E., E., 1989, 1989, Sims8 P. K., K., Van Van Schmus, Schmus8 W. Tectono—stratigraphic evolution Wisconsin magmatic magmatic Tectono-stratigraphic evolution of of the the Early Proterozoic Proterozoic Wisconsin terranes v. terranes of of the the Penokean Pen0kea.nOrogen: Orogen: Canadian Canadian Journal Journal of Earth Sciences, v . 26, p. p. 2145-2158. 2145—2158. petrology of Proterozoic Southwick, Southwick, D. D. L., L., and and Day, Day, W. W. C., C., 1983, 1983, Geology Geology and and petrology Proterozoic mafic mafic dikes, dikes, north—central north-central Minnesota Minnesota and and western western Ontario: Ontario: Canadian Canadian Journal Journal of of Earth v. 20, 20, p. p. 622—638. 622-638. Earth Sciences, v. Southwick, Southwick8 D. D. L., L., and and Morey, G. G. B., B., 1991, 19918 Tectonic Tectonic imbrication imbrication and foredeep foredeep development development in in the the Penokean Penokean Orogen, Orogen, east—central east-central Minnesota——An Minnesota--An interpretation interpretation U. based on on regional regional geophysics geophysics and and the the results results of test—drilling: test-drilling: U . S. Geological Geological Survey Survey Bulletin Bulletin 1904-C, 1904-C8 17 17 p. p. Southwick, L., Geologic map G. B., B., and and McSwiggen, P. P. L ., 1988, 1988# Geologic Southwick8 D. D. L., L., Morey, Morey, G. (scale 1:2508000) 1:250,000) of the Penokean Penokean orogen, orogen, central central and and eastern eastern Minnesota8 Minnesota, and (scale accompanying accompanying Minnesota MinneS0ta Geological Geological Survey Survey Report of Investigations Investigations 37, 3T8 25 25 p. Fluvial origin Southwick, D. Southwick, D. L.. L.. Morey, Morey, G. G. B., B e 8and and Mossier, Mossler, 3. J. H., He, 1986, 1986, Fluvial origin of of the Minnesota: Geological Geological the lower lower Proterozoic Proterozoic Sioux Sioux Quartzite, Quartzite, southwestern southwestern Minnesota: Society of America America Bulletin Bulletin v. v. 97, 97, p. p. 1432—1441. 1432-1441. Society of Southwick, Southwick, D. D. L., L.8 and and Moasler, MoSSler, 3. J. B., H e 81984, 1984, The The Sioux Sioux Quartzite and subjacent subjacent regolith regolith in in the the Cottonwood Cottonwood County County basin, basin8 Minnesota: in Southwick, D. D. L., L., Quartzite (Early (Early (ed.), Contributions to to the Geology of the Sioux Quartzite (ed.)# Shorter Contributions Proterozoic), Southwestern Proterozoic), Southwestern Minnesota: Minnesota: Minnesota Geological Geological Survey Report of of Investigations Inveatigations 32, 32, p. p. 17—44. 17-44. Stille, P. isochron-age and and provenance provenance of of the the N., 1986, 1986, Sin-Nd Sm-Nd isochron-age P - and and Clauer, Clauer, N., Geochimica et argillites lint Iron Formation Formation in Ontario, Canada: Geochimica argillites of of the the Gunf Gunflint Cosmochemica Acta, v. Comochemica v. 50, 50, p. p. 1141—1146. 1141-1146. K. C., Proterozoic R., Bickford, Bickford8 N.E., M.E., and and Condie, Condiet K. C O 8 1993, 19938 Early Proterozoic Van Schmus, Schmus8 W. W- R., crustal Precambrian: crustal evolution: evolution: in in Reed, Reed, J.C., J-C., Jr., Jr., and and six six others, (eda.), (eds.), Precambrian: Conterminous U.S., p. 270-281. Conterminous U.Se8 Geology Geology of of North North America, v. v. C—2, C-2, p . 270-281Pb, Sm-Nd, Sm—Nd, and and zircon zircon Van Wyck, W c k 8 N., N a 81995, 1995, Major Major and and trace trace element, element, conunon common Pb, geochronology pre— and geochronology constraints constraints on on petrogenesis petrogenesis and and tectonic tectonic Betting setting of preand Wisconsin— Early Proterozoic Proterozoic rocks rocks in in Wisconsin: Wisconsin: Ph. Ph. D. D. thesis, University University of Wit3consinp. 47—280. 47-280. Madison, p. Williams, G. G. E., E., and and Schmidt, Schmidt, P. P. W., W., 1997, 1997, Paleomagnetiam Paleoxnagnetism of the the Willims, Paleoproterozoic paleolatitude Paleoproterozoic Gowganda Gowganda and and Lorrain Lorrain formations, formations8 Ontario: Ontario: low low paleolatitude Letters, v v. p. 157. 153, 1538 p. 157for Buronian Huronian glaciation: glaciation: Earth Earth and and Planetary Planetary Science Letters8 16 �_____ 169. J. F F., Monger, J. J. WW. Williams, H., H., Hoffman, P.F., P.F., Lewry, J. ., Monger, . HH, ., and and Rivers, Rivers, T., T., 1991, Anatomy of of North North America: America: thematic geologic portrayals of the in Hilde, Hilde, T. T. W. W. C., C., and and Carison, Carlson, R. L. L. (eds.), (eds.), Silver Silver Anniversary Anniversary continent: in of Plate Plate Tectonics: Tectonics: Tectonophysics, v. 187, 187, P. p. 117—134. 117-134. Winter, B. L., L., and and Knauth, Knauth, L. L. P., P., 1992, 1992, Stable Stable iBotope isotope geochemistry geochemistry of of cherta cherts and lint Iron and carbonates carbonates from from the the2.0 2.0 Ga Ga Gunf Gunflint Iron Formation: implications implications for for the the depositional depositional setting, setting, and and the the effects effects of of diageneBis diagenesis and and metamorphism: Precambrian Precambrian Research, Research, v. v. 59, 59, p. p. 283-313. 283-313. Young, G. M., M., 1970, 1970, An An extensive extensive early early Proterozoic Proterozoic glaciation glaciation in in North North america:? Palaeography, v. 7, p. America:? Palaeography, Palaeoclimatology, Palaeoclimatology, Palaeoecology, v. p. 85—101. 85-101. , 1983, 1983, Tectono—aedimentary Tectono-sedimentary history of early Proterozoic rocks rocks of of the the northern Great northern Great Lakes Lakes region: region: in in Medaris, Medaris, L.G., L.G., Jr., Jr., (ed.), (ed.), Early Early Proterozoic Proterozoic Geology of of the the Great Great Lakes Lakes Region: Region: Geological Geological Society Society of of inerica America Memoir Memoir 160, 160, p. 15—32 p.15-32. 17 �UNDERSTANDING THE UNDERSTANDING THEMIDDLE MIDDLEPROTEROZOIC PROTEROZOIC HISTORY HISTORY OF OF THE THE LAKE LAKE SUPERIOR SUPERIOR REGION: WHAT'S REGION: WHAT'S NEW? NEW? WHAT'S WHAT'S NEXT? NEXT? W.F. Cannon, Cannon, US Geological Geological Survey, Survey, Reston, Reston, VA VA Middle Proterozoic Proterozoic time encompasses 700 million Middle million years years (1600-900 (1600-900Ma) Ma)of ofgeologic geologichistory. history. In the Lake Superior Superior region only a small part of that 1470 Ma Lake that time time is is recorded recorded in inthe therock rockrecord. record. At about 1470 large anorogenic granitic plutons plutons were were emplaced emplaced in innorthern northernWisconsin. Wisconsin. Between 1108 and about about 1108 and 1060 1060 Ma the Midcontinent rift, a 2200 km-long volcanic and subsequent sedimentary basin, formed and was was structurally structurallymodified. modified. AAbrief briefsummary summaryof ofthe thecurrent currentunderstanding understandingof ofthese thesetwo twoevents eventsisis and emphasizing findings during the presented below emphasizing the past past 15 years. years. An extended list of references for the Midcontinent Midcontinent Rift Rift presents presents some some of of the principal publications since the detailed papers in the 1982 1982 Geological Society Societyof of America America Memoir Memoir 156, 156, "Geology and Tectonics Tectonics of the Lake Superior Superior Basin". Geological For anorogenic anorogenic plutons, plutons, references references include include original original research from the 1970's 1970's and and more more recent recent For summary summary papers. papers. Anorogenic Anorogenic plutons AAsuite suiteof oflarge largegranitic graniticplutons plutons was emplaced in a broad belt spanning most of the North American continent to Arizona Arizona between betweenabout about 1500 1500and and 1450 1450Ma. Ma. The continent from Labrador to plutons plutons intruded intruded older older continental continentalcrust crust during a period generally devoid of major orogeny, orogeny, hence the name anorogenic anorogenic plutons. That Thatsuite suiteof of plutons plutons is is represented in the Lake Superior region by the Wolf River River batholith and Waussau and Stettin plutons plutons in in Wisconsin. These Theseplutons plutonswere werestudied studied extensively with the the exception exception of of extensively in the 1970's 1970's but but have have received received relatively relatively little attention since, with being discussed discussed in regional summary papers. The The Wolf Wolf River batholith, with an exposed area of about were emplaced emplaced at at about about 1470 Ma. Ma. The about 10,000 10,000km2, km2, and the smaller plutons were The Wisconsin Wisconsinplutons plutons share share characteristics characteristics with the other members of the suite in being emplaced at shallow depths in Early Proterozoic Proterozoic crust crust and and consisting consistingof of large large volumes volumes of granite granite with rapakivi affinities, affinities, and lesser lesser volumes volumes of of more mafic rocks, largely mangerite mangerite and and anorthosite. anorthosite. The Thegranites granitesof ofthe thesuite suiteare are interpreted (20±10%) of Proterozoic interpreted to have formed by relatively relatively low percentage of partial melting (20±10% granitic granitic rocks rocks in in the the lower lower crust. crust. Anorthosite Anorthosite may be derived from basaltic basaltic magma produced, produced, in part, by partial partial melting melting of mantle lithosphere. Studies Studiesof of the the Wolf Wolf River batholith indicate that mangerite magma C. Crystallization magma was was derived derived at at aa depth depth of of 21-32 21-32 km and and a temperature temperature of 950±90° 950±90C. Crystallizationof of the the granite 0-840°C and 650-840° and at at shallow shallow depths depths of of 2-4 2-4 km. km. The The granite now now exposed exposedoccurred occurredatattemperatures temperaturesof of65 cause cause of of widespread widespread melting melting of of lower lower crust crust in in a belt of continental dimensions dimensions remains obscure. obscure. Midcontinent Midcontinent rift The TheMidcontinent Midcontinentrift rift extends extendsin in an an arc arc from Kansas, through the Lake Superior basin, basin, into into southern southernMichigan. Michigan. The The physical physical character character of the rift (rock types, geometry, structure, structure, approximate decades. Research in the past 15 approximate age) age) have been well known for many decades. 15 years has added critical critical information informationto to allow allow the thekinematic kinematic and and dynamic dynamic aspects aspects of evolution evolution of the rift to be deciphered. Deep crustal seismic surveys, precise age determinations, deciphered. Deep crustal seismic surveys, precise age determinations, petrochemical petrochemical research, and experimental experimentaland and theoretical theoretical studies studiesof of mantle mantle and and lithospheric lithospheric processes can be integrated to understand understandthe the rift rift in in the the broad broad context context of of the the evolution of the North American continent continent and and globalglobalscale scale processes. processes. Seismic comprising the entire crustal Seismic surveys surveys have have shown shown that that the rift is is very deep, in places comprising thickness. thickness. Subaerial Subaerialbasalt basaltflows flowsform formthe thelower lowerpart part of of the the rift-fill rift-fill and are as as much as 20 km thick along km along the rift axis. axis. Continental Continentalclastic clasticsedimentary sedimentaryrocks rocksoverlie overliethe thebasalt basaltand andare areas asmuch muchas as10 10km thick. thick. Basalt Basalteruption eruptionand andcoeval coevalrift riftsubsidence subsidencewas was rapid rapid and and of of relatively relatively short short duration. duration. The The volcanic volcanic phase of of the the rift rift lasted lasted about about 14 14 my (1108-1094 (1 108-1094 Ma). Rates of volcanism and subsidence subsidence were were not entirely entirely uniform uniform and and appear appear to have have been greatest near the close of the volcanic phase. Subsidence Subsidenceof of volcanic volcanic basins, basins, as as inferred inferred from seismic seismic profiles, appears appears to have been by a combination combination of of normal normal faulting faulting and and broad flexure. Large Largevolumes volumesof ofmafic maficmagma magmawere werealso also 19 �emplaced both within the crust and as crustal underplating during during this this same same period. period. Basalt Basalt eruption eruption ceased rather abruptly at about 1094 Ma and subsidence rates rates declined correspondingly. correspondingly. Further filling of the rift was with continental sedimentary rocks, mostly mostly red red sandstone, sandstone, and and minor minor reduced reduced lacustrine rocks. The Theduration durationof ofsedimentation sedimentationisis not not well well constrained constrained but but most most likely likely continued, continued, lacustrine During along with subsidence, at declining rates for at least several tens tens of of millions millions of of years. years. During sedimentation, sedimentation,inversion inversion of of the the central central portions portions of of the the rift rift took took place place along along aa set set of of major majorreverse reverse faults. These Theseevents eventscombined combinedto toform formthe thepresent present geometry geometry of of the the rift. rift. A A central central horst horst contains containsthe the originally of volcanic volcanic rocks. rocks. Flanking originally deeper central parts of the rift, including thick sections of Flanking basins basins contain contain wedges of of thinner thinner volcanic volcanic sequences sequences and and overlying overlying sedimentary sedimentary rocks. rocks. The great volume of basaltic rocks and related intrusive rocks in in the the rift, rift, combined combined with with limited amounts hot during during rifting; rifling; probably amounts of lithoshperic lithoshperic extension imply that the mantle was anomalously hot about 200°C 200° hotter than present day asthenosphere. Petrochemical Petrochemical studies studies indicate indicate that much of of the the magma was generated by partial melting melting of of primitive, primitive,enriched enrichedmantle mantle.. Together, Together, these these features features point to the existence that the the rifting rifling existence of a mantle plume beneath the rift, and more specifically, suggest that the initiation of of aa new new plume plume and andthe the arrival arrival of of aa plume plume head head at at and volcanism was a consequence of the the base of the lithosphere. Modelling and numeric simulation of plume behavior shows that that when aa large mushroom-shaped mushroom-shaped head head of of hot hot new plume forms and rises from depth, it generates aa large asthenosphere. The head grows asthenosphere. grows as as it rises rises slowly slowly and is fed by its its own own narrower narrower but but faster faster rising risingstem. stem. The arrival arrival of a plume head at at the base of the lithosphere lithosphere and at at depths depths where where adiabatic adiabaticpartial partial magma generation. generation. Under suitable melting occurs creates a short period of intense magma suitable stress stress conditions conditions in the lithosphere, the plume can also initiate extension and and rifting. rifting. The The arrival arrival of of aa new new mantle mantle plume at the base of the lithosphere lithosphere at at about about 1108 1108 Ma provides the most most coherent coherentexplanation explanationfor forthe the origin of the rift and its its great great volume volume of of igneous igneous rocks. rocks. than the the volcanic volcanic basin. basin. The Rift sedimentation occurred in basins somewhat broader than The sedimentary sedimentary basins do not appear to be strongly controlled by faulting. Rather, Rather, they they appear appear as as smooth smooth flexural flexural depressions depressions on seismic seismic reflection sections. Subsidence Subsidencewas was most most likely likely aa result result of of cooling cooling of of the the head spread and and cooled cooled conductively. conductively. Sediments lithosphere as the initial plume head Sediments were initially initially derived dominantly progressed, however, however, more more older dominantly from volcanic rocks in the rift. As sedimentation progressed, with continued continued erosion erosion of of rift rift terranes outside outside of the rift were tapped as a sediment source along with volcanic volcanic rocks. Inversion of the central portion of of the the rift rift occurred occurredduring duringthe thelater laterstages stagesofofsedimentation. sedimentation. A A set set of of high angle produced displacements displacements of as angle reverse reverse faults and thrusts, in part reactivated normal faults, produced much as several tens of kilometers. The Thetime timeof offaulting faultingisis imprecisely imprecisely known, known, but but most most movement movement must have been in in the the interval interval 1080-1040 1080-1040Ma. Ma. Viewed on a more more regional scale, the Midcontinent rift has been historically somewhat of an enigma in that it is a major extensional feature feature which formed formed immediately immediately west of of the the seemingly seeminglycoeval coeval Grenville orogen. In recent years, however, precise radiometric dating shows that the short In recent years, however, precise radiometric dating shows that short interval interval (1108-1094 Ma) of extension in the Midcontinent rift appears to coincide with an interval of tectonic tectonic rift appears to coincide with an interval of (1 108-1094 quiescence, orogeny. Thus, quiescence, or possibly extension, in the multi-phase Grenvillian orogeny. Thus, aa mantle mantle plume plume arriving arriving at 1108 1108Ma Ma could could have have begun aa period period of of extension extension during during this this Grenvillian Grenvillianquiescent quiescentperiod. period. was renewed renewed and and aa period period of of northwestnorthwestAt about 1090 1090 Ma compression in the Grenville Province was directed thrusting, the Ottawan orogeny, orogeny, continued continuedfor fortens tensof ofmillions millionsofofyears. years. The The onset onset of of thrusting ininthe theGrenville GrenvilleProvince Provincecoincides coincidesremarkably remarkably closely closelywith with the the end end of of extension extensionin in the the Mideontinent Midcontinent rift rift and and the the onset onset of of compressive compressive deformation. deformation. rift marks marks the the arrival arrival of of aa new new plume plume head head at at the the It appears then that development of the Midcontinent rift at about about 1108 Ma. Ma. Melting base in the lithosphere of the Lake Superior region at Melting of the plume plume head head and and 20 �stresses generated by lateral spread of the plume caused the intensely volcanic rift. Under Undersome some stresses circumstances this event might have led circumstances led to to continental continentalbreakup. breakup. In this case, however, however, initiation of the Ottawan orogeny in the adjacent Grenville Province, transmitted northwest-southeast northwest-southeast directed stresses into the Lake Superior region. This Thisnewly newlyapplied appliedstress stressfield field not not only only terminated terminatedrift rift extension, initiated aa period period of of compressive compressive deformation deformation and and rift rift inversion. inversion. extension, but initiated The processes that formed the rift were also important in forming the major mineral deposits for which the rift is well known. The The vast vast new igneous rocks were fertile starting material for for metalmetalprocesses. Some crystallization of of concentrating processes. Someconcentration concentration occurred occurred early, during fractional crystallization magma. The Thevery verylarge large Cu-Ni Cu-Ni sulfide sulfide deposits deposits of the theDuluth Duluthcomplex complexand and other other intrusions intrusions formed formed at at this stage, as did concentrations of of platinum platinum group groupelements. elements. The rifting and related related processes processes in in the the mantle also provided a large heat engine that drove hydrothermal circulation. Those Thosehydrothermal hydrothermal systems sediment-hosted systems formed the Keweenaw native copper district, the White Pine and related sediment-hosted copper deposits, and polyrnetallic polymetallic vein vein deposits. deposits. The heat generated by the the rift rift also also caused regional regional metamorphism that converted Early Proterozoic iron-formations from non-magnetic to magnetic taconite in places such such as as the the Mesabi Mesabi Range Range and and Gogebic Gogebic Range. Range. Much progress has been made in the past 15 years in understanding fundamental causative factors of refinements the Midcontinent rift. The The data data gathered gathered in in that period lay the foundation for continued refinements of knowledge knowledge of this important structure. Research continues on refining knowledge of the age of rifting events, events, internal stratigraphy stratigraphy of rift units, the nature of plume-lithosphere interaction, and and alteration. alteration. Advances in the detail and precision precision of patterns of regional metamorphism and information information on the geometry, age, and composition of the rift from recent and continuing research, combined quantitative numerical combined with modem modem computational computational techniques, allows allows a new phase of quantitative undertaken. Examples of this new phase of research research are current research on rift evolution to be undertaken. studies studies of the transient transient thermal history of the rift, and the paleohydrology of the rift as it related to formation formation of of mineral mineral deposits. deposits. 21 �References on on the the Midcontinent Midcontinent Rift (post Selected References (post 1982) 1982) Allen, Wi., Dickas, &en, D.J., Hinze, W.J., Dickas,A.B., A.B.,and andMudrey, Mudrey,M.G., M.G., Jr., Jr., 1997, Integrated geophysical modeling of the North American Midcontinent Midcontinent Rift System: System: new interpretations interpretationsfor for western Lake Lake Superior, Superior, in northwestern Wisconsin, Wisconsin, and eastern eastern Minnesota, Minnesota, in Ojakangas, R.W., and others, others, eds., Middle Middle Proterozoic to Cambrian Proterozoic Cambrian rifting, central central North America: Geological Society Society of of America America Special Special Paper 312, p. 47-72. Cannon, Cannon, W.F., and and Hinze, Hinze, W.J., W.J., 1992, 1992,Speculations Speculationson onthe the of the the North North American American Midcontinent Midcontinentrift: rift: origin of Tectonophysics, v. 213, p. 49-55. Hinze, W.J., W.J., and Mariano, Mariano, J., J., 1995, 1995, Allen, D.J., Braile. L.W., Hinze, The Midcontinent Midcontinent rift rift system, system, U.S.A.-a major major Proterozoic in Olsen, Olsen, K.H., K.H., (ed.), (ed.), Proterozoiccontinental continental rift: in Continental rifts: evolution, evolution, structure, structure, tectonics, tectonics, International Lithosphere Lithosphere Program Program Publication Publication no. no. 264, 373-407. 264, p. p. 373-407. Cannon, W.F., W.F., and ten ten others, others, 1990, The The Midcontinent Midcontinent rift beneath Lake Superior from GLIMPCE seismic reflection profiling: Tectonics, Tectonics, v. v. 8, 8, p.305-332. p.305-332. Cannon, showing mineral Cannon, W.F., W.F., and McGervy, T.A., 1991, Map showing Midcontinent rift. rift, Lake Superior deposits of the Midcontinent region, United States and Canada: U.S. Geological Miscellaneous Field Studies Survey Miscellaneous StudiesMap Map MF-2153, MF-2153, 1:500,000. scale 1:500,000. Z.E., and and Sirns, Sims, P.K., P.K., 1993, CrustalCrustalCannon, W.F., Peterman, Z.E., scale thrusting and origin of the Montreal River monocline—a 35-km-thick cross section of the monocline-a Midcontinent rift in northern Michigan and Wisconsin: Tectonics, Tectonics, v. 12, 12, p. p. 728-744. 728-744. Behrendt, J.C., and seven Behrendt, seven others, others, 1988, 1988,Crustal Crustal structure structureof of the the Midcontinent Midcontinent rift rift system: system: results results from from GLIMPCE GLIMPCE seismic reflection profiles: Geology, v. 16, deep seismic 16, p. 81-85. 81-85. P.L., Morey, G.B., Hinze, W.J., W.J., Chandler, V.W., McSwiggen, P.L., and Anderson, R.L., 1989, Interpretation Interpretation of seismic seismic reflection, gravity and magnetic magnetic data across the Middle Proterozoic Proterozoic Midcontinent Rift System System in western Wisconsin, eastern Minnesota, and central Iowa: Iowa: American Association of Petroleum Geologists 261-275. GeologistsBulletin, v. v. 73, 73, p. p. 261-275. Behrendt, Behrendt, J.C., J.C., and seven seven others, others, 1990, 1990,Seismic Seismicreflection reflection evidence of deep (GLIMPCE) evidence deep crustal and upper mantle intrusions and magmatic magmatic underplating underplating associated with the Midcontinent rift system of North America: America: Tectonophysics, Tectonophysics,v. v. 173, 173,p.617-626. p.617-626. Davis, D.W., and Green, J.C., 1997, Geochronology Geochronology of the North American Midcontinent Midcontinent rift in western Lake Superior Superior and implications for its geodynamic geodynamic evolution: Canadian Journal of Earth Sciences, Sciences, v. 34, 476-488. p. 476-488. Berg, J.H., J.H., and and Klewin, Klewin, K.W., K.W., 1988, 1988,High-MgO High-MgOlavas lavasfrom fromthe the Keweenawan Midcontinent rift near Mamainse Mamainse Point, Ontario: Ontario: Geology, Geology, v. 16, 16, p. 1003-1006. 1003-1006. Bomhorst, T.J., 1997, Tectonic context of native copper copper Bornhorst, deposits deposits of the North American American Midcontinent Midcontinent Rift Rift system, Ojakangas, R.W., and and others, others, eds., Middle Middle system, in Ojakangas, Proterozoic Proterozoicto Cambrian Cambrian rifting, central central North America: Geological America Special Special America: Geological Society Society of of America Paper Paper 312, p. 127-136. 127-136. Davis, D.W., and and Sutdliffe, Sutcliffe, R.H., 1985, 1985,U-Pb U-Pb ages agesfrom fromthe the Nipigon plate plate and and northern northernLake LakeSuperior: Superior: Geological Society Society of America America Bulletin, Bulletin,v. v. 96, 96, p. p. 1572-1579. 1572-1579. Implications of of Campbell, I.H., and Griffiths, R.W., 1990, Implications mantle plume structure structurefor for the evolution evolution of of flood flood basalts: Earth and and Planetaiy PlanetaryScience ScienceLetters, Letters, v. v. 99, 99, p. p. 79-93. 79-93. Paces, J.B., J.B., 1990, Time Time resolution resolution of of geologic geologic Davis, D.W., and Paces, events on the Keweenaw Peninsula and implications development of the Midcontinent rift system: system: for the development Midcontinentrift Earth and Planetary Science Science Letters, Letters, v. v. 97, 97, p. p. 54-64. 54-64. Campbell McCuaig, T., T., and and Kissin, Kissin, S.A., S.A., 1997, 1997,The The Port Port Coidwell Coldwell veins, veins, northern northern Ontario: Ontario: Pb-Zn-Ag Pb-Zn-Ag deposits deposits in a rift setting, in Ojakangas. R.W., and others, eds., Middle Proterozoic Proterozoicto to Cambrian Cambrian rifting, rifting, central central North America: America: Geological Geological Society Society of of America America Paper 312, 312, p. 187-196. Special Paper 187-196. Dickas, A.B., 1986, 1986, Comparative Comparative Precambrian Precambrian stratigraphy stratigraphyand and structure along the Mid-Continent Rift: American structure Petroleum Geologists, v. 70, p. 225Association of petroleum 238. 238. 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Tectonophysics, v. 91, p. 413-437. 22 ' �IC., 1989, Green, J.C., 1989,Physical Physicalvolcanology volcanologyof ofmid-Proterozoic mid-Proterozoic plateau lavas: lavas: the Keweenawan KeweenawanNorth North Shore Shore Volcanic Volcanic Group, Minnesota: Geological Society of America Bulletin, 486-500, America Bulletin, v 101, 101, p. p. 486-500. Manson, M.L., and Halls, H.C., 1997, Proterozoic Proterozoic reactivation Superior Province and its role in the of the southern Superior evolution evolution of the Midcontinent Midcontinent rift: Canadian Canadian Journal Earth Sciences, Sciences,v. v.34, 34,p.p.562-5 562-575. of Earth 75. 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Samson, Samson, C., and West, West, G.F., G.F., 1992, 1992,Crustal Crustal structure structureof of the the Midcontinent MidcontinentRift Rift system system in in eastern eastern Lake Lake Superior Superior from controlled-amplitude controlled-amplitudeanalysis analysisof of GLIMPCE GLIMPCE deep deep reflection seismic seismicdata: data: Canadian CanadianJournal Journal of of Earth Earth Sciences, Sciences,v. v. 29, 29, p. p. 636-649. 636-649. Weiblin, P.W., P.W., 1993, 1993,Midcontinent Midcontinentrift riftsystem, system,the theLake Lake Weiblin, Superior region region and and Trans-Hudson Trans-Hudsonorogen, orogen,in inReed, Reed, Superior J.C., J.C., Jr., Jr., and and others, others, eds., eds., Precambrian-Conterminous Precambrian-Conterminous United States: States: Boulder, Colo., GeologicalSociety Societyof of United Cob., Geological v. C2, C2, p. p. America, The The Geology Geology of of North America, America, v. America, 72-8 1. 72-81. 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Sims,P.K., P.K., 1996, 1996,Early Earlyand andMiddle MiddleProterozoic Proterozoicintracratonic intracratonic Sims, rocks, rocks,in in Sims, Sims,P.K. P.K. and and Carter, Carter, L.M.H., L.M.H., eds., eds., Archeanand and Proterozoic Proterozoicgeology geology of of the the Lake Lake Archean Superior region, U.S.A.: U.S.A.: U.S. Geological Geological Survey Survey Superior ProfessionalPaper Paper1556, 1556,p.p.57-60. 57-60. Professional Anderson, Anderson,.LL., J.L., 1980, 1980, Mineral equilibria equilibria and and crystallization crystallization conditions conditionsin in the the late latePrecambrian PrecambrianWolf WolfRiver River rapakivi rapakivi massif, massif, Wisconsin: Wisconsin: American Journal of Science, Science,v. v. 280, 280, p. p. 289-332. 289-332. Van Medaris, L.G., L.G., and andBanks, P.O., 1975, 1975, Van Schmus, Schmus,W.R., W.R., ,,Medaris, Banks, P.O., Chronologyof ofPrecambrian Precambrianrocks rocksininWisconsin, Wisconsin,I:I: Chronology theWolf WolfRiver Riverbatholith, batholith,aarapikivi rapikivimassif massif the approximately1500 1500 m.y. my. old: Geological Geological Society Society of of approximately AmericaBulletin, Bulletin,v.v.86, 86,p.p.907-9 907-914. America 14. Anderson, Anderson,J.L., J.L., and andCullers, Cullers,R.L., R.L.,1978, 1978,Geochemistry Geochemistryand and evolution evolutionof of the the Wolf WolfRiver Riverbatholith, batholith,aalate late Precambrianrapakivi rapakivimassif massifininnorthern northernWisconsin, Wisconsin, Precambrian USA: v.7,7, p.p. 287-324. 287-324. USA: Precambrian PrecambrianResearch, Research,v. 24 �ROCKS IN THE THE NORTHERN NORTHERN PART OF THE THE CENTRAL CENTRAL PALEOZOIC ROCKS MIDCONTINENT OF NORTH NORTH AMERICA AMERICA RUNKEL, RUNKEL, Anthony Anthony C., C., Minnesota Minnesota Geological Geological Survey, Survey,2642 2642University University Ave AveSE, SE,St St Paul, Paul, MN, MN, 55114-1057 55 114-1057 INTRODUCTION Paleozoic Paleozoic strata strata in the central central midcontinent region of North North American American consist consistof of thin thin units of carbonate, carbonate, sandstone, sandstone, and and shale shale distributed across tens of thousands of square square kilometers. kilometers. This This overview overview focuses focuses on the northernmost extent of lower Paleozoic strata which were were deposited deposited on on the the stable stable cratonic cratonic shelf northwest northwest of the Illinois and Michigan Michigan basins sinuous belt of outcrops outcrops in southern southern basins (Figs. (Figs. 11and and 2). 2). They They are are exposed exposed in in a sinuous Minnesota, Minnesota, Wisconsin Wisconsin and and northern northern Michigan, Michigan, on the southern southern flanks flanks of the Transcontinental Transcontinental arch arch and and the the Wisconsin Wisconsin dome dome and and arch. arch. Deposition Late Cambrian Cambriantime. time. Coarse Coarse Depositionof of Paleozoic Paleozoicsediments sedimentsbegan began in in Middle Middleto to Late siliciclastic siliciclastic sediments sediments of the the Mt Mt Simon Simon Sandstone Sandstone covered covered the eroded eroded Precambrian Precambrian surface. surface. Overlying Overlying strata stratawere were deposited deposited in in two broad, laterally equivalent equivalent facies belts across the central inset) (Palmer, (Palmer, 1960). 1960).An An inner innerdetrital detritalbelt belt was was central midcontinent midcontinentregion region (Fig. (Fig.11inset) composed composed of shallow shallow marine marine siiciclastics siliciclasticsderived derived from from subaerially subaerially exposed exposed Precambrian Precambrian shield shield areas areas on on and and totothe thenorth northof ofthe theWisconsin WisconsinDome. Dome. Thin, Thin, laterally laterally extensive extensive units units dominated quartzose sandstone, sandstone, very fme fine sandstone, or dominated by either either fmefine-to tocoarse-grained coarse-grainedquartzose shale shalewere were deposited depositedin in the the inner innerdetrital detritalbelt. belt. The The middle middle carbonate carbonatebelt belt consisted consistedof ofsubtidal subtidal to to intertidal intertidal carbonate carbonate and and shale shale deposits deposits that accumulated accumulated to the south. The boundary between belts shifted, belt sedimentation shifted, with inner detrital belt sedimentation dominant during Cambrian and part part of of Middle MiddleOrdovician Ordovician time, time, and and middle middle carbonate carbonate belt sedimentation sedimentationdominant dominantduring during the as in in Silurian Silurianand and Devonian Devoniantime time (Fig. (Fig. 2). 2). the Early Early and and Late LateOrdovician, Ordovician,as as well well as Early Early Paleozoic Paleozoicdeposition depositionoccurred occurred on on aavirtually virtuallyhorizontal, horizontal,cratonic cratonicshelf shelfwith withaavery very low lOrn1m.y. (Sloss, (Sloss, low subsidence subsidence rate. Late LateCambrian Cambriansubsidence subsidenceaveraged averaged less lessthan thanlOrn/m.y. 1988), 1988),about about one-fifth one-fifth to to one-tenth one-tenth the the rate rate in in the the contemporaneous contemporaneousIllinois IllinoisBasin Basin (Sargent, (Sargent, 1991) 1991) and orders orders of magnitude magnitude slower slower than than that that of better known, known, younger younger basins basins in in North North America. (e.g. Byers Byersand and Dott, Dott, America. Maximum Maximumpaleobathymetry paleobathymetrywas was typically typically less lessthan than100 100m m(e.g. 1995; 1995; Ludvigson Ludvigson and and others, others, 1996) 1996)and and the shelf had a low gradient gradient slope slope of about about 0.1 rn/km. O.lm/km. The The Wisconsin Wisconsinarch arch and and dome dome and and Transcontinental Transcontinentalarch arch were were positive structural structural features featuresthat that influenced influencedearly early Paleozoic Paleozoic sedimentation sedimentation patterns, patterns, and and eventually eventually controlled controlledthe the distribution distribution and and configuration configurationof of gently gently folded folded and and faulted faulted Paleozoic Paleozoic strata strata today. In In northern are northern Iowa, Iowa,southern southernMinnesota, Minnesota,and and southwestern southwesternWisconsin Wisconsin Paleozoic Paleozoic strata strataare preserved preserved in in what what is is known known as as the the Hollandale Hollandale Embayment, which is a broad syncline syncline that lies lies between between these these two two positive positive features. features. South Southand andeast eastof ofthe theWisconsin Wisconsinarch archand anddome dome Paleozoic Paleozoic rocks rocks dip dipless lessthan than 11degree degreeinto into the the Illinois Illinois and and Michigan Michigan basins. basins. DEPOSITIONAL MODELS MODELS The The depositional depositionalhistory history of of lower lowerPaleozoic Paleozoicsiliciclastic siliciclasticstrata strata of of this this region regionremains remains poorly understood despite an despite over 100 100 years of study. Many Many workers workers have have lamented lamented an apparent apparent absence absenceof of modern modem or or ancient ancientdepositional depositionalanalogues. analogues.In In addition, addition,dozens dozensof of local local studies studies have have been conducted conducted (e.g. (e.g. Nelson, Nelson, 1954; 1954; Haddox and Dott, 1990) 1990) but there are few regional-scale regional-scaleinvestigations investigationsthat that incoiporate incorporate several several lithofacies lithofaciesinto into aa temporally temporally constrained constrained stratigraphic stratigraphic framework. framework.Present-day Present-day understanding understanding of early Paleozoic Paleozoic siliciclastic siliciclastic deposition deposition is is based based mostly mostly on on work work conducted conducted since since 1950, 1950,beginning beginning with with the the predominantly (1954), Nelson Nelson (1956), (1956), Berg Berg and and others others predominantly stratigraphic stratigraphic investigations investigations of of Berg Berg (1954), (1956), Bell and others (1956), and Ostrom (1964, 1970). Subsequent work has been (1964,1970). chiefly chiefly sedimentologic, sedimentologic, focusing focusing on the interpretations of near-shore marine facies (Fraser, (Fraser, 1976; 1976; Driese Driese and and others, others, 1981; 1981;Dott Dott and and others, others, 1986; 1986; Haddox Haddox and and Dott, Dott, 1990; 1990;Barnes Barnes and and 25 �Figure1.1.Location Locationmap mapshowing showing Figure earlyPaleozoic Paleozoictectonic tectonicfeatures, features, early major paleotopographic paleotopographichighs highs of of major Precambrian rocks (stippled) and the Precambrian rocks (stippled) and the approximate distribution of approximate distribution of (C),Ordovician Ordovician (0), (0), Cambrian (C), Cambrian Silurian (S), and Devonian (D) Silurian (S), and Devonian (D) stratain in the thenorthern northernpart partof ofthe the strata centralmidcontinent midcontinentregion. region. The The central inset shows the study area relative inset shows the study area relative toto theLate LateCambrian Cambrianinner inner(stipple) (stipple) the detritalbelts belts and and and outer outer(dashes) (dashes)detrital and the middle carbonate belt (block the middle carbonate belt (block pattern)of ofPalmer Palmer(1960). (1960).Modified Modified pattern) from Runkel Runkeland andothers others(1998) (1998) from GROUP! FORMATION LITHOLOGY ; i. Cedar VaHey J — I — —L —I -— I——I Manustique Burnt Bluff Cataract I—I- J —— — . Maquoketa Dubuque Galena Decorah Platteville ood !:!. — •• E •. -: • Figure2.2.Generalized Generalizedstratigraphic stratigraphiccolumn column(no (no Figure scale)for for lower lowerPaleozoic Paleozoicrocks rocksininthe thenorthern northernpart part scale) of the central midcontinent region. The Cambrian of the central midcontinent region. The Cambrian andOrdovician Ordoviciannomenclature nomenclatureisisthat thatused usedinin and southeastern Minnesota Minnesota and and Wisconsin, Wisconsin, the the southeastern Silurianfrom from eastern easternWisconsin Wisconsinand and northern northern Silurian Michigan,and and the the Devonian Devonianfrom from southernmost southernmost Michigan, Minnesotaand andnorthern northernIowa. Iowa. Minnesota Engadune Jde Group Jordan St Lawrence Franconia Ga (Wonewoc) Eau Claire and Bonneterre — . Mt. Simon E l (uatzose -sandstone sandstone sdtstone, shale (] Very Very fine fine s.s.,s.s., siltstone, shale (LoneRock) — (dashedwhere whereshaly) shaly) Carbonate(dashed Carbonate Norecord record No Unconfonnity Unconformity �others, others,1992; 1992;Mossier, Mossler,1992; 1992;Runkel, Runkel,1994). 1994).In Inaavery veryimportant importantand andwidely widelycited citedstudy study Dott Dottand andothers others(1986) (1986)examined examinedthe thetransition transitionfrom fromnonmarine nonmarinetotomarine marineenvironments environments recorded recordedin inquartzose quartzosesandstones, sandstones,and andprovided providedthe thefirst fmt set setof of criteria criteriafor foridentification identificationof of nonmarine facies.They described described an an early early Paleozoic Paleozoic terrestrial terrestrial setting setting with broad braided braided nonmarinefacies.They streams streamsand andeolian eoliansheet sheetand anderg ergsystems systemsthat that delivered delivered sand sand to to aa shallow shallowmarine marine environment environmentdominated dominatedby by small smallthree threedimensional dimensionaldunes. dunes.Dott Dottand andothers others(1986) (1986)stressed stressed the as the the lack lack of of vegetation, vegetation, between between early early Paleozoic Paleozoic depositional depositional the differences, dzfferences, such such as environments A environmentsand andthose those inferred inferredfor forboth both younger younger rocks rocks and and modem modemsettings. settings.A depositional depositional model model ofofaasimple, simple,storm-dominated, storm-dominated,texturally texturallygraded gradedshelf shelfwas wasproposed proposedby by Runkel Runkel and and others others(1998), (1998),and and isis noteworthy noteworthy in in its its similarity similari~to to models modelsbased basedon onboth both younger youngerrocks rocks and andmodem modemsystems. systems.Their Theirstudy studywas was essentially essentiallyaaregional-scale regional-scaleoutgrowth outgrowth of of the the excellent excellentoutcrop outcropwork workof of Charlie CharlieBell Belland andhis his students studentsfrom fromthe the University University of of Minnesota Minnesotain in the the 1950's. 1950's.Runkel Runkeland and others others(1998) (1998)suggested suggestedthat that early early Paleozoic Paleozoic depositional areanalogous analogousto to those thosedepicted depictedin inwell-known well-known depositionalprocesses processesand andfacies faciesdistribution distributionare models modelsof of the the Cretaceous Cretaceousinterior interior seaway and the modem Bering Bering Shelf. Shelf. The The thin widespread widespread siliciclastic chamcteristic of lower lower Paleozoic strata strata result from large largelateral lateralfacies facies siliciclasticunits units characteristic migrations relativesea sealevel. level. migrationswhich whichoccurred o c c m din inresponse responseto tocontinental-scale continental-scalechanges changesininrelative Taylors Falls Precambrian lava flow rrdges, (J,/ Mayor sand 0 — SILIcICLASTIC OFFSHORE SHELF — CARBONATEI — — — —(M0StIV — — SHELF — — — - — — — — — — o — — — Storm—t,anspolt of !° sand. suit. shale !rom shoretace — — 0 — — — — —— = — — - — — 0 — — — 0 — — — — — — Rudge : — — — — - — — — 'mmodks - Tempestltes- 01 0 0 00 — Depth 5Pm = -o — — — — 0 4OUI — -o 2O4O= I •.: 0 00 00 00 : 0 —— — .._- on Arch 0 —0 — — — — source sandstone Tudal - — — FLUVIAL& o . EOLIAN 0 SANDPLAIN sand transport by storms s.. — - Dome • — SHOREFACE 0 — ORE Figure Figure3.3.Conceptual Conceptual source from — — — — 0000 0000 0 0 0 0 (East) 0 depositional depositional model model of Late Late Cambrian Cambrianstorm-dominated, storm-dominated, texturally textxrailygraded gradedshelf. shelf. Quartzose Quartzosefmefme- to to coarsecoarsegrained gained sand sandaccumulated accumulatedin in nearshore nearshoreterresirial terrestrial and and shoreface shorefaceenvironments. environments.Finer Finer grained feldspathic grained,,feldspathic siiciclastic siliciclasticsediments sedimentsand and subtidal subtidalcarbonates carbonates accumulated accumulated in in deeper deeperwater water of the the offshoreshelf. offshoreshelf. Carbonate Carbonaterocks rocks within within the the lower lower Paleozoic Paleozoic sequence sequence have have historically historically been regarded regarded as as more more amenable amenableto to comparison comparisonwith with both both modem modem and and ancient ancientfacies facies models. models. Deposition Deposition occurred occurred in in environments environmentsthat thatrange m g efrom fromevaporitic, evaporitic,supratidal supratidalconditions conditionsfor forparts parts of of the the Prairie du Chien Chien Group Group(Smith (Smithand andothers, others,1993) 1993)to to subtidal subtidalsettings settingsin indepths depthsof of 100 100m mor or Prairie du more more for for parts parts of of units units such suchas asthe theDecorah DecorahShale Shale(Ludvigson (Ludvigsonand andothers, others,1996). 1996).Most Most investigations in scope scoperelative relativeto to the the great g m t lateral lateral extent extent of of these these units units and and investigationshave havebeen been local localin there aretoo too many many to tocite cite them them individually. individually. Ordovician Ordovician carbonate carbonatestrata strata of of the the Hollandale Hollandale thereare embayment embayment are are the the focus focus of of aa monograph monograph edited edited by by Sloan Sloan (1986). (1986). Silurian Siluriancarbonates carbonateson onthe the westem westem flank flankof of the the Michigan Michigan Basin Basin have have recently been studied studied by Harris Harris and and Waldhuetter Waldhuetter (1996). There are many excellent excellent studies studies of Ordovician through Devonian age strata strata in There are northern northem Iowa, Iowa, largely largely conducted conducted by the Iowa Geological Survey; the results can often be extrapolated several papers in Witzke and others, 1996) 1996) extrapolated to to Minnesota Minnesota and and Wisconsin Wisconsin (e.g. several Some Some regional regional scale scalestudies studies have have recently recently been been completed; completed;aa stratigraphic stmtigxaphicframework frameworkhas has been been developed developedfor for the the Prairie Fhkie du du Chien Chien Group Group from the Michigan basin to the Hollandale Hollandale embayment 1996; Barnes embayment (Smith (Smith and others, 1993, 1993,1996; Barnesand and others, others, 1996). 1996).Simo Simoand and others others (1997) are currently currently constructing constructingaa large large scale scale stratigraphic stratigraphic framework framework for for Ordovician Ordovician rocks rocks (1997) are of as identification identification of the the central centralmidcontinent midcontinentin in order order to to address address long-standing long-standing problems problems such such as of the controls responsible for the the apparently synchronous regional-scale changes from from "tropical" to %opicalV1 to "temperate" "temperate1'styles stylesof of carbonate carbonatedeposition. deposition. . 27 �NOTABLE FEATURES FEATURES AND AND LONGSTANDING LONGSTANDING PROBLEMS PROBLEMS NOTABLE LowerPaleozoic Paleozoicstrata strataininthe thecentral centralmidcontinent midcontinentregion regionare areamong amongthe thelongest longeststudied studied Lower sedimentary sedimentaryrocks rocksin in North North America. America. They Theyare arewell wellknown knownto togeologists geologistsoutside outsideof ofthe thearea area forseveral severalenigmatic enigmaticfeatures features(Dott (Dottand andByers, Byers,1980). 1980).Most Mostnotable notableisisthe theextreme extremetextural textural for andmineralogical mineralogicalmaturity maturityofofthe thefme fineto tocoarse-grained coarse-grained sandstones, sandstones,and andthe the sheet-like sheet-like and geometryofofthese theseand andother othersiliciclastic siliciclasticunits. units. The Theoverall overalldearth dearthofofshale shalehas haspuzzled puled geometry sedimentologists, sedimentologists,and andthe thefundamental fundamentalcontrols controlson onthe theepisodic episodicchange changefrom fromsiliciclasticsiliciclasticdominated dominatedto tocarbonate-dominated carbonate-dominatedsedimentation sedimentationremain remain poorly poorly understood. understood. Lastly, Lastly, the the presence, presence,position positionand andmagnitude magnitudeofofunconformities unconformitieshas hasbeen beendebated debatedfor fordecades. decades.The The remainderof ofthis thisabstract abstractsummarizes summarizesthe theprogress progressmade madeininunderstanding understandingthese theseenigmatic enigmatic remainder features featuressince sincethe theoverview overviewpublication publicationby byDott Dottand andByers Byers(1980) (1980)on onlower lowerPaleozoic Paleozoicstrata. strata. Sheet Sheetgeometry geometryAAlong-standing long-standingquestion questionhas hasbeen beenhow howsheet-like sheet-likesiliciclastic siliciclasticlayers layerswere were initially initiallydeposited depositedand andthen thenpreserved preservedacross acrosstens tensof ofthousands thousandsof ofsquare squarekilometers kilometersof ofthe the cratonic cratonicshelf. shelf.Most Mostworkers workershave haveattributed attributedthe theformation formationof ofsuch suchsheets sheetsto todepositional depositional processes aremarkedly markedlydifferent differentfrom fromthose thosedescribed describedfor formost most processesand andenvironments environmentsthat thatare younger youngerrocks rocksand andmodern modernsettings. settings.Lochman-Balk Lochman-Balk(1970) (1970)inferred inferred the the presence presence of of enormous kilometersperpendicular perpendiculartotothe the enormoustidal tidalflats flatsextending extendingwell wellover overtwo twohundred hundredkilometers shoreline. shoreline.Dott Dottand andByers Byers(1980) (1980)suggested suggestedthat that quartzose quartzosesand sandaggraded aggradedmore more or or less less vertically verticallyinto intoaasheet sheetunder underhigh-energy high-energy conditions conditions across across a vast shallow shallow sea. sea. The Themost most widely widelycited citedhypothesis hypothesisisisone onewhich whichattributes attributesthe theorigin originof ofquartzose quartzosesandstone sandstonesheets sheetstoto fluvial fluvialand andeolian eolianprocesses processesthat thatdispersed dispersedsand sandacross acrossaa vegetation vegetation free freelandscape landscapeprior priorto to marine marinereworking reworkingduring duringaatransgression bansgression(Dott (Dottand andothers others1986). 1986).Recent Recentstudies, studies,however, however, have havedemonstrated demonstratedthat thatsome somequartzose quartzosesheets sheetswere weredeposited depositedentirely entirelywithin withinthe themarine marine realm realmunder underregressive regressiveconditions conditions(e.g. (e.g.Runkel, Runkel, 1994, 1994,Hughes Hughes and and Hesselbo, Hesselbo,1997, 1997,Runkel Runkel and and others others1998), 1998),and andthat thatthe thedepositional depositionalprocesses processes responsible responsible for for the the dispersal dispersalof of siliciclastic siliciclasticsediments sedimentswere were similar similar totothose thoseoperating operatingduring duringthe the deposition deposition of of ancient ancient sandstones that are not sheet-like. sheet-like. sandstones The Thelateral lateralpersistence persistenceand andsheet-like sheet-likegeometry geometryof oflower lowerPaleozoic Paleozoicsiliciclastic siliciclasticunits units probably probablyreflect reflectthe theroles rolesof ofbasin basinphysiography physiographyand andtectonics tectonicsin in controlling controllingthe the lithostratigraphic lithostratigmphicarchitecture, architecture,rather ratherthan thanthe theexistence existenceof ofatypical atypicalsedimentary sedimentary environments. environments.Deposition Depositionwas was characterized characterized by a continuous continuous and abundant supply of sediment sedimenttotoaarelatively relativelystable, stable,nearly nearlyfiat flatbasin basin with with aa slow, slow,uniform uniformrate rateof ofsubsidence. subsidence. Individual (e.g.Fig. Fig.3) Individual sheets sheetsof of siliciclastic siliciclasticsediment sediment were were deposited when whendiscrete discretefacies facies(e.g. 3) migrated migratedgreat greatdistances distancesduring duringchanges changesininsea sealevel. level.Deep Deepincision incisionof ofthe theindividual individualsheets sheets during duringepisodes episodesof of subaerial subaerialexposure exposuredid did not not occur, occur, resulting resulting in in more more or or less less uniform uniform preservation. preservation. Textural Texturalmaturity maturitvof ofsandstones sandstonesThe Theextreme extremetextural textural and and mineralogical mineralogical maturity maturity of of the the finefineto to coarsecoarse-grained grainedsandstone sandstoneunits, units, such such as as the the St St Peter Sandstone, Sandstone, may maybe bethe thebest bestknown known and andlongest longeststudied studiedfeature featurein in the the lower lowerPaleozoic Paleozoicstrata strataof ofthe thecentral centralmidcontinent. midcontinent.The The sandstones are moderately moderately to to well wellrounded. rounded. sandstonescontain containmore morethan than 98% 98%quartz quartzand andmost most grains grainsare Such Suchtextural texturaland andcompositional compositionalmaturity maturitycould couldnot not have have been been achieved achievedsolely solelyby by fluvial fluvialand and marine marine abrasion abrasioneven evenover overtransport transportdistances distancesof of hundreds hundreds of of kilometers kilometersifif the the grains grainswere were derived derived directly directly from from crystalline source rocks. Rare Rare grains grains with abraded overgrowths are are reworked reworkedfrom fromolder oldersedimentary sedimentaryrocks, rocks,but butthe thevolumetric volumetricsignificance significanceof of such suchrecycling recyclingisis uncertain uncertain and and aa source source of of suitable suitable sedimentary rock has never been identified. Odom Odom (1975, (1975, 1978) 1978)conducted conductedthe the most mostcomprehensive comprehensivemineralogical mineralogicalstudy studyof of lower lowerPaleozoic Paleozoic sandstones; sandstones;he henoted noted that thatthe thevery very fme finegrained grainedfraction fractionis is feldspathic, feldspathic,whereas whereas the the fine fine to to coarse-grained coarse-grainedfraction fractioncontains containsmore more than than 98% 98%quartz quartz (with (with the exception exception of some some lower lower Mt Simon Simon Sandstone Sandstonebeds). beds). He He suggested suggested that that aa long history of abrasion in a marine setting 28 �could account account for for both the maturity of the quartzose grains and the reduction in size of feldspar first to to clearly clearly identi@ identify the thepresence presence of of feldspar grains. Dott and others (1986) were the fmt substantial eolian deposits quartzose sandstones, and they suggested that deposits within some quarkose eolian abrasion abrasion could contribute contribute to the textural and mineralogic features features described described by Odom Odom (1975, 1978). 1978). Lastly, Lastly,chemical chemicalweathering weatheringin inthe thesource sourcearea area must mustbe be taken taken into into consideration (Morey, consideration (Morey, 1972). 1972). Odom Odom (1975, (1975, 1978) 1978)noted that the the very very fine fine grained, grained, feldspathic sandstones are arerich rich in in K-feldspar K-feldspar but have have only a "trace" "trace" amount of plagioclase grains, even though though plagioclase plagioclase was presumably dominant dominant in in the the source source area area of of the the Precambrian shield. Selective plagioclase grains grains from from the the sandstone Precambrian Selective diagenetic leaching of plagioclase chemical weathering weathering probably preferentially dissolved was discounted by Odom. Thus, chemical plagioclase crystals and reduced reduced the thesize sizeand and amount amount of of other other relatively unstable unstable minerals minerals prior prior to to mechanical mechanicalabrasion abrasionduring during transport transport to to the the shoreline. shoreline. While each of the processes processes described above above could have been responsible responsible in part for for the the mineralogic and textural attributes of lower Paleozoic sandstones, they do not entirely mineralogic that virtually virtually all all fmeaccount for the compositional record that appears to indicate that fine- to coarse-grained sand sand was was exceptionally exceptionally mature mature when itit arrived arrived to to the the early early Paleozoic Paleozoic shoreline. shoreline. Fine- to coarse-grained coarse-grained immature immature sand would have almost certainly been abrasion model modelof ofOdom Odom(1975) (1975)were wereaccurate. accurate. It It is difficult difficult deposited locally if the marine abmion in which whichall all sand abrasion sand is subjected to prolonged eolian abrasion to reconstruct a terrestrial setting in (Dott and others others 1986) 1986) prior to deposition deposition in a marine marine environment. centmlmidcontinent midcontinent region region are are noted noted for for aa Dearth of Shale Shale Lower LowerPaleozoic Paleozoicrocks rocksof of the thecentral dearth of shale shale compared compared to other shallow marine deposits. Two Twovery very different d i f f e ~ nhypotheses hypotheses t have been proposed to account account for this dearth of shale. In a "marine bypassing" model, were delivered to the Pettijohn and others (1973) suggested that clay- and silt-sized particles were shoreline, shoreline, but subsequently subsequently carried carried in suspension suspension by repeated storms across the shallow shallow shelf before final burial in basinward areas. In contrast, Dalrymple Dairymple and others (1985) suggested that strong kilometers strongwinds windsblew blewclay clayand andsilt siltparticles particleshundreds hundredsto to thousands thousands of of kilometers offshore, to be ultimately ultimately deposited deposited in the outer detrital belt (Fig 1). Recent investigations investigations of Upper Cambrian siliciclastic siliciclastic strata support the marine bypassing well known known dearth of shale isis model of Pettijohn and others (1973), demonstrating that the well of the the outcrop outcrop belt on the flanks of the Wisconsin dome and arch characteristic only of (McKay, 1988, Wisconsin arch, subsurface 1988, Runkel and others, 1998). Basinward of the Wisconsin records from Minnesota Minnesota and and Iowa Iowa show show that facies facies dominated by shale shale and and siltstone siltstoneare are equivalents to the shale-poor offshore equivalents shale-poor common. The The shale shale and and siltstone siltstone dominated facies are offshore sandstone facies of the sandstone theoutcrop outcropbelt, belt, and and their their geographic geographic position changed through time in response outcrop belt has response to to changes changes in in the the position position of the storm-fairweather storm-fairweather wave base. The outcrop a dearth of shale shale simply because the depositional depositional record is dominated by highstand shoreface shoreface base. This facies deposited above fairweather wave base. This stratigraphic stratigraphic and sedimentologic sedimentologic attribute is not unique attribute unique to the the lower lower Paleozoic Paleozoic rocks of the central central midcontinent midcontinentregion-it region-it is is landward margins margins of of common in many younger wave-dominated wave-dominated sequences along the landward shale-free early earlyPaleozoic Paleozoicepeiric epeiricsea seaisis a deeply individual basins. The notion of a shale-free entrenched idea ideathat thatsimply simply reflects reflectsthe thebias biasof ofthe theoutcrop outcropbelt. belt. The The dearth dearth of of shale shale in in lower Paleozoic Paleozoic rocks should should be removed from the list of enigmatic enigmatic features unless the scarcity scarcity can can be be demonstrated demonstratedto to exist exist on on aa scale scale larger larger than than that that of of the the outcrop outcropbelt. belt. Siliciclastic-Carbonate Thefundamental fundamentalcontrols controlson on the the transition transition from from nearshore nearshore Siliciclastic-Carbonatecycles The siliciclasticsiliciclastic- to carbonate-dominated carbonate-dominated deposition deposition have have never never been been satisfactorily satisfactorilyunderstood. understood. the For example, example, in Early Ordovician time carbonate deposition apparently dominated across the entire region even in the shallowest water water conditions conditions (Smith and others 1993). Both older Sandstone) and younger (St Peter Sandstone) shallow marine environments were (Jordan Sandstone) dominated dominated by siliciclastics. siliciclastics. Only speculative speculative and vague hypotheses have been suggested suggested to to account account for for such such fundamental fundamental changes. For example, Adams (1978) suggested that the Early Ordovician Ordovician change change in in depositional depositionalstyles styles may have have been in response response to drowning drowning of of the the 29 �siliciclastic siliciclastic source source area by a shallow sea or the result of siliciclastics being "deflected" "deflected" to another l y Paleozoic carbonate-dominated systems another region. b Early systems developed developed following following extended extended highsea sealevel level(Smith (Smithand andothers, others,1993) 1993)which which suggests suggeststhat that the the siliciclastic siliciclastic periods of high source area may have been covered with a blanket of carbonate rocks. rocks. The The spread of certain source forms of terrestrial life such as bacterial encrustation, and later the development development of vascular vascular plants, may may have have also also reduced reduced siliciclastic siliciclasticinput. input. Crvntic of lower lower Paleozoic Paleozoic strata strata of of the the central central C w t i c unconformities Previous investigations of midcontinent region have also been hindered by an inability to recognize midcontinent recognize unconformities. unconformities. The are fairly fairly well well The unconformities unconformities bounding bounding the the major major sequences sequencesof of Sloss Sloss (1963) (1963) are established within the strata of the outcrop belt. The presence and position of "lesser" "lesser" unconformities, within siliciclastic siliciclasticunits, have have been aa matter matter of of considerable considerable unconformities,especially especially within relations and interpreted depositional histories indicate that such debate. Stratigraphic Stratigraphic relations unconformities "should" "should" be present. However, However, little or no evidence evidence for for regionally regionally extensive extensive subaerial erosion has been documented. Such sequence-bounding unconformities unconformities are are they are are contained containedwithin withincoarse coarsesiliciclastics siiciclastics because because they they difficult to recognize where they are texturally and mineralogically similar, similar, and because because separate quartzose quartzose sandstones sandstones that are that occurred occurred on they are relatively flat-reflecting erosion that on aa loose, loose, sandy sandy substrate substrate along along aa low, uniform gradient, gradient, and in a nonvegetated terrestrial terrestrial environment. environment. Furthermore, Furthermore, the the ultra ultra development of a distinctive mature mineral composition composition of the exposed substrate substrate inhibits inhibits development distinctive weathering profile. Recent work has shown some promise for identifying subtle subaerial surfaces of of regional regional erosion. Recognition Recognition of cryptic unconformities requires interpretation of stratigraphic at individual outcrops stratigraphic relations in conjunction with physical evidence collected at and high resolution resolution biostratigraphic biostratigraphic data. Smith and others (1993) interpreted local deposits of silica cement cement in uppermost Cambrian Cambrian and Lower Ordovician Ordovician strata strata as subaerially subaerially formed formed silcrete. Runkel fronton Runkeland andothers others(1998) (1998)suggested suggestedthat that cryptic cryptic unconformities unconformities within the Ironton and at at the the top of the Jordan Jordan Sandstone Sandstoneand andcan canbe be identified only and Galesville Sandstones and the coarsest coarsest bed bed within within nearshore nearshore by overlying lag deposits. 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A., A., and andDay, Day,J., J., Formation, Upper Upper Mississippi Mississippi Valley, in Witzke, eds., eds., Paleozoic Paleozoic Sequence SequenceStratigraphy: Stratigraphy: Views Views from from the the North North American American Craton:Geological Craton:Geological Society Societyof of America AmericaSpecial SpecialPaper Paper306, 306,p.67-86. p.67-86. McKay, McKay, R. R. M., M., 1988, 1988,Stratigraphy Stratigraphyand andlithofacies lithofaciesof of the the Dresbachian Dresbachian(Upper (UpperCambrian) Cambrian)Eau Eau Claire Ludvigson,G. G. A., A., and and Bunker Bunker B. B. Claire Formation Formation in in the the subsurface subsurface of eastern Iowa: in Ludvigson, A., A., eds., eds., New New perspectives perspectives on on the the Paleozoic Paleozoic history history of the Upper Mississippi Mississippi Valley, Valley, Guidebook Guidebookfor forthe the18th 18thField FieldConference Conferenceof of the the Great GreatLakes Lakessection, section,Society Societyof ofEconomic Economic Paleontologists Paleontologistsand andMineralogists, Mineralogists,p. p. 33-53. 33-53. Morey, Sims,P. P.K., K., and andMorey, Morey,G. G. B., B., eds., eds., Morey, G. G. B., B., 1972, 1972,Pre-Mt Pre-Mt Simon Simon Regolith, in Sims, Geology Geology of of Minnesota: Minnesota: A A Centennial CentennialVolume: Volume: Minnesota Minnesota Geological GeologicalSurvey, Survey,p. p. 506-508. 506-508. Mossler, Mossier,J.J. H., H., 1992, 1992,Sedimentary Sedimentaryrocks rocks of of Dresbachian Dresbachian age age (Late (Late Cambrian), Cambrian), Hollandale Hollandale Embayment, Embayment,southeastern southeasternMinnesota: Minnesota:Minnesota Minnesota Geological Geological Survey SurveyReport Reportof of Investigations 71 p. 40,71 p. Investigations40, Nelson, Nelson, C. C. A., A., 1956, 1956,Upper UpperCroixan Croixanstratigraphy, stratigraphy,Upper UpperMississippi MississippiValley: Valley: Geological Geological Society Society of of America America Bulletin, Bulletin,v. v. 67, 67,p. p. 165-183. 165-183. 31 �Odom, I. E., 1975, 1975, Feldspar-grain size relations in Cambrian arenites, Upper Mississippi Valley: Journal Journal of Sedimentary Petrology, v. 45, no. 3, p. 636-650. Odom I. E. 1978, 1978,Mineralogy Mineralogyof of Cambrian Cambriansandstones, sandstones, Upper Upper Mississippi Mississippi Valley: Wisconsin Geological and Natural History Survey Field Trip Guidebook 3, p. 23-45. Ostrom, M. E., 1964, Ostrom, 1964, Pre-Cincinnatian Pre-Cincinnatian Paleozoic cyclic sediments in the Upper Mississippi 1-398. Valley: A A discussion: discussion: Kansas KansasGeological GeologicalSurvey SurveyBulletin Bulletin169, 169,p.p.38 381-398. Ostrom, M. E., 1970, Ostrom, 1970, Sedimentation Sedimentation cycles cycles in Lower Lower Paleozoic Paleozoic rocks of western western Wisconsin: Wisconsin: Wisconsin Geological Geological and and Natural History History Survey Survey Information Information Circular Circular11, 11,p. p. 10-34. 10-34. Palmer, A. R., 1960, 1960,Some Some aspects aspects of the the early early Upper Upper Cambrian Cambrian stratigraphy stratigraphy of of White White Pine Pine County Geology of of east east Central Central Nevada: Intermountain Intermountain County ,, Nevada, and Vicinity, in Geology Association 1lth Annual Field Conference, Conference, p. 53-58. 53-58. Association of Petroleum Petroleum Geologists Geologists Guidebook Guidebook 11th Pettijohn, F. J., Potter, Potter, P. E., E., and and Siever, Siever, R., R., 1973, 1973,Sand Sand and and Sandstone:New Sandstone:New York, York, Springer-Verlag, 618p. 6 18p. Runkel, A. C., 1994, 1994,Deposition Deposition of the uppermost uppermost Cambrian Cambrian (Croixan) (Croixan) Jordan Sandstone, Sandstone, and and the the nature nature of of the the Cambrian-Ordovician Cambrian-Ordovician boundary boundary in in the the Upper Upper Mississippi MississippiValley: Valley: Geological Society Society of America America Bulletin, Bulletin, v. 106, 106, p. 492-506. 492-506. Runkel, A. C., McKay McKayR. R.M., M., and andPalmer, Palmer, A. A. R.,1998, R.,1998, Origin Origin of a classic cratonic sheet sandstone:Stratigraphy across the Sauk 11-Sauk Il-Sauk I11 III boundary in the Upper Mississippi sandstone:Stratigraphy Valley: Geological Geological Society Society of America Bulletin Bulletin v. 110, 110, no. 2, p.188-210 Sargent, M. L., 1991, 1991, Sauk Sequence: Cambrian System through Lower Ordovician Series, F., and Eidel, J. J., J., eds., Interior cratonic in Leighton, M. W., Kolata, D. R., Oltz, D. F., basins: American p.75-86. American Association Association of Petroleum Petroleum Geologists Geologists Memoir 51, p.75-86. P., Byers, C. W., Dott, Doft, R. R. H., H., Jr., and Saylor, B., 1997, 1997, Simo, J. A., Choi, L, Freiberg, P., Sedimentology, Sequence Sedimentology, Sequence Stratigraphy, Stratigraphy, and Paleoceanography of the Middle Ordovician of eastern Wisconsin, Wisconsin, in, Mudrey, M. G., ed, Guide to Field trips in Wisconsin Wisconsin and and adjacent areas areas of Minnesota: Wisconsin Geological Geological and and Natural History History Survey, Survey,p. p. 9595114. 114. Sloan, R. E., ed, 1986, 1986, Middle Middle and Late Ordovician Ordovician lithostratigraphy lithostratigraphy of the Upper Upper 232p. 35,232~. Mississippi Valley: Minnesota Minnesota Geological Geological Survey Survey report report of Investigations Investigations 35, Sloss, L. L., 1963, 1963, Sequences Sequences in the cratonic interior of North America: Geological Society of America Bulletin, America Bulletin, v. v. 74, 74,p.p.93-1 93-114. 14. in Phanerozoic Phanerozoic time, time, in in Sloss, 1988, Tectonic evolution of the craton in Sloss, L.L., ed., Sloss, L. L., 1988, Sedimentary American craton, craton, United United States: States: The The Geology of North Sedimentarycover—North cover-North American America, DNAG America, DNAG Volume Volume D-2, p. 25-51. 25-5 1. Smith, G. L., Byers, C. W., and Dott, R. H., Jr., 1993, 1993, Sequence Sequence stratigraphy of the Lower Ordovician Prairie in the the Michigan MichiganBasin: Basin: Ordovician Prairie du du Chien Chien Group Group on on the the Wisconsin Wisconsin Arch Arch and and in American Association Association of of Petroleum Petroleum Geologists Geologists Bulletin, Bulletin, v. 77, 77, p. 49-67. Smith, G. L., Byers, C. W., and Dott, R. H., Jr., 1996, 1996, Sequence stratigraphy of the Prairie du Chien Group, Group, Lower Lower Ordovician, Midcontinent, USA, in, Witzke, B.J., Ludvigson, Ludvigson, 0. G.A., A., and andDay, Day,J., J.,eds., eds.,Paleozoic PaleozoicSequence SequenceStratigraphy:Views Stratigraphy:Views from from the the North North American American Craton: Geological Geological Society Society of America Special Special Paper 306, p.23-34. Witzke, B. J., Ludvigson, Ludvigson, G. A., and and Day, Day, J., 1991, 1991, eds., eds., Paleozoic Paleozoic Sequence Sequence Stratigraphy:Views from the North American Craton: Geological Society of America 446p. Special Paper 306, 306,446~. 32 �MODELS FOR INTERPRETING INTERPRETING THE THE QUATERNARY QUATERNARY HISTORY OF THE THE LAKE SUPERIOR SUPERIOR REGION PATTERSON, PATTERSON, Carrie Carrie J., Minnesota Minnesota Geological GeologicalSurvey Survey The interpretation interpretation of the Quaternaiy Quaternary glacial and interglacial history for the Lake Superior as aa result result of of two twonew newmodels. models. Firstly, oxygen isotope region is in the midst of change as data have provided evidence leading to the development of a model that indicates a large during the the last lasttwo twomillion millionyears. years. Secondly, a new number of glaciations occurred during mechanical model for the dynamics of ice flow has been developed. In In order orderto to integrate integrate the new models into into our our interpretations, interpretations,aa broad broad geographic geographicperspective perspectiveisis required. required. Rather than provide a summary of the history of the investigations in the Lake Superior in the the context contextof ofthese thesenew newmodels. models. Even ifif region, I will present relevant observations in to look beyond the confines the models are eventually eventually replaced, they will have forced us to of the Upper Midwest Midwest and and the the traditional traditional glacial glacial interpretations. interpretations. Number of Number of glaciations glaciations Evidence indicates indicates that the number of Quaternary glaciations is significantly greater than the turn turn of the century the four-fold glacial chronology devised for North America around the which included the Wisconsinan, Illinoian, Kansan and Nebraskan glaciations (Flint, 1957). The The new new precision precisionisis based based on on nonterrestrial nonterrestrial records records of global global ice ice volume, record of of ocean ocean carbonates. carbonates. During glaciation, 160 is is including the oxygen-isotope record the ice ice sheets, enriching enriching the preferentially evaporated evaporated from the oceans and is stored in the Fluctuationsin in the the amount amount of 160 160 and 180 180 can be measured measured in glacial oceans in 180. Fluctuations used to to determine global ocean sediments sediments and ice cores (Shakleton and others, 1984) and used of oxygenice volume. Based Based on on these these calculations calculations for for global ice volumes, a series of represent isotope stages has been identified. Even Even numbered oxygen-isotopes stages represent periods. There glaciations, and odd numbers represent interglacial periods. There were were 40 40 glaciallinterglacial oscillations volumes between between 2.4 2.4 Ma Ma glacialhterglacial oscillations involving moderate global ice volumes and .9 Ma, and andthere therewere were 22 22 oscillations oscillations involving involvinggreater greaterice icevolumes volumes between between .9 .9 Ma Ma al., 1984). For the most recent 11 glaciations, oxygenand the present (Shackleton et al., 6, 12 2,6, 12 and 16 16 show the greatest ice volumes, possibly possibly corresponding correspondingto to isotope stages 2, traditional four-fold four-fold record record of terrestrial terrestrial glaciations glaciations in in North America. America. that the the most most extensive Another feature of the traditional four-fold record of glaciations is that glaciation formerly formerly recognized, recognized, (the (the Nebraskan) Nebraskan) was was also also interpreted interpreted to to be be the the oldest. oldest. Successively Wisconsinan) were Successively less extensive extensive glaciations, (the Kansan, Illinoian and Wisconsinan) younger (Flint, (Flint, 1957). 1957). This chronology is probably probably an interpreted to be successively younger of terrestrial terrestrial glacial glacial sediments. sediments. While there were clearly more artifact of the preservation of than four glacial periods during the past 0.9 my, each glacial advance obscures, either by of previous, previous, less less extensive extensiveadvances. advances. If, for example, there there erosion or burial, the record of random distance, probability probability were ten successive successive glacial advances, each advancing some random the surface and the oldest anaylsis suggests suggests that only three glacial limits will survive at the surviving advance advance will be the most extensive (Gibbons and others, 1984). ItIt isis therefore therefore 11 most recent glaciations we have historically recognized only not surprising surprising that of the 11 four glacial limits limits at at the the surface. surface. i r t half of the Pleistocene did The oxygen isotope record shows that glaciations in the ffirst (Shaldeton and others, not have as great great a global ice volume as those in the latter half (Shakleton 1984). However, However, these theseearly early advances advances of of ice ice were were apparently apparently extensive extensive enough enough in in North North 33 �America to to reach reach Iowa Iowa and and Nebraska Nebraska (Hallberg, (Hallberg, 1986) 1986)and and the the foothills foothillsof of the the Canadian Canadian America Rockies (Kiassen, (Klassen, 1989). 1989). The Thesediment sedimentof ofthese theseearly earlyadvances advancesmay may be be preserved preserved in in Rockies Minnesota (e.g. (e.g. Meyer, Meyer, 1997; 1997;Patterson, Patterson, 1997) 1997)and and in in Canada Canadain in the the subsurface subsurface(e.g. (e.g. Minnesota Klassen, 1989) 1989)in in areas areasof of net net glacial glacialdeposition, deposition, but but the the record record is is discontinuous discontinuousand and Kiassen, localized localized in in deep, deep, preglacial preglacialvalleys. valleys. Discontinuous,subsurface subsurfaceglacial glacial sediment sediment is is difficult difficultto to place place in in aa stratigraphic stratigraphic Discontinuous, framework because: (1) (1)absolute absolutedating datingof of the theunits units isis difficult; difficult;(2) (2) till till of of different differentglacial glacial framework terranetraversed traversedby by the the periods isis lithologically lithologicallyand andtexturally texturally similar similarifif the the source sourceterrane periods glacier (3)although althoughtill till may may change changecomposition compositiongradually graduallywith withdistance distanceinin glacierisisthe thesame; same;(3) the the ice-flow ice-flow direction, direction,isolated isolatedexposures exposuresof of till till may may be be dissimilar dissimilarenough enoughto toprevent prevent correlation. correlation. Radiocarbon Radiocarbondating datingof oforganic organicremains remainsisis only only useful useful for for Wisconsinan-age Wisconsinan-age deposits scattered predeposits because because of the limitations of the half life of 14C. A few dates from scattered Wisconsinan Wisconsinansamples sampleshave havebeen been secured securedusing using vertebrate vertebratepaleontology paleontology (e.g. (e.g.Klassen, Klassen, 1989), 1989), dating of volcanic ash present in the glacial glacial sediment (summarized (summarized in in Richmond Richmond and 1986),studies studiesof of remnant remnant magnetization magnetizationin in till till and andlake lakesediment sediment(e.g. (e.g. and Fullerton, Fullerton,1986), Baker Baker and and others, others, 1983), 1983),and and cosmosgenic cosmosgenic isotope isotope age age estimates estimates of of striated striatedrock rock surfaces surfaces (Bierman (Bierman and and others, others,1998). 1998). Owing Owingto to the thedifferent differentsubstrates substratesover overwhich whichthe theice iceflowed, flowed,ititisispossible possibleto todistinguish distinguish tills tills using using matrix matrix color, color,texture texture and and mineralogy, and clast lithology. During Duringthe theLate Late Wisconsinan, Wisconsinan,Minnesota Minnesotawas wasnearly nearlyequidistant equidistantfrom from the the two twomajor majorice iceaccumulation accumulation centers centersof of the theLaurentide Laurentideice icesheet sheetand andreceived received ice icefrom fromboth both (Dyke (Dykeand andPrest, Prest,1986). 1986). Minnesota's Minnesota'sunique uniqueposition position has hasfacilitated facilitatedprovenance provenancestudies studiesto to determine determineice-flow ice-flow paths paths and and source sourceareas. areas. The Theglacial glacialstratigraphy stratigraphyof ofCanada Canadaand andMinnesota Minnesota(Fulton, (Fulton, 1989; 1989; Meyer, Meyer,1997) 1997)indicate indicatethat thatice icesheets sheetshad had similar similargeometries geometriesthroughout throughoutthe theQuaternary. Quaternary. At At least leastfive fiveice icelobes lobesadvanced advancedinto intoMinnesota Minnesotaduring duringoxygen-isotope oxygen-isotopestage stage22(Late (Late Wisconsinan). Wisconsinan). Many Manyof ofthese theselobes lobeshad had multiple multiple readvances. During Duringadvance advanceeach eachlobe lobe had had the the potential potentialto toerode erodeolder oldersediment sedimentand androck, rock, and andto to deposit depositits itsown ownglacial glacial sediment. sediment.Therefore, Therefore,aasingle singleglacial glacialperiod periodmay maybe berepresented representedby by ten's ten'sof of compositionally -each each compositionallyand andtexturally texturallydifferent, different,incompletely incompletelypreserved preserved glacial glacialunits units— having having several severaldepositional depositionalfacies. facies. Interpretation Interpretationof of the themost mostrecent recentadvances advancesisismost most straightforward straightforwardbecause becausethe thedeposits deposits are are continuous, continuous,and and the the associated associated landforms are well preserved. For Forthis thisreason, reason, research research in in Minnesota Minnesota and and neighboring neighboring states states has historically focused of the activity of ice ice lobes lobesduring during the the Late LateWisconsinan Wisconsinan(for (forregional regional summaries summariessee seeWright, Wright,1972; 1972;Clayton Clayton and and Moran, Moran, 1982). 1982). Dynamics Dynamicsof ofice iceflow flow During 12 and Duringoxygen-isotope oxygen-isotopestage stage22(Late (LateWisconsinan), Wisconsinan),and andprobably probably during duringstages stages6,6,12 and 16 an ice ice sheet sheet that that extended extended 16 (all (all pre-Late pre-Late Wisconsinan), Wisconsinan),Minnesota Minnesota was was marginal marginal to to an across across most most of of Canada. Canada. Minnesota Minnesotaand andthe theGreat GreatLakes Lakesregion regionwere wereaffected affectedmainly mainlyby by thin, thin, dynamic dynamicice ice lobes lobes that that advanced advanced beyond the main body of the ice sheet. Much Much effort efforthas has been been made madeto tocorrelate correlatethe theadvances advancesof of these theselobes lobes(Clayton (Claytonand andMoran, Moran,1982; 1982; Mickelson Mickelsonand andothers, others,1983) 1983)but butitithas hasbecome becomeapparent apparentthat thatthey they were werenot notsynchronous synchronous on on aa time time scale scaleof of hundreds hundreds to to thousands thousands of of years. Movement Movementof ofthe theice icelobes lobesisis ultimately ultimatelydriven drivenby by the theoverall overallmass massbalance balanceof of the theice icesheet, sheet,which whichisiscontrolled controlledby by climate. climate.Ice Icelobes, lobes,however, however,respond respondquickly quicklytotochanges changesininmass massbalance balanceand andbed bed 34 �conditions of their their respective respective icesheds and may therefore appear to be out of phase with conditions nearby nearby lobes lobesand andregional regionalclimate. climate. Because km Because the the ice icelobes lobeswere werecomparatively comparativelythin—decreasing thin-decreasing from fromapproximately approximately11km where they they left leftthe the ice ice sheet— sheet- exisiting exisiting structural structural and and alluvial alluvial lowlands lowlands controlled controlled the where direction of of ice ice flow. flow. These Theselowlands lowlandswere weredeepened deepened even even more more owing to the enhanced enhanced direction glacial erosion erosion resulting resulting from fast, focused flow of the The Great Great Lakes are well glacial the ice. ice. The known examples examplesof of basins basins that that controlled controlled the flow flow of lobes; lobes; others others include include Great Great Bear known MacKenzie, Lake Lake Lake in in the the Northwest Northwest Territories, Territories, Great Great Slave Slave Lake in the District of MacKenzie, Lake Athabasca, on on the the Alberta-Saskatchewan border, Reindeer Reindeer Lake Lake in Saskatchewan, Saskatchewan, and and Athabasca, Lakes Winnipegosisin inManitoba. Manitoba. Lakes Winnipeg Winnipeg and andWinnipegosis Evidenceindicates indicatesthat that the the development development of of ice ice lobes (or (or 'outlet lobes') may be the result result Evidence of of ice ice streams streams(Patterson, (Patterson,1997). 1997).Ice Iceflow flowhundreds hundredsof ofkm kmup-ice up-icefrom fromthe theoutlet outletlobes lobes may may begin begin to toconverge convergeinto intoaanarrow, narrow,fast-moving fast-movingstreams streamsof ofice ice(Dyke (Dykeand andPrest, Prest,1986; 1986; Fulton, Fulton,1989; 1989;Thorliefsson Thorliefssonand and Kristjansson Kristjansson 1993; 1993; Fulton, 1995). The The nature nature and and distributionof of glacial glacialsediment sedimentand andlandforms landformsimplies impliesthat thatice iceflow flowwas wasmuch muchdifferent differentinin distribution thesenarrow narrowconvergent convergentzones. zones.Till Tillassociated associatedwith withice icestreams streamsisismore moredistally distallyderived, derived, these homogenous, homogenous, traceable traceablefor for hundreds hundreds of of km, and and typically has a level-to-streamlined level-to-streamlined surface surfaceexpression. expression.Tills Tillsdeposited depositedoutside outsidethese thesenarrow narrowconvergent convergentzones zonesare areusually usually thin thinand andlocally locallyderived. derived. are based based on on the the study study of of modem modem ice ice Modelsfor forthe themechanics mechanicsof of ice icemovement movementthat that are Models sheets (Fowler and Johnson, 1995) predict that slow, uniform flow of ice is unstable and sheets (Fowler and Johnson, 1995) thereforeunlikely. unlikely.What Whatisispredicted predictedand andobserved, observed,by bycontrast, contrast,isisaabimodal bimodalstyle styleofofice ice therefore flow, (km/yr)moving movingwithin within slower slower ice ice (cm/yr). (cdyr). The Thelocation locationofofice ice flow,with withfast fastice icestreams streams(km/yr) streams streamsappears appearstotochange changeover overtime, time,but butisisinfluenced influencedby bybed bedtopography topographyand and hydrogeology. Ice Icestreams streamsand andtheir theiroutlet outletlobes lobesare arethe themajor majordischarge dischargeareas areasfor foran anice ice hydrogeology. sheet, sheet,and andtheir theirdevelopment developmentisislargely largely aa function function of of subglacial subglacialwater. Ice Icestreams streamsdraw draw down downthe theice icemass massin inthe theice iceaccumulation accumulationcenters. centers. Ice-lobe Ice-lobeadvances advancestherefore thereforerepresent represent aa redistribution redistributionof ofice, ice,and andmay may actually actually signal signalthe the overall overall decay decay of the the ice ice sheet sheet rather rather than thanan anincrease increaseininvolume volumeofofthe theice icesheet. sheet. The LateWisconsinan Wisconsinan Laurentide Laurentideice ice sheet sheet indicates indicates that that in in the the Thedeglacial deglacialrecord recordof ofthe theLate areas areasof of continuous continuousice icecover coverin inCanada, Canada,ice ice streams streamsdeveloped developed within within the the ice ice sheet sheet and and fed fedthe theice icelobes lobesthat thatmoved movedthrough through the the Great Great Lakes Lakes basins basins into into the the upper upper Midwest Midwest (Dyke Hicockand andDreimanis, Dreimanis,1992; 1992;Thorleifson Thorleifsonand andKristjansson, Kristjansson, (Dykeand andPrest, Prest,1986; 1986;Hicock 1993). 1993).The Theice icestreams streamswere wereactive activethroughout throughoutthe theretreat retreatof ofthe theice iceacross acrossCanada Canadaas as documented documentedin inthe thepattern patternof of moraines moraines(Dyke (Dykeand and Prest, Prest, 1986; 1986;Fulton, Fulton, 1995). 1995).ItItisis unclear growthbecause because the theeffects effectsof of unclearififice icestreams streamswere werealso alsoimportant importantduring duringice-sheet ice-sheetgrowth subglacial subglacialwater waterare aredifficult difficultto toascertain. ascertain.This Thismodel modelofofice iceflow flowcan canbe becautiously cautiously extended extendedto toearlier earlierglaciations, glaciations,bearing bearingininmind mindthat thatbed bedconditions conditionscould couldhave havebeen beenvery very different differentfrom fromthose thoseof ofmore morerecent recentevents. events. The Theadvantages advantagesofofstudying studyingthe thegeological geologicalrecord recordofofQuaternary Quaternaryglaciations glaciationsinclude: include:(1) (1) the (2) the the therelatively relativelyexcellent excellentpreservation, preservation, continuity continuity and and accessibility accessibilityof of the the deposits; deposits; (2) location locationof ofthe thedeposits depositswithin withinaawell wellestablished established paleogeographic, paleogeographic, paleomagnetic, paleomagnetic,and and tectonic (4)records recordsfor forfloral floraland andfaunal faunalsuccession successionand andpluvial pluviallake-level lake-level tectonicsetting; setting;(4) histories (4) direct direct historiesthat thatallow allowthe theconstruction constructionof of predictive predictiveglobal globalcirculation circulationmodels; models; (4) evidence evidenceof ofglobal globalice icevolume volumefrom fromthe theocean oceanoxygen oxygen istope istoperecord record as as well well as as the the record record of ofcrustal crustalrebound; rebound;and and(5) (5)fairly fairlyeasy easyaccess accessto to modem modemanalogs analogs(for (forexample, example,the thestudy study 35 �of Antarctic chamber). Antarctic ice is relatively easy compared to the study of a deep magma chamber). These advantages advantages also provide the greatest greatest challenge challenge to Quaternary researchers, researchers, who are are required to integrate data across a wide range range of of disciplines disciplines and and geographic geographic areas. areas. The ultimate goal is to provide provide a integrated picture of the geosphere, geosphere, hydrosphere and biosphere for a specific specific period of earth's history, and to extend this understanding understanding to more more obscure glacial periods in the geologic record. REFERENCES REFERENCES Baker, R. W., Diehi, Diehl, J. F., Simpson, Simpson, T. W., W., Zelazny, Zelazny, L. L. 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K., K., 1986, 1986,Paleogeography Paleogeographyof northern northern North America, America, 18,000-5000 18,000-5000 years years ago. ago. Geological Survey of Canada, Map Map 1703A, scale scale 11::12,500,000. 12,500,000. Hint, R. F., 1957. 1957. Glacial Glacialand andPleistocene PleistoceneGeology. Geology.New NewYork, York,John JohnWiley Wileyand andSons, Sons,553 553p.p. Flint, 1995, Hydraulic run-away: A mechanism mechanism for thermally regulated surges of Fowler, A. C., and Johnson, C., 1995, run-away: A ice sheets: 1. sheets: Journal JournalofofGlaciology, Glaciology,v.v.41, 41,p.p.554-56 554-561. Fulton, R. J., 1989, 1989, Foreward in Fulton, Fulton,R. R. J., J., ed., ed., Quaternary Quaternary geology geology of Canada Canada and Greenland: Greenland: Ottawa, Ottawa, Geological Survey Survey of Canada, Canada, Geology Geology of Canada series, v. 1;(Geological l;(Geological Society Society of America, America, Geological Geology of North America, v. v. K-1), K-i), p. 1-11. 1-11. Fulton, R. J., 1995, 1995, Surficial Surficial map of Canada: Geological GeologicalSurvey Survey of Canada Canada Map 1880A, 1880A, scale 1:5,000,000. 1:5,000,000. Gibbons, A. B., Megeath, Megeath, J. D., and Pierce, K. L., 1984, 1984, Probability of moraine survival in a succession succession of glacial advances. Geology, Geology,v. v. 12, 12,p. p. 327-330. 327-330. Hallberg, Hallberg, G. G. R., 1986, 1986,Pre-Wisconsin Pre-Wisconsin glacial glacial stratigraphy stratigraphyof the the central central plains plains region region in in Iowa, Iowa, Nebraksa, Nebraksa, Kansas, and Missouri. Quaternary Quaternary Science Science Reviews, Reviews, v. 5, p. 11-15. Dreimanis, A., 1992, Deformation till implications for rapid Hicock, S. T., and Dreimanis, till in in the the Great Great Lakes Lakesregion: region: implications of the the Laurentide Laurentide Ice Ice Sheet. Sheet. Canadian Journal of Earth flow along the south-central margin of Sciences, Sciences, v. 29, 29, p. 1565-1579. 1565-1579. Kiassen, Klassen, R. W., W., 1989, 1989,Quaternary Quaternarygeology geology of of the the southern southern Canadian Canadian interior interior plains, plains, in in Fulton, Fulton, R. R. J., J., ed., ed., and Greenland: Greenland: Ottawa, Quaternary geology of Canada and Ottawa, Geological Survey of Canada, Geology of of America, America,Geology Geologyof ofNorth NorthAmerica), America),v.v.K-1, K-i, p. p. 138Canada series, v. 1; (Geological Society of 174. 174. Mickelson, D. M., Clayton, L., Fullerton, D. S., S., and Boms, Borns, H. H. W. W. Jr., Jr., 1983. 1983. The late Wisconsin glacial S, C., LateLaterecord of the Laurentide ice sheet in the United States, in Wright, H. E., Jr., and Porter, S. Quaternary Environments of of the the United United States, States, Vol. Vol. 1, 1,The TheLate LatePleistocene. Pleistocene. Univeristy of Minneapolis, p. 3-37. Minnesota Press, Minneapolis, Meyer, G. N., 1997, of north-central north-centralMinnesota. Minnesota. Minnesota 1997, Pre-late Wisconsinan till stratigraphy of 48, 67 p. Geological Survey Survey Report of Investigations Investigations no. 48,67 Patterson, in Patterson, Patterson,C. C. J., J., Contributions Contributionsto to Patterson, C. C. J., 1997, 1997,Quaternary Quaternarygeology geology of of southwestern southwesternMinnesota, in the Geology Geology of Southwestern Southwestern Minnesota, Minnesota, Minnesota Geological Geological Survey Report of Investigations Investigations 47, p. 1-45. 1-45. Richmond, Richmond, G. G. M., M., and and Fullerton, Fullerton, D. D. 5., S., 1986, 1986,An An introduction introductionto to Quaternary Quaternaryglaciations glaciationsin in the theUnited UnitedStates States of America, Quaternary Quaternary Science Science Reviews, Reviews, v. 5, p. 3-10. Shackelton, N. J. and others, Shackelton, others, 1984, 1984, Oxygen isotope isotope calibration calibration of the onset of ice-rafting ice-rafting and history history of glaciation in the North Atlantic region: region: Nature, Nature, v. 307, p. 216-219. Thorleifson, L. H., and Kristjansson, Kristjansson, F. J., 1993, 1993, Quaternary Quaternary geology and drift prospecting, prospecting, BeardmoreBeardmoreGeraldton area, Ontario: Geological GeologicalSurvey Survey of of Canada Canada Memoir 435, 146 146 p. of Minnesota, Minnesota, in in Sims, Sims,P. P.K. K.and andMorey, Morey,G. G.B, B,eds., eds.,Geology Geologyof of Wright, H. E. Jr, 1972, 1972, Quaternary History of Minnesota: AAcentennial centennialvolume. volume. Minnesota MinnesotaGeological GeologicalSurvey, Survey,p.p.5515-547. 36 �WHAT'S NEXT FOR GEOLOGY GEOLOGY IN IN THE THE LAKE LAKE SUPERIOR SUPERIOR AREA? WHAT'S NEXT SOUTHWICK,David David L., L., Minnesota Minnesota Geological Geological Survey, Survey, 2642 2642University University Ave. Ave. W., W., St. St. Paul, Paul, MN MN SOUTHWICK, 55114-1057 55114-1057 Marvelous Marvelous progress progress has has been been made madein indeciphering decipheringthe thecomplex, complex,diverse diversegeological geological framework frameworkof of the the Lake Superior Superior region over the past twenty years. In particular, our comprehension comprehension of the Precambrian rock record has progressed progressed remarkably remarkablythrough throughexcellent excellent programs programs of of geologic mapping, regional geochronology, and and related related topical research research supported supported largely by government government and geophysics, geochronology, and justified understanding of on the premise that that geologic understanding of Precambrian terranes terranes will will lead to to discovery discovery of of economic mineral be sustained sustained and and that intellectual and mineral deposits. One hopes that this momentum can be progress toward the goal of finding and developing technological progress developing viable ore deposits deposits will continue. continue. Sustaining it will not not be be easy easy in in the theprevailing prevailingpolitical politicalclimate, climate, however. however. of democratic governments governments are determined Ultimately, albeit indirectly, the policies of determined by by public public opinion that is transmitted transmitted to to elected elected representatives. At the present time the public is not particularly p&ticularly concerned about mineral commodities commodities and therefore minerals issues do not have aa high high political political profile. There are no pressing shortages, prices are moderate moderate and stable, stable, unemployment unemploymentis is generally generally issues greatly greatly outweigh outweigh concerns concerns for for the the long-term long-term low, and concerns concerns for present-day "quality "quality of life" issues of mineral and energy availability of energy resources resources in in the the minds mindsof of most most people. people.As As aa consequence, consequence, elected elected representatives are representatives are being urged by their constituents to preserve and promote promote environmental environmentalquality, quality, provide provide recreational recreational opportunities opportunitiesin inwilderness wildernessareas, areas, improve improveurban urbaninfrastructure, infrastructure,combat combatcrime, crime, opportunites, and reduce taxes. They are are not not being being urged urged to improve health care, extend educational opportunites, of aa mining mining industry industry that we geologists geologists know know is is vital vital to to the the long-term long-term provide for the well-being of sustainability of because there there is is aa powerful powerful human human tendency not to worry about sustainability of the quality quality of life, because about future difficulties until circumstances absolutely demand demand it. Instead of of mining, mining, the the plexus plexus of of future affect human human health health and and happiness will be the primary environmental issues that immediately affect primary driver driver of public resource policy and derivative of derivative geological investigations in the Lake Superior region over the the next twenty twenty years. Although Although metal metal mining and and related related industries industries surely surelywifi will remain remain significant significant to local and will receive passive passive political politicalsupport, support, they they will wifinot notin in themselves themselvesprovide provide the the rationale rationale economies and for increasing public expenditures expenditureson ongeological geologicalinvestigations. investigations. be growth areas for applied geologic thinking thinking and research in the Lake The following will be Lake Superior Superior Detailed characterization of of unconsolidated unconsolidated materials within the uppermost region. (1) Detailed uppermost100 100m m of of the the This work work will involve collaboration among among glacial glacial geologists, geologists, stratigraphers, stratigraphers, geologic section. This hydrogeologists,and and soil soil scientists scientistsand and will will have have direct direct application to a geophysicists, geochemists, hydrogeologists, number number of of societal societalconcerns. concerns. It will will also also benefit mineral exploration, exploration, but itit wifi will not be justified on on that that basis. (2) The The development development and deployment deployment of improved geophysical geophysical tools for obtaining information mapping of about the the shallow shallow subsurface. subsurface.(3) (3) Detailed geologic geologic mapping of surficial deposits, deposits, especially especially in in urban, urban, mapping to to provide provide the stratigraphic framework of of the the urbanizing, and agricultural agricultural areas. Regional mapping Quaternary materials Quaternary materials will will be necessary as well, but the more pressing need will will be for detail. detail. (4) (4) Hydrogeologic studies studies on on aa variety variety of of scales, scales, with particular particular emphasis emphasison onthe thegeological geologicalcontrols controlsof of ground-water flow. be a developing area of of research research in in which which ground-water flow. Fractured-rock Fractured-rock hydrogeology will be sedimentologists, petrologists, sedimentologists, petrologists, and and structural structuralgeologists geologistswill willbecome become increasingly increasinglyinvolved. involved.(5) (5)LowLowtemperature rock-water of surface-water surface-water and and groundgroundtemperature rock-water geochemistry, geochemistry, with applications to problems of The mapping mapping and (6)The water composition composition and and the the transport transportof of dissolved dissolvedchemical chemical species. species. (6) of mined mined land and mine waste, characterization characterizationof of aggregate aggregateresources. resources.(7) (7) Characterization Characterization and control of in which the brought to the full full spectrum spectrumof of hydrogeological hydrogeological and and geochemical geochemical methodologies are brought to bear. bear. (8) (8) Geological and geophysical studies within Lake Superior Superior itself itself that that will will be be predicated predicated on calibration Geological and of the paleoclimate record but but will will extend extend to to investigations investigations of of lake-basin lake-basin evolution. evolution. As the geological profession profession becomes becomes ever evermore moredependent dependent on on government government policies, policies, our our near-term near-term research opportunities inevitably will reflect public priorities. This need not and will not mean opportunities inevitably This need not mean the the total demise of economic economic geology geologyand andthe thehard-rock hard-rockdisciplines disciplinesthat thatsupport supportit.it. However, traditional hard-rock work work will will diminish diminish in in favor favor of of non-traditional non-traditional investigations investigationsin in which which hard-rock hard-rock thinking thinking and skills skills can can be applied. applied.Flexibility Flexibility of training training and andoutlook outlookwifi willbe be critical criticalto to professional professionalsuccess. success. 37 �ACTS ABSTRACTS GENERAL TECHNICAL SESSIONS 39 �PETROGRAPHY AND GEOCHEMISTRY O OF F MIDCONTINENT RIFT RIFT RHYORHYOVOLCANICS) NEAR NEAR CLAM CLAM FALLS, FALLS, WISCONSIN LITE (CHENGWATANA (CHENGWATANA VOLCANICS) R.,Geology Geology Department, Department, ABBOTT, Kathleen M., THOLE, THOLE, Jeffrey Jeffrey T., T., WIRTH, WIRTH, Karl KarlR., Macalester College, St. Paul Paul MN, MN, 55105; 55105; kabbott@macalester.edu; kabbott@macalester.edu; thole@macalester.edu; wirth@macalester.edu The southwest southwest limb of the Midcontinent Rift (MCR) includes includes the the poorly-exposed poorly-exposed Chengwatana Chengwatana Volcanics (CV) (CV) which which are comprised of predominantly tholeiitic basalts (Wirth et al., Volcanics al., 1997, 1997, Naiman et al., this volume), volume), with minor rhyolites which are believed to be the the southernmost southernmost exposed rocks of this type within the the MCR. MCR. Recent analysis of these rhyolites found near Clam exposed Falls, Wisconsin, provides physical, chemical, and isotopic data data which which has has helped helped constrain constrain the the processes (Naiman (Naiman and Wirth, this timing (Wirth and Gehrels, this volume), and magmatic processes and the the southern southernMCR. MCR. These data are also used volume) involved in the generation of the CV and . rhyolites of northern Michigan to compare compare the CV rhyolites rhyolites with the Portage Lake rhyolites Michigan (Nicholson, (Nicholson, 1992, Nicholson Nicholson and Shirey, 1990), and the felsic rocks of the the North North Shore ShoreVolcanic Volcanic Group Group (Green (Green and and Fitz, Fitz, 1993, 1993,Vervoort Vervoort and and Green, Green, 1997). 1997). Two exposures exposures of rhyolite rhyolite are are found just west of Clam Clam Falls Falls including including about about 55 meters of rhyolite (KC-302) which is approximately 640 meters above the base of the exposed volcanic volcanic section. The The only only other otheroutcrop outcropof of rhyolite rhyolite (KC-310) (KC-310) is exposed exposed near the base of of the the section section approximately 3 kilometers south of KC-302 and is is less less than than 10 10meters metersthick. thick. No flow contacts contacts approximately or foliations are are present present but but the the outcrops outcrops appear appear to to be beconcordant concordantwith withsurrounding surroundingbasalts basalts which trend northeast and dip approximately 15 degrees to the northwest in this area. The northeast and dip approximately 15 degrees Thebase base with the underlying basalt basalt and of the outcrop at KC-302 appears to be an intrusive contact with the rhyolite contains contains subangular subangular inclusions inclusionsof ofophitic ophiticbasalt. basalt. The nature of emplacelocally, the ment ment of these these rhyolite rhyolite bodies bodies isis unclear. unclear. porphyritic small phenocrysts phenocrysts(-(—.1mm) The rhyolites rhyolites are generally weakly (<5%) (4%) porphyritic containing small lmm) The euhedral to and trace trace amounts of subhedral of euhedral to subhedral subhedralplagioclase plagioclase(avg. (avg.Ab94 Abo4An2 An2 Or4) and subhedralFe-Ti Fe-Ti locally. Amphiboles, oxides. Quartz Quartzphenocrysts phenocrysts and and albite albite glomerocrysts glomerocrysts are present only locally. Amphiboles, partly replaced replaced by chlorite/epidote/carbonate, chlorite/epidote/carbonate,are are rare. rare. The Thegroundmass groundmassisiscommonly commonlyspheruspherucontaining tabular quartz (tridymite (tridymite paramorphs), paramorphs), with phenocryst phenocryst nuclei, nuclei, containing litic (up to 22-- 3 mm) with Or95),very veryfine-grained fine-grained disseminated disseminated Fe-oxides, Fe-oxides, Ani Org5), dusty, anhedral anhedral alkali alkalifeldspar feldspar(avg. (avg.Ab4 Ab4An1 and local poikilitic anhedral quartz. quartz. Accessory zircon cessory zircon is present present as as minute minute I I I a euhedral prisms prisms in in most most samples. samples. The euhedral The C1fl Falls Clam Falls (CV) (CV) presence of minor epidote epidote and and carbonate carbonate BSa1t a Basalt D within the groundmass groundmass is is ubiquitous. ubiquitous. -3 . . Rhyolite Rhyolite samples contain minor diktytaxitic Some samples contain minor diktytaxitic Some a cavities. The presence of of tridymite tridymite g cavities. paramorphs pararnorphsindicate indicatethese theserocks rocks are are simisimi-Do 22 -lar to some rhyolites of the NSVG which a & erupted at athigh highterntern- 0 C are believed to have erupted I L7 f-4 peratures (Green and Fitz, 1993). No ap00° o na ° parent flow foliation or pyroclastic pyroclastic texn o 1 00 observed in the exposures exposures near tures were observed Falls. Clam Falls. Only basalt and rhyolite are present I I I 0 in the Clam Clam Falls' section; section; no rocks rocks of 50 60 40 50 60 70 70 80 intermediate intermediate composition compositionhave have been been idenidenS.1 2 wt /0 SiO, % tifled. tified. Rocks of of intermediate intermediate composicomposiI I I ^ 1 I 41 - �_______________________________ DI 0 I I 0 NSVG Granophyres \ ocJJ om 0 0a Portage Lake Portage Lak  0a -4 — -8 NSVG Icelandites Icelandi -12 NSVG Rhyolites Clam Clam Falls Falls (CV) (CV) -16 0 Basalt Basalt I Rhyolite Portage Lake Type II -20 40 50 60 70 80 Si02 wt % both the the NSVG NSVG and and the thePortage PortageLake LakeVolcanics. Volcanics. Chengwatana Chengwatana basalt basalt geochemgeochemtions are found in both Naiman et al., a!.,this thisvolume. volume. The The felsic felsic Chengwatana Chengwatana rocks rocks can can be be classified classified istry is discussed by Naiman as tholeiitic rhyolites. The Therocks rocks are are metaluminous metaluminous and and only only one one sample sample has normative normative coruncorundum (0.16%). In In general, general,the therhyolite rhyolite chemistry chemistry is is similar similar to to both both NSVG NSVG and and Type Type I Portage Portage Lake rhyolites. Si02 (7 (71-72%), rhyolites.Notable Notablevariations variationsfrom fromthese thesetwo two groups groups include include slightly less Si02 1-72%), higher 13higher total total Fe Fe (4.87 (4.87 to to 5.78 5.78Fe203%), Fe203%),higher Th (25-27 ppm), and significantly significantlyhigher higherZr Zr(7 (713986 986 ppm). Initial ENd (1100Ma) Ma)values valueson ontwo twoChengwatana Chengwatanarhyolites rhyolitesare are0.95 0.95and and-0.06. -0.06. These ENd (1100 Chengwatana basalts of of the the Clam ClamFalls Fallsregion region(-2 (-2toto+3.4). +3.4).The TheChengwatana Chengwatana values are similar to Chengwatana rhyolite similar to Portage Lake (Type I) rhyolites rhyolites which which range rhyolite ENd ENd values are most similar range from from-0.3 -0.3to to -4.7 (Nicholson (Nicholson and andShirey, Shirey, 1990) 1990)and and are are distinct distinct from rhyolites of the NSVG which range from -2.3 to ENd to -14.8 -14.8 (Vervoort (Vervoort and Green, Green, 1997). 1997). NSVG NSVGgranophyres granophyresand andicelandites icelanditeshave haveENd values with a smaller and these these values values are also lower than smaller range range than NSVG rhyolites rhyolites and rhyolites. Large degrees of crustal melting melting are are invoked invoked as as a major process in in Chengwatana rhyolites. forming forming the the NSVG NSVG rhyolites rhyolitesas asindicated indicatedby bythe thelow lowENd ENd values values (Vervoort (Vervoort and and Green, Green,1997). 1997). The Chengwatana rhyolites at Clam Falls lack the pronounced crustal Nd isotopic isotopic signature signature evident in the NSVG rhyolites rhyolites and are are believed to be fractionates fractionates of a primary basaltic basaltic magma magma derived from an enriched enriched mantle mantle source. References Cited Green, v. 54, 54, p. p. 177-196. Green, J.C. J.C. and and Fitz, Fitz, T.J., T.J., 1993, 1993, Journal of Volcanology and Geothermal Research, v. Nicholson, S.W., S.W., and Shirey, S.B., 1990, Journal of Geophysical Research, v. 95, p. 10,851-10868. Nicholson, S.W., U.S.G.S. Bulletin 57 pp. S.W., 1992, U.S.G.S. Bulletin 1970, 1970,57 K.R., Vervoort, J.D., J.D., Naiman, Z.J., 1997, Canadian Journal of Earth Sciences, v. 34, no. 4, p. 536-548. Wirth, K.R., 536-548. J.C., 1997, Vervoort, J.D., and Green, Green, J.C., 1997, Canadian Journal of Earth Sciences, Sciences, v. 34, p. 521-535. 42 �A PRELIMINARY DETAILED GEOLOGICAL GEOLOGICAL DESCRIPTION DESCRIPTION OF OF THE NEW A PRELIMINARY DETAILED NEW IN THE LUMBY HIGH GRADE SILVER-BASE SILVER-BASE METAL DISCOVERY DISCOVERY IN LUMBY LAKE METAVOLCANIC BELT BELT NORTHEAST METAVOLCANIC NORTHEAST OF ATIKOKAN, ATIKOKAN, ONTARIO, ONTARIO, CANADA BERNATCHEZ, Raymond A., President & Consulting Geologist to Atikokan Resources Inc., P.O. Box Box 1376, 1376,126 126Willow Willow Rd., Rd., Atikokan, Atikokan,Ontario, Ontario,Canada, Canada,POT POT1CO. 1CO. Tel. 807-597-4526, Fax 807-597-4636 (rbernatc@atikokan.lakeheadu.ca) (rbernatc @ atikokan.1akeheadu.ca) A high mineraloccurrence occurrencehas hasbeen beendiscovered discoveredwithin within an an east-west east-west high grade grade silver—zinc—lead silver-zinc-lead mineral stratabound felsic volcaniclastic horizon at the southern edge of the Lumby Lake Metavolcarnc Metavolcanic Belt. Located Locatednorth northof ofthe thecreek creekconnecting connectingLumby Lumbyand and Herontrack HerontrackLakes, Lakes,the thediscovery discovery occurs at the southern margin of a 1.5 1.5 km thick east-west trending felsic volcanic volcanic package package near Marmion Lake tonalite the southern contact of the Lumby Lake Metavolcanic Belt with the Marmion of batholith to the south. The The Lumby Lumby Lake Lake volcanic belt is located 23 air miles northeast of Atikokan, Ontario, Canada and forms the northeasterly extension extension of of the the Steep Rock and Finlayson Lake volcanic stratigraphy. This This discovery discoveryisis contained containedwithin within highly highly (hydrothermally) (hydrothermally) altered felsic volcaniclastic rocks having geological and geochemical geochemicalfeatures features similar to other Archean massive sulphide deposits. However, the felsic volcanic rocks hosting metaloccurrence occurrence have have been been dated dated at 3.0 Ga (Mesoarchean; this high grade grade silver—base silver-base metal (Mesoarchean;Davis Davis and Jackson, 1988), 1988), whereas all other base metal deposits found in the Archean in Ontario have been dated at 2.7 2.7 Ga. The The occurrence occurrence contains contains unusually high silver content with some random grab samples assaying as high as 416 ounces/ton (14,265 (14,265 gm/tonne) gdtonne) or or270 270ozfton ozlton samples assaying as high as 416 ounces/ton over 1.1 1.1 meter (9292 (9292 gm/tonne). gdtonne). The Lumby Lake greenstone greenstone belt is located within the Wabigoon subprovince, 30 km north of the Wabigoon-Quetico Wabigoon—Queticosubprovince subprovinceboundary boundaryand and 37 37 air airkm km northeast northeast of Atikokan, Ontario. Ontario. The Lumby Lake km xx 20 20 km km synclinal synclinalsupracrustal supracrustalsequence sequence Lake greenstone greenstonebelt belt consists consists of of aa 60 60 km of rocks composed of mafic (pillowed and massive), ultramafic (komatiitic), and felsic (tuff, lapili lapillituff, tuff,tuff tuffbreccia, breccia,massive), massive),metavolcanic metavolcanicrocks rockswith with lesser lesseramounts amountsof of metasedimentary metasedimentary rocks (chert, (chert, argillite, argillite, arkose, arkose, conglomerate conglomerateand and iron iron formations). formations).The Themetavolcanic— metavolcanicmetasedimentary assemblage Mannion Lake Batholith to the south and the assemblage is in contact with the Marmion White Otter Batholith to the northwest. The The belt belt has has been been intruded intruded by two larger oval oval and monzodiorite-granite plutons, the Norway Lake and van Nostrand Lake Stock heterogeneous monzodiorite-granite and smaller ones (the Bar Lake and Viking Lake Lake stocks). The Belt has been subjected subjected to four major structural structural events: at least two folding events and two faulting-shearing events. The TheBelt Belthas has had had aa major major synclinal synclinal folding folding event event with with its its axis axis trending east-west east-west through through the central central portion of the the belt through through Seahorse-Garnet Seahorse-GarnetBayBayPinecone-Hematite Lakes system. The The van van Nostrand Lake stock intrudes this axis in the central part of the belt. AAsecond secondfolding foldingevent event occurs occurs within within the the interfiow interflow sedimentary sedimentaryunits. units. belt to to the the west. west. Two The Redpaint Lake Fault truncates the Lumby Lake belt Two east-west east-west Spoon Lake Deformation Deformation Zone and the deformation zones have been noted: the Bufo Lake - Spoon Garnet Garnet Bay-Viking Lake-Hematite Lake-Hematite Lake Lake Deformation Deformation Zone. Zone. The silver—base metaldiscovery discoveryisislocated locatedin inthe thewestern westernblock block of of claims claims known known as the silver-base metal Herontrack Herontrack Lake Lake Block Block and and within within the the southwest southwestportion portion of of the the Lumby LumbyLake Lakegreenstone greenstonebelt. belt. A 130 krn grid has been established established in the the central central portion of this block from Lumby Lumby Lake Lake to to 130 km Hutt Lake. AAdetailed detailedexploration explorationprogram programover overthis this grid grid consisting consistingof of geological geologicalmapping, mapping, lithogeochemical soil geochemical sampling, magnetic and partial VLF EM and IP surveys, lithogeochemical 43 �sampling sampling and overburden overburden mechanical stripping has identified and exposed exposed numerous numerous suiphide sulphide bearing felsic volcaniclastic horizons horizons containing containing economic economic to to subeconomic subeconomicvalues valuesin in zinc, zinc, copper, silver, lead and gold. gold. The detail detail geological geological mapping mapping has identified identified five five rock rock types: mafic mafic volcanic, volcanic, massive massive and and pilowed; pillowed;felsic felsicvolcanic, volcanic,tuff, tuff, lapili lapillituff, tuff,tuff tuffbreccia brecciaand andcoarse coarse breccia, breccia, massive massive rhyolite rhyolite as feldspar feldspar and/or andfor quartz quartz porphyries porphyries and and cherty cherty rhyolite; rhyolite; mafic mafic to to intermediate intermediateintrusive intrusiverocks rocks (gabbro and diorite) as dykes and sills intruding the above; Marmion Lake batholith (tonalite) Lake batholith (tonalite) and finally felsic dikes intruding intruding the the felsic felsic volcanic volcanic rocks. rocks. The bulk of the mineralization is contained within stratabound stratabound interflow interflow sediments. sediments. Pyrite, Pyrite, and in some some interfiow interflow units, units, pyrrhotite pyrrhotitemake makeup upthe thebulk bulkofofthe thesulfides. sulfides.The Thehigh highgrade gradesilver— silverzinc—lead discovery zone contains significant amounts of pyrite, sphalerite, galena, acanthite zinc-lead discovery zone contains significant amounts of pyrite, sphalerite, galena, acanthite and native silver with minor chalcopyrite. This This mineralization mineralization is is contained contained within within highly highly altered felsic volcanic rocks. The The felsic felsic rocks rocks have have been been altered altered to sericite sericite and chlorite chlorite in some some locations. The Thesericite sericitewas waspreviously previouslyinterpreted interpreted as as an an altered altered and and sheared shearedquartz quartz diorite; diorite; itit now appears that this alteration was caused as the result of the footwall alteration associated with massive sulphide deposits. This This has has been been partially partially confirmed confirmed by some some limited limited lithogeochemical lithogeochemicalrock rock sampling. sampling. The exploration exploration program carried out out to date has identified three highly altered base metal mineralized horizons. The The most most economically economically significant significanthorizon identified to date is the Lake—SpoonLake LakeHorizon Horizonwhich whichhosts hosts the the high high grade grade silver silver discovery. Several Lumby Lake-Spoon Several other other been discovered discovered along along this 250 to to significant silver and base metal-bearing occurrences have been 300 meter wide sulphide horizon that has now been traced for a strike length of about about 66 km by surveys. Two additional suiphide base metal mechanical stripping and geophysical surveys. additional altered sulphide bearing felsic volcanic horizons (Delos Lake and Pond Lake Horizon) have been located a few hundred meters north of the silver discovery horizon. Geophysical Survey The Questor Airborne Geophysical Survey carried out by the Ontario Geological Survey in Lake mineralized mineralized 1980 did not identify any input input anomalies anomalies along along the the Lumby Lumby Lake—Spoon Lake-Spoon Lake horizon. However, a broad magnetic low covers the area over the newly identified However, a broad magnetic low covers the area over the newly identified felsic felsic strata. This Thismagnetic magneticlow lowcan canbebetraced tracedeast—west east-west along alongthe thesouthern southernvolcanic—granite volcanic-granite contact contact for over 12 km km from from Bufo Bufo Lake Laketo toHutt Hutt Lake. Lake. Other similar of the Lumby Lake greenstone belt for of over 13 km. km. Similar Similarfelsic felsic magnetic lows can be traced eastward to Old Man Lake a distance of volcanic rocks have been identified in these areas. A new copper—zinc—silver occurrence has rocks have been identified in these areas. A new copper-zinc-silver occurrence been found along this magnetic low response response near a series of airborne input anomalies anomalies at the west end of Old Man Lake. The TheOGS OGSairborne airbornegeophysical geophysicalsurvey survey has has detected detected numerous numerous other anomalies anomalies in the Lumby Lake greenstone greenstone belt, of which most have never been examined or tested. What Whatother otherbase basemetal metaldiscoveries discoverieswill will the the Belt Belt reveal? reveal? References References cited: Davis, D.W., and Jackson, M.C., 1988, 1988, Geochronology of the Lumby Lake greenstone belt: a 3 Ga complex within the Wabigoon Subprovince, northwest Ontario: Bull. G.S.A., G.S.A., v. v. Ontario: Bull. 100, p. 818-824. 44 �L5 r I Ii 0 z 0 -' Ic ii I 45 �DIMENSION STONE PRODUCTS DIMENSION PRODUCTS OF OF MINNESOTA MINNESOTA BOERBOOM, BOERBOOM, Terrence Terrence J., Minnesota Minnesota Geological Geological Survey, Survey, 2642 University University Avenue, Avenue, St. St. Paul, MN 55114; 55114;boerbO01@tc.umn.edu; boerbOOl@tc.umn.edu; and and OBERHELMAN, OBERHELMAN, Matt, Matt, Minnesota Minnesota Division of Minerals, 1525 E. 3rd Street, Hibbing, Department Department of Natural Resources Resources - Division matt.oberhelman@dm.state.mn.us 55746-1461;matt.oberhelman@dnr.state.mn.us MN 55746-1461; The first fmt dimension dimension stone stone quarry was opened in 1868, 1868, to supply gray granite granite from the St. St. Paul Customs Customs House House and and Post Post Office. Office. Since Cloud District for construction of the St. Paul Since then, grown considerably. considerably. At present there are the dimension stone industry in Minnesota has grown are fourteen active fourteen active dimension dimension stone stone quarries quarries in in the the state, state, and and several several others others that that are are active activeon on an an intermittent basis. Dimension Dimension stone stoneproducts products from from Minnesota are marketed worldwide, and are used for for a variety of purposes purposes that that include include interior interior tiling, counter counter tops, monuments monuments and and memorials, "surface memorials, "surface plates" platest' for for precision machine mounts, acid-resistant acid-resistant industrial applications, decorative decorative and structural structural exterior panels for major buildings, and grinding mill liners liners and and balls. balls. The Resources' dimension stone The results of a recent Minnesota Department of Natural Resources' stone inventory potential for for krther further development development of of inventory show show that northern Minnesota offers excellent potential high quality dimension dimension stone products. Field Field investigations investigations have identified twenty-two for quarry quarry development. development. Prospects prospect sites that exhibit potential for Prospectshave havebeen been identified identified in in Middle Proterozoic Proterozoic rocks (ca. 1100 1100 m.y.) of the Duluth Complex and Archean rocks (ca. 2700 m.y.) rock units. units. Prospects may.)of the Vermilion Vermilion Granitic Complex and other granitoid rock Prospects include include black, green, with aa variety variety of of textures. textures. Prospect green, pink, beige, and multi-colored stone with Prospect evaluation evaluation included included outcrop outcrop observations observationsthat that considered consideredjoint spacing, spacing, color, color, texture, texture, and and deleterious deleterious materials. Results Resultsof ofthe theinventory inventoryare aredescribed described in in the the following followingthree three MDNR MDNR reports: Dimension Dimension Stone StoneInventory Inventory of of Northern Northern Minnesota Minnesota 1991, 1991,Report Report 289; 289; Dimension Dimension and Dimension Dimension Stone Inventory Inventory of Stone Inventory of Northern Minnesota 1993, Report 298; and Northern Minnesota Minnesota 1995, 1995, Report Report 298-2. Cold Spring Spring Granite Granite Co. is currently currently leasing three of the prospect sites identified by the have opened opened quarries quarries on ontwo twoof ofthese theseleases. leases. Both dimension stone inventory study, and have utilize gabbroic h m these these sites sites is is marketed gabbroic anorthosite anorthosite of the Duluth Complex; the the stone stone from under Lake Superior SuperiorGreen. Green. under the the names names Mesabi Mesabi Black Black and and Lake This poster display shows shows products from all of the currently active quarries in the state state of Minnesota, along with samples of dimension stone prospects that were collected and prepared Minnesota, along with samples of dimension stone collected and prepared by the Minnesota Minnesota DNR-Minerals Division (see below). The The numbers numbers on on the the samples samples refer refer to locations on the index map. The table on the following page summarizes the geologic The table on the following page summarizes the geologic aspects aspects of the various various dimension stone dimension stoneproducts products of of Minnesota. Minnesota. ACKNOWLEDGMENTS AcmowLEDGMENTs All of the quarry companies listed on companies listed on the the following following table table kindly contributed contributed samples samples of of their their products to the Minnesota Geological Survey for this display. products to the Minnesota Geological Survey for this display. 46 �Sample Sample Company Company Trade Trade Name Name Geologic Geologic Unit 1 1 CSG Mesabi Black Complex Duluth Complex 2 CSG Lake Superior Superior Green Green 3 CSG Indian Iridian 4 CSG 5 Texture -1090 Ma —1090 Dominant Mineralogy P, cpx, urn ilm Duluth Complex Complex -1090 Ma —1090 P, cpx, gp, ilm p, very cgr, porph Isle Granite Isle Granite 18121770 Ma Ma 1812 - 1770 K, P, Q, Q, bi m-cgr, porph porph Charcoal Charcoal Black Reformatory Reformatory granodiorite granodiorite 1812±9 Ma 11 18 1Z?HMa P, K, Q, P, Q, bi, hbl, sph m-cgr, si. sl. porph. porph. CSG Diamond Diamond Pink Rockville Rockville Granite Granite 11812±9 8 1 2 s Ma Ma 11 K, P, Q, Q, bi, hbl, sph m-cgr, porph, rkv, 6 CSG Rockville Rockville Beige Beige Rockville Rockville Granite Granite Ma 11 1812±9 1812&9Ma K, P, Q, Q, bi, hbl, sph cgr, porph, rkv, 7 CSG Rockville Rockville White White Rockville Rockville Granite Granite Ma 11 11812±9 8 1 2 s Ma K, P, Q, Q, bi, hbl, sph cgr, porph, porph, rkv, rkv, 8 CSG Agate Agate Unnamed 2618±1 Ma 22 261833 Ma K, P, Q, Q, bi cgr ClY 9 DGC Bellingham Granite Granite Unnamed 2618±lMa? 2618klMa ? bi K, Q, Q, P, K, P, bi cgr C lY 10 JSC Quartzite Sioux Quartzite 1700Ma 1700 - 1750 Ma Q recrystallized recrystallized quartzite quartzite 11 CSG Rainbow Rainbow Morton Gneiss Gneiss 2600 2600- K, P, Q, bi, hbl gneissic banded, gbl 12 MKS Varieties Varieties of pink-gray Oneota Dolomite Dolomite Earliest Ordovician Earliest Ordovician dolomite dolomite bioturbated bioturbated micro-xln. micro-xln. 13 VSC vsc Varieties pink-gray Varieties of pink-gray Oneota Dolomite Dolomite Earliest Earliest Ordovician dolomite dolomite bioturbated bioturbated micro-xln. micro-xln. 14 BSC Winona Dolomite Dolomite Oneota Dolomite Dolomite Earliest Ordovician Earliest Ordovician dolomite dolomite bioturbated bioturbated micro-xln. micro-xln. Age - - 3600 Ma mgr, lam, lin, un, oph Company abbreviations: abbreviations: CSG -- Cold Spring Granite, JSC JSC -- Jasper Stone Stone Company, DGC - Dakota Granite Company, Company, MKS MKS -- Mankato-Kasota Stone, Inc., Company VSC Co., BSC -- Biesanz Stone Co. VSC -- Vetter Stone Co., Mineral abbreviations: abbreviations: P - plagioclase, plagioclase, K -- potassic feldspars, Q jim - ilmenite, ilmenite, sph sphene, Q - quartz, quartz, cpx - clinopyroxene, hbl -- hornblende, hornblende, bi -- biotite, ilm sph -- sphene, Mineral granophynic quartz/feldspar, gp - granophyric quartdfeldspar, xln xln -- crystalline crystalline Texture abbreviations: abbreviations: mgr mgr - medium-grained, Texture medium-grained, cgr cgr -- coarse-grained, coarse-grained, lam - igneous igneous lamination (cumulus or trachytoid), trachytoid), tin lin -- lineated, lineated, rkv rkv -- rapakivi, gbl-rapakivi, gbl granoblastic, oph oph -- ophitic, ophitic, porph porph -- porphyritic 1U-Pb I u - P ~zircon date (Goldich pers. commun., as reported in Horan and and others, others, 1987) 1987) MassachussettesInstitite Instititeof ofTechnology, Technology, pers. pers. comm., comm., 1998) 22U.Pb ~ - zircon ~ b date (Mark Schmitz, Massachussettes �GROUND GROUND WATER WATER RECHARGE, RECHARGE,DISCHARGE DISCHARGE AND AND RESIDENCE RESIDENCETIME TIMEIN INRICE RICE FOR LAND USE PLANNING IMPLICATIONS COUNTY, COUNTY,MINNESOTA MINNESOTA---- IMPLICATIONS FOR LAND USE PLANNING CAMPION, CAMPION?Moira Moira---- Minnesota Minnesota Department Department of of Natural Natural Resources Resources e-mail moira.campion@d~.state.mn.us e-mail--- moira.campion@dnr.state.mn.us Rice Rice county county is is located located 40 miles miles south south of of the Minneapolis-St. Paul metropolitan metropolitan area. The The county county contains containsurban, urban, suburban, suburban,and and rural rural areas areasand and faces facesincreasing increasingdevelopment developmentpressure pressure for for housing housing as as well as as for for recreational and high intensity agricultural agricultural purposes. Water Watersupply supply in in the the county county isis primarily primarily from fromground groundwater waterand andmost mostof ofthe the1600 1600wells wellsininthe thecounty countydata data base base are are completed completed in in the St. St. Peter-Prairie du Chien-Jordan aquifer. This Thisbedrock bedrockaquifer aquiferisis confined throughout the western and southeastern portions of the county and is unconfined confined throughout the western and southeastern portions of the county and is unconfinedinin the the east-central east-central and and northeast. northeast. The Thepotentiometric potentiometricsurface surfaceshows showsaaregional regionalhigh highin insouthwest southwest Rice Rice County Countyand and lows lowsin inthe the central centraland andnortheast northeastparts partsof ofthe thecounty countywhere wherethe theaquifer aquifer discharges dischargesinto intolocal localstreams. streams. Throughout Throughout most most of of the the county county the the aquifer aquifer isis protected protected from fromdirect directsurface surfacerecharge rechargeby by various consolidated and unconsolidated low permeability materials, except in the northeast various consolidated and unconsolidated low permeability materials, except in the northeast where where the the aquifer aquifer is is exposed exposed at at or or near near the surface. surface. The Thevarious variouslow lowpermeability permeabilitydeposits deposits and and their their distribution distribution result in different different recharge conditions conditions to the bedrock aquifer. In In the the northeast, northeast, where where the the aquifer aquifer is is not not protected protected by by overlying overlying material, material,recharge recharge to to the the aquifer aquifer occurs occurs directly through percolation from the land surface. In Inwestern westernRice Rice County, County,there there are are abundant lakes and wetlands in a hummocky terrain of thick supraglacial tills. Recharge to abundant lakes wetlands supraglacial Recharge to the the bedrock bedrock aquifer occurs occurs in complicated flowpaths flowpaths through the lakes and tills in this part of the the county. county. InInthe thesoutheast, southeast,the theDecorah-Platteville-Glenwood Decorah-Platteville-Glenwoodconfining confiningunit unitand andsome some older older tills tills cover cover the the aquifer. aquifer.Where Where this this relatively relatively thin thin package package of ofshales shalesand andlimestones limestonesisis continuous, continuous7the the St. St. Peter-Prairie Peter-Prairie du du Chien-Jordan Chien-Jordanaquifer aquiferreceives receivesvery verylittle littlevertical verticalrecharge recharge from the surface. Conversely, near the edge of this confining unit, recharge may be as from the surface. Conversely, near the edge of this confining unit, recharge may be asmuch much as fiomthe theaquifer aquifer as 30 30 times times greater greater than underneath this unit (Delin, (Delin, 1991). 1991). Discharge Dischargefrom occurs occurs where where ground ground water water drains drainsinto into the the Cannon CannonRiver, River, the the Straight StraightRiver, River,and andPrairie Prairie Creek. Creek. Residence Residencetime timeofofground groundwater waterwas wasestimated estimatedusing usingtritium tritiumand and14C 1% age-dating. age-dating. These These isotopic isotopic age age estimates estimatesconfirm confirmthe the conceptual conceptualmodel model of ofrecharge rechargein inthe thecounty. county. Ground water is youngest in the northeast where low permeability cover is absent youngest in the northeast where low permeability cover is absent and and oldest oldest in in the the southeast southeast under the Decorah-Platteville-Glenwood confining unit. Isotopic Isotopicresults resultsin in western western Rice Rice County County show showages agesgreater greaterthan thantritium tritium dating datinglimits limitsbut butless lessthan thanaafew few centuriesold. old. centuries Knowledge Knowledge of of these these differing differing recharge recharge conditions, conditions, coupled coupled with with geologic geologic and and hydrologic hydrologic information, provides county planners with an important water resource management information, provides county planners with an important water resource managementtool. tool. This This information information allows allows county county staff staff to to decide decidewhere where modification modificationto to current currentland land use use practices would minimize potential negative impacts on ground water quality. Basing Basing land land use planning decisions on resource management concepts rather than on politically based planning decisions on resource management concepts rather than on politically based situations situationswill will increase increasethe the chance chanceof of resource resource protection. protection. 48 �RICE RICE COUNTY, COUNTY, MINNESOTA Hydrogeology of the Hydrogeology St. Peter-Prairie Peter-Prairie du du Chien-Jordan Chien-Jordan Aquifer Aquifer -5m 5) 5 (0 ln - *- 64 - 0 0 0 2 4 I 1 I 6 Miles I Cross Section Section Legend Cross Legend Map Legend /V Potentiometric Potentiometric contour Cross section section Cross A A Well sampled Well sampled for chemistry + + Well measured for water level, level, but not sampled sampled Saturated thickness in feet LIII 0-100 R E 0 Aquifer absent '1 Aquifer ix Aquiferunconfined; unconfined; aquifer confined to west + 100-200 200-300 300-400 400-500 500-600 From: Rice Counly County Geologic Atlas, Atlas. Part 6.1997 6,1997 Original Scale l1:100,000. : l C J O , O ~ . Fmm: Copyright: Minnesota Minnesota Dept. Dept. of of Natural Natural Resources Cop*ght: 49 Unsaturated Unsaturated Recent waters; waters; tritium tritium >10 sf0TU TU Mixed waters; waters 1< 7c tntium tritium <10 c70 TU TU Vintage waters; tritium c <1 Vintage 7 TU and between 50 50 to 5,000 5,000years old Vintage waters; tritium e <1 l TU and Vintage 5,000to to 10,000 70,000years old more than 5,000 Decorah-Platteville-Glennwood Decorah-Plaffeville-Glennwmd Confining Confining unit unit St. Peter-Prairie Peter-Prairie du Chien-Jordan ChienJordan aquifer — Direction ofofgroundwater Direction groundwater flow flow �THE THE GEOLOGICAL GEOLOGICALSOURCE SOURCE OF OF ARSENIC ARSENIC IN IN GROUND WATER IN SOUTHEASTERN MICHIGAN MICHIGAN W.F. W.F. Cannon Cannon and and Alan Alan Kolker, Kolker, U.S. U.S. Geological Geological Survey, SurveyyReston, Reston?VA VA D.B. Westjohn, Westjohn?U.S. U.S. Geological Geological Survey, SurveyyLansing, Lansing?MI MI The ground ground water water in in parts parts of of nine counties in southeastern Michigan contains anomalous quantities of The dissolved arsenic, arsenic?presumably presumably derived from a natural source. Many Manywells wellstested tested by bythe theMichigan Michigan dissolved Department U.S.Environmental Protection Department of of Community Community Health and by the USGS exceed the U.S.Environmenta1 Agency's maximum maximum contaminant contaminant level level (MCL) of 50 pg/L Extreme values values are are as as Agency's .tg/L for drinking water. water. Extreme high as as 350 350 jtg/L. pgL. In In one one county county (Huron) (Huron) about about 30% of the tested wells exceeded the MCL for arsenic. high Most Sandstone, but other Most wells wells with with elevated elevated arsenic arsenic were completed in the Mississippian Marshall Sandstone? units, units?particularly particularlyglacial glacial aquifers, aquifers?can can also alsoyield yield arsenic-contaminated arsenic-contaminatedwater. water. The nine nine affected affected counties countieshave have aa combined combinedpopulation populationof of more more than than 22 million millionpeople. people.The TheMarshall Marshall The Sandstone Sandstone is is the principal bedrock bedrock aquifer aquifer in in most most of of the the affected affected counties countiesand and in in some someareas areasisisthe the sole-source aquifer. aquifer. These Theseconditions conditionscombine combineto to make make knowledge knowledge of of the the natural natural source source for for arsenic arsenic aa sole-source critical critical aspect aspectin in designing designingaa strategy strategyto to provide provideaa continued continuedsupply supplyof ofsafe safedrinking drinkingwater waterfor forthis this region. region. As As part part of of aa larger larger study study of of this this problem, we have been examining the lithology, mineralogy, and chemistry stratigraphic, and mineralogic chemistry of of the the Marshall Marshall Sandstone Sandstoneto better define the geographic, geographic?stratigraphic? distribution distribution of arsenic arsenic in bedrock. In InOctober October1997, 1997?aa well well was was drilled drilled and and cored cored to to collect collect aa complete complete stratigraphic overlying and and underlying underlying units. units. The stratigraphic section of the Marshall Sandstone and immediately overlying The hole County?near nearone oneof ofthe themost mostcontaminated contaminatedwells wellsknown knownininthe thestudy studyarea. area. hole was was drilled drilledin in Huron HuronCounty, Core Core from from that that hole hole and and cuttings cuttings and and core core from other producing wells have formed the basis for this study. study. The The Marshall Marshall Sandstone Sandstoneis is aa fluvial .fluvialto marginal marine sequence that is present at subcrop in a belt encircling the central part of the encircling the central part of the Michigan Michigan Basin. Arsenic-contaminated Arsenic-contaminatedground groundwater waterisisknown knownonly only along along the the eastern eastern flank flank of of the the basin. basin. As Asseen seenininthe theHuron HuronCounty Countycore, core,the theMarshall Marshallisisaavery very heterogeneous interbedded with massive heterogeneousunit unit of of mediummedium- to to coarse-grained, coarse-grained, gray to brown sandstone sandstone interbedded to to laminated laminated gray gray and and red red siltstone siltstoneand and thin units of black to gray shale. Fossil Fossilplant plantdebris debrisisispresent present and and pyrite pyrite isis common commonin in accessory accessoryamounts amountsin inmany manyunits. units. Arsenic Arsenic isis very very unevenly unevenly distributed distributed in in the Marshall. Highest Highestvalues valuesin inthe theHuron HuronCounty Countycore, core,up upto to 255 mg/kg, are in black shale units. Most sandstone and siltstone have an arsenic content below the 255 m a g yare in black shale units. Most sandstone and siltstone have an arsenic content below the analytically mglkgarsenic. arsenic. analyticallydetectable detectablelimit limit (5 (5 mg/kg), mgkg) but butsome somesandstone sandstonebeds bedscontain containas asmuch muchas as25 25mg/kg Average Average sandstones sandstonescontain contain about about 22 mg/kg mgkg arsenic, arsenic?and so even these relatively low values are anomalous. adjacentLapeer LapeerCounty Countycontain contain as as much much as as 350 350 mg/kg mgkg arsenic. arsenic.The The anomalous. Cuttings Cuttingsfrom fromwells wellsininadjacent strongly strongly anomalous anomalousarsenic arseniccontent content of of the the Marshall Marshall Sandstone Sandstonein in the the area area of of arsenic arseniccontaminated contaminated ground ground water water lends lendsstrong strongsupport supportto to the the earlier earlierbelief belief that that the the source sourceof of arsenic arsenicisisnatural naturaland andwithin within the the Marshall Marshallaquifer. aquifer. Electron Electron microprobe microprobe studies studies of of well cuttings cuttings from Lapeer and Tuscola Counties show that essentially all all arsenic arsenic is is in in pyrite. pyrite. Pyrite Pyriteisisubiquitous ubiquitousininthe theMarshall MarshallSandstone, Sandstone?typically typicallyin in trace traceconcentrations, concentrationsy but locally rock, mostly as porelocally constitutes constitutesfrom from aa few few percent to as much as 20 percent of the rock? occluding occluding cement. cement. Pyrite Pyrite formed formed during during several stages of diagenesis. Early Earlydiagenetic diageneticpyrite pyriteformed formed coatings on detrital grains. Framboidal pyrite formed in intermediate stages of diagenesis and coatings on detrital grains. Framboidal pyrite formed in intermediate stages of diagenesis and precipitated overgrowths. Late precipitated on on authigenic authigeniccarbonate carbonate and chlorite chlorite or on authigenic quartz overgrowths. Latestage stage pyrite pyrite encapsulated encapsulatedframboids framboidsand andin inplaces placesformed formeddisplacive displacivepyrite pyritemasses. masses. 50 �Arsenic Arsenic is very unevenly distributed in pyrite at virtually all scales, even to the limit of resolution of the microprobe. Many Manypyrite pyritegrains grains have have little little or no arsenic arsenic at the limit of detection (about 0.01 mass percent), whereas enrichment. whereas nearby grains grains (within the same rock chip) may have extreme arsenic enrichment. Individual 6.5 mass percent arsenic. Arsenic Arsenic shows a variety of Individual analyzed analyzed points points contain contain as as much much as as 6.5 modes of occurrence, but the most common is as strong enrichments enrichments in rims on individual framboids framboids (see figure). ItItappears appearsthat that aa majority majorityof of arsenic arsenic was introduced during an intermediate stage of pyrite diagenetic growth, at the end of framboidal pyrite formation. Both Both framboid framboid cores cores and and later laterovergrown overgrown pyrite are not enriched in arsenic. Some Someother othertrace traceelements elementsalso alsoshow showenrichment. enrichment.Some Somearsenicarsenicenriched enriched pyrite contains contains as much as 0.7 mass % Ni Ni and and0.5 0.5 mass mass% %Co. Co. A critical critical remaining remaining question question is where and how arsenic is released from pyrite to contaminate ground water. In Ingeneral, general,the theoxidation oxidationof ofarsenic-bearing arsenic-bearingpyrite pyritemust mustbe bethe thefundamental fundamentalcontrol controlof ofarsenic arsenic release. Most Mostarsenic arsenicseems seemsto to be be contained contained in in black shale units, which are not aquifers and have not been observed to be undergoing undergoing oxidation. oxidation. It seems likely, therefore, that arsenic is introduced to concentrations in the coarser sandstones that that form form the the aquifers aquifers within the ground water from smaller concentrations 25 mg/kg mglkg over several Marshall Sandstone. Observed Observedarsenic arseniccontent contentof of coarse coarse sandstone sandstoneisis as as high high as as 25 feet, or tens of feet, of section. The Thesandstones, sandstones,therefore, therefore,have have concentrations concentrationsseveral severalhundred hundredtimes times in quantitative terms terms to to provide provide enough arsenic to greater than the MCL for drinking water and are able in contaminate contaminate a large volume of ground water. Results Results to to date dateindicate indicate that that the the potential potentialfor for natural natural contamination of ground water is controlled by a variety variety of of factors factors including total total arsenic arsenic contamination characteristics of the the rock, rock, and by by poorly poorly know factors such as content of the rock and hydrologic characteristics biological mediation of pyrite solution and variable redox conditions of ground water in both time and place. in arsenic-rich pyrite, in Electron microprobe microprobe map showing showing framboids of arsenic-poor pyrite encased in turn overgrown overgrown by arsenic-poor pyrite. Map of iron distribution (left) outlines large pyrite grains (lightest shade) shade) that have grown in pore space between quartz clasts (black). Authigenic clay (intermediate gray) also fills pore space. space. Arsenic distribution is shown on the the right, right, the the same same field field of of framboids now completely enclosed view as the iron map. Arsenic is concentrated on rims of pyrite frarnboids within late late stage stage pyrite. pyrite. 51 �REiNTERPRETATION REINTERPRETATIONOF OF THE THE PENOKEAN PENOKEAN CONTINENTAL CONTINENTAL MARGIN MARGIN IN IN PART PART OF NORTHERN NORTHERN WISCONSIN WISCONSIN AND AND MICHIGAN MICHIGAN W.F. W.F. Cannon, Cannon, U.S. U.S. Geological GeologicalSurvey, Survey,Reston, Reston,VA VA G.L. G.L. Laberge, Laberge, UW-Oshkosh, UW-Oshkosh, Oshkosh, Oshkosh, WI WI J.J. S. Klasner, Kiasner, Western Illinois Illinois University, University, Macomb, Macomb, IL IL K.J. Schulz, U.S. Geological Survey, Reston, K J. Schulz, U. S. Geological Survey, Reston,VA VA The Thedepositional depositionaland and tectonic tectonic history history of of part part of of the the Penokean Penokean continental continental margin margin has has been clarified clarifiedby by field field studies, studies, and and examination examination of of previously previously proprietary' proprietary1magnetic, magnetic,electroelectromagnetic, drillcore coredata. data. AAcontinental continentalmargin marginterrane, terrane,informally informallycalled calledthe theMarquette Marquette magnetic,and anddrill terrane, terrene, inasmuch inasmuchas asitit isis composed composed largely largely of of rocks rocks of of the Marquette Marquette Range Range Supergroup Supergroup and and its Archeanbasement, basement,consists consistsof ofthree threesubterranes, subterranes,each eachwith withits itsown owncharacteristic characteristicdepodepoitsArchean sitional sitional and and tectonic tectonic history (see figure). The Thesubterranes subterranesare areseparated separatedby bymajor majorPenokean Penokean faults, faults,each eachprobably probablyaanorthward-directed northward-directedthrust. thrust. POWELL POWELLSUBTERRANE SUBTERRANE LAKESUBTERRANE SUBTERRANE PINE LAKE Marquette Vflyj metasedimentary MarquetteRange RangeSupergroup Supergroup metasedirnentary & metavolcanic metavolcanicrocks rocks [i] Graywacke. metavolcanic rocks, Graywacke, metavolcanic rocks,schist schist & Archeangranitic graniticrocks rocks Archean Basal Basalferrugenous ferrugenousunit unit Archean Archeangreenstones greenstones Archean Archean gneiss gneiss WISCONSIN TERRANES WISCONSINMAGMATIC MAGMATICTERRANES PARK PARK FALLS FALLS SUBTERRANE SUBTERRANE ±Xg Granite Graywacke, Graywacke,schist, schist, metavolcanic metavolcanicrocks rocks gi Archeangneiss - Metavolcanic rocks - Keweenwan thrustfaults faults — A.. — Keweenwan thrust Penokean 7 Penokeanthrust thrust faults faults y 1 'We Corporation for permission penuission to We thank thank Cominco ComincoAmerican American Incorporated and and Kerr-McGee Corporation to publish publish detailed detailed aeromagnetic area aeromagneticand and electromagnetic electromagnetic data data for for parts of our study a rea 52 52 �The Marquette terrane includes those areas where the Marquette Range Supergroup was deposited in a tectonically unstable environment for at least part of its depositional history and was subsequently significantly deformed and metamorphosed during the Penokean orogeny. The Theterrane terrane isis bounded bounded on on the north by areas where the Marquette Range Supergroup Supergroup was deposited in a stable cratonic or foreland setting and was not appreciably deformed during the Penokean orogeny (central Gogebic Iron Range for instance), and on the south by the volcanic arcs of the the Pembine-Wausau Pembine-Wausau terrane. terrane. The essential characteristics characteristics of each subterrane subterrane are outlined below. Pine Lake subterrane subterrane 0 Archean granite, granite, greenstone, greenstone, and and metagraywacke. metagraywacke. • Basement is Late Archean 0 Early Proterozoic has quartzite and dolomite of Proterozoic has quartzite and dolomite Chocolay Group at base. • Formation, iron-formation iron-formation including including shallow-water shallow-water oolitic ooliticjasper, jasper, and and • Menominee Group consists of Palms Formation, abundant volcanic volcanic rocks. rocks. Group abundant Group was was deposited deposited in in tectonically tectonically active region, probably in syndepositional grabens. Early Proterozoic rocks were strongly deformed, generally with increasing intensity of deformation deformation to the • south. south. basement rocks rocks were were not not deformed deformedpenetratively penetratively during duringthe thePenokean Penokeanorogeny. orogeny. • Archean basement Penokean granitic rocks are rare. • Penokean granitic rocks are rare. grade ranges ranges from from chlorite chloriteto to garnet garnet (locally (locally staurolite). staurolite). • Metamorphic grade Powell subterrane subterrane Powell • Basement is is Early and and Late Late Archean Archean gneiss. gneiss. 0 Proterozoic rocks widespread basal ferruginous slate slate and and lean leaniron-formation, iron-formation, Early Proterozoic rocks include include a widespread basal unit of ferruginous • Early quartzite, and black suffidic sulfidic slate and an overling succession of metapelitic metapelitic and and lesser lessermetavolcanic metavolcanicrocks. rocks. correlative with the Marquette Range Supergroup, The rocks are probably broadly correlative Supergroup, but details detailsof of correlation correlation are not known. known. basement was penetratively penetratively deformed deformed along along with with Early Early Proterozoic cover during the Penokean Penokean • Archean basement orogeny. orogeny. • Dikes and segregations segregations of of Penokean Penokean granitic granitic rocks rocks are are widespread. widespread. pressure metamorphism metamorphism occurs throughout throughout. Pelitic assemblages are biotitebiotite• High temperature and high pressure gamet-staurolite-kyarnte. garnet-staurolite-kyanite. Park Falls subterrane • Basement is is Archean Archean gneiss. gneiss. 0 politicschist, schist,carbonaceous carbonaceoussulliclic sulfidicslate, slate, and and subordinate subordinatemetavolcanic metavolcanicrocks. rocks. • Early Proterozoic rocks are peitic equivalent to the Marquette Range Supergroup but details of correlation The rocks are probably broadly equivalent correlation are are unknown. unknown. 0 are intensely folded folded in in multiple multiple folding foldingevents. events. • Rocks are 0 segregationsof of Penokean Penokean granitic graniticrocks rocks are are abundant. abundant. • Dikes and segregations Peliticassemblages assemblagesare arebiotite-garnet-sillimanite. biotite-garnet-sillimanite. • Metamorphism is moderate temperature and pressure. Pelitic The assemblage assemblage of subterranes subterranes hereby defined in Wisconsin and Michigan is similar to the assemblage known in analogous parts of the Penokean orogen in Minnesota. In Inparticular, particular, we suggest suggest that the Flambeau Flowage Fault in Wisconsin and Michigan is the eastward extension of the Malmo discontinuity discontinuity in in Minnesota. Minnesota. Both structures structures thrust Archean gneiss and highly metamorphosed Early Proterozoic strata northward over less deformed and metamorphosed Early Proterozoic Proterozoic strata. strata. 53 �GEOGRAPHICINFORMATION INFORMATIONSYSTEM SYSTEMON ONTHE THE GEOLOGY GEOLOGYAND AND COPPER COPPER GEOGRAPHIC DEPOSITS DEPOSITSOF OFTHE THEKEWEENAW KEWEENAW PEMNSULA PENINSULA W.F. W.F.Cannon, Cannon,U.S. U.S.Geological GeologicalSurvey, Survey,Reston, Reston,VA VA Michele MicheleE. E.McRae, McRae,Oak OakRidge RidgeAssociated AssociatedUniversities, Universities,Reston, Reston,VA VA Suzanne Reston, VA VA Suzanne W. W. Nicholson, Nicholson, U.S. U.S. Geological Geological Survey, Survey,Reston, Twonew newproducts productson onthe thegeology geologyand andmineral mineraldeposits depositsof ofthe theKeweenaw KeweenawPeninsula Peninsulaand and Two surroundingarea areahave haverecently recentlybeen beendeveloped: developed:aatraditional traditional1:100,000 1:100,000scale scaleU.S. U. S.Geological Geological surrounding Surveygeologic geologicmap map(now (nowininpress) press)and andaageographic geographicinformation informationsystem system(GIS) (GIs)database. database. Survey These Theseproducts productsare arebased based largely largelyon ondetailed detailedgeologic geologicmaps, maps, many manyatat aascale scaleof of1:24,000, 1:24,000, published during during the the past past 50 50 years. years. They Theypresent presentnew newdata dataand andinterpretations interpretationsininparts partsofofthe the published area.The Thepaper paperproduct productwas wascompiled compileddigitally digitallyand anddigital digitalproduction productiontechniques techniquesare arebeing being area. used usedtotostreamline streamlinethe theprinting printingprocess. process. /1 \ Formations Paleozoic undivided J Jacobsville Sandstone Freda Sandstone Nonesuch Formation Copper Harbor Conglomerate Indiana Felsite Portage Lake Volcanics Diabase dikes Siemens Creek Volcanics Michigamme Formation Granitic gneiss Geology Geologyofofthe dieKeweenaw KeweenawPeninsula Peninsulaand andvicinity vicinitygeneralized generalizedbybyformation. formation. 54 �The The data data were were developed developed using using the Environmental System Resource Institute's Institute's ARC/INFO ARCIINFO softwareand and exported exported to to ArcView. ArcView. ArcView ArcViewisisaadesktop desktopmapping mappingsoftware softwarepackage packagethat that software provides provides aa variety variety of of tools tools for for the display, display, query, analysis, and output of geographically geographically referenced data sets. sets. This Thisparticular particular GIS GIs consists consistsof of coverages coverages and tabular data on on the the geology,structure, structure,mines, mines, mineral mineral deposits, deposits, hydrography, hydrography, and and transportation transportation networks networks of of the the geology, area. Most Mostofofthe thedetail detailfrom fromthe thesource sourcemaps maps has has been incorporated incorporated into the database. database. Map Map area. views showing showingfull fall detail detail can can be be constructed; constructed; however, however, the the data data have have been structured structuredto to allow allow views generalizationby by age, age, rock rock type, type, tectonic tectonic setting, setting, or or stratigraphic stratigraphicrank. rank. The Thefigure figureabove above was was generalization generated in inArcView, ArcView,by by generalizing generalizingthe thegeologic geologicunits unitsbased basedon onstratigraphic stratigraphicformation. formation. generated ArcView ArcView also alsoallows allows the the user user to to access accessinformation information either either by interactively interactivelyselecting selecting features features on on aa map map view, view, or or by by performing performing logical logical selection on the data tables. For Forexample, example,clicking clicking on tool will will open open aa window window that that provides provides tabular on aa mineral mineral deposit deposit with the 'identify' tool information informationon onmines minesthat thatworked workedthe thedeposit, deposit,amount amountof ofproduction, production,years yearsofofproduction, production, and and an an estimate estimate of of the the amount amount and and grade of remaining identified resources. resources. AAlogical logicalsearch search could could be be used to to identify identify native native copper copper lodes lodes with greater than 1% 1% Cu. Finally, Finally,this thisproduct product will will include includegeologic geologiccross crosssections, sections,aa correlation correlation chart, chart, aa description description of of map map units, units, and and interpretative interpretativetext. text. The Thecross crosssections sectionsare aredynamically dynamicallylinked linkedto tothe thecross crosssections sectionslines lineson on the themap mapview. view. 55 �GRAVITY VIRGINIA HORN HORN AREA, AREA, GRAVITY AND AND MAGNETIC MAGNETIC STUDIES STUDIES IN IN THE VIRGINIA MINNESOTA NORTHEASTERN MINNESOTA CHANDLER, Val W Minnesota CHANDLER, Va! W.,.,JIRSA, Mark A., and LIVELY, Richard L. Minnesota Geological Survey, 2642 2642 University Ave., St. St. Paul, Paul, MN MN 55114 551 14 Geological Survey, (chandOO4@maroon.tc.umn.edu) (chand004@maroon.tc.umn.edu) and magnetic magnetic data data were were used used to to supplement supplement geologic geologic field field mapping mapping of of Archean Archean rocks rocks Gravity and of the Virginia Horn area of northeastern Mimesota. Minnesota. Although Although outcrop outcropcontrol controlisis locally locally excellent, gravity gravity and and magnetic magnetic data data assist assist to a minor minor degree degree in mapping mapping areas areas covered covered by by excellent, glacial deposits and mine dumps. More More importantly, importantly, they provide additional information on geologic structure at depth. Preexisting Paleoproterozoic Preexisting subdivisions subdivisionsof the Archean and Paleoproterozoic rocks were used to guide mapping and geophysical work. Although the gross lithologic divisions divisions have have remained remained essentially essentiallyunchanged, unchanged, many many details detailsof of their their stratigraphic stratigraphicand and structural relations are now much better better known. known. Gravity data used in this study consist of of together with with 203 203 new new stations. stations. The new preexisting stations in the state-wide database together gravity stations development of a 50 km stations fill fill gaps in the previous coverage, and allow development northeast-southwest Virginia Horn area, area, together together with northeast-southwest profile profile across across the the Archean rocks of the Virginia (5-15 km) northwest-southeast profiles. The The magnetic magnetic data data are are from from the high shorter (5-15 five shorter resolution aeromagnetic resolution aeromagneticsurvey survey of of Minnesota; Minnesota; line line spacing spacing in in the the Virginia Virginia Horn Horn area area is is 400 400 Subsurfacestructure structurewas wasinvestigated investigatedusing using gravity gravity and and magnetic modeling on the long m. Subsurface profile. The gravity gravity and and magnetic data data were interpreted using grid images of processed data. Unfiltered and Unfiltered and derivative-enhanced derivative-enhanced versions versions of the the gravity and and aeromagnetic aeromagneticgrids grids reveal reveal many details of the bedrock geology. The Thenorthern northern part part of the the study area is underlain by Archean granitic rocks of the Giants Range Batholith. ItIt isis characterized characterizedby by aa strongly strongly negative Bouguer negative Bouguer gravity gravity anomaly anomaly and and aa busy, busy, moderatemoderate- to to high-amplitude high-amplitude magnetic magnetic mafic phases phases within within the the batholith is indicated indicated by signature. The Thepresence presenceof ofintermediate intermediateto to mafic signature. more more magnetic areas areas that that are are associated associated with highs in the derivative-enhanced derivative-enhanced gravity gravity data. Derivative-enhanced magnetic magnetic data data also delineate several previously unidentified northweststriking faults that extend across the batholith. A discontinuous discontinuous sliver sliver of high-grade strildng batholith. A metavolcanic metavolcanic and metasedimentary rocks, the Mimtac Minntac sequence, occurs along the the southern margin of the batholith. AAnegative negativeBouguer Bouguergravity gravity anomaly anomaly implies implies that the supracrustal supracrustal rocks of the Mimtac Minntac sequence are under-plated under-plated by by granitic graniticrocks rocksatatshallow shallowdepths. depths. The Minntac sequence sequence is separated separated from Archean rocks to the south by the east-west striking Laurentian fault. South Laurentian Southof ofthe theLaurentian Laurentianfault faultsubsub- to to low-greenschist low-greenschist grade grade metavolcanic metavolcanic and metasedimentary metasedimentary rocks rocks of the the Archean Archean Mud Lake Lake and and Midway sequences sequences are are characterized by aa positive characterized positive gravity gravity anomaly anomaly and and an an extremely extremely subdued subduedmagnetic magnetic signature. signature. Rocks of the Mud Lake sequence form aa broad broad southwest-plunging southwest-plungingsyncline. syncline. To the south are and west, the supracrustal supracrustal rocks rocks of the the Minntac, Midway and and Mud Lake Lake sequences sequences are Group. Regional covered by the Paleoproterozoic Animikie Group. Regional gravity data indicate that the major belt beltbeneath beneaththe theAnimikie Animikiebasin. basin. The The Biwabik Biwabik Archean rocks extend southwest as aa major Formation of the high-amplitude Iron Formation the lower lower Animilde Animikie Group Group is associated with complex, high-amplitude magnetic signatures; signatures; magnetic magnetichighs highsdelineate delineateoxide-rich oxide-richtaconites taconitesand andmagnetic magneticlows lows delineate natural ores and faults. delineate natural ores and faults. Gravity constmined by surface geologic mapping and rock Gravity and and magnetic modeling was constrained the properties determined from surface samples. The The models indicate that most structures in the Archean rocks have near-vertical dips. The Giants Range Batholith and the low-grade supracrustal extend to to about about 55 km km depth. depth. The supracrustal rocks of the Midway and Mud Lake sequences extend The composition Minntac sequence composition of the the crust crust below 5 km remains uncertain, although the Mimtac (which we infer to have been uplifted along the Laurentian fault) may yield clues because it has been extensively extensively invaded invaded by tonalitic and other early phases of the Giants Range Batholith. Models sedimentaryrocks rocksof of the theMud Mud Lake Lake Modelsclearly clearlyshow showthat thatthe thelow-grade low-gradesedimentary as thick thick as as 1 km km are are underlain underlain sequence lie within a structural structural trough; low-density sediments as 56 �by by moderately moderately high-density high-density rocks rocks inferred inferred to be largely basaltic. Thickness Thicknessof of the the sedimentary rocks rocks increases increases in in stepwise stepwise fashion fashion northwestward northwestward towards the center center of the sedimentary basin against againstnortheast-striking northeast-strikingfaults. faults. Sediment Sedimentthickness thicknessisisalso alsointerpreted interpretedto to increase increase basin appreciably to to the the northeast. northeast. These Theseresults resultsdemonstrate demonstratethat that gravity gravity and and magnetic studies are appreciably valuable valuableto to aa geologic geologicmapping mappingprogram, program,even evenin inareas areasof ofabundant abundantoutcrop outcropcontrol. control. ACKNOWLEDGMENTS ACKNOWLEDGMENTS This This study studywas wassupported supportedby by the theMinnesota MinnesotaLegislature Legislaturethrough throughthe theState StateSpecial Special Appropriation an appropriation appropriationrecommended recommended by the Minnesota Minnesota Minerals Coordinating Coordinating Appropriationand and an Committee. U.S.S.Steel SteelCorporation, Corporation,Inland InlandSteel SteelMining MiningCompany, Company, Committee. The Theauthors authorsthank thankU. Cliffs LTV Mining Mining Company, Company, American American Shield Company, the Cliffs Mining Mining Services ServicesCompany, Company, LTV Duluth Duluth Mesabi Mesabi and and Iron Iron Range Range Railway Railway Company, Company, and and the Minnesota Minnesota Power Power Company Company for for access access to their their properties properties and and for for providing providing elevation data. 57 �MINERAL POTENTIAL POTENTIAL ASSESSMENT ASSESSMENT OF NORTHERN ST.LOUIS ST.LOU1S COUNTY, COUNTY, SOUTHEASTERN KOOCHICHING COUNTY, AND NORTHEASTERN ITASCA COUNTY, SOUTHEASTERN MINNESOTA Va! Chandler, M.A. Jirsa, and G.B. Morey, Minnesota Geological Survey Survey Val W. Chandler, Presented Presented by Tom Tom Lawler, Lawler, Department Department of Natural Resources, Division Division of Minerals Minerals Minnesota Geological Survey The Minnesota Survey in a contract with the Department of Natural Resources, Resources, Division of Minerals Minerals produced a geologic map and mineral-potential assessment assessment of a contiguous contiguous township area twenty-six township area in northern St. Louis, southeastern southeastern Koochiching, and northeastern northeastern Itasca Counties, Counties, Minnesota. Six Six tholeiitic to caic-alkaline calc-alkaline volcanic sequences sequences of the Archean Archean Wawa subprovince subprovince are resolved that are usually separated by faults or metasedimentary belts, and are intruded intruded by a variety of syn- to late tectonic granitoid plutons. Eight criteria criteria are identified identified which indicate indicate potential for twenty-two lode gold deposits; Six Six criteria criteria identify identifj potential potential for for two two iron-formation hosted replacement gold deposits; Seven criteria identify potential for four iron-formation Seven criteria identifj potential four volcanic associated massive sulfide deposits; Seven Seven criteria criteria identify identi@ potential for maficultramafic intrusion intrusion hosted Cu-Ni-PGE deposits; Six Six criteria criteria identify identifj potential potential for for komatiite komatiite associated Ni-Cu-PGE deposits deposits (although (although the criteria criteria were developed only one area with PGE potential was identified); identified); and Two Two criteria identify identifj potential for two kimberlite kimberlite hosted diamond diamond deposits. All of these W h e r evaluation evaluation these areas areas are to be regarded with appropriate caution and further would require require detailed detailed exploration explorationincluding including drilling. The compilation map (Plate compilation of the bedrock geologic map (Plate 6), 61, the magnetic and gravity gravity model crosssections (Plate 7) and the mineral mineralpotential potential assessment assessment map map (Plate (Plate 9) used available available geologic geologic data combined combined with gravity gravity and and airborne airborne magnetic data. The interpretation interpretation used gridded gridded forms forms of of geophysical phenomena. Using geophysical data data that have have been enhanced enhanced to emphasize near-surface geologic phenomena. Using polarization the UTM based grid grid the aeromagnetic aeromagnetic data were enhanced by reduction to vertical polarization and calculation calculation of the second second vertical derivative. These procedures shift anomalies anomalies more directly directly over their sources anomalies to help clarify fiom regional scale anomalies clarifj the sources and eliminate eliminate interference from short wavelength wavelength signatures signatures of shallow shallow sources sources that lie at or near the Precambrian Precambrian surface. surface. With With aa similar similar procedure the gravity data data were enhanced by the calculation of the second second vertical derivative after smoothing by continuation to a level of two kilometers above derivative smoothing continuation kilometers above surface surface to eliminate eliminate "noise" caused caused by by variations variationsin in overburden overburden thickness. thickness. Much Much of of the the quantitative quantitativeanalysis analysisof of this this study are based on the Werner deconvolution method of inverse modeling using the approach approach proprietary software and proprietary software developed developed by by R.J. R.J. Ferderer Ferderer (1988). (1988). The contract resulted in a twenty-seven page open-file report 97-5: Chandler, V.W., Jirsa, M.A. and Morey, G.B., (1997) Mineral potential assessment of northern St. Louis County, southeastern southeastern Koochiching Koochiching County, County, and northeastern Itasca County, Minnesota. The report report includes includes a detailed detailed account of analytical procedures and results, rock property data, six cross cross sectional studies using gravity and magnetic modeling, five tables and nine plates displaying displaying results. This report and the plates plates are available in hard copy and digital digital format format at the Minnesota Minnesota Geological Survey, 2642 University Avenue, St. Paul, Minnesota, 55114-1057, 551 14-1057, Phone (612) (612) 6276274780 also the Minnesota Department of Natural Resources, 1525 Third Avenue East, Hibbing, Minnesota Department of Resources, 1525 Hibbing, Minnesota Minnesota 55746-1461, 55746-1461, Phone Phone (218) (218) 262-6767. 262-6767. 58 �EXTENSION OF THE HURONIAN MAGMATIC SUITE INSIDE INSIDE THE THE GRENVILLE PROVINCE: PROVINCE: NEW ZIRCON ZIRCON U-Pb EVIDENCE FROM THE THE GRENVILLE FRONT TECTONIC TECTONIC ZONE ZONE IN IN STREET STREETTOWNSHIP, TOWNSHIP,SUDBURY SUDBURY REGION, ONTARIO. F. Corfu, Museum, 100 100Queen's Queen'sPark, Park,Toronto, Toronto,ON ON M5S 2C6 and C o f i , Royal Ontario Museum, R.M. Easton, Precambrian Precambrian Geoscience Geoscience Section, Section, Ontario Ontario Geological GeologicalSurvey, Survey,933 933 Ramsey Lake Road, Sudbury, Sudbury, ON ON P3E P3E 6B5 6B5 The Sudbury region is characterized by very complex geological relationships relationships due to to the confluence and overlapping of multiple geological domains ranging in age from Archean to rifling of the Archean crust led to the the deposition of Neoproterozic. Early Paleoproterozoic rifting extensive ian Supergroup and was initially extensive clastic clastic sedimentary sedimentaryassemblages assemblagesof of the the Huron Huronian accompanied by the emplacement emplacement of bimodal mafic mafic and felsic, felsic, intrusive intrusiveand and extrusive extrusiverocks. rocks. Although the distribution distribution and petrogenetic features of these magmatic rocks is well understood in the region west of Sudbury, Sudburyythe fate of the Huronian remains a matter of speculation farther to the Frontythe only only exception exception being being the the previously previously dated dated River RiverValley Valley east and south of the Grenville Grenville Front, gabbro-anorthosite. In conjunction program gabbro-anorthosite. conjunction with an Ontario Ontario Geological Geological Survey S u ~ e mapping mapping y program along alongthe the Southern-Grenville Southern-GrenvilleProvince Province boundary, we have examined examined two examples examples of of metamorphosed metamorphosed granitic bodies and a metapyroxenite plug straddling the Grenville Front Front tectonic tectonic zone in Street 15 km east of Sudbury. Sudbury. Township, roughly 15 The metapyroxenite is part of a suite of small bodiesy bodies, generally less than 500m in size, that occur Coniston and and River River Valley. Valley. Mineralogically, Mineralogically, within the Grenville Grenville Front Front tectonic tectonic zone zone between between Coniston these bodies consist of roughly equal amounts of orthopyroxene phenocrysts (0.5-5 cm in size) in locally olivine phenocrysts are preserved. Metamorphic crystallization in an amphibole matrix; locally these bodies increases with increasing increasing distance from the Grenville Front, consequently, sampling was conducted on a body located only 250m southeast of the Grenville Front. The metapyroxenite contains highly resorbed, prismatic zircon yielding a U-Pb U-Pb data data array array that that points points toward toward an an upper upper intercept age of about 2490 Ma. The age corresponds corresponds approximately approximately to to that that of of the the East-Bull East-BullLake Lake and Shakespeare-Dunlop intrusionsyemplaced emplaced in in Archean crust crust at at the the margin margin Shakespeare-Dunlop (a.k.a. Agnew Lake) intrusions, Huronian basin basin east east of of Sudbury. Sudbury.On On the the basis basis of of SEM SEM examination, examinationymost mostof ofthe thezircon zirconfound found of the Huronian in this sample is located within the orthopyroxene orthopyroxene phenocrysts, in in conjunction conjunctionwith with Cr-spinel Cr-spineland and chromite. In addition, the matrix of the metaproxenite is chemically differentiated. Thus, we are confident that the zircon fraction yielding the upper intercept age of 2490 Ma dates emplacement metapyroxenite was metamorphosed and developed metamorphic zircon during of these rocks. The metapyroxenite an event at about about 1700-1600 1700-1600Ma, Ma, and and was was subsequently subsequentlyoverprinted overprintedby by Grenvillian-age Grenvillian-age metamorphism. metamorphism. Two granitic bodies were sampled. The first was a foliated monzogranite located in an area south of the Ess Creek fault and north of the Grenville Front boundary fault as mapped by Lumbers 59 �(1973). This fault-bounded fault-bounded region has been variously variously assigned assigned to the Southern Southern or or Grenville Grenville provinces, and has been subjected subjected to middle to upper amphibolite amphibolite facies facies metamorphism. metamorphism.The The second body is located about about 15 15 km south of the first, and is is one one of several several similar similar bodies bodies located located within the Grenville Grenville Province. Province. Both sampled granites, granites, as as well as as other other bodies bodies south south of of the the Grenville Grenville plutonic body or a suite of Front, are chemically similar, suggesting they form part of a larger plutonic FeOt0 >35% intrusions. intrusions. In particular, particular, they they are are characterized characterizedby by Si02 Si0266-72%, 66-72%, Al203 A120311.9-12.6%, 11.9-12.6%, FeotO&' >3.5%, CaO >1.5%, La/Yb >IS%, EufEu* Eu/Eu* .55-.70, -55--70,L a b 5-8, and Gd/Yb GdNb 1.2-1.65, 1.2-1-65, and are identical identical in major major and and REE geochemistry with Stobie Formation Formation dacites from both the Sudbury Sudbury and Street Street Township Township areas. areas. On On they plot plot in in the the Within-Plate Within-Plate granite granite field. field. In In various geochemical discrimination diagrams, they contrast, felsic rocks of the Murray and Creighton granites granites and the Copper Copper Cliff Cliff rhyolite rhyolite have have lower Feotoh' FeOt0 contents contentsand andhigher higherSi02 Si02and andalkali alkalicontents. contents.In Inaddition, addition,REE REEdata, data,only onlyavailable available from the Copper Cliff rhyolites, have Eu/Eu* EufEu* c.5, <.5, LLa/Yb <5.5and andGdffb Gd/YbC.75. <.75. The foliated a b -3.5 monzogranite monzogranite defines defines a U-Pb zircon age age of about about 2460-2450 Ma, which overlaps overlaps the the age age of of some some of the youngest magmatic expressions of the Huronian Huronian rifting rifting event event such such as as the the Copper Copper Cliff Cliff rhyolite rhyolite and the Hearst Hearst dyke dyke swarm. swarm. The The granite granite was was overprinted overprinted by by Grenvillian Grenvillianmetamorphism metamorphism that strongly, strongly, but not not totally totally reset reset the the titanite titanite ages. ages. The The zircon zircon data data for for the the second secondgranitic graniticbody body display more pronounced effects of both a 1700-1600 1700-1600 Ma event and the Grenvillian Grenvillian orogeny orogeny at at about 990-980 Ma, but are nevertheless nevertheless consistent consistent with a Huronian Huronian age and with the the chemical chemical similarities similarities between these granitic granitic intrusions. intrusions. are consistent consistent with field field relations relations which which show show aa close close spatial spatial The ages on the bodies reported here are relationship between the metapyroxenites, metapyroxenites,the the granites, granites, and and mesocratic mesocratic to to anorthositic anorthositicgabbros gabbros relationship likely correlative with the ca. 2475 Ma River Valley gabbro-anorthosite. gabbro-anorthosite. In addition, addition, the foliated foliated monzogranite is spatially associated with a thin sliver of mafic and felsic metavolcanic rocks that monzogranite that correlated with the the Huronian Huronian Stobie Stobie Formation. Formation. The The latter latter are are the the only only Huronian Huronian have been correlated volcanic rocks so so far far identified identified east east of of Sudbury. Sudbury. These These field field relationships, relationships,in in conjunction conjunctionwith withthe the geochronological results results reported reported herein, herein, suggest suggest that that the the Huronian Huronian magmatic magmatic province provinceisismore more geochronological extensive extensive east of of Sudbury Sudbury than previously previously recognized. In In addition, addition, felsic felsic magmatism magmatismof ofHuronian Huronian longer confined confined to to the the vicinity vicinity of of Copper Copper Cliff, Cliff, and and indeed, indeed, could could be be more more extensive extensivethan than age is no longer previously thought, thought, particularly particularly in in the the area area of of the the little littlestudied studiedeastern easternCobalt Cobaltplate. plate. previously Reference: 1973. River Valley area; Ontario Ontario Division of Mines, Preliminary Map, P.844. Lumbers, S.B. 1973. P.844. 60 �KINEMATIC KINEMATIC FABRICS FABRICS NEAR MINE MINE CENTRE, CENTRE, ONTARIO: EVIDENCE EVIDENCE FOR A MODIFIED MODIFIED TRANSPRESSION TRANSPRESSION MODEL. MODEL. Czeck, and Hudleston, Hudleston, P. J., Department Department of Geology and Czeck, D. M. and Geophysics, Geophysics, University of Minnesota, Minnesota, 310 3 10 Pillsbury Pillsbury Dr. Dr. SE, SE, Minneapolis, MN 55455 55455 The The boundary boundary between between the the Quetico Quetico and and Wabigoon Wabigoon subprovinces subprovinces of the the Archean Archean Superior Superior Province is characterized by ductily deformed GreenschistGreenschist- Arnphibolite Amphibolitefacies faciesrocks. rocks. The two subprovinces continental accretion accretion processes. processes. The subprovinces have been amalgamated through continental working working kinematic kinematic model model to to describe describe this this area area is is transpression, transpression, which which explains explainsthe the dominant dominant flattening flattening fabric fabric in the vertical vertical plane and the evidence for noncoaxial strain noted in the horizontal plane. Theoretical Theoreticalwork workon onclassical classicaltranspression transpression has has shown shown that that the the long long axis of the the strain strain ellipsoid,' ellipsoid,and either vertical or or axis and thus the mineral lineation, are necessarily either horizontal. horizontal. Structural Structuralfield fieldwork workin inthis thisstudy studyhas hasshown shownthat that the the lineations lineationsalong along the the Wabigoon-Quetico boundary plunge between 0-90' 0-90° within within the the foliation foliationplane. plane. Therefore, a modification modification to to the the three-dimensional three-dimensionaltranspression transpressionmodel model isis necessary necessaryto toadequately adequately describe describe the deformation deformation process. One Onepossible possiblemodification modificationto to transpression transpression which which explains explains the the oblique oblique lineations lineations is is heterogeneous heterogeneous extrusion extrusion due due to anastomosing anastomosing shear shear zones. zones. 61 �New New Aeromagnetic AeromagneticSurveys SurveysininWisconsin Wisconsinby bythe theU.S. U.S.Geological GeologicalSurvey Survey David DavidL. L.Daniels, Daniels,Stephen StephenL. L.Snyder, Snyder,Suzanne SuzanneW. W.Nicholson, Nicholson,William William F. F. Cannon, Cannon,U.S. U.S.Geological Geological Survey, Survey, MS MS 954 954National National Center, Center,Reston, Reston, VA VA20192 20192 Aeromagnetic Geological Aeromagneticsurveying surveyingin in Wisconsin Wisconsin over over the the past past 10 10years yearsby by the theU.S. U. S.Geological Survey Survey(USGS) (USGS)has has added addedconsiderably considerably to to the the coverage coveragein in the the state stateand and to tothe thedigital digital aeromagnetic database of the USGS Mineral Resources Program. Initial efforts aeromagnetic database of the USGS Mineral Resources Program. Initial effortswere weredirected directed toward towardcompleting completingthe thecoverage coverageininthe thenorthern northernpart partofofthe thestate stateininwhich whichPrecambrian Precambrianbedrock bedrockisis atatthe thesurface surfaceor orcovered coveredby byglacial glacialdeposits. deposits.The Theflight-lines flight-lineswere wereflown flownin in aa N-S N-S direction direction because because of of the the predominant predominanteasterly easterly or or northeasterly northeasterly grain grain of of the the geology, geology, were were spaced spaced '/2-mile %-mile apart, apart,and andflown flown at at 500 500or or1000 1000ftftabove aboveterrain. terrain. The Thesurveys surveyswere weredesigned designedto toextend extendthe thelarge large survey 1990), surveyconducted conductedby byJohn JohnKarl Karlofofthe theUniversity UniversityofofWisconsin, Wisconsin,Oshkosh Oshkosh(Karl, (Karl, 1986; 1986;King, King,1990), priorto to1977. 1977. prior In In1988, 1988,the theUSGS USGSflew flewaa3900 3900line-mile line-mileaeromagnetic aeromagneticsurvey surveyin in the thenorthwestern northwesterncorner comer of ofWisconsin Wisconsin south south of of Lake Lake Superior. Superior.In In 1996, 1996,USGS USGSsurveying surveyingwas was continued continued in in two two areas areas adjacent to the 1988 survey (see index map) for an additional 6700 line-miles. These two adjacent to the 1988 survey (see index map) for an additional 6700 line-miles. These twosurveys surveys completed completed the the coverage coverageof ofthe thevolcanic volcanicand andsedimentary sedimentaryrocks rocksin in the theMidcontinent Midcontinentrift riftsystem. system. These Thesenew new data datahave haveled led to tonew newinterpretations interpretationsofofstructures structuresininthe thehighly highlymagnetic magneticKeweenawan Keweenawan basalt basalt flows flows in in the the St. St.Croix Croixhorst horst (Cannon (Cannonand and others, others,1997). 1997).In Inthe themost mostrecent recent(10/97-3/98) (10197-3198) survey, survey, aeromagnetic aeromagneticdata datahave havebeen beenacquired acquiredininthree threeblocks blocksin in aabroad broadswath swaththrough throughthe the central central part part of ofthe the state, state,ininthe theMarinette-Green Marinette-GreenBay Bay area, area, the theWisconsin Wisconsin Rapids Rapids area, area, and and the the Mississippi Mississippi River River area area (about (about16,000 16,000line-miles). line-miles). In In addition, addition,two two small small areas areas along along the the Wisconsin-Michiganborder borderwere werefilled filledin. in. Wisconsin-Michigan In 50m) veneer (<150m) veneer of of In much much of ofthe thearea areacovered coveredby bythe themost mostrecent recentsurvey, survey,aathin thin(<1 magnetically magnetically transparent transparentCambrian Cambriansandstone sandstoneoverlies overliesthe themore morehighly highly magnetic magneticEarly Earlyand andMiddle Middle Proterozoic Proterozoicrocks; rocks;ininthe thewestern westernpart partnon-magnetic non-magneticMiddle MiddleProterozoic Proterozoicsedimentary sedimentaryrocks rocksform form part part of of the the basement. basement. Thus, Thus,although althoughthis thisisisan anarea areaof ofvery very little little outcrop, outcrop, the the aeromagnetic aeromagnetic data data effectively effectively delineate the structure structureand and character characterof ofthe theburied buried basement basement rocks. rocks.The Theenhanced enhanced understanding understandingof of the the basement basement geology geologyprovided providedby by the theaeromagnetic aeromagneticsurvey surveywill will allow allow better better evaluation evaluationof of the the mineral mineral potential potential of of this this region region and and aid aid in in regional correlations correlationsof of basement terranes terranesin in the the region. region. Maps Maps of of the the new new aeromagnetic aeromagneticsurvey survey and the current current aeromagnetic aeromagnetic compilationof ofWisconsin Wisconsinwill will be be shown. shown. compilation References Cited Cited References Cannon, Cannon, W.F., W.F.,Daniels, Daniels, D.L., D.L., Snyder, Snyder,S.L., S.L.,1997, 1997,New Newaeromagnetic aeromagneticmap mapofofthe theMidcontinent Midcontinent Rift Rift in in Northwestern NorthwesternWisconsin Wisconsin and and adjacent adjacent Minnesota; Minnesota;Geological Geological Society Society of of America America 1997 1997 abstractswith with programs, programs, v. v. 29, 29, no. no. 4, 4, p. p. 9.9. abstracts Karl, Karl, J.H., J.H.,1986, 1986,Total Totalmagnetic magneticintensity intensitymap mapof ofnorthern northernWisconsin; Wisconsin;Wisconsin Wisconsin Geological Geological and and Natural History Survey, Map 86-7, scale 1:250,000. Natural History Survey, Map 86-7, scale 1:250,000. King, King, E.R., E.R.,1990, 1990,Precambrian Precambrianterrane terraneofofnorth-central north-centralWisconsin: Wisconsin:an anaeromagnetic aeromagneticperspective; perspective; Canadian Journal Journal of of Earth Earth Science, Science, v. v. 27, 27, pp. pp.1472-1477. 1472-1477. Canadian 62 �Index of Recent Aeromagnetic Aeromagnetic Surveys Surveys in in Wisconsin Wisconsin 93 93- 91 91' 9T 92' 88 88- 89 89' 9O 90' 8T 87' 46 45 44 43 92 0 50 88° 89° 90° 91° 150 100 63 200 KM �POLYMETAMORPHISMOF OF SKARNS SKARNS RELATED RELATED TO TO THE MORIN POLYMETAMORPHISM MORIN ANORTHOSITE ANORTHOSITE COMPLEX, GRENVILLE COMPLEX, GRENVILLE PROVINCE, PROVINCE, QUEBEC. QUEBEC. DEANGELIS1, DEANGELIS l , M. T., PECK, W. H., and VALLEY, VALLEY, J.J. W., W., Department Department of Geology Geology and Geophysics, University of Wisconsin, Wisconsin, Madison, Madison, Madison, Madison, WI, WI, 53706, 53706, william@geology.wisc.edu. william@geology.wisc.edu.1student ^student author caic-silicate assemblages Skarn calc-silicate assemblagesassociated associated with with the the Mona MorinAnorthosite AnorthositeComplex Complexare areexposed exposed—2 -2 km west of the town of St. St. Jovite, Jovite, Quebec, Quebec,and anddisplay displayfield fieldrelations relationsand andreaction reaction textures textureswhich whichindicate indicateaa polymetamorphic origin. small dioritic dioritic and and monzonitic monzonitic intrusive intrusive bodies, bodies, which which are are located located -25 small polymetamorphic origin. A set of —25 between two mapped bodies bodiesofofmangerite mangerite(Martignole (Martignoleand andConiveau, Corriveau,1993) 1993)outcrop outcropinina a—300 -300 meter meter long long These bodies bodies are are rimmed rimmed by by 10-20 cm cm thick thick series of four roadcuts in calcite marble along Highway 117. These skarns containing containing metasomatic metasomatic banding of garnet, diopside, and wollastonite. wollastonite. This This locality locality occurs occurs adjacent adjacent ± 3 Ma (Doig, 1991). to the western margin of the Morin Anorthosite Anorthosite Massif which was emplaced at 1155  bodies that that were were emplaced emplaced 1135 1135 ±3 The anorthosite is associated with mangerite bodies 3 Ma (Doig, 1991). The The area was metamorphosed anorthosite massif metamorphosedunder granulite granulite facies facies conditions conditions following emplacement of the anorthosite of 650-775 650-775 O °C Martignole, 1989). 1989). This to pressures of 6-8 kb and temperatures of C (Indares and Martignole, metamorphism metamorphism has been been dated dated at at 1070-1100 1070-1100Ma Ma by Rb-Sr Rb-Sr whole whole rock isochrons isochrons (see (see Doig, Doig, 1991). 1991). Descriptions of skarns Descriptions of skarns Well developed developedskarns skarns appear appear on both diorite diorite and monzonite bodies. We Weinterpret interpretthese thesebodies bodies as as intrusive relict igneous igneous textures. textures. On intrusive because because of cross-cutting cross-cutting relationships relationships between different intrusions and relict exposed with diameters diameters exposed surfaces, surfaces, diorite diorite bodies bodies vary vary in in both both size size and and shape, shape,but but are are typically typically circular circular to to oval oval with ranging from 11 to 10 10 meters. meters. The Thediorite dioriteintrusives intrusivesare arecomposed composedprimarily primarily of of plagioclase plagioclase with with minor minor amounts of clinopyroxene, amphibole, biotite, magnetite, pyrite, and sphene. Metamorphic Metamorphicminerals minerals and clinozoisite. which are are made made up upof of include calcite, garnet and clinozoisite. Surrounding Surroundingthe the diorite diorite intrusives are skarns which concentric garnet-, clinopyroxene-, cinopyroxene-, and and wollastonite-rich wollastonite-rich bands. Next Next to to the the diorite, diorite, garnet-rich bands are —10cm cmthick. thick.Wollastonite-rich Wollastonite-richbands bands(in (inthe themiddle middleof ofthe theskarn) skarn)are arethinner thinner(51 (1 cm) cm)and andsometimes sometimesare are -10 cmthick thick and gradually not present. Clinopyroxene-rich Clinopyroxene-richbands bands are are —15 -15 cm gradually grade grade into the marble. The Thegarnetgarnetplagioclase, quartz, calcite, sphene, and small amounts of pyrite. pyrite. rich bands contain garnet, clinopyroxene, clinopyroxene, plagioclase, plagioclase, garnet, The wollastonite-nich wollastonite-rich bands are composed of wollastonite, clinopyroxene, calcite, plagioclase, and pyrite. pyrite. The clinopyroxene-rich bands are are made made up up of of quartz, sphene, and small amounts of graphite and clinopyroxene, calcite, garnet, clinopyroxene, garnet, plagioclase, plagioclase, quartz, quartz, sphene, sphene, with minor amounts amounts of graphite and pyrite. monzomte intrusives The monzonite intrusives are composed of potassium feldspar feldspar and plagioclase plagioclase with minor amounts of clinopyroxene, and sphene. Metamorphic quartz, clinopyroxene, Metamorphic minerals minerals include include calcite, calcite, garnet, garnet, and Fe-vesuvianite (Fe/Fe+Mg=0.65 determined determined by electron microprobe). FeFevesuvianite is visibly zoned in hand sample, with Fe-rich rims (Fe/Fe+Mg=0.67) (FeIFe+Mg0.67) and andless less Fe-rich Fe-rich cores (Fe/Fe+Mg=0.61). Fe-vesuviamte Fe-vesuvianitecrystals crystalscan can reach reach lengths cmand andare are found found within within the the monzonite monzonite and lengths of —6 -6 cm the inner most skarn band. Within Withinone onemonzonite monzonitebody, body, an unusual unusual texture texture consisting consisting of of aa cylinder cylinder of of matrix matrix minerals minerals (potassium (potassiumfeldspar, feldspar,plagioclase, plagioclase,garnet, garnet,and and quartz) quartz)encased encasedby byaasingle singlecrystal crystalofofelongate elongate(—2-6 (-2-6 cm cm long, width50 mm)clinopyroxene clinopyroxene(En26Fs23Wo50Ac1) (En2(;Fs23W050Acl) width90mm) occurs. This gives these crystals a "hollow" appearance in thin section and on the outcrop. Monzonite Monzonite occurs occurs both Fragmented diorite dioriteintrusion. intrusion. Figure 1. Fragmented semi-circular bodies (1-10 as semi-circular (1-10 m in diameter) diameter) as as well as Skam is developed Skam developed where where hot hot diorite diorite contact with with marble. marble. Brittle came into contact Brittle dikes which cross cut diorite. Skarns Skarns around the deformation of of diorite and skarn postdeformation monzonite consist of small (3-5 cm) garnet- and intrusion. dates intrusion. clinopyroxene-rich bands. Garnet-rich clinopyroxene-rich Garnet-rich bands contain clinopyroxene, calcite, garnet, clinopyroxene, calcite, potassium potassium feldspar, feldspar, Fe-vesuvianite, and sphene. Clinopyroxene-rich plagioclase, Fe-vesuvianite, Clinopyroxene-rich bands bands contain contain clinopyroxene, clinopyroxene, calcite, calcite, garnet, potassium feldspar, primarily feldspar, plagioclase, plagioclase, and sphene. sphene. Away from the igneous bodies, marble is composed of primarily equigranular calcite with small amounts of clinopyroxene, garnet, sphene, sphene, and and feldspar. feldspar. Trace amounts of equigranular graphite and pyrite are also observed. Bogoch (1997)report reportsimilar similarmineralogies mineralogiesof of calcite, calcite, potassium potassium Bogochetetala1(1997) feldspar, vesuvianite, quartz, clinopyroxene, cinopyroxene, plagioclase, spbene in a body body 2.5 2.5 m m plagioclase,wollastonite, wollastonite, graphite, and sphene long and 50 cm wide in calcite krn west of the field area. calcite marble marble approximately 12 12 km 64 �Deformation Deformation and and mineral mineral reactions reactions The majority of the exposed skarns skarns parallel the edge of the igneous igneous bodies bodies and and maintain uniform uniform thickness. However, However,some someskarns skarnsand and igneous igneous rock are Someigneous igneousbodies bodies and and their their skarns skarns locally deformed. Some are folded and boudined, boudined,2-25 2-25 cm cm size size skarn skarn fragments fragmentsare are common away from from igneous igneous rock; rock; some some of which are are variably folded. Skarn Skarnfragments fragments and and skarn skarn minerals are observed being transported by ductile flow of the marble (e.g. into boudin necks and out of fold hinges). Some Some igneous bodies and their skarns skarns show brittle deformation, breaking both skarn and intrusion intrusion into fragments fragments (see Fig. 1). The intrusionThe lack lack of of skarn skarndevelopment development on on some someintrusionmarble contacts contacts of dismembered dismemberedigneous igneous bodies bodies indicates indicates that brittle deformation deformation (of (of igneous igneous rock rock and and skarn) skarn) Figure 2. Calcite rimmed with garnet occurred after after igneous crystallization and skam skarn formation. formation. (Gç)). This texture (G texture and and garnet garnet rimming nmnung Mineral wolliastonite is Mineral textures textures show show that that original original skarn skarn wopastonite is evidence for the the reaction calcite+ quartz+ quartz+ anorthite+ anorthite+ mineralogies have mineralogies have been been modified modifiedby by aa later later granulite-facies granulite-facies wollastonite-> grossular+ wollastonite-> grossular+CO2. COT metamorphic metamorphic event event (see (see also also Martignole Martignole and and Schriver Schriver 1970). Garnet Garnet(Gr92) (Gr92)rims rimssurrounding surroundingcalcite, calcite, wollastonite, wollastonite,and and plagioclase plagioclaseindicate indicatethe the reaction reaction calcite calcite ++ quartz ++ anorthite anorthite ++ wollastonite wollastonite -> -> grossular + + + wollastonite C 0 2 (see Fig. 2). Garnet-quartz Garnet-quartz intergrowths intergrowthsindicate indicate the the reaction anorthite + ->grossular ++ CO2 wollastomte ->grossular quartz. quartz. The The univariant univariant assemblage assemblageof of garnet garnet(Gr95), (Gr95),plagioclase plagioclase(An19), (An19),quartz, quartz,wollastomte wollastoniteisisobserved observedas as fine-grained intergrowths. Dilution Dilutionof ofthe theanorthite anorthitecomponent componentof of plagioclase plagioclase by albite albite moves moves the fine-grained univariant univariant assemblage assemblage to to lower lower pressures pressures and and temperatures temperatures(Windom (Windom and and Boettcher Boettcher 1976), 1976),consistent consistent with the estimates estimates of regional regional metamorphism metamorphism (Indares (Indares and Martignole 1990). 1990). The Thepresence presenceof of wollastomte+ wollastonite+ vesuvianite, garnet+ plagioclase+ quartz+ wollastonite, wollastomte, clinozoisite+ plagioclase+ plagioclase+ quartz, quartz, and and sphene sphene vesuvianite, indicate metamorphism was was fluid fluid saturated. saturated. These Xu20 ifif metamorphism These assemblages assemblages also also consistent consistent indicate conditions conditions of high high XH2O with estimates of low H2O activityfrom from granulite granulitefacies facies terrains terrains if conditions are fluid absent or if non CH20 activity 0-H fluid 0-H fluid species speciesare are important important(Valley (Valley et et al., al., 1990). 1990). Comparison to the Comparison the Adirondacks Adirondacks Economic wollastonite deposits depositsin in the the Adirondack AdirondackHighlands Highlands(—250 (-250 km Economic wollastonite kmto tothe the south) south) are are skarns skarns associated with the the Marcy Marcy Anorthosite Anorthosite Massif Massifand andrelated relatedgranitic graniticrocks rocks.. Skarn formation adjacent to to the the anorthositewas was due due to to the the infiltration infiltration of of oxidizing oxidizing meteoric meteoric water water into the high temperature contact Marcy anorthosite zone of a shallow (<10km) anorthosite body. The Adirondacks Adirondacks underwent regional granulite facies body. The facies metamorphismwith withhigh highpressure, pressure,fluid-absent fluid-absentconditions conditions—100 -100 Ma later later (McLelland (McLellandand andChiarenzelli, Chiarenzelli, metamorphism 1990), wollastonite and 1990), but wollastonite and other other skarn skarn minerals minerals remained remained stable stable through through this this later later metamorphism metamorphism due due to to fco2 "fluid-absent" "fluid-absent"conditions conditions(Valley (Valley et et al. al. 1990). 1990). Post-intrusion Post-intrusiondeformation deformation and and mineral mineral textures in low fc02 Morin Complex Complexskarns skarnssuggest suggestpolymetamorphism, polymetamorphism,but butpublished publishedgeochronology geochronology(i.e. (i.e. dating datingof ofhigh high Monn temperature temperature metamorphic metamorphicminerals) minerals)atatpresent presentdoes doesnot notallow allowaadistinction distinctionbetween between two twoseparate separate metamorphicevents, events, or or aa continuum continuumof of metamorphism metamorphismunder underchanging changingconditions conditionsfollowing followinganorthosite anorthosite metamorphic intrusion or depth of intrusion. intrusion. References Bogoch, R., Kumarapeli, S., Can Mm Min 35:1269-1275. 351269-1275. S., and Matthews, A. A. (1997) Can Geology 99: 99: 729-738. 729-738. Doig R. (1991) J Geology J., Corriveau L. (1993) Geol Geol Surv Surv Can Can Open Open File 2640. Martignole J., Martignole J., Schrijver Schrijver K. K. (1970) (1970)Geol Geol Soc SocFinland Finland Bull Bull 42: 42: 165-209. 165-209. Chiarenzelli, J. J. (1990) (1990)JJ Geology Geology 98:19-41. 98:19-41. McLelland, J., Chiarenzelli, 1-386. (1989)Can CanJJEarth EarthSci Sci27: 27:37 371-386. Indares A., Martignole MartignoleJ.J. (1989) 1:555-596. R., Essene, Essene, E. E. J., J., and and Lamb, Lamb, W. W. (1990) (1990) J JPetrology Petrology331555-596. Valley, J., Bohlen, S. R., Am Mm Min61:889-896. 61:889-896. Windom, K. E., Boettcher, A. L. (1976) Am 65 �THE OF THE THE GUNFLINT LAPILLI LAPILLI TUFF THE AGE AND PROVENANCE OF TUFF and KISSIN, KISSIN, S.A., S.A., Department Department of of Geology, Geology, Lakehead Lakehead FRALICK, P.W. and University, Thunder Bay, Ontario, P7B University, P7B 5E1, 5E1, and and DAVIS, DAVIS, D.W., Royal Ontario Ontario Museum, Museum, 100 100 Queen's Park, Park, Toronto, Toronto,Ontario, Ontario,M5S M5S 2C6. 2C6. forms the the middle middleunit unit of ofthe the Animikie Animikie Group Group in northwestern The Gunflint Formation forms proximally to to the western end of Ontario, outcropping proximally of Lake Lake Superior. Superior. It consists of an assemblage assemblage of chemical and fine-grained elastic sediments deposited in the strand-proximal zone of a south facing (1996). facing shelf shelf as recently interpreted by Pufahl Pufahl(1996). Previous attempts at assigning an age to the Gunflint Formation (or the conformably conformably overlying Rove Formation) and equivalents equivalentscan can be be classified classified into into three three groups: groups: (1) ages from (Hurley et et a!., al., 1962; 1962;Peterman Peterman 1.556 to 1.63 Ga based on whole-rock Rb/Sr or KIAr K/Ar techniques techniques (Hurley 1969; and Franklin, 1978); 1978); (2) ages from 2.08 to 2.111 2.1 11 Ga Ga based on on 1966; Faure Faure & Kovach, 1969; a!, 1988); and (3) 1.86 1985; Gerlach et al, 1.86 and whole-rock NdJSm NdlSm techniques (Stille & Plauer, 1985; Hemmings et al; 1995). 1995). 1.99 Ga based on whole-rock PbIPb Pb/Pb from the the Virginia Virginia Formation Formation ((Hemmings Petrographic the upper upper Gunflint at Kakabeka Kakabeka Petrographicexamination examination of of aa lapilli lapilli tuff unit present in the Falls identified euhedral zircons forming a small portion of the silt population together with large, monomineralic clasts of of quartz quartz and and sanidine likely from an explosive, volcanic source. source. stratigraphic section section present present here has aa large large algal algal bioherm bioherm complex complex at at its its lowest lowest level level The stratigraphic (Figure sporadic (Figure 1). 1). This Thisisis overlain overlainby by aa thick thick sequence sequence of parallel-laminated black shale with sporadic development of layer rip-ups rip-ups caused causedby bycurrent currentactivity. activity. A A series of what what has been described as lapilli tuff beds beds occurs midway midway through through this thissequence sequence(Shegelski, (Shegelski, 1982). 1982). These are massive to disorganized disorganizedbedded. bedded. Mudstone rip-ups rip-ups are are common. common. The to cross-stratified and graded to The lapilli consist of Fe-rich Fe-rich chlorite chlorite and and are areinternally internallymassive. massive. The The above above strongly suggests suggests that the lapilli are not accretionary volcanic-rainout debris, but but rounded rounded volcaniclastic volcaniclastic mud mud rip-ups, and transported transportedby bystorm-induced storm-inducedcurrents. currents. The The black black shale unit which were eroded, abraded and is correlated with a find-grained, fmd-grained, resedimented, volcaniclastic shale, which which extends throughout upper Gunflint equivalents equivalents in the U.S.A. U.S.A. It may also be correlated correlated with aa small small region region containing containing basaltic basaltic flow flow rocks. rocks. Approximately 100 tuffs, including including altered, 100 zircons were recovered from the reworked tuffs, altered, abraided and euhedral euhedral brown brown populations. populations. Although the majority of the population analysed concordant age of 1878± gave reset Archaean ages, a euhedral zircon gave aa concordant 1878Â2Ma BP (Figure (Figure 2). 2). This most likely represents the age of of volcanism volcanism that was penecontemporaneous penecontemporaneous with sedimentation. sedimentation. volcaniclastic sediment Preliminary geochemical geochemical data data for Gunflint basalts and volcaniclastic sediment indicates indicates possibility of deep mantle mantle source for the melts melts and rules out out any any involvement involvement of the possibility of a deep Similaritieswith with the the Emperor Emperor and and Hemlock Hemlock volcanics volcanics suggest suggest a subducting lithosphere. lithosphere. Similarities eruptive event, event, which which may may in in part part overlap overlap northward time-transgressive, extensional, intraplate eruptive chronologically with the commencement commencement of arc volcanism to the south. south. 66 �References References Faure?G., G.?& & Kovach? SOy 1725-1736. Faure, Kovach,J.J.(1969). (1969). Geol. Geol.SOC. Soc.Amer. Amer.Bull. Bull. , 1725-1736. Franklin, J.M. (1978). Geol. Sum. Can. Pap. 77-14,35-39. Franklin, J.M. (1978). Geol. Surv. Can. Pap. 77-14, 35-39. D.C.? Shirey, 1515. GerlachyD.C., Gerlach, Shirey, S.B. S.B.& &Carlson, Carlson,R.W. R.W.(1988). (1988).EOS EOS@, , 1515. Hemming,S.R., S.R.?McLennan, McLennan,S.M. S.M.& & Hanson, Hanson, G.N. G.N. (1995). (1995). Jour. Jour.Geol. Geol.jQ., 147-168. 147-168. Hemming, Hurley, P.M., Fairbairn, H.W., Pinson? W.HSy & Hower, J. (1962). Jour. Geol. 489-492, Hurley, P.M., Fairbaim, H.W., Pinson, W.H., & Hower, J. (1962). Jour. Geol. 489-492. PetermanyZ.E. Z.E. (1966). (1966). Geol. Geol.Soc. SOC.Amer. Amer. Bull. Bull. fl, 103 lo31-1044. 1-1044. Peterman, Pufahl,P.K. P.K.(1996). (1996).M.Sc. M.Sc.Thesis, Thesis,Lakehead LakeheadUniv., Univ.,167 167 p. Pufahl, p. R.J. (1982). Geol. Assoc. CanJMineral. Assoc. Can.Field FieldTrip TripGuidebook Guidebook4, 4?15-31. 15-31. Shegelski, Shegeiski, R.J. (1982). Geol. Assoc. Can./Mineral. Assoc. Can. my a, , a, Breccia Breccia Stromatolites Stromatojites Wavy Beddin( '' Wavy Beddinc . .34 Cross- '..-.. Cross Stratification Stratification Brown euheclral .338 1878 +I-2 Ma .336 .334 20'Pb / 236U .332 5.2 5.25 5.3 5.35 5.4 5.45 10-01-1997 Fig.2. 2.Pb/U Pb/Uplot plotfor foreuhedral, euhedralybrown brown Fig. zircons from fiomthe thelapilli lapillituff tuffunit. unit. zircons a Granulesto to / Granules .smallPebbles Pebbles small Sandstone Sandstone siltstone .--. Siltstone .-. .:. .:... .. .. .. .. .. .. . .............. . . . . . . Shale Chert Fig. 1.1.Stratigraphic Stratigraphicsection sectionof ofthe theupper upper Fig. GunflintFormation Formationcontaining containinglapilli lapilli Gunflint tuff units in the Kakabeka Gorge. tuff units in the Kakabeka Gorge. 67 �PRE-WISCONSINAN AREA OF THE MINNESOTA PRE-WISCONSINANGRAY GRAY TILL IN THE MANKATO AIZEA MINNESOTA RIVER RIVER VALLEY GRAMSTAD, Sally D., student, Department of Geological Geological and Atmospheric Atmospheric Sciences, Sciences, Iowa Iowa University,Ames, Ames,IA IA5001 50011, sgramstaiastate.edu State University, 1, sgramsta@iastate.edu Exposures of pre-Wisconsinan gray till in the Mankato area of the the Minnesota Minnesota River River Valley Valley show that that continuous. Low shale content, moderate moderate carbonate carbonate this unit is up to 30 m thick and is somewhat continuous. content, and NW-SE trending fabrics fabrics indicate indicate aaWinnipeg Winnipegprovenance. provenance. The The texture texture and and lithology lithology of of this unit are similar to those of other pre-Wisconsinan tills in the Midwest, including the Browerville Browewille and Elmdale tills in north-central north-central and central Minnesota, and unit 1 at Salisbury Hill, which is twenty miles northeast of the study study area. The topography topography of of the bedrock bedrock valley valley that is is present present in in the the Mankato Mankato area area may may have have affected affected ice flow of the glacier that deposited the pre-Wisconsinan gray till unit. Influence Influenceof of this thisbedrock bedrock that the the thick thick till till unit is interrupted valley may explain several several anomalous anomalous fabrics, as well as the fact that by sand and gravel gravel layers layers at at some some sites sites and and is is completely completelyundisturbed undisturbedat at others. others. 68 �A A MINERALOGRAPHIC MINERALOGRAPHICSTUDY STUDYOF OFMAGNETITE MAGNETITEIN IN THE THE BIWABIK BIWABIK IRON-FORMATION, IRON-FORMATION,MESABI MESABI RANGE.M[NNESOTA MrNNESOTA RANGE, T. T.M. M.Han, Han,Senior SeniorResearch ResearchScientist Scientist(Retired), (Retired),Cleveland-Cliffs' Cleveland-Cliffs'Research ResearchLaboratory Laboratory A A substantial substantial number number of ofpolished polishedsections sectionsprepared preparedfrom from specimens specimenscollected collected from from the the Biwabik BiwabikIronIronFormation Formation were were microscopically microscopically examined examined before before and after an induced oxidation procedure. The TheBiwabik BiwabikIronIronFormation Formation is is simply simply classified classified here as cherty and slaty members. ItIt isisconsidered considered aa regionally regionally metamorphosed metamorphosed sediment sediment before before the the the the intrusion intrusion of of the the Duluth Duluth complex. complex. Based Basedon onthe the nature nature and and magnitude magnitude of of the thechanges, changes, the the existing existing iron-formation iron-formationmay may be be divided dividedinto intothree three metamorphosed metamorphosed sectors sectors progressing from west to to east, east, i.e. i.e. hematite functioned functioned as aa regionally, thermally, thermally, and andpyrometasomatically. pyrometasomatically. During During regional regional metamorphism, metamorphism, hematite regionally, "starting much of of the the magnetite magnetitethrough through~Fe Thermal "starting point" point" for for the development development of much e +diffusion. difhsion. + Thermalmetamorphism metamorphism involves involves mineralogical mineralogical transformations transformations of an isochemical isochemical nature, which may be be subdivided subdivided into into transitional, transitional, process involved amphibole, amphibole, and and pyroxene pyroxene zones. zones. Pyrometasomatism Pyrometasomatism process involved advanced advanced recrystallization recrystallization and and replacement replacementby bygabbro gabbroadjacent adjacentto, to,and andwithin, within,the theintrusion. intrusion. This This poster poster focuses focuses on on the the genesis genesisof ofmagnetite magnetiteinin the theregionally regionallymetamorphosed metamorphosed iron-formation iron-formation and and the metamorphismand andpyrometasomatism. pyrometasomatism. Most Most of the the textural textural and and mineralogical mineralogical changes caused by thermal metamorphism features features observed observed during during the the course course of of study study are are photographically and photomicrographically shown. ItIt covers: covers: A. fiomdifferent differentmetamorphic metamorphiczones. zones. A. Lithological Lithologicalcharacteristics characteristicsfrom The The irregularly irregularlyand andevenly evenlybanded bandedmacrostructures macrostructuresofofthe theregionally regionallymetamorphosed metamorphosediron-formation iron-formation show show little little change, change, whereas whereasthe themineralogical mineralogicalcomposition composition and and microstructures microstructures have have experienced experienced significant significant progressive progressive elimination eliminationand andtransformation transformationdue duetotothe thethermal thermalmetamorphism metamorphismand andpyrometasomatism. pyrometasomatism. B. B. Hematite-Magnetite Hematite-MagnetiteRelations Relationsininthe theRegional RegionalMetamorphosed MetamorphosedIron-Formation Iron-Formation occur either Before Induced Induced Oxidation. Oxidation. The hematite hematite and magnetite magnetite occur either in separate separate layers layers or or inin 1. Before 1. intimate intimate relations in in the same same layer. layer. Hematite Hematiteisisalmost almostalways alwaysmuch muchfmer fmerand andless lessabundant abundantthan thanmagnetite. magnetite. The The replacement of of hematite by magnetite is readily evident. The The magnetite magnetite differs differs in in external external morphology, morphology, i.e. i.e. octahedral octahedral and and pseudomorphs pseudbmorphs after afterother otherminerals. minerals. After Induced Induced Oxidation. Oxidation. The Themorphologies morphologiesand andarrangement arrangement of of precursor precursor hematite hematite in in existing existing magnetite magnetite 2. 2. After significantly. In the the evenly evenly banded banded slaty slaty lithology, lithology, the the precursor precursor hematite hematite isis almost almost exclusively exclusively lathlathvary significantly. shaped shaped and exhibits exhibits aa decussate decussate microstructure. In Inthe the irregularly irregularlybanded banded lithology lithology of both the slaty and cherty cherty members, the the precursor precursor hematite hematite exhibits exhibits aawide widevariety varietyofofmorphologies. morphologies. It is is either either randomly randomly arranged arranged or or displays displays vuggy vuggy or or microgeodic microgeodic structures structures within within magnetite magnetite that isis present present as asirregular, irregular,coalesced coalescedcrystals, crystals, granules, or or pinch-and-swell pinch-and-swell layers. layers. The The external external morphology morphology of the present magnetite magnetite is governed governed by by the the granules, hematite. Some Some of the the precursor precursor hematite hematite might might have have been been enlarged enlarged by by authigenesis authigenesis before before precursor hematite. inclusions isis present present in nearly all magnetite development. development. Magnetite Magnetite with precursor precursor hematite hematite inclusions all the the mineral mineral magnetite assemblages fiom assemblages of of the the iron-formation. iron-formation. The Thesize sizeand andmorphologies morphologiesof ofprecursor precursorhematite hematitein inmagnetite magnetite differs differsfrom the the existing existing hematite, hematiteyeither either coexisting coexisting with or or playing host hostto tothe themagnetite. magnetite. C. C. Effect EffectofofThermal ThermalMetamorphism Metamorphismon onHematite Hematiteand andMagnetite Magnetite In In the the transitional transitional zone, zoneymore more than than one one stage stage of of overgrowth overgrowth on euhedral magnetite (with or without the the precursor hematite inclusions) inclusions) is frequently frequently observed. Two Twoto tothree threeexternal externalmorphologies morphologiesof ofmagnetite magnetitewere were also seen in in coexistence. coexistence. The Theinduced inducedoxidation oxidationpattern patternprogressively progressively changes changes from from grain grain boundary boundary oxidation oxidation along planes of of the existing along the the precursor precursor hematite hematite to cleavage cleavage oxidation oxidation along octahedral octahedral planes existing magnetite magnetite as the metamorphic grade grade increases. increases. The Thehematite hematiteofofthe theregionally regionallymetamorphosed metamorphosediron-formation iron-formationisisprogressively progressively replaced by magnetite. magnetite. The Theeuhedral euhedralmagnetite magnetiteisisprogressively progressively changed changed to subangular subangular to nearly round grains. However, the outlines granules are still preserved. Magnetite outlines of of the the magnetite magnetite pseudomorphs pseudomorphs and magnetite granules Magnetite porphyroblasts appear in the fine-grained coalesced subangular magnetite. fine-grained magnetite. Some Some siliceous siliceous magnetite magnetite blades blades or or 69 �cubic cavities are are occasionally occasionally observed observed in in magnetite magnetite distributed distributed in the the pyroxene pyroxene zone. zone. However, However, some some hematite coexisting coexisting with with magnetite magnetitehas has also alsobeen been found foundinin the the pyroxene pyroxenezone. zone. D. Effect Effectof ofPyrometasomatism Pyrometasomatismon on Hematite Hematite and Magnetite Advanced Recrystallized Recrystallized Zone. The Themagnetite magnetite here here is is substantially substantially coarser than 1. Advanced than in the regionally and thermally metamorphosed metamorphosed zones. zones. The hematite, hematite, magnetite magnetite pseudomorphs, and magnetite magnetite granules granules no no longer exist. Two Twogenerations generationsof ofmagnetite magnetiteand andthe theintroduction introductionof ofhercyanite hercyanitealong alongmagnetite magnetitecleavage cleavageplanes planes fmeparallel parallelto tosubparallel subparallelfractures, fractures,whereas whereas the the host hostdoes does are evident. The Themagnetite magnetitegrains grainscommonly commonlyhave havefme not. The Thefractured fracturedmagnetite magnetitesometimes sometimesresembles resembles specular specular hematite. Minute Minuteeuhedral euhedral gangue gangue inclusions inclusions are are commonly present. Cleavage Cleavageoxidation oxidationisistypical. typical. Magnetite Magnetiteinclusions inclusionswithin withinmagnetite magnetiteare areeither eitheroutlined outlinedby by the effect of differential differential oxidation oxidation or or by their their grain grain boundaries. boundaries. The advanced Gabbroized Zone. 2. Gabbroized Zone. The advanced recrystallized recrystallized magnetite magnetite gradationally gradationally transforms transforms to to a 2. titanomagnetite approaching the gabbroized zone. The The latter latter contains contains minute inclusions of hercyanite, ilmenite, and ulvospinel, mineral. Most phases are are products products of of exsolution. exsolution. Both ulvospinel, and an unidentified unidentified mineral. Most of these mineral phases Both magnetite and titanomagnetite may be observed observed in in adjacent adjacent layers layers of of the thesame samespecimen. specimen. Small octahedral octahedral the same composition and texture as inclusions of titanomagnetite are occasionally seen and exhibit essentially the as titanomagnetite contains contains apatite, apatite, pyroxene, pyroxene, and and other other gangue grains; some titanomagnetite host. host. Some titanomagnetite some their titanomagnetite exhibits aa myrmekitic intergrowthtexture textureinin pyroxene; pyroxene;and and some some appears appearstoto be be replaced replaced by by ilmenite and exhibits myrmekitic intergrowth ilmenite and sulfides. sulfides. Economically, regional regional metamorphism metamorphism isis the the key key contributor in in generating generating magnetite magnetite for for the present Economically, Thermal metamorphism metamorphismhas has aa negative negative impact impact on on magnetite magnetite size size liberation liberation but but a positive mining industry. industry. Thermal positive recovery. Advanced effect on magnetite weight recovery. Advanced recrystallization recrystallization has a positive effect on both both size size liberation liberation ore. and weight recovery, whereas whereas the gabbroized gabbroized iron-formation can no longer be considered iron ore, The details details relative relative to to this this study study were were reported reported in in the the following followingpapers papersand andabstracts. abstracts. T. M. Han (1978) "Microstructures "Microstructures of of Magnetite Magnetite as as Guides Guides to Its Origin in Some Precambrian IronFormations." Fortschr. Fortschr. Mineral. Mineral.56, 56,105-142 105-142 (1982) "Iron-Formation of of Precambrian PrecambrianAge: Age: Hematite-Magnetite Hematite-MagnetiteRelationships RelationshipsininSome SomeProterozoic Proterozoic (1 982) "Iron-Formation MicroscopicObservation." Observation."Ore Ore Genesis - State of the Art, Springer-Verlag, Deposits -- A Microscopic Genesis - The The Springer-Verlag, Berlin, Berlin, Iron Deposits Heidelberg, New York. (1988) "Origin of of Magnetite Magnetite in Precambrian Iron-Formations of Low Metamorphic Grade." Proceedings of Dof the Seventh Seventh Quadrennial Quadrennial IAGOD IAGOD Symposium, Symposium, E Schweizerbart'sche Schweizerbart'sche Verlagsbuchhandlung, Verlagsbuchhandlung,D7000 Stuttgart Stuttgart II (1996) "Mineralogical Evolution Evolution of of Precambrian Precambrian Iron-Formation of Low Metamorphic Grade and Its Contribution to the U.S. Steel Steel Industry" (Abstract), (Abstract), 30th IGC, Beijing, China G . Graber, and Ruth Kramer (1992) "Effect of Duluth Gabbro Intrusion on Ore Mineralogy of T. M. Han, R. G. the Biwabik Iron-Formation, Iron-Formation, Lake Superior Superior District," District," USA International International Symposium on Mineralization Related to Mafic and Ultramafic Rocks, Rocks, 8th 8th Quadrennial Quadrennial IAGOD Symposium, Symposium, Orleans, France (Abstract) 70 �FACIES DEPOSITIONAL ENVIRONMENTS ENVIRONMENTSOF OFTHE THEEEARLY PROTEROZOIC FACIES AND DEPOSITIONAL A m Y PROTEROZOIC IRONWOOD IRONWOOD IRON FORMATION, MT. WHITTLESEY WISCONSIN. *EJ Joslin, Dan *EMHensel, Hensely*ck *Rick J o s hand , and DaLehrmann; n LehrmaqDept. Dept.ofofGeology, Geoloa,University Universityof of WisconsinWisconsinOshkosh, .54901 Kl54901 Oshkosh7Oshkosh, Oshkosh, Wi There are numerous models of depositional depositional environments environments of ofEarly EarlyProterozoic Proterozoiciiron fonnation. The k n formation. The puipose of the study was to evaluate which which of of these these models modelsbest bestfit fitthe thesedimentary sedimentaiyfacies faciesand and stratigraphic stratigraphic purpose patterns in the the Ironwood Ironwood iron iron formation formation exposed e x p o d at the Whittlesey, in the patterns in the Berkeshire Mine Ruins, at Mt. Whitfiesey, Gogebic were stripped stripped from from this this area by the the abandoned Gogebic District, near Mellen Wisconsin. Soil and vegetation were mining miningeffort. &ort. Approximately Approximately 100 100 meters meters of of stratigraphic stratigraphicsection sectionwas was described describedbed bed by by bed bed at at aa decimeter decimeter scale. bed in reconnaissance cut and and d e . An An additional additional150 150 meters was descr described reconnaissance sections. Samples were collected, cut described described in in detail detail to to help help understand understanddepositional depositionalenvironments. environments. fades were recognized from outcrop observation observation and and sample sample descriptions. descriptions. These These are are Five different facies summarized facies consists s u m a r i d as as follows. 1) 1) The The horizontal horizontallaminated hmin'atedfiia consistsof ofcontinuous continuousand anddiscontinuous discontinuouslaminae laminae of alternating alternating inagnetite structures include includethin, thin, graded graded laminae, laminae, scour scour marks, marks, vmagnetite and and chert. chert. Sedimentary structures shaped ?), and and discontinuous shaped cracks cracksthat that probably probably resulted resulted from from differential Merentid compaction compaction(j)ossibly (possibly desiccation ?), discontinuous lenses thick and commonly pinch out within a few lenses of granular granularfacies. The lenses lenses range range from fiom a few to 15 cm thick meters laterally. 2) The wavy wavy hminatedfacies consists of wavy wavy laminae laminaeof of magnetite magnetiteand and chert chertwith with few few 2) The laminated facies consists intraclasts of cheit are horizontal horizontal intraclasts chert.Sedimentary Sedimentarystructures structuresinclude includecrinidey crinkleylaminations laminationsthat thatprobably probably are stromatolites, convolute convolutelaminae, laminae,and andlenticular lenticularlayers. layers.3)3)The Theinfracladcfacies intraclasticfacies consists consistsof of intraclasts of of stromatolites, magnetite magnetiteand andchert chertderived derivedfrom fromthe thewavy wavyand andgranular granularfacies. facies.The Theclasts clastswere werecemented cementedearly earlyby bysilica. silica. include, planar cross beds, beds, imbricated clasts, clasts, differential differential syn-sedimentary syn-sedimentaiy compaction, compaction, Sedimentary structures include7 autoclastic penetrating the margins autoclastic breccia, breccia, and abundant abundant v-shaped cracks penetrating margins of of intraclasts. intraclasts. These Thesemay may be be desiccation of the the intraclasts intraclasts are are rounded roundedand andare areconcentrically concentricallycoated coatedwith withchert. cheit 4) 4) The The desiccation cracks. Some of stromatolitefacies contains ~omatolifefacies containsdomal domalstromatolites stromatolitescomposed composed of of chert chert and and magnetite. magnetite. Intraclastic Intraclastic material, containing occursbetween betweenthe the containingstromatolite stromatolite fragments hgments and and clasts clasts of of granular granular fades, facies*isisinterbedded interbeddedwith withand andoccurs stromatolites. 5) facies consists 5)The Thegranular granuhrfacies consistsof ofcoarse coarse to fine fine sand and minor silt sized chert and magnetite grains. ooids. The The granular granular facies grains. Most Mostofofthese thesegrains grainsare arepeloids peloids(featureless (featureless rounded grains), some are mids. appears appears to to be winnowed with little fine grained matrix and locally contains ripple ripple cross-lamination. cross-lamination. The stratigraphic pattern at Mt. Whittlesey is a meter- to decimeter-scale intercalation intercalation The most obvious stratigraphic of the wavy, granular, granular, and and intraclastic intraclasticfacies facies (fig. (fig. 1). 1). Careful Carefid observation obsemtion reveals, however, that that there there is is also a larger-scale are lithologic cycles. These cycles are larger-scale change change in in facies facies associations associations in the the outcrop outcrop that defines 3 lithologic approximately50 m thick. thick Within Within the the cycles cycles there there is a preferential association association in which which the the following following facies facies approximately more frequently granular and and wavy laminated facies, 2) the intraclastic intraclastic and and stromatolitic stromatolitic frequently occur together: 1) the granular three facies associations 3) the the horizontal horizontal laminated laminatedfacies. facies. The The cycles cycles consist of a repetition of the three facies, and and 3) stmmatolitic facies facies above. Interestingly, the cycles are are asymmetric in in the sense that that the intraclastic and stromatolitic associationalways always occurs beneath the the horizontally horizontally laminated laminatedfacies faciesand andnot notabove aboveitit(fig. (fig.2). 2). association Our interpretation that in aa shallow-marine, intertidal Our data data supports supports the interpretation that the the iron formation was deposited in to subtidal subtidal shelf environment. This Thisisissimilar similarto tothe theenvironments environments that that have have been been most most widely interpreted for iron Lougheed, 1983; M LaBerge, (cf. Simonson, 1985; hugheed, e r g e , 1987; Simonson Simonson and and Hassler, Hassler, 1996). 1996). iron formations formations(CL Sedimentary fatures interpretation include the stromatolites, ooids, mi&, ripple ripple cross lamination, lamination, features that that support this interpretation and and cross cross bedding. We interpret interpret that that the theiron ironformation formationformed formed as as aa biochemical biochemical precipitate precipitateof of iron iron and and silica silica minerals marine carbonate supports the minerals from from sea-water. sea-water. The The similarity similarityto to Proterozoic Proterozoic or Early Paleozoic marine carbonate facies supports idea to support the interpretation interpretation that are biochemical biochemical rocks. We found no evidence to that these these were idea that that these these are originally carbonate carbonate sediments sediments that that were were diagenetically diagenetically replaced by h w a t e r deposition that has originally by silica or for hfreshwater been postulated by 1973). by other other authors authors (Hough, (Hough, 1958; 1958;Eugster Eugsterand andChou; Chou;and and Trendall, 1973). In our laminated facies facies formed formed on on the the tidal tidal flats, the granular, granular, our preferred p r e f e d depositional model, the wavy laminated intraclastic, further seaward in shallow, wave agitated subtidal intraclastic, stromatolite, stromatolite7facies facies formed formed progressively progressively fiuther environments environmentsand and the the horizontally horizontallylaminated laminatedfacies faciesformed formed in in deeper deeper environments environmentsbetween nonnal normalwave wavebase base and and storm storm wave wave base base (fig. 3). The The horizontal horizontallaminations laminationsare are interpreted interpretedto tohave haveformed formedin inquiet quietwaters watersbelow below granular facies found found in in the the The abundant abundantscour scour structures structuresand discontinuous lenses of granular normal wave base. The horizontally laminated horizontaIly laminated facies are interpreted interpreted to to represent represent agitation agitation and and "spill "spill over over lobes" lobesnof of granular granularmaterial material 71 �___ Originally we entertained the idea that the horizontally laminated washed seaward during storms (fig. 3). 3). Originally facies formed formed landward landward of of the the oolite oolite shoals shoals in in tidal tidal flat flat ponds. ponds. If If the the v-shaped v-shaped cracks crackswere were desiccation desiccationfeatures, features, facies that that would support support such such an an interpretation. interpretation. The Thev-shaped v-shaped cracks cracks are more commonly associated with syndepositional depositional deformation deformationstructures structureshowever, however, and and the the horizontally horizontallylaminated laminatedfacies faciesisisrarely rarelyassociated associatedwith with laminatedfacies. facies. This, This, along alongwith withthe theasymmetrical asymmetricalpattern pattern of of the thelarge-scale large-scaledepositional depositionalcycles cycles the wavy laminated facies associations associations would represent supports the deeper deeper offshore offshore environment. In this this model, model, the the cycles in facies represent long long term (—million (--million year) intraclastic term year)asymmetric asynunetrictransgressions transgressions and and regressions regressions of ofthe the shelf. shelf. The The stromatolites stromatolites and intraclastic facies formed preferentially during initial transgressions, due to increased wave energy energy and and increasing increasing water Maximum deepening deepening is is represented represented by the horizontally laminated facies and regression is represented depths. Maximum by the shift facies association. association. shift back to to the the wavy laminated laminated - granular facies studies have commonly interpreted the horizontally laminated laminated facies Previous studies facies as as being being aa deep deep water water In some some cases cases itit has has been been interpreted interpretedto tobe be aa vezy very deep, pelagic and turbiditic Our data datasuggests suggests deposit. In turbiditic facies. Our that, at units interbedded interbedded in in the the horizontal horizontal facies are are at Mt. ML Whittlesey Whittlesey at least, this is not the case. The granular units far too discontinuous discontinuousto to represent represent distal distalturbidites turbiditesand andthey they lack lack Bouma Bouma sequences. sequences. - Eugster, H. P., Chou, Chou, I.M., I.M., 1973, 1973,The The depositional depositional environments environments Precambrian banded iron iron formations: formations: Economic Geology and the Bulletin Bulletin of the Society for for Economic Economic Geology, Geology,v. v. 68, 68, n. n. 7, 7, p. p. 1144-1168. 1144-1168. Economic Hough, J. L., L., 1958, of Precambrian Precambrian banded banded iron iron formation: formation: Journal Journal of of 1958, Fresh Freshwater waterenvironment environmentof of deposition of Sedimentary Sedimentary Petrology, v. 28, n. 4, p. p. 414-430. 414-430. LaBerge, G. L., L., Robbins, E. E. I. Schmidt, R K 0., G.,1987, 1987,AAmodel model for for the the biological precipitation of Precambrian iron Pubi., Athens, p. 69-96. iron formations: formations: Precambrian Precambrian Iron Iron Formations, Formations, Theophrastus Theophrastus Publ., 1983, Origin Origin of of Precambrian Precambrian iron iron formations formations in the lake superior superior region: region: Geological Geological Society Lougheed, M. S., 1983, of America Bulletin, Bulletin, v. 94, 94, ii. n. 3, 3, p. 325-340. 325-340. M., 1985, the origins of of Precambrian Precambrian iron formations: Simonson, B. M, 1985, Sedimentological Sedimentological constraints on the Geological Geological Society of America Bulletin, v. 96, n. 2, p. 244-252. Simonson, B. M M. and Hassler, S. W., of large large Precambrian Precambrian iron formations linked to W., 1996, 1996, Was the deposition of major marine marinetransgressions?: transgressions?:Journal Journalof ofGeology, Geology, v. 104, 104,n. n. 6, 6, p. p. 665-676. 665-676. Trendall, A. F.,1973, 1973,Iron Ironformation formationof ofthe theHamersley HamersleyGroup Groupof of Western Western Australia; Australia; type typeexamples examplesof ofvarved varved Trendall, A. F., Earth arth Science Science (Paris), v. 9, p. 257-270. 257-270.evaporites: E Fades Fades TO- ,"- nfradasc Fades Associations 1 HorizontallyE HorizontallyLaminated Intraclastic I Intraclastic Stromatolitic Strornatolitic Wavy Laminated /I Granular 3 I1 urn FIom Figure Figure11 ."-- Figure 2 Fades Wavy Iamânated Wavy laminated Granu [S Intradastic t.nbad&c a HorizontallyLaminated Figure Figure 3: Depositional Depositional Model Model 72 �AGE DEFORMATION OF EARLY PROTEROZOIC PROTEROZOIC QUARTZITES AGE AND DEFORMATION QUARTZITESIN IN THE THE SOUTHERN SOUTHERN LAKE SUPERIOR SUPERIOR REGION: REGION: IMPLICATIONS IMPLICATIONSFOR FOR EXTENT EXTENTOF OF FORELAND FORELAND DEFORMATION DEFORMATION DURING DURING FINAL FINAL ASSEMBLY OF LAURENTIA Daniel Daniel Hoim, Holm,Department DepartmentofofGeology, Geology,Kent KentState StateUniversity, University,Kent, Kent,OH OH44242 44242 David David Schneider, Schneider,Dept. Dept.of ofEarth Earth and and Environmental Sciences, Sciences, Lehigh Lehigh University, University, Bethlehem, PA PA Christopher ChristopherD.D.Coath, Coath,Department DepartmentofofEarth Earthand andSpace SpaceSciences, Sciences,UCLA, UCLA,Los LosAngeles, Angeles,CA CA90095 90095 Post-accretion stabilization stabilization in the Lake Superior region at 1770-1760 1770-1760 Ma resulted in deposition of locally thick successions successions of Early Early Proterozoic Proterozoic mature mature quartzites quartzites in Wisconsin Wisconsin and and southern southern Minnesota. Minnesota. Their Their age age of of deposition deposition and and the theage ageof of the thedeformation deformationwhich which caused causedwidespread widespreadfolding foldingof ofmany manyof ofthe the quartzite units has long been aa matter importance and and controversy. controversy. We matter of of considerable considerable importance We present present new new evidence these quartzites. quartzites. Also, we document evidence for both the maximum and minimum age of these document the spatial coexistence of aa thermal with a deformational front in the thermal front front in in Precambrian Precambrian crystalline crystalline basement basement with deformational front overlying quartzite units. The Theage ageofofthe thefront frontsuggests suggeststhat thatpost-Penokean post-Penokeanshortening shortening of of the thePenokean Penokean province province is is likely likely related related to to the the final final stages stages of formation formation of the Laurentian Laurentian supercontinent supercontinent at at -1650 Ma. 1650 Ma. The The bulk bulk of Laurentia Laurentia formed formed by rapid aggregation aggregation of Archean continents at 1900-1800 1900-1800 Ma during the Trans-Hudson and Penokean orogenies (Hoffman, 1989). Subsequent Subsequent accretion accretion of of juvenile crust crust along along the the southern southern margin margin of of pre-1800 pre-1800Ma Ma Laurentia Laurentiaformed formedthe theTranscontinental TranscontinentalProterozoic Proterozoicprovinces provinceswhich which consist broadly of aa northern northern 1800-1700 1800-1700 Ma inner accretionary belt and a southern 1700-1600 1700-1600 Ma outer tectonic belt. The Thetransition transition zone zone between between the the two two tectonic tectonic belts belts of the the TPP TPP represents represents the region of known Ma during during formation formation of of the outer known pre-1700 pre-1700 Ma Ma rocks rocks metamorphosed metamorphosed and and deformed deformed at at —1650 -1650 Ma tectonic belt. The Theeastward eastwardcontinuation continuation of of this this transition transition zone zone and and of the the outer outer tectonic tectonic belt from the central central plains plains is is problematic problematicas as no no 1800-1600 1800-1600Ma Majuvenile juvenile crust crustexists existsin inthe theentire entiresouthern southernGreat GreatLakes Lakes region region (Van (Van Schmus Schmus et et al., al., 1993). 1993).However, However,on onthe thebasis basisof of1680-1640 1680-1640Ma Maorogenic orogenicdeformation deformationand andthe the existence of 1650 1650 Ma Ma batholithic batholithic intrusive rocks in Labrador, Labrador, Van Schmus et al. al. (1993) (1993) have have proposed proposed that that the the outer outer tectonic tectonic belt belt was was aa single single coherent coherent continental arc extending extending from California California to Labrador. Labrador. The arc/microcontinentcollision collisionalong alongthe the southern southernpassive passivemargin margin The Penokean Penokean orogeny orogeny involved involvedisland island arc/microcontinent of of the the Superior Superior Province Province at at 1870-1830 1870-1830Ma. Ma. InInnorthern northernWisconsin Wisconsinthe thesouth-dipping south-dippingNiagara Niagarafault faultzone zone represents represents the the main main suture suturewhich whichseparates separatesuniformly uniformlymetamorphosed metamorphosed (upper (uppergreenschistllower greenschist/lower amphibolite facies) island arc arc rocks rocks of of the thePembine-Wausau Pembine-Wausauterrane terrane from fromdeformed deformedcontinental continentalmargin margin rocks rocks which whichexhibit exhibitaanodal nodalmetamorphic metamorphicpattern patternimposed imposedduring duringcollapse collapseof ofthe theorogen orogen(Schneider (SchneideretetaL, al., 1996; 1996; Marshak Marshak et et al., al., 1997). 1997). Abundant Abundant mica mica Ar/Ar ArIAr cooling cooling dates dates from from central central Minnesota Minnesota and and northernmost northernmost Wisconsin Wisconsin and and Michigan Michigan indicate indicate that that collapse collapseand andorogenic orogenicunroofing unroofingoccurred occurredatat175017501700 1700 Ma shortly shortly after after an anepisode episodeof ofwidespread widespreadmagmatism magmatismatat1770-1760 1770-1760Ma Ma(Holm (Holmand andLux, Lux,1996; 1996; Schneider Schneider et et al., al., 1996). 1996).InIncontrast, contrast,Rb-Sr Rb-Srwhole wholerock rockisocbron isochronand andbiotite biotitemineral mineraldates datesininnorthern northernand and central central Wisconsin Wisconsin (Peterman (Petermanand and Sims, Sims,1988) 1988)are are mostly mostly Middle Middle Proterozoic Proterozoic (1600-1100 (1600-1100Ma) Ma) and and reflect reflect variable variable thermal thermal resetting resettingassociated associatedwith withaalow-grade low-grade—1630 -1630 Ma metamorphic event (Van Scbmus Schmus and and Woolsey, Woolsey, 1975; Van Van Schmus Schmus et al., al., 1975), 1975), intrusion intrusion of the the 1470 1470 Ma Ma Wolf Wolf River River batholith, batholith, and and Keweenawan Keweenawan activity. activity. Post-accretion Post-accretion rapid rapid stabilization stabilization resulted resulted in in the the accumulation accumulation of of post-tectonic post-tectonic quartz quartz arenites arenites in in the the southern southern Lake Lake Superior Superior region region (Van (Van Schmus Schmus et al., 1993). 1993). Deformed Deformedquartzite quartziteunits units in in central central and and southern southernWisconsin Wisconsin yield yield post-Penokean post-Penokean detrital detrital zircon Pb-Pb ages (Van (Van Wyck, 1995). 1995). The The folded folded Baraboo Baraboo quartzite quartziteis is depositional depositionalon on aa 1752 1752Ma Ma granite granite(Medaris (Medariset et a!., al., 1996) 1996)and and contains contains detrital detrital zircons zircons as as young young as as 1712 1712Ma Ma (Dott (Dott et et a!., al., 1997). 1997). The Theminimum minimumage ageof ofthese thesequartzite quartziteunits unitsisisconstrained constrained only only by by the the fact factthat thatsome someare areintruded intrudedby bythe the1470 1470Ma MaWolf WolfRiver Riverbatholith, batholith,although althoughDott Dott(1983) (1983)and and Van Van Schmus Schmuset et al. al. (1993) (1993)speculated speculatedthat that they they may may have have been been deformed deformed during during the the 1630 1630Ma Ma event. event. The The predominantly predominantly Middle Middle Proterozoic Proterozoic mica mica mineral mineral dates of central central Wisconsin contrast sharply with the the well-grouped well-grouped 1750-1700 1750-1700Ma Ma mica mica dates dates obtained obtainedfrom from central centralMinnesota, Minnesota,northernmost northernmost Wisconsin, Wisconsin, and and northern northern Michigan. Michigan. The The1750-1700 1750-1700Ma Madates datesare arethe theoldest oldestmica micadates datesobtained obtainedfrom fromthe theinternal internal portions portions of of the thePenokean Penokeanorogen orogenand andthus thusalmost almostcertainly certainlyreflect reflect primary primary cooling cooling through through mica mica closure closure temperatures temperatures following following Penokean Penokean metamorphism. metamorphism. Considering Considering that that primary primary cooling cooling atat1750-1700 1750-1700Ma Ma was An—1630 -1630 Ma Maage age was orogen orogen wide, wide, ititisislikely likelythat thatthe theyounger youngermica micadates datesrepresent representthermal thermalresetting. resetting.An contour contour thus thus separates separates basement basement with with typical typical post-Penokean post-Penokean cooling cooling ages to the the north north (and (and west, west, in in Minnesota) Minnesota)from frombasement basement with with thermally thermally reset reset ages ages to the south. The Theeastward eastwardextent extentof ofthe thechrontour chrontourisis not not precisely preciselylocated, located,however, however,north northof ofthe theFlambeau Flambeauquartzite quartziteininnorthwest northwestWisconsin Wisconsinthe thechrontour chrontourisis sharply sharplydefined definedby byRb-Sr, Rb-Sr,K-Ar, K-Ar,and andAr-Ar Ar-Armica micadates. dates. Importantly, Importantly,the theFlambeau Flambeauthermal thermalfront frontin innorthwest northwestWisconsin Wisconsincoincides coincidesspatially spatiallywith withan anapparent apparent deformational deformational front front ininoverlying overlyingpost-Penokean post-Penokeanquartzites. quartzites. In In Minnesota, Minnesota, the thesubhorizontal subhorizontal Sioux Sioux 73 �quartzite quartzitelies liesjust justsouthwest southwestofofPenokean Penokeaninternal internalzone zonerocks rockswhich whichcooled cooledrapidly rapidlythrough throughmica micaclosure closure temperatures Ma. In temperaturesatat—1750 -1750 Ma. Innorthwest northwest Wisconsin, Wisconsin,the theBarron Ban-onquartzite quartziteisisessentially essentiallyflat-lying flat-lyingand andisis depositional depositional on on Precambrian Precambrian basement basement with mica ages between 1730-1700 1730-1700 Ma. South Southof ofthe thethermal thermal front, front,and andonly only25 25km kmsouth southofofthe theBarron Barronquartzite, quartzite,are areexposures exposuresofofsteeply-dipping steeply-dippingFlambeau Flambeauquartzite. quartzite. Here Herethe thequartzite quartziteisisfolded foldedinto intoaamoderately moderatelywest-plunging west-plungingsynform synform(Myers, (Myers,1974) 1974)similar similarto to the thestyle styleof of deformation McCaslin quartzites. quartzites. The Therelatively relativelyundeformed undeformedBarron Barronand and deformationexhibited exhibitedby by the theBaraboo Barabooand andMcCaslin Sioux SiouxProterozoic Proterozoicquartzites quartzitesmust musteither eitherlie lieoutside outsidethe theregion regionofofsignificant significantpost-Penokean post-Penokeandeformation deformation (as (asseems seemssuggested suggested by by the thespatial spatialcoincidence coincidence of of aathermal thermalfront frontwith withaadeformational deformationalfront) front)ororbebe younger younger quartzite quartzitepackages packagesdeposited depositedafter aftersignificant significantpost-Penokean post-Penokean deformation. deformation. To Totest testwhether whetherthe the subhorizontal subhorizontalquartzites quartzitesare arecorrelatable correlatablewith withthe thedeformed deformedquartzites quartziteswe weobtained obtainedsingle-grain, single-grain,singlesinglespot ages spot207Pb/206Pb 2 0 7 ~ b / 2 0 6ages ~ b on detrital zircons separated from from the the Sioux, Sioux,Barron, Barron,and andFlambeau Flambeauquartzites. quartzites. Because Becausewe weare aremostly mostlyinterested interestedininconstraining constrainingthe themaximum maximumage ageofofeach eachquartzite quartzitewe weconcentrated concentratedour our efforts possible. All efforts on ondating dating euhedral euhedral or or subhedral subhedral crystals crystals wherever wherever possible. All three three quartzite quartzite bodies bodies yielded yielded Early Early Proterozoic Proterozoic and and Late Late Archean Archean detrital detrital zircon zircon dates dates comparable comparable to to dates dates obtained obtained by by Van Van Wyck Wyck (1995) (<2000Ma) Ma)dates dates (1995)for fordeformed deformedquartzite quartzitebodies bodiesin in Wisconsin. Wisconsin. Many Manyofofthe thelate lateEarly EarlyProterozoic Proterozoic(<2000 fall fallalong alongaadiscordia discordiawith withaalower lowerintercept interceptatator ornear nearthe theorigin originindicating indicatingrecent recent lead lead loss lossattributed attributedto to upper Proterozoic uppercrustal crustalfluid fluidcirculation. circulation.Reliable Reliable207Pb/206Pb 207Pb/2w~b Proterozoicages agesare arebetween between1730 1730and and1850 1850Ma Mafor for the theSioux Sioux(9 (9grains), grains),between between1714 1714and and1880 1880Ma Mafor forthe theFlambeau Flambeau (9 (9 grains), grains),and and between between 1750 1750and and 1880 1880 Ma Mafor forthe theBarron Barron(6 (6grains). grains).These Thesedata dataattest attesttotothe thefact factthat thatall allthree threequartzite quartzitebodies bodiespost-date post-datethe the1760 1760 Ma Mamagmatic magmaticevent eventin inthe theLake LakeSuperior Superiorregion. region. Thus Thusfar farthere thereisisno noevidence evidencetotosuggest suggestthat thatthe theBarron Ban-on and andSioux Siouxquartzites quartzitesare areyounger youngerthan thanthe thedeformed deformedquartzites quartzitesfound foundthroughout throughoutmost mostofofWisconsin. Wisconsin. Abundant Abundant new new thermocbronologic thermochronologic data in the Lake Superior Superior region allow us to make make aa simple simple but but important importantfirst-order first-orderobservation observationthat thatprovides providesthe thefirst firstdirect directstructural structuralevidence evidencethat thatthe thequartzites quartziteswere were deformed deformedduring duringthe thelow-grade low-grade—1630 -1630 Ma event in the Lake Superior region. We Wenote notethat thatsubhorizontal subhorizontal post-Penokean post-Penokean quartzites quartzites consistently consistently overlie overlie crystalline crystalline basement basement with with primary primary post-Penokean post-Penokean cooling cooling ages, ages, whereas whereas highly highly deformed deformed quartzites quartzites everywhere everywhereoverlie overliecrystalline crystallinebasement basementwith withsecondary secondary (thermally (thermally reset) reset) cooling coolingages. ages.We Weare arefortunate fortunatethat thatthe theproximity proximityofofthe thedeformed deformedFlambeau Flambeauquartzite quartzitetoto the the subhorizontal subhorizontal Barron Barron quartzite quartzite in in northwest northwest Wisconsin Wisconsin allows allows us to to precisely precisely locate locatethis this deformational/thermal deformationalhhermal front. front. An Anage ageofof1650-1630 1650-1630Ma Mafor forthe thedeformation deformationseems seemsreasonable reasonablegiven giventhat that coolingages agessouth southof ofthe thefront frontprobably probablypost-date post-datethe thedeformation deformationsomewhat. somewhat. cooling The The thermal thermal front front extends extends eastward eastward into into northern northern Michigan, Michigan, the the geology geology of of which which isisdominated dominated by by gneiss gneissdomes domesand and classic classic nodal nodal metamorphic metamorphic isograds. No NoEarly EarlyProterozoic Proterozoicpost-Penokean post-Penokeanquartzites quartzitesare are known known north north of of the the McCaslin McCaslin quartzite. quartzite.However, However,it's it'sinteresting interestingtotonote notethat thatthe theRepublic Republicmetamorphic metamorphic node node located locatednorth north of of the thethermal thermalfront frontisisconcentric concentricwhereas whereasthe thePeavy Peavymetamorphic metamorphicnode nodelocated locatedsouth south of the the thermal thermal front frontisiselongate elongateeast-west. east-west. ItIt isis tempting tempting to to speculate speculate that that the the Penokean Penokean isograds isograds of the the of Peavy Peavy metamorphic metamorphic node node have have been been shortened shortenednorth-south north-south and and may may therefore therefore be be yet yetanother anotherstructural structural manifestation of of the the1630 1630Ma Madeformational deformationalevent. event. If If our our interpretations interpretations are are correct, correct, then thenthe thesimilar similar manifestation orientation orientation of of post-Penokean post-Penokean folds folds and and Penokean-age Penokean-age folds (north (north of the the front) front) requires requires that that caution caution be be used usedwhen whenattributing attributingbasement basementstructures structuressouth southofofthe thefront fronttotoPenokean Penokeandeformation. deformation. The Ma metamorphism metamorphism has has been one of the most Thelow-grade low-grade—1630 -1630 Ma most poorly poorly understood understood events events in inthe the Lake Lake Superior Superior region. region. Although Althoughitithas haslong longbeen beenspeculated speculatedupon uponthat thatthe thequartzites quartzitesmay mayhave havebeen been deformed deformed during during this this event event (Dott, (Dott, 1983; 1983; Van Van Schmus Schmus et al., al., 1993), 1993), until now there has been no no direct direct evidence evidence of of any any intrusive intrusive or or deformational deformational event of that age. We Webelieve believethat thatthe thedata datasummarized summarizedhere here provides provides the the missing missing structural structural link link to to that that event. event. The Thetiming timingand andthe thestrong strongapproximately approximatelynorth-south north-south shortening shorteningstyle styleof of post-Penokean post-Penokeandeformation deformationtogether together are are consistent consistentwith with itit being being the theresult resultof offoreland foreland deformation deformation associated associated with emplacement emplacement of the outer outer tectonic tectonic belt belt onto onto the the southernmost southernmost margin margin of of Laurentia Laurentia during the the Mazatzal Mazatzal orogeny orogeny (Van (Van Schmus et al., 1993). 1993). The Therocks rocksofofthe theTranscontinental Transcontinental Proterozoic Proterozoic provinces provinces were were subjected subjected to to aa major major magmatic magmatic event event during during the theMiddle MiddleProterozoic Proterozoicfrom from 1500-1300 1500-1300 Ma. The Theundeformed undeformedWolf WolfRiver Riverbatholith batholithinincentral centralWisconsin Wisconsinisissurrounded surroundedby byand andlocally locally intrudes intrudesthe the deformed deformedquartzite quartzitebodies, bodies,leading leadingsome someto tosuggest suggestthat thatquartzite quartzitedeformation deformationwas wascaused causedby by Middle Middle Proterozoic Proterozoic epeirogenic epeirogenic doming doming and and igneous intrusion (Greenberg and Brown, 1984). However, However, the the existence existenceof of the theFlambeau Rambeau deformational deformationalfront front(located (locatedover over 100 100km km from fromexposures exposuresof of the thebatholith) batholith) shows showsthat that the the deformation deformationdoes does not not wane wane away away from from the the batholith. Rather, Rather,the theabrupt abruptnature natureof ofthe thefront front is is characteristic characteristic of of tectonic, tectonic, not not intrusion intrusion related, deformation. This This study studysupports supportsDott's Dott's (1983) (1983) model model which which attributed attributed post-Penokean post-Penokean deformation deformation in in Wisconsin Wisconsin to to Early Early Proterozoic Proterozoic plate plate collision collisionfrom fromthe the south 1700-1600Ma Ma outer outer tectonic tectonic belt belt south and and supports supports the the hypothesis hypothesis of of Van Van Schmus Schmus et et al. al. (1993) (1993) that that the the 1700-1600 was was aa single single coherent coherentbelt belt extending extendingfrom fromCalifornia Californiato to Labrador. Labrador. References Referenceswill will be be made madeavailable availableatatthe themeeting meetingor orupon uponrequest request(dholm@kent.edu). (dholm@kent.edu). 74 �THE THERECOGNITION RECOGNITIONOF OFAALAVA LAVADOME DOME COMPLEX COMPLEXAND AND ITS ITS RELATIONSHIP RELATIONSHIP TO TO THE THEARCHEAN ARCHEANSTURGEON STURGEONLAKE LAKE CALDERA, CALDERA,NORTHWESTERN NORTHWESTERNONTARIO ONTARIO GEORGE RONALD L. MORTON GEORGEJ.J.HUDAK HUDAKAND AND RONALD MORTON Economic EconomicVolcanology VolcanologyResearch ResearchLab, Lab,Geology GeologyDepartment, Department,University Universityof ofMinnesota Minnesota —-Duluth, Duluth, Duluth, Duluth,Minnesota, Minnesota, USA USA 55812 55812 JAMES JAMES M. M. FRANKLIN FRANKLIN Geological GeologicalSurvey Survey of of Canada, Canada,601 601Booth Booth Street, Street, Ottawa, Ottawa,Ontario, Ontario,Canada CanadaK1A KIA0E8 OE8 Detailed has led to the Detailed volcanic facies mapping mapping has the recognition recognition of of the the Archean Archean Sturgeon Sturgeon Lake Caldera Caldera Complex Complex in northwestern Ontario (Morton This complex complex is isup uptoto Lake (Morton et et al., al., 1991). This 25 kilometers kilometers in in strike strike length, length, contains contains up up to to 4500 4500 meters meters of of caldera calderafill fillmaterial, material,and andhosts hosts 25 six six known known volcanogenic volcanogenic massive massive sulfide sulfide (VMS) (VMS)orebodies orebodiesand andnumerous numeroussubeconomic subeconomic massive sulfide sulfide lenses. The Thevolcanic volcanicrocks rockswithin withinthe thecomplex complexhave havebeen beendivided dividedinto intoten ten massive distinct based on the types distinct stratigraphic stratigraphic successions successions based types of ofvolcanic volcanicand andsedimentary sedimentaryrocks rocks present present (Hudak, (Hudak,1996). 1996). The TheLyon LyonCreek CreekSuccession Successioncomprises comprisesthe theuppermost uppermostof ofthese thesesuccessions. successions.Historically, Historically, these these rocks rocks were were called calledthe theNBU NBUrhyolite rhyolite(Harvey (Harvey and andHinzer, Hinzer, 1981; 1981;Severin, Severin,1982), 1982),and and were were interpreted interpreted as as rhyolite rhyolite tuffs, tuffs,lapilli lapillituffs, tuffs,agglomerates, agglomerates,and andgraphite-rich graphite-richsediments. sediments. However, However, our our detailed detailedfield fieldmapping, mapping,core corelogging, logging,and andpetrographic petrographicinvestigations investigationsindicate indicate that that little littleor ornone noneof ofthese theserocks rocksare arepyroclastic pyroclasticininorigin. origin. Instead, Instead,this thissuccession successionhas hasbeen been interpreted interpretedto torepresent representaasubaqueous subaqueouslava lavadome domecomplex. complex. krn in strike strike length length and and up up to to 540 540 A plagioclase-phyric plagioclase-phyric dacite A dacite lava lava dome dome that that is is 2-3 2-3 km meters meters thick thick forms formsthe thebase baseofofthe thesuccession. succession. This Thisdome domeoccurs occurswithin withinthe thecaldera calderaedifice edifice krn west west of of aa major major caldera caldera margin margin fault. fault. An Anabsence absenceofofflow flowcontacts, contacts, approximately 1-2 1-2 km approximately and andan anincrease increaseininthe thesize sizeofoffeldspar feldsparphenocrysts phenocrystsfrom fromthe themargins marginstoward towardthe the core coreof ofthe the dome, suggests suggests that thatthe thedome's dome'sgrowth growthwas wasendogenous. endogenous.AAseries seriesofofpredominantly predominantlydomedomedome, derived matrix-supportedbreccia breccia derived clastic clastic sediments sediments overlies overliesthe thedome. dome. These Theseinclude: include:a)a)matrix-supported deposits depositswhich which contain contain up up to to75% 75%dome domefragments; fragments;b) b) arkosic arkosicgreywacke greywackedeposits; deposits;c) c) veryveryfine finegrained grainedtuffaceous tuffaceoussandstone sandstoneand andsiltstone siltstonedeposits; deposits;and andd) d)graphite-rich graphite-richshale shaledeposits. deposits. The Theclastic clasticsediments sedimentslack lackan anabundance abundanceofofpumice pumice(rarely (rarely>3%) >3%)and andcross-bedding cross-beddingisisabsent. absent. Silica-, carbonate-, carbonate-, oxide-, oxide-, and/or and/or sulfide-facies sulfide-facies iron iron formations formations and and associated associated chert chert are are Silica-, interlayered interlayeredwith withthe theclastic clasticsediments sedimentsand, and,locally, locally,directly directlyoverlie overliethe thelava lavadome. dome. Detailed Detailedfacies faciesmapping mappingindicates indicatesthat thatthe thebreccia brecciadeposits, deposits,the thegraphite-rich graphite-richshales, shales,and and theiron ironformation formationwere wereformed formed ininrestricted, restricted,fault-bounded fault-bounded basins within the top top of ofthe the the dome. dome.The Theiron ironformation formationresulted resultedfrom fromrelatively relativelylow lowtemperature temperaturehydrothermal hydrothermalactivity activitythat that occurredproximal proximal to to the the basin basin marginal marginal faults. faults. The Thelack lackofofpumice, pumice,the theabsence absenceofofevidence evidence occurred suggestive suggestive of of reworking reworking by by surface surfacecurrents currents(e.g. (e.g.cross-bedding), cross-bedding), and andthe the presence presence of of graphitic graphitic shales shales suggests suggests aarelatively relativelydeep deepwater water(>500 (>500meters), meters),anoxic anoxicenvironment, environment, although althoughno noabsolute absolutewater waterdepth depthestimate estimateisispossible. possible. Detailed studies studies on onfelsic felsicvolcanic volcanic centers centers indicate indicate that that the the final finaltwo twostages stagesofofcaldera caldera Detailed development development involve involve major major ring ring fracture fracture volcanism volcanism and and terminal terminal hot hot spring springand andfumarolic harolic activity activity (Smith (Smith and andBailey, Bailey,1968). 1968). The The strata stratacomprising comprisingthe theLyon LyonCreek CreekSuccession Succession represent these these final final two two evolutionary evolutionary stages stages in in the the development development of of the theSturgeon SturgeonLake Lake represent Caldera CalderaComplex. Complex. 75 �References References Harvey, J. D., and Hinzer, J. J. B., 1981, 1981,Geology Geology of of the the Lyon Lyon Lake Lake ore ore deposits, deposits, Noranda Noranda Mines Mines Ltd., Ltd., Sturgeon SturgeonLake, Lake, Ontario: Ontario:Canadian CanadianInstitute Instituteof ofMining Miningand and Metallurgy Bulletin, Bulletin, v. 74, 74, no. 833, 833, p. 77-84. 77-84. Hudak, G. J., 1996, 1996, The The physical physical volcanology volcanology and and hydrothermal hydrothermal alteration alteration associated with with late late caldera caldera volcanic volcanic and and volcaniclastic volcaniclastic rocks rocks and and volcanogenic volcanogenicmassive massive sulfide sulfide deposits deposits in in the the Sturgeon SturgeonLake Lake region region of of northwestern northwestern Ontario, Ontario, Canada: Canada: unpublished unpublished Ph. Ph. D. D. dissertation, dissertation, University University of of Minnesota, Minnesota, Minneapolis, Minneapolis, MN, MN, 463 463 pages. pages. Morton, Morton, R. L., Walker, Walker, J. J. S., S., Hudak, Hudak, G. G. J., J., and and Franklin, Franklin, J.J. M., M., 1991, 1991,The The early early development developmentof of an an Archean Archean submarine submarine caldera calderacomplex complex with with emphasis emphasison onthe the Mattabi Mattabiash ash flow and its its relationship relationshipto to the the Mattabi Mattabi massive massive sulfide sulfidedeposit: deposit:Economic EconomicGeology, Geology, flow tuff and v. 86,p. 86, p.1002-1011. 1002-1011. Severin, P. W. A., 1981, 1981, Geology Geology of the Sturgeon Sturgeon Lake Lake Cu-Zn-Pb-Ag-Au deposit: deposit: Canadian Canadian Institute Instituteof of Mining Mining and and Metallurgy MetallurgyBulletin, Bulletin, v. v. 75, 75, no. no. 846, 846,p. p. 107-123. 107-123. Smith, R. L., and Bailey, R. A., 1968, of 1968, Resurgent Cauldrons: Geological Society of America 13-662. AmericaMemoir Memoir116, 116,p.p.661 3-662. 76 �GEOLOGIC SETTING OF SUBECONOMIC GOLD GEOLOGIC GOLD DEPOSITS DEPOSITSIN INTHE ThE VIRGINIA HORN, NORTHEASTERN MINNESOTA: MINNESOTA.A AHORN HORNOF OFPLENTY PLENTY OR A HORNSWOGGLE? NORTHEASTERN HORNSWOGGLE? JIRSA, Geological JIRSA, Mark Mark A., BOERBOOM, BOERBOOM,Terrence Terrence J., J.,and and CHANDLER, Val Val W.-Minnesota W.—Minnesota Geological Survey(MGS), (MGS),2642 University Avenue,St. St.Paul, Paul,MN, MN,55114-1057 55114-1057(jirsa001@tc.umn.edu) (nrsaOOl@tc.urnn.edu) Survey University Avenue, Several significant-though, significant—though, to to date date subeconomic-gold subeconomic—gold deposits deposits occur occur within within Archean Archean bedrock bedrock in the area known as the Virginia Horn. Three Three prospects prospects were were worked worked to to varying varying degrees degrees by exploration exploration companies in the late late 1980's, 1980'~ and ~ one of of these, the "Viking prospect", The and prospect",was was extensively extensivelydrilled. drilled. The exploration focused focused on pervasively pervasively altered altered felsic felsicporphyry porphyry intrusions intrusions having having variably variably well well developed deformation envelopes and and associated associated carbonate-sericite alteration. Recent mapping mapping by by the theMGS MGS (Jirsa (Jirsa deformation envelopes alteration. Recent and others, others, 1998), 1998), together together with with geochemical work work by by the the Natural Natural Resources Research Research Institute Institute (Englebert and Hauck, 1991; 1991; and information on on the the lithological lithological and work work in in progress) progress) has has provided provided further further information and structural structuralframework, framework, potential potential sources sources of of Au, and relative timing of mineralization mineralization in these prospects and the surrounding surroundingarea. area. à 'I ''''''I, ,,,,,,,,, ,f/f,, ,,,,,,,,,,, MINNTAC SEQUENCE \- %, 'S .. , .' .' \ \ '. 'S S S 'S ,1 , S.''' / / /1 / /, /1 •5%.'.'\\'SI / / / / / / /1 '''''S.''''' '''''S'S'S'''' '''''''S'S''', ,,/,//,/,,, 'S'S5'S'S'S'S'S 'S 'S 'S 'S'S.' 'S 'Ss 'S 'S '''''S ''''S'S'S' '''"'S /, MUD LAKE SEQUENCE Graywacke (stippled) and volcanic rocks (white) Figure 1—Schematicblock blockdiagram diagramofofthe theVirginia VirginiaHorn. Horn.Map Mapsurface surfacedimensions dimensions approximately approximately Figure 1-Schematic 30X30 km. km. 30x30 The Archean rocks of the Virginia Horn lie within the Wawa subprovince subprovinceof of Superior SuperiorProvince. Province. The rocks are are subdivided subdivided into northern and southern of metamorphic metamorphic grade grade and and southern panels on the basis of deformation style. The The northern northernpanel, panel,immediately immediatelysouth southofofthe theGiants GiantsRange Rangebatholith, batholith,contains contains intensely lineated, schists having having volcanic volcanicand and clastic clasticprotoliths. protoliths. The southern heated, amphibolite-grade schists southern panel that were metamorphosed to much lower grades, panel contains contains lithologically similar rocks that grades, ranging ranging from prehnite-pumpellyite to low greenschist. The two panels are separated by the east-trending, post-metamorphic, Laurentian Laurentianfault fault (Figure (Figure1). 1).The Themetamorphic metamorphiccleavage-forming cleavage-formingevent event in in both both panels of 33major majordeformations-the deformations—theother othertwo twodeformation deformationevents eventsproduced produced no no panels was was the the second second (1)2) (D2) of metamorphic affects. affects. The first (Dl) (Di) involved upright discernible metamorphic upright folding, folding, soft-sediment soft-sediment deformation, deformation, and complex faulting; the third third (D3) (D3) produced produced localized localized semi-brittle semi-brittle crenulation crenulation of of D1 Dl and and D2 D2 structures, brittle fractures, of earlier-formed earlier-formed faults. faults. Amphibolite structures, fractures, and and selective selective reactivation of Amphibolite grade grade sequence; the the low low and and sub-greenschist sub-greenschist grade grade rocks north of the Laurentian fault comprise the Minntac sequence; 77 �strata south of the Laurentian fault are subdivided The Minntac subdivided into Mud Lake and Midway sequences. The sequence contains strongly banded banded schists schists having geochemical geochemical and outcrop-scale outcrop-scale characteristics characteristics of mafic to intermediate volcanic and volcaniclastic volcaniclastic strata, strata, subvolcanic subvolcanicmafic maficsills, sills,and andgraywacke. graywacke. Although of the Minntac sequence, sequence, relict relict grading grading and bedding the possibility of tight folding is great in rocks of Incontrast, contrast,the the Mud Mud Lake Lake sequence sequence forms forms a broad, southward stratigraphic stratigraphic facing. facing. In consistently indicate southward southwest-plunging, D1 D l syncline synclinethat that isis cored cored by by graywacke, graywacke, slate, slate, and and minor minor felsic felsic tuff; and and has has outer outer southwest-plunging, of calc-alkalic calc-alkalic and limbs of and tholeiitic tholeiiticstrata. strata. The Mud Lake strata are cut by several variably The Mud Mud Lake Lake sequence and the intrusions are porphyritic, quartzofeldspathic intrusions. The and are are locally locally in fault contact with, fluvial conglomerate and and subaerially subaerially unconformably overlain by, and deposited trachyandesite trachyandesite flows flows and and pyroclastic pyroclastic rocks that comprise the Midway sequence. seauence. The The deposited Tirniskaming -like strata in the Kirkland Lake and Shebandowan gold attributes of of Timiskaming Midway has many attributes Like the the Timiskaming Timiskaming rocks of mining districts of Ontario. Like of Ontario, those those in in the Virginia Virginia Horn Horn are have been deposited deposited in in aa fault-bounded fault-boundedpull-apart pull-apartbasin basinthat thatformed formedbefore beforethe theonset onsetofof1)2 D2 inferred to have deformation and metamorphism. datingback back to tothe thedays daysof of J.W. J.W. Gruner Gruner and and The Virginia Horn has a long history of of gold "shows", 'shows', dating F.F. Grout Grout (Grout, and some some visible visible gold gold can can still still be be found found locally in in altered altered rocks in and and adjacent (Grout, 1937), and adjacent to quartz quartz veins. Sampling Samplingby byexploration explorationcompanies companiesfocused focused largely largely on the quartzofeldspathic intrusions, and the country rocks were rarely rarely analyzed. analyzed. From those data and the current study, the generalizations can be made about the distribution distribution of of gold gold in in the the region: region: following generalizations 1. Gold 1. Gold is is most abundant abundant in in quartzofeldspathic quartzofeldspathicdikes. dikes. Thegreatest greatestgold goldcontents contents(as (aslarge large as as 50,000 50,000 ppb) 2. The ppb) occur occur in in rocks rocks that that are are pervasively pervasively altered and cut by quartz-rich veins. Anomalousquantities quantitiesofofgold gold(50(50-500 500 ppb) also also exist in sedimentary sedimentary and and volcanic volcanic wall-rocks wall-rocks of of 3. Anomalous the porphyritic intrusions. intrusions. 4. Gold Goldconcentrations concentrationsgreater greaterthan thana a"mineable" "mineable"cut-off cut-offof ofabout about1000 1000ppb ppb (0.029 (0.029 OPT) are recorded exclusively from samples of quartzofeldspathic quartzofeldspathic dikes. dikes. Inrocks rocks uniformly uniformly affected affected by carbonate-sericite alteration, 5. In alteration, gold gold is is most most abundant abundant in zones of of anomalous arsenic content. anomalous arsenic content. carbonate-sericite alteration and The carbonate-sericite alteration associated associated with with gold mineralization mineralization varies from pervasive and having textures that imply strong involvement in shearing. not obviously related to to the the rock rock fabric, to having Pyrite typically is associated with carbonate and sericite; sericite; and arsenopyrite and and chalcopyrite chalcopyrite occur occur locally. Alteration is inferred to have taken place during or just after D2 deformation, as the Alteration is inferred to have taken during or are variably variably affected affected by 82. That alteration is best developed along major fault alteration products are S2. That zones, lithologic contacts, contacts, and and adjacent adjacentto to and and within within the the quartzofeldspathic quartzofeldspathic intrusions. intrusions. Although Although the the shallow subsurface subsurface have been evaluated in in some some detail, detail, comparisons with analog analog deposits deposits surface and shallow imply that that unexplored unexplored potential potential exists; exists; 1) 1) at depth in in the the low-grade low-grade rocks rocks of of the the Midway Midway in Canada imply and and Mud Mud Lake Lake sequences; sequences; and and 2) 2) throughout throughout the thehigh-grade high-gradeMirintac Minntac sequence. sequence. ACKNOWLEDGMENTS Mapping Mapping and and geochemical geochemical study study was was supported supportedby by the the Minnesota Minnesota Legislature Legislatureon on recommendation recommendationof of the Minerals Coordinating CoordinatingCommittee. Committee. REFERENCES REFERENCES Englebert, and Hauck, 1991,Bedrock Bedrockgeochemis geochemistryofofArchean Archeanrocks rocksin innorthern northern Minnesota: Natural Natural Englebert, J.A., J.A., and Hauck, S.A., 1991, Institute Technical Report NRRI/TR-91/12, 200 p. NRRI TR-91/12,200 Resources Research Institute 7 Grout, Petrographic study F.F., 1937, Petrographic studyof of gold goldprospects prospectsofofMinnesota: Minnesota:Economic EconomicGeology, Geology,v.37, v.37,P. p.56-68. 56-68. Grout,F.F., Jirsa, Bedrockgeolo geologic map of of the the Virginia Horn, Horn, Mesabi Ran e,St. St. Jirsa,M.A., Boerboom, Boerboom, T.J., and Morey, Morey, G.B., 1998, Bedrock 'c map Mesabi Iron IronRange, Louis County, County,Minnesota: Minnesota:Minnesota MinnesotaGeological GeologicalSurvey SurveyMiscellaneous MiscellaneousMap MapM-85 M-85(digitial), (digitial),scale scale1:48,000. 1:48,0%. 78 �EFFECT EFFECI' OF OFELECTRIC ELECI'RICPULSE PULSEDISAGGREGATION DISAGGREGATION ON ON MICROFOSSIL-BEARING MICROFOSSIL-BEARING ARGILLACEOUS ARGILLACEOUSLIMESTONE LIMESTOM OF OF THE THE MIDDLE MIDDLE ORDOVICIAN ORDOVICIAN DECORAH DECORAH SHALE SHALE KJERLAND, KJERLAND, Dean Dean W., W., and andKJERLAND, KJERLAND, Marc MarcP., P., amateur amateurpaleontologists, paleontologists, 73563,3520@compuserv.com E-mail: 73563,352O@compuse~.com 8007 MN 55431 S, Bloomington, Bloomington, MN 8007 Xerxes Ave S, 55431 E—mail: The The Middle Middle Ordovician Ordovician Decorah Decorah Shale is a fossiliferous fossiliferous shale with lenses and thin beds beds of of coquinoidal coquinoidal limestone limestone and and calcareous calcareous shale (Rice). The Thecalcitic calciticmacrofossils macrofossilsand andphosphatic phosphatic conodont conodont microfossils microfossils have been been studied studied (Sloan, (Sloan, Webers). Webers). Though Though known known from from acid acid processing processingresidues, residues,other othernon—calcitic non-calcitic microfossils have have not not been beendocumented. documented. We samples of of limestone from Decorah We collected collectedover over250 250typical typicalhand—sized hand-sized samples Decorah Shale Shale beds beds disturbed disturbed during during the the reconstruction reconstruction of Hwys 110, 55 & 13 13 at at Mendota, Mendota, Minnesota Minnesota in in 1993. 1993. Our Our selection selection criteria criteria was was the the presence presence of of phosphatic phosphatic microfossils or fragments fragments visible visible with with Our photographic photographic documentation of 200 of of these these aa hand hand lens lens on oneither eitherororboth bothsurfaces. surfaces, Our surface surface microfossils microfossilsusing using optical optical microscopy reveals a wide variety of microfossils including including lithified lithifiedmud mud internal internalcasts castsof of bryozoans bryozoans(Cuffey), (Cuffey), laminated laminated plates, plates, and and gastropod gastropodsteinkerns. steinkerns. Separation Separation of microfossils microfossils from the the matrix matrix isis necessary necessary for for more more efficient efficientcollection collectionand and documentation. documentation. Full Fullviewing viewingof of specimens specimensisis useful useful for for classification. classification. Mechanical Mechanicalcrushing crushing is is not not an aneffective effectivemethod methodfor forcleanly cleanlyseparating separatingeither eithermacrofossils macrofossils or ormicrofossils microfossilsfrom from matrix. matrix. Acid Acidprocessing processingyields yieldsclean cleanmicrofossil microfossilspecimens specimensbut but artificially artificially selects selects for for either either calcitic or phosphatic material. material. Both Both Ca Ca and P, as well as Fe, 5, S, Al, A,Si, Si, and and Mg, Mg, have have been been confinned confirmed from from our our S.E.M. S.E.M. analyses analyses of of aa sample sample of of several severaldozen dozen typical typical microfossils. microfossils. Saini—Eidukat andWeiblen Weiblenreported reportedthe theuse use of of an an Electric Pulse Pulse Disaggregator (EPD) for Saini-Eidukat and fossil extraction extraction (see (see References). References). In In our our study study we we evaluated evaluated the potential potential of the the EPD EPD for for separating visible microfossils from the surface 'fossil hash' of Decorah Shale limestone and separating microfossils Shale limestone and also for sampling matrix of of this this rock. rock. We sampling for microfossils microfossils buried in the matrix We used the the specialized, specialized, upgraded version EPD EPD at the University of Minnesota which is upgradedlaboratory—scale laboratory-scale version is based based on on the the electric—pulse facility in St. Petersburg, Russia (Saini—Eidukat and Weiblen). electric-pulse facility Petersburg, Russia (Saini-Eidukat Weiblen). A cm long long xx 12.5 12.5 cm cm wide weighing about 1.2 1.2 kg, was quartered quartered A lenticular lenticularslab slab fragment, fragment,16 16cm with aa rock hammer and further fragmented/delaminated with a cold chisel to rock hammer and further fragmentedldelaminated with cold chisel toproduce produce walnut—sized fragments for electric walnut-sized fragments electric pulse pulsedisaggregation. disaggregation. The rock rock consisted consistedofofnon— nonweathered, crystalline calcite calcite with with typical weathered, compact, compact, dark dark blue—gray blue-gray crystalline typical cemented cemented calcitic calcitic macrofossil clay on both sides and macrofossil fragment fragment debris and gray interstitial surface clay and phosphatic phosphatic microfossils microfossils and and fragments fragmentsvisible visible on ononly onlyone onesurface. surface. The The slab slab pieces pieces were were hand hand fed fed in in two two batches batches into into the hollow cathode of the EPD over over aa 66 mm pulses at approximately 100 kV. kV. All mm integral integral sieve sieve and and subjected subjected to approximately approximately 200 pulses All material except except the the suspended suspended fines fines was was air air dried driedand andmechanically mechanicallysorted sorted through through brass brass sieves sieves (Table (Table 1.) 1.) The Thematerial materialwhich whichpassed passedthrough throughthe the0.25 0.25 mm mm sieve sievewas wasprocessed processeddry dry through through aa series series of of teflon teflonmeshes meshes(Table (Table2.). 2.). The aggregate calcite and yellow clay and aggregate produced produced by the the EPD EPD isis fragmented fragmented crystalline calcite and mud-sized fines. fines. Only Only aa small small fraction fraction consists consists of whole whole calcite calcite fossils fossils or or fragments fragments and and mud—sized non—calcitic microfossils and orpartly partlyenclosed enclosed in in calcite calcite matrix). matrix). non-calciticmicrofossils and fragments fragments(either (eithermatrix—free matrix-free or 79 �Table 1: 1:Grading Grading criteria criteria and and results: results: Table 2. Grading of of Class VIII Material Weight(in g) and % % Class Sieve(in mm) Weight(in 31.2 >6.0 31.2 2.5% ~6.0->4.0 297.8 24.0% 24.0% I1 II <6.0—>4.0 297.8 I11 ~4.0->2.0 397.3 32.1% 32.1% III <4.0—>2.0 397.3 IV 207.6 207.6 16.8% 16.8% Iv c2.0->1.0 <2.0—> 1.0 65.6 5.3% ~1.0->.701 vV <1.0—>.701 <.701—>.495 46.7 <.701->.495 46.7 3.8% VI c.495->.250 62.9 5.1% <.495—>.250 62.9 VII <.250 129.1 10.4% 10.4% 129.1 VIII e.250 Total Total 1238.2 1238.2 100.0% 100.0% Note: The material which passed through the Note: 0.25 mm brass brass sieve sieve was wasre—graded re-graded using using meshes. Results teflon meshes. Results are from top of mesh. II Class Class VIlla VIIIa VIIIb VIIIb VIlic VIIIc VIlId VIIId Mesh# (mm) Weight(m Weight(ing) g) and and % 6.4 #60 (>.250) 5.0% 15.9 12.3%; #80 (>.177) (>.I771 15.9 12.3%; #100(>.149) 13.0 13.0 10.1%; 10.1%; thru #100 #lo0 93.8 72.6%. Total 129.1 100.0% Total 100.0% materialsfrom fromthe theteflon teflonmeshes mesheswere werenot notexamined examinedatatthis thistime. time. The VIIIa-d materials The Class VIIIa—d Class ClassII—- VII materials were were examined examined with with an an optical opticalmicroscope microscopeand andsampled sampledfor fora).a).non— nonfossils, fragments fragments and fossil crystalline crystallinecalcite, calcite,b). b).fossil—bearing fossil-bearing calcite, and c). non—calcitic non-calcitic fossils, and unknowns. Based Basedon onsubjective subjectivecriteria criteria (i.e. typical, interesting, unusual or trophy categories) 654 fossils, fragments and unknowns were were collected. collected. Specimen Specimen counts counts are: are: 11.8% 11.8%calcitic calcitic fossils, crystalline calcite, fossils, 9.8% 9.8% phosphatic fossils fossils in crystalline calcite, 74.9% 74.9% loose loose phosphatic phosphatic fossils fossils and fragments, and 3.5% fossils and fragments, 3.5% unknown. unknown. Virtually all of of the thematrix—free matrix-free non—calcitic non-calcitic fossils recovered from from the top of the sieves fragments are from that portion of the aggregate (31%) recovered sieves .250 mm sieve in the the 2.0 2.0mm mm—- -250 sieveset set(Class (ClassIV—VII). IV-VII). Conclusion: provides aa new new method method for for disaggregating disaggregating rocks for for isolating isolating Conclusion:The The EPD EPD provides microfossils mm to to 0.25 0.25 mm. mm. EPD processing microfossils in the size range from 2.0 mm processing effectively effectively separates separates microfossils from allows efficient efficient phosphatic, calcitic, and pyritic microfossils from their calcitic matrix and allows testing of rocks for the the presence presence of buried specimens. Although Although some some specimens specimens may may break break in processing or during preserved in shale are during sample sample preparation, preparation, many fossils preserved are commonly commonly fractured naturally in the matrix. We Webelieve believethat that EPD EPDprocessing processingsimply simply separates separatesalready already damaged fragments or whole whole fossils fossils along along existing existing fractures. fractures. References: References: Cuffey, Roger J., Professor of Paleontology, Department of of Geosciences, Pemsylvania Pennsylvania State correspondence 1997 1997 and and 1998. 1998. University; personal correspondence Rice, William F.; "TheSystematics Systematicsand and Biostratigraphy Biostratigraphy of the Brachiopoda of the Decorah F.; "The St.Pau1, Minnesota", Mimesota", 1985, 1985,Unpublished M.S. thesis, University of Minnesota, Mimesota, Mpls. Shale at St.Paul, Saini-Eidukat, B., Saini—Eidukat, B.,and andWeiblen, Weiblen,P.W., P.W., 1996; 1996; "A "ANew New Method Method of of Fossil Fossil Reparation, Preparation, Using High-Voltage Pulses", references therein. therein. High—Voltage Pulses", Curator Curator 3912, 39/2, and references Sloan, Robert E, E, editor, editor, Middle Middle and and Late LateOrdovician Ordovician Lithostratigraphy Lithostratigraphy and Biostratigraphy Biostratigraphy of the Upper #35, Mimesota Minnesota Geological Survey, Upper Mississippi Mississippi Valley, Report of Investigations #35, University of Minnesota, university Mimesota, 1987. 1987. Webers, Gerald F.; "The Middle Mimesotat': Middle and Upper Ordovician Conodont Faunas of Minnesota": Mimesota Geological Geological Survey Survey Special SpecialPublication PublicationSeries SeriesSP—4, SP-4, 1966 1966 Minnesota 80 �RESULTS OF MODELLING MODELLING PROTEROZOIC PROTEROZOIC THERMAL THERMAL HISTORIES: HISTORIES: THE POSSIBLE POSSIBLEEFFECTS EFFECTS OF OF WOLF WOLF FUVER RIVER BATHOLITH BATHOLITH EVALUATING THE REHEATING THERMOCHRONOLOGIC DATA =HEATING ON THEMOCHRONOLOGIC DATA FROM FROM NORTHERN NORTHERN WISCONSIN WISCONSIN Jeff Jeff Loofboro Loofboro(student) (student) and and Daniel DanielHoim, Holm,Department Departmentof of Geology, Geology, Kent Kent State StateUniversity, University, Kent, OH 44242 Introduction. Mica MicaRb/Sr RblSrand andAr/Ar ArlArthermochronologic thermochronologicresults results across across northern northern Wisconsin Wisconsin and northern Michigan (Peterman and Sims, 1988, 1988, Tectonics; Schneider and and others, others, 1996, 1996, CJES; CJE!S;Hoim Holm and and others, 1997, 1997, GSAA) reveal a 1630-1600 1630-1600 Ma chrontour chrontour which separates separates basement basement rock with with primary primary cooling ages of 1760-1750 Ma Ma to the north from 4<1630 6 3 0 Ma ages to the south. The Thechrontour chrontourcoincides coincides physically with an apparent deformational front in overlying, Early Proterozoic, post-Penokean quartzites Hoim and others (1998, ILSG; and in review) to interpret complete leading Holm interpret the the chrontour chrontour to to represent representcomplete thermal resetting resetting of of micas associated with foreland deformation deformation related related to to accretion accretion from the south. thermal associated with However, we note that the chrontour also appears appears to surround surround the known known subsurface subsurface extent extent of of the the Middle Middle Wolf Mver River batholith batholith(Fig. (Fig. 1) 1) raising raising the the possibility possibilitythat that itit might might be be an an artifact of partial partial Proterozoic Wolf resetting. In Inthis this case, case, the the1630-1600 1630-1600Ma Ma chrontour chrontour may may represent represent aa collection collection of meaningless "mixed" ?nixed'' resulting from from partial partial resetting of of the older primary 1760-1750 Ma dates at 1470 dates resulting 1760-1750 Ma 1470 Ma Ma when when the the batholith intruded. Using Using the the MacArgon MacArgon program (Uster (Listerand andBaldwin, Baldwin,1996, 1996,Tectonophysics) Tectonophysics) we we have have various Proterozoic Proterozoic thermal thermal histories histories in in an attempt to evaluate modelled various evaluate the possible effects effects of of Middle Middle Proterozoic Proterozoic reheating on thermochronologic data data from from northern Wisconsin. Initial Initial conditions conditions and andmodel modelparameters. parameters.We Weinitially initiallyconsider consideraarock rockcontaining containing muscovite muscovite with a plateau ArIAr Ar/Ar date of 1765 Ma and biotite biotite with with a plateau plateau date date of of 1755 Ma. Ma. Precambrian Precambrian basement rock north of the chrontour chrontour in northwest northwest Wisconsin are are near near the the Early Early Proterozoic Proterozoic nonconformity nonconformity suggesting suggesting these rocks were at shallow Ma. Considering this, we chose three shallow crustal depths by —1700 -1700 Ma. three different different ambient temperatures temperatures(loo0, (100°, 150° 150°,and and200') 200°) and and imposed imposedaa thermal thermal pulse pulse at at 1470 Ma Ma to simulate ambient intrusion of the batholith. batholith. We We varied varied the the peak peak temperature temperature of of the the pulse pulse between between 200° 200O and and 450°C 450° (using (using 50°C to 22 my my (using (using 0.5 0.5 my my increments). In In 50° increments) and the duration of heating from instantaneous to all cases the duration of cooling back to ambient temperatures lasted 2 my and hence the total duration duration of the pulse varied in our models models from from 2-4 2-4 my. my. The plutonism on country rock The duration duration of thermal effects effects of plutonism is normally normally shorter than this (Carslaw (Carslaw and Jaeger, Jaeger, 1959, 1959, Clarendon Press), but we chose chose such such long long durations in in order order to to maximize maximize the the effects effects of of partial partial resetting resettingby bythe the batholith. batholith. We assume no other affects after after intrusion intrusion of of the the Wolf Wolf River batholith, batholith, ending ending the the thermal thermal history with thermal overprinting affects slow cooling cooling from from the the chosen chosen ambient ambienttemperature temperaturetotoO° 0°Catat600 600Ma Ma(Fig. (Fig.2). 2). The variables in the modelling thus include the peak temperature obtained, the duration of the thermal pulse, and the the initial initial temperature. The ambient temperature. The affect affect of each each of these these parameters on argon diffusion in muscovite and biotite is is described described below. Results thermal modeling. modeling.AsAsmight mightbebeexpected, expected,the thedominant dominantfactor factorinfluencing inlluencingpartial partial resetting Results of thermal is the peak temperature obtained by by the the rock rock during during the the imposed imposedthermal thermalpulse. pulse. Peak thermal pulses at or below the closure temperature of biotite (300°C) (3W°Cor muscovite (350°C) (350°Chad little affect on on the the initial initial cooling age regardless of the duration of heating. Peak Peakthermal thermalpulses pulsesof of50°C 50°above aboveclosure closuretemperature temperature resulted in considerable considerable partial partial resetting. resetting. In this case the duration of the heating interval did have a moderate degree of resetting total gas gasages ageswhich whichare are moderate affect on the degree resetting with 2 my my heating intervals intervals resulting resulting in in total —50 myyounger youngerthan than in in the case for Because of of the difference in closure -50 my for instantaneous instantaneous heating. heating. Because closure temperature between biotite and muscovite, the modelling reveals that large differences in the degree of partial resetting resetting (and hence apparent ages obtained) are expected for 1470 1470 Ma Ma peak peak thermal thermal pulses pulses between 300 and 450°C 450°C. Temperatures Temperatures100°C 100OCabove above the the mineral's mineral's nominal nominal closure closure temperature temperature resulted in nearly complete resetting resetting of of the the isotopic isotopic systematics systematics regardless regardlessof ofthe theduration durationof ofheating. heating. Varying the initial ambient temperature between 100-200°C 100-200OC had little little affect affect on the apparent apparent ages ages obtained. obtained. Implications. Existing Existingthermochronologic therm6chronologicdata data from from northern northern Wisconsin Wisconsin show nearly concordant muscovite and biotite dates near the chrontour (with muscovite around 1620 1620 Ma and biotite around around 1600 1600 GSAA). We Ma; Romano and others, 1997, GSAA). Weare areunable unableto toobtain obtainnearly nearlyconcordant concordantpartially partiallyreset resetages ages with any of our simulations and conclude that Middle Proterozoic intrusion of of the the Wolf River batholith was probably probably not responsible for generating the 1630-1600 1630-1600 Ma chrontour by partial resetting. This is indirectly indirectly supported supported by by two two independent independent lines lines of ofevidence. evidence. First, the degree of deformation conclusion is deformation Proterozoic quartzites in in Wisconsin Wisconsin does does not not wane away from the the Wolf Wolf River batholith as of the Early Roterozoic deformation. The would be expected for intrusion related deformation. The sharp sharp deformational deformational front front (which (which coincides coincides Second, with the 1630-1600 1630-1600 Ma clirontour) chrontour) is more more characteristic characteristic of tectonic-related tectonic-related deformation. Second, 81 �thennal thermaleffects effectsof ofthe theDuluth DuluthComplex Complexon onArchean Archeancountry countryrock rockininnortheastern northeasternMinnesota Minnesotaexist existonly onlytotoaa map-view distance distance of 10 10 km away from the intrusion (Hanson (Hanwn and others, 1975, GCA). By By comparison, comparison, the 40km kmaway awayfrom fromthe theknown known the 1630-1600 1630-1600Ma Ma chrontour chrontour in in northern northern Wisconsin Wisconsin isis located locatedmore more than than 40 subsurface extent of the Wolf River batholith (l3g. (Fig. 1). Our Ourresults results support supportthe the conclusion conclusion of of Hoim Holm and and others U G )that that the the1630-1600 1630-1600Ma Machrontour chrontourrepresents represents complete completethermal thermal resetting resetting of of micas micas others (1998, (1998, ILSG) tectonism. associated with latest Early Proterozoic tectonism. Lister, Lister, G.S., G.S., and andBaldwin, Baldwin,S.L., S.L., 1996, 1996,Modelling Modellingthe theeffect effectof of arbitrary arbitraryP-T-t P-T-t histories historieson onargon argondiffusion diffbsion in in minerals minerals using using the the MacArgon MacArgonprogram program for for the the Apple Apple Macintosh: Macintosh: Tectonophysics, Tectonophysics, v. 253, p. 83-109. #%. ../ %t %/% %/%/ &S:S:S:::S 3:S::S / . F. /. /. / / / FS. %S.F SaS. —:-xc-t-:.:-: %'..—.. % . KEWEENAWAN S. subhoilzontal, , Ba ffonF % ,, S ,,,- .. .. % % % .. - S. S. S. S. S. S. S. S. S. CM%S.S.S.S.S.S.S.S.1 S. S. S. ' —46 - :Penoke ambeau ightly fold I, fit ,f' a 50km Edge of Late Prol/ Phanerozoic cover / Baraboo qtzite I 1(tightly folded) / Approximate sub . -! surface extent of WRB I 91 I I 90 89 I 88 Figure I.Simplified Simplifiedtectonic tectonicmap mapof of the the central central Penokean Penokeanorogen, northern northern Figure 1. Wisconsin and Michigan, U.S.A. (after Sims, 1992; Holm and others, Wisconsin and Michigan, U.S.A. (after Sims, 1992; Holm and others, in in review). review). CM = continental margin; EPSZ = Eau Pleine shear zone; NSZ = Niagara suture CM = continental margin; EPSZ = Eau Pleine shear zone; NSZ = Niagara suture zone; MT Archean Marshfield Marshfieldterrane; terrane; WRB WRB == Wolf Wolf River River batholith. batholith. MT == Archean E 92 PeakT Peak T 3 + 2 tzE \ a 1 1800 1800 tt == duration duration of thermal thermal pulse pulse AmbientT Ambient T ,t 1470 Age(Ma) Age (Ma) 1470 600 600 Figure Figure 2. Temperature-time Temperature-timegraph graphshowing showing modelled modelledparameters. parameters. 82 �An Archean subaqueous heterolithic debris flow, Irwin, Irwinl Pifher, Pifher! and Meader Townships, Townshipsl Lake Nipigon Nipigon Region, Ontario ft Luther, Whitewater, Wl WI 53190 Frank R. Luther!Geology GeologyDepartment, Departmentl UW-Whitewater, UW-Whitewaterl Whitewatery 53190 lutherf@mail.uww.edu lutherf@mail.uww.edu This extensive body body of volcanic breccia breccia is is located located in in northern northern Irwin, Irwinl southeastern southeastern Meader, Meader! and and aa large large part part of of southern southernand andeastern easternPifher PifherTownships. Townships. It is 10-25 10-25 km east of Lake Lake Nipigon Nipigon and and 17-28 17-28km km north-northeast north-northeastof of Beardmore. Beardmore. Mapping by Mackasey (1975) and Kresz and Zayachivsky (1989) shows this rock to be enclosed in a thick sequence of typical greenstone greenstone assemblage rocks -flows, intermediate to felsic pyroclastics pillowed and massive basalt flowsl pyroclastics and and flows, flowsl and lesser amount amount of of spatially-associated spatially-associatedvolcanogenic volcanogenic sediments. sediments. It is cut by small granitic intrusions through most of its its exposure exposure area and and by by larger larger granitic granitic intrusions in Pifher Twp to to the the northeast. northeast. Metamorphism Increases to to the the northeast, perhaps caused by these these intrusions. Keweenawan northeast! Keweenawanintrusions intrusions which which cut cut the breccia breccia include a large diabase sill which dips gently to the south and a small dike, locally termed greenspar (Luther, Thomas, Kean, Keanl and and Luther, Luther! diabase dike! (Lutherl 1997; Thomasl in preparation). preparation). fragments ranging from from c <1l mm up to over The breccia contains rounded rock fragments 1 Im m in in maximum maximum dimension. dimension. Most fragments are disk-shaped disk-shaped to cigar-shaped cigar-shaped in in form although although irregular irregular on on smaller smaller scale; some some smaller smaller (5-20 (5-20 cm) cm) fragments fragments are are of fragments is, more competent more competent and and nearly nearly spherical. spherical. Sorting and alignment of isl in in some locations, locationsl poorly-developed poorly-developed primary primary bedding while, whilel in other locations, locationsl the sorting and alignment is a result of later strain. The smaller fragments fragments vary in in Larger composition from that of the composition the matrix matrix to to mafic mafic or or ultramafic ultramaficto to carbonate-rich. carbonate-rich. Larger fragments tend to be be similar to to the the matrix matrix in in composition composition although although minor minor differences differences in composition or consolidation consolidation cause the fragments to to weather weather high high or or low. low. The matrix of fine mm), matrix of the breccia is composed of fine quartz quartz grains grains (<0.05 (~0.05 mm)l euhedral to broken 4 . 1 to to euhedrai broken crystals of plagioclase (now albite) ranging in in size size from <0.1 1 mm, a minor pelitic fraction (now muscovite), and, locally, quartz, I muscovite)l and! locallyl fragments of quartzl and/or hornblende hornblende(now (nowchlorite) chlorite)up uptoto0.5 0.5mm. mm. The primary pyroxene andlor primary texture is epidotel actinolite, actinolitel over-printed by a metamorphic metamorphic assemblages of chlorite, chloritel epidote, Representative whole rock analyses of the matrix muscovite, muscovitel and and biotite. biotite. Representative matrix and and fragments are presented Theseanalyses analysesshow showthe theaverage average(igneous (igneous presented in Table 1. These rock equivalent) composition of of the matrix to be dacitic while the fragments vary from from dacitic dacitic to to mafic. mafic. fragments, (2) the relative relative In summary (1) (I) the heterogeneity of the fragments! homogeneity of the matrix, (3) the shape, and rounding of the fragments, matrix?(3) the shape! and rounding the fragmentsl (4) (4) the the 83 �great variability variability in in size size of of the the fragments, fragments, (5) (5) the the poorly poorlysorted sortedcharacter characterof of the thewhole whole great body of of rock, rock, and and(6) (6)the thespatial spatialassociation associationwith withpillowed pillowedvolcanics volcanicsand andbedded bedded body of aasubaqueous subaqueous tuffs lead leadthe the author author to to conclude conclude that that this this rock rock isisthe the product productof tufts debris flow flow or or flows flows off offthe the side side of of aavolcanic volcanic edifice. edifice. The Theslopes slopes presumably presumably debris consisted of of poorly-consolidated poorly-consolidatedvolcanogenic volcanogenic debris debrisincluding includingfinely-crystalline finely-crystalline consisted quartz and and clay clay which which was was transported transported from from nearby nearbyweathered weathered felsic-tofelsic-toquartz intermediate volcanics volcanics and and an an admixed admixedquantity quantityof of pyroclastic pyroclasticdebris. debris. intermediate Table 1. 1.Whole Wholerock rockanalyses analysesofofthe thematrix matrixand andselected selectedfragments fragmentsof of the the Table volcanic breccia. (XRAL) (XRAL) volcanic fraaments matrix matrix fraaments LN97-6-1BB LN97-6-2A ~~97-7-9~* LN97-6-2 LN97-7-9-2 LN97-7-9-2 LN97-6-1 LN97-6-2 LN97-6-2A LN9779A* Si02 Si02 Ti02 Ti02 A1203 A12 0 3 Fe203 Fe203 Feo FeO MnO MnO MgO MgO CaO CaO Na20 Na20 K20 K20 p205 LO1 LOI TOTAL 643 0.49 15.8 1.85 3.2 0.08 2.92 4.87 4.54 1.05 0.10 0.55 99.75 60.5 0.53 63.2 0.51 0.51 16.0 1.38 4.9 0.09 4.63 3.53 4.18 1.15 0.12 2.4 16.5 1.85 16.0 1.73 5.4 0.09 4.36 4.42 3.47 2.18 99.41 3.1 0.07 2.15 6.03 3.53 1.49 0.11 0.85 99.39 57.8 1.45 45.4 0.36 22.2 7.34 0.8 0.12 0.88 17.7 0.88 0.30 0.08 2.0 97.52 98.06 0.11 95%epidote epidote ** 95% REFERENCES REFERENCES Kresz, D.U. D.U. and and Zayachivsky, Zayachivsky, B., B.,1989, 1989,Precambrian Precambriangeology, geology, Barbara, Barbara, Meader Meader Kresz, and Pifher Pifher Townships; Townships;Ontario Ontario Geological Geological Survey, Survey, rpt rpt270 270with withmaps maps2536-2537, 2536-2537, and 91p.p. 91 Mackasey, W.O., W.O., 1975, 1975, Geology Geology of of Dorothea, Dorothea, Sandra, Sandra, and and Irwin IrwinTownships, Townships, District District Mackasey, of Thunder Thunder Bay; Bay;Ontario OntarioDivision Divisionof of Mines, Mines,rpt rpt122 122with withmap map2294, 2294, 83 83 p. p. of F., 1997, 1997, The The Petrology Petrologyof ofgreenspar: greenspar: aaProterozoic Proterozoicporphyritic porphyriticdiabase diabase Luther, F., Luther, dike; Pifher Pifherand andIrwin IrwinTownships, Townships, Lake LakeNipigon NipigonDistrict, District,Ontario Ontario (extended (extended dike; abstract):43rd 43rdAnnual Annual Institute Instituteon onLake LakeSuperior SuperiorGeology Geologymeeting, meeting,Sudbury, Sudbury, abstract): 43. Ontario,v.v.43. Ontario, 84 �UPPER PENINSULA PENINSULA OF NEW FIELD OBSERVATIONS OBSERVATIONS OF THE CLARKSBURG VOLCANICS, UPPER MICHIGAN MICHIGAN MAKI, John C. and Bornhorst, Theodore J., J., Department of Geological Engineering and MAIU, MI 49931 4993 1 Sciences, Michigan Technological TechnologicalUniversity, University,Houghton, Houghton, MI The Clarksburg Volcanics are a member of the the Early Early Proterozoic Proterozoic Michigamme Michigamme Formation, Baraga Baraga Group, Marquette Supergroup and crop crop out near US-4 Group, Marquette Supergroup and US-41I between between Champion Champion and west Ishpeming, Ishpeming, Marquette County, County, Upper Upper Peninsula, Michigan (Cannon, (Cannon, 1974, 1975; Cannon and Klasner, Marquette Peninsula, Michigan Klasner, 1977; 1977; Simmons, 1974). 1974). The TheClarksburg ClarksburgVolcanics Volcanicsare are stratigraphically stratigraphically above above the the Greenwood Greenwood Iron-formation Iron-formation member of of the the Michigamme Michigamme Formation Formation and and are are laterally Member and below the Lower graywacke member restricted over a 19 19 km strike length and only crop out on the southern southern limb limb of of the Marquette Marquette trough. trough. These only provides provides data on on stratigraphic These rocks rocks dip dip about about 60 60 degrees degrees or more, hence the exposed section only and strike parallel variation. Despite metamorphism to the amphibolite amphibolite facies in most most exposures exposures and and fades in greenschist facies in aa few, few, primary primary textures textures are are well preserved in the outcrops. Clarksburg Volcanics Volcanics are composed mostly of volcanic rocks with lesser amounts The Clarksburg amounts of of clastic clastic sedimentary rocks and iron-formation. Field Field observations and available chemical data suggest that the volcanic rocks are dominantly basalt with less amounts amounts of of andesite. andesite. In general, general, the volcanic rocks are tuffs and agglomerates agglomerates containing containing fragments 0.5 to 1.5 1.5 cm in diameter. Near Near the thetowns townsof ofHumboldt Humboldtand and clast size is considerably larger larger than than elsewhere, elsewhere,up upto to 30 30 cm cm in in diameter. diameter. Laterally, Clarksburg, clast Laterally, the the typical clast clast size size is is considerably considerably finer finer in both the extreme eastern and western exposures with argillite argillite being common in the west Ishpeming exposures. These These observations observations suggest suggest a proximal proximal or or near near vent vent environment environment in the central central exposures exposures and a distal environment towards the east and west. Since Sincemafic mafic pyroclastic pyroclastic rocks rocks often often do do not not travel travel large large distances distances from from the volcanic volcanic vent, itit is is likely likely that that the the volcano volcano was quite near the central exposures of the Clarksburg Volcanics. central exposures Clarksburg Within the Clarksburg Volcanics there there are are several areas with Within Clarksburg Volcanics with interbedded interbedded banded banded ironironformation. The layers (I (1 to to44 mm mm Theiron-formation iron-formationisiscomposed composed of of mixed magnetitemagnetite- and detrital-bearing layers (< 1 mm thick). Metamorphism thick) and poorly defined chert layers (< Metamorphism has has produced produced quartzite quartzite textures textures in the iron-fonnation. iron-formation. As Asthe theexposures exposuresof ofiron-formation iron-formationare arein in the the proximal proximal section section of of the the Clarksburg Clarksburg Volcanics, we suggest suggest that the interbedded iron-formation has a volcanogenic volcanogenic origin. origin. Throughout the immediate immediate region, diabase sills, dikes, and other shaped bodies bodies are are common. common. Cannon (1974) (1974) suggested suggested that that the the diabase was was approximately approximately equivalent equivalentinin age age to to the Clarksburg Cannon Volcanics. The Themajor majorelement elementchemical chemical composition composition of the the diabase diabase and and Clarksburg Clarksburg Volcanics Volcanics are are large body body of of diabase diabase with with a surface similar. Just south of the town of Clarksburg Clarksburg is a relatively large exposure of approximately km. This approximately 1.5 1.5 by 1.5 1.5 krn. Thisbody body of of diabase diabasecuts cuts rocks rocks stratigraphically stratigraphicallyolder olderthan than the Clarksburg Volcanics and is spatially adjacent to to the the proximal proximal section. section. We suggest this diabase is part of the subvolcanic subvolcanic roots roots of of the the Clarksburg Clarksburg volcanic volcanic system. system. References Marquette County, County, Michigan: Michigan: U.S. U.S. Cannon, W. F., 1974, 1974, Bedrock geologic map of the Greenwood quadrangle, Marquette Geological 168. Geological Survey Survey Geologic GeologicQuadrangle QuadrangleMap MapGQ-l GQ-1168. Michigan: U.S. U.S. Cannon W. F., 1975, 1975, Bedrock Bedrock geologic geologic map of the the Republic Republic quadrangle, quadrangle, Marquette County, Michigan: Geological Survey Geological Survey Miscellaneous MiscellaneousInvestigation InvestigationSeries SeriesMap Map 1-862. 1-862. Klasner, J. S., 1977, 1977, Bedrock geologic map of the southern part of the Diorite and Champion Cannon, W. F., and Kiasner, minute quadrangles, quadrangles, Marquette Marquette County, County, Michigan: Michigan: U.S. U.S. Geological Geological Survey Survey Miscellaneous Miscellaneous Investigation Investigation Series 7-112 minute Map 1-1058. 1-1058. map of of the the Ishpeming Ishpemingquadrangle, quadrangle,Marquette MarquetteCounty, County,Michigan: Michigan: U.S. Simmons, G. C., 1974, 1974, Bedrock geological map Geological Survey Geological SurveyGeologic GeologicQuadrangle QuadrangleMap MapGQ-1 GQ- 1130. 130. 85 �ROYALE -- WHERE ARE THEY POST-GLACIAL SHORELINES OF ISLE ROYALE THEY NOW? NOW? M.E. McRae, Oak Ridge Associated Universities, Universities, Reston, VA W.F. Cannon, Cannon, U.S. Geological Survey, Reston, VA Woodruff, U.S. Geological Survey, Mounds View, MN L.G. Woodruff, Well-developed Well-developed shoreline shoreline features features at at elevations elevations higher higher than the the present day day lake lake level level are are basin. These well documented in the Lake Superior basin. These shorelines shorelines formed approximately approximately 10,000 10,000 to 4,500 years years ago as the last glacier to occupy western Lake Superior Superior receded to the northeast. Further, Further,mapping mapping of of stranded stranded shoreline shoreline features features has demonstrated demonstrated that these once flat-lying lake planes are now tilted from northeast to southwest as a consequence consequence of differential isostatic rebound. Previous Previousresearchers researchers have been able able to construct construct isobases of better-developed lake lake levels. levels. These Washbum and rebound for several of the better-developed These include include Lakes Washburn Lake Minong B.P.), Beaver Bay Minong(—9500 (-9500 B.P.), Lake Houghton Houghton(—8000 (-8000 B.P.), Beaver Bay(—9800 (-9800 - 9700 B.P.), Lake and Lake Lake Nipissing Nipissing(—5500 (-5500 -4700 - 4700 B.P.). Beach ridges are common features features on Isle Royale, particularly particularly on the lower lower elevations elevations of of the the southwest portion of the island where glacial debris debris is is widespread. widespread. A few wave-cut features features in bedrock have also been mapped in the the northeastern northeastern half half of of the the island. island. However, However, all of and discontinuous. discontinuous. Consequently, these features are scattered and Consequently, the exact exact positions of former shorelines shorelines are not precisely known from observable observable features features for most of the island. island. (GIs) software, we constructed constructed a series series of gridded gridded Using geographic geographic information information systems systems (GIS) surfaces surfaces representing representing lake level level planes from from the isobases of glacioisostatic glacioisostatic rebound described described above. Subtracting Subtractingeach eachgridded gridded surface surfacefrom from the the present-day digital digital elevation elevation model (DEM) (DEM) new DEM7s DEM's showing the island's morphology morphology at at several several of Isle Royale yields a sequence of new different different lake lake stages. stages. We then displayed the modeled shorelines shorelines with the known beach and wave-cut features. features. The The Beaver Bay do not correlate correlate with with two highest modeled shorelines, shorelines, Lake Washburn and Lake Beaver any of the mapped features. This This may may indicate indicatethat that the the island island was not yet free free of ice at these Minong shoreline. shoreline. Lengthy times. All All mapped mapped features features fall fall either either on or below the Lake Minong on the the modeled modeled Minong Minong shore. shore. Evidence sections of mapped beach ridges lie on Evidence also seems seems to shore. No features support the position of the modeled Nipissing shore. features seem seem to correlate correlate with the Houghton Houghton shoreline. shoreline. By overlaying overlaying the the modeled modeled shorelines shorelineson on the the modern modem digital digital elevation elevation model, model, itit isis possible possibleto to the post-glacial post-glacial shores shores around around the the island. island. This determine the approximate elevation of the knowledge could serve serve as a guide to future future mapping particularly if combined with information such as vegetation type, surficial surficial material, abundance of outcrop, outcrop, and and information accessibility accessibility to trails. 5,000 years ago, and possibly possibly earlier. earlier. Lastly, prehistoric mining of native copper copper began about 5,000 the prehistoric prehistoric discovery discovery and and mining mining of of We hypothesize that former lake levels influenced the copper. Copper would have been easily accessible and recognizable in wave-washed Copper would have been easily accessible and recognizable prehistoric shorelines shorelines seems seems probable. probable. Because shoreline rock exposures, so discovery along prehistoric Because wave-washed exposures exposures remain largely barren of vegetative material for for prolonged prolonged periods periods 86 �after afterthey theyare areabandoned, abandoned,they theyremained remainedfavorable favorablepoints pointsfor fordiscovery discoverylong longafter afterthe thelake lake levels levelshad hadreceded. receded.Major Majorprehistoric prehistoricworkings workingsatatthe theMinong MinongMine Mineare areininextensive extensivebedrock bedrock exposures exposuresatatororjust justabove abovethe theprojected projectedMinong Minongshore. shore.During Duringa abrief briefreconnaissance reconnaissanceinin 1997 1997we weobserved observedprehistoric prehistoricworking workinginintwo twoother otherareas areasof ofextensive extensiveexposure exposureatatthe the Minong Minongshore. shore.Did Didearly earlyinhabitants inhabitantsofofthe theLake LakeSuperior Superiorregion, region,such suchasasthe thePlano PianoIndians Indians who whoinhabited inhabitedthe theMinong Minongshore shorenear nearThunder ThunderBay, Bay,visit visitthe theisland islandand anddiscover discovercopper copper duringthe theLake LakeMinong Minongstage, stage,well wellbefore before the the generally generally accepted accepted date of first mining? Or Or during did didbarren barrenrock rockexposures exposuresfrom fromthe theformer formerMinong Minongshore shorefacilitate facilitaterecognition recognitionofofnative native copper eithercase, case,we wesuggest suggestthat thatthe theprojected projectedlocation locationof ofthe the copperthousands thousandsofofyears yearslater? later?InIneither Minong Minongand andyounger youngershorelines shorelinescan canprovide providea aguide guidetotofuture futurearchaeological archaeologicalstudies. studies. Projected Projecteddigital digitalelevation elevationmodel modelof ofIsle IsleRoyale Royaleduring duringthe thetime timeof ofLake LakeMinong. Minong. Shoreline Shorelineof ofthe the modem modemisland islandisisshown shownininwhite. white. 87 �ELECTRON MICROPROBE STUDY STUDY OF THE Pt-Pd Pt-PdAND AND RELATED RELATED MINERALIZATION IN THE Cu-Ni DEPOSIT MINERALIZATION THE MINNAMAX/BABBITT MINNAMAXIBABBITT Cu-Ni McSWIGGEN, Peter L., Minnesota Geological Survey, 2642 University Avenue, St. Paul, Minnesota 55114 551 14 The Minnamax deposit deposit is is one one of several several copper-nickel copper-nickel sulfide sulfide deposits deposits that occur occur along along the the base of the the Duluth Duluth Complex, Complex, which which is is aa series series of mafic intrusions intrusions that are part of the Keweenawan (1100 and Miller, Miller, 1993). The Keweenawan (1 100 Ma) Midcontinent Rift system (Paces and The ore ore body consists inclusions derived derived from from consists of troctolitic and ultramafic rocks, as well as hornfelsic homfelsic inclusions Paleoproterozoic metasedimentary rocks, and unconforrnably unconformably overlying Mesoproterozoic Mesoproterozoic Paleoproterozoic volcanic rocks. The Thecopper copperand andnickel nickel are are contained contained predominantly predominantly in disseminated disseminated sulfides that make rock. The make up between 11 and 5 percent of the rock. The sulfides sulfides consist largely of chalcopyrite, cubanite, pyrrhotite and pentlandite (Severson, 1991; chalcopyrite, 1991; Severson and Barnes, 1991). In In addition additionto tothe thecopper copperand andnickel, nickel,the the deposit depositalso alsocontains containssignificant significant concentrations of platinum concentrations platinum (Pt), (Pt), palladium palladium (Pd), (Pd), gold gold (Au), (Au), silver silver (Ag) (Ag)and and cobalt cobalt(Co). (Co). Sections Sections of core core ranging ranging from from 55 to 10 ft long have as much as 7.0 ppm Pd, 3.1 ppm Pt, and 13.1 13.1 ppm Au. As Aspointed pointed out outby by Severson Severson(1991), (1991), the high values for the platinum group elements other precious precious metals, and Co have been shown by others to be elements (PGE's), other associated associated with the the high-grade high-grade copper copper zones zones (Kuhns (Kuhns and and others, others, 1990). 1990). This This electron electron microprobe microprobe study study has has shown shown that that rocks rocks at at the the Minnamax Minnamax site sitecontain contain at least two platinum group minerals (PGM's) -froodite (PdBi2) and cabriite -- froodite cabriite (Pd2SnCu). (PdzSnCu). They are are commonly commonly associated associated with massive massive sulfide sulfide mineralization and are less common common in in samples samples consisting consisting mostly of silicates. silicates. Of Ofthe the14 14samples samplesinvestigated investigatedin indetail, detail,55 were were found to contain either froodite or cabriite. Although Although the number of PGM grains is small, small, just aa few few of of the the 1-2 1-2micron micron size sizegrains grains could could account account for for the the reported reported whole whole rock rock values. values. Therefore there is no need to invoke invoke PGE-sulfide phase solid solution solution to account for the Therefore there PGE whole-rock whole-rock values values reported reported from from these these rocks. Numerous found in in these these rocks. rocks. The Numerous examples examples of silver mineralization were found The silver silver is typically typically present either either as as solid solid solution solution in maucherite maucherite or as discrete discrete grains grains of native native silver. Significant Significantgold goldwas was found found in in aa few few of the native silver grains. Values Values as as high high as as 16 wt. percent Au were measured in 55 to 100 micron size grains of silver, but values were more typically typically in the 11 percent range. Cobalt Cobaltwas was found foundat at significant significantlevels levels only only in in maucherite maucherite and pentlandite. Detailed Detailedinspections inspections of of these these samples samples shows shows that they contain contain numerous altaite (Ni,As), shadlunite shadlunite[(Pb,Cd)(Fe,Cu)8S8], [(Pb,Cd)(Fe,Cu)$J, altaite numerous rare rare phases phases including includingdienerite dienerite(Ni3As), (PbTe), laurionite (PbTe), laurionite[PbCl(OH)} [PbCl(OH)]and and cotunnite cotunnite(PbCl2). (PbClJ. Kuhns, M.P., Hauck, S.A. and Barnes, R.J., 1990, Origin and occurrence of platinum group elements, copper-nickel mineral group elements, gold and silver, silver, in the South Filson Creek copper-nickel mineral deposit, Lake County, Minnesota. Natural Natural Resources Resources Research Institute, NRRUGMIN-TR-89-15,6Op. 60p. Univ. Minn., Duluth, Duluth, Tech. Tech.Report, Report,NRRI/GMIN-TR-89-15, Paces, J.B. and and Miller, Miller, J.D., J.D., Jr., Jr., 1993, 1993,Precise Precise U-Pb U-Pb ages ages of Duluth Complex and and related related mafic intrusions, intrusions, northeastern Minnesota: Geochronological insights to physical, petrogenetic, paleomagnetic, petrogenetic, paleomagnetic, and tectonomagmatic tectonomagmatic processes associated with with the the 1.1 Midcontinent Rift System. Journal Journal Geophysical Geophysical Research, Research, v. 98, no. B8, 13,997-14,013. p. 13,997-14,013. Severson, MinnamaxlBabbitt Severson, M., 1991, 1991, Geology, Geology, mineralization, mineralization, and geostatitics of the Minnarnax/Babbitt Cu-Ni Deposit (Local Boy Area), Minnesota. Natural Resources Resources Research Research Institute Institute Technical Report NRRIITR-91/13a, 96 96p. p. Severson, Severson, M.J. and Barnes, Barnes, R.J., 1991, 1991, Geology, mineralization, and geostatistics geostatistics of the the Minnamax/Babbitt MinnamaxBabbitt Cu-Ni Cu-Ni deposit deposit (Local (Local Boy Area), Area), Minnesota; Minnesota; Part II: II: Mineralization Mineralization and geostatistics. Natural Natural Resources Resources Research Research Institute Institute Technical Report NRRI/TR-91/13b, NRRIITR-9 1/13b, 216 p. 88 �POST- 1.76 Ga Ga LOW-GRADE LOW-GRADE METAMORPHISM METAMORPHISM OF THE BARABOO QUARTZITE POST-1.76 G., Jr., J., Dept. of Geology Geology & & Geophysics, MEDARIS, MEDA1US,L. L.G., Jr., BROWN, BROWN, P.B. P.B. and BUNGE, BUNGE, R R.J., Wisconsin-Madison,Madison, Madison,WI WI53706; 53706;medaris@geology.wisc.edu medarisgeology.wisc.edu Univ. of Wisconsin-Madison, It has long long been been recognized recognized that the the Baraboo Baraboo Quartzite Quartzite is is folded folded and and metamorphosed, metamorphosed, and recent U-Pb dating of of detrital detrital zircons zircons in the quartzite quartzite requires requires that deformation deformation and and recrystalrecrystallization were were post-1.76 Ga events. Although Although the the structure structureof ofthe theBaraboo Baraboosyncline syncline has been well studied, little attention has been devoted to to metamorphism metamorphism in the Baraboo Baraboo Range, Range, other other identifyingpyrophyllite pyrophyllite in inmetap metapelite and recognizing recognizing that that metamorphism metamorphism was was than identii'ing elite layers and low-grade. low-grade. We Wehave haveundertaken undertakenaapetrologic petrologicinvestigation investigation of of the theBaraboo BarabooQuartzite Quartziteand and post-1.76Ga Gametamorphism. metamorphism. underlying granite and rhyolite to to determine the the conditions of ofpost-1.76 Rock types, chemical compositions, well-developed paleosol paleosol compositions. and and mineral assemblages AAwell-developed occurs in granite and rhyolite at the unconformable base of the Baraboo Quartzite. Intense rhyolite the unconformable the Baraboo Quartzite. Intense chemical weathering and sedimentary chemical weathering sedimentary processes processes Table I1 produce marked geochemical combined to a combined a geochemical Chemical Compositions, Compositions, Baraboo Baraboo Rocks Rocks differentiation among basement basement rocks, paleosol, and avg avg avg pelitic layers in the Baraboo 1). pelitic layers Baraboo Quartzite Quartzite (Table (Table 1). rhyolite granite granite saproliie soil pelite saprolite soil pelite (1) (2) (10) (5) (1) Ca, (1) (2) (10) ( 5) (1 Ca, Na, Na, and and KKwere wereleached leached from from granite granite and and wt% wt% rhyolite, and and A1 Al and Fe were were concentrated concentrated in the the Si02 rhyolite, 5102 70.51 59.70 70.51 56.41 56.41 59.70 72.80 69.25 69.25 72.80 0.26 0.25 0.36 0.87 Ti02 0.26 0.25 0.36 paleosol (saprolite and soil) 0.87 1.03 1.a3 soil) and and pelitic layers in the Ti02 1AJ203 13.30 15.15 17.18 20.89 25.40 A1203 13.30 15.15 17.18 20.89 25.40 sedimentary section, which which consisted of sedimentary section, consisted originally originally of Fe203 2.99 3.46 2.82 10.18 8.04 2.99 3.46 2.82 10.18 8.04 kaolinite and variable amounts of silt-size quartz kaolinite and variable amounts salt-size quartz Fe203 MnO 0.07 0.09 0.00 0.00 0.00 0.01 MnO 0.07 0.09 0.00 0.01 elites MgO aluminousofofthree threeanalysed analysedppelites grains. The Themost mostaluminous MgO 0.14 0.89 0.07 0.38 0.38 0.04 0.14 0.89 0.07 0.04 is listed listed in Table Table 1, 1, and and two two other othersamples samples are are CaO 1.16 1.55 0.14 0.09 0.09 0.03 1.16 1.56 0.14 0.03 CaO 4.93 4.40 0.34 0.32 0.32 0.04 0.34 0.04 Na20 4.93 4.40 equally lowinin Ca, Ca, Na, Na, and meta- Na20 equally low and K During meta3.17 3.14 4.75 5.72 0.21 4.75 5.72 0.21 K20 K20 3.17 3.14 morphism, K K was was reintroduced re-introduced into the paleosol by P205 0.03 0.09 morphism, 0.13 0.10 0.10 0.12 P205 0.03 0.09 0.13 0.12 1120-tich fluids that were H,0-rich fluids that were channeled channeled along along the the LLOl 1.25 1.53 2.51 3.65 4.70 4.70 O1 1.25 1.53 2.51 3.65 sub-B araboo unconformity; unconformity; this K-metasomatism sub-Baraboo K-metasomatism SSum 100.10 99.78 98.80 98.62 um 100.10 99.78 98.80 98.62 99.32 99.32 was orethindiasp diasporewas accompanied accompaniedby by formation formationof ofthin quartz pyrophyffite-white pyrophyllite-white mica veins in basal quartzites. quartzites. The compositions compositions of Baraboo rocks are projected projected into in which which the the positions positions into the the system, system, KASH, KASH, in in Fig. Fig. 1,1,in microcline of selected selected minerals minerals are also also plotted. plotted. The KASH KASH equilibrium metamorphic metamorphic assemblages assemblagesfor for these these rocks equilibrium + quartz + microcline are: granite and and rhyolite, microcline + are: granite rhyolite, quartz muscovite; metapelite, muscovite; paleosol, paleosol, quartz ++ muscovite; metapelite, hydrothermal veins, veins quartz pyrophyllite; and hydrothermal quartz ++ pyrophyllite; + diaspore. diaspore. Kaolinite is pyrophyllite Kaolhute pyrophyllite ++ muscovite + present in elite and hydrothermal in metap metapelite hydrothermal veins, but only only as a retrograde retrograde product. Inhiaddition additiontotoKASH KASHminerals, minerals, granite and rhyolite contain albite, epidote, and chlorite. chlorite. Hematite isis abundant abundant in these these rocks, rocks, especially especially in Hematite K20 A1203 diaspore paleosol common in in paleosol and metapelite, metapelite, and and rutile rutile is common Fig. 1 Compositions Compositions of of Baraboo Baraboo metapelite. metapelite. plane rocks projected projected into into the KAS plane system, KASH KASH of the system, 89 �Metamorphic Metamorphic conditions conditions Mineral reactions and and chemographic chemographic relations relations in m the thesystem, system, KASH for unit unit activity activity of of H20), KO), are aresummarized summarized in in Figure Figure 1.1. Minimum KASH (calculated (calculated for temperatures temperatures of of metamorphism metamorphism are are defined defined by by the themetapelite metapeliteassemblage, assemblage, quartz ++ pyrophyllite, pyrophyllite, which is stable stable above above the reaction, reaction, Kin K h ++ Qtz Qtz == Pr! Prl ++ V, V, and and by the the absence absence of stable kaolinite from all observed T,, assemblages, indicating that temperatures were T- assemblages, indicating that temperatures were above above stable fiom the kaolinite. Maximum the stability stability limit of kaohite. Maximum temperatures temperatures are are defined defined by the the absence absence of of kyanite kyanite ore, in from pyrophyllite ++ diasp diaspore, in hydrothermal hydrothermal veins, vems, which which isis fiom the the assemblage, assemblage, muscovite muscovite ++ pyrophyffite stable below the reaction, Pr! Prl ++ Dsp Dsp == Ky Ky ++ V, V, and and by by the theabsence absencekyanite lqmniteininmetapelite, metapelite, which limitof of pyrophyllite. pyrophyllite. which indicates mdicates that temperatures temperaturesdid didnot not exceed exceedthe thestability stabilitylimit Fluid were analysed from quartz m in a folded vein in inmetapelite. metapelite. The The a d inclusions inclusions were analysed fiom folded quartz quartz vein quartz contains contains aa single single population population of ofabundant abundantaqueous aqueousinclusions mclusions that thathave havefinal finalmelting meltmg points corresponding points of-15 of -15toto-18°C, -lS°C corresponding to to 18 18to to20 20equivalent equivalent wt% wt% NaCL NaCL First Firstmelting meltmg below below -35OC divalent cations. H o m o g ~ t i o temperatures ntemperatureslie lie between between -3 5°C suggests suggests the the presence presence of divalent cations. Homogenization 165 the 175-185°C 175-lW°range. range. 165 and 215°C 215OC with a peak in the Intersection of with the thelimiting limiting mineral mineral reactions reactions constrains constrains of the the fluid fluid inclusion mclusion isochore isochore with temperature-pressure conditions conditions for for the the Baraboo BarabooQuartzite Quartzitetotolieliebetween between—320°C, -320°C2.7 kbar kbar and —385°C, 4.0kbar. kbar. Such values correspond correspond to aa thermal -385OC, 4.0 thermal gradient gradient of of25-30°C/km. 25-30°C/kmwhich is is typical terranes and is notably notably elevated elevated over that for typical for Barrovian-type Barrovian-type metamorphic terranes for stable stable cratons cratons(--17°C/km (-17OCh at comparable comparable depths). depths). 8 6 4 2 0 250 300 350 T,°C 400 450 Fig. Fig. 2 Mineral Mineralassemblages assemblagesand andreactions reactionsin inthe the system, systeml KASH, KASH, aa fluid fluid inclusion inclusionisochore isochorefor for quartz quartzin inaa folded foldedquartz quattzvein, vein, and and metamorphic metamorphicconditions conditions for for the the Baraboo Barabm Quartzite Quarfziie Conclusions Folding and metamorphism metamorphism of the Baraboo Baraboo Quartzite Quartzite mark mark an animportant important Conclusions the age of this post-l.76 post- 1-76Ga Gatectonothermal tectonothermal event event in in the theLake LakeSuperior Superiorregion. region. Although Although the event remains remains uncertain, uncertain, itit could could be be related related to an an eastern eastern extension extension of the the Mazatzal Mazatzal belt at at -1.63 Ga. However, However,andalusite-bearing andahsite-bearingassemblages assemblagesin the the Waterloo Waterloo Quartzite Quartzite are are probably probably -1.63 Ga. due due to to contact contactmetamorphism metamorphismassociated associatedwith withWolf WolfRiver Rivermagmatism magmatismatat—4.43 -1.43 Ga. 90 �SVANBERGITE SVANBERGITEiN INTHE THEBARABOO BAMBOOQUARTZITE: QUARTZITE:SIGNIFICANCE SIGNIFICANCEFOR FORDIAGENETIC DIAGENETIC PROCESSES ANDPHOSPHORUS PHOSPHORUSFLUX FLUXIN INPRECAMBRIAN PRJXAMBRIANOCEANS OCEANS PROCESSESAND MEDARIS, Geophysics, MEDARIS,L.G., L.G.?Jr. Jr.and andFOURNELLE, FOURNELLE?J.H., J.H.,Department DepartmentofofGeology Geology&&Geophysics, University Madison,WWI 53706;medaris@geology.wisc.edu medarisgeology.wisc.edu I 53706; University of of Wisconsin-Madison, Wisconsin-Madison, Madison? Authigenic Authigenicminerals mineralsof ofthe thebeudantite beudantiteand andcrandallite crandallitegroups groupshave haverecently recentlybeen beenrecognized recognizedasas widespread widespreadconstituents constituentsofofArchean ArcheantotoCretaceous Cretaceoussedimentary sedimentaryrocks rocks(Rasmussen, (Rasmussen71996). 1996). Although Althoughthe theabundance abundanceofofthese thesealuininophosphate-sulfate alumhophosphate-dte minerals minerals is is small, small, on the the order order of of wt%ininaagiven givensample, sample7they theyappear appearto tobe bemore moreabundant abundantthan thanauthigenic authigenicapatite apatite 0.2to to0.01 0.01wt% 0.2 and phosphorusbalance balanceininthe theoceans. oceans. andplay playan animportant importantrole roleininphosphorus The general formula i%e beudantite beudantite and andcrandaiite cranddlitemineral mineralgroups w m pThe The general formulafor forthe thebeudantite beudantite groupisisAB3(XO4XSO4XOH)6, AB3(X04)(S04)(OH)6, whereAA ==Ba, Ba7Ca, Ca7Ce, Ce7Pb, Pb7Sr; Sr;BB==Al, Al,Few; Few;and andXX==As, As7P; P; group where and where AB3(X04)2(O13,F)547 whereAA ==Ba, Ba7Bi, Bi,Ca, Ca7Ce, Ce,La, La7Nd, Nd,Sr, Sr7Th; Th; andfor forthe thecrandallite crandallitegroup groupisisAB3(XO4)2(OH,F)5, P, Si. Electron microprobe analysis of Baraboo svanbergite B = Al, Fe3+; and X = As7 P7 S i Electron microprobe analysis of Baraboo svanbergite Fe3+; and X = As, B = Al, demonstrates which demonstratesthat thatits itscomposition compositioncan canbe beportrayed portrayedby byaadistorted distortedpyramid pyramid(Fig. (Fig.1)1)ininwhich members of the beudantite group lie along the front edge of the pyramid and members members of the beudantite group lie along the fiont edge of the pyramid and membersof ofthe the crandallite crandallite group group lie lie in m the the fir fiuface face(note (notethat thatCa Caand andBa Bahave havebeen beencombined combmedfor forprojection projection purposes). purposes). florencite florencite CeAJ3(P04)2(OH)6 ce%p04)2(0H) Crandallite group SrsAJ3Q'Q4 )2(H)5 . HO goyazite (Ca,Ba)A13(P04)(S04)(OH)6 SrAI3(P04)(S04 )(OH)6 svanbergite Fig. Fig. IICompositional Compositionalspace spaceofofBeudantite Beudantiteand andCrandallite Crandallite groupminerals mineralsfrom fromBaraboo Baraboometapelite metapelite group svanbergite Small Occurrenceand andchemical chemical composition compmition of o fBaraboo svanberdte S d amounts amounts of Occurrence svanbergite elite layers layers m in the the Baraboo Baraboo Quartzite7 Quartzite, where where it is inmetap metapelite is svanbergite are are widespread widespreadin associated with pyrophyllite, quartz, hematite, and rutile. Svanbergite grains are equant associated with pyrophylbe7 hematite7 Svanbergite grains are equantand and have smallsize, size7are arereadily readilyvisible vkiile have diameters diametersof of10-20 10-20microns, microns7but butdespite despitetheir theirsmall microscopically microscopically because because of of their their marked marked difference &erence in relief compared to associated associated pyrophyllite. <1 pyrophyllite. Baraboo Baraboosvanbergite svanbergitecontains contains<2 < 2wt% wt%Fe203, Fe203? 4wt% wt%As205, 4 O s 7and andhas hasnegligible negligiile amounts ofAAl3(PO4XSO4XOH)6 solidsolution solution of ALUJPO~)(SO~)(OH)~ amountsof ofBi, Bi,Pb, Pb7Th, Th7Si, Si,and andF;F;itsitscomposition compositionisisa asolid Ca + Ba + REE, which lies near the base of the + Ba + W E 7 which lies near the base of the Ca Sr> where A = AAl&P04)2(OH)5*q07 where A = Sr AAI3(P04)2(OH)5'H20, pyramid in m Fig. 11 between between svanbergite svanbergiteand and goyazite goyazite(Fig. (Fig. 2). 2). - 91 �"crandallite" "crandallite" goyazite goyazite Ba Ba REE REE 0 0 + 0 U) 0 U) Ca Ca 0 0.2 0.4 0.6 0.8 Ba Sr - Fig. 33 Proportions Promtions of of cations cations in in the A-site of Baraboo Bamboo svanbergite-goyazite svanbergite-goyazite 1.0 "woodhouseite" "woodhouseite"Sr/(Sr+Ca+Ba) Srl(Sr+Ca+Ba) svanbergite svanbergite Fig. 2 Projection Projectionof ofmineral mineralcompositions compsitions onto onto the the base of the Beudantite-Crandallite Beudantite-Crandallite prism prism Baraboo svanbergite The The Baraboo svanbergite solid solid solution solution ranges ranges l m m from fiom almost pure svanbergite (beudantite group) to —70% goyazite(crandallite (crandallite group) group) with with a concomitant concomitant -70% goyazite in Sr/(Sr+Ca+Ba) (Fig. 2), decrease m 2)?and and A-site 10000 is dominated dominatedby by Sr Sr(Fig. (Fig.3). 3). Many occupancy is grains are svanbergite grains svanbergite are strongly strongly zoned, zoned, with with rims rimsbeing bemg in crandallite component7 component, m in which whichthe the sum sum of of enriched in reaches 5.3 wt %, La203, Ce203, %? L%O3? Ce203?and and Nd203 N&03reaches amounting to --27% -27% occupancy occupancy of of the the A-site (Fig. (Fig. 3). 3). present, they Although other RE RE elements elements may be present? Nd can't readily re&ly be determined by electron microprobe Fig. 44 Representative Representativechondrite-normalized chondritenormalized techmques due to their techniques their low low abundances abundances and spectral spectral La, contentsof of Baraboo Baraboo La, Ce, and Nd contents svanbergite-goyazite interferences. mterferences. The light REE contents contents in m svanbergite svanbergite 5000 toto40,000 times are 407000 timesgreater greaterthan thanin mchondrites, chondrites7 are -5000 Nd by by aa fhctor factor of 2 to to 3 (Fig. 4). There nomarked markedCe Ceanomaly, anomaly7 and La is enriched over Nd Thereisisno with respect respect to to La and Nd. although two samples samples may have a slight Ce enrichment with Geological simificance significance of svanbergite Precipitation Geolokcal ofsvanberkte Precipitation of ofauthigenic authigenic aluminophosphatesulfate minerals has been ascribed to bacterial decomposition of P-beakg P-bearing organic matter m in an d t e minerals has been ascriied to bacterial decomposition of within the zone of d sulfate methanogenesis ithin the a t e reduction and methanogenesis Al-rich environment, such as shale, shale?w (Rasmussen, so7the theoccurrence occurrenceof ofsvanbergite-goyazite svanbergite-goyazite in m Baraboo metapelites (Rasmussen71996). IfIfso, that such a process process may have been operative m mid-Proterozoic mid-Proterozoictime. time. signifies that operativein The widespread occurrence occurrence of of authigenic authigenic aluniinophosphate-sulfate alumhophosphate-dte minerals represents a unrecognized repository for phosphorus m in the the oceans. Rasmussen previously unrecognized Rasmussen has has estimated estimated that fluxof of7.6 7.6xx1010 10" moles that aluminophosphate alumhophosphateprecipitation precipitation accounts accountsfor for aaphosphorus phosphorusburial burialflux yr, which is comparable to that resulting from authigenic phosphates and P-bearing which is comparable to that resultmg fiom authigenic phosphates and (2.2-9.1 xx 10" moles yfl). yf'). However, However7Rasmussen Rasmussenused used the the composition composition of carbonates (2.2-9.1 florencite florencite (2 (2 moles of of P phi) pfb) in m his his calculation, calculation, and using the compositional compositional range range of of Baraboo Baraboo svanbergite-goyazite (1.0(1.0-1.7 estimate by 15 15 to 50%. 50%. 1.7 moles moles of of P pfli) pfi) reduces reduces the the burial flux estimate Regardless, factor in m oceanic oceanic P-flux. P-flux. Regardless?aluniinophosphate-sulfate aluminophosphate-dte minerals are an important fhctor REFERENCE CITED 296?601-632. 601-632. Rasmussen, B. (1996) (1996) American Journal Journal of of Science, Science?v. 296, . 92 �HIGH-RESOLUTION AEROMAGNETIC DATA DATA FOR USE OF HIGH-RESOLUTION FOR REGIONAL REGIONAL (WHERE'S THE GEOLOGY INVESTIGATIONS, INVESTIGATIONS, SOUThEASTERN SOUTHEASTERN WISCONSIN (WHERE'S KIMBERLITE!) MIJDREY, M.G., Jr., Jr.?Wisconsin WisconsinGeological Geologicaland and Natural NaturalHistory History Survey, Survey73817 3817Mineral Mineral MUDREY, Road, Madison, Point Road? Madison?WU 53705-5 100, 100, mgmudreyfacstaff.wisc.edu mgmudrey@facstaff.wisc.edu Between 1876 Between 1876 and and 1913, 1913, diamonds diamonds were found in at least seven localities in southern and central Wisconsin. All All were were found found in in Pleistocene Pleistocene gravel gravel deposits depositsor orHolocene Holoceneriver rivergravel. gravel. The bedrock unknown, but was presumed to be in bedrock kimberlite source for these diamonds is unknown7 northern northern Canada, Canada?the the only only area area north north of ofWisconsin Wisconsin previously previously known known to to contain containkimberlite. kimberlite. County, Michigan? Michigan, Cannon and With the discovery discovery of the Lake Lake Ellen kimberlite in Iron County? Mudrey (1981) (1981) suggested suggestedthe thedrift driftdiamonds diamondsin in Wisconsin Wisconsin may have come from a more more local source. source. Carison southeastern Wisconsin about 280 m Carlson and Adams (1997) described a kimberlite in southeastern across. The Thepreliminary preliminaryidentification identificationwas wasbased basedon ondrilling drillingsmall, small,highly highly magnetic magnetic anomaly anomaly identified from a little known aeromagnetic survey from the 1980s 1980s (800-meter (800-meter flight-line flight-line have aeromagnetic spacing). Only recently have aeromagneticsurveys surveysbeen been sufficiently sufficiently detailed to determine determine the presence of absence of kimberlite kimberlitein insoutheastern southeasternWisconsin. Wisconsin. Prior Prior to to the the most most recent survey? strong, small small survey, limited flight-line spacing of 110-krn 0-km precluded precluded the the identification identification of strong, magnetic bodies at the the shallow shallow bedrock bedrock surface. surface. Analysis of the aeromagnetic aeromagnetic survey survey indicates indicates that that flight-line flight-line spacing less than 800 800 m m will be ineffective in the identification identification of of small, small?highly magnetic kimberlite at at the the bedrock/surficial bedrock/surficial material material surface surface in southeastern southeasternWisconsin. Wisconsin. The identification identification of the kimberlite, and analysis of available aeromagnetic maps, indicate that other other kimberlitic kimberlitic bodies may occur occur in southeastern southeasternWisconsin and possibly northeastern Illinois and may be the source source for for the the diamond diamond discoveries discoveriesin in Wisconsin Wisconsin and and Illinois. Illinois. However, urbanization However? urbanization in in the the Milwaukee-Chicago Mlwaukee-Chicago corridor corridor may may discourage discourage further hrther geologic geologic and geophysical analysis and competing competing land use may make further hrther exploration explorationand and ultimate ultimate development difficult. development difficult. REFERENCES: REFERENCES: Cannon, W.F., and Mudrey, Cannon? Mudrey, M.G., M.G., Jr., Jr., 1981, 1981,The Thepotential potentialfor fordiamond-bearing diamond-bearingkimberlite kimberlite in northern Michigan and Wisconsin: U.S. Geological Survey Circular 842, 15 15 p. p. Carison, S.M. Carlson, S.M. and Adams, G.W., G.W., 1997, 1997,The Thediamondiferous diamondiferousSix-Pak Six-Pak Ultramafic Ultramafic U.S.A. (abs.): Institute Institute on Lake Superior Lamprophyre Diatreme, Kenosha, Wisconsin, U.S.A. Superior Geology, Proceedings, Part 1-Program Geology?Proceedings? 1-Programand and Abstracts, Abstracts?v. v. 43, 43, p. p. 11 11 Wisconsin, kimberlite, Wisconsin, kimberlite, aeromagnetic data 93 �_____________ AS INDICATORS INDICATORS OF OF INTRUSION INTRUSIONMECHANISMS MECHANISMS XENOLITHOLOGIES AS IN THE THEWAUSAU WAUSAU SYENITE SYENITE COMPLEX, COMPLEX, WISCONSIN WISCONSIN MYERS?Paul E., Geology Department, Department?University of Wisconsin, Eau 54701 MYERS, Eau Claire? Claire, WI WI 54701 area west of Wausauy (2) Wausau, Wausau, In the area Wausau, four alkaline subvolcanic subvolcanicplutons: plutons: (1) Stettin, (2) (Figure)?were intruded in a southeastward southeastward sequence sequence (3) Rib Mountain, and (4) Ninemile (Figure), into Lower Lower Proterozoic Proterozoic metavolcanic, metavolcanic, metasedimentary, and and granitic granitic intrusive intrusive rocks rocks into (Myers and others, 1984). 1984). Whereas Whereas the first three syenite plutons are concentrically concentrically (Myers plutons are zoned and and pipelike in structure, structure, the theyoungest, youngest,Ninemile Ninemilepluton, pluton, although althoughpossessing possessing an an zoned stopedits itsway wayto toaashallow shallowdepth depthunder underthe the aplitic core core rim, rim, isisaastock-like stock-likebody bodywhich whichstoped aplitic volcanoes. This paper shows the connection between magma now-eroded volcanoes. between xenolithologiesy xenolithologies, magma emplacement, emplacement?and andwalirock wallrockalteration. alteration. EXPLANATION EXPLANATION qp qp quartz quartzmonzonite monzoniteporphyry porphyry ng ng Ninemile Ninemile granite granite ga ga granite granite aplite aplite sy sy syenites syenites vv volcanic rocks rocks qq quartzite quartzite bs bs biotite biotiteschist schist fault fault 4 ', , -1 contact, infened contact, dashed where inferred 1 1 0 Scale: Scale:1 - 1 -, 1 2 . Zmiles mles 012-3. 7 -? kilometers kilometers Figure --- Map Map of of Wausau Wausau syenite syeniteplutons plutons The The Stettin Stettin pluton, plutony(Figure) (Figure) which is the oldest, oldest, most alkaline alkaline intrusion of the Wausau of 8.8 and Wausau syenite syenite complex, 8.8 xx 6.4 6.4 km. by and has has aa complexyis oval in plan with dimensions of concordant concordant NE NE elongation. elongation. Its Its outer outer wall zone zone consists of strongly strongly syenitized volcanic volcanic rocks rocks and and syenite syeniteaplite, aplite,which which grade grade inward inward into into concentric, concentricysheet-like sheet-like masses masses of gneissic gneissic nepheline nepheline and and tabular tabular syenites. syenites. The The indistinctly indistinctly bounded bounded intermediate intermediate zone zone consists consists mainly mainly of of flow-lineated flow-lineatedamphibole amphibolesyenite, syenite,and andthe the cylindrical cylindricalcore, core?with with aa diameter diameterof of 22 km kmhas hasaa rim rim of of lineated heated nepheline nephelinesyenite syeniteand and an an inner inner core core of coarse, coarse, pyroxene pyroxene syenite syenite identical identical with Stettin pluton is is separated separated from from the the syenite syenite bodies bodies to to with that that in in the the intermediate intermediatezone. zone. The The Stettin the the SE SE by by aa fault. fault. In the the Wausau Wausau pluton, pluton, coarse, coarse?massive massive pyroxene pyroxene and and amphibole amphibole syenites syenitesform form aa partial partial outer outer rim rim on on the the north and and east sides. AAbroad broad intermediate intermediatezone zone of of lensoidal lensoidal syenite syenite and and quartz quartz syenite syenite are are crowded crowded with lenticular lenticular xenoliths xenoliths of mica schist, schist?sillimanite-bearing sillimanite-bearing 94 �syenitized volcanic rocks. rocks.Xenolith Xenolith volume volume locally locally exceeds exceeds the the volume volume of of quartzite, and syenitized the the quartz quartzsyenite. syenite.As Asthe thecontact contactbetween betweenthe theWausau Wausauand andRib RibMountain Mountainplutons plutonsisis obscured by by aa broad strip strip of of Rib Rib River alluvium, its itscore coremay maynot notbe bevisible visiblein in outcrop. outcrop. obscured The Rib Rib Mountain Mountainpluton pluton produces produces aa crescentic crescenticmap map pattern pattern with with an an opening openingto to the the The south The most most striking strikingfeature feature of of this this south where where itit is engulfed engulfed by younger Ninemile granite. The concentric concentric pluton is the 8km 8km ring of very large, lenticular lenticularquartzite quartzite and and mica mica schist schist xenoliths xenoliths embedded embedded in in foliated foliated quartz quartz syenites syenites in in its its intermediate intermediate zone. zone. The The Ninemile NinemilePluton, Pluton,isisan anelliptical, elliptical, stock-like stock-likebody body which whichwas was intruded intrudedat at 1500 1500 Ma. (Van (Van Schmus Schmusand and Bickford, Bickford, 1981) 1981) into into the core core and south rim of the Wausau Wausau pluton. pluton. According According to to Anderson Anderson (1983) (1983)itit isis comagmatic comagmaticwith with rapakivi rapakivi granites granitesof of the the Wolf Wolf River River batholith. Although Althoughclassed classed as as aa granite, the theNinemile Ninemile pluton is mainly mainlycoarse coarsebiotitebiotiteamphibole amphibolemonzonite monzonitecontaining containingup up to to 30 30percent percent strained, strained,polycrystalline polycrystallinequartzite quartzitegrains grains usually accompanied accompanied by occasional occasional mica schist and quartzite xenoliths. A A crescentic crescentic mass mass of of granite graniteaplite aplite defines defines the the core corerim rim of of the the larger larger southern southernlobe lobe of of the the Ninemile Ninemilepluton. pluton. The The Wausau Wausau plutons plutons thus thus show show aa distinctive distinctive magmatic magmatic differentiation differentiationsequence, sequence, beginning Stettin pluton and and ending ending with with pegmatite pegmatite dikes dikesin in beginning with with nepheline nephelinesyenite syenitein in the the Stettin the the Ninemile Ninemile pluton. pluton. As As these these dikes dikes are are shallow-dipping shallow-dippingand and contain contain miarolitic miarolitic cavities cavitieswith with autoclasts autoclasts of of early early crystalline crystallinephases, phases,Falster Falster (1985) (1985)concluded concludedthat thatthey theycrystallized crystallized shallow shallow enough enough for for hydrothermal boiling. Several small small porphyritic quartz monzonite monzonite plugs plugs cut cut post-syenite post-syenite faults faults outside outside the Wausau complex complex and probably represent the "last gasp" Ninemile magma. magma. gasp" of of the the differentiated differentiatedNinemile Xenoliths Xenoliths in in the the Wausau, Wausau, Rib Rib Mountain Mountain and and Ninemile plutons are unassimilated wallrock wallrock fragments fragmentscarried carriedup up and and down down in in the the magmas magmas during during intrusion. intrusion. Where Wherethere therehas has been been considerable considerablevertical vertical transport, as asfor forinstance instancealong along caldera calderawalls, walls, xenoliths xenoliths show show great great diversity diversity of of protolithology protolithologyand and metamorphic metamorphicgrade. grade. They They include include upper upper amphiboliteamphibolitegrade, amphibolite, metadiorite, andesitic grade, sillimanite-bearing sillimanite-bearing quartzite, quartzite, mica schist, and arnphibolite, andesitic metavolcanics metavolcanicsand andmetasediments, metasediments,and andeven evencognate cognateinclusions inclusionsof ofearlier-phase earlier-phasesyenites. syenites. Their Their shapes shapes are are most most commonly commonly lenticular lenticular and and sheet-like with a preferential orientation orientation parallel Stettinpluton. pluton. parallel to to cylindrical cylindricalwalls. walls. Xenoliths Xenolithsare areuncommon uncommonininthe theStettin In In the the Wisonsin Wisonsin River River channel channel east east of of the the power power dam dam at at Wausau, Wausau, the the relationships relationships between betweenxenoliths xenolithsand andflow flowstructures structuresin in enclosing enclosing felsic felsic and and mafic mafic quartz quartz syenites syenites are are well displayed. with swirled swirledlineation lineation,, give displayed. Biotite amphibolite xenoliths with give way way southward southward in the outcrop outcrop to to sheet-like sheet-like masses masses of of felsic felsic and and mafic mafic rocks. The folded and fragmented mafic mafic xenoliths advanedmetasomatic metasomaticreplacement replacementand anddeformation. deformation. xenolithsare arebiotite-rimmed, biotite-rimmed, showing showingadvaned The Theenclosing enclosingamphibole amphibolequartz quartzsyenite syenitehas has highly highly discordant discordant flow flow lineation lineation with with swirls swirls and and eddies eddiessuggesting suggestingconsiderable considerableviscosity viscosity and andturbulence. turbulence. Late-stage Late-stagesyenite syenitepegmatite pegmatite veins veins with with quartz quartzcores corespobably pobably represent representresidual residual liquid liquid segregations segregations along along incipient incipient thermal thermalcontraction contractionfractures fracturesininquartz quartzsyenites syenitescontaining containingincompletely incompletelyassimilated assimilatedquartzite quartzite xenoliths. xenoliths.The Theoccurrence occurrenceof of several severalsmall smallxenoliths xenoliths of of unaltered, unaltered, porphyritic porphyritic trachyte trachyte in in the the north northend endof ofthe theoutcrop outcropsuggest suggestaadownward downwardmovement movementof ofsome someof ofthe theclasts clastsfrom fromthe the overlying overlyingvolcanic volcanicpile. pile.As Aselsewhere elsewherein inthe theWausau Wausausyenite syenitecomplex, complex,the theconsiderable considerable concentric concentricheterogeneity heterogeneityof ofxenoliths xenolithssuggests suggestsconsiderable considerablevertical, vertical,somewhat somewhatlaminar laminar transport transportof of xenoliths xenolithsalong alongcaldera calderawalls walls as as aa consequence consequence changes changes in the level of magma magma in in the the conduit. conduit. Future Future field fieldstudies studiesshould shouldinclude include detailed, detailed, comprehensive comprehensive mapping mapping of of xenolithologies. xenolithologies . References: References: Anderson, Anderson,J.J.L., L.,1983, 1983,Proterozoic Proterozoicanorogenic anorogenicgranite graniteplutonism plutonismofofNorth NorthAmerica, America,Geological Geological Society Society of of America AmericaMemoir Memoir161, 161, P.p.133-154. 133-154. Myers, Myers,P.E., P.E.,Sood, Sood,M. M. K., K.,Berlin, Berlin,L.A., L.A.,and andFaister, Falster,A.A.U., U.,1984, 1984,The TheWausau Wausausyenite syenitecomplex, complex, central central Wisconsin, Wisconsin,30th 30thAnnual AnnualInstitute Instituteon onLake LakeSuperior SuperiorGeology, Geology,58 58 pages. pages. Van VanSchmus, Schmus,W.R., W.R.,Medaris, P.O.,1975, 1975,Chronology Chronology of of Precambrian Precambrian rocks rocksin in Medaris,L.G., L.G.,and andBanks, Banks,P.O., Wisconsin, TheWolf WolfRiver Riverbatholith, batholith,aarapakivi rapakivimassif massifapproximately approximately1500 1500m.y. m.y.old, old,Geological Geological Wisconsin,I:I:The Society 14. Societyof of America, America,Bulletin, Bulletin,v.v.86, 86,p.p.907-9 907-914. 95 �COMPOSITION COMPOSITIONAND AND SOURCE(S) SOURCE(S)OF O FMIDCONTINENT MIDCONTINENTRIFT RIFTLAVAS LAVAS (CHENGWATANA VOLCANICS) NEAR NEAR CLAM FALLS, WISCONSIN (CHENGWATANA VOLCANICS) NAIMAN, NAIMAN,Zachary ZacharyJ., J.,Department Departmentof ofGeosciences, Geosciences,University Universityof ofArizona, Arizona,Tucson, Tucson,AriArizona, WIRTH, Karl znaiman@geo.arizona.edu; WIRTH, Karl R., R., Geology Geology Department, Department, zona, 85716, 85716, znaiman@geo.arizona.edu; MacalesterCollege, College,St. St.Paul, Paul, Minnesota, Minnesota, 55105, 55 105,wirth@macalester.edu. wirth@macalester.edu. Macalester Most well-exposed volcanics Moststudies studiesof of the the1.1 1.1Ga Ga Midcontinent Midcontinentrift rift (MCR) (MCR) have have focused focused on the well-exposed volcanics in the Lake Superior region from the central part of the rift. Studies of the Chengwatana Volcanics in the Lake Superior region from the central part of the rift. Studies of the Chengwatana Volcanics (CV), (CV),the the southernmost southernmostexposed exposedvolcanics volcanicsof of the the MCR, MCR, provide provide information informationabout about variations variationsin in rift rift processes processesalong alongthe theaxis axisof of the the MCR. MCR. Here Herewe wereport reportmajor majorelement, element,trace traceelement, element,and andNd Nd isotopic isotopicdata datafrom frommafic maficand andfelsic felsicCV CVflows flowsnear near Clam Clam Falls, Falls, Wisconsin. Wisconsin. Approximately Approximately3000 3000 meters of mafic volcanics, minor interfiow sediment, and rare rhyolite are exposed in the Clam meters of mafic volcanics, minor interflow sediment, and rare rhyolite are exposed in the Clam Falls Falls area. area.The Thepetrography petrographyand andgeochemistry geochemistryof ofthe therhyolite rhyoliteare arediscussed discussedby by Abbott Abbott et et al. al. (this (this volume). volume). New, New,precise preciseU-Pb U-Pbzircon zirconages ages(1,102±5 (1,102±Ma) Ma)of of rhyolite rhyolitenear near Clam ClamFalls Falls (Wirth (Wirth and and Gehrels; Gehrels; this this volume) volume) provide provide aa means means for forcorrelation correlation of of the theChengwatana ChengwatanaVolcanics Volcanics from from Clam Clam Falls Falls and and Taylors Taylors Falls Falls with volcanics from other parts of the rift. Recent Recentaeromagnetic aeromagnetic data data (USGS) (USGS)suggest suggestthat that Clam ClamFalls Fallsflows flowsare arestratigraphically stratigraphicallylower lowerand andtherefore thereforeolder olderthan than CV flows flowsexposed exposedin inthe theTaylors TaylorsFalls Fallsregion. region. CV The The mafic mafic volcanics volcanics from from the the Clam Clam Falls Falls region region are are classified classified as as basalt basalt based based on onmajor major and and trace trace element elementabundances. abundances.The Thebasalts basaltsare aremostly mostlyolivine olivinenormative, normative,but butsome someflows flowsconcontain (Mg# = = tain small smallamounts amountsof of normative normative quartz. Most Mostflows flows have have moderately moderately low Mg-numbers Mg-numbers (Mg# and Si02 contents (45-53 wt. %) indicating that they have under0.58) M ~ / [ M ~ + F = ~ 0.40 + ~ ] 0.58) and Si02 contents (45-53 wt. %) indicating that they have under= 0.40 Mg/[Mg+Fe2I gonesignificant significantfractionation, fractionation,similar similarto toflows flowsfrom fromthe the Taylors Taylors Falls Falls section section of the the Chengwatana Chengwatana gone Volcanics1. Volcanicsl. Clam ClamFalls Fallsbasalts basaltsexhibit exhibitincreasing increasingincompatible incompatibleelement elementabundances abundances(e.g., (e.g.,P,P,Ti, Ti, Y) Y) with with decreasing decreasingcompatible compatibleelement element abundances abundances (e.g., (e.g., Mg, Mg, Ni, Ni, Cr) Cr) similar similarto tothose thoseof ofthe the Taylors Taylors Falls Falls region, region, and and can can be be modelled modelled by fractional fractional crystallization processes2. processes2. Clam ClamFalls Falls flows have Ti02 concentrations which are similar to the low-Ti group (<2.3 wt. %) of basalts flows have Ti02 concentrations which are similar to the low-Ti group (42.3 wt. %) of basalts recognizedininthe theTaylors TaylorsFalls Fallssection1. section1. recognized Neodymium Neodymiumisotopic isotopicanalysis analysisof ofeight eightbasalts basaltsand andtwo tworhyolites rhyolitesfrom fromthe theClam ClamFalls Fallsarea area values between -2.0 and 3.4. Initial ENd values decrease with stratiyield initial ENd loo Ma values between -2.0 ""3.4. Initial ENd values decrease with stratiyield initial ENd(1 iOO Ma') graphic ( igure 1), 1 ,and and all all of of the the values values are are in in general general displaced displaced toward toward more more positive positive graphicheight height (1!gure values values relative relative to to those those of of the the overlying overlying flows flows of of the the Taylors Taylors Falls section1 section1 (Figure 2). AlAlthough similarly similarlyhigh highNd Ndvalues values(initial (initialENd ENd = 2) +2)have havebeen beenobserved observedininother othervolcanic volcanicsesethough quences in the Midcontinent rift quences in the Midcontinent rift 3000 3000 I rn I I I (e.g., (e.g., Group Group 66 and and 77 flows flows of of Clam Falls Region Mamainse Mamainse Point3, ~ o i n t 3Portage ,Portage Lake Lake • basalt basalt Volcanics Volcanicsand and "late "late basalts" basalts" of of northnorth- 'a i   '.' Q r yo ite em Wisconsin4), ~isconsin4),flows with with initial initial w em Â¥ . U ENd values > +2 2 are ENd values arerare rareininthe theearly early 2000 2000 .stagesof of rift riftevolution evolution(time (timeequivaequivastages lent to to upper upper Kallander Kallander Creek Creek ForForlent 0 5 lavas). Furthermation or Group mation or Group 5 Further- 3 more, Taylors Taylors Falls Falls flows flows which which 2 more, rn 1000 -overlie the the Clam Clam Falls Falls basalts basalts (and (and ^. 1000 overlie U  maybe becorrelative correlativewith withPortage PortageLake Lake .may cd 0 j=!  Volcanics Volcanics and Group Group 66 flows) flows)have have w epsilonNd Nd values valuesthat thatare aregenerally generally epsilon  45 -ENd == -4.5 more negative negative(initial (initialENd more I I n I 00 44 22 33 11 -1 00 O1) than ""0.1) thanhas hasbeen beenobserved observedinincorcor-2 -2 -1 relativemain mainstage stagelavas lavas(initial (initialENd ENd relative Initial Ed &srd Initial ^ \ s - 6 a 4-à - 96 - �12 -1 -- 4) +4)elsewhere elsewherein in the therift. rift. == -l Most models models of of the the magmagmatic evolution evolution of the the matic Midcontinent rift assume that the Midcontinent rift assume that the large volume volume of of magmas magmas were were produced primarily from from an an enenriched riched mantle mantle plume plume with with initial initial eNdnear zero3'4. zero3'4. Lavas with with ENd negative ENd values have have been been negative ENd modelled by contamination contamination of of mantle mantle plume plume melts melts with with conticontinental nental lithospheric lithosphericmantle mantle(ENd (ENd near near 9) -9)or orwith withcontinental continentalcrust crust -12 -10 -8 -6 -4 (ENd < -10). -10). In In contrast, contrast, lavas lavas (ENd with with positive positiveENd ENd values values has has been been Initial ENd £\ Initial modelled modelled by aa combination combination of of enriched enriched mantle mantle plume plume and and dedepleted pleted asthenospheric asthenosphericmantle mantle(ENd (ENd > 6) that may have been entrained in the plume head5. FolFollowing valuesof ofChengwatana Chengwatana basalts basalts suggest suggest aa progression progression of mantle lowingthis this model, model, the the initial initial ENd ENd values sources sources from from enriched enrichedmantle mantle plume+depleted plume+depletedasthenospheric asthenosphericmantle mantle(flows (flowswith withENd>>11near near the base of the the Clam Clam Falls Falls section) section) to to enriched enriched mantle plume that has been variably variably contamicontaminated nated with with lithosphere lithosphere(the (theremainder remainderof of the theClam ClamFalls Fallssection sectionand andthe the overlying overlyingTaylors TaylorsFalls Falls section). The inferred progression of mantle sources observed in the Chengwatana Volcanics section). The inferred progression of mantle sources observed in the Chengwatana Volcanics (plume+asthenosphere (plume+asthenosphere—> -> plume plume+1+I- continental continental lithosphere) occurs at a time when when mantle mantle sources sources elsewhere elsewherein in the the rift rift are are inferred inferred to to be changing changing from from plume+continental plume+continental lithosphere lithosphereto to plume+asthenosphere. IfIfthe thedepleted depletedmantle mantlecomponent component of of early early Clam Clam Falls Falls flows flows originated originated from from material material that that was was entrained entrainedin in the the plume plume head, head, as as has been suggested suggested by several several for for other other parts the proportion proportion of melts melts produced produced from entrained entrained asthenospheric asthenospheric mantle rift3'4y5 then the mantle parts of the the rift3'4'5 in the plume plume varied varied in in space space and and time time throughout throughout the rift. rift. Alternatively, Alternatively,the thedepleted depletedmantle mantle component component may may have have been differentially incorporated into plume-generated melts as they traveled continental lithosphere. lithosphere. The eled through the the asthenosphere asthenospherebefore reaching the continental The relatively relativelylow low initial values observed observed in flows of the Taylors Taylors Falls Falls and and upper upper Clam Clam Falls Falls sections indicate initial ENd EM values indicate greater greater involvement involvementof of aa continental continentallithosphere lithosphere(crust (crust and/or andlor mantle) mantle) component componentthan than has hasprepreviously been recognized during the early part part of of "Main "Main Stage" Stage" volcanism volcanism in inthe the rift. rift. In all all of these cases, cases, the the observed observed isotopic isotopic differences differences between between the the Chengwatana ChengwatanaVolcanics Volcanics and and other other volcanic "off-axis" position of the Chengwatana volcanic sequences sequencesof of the the MCR MCR might be related to the "off-axis" Volcanics relative to the location of the inferred inferred plume plume head. head. References Cited Cited (1) Jeffrey D., D., and and Naiman, Naiman, Zachary ZacharyJ,J, 1997. (1) Wirth, Karl R., Vervoort, Jeffrey 1997. The TheChengwatana ChengwatanaVolcanics, Volcanics,Wisconsin Wisconsin and Minnesota: Petrogenesis Petrogenesisof ofthe thesouthernmost southernmostvolcanic volcanic rocks rocks exposed exposed in in the the Midcontinent Midcontinent rift. rift. Canadian Canadian Journal 536-548. (2) (2)Naiman, Naiman, Zachary Zachary J., 1997. 1997. Petrogenesis Petrogenesisof of the the ChengwatanaVolcanics: ChengwatanaVolcanics: Journal of Earth Science, Science, 34: 536-548. 1.1 Wisconsin. Bachelors Thesis, Macalester College. (3) 1.1 Ga Midcontinent rift lavas in Minnesota and Wisconsin. (3)Shirey, Shirey, S.B., Klewin, K.W., Berg, J.H., J.H., and and Carlson, Carlson, R.W.. R.W.. 1994. K.W., Berg, 1994. Temporal Temporal changes changes in the the sources sources of of flood flood basalts: basalts: isotopic and 1100Ma Ma old old Keweenawan Keweenawan Mamainse Marnainse Point Formation, Formation, Ontario, Ontario, and trace trace element element evidence evidence from from the the 1100 Canada: Geochimica Geochimica et et Cosmochimica Cosmochimica Acta, Acta, 58: 58: 4475-4490. 4475-4490. (4) Nicholson Nicholson Suzanne Suzanne W., W., Shirey, Shirey, Steven Steven B., B., Shultz, Klaus J., and and Green, Green, John John C., C., 1997. 1997.Rift-wide Rift-widecorrelation correlationofof1.1 1.1Ga GaMidcontinent Midcontinentrift riftsystem systembasalts: basalts: implications for multiple mantle sources during rift development. Canadian Journal of Earth Science, 34: 504520. 520. (5) (5)White, White,Robert RobertS., S.,1997. 1997.Mantle Mantletemperatures temperaturesand andlithospheric lithosphericthinning thinning beneath beneath the the Midcontinent Midcontinent rift system: evidence from magmatism and subsidence. Canadian Journal of of Earth Earth Science, 34: 34: 464-475. 97 �MILLGROUP GROUPREVISITED: REVISITED: BASAL BASALVOLCANIC VOLCANIC ROCKS ROCKS OF OF THE ThE THE POWDER MILL MIDCONTINENT RIFT MIDCONTINENT RIFTSYSTEM SYSTEM ON ON THE THE SOUTH SOUTH SHORE SHOREOF OF LAKE LAKE SUPERIOR SUPERIOR NICHOLSON, SuzanneW. W.USGS, USGS, National NationalCenter, Center,MS MS954, 954,Reston, Reston,VA VA20192 20192 NICHOLSON, Suzanne and WOODRUFF, and WOODRUFF,Laurel LaurelG., G.,USGS, USGS, 2280 2280 Woodale Woodale Drive, Mounds View MN 55112 55112 In northern Wisconsin and Michigan the Powder Mill Group comprises the oldest volcanic Michigan Group oldest volcanic rocks related to the 1.1 Ga Ga Midcontinent Midcontinentrift rift system system (MRS). (MRS). In In the the more more than than twenty years years since Hubbard (1975) (1975) first separated separated the thePowder PowderMill MillGroup Groupfrom fromthe theoverlying overlyingPortage Portage Lake isotopic, and Lake Volcanics, Volcanics, an abundance abundance of of geophysical, geophysical, structural, structural, geochemical, geochemical, isotopic, chronological data data for for Midcontinent Midcontinentrift riftrocks rockshas has become becomeavailable. available. This report integrates integrates new and existing information to to provide provide a better existing information better understanding understanding of the the early earlymagmatic magmatic history historyof of the theMRS. MRS. Powder Mill MillGroup Groupconsists consistsofof the the basal basal Bessemer BessemerQuartzite, Quartzite, and and the reversely The Powder reversely magnetized igneous rocks of the the Siemens Siemens Creek Creek Volcanics Volcanics and and overlying overlying Kallander Kallander Creek Creek Volcanics. The outcrop outcrop distribution distributionextends extendsfor formore morethan than 180 180 km km along strike, from just Volcanics. The west of the Lake WI discontinuously eastward to toSilver Silver Mountain, Mountain, Lake Owen Owen fault fault near near Cable, Cable, WI ML The Thetrue trueextent extent of of the thegroup group is is unknown unknown because or Ml. because itit is is either structurally truncated or unconformably overlain by younger rocks. However, seismic reflection proffles suggest that unconformably by younger rocks. profiles that the Powder Powder Mill Mill volcanic volcanic rocks rocks extend extend laterally laterally beneath beneath Lake Lake Superior. Superior. The Siemens CreekVolcanics Volcanicsisissubdivided subdividedinformally informallyinto intoupper upper and and lower lower The Siemens Creek members and isotopic isotopiccharacteristics. characteristics. The The lower lower member member of of the members based based on on field, field, geochemical, geochemical, and Siemens Creek Creek Volcanics Volcanicsisisdominantly dominantlybasalt, basalt, but but includes indudes recently recently recognized basal highhighMgO has limited limited regional extent, and and MgO picritic flows. The Thelower lower member memberis is thin thin (<50 ( ~ 5m 0 thick), has is distinctive distinctive because because some someflows flowscontain containaugite augitephenocrysts, phenocrysts,uncommon uncommonamong amongyounger younger MRS basalts. basalts. Pillows Pillows formed formed in the the basal few basalt basalt flows flows that that directly overlie the MRS the Bessemer Bessemer Quartzite. Basalt Basalt with minor basaltic andesite and and andesite andesite dominates dominates the the upper uppermember, member, which is more widespread and 1.5km) km)than thanthe thelower lowermember. member. No No ages have and thicker (up to 1.5 for the Siemens Creek of been determined determined for CreekVolcanics, Volcanics,but butby bycorrelation correlationwith withthe the basal basal units of Osler Group in Ontario and the sills, volcanism volcanismprobably probablywas was initiated initiated about the Nipigon Nipigon sills, the Osier 1108 Ma. Ma. High-MgO High-MgO(picritic) (picritic)rocks rocksrelated relatedtoto the the Midcontinent Midcontinentrift rift magmatism magmatism are are now known of the section sectionin inthree threeareas: areas:1) 1)in inthe theNipigon Nipigonarea area in in Ontario known to to occur occur near the base of associated with with dikes dikes and andsills sills(Sutdiffe, (Sutcliffe,1987); 1987); 2) associated 2) at at Mamainse MamainsePoint Point in in the the basal 500 m of the MRS section (Berg (Bergand andKlewin, Kiewin,1988); 1988);and and3)3)ininthe the Club Club Lake, Lake, WI WI area area west of the MRS section the Mineral Lake Lake intrusion intrusion as as recently identified picritic picriticflows flowsnear near the the base base of the recently identified the Siemens Siemens Creek The high-MgO flows in in the Siemens Creek Volcanics Volcanicsare are strongly strongly altered altered to high-MgO flows Siemens Creek Creek. The serpentine, chlorite chlorite and and talc: no primary serpentine, primary mineralogy is is present. present. An average of of three three analyses of these of these high-MgO high-MgO flows (Ti02 (Ti02= = 1.95 1.95 wt wt %; %; A1203 A1203= 8.89 8.89 wt %; %; MgO MgO == 16.09 16.09 wt %) %) is is chemically chemically most most similar similar to to an an analysis analysisof of a Nipigon Nipigon picritic picritic dike dike (Ti02 (Ti02== 1.88 1.88 wt %; A1203 A&03== wt %; 7.72 higher Ti02 Ti02 and and lower A1203and and MgO MgOthan than a 7.72 wt %; %; MgO MgO == 17.1 17.1 wt %) in having higher picritic average wt %; %; A1203 A l a == 9.79 wt %; %; MgO MgO average reported reportedfrom fromMamainse MamainsePoint Point(Ti02 (Ti02== 0.90 wt = 19.89 wt %; and Klewin, = 19.89 %; Berg and Klewin, 1988). 1988). Picritic flows in the the Siemens Siemens Creek Volcanics show with derivation derivation from steep 18.6), consistent consistent with from partial partial steep REE-element REE-element patterns patterns(CeN/YbN (CeN/YbN= 18.6), melting melting of an an enriched enriched mantle mantle source source at at a depth depth of of more more than than about about 80 80 km. Basalts Basalts from fromthe thelower lowerSiemens SiemensCreek Creek Volcanics Volcanics show show moderate moderateTi02, Ti02,lower lowerA1203 higher MgO MgO than and higher than basalts basalts from the the upper upper Siemens SiemensCreek. Creek. REE REEpatterns patterns are steeper Creekthan thanfor foroverlying overlyingunits. units. In In addition, addition, the two = 14.2), two (CeN/YbN 14.2), for the lower Siemens Creek (CeN/YbN = of the Siemens Siemens Creek CreekVolcanics Volcanicscan canbebedistinguished distinguishedon onthe thebasis basisofof Nd Nd isotopic members of composition: lower lower Siemens SiemensCreek Creekbasalts basalts have have initial initial £v Ed == -1 -1 whereas the upper upper Siemens Siemens Creek EM,, == -3.6. Creek basalts basaltshave haveinitial initialENd Volcanics overlies overliesthe theSiemens SiemensCreek CreekVolcanics, Volcanics,and and also also has The Kallander Creek Volcanics has been informally divided into upper and lower members. members. Both Both members membersrange range from from basalt basalt to to andesite and andesite and rhyolite. rhyolite. The Thelowermost lowermost1.5 1.5km km of of the the Kallander Kallander Creek Creek consists consists of flood basalt phenocrysts,which whichlocally, locally,form formlarge largeradiating radiatingclusters. clusters. A typically containing plagioclase phenocrysts, 98 �rhyolite flow near near the the top of the lower Kallander Kallander Creek Creek gives gives an an age age of of 1107.3 rhyolite flow 1107.3 ± Â1.6 1.6 Ma Ma and Green, Green, 1997). 1997). The upper upper member (about 22 krn km thick) thick) is is dominated dominated by andesite (Davis and member (about andesite and is is considered considered to to represent representthe the extrusive extrusive products of of aa localized localized magmatic magmatic system, the the Mellen complex complex(Cannon (Cannonetetal. al.1993). 1993). A A thick thick laterally laterally extensive extensiverhyolite rhyoliteatat the the top of the the upper member upper memberofofthe theKallander KallanderCreek Creekgives givesan anage ageofof1099.0 1099.0±Â2.6 2.6 Ma (Zartman (Zartmanetetal. al.1997). 1997). Basalts of the Volcanics are are characterized characterized by the lower lower member member of the Kallander Creek Volcanics and low MgO, MgO,Cr Crand andNi, Ni,suggesting suggestingstrong strongfractionation. fractionation. Although Although the REE TiODand their high Ti02, patterns for this Creek basalts, basalts, the patterns this group group are are similar similar to those those for for the the lower lower Siemens Siemens Creek elemental REE REEabundances abundancesare aresubstantially substantiallyhigher higherfor forthis thisgroup. group.InInaddition, addition, not not only are incompatible trace trace element elementratios ratiossuch suchas as C CeN/YbN andTa/Th Ta/Th similar similarfor for both both lower incompatible e N / m and lower members of of the their Nd members the Kallander Kallander Creek Creek and andSiemens Siemens Creek CreekVolcanics, Volcanics, their Nd isotopic isotopic compositionsare are similar similar as as well well (initial (initial ENd Nd == -1). In basalts of of the In contrast, contrast, basalts the upper upper compositions Creek show show lower lower incompatible incompatible trace trace element elementratios ratios and and much less steep Kallander Creek steep REE REE patterns than despite the fact that patterns than the thelower lowerKallander Kallander Creek Creek member, member, despite that their theirmajor majorelement element of the the upper upper Kallander Creek yields compositions are similar. The The Nd isotopic composition of yields slightly lower than the an initial initialEyy d == -1.5, slightly the lower lower member. member. The Siemens Creek and and Kallander Creek Volcanics Volcanicsrepresent representthe the initiation initiation of of aa The Siemens Creek Kallander Creek continental upweiling of of aa mantle mantle plume beneath continental rifting event that has been attributed to the upwelling beneath the Lake Superior Superior region. region. The diversity diversity of of basalt basalt compositions, compositions, including induding picrites, picrites, that that are representative the first years ofof rifting rifting are are characteristic of other representative ofof the first several several million million years characteristic of other continental rift settings mantle plumes plumes play play a dominant which mantle dominant role. role. Based Based on the the continental rift settings in which geochemical and isotopic both the the lower lowerSiemens SiemensCreek Creekand and lower Kallander isotopic characteristics, both Kallander Creek units are probably the of partial melting the products products of of varying varying degrees of melting of an an enriched enriched source (mantle plume) at great great depth depth with withthe thelower lowerKallander Kallander Creek Creekhaving havingundergone undergone significant fractionation. fractionation. The upper Siemens Siemens Creek Creek member member probably represents represents larger larger degrees of of partial partial melting meltingof ofaaplume plumesource sourceatatshallower shallowerdepths, depths,producing producingmelts meltsthat that may have interacted with with lithosphere lithosphereand andundergone undergonelimited limitedfractionation. fractionation. The upper Kailander Kallander Creek probably in in shallow crustal Creek appears to to have haveundergone undergone significant significant fractionation fractionation probably crustal magma magma chambers chambersnow now seen seen as as layered layered intrusions. intrusions. References: References: Berg, J.H., J.H, and 1988, High-MgO High-MgOlavas lavasfrom fromthe theKeweenawan Keweenawanmidcontinent midcontinent rift rift near Berg, and Kiewin, Klewin, K.W., K.W., 1988, near Mamainse MarnainsePoint, Point, Ontario: Ontario:Geology, Geology,v.v.16, 16,pp. pp.1003-1006. 1003-1006. Cannon,W.F., W.F., Nicholson, Nicholson, S.W., S.W., Zartman, Zartman, R.E., R.E., Peterman, Peterman,Z.E., Z.E.,and and Davis, Davis, D.W., D.W., 1993, Cannon, 1993, The Kallander remnantof ofaa Keweenawan Keweenawan central central volcano centered near Mellen, Kallander Creek Creek volcanics—a volcanics-a remnant Mellen, Wisconsin: Institute Institute on Lake Superior Superior Geology GeologyProceedings, Proceedings,Program Programand and Abstracts, Abstracts, v. 20v. 39, 39, p. p. 2021. Geochronologyofofthe theNorth North American American Midcontinent Midcontinentrift rift in Davis, D.W., D.W., and andGreen, Green, J.C., J.C., 1997, 1997, Geochronology western Lake Superior Superior and and implications implications for for its geodynamic evolution: Canadian Journal of western Lake geodynamic evolution: Earth Earth Sciences, Sciences,v.v.34, 34, pp. pp.476-488. 476-488. 1975, Lower Lower Keweenawan Keweenawanvolcanic volcanicrocks rocksofofMichigan Michigan and and Wisconsin: Wisconsin: U.S. U.S. Hubbard, H.A., H.A., 1975, Geological Journal of Research, v. v.3, 3, no.5, no. 5,pp. pp.529-541. 529-541. Geological Survey, Journal Sutcliffe, R.H., of Middle Middle Proterozoic Proterozoicdiabases diabasesand andpicrites picrites from from Lake Lake Nipigon, Nipigon, Sutcliffe, R.H., 1987, 1987, Petrology Petrology of Canada: Canada: Contributions ContributionstotoMineralogy Mineralogyand andPetrology, Petrology,v.v.96, 96,pp. pp.201-211. 201-211. Zartman, R. 1997, U-Th-Pb zircon zircon ages ages of Zartman, R. E., E., Nicholson, Nicholson, S.W., S.W., Cannon, W.F., W.F., and Morey, G.B., G.B., 1997, of some some Keweenawan Supergroup Supergrouprocks rocksfrom fromthe thesouth south shore shore of of Lake Lake Superior: Superior: Canadian Canadian Journal Journal of of Earth Earth Sciences, Sciences,v.v. 34, 34, pp. pp.549-561. 549-561. 99 �GIS MINERAL POTENTIAL GIs BASED MINERAL POTENTIALANALYSIS ANALYSIS FOR FOR LODE-GOLD LODE-GOLDAND AND MASSIVE MASSIVE SULFIDE TERRANE OF NORTHERN SULFIDE DEPOSITS DEPOSITS IN IN AN AN ARCHEAN TERRANE NORTHERN MINNESOTA MINNESOTA DEAN M. PETERSON PETERSONand and DR. DR. RONALD RONALD L. L. MORTON DEANM. MORTON Economic Economic Volcanology Volcanology Research Lab, Geology Geology Department, University University of Minnesota - Duluth, Duluth, Duluth, 55812 Duluth, Minnesota, Minnesota,USA USA55812 The last decade change. The decade has been a period of worldwide political and economic change. The globalization globalization of of the world's world's economy economy has has created creatednew new challenges challengesand and opportunities opportunities for the mining and mineral exploration exploration industry. industry. Many Manyareas, areas,which whichpreviously previouslywere were strictly strictly the the domain domain of of nationalist nationalistenterprises enterprises (Southeast Asia, South America, and the former Soviet Union), are now open to mineral exploration (Southeast Asia, South America, and the former Soviet Union), are now open to mineral exploration by companies companies from North America and Europe. Many Many exploration exploration companies companiesare are focusing focusinglarge large portions of their resources resources away from North America and into these recently opened countries. This This switch in regional area selection selection has had aa negative negative impact impact on on the the amount amount of mineral mineral exploration exploration conducted conducted in the Archean terranes terranes of Minnesota. Aside Asidefrom fromthe the changes changesin in global global economics, economics, other other specific specific reasons reasons for the lack of recent mineral mineral exploration exploration in the the Archean Archean terranes terranes of of Minnesota Minnesota include the following: following: > no no local local prospectors are are "beating "beatingthe the bush" bush"and anddiscovering discoveringprospects prospects in in Minnesota Minnesota >>misconception that mine misconception that minepermitting permittingwould wouldbebeasascumbersome cumbersomeasaswith withWisconsin WisconsinVMS VMSdeposits deposits >>absence ofofsuccess absence successininprevious previousgold goldand andmassive massivesulfide sulfideexploration exploration programs programs > most most mineral industry industry geologists geologists have have little little knowledge knowledge of of the the geology geology of of Minnesota, Minnesota,and and > the identification identificationof of specific specificexploration exploration target target areas areas are are normally normally not not included includedin in geological geological ' reports reports and and maps maps The The discovery discovery of economic economiclode-gold lode-gold and and massive massive sulfide sulfidedeposits deposits will will only only occur occurfollowing following prolonged exploration by the mineral mineral industry. industry. To exploration in the Archean terranes of Minnesota by To increase increase exploration exploration activity, activity, state state agencies agenciesin in Minnesota Minnesota have have completed completed extensive extensivegeological geologicaland and geophysical mapping, mapping, completed completed several several mineral mineral potential potential studies, studies, and and currently currentlyare arepromoting promoting geophysical Minnesota's Minnesota's geology geology and and mineral mineralpotential potential to to the the mineral mineral industry. However, However,because becauseof ofextensive extensive glacial glacial cover, cover, an an absence absence of of producing producing mines, mines, and and the the aforementioned aforementionedreasons, reasons, the the mineral mineralindustry industry requires additional Archean additional geological geologicalincentives incentives in in order order to to start start exploration exploration programs programs in in the the Archean terranes terranes of Minnesota. Minnesota. These Theseincentives incentivescould couldinclude includedetailed detailed descriptions descriptionsof of known known prospects, prospects, detailed mineral mineral potential potential studies, studies, and and specific specifictargets targetsand and geologic geologic criteria criteriaupon upon which whichto tobase base detailed exploration exploration programs. programs. This This study study is is an attempt attempt to to generate generatespecific specific lode-gold lode-gold and and massive massive sulfide sulfidetarget targetareas areasthat thatthe the mineral the state. Current mineral industry industry can use as a premise to begin exploration programs in the Currentore ore deposit deposit models GIs databases databasesof of important important Canadian Canadian mining mining camps camps(Timmins, (Tirnrnins, models have have been been integrated integratedinto into GIS Kirkland Lake, Lake, Hemlo, Hernlo, and and Sturgeon Sturgeon Lake Lake(Figure (Figure1)), I)), and and lode-gold lode-gold and and massive massive sulfide sulfideexploration exploration Kirkland models developed from detailed spatial analysis. Exploration target areas in the Minnesota developed detailed Exploration target areas in the Minnesotastudy study area area have have been generated generated from fromthe the integration integrationof of these these models modelsinto intoaa detailed detailedGIS GIs of of aalarge largeArchean Archean tenane 2). terraneof ofnorthern northernMinnesota Minnesota(Figure (Figure2). The The methods methods developed developedto to complete completethis thisstudy studycomprise comprisefive fiveseparate, separate,but but related relatedthemes: themes: >9Thorough research Thorough researchononthethetheory theoryand andmethods methodsofofore oredeposit depositmodeling, modeling,and andthe thegeological geologicalsetting setting of of Archean Archean lode-gold lode-gold and andmassive massivesulfide sulfidedeposits. deposits. 100 �_____________________________________ Standardized from the Superior Province of of Standardized geological compilations compilations of four analog mining camps from Ontario, Canada. These Thesecompilations compilationsare areintegrated integratedwith with Ontario Ontario Geologic GeologicSurvey Survey(OGS) (OGS) drill drill hole, geochemical geochemical and and mineral mineral deposit deposit inventory inventory databases databasesand and have have been been converted convertedinto intoGIS GIs format. format. I ) Standardized geological, Standardized geological,geophysical, geophysical,and geochemical geochemical compilation compilation of the Minnesota study area, area, and and the the conversion conversionof of this this compilation compilation into into GIS GIs format. format. Development of mineral mineral exploration models and targeting targeting criteria generated from knowledge-based queries queries of of the the analog analogGIS GIs datasets. These Thesemodels modelsintegrate integrateArchean Archean massive sulfide lode-gold and massive sulfide deposit deposit models models with spatial features in the analog GIS analog GIs databases. Specific Specificgeological geological criteria criteria have been developed developed that define define the location of the lode-gold and massive sulfide deposits within the analog GIS GIs datasets. datasets. I Figure 11 Location map of the the study study areas. areas. Figure I Thoroughmineral mineralpotential potentialevaluation evaluationfor forlode-gold lode-goldand andmassive massivesulfide sulfidedeposits deposits in in the > Thorough Minnesota study area. This Thisevaluation evaluationisisbased based upon upon spatial spatialanalysis analysisof of the the Minnesota MinnesotaGIS GIs of database using targeting criteria developed from the exploration models generated from queries of the analog analog GIS GIs databases. databases. Simvlified Simolified Geology Geoloey Ely* Ely' Towns ....— 10 Figure Figure 22 0 Major MajorShear S k a Zones Zones ~ 10 20 Kilometers = Proterozoic Protemzaic Rocks Rocks Wawa Subprovince Subpronnce Vennilion Vemilion Granhtic G r a ~ t i cComplex Complex Greenstone Terrane GreenstoneTemne Internal Plutons Plutolw Giants Range Range Granitic Gramtic Complex Complex Mammnt& Simplified geology and location of USGS 1:24,000 Simplified 1 : 2 4 , 0 scale scale quadrangle quadrangle maps maps of of the the Minnesota Minnesotastudy study area. area. 101 �IMPROVED VULNERABILITY ASSESSMENTS ASSESSMENTS OF IMPROVEDGEOLOGIC GEOLOGIC SENSITIVITY SENSITIVITY AND VULNERABILITY OF GROUNDWATER GROUNDWATER POLLUTION POLLUTION POTENTIAL POTENTIALTHROUGH THROUGHAPPLICATION APPLICATIONOF OFFUZZY FUZZYLOGIC LOGIC PFANNKUCH, PFANNKUCH, H.O., H.O., and and PAULSON, PAULSON, Richard, Richard, A., Department Departmentof of Geology Geology and andGeophysics, Geophysics, University of of Minnesota, 310 Pillsbury Drive S.E. Minneapolis, MN University Minnesota, 310 Pillsbury Minneapolis, MN 55455 55455 Vulnerability/sensitivity assessments assessmentsbelong belongto to the the general general problem class of Vulnerability/sensitivity of suitability suitability assessments. In general, these these are management tools to to evaluate evaluate the feasibility, reliability assessments. management tools or risk of of using using aa given given physical physical entity entity or or process. process. In In the the environmental environmental or geologic geologic context context it is is aa decision decision aid aid ininaaresource resourceprotection, protection,or ormanagement managementplan. plan. In generall general, the procedure has three components: components: aa phvsical physical model that describes the process process in a risk analysis analvsisframework, framework, and andaamethodology methodology to to aggregate aggregate individual individual partial partial vulnerability indices indices to to aa global vulnerability alobal vulnerability vulnerabilitv index. index. In In the the context context of of aa vulnerability vulnerability assessment to groundwater contamination contamination the physical physical model model simulates simulates contaminant contaminant transport along pathways from the land surface to the groundwater groundwater body. The pathway pathway is is subdivided into a sequence sequence of of zones zones in in which which different differenttransport transport processes processesand andparameters parameters predominate. These compartments compartments are are surface surface parcell parcel, soil soil zone, zone, vadose zone, capillary fringe, and the groundwater flow zone zone which which may may be be further further subdivided subdivided ifif more more detail detail is fringe, groundwater flow wanted. wanted. In a perfectly perfectly deterministic deterministic world where all transport transport processes processes can be be described described as as mathematically exact, where flow boundary physicoboundary geometry, geometry, boundary boundary conditions conditions and and physicochemical parameters are known everywhere in the domain domain of of interest, interest, the the transport transport process process can be be modeled modeled exactly exactly along along continuous continuous pathways, pathwaysl given given appropriate appropriate computational computational power. power. Then, concentration of the contaminant Its residence residence contaminant everywhere everywhere in space and time is known. known. Its time in in the the system system and and its its exposure exposure to to and and impact impact of of exposure exposure on on the the target target can canbe bequantified. quantified, From this, choices about protection protection of the the resource, resource, the the environment, environment, or or human human targets targets can can be made. This is all that is is needed needed for solving the problem, and no further steps are necessary. necessary. Alas, the world is is not notisotropic, isotropic, homogeneous homogeneousand and perfect, perfect, and and mathematical mathematicalsimulation simulation models even less models less so. so. Therefore, Therefore, severely severely restrictive restrictive approximations approximations and and simplifying simplifying assumptions have have to to be introduced to represent the transport transport process process in in an half-way assumptions represent the adequate manner. The approximations concern the mathematical description of the process, process, limited by insufficient insufficient and and infrequent infrequent information, information, and by inadequate inadequate knowledge of impacts. impacts. the greater greater the the uncertainty that the the model The greater the simplifications, simplificationsl the uncertainty that model results results reflect reflect reality and produce reliable predictions or vulnerability designations. and produce reliable predictions or vulnerability designations. This uncertainty traditionally has been handled by a risk risk analysis analysis approach. approach. The The likelihood likelihood of aa contaminant contaminant particle particle reaching reaching the the groundwater groundwater target and its its likelihood likelihood to to produce produce unwanted unwanted consequences has been expressed in terms of conditional conditional probabilities probabilities and and statistical estimates as confidence limits or ranges. Inadequacies in the geologic database estimates as confidence limits or ranges. Inadequacies in the geologic database have been handled handled by by statistical statistical methods methods such such as as Monte-Carlo Monte-Carloapproaches approaches or or kriging. kriging. A groundwater groundwater system system is is extensive, extensive, three three dimensional, dimensional, dynamic dynamic and and non-homogeneous. non-homogeneous.Its Its properties and states must be be spatially spatially referenced referenced for most most efficient efficient analysis analysis and and map map representation. Georeferencing is best carried out by by aa Geographic Geographic Information InformationSystem System (GIS) (GIs) which also also performs performs aggregation aggregation functions functions able able to to handle handlemap mapoverlay-index overlay-index procedures using built in algorithms. procedures using algorithms. The information information for each hydrogeologic hydrogeologic flow as an an information layer layer in in the the GIsl GIS, and and can can be combined into an compartment is represented as aggregate or monothematic monothematic layer such as aa global global vulnerability vulnerability map map layer. layer. Traditional methods of groundwater translate the the protection afforded Traditional groundwater sensitivity assessment assessment translate by various elements elements of the the geological geological conditions conditions and materials between the surface and the groundwater body body into into vulnerability vulnerability indices, indices, from from which, which, pollution pollution potential potential can can be groundwater 102 �estimated. estimated.One Onesuch suchmethodology methodologyisisUSEPA's USEPA's DRASTIC. DRASTIC.Many Manyof of these theseprocedures procedureslack lack internal consistency, and give no explicit rationale for assigning rating indices, internal consistency, and give no explicit rationale for assigning rating indices, range range intervals and and thresholds, thresholds, weights to the various various factors, and leave leave the choice choice of of an an additive additive intervals aggregation aggregationmodel modelunexplained. unexplained. The Minnesota MinnesotaDepartment Department of of Natural Natural Resources' Resources' (MN (MN DNR) DNR) guidelines guidelines stand stand on on aamuch much The firmer firmer conceptual conceptual basis. basis. They They link link geologic geologic sensitivity sensitivity to to travel travel time time of ofaaconservative conservative tracer tracer from from the the surface surface to to the thegroundwater. groundwater. Long Long travel travel times times are are equated equated to low low sensitivities, and and short short travel travel times times to to high high sensitivity. sensitivity. In In order order to to take take into intoaccount account the the sensitivities, availability of of information information for for mappable mappable factors factors ititmakes makessome somesweeping sweepingsimplifications. simplifications. ItIt availability uses three three factors: factors: depth depth to to water, water, geologic geologic material material in the vadose vadose zone and material material at at the the uses water water table table and andobtains obtainsthe theaggregate aggregateindex indexthrough throughaabinary binarydecision decisiontree treeprocedure. procedure. Because Because of of these these simplifications simplificationsthe the degree degreeof of uncertainty uncertaintyand andthe theconfidence confidencelimits limits are are large. large. Introduction Introduction of of aa fuzzy fuzzy set set methodology methodology will will lead lead to to aa greater greater internal internalconsistency consistency of of the the rating ratingprocess processand andfacilitate facilitate the the use use of of vague vague and and descriptive descriptive data data in in aa more moreappropriate appropriate way. way. Fuzzy Fuzzy logic logic isisaabranch branchof ofset settheory theorythat thatallows allowsobjects objectsdegrees degreesof ofbelonging belongingto toaaset setrather rather than than aabinary binaryyes yesororno nodescription. description.Fuzzy Fuzzynumbers numbersare aredefined definedby bymembership membershipfunctions functions that thatdescribe describetheir their degree degreeof of belonging belongingto to one one set set or or another, another, and and thereby thereby are are able able to to deal deal with with verbal verbal descriptors descriptors or or linguistic linguistic variables, variables, and and to to take take into intoaccount accountthe thenatural natural vagueness vaguenessand anduncertainty uncertaintyinherent inherentiningeologic geologicdata. data.Fuzzy Fuzzymethodology methodologyprovides providesthe the algorithms algorithmsto tooperate operateon onvague vaguerating ratingclasses classesininaaconsistent consistentway. way.Fuzzy Fuzzymethodology methodologywill will also alsogive givemore morerealistic realisticboundary boundarydefinitions definitionsbetween betweenrating ratingcategories categoriesand andclasses. classes. This This research researchcasts caststhe thedefinition definitionof ofthe theMN MNDNR DNRrating ratingfactors factorsinto intoaafuzzy fuzzycontext. context.This This approach more (I) moreadequate adequaterepresentation representation of of linguistic linguistic variables variables such such as as approach isiscapable capableof: of:(1) lithologic lithologic descriptions descriptions from from well well log loginformation informationinto intomanipulable manipulableindex indexnumbers, numbers, (2) (2) combining combining of layer layer information information in in aa GIS GIsthrough throughfuzzy fuzzyrule rulebased basedinstructions, instructions,and and (3) (3) to to extend extendthe thenumber numberof of factors factorsthat thatgo gointo intothe theoverall overallevaluation evaluationto to geohydrologic geohydrologic and and land landuse uselayers. layers. Fuzzy Fuzzy methodology methodology application: application: The The technique technique for for performing performing aa Level Level 22geologic geologicsensitivity sensitivity analysis analysis as as set set forth forthby bythe theMN MNDNR DNRisisrelatively relativelysimple simple and and straightforward. straightforward. The The techniques techniques were were intentionally intentionally designed designed so so that that water water resource resource managers managers (or (or others) others) who who may maynot nothave havetraining trainingon, on,ororaccess accessto, to,a ageographic geographicinformation informationsystem system(GIS), (GIs),would wouldstill still be beable abletotoimplement implementaahand-performed hand-performedoverlay overlayanalysis. analysis. This This can canbe beaavery verytime timeconsuming consuming and andtedious tedioustask taskfor forthe theanalyst. analyst. InInan aneffort efforttotospeed speedup upand andsimplify simplifyespecially especiallythe the preliminary preliminaryassessment assessmentor orproject projectstage, stage,an anExcel Excelspreadsheet spreadsheetbased basedprogram programisisbeing being developed MicrosoffVisual VisualBasic. Basic.ItItaccepts acceptsthe thevarious variousMN MNDNR DNRspecified specifiedvadose vadosezone zone developedusing usingMicrosoft parameters parametersunder underconsideration considerationas as input. input. The Theinput inputdata datalayers layersinclude: include:depth depthtotowater watertable table below belowthe theland landsurface, surface,aquifer aquifermatrix matrixmaterial materialtype typeatatthe thewater watertable, table,cumulative cumulative thickness thicknessofofany anylow lowand andmoderate moderatepermeability permeabilityunits unitsininthe thevadose vadosezone. zone.AAsecond secondversion versionofof the theprogram programincorporates incorporates the the principles principles of of fuzzy fuzzy methodology methodology into the analysis. The The sensitivity sensitivityratings ratingsproduced producedby bythe the"fuzzy" "fuzzy"version versionare arecompared comparedtotothose thoseproduced producedusing using the thepresent presentMN MNDNR DNRtechnique. technique. 103 �SEISMIC EVIDENCE OF Pm-NICKERSON PRE-NICKERSON SEDIMENTS IN SEISMIC WESTERN LAKE SUPERIOR SUPERIOR Deborah E. Rausch and and Nigel J Wattrus Wattrus Large Lakes Observatory, University Universiiy of Minnesota Duluth, MN 55812 558I2 email:nwattrus@d. umn.edu email:nwattrus@dumn.edu The Superior Superior lobe of the Laurentide Laurentide Ice Sheet advanced and retreated out of the western basin of Lake Superior Superior several several times during during the Wisconsin glaciation. glaciation. Wright et al. (1973) recognized recognized four four they are (in order of decreasing age): separate phases of ice advance out of the Lake Superior basin, they the St. Croix; Automba; Split Rock and Nickerson Nickerson phases. phases. The tills of the last two phases show an which represents represents the the incorporation incorporationof of proglacial lacustrine sediments with each enrichment in clay, which advance. As As the the ice ice retreated retreated during during the Nickerson phase, a series of proglacial lakes formed against the edge of the retreating ice. The position of ice margins bordering these lakes have been determined by correlating correlating subaerial subaerial moraines on either side of western Lake Superior Superior (Farrand, (Farrand, 1969; 1969; Isle Royale (Huber, 1973). A Saarnisto, 1974) and Isle A series series of of subaqueous subaqueous recessional recessional moraines, moraines, presumably associated with this sequence of proglacial lakes, have been described in the western arm of Lake Superior Superior near near Isle Isle Royale Royale (Landmesser (Landmesseret et al., al., 1982). 1982). The sediment sediment record contained contained in western Lake Superior Superior is intimately related to the retreat of the An idealized idealized soft soft sediment sediment section section for western Lake Superior based upon Laurentide Ice Sheet. An coring (Farrand, (Farrand, 1963; 1963; Dell, 1971; 1971; Thomas and Dell, 1978) 1978) and high resolution seismic surveying surveying consists of of till till overlain overlain by by aa glaciolacustrine clay (Johnson, 1980; Scholz, 1985; Anderson, 1997), consists sequence followed by a thin post-glacial Holocene clay. Recent Recentdata data collected collectedby by the the Large LargeLake Lake from Observatory (LLO) suggests the presence of a relict sediment section below the till, presumably fiom advances into earlier advances into the Lake Lake Superior Superiorbasin. basin. Since 1996, the Large Lakes Observatory (LLO) has collected over 2500 km km of high resolution single channel seismic reflection data in western Lake Superior. The surveyed area extends from Duluth to Isle Royale and southeast to Houghton, Michigan. Most of this this new data was collected with a ORE Geopulse system. The firing rate was 0.5 seconds and the the average vessel vessel speed was 6.5 milliseconds/sample for later post-survey knots. The data were digitally recorded at rate of 0.5 milliseconds/sample processing. Positioning Positioninginformation information was was derived from fiom the ships GPS navigation system. Images of the recently acquired data show most of the soft sediment section and bedrock-soft sediment interface (acoustic basement). In In water water depths depths of less than 100 100 meters, the development/preservation of the g1aciaVpost-glacial and Holocene clays above the till is negligible negligible developmentlpreservation glacial/post-glacial due to current action on the lake floor. floor. In In the deeper deeper portions of the lake, the near surface reflections are associated with the post-glacial Holocene clays, glaciolacustrine glaciolacustrine clays and a thin basal till (less than six meters thick). Presumably, glaciallpost-glacial sequence is associated with the last Presumably, this glacial/post-glacial advance/retreat in the Lake Superior (Nickerson/post-Nickerson deposition). Many of recent advancehetreat Superior basin (Nickersodpost-Nickerson seismic lines, especially those in the western portion of the survey area, exhibit buried channels containing thick sequences sequences of pre-Nickerson deposits (Figure 1). There is often a well defined unconformity separating the pre-Nickerson sediments sediments from the overlying younger section. The unconformity clearly represents represents a period of erosion, perhaps associated with the last advance advance of ice across across the basin. basin. 104 �Seismic facies analysis suggests that the pre-Nickerson pre-Nickerson material material is is composed composed of of aa sequence sequence of of glacial glacial tills and glaciolacustrine sediments. Presumably Presumably these represent represent relict relict sediments sediments preserved preserved from from earlier advances of the Superior Lobe in in western Lake Lake Superior. Superior. Very few of of the the cores cores collected collected in in Lake Superior penetrated penetrated sediment sediment below below the the glaciolacustrine glaciolacustrine vvarved clays. One a n e d clays. One long long core collected Minnesota North North Shore, Shore, however, however, recorded over 190 of Split Rock on the Minnesota 190 meters of glacial and glaciolacustrine sediments glacio1acustrine sediments (Zumberge and Gast, 1961). 1961). References. Anderson, K.A., K.A., 1997, Lake Superior Superior (M.S. (M.S. Thesis): Thesis): University University of of Anderson? 1997, A seismic stratigraphic study of western Lake Minnesota, Mimesota, Duluth, Minnesota, Minnesota, 82 82 p. p. C.!., 1971, (Ph.D. Dissertation): Dissertation):University Universityof ofMichigan, Michigan, Dell, C.I., 1971, Late Quaternary Quaternary sedimentation sedimentation in in Lake Lake Superior Superior(Ph.D. Ann Arbor, Michigan, Michigan, 184 184 p. W.R., 1963, Preliminary report report of Lake Superior Coring Program, Program, Core Core Study, 33 p. p. Farrand, W.R., W.R., 1969, The Quaternary history of Lake Superior: International Farrand, W.R., InternationalAssociation Association of of Great Great Lakes Lakes Research, p. 181-197. 181-197. Huber, N.K., 1973, 1973, Glacial and postglacial history of Isle Royale National Park, Michigan: U.S. U.S. Geological Geological Survey Professional Professional Paper 754-A. Johnson, T.C., 1980, 1980, Late Late glacial and postglacial sedimentation sedimentation in Lake Superior based on seismic-reflection profiles: Quaternary QuaternaryResearch, Research, p. 380-391. 380-391. Landmesser, Landmesser, C.W., Johnson, Johnson, T.C., T.C., and and Wold, Wold, R.J., R.J., 1982, 1982,Seismic Seismicreflection reflectionstudy studyof ofrecessional recessionalmoraines moraines 173beneath Lake Superior and their relationship to regional deglaciation: Quaternary QuaternaryResearch, Research, p. p. 173190. 190. C.A., 1985, Scholz, C.A., 1985, Sediment Sediment distribution distribution and sedimentation sedimentationrates rates in the the western western arm arm of of Lake LakeSuperior Superiorusing using 3.5 kHz kHzseismic seismicreflection reflectionprofiles profilesand and210Pb ''qb geochronology University of of Minnesota, Minnesota, geochronology (M.S. (M.S. Thesis): Thesis): University Duluth, Minnesota, Minnesota, 129 129 p. Thomas, Thomas, R.L. and and Dell, Dell, C.I., C.I., 1978, 1978,Sediments Sedimentsof of Lake LakeSuperior: Superior: Journal Journal of Great Great Lakes Lakes Research, Research, p. p. 264-275. 264-275. Wright, H.E., H.E., Matsch, C.L., E.J., 1973, Superior and Des Moines Moines Lobes: Lobes: Geological GeologicalSociety Society of of C.L., and Cushing, E.J., America Memoir 136, 136, p. 153-185. 153-185. J.H., and Gast, P.G., P.G., 1961, Geological investigations in Lake Lake Superior: Geotimes, Zumberge, J.H.? Geotimes,p. p. 10-13. 10-13. sP p 0 C" I •1 C I -I -r'" . — -- Figure 1. North Shore southwest southwest of of 1. Geopulse seismic reflection data collected off the Minnesota North Grand Marais, Minnesota. Relict Relict sediments sediments are are clearly clearly preserved p r e s e ~ e in din aa broad broad channel channel and and are are unconformably overlain by by younger till and and glaciolacustrine glaciolacustrine sediments sediments of of the the Nickerson Nickerson phase. phase. 105 �____ PRELIMINARY ORE OREi MINERALOGY OF THE HERONTRACK SILVER-ZINC-COPPER OCCURRENCE, OCCURRENCE, LUMBY LAKE LAKE AREA, AREA?ONTARIO, ONTARIO, CANADA CANADA SAINI-EIDUKAT, Geosciences, North Dakota State SAINI-EIDUKAT?Bernhardt, Bemhardt, Department of Geoscien~es~ University, Fargo, Fargo?ND 58105-5517 USA (sainieid@badlands.nodak.edu). (s~fieid@badlands.nod&.edu). Inc., Box 1376, BERNATCHEZ, Raymond, Atikokan Resources, Inc.? 1376?126 126 Willow Road, Atikokan, Ontario, Canada (rbernatc@atikokan.lakeheadu.ca) Road? (rbernatc @atikokan.lakeheadu.ca) The Herontrack silver-zinc-copper silver-zinc-copper occurrence occurrence occurs near Herontrack Lake Lake in the the Lumby Lumby Lake greenstone belt. It lies in the southwestern part of the Archean Superior Province, near Atikokan, Atikokan?Ontario. Recently discovered in the region of the famous Steep Rock iron mine, the Herontrack occurrence contains numerous stratiform mineralized horizonsy horizons, some of which contain contain significant significant Ag Ag mineralization. mineralization. The Lumby Lake greenstone near its border border greenstone belt occurs occurs in the Wabigoon subprovince, subpro~ince~ near its with the Quetico subprovince (Fig. 1, 1 from Davis and Jackson, 1988). It comprises a 60 km x mafic, ultramafic (komatiitic) and felsic 20 km synclinal supracrustal assemblage of mafic? metavolcanic packages with subordinate metasedimentary units (Jackson and Chevalier, Chevalier? contacts the the older Marmion Lake tonalite batholith to the the southy south, and is intruded by 1985). ItIt contacts north, and by mafic dikes. Felsic units include lapilli the younger Norway Lake granite to the north? tuffs, quartz porphyriesy porphyries, and rhyolite flow breccias. tuffs? breccia. To the west of the Lumby Lake area, area?the northeasterly trending Red Paint Lake fault zone truncates the assemblage. '-..-_.4+.' ..L—r..JJ I *+T —: I ! ,./ \ • * * + + * * Finlays0 Lake '* Belt. • * ++ A * + e't * — . Marmion Lake Batholith * —---—-——- : + * * : --+ kilornetres Figure 1. Geologic map showing the location map of the the western western Wabigoon Wabigoon subprovince, showing location of the Lumby Lumby Lake area. From Davis and Jackson, 1988. 106 �I The The lack lackof of aametamorphic metamorphicaureole aureolein inthe thesupracrustal supracrustalsequence sequence against againstthe theMarmion Marmion Lake Laketonalite tonaliteindicates indicatesthat thatthe thebatholith batholithwas wasaabasement basementunit unit upon upon which whichthe theLumby LumbyLake, Lake, and and possibly possibly the the Steep Steep Rock Rock Lake Lake group, group,were were deposited deposited (Davis (Davis and and Jackson, Jackson, 1988). 1988).Davis Davis and and Jackson Jackson (1988) (1988) dated dated felsic felsic samples samplesfrom from the the Lumby Lumby Lake Lake area area and and the the Marmion Mannion Lake Lake batholith batholith to to approximately approximately 33 Ga, Ga, an an age age older older than than most most greenstone greenstone belts. belts. During 1990's,Atikokan AtikokanResources, Resources,Inc. Inc. prospected prospected the the Lumby LumbyLake Lakearea areaand and During the the mid mid 1990's, discovered discovered aa high-grade high-gradesilver silveroccurrence occurrenceon onthe thewest westside sideof of Herontrack Herontracklake. lake.The The occurrence km thick thick east-west east-westtrending trending intermediate intermediateto to felsic felsicvolcanic volcanic occurrenceisis hosted hosted in inaa1.5 1.5km sequence sequencein in the the area areabetween betweenHerontrack Herontrackand andLumby LumbyLakes Lakes(Staargaard, (Staargaard,1997). 1997).This This sequence sequence thins thinsto to the theeast eastand andwest, west,indicating indicatingititmight mightbe bean aneruptive eruptivecenter. center.The Thefelsic felsic units units are are fragmental, fragmental, often often containing containing quartz quartz eyes, eyes, and and can can contain contain significant significant cherty chertyunits. units. Chip Chip samples samples (over (over one onemeter) meter)indicate indicategreater greaterthan than40 40g/tonne ghonneAg. Ag. Thin Thin and and polished polished block block sections sections of of ore ore horizon horizon samples samples are are being being investigated investigated using using transmitted transmitted and and reflected reflected light lightmicroscopy microscopyanalysis analysis to to determine determine the the host host rock rock and and ore ore mineralogy mineralogy and and genesis. genesis. The Therelationship relationshipbetween between fold fold structures structures recognizable recognizable on onboth both outcrop outcrop and and thin-section thin-section scales scalesand and mineralization mineralizationindicates indicatesthat that the the silver silvermineralization mineralization may may be be locally locally remobilized. remobilized. These Thesefold fold structures, structures,however, however, may may be be related related to to mafic mafic dike dike intrusion intrusion and and not not to to regional regional shear. shear. Mineralization Mineralizationoccurs occurs in in chert chert units units as as disseminated disseminated sphalerite, sphalerite, galena, galena, native native silver, silver,acanthite, acanthite,chalcopyrite chalcopyriteand and pyrite. pyrite. Native Native silver silverand andacanthite acanthite occur pm in diameter diameter and and as as veinlets veinlets 10—20 10 - 20 p.m pm wide. No Au Au was was occur as as isolated isolated grains grains 10 10to to 30 30p.m detected detected in in the the Ag Agor orthe theacanthite acanthiteusing using EDS EDSanalysis. analysis.Electron Electronmicroprobe microprobe analyses analysesare are being being undertaken undertaken to to determine determinethe theamount amountof of Ag Ag contained containedin in galena galena and and trace traceelement element composition composition of of sphalerite. sphalerite.Continued Continuedmapping mappingmay may show showthat that the the Herontrack Herontracksilver silver occurrence occurrence represents represents aa locally locally remobilized remobilized silver-rich silver-rich distal distal portion portion of of aa larger larger massive massive sulfide system. system. sulfide Referencescited: cited: References Jackson, Jackson, M.C. M.C. and and Chevalier, Chevalier, P., P., 1985, 1985,Precambrian Precambrian Geology Geology of of the the Lumby Lumby Lake Lake Area, Area, Western Preliminary Western Part, Part, Kenora Kenora District; District; Ontario OntarioGeological Geological Survey, Survey, Geological Geological Series Series-- Preliminary Map P.2828. P.2828. Map Davis, D.W., and Jackson, M.C., M.C., 1988, 1988,Geochronology Geochronology of of the Lumby Lake Lake greenstone greenstone belt: belt: aa Bull. G.S.A., G.S.A., v. v. 100, 100,p. p. 3 Ga complex within the Wabigoon Subprovince, northwest Ontario: Bull. 8 18-824. 818-824. Staargaard, C.F., 1997, 1997,Private Private report report to to Atikokan Atikokan Resources, Resources, Inc. Staargaard, 107 �ALTERATION AND METAMORPHISM METAMORPHISM IN AN ALTERATION AND AN ARCHEAN ARCHEAN LODE GOLD GOLDDEPOSIT, DEPOSIT, KItEMZAR KRJZMZARMINE, MINE,GOUDREAU-LOCHALSH GOUDREAU-LOCHALSHGOLD GOLDCAMP, CAMP,ONTARIO ONTARIO SALO, R.W. and Lakehead University, andKISSIN, KISSIN,S.A., S.A., Department Departmentof ofGeology, Geology, Lakehead University, SALO, RW.* Thunder P7B SE! SEl ThunderBay, Bay, Ontario, Ontario,P7B The TheKremzar KremzarMine h4heisislocated located45km 45km northeast northeast of of Wawa, Wawa, Ontario Ontarioin in the theMichipicoten Michipicoten Greenstone GreenstoneBelt. Belt.The TheKremzar Kremzarisisone oneofofseveral severalformer formergold-producing gold-producingmines minesin inthe thevicinity vicinity including well as as aa number of smaller properties. The including the Magino and Edwards Mines, as well The mine mine was was most most recently recently operated operatedby by Canamax CanamaxResources ResourcesInc. hc. in in the thelate late1980s, 1 9 8 0with with ~ ~ aa total total production productionof of 46798 46 798oz ozAu Au(Domville, (Domville,1998). 1998). The Thepresent presentstudy studywas was undertaken undertakenwhile whilethe the property is under redevelopment as the Island Gold Project of Patricia Mines Inc. property is under redevelopment as the Island Gold Project of Patricia Mines Inc. The TheNo.2 N0.2 Zone, Zone,aagold-bearing gold-bearingvein veinsystem systemwell well exposed exposed on on the the surface, surface,was was channelchannelsampled sampled in order order to tostudy studythe thealteration alterationassociated associated with with the thequartz-carbonate quartz-carbonate vein. vein. Petrographic Petrographicstudies studieswere werecarried carriedout outon on25 25samples samplescollected collectedatatO.5m OSm intervals; intervals; 13 13of these these were analyses of of major, major, minor minor and and trace elements by XRF and were selected selected for for whole-rock whole-rock analyses and NAA, respectively. respectively. NAA, The Thevein vein system system cuts cuts metavolcanic metavolcanic rocks of intermediate intermediatecomposition, composition,which which contain contain the chlorite chloritezone zonemineral mineralassemblage assemblagechiorite-sericite-albite. chlorite-sericite-albite. Alteration Alteration is is marked marked by by the intense carbonate carbonate and quartz quartz flooding, flooding, as well well as aa number number ofofchanges changesininaccessory accessory mineralogy. Primary Primaryilmenite ilmeniteisisprogressively progressively replaced by sphene, and allanite allanite occurs occurs only only within the the alteration alterationzone. zone. Zoisite, Zoisite, not present in in the the country country rock, rock, is abundant abundant in the the within altered zone. zone. Weakly Weakly pleochroic, fine-grained fie-grained biotite is is closely closely associated associated with with quartz quartz altered veining and andflooding. flooding. veining Among major components, CaO increases increases inward inward toward the the vein vein system, system, whereas components, CaO normally mobile components components Na20 Na20and and K20 K20show show little little variation. Ti02 Ti02decreases decreasesslightly, slightly, Among trace elements, W shows a marked increase. although itit usually usuallyimmobile. immobile. Among elements, shows a marked increase. although Although REE REE are areconsidered consideredtotobe beimmobile immobileiningold goldvein veinsystems systems(McCuaig (McCuaig & & Kerrich, Kemch, 1994), the the light light REEs, LLaa and Ce, are markedly markedly enriched in the alteration alteration zone. zone. The presence and prehnite and abundant presence of of euhedral euhedral zoisite, zoisite, minor minor wollastonite wollastonite and abundant The skarnoid calcite produce an an assemblage assemblage resembling resembling that of of aalow-grade low-gradeskarn. skarn. The skarnoid assemblage is the result result of of regional regional metamorphism metamorphism subsequent to formation formation of of the the vein vein and carbonate-enriched system, which has operated system, which operated on onthe thecompositionally compositionallymodified modified carbonate-enriched alteration zone. zone. Multiple Multiple metamorphic events are consistent consistent with three three deformational deformational alteration regimes &Helmstaedt Helmstaedt(1989). (1989). regimes documented documented by by Arias Arias & References References Arias, Z.G. & of central and east& Helmstaedt, Helmstaedt, H., H., 1989. 1989. Grant 343 343 Structural Structural evolution of eastcentral Michipicoten (Wawa) Greenstone Greenstone Belt, Belt, Superior Superior Province, Province, p. p. 210-226 210-226hj Michipicoten (Wawa) Milne, V.G., Research Grant V.G., ed., Geoscience Research Grant Program, Program,Summary Summary of Research Research 198819881989, 237 p. p. 1989, Ont. Geol. Geol. Surv. Sum. Misc. Misc. Pap. Pap. 143, 143,237 Domville, 1-32. J., 1998. 1998. Patricia Patricia Mines. Mines. Ont. Ont.Prospector Prospector1998, 1998,p.p.331-32. Domville, J., McCuaig, T.C. & Kerrich, of lode gold McCuaig, T.C. Kemch, R., R., 1994. 1994. P-T-t-deformation-fluid P-T-t-deformation-fluid characteristics of gold deposits: Evidence from from alteration alteration systematics, systematics,p.p.339-380 339-380 j Lentz, D.R., ed., ed., deposits: Evidence Lentz, D.R., Alteration AlterationProcesses ProcessesAssociated Associatedwith with Ore-forming Ore-formingProcesses. Processes. Geol. Geol.Assoc. Assoc. Can. Can.Short Short Course Course Notes, Notes, v. v. 11, 11,467p. 467p. *student *studentauthor author 108 �— ADDITIONAL PALEOMAGNETIC RESULTS FOR A 1500 Ma MAFIC DIKE AT WATERLOO WISCONSIN Schaper*, D. , Suess*, W. , Katzer*, L. ,and Kean, W. Department of Geosciences,University of Wisconsin—Milwaukee P.O. Box 413, Milwaukee, Wi. 53201 (* student authors) Recent expansion of the Michels Materials Quartzite Quarry (Gillen Quarry) at Waterloo Wi. has exposed additional outcrops of a near vertical mafic dike which cuts the quartzite in a North-South direction. The new exposure is approximately 1.5 meters wide and about 50 meters long located on the NE top surface of the quarry. The other exposure previously reported by Kean(1994) is on a vertical wall in the Southwest corner of the quarry (Luther,1997). The two exposures are on line and appear to be the same dike. The age of the dike is assumed to be 1500 Ma, which is the age of mafic material from a drill core in the nearby Portland Quarry (Aldrich et.al., 1959) and similar to the age of a pegmatite (1440 Ma, Aldrich 1959) in the area. Luther(personal communication, 1994) identified the dike as basalt which has been metamorphosed to possibly greenshist fades. Thirty six cores were collected from both locations, as well as from the surrounding quartzite. The edges of the dike show evidence of weathering and mineral alteration, so the majority of the mafic samples were collected from the center of the dike. Cores from all sites were subjected to detailed thermal demagnetization to either 600° or 750° C. Several dike samples were also A.F. demagnetized to lOOmT. The demagnetization characteristics and the Saturation Isothermal Remanent Magnetization characteristics (SIRN) indicate that magnetite is the primarily carrier of the magnetism. There is one primary magnetic direction for the dike which is removed with thermal demagnetization to 600°C. The magnetism of the quartzite is carried by hematite, as is evident from thermal demagnetization to 750°C., and SIRM studies.The magnetic directions of all samples including those reported by Kean, 1994, are presented in Figure 1. The dike shows negative inclinations (-30° to -50°)and declinations in the NNW-NNE direction. The quartzites have positive inclinations (30° to 40) and westerly declinations, which is similar to the earlier results of Mercer(1984). The magnetic directions for the dike show streaking, which may represent an alteration component in some of the samples. Nonetheless, the overall direction provides a pole position consistent with other 1400—1600 Ma. rocks in the Lake Superior region,and significantly different than that of the quartzite. 109 �References: References: Aldrich,L.T., Wetherill,G.W., ~etheri1l~G.W.~ Bass, MN.., M.N., Compston, Compston, W., Davis, Aldrich,L.T., Bass, W,Davis, G.L., and and Tilton,G.R.,1959, Tilton,GÈR.,1959Mineral Mineral age age measurements: measurements: G.L., 58, p.245—247. p.245-247. Carnegie Institute Washington Year Book Carnegie Institute Washington Year Book. 58, Kean, WF., W.F., 1994, 1994,Paleomagnetism Paleomagnetismofofa a1500 1500Ma. Ma. mafic maficdike dikeat at Kean, Institute on Lake Superior Geology abstracts Waterloo Wi. Waterloo Wi. Institute on Lake Superior Geology abstracts Vol.40, p.17. p.17. and proceedings, proceedings, Vol.40, and Luther, F., F., 1997, 1997, The The precambrian precambrian Waterloo waterloo quartzite, quartzite, Dodge Dodge and and Luther, Counties, Wisconsin-petrology, structure, and Jefferson Jefferson Counties, Wisconsin—petrology, structure, and Field Trip Trip No.5, No.5, in in Guide Guide to to Field Field Trips Trips in industrial uses, uses, Field industrial Wisconsin and Adjacent Areas of Minnesota. 31st annual Wisconsin and Adjacent Areas of Minnesota. 31st annual meeting of of the the NCGSA, NCGSA, Madison Madison , Wi. Wi. Ed. Ed. M.G. MçG Mudrey, Mudrey, Jr. Jr. meeting , Mercer, D., Paleomagnetism of of the theBaraboo BarabooQuartzite, Quartzite,tJW— UWMercer,. D., 1984, 1984, Paleomagnetism Milwaukee M.S. thesis, 294 p. Milwaukee M.S. thesis, 294 p. FIGURE 11 FIGURE FOR WATERLOO WATERLOO BASALTIC BASALTIC DIKE DIKEAND AND WATERLOO WATERLOO MAGNETIC DIRECTIONS DIRECTIONS FOR MAGNETIC HAS NEGATIVE INCLINATIONS AND NORTHERLY QUARTZITE. DIKE MATERIAL QUARTZITE. DIKE MATERIAL HAS NEGATIVE INCLINATIONS AND NORTHERLY DECLINATIONS. THE QUARTZITE HAS POSITIVE INCLINATIONS AND DECLINATIONS. THE QUARTZITE HAS POSITIVE INCLINATIONS AND WESTERLY DECLINATIONS. THE DATA REPRESENTS TWO DIFFERENT WESTERLY DECLINATIONS. THE DATA REPRESENTS TWO DIFFERENT EXPOSURES IN IN THE THE SAME SAME QUARRY QUARRY EXPOSURES N o EXPOSIJ( H(Z NES DC smir. £ EflU( 1(6 IPC RA.T s. HORIZ EXPO$UI( P06 DC OUNflZITE * WRT OPOSU( P06 DC IW1TZITE 110 I �I METAMORPHISM,HYDROTHERMAL HYDROTHERMALALTERATION ALTERATION AND AND LATERITIC LATERITIC METAMORPHISM, WEATHERING OF OF DRILLED MRS VOLCANIC ROCKS IN IOWA WEATHERING SCHMIDT, Susanne Th.! Th., Mineralogisch-Petrographisches Mineralogisch-Petrographisches Institut, SCHMIDT/ Susanne Institut/ Bernoullistr. Bernoullistr. 30, 30/ CH CH 4056 4056 Basel, Basel/ Switzerland, Switzerland/ schmidts~ubac1u.unibas.ch;SEIFERT, SEIFERTt Karl! schmidts@ubaclu.unibas.ch; Karl, Departement Departement of Geological & Atmospheric AtmosphericSciences, Sciences/ Iowa Iowa State StateUniversity, University/Ames, Ames/IA IA50011, 500111 kseifert@pop-2.iastate.edu. kseifertapop-2.iastate.edu. and cuttings from deep wells into the Precambrian igneous rocks Well cores and of the buried buried Midcontinent MidcontinentRift RiftSystem System in in Iowa Iowa (Iowa (Iowahorst, horst/Anderson, Anderson/1990) 1990) were studied to to identify identify primary primary and and secondary secondary mineral mineral assemblages assemblages and the compositionwas was determined determined by by instrumental instrumental neutron neutron bulk geochemical composition activation analysis (INAA) for trace elements and and by inductively inductively coupled coupled for major major elements. elements. The results indicate a complex plasma (ICP) analysis for alteration history with metamorphic and hydrothermal hydrothermal stages, stages! followed followed by lateritic weathering on the Precambrian erosion surface. surface. Minerals Minerals were analyzed analysis/clay clay minerals minerals by by X-ray X-ray diffraction diffraction analyzed by by electron electron microprobe microprobe analysis, (air-dried and gly~olated)~ and the theisotopic isotopic composition compositionof of calcite calcite was was (air-dried and and glycolated), determined. The large majority of these Midcontinent Rift samples were originally & Anderson, Anderson/ 1996) 1996) compositionally similar to basalts or diabases diabases(Seifert (Seifert & intermediate olivine olivine tholeiites tholeiites as as described described by by Brannon Brannon (1984) (1984) from the exposed north north of Midcontinent Rift or North North Shore Shore Volcanic Volcanic Goup (NSVG) (NSVG) exposed Duluth in Minnesota. Minnesota. Although Although alteration alteration has greatly modified modified the primary samples/ relicts relicts of the original original magmatic magmatic composition and texture texture of of most most samples, mineral assemblage can still be be observed observed in in some some samples. samples. Based on amygdule frequency frequency and and degree degreeof of alteration alteration itit is is possible possible to to differentiate differentiate morphological flow flowunits. units. Flow tops with a large between the various morphological Flow tops number of amygdules and and highest highest degree degree of of alteration alteration can be distinguished distinguished without any amygdules and a less from massive flow interiors without less intensive Massive alteration. In some flow tops no primary igneous texture is visible. Massive of alteration but but the primary texture is flow interiors show various degrees of often preserved. A relativly homogenous regional metamorphic alteration alteration pattern is observed based on the highly amygdaloidal amygdaloidal flow tops and amygdule amygdule minerals. In addition, some massive flow interiors have preserved part of addition/ some of the the early early alteration history. history. The Theassemblage assemblageepidote-Fe-rich-chlorite-albiteepidote-Fe-rich-chlorite-albitequartz±pumpellyite±sericite is characteristic characteristic for for all all studied studied drill sites of of the quartz~umpellyite~ericite facies. The Iowa horst and and indicates indicates conditions conditions of the beginning greenschist facies. The same facies is also observed in the lowermost part of the ca 8 km thick NSVG the lowermost part of the ca 8 k m thick NSVG in Minnesota near Duluth which is interpreted to be the result of of burial metamorphism (Schmidt, 1990; 1993). metamorphism (Schmidt/ 1990; 1993). 111 �The Sharp #1 core documents the complex alteration history that affected at least part of the Midcontinent Rift System in Iowa. A sequence of secondary alteration stages can be established. In the massive flow interior of Sharp #1 (sample 2206.4), an early Fe-poor, Si-rich phyllosilicate replaces pyroxene along grain boundaries. Fe-poor, Si-rich phyllosilicates (smectites) are also reported from massive flow interiors of the NSVG indicating an earlier alteration stage under lower temperatures (Schmidt & Robinson, 1997). The Fe-poor, Si-rich phyllosilicate is in turn replaced by a late Fe-rich chlorite which also occurs in veinlets. This Fe-rich chlorite also forms part of the epidote-Fe-rich-chlorite-albite-quartz ± pumpellyite ± sericite assemblage in the amygdaloidal flow tops. In samples, a late potassic alteration is present with K-feldspar as a frequent overgrowth not only of silicates (albite and pyroxene), but also of chalcopyrite. All samples which were derived directly from the original Precambrian erosion surface are partly intensively altered to kaolinite which is attributed to a tropical lateritic weathering (Seifert & Anderson, 1996). This correlates well with the suggested position of Iowa near the equator at the end of the Precambrian time. No kaolinite is present deeper in the drill cores. Anderson, R.R. (1992) The Midcontinent Rift of Iowa. Ph. D. thesis, University of Iowa, Iowa City, 324p. Brannon, J.C. (1984) Geochemistry of successive lava flows of the Keweenawan North Shore Volcanic Group. Ph. D. Thesis, Washington University, St.Louis, 3l2p. Schmidt, S.Th. (1990) Alteration under conditons of burial metamorphism in the North Shore Volcanic Group, Minnesota - Mineralogical and geochemical zonation. Heidelberger Geowisscnschaftliche Abhandlungen, Band 41, 309 p. Schmidt, S.Th. (1993) Regional and local patterns of low-grade metamorphism in the North Shore Volcanic Group, Minnesota, USA. Journal of metamorphic Geology, 11, 401-414. Schmidt, S.Th. & Robinson, D. (1997) Metamorphic grade and porosity and permeability controls on mafic phyllosilicate distributions in a regional metamorphic zeolite to greenschist facies transition of the North Shore Volcanic Group. Geological Society of America, Bulletin, 109, 683-697. Seifert, K. & Anderson, R.R. (1996) Geochemistry of buried Midcontintent Rift volcanic rocks in Iowa: Data from well samples. Jour. Iowa Acad. Sci. 103 (3-4), 63-7. 112 �CRUSTAL CRUSTALRECYCLING RECYCLINGIN INTHE THEEVOLUTION EVOLUTIONOF OFTHE THEPENOKEAN PENOKEANOROGEN: OROGEN:ISOTOPIC ISOTOPIC EVIDENCE EVIDENCEFOR FORARCHEAN ARCHEAN CONTRIBUTIONS CONTRIBUTIONS TO TO CRUSTAL CRUSTAL GROWTH GROWTH IN IN THE THE PEMBINE-WAUSAU TERRANE, TERRANE, NORTHERN NORTHERN WISCONSIN WISCONSIN PEMBINE-WAUSAU Schulz,Klaus KlausJ.J.and andAyuso, Ayuso,Robert RobertA., A.,U.S. U.S.Geological GeologicalSurvey, Survey,954 954National NationalCenter, Center,Reston, Reston, Schulz, VA20192 20 192(kschulz@usgs.gov) (kschulz@usgs.gov) VA Continental Continentalgrowth growthmodels modelsdepend dependon oninformation informationregarding regardingthe theage ageofofbasement basementininorogenic orogenic belts beltsand andon onestimates estimatesof ofthe theamount amountof ofcrustal crustalrecycling recycling involved involvedin in their theirevolution. evolution. The Thedistribution distribution and androle roleof ofArchean Archeanbasement basementininthe theEarly EarlyProterozoic ProterozoicPenokean Penokeanorogen orogenininthe theLake LakeSuperior Superiorregion region has haslong longbeen been aa topic topic of of debate debate and and speculation. speculation. Early Earlyworkers workersviewed viewed the the Early Early Proterozoic Proterozoic history history of theregion regionin interms termsof ofintracratonic intracratonicdeposition depositionand andreactivation reactivation of of Archean Archean crust crust of of the the Superior Superior the Province Province(e.g., (e.g.,Sims, Sims,1976). 1976).More Morerecently recentlythere therehas hasbeen beenaageneral generalconsensus consensusthat thatthe theEarly Early Proterozoic Proterozoicrocks rocksevolved evolvedthrough throughplate platetectonic tectonicprocesses processesincluding includingcontinental continentalrifling riftingand andsubduction, subduction, with wasaccreted accretedtotothe theArchean Archeancraton craton withformation formationofofsignificant significantvolumes volumesofofjuvenile juvenilecrust crustthat thatwas (Hoffman, (Hoffinan,1988; 1988;Sims Sirns and and others, others, 1989). 1989).However, However,isotopic isotopicstudies studieson onrocks rocksfrom fromthe theWisconsin Wisconsin maginatic magmaticterranes terraneshave haveagain againraised raisedquestions questionsabout aboutthe thedistribution distributionand androle roleofofArchean Archeancrust crustininthe the Penokean Penokeanorogen orogen (Barovich (Barovichand and others, others, 1989; 1989;Van Wyck and Johnson, 1997). 1997). In Inparticular, particular,Van VanWyck Wyck and and Johnson Johnson(1997) (1997)proposed proposedthat thatthe thePenokean Penokeanorogen orogenevolved evolvedthrough throughback-arc back-arcrifling riftingofofthe thesouthern southern Superior SuperiorProvince, Province,followed followedby bycollision collisionof ofaacontinental continentalarc arcterrane terrane(the (theMarshfield Marshfieldterrane) terrane)from fromthe the south. south. One Oneof ofthe theprimary primarylines linesof ofevidence evidenceused usedby byVan VanWyck Wyckand andJohnson Johnson(1997) (1997)totosupport supportaamodel model of of continental continentalback-arc back-arcrifling riftingfor forthe thePembine-Wausau Pembine-Wausauterrane terranewas wasan aninferred inferredcorrelation correlationbetween betweenthe the degree degree of of crustal crustal contamination contamination and and distance distance from the northern margin of the terrane, the Niagara fault zone, (i.e.,€Nd(T) eNd(T)values valuesbecome becomemore morepositive positive zone, in in which whichcontamination contaminationdecreased decreasedsouthward southward(i.e., southwards). southwards). To Totest testthis thismodel modelfor forthe thePembine-Wausau Pembine-Wausauterrane terraneand andfurther furtherrefme refineestimates estimatesfor forthe the involvementof of older oldercrust, crust,14 14volcanic volcanicrocks rocksand and14 14granitic graniticrocks rocksfrom fromacross acrossthe thePembine-Wausau Pembine-Wausau involvement terranein innorthern northernWisconsin Wisconsinwere wereanalyzed analyzedfor forNd Ndand/or andlorPb Pbisotopes. isotopes. These Thesesamples, samples,collected collectedfrom from terrane thethree three principal principal outcrop outcropareas areasin innorthern northern Wisconsin—the Wisconsin-the Dunbar-Pembine Dunbar-Pembine area area located located in in the northeastern northeasternWisconsin Wisconsinjust justsouth southofofthe theNiagara Niagarafault faultzone, zone,the theMonico Monicoarea arealocated locatedabout about45 45 km krn south south of ofthe theNiagara Niagarafault faultzone zoneininnorthcentral northcentralWisconsin, Wisconsin,and andthe theMarathon MarathonCounty Countyarea arealocated locatedatatthe the southern southernmargin marginof ofthe thePembine-Wausau Pembine-Wausauterrane terraneinincentral centralWisconsin—significantly Wisconsin-significantly expand expandthe the sampling sampling density density in in these thesethree threeareas areasand andfor forthe thefirst firsttime timeprovide provideisotope isotopedata datafor forseveral severalvolcanic volcanic units units within within the the Pembine-Wausau Pembine-Wausau terrane. terrane. Results Resultsare aresummarized summarizedininthe thetable tablebelow. below. The Theanalyzed analyzedmafic maficvolcanic volcanicrocks rocks from from the the Monico Monicoand and Marathon Marathon County County areas areasare are light light REEREEenriched from +1.3 +1.3 to to +3 +3 and and relatively relatively primitive primitive p values. These enrichedbut but have havepositive positiveENd(T) ENd(T)from TheseNd Ndisotope isotope data dataare are slightly slightlymore more enriched enriched than than the the Nd isotope isotope results of of Beck and and Murthy Murthy (1991) (199 1) for for the the +4.2 )from fromthe thePembine Pembinearea areaand andsuggest suggestderivation derivationfrom fromdepleted depletedEarly Early Quinnesecbasalts basalts(€Nd(T) (eNd(T) +4.2) Quinnesec Proterozoic (10%) addition contrasttoto Proterozoic mantle mantle with possibly a small (510%) additionofofolder oldercrustal crustalcomponents. components.InIncontrast the the mafic mafic volcanic volcanic rocks, rocks, the the felsic felsic volcanic volcanic rocks rocks from throughout throughout the Pembine-Wausau Pembine-Wausau terrane terrane have eNd(T) values ranging ranging from -0 —0toto-4 -4and andrelatively relativelyhigh highppvalues values >10 >10 suggesting suggesting variable but significant eNd(T) values significant input inputof of older, older, probably probablyArchean Archean crustal crustalcomponents. components. Surprisingly, Surprisingly,the thefelsic felsicvolcanic volcanicrocks rocksfrom fromthe the Monico Monico area area show show the the greatest greatest crustal crustalcontamination. contamination. The Thegranitic graniticrocks, rocks,like likethe thefelsic felsicvolcanic volcanicrocks, rocks, also alsohave havemostly mostlynegative negativeENd(T) eNd(T)values valuesbut butshow showaagreater greaterrange rangefrom from—0 -0 to to—7.4, -7.4, and relatively high high pp values values >10; >lo; younger youngergranites granitestend tendto tohave havethe themost mostnegative negative€Nd(T) e ~ d ( Tand ) highest p values values in in both both the the Dunbar-Pembine Dunbar-Pembine and and Marathon Marathon County County areas. areas. The Theisotope isotopedata datalie liealong alongmixing mixinglines linesbetween betweendepleted depleted Early Proterozoic mantle and Archean Superior Province crust; mixing models suggest from 20 Early Proterozoic mantle and Archean Superior crust; mixing models suggest from to to >70% >70%Archean Archeancrustal crustalcontamination contaminationfor forfelsic felsicvolcanic volcanicand andgranitic graniticrocks. rocks. - 113 I �I Areas Dunbar-Pembine (North) Dunbar-Pembine (North) • Pemene Pemene Rhyolite Rhyolite (2) (2) • Dunbar Dunbar Dome Dome (5) (5) • Bush Bush Lake Lake Granite Granite (1) (1) • Twelve Foot Falls Falls (1) Quartz Quartz Diorite Diorite Monico Monico Basalt (2) (2) • Basalt • Dacite/Rhyolite DaciteRhyolite (3) (3) • Quartz Quartz Porphyry Porphyry (1) (1) Marathon Marathon County County (South) (South) Basalt/Andesite (4) • BasaltIAndesite • DaciteIRhyolite Dacite/Rhyolite (3) (3) • Pre/Syn-Tectonic PrefSyn-TectonicGranite Granite (3) (3) Syn/Post-Tectonic Granite Granite (3) • SynPost-Tectonic TDM TDM(in Ga) Ga) ENd(T) e~d(T.1 - — M.35 +0.35 p (8U/204Pb) (*8~/20"~b) 12 --10.4 11.5 .7.4 -7.4 -3.2 2.3 2.3 2.2 to 2.9 2.9 2.8 +2.1 +2.1 -3.1 -3.1 •1 -4.7 2.1 —2.6 2.6 2.5 --9.811 9.4 +3 to +1.3 +1.3 to -2.0 2.0 -0.8 to 4.0 -1.0 42 -4.2 2.0 to 2.2 2.2 to 2.3 2.3 2.8 2.8 9.8 ---10.6 - 10.9 13.2 -0.9 to -4.2 - -- -- 12 10.4 11.5 - — 9.8 11 9.4 9.8 10.6 10.9 .-. 13.2 The new new data datapresented presented here here do donot notsupport supportaacorrelation correlationof ofincreasing increasing6Nd eNd with distance from Niagara fault zone. zone. The the Niagarafault The felsic felsic volcanic rocks from throughout the terrane show isotopic evidence greatest crustal crustal component component in in rhyolites rhyolites from fromthe theMonico Monicoarea. area. The for crustal contamination with the greatest granitic rocks from throughout the terrane also show isotopic evidence for significant significant crustal contamination. However, However, the the isotope isotope data datado do suggest suggest that that crustal contamination was greatest for syn- to post-tectonic granites emplaced near the northern and southern margins of the Pembine-Wausau terrane. post-tectonic isotope data data for for the Pembine-Wausau terrane suggest suggest that: (1) (1) input input of of Archean crustal crustal The new isotope greater and more widely distributed than previously components to Penokean crust crust formation was greater (2) there there isisno noclear clearcorrelation correlationbetween betweenENd EN^ and and distance from the northern (Niagara) recognized; (2) suture zone, although contamination appears to have been greatest for syn- to post-tectonic granites shown by the emplaced near the margins of the terrane; and (3) the high levels of crustal components shown felsic igneous rocks probably result from crustal assimilation and mixing and not from contamination contamination of a depleted mantle source by subduction of Archean derived sediments. References cited Barovich, KM. Cia KM.,Patchett, Patchett,P.J., P.J.,Peterman, Petennan,Z.E., Z.E.,and andSims, Sims,P.K., P.K.,1989, 1989,Nd Ndisotopes isotopesand andthe theorigin originof of1.9-1.7 1.9-1.7 Ga Penokean Penokean continental continental crust crustof of the the Lake Lake Superior Superiorregion: region: Geological GeologicalSociety Society of of America AmericaBulletin, Bulletin,v. v. 101, 101, p. 333-338. Beck, W. and and Murthy, V.R., V.R, 1991, 1991,Evidence Evidence for for continental continental crustal crustal assimilation assimilation in in the the Hemlock Hemlock Formation Formation flood flood basalts basalts of of the the Early Early Proterozoic ProterozoicPenokean Penokean Orogen, Orogen, Lake Lake Superior Superiorregion: region: U.S. U.S. Geological Geological Survey Survey Bulletin 25p. Bulletin 1904-I, 1904-1,25p. Hoffman, P.F., 1988, Hoffinan, 1988,United United plates plates of of America, America, the the birth birth of craton: craton: Early Proterozoic Proterozoic assembly assembly and and growth growthof of Laurentia: Laurentia:Annual AnnualReviews Reviews of of Earth Earth and and Planetary Planetary Sciences, Sciences, v. 16, 16,p. p. 543-603. 543-603. Sims, Sims, P.K., 1976, 1976, Precambrian Precambrian tectonics tectonics and and mineral deposits, deposits, Lake Lake Superior Superior region: Economic Economic Geology, Geology, v. 71, 71, p. 1092-1177. 1092-1177. P.K., Van Schrnus, W.R., Schulz, KJ., K.J., and Peterman, Petennan, Z.E., 1989, Sims, P.K., Schmus, W.R, 1989, Tectono-stratigraphic Tectono-stratigraphic evolution evolution of the Early Early Proterozoic ProterozoicWisconsin Wisconsin magmatic magmatic terranes terranes of the the Penokean Penokean Orogen: Orogen: Canadian CanadianJournal Journalof of Earth Earth Sciences, v. 26, p. 2145-2158. Van Wyck, N. and Johnson, Johnson, C.M., C.M., 1997, 1997, Common Common lead, lead, Sm-Nd, Sm-Nd, and and U-Pb constraints constraintson on petrogenesis, petrogenesis, crustal crustal architecture, architecture,and and tectonic tectonic setting setting of of the the Penokean Penokean orogeny orogeny (Paleoproterozoic) (Paleoproterozoic)in in Wisconsin: Wisconsin: Geological Geological Society of America Bulletin, Bulletin, v. 109, 109, p. 799-808. , 114 " - II I �I ND ISOTOPE EVIDENCE EVIDENCE FOR FOR MIDDLE MIDDLE AND AND EARLY EARLY ARCHEAN ARCHEAN CRUST CRUST IN THE WAWA SUBPROVINCE OF THE SUPERIOR PROVINCE, MICHIGAN, U.S.A. IN Sims, P.K., Neymark, L.A., L.A., and and Peterman, Petennan, Z.E., Z.E., U.S. U.S. Geological Geological Survey; Survey; Kotov, A.B., A.B., Institute Institute of Precambrian Precambrian Geology Geology and and Geochronology, Geochronology, St. St. Petersburg, Petersburg, Russia Russia Kotov, New Sm-Nd New Sm-Nd isotopic isotopic data on Late Late Archean Archean granitic granitic rocks rocks from from the theWawa Wawasubprovince subprovince(a(agranite-greenstone granite-greenstone terrane) indicate aa Middle to Early Archean crustal source for the rocks. rocks. terrane) of the Superior province, northern Michigan, Michigan, indicate Early Archean model ages between between 2.7 and 3.6 Ga At 2.7 Ga pNd values vary from -6.4 to +3.3, which correspond to depleted mantle mantle model Previous Nd-isotope Nd-isotope studies studies in in granite-greenstone terranes in in the the southern part of the (see table). Previous granite-greenstone terranes the Superior Superior province province indicated that that most most granitoid rocks are juvenile, juvenile, i.e. i.e. mantle derived, with little identifiable participation from older have indicated crust or recycled material. Samples were taken from the Puritan batholith (Fig. I), I), which which lies lies astride astride the Michigan Michigan -- Wisconsin Wisconsin border, batholith (Fig. border, and the northern complex of the Marquette district district (Fig. (Fig. 2); both igneous igneous bodies bodies have have crystallization crystallization ages agesof of—2.7 -2.7 Ga. Ga. Candidatesfor for the the source source of of the Middle Candidates Middle and Early Early Archean Archean rocks rocks in the the Michigan Michigan segment segment of the the Wawa Wawa subprovince have not been been identified, identified, but these rocks mainly constitute ancient ancient continental continental crust, crust, perhaps a proto-craton proto-craton block like that in the Sachigo and Minto subprovinces subprovinces (Percival (Percival and and other, other, 1994) 1994)to to the the north. north. Not unexpectedly, high-grade gneisses from the adjacent Minnesota River Valley subprovince, to to the south, which which contains the oldest rocks in the Superior province, have have comparable comparable old old Nd-depleted Nd-depleted mantle mantlemodel modelages ages(see (seetable), table), ranging from 2.9 to 3.3 Ga. d Table. Sm-Nd Sm-Ndisotope isotopedata datafor forgranites granitesfrom from Wawa WawaSubprovince Subprovinceand andfelsic gneisses and and granites granites from from Minnesota felsic gneisses Subprovince. River Valley Suburovince. '47Sm/ 143Ndt T(Ga) Nd Sample Sm d(t) d(O) TDM TDM '44Nd '44Nd (ppm) (ppm) Subprovince (Granite-Greenstone (Granite-Greenstone Terrane) Wawa Subprovince Terrane) 182B 183B 198 215B 0919-1-89 0919-3-89 0920-4-89 l36R M169 Ml70 177 179 D1044 D1731 D2493 D2494 D2495 2.7 2.7 2.7 2.7 2.7 2.7 2.7 2.7 2.7 2.7 2.7 2.7 2.7 2.7 2.7 2.7 2.7 8.88 19.7 5.70 2.76 4.06 8.08 3.56 0.79 1.60 2.98 40.9 98.2 32.2 17.0 30.2 57.7 17.9 3.11 11.5 17.4 2.53 13.8 1.01 4.67 4.10 16.7 2.08 10.5 1.26 6.48 5.06 33.6 5.60 33.6 0.0980 0.1214 0.1074 0.0982 0.0815 0.0925 0.1205 0.1545 0.0848 0.1041 0.1107 0.1315 0.1486 0.1200 0.1176 0.0913 0.1012 0.510695 (13) 0.511072 (5) 0.510842 (8) 0.510672 (13) 0.510594 (12) 0.510707 (6) 0.511397(10) 0.511781 (9) 0.5 10708 (10) 0.511040(10) 0.510912 (10) 0.511415(9) 0.511572(7) 0.511070(7) 0.511266(7) -3.7 -4.5 0.510928 (7) 0.510792(4) 3.3 -37.9 -30.5 -35.0 -38.4 -39.9 -37.7 -24.2 -16.7 -37.6 -31.2 -33.7 3202 3394 3276 3237 2922 3044 2840 3478 2863 2908 3277 -23.9 -20.8 -30.6 -26.8 -33.4 -36.0 3182 3646 3347 2959 2744 3163 3334 3123 3358 3347 2966 2758 3256 -39.8 -32.1 2971 3037 -31.4 -31.6 3192 3309 3072 3226 3325 3104 -6.4 -36.0 3358 3456 -2.3 -2.3 -31.8 3068 3127 -4.1 -4.2 0.1 -1.5 2.3 -2.1 1.2 1.0 -3.8 -1.2 -4.1 -4.0 0.7 -2.9 213 2.8 2.8 2.8 Subprovince (Gneiss Terrane) Terrane) Minnesota River Valley Valley Subprovince 44.9 0.0841 0.510600(8) 0.8 6.22 44.9 0.0841 0.5 10600 (8) 0.8 0.510993(11) 0.510993 (1 1 ) 2.35 12.8 0.1117 -1.5 12.8 0.11 17 2.35 0.1170 0.511027(10) 1 1027 (10) 0.5 38.2 -2.7 38.2 0.1 170 7.36 0.511018(8) 21.2 0.1089 0.0 0.1089 0.0 3.80 3.80 21.2 3-90 2.6 10.5 10.5 34-90 161-B 211 2.8 3319 3384 3352 3361 3012 3144 2839 3193 2924 2943 Tilden Granite Granite 59.2 0.510791 0.5 1079 1 (8) 0.1078 0.1078 Gwinn Granite 226-89 2.6 5.65 5.65 31.6 31.6 0.511006(10) 0.511006(10) 0.1082 0.1082 2 within-run **)) Data Data corrected to La La Jolla Jolla '43Nd/'44Nd=0.5 '"Nd/'"Nd=0.5 1 11860, 1860, 2,-r within-run errors errors are are given given inin parentheses. parentheses. 12ininthe the source source of of rocks before T Ga ** *) * ) Two-stage Two-stage Nd-model age age assuming assuming47Sm/'41Nd=0. '"Sm/'"Nd=O. 12 Ga ago. ago. 115 �________________________________ W" 89' 88O I 1 LAKE SUPERIOR 47% Figure 1. 1.Geologic Geologicmap mapofofPrecambrian Precambrianrocks rocksininnorthern northernMichigan Michiganand and adjacent adjacent Figure Wisconsin, showing showing localities Sm-Nd samples. Figure 2 is an enlargement of area outWisconsin, - localities of Sm-Nd samples. Figure 2 is an enlargement of area outlined lined south south of of Marquette. Marquette. n EXPLANA11ON EXPLANATION EXPLANATION —Contact Paleozoic Paleozoicrocks, rocks,undivided uncfwidd (1,600-900Ma) Ma) MIDDLEPROTEROZOIC PROTEROZOIC(1.600-900 MIDDLE ROCKS subprovinces '—Mylonde (ca. 1 ,I 00Ma) Ma) Rocksof ofmidcontinent midcontinentrift riftsystem system(ca. Rocks 1,100 Sm-Nd age locality . Wawa / Sub- Palmer EARLY (2,500—I .600 Ma) EARLYPROTEROZOIC PROTEROZOIC (2,500-1,600 Ma) province '.k)lcanic Volcanic.and andgranitoid granitoidrocks rocksofofWisconsin Wisconsin 1618 magmatic zone (—1.880—1,860 (-1.880-1.860Ma) Ma) magmatlc zone Sedimentary Sedimentaryand andvolcanic volcanicrocks rocksofofMarquette Marquette Range RangeSupergroup Supergroup •3.90 Puritanbatholith batholiih (-2,700 Ma) Puritan (—2,700 Ma) Granitoid Granitoidrocks rocksofofnorthern northerncomplex complexofof Marquette district (—2,700 Ma) Marquette district (-2,700 Ma) ' SAND COVER B 828 34-90 ' Minnesota A subprovince ARCHEAN ARCHEAN(2,500 (2,500Ma Maand andolder) older) ':2 PRO TEROZOIC . MinnesotaRivervalley Jacobsville JacobsvilleSandstone Sandstone n 1361 Approximate boundary between Wawa and Valley 21 21 '\\ 5 MILES 5 KILOMETERS Metavolcajijc Metavolcanicrocks rocks "3 7- 1 Gneiss (2,750—2,640 Ma) Gneissand andamphibolite amphiboliie (2.750-2.640 Ma) mat3icgneiss gneissofofMinnesota MinnesotaRiver RiverValley Valley Migmatitic prwlnce(3,550—2,800 (3,550-2,800 Ma) subprovince Ma) GLTZ, GLTZ, Ma, Ma, Mar, Mar, Me, Me, Great GreatLakes Lakestectonic tectoniczone zone Marquette, Marquette,Michigan Michigan Marenisco, Marenism,Michigan Michigan Mellen, Mellen,Wisconsin Wisconsin Sm—Nd Sm-Ndage agelocality locality Figure2.2.Geologic Geologicsketch sketchmap mapofofPrecambrian Precambrian Figure rocksininan anarea areasouth southof ofMarquette, Marquette,showing showing rocks localities of Sm-Nd samples. The Great hkes localities of Sm-Nd samples. The Great Lakes tectoniczone zoneseparates separatesgranite-greenstone granite-greenstonetertertectonic rane(Wawa (Wawasubprovince) subprovince)from fromgneiss gneissterrane terrane rane (MinnesotaRiver RiverValley Valley subprovince). subprovince). (Minnesota 116 I �I A THIN SHEET APPROACH TO A T H I N VISCOUS VISCOUS S HEET A PPROACH T O INVESTIGATE INVESTIGATE THE POST POST OF THE RIFT EVOLUTION O FT H E MIDCONTINENT M I D C O N T I N E N T RIFT RIFT SYSTEM SYSTEM UNDER UNDER THE INFLUENCE OF O F GRENVILLE GRENVILLE OROGENY OROGENY Soofi, M. A., A., and and King, King, S. S.D., D., Department Department of of Earth Earth and Atmospheric Sciences, Purdue Purdue Soofi, M. West Lafayette, Indiana University, West Indiana 47907 47907 The cause of the termination termination of of rifting rifting along along the the Midcontinent Midcontinent Rift Rift system system(MCR) (MCR) and the the presence presence of reverse faults along along the rift margins margins are are still still troublesome troublesome for the the investigators of the MCR. Suggestions for the cause of rifting investigators of Suggestions for rifting range range from fiom aapassive passive mechanism, where where processes processesatat plate plate boundaries responsible (e.g. (e.g. Hinze Hinze et al., mechanism, boundaries were were responsible al., 1982), to to an active mechanism, where where aa mantle mantle plume plume ascended ascended and and initiated initiated rifting (e.g. 19821, (e.g. the formation of reverse reverse faults faults has been suggested Cannon and Hinze, 1992). Similarly, the to be under the loading due to rift be aaconsequence consequence of plate flexure under rift related related rocks rocks (e.g. (e.g. stresses from from the the plate boundaries, which Nyquist, 1986), 19861, or an effect effect of compressive compressive stresses which thrusting along the original rift bounding not only terminated the the rifting but also also caused thrusting normal faults (e.g. (eg. Cannon, Cannon, 1994). 1994). study focuses on the evolution of of the the MCR under the the influence of plate plate boundThis study influence of forces from from the the Grenville Orogeny. We are ary forces, forces, particularly particularly the compressive compressive forces Grenville Orogeny. using the thin using thin viscous viscous sheet sheet model model (TVS) (TVS) of of England England and and McKenzie McKenzie (1983) (1983) which which is implemented in in aa finite element element code code by by Houseman Houseman and and England England (1986). (1986). This model implemented model has been used in the the study studyof of India-Asia India-Asia collision collision (England and Houseman, Houseman, 1986) 1986) and (Sobouti and and Arkani-Hamed, 1996), where where it has successArabia-Eurasia convergence convergence (Sobouti successfully reproduced reproduced the topography and deformation in the overriding Eurasian Eurasian deformation observed observed in plate. The Themodel modeluses usesincompressible, incompressible,vertically vertically averaged, averaged,power-law power-law rheology rheology for the the lithosphere. lithosphere. For a given geometry,boundary boundary conditions, conditions,stress-strain stress-strainexponent exponent(n) (n) and and Argand For given geometry, Number (Ar) (Ar) values, stresses, strain rates and Number values, the the model model calculates calculates crustal thickness, stresses, and rotation. rotation. These These can can then thenbe becorrelated correlatedwith withtopography topography and and deformation deformation in in the theover over riding plate. A assumed such such that that there is no discontinuity in the A continuous continuous medium is assumed velocity field. Fault Fault planes cannot be defined defined explicitly explicitlybut, but, information information on on the the type of of velocity field. faulting can be inferred from from the the stress and strain rate rate distribution. distribution. results indicate indicate that even (i.e. n=10) Our results even in the case case of aa very very weak weak lithosphere lithosphere (i.e. n=lO) stresses from the the Grenille GrenilleEont Front (GF) (GF) can can be be transmitted transmitted inland inland to interact with stresses from with the the processes that that were were occuring occuringalong along the the MCR. MCR. Also, Also, depending dependingon on the thesize sizeof of the the colliding colliding microcontinents (i.e. indenters) indenters) and and their their position position along alongthe the GF GF itit is is possible possiblethat that the microcontinents (i.e. MCR was subjected to different magnitude of of stresses stresses along along its its length length and itit evolved was subjected difFerent magnitude evolved through the the superposition superposition of of these stresses. The Thevarying varying degree degree of thrust thrust faulting faulting obobserved along along the the MCR could style. The models could be a manifestation manifestation of such a collision collision style. models also predict significant of crust crust next to the significant thickening of the indenter, indenter,the thethickening thickeningdecreases decreases away from the collision boundary. For For a comparatively rigid lithosphere lithosphere (n=l,Ar=l) (n=1,Ar=1) away fiom collision boundary. comparatively rigid crustal thickening is as much much as as 2 km where for a weak lithosphere (n=lO,Ar=l) (n=10,Ar=1) thickening is where as for weak lithosphere crustal thickening is as much as 19 km. Assuming kg/m3 and Assuming crustal density density of 2700 2700 kg/m3 mantle density density of of 3300 3300 kg/m3 kg/rn3 and and assuming assumingthe the surface surfaceof ofthe the 35 35 km km thick thick crust to mantle to be at at the thesea sealevel level the thechange changein in crustal crustalelevation elevation is is 0.36 0.36 km for for rigid lithosphere and 3.4 km km for for the relatively weak lithosphere. lithosphere. The high elevations elevations predicted predicted by by the the TVS 3.4 relatively weak for the the Tican initiate local local extension, as suggested by England and McKenzie McKenzie (1982) (1982) for betan betan plateau. plateau. Such Suchaamechanism mechanismmay may had hadbeen beenresponsible responsiblefor for the the late latestage stageextension extension reported for the the Grenville Grenville Orogeny (e.g. (e.g. Easton, Easton, 1992). 1992). 117 �We are also studying along the the GF studying the the effect effect of of oblique oblique convergence convergence along GJ? on on the theevoluevolution of the the MCR. MCR. For For fixed fixed boundary boundary conditions conditions and and rheology, rheology, the length length scale scale of of dede formation decreases with increasing obliquity. As discussed for the normal convergence, formation decreases increasing As discussed the normal convergence, microcontinents convergingobliquely obliquelyalong alongthe the GF GF can produce stresses microcontinents of various sizes converging magnitudes along the the MCR. Oblique convergence convergenceproduces producessame samepattern pattern of of of different magnitudes crustal thickening as observed for normal convergence except that it is not symmetric. observed for normal convergence except that it One between oblique oblique and and normal convergence is the the significant area area One significant significant difference between of (indenter). This thinning repof crustal thinning next to to the the colliding colliding microcontinent microcontinent (indenter). resent extension in the over over riding plate. For For normal normal convergence convergence the thinning is is very very localised and produced produced in a very localised and very small small area area that thatdoes doesnot notchanges changessignificantly significantly with with rheology. this area of rheology. For oblique convergence this of extension extension increases increases for for weaker weaker rheology (increasing nn value). We together with a weak We hypothesize hypothesize that that oblique oblique convergence, convergence, together weak lithosphere (due subduction), may had helped, (due to thermal thermal anomaly anomaly resulting resulting from fiom subduction), helped, if if not initiated, the the rifting rifting process. process. REFERENCES CITED CITED of Grenvillian Cannon, Cannon, W. F., F., 1994, 1994,Closing Closing of the Midcontinent Midcontinent rift rift -- A A far-field effect of compression: Geology, Geology, v. 22, 22, p. p. 155-158. 155-158. on the the origin of of the the North AmerCannon, W. F., and Hinze, Hinze, W. J., 1992, 1992, Speculations on ican Midcontinent rift, in Ziegler, P. A., ed., Geodynaniics of rifting, an Ziegler, P. A., ed., Geodynamics of rifting, Volume Volume 2. 2. Case History History Studies Studies on on Rifts: Rifts: North and and South South America America and and Africa: Africa: TectonoTectonophysics, v. 213, 213, p. 49-55. 49-55. Easton, R. R. M., M., 1992, 1992, The The Grenville Grenville Province and the the Proterozoic Proterozoic history history of of Central Central and Southern Ontario, in an Thurston, Thurston, P. P. C., C., Williams, Williams, H. R., Sutcliffe, Sutcliffe, R. H., H., and Stott, Stott,G. G.M., M.,eds., eds.,Geology Geologyof of Ontario, Ontario,Ontario OntarioGeological GeologicalSurvey, Survey,Special SpecialVolume Volume 4, Part 2, p. 715-904. Part 2, p. 715-904. England, P., and and Houseman, Houseman, G., G., 1986, 1986, Finite strain straincalculations calculationsof of continental continental defordeformation 2. 2. Comparison Comparisonwith with the theIndia-Asia India-Asiacollision collision zone: zone: Journal Journalof ofGeophysical Geophysical Research, v. 91, p.3664-3676. 3664-3676. 91, p. England, P., and and McKenzie, McKenzie, D., D., 1983, 1983, Correction to,: to: A thin thin viscous viscous sheet sheet model model for for continental continental deformation: deformation: Geophysical Geophysical Journal Journalof ofthe theRoyal RoyalAstromomical AstromomicalSociety, Society, v. 73, 73, p. p. 523-532. 523-532. Hinze, W. J., Wold, R. J., J., and and O'Hara, O'Hara, N. N. W., W., 1982, 1982,Gravity Gravity and and magnetic magnetic anomaly anomaly Hinze, W. studies of of Lake Lake Superior, Superior, an in Wold, Wold, R. R. J., J., and and Hinze, Hinze, W. J., J., eds., eds., Geology Geology and and tectonics of the Lake Superior basin: Geological Society of America Memoir 156, the Lake Superior basin: Geological Society of America Memoir 156, 203-222. p. 203-222. Houseman, G., and and England, England, P., 1986, 1986, Finite strain strain calculations calculations of continental deformation 1. Method and general results for convergent 1. Method and general results for convergent zones: zones: Journal Journalof of Geophysical Geophysical Research, v. v. 91, 91,p.p.3651-3663. 3651-3663. of the the Mid-Continent Mid-Continent rift rift [Ph.D. Nyquist, J. E., 1986, 1986, Thermal and mechanical models of thesis]: University Universityof of Wisconsin-Madison, Wisconsin-Madison,193p. 193p. Sobouti, F., and of the the deformation of of and Arkani-Hamed, Arkani-Hamed, J., 1996, 1996, Numerical Numerical modelling of the Iranian plateau: plateau: Geophysical Geophysical Journal Journal International, International, v. v. 126, 126,p. p.805-818. 805-818. 118 I �U PALEOMAGNETIC STUDIES OF AA PROTEROZOIC PORPHYRITIC PORPHYRITIC DIABASE DIABASE DIKE, PIFHER AND IRWIN DIKEf IRWIN TOWNSHIPS, TOWNSHIPS LAKE LAKE NIPIGON NIPIGON DISTRICT, DISTRICT ONTARIO ONTARIO T h ~ m a s *C., C~S fKean, Keanf W., Department Department of of Geosciences, Geosciencesf Thomas*, University of Wisconsin-Milwaukeef 53201 Wisconsin—Milwaukee, Milwaukeef Milwaukee, WI 53201 and Luther, Lutherf F., F e fGeology Geology Department, Departmentf UW—Whitewater, UW-Whitewaterf Whitewater, student author) Whitewaterf WI WI 53190 53190 (* ( * student author) This approximately This approximately 50 50 m m wide wide porphyritic porphyritic diabase diabase dike, dikef outcropping outcropping in western Irwin Irwin and Pifher Pifher Townships Townships in in the the Nipigon district, districtf is is locally locally known known as as greenspar. The The dike dike has has a characteristic characteristic greenish greenish mottled appearance appearance in in outcrop outcrop as as aa result of saussaritized saussaritized plagioclase glomerophenocrysts glomerophenocrysts in in aa diabase (Luther,1997). The The dike dike strikes strikes due due north north diabase groundinass groundmass (Lutherf1997). and dips verticallyf vertically, and is off-set by by is found found as as segments, segmentsf off—set east—west east-west faulting(Mackasey,1975). faulting(Mackasey,l975). There There are are no no radiometric radiometric dates on on this this rock rock or or associated associated rocks, rocks, although, althoughf it it is is cut cut by by middle or late Proterozoic sill a large middle sill in Irwin Irwin Township 1975).. Township(Mackasey, (Mackaseyf1975) Paleomagnetic studies were completed on 2—3 2-3 cores cores from from each of 5 locations. Each location represents represents one one dike dike segment. Samples Samples from each location location were subjected subjected to to both alternating field alternating field (A.F.) (A.F.) and and thermal thermal demagnetization demagnetization studies. studies. The is The samples samples show show one one primary primary magnetic magnetic direction direction which which is removed at demagnetization demagnetization temperatures temperatures of of 5700 570 C. or or by by A.F. fields of 60 mT. All but one location normal polarity fields 60 mT. location shows shows normal with inclinations of with northwesterly northwesterly declinations(200°-300°) declinations(200~-300') and inclinations of 40°-80°. The northern northern most most section section of of the the dike dike which which we we sampled 40'-80° The is reversally reversally magnetized magnetized with with declinations declinations of of about about 90°—100° 90'-100~ and inclinations inclinations of of —75°. -75'- These magnetic directions directions are are consistent with Keweenawan age age paleomagnetic directions directions in in the the Lake Superior Superior Region. Region. References References Luther, Proterozoic Lutherf F.,1997, F.f1997f The The Petrology Petrology of of Greenspar: Greenspar: A Proterozoic Porphyritic Porphyritic Diabase Diabase Dike; Dike; Pifher Pifher and Irwin Irwin Townships, Townshipsf Lake Lake Nipigon District, Districtf Ontario. Institute Institute on on Lake Lake Superior Superior Geology Geology Vol.43. abstracts abstracts and and proceedings proceedings Vo1.43. , Mackasey, Mackaseyf W.O.,1975, W.0.f1975f Geology Geology of of Dorothea, Dorothear Sandra, Sandra, and and Irwin Irwin Townships, Townshipsf District District of of Thunder Thunder Bay; Bay; Ontario Ontario division division of of Mines, Minesf 83 p. p. rpt 122 122 with with map map 2294, 2294# 83 119 �., GRAVITY, MAGNETIC, AND STRUCTURAL STUDY OF TJ3E THE WAKEMUP WAKEMUP BAY A GMVITY, TONALITE, MINNESOTA TIKOFF, Basil, Department of Geology and Geophysics, Rice University, Houston, TX 77005-1892, 770051892, USA, BAUER, Robert Department of Geological Sciences, University of Missouri, Columbia, Columbia, MO, 65211, 652 11, USA, VIGNERESSE, VIGNERESSE, Jean-Louis Jean-Louis Vigneresse, Vigneresse, CREGU, 54501 54501 Vandoeuvre, Vandoeuvre, Nancy Cedex, France, and HAGGEMAN, HAGGEMAN, Nick, Nick, of Mimesota, Minnesota, Minneapolis, Minneapolis, MN MN Department of Geology and Geophysics, University of 55455, USA Wakemup Bay The wakemuP Bay tonalite tonalite is is aa small small intrusive intrusive body that intrudes intrudes amphibolite-grade amphibolite-gradebiotite biotite schist on the extreme extreme southern southern edge of the Quetico sub-province sub-province in the western part of Lake Lake Minnesota. The tonalite is part of of the the Wakemup Wakemup Bay Bay block, block, which which is is bounded bounded by by Vermilion in Minnesota. the Vermilion fault to the north and the Haley fault to the south. The Haley fault has a dip-slip component that separates separates amphibolite-grade amphibolite-grade rocks of the Quetico sub-province to the north greenschist-grade rocks of the Wawa sub-province to to the the south. south. The The primary primary purpose purpose of of from greenschist-grade our investigation was to evaluate the mechanism of emplacement of the Wakemup Bay pluton and its relationship to local doming by determining its 3D shape and internal magnetic fabric. conducted aa gravity gravity survey survey over over the the pluton, and use the gravity gnvity inversion inversion to to evaluate evaluatethe the We conducted pluton shape. shape. We Wecollected collectedanisotropy anisotropyof of magnetic magnetic susceptibility susceptibility(AMS) (AMS) data data to to evaluate eval~latethe the magnetic fabric mdgnetic fabric of the pluton. pluton. Bauer Bauer (1985, (1985, 1986) 1986)reports reports previous previous structural structural analysis analysis and mapping mapping of the the Wakemup Wakemup Bay pluton. The pluton comprises a medium-grained biotite tonalite, with sphene, apatite, magnetite, appearance, magnetite, and and zircon zircon as as accessory accessory minerals. minerals. The tonalite typically has a layered appearance, indicate solidand the microstructures throughout throughout the pluton, particularly at the pluton margin, indicate soliddeformation. Foliation dips outward (20-60°) (20-60') from the middle of the pluton, in a state deformation. plagioclase, quartz, and biotite concentric concentric pattern. pattern. Biotite Biotite schist schist -- consisting dominantly of p1agioclase7 surrounds the tonalite tonalite on on all all sides, sides, and and has has foliation foliation that that also also dips dips away away from from the the center centerof of the the pluton on all sides. On On aa more more regional scale, the foliations of the schist defines a doubly plunging, EW-trending anticline with moderately moderately dipping dipping limbs. limbs. The tonalite is spatially B auer(1985, (1985, 1986) 1986)interpreted interpreted as as an an F3 F3 fold fold associated with the hinge area of this fold, which Bauer in the local deformation biotite schist deformation sequence. A hornblende hornblende diorite unit that intruded the biotite The center of of the pluton pluton is is capped by by outcrops on both the north and south sides of the tonalite. The abovethe thetonalite tonalitecontact. contact.The The roof roof consists consists of both the wallrock that that extends extends—40 -40 mmabove a roof of walirock biotite schist schist and and aa relatively relatively flat-lying flat-lyinglayer layer of of the the hornblende hornblende diorite. diorite. The Anisotropy Anisotropy of Magnetic Susceptibility Susceptibility (AMS) is a technique that is widely used in the study = K x H, where M is defmed by M = study of granitic granitic fabrics. fabrics. The The magnetic magnetic susceptibility is defined the induced magnetization and H is the inducing magnetic field. The variation induced magnetization and H is the inducing magnetic field. The variationof of this thismagnetic magnetic susceptibility with the sample placed in different orientations produces an AMS ellipsoid, sample ellipsoid, kmin, which similar to the finite strain ellipsoid. The principle AMS axes are kmax > > kint > > kmin7 plane) or magnetic lineation kint lineation may be interpreted interpreted in terms terms of a magnetic foliation (kmax (kmax orientation). orientation). The bulk susceptibility values varied widely widely in in the the Wakemup Wakemup Bay tonalite 10-1 SI), SI), interpreted as representing the presence or absence of magnetite. The (5 x 10-4 to 10-1 AMS foliation essentially essentially parallels parallels the measured field foliation. foliation. The The major major insight insight from from the the AMS study comes comes from from the orientation orientation of the magnetic lineation. Throughout the Wakemup Bay tonalite, tonalite, the the magnetic magneticlineation lineationisis oriented oriented dominantly dominantly EW, EW, plunges plunges shallowly, shallowly,and andisis generally parallel to the long long direction direction of the Wakemup Bay pluton and parallel to the trace trace of the F3 fold hinge. This This observation observation has has significance significance with respect respect to to emplacement emplacementmechanism. mechanism. We selected gravity study study because: because: 1) 1)ItIt had had selectedthe the Wakemup Wakemuptonalite tonalite for for our our detailed detailed gravity with aa previous structural structural mapping mapping (Bauer, (Bauer, 1985); 1985); 2) It has a single surrounding surrounding lithology lithology with significant and consistent ± 0.04 for the tonalite and 2.75 k ± 0.04 for the consistent density density contrast contrast (2.67 k surrounding 3) A A walirock wallrock roof exists over the center of the pluton, despite despite the surrounding schists); schists); and and 3) (<40 40 m). m). Thus, Thus, the depth recorded by the gravity inversion relatively low relief of the area (< represents represents the the true true depth depth of of the the pluton, within the limitations limitations of the gravity inversion inversion technique technique (e.g., method of Vigneresse, Vigneresse, 1995). 1995). To achieve resolution obtained in structural measurements, Wakemup pluton and immediate measurements,142 142gravity gravity stations stations were collected collected on the Wakemup immediate 120 I ' �I surroundings surroundingsusing using aa Lacoste Lacoste & & Romberg, Romberg, model model G G gravitimeter. gravitimeter. Laser theodolite theodolite from from benchmarks and the controlled-elevation shoreline Of Lake Lake Vermilion provided the existing benchmarks Bouguer anomalies is is provided provided (Fig. (Fig. la). Using a critical elevation controls. A map of the Bouguer gravimetric three-dimensional gravirnetric three-dimensional iterative technique, resulted in a good first-order picture of the (Fig. ib). lb).Most Mostofofthe thepluton plutonisisvery verythin, thin,less lessthan than0.5 0.5 km km thick. thick. There There are aretwo two root root pluton (Fig. zones, both of which which indicate depths of up to 4.0 km, using the calculated densities. The depth krn anomaly in the southwest southwest part of the pluton has a linear, NW trend and is approximately 5 km thus adjacent to the the Haley Haley fault. fault. The The long. It lies adjacent to the SW part of the pluton and is thus contains aa NW depth anomaly anomalyin in the thecenter centerof ofthe thepluton plutonisisslightly slightlyless lessdeep deep(—3 (-3 km). It also contains NW NW-SE oriented trend. trend, although the depth depth is clearly at a maximum in the SE part of the NW-SE interesting to note that the deepest portion of the tonalite does not sit under the present It is interesting exposure of the pluton. As a result of the structural geology, magnetic analysis, and gravity measurements, the Wakemup Bay pluton is interpreted as intruding a broad anticlinal hinge, hinge, during during the the folding folding Wakemup event (F3). This was one of the possibilities suggested by Bauer (1986) and consistent with the very thin nature of of the the pluton pluton (<0.5 ( ~ 0 . km). 5km).The The walirock wallrock preservation preservation in in the the roof represents representsthe the anticlinal anticlinal hinge. hinge. The The hornblende diorite unit on the north side, south side, and above the pluton is a good indication indication of of this this situation. situation. The The two NW-root zones zones were presumably presumably were were feeder feeder zones for the magma, magma, although although given the very high exposure level this claim is impossible to support by geological may have have initiated initiated on on NW NW geological or or magnetic measurements. The feeder zones may oriented fractures. oriented fractures. This This type type of of cross-faulting cross-faulting is commonly commonly seen seen in in folds, folds, particularly particularly those those with a component component of of hinge-parallel hinge-parallel extension. extension. The The large large southern southern root root zone zone may may have have affected affected the subsequent subsequent movement movement of the Wakemup Wakemup block, between the Haley and Vermilion faults. occurs just south of the deep southern root zone, and the root of the the The Haley fault occurs tonalite may have fault shows tonalite have acted acted as as a strong strong heterogeneity in the schist. The Haley fault indications of some inferredto some dextral dextral strike-slip faulting, which is inferred to have have occurred occurred after afterits its earlier normal normal movement movement (e.g., (e.g., Bauer, 1986). 1986). This type of small rigid block moving between major fault fault systems systems is is inferred inferred in other other orogenic orogenic belts. REFERENCES REFERENCES Minnesota. Minnesota Bauer, R.L., 1985, 1985, Norwegian Bay Quadrangle, Quadrangle, St. Louis county, Minnesota. Minnesota Geological Geological Survey, Survey, Miscellaneous Map Series, Map MapM-59, M-59, 1:24,000. 1:24,000. Bauer, R.L., 1986, 1986,Multiple Multiple folding folding and pluton emplacement emplacement in Archean migmatites rnigmatites of the the southern complex,- northeastern northeasternMinnesota. Minnesota. Canadian Journal of Earth Earth southern Vermilion granitic eranitic com~lex, Sciences, v. 23, 23, p. p. 1753-1764. 1753-1764. I I I I I I I I I I I I 5314.00 5312.00 5310.00 5308.00 5306.0 5304.00 5302.00 5300.00-' I I b ! t I I 53002.00 522.00 524.00 524.00 526.00 526.00 528.00 528.00 530.00 530.00 532.00 532.00 534.00 534.00 536.00 536.00 538.00 538.00 540.00 540.00 542.00 542.00 I 544.00 544.00 Fig. Fig. 1. Gravity Gravityinversion inversion model model for for Wakemup Wakemup Bay tonalite. Heavy Heavy dashed dashed line line represents represents current outcropping outcropping of the pluton. Light Lightlines linesare are inferred inferred depth depth of of the pluton, pluton, contoured contoured for for km. The 0.5 km. Thetonalite tonaliteisisgenerally generallyaathin thinsheet sheet(<0.5 ( ~ 0 . km), 5km), with with two two deep deep root root zones. zones. 121 �THE RELEVANCE OF THE GEOLOGY AND OPHIOLITES TO GEOLOGY OF OF MID-OCEAN MID-OCEAN RIDGES AND UNDERSTANDING OF MIDCONTINENT RIFT: RIFT: THE UNDERSTANDING OF LAYERED LAYERED INTRUSIONS INTRUSIONS IN IN THE MIDCONTINENT AND PETROLOGY PETROLOGY PART I. GEOMETRY; GEOMETRY; PART PART II. 11. INTERNAL STRUCTURE STRUCTURE AND Tatiana TatianaVislova, Vislova,Department DepartmentofofGeology Geologyand andGeophysics, Geophysics,University Universityof of Minnesota, Minnesota, USA USA Part Insightsfrom fromcurrent current research research on on mid-ocean mid-ocean ridges and ophiolites remain to be applied Part I.I.Insights to studies studies of ofintracontinental intracontinental rift rift systems. systems. Dynamic Dynamic magma magma chambers chambers where where fractional fractional crystallization and and formation formation of of layered with spreading are crystallization layered cumulates occur simultaneously simultaneously with being ocean island island and and mid-ocean mid-ocean ridge ridge systems. systems. But But layered layered being defined defined by by seismic data for ocean intrusions in in continental continentalcrust crustare are still still generally generallystudied studiedfrom fromthe the point point of of view view of fixed intrusions fixed geometry. conclusion that the Duluth Duluth Complex Complex and and associated associated geometry. However, However, ifif we we accept the conclusion intrusions such as the Sonju Lake and the Bald Eagle intrusions formed in an an intracontinental intracontinental rift system, the concept concept of of dynamic dynamic magma magma chambers chambers during during crystallization crystallization of of layered layered gabbro gabbro must be considered. considered. There is a growing database on the geometry geometry and dynamic dynamic processes processes of of crystallization crystallization and the formation of layered gabbro based based on seismic studies along along the the fast spreading (>-lo (>-10 cm/yr.) cmlyr.) East Pacific Rise (Sinton, 1992; 1992; Wang, 1996; 1996; Barth, Barth, 1996) 1996) and and the theslow-spreading slow-spreading (<-5 crnlyr.)Mohns Mohns Ridge Ridge (Geli, (Geli, 1994) 1994)and and Mid-Atlantic Mid-Atlantic Ridge Ridge (Rommevaux, (Rommevaux, 1994). 1994).These These (<-5 cm/yr.) studies demonstrate studies demonstrate that active active magma magma chambers: chambers: 1) are are segmented segmented and and centered centered under under and active vents along the ridge axes (McKenzie, 1997 topographic highs and 1997 and and Wright, Wright, 1995), 1995), 2) pinch and swell 15 km (Geli, swell in in plan plan view view with withtypical typicalwidths widthsand andalong-axis along-axislengths lengthsofof5 5—- 15 2.5 km below the seafloor. These features are best 1994), and 3) are are found found at atdepths depthsofof1.5 1.5— - 2.5 developed along slow spreading rifts such as the Mohns Ridge (Geli, 1994). 1994). Because ophiolites are fragments of oceanic crust, they provide an opportunity opportunity to to study study the processes that occur along along ridge axes. axes. Recent Recent detailed detailed mapping mapping and interpretation interpretation of of the the Oman generally confirm confirm the the segmental segmental structure structure of of ridge ridge magma Oman ophiolite ophiolite generally magma chambers chambers as described above above (Nicolas, (Nicolas, 1996 1996and and references referencestherein). therein). The geophysical expressions expressions of present-day oceanic oceanic ridges and the 1.1 1.1 Ga Ga Midcontinent Midcontinent bulls-eye structure on on a scale of 100-1000 Rift in North America America show the same same segmented segmented bulls-eye 100-1000 km. On aa scale scaleof ofI 1—- 100 100 km, the geophysical geophysical data on active active magma magma chambers chambers along along ridge ridge axes and the first first derivative derivative of the the aeromagnetic aeromagnetic data on the the Bald Bald Eagle Eagle Intrusion Intrusion have have aa pinch and and swell geometry. geometry. These These similarities similarities on on large large and and small small scales scales imply imply that that our similar pinch current understanding of the processes processes responsible responsible for for the the structure and and petrologic petrologic features features of of understanding of ridge magma chambers and and layered layered gabbro in ophiolites ophiolites can can be be used to explain the origin of similar features features in in layered rifts. The geometries similar layered intrusions intrusions in intracontinental intracontinental rifts. geometries of intrusions intrusions formed in dynamic or static magma chambers are related to spreading rates and continuity of static With fast, fast, continuous continuous spreading spreadingrates ratesititisis possible possibleto to produce produce layered layered gabbro gabbro at at aa spreading. With lateral scale of many kilometers from a relatively narrow, growing magma chamber which is never more than 1-2 km wide at any p.17,842). On the other any given time (e.g., Nicolas, Nicolas, 1996, p.17,842). hand, rates the the lateral lateral extent extent of layered hand, with with slow, slow, episodic episodic spreading spreading rates layered gabbro gabbro could could be restricted to the dimensions dimensions of the active active magma magma chambers. chambers. Thus Thus the the Sonju Sonju Lake Lakeintrusion, intrusion, with its sill-like could have have formed sill-like geometry geometry (Miller, (Miller, 1996), 1996), could formed in a static static magma magma chamber; chamber; whereas the Bald Eagle intrusion, with its funnel shape, could have formed in a more dynamic dynamic environment. environment. Part II. Part It.The Thefunnel-shaped funnel-shaped layering layering in in the theBald BaldEagle Eagleintrusion intrusioncontrasts contrastsremarkably remarkably with near-horizontallayering layeringofofthe the other other intrusions intrusionsinin the the Duluth Duluth Complex Complex and and in the near-horizontal the Oman Oman ophiolite. Unfortunately the current interpretations of the layering in ophiolites do not provide Unfortunately the current interpretations layering do provide 122 �readyexplanation explanation for for the the layering layering in in the the Bald Bald Eagle Eagle intrusion. intrusion. There aaready Thereisisananactive activedebate debateinin the literature literature concerning concerning the the processes processes that would would lead lead from from the the isotropic isotropic crystal crystal mushes mushes of the of active active ocean-ridge ocean-ridge magma magma chambers chambers to the the near-horizontal near-horizontal layering layering in gabbro gabbro of ofthe theocean ocean floorand andininophiolites ophiolites(Quick, (Quick,1993, 1993,and and Nicolas, Nicolas, 1996). 1996).In Inessence essenceQuick's Quick'sanalysis analysisimplies implies floor that the thelayering layeringand andthe theigneous igneouslamination laminationare arepost-crystallization post-crystallizationphenomena, phenomena,produced produced that whencrystal crystalmush mush isiscarried carried away away from from the the active activemagma magma chamber. chamber. IfIfthis thisidea ideaisisapplicable applicableto to when theDuluth Duluth Complex, Complex, the the Bald Bald Eagle Eagle intrusion intrusion could be aa frozen frozen active active chamber chamber thus thus far far not not the observed in in ophiolites. ophiolites. Layered Layered gabbro gabbro of ofadjacent adjacentSouth SouthKawishiwi Kawishiwiintrusion intrusioncould couldbe bethe the observed equivalent equivalentof oflayered layeredgabbro gabbroininophiolite ophioliteproduced producedduring duringspreading spreadingaway awayfrom fromaaridge ridgeaxis. axis. One One might might expect expect that thatthe thecryptic, cryptic,compositional compositionalvariations variations ofofcumulus cumulusminerals minerals formed formedininstatic staticchambers chambersmight mightdiffer differfrom fromthose thoseformed formedinindynamic dynamicchambers. chambers.AAsuggestion suggestion of ofsuch suchdifferences differencescan can be be seen seenin inFigure Figure1.1.All Allthree threedata datasets setslie lieon onaacommon commontrend. trend.Gabbro Gabbro inthe theOman Omanophiolite ophiolite and and rocks rocks in inthe theBald BaldEagle Eagleintrusion intrusion show show more more restricted restricted ranges ranges of of in differentiation than rocks in the Sonju Lake intrusion, and the Oman magma is the most differentiation than rocks Sonju intrusion, Oman magma is the most primitive. primitive. Additional Additional electron electronmicroprobe microprobe mineral mineral and and minorminor- and and tracetrace-element elementrock rockanalyses analyses ofthe theBald Bald Eagle Eagleintrusion intrusionare areplanned planned to toevaluate evaluatethe thesuggestion suggestionthat thatthe thechemical chemicalvariations variations of produced produced in in dynamic dynamic chambers chambers are are 100 100 definitively definitively distinct distinct from from those those L-..-.-.---L-.-..-----^---.....--i^<---.. . 90 jp. established establishedfor forstatic staticchambers. chambers.  + .ac ::80 ^n- ; - 1..-.....---- ---.--.....L--~-.~.---L-..-......L-------.-.~---------- -3 1 70 70 = 0, 0 5 " 3 - - - - -1 ; ; ; + +--+wt*^.+ Hi"++--?--.: ---------- ; L . -------..... - ------- -. Fig. Fig. 1.1.Mg/(Mg+Fe) Mgl(Mg+Fe) variation variationin inpyroxene pyroxeneand and olivine. All the data are electron microprobe olivine. All the data are electron microprobe ..--.-------------___t+ 50 analyses. analyses. Sonju SonjuLake Lakeintrusion intrusion(Miller, (Miller,1996); 1996); + Sonju Lakelnbusion Lake intrusion d.+f? - - - - - - - - - [ - - - - - - - - +SOOjU 40 --..-.40 points are averages Bald Eagle intrusion data Bald Eagle intrusion data points are averages ++ OBaldEagle Eaglelnfrusion Intrusion OBald So --------.---: ---------.; ----xman . - -ophiolite gabbro SIIISof ofover over200 200analyses analysesof ofrepresentative representativesamples samples I I 20 of oftroctolite, tructolite,olivine olivineand andoxide oxidegabbros; gabbros; Oman Oman 20 40 60 80 loo 40 20 0o ophiolite ophiolite—- data data from from gabbro gabbrosills sills(Korenaga, (Korenaga, fitom% %Mg!(Mg+Fe) Ma/(Mg+Fe)in in olivine olivine Pom 1997). 1997). , 60.-----------~----------p.++ --------~.---------~---------60  - ¥  ¥  ¥  I l D References: References:Barth, Barth,G. G.A., A ,and andJ.J.C.C.Mutter, Mutter,Variability Variabilityininoceanic oceaniccrustal crustalthickness thicknessand andstructure: structure:Multichannel Multichannel seismic resultsfrom fromthe thenorthern northernEast EastPacific Pacific Rise, J. Geophys. Res., 17,951-17,975, seismic reflection results Rise, J. Geophys. Res., 10101, 1 17,95 1 17-975,1996. 1996. Geli, Geli, L., L., and andV. V. Renard, Renard, Ocean Ocean crust crust formation formation process at very slow slow spreading spreading centers: centers: A A model model for for the the Mohns Mohns ridge, 2995-3013, 1994. basedon onmagnetic, magnetic,gravity, gravity,and andseismic seismicdata, data,J.J.Geophys. Geophys.Res., Res.,99, 99,2995-3013, 1994. ridge,near near72 72N, N,based Korenaga, Korenaga, J., J., and and P. P. B. B. Kelemen, Kelemen, Origin Origin of of gabbro gabbro sills sills in in the the Moho Moho transition transition zone zone of of the theOman Omanophiolite: ophiolite: Implications magma transport transportin in the the oceanic oceanic lower lower crust, cmst, J. Geophys. Res., 102,27,729-27,749, 102,27,729-27,749,1997. 1997. Implicationsfor formagma McKenzie, McKenzie, D., and and D. D. Fairhead, Fairhead, estimates estimates of of the the effective effective elastic elastic thickness thickness of of the the continental continental lithosphere lithosphere from from Bouguer 27,523-27,552, 1997. Bouguerand andfree freeair airgravity gravityanomalies, anomalies,J.J.Geophys. Geophys.Res., Res.,102, 102,27,523-27,552, 1997. Miller, Ripley, Layered LayeredIntrusions Intrusionsofofthe theDuluth DuluthComplex, Complex, Minnesota, USA, RG.Cawthorn Cahom Miller, J. J. D., and E. M. Ripley, Minnesota, USA, hi:In: RG. (ed) Layered Layered Intrusions, Intrusions,Elsevier ElsevierScience, Science,1996 1996 (ed.) Nicolas, crustalthickness thickness in inthe theOman Omanophiolite: ophiolite: Implication Implication for for Nicolas, A., A , F. F. Boudier, Boudier, and andB. B.ildefonse, Ildefonse,Variable Variable crustal oceaniccrust, Geophys. Res., Res., 101, 101,17,941-17,950, 17,941-17,950,1996. 1996. oceanic crust, J.J. Geophys. Quick, Quick, J.J. E., E., and and R. R P. P. Denlinger, Denlinger, Ductile Ductile deformation deformation and and the origin origin of layered layered gabbro gabbro in in ophiolites, ophiolites, J. Geophys. Geophys. Res., 98, 98, 14,015-14,027, 14,015-14,027,1993. 1993. Res., Rommevaux, study of of the theMid-Atlantic Mid-AtlanticRidge: Ridge:evolution evolution Ronunevaux,C., C., C. C. Deplus, Deplus, and andP. P. Patriat, Patriat,Three-dimensional Three-dimensional gravity gravity study of 3015-3029, 1994. of the thesegmentation segmentationbetween between 28° 28Oand and29°N 2g0Nduring duringthe thelast last10 10my, my, J.J.Geophys. Geophys.Res., Res., 99, 99,3015-3029,1994. Sinton, and R it S. 197-216, 1992. M yand S.Detrick, Detrick,Mid-ocean Mid-oceanridge ridgemagma magmachambers, chambers,J.J.Geophys. Geophys.Res., Res., 97, 97,197-216,1992. Sinton,J.J. IvL, Cochranand andG.G.A.ABarth, Barth,Gravity Gravityanomalies, anomalies,crustal crustalthickness, thickness,and andthe thepattern pattern of of mantle mantle flow flow at at Wane, X., J.J. itRCochran Wan& Res., the EastPacific PacificRise, Rise,9-10 9-10N: N:evidence evidencefor forthree-dimensional three-dimensionalupwelling, upwelling, J.J.Geophys. Geophys. Res., 101, 101, the fast fastspreading spreadingEast 17,927-17,940,1996. 1996. 17,927-17,940, Wright, D. J., Fomari, Wright, D. J., itR.MM.Haymon, Haymon,and andD.D.J. J. Fornari,Crustal Crustalfissuring fissuringand anditsitsrelationship relationship to tomagmatic magmatic and and hydrothermal processes on the East Pacific Rise crest (9°12' to 54'N), J. Geophys. Res., 100, 6097-6120, 1995. hydrothermal (9O12' to 5479, J. Geophys. Res., 100,6097-6120, 1995. - 123 �PRECISE PRECISE U-Pb U-Pb ZIRCON ZIRCON AGES AGES OF O F MIDCONTINENT RIFT RHYOLITE RHYOLITE (CHENGWATANA VOLCANICS), CLAM FALLS, WI CLAM FALLS, WI WIRTH, Karl Karl R., R.,Geology Geology Department, Department, Macalester Macalester College, College, St. St. Paul, Paul, MN MN55105, 55105, WIRTH, wirth@macalester.edu; E.,Department Departmentof ofGeosciences, Geosciences,UniUniwirth @macalester.edu;and and GEHRELS, GEHRELS,George, George,E., versity versity of of Arizona, Arizona, Tucson, Tucson, AZ 85721, 85721, gehrels@geo.arizona.edu. gehrels@geo.arizona.edu. Recent Recent studies studiesof of the the southwestern southwesternsegment segmentof of the the Keweenawan KeweenawanMidcontinent Midcontinentrift riftalong alongthe theSt. St. Croix River River have have focused focused on on the the structural structural (Leslie (Leslie et et al., al., 1994), 1994),paleomagnetic paleomagnetic(Kean (Keaneteta!., al., 1997), evolution of the poorly-exposed poorly-exposed Chengwatana 1997),and and magmatic magmatic (Wirth (Wirthet et al., 1997) 1997) evolution ChengwatanaVolcanics Volcanics (Minnesota (Minnesotaand and Wisconsin). Wisconsin). Comparison Comparisonof ofChengwatana ChengwatanaVolcanics Volcanicsfrom from this this segment segmentof of the the rift with the those of the better-studied portions of the rift in the Lake Superior region (e.g., the those of the better-studied Superior (e.g., Nicholson Nicholson et al., 1997) 1997) have have been been hindered hindered by the the lack lack of of well-constrained well-constrained ages for for the the Chengwatana ChengwatanaVolcanics. Volcanics. The Theonly onlyprevious previousgeochronologic geochronologicstudy studyof of these thesevolcanics volcanics(Zartman (Zartman et exposed in the Ashland syncline et al., al., 1997) 1997)resulted resulted in in an an age age of 1094.6 1094.6± zk 2.1 Ma for rhyolite exposed syncline in northern Wisconsin; rhyolite from drill core in Hudson-Afton Horst (SE of Minneapolis) in northern Wisconsin; rhyolite drill core in Hudson-Afton Horst (SE of Minneapolis) yielded yielded an an anomalously anomalouslyold old(1130 (1130Ma) Ma) age. age. Here Herewe wereport reportprecise preciseU-Pb U-Pbzircon zirconages ages(1102 (1102±k55 Ma) Ma) for for rhyolites rhyolitesexposed exposedin in the the lower lower part part of of the the volcanic volcanic section section along along the the Lake Lake Owen Owen Fault, Fault, which rhywhich bounds bounds the theeastern easternmargin marginof of the therift. rift. Petrographic Petrographic and and geochemical geochemical studies studies of of the the rhyolitic and basaltic flows of this segment of the rift are described by Abbott et al. and Naiman olitic basaltic flows segment Abbott Naiman et a!. al. (both this volume). volume). Rhyolite exposed one kilometer east of Clam Falls, WI contains phenocrysts of plagioplagioclase spherulitic groundmass of tabular tabular quartz quartz and and potassium potassium feldspar. feldspar. The clase and rare quartz quartz in a spherulitic The rhyolite is typically typically finefine- to to medium-grained medium-grained and massive massive (sample (sample KC-302a), but becomes becomes more coarse-grained coarse-grained near near its its base base (sample (sample KC-302d) KC-302d) and and contains containssubangular subangularclasts clastsof ofbasalt. basalt. Flow structures the large large rhyolites rhyolites of of structuresare are not apparent, apparent, but the rhyolites are otherwise similar to the the the North Shore Shore Volcanic Group. Rhyolite Rhyoliteis is rare rare in in this this portion portion of of the Midcontinent Midcontinentrift rift and and is is estimated estimated to to compose compose less less than than one one percent percent of the the exposed volcanic volcanic and and sedimentary sedimentary sections. sections. Zircons (1ength:width ratios ratios == 2:1 2: 1 to to Zircons from from both samples samples have have relatively simple simple prismatic (length:width 8:1) 8: 1) forms, forms, are are translucent, translucent, and and vary vary in in color color from from reddish-brown, reddish-brown, to to honey honey brown, brown, and andto to pale pale pink. Dark Darkgrains grainstypically typicallycontain containabundant abundant inclusions inclusions and were not selected selected for analysis. analysis. Analyses Analyses were were conducted conducted by conventional conventional isotope isotope dilution-thermal dilution-thermal ionization ionization mass mass spectromspectrometry, as described by Gehrels et al. a!. (1991). Six Six euhedral crystals (175-250 jim pm in length) from KC-302a analyzed as as individual individual grains. grains. Three KC-302awere were abraded abraded to to 75% 75% their original size and were analyzed Three ages of the grains grains yielded yielded concordant concordant ages ages with mean 2o6Pb*P38U 2 0 6 ~ b * / 2 3and and 8 ~2o7Pb*/2o6Pb* 207~b*/206~b* ages of 1102 1102 Ma; an uncertainty of k5 ±5 Ma Ma (2a) uncertainty of (20) is is assigned assigned to this age on the basis of the errors errors of the the individual individual determinations, determinations, rather than the error of the mean of the three concordant concordant analyses. analyses. Three Three additional additional grains grains are are slightly slightly discordant, presumably due to small amounts of lead loss. A discordia through these points, projected from from 1102Ma, Ma,yields yieldsaalower lowerintercept interceptofof196 196±205 5 205 A discordia Ma (MSWD (MSWD == 0.15). 0.15). Analyses of KC-302d were conducted on two multigrain fractions, one Ma unabraded unabraded single singlegrain, grain,and andfive fiveabraded abradedsingle singlegrains. grains.The Thesingle singlegrains grainswere wereallall—200 -200 .tm pminin length jim 125 pm length originally, originally, and and the the multigrain multigrainfractions fractionsconsisted consistedof: of:1)1)seven sevengrains grainsmeasuring measuring—125 in length, and 2) thirty grains —80 jim in 1enth. The three abraded grains are analytically 2) thirty grains -80 pm in length. The three abraded grains are analytically Ma k± 5 Ma. Ma. Three concordant concordant and yield mean mean 2o6Pb*/238U 2 0 6 ~ b * / 2 3and and 8 ~ZO7pb*/2O6pb* 2O7pb*/2O6pb*ages of 1101 Ma Three additional grains grains and and the the two two multigrain multigrain fractions fractions are are slightly slightly discordant; discordant;aa discordia discordiathrough through these ±217 217 Ma Ma (MSWD (MSWD==0.45). 0.45). these points, points, projected projectedfrom from 1101 1101Ma, Ma, yields a lower intercept of 63 k Given the uncertainties of ±5 Ma on each of the ages, the 1 Ma age difference between the two Given the uncertainties of k5 Ma on each 1 difference samples samples is is probably probably not not significant. significant. Analyses of the Chengwatana rhyolites near Clam Falls indicate indicate that magmatism magmatism began began by at least least 1102 1102 Ma in in this this portion portion of the rift, considerably considerably earlier than the age age reported reported by by Zartman et al. (1997) for rhyolite (1094.6 ± 2.1 Ma) exposed near the base of the Chengwatana Zartman et al. (1997) for rhyolite (1094.6 k base of the Chengwatana - 124 - I �U 0.190 0.186 00 en 0.182 0.178 Lower Intercept = Lower Intercept = 196 ±205 Ma (MS WD=0.15) I 0.174 1.82 1.90 I I 2.06 1.98 / 63±217Ma(MSWD=0.45) 1.82 1.90 1.98 2.06 207Pb / 235 u 207pb / 235 u section section in the southeastern limb of the Ashland syncline. This This implies implies that flows flows exposed exposed near near Clam Falls likely formed formed contemporaneously contemporaneously with the Upper Kallander Creek Volcanics and the Mellen Conglomerate of Mellen Complex Complex of of Northern Northern Wisconsin, Wisconsin, and the Group 5 flows and Great Conglomerate Mamainse Point. The Maage ageofofChengwatana ChengwatanaVolcanics Volcanics in in the the Clam ClamFalls Fallsregion region The1102 1102±Â55Ma implies implies that that the the Clam Clam Falls flows flows may have "reversed" paleomagnetic paleomagnetic directions directionssince sincethey they are are coeval with the time of the reverse-to-normal magnetic polarity change (1105-1100 Ma) that the time of the reverse-to-normal magnetic change (1 105-1100 has throughout the Lake Superior region. region. New aeromagnetic has been widely observed observed throughout aeromagnetic data data (USGS) (USGS) suggest Falls, MN, MN, are younger than suggest that Chengwatana Chengwatana Volcanic flows exposed near Taylors Falls, those those near Clam Clam Falls. Flows Flowsnear nearTaylors Taylors Falls Falls have predominantly "normal" paleomagnetic paleomagnetic directions (Kean et al., 1997) and are likely younger than the regionally documented reversedirections (Kean et al., 1997) and are likely younger than the regionally documentedreverseto-normal to-normal polarity polarity shift; shift;these theseflows flowsmay may be be correlative correlativewith with Portage PortageLake LakeVolcanics Volcanics (northern (northern WI) and Group Group 66 flows flows (Mamainse (Mamainse Point). A A few few Taylors Taylors Falls flows have "reversed" paleomagnetic directions (Kean reversal event that that is younger than the mean et al., 1997) 1997) and record a reversal regionally observed reverse-to-normal magnetic regionally observed reverse-to-normal magnetic Upper Mich Mich Michipicoten Is. Is. Minnesota Minnesota polarity change. NW Wisconsin NW Wisc Wisc Mamainse Mamainse Point Point polarity change. ' References Cited Cited Gehrels, G.E., W.C., Samson, Samson, S.D., and G.E., McClelland, McClelland, W.C., Patchett, SciPatchett, P.J., P.J., 1991, Canadian Journal of Earth Sciences, p. 1285-1300. 1285-1300. ences, v. 28, P. Green, J.C. and and Fitz, Fitz, T.J., T.J., 1993, 1993, Journal Journalof ofVolcanology Volcanology and Geothermal 177-196. Geothermal Research, Research, v. 54, p. 177-196. Kean, W.F., W.F., Williams, I., Chan, L., and and Feeney, Feeney, J., J., 1997, 1997, Geophysical Geophysical Research Research Letters, Letters, v. 24, p. 1523-1526. 1523-1526. Leslie, M., Wetzel, Wetzel, T., Wirth, K.R., and and Craddock, Craddock,J.P., J.P., 1994, 40thAnnual Meeting 1994,40thAnnual Meeting of of the the Institute Institute on on Lake Lake Superior Houghton, MI, May 11-14, 11-14, Part Superior Geology, Houghton, II -- Program Abstracts, v. 40, p. 35-36. Program with Abstracts, 35-36. Miller, J.D., Nicholson, Nicholson, S.W., S.W., and and Cannon, Cannon,W.F., W.F., 1995, 1995, Minnesota MinnesotaGeological GeologicalSurvey SurveyGuidebook GuidebookSeries, Series,p.p. 1-22. 1-22. Nicholson, Nicholson, S.W., S.W., Shirey, S.B., S.B., Schulz, K.J., Green, Green, J.C., J.C., 1997, Canadian Journal Journal of Earth Earth Sciences, Sciences,v.v. 34, 34, p. p. 504-520. 504-520. Wirth, K.R., Vervoort, J.D., J.D., Naiman, Z.J., Z.J., 1997, Canadian Canadian Journal of Earth Sciences, Sciences, v. 34, no. 4, p. 536-548. Zartman, Zartman, R.E., Nicholson, Nicholson,S.W., S.W., Cannon, Cannon,W.F., W.F., and Morey, G.B., 1997, 1997, Canadian Canadian Journal Journal of of Earth EarthSciences, Sciences,v.v. 34, p. p. 549-561. 549-561. 125 � https://digitalcollections.lakeheadu.ca/files/original/ef817c5c00f1dd4aa45ca2f7d4b1ff20.pdf e9633852122cc432ccfd00cdfe5f1152 PDF Text Text Minneapolis, Minnesota May 6-10,1998 Organized by MINNESOTA GEOLOGICAL SURVEY OF MINNESOTA UNIVERSITY �44th 44th Annual AnnualMeeting Meeting INSTITUTE ON GEOLOGY INSTITUTE ONLAKE LAKESUPERIOR SUPERIOR GEOLOGY Volume Volume44 44 contains contains the the following followingparts: parts: Part1: 1:Program Programand andAbstracts Abstracts Part 2: Field FieldTrip TripGuidebook Guidebook Part2: Part 1—Early 1-Early Proterozoic Proterozoic intrusive intrusiverocks rocks of of east-central east-centralMinnesota Minnesota 2—Geology 2ÑGeolog of of the the southeastern southeasternportion portionof of the theMidcontinent MidcontinentRift Rift System, stern,eastern easternMinnesota Minnesotaand andwestern westernWisconsin Wisconsin 3—Glacial 3-Glacial exotica exoticaof of the theTwin TwinCities Citiesarea area 4—Stratigraphy &Stratigraphy and andhydrogeology hydrogeologyofofPaleozoic Paleozoicrbcks rocksof of southeastern southeastern Minnesota Minnesota 5—Minnesota 5-Minnesota River River Valley Valley and vicinity, southwestern southwesternMinnesota Minnesota Reference Referenceto to the thematerial materialin inthis thisvolume volumeshould shouldfollow followthe theexample examplebelow: below: Sims, Sims,P.K., P.K., Neymark, Neymark,L.A., L.A., Peterman, Peterman,Z.E., Z.E., and andKotov, Kotov,A.B., A.B., 1998, 1998, Nd isotope isotope evidence evidence for forMiddle Middleand andEarly EarlyArchean Archeancrust crustin inthe theWawa Wawasubprovince subprovinceof of the the Superior SuperiorProvince, Province, Michigan, 44th Michigan,U.S.A., U.S.A., [abstract]: [abstract]:Institute Institute on onLake Lake Superior SuperiorGeology GeologyProceedings, Proceedings,44th Annual MN, AnnualMeeting, Meeting,Minneapolis, Minneapolis, MN,1998; 1998;v.v.44, 44,Part Part1,1,p.p.10-11. 10-11. Volume Volume44 44 is is published publishedby by the the Institute Instituteon onLake LakeSuperior SuperiorGeology Geologyand and distributed distributedby bythe theInstitute InstituteSecretary-Treasurer: Secretary-Treasurer: MarkJirsa Jirsa Mark MinnesotaGeological Geological Survey Survey Minnesota 2642 University University Avenue Avenue 2642 MNUSA USA55114-1057 55114-1057 St.Paul, Paul,MN St. (612)-627-4780 (612)-627-4780 email:jirsa001@tc.umn.edu jirsaOOl@tc.urnn.edu email: /www.geo.mtu.edu/great_lakes great-lakes /ilsg /ilsg // ILSG website http: // /www.geo.mtu.edu/ ILSG website http: ISSN ISSN1042-9964 1042-9964 �INSTITUTE ON LAKE SUPERIOR GEOLOGY 44th 4th Annual Meeting May 6-10, 1998 Minneapolis, Minnesota Sponsored by: Sponsored by: Minnesota Minnesota Geological Survey University University of Minnesota Minnesota Field Trip Guidebook Volume 44 Volume 44 2—FieldTrip Trip Guidebook Guidebook Part 2-Field EDITORS: EDITORS: Terrence J. J. Boerboom Boerboom and and Barbara A. Lusardi Lusardi Terrence Minnesota Minnesota Geological Geological Survey Survey �PROCEEDINGS VOLUME 44, 44, PART 2—FIELD %FIELD TRIPS CONTENTS CONTENTS 1: Early EarlyProterozoic ProterozoicIntrusive IntrusiveRocks Rocks of of East-Central Minnesota Trip 1: Introduction Field Trip Stops 3 18 Leaders Terry Boerboom, Boerboom, Minnesota Minnesota Geological Survey Mark Jirsa, Minnesota Minnesota Geological Geological Survey Daniel K. Hoim, Holm, Kent State State University Trip Trip 2: The TheGeology Geologyof of the the Southeastern Southeastern Portion Portionof of the the Midcontinent MidcontinentRift Rift System, System, Eastern Eastern Minnesota Minnesota and andWestern WesternWisconsin Wisconsin Introduction .................................................................................................. 33 Introduction.. 33 44 Field Trip Stops Stops............................................................................................. 44 Leaders: Karl Wirth, Wirth, Macalester Macalester College College William S. Cordua, Cordua, University University of of Wisconsin-River Wisconsin-River Falls Falls William F. Kean, Kean, University University of of Wisconsin-Milwaukee Wisconsin-Milwaukee Mike Middleton, Middleton, University of Wisconsin-River Falls Zachary J. Naiman, University of Arizona Trip 3: Glacial Trip GlacialExotica Exoticaof of the the Twin Twin Cities Introduction Field Trip Stops Leaders: Howard Hobbs, Hobbs, Minnesota Minnesota Geological Geological Survey Survey Alan Knaeble, Minnesota Minnesota Geological Geological Survey Survey Minnesota Geological Survey Gary Meyer, Minnesota 79 82 Trip 4: 4: Stratigraphy Stratigraphyand andHydrogeology HydrogeologyofofPaleozoic PaleozoicRocks Rocks of of Southeastern Southeastern Minnesota Minnesota Trip Introduction Field Trip Stops 103 113 Leaders: Anthony C. C. Runkel, Runkel, Minnesota Minnesota Geological Geological Survey Robert G. Tipping, Minnesota Geological Robert G. Tipping, Minnesota GeologicalSurvey Survey Trip Trip 5: 5: Archean Archeanand andQuaternary QuaternaryGeology Geologyofofthe theMinnesota MinnesotaRiver RiverValley Valley Introduction to Precambrian Geology 133 Geology.......................................................... 133 Field Trip 137 Trip Stops, Stops, Day Day 11................................................................................ 137 Introduction 148 Introduction to to Quaternary Quaternary Geology Geology............................................................ 148 Field Trip Stops, Day 2 154 Stops, ................................................................................ 154 Leaders: D. L. Southwick, Southwick, Minnesota Minnesota Geological Survey Carrie J. Patterson, Minnesota Minnesota Geological Geological Survey Survey ��FIELD FIELD TRIP TRIP#1 #1 EARLY PROTEROZOIC PROTEROZOIC INTRUSIVE INTRUSIVE ROCKS ROCKS OF OF EAST-CENTRAL EAST-CENTRALMINNESOTA Leaders: Terry Boerboom, Mark Mark Jirsa, Jirsa, and Leaders: and Daniel Hoim Holm INTRODUCTION rocks of the St. Cloud District The Early Proterozoic (Paleoproterozoic) granitoid rocks District in in east-central east-central Minnesota Minnesota(Fig. (Fig.1) 1)have have long long been been aa source source of both building building materials materials and and geologic geologic controversy. Quarrying Quarrying for for dimension dimension stone stone began in the St. Cloud District in the late 1800's 1800's 1930-1940, were some some 18 different differentquarry quarrycompanies companies operating operating and peaked at about 19301940, when there were in the district (Thiel (Thiel and Dutton, 1935). 1935). Currently, Currently, Cold Cold Spring Spring Granite Granite is is the the only only dimension dimension operating, with 5 active quarries stone company operating, quarries here, and and 4 others others in different different parts parts of of the the state. state. Meridian Aggregates Company also operates a large crushed-stone operation in the St. Cloud Cloud TheSt. St.Cloud Cloudarea areacontains containsabundant abundant active active and inactive quarries, as well as natural District. The outcrops. Despite Despitethese theseexposures, exposures,many many of of the the critical critical relationships relationships between various intrusive units are concealed—leaving concealed-leaving details of the magmatic history unknown and speculative. Until Until recently, geologic geologic maps reconnaissance-style (Morey recently, maps of the district were reconnaissance-style (Morey and and others, others, 1981), 1981),and and little geochronologic work had had been been conducted. conducted. This This field field trip highlights the results of more current and thorough thorough mapping mapping endeavors endeavors that utilized quarry and natural exposures, drill core, These include include the the Stearns Steams County Geologic Atlas (Boerboom and geophysical interpretation. These and others, 1995; 1995; Boerboom, Boerboom, 1996a), 1996a),and and mapping mapping north north and east of St. Cloud (Jirsa and others, 1995a; 1995b; Jirsa and Chandler, 1997). In In addition, addition,we we review review both pre-existing pre-existing and and newly newly acquired geochronologic data (e.g., Hoim Holm 1997, 1997, 1998) 1998) in light of the field, field, petrographic, petrographic, and and geophysical observations. observations. Intrusions Intrusions of the the St. St. Cloud Cloud District District were were emplaced emplaced relatively relatively late late in in development developmentof of the the Penokean orogen—a Penokean orogen-a belt belt of of Early Early Proterozoic Proterozoic volcanic, volcanic, sedimentary, sedimentary,and and plutonic plutonic rocks rocks affected affected the Penokean Penokean orogeny, orogeny, which which culminated culminated at approximately approximately 1870 Ma (Van (Van Schmus and by the 1981). Rocks Rocksofofthe theorogen orogenare aredivided dividedfrom fromnorth north to to south south(Fig. (Fig. 1) 1)into intoaavariably variably Bickford, 1981). deformed foreland basin; a fold and thrust belt; and what what has has been been inferred inferred to to be be an accreted broadly equivalent to the Wisconsin Wisconsin magmatic magmatic terranes terranes (Jirsa (Jirsa and others, island-arc terrane, broadly 1995b, Boerboom, 1996b). All All of of these these terranes terranes were were deposited deposited upon or or accreted accreted against against the the southern margin of the Archean Superior Province. Province. Using Using the terminology of Southwick Southwick and into distinct distinct segments on on the the basis basis of of others (1988), (1988), the fold fold and thrust belt is further subdivided into of the Animikie Group and lithologic and structural attributes: 1) an external zone comprised of related outliers; 2) a medial medial zone zone characterized characterized by fault slices of interlayered interlayered volcanic and related clastic including the Cuyuna north internal zone, zone, clastic strata including north and south (iron) ranges; ranges; and 3) an internal containing fault-bounded fault-bounded blocks blocks of of various metamorphic and and plutonic plutonic rocks. rocks. The The Early Proterozoic Proterozoic granitoid granitoid rocks rocks of the St. Cloud District occur within the internal zone of the western Penokean orogen, where they form a physically continuous mass of lateand post-orogenic post-orogenic intrusions. intrusions. They Theyrepresent represent some some of the most deeply emplaced magmas of the 3 �orogenicbelt. belt. Regionally, Regionally, the the Early Early Proterozoic Proterozoic supracrustal supracrustalcountry country rocks—including rocks-including the the orogenic Little Falls Formation to the north and west, and unnamed volcanic and clastic strata to the east Little Falls Formation to the north and west, and unnamed volcanic and clastic strata to the east andsoutheast—were southeast-were metamorphosed metamorphosedatatdepths depthsofof22-25 22-25km krnduring duringthe the Penokean Penokeanorogeny orogeny(Holm (Holm and andSelverstone, Selverstone,1990). 1990).Reconstruction ReconstructionofofP-T-t P-T-thistories historiesindicate indicatethat thatthe therocks rocks currently currentlyexposed exposed and remained at those depths until well after the orogeny, then were rapidly exhumed at about 1770 remained at those depths until well after the orogeny, then were rapidly exhumed at about 1770 Ma during during emplacement emplacement of of post-tectonic post-tectonic magmas magmas (Hoim (Holm and and others, others, 1998). 1998). The Thesignificant significant Ma depth of emplacement and the great volume of igneous rock provide an excellent opportunity to depth of emplacement and the great volume of igneous rock provide an excellent opportunity to midcrustal magmatic magmatic processes processes that that occurred occurred immediately immediately after after the the orogenic orogenic belt belt investigate midcrustal investigate was constructed, constructed,and andlater lateras asthe theorogen orogencollapsed. collapsed. was 950 940 930 92° b IIArchean Archean (A) (A) I I 1 Superior Province 47O 46' sland arc rocks (Equivalent to Wisconsin agma 45O thePenokean Penokeanorogen, orogen,showing showingmajor major Figu 1. Simplified geologic map of)fthe Figure tectcLLL.w.-iLLuLLLo. bciLbuuaL-Lbb~nic Penokeanintrusions intrusionsshown shownininblack. black. tectonic elements. LatetoLu post-tectonic Penokean GEOLOGYOF OFINTRUSIVE INTRUSIVEROCKS ROCKS GEOLOGY Intrusionsof ofthe theSt. St.Cloud CloudDistrict District(Fig. (Fig.2) 2)are arecomprised comprisedof of several several discrete discrete units units that that Intrusions includethe theReformatory Reformatorygranodiorite, granodiorite,the thecharnockitic charnockiticRichmond Richmondgranite, granite,the theRockville RockvilleGranite, Granite, include the St. St.Cloud CloudGranite, Granite,the theFoley Foleybatholith, batholith,and andseveral several types types of of granitic graniticand anddiabasic diabasicdikes. dikes. the Only untry rocks are recognized within the intrusions, Only scattered xenoliths of metamorphic country rocks are recognized within the intrusions, 4 �but numerous numerous mafic maficenclaves enclavesinterpreted interpretedto to be be comagmatic comagmaticwith withthe theenclosing enclosing granitoid granitoidrocks rocks but are present in some units. The intrusions can be divided on the basis of composition and relative are present in some units. The intrusions can be divided on the basis of composition and relative 1) gray gray to to pinkish-gray pinkish-gray to to greenish greenish gray gray granitic, granitic, temporal setting setting into into three three categories: categories: 1) temporal granodioritic,and and dioritic dioriticrocks—Reformatory rocks-Reformatory granodiorite, granodiorite,Richmond Rchmond granite, granite,and and Rockville Rockville granodioritic, Granite; 2) red and pink granitic intrusions-St. Cloud Granite, Foley batholith, and associated Granite; 2) red and pink granitic intrusions—St. Cloud Granite, Foley batholith, and associated aplite; and and 3) 3) diabasic diabasic and and porphyritic porphyritic microgranite microgranite dikes. Colorisis not not always always an an adequate adequate aplite; dikes. Color distinguishing characteristic between various intrusions because components of the "gray" distinguishing characteristic between various intrusions because components of the "gray" intrusionscan canbe be quite quite pink. pink. Other Otherattributes attributesthat that distinguish distinguish "gray" "gray" from from"red" "red" varieties varietiesinclude include intrusions the observation observationthat that "gray" "gray" intrusions intrusionscontain containmafic maficenclaves, enclaves,and andhave have aa better better developed developedand and the more pervasive magmatic foliation than do the "red" ones. These differing attributes have more pervasive magmatic foliation than do the "red" ones. These differing attributes have A description description importantimplications implicationsabout about the the magmatic magmatic history history that that will will be important be discussed discussed below. below. A of individual individualplutonic plutonic units unitsfollows. follows. of EARLYVPROTEROZOIC PARI PRCTFPfl7flI ', NW-striking diabase dike ..NW-strikingdiabasedike Maficto toultramafic ultramaficintrusions intrusions Mafic D St.Cloud CloudGranite Granite St. Foleybatholith batholith Foley RockvilleGranite Granite Rockville Richmondgranite granite Richmond Reformatotygranodionte granodiorite Reformatory Gabbroicintrusions intrusions Gabbroic = 0 Granite,undivided undivided Granite, AnimikieGroup Group(slate) (slate) Animikie \ LittleFalls FallsFormation Formation Little (garnet-stauroliteschist) schist) (gamet-staurolite Volcanicand andclastic clasticrocks, rocks, Volcanic iron-formation; largely large1 of of iron-formation; Mille Lacs Lacs Group, Group, undivided unchided Mule Strike- or or dipdipStrikeslip fault. slip fault. Thrustfault. fault. Thrust El ARCHEAN ARCHEAN Sartell Gneiss(may (maybe beEarly Early Sartell Gneiss Proterozoicininpart) part) Proterozoic 'NS Lithologic Lithologic contact. contact. 0 Gneissterrane terrane 0Gneiss Figure 2. 2. An An extremely extremely busy busy and and largely largely illegible illegibleregional regional geologic geologic map map of of the the Figure area around Steams County (outlined). Inset map references location within area around Steams County (outlined). Inset map references location within 1). Penokeanorogen orogen(Fig. (Fig.1). Penokean 55 �Reformatory Reformatory granodiorite granodiorite Reformatory granodiorite granodiorite (Reformatory (Reformatory Granite 1978) is presently presently The Reformatory Granite of Morey, 1978) (trade name Charcoal Granite), just city of of St. St. extracted from only one quarry (trade just south of the city Cloud. However, However,there thereare aredozens dozensof of inactive inactive pits pits from from which which this this rock rock has been quarried quarried in the the Cloud. past, including those that supplied stone to the the unit's unit's namesake-the namesake—the State State Reformatory! Reformatory! The rock is mediummedium- to dark-gray, mediummedium- to to coarse-grained, coarse-grained, weakly wealdyporphyritic porphyriticbiotite-hornblende biotite-hornblende granodiorite characterized by small small tabular tabular plagioclase plagioclase phenocrysts (oligoclase to andesine; andesine; Johnson, Johnson, 1978) 1978)in in aa groundmass groundmassof of plagioclase, plagioclase, microcline, microcline, homblende, hornblende, biotite, biotite, and and accessory accessory pyroxene, pyroxene, sphene, and apatite. apatite. AAweak, weak,generally generally subhorizontal subhorizontal trachytoid trachytoid fabric in the the granodiorite granodioritecan canbe be observed observed in in many places. Small Smallovoid ovoid mafic enclaves are scattered throughout the the intrusion. intrusion. Richmond granite granite The charnockitic Richmond granite is well exposed between the towns of Richmond and Cold Spring, but has never been significantly exploited as as a dimension stone. Although Although generally generallydark dark greenish-pink, greenish-pink,ititlocally locallyretains retainsaa unique unique deep deep green green color color where where the rock has not been been subjected subjectedto to oxidation oxidationalong alongtight tight brittle brittle fractures. fractures. The Thegranite granitedisplays displaysaa prominent prominentrapakivi rapakivi 2-6 cmlong longK-feldspar K-feldsparmegacrysts, megacrysts,as as well well as as a consistent texture defined defined by plagioclase-mantled, texture plagioclase-mantled, 2-6cm consistent Hypersthene, redeast-northeast magmatic trachytoid fabric defined by by aligned aligned phenocrysts. phenocrysts. Hypersthene, brown biotite, and and green green homblende hornblende are are the the dominant dominant mafic mafic minerals; minerals; apatite, apatite, ilmenite, ilmenite, and and zircon mafic minerals. minerals. Quartz zircon form form abundant abundant accessory accessoryphases phases concentrated concentrated with the late-formed mafic Quartz typically occurs occurs as as more-or-less more-or-less equant, equant, but anhedral-interstitial, anhedral-interstitial,monocrystalline monocrystalline clots clots as as large large typically as 11 cm. cm. Although Althoughelongate elongategrains grainsofofquartz quartzoccur occurin inlocalized, localized,meter-scale meter-scale shear shear bands, bands, the the of the the intrusion intrusion contains contains aawell-developed well-developed magmatic magmatic foliation foliation and no evidence evidence of bulk of metamorphic recrystallization. recrystallization. Scattered Scatteredoutcrops outcropsand and geophysical geophysical maps (Fig. 3) indicate that metamorphic the Richmond charnockitic intrusion intrusion Richmond granite may be be one one component component of of aa large large composite composite charnockitic composed largely of gabbroic and noritic intrusive rocks. composed largely of gabbroic and noritic intrusive Rockville Granite Granite The Rockville Rockville Granite is presently presently taken from from three separate separate quarries and marketed marketed under under the the trade trade names namesof ofDiamond DiamondPink, Pink,Rockville RockvilleBeige, Beige,and andRockville RockvilleWhite. White. It is is aa very very coarse-grained, coarse-grained, pinkish- to grayish-white grayish-white rapakivi granite characterized characterized by zoned 1-3 1-3 cm cm microcline microcline phenocrysts phenocrysts and and smaller smaller plagioclase (oligoclase; Johnson, Johnson, 1978) 1978)phenocrysts phenocrysts in in aa groundmass groundmass of of coarse coarsequartz, quartz,feldspar, feldspar, biotite, biotite, and and hornblende, hornblende, with with accessory accessoryzircon, zircon,apatite, apatite, sphene, epidote, and allanite. The Rockville locally shows a weak trachytoid fabric, defined sphene, epidote, and allanite. The Rockville locally shows a trachytoid fabric, defined by aligned generally N-S N-S and and dips dips variably variablyto to the the west. west. This aligned feldspar phenocrysts, that strikes generally This granite granite contains containsscattered scatteredenclaves enclavesthat that vary vary from from coarse-grained coarse-grainedblack black diorite, diorite, to to fine-grained, fine-grained, gray gray quartz quartz monzonite; monzonite; both both having having abundant abundant homblende hornblende and biotite. The Thedioritic dioriticenclaves enclaves commonly commonlycontain containmicrocline microclinephenocrysts phenocrystsor orxenocrysts; xenocrysts;whereas whereasthe the monzonitic monzoniticones ones contain contain scattered microcline, scatteredplagioclase plagioclasephenocrysts phenocrystsin in aa pristine pristine igneous-textured, igneous-textured, trachytoid trachytoid matrix matrix of microcline, quartz, biotite, and homblende. hornblende. Dikes Dikes5-30 5-30cm cmwide wideof of rock rocklike likethe thecoarse-grained coarse-grained dioritic dioritic phase phaselocally locallycut cut the the Rockville RockvilleGranite. Granite. These Thesetwo twoconflicting conflictingoccurrences occurrencesof of the the coarse-grained coarse-grained diorite (as both rphenocrysts' in in the thecoarsecoarseboth enclaves enclaves and and dikes), dikes), the the presence presence of of microcline microcline 'phenocrysts' grained grained enclaves, enclaves, the pristine pristine trachytoid trachytoid igneous texture of the finer grained enclaves, and the rapakivi mafk and and felsic felsic magmas magmas during during rapakivi texture, texture, all all imply imply an an origin origin by by the the commingling comminglingof of mafic magma magma ascent ascent(see (seeDISCUSSION). DISCUSSION). 66 �Figure anomaly map of Stearns Figure 3. 3. First vertical derivative, derivative, reduced to pole aeromagnetic anomaly S t e m s County (white dashed line, also also see Figure 2) and the fringing area. Outlines Outlinesonly only shown shown for for rock rock units units discussed discussed in in text. text. St. Cloud Granite Granite The The St. St. Cloud Cloud Granite Granite occurs occurs as as aa zone of variably wide dikes and sills that permeated into the Reformatory Reformatory granodiorite, granodiorite,resulting resulting in a complex geometry not easily depicted at small into map map scales. scales.At Atlarger largerscale, scale,dikes dikesof ofSt. St.Cloud CloudGranite Graniteare are irregular irregular in in shape, shape, and and contacts contacts most most commonly trend trend to to the the north north and and northeast. Small Smalldikes dikesand and irregular irregular pods pods of of pink pink aplite aplite that that commonly are associated associated with with the the St. St. Cloud CloudGranite Granite also also cut cut Reformatory Reformatory granodiorite. granodiorite. The St. extensively in in the the past, past, but but no no longer. longer. It is a St. Cloud Cloud Granite has been quarried extensively coarse-grained, coarse-grained,deep-colored, deep-colored,grayish-pink grayish-pinkto tored, red, hornblende hornblendegranite granite having having a weak porphyritic texture texture defined defined by by pink pink microcline microcline phenocrysts phenocrysts only slightly larger than the matrix. The Themain main 19781, quartz, hornblende, microcline, plagioclase (albite to oligoclase; minerals are microcline, oligoclase; Johnson, 1978), and biotite, apatite, zircon, zircon, sphene, sphene, and and rare rare epidote. epidote. Using biotite, with with accessory accessory Fe-Ti oxides, apatite, Using Maitre (1979), (19791, the the St. St. Cloud Cloud varies varies in in modal modalmineralogy mineralogy Streckeisen and and Le Le Maitre terminology of Streckeisen from alkali-feldspar (Fig. 4). 4). A alkali-feldspar granite to syenogranite (Fig. A vague vague trachytoid trachytoid fabric fabric defined defined by by aligned feldspar and hornblende crystals is common and is parallel to the margins of the dikes aligned feldspar and hornblende crystals is common and is parallel to the margins of the dikes and and sills sills in in which which the the St. St. Cloud Cloud Granite Granite occurs. Narrow Narrowdikes dikesof of pink pink aplitic apliticgranite granitelocally locallycut cut the St. St. Cloud Cloud and and Reformatory, Reformatory, and and are are inferred inferred to to be be late late differentiates differentiatesof of the the St. St.Cloud Cloudon onthe the the basis of of lithologic lithologic similarity. similarity. Coarse Coarsepegmatite pegmatiteis is exceedingly exceedingly (and (and conspicuously) rare. The The St. St. Cloud Cloud commonly commonlycontains containsangular angularxenoliths xenoliths of of Reformatory Reformatorygranodiorite, granodiorite,along alongwith withrare rare xenoliths xenoliths of of metamorphic metamorphiccountry countryrock. rock. 77 �Foley batholith batholith Foley The salmon-colored, coarse-grained, coarse-grained, hornblende-biotite homblende-biotite granite TheFoley Foley batholith batholith is is a red to salmon-colored, granite that that is is cut cut by by minor minoramounts amountsof ofgranitic graniticporphyry porphyry and andaplite—similar aplite-similar in in nearly nearly all allrespects respectsto to the km),ovoid ovoidgravity gravitylow lowthat thatextends extendsfrom fromthe the the St. St. Cloud Cloud Granite. Granite. ItItforms formsaalarge large(60 (60xx20 20km), east east side sideof of St. St.Cloud, Cloud, northeastward northeastward to to near Mule Mille Lacs Lake (Jirsa and Chandler, 1997). The The batholith batholith is is moderately moderately well well exposed exposed along along its its western western terminus, terminus, where where its its intrusive intrusive contact contact against againstReformatory Reformatorygranodiorite granodioritecan canbe beseen, seen,and andin inseveral severalplaces placeseast eastof ofthe themap maparea areashown shown on on Fig. Fig. 2. 2. Small Smallquarries quarriesininthe thewestern westernpart partofofthe theunit unitoperated operatedduring duringthe theperiod period1896-1909. 1896-1909. The The Foley Foley isismassive massiveto tovaguely vaguelyfoliated, foliated,having havingaapoorly poorlydeveloped developedand andlocalized localizedtrachytoid trachytoid fabric. fabric. Although Althoughititwill willnot notbe bevisited visitedduring duringthis thisfield fieldtrip, trip,the theFoley Foleyisis described describedhere herebecause because itit isisaalarge largeand anddistinctive distinctiveunit unitthat thatappears appearsto tobe bemagmatically magmatically related related (parental?) (parental?) to to the the St. St. Cloud Granite. Granite. Cloud Porphyritic (AKAQFP) QFP)dikes dikes Porphyriticmicrogranite microgranite(AKA Thin Thin northeast-trending northeast-trendingdikes dikesof of distinctively distinctively textured porphyritic porphyritic microgranite microgranite cut cut the Reformatory Foley batholith. batholith. None of Reformatory granodiorite, granodiorite, Rockville RockvilleGranite, Granite, St. St. Cloud Granite, and Foley these these dikes dikes were were noted noted in in the the Richmond Richmond granite, granite, but but they they would would logically logically post-date that unit. unit. Most 2-4 m m wide, wide, but but one one is is at at least least 30 30 m wide, and and another another may may be as as much much Most of of these these dikes dikesare are 2-4 as as 100 100m m wide, wide, although although correlation correlation of of the the latter latter with this dike set is tenuous. The Themargins marginsof of these dikes dikes are are chilled chilled and and locally locally flow-banded, flow-banded, texturally similar to volcanic rhyolite. The The porphyries porphyries are are characterized characterized by by 3-10 3-10 percent percent quartz quartz phenocrysts as large as 4 mm across across that have primary euhedral have aa primary euhedralshape shapemodified modified by by resorption, resorption,and and 3-10 3-10 percent percent microperthite microperthiteor or sanidine sanidine phenocrysts phenocrysts as as large large as as 10 10mm. mm. The Thefine-grained fine-grainedgroundmass groundmassvaries variesin intexture texturefrom fromanhedralanhedralgranular to spherulitic. spherulitic. InInaddition additiontotothe themain mainquartz quartzand andfeldspar, feldspar,the the rock rock contains contains minor minor amounts of of fine-grained fine-grained biotite, biotite, homblende, hornblende, actinolite, actinolite, and and chlorite, chlorite, and and accessory accessory fluorite, fluorite, apatite, apatite, Fe-Ti Fe-Ti oxides, oxides, epidote, epidote, sphene, sphene, zircon, zircon, and and allanite. allanite. Diabase dikes dikes Diabase There There are are two two main main groups groupsof of diabase diabase dikes dikes recognized recognized in in the the area: a northeast-trending northeast-trending set, and a northwest-trending northwest-trending set. Both Both sets setsare are steeply steeply dipping dipping and are interpreted to be the youngest rocks in the St. youngest Precambrian rocks St. Cloud Cloud area, area, as as they they cut cut nearly nearly all all other other rock rock types. types. Northeast-trending Northeast-trendingdiabase diabasedikes dikesare aretypically typically non-magnetic non-magnetic and andlack lackgeophysical geophysicalexpression, expression, but throughout the area. They but are are exposed exposedin in several several outcrops outcropsand and old old quarries quarries throughout They are are most most commonly commonly 1-3 m thick, but some m,and anddike dikemargins margins are aresharply sharplychilled chilled against against the the some are are as as wide wide as as 88m, neighboring metamorphism neighboringgranitic graniticrocks. rocks. These Thesedikes dikescontain containfresh fresh plagioclase, plagioclase, but low-grade metamorphism or actinolite, chlorite, or deuteric deuteric alteration alteration(?) (?)has has altered alteredthe the primary primary mafic minerals minerals to actinolite, chlorite, and and dusty dusty oxides. oxides. Northwest-trending Northwest-trendingdiabase diabasedikes dikesare arerarely rarely exposed, exposed,but are are inferred inferred from geophysical geophysical data 100m wide. They They are are geophysically geophysicallytraceable traceableby by their their distinctive, distinctive,generally generally data to to be be as as much much as as 100 reversely polarized, aeromagnetic signature (Fig. (Fig. 3). 3). One exposed northwest dike (Fig. F6 of One exposed stop descriptions) has has sharply sharply chilled chilled margins, margins, and and compared compared to to the the northeast-trending northeast-trendingset setisis strongly magnetic magnetic (pyhrrotitic) (pyhrrotitic) and and is is less less altered/metamorphosed, alteredmetamorphosed, having having substantially substantiallymore more fresh clinopyroxene. This Thisdike dikeisisnormally normally polarized polarized and and only 6 meters thick—attributes thick-attributes that contrast somewhat somewhat with the the geophysically-defined geophysically-defined northwest northwest swarm, making correlation correlation 8 �uncertain. Another Anothersmall smalloutcrop outcropof of apatitic apatiticferrodiorite, ferrodiorite,in in northwestern northwestern Stearns Steams County, County, lies over one of the reverse-dike reverse-dike anomalies and is probably part of this swarm, swam, but no no magnetic magnetic polarity tests have been performed. performed. GEOCHEMISTRY A standard standard alkali-silica alkali-silica chemical chemical classification classificationplot characterizes characterizesthe the granitoid granitoidrocks rocksas as subalkaline to alkaline composition. As As shown shown in in Figure Figure 4, 4, both both the the St. St. Cloud Cloud and and Rockville Rockville alkalic Granites plot as subalkalic subalkalic using the dividing line of Irvine and Baragar (1971), but as alkalic Miyashiro (1978). (1978). This alkalic tendency reflects the perthite-dominated perthite-dominated using the dividing line of Miyashiro mineralogy of the St. Cloud Granite. In In addition, addition, the all the granitoid rocks in Stearns Steams County are peraluminous, and I-type, I-type, consistent consistent with with the abundance of biotite peraluminous, calc-alkaline, calc-alkaline, and biotite and and hornblende and lack of muscovite. DISCUSSION DISCUSSION Temporal Relationships—Field Temporal Relationships-Field Evidence Evidence Based on field and petrographic petrographic observations, observations, geophysical geophysical maps and measurements, measurements, and and limited geochronologic geochronologic data, the following following sequence—from sequence-from oldest to youngest—summarizes youngest-summarizes the emplacement history of igneous igneous rocks in the St. St. Cloud Cloud District: 1) Reformatory granodiorite, and Rockville and Richmond granites—emplaced granites+mplaced at at about about 1812 Ma; Granite and associated associated aplite, and Foley batholith+mplaced batholith—emplaced at approximately 2) St. Cloud Granite approximately 1770 Ma; northeast-trending dikes of porphyritic 3) northeast-trending porphyritic microgranite microgranite and diabase; diabase; and 4) northwest-trending northwest-trendingdiabase diabase dikes. dikes. 10 + 0 9 z 5 SO feldspar 70 75 VDiabua dike 8W w a i n R v G ~ P w p b @ c ~ ~ARichond+te t e SL CI-4 w e 0 Refemwary pnodiaite Figure 4. Modal rocks from from the the St. St. Cloud Cloud area. area. (a) Modaland andchemical chemicalvariation variation diagrams of intrusive rocks selected selected modal modal analyses analyses compiled compiled from from Dittman (1971), (1971), Morey (1972), (19721, Johnson (1978), (19781, Skiliman Skillman (1946), and Boerboom (in prep.); (b) (19461, (b)alkali-silica alkali-silicaclassification, classification,with with dividing dividing lines lines of of Miyashiro Miyashiro (1978, solid line) and Irvine k i n e and Baragar (1971, (1971, dashed line). 9 �The TheSt. St.Cloud CloudGranite Graniteintrudes intrudesthe theReformatory Reformatory granodiorite, granodiorite,as as established establishedabove above and and by by earlier earlierworkers workers(Morey, (Morey,1978 1978and and references references therein). therein). The Theintrusive intrusiverelationships relationshipsbetween between the the Rockville Rockville Granite Granite and and other other granitoid granitoid rocks cannot be seen in outcrop. outcrop. Although Although geochronological geochronologicaldata dataimply implythat thatthe theRockville Rockvilleand and Reformatory Reformatory are are generally generally synchronous synchronous(as (as discussed discussedbelow), below),some someoutcrops outcropsof ofRockville RockvilleGranite Granitecontain containinclusions inclusionsof ofrock rockequivocally equivocally similar to to the theReformatory Reformatorygranodiorite. granodiorite. Geophysical Geophysical maps maps imply imply that that the thenon-magnetic non-magnetic similar Rockville Rockville Granite Granite forms forms an an eastward-thinning eastward-thinning wedge wedge that that overlies overlies the the more moremagnetic magnetic Reformatory 3);however, however, the the observations observationscontribute contributelittle little to to their theirrelative relative Reformatorygranodiorite granodiorite(Fig. (Fig.3); emplacementhistory. history. emplacement Porphyritic dikes are inferred inferred to to be either cut by or Porphyritic microgranite microgranite dikes or synchronous synchronous with with northeast-trending northeast-trendingdiabase diabasedikes. dikes.ItItisisinteresting interestingto tonote notethat thatthe the microgranite microgranitedikes dikescommonly commonly have have aa similar similar northeast-trending northeast-trendingdiabase diabase dike dike near them. At At one one locality locality aa thin thin diabase diabase dike dike is is chilled chilledagainst againstthe theRockville RockvilleGranite Graniteon on one one side, side, but but retains retains felty-textured felty-textured plagioclase plagioclase against against the the contact contactwith withaaporphyritic porphyriticmicrogranite microgranitedike dikeon onthe theother, other,implying implyingthat thatthe themicrogranite microgranite was porphyrywas still stillhot hot when when diabase diabase was was emplaced. emplaced. The Thediabase diabasecontains containsabundant abundantxenocrysts xenocrystsof ofporphyryderived derived quartz and feldspar grains adjacent to this contact. These Thesetextures textures indicate indicate that that the the diabase diabasemay may be be comagmatic comagmaticwith with the the microgranite, microgranite, or or that that diabase diabase post-dates post-dates microgranite micrograniteonly only slightly. A northwest-trending diabase dike exposed in a quarry in Waite Park (Fig. F6 of slightly. A northwest-trending diabase dike exposed in a quarry in Waite (Fig. F6 stop stop descriptions) descriptions)unequivocally unequivocally cuts cutsand andisis chilled chilledagainst against aa small smallnortheast-trending northeast-trendingdiabase diabasedike. dike. If If this this northwest-trending northwest-trendingdike dikeisisrepresentative representative of of the the aeromagnetically aeromagneticallydefined defined dikes dikes having having the the same same orientation, orientation,they they are are the the youngest youngest intrusive intrusive rocks in the area. Temporal TemporalRelationships—Geochronologic Relationships~GeochronologicData Data All All the the intrusions intrusionsdescribed describedabove aboveare areinferred inferredto to be be Early Early Proterozoic, Proterozoic,with withthe theexception exception of somewhat equivocal dates. Unfortunately, of diabasic diabasicdikes dikesthat that cut cut the the granitoid granitoid rocks rocks and and yield somewhat Unfortunately, U-Pb data data are are rare, rare, and andfield fieldobservations observations together together with with Ar-Ar Ar-Ar and and K-Ar K-Ar dates dates make make much much of of the the emplacement emplacementhistory historyinferential. inferential.Reported ReportedU-Pb U-Pbdates datesof of1,770 1,770Ma Ma for for the the St. St. Cloud Granite, Granite, and 1,812 Â9Ma Mafor forboth boththe theRockville Rockvilleand andReformatory Reformatory(Goldich, (Goldich,pers. pers.comm., comm.,as asreported reportedin in and 1,812±9 Horan Horan and and others, others, 1987) 1987)are are consistent consistentwith with the the field field observations observationsthat that show show Reformatory Reformatory cut cut by St. St. Cloud Cloud Granite. Granite. Although Althoughnot notdated datedby by the the U-Pb U-Pb method, method, the Richmond granite has Nd and Pb isotope and trace element systematics consistent with and Pb isotope and trace element systematics consistent with it being Early Proterozoic (Spencer, (Spencer, 1987). 1987). Most Most controversial controversial are are the dates dates for diabasic dikes. Hanson Hanson(1968) (1968)gives gives K-Ar K-Ar wholewholerock ages northeast-trending diabase diabase dikes. dikes. Of these, the ages of 1280, 1280, 1460, 1460, and 1570 1570 Ma for the northeast-trending 1570 considered aa minimum consistent 1570Ma Ma date date is considered minimum age, age, and and some some of the dikes yield Pb isotope data consistent with northeastwith an an age age of approximately approximately1800 1800Ma Ma (Horan (Horan and others, 1987). 1987). Using Using these these data, data, the northeasttrending with enclosing enclosing granitic granitic rocks. rocks. By trending diabasic dikes may be more or less comagmatic with By contrast, contrast, Holm Holm and andLux Lux (1997) (1997)report reportAr-Ar Ar-Ar whole-rock ages of 1164±12 1164k12 Ma and 1190±9 1190±Ma two of of the thenortheast-trending northeast-trendingdiabase diabasedikes. dikes. Field relationships relationships do not permit us to to from two However, some field, geophysical, and unequivocally unequivocally resolve resolve these these contrasting contrasting age age dates. dates. However, and petrographic petrographicobservations observationsraise raisequestions questionsabout aboutthe theyounger younger(Keweenawan) (Keweenawan)emplacement emplacementdate. date. For example, example, nearly nearly all all of the diabase diabase dikes—including dikes-including those those dated dated by Holm and Lux (1997)— (1997)show alteration of mafic minerals to actinolite. The The northeast-trending northeast-trending dikes dikes in in the the St. St. Cloud Cloud District dikes exposed elsewhere elsewhere Districtare are only only weakly weakly to to non-magnetic, non-magnetic,in in contrast contrast with Keweenawan Keweenawan dikes that are strongly magnetic. Furthermore, paleomagnetic measurements on a limited suite of are strongly magnetic. Furthermore, paleomagnetic 10 10 �samples samples failed failed to to isolate isolate any any magnetization magnetization direction direction that that is is consistent consistent with with either either the the reversed reversed or normal normal directions directions typical typical of of Keweenawan Keweenawan dikes dikes (Val (Val Chandler, Chandler, unpub. data, Minnesota Minnesota Geological GeologicalSurvey). Survey).The Thegranites granitessurrounding surroundingthe thediabase diabasedikes dikesare are not metamorphosed, metamorphosed,implying implying that the the alteration alteration of of mafic mafic minerals minerals to to actinolite actinolite in the diabase diabase may be of of deuteric deuteric rather rather than than metamorphic origin. In Ar-Ar ages ages in in the the range range of of 1152-1199 1152-1199 Ma Ma may may indeed indeed Inthis thiscase casethe theAr-Ar reflect emplacement, related to the onset emplacement, or alternatively alternatively a weak metamorphic metamorphic overprint related onset of of Keweenawan different ages of northeastnortheastKeweenawanigneous igneousactivity activityto to the the east. A A third third scenario scenariois is that two different trending trending dikes dikes exist; exist; however, however, no systematic systematic differences differences between dikes of this trend have been observed observed in the field field or during during subsequent subsequent petrographic and geochemical study. The The apparent apparent conflict conflict of of dates dates and and observations observationsfrom from diabasic diabasic and and quartzofeldspathic quartzofeldspathicdikes, dikes,and and uncertainties uncertainties about the age age of of other other plutonic plutonic elements elements in in east-central east-central Minnesota, Minnesota, underscores underscores the need need for for modern modem U-Pb U-Pb zircon zircon or or baddelyite baddelyitedates. dates. Mafic microgranular microgranularenclaves-evidence enclaves-evidence for for magma magma mingling mingling Mafic Mafic microgranular microgranular enclaves that occur in many intrusions of the St. Cloud area are interpreted interpreted as as the the product product of of commingled, commingled, coeval felsic and mafic magmas. The Thetextural texturaland and mineralogical attributes of mafic mafic microgranular microgranular enclaves enclaves in the Rockville Rockville Granite Granite and and Reformatory rapakivitexture textureof of the the Rockville Rockvilleand and Richmond Richmondgranites, granites,are are Reformatorygranodiorite, granodiorite,and andthe therapakivi similar commingling of mafic and felsic magmas. Although similarto to features featuresattributed attributedelsewhere elsewhereto to the commingling Although some some of of the the enclaves enclavesmay may have have originated originatedby by the the reincorporation reincorporationof of chilled chilled intrusion intrusionmargins margins by upwelling upwelling magma, magma, textural texturalevidence evidenceclearly clearly shows shows that that some some of the the enclaves enclaves coexisted coexisted as as aa melt melt with with the the host host granite granite magma. magma. Textures Texturesimplying implyingcommingling comminglingof ofmafic maficand andfelsic felsicmagmas magmas beg the question: Under what conditions are these coeval yet disparate magmas generated? beg question: Under conditions coeval yet disparate magmas generated? The mingling mingling of of mafic mafic and and felsic felsic magmas magmas is is most likely likely to occur in regions where crustal melts are generated generatedby by underplating underplatingof of continental continentalcrust crust by mafic mantle-derived magma. Melt Meltgenerated generated by this process process and and in in aa quantity quantitysufficient sufficient to to accumulate accumulate at at the the base base of of the the crust crust can can become become fully (Cruden fully mobilized mobilized and and ascend ascend rapidly, rapidly, entraining entraining the underlying underlying mafic magma as it rises (Cruden and and others, others, 1995, 1995,and and references referencestherein). therein). We suggest suggest that that the the numerous numerous mafic mafic enclaves enclavespresent present in in the the 1812 1812 Ma intrusive intrusive suite suite give give evidence evidence that that melting meltingof of the the lower lower crust crust by mafic mafic mantle mantle underplating underplatinggave gave rise rise to to the the latelatetectonic tectonicsuite suiteof of granitic graniticintrusions, intrusions,during duringthe the waning waning compressive compressivestages stagesof of Penokean Penokeanorogeny. orogeny. Furthermore, Furthermore, the numerous numerous gabbroic to noritic intrusions such as that that associated associated with with the the Richmond Richmond granite granite (Fig. (Fig. 2) 2) may may represent represent mafic mafic end-members end-members of this same same late-Penokean late-Penokean suite suite of intrusions. intrusions. of In the case Masuite suite of ofpost-tectonic post-tectonic granites, granites, mantle mantle underplating underplating as the case of of the the —1770 -1770 Ma result of mantle (e.g., Holm Hoim and and Dahl, Dahl, 1996; Cruden mantle lithospheric lithospheric delamination (e.g., Cruden and andothers, others, 1995; Turner and others, 1992) may have generated the melts. In this model, delamination 1995; Turner and others, 1992) may generated In this model, delaminationand and thinning of the the orogenically orogenically overthickened overthickened crust allows hot asthenosphere to well up, up, raising raising the asthenosphere-lithosphere asthenosphere-lithosphereboundary and increasing the thermal input into into the the base base of of the the crust. This Thisprocess processisisattractive attractivebecause because granitic granitic melt melt generation is delayed until some 40-50 m.y. after the peak of orogenesis, orogenesis, coincident coincident with the time necessary for orogenic collapse and thinning of the mantle lithosphere thinning of the mantle lithosphere(Turner (Turner and and others, others, 1992). 1992). There are post-orogenic granites of the are several several lines of evidence which indicate that the post-orogenic St. Cloud area may have formed from crustal crustal underplating underplating by by high-temperature high-temperature mantle material material following following crustal crustal collapse collapse and and mantle mantle lithospheric lithosphericdelamination. delamination. - 11 �high temperatures temperatures 1. The The granite granite melts are are inferred by Spencer (1987) to have formed at high (800-1000°C), and and are nearly coeval with the (800-1000°C) the isotopically isotopically similar similar mantle-derived mantle-derived diabasic diabasic rocks rocks (Horan (Horan and and others, others, 1987). 1987). 2. The Theclose closeand andprobable probablecogenetic cogeneticassociation associationof ofthe theporphyritic porphyritic microgranite microgranitedikes dikes with diabase dikes. This This may may reflect reflect bimodal bimodal magma generation, a common feature of post-orogenic post-orogenic plutonic plutonic complexes complexeselsewhere elsewhere (Turner (Turner and and others, others,1992). 1992). 3. The Theemplacement emplacementofofgranite granitelags lagsbehind behindpeak peakorogenesis orogenesisby by—50 -50 Ma. 4. Holm 4. Holm and and others others (1998) (1998) concluded concluded from garnet garnet and and staurolite staurolite core-rim core-rim thermobarometric, geobarometric, geobarometric, and and thermochronologic thermochronologic studies studies (see following thermobarometric, section) that crust crust thickened thickened by the the Penokean Penokean orogeny orogeny remained remained so so for for50-60 50-60m.y. m.y. before collapse, collapse, which then may then have triggered sudden lower crustal melting. 5. Spencer Spencer(1987, (1987,p. p.174, 174,e.g.) e.g.) interpreted interpreted from from isotopic isotopic evidence evidence that the granite melts were generated at aa convergent convergent continental margin that recycled a source source material material with a short-lived crustal history. However, he allows for an extensional extensional environment environment superimposed superimposedon on an an earlier earlier orogenic orogenic event, event, to produce produce basic mantle mantle melts melts beneath beneaththe the crust to melt the crustal rocks. the crustal rocks. Thermobarometric data The significant significant proportion of igneous rocks, together with the regional staurolite grade of metamorphism of of the country rocks, implies implies that that outcrops outcrops in this area represent one of metamorphism of the the deepest exposed levels of the entire entire Penokean Penokean orogenic orogenic belt. belt. Holm Hoim and others (1998) recognized recognized deepest that Early Proterozoic country rock within the internal internal zone zone (Little (Little Falls Falls Formation) Formation) were were metamorphosed twice. Thermobarometric Therrnobarometricestimates estimatesindicate indicate that early, Penokean-age, garnetgrade (Ml) metamorphism occurred at pressures of 5-6 kbar and temperatures of 450-500°C 450-500°C. (Ml) metamorphism occurred at pressures Thermobarometric estimates metamorphism yield similar pressures, pressures, and and only only slightly slightly Thermobarometric estimatesof the M2 metamorphism temperatures (500-550°C) (500-550°C). This indicates plutons exposed exposed in in the St. higher temperatures indicates that Penokean plutons District were Cloud District were emplaced emplaced during during the the interim interim between between the the two metamorphic metamorphic events events at at 19-23 19-23 depths. The km midcrustal orogenic depths. The age age of of M2 M2 metamorphism must be older than the 1750Ma mica mica Ar/Ar Ar/Ar cooling cooling ages obtained obtained throughout throughout the the region region because because of of the the 300° 300°C closure closure 1760 Ma temperature of biotite Hoim and Lux, 1997;Holm Holm and and others, others, 1998). These These ages indicate indicate temperature biotite (Fig. (Fig. 5; Holm been reheated reheated to temperatures temperatures above 300° 300°C since since that that time. time. Five hornblende hornblende that the area has not been Ar/Ar dates obtained from central Minnesota are concordant with the 1760-1750 Ar/Ar 1760-1750 Ma mica mica temperatures dates. Hornblende Hornblendehas hasaa typical typical closure closure temperature temperature of 500°C, 500°Cwhich matches the temperatures obtained for M2 metamorphism (500-550°C). This is strong evidence that the rocks of the strong the metamorphism (500-550°C) remetamorphosed to to staurolite internal zone of the orogen in central central Minnesota were widely remetamorphosed grade during the same same event event responsible for for generating generating the post-tectonic magmas at 1770 1770Ma. Ma. 5-6 kbars kbars indicates indicates that little or or no no unroofing unroofing of of the the Penokean Penokean The M2 pressure estimate of 5-6 midcrustal root occurred occurred between between about about 1820 1820and 1770 1770 Ma. Emplacement Emplacement pressure estimates estimates using an igneous barometer indicate that some of the 1770 Ma post-Penokean plutons were intruded at 4.6 kbar pressures (17 km depth); depth); whereas, whereas, others were emplaced at lower pressures of 3.5 kbar, or about 13 km depth (Darrah, lower kbar, about 13 km depth (Darrah, 1996). 1996). These contrasting contrasting pressure estimates—derived estimatesÑderive from suites of rock tentatively inferred to be be comagmatic—indicate comagmatic-indicate that post-tectonic magma emplacement was synchronous with crustal uplift (Fig. (Fig. 6). 6). 12 �________ _________________________________________ Early Proterozoic Proterozoic tectonomagmatic tectonomagmaticmodel Our mapping observations and analytical results of the last five years indicate that there significant differences in the overall character of the & vs. -Penokean plutons are significant m-Penokean plutons(Table (Table that must be explained in any tectonic model. model. We believe these differences differences reflect two very 1) that tectonomagmatic settings; different tectonomagmatic settings; one that occurred at the end of orogenic orogenic belt construction, construction, and one during its demise demise approximately approximately 40-50 40-50 my later. (I)- ci) 4-- 0 0 "0- S I- a) E z 1800 Ml metamor hism Late- Penokean plutonism ) ) ) I I I II I I '1 11 j Ar/Ar, ArIAr,hornblende hornblende H Ar/Ar, mica McGrath gneiss dome dates S Ii' 1.1.1.1 ——l I 1700 I 1600 I 1500 AGE (Ma) Post-tectonic plutonism, M2 metamorphism metamorphism Figure Figure 5. Histogram Histogramof ofAr/Ar ArlAr dates dates from from the the EarlyProterozoic EarlyProterozoic of central Minnesota Minnesota (after Holm and Lux, 1996; 1996; Holm Holm and and others, others,1998). 1998). Figure 7 presents a Temperature (*C) (C) schematic synopsis of of our schematic synopsis our interpretation of pluton 300 400 500 600 300 400 the emplacement after compressive phase phase (Fig. (Fig. 7A) 7A) of compressive semi-brittle shears Penokean deformation in central n Rapid cooling Minnesota. The Richmond, Richmond, Reformatory, and Rockville-the Rockville—the Reformatory, 1770-1760 Ma "gray granites"—represent lower granites9'-represent \ 1 post-tectonic crustal crustal melts intruded into the the midcrust (20-22 km) km) of the midcrust (20-22 the Penokean orogen (Fig 7B). These These Penokean magmas were generated during generated during metamorphism Ml the waning stages stages of of Penokean Penokean compression hence, compression and 1 late-tectonic plutons developed a moderate magmatic fabric. fabric. Figure 6. Summary Summaryof of P-T-t P-T-t diagram diagram showing showing the relation The The evidence for (M 1and andM2), M2),plutonism, plutonism,and and forforbetween metamorphism metamorphism (Ml commingled commingled mafic mafic and felsic mation of semi-brittle shears in the internal zone of the these rocks indicates magmas in Penokena orogen Penokena orogen (modified (modifiedafter after Hoim Holm and and others, others, 1998). 1998). 13 13 �TABLE 1—Comparison post-Penokean intrusions intrusions 1-Comparison of late and post-Penokean TYPEIAGE TYPE/AGE Composition/Color Composition/Color LATE LATE PENOKEAN/—1812 PENOKEXNI- 1812 Ma Ma Granodiorite-granite——typically Granodiorite-granite-typically gray—with gray-with mafic maficenclaves enclaves POST-PENOKEAN/--1770 POST-PENOKEANI- 1770 Ma Granite Granite (alkali-feldspar (alkali-feldspargranite granite to to syenogranite)—typically syenogranitel-typically red— redwith with few few mafic mafic enclaves enclaves Magmatic Fabric Fabric Magmatic Moderately Moderatelydeveloped, developed, NE NE orientation, orientation,commonly commonlyflat flat Very weak to absent absent Pluton Pluton Shapes Shapes Broad Broad and and irregular irregular Dikes, Dikes, sills, sills, and and larger larger plutons plutons with a tendency for for NE orientation orientation Geophysical Characteristics Characteristics Variable Variable -- moderate moderate and busy busy magnetic magnetic signature; signature;dense dense Typically non-magnetic, non-magnetic, pronounced pronounced gravity gravitylows lows Depth Depth Emplaced Emplaced 20-22 20-22 km km(5-6 (5-6 kbar) kbar) 13-17 13-17 km (3.5-4.5 (3.5-4.5 kbar) kbar) Associated Metamorphism Metamorphism Garnet Garnet grade grade Ml M 1(5-6 (5-6 kbar) kbar) Staurolite M2 (5-6 (5-6 kbar) kbar) Staurolitegrade gradeM2 Solid-state Solid-state Fabric Fabric Cut Cut by by semi-brittle semi-brittleshears shears Cut Cut by semi-brittle semi-brittle shears shears that that crustal crustal underplating underplatingmay may have have played played an an important important role in their generation. However, However, these these crustal melts were not able to penetrate the stronger upper crust of the orogen, but instead not able to penetrate the stronger the orogen, but instead formed formed irregular irregularshaped shaped plutons plutons at at depths depths of of 20-22 20-22 km km where where they remained for approximately approximately 40 Penokean orogeny 40 m.y. The Theperiod period of of tectonic tectonic quiescence quiescenceand and amagmatism amagmatismafter after the Penokean orogeny (during (during the the period period approximately approximately1812-1770 1812-1770Ma) Ma)was wasterminated terminatedby byaashort-lived short-livedperiod periodof of post-tectonic post-tectonic magma magma generation, generation,metamorphism, metamorphism,and and rapid rapid midcrustal midcrustal uplift uplift and and cooling coolingat at about about 1770 1770Ma. Ma. This This abrupt abrupt episode episode may may have been triggered by mantle-lithospheric mantle-lithospheric delamination delaminationthat that would would have midcrustto to temperatures temperatures have caused causedboth bothmelting meltingof ofthe thelower lowercrust crust(Fig. (Fig. 7C) 7C)and and heating heatingof of the the midcrust above above 500°C 5OO0Cduring during M2 M2 metamorphism. metamorphism. This Thisthermal thermalheating heatingsoftened softenedthe the overthickened overthickenedcrust, crust, causing At this this time time significant significant unroofing occurred and shears shears causing itit to collapse collapse and and thin (Fig. 7D). At formed as as the the rocks rocks cooled cooled and and became more brittle. The TheSt. St.Cloud CloudGranite, Granite,Foley Foley batholith, batholith, and associated associated plutons—the plutons-the "red, "red, massive massive granites"—were granites9'-were advected advected during during this this event event into into uplifting orogenic shortening uplifting crust crustthat that was was extending extendingNW-SE, NW-SE, parallel parallel to to the the previous orogenic shorteningdirection. direction. Early Proterozoic Proterozoic diabasic diabasic and and quartzofeldspathic quartzofeldspathic dikes apparently lagged behind a bit bit and and were emplaced just after after brittle brittle shears shearsformed, formed, using using the the shears shearsas as conduits conduits(Fig. (Fig. 7E). 7E). were emplaced ACKNOWLEDGMENTS ACKNOWLEDGMENTS This This field field guide guideis is an an outgrowth outgrowth of studies studies by the Minnesota Geological Survey Survey (MGS) (MGS) that were were supported supportedby by several several programs programs of the State Legislature. The The Stearns StearnsCounty County segment segment (Boerboom and others, 1995, 1996a) was funded through the Legislative Commission 1995, 1996a) was funded through the Legislative Commission on on Minnesota Resources; funding for drilling drilling and and mapping mapping east of of St. St. Cloud Cloud (Jirsa (Jirsaand andothers, others, 1995a) was made available available on on recommendation recommendation of the the Minnesota Minnesota Minerals Minerals Coordinating Coordinating Committee. On-going On-goingmapping mapping and and analytical analytical work work in in both areas areas has been supported supported by the MGS. was supported supported thermobarometricand andgeochronologic geochronologicwork work of of Daniel Daniel Holm and others was MGS. The Thethermobarometric by a National Science Foundation grant (EAR-9304070). We are grateful to Mr. Frank Lyons Science We and and the the Meridian MeridianAggregates AggregatesCompany Companyfor foraccess accessand andguidance guidancein in the theaggregate aggregatequarry, quarry,and andfor for permission to to visit visit their their developing developingsouthern southern property property (before (before the the natural natural outcrops outcropsare aregone!). gone!). A very special special thanks thanks to to Charles Charles Muehlbauer Muehlbauer and and other other employees employees of the the Cold Cold Spring SpringGranite Granite Company Company for for assistance, assistance,advice, advice, samples, samples, permission, permission, and and guidance guidance (on their their day day off!). off!). 14 �___ Schematic Schematic N ++ + — Timing Timing Penokean orogeny Penokean orogeny Mj Mi metamorphism metamorphism \ crust cmst mantle- B s* s Penokean Penokean highlands Orogenic Orogenic features features —1850Ma Ma -1850 strong upper ccrust wt —_ Late-Penokean magma emplacement emplacement _..______S2022 datum 20-22 km depth depth datum mantle km manti —1812Ma Ma -18l.2 basaltic underplating? ---- ———, I --—-—- M2 metamorpinsin metamorph Generation Generation of post-tectonic post-tectonic magmas in the lower crust 1775-1770 Ma 1775-1770 Ma Mantle delamination, basaltic underplating? underplating? D E —- H — - - a- a- magma emplacement emplacement Post-tectonic magma Crustal unroofing/cooling crustal ~ o f ~ / c o o ~ Semi-brittle shears shears developed Semi-brittle Ma km depth depth datum datum 1770-1750 \20-22 20-22 km 1770-1750 Ma Diahase and QFP dikes <1750 MaKeweenawan? —. post orogenic plutons, plutons, Figure 7. Proposed Proposed tectonomagmatic tectonomagmaticmode mode for for generation generation of late- and post central Minnesota. Minnesota. Heavy dashed lin un represents 20internal zone of the Penokean orogen, central 22 km depth datum prior to crustal crustal unroofing unroofing (B (B and andC). C). Crustal Crustal unroofing unroofing and and exhumation exhumation causes upwarping upwarping of this this datum datum livel live1 in (D (D and E). E). 15 �REFERENCES FWFERENCES CITED CITED B arbarin, B., B., and and Didier, J., 1991, Macroscopic features of mafic microgranular enclaves, Barbarin, enclaves,in in Didier, J., and Barbarin, Barbarin, B., eds., Enclaves and granite petrology: Elsevier, Elsevier,p. p. 253-262. 253-262. in Meyer, Meyer, G.N., G.N., Boerboom, T.J., 1996a, 1996a, Precambrian geology of Steams S t e m s County, County, Minnesota, in and Swanson, supplement to the Geologic Atlas, Stearns Steams County, Swanson,L., eds; eds; Text supplement County, Minnesota: Minnesota: Survey County CountyAtlas AtlasSeries SeriesC-10, C-b, Part C, p. 1-6. Minnesota Geological Survey Boerboom, T.J., 1996b, Boerboom, 1996b, Southward Southward extension of the Penokean terrane through Stearns Steams County, County, Part 1- programs and abstracts; central Minnesota: Institute on Lake Superior Geology, Part 42nd annual annual meeting, meeting, Cable, Cable, Wisconsin. Wisconsin. Boerboom, T.J., Setterhoim, f Boerboom, Setterholm,D.R., D.R., and andChandler, Chandler,V.W., V.W., 1995, 1995, Bedrock geologic map, plate 2 oof GeologicAtlas Atlasof ofStearns SteamsCounty, County,Minnesota: Minnesota: Minnesota Minnesota Meyer, G.N., project manager, Geologic Geological Survey County County Atlas AtlasSeries SeriesC-10, C-b, Part A, scales 1:200,000 and 1:100,000. Part scales 1:200,000 and 1:100,000. A.R., Koyi, H., and Schmeling, Cruden, A.R., Schmeling, H., 1995, 1995, Diapiric basal entrainment entrainment of mafic mafic into into 321-340. felsic magmas: Earth Earthand andPlanetary PlanetaryScience ScienceLetters Letters 131, 131, p. 321-340. internal zone zone of of the the Early Early Proterozoic Proterozoic (1870Darrah, K.S., 1996, 1996,An exhumation history of the internal 1830 Ma.) Penokean orogenic belt, central central Minnesota: Minnesota: Unpublished Unpublished M.S. M.S. thesis, thesis, Kent Kent State State University, University, 99 99 p. Hanson, G.N., 1968, 1968, K-Ar ages for hornblende hornblende from granites and gneisses and for basaltic intrusives in Minnesota: Minnesota 8, 20 p. Minnesota Geological Geological Survey Survey Report of Investigations 8,20 Hoim D.K., and Selverstone, synkinematic Holm Selverstone,J., 1990, 1990,Rapid growth growth and strain rates inferred from synkinematic garnets, garnets, Penokean orogeny, Minnesota: Geology, Geology, v. v. 18, 18, p. 166-169. 166-169. Hoim D.K., and Dahl, delamination an an important important process process in the Holm Dahl, P.S., P.S., 1996, 1996, Was lithospheric delamination evolution of Early Proterozoic collisional orogens? Institute on Lake Superior Institute on Lake Superior Geology, Part 11- programs and abstracts; 42nd 42nd annual annual meeting, meeting, Cable, Cable, Wisconsin. proposed for gneiss gneiss dome dome development development Holm D.K., and Lux, D.R., 1996, 1996, Core complex model proposed during collapse v.24, 24, no. no. during collapseof of the the paleoproterozoic paleoproterozoicPenokean Penokeanorogen, orogen,Minnesota: Minnesota:Geology, Geology,-v. 4, p. 343-346. Minnesota and Holm D.K., and and Lux, Lux, D.R., 1997, 1997,Results Results of of Ar/Ar ArIAr dating of dikes in central Minnesota and the the Minnesota River Valley: Valley: Institute on Lake Lake Superior SuperiorGeology, Geology,Part Part11-program - program and abstracts; Minnesota 43rd annual annual meeting, meeting, Sudbury, Sudbury, Engineers, Engineers, Reston, Reston, Va., 141 141 p. Holm D.K., D.K., Darrah, Darrah,K.S., K.S., and andLux, Lux,D.R., D.R., 1998, 1998,Evidence Evidencefor forwidespread widespread—1760 -1760 Ma metamormetamorphism and rapid crustal (1870-1820 crustal stabilization stabilization of the early Proterozoic (1 870- 1820 Ma) Penokean orogen, 298, p. 60-81. orogen, Minnesota: American AmericanJournal Journal of of Science, Science,vol ~01298, 60-8 1. Horan, M.F., M.F., Hanson Hanson G.N., G.N., and Spencer, K.J., 1987, Pb Pb and Nd isotope and trace element Spencer, K.J., element constraints constraints on on the the origin origin of of basic basic rocks rocks in an early Proterozoic Roterozoic igneous igneous complex, Minnesota: Precambrian PrecambrianResearch, Research,v. v. 37, 37, p. 323-342. 323-342. Irvine, W.R.A., 1971, A guide guide to to the the chemical chemical classification classification of of the the common common Irvine, T.N., and Baragar, W.R.A., 1971, A volcanic rocks: Canadian Journal of Earth Sciences, v. 8, p. 523-543. 16 �Jirsa, M.J., Chandler, J.M., and Meints, J.P., J.P., 1995a, Bedrock geologic map of Chandler, V.W., V.W., Cleland, J.M., east-central Minnesota: Minnesota east-central Minnesota: Minnesota Geological Geological Survey Survey Open-file Open-file Report 95-1, 95- 1, scale scale :100,000. 11:100,000. Jirsa, T.J., 1995b, Jirsa, M.J., Chandler, Chandler,V.W., V.W., and Boerboom, T.J., 1995b, Extension of the Wisconsin Magmatic Magmatic Terranes into the Minnesota segment of the Penokean orogen: orogen: Institute Institute on Lake Lake Superior Geology, Part 1- programs and abstracts; 41st 41st annual annual meeting, Marathon, Marathon, Ontario. Ontario. test drilling and mapping in east-central Jirsa, M.J., and and Chandler, Chandler, V.W., V.W., 1997, Scientific test east-centralMinMinnesota, 1994-1995: 1994-1995: Summary of lithologic results: Minnesota Geological Survey Information Circular Circular 42, 42, 105 105p. Johnson, M.C., east-central MinJohnson, M.C., 1978, 1978, Mineral Mineral chemistry chemistry of four quartz-bearing monzonites in east-central Minnesota: Unpublished UnpublishedM.S. M.S. thesis, thesis,University Universityof of Iowa, Iowa, 227 227 p. Miyashiro, A., 1978, Nature of alkalic volcanic volcanic rock rock series: series: Contributions Contributions to mineralogy mineralogy and petrology, 1-104. petrology, v. v. 66, 66,p. p. 991-104. Morey, G.B., 1978, Middle Precambrian Precambrian stratigraphic stratigraphic nomenclature nomenclature for east-central east-central 1978, Lower and Middle Minnesota: Minnesota 52 p. MinnesotaGeological GeologicalSurvey SurveyReport Report of of Investigations Investigations 21, 21,52 Morey, G.B., Olson, B.M., and Southwick, Southwick, D.L., 1981, 1981, Geologic map of Minnesota, Minnesota, east-ceneast-central Minnesota, bedrock geology: Minnesota Geological Survey, scale 1:250,000. Minnesota, Minnesota Geological Survey, scale 1:250,000. Muehlbauer, C.J., and Fuchs, J.P., J.P., 1997, 1997, Modern dimension stone quarrying and fabrication fabrication technologies, in Labuz, J.E, J.F.,ed., ed.,Degradation Degradationof ofnatural naturalbuilding buildingstone: stone:proceedings proceedingsof of22 technologies, in sessions sponsored by the Rock Mechanics Committee of the Geo-Institute Geo-Institute of the Amerisessions can Minneapolis, can Society Society of Civil Civil Engineers Engineers in conjunction conjunction with the ASCE Convention in Minneapolis, Minnesota, Reston,Va., Va.,141 141p. p. Minnesota,October October 5-8, 5-8, 1997: 1997:American AmericanSociety SocietyofofCivil CivilEngineers, Engineers,Reston, Southwick, D.L., Morey, G.B., and McSwiggen, P.L., 1988, Geologic Geologic map map (scale 1:250,000) Southwick, 1:250,000) of the Penokean orogen, accompanying text: text: Minnesota orogen, central and eastern Minnesota, and accompanying Minnesota Geological 25 p. Geological Survey Survey Report Report of of Investigations Investigations37, 37,25 p. Spencer, K.J., 1987, constraints on the sources of granites in 1987, Isotopic, Isotopic, major, and trace element constraints an 1800 near St. Cloud, Minnesota: 1800 Ma-old Ma-old igneous igneous complex complex near Minnesota: Unpublished Unpublished Ph.D. Ph.D. dissertation, dissertation, SUNY-Stony SUNY-Stony Brook. Brook. Streckeisen, A chemical chemical approximation to to the modal QAPF Streckeisen, A.L., and Le Maitre, Maitre, R.W., R.W., 1979, A classification classificationof of the the igneous igneousrocks: rocks:N. N. Jb. Jb. Miner. Miner. Abh., Abh., v. v. 136, 136, p. 169-206. 169-206. Thiel, G.A., and Dutton, C.E., 1935, monumental stones of of 1935, The architectural, structural, and monumental Minnesota: Minnesota MinnesotaGeological GeologicalSurvey Survey Bulletin Bulletin 25, 25, p. 63-87. Turner, Sandiford, M, and Foden, J., 1992, Some geodynamic geodynamic and compositional compositional constraints constraints Turner, S., Sandiford, on "postorogenic" magmatism: magmatism: Geology, Geology,v.v.20, 20,p.p.93 931-934. 1-934. Van Schmus, W.R., W.R., and Bickford, M.E., M.E., 1981, Van 1981, Proterozoic chronology and evolution of the the Midcontinent region, Precambrian plate in Kroner, Kroner, A., ed., Precambrian plate tectonics: tectonics: New New Midcontinent region,North North America, America,in York, Elsevier, p. 261-296. 261-296. 17 �FIELD FIELD TRIP TRIP STOPS STOPS The shown on on figure figureFFl. The general general locations locations of all stops are shown l. A A more more detailed detailed location and geologic geologic map map is is included included with each each stop stop description. description. The Thevarious various rock rock units units are are fully fully described in in the the field field trip trip introduction, introduction,and and only only the the details details pertinent pertinent to to the the individual individualsites sites described are given given below. below. are I A KILOMETERS MILES 1 ------- 1 0 0 2 1 1 3 4 2 8 6 - 3 4 7 8 5 0 10 6 Figure Fl. Fl. Locations Locationsof offield fieldtrip trip stops. stops. STOP STOP 1. 1. STEARNS STEARNSCOUNTY COUNTYQUARRY QUARRY PARK • Location: Location:T.T.124 124N., N.,R.R.2828W., W.,Section Section19 19DDA. DDA. • St. St.Cloud Cloud(red) (red)Granite, Granite,diabase diabasedikes, dikes,semi-brittle semi-brittleshears shearsin in granite, granite, outcrops. glacially polished outcrops. This This area area contains containsseveral severalinactive inactivequarries quarries(Figs. (Figs. F2 F2 and and F3), F3), and and was was recently recently made made into into a unique unique county county park. The Thepark parkprovides providesexcellent excellent exposures exposures in which which one can can view view the the relationship between the Reformatory granodiorite and the St. Cloud Granite, as well as several relationship between the Reformatory granodiorite and the St. Cloud Granite, as well as several diabase dikes. Although Althoughthe thepark parkhas hasexposures exposuresof ofboth bothnortheastnortheast- and andnorthwest-trending northwest-trending diabase dikes, we will will only only see seenortheast-trending northeast-trending ones and St. St. Cloud Cloud Granite, Granite, due due to to time time constraints. constraints. 18 18 �________-- Diabase dike (single line for thin dike; dashed where inferred) Porphyritic microgranite Outcrop IA Ii —450 32 30 .4 QUirri - I DM7 4 0 092 -. / C J -- — z I /Y kI -'zr? )( (JU :-- Q'II. rI 0 -'S 1094 - '':i • t074 p - ç— — I c..j Â¥ Mhi =;, ON jl FÑ 1 3.',, 3 1,- ' 6282 kilLS MILS 15 15MIS MgLS I ,' i 00 ^ ^ ^ - - . 2 - - , 0 1000 1000 , È I - 1 -0 I1 - - 1000 1 2000 200C 3000 3000 4SOO 4001) 5 00 .55 - - - - - , 1 MILC MILE - - 5000 5000 6000 7000FEfT 701.51 FEri 1 I KILOMETRE 11KILOMETRE i CONTOUR CONTOUR INTERVAL INTERVAL 10 10FEET FEET DOTTED LINES RPR.SNT 5.FOO1 CONTOURS DOTTED LINES REPRrSFNT 5-FOOT CONTOURS Figure FigureF2. F2. Map MapofofWaite WaitePark, Park,southwest southwestof ofSt St.Cloud, Cloud,showing showinglocations locationsof ofoutcrops outcropsand anddikes dikes in 1:24,000. in parts parts of of the theSt. St.Joseph Joseph and andSt. St.Cloud Cloud 7.5-minute 7.5-minute quadrangles. quadrangles. Scale Scalereduced reduced from from 1:24,000. 19 �2, and 3. Scale Figure F3. Location Locationmap map for for stops stops 1, 1,2, Scale1:24,000; 1:24,000;St. St. Cloud Cloud 7.5-minute quadrangle. quadrangle. At least seven different different quarry companies were active in what is now the park area—all area-all utilizing the St. Cloud Granite. Production Production started in the early 1900's, peaked in about 1940, variety of of "red" "red" and ceased in the mid-1950's. The Thestone stonethey they produced was marketed under a variety "Mahogany Red," Red," "Indian "Indian Red," Red," and and"Rose "Rose Red." Red." Most of names, including "North Star Red," Red," "Mahogany the pits were (and (and still still are!) 60 60 to to more more than 100 100 feet feet deep deep (Thiel (Thiel and Dutton, Dutton, 1935). 1935). PLEASE PILES ARE ARE NOT NOT PLEASE EXERCISE EXTREME CAUTION! THE THEQUARRY QUARRY PILES STABLE, AND AND THE THE PITS PITS ARE ARE DEEP! DEEP! parking area. From Follow the park road south from the park entrance to the parking From here here walk walk trail on on the the right right (west) (west)that thatleads leadsup upto toquarried quarriedarea. area. Proceed 400 feet south on a dirt road to a trail up this trail to the edge edge of of aa small small quarry quarry and and Stop Stop 1A 1A (Fig. (Fig. F4). F4). 20 �Diabase Dike St. Cloud (Red) Granite Reformatory (Grey) Granite Quarry Figure F4. Outcrop Outcrop map map of Stop 1A and lB. IB. STOP lA—Three-dimensional 1A-Three-dimensional view view of diabase and quartz-epidoteshears shearsin inSt. St.Cloud Cloud STOP and quartz-epidote Granite. Granite. Directly Directlywest, west, across across the the rubble rubble in the pit, is an excellent exposure in pit, is an excellent exposure of a northeast-striking, northeast-striking, steeply steeply southsouthdipping, dipping,meter-thick meter-thickdiabase diabasedike dikethat that cuts cuts St. St. Cloud Cloud Granite. Granite. The Thedike dikewas was sampled sampledfor for both both paleomagnetic paleomagneticstudy study and and Ar/Ar ArIAr dating dating (see (seeintroduction). introduction). This This is is typical typical of of the the diabases diabases in in the the area, area, having having chilled chilled margins margins and and Diabase dikes ~iab&e dikes Quartz-epidote Quartz-epidoteshears shears scattered cm-scalexenoliths xenolithsof ofgranite granite scatteredcm-scale wallrock. wallrock. The Thegranite graniteadjacent adjacentto tothe the Figure F5. F5. Stereographic Stereographicprojections projectionsof oforientations orientations Figure dike dike contains contains numerous numerous thin, thin, diabase dikes dikes (A) and and quartz-epidote-filled quartz-epidote-filledsemiserniof diabase northeast-trending, northeast-trending, quartzquartz- and and brittle brittle shears shears(B). (B). epidote-lined, epidote-lined,semi-ductile semi-ductileshears shearsthat that 21 �truncated by by and are probably probably in in part part occupied occupied by by the the diabase diabase dike. dike. This are clearly truncated This nearly nearly coincident trend typical of the regional pattern shown on the stereoplots stereoplots in coincident trend of dikes dikes and and shears shears is typical figure F5. Two Two other other diabase diabasedikes, dikes, up up to to 22 meters meters thick, thick, can can be be seen seen north north of of this this dike. dike. Although the majority of blocks in the the waste waste rubble rubble before you are are indigenous, indigenous, several several exotic rock types are present, including including blocks of Reformatory granodiorite granodiorite (gray) (gray) that we we will will see in place at Stop 3. The Reformatory granodiorite is presently extracted from a quarry The Reformatory granodiorite is presently extracted quarry just by the Cold Spring Granite south of the city of of St. St. Cloud, Cloud, marketed marketed as "Charcoal "Charcoal Granite" Granite" by Company. The Company. The maroon-colored maroon-colored granite granite blocks are probably probably imported from quarries near South Dakota. Dakota. Blocks of grayish-pink, complexly banded Ortonville, Minnesota and Milbank, South Morton gneiss are are from from the the Minnesota Minnesota River River Valley. Valley. Several Several other blocks of pink granite granite and and pale pink gneiss are from unknown localities, but are not indigenous. Return to the dirt road, Return road, and and walk walk south south (to (to the the right) right) approximately approximately 250 feet to to the the switchback right. Note the spheroidally-weathered granite along along the the switchback trail on the right. spheroidally-weatheredoutcrops of red granite west (right) edge of the road between the two trails. The The aggregate aggregatecovering covering the the switch-back switch-back trail illustrates illustrates one of the many uses of crushed stone from the Meridian Aggregates one stone Aggregates Quarry Quarry that that polished outcrop on on the the north north we will visit at Stop 2. At At the the next quarry proceed to a glacially polished (right) side of the pit. pit. STOP Granite. STOP 1B—Diabase 1B-Diabase dike in St. Cloud Granite. The diabase dike splits and rejoins along its length, and has small, 4-10 cm, north-south 'jogs' at at its its northeast northeasttrend. trend.There Thereare areno noobvious obviouscross-fractures cross-fracturesin in the the granite granite that that might might have have controlled the these small small offsets, offsets, making them somewhat enigmatic. xenoliths, as well as This stop stop affords affords a better look look at the chilled dike margins and granite xenoliths, of granite wallrock walirock torn torn partly partly loose loose during during dike dike emplacement. emplacement. Granite xenoliths in slivers of various stages of assimilation assimilation can be seen, seen, and xenoliths xenoliths are concentrated concentrated in the the center center of of the the ±0.5 main dike, presumably by flow entrainment. Also Also visible here, with some searching, are ±0. cm amygdules filled with fibrous fibrous actinolitic actinolitic amphibole. side, where where two two subparallel, subparallel, northeast-trending northeast-trending diabase Walk around the quarry to its south side, diabase approximately 3 m thick—the this thick-the maximum thickness of dikes in this dikes occur. These These dikes dikes are approximately set. They They are are cut cut by by thin, thin, white, white,silicic, silicic,and and sugary-textured sugary-textured veinlets veinletsthat that emanate emanatefrom from the the dike dike margins and pinch out in the dike interiors. The Theveinlets—interpreted veinlets-interpreted as partial melts of of the the presumably because because narrower wallrock granite—are granite-are rarely rarely present present in in dikes dikes less less than 2.5 m thick, presumably narrower dikes were not capable of heating the wallrock to temperatures sufficient for melt generation. polished outcrop mineralogy and The polished outcropsurface surfaceprovides provides aa good good look look at at the mineralogy and coarse coarse texture texture of black and white white mottled, mottled, red red color. color. The the St. Cloud Granite, characterized characterized by its distinctive black The imparted by microcline, red color is imparted microcline,the the black black by hornblende hornblendeand and minor minor biotite, biotite, and and the the white white by by saussuritized plagioclase. The The granite granite has has aa very very weak weak trachytoid trachytoid foliation, foliation, via alignment alignment of blocky feldspar and hornblende crystals. Where Where discernible, discernible, this fabric parallels the granite granite coarse-grained phase) phase) dike or sill margins. This This granite granite has has an amazing amazing lack of pegmatite (very coarse-grained and a preponderance preponderance of homblende hornblendeas as the the mafic mafic phase. Glacial features are are well well displayed displayed here here and and include include polished polished outcrops, outcrops, striations, striations, and and differential diabase/granite contacts. contacts. Most Mostof of the the subsurface subsurfacebedrock bedrock in in Minnesota Minnesota differential scouring scouring of the diabaselgranite is covered by variable variable thicknesses thicknesses of of weathered weathered bedrock bedrock residuum (saprolite) (saprolite) that has has been been highs by by glacial scouring. scouring. Saprolite stripped away from bedrock topographic highs Saprolite developed developed on on 22 22 �granite is typically pale gray-green. Many Many of of the the active active quarries in this area have exposures of granite of this saprolite saprolite along along the the margins margins of of the the pits. pits. interesting hydrologic hydrologic observation is the approximately 10-foot 10-foot difference in water An interesting level level between this pit and the small one to the south. The The two two quarries quarries are are separated separated by little little more than than the the diabase diabase dike's dike's width, width,and and the the hydrologic hydrologic gradient gradient exists exists despite despite the the abundance abundanceof of more cross-fractures cross-fractures in in the the diabase. diabase. Addendum Addendumto toStop Stop11 The The sketch sketch map shown shown on figure figure F6 is included for those who wish to visit the park to Of particular particularinterest interestisis aa pit pitatatthe theeast eastside sideof ofthe thepark park view other exposed geologic features. Of northwest-trending diabase to the the where aa northwest-trending diabase dike dike cuts cuts aa northeast-trending northeast-trendingone. one. The next pit to northwest of that thatshows showsSt. St.Cloud CloudGranite Granitehaving havingmany manyangular, angular,meter-scale meter-scale xenoliths xenoliths of of Reformatory Reformatory granodiorite—typical granodiorite-typical of of regional regional intrusive intrusiverelationships relationships between between the the two twounits. units. Diabase Dike St.Cioud(red) Granite ' Reformatory(gray) granodiorite j Mixed St. Cloud Granite and Reformatory granodiorite .# Cross—country ski trails Figure Figure F6. F6. Sketch Sketchmap mapofofthe theQuarry QuarryPark Parkshowing showingoutcrop outcropdistribution distributionand andsimplified simplifiedbedrock bedrock geology. geology. Modified Modifiedfrom fromStearns SteamsCounty CountyPark Parkwinter wintertrail trailmap. map. 23 23 �STOP STOP 2. 2. MERIDIAN MERIDIANAGGREGATES AGGREGATESQUARRY QUARRY • Location: Location:T.T.124 124N., N.,R.R.28 28W., W.,south southhalf halfofofSection Section18. 18. • Quarry Quarryoverlook, overlook,crushing crushingfacilities, facilities,restrooms. restrooms. Due to constraints constraints of time, time, safety, safety, and group size, we will will not not go go into into the the Meridian Meridian Aggregates Aggregates quarry, quarry, but we we will will get get an an excellent excellentview view of of the the pit pit from froman anoverlook overlookpoint. point. 1.2 million million tons tons of of crushed crushed Meridian Aggregates Aggregates Company produces an average average of 1.2 The Meridian rock aggregate aggregate per year. Mining Miningand andcrushing crushingoperations operationsrun run 77 months months of of the the year, year, although although stockpiled stockpiledproduct productisis shipped shippedyear-around. year-around. This Thisquarry quarryutilizes utilizes the the complex complex mixture mixture of igneous igneous rock rock types types present present in in the the pit, pit, mainly mainly the the Reformatory Reformatory granodiorite granodiorite and St. Cloud Red Granite, and and lesser lesser proportions proportions of of diabase diabaseand andquartz-feldspar quartz-feldsparporphyry porphyry dikes, dikes, such such as as will will be be seen seenatat Stop Stop 3. 3. Unlike Unlikedimension dimensionstone stonequarries, quarries,joints jointsand andfractures fracturesin inthe therock rock are are not not detrimental— detrimentalblast blast away! away! Quarrying Quarryingmethods methodsinvolve involvedrilling drillingand andblasting, blasting,primary primary crushing crushingin inaagyratory gyratory crusher, crusher, and and secondary secondary crushing crushing to various sizes. The The primary primary use use of of the the aggregate aggregate is is railroad railroad ballast, ballast, followed followed by by road road construction construction and and other other uses, uses, including including breakwater breakwater walls, decorative decorative stone, stone, and and driveway drivewaymaterial. material. A A substantial substantialfraction fractionof of the therock rockin in this this quarry quarry consists consistsof of fine-grained fine-grainedgray gray granodiorite granodiorite interpreted interpreted by by earlier earlierworkers workersas asinclusions inclusionsofofmetamorphosed metamorphosedand andmetasomatically-altered metasomatically-altered country rock in in the the Reformatory Reformatory granodiorite. granodiorite. Although Although there there are are undoubtedly undoubtedly some some small small xenoliths, finexenoliths,textural texturaland andgeochemical geochemicalevidence evidenceindicates indicatesthat thatthe thebulk bulkof ofthis thisgray graymaterial materialisisfinegrained grained border border phase phase of of the the Reformatory Reformatory granodiorite. granodiorite. If If the the light lightconditions conditionsare areproper, proper,aacross-section cross-sectionisisvisible visibleon onthe thefar farwall wallof of the the pit pit showing showing fresh fresh rock, rock, transitionally transitionallyoverlain overlainby weathered weathered bedrock residuum residuum (saprolite), (saprolite),overlain by glacial deposits. deposits. STOP STOP3. 3. MERIDIAN MERIDIANAGGREGATES AGGREGATESCOMPANY—SOUTH COMPANYÑSOUT PROPERTY PROPERTY • Location: Location:T.T.124 124N., N.,R.R.2828W., W.,Section Section19 19AB. AB. • St. quartzSt.Cloud Cloud(red) (red) Granite, Granite,aplite, aplite, Reformatory Reformatory granodiorite, granodiorite,diabase diabase dikes, quartzfeldspar feldsparporphyry porphyry(aka (akaporphyritic porphyriticmicrogranite) microgranite)dikes. dikes. This This stop stopisislocated locatedin inan anarea areaof of planned planned large-scale large-scalemining mining like like that that in in Meridian's Meridian's main main pit pit (Stop (Stop2) 2) just across acrossHighway Highway 23 23 to to the the north. north. There Thereare areaafew fewsmall smallabandoned abandonedquarries quarrieson on the the property, property, but but most most of of the the outcrops outcrops are natural (Fig. F7). Permission Permission must must be be obtained obtainedfrom from Meridian Meridian Aggregate Aggregate Company, Company, which has kindly kindly granted granted access access for for this this trip, trip, before before entering entering their their property, property,but but these these outcrops outcropswill will soon soonbe be mined mined out. out. STOP Cloud (red) (red)Granite Granite intrusive intrusive into into Reformatory Reformatory STOP3A—NE-trending 3A-NE-trending dikes dikes of St. Cloud (gray) (gray)granodiorite. granodiorite. The TheSt. St.Cloud CloudGranite Graniteisisnot notaadistinct distinctsingle singlebody, body, but but rather rather an an intricate intricate series series of of vertical vertical and and horizontal horizontal dikes dikes emplaced emplaced into into the Reformatory granodiorite. As As represented represented in this series series outcrops, outcrops,the theintrusions intrusionshave havecomplex complexgeometries geometriesand andvaried variedthicknesses thicknessesfrom fromfew fewcentimeters centimeters to to more more than than 50 50meters. meters. 24 �3B-A variety units, including including (oldest (oldest to toyoungest) youngest) STOP 3B—A variety of of intrusive rock units, St. Cloud Cloud Reformatory granodiorite, St. Cloud Granite, aplite related to the St. Granite, Granite,and anddiabase. diabase. The aplite aplite occurs occurs as as small, small,irregular irregularpod-shaped pod-shaped masses masses that that apparently apparentlycut cutboth boththe thered red The and gray gray intrusions. intrusions. Although Althoughthe thetiming timingof of emplacement emplacement of of the the aplites aplites relative to that of the and quartz-feldspar porphyry porphyry and and diabase diabase dikes dikes is is uncertain, uncertain, the the irregular irregular shapes shapes of of the the former former vs. vs. quartz-feldspar the straight straight and andcontinuous continuous(fracture-controlled (fracture-controlled emplacement) of the latter two two leads leads to to the the the inference that that the the aplites aplites are are a late late differentiate differentiate of the St. Cloud Granite. At this this site site and and the the inference Granite. At next (stop (stop 3C), 3C),note note the the contrast contrast in in jointing jointing pattern pattern of the aplite aplite and porphyry porphyry compared compared to to the the next surrounding surroundingplutonic plutonicrocks. rocks. Early Proterozoic Intrusive Rocks --------e Diabase dikes QFP (Porphyritic microgranite) dikes Aplite pods related to St. Cloud Granite (?) St. Cloud Granite Ref ormatory granodiorite Outcrop Geolo ical contacts, \ - - dashe where inferrec Small or discontinues diabase dike 0 8 ' 200 feet I 50meten I . Trails I Figure FigureF7. F7.Outcrop Outcropand andgeologic geologicmap mapofofStop Stop3.3. 25 % �STOP 3C-Porphyritic 3C—Porphyritic microgranite (aka quartz-feldspar quartz-feldspar porphyry). porphyry). This dike strikes strikes N45E, is 4-5 4-5 m thick, and has 4-6 percent percent glassy glassy subhedral subhedral quartz quartz phenocrysts and 3-4 percent subhedral phenocrysts in in an aphanitic, siliceous, phenocrysts subhedral K-feldspar K-feldspar phenocrysts groundmass. Dikes Dikes such suchas asthis thisare arescattered scattered around around the the St. St. Cloud Cloud area, area, and like the diabase the St. St. Cloud Cloud Granite. Granite. The dikes, they cut the Reformatory granodiorite, Rockville Granite and the phenocrysts vary from the 2-4 mm cm elsewhere. elsewhere. The margins phenocrysts rnm size here, to as large as 22 cm margins of the quartz-feldspar dikes are chilled, and in some cases flow-banded. A similar dike in quartz-feldspar dikes are chilled, and in some cases flow-banded. A similar dike in the the aggregate aggregate quarry north of here is clearly clearly comagmatic comagmatic and commingled with a diabase dike that contains fresh ophitic clinopyroxene, olivine, and chromite. However, However, that diabase dike contrasts with not altered/metamorphosed altered/metamorphosed all the other diabase diabase dikes dikes in this area in that the mafic minerals are not to actinolitic actinolitic amphibole. amphibole. STOP xenolith of of garnet garnet amphibolite amphibolite in St. Cloud Granite. Granite. STOP 3D—Small 3DÑSmal xenolith True xenoliths of external origin (vs. cogenetic mafic enclaves) are are rare rare in in all of the St. Cloud District intrusions. Xenolith types noted in the St. Cloud area include garnet-magnetiteCloud District intrusions. Xenolith types noted in the St. Cloud area include garnet-magnetiteamphibole schist (probably (probably metamorphosed metamorphosed iron-formation), biotite-quartz-feldspar schist of graywacke magnetite, and abundant graywacke protolith, protolith, granulitic granuliticgneiss gneiss that that contains contains garnet, sillimanite, sillimanite, magnetite, abundant cordierite, charnockitic garnet-biotite-orthopyroxene garnet-biotite-orthopyroxenegranofels. The The general general metamorphic metamorphic cordierite, and chamockitic mineral assemblages indicate that the country rock was metamorphosed to amphibolite and higher retrograde metamorphism metamorphism caused higher grade grade prior prior to to incorporation incorporationinto into the granites, granites, with minor retrograde caused by contact with with granite granite magma. magma. On the way to Stop 4 watch for the the derrick derrick in in the the deep deep quarry quarry north north (right) (right) of of the the highway highway on the east edge of the town of Rockville. Rockville. This This is the "Rockville Beige" quarry operated operated by the Cold Spring Spring Granite Granite Company. Company. STOP STOP 4. COLD COLDSPRING SPRINGGRANITE GRANITEQUARRY QUARRYAND AND PROCESSING PROCESSINGPLANT PLANT • Location: T.T.123 Location:(quarry) (quarry) 123N., N.,R.R.29 29W., W.,Section Section19 19BDAB. BDAB. • Rockville Rockville Granite, Granite,quarry quarrymethods, methods,production productionof offinished finisheddimension dimensionstone. stone. -- '—, —..__/ .1 -/ J/4 ((Gr.v • — u)j Highway 23')c-StOp 4A Figure F8. Location Location of of Stop Stop 4A. Other Otheroutoutcrops of Rockville Granite shown in black, Granite shown in black, except over the two quarries. STOP 4A—Cold 4A-Cold Spring Granite Granite Rockville Rockville White quarry quarry(Fig. (Fig. F8), F8), Rockville Rockville Granite, Granite, mafic mafic enclaves. enclaves. This is the "Rockville L'RockvilleWhite" quarry, quarry, one one of the three Cold of Cold Spring Spring Granite Granite quarries quarries developed granite developed in in Rockville Rockville Granite. Granite. The granite from the other Rockville quarries is marketed Beige" and and "Diamond "Diamond Pink." Pink." Due as "Rockville Beige" we will not be able to enter to safety concerns we the quarry, but will have ample opportunity to view the Rockville Granite Granite up close. close. This quarry uses the "drive-in This "drive-in quarry quarry method," method," a system that replaces the traditional cable-operated cable-operated derrick derrick method method of stone stone removal. Surprisingly, Surprisingly, the method was developed only in 26 �the mid-1970's mid-1970's (Muehlbauer (Muehlbauerand andFuchs, Fuchs,1997). 1997).The Thedrive-in drive-inmethod method utilizes utilizes aa series series of benches, the from which which the the stone stone is is removed removed as a series series in large "loaves" "loaves" that vary in size—15-25 size-15-25 feet (5from 8m) high high xx 20 20 feet feet (6m) (6m) wide wide xx 30-150 30-150feet feet (lO-50m) (10-50m) long. long. These Theseloaves loavesare aresubsequently subsequently 5.5 x 5.5 5.5 x 10.5 drilled off into smaller blocks that that are optimally optimally 5.5 10.5 feet feet in in size, size, weighing in at approximately 25,000 kg, or nearly 28 tons. This Thissize sizeisissmall smallenough enoughto totransport transportlegally legallyby by approximately flatbed trailer trailer without without aa special specialpermit, permit, and and allows allows for for minimum minimum wastage wastage during during processing. processing. flatbed Charles Charles Muehlbauer of Cold Cold Spring Spring Granite Granite will give a more extensive overview of the the quarry, quarry, and will will also also answer answer questions questions about about the the quarry quarry and andstone stone quarrying process at the products products in in general. general. There are many near the quarry viewing area to many blocks blocks of of Rockville Rockville Granite stacked near examine. examine. The Thefollowing followingfeatures featurescan canbe beseen seenin inthe theblocks: blocks: 1. Porphyritic Porphyritictexture, texture,rapakivi rapakivifeldspars. feldspars. 2. Mafic Maficenclaves, enclaves,some somewith with feldspar feldspar phenocrysts phenocrysts in them. The Theenclaves enclavesare areinterpreted interpreted as as the the product product of of the themingling minglingof ofmafic maficand andfelsic felsicmagmas magmas(see (seeINTRODUCTION). INTRODUCTION). Most Most occur occur as as ovoid ovoid inclusions, inclusions, although although discontinuous discontinuousand and irregular irregular dike-like dike-like masses masses of of the the same same composition compositionhave have been been noted noted in in another another quany. quarry. 3. Weak phenocrysts. This Weak trachytoid trachytoidtexture texturedefined defined by aligned aligned feldspar feldspar phenocrysts. Thisisistypical typicalof ofthe the "gray g r a y granites." granites." Stop Granite Company Processing and and Fabrication Fabrication Plant. Stop 4B—Cold 4BÑCol Spring Granite Plant. Cold two different different buildings. buildings. One Cold Spring Springpersonnel personnelwill will guide guide us in small groups through two One is is the the facing facing plant, plant, where where rough rough quarry quarry blocks blocks are are cut, cut, finished finished (polished (polished vs. vs. the the rougher rougher "fire"firefinish"), product specifications. The finish"), and and made made into into facing facing panels of varied size, depending on product The other polished, and and engraved. engraved. Notice other is the the monument monument plant, where the stone is cut, shaped, polished, surprisingly surprisinglyornate ornateworks! works! ****PLEASE * *PLEASE OBSERVE OBSERVESAFETY SAFETY REGULATIONS— REGULATIONS- HARD HARDHATAND HAT ANDSAFETY SAFETYGLASSES GLASSESMANDATORY*** MANDATORY*** STOP STOP5. 5. RICHMOND RICHMONDGRANITE GRANITE • Location: Location:T.T.123 123N., N.,R.R.3030W., W.,Section Section29 29BB BB center. center. • Charnockitic, prominent trachytoid trachytoid K-feldspar Charnockitic,rapakivi rapakivi granite granitewith with prominent K-feldspar phenocrysts. phenocrysts. ***PRIVATE PERMISSION OF *** ***PRIVATEPROPERTY—MUST PROPERTY-MUST HAVE HAVE PERMISSION OFHOMEOWNER HOMEOWNERTO TOENTER ENTER*** —HAMMERING -HAMMERING AND AND SAMPLING SAMPLJNG PROHIBITED— PROHIBITED- The TheRichmond Richmondgranite granitewas wasinterpreted interpretedby byearlier earlierworkers workersas asaahigh-grade high-grademetamorphic metamorphic gneiss gneissof ofArchean Archeanage. age. By Bycontrast, contrast,this thisstop stopdemonstrates demonstratesthat thatthe thegranite granitehas hasaa primary primary igneous igneous texture, texture, which which isis typical typical of of the the unit unit overall. overall. ItItcontains containsundeformed undeformedunit unitquartz quartzgrains grainsas aslarge large as 1 cm and euhedral feldspar phenocrysts as large as 5 cm. Because quartz is one of the as 1 cm and euhedral feldspar phenocrysts Because quartz is one of the first first minerals mineralsto toexhibit exhibitstrain strainand and recrystallization recrystallizationduring during deformation deformationand and metamorphism, metamorphism,the the rock rock clearly semiclearly has has not notexperienced experienced substantial substantial amounts amounts of of either either process, process, and and only only localized localized semibrittle brittle shearing shearing exists. exists. We Weinterpret interpretthis thisand andother otherlithologic lithologic evidence evidence to to indicate indicate that that the the Richmond emplacedafter aftermost mostof of the the regional regional deformation deformationceased, ceased, and and infer infer that that itit Richmondgranite granitewas wasemplaced probably probablyhad hadan anemplacement emplacementhistory historylike likethat thatof of the theReformatory Reformatorygranodiorite granodioriteand andthe theRockville Rockville Granite. Granite. 27 �Key features features at at stop stop 5: 5: 1. Dark green charnockitic charnockitic granite. This Thiscolor colorphase phasegrades gradesinto intothe the more moretypical typicalpink-tinted pink-tinted 1. Richmond granite, Richmond granite, due due to oxidation oxidation introduced introduced along along fracture fracture planes. At At first first glance, glance, the the green green phase looks like gabbro, gabbro, but if you trace trace across the gradation gradation to the pinker pinker phase, phase, you will will see see that it actually actually contains contains abundant abundant quartz quartzand and K-feldspar. K-feldspar. 2. Euhedral, Euhedral, carlsbad-twinned carlsbad-twinnedK-feldspar K-feldspar (microperthite) (microperthite) phenocrysts. Some Someof these are mantled by a thin rim of plagioclase, plagioclase, giving giving rise rise to rapakivi texture—best texture-best observed observed on on vertical, vertical, slightly slightly weathered faces, where plagioclase plagioclase is bleached white. 3. Magmatic-trachytoid Magmatic-trachytoidalignment alignmentof of feldspar feldsparphenocrysts phenocrysts (see (see Fig. F9). dark-colored mafic mafic enclaves. enclaves. From From aa petrographic petrographic standpoint, standpoint, these enclaves are 4. Small dark-colored mineralogically identical to aa fine-grained, mineralogically fine-grained, trachytoid, trachytoid, apatitic, apatitic,quartz-orthopyroxenequartz-orthopyroxeneclinopyroxene ferrodionte outcrops clinopyroxene ferrodiorite(orjotunite, (orjotunite,in incharnockite charnockiteterminology) terminology)that that occurs occurs in several outcrops 1/4 mile to the the west west of of this this location. location. This diorite diorite contains contains abundant abundant zircon zircon and small phenocrysts 114mile small phenocrysts phase that is of both plagioclase plagioclase and K-feldspar, K-feldspar, and locally grades into a coarser-grained coarser-grained phase compositionally and compositionally and texturally texturally similar similar to the Richmond granite as exposed here. The Thediorite dioriteto to the west is inferred inferred to to be be aaborder border phase phase of of the theRichmond, Richmond,and andthe the small smallenclaves enclavesscattered scattered throughout the Richmond throughout Richmond are are interpreted interpreted as as cognate cognate xenoliths derived from from this dioritic dioritic border border phase. •END FiELD TRIP. TRIP. THANKYOUFORATITENDING! END OF FIELD THANK YOU FOR ATTENDING!---------------You are are encouraged encouraged to to visit the poster titled You "DIMENSION "DIMENSION STONE STONE PRODUCTS PRODUCTS OF OF MINNESOTA" MINNESOTA" on display at the poster session. 28 �A ——- Strike and dip of ductile shear fabric Strike and dip of brittle shear fabric Strike and dip of trachytoid foliation vertical, inclined Figure F9. Map of central part of the Cold Spring 7.5-minute quadrangle, showing outcrops of Richmond granite. Structure symbols touch the outcrop from which they were taken. OAD �PHOTOGRAPHS OF QUARRIES QUARRIESININTHE THEST. ST.CLOUD CLOUDAREA AREAFROM FROMTHE THE EARLY 1900's. Top, QUARRIES PHOTOGRAPHS OF EARLY 1900's. TOP, QUARRIESOPERATED OPERATEDBY BY NORTH STAR GRANITE COMPANY, NOW OVERRUN AGGREGATES QUARRY?; NORTH STAR GRANITE COMPANY, NOW OVERRUNBY BYTHE THEPRESENT-DAY PRESENT-DAY MERIDIAN MERIDIAN AGGREGATES QUARRY?; BOTBOTTOM,AAQUARRY QUARRY OPERATED OPERATED BY GRANITE COMPANY, LOCATED IN FIELD TOM, BY THE MELROSE MELROSE GRANITE COMPANY, LOCATED IN THE THE VICINITY VICINITYOF OFSTOP STOP 1 1 OF FIELD TRIP 1.1. REPRODUCED FROM JOURNAL COLORED GRANITES FOUND IN TRIP REPRODUCED FROM JOURNALARTICLE ARTICLE OF OFTHE THEBRILLIANT BRILLIANT COLORED GRANITES FOUND IN AMERICA'S AMERICA'S GREAT NORTHWEST AMERICAN STONE STONE TRADE, PUBLISHED GREAT NORTHWEST ININ AMERICAN TRADE, PUBLISHEDMAY, MAY, 1931. 1931. 30 30 ��FIELD TRIP TRIP #2 FIELD THE SOUTHEASTERN FIELD GUIDE GUIDE TO THE GEOLOGY OF THE RIFT SYSTEM, PORTION OF OF THE THE MIDCONTINENT RIFT SYSTEM, EASTERN AND WESTERN WESTERN WISCONSIN WISCONSIN MINNESOTA AND Leaders: Leaders: Karl KarlR.R.Wirth, Wirth,William WilliamS.S.Cordua, Cordua,William WilliamF. F. Kean, Kean, Mike Middleton, Zachary Zachary J. J. Naiman Naiman INTRODUCTION The Middle Proterozoic Midcontinent rift rift system system extends extends over over 2,000 Proterozoic (Keweenawan) (Keweenawan) Midcontinent kilometers in an arc across central North America America from from Kansas Kansas to tocentral centralMichigan. Michigan. Magmatic kilometers Magmatic continental lithosphere lithosphere and sedimentary sedimentary rocks rocks in in this this major major tectonic tectonic feature feature record the evolution of continental million years years ago. ago. Rifting as it interacted with a mantle plume 1100 million Rifting was was aborted aborted before the production of oceanic lithosphere lithosphere began. Field, production Field, geochemical, geochemical, geochronologic, geochronologic, and and geophysical geophysical studies during the past decade have made significant contributions contributions to our understanding understanding of the evolution of of the Midcontinent rift rift system. system. The interested reader is referred to several recent evolution reviews (Van Schmus Schmus and Hinze, 1985), volumes (Tectonophysics, 213, 1992; Canadian Canadian reviews 1985), special volumes (Tectonophysics,v. 213,1992; Journal of Earth Science, Science, v. v.31, 1994; Canadian 34, 1997; Ojakangas Ojakangas Journal 3 1,1994; Canadian Journal Journal of Earth Science, Science, v. 34,1997; et al., 1997), 1997), and and guidebooks guidebooks (Miller (Miller et al., al., 1995) 1995) on on the the Midcontinent Midcontinent rift rift for for additional additional information. information. Geophysical Geophysical studies studies have provided much information about the nature of the rift, which lies buried beneath younger deposits along much much of of its its length. length. Regional gravity and magnetic surveys were important in establishing the extent and character of the rift (e.g., Hinze Hinze et et al., al., 1992). Our Our knowledge knowledge of of the the detailed detailed structure structure and and stratigraphy stratigraphy of the rift has has been been greatly greatly of the COCORP (Serpa et al., 1984; enhanced by several seismic surveys, most notably those of 1984; Zhu and and Brown, 1986) 1986)and and GLIMPCE GLIMPCE (Behrendt (Behrendt et al., 1988; 1988; Cannon et al., 1989) 1989)programs. programs. These surveys basins filled filled with with thick sequences of surveys revealed the presence of fault-bounded basins sedimentary rock. Detailed Superior volcanic and sedimentary Detailedseismic seismicimages imagesof the eastern portion of Lake Superior indicate the percent of oforiginal original thickness) thickness) in in some portions portions of the indicate the extent extentof of crustal crustalthinning thinning(—30 (-30 percent kilometers deep deep and and consists consists of of roughly roughly 20 kilometers kilometers rift; the rift in this region is more than 30 kilometers of basalt overlain by 10 10 kilometers of Keweenawan sedimentary rock. The voluminous tholeiitic basalt flows voluminous volcanic volcanic rocks of the rift consist predominantly of tholeiitic flows and minor rhyolite (Green, (Green, 1977; 1977; 1983) 1983) that were erupted during a relatively short short time time span span (1110-1090 Ma; Davis and Green, 1997). Trace element and isotopic studies indicate that the (1 110-1090 Trace element and isotopic studies indicate the basalts were derived from mantle melts that basalts that were were variably variably contaminated contaminated by continental continental lithospheric mantle Nicholson et lithospheric mantle and and crust crust (Nicholson (Nicholsonand and Shirey, Shirey, 1990; 1990;Shirey Shirey et al., 1994; 1994; Nicholson et al., 1997). The Thecombined combinedpetrologic, petrologic,structural, structural, and and geophysical geophysical evidence are consistent with a "hot-spot" "hot-spot" origin originfor for the the Midcontinent Midcontinentrift rift system system(Hutchison (Hutchisonet et al., al., 1990). 1990). 33 �SOUTHWESTERN ARM OF THE MIDCONTINENT RIFT SYSTEM SOUTHWESTERN THE MIDCONTINENT RIFT SYSTEM Most Most ground-based ground-based studies studies of the the Midcontinent Midcontinent rift have have been been conducted conducted in in the the Lake Lake Superior Superior region region where where Keweenawan Keweenawan volcanic and sedimentary rocks are well-exposed. Along Along much much of of the the southeastern southeastern (Michigan) (Michigan) and and southwestern southwestern (southern (southern Minnesota Minnesota to Kansas) Kansas) extensions extensions of the rift, rift, these these rocks rocks are are largely largely buried beneath thick Phanerozoic deposits. The The objective objectiveof of this this field fieldtrip trip is is to to provide provide an an overview overview of of recent recent studies studiesof of the the Midcontinent Midcontinentrift riftin in east-central east-centralMinnesota Minnesotaand andwest-central west-centralWisconsin. Wisconsin. Despite Despitethe therelatively relativelypoor poorexposure exposurein inthis this region, region, there there are are several several compelling compelling reasons reasons for for studying studying this portion of the rift. Most Most studies studies of of the rift in of the rift formed near the in the the Lake Lake Superior Superior region region have focused on the portion of location Peterman and Sims, Sims, locationof of the the inferred inferred Keweenaw Keweenaw plume plume beneath northern northern Wisconsin (e.g., Peterman 1988). New (e.g., Campbell Campbell and and Giffiths, Giffiths, 1990) 1990) have have New models modelsof ofmantle mantleplume plumeprocesses processes (e.g., contributed contributed significantly significantly to our understanding understanding of large igneous provinces and suggest that rift processes processes may vary with distance distance from the plume center. Unfortunately, Unfortunately, the distal portions of the Midcontinent rift system are buried, making geologic study difficult and costly. The Midcontinent rift system are geologic The rocks rocks of the the Taylors Taylors Falls Falls-- Clam Clam Falls Falls region region are are the southernmost southernmostexposures exposures of the Midcontinent Midcontinentrift rift of system system and and provide provide an an opportunity opportunity to to examine examine variations variations in rift geology geology and and processes processes along along the length length of of the the rift. rift. AAsecond secondreason reasonfor forstudying studyingthis thissegment segment of of the the rift rift relates relates to to regional regional geologic geologic provinces. provinces. The TheMidcontinent Midcontinentrift riftsystem systemcrosses crossesseveral severalmajor majorgeologic geologicprovinces provincesas as itit traverses In northern northern Minnesota Minnesotaand and Ontario Ontario traverses from from Minnesota Minnesotato to Kansas Kansas (Van Schmus, 1992). In the the rift rift is superimposed superimposedon on Late Late Archean Archean granite-greenstone granite-greenstoneterranes terranes (2.6-2.8 (2.6-2.8 Ga) Ga) of of the the Superior Superior Province. Province.South SouthofofLake LakeSuperior, Superior,the therift riftcrosses crossesaa younger younger east-west east-west belt belt of of immature immaturevolcanic volcanic and southward-dipping subduction and sedimentary sedimentaryrocks rocks (Southwick (Southwicket et al., al., 1989) 1989)that formed formed in a southward-dipping subduction zone Ga). Subduction Subduction processes processes during zone during duringthe the Penokean Penokeanorogeny orogeny(—1.85 (-1.85 Ga). during the Penokean Penokean may may have modified the mantle beneath these terranes, and thus might have had an effect on mantle an effect on the the Keweenawan magmas erupted through them. Studies Studiesof of Keweenawan Keweenawan volcanics south of the Malmo Structural Structural Discontinuity Discontinuity (Minnesota) (Minnesota) and and Niagara Niagara Fault Fault Zone Zone (Wisconsin) (Wisconsin) provide provide an an opportunity opportunity to to study study these these effects. effects. PREVIOUS PREVIOUS STUDIES STUDIES Studies of the the Taylors Taylors Falls - Clam Clam Falls region date back to the time before Minnesota became became aa state state in in 1858. 1858.AAthorough thoroughreview reviewof ofthe thehistory historyof ofinvestigations investigationsisis beyond beyondthe thescope scope of this guide, and the interested reader is referred to the review by Craddock (1972). Since this guide, and the interested reader review by Craddock (1972). Since the early 1900'sitithas hasbeen beenrecognized recognizedthat thatthe therocks rocksof ofthe theTaylors Taylors Falls Falls - Pine early 1900's Pine City City region region constitute constitute a thick, fault-bounded fault-bounded volcanic and sedimentary sedimentary sequence that has been broadly folded into a synform Hall, 1901). The synforrn (Strong, 1880; 1880; Berkey, 1897, 1898; Hall, The term term "Chengwatana" "Chengwatana" was was first first assigned by Hall in 1901 1901 to to refer refer to to aa sequence sequence of flows flows and interfiow interflow sediments of "unusual extent" that are exposed along the Snake River east east of of Pine Pine City City (Fig. (Fig. 1). As As stated stated by by Hall Hall (1901) (1901) "The flood floodof of 1898, 1898,which whichtore toreaway away the the dam dam at at the the foot foot of Cross Cross lake lake and and poured poured down down the river gorge gorge a vast volume volume of water, cleaned cleaned out in an admirable admirable manner manner for for examination examinationthe the channel channel of the the stream stream for for several several miles." At At the the time, time, Hall Hall (1901) (1901) was was able able to to describe describe aa nearly nearly continuous continuous sequence sequence consisting consistingof of 65 65lava lava flows flows and and 55 interfiow intefflow sedimentary sedimentaryunits, units, as aswell wellas as the relationships relationships of the bounding Douglas fault. He also recognized the typical three-fold flow He also morphology and described the igneous and metamorphic minerals. minerals. Unfortunately, Unfortunately, the rocks rocks along the Snake Snake River River are not not nearly nearly so so well-exposed well-exposed today. today. Later, Later, the the term term "Chengwatana "Chengwatana volcanics" volcanics" was wasused usedto torefer referto to Keweenawan Keweenawanvolcanic volcanicrocks rocks exposed exposed over over aa much much broader broader region region 34 �_______ ______ _______ ______ 2: Croix Falls 1982) (Modified from Morey Morey eta], eta!, 1982) 0 I I kilometers kilometers I I I 50 50 I Q .:. .:. .:. .;. ........... +;,:>:..:: .... :..:... .......... * * * * Ordovician Ordovician 0 N 0 Lower-Middle Lower-Middle Proterozoic Quartzite Proterozoic Cambrian Metavolcanic Rocks Metavolcanic Rocks U. Animikie Animikie Group Group Slate Metagreywacke Slate & Metagreywacke Bayfield Baytield Group Group Copper Copper Harbor Harbor Iron Iron Formation Formation Conglomerate Conglomerate Group L. Animikie Group Quartzite & wacke Duluth Duluth Complex Complex Gabbro & Anorthosite Gabbro Anorthosite F,,, - 5) Prot. Archean-L. h ot. Granite & Gneiss Mellen Complex, Complex, Basalt & Sediment Sediment Basalt Basalt (NSVG and and Chengwatana ChengwatanaVolcanics) Volcanics) 1. Generalized Generalizedbedrock bedrockgeology geologyof ofthe thesouthern southernLake Lake Superior Superiorregion region showing showing Figure 1. location of of the the field fieldtrip tripin inthe theTaylors Taylors Falls Falls -- Clam Clam Falls region. (Modified (Modified from from the location Morey et al., 1982). al., 1982). 35 35 �between the Douglas fault (west) and Lake Owen fault (east) in east-central Minnesota and between west-central Wisconsin (Morey west-central (Morey and Mudrey, 1972; 1972; Hassan and Mudrey, 1980). 1980). The distribution distribution and stratigraphy stratigraphy of the Chengwatana volcanics in the Taylors Falls - St. St. Cordua (1989a and b; b; unpublished unpublished mapping). mapping). He Croix Falls region was established by Cordua He divided divided the nearly 3,000 meter thick thick volcanic volcanic section section into into seven seven flow units based on on field field and and textural textural relationships (Fig. 2). The by Themapping matmin~ bvCordua Corduaalso alsodelineated delineated several several east-west east-west faults faults in in the the region. Nearly 3,000 meters of volcanic and sedimentary rock are also dso exposed in the Clam Nearly 3,O region, however corresponding mapping and stratigraphic been ~ h i cstudies have not been Falls Frederic regi Falls -- Frederic conducted conducted there there yet. ye1 meters above base Figure 2. Lithostratigraphic column of Chengwatana volcanics in the Taylors Falls region (Modified from Wirth et al., 1997). Top and bottom 2500 of the section are unexposed. Geochemical sample locations are shown with tick marks along the right side of the column. Flow unit abbreviations are from Cordua 2000 (1989): K!, Lotus lake; Kd, Dresser; Kt, Traprock Alley; Kep, Eagle Peak; Ks, Skitrail; Kp, Pipeline; Ky, unnamed. 1500 1000 Unexposed Interfiow Sediment Interflow Sediment Intersertal to Ophitic Ophitic Plag. phyric, intersertal 500 ....... ....... ....... Intersertal Intersertd ... Ophitic Ophitic [ Sub-ophitic Sub-ophitic 0 36 GEOPHYSICAL STUDIES Gravity, magnetic, ~agnetic,and and seismic studies lies were essential to developing developing detailed models of the buried the buried zontinent parts of the Midcontinent rift system in Minnesota mesota and and Wisconsin (see:review by Craddock, 1972). 172). The regional magnetic tic character of the Keweenawan iwan Rift E f t in eastern Minnesota lesota and and western Wisconsin sin is given given in Chandler et In Lnanuler eL a!. al. (1989) and Allen et al. al. (1997). Allen et (1997). The The rocks of the Taylors Falls Clam Clam Falls Falls region are part of the St. Croix horst, which is is bounded by by the Douglas bounded Douglas (northwest) and Hastings Hastings (northwest) (southeast) faults (Fig. 3). (southeast) 3). On On the the basis basis of of threethreedimensional dimensional gravity gravity models, models, the thickness ooff Chengwatana volcanics volcanics in Chengwatana this region ranges from 4 kilometers at Clam Falls to to 14 kilometers north of 14 kilometers north Frederic, and vertical uplift of the horst ranges from 3 kilometers in the northwest northwest to 8 kilometers in �Emerald Basin + + 0 20 kilometers strike/dip of flows and bedding I trend of aeromagnetic anomalies inferred structuraJ/strañgraphic I discontinuity 450 15' + + 920 15' 92° 00' Falls - Clam Falls region Figure 3. Sketch Sketchmap mapof ofaeromagnetic aeromagneticanomalies anomalies in the Taylors Falls interpreted from interpreted from new new aeromagnetic aeromagneticmaps mapsof of western western Wisconsin Wisconsin (Cannon (Cannonet et al., al., 1997; 1997;in in prep). prep). the southeast southeast(Allen (Allenetetal., al.,1997). 1997).Thick Thick(—5 (-5 km), wedge-shaped wedge-shaped accumulations accumulationsof of Keweenawan Keweenawan sediment (Oronto (Oronto and Bayfield Bayfield Groups) Groups) occur occur in in basins basins on the margins of St. Croix sediment Croix Horst Horst (Allen et a!., al., 1997). 1997). The magnetic character of Polk County is provided by Reich (1989), (19891, who conducted aa primarily N-S ground magnetic magnetic survey survey at 0.1 mile intervals, transecting the county along seven primarily Time-corrected raw data and 3-point smoothed data for line one are and E-W lines (Fig. 4). Time-corrected presented in Fig. 5. This This line covers some of the outcrops seen on this this field trip, trip, and shows the strong magnetic signature of the Chengwatana flows that is about 1000 nanotesla (nT) above the regional value. The Theminimum minimumin in the the magnetic magnetic line line at approximately approximately 15 15 kilometers kilometers from from the the 37 �___________ in the the bedrock bedrock caused caused west end of the line is interpreted interpreted by Reich (1989) as the result of offset in by the Cottage Grove fault. The Thehigh-frequency high-frequency nature nature of of the the magnetic magnetic signal signal on on the the west west end end of the flows. flows. These of the line is common to all the lines that cross outcrops of These high-frequency high-frequency by lightening. lightening. Lightening magnetic "spikes" may in part represent locations hit by Lightening strikes strikes on highly magnetic rock can produce produce large large localized localized anomalies. Many Many outcrops outcropsin in this thisregion regionare aremagnetically magnetically significantly deflect a compass! compass! Reich variations in the strong enough to significantly Reich (1989) interpreted interpreted the variations half-graben faults faults that thatparallel parallelthe theCottage CottageGrove Grovefault. fault. Recent Recent filtered data as resulting from half-graben work by Cannon et al. (1997; in prep.) suggest that these features are the result of folding work Cannon et (1997; suggest these features folding within within in the the magnetic susceptibility of of the the different different flows flows may may also be aa the flows. flows. Variations Variations in magnetic susceptibility contributing factor. Recent Recentstudies studiesby by Kean Kean (1992, (1992, 1993, 1993,1995) 1995)and and Kean Kean et et al. al. (1997) (1997) on on the the paleomagnetic paleomagnetic character characterof of Chengwatana Chengwatanaflows flows in in the the Taylors Taylors Falls region are described described in in the the 2. section for Stop Stop 2. et al., al., 1997; in prep.) provide New aeromagnetic data from western Wisconsin (Cannon et additional constraints on the stratigraphy stratigraphy and structure of the Chengwatana Chengwatana volcanics in the the Falls region. Previously, the relationship between the stratigraphic sections Taylors Falls Falls -- Clam Clam Previously, relationshipbetween the stratigraphic sections Taylors Taylors Falls Falls and and Clam Clam Falls Falls regions regions was wasnot notwell wellunderstood. understood. Preliminary interpretation interpretation in the Taylors suggest that the stratigraphy stratigraphy continues trending of the data suggest continuesnorth north of of the the Taylors Falls region before trending to the east east around around aa northeastnortheastsouthwest southwest antiformal antiformalstructure structure(Fig. (Fig. 3). No Nomajor majorstructural structuralbreaks breaks are are STUDY AREA POW COUNTT apparent. apparent. If this this interpretation interpretation is correct, then then the correct, the flows flows in the the Frederic - Clam Falls region are Frederic are stratigraphically below those of the stratigraphically the Falls section. section. Also apparent apparent Taylors Falls aeromagnetic map on the aeromagnetic map are are several several stratigraphic structural or stratigraphic discontinuities surrounding surrounding the the Ashland syncline, syncline, and northwest of Frederic. These relationships, relationships, combined with the results of recent geochemical geochemical and geochronologic geochronologic studies, suggest that that there may be significant differences between the flow flow sequences sequences and that further further stratigraphic subdivision of the stratigraphic subdivision the ICALI I US.SC CMLII • Chengwatana volcanics volcanics may be • C S ISKI.OMITICS warranted. warranted. U U SA8R STATION Location map map for Figure 4. 4. Location magnetic profiles of Polk magnetic profiles Polk Co., Co., 1989). Wisconsin (after (after Reich, Reich, 1989). 38 �WI., LVIE I A. A GAMMAS I .J'jii*w DATA 61500.0 •:". U.TIRCD DATA 60500.0 MM.I$ Plot of raw and filtered data for line 1 (A—A'I. - Figure Figure 5. 5. -- Magnetic Magnetic profile profile of Line Line 11 in in Figure Figure 44 (after (after Reich, Reich, 1989). 1989). METAMORPHISM IVETAMORPHISMAND AND MINERALIZATION MINEXALIZATION The The secondary s e c o n d q minerals minerals in in the the Keweenawan Keweenawan volcanic rocks form by aa combination combination of of burial metamorphism, activity and and contact contact metamorphism. metamorphism. They metamorphism, hydrothermal hydrothermal activity They form form 20-80 20-80 percent percent of of aa typical typical sample. sample. They Theyreplace replacephenocrysts phenocrystsand andgroundmass, groundmass,fill fillamygdules, amygdules,form form veins and line line joint and and fault fault planes. planes. The Theminerals mineralsreplacing replacing ground ground mass mass and and phenocrysts phenocrysts typically albite epidote+actino1ite~hlorite+qu~z+ albite+1+I- calcite calcite +1+Itypically consist consist of ofthe theassemblage assemblageepidote+actinolite+chlorite+quartz+ muscovite +/-titanite +1Fe-Ti muscovite +/-titanite +I- Fe-Ti oxides. oxides. The Thecommon commonminerals mineralsfilling filling amygdules amygdules are are quartz, quartz, chlorite, crystalline material chlorite,epidote, epidote,K-feldspar K-feldsparand andcalcite. calcite.The Thequartz quartz may may be present as coarse crystalline material or, or, more rarely, as agate. Joint Jointsurfaces surfacesand and fault fault planes planes may have veins or coatings of any of the and chrysotile. chrysotile. Minor the above above mentioned mentioned minerals, minerals, but may also show tremolite, tremolite, and Minor copper copper mineralization mineralizationin inthe theform formof of native native copper, copper, chalcopyrite, chalcopyrite, bornite, bornite, chalcocite chalcocite and and malachite malachite and and azurite occurs in amygdules, flow-top breccias or later gash veins (Grant, 1901; Dutton, 1972; azurite occurs in amygdules, flow-top breccias or later gash veins (Grant, 1901; Dutton, 1972; White, White, 1978; 1978;Cordua CorduaetetaL, al., 1979). 1979). Epidote Epidote occurs occurs as as both both granular granularand and crystalline crystalline grains. grains. Granular Granularepidote epidoteisiscommonly commonly observed observed in in the the groundmass groundmassor orasasalteration alterationofofthe theplagioclase, plagioclase,whereas whereascrystalline crystallineepidote epidote occurs occurswithin withinthe theamygdules. amygdules.Actinolite Actinoliteisispresent presentmainly mainlyininthe thegroundmass, groundmass,but butalso alsoreplaces replaces clinopyroxene clinopyroxeneand andoccurs occursin inamygdules. amygdules.Chlorite Chloriteisisubiquitous ubiquitousininall allof of the the flows flows and and is is present present in intwo two forms: forms: ripidolite ripidolite(brown (brownbirefringence) birefringence)and andpycnochlorite pycnochlorite(anomalous (anomalousblue bluebirefringence). birefringence). Although both types are present throughout the sequence of Chengwatana flows Although both types are present throughout the sequence of Chengwatana flowsthe theFe-poor Fe-poor variety variety (pycnochlorite) (pycnochlorite) is is most most abundant abundant in in the theuppermost uppermostflows, flows, and andthe thehigh-iron high-ironvariety variety (ripidolite) (ripidolite)isis more morecommon commonin inamygdules amygdules(Wirth (Wirthet. et. al., al., 1996). 1996). The The pressure pressure and andtemperature temperature conditions conditions during during metamorphism metamorphism in in these these rocks rocksare are constrained the actinolite. actinolite. The constrainedby bymineral mineralreactions reactions(Liou (Liouet etal., al., 1987) 1987)and and by the Na content of the The minimum minimum temperature temperatureof ofmetamorphism metamorphismof of the theChengwatana Chengwatanavolcanics volcanics isis constrained constrainedby bythe the 39 39 �presence of actinolite and epidote (Fig. 6) and presence and by by the the absence absence of of coexisting coexisting prehnite prehnite and and pumpellyite. The upper temperature temperature boundary of metamorphism is constrained by the lack of with epidote, chlorite, actinolite actinolite and and quartz. quartz. The hornblende coexisting with The maximum maximum pressure pressure conditions of metamorphism metamorphism (4-6 kbar) are constrained constrainedby bythe theabsence absenceofofglaucophane. glaucophane. Further Further conditions constraints on the pressure constraints pressure conditions conditions during during metamorphism metamorphism can can be estimated estimated from from the Na and and Al contents of the calcic amphiboles in the presence of of quartz + + albite + + chlorite + + magnetite A1 (Brown, 1977). Analyses (SEM-EDS) of actinolite indicate that it contains Na (M-4 site) 1977). Analyses (SEM-EDS) of actinolite indicate site) and tetrahedral A1 Al (AlIV). (Ala'). The found in in the tetrahedral Theresults resultsare are similar similar to to the the composition composition of amphiboles found Batholith and suggest suggest low low pressure pressure burial burialmetamorphism metamorphism contact aureoles aureoles of the Sierra Nevada Batholith Group. This of the Chengwatana Volcanic Volcanic Group. This suggests suggests that the the presently presently exposed exposed Chengwatana Chengwatana sediment. This flows were overlain by an additional 6-7 kilometers of volcanic flows or sediment. This estimate estimate is greater than the estimated burial depths made by Cordua (1980; 1989b) and Cavaleri (1987) by analogy Group in the Keweenaw Peninsula, Peninsula, but are consistent consistent analogy with with the the Portage PortageLake LakeVolcanic Group with the amount of uplift (<8 km) (<8 km) estimated from geophysical geophysical models models al., 1997). Assuming Assuming a peak (Allen et al., metamorphic temperature of approximately350' 350° C and a burial approximately km., the depth of approximately 7.5 km., metamorphic data from the Chengwatana flows suggest Chengwatana flows suggest aa geothermal gradient of approximately geothermal approximately 0.6 45-50° 45-50' CCwithin within this this portion portion of the midcontinental midcontinental rift. rift. Similar results were were obtained obtained by Livnat (1983) (1983) using using oxygen isotopes in the Portage Lake volcanic sequence sequence on on the the Keweenaw Keweenaw Peninsula. Peninsula. The metamorphic minerals in Polk County are are distinctly distinctly different different from those those seen seen further from further north in content of aci Wisconsin. Wisconsin. In the volcanic volcanic rocks rocks pr-s exposed in northern Douglas County cz-i-tr+H20 (south shore of Lake (south Lake Superior), Superior), \X, prehnite, laumontite and other prehnite, laumontite and other X #' \X zeolites are common common secondary secondary 9 .1. minerals (Grant, 1901, 1972, minerals (Grant, 1901, Dutton, 1972, 0 400 500 300 200 300 100 Cordua, 1990,1991). 1990,1991). In White, 1978; Cordua, southern Douglas County, southern Douglas County, in the Temperature Temperature (°C) (OC) region between Dairyland to Solon region Solon Figure 6. P-T P-Tdiagram diagramfor forunivariant univariant reactions reactionsrelevant relevant Springs, prehnite is found, but the Springs, prehnite the to low-grade low-grade metamorphism metamorphism of of mafic mafic volcanic volcanic rocks rocks zeolites zeolites are rare to absent absent (Grant, (Grant, (modified from from Wirth Wirth et al., (modified al., 1997). 1997). Estimated 1901). 1901). To To the the east, east, in in the the Minong Minong conditions conditionsof of metamorphism metamorphismof of Chengwatana Chengwatanavolcanics volcanics Copper Range, which stretches from are shown in shaded regions. Minong Minong through through Grandview Grandview in in 40 �Washburn, Washburn, Bayfield and Douglas Douglas Counties, Counties, prehnite is is common common and and pumpellyite pumpellyite has hasbeen been reported. Mi, 1982). Zeolites reported. (Grant, (Grant, 1901; 1901;Smith, Smith, 1947; 1947; Dutton, 1972; White, 1978; AH, Zeolites such such as as natrolite natroliteoccur occuralong alonglater laterjoint joint surfaces surfacesnear near Chittamo Chittamo and and heulandite heulandite and and natrolite natroliteare are reported reported occurring occurring in in amygdules amygdules with with quartz, quartz, epidote epidote and and chlorite chlorite near nearGrandview Grandview (LaPoint, (Lapoint, 1976). 1976). South South of of Grandview, Grandview, southeast southeast of of the the Lake Lake Owen Owenfault, fault,epidote, epidote,chlorite, chlorite,actinolite, actinolite,quartz, quartz, biotite zeolites (LePoint, biotiteand and ferrostilpnomelane ferrostilpnomelaneoccur, occur,with with no no prehnite, pumpellyite or zeolites (LePoint, 1976). 1976). A hornblende-epidote-biotiteassemblage assemblageisislikely likelydue duetotothe thepresence presenceof ofnearby nearbyMellen MellenIntrusive Intrusive A hornblende-epidote-biotite Complex plutons (Cannon et al., 1996). Toward the Michigan border, at Saxon Falls Complex al., 1996). Toward the Michigan border, at Saxon Fallsnear near Hurley, Hurley, prehnite prehnite and and zeolites, zeolites, such such as as thomsonite thomsonite and and laumontite, laumontite,are areagain againreported reported(Irving, (Irving, 1883; 1883;Cannon, Cannon,1996). 1996). The The higher higher metamorphic metamorphic grade grade of of the the Chengwatana Chengwatana basalts could could reflect reflect either either deeper deeper burial burialin inthe thevolcanic volcanicpile pilethan thanrocks rocksto tothe thenorth, north,or or the the presence presence of of aa higher higher geothermal geothermalgradient gradient in in that that part part of of the the Keweenawan Keweenawan terrain. Allen Allen et etal. al. (1997) (1997)estimate estimatethat that the the St. St. Croix CroixHorst Horst has has undergone undergone 3-8 3-8kilometers kilometers of of uplift uplift in in the the Taylors Taylors Falls-Clam Falls region. This This contrasts contrastswith with estimated estimateduplift upliftofof2-4 2-4kilometers kilometersininthe theAshland Ashlandsyncline synclineand and1-2 1-2kilometers kilometersininthe theTwin TwinCities Cities Basin Basin(SE (SEMinnesota). Minnesota). GEOCHEMISTRY GEOCHEMISTRY Petrographic Petrographicand andgeochemical geochemicalstudies studiesof ofthe theChengwatana Chengwatanavolcanics volcanicsin inthe theTaylors TaylorsFalls Falls -- Clam Clam Falls Falls region region have have been been conducted conducted by by Cordua Cordua(1980; (1980;1989b), 1989b),Cavaleri Cavaleri(1987), (1987),Leslie Leslieetet al. (1994), (1994),Wirth Wirthet et al. al. (1995; (1995;1996; 1996;1997), 1997),Naiman Naiman et et al. al. (1996; (1996;1997; 1997;in in press), press), and and Abbott Abbott et et al. al. al.(in (in press). press). These Thesestudies studiesestablished establishedthe thetholeiitic, tholeiitic,high-alumina high-aluminaand andhigh-iron high-iron character characterof of the the basalts basaltsin inthe theregion region(Table (Table1;1;Fig. Fig. 7); 7);intermediate intermediate and and felsic felsicrocks, rocks, with with the the exception exceptionof of rare rarerhyolite rhyolitenear nearClam ClamFalls, Falls, are are not observed. observed. Most Mostflows flows are are weakly weakly olivine-normative olivine-normative (0-15 (0-15 percent percent norm norm ol) 01) and and the theremaining remaining flows flows have have trace trace amounts amounts of quartz quartz in in their their norms norms (0-5 (0-5 percent percentnorm normqz). qz). Nickel Nickel abundances abundances (36 (36 -185 185ppm) ppm)and andMg#'s MgWs(Mg# (Mg#==Mg! Mg/ [Mg+Fe2] [Mg+Fe+2]== 0.37 0.37 -- 0.58) 0.58) are are Fe2 F ~ ++ Fe3 + Ti generally generallylow, low,suggesting suggestingthat thatthe the Chengwatana Chengwatana Volcanic Volcanic Group Group flows flowshave haveundergone undergonesignificant significant fractionation. fractionation. Chengwatana Chengwatana basalts can be subdivided basalts can be subdividedon onthe the basis basis of of TiO2 T i 0 2 (less (less than than and and greater greater than than 2.3 2.3 weight weight %), %), aa distinction distinction that that has has been been recognized recognized elsewhere elsewhere in in the the Midcontinent Midcontinentrift. rift.InIngeneral, general,the the high-Ti02 high-Ti02 basalts basalts are aremore more abundant in the upper part of abundant in the upper part ofthe the St. Croix Croix Falls Fallssection sectionand andare are St. characterized characterizedby byhaving havinggenerally generally low low Mg# Mg# (<0.5) (<0.5) and and high high A Al A1 Figure Figure7.7.Plot PlotofofChengwatana Chengwatanavolcanics volcanicsfrom fromthe theTaylors Taylors Falls region on a Jensen cation plot (Jensen, 1976) (after Falls region on a Jensen cation plot (Jensen, 1976) (after Wirth et al., 1997). Wirthetal., 1997). 41 �Table 1. Representative Representative analyses analyses of basalt and sediment from the Taylors Taylors Falls and Clam Clam Falls Falls region. region. Si02 Si02 Ti02 A1203 *l2O3 Fe203 Fe203 MnO MnO MgO MgO CaO CaO Na20 Na20 K20 K20 P2° LOT LO1 basalt KC-lb basalt KC-7 basalt KC-70 KC-70 47.60 48.30 1.69 15.57 13.34 1.71 48.13 2.64 14.07 16.40 0.21 5.17 15.65 13.61 0.19 6.69 9.56 0.19 7.48 8.14 2.38 0.16 3.09 64.75 0.93 59.64 0.84 11.11 13.55 8.75 1.63 8.41 2.45 1.43 0.31 1.25 7.37 0.08 0.97 11.92 0.21 0.73 0.10 2.02 2.60 0.55 0.19 1.13 sediment sediment sediment KC-331f KC-330g KC-330g KC-33 1f 0.10 2.66 11.55 1.28 0.61 0.13 1.59 Total Total 100.77 100.68 100.47 100.19 100.70 Mg# Mg# 0.57 0.43 0.42 0.23 0.48 39.54 0.57 — qz qz — — — — — — hy hy ol 01 17.73 17.01 20.38 9.24 6.41 2.66 ne Rb Ba Th Nb La Sm Sm Yb Zr Y 42 206 Cr Cr Ni — 9 26.68 — 16 15 128 — 206 — 13 9 11 — — — — — — — — — 108 23 121 209 42 122 23 142 165 185 125 124 128 79 67 105 248 254 169 161 1.03 9.58 3.50 2.15 Initial ENd Initial CNd+0.101 Locations: Sample Sample Locations: -KC-lb KC-1b KC-7 KC-7 KC-70 KC-70 KC-330g KC-310 48 546 14 11 V v 277 — -- -- -- 6.94 26 82 318 -1.7— -1.7 - — 19 -1.86 -1.86 NW1/4, section 5, T T 33 33 N, N, R R 18 18W NE114, NW114, W NE1/4, 1/4, NE NE 114, 1/4, section 6, T T 33 33 N, N, R R 18 18W SE W (Stop (Stop 1) 1) SE 114, NW 114, 1/4, section 14, T T 33 33 N, N, R R 19 19W NW 1/4, 114, NW W T 33 N, N, R R 18 18W NEll4, NEl14, section 6, T W NE1/4, NE1/4, T 37 37 N, N, R R 17 17W NE114, SW114 of section 11, T W (Stop 5) NE1/4, SW1/4 42 — 50 �the Taylors Taylors Falls basalts are are subsubincompatible trace-element trace-element abundances. abundances. REE patterns of the and variably variably enriched enriched in in the the light light REE, REE, with with abundance abundance levels levels 40-100 40- 100times times chondritic chondritic parallel and values for La, and from Most samples samples have have prominent prominentnegative negative from 12-22 12-22 times chondrites chondrites for Yb. Most Eu anomalies, feature that is consistent with the widespread petrographic evidence of plagioclase anomalies, aa feature petrographic evidence plagioclase Normalized trace trace element element abundances abundances (Fig. 8) of the flows are enriched in the fractionation. Normalized highly incompatible elements (e.g., Th, Nb, La) relative to the the less less incompatible incompatible trace elements incompatible elements (e.g., Th, I.) a -4 10 ID I I I I I Nd La Ce 5o I I I I I I I I I YbLu Tb Sm Eu I b : 10 I I I I I I I I I I I I I I I I I Th Nb Ta La Ce Sr P Nd Sm Zr Hf Eu Ti Th Y Yb Lu Figure 8. (a) (a)Chondrite-normalized Chondrite-normalizedplot plotof of REE REE abundances abundancesin in representative Figure 8. volcanics from from the Taylors Taylors Falls Falls region region (after Wirth Wirth et al., Chengwatana volcanics trace-element abundances normalized to primitive mantle. (b) Plot Plot of trace-element abundances normalized 1997). (b) (e.g., Zr, Y, Y,Yb); Yb);Ta, Ta,Nb, Nb,and andSr Srare arerelatively relativelydepleted. depleted. These These relationships relationships suggest that at least some of the major major and and trace trace element element variations variations exhibited by the Chengwatana Chengwatana volcanics volcanics are are aa fractional crystallization contamination. Basaltic result of fractional crystallizationand variable contamination. Basalticflows flows of the the Chengwatana Chengwatana volcanics exhibit a relatively narrow narrow range range of of Nd Nd isotopic isotopic compositions compositions (Fig. (Fig. 9). 9). Although Although flows range range from from+3.4 3.4 to initial ENd ENd values of the flows to 4.5, -4.5,the themajority majority of of samples samples plot within a initial more limited range (-1.5 and -3.0). -3.0). The The combined combined geochemical geochemical data suggest that the basalts originated contaminated by by continental continental lithospheric lithospheric originated from from plume-derived plume-derived melts that were variably contaminated mantle EM values mantle or or crust crust (Wirth (Wirth et et al., 1997). 1997).Rhyolites Rhyolitesfrom fromthe theClam ClamFalls Fallsregion regionhas hasinitial initialENd ENd of ++1.0 Thesevalues valuesare areclose closeto tothe thecomposition compositionof ofthe theinferred inferredplume plume(initial (initialENd 1.0 and -0.1. These value = = 0) 0) implying that the rhyolites formed by crystal fractionation fractionation (Abbott (Abbott et al., al., in in press). press). ' 43 43 �12 Clam Falls Rhyolite • Clam Falls Basalt 10 Falls Basalt 8 6 L 4 2 0 -12 -10 -8 -4 -6 0 6 Initial Nd £\ Initial Figure Figure 9. 9. Histogram Histogramofofinitial initialENd EM values values (1100 (1100Ma) Ma) of Chengwatana Chengwatana volcanics volcanics from from the the Taylors TaylorsFalls Falls and and Clam ClamFalls Falls regions regions(after (afterNaiman Naiman etetal., al.,in inpress). press). ITINERARY ITINERARY This in Minneapolis, Minneapolis, Minnesota. Minnesota. A This guide guide describes describes aa one-day one-day trip beginning and ending in regional regionalmap mapof ofthe theroute routeisisgiven givenin inFigure Figure10, 10,and andmore moredetailed detailedmaps mapsof ofthe thestops stopsare aregiven giveninin Figures Figures11 11and and12. 12.AAbrief briefdescription descriptionofofthe theroute routeisisgiven givenbelow: below: Proceed from from Minneapolis Minneapolis about 45 miles to Osceola Wisconsin. One One route route to to Osceola Osceola Proceed would wouldbe beas asfollows: follows:Take Take 1-35 1-35 north to the exit for Minnesota 97 east bound. Follow FollowRoute Route97 97 for 11 11miles miles to to its its intersection intersection with with Minnesota 95. Turn Turn left left (north) (north) on on Minnesota Minnesota 95 for 66 for miles. Turn Turnright righton onroute route243, 243,cross crossthe theSt. St.Croix CroixRiver Riverand andfollow followititto toits itsintersection intersectionwith with miles. Wisconsin Route 35. Wisconsin Route 35. Go Go north north on on Route Route35. 35. InInabout about4.5 4.5miles miles(about (about11mile milenorth northof ofDresser DresserWisconsin) Wisconsin)turn turnright right on Ravine Drive. Follow Ravine Drive a short distance to the entrance of the Dresser Trap Rock on Ravine Drive. Follow Ravine Drive a short distance to the entrance of the Dresser Trap Rock Company CompanyQuarry Quarry(Stop (Stop1;1;Fig. Fig.13). 13). Return Return to to Route Route 35. 35. Turn Turnleft left(south). (south). Go Go1 1mile miletotoState StateStreet. Street.Turn Turnright right(west) (west)on onState State Street. milestotothe theintersection intersection Street. This Thissoon soonbecomes becomes100th 100thAvenue. Avenue. Follow Followthis thisroad roadabout about33miles with with County County S. S.Turn Turnnorth northand andgo goabout about1/2 112mile miletotothe thepipeline pipelinecrossing crossingofofCount CountSS(Stop (Stop2;2; Fig. Fig. 15). 15). Return Return to to Route Route 35. 35. Turn Turnleft left(north). (north).Go Gothree threemiles milestotothe thecity citylimits limitsof ofSt. St.Croix CroixFalls. Falls. Turn Turn left leftinto intoInterstate InterstatePark, Park,Wisconsin Wisconsin side side (fee (fee area). area). Follow Followthe thepark parkroad road to toEagle EaglePeak Peakand andthe the group groupcamp camparea area(Stops (Stops3a 3aand and3b; 3b;Fig. Fig.17). 17). 44 �Figure Figure10. 10.Scanned Scannedimage image(not (notshown showntotoscale) scale)ofofUSGS USGSStiliwater, Stillwater,Minnesota Minnesota- -Wisconsin Wisconsin topographic topographicquadrangle quadrangle(1 (1xx22degree degreeseries; series;1:250,000 1:250,000scale) scale)showing showingthe thelocations locationsofofthe the field fieldtrip tripstops. stops. Return ReturntotoRoute Route35. 35.Turn Turnleft. left.Follow Followthe thesigns signstotomerge mergeonto ontoU.S. U.S.Highway Highway8 8- -WEST bound. WEST bound. Cross Crossthe theSt. St.Croix CroixRiver Riverinto intoMinnesota. Minnesota.Immediately Immediatelyafter afterthe thebridge bridgeturn turnleft leftatatthe thetraffic traffic light lightinto intoInterstate InterstatePark Park- -Minnesota Minnesotaside side(a(adifferent differentfee feearea) area)(Stop (Stop4;4;Fig. Fig.17). 17). Return Turnright right(east). (east).Recross Recrossthe theSt. St.Croix CroixRiver. River.Follow FollowU.S. U.S.88for for55miles miles ReturntotoHighway Highway8.8.Turn totothe theexit exitfor forRoute Route35 35north. north.Follow FollowRoute Route35 35north northabout about25 25miles. miles.About About2.5 2.5miles milesnorth northof of Frederic, Frederic,turn turnleft leftonto onto130th 130thStreet. Street.InInabout about0.5 0.5miles milesturn turnleft lefton on345th 345thStreet. Street.InIn0.7 0.7miles, miles, look anoutcrop outcropininthe thefield fieldtotothe thenorth north(Stop (Stop5;5;Fig. Fig.19). 19). lookfor foran Return for Returneast easton on345th 345thStreet StreettotoLewis. Lewis.Cross CrossRoute Route3535and andcontinue continueeast eastononCounty CountyRoad RoadEEfor 55miles; turn south on 65th Street to the town of Clam Falls. Turn west at the junction with miles; turn south on 65th Street to the town of Clam Falls. Turn west at the junction with County CountyRoad RoadI.I.Stop Stop55isisNNE NNEofofthe thejunctioin junctioinwith with73rd 73rdStreet. Street.(Stop (Stop6;6;Fig. Fig.20). 20). 45 �Figure 11. 11. Scanned Scannedimage imageof of aaportion portion of of the the USGS USGS Stiliwater, Stillwater, MinnesotaMinnesotaWisconsin topographic quadrangle (30 x 60-minute series; 1:100,000 1:100,000 scale) scale) image (not (not shown shown to to scale) Figure 12. 12. Scanned Scanned image scale) of a portion portion of of the the USGS USGS topographic quadrangle (30 x 60-minute series; Grantsburg, Wisconsin Minnesota Grantsburg, topographic quadrangle (30 60-minute series; . 1: 100,000 scale) scale) showing showing the locations locations of the the field field trip trip stops stops 5-7. 5-7. 1:100,000 46 �AlternateStop Stop66isisreached reachedfrom fromstop stop66by by continuing continuingsouth southon on73rd 73rdto tothe thejunction junction with with3315th Alternate 15th Ave. Continue Mckenzie Trail south and around Continuewest weston on315th 3 15thAve Ave to Mckenzie Trail. Follow Mckenzie the bend to to the the east. east. The Theroad roadveers veerssouth southaround around an an outcrop outcropon on the the north north side side of the the road road (Stop (Stop the 6b; 6b; Fig. Fig. 23). 23). 3 15th Ave and continue west to 90th Street along the east side side of of Sommers Sommers Lake. Lake. Return to 315th Turn north north and and continue continueon on 90th 90th Street Street to to the junction with 320th Ave. Continuewest west on on 320th 320th Turn Ave. Continue 15thAve. and on County Road I until the junction junction with with 3315th Ave. Continue Continue west west on on 315thAve. 315th Ave. Outcrops Outcrops on on north north side sideof of road road near neartop topof ofhill hill(Stop (Stop7;7;Fig. Fig.24). 24). Return 15th Ave., Return to to Frederic Fredericand andRoute Route35 35by bytravelling travellingwest weston on3315th Ave., south south on on120th 120thAve., Ave., and and west west on on 310th 3 10thAve. Ave. A Asimple simpleway way to to return return to to Minneapolis Minneapolis isis to to follow follow Route Route 35 35 south southto to U.S. U.S. Highway Highway 8. 8. Follow FollowU.S. U.S.88east easttotoits itsintersection intersectionwith with1-35. 1-35. 1-35 1-35southbound southboundleads leads direcily directly to to the the Twin Twin Cities Cities of of Minneapolis Minneapolisand andSt. St.Paul. Paul. Stop Trap Rock Quarries. Stop 1—Chengwatana 1-Chengwatana Lava Lava Flows Flows in the Dresser Trap Quarries. Location: NW 1/4 114Sec. Sec.55 Location: Approximately Approximatelyone onemile mileNNE NNE of of Dresser, Dresser, Wisconsin. North North Quarry Quarry -- NW andNEl/4Sec.6,T33N,R18W. and NE 114 Sec. 6, T 33 N, R 18W.EastQuarriesEast Quarries - SW1/4Sec.5,T33N,R18W. SW 114 Sec. 5, T 33 N, R 18 W. The The lava lava flows flows at at Dresser Dresserhave havebeen been mined mined for "trap rock" since "trap rock" since 1855. The Thelarge largequarry quarry complex, complex, owned owned by by Dresser Dresser Trap Trap Rock Rock Inc., Inc., currently produces currently produces 750,000 750,000 tons tons per per year year in in crushed crushedstone stoneof ofall allsizes. sizes. The rock rock isis extremely extremely tough an4 durable, duein in tough and durable,due large large part part to to the the interlocking of of microscopic microscopic unoriented unoriented crystals crystals of of chlorite chlorite and and actinolite. actinolite.All Allvisitors visitorsare are urged urg6d to to seek seekpermission permission to to enter, enter, and and to to use use Figure WIFigure 13. 13.Scanned Scannedimage imageof. of portions portions of of the the USGS USGS Osceola, Osceola,WIfundamental rules of fundamental rules of MN MN and and St. St.Croix CroixDalles, Dalles,WI-MN WI-MN topographic topographicquadrangles quadrangles(7.5(7.5caution. caution. The Therock rockwalls walls minute minuteseries; series;1:24,000 1:24,000scale) scale)showing showing the the location locationof of Stop Stop1.1. are are shear, shear, blasting blasting isis frequent, frequent,rock rockpiles pilesare areunstable, unstable,and andquarry quarrytruck truckdrivers driversexpect expectyou you to to yield yield right-of-way. right-of-way. We We will will visit visitseveral severalspots spotsininthe thequarry, quarry,the theexact exact localities localitiesdependent dependenton onthe theareas areasaccessible accessibleatatthe the time of the field trip. time of the field trip. Both Both quarries quarries expose expose basaltic basaltic lava lava flows flows that that have have been been recrystallized recrystallized incipiently incipiently to to completely completelyto togreenschist greenschistfacies ficiesminerals mineralsby bystatic staticburial burialmetamorphism, metamorphism,due duetotoburial burialwithin within the thevolcanic volcanicpile. pile. 47 �Geology of of the the north north quarry quarry The north north quarry quarry is is aa large largequarry quarry cut cut into into aa single singlelava lava flow flow over over 35 35 meters meters thick, thick, which which The is informally informally named the Trap Rock Alley flow. The flow is a generally subophitic subophitic to diabasic diabasic porphyritic basalt. The Themajority majority of of the the phenocrysts are plagioclase. Augite Augite shows shows up as lighter porphyritic patches on on weathered weathered surfaces, surfaces, giving giving the rock aa distinctly distinctly mottled appearance appearance (Fig. (Fig. 14 14aa gray patches Otherprimary primary igneous igneous minerals minerals are are plagioclase and ilmenite. In In places places these minerals minerals and b). Other are relatively fresh, but usually they are incipiently to completely replaced replaced by by a mixture of chlorite, titanite. The groundmass usually consists entirely chlorite, epidote, epidote, actinolite, actinolite, albite, albite, zoisite and titanite. of this mix of secondary secondary minerals minerals .Locally, bodies of coarse gabbro are present as sill-like sill-like masses. masses. Particularly Particularly common common on on the lowest lowest level level of of the the quarry, quarry, they they average average 0.5-1.0 0.5-1.0 meters meters in in thickness, thickness, and and consist consistof ofcoarse coarse augite, plagioclase and magnetite. Elongated to 44cm cmlong. long. Secondary augite, plagioclase Elongated augite augitecrystals crystals may be up to minerals, commonly developed minerals, such such as as those those found found in the surrounding surroundingbasalt, basalt, are are commonly developed at at the expense expense of the primary minerals. Angular Angularvesicles vesicles occur occur in in these these gabbros, gabbros, and are filled with euhedral quartz, quartz, epidote epidote and and felted felted masses of chlorite. chlorite. These Thesegabbros gabbrosare areinterpreted interpretedas as lenses lensesof of slowly slowly cooled intrusions. The cooled magma magma trapped trapped within within this this exceptionally exceptionallythick thick flow, flow, rather than as later intrusions. The lack lack of of chilled chilled margins margins in in the the gabbro gabbro against against the the basalt basalt support support this this conclusion. conclusion. Flow-top quarry. Here an interfiow Flow-top features features are are common common along the west wall of the quarry. interflow zone is found, basalt. The found, containing containing clasts clasts of of fine-grained fine-grained and extremely amygdaloidal basalt. The clasts clasts are are angular consisting angularand and up up to to 20 20 cm cm in diameter. Interstitial Interstitialto to these these clasts clasts in a fine-grained matrix consisting of of angular angular quartz quartz and and feldspar. feldspar. This Thismay maybe bean aninterfiow interflowsediment sedimentconsisting consistingof ofwind-blown wind-blown scoriaceous scoriaceous flow-top flow-top material material or or perhaps perhaps pyroclastic pyroclastic debris debris from a nearby cinder cone. Burial Burial metamorphism has resulted in the recrystallization of the matrix and growth of secondary the recrystallization matrix and growth of secondary minerals, minerals,especially especiallyquartz, quartz,epidote, epidote,and and chlorite. chlorite. Pay Payclose closeattention attentionto to the the sedimentary sedimentaryfeatures features at at this this stop stop for for later later comparison comparisonwith with sediments sedimentsexposed exposed at at Stop Stop 5. 5. Amygdules Amygdules are are ubiquitous ubiquitous throughout throughout the the flow, flow, but but increase increase in in size size and andnumber numbertoward toward the top of the the flow. flow. The Theminerals mineralscommonly commonly found found filling filling the the amygdules amygdules are are quartz, chlorite, epidote, K-feldspar, calcite and actinolite. The Theamygdules amygdulesare are usually usually zoned, zoned, with with chlorite chlorite forming forming the the rinds. rinds. Growing Growingon onthese theserinds rindsare areinward inward projecting projecting crystals crystals of of quartz, quartz, epidote epidote and and pink pink perthitic perthitic K-feldspar. K-feldspar. Calcite, Calcite,or oraasecond secondgeneration generation of of chlorite, chlorite, occupies occupiesthe the centers centers of the amygdules. Actinolite Actinoliteoccurs occursas asmicroscopic microscopic fibers fibers projecting from the groundmass into the amygdules amygdules and and intergrown intergrown with with the the other other amygdule amygdule minerals. Another joint surfaces surfaceswithin withinthe thebasalt. basalt. The Another group group of minerals minerals form form veins or occur along joint most prominent veins are a series reverse faults. faults. These series of of quartz quartz veins veins formed along reverse These veins veins range from 10-40 10-40 cm cm in in thickness thickness and andare aresurrounded surrounded by by zones zonesof ofparticularly particularly extensive extensive chioritization chloritization and and epidotization epidotization of the basalt. The Thequartz quartzisis coarsely coarsely crystalline crystalline and and milky. milky. At At times crystals up to 15 cm long. long. Locally Locally times the the veins veins open open up up into into vugs vugs containing containing euhedral euhedral quartz quartz crystals calcite occurs occurs on on the the quartz quartz as asyellow-green yellow-green flattened flattened rhombohedral rhombohedral or globular clusters of radiating crystals. Pink Pinktotowhite whiteK-feldspar K-feldspardruses, druses,radial radialgroups groups of of dark-green dark-green chlorite, chlorite, and and copper minerals such such as as chalcocite, chalcocite, cuprite and malachite also occur from time to time in the veins. veins. Joint chlorite, hematite, hematite, tremolite Joint surfaces surfacesmay may be be coated coated by by aa variety of minerals, including chlorite, tremolite (growing (growing in in fibers fibers up up to to 33cm cmlong), long),white whitecleavable cleavablecalcite, calcite,chrysotile, chrysotile,chalcopyrite, chalcopyrite,bornite, bornite, malachite, malachite,and andnative native copper. copper. 48 �Figure Figure 14. 14.(a) (a)Photomicrograph Photomicrograph(crossed (crossedpolars) polars)of of "ophimottled" "ophimottled"basalt basalt(scale (scalebar bar along alongleft left mrn long). long). (b) Photomicrograph Photomicrograph (uncrossed polars) of augite augite exhibiting exhibiting ophitic ophitic side is 55 mm mm long). Groundmass in (a) and (b) contains plagioclase texture (scale bar along left side is 2.5 texture (scale bar along left side is 2.5 rnrn long). Groundmass in (a) and (b) contains plagioclase microcrysts, microcrysts, Fe-Ti oxides, oxides, chlorite, chlorite, quartz, quartz, epidote, epidote, actinolite, actinolite, and and calcite. calcite. 49 �Nuggets Nuggets of native copper copper massing up to several kilograms have been found in the quarry, but the author has not seen any in place. place. These Thesereportedly reportedly are are most most common common when when quarry quarry corner of the quarry. These operations are active in the flow-top area in the northwestern comer These can can effects on the crusher, and are thus not viewed as a resource have disastrous effects resource by the the quarry quarry owner. quarry are arecut cutby bynumerous numerousfaults. faults. Numerous Numerouseast-dipping east-dipping(45O (45°)) The flows of the north quarry cross-cut by a west-dipping (35° north-south across thrust faults are cross-cut (35O ) thrust fault that trends north-south across the center of the quarry (Leslie et al., 1994). Along most of the west-dipping fault surface is (Leslie 1994). Along most of west-dipping fault surface is massive massive and milky-white milky-white quartz. epidote-filled en-echelon en-echelon fractures, fractures, quartz. Also Alsofound found within within the the gouge gouge zone are epidote-filled striated and stepped chlorite-quartz-epidote chlorite-quartz-epidote surfaces, and late-stage syntaxial calcite fillings. kinematic indicators indicators indicate indicate that the hanging wall moved up and and east east relative relative to to All of these kinematic the footwall. Motion Motionalong alongthis thissurface surfaceoffsets offsets other other thrust faults in the quarry that dip to the east; the magnitude of the motion is not known known but but is is likely likely minor. minor. The age of faulting is not known, but the similar metamorphic minerals found in both the host rock and the gouge zone suggest that motion occurred occurred while the rocks were still relatively deeply buried. Geology of of the the east east quarries quarries across the the railroad railroad tracks, tracks, is another Approximately 0.5 0.5 km km SSE of the north quarry, across complex. These quarry complex. Thesequarries quarriesexpose exposetwo twoflows flowsunderlying underlyingthe theTrap TrapRock RockAlley Alley flow flow seen seen in in the north quarry. These These flows flows are are informally informally named the Dresser flows. Ten to twelve meters of each flow are exposed. The flows The flows dip dip westerly at about 10 10 degrees. The The contact contact between between the the two flows is well exposed. exposed. been converted Both flows flows are are subophitic subophiticdiabase, diabase,and andlike likethe the Trap Trap Rock Rock Alley flow, have been to greenstones greenstones during burial metamorphism. metamorphism. The The lower lower flow flow contains contains aa primary primary igneous igneous ilmenite. The rock is microporphyritic. microporphyritic. The assemblage of augite, plagioclase and ilmenite. The groundmass groundmass phenocrysts are titanite, and phenocrysts are incipiently incipiently to completely completely replaced replaced by a mixture of chlorite, epidote, titanite, actinolite, albite albite and and zoisite. zoisite. The plus white white quartz quartz and and pink pink K actinolite, The same same mineral mineral assemblage, plus Feldspar occur in the amygdules. The top of this flow is well exposed, and has been virtually amygdules. The top of this flow is well exposed, and has been virtually entirely entirely recrystallized recrystallizedto to aa metamorphic metamorphic greenstone. greenstone. Large Largeamygdules amygdulesare areabundant, abundant,and and contain contain coarse-grained assemblage yellowan attractive coarse-grained assemblageof white white quartz, quartz, pink K-feldspar, K-feldspar, red hematite, hematite, yellowgreen epidote, and dark green chlorite. Only Onlyminor minor flow-top flow-top breccia breccia can be seen. seen. subophitic The upper flow has a fine-grained chilled base grading upward into a diabasic subophitic interior. The Theprimary primaryigneous igneousand andsecondary secondary minerals minerals are are the the same same as as that that of of the the lower lower flow. flow. The The upper flow flow contains contains fewer fewer amygdules, amygdules, and and these these are are dominated dominated by nearly isotropic isotropic chlorite chlorite with minor intergrown epidote and quartz. The Thetop topof of this thisflow flow isis not not exposed. exposed. 50 �Stop %Magnetic Characteristics of the the Chengwatana ChengwatanaLava LavaFlows. Flows. Stop 2—Magnetic Characteristics of Location: Outcrops are are located located on on both both sides sides of of the the road road near near the the intersection intersection between between the the Location: Outcrops NE 1/4, 114, NE 1/4, 114, Sec. 11, 11, T 33 N, R 19W. 19 W. pipeline and County Road S. NE Figure 15. 15. Scanned Scannedimage imageof ofaaportion portionof ofthe theUSGS USGS Osceola, Osceola,WI-MN WI-MN topographic topographic quadrangle (7.5-minute (7.5-minute series; series;1:24,000 1:24,000 scale) scale) showing showing the the location location of of Stop Stop 2. 2. quadrangle examine and discuss the magnetic characteristics characteristics of the Chengwatana Chengwatana At this stop we will examine lava flows as exposed in Polk County, Wisconsin. Wisconsin. Paleomagnetic studies have been been conducted conducted in this region over the past 10 relationship of these 10 years to better understand the stratigraphic relationship flows within within the the context context of of the the regional regional Keweenawan Keweenawan magmatic sequence. paleomagnetic studies studies for for this this region region are arereported reportedby byKean Keanetetal. al.(1997). (1997). Here Detailed paleomagnetic only on on the the general general interpretation interpretation of of the the paleomagnetic paleomagnetic results results that that help helpto to place place we concentrate concentrate only the Chengwatana flows in the context context of of the the other other Keweenawan Keweenawan rocks in the Lake Lake Superior Superior region. Keweenawan Keweenawan paleopole paleopole positions positions for the craton are well known and a major polarity reverse to normal transition from fromreverse normal occurred occurred during during the the middle middle Keweenawan Keweenawan (1105-1102 (1 105-1102 Ma) has been documented by Palmer (1970) and Halls and Pesonen (1982). Table Table 22 shows shows this this Lake Superior polarity change change as as determined determined in some some of the major basalt flows of the southern Lake predominantly region. Feeney Feeney(1990) (1990)determined determinedthat that the the lava lava flows throughout Polk Co. have predominantly a-95=15.5° ;;which is consistent D=27S0 ,,1=41.5° 1=41S0,, a-95=15.5O normal polarities, polarities, with with aa mean direction direction of D=275° consistent Pesonen, 1982) 1982) such as the the North North Shore with other other Keweenawan Keweenawan directions directions(Table (Table 2) (Halls and Pesonen, Volcanic Group Group (Books, (Books, 1972). 1972). He Volcanic He also also noted noted several several locations locations with with reversed reversed directions. directions. St. Croix CroixFalls Fallsrendered renderedamore amore precise correlation correlation Insufficient geologic geologic control controlnorth north of the city of St. impossible impossible for for those those locations. locations.However, However,the thevolcanics volcanicssouth southof of St. St. Croix Croix Falls Falls are are better exposed exposed and have been mapped in detail detail by Cordua Cordua (1989a and b) which allowed for a more detailed study. Sixty-five Sixty-fiveoriented orientedcores coreswere were collected collectedat at the 66 sites noted in ~FIgure i g u r e16. Sampling Samplingwas was 51 �Table 2. Magnetic Magnetic polarity polarity and anddirections directionsfor formany many Keweenawan Keweenawan rocks rocks in in the the Lake Lake Superior region (from Superior (from Halls Halls and and Pesonen, Pesonen, 1982). 1982). Formation DeclinDeclination Jacobsville Jacobsville Sandstone Sandstone 263 263 Freda Sandstone Sandstone Apha 95 Pole Position Polarity -11 6 183°E, -0.9°S N 271.3 271.3 0.7 2.8 179.5°E, 1.2°N N Nonesuch Shale Shale 279.8 279.8 9.8 6 176.5°E, 10.3°N N Portage Volc (Avg) (Avg) Portage Lake Lake VoIc 288.6 34.9 2.5 181.2°E, 26.5°N N Upper North Shore Shore Vol. Vol. (Avg) (Avg) 290.3 290.3 44.5 4.7 183.8°E, 32.4°N N Lower Lower North Shore Shore Vol. Vol. (Avg) (Avg) 120.9 120.9 -63 7.8 197.8°E, 9.6°N N Logan Logan Sills Sills 1111 11 -72 2.5 219°E, 49.4°N N 74 74 -71.5 4.8 232.4°E, 28.9°N N Upper Powder Mill Gr. Gr. InclinInclination and 2), 2), and and concentrated in the areas areas where where Feeney Feeney (1990) (1990) found found reversed reversed directions directions (sites (sites 11 and equivalent. Most which are considered stratigraphically equivalent. Most of of the the samples samples (Table (Table 3) 3) have have high high intensities of natural remanent magnetism (NRM) (1.0-2,0 AIm) and volume magnetic natural remanent magnetism (NRM) (1.0-2.0 Alm) and volume magnetic susceptibility (4 x 10-2 SI). SI). The Themagnetic magneticproperties propertiesdiffer differ somewhat somewhat between between flows.. flows. The The remanent intensities middle flows flows (Pothole (Potholetrail, trail, Trap Trap Rock Rock Alley and Dresser flows) have remanent intensities and and which are are at least an order of magnitude less than the other magnetic susceptibilities which other flows flows (Table 3). For Forsamples sampleswith withvery very strong strong remanent remanent values, values, the intensities intensities are typically reduced A.F. demagnetization to to 20 20 millitesla millitesla (mT). (mT). Petrographic studies 100 fold with A.F..demagnetization studies of the the opaque opaque minerals in samples from each each site site also also show show differences differences which are consistent with the bulk magnetic parameters of susceptibility susceptibility and intensity. intensity. The The upper upper lava lava flows flows (sites (sites 1-4; 1-4; Fig. 16) 16) have a high percentage percentage of coarse-grained magnetic minerals (25 percent), which are generally coarse-grained magnetic minerals (25 percent), which are generally more altered than the older flows (sites 5 and 6), 6),and and which appear to have been produced during metamorphism. metamorphism. Samples during Samplesfrom fromsites sites55and and66have haveonly only about about 10 10percent percent magnetite magnetitegrains grains and the grains are smaller smaller than the upper flows. Principal Principalcomponent componentanalysis analysisof of the the magnetic magnetic directions directions (Kirschvink, (Kirschvink,1980) 1980)for for samples samplesfrom fromthe the various various sites sitesreveals reveals two two directions directionsthat that are are approximately antiparallel to to each other. other. The most prominent direction, after removal of The most prominent direction, after removal of aa viscous component is a northwesterly with inclinations of of about 430 43O (normal (normal northwesterly declination, with magnetization). A approximately -50 500 A second seconddirection direction with with aa southeasterly southeasterly declination and approximately inclination (reverse in some some samples samples at at sites sites 11and and2.2. There are (reverse magnetization) is present only in no significant significant differences petrographic characteristics characteristics or in the the rock rock magnetic magnetic properties properties differences either either in petrographic between the normal magnetized samples and the reversely magnetized samples at both sites 11 normal samples and 2. Wirth the entire entire sequence sequence of of Wirth et et al. al. (1997) (1997)report report only minor geochemical differences for the flows. The Thedetailed detailedmagnetic magneticinformation information for for these these sites sites is is given given in Table 4. Combined Combined data data from both components yield yield a Virtual Virtual Geomagnetic GeomagneticPole Pole(VGP) (VGP)atat30.9' 30.9° N, N, 186' 186° E, which which 52 �92 42 3O Oc 1 Ouarternary Alluvium. Colluviurn. Drift d 45 25 ST CROIX FALLS 8 PRECAMBRIAN PRECAMBRIAN KEWEENAWAN KEWEENAWANVOLCANIC VOLCANIC SERIES SERIES Ky Kv 0Kp Kp 0KsKs 0Kep Kep tO Kt Kd Kd Kpt Kpt --0 Q Unnamed Unnamed Flows Flows Pipeline P~pehneFlows Flows Skitrail Skltra!lFlows Flows Eagle Eagle Peak Peak Flows Flows Traprock TraprockAlley Alley Flows Flows Dresser Dresser Flows Flows Pothole Pothole Trail Tra~lFlows Flows Exposed Exposed Contact Contact Unexposed Contact Contact Unexposed Sample Location LocatlonNormal Normal Sample Location Locat!onReversed Reversed Sample Location LocatlonMixed Mlxed 1 MILE G 0 iKM t 45 20 92 $2'42 42'30 3W 92 37 30 Figure Figure 16. 16. Map Mapshowing showingpaleomagnetic paleomagneticsampling samplingsites sites(after (after Kean Kean et et al., 1997). 1997). 53 �Table 3. NRM NRM intensities intensitiesand and susceptibility susceptibility values for the Chengwatana volcanics in the St. St. Croix Croix Falls Falls area. area. Flow Name Number of samples samples Ky Kv NRM Intensti Intenstity ty AIM A514 Magnetic Susceptibility x10i5 Volume S.I. units xlO-5 9 2.3 3591 Pipeline Pipeline 14 2.0 5118 SkiTrail Ski Trail 16 2.1 5326 Eagle Peak Peak Eagle 14 0.15 1061 6 0.14 23 0.057 299 742 Trap Rock Alley Dresser 11 Pothole Trail 6 0.05 LotusLake h t u s Lake 6 2.1 3647 Paleomagnetic data for the sites indicated in Figure 16 Paleomagnetic 16 (after Kean et a!., al., 1997). 1997). Table 4. N DecinDeclination Inclination K 288.9 49.5 5.2 6.9 29.2 36.7 17 Apha -95 (R) (3) 7 7 114.8 55.0 -57.8 Site 2 (N) (N) 7 274.0 51.1 13 -47.5 33.2 14 23.1 20.8 31 16.3 14.1 45.5 42.6 43.4 45.8 11.2 18.8 11.2 Site I1 (N) (N) (R) (3) Site 33 Site 4 Site 55 Site 66 (N) Avg (N) (N&R) Avg @&R) 10 10 88 106.7 5 280.0 88 77 88 285.1 306 6 6 88 287.9 286.8 287.5 6.7 25.4 43.9 48.5 10.2 8.04 VGP Lat(N) L atO Long(E) Long@) SITE SITE L ato L ong0 Lat(N) Long(W) 45.33 92.65 24.6 31.2 193.4 193.4 198.4 187.9 45.37 92.67 19.9 183 22 43 178.9 29.6 29.7 30.9 183.6 184.9 186.1 45.39 45.39 45.36 45.37 92.66 92.66 92.64 92.63 41 173 agrees well with published published Keweenawan Keweenawan paleopoles for stable North American (Halls and and Pesonen, the area, area, because because Pesonen,1982). 1982).ItItisispossible possiblethere thereare areother other exposures exposuresof of the reversed flows in the detailed magnetic studies have not been conducted over the full length of the two prominent ridges in the area. area. Paleomagnetic Correlation Correlation The appear wimn within aa thick thick series series of of The reversed flows in this area are important because they appear flows that are normally polarized and considered to be equivalent in age, or younger than, the 54 �NorthShore Shorevolcanics. volcanics.Past Pastinterpretations interpretationssuggested suggestedthat thatallallthe theKeweenawan-age Keweenawan-ageflows flowsequivaequivaNorth lentororyounger youngerthan thanthe theNorth NorthShore Shorevolcanics volcanicswere werenormally normallypolarized polarized(Green, (Green,1977; 1977;Halls Halls lent and andPesonen, Pesonen,1982), 19821,and andthose thoseflows flowsolder olderthan thanthe theNorth NorthShore Shorevolcanics volcanicswere werereversely reverselypolarpolarized. ized.Similar Similarshort shortreversals reversalsatatapparent apparentequivalent equivalentstratigraphic stratigraphiclevels levelshave havebeen been documented documented onlyaafew fewother otherlocations locationsin inthe theLake LakeSuperior Superiorregion. region. The Thebasalt basaltflows flowsatatMamainse MamainsePoint Point atatonly theeastern easternLake LakeSuperior Superiorregion regionshow showa asimilar similarshort shortreversal reversal(Palmer, (Palmer,1970; 1970;Robertson, Robertson, ininthe 1973). 1973).The Thedikes dikesininthe thealkali alkalisyenite-carbonatite syenite-carbonatitecomplexes complexesininthe theKapuskasing Kapuskasingstructural structural zone zoneininCanada Canadadated datedatat1097 1097Ma Mayears yearsshow showreversals reversalsin in aanormal normal polarity polarity sequence sequence(Symons (Symons etetal. al.1994). 1994).The Thegeochemical geochemicaldata dataofofWirth Wirthetetal. al.(1997) (1997)are areconsistent consistentwith withthis thisequivalence equivalenceinin age agebetween betweenthe theChengwatana Chengwatanaflows flowsand andthe themiddle middlesection sectionat atMamainse MamainsePoint. Point.AAshort shortreverreversal salatatthis thistime timeisisalso alsoconsistent consistentwith withrecent recentages agesby by Wirth Wirth and and Gehrels Gehrels (in (in press). press). They Theyreport report Mafor forslightly slightlyolder olderChengwatana Chengwatanarhyolites rhyolitesnear near preciseU-Pb U-Pb zircon zircon ages ages of of 1102 1102Ma Ma ± 55Ma precise Clam ClamFalls, Falls,which whichisison onthe theeastern easternextreme extremeofofthe theChengwatana Chengwatanaexposures. exposures. Field FieldIdentification IdentificationofofReversed ReversedFlows Flows Unfortunately, Unfortunately,ititisisnot notpossible possibleto tovisually visuallyrecognize recognizenormalnormal-from fromreverse-polarity reverse-polarityrocks rocks ininthe thefield. field.Occasionally, Occasionally,the thereversed reversedflows flowsininthis thisarea areawill willcause causeaacompass compassneedle needleto todeflect deflect by but bymore morethan than90°, 90° butthen thenso sowill will areas areasstruck struck by lightening. lightening. Only Onlydetailed detaileddemagnetization demagnetizationof of samplesin inthe thelaboratory laboratorycan canresolve resolvethe thepolarity polarityquestion. question. samples Stop Interstate Park, Stop3a—Chengwatana 3a-Chengwatana Volcanic Volcanic Flows Flows of Interstate Park,WI. WI. Location: Location: Access AccesstotoEagle EaglePeak Peakisisfrom froma ahiking hikingtrail trailleading leadingwest westfrom fromthe thegroup groupcamping camping area, (WI).NW NW1/4, 114,SE SE1/4, 114,Sec. Sec.36, 36,TT3434N,N,RR1919W. W.(Fig. (Fig.17). 17). area,Interstate InterstatePark Park(WI). NOTE: NOTE: Specimen Specimencollecting collectingisisnot notallowed allowedininthe thepark! park! Thecrest crestof ofEagle EaglePeak Peakisison ontop topof of the thedipping dippingEagle EaglePeak Peakflow, flow, aa porphyritic porphyritic basalt basalt with with The large largeplagioclase plagioclase phenocrysts. phenocrysts. The Thepanoramic panoramicview viewfrom fromthe thecrest crestallows allowsvisitors visitorstotosee seethe the contrasting contrastingtopography topographyon oneast-facing east-facingflow flowfronts frontsversus versuswest-sloping west-slopingflow flowtops, tops,the thegeneral general distribution distributionof ofCambrian Cambriansedimentary sedimentaryrocks rocksdeposited depositedaround aroundbasaltic basalticislands, islands,and and the the Quaternary Quaternary featuresof ofthe theDalles Dallesofofthe theSt. St.Croix CroixRiver. River. features TheEagle EaglePeak Peakflow flowmap mapunit unitconsists consistsof ofseveral severalflow flow units units containing containingconspicuous conspicuouspink pink The plagioclasephenocrysts phenocrystsup uptoto66cm cmlong longin inaafine fine crystalline crystallinematrix. matrix. The Thematrix matrixand andphenocrysts phenocrysts plagioclase minerals such as epidote, arepartly partlyto tocompletely completelyreplaced replacedby bysecondary secondarymetamorphic metamorphic minerals such as epidote,chlorite, chlorite, are actinolite Kactinolite and and albite. albite. The Theflow flowtop topcontains containsmany manyamygdules amygdulesfilled filledwith withquartz, quartz,epidote, epidote,Kfeldspar feldsparand andchlorite. chlorite.The Theflows flowsdip dipgently gentlywestward westwardatatan anangle angleofofabout about15 15degrees. degrees. This Thisflow flowisisan animportant importantstratigraphic stratigraphicmarker, marker,traceable traceablein inthe thearea areafor forover over99kilometers kilometers along alongstrike. strike. InInplaces placesthe theunit unitconsists consistsofofonly onlyone oneflow; flow;in inothers othersititthickens thickensto to as asmuch muchas as60 60 meters meters and and includes includesat atleast least33 flow flow units, units, one one on on top top of the other. In Inthe theEagle EaglePeak Peakarea, area,only only oneflow flowisisevident. evident. one The Theslope slopecontinuing continuingdown downto tothe thewest westisisthe thedip dipslope slopemarking markingthe thetop topof ofthe theEagle EaglePeak Peak flow. flow. This Thisisisinincontrast contrasttotothe thesteep steepeast-facing east-facingescarpment escarpmentone oneascends ascendstotoreach reachthe thesummit summit from the group camping area. A small escarpment in the trees marks a quarry exposing from the group camping area. A small escarpment in the trees marks a quarry exposing the the overlying overlyingflow. flow. This Thisemphasizes emphasizesthe thestair-step stair-steptopography topographyof of the the terrain terrain formed formed by the dipping dipping flows. flows. 55 �Figure 17. 17. Scanned Scannedimage imageof of aaportion portion of of the the USGS USGS St. St. Croix Croix Dalles, Dalles, WItopographic quadrangle MN topographic quadrangle(7.5-minute (7.5-minute series; series; 1:24,000 1:24,000 scale) scale) showing showing the locations of Stops Stops 3a, 3a, 3b, and 4. One can see see outcrops outcrops of of Cambrian Cambrian sediments sediments deposited unconformably on the complex in the Chengwatana Chengwatana flows. flows. Looking slightly south of west, across the landscape developed in sandstones exposed in road cuts along U.S. river, one sees buff-colored Cambrian Mazomanie sandstones Highway 8. Cambrian Cambrianstrata strata continue continue down down to river level on the west side of the St. Croix Croix Highway River. The fiver. The sandstone sandstoneisistraceable traceablethrough through the the trees trees along along the the bluffs north nearly to the town of Taylors Falls. Falls. Here Taylors Hereaaridge ridgeofofbasalts basalts(predominantly (predominantlythe the Eagle EaglePeak Peak and andTrap TrapRock RockAlley Alley flows) rise up from which the the town town rests. rests. The scenic gorge called from the river to form the hills on which the St. Croix Dalles is cut cut through through these flows. Locally Locally along along the the contact contact of of the the Cambrian Cambrian sediment, is aa coarse coarse basalt basalt boulder boulder conglomerate conglomerate facies called the Mill Street Street conglomerate. conglomerate. the next next stop. stop. Another ridge of basalt is found near This is not visible here, but will be visited at the Northern States Falls is is built. built. East the Northern States Power Power Plant Plant and forms the highlands on which St. Croix Falls East of the river are many outcrops A few few exposures exposuresof of Cambrian Cambrian sandstone, sandstone,particularly particularly outcrops of basalt. A along along the bluffs bluffs to to the the east, east, can can also also be be found. found. 56 �Reconstruction Reconstructionof of the the paleogeography paleogeography of of the the Cambrian-Precambrian Cambrian-Precambrian unconformity unconformity was was done done using using outcrop outcrop and and water-well water-well data. The Theunconformity unconformity is is complex complex and and shows shows aa relief relief of of over over 100 100meters meters (Scott (Scott and and Anderson, Anderson, 1983). 1983). In Insome someareas, areas,the the relief relief occurs occurs along along buried buried shear shear cliffs, Cambrian sea rose. The as the Cambrian The Mill Mill Street Street conglomerate conglomerate cliffs?which whichwere wereprogressively progressively covered covered as marks these environments. In other areas, calmer embayments and lagoons formed marks these environments. In other areas, calmer embayments and lagoons formed in in areas areas of lower lowerrelief, relief?sometimes sometimesisolated isolated behind behind basaltic basaltic islands. islands. Fine Finesandstones sandstonesand andshales shalesof ofthe theEau Eau Claire Claireand and Mazomanie MazomanieFormations Formations were were deposited deposited in in these these areas. areas. The Theshapes shapesofofthese theseislands islands were of the the flows? flows,joint joint sets, sets, and and small small faults. faults. The were controlled controlled by the the stair-step stair-step topography topography of The continuity continuity of of the the Eagle Eagle Peak Peak flow flow from from island island to toisland island suggests suggests that thatfaults faultswith withmajor major displacement displacementdid didnot notcontrol controlthe theshapes shapesof ofthe theislands. islands. Knowledge Knowledge of the the distribution distribution of of basalt basalt in inthe thesubsurface subsurfacehas hasconsiderable considerablepractical practical importance. A company building a pipeline through the area in the 1970's went bankrupt importance. A company building a pipeline through the area in the 1970's went bankruptbecause because they they failed failedto totake takeinto intoaccount accountthe theexpenses expensesinvolved involved in in blasting blastingthrough throughthese theseburied buriedbasalt basalt ridges ridgeswhen when submitting submittingtheir theirbid. bid. ItItisisalso alsonot notuncommon uncommonfor forone oneparcel parcel of of land land to to have have basalt near near the the surface surfaceto to have have little little or or no no ground ground water, while a neighboring parcel a few 100 100 meters away away will will have have aa plentiful plentifulsupply supply of of water water from fromaathick thicksection sectionof ofPleistocene Pleistoceneand andCambrian Cambrian sediments. sediments. The The scenic scenic dalles dalles of of the the St. St.Croix CroixRiver River are arewhere wherethe theriver, river,after afterexcavating excavating the the soft soft Cambrian sediments in a gap between paleo-islands, has finally cut down to the hard basaltic Cambrian sediments in a gap between paleo-islands, has finally cut down to the hard basaltic shoal shoal separating separatingdeeper deeperCambrian Cambrianembayments. embayments. Immediately Dalles, aa possible possible whirlpool whirlpool or Immediately to the north, one can see see the Lake Lake of the the Dalles, plunge more easterly easterly course. course. Finally, numerous plungepool pool formed formedwhen whenthe the St. St. Croix Croix flowed along a more glacial glacial striations striationsand andchatter chattermarks marks can canbe be found foundon on the the bedrock bedrock surface surfaceat atEagle EaglePeak. Peak. Stop Interstate Park, Stop 3b—Cambrian 3b-cambrian Rocky Rocky Shoreline Shoreline Deposits of Interstate Park,WI. WI. See Figure Figure 17 17for forlocation locationmap. map. See Location: Lmation: Ravine Ravineimmediately immediatelysouth southofofSkyline SkylineTrail, Trail,approximately approximately 400 400 m m from from trailhead trailhead at at group Park (WI). (WI). SE1/4, SE1/4, Sec. 36, 36, TT 34.N7 34N, R 19W. group campground in Interstate Park SEl14, SElI4, 19W. NOTE: Specimen Specimencollecting collectingisisnot notallowed allowedin inthe the park! park! The meters. ItIt then The Skyline SkylineTrail Trail skirts skirts aa low, marshy area for its first 150 meters. then begins begins its its slow slow ascent ascent onto onto the the Trap Trap Rock Rock Alley flow of the Precambrian Chengwatana Chengwatana basalt, basalt, with with outcrops outcropsof of basalt basalt prominent prominent on on both both sides sides of of the the trail. After Afterapproximately approximately400 400 m, m, aa steep-walled, steep-walled,narrow narrow ravine can be be seen seen by by looking lookingdown down to to the the right right (south) (south) of of the the trail. trail. This ravine ravine marks marks the the approximate approximatecontact contactbetween between Precambrian Precambrian basalts basalts and Cambrian sedimentary deposits. deposits. Basalt Basalt outcrops outcropsoccur occuron on the the floor floor of of the the ravine ravine and along the north wall. Along Along the the south south wall, wall, 88 m of Upper Mazomanie Formation Formation UpperCambrian Cambrianconglomerates conglomeratesand andsandstones sandstonestentatively tentatively assigned assigned to the Mazomanie of of the the Tunnel Tunnel City City Group Group (Mazomanie (Mazomanie Member Member of the Franconia Franconia Formation in Minnesota) Minnesota) lie lie directly directlyabove aboveand andlateral lateralto to the the basalts. basalts. The TheCambrian Cambriansediments sedimentscan canbe betraced tracedfor forsome some240 240m m to to the the east east up up the theravine, ravine,but but the the best best exposures exposuresare are in in the the first first 70 70 m. m. On the south south wail wall of of the the ravine, ravine, aa basalt basalt boulder boulder conglomerate conglomerate facies ("the Mill Mill Street Street conglomerate" of of Berkey, Berkey, 1897) 1897)lies lies against against the the lava lava flows and grades grades vertically vertically and and laterally laterally into in this this area area (Fig. (Fig. 18). In into the sandstone sandstone facies facies more typical of the Cambrian section in In sharp sharp contrast contrastto to the the gray-green gray-greenbasalt basaltflow flowoutcrops outcropson onthe the north north side sideof of the the ravine, ravine, the the basalt basalt boulders boulders in the conglomerate are heavily weathered and stained orange-brown by iron oxides. The conglomerate are heavily weathered and stained Thelargest largest 57 57 �- - - - - I 10 meters meters Figure 18. Sketch Sketch of south south wall wall of of ravine ravine along along Skyline Skyline Trail (Stop 3b) showing vertical and and boulder conglomerate conglomerate and and sandstone sandstonefacies. facies. Covered areas lateral relationships between basalt boulder indicated by lack of pattern. No No vertical vertical exaggeration. exaggeration. boulders boulders near the the base base of the exposure exposure are over 1 m in diameter. The boulders are rounded but perhaps due to to original originaljointing jointing in in the thebasalt. basalt. A quartz sandstone matrix with of low sphericity, perhaps inarticulate brachiopods brachiopods fills boulders. No abundant inarticulate fills the spaces between the boulders. No trace trace of bedding bedding is is present within the main body of the conglomerate, although a few thin conglomerate beds present the conglomerate, extend out into the sandstones. These These beds beds contain contain rip-up clasts of sandstone as well as basalt cobbles and pebbles, pebbles, in basalt conglomerate conglomerate in which sandstone sandstone cobbles in contrast contrast to to the main body of the basalt clasts have not been seen. They Theyalso alsoshow showweak weakimbrication imbricationsuggesting suggesting current current flow flow to to the the west. conglomerate and and sandstone sandstonefacies faciesisissurprisingly surprisinglysharp. sharp. The The contact between the conglomerate The sandstone sandstone beds beds thin- to medium-bedded quartz arenites. arenites. The sandstones are orange-brown, thinmedium-bedded quartz vary in texture from fine- to coarse-grained, coarse-grained, from sub-rounded to rounded, rounded, and from moderately moderately to well-sorted. Some Somefinefine-to to medium-grained medium-grained sandstone sandstoneunits units contain contain scattered scattered coarse, coarse, frosted frosted quartz grains. A A few few beds beds are aregraded, graded, and and some some contain contain quartz pebbles and rip-up clasts of sandstone with foresets foresets dipping dipping sandstone and siltstone. Many Many units units show show high-angle planar cross-bedding, with to the west. fron-oxide Iron-oxidestaining stainingand andconcretions concretions are are common, common, as are inarticulate brachiopod shell- hash layers. AAlarge trough cross-bed set (or possibly a slump) near the center of the large trough cross-bed set (or exposure exposure is indicated indicated by aa curved curved erosional erosional surface surface marked by basalt cobbles near its base, and sandstone beds which dip slightly to the east, in contrast to the slight westward westward dip dip of of most of the sandstone sandstone beds in in the the outcrop. outcrop. Interpretation Interpretation The Taylors Falls-St. Falls-St. Croix Croix Falls Falls area of Minnesota and and Wisconsin Wisconsin isis one one of the few localities in North North America America where where Upper Upper Cambrian Cambrian conglomerates conglomerates lie lie unconformably unconformably on on Precambrian rocks rocks (Webers (Webers and and Austin, Austin, 1972; 1972;Cavaleri Cavaleri et. al., 1987). 1987). 58 �Apparently, Apparently, the the Cambrian Cambrian Sauk Sauksea seatransgressed transgressedonto ontoaaland landsurface surfaceof ofvery verylow lowrelief reliefas as itit flooded advanced. At a few localities localities flooded the the North North American American craton, craton, leaving leaving a blanket of sand as itit advanced. such such as as Taylors TaylorsFalls-St. Falls-St.Croix CroixFalls Fallsand andBaraboo, Baraboo,Wisconsin Wisconsin (Dalziel (Dalzieland andDott, Dott,1970; 1970;Dott, Dott, 1974), 1974), resistant bedrock bedrock hills hills stood stood above above the the subdued subdued land land surface surface and and acted actedas aslocal localsources sources for for coarse coarse conglomerate conglomeratedeposits depositsas as the sea advanced. In In Baraboo, Baraboo, the conglomerate conglomeratewas was formed formed of quartzite quartzite boulders boulders from from local local outcrops; outcrops; in in the the Taylors Taylors Falls-St. Falls-St. Croix Croix Falls Falls area, area, the the conglomerate conglomerate was was formed formed of of basalt basalt boulders boulders from from the the local local lava lava flows. flows. The basalt boulder boulder conglomerates, conglomerates, informally called the "Mill Street conglomerate" are are exposed exposed at at only only aa handful handful of of sites sites on on both both sides sidesof of the the St. St. Croix Croix River River south southof of Taylors Taylors Falls-St. Falls-St. Croix Croix Falls. Falls. Of Ofthese thesesites, sites,the theSkyline SkylineTrail Traillocality, locality,shows showsmost most clearly clearlythe the vertical verticaland andlateral lateral relationships relationships between between the Precambrian Precambrian basalts and Upper Upper Cambrian Cambrian conglomerates conglomerates and sandstones. sandstones. As Ascan canbe beseen seenin in the the ravine, ravine, the the basalt boulder conglomerate conglomerate was deposited deposited on on top of and and against against aa steep steep face face cut cut into into the the basalt basalt lava lava flows. Very Very high high energy energy conditions conditionsmust musthave have been been present present to to round round the the corners comers of the basalt boulders. Dott Dott(1974) (1974)estimated estimatedthe theheight heightof ofthe the waves required to round boulders of similar size in Baraboo. Baraboo. His His conservative conservative estimates estimates of m high suggest suggest storms storms were important in producing producing these conglomerates. conglomerates. A A waves 55 m paleogeographic paleogeographic reconstruction reconstructionof of the the Taylors Taylors Falls-St. Croix Falls area as the Sauk Sauk sea sea began began to submerge submerge the the basalt basalt highlands highlands shows shows that the the lava flows along the Skyline Trail would have been fully exposed to waves from the west or southwest. ItIt isis tempting tempting to to envision envision basalt basalt sea sea cliffs on the windward windward side side of of islands islands or or headlands, headlands,with with storm-generated storm-generatedwaves waves crashing crashinginto into and the base base being being pounded pounded and jostled jostled and undercutting undercuttingthe the cliffs, cliffs, and and the the rubble rubble in the surf zone at the to produce rounded boulders. Such an environment evokes images of the Hawaiian Islands or rounded Such an environment evokes images the Hawaiian or perhaps perhaps the the Pacific Pacific Northwest Northwest coast coast today. today. However, However, very very little little has been written written in the geologic geologic literature literature on on the characteristics characteristics of of rocky shoreline shoreline deposits (Johnson, 1988) 1988) and care should be taken in reconstructing reconstructing the the exact exact depositional depositionalenvironment. environment. The The sharp sharp contact contact between between the conglomerate conglomerateand and sandstone sandstone and the difference in lithology between between the the two two facies facies suggest suggestthat that the the sands sands came came from from a more distant distant source source and and were were washed washed along basalt boulders. boulders. The along the shoreline shoreline and and deposited deposited against against and between the basalt The graded graded bedding, bedding, rip-up clasts and shell-hash layers show that periodic storms may have been more important and shell-hash layers been more important in deposition deposition of of the the sandstone sandstone beds beds than normal day-to-day events. Storms Stormscould couldalso also account accountfor for the two conglomerate beds extending out into the sandstone; each each bed bed with a mix of basalt basalt cobbles and sandstone rip-up clasts from the ocean floor. and sandstone rip-up clasts from the ocean floor. The The sandstones sandstones are are tentatively tentatively assigned assigned to to the the Mazomanie MazomanieFormation Formationof of the theTunnel TunnelCity City Group Group by their their similarity similarity to to outcrops outcrops of of that formation formation across across the St. Croix River in Minnesota. However, they they may represent a near-shore Ironton Member Member of ofthe theWonewoc Wonewoc near-shore facies facies of of the the fronton Formation as well. The Mill Street conglomerate varies in age from Dresbachian to Franconian Formation as well. The Mill Street conglomerate varies (Webers and Austin, 1972) 1972) and and thus thus may may grade grade laterally laterally into into sandstones sandstonesof of either eitherformation. formation. Detailed Detailed study of of the the fossil fossil assemblages, assemblages, particularly particularly the trilobites, trilobites, in the the sandstone sandstone and and conglomerate would be the best method method to tell the age age and and formation, formation, but as as yet yet this this has has not not been attempted. attempted. Such Suchaastudy studywould would be be especially especially valuable valuable since the Mill Street conglomerate is known known to to contain contain an an unusual unusual assemblage assemblage of of trilobites, trilobites, inarticulate inarticulate brachiopods brachiopods and and monoplacophoran monoplacophoran molluscs molluscs representing representing an an intertidal, intertidal, shoreline shoreline environment environment (Webers, (Webers, 1972). 1972). According to Johnson (1988), the oldest known known rocky-shore rocky-shorefaunas faunasare areOrdovician Ordovicianininage. age. It may well be be that that the theunusual unusualUpper Upper Cambrian Cambrian conglomerate conglomerate deposits deposits around around St. St. Croix Croix Falls Falls and Taylors Falls contain contain the the oldest oldest rocky rocky shoreline shorelinefaunas faunasin in the the world. world. 59 �Stop Stop4—Potholes &Potholes of ofInterstate InterstatePark, Park,MN. MN. SeeFigure Figure17 17for forlocation locationmap. map. See Location: Paths Pathsleading leadingfrom fromthe theparking parkinglot lotbybythe theinterpretative interpretativecenter, center,Interstate InterstatePark Park Location: (Minnesota). SW 1/4, SW 1/4, Sec. 30, T 34 N, R 18 W. (Minnesota). SW 114, SW 114, Sec. 30, T 34 N, R 18 W. NOTE: NOTE:Specimen Specimencollecting collectingisisnot notallowed allowedininthe thepark! park! This Thisstop stopprovides providesan anopportunity opportunity totoexamine examineoutcrops outcropsof ofbasaltic basalticlava lavaflows flowswith with spectacular spectacular potholes. potholes. From Fromthe theparking parkinglot, lot,follow followthe theservice serviceroad road(also (alsocalled calledTrap TrapRock Rock Alley) Alley)aashort shortdistance. distance.Many Manyshort, short,well-marked well-markedtrails trailstotothe theeast eastimaginatively imaginativelyand andconveniently conveniently lead over, around and through world-class potholes cut in the top of the Dresser basaltic lead over, around and through world-class potholes cut in the top of the Dresser basalticlava lava flow. flow. The Thebase baseofofthe theTrap TrapRock RockAlley Alleyflow, flow,here here at at its its type typelocality, locality, is is well well exposed exposedalong alongthe the west westside sideof ofTrap TrapRock Rock Alley. Alley. The Thetop topof of the the Dresser Dresser flows flows is exposed to the east. This Thisflow flow dips dips gently gently west westunder underthe theTrap TrapRock Rock Alley. Alley. The Theflow flowtop topisistypically typicallyamygdaloidal amygdaloidaland and extensively extensivelyepidotized. epidotized.ItItisiswell wellexposed exposedininabundant abundantoutcrops, outcrops,asaswell wellasasalong alongthe thesides sidesof ofthe the manyenormous enormouspotholes. potholes. many The Thepotholes potholesformed formedon onthe theDresser Dresserflows flows are arethought thought to to be be some someof of the thedeepest deepestin inthe the world world(Crawford, (Crawford,undated). undated).They Theyrange rangefrom fromfist-size fist-sizedepressions depressionsto to"giant's "giant's kettles" kettles"that thatcan can be beover over66meters metersacross acrossand andmore morethan than 20 20 meters meters deep. deep. The Thepotholes potholesare aregenerally generallypartly partly filled filled with withaamixture mixtureof ofsilt, silt,mud, mud,peat peatand andcoarse coarsegrind grindstones stonesranging rangingfrom frompebble pebbletotoboulder bouldersize. size. The Thesediments, sediments,swirled swirledby bythe theturbulence turbulenceof ofthe theriver riveras asititraced racedover overthe the basalt, basalt,were werethe thetools tools cuttingthese thesepotholes. potholes. cutting These Thesepotholes potholesare arepart partofofaalarger largerregion regionof of river-scoured river-scouredterrain. terrain. InInaddition additiontotothem, them,the the bedrock bedrocksurface surfaceisisscoured, scoured,smoothed smoothedand andpolished polished in in many areas. The Thepotholes potholes were were produced produced when when localized localized areas, areas, facilitated facilitated by by joint joint intersections, intersections, wore wore down down slightly slightly faster faster than than the the surrounding rock. Eddies formed over these low spots, trapping sediment. Large boulders surrounding rock. Eddies formed over these low spots, trapping sediment. Large boulders occasionally occasionally were were stranded strandedin in these these depressions. depressions. The Thestrong strongcurrent currentswirled swirledthem themabout, about,but but lacked lackedthe theforce forceto to free free them. them. This Thisaction actioncut cutthe thepotholes. potholes. Notice Noticeininplaces placesthe thegrooves groovescut cutin in the the sides sidesof ofthe thepotholes potholesas aslarge largeboulders boulders ground ground their their way way down. down. The Theboulders bouldersthemselves themselves were were shaped shaped by by the theprocess. process. Grind Grindstones stonesrecovered recoveredfrom fromthe thepotholes potholesare areasassmooth smooth and and roundedas ascannon cannonballs. balls. rounded The Thepotholes potholes here hereare are7.5-18 7.5-18 meters metersabove above the the current current river river level. level. Some Somepotholes potholeshave have beenfound foundasashigh highasas34 34meters metersabove aboveriver riverlevel. level. been The Thepotholes potholesformed formedwhen whenwater waterfrom fromthe themelting meltingglaciers glaciersfilled filledGlacial GlacialLake LakeDuluth Duluthto to the thenorth north(Cahow, (Cahow,1975; 1975;Ojakangas Ojakangasand andMatsch, Matsch,1982). 1982).The Thewater waterovertopping overtoppingthis thislake lakeflowed flowed south southdown downthe the ancestral ancestralSt. St.Croix CroixRiver. River. At AtInterstate InterstatePark, Park,these thesewaters waterswere werefurther furtherfunneled funneled down down the the narrow narrow channel channel now now seen seen as as the Dalles. Dalles. Below Belowthe theDalles, Dalles,the the river river encountered encounteredsoft soft Cambrian Cambriansandstones sandstonesand andshales, shales,which whichcut cutaway awayfaster fasterthan than the the basalt. This Thisresulted resultedininaamajor major knickpoint in in the the St. St.Croix Croixatatthe the Dalles. Dalles. This Thishigh highgradient gradientsped spedup upthe thewater, water, increasing increasing its its knickpoint ability abilityto to gouge gougeout outthe thepotholes potholesas asititexcavated excavatedits its valley valley into into the the resistant resistant basaltic basaltic bedrock. bedrock. Many Many of of the thepotholes potholeshere herehave have been been given given names names by the park service. service. Be Besure suretotoenjoy enjoy the the Lily Lily Pond, Pond,Devil's Devil'sParlor, Parlor,Cauldron, Cauldron,Bottomless BottomlessPit Pit and and Bake Bake Oven Oven as as time time permits. permits. Also Also note note the the west-dipping west-dipping thrust thrust fault fault exposed exposed in in the the cliff cliff by by the the riverboat riverboat dock dock just west west of of the the potholesarea. area. potholes 60 60 �Stop Stop 5—Volcanic 5-Volcanic Flows and Interfiow Interflow Sediments Sedimentswest west of of Lewis, WI. Location: Outcrops Outcropsare arelocated locatedon on345th 345thAve AveOne-half one-half mile west of the intersection intersection with with 130th 130th Location: Street. Street. NN1/2, 112,SE SE1/4 114and and5S1/2, 112,NE NE1/4, 114,Sec. Sec.11, 11,TT37 37N, N, RR 17 17W; W, Lat. Lat. 450 45' 42' 42' 07.6" 07.6" N, N, Long. Long. 092° 092' 26' 26'25.8" 25.8"W. W. Figure 19. Scanned Scanned image image of of a portion of the Figure 19. the USGS USGS Frederic, Frederic, Wisconsin Wisconsin topographic topographicquadrangle quadrangle(7.5-minute (7.5-minuteSeries; Series;1:24,000 1:24,000scale) scale)showing showing the the location location of of StopS. Stop 5. These permission before before entering. entering. Basalt Theseoutcrops outcropsare areon on private private land land and you should seek permission Basalt and and interfiow intefflow sediments sedimentsare areexposed exposedin inaaseries seriesof ofoutcrops outcrops20-100 20-100meters metersnorth northof ofthe theroad. road. Near Near the the road, road,fine-grained fine-grainedbasalt basalt isis exposed exposed in in aa flow that is at least 4 meters thick. Near Near the amygdules. the top top of of the theflow, flow, the the basalt basalt contains containsrare rare large large quartz-filled quartz-tilledamygdules. Interflow Intefflow sediment sedimentisis exposed exposed further furthernorth north and andisisparticularly particularly well-exposed well-exposed in inan aneasteastwest west trending trendingcliff cliff face. face. Please Pleasedo donot nothammer hammeron onthis this face. face. Excellent Excellentexamples examplesofofthe theinterfiow interflow sediment sediment can be found found in in the the many many loose loose blocks along the base of the cliff. The Thebasalt basaltisis overlain Thesediment sediment overlain by aa mixed mixed basalt basalt and and sediment sediment zone zone that is roughly 3 meters thick. The weathers weatherspale palereddish-orange reddish-orangeand andconsists consistsof offine-grained, fine-grained,poorly poorly sorted, sorted,and andthinly thinlylaminated laminated quartz, quartz, feldspar, feldspar, and and volcanic volcanic fragments. fragments. The Thefine-grained fine-grainedmatrix matrixmaterial materialisiscompletely completely recrystallized minerals. Beds recrystallized to epidote epidote and and other other greenschist greenschist facies minerals. Beds typically typically show show planar planar bedding bedding structures, structures,although although some somecross-beds cross-beds(ripple (ripplestructures), structures),channel-fill channel-fillstructures, structures,and and convoluted convoluted beds are are also also visible. Bedding Beddingstructures structuresoften often trend trend uninterrupted uninterrupted right up to the margins margins of of clasts, clasts, though though in in some someplaces places bedding bedding surfaces surfaces appear appear to to be be deflected deflected by by clasts. clasts. There There are are also also patches patches of of sediment sedimentthat that are are surrounded surrounded by basalt and appear "isolated" in in the the two-dimensional two-dimensionaloutcrop outcropface. face.'These, These,asaswell wellas asmany many narrow narrow sub-vertical sub-vertical"veins" of of sediment, sediment, exhibit exhibitwell-defined, well-defined,sub-horizontal sub-horizontallayering layeringthat thatisissharply sharplytruncated truncatedalong alongits itsmargins. margins. 61 , �Fragments of basalt range from less than than aa millimeter millimeter to to more morethan than 15 15centimeters. centimeters. The microcrystalline plagioclase, plagioclase, and are are highly highly vesicular vesicular clasts are typically sub-angular, consist of microcrystalline (1-5 mm mrn diameter); the outer outer surfaces surfaces of many many clasts are are highly highly embayed embayed and and exhibit exhibit very very "sponge-like" textures. textures. Some delicate "sponge-like" Some clasts clasts are are sub-rounded sub-rounded and exhibit decreasing vesicle sizes near their outer edges; the long long axes axes of of highly highly elliptical elliptical vesicles also parallel the clast clast surfaces. Many Many of of these thesefeatures featuresare aresuggestive suggestiveof of chilled chilled margins margins surrounding surrounding some of the clasts. clasts. Many Manylarger largerclasts clastsalso also have have numerous numerous small small "floating" fragments fragments around around their margins. margins. Viewed closely, many of these these fragments fragments appear appear to to be bedisrupted disrupted"glassy" "glassy" walls walls between between adjacent adjacent vesicles. fragments are typically filled with with coarse coarse epidote. epidote. Near the vesicles. Vesicles Vesicles in in the interiors interiors of fragments continuous layer of vesicular basalt has a highly irregular top of the outcrop, a nearly continuous irregular base base that that in some places cross-cuts layering in the underlying sediment. All All of of these these features features point point to to aa highly immature sediment. Elsewhere Elsewherein in the the rift, rift, interflow sediments are interpreted to record deposition in predominantly environments (e.g., (e.g., Jirsa, Jirsa, 1984). However, predominantly sedimentary environments However, some some features features at at this this stop stop are are suggestive suggestiveof hyaloclastites, hyaloclastites,in in which which basaltic basaltic melt melt interacts interactswith with water, water, or water-saturated water-saturated sediment. sediment.Preliminary Preliminaryinitial initialCNd EM^values valuesof ofthese thesesediments sediments(—-2.0; (--2.0; Naiman, unpublished data) are are similar similar to to those those of of the the surrounding surrounding basalts (Table 5) suggesting that the source of the sediments sediments is primarily immature rift volcanics. Stop Stop 6a—Rhyolite 6a-Rhyolite and Basalt Basalt near near Clam ClamFalls. Falls. Location: 435 435m mNNE NNE of of the the intersection intersection between County Rd I and 73rd St. SE SE 1/4, 114,SE SE 1/4, 114, 09.8" N, N, Long. Long. 092' 092° 18' 27.4"W. Sec. 14, T 37 N, R 16W; 16W,Lat. Lat. 450 45O 41' 41'09.8" 18'27.4" W. image of of a portion Figure 20. 20. Scanned image portion of the the USGS USGS Clam Clam Falls, Falls, Wisconsin topographic topographic quadrangle quadrangle (7.5 minute minute series; series; 1:24,000 1:24,000 scale) scale) showing the location of Stop Stop 6a. 6a. 62 62 �Table Table 5. 5. Representative Representativeanalyses analysesof ofbasalt basaltand andrhyolite rhyolitefrom fromthe theClam ClamFalls Fallsregion. region. Si02 Si02 Ti02 Ti02 Al203 *l2O3 Fe203 Fe203 MnO MnO MgO MgO CaO CaO Na20 Na20 K20 K20 basalt basalt KC-301b KC-301b basalt basalt KC-303 KC-303 rhyolite rhyolite KC-302a KC-302a rhyolite rhyolite KC-302d KC-302d rhyolite rhyolite KC-310 KC-3 10 47.08 47.08 49.89 49.89 1.60 15.66 14.10 0.18 1.84 14.91 13.61 72.46 72.46 0.49 71.34 7 1.34 0.49 11.52 5.30 0.06 72.18 72.18 0.48 11.93 5.78 0.12 0.40 '25 P2° 0.56 0.15 LOl LO1 1.72 0.17 5.10 8.61 3.17 0.55 0.20 2.31 Total Total 100.20 100.36 Mg# Mg# 0.53 6.84 10.00 2.31 qz qz or ab ab an an hy hy 01 ol 3.41 20.08 31.54 14.07 9.23 4.87 0.09 0.48 1.36 2.32 2.63 4.11 1.01 1.32 3.52 4.21 0.09 0.40 99.69 100.22 100.43 0.47 0.19 0.37 0.14 0.56 3.36 27.66 25.60 21.60 31.39 30.56 24.75 3.65 6.43 31.85 24.62 22.51 7.55 29.75 25.02 29.90 4.30 7.24 1.08 2.89 5.10 0.08 0.54 0.08 8.21 13 151 91 82 216 1036 80 889 123 831 108 90 12 178 68 794 62 713 38 141 118 67 965 155 205 117 24 133 281 76 299 14 6 21 Rb Rb Ba Ba Sr Sr 19 115 Nb Zr Y Y 8 Cr Cr Ni Ni v V InitialENd EN^ Initial 11.61 164 111 31 +34 "'"3.4 — -0.10 Sample Sample Locations: Locations: T 37 N, R 16W. 16 W. SW114, SW1/4, SW114, section section 13 13 KC-301b KC-301b -- SW1/4, SE 1/4, 114, SE 1/4, 114, section section 14 14 (Stop (Stop 6) 6) KC-302a -- SE KC-302a KC-302d -- SE SE 1/4, 114, SE 1/4, 114, section 14 14 (Stop (Stop 6) 6) KC-302d SE114, NW1/4, NW114, section section 13 13 KC-303 -- SE1/4, KC-303 SE114, SE1/4, SE114,section section 26 26 (Stop (Stop 66 Alt.) Alt.) KC-310 KC-310 -- SE1/4, 63 14 26 19 9 17 095 �These outcrops outcrops are are on on private private land and permission to access access them them should should be sought sought before before the intersection intersection of of Country Country entering. The The outcrops outcropscan can be be accessed accessed from from the property (north of the 73rd St. approximately 1 mile mile west west of of Clam ClamFalls. Falls. Direct access to the the outcrops outcrops from Rd I with 73rd County Rd Rd I requires landowner. An alternate County requires permission permission from another another landowner. alternate stop (6b) (6b) near near the the McKenzie McKenzie Creek Creek State State Hunting HuntingGrounds Groundsisisgiven given below. below. The purpose of this stop is to examine an example example of ofrhyolite. rhyolite. Rhyolite is extremely rare in this part of the rift rift and and only only two two localities localitiesare are known known in in the the area area extending extendingfrom fromTaylors TaylorsFalls Falls to Clam Falls. This Thisisisin instark starkcontrast contrastto tothe the relatively relatively abundant abundant rhyolites rhyolites (up (up to 25 25 percent percent of of the volcanic volcanic section; section;Green Greenand andFitz, Fitz, 1993) 1993)that that are are exposed exposed on on the North Shore Shore of Lake Lake Superior. Superior. This locality was also also sampled sampled for for U-Pb zircon studies studies (see (see below). At this exposure, that measures measures approximately approximately 150 x exposure, the rhyolite is exposed over an area that 75 meters. The the exposure exposure trends trends N N 50 50° E and Theupper uppersurface surfaceof of the the outcrop outcrop at at the north end of the dips 15° 15O NW, NW, sub-parallel sub-parallelto to the the trend of flow layering in the area. At the southern southern end of the outcrop, exposures outcrop, the the basal basal contact contact with with the underlying underlying basalt basalt flow can be seen. In a few isolated exposures approximately 3-4 3-4 meters meters below below the the top top of of the knoll one can observe isolated exposures exposures in in approximately which basalt and rhyolite are complexly inter-fingered. Sub-angular Sub-angularto to rounded rounded clasts clasts consist consist of fine-grained basalt, up to 15 cm in diameter, diameter, can can be befound foundin inrhyolite. rhyolite. The upper upper contact of of the rhyolite rhyolite with with the the overlying overlying flows flows isis not not exposed. exposed. Weakly porphyritic (An2Abo40r4)and porphyritic rhyolite rhyolite consists consistsof of phenocrysts phenocrystsof of euhedral euhedralalbite albite(An2Ab94Or4) rare quartz quartz occur occur in in aa groundmass groundmassof ofintergrown intergrownquartz quartzand andpotassium potassiumfeldspar feldspar(An0Ab5Or95); textures spherulitic (Fig. 21). textures range from from fine-grained fine-grained intergranular intergranular to medium-grained medium-grained spherulitic Spherulitic Spheruliticintergrowths intergrowths are are commonly commonly nucleated nucleated on on phenocrysts. phenocrysts. Minor Minoranhedral anhedralFe-Ti Fe-Tioxides, oxides, rare calcic amphibole and accessory apatite and zircon are amphibole (ferro-edenite-hornblende), (ferro-edenite-hornblende), and are also also commonly commonly present. present. Groundmass Groundmassquartz quartzisistypically typicallyeuhedral euhedralto to subhedral subhedral and tabular to elongate (length:width (1ength:width ratios == 10:1 10:1 to 50:1) 50: 1) indicating crystallization as tridymite, the orthorhombic, high temperature (>867O (>867° C) C) form form of of quartz. quartz. The Thepreservation preservation of of these these delicate delicate devitrification textures is remarkable remarkable given given the metamorphic metamorphic alteration alteration and and recrystallization recrystallizationthat that has has occurred occurred in this portion of the rift. The rhyolites of the Clam Clam Falls Falls region region are classified as rhyolite or rhyodacite on most diagrams (Abbott (Abbottetetal., al.,ininpress). press). The major and trace major and trace element discriminant diagrams element compositions icelandites and granophyres granophyres from the North element compositions(Table (Table 5) 5) are are similar similar to some icelandites Shore Green, 1997) to type type IIrhyolites rhyolites from from the the Portage Portage Lake Lake Shore Volcanic Group (Vervoort and Green, 1997) and to volcanics (Nicholson, (Nicholson, 1992; 1992; Nicholson and Shirey, 1990). Nd Nd isotopic isotopic studies studiesof of the the rhyolites rhyolites (Abbott ENd values = (Abbott et et al., al., in in press; press; Naiman Naiman and andWirth, Wirth, in in press) press) indicate indicatethat that they they have have initial initialENd This evidence, combined with their relatively minor abundance in the volcanic 0. their relatively abundance the volcanic section, section, 0. by magmatic fractionation. fractionation. This suggests that they originated as residual melts by This is is in contrast contrast to to many values and are interpreted interpreted many of of the the rhyolites rhyoliteson onthe theNorth NorthShore Shorethat thathave havenegative negativeinitial initialENd ENd values to be the and Green, Green, 1997). 1997). Basalt from this part of the the result result of of crustal crustal melting melting (Vervoort (Vervoort and volcanic volcanic section section (e.g., (e.g., KC-301b KC-301band andKC-303; KC-303;Table Table5) 5) isis similar similarto to low-Ti low-Ti basalt basalt of of the the Taylors Taylors Falls region and has initial ENd valuesranging rangingfrom from00toto+3.4, 3.4, consistent ENd values consistent with with derivation derivation from multiple asthenosphere (Naiman multiple mantle mantle sources, sources, including includingenriched enriched mantle mantle plume plume and depleted asthenosphere (Naiman and Wirth, in press). 64 �Figure21. 21.(a) (a) Photomicrograph Photomicrograph (plane-polarized (plane-polarized light) light) of of spherulitic Figure intergrowths of of tridymite pararnorphs paramorphs and and feldspar feldspar in Clam Falls rhyolite intergrowths bar along (sample KC-302a). KC-302a). Scale bar along left side is 0.25 0.25 mm mm long. long. (b) (b) Photomicrograph showing plagioclase (albite) phenocryst with spherulitic spherulitic mrn long. sideis 1.25 1.25 mm intergrowths around the margin. Scale Scale bar bar along along left sideis 65 �One of the major difficulties in integrating geologic information from this portion of the rift with models of of the the rift rift has has been been the thelack lackof ofgeochronologic geochronologic control control in in the the Chengwatana Chengwatana volcanic s. With this objective collected from both Stop volcanics. objective in mind, large samples of rhyolite were collected Stop 10) has not 6a and Stop 6b for U-Pb zircon dating. The Thesample samplematerial materialfrom fromStop Stop6b 6b(KC-3 (KC-310) been processed processed at at this this time, time, but two, two, nearly identical identical ages ages were determined determined for for different different rhyolite rhyolite phases (KC-302a and and KC-302d) KC-302d) from from Stop Stop 6a. 6a. Zircons from both samples samples have have relatively relatively simple reddish-brown, to honey brown, simple prismatic prismatic forms, forms,are are translucent, translucent,and and vary vary in in color color from reddish-brown, brown, and pale pink. Three Threezircon zircongrains grainsfrom fromKC-302a KC-302a yielded yielded concordant concordant ages ages (Fig. (Fig. 22) 22) with mean mean 2O6pb*/238U and 2o7Pb*PO6Pb* of 1102 k ± 5 Ma (2a). 206Pb*/238U and 207~b*/206Pb* ages of (20). Three Threeadditional additionalgrains grainsare are slightly slightly discordant, discordant,presumably presumablydue dueto to small smallamounts amountsof of lead lead loss, loss, and and aa discordia discordiathrough through these thesepoints, points, projected from ± 205 Analyses 205 Ma Ma (MSWD (MSWD== 0.15). 0.15). Analyses from 1102 1102Ma, Ma, yields yields aa lower lower intercept of 196 196 k of three and yield mean 2O6Pb*/238U three abraded abradedgrains grainsfrom fromKC-302d KC-302dare areanalytically analyticallyconcordant concordant and yield mean ^Pb*/238U ages 1101Ma Mak ±55Ma Ma(Fig. (Fig.22). 22). Three additional grains and the two and 2o7Pb*PooPb* 207~b*/206Pb*ages ofof1101 multigrain fractions are slightly discordant; a discordia through these points, projected from uncertainties o of± 1101 Ma, Ma, yields yields a lower intercept intercept of 63 63 k± 217 Ma (MSWD = 0.45). 0.45). Given the uncertainties 1101 ft 5 Ma on each of of the the ages, ages, the the 11Ma Ma age agedifference difference between between the the two two samples samples is is probably probably not not significant. significant. 0.190 Rhyolite Rhyolite 0.186 00 I Age = Age = 1080 1102 ±5Ma 1080 1101 ±5Ma 0.182 0.178 Lower Intercept 196 ±205 Ma (MSWD=0.15) 0.174 I I Lower Intercept = 63 ±217Ma (MSWD=0.45) • 1.98 2.06 1.98 1.82 1.90 1.90 1.90 1.98 2.06 1.82 1.90 1.98 2.06 2O7pb 235 u 2O7pb 235 u 207Pb / 235 U 207Pb / U Figure 22. Concordia Concordiadiagrams diagramsfor forChengwatana Chengwatanavolcanics volcanics from from the the Clam Clam Falls Falls area area (Stop (Stop6a). 6a). Error ellipses ellipses and and regression regression age age uncertainties uncertainties represent represent 95 95 percent percent confidence confidencelimits limits(after (afterWirth Wirth and Gehrels, in press). 1.82 1.82 Analyses of the the Chengwatana Chengwatana rhyolites near Clam Clam Falls indicate indicate that magmatism magmatism began began by at least 1102 1102 Ma Ma in in this this portion portion of of the the rift, rift, considerably considerably earlier than the age reported by Zartman et ± 2.1 Zartman et al. (1997) (1997) for for rhyolite rhyolite (1094.6 2 2.1Ma) Ma)exposed exposednear near the the base base of the the Chengwatana Chengwatana section section in the southeastern southeasternlimb limb of the Ashland syncline. This This implies implies that that lower lower flows flows exposed exposed near Clam Clam Falls Falls likely likely formed formed contemporaneous contemporaneouswith with the the Upper Upper Kallander Kallander Creek Creek volcanics volcanicsand and Conglomerate of the Mellen Complex Complex of of Northern Northern Wisconsin, Wisconsin, and the Group 5 flows and Great Conglomerate Mamainse Point (Fig. 23). The The 1102± 1102 k55Ma Maage ageofofChengwatana Chengwatanavolcanics volcanics in in the Clam Falls 66 �Age (Ma) Minnesota Wisconsin Wisconsin Upper Mich Michipicoten Is. Is. NW Wise Wisc Mamainse Point Point 1085 1090 1095 1100 1105 1110 Figure23. 23. Diagram Diagramillustrating illustratingthe thecorrelation correlationof ofMidcontinent Midcontinentrift riftrocks rocks from from Figure Taylors Falls-Clam Falls region with those those of of northern northern Wisconsin Wisconsin and and the Taylors Superior. The The upper upper limit limit of of the theChengwatana Chengwatana volcanics volcanics is eastern Lake Superior. Zartman et et al. al. (1997) (1997) in in the the estimated on on the the basis basis of of U-Pb U-Pb zircon zircon studies studies by by Zartman estimated Ashland syncline; syncline; the the lower lower limit limit is is based on on the the age age of of Clam Clam Falls Falls rhyolite. rhyolite. Ashland The The age age of of Taylors TaylorsFalls Falls flows flows isisbased basedon ontheir theirpredominantly predominantly "normal" "normal" paleomagnetic paleomagneticsignature signature(Kean (Keanetetal., al.,1997) 1997)(after (afterWirth Wirthand andGehrels, Gehrels,in inpress). press). 67 �region implies that the lower Clam Falls flows may may have have "reversed" "reversed" paleomagnetic paleomagnetic directions directions since they are approximately 105approximately coeval with the the reverse-to-normal reverse-to-normal magnetic magnetic polarity polarity change (1 (11051100 Ma) zk 55 Ma) that that has has been been widely widely observed observedthroughout throughoutthe theLake LakeSuperior Superiorregion. region.The The 1102 1102± age of the the Clam Clam Falls Falls rhyolites rhyolitesalso also implies impliesthat that this this section section of of the the Chengwatana ChengwatanavOlcanics volcanics Ma age during a period regarded as the was erupted erupted during the transition transition between between the the"latent" "latent" and and "main-stage" "main-stage" of rift magmatism (Millerand 1996). magmatism (Miller andVervoort, Vervoort, 1996). Stop 6b -(Alternate) —(Alternate) Rhyolite Rhyolite near near the McKenzie McKenzie Creek Creek State State Hunting Hunting Grounds. Outcrops Outcrops are located on on 310th 3 10th Ave approximately 0.8 miles south and east of the intersection intersection Ave. SE with 315th Ave. SE 1/4, 114,SE SE 1/4, 114, Sec. 26, T 37 N, R 16W; 16 W; Lat. Lat. 450 45O 39' 15.1" N, 092° 18' Long. 092O 18'28.4" 28.4" W. W. Scannedimage imageof of aaportion portion of of the the USGS USGS Clam Clam Falls, Falls, Wisconsin Wisconsin topographic topographic Figure 24. Scanned quadrangle (7.5 minute series; quadrangle series; 1:24,000 1:24,000 scale) scale) showing showing the location of Stop 6b. This stop is an region. Although an alternate alternate stop stop in the the rhyolites rhyolites of the Clam Falls region. Although the the contact stop does does permit permit examination examination contact with with surrounding surroundingbasalts basaltsisisnot not exposed exposed at at this locality, the stop of a large exposure exposure of rhyolite. The Theoutcrops outcropsare arelocated locatedalong alongthe thenorth northside sideof of 310th 3 10thAve Ave after after the end of the pavement near near where where the the road curves south south around around outcrop. outcrop. This outcrop is the the eastemmost easternmostexposure exposure of of Chengwatana Chengwatana volcanics in the Clam Falls Falls region and defines the base of the region the exposed exposed section. At At this thislocation, location,aaseveral-meter-thick several-meter-thick section of rhyolite is exposed over an area area several severalhundred hundredsquare squaremeters. meters. The The rock rock consists consists of of rhyolite. No layering is is observed. observed. The pale purple and aphanitic rhyolite. No compositional compositional or textural textural layering outcrop outcrop is cut by several sets of closely-spaced sub-vertical sub-verticalfractures fracturesthat that have have coatings coatings of iron iron oxides and other alteration alteration minerals. Quartz-rich Quartz-richveins veinsup up to to several several millimeters millimetersthick thick are are also also commonly observed. commonly 68 �Stop near Godfrey Stop 7—Porphyritic 7-Porphyritic flows near Godfrey Lake, Lake, WI. Outcrops are located 0.72 miles west of of County County Rd RdIIon on 315 St. SE SE1/4, 1/4,NW NW1/4, 1/4,Sec. Sec.29, 29,TT 37 37 N, R 16 W; Lat. Lat. 45O 45° 39' 43.0" N, Long. 092O 092° 22' 16 W, 22' 43.4" 43.4" W. W. purpose of this stop is to examine some of the strongly plagioclase-porphyritic plagioclase-porphyritic flows The purpose flows features can be observed in the exposures of the Clam Falls region. Several Severalinteresting, interesting-features exposures along along the north north side side of of the road road at this stop. The the Theeastern eastern end end of of the the exposure exposure consists consists of coarse basalt with porphyritic basalt* large (<3 cm cm long) long) large plagioclase phenocrysts phenocrysts plagioclase (40-60 percent) in aa (40-60 percent) groundmass groundmass consisting consisting of microcrysts of and plagioclase secondary minerals; secondary minerals; no minerals primary mafic minerals are present. Possible zoning structures are zoning still apparent is some of the feldspar phenocrysts. The The rock has been extensively extensively altered as evidenced evidenced by altered 25. Scanned image image of a portion of the strongly Figure 25. the USGS USGS Clam Clam Falls, Falls, the tpographic quadrangle and 1:24,000scale) scale) saussuritized Wisconsin topographic quadrangle(7.5-minute (7.5-minuteseries; series;1:24,000 showing the location epidotized plagioclase, plagioclase, location of Stop Stop 7. abundant chlorite, disseminated iron-oxides, quartz, and secondary feldspar (pink). Near the top of the the porphyritic porphyritic disseminated iron-oxides, quartz, centimeter thick "epidosite" "epidosite" that is is sub-parallel sub-parallel to toflow flowlayering. layering. This This epidosite epidosite is basalt is a ten centimeter similar interfiow sediments sediments seen at other localities. localities. Further similar to many intefflow Further west is a sparsely porphyritic basalt and vesicular basalt that basalt, which is overlain overlain by repeating layers of fine-grained basalt might represent several thin flow units. Some Somecross-cutting cross-cuttingvesicular vesicular basalt is also also observed. observed. Other coarse coarse porphyritic porphyritic basalts basalts can be found found several hundred meters south south of this this stop. stop. plagioclase phenocrysts phenocrysts typically comprise 15-25 percent percent of ofthe therock. rock. Intefflow Interfiow sediment sediment There, plagioclase is also found. Other exposures of coarse porphyritic basalt are also found further south and Other exposures of coarse porphyritic west of this stop (one mile NW of Straight Lake). Lake). The The orientations orientations of flows in this area are NW On poorly known, known, but but they theygenerally generallytrend trendNNE NNEand anddip dipgently gently(—15° (-15' ) to the NW. On the the basis of these considered to be these general general trends, trends, and and the the similarity similarityof rock types, these units are tentatively considered the same same stratigraphic stratigraphicunit. Considering Consideringthat thatflows flowswith with coarse coarse porphyritic porphyritic textures textures are are relatively relatively rare in the Chengwatana volcanics (Eagle Peak flows near St. Croix Falls and stop in the Clam Clam Chengwatana Falls in the region), it is also Falls region), also tempting tempting to suggest suggest that these geographically disparate disparate flow units units might might event. A be a roughly roughly coeval coeval eruptive event. A large large sample sample from this outcrop outcrop was processed processed for baddeleyite and zircon, but did not baddeleyite and not yield yield either either in in sufficient sufficient quantity quantity for for U-Pb U-Pb analysis. analysis. Preliminary Preliminaryinterpretation interpretationof of new new USGS USGS aeromagnetic aeromagneticdata data suggests suggeststhat that the the porphyritic porphyritic basalts basalts at Stop 7 are are stratigraphically stratigraphically below those of Stop Stop 3a. 3a. 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Report of Investigations 4088,7 Southwick, D.L., D.L., Morey, G.B., G.B., and McSwiggen, P.L., P.L., 1989, Geologic Geologic map map of the Penokean orogen, central central and eastern Minnesota: Report of of orogen, Minnesota: Minnesota Minnesota Geological Geological Survey Survey Report Investigations 37, Investigations 37, scale scale 1:250,000. 1:250,000. 74 �Strong, Moses, 1880, 1880, The geology of the the upper upper Saint Saint Croix Croix district: district: Geology Geology of of Wisconsin, Wisconsin, Wisconsin Wisconsin Geologic GeologicSurvey, Survey,v. v. III, Ill, p. p. 363-428. 363-428. Symons, D.T.A., Symons, D.T.A., Lewchuk, Lewchuk, M.T., Dunlop, Dunlop, D.J., Costanzo-Alvarez, Costanzo-Alvarez,V., V., Halls, Halls, H.C., H.C., Bates, Bates, M.P., M.P., Palmer, H.C., H.C., and Vandall, T.A., 1994, 1994, Synopsis Synopsis of of paleomagnetic paleomagnetic studies studies in in the Palmer, Vandall, T.A., Kapuskasing structural zone: Canadian Canadian Journal Journal of Earth Earth Science, Science, v. 31, 3 1, p. 1206-121. 1206-121. Van Schmus, W.R., W.R., 1992, Tectonic Tectonic setting setting of of the the Midcontinent Midcontinent rift rift system: Tectonophysics, Tectonophysics,v. v. 1-15. 213, p. 1-15. Van W.R. and Hinze, W.J., W.J., 1985, The The Midcontinent Midcontinent rift rift system: system: Annual Annual Review Review of of Van Schmus, W.R. Earth and and Planetary PlanetarySciences, Sciences,v. v. 13, 13,p. p. 345-383. 345-383. Vervoort, J.D. and Green, J.C., 1997, of evolved evolved magmas magmas in inthe theMidcontinent Midcontinent rift rift system, system, 1997, Origin of northeastern Minnesota: Nd-isotope Nd-isotope evidence evidence for for melting melting of of Archean Archean crust: crust: Canadian Canadian Journal Journal of of Earth Earth Science, Science,v. v. 34, 34, p. p. 521-535. 521-535. Webers, G., 1972, of Minnesota, Minnesota, in Sims, 1972, Paleoecology of the Cambrian and Ordovician strata of Sims, P.K., and Morey, Morey, G.B., G.B., eds., Geology of Minnesota: A centennial volume: Minnesota P.K., Geological Survey, p. 474-484. G.S., 1972, Webers, G., and Austin, G.S., 1972, Field trip guidebook for Paleozoic and Mesozoic rocks of 4, 91 p. southeastern Minnesota: Minnesota Geological Geological Survey Guidebook Series 4,91 theoretical basis for exploration White, W.S., 1978, 1978,A theoretical exploration for for native copper copper in in northern northernWisconsin: Wisconsin: U.S. Geological Survey Circular 769, 19 p. Geological Survey Circular 769, 19 p. J.D., 1995, Geochemistry Geochemistry of southernmost Wirth, K.R., Grotta, Grotta, S., S., Sadofsky, Sadofsky, S., and and Vervoort, J.D., southernmost Midcontinent Midcontinent rift lavas lavas in Minnesota Minnesota and and Wisconsin: International Field Conference Conference and and Symposium on the Petrology and Metallogeny Metallogeny of Volcanic and Intrusive Rocks of the the Midcontinent p.211-212. Midcontinent Rift Rift System: System: Aug. 19-Sept. 19-Sept. 1, Duluth, Minnesota, Proceedings, p. 21 1-212. Wirth, Karl R., Naiman, J.D., Miller, James D., and Naiman, Zachary, Zachary, Vervoort, J.D., and Morey, Morey, G.B., G.B., 1996, 1996, Volcanic Group Group near near Taylors Taylors Falls Falls and from Osseo drill Geochemistry of Chengwatana Chengwatana Volcanic core: core: 42nd Annual Meeting of the the Institute Institute on on Lake Lake Superior Superior Geology, Geology, Cable, Cable, WI, WI, Proceedings, Proceedings, v. v. 42, p. 66-67. 66-67. Wirth, Karl, Vervoort, J.D., and and Naiman Naiman Z.J., Z.J., 1997, Petrography Petrography and and geochemistry geochemistry of of the the Wirth, Vervoort, J.D., southernmost volcanic rocks exposed in the the Midcontinent Midcontinent rift: rift: Canadian southernmost Canadian Journal Journal of Earth Science, v. 34, p. 536-548. 536-548. of Midcontinent Midcontinent rift rift rhyolite rhyolite Wirth, K.R. and Gehrels, G.E., in press, Precise U-Pb zircon ages of (Chengwatana volcanics), Annual Institute on Lake Superior Superior Geology, 44thAnnual (Chengwatana volcanics),Clam Clam Falls, WI: 44th Proceedings. Zartman, Zartman, R.E., R.E., Nicholson, Nicholson,S.W., S.W., Cannon, Cannon,W.F., W.F., and Morey, G.B., 1997, 1997, U-Th-Pb zircon zircon ages ages of of rocksfrom fromthe thesouth southshore shoreofofLake LakeSuperior: Superior: Canadian some Keweenawan Supergroup rocks Journal of Earth Earth Science, Science, v. v. 34, 34, p. 562-575. 562-575. Zhu, Consortium for continental continental reflection reflection profiling Michigan Michigan surveys: Zhu, T., and Brown, L., 1986, 1986, Consortium surveys: reprocessing and results: results: Journal of Geophysical Geophysical Research, Research, v. 91, p. 11477-11495. 11477-11495. 75 ��FIELD FIELD TRIP TRIP#3 #3 GLACIAL GLACIAL EXOTICA OF OF THE THE TWIN TWIN CITIES CITIES AREA Leaders: Leaders: Howard HowardHobbs, Hobbs, Alan Alan Knaeble, Knaeble, Gary Gary Meyer Meyer OVERVIEW OF OF LATE QUATERNARY QUATERNARY GEOLOGIC OVERVIEW GEOLOGIC HISTORY Howard Howard Hobbs Hobbs The The landforms landformsand andsurface surfacesediments sedimentsof of this this area area formed formed during during the the most most recent recent glaciation— glaciation- the late Wisconsinan. The Thearea areawas was covered covered by by previous previous glaciations some 10 10 to 20 times, but sediments sediments from from these these earlier earlier glaciations glaciationshave have been been partially partially eroded eroded by by subsequent subsequentglaciations glaciations and are are now now deeply deeply buried buried by sediments sediments deposited during the last glaciation. Although Although the the volume of late Wisconsinan drift in Minnesota is less than half the volume of all the older drifts volume of late Wisconsinan drift in Minnesota is less than the volume all older drifts put put together, together, the the amount amountremaining remainingper per glaciation glaciationisisso somuch muchmore morethat that itit can can be be explained explainedonly only by recycling new drift drift sheet. In recycling large large amounts amounts of older glacial sediment into each new In other other words, words, only aa portion portion of of the the sediment sediment that that we we will will see see was was brought brought from from its bedrock bedrock source source to its its present present position position in in one one glaciation. glaciation. The The Twin Twin Cities-St. Cities-St. Cloud Cloud area area is is dominated dominated by by the the deposits deposits of of two two ice ice lobes, lobes, each each from fromaa different direction (Fig. 1). 1). The TheSuperior Superiorlobe lobeadvanced advancedinto intocentral centralMinnesota Minnesotathrough throughthe the Lake Superior Superior basin from from northeast. Its Itstill tillisisreddish-brown, reddish-brown,sandy sandyto toloamy, loamy,and andrich rich in inred red and and black black rocks rocks from from the the Superior Superiorbasin and and the north shore of Lake Superior. Typical Typical rocks are red sandstone basalt and and gabbro. gabbro. Within the Superior sandstone and siltstone, rhyolite and granophyre, granophyre, basalt basin, basin, the the Superior Superiorlobe lobedrift drift contains containspractically practically no no carbonate carbonaterocks rocks or or matrix matrixcarbonate, carbonate,but butin in the field field trip trip area area ititcontains containsaamodest modestamount, amount,presumably presumably recycled recycledfrom fromolder, older,calcareous calcareous drifts. drifts. The St. St. Croix Croix moraine moraine roughly roughly marks marks the the late late Wisconsinan Wisconsinan maximum of the Superior Superior lobe. lobe. There Thereisisevidence evidencefrom frombeyond beyondthe themoraine moraineof of aa somewhat somewhat more more extensive extensive lobe that may have preceded moraine-building, but but this this zone zone is is not not very very wide. wide. On the southeast southeast side of the the lobe, the moraine moraine is is wide wide and andhigh. high. It ranges lobe, from from south south of Minneapolis Minneapolis to the St. Croix River, the from 5-10 5-10 miles miles wide, wide, and and the the thickness thicknessof of morainic morainicmaterial material ranges ranges from from100-300 100-300feet. feet. Its Its surface development surface morphology morphology is is highly highly collapsed, collapsed, indicating indicating that the final event of moraine development was was the the melting melting of of stagnant stagnantice icefrom frombemeath bemeath thick thickdebris. debris. At the west west end end of this this same same segment, segment, the moraine moraine turns sharply sharply and and runs northwest northwest to to the the St. Cloud area. Most Mostof ofthis thissegment segmentisisburied buried by by glacial glacial sediment sediment of of the the Des Des Moines Moines lobe, lobe, so so is not known in detail. Only the highest parts (generally kames) are exposed at the surface (for Only the highest parts (generally kames) are exposed surface example, Stop 1). 1). These Thesekames kamesmay may represent represent fans fans of of sand sand and and gravel built at the edge of the ice by subglacial subglacial tunnel tunnel valleys valleys (Fig. (Fig. 1.1). 1.1). The Thetop topof ofthe themoraine morainein inthis thissegment segmentisislower, lower,due due to a combination combination of the following following factors: the thebase baseon on which whichitit was was built built seems seems to to be lower; lower; the the average thickness of moraine material is less; and some of the material was eroded off by the overriding overridingDes Des Moines Moines lobe. lobe. Inasmuch Inasmuchas asthis this segment segmentrepresents represents the frontal frontal part of the moraine, the debris debris may may have have been been spread spread over over aa wider wider zone zone by minor minor fluctuations fluctuations of of the the ice ice front. front. 79 �EII1 Park 1/ 4 - do . '- :' 4Bodu I, ok A pr1 pers C 0O 0 EXPLANATION hp td do Terraces of the Mississippi River Des Moines lobe outwash (includes sandy lake sediment in eastern part) dag, dpg, Des Moines lobe ground moraine dbg Des Moines lobe stagnation moraine das dpe, dbe Des Moines lobe end moraine Superior lobe outwash so Superior lobe ground moraine ssg Superior lobe end moraine sse Figure Figure 1. 1.Simplified SimplifiedQuaternary Quaternarygeology geologyofofthe thefield fieldtrip triparea, area,showing showingmajor majorroads roadsand andlocation locationofofstops. stops. �About 15 15 miles miles south south of of St. St. Cloud, Cloud, the the moraine moraine begins begins to to emerge emerge from from under under its its Des Des About Moines Moines lobe lobe cover. cover. The Thehigher higherparts partsof ofthe themoraine moraineform formisolated isolated bumpy bumpy knobs, knobs, while while the the lower lowerparts partsare arecovered coveredwith withoutwash outwashof of the the Des Des Moines Moines lobe. lobe. Many Manyof ofthe thehigher higherparts parts appear appear to to be be ice-thrust ice-thrustfeatures, features,such suchas asthe theone oneatatStop Stop2.2. The The Des Des Moines Moineslobe lobeadvanced advanced from from the the northwest, northwest,following following the the broad broad lowland lowland now now occupied occupiedby bythe theMinnesota MinnesotaRiver RiverValley. Valley. Its Its till till isisgray gray(oxidizing (oxidizingto toolive olivebrown), brown), loamy loamy to to clayey, clayey, and and rich rich in in sedimentary sedimentaryrock rock fragments—mainly fragments-mainly carbonate carbonate and and gray shale. shale. Granite Graniteand and Anoffshoot offshootof ofthe theDes DesMoines Moineslobe, lobe,called calledthe the greenstonefragments fragmentsare are also alsofairly fairlycommon. common. An greenstone Grantsburg Grantsburgsublobe, sublobe,extended extendednortheast northeastfrom fromthe themain mainlobe, lobe,burying buryingthe theSt. St.Croix Croixmoraine, moraine,and and advancing over land that had recently been vacated by the Superior lobe. advancing over land that had recently been vacated by the Superior lobe. ItIt appears appearsthat thatthe theGrantsburg Grantsburg sublobe sublobe was was aa late late advance, advance, during a time when when the the main main Des Moines lobe was retreating. The retreat was interrupted by many minor re-advances, each Des Moines lobe was retreating. The retreat was interrupted by many minor re-advances, each one lobeApparently the the Bemis Bemis advance advance of of the the Des DesMoines Moineslobe— one less less extensive extensive than than the thelast. last. Apparently 14,000 14,000years years ago— ago- was was blocked blocked and and diverted diverted by the St. Croix moraine. How Howwas wasthis thismoraine moraine able ableto toblock blockthe theearliest, earliest,most mostextensive extensiveadvance, advance,and andyet yet was was overridden overriddenby by aa later, later, less less powerful powerful pulse? pulse? The Themost mostreasonable reasonableexplanation explanationisisthat thatearly earlyon onstagnant stagnantice iceburied buriedininthe themoraine moraine made madeititeffectively effectivelyhigher. higher.As Asthe theice icemelted, melted,the thebarrier barrierbecame becamelow lowenough enoughto tobe bebreached breachedby by the theadvancing advancingice. ice. One One could could postulate postulate that that at at the the time time of of the theBemis Bemisadvance, advance, the the St. St. Croix Croixmoraine moraine was was backed sublobeto to backedby byactive activeglacier glacierice, ice,which whichlater laterretreated retreatedenough enoughto toallow allowthe theGrantsburg Grantsburgsublobe cross crossthe themoraine. moraine.However, However,glacial glaciallake lakedeposits depositshave havebeen beendiscovered discoveredwell well back back from fromthe the St. St. Croix moraine, underneath sediments of the Grantsburg sublobe. Johnson and Hemstad (in Croix moraine, underneath sediments of the Grantsburg sublobe. Johnson and Hemstad (in prep.) varve couplets couplets from from the the thickest thickest part part of of the the lake lake sediments sediments as as prep.) estimate estimate at at least least 900 900varve extrapolated extrapolatedfrom fromthinner thinnercounted countedsections. sections.This Thissuggests suggeststhat thatactive activeice ice had had melted melted back back from from the themoraine morainelong longbefore beforethe theGrantsburg Grantsburgadvance. advance. The TheDes DesMoines Moineslobe lobeadvance advanceover overthe theSt. St.Croix Croixmoraine morainewas was in in two two phases: phases:first firsttotocross cross was wasthe theDuelm DuelmBulge Bulge(Stops (Stops44and and5). 5). The Thenorthern northern limit limit of of this thisadvance advanceisisdefined definedby by the the Duelm Duelmchannel, channel,which whichcarried carriedthe thedischarge dischargeof ofthe theupper upperMississippi MississippiRiver Riveraround aroundthe thebulge bulgeof of ice. The eastern limit of the bulge is less certain, but it may have been pinned by the high ice. The eastern limit of the bulge is less certain, but it may have been pinned by the high ground groundnorth northofofElk ElkRiver River(Stop (Stop7). 7).This Thisadvance advanceappears appearstotohave havebeen beenshort-lived, short-lived,and andquickly quickly succeeded succeededby bythe theadvance advanceofofthe theGrantsburg Grantsburgsublobe. sublobe. The TheGrantsburg Grantsburgsublobe sublobecrossed crossedthe theSt. St.Croix Croixmoraine moraineover overaabroad broadfront, front,and andadvanced advancedtoto the thenortheast, northeast,past pastthe theSt. St.Croix Croixriver rivertotothe thetown townof ofGrantsburg, Grantsburg,Wisconsin. Wisconsin. ItItwas washemmed hemmedinin by bythe theback backside sideofofthe theSt. St.Croix Croixmoraine moraineon onthe thesoutheast southeastside, side,and andby byhigh highground groundtotothe thenorth. north. The TheGrantsburg Grantsburgappears appearstotohave havebeen beenone onemain mainpulse, pulse,followed followedby bywidespread widespreadstagnation stagnationand and melting. melting. Till Tillof ofthe theGrantsburg Grantsburgadvance advanceisisquite quitevariable variablein in composition; composition;ininplaces, places,ititisisessentially essentially the thesame sameasastill tillofofthe theDes DesMoines Moineslobe. lobe.InInothers, others,ititisisbanded bandedred redand andgray, gray,on onthe thescale scaleofoffeet feet totoinches. inches.InInother otherplaces, places,ititappears appearsthe thesame sameasastill tillofofthe theSuperior Superiorlobe, lobe,except exceptfor foraatrace traceof of shale. sublobeincorporated incorporatedaalarge largeamount amountof ofSuperior Superior shale.Apparently, Apparently,the theice iceofofthe theGrantsburg Grantsburgsublobe lobe lobedebris debrisasasititwas waspassing passingover overthe theSt. St.Croix Croixmoraine. moraine. This Thisdebris debriswas waspartially, partially,but butnot not completely, completely,mixed mixedwith withsediment sedimentalready already in in the the ice. ice. InInplaces, places,especially especiallyininthe thecenter centerofofthe the lobe, lobe,Grantsburg Grantsburgtill tillisisthin, thin,orormissing missingaltogether. altogether. 81 �The ice melted melted more rapidly in the center center than along along the margins, presumably presumably because it GlacialLake Lake Anoka Anoka formed formed in the center center of the sublobe, sublobe, fed by large large had less of a debris cover. Glacial amounts Of of meltwater amounts meltwater from the upper Mississippi (a continuation of the same flow that eroded the Duelm Channel). Channel). The Thelake lakedeclined declinedin instages stagesas asice icemelted melted out out of of the the margins, margins,uncovering uncovering successively lower outlets into the St. Croix Croix River, River, and finally finally drained drained altogether altogether down down the the Mississippi River. This This drainage drainageevent event connected connectedthe the upper upper and and lower lower parts parts of the the Mississippi Mississippi for the first time in its modern course. course. of two two parts: parts: the The Anoka Sand Plain is composed of the lakebottom lakebottom sediment sediment (mostly (mostly fine fine plain-delta which extends from the Mississippi valley train train into the outwash plain-delta sand), and a sandy outwash lake. The Thelake lakewas wasshallow, shallow,and and apparently apparentlymost most of of the the silt silt and and clay clay from from the the meitwater meltwater stayed stayed until it was carried downstream. between the the delta and the in suspension suspension until downstream. The The boundary boundary between lakebottom sediment lakebottom sedimentisisdifficult difficultto to pin pin down, down, because becausethe the texture textureof of the the sand sand is is not much much different, different, and because the boundary boundary shifted shifted as as the lake filled in. STOP 1—Superior ValleyFan Fan Sand Sand and and Gravel Buried by Superior 1ÑSuperio Lobe Tunnel Valley SuperiorLobe Lobe and and Grantsburg GrantsburgSublobe SublobeTill. Till.(Gary (GaryMeyer) Meyer) A radiocarbon radiocarbon date 32,300±2000 obtained from from wood fragments fragments date of 32,300 k2000years yearsB.P. B.P. (Beta-40098) (Beta-40098) obtained in a core core sample sample taken taken below below 130 130 feet feet of of Superior Superior lobe lobe sand sand and and gravel gravel in Ramsey Ramsey County County (Meyer, 1992), 1992), gives a possible maximum age for the advance advance of the Superior Superior lobe lobe into into easteastcentral Minnesota. As Asthe thefront frontof of the the Superior Superiorlobe lobe became stabilized, stabilized, it formed the St. Croix moraine—a complex the east, east, south, south, and and moraine-a complexlinear linear series seriesof of high high hills encircling encircling the Twin Cities on the paralleling the Mississippi Cloud area area (Fig. (Fig. 1.1). 1.1). During the eventual west, and paralleling Mississippi River to the St. Cloud retreat of the ice front, front, meltwater meltwater issuing issuing from the Superior lobe became channelized through the moraine. The TheSuperior-provenance Superior-provenance(Table (Table 1.1) 1.1) sand sand and gravel deposit at Maple Grove in northeast Hennepin Hennepin County County (Fig. (Fig. 1.1), 1.l), extensively exposed in gravel pits (Fig. 1.2), was likely deposited during formation of the North 1992),which which mark mark a retreatal retreatal deposited during formation of the North Ramsey Ramsey mounds mounds (Patterson, (Patterson, 1992), position of the Superior Superior lobe lobe behind the the St. St. Croix Croix moraine. Table 1.1. General Generalcharacteristics characteristicsof of mapped mapped glacial glacial deposits of ofthe theTwin Twin Cities Cities area. area. texture Till texture Mountain Riding Mountain Provenance Provenance loamy Superior Superior Provenance Provenance sandy sandy Color oxidized oxidized unoxidized unoxidized yellow brown to olive olive brown gray gray red brown gray to to red red gray gray gray common common uncommon to common common rare to uncommon common to abundant abundant rare to uncommon uncommon uncommon to abundant abundant common absent absent Feature Pebble type white to to buff carbonate carbonate dark gray to gray-green rocks red felsite and sandstone sandstone gray shale shale 82 �u lMTED STATES Figure moraine in east-central east-central Minnesota Figure 1.1. 1.1. Tunnel Tunnelvalleys, valleys,valley-mouth valley-mouthfans, fans, and and the St. Croix moraine and adjoining counties in Wisconsin. Wisconsin. Lettered features are landforms landforms discussed discussed in inthe thetext: text: M, Maple Grove fan; E, Elk River fan complex. complex. Modified Modified from Patterson (1994). The The Maple Maple Grove Grove sand sand and and gravel gravel deposit depositwas was laid laid down down as as aa fan fan at at the the mouth mouth of of aa tunnel tunnel valley—a drainageway (Patterson, (Patterson, 1994). 1994). The trend valley-a deeply incised, broad, subglacial drainageway trend of of the the tunnel valley that fed the fan is is marked marked to to the the northeast northeast in in Anoka County by aa chain chain of of lakes lakes (Fig. 1.1) 1.1) formed formed when thick thick ice filling filling the valley later melted. The The sand sand and and gravel gravel laid laid down down at the mouth of the valley evidently buried stagnant ice, as the fan deposit is deeply pitted (Fig. 1.2). The The buried buried ice ice was was well-insulated, well-insulated, as as it apparently was still melting during a readvance of the Superior gravel below reddish reddish sandy till, and then then during during an Superior lobe, lobe, which which buried buried the the sand sand and grave1 which further buried buried the the sand and gravel with yellowish advance of the Grantsburg sublobe, which clayey till. The Thesand sandand andgravel gravelisis thickest thickest where where the the buried ice was thin, forming ridges in the postglacial landscape. landscape. Areas Areasunderlain underlain by by the the thickest thickest ice became depressions into which first Superior lobe till from Superior from the the readvance readvance (Automba?) (Automba?) phase flowed, flowed, and and then, then, following following final final deglaciation, both finally completely completely deglaciation, both Superior Superiorlobe lobe and and Grantsburg Grantsburg sublobe sublobe tills flowed flowed as the ice finally melted, deposited. A log at the base of collapsed melted, apparently apparently thousands thousandsof of years years after after it was first deposited. lake sediments and Superior Superior lobe lobe tills, tills, exposed in a Maple sediments overlying overlying collapsed Grantsburg Grantsburg and Maple Grove fan pit, yielded a date date of of 11,930±60 11,93e60radiocarbon radiocarbon years years B.P. B.P. (Beta-23746; Meyer and Hobbs, 1989), 1989), indicating indicating that that buried buried St. St. Croix Croix phase ice was still melting less than 12,000 12,000 years years ago. ago. 83 83 �9/ yr- jj ci o a Q J)I Ik0 TH II 0 0 / a 0riggI lemT I t U— - - r Y.°'— .'c 4r'/t9r( _.; . .. . . . Figure 1.2. 1.2. Topographic Topographicmap mapwith with Maple Maple Grove Grove fan deposit outlined. The The landform landform likely likely extended extended to to the Figure sublobe meltwater. meltwater. Area shown is is about about 2.8 2.8 miles miles wide; wide; northeast prior to being planed off by Grantsburg sublobe contour contour interval interval 10 10 feet. feet. (U.S. (U.S. Geological Geological Survey Survey Osseo Osseo quadrangle, quadrangle, 7.5-minute series, series, 1967.) 1967.) The movement depressions during during differential differential ice-block ice-block movement of the bulk of overlying tills into depressions melt-out melt-out reduced reducedthe the"overburden" "overburden7'thickness thicknessabove abovethe thesand sandand andgravel, gravel,allowing allowingitit to to be exploited exploited for construction construction aggregate. aggregate. Gravel Gravelmining mininghas hasinverted inverted the the topography once once again, again, turning the gravel ridges into deep pits and the till-filled depressions into into hills. hills. Gravel from the Maple till-filled depressions Grove Cities area area as as ititconsists consistsmostly mostly of ofPrecambrian Precambrian Grove fan fan deposit deposit is is the most durable durable in the Twin Cities rock clasts (Meyer and Jirsa7 ursa, 1984). 1984). Superior Superiorlobe lobe deposits deposits to to the the east east and and southeast southeast contain greater greater amounts amountsof of locally-derived, locally-derived,relatively relativelysoft softPaleozoic Paleozoicclasts, clasts,eroded erodedas asthe thelobe lobemoved movedup up the escarpment others, 1986). Des Moines lobe and escarpment formed formed by the Oneota Dolomite (Jirsa and others, Grantsburg sublobe deposits contain clasts of both Paleozoic carbonate and Cretaceous shale, as they are of Riding Riding Mountain Mountainprovenance provenance (Table (Table 1.1). 1.1). 84 �%Powder Ridge Site-Glacial Thrusting Cretaceous STOP 2—Powder Ridge Borrow Borrow Pit Site—Glacial Thrusting of of Drift and Cretaceous (Alan Knaeble) Knaeble) Bedrock. (Alan A located in the St. Croix moraine (Fig. 2.1). The moraine was deposited A large large borrow borrow pit pit is located deposited prior prior to to 16,150 16,150years years BP BP (Birks, (Birks,1976) 1976)when when the the Superior Superior lobe was at its maximum. This Thissite siteisis perched Moines lobe lobe outwash outwash plain plain (Fig. (Fig. 2.2). 2.2). The perched about about 225 ftft above above the surrounding Des Moines borrow to0build up the summit of the ski hill and and regrade borrow pit pit was was excavated excavated to to supply supply material 1 existing existing ski-run slopes. The The pit pit isis 1/4 114mile mile long long and and oriented oriented north-south. north-south. There There are are good good exposures wails (Fig. 2.3). 2.3). Six texturally and lithologically distinct exposureson on the the north, north, west, and east walls (K); pre pre Wisconsin Wisconsin sand sand (S); (S); are recognized recognized in in the the pit pit including: including: Cretaceous Cretaceous shale shale (K); units are unoxidized, dark dark gray, gray, clayey clayey pre-Wisconsin pre-Wisconsin till (Elmdale (Elmdale till) till) (wt-w); (wt-w); unoxidized, unoxidized,dark darkredredunoxidized, brown pre-Wisconsin till ("Old ("Old Red Red till") till") (st-x); (st-x);oxidized, oxidized,yellow-brown yellow-brown or orunoxidized, unoxidized,gray gray pre-Wisconsin pre-Wisconsin till (wt-x); (wt-x); and and reddish-brown, reddish-brown, sandy sandy late late Wisconsin Wisconsin till, till, lake lake sediments, sediments,and and sandlgravel identification sand/gravel (Superior (Superior lobe deposits) (st). Fossil Fossil and and mineral mineral content content have helped identification of of the Cretaceous Cretaceousdeposits, deposits,and and texture texture and and grain grain count count analyses analysesindicate indicate that that at at least least four four glacial glacial advances advances are are represented represented(Table (Table2.1; 2.1; Fig. Fig. 2.4) 2.4) (Knaeble, (Knaeble,1996). 1996). - E St. Croix moraine Payn.wC. Thrusthills IOMILES o • Thrust site I Fo a 10 - --- 15 KMOMETERS . . Figure 2.1. Simplified Simplifiedmap mapof ofStearns steamsCounty Countyshowing showingthe thelocation locationof of thrust thrust masses masses Figure (hills) (hills) within the St. St. Croix Croix Moraine and 22 thrust sites. From FromKnaeble Knaeble(1996). (1996). Exposures in the the pit pit walls walls show show that that these these sediments sediments form slabs slabs 50-250 50-250 ft thick, thick, which which appear appear to extend extend laterally for more than 400 ft. The The slab slab contacts contacts dip dip 30°-60° 30°-60north-northeast, north-northeast, in for the the Superior Superiorlobe. lobe. The The internal internal stratification stratification in what would would have been the up-glacier direction for ft 50-100 ft within these slabs slabs largely largely subparailels subparallels slab slab boundaries, although although two zones, each 50-100 withiI these thick, are intensely deformed; the sediments are sheared, streaked, mixed and, in the intensely eaked, mixed and, in the intensely thick, are intensely deformed; the sediments are sheared, str rned zone, 7nne dicnlmr distorted dictnrtpd overturned nvprhirnpd fnldc Rnqpd on deformed display folds. Based ----on comparisons comparisons with with undeformed undeformed defonAawu uALw, exposures exposures in in Stearns SteamsCounty, County, the the sequence sequence of sediments sediments in in this pit can be divided into at least 6 thrust blocks. Each Eachthrust thrustblock blockcontains containstwo twoor ormore moredistinct distinctunits unitsdifferentiated differentiatedby by color, color, texture, and lithology. block. Superior lithology. The The youngest youngest till (unit st) caps each thrust block. Superior lobe lobe ice, ice, associated with deposition of this youngest till, is interpreted to have caused the thrusting associated deposition of youngest (Knaeble, (Knaeble, 1996). 1996). 85 85 uawy*aJ -au..-A.-- �I I glaciotectonic thrusting Figure 2.2. 2.2. Topographic Topographicmap map showing showing the powder ridge ski pit, a site of glaciotectonic Figure on N., R. R. 29 29W.). on the the St. St. Croix Croix Moraine Moraine (sec. (sec. 27, 27, T. 22 N., W.). Hachured Hachured lines lines indicate indicate scarps; scarps; hachures hachures on on downslope downslope side. Area Areashown shownisis2.3 2.3 miles miles wide; wide; contour contourinterval interval10 10feet feet(U.S. (U.S.Geological Geological Survey Kimball quadrangle, 7.5-minute series, 1967). From Knaeble (1996). From Knaeble (1996). 86 �EXPLANATION Fill Unexpose area or Slope wash Superior lobe lull (Pierz). in places Containing inlerbegs of Superior lobe lacuustrine sedumenf (.1) and Superior lobe sand and gravel deposits (so) Winnipeg provenance n till )Sauk Centre or Meyer Lake) v till (Old Red) Winnipeg provenance w till (Elmdale) Sand (pre-lafe Wisconsin) Cretaceous marine Shale Thrust fault; sawteeth in upper plate Fault, Showing relative horizontal motion; approximate location where dashed —— — Unit confacl, approximate location where dashed Highly deformed mined malerial Superior provenance I. 0 tOO 300 feet Vertical exaggera(l Figure thrust blocks. blocks. Quaternary sediments sediments and Cretaceous Figure 2.3. Powder PowderRidge Ridgeski ski pit showing showing interpreted thrust clays are exposed on the north, east, and west west walls walls of of the the pit; pit; the exposure exposure on the west wall has been extended through to the outside face face of ofthe theblock blockdiagram. diagram. See Seefigures figures 2.1 2.1 and.2.2 and 2.2 for forpit pitlocation. location. From Knaeble Knaeble (1996). (1996). Table 2.1. Matrix Matrixtexture textureof of glacial glacialtills tills in in the the Powder Powder Ridge Ridge ski ski pit. Unit Percent of Sand Sand Silt No. of Samples Samples Clay Clay wt-w 4 29 29 40 31 31 st-x st-x 6 41 41 34 34 25 25 Meyer Lake 5 28 57 57 15 15 Sauk Sauk Centre Centre 8 8 41 41 41 41 18 18 20 58 58 29 29 wt-x wt-x St st 87 . 13 13 �Clay Clay 100% 100% UMTS • wt-w + st-x • wt-x o wt-x St Figure 2.4. Triangular Triangular plot of matrix texture of glacial till units in the Powder Ridge ski ski units Powder Ridge pit. From FromKnaeble Knaeble (in (in prep.). U.. U ••S• c&o • 100% Sand Sand 100% 50% Silt The The exposure exposure on on the west west wall at at the south south end of the pit, shows Cretaceous marine shale shale 10-foot-thick packet of deformed deformed Superior lobe till, which contains contains streaks streaks of of overlying a 10-foot-thick incorporated older till. The deformed Superior lobe till overlies 25-30 ft of very well sorted, The deformed Superior finely bedded, finepre-late Wisconsin, Wisconsin, which in turn finely bedded, fine- to medium-grained medium-grained sand sand interpreted interpreted to to be pre-late overlies overlies more Cretaceous Cretaceous shale. shale. The Thecontacts contactsbetween betweenthese theseunits units dip dip 30°-60° 30°-60north and and indicate indicate south-directed thrust block block overlying overlying younger south-directedthrusting thrustingwith withaa Cretaceous Cretaceousunit unit at at the base of one thrust units in another another thrust thrust block. Drill Drillcore coreof of the the Cretaceous Cretaceousshale shale at at the south south end of the pit shows them to extend to a depth of at least 56 ft, where the drill core ended. The elevation at the the top of extend ft, where the drill core ended. the Cretaceous shale is about about 1300 1300 ft; ft; yet well well logs logs show show the highest undisturbed Cretaceous level. Some Some of the thrust blocks contain contain bedrock in the region to be less than 1100 1100 ft above sea level. Cretaceous top of of other other thrust thrust Cretaceous shale, shale, which which is is interpreted interpreted to have been exhumed and stacked on top blocks to form form the moraine moraine during during ice ice advance advance (Knaeble, (Knaeble, 1996). 1996). wide at the the Powder PowderRidge Ridge ski skipit. pit. Water-well Water-well The St. Croix end moraine is about one mile wide records for mile northwest northwest records for three three wells wells located located on on the flanks flanks of the end moraine (two about a half mile of the pit, one one located located about about aa quarter quarter mile northeast northeast of the pit) also describe materials that appear appear to be thrusted thrusted (i.e., (i.e., Cretaceous Cretaceousdeposits depositsover over till, till, and and repetitive repetitive sequential sequentialcolor color changes changes in the till units). units). There is evidence evidence that that the the presence presence of permafrost (Mackay (Mackay and Mathews, Mathews, 1964; 1964; Clayton Clayton increase in in pore-water pore-water pressure pressure and Moran, 1974; 1974; Bluemle and Clayton, Clayton, 1984; 1984;Aber, 1988), an increase in the underlying underlying sediment sediment(Clayton (Claytonand andMoran, Moran,1974; 1974;Bluemle Bluemleand andClayton, Clayton,1984; 1984;Aber, Aber,1988), 1988), Aber, 1988) are conditions that and sufficient ice-flow velocities (Clayton and Moran, 1974; Aber, contribute to thrusting thrusting of substrata substrata at ice margins. When Whenthe theSuperior Superiorlobe lobeadvanced advancedover over soft soft bedrock, such as Cretaceous shale, or older glacial deposits, these conditions may have been as Cretaceous shale, or older glacial deposits, these conditions have been present and appear appear to to have have fostered fostered thrusting thrusting (Fig. (Fig. 2.5) during during the formation formation of the the St. St. Croix Croix moraine at Powder Powder Ridge. Ridge. 88 �Zuul—. 'I // \—_;.u__ \'_ — — —— 7, .. ,, -u '' 7,s_... • /\ 7/._.. . , _'•- —' — — - #•%S _ /' - — _% 'ui — , %_ \ 'S - 1s __u_u— — —I —S — -. _ .. — F I Is/i ,%7.,I, — 55 .2s I5./ ,./ — .2 .. — — '.. I ..S_I_\ — sI —,.;.. * — -' — %s '%S '\ ,%—;_ S_ — .. ',, \S S Ss1 — ' 7 — —-' ,• .'' _'L. — .2 •S__4•. I S , / 5, '5 — _.g_l' — :L L''-'.7' '•'_i r''——— '—''——— '—'r5 — Bedrock Surface Cretaceous Precambrian — — 5,5 J ———'5' 7,5,,,—5—— — —— i, — I_,,\ \_ 7, I_5—%_'S_ 5, SJ 1_ — — . .2 ': %___ ,: — — -__S... S — • _''_—— —' s._ ''SA \__ '_/t _.ez.' 'ui SS .— . ,','_',/_'. _,'..'/_!.I — __ _SS — __ — — I !. '—S . _,— L .2 .. ' —— '\ '11ui'' ' S/*'S'' I_ \__ '_'—, — '—— ,./ —— I, 5 __/% —,';— •__ us/u / z _;'u•_ ,— — .b —— — — ;_ : I—I / .j. ---I... _'5. Ice-Thrust Sites Figure 2.5. 2.5. Geologic Geologicmap mapofofSteams StemsCounty Countyshowing showingthe theSt. St.Croix Croix Figure moraine and the association of ice-thrusts with the underlying moraine and the association of ice-thrusts with the underlyingbedrock. bedrock. Powder POW^& Ridge Ridge Borrow Borrow Pit Pit STOP Thrusting of Cretaceous STOP3—Merden 3-Merden Lake Lake Esker EskerGravel GravelPit—Small-scale Pitamall-scale Thrusting Cretaceous Bedrock Bedrock and and Glacial Glacial Drift. Drift. (Alan (Alan Knaeble) Knaeble) The gravel gravel pit cuts through a section section of the Merden Lake esker and provides evidence for small-scale thrusting that is not associated with with end-moraine end-moraine formation formation(Fig. (Fig.2.1). 2.1). The esker formed formed beneath beneath the the Superior Superiorlobe lobeas asthe the ice ice advanced advanced towards towards the the southwest. southwest. Typical esker esker deposits deposits are are exposed exposedalong alongthe theeast eastwall wallof ofthe the pit. pit. Here, Here, about about 20 20 ftft of of Superior Superiorlobe lobe sand sand and and gravel gravelare are overlain overlain by aa thin 5-foot 5-foot layer layer of sandy sandy Superior Superiorlobe lobe till till (Fig. (Fig. 3.1). In represent Inthe the northwest northwestwall, wall,aa Superior-lobe-source Superior-lobe-sourcesand sand and and gravel gravel is also interpreted to represent the Superior lobe lobe till that has incorporated incorporated the core core of an an esker. Mantling Mantlingthis thiscore coreisis aa 5-10-foot 5- 10-footcap cap of Superior aa 3-5-foot Cretaceous shale 3-5-foot slab slab of old 'Elmdale 'Elmdale till' till' of of Meyer (1986). Thin Thin layers layers of dark gray Cretaceous are present present at the base of the Superior Superior lobe till cap. The The Cretaceous Cretaceous shale shaleand and the the older older Elmdale Elmdale till till are are interpreted interpretedas as substrata substratathat that were were picked up up by Superior-lobe Superior-lobe ice, transported transported at the base of the glacier, glacier, and and then deposited deposited on top top of the esker esker as as the ice ice wasted wasted (Knaeble, (Knaeble, 1996). 1996). Scattered in the sand and gravel on the pit floor you can find pebbles and cobbles of pisolitic lateriticclay. clay. These Theseclasts clastsare areinterpreted interpretedto tobe be derived derived from from the the uppermost uppermost weathering weathering pisolitic lateritic profile Precambrian igneous saprolith, and transported transported here by by Superior Superior profile of the Precambrian igneous and metamorphic saprolith, lobe landscape lobe ice ice and and meitwater. meltwater. Setterholm Setterholm(1990) (1990)states, states,"The "The pisolitic pisolitic layer layer marks marks aa soil soil of the landscape upon which which the the bulk of of the the Upper Upper Cretaceous Cretaceous rocks rocks in in Steams S t e m sCounty Countywere weredeposited." deposited.'' 89 �andravel east ____— west Cretaceous Cretaceous shale shale iiorlobetil1_ Superior lobe till sand and gravel . . . . . . .. Figure 3.1. Merden MerdenLake Lake Esker Esker gravel gravel pit: profile profile of of exposed exposed east and west walls. Brothers Gravel STOP STOP 4— 4- Bauerly Brothers Gravel Pit. Pit. (Howard (Howard Hobbs) lobe drumlin drumlin (Fig. (Fig.4.1). 4.1). The near side of the This pit is dug into the side of a Superior lobe drumlin is truncated by the the edge edge of of the theMississippi Mississippivalley valley train. train. There is about about 25 25 feet feet of Superior outwash overlain by by as much as 25 feet of reddish-brown till. The till cover reddish-brown till. cover gets thinner on the lower flanks of the drumlin. ItItisisnot not unusual unusual for for drumlins drumlins of of the the Pierz Pierz drumlin drumlin field to contain meltwater meltwater sediment, sediment, presumably deposited deposited in an earlier phase of glaciation, glaciation, as as well as till. are typical typical of ofSuperior-provenance Superior-provenancedeposits. deposits. They are reddish reddish Both the till and the gravel are brown, and contain many many red and black pebbles; pebbles; carbonate carbonatepebbles pebblesare aresparse. sparse. The till is aa brown, rocky gravelly gravelly sandy sandy loam. In Insharp sharpcontrast, contrast,this thissequence sequenceisis overlain overlain in in places places by aa thin layer layer of buff-colored buff-colored loamy till, which which contains contains only a few rocks and pebbles. This material material is is interpreted interpreted as as till deposited deposited by the Duelm Duelm bulge of the Des Moines lobe. This This site site is is only only aa few few miles from Benton and Sherburne Counties, from the the edge edge of the bulge, bulge, judged by the soil surveys of Benton and by the position of the Duelm channel. The interpreted as Thethin thin and and patchy patchy nature nature of the till is interpreted as a sign that the the ice ice did did not not persist persist long. long. 90 �I- 4 ) H .7 / Wa?j% P.... h- t: 6 ____arr t \1C4Ie 309\ t-- / _ LJ c 31 0 0w . — ?—4 - . (: UIN1 cl.1BENTON rr hl: '' M& c-o. . ii// Figure 4.1. Duelm Channel and Mississippi valley train. ________ ._/ ). r y BovJ sr c j, o.i �_ STOP STOP 5— 5- Duelm Channel Channel (Howard (Howard Hobbs) Hobbs) vantage point, on on an an erosional erosional remnant of till, till, the the essential essential elements elements of of the the From this vantage 4. I). The Thechannel channelstretches stretchesas asfar faras asthe the eye eye can can see see to to the the east east Duelm channel channel can can be be seen seen (Fig. (Fig. 4.1). Duelm Thenorthern northernbank bank of ofthe thechannel channel isis about about 1/2 I12 mile mile away, away, rising from 30-60 feet and west. The floor. The The land landsurface surface to to the the north north isismade madeup upofofdrumlinized drumlinizedtill, till, above the flat channel floor. underlain in places by outwash, outwash, of the Superior lobe. To To the the south, south, the edge edge of the channel channel is is underlain not so so well well defined. defined. In Inplaces, places,the thechannel channelcuts cutsseveral severaltens tens of of feet feet into into a drumlinized drumlinized topography topography not similar similar to the north north side, side, but but in in other other places places there there is is scarcely scarcely any any elevation elevation difference difference between between the channel channel bottom bottomand and the the land land outside outside the the channel. channel. In Insome someplaces, places,the the land land actually actuallydrops dropsoff off the to dificult to to see see how how the the channel channel could could have have held in any any water water unless unless itit was was to the the south. south. ItIt is is difficult fronted fronted by by glacial glacial ice ice on on the the south southside. side. This This channel channel defines defines Duelm channel ,Duelm channel the limit limit of of what what II have have Princeton0 called called the "Duelm bulge" bulge'' (Fig. 5.1). 5.1). ItItisislobate, lobate,but but (Fig. too small small to to be be an an ice ice lobe lobe too or even even aa sublobe, sublobe, in in the the usual usual sense. sense. All the the Duelm meltwater flowing down meltwater flowing down 0 /1 the the Mississippi Mississippi valley valley 0 0 bulge train was diverted around train was diverted around this this bulge bulge in in the the ice ice front, front, on on its its way way to to the the Mississippi Mississippi south south of of St. St. Paul. Paul. The The thin thin skim skim of of -. gray, gray, shale-bearing shale-bearing till till atat Stop Stop 44 indicates indicates that that this this was was aa bulge bulge of of the the Des Des Figure Figure 5.1. 5.1. Duelm Duelmchannel channeland andDuelm Duelmbulge. bulge. Moines Moines lobe, lobe, which which was was otherwiseheld heldback backby by the the otherwise St. St. Croix Croixmoraine. moraine. Because the till till is is thin, thin, and and has has not notaltered alteredthe theunderlying underlyingdrumlinized drumlinized topography topographyinherited inheritedfrom fromthe theSuperior Superiorlobe, lobe,IIinterpret interpretthe theDuelm Duelmbulge bulgeas asaashort-lived short-livedevent. event. ItIt was was probably probably aasingle singlepush pushfollowed followedby by stagnation. stagnation. \ The The Duelm Duelm channel channel originates originates just east east of of St. St.Cloud. Cloud. Its Its original original junction junction with with the the Mississippi Mississippi valley valley train train cannot cannot be beobserved, observed,because becauseof of subsequent subsequenterosion erosionalong alongthe thevalley valley train. train.At Atthe theupper upperend, end,the thewatercourse watercourseisisbroad broadand andits itsedge edgeisispoorly poorly defined, defined,suggesting suggestingthat that itit was Inthe themiddle middlesection, section, itit isis as aswe we see seeitithere—wellhere-wellwas not not very very erosive erosive in this this section. section. In defined definedand anderosive erosiveon on the the north northside, side,variable variable on on the the south south side. side. At Atits itslower lowerend, end,the thechannel channel gradually Anoka Sand Sand Plain. Plain. South graduallyloses losesits itsidentity identityas asitit is is buried buried by younger deposits deposits of the Anoka South of the the Duelm Duelm channel channelisisaa set setof of smaller, smaller,anastamosing anastamosingchannels channels at lower elevations. They They range range from fromwell-defined well-definedto toobscure, obscure,and andcontain containmany manyshallow shallowdepressions, depressions,apparently apparentlyaaresult resultof ofice ice collapse. Like the main channel, they trend east to southeast, and disappear beneath the Anoka collapse. Like the main channel, they trend east to southeast, and disappear beneath the Anoka Sand SandPlain. Plain.These Thesechannels channelsrepresent representshort-lived short-liveddiversions diversionsaround aroundthe theice iceas asitit was was advancing, advancing, and andpossibly possiblyalso alsoas asititwas wasmelting meltingback. back. 92 �northwestern part part of the the Duelm Duelm bulge advanced over relatively high drumlinized drurnlinized till The northwestern subsequently covered after the ice melted off. By By contrast, contrast, of the Superior lobe, which was not subsequently the southern and eastern eastern parts parts of of the the bulge bulge passed passed over over lower lower ground, ground, which which was was covered coveredby by Here, itit is is impossible impossible to to tell tell where where the the sand of the Anoka Sand Plain after the ice melted off. off. Here, boundary of the bulge was, or where the Duelm channel went. Clearly, Clearly, the the water water must must have have found its way eventually eventually to to the the Mississippi MississippiRiver River below below the the Twin Twin Cities. Cities. Stop &The 6—The Lake LakeAnn AnnDunes, Dunes,East-Central East-Central Sherburne Sherburne County, Minnesota. Minnesota. (Gary (Gary Meyer) Meyer) see figure figure 7.1 for location]. [From Stop 2 by Kerry Keen in Goldstein (1987); see Sand dunes are an uncommon uncommon feature feature of of Minnesota's Minnesota's landscape. landscape. They typically occur as small distinct areas on much much larger larger glacial outwash plains or on terraces terraces along along rivers rivers (Cooper, (Cooper, Grigal and and others, others, 1976). 1976). Dunes also occur adjacent to to lakes lakes and and on beach beach ridges ridges of of 1935; Grigal Glacial Lake Agassiz in northwestern Minnesota. Some Some of of the the largest largest tracts tracts of well developed developed dunes are scattered scattered across across the the Anoka Anoka Sand Sand Plain, Plain, just north north of of the theTwin Twin Cities CitiesMetropolitan Metropolitan Area. Of Ofthese, these,the thelargest largestareas areasof of dunes dunesare are north north of of Elk Elk River River in eastern eastern Sherburne Sherburne County. These dune areas are best best described described as parabolic parabolic dune blankets (David, 1977) that contain narrow, elongate, parabolic parabolic dunes dunes and and en en echelon echelon dune dune ridges. ridges. the typical typical geometry geometry of of dune dune blankets blankets on on the the Anoka Anoka The Lake Ann dunes (Fig. 6.1) display the Sand Plain (Fig. 6.2A). This Thisdune duneblanket's blanket's distinct distinctsoutheast southeastlobe lobeappears appearsto tohave have advanced advanced Ann. The dune blanket is highly asymmetric, with an indistinct into the southern area of Lake Ann. wing. ItIt isis composed southeastsouthwest margin and a well-developed northeast wing. composedof of several severalsoutheasttrending dune dune ridges, ridges, which with northeast northeast slopes slopes steeper steeper than than trending which also are very asymmetric, asymmetric, with outwash plain, plain, southwest slopes. The Thedune duneblanket blanket grades gradesnorthwestward northwestward into into wind-deflated wind-deflated outwash containing a number number of northwest-southeast elongate elongate deflation deflation depressions. depressions. The eolian features of the Anoka Sand Plain were originally attributed to formation by Cooper, 1935). 1935). However, study of air photos southwest winds (Leverett and Sardeson, 1932; Cooper, — the dune blankets and other data indicates that the major eolian features of the sand plain — were were formed by northwest winds (Keen, 1985). Modification Modification by by west, west, southwest, southwest, and and south south winds created the asymmetry asymmetry of of the the dune dune blankets blankets and and dune dune ridges. ridges. Sand was eroded and transported transported to the the northeast northeast over over the the dune dune ridges, ridges, steepening steepening their their northeast northeast slopes. slopes. This modification was so parabolic dune shapes were nearly obliterated modification so severe severe that the original parabolic obliterated (Fig. (Fig. 6.2B). The Thepresent presentwind windregime regime of of the thesand sandplain plain isisdominated dominated by by northwest northwest winds winds that that are are strongest in spring and fall. During Duringthe the summer, summer, winds winds from from the west and south would result in of sand. sand. The present wind appears to be similar to that a smaller net northeastward movement of responsible for eolian activity on the Anoka Sand Plain, although components of this regime regime probably varied in importance importance during during the Holocene. Holocene. A number of vegetational vegetational communities occur on the dunes of the Anoka Sand Plain and are well displayed in the Lake Ann Ann area. area. Prairie of Prairie grows on the dry sunny southwest sides of dune ridges, whereas oak woods occupy the moister northeast slopes. An An area area of of low low dunes dunes in in Ann dunes dunes supports an oak oak savanna savannacommunity. community. Various Variouswetland wetlandcommunities communities occupy occupy the Lake Ann dune depressions. depressions. Sediments from from Lake Lake Ann were studied studied with the the goal goal of of interpreting interpreting the the vegetation vegetationand and eolian history of the adjacent Lake Ann Ann dunes dunes (Keen (Keen and and Shane, Shane, 1990). 1990). As determined determined by 93 �Ann dune field. field. Area Figure 6.1. Topogaphic Area Topogaphic map map showing showing part of the Lake Ann shown (U.S. Geological GeologicalSurvey Survey shown is about 2.8 miles wide; contour contour interval interval 10 10 feet. (U.S. Orrock Orrock quadrangle, quadrangle, 7.5-minute 7.5-minute series, series, 1991). 1991). 94 �I\. Deflation area limb Obscure southwest southwasl margin parabolic dunes 4i 1 . B. WENDS WINDS 1km m .k MAP MAPVIEW VIEW CROSSSECTION SECTION CROSS Figure 6.2. 6.2. A. A.Typical Typicalasymmetic asymmeticdune dune blanket on the Anoka Proposed stages stages Figure Anoka Sand Sand Plain. Plain. B. Proposed in in the thedevelopment developmentof ofmodified modifiedparabolic parabolicdunes: dunes: A. A. Initial Initial development developmentof of symmetric symmetricparabolic parabolic dunes dunes by by strong strong northwest northwestwinds. winds. B. Modification Modificationby bycross-winds. cross-winds.Northwest Northwestdunes dunesare arestill stillstrong, strong,but butan animportant importantsouthsouthB. west wind component exists. west wind component exists. C. Stabilization Stabilizationand andrevegetation revegetation of of the the dunes. dunes. Minor Minoreolian eolianerosion erosion under under variable variable wind wind C. directions. directions. Steep Steep slope slope (slipfaces) (slipfaces)represented represented by by lined linedpattern; pattern; less less steep, steep,eroding eroding slopes slopes(backslopes) (backslopes)represented representedby by dotted dottedpattern. pattern. (Stop (Stop 22 by by Keen, Keen,from fromGoldstein, Goldstein,1987) 1987) 95 �O\ "S [H [TLTi. p.,..., •i •i•i ... —.-. I. ,:$ ,P s •' lI0 'be' !. - 'il-::j - --F— -, Istiflid b t C S $54.5. IRS, '1.! — I- ;Q' , 0.s (or rsd Din.) forest Birch-Aider forest Spruce woodland — Jack pine Prairie Oak savanna Oak I VEGETATION TYPES and sample of the spruce pollen decline). From Keen (1985). The estimated time scale was constructed by linear extrapolation between dated materials (surface lacustrine sediment, radiocarbon dated samples, Figure 6.3. A. Abbreviated pollen diagram for Lake Ann, Sherburne County, Minnesota: B. Eolian component of magnetic susceptibillity of core F, Lake Ann. Depth is estimated from the frozen lake surface. "1 4..— — 'S.— 'S..— '405— '7,.— — 6 Shi'burns Coirnuy . UInn.,oI. •5SS— CoreA lw's.. aOl ? A. CorSF C-' D??S LAKE ANN 1400- 1300. 1200. 1100. 900. SOD' 700 I 10 I 9 II I 20 I -3000 -2000 -bOO (yr. B.P.) Estkn.t.d 'C B?) (WIS-I4S2 7420*90 (WIS-1453) 43910 (yr. —8000 —4000 W — 10.000 — 9000 $000 -7000 -.000 0 w z U I- .. Radiocarbon dates Dipm AdusI.d Inagnstic auscepIty (ciTu) (.muIO.) a 1O bsss of B EOLIAN COMPONENT OF MAGNETIC SUSCEPTIBILITY CORE F. LAKE ANN, SHERBURNE COUNTY. MINNESOTA ___________ �pollen analysis (Fig. 6.3A), the postglacial vegetation vegetation history history of of spruce spruce woodland, woodland, birch-alder birch-alder forest, pine forest, and finally oak woodland other studies studies forest, prairie, and woodland is similar similar to that inferred from from other Minnesota. The in east-central Minnesota. The degree degree of of representation representation of prairie-indicator prairie-indicator species implies conditions on on the the Anoka Sand Plain during the mid-Holocene. mid-Holocene. very dry conditions The chronology of eolian eolian activity activity for the dunes dunes near Lake Ann, derived from analyzing lake sediment for eolian coarse silt and and very very fine fine sand, sand, correlates correlates extremely well with the vegetation history determined from pollen analysis. Because sediment is found history determined Because no wind-derived sediment in early Holocene Holocene sediments, present on the the sandplain sandplain in late late sediments, it appears appears unlikely that dunes were present glacial or early Holocene time, when forest covered the land. land. Eolian Eolian activity activity appears appears to to have have begun around 8000 8000 years ago, ago, when the percentage of tree pollen falls to its lowest postglacial 6.3B), Majoreolian eolianactivity, activity,as as shown shown best best by by the the magnetic magnetic susceptibility susceptibility curve curve (Fig. (Fig. 6.3B), value. Major occurs during prairie conditions occurs conditions of the mid-Holocene, mid-Holocene, until until about about4000 4000years yearsago. ago. Minor eolian activity activity follows follows throughout throughout the the late late Holocene. Holocene. Stop 7. The The "Feature" "Feature"(Howard (HowardHobbs) Hobbs) North of Elk River, an extensive extensive highland rises above the Anoka Sand Plain (Fig. 7.1). 7.1). Its largest dimensions east-west direction and a little less than 15 dimensions are are aa little little over 15 15 miles in the east-west miles north-south. Its about 100 feet; feet; local relief ranges Itsaverage average height height above the sandplain is about up to 100 100 feet, feet, but but many many parts parts are areflatter. flatter. highland has been interpreted interpreted as a tunnel-valley fan (Fig. 1). However, The origin origin of this highland However, it has been mantled mantled and and modified modified since since its its formation, formation,so so its surficial surficial sediments sedimentsare are quite quite variable. variable. Much of it has been mantled by reddish-brown sandy till, similar to till till of of the the Superior Superior lobe. lobe. In In places, places, banded banded red red and and gray gray till has been observed. The The till-covered till-covered part part of of the the feature feature is is crossed crossed by eskers, eskers, some from the Superior some of which which appear appearto to be Grantsburg, Grantsburg, some some of which which are are left left over over from Superior lobe. On gravel. They are similar Onthe thewest westside sideof of the the highland highland is is aa set of north-south ridges of gravel. to eskers, but are straighter. Stop Stop77isisaalarge largegravel gravelpit pit in in one oneof of them. them. in most most of of the the pit pit at The gravel is clean and rather coarse in at first first glance, glance, itit looks looks just like like Superior gravel. gravel. It has lots lots of of black black and and red red pebbles pebbles from from the the Superior Superior basin basin and and the the North North Shore. But Butlook lookclosely, closely,and andyou you will will find find aa few few gray gray shale shale pebbles, pebbles, which are are never found in pure Superior Superior gravels. ItItappears appearsthat thatmost most ifif not not all all the shale shale is coming out of the upper part of the exposure, but this is difficult to confirm, because the lower parts slump over so quickly. Our best interpretation interpretation of these ridges is that they were formed as a sort of ice-marginal meitwater by the the highland. highland. Most meltwater deposit where the Duelm bulge was hemmed in by Most of of the the gravel gravel is reworked from the existing existing fan, but aa little little gravel gravel was was derived derived from from the the Des Des Moines Moines lobe. lobe. This is where where the the shale shale came came from. from. 97 �Figure 7.1. Location Locationmap mapfor forstops stops66 and and 7. 7. 98 98 �REFERENCES CITED Aber, J. S., 1988, with glaciotectonic glaciotectonic examples: examples: Winston-Salem, Winston-Salem, 1988, Structural Structural geology exercises with N.C., Hunter HunterTextbooks, Textbooks,p.p.881-84. 1-84. Birks, H.J.B., 1976, 1976, Late LateWisconsin Wisconsinvegetational vegetational history history at at Wolf Wolf Creek, central Minnesota: Minnesota: Ecological Ecological Monographs, Monographs, v. v. 46, p. 495-529. glacial thrusting and related processes in Bluemle, J.P., J.P., and Clayton, L., 1984, 1984, Large-scale glacial North Dakota: Boreas, Boreas,v.v. 13, 13,p. p. 279-299. 279-299. Clayton, process-form model, Clayton, L., and and Moran, Moran, S.R., S.R., 1974, 1974,A glacial process-form model, in in Coates, Coates,D. D. R., ed., ed., Glacial Glacial geomorphology—Geomorphology Binghamton, N.Y., N.Y., 1974: 1974: Binghamton, geomorphology-Geomorphology Symposium, Symposium,5th, 5th, Binghamton, 89-119. State University University of New York, p. 89119. Cooper, W.S., 1935, Mississippi River in late Wisconsin Wisconsin and postglacial postglacial Cooper, W.S., 1935,The history of the upper Mississippi time: Minnesota MinnesotaGeological GeologicalSurvey SurveyBulletin Bulletin 26, 26, 116 116p. p. David, P.P., Sand dune dune occurrence occurrencein inCanada: Canada: A theme and resource resource inventory study study of of P.P., 1977, Sand eolian David, Dept. Dept. of Geology, Geology, University University eolian landforms landformsof of Canada: Canada: Available Availablefrom fromDr. Dr. Peter Peter P. David, of Montreal, 183 183 p. Goldstein, Goldstein, B., 1987, 1987, Geomorphology Geomorphology and and Pleistocene Pleistoceneglacial glacial geology geology of of central central Minnesota, Minnesota,in in Balaban, N.H., N.H., ed., Field trip guidebook for Quaternary and Cretaceous geology of westcentral Minnesota Minnesota and adjoining South Dakota: Minnesota Minnesota Geological GeologicalSurvey Survey Guidebook Guidebook Series No. 16, 16, p. 16-19 16-19 (Stop (Stop 2). Grigal, Grigal, D.F., Severson, Severson, R.C., and Goltz, G.E., 1976, 1976, Evidence of eolian activity in north-central Minnesota 8,000 to 5,000 years years ago: ago: Geological Geological Society Society of of America America Bulletin, v. v. 87, p. 125 1-1254. 1251-1254. Bedrock geologic geologic and topographic topographic maps Jirsa, M.A., Olsen, Olsen, B.M., and Bloomgren, B.A., 1986, Bedrock of the seven-county seven-county Twin Cities Cities Metropolitan MetropolitanArea, Area,Minnesota: Minnesota: Minnesota Minnesota Geological Geological Survey Survey Miscellaneous Miscellaneous Map Map M-55, scale scale 1:125,000. 1:125,000. Johnson, M.D., M.D., and Hemstad, Chris, in prep., Glacial Lake Grantsburg: a short-lived lake Johnson, recording recording the advance and retreat of the the Grantsburg Grantsburg sublobe, sublobe, in in Patterson, Patterson, C.J., C.J., ed., ed., Contributions to the Quaternary of Minnesota: Minnesota: Minnesota Quaternary of Minnesota Geological Survey Report of Investigations Investigations49. 49. Keen, K.L., 1985, Plain: Unpublished 1985, Sand dunes on the Anoka Sand Plain: Unpublished M.S. M.S. thesis, thesis, University University of Minnesota, Minneapolis, 191 p. Minnesota, Minneapolis, 191 Keen, K.L., and Shane, Shane, L.C.K., L.C.K., 1990, 1990,A A continuous continuous record record of of Holocene Holocene eolian eolian activity activity and and vegetation change at Lake Ann, east-central Minnesota: Minnesota: Geological Geological Society Society of of America America Bulletin, Bulletin, v. v. 102, 102,p. p. 1646-1657. 1646-1657. A.R., 1996, Knaeble, A.R., 1996, Glaciotectonic thrusting along the St. St. Croix Croix moraine, moraine, Stearns StearnsCounty, County, Minnesota, Geologic Atlas, in Meyer, Meyer, G. G. N., and and Swanson, Swanson, L., eds., Text supplement to the Geologic Minnesota, in Stearns S t e m s County, Minnesota: Minnesota MinnesotaGeological GeologicalSurvey SurveyCounty CountyAtlas Atlas Series SeriesC-1O, C-10, Part C, p. 40-47. Knaeble, A.R., in prep., Superior Knaeble, Superior lobe glacial thrusting of drift and bedrock along the St. Croix Croix moraine, Stearns County, Minnesota, in in Patterson, Patterson, C. J., County, Minnesota, moraine, J., editor, Contributions Contributions to the the Quatemary Quaternary geology of Minnesota: Minnesota MinnesotaGeological Geological Survey Survey Report Report of Investigations Investigations 49. 99 �Leverett, F., and Sardeson, Sardeson, F.W., Minnesota and parts Leverett, F.W., 1932, Quaternary geology of Minnesota parts of adjacent adjacent states: U.S. U.S. Geological GeologicalSurvey Survey Professional Professional Paper Paper 161, 161, 149 149 p. Mackay, K.R., and Mathews, W. W. H., H., 1964, The The role role of of permafrost permafrost in in ice ice thrusting: thrusting: Journal Journal of of Geology, v. 72, p. 378-380. p. 378-380. Meyer, G.N., 1986, 1986, Subsurface Subsurface till till stratigraphy stratigraphy of of the the Todd Todd County County area, area, central central Minnesota: Minnesota: Minnesota 40 p. Minnesota Geological GeologicalSurvey SurveyReportof ReportofInvestigation Investigation34, 34,40 p. Meyer, G.N., 1992, plate 55 in in Meyer, 1992, Quaternary stratigraphy, stratigraphy, plate Meyer, G.N., G.N., and and Swanson, Swanson, L., L., eds., eds., Geologic atlas of Ramsey County, Minnesota: Minnesota MinnesotaGeological GeologicalSurvey Survey County CountyAtlas Atlas Series C-7. Meyer, G.N., in Balaban, G.N., and Hobbs, Hobbs, H.C., 1989, 1989, Surficial Suficial geology, plate 3 in Balaban, N.H., ed., Geologic Geologic atlas of Hennepin County, Minnesota: Minnesota MinnesotaGeological GeologicalSurvey Survey County County Atlas Atlas Series Series C-4, scale 1:100,000. 1:100,000. Twin Cities Metropolitan Meyer, G.N., and Jirsa, M.A., 1984, 1984,Aggregate resources inventory, Twin Area, Minnesota: Minnesota MinnesotaGeological GeologicalSurvey Survey Information Information Circular 20, 16 16 p. Patterson, C.J., 1992, in Meyer, G.N., G.N., and and Swanson, Swanson, L., L., eds., eds., Geologic Geologic Patterson, 1992, Surficial Surficial geology, plate 33 in atlas of Ramsey County, Minnesota: Minnesota MinnesotaGeological GeologicalSurvey SurveyCounty CountyAtlas Atlas Series Series CC7, scale 1:48,000. 1:48,000. Patterson, C.J., 1994, Tunnel-valley fans of the the St. St.Croix Croixmoraine, moraine,east-central east-centralMinnesota, Minnesota, U.S.A., U.S.A., Patterson, 1994,Tmnel-valley in Warren, W.P., W.P., and and Croot, D.G., D.G., eds., Formation and deformation of glacial glacial deposits: deposits: Rotterdam, Balkema, Rotterdam, Balkema,p.p.69—87. 69-87. Setterhoim, D. R., 1996, Setterholm, 1996, Geology Geology of of the the Late Late Cretaceous Cretaceous Strata Strata and and Pre-Late Pre-Late Cretaceous Cretaceous Weathering Profile, Steams Stearns County, County, Minnesota, Minnesota, in in Meyer, Meyer,G. G. N., N., and and Swanson, Swanson, L., L., eds., Weathering Atlas, SStearns County,Minnesota: Minnesota: Minnesota Minnesota Geological Geological Text supplement to the Geologic Atlas, t e m s County, Survey County Atlas Atlas Series Series CC-b, 10,Part PartC, C,p. p. 7-15. 7- 15. 100 ��FIELD FIELD TRIP TRIP #4 #4 STRATIGRAPHY STRATIGRAPHYAND AND HYDROGEOLOGY HYDROGEOLOGY OF OF PALEOZOIC PALEOZOICROCKS ROCKS OF OF SOUTHEASTERN SOUTHEASTERNMINNESOTA MINNESOTA Leaders: Leaders: Anthony AnthonyC. C.Runkel Runkeland andRobert RobertG. G. Tipping Tipping Paleozoic Paleozoicstrata strataof of the thecentral centralmidcontinent midcontinentregion regionare areamong amongthe thelongest longeststudied studiedand andbest best known America. This known sedimentary sedimentary rocks in North America. This field field trip tripwill willprovide provide an anopportunity opportunityto to examine examinethe thediverse diversesuite suiteof of lower lowerPaleozoic Paleozoicrocks rocks exposed exposedalong alongthe the Mississippi MississippiRiver Riverand andits its 1) the depositional tributaries in southeastern Minnesota, focusing on two interrelated topics: tributaries in southeastern Minnesota, focusing on two interrelated topics: 1) the depositional history history of of these thesestrata, strata,highlighting highlightingadvances advancesmade madeover overthe thepast pastfifteen fifteenyears yearsin inunderstanding understanding the the origin originof of their their well well documented documented enigmatic enigmatic features, features, and 2) 2)the thehydrogeologic hydrogeologicproperties propertiesof of these these strata, strata,with withparticular particularemphasis emphasison oncharacterization characterizationof ofhydrostratigraphic hydrostratigraphiccomponents. components. INTRODUCTION INTRODUCTION Paleozoic Paleozoicstrata stratain inthe thecentral centralmidcontinent midcontinentregion regionof ofNorth NorthAmerica Americaconsist consistof ofthin thinunits units of of carbonate, carbonate, sandstone, sandstone,and and shale shaledistributed distributed across across tens tens of of thousands thousands of of square squarekilometers. kilometers. This Thisoverview overviewfocuses focuseson onthe thenorthernmost northernmostextent extentof of lower lowerPaleozoic Paleozoicstrata stratathat thatwere weredeposited deposited on the stable cratonic shelf northwest of the illinois and Michigan basins (Figs. 1 and 2). The on the stable cratonic shelf Illinois basins (Figs. and 2). The rocks rocks are areexposed exposedin in aa sinuous sinuousbelt beltof of outcrops outcropsalong alongthe the southern southernflank flankof of the theTranscontinental Transcontinental arch Minnesota, Wisconsin and northern Michigan. Michigan. archand and the the Wisconsin Wisconsindome dome and and arch in southern Minnesota, Deposition began in in the the Middle Middle to Late Cambrian. Deposition of Paleozoic Paleozoic sediments sediments began Cambrian. Coarse Coarse siliciclastic Sandstone covered the eroded Precambrian Precambrian siliciclasticsediments sedimentsof of what whatisis now now the Mt. Simon Sandstone surface. surface. Overlying Overlyingstrata stratawere weredeposited depositedinintwo twobroad, broad,laterally laterally equivalent equivalent facies facies belts belts across across the composed the central central midcontinent midcontinentregion region (Fig. (Fig.11 inset) inset) (Palmer, 1960). An inner detrital belt was composed of of shallow shallowmarine marinesiliciclastics siliciclasticsderived derived from from subaerially subaerially exposed exposed Precambrian Precambrian Shield Shieldareas areason on and to to the the north north of of the theWisconsin Wisconsin Dome. Dome. Thin, Thin,laterally laterallyextensive extensiveunits unitsdominated dominatedby by either either and fineto coarse-grained quartzose sandstone, very fine gralned sandstone, or shale were deposited fine- to coarse-grained quartzose sandstone, very fine grained sandstone, in intertidal carbonate carbonate subtidal to intertidal in this this inner inner detrital detrital belt. The Themiddle middlecarbonate carbonatebelt belt consisted consisted of subtidal and and shale shale that that accumulated accumulated to the south. south. Over Overtime, time,the theboundary boundary between between these thesedepositional depositional belts shifted: shifted: sedimentation sedimentationininthe theinner innerdetrital detritalbelt beltwas wasdominant dominantduring during the theCambrian Cambrianand and part of of the the Middle Middle Ordovician; Ordovician; and and sedimentation sedimentation in in the the middle middle carbonate carbonate belt belt was was dominant dominant during during the the Early Early and and Late LateOrdovician, Ordovician,as aswell well as asin in the theSilurian Silurianand andDevonian Devonian(Fig. (Fig.2). 2). Early Early Paleozoic Paleozoicdeposition depositionoccurred occurredon on aa virtually virtually horizontal, horizontal, cratonic cratonic shelf shelf that that subsided subsided very slowly. slowly. Late LateCambrian Cambriansubsidence subsidenceaveraged averaged less less than than 10 10m/m.y. m/m.y. (Sloss, (Sloss,1988)—about 1988)-about one-fifthto to one-tenth one-tenth the the rate rate in the contemporaneous Illinois 199I), and orders one-fifth illinois basin (Sargent, (Sargent, 1991), magnitude slower slower than that that of of better known, younger basins in North America. Maximum Maximum of magnitude 1995; Ludvigson and typically less than 100 m (e.g., Byers and Dott, 1995; paleobathymetry was typically others, 1996) 1996)and and the theshelf shelfhad hadaalow low gradient gradientslope slopeof of about about0.1 0.1 rn/km. mlkrn. others, The Wisconsin Wisconsin dome dome and and arch arch and Transcontinental Transcontinental arch were positive structural The structural features features influenced patterns patterns of of early early Paleozoic Paleozoic sedimentation, sedimentation, and and eventually eventually controlled controlled the the that influenced distributionand and configuration configurationof the gently folded and faulted Paleozoic distribution Paleozoic strata we we see see today. today. In 103 �____ Figure 1.1.Location Location map map showing showing Figure early Paleozoic Paleozoic tectonic tectonic features, features, early major paleotopographic pdeotopographic highs of major Precambrian rocks rocks (stippled) (stippled) and and the the Precambrian approximate distribution dismbution of approximate Cambrian (C) Ordovician (0), Cambrian (C),, Ordovician (0), ( S ) ,and and Devonian Devonian (D) (D) Silurian (S), strata in the northern part of the central midcontinent midcontinent region. region. The The central area relative relative to to shows the study study area inset shows the Late Late Cambrian Cambrianinner inner (stipple) (stipple) the detrital belts belts and and and outer outer (dashes) (dashes)detrital and the the middle middle carbonate carbonatebelt (block (block Palmer (1960). (1960). Modified Modified pattern) of Palmer others (1998). from Runkel and others GROUP! FORMATION UTHOLOGY .e. < Cedar Valley J ::::" — —l -— Burnt Bluff Cataract -——— —— Maquoketa Dubuque J —— Figure Figure2.2.Generalized Generalizedstratigraphic stratigraphiccolumn column(no (no scale) scale) for for lower lower Paleozoic Paleozoicrocks rocksininthe thenorthern northernpart part of the the central central midcontinent midcontinentregion. region. The The Cambrian Cambrian and and Ordovician Ordoviciannomenclature nomenclatureisis that that used used in in southeastern southeastern Minnesota and Wisconsin, the the Silurian from eastern eastern Wisconsin Wisconsinand and northern northern Silurian from Michigan, Michigan, and and the the Devonian Devonianfrom fromsouthernmost southernmost Minnesota Minnesota and and northern northern Iowa. Iowa. ngadine Manistique ——— Galena Decorah PttevilIe - St Peter ShakoPeejPrane O' I j-L--. — 2 - \_ ..: . —. —. . . Group Jordan St Lawrence Franconia (Lone Koch) (Worwwoc) EauClaireand Bonneterre • Mt. Simon Quwtzose sandstone @atzosesandstone Very shale Very fine fines.s., s.s., siltstone. s~lmone, shale - Carbonate (dashedwhere whereshahy) sbl~) Carbonate(dashed No Norecord record Unconformity Unconfonn~ty 104 �northern Iowa, southern Minnesota, Minnesota, and southwestern southwestern Wisconsin, Wisconsin, Paleozoic Paleozoic strata are are preserved preserved northern in what is known known as as the the Hollandale Hollandale embayment, embayment, which is aa broad broad syncline syncline that that lies lies between between these two positive features. South Southand andeast eastof of the theWisconsin Wisconsin dome dome and and arch, arch, Paleozoic Paleozoic rocks rocks dip less than 11 degree degree into into the Illinois Illinois and and Michigan Michigan basins. DEPOSITIONAL MODELS DEPOSITIONAL MODELS Despite over 100 100 years of study, study, the depositional depositional history of lower lower Paleozoic Paleozoic siliciclastic siliciclastic strata of this region remains poorly understood. Many poorly understood. Many workers workers have lamented an apparent apparent absence of modern or ancient depositional analogues. In addition, addition, while dozens of local studies have been conducted (e.g., Nelson, 1956; 1956; Haddox and Dott, Dott, 1990), 1990), few few are are regional-scale regional-scale investigations that incorporate several lithofacies into a temporally constrained stratigraphic framework. framework. Present-day Present-dayunderstanding understandingof of early early Paleozoic Paleozoic siliciclastic siliciclasticdeposition depositionis is based mostly mostly on work conducted since since 1950, 1950,beginning beginning with the predominantly predominantly stratigraphic stratigraphic investigations investigations of Berg (1954), (1956), Bell Bell and others (19561, (1956), and Ostrom (19541, Nelson (1956), (19561, Berg and others (19561, (1964, 1970). Subsequent sedimentologic—focusing on the interpretations interpretations (1964,1970). Subsequentwork work has has been chiefly sedimentologic-focusing of near-shore marine facies (Fraser, (Fraser, 1976; 1976; Driese and others, 1981; 1981; Dott Dott and and others, others, 1986; 1986; Haddox and Dott, 1990; 1990;Barnes Barnes and and others, others, 1992; 1992;Mossler, 1992; 1992; Runkel, Runkel, 1994). 1994). In a very important important and widely cited examined the transition cited study, study, Dott and others (1986) examined transition from nonmarine to marine environments recorded recorded in quartzose sandstones, and provided the of nonmarine nonmarine facies. facies. They described an early Paleozoic first set of criteria for identification of terrestrial setting with broad braided streams and eolian sheet and erg systems that delivered sand to a shallow marine environment dominated dominated by by small smallthree-dimensional three-dimensionaldunes. dunes. Dott and of vegetation, between between early early Paleozoic others (1986) stressed the differences, difherences, such as the lack of depositional environments environments and those inferred inferred for both younger rocks and and modern modern settings. settings. depositional model A depositional model of a simple, simple, storm-dominated, storm-dominated, texturally texturally graded graded shelf shelf was was proposed proposed by Runkel and others (1998) (Fig. 31, 3), and is noteworthy noteworthyin inits itssimilarity similarity to models based on both younger younger rocks regional-scale outgrowth rocks and modern systems. Their Their study study was essentially a regional-scale of the excellent students from the University University of Minnesota Minnesota excellent outcrop outcrop work work of Charlie Charlie Bell Bell and his students in the 1950's. Runkel Runkeland andothers others(1998) (1998)suggested suggestedthat that early early Paleozoic Paleozoic depositional depositional processes distribution are analogous analogous to those depicted in well-known and facies distribution well-known models models of of the the Cretaceous Cretaceous interior seaway and the modern Bering Shelf. Shelf. The thin, widespread siliciclastic seaway and modern Bering The thin, widespread siliciclastic units units characteristic migrations that occurred characteristic of lower lower Paleozoic Paleozoic strata strata result from large lateral facies migrations in response to to continental-scale continental-scalechanges changes in in relative relative sea sea level. Carbonate rocks within within the lower lower Paleozoic sequence sequence historically historically have have been regarded regarded as as more amenable comparison with both modern and ancient ancient facies facies models. models. Deposition occurred amenableto comparison occurred in environments supratidal conditions conditionsfor for parts parts of of the the Prairie Prairie du environments that range from evaporitic, evaporitic, supratidal Chien Group Group (Smith (Smith and and others, others,1993) 1993)to to subtidal subtidalsettings settingsin in depths depths of of 100 100m m or or more more for for parts parts of the Decorah Shale (Ludvigson and others, 1996). Most Most investigations investigations have have been local local in in scope relative relative to to the great lateral extent extent of of these these units, units, and and there there are are too too many many to cite them scope individually. Ordovician individually. Ordovician carbonate carbonate strata strata of of the the Hollandale Hollandale embayment embayment are are the the focus focus of a monograph edited by Sloan (1986). Silurian Siluriancarbonates carbonates on the western flank of the Michigan basin have recently been studied by Harris and Waldhuetter Waldhuetter (1996). (1996). There are many excellent studies of OrdovicianOrdovician- through through Devonian-age Devonian-age strata strata in northern northern Iowa, Iowa, largely largely conducted conducted by by the the Iowa Geological extrapolated to Minnesota and Wisconsin (for Geological Survey; Survey; the the results results can often be extrapolated 105 �Taylors FaNs Precambrran ava flow ndq SILICICLASTIC (WSMOPE SHELF - — — MO3ft — — — — — — sand — — — -4,:;— — - — — — — 0 trom ahotataco — — — —— ' —o Q\AILW%.PUI Iranspolt by storms Sand 0 — — — '' Storm — naport ot fn sand. Ol. srral. — — — — .'.,, 0 0 - Ternp,sIiI.I — D Wasfi Figure3.3.Conceptual Conceptualdepositional depositionalmodel modelofofLate LateCambrian Cambrianstorm-dominated, storm-dominated, texturally Figure texturally graded shelf. Quartzose fineto coarse-grained sand accumulated nearshore terrestrial graded shelf. Quartzose fine- to coarse-grained sand accumulated ininnearshore terrestrial andshoreface shorefaceenvironments. environments.Finer Finergrained, grained,feldspathic feldspathicsiliciclastic siliciclasticsediments sedimentsand and subtidal and subtidal carbonatesaccumulated accumulatedinindeeper deeperwater waterofofthe theoffshore offshoreshelf. shelf. carbonates example,several severalpapers papersininWitzke Witzkeand andothers, others,1996). 1996).Some Someregional-scale regional-scalestudies studieshave have recently example, recently been completed; a stratigraphic framework has been developed for the Prairie du Chien Group been completed; a stratigraphic framework has been developed for the Prairie du Chien Group fromthe theMichigan Michiganbasin basintotothe theHollandale Hollandaleembayment embayment(Smith (Smithand andothers, others,1993, 1993, 1996; Barnes from 1996; Barnes andothers, others,1996). 1996).Simo Simoand andothers others(1997) (1997)are arecurrently currentlyconstructing constructingaalarge largescale scalestratigraphic stratigraphic and frameworkfor forOrdovician Ordovicianrocks rocksofofthe thecentral centralmidcontinent midcontinentininorder orderto toaddress addresslong-standing long-standing framework problemssuch suchasasidentification identificationof ofthe thecontrols controlsresponsible responsible for forthe theapparently apparently synchronous problems synchronous regional-scale changes from "tropical" to "temperate" styles of carbonate deposition. regional-scale changes from "tropical" to "temperate" styles of carbonate deposition. NOTABLEFEATURES FEATURESAND ANDLONGSTANDING LONGSTANDINGPROBLEMS PROBLEMS NOTABLE LowerPaleozoic Paleozoicstrata strataininthe thecentral centralmidcontinent midcontinentregion regionare arewell wellknown knowntotogeologists geologists Lower outsideof ofthe thearea areafor forseveral severalenigmatic enigmatic features features(Dott (Dott and and Byers, Byers, 1980). 1980). Most Most notable is the outside notable is the extreme textural and mineralogical maturity of the fineto coarse-grained sandstones, and the the extreme textural and mineralogical maturity of the fine- to coarse-grained sandstones, and sheet-likegeometry geometryofofthese theseand andother othersiliciclastic siliciclasticunits. units.The Theoverall overalldearth dearthofofshale shale has puzzled sheet-like has puzzled sedimentologistsyand and the thefundamental fundamentalcontrols controls on onthe theepisodic episodicchange changefrom from siliciclasticsedimentologists, siliciclasticdominatedtotocarbonate-dominated carbonate-dominatedsedimentation sedimentationremain remainpoorly poorlyunderstood. understood.Lastly, LastIy, the presence, dominated the presence, position,and andmagnitude magnitudeofofunconformities unconfonnitieshas hasbeen been debated debatedfor for decades. decades. The Theremainder remainder of this position, of this discussion summarizes the progress made since Dott and Byers (1980) published a similar discussion summarizes the progress made since Dott and Byers (1980) published a similar overviewyand andoffers offersaaguide guideto totopics topicsthat thatcan canbe bediscussed discussedatatthe theindividual individualfield fieldtrip trip stops. overview, stops. Texturalmaturity maturityofofsandstones sandstones Textural Theextreme extremetextural texturaland andmineralogical mineralogicalmaturity maturityofofthe thefinefine-totocoarsecoarse-grained grainedsandstone sandstone The units,such suchasasthe theSt. St.Peter PeterSandstone, Sandstone,may maybe bethe thebest bestknown knownand andlongest longeststudied studied feature in the units, feature in the lower Paleozoic strata of the central midcontinent. The sandstones contain more than 98 percent lower Paleozoic strata of the central midcontinent. The sandstones contain more than 98 percent quartzand andmost mostgrains grainsare aremoderately moderatelyto towell wellrounded. rounded. Such Suchtextural texturaland andcompositional compositionalmaturity maturity quartz could not have been achieved solely by fluvial and marine abrasion, even over transport distances could not have been achieved solely by fluvial and marine abrasion, even over transport distances 106 �of hundreds of kilometers, if the grains grains were were derived derived directly from crystalline source rocks. Rare grains with abraded abraded overgrowths overgrowths are reworked reworked from older sedimentary rocks, but the the volumetric significance of suitable suitable sedimentq sedimentary rock volumetric significanceof such such recycling is uncertain and a source of been identified. identified. Odom 1978) conducted the most comprehensive comprehensive mineralogical mineralogical has never been Odom (1975, (1975,1978) Paleozoic sandstones. He fine grained grained fraction fraction is is feldspathic, feldspathic, study of lower Paleozoic He noted that the very fine whereas the fine- to coarse-grained contains more more than than 98 percent percent quartz (with the coarse-grained fraction contains exception of some lower Mt. Mt. Simon Simon Sandstone Sandstonebeds). beds). He suggested exception of suggested that a long long history history of of abrasion abrasion in aa marine marine setting setting could could account account for for both both the maturity of the quartzose quartzose grains grains and and the the reduction in size of feldspar grains. Dott Dott and and others others (1986) (1986) were the first to clearly identify the presence of substantial substantial eolian eolian deposits deposits within within some some quartzose quartzose sandstones, sandstones, and and they they suggested suggested that eolian mineralogic features features described described by Odom eolian abrasion abrasion could could contribute contributeto the textural and mineralogic Odom be taken taken into into consideration consideration (1975, 1978). Lastly, Lastly, chemical chemical weathering weathering in the source area must be 1978) noted that the very fine grained, feldspathic sandstones sandstones are (Morey, 1972). Odom Odom(1975, (1975,1978) rich in K-feldspar "trace" amount of of plagioclase plagioclase grains, grains, even even though though plagioclase plagioclase K-feldspar but have only a "trace" of the Precambrian Precambrian Shield. Shield. Selective was presumably dominant in the source area of Selective diagenetic diagenetic leaching of of plagioclase plagioclase grains grains from from the the sandstone sandstone was was discounted discountedby by Odom Odom (1978). (1978). Thus, leaching Thus, chemical weathering probably preferentially dissolved plagioclase crystals and reduced reduced the the amount of other relatively unstable unstable minerals prior to mechanical mechanical abrasion abrasion during during transport size and amount transport to the shoreline. shoreline. been responsible responsible in part for the While each of the processes described above could have been mineralogic mineralogic and and textural textural attributes attributes of lower Paleozoic sandstones, they do not entirely account for the compositional record that appears to indicate that virtually all fine- to coarse-grained coarse-grained exceptionally mature the early early Paleozoic Paleozoic shoreline. shoreline. Finesand was exceptionally mature when it arrived to the Fine- to to coarsecoarsegrained immature sand would have almost certainly been deposited locally if the marine abrasion grained immature sand would have almost certainly been deposited locally marine abrasion model accurate. Similarly, terrestrial setting model of Odom Odom (1975) (1975) were accurate. Similarly,itit is difficult to reconstruct a terrestrial in which all all sand sand isissubjected subjectedto toprolonged prolonged eolian eolian abrasion abrasion prior prior to to deposition deposition in in aa marine marine environment environment as suggested suggested by Dott Dott and and others others (1986). (1986). Sheet geometry geometry layers were were initially initially deposited deposited Another long-standing long-standing question question is how sheet-like siliciclastic layers of thousands of of square kilometers kilometers of of the the cratonic cratonic shelf. shelf. Most and then preserved across tens of workers have attributed the formation of such sheets to depositional processes and environments workers have attributed the formation such sheets processes and environments that are markedly markedly different different from those described for most younger rocks and modern settings. Lochman-Balk (1970) inferred the presence of enormous tidal flats extending well over over two two the shoreline. shoreline. Dott and Byers (1980) (1980) suggested suggested that that hundred kilometers perpendicular to the quartzose sand under high-energy high-energy conditions conditions across quartzose sand aggraded aggradedmore more or or less less vertically into a sheet under across a vast shallow sea. The most widely cited hypothesis is one that attributes the origin of quartzose The widely cited that attributes the origin of quartzose sandstone sheets to fluvial fluvial and and eolian eolian processes processes that that dispersed dispersed sand sand across across aavegetation-free vegetation-free reworking during during aa transgression transgression(Dott (Dottand andothers, others, 1986). 1986). Recent landscape prior to marine reworking studies, however, have demonstrated demonstrated that that some some quartzose quartzose sheets were deposited entirely within the marine realm under under regressive conditions conditions (e.g., Runkel, Runkel, 1994; 1994; Hughes and Hesselbo, Hesselbo, 1997; 1997; Runkel and others, 1998), and that the depositional processes responsible for the dispersal of 1998), depositional siliciclastic ancient sandstones sandstones siliciclasticsediments sedimentswere were similar similarto to those those operating operating during during the deposition of ancient sheet-like. that are not sheet-like. 107 �The lateral lateral persistence persistence and and sheet-like sheet-like geometry geometry of of lower lower Paleozoic Paleozoic siliciclastic siliciclastic units units probablyreflect reflectthe theroles rolesof of basin basin physiography physiographyand and tectonics tectonics in controlling controlling the lithostratigraphic probably lithostratigraphic architecture, rather rather than than the the existence existence of atypical atypical sedimentary environments. Deposition Deposition was was architecture, characterizedby byaacontinuous continuousand andabundant abundantsupply supplyof of sediment sedimentto to aa relatively stable, stable, nearly flat flat characterized basin that that had had aa slow, slow, uniform uniform rate rate of of subsidence. subsidence. Individual basin Individualsheets sheetsof ofsiliciclastic siliciclasticsediment sediment (e.g., Fig. Fig. 3) 3) migrated migrated great great distances distances during duringchanges changesin in were deposited deposited when when discrete discrete facies facies (e.g., were sea level. level. Deep Deepincision incisionofofthe theindividual individualsheets sheetsduring duringepisodes episodesof ofsubaerial subaerialexposure exposuredid didnot not sea occur, resulting in more or less uniform preservation. occur, resulting in more or less uniform preservation. Dearth Dearthof ofShale Shale LowerPaleozoic Paleozoicrocks rocksof ofthe thecentral centralmidcontinent midcontinentregion regionare arenoted notedfor foraadearth dearthofofshale shale Lower compared comparedto toother othershallow shallowmarine marinedeposits. deposits.Two Twovery verydifferent differenthypotheses hypotheseshave havebeen beenproposed proposed to "marinebypassing" bypassing" model, model,Pettijohn Pettijohnand and others others (1973) (1973) to account accountfor for this this dearth dearth of of shale. shale. In Inaa"marine suggested that that clayclay-and andsilt-sized silt-sizedparticles particleswere weredelivered delivered to to the the shoreline, shoreline,but but subsequently subsequently suggested carriedin insuspension suspensionby byrepeated repeatedstorms stormsacross acrossthe theshallow shallowshelf shelfbefore beforefinal finalburial burial in in basinward basinward carried areas.InIncontrast, contrast,Dairymple Dalrympleand andothers others(1985) (1985)suggested suggestedthat thatstrong strongwinds windsblew blewclay clayand andsilt silt areas. particles hundreds hundredsto to thousands thousandsof of kilometers kilometersoffshore, offshore, to to be ultimately ultimately deposited deposited in in the the outer outer particles detrital detrital belt belt (Fig. (Fig.1). 1). Recentinvestigations investigationsof of Upper Upper Cambrian Cambrian siliciclastic siIiciclastic strata strata support support the marine bypassing Recent model model of of Pettijohn Pettijohnand andothers others(1973), (1973),demonstrating demonstratingthat thatthe theabsence absenceof ofshale shaleisischaracteristic characteristic only only of of the the outcrop outcropbelt belt on on the the flanks flanksof of the the Wisconsin Wisconsin dome dome and and arch arch (McKay, (McKay, 1988; 1988; Runkel Runkel and and others, others, 1998). 1998).Basinward Basinwardofofthe theWisconsin Wisconsinarch, arch,subsurface subsurfacerecords records from from Minnesota Minnesota and and Theseshale shaleand and siltstone siltstone Iowashow showthat that facies faciesdominated dominatedby by shale shale and and siltstone siltstone are common. These Iowa facies facies are are the the offshore offshoreequivalent equivalent of of the the shale-poor shale-poor sandstone sandstone facies facies of of the the outcrop outcrop belt, belt, and and their geographic geographicposition position changed changed through through time time in in response response to to changes changes in in the the position position of of the the their storm-fairweather wave storm-fairweather wave base. base. The The outcrop outcrop belt belt has has aadearth dearth of of shale shalesimply simply because because the the depositional depositional record record isisdominated dominatedby byhighstand highstandshoreface shorefacefacies faciesdeposited depositedabove abovefairweather fairweather wavebase. base.This Thisstratigraphic stratigraphicand andsedimentologic sedimentologicattribute attributeisisnot notunique uniquetotothe thelower lowerPaleozoic Paleozoic wave rocks rocks of of the thecentral centralmidcontinent midcontinentregion—it region-it is is common common in many many younger wave-dominated wave-dominated sequences along along the the landward landward margins margins of of individual individual basins. The Thenotion notionof ofaashale-free shale-freeearly early sequences Paleozoic epeiric epeiric sea seaisisaadeeply deeplyentrenched entrenchedidea ideathat thatsimply simplyreflects reflectsthe thebias biasof ofthe theoutcrop outcrop Paleozoic belt. belt.The Thedearth dearthofofshale shaleininlower lowerPaleozoic Paleozoicrocks rocksshould shouldbe beremoved removedfrom fromthe thelist listofofenigmatic enigmatic featuresunless unlessthe thescarcity scarcitycan canbe bedemonstrated demonstratedtotoexist existon onaa scale scalelarger largerthan than that that of the outcrop features outcrop belt. belt. Siliciclastic-Carbonate Siliciclastic-Carbonatecycles cycles The The fundamental fundamental controls controls on onthe thetransition transitionfrom fromnearshore nearshoresiliciclasticsiliciclastic-to tocarbonatecarbonatedominated understood. For dominated deposition deposition have have never never been satisfactorily satisfactorily understood. For example, example, in in the the Early Early Ordovician, carbonate carbonate deposition deposition apparently apparently dominated dominated across across the the entire entire region, region, even even in in the the Ordovician, shallowestwater waterconditions conditions(Smith (Smithand andothers, others,1993). 1993).Both Botholder older(Jordan (JordanSandstone) Sandstone)and andyounger younger shallowest (St. (St. Peter PeterSandstone) Sandstone)shallow-marine shallow-marineenvironments environmentswere weredominated dominatedby bysiliciclastics. siliciclastics. Only Only speculative kndamentalchanges. changes. speculativeand andvague vaguehypotheses hypotheseshave havebeen beensuggested suggestedto toaccount accountfor forsuch suchfundamental For Forexample, example,Adams Adams(1978) (1978)suggested suggestedthat thatthe theEarly EarlyOrdovician Ordovicianchange changeinindepositional depositionalstyles styles may mayhave havebeen beenin inresponse responsetotodrowning drowningof of the thesiliciclastic siliciclasticsource sourcearea areaby by aa shallow shallow sea sea or orthe the result resultof ofsiliciclastics siliciclasticsbeing being"deflected" "deflected"to toanother anotherregion. region. Early EarlyPaleozoic Paleozoiccarbonate-dominated carbonate-dominated 108 �systems developed following level (Smith (Smith and and others, others, 1993), which which systems following extended periods of high sea level siliciclastic source area may have been covered by a blanket of of carbonate carbonate suggests that the siliciclastic rocks. The Thespread spreadof of certain certainforms formsof of terrestrial terrestriallife life such such as as bacterial bacterial encrustation, encrustation, and and later later the the development development of vascular vascular plants, may have also reduced siliciclastic siliciclastic input. Cryptic Cryptic unconformities unconformities Previous investigations investigations of lower Paleozoic strata of the central midcontinent region have also been hindered by an inability to recognize unconformities. unconformities. The unconformities bounding the major sequences sequences of Sloss Sloss (1963) (1963) are are fairly well established established within the strata strata of of the the outcrop outcrop belt. The The presence presence and and position position of "lesser" "lesser" unconformities, unconformities, especially especially within siliciclastic units, have been a matter of considerable debate. Stratigraphic Stratigraphicrelations relations and and interpreted interpreted depositional depositional histories indicate that such unconformities "should" be present. However, However, little little or or no evidence evidence for regionally extensive subaerial subaerial erosion erosion has has been been documented. documented. Such Such sequence-bounding sequence-bounding they are contained within coarse siliciclastics unconformities are difficult to recognize where they texturally and and mineralogically mineralogically similar, and and sandstones that are texturally because they separate quartzose sandstones because they are relatively flat—reflecting erosion that occurred on a loose, sandy substrate relatively flat-reflecting sandy substrate along a low, uniform uniform gradient, gradient, and and in in aa nonvegetated nonvegetatedterrestrial terrestrialenvironment. environment. Furthermore, Furthermore, the ultra-mature mineral ultra-mature mineral composition compositionof of the the exposed exposed substrate substrateinhibits inhibits development developmentof of aa distinctive distinctive weathering profile. Recent work has shown some promise for identifying subtle subaerial erosion surfaces. Recognition of cryptic unconformities interpretation of regional stratigraphic stratigraphic relations Recognition unconformities requires requires interpretation outcrops and high resolution in conjunction with physical evidence collected at individual outcrops biostratigraphic data. data. Smith deposits of of silica cement cement in biostratigraphic Smith and and others others (1993) (1993) interpreted local deposits formed silcrete. Runkel uppermost Cambrian and Lower Ordovician strata as subaerially formed Runkel and and others (1998) suggested that cryptic unconformities within the fronton and Galesville Sandstones Ironton Galesville Sandstones others (1998) suggested that cryptic unconformities within and at the top top of of the the Jordan Jordan Sandstone Sandstone and and can can be be identified identified only by overlying overlying lag deposits. deposits. These lags deposits are the coarsest bed within nearshore sandstone successions; they separate a regionally traceable, traceable, decameter-scale, decameter-scale, coarsening-upward interval below from a decameterdecameterscale, fining-upward sequence above. above. Preliminary Preliminary results of of high high resolution resolution biostratigraphic biostratigraphic verified the the presence presence of of an an erosion erosion surface surface on on top top of of the Jordan dating using conodonts has verified Sandstone, and magnitude of such cryptic cryptic unconformities unconformities Sandstone, and demonstrates demonstratespromise promise for for measuring the magnitude with detailed paleontologic paleontologic work. HYDROGEOLOGY The Paleozoic Minnesota are are the the most most widely widely used used source of Paleozoic strata of southeastern southeastern Minnesota groundwater in the state. state. Groundwater Groundwatermanagement management and andscientific scientificinvestigations, investigations, including including ground water models, models, estimates estimates of of aquifer yields and predictions of contaminant transport, ground water well construction codes have, in the past, relied on a generally accepted hydrogeologic framework that we believe believe is inaccurate inaccurate in in many many important important respects. respects. This commonly framework that commonly used classification of aquifers and confining beds beds (e.g., (e.g., Kanivetsky Kanivetskyand andWalton, Walton,1979; 1979; Delin and Woodward, 1985) assumption that Paleozoic lithostratigraphic lithostratigraphic units in Minnesota Minnesota Woodward, 1985)is based on the assumption are more or or less less internally internally homogeneous homogeneous in in hydrogeologic hydrogeologic character, character, and that they they have have boundaries. Furthermore, this paradigm is boundaries that correspond to hydrostratigraphic boundaries. based chiefly on the the hydrogeologic hydrogeologic characteristics of the Paleozoic strata in the Twin Cities Metropolitan from equivalent equivalent strata stratain insoutheastern southeasternMinnesota. Minnesota. A Metropolitan Area, which differ markedly from 109 �more accurate accurate hydrogeologic hydrogeologic framework framework is necessary to advance our understanding of groundwater flow in this region. region. We have have recently changes in the methods We recently made fundamental fundamental changes methods used used to to characterize characterize hydrogeologic attributes focusingon onhydrostratigraphic hydrostratigraphic components components rather rather hydrogeologic attributes of Paleozoic strata, focusing than lithostratigraphic lithostratigraphic units. Fig. 4 shows our preliminary results in delineating hydrostratigraphic Fig. 4 shows in delineating hydrostratigraphic components, permeability. The Paleozoic components, distinguished distinguishedand and characterized characterized by their porosity and permeability. bedrock hydrostratigraphic components components that bedrock of southeastern southeastern Minnesota Minnesota consists consists of four distinct hydrostratigraphic have been described described in in studies studies at at both both the regional regional and local scale scale (e.g., Setterholm Setterholm and and others, others, Miller and and Delin, Delin, 1993; Runkel, Runkel, 1996a, 1996b). 1996b). They are: 1) fine clastic; 2) coarse 1991; Miller coarse clastic, 3) carbonate rock, rock, and 4) mixed mixed carbonate carbonate and and clastic. clastic. The values for porosity and permeability permeability of these these components, components,discussed discussed below, below, have been determined determined through through laboratory laboratory tests of plug samples samples and and through through hydraulic hydraulic testing testing of of boreholes boreholes in in southeastern southeasternMinnesota. Minnesota. grained, feldspathic feldspathic sandstone, sandstone, siltstone The fine-clastic component consists of very fine grained, strongly to to moderately moderatelycemented. cemented. This component and shale in thin to medium beds that are strongly orders of of magnitude less than that of the has low to very very low low relative relative permeability—several permeability-several orders coarser-grained sandstone coarser-grained sandstone of the quartzose quartzose component component described described below. Vertical Vertical conductivity conductivity based on on pumping pumpingtests testscommonly commonlyranges ranges from i0 to i0 ft/day for interbedded from 1 0 to 10'~ft/day for interbedded very very fine sandstone and sandstone and shale shale (Miller (Millerand and Delin, Delin, 1993), 1993),to to as low as iO7 10'~ft/day ft/day for units composed composed almost almost entirely entirely of shale shale (Freeze (Freeze and and Cherry, 1979). In In the the former, former, horizontal horizontal permeability permeability is is typically typically more than 100 100times times greater greater than than vertical vertical permeability permeability (Miller, (Miller, 1984; 1984;Setterholm Setterholm and and others, others, 1991; 1993). 199 1;Miller and Delin, 1993). coarse-clastic component The coarse-clastic componentis is aa mostly uncemented, uncemented, moderately moderately to to well-sorted, well-sorted,finefine-to to coarse-grained sandstone composed of about 98 percent quartz. Plug-sample Plug-sampletests tests indicate indicate itit has aa high high to tovery veryhigh highpermeability permeability and andporosity porosity due due to torelatively relatively large, large, well-connected well-connected intergranular intergranular pore spaces. spaces. Pump Pumptests testsof ofwells wellsopen openmostly mostlyto tothis thiscomponent componenttypically typicallyrange range from from about about 2-20 2 -20ft/day, ft/day, indicating indicatingaamoderate moderateto to high high conductivity, conductivity, corroborating corroborating the results results of the plug tests 1 996a). tests (Miller, (Miller, 1984; 1984;Setterholm Setterholmand and others, others, 1991; 1991;Miller Miller and and Delin, Delin,1993; 1993;Runkel Runkel1996a). The carbonate-rock component consists of limestone or dolostone with minor shale and sandstone. Porosity features, and karst features. sandstone. Porosityand andpermeability permeabilityisisdue dueto to fractures fracturesand solution features, The permeability permeability varies varies substantially substantiallyfrom from place place to to place place depending dependingon on the the size, size, extent, extent, degree degree and interconnectivity interconnectivityof of fractures fracturesand andsolution solutionfeatures features(Libra (Libraand andHallberg, Hallberg,1985; 1985;Visocky Visockyand and others, 1985). Pumping Pumping tests tests indicate indicate that that this this component component in most places is moderately moderately to highly permeable permeable where where such such features features are are well developed—typically developed-typically ranging from 1-40 1-40 ft/day Woodward, 1985). 1985). However, (Delin and Woodward, However, in places where fractures and solution features are minimally developed, developed, such such as as where where deeply deeply buried by younger bedrock, the component component has has aa very low conductivity, even at a large scale (Libra and Hallberg, 1985; Visocky and others, large scale (Libra and Hallberg, 1985; Visocky and others, 1985). 1985). The mixed carbonate and clastic component is composed of interbedded siltstone, very sandstone, sandy dolostone, dolostone, and shale (Setterholm (Setterholm and others, 1991; fine to very coarse grained sandstone, 1991; Cementationisisvariable; variable; beds beds of of mediummedium- to to coarse-grained coarse-grained sandstone sandstone are are Runkel, 1996b). Cementation typically friable, but very fine to fine-grained sandstone and siltstone are commonly strongly permeability from from bed bed to tobed. bed. Coarsecemented. As As aa heterolithic heterolithic unit, unit, it varies markedly in permeability grained grained sandstone sandstone beds beds that that are are too too weakly weakly cemented cemented to to provide provide coherent coherent samples samplesare are likely likelyto to be highly permeable. Laboratory Laboratorytests testsof ofthe themore morestrongly stronglycemented, cemented,finer-grained, finer-grained, clastic clastic 110 �0 Group, Formation. Member - ,.-% 5 - Natural Gamma Log D Lithology Increasingcount LIMESTONE LIMESTONE 100 API-G units DOLOSTONE DOLOSTONE SANDY SANDY SANDSTONE SANDSTONE TO FINE VERY FINE FINETO FINE Prosser Limestone FINE TO MEDIUM FI NE TO MEDIUM M EDIUMTO COARSE MEDIUM SHALY Cummingsville Formation SILTSTONE SILTSTONE SHALE Vugs Vugs (commonly (commonlytilled filledwith with coarse coarse calcite) calcite) Decorah Shale Chert Chert K-bentonile K-bentonitebed bed(altered (altered volcanic volcanic ash ash bed bed Oolites Oolites Glaucorrite Glauconite Iron Ironstain stain Goethite-hematite ore Goethite-hematite St. Peter Sandstone Phosphate pellets Phosphate pellets AaI mats Abal mats atromatolites Algal domes; stromatolltes Fossiliferous; fossils (symbols Fossiliferous; (symbolsnot not limestone and dotostone dolostone used in limestone units) units) bored Worm bored Pebbles (gravel Pebbles (gravelIn in unconsolidated units) unconsolidated Shakopee Formation Flat-pebble conglomerate Flat-pebble Cross-bedded Cross-bedded(testoon) (festoon) Cross-bedded (planar to tangential) - Ripple cross-laiThnatlons "TT^- Ripple cross-laminations ^S- 7 J- -r 7 J. J. Dolomitic Dolomitic Calcereous Calcareous Contact Contact marks marks aa major majorerosional erosional surface surface ,,'\ .f': .-"ÂFades Fadeschange change Low permeability permeability and porosity; Low hodzontal horizontal bar shortened shortened where lateral lateralextent extent is is limited limited high permeability Moderate to high permeability end porosity porosity and Oneota Dolomite l a Outcrop Intervals. intervals. Number Number refers refersto stop number number In the the field field guide guide in Coon valley Member column showing showing units units from from the the Prosser Prosser Limestone Limestone of of the Figure Figure 4. 4. Bedrock stratigraphic column Upper Ordovician Ordovician Galena Galena Group Group to the Upper Upper Upper Cambrian CambrianEau EauClaire ClaireFormation. Formation. Column Colunm includes hydrostratigraphic hydrostratigraphicunits units based based on on estimated estimated permeability permeability and and porosity. porosity. 111 �Group, Formation, Member - Natural Gamma Log Increasingcount - O 100 API-G units Coon Valle) Member Jordan Sandstone St. Lawrence Formation Birkmose Member Ironton and Galesville Sandstones Eau Claire Formation Figure 4. Continued Continuedfrom fromprevious previous page. beds, indicate aa low beds, low permeability permeability (Setterholm and and others, others, 1991). 1991). These These latter beds beds make make up up the the bulk latter bulk of this heterolithic meager heterolithic component, and meager pumping data data indicates a horizontal pumping horizontal conductivity conductivity of of about one-fifth that of the coarse coarse clastic clastic facies facies (Runkel, (Runkel, 1996a). 1996a). Lateral and vertical variability variability in abundance and interconnectivity of abundance and fractures can markedly markedly affect affect the the hydrologic behavior of each of the four components described above. above. Such features features are most abundant abundant and best best interconnected where the bedrock is at or near (within (within 100 100 feet) feet) the the surface. surface. Siliciclastic components componentssuch such as as the fine Siliciclastic which has low to clastic component, component, which very low intergranular intergranular permeability, may be orders orders of of magnitude magnitude higher higher in in conductivity where they they lie near the conductivity where the surface because because there there is a substantial surface substantial amount of flow along fractures. amount of flow along fractures. Conversely, some carbonate units may may have a relatively relatively low low conductivity conductivity and and act as confining confining beds where they they are are covered by younger covered by younger bedrock bedrock and and secondary porosity is not well developed secondary porosity is developed (Libra (Libra and Hallberg, Hallberg, 1985; 1985;Visocky and others, 1985). 1985). Additionally, Additionally, fracture flow may be be dominant even in the flow may dominant even coarse-clastic component, which which has a high intergranular intergranular permeability permeability where it lies near the surface. surface. aquifers and Delineation of aquifers and confining confining beds Given the hydrostratigraphic hydrostratigraphiccharacter character of the components components described described above, above, the Paleozoic Paleozoic section can be divided and low low permeability permeabilityunits units(Fig. (Fig.4). 4). The The coarse coarse divided into moderate/high moderatehigh and clastic that contribute contribute most most clastic and carbonate carbonate rock rock component component (where (where karstic) karstic) are likely the sources that of the yield yield to to water water wells wells developed developed in in Paleozoic Paleozoic strata. The Thefine-clastic fine-clasticcomponent component can can potentially yield particular where it is fractured near the surface, potentially yield moderate moderatequantities quantitiesof of water, water, in particular but more importantly itit acts acts as as aa confining confiningunit unit separating separatingcoarse-clastic coarse-clastic and and karstic karstic aquifers aquifers (e.g., Wenck and Associates, Associates, Inc., 1997). The component contains The mixed carbonate carbonate and clastic component contains individual beds that can yield moderate quantities of water, but where greater than 10 feet individual beds that can yield moderate quantities of water, but where greater than 10 feetthick, thick, this unit apparently apparently also (Setterhoim and and others, others, 1991). Unfractured Unfractured carbonate also acts as an aquitard (Setterholm carbonate rock can also Visockyand andothers, others, 1985; 1985;Donahue Donahueand andAssociates, also serve serve as a confining bed (e.g., Visocky Associates, 1991; Barr Engineering, Engineering, 1996). 199 1;Ban1996). 112 �Of particular particular importance this more more rigorous rigorous hydrogeologic hydrogeologic approach importanceto to this this field field trip is that this approach indicates that that two two widely widely used used aquifers, aquifers,the the Prairie Prairie du du Chien-Jordan Chien-JordanAquifer Aquifer and and the the FranconiaFranconiaindicates Ironton-GalesvilleAquifer, Aquifer, are are not single, hydraulically connected aquifer systems as commonly Ironton-Galesville commonly believed believed (e.g., (e.g., Kanivetsky Kanivetsky and and Walton, 1979). Pumping Pumping tests (Miller, (Miller, 1984; 1984;Delta Environmental Consultants, Inc., Inc., 1992; 1992;Miller Miller and and Delin, Delin, 1993) 1993)and and carefully carefullycollected collectedlocal localstatic staticwater waterlevel level Consultants, measurements measurements(Delta (DeltaEnvironmental EnvironmentalConsultants, Consultants,Inc., Inc.,1992; 1992;Wenck Wenckand andAssociates, Associates,Inc., Inc.,1997) 1997) demonstrate that that the the fine fineclastics clasticsof ofthe theFranconia FranconiaFormation Formationhydraulically hydraulicallyseparate separate clearly demonstrate ground ground water water in in the the fractured, fractured, upper upper part part of of the the Franconia Franconia Formation Formation from from ground ground water water in in coarse below. Some fractured, fractured, carbonate-cemented carbonate-cemented coarseclastics clastics of the Ironton-Galesville Sandstones below. rock rock in in the the lower lower part part of of the the Franconia, Franconia, where it occurs at or near the surface, is the source of many many springs springs in in the the area area and andisisperhaps perhapsthe theonly onlyhighly highlypermeable permeableconduit conduitfor forgroundwater groundwater within the the Franconia Franconia Formation. Formation. The ThePrairie Prairiedu duChien-Jordan Chien-JordanAquifer Aquiferisis likewise likewisetwo two distinct distinct within and coarse clastic clastic aquifer-separated aquifer—separated and separate separateaquifers—an aquifers-an upper upper carbonate carbonateaquifer aquiferand and a lower, coarse by clastic component. component. Hydraulic by an an intervening intervening aquitard aquitard composed composed of the mixed carbonate and clastic Hydraulic separation separationof of the the carbonate carbonateand and coarse-clastic coarse-clasticaquifers aquifersisis indicated indicatedby by several severallines lines of hydrologic hydrologic evidence including: Donahue and andAssociates, Associates,1991; 1991; including: potentiometric potentiometric data data (Kanivetsky, (Kanivetsky, 1988; 1988; Donahue N.O. pumping tests (Barr N.O. Janick Janick ,,Winona Winona State University, University, oral communication communication 1994), pumping (Barr Engineering, Engineering, 1996; 1996;N.O. N.O. Janick, Janick,Winona Winona State StateUniversity, University, oral oral communication, communication,1994), 1994),and andby by ground-water ground-waterchemistry chemistry(Alexander, (Alexander,1990; 1990;Setterholm Setterholmand andothers, others,1991, 1991,Wall Wall and and Regan, Regan, 1994). 1994). FIELD FIELDTRIP TRIPSTOPS STOPS Introduction Introduction As enigmatic features As we we examine examinethese these rock rock exposures, exposures,think think about about the enigmatic features and and long-standing long-standing sedimentologic sedimentologic problems associated with these units. For For example, example,what what created created the the extreme extreme maturity of the fine to coarse-grained sandstones? sandstones? Is there really a dearth dearth of of shale? shale? Why is it difficult to place your hand on an unconformity in these rocks? In addition, difficult unconformity in these rocks? In addition, think think about about the water-bearing water-bearing characteristics that are are determined determined by grain grain size, size, cementation, cementation, fractures, fractures, and and dissolution dissolutionfeatures. features.With Withthis thisininmind, mind,judge judgefor foryourself yourselfthe thevalidity validityof of some someof of the the commonly commonly accepted accepted depictions depictions of of the the hydrogeologic hydrogeologiccharacteristics characteristics of the Paleozoic Paleozoic rocks. For Forexample, example, does doesthe thePlatteville PlattevilleFormation Formationlook looklike likeaaconfining confiningunit unit that that will will impede impedethe the downward downwardtransport transport of of contaminants, contaminants,as asititisis commonly commonlyshown shownto to be on maps? maps? Compare Comparethe theFranconia FranconiaFormation Formationtoto the try to to determine determine why the former is most often often regarded as an an the Eau Eau Claire Claire Formation, Formation, and and try aquifer aquifer and and the the latter latteras asaaconfining confiningbed. bed. Examine Examinethe thedramatic dramaticvariability variabilityininthe theporosity porosityand and permeability ChienGroup Group and and Jordan Jordan Sandstone Sandstone and ask yourself whether permeabilitywithin withinthe thePrairie Prairiedu du Chien the the commonly commonly accepted accepted hydrogeologic hydrogeologic depiction depiction of of these these units units as asinternally internallyhomogenous, homogenous, hydraulically connected aquifers is accurate. hydraulically connected aquifers is accurate. The 8, 10, Thelocation locationof of individual individualstops stops is is shown shown on Figures 5, 7, 7,8, 10,and and 11. 11. Directions Directionsfrom from major major road road intersections, intersections,or orstreet streetaddresses, addresses,are arealso alsoprovided providedfor foreach eachstop. stop. STOP STOP1—Rochester I-Rochester Public PublicUtilities, Utilities,4000 4000E.E.River RiverRoad RoadNE, NE,Rochester, Rochester, Minnesota. Minnesota. An An overview overview of of the thedepositional depositionalhistory history and andhydrogeologic hydrogeologicattributes attributes of of the thePaleozoic Paleozoic strata strataof of southeastern southeasternMinnesota Minnesotawill willbe bepresented presentedatatthis this stop. stop. Paleozoic Paleozoicbedrock bedrockininthe theRochester Rochester area areaare arenearly nearly flat flat lying, lying, and and have have been eroded into an upper and lower plateau. The The resistant resistant limestone and dolomite formations of the Galena Group form an upper plateau that skirts limestone and dolomite formations of the Galena Group form an upper plateau that skirtsthe the 113 �8, 10, Figure 5. 5. Index Index map map of of field field stops. Black Blackboxes boxes refer refer to to maps maps in in Figures Figures 7, 7,8, 10,and and 11. 11. Figure perimeter perimeter of of Rochester. Rochester. The Themostly mostlycarbonate carbonaterocks rocksof of the the Prairie Prairie du du Chien Chien Group Group form form a lower plateau along the South Fork of the Zumbro River and the lower ends of its tributaries, in and along the South Fork of the Zumbro around around the the city city of Rochester. These Thesetwo twoplateaus plateausare areseparated separatedby by an an escarpment, escarpment, composed composed of of Decorah Sandstone, which exposed DecorahShale, Shale,Platteville PlattevilleFormation, Formation,Glenwood GlenwoodShale, Shale,and and St. St. Peter Peter Sandstone, which is exposed on steep city. We will examine most steep bluffs within and around the city. most of of these these units units on on the the trip trip today, as well as as several several older older units, units, such such as as the Jordan Sandstone. Sandstone. The hydrostratigraphic attributes of of many many of the Paleozoic units that we will will examine examine today have have aa direct direct or orindirect indirectimpact impacton onthe theavailable availablewater watersupply supplyfor forthe thecity cityof ofRochester. Rochester. The understanding the The city city has has devoted devoted aa considerable considerable amount amount of of effort effort and resources to understanding the geologic geologic controls controlson on ground-water ground-waterquality qualityand andquantity quantityin in their their region. region. An Aninvestigation investigationof of variable variableyield yield from Dolomite from city city wells wells that that draw draw water water from from the Jordan Sandstone Sandstone and and lower part of the Oneota Dolomite (Runkel, 1996a) 1996a) provides provides an an example example of of where where lithostratigraphic lithostratigraphic and and hydrostratigraphic hydrostratigraphic boundaries do not coincide. coincide. The Theopen-hole open-holeinterval interval of of these these city city wells wells cross cross three three or or more more distinct hydrostratigraphic hydrostratigraphic components—the components-the fine-clastic, fine-clastic, coarse-clastic, coarse-clastic, and mixed carbonate carbonate 114 �and clastic components (Fig. 6). Permeability Permeability values values of of these these components components vary by as much as four orders of magnitude. magnitude. Grain permeability Grainsize, size,sorting sortingand and degree degree of cementation cementation affect affect the permeability of these rocks, all within boundaries of what is currently designated as a single aquifer unit— unitthe Prairie du Chien-Jordan Aquifer. Pumping records of municipal wells finished in these Chien-Jordan Aquifer. Pumping municipal components, all three components, all considered considered "Jordan" wells, wells, show show that the productivity productivity of individual individual wells wells is directly proportional to the thickness of the coarse-clastic component exposed in the openhole interval (Runkel, (Runkel, 1996a). 1996a). This stop Formation in the the large large quarry quarry west west of of stop shows shows the sandy dolomite of the Shakopee Formation the road. Notable Notablefeatures featuresinclude includethe thethin thincover coverof of the the bedrock bedrock and and the the highly highly fractured fractured nature nature rock hydrostratigraphic hydrostratigraphic component. component. The high density density of of fractures fractures isis typical of of the carbonate rock all bedrock units near the land surface surface in this region. region. Also visible visible to the southeast southeast is the quartzose quartzose facies of the St. Peter Sandstone Sandstone and the overlying Glenwood Shale and Platteville Limestone. recharge to to the the Prairie Prairie du du Chien Group and Jordan Delin (1991) showed that ground-water ground-water recharge Sandstone is focused along along the the edge edge of of the the plateau plateau above abovethe the St. St. Peter Peter Sandstone. Sandstone. Ongoing investigations into into the the phenomena phenomena of of focused focused recharge recharge by by the the USGS USGS based based on earlier work investigations (Delin, 1991; 1991; Delin and Almendinger, 1991) 1991) will provide better data on the hydrologic budget of the region by quantifying quantifying the amount amount of water recharging recharging from from upper plateau. plateau. STOP 2—Bailey Quarry near STOP %Bailey Quarry nearSt. St.Charles, Charles,Minnesota. Minnesota.West Westside sideof ofMinnesota Minnesota Highway 74, about 1.2 1.2 miles south south of Interstate Interstate 90. Winona County, Minnesota (Fig. 7). This quarry has one one of of the the most most accessible, accessible, continuous continuous exposures across the upper upper St. St. Peter Sandstone, Glenwood Shale, and Platteville Formation in Minnesota. Our work on this part of the Paleozoic reconnaissance nature at this time. Most Paleozoic section section is of a reconnaissance Most workers workerswho whohave have studied these units have suggested suggested that they are part of an overall transgressive sequence (e.g., Dott and others 1986; Mossler, 1985). A 1986; Mossier, 1985). A rise rise in in sea sea level level is is recorded recorded by the the facies facies change change upsection from fine- to coarse-grained coarse-grained quartzose sandstone deposited in a shoreface (St. Peter deposited in deeper offshore shelf areas (Glenwood (Glenwood Shale), culminating culminating in rnicritic micritic SS.), to shale deposited carbonates offshoreconditions conditions (Platteville (PlattevilleFormation). Formation). While While carbonatesthat that accumulated accumulated in the most distal offshore this scenario scenario is plausible, plausible, some some features features suggest that the depositional depositional history may be more more complex. For example the upper half to two-thirds of the St. Peter Sandstone coarsens upward For example the upper half to two-thirds of the St. Peter Sandstone coarsens upward in southeastern wh,ich in in other other sheet sheet sandstones sandstones is is indicative indicative of shallowing shallowing rather rather southeastern Minnesota, Minnesota, wh,ich than deepening. Workers Workersin inother otherstates states(e.g., (e.g., Simo Simoand and others, others,1997) 1997)have have suggested suggestedthat that the the St. Peter Sandstone Sandstone is capped by an unconformity, which also suggests that its deposition was culminated by a regressive event. Additionally, Additionally, the Glenwood Glenwood Shale contains discrete beds of medium- to coarse-grained sandstone, some with with a channel-shape, channel-shape, and and the the lower lower part part of the Platteville Formation Formation contains contains matrix-supported, matrix-supported,coarse coarsequartz quartzgrains. grains. These attributes are incompatible incompatible with with deposition depositionin in aa relatively relatively deep, deep, distal distal offshore offshore shelf shelf setting. setting. here. The There are three hydrostratigraphic hydrostratigraphic components exposed here. The Platteville Platteville Formation Formation consists fractured carbonate carbonate rock component, the Glenwood Glenwood Shale Shale consists consists mostly mostly consists chiefly chiefly of the fractured of the fine clastic clastic component, component, and Sandstone consists coarse clastic and the the St. St. Peter Sandstone consists of the coarse clastic component. component. Hence, across this part of of the the Paleozoic Paleozoic section section lithostratigraphic lithostratigraphic boundaries nearly (within a meter) coincide with the principle hydrostratigraphic boundaries. We We will see examples at principle hydrostratigraphic boundaries. subsequent stops where the lithostratigraphic lithostratigraphic boundaries do not correspond to the principal principal hydrostratigraphic hydrostratigraphic boundaries. boundaries. 115 �____ ____ _____ NORTH /—/ f • - - . . . ___ .. . . . . - S . a — . ••' * _z___7__. . . . .-r in - . ,— . ci - •—---— • s . . . coarse clastic . ._.— . .—- •'. ._._—e—t'-—-':; . .. s. — — ———— — • / . . . . . • coarse clastic . . - . mixed carbonate and clastic.,- ' ' ——-k SOUTI+ . ., __ - coarse clastic ——— .--fineclastj,. - — — . St. Lawrence Formation St. Lawrence Formation L Lines on section dashed where control is poor 434041 161425 mcc rncct 220166 1 mcc mcc cc Ic fc I I Ic xl 2C64 21ca11 222525 2226S - - mcc cc cc E)QLANATION mcc mixed mixedciastic clasticand andcarbonate carbonatecomponent component Ic mixed clastic ciastic and and carbonate carbonatecomponent component fc cc cc mixed clastic clastic and and carbonate carbonate component component mcc SI St. Lawrence Formation sl St. Lawrence Formation - - Ic fC — cc cc Ic fc Ic cc Ic SI Figure 6. West-east West-eaststratigraphic stratigraphiccross-section cross-sectionand andcorresponding correspondinggamma gammalogs logsfor forthe theJordan JordanSandstone Sandstoneand andthe thelower lowerpart partof ofthe theOneota Oneota Figure Dolomite in the Rochester Metropolitan area, showing the variable thickness of the coarse-clastic and fine-clastic fine-clastic components of the Jordan beneath the mixed carbonate and clastic Coon Valley Valley Member Member of of the the Oneota. Oneota. (Modified from from Runkel, Runkel, 1996a.) 1996a.) �Figure 7. Map Map11on onindex indexmap map(Fig. (Fig. 5) 5) showing showing the the location location of of stop stop 2. 2. quarry is a good example example of the geologic geologic controls on ground-water ground-water recharge recharge discussed This quarry discussed carbonate Platteville Formation is through through horizontal at Stop 1. Ground-water Ground-waterflow flow through through the carbonate vertical joints. joints. Matrix fractures along bedding planes and vertical Matrix porosity and permeability does not contribute substantially Platteville bench contribute substantiallyto to ground-water ground-water flow. flow. Water Water pools pools on on top of the lower Platteville because the underlying underlying Glenwood Glenwood Shale Shale restricts restricts the downward downward movement of ground ground water. water. conductivity of of the the Glenwood Shale Shale is is estimated estimated to to be be similar to values for shale Hydraulic conductivity reported in in the the literature literatureof of iO to toiO rn/day &day(Freeze (Freezeand andCherry, Cherry,1979). 1979). The Thesurface surfacewater water Platteville bench bench and and onto onto the the top top of of the Glenwood Shale entering the quarry runs across the Platteville before spilling quarry. This stream does not account for all the spilling into the St. Peter section of the quarry. recharging the St. Sandstone. Joints water recharging St. Peter Sandstone. Jointsare arevisible visiblein in the the Platteville Plattevillethat that extend extend into into the the Glenwood Shale. The ThePlatteville PlattevilleFormation Formation and and Glenwood Glenwood Shale form aa flat flat plateau plateau across across much of the Twin Cities area. The Glenwood Shale is an important confining bed in Twin area. The Glenwood an important bed that it restricts contaminant contaminant transport transport to to lower lower bedrock aquifers aquifers where where it is is not not crossed crossed by by fractures. fractures. STOP 3—Road >Road Cut Cut near nearHomer HomerMinnesota. Minnesota.From Fromintersection intersectionofofState StateHighway Highway 43 43 and and U.S. 61 61 inWinona, in Winona,take takeState StateHighway Highway 61 61 south south for 3.5 miles. Turn right on County Road 15 (at Homer) and travel 2.2 miles to large large road cut (Fig. (Fig. 8). 8). This exposures of the Jordan Sandstone This is one one of the most complete, complete, readily accessible accessible exposures Sandstone in the entire central mid-continent region. The mid-continent region. The section section is is continuously continuously exposed from the upper part of the St. Lawrence Lawrence Formation, Formation, through the entire Jordan Sandstone, Sandstone, and most of the the Oneota Dolomite. cycleisisrecorded. recorded. The very fine grained complete regressive-transgressive regressive-transgressive cycle grained Dolomite. AA complete sandstone, shale and dolostone dolostone of the St. Lawrence Lawrence Formation Formation was deposited deposited in relatively relatively deep deep water during a high high stand stand of of sea sealevel level (Hughes (Hughes and and Hesslbo, Hesslbo, 1997), 19971,which which was was followed followed by by 117 �KILoMmERs MILES 1 -1 - 0 - 1 0 - 2 I 3 4 2 5 3 6 1 4 7 8 5 9 $0 6 Map22on onindex indexmap map(Figure (Figure5) 5) showing showing the the location location of of Stop Stop3. 3. Figure 8. Map progressive shallowing recorded in the coarsening coarsening upward Jordan Sandstone, culminated by subaerial erosion marked by aa pebbly pebbly sandstone sandstone lag. lag. The Oneota Oneota Dolomite Dolomite above above the the unconformity unconformityrecords recordsthe thereturn returnof ofthe theshoreline shorelineand andgradual gradualdeepening deepeningin inthe theEarly EarlyOrdovician. Ordovician. Lowermost Oneota strata (Coon Valley Member) are mixed clastic carbonate deposits that Oneota strata (Coon Valley accumulated in supratidal to shallow subtidal conditions. conditions. Upper Upper Oneota Oneota strata strata (Hagar (Hagar City City Member) dolostonedeposited depositedin in deeper, deeper, entirely entirely subtidal subtidal conditions. conditions. Member) are are mostly mostly sand-free sand-freedolostone Particularly include large-scale, large-scale, high-angle high-angle Particularly interesting interestingsedimentologic sedimentologicfeatures features at this stop include cross cross strata stratawith with reactivation reactivationsurfaces surfacesand and shale shaledrapes drapesin in the the Jordan Jordan Sandstone Sandstonethat that may may record record a strong influence of tidal currents, and bbcabbage-head" "cabbage-head" stromatolites stromatolites in the lower Oneota. Oneota. The The depositional can account account for for the the sedimentologic sedimentologic and stratigraphic stratigraphic depositional model depicted depicted in in Figure Figure 33 can attributes of the St. Lawrence Formation and Jordan Sandstone, but does not readily explain the attributes Lawrence Formation and Jordan Sandstone, attributes attributes of the overlying overlying Oneota Oneota Dolomite Dolomite This exposure example,whereaa major major hydrostratigraphic hydrostratigraphicboundary boundary does does not not exposure includes includes an an example.where correspond hydrostratigraphic variability correspondto to aa lithostratigraphic lithostratigraphicboundary, boundq, and and also also shows shows the great hydrostratigraphic variability within internally homogenous homogenous in in hydrogeologic hydrogeologic within lithostratigraphic lithostratigraphicunits units that that are are widely regarded as internally properties. properties. The TheSt. St.Lawrence Lawrence Formation Formation and and lower lower part of the the Jordan Jordan Sandstone Sandstone are both composed confining composedof of the the fine-clastic fine-clastic component. component. The TheSt. St.Lawrence Lawrence is is commonly commonly regarded regarded as as a confining bed and the the Jordan Jordan as as an an aquifer, aquifer, yet yet there there is is no no distinct distinct hydrogeologic hydrogeologic boundary between the two lithostratigraphic units as is commonly believed. believed. As As you you walk walk up up the the outcrop, outcrop, consider consider where where you would would define define the the bottom bottom and and the the top top of the "Jordan Aquifer." Aquifer.'' The The mixed mixed carbonate carbonate and and clastic clastic component componentthat that composes composesthe the Coon Coon Valley Member of the Oneota Dolomite (Prairie (Prairie du du Chien Chien Group) Group) isis markedly markedly lower lower in in porosity porosity and and permeability permeability than than the the coarse coarseclastics clasticsof ofthe the uppermost Jordan Sandstone. The Theoverlying overlying carbonate carbonate rock rock component component of of the the Hagar Hagar City City Member fractures. Fracture Member is tightly cemented, cemented, with primarily horizontal fractures. Fracture tops show evidence 118 �of dissolution. Larger scale scale vertical vertical dissolution along dissolution. Larger along aa vertical verticaljoint joint isis also also visible visible here. here. If such fractures and dissolution dissolution features features were not developed in the subsurface subsurface this unit would be be a confining bed. BIOSTRATIGRAPHY OF OF CONODONTS CONODONTS FROM FROM JORDAN JORDAN SANDSTONE SANDSTONEAND AND LOWERMOST ONEOTA LOWERMOST ONEOTA DOLOMITE DOLOMITENEAR NEAR HOMER, HOMER,MINNESOTA MINNESOTA J.F. Miller* and and Anthony C. C. Runkel Runkel *Southwest *Southwest Missouri Missouri State State University, University, Department Departmentof of Geography, Geography,Geology, Geology, and and Planning, 901 South South National National Avenue, Springfield, Missouri 65804-0089 The physical evidence for the presence presence of aa large large magnitude, magnitude, regional regional unconformity unconformity associated with the Jordan Sandstone has been been debated for decades. Smith Smith and and others others (1993) (1993) described subaerially formed silcrete that occurred at or or below below the the Jordan Jordan Sandstone-Oneota Sandstone-Oneota Dolomite contact at at a few outcrops Wisconsin. Runkel that a pebbly Dolomite contact outcrops in Wisconsin. Runkel (1994) suggested suggested that sandstone that caps the Jordan Jordan Sandstone Sandstone at many outcrops in Wisconsin and Minnesota is an erosional lag of regional extent. ItIt everywhere everywhere separates separates a major, decameter-scale coarsening decameter-scale fining upward upward sequence sequence above, above, and and was was formed formed upward sequence sequence below from a decameter-scale extreme basinward basinward positions positions in inlatest latestCambrian Cambriantime. time. The when the regressive shoreline was in extreme to be be more more deeply deeply truncated beneath this lag on the margins of of Jordan Sandstone was shown to the Hollandale Embayment Embayment (Runkel, (Runkel, 1994). 1994). The work described above suggests that that an unconformity unconformity is is present present near near or or at at the the top top of of evidence is subtle and and cannot cannot be be recognized recognized at at all all outcrops outcrops the Jordan Sandstone Sandstone but the physical evidence (Fig. 9). In unconformity and and determine determine its magnitude, magnitude, In an an effort effort to substantiate substantiate the presence of an unconformity Jordan Sandstone and from the conodont samples samples were were collected collected at the Homer section from the Jordan overlying Coon Valley Member of the Oneota Dolomite overlying Coon Dolomite by A. C. C. Runkel Runkel and were processed processed by J.F. Miller. Samples J.F. Samples from the Jordan Sandstone Sandstone contain contain only two conodont conodont species, species, Proconodontus muelleri muelleri (Miller) Proconodontus (Miller) and and Eoconodontus Eoconodontus notchpeakensis notchpeakensis (Miller), (Miller), which which range range America and and are are diagnostic diagnostic of of throughout the Jordan. These These species species are widespread in North America of the theEoconodontus Eoconodontus Zone, Zone, approximately approximately of middle middle the Eoconodontus notchpeakensis Subzone of Age. This from samples samples 1 through through 10. 10. Sample 11 Trempealeauan Age. This fauna fauna has been recovered from 11 is from the Coon Coon Valley Valley Member of the Oneota Oneota Dolomite Dolomite and and yielded yielded aa completely completely different different conodont fauna. This Thissample sampleincludes includesAcanthodus uncinatus uncinatus (Furnish), (Furnish),Aloxoconus Aloxoconus iowensis iowensis (Furnish), Aloxoconuspropinquus (Furnish), Cordylodus intermedius (Furnish), (Furnish), Aloxoconuspropinquus (Furnish), Aloxoconus sp., Cordylodus (Furnish), Cordylodus lindstromi lindstromi (Druce (Druce & & Jones), Jones), aa new species of Cordylodus known known from from Utah Utah and and Polycostatus oneotensis oneotensis (Furnish). Many Texas, and Polycostatus Many of of these these species species were named by Furnish (1938) (1938) from from the Oneota Oneota in the Iowa-Minnesota area. The The presence presence of of these these species species in in the the Coon Coon Valley Member indicates a close age relationship between sandstones of the Coon Valley and Valley overlying dolomite the assignment assignment of these these sandstones sandstones the overlying dolomite member of the Oneota, and supports the to the Oneota rather than to the Jordan. This This assemblage assemblage of species species is at least as young as the Cordylodus angulatus angulatus Zone Rossodus manitouensis manitouensis Zone. Cordylodus Zone but but could could be from from the the overlying overlying Rossodus These two zones are are from from the the middle middle to to upper upper part part of of the the Skullrockian Skullrockian Stage Stage of of the the Ibexian Ibexian Series (Lower (Lower Ordovician) Ordovician) in the Ibex Ibex area area of western Utah (Ross (Ross and and others, others, 1997). 1997). Sandstone and Coon Valley Valley Member Member are are separated separated These faunas indicate indicate that the Jordan Sandstone by a large hiatus hiatus compared compared with with the the continuous continuous succession successionin in the the Ibex Ibex area area of of Utah, Utah, which which was was 119 �ZONATION CONODONT CONODONT ZONATION MIller MIIler (1988) ( 1 988) one I oneI z e = conodonts conodonts LU <I-. 0 wO a z-J 0 Rossodusmanitouensis Ii z 0 I— (1, 0 z Cordylodus lindstromi . 20 15 I.—. 'Jb z 0 0 . . , .5 .4 '3 C,, 7 I,,,,, It 1 1 7 .1 & 7' T1 0• liii VF FMCVC pJg Burrows B Intraclasts gpJ l r l ~ l a s t s Hunmocky cross-strata @Dolostone O ~ o r l e Ripple cross-strata R i i cross-strala =EEzL Z hlntzei HirsutodontUS simplex ... Clavohamulus elongatus d1 -. )< LU Fryxellodontus inornatus Hirsutodontus 10 z< Clavohamulus hirsutus Cambroistodus minutus 5. • LU lapetog,wthus w C-) UJ Cordylodusangulatus 25 z Subzone Subzone 1t•D• 5 < I- EoconodontUS notchpeakensis — z= < < <x WQ ILl o '- Proconodontus mueller! Trou mTang8nMl o w cross-strata cross-stram Tangentlel cross-strata cross-stmm thick thick hnes h e s are are shale shale drapes drapes MedP.sn to ccoarse-graied M d b m to o a r s w n e dS.S. S.S. m .•: nFimt+gmmd S.S. Fine-gravied S.S. Pebbles Po- Figure9. 9.Measured Measuredsection sectionofofthe theJordan JordanSandstone Sandstoneand andadjacent adjacentunits unitsatatHomer, Homer, Minnesota Minnesota Figure outcropyhighlighting highlightingbiostratigraphic biostratigraphicinterpretation interpretationbased basedon onconodonts conodontsasasreported reportedherein. herein. outcrop, Thevertical verticallines linesshow showthe therelative relativemagnitude magnitudeof of the the hiatus hiatus represented The represented by the unconformity unconformity on top of the Jordan Sandstone. on top of the Jordan Sandstone. deposited rapidly subsiding subsidingmiogeoclinal miogeoclinal carbonate platform. The Thefollowing followingconodont conodont deposited on on aa rapidly units known known in in Utah Utahare aremissing missingbetween betweenthe theJordan Jordanand andCoon CoonValley ValleyatatHomer: Homer: biozonal units Cambrooistodus Cambrooistodus minutus Subzone Subzoneof ofthe theEoconodontus Eoconodontus Zone Zone(uppermost (uppermostTrempealeauan, Trempealeauan, Upper Cordylodusproavus Zone Zone(basal (basalSkullrockian, Skullrockian,Lower Lower Upper Cambrian), Cambrian),three three subzones subzonesof of the Cordylodusproavus Ordovician), Ordovician), two two subzones subzones of the Cordylodus intermedius Zone, Zone, the the Cordylodusprolindstromi Cordylodusprolindstromi Zone, Zone, the Cordylodus Cordylodus lindstromi lindstromi Zone, Zone,and andthe thelapetognathus IapetognathusZone Zone(approximately (approximatelymiddle middle Skulirockian). Skullrockian). InInthe theIbex Ibexarea areaofofUtah, UtahyUpper UpperCambrian Cambriancarbonate carbonatestrata strataare areapproximately approximately 2850 2850ftft (870 (870m) m)thick thickand andare areoverlain overlainby by approximately approximately5000 5000ftft(1525 (1525m) m)of ofOrdovician Ordovicianstrata. strata. The The missing missinginterval intervalat atHomer Homerisisequivalent equivalentto to more more than than 500 500 ftft (150 (150 m) m) of of limestone limestonein in Utah. Utah. The The interval intervalincludes includesseveral severalstratigraphic stratigraphicsequences sequencesthat that include include at at least least two two major major lowstands lowstands of A similar similarlarge large hiatus hiatus is is of sea sealevel, level, as as well well as as several several transgressive transgressive and highstand sequences. A known known on on the the crest crestof ofthe theTranscontinental Transcontinentalarch archin inwestern westernColorado Colorado(Myrow, (Myrow, Ethington, Ethington,& & Miller, Miller,1995), 19951,which whichisisaawestern western extension extensionof of the the Minnesota Minnesota craton. craton. 120 �STOP 4—Road &Road cut cut along alongnorth northside sideofofCounty CountyRoad Road3030(time (timepermitting). permitting).From From County County STOP road 14, 14,travel travel east east on on County County road road 88 for for one one mile mile (becomes (becomesCounty Countyroad road 30 30in inWinona Winona road Continueeast easton onCounty Countyroad road 30 30for for about about 0.7 0.7 miles miles to to road road cut cut (Fig. (Fig. 10). 10). County). Continue The upper upper part part of of Oneota OneotaDolomite Dolomiteand and lowermost lowermost Shakopee ShakopeeFormation Formationof of the the Prairie Prairiedu du The Chien Group are exposed at this stop. The TheOneota OneotaDolomite Dolomite consists consists chiefly chiefly of of tan tan to to gray gray microcrystalline dolostone dolostone in thick to medium irregular beds. The Shakopee Shakopee consists of sandy, microcrystalline beds. The The New Richmond Sandstone Sandstone oolitic and intraclastic dolostone, with intercalated sandstone. The of the Shakopee uppermost part part of of this this exposure. exposure. Deposition Shakopee Formation forms the uppermost Deposition of of these these strata occurred occurred on a carbonate-dominated, laterally extensive strata carbonate-dominated, laterally extensive platform in environments ranging from from supratidal supratidal to to shallow shallow subtidal subtidal (Smith and others, 1993). The The Oneota Oneota Dolomite Dolomite and and Shakopee Shakopee Formation are separated by an unconformity unconformity less meters below below the the New New Richmond Richmond less than than 22meters Sandstone. Features Featuresdiagnostic diagnosticof ofdepositional depositionalorigin, origin,as aswell wellas asthe theunconformity, unconformity, are arelargely largely Sandstone. Stop99will willprovide provide aa better better opportunity opportunity to to more more closely closely inaccessible in this steep road cut. Stop examine the Prairie Prairie du Chien Chien Group. Group. The primary primary purpose purpose of this this stop stop is is to to discuss discuss the the karst karst features features exposed exposed in in this this road roadcut. cut. A well developed developed cave in the Oneota exists at the solution solution horizon near the Oneota-Shakopee Oneota-Shakopee contact. The Theunconformable unconformablecontact contactshows showssubaerial subaerialexposure, exposure,as as evidenced evidenced by by considerable considerable karst development development below below it, and and is is characteristic characteristic of of this this contact contact throughout throughout southeastern southeastern Minnesota and and western western Wisconsin (Smith and others, 1993, 1996). Sinkholes Sinkholes occur occur near near this this contact Maki, 1988; 1988;Magdeline Magdeline and and Alexander, Alexander, contact (Dalgleish (Dalgleishand andAlexander, Alexander,1984; 1984;Alexander Alexander and and Maki, 1995) catastrophic collapse treatment lagoons 1995) and have resulted in catastrophic collapse of several several sewage treatment lagoons (Alexander (Alexander and and Book, Book, 1984; 1984;Alexander Alexander and and others, others, 1993; 1993;Jannik Jannik and and others, others, 1991). 1991). The SW. Evidence for the The cave cave at this outcrop apparently formed in aajoint joint trending trending NE to SW. development development of this solution feature is visible. Ground Groundwater water originally originally flowed flowed horizontally horizontally along along aa permeable permeable bedding beddingplain, plain,widening wideningitself itself through throughdissolution dissolutionas as itit became became the the dominant dominant hydraulic conduit at this horizon. At the intersection of a vertical joint, water moved downward, hydraulic conduit at this horizon. At the intersection of joint, downward, dissolving dissolving the the bedrock bedrock and and increasing increasing the size of the cavity. This This feature feature widened widened from from top top to to bottom, ground-water flow. Characteristic bottom, as as the the conduit conduit captured captured increasing increasing amounts amounts of ground-water Characteristicfeatures features include fracture—and sinuous include aa flat-topped flat-topped ceiling—top ceiling-top of of the original original hydraulic fracture-and sinuous walls formed by the water water dissolving dissolving beds beds of of variable variable permeability. permeability. A A large largecollapse collapse adjacent adjacent to to the thecave, cave, presumably into a void extending into the outcrop, and the alignment of this feature with void extending with aa creek dissolution creek bed on on south south side side of of the the highway, highway, indicate indicate the extensive extensive nature of this type of dissolution within within the the Prairie Prairie du du Chien. Chien. The regional regional direction direction of ground-water ground-water flow with the Prairie du Chien Group is is to to the the southeast—perpendicular southeast-perpendicular to to the the trend of this large dissolution feature. Monitoring Monitoringof of groundgroundwater quality quality within within the the Prairie Prairie du du Chien Chien is complicated complicated by these types of features throughout southeastern southeastern Minnesota. Dye-trace Dye-trace studies studies have have documented documented cases where local flow is in aa direction perpendicular to the regional gradient (Donohue 1991). The The presence presence direction perpendicular to the regional gradient (Donohue and Associates, 1991). of of these these large-scale large-scaledissolution dissolutionfeatures featuresleads leads to to extreme extreme variability in transmissivity, and preclude the isotropic porous media in ground-water ground-water monitoring the treatment treatmentof of the the Prairie Prairie du du Chien Chien Group Group as as isotropic monitoring and and modeling. modeling. 121 �KILOMETERS MILES 1 1 - -0 0 2 - 1 1 3 4 2 6 .-7 8 3 ' 4 8 5 0 10 6 Figure 10. 10. Map Map33on onindex indexmap map (Figure (Figure 5) 5) showing showingthe the locations locationsof of stops stops44 through through 8. 8. STOP overlook of of Mississippi Mississippi River River Valley Valleynear nearWabasha. Wabasha. On STOP 5—Scenic 5ÑSceni overlook On north side of State State Highway Highway 60 60 about about 1.3 1.3miles miles east east of of U.S. U.S. 61 61 (Fig. (Fig. 10). 10). This This overlook overlook provides provides aa visual visual estimate estimate of of the the thickness thickness of of the the lower lower Jordan Jordan Sandstone, Sandstone, St. that lie lie below below our our feet. feet. The St. Lawrence, and Franconia Formations that The upper upper 50 50 ftftof ofJordan Jordan Sandstone, Sandstone,and andlower lower20+ 20+ftftof ofOneota OneotaDolomite Dolomite(Coon (CoonValley Valley Member) Member)are areexposed exposedhere. here.This This outcrop provides an excellent opportunity to examine the sequence bounding unconformity provides an excellent opportunity to examine the sequence bounding unconformity that quartzose Jordan Jordan Sandstone Sandstone below from from the that separates separates well-sorted, well-sorted,finefine- to to coarse-grained, coarse-grained,quartzose overlying overlyingheterolithic heterolithicCoon CoonValley Valley Member. Member. The TheCoon CoonValley Valley Member Member consists consists of very finefine- to coarse-grained coarse-grainedsandstone, sandstone,siltstone, siltstone,shale, shale, and and sandy dolostone. dolostone. The The erosional erosional lag lag marking marking the the unconformity Minnesota (Stop (Stop 3) 3) but but here consists of an unconformity was poorly developed developed at Homer, Minnesota an 2 m thick—that contains intraclastic, poorly sorted, complexly cross-bedded sandstone—i - 2 thick-that contains cross-bedded sandstone-1 abundant abundant pebbles pebbles of of Precambrian Precambrianrocks rocksas aslarge largeas as22cm cminindiameter. diameter. 122 �Note the the considerable considerable difference difference in grain grain size size and and degree degree of of cementation cementation between between the the Note Jordan JordanSandstone Sandstoneand andthe theCoon CoonValley Valley Member. The Theformer formerisisdominated dominatedby bythe the coarse coarseclastic clastic hydrostratigraphic hydrostratigraphic component, the latter by the the mixed mixed carbonate carbonate and and clastic clastic component. component. Permeability of the the mixed mixed carbonate carbonate and clastic component component is as much as three three orders orders of of Permeability magnitude magnitude less less than than that that in in the the underlying underlying coarse clastics. In Inunfractured unfracturedsubsurface subsurfacesettings, settings, this this unit unit and and overlying overlyingunfractured unfractured carbonate carbonate rocks rocks of of the the Hagar Hagar City City Member Member of of the theOneota Oneota Dolomite Dolomite can can act actas asaaconfining confiningbeds, beds, hydraulically hydraulically isolating isolating ground ground water water in in the the Jordan Jordan from from ground groundwater waterininthe theupper upperPrairie Prairiedu duChien. Chien.This Thisseparation separationcan canbe beseen seenininchemical chemical(Alexander, (Alexander, 1990; Setterholm and others, 1991; Smith and Nemitz, 1996; Wall and Regan, 1990; Setterholm and others, 1991; Smith and Nemitz, 1996; Wall and Regan, 1995) 1995) and and hydraulic hydraulicdata data(Barr (Ban-Engineering, Engineering,1996). 1996). STOP STOP6—Lower &Lower Franconia FranconiaFormation Formationnear nearWabasha, Wabasha,Minnesota. Minnesota.Outcrop Outcropisisalong alongwest west side sideof of U.S. U.S. Highway Highway61, 61,1.2 1.2miles milesnorth northof ofState StateHighway Highway60 60(Fig. (Fig.10). 10). The Thelower lowerFranconia FranconiaFormation Formationatat this thisstop stopisisan anexcellent excellentexample exampleof ofthe theheterolithic, heterolithic, very very fine finegrained grainedsandstone sandstoneand andshale shalefacies faciescharacteristic characteristicof of Cambrian Cambrian storm storm and and fairweather fairweather deposits that accumulated on the offshore shelf seaward of the quartzose shoreface sands. deposits that accumulated on the offshore shelf seaward of the quartzose shoreface sands. Thin Thin to tomedium mediumbeds bedsof offeldspathic, feldspathic,variably variablyglauconitic glauconiticsandstone, sandstone,siltstone, siltstone,and andshale shalecommonly commonly occur occurin innormally normallygraded gradedsequences sequencesas asmuch muchas as30 30cm cm thick. thick. Sandstone Sandstonebeds bedspinch pinchand andswell swellasas form form sets setsofofsmall-scale small-scalehummocky hummockycross-stratification, cross-stratification, which which in in aacomplete complete depositional depositional sequence, sequence,pass passtransitionally transitionallyupward upwardinto intoripple ripplecross-stratified cross-stratifiedor orstructureless, structureless,very veryfine finegrained grained sandstone sandstone and andsiltstone, siltstone,which which in in turn turn passes passes upward upward to to shale. shale. Bioturbation Bioturbationisiscommon, common,and and ranges rangesfrom fromisolated isolatedburrows burrows(Planolites (Planolitesand andSkolithos) Skolithos)totonearly nearlyhomogenized homogenizedsediment. sediment. The Thefine-clastic fine-clasticcomponent componentofofthe thelower lowerFranconia FranconiaFormation Formationisishydrostratigraphically hydrostratigraphically similar similarto tothe thesame samecomponent componentthat thatmakes makesup upthe thebulk bulk of of the theSt. St.Lawrence LawrenceFormation Formationseen seenatat Stop Stop3.3.The TheSt. St.Lawrence Lawrenceisiswidely widelyregarded regardedasasaaconfining confiningbed, bed,yet yetthe theFranconia Franconiaisiscommonly commonly designated designatedasasan anaquifer aquiferalong alongwith withthe theunderlying underlyingcoarse coarseclastics clasticsofofthe thefronton Irontonand andGalesville Galesville Sandstones. Sandstones.We Webelieve believethat thatthis thischaracterization characterizationof of the the Franconia Franconia is inaccurate. This Thispart partof of the onia has theFranc Franconia has permeability permeabilityvalues valuesseveral severalorders ordersof of magnitude magnitudelower lowerthan than underlying underlyingcoarse coarse sandstones sandstones(Miller (Millerand and Delin, Delin, 1993). 1993).Core Coresamples samplestaken takenfrom fromoutcrop outcrophad had permeabilites permeabilites of of 0.01 0.006md. md.(MGS (MGSunpublished unpublisheddata, data,1997). 1997).InInaddition, addition,wells wellsfinished finishedabove aboveand andbelow below 0.01--0.006 this thispart partofofthe theFranconia Franconiahave haveover overaa40-foot 40-footdifference differenceininhydraulic hydraulichead head(Wenck (Wenckand andAssoc., Assoc., 1997). 1997). STOP STOP7—Road 7-Road cut cuton onU.S. U.S.Highway Highway61 61near nearWabasha. Wabasha.From FromState StateHighway Highway60, 60,take takeState State Highway Highway61 61south south1.8 1.8miles milestotoroad roadcut cuton onwest westside sideofofroad road(Fig. (Fig.10). 10). The metersofoffronton IrontonSandstone Sandstoneand andabout about44meters metersof ofthe theoverlying overlyingFranconia Franconia Theuppermost uppermost55meters Formation are exposed here in a steep road cut. The fronton consists of poorly sorted sandstone Formation are exposed here in a steep road cut. The Ironton consists of poorly sorted sandstone that thathas hasaapervasive pervasivebioturbated bioturbatedtexture, texture,with withburrows burrowsasasmuch muchasasa acentimeter centimeterinindiameter. diameter. Shale Shaleand andsiltstone siltstoneoccur occuras asaamatrix matrixbetween between sand sandgrains grains and and as as lenticles. lenticles. Moderately Moderatelytotowellwellsorted sortedsandstone sandstonebeds bedsare areinternally internallystructureless structurelessororcontain containill-defined ill-definedtrough troughand andtangential tangential cross-strata cross-stratawith withrare rareshale shaledrapes drapesand andreactivation reactivation surfaces. surfaces. These Thesefeatures featuresare areindicative indicativeofof deposition deposition in inaashoreface shorefaceand andtidal tidalflat flatenvironment. environment. The Theoverlying overlyingstrata strataofofthe theFranconia Franconia Formation Formationconsists consistsmostly mostlyofoffeldspathic, feldspathic,glauconitic, glauconitic,finefine-totovery veryfine finegrained grainedsandstone sandstonewith with hummocky hummockycross-strata cross-strataand andtempestites tempestitesthat thatwere weredeposited depositedon onthe theoffshore offshoreshelf. shelf.These Theselower lower 123 �Franconia Franconia Formation Formation strata strata are are better better exposed exposed at at Stop Stop 6. 6. The The contact contact between between the the Ironton Ironton Sandstoneand andFranconia FranconiaFormation Formationisistransitional transitionaland and records records gradual gradual flooding flooding during duringan an overall overall Sandstone rise rise in in sea sealevel. level. The quartzose quartzosesandstone sandstoneof of the the fronton Ironton exposed exposed includes includesaa pebbly pebbly sandstone sandstonebed bed that that may may The mark aa regional regional unconformity. unconformity. The Theupper upper part part of ofthe theunderlying underlyingEau Eau Claire ClaireFormation Formation and and mark lower lower approximately approximately two-thirds two-thirds of of the the fronton/Galesville Ironton/Galesville Sandstones Sandstones (below (below level level of of this this exposure)form formaacoarsening-upward coarsening-upwardsequence sequencethat thatrecords recordsdeposition depositionininprogressively progressivelyshallower shallower exposure) water Ironton/GalesvilleSandstones Sandstones fines fines upward, upward, water conditions. conditions. The Theupper upperone-third one-thirdofofthe thefrontonlGalesville recordingdeeper deeperwater waterconditions. conditions.The Thenearly nearlystructureless, structureless,resistant resistantbed bedabout about22mmabove abovethe the recording base base of of this thisoutcrop outcropisisaa1.5-2 1.5-2mmpebbly pebblysandstone sandstonelag lagthat thatseparates separatesthese thesedecameter-scale decameter-scale sequences. sequences.This Thispebbly pebblylag lagcan canbe bephysically physicallytraced tracedfrom fromthe theTwin TwinCities Citiesarea areasouth southinto intoIowa, Iowa, and andfrom fromsouthwestern southwesternWisconsin Wisconsinwestward westwardatatleast least80 80kilometers kilometersinto intothe thesubsurface subsurfaceof ofsouthsouthcentral centralMinnesota. Minnesota.ItItmay mayrepresent representaatransgressively transgressivelyre-worked re-worked lag lag that that developed developed subaerially subaerially when when the the "Ironton-Galesville "Ironton-Galesville shoreline" shoreline"was wasininextreme extremebasinward basinwardpositions. positions. Compare Compare the the hydrostratigraphic hydrostratigraphic properties of the the Franconia Franconia Formation Formation and and Ironton Ironton Sandstone.The Thefronton Irontonisiscomposed composedmostly mostlyof ofthe thecoarse-clastic coarse-clasticcomponent, component,specifically specificallyof of aa Sandstone. poorly poorlycemented cementedmostly mostlyfine fine-- very verycoarse coarsegrained, grained,shaly shalysandstone sandstonewith withmoderate moderateporosity porosityand and permeability. The TheFranconia Franconiaabove aboveisisdominated dominatedby by the thefine fineclastic clastic component, component, which which is is finer finer permeability. grained Ironton,and and contains contains discrete, discrete, continuous continuous laminations laminations of of grainedand andbetter bettercemented cementedthan than the the fronton, shale. fronton. The shale.ItItisismarkedly markedlylower lowerin in porosity porosity and and permeability than the Ironton. The common common practice practice of of lumping lumpingthese thesetwo twounits unitstogether togetheras asaasingle singleaquifer aquiferis is not not reasonable, reasonable,and and gives gives the the erroneous erroneous impressionthat thatthey theyshare sharesimilar similar hydrogeologic hydrogeologicattributes attributes (see (see Stop 6 for impression for additional additional discussion). discussion) STOP STOP8—Road %Road cut cuton onU.S. U.S.Highway Highway61 61near nearWabasha. Wabasha.From FromState StateHighway Highway60, 60,take takeU.S. U.S. 61 61south south2.3 2.3miles milesto toroad roadcut cuton onwest westside sideof ofroad road(Fig. (Fig.10). 10). Intethngering InterfingeringEau EauClaire ClaireFormation Formationand andIronton-Galesville Ironton-Galesville(Wonewoc) (Wonewoc)Sandstones Sandstonesare are exposed in this long road cut. There are several interesting sedimentologic features, including exposed in this long road cut. There are several interesting sedimentologic features, including hummocky cross-strata, cross-strata, tempestites, tempestites, trough trough cross cross stratified stratified sandstone, sandstone, and and coarse coarse sand sanddune dune hummocky forms formsdraped drapedby byshale. shale.Trilobite Trilobitemolds moldsare areabundant abundantatatthis thisstop stopininthe thehummocky hummockystratified stratified sandstone sandstonefacies. facies.This Thisoutcrop outcropisisone oneofofonly onlytwo twoknown knownexposures exposuresininthis thisarea areathat thatrecord recordthe the boundary boundarybetween betweenthe theMarjumiid Marjumiidand andPterocephaliid Pterocephaliidbiomeres, biomeres,aamajor majorisochronous isochronousextinction extinction event correlatable across all of North America. event correlatable across all of North America. This Thisexposure exposureisisaagood goodexample exampleofofthe thesame samefine-clastic fine-clastichydrostratigraphic hydrostratigraphiccomponent component that thatdominates dominatesthe thelower lowerFranconia Franconia and and St. St. Lawrence Lawrence Formations seen at stops 3 and 6. Core Core samples samples from fromall allthree threeunits unitsshow showaaconsiderably considerablylower lowerdensity densityofoffractures fracturesalong alongbedding bedding planes. planes. STOP west STOP9—Vern 9-Vern Keller KellerQuarry. Quarry.Along Along westside sideofofCounty CountyRoad Road6,6,1.15 1.15miles milessouth southof ofState State Highway Highway19. 19.Goodhue GoodhueCounty County(Fig. (Fig.11). 11). About About30 30mmofofthe themiddle middlepart partofofthe thePrairie Prairiedu duChien ChienGroup Groupisisexposed exposedininthis thisquarry. quarry. Relatively Relativelypure puredolostone dolostonebeds bedsof ofthe theuppermost uppermostOneota OneotaDolomite Dolomiteare areunconformably unconformablyoverlain overlain by ShakopeeFormation Formationabout about22meters bysandy sandydolostone dolostoneand andsandstone sandstoneofofthe theShakopee metersabove abovethe thefloor floorofof the thequarry. quarry. This Thisunconformity unconformityisisregional regionalininextent, extent,traced tracedfrom fromthis thisarea areainto intothe theMichigan Michigan basin basin by bySmith Smithand andothers others(1993). (1993).Deposition Depositionofofthe thePrairie Prairiedu duChien ChienGroup Groupoccurred occurredon onaa shallow shallowcarbonate carbonateplatform platformduring duringaarelatively relativelyhighstand highstandof ofsea sealevel levelthat thatflooded floodedmost mostof of North North 124 �Map 4 KILOMETERS MILES 11 1 00 00 I1 — 22 1 1 33 — 22 44 = 55 33 6B = It 17 88 55 90 —10$0 6 Figure Figure 11. 11.Map Map44on onindex indexmap map(Figure (Figure5) 5) showing showingthe the locations locationsof of stops stops99and and10. 10. Americaduring duringthe the Early Early Ordovician Ordovician (Smith (Smith and and others, others, 1993; 1993; Smith Smith and Clark, 1997). 1997). These These America strataare are typical typical of of "tropical" "tropical" carbonate carbonatesystems, systems,dominated dominatedby oolitic oolitic and peloidal grainstones grainstones strata subtidal andpackstones, packstones,and andstromatolitic stromatoliticand andwavy-laminated wavy-laminatedboundstones boundstonesdeposited depositedininshallow shallowsubtidal and tosupratidal supratidalsettings. settings.Stromatolites Stromatolitesare areabundant abundantininthis thisquarry: quarry:digitate digitateforms formscan can be be discerned discerned to inaafew fewplaces placesininthe theuppermost uppermostOneota, Oneota,and andcabbage-head cabbage-headstromatolites stromatolitesare arecommon commonininthe the in Shakopee.Evidence Evidencefor forsubaerial subaerialexposure exposureincludes includesabundant abundantmud mudcracks, cracks,intraclastic intraclasticbreccias, breccias, Shakopee. and andsilicified silicifiedand andmoldic moldicanhydrite. anhydrite. Thereare aresome someinteresting interestingquestions questionsthat thathave haveyet yetto tobe be answered answeredabout aboutthe thedeposition depositionof of There the ChienGroup: Group: thePrairie Prairiedu duChien 1) 1)What What isis the the fundamental fundamentalcontrol control that that blocked blocked detrital detrital input input when when most most of of the the Oneota Oneota was deposited? deposited?Much Muchofofthe theOneota Oneotaconsists consistsofofstrata stratathat thatwere wereapparently apparentlydeposited depositedalong alongaa was regional shoreline in which siliciclastics were nearly absent. regional shoreline in which siliciclastics were nearly absent. 2)What What are arethe thefundamental fundamental controls controls that that led led to to an an arid, arid, tropical tropical carbonate carbonate style style of of 2) deposition,when whenboth bothyounger youngerand andolder oldercarbonate carbonatedeposition depositionwas wasreminiscent reminiscentof of modern modemcoolcooldeposition, water, water,temperate temperateconditions? conditions? This Thispart partof ofthe thePrairie Prairiedu duChien ChienGroup Groupconsists consistschiefly chieflyof of the the carbonate-rock carbonate-rockcomponent. component. ItItisisan anexcellent excellentexample exampleof of the the importance importancein in delineating delineatingthe the presence presence and and position position of of fractures fractures that that are arethe theprincipal principalgroundwater groundwaterconduits. conduits. AAprominent prominenthorizontal horizontalinterval intervalofofdissolution dissolution features, features,some somewith withstalactites, stalactites,occurs occursalong alongthe theOneota-Shakopee Oneota-Shakopeeunconformity unconformityininthis thisquarry. quarry. AAsecond seconddissolution dissolutionlayer layerisisvisible visiblehigh highon onthe thequarry's quarry's south southwall, wall,just just below belowaa1-2 1-2m mbed bedof of coarse coarsesandstone. sandstone.Work Workby byCalvin CalvinAlexander Alexanderfrom fromthe theUniversity University of of Minnesota Minnesota suggests suggests that that these these dissolution dissolution horizons horizons have have an animportant importantcontrol control on on the thehydrogeologic hydrogeologicattributes attributes of of the the Prairie Theyare arelikely likelymajor majorconduits conduitsfor forground-water ground-waterflow, flow,and andenhance enhancethe the Chien. They Prairie du du Chien. development developmentof ofsinkholes sinkholeswhere wherethey they are are nearer nearer the surface. surface. Other Othernotable notablefeatures featuresinclude includethe the 125 �the carbonate carbonate rock rock exposed exposed on the the south south wall wall of of the thequarry—in quarry-in tight, unfractured nature of the contrast with with the the carbonate carbonaterock rock of of the the Shakopee Shakopeeseen seen at at Stop Stop 11 where it is closer to the surface, contrast surface, and and secondary secondary porosity porosity isisbetter betterdeveloped. developed. Stop 10—Spring 10ÑSprin near nearVern VernKeller KellerQuarry. Quarry.From Fromquarry quarrycontinue continuesouth south0.7 0.7 miles miles on County Stop Road Road 6. 6. Turn Turneast easton onto togravel gravel road road and and travel travel 0.1 miles (Fig. 11). 11). Spring Springisison on north northside side of road on PRIVATE PROPERTY. of road on PRIVATE PROPERTY. Elevation Elevationof of this this resurgent resurgent spring spring approximately approximatelythe the same same as as the Oneota-Shakopee Oneota-Shakopeecontact contact seen seen at at the the previous previous stop. stop. This supports supports the hypothesis hypothesis that dissolution dissolution features along along the the unconformity unconforrnitymay maybe beaamajor majorconduit conduitfor forgroundwater groundwaterflow. flow. REFERENCES REFERENCES CITED CITED Adams, R. R. L., L., 1978, 1978,Stratigraphy Stratigraphy and and petrology petrology of of the the lower lower Oneota Oneota Dolomite Dolomite(Ordovician), (Ordovician), south-central Wisconsin: Wisconsin Wisconsin Geological Geological and and Natural Natural History Survey Field Trip Guidebook Guidebook3, 3, p. p. 82-90. 82-90. 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Nelson, Nelson, C.A., C.A., 1956, 1956,Upper UpperCroixan Croixanstratigraphy, stratigraphy,Upper UpperMississippi MississippiValley: Valley: Geological GeologicalSociety Society of America Bulletin, Bulletin, v. v. 67, 67, p. 165-183. 165-183. Odom, Odom, I.E., 1975, 1975,Feldspar-grain Feldspar-grainsize sizerelations relationsin inCambrian Cambrianarenites, arenites,Upper UpperMississippi MississippiValley: Valley: Journal Journal of of Sedimentary SedimentaryPetrology, Petrology, v. v. 45, 45, no. no. 3, 3, p. p. 636-650. 636-650. Odom, I.E., 1978, 1978, Mineralogy Mineralogy of of Cambrian Cambrian sandstones, sandstones, Upper Upper Mississippi Mississippi Valley: Wisconsin Wisconsin Geological Geological and and Natural Natural History History Survey Survey Field Trip Guidebook 3, p. 23-45. Ostrom, Ostrom, M.E., 1964, 1964,Pre-Cincinnatian Pre-CincinnatianPaleozoic Paleozoiccyclic cyclicsediments sedimentsin in the the Upper Upper Mississippi MississippiValley: A 1-398. A discussion: discussion:Kansas KansasGeological GeologicalSurvey SurveyBulletin Bulletin169, 169,p.p.38 381-398. Ostrom, M.E., M.E., 1970, 1970,Sedimentation Sedimentation cycles cycles in in lower lower Paleozoic Paleozoic rocks rocks of of western westernWisconsin: Wisconsin: Ostrom, Wisconsin Wisconsin Geological Geologicaland and Natural Natural History History Survey Survey Information Information Circular Circular11, 11,p. p. 10-34. 10-34. Palmer, Palmer, A.R., 1960, 1960,Some Someaspects aspectsof of the the early early Upper Upper Cambrian Cambrian stratigraphy stratigraphyof of White WhitePine PineCounty County ,Nevada, Nevada, and and vicinity, vicinity, in Geology Geologyof of east eastcentral central Nevada: Nevada: Intermountain Intermountain Association of Petroleum PetroleumGeologists GeologistsGuidebook Guidebook11th 11thAnnual Annual Field Field Conference, Conference, p. 53-58. 53-58. 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Runkel, Runkel, A.C., 1994, 1994, Deposition Deposition of of the the uppermost uppermost Cambrian Cambrian (Croixan) (Croixan) Jordan Jordan Sandstone, Sandstone, and and the the nature natureof of the the Cambrian-Ordovician Cambrian-Ordovicianboundary boundaryin inthe theUpper UpperMississippi MississippiValley: Valley: Geological Geological Society Societyof of America AmericaBulletin, Bulletin,v.v. 106, 106,p. p. 492-506. 492-506. Runkel,A.C., Runkel,A.C.,1996a, 1996a,Geologic Geologicinvestigations investigationsapplicable applicableto to groundwater groundwatermanagement, management,Rochester Rochester Metropolitan Metropolitanarea, area,Minnesota: Minnesota:Minnesota MinnesotaGeological GeologicalSurvey SurveyOpen-File Open-FileReport Report96-1, 96- 1, 27p. 27 p. Runkel., Minnesota: Minnesota Runkel., A.C., 1996b, 1996b,Bedrock Bedrock geology of Houston County. Minnesota: Minnesota Geological Geological Survey Survey Open File Report 96-4, 1lip. lp. 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Thesis, University Sargent, M.L., 1991, 1991, Sauk Sequence: Sequence: Cambrian System through Lower Ordovician Series, in D.F., and Eidel, J.J., J.J., eds., Interior cratonic basins: Leighton, M.W., Kolata, D.R., Oltz, D.F., basins: American Association of Petroleum Geologists Memoir 551, 1, p. 75-86. Setterholm, D.R., Runkel, Runkel, A.C., Cleland, Cleland, J.M., Tipping, R., Mossier, J.M., Kanivetsky, R., and Hobbs, H. C., 1991, 1991, Geologic Geologic factors affecting the sensitivity sensitivity of of the Prairie du ChienJordan Jordan Aquifer: Aquifer: Minnesota MinnesotaGeological GeologicalSurvey SurveyOpen-File Open-FileReport Report991-5,18 1-5,18 p. Simo, J.A., J.A., Choi, L., Freiberg, Simo, Freiberg, P., P., Byers, C.W., C.W., Dott, R.H., R.H., Jr., and and Saylor, Saylor, B., B., 1997, 1997, Sedimentology, sequence stratigraphy, and paleoceanography of the Middle Sedimentology, Middle Ordovician Ordovician Wisconsin, in Mudrey, M.G.,ed., M.G.,ed., Guide to field trips trips in in Wisconsin Wisconsin and and adjacent adjacent of eastern Wisconsin, areas of Minnesota: Minnesota: Wisconsin Geological Geological and and Natural Natural History History Survey, Survey, p. 95-114. 95-1 14. Sloan, R.E., ed., 1986, 1986, Middle and Late Ordovician lithostratigraphy of the Upper Mississippi Valley: Minnesota Geological Survey Report of Investigations 3 5 ,232p. 232~. Valley: Investigations 35, Sloss, L.L., 1963, 1963, Sequences in the cratonic interior of North America: Geological Society of America Bulletin, Bulletin, v. 74, p. 93-114. 93-1 14. 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Investigations 95-41 15,76 Visocky, A.P., A.P., Sherrill, Sherrill, M.G., M.G., and Cartwright, Cartwright, K., 1985, 1985, Geology, hydrology, and water quality quality of the Cambrian Cambrian and and Ordovician Ordovician Systems in northen northen Illinois: illinois Illinois State State Geological Geological Survey and Illinois Illinois State State Water Survey Cooperative Groundwater Groundwater Report Report 10, 10, 136 136p. p. Wall, D.B., and Regan, C.P., C.P., 1994, 1994, Water quality and sensitivy of the Prairie du Chien Chien /Jordan /Jordan and Regan, Aquifer ininwestern westernWinona WinonaCounty, County,Minnesota: Minnesota: Unpublished Unpublished report of the the Minnesota Minnesota Pollution Control MN. Pollution ControlAgency, Agency, Division Division of of Water Water Quality, Quality, St St Paul, Paul, MN. Wenck and Associates, Associates, Inc., Inc., 1997, Phase 11: II: Detailed site investigation report and Phase II Wenck investigation report I1 workplan for the hydrogeologic of the proposed proposed Red Wing Wing ash disposal hydrogeologic investigation investigation of facility facility expansion, expansion, 36 36 p. p. Witzke, B.J., Ludvigson, Ludvigson, G.A., G.A., and and Day, Day, J., eds., 1996, 1996,Paleozoic Paleozoic sequence sequencestratigraphy: stratigraphy:Views Views from from the North North American American craton: Geological Geological Society Society of America Special Paper 306, 446 p. 130 ��FIELD FIELD TRIP TRIP#5 #5 MINNESOTA MINNESOTA RIVER RIVERVALLEY VALLEYAND AND VICINITY, VICINITY, SOUTHWESTERNMINNESOTA MINNESOTA SOUTHWESTERN Leaders: D.L. D.L.Southwick Southwick and and Carrie CarrieJ. J. Patterson Patterson Leaders: INTRODUCTIONTO TOTHE THEGEOLOGY GEOLOGYOF OFPRECAMBRIAN PRECAMBRIANROCKS ROCKSIN INTHE THE INTRODUCTION MINNESOTA RIVER VALLEY MINNESOTA RIVER VALLEY D. D.L. L.Southwick Southwick The Precambrian Precambrian rocks rocks exposed exposed in inthe theMinnesota MinnesotaRiver RiverValley Valley are are within within an anArchean Archean The gneiss terrane terranethat thatconstitutes constitutesthe thesouthernmost southernmostsubprovince subprovince of of the the Superior SuperiorProvince Provinceof ofthe the gneiss CanadianShield. Shield.The TheMinnesota MinnesotaRiver RiverValley Valley(MRV) (MRV) subprovince subprovince is is further further subdivided subdivided into into Canadian fourtectonic tectonicblocks blocks by byregional regionalENE-trending ENE-trending shear shear zones zones (Fig. (Fig.1;1;Southwick Southwickand andChandler, Chandler, four 1996).This Thistrip tripwill willfocus focuson onexposed exposedrocks rocksof ofthe theMorton Mortonand andMontevideo Montevideoblocks, blocks,which whichare are 1996). EXPLANATION' EXPLANATION TECTONIC TECTONICELEMENT ELEMENT Sioux Quartzlto P.nok.an Ponokoanoreg.n orogon (undlvld.d) (undivided) ROCKTYPES TYPES ROCK AGE AGE Red sandstone and shale Middle Middle Proterozotc Proterozoic a (51,100Ma) Ma) (1,100 Quartzite Quartzite Early Early Pmterozok Proterozoic (1,630-1,770Ma) Ma) (1,630.1,770 'fl /1 Supracrustal SuPracrustal endIntrusive Intrusiverocks rocks and manytypes; types: ofofmany alsoArchean Archeangnelss gneiss also Penokean rewwked reworked InInPenokean events events Early Early Proterozoic Proterozoic (depositional (depositional andemplacement emplacement and 80681.770-2.200 1,770-2.200 ages Ma) Ma) Greenstone-belt Greenstone-belt 1tNcassociation. association, Nthlc granitoidIntrusions Intrusions granitold LateArchean Archean Late Ma) ('2.700Ma) (2,700 Greenatone-beft NtNc association, Uncertain;Late Late Uncertain; Archeanand/or and/or Arctiean EarlyProterozoic Proterozoic Early SuperiorProvince Province Superior Wawa W a w subprovlno. aubprovlnco (undivided) (undlvldod) ' VaMoy mibprovlnce ffffl'Jffl) Ilifirnillil lowtotomoderate moderate low orade rnetarnor~hic metamorphic . grade 4-; Location Map Regionalshear shearzone zoneorortectonic tectoniccontact; contact;barbs barbs Regional indicatedirection directionofofdip dipasasInterpreted interpreted from Indicate from geophysical models. geophysical models. IOWA 0 30 - Quartzofeldspathic Quartzofeldspathic MiddletotoLate Late Middle gneiss,granitold granitoid gnelsa, Archean(3,600(3,600Archean ~ ~ ~ I U S I O ~ S Intrusions 2,600Ma) Ma) 2,600 60 KNOm.tws Figure Figure1.1.Tectonic Tectonicsketch sketchmap mapof ofPrecambrian Precambrianterranes terranesin insouthwestern southwesternMinnesota. Minnesota.The TheMinnesota Minnesota River RiverValley Valley subprovince subprovinceconsists consistsof of the the Benson, Benson, Montevideo, Montevideo, Morton, Morton, and and Jeffers Jeffers blocks. The The Taunton Tauntonbelt beltisisa anarrow narrowseptum septumofofrelatively relativelylow lowgrade grademetavolcanic metavolcanicrocks rocksalong alongthe theYellow Yellow Medicine shear zone, which marks the boundary between the Montevideo and Morton blocks. Medicine shear zone, which marks the boundary between the Montevideo and Morton blocks. The Theline lineindicates indicatesthe thelocation locationofofgeophysical geophysicalprofiles. profiles.From FromSouthwick Southwickand andChandler Chandler(1996). (1996). 133 �central two two blocks blocks of the the subprovince. subprovince. The Theboundary boundarybetween betweenthese theseisisthe theYellow Yellow Medicine Medicine the central shear zone (YMSZ), (YMSZ),aamajor majorcrustal crustal feature feature that that is is well well delineated delineated aeromagnetically aeromagnetically but does does not crop crop out. The TheYMSZ YMSZcrosses crossesthe the Minnesota MinnesotaRiver River between betweentrip trip stops stops66 and and 77 (Figs. (Figs. 11 and and 2). 2). At stops stops 11 through through 6, 6, south south of the the YMSZ, we will see features of the Morton block and at Stops 6 through ii11we wewill willsee seefeatures featuresof ofthe theMontevideo Montevideoblock. block. The characteristic characteristicrock rock type type of of both blocks blocks is a modally layered gneiss gneiss that falls falls generally generally tonalite to granodiorite granodiorite range in bulk composition (Goldich and others, 1980a 1980a and b). within the tonalite irregular blocks of mafic gneiss, gneiss, This rock type, together together with less less abundant abundant layers, layers, lenses, lenses, and irregular amphibolite, constitutes that Morton Gneiss amphibolite,and and various various types types of aluminous alurninous gneiss, constitutes Gneiss south south of the YMSZ and the Montevideo Montevideo Gneiss north of it. Alert readers will note note the the correspondence correspondence of the the principal principal map mapunit unitwithin withinit. it. Mineral-assemblage between the block name and the name of data indicate that the Morton and Montevideo gneisses were metamorphosed metamorphosed under under conditions conditions of the upper upper amphibolite amphibolite and and granulitic granulitic facies (Grant, (Grant, 1973; 1973; Perkins and Chipera, Chipera, 1985). 1985). Retrograde processes Montevideo Gneiss Retrograde processeshave have affected affectedaa considerable considerablearea area of the Montevideo Gneissbut are are evident evident only locally in the Morton. The Morton and by granite (adamellite, and Montevideo Montevideo gneisses were invaded by (adamellite, in the the terminology favored favored by by Goldich Goldich and and others, others, 1980a and and b) b) at two different different times during the terminology Archean. 1 of 980a) Archean. The Thefirst firstepisode episodeof ofgranite graniteemplacement emplacement(adamellite(adamellite-1 of Goldich Goldichand and others, others,11980a) fabric in in the gneissic host rocks; preceded the development of the predominant metamorphic fabric that fabric passes passes through the the granite granite bodies, bodies, most most of of which which are are aplitic aplitic or or pegmatitic, pegmatitic,without without discernable change in in orientation. orientation. In addition, addition, much granite of this this generation generation possesses possesses of Goldich metamorphic texture. The The second second episode episode of of granite granite emplacement emplacement (adamellite-2 of and others, 11980a) 980a) occurred occurred after after the the main main fabric-forming fabric-forming events. events. Most intrusions intrusions of of this this generation generationlack lack internal internalfabric, fabric,although although some someshow show aa weak foliation foliation and therefore therefore may be latelateAdamellite-2 intrusions intrusions range from to post-tectonic. post-tectonic. Good Good igneous igneous textures textures are the norm. Adamellite-2 aplitic to medium-grained granitic in grain size and from thin dikes and sills to batholiths in form and scale. The TheSacred SacredHeart HeartGranite Granite(Stop (Stop6) 6)forms formsaa regional-scale, regional-scale, sheet-like sheet-like intrusion intrusion several kilometers kilometers in in thickness thickness that that is is interpreted interpreted to to be be of of the adamellite-2 generation. generation. The Ortonville and Fort Ridgeley granites are late- to post-tectonic post-tectonic masses that also are of of the the adamellite-2 adamellite-2 type and and are are assumed assumed to to be approximately approximately coeval with the Sacred Sacred Heart. Between colleagues devoted huge efforts efforts to to pioneering pioneering Between 1950 1950 and 1980, 1980, S.S. Goldich and colleagues geochronologic studies geochronologic studies of the the Morton Morton and and Montevideo Montevideo gneisses gneisses and and the various various granitic granitic rocks rocks that are associated associated with with them them (Goldich (Goldich and and Wooden, Wooden, 1980; 1980; Goldich and others, others, 1980a 1980a and and references therein). components of both the Morton references therein). The Thegneisses gneissesproved provedto tobe be (1) (1)very very old, old, with components and Montevideo as old as about 3,600 Ma, and (2) geochronologically as about 3,600 Ma, and (2) geochronologically complex, complex, with with several several Archean events events recorded recorded isotopically. isotopically. Moreover, Moreover, the the Goldich Goldich group group found found the discernable Archean "adamellite 1" the geologically geologically straightforwardstraightforward"adamellite 1" rocks rocks to to be be isotopically isotopically complex complexas as well, and even the "adamellite 2" rocks rocks to to yield yield less less than thandefinitive definitive crystallization crystallization ages. ages. Goldich's appearing "adamellite interpretation of interpretation of the the geologic geologichistory historyof of the theMRV MRV subprovince subprovinceisis presented presentedin inTable Table1.1. Goldich emphatically type represented represented genuine Goldich emphaticallybelieved believedthat that the the granite graniteof the the adamelliteadamellite- 1 type igneous i.e., true true intrusion. intrusion. Others contended Others have contended igneous importation importationof of magma magma from from a distant source; i.e., that some, some, if not not all, all, of the the early early granite granite was derived more or less locally through partial partial melting melting of the gneis sichost. host. A major question persists as to to whether whether the the pink pink leucosomatic leucosomatic components components gneissic of the Morton 1 Morton Uneiss Gneissin inthe thevicinity vicinityof ofMorton Mortoncrystallized crystallizedfrom frominjected injectedmelt meltofofadamelliteadamellite-1 134 �Figure 2. Locations of field-trip stops for Day 1. More detailed location maps accompany the individual stop descriptions. �Table1.1.Summary Summaryofofprincipal principalPrecambrian Precambrianevents eventsininthe theMinnesota MinnesotaRiver RiverValley Valley subprovince. subprovince. Table Modified and and interpreted interpreted from from Goldich Goldich and and Wooden Wooden (1980); Goldich and others others (1980a). (1980a). Modified 1800 Ma Ma event event(Proterozoic): (Proterozoic): Emplacement Emplacement of of small small intrusions; intrusions; local local 1800 retrogade retrogademetamorphism, metamorphism,shearing shearing 2600 2600Ma Maevent eventEmplacement Emplacementofofpost-kinematic post-kinematicaplite apliteand andpegmatite pegmatitedikes dikes Emp1acemen.tof of Sacred SacredHeart Heart Granite, Granite, other other granite granitebatholiths, batholiths,and and Emplacemen.t associated associated minor minor intrusions intrusions ("adamellite-2"; ("adamellite-2"; late-kinematic) late-kinematic) High-grade High-grade metamorphism, metamorphism, deformation deformation of of gneiss gneiss 3100 Ma event 3100Maevent High-grade High-grademetamorphism, metamorphism,deformation deformationof of gneiss gneiss Emplacement Emplacementof ofminor minorgranitoid granitoidintrusions intrusions("adamellite("adamellite-1") 1") 3600 3600 Ma Ma event event Intrusion Intrusionof oftonalite, tonalite,granodiorite granodioriteinto intoheterolithic heterolithicprecursor precursorof of layered layered gneiss gneiss typeor orfrom frommelts meltsdeveloped developedthrough throughanatexis anatexisof ofpre-existing pre-existinggranodioritic granodioritictototonalitic tonaliticgneiss. gneiss. type We and2A. 2A. We will will have have an anopportunity opportunityto toform formour ourown ownconclusions conclusionsatatstops stops22and Although the theprincipal principalrock-forming rock-forming events events responsible responsible for for the theformation formationof ofthe theMRV MRV Although subprovinceoccurred occurredover overaabillion-year billion-yearinterval intervalof ofArchean Archeantime, time,there thereare areclear clearindications indicationsof of subprovince further furthergeologic geologicactivity activityin in the the Early Early Proterozoic. Proterozoic. The Thesubprovince subprovincelay lay in in the the cratonic cratonicforeland foreland (Superiorcraton) craton)with with respect respectto toPenokean Penokeantectonism tectonism in in the the interval interval between between 2.1 2.1 and and 1.7 1.7Ga. Ga. (Superior We are arejust just beginning beginningto torecognize recognizeand andquantify quantifyevents eventsand and responses responses recorded recorded in in the the foreland foreland We rocks rocksthat thatwere wereengendered engenderedby bytectonic tectonicprocesses processeswithin withinthe thePenokean Penokeanorogen orogen (Southwick (Southwickand and Chandler,1996; 1996;Holm Holmand andothers, others,1998), 1998),the the axis axis of of which which lies lies only a few 10's 10's of kilometers kilometers to to Chandler, theeast eastof ofpresent presentMRV MRV exposures. exposures. Proterozoic Proterozoicevents eventsinclude include(1) (1)the theemplacement emplacementof of at at least least the twoand andpossibly possiblyasasmany manyas asfour fourswarms swarmsof ofdiabase diabasedikes; dikes;(2) (2)the the emplacement emplacementof of small smallintrusive intrusive two plugsthat thatrange rangein incomposition compositionfrom fromperidotite peridotiteto togranite; granite;and and(3) (3) differential differential vertical vertical movement movement plugs on onblock-bounding block-boundingshear shearzones, zones,with withconcomitant concomitantdevelopment developmentof of brittle brittlestructures structuresand and retrograde retrograde metamorphic metamorphiceffects. effects. No No discussion discussionofofthe theMRV MRVsubprovince, subprovince,regardless regardlessofofbrevity,, brevity,.is is complete completewithout withoutan an acknowledgment 1956) over acknowledgmentof ofthe theexcellent excellentgeologic geologicmapping mappingdone doneby by Ernest ErnestLund Lund (1950, (1950,1956) over45 45 years Lund'swork workwas wasthe thestarting startingpoint pointfor forsubsequent subsequentgenerations generationsof offield fieldinvestigations investigations yearsago. ago.Lund's (Himmelberg, (Hirnmelberg, 1968; 1968; Grant, Grant, 1972; 1972; Bauer, Bauer, 1980) 1980) and and was was the the principal principal framework framework for for the the geochronologicinvestigations investigationsofofGoldich Goldichand andcolleagues. colleagues.Those Thoseofofus usworking workingtoday todayfind findLund's Lund7s geochronologic maps mapstotobe beproof proofofofthe themantra mantrathat thatcareful carefulgeologic geologicobservations observationsand anddescriptions descriptionsare aretimeless; timeless; their theirvalue valuewill willoutlast outlastthe theinterpretational interpretationalframework frameworkwithin withinwhich whichthey theywere weremade. made. 136 �FIELD TRIP FIELD TRIPSTOPS—DAY STOPS-DAY 11 Stop 1—MRV 1-MRV geomorphology; geomorphology; Proterozoic diabase dikes and and walirock wallrock of of Archean Archean Morton Morton Stop Morganquadrangle, quadrangle,T. T.112 112N.-R. N.-R. 34 34W.-Section W.-Section 23AAC. 23AAC. Gneiss. Morgan At this locality locality south Franklin, newcomers can readily comprehend comprehend several south of Franklin, several elements elements of post-Precambrian geologicalhistory history that that bear bear on the condition and distribution post-Precambrian geological distribution of the the Precambrian Precambrian rock outcrops on the valley Point (1): (1): The ThePrecambrian Precambrianrocks rocks were were deeply deeply weathered weathered valley floor. floor. Point prior to continental glaciation in the Quaternary. Quaternary. Actually, Actually, most of the weathering weathering occurred prior to the Late Cretaceous. ManyMRV MRV outcrops, outcrops, such such as these, are incipiently substantially Cretaceous. Many incipiently to substantially weathered; they represent material that lay just pre-Cretaceous weathering just at the base of the pre-Cretaceous profile. Upper the Upper parts parts of of the weathering profile, remnants of of weathering Late Cretaceous marine strata, and the overlying glacial deposits deposits were were stripped away as the Glacial River Warren (a high-discharge, Warren high-discharge, lowlowgradient gradient meltwater meltwater river river ancestral ancestralto to the Minnesota) eroded downward. downward. River River downcutting downcutting slowed slowed or or perhaps ceased perhaps ceased where where hard rock was encountered at the the base of encountered at of the the (2): The The weathered section. section. Point (2'): present valley-floor outcrops were rapids and islands rapids islands in the Glacial Glacial River Warren. Warren. Their morphology morphology is due primarily due primarily to river river erosion. erosion. (31: Because Because of of the the Scoured cuts (former shoots in rapids) and and potholes potholes are are common. common. Point (3): history knobs of approximately history discussed discussedin inpoints points(1) (1)and and(2), (21, outcrops outcropstend tend to to be clusters clustersof low knobs approximately the same height. InIngeneral generalthey theydo donot notoccur occuron onthe thevalley valley walls, walls,Grand-Canyon Grand-Canyon style, style, but instead are located toward the middle middle of the the valley valley floor floor where where the the stream stream velocity velocity and and downcutting greatest. The commonly downcuttingpower power of of the the River River Warren were greatest. The sides sides of the valley floor are commonly occupied by constructional terraces (as here) and the valley walls are chiefly the Quaternary sediments sediments through through which whichthe the River RiverWarren Warren cut. cut. Diabase dikes of of Proterozoic Proterozoic age age form form prominent prominent valley-floor valley-floor ridges ridges at at this thislocality. locality. Compositionally, tholeiites. They are very similar in in composition composition Compositionally,the dikes dikes are good continental tholeiites. and petrographic characteristics characteristics to to tholeiitic tholeiitic dikes dikes near Granite Granite Falls, Falls, some some 40 40 miles miles up-river, up-river, that yield K-Ar dates of about 2,080 Ma (Hanson and Himmelberg, 1967). Several of of the the larger larger az. 095-100, approximately parallel to the dikes dikes here tholeiite dikes dikes at at Granite Granite Falls Falls strike strike about about az. tholeiite approximately parallel at Franklin. Franklin. Some Somebetter bettergeochronology geochronologyand andaalittle littlepaleomagnetic paleomagneticwork workwould wouldbe bevery very helpful helpful in deciding Falls tholeiitic tholeiitic diabase diabase dikes dikes are are or or are not deciding whether whether the Franklin Franklin and Granite Granite Falls genetically genetically related. related. that is held up up by by the the Cedar About a mile northwest northwest of Stop 11 is a prominent brushy knob that Mountain Complex, a compositionally zoned zoned igneous igneous plug plugof ofProterozoic Proterozoicage. age. The outer part of the plug plug isis melanocratic melanocratic hornblende hornblende diorite that has aa chilled chilled external external rind rind of of olivine olivine trachybasalt homblende trachybasalt porphyry. The Thecore core of of the the plug is granite and granodiorite. Biotite and hornblende from the core core yield yield essentially essentially identical identicalK-Ar K-Ar ages ages of of 1,750 1,750Ma Ma (Hanson, (Hanson,1968). 1968). from :&, 137 �1.5 miles to the east of Stop 11 is a small plug of highly silicified and carbonatized About 1.5 Thisbody body isispost-Archean post-Archean but but is is unconstrained unconstrained otherwise otherwise as to age. serpentinite. This wallrock to the dikes and other intrusions is a granodioritic granodioritic variant The walirock variant of the middle Archean Morton Gneiss. Gneiss. Because Becausethe thegneiss gneisshere hereisis in in such such poor condition (incipient (incipient weathering), Archean Morton weathering), it has not been studied in any great detail. We We will see much better outcrops of the Morton at 4, and Stops 2, 2,4, and 5. 5. Features to see: see: • Grain Grain size sizeand andfabric fabricvariations variationswithin within diabase diabasedikes; dikes; chilled chilled margins. margins. • Paleomagnetic Paleomagneticdrill drillholes: holes: Where Where are are the the paleomagnetic paliomagnetic data?? data?? owned and operated operated by by the Cold Spring Stop 2—Morton %Morton Gneiss, Morton Quarry owned Spring Granite Granite Company. Morton W.-section 3lDAA. 31DAA. Hard hats must be Morton quadrangle, quadrangle, T. 113 113 N.-R. 34 W.-section worn everywhere everywhere on company company property. quarried here here isis aa variant variantof ofthe theMorton MortonGneiss. Gneiss. It is a The flamboyant dimension stone quarried classic migmatite migmatite in which a pink, granitic of the neosome classic granitic to pegmatitic pegmatitic component component of neosome (the "adamellite-1" rock suite of Goldich and others, 1980b) is unusually unusually abundant. More "adamellite-1" More typical typical Morton Gneiss from the standpoint standpoint of areal areal abundance abundance is aa predominantly predominantly gray rock of of granodioritic to to tonalitic tonalitic composition composition that that is is more more uniform uniform in in texture texture than than the the gneiss gneiss in the granodioritic Morton complex metamorphic metamorphic Morton area. area. This Thisisisanother anothercase casewhere where the the concept concept of "type locality" for a complex rock turns out to be flawed. flawed. The TheMorton Mortonarea areasupplied suppliedthe the name name for for the the gneiss gneiss because because the the many quarries provided accessible, unweathered, unweathered, clean exposures to study, study, not not because because the rock exposed is particularly exposed is particularly typical of aa mappable mappable geologic geologic unit. gneiss from u q The gneiss from this qquarry is marketed marketed under under the the trade trade name name granite." ItIt can "rainbow granite.'' can be seen ornamental stone as a facing and ornamental stone on buildings throughout buildings throughout the the Nation, Nation, and and in in recent recent years years itit has become a favorite favorite material material for for up-scale up-scale kitchen counters counters and and tabletops. The patterns, plastic, suggestive of inhomogeneous bulk inhomogeneous bulk deformation deformationunder under conditions conditionsat at which which the the rock rock was was in in aa partially partially molten molten state, attractive and intriguing intriguing to architects architects and interior designersas designers as they are to to geologists. geologists. state, are as attractive Features to to see: see: • Paleosomatic Paleosomatic"enclaves" "enclaves" of of several several types. types. • Evidence Evidenceof of rheological rheologicalcontrasts contrastsamong amongdifferent differentrock rock types during partial melting and deformatio.n. deformati0.n. • Gently dipping, tight folds folds reoriented reoriented into the dipping, broadly undulating gneissosity; small, tight undulating undulating "regional" "regional" fabric. fabric. 138 �• Zones Zones of of extensional extensional ductile ductile shear, shear, many many of of which which contain contain granitoid granitoid segregations segregations interpreted interpreted to to have have formed formed as as partial partial melts. melts. Stop Stop 2A 2A (Alternative (Alternative to to Stop Stop 2)—Morton 2)-Morton Gneiss, Gneiss, small small quarry quarry behind behind former former school school building in in town building town of Morton. Morton. Morton Morton quadrangle, quadrangle, T. T. 113 113 N.-R. N.-R. 34 34 W.-section W.-section 3 1BCBA. 1BCBA. Because of insurance insurance liability liability considerations, considerations, the Cold Spring Granite Company does not quarry. As of press time we were not normally permit field-trip field-trip groups groups into the active Rainbow quarry. many of of the cleared for quarry access. The The small small quarry quarry behind the old Morton school shows many described under Stop 2 (above), but but the the rock rock surfaces surfaces are are smaller smaller and and less less features of the gneiss described spectacular than those in the Rainbow quarry. Please spectacular Please read read the the discussion discussion of of Stop Stop 22 and and transfer transfer it to the Stop 2A exposures. exposures. move about about Stop Stop 2A. 2A. Rock surfaces that are shaded most of the Be very careful as you move time acquire a slimy slimy coating coating that can be treacherously treacherously slick. slick. Stop 3—Weathering Morton Gneiss Gneissprior priorto tothe theLate LateCretaceous. Cretaceous. Redwood Redwood Stop &Weathering profile developed on Morton Falls Falls quadrangle, quadrangle,T. T. 113 113N.-R. N.-R.35 35W.-section W.-section3ODAB. 30DAB. Clay-rich saprolith of the general type exposed here here occurs occurs widely widely in in the the subsurface of of southwestern Minnesota. southwestern Minnesota. Where WhereLate LateCretaceous Cretaceousmarine marinestrata stratahave havenot notbeen been removed removedby by postpostCretaceous erosion they overlie the saprolith saprolith directly, confirming that most of the weathering weathering occurred before Late Cretaceous Cretaceous marine transgression transgression and the the deposition deposition of of marine marine sedimentary sedimentary occurred rocks. In places where where the Cretaceous Cretaceous rocks rocks were eroded away prior to glaciation, remnants of the weathering weathering profile profile directly underlie Quaternary glacial deposits. The The clay, clay, grus, and corestones from from the the weathered Precambrian rocks undoubtedly contributed contributed substantially substantially to the mass of subsequent Cretaceous shales and and Quaternary tills. Quaternary Reworked and inReworked deposits of Late situ clay deposits Cretaceous and postCretaceous Cretaceous age are mined at several sites mined sites along the Minnesota along Minnesota River, including one River, one about a mile southeast of 139 �these exposures. Theclay clayisisused used mainly mainly in in the the manufacture manufacture of portland portland cement cement and and for for various various exposures. The agricultural purposes. The weathering profile at this stop was was studied studiedby bySam SamGoldich Goldichininthe the1930's; 1930's; his classic the weathering weathering stability stability of of rock-forming rock-forming minerals minerals (Goldich, (Goldich, 1938) 1938) was was based based on on paper on the Thatfundamental fundamentalpaper paper on onweathering weathering has has probably probably achieved achieved wider wider materials collected here. That all of of Sam's Sam's geochronological geochronologicalcontributions contributionscombined. combined. notoriety than all Features Features to to see: see: Upwardloss lossof ofsource-rock source-rockminerals mineralsand andfabric fabricin in the the bottom bottom two-thirds two-thirds of the weathering • Upward weathering profile. profile. • Pisolitic Pisoliticclay claylayer layertoward towardthe thetop top of of the the section. section. Beddedclay clay(reworked (reworkedby by streams?) streams?)above abovethe the pisolitic pisolitic layer layer and and below Quaternary Quaternarytill. till. • Bedded Stop Stop4—Morton &Morton Gneiss Gneisscut cut by by adamellite adamellitedikes. dikes. Vicksburg quadrangle, quadrangle,T. T. 114 114N.-R. 36 36 W.-section W.-section 33DDD. 33DDD. The gray tonalitic gneiss exposed in these outcrops is a common, widespread variant of of the Morton. Much Muchof ofthe therock rock mapped mapped as as Morton Morton Gneiss Gneiss is basically basically this lithology lithology with varying included mafic "enclaves" "enclaves7'and and varying degrees degrees of intrusion intrusion by younger younger granitoid granitoid quantities of included rock types. The The gray gray gneiss gneiss inclusionhere is about as inclusionas it free gets. Furthermore,this this is is a Furthermore7 locality where where there there is a locality intrusive clear-cut relationship between between .late late relationship granite of the Sacred Heart type (sharp-walled dikes, dikes, including an easily accessible one about two accessible meters thick) thick) and meters and the the can tonalitic Morton Morton Gneiss. Gneiss. The Therelative relativeage ageof of the the two two is is not a matter of great debate, in that it can be reliably reliably inferred inferred from from textural textural evidence evidence in the rocks and from field relationships observed at a number of places in the Valley. Valley. Accessible outcrops that show the critical field relations are rather rare7however. however. rather rare, Samples of tonalitic Morton Gneiss from this this site site form form part part of of the the dataset dataset for for the the "old" Rb-Sr isochron age of about about 3,500 3,500 Ma (Goldich (Goldich and Wooden, 1980) that is widely cited in the literature. Data the Rb-Sr Rb-Sr diagram diagram (Goldich (Goldich literature. Datafrom fromhere hereanchor anchorthe the lower lower or less radiogenic end of the and Wooden? Wooden, 1980; 1980; their their fig. fig. 2 and and data data from from locality locality 5). 5). In addition, addition, zircons from from the gneiss at this locality yield an interpreted interpreted U-Pb age age of 3,662 3,662+1+I-42 42 Ma (Goldich (Goldich and and Fischer, Fischer, 1986). 1986). details is beyond beyond the scope and purpose of this Lengthy discussion of geochronologic details this out7however, however, that that healthy disagreements exist as to the exact field guide. ItItmust mustbe bepointed pointedout, antiquity of the Morton Morton Gneiss Gneiss and and the the significance significanceto to be be attached attached to to the the dates dates determined. determined.A A derives from the the complexity complexity of of the the neosomatic neosomatic components components of of major source of controversy derives migmatitic rocks rocks (as seen in the quarries migmatitic quarries at at Stops Stops 22 and and 2A, 2A, for forexample) example) and andconflicting conflicting sequence of ofprocesses processesinvolved involvedinin neosome neosome genesis. genesis. The interpretations of the processes and sequence 140 �more straightforward straightforward sequence sequence of of cross-cutting cross-cutting relationships relationships displayed at the the present present stop stop isis more informative informativebecause becauseitit eliminates eliminatessome someof of the theinterpretational interpretationalambiguities ambiguitiesassociated associatedwith withthe the more morecomplex complexphases phasesof ofthe theMorton. Morton. Featuresto tosee: see: Features • Fabric Fabricand andfabric fabricvariations variationsinintonalite tonalitegneiss. gneiss. • Folded Foldedmafic maficlayer layerinterpreted interpretedas asaadeformed deformeddiabase diabasedike. dike.(Do (Doyou youagree?) agree?) • Textural Texturaland andfabric fabricvariations variationswithin withinpostpost-Morton Mortonadamellite adamelliteintrusions. intrusions. Stop5—Morton 5-Morton Gneiss Gneissthat thatdisplays displaysaavariety varietyofofenclaves enclavesand andsmall-scale small-scalestructures. structures. Stop Iverson IversonLake Lakequadrangle, quadrangle,T. T.114 114N.-R. N.-R. 37 37W.W.- section section21CB. 21CB. These 0.5mile mile south southof of the the the the largest largestexposed exposedmass massof of Sacred Sacred Theseoutcrops outcropsare arelocated locatedabout about0.5 Heart Heart Granite Granite in in the the Minnesota Minnesota River River Valley. Valley. The The gneiss gneiss here here isis characterized characterized by by abundant abundant amphibolitic amphibolitic inclusions inclusions of of tholeiitic tholeiitic and andkomatiitic komatiiticcomposition, composition, complex complex fold foldstructures structures indicative indicative of of multiple multiple folding folding events, events,deformed deformed(boudinaged, (boudinaged,folded) folded) aplitic aplitic dikes dikes presumably presumably of the "adamellite 1" suite, and straight, undeformed granite dikes of Sacred Heart the "adamellite 1" suite, and straight, undeformed granite dikes of Sacred HeartGranite. Granite. The The quartzofeldspathic quartzofeldspathic gneiss gneiss that that encloses encloses the various various mafic rock types is variable variable in modal modal composition composition and and texture. texture. Its Itsoverall overallcomposition compositionisisapproximately approximatelyin in the the granodiorite granodioriterange. range. Wander Wander around among the cedars cedars and and thombushes thornbushes to to find find examples examples of of the thefeatures features mentioned above. Look before you kneel or sit! Little cacti with big spikes grow all over these mentioned above. Look before vou kneel or sit! Little cacti with big spikes grow all knobs. knobs. Stop Stop6—Sacred &Sacred Heart Heart Granite Granite and and associated associated rock types. Iverson Iverson Lake Lake quadrangle, quadrangle, T. 114 114 N.-R. 37 37 W.-section 7DD, 7DD, near prominent prominent knob knob named named Middag MiddagKnutea. Knutea. The The Sacred SacredHeart HeartGranite Graniteisisone oneof of several severallarge large granite granite masses masses that that intruded intrudedMRV MRV gneisses gneisses 2.55 -- 2.7 2.7 Ga Ga time time interval. interval. Available Availableradiometric radiometricage age determinations determinationson on these these intrusions intrusions in the the 2.55 in are rather imprecise, owing to the scarcity and poor poor quality quality of of the the contained contained zircons. zircons. Further efforts to obtain high-precision dates would be most welcome. efforts obtain high-precision dates would be most welcome. 141 �I / :::: Most of of the the Sacred Sacred Heart Heart is is aa Most rather ordinary ordinary medium-grained medium-grained rather granite that that consists consists of of subequal subequal granite amountsof of quartz, quartz,oligoclase, oligoclase,and andKKamounts I '7 M —p \) c !'sA - - -- 8 - N , —_.) ))c ,J) - feldspar. It was quarried as dimension stone in an earlier era but is not being worked now. Although much of the rock mapped mappedas asSacred SacredHeart Heartisisquite quite rock uniform in in texture texture and andcomposition, composition, uniform thereare areparts partsof ofthe themass massthat thatdisplay display there '-'c.-zz C' quartzstronglygneissose gneissosefabric fabricand andquartzstrongly ° poor compositions compositions trending trending toward toward poor ) " ' monzonite. Some Somefeatures featuresindicative indicative monzonite of aa complex complex intrusive intrusive history history are are of displayedin in the the road roadcuts cutsatatthis thisstop. stop. displayed Featuresto tosee: see: Features • Massive, Massive,uniform uniformSacred SacredHeart HeartGranite Granite(road (roadcuts cutsabout about1,000 1,000ftftsouth southof of Middag MiddagKnutea). Knutea). • Gneissose Gneissosefabric fabriciningranite; granite;modal modaland andtextural texturallayering layering(SE (SEflank flankof ofMiddag MiddagKnutea). Knutea). • Monzonite Monzonitewith withpyroxene pyroxenegranulite granuliteinclusions. inclusions. ;Q I 'ci, tfl i U — I Drive DrivetotoStop Stop7—The 7-The bedrock bedrocksurface surfaceexposed exposedhere herewas wasexhumed exhumedby byGlacial GlacialRiver RiverWarren, Warren, however, however, significant erosion of fresh rock was not required to form form this smoothly smoothly undulating undulating bedrock bedrocksurface surfacewith with rounded rounded bedrock bedrock knobs and boulders. Such Suchsurfaces surfacescan can be formed simply by by the the removal removal of of deeply deeply weathered weathered bedrock. bedrock. Large Largerounded roundedboulders boulderswere werenot notshaped shapedduring during fluvial fluvial and and glacial glacial transport; transport; they they represent represent chemically chemically rounded corestones resting at or near their source. source. their Pre-Cretaceous weathering penetrated to an average depth of 30 m, but the rock, the fresh fresh rock/ of relief. Joints m weathered rock interface is irregular and undulates with as much as 45 Joints and and weathered rock interface is irregular and undulates with as much as 45 m fractures isolating fracturesare are preferentially preferentiallyexploited exploitedand andpenetrated penetratedto to depths depthsof of 60 60 m in places, locally isolating meter-sized volumes volumes of fresh fresh rock. The Therounded, rounded,fresh fresh rock rock remnants remnants are are known as corestones corestones and are are aa common common feature feature of of the theweathered weathered bedrock bedrock residuum residuum in in Minnesota Minnesota and and when when incorporated incorporated into into glacial glacialsediment, sediment,may may be be misinterpreted. misinterpreted. On Homme-Kollin Unit, Scientific Scientificand and Natural Natural On the south south side side of the road is Swedes Forest, Homme-Kollin Area. quarries that that are are hibernating hibernating Area. Its Itsmain mainscientific scientificsignificance significanceisisthat thatititisisthe the site site of several old quarries areas for the rare, blue-tailed lizards lizards and and "blue "blue devils"). devils"). They rare, five-lined five-lined skink (also called blue-tailed They prefer sunny woodlands. The sunny bedrock exposures near oak woodlands. The main main range range of of this this species species is is the the eastern eastern United United States Statesand andthese theseare arean anisolated isolatedpopulation. population. 142 �Stop7—Garnet-biotite-quartz-feldspar 7-Garnet-biotite-quartz-feldspar gneiss gneiss (Montevideo Gneiss). Granite Granite Falls quadrangle, quadrangle, Stop T. 115 N.-R. 39 W.-section W.-section 10AA. bAA. 115 N.-R. The Yellow Medicine Minnesota The Medicine shear zone (YMSZ), a major crustal structure structure within the Minnesota River Valley subprovince subprovince (Southwick (Southwick and and Chandler, Chandler, 1996), 1996),crosses crosses the the Minnesota MinnesotaRiver Riverabout about River two miles miles southeast southeast of here. The The shear shear zone zone rocks rocks do do not two crop out; out; the the zone zone was first recognized from geophysical geophysical crop recognized from mapping and and the existence existence of sheared sheared rock within within itit was mapping later verified verified through core drilling. The TheYMSZ YMSZ isisnow now later informally defined defined as as the the boundary between between the the Morton Morton informally Gneiss Gneiss (to (to the the south) south) and and the the Montevideo Montevideo Gneiss Gneiss (to (tothe the north). north). The The rock rock in the rubbly rubbly road road cuts cuts at at this this locality locality is is aa garnet-biotite-quartz-plagioclasegneiss, gneiss,aamappable mappablesubsubgarnet-biotite-quartz-plagioclase unit unit of of the the Montevideo Montevideo Gneiss Gneiss that that is is fairly fairly abundant abundant in in the (Himmelberg, 1968). the Granite Granite Falls area (Hirnmelberg, 1968). Lund Lund (1950) (1950) mapped mappeditit as as the Granite Granite Falls Falls garnetiferous garnetiferousquartz quartzdiorite diorite gneiss, aa name name that never caught on. The The protolith protolithof of the the gneiss, unit as a whole is not immediately apparent. Parts Parts of of itit unit are are quite quite aluminous, aluminous, suggestive suggestive of a sedimentary sedimentary origin, origin, and and other other parts parts are are very very feldspathic, feldspathic,at at least least locally locally suggestive suggestiveof of igneous igneous derivation. derivation. This This and and other other rock rock units units in in the the Granite Granite Falls Falls area area are are folded folded broadly broadly about about east-trending, east-trending, gently F2 structures. structures. gently east-plunging east-plungingaxes axes(Himmelberg, (Himmelberg,1968) 1968)that that Bauer Bauer (1980) (1980) interpreted interpreted as as F2 The Thecomplete completedeformational deformationalhistory historyinvolves involvesfour four folding foldingevents, events, which which Bauer Bauer (1980) (1980) discusses discusses in in detail. detail. Faults Faultsand andbrittle-ductile brittle-ductileshears shearsatatand andnear nearthe thesouth southedge edgeof of the the garnet garnet gneiss gneiss outcrop outcrop belt belt are are probably probably related related to to late late deformation deformationalong along the the nearby nearby YMSZ. There Therealso alsoisisscattered scattered evidence evidence of of earlier, earlier,more more deep-seated deep-seated shear sheardeformation deformationthat that may may have have been been related relatedto toearlier earlier YMSZ activity. YMSZ activity. Features Featuresto tosee: see: • Lithologic Lithologicvariations variationsin in the the gneiss. gneiss. • Late Lateshear shearzones. zones. • Rotational Rotationalstructures structuresindicative indicativeof ofductile ductileshear. shear. Stop Stop8—Granulite-facies 8-Granulite-facies mafic mafic and and pelitic pelitic gneiss gneiss (Montevideo (Montevideo Gneiss). Gneiss). Granite GraniteFalls Fallsquadrangle, quadrangle, T. 3BBD. T. 115 115N.-R. N.-R. 39 39W.-section W.-section 3BBD. Garnet-bearing Garnet-bearinggneiss gneisssimilar similarto tothat thatatatStop Stop77 is is in in contact contactwith withgranulite-grade granulite-grademafic maficgneiss gneiss(cpx(cpxopx-plag) opx-plag)in inthese theseroad road cuts. cuts.Small Smallamounts amountsof ofbiotite biotite in in the the granulite granulite may may record record retrograde retrograde rereequilibration. The garnet gneiss is quite micaceous equilibration. The garnet gneiss is quite micaceous and and well well layered, layered, and and has has been been regarded regarded as as aa metamorphosed metamorphosedsedimentary sedimentaryrock. rock.The Themafic maficgneiss gneiss may mayhave havebeen beenaabasalt basaltflow floworiginally, originally,although althoughother other mafic maficprotoliths protolithsare arecertainly certainlypossible. possible. 143 �Stop 9—Mafic 9-Mafic gneiss gneiss (Montevideo Gneiss). Shear Shear zones zones and pseudotachylite veins. Granite Granite Stop 4AAB. Falls quadrangle, quadrangle, T. T. 115 115 N.-R. 39 39 W.-section 4AAB. Shear structures in these outcrops have been studied by John Craddock and several of his Thefollowing followingsummary summary is is taken taken from from material material provided provided by by students at Macalester College. The John. Twenty-two discrete discrete shear zones have been Twenty-two found here that contain pseudotachylite seams. The The subparallel, trend 070 on on average, average, zones are subparallel, trend about about az. az. 070 and dip and dip subvertically. subvertically. This This orientation orientation is is approximately that of approximately of the the regional-scale regional-scale Yellow Yellow Medicine shear zone and several of the Proterozoic diabase dikes dikes in in the the area. Within diabase Within aa given given zone the individual pseudotachylite pseudotachylite seams seams (black) (black) are of individual diverse orientations. orientations. pseudotachylite matrix is compositionally compositionally The pseudotachylite layered and preserves preserves flow-foliation layered flow-foliation swirls swirlsand and relics relics of glass. Dextral Dextralwinged wingedporphyroclasts porphyroclastsin in the the pseudotachylite pseudotachylite preserve dextral and sinistral kinematic kinematic displacement, displacement, primarily primarily opposite opposite the the sinistral sinistral sense sense of of S-C S-C structures structuresin in the the country country rock and and of sinistral rock sinistral fault fault drag drag indicators indicators along the strike-slip strike-slip zones that contain the pseudotachylite seams. Seam-margin pseudotachylite seams. Seam-margin forking forking directions directions are are dominantly dominantly toward toward the the west; west; poryhyroclast imbrication imbrication within the pseudotachylite is dominantly dominantly up and easterly. pseudotachylite seams yield Calcite in veins that appear to be contemporaneous with the pseudotachylite twinning strains indicative indicative of zone-parallel and zone-normal horizontal shortening. Magnetic Magnetic pseudotachylite seams give Krnax Kmax subvertical, Krnin Kmin subhorizontal fabric meaurements on the pseudotachylite and zone-normal. zone-normal. IfIfthe themagnetic magneticfabric fabriccorrelates correlateswith withflow, flow, these these results results indicate indicate that the flow of pseudotachylite pseudotachylite glass glass was was upward upward within withinthe thezone zoneof ofshear. shear. Features Features to to see: see: • Discrete Discrete shear shearzones zones (many (many are are reddened). reddened). • Pseudotachylite Pseudotachyliteseams. seams. • Sense-of-shear Sense-of-shearindicators indicatorsin in shear shear zones. zones. Stop lO—Proterozoic Gneiss. Granite Stop 10ÑProterozoi "Section "Section 28" intrusion and wallrocks of Montevideo Gneiss. Granite Falls quadrangle, quadrangle,T. T. 116 116N.-R. 39 39 W.-section 28BCA. At this locality a small plug of Proterozoic granite is in complex contact contact with with a body body of hornblende hornblende andesite andesite (also (also Proterozoic). Proterozoic). Contacts Contactswith withthe the Montevideo Montevideogneiss gneiss are are not not exposed, exposed, but they can be mapped rather closely. closely. The The granite granite yields a zircon Pb-Pb age of 1825 1825 Ma (Catanzaro, 1963). 1963). The standard standard explanation explanation of of the the relationships relationships seen seen here is as follows: andesite. Dikes (1) The body of dark rock is a dike of hornblende andesite. Dikes of of this this composition composition occur elsewhere elsewhere in the the Granite Granite Falls area area (e.g., (e.g., Stop Stop 11). 11). (2) The granite intrudes the dike and thus is the younger rock, by classical geological reasoning. reasoning. contact relations relations necessarily necessarily imply imply the the interpretation interpretation outlined outlined Do we agree that the observed contact above? above? 144 �______ _______ Stop Gneiss,Proterozoic Proterozoic dikes dikes in inthe theYellow Yellow Medicine Medicine quarry quarry owned owned and an( Stop11—Montvideo 11- -MontvideoGneiss, 115N.-R. N.-R.39 39 operatedby bythe theMeridian MeridianAggregates AggregatesCompany. Company.Granite GraniteFalls Fallsquadrangle, quadrangle,T.T.115 operated W.-section W.-section 33BB. 33BB.Hard Hardhats hatsmust mustbebeworn worneverywhere everywhereon oncompany companyproperty. property. TheYellow Yellow Medicine Medicine quarry produces crushed stone, much of which which is is used used as as railroad railroad The ballast ballast for for the theBurlington Burlington Northern Northern Railroad. Railroad. Aggregate Aggregatefrom fromhere here isisused used on onrailroad railroadtracks tracks across acrossthe theDakotas Dakotasand andMontana Montanatotothe theRocky RockyMountain Mountainfront. front. The principal principal rock rock in in the the quarry quarry isis aa The granitic granitic gneiss gneiss composed composed of of quartz, quartz, plagioclase, microcline, microcline, and and biotite biotite that that isis plagioclase, modally layered layered on on various various scales. scales. Scattered Scattered modally withinititare areconformable conformablelenses lensesand and layers layersof of within hornblende-pyroxenegneiss. gneiss.This Thisgeneral generalrock rock homblende-pyroxene '' type is is the thecommonest commonest variant variant of of the the type MontevideoGneiss Gneissin in terms termsof ofmap maparea areaand and Montevideo D / essentiallythe therock rockexposed exposedup-river up-riveratatthe the isisessentially 33L4F "type locality" locality" outcrops outcrops near near the thetown town of of "type Montevideo. Samples Samplesof ofgneiss gneissfrom fromthe the Montevideo. quarry were were used used by by Goldich Goldich and andothers others quarry = (1980a, locality 4) 4) to to identify identifyaasequence sequence (1 980a, their locality ofRb-Sr Rb-Srisotopic isotopicevents eventsthat thatrange rangefrom from3,530 3,530 of toto2,265 2,265Ma. Ma.Various Variousinterpretations interpretationsofofthese these v' )\ ranité11s rriS I \ ) iriYfA 1ru • I I :11: E5!T 145 �I isotopic results results are are discussed discussed at at length length by the original authors. U-Pb zircon data reported for an isotopic "older" adamellite adarnelliteintrusion intrusioninto into the the layered layered gneiss gneiss yield an interpreted age of 3,230 3,230 Ma Ma (Goldich (Goldich and others, 1980a). others, 1980a). Dikes of of Proterozoic Proterozoic hornblende hornblende andesite andesite are are prominently prominently displayed displayed in in the the quarry quarrywalls. walls. Dikes all other other rocks rocks in in the the quarry quarry are are shot shot through through with chioritized, chloritized, slickensided, slickensided, brittle These and all shears on all all orientations. orientations.This Thistype typebrittle brittleshearing shearingand andassociated associatedevidence evidenceof ofhydrothermal hydrothermal shears activity (chlorite (chlorite films; films; calcite-quartz calcite-quartz veins) veins) are are associated associated with a pronounced reddening of the activity disseminated hematite. The Thereddening reddeningphenomenon phenomenon affects affects many many rocks, presumably due to disseminated MRV exposures exposures north north of of the the YMSZ YMSZ but is uncommon uncommon south south of it. it. END OF OF DAY DAY ONE. REFERENCES REFERENCES CITED CITED Bauer, R.L., 1980, 1980, Multiphase deformation in the Granite Granite Falls-Montevideo area, Minnesota River in Morey, Morey,G.B., G.B.,and andHanson, Hanson,G.N., G.N.,eds., eds.,Selected Selected studies studies ofkchean ofArchean gneisses River Valley, in gneisses and lower Proterozoic rocks in the southern Canadian Shield: Geological Society lower Proterozoic the southern Canadian Society of America America Special SpecialPaper Paper 182, 182,p. p. 1-17. 1-17. Catanzaro, southwestern Minnesota: Journal of Geophysical Geophysical Research, Catanzaro,E.J, E.J, 1963, 1963,Zircon Zircon ages ages in southwestern Research, v. 68, p. 2045-2048. 2045-2048. Goldich, Goldich, S.S., S.S., 1938, 1938,A A study study of of rock rock weathering: weathering:Journal Journalof of Geology, Geology,v. v. 46, 46, p. p. 17-56. 17-56. Goldich, S.S., and and Fischer, Fischer, L.B., L.B., 1986, 1986,Air-abraison Air-abraison experiments experiments in U-Pb U-Pb dating dating of ofzircon: zircon: Chemical ChemicalGeology, Geology, v. v. 58, 58, p. 195-215. 195-215. Goldich, J.B., and North, R.M., 1980a, Goldich, S.S., S.S., Hedge, Hedge, C.E., C.E., Stern, Stem,T.W., T.W., Wooden, J.L., Bodkin, J.B., 1980a, Archean rocks of of the the Granite GraniteFalls Falls area, area, southwestern southwestern Minnesota, Minnesota, in Morey, Morey, G.B., and Hanson, G.N., G.N., eds., eds., Selected Selected studies studies of of Archean genisses and lower Proterozoic rocks, southern southern Canadian Canadian Shield: Geological GeologicalSociety Societyof of America America Special Special Paper 182, 182, p. 19-43. 19-43. Goldich, Goldich, S.S., and and Wooden, J.L., 1980, 1980, Origin of the Morton Gneiss, southwestern southwestern Minnesota: Minnesota: Part Archean Part 3. Geochronology, Geochronology,ininMorey, Morey,G.B., G.B., and andHanson, Hanson,G.N., G.N., eds., eds., Selected Selectedstudies studiesof ofkchean gneisses and lower Proterozoic rocks, southern Canadian Shield: Geological Society of gneisses Canadian Shield: America America Special Special Paper Paper 182, 182,p. 77-94. 77-94. Goldich, Goldich,S.S., S.S., Wooden, Wooden,J.L., J.L.,Ankenbauer, Ankenbauer,G.A., G.A.,Jr., Jr., Levey, Levey, T.M., and Suda, Suda, R.U., 1980b, 1980b,Origin Origin of the Morton Morey, G.B., G.B., and and Morton Gneiss, Gneiss, southwestern Minnesota: Part Part 1. 1. Lithology, Lithology,ininMorey, Hanson, G.N., eds., eds., Selected Selected studies studies of of Archean Archean gneiss and lower lower Proterozoic Proterozoic rocks, southern southern Canadian Canadian Shield: Shield: Geological GeologicalSociety SocietyofofAmerica, America,Special SpecialPaper Paper182, 182,p.p.45-56. 45-56. Grant, Grant, J.A., J.A., 1972, 1972,Minnesota MinnesotaRiver RiverValley, Valley, southwestern southwestern Minnesota, Minnesota,in in Sims, Sims,P.K., P.K., and and Morey, Morey, G.B., eds., Geology of Minnesota: A A centennial centennial volume: Minnesota MinnesotaGeological GeologicalSurvey, Survey, 177-196. p. 177-196. Grant, Grant, J.A., 1973, 1973,Phase Phase equilibria equilibriain in high-grade high-grade metamorphism metamorphism and partial melting of pelitic pelitic rocks: rocks: American American Journal Journalof of Science, Science,v. v. 273, 273, p. p. 289-317. 289-3 17. Hanson, G.N., 1968, 1968, K-Ar K-Ar ages ages for for hornblende hornblende from from granites granites and gneisses gneisses and and for for basaltic basaltic intrusives 20 p.p. intrusives in in Minnesota: Minnesota: Minnesota MinnesotaGeological GeologicalSurvey SurveyReport ReportofofInvestigations Investigations8,8,20 Hanson, Granite Falls, Minnesota: Minnesota: Hanson,G.N., G.N., and andHimmelberg, Himmelberg,G.R., G.R., 1967, 1967,Ages Ages of mafic mafic dikes near Granite Geological GeologicalSociety Societyof ofAmerica AmericaBulletin, Bulletin,v.v. 78, 78,p. p. 1429-1432. 1429-1432. 146 �G.R., 1968, Geology Geology of Precambrian rocks, Granite Granite Falls - Montevideo Himmelberg, G.R., Precambrian rocks, Montevideo area, area, southwestern Minnesota: Minnesota Geological Survey Special Publication Series Series SP-5, SP-5, 33 p. 33 Hoim, D.K., Holm, D.K., Darrah,K.S., Darrah,K.S., and and Lux, Lux, D.R., D.R., 1998, 1998,Evidence Evidencefor forwidespread widespread—1760 -1760 Ma metamorphism and rapid crustal stabilization of the Early Proterozoic (1870-1820 Proterozoic (1870-1820 Ma) Ma) Penokean orogen, orogen, Minnesota: Minnesota: American American Journal Journal of of Science, Science,v. v. 298. 298. p. p. 60-8 60-81. 1. Igneous and metamorphic rocks of the Minnesota Minnesota River River Valley: Valley: Unpublished Unpublished Lund, E.H., 1950, 1950, Igneous Minneapolis. Ph.D. dissertation, dissertation, University of Minnesota, Minneapolis. Valley: Geological Lund, E.H., 1956, 1956, Igneous Igneous and metamorphic rocks of the Minnesota River Valley: Geological Society Society of America Bulletin, Bulletin, v. 67, p. 1475-1490. 1475-1490. Moecher, D.P., ffi, Leier-Englehardt, Leier-Englehardt, P.J., and and Medaris, Medaris, L.G., L.G., Jr., Jr., 1986, Metamorphic Metamorphic Moecher, D.P., Perkins, D. in, conditions of late high-grade gneisses, conditions late Archean high-grade gneisses, Minnesota Minnesota River River valley, U.S.A.: Canadian Canadian Journal of Earth Journal Earth Sciences, Sciences,v. v. 23, 23, p. 633-645. 633-645. Perkins, D., ifi, in,and and Chipera, Chipera, S.J., S.J., 1985, 1985,Garnet-orthopyroxene-plagioclase-quartz Gmet-orthopyroxene-plagioclase-quartz barometry: Refinement and application to the English River subprovince and the Minnesota River Valley: Contributions to Mineralogy and Petrology, Petrology, v. 89, p. 69-80. 69-80. Southwick, D.L., and architecture of the Minnesota Minnesota Southwick, and Chandler, Chandler,V.C., V.C., 1996, Block and shear-zone architecture Valley subprovince: subprovince: Implications for Late Archean Archean accretionary accretionary tectonics: Canadian Canadian River Valley Journal of Earth v. 33, 33, p. 831-847. 831-847. Journal Earth Sciences, Sciences,v. 147 �I INTRODUCTION TO THE INTRODUCTION THE GLACIAL GLACIAL HISTORY OF OF THE THE MINNESOTA RIVER VALLEY Carrie Carrie J. Patterson Patterson Contrary to the four-fold devised around around the the turn of the century for four-fold glacial chronology devised terrestrial glacial sediments (Wisconsin, Illinoian, Kansan Kansan and and Nebraskan Nebraskan (Flint, 1957)), 195711, the current model for the Quaternary Quaternary record of glaciations is much more elaborate (Ruddiman and more elaborate Wright, 1987). 1987). The Theoxygen oxygenisotope isotoperecord record of of ocean ocean carbonate carbonate sediments sediments records records the the effects effects of glaciations. glaciations.During Duringglaciations, glaciations,160, 160,which whichisispreferentially preferentiallyevaporated evaporatedfrom from the the oceans oceans because because of it lesser mass, is stored enriching the glacial glacial oceans stored on land in the ice sheets, enriching oceansin in 180. 180. According to this record record of of global globalice icevolume, volume,there therewere were40 40glacial/interglacial glacialhnterglacialoscillations oscillationsinvolving involving moderate global Ma and and there therewere were22 22oscillations oscillations involving involving moderate global ice ice volumes volumes between 2.4 2.4 Ma and 0.9 Ma greater ice volumes from .9 Ma to the present present (Fig. (Fig. 3) 3) (Shackleton (Shackleton et et al., al., 1984). 1984). Counting back from our current oxygen isotope stage, stage 1, odd-numbered stages represent interglaciations interglaciations stages, glaciations. glaciations.Oxygen-isotope Oxygen-isotopestages stages2,2,6,12 and16 16show show the the greatest greatest and even-numbered even-numbered stages, 6, 12 and ice volumes, perhaps perhapsexplaining explainingthe the historical historical recognition of a four-fold record of terrestrial glaciation. glaciation. SPECMAP SPECMAP COMPOS!TE. COMPOSITE. 4 0.0 6180 6"0 (cr) (a) 0 2 —2 6"=0 ö'o (c) (a) 4 —4 0.0 • $_ 7 , $ —2 --4 7 10 0.5 0.5 a 2$-uz 1.0 0 2 25 1.0 1 .o - • 1.5 - 52 ' • 60 • 52 63 - Figure 3. Oxygen-isotope Oxygen-isotope profile derived from four cores (2 Atlantic Atlantic and 2 Pacific), Pacific), showing showing the the dominance dominance cores of the 41,000-year 41,000-year frequency before about 700,000 the 100,000-year 100,000-year frequency frequency after. after. Note years ago, and the the higher values values (and thus larger ice volumes) volumes) for 12, and and 16, 16,perhaps perhaps representing representing times times stages 2, 6, 12, when the Laurentide Laurentide ice sheet extended extended into the Great Lakes region and and beyond (from (from Williams Williams et et a!; al; 1988). 1988). Lakes data are compared compared with the the SPECMAP SPECMAP These data compilation compilation (Imbrie et al., 1984). 1984). . 2.0 148 . �oxygen-isotopestage stage 2 (the late Wisconsin7 During oxygen-isotope Wisconsin, retained retained from from the the former former chronology) chronology) and possibly possibly during during stages stages6, 6?12 12and and 16, 167Minnesota Minnesota was at the edge of an ice sheet that covered and most most of of Canada Canada (Fig. (Fig. 4). 4). thin7dynamic dynamic ice ice lobes lobes that that advanced, advanced?stagnated, stagnated?and and Minnesota was was affected affectedmainly mainly by by thin, Minnesota retreated independently independently of one another another (Wright, (Wright?1972). 1972). Ice-lobe Ice-lobedynamics dynamics were were controlled controlled by by retreated the mass mass balance balance and and bed conditions conditions of their respective icesheds. Owingto to the the different different substrates substrates the icesheds. Owing the ice ice flowed flowed over, over7it is possible possible to to distinguish distinguish the till of of the the different different ice ice lobes lobes using using matrix matrix color?texture texture and and mineralogy, mineralogy?and and clast clast lithology, lithology7and and thus thus reconstruct reconstructthe the activity activityof of the the lobes. lobes. color, few advances and aid in the reconstruction of the nature of ice ice Landforms remain for the last few advance advance and and retreat. retreat. Figure 4. Laurentide Laurentideice icesheet sheetatat14 14Ka. Ka. (Modified (Modifiedfrom fromDyke Dykeand andPrest, Prest?1986). 1986). Figure 4. Absolute dating dating of of the the late lateWisconsin Wisconsin glacial glacial sediments sediments is is possible possible using using radiocarbonradiocarbondating methods ifif organic organic remains remains are are found. found. Pre-late Pre-late Wisconsin units are difficult difficult to to date date absolutely Wright?1987). 1987). AAfew fewscattered scattereddates dateshave have been been secured securedin in the the area area absolutely (Ruddiman (Ruddiman and and Wright, using usingthe the presence presenceof of volcanic volcanicash ash (Richmond (Richmondand and Fullerton, Fullerton71986), 1986)?magnetic magneticreversals reversals preserved preserved in till and lake sediment (Patterson, 1993), amino-acid dating of shells (Gilbertson, 1990) and lake sediment (Patterson?1993)?amino-acid (Gilbertson71990) and cosmosgenic cosmosgenic isotope isotope age age estimates estimatesof of striated striatedrock rock surfaces surfaces(Bierman (Bierman et et al., al.?in in press). press). 149 �The basic stratigraphy stratigraphy was was described described by Matsch Matsch (1972). The history history of of work work in this area and the basic oldest glacial glacial sediment sediment in in southwestern southwestern Minnesota Minnesota is at least of mid-Pleistocene age age (Fig. (Fig. The oldest (Patterson,1997) 1997)and and may may even even be be of of Late Late PliocenefEarly Pliocene/Early Pleistocene Pleistoceneage age(2.1-1.2 (2.1-1.2 55 A and B) (Patterson, Ma) based based on on correlations correlations with glacial sediment in Ma) in Iowa Iowaand andNebraska Nebraska(Hallberg, (Hallberg,1986). 1986). These depositsare are attributed attributedto to northwest-sourced northwest-sourcedice iceadvances, advances,which which deposited depositedgray, gray, loam-to-clayloam-to-claydeposits loam tills tills containing containingclasts clasts of of Paleozoic Paleozoic carbonate carbonate and Cretaceous Cretaceous shale. There Thereare areatatleast leasttwo two loam tills tills of this age age that are are difficult diflicult to differentiate. Similar Similartills tills in South South Dakota are thought to be .6 Ma to 2.1 Ma (Gilbertson, 1990). (Gilbertson, 1990). / Figure 5. Ice Iceadvances advancesinto intothe the region. region. A. A.Early EarlyPleistocene Pleistoceneadvances, advances,greater greater that 0.6 Ma; B. B. Ice Ice Figure5. advance advance from from the northwest; C. C. Ice Ice advance advance from the northeast; D. D. Ice Iceadvance advancefrom fromthe thenorth, north, deposition 0-20 depositionof ofGranite GraniteFalls Fallstill till>40 >40ka; ka; E. E.Late LateWisconsin Wisconsinadvance advanceofofearly earlyDes DesMoine Moinelobe, lobe,330-20 ka; F. Late Wisconsin advance of the Des Moine lobe, 14 ka. (From Patterson, 1993). ka; F. Late Wisconsin advance of the Des Moine lobe, 14 ka. (From Patterson, 1993). 150 �Stratigraphicallyabove above these these gray gray tills tills is is aa northeast-sourced northeast-sourced glacial glacial sediment sediment(Fig. (Fig.5C) 5C) Stratigraphically that can can be be distinguished distinguishedby by its itsred-brown red-brown color, color, sandier sandier texture, texture, and and clasts clasts originating originating in in the the that Lake Superior Superiorarea area including including banded banded iron iron formation, formation, agate, agate, red Thisunit, unit, Lake red clastics clastics and and basalt. basalt. This the Hawk Creek till (Matsch, 1972) is only locally preserved and its southwestern extent is not the Hawk Creek till (Matsch, 1972) is only locally preserved and its southwestern extent is not known. ItItisisthought thoughtto tobe be >50 >50 ka ka (Gilbertson, (Gilbertson,1990). 1990). known. Thelast lastpre-late pre-lateWisconsin Wisconsinglacial glacial advance advancewas was from from the the north-northwest (Fig. 5D) 5D) and and is is The north-northwest (Fig. similarto to the theolder oldergray grayunits unitsbut but has has less less Cretaceous Cretaceousshale. shale.Wood Woodininthis, this,the theGranite GraniteFalls Fallstill, till, similar is A0,OOO years old (Matsch, 1972). is >40,000 years old (Matsch, 1972). The surficial surficial glacial glacial sediment sediment in in the the Minnesota Minnesota River River basin basin was was deposited deposited by by the the late late The Wisconsin Des Moines lobe, which advanced, stagnated and retreated repeatedly. Its first advance Wisconsin Des Moines lobe, which advanced, stagnated and retreated repeatedly. Its first advance may have have been been as as early early as as 30-20 30-20 ka ka (Fig. (Fig. 5E) 5E) (Gilbertson, (Gilbertson, 1990) 1990) The Theadvance advanceto to Des Des Moines, Moines, may Iowa is is dated dated at at 14 14ka ka (Fig. (Fig. SF) 5F) (Clayton (Clayton and 1982; Hallberg The Iowa and Moran, Moran, 1982; Hallberg and and Kemmis, Kenimis, 1986). 1986). The loam-textured till is gray when unoxidized and has Cretaceous shale and Paleozoic carbonate loam-textured till is gray when unoxidized and has Cretaceous shale and Paleozoic carbonate clasts.ItItgenerally generallycontains containsPierre PierreShale, Shale,whereas whereasthe theolder oldergray graytills tillscontain containother otherCretaceous Cretaceous clasts. formations such as the Greenhorn and Carlisle. The base of the Des Moines lobe till is locally locally formations such as the Greenhorn and Carlisle. The base of the Des Moines lobe till is marked by by aa planar planar concentration concentrationof offaceted, faceted,striated striatedboulders. boulders. marked GlacialLake LakeAgassiz Agassiz and and Glacial Glacial River River Warren Warren Glacial commonfor forlakes lakes to toform formin infront frontof ofaaretreating retreatingglacier, glacier, with with meltwater meltwater ponding ponding ItIt isiscommon between aa moraine moraine and and the the ice ice front. front. AAproglacial proglaciallake lakemay maynot notbe bevery verylarge large or or long-lived long-lived between because of the instability of the moraine dam and ice margin. However, an unusually stableand and because of the instability of the moraine dam and ice margin. However, an unusually stable large proglacial proglaciallake lakebegan began to to form form in in west-central west-central Minnesota Minnesota at approximately approximately12 12ka ka as as the theice ice large retreatednorth north of of the the Big Big Stone StoneMoraine Moraine and and the the nonspectacular nonspectacular continental continental divide divide at at Brown's Brown's retreated Valley (Fig. 6). Valley (Fig. 6). For much muchof ofits itsearly earlyhistory, history,Glacial GlacialLake LakeAgassiz Agassizwas wasdrained drainedby byGlacial GlacialRiver RiverWarren, Warren, For which flowed southeast from the southern tip of the lake (Upham, 1883, 1895; Matsch and which flowed southeast from the southern tip of the lake (Upham, 1883, 1895; Matsch and Wright, 1967). 1967). Initially Initially Glacial Glacial River Rver Warren Warren cut series of of anastomosing anastomosing channels channels with with Wright, cut aa series streamlined residual bars and boulder lags (Matsch, 1983). The style of channel formation streamlined residual bars and boulder lags (Matsch, 1983). The style of channel formation isis characteristicof ofsudden suddenand andlarge largedischarge dischargefrom fromaa lake lake that that overwhelms overwhelms the the existing existing drainage drainage characteristic system (Kehew (Kehew and and Lord, Lord, 1986). 1986). Flow Flowwas waseventually eventuallyfocused focused in inone onemain mainspillway spillwaywhich which system became more deeply incised, stranding earlier channels (Fig. 7). became more deeply incised, stranding earlier channels (Fig. 7). Continuedretreat retreatof ofthe theice icefront fronteventually eventuallyopened openedlower lower outlets outletsfor for Glacial GlacialLake Lake Agassiz Agassiz Continued to the northeast (Clayton, 1983) and possibly the northwest (Smith and Fisher, 1993) and to the northeast (Clayton, 1983) and possibly the northwest (Smith and Fisher, 1993) and Glacial Glacial River Warren was abandoned abandoned as as an an outlet. outlet. Tributaries Tributaries to to Glacial Glacial River River Warren, Warren, which which had had River steepened their their gradients gradients in in response response to tothe thedowncutting, downcutting,were were now now contributing contributingtoo toomuch much steepened sediment to be carried away by the reduced flow of the river. Fans spread across the valley floor sediment to be carried away by the reduced flow of the river. Fans spread across the valley floor partiallydamming dammingit,it,forming formingaaseries seriesof oflong longlakes lakes(Wright, (Wright,1972; 1972;1990) 1990)including includingLake LakeTraverse, Traverse, partially Big Stone Lake, Marsh Lake and Lac qui Parle. The levels of these lakes are now controlled by Big Stone Lake, Marsh Lake and Lac qui Parle. The levels of these lakes are now controlled by damsfor for recreation recreationand andflood floodabatement. abatement. dams Thefield fieldstops stopswill willfirst firstaddress addressthe the most most recent recent event event related related to to glaciation, glaciation,the the formation formation The of the the Minnesota MinnesotaRiver RiverValley, Valley, and then move move to to progressively progressively older older events events that that are are exposed exposed of because of of river river downcutting. downcutting. See Seeplate plate11(page (page168) 168)for forstop stoplocations. locations. because 151 �KM Figure Figure6. 6.Early Earlystages stagesofofGlacial Glaciallake lakeAgassiz. Agassiz.(Adapted (Adaptedfrom fromTeller, Teller,1987). 1987). 152 �pPpLrmw hf Hermanstage stagedownstream downstreamfrom fromOrtonville. Ortonville. Herman Thewide wideshallow shallowRiver RiverWarren Warren(in (inblack) black) The flowsacross acrossaaflat flatstretch stretchofoftopography, topography, flows "'i" around branching aroundislands islandsofofdrift. drift. r-d i—J 1 I I0 ost-Tintah stage downstream from rtonville. The auxiliary channels are bandoned as River Warren (in black) enches more deeply. A few islands, ome of bedrock, appear in the channel ownstream from Ortonville. 7 r-l- .-A resent valley. Alluviation by tributarie as segmented the valley abandoned by Warren into a series of long, shallow lakes, connected by the Minnesota River. r - Figure Figure 7.7.A.A.Initial Initialstages stagesofofdevelopment developmentof ofGlacial Glacial River Warren. Warren. B. B. Formation Formationofofmain mainriver rivertrenches. trenches. Abandoned Abandoned channels channels may may be be marked marked by river lags. C. C. Present-day Present-day Minnesota MinnesotaRiver River Valley. Reproduced Reproduced from from Matsch, Matsch, 1983. 1983. 153 �FIELD TRIP FIELD TRIPSTOPS—DAY STOPS-DAY 2 Stop 1—Ingebretsen's 1-Ingebretsen's Landing, Landing, or "the clay banks" on Lac qui Parle. Milanquadrangle, quadrangle, Stop Pane. Milan T. 119 42 W.-section 32 32 119 N.-R. 42 and low bank are formed in 2-3 m of reddish matrix has 43The beach and reddish brown brown till. till. The till matrix 48 percent sand and and the the clasts clasts have have aa northeastern northeastern provenance; provenance; you may find find Lake Lake Superior Superior clastic rocks on the beach. This Thiscolor, color,texture textureand and agates, banded iron formation, formation,basalt basalt and and red clastic agates, banded iron grain type are unusual for tills in this general area. area. This is not the surface till in the region but but is normally found deeper deeper in the glacial glacial section section and was exhumed by river downcutting. In places there are are remnants remnants of of another anothertill till overlying overlying this this red red till. till. It can be distinguished distinguished by its siltier northwest, including siltier texture texture and and clasts clasts typical typical of of an an ice ice advance advance from from the northwest, includingPaleozoic Paleozoic carbonate and Cretaceous Cretaceous shale. shale. discontinuous boulder A discontinuous boulder lag lag represents represents the erosional discontinuity created as Glacial River Warren, Agassiz, cut into the the glacial glacial sediments, sediments, selectively removing removing Warren, the spillway spillwayfor for Glacial Glacial Lake Lake Agassiz, the finer grains. The Thefollowing followingsections sectionsfrom from aa paper paper by Kehew Kehew and Lord (1986) describe the general formation of glacial-lake glacial-lake spiliways spillways (Fig. 8). The instability of the the spillway spillway rivers rivers was was exceptional; exceptional; torrential torrential discharges discharges no sediment from glacial-lake glacial-lake outlets, following following dam failure, had high energy and no load. Consequently, Consequently,flows flowswhich whichincised incisedspillways spillwayswere were highly highly erosive, erosive, and and channel channel sediment from these events is scarce. The The flood flood deposits deposits which do exist consist of homogeneous masses of very poorly sorted, pebbly homogeneous masses pebbly cobble cobble gravel, gravel, which indicates water. p. 165 rapid aggradation in very turbulent water. 165 154 �The morphological morphologicd characteristics characteristics of of spiliways. spillways....indicate indicate that the spiliways spillways were channels that that contained contained flow flow at at bankfull bankfull stage stage during during one one or more highly Thesize sizeof of the thespillways spillwaysqualitatively qualitatively demonstrates demonstrates that the the flood flood erosive floods. The discharges were enormous, and the estimated volumes of most proglacial proglacial lakes lakes (Kehew and Clayton, 1983) require that that bankfbll banklull discharges couldn't have been (Kehew sustained for more than aa few few weeks. weeks. In short, spiliways spillways in the the mid-continent mid-continent region geologically instantaneous instantaneous events of colossal colossal magnitude magnitude region were were incised incised by a few, geologically in comparison comparison to modern modern river discharges. p. 165 165 . At this location in Glacial Glacial River River Warren, two subparallel channels were incised rather than one main channel: channel: Lac Parleand andWatson Watson Sag. Sag. They Theyare areseparated separated by the erosional Lac qui qui Pale residual is located located on. on. According to Kehew and and Lord, Lord, (1986) (1986) erosional erosional residua1that the the town of Watson is residuals are key to identifying floods that overwhelmed existing drainage systems. residuals are identifying floods that overwhelmed existing drainage systems. organic horizon horizon associated associated with with the theboulder boulder lag. lag. A A silty silty lake lake sediment sediment In places there is an organic caps the section. The organic horizon and lake sediment may represent Glacial River section. The organic horizon and lake sediment may represent Glacial River Warren overbank deposits deposits or more recent overbank E X PP L AANAT N A T IION ON Holocene deposits. An examination examination of the organics of organics for pollen pollen to to determine their approximate determine approximate age age fihallow Channel before radiocarbon before radiocarbon dating was was considered yielded no identifiable considered yielded identifiable 9 Erosional Erosional Residual Residual grains. The bank The bank has has retreated significantly in recent years and the DNR-fisheries is planning to riprap Longitudinal it to prevent prevent further further retreat. retreat. Their Groove concern is that sediment loading of lake is negatively the negatively affecting affecting fish fish Boulder Lag habitat. habitat. Features to see: Features see: • Lake LakeSuperior Superioragates, agates, banded iron formation, basalt basalt and red elastic formation7 clastic rocks on the beach indicative indicative of a northeastern provenance provenance for the northeastern till. • Joints Joints in in till till with with narrow zones of reduced indicating reduced till indicating water water Figure 8. There Thereare are two two basic spillway levels: (1) (1) the movement along the joints. trench-like, channel; and (2) the trench-like, low sinuosity, inner channel; • Boulder lag and associated associated organic organic broad outer zone with: (a) slighity of slighlty scoured areas of honzon. horizon. channels; and anastamosing channels; and (b) (b) the the deeply deeply scoured scoured v / displays longitudinal longitudinal grooves, zone which displays grooves7streamlined erosional residuals residuals and and boulder boulder lags. lags. From erosional From Kehew Kehew and Lord (1986). (1986). 155 �Stop2—Glacial %Glacial Lake Lake Benson Benson sediment sediment exposed exposed along the Chippewa River. Bend City City Stop River. Big Bend quadrangle, T. T. 120 120N.-R. N.-R. 41 41 W-section W-section 36 36 Glacial Lake Lake Benson, a moraineGlacial morainedammed, 2800 sq km, proglacial lake in dammed, 2800 west-central Minnesota, formed formed during during the the west-central Minnesota, late Wisconsin Wisconsin retreat retreat of of the Des Moines lobe (Fig. 9). It was the last in a series of of retreated lakes before the Des Moines lobe retreated north of the divide to form form Glacial Glacial Lake Lake Agassiz (Diedrick and and Rust, Rust, 1975; 1975; Agassiz (Diedrick Patterson, Cotter Cotter and Knaeble, Patterson, Knaeble, 1998; 1998; Rittenour, Geiger and Cotter, Cotter, in prep.) Two-rn-thick exposures exposures of of lake Two-m-thick lake sediment Chippewa River in Swift sediment along along the Chippewa and Chippewa counties counties show show as many as 23 23 rhythmically bedded couplets interpreted as annual interpreted annual layers layers (varves) (varves) by Des Moines lobe till. In a underlain by series of undergraduate undergraduate and and NSF-sponsored NSF-sponsored for REU (Reseach (Reseach Experience supervised by Jim Undergraduates) studies studies supervised Cotter of University of Minnesota, Minnesota, Morris, Morris, students students have described described and counted counted varves at five five sites; 44 4 4 varves were were correlated correlated (Rittenour, (Rittenour, 1994; 1994;1995). 1995). exposure you will note that in some areas the beds beds are are overturned. overturned. We interpret interpret this In this exposure this as a result of the lake forming forming in an area where there was stagnant glacial ice which melted out, out, been deposited deposited in in a disrupting some of the beds. The Theupper, upper, massive massive silt and clay may have been shallower lake that was was unfavorable varve to development because the wave base base disturbed disturbed the the bottom bottom sediment. sediment. Features to see: see: • Difference in grain size of the winter and summer layers. • Upward decrease in thickness of summer layer indicating lessening sediment load and aid retreating glacier. retreating glacier. • Overturned beds. • Dropstones. Dropstones. • Nature of of contact contact with underlying Des Moines lobe lobe Figure 9. Approximate Approximateextent extent of of Glacial Glacial Lake Lake Benson till. till. (from Rittenour Rittenour et al., al., in in prep). prep). 1 156 �Stop 3—Ice-confined &Ice-confined streams. Montivideo Montivideo landfill landfill and nearby pits. Montevideo Montevideoquadrangle, quadrangle, Stop 117 N.-R. 40 W.-section 12; Asbury W.- section section 13 13and and T. T. T. 117 Asbury quadrangle, quadrangle, T. 1. 117 N.-R. N.-R. 40 40W.117 117 N.- R. R. 39 39 W.-section W.-section 33. 33. These These three three pits pits have have been been developed developed in in southeast-oriented, southeast-oriented?discontinuous discontinuousridges ridgesthat thatare are generally less less than than 77 m high. We We may may only only visit visit one one or two of the pits depending generally depending on the quality of the exposures exposures and time constraints. These transverse to them form These ridges ridges and others oriented transverse a rectilinear rectilinear pattern pattern that that is is common common in in the the interior interiorof of the the Des Des Moines Moines lobe. lobe. Ridges Ridges parallel to to ice ice flow, flow, and therefore to former ice surface surface slope, slope?are are predominantly predominantly composed of sorted sorted sediments. The Thetransverse transverse ridges ridges are are composed composed of sediment sediment ranging ranging from from diamicton to to sand sand and and gravel. gravel. Most Mostof of the thesampled sampledtransverse transverse ridges ridges were were only only slightly slightlycoarser coarser diamicton and more more sorted sorted than than the the underlying underlying and and surrounding surrounding till. till. ridges are result of The ridges are intepreted intepreted to to be be a result the pervasively pervasively crevassed crevassed deposition localized in the stagnant stagnant ice of the Des Des Moines Moines lobe lobe (Fig. (Fig. 10) 10) (Matsch, (Matsch, 1972; 1972; Patterson, Patterson?1997). 1997). Crevasses oriented oriented paralled paralled to to the the ice ice surface surface Crevasses slope were preferentially used by by supraglacial supraglacial streams. streams. Final melting melting of the ice ice walls walls of of the the streams inverted the the topography topography and left sorted sorted stream sediment sediment as a positive positive element element in in the the landscape. landscape. iceBenson outlets were were iceGlacial Lake Benson confined and the pits east and north of the landfill landfill are interpreted as part part of a late-stage interpreted as late-stage outlet of Glacial Lake northern pit, pit, well well Glacial Lake Benson. Benson. In the northern sorted sand is unconformably unconformably overlain by poorly sorted sorted pebbly pebbly sand which which has an an indistinct, indistinct, conformable contact with with the the overlying diamicton. This is is overlying diamicton. This interpretedas as steady steady discharge discharge interpreted followedby by aa larger, larger?short-lived followed short-lived discharge causing causing the the collapse collapse discharge of of stagnant stagnantice ice resulting resultingin inflow flow of diamicton into the channel. channel. Features Featuresto to see: see: • Climbing Climbingripples. ripples. • Uncollapsed Uncollapsedbeds beds indicating indicating no ice ice beneath beneath the the stream stream when when the sediments sediments were were deposited. deposited. 157 157 �Figure 10. 10. Heavily crevassed, postsurge Bering Glacier, surge ice surface surface of the Bering Glacier, Alaska. Photograph reproduced Photograph reproduced with with the the permission permission of of B. B. Molnia. Molnia. 158 �Stop4—Glacial &Glacial Stratigraphy, Stratigraphy,Upper UpperSioux SiouxAgency Agency State StatePark, Park, exposure exposureon on the theyellow Stop Yellow Medicine Medicine LoneTree TreeLake Lakequadrangle, quadrangle,T. T. 115 115 N.-R. 38 38 W.-section 30 River. Lone WARNING This is an unstable Be aware awareof of the the position position of others on the slope. Do not unstable outcrop. Be another person before digging digging or descending. descending. follow another personup upaagully. gully. Look Lookfor forpeople peoplebelow below you before Climbing up up is is easier easier than than getting getting down. down. Hardhats Hardhats are are recommended. If you chose not to climb around on this outcrop, samples of the till and and washed washed pebbles from the different different units will be provided for for viewing viewingon ontop topof ofthe thebluff. bluff. Do not step too close There are are rotational rotational slump slump blocks blocks waiting to descend; avoid close to to the the edge. edge. There becoming colluvium. colluvium. Nearly of glacial glacial sediment sediment is is exposured exposured along this meader bend of of the the Yellow Yellow Nearly 100 ft of Medicine River (Fig. 11). This This is almost almost the entire thickness of glacial glacial sediment at this this location. location. constructed from from waterwaterCross sections constructed well data show show the regolith regolith surface surface at at approximately immediate approximately 930 930 ft ft in the immediate just a few feet below the river area; this is just bed. bed. uppermost unit is a 2-3 m layer The uppermost of Des Moines lobe till. It accessible It is not accessible from this outcrop. Please do not Please do not try! try! There is aa discontinuous There discontinuous boulder boulder pavement pavement at the base of the Des Des Moines Moines lobe till. till. The boulders are faceted and and striated and and form form aa planar planar surface. surface. The The boulder pavement, although not continuous, is found at this stratigraphic stratigraphic position the position over over most most of of the interior of the I/i ,—ih,Des Moines lobe in Minnesota (Wright (Wright et et 1973). The Thefaceting facetingand andstriating striatinghad had to todevelop develop beneath beneath aa moving moving glacier glacier that did did not, not, al., 1973). however, however, have the shear stress to move move the theboulders boulders very very far farbecause becauseunderlying underlying beds beds are are generally generally not disturbed. Theboulders bouldersmay mayhave havebeen been concentrated concentratedat at the the surface surfacebefore before the glacier glacier overrode overrode disturbed. The them by water or periglacial processes. processes. Alternatively, some have proposed that the Alternatively, some have proposed that the boulder boulder concentration settling through an incompetent incompetent till matrix concentrationdeveloped developedsubglacially, subglacially, by large large clasts settling (Clark, 1991). 1991). The Theissue issueisisstill stillunresolved. unresolved. The exposure of the The next next unit unit is exposed exposed is is the the Granite Granite Falls Falls till. till. This may be an atypical exposure Granite Falls till; it is siltier than normal and layered layered with with sorted sorted sediment. sediment. Toward the base base of this unit, near near the the contact contact with with the the underlying underlying fine fine sand, sand, discrete discrete lobes of of diamict diamict can can be be recognized. These Thesefeatures featuresare areinterpreted interpretedas as the the result result of of flow flow of of the the till till into into standing standing water. water. This is a very plausible scenario given the unit immediately below which has been interpreted plausible scenario given unit which has been interpreted as a lake sediment. sediment. is mainly mainly aa fine fine sand sand with with silt silt and and some some clay. clay. In The unit interpreted as lake sediment is In places it is finely finely bedded. bedded. The Theextent extentof of the the lake lake sediment sediment beyond beyond this outcrop is not well 159 �Figure 11. 11. Yellow Yellow Medicine Medicine River River exposure exposure in Upper Sioux Sioux Agency State Park looking downriver. Photograph Photographby by Star Star Mulder known. From Fromthis thisexposure exposureitit appears appearsto to be be aarelatively relatively deep deep lake and therefore could have covered a large large area. area. Beneath the the lake lake sediment sedimentis a thick, gray loamy Beneath loamy till. till. Note the many well-striated Paleozoic Paleozoic carbonate clasts. clasts. The Thelower lowertill tillhas hasnot not been been well well exposed exposed here here but at other cuts along this river carbonate there are are two two gray tills tills separated separatedby aa glacial glacial stream stream sediment sediment at at this stratigraphic stratigraphicposition. Features Features to to see: see: • Striated, Striated,bullet-shaped bullet-shaped clasts clastsof of Paleozoic Paleozoic limestone limestonefrom from lower lower till. till. • Path Path of of groundwater groundwater flow through glacial units. Note Note areas areas of of lateral lateral flow. flow. • Contact of the Granite Falls till with underlying lake sediment. Contact of the Granite Falls till with underlying lake sediment. • Evidence Evidence for for depositional depositional environment environmentof of Granite GraniteFalls Falls till. • Boulder Boulder pavement pavement (from (from aa distance, distance,please). please). 160 �Stop5—Inge 5-Inge Kea's Kea's climbing climbingripples. ripples. Iverson IversonLake Lakequadrangle, quadrangle,T. T. 114 114 N.-R. 37 W.-section 23 Stop (this stop is out of stratigraphic stratigraphic order along the field trip route) located in an an This sand pit is located upper terrace along the Minnesota Minnesota The deep deep channel channel below us is River. The the Glacial Glacial River River Warren Warren part of the spillway. spillway. Glacial outwash outwash streams streams flowed from from the retreating retreating Des Des flowed Moines general area of Moines lobe lobe in the general Glacial Warren prior prior to its Glacial River River Warren formation. formation. This exposure is most most likely likely a remnant of an earlier earlier outwash stream. stream. The The depositional depositionalenvironment environment is distinctly different different from the first stop of the the day. day. Features to see: Variation in migration and migration and aggradationrates rates (angle (angle of climb). climb). aggradation Stop6—Rush &Rush River River Wayside; Deformation of Henderson quadrangle quadrangle T. 112 Stop of glacial glacial sediment. sediment. Henderson N.-R. 26W-section 15 The downcutting of this east-flowing east-flowing Minnesota River has exposed exposed tributary to the Minnesota glacial units glacial units that display display deformation deformation induced by the advance a glacier. induced by the advance a glacier. Mark Mark Johnson Johnson of Gustavus Gustavus Adolphus College has directed undergraduates from his school directed undergraduates from school and from an NSF-sponsored NSF-sponsored field program program in in work work on the details details of this outcrop outcrop (Fig. (Fig. 12). 12). The lowest lowest unit is a gray The gray loamy loamy till till and it is conformably conformably overlain by lake sediment, sediment, that, judging judging by the color, formed in front of the retreating, gray-till-bearing gray-till-bearing ice lobe. lobe. The gray lake sediment sediment grades into a red red layers. This sandy unit records sand with silt layers. the northeast. the advance advance of an ice lobe from the northeast. The next unit is a mixture of the underlying sand sand with with aa red red sandy sandyloam loamtill. till. There is a sharp contact between this and the final unit exposed, exposed, a homogenous red sandy till. Folds: The lower two units are folded into three anticlines anticlines that span the outcrop. outcrop. sand displays displays a subparallel subparallel series series of high-angle high-angle normal faults. faults. Faults: The red sand Faults: Fabric: The long axis of prolate pebbles in a till till are are commonly commonly measured measured and plotted plotted on Fabric: a Rose diagram. Pebbles Pebblesin in aa subglacial subglacialtill till may be oriented oriented by the the shear shear stress stress of the overriding overriding glacier; glacier; pebbles pebbles are are generally generally parallel parallel to to flow, flow, with a slight slight upsuggesting ice flow from from the the north-northeast. north-northeast. glacier dip. The The red red till till has a fabric suggesting 161 - ll rn �Si .5Z $2 .38 53 .10 SI .4 53 .44 53 .o Elgen Values Si .55 51 .5S 52 .38 SZ .31 53 .13 53 .0? * F,t Ta., • zs Mlyi Siiuple T.n w 0000 OlyL1y MSfldOnud RhvwO (rscxit) DdR.d Old Grey Grey EJ Hs$d LayW Leysre eI 1*. Sam.nts iiwougl.on — S Faà. Tp-.* sew Figure Figure12. 12.Structural Structuraldata datafor forRush RushRiver Riveroutcrop. outcrop.Unpublished Unpublishedwork workofofAmy AmyMoe, Moe,Gustavus Gustavus Adolphus AdolphusCollege Collegestudent, student,1996. 1996. 162 �Ouestion structural data consistent with the simple interpretation of proglacial deformation Is the structural and eventual overriding overriding by the advance of the the red-till-bearing red-till-bearing ice ice lobe lobe from from the the north-northeast north-northeast (Fig. (Fig. 13)? 13)? - p_se. — -.p mmmbwlI@ll .I—_ =-- V v - —_ V v Vv 1401 wt-mmma A. Advacing Advacing glacial glacial ice with attached frozen frozen-unfrozen substrate. Shear Shear forces forces along the frozen-unfrozen boundaryat boundaryat the base base of the slab slab initiate i ~ t i a t thrustthmste block movement. movement. —— \ • B. Thrusted Tbrustedsubglacial subglacialslabs slabs are are deformed deformed and attacked Snout. attacked at the the glaciers glaciers~ snout. C. Glacial Glacialice ice ovemdes ovenides the the thrust thrust slabs, causing more more deformation. deformation. 13. Sequence Sequenceof ofproglacial proglacialdeformation deformationA A and and B B with with eventual eventual overriding by Figure 13. advancing glacier glacier (from (fromAber, Aber, 1988). 1988). the advancing TERRACES THE MINNESOTA RIVER NEAR SHAKOPEE, SHAKOPEE,MINNESOTA MINNESOTA TERRACES ALONG THE Barbara Lusardi Lusardi The Minnesota Minnesota River River Valley near near Shakopee is almost almost 200 200 feet feet deep deep and and over over 33 miles miles wide wide in places. highlands on on either either side side of of the valley rise to an elevation places. Till highlands valley rise elevation of over 900 feet. Distinct terraces terraces step step down into into the valley where the undefiit across underfit Minnesota River meanders across a broad alluvial alluvial plain. based on on elevation. elevation. The Three terraces are distinguished based The uppermost uppermost terrace, terrace 3 (Qft3), is visible just to the the south south of of highway highway 169 169 between between Marschall Marschall Road and Marystown Marystown Terrace33 is is at at an an elevation elevation of about 850 feet-150 Road. Terrace feet—iSO feet feet above abovethe themodern modernfloodplain. floodplain. A distinct scarp separates the terrace from the till upland to the south, and smaller channel scars crisscross the surface "islands" above terrace above the level of terrace crisscross surface breaking breaking the the terrace terrace up into three small ''islands" thick over overbedrock. bedrock. Data from water 2 (Qft2). Alluvial Alluvial sediments sediments of of terrace terrace 3 are up to 40 feet thick well logs indicate that sand and gravel extends suggests that extends south beneath beneath the the till till upland. upland. This suggests the terrace sediments outwash deposits deposits that that have have been eroded eroded to form form the the terrace. terrace. sediments may may be be outwash follows the middle terrace, terrace, terrace terrace 2, 2, at atan anelevation elevationof ofapproximately approximately The new highway 169 169 follows feet—i 10 feet above the modern modern floodplain. Numerous 810 feet-1 Numerous shallow shallow channels crisscross the terrace surface. Alluvial Paleozoic bedrock. bedrock. Just south of Alluvial sediments sediments are are 10-50 10-50 feet thick over Paleozoic Shakopee, terrace miles wide. wide. It narrows to the southwest southwest and and eventually eventually disappears disappears Shakopee, terrace 2 is about 1.5 miles (Qftl) near Meniam. Many Manygravel gravel pit pit operations operations occur occur within sediments of against terrace 1 (Qftl) near Merriam. terrace 2 and and into into the the bedrock bedrock below. below. 163 �_ ___ 14. Terraces Terracesof ofthe theMinnesota MinnesotaRiver River Valley Valley near Shakopee and Chaska. Figure 14. ; \G1ajidepsits \i . ' ;7i / 2 / I :/ / ' Qf / ( / /_ /I * wa f -., — . SCALE 1:62 162500 SCALE 500 2 1/2 1 1 1 ~ (sand and gravel and till) i .. 3/4 — : I . }/' 1 / ... _,$7 I' - •— 1.1 — ikt j $ r — . L 1 . / . Lower terraces cut into glacial p- sediments and bedrock I .. : I 1 KILOMmER KILOMETER preserved as terraces above the floodplain of the modern Minnesota River Highest terrace cut into glacial sediments Z / I 0 : ALLUVIAL TERRACES—Cilacial River Warren sediments - / -.. U 11MILE MILE 0 5 .5 H - 1 Qft3 Alluvium of Terrace 3—Elevation —850 ft 150 ft (46 m) above present floodplain Silty loam to sandy loam (fine grained in shallow channels) grading into loamy shale; increasing percentage of gravel with depth. Qft2 above present floodplain Loam to sandy loam (fine grained in shallow channels) 1 2mm coarse sand than 1 percent percent shale; shale increasing fraction contains less than percentage of gravel with depth Qftl Alluvium of Terrace 1—Elevation 750 ft 50 ft (15 m) above present floodplain Variable thickness of predominantly medium to coarse coarse sand. sand. 1 / c I 1 / GLACIAL DEPOSITS—Sediment deposited by the Des / Moines lobe Contains abundant shale fragments .- 1 PALEOZOIC BEDROCK—Prairie du Chien dolostone and Jordan Sandstone mapped within 10 feet of surface. L This map consists of portions of the Shakopee and Jordan East 7.5-minute quadrangles that have been modified and reduced in scale Linework and descriptions are taken from Lusardi (1997) and Lusardi (in prep). Hennepin I Carver ---I)ak ota Scott L -Dig ram Location Digram I@ 164 �The lowest lowest terrace terrace is is at at an elevation elevation of approximately 750 feet—50 feet-50 feet feet above above the the modern modern The approximately 750 floodplain. In Inmany manyplaces places the the underlying underlying bedrock is at or near the Ordovician Prairie Prairie floodplain. the surface. surface. Ordovician du Chien dolostone is the principal source for crushed stone. Cambrian Cambrian Jordan Jordan Sandstone Sandstoneisis exposed limited areas just west exposed in limited areas near Merriam and Baden. The The only only known sandstone sandstone quarry, just of Baden, Baden, is is now now abandoned. abandoned. On the opposite terraces are narrow narrow or or obscured. obscured. Just northeast opposite side of the river, the terraces northeast of Chaska, sediments sediments of terrace terrace 11 are are buried by colluvial sediments eroded from from the the valley valley wall. Chaska, small remnants remnants of this this lowest lowest terrace terrace are visible above the floodplain. Terrace22 is is present present Only small floodplain. Terrace 114 mile as a very narrow strip, less than 1/4 mile wide, wide, between between Chaska Chaska and and Carver. Carver. Terrace 3 is is present present south of Chaska dramatically south south of Carver. Sand Sandat at the the same same elevation elevation of of terrace terrace south Chaska and widens dramatically 3 continues to the south south in aa band band almost almost 2.5 2.5 miles miles wide wide along along the the river, river, although although no no distinct distinct scarp is obvious. Unlikethe the other other terrace terracesurfaces, surfaces, this this area is pitted and channeled, scarp obvious. Unlike channeled, and may be related to to an an earlier earlier flood flood event. Similarly, Similarly,thick thick sand sand buried buried by 50-100 50-100feet feetof of glacial glacialtill till on on the the related north side side of of the the valley, valley, north north of of Shakopee, Shakopee, suggests suggests that that the the river river valley valley at at one one time timeextended extended north further further to the the north. The Thesand sandwas wascovered coveredby by glacial glacial sediment sediment during during the the last last glacial glacial advance advance and was never re-excavated re-excavated by subsequent subsequent floods. floods. REFERENCES WFEWNCES CITED CITED Aber J.S., 1988, 1988, Structural Structural geology exercises with glaciotetonic examples: WinstonSalem, 1-84. Salem, North North Carolina, Carolina,Hunter HunterTextbooks, Textbooks,p.p.881-84. Bierman, Bierman,P.R., P.R., Marsella, Marsella, K.A., K.A., Patterson, Patterson, C., C.,Davis, Davis,P.T., P.T., Caffee, M., in press, press, MidMidPleistocene Pleistocenecosmogenic cosmogenicminimum-age minimum-agelimits limitsfor for pre-Wisconsinan pre-Wisconsinan glacial glacialsurfaces surfacesin in southwestern southwestern Minnesota Minnesota and and southern southern Baffin Island—a Island-a multiple nuclide nuclide approach: approach: Geomorphology. Geomorphology. Clark, pavements: Products Clark, P.U., P.U., 1991, Striated clast pavements: Products of deforming subglacial subglacial sediment? sediment? Geology, Geology, v. v. 19, 19,p. p. 530-533. 530-533. Clayton, Clayton, Lee, Lee, 1983, 1983,Chronology Chronologyof ofLake LakeAgassiz Agassizdrainage drainagetotoLake LakeSuperior, Superior,ininTeller, Teller, J.T., and Clayton, Lee, eds., Glacial Lake Agassiz: Agassiz: Geological Association of Canada Special 1-307. 291-307. SpecialPaper Paper26, 26,p.p.29 Clayton, Clayton, L., and and Moran, Moran, S.R., S.R., 1982, 1982,Chronology Chronology of of late late Wisconsin Wisconsin glaciation glaciation in in middle middle North America: Quaternary QuaternaryScience ScienceReviews, Reviews,v.v. 1,1,p. p. 55-82. 55-82. Diedrick, Diedrick,R.T., R.T., and and Rust, Rust, R.H., R.H., 1975, 1975,Glacial Glaciallake lake evidence evidencein in western western Minnesota Minnesotaas as interpreted interpreted from from the the soil soil survey: Journal Journalof of the the Minnesota Minnesota Academy Academy of Science, Science, v. v. 41, 9-12. p. 9-12. Dyke Dyke A.S., and and Prest, Prest, V.K., V.K., 1986, 1986, Paleogeography Paleogeography of northern northern North North America, America, 18,00018,0005000 5000 years years ago: ago: Geological GeologicalSurvey Surveyof ofCanada CanadaMap Map1703A, 1703A,scale scale1:12,500,000. 1:12,500,000. Flint, Flint, R.F., R.F., 1957, 1957, Glacial Glacial and and Pleistocene Pleistocenegeology: geology: New NewYork, York, John John Wiley and Sons, Sons, 553 553 p. p. Gilbertson, Gilbertson,J.P., J.P., 1990, 1990, Quaternary Quaternary geology along along the eastern flank flank of the Coteau Coteau des des Prairies, Prairies, Grant Grant County, County, South Dakota: Unpublished UnpublishedM.S. M.S. thesis, thesis, Univeristy Univeristy of of Minnesota, Duluth, 108 p. Minnesota, Duluth, 108 p. Hallberg, Hallberg, G.R., G.R., 1986, 1986,Pre-Wisconsin Pre-Wisconsin glacial glacial stratigraphy stratigraphy of of the the central central plains plains region region in in Iowa, Iowa, Nebraksa, Kansas, Kansas, and Missouri: Missouri: Quaternary QuaternaryScience ScienceReviews, Reviews, v. v. 5, 5, p. 11-15. 11- 15. 165 i m-' �Hallberg, G.R., and and KenuTlis, Kemmis, T.J., glacial T.J., 1986, Stratigraphy Stratigraphy and correlation of the glacial deposits of the Des Moines and James lobes and adjacent areas in North Dakota, Minnesota,and and Iowa: Iowa: Quaternary QuaternaryScience ScienceReviews, Reviews,v. v. 5, 5, p. 65-68. 65-68. Minnesota, Imbrie, J., and and others, others, 1984, 1984,The The orbital orbital theory of Pleistocene climate; climate; Support Support from from aa Imbrie, n Berger, A.L., the marine marine 8 8 0 record, iin revised chronology of the A.L., and others, eds., Boston,Mass., Mass., D. D. Reidel, Reidel, p. p. 269-305. 269-305. Milankovitch and climate: Boston, 1986, Origin and large-scale erosional features of glacialKehew A.E., and Lord, M.L., 1986, lake spillways spillways in the northern Great Plains: Geological Society of America Bulletin 97, p. 162-177. 162-177. Lusardi, B.A., 1997, quadrangle: Carver, Scott, and 1997?Surficial geology of the Shakopee quadrangle: Counties?Minnesota: Minnesota MinnesotaGeological Geological Survey Survey Open-File Open-File Report Report 97-6, 97-6? Hennepin Counties, scale scale 1:24,000. 1:24,000. of the the Jordan Jordan East East quadrangle: quadrangle: Scott Lusardi, B.A., in prep., Surficial geology of Scott County, County7 Minnesota: Minnesota Geological Survey, scale 1:24,000. Minnesota: Minnesota Geological Survev. scale 1:24.000. " geology Minnesota, in Matsch, C.L., 1972, 1972, Quaternary gec )logy of southwestern Minnesota, in Sims, Sinns, P.K. and nK:....-"-+,.. A ...:-I -.-I..--. nK:-* Morey, G.B, G.B, eds., eds., Geology Geology of of lvuuuc>uLa. Minnesota: fi A centennial volume: Minnesota Geological LCLILCIIIIW V U ~ U I I I G . 1~111111esota Geological Survey, Survey?p. 548-560. 548-560. Matsch, C.L., 1983, 1983,River River Warren, the southern southern outlet outlet of Glacial Glacial Lake Lake Agassiz, Agassiz, in in Teller, Teller, J.T., and Clayton, Lee, eds.? eds., Glacial Lake Lake Agassiz: Agassiz: Geological Association Association of of Canada Canada J.T., Special Special Paper 26, p. 231-244. C.J., 1993. Mapping Patterson, C.J., Mappingglacial glacialterrain, terrain, southwestern southwestern Minnesota, Minnesota, U.S.A., U.S.A.7 in J.S., ed., Glaciotectonics Aber, J.S., Glaciotectonicsand and mapping mapping glacial glacial deposits: deposits: Regina, Saskatchewan, Saskaichewan, University of Regina, Regina, Canadian Canadian Plains Plains Research Research Center, Center, p. p. 155-176. 155-176. Patterson, C.J., 1997, 1997, Quaternary Quaternary geology geology of southwestern Minnesota, in Patterson, C.J., Contributions to the geology Contributions geology of southwestern southwestern Minnesota: Minnesota Geological Geological Survey Report Report of Investigations Investigations 47, 47?p. 1-45. 1-45. Patterson, Patterson, C.J., C.J., Cotter, Cotter,J.F.P., J.F.P., and Knaeble, Knaeble?A.R., 1998, 1998, Des Moines lobe advanced advanced into into Glacial Lake Benson to form the Big Stone Stone Moraine, Moraine?west-central Minnesota: Geological Society Geological Society of of America America Abstracts Abstracts with Program, Program, v. v. 30, 30, no. 2, p. 66-67. 66-67. Richmond, Richmond, G.M., and and Fullerton, Fullerton,D.S., D.S., 1986, 1986,An introduction introduction to Quaternary Quaternary glaciations glaciations in in the the United States States of America: America: Quaternary Quaternary Science Science Reviews, Reviews, v. v. 5, 5, p. 3-10. 3-10. Rittenour, T.M., 1994, 1994, Lacustrine Lacustrinedeposits depositsin in the the Minnesota MinnesotaRiver River Valley, Valley, west-central Minnesota; evidence for Glacial Lake Benson? Abstracts Abstractswith with Program, Program, 5th 5thAnnual Annual Minnesota; evidence Argonne Symposium Symposium for Undergraduates Undergraduates in Science, Science, p. 102. 102. 1995, Strand lines and lacustrine lacustrine deposits deposits in in the the Minnesota Minnesota River River Valley, Valley? Rittenour, T.M, 1995, Benson exist? exist? Geological Society west central Minnesota; Minnesota: Did Glacial Lake Benson Society of America no. 3, 3, p. 82. 82. An 2l7?no. ierica Abstracts Abstracts with with Programs, Programs, v. v. 27, Rittenour, Geiger, K.L., K.L., and Cotter, J.J.F.P., prep., Evidence Evidence for Glacial Lake Lake Benson, F.P., ininprep., r, T.M., Geiger? Rittenou -+ ..-I XK:....--..+,. L. Dn++a..nAwest-central in W ~ ~ L - L G I I Minnesota, ~ LVLU ~ U EJ W L ~ , w Patterson, =UUWU,C. C. J., ed., Contributions to the Quaternary geology of Minnesota: Minnesota MinnesotaGeological Geological Survey Survey Report of Investigations 49. d d 166 , �Ruddiman, W.F., and Wright, 1, in Ruddiman, W.F., and Wright, H.E., H.E., Jr., 1987, Introduction, Chap. 1, Ruddiman, W.F., H.E., Jr., Jr., eds., North America and the adjacent oceans during the last Wright, H.E., Wright, TheGeology Geologyof ofNorth NorthAmerica, America, volume volume K-3, Geological Geological Society Society of deglaciation: The America, America, p. p. 1-12. 1-12. Shackelton, N.J., and and others, others, 1984, 1984,Oxygen Oxygen isotope isotope calibration calibrationof of the the onset onset of of ice-rafting ice-raftingand and Shackelton, history of glaciation region: Nature, glaciation in the North Atlantic region: Nature, v. v. 307, p. 216-219. 216-219. Smith, D.G., and and Fisher, T.G., 1993, 1993, Glacial Lake Agassiz: The The northwestern northwestern outlet outletand and Smith, paleoflood: paleoflood: Geology, Geology,v. v. 21, 21, p. p. 9-12. 9-12. Teller, J.T., J.T., 1987, Proglacial lakes and the southern margin of of the Laurentide Laurentide Ice Sheet. Ch. Ch. 3, in Ruddiman, Ruddiman,W.F., W.F., and Wright, H.E., Jr., eds, North America and the adjacent adjacent 3, in oceans oceans during during the the last last deglaciation: deglaciation: The TheGeology GeologyofofNorth NorthAmerica, America,volume volumeK-3, K-3, Geological GeologicalSociety Societyof of America, America, p. p. 39-69. 39-69. Upham, Upham, Warren, 1883, 1883, The The Minnesota Minnesota valley valley in in the the ice ice age: age: American American Association Association for forthe the Advancement 1. Advancementof of Science ScienceProceedings, Proceedings,v.v.32, 32,p.p.213-23 213-231. Upham, Agassiz: U.S. Upharn, Warren, 1895, 1895, The Glacial Lake Agassiz: U.S. Geological Geological Survey Survey Monograph Monograph25, 25, 658 p. Williams, Thunell, R.C., Tappa, E., Rio, D., and Raffi, I., 1988, 1988, Chronology Chronology of of the the Williams, F.F., F.F., Thunell, Pleistocene Pleistocene oxygen isotope record: 0-1.88 0-1.88 my. my. B.P.: B.P.: Paleogeography, Paleogeography, Paleoclimatology, Paleoclimatology, Paleoecology, Paleoecology, v. 64, no. 3-4, p. 221-240. Wright, in Sims, Sims,P.K., P.K., and Morey, G.B., Wright, H.E., H.E., Jr, Jr, 1972, 1972,Quaternary Quaternary history history of of Minnesota, Minnesota, in eds., Geology of Minnesota: A centennial volume: Minnesota eds., Geology Minnesota: A centennial MinnesotaGeological GeologicalSurvey, Survey, p.515-547. p.515-547. Wright, Jr. 1990, 1990,Geologic Geologichistory history of of Minnesota Minnesota rivers: rivers: Minnesota Minnesota Geological GeologicalSurvey Survey Wright, H.E., H.E., Jr. Educational 20 p. EducationalSeries SeriesNo. No. 7, 7,20 p. Wright, E.J., 1973. Superior in Wright, H.E., Jr., Matsch, Matsch, C.L., and Cushing, E.J., Superiorand and Des Des Moines Moines lobes, lobes, in Black, H.B., eds., The Wisconsinan Black, R.F., R.F., Goldthwait, Goldthwait,R.P., R.P., and Whillman, H.B., Wisconsinanstage: stage: Geological GeologicalSociety Societyof ofAmerica AmericaMemoir Memoir136, 136,p.p.153-185. 153-185. 167 i m- �..:. '(1 \'' \\\(\ Ir Plate Plate 1. 1. Preliminary Preliminarysurficial surficialgeologic geologicmap mapof of the theupper upper Minnesota Minnesota River River basin showing showing stop locations. locations. 168 � Dublin Core The Dublin Core metadata element set is common to all Omeka records, including items, files, and collections. For more information see, http://dublincore.org/documents/dces/. Title A name given to the resource Institute on Lake Superior Geology Dublin Core The Dublin Core metadata element set is common to all Omeka records, including items, files, and collections. For more information see, http://dublincore.org/documents/dces/. Title A name given to the resource Institute on Lake Superior Geology: Proceedings, 1998 Description An account of the resource Institute on Lake Superior Geology. Minneapolis, Minnesota. May 6-10, 1998. Creator An entity primarily responsible for making the resource Institute on Lake Superior Geology Date A point or period of time associated with an event in the lifecycle of the resource 1998 Format The file format, physical medium, or dimensions of the resource PDF Language A language of the resource English https://digitalcollections.lakeheadu.ca/files/original/9660caf940f66fd29e7fe32eae6eae00.pdf 6d73e78d6c61bec84aba951e925d06e6 PDF Text Text ~ake Institute on Lake Superior Geology 45th 45th Annual Annual Meeting Meeting Ramada mi Ramada IInn Marquette, Maquette, Michigan Michigan 1999 May 4-8, 4-8, 1999 Sponsored Sponsoredby Northern Northern Michigan Michigan University and University and Michigan Michigan Technological Technological University Proceedings Volume 45: Program and Abstracts Robert S. Regis and Theodore J. Bornhorst, editors �45TH ANNUAL MEETING INSTITUTE ON LAKE SUPERIOR GEOLOGY Volume Volume 45 consists of Pan 1: Program Partl: Programand andAbstracts Abstracts Pan Part2: 2: Field FieldTrip TripGuidebook Guidebook Reference to material material in this this volume should should follow follow the the example example below: Ams, Arns, D. and Hoim, Holm, D., 1999, 1999, Characterization Characterization and timing constraints constraints of post-Penokean post-Penokean meso-scale structures in the Watersmeet and Republic gneiss domes structures domes of northern northern Michigan (abst.): Institute Instituteon on Lake Lake Superior Superior Geology Proceedings, 45th Annual Meeting, Marquette, Marquette,MI, MLv.v.45, part 1,I, p. p.2. 2. 45, pan distributed by Volume Volume 45 45 Published Published and distributed by Institute Institute on Lake Lake Superior SuperiorGeology Geology Mark Jirsa, Jirsa, Secretary-Treasurer, Secretary-Treasurer,I.L.S.G. I.L.S.G. Minneosta Minneosta Geological Geological Survey Survey 2642 University University Avenue Avenue St. Paul, MN USA USA 55114-1057 551 14-1057 (612)-627-4780 (61 2)-627-4780 email: jirsaOOl jirsaOOl@tc.umn.edu @tc.umn.edu ILSG websitehttp://www.eeo.mtu.edu/ereat http://www.geo.mtu.edu/great lakes/ilsg/ ILSG website lakes/Us$ ISSN 1042-9964 1042-9964 All volumes are are available available for photocopying costs All costs from Michigan Technological TechnologicalUniversity UniversityLibrary Library Archives �INSTITUTE ON LAKE SUPERIOR GEOLOGY PROCEEDINGS Volume 45 AND ABSTRACTS ABSTRACTS Part 1: 1 :PROGRAM PROGRAM AND *~ ~ ~ .- .> . . .. . -.. . ... ~, . .. .. .~ , , 1 !; ! I Editors: Robert S. Regis and Theodore Theodore J. J. Bornhorst Bornhorst Editors: �CONTENTS CONTENTS PROCEEDINGS VOLUME VOLUME 45 45 PROCEEDINGS ABSTRACTS PART 1 1 -- PROGRAM PART PROGRAM AND ABSTRACTS Editors: Robert S. Regis and Theodore Theodore J. J. Bornhorst Bomhorst Institutes Institutes on on Lake Lake Superior SuperiorGeology Geology to to 1955-99 1955-99......................................... Constitution Constitution of of the the Institute Institute on on Lake Lake Superior Superior Geology Geology...................................... ii iii By-Laws BY-Lawsof of the the Institute Institute on on Lake Lake Superior Superior Geology Geology ..........................................................iii iv Goldich Goldich Medal Medal Guidelines Guidelines ................................................................................................. iv Goldich Goldich Medal Medal Committee Committee.................................................................. .................v Past Goldich Past Goldich Medalists Medalists ......................................................... vi ................vi 1999 Goldich Goldich Medal Medal Recipient 1999 Recipient ............................. ....................... VIvi .. vii ............vll Citation Citation for for 1999 1999Goldich Goldich Medal Medal Recipient Recipient ............. Student Paper Paper Awards Student Awards .................................................................. ........ ... Viii .............vlll ... Student Student Paper Paper Awards Awards Committee Committee ...................................................................................~Viff 111 Student Travel Travel Award Student Award ......................................................................................... Student Travel Travel Award Student Award Application Application Form Form ............................................................ ........ ix IX. . ix ix Board of of Directors Directors ............................................................................................................... xx Board x Local Local Committees Committees ...............................................................................................................x xi Banquet Banquet Speaker Speaker................................................................................................................. xi xii Report of the Chair Chair of the the 44th 44th Annual Annual Institute Institute ...............................................................xii Program Program xv ............................................................................................................................ xv Abstracts ....................................................................................................................... 1 Abstracts �INSTITUTE ON LAKE SUPERIOR GEOLOGY DATE PLACE CHAIRS 4 1955 1956 1957 1958 5 1959 6 1960 7 8 1961 Minneapolis, Minnesota Minneapolis, Minnesota Houghton. Michigan Houghton, East Lansing, Lansing, Michigan Michigan East Duluth, Minnesota Minneapolis, Minnesota Madison, Wisconsin Madison. Port Arthur, Arthur. Ontario Houghton. Michigan Houghton, Duluth, Minnesota Ishpeming, Michigan Ishpeming, Michigan St. Paul, Minnesota Marie. Michigan Sault Ste. Marie, East Lansing. Michigan Superior. Wisconsin Superior, Wisconsin Oshkosh, Wisconsin Oshkosh. Thunder Bay. Ontario Thunder Duluth, Minnesota Duluth. Houghton. Michigan Madison, Wisconsin Madison. Marie, Ontario Sault Ste. Marie. Marquette. Michigan Paul. Minnesota St. Paul, Thunder Bay. Bay. Ontario Ontario Milwaukee. Wisconsin Milwaukee. Duluth. Minnesota Duluth, Eau Claire. Wisconsin East Lansing. Michigan Falls, Minnesota International Falls. Houghton. Michigan Wausau. Wisconsin Wausau. Kenora. Ontario Ontario Kenora, Wisconsin Rapids. Wisconsin Wisconsin Wawa, Ontario Marquette, Michigan Marquette. Duluth, Minnesota Thunder Bay, Bay. Ontario Thunder Eau Claire. Claire, Wisconsin Eau Hurley, Wisconsin Eveleth. Minnesota Eveleth, Houghton, Michigan Houghton. Michigan Marathon, Ontario Marathon. Cable, Wisconsin Sudbury. Ontario Minneapolis, Minnesota Marquette, Michigan C.E. Dutton . . . AK. Snelgrove A.K. Snelgrove B.T. Sandeflir Sandefur R.W. Marsden R.W. E.N. Cameron & & R.A. Hoppin E.N. E.N. Cameron E.N. E.G. Pye E.G. A.K. Snelerove Snelgrove *,. . A.K. H. L Lepp H. ~PP A.T. Broderick A.T. P.K. Sims & & R.K. R.K. Hogberg P.K. R.W. White R.W. W.J. Hinze A.B. A.B. Dickas G.L. G.L. LaBerge M.W. Bartley & E. Mercy Bardey & D.M. Davidson D.M. J. Kafliokoski Kalliokoski M.E. Ostrom Osuom P.E. Giblin P.E. J.D. Hughes M. Walton M.M. Kehlenbeck M.M. C. Mursky G. D.M. Davidson i-'fr ' D.M. P.E. Myers P.E. W.C. Cambray W.C. DL. Southwick D.L. Southwick T.J. Bornhorst T.J. Bomhorst -' -st CL. LaBerge G.L. LaBerge CE. Blackburn C.E. Blackburn J.K. Greenberg J.K. E.D. Prey Frey & R.P. R.P. Sage E.D. J. S. Klasner .J.C. Green Green J.C. M.M. Kehlenbeck M.M. P.E. Meyers P.E. A.B. Dickas Dickas A.B. DL. Southwick D.L. Southwick T.J. Bornhorst Bomhorst M.C. Smyk M.C. L.G. Woodruff L.G. R.P. Sage & W. Meyer R.P.Sage&W.Meyer J.D. Miller Miller & M.A. M.A. Jirsa ursa J.D. T.J. Bornhorst Bomhorst & & R.S. Regis Regis INSTITUTE NUMBER INSTITUTE NUMBER 1 2 3 9 10 11 12 13 14 15 16 17 18 19 20 2] 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 1962 1963 1964 1965 1966 1967 1968 1969 1970 1971 1972 1973 1974 1975 1976 1977 1978 1979 1980 1981 t982 1983 1984 1985 1986 1987 1988 1989 1990 1991 1992 1993 1994 1995 1996 1997 1998 1999 ~--., �CONSTITUTION OF OF INSTITUTE INSTITUTE ON LAKE SUPERIOR GEOLOGY CONSTITUTION Article Article II Name Nams The be the the "Institute "Institute on onLake LakeSuperior SuperiorGeology". Geology. The name of the organization shall be Article I IIl Article Article IU III Article Objectives Obiectlves The objectives objectives of of this organization organization are: are: geologists in in the the Great Great Lakes Lakes region region may may exchange exchange ideas ideas and and A. To provide a means whereby geologists scientific data. scientific data. B. Superior region. B. To promote better understanding understanding of the geology of the Lake Superior C. To plan plan and conduct C. To conduct geological geological field trips. Status Sam? No part of to the benefit benefit of any member or individual. of the the income income of the organization shall insure to In the event of dissolution the assets of the organization shall be distributed to ______________ tax free organization). organization). (some (some tax (To avoid Federal and State State income taxes, the organization should be not only only "scientific "scientific" or also "non-profit".) "educational, but also "non-profit".) .. ,2.. Minn. Stat. Slat. Anno. 290.01, subd. subd. 44 Minn. Stat. 290.05(9) S t a Anno. ~ Internal Revenue 1(c)(3) 1954 Internal RevenueCode Code5.50 s.501(~)(3) Article Article IV IV ,. Membership rasmkmm The membership of the organization shall consist of persons who have registered for an an annual annual meeting or who have indicated interest in being a member according according to to membership membership guidelines guidelines approved by the board approved board of directors directors and have paid any applicable applicable dues. Article V Meetin2s &!dlws The organization shall shall meet meet once once aa year, year, preferably preferablyduring duringthe themonth monthof ofApril. April. The The place place and and exact directors. exact date date of of each each meeting meeting will be designated by the board of directors. Article VI Article VI Directors Directors The board and the the last last three three past board of of directors directors shall shall consist consist of the the Chair, Chair, Secretary-Treasurer, Secretary-Treasurer, and Chair; but if the by reason reason of Chair, but the board board should should at any any time time consist consist of fewer fewer than five persons, persons, by unwillingness or inability of any of the above persons to serve as as directors, directo& the the vacancies vacakies on on the the board may board up to five members. may be be filled filled by by Chair Chair so as to 10 bring the the membership of the board Article VH Officers smcsls The The officers officersof this this organization organization shall be a Chair and Secretary-Treasurer. A. be elected of directors, A. The Chair Chair shall shallbe elected each each year year by by the the board boardof directors, who who shall give due due consideration to the wishes of any group DUUD that that may may be be promoting promoting the the next next annual annualmeeting. meetine. His/her terminate at at the cl&c close of theannual the annual meeting over which Hisher term of office office as Chair Chair will $lt&nate he/she presides or when hisher his/her successor shall have have been been appointed. appointed. He/she hdshe presides Hdshe will willthen thenserve serve for for a period period of of three three years years as as aa member memberof of the theboard boardof of directors. directors. B. shallbe beelected electedby by aa majority majority vote of of members B. The Secretary-Treasurer Secretary-Treasurer shall members at the the annual annual . . vote meeting. His/her of years or ~ i s / h eterm term r ofoffice officeshall shall be be four fouryears or until until his/her hisher successor successorshall shall have have been been appointed. appointed. Article VIII Amendments This may be be amended amended by by aa majority of those This constitution constitution may majority vote vote (majority (majority of those voting) voting) of of the the membership membership of of the the organization. organization. �BY-LAWS OF OF INSTITUTE INSTITUTE ON LAKE LAKE SUPERIOR SUPERIOR GEOLOGY "9.. !!i !',vp..,. Duties of the the Officers and Directors Directors I. Duties A. It shall be the duty of the the Annual Annual Chair Chair to: to: >, .,,, , . 1 -"-< I.. Preside at the annual meeting. - ,, Appoint all committees committees needed for the organization organization of the annual meeting. . . ..,.&;, 2. Appoint .. 3. Assume and of the the annual *. . ! 3. Assumecomplete completeresponsibility responsibility for for the the organization organization and financing financine annual meeting meetine - of over which he/she h&he presides. B. It shall be the duty of the B. the Secretary-Treasurer Secretary-Treasurerto: to: 1. 1. Keep accurate accurke attendance attendance records &cords of all annual meetings. 2. Keep Keep accurate accurate records records of of all meetings of, and correspondence between, the the board board of of 2. meetings of, correspondence between, directors. directors. 3. Hold all funds that may may accrue accrue as as profits profits from from annual annual meetings meetings or or field field trips trips and and to make 3. these funds available available for the organization and operation operation of future future meetings meetings as as required. required. C. It shall be the duty of the board of directors to plan locations locations of annual meetings and to advise on the organization organization and and financing financingof of all all meetings. meetings. 8 ,, Expenses and E IH. I. Duties and xuee s - I. Regular lesson 1. Regularmembership membership dues dues of $5.00 $5.00 or or less on an an annual annual basis basis shall shall be be assessed assessed each member member as determined by the board board of directors. directors. 2. Registration Registration fees for the annual meetings shall shall be be determined determined by by the Chair in consultation with the board of The registration fees can can include expenses to cover the of directors. directors. The registration fees expenses to cover operations operations outside of of the annual outside annual meeting meeting as as determined determined by the the board hoard of of directors. directors. It is strongly strongly recommendedthat thatregistration registrationfees feesbebekept keptatat aa minimum to encourage attendance of of recommended minimum to encourage attendance graduate students. ILL. Rulesof ofOrder Order ;z F .lQW The rules contained in Robert's Rules of Order shall govern this organization in all cases to which The rules contained in Robert's Rules of Order shall govern this organization in all cases to which they are are applicable. applicable. LV. Anw>nflnw*nfc Amendments N. . I , These by-laws may be amended by by aa majority majority vote vote (majority (majority of of those those voting) voting) of of the the membership membership of the organization; provided provided that that such such modifications shall shall not not conflict conflict with with the the constitution as as ;;-of adopted or subsequently amended. 5 ~ i i ~ .presently presently is adopted or subsequently amended. . . , . ..;. Last Amended May, 1996 Amended -- May, 1996 .'t . �GOLDICH GOLDICH MEDAL GUIDELINES GUIDELINES Preamble Preamble Institute on on Lake The Institute Lake Superior Superior Geology Geology was was born born on on or or around around 1955, 1955, as as documented documented by by the the fact fact that that the the 27th 27th The annual meeting annual meeting was was held held in in 1981. 1981. The TheInstitutes Institutesare areexemplary exemplaryin intheir theircontinuing continuingobjectives objectivesof ofdealing dealingwith withthose those aspects of aspects of geology geology that that are are related related geographically geographically to to Lake ~ a k eSuperior; ~ u p e r i oof ofr ;encouraging encouraging the the discussion discussion of of subjects subjects and and sponsoring field trips which will bring surveys, and industry; and of swnsoring brine together together geologists eeoloeists from academia, government surveys. maintaining an an exceedingly exceedingly informal but highly effective mode mode of of operation. operation. maintaining i n f o d buthighiyeffective During the course of of its existence, existence. the membership membership of the Institute (that is, those geologists who indicate an interest colleagues have made in the objectives of the ILSG by by attending) attending) has has become aware aware of the fact that certain of their colleagues made particularly noteworthy noteworthy and of Lake Lake Superior and particulaily and meritorious meritorious contributions contributions to to the the understanding understanding of Superior fgeology $eolo&' and mineral mineral deposits. deposits. The toSam SamGoldich Goldichin in 1979 1979for forhis hismany many contributions contributionsto to the the geology geologyof ofthe theregion region The first award award was was made made by by ILSG ILSG to extending below. extending over about 50 50 years. Subsequent Subsequentmedalists medalistsand and this this year's year's recipient are listed in the table below. Award Award Guidelines Guidelines I) The medal shall to a geologist whose whose name name is is associated associated 1) shall be awarded awarded annually by the ILSG Board of Directors to contribution to, the geology of the Lake Lake Superior region. with a substantial interest in, and contribution 2) The Board Committee. The three Board of of Directors Directors shall shall appoint appoint the Goldich Medal Committee. The initial initial appointment appointment will be of three members, members, one to serve for three three years, years, one for for two two years, years, and and one one for for one one year. year. The member with the the briefest briefest incumbency shall be chair of the firstyear, year,the the Board Boardof ofDirectors Directorsshall shallappoint appoint the Nominating Committee. After Afterthe the first at each spring three years. In his/her hidher third year year this member member shall shall be be spring meeting meeting one one new new member member who who will will serve serve for for three the chair. The Committee of interest interest and and geographic geographic distribution distribution of of ILSG ILSG Committee membership membership should reflect the main fields of membership. membership. 3) By to the the Chair Chair of of the 3) By the the end end of of November, November, the the Goldich Goldich Medal Medal Committee Committee shall shall make make its its recommendation recommendation to the Board of Directors, Directors, who who will then inform inform the Board of the nominee. 4) The 4) The Board Board of ofDirectors Directorsnormally normally will will accept accept the thenominee nominee of ofthe theCommittee, Committee. will will inform inform the themedalist medalist immediately, and will have one medal engraved appropriately appropriately for presentation at the next meeting of the Institute. 5) It is recommended recommended that that the the Institute Institute set set aside aside annually annually from from whatever whatever sources, such funds as will be be required required to to continuing costs of this award. support the continuing Nomination Procedures Procedures Nomination Nominations shall be taken 1) Nominations taken at at any anytime timeby bythe theGoldich GoldichMedal MedalCon-imittee. Committee. Committee Committeemembers membersmay may themselves themselves candidates. The nominate candidates. The deadline deadline for for nominations nominations is is November 1. 1. 2) Nominations Nominations must be in writing and supported by appropriate appropriate documentation such as letters of recommendation, recommendation, publications. curriculum contributions to Lake Lake Superior geology and to to the Institute. lists of publications, curriculum vita's, and evidence evidence of contributions are not not restricted restricted to to Institute Institute attendees, attendees, but are are open open to to anyone anyone who who has has worked worked on on and and contributed contributed 3) Nominations Nominations are to the understanding understanding of of Lake Lake Superior Superiorgeology. geology. iv �Selection Guidelines Nominees are to be evaluated 1) Nominees evaluated on the basis of their contributions contributions to Lake Superior Superior geology geology (sensu lato) lato) including: including: a) importance importance of relevant relevant publications; publications; b) b) promotion promotionof of discovery discoveryand andutilization utilizationof ofnatural natural resources; resources; c) contributions contributions to to understanding understandingof of the the natural natural history history and and environment environmentof of the the region; d) generation generation of new ideas ideas and concepts; concepts; and e) contributions contributions to to the the training training and education educationof of geoscientists and the the public. nublic. - and -geoscientistsand # ., ...,:,{ m, . P,:~:, ,y 2 : 2) 2) Nominees Nominees are are to tobe beevaluated evaluatedon ontheir theircontributions contributionsto tothe theInstitute Instituteas asdemonstrated demonstratedby byattendance attendanceatatInstitute Institute meetings, meetings, presentation presentationof of talks talksand andposters, posters. and andservice serviceon onInstitute Instituteboards, boards, committees, committees,and andfield fieldtrips. trips. 3) 3) The The relative relative weights weights given given to to each each of of the theforegoing foregoing criteria criteria must must remain remain flexible and at the discretion discretion of of the the Cornniittee Committee members. members. - . ..q .* ? ,' 4) 4) There There are are several several points points to to considered considered by by the the Goldich Goldich Medal Committee: . "...., * . . . a) of the a) An An attempt attempt should should be be made madeto to maintain maintain aa balance balanceof of medal medal recipients recipientsfrom from each each'of thethree threeestates-industry, estates-industry, academia, academia, and government. government. b) It It must must be be noted noted that thatindustry industry geoscientists geoscientistsare areat at aa disadvantage disadvantagein in that that much much of of their their work work is is not not published. published. .# 5) 5 )Lake Lake Superior Superiorhas hastwo twosides, sides,one onethe theU.S., US., and andthe theother otherCanada. Canada. This Thisisisundoubtedly undoubtedlyone one of ofthe theInstitute's Institute's great great strengths strengths and should should be be nurtured nurtured by by equitable equitablerecognition recognition of of excellence excellencein in both both countries. countries. Last Last Amended Amended 1997 1997 GOLDICH GOLDICHMEDAL MEDAL COMMITTEE COMMITTEE1998-99 1998-99 John John Klasner Klasner (1999) (1999) Western Western Illinois IllinoisUniversity, University, Macomb, Macomb, Illinois Illinois Mark Smyk MarkSmyk (2000) (2000) Ontario Ontario Geological Geological Survey, Survey, Thunder Thunder Bay, Bay, Ontario Ontario Rod Johnson Johnson (2001) (2001) Rod Rod Johnson Johnson and and Associates, Associates, Negaunee, Negaunee, Michigan ~ichi'n V *' k' * �,; :G?L GOLDICH GOLDICH MEDALISTS MEDALISTS '' 1991 991 William WilliamJ. Hinze 1992 William F. Cannon Cannon 992 F. 1993 993 Donald W. W. Davis 1994 994 Cedric Cedric Iverson 1995 995 Gene Gene LaBerge 1996 David L Southwick 996 L. Southwick 1997 997 Ronald P. Sage 1998 Zell Peterman Petennan 998 Zell 1999 Tsu-Ming Han 999 Tsu-Ming Hun 1979 Samuel S. £ Goldich Goldich 1980 not awarded E. Dutton, Jr. Jr. 1981 Carl Carl IL 1982 Ralph W. Ma Marsden 1983 Burton 1983 Burton Boyum Boyu 1984 Richard Richard W. W Ojakangas Ojakangas 1985 Paul Paul K. 1985 K. Sims Sims 1986 1986 G.B. Morey 1987 Henry H. Halls 1988 Walter £ White Walter S. White 1989 JormaKalliokoski Kalliokoski 1989 Jonna 1990 1990 Kenneth C. Card Card '' 1999 19999 Goldich Medal Recipient -.. Tsu-Ming Han vi !:- �- I I : ,.. . . ,. Citation Citation Tsu-Ming HHan an 1999 Recipient 9 Goldich Medal Recipien The 1999 1999 c3oldich Goldich Medal recipient epitomizes the characteristics characteristics required to receive receive this unique and prestigious award. He life to to solving nature's nature's this prestigious award. He has has devoted devoted his professional professional life myriad challenges challenges in in the field myriad field of of geology geology and and sharing sharing his his findings findings with with colleagues colleagues both both verbally and through published and unpublished unpublished mineral mineral papers. r He born during the 1920's of China. China. His He was was born during the 1920's in in the the Hunan Hunan Province Province of His family familystressed stressed the importance importance of of education. education. He the He pursued pursued his his education education during during a series series of of difficult difficult periods periods that included being kidnapped kidnapped and and held held by by bandits, pursued by by Japanese Japanese forces, forces, and and the that included being bandits, pursued imposition of of Nationalist Nationalist control control followed followed by by the the cultural cultural upheaval upheaval caused caused by by the the ascendancy ascendancy imposition of the Communists from Northwest Northwest University in Sian of Communists after after World War War II. U. After graduating from Province in in 1945 Province 1945 and a brief stint stint with with the the Bureau Bureau of of Mineral Mineral Exploration, he immigrated immigrated to to the U.S. the U.S. in in 1947 1947 to tocomplete complete graduate graduate work work at at the the University University of of Cincinnati Cincinnati and and the the University of Minnesota. Minnesota. His Drs. Goldich, His mentors mentors at the University of Minnesota included Drs. Gruner, and Schwartz. Gmner, Schwartz. ;, ,. ,,, After summer employment with Clevcland-Cliffs in 1952, After Cleveland-Cliffs in 1952, he he accepted accepted permanent permanent employment at at the the Ishpeming Ishpeming Research Researchfacility. facility. Soon Soon after, after, he he met met and and married married Joy. Joy. They They employment have have advanced have three three children children who who,, have also alsobenefited beqegted,professionally professionally by b yachieving .achiev&g *-* advanced .,.~ , ,. educational educational degrees. degrees. , t He has published numerous articles on the genesis of iron formations with emphasis on textural textural relations relations during duringdiagenesis diagenesisand and metamorphism. metamorphism. What is not generally known known is that he is an expert on all facets of the beneficiation and pelletizing pelletizing process process that that has has dominated dominated the the North North American Americaniron ironore ore industry industry for for half half aa and His studies have assisted in the pelletizing process to century. century. His assisted in continual continual improvement improvement in industry competitive. keep the industry competitive. He in several He has has aa special special interest interest in in the the preserved preserved algae algae present present in several areas areas of of the the Negaunee Iron-formation Iron-formation at at the the Empire Empire Mine Mine and and has has published his his findings. findings. It should be noted noted that he delivered delivered a paper at the first Institute Institute meeting in 1955 1955 and and continues his scientific inquiry as evidenced by his current presentation at the Institute. continues his scientific inquiry evidenced by current presentation the Institute. his formal formal retirement retirement in in 1992 is is that that he he now now wears Indeed, the only change noticeable since his tennis shoes shoes to the office. office. It is my pleasure to to introduce introduce to the Institute Institute the the 1999 1999 recipient recipient of the the Goldich Goldich Medal, Medal, friend and our my friend our colleague, colleague, Tsu-Ming Tsu-Ming Han. Han. Tom Wagonner vii �STUI)ENT STUDENT PAPER PAPER AWARDS AWARDS Each year, the Institute selects the best of the and honors presenters presenters with with aa monetary award. Each the student student presentations and Funding for for the Funding the award award is is generated generated from from registrations registrations of of the the annual annual meeting. meeting. The The Student Student Paper Paper Committee Committee isis appointed by appointed by the the annual annual meeting meeting Chair Chair in in such such aa manner manner as as to to represent represent aa broad broad range range of of professional professionaland andgeologic geologic expertise. Criteria expertise. Criteria for for best best student student paper-last paper-last modified modified by the the Board in 1997-follow: 1997-follow: 1) The The contribution contribution must 1) must be be demonstrably demonstrablythe the work work of of the thestudent. student, 2) The The student student must present the contribution 2) contribution in-person. 3) The Student shall decide decide how how many many awards awardsto to grant, grant, and and whether whether or or not not to give separate 3) Student Paper Committee shall separate awards awards for for poster poster vs. vs. oral oral presentations. presentations. 4) In will be be made made to to the the senior author, author, or or the the award will be 4) In cases cases of of multiple multiple student student authors, the award will be shared shared equally equally by all authors authors of of the the contribution. contribution. 5) The but The total total amount amount of of the the awards awards isisleft lefttotothe thediscretion discretionof ofthe themeeting meetingChair Chairand andSecretary-Treasurer, Secretary-Treasurer, but typically is in the amount of about $300 $300 US. 6) The maintains, and and will will supply supply to to the 6) The Secretary-Treasurer Secretary-Treasurer maintains, the Conmiittee. Committee, aa form form for for the the numerical numerical ranking ranking of of presentations. This form form was was created and modified modified by Student Student Paper Paper Committees Committees over several years in in an an effort effort to to reduce the the difficulties that that may may arise arise from selection by by raters raters of of diverse background. background. The The me "Se of of the the form form is not reduce required, but but is is left left to to the the discretion discretion of of the the Committee. Committee. 7) The 7) The names names of of award award recipients recipients shall shall be be included included as a s part part of of the the annual annual Chair's Chair's report that that appears appears in in the the next next volume volume of of the the Institute. Institute. STUDENT PAPER PAPER COMMITTEE COMMITTEE 1999 STUDENT .~ .. ~,,. Allan Blaske, STS STS Consultants, Consultants, LTD. LTD,Lansing, Lansing, MI MI Woodruff, U.S. Laurel Woodruff, U.S.Geological Geological Survey, Survey, St. Paul, MN vii . ' . B; .. , . .. . , . . .: ,, .. �I 1 STUT)ENT TRAVEL TRAVEL AWARD STUDENT AWARD The Travel Award Award to to support student participation participation at at the the The 1986 1986Board Board of of Directors Directorsestablished established the the LL.S.G. I.L.S.G. Student Student Travel support student annual find set annual Institutes. Institutes. The The awards awardswill will be be made made from from aa special special fund set up up for for this this purpose. purpose. This Thisaward awardisisintended intendedtoto help help defray defray some some of of the the direct direct travel travel costs costs to to the the Institute Institute and and includes includes aa waiver waiver of of registration registration fees, fees, but but excludes excludes expenses and field field trip trip registration. registration. The and value by the the expenses for for meals, meals, lodging, lodging, and The number number of of awards awards and value are are determined determined by annual annual Chairman Chairman in in consultation consultationwith with the the Secretary-Treasurer Secretary-Treasurerand and will will be be announced announcedat at the the annual annualbanquet. banquet. The beconsidered consideredby bythe theannual annualChairman, Chairman,who whoisisresponsible responsiblefor forthe theselection: selection: Thefollowing followinggeneral generalcriteria criteriawill willbe 1) 1) The or graduate) graduate) student student status status at at the the time time of of the the The applicants applicants must must have have active active resident resident (undergraduate (undergraduate or Institute, Institute, certified certified by by the the department department head. head. who are are the the senior author on on either either an an oral 2) Students who senior author oral or or poster poster paper paper will will be be given given favored favored 2 ) Students consideration. consideration. 3) is desirable desirablefor fortwo two or or more more students students tojointly to jointly request requesttravel travel assistance. assistance. 3) ItIt is In general, general,priority priority will will be be given given to to those thosein in the the Institute Institute region region who who are are farthest farthest away. 4) 4) In with an an explanation of 5) Each travel travel award award request request shall shall be be made made in in writing, writing, to to the the annual annual Chairman, Chairman, with explanation of 5 ) Each need, need, possible possibleauthor authorstatus statusor orother othersignificant significantdetails. details. Successful Successfulapplicants applicantswill willreceive receivetheir theirawards awardsat atthe thetime timeof of registration registration for forthe the Meeting. Meeting. INSTtTUTh ON SUPERIOR GEOLOGY ONLAKE -SUPERIOR GEOLOGY Student A want Application Student Travel TravetAwardAppUcdon Please Pleaseprint: print: Student Student Name: Name: _______________________________ Date: Date: _______________ Address: Address: _______________________________________________________ :. Icertify 1certifythat thatthe theabove abovenamed namedperson personisIsan anactive activeresident residentstudent. student. .; ;; .,>'. , .. .,." v.., Department DepartmentHead Head--Typed Typed .. - ..>i.; ;.( <: ... , ,, Date Date Department DepartmentHead Head- Signature Signature L Educational Educational Status: Status:___________________ Are an oral reyou you the theSenior Senior Author Author of ofan oral or orposter poster paper? paper? Yes Yes Will Willany anyother otherstudents studentswill willbe betraveliag (revelingwith withyou? you? c . ~,.. : ___ ___ No No-_____ How Howmany? many? - Statement (If:(Ifyou statementofofNeed: ~eed youneed needmole moreloom, room,please pleaseuse usethe theback backof ofthe thepage.) Page.) Other OtherSignificant SignificantDetails: Details: Please Please return returnto: to: ix : �BOARD BOARD OF OF DIRECTORS DIRECTORS fheodoreJ. J. Bornhorst, Bornhorst, Chair Chair(2002) (2002) Theodore Michigan MichiganTechnological TechnologicalUniversity, University,Houghton, Houghton,Michigan Michigan James JamesD. D.Miller Miller(2001) (2001) Minnesota Minnesota Geological GeologicalSurvey, Survey,St. St.Paul, Paul,Minnesota Minnesota Ronald RonaldP. P.Sage Sage(2000) (2000) Ontario OntarioGeological GeologicalSurvey, Survey,Sudbury, Sudbury,Ontario Ontario <. Laurel LaurelG. G. Woodruff Woodruff(1999) (1999) U.S. US. Geological GeologicalSurvey, Survey,Mounds MoundsView, View,Minneapolis Minneapolis Mark MarkA. A.Jirsa J i m(2000) (2000)Institute InstituteSecretary-Treasurer Secretary-Treasurer Minnesota MinnesotaGeological GeologicalSurvey, Survey,St. St.Paul, Paul,Minnesota Minnesota LOCAL LOCAL COMMITTEES COMMITTEES GENERAL Co-CHAIRS Robert RobertS.S.Regis Regis Department Northern Michigan Departmentof ofGeography/Earth Gwgraphy/EarthScience, Science,Northern MichiganUniversity, University, Marquette, Marquette,Michigan Michigan49855 49855 Theodore TheodoreJ. J. Bornhorst Bornhorst Department Department of of Geological GeologicalEngineering Engineeringand andSciences, Sciences,Michigan MichiganTechnological TechnologicalUniversity, University.Houghton, Houghton, Michigan Michigan 49931 49931 PROGRAM AND EDITORS PROGRAM AND ABSTRACTS EDITORS ,* . Robert RobertS. S.Regis Regis Department Departmentof ofGeography/Earth Geography/EarthScience, Science,Northern Northern Michigan MichiganUniversity, University, Marquette, Marquette,Michigan Michigan 49855 49855 Theodore TheodoreJ. J. Bornhorst Bornhorst Department of of Geological GeologicalEngineering Engineering and andSciences, Sciences,Michigan MichiganTechnological TechnologicalUniversity. University, Houghton, Houghton, Michigan Michigan 49931 49931 FIELD TRIP GUIDEBOOK EDITOR Theodore Theodore J. J. Bornhorst Bornhocst Department of of Geological Geological Engineering Engineering and andSciences, Sciences,Michigan MichiganTechnological TechnologicalUniversity, University,Houghton, Houghton, Michigan 49931 49931 x �SESSION CHAiRS SESSION CHAIKS Dave DaveBaxter, Baxter,PayDay PayDayResources, Resources,Lansing, Lansing,MI MI Shawn Shawn Carison, Carlson, Ashton AshtonMining, Mining,North North Vancouver, Vancouver,BC, BC, Canada Canada Ron Ron Graber, Graber, Cliffs CliffsMining Mining Services ServicesCompany, Company, Ishpeming, Ishpeming, MI MI John John Green, Green,University Universityof of Minnesota, Minnesota, Duluth, Duluth, MN MN Rod Rod Johnson, Johnson, Rod RodJohnson Johnson& &Associates, Associates,Inc., Inc.,Negaunee, Negaunee, MI MI Gene Gene Laberge, Laberge, University Universityof of Wisconsin, Wisconsin,Oshkosh, Oshkosh, WI WI Jim Jim Small, Small, Edward Edward Kraemer Kraemer & &Sons, Sons, Burnsville, Burnsville, MI MI Tom Tom Waggoner, Waggoner, retired retired Cliffs CliffsMining MiningServices ServicesCompany, Company,Ishpeming, Ishpeming, MI MI " a, 1999 999 BANQUET BANQUET SPEAKER SPEAKER ' Nelson R. R. Ham Ham Department Department of Geology Geology St. Norbert College St. College De De Pere, Pere, Wisconsin Wisconsin , . . , Ice-Flow Dynamics and Landform Landform Development Development Along the Southern Southern Margin Margin of of the the Laurentide LaurentideIce Ice Sheet Sheet xi , �REPORT REPORTON ONTHE THE44th 44thANNUAL ANNUAL MEETING MEETINGOF OFTHE THE INSTITUTE INSTITUTEON ONLAKE LAKESUPERIOR SUPERIORGEOLOGY GEOLOGY MINNEAPOLIS, MINNEAPOLIS,MINNESOTA MINNESOTA The The44th 44thAnnual AnnualMeeting Meetingof ofthe theInstitute Instituteon onLake LakeSuperior SuperiorGeology Geologywas washeld heldinin Minneapolis, Minneapolis,Minnesota Minnesotaon on May May 6-10, 6-10, 1998. 1998. The Themeeting meeting was was sponsored sponsored by by the the Minnesota Minnesota Geological GeologicalSurvey Surveyand andwas washeld held at atthe the Holiday Holiday Inn Inn on on the the West West Bank Bank of of the the University University of of Minnesota Minnesotacampus. campus. Proceedings Volume44 44of ofthe themeeting meetingwas waspublished publishedinintwo twoparts: parts: ProceedingsVolume Pan Abstracts Part1:1:Program Programand and Abstracts(including (includingextended extendedabstracts abstractsofofthe thespecial specialoverview overview session) session) Part Part2:2:Field FieldTrip TripGuidebook Guidebook 1—Early 1-Early Proterozoic Proterozoicintrusive intrusiverocks rocksof of east-central east-centralMinnesota Minnesota 2—Geology 2-Geology of of the the southeastern southeasternportion portionofofthe theMidcontinent MidcontinentRift RiftSystem. System,eastern eastern Minnesota Minnesotaand andwestern westernWisconsin Wisconsin 3—Glacial ofthe theTwin TwinCities Cities area area 3ÑGlacia exotica exoticaof 4—Stratigraphy hydrogeology of M t r a t i g r a p h y and andhydrogeology of the the Paleozoic Paleozoic rocks rocks of of southeastern southeastern Minnesota Minnesota 5—Minnesota River Valley and vicinity, southwestern Minnesota (Precambrian and 5-Minnesota River Valley and vicinity, southwestern Minnesota (Precambrian and Quaternary Quaternarygeology) geology) By By most most measures, measures,the themeeting meetingwas wasaagreat great success. success. We Wesaw sawaaconsiderable considerablejump jumpinin attendance attendancethis thisyear yearto to200 200participants, participants.compared comparedwith withrecent recentaverage averageattendance attendanceon onthe the order of 125. Fifty-six participants were first-time attendees to the ISLG; split about order of 125. Fifty-six participants were first-time attendees to the ISLG. split aboutequally equally between betweenstudents studentsand andrelated relatedfields fieldspeople—that people-that is. is, those those involved involved in in Quaternary, Quaternary, Paleozoic, Paleozoic, environmental, are not not traditional traditional topics topics of the the Institute. Institute. We We environmental,and andengineering engineeringgeology geology that that are attribute attributesome someof of this thisincrease increasesimply simplyto to the the metropolitan metropolitan location location of the the meeting meeting and and our our fairly fairly aggressive aggressiveappeal appealto to the thelocal localgeoscience geosciencecommunity. community. To Toattract attractlocal localand andmore more broadly broadlybased basedinterest, interest,we webroke brokesomewhat somewhatwith withtradition traditionby byconducting conductingaaspecial specialhalf-day half-day session region. To session overviewing overviewingthe geology of the Lake Superior region. Tomake makethe themeeting meetingeven even more moreattractive attractiveto tonew-comers, new-comers,we weoffered offeredaafirst-day-only first-day-onlyregistration registrationatataareduced reducedrate ratefor for those thoseinterested interestedin inattending attendingjust justthe thespecial specialoverview overviewsession; session;however, however,few fewtook tookadvantage advantage of of the the offer. offer. The talksthat thatoutlined outlinedcurrent currentideas ideasand and The special specialoverview overviewsession sessionconsisted consistedof ofsix six30 30minute minutetalks new new research researchdirections directionson onthe themain maingeologic geologicprovinces provincesof of the theLake LakeSuperior Superiorregion. region. Presentations (Archean),Dick DickOjakangas Ojakangas(Early (EarlyProterozoic), Proterozoic),Bill Bill Presentationswere weregiven givenby by Ken KenCard Card(Archean), Cannon Cannon(Middle (MiddleProterozoic), Proterozoic),Tony TonyRunkel Runkel(Paleozoic), (Paleozoic),Carrie CamePatterson Patterson(Quaternary), (Quaternary),and and Dave talkswere werewell wellpresented presented Dave Southwick Southwick(New (Newdirections directionsin in Lake Lake Superior Superior geology). The Thetalks and and well well received; received; comments commentsfrom fromthe the participants participants were overwhelmingly overwhelmingly favorable. The The general 23oral oralpresentations presentationscovering coveringnot not only only the the typical typical fare fareof of general sessions sessionsincluded included23 Precambrian to groundwater. groundwater. In Inaddition, addition,24 24 Precambriantopics, topics,but but also alsoincluded included several severaltalks talks related related to poster of the the meeting. meeting. The poster presentation presentation were were on on display display during during the course of Thebanquet banquet speaker speaker was was Dr. Dr. Bevan Bevan French Frenchof ofthe theSmithsonian SmithsonianInstitution, Institution,who whogave gavean anexcellent excellenttalk talkon onthe therole role of of meteorite meteoriteimpacts impactson on the the geologic geologic history history of earth earth and other planets. At At the thebanquet, banquet,Zell Zell Peterman Petennan of of the theUSGS USGSwas wasawarded awardedthe theGoldich GoldichMedal Medalfor forhis his important importantgeochronologic geochronologicand and xii �geologic studies studies of of Precambrian Precambrian geology geology in in the the Lake LakeSuperior Superiorregion. region. Another Another highlight highlight of of geologic the meeting for 40 40 participants participants was was aa night night of of baseball baseball at at the the Metrodome. Metrodome. This meeting excursions that covered a meeting also also broke broke the the mold mold a bit by offering five field excursions similarly wide breadth similarly breadth of geology gwlogy as as was was presented in the the special special overview overview session. session. Although the emphasis highlighting the Paleozoic Although-the emphasis remained remained with Precambrian geology, trips highlighting and Quaternary geology of central and southern Minnesota Minnesota were were also also included. included. Three Threeprepremeeting the Early Early Proterozoic Proterozoic gwlogy geology of meeting field field trips trips were were run run on on Wednesday, Wednesday,May May 6th; 6th. 1) the east-central Minnesota Minnesota led by Terry Boerboom, Mark Jirsa, and Daniel Holm (26 participants); Wirth, Bill participants); 2) the Keweenawan geology of the Taylor's Falls area led by Karl Wirth, Cordua, Cordua, Bill Kean, Kean, Mike Mike Middleton, Middleton, and Zach Naiman Nairnan (46 (46 participants); and 3) Glacial exotica exotica of the the Twin Twin Cites Citesarea area led led by by Howard Howard Hobbs, Hobbs, Alan Alan Knaeble Knaebleand and Gary GaryMeyer Meyer(21 (21 participants). Two the Paleozoic Paleozoic stratigraphy, stratigraphy, Twopost-meeting post-meetingtrips trips included included aa one-day trip on the sedimentology, sedimentology,and hydrogeology hydrogeology of southeastern southeastern Minnesota led by Tony Runkel and Bob Tipping Tipping (11 (1 1 participants), and a two-day excursion investigating the Quaternary and Archean geology of the Minnesota Minnesota River Valley led by Carrie Patterson and David Southwick (33 participants). participants). The meeting was also is to to at least also a financial success; that is, if your measure of success is break even (which has been the traditionally held held view). view). We actually turned turned aa small small profit profit of of several hundred dollars. dollars. Although Althoughregistration registrationwas wasmore morecostly costlythan than we we had had hoped, hoped, the thecost cost was unavoidable unavoidable given the metropolitan metropolitan location. Part Partof of the theregistration registrationwe we all all pay pay is is applied to encouraging Institute by by granting granting awards awards for for student student encouraging student student participation in the Institute travel and best student student papers. Eight Eighttravel travelawards awardstotaling totaling$750, $750, and and two two best best paper paperawards awards of $150 each were granted. granted. Best Bestpaper paperawards awardswent went to to Kathleen Kathleen Abbott Abbott (Macalester (MacalesterCollege) College) for her undergraduate undergraduate work work on on geochemistry geochemistryand and petrography petrography of of Keweenawan Keweenawan Chengwatana Chengwatana volcanic rocks of Minnesota and Wisconsin, and to Dean Peterson (University of MinnesotaMinnesota Duluth) Duluth) for for his his graduate graduate presentation presentationon on (3IS-based GIs-based mineral potential analyses analyses of Archean Archean rocks in Minnesota. Congratulations Congratulationsto to you you both! both!. The Institute's Institute's Board Board of Directors Directors met on May 7th, 7th. and the following is generalized from minutes of that meeting: 1. Accepted Acceptedthe the Report Report of of the the Chair Chair 43rd 43rd ILSG ILSG 2. Accepted Acceptedthe the1997-1998 1997-1998JLSG ILSG Financial Financial Report. Report. 3. Approved ro rovedZell ZellE. E.Peterman Petermanas as1998 1998Goldich Goldich Medal Medal recipient. recipient. 4. Modified 4. Modifiedthe thelanguage languagefor forGoldich GoldichAwards Awards regarding regarding dates dates for for receipt receipt of nominations nominations (now November 1) 1) and final decision (now the end of November). 5. Approved Approvedthe theend-of-term end-of-termreplacement replacement of of Dan Dan England England (Eveleth Fee Office) Office) as committee member member hy y Rodney Goldich Medal committee RodneyJohnson Johnson (Trans (Trans Superior Superior Resources). Rod begins a 3-year term in Novemuer Novemner of 1998. 1998. title to to "Eisenbrey "EisenbreyStudent StudentTravel TravelAwards". Awards'. This 6. Changed Changedthe the student student travel award's title satisfies a request from satisfies from individual individual and corporate corporate contributors contributors to the 1996 1996 meeting meeting that that such a fund be established in honor of Ned Eisenbrey, and permits the use of & l established =senbrey, investment income income for for encouraging encouraging student student participation participation in the Institute. ILSG meeting. meeting. Co-chairs will 7. Approved Approvedthe the host host location—Marquette—for location-Marquette~for the 1999 ILSG will Bomhorst (Michigan Bob Regis Regis (Northern be Ted Bomhorst (Michigan Technological University) and Bob Michigan University). University). xiii xiii �8.8.Discussed Discusseda apotential potentialY2K Y2Kmeeting meetinglocation—Thunder location-Thunder Bay Bayororother otheraccess accesspoint pointtoto the theAtikoken Atikokenarea. area. 9. 9.Discussed Discusseda apotential potential2001 2001meeting meetinglocation—Sault 1ocationÑSaulSte. Ste.Marie, Marie,MI. MI. 10. the 10. Other Otherbusiness—contact busines-ontact thesecretary-treasurer secretary-treasurerfor fordetails details We Wehope hopethat thatwith withthe thesuccess successof ofthe the1998 1998meeting, meeting, the the ILSO ILSGtook took an an important important step steptoward toward achieving achievingthe thegoal goalof ofexpanding expandingits itsreach, reach,both both in in terms termsof of the the range range of of geological geological topics topics and and the thebackground backgroundof of participants. participants. While Whilewe wemay maynot notbe beable ableto torepeat repeat the the attendance attendancesuccess success of of this thismeeting meetingas aswe wemove moveto tothe themore moretypically typicallyremote remoteconference conferencesites, sites, future futureorganizers organizersand and those thoseof ofus uswho whoare arelong-time long-timeparticipants participantsmust mustdo doall allwe we can can to to actively actively promote promote the the ]LSG ILSG to the broadest possible audience. If we had to pinpoint one reason for the success to the broadest possible audience. If we had to pinpoint one reason for the successofofthe the 1998 1998 meeting, meeting, itit would would be be our ourrelentless relentlesspromotion promotionof ofthe themeeting meetingto tolocal localgeoscience geoscience organizations, organizations,colleges, colleges,and andindividuals. individuals.For Forour ourpart, part,we wewill willencourage encourageTwin TwinCities Cities geoscientists geoscientiststo tocontinue continuetheir theirinvolvement, involvement,now nowthat thatthey they have have been been exposed exposed to to what what the the ILSO ILSGhas hasto tooffer. offer. We Wewish wishto tothank thankall allof ofthe thepresenters, presenters,in inparticular particularthe the special special session session speakers speakerswho who wrote wrote extended extendedabstracts abstractsthat thatwill willserve serveas assummaries summariesof of their their fields fieldsfor for years years to to come. come. This This institute institutewas was built built on onits itstradition traditionof of fine finefield field trips, trips, and and this this year's year's trips trips maintained maintained that that tradition, tradition,thanks thanksin inlarge largepart partto toefforts effortsof of the theleaders. leaders. Acknowledgment Acknowledgmentisisalso alsodue duetotothe the session sessionchairs, chairs,the thebest beststudent studentpaper paperaward awardcommittee, committee,the thelocal localplanning planningcommittee, committee,and andthe the LLSG board members members for for making jobs much easier by by doing theirs well. ILSG board making our our jobs much easier doing theirs well. AAspecial specialthanks thanks to to Terry Terry Boerboom Boerboomfor forhis hisflawless flawlessorganization organizationof ofthe thefield fieldtrips tripsand andguidebook, guidebook,and andtotoLori Lori Day, it takes. takes. Finally Day, the the meeting meeting coordinator, coordinator, for for doing doing all all that that it Finally we we want want to to thank thank our our director directorof ofthe theMinnesota MinnesotaGeological GeologicalSurvey, Survey,David David Southwick, Southwick, for for giving giving us us the the freeboard freeboard and andstaff stafftime timeneeded neededto topull pullthe themeeting meetingtogether. together. Jim JimMiller Millerand andMark MarkJirsa Jirsa Co-chairs Co-chairsof ofthe the44th 44thAnnual AnnualILSG ILSG xiv xiv �45TH 4 5ANNUAL ANNUAL ~ ~ MEETING MEETING INSTITUTE GEOLOGY INSTITUTEON ON LAKE LAKE SUPERIOR SUPERIOR GEOLOGY Program Program �Program Program of of Events Tuesday, Tuesday, May May 4 4 0800-1730 0800-1730 Field Trip 2 Field Trip 2: Archean Ishpeming Greenstone Belt and Gold Mineralization, D.J. Duskin, R.C. Mineralization, Michigan - Leader T.J. Bornhorst, D.J. Johnson, R.A. Mahin, T.O. Quigley, and G.W. Scott Mahin, T.O. Quigley, Scott Wednesday, May Wednesday, May 5 5 ,:-3. ,.. :. .;:, ;+?, 0800-1730 0800- 1730 Field Trip 1I and 2 Field Trip Trip 1: 1: Early Early Proterozoic Proterozoic Strata Strata of the Marquette Marquette Iron Iron Range, Range, Michigan Leader: W.F. Cannon Michigan - Greenstone Belt and Gold Field Trip 2: Archean Ishpeming Greenstone Leaders: T.J. T.J. Bornhorst, D.J. Duskin, R.C. Mineralization, Michigan Michigan - Leaders: Johnson, R.A. Mahin, T.O. Quigley, and G.W. Scott - Registration -- Ramada Inn, Inn, Marquette, Marquette, Michigan Michigan 1700-2000 Registration 1700-2000 1900-2100 Poster Session and cash bar in Ramada Inn 1900-2100 (Authors at posters 1930 1930 to 2100) xv �1 J Thursday, Thursday,May Mav 66 All All technical technical sessions sessions are arein inRamada RamadaInn, Inn,Marquette, Marquette,Michigan Michigan 0730-1600 0730-1600 J Registration Registration-- Ramada Ramada Inn Inn Technical Technical Session SessionII Session Session Chair: Chair: Gene Gene LaBerge LaBerge (University (University of Wisconsin, Wisconsin, Oshkosh) Oshkosh) Shawn Shawn Carison Carlson (Ashton (AshtonMining) Mining) 0820-0830 Opening Opening-- 45 45thAnnual Annual Institute Instituteon on Lake Lake Superior Superior Geology Geology R. R. S. S. Regis Regis and and T.J. T.J. Bornhorst, Bornhorst, Co-Chairs Co-Chairs J J 0830-0930 0830-0930 Invited Invited Presentation Presentation Sarah Sarah A. A. Green Green and and Judy Judy Wells-Budd Wells-Budd Cross Cross Margin Margin Transport Transportin in Lake LakeSuperior Superior . !' .,: . ' . ... . 0930-1000 0930- 1000 Invited InvitedPresentation Presentation Charles Kerfoot, W. : ~. W. Charles Kerfoot,John John A. A. Green, Green, and and Lawrence Lawrence J. J. Weider Weider , A New Approach to Historical Reconstruction: Combining A Approach to Historical Reconstruction: Combining Descriptive Descriptiveand and Experimental ExperimentalPaleolimnology Paleolimnology J 1000-1030 1000-1030 Coffee CoffeeBreak Break J " . 1030-1050 1030-1050 Ojakangas, Ojakangas, R.W. R.W. Sedimentology Sedimentology of of two two Deep Deep Wells Wells in in the the Keweenawan Keweenawan Midcontinent Midcontinent Rift Rift System System Near Munising, Munising, Upper Peninsula, Peninsula, Michigan Michigan 3'. 1050-1110 Puschner,U., U., Schmidt, Schmidt,S.Th., S.Th., and and Bornhorst, Bornhorst,T.J. T.J. 1050-1110 Puschner, Low Grade Metamorphism and Hydrothermal Low Grade Metamorphism and Hydrothermal Alteration Alteration of the the Upper Upper Keweenawan Keweenawan Portage Portage Lake Lake Volcanics, Michigan J 1110-1130 1110-1130 Maki, Maki,J.C. J.C.and andBornhorst, Bornhorst,T.J. T.J. The Gratiot Chalcocite Chalcocite Deposit, Keweenaw Peninsula, Michigan 1200-1340 LunchBreak Break 1200-1340 Lunch 1200-1340 1200-1340 Board BoardofofDirectors DirectorsMeeting Meeting xvH xvi i J �Technical II Technical Session Session H Session Chairs: Rod Johnson (Rod (Rod Johnson & & Associates, Associates, Inc.) Inc.) Jim Small (Edward Jim (Edward Kraemer Kraemer & & Sons) Sons) 1340-1400 Easton, 1340-1400 Easton, R.M. R.M. Metamorphic Map Map of the Canadian Canadian Shield Shield of Ontario, Ontario, Michigan, Michigan, Minnesota, Minnesota, and and Wisconsin Wisconsin 1400-1420 Vitton, 1400-1426 itt ton, S.J. and and Subhash, Subhash. G. G. Dynamic and Static Strength of of Aggregates: Aggregates: An Estimate Estimate of of Static Strength Strength Rate Sensitivity of Geological Materials Rate Sensitivity Geological Materials . ,. . .. . . , : .: :>: , , i.#&: ..' , 3B ?:'$ .A, '3 1420-1440 1420-1440 Yeo, Yeo, G.M. Is the Janice Lake Unconformity a Link between the Hearne Craton and the La Ronge Ronge -- Lynn Lynn Lake Volcanic Arc? . .. . . .. . ! I . - . .... : 1440-1510 1440- 15 10 Coffee CoffeeBreak Break 15 10-1530 Czeck, 1510-1530 Czeck, D.M. and and Hudleston, Hudleston, P.J. P.J. Structural Structural Fabric Fabric and and Strain Strain for for the the Seine Seine River River Conglomerates Conglomeratesat at the the Wabigoon-Quetico Wabigoon-QueticoSubprovince Subprovince Boundary Boundary Near Mine Mine Centre, Centre, Ontario Ontario 1530-1550 Cannon, Cannon,W.F. W.F.and andWoodruff, Woodruff,L.G. L.G. Isle Mercury Distribution in Bedrock, Distribution in Bedrock, Native Copper Copper Ore Ore and and Soils Soils -- Isle Royale National Park, Michigan Michigan 1830-1930 Social Cash Bar 1830-1930 Social - Cash . . . . . . . ?:. 1930-2130 Annual Banquet at Ramada Inn xvii i xvii .:i"> ,. : . . .S t . + . . . ., . . , . . ,. . . .. . . .,. , . "' �j Friday, Friday, May 7 Technical Session ffl III Technical r-Â¥f Session Chair. Chair: Ron Graber (Cliffs Mining Services Co.) Tom Waggoner (Cliffs (Cliffs Mining Services Services Co.) 0830-0850 LaBerge, 0830-0850 LaBerge,G.L. G.L. Regional Patterns on the Peno Penokean Continental Margin in the ~e~ional Southern Lake Superior Superior Region Regio 0850-0910 0850-0910 Ottke, D. Ottke,D. i.g,. , ,, , .~*: Early Descriptions of the Natural Features on the Marquette 1Iron r o Range n ~ a n ~- e ,: --. J J U j L 0910-0930 Webster, Webster,C., C.,Cambray, Cambray,W., W., Scott, Scott,0., G.,Nordstrom, Nordstrom,P., P., Wilson, Wilson, E. E. Palmer Gneiss: A Large, Low-grade Low-grade Shear Shear Zone Zone ., , '.!, , 0930-0950 Diedrich, Diedrich,T.R., T.R., and andMorton, Morton,P. P. Investigation of CaO at Thunderbird Mine, Mesabi Range: Range: Mineral and Stratigraphic StratigraphicRelationships Relationships j 0950-1020 0950- 1020 Coffee CoffeeBreak Break 1020-1040 Medaris, Medaris,L.G., L.G., Fournelle, Foumelle,J., J., Boszhardt, Boszhardt, R., R., and and Broihahn, Broihahn, J. T* Chemical and Mineralogical Comparison Comparison of Baraboo, Barron, Ban-on, and Sioux Sioux Argillite, Metapelite, Metapelite, and Pipestone Pipestone 1040-1100 1040-1100 Graber, Graber,R.G. R.G.and andStrandlie, Strandlie,A.J. A.J. Where are the Metamorphosed Natural Orebodies of the Mesabi Range? Range? j 1100-1120 1100-1120 Scott, G.W. and Lukey, Lukey, H.M. Geology of the Tilden Mine, Marquette iron range, Michigan J 1120-1140 1120-1140 Meier, Meier,J.G. J.G. Republic Wetland Preserve 1140-1300 1 140-1300 Lunch Lunch U J xix j �I Technical TechnicalSession SessionIV IV Session Session Chair: Chair: John John Green Green (University (University of of Minnesota, Minnesota,Duluth) Duluth) Dave DaveBaxter Baxter(PayDay (PayDayResources) Resources) 1300-1320 1300-1320 Boerboom, Boerboom,T.J. T.J.And AndSeverson, Severson,M. M. Geologic Geologic Map Map of of the the Western Western Penokean Penokean Orogen, Orogen, East-Central East-Central Minnesota Minnesota :. 4 8 -?-# 1320-1340 1320- 1340 Daniels, Daniels,D.L., D.L.,Nicholson, Nicholson,S.W., S.W.,Cannon, Cannon,W.F., W.F., and andBracken, Bracken,R.E. R.E. Preliminary Aeromagnetic Map of Wisconsin Preliminary Aeromagnetic Map of Wisconsin 1340-1400 1400 Johnson, Johnson,R.C. R.C.and andBornhorst, Bomhorst, T.J. T.J. Ishpeming Ishpeming greenstone greenstone belt belt -- Evidence Evidence for for Archean Archean tectonic tectonic evolution evolution of the southern edge of the Superior Province in Michigan of the southern edge of the Superior Province in Michigan 1400-1420 1420 Yeo, Yeo,G.M. G.M. Low-Resolution Low-Resolution Sequence Sequence Stratigraphy Stratigraphyof of Early Early Proterozoic Proterozoic Paragneisses, Paragneisses, Wollaston Wollaston Domain, Domain, Saskatchewan Saskatchewan I I I I I I 1420-1450 1420- 1450 Coffee CoffeeBreak Break 1450-15 10 Bickford, 1450-1510 Bickford, M.E. M.E. and and Steinhart, Steinhart,W.E. W.E. Distribution Distribution of of the the Archean Archean to to earliest earliest Paleoproterozoic Paleoproterozoic Sask Saskcraton craton beneath beneath deformed deformed orogenic orogenic rocks rocks in in the the Trans-Hudson Trans-Hudson orogen orogen and andits its tectonic implications: Evidence from common Pb and Sm-Nd isotopic tectonic implications: Evidence from common Pb and Sm-Nd isotopic data data 1510-1530 Miller, Miller, J.D. J.D. Jr. Jr. 1510-1530 Potential Potential for for stratiform stratiformPGE PGE mineralization mineralization in in mafic mafic layered layered intrusions intrusions of of the the Duluth Duluth Complex Complex - 1530-1550 Peterson, Peterson.D.M. D.M.and andMorton, Morton,R.L. R.L. Development Development of of Volcanogenic Volcanogenic Massive Massive Sulfide Sulfide Deposit Deposit Exploration Exploration Targets Targets in in Northern Northern Minnesota Minnesotafrom from GIS GIs Spatial SpatialAnalysis Analysis of of Geological, Geological, Geochemical, Geochemical, and Geophysical Geophysical Criteria 1550-1610 1550-16 10 Loughry, Loughry, J.E., Johnson, Johnson, Matthew Matthew M., and Cotter, J.F.P A Geochemical Geochemical and and Petrologic Petrologic Study Study to Determine the Origin of the the Crowduck Crowduck Lake Lake Group, Group, Kenora, Kenora, Ontario: Ontario: A A Problematic Problematic Metaconglomerate Metaconglomerate xx �—I Poster Session Poster Session J Posters will be Friday 1200 Posters be up up from from Wednesday Wednesday 1900 1900 to to Friday 1200 Authors will will be be at at posters posterson onWednesday Wednesdayfrom from1930 1930to to 2100 Authors Ams, D. and Holm, D., Characterization Characterization and Timing Timing Constraints Constraints of Post-Penokean Post-Penokean Meso-Scale Structures in the Watersmeet and Republic Gneiss Domes of Northern Structures Michigan Barber-Delach, R.D. and and Cannon, Cannon, W.F., Re-examining Stream Stream Sediment Sediment Geochemical Data from the National Uranium Resource Evaluation Program Program Geochemical (NURE), Wisconsin and Northern Michigan (NURE), and Michigan Han, T.M., T.M., Megascopic Megascopic Fossils and Their Their Possible Possible Contribution Contribution to to the the Han, Development of the Silicate Silicate Unit Unit of of the the Negaunee Negaunee Iron Iron Formation, Formation, Empire Empire Mine, Mine, Marquette Range, North Michigan Marquette Michigan Holm, D., Romano, D., and Mancusco, C., Comparison of Mica Ar/Ar AdAr and Rb/Sr Thennochronology Results from Northern Wisconsin and Northern Michigan j J J lUasner, J.S., Klasner, J.S., Cannon, Cannon, W.F., Schulz, Schulz, K.J., and LaBerge, G.L., G.L., The Iron River Syncline: An Allochthonous Structural in the the Penokean Penokean Foreland Foreland of of Structural Panel in Syncline: Northern Michigan Miller, J.D. Jr, and Miller, and Chandler, Chandler, V.W., V.W., New Geologic Geologic Map of the Central Central Duluth Duluth Complex Complex Rausch, D.E., and Wattrus, N.J., Rausch, N.J., Lake Superior's Rings: Clues to the Origin of Polygonal Fault Systems Polygo J J j xxi j �Saturday. May Saturday. Mav 8 8 0800-1730 0800-1730 Field and 4 Field Trip Trip 3 and Field of the the Marquette Marquette Iron Iron Range, Range, Field Trip Trip 3: 3: Tilden Tilden and and Empire Mines of Michigan G.W. Scott, Scott, P.M. P.M. Nordstrom Nordstrom and and H.M. H.M. Lukey Lukey Leaders: G.W. Michigan -- Leaders: Field Trip 4: Paleozoic and and Glacial Geology from Au Train to Grand Trip 4: Marais, R.S. Regis Regis and and J.B. LB. Anderton Anderton Leaders: R.S. Marais, Michigan Michigan -- Leaders: xxi xxi i �45TH ANNUAL MEETING INSTITUTE ON LAKE SUPERIOR GEOLOGY Abstracts Abstracts �CHARACTERIZATION AND AND TIMING TIMING CONSTRAINTS CHARACTERIZATION CONSTRAINTS OF POST-PENOKEAN POST-PENOKEAN MESO-SCALE STRUCTURES STRUCTURES IN IN T THE MESO-SCALE H EWATERSMEET WATERSMEET AND REPUBLIC REPUBLI~GNEISS GNEISS DOMES OF OF NORTHERN MICHIGAN MICHIGAN David Ams (undergraduate student) and Daniel Hoim, Holm, Department Department of Geology, Kent State Ams (undergraduate University, Kent OH 44242 OH 44242 We have measured late, meso-scale, structures present present in in Early Proterozoic Proterozoic gneiss gneiss meso-scale, ductile and brittle structures in order to to assess assess their their origin. origin. The Watersmeet and Republic gneiss gneiss domes domes domes of northern Michigan in lie north north of of the the region regionofofpervasive pervasivepost-Penokean post-Penokean 1600-1650 1600-1650 Ma shortening shortening (Hoim (Holm et a!., al., 1998, 1998, Geology) and southeast which closed the Keweenawan Keweenawan rift rift at ca. 1080-1860 southeast of thick-skinned thrusting which whether meso-scale meso-scalebrittle brittle and andductile ductile 1994, Geology). The The challenge challenge then is to determine whether Ma (Cannon, 1994, shear zones formed during during the late stages stages of Early Proterozoic gneiss dome formation or if they represent deformation associated defamation associated with these these younger younger events. events. Watersmeet gneiss Watersmeet gneiss dome. observations were made on the north-east side of the dome, south of its contact with the overlying Our observations metasedimentary rocks rocks (Hwy (Hwy 45 45 exposures). exposures). The dominant steep east-west fabric fabric in in Archean Archean rocks rocks of of metasedimentary brittle shear shear zones. zones. The ductile the dome are cross-cut by steep ductile, semi-brittle, and brittle ductile and larger semiand dip dip steeply steeply both both north north and and brittle to brittle shear zones show a dominant N70-80E strike orientation and etc.), the apparent sense sense south (Fig. 1). Where Where relative relativemotion motion indicators indicators exist (offset dikes, pegmatites, etc.), up. Small to be be oriented oriented NS NS (with (with steep steep east east of motion is south-side up. Small scale scale brittle brittle faults and fractures tend to dips) dips) or NW (with steep steep southwest dips). Slickenlines Slickenlineson on the the NW NW oriented oriented set set plunge plunge gently gently to to the the NW NW Pie. 1 (Fig. 1). .--o- *1 The coarse, more gentle gentle to to the the north north toward toward the the contact contact coarse, steep, steep, EW fabric fabric of the dome interior becomes more rocks and and shows shows aareduction reductioniningrain grainsize sizedue duetotoductile ductileshearing. shearing.We Weattribute attribute with the metasedimentary rocks this to ductile ductile overprinting shear zone. zone. The overprinting of the steep fabric along a basement-cover shear The timing timing of shearing shearing during gneiss gneiss dome dome formation formation is is constrained constrained by aa 1765 1765 Ma Ma hornblende hornblende Ar/Ar ArIAr plateau date date obtained obtained from from the core rocksjust just from aa concordant concordant muscovite plateau date obtained from metasedimentary rocks core rocks and from north of the see also also Schneider Schneider et et al., al., 1996, 1996, CJES). CJES). the contact contact (Fig. (Fig. 2; 2; see We propose that ductile and semi-brittle shear zones zones Conned formed during during the thelate latestages stagesof ofunroofing unroofingofof thal the theductile of the the footwall footwall In our our model model they thev represent remesent internal deformation of the gneiss dome (at ca. 1765-1755 1765-1755 Ma). In dome rocks as they were unroofed from beneath the metasedimentary cover rocks along a north-dipping detachment fault fault at at the basement-cover contact. The brittle shear zones have a completely different detachment basement-cover contact. ones. Their orientation from the ductile and semi-brittle ones. Their orientations and subhorizontal lineations suggest rift. they may be related to closure of the Keweenawan rift. Republic gneiss dome. Republic fracture zones zones which which occur occur in in the the Republic We focused on the numerous chlorite mineralized brittle fracture Ma post-tectonic post-tectonic alkali alkali red red granite granite gneiss dome north of Republic (Fig. 3). They Theycross-cut cross-cutthe the—1735 -1735 Ma be younger younger than than mica mica cooling cooling ages ages within within the the dome dome (1680-1720 (1680-1720 Ma). Ma). (Xgaf of Sims. Sims, 1992) 1992) and must must be They have a dominant north-northwest north-northwest strike strikeand anddip dip moderately moderatelytotosteeply steeplytotothe thewest. west. Most of the They lineations plunge gently gently to to the the northwest. northwest. Kinematic fiber steps) steps) on on a few few of these Kinematic indicators (crystal fiber show left-lateral, reverse motion. Ductile Ductileshear shear zones zones within within the dome dome strike dominantly northwest and dip steeply and must be older older than the mica cooling coo1i.i; ages. ages. related to to the older ductile shear zones along The brittle fractures do not appear to be kinc:iiatically kincniatically related uplifted. The which the gneiss dome block was probably uplifted. Thedominant dominant left-lateral left-lateral strike-slip strike-slip motion and be defonnational deformational features features associated associated with withclosure closureof of north-northwest attitude indicates they might be also be the Keweenawan rift. This Thisinterpretation interpretationisisconsistent consistentwith with prior prior thermochronologic thennochronologic evidence evidence for a low temperature Keweenawan CJES). temperature Keweenawan age age disturbance disturbance of this region (Schneider (Schneider et al., 1996, 1996, CJES). 2 �Ductile shear zones Smaller britile fracture zones Fig. Fig. 1. Stereonet Stereonet plots of of ductile, ductile, semi-brittle, semi-brittle, and and brittle brittle shear shear zones zones within the Watersmeet the Watersmeet gneiss gneiss dome. 1 -1 Schist outside of the dome — 2000J 2000: Amphibolite imnhibolite within within the the dome AGE 1 Ma 1500 - - 1000-0_ 94-MI-3-H 94-MI-3-H Hornblende Hornblende Tg=1751±l3Ma T g = 1751k13Ma - Tp=1765±l3Ma %39Ar 100 0 UP-i OA-M UP-1 0A-M Muscovite Muscovite Tg=1760±i4Ma Tp=1767±l7Ma 100 %39Ar Fig. 2. Ar/Ar mineral Fig. mineral age age spectra from from the the Watersmeet Watersmeet gneiss gneiss dome region. region. date. Tg Tg Is is total gas Tp is plateau date. gas date. Fig. 3. 3. Stereonet plots plots of ofrepresentative representativeductile ductileshear shear zones zones and and mineralized mineralized Fig. brittle fracture brittle fracturezones, zones. Republic Republic gneiss gneiss dome dome region. region. 3 1 �Re-examining stream sediment data ffrom National U Uranium Re-examining sediment geochemical geochemical data r o m tthe h e National r a n i u m Resource Resource Evaluation Program and nnorthern o r t h e r n Michigan Michigan Evaluation P r o g r a m (NURE), (NURE), Wisconsin Wisconsin and Robert D. Barber-Delach, Oak Oak Ridge Ridge Associated Associated Universities, Universities, at at U.S. U.S. Geological Geological Survey. Survey, Mail Mail Stop Stop 954, Reston, VA VA 20192 20192 W.F. W.F. Cannon, U.S. Geological Geological Survey, Survey, Mail Mail Stop Stop 954, 954, Reston, Reston, VA VA 20192 20192 In the In the latter latter 1970's 1970's a astream streamsediment sedimentgeochemical geochemical survey survey was was conducted conducted in in parts parts of ofnorthern northern the United United States Department Department of of Energy. Energy. A A Wisconsin and northern Michigan by the NURE program of the data set consisting I °x2° data consisting of of multi-element multi-element analyses analyses of of 3185 3 185 samples samples was was developed developed spanning spanning eight eight l0x2' quadrangles. The but also quadrangles. The data datawere wereintended intended for foruse use ininevaluating evaluatingundiscovered undiscovered uranium uranium resources, resources, but have application geochemical background background and and baseline have application for for establishing establishing regional regional variations variations in geochemical baseline concentrations. The The U.S. is concen&itions. U.S. Geological ~ e o l o ~ i c Survey Survey al is ____________________________________________ expanding research research on on regional regional geochemical geochemical Figure I. 1. Comparison of unadjusted (a) (a) and patterns, and and the the NURE data set patterns, MURE data set is is being being rerenormalized (b) (b) cobalt cobalt concentrations concentrations for for use use in in normalized examined as as part of of that that effort. effort. displaying NURE stream sediment sediment data. data. In many places places the the NURE NURE data datashows showsobvious obvious biases in in values values between between adjacent adjacent quadrangles, quadrangles, visual in some some cases cases apparent only by visual examination of element concentration maps. For instance, Figure llaa shows shows significant discontinuities of cobalt values values between quadrangles in the original original NURE NURE data. data. Biases were probably introduced introduced by by somewhat somewhat different sampling, processing, sampling, processing, and analytic analytic techniques techniques between various quadrangles, between quadrangles, and probably also changes in analytical by time-dependent time-dependent changes instrument calibration that that appear appear not not to have instrument calibration have been fully accounted for over the duration of the NURE program. program. These Thesequadrangle-based quadrangle-based biases biases render use of render of the thedata dataproblematical problematical without without careful assessment careful assessment and correction correction of of analytical analytical biases. Here Here we present present two two approaches approaches by by which the NURE NURE data data set set can can be be corrected corrected for for which the quadrangle biases. in analytical data First, systematic biases in between can be normalized between quadrangles quadrangles can normalized by by quadrangle as as a displaying data for each each quadrangle function of the statistical function statistical distribution distribution of values values for only that quadrangle. Figure lb for quadrangle. Figure I b shows shows the the same data for cobalt as shown in Figure Ia, same la, but but each of with the values within within each of the the eight separately into quadrangles quadrangles classified separately percentiles of the data data set set from from that that quadrangle. quadrangle. The between-quadrangle bias bias is is largely largely removed removed and natural patterns patterns of of cobalt cobalt variation variation are are more more 4 a. Unadjusted data . . ,do.- adom. b. Data normalized within quadrangles �evident. that standard standard desktop desktop G GIS software evident. This Thistechnique technique has has the the advantage advantage of of ease ease and and simplicity simplicity in in that I s software can perform statistical manipulation manipulation of of data data and and time time required required for for perform and display the results with minimal statistical processing. Also, Also, the technique However, two two technique does not require acquisition acquisition of new analytical analytical data. However, important shortcomings shortcomingsof of the the technique only relative of element are: 1) presents only relative variations variations of element important technique are: I) itit presents concentrations and and does does not not improve the the overall overall accuracy accuracy of of the the NURE NURE data, data, 2) 2) itit masks masks true true variations variations concentrations quadrangle. that occur at the approximate scale of a l°x2° l0x2"quadrangle. A second In the the 1980's, A second technique technique requires requires new new analytical analytical data. data. In 1980's, the the USGS USGS became became the the official official archiving agency agency for for NURE NIJRE data and maintains repository in in Denver, Denver, Colorado archiving data and and samples, samples, and maintains aa sample sample repository Colorado in which all N'URE samples samples are are accessible accessiblefor for restudy. restudy. We re-analyzed aa subset subset of of those those samples samples We have have re-analyzed in which all NURE for the Ashland and Rice Rice Lake Lake l°x2° Iox2' quadrangles quadrangles in northern Wisconsin and compared the results of our re-analyses to to the the original original data data reported reported by by the the NURE NUREprogram. program. Our Our analyses analyses were were done done using using routine routine re-analyses 40-element inductively 40-element inductively coupled coupled plasmaplasmaatomic emission spectroscopy Figure 2. 2. Scatterplot Scatterplot of of magnesium magnesium concentration concentration spectroscopy (ICP-AES) (ICP-AES) Figure technique supplemented supplemented by by more (ppm) demonstrating demonstrating the the quad quad bias bias of of original original NURE NURE technique more precise precise (ppm) single-element techniques for arsenic and data, with with fitted fined regression regression lines lines and and correlation correlation single-element techniques and data, selenium. Analytical precision and and Analytical indices (R2). indices (R'). accuracy were monitored accuracy were monitored by by replicate replicate 2.1 2.1 analyses of standard samples. ,, 1 , -, — 1 Comparison of our new new values values to to 1.8 •0 concentrations reported reported by by NURE NURE show show $b —, quadrangle-based quadrangle-based biases in virtually all 1.5 elements elements for which which aa significant significant number number —— 000 of samples exceed exceed detection limits (about (about ,. elements). Figure 20 elements). Figure 2 shows shows an extreme 0 case in which NURE magnesium analyses 09 are strongly and and consistently consistently quadranglequadrangle0.9 dependent and in which which both both quadrangles quadrangles vary significantly from our new analyses. j, vary significantly from analyses. of bias bias within within aa 0.6 This consistency of quadrangle allows derivation of equations •Rice Lake Lake Quad Quad Â¥Ri that can adjust the original original NURE data to 03 correct for previous analytical biases and and oAshland Quad Quad OAshland , new produce a better accord with new 0 data. Although Although this technique analytical analytical data. technique 1.8 2.1 0.6 0.9 1,2 1.5 0.3 has 00 0.3 0 .6 0.9 1.2 1.5 1.8 2.1 has inherent inherent statistical statistical uncertainty, uncertainty, that that the and the uncertainty is quantifiable, and Re-Analyzed Mg MgConcentration Concentration Re-Analyzed element maps are resulting element are significantly significantly L more accurate accurate than than those made from more from the the Although this this technique techniquedoes doesrequire requirethe the cost cost and and time time of original NURE data. of re-analyzing re-analyzing aa original data. Although significant number number of of NURE NURE samples, samples, the the result result produces producesaamuch much improved improveddata dataset setwithout withoutthe thecost costof of re-analyzing the entire sample set. We plan to proceed with this technique during the coming year. re-analyzing the entire set. We to the year. , . 7 • , 7 i. • — - 7 5 I �Distribution Distributionof ofthe theArchean Archean to to Earliest Earliest Paleoproterozoic PaleoproterozoicSask Sask Craton Craton Beneath Beneath Deformed Deformed Orogenic OrogenicRocks Rocksin inthe theTrans-Hudson Trans-HudsonOrogen Orogenand andits itsTectonic TectonicImplications: Implications:Evidence Evidencefrom from Common Common Pb Pb and and Sm-Nd Sm-Nd Isotopic IsotopicData Data M. E. Steinhart, III, ifi, Department M. E. E. Bickford Bickford and and William William E. Departmentof of Earth Earth Sciences, Sciences, Heroy Heroy Geology Geology Laboratory, Syracuse University, Syracuse, NY 13244-1070 Laboratory, Syracuse University, Syracuse, NY 13244-1070 Late, Late, undeformed, undefonned ,ca. ca.1.8 1.8Ga Gapegmatites, pegmatites,leucogranitic leucograniticsheets, sheets, and and post-orogenic post-orogenic plutons plutons in in the Glennie, Hanson Lake, and La Ronge Domains, and parts of the Hearne Province, were studied Glennie, Hanson Lake, and La Ronge Domains, and parts of the Hearne Province, were studied to melting ofjuvenile ofjuvenile orogenic orogenic crust crust or or of Archean todetermine determinewhether whetherthey they were werederived derived by melting Archean lower structuralwindows windowsin inthe theGlennie Glennieand andHanson Hanson lower crustal crustalrocks rocksequivalent equivalentto tothose thoseexposed exposedin instructural Lake isotopic composition of of PbPb from feldspars (206Pb/2°4Pb == 14.3 14.3-- 15.2; 15.2; LakeDomains. Domains.The The isotopic composition from feldspars (20Èpb/== 15.1 15.1-- 15.25; 15.25;208Pbf°4Pb ^"Pb/'^Pb ==34.4-36.4) 34.4 - 36.4) and andSm-Nd Sm-NdTDM TDM ages of of ca. ca. 3.2 3.2 Ga Ga m7~b/2d4pb ages for forca. ca.1.8 1.8Ga Gapost-orogenic post-orogenicintrusions intrusionsreveal revealthat thatArchean Archean rocks rocks are arenot not only onlyexposed exposedin inthe the windows, windows,but butalso alsoextensively extensivelyunderlie underlieparts partsof ofthe theGlennie Glennieand andHanson HansonLake LakeDomains Domainsininwhich which only Incontrast, contrast,feldspar feld arPb Pbfrom frompegmatites pegmatitesin inthe the only juvenile Paleoproterozoic Paleoproterozoicrocks rocksare areexposed. exposed. In La similar == 15.1 b/-b 15.1-- 15.2; 15.2; 15.4 - 15.6; 15.6;207Pb/2"Pb LaRonge Ron eDomain Domainisisisotopically isotopically similar(2°6Pb/2°'Pb ('"'Pb/^'Pb ==15.4208Pb/204Pb plutons with TDM "'PW b =34.8 34.8-- 35.2) 35.2)to tothat thatofjuvenile, ofjuvenile,ca. ca.1.85 1.85Ga GaPaleoproterozoic Paleoproterozoic plutons with TDM ages oceanic materials. materials. Sm-Nd data agesof ofca. ca.1.80-2.0 1.80-2.0Ga, Ga,indicating indicatingderivation derivation from similar oceanic data from from two yield TDM ages twoLa LaRonge RongeDomain Domainaplites, aplites,ininwhich whichSm Smand andNd Ndare areapparently apparentlyunfractionated, unfl-actionated, yield TDM ages of 19 Ga. Surprisingly, feldspar Pb data (2°'Pb/2°4Pb 207Pb/204Pb = 15.1 Surprisingly,feldsparPbdata (""Pb/^Pb== 15.515.5 - 15.8; 15.8;^Pb/^'Pb= 15.1-- 15.2; 15.2; of1.8-. 1.8-.19Ga. 35.0--35.2) 35.2) from frompegmatites pegmatitesthat that intrude intrudeArchean Archean rocks rocksof ofthe theHearne HeameProvince, Province,in in m'~b/-b ==35.0 the thehinterland hinterlandwest westofofthe theNeedle NeedleFalls FallsShear ShearZone, Zone,also alsoindicate indicatederivation derivationfrom fromjuvenile juvenilesources. sources. Thus, viewthat thatan anArchean Archeanmicrocontinent microcontinent("Sask ("SaskCraton") Craton") Thus,while whilethese thesedata datasupport supportthe theview underlies underliesparts partsof ofGlennie Glennieand andHanson HansonLake LakeDomains, Domains, they they suggest suggest that that crust crustbeneath beneathLa LaRonge Ronge Domain, Domain,and andalso alsobeneath beneathatatleast leastparts partsofofHearne HeameProvince, Province,isisofjuvenile ofjuvenilemantle mantlederivation. derivation. Alternatively, LaRonge RongeDomain Domainand andHearne HearneProvince, Province, Alternatively,Archean Archeancrust crustmay maybe bepresent presentbeneath beneaththe theLa but ca.1.8 1.8Ga Gapegmatites pegmatiteswere wereformed. formed.These These butwas wasbelow belowthe thezone zoneofofmelting meltingwhen whenthe theca. observations observationsare areconsistent consistentwith withinterpretation interpretationofofnorthwesterly-dipping northwesterly-dippingreflectors reflectorsbeneath beneath Hearne revealedby byCanadian CanadianLithoprobe Lithoprobeseismic seismic data, data, as asrepresenting representingsubducted subducted H e m eProvince, Province,asasrevealed oceanic oceaniclithosphere. lithosphere.The Thepresence presenceofofoceanic oceaniclithosphere lithospherebetween betweenHearne HeameProvince Provinceand andGlennie Glennie Domain Archeanmicrocontinent microcontinentbeneath beneaththe theGlennie GlennieDomain Domainisisprobably probablynot not Domainindicates indicatesthat thatthe theArchean subducted subductedHearne H e m ecrust, crust,but butmore morelikely likelyan anexotic exoticcrustal crustalfragment. fragment. =% 4 6 �GEOLOGIC MAP GEOLOGIC MAP OF OF THE THEWESTERN WESTERN PENOKEAN PENOKEAN OROGEN, OROGEN, EAST-CENTRAL EAST-CENTRAL MINNESOTA BOERBOOM, Terrence Terrence J., J., Minnesota Minnesota Geological Geological Survey, Survey,2642 2642 University UniversityAve., Ave.,St. St.Paul, Paul,MN MN 55114; BOERBOOM, 55114; boerboOl @maroon.tc.umn.edu; @maroon.tc.umn.edu; and boerb00l and SEVERSON. SEVERSON, Mark, Mark, Natural Resources Resources Research Institute, Institute, University University of Minnesota, Duluth. Duluth, MN 55811; 5581 1;mseverso@sage.nrri.unm.edu mseverso@sage.nrri.umn.edu The Natural Resources Resources Research Research Institute, Institute, has has recently recently The Minnesota MinnesotaGeological Geological Survey, Survey, in cooperation with the Natural completed Orogen in east-central east-central Minnesota. Minnesota. comnleted aa revised revised geologic eeoloeicmap man of the the western portion nortion of the Penokean Oroeen The geologic framework western Penokean framework for for the thewestern ~ e n o k e Orogen kOrogen has has been been previously previously interpreted interpreted by by Southwick Southwick and others (1988) using plate-tectonic theory theory (see discussion discussion below). below). This This map map builds builds on on that that base base by by data. Although utilizing new drilling information and better geophysical geophysical data. Although thousands thousands of of exploratory exploratory holes holes were drilled in this area area from the late l800s 1800sto tothe the 1950s, 1950s.nearly nearly all all focused focused on locating locating iron, iron, manganese, manganese, or or sulfur ore. As Asaaresult, result, the thedistribution distributionand and form form of of the the major major iron-formations both within and outside the iron-mining districts are fairly well established, but but little little is is known known about aboutthe the areas areas in in between. between. Thus, any geologic compilation compilation necessarily relies relies heavily on geophysical interpretations. interpretations. GEOLOGIC FRAMEWORK Southwick (1988) interpreted interpreted the Penokean Orogen to consist of several structural panels that range from sedimentary sedimentary rocks rocks filling filling aa foreland foreland basin, basin, through through aa main main fold-and-thrust fold-and-thrust belt belt of sedimentary sedimentaryand and volcanic volcanic rocks, to a complex terrane. The major terranes, referred referred to as panels in the list rocks, complex metamorphic-plutonic metamorphic-plutonic terrane. list below, are separated by linear, linear, northeast-trending northeast-trending aeromagnetic aeromagnetic anomalies, which are are interpreted interpreted as as thrust thrust faults that truncate stratigraphy-related stratigraphy-relatedaeromagnetic a e r ~ r n a ~ e tanomalies ainc o d i e s within the panels. The Thefollowing followingsummary summary of the structural I), and modified accordingly accordingly structural panels panels is is condensed condensed from from Southwick Southwick and others others (1988) (1988) (Fig. (Fig. 1), for this study study based based on on new new information. information. 1. The Animikie basin is filled with essentially essentially unmetamorphosed unmetamorphosed sedimentary 1. The Animikie sedimentary rocks rocks (Pokegama (Pokegama Quartzite, Quartzite, Biwabik Iron Formation, Formation,and and Virginia Formation). The TheAnimikie Animikie strata strata generally generally have have aa shallow shallow south south dip, but along along the the southern southern basin basin margin, margin, and and hence hence this this map map area, area, are are deformed deformed into into fairly fairly tight tight upright upright folds. folds. In Inthis thisarea areaofofthe themap, map,these thesestrata strataunconformably unconformablyoverlie overlierocks rocks of of the the foldfold- and and thrust-belt. thrust-belt. 2. The North Range 2. Range panel panel isisdominated dominatedby byweakly weaklymetamorphosed metamorphosedargillite, argillite, siltstone, siltstone, quartzite, quartzite,ironironformation, graphitic slate, graywacke, and minor limestone and and chert. chert. Volcanic and hypabyssal mafic rocks rocks are are a minor component componentof the the North Range. Structurally, Structurally,the the North North Range Range is is dominated dominatedby by aa large large northwest-inclined, northwest-inclined, doubly plunging synclinorium. synclinorium. Geophysical Geophysicalmodels models (Carlson, (Carison, 1985) 1985) show that the folded Animikie Basin. The folded Trommald Trommaldiron-formation iron-formationcontinues continuesto tothe theeast eastbeneath beneath rocks rocks of of the thehimikie Thestructural structural of those deposited in an external and stratigraphic attributes of North Range rocks are characteristic of tectonic zone. zone. 3. The 3. The South South Range Rangepanel panel also alsocontains containsan an abundance abundanceof of slaty slaty and and argillaceous argillaceousrocks, rocks, but but unlike unlike the the North North Range, rocks, all of which Ranee. it has aa substantial substantial component comoonent of mafic rnafic volcanic volcanic and hypabyssal hvpabyssal intrusive rocks, have undergone low-grade inthe theSouth SouthRange Rangeresembles resemblesAlgomaAlgomahaveundergone low-grade metamorphism. metakorphism. The Theiron-formation iron-formationin type iron-formations iron-formations in in that that itit occurs occurs as as aa series seriesof of Jenses lenses closely associated with mafic volcanic rocks and graphitic anomalies. The graphitic slate. slate. This Thispanel panel isis characterized characterizedby narrow linear aeromagnetic anomalies. The structure structure of the the South South Range Range isis dominated dominatedby by elongate elongateeast-northeast-trending east-northeast-trending overturned overturnedfolds. folds. The South Township panel panel to to the the south south by byaa South Range Range panel panel is is separated separated from from the Moose Lake-Glen Township narrow zone of graphite-rich, graphite-rich, crenulated crenulated phyllitic schist that curves from northeast to east-west. This This graphitic schist schist may have absorbed absorbed aa great great deal deal of strain strain during during thrust thrust faulting. faulting. 4. The TheMoose MooseLake-Glen Lake-GlenTownship Townshippanel panel isis dominated dominated by by quartz-rich quartz-rich metaclastic rocks and by mafic mafic volcanic graphitic argillite argillite and and schist; schist; all were subjected volcanic and hypabyssal intrusive rocks, along with graphitic subjected to lower greenschist-facies greensehist-facies metamorphism. This Thispanel panel includes includes the the Glen Glen Township Formation, a sulfiderich graphitic schist schist grading grading into into aa sulfide sulfideiron-formation iron-formation that that contains contains pyrrhotite, pyrrhotite, pyrite, pyrite, lesser lesser chalcopyrite, and consists of ofamygdaloidal amygdaloidal chalcopyrite, and minor minor sphalerite. sphalerite. The Thestratigraphic stratigraphicsection section at at Glen Township consists basalt overlying overlying the the sulfidic-graphitic sulfidic-graphiticschist, which in turn overlies graywacke. In In places places the the latter lattertwo two are separated by slaty iron-formation. iron-formation. The Thebase base of of the thesequence sequencecomprises comprises quartz-rich quartz-rich sedimentary sedimentary moderate magnetic magnetic anomaly. rocks that typically contain contain up up to several several percent magnetite, which causes a moderate Several prominent linear linear aeromagnetic anomalies anomalies apparently reflect some combination of thrust faults faults with relatively minor displacement, displacement, and stratigraphic and lithologic variation. variation. The GlenTownship Glen Township strata strata have undergone undergone at least least two two generations generationsof of folding folding that that produce produce complex complex aeromagnetic aeromagneticpatterns. patterns. �A previously unrecognized, synsyn- to to late-orogenic late-orogenic monzonitic intrusion intrusion with with aa well-defined well-defined circular circular aeromagnetic anomaly core drilline drilling iust just northwest northwest of ofMille Mule Lacs Lacs Lake. Lake. Another Another core core aeromaenetic anomalv was intersected by bv core hole hole drilled drilled on on this this anomaly anomaly intersected intersected ten ten feet feet of o faabrick-red, brick-red,unmetamorphosed unmetamorphosed quartz-pebble quartz-pebble conglomerate. This Thisunit unitisisgeophysically geophysicallyinvisible invisibleand and its its extent extent is is thus thus unknown, unknown, but but itit may may represent represent conglomerate that was deposited durine during Meso~roterozoic Mesoproterozoic time time in in aa shallow shallow basin basin on on the the backside backside of of aa conelomerate the Midcontinent Midcontinent rift, and the and thus thus is is correlative correlative with with Keweenawan Keweenawan rocks rocks to to the the east. east 5. The McGrath-Little 5. The McGrath-Little Falls Falls panel, panel, the the southernsouthern- and and internal-most internal-most component component of of the the foldfold- and and thrust-belt, thrust-belt, comprises comnrises granitic eranitic to to tonalitic tonalitic gneiss, eneiss. amphibolite-facies amnhibolite-facies pelitic nelitic schist, schist. and and latelate- to post-tectonic nost-tectonic granitic eranitic intrusions. An uncommon dike that Penokean granites of fresh, comnosed fresh. intr6sions.~n uncommon that nost-dates ~enokekn =m~ i t e s is composed -~~ ~- ~ ~ ~lamprophyre -la&ronhvredike -~~~~~ r~ ~ - r ~ ~- , ~ ~~~-~~ ~ post-dates - -~~ -~~~~-~~~ ~ euhedral be traced across across the entire entire map area area euhedral clinopyroxene clinopyroxenein in aa groundmass groundmass of of poikilitic feldspar; feldspar; it can be by its its pronounced pronounced reverse reverse aeromagnetic aeromagnetic anomaly. Abundant Abundant small small circular circular to to elongate elongate positive positive magmagnetic anomalies anomalies are areindicative indicative of of mafic-ultramafic mafic-ultramafic plugs plugs similar similar to to those that have been drilled at several locations to to the the south locations south and and east. east. Based Basedon onaeromagnetic aerom&$etic data, data, these these plugs plugs post-date post-date the the lamprophyre lamprophyre dike. The Thedike dikeisisconjectured conjecturedtotobe berelated relatedto tothe thewaning waningstages stagesof ofPenokean Penokean granite granitemagmatism. magmatism. ~ ~ ~~~~ -~ ~~~~ ~ ~ is ~ ~ References: References: Carlson, Carlson, K.E., K.E.,1985, 1985, A A combined combined analysis analysis of of gravity gravity and and magnetic magnetic anomalies anomalies in in east-central east-central Minnesota: Minnesota: M.S. 138p. p. M S . thesis, thesis. University University of of Minnesota, Minnesota, Minneapolis, Minneapolis, 138 Southwick, Geologic map map (scale (scale 11:250,000) of the the Penokean Penokean Southwick, D.L., Morey, Morey, G.B., and McSwiggen, McSwiggen, P.L., P.L., 1988, Geologic :250,000) of Orogen, and accompanying accompanying text: text: Minnesota Report Orogen, central central and and eastern eastern Minnesota, Minnesota, and Minnesota Geological Geological Survey Survey Report of Investigations 37, 25 p. 37.25 p. Figure 1. 1. Regional Regional tectonic tectonicinterpretation interpretation elements discussed in in showing the tectonic elements the abstract- From Southwick and others (1998). This map does not reflect changes made on the map accompanying this poster. Area of revised geologic map 8 �Mercury distribution National Park, Park, Mercury distributionin inbedrock, bedrock,native nativecopper copperore, ore, and andsoils—Isle soils-Isle Royale National Michigan Michigan W.F. Cannon, U.S. W.F. U.S. Geological Geological Survey, Survey, Reston, Va L.G. Woodruff, U.S. Geological Geological Survey, Survey, St. Paul, MN In response response to recent recent findings findings of elevated elevated mercury in fish in some inland lakes on Isle Royale, we have begun a study of mercury concentration study of concentration in natural geologic materials of the island. Initially Initially we aimed to determine determine if elevated elevated mercury from native copper deposits could be contributing mercury to the impacted lakes. Small Smallnative nativecopper copperdeposits depositson onthe the island island were were mined mined the 1800's. Those sporadically in the Thosedeposits, deposits,waste waste dumps dumps at at abandoned abandoned mines, and wastes from small processing operations, do contain anomalous amounts of of mercury. mercury. Our Our analyses analyses have have found individual as much as 14 14 parts per million (ppm) mercury, and stamp sands individual samples samples with as were found to contain contain from 0.6 to 0.7 ppm. In Incontrast, contrast,typical typicalbedrock bedrockof of the the island, island, aa sequence sequence of volcanic Sampleswe we have have volcanic basalt flows, appears appears to be uniformly very low in mercury. Samples analyzed all had no detectable parts per billion (ppb). detectable mercury at at aa detection detection limit limit of of 55 parts (ppb). determine if mercury contained To determine contained in in mineral mineral deposits deposits could wuld be be aa source source of of mercury mercury to to impacted impacted lakes we sampled and analyzed analyzed soil soil and and glacial glacial deposits deposits on on which which the the soils soils formed formed in in two two test test wextaken takenaround aroundthe theMinong Minong mine, mine, the the largest largest mine mine on on the the island, island, to to determine determine areas. Samples Sampleswere the extent extent to which which anomalous anomalous metal content content of the ore and surrounding altered rocks affected the drainage drainage basins basins of of the trace element content of soils. Also, Also, samples samples were taken within the mercury in in fish. fish. No copper Sargent Lake and Lake Wagejo, two of the lakes with elevated mercury copper basins, but but deposits depositscould wuld be concealed concealed beneath beneath extensive extensive deposits are known known within within those those basins, mercury. In glacial deposits, and, if present, could be a contributor of mercury. In total, total, samples samples were were taken taken was taken from from the theAAsoil soilhorizon, horizon, aa dark dark organic organic mineral soil, soil, at 65 sites. At Ateach eachsite siteaa sample samplewas 1-6 inched below the surface. A second sample was taken from a depth of about 2 feet, A second sample was taken from depth consisting of either consisting either reddish reddish sandy sandy glacial glacial till till or or till till slightly slightly modified by soil-forming soil-forming processes processes (referred to here as BC horizon). as BC (referred Results show Results show that that the the copper copper deposit depositat at Minong Minong mine mine produces produces aa very very distinct distinct trace trace element element anomaly in soil, soil, especially especially the copper copper content of the BC horizon. Mercury Mercury also also is is somewhat somewhat elevated in samples closest to tothe thecopper copperdeposit. deposit. Mean Mean copper copper content content of of BC samples of the BC horizon closest ppm and that of of mercury mercury is is 44 44ppb. ppb. Highest values are 1160 1160 soils in the Minong mine area is 342 pprn ppm copper and 110 ppb mercury. The A soil horizon near the Minong mine averages 290 ppm pprn 110 The A soil horizon near the Minong averages pprn Cu and 70 thedrainage drainagebasins basinsfeeding feedingLake LakeWagejo Wagejoand and Sargent Sargent Lake, BC soils 70 ppb ppb Hg. Hg .InInthe ppm Cu, nearly five times lower than near Minong Minong mine, mine, and and 38 ppb Hg, essentially essentially average 60 pprn A-horizon soils soilsin inthe the Sargent-Wagejo Sargent-Wagejo drainage drainage average average 63 63 ppm pprn the same as at Minong mine. A-horizon Cu and 133 133 ppb ppb Hg. Hg. The The maximum maximum value value for for Hg Hg is is 370 370 ppb, ppb, an an exceptionally exceptionally high high value value for for soil soil For comparison, similar soil geochemical studies that we are conducting in the in this this region. region. conducting Chequamegon National Forest in Chequamegon in northern northern Wisconsin show A-horizon soils soils to have a mean mean Hg content of about 54 ppb with a maximum detected concentration of 260 ppb. C-horizon content about 54 of 260 ppb. C-horizon soils soils in in that area have a mean of 19 ppb. With 19ppb ppbHg Hg and and aa maximum maximum of 80 ppb. With respect respect to to soils, soils, Isle Isle 9 �than northern northern Wisconsin. Both Royale appears to be a more Hg-rich environment than Both A A and and BC BC horizon soils soils are are at least least twice twice as as high high on on the the island island as as in in northern northern Wisconsin. Wisconsin. The results results suggest suggest that the very elevated mercury content of soils in the Sargent Sargent Lake-Lake Wagejo area is not caused by concealed concealed native native copper copper deposits depositsbecause because there there is is little littleor orno no elevated elevated copper copper content of those soils. soils. Results from the Minong mine area show that concealed deposits, if present, would produce readily detectable elevated copper content of the soils. Neither is there reason reason to conclude conclude that local bedrock is the source for mercury because all tested chemically very uniform bedrock have very low mercury mercury content. content. Because samples of the chemically Becauseof of the the general lack of mercury in the most common occurrence common rocks of the island and the very limited occurrence of native copper copper deposits deposits that that do do contain some mercury, the mercury content of the soils on Isle Royale seems very very likely likely to to result result largely largely from from airborne airborne deposition. deposition. The The processes processes causing causing the the great variability variability of mercury content content of similar similar appearing soils over short distances that thatwe wehave have observed in our survey remain only speculative. Nevertheless, it appears certain that mercury must be very mobile in the soil soil zone zone in order to redistribute what must be a relatively uniform mobile in amount of deposited mercury into the highly variable observed concentrations. 10 10 �STRUCTURAL STRUCTURALFABRIC FABRICAND AND STRAIN STRAINFOR FOR THE THE SEINE SEINERIVER RIVER CONGLOMERATES CONGLOMERATESAT AT TIlE THE WABI000NQUETICO WABIGOONQUETICOSUBPROVINCE SUBPROVINCEBOUNDARY BOUNDARYNEAR NEARMINE MINECENTRE, CENTRE,ONTARIO. ONTARIO. CZECK, Peter I., J., Department Department of of Geology Geology and M. and and HTJDLESTON, HUDLESTON, Peter and Geophysics, Geophysics,University University of of CZECK, Dyanna Dyanna M. Minnesota, Minnesota, 310 310 Pillsbury Dr. SE, Minneapolis, MN 55455, 55455, dyanna@geolab.geo.umn.edu dyanna@geolab.geo.unm.edu INTRODUCTION The The Superior Superior Province Province consists consistsof of approximately approximatelyeast-west east-west trending trending subprovinces subprovinces defined defined by by lithological lithological differences, & Ciesielski Ciesielski 1986). This This study study differences,metamorphic metamorphic grade, and structural boundaries (Card & concentrates concentrates on on the the boundary between between the the Quetico Quetico metasedimentary metasedimentary subprovince subprovince and and the the Wabigoon Wabigoon metavolcanic subprovince. The Seine River Metasedimentary Group, including the Seine River metavolcanic The Seine River Metasedimentary Group, conglomerates, are distinctive rocks found within a wedge along this boundary. along this conglomerates, are distinctive rocks found within a Structural Structural work along the Quetico Quetico and Wabigoon describes subvertical foliation overprinting overprinting large Hudieston 1991). 1991). These These structures structures indicate a strain large lithological folds (Poulsen 1986, 1986, Tabor & Hudleston history history consisting consisting of an early early recumbent recumbent nappe nappe deformation deformation followed by a more more ubiquitous ubiquitous overprinting overprinting of a subvertical flattening fabric and shear zones attributed to dextral transpression. Strain is pervasive flattening attributed to dextral transpression. throughout throughout the the boundary, boundary, but but also also localized localized into into more more discrete discrete shear zones zones including including two two main, main, connecting connecting shear shear zones zones coincident coincidentwith with the the Rainy Rainy Lake-Seine Lake-Seine River River and Quetico Quetico Faults. These Theselarge large shear shear zones zones are are interconnected interconnected with with smaller smaller shear shear zones zones forming an anastomosing anastomosing pattern. The TheSeine Seine River conglomerates conglomerates are are located located in in aa wedge wedge between between these two shear shear zones zones west west of their intersection. intersection. Poulsen (1986) (1986) interpreted interpreted the the Seine Seine River River conglomerates conglomeratesto to have have formed formed syn-kinematically syn-kinematically during during transpression, transpression, possibly possibly in in structures structuressimilar similarto topull-apart pull-apanbasins. basins. This This preliminary preliminary structural structuralwork work made made itit clear clear that that the the WabigoonWabigoon- Quetico Quetico subprovince subprovince boundary is is not not merely aa discrete discrete suture suturebetween between two two tectonic tectonic microplates, microplates, but is instead instead a complex complex network of shear zones which together accommodated oblique collision. The Thegoal goalof ofthis thisstudy studyisisto todescribe describehow how this complex shear zone geometry is reflected in spatially variable strain magnitudes and structural complex shear zone geometry is reflected in spatially variable magnitudes structural fabrics. fabrics. - STRUCTURAL FABRIC Foliations Foliations in in the the field field show show aa consistent consistent regional regional orientation orientation with strike strike of approximately approximately 080 080 and and subvertical dips. This Thisstrike strikeisisconsistent consistent with with the the dextral dextral transpression model. One Oneexception exceptionto to this this is is in the area of Shoal 045,creating creatingan anoverall overallS-like S-likegeometry geometry Shoal Lake Lake where where the the strike strikechanges changesto toapproximately approximately045, with a map pattern analogous analogous to to a dextral shear sense indicator. The Thesame sameshear shearsense senseisisobserved observedatataa smaller scale within the conglomerate clasts that often form sigma and delta dextral shear smaller scale within the conglomerate clasts that often form sigma and delta dextral shearsense senseindicators indicators on the sub-horizontal sub-horizontalplane. plane. Mineral chlorite and amphiboles. Mineral lineations lineationsin in the field field are are predominantly defined by chlorite amphiboles. General General transpression 1993). However, However, transpression theory predicts either vertical or horizontal lineations (Fossen & Tikoff 1993). lineation orientations orientations in the field field vary remarkably within the foliation plane. Typically, Typically,the theSeine SeineGroup Group lineations are spatially similar on the scale of 0.5-1 km. Therefore, the lineation variations are not Therefore, the lineation variations are not caused caused similar by small-scale-phenomena by some regional regional phenomenon. phenomenon. Rather small-scalephenomena such as clast interaction, but by Rather than than reflecting different different bulk kinematic kinematic conditions conditions along the boundary (such as partitioned triclinic transpression). transpression), the lineation lineation variations variations may reflect reflect anastomosing anastomosing shear zone patterns and variable pressure gradients gradients within within the therock. rock. 11 �Taken together, the finite strain ellipsoid Taken together. foliation and lineation match the variations in the orientation. The Thefoliation foliationpole polealigns alignswith withthe theminimum minimumstretching stretchingdirection, direction,and andthe thelineations lineationsparallel parallel the maximum stretching direction. direction. STRAIN ANALYSIS The Seine River conglomerates are useful strain recorders. recorders. Qualitative observations and quantitative strain analyses indicate heterogeneous heterogeneous strain distributions within the Seine River conglomerates. Analysis Analysis confinns confirmsaaflattening flatteningstyle stylestrain strainthat that could could only only be aa result result of of aa threethreedimensional deformational phenomenon such as transpression rather than the two-dimensional strain strain produced by wrench or thrust movements. Results to date show that the longest axis corresponds to the mineral lineation longest lineation measured . principal in the field and the shortest principal axis corresponds well with the foliation pole. This Thissupports supportsthe theidea idea that structural fabric measured in the field may reoresent the orientation of the finite finite strain mav be used to represent ellipsoid. ellipsoid. The variations in strain ellipsoid orientations orientations and magnitudes could be used to argue argue for multiple multiple deformation events or complex and variable kinematic kinematic boundary boundaryconditions. conditions. However, the geometry of of the anastomosing shear zone pattern can be used to explain the variations in the orientation of the strain ellipsoid and and the the heterogeneous heterogeneous strain magnitudes within the Seine Seine Group Group within a simple dextral ellipsoid transpressional setting. Poles to to foliation foliation 138 Measurements Measurements (equal (equal area) area) Mineral lineations 113 Measurements Measurements (eaual (equal area) Card. K. IC.D. D.& &Ciesielski, Ciesielski, A. A. 1986. 1986. DNAG DNAG Subdivisions Subdivisions of of the the Superior Superior Province Province of the Canadian Card, Geoscience Canada Canada 13, 5-13. Shield. Geoscience 13.5-13. Fossen, H. & Tikoff, B. 1993. 1993. The deformation matrix for simultaneous simple shearing, pure shearing and volume change, and its application to transpression- transtension tectonics. tectonics Journal 15, 413-422. Journal of o fStructural Structural Geology Geoloxv IS. 4 13-422. -. Poulsen. example of of an an Archean Archean Subprovince Subprovince boundary boundary Poulsen, K. H. 1986. 1986. Rainy Lake Wrench Zone: An example in Northwestern Ontario. Tectonic evolution evolution of greenstone belts Technical Technical Report Report (edited (edited Ontario. In: In: Tectonic Ashwal, L. L. D.) D.) 86-10. Houston TX, TX, Lunar and planetary Inst., 177-179. 1. Sc & Ashwal, 177-179. by de Wit, M. J. Tabor. J. J. R. & & Hudleston, P. 1 J.. 1991. Deformation at an an Archean subprovince boundary, boundary, northern Tabor, Minnesota. Canadian Canadian Journal 292-307. Journal of of Earth EarthSciences Sciences 28, 28,292-307. 12 �Preliminary PreliminaryAeromagnetic AeromagneticMap Mapof ofWisconsin Wisconsin David DavidL. L. Daniels, Daniels,Suzanne SuzanneW. W.Nicholson, Nicholson,William WilliamF. F.Cannon, Cannon,U.S. US. Geological GeologicalSurvey. Survey,MS MS 954 954National National Center, E.Bracken, Bracken,U.S. U.S. Geological GeologicalSurvey, Survey,MS MS 964, 964, DFC DFCBox Box 25046, 25046, Center,Reston, Reston,VA VA20192, 20192,Robert RobertE. Denver, Denver,CO CO80225 80225 The The Mineral MineralResources ResourcesProgram Program of of the the U.S. U.S. Geological GeologicalSurvey Survey (USGS) (USGS) has has conducted conducted aeromagnetic the magnetic coverage coverage of of the the aeromagneticsurveys surveys in in Wisconsin Wisconsin during during the past three years to improve the state. state. State Statecoverage coveragewas was completed completed with with aa survey survey carried out in 1998/1999. 199811999. The The new new aeromagnetic aeromagnetic survey survey fills fills the the southern southernthird third of of the the state statenot not covered covered by existing existing good quality surveys (see figure). Right are:north-south north-southflight flightlines linesatat½Vimile mile(800 (800m) m) separation separation draped draped at at 1000 1000ftft (305 (305 m) m) Flightspecifications specificationsare: mean mean terrain terrain clearance. clearance. Right Flightlines linesare areeast-west east-westfor foraapart partof ofsoutheast southeast Wisconsin. Wisconsin. The 4' meeting of the ILSG in 1998 1998 The results resultsof ofthe thefirst firsttwo twoyears yearsofofflying flyingwere wereshown shownatat44th (Daniels and others, 1998). These data have been released since that meeting as paper contour (Daniels and others, 1998). These data have been released since that meeting as paper contourmaps maps (Snyder, (Snyder,1998; 1998;USGS USGS Open-File Open-File Reports Reports 98-431 through 439). Digital Digital data data for for the the 1997/1998 199711998survey survey have have now now been been released released(Open-File (Open-FileReport Report99-28) 99-28)on on CD-ROM CD-ROM (Daniels, (Daniels, Nicholson, Nicholson, and and Cannon, Cannon, 1999). 1999). The accompanying figure shows a shaded image of the aeromagnetic field for current data in The accompanying figure shows a shaded image the aeromagnetic field for current data in Wisconsin years data data are are blocked and labeled. Three Threeaeromagnetic aeromagneticsurveys surveys Wisconsin and and the the areas areas of of the the first first22 years obtained (M.Mudrey, Mudrey, obtainedfrom fromindustry industrysources sourcesby by the theWisconsin WisconsinGeological Geologicaland andNatural NaturalHistory HistorySurvey Survey(M. personal for the the new new survey survey are are still still personal communication, communication, 1997) 1997)are are shown shown in southern Wisconsin. The data for preliminary. Blocks 1-5 and A-D represent the areas of the new survey that will be shown and the will Blocks 1-5 and A-D represent the areas of the new survey contour be available available later later in in 1999. 1999. contour maps maps that that will will be The been to to provide provide higher higher resolution resolution data data The rationale rationale for for continued continued aeromagnetic aeromagnetic surveying has been with with which which to to interpret interpretbasement basementgeology geologyin inWisconsin. Wisconsin.The Theaeromagnetic aeromagneticdata data image image basement basement structures by glacial glacial structures in in detail detail and and give give clues clues to to the the structural structural evolution of the Precambrian crust, covered by and and Paleozoic Paleozoiccover. cover. References References D.L., Nicholson, Nicholson,S.W., S.W., Cannon, Cannon,W.F., W.F., 1999, 1999,Aeromagnetic ~eromahetic surveying in Wisconsin Wisconsin 1997-98: 1997-98: Daniels, D.L., Daniels, surveying Digital Digital data datafiles: files:U.S. U.S. Geological GeologicalSurvey SurveyOpen-File Open-FileReport Report99-28, 99-28, CD-ROM. CD-ROM. Daniels,D.L., D.L., Snyder, Snyder,S.L., S.L., Nicholson, Nicholson,S.W., S.W., Cannon, Cannon,W.F., W.F., 1998, 1998,New New aeromagnetic aeromagnetic surveys surveysin in Daniels, Wisconsin part 1, 1, Wisconsin by by the theU.S. U.S. Geological GeologicalSurvey: Survey:Institute Instituteon on Lake Lake Superior SuperiorGeology Geology Proceedings Proceedings v. 44, part p. 62-63. 62-63. p. Snyder, S.L., 1998, areas: 1998, Aeromagnetic Aeromagnetic map map of of part part of of northwestern Wisconsin and and adjacent areas: U.S. U S . Geological Survey Survey Open-File Open-File Report Report 98-228, 98-228, Scale Scale 1:125,000, 1:125,000,22 sheets. sheets. 13 �Index Index Map Mapof of'Wisconsin Wisconsin Aeromagnetic Data Data 93E 936 92E 926 91E 916 89 9oE cct SEE 87E 46E 46E 45E 45E 44E 43E 43E 92E me. 9oE 90fi 91E 916 ssE 'O'5°20 KM 50 50 0 89E 100 • 14 150 200 KM siE 876 �INVESTIGATION INVESTIGATIONOF OFCaO CaOAT ATTHUNDERBIRD THUNDERBIRDMINE, MINE,MESABI MESABIRANGE: RANGE:MINERAL MINERALAND AND STRATIGRAPHIC STRATIGRAPHICRELATIONSHIPS RELATIONSHIPS DIEDRICH, DIEDRICH,Tamara TamaraR., R.,and andMORTON, MORTON,Penelope, Penelope,Dept. Dept.of ofGeology, Geology,University Universityof ofMinnesota Minnesota Duluth,Duluth, Duluth,MN, MN,55812, 55812, tdiedric@unnd.edu tdiedric@umn.d.eduand andpmorton@unmA.edu pmorton@umn.d.edu Duluth, Mine Minegeologists oeolomstsatatEVTAC's EVTAC'sThunderbird ThunderbirdMine, Mine,aataconite taconitemine mineininEveleth, Eveleth,Minnesota, Minnesota,have havebeen been tracking variation ofofnaturally trackingthe thevariation naturallyoccurring occurringCaO CaOinmiron ironore oreconcentrate concentratefor foratatleast leastnine ninemonths. months. Information Informationabout aboutthe theCaO CaOisishelpful helnfulininformulating formulatino thepartial fluxpellets nelleis that that EVTAC EVTAC produces. produces. The The -the .vartialflux CaO-bearing CaO-bearinephase phasewas wasunidentified, unidentified,but butpresumed presumedto to be be aa carbonate. carbonate. The Theobjective objectiveof ofthis thisstudy studywas wasto to investigate investigatethe thenature natureof ofthis thisCaO CaOininterms termsof: of:1.) I .)The The identification identificationof of its its phase or phases; 2.) Location of major majorsiratigraphic stratigraphiccontributors; contributors;and and3.) 3.)The Theininsitu situtextural texturalrelationship relationshipbetween betweenthe theCaO-bearing CaO-beanng phase(s) phase(s)and andthe themagnetite. magnetite. Manual Manualinterpretation interpretationof ofX-ray X-raydiffraction diffractionresults resultsidentified identifiedthe theCaO-bearing CaO-bearingphase phasein inthe the concentrate concentrateto tobe beankerite. ankerite.Other Otherconstituent constituentminerals mineralsinclude includequartz, quartz.hematite, hematite,siderite, siderite.greenalite, greenalite, stilpnomelane, stilpnomelane,talc, talc,and andgoethite. goethite. Thunderbird ThunderbirdMine Mineexcavates excavatesore orefrom fromthe theBiwabik BiwabikIron IronFormation, Formation,aaPrecambrian Precambrianunit unitcomposed composed of areUpper UpperUpper Upper ofseveral severalhorizons horizonsof ofbanded bandediron ironformation. formation.From Fromtop toptotobottom, bottom,these thesehorizons horizonsare Cherty, Bottom Lower Lower Cherty,Middle MiddleUpper UpperCherty, Cherty,Lower LowerUpper UpperCherty, Cherty, Lower Lower Slaty, Slaty, Top Top Lower Cherty, Cherty,and Bottom Cherty. Cherty.Horizons Horizonsdiffer differininphysical physicalcharacteristics, characteristics,such suchasasthickness thicknessand andtexture, texture,and andchemical chemical composition. areblasted blasted and and composition.When Whencollecting collectingore orefor forthe theinitial initialore oremix, mix,aacombination combinationof ofhorizons horizonsare blended achieveaadesirable desirablemagnetic magneticiron ironconcentration. concentration.Statistical Statisticalanalysis analysisdemonstrated demonstratedaastrong strong blendedtotoachieve positive the amount amount of of positiverelationship relationshipbetween betweenthe thepercentage percentageof ofore orederived derived from from the the Top Top Lower Lower Cherty Cherty and and the ankerite ankeritein inthe theresulting resuitingconcentrate. ~oncen~te. Textural Texturalrelationships relationshiosbetween betweenthe theankerite ankeriteand andmagnetite mametitewere wereobserved observedand andphotographed. photographed. Ankerite ankerite Ankexiteoccurs occursininatatleast leastfour fourdistinct distincthabits, habits,relative relativethe themagnetite: magnetite:1.) 1.)Rhombohedral ~hombohedrd ankeritecrystals crystals are granoblastic,recrystallized recrystallizedquartz, aresurrounded surroundedby bymuch muchsmaller, smaller,granoblastic, quartz,and andminor minormagnetite; magnetite;2.) 2.) FineFinegrained, areintergrown intergrownwith withmagnetite magnetiteof ofapproximately approximatelythe thesame samesize; size;3.) 3.)An An grained,irregular irregularankerite ankeritecrystals, crystals,are ankerite ankeritecrystal crystalcan canbe beentirely entirelyenclosed enclosedwithin withinaasingle singleor orcluster clusterof ofmagnetite magnetitecrystals; crystals;and and4.) 4.)A Asingle single or orcluster clusterof i fankerite ankeritecrystals crystalsencapsulates &apsulates aamagnetite mapetite crystal. crystal. The Theiron ironore oreat atEVTAC EVTACis isprocessed processed by by magnetic mameticseparation. senaration.Examining Examininothe thetextural texturalrelationship relationshipbetween betweenthese thesetwo twominerals mineralscan can produce produce information informationrelevant relevanttotomake makethe theisolation isolationof ofmagnetite magnetitemore moreefficient. efficient. ~~ ---- ~~~ - - - .~ ~ ~ ~ ~ 15 �METAMORPHIC THE CANADIAN SHIELD SHIELD OF OF ONTARIO, METAMORPHIC MAP MAP OF THE ONTARIO, MICHIGAN, MICHIGAN, MINNESOTA MINNESOTA AND AND WISCONSIN WISCONSIN R.M Easton, Ontario R.M. Easton, Ontario OntarioGeological GeologicalSurvey, Survey,933 933Ramsey RamseyLake Lake Road, Road, Sue/bury, Sudbuty, Ontario J'3E 6B5, and R. G. Berrnan. Berman, Geological Geological Survey P3E 6B5, eastonrm@vianet.Ofl.Ca eastonrm@yianet.on.ca and R G. Survey of of Canada, Canada, 601 Booth Booth Street. Street, Ottawa, OE8 607 Ottawa. Ontario Ontario K1A KIA 0E8 The Geological The Geological Survey Surveyof ofCanada's Canada's undertook undertookaaproject projectseveral severalyears yearsago ago to toproduce produce an an updated updated metamorphic map for for the Canadian Canadian Shield Shield (GSC (GSC Map Map 1475A), l475A), which which would wouldalso alsobe be used used to produce aa metamorphic map map of of the the world world (in (in conjunction conjunction with with the for the Geologic M Map World). ap of of the the World). metamorphic the Commission Commission for the Geologic At of the Geological Survey Ontario was was asked askedto to compile compile aa metamorphic metamorphic map map of of At the the request request of the Geological Survey of of Canada, Canada, Ontario the Canadian Canadian Shield Shield in in Ontario. the Ontario. In addition addition to to simply simply compiling this project project with with In compiling metamorphic metamorphic information, information, Ontario Ontarioapproached approached this the goal of the goal of attempting attempting to to integrate integrate metamorphic metamorphic information informationwith withthe thetectonic tectonicsynthesis synthesisproduced produced as a s part part of the Ontario project, with the aim of of developing mineral exploration exploration models. of the Geology Geology o f Ontario project, with the aim developing improved improved mineral models. As As aa of consequence,the the metamorphic metamorphic map map of of Ontario as to to complement complement the existing existing set set of of consequence, Ontario was was designed so as 1: 1.000,000 1.000,000bedrock, bedrock, suficial surficial geology, geology, geophysical, geophysical,and andtectonic tectonicassemblage assemblagemaps mapsand andtime-space time-space charts charts released in in 1991-92 part of of the the Geology Geology o Ontario series. released 1991-92 aas s part f Ontario series. A draft draft of of this this map, map, at roughly roughly 1:2,500,000 1:2,500,000 of scale, will will be scale, be presented presented here. here. Also at of the Geological Survey to produce produce aa Also at the the request request of the Geological Survey of ofCanada, Canada, Ontario Ontario has has undertaken undertaken to preliminary in Wisconsin, Wisconsin, Michigan, preliminary metamorphic metamorphicmap mapof ofthose those portions portions of ofthe theCanadian Canadian Shield Shield exposed exposed in Michigan, and Minnesota. One One of ofthe thereasons reasons for requesting reauestine the involvement of of the the Ontario Ontario Geological Geological Survey Survey in in this compilation, wasso soas as to to best best integrate integrate the metamorphic met-orphic pattern compilation,as asopposed opposed to toother otherorganizations, or&izations, was present in the the shield shield in in the the United United States with that that oresent present across acrossthe theborder borderininOntario. Ontario. In In addition. addition, fast fast present in States with approaching deadlines for completion of deadlines for of the the project project factored factored into into this this decision. decision. Thus. the main focus of this presentation will be preliminary draft Thus, presentation will be on on presentation presentation of a preliminary draft of ofthe the adjoining Ontario, metamorphic map for for the the shield shield rocks rocks in in the the areas areas adjoining Ontario, for forthe thepurposes purposes of of discussion discussion regarding: regarding: the style style of presentation, 1) the ,,,:~ i. . , , 2) the accuracy accuracy of ofthe the data data presented, presented, and 3) solicitation bringing this solicitation of ofpossible possible assistance assistance in bringing this project project to to aa conclusion. concl&on. The metamorphic map of the Shield is being being produced produceddigitally. digitally. In Inthe the case case of Ontario, the Tectonic used as the geologicalbase. geological base. Key aspects of of the project include as the Key digital digitalaspects the project include Tectonic Map Map of ofOntario 0ntariowas wasused digitization of representing different metamorphic facies (grade) and of linework (e.g. dieitization ofpolygons nolveons reoresentine different metamomhic facies (grade) and of linework (e.e. isoerads. . . . - isograds, facies boundary boundary information), information), into a-CAD a CAD program. facies program. In In addition, addition, point-source point-source information information (e.g. (e.g. assemblage data.P-T P-Tdeterminations) determinations) is is beinginput being input into a database. database. The final final map product will willbe bean an assemblage data. attributed map. releasedon onCD-ROM. CD-ROM.containinc containingall allthe thecom~iled compiledinformation. information. The artnbuted attributed map map will will mao. released accompany aa standard standardcoloured, coloured,hard hardcopy copymap, map,which whichwill will mainly mainly display display metamorphic metamorphic facies facies distribution. will be distribution. This Thissame sameapproach approach will be taken taken in compiling compiling the the information information for forWisconsin Wisconsin Michigan Michiganand and ofofCanada, based Minnesota, except that here, the digital digital base base is being being supplied supplied by by the the Geological GeologicalSurvey Survey Canada, based , . on a previously previously released released US geological compilation compilationmap mapof ofthe theregion. region. -- - in the Two Canadian Mineralogist on "Tectonometamorphic Twospecial special issues issues of of The The CanadianMineralogist "~ectonom&&phic Studies Studiesin the Canadian Shield Shield" are are being being produced producedaas partofthis of thisproject. project. The first (vol. (vol. 34, 34, part pan 5, 5, October October 1997), 1997). Canadian s part includes results results obtained obtained from from aa variety variety of of ancillary to the the compilation compilation effort. includes ancillary metamorphic metamorphic studies studies related related to effort The second issue, issue, which which is is in in the the process process of of being being assembled, assembled, includes regional overviews overviewsrelated related to tothe the metamorphic map well as map of of the the Canadian Canadian Shield, Shield, as as well a s additional, additional, detailed detailed metamorphic metamorphic studies. studies. 16 16 �WHERE ARE OREBODIES WHERE ARE THE THE METAMORPHOSED METAMORPHOSED NATURAL NATURAL OREBODIES OF THE MESABI RANGE? OF THE MESABI RANGE? RONALD G. 0. GRABER RONALD GRABER AND AND ALAN ALAN J. J. STRANDLJE STRANDLIE CLIFFS COMPANY,ISHPEMING, ISIIPEMING, MI. ML 49849 49849 C U F F S MINING MINING SERVICES SERVICES COMPANY. (graber@ponup.com) (graber@portup.corn) The nearly nearly century-old century-old debate regarding The regarding the genesis genesis of the hematite-goethite hematite-goethite iron iron ore deposits the Mesabi Mesabi Range Range has has recently recently been been revisited revisitedby byMorey Morey(1999). (1999). The The ore deposits of of the historic debate for the the combined combined oxidation oxidation historic debate centers centers on on the the origin origin of of the the fluids fluids responsible responsible for and leaching of the Biwabik iron-formation to form the deposits — they upward were and leaching of the Biwabik iron-formation to form the deposits moving hydrothermal moving hydrothermal fluids fluids (hypogene) (hypogene)or or downward downward moving movingmeteoric meteoricwaters waters (supergene)? (supergene)? Morey presents conceptual model model for for the the genesis genesis of of the the ores ores that that Morey presents an an interesting interesting conceptual utilizes Early Proterozoic, Proterozoic, driven driven by by uplift utilizes continental-scale continental-scale groundwater groundwater flow flow during during the the Early uplift in fold-thrust belt belt to to the the south south of of the the Mesabi Mesabi Range. Range. This This model model relies relies on on in the the Penokean Penokean fold-thrust the as aa regional regional the Pokegama Pokegama Quartzite, Quartzite, which which underlies underlies the the Biwabik Biwabik iron-formation, iron-formation, as aquifer for for the aquifer the movement movement of of basinal basinal waters waters to to the the northern northern margin margin of of the the Animike Animike basin. basin. A Ma when when loss loss of the A minimum minimum age age for for ore ore genesis genesis in in this this model model is is believed believed to to be be 1650 1650 Ma of the hydraulic gradient for the groundwater flow system occurred due to erosion of the hydraulic gradient for the groundwater flow system recharge area. This ThisEarly EarlyProterozoic Proterozoicage age for for ore ore genesis genesis is significantly significantly older than the Jurassic-Cretaceous over the Jurassic-Cretaceous age age that has been generally, generally, albeit not universally, accepted over last 30 plus plus years years (Sloan, (Sloan, 1964; 1964;Morey. Morey, 1972). 1972). last Constraints Constraints on on the the timing timing of of the the hematite-goethite hematite-goethiteores ores are are few few due due to to the the scarcity scarcity of geologic geologic events events impacting the the Mesabi Mesabi Range Range between between the the Early Early Proterozoic Proterozoic and and the the of Late Cretaceous. ItItisison onthe theeast eastend endof of the theMesabi Mesabi Range Range where where intrusive intrusiveevents eventsand and contact metamorphism associated with the Middle Proterozoic Duluth Duluth Complex provide a potential opportunity to put additional time time constraints constraints on onthe thegenesis genesisof ofthe theores. ores. Hence Hence the title of this paper. IfIf ore oreformation formation occurred occurred prior to the Middle Proterozoic, the opportunity equivalents of of the the soft soft hematite-goethite hematite-goethite opportunity should exist to find metamorphosed equivalents ores. Detailed Detaileddrilling drillingboth bothalong alongthe theiron-formation iron-formation outcrop outcropbelt belt and and downclip downdip as part of exploration to find these metamorphosed metamorphosed equivalents. equivalents. In In exploration for for Cu-Ni Cu-Ni deposits deposits has has failed failed to find these fact the distinct distinct absence absence of of enriched enriched orebodies orebodies of any sort east of the Duluth Complex's post-Middle Proterozoic Proterozoic age age metamorphic aureole aureole has long been utilized as support for aa post-Middle for ore ore genesis. genesis. Alternatively, Alternatively, thinning thinningof of the the Pokegama Pokegamaquartzite quartzitein in this thissame samegeneral general area is cited by Morey Morey to to explain explain the the absence absence of enriched enriched ores ores on on the the East East Mesabi. Mesabi. The The relative relative abrupt abrupt absence absence of of enriched enriched ores ores in in the the Biwabik Biwabik iron-formation iron-formationoccurs occurs within the mining operations Mining Company, Company, managed managed by by aa subsidiary subsidiary of of operations of LTV Steel Mining Cleveland-Cliffs, which has been active 1). Detailed Detaileddata data active for over 40 years (Figure 1). acquired acquired through through both both field field observations observationsand and thousands thousands of of drill drill holes holes provide provideinsight insighton on the controls controls of the the ore-forming ore-forming process. The Thefollowing followingfeatures featuresof of the the geology geology at at LTV LTV Steel Mining Company are are in in conflict conflict with with an an Early Proterozoic Proterozoic genesis genesis of the the hematitehematitegoethite ores: goethite ores: 17 �1. 1. Due to the economic economic significance significance that metamorphism has on the processing of the magnetic taconites, considerable effort is placed on mapping the metamorphic isograds at this operation. Further Further refinement refinement of the original zonation of the Duluth Complex's contact resulted. The Complex's contact metamorphic metamorphic aureole (French, 1968) has resulted. The relationship of metamorphic metamorphic grade with the the eastern eastern limit limit of of iron-formation iron-formation enrichment enrichment relationship stronger than the correlation with either the thickness or distribution of the appears stronger Pokegama Pokegama Quartzite. This Thisisismanifested manifestedby: by: the abrupt termination of enrichment enrichment and oxidation oxidation along along the the Wentworth Wentworth a) the abrupt termination a) structure structure due due to increasing increasing metamorphic metamorphic grade; grade; and, and, b) the b) the thepresence presenceof ofenrichment enrichmenteast eastof ofthe the Siphon Siphon structure structure which which is is the controlling structure for aa dramatic dramatic decrease decrease in in Pokegama Pokegama Quartzite Quartzite thickness. thickness. controlling structure for 2. the Biwabik Biwabik iron-formation in 2. The Aurora sill, sill, aa sizeable sizeable syenitic syenitic body that intrudes the the western portion of the mining operation, appears to have contributed to the localization James and and the the Miller-Mohawk Miller-Mohawk mines. mines. This sill localization of ore formation in the St. James has visual similarities to granophyres associated elsewhere with the Duluth Complex similarities granophyres elsewhere and as such has long been considered Keweenawan (White. 1954). Jf ore genesis in long (White, 1954). If ore genesisin these mines constrain ore mines were Early Early Proterozoic, how could a Keweenawan sill constrain formation? formation? Likewise, Likewise,no nometamorphic metamorphic overprint overprint has has been reported from these % orebodies. Definitive Definitiveage agedating dating though though is is lacking lacking for for this intrusive. ri 3. AAlarge largenumber numberofofthe theenriched enrichedorebodies orebodiesat at the the LTV LTV Steel Steel Mining Company operation are very shallow. Drilling of a Drilling has has been been conducted conducted through the bottom of number of the natural ore magnetic taconite taconite ore pits successfully successfully finding fresh, unaltered magnetic reserves below. The Thelack lackof of alteration alteration between between the the Pokegama Pokegama Quartzite Quartzite and the orebodies orebodies is is problematical problematical for for ascending ascendinggroundwater groundwaterflow flowmodels. models. French, B.M. 1968, of the the Biwabik Biwabik iron-formation, iron-formation, 1968, Progressive Progressive contact metamorphism of Mesabi Range, Minnesota, p.103. Minnesota, Minnesota Minnesota Geological Survey Bulletin 45, p. 103. Morey. Morey, eds.. eds., Geology Geology of of Morey, G.B., G.B., 1972, 1972, Mesabi Range; Range; in P.K. Sims Sims and G.B. Morey, Minnesota: Minnesota: A A Centennial Centennial Volume, Volume, Minnesota MinnesotaGeological GeologicalSurvey. Survey,pp. pp. 204-217. 204-217. Morey, Mesabi Range, Range, MinnesotaMinnesotaMorey, G.B., G.B., 1999, 1999, High-grade High-grade iron iron ore ore deposits deposits of of the the Mesabi Product of a continental-scale ground-water system. Econ. Geology, vol. 94, pp 133-142. continental-scale ground-water system, Geological Survey Sloan, R.E., R.E., 1964, 1964, The Cretaceous system in Minnesota: Minnesota Geological 5 . 64p. 64~. Report of Investigations Investigations 5, White, D.A., White, D.A., 1954, 1954,The The stratigraphy stratigraphyand and structure structureof of the the Mesabi Mesabi Range, Range, Minnesota: Minnesota: Minnesota 92p. Minnesota Geological Geological Survey Survey Bulletin Bulletin 38, 38,92p. 18 �Figure 1. Map of of LTV Steel Steel Mining Mining Company Company Figure 1. Geologic Geologic Map 19 �Cross Cross Margin Margin Transport Transport in in Lake Lake Superior Superior GREEN, GREEN,Sarah Sarah A. A. and and BUDD, BUDD, Judith Judith W., W., Dept. Dept. of of Chemistry Chemistry and Dept. of Geological Geological Engineering Engineeringand andSciences, Sciences,Michigan MichiganTechnological TechnologicalUniversity, University, Houghton, Houghton,MI MI49931 4993 1 The The Keweenaw Keweenaw Interdisciplinary InterdisciplinaryTransport Transport Experiment Experiment in Superior Superior (KITES) (KITES) is focused focused on on cross-margin cross-margintransport transportprocesses processesalong alongthe thewestern westernshore shoreof ofLake LakeSuperior's Superior's Keweenaw Keweenaw Peninsula. Peninsula. The Thedominant dominantfeature featureofofthis thisregion regionisisthe theshore-parallel shore-parallel Keweenaw Keweenaw Current, Current,which whichflows flowsto tothe thenortheast northeastand andisisstongest stongestnear nearEagle EagleHarbor. Harbor. Water, Water, sediment, sediment,and andhydrographic hydrographicdata dataare arebeing beingcorrelated correlatedwith with satellite satelliteimagery imageryto to obtain obtain an an integrated integrated view view of of transport transport of of suspended suspended sediments, sediments, nutrients, and organic organic material material near near and and across acrossthe thecurrent. current. Time show cross cross margin margin transport Time series series SeaWiFS SeaWiFS images from May to September, 1998 show events in Lake Superior. These chlorophyll and turbidity maps reveal a highly events in Lake Superior. These chlorophyll and turbidity maps reveal a highly productive productive southern of the the Keweenaw. southern corridor corridor from Duluth Harbor to the tip of Keweenaw. Distinctive Distinctivesediment sediment and and chlorophyll chlorophyll plumes plumes can can be be seen seenoffshore offshorewest west of of the the Ontonagon Ontonagon River Riverand andnear nearthe the tip of the the Keweenaw Keweenaw Peninsula. Movement Movementofofthe theplumes plumesoffshore offshorewas washighly highlyvariable variable depending dependingupon upon the thedirection directionofofprevailing prevailingwinds windsprior priortotothe thesatellite satelliteband bandpass. pass. Simultaneously Simultaneouslyacquired acquiredSeaWiPS SeaWiFS(Sea-viewing (Sea-viewing Wide Wide Field-of-View Sensor) Sensor) and AVHRR 23,1998 1998were were AVHRR(Advanced (AdvancedVery VeryHigh HighResolution ResolutionRadiometer) Radiometer)images imagesfrom fromMay May23, used used to to verify verify cross cross margin margin transport transport events events in in Lake Lake Superior. Superior. The TheAVHRR AVHRRlake lakesurface surface temperature temperatureimage imagereveals reveals aa dramatic dramatic northward northward flowing flowing offshore offshore eddy eddycurrent currentat atthe thetip tip of of the the Keweenaw Keweenaw Peninsula. Peninsula. AASeaWiFS SeaWiFSturbidity turbidity map mapacquired acquiredwithin withinhours hoursof ofthe the AVHRR AVHRR SST SSTimage imagesuggests suggeststhat that materials materials were weretransported transportedoffshore offshorenorth northof ofEagle Eagle Harbor, Harbor, providing providingevidence evidenceof of crosscross- margin margin transport. transport. These Thesepatterns patternswere werenot notpresent presentin in AVHRR 23rdevent event(on (onMay May20 20 AVHRR and and SeaWiFS SeaWiFSimages imagesobtained obtainedbefore beforeor orafter afterthe theMay May23rd and and May May 27). 27). Sediment Sedimentpatterns, patterns,in-water in-wateroptical opticalmeasurements, measurements,and andphysical physicalmodels modelsare arehelping helping clarify in the the KITES KITESstudy study region. region. clarify transport transport mechanisms mechanismsand andpathways pathwaysin 20 �Megascopic Fossils and and Their Megaswpic Fossils Their Possible Possible Contribution Contribution to to the theDevelopment Development of of the theSilicate SilicateUnit Unit of Iron-Formation, Empire of the the Negaunee Negaunee Iron-Formation, Empire Mine, Mine, Marquette MarquetteRange, Range, North NorthMichigan Michigan T. M. Han, Senior Research Scientist (Emeritus), Cleveland-Cliffs Inc. Abstract The fossils discovered discoveredin in the the Early Early Proterozoic Negaunee Iron-Formation Iron-Formation are The megascopic megascopic fossils Proterozoic Negaunee are the the world's have been been reported reported as as eukaryotic eukaryotic algae algae similar similar to to world's oldest oldest known known fossils. fossils. These These fossils fossils have Grypania may have have played Grypania spiralis spiralis (Han (Han and and Runnegar Runnegar 1992). 1992). Their Their existence existence may played a a key key role role in in the the development of of the the thin thin banded banded "silicate unit" unit" of the the Negaunee Negaunee Iron-Formation Iron-Formation at at the the Empire Empire Mine. Mine. This of magnetite-rich magnetite-rich layers layers alternating alternating with layers having This unit is is composed wmposed of having a mineral mineralassemblage assemblage of of chert, chert, siderite, siderite, ankerite, ankerite,minnesotaite ininnesotaiteand and stilpnomelane stilpnomelane in various various proportions. proportions. Two fossil types typesare are recognized. recognized. One filaments that that are long One type type is is fine fine filaments long and and uniform uniform in in width width Two fossil and "springs". The The other other type type is is short, short, coarse, coarse, in inwhole whole and andsectional sectional forms, forms, and and and coiled wiled like like "springs". resembles "coiled garden garden worms". worms". These were apparently apparently transported transported by resembles "coiled Thesefossils fossils were by direct direct current current and and deposited at at distances from their origin. Based on the relationship between the current marks distances between the marks and and the orientation coils on on the the outcrops outcrops measured, measured, the direction orientation of of the the fossil fossil patches patches and and oval-shaped oval-shaped coils of the paleocurrent where Archean rocks paleocurrent at at the the time timeof of sedimentation sedimentation was from from the the southwest southwest where rocks are are distributed. distributed. • 'a-".: z"& ,. Fossil remains resembling resembhg "coiled "coiledgarden garden worms" worms" 21 �An An induced induced oxidation oxidation study study reveals reveals that that much much of of the themagnetite magnetitewas wasdeveloped developed and andenriched enriched through Fe+ nuclei. These These laths laths are are randomly randomly arranged, arranged, through Fe+ + diffusion, diffusion, using using lath-shaped lath-shaped hematite hematite as as nuclei. either scattered, either scattered, or or in in irregular irregularclusters clustersand andexisted existedbefore beforethe themagnetite magnetitedevelopment. development. The gangue layers are believed to be derived from a highly sfficeous gel with with carbonaceous carbonaceous matter The gangue layers are believed to be derived from a highly siliceous gel matter and other and replaced and other impurities. impurities. They Theywere weresubsequently subsequently recrystallized recrystallized and replaced by by siderite, siderite, ankerite, ankerite, minnesotaite and and stilpnomelane and low-grade regional metamorphism. minnesotaite stilpnomelane during during diagenesis diagenesis and low-grade regional metamorphism. + --f -. Magn eliteand and magnetite magn elitegranule granule layers, white; Microstructrure of Magnetite white; 250x Micmstructrure of aa magnetite magnetite layer. layer. 250x gangue layers, dark. Magnetite, gray; gray; hematite grayish white dark. and gangue, gangue, black. black. Magnetite, hematite grayish white and According to LaBarge LaBarge et et al is reasonable According to a1(1987), (1989, it it is reasonable to to assume assume that that the theheavily heavilypopulated populated megascopic eukaryotic eukaryotic algae algae were were probably probably one the principal megascopic one of of the principal oxygen oxygen suppliers suppliers for for precipitating precipitating Ee+ + ± as as Fe(OH)3. Fe(OH)3. The Theclusters clustersof ofthe thelath-shaped lath-shapedmagnetite magnetite pseudorph pseudorph in in magnetite magnetitelaininae laminae and and Fe+ granules hematite . The effect of granules probably probably represent represent dehydrated dehydratedand andcrystallized crystallized Fe(OH)3 Fe(OH)3 flocculi, flocculi, hematite flocculation, if any, any, would flocculation. if would cause cause the the segregation segregation between between the the siliceous siliceous gel gel and and the theEe(OH)3. Fe(Om3. Furthermore, the gravity of of the theFe(OH)3 Fe(Om3 is is significantly significantly greater greater than thanthe thesificeous siliceousgel. gel. the specific specific gravity Consequently,the the interbanded interbanded structure structure of of the unit is Consequently, the lithological lithologic111 unit is believed believed to to be be deposited deposited simultaneously through processes of selective flocculation and and differential differential settling between simultaneously through processes of selective flocculation between the Fe(OH)3 and siliceous gelunder under aa rhymatic rhymatic and and cyclic cyclic manner maimer regulated regulated by by the the life life and and death Fe(OH)3 and siliceous gel death of of the organism, i.e. the off-season is aa period period of growing season season is aa period period of of deposition deposition while the off-season is the i.e. the the growing solution. Furthermore, Furthermore, the solution. the carbonaceous carbonaceous matter associated associated with the precipitates precipitates may may generate generate Fe+ ++during duringdiagenesis diagenesisand andmetamorphism metamorphismfor forthe thedevelopment development of of various various types types of hon iron minerals, minerals, particularly, particularly, the the development development and and enrichment enrichment of of magnetite. magnetite. . References ,. , . 1. Han, T. M. 1. M. and andRunnegar, Runnegar,B. B.(1992) (1%) Megascopic MegascopicEukaryotic EukaryotiiAlgae &ae from fromthe the2.1 2.1 Billion-YearBillion-YearAmerican Association for the Advancement Oldd Negaunee Iron-Formation, Iron-Formation.Michigan. Michigan. American Association for the Advancement of Science, science, Vol. Vol. 237, 237, pp. pp..232-235 .232-235 2. 2. Han, T. M. M. (1978) (1978) Microstructures Microstructuresof ofMaguetite Magnetite as as Guides Guides to to Its Its Origin Origin in in Some Some Precambrian Precambrian Iron-Formations. Fortschr.Miner. Miner.Vol. Vol.56 56pp. on.105-142 105-142 Iron-Formations. Fortschr. (1988) Origin of Magnetite Magnetite in inPrecambrian Precambrian Iron-Formations Iron-Formations of Low Low Metamorphic Metamorphic Grade Grade (1988) Proceedings of the Seventh Symposium. pp.641-656 Seventh Quadrennial JAGOD IAGOD Symposium. pp.641-656 3. Laflerge, LaBerge, C. G. L., L., Robbins, Robbins, E. E. I., I.,and andHan, Han,T.T.M. M.(1987) (1987)AAModel Modelfor forthe theBiological Biological Precipitation Precambrian Iron-Formations Evidence. Precambrian Precambrian Iron of Precambrian Iron-Formations- A: GeologicalEvidence. IronFormations. Formatt.ons. Publication, SA. Athens, Greece. Editors: Peter and Gene Gene LaBarge. LaBarge. Theophrastus Publication, SA. Athens, Peter Appel Appel and pp.69-96 pp. 69-96 ~ - 22 �COMPARISON OF O F MICA Ar/Ar ArIAr AND AND Rb/Sr RblSr THERMOCHRONOLOGY THERMOCHRONOLOGY RESULTS RESULTS FROM NORTHERN WISCONSIN AND NORTHERN MICHIGAN WISCONSIN AND Daniel HoIm, Holm, Denise Romano, Romano, and andCraig CraigManeuso, Mancuso,Dept. Dept.ofofGeology, Geology,Kent KentState StateUniversity, University, Kent, OH 44242; Ken Foland, Dept. of Geological Sciences, The Ohio State Poland, Dept. of Geological Sciences, The Ohio State University, University, Columbus, OH OH 43210. 43210. Columbus, Thermochronologic data from from the the southern Lake Superior Thermochronologic data Superior region has historically historically been been dominated by the RblSr Rb/Sr method method on biotite (Fig. (Fig. 1; Peterman Peterman and and Sims, Sims. 1988, 1988, ~&Q&J. Tectonics). We We summarize the results of 45 45 new new mica mica Ar/Ar ArlAr age age dates dates from from northern northern Wisconsin Wisconsin and and northern northern Michigan (Fig. Rb/Sr data. data. Because (Fig. 2) and compare these with the RbISr Because the Rb/Sr RbISr and K/Ar systems in biotite thissummary summaryprovides providesan an biotite are are known known to to have have similar similarclosure closuretemperatures temperatures(300°±50°C), (300¡±50°this excellent opportunity opportunity to to compare how susceptible these these systems systems are are to to partial partial or or complete complete excellent resetting. Northwest to 1730 M ML Northwest Wisconsin. Wisconsin. Rb/Sr RbISrbiotite biotitedates datesfrom fromthis thisregion region vary vary from from 1309 1309 to a In In contrast, Ar/Ar ArIAr mica mica dates dates fall fall tightly tightlyinto intotwo twogroups, groups,an anolder older—1755 -1755 Ma group and a younger —1600Ma Magroup. group. The two groups of Ar/Ar -1600 Ar/Ar dates dates are are separated separated by by aa sharp sharppost-Penokean post-Penokean deforinational front in the overlying defonnationallthennal defonnational front overlying Early Proterozoic quartzites. The ThedeformationalJthermal in the front here probably probably represents represents the northern northern limit of of Mazatzal Mazatzal foreland foreland deformation deformation in southern Lake Superior Superior region. Northern 1630-1650 Ma ArIArchrontours, chrontours,which whichcoincide coincidein in Northern Michigan. Michigan.The The 1630-1650 MaRb/Sr RbISrand andAr/Ar northwest Wisconsin, diverge diverge eastward eastward into into northern northern Michigan. Michigan. Given northwest Wisconsin, Given the the absence absence of of postpostPenokean quartzites quartzites in in this region, region, we suggest that the Ar/Ar proxy for for Penokean ArIAr ages can serve as aa proxy determining the northern limit of Mazatzal deformation. We suggest that the Republic area determining the northern limit of Mazatzal deformation. area escaped significant Mazatzal related deformation deformation and higher-temperature higher-temperature metamorphic affects but did undergo some form of lower-temperature, possibly hydrothermal, metamorphism metamorphism at undergo some form of lower-temperature, possibly hydrothermal, —1630 1630 Ma. - Northeast Wisconsin. largearea areaofof<1200 el200Ma MaRb/Sr Rb/Srbiotite biotitedates dates(the (theGoodman GoodmanSwell) Swell) Northeast Wisconsin. AAlarge north of the Wolf River batholith has been been interpreted as an uplifted flexural bulge created by rapid loading along Fig. 1). In In contrast, contrast, along the mid-continent rift axis to the north (dashed ellipse of Fig. Ar/Ar dates mica ArIAr dates from the the same same region region define define aa much much smaller smaller region region of <1200 c1200 Ma Ma dates dates (dashed (dashed ellipse of Fig. 2). An isolated 1170 Ma Ar/Ar biotite date has also been obtained from basement An isolated 1170 Ma ArlAr biotite date has also swell. We over 100 100 km southwest of the swell. Weinterpret interpretthe the <1200 c1200 Ma dates for both systems to reflect shallow intrusion-related resetting. The larger locus of The larger locus of anomalously anomalously young young Rb/Sr RbISr dates dates probably reflects reflects the the fact fact that that the the Rb/Sr RWSrsystem systemisismore moresusceptible susceptibleto tolower-temperature lower-temperatureresetting resettingthan thanthe the Ar/Ar system. This Thisinterpretation interpretationalso alsoprovides providesan anexplanation explanation for for the the problematic problematic Rb/Sr RbISr and and AdAr Ar/Ar dates that fall between between 1200 and and 1400 Ma. Ma. Because AdAr Because much of the 1470 1470 Ma Wolf River batholith and associated intruded into into shallow shallow crust and batholith associated plutons (Wausau (Wausau Syenite complex) complex) intruded cooled through Ma (Fig. (Fig. 1 and 2). 2), it is likely through 300°C 300OCby by —1400 -1400 Ma likely that that the the surrounding surroundingPrecambrian Precambrian country rock to the north and west was also shallow. We We suggest, suggest, therefore, therefore, that the 1200-1400 1200-1400 Ma country rock mineral dates for for both systems systems indicate indicate incomplete mineral resetting related to shallow Keweenawan intrusions. 23 �Fig. Fig.1 1Rb/Sr RbISrBIOTITE BIOTITEAGE AGEDATA DATA Republic iis 4'— KEWEENAWAN 4 - ,,____,__,__ S'S.. — - — 1686. Peavy -1018=-— W:.1537+4+!.&ioa.thJ. ifs8l c*rtJL:i 4. +.ff rj¼l63:.llss.. '..5%& 1l03j.j..j tmbeau quartz'te 1249, r ' tfQightly foldedrL!:.', .'i'!! 1516 'us-i 620 ti's 1354S 1739 IZ3Sbj 1354 1360 1384"74// a, g 408 4/ .:.LLJ.:L1.J.J.:.Lth1455 'IV. ::15e2 1385 Edge of Late Proterozol Phanerozoic cover' After Peterman and Sims (1988) but excluding data of Aldrich et al. (1965) • Biotite Fig. 2 Ar/Ar MICA AGE DATA <4 ff011 '111 4', % — —.-- KEWEENAWAN "p ,',',',','.\.'.','l 696-,' 0 MuscovIte ___ ept I R7A "'%"' 10,natIonah11ft0i , , '..'' - IA! — tTrrrrrrrw1576;n.:.E.:n cm067'r*101 r.trhTrTnT.Tr:!Tr:,Tr:tT:-r-'.r' - 1358t -. Qua 1605-— _._.._j_ _,ø.__; -- -— r,-n11366rrtt1456 -'--1 HFlambeau quarizute :1-1372t:h-htr t1753I'r!." — 4 (tughtlyfolded) 1581 - S LJ.:1461 -! - 1A7 1616 415 Edge of Late Proti Phanerozoic covei Compiled Compiledfrom fromRomano Romano(1999, (1999.Kent KentState StateM.S. M.S.thesis), thesis),Mancuso Mancuso(1999. (1099.Kent Kent State CJES), StateM.S. M.S.thesis), thesis).Hoim Holmand andLux Lux(1998, (1998. CJES).Hoim Holmetelal. al.(1996, (1998.GSAA). GSAA),and and . Schneideretetal. al.(1996, (1996,CJES). CJES). Schneider 24 24 �ISHPEMING ISHPEMING GREENSTONE GREENSTONE BELT BELT --EVIDENCE EVIDENCEFOR FOR ARCHEAN ARCHEANTECTONIC TECTONIC EVOLUTION OF THE SOUTHERN EDGE OF THE SUPERIOR EVOLUTION OF THE SOUTHERN EDGE OF THE SUPERIOR PROVINCE PROVINCE IN IN MICHIGAN MICHIGAN JOHNSON, JOHNSON,Rodney RodneyC., C., Rod Rod Johnson Johnson& &Associates, Associates,Inc., Inc., Negaunee, Negaunee, MI MI 49866, 49866, MinerDoc@aol.com; MinerDoc@aol.com;and andBORNHORST, BORNHORST, Theodore Theodore J., J., Department Department of of Geological Geological Engineering Engineeringand and Sciences, Sciences,Michigan MichiganTechnological Technological University, University, Houghton, Houghton, MI MI 49931, 4993 1, tjbomho@mtu.edu tjbomho@mtu.edu The The Ishpeming Ishpeminggreenstone greenstonebelt belt is is the the southernmost southernmostgreenstone greenstone belt of of the the Superior Superior Province. The southern boundary of the Superior Province and the Ishpeming Province. The southern boundary of the Superior Province and the Ishpeming greenstone greenstone belt zone. Late k m long long Great Great Lakes Lakes tectonic tectonic zone. LateArchean Archean greenstone greenstone and i d belt is is the the 1,000 1,000km granite graniteterrane terraneto tothe thenorth north(Ishpeming (Ishpeminggreenstone greenstone belt) belt) are are juxtaposed against against Early Early to to Middle migmatite-gneiss-amphiboliteand and Late Late Archean Archean granite granite terrane terrane MiddleArchean Archeanmigmatite-gneiss-amphibolite (southern (southern complex). complex). The TheIshpeming Ishpeminggreenstone greenstonebelt belt consists consistsof of subaqueous subaqueous tholeiitic tholeiitic basalt thickness. New calc-alkalic rhyolite, rhyolite, 10-15 10-15km in total thickness. basalt to to calc-alkalic New U-Pb U-Pb zircon zircon data data establish establishthe the age ageof of volcanism volcanism at at 2705.8+/-1.6 2705.8+/-1.6 Ma. (Table (Table 1) Recent Recent field field studies studiesdefine define aa sequence sequenceof of multiple multipledeformation deformationand and intrusive intrusiveevents events following followingvolcanism. volcanism. The The volcanic volcanic rocks rockswere wereenveloped envelopedby by aatonalite tonalitesuite suite just before before and and during during the the northnorthdirected directed thrusting thrustingand and nappe nappe formation. formation. This Thiswas wasfollowed followedby bydevelopment developmentof ofstrike-slip strike-slip shear zones and the deposition of clastic sediments into pull-apart basins. A second second shear zones and the deposition pull-apart basins. phase suite intruded the belt phase of of folding folding produced upright folds. A Atrondhjemite trondhjemiteto to granite suite and and deformed deformedearlier earlierfabrics. fabrics. The Thetiming timingof ofdeformation deformationisisconstrained constrainedwith withnew newU-Pb U-Pb zircon zircon data data yielding yielding an an age age of 2668.4÷2.l/-l.8 2668.4+2.1/-1.8 Ma Mafor foran anintrusion intrusionin inthis thissuite. suite. Intrusions Intrusionsof of hornblendite homblenditeto to syenite syenite (appinite (appinite suite) suite) and and continued movement along along shear shear zones zones represent represent the the end end of of deformation. deformation.An Anundeformed undeformedpost-tectonic post-tectonicgranite graniteintrusion intrusion has has an an age ageof of 2585 2585(Sims (Simsand andPeterman, Peteman, 1992). 1992). This are readily readily interpreted in a This sequence sequenceof of deformation deformationmagmatic/volcanic magmatic/volcanicevents events are modern modem plate plate tectonic tectonic context. context. The Thevolcanic volcanicarc arcrocks rocksare arethe theresult resultof of north-directed north-directed subduction. Tonalite-suite plutons intruded the arc just prior to collision subduction. Tonalite-suite plutons intruded the arc just prior to collisionof ofaasmall small continent from the south (southern complex) along the Great Lakes tectonic continent from the south (southern complex) along the Great Lakes tectoniczone zone (suture). (suture). Collision Collisionoccurred occurredover overan anextended extendedperiod periodof oftime timewith withmultiple multipledeformation deformation and and magmatic magmatic events. events. The Theappinite appinitesuite suiteisischaracteristic characteristicof ofmodern modemcollision-related collision-related magmatism. magmatism. The Thefield-based field-basedsequence sequenceof ofevents eventsand andnew new age agedates datesare areimportant importantdata datain in continuing continuing to to unravel unravel the the tectonic tectonic evolution evolution of the southern southern edge of the Superior Superior Province. sProvince. References: Sims, Sims, P.K. P.K. and and Peterman, Peterman, Z., Z., 1992, 1992, Guide Guideto tothe thegeology geologyof of the theGreat GreatLakes Lakestectonic tectonic paleosuture: Institute zone zone in in the the Marquette Marquettearea, area,Michigan Michigan -- A A late late Archean Archean paleosuture: Instituteon on Lake LakeSuperior SuperiorGeology GeologyProceedings, Proceedings,38th 38"' Annual Annual Meeting, Meeting, Hurley, Hurley, WI, WI, v. v. 38. 38, part part 2, 2, p. p. 105-135. 105-135. 25 �1 Table 1. and constraining constraining age age dates dates for for the the Table 1.Summary Summaryof ofdeformation deformation sequence, sequence, volcanic/magmatic volcanic/magmatic activity activity and Jshepming greenstone Ishepming greenstone belt. belt. Event Characteristic ., VolcanicfMagmatic Vnlcanic~MaematicActivity Activity Age Dates Undeformed Undeformed post-tectonic post-tectonic granite granite 2585 Ma Kink bands Kink bands with with north-easterly north-easterly striking kink kink planes planes and striking and steeply steeply plunging hinges :,'',,->$ '.f03'] D5 Ds Dip slip motion along shear zones. U4 D4 Folding associated associated with Folding with intrusion of plutons. D3 D3 Upright folding. Appinite suite Di U2 Strike-slip shearing. Trondjhemite-granite suite Tmndjhemite-granite suite U1 Di Recumbent folding. Recumbent folding. Tonalite suite Tonalite suite : yw; .8fel. Extrusion of mafic ma ic and an felsic sic volcanic rocks. 26 2668.4+2.11-1.8 2668.4+2.1/- 1.8 Ma Ma ,". ,,. , . . , : ,. :* : : 2705.8+/-1.6 Ma ; , , b �A NEW APPROACH APPROACH TO TO HISTORICAL HISTORICAL RECONSTRUCTION: COMBINING DESCRIPTIVE AND DESCRIPTIVE AND EXPERIMENTAL EXPERIMENTAL PALEOLIMNOLOGY W. W. Charles CharlesKerfoot, Kerfoot,Lake LakeSuperior SuperiorEcosystem EcosystemResearch Research Center Center and and Department Department of of Biological BiologicalSciences, Sciences,Michigan MichiganTechnological TechnologicalUniversity, University, Houghton, Houghton, MI MI 49931 4993 1 John John A. A. Robbins, Robbins,NOAA NOAAGreat GreatLakes LakesEnvironmental EnvironmentalResearch Research Laboratory, Laboratory, 2205 2205 Commonwealth CommonwealthBlvd., Blvd., Ann Ann Arbor, Arbor,MI MI 48105 48105 Lawrence LawrenceJ. 1.Welder, Weider,Max-Planck-Institut Max-Planck-Institutfür f i rLimnologie, Limnologie,Postfach Postfach165, 165,D-24302 D-24302PlOn, PlOn, Germany* Germany* Here Here we we introduce introduce aa combined combined experimental experimental and and descriptive descriptive approach (termed "Resurrection Ecology") Ecology") to toreconstructing reconstructinghistorical historicalperturbations, perturbations,pointing pointing out out how how direct direct tests tests with with sediments sediments and and hatched hatched resting resting eggs eggs complement complement the traditional descriptive calculation of microfossil microfossil fluxes. fluxes. This Thisapproach approachisisbeing beingstudied studiedin in both both NSFINOAA NSF/NOAA Cooperative sites, the KITES Project in in Lake LakeMichigan. Michigan. Additional core KITES Project in Lake Superior Superior and the EGLEE Project studies studies involve involveBaltic Baltic German German lakes lakes and and the Caspian Sea. In the the Keweenaw Keweenaw Waterway, Waterway, aa freshwater freshwater estuary estuary off Lake Superior, turn-of-the-century copper coppermining mining impacted impactedthe the resident residentbiota. biota. Remain Remain fluxes fluxes document document that that diatom, diatom, rhizopod. rhizopod, and production all declined declined during stamp sand discharges, but recovered rapidly and Bosmina production after moving above background levels due to developing developing eutrophication. eutrophication. In addition addition after WWLI, WWII, moving to biogenic biogenic silica, silica, we we discovered discovered that that bromine bromine flux holds promise as an indicator of diatom production production and and confirmed confirmed that that this this element element is present in several genera. Fluxes of Daphnia resting eggs also the 1940's. 1940's, dominated by by aa hybrid hybrid apparently apparently also increased dramatically since the produced produced from from crosses crosses between offshore offshore and interior interior Waterway species, after channeling promoted promoted greater greater mixing mixing of of water water masses. masses. Toxicity Toxicity studies studieswith with sediments sediments and and Daphnia Daphnia clones clones directly directly tested tested recovery recovery of environments environments after concentrations and after cessation cessation of of mining mining activities. activities. The The studies studies document document that increased concentrations fluxes fluxes of of copper copper in in the the Waterway Waterway during during mining mining discharges discharges were toxic to invertebrates. Once stamp stamp sand sand discharges discharges ceased, ceased, the the biota biota recovered recovered rapidly due to a combination of decreased copper copper cycling cycling and and organic organiccomplexation. complexation. Although Although sedimentation sedimentation has returned to nearbackground background conditions conditionsand and surficial surficial sediments sediments in much of Portage Lake are no longer toxic, eutrophication eutrophicationand and faunal faunal exchange exchange with with Lake Lake Superior Superior make it unlikely that the original zooplankton zooplankton community communitycomposition composition will will return return to to the Waterway system. 27 �THE IRON IRON RIVER RIVER SYNCLINE: AN AN ALLOCHTHONOUS ALLOCHTHONOUSSTRUCTURAL STRUCTURALPANEL PANELIN INTHE THE PENOKEAN PENOKEANFORELAND FORELANDOF OF NORTHERN NORTHERN MICHIGAN MICHIGAN KLASNER, John S., Survey Western S., Department Department of of Geology Geology and U. S. Geological Survey, Western Illinois Illinois University, University. Macomb, Macomb, IL IL61455, 61455. jklasner@macomb.com; jklasner@macomb.com; CANNON, CANNON, William William F. F. and and SCHULZ, SCHULZ, Klaus Klaus J., U. U. S. Geological Geological Survey, Survey, National NationalCenter, Center, MS. MS. 954, 954, Reston, Reston, VA VA 20192; 20192; and and LABERGE, S. Geological Geological Survey, Survey, University Universityof of LABERGE, Gene Gene L., L., Department Department of of Geology Geology and and U. U. S. Wisconsin 54901 Oshkosh, Oshkosh, Oshkosh,WI Wl54901 Wisconsin -- Oshkosh, The The Iron IronRiver Riversyncline syncline(James (Jamesand andothers, others, 1968) 1968)lies liesnear nearthe the southern southernmargin marginof ofthe the Penokean strata of of the Penokeanfold fold and and thrust thrust belt beltin innorthern northernMichigan. Michigan. It It contains sedimentary strata the Paint Paint River River Group Group and and underlying Badwater BadwaterGreenstone. Greenstone. The Thesyncline synclinehas has aa triangular triangular map map pattern pattern and and is is flanked flankedby by strata strataof ofthe theMichigamme MichigammeFormation Formationon onits itsnorth northand andeast eastsides sidesand andby by intensely comolex. intensely deformed deformed Early Earlv Proterozoic Proterozoic strata on its southwest side. An An unusually unusuallvcomplex, multiply-folded structure within the multiply~folded structurewithin the syncline synclinehas hasbeen beenrecognized recognizedsince since the the detailed detailedstudies studiesby by James James and and others others (1965). (1968). Traditional Traditionalstratigraphic stratigraphicinterpretation interpretationhas hasbeen beenthat that the the strata stratain inthe the syncline syncline are are stratigraphically stratigraphicallyabove abovethe the Baraga BaragaGroup Groupand and that that the the Badwater BadwaterGreenstone Greenstoneand and Paint Paint River River Group Group are are the the youngest youngest parts parts of the Marquette Marquette Range Supergroup. More Morerecently, recently, an an allochthonous allochthonousorigin originfor forthe thesyncline syncline has hasbeen beenadvocated advocated(Sims, (Sims, 1996) 1996)and andthe the exact exact correlation correlationof of units unitsin inthe thesyncline synclinewith with autochthonous autochthonousunits unitselsewhere elsewhere in inthe the foreland foreland is is uncertain. uncertain. Our Ourrecent recentre-examination re-examinationof of the the region region lends lends support to tothe theview view that that the the syncline syncline is is an anallochthon allochthonemplaced emplacedby bygenerally generallynorthward-directed northward-directed thrusting. A A thrust thrust of of considerable considerable magnitude This thrust thrust forms forms the the magnitude is is interpreted interpretedto to lie lie at at the the base base of the Badwater Greenstone. This base base of of the the allocthon allocthonand andseparates separatescomplexly complexlydeformed deformedstrata strataabove abovefrom from more moresimply simply deformed deformed strata strata below. below. Several Severalsets setsof ofstructural structuralobservations observationsargue arguefor for the the allochthonous allochthonous nature nature of of the the Iron IronRiver Riversyncline, syncline,the theprincipal principalargument argumentbeing beingthat that the the syncline synclinehas hasaafolding folding history history and and fold fold geometry geometrymore morecomplex complexthan thansurrounding, surrounding,and andpresumably presumablyunderlying underlyingrocks. rocks. ItIt must must therefore thereforehave haveacquired acquiredsome someaspect aspectof ofits itsstructure structureeither eitheras asaageographically geographicallyseparated separated terrane terrane or or during duringthin-skinned thin-skinnedemplacement emplacementover overthe thefootwall footwallrocks. rocks. ~~~~ Structures Structures in in the the allocthon allocthon Studies Studies of of outcrops outcropsof ofthe thePaint PaintRiver RiverGroup Groupshow showthat that at atleast leasttwo twoand andprobably probablythree threeor ormore more generations generations of of fold fold axes axes occur occur in in the the Iron Iron River River syncline. Most Mostfolds folds are are tight tight to to isoclinal isoclinalwith with steeply-plunging steeply-plungingaxes. axes. Similar Similarsteeply-plunging steeply-plunging fold fold axes axes are are common common in in fault fault panels panelswithin within the the Niagara Niagara fault fault complex, complex, part partof of which which bounds bounds the the syncline syncline on on the the south, south, but but are are rare rare elsewhere elsewhere in in the the foreland. Bedding Beddingand andaxial axialplanar planarfoliation foliationare are variably variably oriented, oriented, but but generally generally dip dip steeply. steeply. Remnants Remnantsof of sub-horizontal sub-horizontal foliation foliation occur occur in in aa few places places suggesting suggesting that that recumbent recumbent folds of folding. folding. AAcross folds may may have have been been significant significant during early stages of crosssection section(James (Jamesand and others, synclinenear near others,1968) 1968)from fromiron ironmine mineworkings workingsat atthe thewest westend endof ofthe theIron IronRiver Riversyncline Staumbaugh, steeplyStaumbaugh, Michigan Michigan shows shows a a recumbent recumbentfold foldthat thatisisonly only moderately moderately overprinted overprinted by by steeplydipping dipping structures. structures. The The Badwater BadwaterGreenstone, Greenstone,although althoughlargely largelymassive, massive,does doescontain containstructures structuressimilar similarto tothose those shown history. The shown in in the the Paint Paint River River Group Group and and appears appears to have the same structural history. The Badwater Badwater Greenstone Greenstoneis is therefore thereforeconsidered consideredpart partof ofthe theallochthon. allochthon. 28 �syncline Structures iinn rocks surrounding the Iron Iron River syncline Rocks within the Niagara fault fault complex, south south of of the the syncline, syncline, have havenorthwest-striking, northwest-striking,steeply steeply south-dipping foliation and tight tight to to isoclinal folds folds that that are are steeply steeply plunging, plunging,like likethose thosewithin withinthe the Structures in Baraga Group rocks (primarily (primarily Michigamme Michigamme Formation), Formation),which whichbound boundthe the syncline. Structures the north and east, are much different and and generally generally have havewest-northwest-striking west-northwest-striking syncline on the foliation to sub-horizontal sub-horizontal fold fold axes axes that that foliation that dips moderately to steeply south, and horizontal to trend fold axes axes are are rare rare in in the the Iron Iron River River trend west-northwest. Such Such sub-horizontal, west-trending fold first generation recumbent folding foldingwith with sub-horizontal sub-horizontalaxial axialplanar planar syncline. Several areas of first foliation foliation have have been been found found over over the the past past several several years years within within the the Baraga Baraga Group Group rocks, rocks, small recumbent recumbentfolds foldswith with sub-horizontal sub-horizontal suggesting the formation of nappes. Most recently, small foliation of the the Iron Iron River River foliation have have been been documented documented near Watersmeet, Michigan, northwest of structures north north and andeast eastof ofthe the Iron Iron syncline. Together Together with with previous previous observations observations of similar structures River syncline, there is now widespread evidence evidence of of an early phase of recumbent folding and an early phase foliation, now now variably variably overprinted overprintedby bymore moreupright upright generation of low angle axial planar foliation, structures. structures. Interpretation Interpretation Recumbent Recumbent folds documented documentedby by underground underground mapping mapping in in the Iron Iron River River syncline syncline (James (James and and others, 1968) and remnants of flat-lying foliation found in outcrops of the Paint River Group remnants found in outcrops of the Paint River Group Baraga Group Group had had aa similar similarearly early suggest that both both the Iron Iron River syncline and adjacent Baraga structural history history of recumbent folding and development of of low low angle anglefoliation. foliation. However, structural However, multiple generations generations of of steeply-plunging steeply-plungingfold axes axes and and steeply-dipping, variably-oriented variably-oriented axial axial planar foliations of the Iron River syncline, are distinct from the gently west-plunging fold axes Iron distinct from the gently west-plunging fold axes found in the the Michigamme Michigamme Formation Formation north northand andeast eastof of with south-dipping south-dipping axial planar foliation found the syncline. Similar Similarsteeply steeplyplunging plungingfold foldaxes axes are are common common in in very highly highly strained rocks rocks along to events events related related to to suturing suturing of ofthe thevolcanic volcanic the Niagara Niagara Fault Fault and seem clearly to be integral to terranes south south of the fault. This Thissuggests suggeststhat thatthe theIron IronRiver Riversyncline syncline was was detached detached from from folding history. history. The base interpreted to underlying rocks during much of its folding base of the allocthon is interpreted be a thrust fault along the the base base of of the the Badwater Badwater Greenstone, Greenstone, along which the allochthon allochthon has has been thrust thrust northward over foreland basin turbidite turbidite deposits deposits of ofthe the Michigamme MichigammeFormation. Formation. We folding within within the the Iron Iron River Riversyncline synclineisisaaresult resultof of suggest that the unusual unusual complexity of folding zone. During thrusting of earlier earlierdeformed deformedrocks rocks northward northward from the suture zone. During this thrusting, an earlier set of recumbent folds was intensely redeformed. In In contrast, contrast, rocks rocks in in the structural structural the fact fact that that the the Iron Iron River Riversyncline synclinecross-cuts cross-cutsthe the footwall were little little deformed as shown by the west-trending, sub-horizontal west-trending, sub-horizontal fold fold axes axes in in the the adjacent adjacent Michigamme Michigamme Formation. Formation. REFERENCES REFERENCES J., and Wier, Wier, K. K. L., L., 1968, 1968, Geology Geology and andOre Ore Deposits Depositsof of James, H. L., L., Dutton, C. E., E., Pettijohn, F. J., the Iron Iron River-Crystal River-Crystal Falls Falls District, District, Iron Iron county, county, Michigan: Michigan: U. S. Geological Geological Survey Professional Paper 570, 134 134 p. P.K., 1996, L.M.H., eds., Sims, P.K., 1996,Structure Structureof of continental continentalmargin, margin, in in Sims, P.K., P.K., and Carter, L.M.H., Archean and Proterozoic geology of the Lake Superior region, U.S.A., 1993: Proterozoic of the Lake Superior region, U.S.A., 1993: U.S. Geological Professional Paper Paper 1556, 1556, p. p.44-51. Survey Professional 44-51. 29 �REGIONAL PATTERNS PAYIERNS ON THE ON THE THE PENOKEAN PENOKEAN CONTINENTAL MARGIN IN THE SOUTHERN SOUTHERN LAKE SUPERIOR REGION Gene , Oshkosh, Oshkosh, WI L. LaBerge, M e r g e , UW UW Oshkosh Oshkosh , W I 54901 and U. U.S. S. Geological Geological Survey Survey Gene L. Studies of outcrops outcrops and exploration drill cores reveal several cores during the past decade decade reveal several regional patterns in the deposition deposition and subsequent deformation deformation and metamorphism metamorphism of of the the Early Proterozoic Earl Proterozoic Penokean continental continental margin margin rocks rocks in in northern northern Wisconsin Wisconsin and and northern northern Michigan. These datahelp helpconstrain constrain models models of of the the depositional depositional and tectonic history of the ~ichigan. Thesedata region. . region. I. Regional depositional depositional patterns. patterns. A. Thinning westward of the basal arenite of of the the Chocolav Chocolay Grouo. Group. The A. The Mesnard and Sturgeon Formations are are prominent arenite arenite units in the Marquette ~ a r ~ b e tand te Sturge& Formations Menominee districts, Menominee districts. respectively, resuectivelv. and the the Sunday Sundav Quartzite Ouartzite forms forms a thin basal unit on the eastern Gogebic &nee. range. However, basal arenite &&te is is absent absent on on the thewestern rfowever, aabasal Gogebic range, where the the the dolomite dolomite unit characteristic characteristic of the upper part of the Gogebic range, Group rests directly on on Archean basement. basement. Drill Chocolay Group Drill core coredata data from from the the Park Park Falls -- Mercer area of northern Falls northern Wisconsin suggests suggests that this this pattern pattern extends extends southward toward toward the the proposed continental continental margin. southward increase in politic pelitic rocks rocks southward toward the proposed continental B. An increase margin. Drill pelitic ParkFalls Falls -- Mercer area intersect abundant ~elitic marein. Drillcores coresfrom from the the Park schists, some of which contain interbedded carbonate carbonate units. units. Bedded Bedded sulfides sulfides are are present locally within the politic pelitic rocks. rocks. The Thestratigraphic stratigraphicposition positionof of the thepelitic politicunits units has not been ascertained, but they may be broadly correlative correlative with the Chocolay (Cannon and others, 1998). 1998). Group (Cannon C. A consistent pattern of litholoeies lithologies within the Palms formation of the Menominee Menominee Penokean platform. platform. The Group throughout the Penokean The thin-bedded argillaceous lower member and the thick-bedded thick-bedded orthoquartzite are recognizable orthoauartzite upper uooer member membea are r e c o b b l e from from member the Marenisco are also ~amekaion.These Thesemembers membekare also Marenisco area westward to Lake Namekagon. recognizable recoenizable in drill drill cores cores from from the the Pine PineLake LakeSubterrane Subterrane(Cannon (Cannonand andothers, others. 1998) from the Lake Gogebic Gogebic area southwestward WI area, area, southwestward at least to the Butternut, WI suggesting a uniform platformal depositional environment. platf-1 suggesting D. Rift-related ironRift-relatedvolcanic volcanicrocks rocks(Sims (Sims and and others, 1989) 1989) are are associated with ironformation of the Menoninee ~Group G u on p the proposed shelf. The The Emperor Emperor Volcanics Volcanics are interbedded interbedded with iron-formation on the the eastern eastern Gogebic Gogebic (LaBerge (LaBereeand and Klasner, Klasner, 1994), and volcanics are present within the iron-formation iron-formation on & the western w-&tern end end of the Gogebic ((LaBerge M e r g e and others, 1995). Volcanic Volcanic rocks rocks as as well as carbonaceous sediments are associated with iron-formation south of the Gogebic range in a belt that extends extends from from near near Lake Lake Gogebic Gogebic southwestward southwestward at at least least to to the the Butternut, Butternut, Wisconsin area, (LaBerge, (JaBer e, 1997). This Thissuggests suggeststhat that rifting, rifting, with with associated volcanism and stagnant stagnant basin development, development, occurred occurredafter after deposition deposition of of the the Palms Palms Formation on the continental margin. On Onthe themain mainGogebic Gogebicrange, range,then, then, the the ironironformation accumulated accumulated on a shallow shallow platform bounded bounded on on the the east, east, south south and and west west basins with active active volcanism. by rift basins II. deformation/metamorhpic 11. Regional Regional defonnation/metamorhmcpatterns. " A. Metamorphism ~ & o r p h i s m of ofcontinent &tin& margin margin sediments sedimentsthat that increases increasesin in intensity intensity associated with with intense intense folding foldingand andnorth-directed north-directedthrusting. thrusting. A A zone zone of of southward associated high pressure pressure metamorphism metamorphism characterized characterized by kyanite and a high temperature zone 30 �sillimanite(the Powell Subtenane Subterrane and the Park Falls Subterrane, Subterrane, characterized by sillimanitefthe respectively of Cannon and others, 1998). 1998). pegmatitic, granites, some of of B. Emplacement of post-tectonic potassic, commonly pegmatitic, two-mica granites, or garnet, garnet,typical typicalof of which are two-mica granites, or which contain sillimanite or anatectic granites. later deformational deformational event eventwith withassociated associatedretrograde retrogrademetamorphism. metamorphism.This Thisisis C. A later widespread alteration alteration of of high grade minerals such such as as sillimanite sillimaniteand and expressed as widespread rocks)to topyrophyllite pyrophylliteand andserpentine, serpentine,respectively. respectively. This This olivine (in carbonate rocks) the post-tectonic post-tectonic granites granitesassociated associatedwith withthe theearlier earlier deformation has locally affected the deformation. References: Cannon, W.F., W.F., LaBerge, G.L., G.L., Klasner, Kiasner, J.S., J.S., and Schulz, K.J., K.J., 1998, Reinterpretation Reinterpretation of the Penokean continental margin in part of northern Wisconsin and Michigan (Abstract): 44th Annual Institute on Lake Superior Geology, vol. vol. 44, 44, part part 1, p. p. 52-53. J.S., and M LaBerge, G.L., 1994, Klasner, J.S., e r g e , G.L., 1994, Structural evolution of the eastern Gogebic Michigan (Abstract): (Abstract): 40th 40th Annual AnnualInstitute Instituteon onLake LakeSuperior Superiot range, northern Michigan vol. 40, part part 1, p. 23-24. Geology, vol. LaBerge, G.L., G.L., 1997, break-up of of the the Superior SuperiorCraton: Craton:Implications Implicationsofof Merge, 1997, Early Proterozoic break-up drill core and geophysical data south of of the the Gogebic range, range, northern northern Wisconsin Wisconsin (Abstract), 43rd Annual Annual Institute Instituteon onLake LakeSuperior SuperiorGeology, Geology,vol. vol.43, 43,part part1,1,p.p. 3 1-32. 31-32. LaBerge, G.L., G.L., Cannon, Cannon, W.F., and andKiasner, Klasner,J.S., J.S., 1995, 1995,New New observations observations on the geology of the western Gogebic range (Abstract): Institute on Lake (Abstract): 41st Annual Institute Superior Geology, vol. 41, part I,1,p.p.331-32. 1-32. LaBerge, G.L. G.L. and Klasner, J.S., J.S., 1994, Tectonic Tectonic implications implications of the Early Proterozoic lithostratigraphy on the eastern Gogebic range, northern Michigan (Abstract): 41st on the eastern Gogebic Annual Institute on Lake Superior Geology, vol. vol. 41, part part 1, p. p. 33-34. Sims, P.K., P.K., Van Schmus, W.R., W.R., Schulz, K.J., K.J., and Peterman, Z.E., Z.E., 1989, TectonoTectonostratigraphic evolution evolution of of the the Early Early Proterozoic Proterozoic Wisconsin Wisconsin magmatic magmatictenanes terranesof ofthe the Penokean Orogen: Canadian Journal of Earth Sciences, v. 26, p. 2 145-2158. Orogen: Canadian Journal of Earth Sciences, v. 26, p. 2145-2158. 31 �1 I DETERMINE THE THE ORIGIN ORIGIN OF A GEOCHEMICAL AND PETROLOGIC STUDY TO DETERMINE CROWDUCK LAKE THE CROWDUCK LAKE GROUP, GROUP. KENORA, ONTARIO: A PROBLEMATIC METACONGLOMERATE. METACONGLOMERATE. JOHNSON, Matthew M. M.and and COTTER, COTTER, J.F.P., J.F.P., LOUGHRY, Joy LOUGHRY, Joy E., JOHNSON, Geology Geology Discipline, Discipline, University University of of Minnesota, Minnesota, Morris, Morris, Morris 56267 Morris MN M N 56267 The The Crowduck Crowduck LakeLake Group is is a sequence sequence of of argillite argillite and aa poorly poorly sorted sorted conglomerate (Archean (Archean ? age) age) exposed exposed near near Kenora, Kenora, Ontario. Ontario. Smith Smith (1988) may be be a debris debris flow flow (1988) suggested suggested that that the the Crowduck Crowduck Lake Lake Group Group may deposit, deposit, however however lithology lithology and and geographic geographic location location suggest suggest that that it may may be be aa correlative correlative of of the the"Gowganda "Gowganda tillites' tillites" (polymictic (polymictic conglomerates conglomerates deposited deposited during during the the Gowganda Gowganda glaciation glaciation 1.8 1.8 billion billion years years ago). ago). The goal goal of Crowduck Lake Lake Group Group is is glacial glacial in in of this this study study is is to todetermine determine ifif the theCrowduck origin. origin. Extensive research has has been been done done on Extensive research on the the deposits deposits of of the the Gowganda Gowganda Glaciation of the Glaciation (Summarized (Summarized by by Young Young 1969, 1969, 1973. 1973, 1999). 1999). Outcrops Outcrops of the Gowganda Gowganda are are located located in in Chibougamau, Chibougamau, Quebec, Quebec, Wyoming. Wyoming, and and Northern Northern Michigan. Geochemical analysis analysis indicate indicate that that there Geochemical there are are broad broad similarities similarities in diamictite constituents. Additionally. Chemical Index in constituents. Additionally, Chemical Index Alteration Alteration studies studies provide provide evidence evidence of of regionally regionally cold cold climatic climatic conditions conditions (Young, (Young, 1999). 1999). Young on the Young (1969), (1969). on the basis basis of of outcrop outcrop distribution, distribution, suggests suggests that that elsewhere in Canada there elsewhere in Canada there are arepolymictic polymictic conglomerates conglomerates which which on on detailed detailed analysis may well turn out to be tillites. analysis may well turn out to be tillites. For For this this study study an an outcrop outcrop at at the the type type locality locality of of the theCrowduck Crowduck Lake Lake Group Group was was described described and and sampled. sampled. Hand Hand samples samples were were analyzed analyzed for for sedimentary structures, Geochemistry structures, clast provenance provenance and and clast clast shape. shape. Geochemistry of matrix matrix samples samples was was determined determined using using ICP. ICP. Thin Thin sections sections of of matrix matrix were were used used for for petrographic petrographic analyis. analyis. Geochemistry of the Crowduck Lake Lake Group Group is is similar similar to to that that of of the the Geochemistry of the Crowduck type of these type Gowganda Gowganda Fotmation Fofmation of of Ontario. Ontario. However, However, interpretation interpretation of these results is results is restricted restricted because because little little is is known known about about the the geochemistry geochemistry of of the the bedrock at at the Additionally, the age age of of the the Crowduck bedrock the time time of ofdeposition. deposition. Crowduck Additionally, the Lake Group Lake Group is is poorly poorly constrained. constrained. Thus, Thus, several several possible possible origins origins of the the Crowduck Crowduck Lake Lake Group Group remain remain plausible: plausible: glacial glacial tillite, tillite, turbidite/debris turbiditeldebris flow, and flow, and basal basal conglomerate. conglomerate. Although Although the sedimentology. sedimentology, location location and and age of of the the Crowduck Crowduck Lake Lake Group Group make make aaglacial glacial origin originattractive, attractive, evidence evidence is Additional is not conclusive. conclusive. Additional petrographic petrographic analysis analysis are are underway. underway. 32 �THE GRATIOT CHALCOCITE DEPOSIT, KEWEENAW PENINSULA, MICHIGAN MAKI, John C., Department of of Geological Geological Engineering Engineeringand andSciences, Sciences,Michigan Michigan Technological Technological University. Houghton, MI 49931, jcmaki@mtu.edu; and BORNHORST, Theodore J., Department Department of of University, 4993 1Jcmaki@mtu.edu; and BORNHORST, Theodore J., Geological University, Houghton, Houghton, MI 49931, Geological Engineering and Sciences, Sciences, Michigan Technological University, tjbomho@mtu.edu tjbomho@mtu.edu ABSTRACT ABSTRACT Michigans Michigan's Keweenaw Keweenaw Peninsula Peninsula is is well well known for world-class world-class native copper deposits and the lack of significant amounts of copper sulfides. Twelve copper Twelve copper sulfide sulfide (chalcocite-dominated) (chalcocite-dominated) deposits depositshave have Peninsula. Robertson (1975) described one small deposit near Mt. been discovered in the Keweenaw Peninsula. Bohemia. Chalcocite-dominated deposits are are concentrated concentratedininthe the lower lowerquarter quarter of of the the Portage Portage Lake Lake Bohemia. Chalcocite-dominated deposits to Mt. Mt. Bohemia Bohemia (Figure (Figure 1). 1). The Gratiot chalcocite Volcanics from Suffolk to chalcocite deposit (previously termed 543-S) is the largest of the deposits and and contains about about 4.5 4.5 million metric 5434) the copper copper sulfide sulfide dominated dominated deposits tons of ore with an average average grade grade of of 2.3% 2.3% copper. copper. The The Gratiot chalcocite chalcocite deposit deposit is is hosted hosted by the Portage Lake Volcanics and is about 1.4 1.4 km from from the In vicinity of the ore, basalt lava flows are Keweenaw fault, a major reverse fault of regional extent. reverse fault of regional In vicinity of dikes. These to the the orientation orientation of of the the lava lava flows. flows. cut by two dacite-andesite dikes. These dikes are nearly subparallel to flow tops, although lesser amounts are Ore grade intercepts occur mostly in brecciated brecciated amygdaloidal flow found in flow interiors and and dikes. dikes. The both dikes are present present The highest highest grade and tonnage exists where both both dikes dikes are are thick. thick. Faulting and both dikes dikes and where both and fracturing fracturing are most prevalent in rocks where both exist. The deposit zone, the the Gratiot-Suffolk Gratiot-Suffolkfault, fault, that has a stratigraphic exist. deposit is within a 12 12 km long fault zone, displacement of about 7 meters and is sub-parallel to to the the attitude attitude of of the the basalt basalt flows flows and and sub-parallel to to fault. Two deposit are are the the Cross-Gratiot Cross-Gratiot fault fault that that is is the Keweenaw fault. Two other other significant significant faults that cut the deposit basalt flows flows with with aa stratigraphic stratigraphic displacement displacement of of about roughly perpendicular to the attitude of the basalt about 15 15 meters and and the the Gratiot fault that that is sub-parallel to the the attitude attitude of of the the basalt basalt flows flows with with very meters Gratiot fault sub-parallel to very little little The highest grades are associated with the intersection of the Gratiotstratigraphic displacement. displacement. highest grades associated with the intersection the GratiotSuffolk fault, the Gratiot Gratiot fault fault and and the the Cross-Gratiot Cross-Gratiot fault. fault. fill amygdules amygdules and and fractures fractures within within the the basalt lava A suite suite of of secondary secondary hydrothermal hydrothermal minerals minerals fill lava flows and dikes. Chlorite was the earliest secondary mineral, followed by epidote, potassium feldspar, Chlorite was the earliest secondary by epidote, potassium feldspar, Deposition of of native copper and native silver, prehnite prehnite and quartz and calcite (approximate order). Deposition pyrite clearly follows native copper and was itself followed by by chalcopyrite, bomite, bornite, chalcocite chalcocite and and hematite. The Thelast lastphase phaseof ofsecondary secondarymineral mineral deposition deposition was adularia, laumontite and more calcite. Chalcocite Chalcocite is by far far the the major majorcopper-bearing copper-bearing mineral mineral in the Gratiot Gratiot deposit, deposit, other other copper-bearing copper-bearing minerals are trace to rare in occurrence. The deposit The relative relative age of mineral deposition in the Gratiot deposit matches the relative age of mineral mineral deposition deposition in the large native copper deposits in the the Keweenaw Keweenaw Peninsula. Butler an early early suite of of minerals associated associated with with native native Butler and and Burbank Burbank (1929) (1929) documented documented an Native copper copper in in the copper followed by late adularia, adularia, laumontite and calcite. Native by chalcocite and then late Keweenaw Peninsula is interpreted to be temporally and and genetically genetically related related to to compressional tectonics The close temporal produced reverse motion motion along along the the Keweenaw Keweenaw fault (Bornhorst, (Bomhorst, 1997). 1997). The temporal that produced also chalcocite is also relationship of native copper and chalcocite relationship of chalcocite in the Gratiot deposit suggests that chalcocite are interpreted interpreted as as very Native copper copper ore-depositing ore-depositing fluids are very tectonics. Native related to to compressional compressional tectonics. related Chalcocite ore must Chalcocite ore fluids must sulfur poor and derived from basalts within the rift (Bomhorst, 1997). sulfur poor and derived from within the rift (Bomhorst, 1997). 33 �have have carried carried more moresulfur sulfurthan thannative nativecopper copperfluids. fluids. However, However, the the genesis genesis of offluids fluidsgenerating generatingthe the chalcocite chalcocitedeposits depositsisiscurrently currentlyspeculative. speculative. Gratiot-Suffolk Fault Gratiot Lake Mt Bohemia Deposit Gratiot GratiotDeposit Deposit Suffolk Deposit 1111111 Jacobsville Sandstone KXI Oronto GrOLQ I Portage Lake Volcanics I 20 0 km FIGURE FIGURE 1: 1: LOCATION LOCATIONOF OFCOPPER COPPERSULFIDE SULFIDEDEPOSITS DEPOSITS References References - ,< . Bornhorst, Bomhorst, T. T. J., J., 1997, 1997,Tectonic Tectoniccontext contextof ofnative nativecopper copperdeposits deposits of of the the North North American American Midcontinent Midcontinent Rift Rift System: System: Geological GeologicalSociety Societyof ofAmerica AmericaSpecial SpecialPaper Paper 312, 312, p. p. 127-136. 127-136 Butler, deposits of of Michigan: Michigan: U. S., 1929, 1929, The copper deposits U. S. S. Geol. Geol. Survey Survey Prof. Prof. Butler, B. S. and Burbank, W. 5., Paper 238 p.p. Paper 144, 144,238 Robertson, Robertson, J. M., M., 1975, 1975, Geology Geologyand andmineralogy mineralogy of of some somecopper coppersulfide sulfidedeposits depositsnear near Mount Mount Bohemia, Bohemia, Keweenaw Keweenaw County. County, Michigan: Economic Economic Geology, Geology, v. v. 70, 70, p.p.1202-1224. 1202-1224. 34 �CHEMICAL AND AND MINERALOGICAL MINERALOGICAL COMPARISON COMPARISON OF OF BARABOO, BARABOO, BARRON, BARRON, AND AND SIOUX SIOUX CHEMICAL ARGILLITE, METAPELITE AND PIPESTONE ARGILLITE, METAPELITE AND PIPESTONE MEDARJS, L.G., Jr., of MEDARIS, L.G., Jr., and and FOURNELLE, FOURNELLE, J.H., J.H., Dept. Dept. of of Geology Geology & & Geophysics,Univ. Geophysics,Univ. of Wisconsin-Madison,53706, 53706,medaris@geology.wisc.edu, inedarisgeology.wisc.edu, johnf@geology.wisc.edu; johnfgeo1ogy.wisc.edu; Wisconsin-Madison, BOSZHARDT, BOSZHARDT, RI., RF.,Mississippi MississippiValley ValleyArchaeology ArchaeologyCenter, Center,Univ. Univ.ofofWisconsin-La Wisconsin-LaCrosse, Crosse, 54601, rboszhar@uwlax.edu; J.H., State rboszhar@uwlax.edu, BROII{AHM, BROBHAHN, J.H., State Historical Society Society of of Wisconsin-Madison, 53706, John.Broihahn@ccmail.adp.wisc.edu 53706, John.Broihahn@ccmail.adp.wisc.edu Early Early Proterozoic Proterozoic (1760-1630 (1760-1630 Ma) Ma) red red quartzites quartzitesin in the the southern southern Lake Lake Superior Superiorregion region place place important important constraints on the climatic, sedimentary, and tectonic history of North America, and fine-grained constraints on the climatic, sedimentary, and tectonic history of North America, and fine-grained sedimentary and hydrothemially hydrothermally altered rocks in sedimentaly in the quartzite sequences sequences have provided material for for Native Native artihcts. Although American artifacts. Althoughargillites argilhtesand andpipestones pipestonesfrom fromseveral severallocalities localities have have been been investigated investigated freviously by previously by X-ray X-ray diffiaction, diffraction, little littleattention attentionhas hasbeen beenpaid paid so sofar firto totheir theirchemical chemical compositions compositions and and textural details. Representative samples of Baraboo, Barron, and Sioux argillite, metapelite, and pipestone Representative samples of Barabw, Ban-on, and Sioux have been investigated by by petrographic petrographic microscope, XRF, XRD, and EMP to determine textural characteristics to determine their textural characteristics and and chemical and and mineralogical mineralogical compositions. compositions. Such chemical Such information information provides provides aa basis basis ibr for evaluating evaluatingpossible possibleregional regional variations variations in in chemical compositions and metamorphic metamorphic conditions among conditions among the artifact determining artifact the quartzite quartzite localities localities and and for for determining provenances. provenances. Bamboo: fine-grained metasedimentary metasedimentary layers, Barabw: layers, several several to several several feet feet in inthickness, thckness, are interbedded interbedded with inches to quartzite and vary varyfrom frompink pink argillite argillite(metasiltstone) (metasiltstone) to gray phyllonite (metapelite), depending on on the the proportions proportions of quartz and pyrophyllite. Pipestone occurs Pipestone occursin in several several small pipestone quarries and one outcrop near the base of the quartzite sequence sequence in the south south limb of the the Bamboo Baraboo syncline. syncline. The pipestone is a dark purplish-red argillite, aigillite, consisting of quartz, quartz, pyrophyllite, and and hematite, hematite, which which is is cut cut by by thin thin white white hydrothermal veins containing pyrophyffite, muscovite, and hydrothermal containing pyrophyllite, and diaspore. In several pipestone samples, argillite itself has In several pipestone samples, argillite been altered to an assemblage assemblage of of muscovite-pyrophyllitemuscovite-pyrophyllitediasp ore-hematite, in in which which quartz quartz has been replaced diaspore-hematite, replaced largely largely by pyrophyllite (Fig. 1). Small amounts of kaolinite in 1). Small amounts of kaolinite inthe the metasedimentary rocks and and pipestone pipestone are are retrograde retrogradein in origin, origin, replacing replacing pyrophyllite pyrophyllite or or muscovite. muscovite. Barron: four samples fow samples of of discarded discardedpipestone pipestone were collected in the vicinity of a pipestone pipestone quarry quarryin in the the Doyle Doyle Barron County. The Forest Unit, Barren Thepipestone pipestoneisis aamassive massive to laminated red argillite, which contains quark, quartz, hematite, hematite, and and large vermicular grains of vermicular-grains of kaolinite kaolmite (Fig. 2). 2). Sioux: two samples M: samples of of pipestone pipestone from from Pipestone Pipestone National Monument and one of flaggy aigillite argillite from the Jasper quadquadrangle (sec. 32, Tl 04N, R4W) T104N, R4W) were were provided by David and Tony Tony Runkel. Runkel. The Southwick and Thepipestone pipestone samples samples are are typical catlinite, catlinite, being being fine-grained fine-grainedand and deep deepred red in in color, color, m: 35 �I locally with small pale orange-red reduction spots and pale gray elliptical domains. The Thepipestone pipestone mineral mineral assemblage assemblage is pyrophyllite-diaspore-muscovite-hematite, pyrophyllite-diaspore-muscovite-hematite,and the pale pale gray gray elliptical elliptical domains domains are are largely largely pyrophyllite with minor diaspore and muscovite (Fig. 3). Small Smallamounts amountsof ofkaolinite kaoliniteare are retrograde retrogradeafter after argillitecontains containsquartz, quartz,hematite, hematite,pyrophyllite, pyrophyllite,and and traces tracesof of detrital detrital pyrophyllite and muscovite. The Theargillite muscovite. muscovite. Chemical Comoosition Composition Six are Six samples samples of Baraboo, Barron, Barron, and Sioux Sioux argillite and metapelite are of Na,0 Na20 and CaO CaO and and contain wntain less than than essentially devoid of 0.39 wt% wt% K20, K,0, attesting attestingto totheir theirextreme extreme chemical chemical Rock Compositions in the q Baraboo Baron ICASH System matunty and maturity and contrasting contrastingmarkedly markedly with with the the composition composition of Projected onto tle KAS Plane Sioux average shale (Fig. (Fig. 4). Relative argillite and average Relative to to argiuite shale, the K-rich and Si-poor Si-poor compositions wmpositions of Bamboo Baraboo and and 19 Si Sioux pipestones (0.66-5.62 wt% lC,O Sioux K,0 and 40.90-54.20 wt% SiOJ 5i02) indicate wt% indicate that they may have have formed from ppestone argillite by addition of K and removal of Si through argilhte hydrothermal activity. Such Suchaa process processcould could account account for kin estone and replacement of quartz quartzin inBaraboo Baraboopip pipestone and the replacement suggests suggests that that the the elliptical ellipticalpyrophyllite pyrophyllite domains domains in in Sioux Sioux K pipestone may also be the result of quartz pipestone replacement. replacement. 8 Metamorphic Metamomhic Conditions: the Barron Ban-on argillite argiUite assemblage, quartz-kaolinite, assemblage, quartz-kaolimte, is limited to 6 at 22 kbar kbar (Fig. (Fig. 5). 5). The temperatures below 3300°C 0 0 T at The Bamboo and Baraboo and Sioux Siouxargilhite argillite assemblage, quartzquartzpyrophyllite, is stable stable between 300 and 390°C 3 9 0 T at 2 -. kbar, and and the the pipestone pipestone assemblage, assemblage, pyrophyllitepyropbyllite22 muscovite-diaspore, is is more more narrowly narrowlyconfined confined between 3315 and 360° 360°C (Fig. (Fig. 5). 5). The Baraboo and hetween 15 and Sioux assemblages assemblages cannot cannotbe be due due to to burial burial alone, alone, o o 450 350 400 250 300 because depths on the order of 18-19 18-19 km k m would be 250 300 350 400 450 T C T, "C required to reach reach 300°C 'raton quiredm 3000c for a typical stable craton 5 Reactions Fig. 5 Fig. Reactions in in the the KASH KASH system system and and assemblages assemblages conductive g geotherm. conductive ~ t h e n n The .Theage ageand andsource source of the u Bamboo, Barron, in Ban-on, and and Sioux Sioux rocks rocks thermal pulse responsible responsible for for Baraboo Baraboo and and Sioux Sioux metamorphism remains uncertain. In Inaddition, addition,kaolinite kaolinite is is widely reported in the Sioux Quartzite, and it is was ubiquitous in the the Sioux Quartzite (as it was was in the Baraboo quartzite), unclear whether metamorphism was or restricted restricted to to zones zones of of hydrothermal hydrothermal activity, activity, perhaps perhapsrelated relatedto tofaulting. faulting. Conclusions: Conclusions: the thechemical chemicalcompositions wmpositionsof ofargillite argilliteand andmetapelite metapeliteconfirm confirmthe the chemical chemicalmaturity maturity of of all all sedimentary members of the Bamboo, Barron, and Sioux sequences, consistent with derivation from a Baraboo, Barren, and Sioux sequences, consistent with derivation from a deeply weathered, weathered, low-relief low-relief source source in in an an Early Early Proterozoic Proterozoic warm, warm, humid humid climate. climate. Comparable Comparable mineral assemblages in Bamboo assemblages Baraboo and and Sioux Siouxpipestones pipestonesdemonstrate demonstratethat thatthe thepromotmg promotinghydrothennal hydrothermalactivity activitydoes does not coincide with the 1630 1630 Ma thermal front in the southern Lake Lake Superior Superiorregion, region, postulated postulatedby by Hoim Holm et et al. (1998); (1998); whether whether they are are contemporaneous remains remains to be seen. Regarding Regarding artifact artifactprovenance, provenance, Barron Barron pipestone is easily easily distinguished distinguished from Bamboo Baraboo and and Sioux Siouxpipestone pipestone by by the the presence presence of of vermicular vermicular kaolinite. kaolinite. Comparable Comparable mineral mineral assemblages assemblagesand and textures texturesmake makediscrimination discriminationbetween between Baraboo Baraboo and and Sioux Siouxpipestones pipestones more difficult. Baraboo Baraboopipestone pipestonemay maycontain wntainquartz, quartz,isislocally locallycut cutby bythin, thin,white white veins, veins, and and is is dark dark purplish purplish red red in in color; color; Sioux Siouxpipestone pipestoneis isdevoid devoid of of quartz quartzand andveins, veins, commonly commonly has has reduction reduction spots spotsand and conspicuous, conspicuous, small, small, pale pale gray, gray,elliptical ellipticalpyrophyllite-rich pyropbylhte-rich domains, domains, and and isis deep deep red red to to orange orangein in color. color. 36 �REPUBLIC REPUBLIC WETLAND PRESERVE John G. G. Meier - District DistrictManager Manager— Environmental Environmental Affairs Affairs Cliffs Cliffs Mining Milling Services Company Iron Iron ore ore mining, mining, by by its its very very nature, nature, causes causes large large potential impacts to natural resources. Development Developmentof of mine mine pits, pits, rock rock stockpiles stockpiles and and tailings tailings basins basins impacts impacts wetlands wetlands from time to to time. time. Permits Permitstotoimpact impactwetlands wetlandsare areissued issuedby by the the Michigan Michigan Department Department of Environmental EnvironmentalQuality Quality ifif the the impacts impacts are are "unavoidable" "unavoidable" and and are are "minimized "minimized to to the the greatest greatest extent extent possible". possible". Each Eachpermit permitrequires requiresthat that"compensatory "compensatory wetland wetland mitigation" mitigation" be be provided. provided. The The Republic RepublicWetland WetlandPreserve Preserveisis being being created created at at the the former former Republic Republic Mine Mine tailings tailings basin basin to to provide providecompensatory compensatorywetland wetland mitigation mitigation for for those unavoidable unavoidable impacts to wetlands wetlands at at other other mining operations. operations. Instead Insteadof of merely merely draining draining the water from the various various tailings tailings and and water water clarification clarification ponds and converting the land to upland at Republic, Cliffs, with MDEQ oversight, is in these these areas. areas. Several is constructing wetlands in hundred hundred acres acres of creditable creditable wetland will be created. This This wetland area, area, along along with adjacent upland and external external preservation area, will be placed in a Conservation Easement Easement for for the the benefit benefit of the the State State for long term protection. 37 �POTENTIAL PGE IN POTENTIALFOR FORSTRATIFORM STRATIFORM PGEMINERALIZATION MINERALIZATION IN MAFIC LAYERED INTRUSIONS COMPLEX MAFIC LAYERED INTRUSIONSOF OFTHE THEDULUTh DULUTH COMPLEX MILLER, 55114 MILLER,James JamesD., D.,Jr., Jr.,Minnesota MinnesotaGeological GeologicalSurvey, Survey,2642 2642University UniversityAve., Ave.,St. St.Paul, Paul,MN MN 55114 (mille066@maroon.tc.unm.edu) (mille066@maroon.tc.umn.edu) Economic Economicconcentrations concentrationsof ofplatinum platinumgroup groupelements elements(PGEs) (PGEs)ininmeter-thick, meter-thick,stratiform, stratiform,sulfide-bearing sulfide-bearing horizons horizons(reefs) (reefs)have havelong lonebeen beenknown knowntotobebeassociated associatedwith withultramafic-mafic ultramafic-maficlayered layeredintrusions intrusionssuch suchasas the theBushveld ~ u s h i e land dA dStillwater Stillwatercomplexes. complexes. Recent Recentdiscoveries discoveriesofofPGE PGEmineralization minerali&on ininthe theSkaergaard Skaergaard Intrusion Intrusionand andrelated relatedbodies bodiesininGreenland Greenland(Bird (Birdetetal., al.,1991, 1991,1995; 1995;Neilsen Neilsenand andBrooks, Brooks,1995; 1995;Aranson, Aranson,etet - al., al., 1997; 1997;Andersen Andersenetetal., al.,1998) 1998)have haveshown shownthat thatstratiform stratiformPGE PGEmineralization mineralization can can also alsooccur occurinin tholeiitic tholeiiticlayered layeredintrusions. intrusions.The Thepresence presenceofofmany manytholeiitic tholeiiticmafic maficlayered layeredintrusions intrusionsassociated associatedwith withthe the 1.1 1.1 Ga GaMidcontinent MidcontinentRift Riftsuggests suggeststhat thatthe theLake LakeSuperior Superiorregion region isisfertile fertileground groundfor forexploration explorationof ofthis this newly newlyrecognized recognizedtype typeof ofPGE PGEmineralization. mineralization. With Withthe thesupport supportofofthe theState StateofofMinnesota's Minnesota'sMinerals Minerals Coordinating the been assessing coordinatingCommittee ~ommi'ttee theMinnesota MinnesotaGeological GeologicalSurvey Surveyhas hasbeen assessingthe thepotential potentialfor forstratiform stratiform PGE PGE mineralization mineralization in in two twointrusions intrusionsof ofthe theDuluth DuluthComplex—the Complex-the Layered Layered Series Series at at Duluth Duluth and andthe the Sonju SonjuLake Lakeintrusion intrusion(Miller (Millerand andRipley, Ripley.1996). 1996). Based Skaergaardand andother othertholeiitic tholeiitic Based on onempirical empiricalobservations observations of ofPGE PGEmineralization mineralizationin inthe theSkaergaard intrusions, intrusions, and andon ontheoretical theoreticalconsiderations considerationsof ofsulfur sulfurand andPGE PGEbehavior behaviorinindynamic, dynamic,differentiating differentiating intrusions, intrusions, the the conditions conditions that that favor favorthe theformation formationofofPGE-enriched PGE-enrichedhorizons horizonsinintholeiitic tholeiiticlayered layered intrusions intrusionsare: are: 1.1.The undersaturated Theparent parentmagma magmaisisinitially initiallysulfide sulfideundersaturated. 2.2.The parent magma has a high initial PGE experiences &h experiencesaaconsiderable considerableamount amount The parent magma has a high initial PGEconcentration concentrationand/or of offractional fractionalcrystallization crystallizationtotobuild buildup upnoble noblemetal metalconcentrations concentrationsprior priorto tosulfide sulfidesaturation. saturation. of sulfide 3.3. The Theinitial initial segregation segregation of sulfide melt melt is is triggered triggered by by aaprocess processsuch suchasasmagma magmamixing, mixing, decompression, decompression, assimilation, assimilation, or or simple simple differentiation differentiation that that promotes promotes aa large large R-factor R-factor (silicatdsulfidemelt meltratio). ratio). (silicate/sulfide These Theseconditions conditionsimply implythat thatan anintrusion intrusionthat thatformed formedfrom fromananinitially initiallysulfide-undersaturated, sulfide-undersaturated,tholeiitic tholeiitic parent parentmagma magmahas hasthe thebest bestchance chancefor forsignificant significantPGE PGEmineralization mineralizationin in the themidmid- to toupper-level upper-level horizon horizon that that marks marksthe thefirst first"cumulus "cumulusarrival" arrival"ofofimmiscible immisciblesulfide sulfidemelt. melt. Theoretically, Theoretically, aa gabbro gabbrocumulate cumulate crystallized crystallizedfrom fromaamagma magmasaturated saturatedininsulfide sulfideshould shouldcontain containgreater greaterthan than400 400ppm ppmsulfur sulfur(Boudreau (Boudreauand and McCallum, McCallum, 1992). 1992).Regardless Regardlessofofhow howsulfide sulfidesaturation saturationisistriggered, triggered,ororthe theway wayininwhich whichsulfide sulfide melt melt arrives arrives at atthe themagma magmachamber chamberfloor, floor,ititisislikely likelythat thatthe thefirst firstsignificant significantsulfide-saturated sulfide-saturated melt melt has has the the greatest greatestchance chanceof ofencountering encounteringthe themost mostPGE-enriched PGE-enriched silicate silicate magma. magma. Thus, Thus, exploration exploration for foraaPGEPGEenriched enrichedhorizon horizonshould shouldattempt attempttotoseek seekout outthe thestratigraphically stratigraphicallylowest lowestgabbroic gabbroiccumulates cumulatesthat thatcontain contain 400 ppm ppm SSor ormore. more. The The Cu/Pd Cfld ratio ratioindicates indicatesthe theeffectiveness effectiveness of of the thesulfide-saturated suicide-saturated melt melt inin 400 scavenging of magnitude scavengingchalcophile chalcophilemetals metalsfrom fromthe thesilicate silicatemagma. magma. Because BecausePd Pdisisseveral severalorders. ordersof magnitude more more compatible Cu,an anefficiently efficientlyscavenged scavengedsilicate silicatemelt meltshould shouldrecord recorda asignficant signficant compatiblewith with sulfide sulfidemelt meltthan thanCu, increase increasein inCu/Pd CuIPdafter afteraasulfide-segregation sulfide-segregationevent. event. These (DLS,Miller, Miller,1998). 1998). Thesegeochemical geochemicalcriteria criteriawere werefirst firstapplied appliedtotothe theLayered LayeredSeries SeriesatatDuluth Duluth(DLS, The TheDLS DLSisisaa3.53.5-toto4-km-thick, 4-km-thick,well-differentiated, well-differentiated,layered layeredintrusion intrusionemplaced emplaced into into the the basal basal section section of of comagmatic Keweenawan Keweenawan volcanics volcanics in in the the vicinity vicinity of of Duluth. Duluth. The The DLS DLS isis composed composed of of aa comagmatic unidirectionally troctolite(P1+01) (Pl+01) to gabbro gabbro unidirectionally differentiated differentiatedsuite suiteof of mafic maficcumulates cumulatesthat that grades grades up up from from troctolite and (Pl+Aug+Fem±O1±Ap and displays displays aa complementary complementary cryptic cryptic variation variation inin cumulus cumulus mineral mineral (Pl+Aug+Fe0±0l±Ap), compositions. 1-km-thickinterval interval compositions. The Thetransition transitionfrom fromtroctolitic troctolitictotogabbroic gabbroiccumulates cumulatesoccurs occurs in inan an1-km-thick called called the thecyclic cycliczone zonewherein whereinP1+01 Pl+01cumulates cumulatesgrade gradeupward upwardto toPl+Aug+Fe0,,+0l Pl+Aug+Fe-+01 cumlates, cumlates, and and regress regress abruptly abruptly back back to to P1+01 Pl+01 cumulates. cumulates. The Thecyclic cyclic zone zone isismade made up upof ofasasmany manyasassix sixsuch suchmacrocycles, macrocycles, 38 �which implies that despite despite being being well-differentiated, well-differentiated, the DLS magma system was open open to to recharge rechargeand and venting (Miller and Ripley, 1996). (Miller and Ripley, 1996). Sulfur concentrations indicate that that the DLS was initially sulfide undersaturated undersaturated and and did did not reach Cu/Pd ratios begin to show sulfide saturation until the onset begin show irregular irregular onset of of cyclic cyclic zone zonecrystallization. crystallization. CuRd upsection from from the the base base of of the the cyclic cyclic zone. zone. The though significant increases upsection The irregular irregular increase in Cu/Pd CuIPd ratios probably reflects the open nature of the DLS system. Interestingly, Interestingly,the theanomolous anomolous concentrations concentrations of sulfur sulfur and PGEs occur occur at macrocycle macrocycleboundaries, which I interpret interpret to to indicate indicate venting venting and/or and/or recharge recharge events. These observations suggest that a PGE-enriched sulfide reef may exist near the base of cyclic These observations suggest that a PGE-enriched reef may zone, and may correspond correspond to to aa horizon horizon indicative indicativeof of open-system open-system perturbations perturbations to to the the DLS DLSmagma. magma. the stratiform PGE PCE potential potential of of the Sonju Lake Geochemical studies were recently initiated to study the intrusion (SLI) near Finland, Minnesota. The The SLI SLI isis aa 1-km 1-km thick, sheet-like sheet-like intrusion that was emplaced beneath beneath a granophyre granophyre body. body. It is is aa completely completely differentiated differentiated intrusion intrusion that displays a very very regular, regular, unidirectional cumulus paragenesis: Ol—>Pl+Ol—>Pl÷Aug+Ol—>Pl+Aug+Fe—>Pl+Aug+Fe+Ol+ unidirectional paragenesis: 01->P1+01->Pl+Aug+01->Pl+Aug+Fe_->Pl+Ang+Fe_+Ol+ Ap. This Thisphase phaseprogression progressionand andaasmooth smoothcryptic crypticvariation variationin inmineral mineral composition composition indicate indicate that that the the SLI SLI crystallized as an almost The SLI is the intrusion most most similar to the crystallized almost closed closed system. system. The the Keweenawan Keweenawan intrusion the Skaergaard. Geochemical analyses of sulfur and PGEs have not yet been completed for the SLI. Skaergaard. Geochemical analyses of sulfur and PGEs have not yet been completed for SLI. Previous analyses included Cu which provides indirect evidence for for the the abundance abundance of of sulfide in in the SLI cumulates. The TheCu Cuconcentration concentrationshows shows aa dramatic dramatic 5-fold Sfold increase increase (from cl0Oppm e100ppm to >500 >500 ppm) ppm) at at aa level equal to 2/3 2.13 of of its itsthickness. thickness. This change is level above above the base base of of the theintrusion intrusion approximately approximately equal approximately midway midway through cumulate interval; interval; notably, notably, it is at approximately through the Pl+Aug+Fe0, Pl+Aug+Fe cumulate at the theequivalent equivalent stratigraphic level, and within the same cumulate type as the Platinova reef of the Skaergaard stratigraphic the same cumulate as the Platinova reef of the SkaergaardIntrusion Intrusion ILSGmeeting. meeting. (Andersen et al., 1998). 1998). I anticipate anticipate reporting reporting geochemical analyses for the SLI SLI at at the theILSG horizon in They will provide more direct evidence of the potential potential for aa PGE-enriched PGE-enriched sulfide-bearing horizon the upper part of SLI. may exist in the In conclusion, these studies studies suggest suggest that that significant significant PGE mineralization mineralization may the medial medial orupper parts of the DLS and SLI intrusions, as well as in other tholeiitic layered intrusions of the the orupper parts of DLS and SLI intrusions, as well as in other tholeiitic layered intrusions of Midcontinent Rift. Moreover, demonstrate that that geochemical geochemical criteria criteria can can be be used (1) to Moreover, these studies demonstrate to evaluate the overall potential for stratiform stratiform PGE mineralization in tholeiitic mafic intrusions, and (2) to Because potential PGEassist in assist in identification identification of of favorable favorableintervals intervalswithin within individual individual intrusions. intrusions. Because PGEmineralized horizons horizons are likely likely to be meter-scale and contain contain only only a few modal percent meter-scale in thickness, thickness, and sulfide, core drilling drilling and and systematic systematicgeochemical geochemical sampling sampling are are necessary necessary to to confirm confirmtheir their existence. existence. References :.,!, J.C.ø., Rasmussen, J.G., 1998, The Triple Group and the Platinova gold and palladium Andersen, J.C.0.. Rasmussen, H., H., Neilsen, Neilsen, T.F.D., T.F.D., Rønsbo, R~nsbo.J.G., reefs in relations: ECONOMIC ECONOMIC GEOLOGY, 488-509. reefs in the the Skaergaard SkaergaardIntusion—stratigraphic Intusion-stratigraphicand andpetrographic petrographic relations: GEOLOGY, v.93, v.93, p. 488—509. DX., Bernstein, PB., 1997, J.G., Bird, D.K., Bernstein, S. and and Kelemen, Kelemen, P.B., 1997, Gold Goldand andplatinum-group platinum-groupelement element mineralization mineralization in the Aranson, J.G., Kruuse ECONOMIC Kmuse Fjord FjordGabbro Gabbrocomplex. complex.East EastGreenland: Greenland: ECONOMICGEOLOGY, 490-501. GEOLOGY,v.92, v.92, p. 490—501. Bird, D.K., Bird, D.K., Brooks, C.K., C.K., Gannicott, Gannicott, R.A., R.A., Turner, P.A., P.A., 1991, 1991, A A gold-bearing gold-bearing horizon horizon in the the Skaergaard Skaergaard Intrusion, Intrusion, East East Greenland: GEOLOGY, v. 092. ECONOMIC GEOLOGY, v. 86, 86,p.p.1083—1 1083-1092. Greenland:ECONOMIC Brandriss. ME., M.E., Nevle, Nevle, R.J., Kelerotn, P.R., P.B., 1995, 1995, Bird, Bird, D.K., D.K., Aranson, J.G., IC., Brandriss, It)., Radford, G., C., Bernstein, S., Gannicott, R.A.. R.A., and Kelemen, A gold-bearing gold-bearing horizon East Greenland: ECONOMIC ECONOMICGEOLOGY, 90. p. 1288—1300. 1288-1300. A horizonininthe theKap KapEdvard EdvardHoIm HolmComplex, Complex, East Greenland: GEOLOGY,v.v.90, by magmatic fluids in layered intrusions: Boudreau, A.E. A.E. and McCallum, McCallum, 1.8., IS., 1992, 1992, Concentration of platinum-group elements by intrusions: ECONOMIC GEOLOGY, v. 87, ECONOMICGEOLOGY, 87.p.p.1830—1848. 1830-1848. J.D., Jr., 1998, 1998,Potential Potential for for stratiform stratiform POE PGE deposits deposits in sulfide-undersaturated, sulfide-undersaturated, tholeiitic layered intrusions of the Duluth Miller, J.D.. Complex. Complex, Minnesota, Minnesota, USA. USA. 8th 8th International International Platinum Platinum Symposium Symposium Abstracts, Abstracts, Rustenburg, Rustenburg, South South Africa, Africa, GSSA GSSA and and SAIMM Symposium Symposium Series Series 518. S18,p.263—266. p. 263-266. J.D.. Jr.. Jr., and Ripley, Ripley, E.M., E.M., 1996, 1996,Layered Layeredintrusions intrusions of of the the Duluth Duluth Complex, Complex, Minnesota, Minnesota, USA, USA, in in Cawthorne, R .G.,ed., Miller, J.D., R.G., Layered Layered Intrusions: Intrusions:Amsterdam, Amsterdam,Elsevier ElsevierSci., Sci..p.p.257—301. 257-301. T.F.D. and Brooks, East Greenland: Greenland: Factors Factors important important to tothe themineralization mineralization Neilsen, T.F.D. Brooks, C.K., C.K., 1995, 1995,Precious Preciousmetals metals in in magmas magmas of of East in ECONOMIC GEOLOGY, v. 90, ECONOMICGEOLOGY, 90,p.p.1911—1917. 1911-1917. in the theSkaergaard SkaergaardIntrusion: Intrusion: 39 �NEW GEOLOGIC MAP OF THE CENTRAL DULUTH COMPLEX MILLER, James D., D., Jr., Jr., and and CHANDLER, CHANDLER, Val. Val. W., Minnesota Minnesota Geological Geological Survey, Survey, University of of Minnesota, 2642 University Ave., Ave., St. Paul, MN MN 55114 orchand004@tc.umn.edu) 551 14(milleO66 (mille066 or chand004@tc.umn.edu) The Minnesota The Minnesota Geological Geological Survey Survey is is preparing preparing aa new new interpretation interpretation of of the the geology geology of of the the central central part pan of of the Duluth Complex, 00,000-scale man mapthis thissummer. summer. The map 1: 100.000-scale mao will cover cover Comnlex. which which will be published nublished as a 1:1 and lat. rectangular area and 9101510011 aa rectangular areaof ofabout about1,100 1,100square squaremiles milesbounded boundedbybylong. long.92°07'30" 92007'30 and 91°15'00 andlat. 47°37'30" and Both the the southeastern southeastern comer corner of of the the map map area, area, which which is is anchored anchored to to the the Lake Lake 47'37'30 and 47°15'OO". 47°15'00" Both Superior shoreline contact of Superior shoreline near near Silver Silver Bay, Bay, and and the the northwestern northwestern corner, comer, which which covers the the basal basal contact of the the Duluth Complex, Duluth Complex, have have adequate adequatebedrock bedrock exposure exposure that that has has been been mapped mapped at at the the scale scale of of 1:24,000 1:24,000 (Miller, (Miller, Miller and others, 1993; 1988; Miller 1993; Severson and Hauck, 1990; Severson and Miller, 1999). However, However, the the intervening area, area, roughly roughly 90% 90% of of the the map map area, area, contains contains little little or orno nobedrock bedrockexposure. exposure. Geologic Geologic intervening evaluation of of aeromagnetic aeromagneticand andgravity gravitydata. data. Geologic interpretations in in this area largely depend on evaluation control for the the geophysical geophysical data data is is limited limited to to widely widely and and unevenly unevenly dispersed dispersed drill cores as as well well as as scattered scattered outcrop (Severson, 1971). areas of outcrop (Severson, 1995; 1995; Chandler Chandler and others, others, 1991; 1991;Bonnichsen, 1971). The bedrock geology geology of the the map area area is is dominated by intrusive intrusive rocks that were emplaced emplaced into into the the basaltic North North Shore Shore Volcanic Volcanic Group Group (NSVG) (NSVG) during during the the main main lower and medial portionS portions of the largely basaltic stages of the Midcontinent Rift magmatism (Paces and and Miller, Miller, 1993). 1993). The intrusive rocks can be grossly subdivided into those belonging to the more plutonic Duluth Complex and those more subdivided into those belonging to the more plutonic Duluth Complex and those composing composing the the more intrusions of the Beaver Bay Complex. The complexes hypabyssal intrusions The boundary boundary between between two intrusive complexes corresponds to a semi-continuous semi-continuous septa septa of strongly hornfelsed homfelsed volcanic rocks, locally containing minor corresponds the middle middle of of the the map maparea area(Fig. (Fig. 1). 1). Large-scale intrusions of of intrusions, that trends northeasterly through the differentiated mafic cumulates, cumulates, gabbroic gabbroic anorthosites, &orthosites. gabbros, gabbros, and &d granophyres pnophyres compose the Duluth Complex northwest of the volcanic septa. Southeast Southeast of of the the volcanic volcanic septa, septa, smaller scale, sheet-like bodies and dikes dikes of mafic mafic cumulate cumulate rocks, rocks, gabbro, gabbro,diabase. diabase, diorite dionte and granophyre granophyre constitute constitute multiple multiple intrusions intrusions of the Beaver Beaver Bay Bay Complex Complex that that were were emplaced emplaced into into higher higher levels levels of the the volcanic volcanic edifice. edifice. A number of intrusive components can be be distinguished distinguished within within the theDuluth DuluthComplex. Complex. The oldest is a structurally structurally complex complex assemblage assemblageof of mostly mostly leucogabbroic leucogabbroic to to anorthositic anorthositic rocks, small bodies of olivine olivine oxide hornfels (collectively (collectivelytermed termedAGV AGVin inFigure Figure IA). 1A). This oxide gabbro, and scattered inclusions of volcanic homfels assemblage assemblage corresponds correspondsto to aa very very heterogeneous heterogeneous aeromagnetic aeromagneticsignature signature of variable variable amplitude amplitude in the to aa more more subdued subdued signature signaturetotothe theeast east(upsection). (upsection). The The western part of the complex but gives rise to consistently anorthositic anorthositic compositions. compositions. Irregular masses of change may indicate a transition to more consistently granophyre granophyre occur occur within the the eastern eastern part of the the AGV, AGV, but contact contact relationships relationships are not exposed in the study area. Aeromagnetic Aeromagneticpatterns patternssuggest suggestthat thatthe thesubcircular subcircularto tolensoidal lensoidalgranophyre granophyrebodies bodieswere were emplaced emplaced into into the the AGV, AGV, but but exposures exposures outside outside the map map area (Boerboom (Boerboom and Miller, 1994) 1994) indicate indicate that large granophyre granophyrebodies bodies can can be be older olderthan than the the anorthositic anorthositic rocks. More than half half of of the the Duluth Duluth Complex Complex in in the the map map area area is composed of six discrete mafic layered layered intrusions intrusions which were were emplaced emplaced beneath beneath and and within the AGV and, in one case, beneath a body of granophyre. granophyre. The Thestratiform stratiforminternal internalstructure structureofofthese theselayered layeredintrusions intrusionsgives givesrise riseto toaacrudely crudelybanded banded aeromagnetic aeromagnetic pattern. pattern. Truncations Truncationsofofthe thepatterns patternsimply implyaageneral generalsequence sequenceof ofemplacement emplacementand andsuggest suggest that successive successiveintrusions intrusions overplated overplated previous intrusions. intrusions. Although Althoughthe theigneous igneousstratigraphy stratigraphyof ofeach each intrusion is generally generally poorly known, known, some some notable differences differences are evident. Apparently, Apparently, the theoldest oldestlayered layered mafic intrusion intrusion is is the the Partridge Partridge River River intrusion intrusion (PRI), which forms the basal contact in the northwestern by frequent frequent PRI suggests suggests that it formed by part of the map area. The Thepreponderance preponderanceof of troctolite troctolitein in the the FRI truncated by by the impulses of magma and little internal differentiation. The The northeast end of the PRI is truncated South Kawishiwi South Kawishiwi intrusion intrusion (SKI). (SKI). Where Whereititisismore morecompletely completelyexposed exposedin inthe theGabbro GabbmLake Lakequadrangle quadrangle dominatedby bytroctolite. troctolite. At its southern end, end, the the to the north (Green and others, 1966), 1966). the SKI is also dominated PRI is overplated overplated and and ultimately cut cut out out by another another intrusive intrusive body that is almost entirely unexposed except for a few drill except drill holes holes along along its its basal basal contact contact and some some troctolite emplaced into the AGV hanging wall of the PRI. This Thisintrusion, intrusion,which whichwe wetentatively tentativelycall callthe theWest-central West-centralmargin marginintrusion, intrusion,has hasaa subdued subdued aeromagnetic aeromagnetic signature signature indicative indicative of troctolitic troctolitic cumulates. cumulates. The Thesubdued subduedpattern pattern passes passesupsection upsection into a busy, high-amplitude high-amplitude signature signature that that shows shows some some banding and thus may indicate the presence of roof zone. The upper gabbroic cumulates beneath an AGV roof The Greenwood Lake intrusion (GLI) is a somewhat isolated somewhat isolated intrusion intrusion that that truncates truncates the the SKI SKI but otherwise otherwise intrudes AGV and granophyre rocks. troctolite The GLI is unique in in that that itit contains contains aa complete complete differentiation differentiation sequence sequence that grades from lower troctolite 40 �cumulates cumulatesto to upper upper oxide oxide gabbro gabbro cumulates. The Thenorthern northern extent extent of of the the GLI GLI is is truncated by the southern margin margin of of the the troctolitic troctolitic Bald BaldEagle Eagleintrusion, intrusion,apparently apparentlythe the youngest youngest major major mafic mafic layered layered intrusion intrusion in in the the map map area. area. The TheOsier OsierLake Lakeintrusion intrusionisisaasmall, small,plug-like plug-likebody body of of troctolite troctolite cored by gabbro gabbro cumulates that that is is known known from from two two drill drill core core and a bull's-eye aeromagnetic signature. It It was was emplaced entirely entirely into anorthositic anorthositicrocks rocks of of the the AGV, AGV, and andthus, thus,its itsage agerelative relative to to other other layered layered intrusions intrusions is is unknown. unknown. Intrusions Intrusionsof of the the Beaver BeaverBay Bay Complex Complexoccur occuras asseveral severalsuites suites of of east-dipping, east-dipping, half-saucer-shaped half-saucer-shaped sheets, anomaly patterns. patterns. The largest and sheets, which which produce produce very very distinctive, concentric concentric aeromagnetic anomaly earliest to be be aa nested nested set set of of earliestintrusive intrusivesuite suiteis is the the Cloquet Cloquet Lake Lake layered layered series (CLLS), which appears to sheet-like sheet-like intrusions. intrusions.ItItisisdifficult difficulttotoaccurately accuratelydetermine determinethe thecompositional compositionalvariability variability of of the the CLLS CLLS because dozen or so drill drill core. core. In In general, general, the the lower lower becauseitit is is completely completely unexposed unexposed and and penetrated penetrated by only a dozenor part part of of the the series seriesappears appearsto tobe becomposed composedof ofatatleast leasttwo twodifferentiated differentiatedsequences sequencesof of troctolitic troctolitic to to gabbroic gabbroic cumulates. cumulates.The Theupper upperpart partofofthe theseries seriesappears appearstotocontain containmore moreevolved evolvedintrusive intrusiverocks, rocks, including including gabbro, ferrodiorite,monzodiorite, monzodiorite,and andgranophyre, granophyre,as aswell wellas gabbro, ferrodiorite, asan an unknown unknown amount amountof of volcanic volcanic hornfels. hornfels. A A complex complexaeromagnetic aeromagneticpattern pattern emanating emanatingfrom fromthe thesouthern southernmargin margin of of the the CLLS CLLS may may be be caused caused by by numerous numeroussatellite satellitedikes dikesand and sheets sheetsemplaced emplaced into into volcanic rocks. The Theeastern easternside side of of the the CLLS CLLS is is cut cut by another anothersheet-like sheet-likebody—the body-the Sonju Sonju Lake Lake intrusion intrusion (SLI). This Thisstrongly stronglydifferentiated differentiated mafic mafii layered layered intrusion in the theFinland Finland quadrangle quadrangle(Miller (Millerand and others, others, intrusion isiswell wellexposed exposedjust just to tothe theeast eastof ofthe themap maparea areain 1993) of the the Finland Finland granite. granite. Good exposure 1993) and is is capped capped by ferromonzonitic to granophyric rocks of exposure in the the southern southernDoyle DoyleLake Lakeand andSilver SilverBay Bayquadrangles quadrangles(Miller, (Miller,1988; 1988;Miller Millerand and others. others, 1993) 1993)shows showsthat that the of the the Lax Lax Lake Lake gabbro. gabbro. Both the Finland Finlandgranite granitecuts cutsan an early early suite suiteof of gabbroic gabbroic to ferromonzonitic rocks of the the Finland Finlandgranite graniteand andthe theLax LaxLake Lakegabbro gabbromay mayoriginally originallyhave havebeen been part part of of the the CLLS CLLS but but were were disassociated are the disassociatedfrom fromitit by by the the intrusion intrusion of of the the SLI. SLI. The Theyoungest youngestintrusions intrusionsin in the the map map area area are anorthosite-inclusion-bearing is anorthosite-inclusion-bearing dikes dikes and and sills sills of the Beaver River diabase. This This intrusive intrusive swarm, swarm, which which is well exposed exposed in in the the southeastern southeastern corner comer of of the the map map area, area, is is bounded on the west by a prominent dike dike that feeds feeds into into southeast-dipping southeast-dipping sheets. sheets. The Theupper upperparts partsof ofthese thesesheets sheetscommonly commonly contain contain ferrogabbroic ferrogabbroic cumulate cumulatebodies, bodies, collectively collectivelytermed termedthe theSilver SilverBay Bay intrusions. intrusions. The 00,000-scale map of of the central Duluth Duluth Complex Complex will will represent represent aa significant significant improvement improvement on on The 1:1 1:100,000-scale previous previous regional regional geologic geologic maps maps of of the the complex. complex. Because Becausethis this map map will will be be digitally digitally compiled, compiled, we intend to to revise revise itit periodically periodically as as new new data data become become available. An Animportant importantcontribution contribution of this this new geologic map map isis that that itit will willidentify identifymany manypreviously previouslyunrecognized unrecognizedintrusive intrusivebodies bodies that that should should provide provide new new exploration explorationtargets targetsfor forstratiform stratiformPGE PGEdeposits. deposits. References References Bonnichsen, Bonnichsen, 8., B.,1971, 1971,Outcrop Outcropmap mapofofsouthern southernpart partofofDuluth DuluthComplex Complexand andassociated associatedKeweenawan Keweenawan rocks, rocks,St. St. Louis 1, scale Louis and and Lake LakeCounties, Counties,Minnesota: Minnesota:Minn. Minn. Geol. Geol. Surv. Surv. Misc. Misc. Map Map M-l M-11, scale 1:24,000. 1:24,000. Boerboom, Boerboom, T.J., T.J., and and Miller, Miller,J.D., J.D., Jr., Jr., 1994, 1994,Geologic Geologicmap map of of the the Wilson Lake Lake quadrangle and parts of the Silver Silver Island Lake and Toohey Lake quadrangles. quadrangles, Lake and and Cook Cook Counties, Counties,Minnesota: Minnesota: Minn. Minn. Geol. Geol. SUN. Surv. Misc. Misc. M-81, scale scale 1:24,000. 1:24,000. Map M-81, Map Chandler, V.W.,Miller, Miller,J.D., J.D., Jr., Jr.,and and Venzke, Venzke,E. E. A., A,,1991, 1991,Central Central Duluith Dululth Complex drilling drilling project; Minn. Geol. Chandler,V.W., S w . OFR 91-4,2 sheets,accompanying accompanyingtext. text. Surv. 91-4,2 sheets, Green, County, Minnesota: Minn. W.C., and and Weiblen, Weiblen,P.W., P.W., 1966, 1966,Gabbro GabbroLake Lake quadrangle, quadrangle. Lake County, Green, J.C., J.C., Phinney, Phinney,W.C., Surv. Misc. Misc. Map Map M-2, M-2, scale scale 1:24,000. 1:24,000. Geol. Surv. Miller, County, quadrangles. Lake County, Miller, J.D., J.D., Jr., Jr., 1988, 1988,Geologic Geologicmap mapof of the the Silver SilverBay Bay and and Split Split Rock Rock Point NE quadrangles, Minnesota: Minn. Minn. Geol. Geol. Surv. SUN.Misc. Misc. Map Map M-65, M-65, scale scale 1:24,000. 1:24,000. Minnesota: Miller, J.D., J.D., Jr., Jr., Green, Green,J.C., J.C., Chandler, Chandler,V.W., V.W., and and Boerboom, Boerboom, T.J., T.J., 1993, 1993,Geologic Geologic map of the Finland and Doyle Miller, Lake Lake quadrangles, quadrangles, Lake Lake County, County,Minnesota: Minnesota: Minn. Minn. Geol. Surv. Misc. Map M-72, scale 1:24,000. Paces, intrusions, Paces, JR., J.B., and andMiller, Miller,J.D., J.D.,Jr., Jr.,1993, 1993,Precise PreciseU-Pb U-Pbages agesof of Duluth Duluth Complex and related mafic intrusions, northeastern, northeastern, Minnesota: Minnesota: new new insights insightsfor for physical, physical, petrogenetic, paleomagnetic and tectono-magmatic 13997-14013. processes rifting: J. J. Geophys. Geophys.Res., Res.,v.v.98, p. 13 processes associated associated with 1.1 1.1 Ga Midcontinent rifling: 98, p. 997-14 013. Severson, Severson, M.J., 1995, 1995,Geology Geology of of the the southern southern portion portion of of the Duluth Complex: Univ. of Minn. Natural Resources Res. Inst., Inst.,Tech. Tech.Rept. Rept.NRRITI'R-95126, NRRI/TR-95/26, 185 185 p. Res. Severson, Severson, M.J., MJ., and and Hauck, Hauck, S.A., S.A., 1990, 1990,Geology, Geology, geochemistry, geochemistry, and stratigraphy of a portion of the Partridge River NRRIIGMIN-TR-89-l 1,236 p. intrusion: Univ. of of Minn. Minn. Natural Resources Resources Res. Inst., Tech. Rept. NRRIIGMIN-TR-89-11.236 Severson, quadrangle, Minnesota: Minn. Geol. M.J.. and and Miller, Miller, J.D., J.D., Jr., Jr., 1999, 1999,Bedrock Bedrock geologic geologic map of the Allen quadrangle, Severson, M.J., Surv. Misc. Map M-91, M-91, scale scale 1:24,000. 1:24,000. 41 �A. —fSBl Footwall Beaver Bay complex Miscellaneous Volcanic Shale Iron-formation Grariute Duluth Complex NSVG —-" — "BRD Mafic Granophyre Anohositic Rocks ftGranophyre Rocks Gabbroic Rocks Gabbroic Cumulates Gabbro, Ferrodiotite, Monzodiorite Fault Volcanic Homlels LilTroctolite Cumulates Diabase, 01 Gabbro, Troctolite • Oxide Ultramatic Metavolcanic Rocks 10 Miles =20 Kilometers FIGURE 1. A) Preliminary generalized geologic map of the central Duluth Complex. Specific intrusive units are: AGV-Anorthositic-gabbroicvolcanic assemblage (rock types distinguished in the northwest area), PRI-Partidge River intrusion, WCMI-West-central margin intrusion, SKI-South Kawishiwi intrusion,OLl-Oreenwood Lake intrusion. BEt-Bald Eagle intrusion, OLI-Osier Lake intrusion, CLLS-Cloquet Lake layered series. SLISonju Lake intrusion, FO-Finland granite, LLG-Lax Lake gabbro, BRD-Beaver River diabase, SBI-Silver Bay intrusions. Crosses mark 7.5' quadrangle corners. B) First-vertical-derivative, reduced-to-pole image of data, which forms basis for the geologic interpretation shown in A. aeromaic �SEDIMENTOLOGY OF TWO DEEP MIDGONTINENT SEDIMENTOLOGY DEEP WELLS IN THE KEEWANAWAN MIDCONTINENT RIFT SYSTEM NEAR MUNISING, UPPER RIFT UPPERPENINSULA, PENINSULA,MICHIGAN MICHIGAN OJAKANGAS. Richard Richard W., W., Department Department of of Geology, OJAKANGAS, Geology, University of Minnesota-Duluth, Duluth, MN 55812, rojakang@d.umn.edu Minnesota-Duluth, MN 55812, rojakang@d.umn.edu Amoco Production Production Company Companydrilled drilled the the St. St. Amour Amoco Amour stratigraphic stratigraphic test well well in 1987. six miles south-southeast of Munising, Ml. The well bottomed well bottomed at at 1987, miles south-southeast Munising, MI. Eight mites to the southeast 7,241 ft. ft. Eight miles to southeast of the the St. St. Amour Amour welt, well, at at Mickey Hickey 7,241 Creek, Cliffs Cliffs Mining Mining Services Services Company Companyhad haddrilled drilledaa 5,345 5.345 ftft deep Creek, deep well well in in 1969. 1969. These These wells wells are located located on on the the southwest southwest flank flank of of the theMidcontinent Midcontinent Rift System where the the rift Rift System (MRS) (MRS) where rift starts starts bending bending towards towards the the south. south. Except for for the the Pleistocene (110ftft thick thick in in the the St. Except Pleistocene (110 St. Amour Amour and and 88 ft thick thick in in the Mickey Creek), both both wells wells were the Hickey Creek), were cored from from top to to bottom. bottom. The The youngest youngest bedrock is is the the Ordovician Au Train Train Formation, Formation,about about280 280ftft thick thick in in the St. bedrock Ordovician Au St. Amour well well and and 235 Amour 235 ft thick thick in inthe theMickey Hickey Creek Creek well. well. The The Au Au Train Train overties the the Upper (?) Munising Munising Formation, Formation, a quartz quartz arenite arenite unit unit overlies Upper Cambrian Cambrian (?) that is 135 ft thick in the St. Amour and 310 ft thick in the Hickey Creek. that 135 thick in the St. Amour and 310 ft thick in the Hickey Creek. The Keweenawan rocks in in the St. Keweenawan rocks St. Amour Amour well well from from the thebase basedownward downward include QIF/L= =2200 ft of feldspatholithic sandstone (N=8: QlF/L= 72.2/20.7/ 72.2120.71 include -2200 feldspatholithic sandstone (N=8: interpreted as as Jacobsville Jacobsville Fm.; Fm.; =3000 -3000 ft of of lithofeldspathic lithofeldspathic 7.2) interpreted 725 ft sandstone (N=7: (N=7: Q/F/L=58.1/19.3/22.6) interpreted as Freda Freda Fm.; Fm.; 725 ft sandstone QIF/L=58.1/19.3/22.6) interpreted of basalt flows 400 ftft of basalt flows of quartz .4/5.0): 400 of quartz sandstone sandstone(N=4: (N=4:Q/F/L=93.6/1 QlFIL=93.611.4/5.0); with interflow with interflow black black shales shales and and red red to tobrown browncoarse coarseclastics elasticsincluding including conglomerateand and lithic lithic sandstone sandstone (N=2: (N=2: QlFlL=65.010.5134.5); QIFIL65.0I0.5/34.5); and and 300 300 ftft conglomerate of of dacitic dacitic (?) (?) ignimbritic flows. flows. - The Keweenawan rocks in in the The Keweenawan rocks the Hickey Hickey Creek Creek welt well from from the the base basedownward downward include include =1720 -1720 ft ft of of dominantly dominantly feldspatholithic feldspatholithic sandstone sandstone (N=6: (N=6: Q/F/L=78.2/16.7/5.1) interpreted interpreted as as Jacobsville Q/F/L=78.2116.715.1) Jacobsville Fm. Fm. and and —2845 52845 ft ft of dominantly lithofefdspathic sandstone (N=9: QIF/L= 54.8/19.0/26.3) dominantly lithofeldspathic sandstone (N=9: Q/FlL= 54.8119.0126.3) interpreted as Freda main two two types types of of sand-sized sand-sized rock rock interpreted as Freda Fm. Fm. The main In the fragments in the two fragments in two wells wells are aremetamorphic metamorphic and and fetsic felsic volcanic. volcanic. In the St. St. Amour well, metamorphic rock fragments (schist and greenstone) are on Amour well, metamorphic rock fragments (schist and greenstone) are on average twice as abundant average twice abundant as as felsic felsic volcanic volcanic fragments, fragments, whereas whereas in in the the Mickey Creek Creek well, well, felsic fetsic volcanics volcanics are are three three times times as Hickey as abundant abundant as as metamorphic rock fragments. metamorphic rock fragments. Porosity Porosity decreases decreases downward downward in both both wells, wells, with with virtually virtually no no porosity porosity present present below below 2750 2750 ft. ft. 43 �I I The in the the two The mineralogy mineralogy in two wells wells is is quite quite similar similar for for the the upper upper 5300 5300 ftftand and the formations, not unexpectedly, correlate well. They also correlate well the formations, not unexpectedly, correlate well. They also correlate well with with Keweenawan Keweenawan outcrops outcrops in the the Lake LakeSuperior Superior region region(Ojakangas, (Ojakangas, 1986; 1986; However, the lower portion of the St. Amour does not Adamson, 1997). However, the lower portion of the St. Amour does not Adamson, 1997). correlate correlate well well with with the theexposed exposedBayfield Bayfield and andOronto OrontoGroups. Groups. Quartz Quartz sandstones occur low low in the sandstones occur the well, well, in in direct direct contrast contrast to toexposed exposedsections sections where deep in in the rift where they they are are near near the the top. top. Quartzose Quartzose sediments sediments deep rift are arealso also present present in in the the Eischeid Eischeid ## 11 well well in in Iowa Iowa(Ludvigson (Ludvigson et et at, al, 1990). 1990).Clearly, Clearly, the the search search for for uniformity uniformity and andcorrelation correlationwhere wheredeposition deposition likely occurred occurred in in aaseries seriesofofsub-basins sub-basins(haif-grabens) (half-grabens) is is aa tenuous tenuous pursuit, pursuit, as asnoted noted earlier earlier by by Mauk Mauk(1991). (1991). Soreghan Soreghan and and Cohen Cohen (1993) (1993) interpreted interpreted relatively relatively quartzose quartzose sands sands (Q (Q to to 79%) 79%) on onhinged hingedmargins marginsofofmodern modernLake LakeTanganyika Tanganyika to to be be the theresult resultofofreworking reworkingininshallow shallowwater. water. This This may may be be aa partial partial analogue for these but eolian analogue for these quartz quartz sandstones, sandstones, but eolian activity activity in in the the vegetationless vegetationless Middle Middle Proterozoic Proterozoic terrestrial terrestrial environment environment is is also also likely. likely. Cliffs Cliffs Mining Mining Services Services Company Company kindly kindly purchased purchased the the thin thin sections. sections. REFERENCES REFERENCES Adamson, k.F, 1997, Adamson, K.F., 1997,Petrology, Petrology, stratigraphy, stratigraphy, and and sedimentation sedimentation of of the the Middle Middle Proterozoic Proterozoic Bayfield Bayfield Group. Group, Northwestern NorthwesternWisconsin: Wisconsin: Unpublished M.S. thesis. thesis, University of Minnesota, Unpublished M.S. University of Minnesota, Duluth, Duluth, 203 p. p. Ludvigson, Ludvigson, G.A., G.A., Mckay, McKay, H.M., P.M., and andAnderson, Anderson, R.R., R.R., 1990, 1990,Pekrology Petrology of of Keweenawan sedimentaryrocks rocksinin the the MG. drillhole: in in Keweenawan sedimentary M.G. Eischeid Eischeid ## 1 drillhole: Anderson, DeepPetroleum PetroleumTest, Test, Anderson, R.R., R.R., ed., ed.. The The Amoco Amoco M.G. M.G. Eischeid Eischeid ## 11Deep Carroll Carroll County, County, Iowa, Iowa, Iowa Iowa Department Department of of Natural NaturalResources Resources Special Special Report Report Series Series No.. No., 2, p. p. 77-112. 77-112. Mauk, J. J. L., L., 1991, 1991, Sub-basins Sub-basins in in the theProterozoic Proterozoic Midcontinent Midcontinent Rift: Rift: Mauk, Stratigraphic Stratigraphic evidence evidence from from Upper Upper Michigan Michigan (Abs.): (Abs.): Geological Geological Society Society of of America America Abstracts Abstracts with with Programs, Programs, San San Diego, Diego, CA, CA, p. p. A59. A59. Ojakangas, R.W., 1986, Reservoir characteristics of the keweenawan Ojakangas, R.W., 1986, Reservoir characteristics the Keweenawan MG. Jr., Supergroup, in Mudrey, M.G. Jr., ed., ed., Supergroup, Lake Superior Superior region: region: in Precambrian Precambrian Petroleum Petroleum Potential, Potential, Wisconsin Wisconsin and and Michigan. Michigan, Geoscience Wisconsin, V. V. 11, 11. p. p. 25-31. 25-31. Geoscience Wisconsin. Soreghan, M.J.. and Cohen, Soreghan, M.J., Cohen, A.S., A.S., 1993, 1993, The The effects effects of of basin basinasymmetry asymmetry on on in Examples from from Lake Lake Tanganyika. Tanganyika, Africa: Africa: in sand sand composition: composition: Examples Johnsson, Johnsson, M.J., M.J., and and Basu, Basu, A.. A., eds.. eds., Processes ProcessesControlling Controlling the the Geological Composition Composition of Clastic Clastic Sediments: Sediments: Geological Society Society of of America America Special Special Paper 284. 284, p. p. 285-301. 285-301. 1 44 �DESCRIPTIONS OF MARQUETTE EARLY DESCRIPTIONS OF THE THE NATURAL NATURAL FEATURES ON THE MARQUETTE IRON RANGE Doug Ottke, U.S. Geological Survey, 12201 Sunrise SunriseValley ValleyDr. Dr. Reston, Reston, Virginia Virginia 20192 -, -- -- r The peninsula of of Michigan Michigan is is integrally integrally linked linked to to The history history of the Marquette Iron Range in the upper peninsula the environment. The the mode mode of of production production on Thenatural naturalfeatures features of of the the Marquette Marquette Range defined the on the the Range, Range, and and conversely, conversely, as as human human systems systems became more adept in these modes of production they they became became the the most most important importantmodifiers modifiersof of the the natural natural systems. systems. Settlement natural Settlement on the the Marquette Marquette Iron Iron Range was closely related to two factors of natural environment: environment: the the iron iron ore ore formations formationsand and the the hardwood hardwood forest. The distribution of three iron ore ore formations--principally formations-principally the the Negaunee, Negaunee, but but also also the the Bijiki Biiiki and other other Iron-formations Iron-formations within the Michigamme --determined the the locations locations of of the sites sites of of extraction of iron ore Michigamme Formation Formation --determined ore in the the area. area. Stands Standsof of hardwood hardwood forest, forest, particularly particularly maple maple and yellow birch were the major factor determining determiningthe the location location for for processing pro&ssing operations operations that converted iron ore into pig pig iron. iron. The location of beehive kilns where the hardwood was converted into charcoal, the early forges, and and beehive kilns charcoal, the early forges, the of hardwood. hardwood. The iron ore formations the blast blast furnaces furnaces were reliant foremost on the availability of formations and and the the hardwood hardwood forest forest of of the the Range Range defined defined the physical subdivision of the land into tracts owned the mines, mines, forges, forges, owned by individuals. individuals. Because Becauseaareadily readilyavailable available workforce workforce was needed at the kilns, kilns, and and furnaces furnaces of of the the area, area, locations locations of of settlement settlement on the Range were within very close proximity proximity to to the the sites sites of of extraction and processing operations. Transportation, from the earliest trails to the plank road, trails to the plank road, strap straprailroad railroad and and the the Iron Iron Mountain Railroad completed in the 1857 1857 were were defined defined by by the the natural natural location location of of the the ore ore and and the processes processes involved with extracting it. In 1850's, with withadvances advancesinintransportation transportationassociated associatedwith with the the completion completion of of the the railroad railroad In the the mid mid 1850's, to to the the mining mining areas areasnear near Negaunee Negaunee and and lshpeming Ishpeming and the completion of the Sault Locks near Sault By 1868 that that Sault Saint SaintMarie, Marie, the the production production of of iron iron ore ore reached reached a level of 11,343 tons per year. By number 508,000 tons mined. The Thedepression depression of of 1873 I873 caused aa sharp sharp drop drop number had had reached reached aa level level of of 508,000 in in production. production. However, However,for forthe theyear yearbefore beforethe thedrop dropone onemillion million tons tonshad had been been withdrawn withdrawn from from 40 rose to to 40 pits pits carved carved into into the ore bodies. In In 1880 1880two two million million tons were mined and that number rose seven seven million million tons tonsmined mined during duringthe the year year of of 1890. 1890. The Thequarrying quarryingoperations operationsprogressed progressed deeper deeper into into the earth earth until until by by the the 1880's 1880's shaft shaftmining miningbecame became aa necessity, necessity, calling calling for for advancement advancement in in technological applications and forcing many of the less wealthy operations out of business. The technological applications wealthy operations out of business. The large large amounts amounts of of capital capital involved involved in in diamond drilling drilling exploration, and the operations underground underground forced forced industrial industrial consolidation consolidation of of the many small operations into a few large companies companiescommanding commandinglarge largeresources. resources. As Asmines mineswent wentunderground, underground,the the need need for for timber timber also also increased became aa necessity. necessity. Between .72 and .92 increased as as supports supports for for the underground workings became cubic cubicfeet feetof oftimber timberwas wasneeded neededper perton tonof ofore oreextracted. extracted. In In 1868 1868eleven elevenblast blast furnaces furnaceswere were in in operation operation on the Marquette Range. Twenty Twentyfive fivefurnaces furnaces total total were were built built ininMarquette MarquetteCounty. County.Numerous Numerous beehive beehive kilns kilns dotted the countryside. These These kilns pine, and and other softwoods softwoods kilns converted converted maple, maple, yellow yellow birch birch and, and, in in some instances, hemlock, pine, into iron produced produced in in furnaces furnaces varied varied from from 110 110 into charcoal. charcoal. The Thecharcoal charcoalconsumed consumedper per ton ton of of iron bushels to 140 bushels, with a bushel consisting of 20 pounds of charcoal. The Pioneer Furnace, bushels to 140 bushels, with a bushel consisting of 20 pounds of charcoal. The Pioneer Furnace, the theoriginal originalblast blastfurnace furnaceininthe thearea arealocated locatedin in Negaunee, Negaunee, used used the timber from 1,500 1,500 acres in the year year of of 1869 1869to to produce produce 9,500 9,500 tons tons of pig iron. One Oneacre acreof ofwood wood could could produce produce 14 14 tons of iron. iron. ItIt isis estimated the kilns of the the estimatedthat thatby by 1903 1903thirty thirty acres acresof of hardwood hardwood per day was needed to supply the Marquette MarquetteRange. Range.InInthe thefirst firsthalf halfcentury centuryofofiron ironproduction production330,000 330,000acres acreswere were cut. cut. In In order orderto to understand understand more more thoroughly thoroughly how natural and human systems have modified each other on pre-major European European settlement settlement natural environment must be on the the Marquette MarquetteRange, Range, the the pre-major 45 �I delineated. delineated. Beginning Beginninginin1838, 1838,the theMichigan MichiganGeological GeologicalSurvey Surveyand andthe the Linear LinearSurvey Surveyof ofthe the U.S. U.S.Land Land Office Officecreated createddescriptions descriptions of ofthe thenatural naturalenvironment environmentof ofthe theMarquette MarquetteRange. Range. These These descriptions descriptionsbetter betterenable enablethe theunderstanding understanding of ofthe thepre-major pre-majorsettlement settlementnatural naturalenvironment. environment. The Thedescriptions descriptions contained contained within withinthese these reports reports of of the location location of of the the original originaloutcrops outcropsof ofiron ironore ore and andthe thestands stands of of trees trees shows shows how how important importantthese these factors factors were were to to the the early early settlement settlement of ofthe the Marquette MarquetteRange. Range. The Thedescriptions descriptionsalso alsoallow allowus usto tosee see how how influential influentialthat thatsettlement settlementwas wasin in modi1'ing modifyingthe thenatural naturalsystems systemsofofthe theRange. Range. 46 �DEVELOPMENT OF VOLCANOGENIC VOLCANOGENIC MASSIVE MASSIVE SULFIDE SULFIDEDEPOSIT DEPOSITEXPLORATION EXPLORATION OF TARGETS IN NORTHERN MINNESOTA FROM GIS GIs SPATIAL SPATIAL ANALYSIS OF GEOLOGICAL, GEOCHEMICAL, GEOPHYSICALCRITERIA CRITERIA AND GEOPHYSICAL GEOLOGICAL, GEOCHEMICAL, AND DEANM. M. PETERSON PETERSONand andDR. DR. RONALD RONALDL. L. MORTON MORTON DEAN Economic Volcanology Research Research Lab, Lab, Geology Department, Department, University ofMinnesota of Minnesota --Duluth, Duluth, Economic Duluth, Minnesota, Minnesota, USA USA 55812 massive sulfide (VMS) deposits are are syngenetic syngenetic stratifm stratiformiron ironand andbase-metal base-metal(Cu-Zn-Pb) (Cu-Zn-Pb) Volcanogenic massive systems in in subaqueous subaqueousvolcanic volcanicenvironments. environments. At the accumulations that form out of large geothermal systems "bottom" of VMS-producing systems are subvolcanic intrusions, which which produce produce focused focusedheat heatsources sourcesthat that "bottom" provide the energy for circulating hydrothermal fluids and leaching reactions, reactions, and and may may add addbase-metals base-metals into the geothermal system. Above Above the the subvolcanic subvolcanicintrusions, intrusions, the strata have undergone extensive highmetal depletion, alkali alkalimodification, modification,and andextensive extensive temperature alteration, which can include metal silicification. silicification. Over the last twenty years, a VMS ore ore deposit deposit model has been developed from the work of many researchers. Important features of the model Important features of the model include include the the following: following: • • • • • • deposits are associated VMS deposits associated with with submarine submarine volcanic volcanic rocks, and typically are are spatially spatially associated associated with felsic volcanic rocks in greenstone terranes. with age age or or petrochemistry petrochemistrybut butdo dooccur occurin indistinct distinct VMS deposits occur with no obvious correlation with provinces, camps or clusters. Deposits often occur at one or more distinctive favorable stratigraphic stratigraphichorizons horizonswithin withinaacamp. camp. These Deposits represent quiescent horizons represent quiescentperiods periods in in volcanic volcanic activity, activity, tops tops of volcanic volcanic cycles, cycles, or a major volcanicor aa sediment interface. The Thedistal distal extent extentof of ore ore horizons horizons may be marked by a siliceous, ferruginous, or tuff. base metal bearing bearing sediment sediment and/or and/or felsic felsic tuff. Footwall subvolcanic subvolcanic intrusions intrusionsare are typically typically sill-like, sill-like, with with irregularly irregularly distributed distributed porphyritic and non-porphyritic phases. The intrusions may contain minor porphyry copper occurrences. The intrusions may contain minor Synvolcanic fault controls are recognized in some deposits, and may control the location of rhyolite some Synvolcanic controls deposits. Proximal facies volcanic rocks associated with with domes that occur in the footwall of some deposits. synvolcanic faults are generally generally the most favorable favorable horizons for ore deposition. alteration may include semi-conformable and cloud-like Footwall alteration include a pipe-like zone and/or andlor widespread semi-confmable alteration. alteration. The massive-sulfide nature of the ore ore typically makes them conductors conductors of electricity, and therefore can be detected by airborne and ground-based electro-magnetic (EM) surveys. airborne feature of the ore deposit deposits have been based on only one feature Many exploration programs for for VMS deposits specifically, the blind drilling of airborne EM EM conductors. conductors. Although this method of exploration model, specifically, has discovered many major major deposits deposits in the the past, strictly strictly EM-based VMS exploration has many shortcomings. The The drawbacks drawbacks include include any any or or all of the following: • • • • Poor geologic control of conductor location block Poor ranking of conductors in a survey block High cost of drilling tens tens to hundreds hundreds of barren or graphitic EM conductors prior to discovery 1% of drilled EM conductors conductors lead to mines) Poor rate of discovery discovery (less than 1% 47 �This study study formulates formulates a GIS-based GIs-based exploration exploration model model that that incorporates incorporates all all facets facets of of the the VMS VMS ore deposit deposit Thesemaps maps have have ultimately ultimately led led to to the generation of specific s p e c i f VMS icps model into a series of digital maps. These exploration targets in the study area of northern Minnesota. The km The study study integrates integrates a new 5880 5880 km geologic compilation map with with mapped mapped alteration alteration zones, zones, over over 5400 5400 ground ground and airbome airborne EM EM anomalies, anomalies, and approximately 21,000 copper and zinc assays. Intermediate Intermediate maps maps used to predict VMS potential include stratigraphy, stratigraphy, heat generation, generation, alteration, Cu-Zn Cu-Zn geochemistry, geochemistry, and and EM EM conductors. conductors. The methodology inFigure ~ i &1.1. e methodology used used to to create create the the 015-based GIs-basedmodel modelisispresented presentedin STEP STEP I1 Build luild Spatial Spatial Data Base Base STEP STEP22 Collect Collect spatial Spatial Data Data and and Input Input into into GIS CIS Extraction of 015 CIS Extraction of Features Relevant Relevant to the VMS Ore to the VMS Ore Deposit Deposit Model Model S S BEDROCK BEDROCK GEOLOGY GEOLOGY S MAPPED MAPPED ALTERATION ALTERATION ZONES ZONES -H———— ———--H— I. Extractqtz.cpidote 2. Extract chlorite 2.Extractchlonu t.1.Reclassii RecUmfy 2. 2 Extract . m - contacts 3. Qeale buffers 3.0cçEbufiei 3. 3 .CYeate O m e bbuffers ufim I.1.Classifymiervals aassi& intervals 2. Grid soil & lake aSs 2.Gndsoil&lateseds 3. Buffer rock & axe 3.Bufferrock&core Data Data Processing Processing Preliminary Preliminary Maps Maps of of Selected Selected GIS GIs Features Features S ROCK, CORE, SOIL SOIL AIRBORNE ROCK. CORE. AIRBORNEAND AND & & LAKE LAKE SEDIMENT SEDIMENT GROUND GROUND EM EM CONDUCTORS GEOCHEMISTRY CONDUCTORS tontacts ;contscts Volcanic-Sedin.t contacts Greanstone Subvókar.ac 5eq lntrusio,.s Qsarfl- Chlorite A -A- Cu Zn Cu Zn Cu C"aC"a m Zna Epidote I I. Extnct ground EM 1-ExtractcrowdEM 2. airborne EM 2. Classil5, Classify airbornem soils Soik Lake Lake Rocks Reeks Gromd t EM EM EM EM Assign Assign Weights Weights of ofEvidence Evidence hny,gIits(O.on . t.) F-wriflte(0m-lm) STEP STEP33 Integration Integration Modelling Modelling Map Map Overlay Overlay to Produce to Produce Interrnedtate Intermediate Factor Factor Maps Maps 1 STRATIGRAPHY STRATIGRAPHY HEAT HEAT Factor Factor Factor Factor 1 ALTERATION ALTERATION Factor Factor 1 GEOCHEMICAL GEOCHEMICAL Factor Factor 1 EM EM Factor Factor Overlay of Overlay of Intermediate Intermediate Factor Factor Maps Maps to to Produce Producethe the Final Predictive Final Predictive Map Map Figure Figure 1. 1. VMS NJFEWflAL MAP VMS NERAL MINERAL-POTENTIAL MAP L Flowchart Flowchart for for the the 3-step 3-step GIS GIs modelling modelling of the VMS potential of the Archean Vermilion District District and and its its western western extension, extension, northeastern, northeastern, Minnesota. Minnesota. The Thethree threesteps stepsin inthe thestudy study are: are: 1) 1)Detailed Detailedgeologic geologicmapping mappingand andcompilation compilationof ofall allavailable availablegeological, geological, geochemical, geochemical,and and geophysical geophysical data. data. Conversion Conversionof ofall alldata datainto intoprimary primaryGIS GIsdatasets; datasets; 2) 2) Extracting Extractingand and enhancing enhancing the the features featuresof of the the primary primary datasets datasets that are important important for predicting VMS and 3) 3) Integration Integration of of the preliminary prelimhry maps using GIS GIs modelling p~dicting VMS deposits; deposits;and techniques techniquesthat that predict predictmineral mineralpotential. potential. 48 �LOW-GRADE LOW-GRADEMETAMORPHISM METAMORPHISMAND AND HYDROTHERMAL HYDROTHERMAL ALTERATION ALTERATION OF OF THE THE UPPER KEWEENAWAN PORTAGE LAKE VOLCANICS, MICHIGAN UPPER KEWEENAWAN PORTAGE LAKE VOLCANICS, MICHIGAN PUSCHNER, PUSCHNER, Ulrich, Ulrich, SCHMIDT, SCHMIDT,Susanne SusanneTh., Th., Mineralogisch-Petrographisches Mineralogisch-PetrographischesInstitut, Institut, Base!, J.. Department Department of Geological Basel. Switzerland Switzerlandand and BORNHORST, BORNHORST. Theodore Theodore J., Engineering Sciences, University, ~ n ~ i n e e rand and in~ Sciences,Michigan Michigan Technological ~echnolo~ical university, Houghton, ~ o u ~ h t o Michigan n,-~ichi~an 49931 4993 1 The ThePortage PortageLake LakeVolcanics Volcanicsin inthe theKeweenaw KeweenawPeninsu!a Peninsula of Michigan Michigan consists consists of aa thick thick succession interfiow sedimentary sedimentary successionof of subaerial subaerialtho!eiitic tholeiiticbasalt basalt !ava lava flows with scattered interflow !ayers. layers. These Theserocks rockshave havebeen beensubjected subjectedtotolow-grade low-grademetamorphic metamorphicand andhydrothermal hydrothermal alteration. emplaced during during this alteration alteration alteration.The Theworld-class world-classnative nativecopper copperdeposits depositswere were emplaced event. In the Keweenaw Peninsula, and elsewhere, the Portage Lake Volcanics are not event. In the Keweenaw Peninsula, and elsewhere, the widely widely exposed exposed at at the the surface surface because because of overlying overlying unconsolidated glacial sediments. However, Peninsula during However, subsurface subsurfacedrill drill core core were were obtained obtained in the Keweenaw Peninsula during exploration explorationfor for native native copper. Much Muchdrill drillcore, core,some someover over 100 100years old, still exists in excellent and locations. locations. Mr. Gordon Peterson excellent condition condition and and with original dri!l drill core logs and of of Calumet Calumetowns ownsand and continues continuesto to maintain maintain much much of the the existing existing drill drill core core and and allowed allowed us us to to sample samnlethe the core core for for our our research. Stoiber Stoiberand and Davidson Davidson (1959a, (l959a. b), in part, part. used a drill core portage Lake Lake Volcanics. Volcanics. corecross-section cross-sectionto topostu!ate postulatemetamorphic metamorphic zonation zonation within within the the Portage Four Fourdrill drillcore corecross crosssections sectionsthrough through the thePortage PortageLake Lake Volcanic Volcanic have been studied studied using using aa combination combinationof of microscopic microscopicinvestigation, investigation, XRD XRD technique, technique, and electron electron microprobe analysis, by Stoiber Stoiber & &Davidson Davidson(1959a. (1959a,b). b). These analysis, including including the drill core section studied by four are located located between Ahmeek and Copper Harbor and four dril! drill core core cross cross sections sections are provide km provide coverage coveragethrough through 3000m 3000m of of the the Portage Portage Lake Volcanics over a distance of 60 k m along alongstrike. strike. Interlayered Interlayeredsediments sedimentsand andse!ected selectedlava lavaflows flows can can be be used used as as marker marker horizons horizonsto to corre!ate correlatethe the stratigraphic stratigraphic zones zones between the different individual drill holes. Initial distinguished within Initial results resultsdemonstrate demonstratethat that two two main main minera! mineral associations associations can be distinguished the the amygdaloidal amygdaloidal tops tops of of the the basaltic basaltic !ava lava flows of the upper part of the Portage Lake Vo!canics Volcanics (above (above the the Greenstone Greenstone flow) flow) in the Copper Harbor to Ahmeek sections: (1) a zeolite-dominated laumontite-chlorite-corrensite±wairakite±quartz± zeolite-dominated assemb!age assemblage with laumontite-chlorite-corrensite±wairakite±quart calcite, with chloriteiquartz* chlorite±quartz± calcite, and and (2) (2) aa pumpellyite-epidote-dominated assemblage with calcite±prehnite±laumontite. The zeolite-dominated assemblage is more frequent in the the calcite±prehnite±laumontit upper upper part part of of the the section, section,but butwairakite wairakiteoccurs occurs only below the Hancock Conglomerate. The pumpellyite-epidote-dominated assemblage of the the lower part of the The pumpellyite-epidote-dominated assemblage is characteristic of sequence. sequence. Zeolite Zeoliteminerals mineralsare arepresent present throughout throughout the whole vertical section. Along strike, strike, aa temperature temperature gradient gradient is is observed observed with lower temperature conditions in the Copper Copper Harbor Harbor section section and and higher higher temperature conditions in the Ahmeek section near Ahmeek Ahrneek to the southwest. southwest. This Thiscorrelates correlateswith with the the distribution of native copper deposits increasing in frequency and size from Copper Harbor Ahmeek. increasing in frequency and size from Copper Harbor towards towards Ahmeek. The The most most abundant abundantphyllosilicates phyllosilicates in in the the upper part of the Portage Lake Volcanics are chlinochlore units of of aa lava lava chlinochlore and corrensite. Chlinoc!ore Chlinoclore is present in all morphological units flow, within all flow, i.e. in in the the amygdaloidal amygdaloidal flow top and in the massive interior, and within stratigraphic as determined determined by by electron electron stratigraphichorizons. horizons. The Themean meanof ofthe theinterlayered interlayeredcations cationsas microprobe microprobe analysis analysisis is around around 0.1 0.1 indicating indicatingon!y only very low mixed-layered mixed-layered components. components. Corrensite amygdaloidal flow flowtops. tops. In the eastern eastern most most Copper Copper Corrensite is more abundant in the amygdaloidal 49 �Harbor Harbor section, section, smectites smectites (saponite, (saponite,montmorillonite) montmorillonite)as as well well as asparagonite paragoniteand and pyrophyllite pyrophyllite are are also also present present in in the the zeolite-dominated zeolite-dominatedassemblage. assemblage. The complexmetamorphic metamorphicand andhydrothermal hydrothermal The Portage Portage Lake Lake Volcanics Volcanicswas was subjected subjectedto to aacomplex alteration event (Stoiber & Davidson, 1959, Bornhorst, 1997). The initial 1997). The initialresults resultsof ofthis this alteration event (Stoiber & Davidson, 1959, continuing continuing research research suggest suggest that the abundant laumontite-chlorite assemblage in most of the the upper upper part part of of the the Portage Portage Lake Lake Volcanics Volcanicswas was likely likely the the result result of of regional regional zeolite zeolite fades pumpellyite-prehnite-epidoteassemblage assemblageis is faciesmetamorphism metamorphism during duringburial. burial. The Thepumpellyite-prehnite-epidote likely In the the Copper CopperHarbor Harbor to to Ahmeek Ahmeek section sectionthe the likely related to a hydrothermal hydrothermal phase. In hydrothermal hydrothermalevent eventoccurs occursonly onlylocally, locally,but but when when present present itit is ispervasive. pervasive. References References . Bornhorst, Bornhorst, T.J., T.J., 1997, 1997,Tectonic Tectoniccontext context of of native native copper copper deposits depositsof of the the North NorthAmerican American Midcontinent Midcontinent rift rift system: system: Geological Geological Society Society of America Special Paper, 312, 312, p. p. 127127136. 136. Stoiber, E.S., l959a, 1959a.Amygdule Amygdulemineral mineralzoning zoningin inthe thePortage PortageLake Lake Stoiber, R.E. R.E. and and Davidson, Davidson, E.S., Lava v. 54, 54. p.1250Lava Series, Series, Michigan Copper Copper district. district. Part I: Economic Geology, v. p.12501277. 1277. Stoiber, R.E. and and Davidson, Davidson, E.S., E.S., l959b, 1959b.Amygdule Amygdulemineral mineralzoning zoningin in the thePortage PortageLake Lake Stoiber, R.E. Lava Lava Series, Series, Michigan Michigan Copper Copper district. district.Part Part H: IT Economic Economic Geology, v. 54, 54, p. p. 144414441460. 1460. 50 �Lake Superior's Superior's lUngs: Fault Systems Lake Rings: Clues Clues to to the the origin origin of of Polygonal Polygonal Fault Systems Deborah J. Wattrus Deborah E. E. Rausch Rausch and and N/gel NigeI J. Wattrus Large Lakes Minnesota Large Lakes Observatory, Observatory, University University of ofMinnesota Duluth MN 55812 55812 Duluth MN email: drausch2(did.umn.edu Polygonal Fault Fault Systems Systems (PFS) (PFS) are are aa recently recently recoenized recognized class class of of soft-sediment soft-sedimentstructures. structures. They result They result Polygonal from volumetric contraction contraction triggered triggered by by s&eresis-during syneresis during early early compaction compactionof ofultra-fine ultra-finesediments. sediments. PFS PFS from-volumetric were first described in Paleoeene Paleogene clavstones claystones from from the the North North Sea Seabasin basin (Cartwrieht. (Cartwright, 1994). In 2D cross1994). . sections, PES appear appear be be small small extensional extensional faults and in in map map view, view, the the faults faults have have aa polygonal polygonal appearance. sections, PFS faults and appearance. Cartwright and and Lonergan Lonergan (1996) measured measured the extensional Camwight extensional strain and determined determined that apparent apparent extension extension on any any given given horizon horizon was was uniform uniform in in all all directions. directions. They this that that the the fault fault systems systems could could on They concluded concluded from from this not not have have aa tectonic tectonic origin origin and and that that the the faulting faulting was was related related to to volumetric volumetric contraction contraction of of sediments sedimentsduring during early burial burial and and compaction. compaction. From North Sea, Cartwright Cartwright and and Dewhurst Dewhurst early From 3D 3D seismic seismic data data collected collected in the North (1998) identified identified specific specific criteria criteria of of PFS. PFS. These in other other (1998) These criteria criteria are are used used to to delineate delineate systems systems in sedimentary basins. Based normal faults faults with with small small sedimentary basins. Based on on these these criteria, criteria, PFS PFS are are typically typically close close networks networks of of normal throws that that occur occur over over aa large large area area in in sedimentary sedimentary basins. basins. The bound and and are are throws The systems systems are are layer layer bound occasionally tiered. They Theyonly onlyoccur occurin in very very fine-grained fine-grained sediments sediments (<2 (<2 micron). There Thereare areno noknown known modern analogues. analogues. - < Doughnut-shaped rings rings and and subcircular depressions have been observed in in the the side-scan records collected Doughnut-shaped subcircular depressions side-scan records collected in Lake Lake Superior (Bergson (Bergson and Clay, 1973; et al., 1984; Flood and and Johnson, Johnson, 1984; in 1973; Johnson et 1984; Flood 1984; Flood, 1989; 1989; and Anderson, 1997). The The described describedfeatures features are are 100-300 100-300 meters in diameter. diameter, 10-3- meters wide and 5 meters deep. Side-scan Side-scandata datacollected collectedby by the the Large Large Lakes Lakes Observatory Observatory (LLO) confirms confirms the widespread development of of ring ring structures structures throughout throughout much much of of the the basin. basin. The rings rings commonly commonly occur occur wherever wherever finefinedevelopment grained glacio-lacustrine glacio-lacustrine sediments sediments are are found. found. High-resolution reflection data data collected collected with with grained High-resolution seismic reflection boomer A and d echosounder echosounder systems systems show show that that the the nngs ringsare areassociated associated with with deformation deformationthat thattypically typically disrupts the the thir thifl Holocene Ilolocene surface sediments sediments and and elacio-lacustrine glacio-lacustrinesediments sedimentsbelow. below. The echosounder dismots data clearly shows that the underlying underlying glacio-lacustrine glacio-lacusmne exhibits extensive fracturing and small-scale small-scale ring or or faulting. Some Someof of these these fractures fractures and and faults faults continue to the surface where they coincide with a ring partial ring structure. Many, Many,however, however,are aretruncated truncated at at the the Holocene Holocene boundary. Throws Throwson onthe thesmall small faults are often less than 50 cm and the apparent displacement on these faults is typically normal. Some Some echosounder records show evidence apparently genetically unique deformation deformation sequences sequences in the of the echosounder evidence of apparently fine-grained sediments. sediments. These poorly resolved resolved horizon horizon with with little little coherent coherent These sequences sequencesare are separated separated by a poorly internal reflections. reflections. The well developed Thesequences sequencesabove aboveand andbelow belowexhibit exhibitwell developedinternal internalreflections reflectionsthat thatdo do not appear appear to be concordant. concordant: Both Bothsystems systemsshow showwell-developed well-developedfracture fractureand andmicro-faulting micro-faultingpatterns. patterns. observation suggests that these systems in the subsurface, and are This observation systems are confined to distinct intervals in therefore genetically genetically unique. unique. . ~ ~ ~ ~~ - ~ ~ It is proposed that the rings in Lake Superior expressions of PFS developed in the near surface surface Superior are surface expressions clays. AAcomparison comparisonwith withthe thecriteria criteriaoutlined outlinedby byCartwright Camwightand andDewhurst Dewhurst(1998) (1998)show showthat thatthe thenearnearsurface requirements for PFS development. surface sediment sediment and data from Lake Lake Superior Superior meet nearly all of the requirements development. The seismic data collected thus far indicate indicate that there are basinwide layer bound normal fault systems systems with small throws. The TheLake LakeSuperior Superiorglacio-lacustrine glacio-lacustrinesediments sedimentsare arecharacterized characterizedby by fine finegrain grainsize, size, high water content, content, and and aa clay clay fraction fractioncomposed composedpredominantly predominantlyof ofillite. illite. 51 �The following following model is proposed proposed to explain explain the the origin origin of the the rings rings on the floor of Lake Superior. High High sedimentation sedimentation rates associated with the retreat of ice ice out of the basin produced produced deposits deposits with with high high water water Sometimeafter after deposition, deposition, syneresis syneresis in the sediments sediments contents, which behaved like a colloidal fluid. Sometime tothe thedevelopment developmentof of fractures fracturesand and faulting faultingin in the the initiated volumetric volumetric contraction. This Thisprocess pocess led ledto initiated clays. The Thegrowth-fault growth-faultappearance appearanceof ofsome someof ofthe the faults faultssuggests suggests that that deformation deformation and and faulting faulting was was clays. syndepositional syndepositional and continued for some time. Since Since many of of the fractures fractures and and faults faults truncate truncate against against the the Holocene the deposition of Holocene boundary, we believe that most of the volumetric contraction ceased before the the the Holocene Holocene sediment. sediment. Some Somefractures fractureswhich whichcontinue continueto tothe thesurface surface appear appear to to act act as asconduits conduitsfor forthe the expressed expressed water. This Thisisissupported supportedby bysubmersible submersibleobservations observations(Flood, (Flood, 1989) 1989) that that appear appear to to suggest suggestthat that water in water venting venting from from the the lake lake floor floorremoved removed or or prevented prevented the the deposition depositionof of the the fine fineHolocene Holocenematerial materialin the the vicinity vicinity of of the the ring. ring. REFERENCES REFERENCES Anderson, graphic study Anderson,K.A., K.A., 1997, 1997,A A seismic seismic strati stratigraphic study of of western western Lake Superior Superior(M.S. (M.S. thesis). thesis): University University of of Minnesota, 74p. 74p. and Clay, Clay. C.S., C.S., 1973, 1973. Possible Possiblesyneresis syneresisorigin originof ofvalleys valleyson on the thefloor of ofLake Superior: Berkson, J.M.. f.M., and Lake Superior: Nature, Nature, 245:89-91. 24589-91. Cartwright, from geopressured Cartwright,f.A.. J.A., 1994, 1994.Episodic Episodicbasin-wide basin-widefluid fluid expulsion expulsionÂ¥fro geopressuredshale shale sequence sequencein in the the North 2222:447-450. :44 7-450. NorthSea Seabasin: basin:Geology, Geology, J.A., and sediments: Cartwright,.J.A., Cartwright. and Dewhursi, Dewhurst, D.N., D.N., 1998. 1998, Layer-bound Layer-bound compactionfaults faults infine-grained infine-grained sediments: Geol. 7. Geol.Soc. Soc. Am. Am. Bull., Bull., 110:1242-125 110:1242-1257. Cart-wright, .14. and Lonergan. Lonergan, L., Cartwright,J.A. L., 1996, 1996,Volumetric Volumetriccontraction contractionduring duringthe thecompaction compactionofofmudroc/cy: mudrocks: AA mechanism cale polygonal polygonalfault mechanismfor the the development development of regional-s regional-scale fault systems: systems: Basin BasinResearch, Research,v.8, v.8, p 183-193. 183-193. Flood. topography in Lake Superior: Superior: .1 Flood, RD., R.D., 1989. I989,Submersible Submersiblestudies studiesof of current-modified current-modified bottom topography J. Great GreatLakes Lakes Res., Res., 15:3-14. 15:3-14. Flood. C., 1984, for bedforms and Flood. R. R. D. and and Johnson, Johnson,TT.C., 1984,Side-scan Side-scan targets targetsin in Lake Lake SuperiorSuperior- evidence evidencefor sediment sediment transport: transport:Sedimentology, Sedimentology,v.v.31, 31,p. p. 311-333. 311-333. Johnson, and currents andfish Johnson,T. T.C.. C.,Halfman, Hal/man,J.D., J.D., Busch, Busch,W.H., W.H., and Flood, Flood,R.D., R.D., 1984, 1984,Effects Effects of bottom currents and fish on on sedimentation sedimentationin inaadeep-water. deepwater,lacustrine lacustrineenvironment.' environment:Geol. Geol.Soc. Soc.Am. Am.BulL, Bull., 95:1425-1436, 95:1425-1436. Mollard, patterns ononthe J.D.,1983, 1983,The Theorigin originofofreticulate reticulateand andorbicular orbicularpatterns thefloor floorofofthe theLake LakeAgassiz Agassiz basin basin Mollard. ID., in IT. and in Teller, Teller, J.T. andClayton, Clayton,L., L., eds.. eds.. Glacial GlacialLake Lake Agassiz: GeoL Geol. Assoc. Can. Can. Sp Sp. Paper, Paper,p. p. 355355374. 3 74. 52 �GEOLOGY OF THE TILDEN MINE, MINE,MARQUETTE MARQUEflE IRON IRONRANGE, RANGE, MICHIGAN MICHIGAN Glenn W. Scott Scott and Helene Helene M. Lukey, Lukey, Mine Engineering Engineering Department, Department, Tilden Tilden Mining Mining Company, P.O. Box 2000, 2000, Ishpeming, MI 49849 The Tilden hon Formation, Tilden Mine Mine produces produces iron iron ore ore from from the Negaunee Iron Formation, Menominee Menominee Group, Group, Marquette Range Supergroup in the Upper Peninsula of Michigan. As the base of the iron peninsula iron Marquette ~ a n ~ e ~ u p e r ~ r o u p formation is not exposed exposed at at the the Tilden Tilden Mine, the stratigraphic thickness is unknown. The The thickness exceeds 1000 feet and is probably underlain by and is gradational into thickness exceeds 1000 feet and is probably underlain bfand is gradational into Mine. The undifferentiated elastics and iron formation of the Empire Mine. The iron iron ore ore deposit deposit at at the the Tilden Mine hut, more Mine has has been divided divided into into geologic geologic domains based in part on lithology but, importantly on on the the metallurgical metallurgical response response based based on on bench bench tests tests and and in in the the processing processingplant. plant. The interaction of sedimentation sedimentation and diagenesis within growth fault controlled basin, metamorphism and metamorphism and supergene supergeneoxidation oxidationhas has resulted resulted in in aa complex complexsuite suiteof of ore oretypes, types,each each with specific, problems. Production specific, if not entirely entirely objective, blending characteristics and problems. Production since 1974 million long long tons tons of ore at a 1974 has been 126 126 million long tons of pellets from 355 million 1999, the Asof ofJanuary January1,1,1999, the proven proven and and probable long long range (30 (30 year) stripping ratio of 0.94. As mine mine plan reserve reserve was 628 628 million long tons of ore containing 233 million long tons of pellets at a stripping ratio 0.77. at a stripping ratio of of 0.77. Chlorite Chlorite schist schist defines defines the footwall footwall of the Tilden ore body. The The Martite Martite and and main main pit pit Carbonate Carbonate domains domainsdomains domainslie lie stratigraphically stratigraphicallybelow below the the CDffl CDffl Footwall Footwall and and Main Main Pit Pit Hanging wall intrusives. This is metallurgically "good ore" and is typically characterized This is metallurgically "good ore" and is typically characterizedby by high weight recovery (35-45+%), (35-45+%), low phosphorous, phosphorous, low slime slime iron and good grinding grinding media. The West PitJCDffl Pit/CDin Hematite domain in the west pit is stratigraphically stratigraphically between the CDffl CDIII this is is metallurgically metallurgically 'poor' 'poor' In contrast contrast to the martite domain, this hanging wall and footwall. In ore with higher slime iron, phosphorous and poor grinding. Mineralogically Mineralogically and and texturally, martite domain domain in in being being dominantly dominantly platey hematite hematite with with thin thin this domain domain differs differs from from the the martite (mm scale) chert laminae. The equivalent to the (mrn The Magnetite Magnetite domain domain is is the the stratigraphically stratigraphically equivalent West PitJCDIII. Pit/CDffl. Mineralogically, Mineralogically,the the ore oreconsists consistsprimarily primarily of of magnetite-siderite-chert magnetite-siderite-chertwith with variable hematite and silicates. silicates. This Thismineralogy, mineralogy, along along with with the the thin laminations, laminations,appears appears to to indicate a restricted basin and a reduced environment of deposition. environment There are several igneous igneous horizons horizonsatatthe theTilden TildenMine. Mine.The Theterm term'intrusive' 'intrusive' or or 'dike' 'dike' is is used for diabasic to porphyritic porphyritic to aphanitic aphanitic bodies, which vary from (semi) conformable sill-like horizons, usually interpreted as interpreted as synsedimentary sills but may be flows, to obviously crosscutting bodies, interpreted as dikes that may may be be feeders. feeders. The sills and majority of the crosscutting andlor the dikes appear appear to be of early early Proterozoic Proterozoic age, related to the Clarksburg Clarksburg Volcanics and/or Hemlock and Emperor Emperor Volcanics, but there there are are several several dikes that are interpreted interpreted to be of Keweenawan based on Keweenawan age agebased on the the magnetic magnetic signature. signature. 53 �AN ESTIMATE OF RATE DYNAMIC AND STATIC STATICSTRENGTH STRENGTH OF AGGREGATES: AN SENITIVITY OF SENITIVITY OF GEOLOGIC GEOLOGIC MATERIALS MATERIALS STANLEY J. VITTON, Department of & &Environmental Environmental Engineering, Engineering,GHATUPARTHJ GHATUPARTHI STANLEY J. S UBHASH, Department Mechanics, Michigan Michigan SUBHASH, DepartmentofofMechanical MechanicalEngineering—Engineering Engineering-Engineering Mechanics, Technological University, Technological University,Floughton, Houghton, Michigan Michigan49931 4993 1 The Michigan Michigan Department Department of ofTransportation Transportation (MDOT) (MDOT)has has initiated initiatedresearch research into into the dynamic dynamic fracture fracture characteristics of cement concrete concrete(PCC) (PCC) pavements. pavements. The main focus of this characteristics of aggregates aggregates in Portland cement this aggregateportion portion in PCC. research is to study the fracture fractureand and strength strcngth characteristics of the coarse aggregate wide range Due to the wide range of of rock rock types types inin Michigan, Michigan,there thereisisaacorresponding correspondingrange range of ofcoarse coarse aggregate aggregate used PCC. PCC. In used In addition, addition,aasignificant significant amount amountofofblast blastfurnace furnaceslag slag isis produced produced and used used in PCC. To study unconfined uniaxial uniaxial compressive of study the static static and dynamic dynan~icstrength strength of of the the aggregates. aggregates, unconfined compressive strength of three limestones, limestones, four fourdolomites. dolomites,two twobasalts basaltsand andthree three blast blastfurnace furnaceslags slags were were conducted. conducted. InIn addition, conditions. The addition,tests tests were wcre also also conducted conducted under dry dry and and saturated saturated conditions. The studies studies revealed that that the the aggregates exhibited exhibited the lowest compressive strcngth, strength,followed followed by the limestones and dolomites. slag aggrcgates aggregates exhibited exhibited the the highest highestcompressive compressivestrength. strength. The The compressive compressive strcngth strength data dataof of The basalt aggregates rocks were were found found to to have haveaastrong strongcorrelation correlationtotothe thebulk bulkdensities. densities. Both the dry thy dry and saturated rocks and saturated aggregates revealed revealed aahigher higher compressive compressive strength strength under under dynamic dynamic loads compared compared to to in dynamic compressive strcngth strength over over its static strength is the static loads. The Thepercentage percentage increase increase in identified as which may identified as aa measure measure of the rate sensitivity sensitivityofofthese these aggregates, aggregates, which may have have considerable considerable geologic interpretation. relevance in applications applicationssuch such as rock blasting, underground construction, and geologic interpretation. The aggregate used used in in the thestudy studywere wereobtained obtainedfrom fromquarries quarriesininMichigan, Michigan, Ohio Ohio and and Ontario, Ontario, while while blast furnnace ftrnnace slags obtainedfrom from steel steelmills mills in in Sault Stc. Ste.Marie. Marie, Ontario Ontario and and Detroit. Detroit, the blast slam were obtained Michigan. The limestones investigated Michigan. Thethree threelimestones investigated were from the Fibron Limestone Limestone Formation of of middle middle Silurain City Limestone Silurain age age (Port Inland Inland Quarry), Quarry), the the Roger City Limestone Formation of of middle middle Devonian Devonian age age (Presque Isle Quarry), Quarry), and the the Bay Bay Port Port Limestone Limestone of of late Mississippian Mississippian age age (Bay (Bay County County ~ Road (Presquc Isle oad Commission Quarry). The Dolomite Formation of middle Thedolomites dolomiteswere wcre from from the the Engadine Dolomite middle Silurian Silurian (Cedarville Quarry), age (Cedarvillc Quarry), the the Raisin Raisin River River Dolomite DolomiteFormation Formationofoflate lateSilurian Silurianage age(France (FranceStone Stone Quarry). the Lucas Dolomite Dolomite Formation of Quan-y), of middle middleDevonian Devonian age age (Rockwood Quarry), Quarry), and a stratigraphically later dolomite from the Lucas Formation (Denniston Quany). stratigraphically later dolomite from the Lucas Formation (Denniston Quarry).The Theigneous igneous rocks rocks tested were were from from the Portage Lake Lake Volcanics Volcanics (Moyle (Moyle Quarry) Quarry)and and the the Paleoproterozic Paleoprotcrozic volcanics near near Bruce Mines, Ontario Ontario (Ontario (OntarioTraprock Traprock Quarry). Quarry). The aggregates weresubjected subjectedtotouniaxial uniaxial compressive compressiveloads loadsatattwo twodifferent different strain strain rates. rates. Low Low strain aggrcgates were strain rate (static) wcre were conducted conducted on on aa MTS servohydraulic and high strain rate experiments experiments (static) sc~ohydraulicmachine machine and strain rate rate experiments (dynamic) (dynamic) were conducted conducted on on aa modified modified split Hopkinson Hopkinson pressure pressure bar (MSHPB). (MSHPB). The The experiments Split bar (also çalsocalled calledaa Kolsky Kolsky bar, bar, Kolsky, 1949) Split Hopkinson Hopkinson pressure pressure bar 1949)technique technique has has been been widely used for for dynamic testing testing of of materials materialsatathigh highstrain strainrates ratesininthe therange rangeofof10'-104 IO'-l 4 s"' s' (Ravichandran used (Ravichandran and and Subhash, 1995). It consists consists of aa striker strikerbar, bar, an anincident incidcntbar barand andaatransmission transmission bar, bar, as as shown shown Subhash, 1995). schematically in Figure I.1. The schematically in Thespecimen specimen totobe becharacterized characterized isis placed placed between between the incident incident and and transmission bars. bars.The Thefree freeend endof of the theincident incident bar bar isis impacted impactedby by the the striker striker bar, bar, which which is launched transmission launched from aa gas gun, at aa predetermined predetermined velocity. velocity. The pulse in in the incidcnt incident The impact impact generates generates aa compression pulsc from specimen,subjecting subjectingitit to to the the required required compressive compressiveloading. loading.AApart part of of bar which travels towards the specimcn, and the the rest rest is is rcflected reflected back back into into the the incident bar as a this pulse is transmitted to the transmitter bar and tensile pulsc. pulse. Strain Strain gages gages are are mounted mountedat at the the center center of of each bar to measure the magnitude and tensile each bar measure the magnitude and duration of of these these stress stress pulses. pulses. Based Based on on one-dimensional one-dimensional calculations, calculations, it can can be be shown shown that that the the magnitude of the transmitted pulse gives a measure of the stress to which the specimen is subjected the transmitted pulsc gives a measure which the specimen is subjected and the the magnitude and magnitude of the reflected reflected wave gives aa measure measure of the the strain strain rate rate within withinthe thespecimen. specimen. 54 �integrating Integratingthe the strain strainrate ratewith withrespect respecttototime timeyields yieldsthe thestrain strainin in the the specimen. specimen.Thus, Thus. the thestress-strain stress-strain a material can be obtained at high strain rates. response response of a material can be obtained at high strain rates. A A minimum minimum often of tensamples sampleswere weretested testedfor foreach eachaggregate aggregatetype type in in each each condition, condition, e.g. e.g. thy, dry,saturated, saturated, static, and dynamic dynamic conditions. The Theresults results of of the the static static and and dynamic dynamic testing for thy dry conditions conditions are arc presented in Figure slags arc are identified identifiedas as sample sampletypes types I.1. 2, 2, and 3; the 2, where whcre the the blast blast fi1rnace furnace sla&s the Figure 2, and the basalt and 6; the dolomites are sample types 7 through 10; lirnestones are sample types 4, 5, limestones are sample types 4, 5. and the dolomites arc 10; and the basalt sample sample types are II11and and12. 12. In addition, the bulk density of the rock types are are also alsopresented. presented. ItIt can can be be seen seen from from this thisdata datathat thatthe theslags slagsexhibited exhibitedthe thelowest lowest strength strength followed followed by the the limestones limestones and and addition, itit can can be be sccn seen that that there there is is aa good dolomites dolomites with withthe thebasalts basaltshaving havingthe thehighest higheststrength. strength. In In addition, good of the the slag!,, slags, all of the correlation with with bulk bulk density. density. With the partial exception cxception of the materials materials tested tested showed an increase indicating that that these materials are increase in in dynamic dynamic strength strength over o v a the static strength, strength, indicating rate rate sensitive. sensitive. The blast blast furnace furnacc slag slag showed showed relatively relatively low low strength strength both both in in satic satictesting testingand anddynamic dynamictesting. testing. However, it can be strength and strength in the range of the be seen that that the the air air cooled cooled slag had both low strcngth the limestoncs dolomites. The liniestones and dolomites. The two two data data sets sets shown shown for for the the air air cooled cooled slag slag represent represent samples samples form form two different blocks of slag slag material material assumed assunicd to have been been cooled cooled at different rates depending on where it was deposited. The blast fijrnacc slag is formed from the gangue gangue and and secondary secondaryconstiuents constiuents whcre deposited The blast furnacc slag is formed from the in iron ore as and has has aa chemical chemicalcomposition compositionof ofCaO, CaO,Si02, Si02, A103 Al03 as well as coke residue and limestone and and MgO with trace amounts of of.sulphur and some some alkalis alkalis (Smolczyk, (Smolczyk,1980). 1980). The final structure of sulphur and the slag depends on the cooling conditions conditionsof ofthe themolten moltenslag. slag. When When itit is allowed to cool slowly it forms into into aadense densecrystalline crystallinestructure structurewith with properties properties similar similartotorock. rock. When the molten molten slag slag isis quenshed quickly with limited amonts of water, it traps steam in the mass and produces a porous, quenshed quickly with limited amonts of water, mass and produces a porous, glassy properties. However, slag is formed it also glassy material material with poor mechanical propcriies. Howcvcr, when the air cooled slag has different rates of cooling depending on its location when when deposited deposited for for cooling. cooling. The The molten moltenslag slag exposed to the then the slag at the the atmosphere atmosphere (top) will cool more more quickly then the bottom bottom of ofthe thedeposit. deposit. The appearance of pores. The statification statification when when cooling cooling isis cieariy clearly observed observed by a color straification and the appearance The test data data shows shows this this with with aa significant significant increase increase in strength strcngth with test samples from two different blocks from from the the same same deposit. deposit, i.e., i.e., top topand and bottom bottom locations. locations. In the case of the tested, itit can can be be sccn seen that that the the trap trap rock rock basalt basalt has aa higher strength then the the basalt.s basalts tested, Portage Portage Lake Lake volcanic volcanic basalt. basalt. in In a simplied simplied framework it is assumed that the cooling rate of the trap trap rock basalt was longer which were were formed formed formed formed near near or or at the longer than the Portage Portage Lake voleanics, volcanics, which the surface. surface. This is also also seen in in the the crystalline crystallinc structure structurc of the two basalts, with the trap trap rock rock basalt basalt having a more uniform crystallinc crystalline structure structure and and the the Portage Lake Lake volcanics volcanics a more inconsistent and random crystalline crystallinestructure. structure. The The sedimentary sedimentarylimestones limestones and and dolomites dolomitesalso alsoshow showrate ratesensitivity. sensitivity. It is interesting interesting to note in the the limestones that the the static strength strength for the three three limestones limestones tested tested are relatively relatively close, close, while the the limestones that dynamic dynamic strength strength are archigher. higher. In particular, the Silurian limestone (Port Inland) showed significantly significantly higher rate sensitivity than does the Devonian limestone (Preque Isle) or the Mississippian limestone sensitivity (Prcque Islc) limestone With the exception However, this same trend is not seen in the doloinites. trend seen in the dolomites. With cxception of the the (Bay County). County). Howcvcr, this Silurian dolomite (Cedarville) (Cedarvillc)there thereisis an an increase increase in in both Silurian dolomite both the static static and and dyanmic dyanmic strength strength with with geologic geologic age. age. Previous research has has shown shown that that for Previous research for aa brittle brittle material, material, the the damage damage evolution evolution under under applied applied compressive microeracking at defects such a pores, inclusions, second compressive loading is intimately related to microcracking second phase particles, twin grain boundary intersetcions and triple point grain boundary boundary junctions junctions (Lanford, (Lanford, 1977). However, strain rate the the rate rate sensitivity of a However, under dynamic loading conditions above a critical strain atiributted to to the the inertia-dominated inertia-dominateddynamic dynamiccrack crackgrowth growthfrom fromprc-existing pre-existingflaws. flaws. Thus, material is attributted 55 �response responseofofaadefect defecttotoloading loadingisisinertia inertiadependent, dependent,i.e. i.e,the thetime timeitittakes takestotoovercome overcomethe theinertia inertiaofofthe the strength. Therefore, microcrack, more defects are loaded in the material leading to higher microcrack, more defects are loaded in the material leading to higher strength. Therefore, ititisis speculated speculated that thatififdynamic dynamicloading loadingstresses stressesaalarger largerportion portionofofa amaterial's material'sdefects, defects,then thenititmay maybebe lithification may possible possiblethat thatgeologic geologicmechanism mechanismsuch suchasasformational formationalhistory, history,compaction compactionand and lithification maybebe better bcncrobserved observedunder underdynamic dynamicfracture fracturetesting. testing. References References Koisky, Kolsky,H., H.,1949, 1949,AnAnInvestigation Investigationofofthe theMechanical Mechanicalproperties propertiesof ofMaterials MaterialsatatVery VeryHigh HighRates Ratesofof Loading. Proc.R.R.Soc. Sue.London, London,B62, B62,pp. pp.676-700. 676-700. Loading,Pmc. Ravichandran. Ravichandran,G. G.and andSubhash, Subhash, G., G., 1995, 1995, A A Micromechanical MicromechanicalModel Modclfor forHigh HighStrain StrainRate RateBehavior Behavior 32 Ceramics,lifiernalional International.Journal JournalofofSolids Solidsand andSiructures. S/ruc/ure.~. 32[17/IS], [I 71181,pp. pp.2627-2646. 2627-2646. ofofCeramics, Smolczyk, 1950, Smolczyk,H.G.. H.G., 1980.Slag SlagStrcture Strctureand andIdentification IdentificationofofSlags, Slags,Inter. Inter.Congress Congressononthe theChcmistry Chemistryofof Cement, editions Septima, Cement,7"7*ed. ed.1980. 1980.Paris Parisa aeditions Septima,pp. pp.3-17. 3-17. High HighSpeed, Speed,44Channel Channel Digital DigitalOscilloscope Oscilloscope PR040) (NicoletPRO4O) (Nicolet I I Wheatstone Bridge Strain gage - 1 Striker StrikerBar Bar - specimen m m Incident IncidentBar Bar I Transmission TransmissionBar Bar Modifidied ModifidiedSplit SplitHopkinson HopkinsonPressure PressureBar Bdrwit witMomentum MomentumTrap. Trap. Figure Figure I 1 0 = 0 S d 22 Q F - 700 V 0 H 0 ii Ji 1' 3.5 ID — 600 m U. 5 C 0 3.0 Stat 500 C., E Dens 0 0 > 0 C 0 1 400 I I 300 I .4: 2.5C I 0 C, V C 1 I I; 200 2' VA = 0 C 2.0 00 0 0 1.5 1 2 3 4 5 6 7 6 9 10 11 Sample SampleType Type Figure Figure22 Dynamic Dry Conditions. Dynamicand and Static Static Strength Strength Tests Tests in Dry Conditions. 56 56 12 13 �8 Palmer Palmer Gneiss; Gneiss; aa large, large, low-grade low-grade shear shear zone zone ' 1 ~ e b s t e rC. C. , L., 'Cambray 'cambray W. W. F., F., 2Scott, '~cott,0., G.,'~ordstrom, 'Webster, 2Nordstrom, P. P. 'Widson, 'Wilson, E. 'Dept. Sciences, Lansing, MI 48824 ' ~ e ~Geological Geological t. Sciences, Michigan State State University, University, East Lansing, 22Cleveland Cliffs Mining Co, lshpeming, MI Cleveland Cliffs Ishpeming, MI The Marquette Marquette Trough Trough is is interpreted interpreted to to be be an an asymmetric asymmetricrift-related rift-related basin; basin, truncated truncatedstratigraphy stratigraphy southern margin and a rollover on the southern rollover structure structure to to the the north north provides provides evidence evidencefor for this this interpretation, Marking interpretation. Markingthe thesouthern southernboundary, boundary,between between the the Archean Archeangneiss gneiss and and the the Early Early Proterozoic Proterozoic metasedimentary metasedimentary rocks of the Marquette Marquette Range Supergroup, is the Palmer Gneiss (PG). Van Hiseand andBayley Bayley(1897) (1897)first firstinterpreted interpretedthe the PG PG as as aa comminuited, comminuited, sericitzed and VanRise partly silicified silicified phase of of the lower lower Precambrian Precambrian gneiss. In In1968, 1968,Gair Gairand andSimmons Simmonsconcurred concurred with theft their interpretation and offered offered three three possible modes of genesis: (1) alteration and shearing of Precambrian Precambrian rock during during faulting, faulting, (2) (2) migration migrationof of fluids the contact contactbetween betweenlower lowerand and fluids along along the middle Precambrian rocks, and (3) alteration of of aa regolith regolith during duringfolding. folding. Since the the time time of of mapping by Gair Gair and Simmons, Simmons, Tilden Tilden open pit mining mining operations have exposed the PG. Large Large shear bands, with approximately approximately2.5 2.5 meter meter spacing, spacing,indicate indicatethe the importance importanceof of ductile ductile zone (Figure (Figure 1). Foliation deformation during the formation formation of the PG in a low-grade shear zone Foliation measurements show measurements show aa steep steep NNE NNE dipping dippingS-foliation S-foliation being being cut cutby by aa shallow shallowNNE NNE shear shearband, band, indicating a reverse sense sense of shear (Figure 2). The Thefolds foldsmeasured measuredin in the the adjacent adjacent iron ironformation, formation, at the Tilden Tilden and and Empire Empire mines, mines, consistently consistentlyplunge plunge gently gently towards towardsthe the WNW, WNW,reflecting reflectingthat that they were formed zone. The formed under under the same strain strain conditions conditions as the shear zone. TheNNE-SSW NNE-SSW compressive compressive direction direction corresponds corresponds to previous studies in the area (Myers, 1984). Whole Whole rock rock chemical analysis chemical analysis of of the PG PG suggests suggeststhat that these these altered altered rocks rocks are are not not granitic granitic in in origin, origin, but but rather rather basaltic. The age. The The basaltic basalticnature nature indicates indicates that the PG is of Proterozoic age. The Penokeon Penokeon Orogeny, collision of an island island arc arc with with the the Lake Lake Superior Superior Craton, Craton,caused caused closure closure of of the the Marquette MarquetteTrough Trough that reactivated preexisting normal faults and resulted in a reverse dip dip slip. slip. Strain Strain was was concentrated concentrated in in aa portion portion of of aa metadiabase metadiabasesill sillthat that was was dragged dragged into into the the shear shearzone zone causing causing 57 �alterationand andshearing shearingofofthe therock rocktotoform formthe the PG. A 34% loss of volume is the calculated effect alteration PG. A 34% loss of volume is the calculated effect alterationfrom fromthe themetadiabase metadiabaseprotolith protolith to the PG (Gresens, 1967). ofofalteration to the PG (Gresens, 1967). References: References: Gair, J. E., and Simmons, G. C, 1968, Palmer Gneiss-an example of retrograde metamorphism Gair, J. E., and Simmons, G. C, 1968, Palmer Gneiss-an example of retrograde metamorphism alongan anunconformity: unconfonnity:U.S. U.S.Geological GeologicalSurvey Survey Professional Paper, 600-D, p. D186along Professional Paper, 600-D, p. D186D194. D194. Gresens, R L., 1967, Composition-volume relationships of metasomatism: Chemical Geology, v. Gresens, R. L., 1967, Composition-volume relationships of metasomatism: Chemical Geology, v. 47-65. 2,2,p.p.47-65. G., 1984, Structural analysis of foliated Proterozoic metadiabase dikes in the MarquetteMyers, Myers, G., 1984, Structural analysis of foliated Proterozoic metadiabase dikes in the MarquetteRepublicregion regionofofNorthern NorthernMichigan: Michigan:Master's Master's Thesis, Michigan State University. Republic Thesis, Michigan StateofUniversity. Van Hise, C. R . , and Bayley, W. S., 1895, The Marquette iron-bearing district Michigan: U.S. Van Hise, C. R., and Bayley, W. S., 1895, The Marquette iron-bearing district of Michigan: U.S. 28, p. 608. GeologicalSurvey SurveyMonograph Monograph28, Geological p. 608. East West 2.5 Fig.11Footwall FootwallShear ShearZone, Zone,Tilden TildenMine Mine Fig. N\ . -*- (Palmer Gneiss) (Palmer Onees} o • Pole to mean C'-foliation Pole to mean C-foliation Pole to mean S-foliation Pole to mean S-foliation Slip direction Mean S-C' intersection A Slip direction * Mean S-C. intersection S-C' intersections S-foliation plane S-foliation plane Top of shear zone S-C' intersections \ Top of shear zone C'-foliation plane C-foliation plane StereonetofofFootwall FootwallShear ShearZone, Zone,Tilden Tilden Fig.22Stereonet Fig. 58 58 �IS ISTHE THEJANICE JANICELAKE LAKEUNCONFORMITY UNCONFORMITYAALINK LINKBETWEEN BETWEENTHE THEHEARNE HEARNE LAKE VOLCANIC ARC? CRATON CRATONAND ANDTHE THELA LARONGE RONGE- LYNN LYNN LAKE VOLCANIC ARC? YEO. YEO,Gary GaryM., M.,Saskatchewan SaskatchewanEnergy Energyand andMines, Mines, 1914 1914Hamilton HamiltonSt., St.,Regina, Regina,SK, SK, - S4P 4V4, gary.yeo@sem.gov.sk.ca The TheWollaston WollastonDomain, Domain,aaNE-trending, NE-trending, 75km 75 kmwide widebelt beltofof2076-1860? 2076-1860?Ma Maparagneisses, paragneisses, overlying Archean orthogneisses along the eastern edge of the Heame Craton overlying Archean orthogneisses along the eastern edge of the Hearne Cratonin in Saskatchewan, Saskatchewan,isis separated from 1910-1875 Ma arc volcanics and sediments of the La Ronge Domain by (a) (a) separated from 1910-1875 Ma arc volcanics and sediments of the La Ronge Domain by Archean Archeanorthogneisses, orthogneisses,poorly poorlyknown known supracrustal supracrustalrocks, rocks, and and minor minor Proterozoic Proterozoic plutons plutons of of the the Peter PeterLake LakeDomain, Domain,(b) (b)1855 1855Ma Mamonzogranite monzograniteto toquartz quartzdiorite diorite of of the the Wathaman Wathaman Batholith, Batholith, and and (c) (c)the theRottenstone RottenstoneDomain, Domain,aamigmatitic migmatiticbelt beltof of sediments, sediments,similar similarto to those those of of the the La La Ronge Ronge Domain, Domain, intruded intrudedby by tonalite. tonalite. The Theboundary boundarybetween betweenWathaman Wathaman Batholith Batholith and and Wollaston and Lake Shear Zone. While this Parker Peter PeterLake Lakedomains domainsisisthe theNeedle NeedleFalls Falls-- Parker Lake Shear Zone. While thisisisaafundamental fundamental break breakbetween betweenancient ancientcrust crustto tothe thewest westand andjuvenile juvenile crust crustof of Trans-Hudson Trans-Hudson Orogen Orogen to to the the east, east, there thereisisno noevidence evidencethat thatititisisaacollisional collisionalsuture. suture. Within Within the theWollaston Wollastonsupracrustal supracrustalsuccession, succession,the the Janice Janice Lake Lake Conglomerate, Conglomerate, which can be traced discontinuously for 245 km along the eastern margin of the belt, be traced discontinuously for 245 km along the eastern margin of the belt, marks marks aa major major unconformity. The conglomerate is polymictic, with clasts derived from underlying unconformity. The conglomerate is polymictic, with clasts derived from underlying strata strata predominating. predominating.Locally, Locally,ititincludes includesfanglomerate. fanglomerate.Although Althoughthe theconglomerate conglomeratecannot cannotbe betraced traced westward, westward,younger youngercalc-silicate calc-silicatebearing bearingstrata, strata,locally locally resting restingon on various various older olderlithostratigraphic lithostratigraphic units, units,mark markthe thepresence presence of of aa profound profound unconformity. AAcorrelative correlativeunconformity unconformityhas hasbeen been recognized recognizedininthe theManitoba Manitobasegment segmentof of Wollaston Wollaston Domain, Domain, another another200 200 km km to to the the northeast. northeast. In In the the absence absence of of any any evidence evidence for for thermal thermal uplift (ie. igneous igneous activity), uplift and extension extensionin in Janice Janice Lake Lake time time must must be be due due to to mechanical mechanical flexure flexure of the crust. AAprobable probablecause causeisis Lynn Lake tectonic tectonicloading loadingof of the the eastern eastern margin margin of of the the Hearne H e m e craton craton as as the the La Ronge --Lynn Lake volcanic volcanic arc LaRonge Ronge-arcconverged convergedtowards towardsitit over overan an east-dipping east-dippingsubduction subduction zone. zone. Volcanism Volcanismininthe theLa Lynn LynnLake Lakearc arcbegan beganabout about1910 1910Ma Maand andreached reachedaa peak peak about about 1880 1880Ma. Ma. Following Followingarc-craton arc-craton collision collisionat at about about1860 1860Ma, Ma, the the sense senseof of subduction subductionwas was reversed reversed and the Wathaman Batholith was was emplaced emplaced at at about about 1855 1855 Ma. Geochemical Geochemicalevidence evidencesuggests suggests that the La Ronge segment of the thearc arcdeveloped developedin in aatransitional transitionalcrust crust setting, setting, close close to to or or partly partly over marginal continental crust. Tectonic Tectonic loading loadingof of the the outboard outboard margin margin of of the the Heame Heame Craton Craton would have resulted in an inboard flexural bulge, with consequent normal faulting and erosion over its crest and deposition inboard flexural bulge, with consequent normal faulting of coarse clastics on its flanks. As convergence proceeded, the bulge of coarse clastics on its flanks. As convergence proceeded, the bulgewould would have have migrated migrated cratonward cratonward and and died died out, out, creating creatingaa diachronous diachronous regional unconformity. Preservation Preservationof of coarse coarse clastics clasticswould would be be favoured favoured only only on the the trailing, eastern flank of the bulge, however. The The approaching approachingvolcanic volcanic arc arc would would have have become a bather barrierto tothe the open open ocean, ocean, and and accumulation accumulation of evaporites evaporitesand and carbonates carbonates in in the the resulting resulting restricted restricted basin would have been increasingly favoured. This by the the This hypothesis hypothesisalso also explains explains the the dramatic dramatic change change in sedimentation recorded by Wollaston of Wollastonparagneisses. paragneisses. Following Following2100 2100Ma Marifting, rifting, the the widespread widespread Lower Sequence of psammopelites, psammopelites,pelites, pelites, and and feldspathic feldspathic psammites accumulated accumulated on a passive margin. As As arcarcahead of of craton craton convergence convergenceproceeded, proceeded,coarse coarseclastics clastics were were shed shedoff off aa migrating migrating flexural flexural bulge bulge ahead the arc. Upper Sequence calc-silicate rich strata subsequently accumulated in the developing the arc. Upper Sequence calc-silicate subsequently in the developing foreland basin. basin. foreland 59 �- (a) Rift Rift Sequence (Courtenay (Courtenay - Cairns Cairns Lake LakeBelt): Belt):2100 2100 Ma Ma Rift Stretched continental crust sediments—_ * + t ÷ j* + %+ + L+ + ± Superior Cratori? - Hearne Craton ÷+ ÷ + %+ + A+ + + ±1 ++ ÷ 4• + Oceanic crust - ,.., La Range Volcanic Volcanic Arc Arc (1910- 1860 Ma) (b) Lower LowerSequence: Sequence:2100 2100- 1880 1880Ma I - (c) Upper Sequence: 1880 1880-1860 1860 Ma Ma Restricted basin Restricted basin Uplift and erosion (uncónforrMy) Uplift (uncbnformity) (d) Cord illeran Margin: 1860 - 1830 Ma Foreland sedimentation tharnan (1855 Ma) Reference Reference +'>, : <;s Yeo, ci. G. 1998. 1998 A systems tract approach oach to totthe stratigraphy of paragneisses isses in in the the southeastern southeastern Wollaston Domain: Wollaston Domain: Saskatchewan Saskatchewan Energy Energy and and Mines, Mines, Misc. Misc. Rep. Rep. 98-4, 98-4, p36-47. p36-47. 60 �LOW-RESOLUTION OFF EARLY PROTEROZOJC LOW-RESOLUTION SEQUENCE SEQUENCE STRATIGRAPHY STRATIGRAPHY O EARLY PROTEROZOIC PARAGNEISSES, PARAGNEISSES, WOLLASTON WOLLASTON DOMAIN, DOMAIN, SASKATCHEWAN SASKATCHEWAN YEO, Saskatchewan YEO, Gary Gary M., M., SaskatchewanEnergy Energy and andMines, Mines,1914 1914Hamilton HamiltonSt., St.,Regina, Regina,SIC, SK. S4P S4P4V4, 4V4, gary.yeo @sem.ov.sk.ca The Wollaston Wollaston Domain 75 km km wide wide belt belt of of of of early early Proterozoic Proterozoic paragneisses, paragneisses, The Domain is is aa NE-trending, NE-trending, 75 overlying Archean orthogneisses the eastern eastern edge edge of of the overlying Archean orthogneisses along along the the Hearne Hearne Craton; Craton; west west of of the the TransTransHudson Hudson Orogen. Orogen. Bimodal Bimodal volcanics volcanics near near the the base base of of the the paragneiss paragneiss succession succession give give aa U-Pb U-Pb zircon zircon age granitic plutons plutons range range from from 1.81 to 1.84 Ga. A age of of 2.08 2.08 Ga. Ga, while while minor minor gabbro gabbro and and granitic 1.81 to 1.84 Ga. A threethreeyear, year, 1:20,000 1:20,000 scale scale mapping mapping project project was was begun begun in in 1997 1997in in the the southern southern part part of of Wollaston Wollaston Domain Domain to to improve improve understanding understanding of of the the stratigraphy stratigraphy and and structure structure of of the the guesses, gnesses, which which underlie underlie the unconformity-type unconformity-type uranium the uranium deposits deposits of of Athabasca Athabasca Basin. Basin. A A basic basic strategy strategy of of the the project project is is to to map outward from Archean inliers so as to be able to work out the stratigraphic succession in map outward from Archean inliers so as to be able to work out the stratigraphic succession in spite of of complex complex deformation deformation and spite and high high metamorphic metamorphic grade. grade. Four episodes of of regional regional deformation deformation can can be be distinguished. distinguished. D Dll involved Four episodes involved isoclinal isoclinal folding, local local basement basement ovenhmsting, overthrusting, and and transposition transposition of of primary primary layering layering into into the the SSIl foliation, foliation. folding, D2 involved involved tight tight to D2 to isoclinal isoclinal folding folding about about NE-trending NE-trending axes, axes, superposition superposition of of aa strong strong 52 S2 foliation, and and local local thrust thrust faulting. faulting. D3 foliation, D3 involved involved local local open open folding folding about about SW SW to to NW N W axes, axes, and and local brittle-ductile fault fault movement. movement. D4 D4 involved involved minor minor sinistral sinistral offset offset on on aa series series of of N N to to NNW NNW local brittle-ductile trending brittle trending brittle faults. faults. Two lower granulite facies) (upper amphiboIite amphibolite - lower Two episodes episodes of of high high T T -- low low P (upper metamorphism are associated associated with Dl and Peak with Dl a n 1)2 d ~ deformation. def&mation. 2 Peak P-T PITconditions, conditions. reached reached during during metamorphisk are D2, 750°C and and 55 kbar. kbar. Along the eastern margin of the belt, however, metamorphic D2, were were about about 750° Alone the eastern margin of the belt. however, metamorphic grades are are relatively relatively low lower amphibolite facies). grades low (upper (upper greenschist greenschist - lower Two widespread Two widespread paragneiss paragneiss successions successions are are distinguished distinguished in in Wollaston Wollaston Domain: Domain: aa lower lower Pelite Pelite Unit, Unit, and and an overlying overlying Psammite Psammite Unit. Unit. These These can can be be subdivided subdivided into into at at least least eight eight subunits subunits in the the Foster Foster -- Daly lakes area. Two lakes area. Tworestricted restricted successions successions are are also also recognized: recognized: aa basal basal package package in (Courtenay Lake Lake and (Courtenay and Souter Souter Lake Lake Formations), Formations). preserved preserved locally locally along along the the eastern eastern margin margin of of the the domain, and the heterogenous Hidden Bay Assemblage of interlayered quartzites, pelites. domain. pelites, amphibolites. calc-silicates, amphibolites, calc-silicates, and and marbles, marbles, which which likely likely overlies overlies or or is is correlative correlative with with the the Psammite Unit Unit near near Wollaston Wollaston Lake. Lake. The demonstrated to to Psammite TheCourtenay Courtenay Lake Lake Formation Formation has has been been demonstrated be a rift succession, while a passive margin margin setting is inferred inferred for for the the overlying overlying Pelite and Attempts to to determine the depositional setting of individual lithologic units, Psanunite units. Attempts Psammite however, have been restricted to to the the low-grade low-grade rocks rocks along along the eastern margin of of the the domain. domain. Although sequence Although sequence stratigraphy stratigraphy has has become become aa standard standard technique technique for for analysis analysis of of platform platform and craton margin strata, there have been few attempts to apply it to metamorphosed and deformed rocks. rocks. As which deformed As demonstrated demonstrated here, here, itit has has great great potential potential in in interpreting interpreting strata strata in in which obliteration of primary primary features limits application of facies models or comparison with modern obliteration modem sedimentary environments. environments. Two major sequence boundaries subdivide the succession. succession. The The unconformity on Archean basement can be recognized recognized without without difficulty. difficulty. The Thebase baseof ofthe theJanice JaniceLake LakeConglomerate Conglomerate(Unit (Unit Wo) marks a second unconformity. unconformity. To To the the west, west, where where the the conglomerate conglomerate is is absent, this unconformity corresponds to the base base of of the the calcareous rocks rocks that that overlie overlie it. it. Within each unconformity sequence, the mapped lithofacies lithofacies units can be asigned to a succession of of systems systems tracts. 61 �Lower Sequence: Lower Sequence:Ferruginous Ferruginous(garnet), (garnet),anoxic anoxic(graphite), (graphite), muddy muddy sediments sediments of Unit Wna fine upward upward into aluminous (clay-rich) (clay-rich) muddy muddy sediments sediments of of Unit Unit Wnps. Wnps. Such retrogradation is consistent with transgressive systems is consistent with aa transgressive systems tract. tract. The quartzite quartzite beds in Unit Unit Wna may be stormstormgenerated flows. Less aluminous muddy sediments of Unit Wns are transitional through Unit Wnsp to Unit Wrn Wm sands. Such a progradational sequence is consistent with a highstand systems systems tract. Upper Sequence: Upper Sequence:Polymict Polymictconglomerate conglomerateof ofUnit UnitWo Womarks marksaaperiod periodof of uplift uplift and and succession. Although erosion. Most Most clasts clasts are are derived derived from the underlying sedimentary succession. restricted to the eastern margin of Wollaston Domain, Domain, the Janice Janice Lake Lake Conglomerate Conglomerate can can be be for at at least least 245 245 km. km. This unit is interpreted interpreted as as alluvial alluvial fan fan deposits. deposits. Nontraced along strike for tract. An marine conditions indicate that it is a lowstand systems tract. An upward upward decrease decrease in in clastic input is suggested between calc-silicate calc-silicate bearing bearing Unit Wmc Wrnc and and calc-silicate calc-silicate rich rich Unit Unit Wnc. Wnc. This suggests another transgressive transgressive systems tract. tract. The rocks may may be evaporitic The calc-silicate calc-silicate rich rich rocks deposits. LIthelpay LuhtMY C, 0 C C, C. C, Cl) IC, C. a Wnc lnterDretatipn Gale-silicate Gale-silicate rocks rocks Wrnc Wo Transgressive Transgressive Systems Tract Systems Tract Gale-silicate -bee ring Calc-silicate-bearing arkose 1 I - Gale-silicate-bearing Calc-silicate-bearing conglomerate and arkose Lowstand Lowstand Systems Tract Systems Tract C, 0 C C, Wnsp = C. C, Cl) Wns C, -I0 Wnps Wna I Arid zone zone alluvial fan deposits alluvial deposits Coastal sands sands Arkose and subarkose wbarkose Highstand Highstand Systems Tract Systems Tract Biotite psarn mite and psammopelite Transitionat Transitional shell shelf sands sands and muddy muddy sands and Biotite psammopeiite psammopelite and psammite psammite Shelf muddy sands Shell Sillimanite-cordieriteiimanite-cordieritebiotule psammopelite biotite ~ sammo~eiite and psammite Graphite-garnet-biotute psammopelite and psammopeiite and pelite pelite with quartzite interbeds shell muddy Outer shelf muddy sands sands and sandy muds Transgressive Transgressive Systems Tract Unconformity strain zone) (and high high strai Unconformity (and Basement 1 Carbonate-cemented Carbonate-cemented coastal sands coastal Uplift Uplift and and erosion erosion Unconformity Unconformity Wrn Sauna or restricted restricted basin basin Salina calcareous sediments calcareous sediments and and evaporites evaporites Anoxic shell shelf muds muds and and sands sands Uplift and erosion erosion Granitoid rocks rocks with with local local amphibolite, amphibolite, metased. metased. xenoliths, chsrnockie xenoliths, and charnockile References Delaney. G GD.. and Tisdale. Tisdale, D D., 1997, Geological investigations investigationsof ofthe theCounenay CourtenayLake. Lake. D Jankovic, Jankovic, Z., Z . MacNeil, MacNol. A.. A . McGowan, McGowan. J.. J .and 1997. Geological Cairnss Lake Fold Belt and the H Hill Embayment, Johnson Johnson River River Intier. Intier, Wollasion Wollaston Domain. Domain, northern northern Saskatchewan. Saskatchewan: C i l l Lake Embayment, Saskatchewan SaskatchewanEnergy Energy and and Mines, Mines. Misc. Misc Rep. Rep 97.4. 97-4,p90-1O1. p90-101 Tran, G.M., Geology of of the the Burtudge BurbidgeLake Lake'- northern Lake area, aica. eastern eastern Wollaston Domain Yeo, O M . . 1997. 1997. Geology northern Upper Upper Foster Lake Wollasion D omn Tran, H.T. H T and and Yeo, (NTS 74A-14): Saskatchewan Energy and Mines. Misc. Rep. 97-4. 97.4. p72-89. N T S 74A-14)- Saskatchewan Tran, H.T., Yco, G., Bradley. S. and Lowry, Jl*, 1998. Geology of the Daly-suttle-Middle Foster lakes asea, eastern wollaston S. and Lewry. J.F. 1998. o f the My-Sutile-Middle area. eastern Wollasion Tran. H.T.. Yeo. G.. and.12): -12)Saskatchewan Saskatchewan Energy E n e m and and Mines, Mmcs, Misc. Misc Rep. Rep 98-4. p36-47. Domajn (NTS Domain (NTS 74A-5, 74A-5, -I -Il.I, and p36.47. paragneisses iinn the the southeastern southeastern Wollaason Domain: Saskaichewal Saskatchewan G., 1998. A systems systems tract approach to to the stratigraphy of of para&sses Yeo, G.. 1998, A ~oliaston Domain: Energy and Mines, Misc, Rep. 98.4. Mines. Misc. 984. p36.47. p3647. . . 62 � https://digitalcollections.lakeheadu.ca/files/original/23d76f1727e6bc080350abdf1335866d.pdf 54d5b014057f0f987f6c366c6fc057ee PDF Text Text Trip 1: Early EarlyProterozoic Proterozoic Strata Strata of the Maquette Marquette Iron of Range, Michigan Ishpeming Trip 22:: Archean Arc1 Greenstone Belt and Ore, G01d Golf Mineralization H-<o<a 3: Tilden Trip 3: Tilden and and Empire Empire A tc.* ~ c . \6 6 A\~ Mines 0f the Marquette Mines of Marpette Iron Range, Michigan Trip 4: Paleozoic andIGlacial Glacial Geology from1 Au Train to to Grand Marais,3, Michigan I on ~Lake Institute on ake Superior Geology 45th 45th Annual Annual Meeting Meeting Ramada da IInn nn Rama Marquette,,Michigan Maquette ~ichigan May 4-8, 4-8, 1999 1999 Sponsored by Sponsored Northern Northern Michigan Michigan University and Michigan University and Michigan Technological University Proceedings Volume 45: Field Trip Guidebook Theodore J. Bornhorst, editor �45TH ANNUAL MEETING SUPERIOR GEOLOGY GEOLOGY INSTITUTE ON LAKE SUPERIOR Volume 45 consists of Part Part 1: 1:Program Programand and Abstracts Abstracts Part 2: 2: Field FieldTrip Trip Guidebook Guidebook Reference to material in this volume should follow the example below: Holm, D., 1999, 1999, Characterization and timing constraints of post-Penokean Ams, D. and Hoim, meso-scale structures in the Watersmeet and Republic gneiss domes of northern Michigan (abst.): (ahst.): Institute Institute on on Lake Lake Superior Superior Geology Proceedings, 45th Annual Meeting, Marquette, MI, v. 45, part 1, 1, p. 2. 2. Volume 45 Published and distributed by Institute on Lake Superior Geology Mark .G. Mark Jirsa, Jirsa, Secretary-Treasurer, Secretary-Treasurer,I.L.S I.L.S.G. Minneosta Geological Survey 2642 University Avenue St. Paul, MN USA 55114-1057 551 14-1057 (612)-627-4780 email: jjrsaOOl @tc.umn.edu email: jirsaOOl @tc.umn.edu ILSGwebsite websitehtto://www.eeo.mtu.edu/ereat http://www.geo.mtu.edu/great lakes/ilse/ lakes/ilsg/ ILSG ISSN 1042-9964 1042-9964 All volumes volumes are are available for photocopying All photocopying costs costs from Michigan Technological Technological University University Library Library Archives Archives �INSTITUTE ON LAKE SUPERIOR GEOLOGY PROCEEDINGS Volume 45 45 Part 2: Field Trip Guidebook �CONTENTS PROCEEDINGS VOLUME VOLUME 45 PROCEEDINGS PART 2: FIELD TRIP GUIDEBOOK GUIDEBOOK PART2: FIELDTRIP Editor: Theodore J. Bornhorst Field Trip 1 :: Early Proterozoic Strata Strata of the Marquette Marquette Iron Iron Range, Range, Michigan Leader: W.F. W.F. Cannon Early Proterozoic Strata Strata of the Marquette Iron Range by W.F. Cannon ........................ 22 Field Trip Trip 2: 2: Archean Archean Ishpeming Ishpeming Greenstone GreenstoneBelt Belt and and Gold Gold Mineralization, Mineralization,Michigan Michigan Leaders: T.J. Bornhorst, D.J. Duskin, R.C. Johnson, R.A. R.A. Mahin, Mahin, T.O. TO. Quigley, Quigley, and and G.W. G.W. Scott and An Introduction to the Archean Ishpeming Greenstone Belt, Michigan by R.C. Johnson and 12 T.J. Bornhorst .......................................................................................... 12 Introduction to the Ropes Gold Deposit in the Ishpeming Greenstone Belt, Michigan abstracted from R.A. Brozdowski by T.J. Bornhorst, S.E. Bair, and G. W. Scott ............ 29 29 Geologic Field Excursion to the Ishpeming Greenstone Belt by R.C. Johnson and T.J. T.J. 45 Bornhorst ............................................................................................... Bomhorst 45 Shear Zones and Gold Mineralization in the South Half of the Ishpeming Greenstone Belt, Michigan by D.J. Duskin and T.O. Quigley ................................................57 Examples of Gold Mineralization in the Northern Block of the Ishpeming Greenstone 97 Belt by T.O. Quigley and R.A. R.A. Mahin ............................................................... 97 of the the Marquette Marquette Iron Range, Michigan Field Trip 3: Tilden and Empire Empire Mines of Leaders: G.W. Scott, P.M. Nordstrom and H.M. Lukey Geologic setting of the Tilden and Empire Mines, Michigan by T.J. Bornhorst ............ 108 108 Geologic Field Trip to the Tilden Mine by G.W. Scott and H.M. Lukey .................... 114 114 Geologic Field Trip to the Empire Mine by P.M. Nordstrom ..................................129 129 Trip 4: Paleozoic and and Glacial Glacial Strata Strata from Au Au Train Train to Grand Grand Marais, Field Trip Marais, Michigan Michigan Leaders: R.S. Regis and J. Anderton Regis and J. Anderton Paleozoic and Glacial Geology from Au Train to Grand Marais, Michigan by R.S. Regis and J. J. Anderton ......................................................................136 136 �Field Trip Trip11 Early Early Proterozoic Proterozoic Strata Strataof of the the Marquette MarquetteIron IronRange, Range,Michigan Michigan Leader: Leader:W.F. W.F. Cannon Cannon 2 �FIELD TRIP #1 EARLY PROTEROZOIC PROTEROZOICSTRATA STRATA OF OF THE THEMARQUETTE MARQUETTEIRON IRONRANGE RANGE LEADER: W.F. GEOLOGICAL SURVEY W.F.CANNON, CANNON, U.S. GEOLOGICAL INTRODUCTION preserved in the Marquette Iron Range Early Proterozoic strata of the Marquette Range Supergroup preserved the south edge of the the Archean Superior craton. record the tectonic evolution of a continental margin along the That evolution spans an imprecisely known period culminating in suturing with volcanic arcs to the south at about 1855 Ma. Ma. Lower the Chocolay Chocolay Group Group(Stops (Stops1,2,3,5), 1,2,3, 5), are mostly a sequence of Lower parts parts of the section, the pure quartzite, dolomite, and shale believed to have formed in a stable cratonic setting. They They were were deposited deposited now most commonly a fault (Stop I). unconformably on Archean greenstone and granite, but the contact is now 1). A low angle unconformity separates the Chocolay Group from the overlying overlying Menominee Group (Stop 5). The Menominee Group consists of a basal quartzite-shale unit (Stop 5) overlain overlain by the principal principal ironproducing unit in the range, the Negaunee Iron-formation The Menominee Menominee Group Groupwas was Iron-formation (Stops 6, 7, 10). The deposited in actively subsiding grabens, probably on the rifting continental margin, although a foreland researchers in in the the region. region. Strata basin setting is possible and is favored by some current researchers Strata of of the the Baraga Baraga 9, 11) are widely accepted accepted as products products of sedimentation sedimentation in in aa foreland foreland basin basin during during 8,9, Group (Stops 4, 8, preserved in in northern northern Wisconsin. Wisconsin. The accretion of volcanic terranes now preserved The Baraga Baraga Group Group which lies lies with with aa prominent low angle unconformity unconformity on rocks of the the Menominee Menominee Group Group (Stop (Stop 4), 4), is is composed composed mostly mostly of a prominent turbidite sequence of graywacke and shale (stop 11), and conglomerate conglomerate (stop (stop 4), 4), lesser 1I), quartzite and lesser black black shale shale (stop 8), and minor volcanic rocks rocks (stop (stop 9). 9). The Marquette Iron Range Range is is aa complexly complexly folded folded and faulted, faulted, gently gently west-plunging west-plunging synclinorium synclinorium composed of strata of the Marquette Range Supergroup and intrusive intrusive diabase diabase sheets. sheets. Deformation Deformation occurred occurred during the Penokean orogeny at about 1850 Ma. The synclinorium is bounded on both the north and 1850 Ma, The synclinorium is bounded on both the north and south south by Archean volcanic and granitic rocks, which are most most commonly in in fault fault contact contact with with the the Early Early Proterozoic strata. The Theintense intense penetrative penetrative deformation deformation seen seen in in the the Early Early Proterozoic Proterozoic strata strata isis not not present present in in the Archean basement rocks, which were last penetratively deformed in in Lake Lake Archean Archean time. time. This has led to penetratively deformed the interpretation that the Archean rocks behaved as relatively relatively rigid, rigid, fault-bounded fault-bounded blocks blocks during the Penokean orogeny, and were structuraliy highly deformed deformed Early Early Proterozoic Proterozoic strata. By structurally decoupled from the highly By that interpretation, the Marquette synclinorium is a graben with with respect respect to to Archean Archean basement basement rocks. rocks. The synclinorium synclinorium of of Early Early Proterozoic Proterozoic rocks rocks lies lies within within that that graben. graben. localities that that have have been been visited visited by by literally literally The Marquette area contains many classic geologic localities thousands of geologists during the past century. The TheInstitute Institute on on Lake Lake Superior SuperiorGeology Geology has has visited visited the the area area during several past meetings, but the the Marquette Marquette Range stratigraphy has has not not been been examined examined since sincethe the Twenty-first Annual Meeting in 1975. 1975. This Thisguidebook guidebook isis based based very very largely largely on on the the guidebook guidebook prepared prepared for for that meeting and other guidebooks guidebooks (Cannon (Cannon and and others, others, 1975; 1975; Prinz, Prinz, and and others, others, 1975; 1975;Margeson, Margeson,1989; 1989; Morey, 1989). 1989). For Forthose thosewho whohave havetoured toured the the region region before, before, the the stops stops will will be be largely largely the the same same and and the the rocks rocks familiar; only the interpretations have changed. The stops are arranged, arranged, to to the the extent extent practical, practical, to to view view the the beginning at the base of the the section section and and progressing progressing up-section. up-section. To streamline logistics and stratigraphy beginning minimize driving distances a few stops are out of proper stratigraphic order. 3 �a n - 00 1 1 22 33 44 1 5 miles 5miles 4- C; �frt? + C- 7p2 5 �Stop 1. Enchantment EnchantmentLake LakeFormation Formationand andArchean Archeanvolcanic volcanic rocks. rocks. The Enchantment Lake Formation is is a discontinuous unit at the base of of the Marquette Marquette Range Range Supergroup. ItIt consists arkose, and and slate. slate. Most geologists who have studied it Supergroup. consists of of conglomerate, conglomerate, graywacke, arkose, believe that itit is of of glacial glacial origin, origin, although although that that interpretation interpretation remains remains in in dispute. dispute. It conformably underlies underlies hills immediately immediately south south of of stop stop 1, I, but the Mesnard Quartzite. The The transition transition to the Mesnard can be seen in hills will not be visited on this trip. hip. Immediately north of the Old State State Road are are several exposures of of basal basal conglomerate conglomerate of of the the fragments of of tonalitic tonalitic gneiss gneiss and and greenstone. greenstone. The matrix is Enchantment Lake Formation, containing fragments is rich rich in in chlorite. The The conglomerate conglomerate can can be be seen seen in in sharp sharp vertical vertical contact contact with slaty, highly sheared greenstone greenstone of the underlying Mona Schist (Archean). About About 100 100 feet feet north of the contact, the Mona becomes mostly massive massive greenstone. Both Both the the greenstone greenstoneand and conglomerate conglomerate are are strongly strongly foliated foliated near the contact and and steeply steeply plunging to vertical lineations lineations are are common on on foliation surfaces. surfaces. The contact of the Mona Schist and Enchantment Lake Lake Formation Formation has has been been interpreted interpreted as as aa fault. In In addition to the highly sheared rocks along along the contact, contact, the two units units are are stratigraphically stratigraphically "back "back to to back". back". Pillows in the Mona Schist Schist in in nearby nearby outcrops outcrops are are uniformly uniformly north-facing, north-facing, whereas whereas the the Enchantment Enchantment Lake Lake and overlying formations are south-facing. The present attitude of the rocks is probably a result of vertical The present attitude of rocks is probably a of vertical rise of aafault faultblock blockof ofMona MonaSchist Schistand and passive passive draping draping of of the the Enchantment Enchantment Lake Lake Formation Formation over over the block. block. Stop 2. Mesnard Quartzite Quartzite and and Jacohsvitle Jacobsville Sandstone. Sandstone. In this lakeshore outcrop the Mesnard Quartzite, the basal orthoquartzite unit of of the the Chocolay Chocolay Group, is overlain with with aa sharp sharp angular angular unconformity unconformity by by the the Middle Middle Proterozoic Proterozoic Jacobsville Jacobsville Sandstone. Sandstone. strikes eastward and and dips dips White-weathering vitreous Mesnard Quartzite in beds 4 to 88 inches thick strikes 80°S to vertically. vertically. Cross 80's to Cross beds beds and and ripple ripple marks indicate top direction to the south, in conformance with the position of the quartzite on the north limb limb of the Marquette synclinorium. Reddish Jacobsvillle Jacobsvillle Sandstone Sandstone dips 10-15° 10-15' eastward to southeastward and the contact with the Mesnard is visible at several places on on the the outcrop. Patches of Jacobsville are plastered against the north side of the quartzite outcrop, and on the south side outcrop, and on the south side the contact is steep. Evidently Evidently during during deposition deposition of of the the Jacobsville, Jacobsville, the Mesnard at this locality formed formed a low topographic ridge, much as it does now. Flat-lying Flat-lying Jacobsville Jacobsville is is on the flank of Mt. Mesnard, about about 3/4 miles west of here and 370 feet above current lake level, which indicates a pre-Jacobsville topographic Vs miles relief and ruggedness approximately the same same or or greater than that adjacent to the present present shore shore of of Lake Lake Superior. Superior. 3. Kona Kona Dolomite Dolomite Stop 3. on the the Mesnard Mesnard Quartzite. Quartzite. The formation is mostly dolomite, The Kona Dolomite lies conformably on fine- to to medium-grained medium-grained clastic clastic rocks. rocks. The outcrops on the north siliceous dolomite, and lesser amounts of fineside of the highway show exceptionally exceptionally well preserved sedimentary textures indicative of of aa shallow shallow water water to to intratidal environment, probably open tidal tidal flats at at this this stratigraphic stratigraphic interval. interval. Many beds are algal carbonates with large stromatolites stromatolites exceptionally well displayed and accentuated by differential differential weathering. weathering. visitors. Other Please help preserve these features for future visitors. Other well preserved features features include dessication and rip-up structures, ripple marks, and rip-up beds beds probably probably produced produced by tidal currents. 6 �4. Goodrich Quartzite Stop 4. This stop, for the sake of economizing economizing driving drivingtime, time, isisnot notininproper properstratigraphic stratigraphicorder. order. We We have have temporarily skipped over the Menominee Group and will examine the basal conglomerate of the Baraga Group. At At this this stop, stop,just just south southof ofthe the village village of of Palmer Palmer and and near near the the old old Isabella Isabella Mine, Mine, coarse coarse conglomeratic conglomeratic Goodrich Quartzite are exposed. exposed. The rocks forming the lower part of the Goodrich The Goodrich Goodrich Quartzite, Quartzite, the the basal basal unit unit of the Baraga Group, unconformably overlies the Negaunee Iron-formation. Here Here aa basal basal conglomerate containing clasts of iron-formation iron-formation as as much as 0.5 0.5 m m diameter can be seen. The angular angular clasts clasts have have features features seen. The indicative of brittle fracturing, implying that the Negaunee Negaunee was was well well lithified lithified prior prior to to the the time that that these clasts were eroded. Well Wellrounded rounded clasts clastsof ofvein vein quartz quartz are are also also common, common, most most likely likely derived derived from from aa locally locally exposed basement basement terrane. terrane. The lack of other basement rock types in clasts may mean that the surface of The lack of in clasts may mean that the surface of vein material material persisted persisted in coarse fragments. The exposed basement rocks was deeply weathered so that only vein The exposures seen here are only a few feet above the unconformity and and Negaunee Negaunee Iron-formation Iron-formation was mined from small pits immediately immediately south south of of the the outcrop. outcrop. Conglomerate Conglomerate units such as seen here are typically lenticular. They range up to a few hundred feet thick locally but pinch out along strike so that quartzite commonly lies on the Negaunee with with little or no conglomerate. The Thecoarse coarseconglomerate conglomeratelenses lenses may mayhave have been been alluvial alluvial fans fans along along the the scarps scarpsof offaults faultsthat that were active during deposition. The Thefeatures featuresseen seenhere here suggest suggestaa rather rather long long time time interval interval across across the the unconformity and renewed deposition during reactivation reactivation of basement faults. One One interpretation interpretation isisthat that the the Menominee Group was deposited during continental margin and that the Baraga Group, continental breakup on a rifting margin beginning with the Goodrich Quartzite, was deposited deposited in in aa foreland foreland basin basin at at the the outset outset of of collision collision with with volcanic terranes now now seen seen in in northern northern Wisconsin. Wisconsin. 5. Chocolay Group and lower Group (Ajibik Quartzite Quartzite and Siamo Slate) lower part part of of Menominee Group Stop 5. The series of roadcuts along U.S. Highway much of the the stratigraphy stratigraphy of the the lower part of Highway 41 exposes much the Marquette Range Supergroup. The Theeasternmost easternmost cut cut shows shows aa few few tens tens of of feet feet of of green green chloritic chloritic slate slate Formation. Here mapped as the upper part of the Enchantment Lake Formation. Here the the Enchantment Enchantment Lake Lake differs differs significantly from that seen at stop I1 in in being being much much thinner, probably not much thicker than the section section exposed here, and it lacks conglomerate beds. The The Enchantment Enchantment Lake Lake grades grades over over aa few few feet feet into into the the overlying vitreous quartzite of the Mesnard Mesnard Quartzite, essentially similar similar to to that that seen seen at at stop stop 2. 2. The The Ajibik Ajibik Quartzite is exposed in the next set of roadcuts to the west. Although Although similar similar in in appearance appearance to to the the Mesnard, Mesnard, the Ajibik in general is somewhat more feldspathic. The The geology geology near near here here was was mapped mapped in in detail detail by by Willard Willard Puffett Puffen to document the rdationship relationshipbetween between the the two two quartzite quartzite units. units. Puffett Puffett was was able able to to trace trace aa distinctive distinctive granule bed, about 10 Ajibik and show that the the Ajibik Ajibik cuts across the 10 inches inches thick near the base of the Ajibik Mesnard at a low angle, demonstrating the angular unconformable nature of the the contact. contact. The The thinness thinnessof ofthe the Chocolay Group here and the absence of the Kona Dolomite reflect reflect the westward westward beveling of the group by the Ajibik. Within Withinaamile milewest westof ofhere herethe theChocolay ChocolayGroup Group isis absent absent and and the the Ajibik Ajibik rests rests directly directly on on Archean rocks. The Ajibik grades upward into the Siamo Slate seen in in roadcuts roadcuts about about 1000 feet feet farther farther west west on the south side ofthe of the highway. highway. The The Siamo Siamo is is a lithologic lithologic mixture of slate, slate, arkosic arkosic quartzite, and graywacke, generally in beds from a few inches to a few feet thick. thick. The The rock rock here here has has aa prominent prominent cleavage cleavage that that dips dips southward more steeply than bedding, consistent with the location location on the north limb limb of of the the Marquette Marquette synclinorium. An An interesting interesting and and controversial controversial feature feature of of this outcrop outcrop is is lenses lenses of graywacke that lie lie within 7 �the cleavage and transect bedding. Various Variousauthors authors have have interpreted interpreted these these as as clastic clastic dikes dikes or or as as lithified lithified beds beds tectonically forced into into cleavage cleavage planes. planes. Stop 6. 6. Negaunee Iron-formation (carbonate fades) facies) This stop, near the old Athens Mine, shows carbonate carbonate facies facies iron-formation iron-formation typical typical of of much much of of the the lower lower part of the Negaunee Iron-formation. Iron-formation. The here consists consists mainly mainly of of alternating alternating laminae laminae of of The iron-formation iron-formation seen here sideritic carbonate and 5% minnesotaite, which imparts a and chert, chert, but but some some layers layers contain contain as as much much as as 115% greenish color. Some Somelayers layerscontain contain small smallamounts amounts of of magnetite, magnetite, but but in in general general the the rock rock isis only only weakly weakly foot thick, are are also also present present in in the exposure. exposure. magnetic. Thin Thin sills sillsof ofaltered altered metadiabase, metadiabase, less less than than aa foot This exposure provides striking striking examples of the effects of of surface surface weathering weathering and and oxidation oxidation and and replacement of sideritic iron-formation. iron-formation. The The weathering weathering has has taken place in in the relatively few decades decades since since the road cut (originally a railroad cut) was excavated. Oxidation Oxidation has has advanced advanced inward inward from from cracks cracks and and exposed surfaces, first converting converting layers layers rich rich in in carbonate carbonate into into yellow yellow brown brown to to reddish reddish brown brown goethitic goethiticiron iron laminae into iron iron oxide. oxide. These oxide, and eventually changing even chert laminae These surficial surficial effects effects are analogous analogous to to those that formed the "soft ores" of the region. The major ore bodies in the eastern end of the iron range, The major ore bodies in the eastern end of the iron range, including those in the immediate immediate vicinity vicinity of of this stop, stop, were replacement masses of of iron iron oxides oxides and and hydroxides formed by low low temperature alteration alteration of of carbonate carbonate and and silicate silicate iron-formation iron-formation accompanied accompanied by by dissolution and replacement replacement of of chert. chert. Stop 7. Negaunee Negaunee Iron-formation (hematite-jasper (hematite-jasper fades) facies) Classic exposures exposures of of the jaspillitic upper upper part part of of the the Negaunee Iron-formation Iron-formation are are seen seen on on Jasper Jasper Knob. Knob. These exposures just north north of of the the major major fold fold axis of the exposures are in in the central part of the Marquette synclinorium, just district. The Theknob knob itself itself isison on aa west-plunging west-plunging anticline anticline so so that the base of the Goodrich Goodricb Quartzite wraps around the west end of the knob and is is exposed in in some of the fenced mined areas areas near near the the base base of of the the west west slope. The alternating thin thin beds beds of of specular hematite and bright The iron-formation iron-formation here here characteristically characteristically has alternating jasper. Specularite red jasper. Speculariteplates plates are are strongly strongly oriented oriented parallel parallel to bedding in the hematitic layers. Folds having drag folds on their limbs and themselves being drag folds on the limbs of still still larger larger folds are strikingly shown shown in in many many exposures. exposures. Fold axes are horizontal horizontal to to gently gently plunging. plunging. Small breccia zones are common and appear to lie roughly along axial axial planes planes of of folds. folds. In these zones fractured jasper beds are surrounded by crystalline hematite. hematite, theories have have been been advanced advancedfor forthe theorigin originofofthejaspillite. oxidation of Two theories the jaspillite. One advocates oxidation siderite-chert iron-formation iron-formation during the post-Negaunee erosional interval and its recrystallization recrystallization to to Penokean deformation deformation and and metamorphism. metamorphism. This theory accounts for patches of specularite-jasper during Penokean specularite-jasper within carbonate facies iron-formation near contacts between the two rock types, types, as, as, for for example, in the Cliffs Shaft mine about '/2 ¼ mile mile to to the the west. west. The second theory advocates a primary origin for the hematite and jasper in in a more more oxidizing oxidizing depositional depositional environment than that responsible responsible for for carbonate carbonate iron-formation. The Theeven-bedded even-bedded and and thin-bedded thin-bedded nature nature of of the jaspillite on Jasper Knob is very similar to iron-formation. ItIt contrasts the bedding characteristics of carbonate iron-formation. contrasts sharply sharply with wavy bedding and oolitic structure common common in injaspillite jaspillite elsewhere elsewhere in the district. district. At At the the Kloman Kloman Mine, near Republic (stop 10), lo), a convincing case can be made made for aa primary primary depositional depositionalorigin originofjaspillite. ofjaspillite. Here, at Jasper Knob, an origin origin by oxidation of carbonate iron-formation iron-formation is more possible. 8 �Stop 8. Michigamme Michigamme Formation, Formation, lower lower slate slate member. member. black sulfidic slate well well represented by the The lower part of the Michigamme Formation consists of black outcrops along the south side of Highway 41. This Thisoutcrop outcropisisnear near the the axis axisof of the the Marquette Marquette synclinorium, synclinorium. Subtle beds show mostly low dips and gentle folds with nearly horizontal axes. A A steep steepaxial axial plane planecleavage cleavage is well developed. Very Very fine-grained fine-grained pyrite pyrite is is abundant in many beds. This This black black slate slate facies facies lies lies on on the the Goodrich Quartzite and is overlain by the Greenwood Iron-formation Iron-formation Member, a lean silicate-magnetite iron-formation. iron-formation. Stop 9. Michigamme Michigamme Formation, Formation, Clarksburg ClarksburgVolcanics Volcanics Member. Member. The Clarksburg Volcanics is is a local unit resting on the Greenwood Iron-formation Member. The volcanic rocks are restricted to the south limb of the Marquette synclinorium, where they are exposed along length of about about 15 miles miles and and range range up upto toabout about 1I mile mile thick. thick. The absence of volcanic rocks on the a strike length away, shows that that deposition deposition in in the the Marquette trough trough north limb of the synclinorium, only a few kilometers away, was very assymetrical at this time and and that that the the trough trough was was probably probablymuch muchdeeper deeperon onthe thesouth. south. Lenses of lean iron-formation horizons throughout throughout the the volcanic volcanic section section indicate that that iron-formation at numerous stratigraphic horizons volcanism was mostly or or entirely entirely submarine. submarine. The volcanics are almost exclusively mafic and pyroclastic. pyroclastic. This This outcrop outcrop along alongthe the north north side sideof ofthe the which layering is shown shown distinctly by by variations in abandoned railroad grade is representative of the unit in which highly vesicular mafic rock, rock, and and the the matrix is rich in fragment size, most fragments are angular pieces of highly carbonate minerals. Fragments of argillite and chert are also present. Rocks here are Fragments of argillite and Rocks here are metamorphosed metamorphosed to to garnet grade and original mafic minerals are converted to amphibole and biotite. biotite. In In spite spite of ofthe the recrystallization, original igneous textures are very well preserved, even at microscopic microscopic scales. Low Low outcrops south of the railroad grade show lean, impure iron-formation typical of lenses that that are widespread iron-formation typical in the the Clarksburg Volcanics. Volcanics. The rocks consist of of alternating alternating layers layers of of magnetic magnetic biotite biotite argillite argillite and and siliceous in beds with abundant abundant fine-grained fine-grained muscovite. muscovite. Stop 10. Negaunee Iron-formation at a t Kioman Kloman Mine. Mine. the Negaunee Negaunee Iron-formation. Iron-formation. Interbedded Exposures here are of the uppermost units of the Interbedded on on aa scale scale iron-formation, aa wavy-bedded, wavy-bedded, oolitic oolitic jaspillite jaspillite of one to three feet are two contrasting lithologic types of iron-formation, and even-bedded cherty grunerite-magnetite gmnerite-magnetite iron-formation. The The features features seen seen in in this this exposure exposure were were instrumental in Hal James' formulation formulation in in the 1950's 1950'sof ofhis his concepts concepts of of sedimentary sedimentary facies facies of ofiron-formation iron-formation mineral assemblages assemblages during during high high grade grade metamorphism. metamorphism. A as well as oxygen-buffering by contrasting mineral A critical feature feature very well shown shown here here isis aa correspondence correspondence between between bedding bedding characteristics characteristics and andoxidation oxidation state. Relatively Relatively reduced reduced rocks, rocks, now now grunerite-magnetite grunerite-magnetite assemblages, assemblages, are invariably invariably in thin, even beds, beds, probably reflecting deposition in in quiet, quiet, poorly poorly oxygenated oxygenatedwater. water. Interbeds ofjaspillite ofjaspillite invariably invariably show show irregular wavy wavy beds and oolites are common, common, especially especially in in thicker thickerjasper jasper beds. beds. These These units are are believed believed to to formed in agitated, more oxygenated oxygenated water. water. James have formed James used used this correspondence of sedimentary sedimentary features features and mineral assemblages to argue argue that the different different lithologies lithologies and and their oxidation oxidation states, states, although although metamorphosed to sillimanite grade grade here, here, still still reflect reflect differences differences in in primary primary depositional depositional settings. settings. 9 �Stop 11. Michigamme Michigamme Formation. the Michigamme Michigamme Formation Formation in in the the axis axis of the the This roadcut shows very highly deformed deformed schist of the northwest-plunging Republic trough. The The rock rock here here consists consists of of iron-rich iron-rich metasediments, now now consisting of of biotite-garnet-amphibole schist. The The light-colored light-colored bladed bladed amphibole amphibole is is commonly commonly mistaken for for sillimanite, sillimanite, but although this exposure is is within the sillimanite sillimanite metamorphic zone, detailed petrographic petrographic examination examination failed to find sillimanite in this outcrop. Thicker has failed Thicker beds, beds, up up to a few few inches, inches, of impure impure quartzite form form readily traceable marker beds and reveal very tight folds with amplitudes many times greater than beds and reveal very folds with amplitudes many times greater than wavelength, and highly attenuated limbs. Fold Fold axes, axes, even even in in adjacent adjacent folds, folds, diverge diverge by by as as much much as as 600. 60'. The The compression of of the the metasediments metasediments between between two two blocks blocks of of very tight folding is caused, in large part, by compression Archean gneissic rocks that flank flank the Republic Republic trough on on the northeast northeast and and southwest southwest sides. sides. References Cannon, W.F., Gair, J.E., Klasner, J.S., and Boyum, B.H., 1978, Marquette Marquette Iron Iron Range: Range: Twenty-First Twenty-First Annual Institute on Lake Superior Geology, Field Trip Guidebook, p. 125-173. 125-173. Prinz, W.C., Gair, J.E., and Cannon, W.F., 1975, 1975, Greenstone: Twenty-First Annual Institute Institute on on Lake Lake p.41-85. Superior Geology, Field Trip Guidebook, p. 41-85. and metal metal occurrences, occurrences, Michigan's Michigan's upper peninsula: Society of Margeson, G.B., 1989, Precambrian Precambrian geology and Economic Geologists Geologists Fall Field Conference, 154 154 p. Morey, G.B., 1989, 28"' International Geological 1989, Early Proterozoic rocks of the Great Lakes region: 28th 63 p. Congress Field Trip Guidebook T145, T145,63 10 �Field Field Trip Trip22 Archean ArcheanIshpeming IshpemingGreenstone GreenstoneBelt Beltand andGold Gold Mineralization, Mineralization,Michigan Michigan Leaders: Leaders:T.J. T.J.Bornhorst, Bornhorst,DJ. D.J.Duskin, Duskin,ftC. R.C.Johnson, Johnson,R.A. R.A. Mahin, Mahin,T.O. T.O.Quigley, Quigley,and andG.W. G.W.Scott Scott 11 �An Introduction Introduction to to the the Archean Archean Ishpeming Ishpeming Greenstone GreenstoneBelt, Belt, Michigan Michigan Rodney Johnson & & Associates, Associates, Inc., 1550 1550 Baldwin Baldwin Ave., Ave., Negaunee, Negaunee, MI MI Rodney C. Johnson, Rod Johnson 49866 Theodore of Geological Theodore J. J. Bornhorst, Bornhorst, Department Department of Geological Engineering Engineering and and Sciences, Sciences, Michigan Technological Technological University, University, Houghton, Houghton, MI MI 49931 49931 Introduction Introduction The Ishpeming belt (IGB) (1GB)covers coversan anarea area of of about about 300 300 km2 km2 and and is located Ishpeming greenstone greenstone belt located in Michigan's Upper Upper Peninsula. Peninsula. It is is on on the the southernmost southernmost edge of the Superior Superior province and is is part of the composed of of tholeiitic tholeiitic pillowed pillowed basalt basalt the Wawa Wawa subprovince subprovince (Figure 1). 1). The belt is composed flows and lesser amounts to felsic volcanic flows amounts of intermediate intermediate to volcanic rocks rocks and minor minor clastic clastic and and chemical sedimentary sedimentary rocks. rocks. The 1GB IGB is about 2,700 2,700 Ma Ma (Bornhorst (Bornhorst and and Johnson, Johnson, 1998; 1998; Hammond, 1978). 1978). The The1GB IGB is is north north of of the the Great Great Lakes tectonic zone, an Archean Archean continentcontinentcontinent In Michigan, the Archean rocks south Michigan, the Archean rocks south of the the Great Great Lake Lake continent suture suture (Sims, (Sims, 1991). In tectonic tectonic zone zone are composed composed of old old Archean Archean gneiss gneiss and and migmatite migmatite intruded intruded by younger younger Archean granites granites and and is is part part of of the the Minnesota Minnesota River River Valley Valley Subprovince Subprovince(Sims, (Sims,1996). 1996). Tholeiitic to caic-alkalic calc-alkalic volcanism volcanism of of the the 1GB IGB belt resulted resulted from from north-directed north-directed subduction subduction (Hoffman, 1989; Card, 1990) Archean time. Successive Archean Archean accretion resulted in 1990) during Archean southward younging younging of of greenstone greenstone belts belts in in the the Superior Superior province. province. The Great Lakes tectonic tectonic zone (GLTZ) km long longArchean Archean paleosuture paleosuture (Sims, (Sims, 1991), 1991), the the most most significant significant (GLTZ) is aa 1,000 1,000km Archean boundary within within the the U.S.A. U.S.A. Sims Archean tectonic tectonic boundary Sims (1991) (1991) has has studied studied aasignificant significant shear shear zone, just south south of of the the 1GB, IGB, that he has interpreted as the only exposed segment of of the the GLTZ GLTZ (Figure 1). The buried. A The Minnesota Minnesota segment segment of the GLTZ is buried. A result result of of detailed detailed and andregional regional field studies, studies, including including structural structural geology, geology, is is the the synthesis synthesis of of the the lithostratigraphy lithostratigraphyof ofthe the1GB IGB in close close proximity proximity to to the the Great Great Lakes Lakes tectonic tectonic zone. zone. Structure Structure stratigraphic correlation correlation depends depends on on good good understanding understanding of of deformation deformationhistory. history. Accurate stratigraphic studies have have shown shown that that the the rocks rocks of of the the 1GB IGB have been effected by six periods of of Recent studies deformation (Table (Table 1)(Johnson, l)(Johnson, 1993; 1993;Nachatilo Nachatilo and and Bauer, Bauer, 1993). 1993).D1 Dldeformation deformation Archean deformation produced axial-planar cleavage (Johnson produced recumbent folds with a flat-lying penetrative, nearly axial-planar and Bornhorst, 1991). 1991). D2 D; deformation deformation produced large-scale strike-slip strike-slip shear shear zones zones that that Dadeformation deformation produced produced upright uprightfolds folds define the the boundaries boundaries of of lithostratigraphic lithostratigraphic blocks. blocks. D3 define axial-planar cleavage cleavage that is is developed best best in in felsic felsic volcanic volcanic (Figure 2) with a near-vertical axial-planar D4 deformation is associated with the intrusion of late interflow sedimentary units. D4 and interfiow trondjhemite-granite suite suite plutons plutons that that reorient reorient earlier earlier fabrics. fabrics. D5 Dsdeformation deformation produced produceddipdiptrondjhemite-granite slip motion in shear shear zones. zones. D6 D6 deformation deformation produced produced crenulation cleavage, cleavage, local local kink kink bands, bands, Archean rocks rocks of of the the 1GB IGB were not significantly deformed TheArchean and strike-slip shear zones. The Orogeny (Nachatilo (Nachatilo and and Bauer, Bauer, 1993). 1993). during the Early Proterozoic Penokean Orogeny strata of the southwest southwest block (Figure (Figure 2) 2) form form aa steeply steeply west-plunging synformal synformal The strata This fold foldisisdefined defined by by the the orientation orientation of bedding. Fieldwork Fieldwork has has identified identified northnorthanticline. This 12 �' I '00 700 I I 700KM Explanation Explanation Phanerozoic Phanerozoic 111111 - Precambrian Precambrian 1----] Middle Proterozoic Proterozoic volcanic and sedimentary sedimentary rocks rocks Early Proterozoic Proterozoic sedimentary and volcanic rocks V//A - Grenville front boundary boundary fault fault Sedimentary rocks rocks -- Fault Margins of Great Lakes Lakes tectonic tectonic zone; zone; short dashed where inferred inferred or or covered covered greenstone-granite complexes Archean greenstone-granite complexes Archean gneiss gneiss and and local local granitoid granitoid rocks rocks Regional geologic setting of the Archean Ishpeming greenstone belt and Archean Figure Figure 1: Regional Great Lakes tectonic zone. 13 �____ 87°30' - 0 I T. 50 2 Mi. 0 1 2 3 K m . N T. 49 N ++++++ T. ++++++ +++++++ 48 N. 46°30 Explanation Explanation Mona Mona Formation Formation Upper tuff unit lapilli-tuff unit unit and and lapilli-tuff IN '1 Basalt flow unit unit Kitchi Formation Kitchl Formation Tuff unit and lahar I- — — —l lahar unit unit Basalt flow unit Proterozoic Proterozoic Sedimentary Sedimentary rocks rocks Archean Archean Intrusive Rocks intrusive Rocks Granodiorite k'."J Granodiorite Ii Tonalite Tonalite Deer Lake Lake Peridotite Peridotite P Sedimentary Rocks Rocks £S&S1 Timiskaming-type Timiskaming-type sedimentary sedimentary rocks Volcanic Rocks Rocks Lighthouse Lighthouse Point Point Basalt Basalt Basalt Basalt V//I Reany Lake pyroclastic Reany Lake pyroclasticunit unitand and Fire Center mine iron-formation iron-formation unit unit PL.JLJ Nash Creek glomerophyric glomerophyric basalt unit unit a I\ /1 0 I I a I Bedding Bedding Overturned Overturned bedding bedding Facing of pillows pillows 'C Plunging anticline anticline syncline 'C Plunging syncline Plunging overturned anticline anticline \ Shear zone & - 87 f 87+ A % Figure 2: Generalized Figure Generalized geologic geologic map map of o f the the Ishpeming Ishpeminggreenstone greenstone belt. belt. 14 �Table Table1.1.Summary Summaryofofdeformation deformationsequence sequenceand andvolcanic/magmatic volcanic/magmaticactivity activity and and constraining constraining age agedates datesfor forthe the Ishepming greenstone belt. belt. Event Event - Characteristic Characteristic Volcanic/Magmatic Activity Volcanic/Ma~matic Activity Age Dates Ace Dates Undeformed post-tectonic post-tectonic granite granite 2585 Ma Ma D6 Kink Kink bands bands with with north-easterly north-easterly striking kink kmk planes and steeply plunging hinges D5 Ds Dip slip motion along shear shear zones. D4 D4 Folding associated Folding associated with with intrusion of plutons. plutons. D3 Upright Upright folding. folding. Appinite suite D2 Strike-slip Strike-slip shearing. shearing. Trondjheniite-granite suite Trondjhemite-granite DI Recumbent Recumbent folding. folding. Tonalite suite Extrusion of mafic and felsic volcanic rocks. 15 2668.4+2.11-1.8 Ma 2668.4+2.1/-1.8 2705.8+/-1.6 Ma �northeast-lacing beds in tuffaceous tuffaceous units on the northern northern limb limb of of th'is this D3 D3fold. fold. Tuffs Tuffs of and northeast-facing the southwest block have a well-developed axial planar foliation foliation (S4. (53). Pillow basalts of of the the southeast block consistently consistently young to the north and and have have aa poorly poorly developed developed cleavage. cleavage. Interfiow sedimentary rocks rocks dip dip steeply steeply to to the the north. north. Tuffs that overlie the basalts basalts have two Interflow well-developed cleaviges cleavages that defini define a-moderately a moderately plunging plunging D3 D3synform. synform. The The strata of the well-developed sedimentary and felsic volcaniclastic volcaniclastic rocks define a north block have been re-folded, and sedimentary pattern (Johnson (Johnson and and Bornhorst, Bornhorst, 1991). 1991). The low density of broad Z-shaped outcrop pattern sedimentary rocks necessitates relying on pillows pillows in pillow pillow lava for defining younging directions (Figure 2). AAwell-developed well-developed foliation foliation in in amphibolite-facies amphibolite-faciesbasalt basalt was was subsequently refolded by D3 deformation. deformation. D3 folds are are upright, upright, open open to to tight tight and have D3 folds shallow to steeply plunging fold axes. axes. Stratified Rocks Stratified lithostratigraphic blocks that comprise Bornhorst (1988) subdivided the 1GB IGB into three lithostratigraphic comprise units bounded boundedby bydeformation deformationzones zones (Figure 3). 3). As internally consistent stratigraphic units As aa whole, the belt is bounded to the south by Early Proterozoic Proterozoic sedimentary rocks along the Carp River Falls shear zone, a structure that was active from the Archean Archean through the Proterozoic (Puffett, 1974). 1974). The Thesouthwest southwest block block isis bounded bounded to to the the west west by by Archean Archean granitoid rocks. This Thiscontact contact may may be be aafault fault since since the the boundary boundary is is not not transitional transitional lit-par-lit lit-par-lit as found near the intrusive greenstone-granitoid contact of of the the north north block block of of the greenstone greenstone-granitoid contact belt (Johnson and Bornhorst, Bomhorst, 1991). The The Carp Carp River River shear zone separates the southwest interpreted to be a dextral shear zone with uncertain block from the southeast southeast block. It is interpreted displacement. The stratigraphic displacement. The dextral dextral Dead Dead River River shear shear zone separates separates the two southern southern blocks from the north block. The north block is bounded bounded to the east, north north and west by Archean granitoid rocks that have intrusive relationships relationships with with the volcanic rocks rocks (Wilkins and Bornhorst, 1992; 1992; Johnson and Bomhorst, Bornhorst, 1991). 1991). Southwest Block The southwest block is composed of mafic flows and intermediate to to felsic volcanic and volcaniclastic rocks of the Kitchi Formation which are subdivided into vokaniclastic into three three informal informal units: units: basalt flow, tuff, and lahar units (Figure 44 and 5). The The basalt flow unit, at at the base of of the the Kitchi Formation is composed of 1,800 1,800 meters of dominantly pillowed basalt flows, flows, but but includes massive basalt flows as well. The The basalts basalts are are dominantly dominantly magnesian tholeiites tholeiites composed of hornblende-actinolite-albite-chlorite-clinozoisite hornblende-actinolite-albite-chlorite-clinozoisitewith minor amounts amounts of of sphene, sphene, magnetite, and (or) pyrite. The The base base of of the the basalt basalt flow flow unit unit is is in probable fault fault contact contact with with beds of of chert and and dacite dacite to to rhyolite rhyolite tuff tuff are are interlayered interlayered Archean granitoid rocks. Several thin beds basalt flow unit. Near near the middle of the hasalt Near the the top ton of of the the basalt flow flow unit is is aa 30-meter30-meterplagioclase phenocrysts phenocrysts up up to to 22 cm cm in in diameter. diameter. The The thick glomerophyric flow containing plagioclase uppermost basalt flows intercalate with intermediate volcanic rocks of the overlying tuff intermediate overlying unit. - - tuff unit. Formation is composed composed of of 5,000 meters meters of of tuff tuff with with lesser lesser amounts amounts ~Thei tuff e unit of the Kitchi Formation of interlayered lahar with the thicker beds of lahar separated separated into into the the lahar lahar unit. unit. The The tuff tuff unit unit ash tuffs, tuffs, dominantly dominantly calccalcand lithic lithic tuffs, with minor lapilli-ash and ash consists of crystal and alkalic andesite in composition. The Therocks rocks are are schist schist composed composed of of quartz-feldspar-sericitequartz-feldspar-sericitechlorite containing quartz and feldspar phenocrysts. phenocrysts. Pillowed Pillowed basalt basalt flows flows interfinger interfinger with with 16 �T 50 N T 49 N T 48 N 4630 R2SW R2JW 0 R26W 5 111111 R25W 10 KILOMETERS Explanation Explanation Middle Proterozoic Proterozoic (900-1,600 (900-1,600 Ma) Ma) Metavolcanic rocks Metavolcanic rocks LAttJ ,Jacobsville JacobsvilleSanstone Sanstone(Midcontinent (Midcontinentrift rift system) system) Early Proterozoic Proterozoic (1,600-2,500 (I ,600-2,500 Ma) Ma) I Sedimentav Sedimentary rocks 0 rocks of of Marquette MarquetteRange RangeSupergroup Supergroup I Archean -- - Contact Contact +f - Shear zone Approximate trace of of axial axial plane of plunging plunging anticline anticline +i f- Approximate trace of axial axial — plane planeof ofplunging plungingsyncline syncline I÷++4 Granitoid Granitoid rocks rocks Figure 3: Lithostratigraphic Figure Lithostratigraphicblocks blocks of the the Ishpeming Ishpeminggreenstone greenstone belt. belt. 17 �8r4 8fl0 AAA A Y 4t32'30" 66 A AA A Aa A A'St'/?s —4 A A A A A A A'S {/? z A A A A A 2- A A A A A% M&io - - r4 2' - A A 'a a FJA.Je5 A C - - eq -, -— aa , V 0lshpemiig e3cy 0 88 KILOMETERS KILOMETERS 0 I Explanation Explanation Early Proterozoic Proterozoic 0Undifferentiated Undifferentiated metasedimentary metasedimentary rocks rocks I LAAAAAJ Tuff unit Tuff unit ---- Basalt flow flow unit unit Basalt + App~ximate Approximate trace of axial plane of anticline anttcl~ne I Archean Archean - Contact Contact Undifferentiated Undifferentiatedrocks rocks —r Metagabbro Metagabbro 65 Strike and dip dip of of beds beds "- Shear zone Shear zone Deer Lake Peridotite Peridotite Kitchi Formation Formation Lahar unit unit #— Note: All rocks are metamorphosed metamorphosed Figure 4: 4: Generalized geologic map of southwest block block of the Ishpming n s t o n e belt. Mi. of the southwest lshpeming p greenstone 18 �METERS METE1 0 0 500 500] 1000 1000 Tuff unit Lahar unit unil unit cc: Lahar unit J Basalt flow unit Formation within the southwest block Figure Figure 5: Generalized stratigraphy of the Kitchi Formation of the Ishpeming greenstone greenstone belt. belt. 19 �the tuff unit near the top and base of the unit. The Thelahar lahar unit unit of of the the Kitchi Kitchi Formation Formation isis composed of of beds and and lenses lenses of of polymictic volcanic conglomerate containing clasts of thinly laminated, laminated, porphyritic, porphyritic, and and holocrystaline holocrystaline rocks that are calc-alkalic andesite to dacite dacite in in composition. The polymict volcanic volcanic conglomerates conglomerates are are more more common near the base of the Thepolymict tuff unit unit and and are are interpreted interpreted as as lahar lahar deposits deposits (Bornhorst (Bomhorst and andJohnson, Johnson,1993). 1993). Southeast Southeast Block Block The southeast southeast block is is composed of basalt flows and felsic volcanic and volcaniclastic rocks of the Mona Formation, which which is subdivided subdivided into informal units: basalt flow, lapiffi-tuff, and and upper tuff units (Figure 6). The Thebasalt basalt flow flow unit, unit, at at the the base of the Mona Formation, is a 5,500-meter-thick 5,500-meter-thick sequence of pillowed with minor massive basalt flows. The basalts are dominantly magnesian tholeiite basalt flows. Within the basalt flow unit are thin interfiow interflow chert-magnetite iron formations and schistose schistose quartz-sericite quartz-sericiterocks rocks (tuffs). (tuffs). The most notable occurrence of interflow sedimentary sedimentary rocks in the Mona Formation occurs north of the Pine Hill Hill Quarry Quarry (Figure (Figure 6). 6). At Atthis thislocation, location,chert-magnetite chert-magnetiteand andchert-pyrite chert-pyriteiron-formation iron-formationare are intercalated with graphite and quartz-sericite schist (tuffs) (tuffs) as as interflow interfiow units. units. Diamond quartz-sericite schist drilling drilling along along this interval interval has indicated that these units have a combined thickness of approximately approximately 10 10 meters. meters. The Thelapilli-tuff lapilli-tuffunit unitoverlies overliesthe thebasalt basalt flow flowunit unit (Figure (Figure7) 7)and andisis composed of calc-alkalic rhyolite lapilli in a quartz-sericite-chlorite matrix supporting quartz of calc-alkalic quartz-sericite-chlorite and, less commonly, feldspar phenocrysts. This unit is interpreted as subaqueous pyroclastic flow and fall fall deposits deposits (Bornhorst (Bornhorst and Johnson, 1993). 1993). The Thelapilli-tuff lapilli-tuff unit unit grades gradeslaterally laterally and vertically into the upper tuff unit. This quartz-feldspar-sericiteThisunit unitisiscomposed composedof of quartz-feldspar-sericitechlorite chlorite schist schist with with aa bulk bulk calc-alkalic calc-alkalic dacite dacite composition. composition. It is interpreted as interbedded tuffs tuffs and and volcanic volcanic derived derived graywacke (Bomhorst and Johnson, 1993). The The combined combined thickness thickness of of these these felsic felsicvolcanic volcanic and andvolcaniclastic volcaniclastic units units isis900 900meters. meters. North North Block Block The The north north block block isis composed composed of of the the 3,100-meter-thick 3,100-meter-thick Lighthouse Point Basalt (Figure 8). 8). The Lighthouse Point Basalt is dominantly pillowed tholeiitic-magnesian basalt flows with The Lighthouse Point Basalt is dominantly with minor minor massive massive flows. flows. AAglomerophyric glomerophyric(Nash (NashCreek) Creek)basalt basaltflow flowoccurs occursnear nearthe thebase base (Figure 9). 9). Within Withinthe theLighthouse LighthousePoint PointBasalt, Basalt,the theReany ReanyLake Lakepyroclastic pyroclastic unit unitisiscomposed composed (Figure of interbedded interbedded ash ash to to lapilli lapilli ash ash tuffs tuffs of of caic-alkalic calc-alkalic dacite composition. ItItisisininturn tumoverlain overlain of by thinly bedded chert-magnetite chert-magnetiteiron-formation iron-formation by the the Fire FireCenter Centermine mineiron-formation iron-formationunit unit—- aa thinly with with lesser lesseramounts amountsof ofassociated associatedchlorite-magnetite chlorite-magnetite schist schistand andchert-pyrite chert-pyrite iron-formation. iron-formation. Over-lying Over-lyingthe the iron-formation iron-formation isisintercalated intercalated chlorite-carbonate-feldspar chlorite-carbonate-feldspar and andquartz-chlorite quartz-chlorite schist schist (tuffs). (tuffs). Above Aboveand andbelow belowthe theiron-formation iron-formationare areisolated isolatedlenses lensesand andpods podsof ofgraphitegraphitepyrite pyrite schist. schist. This Thisinterval internalofofsedimentary sedimentaryrocks rocksisispoorly poorlyexposed, exposed,but buthas hasan anestimated estimated thickness thickness of of approximately approximately 100 100meters. meters. The TheReany ReanyLake Lakepyroclastic pyroclastic unit unitalso alsocrops cropsout outinin the the vicinity vicinity of of Hills Hills Lakes Lakes where where itit is is composed composed of lapilli and ash tuffs of calc-alkalic dacite to to rhyolite rhyolite composition. composition. The TheLighthouse LighthousePoint PointBasalt Basaltrepresents representsaasuccession successionofofsubaqueous subaqueous tholehite tholeliitebasalt basalt flows flowswith with intercalated intercalated distal distal to to nearly nearly proximal proximal felsic felsic volcanic volcanic rocks rocks (Johnson (Johnson and andBornhorst, Bornhorst,1991). 1991). 20 �3fl5 8740 a 4 ___ -A t ......................... A A A A A A £e/Lt, —— A A fr - & DeadRiver StorageBasin AA 8t25 87% 87'30 \D A A. -- - A A A Ah —---" A A A A A SMarquette -_ 4632 30 - - - -C4 • - - - - - - - "s/i CARP RIVER FALLS SHEAR ZONE 0Negaunee 10lshpeming 4630 10 KILOMETERS KILOMETERS j0 5 0 1 Explanation Explanation 0Undifferentiated Undifferentiated metasedimentary rnetasedimentary rocks rocks I I V//A Lapilli-tuff unit unit Basalt flow unit unit ARCH EAN ARCHEAN - -- L1 Undifferentiated rocks Undifferentiated rocks - Metagabbro Metagabbro Mona Formation Formation '4-+ unit LA.AI Upper tuff unit — Contact--Dashed where concealed concealed Shear zone Approximate trace of axial axial plane plane of of plunging syncline plunging syncline Note: All rocks rocks are metamorphosed metamorphosed Figure 6: Generalized geolgic map of off the Ishpeming greenstone greenstone belt. o f the southeast block o 21 �Upper upper tuff unit *tuff unit Lapilli-tuff Lapilli-tuff unit unit METERS METERS 0 Basalt Basalt * flow flow unit unit 500 1000 Figure 7: 7: Generalized Generalizedstratigraphy stratigraphy of of the the Mona Mona Formation Formation within within the the southeast southeast block block Figure the Ishpeming Ishpeming greenstone greenstone belt. belt. of the 22 �_____ ______ ______ 0 10 5 Explanation Explanation 0Sedimentav rocks of Middle and EaW Proterozoic ages ages Sedimentary rocks of Middle and Early I Fire Center center mine iron-formation and and Reany Lake pyroclastic pyroclastic units units I ARCHEAN ARCHEAN a to a a] Nash Nash Creek glomerophyric glotnerophyric basalt basalt unit unit where inferred - Fault—Dashed Fault-Dashed where inferred --- Reany Creek Reany Creek Formation Formation Granodiorite near Rocking Granodiorite Rocking Chair Lakes Lakes Gneissic granite Gneissic granite to to tonalite tonalite Strike and dip of overturned overturned bedding bedding %5 +f I.. Lighthouse Point Lighthouse Point Basalt Basalt Hills Lakes Hills Lakes pyroclastic pyrodastic unit unit Shear Shear zone zone — '-{T - Approximate Approximate trace of axial plane plane of plunging plunging anticline anticline Approximate Approximate trace trace of of axial axial plane planeof of plunging syncline plunging syncline Figure 8: Generalized geologic map map of of the north block of of the Ishpeming Ishpeming greenstone greenstone belt. belt. 23 �Local unconformil unconformity + Hills Lakes pyroclastic unit unit Main lithology of Lighthouse Point Basalt Fire Center mine iron-formation unit Reany Lake pyroclastic pyroclastic unit unit Nash Creek glomerphyric basalt unit Base unknown unknown Figure 9: Generalized stratigraphy of the Lighthouse Point Basalt within the north block of the Ishpeming greenstone belt. 24 �Stratigraphic Relationships Stratigraphic Relationships Among Among Lithostratigraphic Blocks Blocks Stratigraphic correlations made across major maior shear zones are tenuous. The folded rocks in in the the southwest block comprise a steep westward plunging synformal anticline, with tops to bedding on the north limb facing northward (Figure (Figure 2). 2). Pillows Pillows in in the the southeast southeast block block consistently consist&tly young to the north, thus strata strata of the southeast block could be be interpreted interpreted as as younger than and overlying strata of the southwest southwest block. block. Displacement Displacement along along the the Carp Carp River shear zone may have eliminated eliminated some of of the the stratigraphic stratigraphic section. section. However, itit could could also be argued that the stratigraphy of the southwest and southeast blocks may have been juxtaposed by thrusting along the Carp River shear zone making stratigraphic relationships between them indeterminate but evidence for thrusting is lacking. & The stratigraphic stratigraphic units of the north block and the southeast block face each other other across across the the Dead River Basin, Basin, but but are separated separated by bythe theDead DeadRiver Rivershear shearzone zone (Figure (Figure 2). 2). The strata strata of the southeast block consist of pillowed and massive tholeiitic basalt flows overlain calcoverlain by by calcalkalic tuffs and lapilli-tuff. lapilli-tuff. The alkalic The Lighthouse Lighthouse Point Basalt and the Mona Formation may represent the opposing limbs of a synform. This This is is much much more more speculative speculative than the stratigraphic correlation between the southeast southeast and and southwest southwest block. block. If each block is stratigraphically unique and represents distinct and separate separate strata, strata, the the total total stratigraphic thickness is 16,000 16,000 meters. If all three blocks are correlatable with one another, the cumulative cumulative thickness thichess isis 13,000 13.000meters. meters. Intrusive Intrusive Rocks Rocks have been been intmded intruded by by multiple multiple episodes episodes of of Archean Archean mafic and felsic The rocks of the 1GB IGB have magmas. The and peridotite peridotite sills. sills. The gabbros Theoldest oldest intrusive intmsive rocks rocks are synvolcanic gabbro and are chemically indistinguishable from the surrounding basalt flows and likely represent subvolcanic intmsions intrusions (Bornhorst (Bornhorst and and Johnson, Johnson, 1993). 1993). The Deer Lake Peridotite is intmded intruded subvolcanic between the basalt and tuff units of the Kitchi Formation. Formation. Contacts with surrounding volcanic rocks are conformable, conformable, but lack of quench textures (spinifex), pillow structures, structures, or or other features typical tpical of ultramafic flows lead to the interpretation of the peridotite body as as aa (Bornhorst and and Johnson, Johnson, 1993; 1993; Brozdowski, Brozdowski, 1990, 1990,Bornhorst Bomhorstet et al., al., 1986). 1986). The sill complex (Bornhorst peridotite is lherzolite lherzolite to harzburgite in composition (Rossell, 1983) 1983) and similar to ultramafic ultramafk flows and sills from other Archean greenstone belts. sills from other Archean greenstone belts. The oldest felsic intrusive intmsive bodies are foliated diorite to granite gneiss batholiths that intrude intmde the margins of the greenstone belt. These These intrusions intmsions post-date post-date mafic volcanism in the greenstone belt and were deformed along with volcanic rocks during the earliest stage of quartz-feldspar porphyry dikes cut deformation. Archean granodiorite to syenite stocks and quartz-feldspar greenstone belt and Dzthrough through D4 D4deformation deformation the greenstone and are are interpreted interpreted to tobe besynchronous synchronouswith withD2 (Wilkin and Bornhorst, Bornhorst, 1992). 1992). 25 �Discussion Structural Stmctural studies studies in the 1GB IGB have led to a more accurate picture of stratigraphic thickness within lithostratigraphic Iithostratigraphic blocks and and possible possible correlations correlations between between blocks. blocks. Geological studies prior to 1988 1988 (Bornhorst) (Bomhorst) did not recognize the stratigraphic significance of lithostratigraphic Iithostratigraphic blocks. The Therecognition recognition of of the the synformal synfonnal anticline anticline in in the the southwest southwest block allows the true thickness of the volcanic strata of the Kitchi Kitchi Formation to be estimated 1,500 meter thickness estimated by Morgan at 6,800 6,800 meters, a four fold increase increase over over the the ++1,500 and DeCristoforo (1980). polyphase deformation in the Lighthouse Point (1980). The recognition of polyphase Basalt of the north block lead to a thickness estimate of 3,000 meters, compared to an earlier estimate of 4,500 meters (Morgan (Morgan and DeCristoforo, DeCristoforo, 1980). 1980). The stratigraphy of the 1GB can be be compared compared to tothat thatof ofthe theAbitibi Abitibigreenstone greenstonebelt. belt. In IGB can particular, the volcanic stratigraphy can be compared to the Tisdale Group, which stratigraphy compared the Tisdale Group, which isis composed of komatiites and basaltic komatiites at the base overlain overlain by tholeiitic basalts, calc-alkalic volcaniclastic volcaniclastic rocks rocks (Pyke, (Pyke, 1982). The Tisdale subsequently overlain by calc-alkalic Tisdale Group Group has a total thickness of from 950 to 4,000 meters. The The 1GB IGB has a similar volcanic stratigraphy: tholeiitic basalt (the basalt basalt flow units units of of the the Kitchi Kitchi and and Mona Mona Formations, Formations, and the Lighthouse Point Basalt) at the base, succeeded by calc-alkalic volcaniclastic rocks rocks (the (the tuff unit of the Kitchi Gtchi and and the upper upper tuff tuff unit unit of the Mona Mona Formations, Formations, and and the the Reany Reany Lake Lake pyroclastic unit of the Lighthouse Point Point Basalt). Basalt). The stratigraphy is even more comparable ifif the Deer Lake Lake Peridotite Peridotite represents represents subvolcanic subvolcanic sills sills analogous analogous with with komatiitic komatiitic volcanism. volcanism. Thus, in terms of lithology lithology and and thickness thickness the the stratigraphy stratigraphy of of the the 1GB IGB is directly comparable comparable to the Abitibi greenstone belt. The The1GB IGB represents an Archean volcanic arc assemblage as characterized characterized by Thurston Thurston and and Chievers Chievers (1990). (1990). The environment of deposition is important in identifying identifying potential potential ore deposits deposits with'in within the JOB. Significant occurrences of volcanogenic massive sulfide deposits are not known in the IGB. the 1GB. Chalcopyrite and sphalerite associated with chert in the Reany Lake pyroclastic unit of IGB. Chalcopyrite the Lighthouse Point Basalt was interpreted by Johnson and Bomhorst Bornhorst (1991) as a massive sulfide deposit incorporated incorporated in the pyroclastic pyroclastic flow. flow. Typically, Typically, volcanogenic massive greenstone belts belts that that have have aa greater greater than than average average volume volume of of sulfides are hosted in greenstone volcanic and sedimentary sedimentary rocks rocks (Franklin, (Franklin, 1990). The intermediate volcanic, felsic volcanic The JOB IGB is favorable for VMS deposits because of its considerable considerable stratigraphic stratigraphic thickness. thickness. The The Ropes Ropes 18901s,and more recently from 1985 1985 to to 1989, 1989,is is gold mine, which was in production in the 1890's, 1990). controlled by a shear zone (Bornhorst (Bomhorst et al., 1986; 1986; Brozdowski, 1990). Card (1990) suggested that the Superior province grew by Archean accretion, accretion, and and that that of north directed directed subduction. subduction. A similar sequence of Archean volcanism was the result of of events events could explain the Archean geology of the IGB. 1GB. The mafic to felsic volcanism could have subduction. Extra-belt been the result of northward directed subduction. Extra-belt tonalite tonalite batholiths, batholiths, intra-belt intra-belt granodiorite stocks, and appinite stocks intrude intrude the the greenstone greenstone belt. belt. The transition transition from from subduction to collision is is preserved by the volcanic rocks (subduction (subduction related arc) arc) and and by by intrusive rocks as described by Wilkin and and Bornhorst (1992) (1992) (transition from from subduction subduction to to collision). 26 �1GBcan canbe beplaced placedininan ananalogous analogousmodem modemenvironment. environment. As As a The volcanic strata of the IGB directed subduction subduction thick thick accumulations accumulations of pillowed tholeiitic tholeiitic basalt basalt flows flows result of north directed (basalt flow units of the Kitchi and Mona Formations and the Lighthouse Point Basalt) were were Subsequently, dome dome complexes complexes developed developed on on the the mafic mafic erupted from shield volcanoes. Subsequently, shield volcanoes. Subaqueous pyroclastic and lahar flows (tuff and lahar units of the Kitchi Kitchi Formation, upper tuff and lapilli-tuff units of the Mona Mona Formation, Formation, and and pyroclastic pyroclastic units units of of the Lighthouse Point Basalt) erupted erupted from the dome complexes. The Therocks rocksofofthe the1GB IGB Continent-continent collision collision caused caused the the represent coalescing volcanoes in an arc complex. complex. Continent-continent cessation of volcanism volcanism and and complex complex post-deposition post-deposition deformation. deformation. Summary Summary The Tshpeming Ishpeming greenstone belt consists of subaqueous tholeiitic basalt to calc-alkalic calc-alkalic rhyolite, 10-15 !an in total thickness. thichess. U-Pb U-Pb zircon zircon data data establish establish the the age age of of volcanism volcanism at at 10-15 km 2705.8 +1—i .6 Ma Ma (Bornhorst Johnson, 1998). The 2705.8+/-1.6 (Bomhorst and Johnson, The volcanic rocks were enveloped by tonalite suite suite plutons just before before and and during the beginning of recumbent folding folding (Table (Table 1). 1). Strike-slip Stnke-slip shear shear zones zones and and the the deposition deposition of clastic sediments into pull-apart basins followed followed recumbent folding. The folded. A The belt belt rocks rocks were were then upright folded. A trondhjemite trondhjemite to granite suite suite intruded the belt and folded earlier fabrics. The timing of deformation is constrained with UThe timing of deformation is with Udata yielding yielding an an age age of of 2668.4+2.1/-1.8 2668.4+2.1/-1.8 Ma for an intrusion in this suite suite (Bornhorst (Bornhorst Pb zircon data and Johnson, 1998). 1998). Intrusions Intrusions of of hornblendite homblendite to to syenite syenite (appinite (appinite suite) suite) and and continued continued movement along shear zones represent represent the end of of deformation. deformation. An undeformed post-tectonic granite (Sims,1991). 1991). granite intrusion intrusion has has an an age age of of 2585 2585 (Sims, These events are readily interpreted in a modem modern plate plate tectonic tectonic context. context. North-directed arc. Subduction-related subduction produced a volcanic arc. Subduction-related tonalite intruded the arc just prior to collision of a small km long long small continent continent from from the south (southern complex) along the 1000 1000 kin Great Lakes tectonic zone (suture). Collision Collision occurred occurred over over an an extended period of time with multiple deformation and magmatic events. events. The The appinite appinite suite suite is characteristic of modem collision-related magmatism. magmatism. Continuing Continuingstudies studiesof ofthe the1GB IGB and and vicinity vicinity will will help help to to unravel unravel the tectonic evolution evolution of of the the southern southem edge edge of of the the Superior SuperiorProvince. Province. Acknowledgments Acknowledgments We thank thank Shannon Shannon E. E. Bair Bair for forcomputer computerdrafting drafting of of the thefigures. figures. We References References T.J., 1988, 1988,Geological Geological overview overview of of the Marquette greenstone greenstone belt, Michigan Michigan ThirtyThirtyBornhorst, T.J., annual meeting, meeting, Institute Institute on Lake L&e Superior Geology, Field Trip Guide Books, Books, part part 2, 2, p. p, fourth annual Al-A31. ALA3 1. 1998, Archean evolution of the southern southem edge of the Superior Superior Bornhorst, T.J., and Johnson, R.C., 1998, 30, p. AProvince in Michigan: Geological Society of America Abstracts with Programs, v. 30, 159. 159. and Johnson, R.C., 1993, 1993, Geology of volcanic rocks in the southern half of of the the Bornhorst, T.J. and U S . Geological Survey Bulletin 1904-P, 1904-P, l3p. 13p. Ishpeming greenstone belt, Michigan: U.S. 27 �Bornhorst, T.J., Shepeck, Shepeck, A.W., and Rossell, D.M., 1986, 1986, The Ropes gold mine, Marquette County, Michigan, U.S.A.-- an Archean hosted lode gold deposit: MacDonald, A.J. (ed), (ed.), Proceedings of Gold '86, an International Symposium on the Geology of Gold, Toronto, p.213-227. bend, Marquette greenstone Brozdowski, WA., R.A., 1990, 1990, Ropes pyritic gold deposit in a dilational bend, belt, Michigan: University of Western Ontario, London, Ph.D. dissertation, 592 p. Card, K.D., 1990, 1990, A review of the Superior Province of the Canadian Shield, a product of of Archean Archean accretion: Precambrian 56. accretion: PrecambrianResearch, Research,v.48, v.48,p.99-1 p.99-156. Card, K.D. and Ciesielski, A., A,, 1986, 1986, DNAG No.1. Subdivisions of the Superior Superior Province Province of of the the Canadian Shield. Shield. Geoscience Geoscience Canada, Canada, v.13, v.13, p.5-13. Franklin, J.M., 1990, massive sulphide sulphidedeposits, deposits,inin Ho, Ho, S.E., SE., Robert, 1990, Volcanic-associated massive Robert, F., F., and and Groves D.I. (eds.), Gold and and Base-Metal Base-Metal Mineralization in the Abitibi Ahitibi Subprovince, Subprovince, Canada, Canada, With Emphasis 1-242. Emphasis on on the the Quebec Quebec Segment, Segment,Short ShortCourse CourseNotes, Notes,p.21 p.211-242. Hammond, R.D., 1978, 1978, Geochronology and origin of Archean rocks in Marquette County, Upper Upper Michigan: University of Kansas, Lawrence, Kansas, M.S. thesis, 69 p. University Kansas, Lawrence, Kansas, M.S. thesis, 69 p. Hoffman, P.F., 1989, 1989, Precambrian Precambrian geology and tectonic tectonic history history of North America, America, in in Bally, Bally, A.W., A.W., and Palmer, A.R. (eds.), (eds.), The geology geology of North North America: America: an an overview: overview: Boulder, Boulder, Colorado, Colorado, Geological society society of America, The Geology Geology of North America, America, v.4, v.4, p.447-512. p.447-512. Johnson, R.C., 1993, structural, tectonic, tectonic, and and economic economic studies studies of the Archean Johnson, R.C., 1993, Stratigraphic, Stratigraphic, structural, the Archean Ispheming greenstone belt, Marquette County, Michigan: Michigan Technological University, University, Houghton, Ph.D. Dissertation, Dissertation, 119 119 p. Johnson, R.C. and Bornhorst, of the the Ishpeming Ishpeming Bomhorst, T.J., 1991, 1991, Archean geology of the northern block of Bulletin 1904-F, 20 p. greenstone belt, Marquette County, Michigan: U.S. Geological Survey Bulletin Morgan, J.P., J.P., and and DeCristoforo, DeCristoforo, D.T., 1980, 1980, Geological Geological evolution of the the Ishpeming Ishpeming Greenstone Greenstone Belt, Michigan, Michigan, U.S.A.: U.S.A.: Precambrian Research, Research, v.11, v.11, p.23-41. p.23-41. Nachatilo, Nachatilo, S.A., and Bauer, R.L., 1993, 1993, Structural Structural analyses analyses of Archean Archean rocks rocks in in the theNegaunee Negaunee area, Michigan ---- constraints constraints on Archean versus versus Proterozoic Proterozoic deformation: deformation: U.S. U.S. Geological Geological Survey Survey Bulletin Bulletin 1904-0. 1904-0. Puffett, W. p., U.S. P., 1974, 1974, Geology of the Negaunee Quadrangle, Marquette County, Michigan: U S. Geol. Survey Professional Paper 788, 53 p. Survey Professional Paper 788,53 Pyke, D.R., 1982, Timmins area, District of Cochrane: Ontario Geological Survey 1982, Geology of the Tirnrnins Report 219, 219, l4lp. 141p. Rossell, Rossell, D.M., 1983, 1983, Alteration of the Deer Lake peridotite in the vicinity vicinity of the the Ropes Ropes mine, mine, Marquette County, Michigan: Michigan Technological University, Houghton, Michigan, County, Michigan: Michigan Technological University, Houghton, Michigan, M.S. M.S. thesis, thesis, 83 83 p. p. Subprovince (Archean (Archean Gneiss Gneiss Terrane): Terrane): in in Archean Archean and and Sims, P.K., 1996, 1996, Minnesota River Valley Suhprovince Proterozoic Proterozoic Geology of the Lake Superior Superior Region, U.S.A., U.S.A., 1993: 1993: U.S. U.S. Geological GeologicalSurvey Survey Professional Professional Paper Paper 1556, 1556,p. p. 14-23. 14-23. Sims, P.K., 1991, Great Lakes Lakes tectonic tectonic zone zonein inMarquette Marquettearea, area,Michigan Michigan--implications - implications for for Archean tectonics in north-central United States: U.S. US. Geological Geological Survey Survey Bulletinl9O4-E, Bulletin1904-E, 77 p. p. Thurston, P.C., and Chievers, K.M., 1990, Secular variations in greenstone sequence development, P.C., Chievers, 1990, Secular variations greenstone sequence development, emphasizing emphasizing Superior Superior Province, Province, Canada: Canada: Precambrian Research, Research, v.46, v.46, p. 21-58. 21-58. Geology and and geochemistry geochemistry of of granitoid rocks in the T.3., 1992, Geology Wilkin, R.T., R.T., and Bornhorst, Bornhorst, 713., Archean Northern complex, complex, Michigan, Michigan, U.S.A.: U.S.A.: Can. Journal of Earth Science, Science, v. v. 29, 29, p. 167416741685. 1685. 28 �INTRODUCTION INTRODUCTION TO THE THE ROPES GOLD DEPOSIT DEPOSIT IN THE THE ISHPEMING GREENSTONE GREENSTONE BELT, MICHIGAN ABSTRACTED H PERMISSION FROM GEOLOGY OF ABSTRACTED WIT WITH OF THE ROPES ROPES GOLD GOLD DEPOSIT BY R.A. BROZDOWSKI BROZDOWSKI (1988) (1988) Theodore J. Bornhorst and Shannon E. Bair, Department of Geological Engineering Engineering and and Sciences, Michigan Technological University, Houghton, MI 49931; 4993 1; and Glenn Glenn Scott, Scott, Tilden Tilden Mining Company, company, Ishpeming, MI 49849 Introduction Introduction The southwest part of the greenstone belt (Figure 1) 1) consists of, of, from west west to to east: east: pillowed and massive basalt, hypabyssal gabbro, dacite tuff and subordinate tuff breccia, breccia, fine-grained peridotite peridotite of of the the Deer Deer Lake Lake Peridotite. Peridotite. Volcanic rocks strike serpentinitic, fine-grained northeast, with a major bend to the east northeast at the Bjork-Lundeen prospect, 1.5 1.5km km west west of the Ropes deposit. Rocks face consistently to the southeast, based on pillows and graded and graded bedding The Ropes deposit is southeast of a transition from dominantly basalt to the the northwest northwest to dominantly dacite tuft to the southeast (Figure (Figure 2). 2). Meter-thick banded iron formation formation and and several meter thick greywacke are within the dacite up section from the interlayered basalt basalt and dacite. Sericite Sericiteprogressively progressively overprints overprints and and finally finally totally pesudomorphs feldspar feldspar phenocrysts in dacite tuff as the Ropes gold deposit is approached from the west. The deposit is in quartz-sericite-chlorite quartz-sericite-chloriterock which is interpreted as quartz-sericite altered altered dacite dacite tuff. tuff. Major Rock Types within Major within the the Ropes Ropes Deposit The four major rock types in or immediately bounding the Ropes deposit are are (Figures (Figures quartz-sericite-chlorite rock which encloses ore, strikes 070' 070° 3 and 4): 1.) fine grained quartz-serieite-chlorite overall, but 080' 080° where where it hosts the the Ropes deposit, deposit, and and dips dips steeply steeply south south or vertical. This This rock type is bounded north and south by 2.) fine grained carbonate-quartz-chlorite rock which is massive to compositionally layered on a scale of several millimeters. It and the the quartz-sericite-chlorite rock are locally complexly interlayered, particularly in the west part quartz-sericite-chlorite of the deposit, and have have generally generally sharp sharp contacts. contacts. Carbonate-quartz-chlorite rock is flanked successively, on both the north and south sides by, 3.) fine grained, massive to moderately rock, and 4.) 4.) fine foliated, carbonate-talc rock, fine grained, grained, serpentinitic peridotite which commonly original olivine olivine and and lesser lesserpyroxene. pyroxene. This is variably has pesudomorph texture after original with carbonate-talc carbonate-talc rock. rock. Contacts between carbonatecarbonate-bearing near its contacts with quartz-chlorite rock and carbonate-talc rock and between the carbonate-talc rock and the serpentinitic peridotite are generally gradational over one to several meters. Quartz-Sericite-Chlorite Quartz-Sericite-ChloriteRock Rock The main host for gold is light green, massive to slightly foliated, fine grained, quartz-sericite-chlorite thick on the 800 quartz-sericite-chlorite rock. This This rock rock is is aa 080°-striking 080'-striking layer up to 40 m thick mine level, but narrows toward the surface and toward the east to less than 6 m thick. It is is level. 29 �0 km 2 EXPLANATION EXPLANATION PROTEROZOIC PROTEROZOIC 1 graywacke and slate 2 quartalte ARCH LAN 3 serpentinillc peridotila 4 volcanIc conglomerate, subordinate daclte tuti 5 banded Iron lorniatton 6 daclle tutt, lull breccta and ltows 7 tonallIe and granodlorlte a gabbro 9 basalt 10 gtornerophyrlc basalt Figure1:1:Geologic Geologicsetting setting theRopes Ropesmine mineininthe thesouthwest southwestblock blockofofthe theIshpeming Ishpeming Figure ofofthe greenstone greenstonebelt. belt. 30 , �EXPLANI4 TION EXPLANA JION 0 0 0 ii GRAYWACKE GRAYWACKE 10 QUARTZITE QUARTZITE w F- 0 a- SERPENTINITIC PERIDOTITE LJ SERPENTINI11C PERIDOTITE EIJ CARBONATE RICH, SERPENnNITIC CARBONATE RICH, SERPENTINITICPERIDOTITE PERIDOTITE 1 a - CARBONATE TALCROCK ROCK ED CARBONATE-TALC COMPOSITIONALLY LAYERED TO MASSIVE COMPOSKIONALLY LAYERED MASSIVE CARBONATE QUARTZ - CHLORITE CHLORITE ROCK ROCK CARBONATE- QUARTZ - - TUFF, TUFF TUFF BRECCIA, BRECCIA, AND FLOWS; FLOWS; DACITE TIJFF, (ALTERED TO QUARTZQUARTZ-SERICITESERICITE- CHLORITE CHLORITE ROCK IN INROPES ROPESDEPOSE!) DEPOSIn S " = - ED BANDED BANDEDQUARTZ QUARTZ - MAGNETrrE MAGNETITE IRON FORMATION FORMATION GRAYWACKE ANDSILTSTONE SILTSTONE ED GRAYWACKE AND E1J FINE GRAINED FINE GRAINEDGABBRO GABBRO 1' L S BASALT (INCLUDES (INCLUDES PILLOWED PILLOWED AND GLOMEROPHYRIC VARIETIES) VARIETIES) PROJECTION TO SURFACE OF OF OREBODIES OREBODIES UPDIP PROJECTION TO SURFACE A = main main ore ore zone zone northwest ore B = northwest ore zone zone Figure 2: Surface Surfacegeologic geologic map mapof o f the the Ropes Ropes mine m i n e and vicinity. 31 �1 300 level 1152 level 200 Ft CI I 61 M I N 200E 400E 6006 BODE I000E 12006 EXPLANATION EXPLANATION I i I I 2 I i 3 i a [5 a Quartz-Sericite SerpentiniticFeridotite Peridotite L41 Quartz-Seridte chlorite Rock -. Serpentinitic Chlorite Rock locally carbonate carbonate rich rich locally Carbonate-Talc Carbonate-Talc Rock Rock Carbonate-Quartz -Carbonate-Quadz Chlorite Rock Rock Chlorite I Orebody Orebody >2 2 , g /tonne ,tonne Au Au Figure 3: Geologic Geologicplan planmap mapof ofthe the300 300and and1152 1152levels levels of of the the Ropes Ropes mine. mine. Figure 32 �ROPES R O P E S MINE MINE 600 E E Cross-Section Cross-Section Looking LookingS80°W S80° i Elevation Elevation(ft) ( 1 Serpentinitic Peridotite Peridotite Serpentinitic locallycarbonate carbonaterich rich locally I a 121 Carbonate-Talc Carbonate-TalcRock Rock 1400 1401 I 1200 1201 Carbonate-Quaflz -Carbonate-Quartz Chlorite Rock Rock Chlorite 3 4 i Quartz-Sericite Quartz-Sericite ChloriteRock Rock Chlorite Orebody 151 Orebody gltonneAu Au >>22g/tonne 1000 1001 C 0mine minelevels levels 800 80C Scale 0 600 600 100 200ff 61 m 100 400 40C 200 ft 61 m 200 200 Sea SeaLevel Level -200 -200 Figure Figure4:4:Geologic Geologiccross crosssection sectionofofthe theRopes Ropesmine minelooking loohngS80°W S80° along alongthe the600E 600Esection. section, 33 �complexly interlayered with carbonate-quartz-chlorite rock, especially west of the Ropes main ore zone and in the mine. Randomly Randomlyoriented orientedto tomoderately moderately aligned, aligned, 11to to22 mm, mm, angular, rectangular mats of felted sericite up to 2 mm in length, comprised of individual sericite grains less than 10 10 microns in size, and minor quartz, are enveloped in this matrix and have an external habit identical to plagioclase In dacite dacite tuff tuff immediately immediately plagioclasephenocryst. phenocryst. In west of the deposit there are plagioclase phenocrysts. The Therectangular rectangular mats matsare areinterpreted interpreted as as pseudomorphs after the plagioclase phenocrysts. phenocrysts. The rock is layered locally with 5 mm thick, lens-like, sericite-rich sericite-rich and and alternating alternating more more chlorite-rich chlorite-rich laminae. laminae. Sericite quartz-sericite-chloriterock rock decreases decreases Sericite in in relict relict feldspar feldspar and and lithic lithic clasts clasts in in the the quartz-sericite-chlorite gradationally westward from the Ropes main ore zone over a distance of of several hundred meters into aa large large body of of dacite dacite tuff tuff that that has has moderately moderately aligned aligned twinned twinned plagioclase plagioclase phenocrysts phenocrysts with with only only very very minor minor sericite sericite internal to the phenocrysts, bipyramidal quartz, and volcanic volcanic rock rock fragments fragments in in an an aphanitic aphanitic quartz-sericite feldspar-chlorite matrix. The Thedacite dacite tuff outside of the Ropes deposit, proper, has local lapilli-sized fragments as well as tuff tuff outside of the Ropes breccia breccia layers. layers. Gold abundance abundance is generally greatest where very fine to aphanitic pyrite is 5 to 8% 8% of the the rock, rock, quartz quartz and and sericite sericite are are most most abundant, and chlorite is least abundant. However, However,this this generality generality does does not not apply apply to to the the chioritic, chloritic, pyritic, pyritic, eastern eastern most most rim rim of of the the Ropes Ropesmain mainore ore zone. zone. Anastomosing Anastomosingquartz quartzveinlets veinletsless lessthan than11mm mmthick thickmake makeup upseveral severalpercent percentof ofthe the rock. rock, Rock Rockoutside outsideofofthe theore orezones zonescontains containsless lessthan than2% 2%very very fine finepyrite. pyrite. The The overall overall 070° quartz-sericite-chlorite rock rock which which hosts hosts the theRopes Ropes 070' striking striking trend trend of of quartz-sericite-chlorite main main and and northwest northwest ore ore zones zones interfingers interfingers with with carbonate-quartz carbonate-quartz chlorite chloriterock rockwest westof ofthe the deposit, and does not continue west of the northwest ore zone (Figure 2). East of the deposit, deposit, and does not continue west of the northwest ore zone (Figure 2). East of the deposit, the the trend trend of of quartz-sericite-chlorite quartz-sericite-chlorite rock does not continue at surface beyond 300 m east of the the Ropes Ropes main main ore ore zone. zone. A A zone zone of of carbonate-talc carbonate-talc rock rock within within the the serpentinitic serpentinitic peridotite peridotite marks marks the the east-northeast east-northeastprojection projection of ofthe thetrend. trend. Carbonate-Quartz-Chlorite Rock Carbonate-Quartz-Chlorite Rock Carbonate-quartz-chlorite Carbonate-quartz-chloriterock rock envelopes envelopes the the quartz-sericite-chlorite quartz-sericite-chloriterock rockand andisis complexly complexly interlayered interlayered with with it, it, particularly particularly toward toward the the west west end end of of the the Ropes Ropesdeposit. aeposit. Carbonate-quartz-chlorite rock rock isis restricted restricted largely largely to to the the deposit deposit although although layers layersup uptoto22mm Carbonate-quartz-chlorite thick thick occur occur up up to to 400 400 m m west of the Ropes main ore zone. The The thickest thickest layers layersof of carbonatecarbonatetalc talc rock rock are are immediately immediately north north and and south south of of the the deposit; deposit; however, however, thin thin layers layersof oftalc-rich talc-rich rock rock are are at at numerous numerous localities localities atat the the contacts contacts of, of, and and also also within within serpentinitic serpentiniticperidotite peridotite along along the the northwest northwest contact contact of of the the peridotite peridotite up up to to 500 500 m m away away from from the the deposit. deposit. Carbonate-quartz-chlorite Carbonate-quartz-chlorite rock rock contains contains abundant abundant ferroan ferroan dolomite, dolomite, and andlesser lesserquartz quartz and and chlorite. chlorite. Minor Minorsericite sericiteisisininsome someparts partsand andvariable variable amounts amounts of of talc talc in inothers, others,but butthese these two quartz-sericite-chloriterock rock two minerals minerals are are generally generally mutually exclusive. Contacts Contactswith with quartz-sericite-chlorite are are sharp sharp in in aa direction direction across acrossthe the strike strikeof of the the rock rock type, type, but but are arelocally locallygradational gradationalalong along strike. strike. Barren Barrenmilky milkyquartz quartzveins veinsup uptoto10 10cm cmthick thickoccur occurlocally locallyand andare areconformable conformabletotothe the contact. contact. Minor Minorcarbonate carbonateminerals mineralsare arepresent presentininthe thequartzquartz-sericite-chlorite sericite-chloriterock rocknear nearits its contacts contacts with with the the carbonate-quartz-chlorite carbonate-quartz-chloriterock, rock, and and minor minor sericite sericiteisispresent presentininthe the carbonate-quartz-chlorite carbonate-quartz-chlorite rock rock near near its itscontacts contactswith with quartz-sericitequartz-sericite-chlorite chloriterock. rock. Carbonate-quartz-chlorite rock rock has has up up to to150 150ppb ppb Au, Au, and and quartz quartzrich richparts partsof ofthe thecarbonatecarbonateCarbonate-quartz-chlorite 34 �quartz-chlorite rock only very locally contain several percent pyrite and up to 11 ppm Au. Locally the carbonate-quartz-chlorite rock is brecciated, with angular fragments of carbonate carbonate veined carbonate-quartz-chlorite rock in a chlorite rich matrix particularly at the south south side side of of the deposit. Carbonate-quartz-chlorite rock is generally compositionally layered on a scale of several millimeters, but but locally locally is is massive. massive. Layering is defined by hy fine to medium grained white cxbonate carbonate lenses, chlorite foliation, foliation, and and quartz-chlorite quartz-chloriterich richlaminae. laminae. The rock is white increasingly talcose toward the contact with carbonate-talc rock. Coarse grained, barren, white dolomite veins up to 5 cm thick cut across all other features and are several percent of rock. Carbonatethe rock. Carbonate- quartz-chlorite quartz-chlorite rock rock is is not only within the deposit but also in a zone up to 60 m thick on its north side, where it contains thin layers of the other three main rock types. Carbonate-quartz-chlorite types. Carbonate-quartz-chlorite rock rock is is in local lenses along the northeast striking contact of and northwest northwest of of the the Ropes Ropesdeposit. deposit. The carbonatethe Deer Lake Peridotite, southwest and quartz-chlorite rock is interpreted as an alteration product of a serpentinitic peridotite protolith. Serpentinitic Peridotite and Carbonate-Talc Serpenrinitic Carbonate-Talc Rock Rock quartz-sericite-chlorite rock and carbonate-quartz-chlorite rocks are The interlayered quartz-sericite-ihlorite are bounded on north and south by elongate masses of serpentinitic peridotite. There are also several smaller serpentinitic peridotite bodies enclosed within the carbonate-quartz-chlorite of the Ropes Ropes deposit. deposit. The largest of these bodies is the north wall of rock on the north side of the Ropes deposit. The The rock rock is is dark dark gray gray to green, green, mostly fine grained, with major serpentine, subordinate talc and carbonate, carhonate, minor chlorite, and accessory chromite and magnetite. The The serpentine serpentine isis aa mixture mixture of of felted felted chrysotile and oriented plates of antigorite. Commonly it has a relict texture of 11 to 3 mm serpentine pseudomorphs after major olivine pyroxene. The and subordinate pyroxene. The pseudomorphs pseudomorphs are surrounded by rims of talc, carbonate and accessory accessory fine-grained fine-grained magnetite magnetiteand andchromite. chromite. Locally the the rock rock is is dark green, minerals and felted textured serpentine which which lacks lacks aa pseudomorphic pseudomorphic texture. texture. The serpentinitic peridotite is increasingly carbonate-rich toward its borders, although the relict texture is commonly preserved. Fibrous continuously preserved. Fibrous chrysotile chrysotile veinlets in the serpentinite are locally pseudomorphed by carbonate. Au abundance is typically less than 30 ppb, even in close proximity to the deposit. deposit. Massive to well foliated, gray to dark green, very fine grained carbonate-talc rock margins of of serpentinitic serpentinitic peridotite. peridotite. Chlorite, serpentine, magnetite and occurs around the margins pyrite are minor phases. phases. The carbonate-talc The carbonate-talc rock has gradational contacts over one to several meters with serpentinitic peridotite and with talc-rich parts of the carbonate-quartz-chlorite subequal. The carbonate rock. Talc Talc and and carbonate carbonate contents contents are generally generally subequal. carhonate mineral in the ferroan dolomite dolomite with with minor minormagnesite. magnesite. Au abundance is carbonate-talc rock is dominantly ferroan from less than 30 ppb to approximately 100 100 ppb locally in the carbonate-talc rock. The Gold Ore g/ton Au, including production and The Ropes deposit is 2.8 million tonnes with 3.24 glton reserves. There Ninety five percent percent of the ore all categories of reserves. There are are two two main types of ore: 1.) 1.) Ninety dispersed pyrite pyrite in in quartz-sericite-chlorite quartz-sericite-chloriterock. rock. This ore has several subtypes is gold with dispersed proportions of of quartz, quartz, sericite, sericite, chlorite, chlorite, and andpyrite. pyrite. 2.) Five percent of the ore is with varying proportions 35 �auriferous quartz veins with saccharoidal saccharoidal texture and tetrahedrite, pyrite, galena, galena, and and chalcopyrite. ItItisisgenerally generallyatator ornear nearthe thesouth southside sideof of the the deposit. deposit. Dispersed Pyrite in Quartz-Sericite-Chlorite Gold With Dispersed Quartz-Sericite-ChloriteRock Rock The Ropes main ore zone is steeply dipping, 335 m in maximum strike length, 12 12 m in average thickness, and 600 m in known down dip extent (Figures 4). It is within the quartz-sericite-chlorite rock, and gold is associated associated with dispersed pyrite with only minor quartz veins. veins. The Ropes main ore zone can be divided longitudinally into three ore subtypes section. Subtype (Figure 5). These These subtypes subtypes are, are, from west to east, in long section. Subtype 11 is is light light gray gray to to pale green, siliceous quartz-sericite rock, containing minor lenses of of light gray cherty quartz rock with pyrite, tetrahedrite, chalcopyrite and galena. galena. Pyrite Pyrite abundance abundance does does not not correlate correlate with gold grade. Subtype quartz-sericite-chlorite Subtype11has hasan aninterdigitating interdigitatingcontact contact with with barren barren quartz-sericite-chlorite and carbonate-quartz-chlorite rock to the west, and a gradational contact to the east with is 6.8 6.8 glton. g/ton. Subtype subtype 2. The average gold concentration is Subtype 2 is is light green green quartzquartzsericite-chlorite-pyrite rock with a positive correlation between fine-grained pyrite pyrite content content and Au abundance. Subtype 2 is the thickest part of the ore zone and, therefore, therefore, the most volumetrically important. ItIt has with subtype 3. The has aa relatively relatively sharp contact to the east with The average Au concentration ranges from 2.6 glton, g/ton, rarely up to 6.2 glton. g/ton. Subtype dark Subtype33isisdark green quartz-chlorite-pyrite consistently large fine-grained fine-grained pyrite pyrite content. ItIt has quartz-chlorite-pyrite rock with a consistently has barren quartz-sericite-chlorite rock rock to to the the east. east. The a sharp contact with barren The average average Au Au concentration is is 10.3 10.3g/ton. glton. Zones of greater than 4 g/ton glton Au abundance, defined by assay data, are are contained contained centrally within the Ropes main ore zone. The middle parts of these greater than The middle parts of these greater than 44 g/ton glton Au Au zones strike echelon fashion at approximately strike across the 080° 080' trend of the orebody in en echelon 055°, 055', whereas their extremities have a nearly 070° 070' strike, thus forming forming a low low angle angle sigmoidal sigmoidal pattern across the ore ore zone. zone. This This pattern pattern is is most most pronounced pronounced at at and and below below the the 1152 1152level level toward the east end of of the the Ropes Ropes main main ore ore zone zone (Figure (Figure 6). 6). Above the 650 level, ore is separated from carbonate-quartz-chlorite rock on on the the north north by slightly auriferous quartz-sericite-chlorite rock, but but below below the the 650 level level the east end of the ore is in contact with carbonate-quartz-chlorite carbonate-quartz-chlorite rock (Figure 3). 3). The north side side of of the the ore ore strikes 070° 070" and dips very steeply north whereas the contact between quartz-sericite-chlorite quartz-sericite-chlorite rock and the carbonate-quartz-chlorite rock strikes 080° 080Âwithin the deposit and dips dips steeply steeply south. Therefore, Therefore, atatdepth, depth, the the ore ore abuts abuts the the carbonate-quartz-chlorite carbonate-quartz-chlorite rock contact contact on on the the north, with the east limit of the Ropes main ore zone plunging to the west at at deeper deeper levels levels along the line defined by the intersection of the planes of the orebody and the the carbonatecarbonatequartz-chlorite rock contact on the north. Below Below the the 1284 1284 level, the 25 25 to 40 m m thick quartzquartzsericite-chlorite rock thins markedly to the east and interfingers along strike strike to to the the east east with with quartz-sericite-chlorite rock rock plunges plunges carbonate-quartz-chlorite rock. The The thickest thickest part part of of the the quartz-sericite-chlorite approximately 45° 45' east and is coincident with the bend in strike of the trend of quartz-sericite-chlorite rock from 080° 070° east of the main ore zone. 080' within the deposit back to 070' zone. There are several other gold bearing bodies bodies near the the main main ore ore zone zone (Figure (Figure 5). The The northwest ore zone is a small ore zone of 101,000 tons tons with with 4.6 4.6 glton g/ton Au, Au, 170 m m northwest northwest of of the Ropes main ore zone, and is dominantly ore subtype 2. 2. Auriferous, Auriferous, pyritic pyritic quartzquartz36 �_____ _____ long section section of of the the Ropes Ropes deposit in in the the Vertical long N80° plane, with gold gold ore ore subtypes: subtypes: N80°E 1 1 2 3 - QUARTZ SERICITE SERICITE ROCK, ROCK, QUARTZWITH WITH GRAY GRAY QUARTZ QUARTZ LENSES LENSES QUARTZ SERICITE -- CHLORITE CHLORITE ROCK, ROCK, QUARTZ -- SERICITE GOOD Au AU :: PYRITE CORRELATION CORRELATION - QUARTZ CHLORITE - PYRITE PYRITE ROCK ROCK QUARTZ -- CHLORITE FigureS: Figure 5 : Vertical Vertical long long section section of of the the Ropes Ropes mine mine in in the the N80°E N8O0E showing gold gold ore ore subtypes. subtypes. 37 37 �0 50 meters meters ROPESMINE MINE 1152 1152 LEVEL LEVELPLAN PLAN ROPES tonne Au Au ore orezones zones >> 44 gg I1tonne I 0quartz quartz-- sericite sericite-- chlorite chloriterock rock 1 Figure6:6:Geologic Geologicplan planmap mapofofthe the1152 1152level levelofofthe theRopes Ropesmine mineshowing showinghigh highgrade gradeore orezones. zones Figure 38 �Ropes Ropes Mine Mine Level 1620 Level Geologic Plan Geologic Plan IN ul m C L, + cu "1" 50 50 m EXPLANATION EXPLANATION serpentinitic peridotite a serpenthitic peridotite C >2g/tonneAu 0 > 2 g I tonne Au carbonate - talc rock C] >4g/tonneAu 0 > 4 g I tonne Au a carbonate - quartz - chlorite rock rock - A,, Au LIII quartz rock quartz -- sericite -- chlorite rock auriferous quartz vein (Lower Secondary Secondary Drift Drift Vein) Vein) LI microcrystalline a rnicrocrystallinecarbonate carbonate - quartz rock rock Figure 7: Geologic Geologic plan plan map map of of the the 1620 1620 level of the Ropes mine. mine 39 �south south of of the the central central part part of of the the main main ore ore zone. zone, Non-Aunferous Non-Aur$erous Veins Veins Milky white, white, vitreous, vitreous, medium to coarse-grained quartz veins commonly cut the east northeast foliation in the quartz-sericite-chlorite quartz-sericite-chlorite rock at a high angle. Some Somedip dipsteeply, steeply, whereas others are shallowly dipping veins offset in north side up stepwise fashion along foliation parallel structures. The The veins veins are are not not auriferous auriferous and are commonly up to 10cm 10 cm thick and several meters in length. They are approximately 1% of the quartz-sericite-chlorite quartz-sericite-chlorite rock. rock. Quartz Quartzininthe theveins veinshas hasfull fullextinction extinctionunder undercrossed crossedpolars, polars,simple simplegrain grainboundaries, boundaries, and locally locally has has minor minor pyrite. pyrite. Banded dolomite veins commonly strike 015' 015° and dip nearly vertical. vertical. They cut the auriferous quartz veins. Massive, planar sided, coarse crystalline white white dolomite veins up to 10 10 cm thick thick cut cut all all other other veins veins and andare areundeformed. undefonned. Structure Structure An 065° 065' striking striking near vertical foliation is defined by planar alignment of sericite and chlorite chlorite in in the the quartz-sericite-chlorite quartz-sericite-chlorite rock. This Thisfoliation foliationisisinterpreted interpreted as astectonic tectonic schistosity schistosity or or SS fabric fabricbecause because the the sericite sericite and and chlorite chloriteare aresecondary secondaryminerals mineralsthat thatcut cutand and locally locally displace displace relict relict primary primary magmatic features, such as domains of former feldspar phenocrysts, phenocrysts, and and lithic lithic fragments. fragments. Locally LocallyS-C S-Cfabric fabricisisdeveloped, developed, especially especiallyin incarbonatecarbonatetalc talc and and carbonate-quartz-chlorite carbonate-quartz-chlorite rocks. rocks. Contacts Contacts between between the the quartz-sericite-chlorite quartz-sericite-chlorite rock rock and and rocks rocks derived derived from fromaaperidotite peridotite protolith protolith defined defined planes planes of of weakness weakness that favored development of a shear zone. The The orientation orientation of of reactivated reactivated zones zones of of weakness such as contacts between rock types are not strictly strictly governed governed by by the the exact exact orientation orientation of of the the stress stress that that causes causesthe the movement. movement. Ore Ore Related Related Structure Structure The The Ropes Ropes main main ore orezone zone trends trends 080° 080' overall, overall, but but is is internally internally comprised comprised of of 055° 055' to to 065° 065O trending trending zones zones of of greater greater Au concentration, concentration, which host most of the gold. These Theseoccur occur in glton Au Au concentration concentrationwithin within ore ore in low low angle angle sigmoidal sigmoidalzones zones of of greater greater than than 44 g/ton characterized characterized by by dispersed dispersedpyrite pyrite or or in in auriferous auriferous quartz-tetrahedrite quartz-tetrahedrite oblique obliqueshear shearveins veinswith with similar similar geometry geometryand andorientation. orientation. Zones Zones with withgreater greaterthan than44g/ton @on gold goldconcentration1 concentration, defined defined by by assay assaydata, data,are aremore more centrally centrally within within the the Ropes Ropes main main ore zone (Figures 6 and 7). The Themiddle middle parts partsof ofthese thesehigher higher grade grade zones zones strike strikeen en echelon echelon across acrossthe the overall overall 080° 080" trend trend of of the the ore orebody bodyatatapproximately approximately 055" whereas their extremities extremities nearer nearer the contacts contacts with the the carbonate-quartz-chlorite carbonate-quartz-chlorite rock rock 0550 strike strike approximately approximately070°, 070°forming formingaalow low angle angle sigmoidal sigmoidal pattern pattern across acrossthe thezone, zone,which whichisis most most prominent prominent on onthe theeast eastend endof ofthe the1152 1152level level (Figure (Figure6). 6).This Thisgeometry geometryisisconsistent consistentwith with greater movement movementbeing beingaccommodated accommodated near nearthe themargin margin of ofmore moreductile ductiledeforming deforming greater carbonate-quartz-chlorite carbonate-quartz-chloriterock, rock,where wherethe theoriginally originally formed formed 055° 055' to to065° 065' schistosity schistositywas was flattened 080' plane plane of of shear, shear, represented represented by by the the contact contact between between contrasting contrastingrock rock flattened to tothe thelocal local080° types. types. 40 �sericite-chiorite sericite-chlorite rock rock was was encountered encountered in in deep deep drilling drilling at at the the Ropes Ropes deposit, deposit, in in aa zone zone separate separate from, from, and and deeper deeper to to the the east east of, of, the the Ropes Ropes main main ore ore zone. zone. Ore Ore Minerals Minerals and and Textures Textures and and Metal Metal Distribution Distribution Gold is with pyrite pyrite less less than than 100 100 microns microns in in diameter diameter dispersed dispersed throughout throughout the the mass mass of of the the quartz-sericite-chlorite quartz-sericite-chloriterock, rock, and and with with this this pyrite pyrite on on fractures, fractures, foliations, foliations,and and within within and and along the margins of millimeter-thick quartz veinlets. veinlets. Native Native gold, gold, of of variable variable fineness, fineness, isis 11 to to 10 10micron micron grains grains isis attached attached to to the the surface surface of of the the fine fine grained grained pyrite, pyrite, included included as asround round blebs hlebs within within fine fine grained grained pyrite, pyrite, on on fractures fractures within within fine fine grained grained pyrite, pyrite, and andatatgrain grain boundaries boundaries of of fine fine grained grained quartz quartz and and sericite. Minor Minorcoarse coarsegold goldisison onfractures fracturesin inquartz quartz veins. veins. Silver Silver isis in in electrum, electrum, native native silver silver isis with with fine fine pyrite, pyrite, argentiferous argentiferous tetrahedrite, tetrahedrite, argentiferous argentiferousgalena, galena,and andrare raredyscrasite. dyscrasite. Pyrite Argentiferous galena, galena, Pyrite is is 97% 97% of of the the metallic metallic minerals followed by 1% chalcopyrite. Argentiferous argentiferous tetrahedrite, tetrahedrite, sphalerite, millerite, bravoite, magnetite, and argentiferous tetrahedrite, tetrahedrite, sphalerite, millerite, bravoite, magnetite, and rutile rutile are are present present in in trace trace amounts. amounts. The The gold gold is is silver silver bearing and metallic silver is gold bearing. bearing, The The low low bulk bulk Au/Ag AulAg of of 0.65 0.65 for for the the Ropes Ropes gold gold deposit deposit differs differs from from ratios ratios reported reported for for Precambrian Precambrian gold-quartz gold-quartz veins veins and and lodes lodes (Boyle, (Boyle, 1979), 19791,which which range range from from1.37 1.37to to12.5 12.5and and average average about about 4.2. 4.2. Both BothAu Auand andAg Aghave havecontinuous continuouspositively positivelyskewed skewed log log normal normal distributions, distributions, each each with with aa single singlemaximum, maximum, interpreted interpretedasasindicating indicatingonly onlyone oneperiod periodof of mineralization. mineralization. Distribution. Distribution.Geometry Geometryand andAu Au Concentration ConcentrationofofAur?ferous Auriferous Quartz QuartzVeins Veins Auriferous Auriferous quartz quartz veins veins are are concentrated concentrated at the south side of the deposit. Individual Individual veins average 20 cm thick and extend 12 m horizontally and 15 m vertically, but collectively veins average 20 cm thick and extend 12 m horizontally and 15 m vertically, but collectively these these veins veins are aregrouped groupeden enechelon, echelon,and andlocally locally they they form formore oreshoots shoots88to to11 11mmthick, thick,with withthe the quartz quartz-sericite-chlorite rock. The Theveins veinsstrike strikeen en quartz veins veins separated separated by by auriferous auriferous foliated foliated quartz-sericite-chlorite echelon echelonatat055° 055' to to065° 065' across acrossthe the080° 080' trend trend of of the the quartz-sericite-chlorite quartz-sericite-chloriterock rocktype, type,dip dip vertically geometry. They vertically to to 85° 85' south, south, and and have a slight sigmoidal geometry. They occur occur progressively progressively further further east east in in successively successively deeper deeper mine mine levels. Eight Eightmajor majorshoots shootsmade madeup upof of these these veins veins were were mined mined in in the the 1800's 1800'sand and 1890's 1890's above above the 800 level. Broderick Broderick (1945) (1945)implied implied that that single single large largequartz quartz veins veinsranged ranged up up to to11 11m m thick, thick, 60 60m m in in horizontal horizontal extent, extent,and and76 76m m vertical vertical extent, extent,but but examination examinationof of the the old old mine mine workings workings concurrent concurrent with with development developmentof ofthe the modern modern Ropes Ropes mine, mine, and anddetailed detailedhistoric historic descriptions descriptions indicate indicate the the old old stopes stopeswere were ore oreshoots shoots made made up upof of aaseries seriesof ofsmaller smallerindividual individualquartz quartz veins veins and and intervening interveningauriferous auriferousfoliated foliated quartz-sericite-chlorite quartz-sericite-chlorite rock. rock. The Theveins veinsare aresaccharoidal saccharoidalwhite white to tolight lightgray grayquartz, quartz,with with pyrite pyrite and andminor minorargentiferous argentiferoustetrahedrite, tetrahedrite, galena, galena, and and chalcopyrite; chalcopyrite;and and rare rare free freegold, gold, molybdenite, molybdenite, dyscrasite, dyscrasite, tourmaline, tourmaline, and and native silver. Overall, Overall,metal metal concentrations concentrations in inthe the veins veins range rangefrom from20 20to to75 75g/ton gltonAu Au with with Au/Ag AulAgratio ratio from from 0.08 0.08 to to 1.76. 1.76. Thequartz quartzveins veinshave havegreater greaterconcentrations concentrationsof ofgold goldthan thanmost mostof ofthe thegold goldwith withdispersed dispersed The quartz-sericite-chloriterock, rock,but butthe thezones zonesof ofgreater greaterthan than44g/tonne gltonneAu Au pyriteininquartz-sericite-chlorite pyrite concentrationin inthe thequartz-sericite-chlorite quartz-sericite-chloriterock rock are are not not generally generally zoned zoned about about the theveins, veins, concentration rather,they they occur occurmore morecentrally centrallywithin within the the quartz-sericite-chlorite quartz-sericite-chloriterock rock north northof ofthe theveins. veins.In In rather, some instances, Au concentrations of greater than 4 glton in the gold with dispersed pyrite in some instances, Au concentrations of greater than 4 g/ton in the gold with dispersed pyrite in quartz-sericite- chlorite chloriterock rockextend extendalong alongthe the same same055° 055' to to 065° 065' trend trend eastward eastwardfrom fromthe the quartz-sericitewest end endof ofold oldstopes stopeswhich which mark markconcentrations concentrations of of quartz quartz veins, veins,particularly particularlyfor forold oldstopes stopes west 41 �westward plunging plunging auriferous auriferous quartz-tetrahedrite quartz-tetrahedrite veins Vertically dipping, steeply westward occur progressively further east in successively deeper levels of the mine. These banded, auriferous, tetrahedrite-bearing tetrahedrite-bearing quartz veins with aligned schistose inclusions of sericitequartz-chlorite wall rock are at or near the south side of the main main ore zone and have an orientation the same as the zones of schistosity parallel gold concentration with dispersed pyrite, which are more centrally within within the the trend trend of of quartz-sericite-chlorite quartz-sericite-chloriterock. rock. The veins are oriented nearly parallel to the schistosity, and therefore therefore nearly nearly perpendicular to the inferred maximum principal principal stress. They They contain schistose septa identical in composition to the quartz-sericite-chlorlte wall rock and have quartz with undulose undulose extinction and subgrain development textures indicating grain size reduction. reduction. These characteristics are compatible with an origin as oblique shear veins formed in the direction of of shear movement movement (Hodgson, 1989). Oblique shears Oblique shear shear veins veins are are inclined inclined to to shear shear zone zone margins margins in the same same way as as PP shears and show the same sense of en echelon stepping as the sense of of movement movement across the zone containing them (Hodgson, 1989). In In the case of the Ropes deposit, this indicates a dextral component in plan view. An An origin origin for for the the quartz-tetrahedrite quartz-tetrahedrite veins, veins, and and the the en en echelon echelon zones of Au concentration with dispersed pyrite, pyrite, as tension tension shears, extension extension veins, or Riedel shears in a sinistral shear zone is not indicated indicated because the the low low angle orientation of the tips of the veins with respect to the shear zone margin, margin, and the similar orientation of of the ends of the en echelon zones of Au concentration with dispersed dispersed pyrite, pyrite, is not not consistent with the sense of rotation expected in sinistral sinistral shear. shear. The sigmoidal zones of gold concentration with dispersed dispersed pyrite pyrite and the oblique shear veins have orientations nearly parallel parallel to the S fabric, fabric, consistent with with an origin as P shears. PP shears commonly form at approximately 10° 10' to the shear shear zone zone boundaries, boundaries, after after peak peak deformation, when resistance to shear is decreased decreased by by the the presence presence of of well well developed planar fabric (Tchalenko, (Tchalenko, 1970). 1970). Inferred Direction of Shear Movement direction in aa shear zone is commonly considered considered to to be he in in the the line line perpendicular to the intersection of of the shear zone margin with the plane plane of of the the oblique obliqueSS fabric, and the sense of movement is inferred from the the sense of of obliquity obliquity of of the the fabric fabric to the shear zone margin. In In aaductile ductile environment environmentthe the acute acute angle angle between between the the SS fabric fabric and and the the shear plane faces away from the direction of movement. The The sigmoidal sigmoidal zones zones of of greater greater gold gold concentration with dispersed pyrite follow an SS fabric, fabric, interpreted as as aa largely largely compressive, compressive, ductile feature. Contacts Contactswith with nonfoliated nonfoliated serpentinitic serpentinitic peridotite peridotite north north and and south south of of the the Ropes deposit are considered considered shear planes parallel to the C C direction. direction. The The orientation orientation of of the the SS fabric relative to the C direction indicates a dextral dextral component component of of movement movement when when viewed in the horizontal plane, with the south south side side of of the zone moving west southwest southwest and and the the north north side moving east northeast. (Figure 8). Offsets Offsets along along northeast northeast trending trending faults faults in in the the deposit, deposit, and the Z sense of warping of layering between between the the rock rock types types at at the the south south side of of the the deposit (Figure 7) 7) also support support a dextral component of movement. Localization of the Deposit Within Within a Dilational Jog quartz-sericite-chlorite rock strikes strikes 070° 070' overall overall but but 080° 080" where where itithosts hosts The trend of quartz-sericite-chlorite the main ore zone (Figure 8). This This080° 080Âpart part of of the the trend trend acted acted as as aa dilational dilational jog or or releasing releasing of movement movement in in plan view view (Figure (Figure 8). 8). bend during the indicated dextral component of Releasing bends are are commonly commonly sites sites for for ore ore deposits, deposits, even even if if the the main main fault fault trend trend isis barren barren 42 �0 1 km r N 2 3 1 1 Ropes deposit quartz vein prospect - 18 svucture anspg, s'rn obliqu, m, v.i,,., nd.s nht Loan 01 gvSr Au conc.,Wi,flon slTh .p.nnpjfl, Numbered quadrants mathed by dashed lines are ranges of possible orientations of horizontal components of maximum principal stresses which could account for dextral components of strain at: I. Bjork -- Lundeen prospect 1. Lundeen prospect 2. 2. I-I -18 18Structure Structure 3. Ropes Ropesdeposit deposit 4. range 4 Possible Poss~ole rangeof 01 horizontal horizontalcomponent component 01 maximum maxfmumprincipal pr,nc~paI stress which wnlcn could co~ld of stress s ~ m ~ l t a n e o usatisfy sat~sfv s l ~ requirements requmvnentsfor lor simultaneously sites 2, and sqles 1, 1.2. and33 above above Figure 8: 8: Structural Structuralmodel model for for the the Ropes Ropes mine, mine. 43 �(Sibson, 1987). Both Both the the sigmoidal sigmoidal zones zones of of Au Au concentration concentration with with dispersed dispersed pyrite, pyrite, and and the the auriferous quartz veins are interpreted as indicating local extension within aa dilational dilational jog. jog. There is a component of positive volume change in the shear zone, in an otherwise compressive tectonic regime. Increased Increased pore pore pressure pressure within within the the shear shear zone zone as as microfractures filled with fluid, combined with the extensional effect effect of of the dilational jog, jog, local extension. extension. Slip jogs involves extensional may have contributed to local Slip transfer in dilational jogs fracture openings localized in the jog, jog, or step over. Formation Formation of of dilational dilational jogs involves involves local loss of cohesion, or brittle failure, in an an otherwise ductile ductile environment. environment. The trend of quartz-sericite-chlorite rock which hosts hosts the Ropes main ore zone narrows to the east of the deposit, as well as toward toward surface up up dip from the deposit, where it 70° south dip at shallow shallow levels. levels. This bends from a near vertical dip at depth to a 70" This change change in in thickenss and attitude may have caused barrier barrier conditions conditions for ascending hydrothermal fluids, thickens addition to to the the dilational jog jog controlling resulting in another control on localization of ore in addition of the overall setting setting of of the the deposit. deposit. References References Anderson,E.M., Anderson, E.M., 1951, 1951,The The Dynamics Dynamics of of Faulting: Faulting: London, England. Oliver and Boyd, Boyd, 191 191 p. p, Geochemistry of Gold and Its Deposits: Deposits: Geological Geological Survey of Boyle, R.W., 1979, 1979, The Geochemistry Canada Bulletin 280, 584 p. 280,584 p. Broderick, T.M., 1945, 1945, Geology Geology of the Ropes Ropes Gold Mine, Mine, Marquette Marquette County, County, Michigan: Michigan: Economic Geology, Geology, v.40, v.40, p.115-128. p.115-128. of Economic Brozdowski, R.A., 1989, 1989, Geology of The Ropes Mine, Society of Economic Geologists Geologists Fall Fall Field Conference Guidebook, Guidebook, Precambrian Geology and and Metal Metal Occurrences, Occurrences, Michigan's Michigan's Upper Peninsula Field Conference, Conference, p. 38-75. Groshong, R.H., Jr., 1988, 1988, Low Temperature Temperature Deformation Mechanisms Mechanisms and and Their Their v. 100, p. 1329-1360. 1329-1360. Interpretation: Geological Society of America Bulletin, v.100, Hodgson, C.J., 1989, 1989, Patterns Patterns of of Mineralization, Chapter Chapter 3, 3, in: in: Mineralization and Shear Zones, Geological Association of Notes v.6, Montreal, Quebec, May 12-14, 12-14, p.51-88. Lisle, R.J., 1989, Dike Sets: Geol. 1989, Paleostress Analysis from Sheared Dike Geol. Soc. Soc. Am. Am. Bulletin, Bulletin, v. v. 101, p. 968-972. Sibson, R.H.,1987, Earthquake Rupturing as a Mineralizing Agent in Hydrothermal Systems: Systems: Geology, v.15, v. 15, p 701-704. 701-704. Tchalenko, J.S., 1970, 1970, Similarities Similarities Between Shear Shear Zones of Different Magnitudes: Magnitudes: 625-1640. Geological Society Society of of America America Bulletin, Bulletin,v.81, v.81,p.1 p.1625-1640. 44 �Geologic Field Field Excursion Excursion to to the the Ispheming Greenstone Greenstone Belt Rodney C. Johnson, Johnson, Rod Rod Johnson Johnson & & Associates, Associates, Inc., Inc., Negaunee, MI MI 49866 49866 Theodore J. Bornhorst, Department Department of Geological Geological Engineering Engineering and and Sciences, Sciences, Michigan Michigan Technological Technological University, University, Houghton, Houghton,MI MI49931 4993 1 Introduction Introduction This geologic field excursion to the Ishpeming Ishpeming greenstone belt consists consists of of 88 selected selected stops stops (Figure 1). These These stops stops are are designed designed to to cover cover the major varieties of volcanic lithologies found in the belt and several localities of structural structural significance. significance. Johnson and and Bornhorst Bomhorst (this volume) provide an overview of the greenstone belt and explanation of stratigraphic stratigraphic terminology used in this guide. AA detailed detailed topographic topographic map map is is provided provided to to identify identify the the location of the stops, however users should refer to larger scale maps in order to navigate stops, order to navigate roads to the stops. stops. Trip Stops Field Trip Stops Stop Stop A -- Lighthouse Point Purpose: View: View:1)1)amphibolite amphibolite schist schist of of Lighthouse Lighthouse Point Point Basalt, Basalt, 2) 2) Dead Dead River Shear Shear Zone, Zone, and 3) cross-cutting relationships of Archean and Proterozoic rocks (Figure 2). Note: You Guard to to visit visit this this locality. locality. No rock You must must obtain obtain permission permission from from the U.S. Coast Guard rock hammers or specimen collecting are allowed at this this stop. Park Park in in the the parking lot across across from from the Coast Coast Guard Guard office. office. At this stop excellent shoreline exposures on Lighthouse Point and along the adjacent beach provide a view of Archean and Proterozoic Proterozoic rocks rocks (Figure (Figure 3). 3). Gair Gair and and Thaden (1968) (1968) mapped these rocks in detail. detail. Part I. The Theoutcrop outcrop in in the the middle middle of of the the beach beach near the parking lot is composed of Archean thinly layered, amphibolite schist (basalt). The basalt here is part of the Lighthouse Point generally strike E-W E-W and and dip dip 70°N 70°N. The layers in Basalt. The The layers layers on on Lighthouse Lighthouse Point generally highly flattened flattened pillows. pillows. The flattening is interpreted to be a the basalt are interpreted as highly result of north verging recumbent folding (Johnson and Bomhorst, 1991). 1991). Part 11. II. The Theoutcrop outcropon on the the southwest southwest end end of of the beach is composed of chlorite-sericite schist, again part of the Lighthouse Point Basalt (see Johnson and Bornhorst, Bomhorst, this volume). The chlorite-sericite schist is interpreted to be deformed pillow basalt and are Kinematic indicators indicators (S-C fabric in particular) metamorphosed to greenschist facies. metamorphosed facies. Kinematic indicate a dominantly left-lateral shear sense, but on close inspection right-lateral and northnorthindicators are also present. present. This locality is interpreted to be the eastern extension of side-up indicators block of of the Ispheming greenstone the Dead River Shear Zone that separates the northern block belt from the southern 1). southern two two blocks blocks (Figure (Figure 1). 45 �____ T. 50 N T. 49 N T. 48 N. 46°30' R.28W. R.27W. R.26W. R.25W. Explanation Explanation Proterozoic Proterozoic Sedimentary rocks 0Sedimentary rocks I Mona Mona Formation Formation Upper tuff unit unit and lapilli-tuff lapilli-tuff unit unit Basalt Basalt flow unit unit Kitchi Formation Formation Kitchi Tuff unit and lahar unit Basalt unit Basalt flow unit l\ /1 I Archean Intrusive Intrusive Rocks Rocks k''-4 Granodiorite Granodiorite 177771 Tonalite Tonalite 1 Deer Lake Peridotite Deer Lake Peridotite Sedimentary Rocks Sedimentary Rocks K"Xl Timiskaming-type Timiskaming-typesedimentary sedimentaryrocks rocks Volcanic Rocks Rocks Lighthouse Lighthouse Point Point Basalt Basalt Basalt Basalt V/A Reany Reany Lake pyroclastic pyroclastic unit unit and and Fire Center mine mine iron-formation iron-formation unit unit HP_Li Nash NashCreek Creek glomerophyric glomerophyric basalt basalt unit unit 3 L\1 m Bedding Bedding 87 f Overturned bedding bedding 87+ Facing of pillows A Facing pillows Plunging anticline Plunging anticline Plunging syncline syncline 'C Plunging overturned anticline Plunging overturned Shear zone 1 @ Location Location of stops stops & - A % Figure 1: 1: Generalized geologic geologic map of the Ishpeming greenstone belt showing location location of stops. stops. 46 �R. 25W. T. 48 N. Figure 2: 2: Stop StopAA- Lighthouse Lighthouse Point Point Figure 47 �100 0 200m 0 50rn I Explanation Middle Middle Proterozoic Proterozoic /,%j Keweenawan Keweenawandiabase diabasedike dike Early Early Proterozoic Proterozoic 'dt*S Metadiabase Metadiabasedike dike Archean Archean I Intrusive IntrusiveRocks Rocks Rhyolite Rhyolite 0 I Lighthouse Lighthouse Point PointBasalt Basalt Basalt, Basalt,outcrops outcropsinindarker darkershade shade Figure Figure3: 3:Geologic Geologicmap mapof of Lighthouse LighthousePoint Point (modified (modifiedfrom fromGair, Gair,1959). 1959). 48 I �Within the basalt dominated outcrop there are lenticular pods of quartz-chert (hematite (hematite The interpretation of the the quartz-chert stained) and small texturally different different quartz quartz veins. veins. The with deposition deposition of of the the basalts. basalts. Small Small quartz quartz pods is not clear, they could be synchronous with veins are found in rocks throughout throughout the the Ishpeming Ishpeming greenstone greenstone belt. belt. Most of of these were were Archean deformation deformation and and metamorphism. metamorphism. However, at at least some some likely emplaced during Archean 1998). were emplaced during the Proterozoic (Bornhorst (Bomhorst and others, 1998). Part III. 111. The main outcrops of Lighthouse Point are northeast of the first two localities. localities. This trip will only only visit visit the the shorline shorline ouctrops ouctrops on on the the northeast end of of the the beach, beach, near near aa house. house. Here, Archean thinly layered, amphibolite schist (basalt) is cut by a tabular, porphyritic rhyolite dike trending roughly parallel to the layering. The layered basalt is part of the the Lighthouse Point Basalt and the rhyolite is interpreted as synchronous with the synorogenic late trondjhemite-granite suite plutons that reorient earlier fabrics. are The Archean rocks are cut by two N-S trending Proterozoic diabase dikes that are metamorphosed to greenschist facies as compared to the surrounding Archean rocks that are are metamorphosed to amphibolite facies. The The crest crest of the ridge (not visited today) is underlain by a relatively unmetamorphosed E-W E-W trending diabase dike dike of Keweenawan Keweenawan age. age. White Bear Drive Stop B -- White Drive Purpose: View Viewthe theupper uppertuff tuffunit unitof ofthe theMona Mona Formation Formation and andS3 S3crenulation cleavage cleavage (Figure (Figure 4). 4). The rocks at this stop are part part of of the the upper upper tuff tuff unit unit of of the the Mona MonaFormation. Formation. The rocks of the quartz-feldspar-sericite-chlorite schist. schist. Thin primary layering subupper tuff unit consist of quartz-feldspar-sericite-chlorite parallel to S S,foliation foliationcan canbe beobserved observed in in some some of the outcrop in this area. Based Based on on the the presence of sand-sized, sand-sized, lenticular lenticular volcanic volcanic fragments, and lack of sand-sized quartz quartz and and feldspar in an intact framework, most of these schist beds are interpreted as tuff. On the north side of the outcrop nearest White Bear Drive we can see the hinge of a fold. This allows us to see S3 crenulation crenulationcleavage. cleavage. On the limbs of westward plunging F3 fold. S and Bornhorst, this volume, andS3 S3are are parallel parallel and and indistinguishable (see Johnson and Bomhorst, the fold S, Table 1). 1). Stop C - Tower Purpose: View Viewthe thelapilli-tuff lapilli-tuff unit unitof ofthe theMona MonaFormation Formation and andS3 S3crenulation cleavage cleavage (Figure 5). 5). Note: Park Parkatatthe thecommunication communicationtower towerand andwalk walkabout about lOOm loom downhill in a southerly direction to aa series series of of outcrops outcrops alongside alongside the the hill. hill. The rocks at this stop are part of the lapilli-tuff lapilli-tuff unit unit of of the the Mona MonaFormation. Formation. The rock is composed of calc-alkalic rhyolite lapilli in a quartz-sericite-chlorite matrix with quartz and and 49 �R. 26W. T. 48 N. Figure 4: Stop Stop B-White B-White Bear Drive Drive R. 26W. T. 48 N. Figure Figure 5: 5: Stop Stop C-Tower C-Tower 50 �R. 26W. 1.48 N. Figure Figure 6: 6:Stop Stop D-Shunk D-Shunk Furniture Furniture R. 26W. T. 48 N. StopE-Tuff E-Tuff Unit Unitof ofthe theKitchi KitchiFormation Formation Figure7:7:Stop Figure 51 �less commonly, feldspar phenocrysts. Flattened Flattened apple apple green green lapilli lapilli (muscovite (muscoviteand and chlorite; chlorite; Puffet, 1974) are also common at this stop. This This unit unit isis interpreted interpreted as as subaqueous subaqueous pyroclastic flow and fall deposits. At this stop an earlier shallowly easterly dipping foliation (S1) (Si) is crenulated by a later E-W foliation and and elongated elongated in the (S3). The The lapilli lapilli are are flattened along the S1 S, foliation trending foliation (53). direction of the intersection of Si and S3. The Dead River Shear zone (D2, D4) is interpreted 83. The Dead River Shear zone (Dz,D4) to be located on the north side of the tower hill. Stop D - Shunk Furniture Purpose: View Viewpillowed pillowedbasalt basalt of ofthe theMona MonaFormation Formation (Figure (Figure 6) 6) Note: Park Parkalongside alongsideof ofthe theroad roadacross acrossfrom fromShunk ShunkFurniture, Furniture, but but be be very very careful careful of oftraffic. traffic. There are excellent views of relatively undeformed pillowed pillowed tholeiitic basalt in outcrops pillowed basalts are part part of of the the basalt basalt flow flow unit unit of of the the Mona Mona alongside of U.S. The pillowed 30 cm cm X X 1.5 1.5 m; m; Formation. The Thepillows pillows are are ellipsoidal ellipsoidal in in shape shape with with dimensions dimensions about about 30 E-W and and dips dips 85' 85° N. N. Cusps on pillows indicate attitude of bedding strikes approximately E-W that stratigraphic top is to the north. There There are are characteristic characteristic well-developed well-developed pillow pillow rinds, rinds, radial fractures, and interpillow void spaces filled with quartz and carbonate. carbonate. Overall, Overall, pillowed and massive tholeiitic basalt is the dominant lithology in the Ishpeming greenstone belt. Stop EE— Kitchi Formation Stop - Tuff Unit of the Kitchi Purpose: View View tuff tuff unit unit of of the the Kitchi Kitchi Formation Formation and and evidence evidence for for superposed superposed folding folding (Figure 7). 7). Kitchi At this stop we will see some of the lithologic variation within the tuff unit of of the the Kitchi folding. Cross-bedding, Formation and evidence for large scale folding. Cross-bedding, graded graded bedding, and and cut cut and and Kitchi Formation, Formation, but but in in this this area area clearly clearly indicate indicate tops tops to to fill structures are uncommon in the Kitchi the east. AA foliation foliation atatright right angles angles to to bedding bedding indicates indicates this this area area is is near aa vertically vertically plunging fold nose. Stop F - Teal Teal Lake Purpose: View View the theCarp CarpRiver River Falls Falls shear shear zone, zone, tuff tuff unit unit of of the Kitchi Kitchi Formation and and Ajibik Ajibik 8). Quartzite of the Menominee Group of the Marquette Range Supergroup (Figure (Figure 8). At this stop we will cross the Carp Carp River Falls shear zone from Lower Proterozoic metasedimentary rocks into Archean We will will begin the the traverse in in the the Archean metavolcanic metavolcanic rocks. rocks. We steeply dipping Ajibik Quartzite of the Lower Proterozoic Marquette Marquette relatively undeformed steeply TheCarp CarpRiver River Falls Falls shear shear zone zone is is aa high high strain strain zone zone indicated indicated by by Range Supergroup. The The foliation foliation in in the the schist schist is is near near vertical vertical and and has has aa quartz-sericite-feldspar-chlorite schist. The steep mineral lineation. As As the the shear shearzone zone isis traversed traversed there there is is aa noticeable noticeable increase increase in in the the 52 �R. 27W. T. 48 N. Figure 8: 8: Stop Stop F-Teal F-Teal Lake Lake R. 27W. T. 48 N. Figure Figure 9: 9: Stop Stop G-Alorig G-Along Deer Deer Lake Lake 53 �amount of chlorite in the schist. On Onthe thenorth north side side of of the the Carp Carp River River Falls Falls shear shear zone zone isis quartz-feldspar-sericite-chlorite schist schist of of the the tuff tuff unit unit of of the the Kitchi Kitchi Formation. Formation. Stop G --Along Along Deer Lake Lake Purpose: View View lahar laharunit unitof ofthe theKitchi Kitchi Formation Formation (Figure (Figure 9). 9). At this stop polymictic volcanic conglomerate is exposed in in a glacially glacially polished polished outcrop along the north side the road road towards towards Deer Deer Lake. Lake. Park alongside of the road. road. This This volcanic volcanic part of the the lahar lahar unit unit of of the the Kitchi KitchiFormation. Formation. On the polished polished surface, the conglomerate is part volcanic clasts vary from 25 cm X 35 cm in cross section, section, down down to to the the size of the matrix grains. Larger 1.2mminincross crosssection, section, are are present present in in the the nearby nearby lake lake Larger clasts, clasts, up up to to 60cm 60 cmXX1.2 shore outcrops. Clasts Clastsgreater greater than than 11cm cm make make up up about about 20 20 % % of of the the rock rock and and there there isis an an obvious stratification in clast clast size. Shape very angular to to rounded. rounded. The Shape of clasts varies from very The volcanic clasts are caic-alkalic calc-alkalic andesite andesite to dacite dacite in composition with with most most clasts clasts at at this this locality being near the andesite to dacite division division with with small small chemical chemical variation variation (Bomhorst (Bornhorst unpublished holocrystalline. The unpublished data). Most Most clasts clasts are are porphyritic and some are holocrystalline. The volcanic volcanic conglomerate is interpreted as a subaqueous lahar deposit. deposit. Stop H - Shoreline of Deer Lake Purpose: View ViewDeer DeerLake LakePeridotite Peridotite (Figure (Figure10). 10). road. Park Note: There There isis aa small small pullover pullover on on the east side of the road. Park and and walk walk along along the the road road to to the north where you can find a small small trail that leads through the woods to to the the tip tip of of the the point. point. Outcrops occur along the shoreline of this small point into into Deer Lake. At this this stop stop serpentized peridotite of the Deer Lake Peridotite is exposed along the shore shore of of Deer Deer Lake. Lake. Elongate pods of massive serpentized peridotite with closely spaced spaced fractures fractures are are surrounded surrounded by 2 to 5 cm wide ribbons of 11 to 22 mm subparallel veins of cross cross cross-fiber serpentine serpentine (Bornhorst fine(Bomhorst and others, 1986). 1986). The Thedark dark grey grey to to green green massive massive serpentized serpentized peridotite peridotite is is fineto medium-grained and lacks obvious foliation. lit In hand sample one can find well-developed well-developed 1 to to 55 mm mm pseudomorphs pseudomorphs after olivine and and pyroxene pyroxene outlined outlined by by thin thin selvages of white carbonate or talc. No No spinifex spinifex or or pyroxene "string beef' beef' textures textures indicative indicative of of komatiite komatiite flows have been found. The Thechemical chemical composition composition indicates indicates an an olivine olivine to to pyroxene ratio ratio from about 0.25 to 2 and most samples samples are are in the harzburgite field and and some some are are in in the the Iherzolite lherzolite field. The The Deer Deer Lake Lake Peridotite Peridotite is is interpreted interpreted as as a sill complex. This locality is only a few 100 Ropes gold gold mine. mine. The 100 meters from the Ropes The shear shear zone zone that that hosts hosts the Ropes gold mine projects immediately immediately north north of of this this small small point. point. The The serpentized serpentized peridotite has a strong, veinlets and and streaks streaks strong, contorted contorted foliation with magnetite as irregular irregular veinlets along the foliation foliation planes indicating the shear zone that hosts gold at at the Ropes ~ o ~mine mine e s continues into the Deer Lake Peridotite. Adjacent Adjacent to to the the gold gold ore ore body body the the serpentized serpentized peridotite is altered altered to a talc-carbonate rock (Bornhorst (Bornhorst and and others, this this volume). volume). 54 �R. 26W. T. 48. N. Figure 10: 10:Stop Stop HH- Shoreline Shoreline of of Deer Deer Lake Lake Figure R. 26W. T. 48 N. Figure 11: 11:Stop StopI-I-County CountyRoad Road510 510 Figure 55 �StopiStop I -County County Road Road 510 Purpose: View Purpose: View fire fire Center Center Mine Mine iron-formation iron-formation of the Lighthouse Point Basalt (Figure (Figure 11). 11). Note: Park Parkalongside alongsideof ofthe theroad, road, but but be be careful careful to to watch watch for for logging logging trucks trucks moving moving at at high high speeds. There are several outcrops outcrops on both sides of County Road 510 510 at at this stop. stop. The The particular particular outcrop of interest is near the top of the slope slope on the east side of the road, itit may may take take aa little little effort to find the iron-formation. iron-formation. At At this this stop stop the the Fire Fire Center Center Mine Mine iron-formation iron-formation unit unit of of the the Lighthouse Point Basalt is overlain and underlain by massive tholeiitic basalt of of the the Lighthouse Point Basalt. The Theiron-formation iron-formation isis approximately approximately 1.5 1.5 m m thick thick and and strikes strikes N30°W. N30¡WItIt isis composed composed of of fine, fine, black black chert chert that contains scattered magnetite grains and pyrite. To Tothe thewest west of of this thislocality, locality, the the iron-formation iron-formation is is layered layered with 1.5 1.5 cm cm thick chert chert and and magnetite bands. Despite Despitevariable variable magnetite magnetite content, content, this this iron-formation iron-formation produces produces aa strong strong magnetic signature signature and can be traced from north to south in this stratigraphic stratigraphic block block of of the the greenstone belt. This marker. The This iron-formation iron-formation is an excellent stratigraphic marker. The basalt is dark dark amphibolite green to black, fine-grained and relatively non-foliated and metamorphosed to amphibolite grade. grade. Acknowledgments We thank Shannon E. Bair for computer drafting of the figures. References Bomhorst T.J., T.J., Shepeck, Shepeck, A.W., A.W., and and Rossell, Rossell, D.M., D.M., 1986, 1986, The The Ropes Ropes gold gold mine, mine, Marquette Marquette County, Michigan, gold deposit: deposit: MacDonald, - an Archean hosted lode gold MacDonald, E.J. E.J. Michigan, U.S.A -(ed.), Proceedings of Gold '86, an International Symposium on the Geology of Gold, Toronto, p. 13-227. Toronto, p. 2213-227. Bornhorst, Bomhorst, T.J., Thorpe, R.I., R.I., and Johnson, R.C., 1998, 1998, Lead isotope study of veins in in the the Archean Ishpeming greenstone belt, Michigan: Econ. Geol., v. 93, pp. 102-107. 102-107. Gair, J.E. and Thaden, R.E., 1968, 1968, Geology of the Marquette and Sands Sands Quadrangles, Quadrangles, Marquette County, Michigan: U.S. Geol. Survey Professional Paper397, 77 p. Johnson, R.C. and Bornhorst, T.J., 1991, Archean Archean geology geology of of the the northern Johnson, R.C. Bomhorst, T.J., northern block block of the the Ishpeming belt, Marquette Ishpeming greenstone greenstone belt, Marquette County, County, Michigan: Michigan: U.S. U S . Geological Geological Survey Survey Bulletin 1904-F, 1904-F, 20 20 p. p. Puffett, W. P., 1974, 1974, Geology of the Negaunee Quadrangle, Marquette County, Michigan: U.S. 53 p. U S . Geol. Survey Survey Professional Professional Paper Paper 788, 788,53 p. 56 �Shear Shear Zones Zones and and Gold Gold Mineralization Mineralization in the the South South Half Half of of the the Ishpeming Ishpeming Greenstone GreenstoneBelt, Belt, Michigan Michigan by D.J. Duskin Duskin Consulting Consulting Geologist Geologist 210 21 0 Union Street Street Camden, SC 29020 29020 and and T.O. T.O. Quigley President Minerals Minerals Processing Processing Corporation Corporation 4547 4547 County County Road Road 601 60 1 Champion, MI 49814 49814 57 �Foreword Foreword Much of this field trip is devoted to gold occurrences. occunences. At Atmost moststops, stops,the theguidebook guidebookdescriptions descriptions will include the the results results of of sampling sampling and and assaying assayingfor forgold. gold. The term "grab sample" means a small reconnaissance-style sample deliberately chosen chosen by by an an exploration exploration geologist to have, in his experience, the maximum chance of yielding gold in the assay because of the presence of alteration, sulfides, sulfides, gossan, gossan, etc.. etc.. If our reported result contains contains gold, gold, this this doesn't doesn't necessarily mean mean that that someone someone else's else's subsequent sample the same value. value. This phase of sampling is deliberately subjective, and and gold gold distribution distribution is is far far will give the from uniform in Archean deposits, deposits, varying varying greatly greatlywithin withinsmall smalldomains, domains,even evenatatproducing producingmines. mines. More representative sampling will will be be discussed at some of the field trip stops as either "channel" or "chip" samples across an exposure. exposure. Channel front diamond blade rock saw cuts or hand-cut Channel samples, samples, taken either from by hammer and moil, are meant to be volumetrically equivalent to a ¼ '/2 split of BQ (1.5-inch (1 S-inch diameter) drill core. Chip Chipsamples samples are are more more representative representative of the exposure than a grab sample, but not as rigorously taken as a channel sample. sample. Unless otherwise specifically noted, all gold values reported herein are from samples samples crushed, ground, split and assayed at the former Callahan Mining Corporation assay lab in the Humboldt (Ropes) Gold Mill, now owned and operated by Minerals Processing Processing Corporation Corporation (MPC). (MPC). MPC's MPC's assays assays were were all all done by the fire fife assay-gravimetric finish finish method, method, using usingaa 1-assay I-assay ton ton (29.167 (29.167 gram) gram) subsplit. subsplit. MPC's MPC's lower detection limit by by this this technique technique isis ,003 .003 odton oz/ton (103 (103 ppb) ppb) Au. Au. The terms "no gold", gold, or or "below "below detection" refer to this limit. In Insome somecases caseswhere wherewe we felt feltititimportant importantto toknow knowthe thepresence presenceof ofeven evenlower lower Au values, separate subsplits were sent to Chemex Labs in Vancouver, B.C. for analysis by a lower detection limit technique, noted herein where so done. This This technique technique is is the the fire fire assay assay -- atomic absorption finish fmish process (FA-AA), (FA-AA), and has has aa lower lower detection detection limit limit of of 10 10ppb. ppb. Chemex Labs also performed whole rock rock major major oxide analyses. analyses. Results Results from samples samples taken at (Grunsky, 1983; Jensen, 1976) some of the field trip stops are shown on Jensen cation plots (Gnmsky, 1976) that have been routinely used for characterizing the lithochemisby lithochemistry of of the the rocks rocks from from this this region (Bomhorst (Bornhorst and Johnson, 1993). Figure lisa 1993). 1 is atemplate templateJensen Jensenplot. plot.The TheJensen Jensenplots plotswere weredone doneby byconsulting consulting geologist geologist R.A. Campbell, Burlington, Ontario, using "Newpet" "Newpet" software developed and distributed by the Earth Sciences Sciences Department of Memorial Memorial University Universityof ofNewfoundland Newfoundland.. Mr. Mr. Campbell's Campbell's assistance assistance is is gratefully acknowledged. acknowledged. 58 �Chemex Chemexalso alsodid didaa32-trace 32-traceelement elementanalysis analysisusing usingthe theX-ray X-rayfluorescence fluorescencetechnique techniquefor forall all samples samplessubmitted submittedfor forassay; assay;results resultsare arediscussed discussedwhere wheresignificant. significant. All thinsections sectionsexamined examinedwith withthe theassistance assistanceofofR.L. R.L. Allpetrographic petrographicdescriptions descriptionsare arefrom frompolished polishedthin Bamett BamettofofBameti BamettGeological GeologicalConsulting, Consulting,London, London,Ontario. Ontario. Mineral Mineralcompositions compositionswere weredetermined determined using JEOLModel Model733 733five fivespectrometer spectrometerscanning scanningelectron electronmicroprobe. microprobe.Mineral Mineral usingBaniett BamettGeological's Geological'sJEOL percentages percentagesare arevisual visualestimates; estimates;no no point point counts counts were done. Mr. Mr.Bamett's Barnett'svaluable valuablehelp helpisisalso alsogratefldly gratefully acknowledged. acknowledged. FeO* + 1102 Cation % Jensen (1976) PJ203 A1203 Mgo MgO Figure 1: 1 :Fields Plot Figure Fieldsfor forthe theJensen JensenCation Cation Plot 595 9 I �CONTOUR INTERVAL 20 FEET 0.. ) 20 Zr.C .5 r CQ 0 t%Z 0 0 �Stop SC-I: SG1: Variably basalt of ol'Mona Mona Formation Formation near near M Marquette Harbor Variably sheared sheared pillow basalt a q u e t t e Harbor (Location 2). (Location map, Figure Figure 2). Gair and (1968) and Thaden Thaden (1 968) last mapped this locality and assigned it to the lower member of the Mona Schist. Recently (1993)have have revised revised the the stratigraphic stratigraphic nomenclature nomenclature of of the the Recently Bornhorst Bomhorst and and Johnson Johnson (1993) lshpeming Ishpeming Greenstone Belt; this locality would now be assigned to the informal basalt flow of the Mona lowermost unit unit.. Pillowed Formation, its lowermost Pillowedmetabasalts metahasaltsof ofgreenschist greenschistfacies facies are are the the predominant Ethology lithology in this this unit. unit. The exposures here are best seen in a three-part sequence. After After parking in in the the abandoned abandoned railroad railroad yard, head east and take the trail along the south side of of Whetstone Whetstone Brook Brook to to the the lakeshore lakeshoreto tosee seeglacially glacially polished outcrops of pillow lavas. The Theoutcrops outcropsdisplay displaywell wellpreserved preservedglacial glacial grooves grooves and andstriae striaetrending trending 198°; 19S0; some of the grooves contain contain classic classic examples examples of of crescent-shaped crescent-shaped chaffer chatter marks pointing down-ice. down-ice. The two outcrops here show show a layer of massive massive non-pillowed non-pillowed basalt basalt conformably conformably sandwiched sandwiched between two pillowed pillowed layers. layers. The layering shown by by this "sandwich" "sandwich" trends trends approximately approximately 305'. 305°. The The pillows are pristine and and undeformed, undeformed, some some of of them them up up to to six six feet feet across. across. They display internal cooling cooling fractures, well preserved rinds, and cusps cusps consistently consistently showing showing tops to to the the north. north. The next point of interest is about about 100 feet feet south south on on the the rocky rockypoint pointof of the thelakeshore. lakeshore. Please he be careful while making your wav way southward over over this this slioperv slippery outcro~. outcrop. On On the the south south side side of of this this rocky rocky point point are pillowed basalt and thin discontinuous lenses of chert interbedded interbedded with the pillows, pillows, some someforming forming pillow selvages. Some brecciated red Someof ofthe thechert chertcontains contains patches patches of ofbrecciated red jasper; this this texture is is probably the the deformation. None of result of soft sediment deformation. of these cherts is magnetic. A A great great deal of of excess calcite is also present with the pillows. This This probably probably contributed contributed to to the the development development of of shearing, shearing, which which can can be be to be increasing rapidly rapidly in in intensity intensity southward southwardin inthis thisoutcrop. outcrop. We think that the calcite and clearly seen to the result result of of degassing degassing and and seawater seawaterprecipitation precipitationininand andnear nearaaflow flowtop. top. In our experience chert lenses are the such interpillow zones containing discontinuous thin cherts are very common. path from the beach beach westward westward back back to to the the railroad railroadyard yard the the progressive progressive deformation deformation of of Taking the path best seen. seen. Entering pillow basalt here is perhaps best Entering the yard, the outcrop exposure on the right (north) again marks the north edge of the developing shearing. Here Here the rock is moderately and variably sheared but the outlines of pillows can still be seen seen despite a penetrative penetrative foliation striking striking 290°, 290°85°N 85'N (photo, (photo,Figure Figure3). 3). The pillow rinds are pinkish weathering calcite, and the pillows here are much smaller than those earlier seen to the north, again a possible contributing contributing factor to the development development of of shearing shearing here. here. 61 �Figure northwest Figure3.3.Looking Looking northwestatatsheared shearedgreenstone greenstoneoutcrop outcropononeast eastside sideofofrail railyard, yard,Stop StopSG-1. SG-1. Hammer Hammerpoint pointtouching touchingcalcareous calcareousflattened flattenedpillow pillowrind. rind. Moving is is itsitswest Movingwest westacross acrossthe therailroad railroadyard, yard,the thethird thirdpart partofofthis thisstop stop westwall. wall.The The features here features here 50yards yardswest westofofhere hereand andabove aboveususininthe theU.S. U.S.Highway Highway4141road roadcut; cut; aremore morecontinuously continuouslyexposed exposedabout about50 are that vexydangerous dangeroushigh highspeed speedIraffic trafficlocation locationand andwe've we'vechosen chosentotoshow showthe thesame sameunits unitsinindetail detailatat thatisisa avery this instead. thisrail railyard yardexposure exposure instead. 62 �'V p/I/sawed 4.ilr 1 n.bbl caicgreo4Jt —-—---— ZontS ii 4n14 a 71 Careen /1/1 Th— r--sheand 2 i4/ pt/al- p//Iota c,_.rinds —'-c re/ic4.. p1/ala 0 20 —'- Peer 7R2-2 - -4-- /1/in Jo.sper £he-rt 71 P/I/a Ec/kt p//loots v Shea rtd X Acsay .capIe ® u/kale- rock mj#trtJ ,tiaiQa d1 te. e-'-- ,-._, _iCoeapsss and Tape. ao Figure Figure4. 4. Compass Compassand andtape tapemap mapofofwest westwall wall of of railroad railroad yard, Stop SG-l. SG-1 63 Ca inple -Thea £ —A... ....LL__ C -at ny �Figure 4 is a map of the rail rail yard yard exposure. exposure. From From north north to to south, south, the the first exposed exposed unit unit is is dark blackish green non-amygdaloidal non-aniygdaloidal pillowed pillowed basalt basalt with with calcareous calcareousepidote-rich epidote-richpillow pillowrinds. rinds. The pillows are quite large, some up to four feet across. Blobs Blobs of ofcalcite calcite and and calcite-cemented calcite-cemented breccia fill some some of the pillow interstices. Within Withinthis thisunit unitthere thereare areshallow shallownorth-dipping north-dipping rubbly rubbly zones zonesthat thatmay may represent represent irregular flow tops. Many Many of ofthe thepillow pillowcusps cuspsindicate indicatefacing facingto to the thenorth, north, but butthis thisisiseasily easilyarguable arguableatatthis this outcrop. The Thepillows pillows themselves themselvesare arenot not megascopically megascopically foliated. foliated. Moving southward, there is an 8-foot covered interval critical to the relationship between the pillowed basalt and the next unit. unit, In In the the Highway Highway 41 exposure exposure to the west, this zone is occupied by a sheared-off lens of gray chert and highly sheared rusty weathering chlorite chlorite rock rock with with abundant abundant oxidized oxidized pyrite along along shear shearplanes. planes. (grab (grab sample sample HIWAY-1, HIWAY-l, .013 fine cubic pyrite ,013 ozlton Au). The The remainder remainder of the unit, exposed past the covered interval here, is highly sheared and light gray-green, with with aa strong Si S foliation foliation striking 269", 269°, 8O0N, 80°N, defined by chloritic slip planes with vertically plunging lineations. Oblique Obliqueto toS1 Sl and dipping more shallowly to the north are discontinuous blobs of white calcite and feathery seams of light brow!] ankerite. ankerite. These appear to to be flattened and and sheared-out sheared-out pillow pillowrinds. rinds. Both textural features are cut brown S1,striking strikingapproximately approximately300' 300°and and dipping dipping 30'-4O0N, 30°-40°N, defined by by a tensional cleavage conjugate to Si, seamlets. There thin fibrous calcite searnlets. There are are also also wide wide spaced spaced flat-dipping flat-dipping relief relief fractures fractures with with fibrous fibrouscalcite. calcite. At first sight this this rock rock might mightbe betaken takenfor foraamafic mafictuff. tuft However, However, itit lacks definitive features of such a protolith, i.e., lapilli, crystals, lithic fragments or bedding. Instead, Instead,itit appears appearsto tohave have been been derived derived from shearing of massive rock, save for the relict pillow rinds, which here indicate that the pillows were quite small and probably more susceptible to shearing than the more massive large pillows to the north. Southward there is another another 10-foot covered covered interval. interval, in In the Highway 41 exposure to the west, a highly sheared rusty sericite-chlorite-ankerite sericite-chlorite-ankeritezone with traces of oxidized cubic cubic pyrite pyrite occupies occupies this. this. (grab sample HIWAY-2, .009 odton ozlton Au). Past Past this this covered covered interval, the exposure is of moderately sheared gray-green rock. rock. SSifoliation vertical; foliationisisapproximately approximately270°, 270° vertical;the theshallow shallowdipping dipping cleavage cleavage isis weakly developed. Blobs Blobsof ofchlorite chlorite in in the the plane plane of SSlshow showvertical verticalalignment, alignment,and and the the rock rock carries carries disseminated coarse cubic pyrite with vertically aligned aligned calcite calcite pressure pressure shadows; shadows; in in thin thin section section both both of of these exhibit porphyroblastic development, rather than a pre-existing textural fabric. This Thischlorite-spotted chlorite-spotted unit has a higher MgO content than the adjacent rocks, plotting in in the the komatiitic field field (see (seeJensen Jensencation cation plot, Figure Figure 5). 5). Further south within this sheared rock rock is a 1.5 -foot bed of non-magnetic jasper chert that almost 285°, dipping 73'N. 73°N. The surely surely defmes defines an an original originallayering layering(So). (So). It strikes 285', Thepatchy patchy bright bright red red jasper zones zones 64 �in this chert are brecciated in in places, as seen seen in in the the outcrop outcrop east east across across the the railroad railroad tracks. tracks. The chert is is not foliated, but carries a trace of fine cubic pyrite on late white quartz fractures. A A grab grab sample sample here here yielded yielded oziton gold gold;;FA-AA 0.003 0 3 odton FA-AA re-analysis re-analysis by by Chemex Chernex gave gave 51 5 1ppb ppb Au. Au. Good examples of relict pillows are a couple of feet north of the hanging wall of the chert. This sheared lithology southern contact contact is is hthoáogy grades grades southward southward into intonon-foliated non-foliatedpillowed pillowedbasalt. basalt. The basalt's southern This a thin discontinuous 0-4" 0-4" nonmagnetic non-magnetic chert-jasper breccia breccia that that gave gave no no gold gold in in aa grab grab sample. sample. This Beyond its its cherty cherty southern southern contact contact the the foliation-resistant pillow basalt unit is about 15 feet thick. Beyond remainder of the exposure consists consists of of highly highly sheared, sheared, light light gray-green gray-green rock with arguable arguable relict relict pillow pillow "vein" S i at 260°, 260°70°N. 70°NWithin this southernmost part of the exposure is a 2-foot calcareous "vein" textures, S1 oblique to S,, S, strike foliation. A grab sample strike 315°, 3 15O, 72°N. 72'N. ItItexhibits exhibitsslickensides slickensides and and drag of the S1 S, foliation. yielded no gold. In In thin thin section sectionthis this rock rock consists consists of of alternating alternating parallel bands of of fine fine grained grained calcite and and plagioclase aggregates in nearly equal amounts, both carrying interstitial high magnesian chlorite that constitutes about 10% 10% of the rock. The Thecalcite calcitebands bands contain contain lozenge-shaped lozenge-shaped ankeritic ankeritic domains. Accessory minerals include apatite, zinc-rich cbromite chromite and abundant chromian titanornagnetite titanomagnetite commonly displaying atoll textures, a feature of of ultramafic rocks. rocks. Other Other indications indications of of an an ultramafic ultramafic parentage parentage are are the the high magnesian chlorite and a trace element analysis that includes 296 ppm Ni, an unusually high result in comparison to the nickel content found in in the dozens dozens of of other other rocks rocks analyzed analyzed in in the the study studyfor forthis thisfield field trip. We altered ultramafic ultramafic dike. dike. Gair and Thaden (1968, Wethus thus consider consider this this "vein" to be be a hydrotherrnally hydrothemally altered pl. 1) showed southernmost end of of what what was was then then the the p1.1) showed an an outcrop outcrop of of "hornblende "hornblende lamprophyre" at the southernmost Highway 41 road cut. Their Their outcrop outcrop cannot cannot be be found found today, today, but hut this this dike dike may may represent represent its its eastward eastward extension. extension. Marked on Figure 4 are five samples taken for for whole rock major oxide oxide and and 32-element 32-element trace trace analysis. Two Two are are from from unfoliated unfoliated pillow pillow basalts, basalts, two are are from from the the sheared sheared lithologies, and the fifth is The whole whole rock rock results results are are shown shown on Figure 5. from the ultramafic dike. The Discussion In this exposure chemically very similar rock rock units unitsexhibit exhibit shearing shearingthat that isispreferentially preferentially developed in weaker units (zones of small pillows, lava interfiow interflow beds, more more magnesian magnesian layers). layers). to shearing. The Intervening more massive buttress units are resistant to The sense sense of of shearing shearingisis nearly nearly vertical. vertical 65 �FeO* + 1102 SAMPLES Cation % Cation % Jensen Jensen(1 (1 976) 976) S RRCVN • PR-i A V RR-2 RR-3 • RR-4 S BK V A1203 MgO Figure 5: Stop SG-1 Figure 5: Stop SG-1 66 �Gait outcrop on on their their map map of of the the Marquette Marquette quadrangle, quadrangle,but but didn't didn't Gair and Thaden (1968) noted this outcrop indicate shearing or or slaty lithology lithology here. here. A couple of of miles miles to to the the southwest southwest they did describe describe east-west shearing at the southern contact of the Mona greenstones and the overlying overlying Proterozoic Proterozoic Enchantment EnchantmentLake Lake conglomerate. Mapping Fails Mapping the the next next quadrangle quadrangle west, Puffett (1974, p.43) recognized the Carp River Falls shear zone near that same contact and correlated it with the shearing in the Marquette quadrangle quadrangle by Gair and Thaden. Both previously noted by Both authors authors pointed pointed out out that that the the sense sense of of shearing shearing isis strongly strongly vertical. Puffett and noted noted (p. (p. 45), 45), "The "The Puffett (1974) (1974) also also recognized recognized and named the Dead River shear zone and projection of the shear zone to the southeast southeast across the Marquette quadrangle quadrangle meets meets aa conspicuous conspicuous rereentrant in the shoreline of of Lake Lake Superior." Superior." Thus Thus neither neither of of these these two two major major later-recognized later-recognized block boundary shear zones is actually actually shown shown on onGair Gait and andThaden's Thaden's 1968 map. map. This This was was left left to to later later authors of maps at various smaller scales, who usually place the Dead River shear shear zone zone as as aa west-northwest west-northwest trend trend meeting the lakeshore at the approximate contact with the Mona formation basalt basalt flow unit of the southern unit of of the the northern northern block block of of the the Ishpeming lshpeming Greenstone Belt. This block and the Lighthouse Point basalt unit This the Dead Dead River River shear shear zone zoneabout about'/< ¾mile miledue duenorth northof ofthis thisfield fieldtrip tripstop. stop. (Figure 2) 2) The would place the The zone seen here is a probable parallel, sympathetic sympathetic structure. Discussing the structural framework of the Ishpeming Greenstone Belt, Bornhorst Bomhorst and and Johnson Johnson (1993, event (Dl) (Di) was was recumbent recumbent folding. folding. This was followed by (1993, p. 4) stated, stated, "The oldest recognized event axes (Dz). (D2). Shear zones are interpreted to to have formed during and upright folding about east-west oriented axes later than 1)2 andmay mayhave havebeen beenreactivated reactivatedduring duringthe theearly earlyProterozoic Proterozoic Penokean Penokean deformation." deformation." They D; and They "Rock units in all blocks are also cut by by minor shear zones. zones. These went on to point out, out, "Rock These high-strain high-strain zones zones are characterized by by rocks that that are more more intensely intensely foliated foliatedthan thanthe thesurrounding surroundingrocks." rocks." We agree with these interpretations and offer the exposure at this stop as a case in point. point. Whether Whether or or not not this this particular particular major or minor one has yet yet to to be be determined. To shear zone is a major To the the west west itit projects projects into into an an urbanized urbanized area area with no outcrop. outcrop. The sheared lithologies at this locality exhibit varying levels of propylitic alteration (pyrite, carbonate, chlorite); significant significant trace amounts of gold can can be found where pyrite andlor carbonate are are well developed. As Asaapractical practicalmatter, matter, further further exploration exploration for for gold gold in in this this shear shear zone zone isis ruled ruled out out by by its its location. 67 �56-2: Stop SG2: Dead with gold gold mineralization mineralization at at Marquette Marquette Mall (Location map, Dead River Shear Zone with Figure 2). Figure 2). After parking at the head of the ski trail in the southeast comer corner of the Marquette Mall parking lot, walk about 500 feet ESE up the trail to an outcrop knob knob of undeformed metabasalt. This This greenstone greenstone has unusually high high number number of of blocky blocky hematitic hematiticfractures. fractures. The northern limit limit of of this this outcrop outcrop is isaa cliff an unusually cliff face face that is controlled by by foliation foliation planes planes striking striking280° 280°,85% 85°S. This cliff cliff face face represents representsthe thesouthern southern margin margin of of was exposed exposed in man-made outcrops in the bank of the Holiday Inn parking lot until it was shearing that was recently covered covered by by landscaping. landscaping. R. Brozdowski (personal communication, 1988) reported anomalous recently gold values from Callahan's Callahan's sampling sampling of of that that sheared sheared rock. rock. Returning about 400 feet westward down the trail, a makeshift wooden bridge crosses crosses the stream leading to the motel's duck pond. Intermittently Intermittentlyexposed exposed along along the the stream stream are are small outcrops outcrops of sheared chiorite-sericite rock rock with with brown brown carbonate carbonate weathering weathering rinds rinds and and oblique oblique quartz quartz veinlets. veinlets. Some chlorite-sericite Some of of this this phenocrysts, indicating aa crystal crystal tuff tuff protolith. protolith. Of rock has small gray quartz phenocrysts, Of three threewidely widely spaced spacedgrab grab took here, here, one one gave gave ,023 .023 odton or/ton Au, the the other other two two were were below below MPC's MPC's detection limits. The samples we took The sample that yielded the gold value was taken aa couple of feet below the little wooden bridge. Mail parking lot and moving west along its south bank, bank, there is a 650 foot Back at the Marquette Mall rock. Bornhorst long exposure of highly sheared rock. Bomhorst and Johnson (1993, p. 9) 9) gave aa brief description of this "..... tuffaceous rock and a graphitic zone crop out." outcrop: ". rock is badly badly slumped northward towards the the parking parking lot throughout throughout This sheared phyllonitic rock much of its length. At At its its eastern easternend end itit is is more more hematitic hematitic than elsewhere, elsewhere, with reddish reddish foliation foliation planes planes in the the relatively relatively underformed underformed greenstone greenstone to to the the east. east. Throughout resembling the fractures in Throughout its its entirety entirety there on foliation planes, planes, with with much much of the rock exhibiting a is a strong presence of chlorite and sporadic sericite on color due due to to weathering weathering of of chlorite chloriteand andferroan ferroancarbonate. carbonate. Where not not slumped, slumped, foliation maroon-reddish color measurements measurements cluster cluster closely closely about about 280°, 280°vertical. vertical. probable tuff There are some zones of chlorite-poor rock with small quartz eyes indicating aa probable protolith, similar to that found in the stream to the east. Near Near the the eastern eastern end end of of the the outcrop outcropisisan an irregular irregular to 2 feet layer of nearly pure graphite. Our Our grab sample of the graphite gave foliation-parallel two inches to no Au. One Oneorortwo twofeet feetacross acrossfoliation foliationfrom fromthe thegraphite graphiteisisaathin thinsemi-parallel semi-parallel layer layer of of rusty rusty to to black gossan with selvages of massive and semi-massive semi-massive pyrite carbonate carbonate breccia. breccia. From From the the pyrite-gossan pyrite-gossanzone, zone, Gleason (1986) reported values values up up to to 22 gmltonne gmltonne (.06 (.06 ozlton) or/ton) Au. Au. Our Our grab grab sample sample of of the the gossan g o w n gave gave .037 gave .028 .028 odton or/ton Au. Au. A 0 3 7 or/ton odton Au, Au, while our sample of pyrite breccia selvages gave A polished polished thin thin section section sample of the pyrite breccia shows shows that there are are two generations generations of of pyrite pyrite in in aa quartz-calcite-chlorite quartz-calcite-chlorite 68 �gangue, with the calcite late late in in the the paragenetic paragenetic sequence. sequence. The first generation pyrite is large and often framboidal, corroded and and partially partially replaced replaced by by quartz quartz and and second secondgeneration generationpyrite pyrite in in smaller, smaller,euliedral euhedral crystals. Heavy as inclusions inclusions in the second generation pyrite and as tiny Heavy traces traces of of covellite covellite (CuS) (CuS) occur occur as gangue. Other free grains in the gangue. Other inclusions inclusionswithin within pyrite pyrite found found by by the the microprobe microprobe include include chalcopyrite and sphalerite as as lesser trace sulfides. Accessory Accessory minerals minerals found found in in this this breccia breccia are are monazite monazite and and ilmenite ilmenite rutile, a common hydrothermal alteration. alteration. No grains common result of hydrothermal partially altered to mtile, grains of of free gold were found in this thin section sample. Besides Besides the the highly anomalous gold in in the corresponding corresponding assay assay grab grab sample, sample, anomalous trace trace elements elementswere werepresent present(ppm): (ppm): Ag-3; Ag-3; As-252; As-252; Cu-1700; Cu-l700; Pb-68; Zn-124; Uthe following anomalous 10. 10. About 150 150 feet from the western end of this exposure is a 2-foot complexly brecciated chloritecalcite-quartz-graphite vein vein with with strong strong vertical verticalhematitic hematiticslickensides slickensidesand andminor minorcopper copperstain. stain. The slickensided hangingwall of of this this vein vein strikes, strikes, 290' 290° 75'N. 75°N. Our Our grab grab sample sample yielded .005 .005 ozlton odton Au, Au, as aswell well as 244 pprn ppm Cu and 100 ppm Zn. Study Study of ofaa corresponding corresponding polished thin section did not fmd any gold grains but confirmed the presence of of very fine grained grained chalcopyrite chalcopyrite and and covellite covellite in in irregular irregular trains trains following late fractures and rimming graphite. This This vein vein appears to be cut cut off off by by aa northerly northerly cross cross fault. fault. About 75 feet from the western end of the exposure is a thin discontinuous vein vein of similar composition; our grab sample sample yielded yielded no no Au. Au. About 100 100 yards southward and uphill uphill from the west end off the Mall exposure is a slumped-in and partially flooded small open open cut cut next next to to the the north-flowing creek. In to the the south south wall of of this old mine pit there is an exposed patch of of rusty rusty weathering, weathering, ankeritic phyllonite similar to the Mall exposure exposure lithology. lithology of the the ore ore mined. mined. This There are no dumps or other present evidence of This is is the the Eureka Eureka mine mine (Williams, (Williams, 1890). 1890). Gair and Thaden (1968, p. 69) provided the following: "The "Theprincipal principaloccurrence occurrenceof ofiron ironininthe the Marquette-Sands area was at the old Eureka mine ... ... Perhaps Perhaps as much as several hundred tons of earthy goethitic iron ore was mined from from aa shear shear zone zone about about 55 feet feet wide wide in in chloritic chloritic slaty slatygreenstone greenstone (Mona (Mona Schist). Secondary Secondaryquartz quartz and and iron-bearing iron-bearing carbonate carbonate were deposited along the shear zone in places, prior to formation of of the iron ore. The Theore oreresulted resultedfrom fromoxidation oxidationof ofcarbonate carbonateand andchlorite, chlorite,the theconcentration concentration of iron, iron, and and the the removal removal of of silica, silica, MgO, MgO, CaO CaOand and alumina alumina by by ground groundwater watercirculating circulatingalong alongthe theshear shear zone. Virtually Virtually all all mining mining was was done done prior to to 1880, 1880,and and whatever whatever ore ore was extracted was shipped shipped to to local smelters. There were several unsuccessful attempts to to renew renew mining mining in in the the 1880's and charcoal-burning smelters. three test holes were drilled at the site in the 1920's". 1920's". 69 �Discussion Discussion This (1968, P1, 1). Their Thislocality locality was was last last mapped by (3air Gair and Thaden (1968, PI. 1). Their map shows shows only only aa couple couple of members of of small small exposures exposureshere, here, marking marking the contact between their Lower and Lighthouse Point members of the the Mona MonaSchist. Schist.We Webelieve believethat thatthe theoutcrops outcropshere hererepresent representthe thesouthern southernmargin marginof ofthe theDead DeadRiver Rivershear shear zone. zone. The Thepresence presenceofofgold goldand andbase basemetals metalsininthe theMaIl Mallexposure exposureisisdirect directevidence evidence of of their their localization localization by by major major shear shearzones, zones, and and we we suspect suspect that some some of of the the ore ore produced produced by by the the Eureka Eureka mine mine may have have been, been, in in aftersuluides. sulfides. part,gossan gossanafter part, The The trend trend of of shearing shearingprojects projects from from here here westward westward along along the the valley of an E-W creek. creek. No No exposures exposures could could be be found found along along itit except except aa few few outcrops outcropsof of aanarrow narrowE-W E-W magnetic magnetic diabase diabase dike dikeon on its its south 4,200feet feetwest west of ofhere, here, probably probably emplaced emplaced atator orclose closeto tothe thesouthern southernmargin margin of of the theshear shearzone. zone. southside side4,200 Thatdiabase diabaseisisnot noton onany anypublished publishedmap. map. That StopSG—3: SG3: Stop Archean metavolcanics metavolcanics (Location map, Keweenawan diabase in hornfelsed, foliated Archean (Location map, Figure Figure2). 2). Loojeuvs &4.cr '4 C -c -a C U '4 '7 sphero,Sc 'a 0" S'a 6atc h. h b It pg S -c 1 -z Lj :W40/e t-k/Occay scnsp.'e SM 0 U. a m rr AFPCg m&>C o% . reE Figure6. 6. Sketch Sketch cross cross section of outcrop outcrop at at Stop StopSG-3, SG-3,looking lookingeast. east. Figure 70 �This outcrop was last mapped by by Gair Gair and and Thaden Thaden (1968, (1968,P1. PI. 1) 1) as as Late Late Precambrian Precambrian diabase diabase with with a small adjoining patch of site" belonging to their lower unit of the Lighthouse Point Member of "fel "felsite" Member of of the the Mona Schist. There There is no outcrop description in their text. This This one one is is part of of a series series of outcrops outcrops of of a long narrow diabase dike that Gair and and Thaden traced eastward eastward into into Lake Lake Superior Superior at atLighhouse Lighhouse Point. Point. Here it strikes 250° 250°, dip 8O0N. 80°N. ItIt appears not appears to to be be about about 50 50 feet feet thick, thick, although its southern contact is not exposed. The Thediabase diabaseisisnon-foliated non-foliatedand andisismagnetic magneticthroughout. throughout. Figure 6 isisaa sketch sketch cross cross section section of this exposure. At Atthe thesouth south end end the the diabase diabase is is medium medium jointing grained, has a felty texture and contains rare vugs lined with drusy calcite. calcite. It shows shows rectangular rectangularjointing that controls incipient spheroidal spheroidal weathering weathering at the erosion surface; surface; the joint planes planes are are hematitic hematitic and and calcareous. The The diabase diabase grain grain size size lessens lessens northward to a fme fine grained but still magnetic chilled margin at the host rock contact. This Thiscontact contactisisstrongly strongly foliated foliated parallel parallel to to the the dike dike margin margin for for aa few few inches. inches. Beyond that the immediate immediate host host rock rock is is aablack, black,non-magnetic, non-magnetic,aphanitic aphanitichomfels homfelswith with strong strong foliation foliation defined mostly by prominent pink K-spar-quartz laminae. This Thisrock rock carries carries aa trace trace of of disseminated disseminated extremely fine-grained pyrite, and some some discontinous discontinous foliation-parallel foliation-parallel lenses lenses of of coarsely coarselyciystallized crystallized quartz. greenish gray. gray. Outward to the north, the host rock becomes rusty weathering, quartz. It weathers light greenish "baked"-lookthg, all the while exhibiting strong foliation planes closely slaty and less "baked"-looking, closely clustered clustered around around 280°, 80%. 80°N. The source 280" source of of the rusty color appears to be numerous foliation partings of ferroan carbonate; no pyrite is visible on a fresh surface. An An irregular irregular 4-6 4-6 inch inch foliation-parallel foliation-parallel quartz-iron oxide oxide vein marks marks the transition northward to non-thennally non-thermally altered altered grainy-light grainy-light greenish-gray greenish-gray sheared sheared rock rock with with rusty rusty 275°, 85¡ 85°N continuing continuing to the northern limit of the exposure. exposure. foliation planes at 275¡ Four grab samples of the host rock are shown on the sketch sketch cross cross section. section. Two Two of of these these were were clearly below below MPC's MPC's detection limit for gold (samples DBS-2 DBS-2 and and 3). 3). The other two returned values at or near the detection limit and were re-analyzed by Chemex using FA-AA, returning weakly anomalous gold values: DBS-l, DBS-1,51 5 1ppb; ppb;HFEL, HFEL,33 33ppb. ppb.No Nounusual unusualtrace traceelement elementsignatures signatureswere werepresent presentininany anyof ofthese these samples. samples. Study of a polished thin section of a sample corresponding to assay sample HFEL HEEL confirmed that that the pink bands consist of quartz phenocrysts phenoctysts in a K-spar groundmass. The The darker-colored darker-colored domains domains of of this this phenociysts/ciystals of albite-oligoclase, rock have a porphyritic texture with scattered phenocrysts/crystals albite-oligoclase, quartz quartz (often (often in in with pyrite), pyrite), and and composite composite large large grains grains or or fragments fragments of of quartzquartz- plagioclase. plagioclase. The dark biminerallic grains with color appears to be mainly due to biotization biotization of of numerous numerous foliation-defining foliation-defining chlorite-quartz-plagioclase chlorite-quartz-plagioclase to ruhle. rutile. The laminae and to an overall content of about 5% opaques: pyrite and ilmenite altered partially to The nature of the coarse grained components suggests that that this this rock rock was was originally originallyaa crystal crystallithic lithictuff. tuff. The 71 �thermal metamorphic effects effects near the contact of the diabase diabase dike dike appear appear to be limited limited to to prograde prograde alteration of chlorite to biotite biotite and recrystallization recrystallization of quartz and feldspar. feldspar. Figure 7 is a Jensen cation plot of of the the whole rock analyses analyses of the four four samples samples taken at this stop. stop. Discussion Discussion The foliation in the weakly hornfelsed country rock here is at an oblique angle to the diabase diabase dike, can best best be be seen seen at at the the top top of of the the outcrop outcropknob). knob). Because of this, we (which can webelieve believethis thisfoliation foliationprepreexisted the emplacement of the dike. We We also also believe believe that much of the foliation foliation in the host rock here is the result of shearing, shearing, and that this outcrop lies near the middle of the Dead River River shear shear zone. The The southern southern boundary of this shear zone would lie lie near near the the Marquette Marquette Mall Mall outcrop outcropatatStop Stop SG-2. SG-2. The emplacement of this diabase diabase dike dike within such such aa large large zone zone of of weakness weaknesswould would not notbe beunexpected. unexpected. Gaff and and Thaden Thaden (1968), (1968), though noting shearing in in their their text text from from place place to to place in the Archean Gair Quadrangle, did did not not emphasize emphasize its its importance, importance,nor norillustrate illustrateititon ontheir theirmap. map. They They rocks of the Marquette Quadrangle, also found very few outcrops of their lower unit of the Lighthouse Point Member, most of which are are shown as "felsite". "felsite". About About 1200 1200feet feet NNW NNW of ofhere, here, theft their map map shows showsaa cluster cluster of of 44 small small outcrops outcrops on on aa low low bill, "felsite". The hill, marked as ""felsite". TheWestwood WestwoodMall Mall and and its its parking parking lots lots now cover cover them, but we suspect that have exhibited exhibited shearing shearingsimilar similartotohere. here. About 500 feet further north in in the the woods woods these outcrops would have and sewer line line were were being being constructed constructed in in the the fall fall of of 1998. The behind the Mall, a new east-west street and The construction equipment tore up the tops of several small subcrops of sheared rock whose composition chioritic to nearly pure pure massive massive sericite. ItIt was was not not possible possible to to obtain obtain dips, but the strike varies from highly chloritic of the shearing is east-west. east-west. These exposures lie he near the probable northern contact contact of of the the Dead Dead River River shear zone. Since Since it's it's unlikely unlikely that that they'll they'll be bestill still available availablein in the the spring spring of of 1999, 1999, we we offer offer Stop Stop SG-4 SG-4 as as an alternative. alternative. 72 �FeO* + 1102 SAMPLES • • Cation Cation % % Jensen (1976) Jensen (1 976) A DBS-1 DBS-2 DBS-3 v HEEL BK A1203 A1203 MgO Figure 7: Stop SG-3 Figure 7; Stop SG-3 73 �Stop Stop SG-4: SG4: margin of Dead River Shear Northern margin Shear Zone on Wright Wright Street Street (Location map, Figure Figure 2). 2). This is an optional optional stop stop that that is is included included here here for for those those interested interestedin in seeing seeing more moreof of the theDead DeadRiver River Zone in in the the Marquette Marquette area. area. This exposure be Shear Zone exposure is very close to a busy highway, and care should be exercised when when visiting visitingit. it. About About 65 65 feet feet of of sheared sheared greenstone greenstone is exposed here on the east side of Wright Street. The The lower lower level level of of the the exposure exposurewas wasrecently recently created created by by widening wideningthe the road, road, and andwas wasnot notavailable available to Gair and Thaden (1968), who showed showed the the upper upper part part of of the the exposure exposureas as aa lithology lithologylabeled labeled"interlayered "interlayered ) massive basalt(?)" on on their their map map(P1. (PI. I1). The degree of shearing is variable here, here, but but much much of of itit is is intense. intense. Foliation The Foliation becomes generally more strongly developed from north to south, and strikes E-W, E-W, nearly nearly vertical. vertical, hi In the the small small cut above above the forms similar to to the the sheared shearedpillows pillows at at Stop StopSG-1 SO-i are present. Figure lower ledge, curvilinear sheared forms Figure 88 isis a photograph of pencil cleavage cleavage developed developed further further south south as as shearing shearing intensifies. intensifies. There Thereisisweak weakcarbonate carbonate alteration in some of the most heavily sheared rock, but it is not pyritic; we didn't sample samplefor forgold goldhere. here. Figure 8. Figure 8. Looking Lookingdue dueeast eastatatpencil pencilcleavage cleavagedeveloped developedby by shearing shearingin in greenstone greenstonein in low low roadcut, east side side of of Wright Wright Street, Street, Stop StopSG-4. SG-4. 74 �The northern part of this outcrop consists of nearly chaotic chloritic foliation that appears to result from the contact with a shear-resistant dike of non-magnetic gabbro that is only weakly foliated. Only Onlyaa couple of feet of this gabbro gabbro are exposed exposed in the roadcut, but a larger, glacially smoothed outcrop outcrop of of itit lies lies above above and and aa few few yards yards east east of of here. here. ii D is c u S 5 Discusssion About 400 feet to the north, on the east side of of the road road is an an outcrop outcrop of of relatively undeformed metabasalt; glacially polished outcrops outcrops of similar rock are exposed exposed in the south side side of the gravel pit being development aa couple couple of of hundred hundred yards yards further furtherENE. ENE. These rocks appear appear to to be be converted to a housing development Point basalt basalt typical typical of of this this area area(Johnson (Johnsonand andBomhorst, Bornborst,1991). 1991). So we would would place place the the Lighthouse Point northern boundary of the Dead River Shear Zone, if not at this outcrop, then no more than a few hundred feet north of here. Figure Figure22shows showswhat what we we think think are are the the approximate approximatelimits limits of of the the shear shear zone, zone, which which corresponds roughly to the lower unit imit of the Lighthouse Point Point Member of of the the Mona Mona Schist of of Gair and corresponds Thaden (1968), (1968), in turn corresponding roughly to the "Eureka Group" of Williams Williams (1890), nomenclature nomenclature that was discarded by Van Hise and Bayley (1897). This Thiswould wouldmake makethe theDead DeadRiver RiverShear ShearZone Zone3,000 3,000 feet wide at this point. Puffett Puffett (1974, (1974, p. p. 44) 44) noted noted that that the the Dead Dead River River Shear Shear Zone four miles west- northwest of here is about 3,400 3,400 feet feet wide. wide. To better define define and and understand understand the the Dead Dead River River Shear ShearZone Zone in in this this important importanthinge hinge area areabetween between the northern and southern blocks of the Ishpeming Greenstone Belt, Belt, remapping re-mapping and and structural study study of of existing and newly newly created created outcrops outcrops are areneeded, needed,before beforeit's it's too too late. late. The ex-urban growth around Marquette, Marquette, although presently presently creating creating new outcrops, outcrops, will will eventually eventually result in a net loss loss of of exposures. exposures. 75 I I I �Figure 9. Location map for Stops SG-5,6 and? 76 �Stop SG-5: Stop SG5: Progressively shearedlaltered sheared/altered metavolcanics metavolcanics in Carp River Falls Shear Shear Zone. 9). (Location map, Figure Figure 9). Puffett Puffett (1974) (1974) last mapped this this locality locality as as "undifferentiated "undifferentiated greenstone" greenstone" within within the Carp River Falls shear zone. Dealing Dealing with with this this exposure exposurespecifically, specifically,he he included included aa photograph photograph of ofits itsmost mostsheared sheared part, and described it as follows (p. 43): "Sericite, and altered part. "Sericite,chlorite, chlorite,carbonate, carbonate,and andleucoxene leucoxeneare arethe the products. Weathered brown from from oxidized oxidized most conspicuous alteration products. Weathered surfaces are commonly stained brown minerals. Quartz-carbonate iron minerals. Quartz-carbonate veinlets fomi form an an anastomosing network in some rock. Copper Copper minerals minerals are present locally. Analytical Analytical data datasuggest suggestthat that the the altered altered rocks rocks are are enriched enriched in CaO CaO and Co2 Co2(Table 12)." value, 90 90 ppm. ppm. W.A. Puffett's analysis from here gave an anomalous copper value, W.A. Bodwell Bodwell (personal (personal communication, 1998) 1998) reports having noted trace chalcopyrite and copper staining here, hut but they are not not easily found. found. This exposure was a 1988 follows (Bornhorst (Bomhorst and 1988 I.L.S.G. field trip stop stop described, described, in part, as follows others, 1988): 1988): "The "The rocks rocksin in this this roadcut roadcut have have aa well developed close-spaced foliation (N75-88W, dip 7089°S) which produces produces a slate-like appearance. appearance. These 89OS) These rocks rocks are are within within the Archean Carp River Falls Shear Zone. There two lithologies lithologiesin in this outcrop: chlorite chloriteschist schistfrom fromaabasaltic basaltic parent, parent, and and quartz-sericite quartz-sericite Thereare are two schist from a rhyolitic parent." Bornhorst Bomhorst and others (1988) also pointed out that near the very eastern end of the outcrop are probable relict pillow rinds. As probable Asseen seenelsewhere elsewhereon onthis thisfield fieldtrip, trip,these these are are gradually gradually obliterated obliterated by by shearing as one moves westward westward along the outcrop. outcrop. The The chioritic chloritic sheared sheared metabasalt metabasalt gives way progressively to more and and more more rusty rusty weathering weathering carbonate-sericite carbonate-sericitealtered altered rock; rock; we we believe believe itit represents represents aa progressively progressive change from from propylitic propylitic alteration alterationto to weak weak potassic potassicalteration alterationin in aa rock rock of ofthe thesame sameparentage. parentage. progressive lighter colored colored carhonate-sericite carbonate-sericitealtered alteredrock rocknear nearthe thewestern westernend endthere thereisisaa 6-inch 6-inch pyritic In the lighter pyritic carbonate zone. Our Our grab grab sample sample of of this this gave .005 oz/ton odton Au (sample STOP 3). AA70-foot 70-footchip chip sample sample across across the entire entire sericite-carbonate sericite-carbonate altered altered zone here (not including including the pyritic pyritic grab grab sample) sample) gave gave undetectable AU Au (sample STOP-3A) STOP-3A)..An AnFA-AA FA-AAre-analysis re-analysisby by Chemex Chemex of of the the pyritic pyritic grab sample gave a value of 90 ppb Au, Au, confirming MPC's MPC's results. We Wealso alsotook tookwhole wholerock rocksamples samplesfrom fromthe thevery veryeastern eastern exposure in the pillowed pillowed greenstone greenstone(sample (sample 5-1), 5-l), one onefrom frommoderately moderatelysheared shearedrock rocknear nearthe the end of the exposure (5-I), and one at the western end of the outcrop in approximately the same spot sampled and middle (5-1), photographed by Puffett (our sample 5-3). Whole Whole rock analyses analyseswere were also also done done on on the the two samples samples taken for gold assay; sample STOP-3A is the themost mostrepresentative representativeof of the the light light colored colored sheared sheared rock at at the western end of the exposure, exposure, since since itit was aa composite composite chip chip sample sampleacross across 70 70 feet feetof ofit. it. Figure 10 10 is a 77 �Jensen plot showing the Note that that sample sample STOP STOP33 is is anomalously anomalously high high in in iron iron because becauseititwas was Jensen the results. results. ((Note chosen chosen for for best bestpyrite pyritecontent). content). + FeO* FeO* + 1102 Ti02 Cation% % Cation Jensen (1976) (1 976) Jensen SAMPLES SAMPLES • 5-1 5-1 • 5-2 5-2 5-3 5-3 "v STOP3 STOP 3 A A • STOP-3A STOP-3A PJ203 MgO Figure Figure 10: 10: Stop Stop SG-5 SG-5 78 �A polished thin section was made of a specimen corresponding corresponding to to pyntic pyritic grab grab sample sample STOP STOP 33 that yielded anomalous gold. Megascopically Megascopicallythis thisspecimen specimenisisaa chlorite-sericite chlorite-sericiteschist schist hosting hostingaa foliationfoliation¼-inch veinlet veinlet of of carbonate. carbonate. Under conformable %-inch Under the microscope microscope and electron microprobe the host rock is 1%tiny tiny a fine grained mixture of 50% quartz, 30% 30% chlorite chlorite and 20% 20% niuscovite/sericite, muscovite/sericite, containing containing about about 1% rutile grains. The grains of disseminated chalcopyrite, as well as trace amounts of tiny disseminated mtile The dolomite with high-manganese cores, with about carbonate veinlet is a mosaic of coarse grains of zoned dolomite 10% high-iron chlorite. chlorite. This 10% interstitial high-iron This vein vein assemblage assemblage hosts hosts schlieren texturally similar to the host rock except that these fragments have no quartz. quartz, consist primarily of zoned ankerite with dolomitic cores and contain about 25% opaques, mostly Mn and Fe oxides, but also abundant fine fine grained euhedral pyrite and subordinate chalcopyrite. One Oneof of the thechalcopyrite chalcopyritegrains grains was was found found to to have have inclusions inclusions of of nonnonand one 3-micron grain of of high-gold high-gold electrum electrum (photo, (photo, Figure 11). This argentiferous tetrahedrite and Thiswas was the the only gold grain found in in this this sample. sampie Arsenopyrite Arsenopyritewas wasnot notfound, found,but but trace traceelement elementanalysis analysis of of the the corresponding assay sample yielded 170 170 ppm As. 'I, 3e+ Figure 3, White Figure II. 11.Polaroid Polaroidphoto photoofofbackscattered backscatteredelectron electrondetector detectorimage, image, sample sample STOP 3. White vertical scale bar at lower left is 10 10 microns. Bright 3-micron grain of of high gold gold electrum electrum in in (teØ. Black chalcopyrite (cpy) that also contains larger inclusions of tetrahedrite (tet). Black areas areasare are gangue. gangue. 79 �Discussion Puffett (1974, (1974, P. p. 43-44) 43-44) noted noted copper copper minerals minerals at at more more than one locality in the Carp Carp River Falls shear zone, an encouraging base metal association from kom the gold exploration explorationpoint point of ofview, view,since sincegold gold mineral here. here. This occurs directly with a copper mineral This outcrop outcrop is is close close to to the the north notth margin margin of the shear shear zone. zone. margin appears to be marked by bluffs that are coneolled controlled by by E-W foliated greenstone, across across The south margin behind Ball Moving and Storage, makiig making the the zone zone about about 400 400 feet wide wide at at this this point point, mostly mostly the highway behind covered by U.S.Highway 441. 1. We Wewill will cross crossthe the highway highway here to to see see more more evidence evidence of of gold gold mineralization. mineralization. Stop SG-6: Stop SG& Gold-bearing gtacial erratic erratic (Bill Bodwell'sBoulder) Boulder).. Location Gold-bearing glacial (Bii Bodwell's Location map, map, Figure Figure 9. first noticed noticed and and sampled sampled by by Bill BillBodwell Bodwellininthe the1980's. 1980's. His This was fust His attempts attempts to find fmd a bedrock source in the immediate immediate vicinity were unsuccessfid. unsuccessful. However, However, judging judging by byits itslarge largesize sizeand andangularity, angularity,this this boulder hasn't traveled traveled very very far. far. The Theeastern easternend endof ofthe theboulder bouldershows showsthe thepreserved preservedremains remainsof ofan an original bedrock surface. snrface. This rectangular 5 by 10 I0 foot foot block block was was unearthed unearthed in in sandy sandy glacio-fluvial glacio-fluvial sediments sedimentsduring during site site clearing for the moving and storage facilities, and and has has lain lain in inits itspresent presentposition positionfor forabout about 30 30years. years. It up to to one one foot thick. thick. The consists of about about 50% 50% close-spaced, close-spaced, sub-parallel sub-parallelen en echelon white quartz veins up veins contain l0%-20% 10%-20%light lightbrown brownweathering weathehgferroan ferroancarbonate carbonateininblobs blobsand andseamlets, seamlets,lesser lessersmall small masses of dark green euhedral euhedral chlorite, chlorite, and rare rare small small blobs blobs of of very very late late stage stage black tourmaline. tourmaline. Interstitial to the quartz veins, veins, the the other 50% 50% of of the the boulder boulder is is made made up up of of highly highly foliated foliated "horses" "horses" of of chloritic greenstone, showing an impressive impressive internal internal continuity continuity of of foliation throughout carbonate-altered cblontic with oblique tensional development in a boulder. The vein g", consistent with the boulder. The style style of veining is "ladder veining", sheared sheared rock. rock. chalcopyrite, and abundant malachite The quartz veins contain contain patchy blobs of pyrite with lesser chalcopyrite, staining. Bill Bill Bodwell's Bodwell'sinitial initialgrab g a bsample sampleof ofthe thesulfide-bearing sulfide-bearingquartz quartz gave gave .267 ,267oz/ton odton Au; Au; two later later 10,000 ppm Cu, samples odton and .006 01/ton, odton, respectively. All All of of these these samples samples yielded ++lO,OOO samples yielded .036 oz/ton Ch showing that copper, although obviously mineralogically associated with gold here, does not necessarily have a direct assay correlation (Bodwell, 1988, written written communication). communication). Our grab sample sample of the quartz.006 odton oz/ton Au. Au. Our greenstone yielded 005 sulfide gave ,006 Our sample sample of of the the barren-looking host greenstone ,005o1/ton odton Au. Au. 80 �This This wide range of gold gold assay results demonstrates the "nuggety" distribution dihbution of gold gold within within this this boulder, boulder, aa phenomenon phenomenon that that requires requires special special assaying assaying techniques techniquesto toobtain obtainaarepresentative representativevalue. value. However, Carp However, the the main point of of this this field fieldtrip trip stop stopisisthat that this this boulder boulderlikely lkeiy caine cameeither eitherfrom from the the Carp River from a similar zone nearby. It's River Falls Falls shear zone or &om It'sinteresting interestingto to note notethat that glacial glacialstriae striae on on the the pillowed greenstone greenstone near near the USGS USGS benchmark benchmark at at the eastern eastern end end of of the theStop StopSG-5 SG-5outcrop outcrop across across the the pillowed highway highway are are nearly nearly east-west, east-west, paralleling the shear zone. The Thestrongest strongestinference inferencefrom h m the theevidence evidenceatat both both this this stop stopand and the the preceding preceding one one isis that that the the Carp CarpRiver River Falls Fallsshear shear zone zone isis in in itself itself aagold goldexploration exploration target. target. Stop StopSG-7: SG7: Basal Basal Proterozoic Proterozoic Enchantment EnchantmentLake Lakeconglomerate conglomeratein in contact contact with Carp Carp River River Falls Falls shear shear zone zone in in Archean Archean metabasalt. metabasalt. (Location (Locationmap, map,Figure Figure9). 9). This This spot spot has has been been aa classic classic field field trip trip stop stop for for seeing seeingthe the features features of of the the Mesnard Mesnard and and Ajibik Ajibk quartzites U.S 41 41roadcut. roadcut.But Butour ourinterest interestlies liesthither furtherdown-section down-sectionininthe theProterozoic, Proterozoic,atatits its quartzites in the US. contact contact with with the Archean. This Thislocality localitywas waslast lastmapped mappedby byPuffett hffett(1974), (1974),who whoshowed showedthe theArchean Archean rocks rockshere here as as Mona Mona Schist, Schist, now now included included in in the the informal informal lower lower basalt flow flow unit unit of of the Mona Mona Formation Formation of of Bornhorst Bomhorst and and Johnson Johnson (1993). (1993).Puffett's Puffett'smap map(P1. (PI.1)1)shows showsthe theCarp CarpRiver RiverFalls Fallsshear shearzone zoneasasaaline line passing passingabout ahoutaa half half mile mile north north of ofhere, here, but but he hestated statedin in his his text text (p.43), (p.431, "The "The zone zoneisis indicated indicatedon on the the map map as asaanarrow, narrow,well well defmed defmedstructure, structure,but but the the symbol symbolmarks marks only only the the north north limit limit of of aa broad broad zone zoneof of sheared sheared and andaltered alteredlower lowerPrecambrian Precambrianrocks." rocks." After M e rparking parking at atthe the intersection intersectionof of U.S. U.S. 41 4 1and andChippewa ChippewaDrive, Drive, walk walk about about100 100feet feetnorthwest northwest past pastthe thebillboard billboardto to aaseries seriesof oflow lowoutcrops outcropsininthe thewoods. woods.The Thefirst fistone oneencountered encounteredisisglacially glaciallypolished, polishe4 and andexposes exposesthe theCarp CarpRiver RiverFalls Fallsshear shearzone zoneinincontact contactwith withthe theoverlying overlyingbasal basalconglomerate conglomerateofofthe the Enchantment EnchantmentLake L&e Formation. Formation.Both Botheast eastand andwest westofofhere herethere thereare arenumerous numerousnearby nearbyexposures exposuresofofthe the shear shearzone zonelying lyingnorth north of of this this contact. contact. AAwidth widthofofabout about200 200feet feetofofthe theshear shearzone zoneisisexposed exposedininthe the immediate immediatevicinity. vicinity. Shearing Shearingintensity intensity isis variable; variable; relict relict pillow pillow textures texturesare are present present in in exposures exposuresabout about 150 150yards yardsto to the the east. east. Here Hereatatthis thisexposure, exposure,the theArchean Archeangreenstone greenstoneshows showsstrong strongfoliation foliationstriking striking280°, 280° 85° 85' S. S.AAparallel parallelfoliation foliationalso alsoaffects a f k t sthe thelowermost lowermostpart partofofthe theoverlying overlyingconglomerate. conglomerate. The Theconglomerate conglomerateisisabout about55feet feetthick, thickbut butisissomewhat somewhatpatchy patchyand anddiscontinuous, discontinuous,grading grading intermittently intermittentlyboth bothupwards upwardsand andlaterally laterallyinto intocoarse coarsegrained gainedquartzite quartzitecontaining containingonly onlyoccasional occasionalsmall small 81 �cobbles or pebbles. The Theentire entireunit, unit, including includingthe the quartzite, quartzite,isis20-50 20-50 feet feetthick, thick forming formingan an erosionally erosionally resistant E-W ledge. South South of of it, it, aa 100-foot-wide 100-foot-widelow lowswale swaleoccupies occupiesthe theinterval interval presumed presumed to to represent represent erosionally recessive sericite slate that constitutes the upper part of erosionally of the the Enchantment Enchantment Lake Formation Fornation in in this area (Puffett, 1974); 1974); the very uppermost uppermost part part of of this thislithology lithologycan canbe beseen seenbelow belowthe theMesnard Mesnardquartzite quartzite back at the the highway. highway. The basal conglomerate conglomerate can be traced traced westward westward from fromhere here at at the the initial initial outcrop outcrop for forabout about250 250feet. feet. layers of of itit consist consist of of +80% The coarsest layers +8O% white vein qquartz u a cobbles. ItIt bears bears aa striking striking physical resemblance to the low-pyrite varieties of the Witwatersrand resemblance Witwatersrand conglomerate conglomerate of of South South Africa, Afiica, and and occurs occurs in in a similar geologic setting. setting. We We took tookthree threegrab grabsamples samplesof of conglomerate ffom from these these outcrops. outcrops. Two of them retumed returned detectable gold: gold: ,003 .003 odton ozlton and and ,005 .005 odton. or/ton. These These two two were were re-analyzed by Chemex and returned retumed 65 ppb and 37 ppb Au, respectively. respectively, These Theseresults resultssuggest suggestaa problem problem with with nugget nugget effect effect at the low end of the detectability scale, which would not be surprising surprising in the case of placer gold. No sulfides sulfides are are megascopically visible in this rock, nor were any found found under under the the binocular binocular microscope microscope in in an an examination examination crushed rejects rejects from from our our grab grabsamples, samples. We of the cmshed Wehave havenot not done doneany any further further testing to ddetermine e t d e the internal domains hosting these low but anomalous gold values. intemal Discussion Diicussion Although it may tum turn out that the the traces traces of gold gold in this rock are caused solely by the foliation event it, aa paleoplacer paleoplacer origin originseems seemstotous ustotobe be much more more likely. likely. For economic concentrations of of that affects it, paleoplacer gold to be found found in in the the Enchantment Enchantment Lake Lake conglomerate, conglomerate, the first fust consideration consideration would be be deposits in the Archean tmane terrane were actually in existence prior prior to to the erosional events whether or not gold deposits deposition of of the the conglomerate. conglomerate. The in that led to the deposition Theonly onlyknown known significant significant gold mineralization in region occws occurs in veins at the Champion iron mine; the Proterozoic rocks in this region the Proterozoic Proterozoicisis otherwise otherwise notable for its paucity of gold showings. Bornhorst Bomhorst and and others others(1998) (1998) have have attempted attempted to constrain constrain the dates for some some of the mineralization in the Archean rocks by lead isotope studies, obtaining obtaining a model model age age 2,455 to to 2,510 2,s 10Ma Ma for forgalena galenathat thatoccurs occurswith with gold goldin inthe theRopes Ropesmine, mine, but but also alsomentioning mentioningstructural stn~ctural of 2,455 evidence suggesting that that the the Ropes Ropes gold gold was was deposited deposited at at about about 2,690 2,690 Ma. Ma. They also pointed out that ages are poorly constrained for the timing timing of the the rifting that that initiated initiated the earliest Marquette MarquetteRange RangeSupergroup Supergroup sedimentation that this conglomerate represents. Whatever the absolute age(s) of the thegold-bearing g o l d - b e ~veins gveinsin in the the Archean Archean rocks rocks of of the the Ishpeming Ishpeming belt, this this conglomerate conglomerateprobably probablypost-dates post-datesthem. them. Evidence for this is is the the high high preponderance preponderance greenstone belt, 82 �of vein quartz within it at this this locality, locality, the the presence presenceof of anomalous anomalous gold gold in in it, it, and its apparently unconformable relationship with the Carp River Falls shear zone, which was demonskated demonstrated to be goldpaleoplacer-typegold golddeposit depositwithin withinthis this mineralized at Stop SG-5 Whether or or not not a paleoplacer-type SO-S of of this field field hip. trip. Whether for exploration exploration is is another another matter. There Thereare arevery veryfew fewexposures exposuresofofthe theEnchaniment Enchantment unit is a prime target for Lake Formation, and especially few hin conglomeratic few of of this this tthin conglomeraticphase. phase. The many samples needed needed for for assaying, provenance provenancestudies studiesand andthe thelike likewould would nearly nearly all all have have to to be be obtained obtainedby byexpensive expensivesubsurface subsurface assaying, means means over over aa wide wide area. area. Stop Stop SC-8: SG8: Lithology-seleetive Lithology-selectiveductile ductile shearing s h e a ~ with g boudinage i in n the Carp Carp River River Falls F a h shear shear 12). zone. (Location (Locationmap, map,Figure Figure12). This This locality locality was last mapped mapped by Cannon and and Klasner Klasner (1977), (1977), shown shown as as part part of of their their Precambrian Precambrian mafic-uleamafic complex. complex. The Therevised revisedstratigraphy stratigraphyof ofthe theArchean Archeanrocks rocksof ofthe theIshpeming Ishpeminggreenstone greenstone W mafic-ultramafic belt (Bomhorst (Bomhorst and and Johnson, Johnson, 1993) 1993)assigns assignsitit to to the the informal informal basalt basalt flow flow unit unit of of the the Kitchi Kitchi Formation. Formation. Beginning about us 118 mile mile east east of of here, Cannon and Klasner mapped a large area area of of Precambrian W serpentinite, serpentinite, now considered considered part of the Deer Lake peridotite. About About1/4 I14 mile to the northeast are a number of outcrops outcrops of of aa very very fresh fiesh looking, looking, nearly nearly unfoliated biotite biotite tonalite tonalite intrusion inhusion that we informally refer to as the "Mockler tonalite", named named for for an an adjacent adjacent small gold gold prospect; Cannon Cannon and and Klasner Klasner mapped mapped that as Only a few hundred feet south of here Cannon and Klasner's outcrop area as Precambrian W felsic rocks. rocks. Only Klasner's map shows shows a fault fault contact contact between the Archean and the Proterozoic. Bornhorst Bomhorstand andJohnson Johnson(1993) (1993) included included this this in the Carp Carp River River falls falls shear shear zone. zone. This expowe was was not not available available to previous workers. ItItwas wascreated createdonly onlyvery very recently, recently, when when the This exposure Marquette Marquette County County Road RoadCommission Commissionstraightened straightenedthe the approach approachto tothe therailway railwayunderpass underpassimmediately immediately south of of us. The TheRoad RoadCommission Commissiondumped dumpedaavery very large large pile pile of of excess excess blasted blasted rock from fiom this new south roadcut roadcut in aa gravel pit that lies a couple of hundred hundredyards yardssoutheast. southeast. Figure 13 13 is a detailed detailed map of of this this exposure. exposure. ItItshows showsaawide widevariety varietyof ofrock rocktypes, types,which which are are affected affected by by an an east-west east-west zone zoneof ofductile ductileshearing shearingthat that varies varies from fiom weakly weakly to to intensely intenselydeveloped, developed, dependiig on the rock type. There Thereisisevidence evidencehere here for formultiple multiple deformation: deformation: aa nearly nearly horizontal horizontal 52 S2 depending crenulation crenulationcleavage cleavageisis superimposed superimposedon onaavertical verticalS1 S, cleavage, and and is is mimicked mimickedatatall allscales scalesby bynearnear- horizontal horizontal boudins boudinsof offoliation-resistant foliation-resistantveins veinsand androck rockunits units (see (seephoto, photo,Figure Figure15). 15). 83 �___ _____ Figure 12. Location map for Stops SG-8, 9 and 10. 32'30' -______ 16/8 I ii I ." •- -: r a H o ?& 0 "N 7r"X)r 0 002 —C S 0 1000 - 60 - —-—— 2000 0 — ,g) 45 3000 I -5 I— - 2/± - —. T. 48 N. T. 47 W 1 MILE 3 601)0 7000 FEET i KILOHErER CONTOUR INTERVAL 20 FEET 47'JO' GREENWOOD 1.2 ML I,rrrnlOB—GE0LOGICAL SUSVEV - WASHING TON, Oj._ISSS—NS SI 5,3565 84 46030) 87°45' �I Figure Figure 13. 13. Plan Planmap map of of Marquette Marquette County Highway 8. Higbway "CL" roadcut, Stop SGSO-S. AT noMttrEtY $$(AC merA&454Lr .2 tocM1, LI/E4%'Y rot,4r6) o — 4u•rt1 E . yo Sd' m'Ms.4Lr ed fri 6Th 54$4tr So uOiW3 p0SN}fRY — -. 'tI—.& /tt1 c. A cm.' "/ ftttt H ti7t,t $4F1c r.mb4/c ch(orb'è jAta.rtd ..,&caJt -J 4 0 iay .cwt#4e6D MErA34re4. r >- L o I piEr I 'U mer4 ,nE.'r5 x .45S0-q SancpI' wI'ok rock sQflpI& T 0 50 5' Pit 1-owib flttT$ &4At- wE'Y C.npast and flp'. JA /0/98 C) 85 �Figure IS. 50-8. Near Figure 15.Looking Lookingeastward eastwardat at roadcut roadcut exposure, Stop SG-8. Nearcenter centerof of photo photo is is mega-boudined blocky tonalite porphyry with with brecciated south south margin margin of of tonalite tonalite fragments, fragments, quartz, chlorite and tourmaline. tounnaline. Tonalite Tonalitemega-boudin mega-boudinisisenveloped envelopedin in highly highly sheared sheared basalt basalt that also hosts horizontally horizontally boudined boudined quartz-carbonate quartz-carbonatevein veinnear nearleft leftside sideof ofphoto. photo. Highly sheared talcose ultramafic ultramafic is is at far far right. right. This exposure exhibits lithologic and structural features too numerous to be described described in detail in will be be briefly briefly mentioned. mentioned. Near the south end, end, a 15-foot this paper; the highlights will %foot layer of virtually piliowed metabasalt and undeformed graywacke and minor pink chert lies between weakly foliated pillowed moderately sheared metabasalt. rnetabasalt The not clear. clear. The southern Thegraywacke grayacke has graded bedding, but tops are not contact of the sediments sediments with the basalt appears to be conformable, conformable, but the northern contact contact with the by pyritic pyritic slickensides. slickensides. Moving northward past a mbbly rubbly interval of moderately sheared basalt is marked by near-outcropping sheared sheared basalt, shearing becomes progressively more intense, and seems to be centered on a 4-foot none can be be found at the 4-foot zone of talcose. talcose,papery-thin papery-thin sheared sheared ultrarnafic ultramafic rock. Although none outcrop itself, aapiece pieceof ofthis thisrock rock found foundin in the the gravel gravel pit pit waste waste pile pile contained contained cross-fiber cross-fiber chrysotile. On On the Jensen Jensen cation cation plot plotof ofour ourwhole wholerock rockanalyses analysesfrom fromthis thisexposure, exposure,the thesample samplefrom from this talcose material material 86 �plots in the peridotitic komatiite field (see Figure 14). This This rock rock isis either either an apophysis apophysis of the Deer Lake peridotite, or a tectonically emplaced slice slice of it; it; it exhibits exhibits vertical vertical rodding rodding but but horizontal horizontal slickensides. slickensides. Because of the structural deformation here, it's problematic problematicwhether whether the the boudined bondined tonalite tonalite porphyry is a dike or a sill. This Thisisisaafme fmegrained grained dark dark pinkish pinkish gray gray rock with up to about 20% small phenoctysts, which which in in thin thin section sectionare areall allhighly highlysericitized sericitizedalbite-oligoclase. albite-oligoclasa The feldspar phenocrysts, The groundmass composition is: a few few percent opaques, opaques, (about (about ¾ % rutile rude pseudomorphing pseudomorphing ilmenite ilmenite and ¼ '/4 porphyroblastic porphyroblastic cubic pyrite); one third anhedral quartz; quartz; one one third third sericitized sericitized albitic albitic plagioclase; plagioclase;and andone onethird thirdinterstitial interstitial chlorite, sometimes as pressure shadows of pyrite, defining a clear thin section-scale foliation. This This isis an an albitic rock that yielded yielded 6.04% 6.04% Na20, Na20, the study. A the highest highest of any of the whole rock analyses done for this study. A K20 content of 1.39% K20 1.39% is is probably probably entirely entirely due due to to sericite; sericite; no no K-spar K-spar was was found. found. A zone of of interest interest in in the the sheared sheared metabasalt metabasaltand and marked marked on onthe themap mapisisaathin thininterval intervalrich richinin disseminated disseminated coarse coarse magnetite magnetite coexisting coexisting with randomly randomly oriented oriented coarse coarsecubic cubicpyrite pyrite that thatappears appearsto tohave have developed porhyroblastically porhyroblastically without pressure shadows in a low strain environment. Another Another isis aa few few feet feet of sheared sheared greenstone greenstone with minor minor iron iron carbonate, carbonate, aa trace trace of of fine finedisseminated disseminatedpyrite pyriteand andrare raremalachite malachite spotting. spotting. This exposure has been sampled for gold more than once by MPC; MPC; the locations locations of of the latest three grab samples are shown on the map. None None of of the the samples samples yielded yielded gold above above detection limits. Despite Despite the favorable-looking favorable-looking shearing, shearing,the the lack lack of of significant significantaccompanying accompanyingcarbonate carbonatealteration alterationmay maybe hean an important reason for the lack of of detectable detectablegold gold in in it, it, even even where where copper copperminerals mineralsare arepresent. present. Figure 14, 14, the Jensen Jensen plot plot for for the the whole whole rock rock samples samplestaken takenfrom fromthis thisexposure, exposure,illustrates illustratesthat thatthe the greenstone samples, samples,regardless regardless of of degree degreeof of shearing, shearing, plot plot closely closely together together in in the the high iron tholeiite tholeiite field. Our sample of the tonalite porphyry from here is shown repeated on the Jensen plot of Figure 16 for the purpose of comparison comparison with with two two other other felsic felsic intrusive intrusive bodies bodies in in this this vicinity, vicinity, the the Mockler Mockler tonalite tonalite(sample (sample "MOCK") mine (sample (sample"PG-1"). "PG-I"). (Note: "MOCK) and andthe the tonalite tonalite porphyry at the Peninsula Peninsula mine (Note: Accessory Accessory zircon zircon was noted in thin sections sections of all of of these these rocks). rocks). The shearing be traced westward only shearing seen here cannot be Iraced traced eastward, and can he only a few few hundred feet, where it is partially exposed in the old highway highway cut. Beyond Beyond that that point, point, scattered scatteredoutcrops outcrops in in the the hills to the west are of unfoliated metabasalt. The Theductile ductileshearing shearingseen seen at at this this stop stop might might represent represent only only a branching splay of the Carp Carp River River Falls Falls shear shear zone, whose whose main expression expression may may well well lie lie south southof of here here at at the Proterozoic Proterozoiccontact. contact. 87 �FeO* + 1102 SAMPLES Cation % Cation YO Jensen Jensen (1976) (1 976) • PC-B-i • PC-B-2 £ PC-8-3 V PC-UM • PC-PFWO AJ203 MgO Figure 114: 4: Stop Stop SG-8 SG-8 Fe0* FeO*++1102 m02 Cation Cation % % Jensen Jensen (1976) ( 1 976) . w SAMPLES • MOCK K C K • RC-PI-WO m K-RtNO £ PJ203 A203 PG-I MgO Figure 6 Figure116 88 �Stop SG9: SG.9: Peninsula Peninsula gold gold deposit (Location (Location map, map, Figure Figure 12). 12). In In contrast to the broad anastomosing anastomosing ductile shear shear zones seell seen so far on this field trip, the Peninsula gold deposit occurs in a discrete brittle-ductile structure. Also Alsoin in contrast contrast to to the the nearly nearly east east -west regional shear zones seen so so far, the Peninsula Peninsula structure structure strikes strikes north north -- northeast. northeast. This structure structure cuts a by Cannon Cannou variety of host hostrocks, rocks, regionally regionally mapped mapped as as Precambrian Precambrian W massive massive and layered felsic rocks by and Klasner (1977) and subsequently subsequently assigned to the informal basalt flow flow unit of the Kitchi Formation (Bornhorst 1993). At (Bomhorst and Jobnson( Johnson(l993). At aa scale scale useful usefbl for exploration, exploration, the the geology geology is is quite quite complex. complex. History Gold was discovered at the Peninsula in the 1880's, 1 8 8 0 ' but ~but ~ there there was was never never any any commercial commercial production. All Allinformation informationon onthis thisperiod periodconsists consistsof ofold oldnewspaper newspaperarticles articleswith withvery verylittle littleuseful useful technical data except the probable depths of the two old main shafts on the property, 69 feet for the North shaft and 80 feet for the South Shaft (Fountain, (Fountain, 1992). 1992). There Therewas wasno nomodem-day modem-dayactivity activityat at the the Peninsula Peninsula by Callahan Miing Mining Corp. in 1981. MPC until it was purchased by MPCpurchased purchasedthe thetracts tractsencompassing encompassingthe the Peninsula and the nearby Michigan gold mine mine from from Callahan Callaban in in 1995; 1995;included includedin inthis thisacquisition acquisitionwere wereall all reports on these properties. properties. The following of Callahan's Callahan's drill d d l core, core, exploration data data and internal rqorts following synopsis part of a of the work done by Callahan is based on an analysis and summary of this acquired data in p~ detailed report for MPC (Duskin, (Duskin, 1997). 1997). detailed mapping, rock sampling and and Between 1981 1981 and 1984 1984 Callahan conducted surface reconnaisssance recomaisssance mapping geophysics. An An early early phase, phase,called calledthe the "granitoid "granitoid program" program'' was wasfocused focusedon onintensive intensivechip chipand and channel channel sampling of the tonalite porphyry, thought to be a pluglike intrusion with potential for large tonnage, tonnage, open inmsion with open pittable gold mineralization. Disappointing pittahle Disappointingresults resultsled led to to aare-focus re-focus on on the the steeply steeplydipping dipping"siliceous "siliceous exhalite" originally tested by the oldtimers, termed tenned the "Target exbalite" "Target Zone" by Callahan. Callahan. The The subsequent subsequent testing No detailed mapping or trenching Irenching were were done. done. Three program consisted entirely of angle core drilling. No mee shallow test holes under the old workings workings in 1984 1984returned returned sub-ore sub-oregrade gradeassay assayresults resultsbut but encouraging encouraging Shaft, returned returned 15.6 slant feet feet grading grading .216 thicknesses. In In 1985 1985the the fourth fourth hole, under the old South Shak ,216 oz/ton odton Au. Intensive Intensiveclose close spaced spaced drilling drillingwas wasthen then carried carried out out through through 1987, 1987, resulting resulting in about 20,000 feet of core in a total of 37 37 holes. boles. During D U Mthe the ~ course courseof ofthis thisdrilling drillingaapresumed presumedblind bliid en enechelon echelon termed the the "Back Zone", was was discovered. stratabound zone zone of of mineralization, mineralization, tenned The purpose purpose of of the the drilling drilling was was to to quickly quickly prove prove up up aa ramp-minable ramp-minableshallow shallowtonnage tonnageof ofhigh higb grade grade ore to augment augment or eventually eventually replace the ore being fed to the mill by the Callahan's mining operation 89 �o -. + • 441+ .7, -c - +- '"ir' '.4 .+ _+4'4 ,.—r' + 4 ++ + - ++ 4 5 + + 4 *4, - - - : 4 + - +4 + : -J 4 + • + + 4 4 + '4 4 , • + 4 + 4 + + 4* 4 o 4 4 .:-:+ ';* 55*4., 44 4 4 + •4 4 'i, 4 v-I i' +',. ,.' -4, 4 + 4 '"Mbc+ - " : + + 4 4 + + + I + + 44 4* ,1 V t -4+- '1-c-ct 7-c'? ++44•V +44 V 4,1-c-c 4 '4 -, 'ç+-c," "v' 414+ +4 "4 v,'ç.,'ç'v,'çc,v,vvv. v.vV'+ 744 +VT+ vvvV'?41vc,# 4', vvvuv c,'?c, :++ + SVV"V+IZQPQV 43'? '+24 WV. v tIn''? Vt ct -. +_.: _..., c,t 'Vt WV' 4 ' :- I \ 441*4 V14V 4 +444+4 ,'1vvvu vvvVvVtvv'?cvVtIc, Vvtv+,+-vvvVvtv,-V 'VVYVU" + Ct.'. 4 • + +-'. 44 4+-.' \\ c,t —': :'47—WãWet ,c-c1 +444+' 4; .>VQ,V+ 4 -: 4 + ' -'v-ct'-c-c VVvr+v +WtVVv V VWWVV WVV'?" V vcVvvvv V-c VvvV W4,VVv" 4' + ;+, 4 '.,tc':::4.'c:: Qc,vvvvVv'?M'?%4V?(,+ '—_.,.i,,,, + + jI V" '+++4I* '4*'• 4 wv,,-+ 9FtV++ 14 V4+- ..''?.t,,' "-cv — 43 ,, -'4" 0 .c(V4,VVV vc'vo vwt V-c 4-c vW+4.4..,v++% •-cfl-c ' Vt''? vwv 554,4 4 -' C" 'C 44+4* +44 4. 4444 +4 ',1W'-4-4-4'-4 w +44444444 '''.,.'.' t+* ' * 4 + 4 ++ +'+ 4+4+4+ -i B Zârie 1'+ 7+44. J -.f+JTh 4, .r+ -r 4 4 4 444''' ++ 4-- 4 + + -u'1°'' 'inC cm:. (.,U,4w vc, 1 •-'..C•0 0 7449?V 4* *4 r ' U'OO 4i4444'4+5 44_•+ .' C>>t>000( wvvv ,'', • +4.4+4+ + + 4 54+•4.'+ 1+4 ,I+ 44+4+4+5 — +4' 4-474 + 4- 4+ + 4 f'- I:$4f] ., 4+44+4+44.4 t. mafic intrusive 200 feet Geology Peninsula Gold Project Minaals Processing Corporation 100 Trench Outcrop Fault Gold—bearing zone Laminated felsic tuf I Greenstone Metagabbro Magnetic Figure 17: Stop SG-9 0 r Tonalite porphyry �at the the Ropes Ropes deposit. deposit. There Therewas wasno noattempt attemptatatstepout stepoutdrilling, drilling,and andthe the deposit deposit remains remains open open at at depth depth and and at in both both directions directions along along strike. strike. Callahan Callahan eventually eventually calculated calculated a reserve of 51,700 5 1,700tons tons grading grading .141 ,141 01/ton odton in in in the the outcropping outcropping Target Target Zone Zone segment segment of of the the structure, structure, and and an an additional additional 41,200 41,200 tons tonsgrading grading.082 ,082 oz/ton asfar far as as obtaining obtaining aa mining mining permit in 1988 1988 from from the first fust odton in in the the Back Zone. Mining Miingplans planswent went as level level of of authority, authority, Marquette County. But Butthe thedeclining decliningfortunes fortunesof of the the Ropes Ropes mine mine and and ofofthe the corporationitself itself led ledtotoaasuspension suspensionofofactivity activityatatthe thePeninsula Peninsulafrom fromthen thenuntil untilthe thesale saletotoMPC. MPC. corporation Taking in the the early early Taking aa new new approach approach not influenced influencedby bythe thestratabound strataboundgold goldmodels modelsin in vogue vogue in 1980's, MPC MPCbegan began its its re-evaluation re-evaluation of of the the property property by rock sampling sampling and mapping mappingon onaagrid gridat atl"=lOO' l"=lOO' 1980's, in in 1996. 1996.This Thisled ledtotothe thediscovery d i s w v wof ofthe theBack BackZone Zoneininoutcrop outcrop(now (nowrenamed renamed the the "B "B Zone"), Zone"), and and the the recognition recognition that that itit is is simply simply aa fault fault offset offset of of the the Peninsula Peninsula structure. structure. Further Furtherwork workincluded includeddigging diggingand and channel "=20' mapping channel sampling sampling 11 11backhoe backhoe trenches, trenches, detailed detailed11"=20' mappingalong alongthe theentire entireexposed exposedstructure, strncture, petrographic petrographic and polished section studies studies of mineralized core intervals, complete re-logging of many of the thecore coreholes, holes,and andcorrelation correlationof ofthe therevised revisedcore corelog loggeology geologywith withthe thesurface surfacemapping. mapping. Figure Figure17 17isisaa geologic geologicmap mapcompiled compiledfrom fromthis thiswork. work. Lithology Lithology The The oldest oldest of of the the rocks rocks hosting hosting the the deposit deposit area area appear appear to to be be an an interlayered interlayered sequence sequence of of greenstones greenstones and a laminated felsic felsic tuft'fragmental tuWfiagmental unit. unit. The Thetuff'fragmental tuWEapentd isisnon-magnetic non-magnetic and and erosionally one very v q small outcrop outcrop just east of the North Shaft Shaft can be found found on on surface; snrface; it erosionallyrecessive. recessive. Only one was wasalso alsoencountered encounteredin in Trench Trench 77 northwest northwest of of there. there. InIndrill drillcore corethis thisgray grayrock rockisisextremely extremelywell wellbanded banded and andoften oftencarries canies coarsely coarselyfragmental kagmental heterolithic heterolithic layers. layers. ItItexhibits exhibitsgraded gradedbedding, bedding,but buttops topsand andbottoms bottoms in inthis thissequence sequencehave have not not yet yet been worked worked out. out. The Thegreenstones greenstonesare aretypical typicalmetabasalts metabasaltsand andoften oftenexhibit exhibit amygdules amygdulesin in drill drill core. core. The Themany manystructural structuraldislocations dislocationsininthe theimmediate immediatePeninsula Peninsulavicinity vicinitymake makeitit difficult difficultto todetermine determineaastrike striketrend aendfor forthese theseunits, nnits,but butaadistinctive distinctivebedded beddedchert cherthorizon horizonwithin withinthis this sequence sequencethat that outcrops outcropsabout about1000 1000feet feetnorthwest northwestgives givesan anattitude attitudeof of035°, 035",72°SE. 72"SE. The Thecoarse coarsegrained grainedmetagabbro metagabbrowest westofofthe theNorth NorthShaft Shaftappears appearstotobe beaasmall smallplug plugororsill sillintruding inin~diig the thegreenstone; greenstone;itit contains containslarge large angular angular fragments Eagments of of greenstone. greenstone.This Thismetagabbro metagabbroisisnon-magnetic non-magneticand and completely completelyamphibolitized, amphibolitizedwith withpseudomorphs pseudomorphsofofcalcic calcicamphibole amphiboleafter afterorthopyroxene orthopyroxenefaintly faintlypreserved. presewed. ItIt contains contains 2-5% 2-5Yo coarse coarse cubic cubic porphyroblastic porphyroblastic pyrite pyrite that that often often hosts microscopic inclusions inclusions of of 6 chalcopyrite; chalcopyite; tiny tinyfree Eeegrains grainsof ofchalcopyrite chalcopyriteare arealso also present present in in traces. The Therock rockcontains containsabout about5% 5% chlorite chloritereplacing replacing amphibole, amphibole, indicating indicatingretrograde retrogrademetamorphism. metamorphism. 91 �The porphyry. This The most most erosionally erosionally resistant resistant of of the the Peninsula Peninsula structure structure host rocks is the tonalite porphy~~. This rock rock has has been been affected affectedby by both both metamorphism metamorphismand andhydrothermal hydrothermalprocesses, processes,especially especiallywhere whereititlies liesclose close to the the auriferous auriferous structure, structure, where gold values ranging from fiom a few to a few hundred ppb can often be found to in init. it. In In mapping mapping near near this this structure, structure, itit is is often often difficult diff~cultto todistinguish distinguishaadivision divisionbetween between the the two two alteration alteration effects, effects, but but one one of of the the principal principal hallmarks hallmarks of of the thehydrothermal hydrothermalalteration alterationisis an an increase increasein in chlorite chloriteas as replacements, replacements, seamlets, s e d e t s ,enhanced enhanced foliation foliation partings p d g s and and slickensides. Other Other such such effects effects are are elevated elevated content content of of fme fine grained grained disseminated disseminatedpyrite, pyrite,carbonate carbonatereplacement replacementof ofthe thegroundmass, groundmass,and andwhite whitequartz quark veining. veining. Strong Strongalteration alterationseldom seldompersists persistsfor formore morethan thanaafew fewfeet f& from fromstructural structuralcontacts. contacts. The Theporphyritic porphyriticnature natureof ofthis thisrock rock isisoften oftentoo toosubtle subtletotoreadily readilydiscern discernininhand handspecimens, specimens,even even in in relatively relatively fresh fiesh samples. In Inthin thinsections sectionsof ofthese, these,the thephenocryst phenocrystcontent contentvaries variesfrom from5% 5%to to 30%, 30%, and and these these are are all all heavily sericitized, sericitized, corroded albite-oligoclase albite-oligoclase crystals. The The groundmass groundmasshas has about about 20% 20% anhedral anhedral quartz, quark, within within aa very very fme fme grained grained mixture mixtureof ofbiotite biotitealtering alteringto to chlorite, chlorite, chlorite, chlorite,albite, albite, muscovite/sericite, primarily of of rutile rutile and and pyrite. Very muscovitelsericite, and opaques consisting primarily Very rare rare tiny tiny grains grains of of probable thin probablemolybdenite molybde~tehave been found in a few hand specimens. In In one polished t hin section of altered altered tonalite, tonalite,microscopic microscopicinclusions inclusionsof ofmixed mixedchalcopyrite-pyrrhotite chalwpyrite-pymhotitewere werefound foundininpyrite. pyrite. Because Becauseof ofits itsrelative relativeerosional erosionalresistance, resistance,this thisunit unit has hasbeen been "overmapped" "overmapped"ininthe thepast, past,and andisis probably probablyalso alsosomewhat somewhatovermapped overmappedas asdepicted depictedon onFigure Figure 17. 17. InInseveral severaldrill drillholes holespassing passingunder under outcrops outcropsof oftonalite, tonalite, none none was was encountered encountered in the subsurface. subsnrface. In Insome someof ofthe thetrenches trenchesitit was was found foundthat that low by outcrops outcropsof oftonalite tonalitewere wereunderlain underlamby bysubcrop subaopof ofthe theolder oldergreenstone-tuff greenstone-tuff lowareas areassurrounded surroundedby sequence sequencethat thatthis thishypabyssal hypabyssalintrusive intrusiveinvades. invades. In In drill drillcore coreintercepts, intercepts, its itscontacts contactswith withthis thissequence sequence are areusually usuallybrecciated brecciated and/or and/or slickensided, slickensided, but butaafew fewof ofthem themshow showinjections injectionsof ofthe thetonalite tonaliteinto intothe the greenstone. greenstone. The Thetonalite tonaliteporphyry porphyryisisnot notaamassive massiveplug, plug,but butrather ratheraacluster cluster of of dikes/sills. diiedsills. The Theyoungest youngestrock rock unit unitisismapped mappedas as"magnetic "magneticmafic mafic intrusive", intrusive", but butititisisprobably probablyaametadiabase. metadiabase. This Thisblack blackrock rockisisvery veryweakly weaklyfoliated foliated(except (exceptimmediately immediatelyadjacent adjacenttotocontacts), contacts),exhibits exhibitsan an equigranular equigranular texture, texture,and andcontains containsmegascopic megascopicfresh fieshbiotite. biotite. ItItcarries carriesaafew fewpercent percentcoarse coarseeuhedral euhedralpyrite, pyrite,asaswell wellasas ubiquitousdisseminated disseminated magnetite, magnetite, sometimes sometimes up up to to 10%. 10Y0.InIndrill drillcore coreititcontains containstrains bainsand andscreens screensof of ubiquitous angular fragmentsofofthe thetonalite. tonalite. angularfragments 92 �Structure Mineralization Structure and and Mineralization The Peninsula Peninsula fault fault structure structure affects affects all of of the the rock rock types, types, inclusions inclusionsof ofwhich whichcan canbe be found foundwithin within it. We Werecognize recognize two two basic basic lithotypes within the structure: quartz-carbonate quartz-carbonate ("q-c"), ("q-c"), and chlorite("ccpy"). Angular carbonate-pyrite ("copy"). Angular breccias are common in the q-c lithotype. Host Hostrock rock fragments fragments are are less abundant, but sometimes ccpy lithotype, usually as boudins. The sometimes present present in the copy Theq-c q-clithology lithology predominates Target Zone; Zone; itit exhibits predominates where the fault fault structure structure intersects tonalite, primarily in the Target exhibitsmostly mostly brittle brittle texures and has abundant abundant albite as veinlets and breccia matrix. The Theprimary primary carbonate carbonate is is dolomite, dolomite, with lesser ankerite, rhodochrosite and and late late calcite. calcite. Silica content is highly variable. variable. The q-c usually contains chioritic slip planes planes,,and contains chloritic and sometimes sometimes lenses lenses or intetfingering interfmgering layers of copy. Megascopic Megascopic metallic minerals in the q-c are pyrite, very minor chalcopyrite, minerals chalcopyrite, and, and, rarely, visible visible gold. gold. There Thereisis aa strong strong conelation correlationof ofgold gold assays assays with with pyrite, but it is not 1:1. 1:1. In Inmicroscope microscopeexamination examinationof of high high gold gold -- high pyrite samples, gold gold is is found found as as tiny tiny inclusions in pyrite, either alone or with sphalerite. Other Otherinclusions inclusions in pyrite samples with visible gold, the pyrite are are argentiferous argentiferous galena, galena- pyrrhotite pyrrhotite and and chalcopyrite. chalcopyrite. In low pyrite samples gold appears appears to to be be later later than than pyrite, pyrite, occurring occurring as as free freegrains grains in in chlorite chloriteand and carbonate, carbonate,associated associatedwith with chalcopyrite. chalcopyrite. characteristically displays The dominant mineral in the copy ccpy lithology is chlorite, and this rock characteristically ductile textures. This Thislithology lithologyseems seemsto to dominate dominatethe the fault fault zone zone where where itit intersects intersects greenstone or and in in the the deeper deeper levels levels of of the the Target Target Zone Zone segment. segment. There is metadiabase, both in the B Zone segment and albite in the matrix of this rock, rock, but but virtually virtuallyno noquartz. quartz. In the B Zone, Zone, most most of which which involves involves faulting adjacent to the metadiabase, much of the chlorite can be be seen in thin thin section to to be be replacing replacing biotite. biotite. The The ccpy is generally much higher in pyrite than the q-c, and also contains copy contains several several percent percent magnetite in the B Zone segment, probably probably derived derived directly from the metadiabase. In Inpolished polished section sectionmagnetite magnetite and and pyrite pyrite exhibit coexisting mutual mutual textures. textures. Chalocopyrite in this thislithology. lithology. Gold, Chalocopyrite also occurs as aa minor sulfide in where found so far, occurs occurs as as inclusions in pyrite, and in quartz and and carbonate carbonate veinlets. that the the composition composition of of the the Peninsula Peninsula gold gold structure's structure's gangue is is very very host host The clear impression is that rock-dependent. ItIt appears appearsthat that aa great great deal deal of of host host rock has has been been assimilated assimilated into into the structure, with the the metatonalite metatonalite contributing contributingto tothe thequartz quartzin inthe theq-c q-clithology. lithology. Similarly, the the availability of free silica in the of ferromagnesians fenomagnesians in more mafic host rocks promoted the lack of free silica and the abundance of rocks were were intersected. intersected. The abundance of dolomite in the q-c and of development of chlorite where those rocks chlorite cepy indicates introduction of magnesium chlorite in the copy indicates a very strong introduction magnesium into into the the hydrothermal system system that that operated within the operated the Peninsula Peninsula fault fault structure. structure. 93 �Zone strikes 020' 020° and dips steeply SE. On The Target Zone Onthe thesouthwest southwestititisisoffset offsetby by aa later laterhigh high angle fault which also rotates it into Zone). into an an orientation orientation trending trending 050°, 050°still stilldipping dippingsteeply steeplySE SE(the (theBBZone). Vertical movement on on this this cross crossfault faulthas has exposed exposedthe thegold goldstructure structurehere hereatataadifferent differentdepth depthlevel, level, porphyry. Where involving mostly mostly the the magnetic magnetic metadiabase in its footwall instead of the tonalite porphyry. Where intersected of breccia. These intersected in drilling, late faults such as this one consist of narrow zones of Thesefaults faults form form an an interconnecting pattern. Their interconnecting Their traces traces in in some somecases cases yield yield anomalous anomalous gold gold in in grab grab sampling, sampling, but it's not not clear whether this represents a later later mineralizing mineralizing event or mineralization mineralization remobilized remobilized from from the the Peninsula Peninsula structure. structure. SG-1O: Michigan Michigan Gold Mine Mine (Location Stop SG10: (Location map, map, Figure Figure12). 12). MPC has done only a limited amount of work so far on this gold occurrence, MFC occurrence. ItItisisincluded included as as an an optional field trip stop stop if time permits. There Thereare arevery veryfew fewoutcrops outcropsin inthe theimmediate immediatemine mine vicinity; vicinity; most most of them are metabasalts metabasalts of the the Kitchi Kitchi Formation Formation informal informal basalt basalt flow flowunit, unit, cut cutby by tonalite tonaliteporphyry porphyrysimilar similar to that at the Peninsula mine. These Theserocks rocksare are cut cut by by at at least least five five parallel, east-west, nearly vertical quartz veins. Compared Comparedto toother othergold golddeposits depositsininthis thisarea, area, the theMichigan Michigan veins veins are are very very low low in in pyrite, and represent a low sulfide sulfide hydrothermal system. There Thereisis no no particular particular correlation correlation of of gold gold with with pyrite, and and this deposit represents a case of severe nugget nugget effect. effect. These These veins veins are are famous famous for for carrying carrying free free gold, which can only be be found today today through through very verydiligent diligenteffort efforton onthe theold oldmine minedump. dump. Examination of of the the dump rocks and three core holes drilled by Callahan in the the 1980's 1980's shows shows that the theveins veinsrepresent representbrittle brittle structures. Angular are open open space space filling filling textures. Black Blacktourmaline tourmalineisisaacommon common Angular breccia breccia is is common, common, as as are vein mineral here; other exotic exotic minerals minerals found found here include include coarse coarse molybdenite, molybdenite, powellite, powellite, scheelite, scheelite, chalcopyrite chalcopyrite and a bismuth telluride. This Thismineralogy mineralogy is is typical of of the the igneous igneous assemblage often found in the roots roots of of porphyry porphyry copper copper deposits. deposits. Recorded 19th 19&Century production from from here was 856 856 ounces ounces of gold. Most Most of ofthis this appears appears to have come come from from the the No. No. 66 Shaft Shafton onthe the "main" "main"vein, vein,which whichwas wasmined minedfrom fromthe the55-foot 55-footlevel levelupwards. upwards. the property property by by MPC, MPC, nothing According to records inherited with the nothing happened at at this this mine again until the 1930's, when aa financially financially struggling strugglingsmall local stock company company deepened deepened the the No. No. 66to to 250 250feet feetand and drifted laterally east and west along the the vein. vein. The blocked-out ore was never mined except for bulk sample sample tests. tests. It is not clear exactly exactlywhere where in in the the mine the bulk samples came from. from. The Thereason reasonthat thatthe the bulk tests were done done is that the company's company's underground underground grab grab and and channel channelsamples samplesall allshowed showedextreme extreme 94 �assay variability. variability. Two Two bulk tests, tests, first first of of aa 1-ton 1-ton sample sample and and then of a 10-ton 10-ton sample, were done in Floughton by by Michigan Michigan Tech., Tech., which which determined determined aa grade grade of of approximately approximately .3 odton oz/ton Au. Au. A Houghton A third third test test was was done in 1937 at a flotation flotation mill SI! on-site Tech.. This on-site under under the the supervision supervision of Michigan Tech.. This also indicated a oziton. At Atthis this point point the the stock stock company company tried tried to to pay pay its its debts debts and move to commercial mining grade of .3 odton. by floating a new stock issue in a difficult fmancial financial and regulatory environment. The The various variousrecords records and and correspondence in MPC's files files show showthat that this this company companywas was still still frying trying to get approval to market its stock the summer of of 1941. As began, the the War War Production Production Board Board prohibited all as late as the Assoon soonas asWorld WorldWar War11 TI began, gold nothing apparently apparently ever ever happened happenedat atthe the Michigan Michigan after afterthat thatexcept exceptthe thethree threecore core gold mining in the U.S.; nothing holes by Callahan. Callahan. holes drilled drilled by 95 �References References Cited Cited Bornhorst, Bornhorst, T.J., T.J., Thorpe, Thorpe, R.I. R.I. and and Johnson, Johnson,R.C., R.C., 1998, 1998,Lead LeadIsotope Isotopestudy studyof ofveins veinsin inthe theArchean Archean Ishpeming Ishpeming(}reenstone GreenstoneBelt, Belt,Michigan: Michigan:Economic EconomicGeology, Geology,vol.93, vol.93,p.102-107. p.102-107. Cannon,W.F., W.F., and and Klasner, Klasner, J.S., J.S., 1977, 1977,Bedrock BedrockGeologic Geologicmap mapof ofthe thesouthern southernpart part of ofthe theDiorite Diorite Cannon, and Champion 7 Vz-minute quadrangles, Marquette County, Michigan: U.S. Geological and Champion 7 %-minute quadrangles, Geological Survey Survey Miscellaneous MiscellaneousInvestigations InvestigationsSeries SeriesMap Map1-1058, 1-1058,scale scale1:24,000. 1:24,000. Duskin, D.J., D.J.,1997, 1997,Peninsula Peninsula gold gold prospect: prospect: private privatereport reportfor forMinerals MineralsProcessing Processing Corporation, Corporation, Duskin, 21p. 2lp. in the the Upper Upper Peninsula: Peninsula: Lake Lake Superior Superior Port Port Cities Cities Fountain, W., 1992, 1992,Michigan Michigan gold gold mining mining in Fountain, Press, Press, l68p. l68p. Gair, Gair, J.E., and and Thaden, Thaden, R.E., R.E., 1968, 1968,Geology Geology of of the the Marquette Marquetteand and Sands SandsQuadrangles, Quadrangles, Marquette Marquette County, Tip., scale County, Michigan: Michigan: U.S. US. Geological GeologicalSurvey SurveyProfessional Professionalpaper paper 397, 397,77p., scale1:24,000. 1:24,000. Gleason, Gleason, R.J., R.J., 1986, 1986,Extended Extended Phase Phase 11Exploration Explorationof of the the Dead Dead RiverRiver- Ishpeming Ishpeming Greenstone Greenstone Belt, CallahanMining Mining Corp. Corp. private privatereport, report, 57p. 57p. Belt,Marquette Marquette County, County, Michigan: Michigan:Callahan Grunsky, E.C., 1981, 1981, No.16No. 16- An algorithm algorithm for for the classification classification of subalkalic subalkalic volcanic rocks Grunsky, using 1using the the Jensen Jensen cation cationplot: plot: Ontario OntarioGeological GeologicalSurvey SurveyMiscellaneous MiscellaneousPaper Paper100, 100,p.6 p.6165. 65. subalkalicvolcanic volcanicrocks: rocks: Ontario Ontario 1976, A new cation plot for classifying Jensen, L.S., 1976, c1assi'ing subalkalic Division 66,22p. 22p. Division of of Mines Mines Misc. Misc.Publication Publication##66, Johnson, Johnson, R.C., R.C., and and Bornhorst, Bomhorst, T.J. 1991, 1991,Archean Archean geology geology of of the the northern northern block of of the Ishpeming Ishpeming greenstone belt, Marquette County, Michigan: U.S. Geological Survey Bulletin 1904-F, greenstone belt, Marquette County, Michigan: US. Geological Survey Bulletin 1904-F, 20p. 20p. Puffet, Puffet, W.P., W.P., 1974, 1974,Geology Geologyof ofthe theNegaunee NegauneeQuadrangle, Quadrangle,Marquette MarquetteCounty, County,Michigan: Michigan:U.S. U.S Geological Geological Survey Survey Professional Professional Paper Paper 788, 788,53p., 53p.,1:24,000. 1:24,000. Van Van Hise, Hise, C.R., C.R., and and Bayley, Bayley ,W.S., W.S.,1897, 1897,The TheMarquette Marquetteironiron-bearing bearingdistrict districtof ofMichigan: Michigan:U.S. U.S. Geological 6O8p. Geological Survey SurveyMonograph Monograph28, 28,608~. Williams, G.H., 1890, 1890, The greenstone greenstone schist areas of the Menominee and Marquette regions of Michigan: 62, 2'llp. Michigan: U.S. Geological Survey Bulletin 62,241~. 96 �Examples of of Gold Gold Mineralization in the N orthern Mineralization in Northern Block of of the the Isbpeming Ishpeming Greenstonc Greenstone Belt Thomas 0. 0. Quigley and A. Mnhin Mahin and Robert Robed A. Minerals Minerals Processing Corporation, Champion MI Corporation, Champion 97 �Minerals Processing Corporation's High High Point, Point., Silver Silver Creek West, and Gold Bluff Bluff gold properties properties the in in the the northern northern m arm of of the the Ishpeming Jshpeminggreenstone greenstonebelt. belt. The field trip stops are intended to to all lie in the illudrate Host lithologies, structure, illustrate the the various various styles styles of of gold gold mineralization mineralization found found in in this thispart part of of the the belt. belt. Host mineralization, and alteration discus^ and and compared. compared. controls of mineralizatioq alteration will be discussed High Point Gold Prospect The High Point prospect was discovered diswvered by by MPC MPC during duringreconnaissance rewnnaissanceexploration explorationactivities activities from Callahan Callahan Mining Corp's working out fiom Corp's Silver SilverCreek CreekWest Westoccurrence occurrencelocated located1500 1500ft. ft.totothe thesoutheast. southeast, High grade surface mineralization at High Point is hosted by aa prominent knob knob of of intrusive intrusive felsic felsic porphyry porphy~~ escarpment of the the Dead Dead River Shear Zone Zone (DRSZ). (DRSZ). Subsequent along the topographic escaynent Subsequent exploration activities at the prospect included detailed mapping and and sampling, sampling, geochemical surveys, trenching, and diamond drilling. Figures Figures 11and 22 show show the the geology geology of of the the High High Point Point prospect. prospect. Lithology Rock types rocks, types at the High Point Point prospect prospect consist wnsist of of felsic, felsic, porphyritic porphy5ticintrusive in-ive rocks, within within aa sheared sheared of matic mafic flows and tuffacwus tuffaceous rocks and minor interfiow sequence of interflow sediments sediments corresponding correspondingto to the the Lighthouse Point Basalt of Johnson and Bomhorst Bornhorst (1991). The TheHigh High Point Point intrusive intrusiveis is aa fme fme to to medium medium grained, massive to weakly foliated foliated feldspar feldspar porphyry porphyq stock stock consisting consisting of of small small phenocrysts phenoaysts of of albite albitein in aa matrix of quartz, albite, potassium feldspar and carbonate. In thin In addition additionto to the the main main stock, stock, numerous numerous thin stringers of pporphyry o ~ h y r yof similar composition composition are are present present in the surrounding mounding volcanics. These mafic volcanic volcanic rocks consist of fine h e grained, chlorite, chlorite, sericite, sericite, and and amphibole amphibole schists, schists, and and are are probably probably altered altered basalts and related kff"wus tuffaceous rocks that have been variably sheared and deformed. Structure types defonnation related All rock t ypes at the High Point prospect have been subjected to shearing and deformation related to to the DRSZ. Mafic units exhibit steeply dipping shear related foliations striking NW-SE, parallel to the Mafk units exhibit steeply dipping shem foliations the ancillary shearing oblique obliqueto tothe themain main DRSZ DRSZtrend. trend. This shearing is main DRSZ, as well as E -- W striking ancillaq~ through 33 (see Figure 21, 2), which expose the flanking volcanic d section well exposed in backhoe trenches 11 &rough o n to the High High Point Point iintrusive. and dikes exhibit exhibit adjacent to n h i v e . The The High High Point Point Intrusive I n h i v e body and related sills and intense brittle deformation deformation manifested manifested by irregular stockwork fracturing, quartz -- carbonate carbonate veining, veining, and and brecciation. Irregular Irregularcontacts contactsof ofthese these felsic felsicunits unitsobserved observedin indrill drillcore, core,as aswell weU as as aa lack lackof ofcontinuity continuity between pporphyry units have been o r p h y ~units ~ in outcrops, drill holes, and trenches, kenches, suggest that these felsic units extensively disrupted and possibly rotated as as large competent wmpetent blocks within this portion of the DRSZ. Alteration Alteration Ubiquitous Ubiquitous carbonate carbonate alteration alteration consisting consisling of of calcite calcite and dolomite-ankerite is present throughout the the High High Point Point P Prospect, pervasive replacement replacement of of rock rock matrix, and as sheared section at the r o s p q occurring as a pmasive discrete fillings in both mafic and felsic muscovite, as discrete veins and fracture fiacture mlings felsic units. Coarse, secondary muswvite, as well as black shiny carbon mineral are wmmonly commonly associated with with carbonate carbonate veining veining in in the the High High an unknown black Point area. Examples of the carbon mineral mineralcan be readily readily found in the talus slope below the the mineralized that mineral is present present throughout throughout the the ha! this mineral outcrops of High Point intrusive, intrusive, and drilling has revealed t 98 �________ VVVVVVV vVVVVvVVVVVVvVVvVVVvyvVVtVVtvvVVvVvvVVVVVVVVVflVVVVVVVVVVV V V V V 9 V V V V V 9 V V V V V V V V V V VV V V V V V V V V V V V V V V V V V V V V V V V V V V V V V V V V V V V VVVVVVVVVV VV VVVWVVVVVVVVVVVVVVVVVVVVVVVVVVVVWVVVVVVVVVVVVVVVVVVVVVVVVVVVV VVVVVVVVV VVVVVVVVVVVVVVVVVWWWVVGVVV v VVVVVVVVVVVVVV V VVVVVV MINERALS PROCESSINGv' VcVVVVVVVV VVVVVVVVVVVVVVV74VVVVVVVV 9VVVVVVVVVVVVVVVVVVVVVVVV 7VVVVVVVVVV VVVVV CORPORATION Geology of the High Point Prospect ala t'ia eei.Iila Pi 11aM Rnjn 4n %0 — .'J — dd tone ci shearing. Strike and dip of inflation. 0 ¼0 Stzika end dip *1 .i or joint. VWVVVVVVVVVVVVVVVVVVVVVVVVVVVVVVVVVVWVVVVVVVVVVVVWVVVVWVVVVVVV VVVVI V cv V V V V V V V V V V V V V V V V V V V V 9 V V V V V V V V V V V V V V V V V WV V V V V V V V V V V V V V WV 49 V V V ' V V V flY V V V V V V V V V V V VV V V V V V V V V V V cv c V V V iii VVVVr '' ea',,T, V igure narge VVVVVVVVVVVVVVV EVVVV 4VVVV VVV V r' I VVVVVVVVVVVVVvVVVVVVTwwVVVVVVVVVV VVVVVVVVVVVVVVVVVV VVVVVVVVVV - Thvv44 cv?,y1j.t,t÷ V VVV - 'VWVWVV&V \r.VVV*1 \74 ttt 4 V + 4 4 + % i " 4 4 V + + 4 4 4, • c + +* Hiab Point Intrusive Porpbyiy, Slice to madimu pained, reddish brown porphyriuo rock p,mpo.ed of 1 to 5 = sibite pbgiooryat. in a matrix of elba.. K—feitpar. a + * t '+ . VVVV VVVVVVVVVVVV VVV VVWVVVVVVV VVVVVVVVVVVV VV VVVVVVVVVV VVVVVVVVVVVV3'VV VVVVVVVVVV VVVVVV 3VVVVw. 9VVVVVVVVV + + * -€ - VVVWiVtI4 VVVSq4/VV9tN44 IVVVV4'W4iVV VVVVVVVVVV 9 VVVVVrVnVVVVV VVVVVVVVVV + VVVVVVVVVVVV t 9 1 4\VVWVWVV9VVVVVVWVVVVVV tt"VJPV?VVVVVVVVVWVVVVVVVVVVV 'V9JryV VV"?.flVV9VVVI "VW VVV V V V V 9' Fgpa_r V quarts, otuacovite and carbonat.. Parnitvely franturod, end veined with quartz, ten-can dolornito. ankorita. end en action black carbon minaret. liii j4j4j }li.h Point Intrusive Bericit. end cerbonata alias-ed porph1ry, cut by bieguler etockwork Veina and mesas of gray quartz. iron carbonates, minor pyrita, minor guiana, bismuth tafluride., and gold. VVVV VVV VVWVVV VVr,4VV.W VVVVVVVVVV rVVVV)_J,tc%.VV 44 VVVVVVVV t 4vvvc-vint VVr%nV gVVVVVVVVV VVt VVVVVVVVV VVWVVVVVVVV VVVVVVVVVV * 'VVVVV VVVt VVVVVV' VVVVVVVVV VVVVVVVVVV VVVV$t.'V-M, VVVVV VVVVVVVVVV VVVVVVVVVV flVVVVVV-t -VtflVWttt$VVV V%VPVVVWVVV VVVVVVVVVV VVVVVSVq VVVVVVVVVV t'Q.b7J VØ V VVV V 499 Vt V VVvVV-yg.VVVlV LVuvv',aVareVvVVVVVVVVVV VVVVVVVVVV 4 tVtV4VV-, VVVVVV 44 V' t.%fl Vflfi-VV Fj.+*9 + VVVVVVW V V; t$VVVY,VVVVV4V . tV,r-VVVVVV%V V uVVVVVVVVVV9V VVVVWVVVVVVVVW VVVVVVtVVVVVVV tI4SVVVVVVVVVV.aL \ViVVVVVVVVI V'VVVVVVVV \VLVVVVVfl VVV'VW WVVVVVVVVV Id WVVVVVVVVV VVT/V V 4LVVV V V VV'V VVVVVV VVVVVVV Ii V V - - 4 9 ÷ 9+ 9 -r 9 VVVVV + + -4 - wVr' -. - t - 'LV'kVV VV 1 t - - + 9 4 4 V4kVJV 'tJLVvN V VVV 4 9 V / tV VVV/ V '%VLVVVV V VVVVVVVVVVVVVVVVVV T''VVVVVVVVV1 VVVVVVVV' VVVVVVVVVV N o 25 - rVV -, V VVVVVVVV V V V V V V 44 V V V VV VVVVVVV V V V V V V V V VVV 50 Scala In S'bet Basalt. Indesita EJ - Fine grelnad chlorite, earlclt carbonate ecbi.te. Massive to roustad end fractured with atockwork carbonate — carbon mineral yams and dissemlatatad pyrtte where .haared, Locaily containing gray quarts veining ecd gold inlnarellsauon, Sequence contains minor mntarfior shexty. pyritln sediments- I Figure Figure 1. 1. Geology of High High Point Point �0 0 '4 + 4 4 4 4 4 4-4-4 MPC Trench in ppb. 7 4+4 444 1 + + ÷ + -1- -4- ± +4- —E 'Intt. 4 4 4 ——3— 4. ± Gold Values (ppb) CORPORATION Oda\E.ctMc Psat Geel 0 25 0 IT I Scale in Feet 0 Channel Chip and Trench Samples Figure 2. Detailed Geology of High Point 4 44 tt* 4+4444 4 44444444 * 4 rTTI Channel sample with gold value Basalt, Andesite 4 4 +t.tt.t-,-ttttt4 444 4-4+4 4 4 T:] High Point Intrusive IThrfl vfl C 4+44 Trench 1 50 MINERALS PROCESSING __ �flanking volcanic section as well. Within Withinthe themineralized mineralizedportion portionof ofthe theHigh HighPoint Pointintnisive, intmsive,microprobe microprobe analysis has shown that zoned zoned dolomite-ankerite dolomite-ankeriteis isintimately intimatelyintergrown intergrownwith with barium bariumbearing bearingK-feldspar K-feldspar Tourmaline is also locally present in quartz veins, in the matrix matrix of brecciated porphyry, and muscovite. Tourmaline and intergrown intergrown with chlorite chlorite along along fracture ffacture surfaces surfacesin in sheared sheared volcanic volcanicrocks. rocks. Mineralization Mineralization gray Surface mineralization at High Point is confmed to the porphyry, and consists of irregular gray quartz veining in altered porphyry porphyry on on the the southeast southeast side sideof ofthe themain mainknob. knob. Here channel chip chip sampling sampling of of exposed exposed outcrops outcrops (Chip (Chip Samples Samples A, A, B, B, and and C) C) returned retumed significant significant gold gold values values including 28 ft. &. of of .09 .09 ozlton, .35 oz/ton odton including including 4 ft of 1.25 1.25 ozlton odton (Figure 2). The Themineralized mineralized quartz quartz from ffom these odton, and 14 14 ft. of .35 exposures gay, cut cut by by iron ironcarbonate carbonateveinlets, veinlets, and andcontains containssmall smallamounts amountsof ofpyrite, pyite, chalcopyrite, chalcopyrite, exposures is dark dark gray, galena, sphalerite, galenq sphalerite, and electrum electnun as as well well as as an an exotic exoticsuite suiteof of bismuth bismuth tellurides, tellurides,lead leadbismuth bismuth tellurides, tellurides, and an unknown lead-bismuth-silver sulfide. The Thegeometry geometryof ofthis thismineralized mineralizedzone zonehas has not not yet yet been been defined, and defmed, although although its its extent extent has has been been partially patially confined confmedby by trenching ~~enching andwide widespaced spaceddrilling. drilling. Silver Creek Creek West Fiver Silver Creek West is a gold occurrence variably altered and and foliated foliated mafic mafic rocks. rocks. In occmnce within variably In 1988 1988 million tons @O.O37optAu @0.037optAu for Silver I. 1 &ion Silver Creek Callahan Mining Corporation calculated a resource of 1.1 controls. Surface West but never exploited it because of unresolved concerns over gold continuity and coneols. Surface trenching exposes exposes gold mineralization eenching mineralidon in in ductile ductile sheared sheared and and carbonate-chlorite-sericite-pyrite carbonate-chlonte-sericite-pyritealtered altered basalt near the margin of a felsic porphyry. In Indrill drillhole hole intersections, intersection&mineralization mineralizationappears appears to to be stratabound seatabound within 170 170 foot foot section section of ofmoderately moderatelycarbonate carbonatealtered, altered,massive massivemedium mediumgrained grainedmafics. mafics, Mineralization in both trenches eenches and and drill drill core core will be be observed observed at at this this stop. stop.The Thegeneral general geology geologyof ofSilver Silver Creek West is 3. is shown shown in in Figure Figure3. Lithology The lithologies in the immediate vicinity of the Silver Creek Creek West West prospect prospect consist consist of of aa number number of of generally generally northwest striking, striking steeply dipping dipping units, largely largely of the Archean Lighthouse Lighthouse Point Basalt (Johnson and Bornhorst, largeexpanse expanseof offine finegrained, graind Bomhorst, 1991). 1991).To Tothe thenortheast northeastof ofthe theSCW SCWprospect prospectisisaalarge pillowed basalt. Nearer Nearerto tothe theprospect prospectoccurs occursaamedium mediumto tofine finegrained grainedequigranular equigranularchiorite-albitechlorite-albitecarbonate carbonate unit, variously interpreted interpreted as as an ophitic ophitic basalt, aa sheared sheared carbonated carbonatedbasalt, basalt, and and aa hypabyssal hypabysd mafic pyrrhotite and hosts gold mafic intrusive intrusive or sill. The Theunit unit isisgenerally generally massive, massive, contains contains significant significant pynhotite mineralization mineralization at depth in drill core. The Thenext nextunit unit to to the the southwest southwestis is aa narrow narrow band of of chlorite-albitechlorite-albitephyllite interpreted interpreted as as aa ductile ductile sheared shearedbasalt. basalt. This unit hosts hosts gold mineralization mineralization sericite-carbonatephyllite trenches. This exposed in surface trenches. Thisbasalt basalt is is bounded bounded to to the the southwest southwest along along the cliff cliff face face by aa rhyodacite rhyodacite porphyry which which consists consists of of quartz, q w feldspar, feldspar,and andchlorite chloritephenocrysts phenocrystsin in aa felsic felsicgroundmass. groundmass.Drill Bill intercepts show an additional sequence sequence of chiorite-albite-sericite chlonte-albite-sericite phyllite and quartz-feldspar quartz-feldspar intrusive intrusive to the southwest. In Inatatleast least one onehole holethe the latter latter felsic felsic is is in in fault fault contact contact with Proterozoic Proterozoic sediments sediments which have have been down-thrown dom-thrown to form form the the basin basin to to the the southwest. southwest. 101 �_ __ ___ ____ VVVVVVVVVVV VVVVVVVVVP VVVVVVVV VVVVVV VVVV MINERALS PROCESSING CORPORATION --vvwVvvVvVt VVVnVflVVV vVVVVVVVVVVV VVVVVVVVVVVVV. uqVVVVVVVVVVVVV VVVV VV VV Vt Vt Vt V VV 1 —— V V V V V V V Vt PVV VVV % V V V V VVV VPVVV VVVV Silver Creek West — a'—.- 1, 1VVVVVVVV VVVVVVVPV 'VVVVVVVV Dt V V V V V V V V V V V V V V V 'VVVVVVVVVVVVVV V V V V V V V V V V V V V V V V! V V V V V V V V V V V V V V rt' °o°bZj V V V V V VP VVV V VY V V Geology — ni-la VVVVVVVVVVVVVW%R%i - VVVVVVVVVVVVV0 p V V V V V V V V V,S V V V V V V VVVVVVVV•&. qa4VV LV V VV V Vt VS%E VVVVV VVVVVV9V '1 r VVVVV Me Reversely polarized 0 a N441 Sedimantan rock. S*cii4 Undifferentiated. Berega Group V÷A FeolnaiRocks I Mafic Volcanic Rook. lv • Hvnabvsai Vafic Intnstve Rocks • Enterwediate Vo4genãc ggçp SedimoctmHoon • — Fault ihowing downthron aide Outcrop Shearing Trench — 200 0 Figure 3. 3. Geology Geology of of Silver Silver Creek Creek West West Figure 200 Scale in feet 400 V Vi �Structure and mineralization mineralization At the surface, gold mineralization exposed exposed in trenches by Callahan occurs within a ductile ductile sheared mafic mafic volcanic volcanic near the margin of of aa felsic felsic porphyry. This Thisshearing shearingstrikes strikes300° 300' and andmineralization mineralization is is considered C-type replacement. In Incontrast contrastto tosurface surfaceexposures, exposures,mineralized mineralizedintervals intervalsin in drill drill core core are are in in an unfbliated, weakly altered altered medium medium grained grained mafic maficunit; unit; there thereisislittle littleresemblance resemblanceto to mineralization mineralizationin in unfoliated, weakly depth to to the the easthortheast east/northeast from from the sheared basalt. Gold-bearing intervals that in drill intercepts occur at depth the trenched intervals intervals do not project project upwards upwards along alongobvious obviousstructural structuralplanes planesto tothe thesurface surfaceworkings. workings. The exact controls to the mineralization at at depth depth have havenot not been beenproved. proved. Intersection lineations lineations of of plunge down to to the east and offer offer one possible explanation for joining joining surface various structural features plunge and drill-hole gold (Johnson, 1991). MF'C has hasshown shownthat thatanomalous anomalousmineralization mineralization fJohnson 19911Limited Limitedwork workby bvMPC . occurs in outcrop outcrop to to the the east eastof o fthe thehigh gradetrenches trenchesatatthe theup-dip up-dip(along (alongSSlfoliation) projection of of the the occurs high grade 1 foliation) projection mineralized drill core mineralized core intervals, intervals, suggesting suggesting that the trench and and drill drill core core intercepts interceptsare are not connected. connected. Alteration The mineralized zone The mineralized zone is is associated associated with with weakly weakly disseminated disseminatedcalcite+chlorite+sericite+pyrite calcite+chlorite+sericite+pyrite alteration. Locally, Locally,minor minorFe-carbonate Fe-carbonateisisobserved observedatatsurface surfaceand andin infelsic felsicunits units encountered encountered in in drilling. drilling. Additionally, Additionally, Callahan Callahan geologists geologists identified identified an an early early epidote-pyrrhotite epidote-pynhotite(spilite) (spilite)event eventin in the the basalts. basalts. Gold Gold Bluff BluffProspect Prospect Gold Bluff Bluff is one of Minerals Processing Corporation's Corporation's active gold properties properties (see (see Figure Figure4). 4). Gold Bluff trending, 1000 foot wide shear zone in mafic mafic volcanics. volcanics. A A 100 to to 200 foot Bluff is is located located within a 3000 300' trending, wide wide felsic felsic porphyry porphyry (the (the GB GBporphyry) porphyry) intrudes intrudesthe theshear shearzone. zone.Within Withinthe thebounding boundingshear shearoccur occureasteastwest and northeast striking mineralized subsidiary shear zones. zones. Outcrop Outcropsampling sampling routinely yields yields gold in the Oppm range. range. Trenching the lppm lppmto to1lOppm 1998 intersected intersected significant significant widths of disseminated Trenching and drilling drilling in 1998 low low grade gold gold mineralization mineralization the GB porphyry and higher grade gold in mafic host rock. Mineralization in both mafic felsic hosts hosts in in different different structural structural orientations orientations will will be be seen seen at at Gold Gold Bluff. Bluff. mafic and felsic Lithology Three lithologies are found at Gold Gold Bluff: Bluff:fine-grained fine-grained mafic mafic volcanic; volcanic; medium medium to tocoarse-grained coarse-grained mafic volcanic, referred to as aa gabbro; volcanic, referred gabbro; and andfelsic felsicporphyry. porphyry. The The mafic maficunits units are aremetamorphosed metamorphosed to to facies and both both can be massive massive to to strongly strongly foliated. foliated. They greenschist fades They belong belong to to Lighthouse Lighthouse Point Point Basalt Basalt as as described by by Johnson and Bonthorst (1991). The felsic unit described Johnson and Bornhorst (1991). unit isis aarhyodacite rhyodacite porphyry porphyry interpreted interpreted as as intrusive. Where unit that that divides the the two two mafic mafic units, units, itit is is dubbed dubbed the the GB intrusive. Where it appears appears to be aa continuous continuous unit throughout the theproperty. property. Contacts porphyry. Smaller Smallerfelsic felsic dikes dikes are are also observed in various orientations throughout Contacts strike northwest and have have steep dips. A Areversely reverselypolarized polarized dike dikeof ofKeeweenawan Keeweenawan age age is is interpreted interpreted from from data to lie just just to the north of the outcropping rocks. rocks. The magnetic data The only only other other unit unit of of significance significance in in the the area is the Reany Lake Pyroclastic (Johnson (Johnson and and Bomhorst, Bomhorst, 1991) which which occurs occursjust just off off the Gold Bluff property to the the north and and west west in in association association with with gabbro gabbro flows. flows. 103 �104 Bluff Gold of Geology — .tgnlflcnt I thoy Figure 4. soda- tat wits. — .siclt. flax. Isyaxat a .aanta acp.alUon. .od.duo to basaitia pobabi. of rook mle4 and The.. u4—eet.d rse,. patoad. o.tdf to Ito. Rnnko Vnlnin MaNe Locally 33 Sec 28 Sec — — foto gr4. inn to coax.. iocr.iln .44 sonata. &aiztt.). (t. t.rbcats S44h .lnd .04 1.t.d broesalad. fr.osr.d. locally qwtL and/ot Mltpc or pb.toetyM. otth pakUo to SqWjnmiIar bO4a th04o .04 — dfr. rflo]a to t.Itth rot to wtittt nedja to vest jeus. Rocks Intrusive Feisic palnb.d Vfl 0 4 Ir' 4 0 0 • 44 + 4 V H '-•t• 01' 4t ciw g- flçf -, V V '7 VVVVV V V S÷ '4 :÷. V '-——V c'flu V — :rn7t; a-+-.. -. ?bfl ?V fl) t;vytV - • - w 4 VV +, 4 VVV o' -t 4 4 4 47 4÷ — 4 fl3 V 01 •vv-r 4_, , .4_ .4, 4__4 t hJt& + • 0 1çJ •lC. t9-ç, VV +, 4 ¶VV1.V • V9VVfl' C VW C" 1'- - + VVVVV C) flt * 4 2 4 vVVW VVV9? q feet in 300 200 .—Iy 9U Scale 100 4Sa 0 100 —I 0*t4M. GEOLOGY Project Bluff Gold Corporation Processing Minerals —. S WE N �Structure The orientation orientation of of brittle brittle and and ductile ductile shear shear structures, structure&felsic felsicporphyries, porphyries, and and quartz quartzveins veinsisis with a system of of conjugate shears shears that that control control gold gold mineralization, mineralization. Bounding geometrically consistent with shear features, mostly penetrative foliation in mafic rocks rocks and along felsic contacts, contacts, strike strike 300' 300°. . Within this, subsidiary stnctures structures and a variety of of mineralization mineralization styles are are observed. observed. For For example, example, the the GB GB trends 3200 and appears porphyry m d s 320' appears to occupy an oblique shear shear position (probably R-type Reidel). Mineralization 300 °and and is C-type Mineralization in Trench 5 and DDH GB-3, and along felsic contacts, strikes 300' replacement veining. R'-type R'-typeshears shearsare arepresent presentas asnortheast northeaststriking strikingductile ductilemicro-shears micro-shears and and as as numerous numerous mineralized quartz veins. Numerous Numerousductile ductileshears shearsand and minor minor felsic felsic porphyries porphyries that that strike strike 080° 080' to 1000 100' or S-type S-type structures. structures. may be either either P or quartz-carbonate-tounnaline veins White quartz-carbonate-towmaline veins with with fibrous fibrousstructure structnreperpendicular peqendicular to to the the vein vein walls walls are are interpreted features. These intqreted as extensional fmtures. Thesetypically typically dip dip in in the the 30° 30' to to40° 40' range rangeand andindicate indicateaahigh highangle angle component veins. Gray Gray quartz quartz veins veins are are often often mineralized, component to the shearing event responsible for these veins. defonned, deformed, and andcross-cut cross-cutby bywhite whitequartz quartzveins veinsindicating indicatingmultiple multipleshearing shearingand andvein veindeposition depositionevents. events. Alteration Alteration A zoned carbonate alterationhalo halo occurs occursat atGold GoldBid. Bluff Distal Distalalteration alterationin in the the mafic ma& volcanics consists cousists of of disseminated disseminated calcite calciteand and weak weak Fe-carbonate, Fe-carbonate, (ankerite-dolomite). (ankerite-dolomite). As As the the GB GB porphyry porphyryisis approached, Fe-carbonate approached, Fe-carbonate increases increases and can can be pervasive to the point point of of flooding floodingand and the theassemblage assemblage sericite+white quartz+pyrit&tourmaline quartz+pyrite+tounnaline appears, sencitewhite appears, largely largely in in the the felsics. felsics. Lithologic Lithologic textures texturesare are generally generally intact. Within Withinthe theGB GBporphyry poxphyryaazone zoneof ofstrong saongsericite+pyrite+Fe-carbonate sericite+pyrite+Fecarbonate occurs occurswith with porphyritic porphyritic sometimes completely completely replaced by fine textures sometimes fine grained gained sericite. sericite. Mineralization Mineralization occurs in all three lithologies lithologies and consists consists of quartz+gold+pyrite+Ag&Bi-tellurides. qm?z+gold+pyrite+Ag&Bi-tellurides. mineralization (i.e., In the metabasalts C-type replacement mineralkalion (i.e., highly silicified and sulfidized sulfidized zones wnes with with is generally generally confined confined to thin thin ductile ductile shears shears at at or or narrow foliation-parallel foliation-parallel quartz quartz veins, lenses lenses and pods) is proximal proximal to to felsic felsic contacts. contacts.Similar, Similar, although althoughoften oftenhigher higher grade, grade, mineralization minerahation occurs occursat atthe thegabbro/felsic gabbro/felsic contact. Significant SignificantC-type C-typevein vein mineralization mineralizationnot associated associated with a felsic contact also occurs within sheared gabbro south of the GB porphyry (S.7'@O. 188opt optAu Auand and17'@0.077 l7'@0.077 opt sheaxed (S.T@O. 188 opt including including 7.5'@0.1480pt w/VG). wNG). 7.5'@0.l4Sopt In In the GB porphyry, mineralization mineraIizatiou is is found found in in quartz quartz vein vein stockwork stockwork and and tends tends to to be be associated associated with disseminated pyrite and strong alteration. Gold-bearing Gold-bearing veins veins are gray g a y colored compared compared to to barren veins, although although white whitequartz quartzveins veinsare arean animportant importantindicator. indicator. One ggray ay white quartz-carbonate-tourmaline veins, quartz vein 0.4 feet wide assays 20-50 opt Au and has yielded impressive impressive visible visible gold gold specimens. Recent Recent drilling in the GB porphyry by MF' MPC significant m mineralization (224'@0.Ol8opt including C intersected sigificant i n e r h t i o n (224'@0.018opt including 1l'@O,l78 and 3'@0.l22 3'@0.122 opt). opt). ll'@O.178 105 �References R.C., 1991. proposal: Stage Johnson, KC., 1991. Silver Creek West drilling proposal: Stage III. 111. Western Western Mining CorporationlCallahan CorporatiodCallahanMining Corporation Corporation unpublished unpublished report, report, February, F e b m ~1991. 1991. , R.C., and Bodorst, Bornhorst, T.J., Johnson, R.C., T.J., 1991, 1991, Archean geology geology of of the northern northern block of of the Ishpeming Greenstone belt, Marquette Marquette County, County, Michigan: Michigan:U.S. U.S.Geological GeologicalSurvey SurveyBulletin Bulletin1904-F, 1904-F,2Op. 20p. 106 �Field Field Trip Trip33 Tilden Marquette Iron Tilden and and Empire EmpireMines Mines of the Marquette Iron Range, Range,Michigan Michigan Leaders: Leaders:G.W. G.W.Scott, Scott, P.M. P.M. Nordstrom Nordstrom and andH.M. H.M. Lukey Lukey 107 �Setting of of the the Tilden Tilden and and Empire Empire Mines, Michigan Michigan Geologic Setting Theodore Theodore J. Bornhorst, Bornhorst, Department Department of of Geological Geological Engineering Engineering and and Sciences, Sciences, Michigan Michigan Technological Technological University, University, Houghton, Houghton, MI MI 49931 4993 1 Introduction Introduction The Tilden and Empire Mines are located in the Marquette Iron hon Range Range of Michigan's Michigan's Upper Upper Peninsula (Figure (Figure 1). 1). Mining Miningbegan beganatatthe theEmpire EmpireMine Minein in 1963 1963and and at at the the Tilden TildenMine Minein in 1974. This This is is the the first first Institute Institute of of Lake Lake Superior Superior Geology Geology field trip to either of these iron mines. The TheMarquette Marquette hon IronRange Rangehas hashad had aalong long and and varied varied mining history (Boyum, (Boyum, 1988). 1988). reserves are are sufficient sufficient to to sustain iron mining Iron mining began in the mid-1800's and current reserves until at at least least 2030. 2030. Stratigraphic Setting Stratigraphic Marquette Marquette Range Range Supergroup Supergroup The Tilden and Empire Mines produce iron ores from the Early Proterozoic rocks of the Marquette Range Supergroup (Figure 2). The The Marquette Range Supergroup consists of sedimentary sedimentary rocks with minor minor amounts amounts of cf volcanic volcanic rocks and is is subdivided subdivided into into three three groups: groups: to youngest. youngest. The Chocolay, Menominee and Baraga Groups, from oldest to The rocks rocks of of the the on older older Archean Archean basement. basement. Marquette Range Supergroup were unconformably deposited on are separated separated by by minor minor angular angular The three groups of the Marquette Range Supergroup are and informal informal units. units. The unconformities. The The groups groups are are subdivided subdivided into formal formations and The from the base upward, of conglomerate Chocolay Group Group consists, consists, from conglomerate (Enchantment (EnchantmentLake Lake Formation), quartzite quartzite (Mesnard (Mesnard Quartzite), Quartzite), dolomite dolomite (Kona (Kona Dolomite), Dolomite),and and slate slate (Wewe (Wewe Slate). Slate). The TheMenominee MenomineeGroup Groupunconformably unconformably overlies overlies the the Chocolay Chocolay Group Group and and consists, consists, from the base upwards, upwards, of local local conglomerate, conglomerate, quartzite quartzite (Ajibik (Ajibik Quartzite), Quartzite),slate slate (Siamo (Siamo Slate), and iron formation (Neguanee Iron IronFormation). Formation). The Baraga Group is is the the youngest youngest of of Menominee Group. Group. The the three groups and unconformably overlies the Menominee The Baraga Baraga Group Group includes a variety of stratigraphic units. In In the the Marquette Marquette area area itit consists, consists,from from the the base base upwards, of quartzite quartzite (Goodrich (Goodrich Quartzite), Quartzite), slate slate (Lower (Lower Slate Slate of the the Michigamme Formation), iron formation (Greenwood Iron hon Formation), Formation), Formation), mafic pyroclastics (Clarksburg (Clarksburg Volcanics), Volcanics), iron formation, formation, slate slate (Upper (Upper Slate Slate of the Michigamme Michigamme Formation), Formation),and and iron iron formation (Bijiki Iron Formation). hon Ironore orehas has been been mined mined from from iron formations within the Menominee and Baraga Groups. However, However, most most production production has has come come from from the the Negaunee Negaunee hon Formation Iron Formation of of the the Menominee Menominee Group, Group, including the Tilden and Empire Mines. Diabase Dikes Dikes and and Sills Sills stratified units of the Marquette The stratified Marquette Range Supergroup Supergroup are commonly commonly intruded intruded by Early Early the form form of of dikes dikes and and sills. sills. Early Proterozoic diabase (metamorphosed) in the Early Proterozoic Proterozoic diabase dikes and sills sills are particularly particularly common in vicinity of the Tilden and and Empire Empire Mines. Mines. Volcanics of of the the Baraga Baraga Group, Group, 10 to to 20 20 km km Diabase is also associated with the Clarksburg Volcanics 108 �% LAKE SUPERIOR srow or EXPLANATION EXPLANATION Paleozoic Paleozoic Undifferentiated Paleozoic Undifferentiated Paleozoic Rocks Rocks Keweenawan Keweenawan UndifferentiatedKeweenawan Keweenawan Rocks Rocks [----1 Undifferentiated Early Proterozoic Early_Proterozoic ji Undifferentiated UndifferentiitedEarly EarlyProterozoic ProterozoicRocks Rocks Archean Archean Undifferentiated Undifferentiated Archean Rocks Rocks I I Marquette iron Figure 1: Geologic setting of the Marquette Figure iron range. range 109 �Explanation Explanation Archean Proterozoic Proterozoic Middle Proterozoic Early Proterozoic Archean Metadiabase Undifferentiated Keweenawan sandstone ItLIMI Undifferentiated Keweenawan sandstone Metadlabase I and diabase diabase Marquette Range Supergroup Marquette Range Supergroup Baraga Group Group Baraga rc::.i Undifferentiated Undifferentiated Menominee Group Group Menornmee Negaunee Iron Negaunee Iron Formation Formation Siate I>'">I Siamo Slate Quartzite LL.Jj.JI Ajibik Quartzite Chocolay Group Group Chocolay Undifferentiated Undifferentiated 1++1 0 I !1 Generalized geology in vicinity Figure 2: Generalized vicinity of the Tilden Tilden and and Empire Empire Mines. Mines. 110 �west of the mines. Several Severalgeologists geologists have have suggested suggested that Early Proterozoic Proterozoic diabase diabase intrusions intrusions throughout the Marquette region are the same age as the Clarksburg Clarksburg Volcanics Volcanics of of younger than than the theNegaunee NegauneeIron hon Formation. Formation. However, some of the the Baraga Group and younger diabase sills at the Tilden and Empire Mines may have been lava flows (Scott (Scott and Lukey, Lukey, this volume). This Thisinterpretation suggestsmultiple ages of Early Proterozoic Proterozoic diabase diabase and interpretation suggests multiple ages of deposition of of iron iron formation. formation. The Hemlock Formation, mafic magmatism during the time of Formation, south of the Marquette area in the Iron hon Mountain area, consists of mafic volcanics that is (Morey, 1996). This supports correlative with the Menominee Group (Morey, supports the interpretation interpretation of mafic magmatism during the Menominee Group in the Marquette area. metamorphosed) UKC> dikes also {UUL LLLCLUWL~LLUXAI, uu cut LUL the rocks rocks diabas~(not Later Middle Proterozoic Proterozoic Keweenawan diabase and cut cut the the Negaunee Negaunee Iron hon Formation at the Tilden and of the Marquette Range Supergroup and Empire Empire Mines. Mines. Negaunee Fonnation Negaunee Iron Formation The Neguanee hon Iron Formation Formation consists consists of of aa variety of iron rich rocks in the Marquette Marquette area (Figure 2). The Themajor major types types of of iron iron formation formation are are carbonate iron-formation (iron carbonate carbonate and chert with minor magnetite), oxide iron formation (hematite or magnetite and chert), magnetite-banded iron formation (laminated magnetite and chert), hematite banded iron formation (laminated hematite and chert), silicate iron formation (iron silicate minerals formation minerals and types (Gair, (Gair, 1975). The TheNegaunee NegauneeIron hon Formation is chert) and combinations of these types described in detail by Scott and Lukey (this volume), Nordstrom (this volume), and Gair (1975). The Theorigin originof of the the iron iron minerals minerals in in the the Negaunee hon Iron Formation Formation isis aa complex complex processes. combination of primary sedimentary depositional, diagenetic, and metamorphic processes. The The maximum maximum thickness thickness of of the the Negaunee Negaunee Iron Formation is about about 1150 1150meters, meters, although although to assess assess (Gair, (Gair, 1975). 1975). The Negaunee hon folds and faults make thickness difficult to Iron Formation is thickest thickest in in vicinity vicinity of the Tilden and Empire Mines where is occurs occurs in in the the nose nose km across across (Figure (Figure2). 2). of a regional west plunging plunging syneline synclineabout about 66 km Age of the Marquette Range Supergroup Morey (1996) has provided a stratigraphic synthesis of the Marquette Range Supergroup. Supergroup. Supergroup is Although the age of the onset of sedimentation of the Marquette Range Supergroup 2,219+1-4Ma. Ma. The age uncertain, he has suggested that the Chocolay Group is younger than 2,219+/-4 age the Menominee Menominee Group Groupisis 1,910+/-10 1,910+/-10Ma. Ma. Deposition of the of volcanic rocks correlated with the Baraga Group Baraga Group ended endedby by1,852+1-6 1,852+/-6Ma. Ma. Depositional and and Tectonic Tectonic Setting Setting The Marquette Range Supergroup is interpreted to have been deposited in several stages (Morey, 1996; Schulz and and others, others, 1993). 1993). The Thesediments sedimentsof of the the Chocolay Chocolay Group Groupwere were deposited or intrarift intrarift stage stage (Figure (Figure3). 3). The sediments deposited during a late intracratonic or sediments of the Menominee Group were deposited on a passive continental margin in normal listric fault bounded rift basins (Cambray, 1991). The The Negaunee Negaunee hon Iron Formation Formation mined mined at at the the Tilden Tildenand and 111 �Late lntracratonic Intracratonic or Intrarift lntrarift Stage Stage Chocolay Group Archean Basement Basement Rift Stage Rift Stage Menominee Group Group Spreading Spreading Center Archean Basement Foredeep Foredeep Basin Basin Stage Stage Archean Basement Continent-arc Continent-arc Collision matic Oceanic Crust Figure Figure 3: Depositional Depositional and and tectonic tectonic setting of the Marquette Marquette Range Range Supergroup Supergroup (modified (modified from from Morey, Morey, 1996). 1996). 112 �Empire Mines was deposited deposited during this stage stage and some some faults faults at the mines may may be be related related to to this stage (Scott and Lukey, this volume). Elsewhere, Elsewhere, and and perhaps perhaps in in the Marquette Marquette area area too, too, tholeiitic basaltic basaltic magmatism also also accumulated in these rift basins. The Negaunee Negaunee Iron Iron Formation basin(s) are are located along the Great Great Lakes tectonic tectonic zone, zone, aa late late Formation depositional depositional basin(s) others, 1980). Passive margin deposition transitioned into Archean suture zone (Sims and others, deposition deposition of sediments sediments and and minor volcanic rocks in a foredeep foredeep basin stage stage that that formed formed as as aa result of Penokean collision collision of the Wisconsin Wisconsin magmatic arc with the edge edge of the the continent continent (Morey, 1996). The The continent-arc continent-arcsuture suture zone zone approximately approximately follows the MichiganWisconsin border. The TheBaraga BaragaGroup Groupwas was mostly mostly deposited deposited during during the foredeep foredeep stage stage as as turbdites. turbdites. The Marquette Range t h s t belt of the 1850 1850Ma Ma Penokean Penokean Range Supergroup Supergroup is is within the fold and thrust orogen (Sims, 1996). The The Tilden Tilden and and Empire Empire Mines are located on the south limb of the Marquette Synclinorium, an east-west trending, west plunging syncline that is about 6 km km across and 55 lun km long long parallel parallel to tothe thefold foldaxis. axis. The synclinorium, like likethe theNegaunee NegauneeIron hon Formation depositional basin(s), may have been controlled by the Archean Great Lakes tectonic zone. The Archean structures structures were subsequently folded during The iron iron formation formationand and Archean the Penokean Orogeny. The The Penokean Penokean orogenic orogenic event produced complex folds and faults and greenschist facies metamorphsim metamorphsim of the rocks at the Tilden and Empire Mines Acknowidegments Acknowldegments for comments comments on on aa version versionof ofthis thispaper. paper. Shannon Bair I thank Rod Johnson and Glenn Scott for and Chris Pascoe Pascoe helped helped with with drafting draftingof of the the figures. figures. References References Boyum, B.H., 1988, 1988, Marquette Marquette Mineral District of Michigan Mining History and Geology: Geology: Meeting, Institute on Lake Lake Superior Superior Geology Geology Proceedings, Proceedings, 34th 3 4 Annual Annual ~ Meeting, Marquette, Marquette, MI, MI, v. v. 34, part 2, p. B1-B33. Bl-B33. Cambray, F.W., Mancusco, J.J., J.J., and Slitor, W., 1991, 1991, Detachment faulting and the origin of asymmetric depositional depositional pattern of the Marquette trough (abstract): Institute on Lake Clalre, WI, v. 37, part 1, Superior Superior Geology Geology Proceedings, Proceedings, 337th7 Annual Annual ~ Meeting, Eau Claire, 1, p. 17-18. 17-18. Gair, J.E., J.E., 1975, 1975, Bedrock Bedrock geology and ore deposits of the Palmer Quadrangle, Quadrangle, Marquette Marquette County, Michigan: U.S. U S Geological Survey Professional Paper 769, l59p. 159p. Continental Margin Assemblage: Morey, G.B., 1996, Assemblage: 1996, Early Early Proterozoic Proterozoic Penokean Orogen - Continental U.S. U S . Geological Geological Survey Survey Professional Professional Paper Paper 1556, 1556,p. p. 30-44. 30-44. Sims, P.K., Card, K.D., Morey, G.B., and Peterman, Z.E., Z.E., 1980, The Great Lakes tectonic major crustal crustal structure structure in in central central North North America: Geological Society -A major Society of zone —A v.91, p.690-698. America Bulletin, v. 91, Pt. pt. 1, p. 690-698. Structure of the Continental Sims, P.K., 1996, Continental Margin: Sims, 1996,Early Early Proterozoic ProterozoicPenokean Penokean Orogen Orogen -- Structure U.S. p.44-51. U S . Geological Survey Professional Paper 1556, p. 44-51. 113 �GEOLOGIC GEOLOGIC FIELD TRIP TRIP TO THE THE TILDEN MINE Engineering Department, Tilden Mining Glenn W. Scott and Helene M. Lukey, Mine Engineering Mining Company, P.O. Box 2000, Ishpeniing, MI 49849 Ishpeming, Introduction Introduction This geologic primary structural and geologic field trip to the Tilden Mine is designed to show the primary stratigraphic features of the iron ore bodies and the implication implication of these geologic stratigraphic geologic features features in mine planning and ore control. The The interaction interaction of sedimentation sedimentation and and diagenesis diagenesis within within and supergene oxidation oxidation has has resulted resulted in in aa growth fault controlled basin, metamorphism and complex suite of ore types, each with specific, specific, if not entirely entirely objective, blending blending characteristics and problems. Although the mining operation tends toward characteristics Although the mining operation tends toward "brute "bruteforce", force", some of the blending concerns can be quite subtle and sensitive. sensitive. For the purpose of mine modeling, the deposit has been divided divided into into geologic geologic domains domains 3;Table Table1) 1)based based in in part part on on lithology lithology but, more importantly importantly on the (Figures 1,2 1 , 2and and3; bench tests tests and and in in the the processing processing plant plant (Table (Table 2). 2). The metallurgical response based on bench The primary p r i m w ore/waste orelwaste parameters are weight recovery (the percentage of each ton of ore that is turned into concentrate concentrate and pellets; i.e. the value of that ton of ore) and grade grade (does (does the the ore contain sufficient sufficient iron and silica silica grade). Other factors which can effect the plant operation and pellet quality are mineralogy (as related to total oxides and loss on ignition); trace chemical ignition); chemical composition (in particular phosphorous but also also Mn and and alkalis); alkalis); crude, magnetic and slime iron; and autogenous grinding feed. It should be noted that essentially all based on rather involved bench tests that may not directly these data are essentially directly reflect the plant response. response. Structural Geology Geology Ththis thisregion, region,the the Marquette Marquette Range Range Supergroup Supergroup is is in in aa narrow narrow east east west trending basin In basin known as the Marquette Synclinorium. This basin lies along the Great Lakes Tectonic This lies along originally defined by Sims and others (1980) as a Late Archean crustal scale Zone as originally suture with Superior Superior Province Province granite-greenstone granite-greenstone terrain to the north and older older Southern Southern Complex gneiss gneiss to the the south. south. The The northern northern margin displays a more or less complete complete stratigraphic stratigraphic succession from the base of the Chocolay Group through to the top of the Menominee Group. The Thesouthern southernmargin margin is is truncated; truncate& the the Negaunee Iron Formation Formation at Menominee group abuts directly against the high grade Archean Gneiss. Gneiss. the top of the Menominee This sharp sharp contact contact is is marked marked by outcrops outcrops of the Palmer Gneiss, Gneiss, described described as as a "comminuted, sericitised sericitised and partly silicified phase of the lower Precambrian gneiss" "comminuted, gneiss" use and (Van Hise andBayley, Bayley, 1897). 1897). since that time time has exposed a large face (Stop2) (Stop2) of the chioritic chloritic schists schists Mining activity since that form part of the Palmer Gneiss. ItIt displays displays mega-shear mega-shear bands, the spacing spacing between 114 �NORTH INTRUSIVE 4-- - 35 I.A±J -, — — -4' - HEI'l �F1 : H lN 1 rC it. 4. CDIII PIT MAGNETIU CD-Ill I 420 L?1AIN /3 1/ — a H 1420 / / H DOOIAIN vii Jat 2 7/ / (_ CROSS SECN' 'N iT I OOP$A1S1 V 2 zi IIAIH 'F 7- CN- N, L — 3 JF -' 'H' 1 (i11T"fH ,-_ -! - IZO F — — TILDEN MINE Figure 1-21.000 DATE: 1 3/11/99 " IDSnAINJ: v1 '' - .1 400 0 I = *ivwW C:: g - 000 I ) .( 1 — 20 - ' PIT F = 800 I 1000 C w OanoIa BoeIdorIts :: flT Me Tot �TILDEN HEMATITE NORTH-SOUTH CROSS-SECTION -13,100 -13,10( - TILDEN MAGNETITE MAGNETITE EAST-WEST CROSS-SECTION CROSS-SECTION -16,000 WES WE' — �________ _________ PIT PIT I LOOKING WEST WEST LOOKING NORTIOWEST DOMAIN (500) HANGINGWALL ZONE (470) L MAGP11TITI DOMAIN 1(420) x4 rooTwALi. ZONE Li ri (410) HEMATITh DOMAIN $NOWAU. CONTACT 20111 DOMAIN INTRUSOVE (200) (230)(240) I_____ L CLAY ZONE (350) HEMATITE - MARTIn DOMAIN (350) MAIN PIT CARIONATE IRON FOMIATIOII (340) FOOTWALL CLASTICS (480) FOOTWALI. IRON FOM4ATIOII DOMAIN — I (310) FOOTWAU. AND MANOINOWALI. (12Q(250) 200 400 600 800 L FIGURI 2 CDIII PIT PIT CDIII LT LnqKING NORTH NORTH LOOKING I -. - ORIGINAL GR0tMD r I CDIII HANGINGWALL AND FOOTWALL E-:J (230) (250) ,/ HEMATITE r' / (440) 1 INTRUSIVE (460) HAGNETITE (420) Figure 2 HANGING WALL ZONE (470) 0 200 I I 400 I 600 I 800 I FIGuRE 5 000 FT. 1000 F �North North S outh South coolly UT PIT .tt I FT NW UUVU 600 rT EAST PIT +1200 FT a DIAGRAMATIC STRATIGRAPHIC STRATIGRAPHIC SECTION SECTION OF OF TILDEN DIAGRAMATIC T I L D E N MINE MINE West Looking Lookin9 est - W Refer R e f e r to t o tcxbIe t ~ k d e11 Figure 33 �Mine. The Table 1: 1: Geologic domains domains and subdomains at the Tilden Mine. The domains domainsare arebased based on on lithology and metallurgical response. The numbers for each domain correspond to those lithology metallurgical The numbers for each domain correspond to those shown on Figures 1, 2, and 3 and are used as drill core codes and in modeling of the deposit 1,2, using MEDSYSTEM. MEDSYSTEM. NORTHWESTDOMAIN DOMAIN 500 NORTHWEST The Northwest Domain is stratigraphically above CD IIll/West I W e s t pit hanging wall metadiabase metadiabase (250) and below North Intrusive Intrusive (270); (270); this this domain domain includes includes numerous numerous dikes dikes and and one one mappable igneous igneous horizon, horizon, the the West Intrusive Intrusive (260). (260). 550 West Hematite 550 Hematitedomain, domain,restricted restrictedto tothe theFar Far West West Extension, Extension, is dominantly 40% and and variable variable but but elevated elevated hematite chert with mixed goethite, recoveries around 40% and metallurgical metallurgical phosphorous. Contact Contact with with 530 530 domain is defined by a thin intrusive and change. change. 530 (Hematite)-Goethite (Hematitel-Goethitedomain domainincludes includesflot flot"ore" "ore"(531) (531)and and WIF WIF (532). (532). 531 Plot Flot"ore" "ore"that thatisisdominantly dominantlygoethite-chert goethite-chert with with weight weight recovery recovery of of iron iron in in the the low 30 to -mid 40 40 %; %; variable, but generally generally high silica silica and and phosphorous. phosphorous. 532 WIF WIF"ore" "ore"isisoxidized oxidizedmartite/goethite; martitelgoethite;low low weight weight recovery, recovery,high high silica silica and and phosphorous; low heads indicate original iron formation may have been carbonate(?). heads formation have been carbonate(?). Sulfates Sulfates are are locally locally common common in in bench bench faces. faces. 520 Magnetite horizons. This Magnetitedomain domainisisdominantly dominantlymagnetite-carbonate magnetite-carbonate with silicate horizons. may be flot and/or andor mag ore in part depending on liberation. liberation. 510 Clastic horizon is at the contact with top of 5 10 Clastic horizon is at the contact with top of the the CDffl/West CDIIT/West pit pit hanging hanging wall (250) syncline.This This horizon horizon isis in in part part flot lot ore. in a local ('1) (?) syncline. ore. 400 CDIII-WEST CDIII-WESTPIT PITDOMAIN DOMAIN This domain is stratigraphically stratigraphically between CDIIJIWest C D W e s t pit hanging wall metadiabase metadiabase (250) (250) and and Thisdomain domainincludes includesnumerous numerous small small dikes dikes and and sills, sills, aa Keweenawan Keweenawan CDIII footwall (230). This dike and the West Pit Marker horizon (240). Footwallclastic clasticzone zonealong alongMain Mainpit pit footwall footwall (100). (100). Consists of dominant martite 480 Footwall clastics with coarse coarse quartzite/conglomerate quartzitelconglomerate and interbedded martite-hematite martite-hematitechert. chert. 470 Hanging Hangingwall wallzone zonealong alongbase baseofofCDIII/West CDIIIlWestpit pithanging hangingwall wallmetadiabase metadiabase(250). (250). WIF Defined as W F due to very fine grain size andlor andor oxidization. Dikedomain domainisisdefined definedasasaanortheast northeasttrending trendingzone zone of of chioritic chloritic dikes dikes and and 460 Dike associated oxidized associated oxidized and unoxidized iron formation. 450 South South Hematite Hematitedomain domainoccurs occursininthe thesouth southpart part of of CDffl CDIII and and the the West pit. It contains flot oreof of variable variablemetallurgy metallurgy and and WIF and is dominantly thin bedded, fine lot ore grained hematite-martite chert although some zones may be oxidized oxidized carbonate. carbonate. 451 Goethite Goethitezones zoneswithin withinhematite hematitedomain. domain.These Thesezones zonesare areassociated associatedwith with folding folding and faulting. A goethite zone along the footwall is present but not broken out as A goethite zone along the footwall as aa domain domain at at this this time. time. 452 Goethite Goethitezone zonealong alongCDIII CDIIIfootwall footwallsouth southof ofKeweenawan Keweenawan dike. This This zone zone typically typically has high slime slime Fe, Fe, may be oxidized oxidized Carbonate Carbonate (430) (430) domain domain along along intersection of dike and footwall. dike footwall. 118 �440 North Northhematite hematitedomain domainconsists consistsofoffine finegrained grainedoxidized oxidizedmartite-hematite martite-hematite chert with numerous dikes. The Theboundary boundary between between this this domain domain and the Magnetite Magnetite domain domain (420) trends northeast and dips steeply Plot ore in part. steeply south. Flot Carbonatedomain domainisiscarbonate carbonateflot flotore orewith withlow lowmagnetite magnetite content, high weight 430 Carbonate recovery and low concentrate grade. Fault Fault bounded bounded on on north and south south but apparently apparently gradational down dip to the west into magnetite domain (420). gradational (420). 420 Magnetite Magnetitedomain domainconsists consistsofofmagnetite-carbonate magnetite-carbonateand and magnetite magnetite silicate-chert silicate-chert with variable variable oxidation and grain size. size. This domain has relatively sharp sharp boundaries boundaries with with other domains. Domain Domaingenerally generallydefined defined by by magnetite magnetite content, content, not ore type, so so it contains potential flot contains flot ore. ore. 421 West Westpit pitmagnetite magnetitedomain domainisisananisolated(?) isolated(?)zone zoneof ofhigh highgrade grademagnetite magnetite in the west pit. It is defined defined by drilling drilling and and blast blast pattern pattern data. data. Footwallzone zoneisisdefined definedasasthe themagnetite-silicate magnetite-silicate horizon horizon at at the contact contact with the 410 Footwall CDIII Footwall metadiabase metadiabase (230). (230). It is typically waste or low grade grade due to low low magnetite content or poor liberation. content or poor liberation. MAIN PIT PIT DOMAIN DOMAIN 300 MAIN The Main Pit Pit Domain Domain contains contains iron iron formation formation units stratigraphically stratigraphically below the the CDffl CDIII footwall metadiabase (230) and/or the East pit hanging wall metadiabase (200). (200). This domain domain includes numerous includes numerous small small mafic mafic intrusives. intrusives. 370 Hanging Hangingwall wallcontact contactincludes includeszones zonesof oferratic erratic metallurgy metallurgy along along the base of the CDffl footwall CDIII footwall (230) (230) or or East East pit pit hangingwall hangingwall(200). (200). 360 Transition Transitionzone zonebetween betweenCDffl CDIIIfootwall footwall(230) (230)and and East East pit hanging wall (200). This zone consists consists of variably variably oxidized oxidized hematite hematite iron formation formation and mafic intrusives. intrusives. Restricted to north side side of East East pit. 350 Hematite-martite Hematite-martitedomain domainininEast Eastpit pitconsists consistsofofvarious varioustypes types of of martite martite chert. This domain includes includes horizons of magnetite-carbonate iron formation and thin dikes. Gradational transition over 20-50 feet to Carbonate iron formation (340). Gradational 340 Carbonate is is stratigraphically Carbonateiron ironformation formation stratigraphicallybelow belowthe thehematite-martite hematite-martitedomain domain It consists of martite-carbonate-chert with variable in East pit. (350) (350) East pit. consists martite-carbonate-chert variable magnetite/martitelFe silicate content. This magnetite1martiteFe This unit is defined by magnetic Fe, weight recovery and total oxides. ItIt has has lower lower weight recovery and higher concentrate grade than CDIII CDIII carbonates carbonates (430) (430) and and may may be be magnetite magnetite ore ore in in part. part. 330 Clay Clayzone zoneisisdefined definedasasthe thehorizons horizonsof of iron ironformation formationoutlined outlinedas as waste waste due due to to high high silica from montmorillonite (or other) interference. interference. This does not differentiate differentiate nonliberating hematite material. This zone may be stratigraphically stratigraphically controlled. controlled. Includes nonliberating Includes some some flot flot ore ore within within boundaries. boundaries. 320 East East pit pitclastics clasticsare aremixed mixedsiliceous siliceous clastics clastics and iron formation. This This unit unit includes includes oxide and carbonate horizons. ItIt may may be be the the stratigraphic stratigraphic equivalent equivalent of carbonate domain (340) down plunge to the west (7). (340) down plunge to the west (?). 321 Clay similar Clay zone zone in in clastics.is c1astics.i~ similarto to clay clay zone zone (330) (330) but in clastic clastic domain. domain. Footwalliron ironformation formationdomain domainconsists consistsofofvariably variablyoxidized oxidizedoxide oxide iron iron 310 Footwall by erratic metallurgy. formation and coarse clastics. This domain is typified by 311 31 1 Earthy Earthyfines finesare arehigh highgrade grade (>50 (>50 weight recovery recovev and >50 head Fe) oxidized zones zones are are controlled controlledby structures structures within within the the footwall footwall domain. domain. 119 �200 INTRUSIVE INTRUSIVEDOMAINS DOMAINS These domains are used for correlations of the iron formation domains, and structural trends. They appear to be conformable at the the scale scale of of the the ore orebody. body. These rocks are generally which vary vary from from diabasic diabasic to to porphyritic porphyritic interpreted as intrusives, they consist of mafic rocks which to aphanitic. All horizons appear to thin to the west and south. Contacts tend to be All horizons appear Contacts tend to be sheared sheared if and locally oxidized. Contact Contact metamorphism metamorphism of the iron formation is minimal and, if present, results in finer grained iron iron formation. Synclinal structures and intersections with Synclinal dikes have focused oxidation of the iron formation. formation. 270 North intrusive is a poorly defined North intrusive is a poorly definedhorizon horizonatatthe thetop topof of the the Northwest Northwest zone zone (500). (500). West intrusive 260 West intrusiveisisaapoorly poorlydefined definedbut but mappable mappable horizon within the Northwest zone zone (500). (500). CDIIIIWest pit 250 CDIII/West pithanging hangingwall wallisisaarelatively relativelyeasily easilymappable mappablehorizon horizon and and along along principle horizons for stratigraphic with the CDIII footwall footwall (230) (230) is one of the principle stratigraphic correlations between the CDffl correlations CDIII pit and the the Main Main pit. 240 West Westpit pitmarker markerisisa athin thinbut butcontinuous continuoushorizon horizon within within the the CDIII/West CDin/West pit stratigraphy (300). ItIt isis interpreted interpreted to to extend extend from from the the Foster Foster Lake Lake slot slot through through the the West West pit. 230 Top Topof ofthe theCDIII CDIIIfootwall footwalldefines definesthe thebase baseofofthe theCDIIIfWest CDIO/West pit pit domain domain (400) (400) while the base defines the top of the Main pit east domain (300). (300). 220 Chloritic Chloriticand anddiabase diabasedikes dikesand andthin thinsills sillsoccur occurininall alldomains. domains. This Thisunit unitincludes includes east-west trending 30+ foot thick Keweenawan Keweenawan dike in CDIII. 200 East Eastpit pithanging hangingwall wallisisseparated separatedfrom fromthe theCDffl CDIIIfootwall footwall (230) (230) by the Transition zone (360) iron formation. This Thisunit unit occurs occurs along along the the north north side side of of the the East East pit, pit, the the base base Main pit pit East East domain domain (300) (300) for for mining mining and and planning planning of this horizon marks the top of the Main purposes PIT FOOT WALL DOMAIN 100 MAIN MAIN PIT FOOTWALL 100 rocks which which are are separated separated from from the the iron iron This domain consists of Archean metamorphic rocks formation formation domains domains by an an east-west east-west trending, north-dipping north-dipping high angle angle fault. fault. 121 Chloritic Chloriticschist schistisisthe thedominant dominantfootwall footwallrock rocktype typeexposed exposed within within the the pit pit and and in in of the the CDIII CDffl footwall horizon horizon (230) within the drill holes. This rock may the extension of the fault zone. zone. 111 111 Granite Granitegneiss gneissoccurs occurssouth southofofthe thechloritic chloriticschist schist(121) (121)but but isisonly onlypoorly poorly exposed exposed in the pit. This Thisdomain domainhas hasnot not been been used used in in the the drill drill hole hole codes. codes. 999 OVERBURDEN OVERBURDENDOMAIN DOMAIN This domain domain consists consists of of Quaternary Quaternary overburden, overburden, rock rock fill fill and and broken broken bench bench material. material. 120 �Table Table 2: Glossary Glossary of terms terms and and abbreviations. abbreviations, Natural The amount of material recovered from the material fed Natural Weight Weight Recovery Recovery -- The fed into into the the concentrator In other words, words, it's the tons of concentrate concentrate made made (measured (measuredas as filter filter concentrator circuit. circuit. In cake) from tons of crude crude ore ore used (measured (measured by #3 belt scale). scale). Metallurgical Metallurgical Weight Weight Recovery Recovery (Met. (Met. Wt. Wt. Rec.) Rec.) - Calculated Calculated by comparing comparing the iron losses losses (as tailings) tailings) with the iron iron content content of the crude crude ore fed into into the concentrator concentrator circuit circuit (i.e., (i.e., the the head Fe). The formula formula used for for this this calculation calculation is called the iron balance balance formula, formula, or or sometimes sometimes called called the the concentration concentration formula. formula. (Head Fe - Tail Fe) Wt. Rec. = x 100 (Grade - Tail Fe) Grade Grade -- Also Also called the concentrate grade, is a chemical measurement (assay) of the total total iron oxide oxide of the concentrate. Iron oxide oxide is found in iron minerals such such as hematite hematite (Fe203), (Fe203), magnetite magnetite (Fe304), (Fe304),geothite geothite(Fe203 (Fez03** OH), OH), and iron iron carbonate carbonate(FeCO3). (FeC03). Concentrate Silica Grade Grade - The chemical Concentrate chemical measurement measurement (assay) (assay)of of the the % % SiO2 Si02in the the concentrate. concentrate. When When aalower lowerconcentrate concentratesilica silicagrade grade is is achieved, achieved, the losses losses in iron units (tailings) (tailings) increases. increases. content of the crude ore fed into the concentrator concentrator circuit. circuit, Grade -- The assayed iron content Head Grade concentrator's ability Iron Iron Recovery Recovery(Fe (FeRec.) Rec.) -- A calculation of the efficiency of the concentrator's ability to recover the iron available. This is calculated by comparing the Met. Wt. Rec., at some iron available. grade, with the head Fe of the crude crude ore. For example, (Met. Wt. Rec. x Grade % Fe) Grade % % = .................................. % Fe Rec, Rec. = (Head (Head % Fe) Percent Percent Magnetic Magnetic Iron Iron Recovered Recovered (% (% Mag. Fe Rec.) - The calculation calculation of the efficiency of recovering recovering the magnetic magnetic iron that was in the feed (crude ore). The Met. Wt. Rec., Rec., at at some some iron grade, is compared compared with the magnetic potential (i.e. (i.e. head) of the crude crude ore. For example, example, (Met. Wt. WI Rec. % Fe) Rec. xx Grade Grade % Rec = .................................. % Mag Fe Re (Head Mag % Fe) Tailings Tailings -- The The product lost in the process. Tailings always includes iron, because iron is always associated with many other minerals (silica, phosphate, carbonate, etc.). 121 �Flot (flotation) -- Flot ores are are the martite, martite, hematite, hematite, geothite geothite and and carbonates, carbonates that are are treated treated The final stage of the by selective chemical chemical processes to achieve Fe and silica grade. The magnetite process magnetite process is is flotation flotation to to achieve achieve target target silica silica grade. grade. to low low weight weight recovery recovery andlor and/or high WIF (waste iron formation) formation) -- hon Iron formation that due to silica cannot be treated in the plant to produce economic economic concentrate. concentrate.Rarely, Rarely, phosphorous phosphorous levels are too high to be treated. treated. The percent of the crude iron that that is concentrated concentrated in in the the Davis Davis Magnetic Magnetic Magnetic iron - The Tube Test (DMTT). (DMTT). %MagFe %MagFe == DMTT Wt. Rec. Rec. x DMTT Grade Grade However, in in the the Tilden Tilden ores ores an The assumption assumption is that all of this occurs as magnetite. However, appreciable and is is carried carried into the DMTT appreciable amount of hematite is up locked with the magnetite and Fe content by by 1-2% points points and concentrate. This tends to over estimate the magnetic Fe therefore therefore the over over estimate estimate weight weight recovery. Satmagan susceptibility and and is is the the Satmagan - The satmagan magnetic iron content is measured using susceptibility actual magnetite content content of of the the crude crude or or concentrate. concentrate. Domain - The The deposit deposit is divided into volumes of rock with similar similar metallurgical metallurgicalresponse. response. These are usually stratigraphic stratigraphichorizons horizons but may be fault fault bounded bounded or or nonconformable nonconfonnable alteration/oxidation alteratiodoxidation zones. The The domains domains are are the basis for for the economic economic and and planning planning models. models. 122 �CIstructures structuresisison onthe theorder orderofof2.5 2.5meters, meters,most mostcommonly commonlysuch suchstructures structuresare arehand hand Cl specimen specimentotomicroscopic microscopicininscale. scale.They Theyindicate indicatethe thepresence presenceofofa alarge, large,reverse reversedip dipslip, slip, ductile ductileshear shearzone zonewith withaaNNE NNEtotoSSW SSWtransport transportdirection. direction.The Thefact factthat thatthe theNegaunee Negaunee hon IronFormation Formationisisthrust thrustup upon ontotothe theolder olderArchean ArcheanGneiss Gneissindicates indicatesthat thatthere theremust musthave have been beenprior priorlocal localsubsidence subsidencehere heretotoform formthe thesedimentary sedimentarybasin, basin,aaclassic classicbasin basininversion inversion pattern pattern(Gillchrist (Gillchristand andothers, others,1987). 1987). Folds Foldsmeasured measuredwith withininthe theNegaunee NegauneeIron IronFormation Formationhave haveaxial axialsurfaces surfacesand andhinge hingelines lines that WNW,indicating indicatingaasimilar similarstrain strainenvironment environmenttotothat thatdetermined determined thattrend trendeast-west east-westtotoWNW, from the shear zone. The folding and shearing are thought to have occurred at from the shear zone. The folding and shearing are thought to have occurred atthe thesame same time. time. The Theiron ironformation formationisismostly mostlyaachemical chemicalor or biochemical biochemical deposit. deposit. The Theclastic clasticlenses lensesthat that in the south, thinning and occur occurininthe theformation formationare arethickest thickestand andmost mostnumerous numerous in the south, thinning and becoming becomingless lessfrequent frequentto tothe thenorth north (Breithart, (Breithart, 1983). 1983). The Thepattern patternsuggests suggestsan an asymmetric asymmetricrift riftbasin basinwith withaabreakaway breakawayfault faulton on the thesouthern southernmargin margin and andaarollover rolloveron onthe the north side. The principal source of clastic sediments would have been derived from the north side. The principal source of clastic sediments would have been derived from the southern southernmargin marginthat thatwas wasbeing being uplifted uplifted along along the the fault. fault. This Thisepisode episodeisisrelated relatedto tothe the development of a passive margin during the early Proterozoic. Subsequent compression development of a passive margin during the early Proterozoic. Subsequent compression during duringthe thePenokean PenokeanOrogeny Orogenyinverted invertedthe thebasin basinand andinitiated initiatedreverse reversefaulting faultingthat thatgave gave rise to the shear zone (Cambray, 1978). To the east, in the Harvey Quarry, a similar rise to the shear zone (Cambray, 1978). To the east, in the Harvey Quarry, a similar pattern patternof ofyounger youngerover overolder olderthrusting thrustingisisobserved observedsuggesting suggestingthat that this thisrelationship relationshipisis rift and later thrusting common commonalong alongthe theSynclinorium Synclinoriumand andconfirms confirmsthe theearly early rift and later thrustingpattern. pattern. Mining Mining Ore 50'x50'x45' Orereserve reserveand and long long range range mine mine planning is done in MEDSYSTEM using 5O'x50'x45' blocks based primarily on development drill holes which are on a nominal 300 blocks based primarily on development drill holes which are on a nominal 300foot foot spacing. spacing.Weekly Weeklyplans plansand anddaily dailyore orepredictions predictionsare arebased basedon onblast blastpattern patternsamples, samples, which which are areon on about about 90 90 foot foot centers. centers. Reconciliation Reconciliationof of ore, ore,waste wasteand and pellet pellet production production between betweenthe the'model" "model"and andactual actualproduction productionshows showsless lessthan than1% 1%difference. difference. The Theannual annualmining miningtask taskisisto tomove moveapproximately approximately38 38million million long longtons, tons, about about20 20million million long longtons tonsof ofore oreand and18 18million millionlong longtons tonsof ofstripping strippingwaste, waste,to to produce produce 7.8 7.8million millionlong long tons tonsof of flux fluxpellets pellets per per year. year. Production Productionsince since1974 1974has hasbeen been 126 126million million long longtons tonsof of pellets pellets from from355 355million million long long tons tons of of ore ore at at aa stripping stripping ratio of 0.94. As As of of January January1,1, 1999, 1999,the the proven proven and and probable probablelong longrange range (30 (30year) year) mine mine plan plan reserve reservewas was628 628million million long long tons tons of of ore ore containing containing233 233 million million long long tons tons of of pellets pellets at at aa stripping strippingratio ratio of of 0.77. 0.77. The P&H 2800 2800(38 (38 cubic cubic yard) yard) cable cable shovels, shovels, three three P&H P&H Theloading loadingfleet fleetconsists consistsof of two twoP&H 2100 2100 (l7cubic (17cubicyard) yard)cable cableshovels shovelsand andtwo two994 994(21 (21cubic cubicyard) yard)Caterpillar Caterpillarwheel wheel loaders. loaders. The The hauling haulingfleet fleetconsists consistsof of three three 793 793 (240 (240 ton) ton) Caterpillar Caterpillar trucks, trucks, seven seven 789 789 (190 (190 ton) ton) Caterpillar trucks and six Haulpack 630E (170 ton) trucks. Drilling is done with one trucks. Drilling is done with one Caterpillar trucks GD120 120drill. drill. P&H and and one oneGD P&H 123 �Field Trip Trip Stops Stops - . stops to be visited and their locations cannot he be determined determined until until iust just urior prior to The actual stoos the field trip. The generic stop descriptions are provided in this guide and the actual The generic stop descriptions are provided in this guide and the actual localities to be visited will be provided provided to participants on on the the day day of the the field field trip. trip. Stop 1 - Pit Service Building Before beginning the tour of the Tilden pit, the mine safety rules will be reviewed and and aa short video of the Tilden Tilden Mine Mine operation operation will be shown. shown. The The video, not not particularly particularly geologic, describes pelletizing processes that have describes the mining cycle, milling and pelletizing have aa major major impact on the ore quality determinations. determinations. Stop 2 -- Main Main Pit Footwall Shear Shear Zone Zone Chlorite schist defines the footwall of the Tilden ore body. body. This This chlorite chlorite schist schist is is described described in the literature literature (Van Hise and Bayley, 1897; 1897; Gair, 1975) 1975) as part of the Palmer Palmer Gneiss and marks the boundary between the Archean Compeau Creek gneiss gneiss of the the Southern complex and the early Proterozoic sediments. This This contact contact extends extends for for approximately seven miles east from the the Tilden Mine. Gair Gair and Simmons Simmons (1968) (1968) made madeaa complete complete study study of this rock and proposed three possible modes of origin: 1) 1)alteration alterationand and shearing shearing of Precambrian rock during during faulting; faulting; 2) migration of fluids fluids along along the contact contact between lower and middle Precambrian rocks; and 3) alteration of a regolith during lower Precambrian alteration regolith during folding. folding. At Atthe theTilden TildenMine, Mine,there thereappear appearto to be be two two varieties varieties of of gneiss, gneiss, aa southern southern sericitic phase related to a granitic protolith and a northern chloritic phase with a diabasic diabasic protolith. protolith. At this locality surface cut by the the more more locality one one can see see the dominant, dominant, steep steep north dipping dipping S surface gently north dipping Cl 4). The C/ surface (Figure 4). The intersection intersection between the S and Cl C/ plunges plunges WNW. The gently to the WNW. The movement movement plane plane on the shear shear zone is at right angles to this intersection and the intersection of this plane and the boundary of the shear zone (determined from drill records) gives the direction of movement (marked with a filled (determined filled triangle on Figure 5). The Thepattern patternof of the the SS surfaces surfaces and and shear shear bands bands give the sense sense of movement (Figure 4). Chemical Chemical analyses analyses indicate that the protolith for the shear zone was most likely to have been one of the diabase bodies found interlayered with the banded iron formation. formation. (-60') foliation foliation in the chlorite schist creates a bench and slope slope The steep steepnorth northdipping dipping(—60°) stability concern. This 45° final wall slope with 35 Thisisis controlled controlled by by triple triple benching to a 45" 35 foot catchers. Proper Properclean cleanup up along alongthe the toe toe line line is is critical critical to avoid "undercutting" the the foliation. foliation. 124 �West 2.5 Shear Zone (Palmer IPaImrGness) GneW Figure Figure 4: 4: Footwall Footwallshear shearzone, zone,Tilden TildenMine. Mine. Pole Poleto to mean mean C-foliation C'-foliation S * U Pole poleto tomean meanS-foliation ~-fo~atim Slip direction Mean ~ e a S-C S-C. n intersection intersection S-C intersections S-foliafion plane Top of shear zone ' .C-foliation C'-foliation plane p4ane "Nonnal intersection \ N o m d totoS-C' S-C/intersection Figure5: 5: Stereo Stereo projection projection of of shear shearzone zonestructures. structures, Figure 125 �Stop 3 -- Martite and Main Pit Pit Carbonate CarbonateDomains Domains The Martite and main pit Carbonate Carbonatedomains domains lie lie stratigraphically stratigraphically below below the the CDffl CDEI Footwall and Main Pit Hangingwall intrusives. This This is is metallurgically metallurgically "good "good ore" ore" and and isis typically characterized characterized by high weight recovery (35-45+%), (35-45÷%), low phosphorous, low slime slime iron and good grinding media. With Withcrude crudeFe Fe around around 35%, 35%, iron iron recovery recovev averages averages over over 70%. The The'best' 'best'ore oreisiscentered centeredon onthe theMain MainPit Pitanticline anticlineand andconsists consistsof of thick thick bedded bedded (2(24 cm) chert with variable variable martite martite and magnetite magnetite plus subordinate subordinatecarbonates carbonatesand and silicates. silicates. The boundary between the Martite and Carbonate domains is based on higher magnetite Carbonate domains higher magnetite content; content; the Carbonate Carbonate domain domain contains contains low calculated calculated total oxides oxides that that may may be be due due to to iron silicates. silicates. The Thevariation variationin inmagnetite magnetitecontent content may may reflect reflect either either the the environment environment of of deposition deposition or or diagenesis; diagenesis;itit is is unlikely unlikely to be due due to supergene supergene effects. This domain comprises reserve. The mine plan comprises about 56% of the ore reserve. The~mine plan attempts attempts to to control control the blend percentages to about 50% of this domain. This This has has been been only only partially partially successful due to pellet quality concerns when blending with other types of ore. The successful planned final final depth depth of of the the Main Main pit pit is is about about sea sea level level so so the the pit will will be be about about 1000 1000feet feet deeper. deeper. As the base of the iron formation is not exposed at the Tilden Mine, the stratigraphic stratigraphic thickness is unknown. The Thethickness thickness exceeds exceeds 1000 1000feet feet and and is probably underlain by and is gradational into undifferentiated clastics and iron formation formation of the Empire Empire Mine. "Intrusive" Igneous Horizons Stop 4 - Mafic "Intrusive" formation and the rapid Due to the lack of clear stratigraphic markers within the iron formation rapid facies changes in the iron formation, several igneous horizons are used for stratigraphic stratigraphic and structural correlation correlation(Figure (Figure 1). 1). The term 'intrusive' 'intrusive' or or'dike' 'dike'isisused usedfor forgreen greenand andgray-green gray-green mafic mafic igneous igneous rocks, which vary from (semi) (semi) conformable sill-like sill-like horizons to obviously crosscutting crosscutting bodies. bodies. Since the fabric varies from diabasic diabasic to porphyritic to aphanitic, the conformable conformable bodies bodies are usually interpreted as synsedimentary sills sills but but may maybe beflows. flows. The sills range in thickness thickness from a few tens of feet to at least 600 600 feet with the thicker horizons horizons thinning thinning to to the south. Dikes, typically 55 to to 20 20 feet feetthick. thick. The Dikes,obviously obviously crosscutting crosscutting bodies, are typically dikes may be feeders. feeders. The dikes and thinner parts of the sills are commonly altered altered to chlorite and carbonate retain primary primary igneous igneoustextures. textures. Contacts cabonate while the thicker parts retain Contacts with the iron formation are variably sheared and altered. the iron formation are variably sheared and altered. The principal principal sills sills are are the the Main pit pit hangingwall, hangingwall, CDffl CDEI footwall footwall and the CDffl CDEI hangingwall. hangingwall. The Thesills sillsand andmajority majorityof of the the dikes dikes appear appear to be of early Proterozoic Proterozoic age but, there are several dikes that are interpreted to be of Keweenawan age based on the and fracture fracture zones. zones. The igneous event magnetic signature. Dikes Dikes commonly fill faults and Clarksburg, that emplaced emplaced the sills sills and majority of the dikes may be related to the Clarksburg, Hemlock and Emperor Volcanics. 126 �Dilution from dikes, especially along shallowly dipping contacts, is the most common internal waste. waste. kcipient type of internal Incipientrecrystallization recrystallization due due to to contact contact metamorphism metamo~hismand hangingwall. quartz overgrowing magnetite results in high silica waste along the CDIII hangingwall, Stop 5 - West West Pit/CDIJI Pit/CDZZZ Hematite Hematite Domain The West Pit/CDffl PivCDIII Hematite Hematite domain domain in in the the west pit is is stratigraphically stratigraphicallybetween between the the CDffl hangingwall and footwall. This domain extends from CDffl along the north limb CDIII This domain extends CDIII pit anticline. In contrast to the martite domain, this is and over the crest of the Main pit metallurgically 'poor' ore orewith with higher higher slime slime iron, iron, phosphorous and poor grinding. Fe), due to the the high crude Fe Although weight recoveries are relatively good (about 36% Fe), below 60%. 60%. Mineralogically of 40%, the iron in this domain is below Mineralogically and texturally, this domain differs from the martite domain in being dominantly platey hematite with thin (mm scale) chert laminae. Presumably, the bedding thickness reflects the original sedimentary sedimentary features but it is unclear as to the nature of the oxidation event that produced the hematite hematite (related (related to to deposition, deposition,diagenesis diagenesisor or supergene supergenealteration). alteration). With a thickness thickness of about about 600 600 feet, this domain contains contains 27% of the ore reserve but, due due to blending concerns for phosphorous, slimes or grinding, it is often difficult to maintain phosphorous, maintain that percentage percentage in in the the blend blend going going into into the the processing processing plant. plant. Stop 66 -- Magnetite Domain The Magnetite PitJCDffl hematite hematite Magnetite domain domain is the stratigraphically equivalent of the West PivCDIII but is essentially essentially restricted to the CDffl CDIII syncline (basin?). Magnetite Magnetiteore orequality qualityisis determined (magnetic determined by the percentage of the crude iron that occurs as magnetic iron (mapetic concentrate determined by the Davis Magnetic Magnetic Tube TubeTest). Test). On average, the Magnetite domain contains 27% magnetic iron with 37% total total crude crude iron. iron. With about 90% magnetic magnetic iron recovery recovery in the plant, weight recoveries are 34-36% iron. Mineralogically, Mineralogically, the ore consists primarily of magnetite-siderite-chert with variable hematite and silicates. consists primarily silicates. This This mineralogy, along along with the thin laminations, laminations, appears to indicate a restricted basin and a reduced environment environment of deposition. deposition. respect to to the There is some scientific scientific controversy as to the role of diagenesis with respect hematite and and siderite. siderite. Within the Magnetite domain relationship between magnetite, hematite there is a faultldike-bounded faulvdike-bounded zone of low magnetite siderite ore; it is uncertain whether this is the protolith of the magnetite ore. The The southern southern extension of the CDffl CDIII magnetite into the hematite domain contains the highest highest grades grades (-30 (-30 magnetic iron). The The sharp sharp contact, not structural, structural, indicates indicates that this is some sort of redox front but it is unknown unknown whether it is is of of diagenetic diageneticor or supergene supergene origin. origin. Approximately reserves are are in in magnetite. magnetite. Development of the Approximately 23% of the Tilden ore reserves of pushbacks pushbacks along along the thewest westwall wallininthe theintrusive. intrusive. The The wall is reserve involves a series of planned planned to move move back about about 800 800 feet and the pit is to be he deepened about 600 feet. 127 �Acknowledgments Acknowledgments We thank Bill Cambray Cambray and Cheryl Webster for their contribution of the Structural Stmctural Geology section in the Introduction and structural structural discussion in Stop Stop 2. References References Cambray, F. W., 1978, 1978, Plate Tectonics as a model for the environment environment of deposition deposition and and deformation Northern Michigan: Michigan: deformation of the the early early Proterozoic Proterozoic (Precambrian X) of Northern Geological 7, p. 376. 376. Geological Society Society of America Abstracts with Programs, Programs, v.10, no. 7, Breithart, M. S., S., 1983, 1983,Significance Significanceof of the the distribution distribution of of clastic clastic lenses lenses within within the the Breithart, Negaunee Iron Formation Formation at the eastern end of the of the Palmer Basin, Marquette Marquette Synclinorium, Synclinorium, Northern Michigan: Masters Masters thesis, Michigan Michigan State State University. University. Gair, J.E., J.E., 1975, 1975,Bedrock Bedrock geology geology and ore deposits deposits of the Palmer Palmer Quadrangle, Quadrangle, Marquette Marquette County, Michigan: U.S. U S . Geological Geological Survey Survey Professional Professional Paper 769, lS9p. 159p. Gair, J. E. and and G. G. C. C. Simmons, Simmons, 1968, 1968,Palmer Palmer Gneiss Gneiss -- an an example of retrograde retrograde metamorphism metamorphism along along and and unconformity: U.S. US. Geological Geological Survey Survey Professional Professional Paper, Paper, 600-D, 600-D, p. D186D186- D194. D194. Gillchrist, Gillchrist, Ralph, Ralph, Mike Mike Coward Coward and and Jean-Louis Mugnier, Mugnier, 1987, 1987,Structural Structural inversion inversionand and its controls: controls: examples examples from from the the French French Alpine foreland foreland and and the the French French Alps: Alps: Geodinamica Acta (Paris) v.1, no. 1, p. p.5-34. 5-34. Sims, P.K., Card, K.D., Morey, G.B., and Peterman, Z.E., 1980, The Great Lakes tectonic zone A major crustal cmstal structure structure in central North America: Geological Society of zone -- A America bulletin, V. V.91, 91, Pt. pt. 1, 1, P.690-698. p. 690-698. Van Hise, C.R., and C.R., and Bayley, W.W., 1897, 1897, The Marquette iron-bearing district of Michigan: Michigan: U.S. U.S. Geological GeologicalSurvey Survey Monograph Monograph 28, 2 8 ,608p. 608~. 128 �Geologic Field Field Trip Trip to the Empire Empire Mine Mine , M. Nordstrom, Nordstrom, Empire Empire hon IronMining MiningPartnership, Partnership,P.O. P.O. Box Box 38, 38, Palmer, Palmer, MI MI 49871 49871 Paul M. Introduction Introduction Empire mine commenced operations in 1963; 1963; over the past thirty-five years the operation The Empire has produced nearly 200 200 million long tons of pelletized iron concentrates. The TheEmpire EmpireMine Mine represents repr&ents a partnership partnekhip of steel making m G n g and iron iion mining interests and is partially oowned h e d and operated by the Cleveland-Cliffs Iron hon Company. The Thereserve reserveis is about about 600 600 million million long long tons tons of magnetite magnetite ore. ore. The Thecurrent currentannual annualproduction productionisis8.4 8.4million million long longtons tonsof of pellets pelletsfrom from27.5 27.5 million long tons of ore. Han hon Han (1975) (1975)provides provides aa detailed description of the Negaunee Iron Formation at at the the Empire Empire Mine. Mine. Stratigraphic hon Formation Stratigraphicrelationships relationships within the Negaunee Iron Formation in in the the vicinity vicinity of of the the Empire Empire Mine Mine are: are: • Upper UpperUndifferentiated UndifferentiatedSeries Series(+ (+1500'): 1500'):intermixed intermixedsequence sequenceof ofcarbonate, carbonate,silicate, silicate, clastic clastic and "lean" "lean" carbonate carbonateassemblages. assemblages. • Clastic Clastic horizon (200-300'); (200-300'); graywacke graywackeand and feldspathic feldspathicquartzite quartzite interbedded interbedded with with chert, iron carbonate carbonate minerals minerals and and magnetite. magnetite. • Carbonate Carbonate horizon horizon (350-500'): (350-500'): alternating alternating bands bands of of magnetite-chert magnetite-chert and and chert, chert, with with siderite siderite or or ankerite ankerite distributed distributedthroughout. throughout. Local, Local, minor minor beds beds of of riebeckite riebeckiteand and aegerine-augite aegerine-augite are present contact. present near near the the upper upper contact. .. • Silicate Silicate horizon horizon (400-500'): alternating alternating laminae laminae of of magnetite, magnetite, carbonate, carbonate, greenish greenish microstilpnomelane), and chert. micro- to to sub-microscopic sub-microscopiciron iron silicate silicateminerals minerals(principally (principally stilpnomelane), and chert. - . • Lower h w e r Undifferentiated undkferentiated Series Series (700-1500'): (700-1500'): intermixed intermixid sequence sequence of carbonate, carbonate, silicate silicate minerals and and clastics clastics (clastics (clasticsincrease increasetoward toward base base of of interval). internal). The The basal basal contact contact of of the the Lower Lower Series Series is is transitional with the underlying Siamo Slate. The The Siamo Slate is represented in the mine area by quartz-arkose and graywacke. Siamo Slate is represented in the mine area graywacke. A A geologic geologicmap map and and section sectionof of the theEmpire EmpireMine Mine(Figure (Figure11and and 2) 2) illustrate illustratethe therelationships relationships between between the the various variouslithologic lithologicunits. units. hon Ironformation formationatatthe theEmpire EmpireMine Mineisistransected transectedby by aa number number of of near-vertical, near-vertical, chioritized chloritized metadiabase are metadiabase dikes. dikes.The Thedikes dikesoccupy occupyfaults, faults,believed believed to to be be of of early earlyProterozoic Proterozoicage, age,which which are probably related related to to basin basin development. development. The Thedikes dikeshave havehad hadaasignificant significantlocalized localizedimpact impact on on ore ore probably processes. processes. The Thefine finegrain grainsize sizeofofmagnetite magnetite(5 (5p.) p)in in iron iron formation formationadjacent adjacentto tothe thedikes dikes represents represents aa "selvage" "selvage" which which was was apparently apparently impervious impewious to subsequent subsequent processes that influenced influenced growth of of the the magnetite magnetite grains grains in in other portions of the iron formation. Effective Effectiveliberation liberationof of growth magnetite in in these these"fine-gralned" "fine-grained"rocks rockscan canrarely rarelybe beachieved. achieved. magnetite The iron iron content content of of the the iron iron formation formation at at the Empire Empire mine is fairly uniform, about 32-35%. The The The amount amount and and grain-size grain-size of of magnetite magnetite determines determines ore quality. Ore-forming Ore-formingprocesses processescontributed contributed and remobilized remobilizediron ironby bydiagenetic diageneticor orlow-grade low-grademetamorphic metamorphicreactions reactionsof of recrystallization recrystallizationand and and replacement. Oxidation Oxidationofofsiderite sideritehas hasresulted resultedininlarge-scale large-scalereplacement replacementby by magnetite, magnetite,but but replacement. 129 �N N N N P1010ED 04/05/99 Formation Iron Fine—Grained 2000 Horizon Carbonate UOji.OWtiOJ Iron UOJI Oxidized PdZlplXn Formation Horizon Ctastics Series Undifferentiated Upper Siamo 1 Figure Series Undifferentiated Lower Horizon Silicate \ Dike Diabase Keweenawan SiLt/Dike Mc-taciiobase - LEGEND GEOLOGIC —- '9tfV.K 's.-.) ' Eevation) Bench (+940 —22000 ---r- ç—1j . - \(iJ l — -. GEOLOGY MINE EMPIRE —18000 (7bt -- 20 t 'tion _J 'A' -- —14000 Resource IV CD —10000 Cu 0 0 0 Li 00 0 nJ o o o Li Li EIIJ ��of the the magnetite magnetite in in these these enriched enriched chert layers are also replaced by magnetite; the grain size of zones is coarser than magnetite in zones not effected by replacement. coarser magnetite zones effected replacement. the Empire Empire Mine. Mine. NonSecondary oxidation has a profound impact on ore quality at the Non- or or weakly weakly characteristic of of oxidized oxidized zones zones are are typically magnetic iron minerals (e.g., martite, hematite) characteristic rejected during primary magnetic separation. Incipient Incipient or or partial partial oxidation oxidation of of magnetite magnetitegrains grains then in flotation flotation stages. may cause them also to be rejected, if not in magnetic separation, then extent of of oxidation oxidation and and predict predict its its impact impact on on plant plant However, it is often difficult to recognize the extent recovery. The Theoxidation oxidationisisthought thoughtto to be be largely, largely,ifif not not entirely, entirely, the the result result of of supergene supergene processes. processes. Circulation Circulationof ofthe theoxidizing oxidizingfluids fluidswas wascontrolled controlled by by faults, faults,dike dikecontacts contactsand andclastic clastic beds and lenses. However, the boundaries of oxidized zones are very irregular and difficult to However, the boundaries of oxidized define. define. all Empire Empire iron iron ores, ores, including including the the Due to the very fine grain size of magnetite in virtually all carbonate ores, extremely carbonate extremely fine fine grinding grinding (93-95% (93-95% passing 500 500 mesh) is is required required to to achieve achieve sufficient sufficient liberation of magnetite for product specifications. Process Process control control is is dominated dominated by by the the specification for Si02 Si02 in the final product. product. Smaller Smalleraverage average grain grain size size of magnetite magnetite in in silicatesilicateliberation. In type ores means that they must be ground finer to achieve acceptable liberation. In general, general,the the becomes significantly significantly more finer grain size also implies increased work index so that grinding becomes costly. costly. Field Trip Trip Stops Stops be determined determined until untiljust just prior prior to the field The actual stops to be visited and their locations cannot be trip. The Thegeneric genericstop stopdescriptions descriptionsare areprovided provided in in this this guide guideand and the the actual actual localities localities to to be be visited will be provided to to participants participants on on the the day day of the the field field trip. trip. Stop Overlook Stop 11 -- Dispatch Overlook Mining development pit, with with significant contributions contributions from development at Empire has focused on the Main pit, satellite satellite pits to the north north (CD-I), (CD-I), east east (Section (Section 20) 20) and and west (Southwest (Southwest Extension), Extension),and and expanding expanding development development to the northwest (CD-V). The The bottom bottom bench bench of of the the Main Main pit pit is is approximately pit will will ultimately ultimately be be developed approximately 1,000 1,000 feet below the dispatch overlook, and the pit 750 feet below the present mining mining level. level. entirely in in the the Carbonate Carbonate and and Silicate Silicate The bottom bench of the Main pit is developed almost entirely horizons. horizons. The The iron iron formation formation in in this this area area strikes strikes about about N35°E N35"E and and dips dips 30-35° 30-35' to to the the northwest. northwest. Stop 2 -- First Class Carbonate Carbonate The Carbonate i) Carbonate unit is gray to dark gray, relatively coarse-grained (magnetite grain size: 20-30 p) and characterized characterized by "thick" (5-25 mm), indistinct magnetite-rich and chert-rich layers with subordinate The term term "carbonate" "carbonate" is is utilized utilized at at the the Empire Empire Mine Mine to to subordinate siderite and ankerite. The c 10) 10) with very good liberation characteristics (low concentrate of indicate soft ores (work index < Si02). These high-grade ores ores have havebeen beenthe the"life-blood" life-blood' of Si02). of Empire's Empire's production. production. 132 �Stop 33 -- First Class Silicate Class Silicate Silicate iron ironformation formationconsists consists thin laminae (2 mm) of magnetite (minor tominor very minor of of thin laminae (2 mm) of magnetite (minor to very amounts greenish or or brownish-gray brownish-gray mixtures mixtures of of amounts of silicate, carbonate, chert, and clastics) and greenish silicate minerals, siderite, magnetite, chert and clastics. The The silicate silicate minerals minerals are are dominantly dominantly stilpnomelane stilpnomelane and and minnesotaite. The TheSilicate Silicatehorizon horizoncommonly commonlyhas has aa greater greaterabundance abundanceof of carbonate p) is finer carbonate minerals minerals than the Carbonate Carbonate zone. The Thegrain grainsize sizeof of the the magnetite magnetite(5-20 (5-20 L') than in the Carbonate-type. The term "silicate" at the Empire Mine is applied to ores Carbonate-type. The term "silicate" at the Empire Mine is applied to oreswith withwork work index> 10and andliberation liberationcharacteristics characteristicsthat thatare areinferior inferiorto to carbonate carbonateores; ores; silicate silicate or or yield yield index >10 higher higher concentrate concentrate of of Si02. Si02. Stop4Stop 4 -CD-V CD-V Future development in two areas: the the "pillar" "pillar" between the development of the mine will be principally focused in Main Main pit and and the the Section Section 20 20 pit pit (west (west wall), wall), and and the the north north and and northwest northwest areas areas of of the the Main Main pit pit termed CD-V. CD-V. Development Developmentof ofthe thewest westwall wallincludes includesrelocation relocation of of the the existing existing rail rail lines linesaround around the the east side side of the Section Section 20 pit; the "pillar" area will then be excavated to expose ores in the wall and, and, more more importantly, importantly,below below the the bottom bottom of of the the present present pit. pit. The The CD-V CD-V pit pit is is being being developed developed in in the the Upper Upper Series Series horizon, horizon, characterized characterizedprincipally principallyby by carbonate-type ores and clastic bands and lenses. Much of the yellowish carbonate material carbonate-type Much of the yellowish carbonate material contains contains very very little little magnetite magnetite ("lean" ("lean" carbonate), carbonate),consisting consistingdominantly dominantlyof of siderite sideriteand andchert. chert. However, very very rich rich carbonate carbonate ores ores are are also also present present in in the the push-back of of the the Main Main pit pit wall. wall. However, Current Current development development is is just below below aa large large diabase diabase sill sill that that is is 200-400 200-400 feet feet thick. thick. Several Several of of these these large, generally generally conformable, conformable, tabular tabular diabase diabase bodies bodies intrude intrude the the Negaunee Negaunee Iron Iron Formation Formation in in this this large, area of the mine. Predictably, Predictably, "fine-grained" "fine-grainer effects effectsare are extensive extensiveadjacent adjacentto to these these large largeigneous igneous bodies. bodies. In In the the CD-V CD-V area areaof of the themine, mine, iron ironformation formationand and interlayered interlayeredsills sillshave have been been folded foldedinto intoseveral several smallsmall- to moderate-scale moderate-scale anticlinal anticlinal and synclinal features. Fold Fold axes axes plunge plunge 10-20° 10-20' toward toward the the northwest. northwest. Bounding BoundingCD-V CD-V to tothe thenorth northisisaalarge largearea areaunderlain underlain by by magnetite-bearing magnetite-bearingiron iron formation formationthat, that, because because of of its its extreme extremehardness hardness (work (workindex index18-20) 18-20)and and poor poor liberating liberatingqualities, qualities,isispresently presently regarded regarded as as aa resource, resource, not not aa reserve. reserve. The Thenature natureof ofthe themetallurgical metallurgicalproblems problemsin in processing processing these these ores ores isis under under investigation investigationby by Cleveland ClevelandCliffs' Cliffs'research researchgroup. group. Stop 5- CD-I CD-I CD-I has has been been an an important importantsource sourceof of very veryhigh high quality quality(high (high weight weight recovery, recovery,low lowconcentrate concentrate Si02)carbonate carbonatematerial materialfor forblending blendingwith with lower lowerquality qualityores ores from from other otherlocations locationsin in the themine. mine. Si02) Ironformation formationininCD-I CD-Istrikes strikesnorth-south north-southand anddips dipsabout about30° 30' to to the the west. west. Two TwoKeweenawan Keweenawan hon age (1.1 (1.1 Ga) Ga) diabase diabase dikes dikes cross the pit in a westerly to southwesterly direction. These two two dikes dikes age direction. These are are coarser-grained coarser-grainedand and fresher fresherin in appearance appearancethan than the the other, other, older older early early Proterozoic Proterozoic diabase diabase dikes. dikes. 133 �The current phase of pit development development in CD-I will be completed in 1999. High High quality qualitycarbonate carbonate but its potential potential development development is is hindered hindered by by the the large large ore extends to the west beneath the pit wall but amount of stripping required. About About 750 750feet feet of of overlying overlying waste waste rock rock would would have have to to be be mined mined in in order to access access the ore. ore. References References Han, Tsu-Ming, 1975, Petrology of of Iron-Formation hon-Formation at the Empire 1975, Lithology, Stratigraphy, and Petrology Deposits of of the the Palmer Palmer Quadrangle, Mine, in Gair, Jacob E., Bedrock Geology and Ore Deposits Marquette Marquette County, County, Michigan, Michigan, U.S.G.S. U.S.G.S. Prof. Prof. Paper Paper 769, 769, pp. pp. 76-106. 76-106. 134 �Field Trip Trip 4 and Glacial Geology Geology from from Au Au Train Train to Paleozoic and Grand Marais, Grand Marais, Michigan Leaders: and J. J. Anderton Anderton Leaders: R.S. Regis and �______ ______ ____ ______ _____0144 ____On ______________________________________ ___________ ____________________________ ________ Pt(ISIOCENE NOMENCLATURE SYSTEM ERA a S z STAGE SERIES RRCMI U w_ i QUATERNARY kRISTOCINR EM STRATIGRAPHIC IN MICHIGAN MICHIGAN STFUTIGRAPHIC SUCCESSION SUCCESSION IN PPAUOZOIC ~ Z C Mmmi U THkOl &E4T 8 m . •• — I________ I__________ ——— DNI 3 DNR CSD I OUTCROP NOMENClATURE SUSSURFAa NOMtNCLATURE IECWW SCPtI11CJTOfflThI*tItSOOflS IWF 0. L GROIOGIC ITIMnTRAIIGAAPHFCI TIME F &LF4UFU& ORUET 0IT FORMATION MEMBER - R T44 kpl, — •.s — -19- .4- - coaflflI INFOPJI&AI. TERMS •fl 9 942 —fl — —d — — I....a — 4.4 04.44 •— •Afl •SC4MAL l1LU SILATGEAWIIC poslifli 4- 09,4 —. I-—. — 4-1 1, 1=- — ii 0._a. Rh 4.. b.,,Cs0L4 04442* 021 442 Tt 1Ja' ...u_o ._0fl4 — .4 S. — Os.— -.4-S— — ____._....__O4 4 ca hød5.S.. 44-,— .1 4-2 *4 —_____ - w.—9 89- -, — '4— 02S4 4I Go 04 SR. _•4_ — 0— O'la EXPLANATION C- — — — -' I flICMdfl p—,.— %%,— 4- 0-4.4 — waaflø fl.,O —. —, — — — —. a — .- 4d 4—— —, — # . . . — —I 42 --- CHART CHART 11 1964 ¶964 2071 em �ILSG Field Field Tdp Trip ##4from 1999 ZLSG 4 -Paleozoic Paleozoic and andPleistocene Pleistocene Geology Geologyfrom Au Train Train to Grand Grand Marais, Michigan Road log log Overview Ovewiew - - Au Train Train channel Profile of Au Stop 11 stop -- Au Au Train Train Falls Falls Stop stop 22 - - Beach Beach ridges and and Stop stop 33 -- Au Train-Whitefish Train-Whitefish Channel Channel Grand Grand Island Overlook Overlook Stop stop 44 -- Stop stop 55 -- Stop 6 -- Stop 77 stop -- Break Stop 88 stop -- Stop 9 stop Stop 10 stop 10 Stop 11 stop 11 ---- Stop 12 stop 12 -- US4 US41I S. (view to east at 2.3-3 ml.) mi.) continue 16.2 ml to M94, F. then E. 16.2 mi 18.2 mi. ml. to Forest Forest Lk. Rd. Rd. Return to Forest Lk. Rd. N 7.4 mi. to M28 M28 F. 2.5 mi. to H58, then to M28 E. Washington St. St. (1.2 mi.), to Munising Munising Falls (0.55 (0.55 mi.) mi.) Munising Munising Falls Falls Return to H58 (0.55 mi.), E to Miners Castle Rd (3.7 mi.), then N to Miners Castle Castle (4.9 mi.) mi.) Miners Miners Castle Castle Return to H58, continue continue F E to to Bear Bear Trap Inn 9 (3.6 mi.), mi.), keep keep left left and and continue on H58 (end of pavement another 4.3 mi.) to Kingston Corner Comer (11.2 (1 I .2 mi. beyond pavement end) Kingston Kingston Outwash Outwash Plains Plains N on H58 to 2-track on left (7.1 mi.) Proceed on 2 track 0.1 mi. & park park mi. & Walk due W 400 yds (strenuous) (strenuous) Turtle Return to H58,2.1 H58, 2.1 mi. to dropoff Turtle Lake Kettle into channel, @ 6.7 mi. is edge of upper outwash terrace, @ @ 8.7 mi. turn left on Log Slide Slide Rd.. Continue Continue to Log Slide Slide (0.75 ml.) mi.) Picnic area area @ Grand Sable @ NW side Grand Sable Lk. Log Slide Slide Return to to H58. H58. FE on on H58 H58 to to parking lot for Sable Creek falls and Ghost forest (5.6 mi.). Ghost Ghost Forest Sable Sable Falls Falls To Grand Marais (1.7 (1.7 mi.) Grand Harbor Grand Marais Harbor Nipissing Bluff E-W M77 to M28 (22.6 E-W channels channels crossed crossed by by M77 M77 (22.6 mi.) To Munising (22.4 mi.) To Marquette (44 mi.) 137 �Detailed Detailed Road Road Log. Log. of Au Au Train Train Whitefish Channel Overview of From the WashingtonfBaraga Washingtonmaraga St. St. intersection in downtown Marquette travel S on baraga St St US41). Along (turns into US4l). Along U.S. U S . 41 41 at at about about 2-3 2-3 miles miles south south of Marquette, a view to the east reveals a profile of channel cut by proglacial meltwater that flowed eastward along the margin of the Marquette (Grand Marais) ice. ice. The the Onota The feature feature was referred to by Hughes (1971) as the outlier. Water Waterspilled spilledinto intothe theAu Au Train TrainWhitefish Whitefish channel channel southward southward to to (present) (present) Lake Lake Michigan after passing through this channel. Continue on U.S. 41 south 16.2 miles to M94, turn east. Continue 16.2 Travel to 29.9 29.9 mi. to to Chatham, Chatham, turn turn SS at at stopsign, stopsign, travel travel to 30.9 30.9 mi and and turn FE on on M94, M94, continue continue to 34.4 34.4 mi and and turn N N on on Forest Forest lake lake rd., travel 0.1 mi to dirt road on right, follow to to gated gated parking area. Walk Walkto to falls. falls. Au Train Train Formation Formationand andAu AuTrain-Whitefish Train-WhitefishChannel, Channel,Beach Beachridge ridgecomplex complex Return to Forest Forest lake lake Rd., Rd., turn N. Follow Follow Forest Forest Lake Rd. At 6.3 miles and all the way to M28, note the beach ridge complex. Turn TurnEE on on M28 M28 and and travel travel to to the Grand Island overlook parking lot on the N side side of M28. M28. Grand Island Island Overlook Overlook From the Grand Island overlook, return return to M-28 and and travel travel east east 2.5 2.5 miles milesto toMunising. Munising. Turn on Dogpatch restaurant restaurant is on Ge the right at H-58 after passing the Holiday gas station on the left (the Dogpatch the intersection...excellent vittles! In In aa rustic, Li'l Abner Abner setting). setting). Continueon on H-58 H-58 an an additional additional intersection ...excellent vittles! . Continue 0.55 miles to to Washington Washington St., St., turn turn left left and and proceed to Munising Munising Falls Falls visitors visitors center center parking lot lot (0.3 miles). miles). Munising Falls Return to H-58 from the parking lot and and proceed proceed north north 3.7 3.7miles milesto toMiners MinersCastle CastleRoad. Road. Turn left. Travel Travel 4.9 4.9 miles miles to to the the Miners Miners Castle Castle parking parking lot. Miners Castle turn east (left). (left). Travel 5.9 miles to the Bear Trap Inn, veer left to to Return to H-58 (4.9 miles) and turn stay on H-58. End End of of pavement pavement 4.4 4.4 miles miles from the Bear Trap Inn. Continue Continueto to Kingston Kingston Corner Comer junction (11.2 (1 1.2 miles). Kingston Plain Travel north on H-58 7.1 miles to the small 2-track road on the left. Proceed Proceed about about50 50yards yardson on the road and park. Walk Walk about about 55 minutes minutes due due west (this (this walk may be strenuous for some). We We will remain at this stop for about ½ hour to allow time to walk to the bottom of the kettle. stop ?h NOTE: At 2.1 miles miles drop-off drop-off onto ontosurface surfaceB B (Hughes). (Hughes). NOTE: At 6.7 miles miles steep steephill hill marking markingedge edge of of surface surface C. C. Turtle Lake Return to H-58 and continue north. north. Travel 8.75 miles to the the Log Log Slide SlideRoad. Road. Turn north. Travel Travel 0.75 miles to the the Log h g Slide Slide parking lot. 139 �Log Slide Slide Return to H-58. Proceed Proceed east. east. NOTE: At 3.7 miles, the Grand Grand Sable Sable dunes dunes are areon onthe theleft left(north). (north). At At the the intersection intersection of of Newburg and William Hill roads, turn north on William Hill road and travel 0.7 miles to the Sable Falls parking lot. Walk Walkto tothe theGhost Ghostforest forest then then to to Sable Sable Falls. Falls. Ghost Forest and and Sable Sable falls Return to parking parking lot lot and and travel travel to to Grand Grand Marais Marais (east). (east), harbor Grand Marais harbor Follow M77 to M28, M28, turn turn e, e, follow follow to to US41, US41, N N to to Marquette. Marquette. Meitwater Meltwater channels channels Observe the outwash channels along M-77 appearance M-77 as as we we proceed proceed south. south. The "terrace"-like appearance of the topography is due due to M77 M77 crossing crossing proglacial meltwater meltwater terraces at right angles. angles. Streamfiow was to the east. Note Streamflow Note the the gentle gentle southward southward slope slope of individual individual terraces, marked by drained, swampy swampy areas areas near near their their southern southernedge. edge. poorly drained, 98 miles to Marquette. Sleep! Sleep! Grand Marais to M-28 M-28 south south on on M-77 M-77 West on M-28 M-28 to to U.S. U.S. 41 41 North on U.S. 41 to to Marquette Marquette 140 �—— — o — .r HIAWATHA InKEe - sera I. HP a Cenle 33 . FOREST 1 C —;-__--_---- NATIONAL -p /t t jIIu —H- -, _\_ 1 / LftlIaReavat - _ — . S -H ogon '° I-vanM -' t9 Ø4jfrurcShk . . -- a I I C C •— Ct-p I ft jt" rLi /' (\ "]' ' U\ In SI q Visitot Information Center a.0suadUtFI 0eSS— Mlnerecautle Stop 5 ta ° :1* diiiL ayeH ml - 4:) - r..r° ra TSI — tC Pu,u4LS.u.Hur '55d F PISM urea. LAKESUPERIOR UP Huu.p.flntS M,nuIee Falls 6*8.0 W5.0. wtt MUNISING HRHO 32*3)4* A re,pr'..d rt°t:d unttt _ _____ 3 C — ' 1 t / ( . C '>' - S I I C a - IA -- SUPERIOR C C -. S . STATE '\' A.a.uPuH . - . .- . FOREST '. .u Stop 9 -- s__s I 23 --— . j. ___1iS I. ¼ H- - -- I C / SIeP.IIS o 0LE' Ø1 "C-\' Log SI' ;r . S'.. ,CCk . SENEY NATIONAL WILDUFE REFUIE H LAKE r-t. ( 4' Hurricane River Stop 8 ___________________________________ jSop7 / 4)-Stop6 '— 'a CO&1 IWulvurulle Beach _____ — -- - STATEFOREST uurwPa.Heef - A 3 Sane 3 _eSdue lAKE SUPERIOR EuThHuth — -C. .H 5-' top 11 nterStop 12 Grand Sable GRAND t3ais rfiIrnCTMUSeUnt _______ �and Pleistocene Geology Geologyfrom fromAu AuTrain Trainto toGrand Grand Marais, Marais, Michigan Michigan Paleozoic and (FIELD TRIP #4) (FIELD TRIP#4) by Robert S. Regis and John B. B. Anderton Anderton Northern Michigan University University The geological history of the Pictured Rocks National Lakeshore (PRNL) (PRNL) is limited limited to to intervals of geologic two intervals geologic time; time; the Pleistocene Pleistocene epoch epoch when glaciers reworked reworked and and mantled mantled the the underlying underlying bedrock bedrock with with aa nearly nearly continuous continuous veneer veneer of drift, drift, and the the late late Proterozoic, Proterozoic,Cambrian Cambrian and early Ordovician periods when sediments deposited in shallow seas became the the sandstones sandstones that form the "pictured rocks" section section of of the the lakeshore. lakeshore. Late the Central Upper Late ProterozoiclCambrian/Ordovician Proterozoic/Cambrian/OrdovicianHistory of the Peninsula Peninsula including including PRNL PRNL Hamblin (1958), who who performed performed a Most material for this section was compiled from Hamblin detailed study of the Cambrian rocks outcropping in the PRNL and elsewhere elsewhere in northern Michigan. Michigan. The The Paleozoic Paleozoicgeologic geologic history history of of the the PRNL PRNL is is best described described as as aa period period of of eroding eroding highlands highlands and sedimentary sedimentary deposition deposition into into transgressing transgressing empeiric empeiric seas. seas. The The Northern Northern Michigan Michigan Highlands Highlands and the the Wisconsin Wisconsin Arch Arch stood stood as as eroding erodingremnants remnants of of former former highlands highlandsand and mountains, trending east-west across northern Michigan and more north-south across Wisconsin, trending east-west across northern Michigan and more north-south across Wisconsin. respectively. Encroaching respectively. Encroachingshallow shallowseas seas(the (theSauk Sauk transgression) transgression) during during the late Proterozoic Proterozoic and and throughout the Cambrian were depositional journey's end for of eroded sediments. the journey's most the sediments. Bedrock Bedrock is is best best exposed exposed in in the the pictured pictured rock rock section section where where bluffs bluffs rise rise up up to to 200' 200' above above short Lake Superior and extend seventeen miles from Munising to to the the Beaver Beaver Basin. Basin. For aa short distance distance inland from from the the escarpment, escarpment, usually usually no more than several several hundred hundred yards, bedrock may may occasional outcroppings. outcroppings. Elsewhere Elsewherein in the the National National Lakeshore Lakeshore bedrock is is only only found found be seen in occasional in the vicinity of the the Grand Grand Sable Sable bank, where where it forms a low bluff around around the the north north and and east east side side of Au Sable Point, Point, and and in in the the gorge gorge at at Sable Sable Falls. On this field trip, we will observe the rock rock formations formations in in reverse reverse order. order. The first rocks we will see are the youngest youngest exposed in the the park (western (western end) and last rocks we see see are are the oldest (eastern end). The TheJacobsville Jacobsvillesandstone, sandstone,of of questionable questionablelate-Proterozoic late-Proterozoicto to lower lower and and age, is is the the oldest oldest formation formation in in the the lakeshore lakeshore (more (more than 520,000,000 520,000,000years years old). old). middle Cambrian age, It is a feldspar-rich, quartz quartz sandstone, sandstone, deep deep red in color color with white mottlings. Although Although the the Jacobsville has a thickness thickness of of 1100 1100feet, feet, only only the top several several feet rise above above lake level, level, and and only only Jacobsville Onthis thistrip, trip,we we will will see see the the Jacobsville Jacobsville at at Sable Sable Falls Falls (Stop (Stop 10). 10). in the eastern part of the park. On The early-to-middle early-to-middle Cambrian-age Cambrian-age Munising- formation underlies most of the the lakeshore, lakeshore, mostof and forms most of the significant bedrock outcroppings in in the the park. park. It lies unconformably on top of the Jacobsville Jacobsville sandstone. The TheMunising MunisingFormation Formation isis divided divided into into two two members, members, the the lower lower and 5) 5) members members (500 (500 -Chapel Rock Rock (Stops (Stops 10 10and and 5) 5) and and the the upper upper Miners Miners Castle Castle (Stops (Stops 44 and 520,000,000 520,000,000 years old). old). Except Except where where the friable Miners Castle member is being rapidly rapidly undermined by wave action it forms slopes rather than cliffs. undermined forms slopes rather cliffs. In the western half of the "pictured rocks" the late Cambrian Au Train formation formation cropscropsout only along the top edge of the cliff (480 The Au Au Train Train is is aa light light along edge (480 500,000,000 500,000,000 years old). The brown or white, hard, dolomitic dolomitic sandstone sandstone usually highly present, it forms forms a highly glauconitic. glauconitic. Where present, - 142 �cap cap rock rock on on the the weaker weaker Miners Miners Castle Castle member. We Wewill will observe observethe the"type "type locality" locality" of ofthe theAu Au Train Trainformation formationatatAu AuTrain TrainFalls Falls(stop (stop1)1)on onthis thisfield fieldtrip. trip. All All formations formationsdip diptoward towardthe thesouth southaadegree degreeor ortwo twoas as shown shownin in the thephoto photohere here(view (viewisis toward toward the the east). east). All Allthe theformations formationsalso alsoarise ariseeastward eastwardso sothat thatthe theAu Au Train Trainformation formationisismissing missing east of of Miners MinersCastle castlebut but east the the Jacobsville, Jacobsville,which whichisis below below lake lake level levelat atMiners Miners Castle, Castle,carries carriesabove abovelake lake level. East Eastof ofMiners Miners level. beach, it is well exposed beach, it is well exposed beneath beneath the the conglomerate conglomerateof of ChapelRock Rockand andin inthe the Chapel gorgeat atSable SableFalls. Falls. gorge Thereare aremany many There waterfalls along along the the waterfalls escarpment escarpmentformed formed mostly mostly by the the Au Au Train Trainformation, formation, by but all all are arefed fedby by small small but streamswith with small small streams watersheds and and are are only only watersheds imposingin in the the spring springand and imposing during wet wet periods. periods. during MunisingFalls Falls(stop (stop4) 4) isis Munising view View along along the thePictured PicturedRocks Rocksshowing showing the the Munisiug Munisine formation formation dipping dipping to to the the the most most unusual unusual and and the south south at at aalow lowangle. angle. interesting of the the falls. falls. ItIt isis interesting - of an an extremely extremelywell-developed well-developedcap-rock cap-rockwaterfall waterfall with withthe the Au Au train train Formation Formation forming forming aa shelf shelf that that overhangs overhangs the the Miners Miners Castle Castle member member by by 25 25 to to 30 30 feet feet permitting observers observers to walk behind behind the the torrent torrent which which falls falls from fromthe the center center of of the the overhang overhang as as aa concentrated concentrated stream stream and then then descends descends another another 30 30 to to 40 40 feet feet in in aa series series of cascades. AArecent recent collapse collapseof of aa section section of this formation formation onto onto the walkway prompted Park officials to close a part of the walkway. Some well developed the walkway officials of the walkway. Some potholes potholes may may be seen seen in the cataract section. Miners MinersFalls Falls has has developed developed where where the Miners Miners River River drops from the upper to the broad lower valley. The fall is vertical and about 30 feet high. drops from the upper to the broad lower valley. The fall is vertical and about 30 feet high. Chapel Chapel Falls Falls isis fed fed by by aa tributary tributary to to Chapel Chapel Lake Lake that courses down the valley slope where there is no cap rock. The fall is a long cascade, about The fall is a long cascade, about 90 90 feet feet high that broadens fan-like from ten feet at the top top to to 30 30 feet feet at at the the bottom. bottom. Bridalveil Bridalveil Falls Falls and Spray Spray Falls are formed where streams streams fall, fall, about 90 feet, directly into Lake Superior, adding greatly to the beauty of the Pictured Rocks. At about 90 feet, directly into Lake Superior, of At Sable Sable Falls, Falls, the the stream stream draining draining Grand Grand Sable Sable Lake Lake cut into the Chapel Rock and Jacobsville Jacobsville formations formations where where they they lie lie beneath beneath sand sand dunes. dunes. The Thedeeply deeplywooded woodedsetting settingisisexceptionally exceptionally beautiful beautiful and and is is but but aa short shortwalk walk from from the the lakeshore lakeshore and and the the parking lot. The The Pictured Pictured Rock Rock escarpment escarpmenthas has been been carved, carved, by frost action and wave erosion erosion of the the present present lake, lake, as as well well as as higher higher stages, stages,into into aa variety variety of shore shore cliff features features such as: stacks, stacks, caves, caves, sea arches, and promontories. These Thesefeatures features have have been named: named: Lovers LoversLeap, Leap,Rainbow RainbowCave, Cave, Grand Grand Portal, Portal, Miners Miners Castle, Castle, Chapel Chapel Rock, Rock, The The Battleships, Battleships, Flower Vase and Indian Drum Cave. Cave. Most Most of of the the features features can can be be reached reached by hiking but only Miners Castle is accessible accessible by automobile. The The best way to appreciate appreciate the cliffs cliffs is by boat tour. Increased Increased accessibility accessibilityby by land land will will not not diminish diminish the the advantage advantageof of viewing viewingthe thecliffs cliffsfrom fromthe thewater. water. 143 �Late Quaternary QuaternaryHistory Historyof of the the Central CentralUpper UpperPeninula Peninulaincluding includingPRNL PRNL The Great Lakes region experienced experienced repeated glaciations glaciations and concommittant concommittant inundation inundation The the Quaternary. Quaternary. For by proglacial lakes throughout the For the the purposes purposes of of this fieldtrip, the final major (i.e. 11,800 BP) BP) marks marks the the beginning beginning of of deglaciation of the area during post-Twocreekan times (i.e. is most most relevant. relevant. Between 11,800 the portion of Late Quaternary history that is 11,800and 11,500 11,500 the Superior covered the the Upper Peninsula (Farrand and Drexler 1985). Superior Ice Lobe nearly completely covered 1985). By about 11,500 11,500 BP, retreating retreating glacial ice, followed followed closely by the high stands stands of Glacial Lake Lake Futyma, 1981). 1981). The retreat of ice continued, Algonquin, had nearly left the region (Larsen, 1987; Futyrna, opening up large portions of the Lake Superior basin in what is large portions the Lake Superior is known as as Glacial Glacial Lake Lake Duluth Duluth (Phases A and B), allowing allowing discharge discharge from from Glacial Glacial Agassiz during during Post Algonquin Algonquin times times (ca. (ca. 10,700 BP); however, evidence of this period was largely obliterated by a final readvance of ice into the Lake Superior Superior basin. The Theglacial glacialreadvance readvance is is known known as as the the Marquette Marquette advance advance (Drexler (Drexler et al. 1983). 1983). Shoreline features created by these earlier lake stages in the Lake Superior Superior basin were Shoreline largely destroyed during during the Marquette Marquette Advance (Hughes, 1978; Drexler, 1981; 1981; Farrand and and Drexler, 1985). 1985). By Byabout about9800 9800BP, BP, the theice icehad had begun begun to to retreat retreat again, again, resulting in a stepwise stepwise drop in lake lake levels levels which initiated initiated the the Post Post Duluth Duluth Phase Phase lakes lakes (Farrand (Farrand and and Drexler Drexler 1985). 1985). After about 9,800 BP, Marquette Advance ice had retreated far enough to the north to 9,800 Marquette Advance ice north to allow allow lake lake water from the western part part of Superior Superior basin to drain eastward and southward, southward, eventually eventually However, catastrophic catastrophic discharge discharge creating the Main Minong Phase (Farrand and Dexler, 1985). However, from Lake Agassiz early in the Nipigon Phase is thought to have breached a till barrier at at the the east east end of the Lake Superior Superior basin, basin, causing causing aa decline decline in Lake Minong resulting in at least least five five or or six six Teller and and Thorleifson, Thorleifson, 1983). The The post-Minong levels levels in the Superior Superior basin (Farrand, 1960; Teller lowering was finally finally stopped stopped as resistant resistant bedrock at the Sault Sault outlet outlet was reached, reached, culminating culminatingat at the Houghton Houghton Low around around 8000 8000 BP, BP, the the lowest lowest lake lake phase in the Superior Superiorbasin. basin. Finally, Finally, as as the the ice left the south south shore shore of of the the basin, basin, Glacial Glacial Lake Lake Minong formed formed along the margins margins of the the retreating glacier reaching its maximum expression by about 9500 BP; however, shortly reaching expression 9500 shortly afterwards afterwards the retreating retreating ice ice front front in the eastern eastern Great Lakes revealed the isostatically depressed depressed known as as the the Houghton HoughtonLow. Low. During this North Bay outlet, resulting in falling lake levels known period, lake lake levels levels in the the Superior Superiorbasin dropped to their their all all time time lowest lowest elevation, elevation, which which may may their valley valley channels. channels. By about 8000 BP the bedrock have allowed many rivers to deeply incise their sill at the Sault Sault acted acted to to halt halt falling falling lake lake levels levels in in the the Lake Superior Superior basin; however, however, by then isostatic isostatic uplift had had acted acted to to raise raise the the elevation elevation of of the the North Bay outlet, outlet, resulting resulting in rising rising lake lake levels in the southern southern basins. Eventually, Eventually, the the rising rising lake lake levels levels reached the elevation elevation of the Sault Sault Outlet Outlet and and lake lake levels levels in the Superior Superior basin began to gain in elevation. During During this this period, period, known as as the the "Nipissing "Nipissing Great Lakes," water in the basins basins of Lake Superior Superior and Lakes Huron and Michigan joined together to create create one one huge lake, lake, which which was controlled controlled by the North Bay outlet. Notwithstanding, Notwithstanding, the the North North Bay Bay outlet outlet continued continued to to rise rise and and eventually eventually lower lower drainages drainages to to the the south became active active commencing commencing the three-outlet (Chicago, (Chicago, Port Huron, and North Bay) phase of Lake Nipissing (Nipissing (Nipissing I), I),which reached its maximum elevation between 4700 and 4000 BP BP (Hansel et al. 1985). 1985). During Duringthe the Nipissing Nipissing Maximum, Maximum, flooding flooding of many tributary river valleys embayments along the coastal areas of the Upper Peninsula (Anderton 1993a). created large embayments 1993a). The Nipissing II IIphase, marking a slight drop in levels, was attained about 4000 years BP as continued continued isostatic isostatic uplift uplift raised the North Bay outlet above the altitude of the two southern southern II phase, lake-levels began to outlets (Hansel et al. 1985, 1985, Larsen 1985b). Following Following the the Nipissing II w �fall as as downcutting downcuttingprogressively progressively lowered lowered the Port Huron outlet and water volumes fluctuated fluctuated in in the the basins. basins. AAshort shortpeak peakininlake-levels lake-levelsatatabout about3200 3200BP BPresulted resulted in in the the Algoma Algoma phase, phase, but but by by about 2200 2200 BP BP lake-levels lake-levels in in the the Lake Lake Michigan-Huron basin had fallen below the elevation elevation of of the the rebounding rebounding sill sill at at the theSault, Sault,separating separatingthe the Superior Superiorbasin basin from from the the lower lowerGreat Great Lakes Lakesand and initiating 1960). Modern Modem lake-levels lake-levels in in both the the Lake Superior Superior and Lake initiating the Sault Sault level (Farrand 1960). Michigan-Huron Michigan-Huronbasins basinswere werefinally finallyattained attainedby byabout about2000 2000years yearsago. ago. Larsen Larsen (1985), (1985), working working in the the southern southern portions of the Lake Michigan-Huron basins, has has also also proposed an an alternative alternativemodel model of of Holocene Holocene lake-level lake-level fluctuations, fluctuations, which suggests suggests aa complex record of climate-related changes that lasted between 200 and 300 years complex record of climate-related changes that lasted between 200 and 300 years each each and and fluctuated fluctuated with with an an amplitude amplitudeof of 11to to 22 meters above the apparent mean lake level. In In the the last last 7000 7000 years at least least eight eight episodes episodes of high water periods separated by intervening low water periods are are recognized recognized (Larsen (Larsen 1985). 1985). periods Stop 1. Au Au Train TrainFormation Formationat atAu Au Train TrainFalls Falls At At Au Au Train Train Falls, Falls, aa 30 30 meter meter thick thick section section of the 100 100 meter thick early Ordovician Ordovician Au Train Formation (aka Trempealeau Formation) is exposed. exposed. The The formation consists consists of 2 parts, the upper and lower members. At Atthis thisstop, stop,we we will will examine examine the the lower lower section section at the lower lower falls, falls, and walk to to an overview overview of of the the upper upper section, section, which is is exposed about 200 200 meters upstream, upstream, but is is relatively inaccessible. inaccessible. The TheAu Au Train TrainFormation Formation lies lies unconformably unconformably upon the Munising Formation, Formation, and and is is representative representative of of the the continued continued Sauk Sauk sea sea marine marine transgression transgression that that began began in in the the late late Proterozoic. The environment of The environment of depositionwas was aa shallow shallow shelf shelf deposition platform platform with with fluctuating fluctuatingsea sea levels. levels. Paleogeographically, Paleogeographically,the theregion region was was equatorial with with the the equator equatortrending trending equatorial nearly north-south north-south compared compared to to nearly modern modem orientation. orientation. Note the the step-like step-like character character of falls (also (also in in the the upper upperfalls) falls) the falls created by the alternating alternating layers layers of of dolomite, dolomite, shale, shale, and and sandstone sandstoneof of varying varyingdegrees degrees of of resistance. Near areaaseries seriesof ofthin thinbeds bedsof of glauconitic glauconiticsandstone sandstone Nearthe thebase baseofofthe thelower lowerfalls fallsare (hydrous (hydrous silicate silicate of iron iron and potassium) potassium) and shale. Glauconite Glauconiteisisdisseminated disseminatedas asflakes flakes throughout the sandstone. sandstone.Glauconite Glauconite comprises comprises as much as 35% of some beds in the lower lower Individual beds Individual beds vary vary section and imparts a speckled green to dark green color to the formation. section and imparts a speckled green to dark green color to the formation. from pure sandstone sandstone to pure dolomite (Hamblin, 1958). Dolomitic Dolomitic beds are are bluish gray in color. An intraformational conglomerate(?) with pebbles of sandstone and dolomitic intraformational conglomerate(?) dolomitic sandstone sandstone are are found in a few of the units near the base of of the section (see (see cross cross section sectionon onnext nextpage). page). At the base of the lower lower Au Au Train, Train, the the contact contact with the underlying Miners Castle member of the Munising Formation is easy to recognize because the friable sandstone is quite quite different in Munising appearance from the hard, resistant dolomitic sandstone sandstone of the Au Train. Fossils are rare in the formations. Following deposition of the Au Train Au Train but become abundant in later formations. Formation was was aa minor minor regression regression that that formed formed an an unconformity. unconformity. 145 �eq a. a Cl) I- a a Cl) �Footage Footage Section section - top Upper Train rep of of ~ m Au AU s~ r r i nr7.11. a n Sandy grayi.h..blu. to to dark 4-10 Inch*. inches [hick. thick, some M d y dolomite, dtilmnitq, grayi#h-blu. dark blue, h h à §b.ds bed# 4-10 miu interbedded buff fin., ttoo mediurn.grained 1 iwft finemedium-grained sandstone Â¥andçtounits. ualte, .everal ¥¥vr horizons contain contain abundant • '/. 120 120 Description Detcription of of lithology lithology ,1auconite and and a uthl'enic pyrite authigenic pyrite Iglauconit. Olagco.ddc Gl.ueonldc . Sand.tone bed6""thick, S u d i t o i r bed thick, buff buff to to light gray, medium- to flne-grain.d, fine-grxincd, well wellrounded rounded well sorted and well sorted Sand.tone bed, same above S a d i t o n e bad, #Â¥mas above 110 110 Sandstonebed, bed, mame same ,a.iabove Suidçton above Ito 110 Authigenic pyrite filling vu ge Pure dolomite I::.: • 90 90 - :1 Highly glauconitic Authigenic pyrite filling wg. 80 80 70 70 - Sandstoneb ibed thick,finefine-totomedium-(rained, medium-grained,buff bufftotolight light gny, gray, well rounded thick, rounded Skndatonà d 8"8" sad well a dw e l l sorted sorted _ Abundant tuthigenic pyrite -: • - 60 60 Highly glauconitic of Uppç Upper An Au Train Train FP41. 1Base !am ef dln interysi (Covered :overed interval - 50. 50 40 40 - betweenUpper Upperaud andLowr LowerAu AuTrain Train fills Falls between -2 and" dolomite thick,generally generally Sandy dolomit,to todolomitic dolomiticsanditone, sandstone,buff bufftotobluish-#ray, bluieh-gray,bçd beds2"-t" 2"-" thick, separated by thin thin !.me* lenses of of silt silt or c p r t t e d by or clay, clay, bedding bedding planes plane* are ere undulatory, undulatory, percent of sand sand b e ' à § r lthroughout throughout à the section, #action, glauconite gluuconit. extremely extremelyabundant abundant mmpeclaily vane, the especially near the base Glauconità Glauconit. and clay galls Crest of of 1.ow.r lower Au Train Train Falls Crçs Fall. 30 30 Olauconit. concentrated along several horizons, sandy units ezhitat email-scale croci bedding, thin shale lense. separate unite 20 20 10 10 00 - _ _ Clauconite is is extremely 10-30 percent percent of of many many extremely abundant abundant as iitt conslitutee Gl*ucÈnit coirtltu1.m between bçtwç10-30 unit. thin uaite Had, weather, dark brown, beds Iron. thick, several horizons contain pebbles of .and.tone and dolomitic .sndstone which ,.pparently constitute an intraformational conglomerate IBase of Lower Au Train F'41s Columnar Columnarsection sectionofofthe theAu AuTrain TrainFormation FormationatatAu AuTrain Trainfalls falls(1-tamblin, [Hamblin, 1958) 1958) 147 147 �Stop Stop 2. Au Au Train-Whitefish Train-WhitefishChannel, Channel, Barrier, Barrier,and andBeach BeachRidge RidgeComplex Complex Train Whitefish Whitefish Channel Channel Au Train The The Whitefish-Au Whitefish-Au Train Train Channel Channel isis aa former formerproglacial proglacial lake lake spillway spillwaythat that drained drainedacross across the the central central Upper Upper Peninsula. Peninsula. From FromLittle LittleBay BayDe DeNoc, Noc,north northto toAu Au Train TrainBay Bay on on Lake Lake Superior, Superior, kilometers the channel is over 60 kilometers (36 miles) in length and ranges between about 2.5 the channel is over 60 kilometers (36 miles) in length and ranges between about 2.5 kilometers (1.5 miles) to 6.7 6.7 kilometers kilometers (4 (4 miles) miles) in width. The TheWhitefish WhitefishRiver, River,aatributary tributaryto to Little LittleBay Bay De De Noc, Noc, drains drains the the southern southerntwo-thirds two-thirds of of the the Channel. Channel. The Thenorthern northernthird thirdisisdrained drainedby bythe theAu Au Train Train River, River, aa tributary tributary to to Lake Lake Superior. Superior. Most Mostof ofthe thechannel channelbottom bottomisisunderlain underlainby by thin thin deposits of of gravel gravel or or till till over over bedrock. bedrock. deposits The The lowlands lowlands of of the the Au Au Train-Whitefish Train-WhitefishChannel Channel were were first first noted notedby by Foster Fosterand andWhitney Whitney (1851), (1851), but itit was was Winchell Winchell (1871) (1871) who who interpreted interpreted the feature as a meltwater spillway. Russell Russell (1904), (1904), however, identified identified the the channel channel sides sides as as kame kame terraces terraces having having been been deposited deposited by by aa thin thin lobe of ice that had stretched stretched across the Upper Peninsula. The The channel channel has has since since been been studied studied by by a number (1929), Hough Hough (1958), (1958), Drexler Drexler et et al. al. (1983), (1983), Farrand Farrand and and number of workers workers including including Leverett Leverett (1929), Drexler (1985), (1985), and Hughes Hughes (1990). (1990). Incidently, Incidently,Leverett Leverett (1929) (1929) indicates indicates that during during the 1920s, 1920s, government government engineers engineers considered considered cutting cutting aa ship ship canal canal through through the the Au Au Train-Whitefish Train-WhitefishChannel Channel and connecting connecting Lake Lake Superior Superior to to Lake Lake Michigan, thus avoiding avoiding the Sault Sault Locks. According to Hughes (1990), (1990), the Au Train-Whitefish Channel reached its its full expression expression According during during the Marquette Marquette Advance Advance about 10,000 10,000 BP. At At this this time, time, lake lakelevels levels in in the the Lake Lake MichiganMichiganHuron basins as retreating retreating ice ice had revealed revealed the the basins were were extremely extremely low low (Chippewa-Stanley (Chippewa-Stanley Low) as isostatically isostatically depressed depressed North North Bay Bay outlet, outlet, allowing allowing water water to nearly drain from the southern southern basins. basins. Before, Before, during, during, and, and, for for an an unknown unknown period period after after the the Marquette Marquette Advance, Advance, proglacial proglacial lake lake water water drained across the central Upper Peninsula to the lower lakes, creating the Au Train-Whitefish central Upper Peninsula lakes, creating Train-Whitefish Channel. Hughes Hughes(1990) (1990)has hassuggested suggestedthe the Channel Channel extends extends under Little Bay De Noc and Green Bay to a large, Chippewa-level off the east east side side of of the the Door Door Peninsula. Peninsula. The Chippewa-level delta submerged off The Channel was abandoned abandoned at at around around 9700 9700 BP when retreating retreating ice allowed allowed lake water to reach the the Sault Outlet Outlet on the the east east end end of of the the Superior Superior basin. Barrier Au Train Barrier During Nipissing Nipissing times, times, lake lake water water flooded flooded some some 66 kilometers kilometers (3.6 miles) miles) into into the the northern end of the the Au Train-Whitefish Train-Whitefish Channel Channel creating creating Au Train Relict Relict Bay, which is is one one of of Nipissing II wave-cut bluffs the largest Nipissing embayments in the central Upper Upper Peninsula. Peninsula. Nipissing and cliffs, cut cut in bedrock bedrock and and unconsolidated unconsolidated sediments sediments at at 192 192meters, meters, rim much much of of the the east east and and west sides of the former embayment; however, in places along the southeast fringes, the shoreline sides the former embayment; southeast fringes, the shoreline is less developed, appearing by eolian eolian activity. activity. In fact, small relict appearing to have been modified by along the the southeast southeast side of Au foredunes may be present along Au Train Lake. Lake. A massive mid-bay barrier extends extends from from northwest northwest of of Paulson Paulson Lake, Lake, east east to to Joel Joel Creek, Creek, forming forming the the northern northern boundary boundary of of modern Au Train Lake. The Thebarrier, barrier, having having an an elevation elevation of 186 186 meters on its north side side and 189 189 its south south side, side, reaches reaches an an elevation elevation at at its its crest crest between 195 195 and and 192 192 meters meters and and aa meters on its maximum elevation dune remnant. remnant. In elevation of 201 meters on what appears to be a dune In places, places, the barrier severely eroded eroded by by the the Au Au Train Train River. River. has been severely The barrier barrier created created aa huge huge lagoon lagoon between the barrier proper and the southern southern rim of of the the The bay, now occupied occupiedby byAu Au Train TrainLake, Lake, Paulson Paulson Lake, Lake, and surrounding surrounding wetlands. Based on the depth of Au Train Train Lake Lake (USDA, (USDA, 1938), 1938),during during Nipissing II times, times, the lagoon would have have had had aa maximum maximum depth depth of of at at least least7.5 7.5 meters meters (25 (25feet), feet), an an average average depth depth of 33 to to 44 meters meters (9.8 (9.8 to to 13 13feet), feet), miles). Drainage may have exited from the and covered about 6 square kilometers (2 square miles). 148 148 �Au Train Lake $Iapnck Cr. AU TRAIN- CisySand Cliffs Baa n SPI LLWAY Cr. WhIt.fish P. SCALE SCALE kilomstsrs I a , j I 0 -I $ IQ Ovation In ff11 vs Little Bay Do Noc AuTrain-Wiifeflsh Spiliway AuTrain-Whitefish Spillway (Hughes, (Hughes, 1971) 1971) 149 �D Moraines and channels in the Marquette area and the Eben-Chatham channels (Hughes, 1971) �SUBMARINE VALLEY IN IN THE THE FLOOR FLOOR OF GREEN GREEN BAY BAY I 11 SCALE I. I. ItI• KIlO S•I SI I SSIk,Ic lIt,SI - S S4—• 151 �lagoon on its its northeast northeast corner comer near near the the eastern eastern end end of of the the Au Au Train Train Barrier Barrier or or at at some somemidmidposition breach in the barrier, where the Au Train River runs through today. today. Nipissing Nipissing II IIlevels levels may have modified the the northern northern edge edge of the the barrier, which is is at an an elevation elevation of of 186 186meters. meters. Au Train TrainBeach BeachRidge Ridge Complex Complex The The Au Train Train Beach Beach Ridge Ridge Complex Complex occupies occupies the the area area between between the the barrier barrier and and the the modern shoreline of Lake Superior. The complex is composed of some 50 separate recessional modem shoreline Superior. The complex is composed of some 50 separate recessional ridges which form a compact, arcuate shaped "corrugated plain" plain' as first first termed by Bergquist Bergquist (1936). The rIdges, which range in elevation between 186 and 184 meters, are currently being (1936). The ridges, which range in 186 184 eroded eroded by Lake Lake Superior, Superior, which has has created created an irregular irregular line of actively forming coastal coastal foredunes on the northern end of the complex. The The Au Au Train Train River has also also meandered through the ridges ridges resulting resulting in in erosion erosion and and truncation, truncation, suggesting suggesting that that the the river's river's present present course course isis relatively recent. The Theridges ridgesare areparallel parallel to toeach each other, other, and and there there is is no no evidence evidence of cross-cutting cross-cutting relationships, relationships, indicating indicatingfluctuating fluctuatinglake lake levels. levels. Grand Island/Powell Stop 3. Grand Island/PowellPoint Point Scenic Scenic Overlook moraine. The This stop stop is on the crest of a Marquette Advance moraine. The overlook overlook affords affords aa view view of Grand Island, Island, Grand island Island Harbor, Harbor, Murray Bay, and Sand Point. Sand Point, a large cuspate spit, is visible in the east channel of Grand Island Harbor. Harbor. The The spit, spit, which ranges in elevation elevation between 185 185 and 183 183 meters, appears appears to to have formed in post-Nipissing times, times, and and is is still still being being actively modified by wave-action wave-action from from Lake Lake Superior. Superior. It is composed of a number of lesser bathers that deve]opment of of the the spit. A sandy barriers that appear appear to to have have created smaller smaller lagoons during the development A massive Nipissing I, wave-cut bluff at 192 meters is present along the southeast side of the spit, 192 southeast side the spit, Nipissing I, which extend extend to the the northeast northeast from marking the start of the modem cliffs of the Pictured Rocks, which Sand Point. Point. On Grand Island, Island, Nipissing Nipissing I wave-cut bluffs developed in bedrock at 192 192 meters meters rim rim much of the southern portions of island. Wave-cut Wave-cut caves, caves, shoreline shorelinestacks stacks and and arches, arches, and pocket pocket shoreline along beaches are present along the Nipissing I shoreline along the west side of Murray Bay. WaveWavecut bluffs at 192 192 meters meters rim portions portions of the the Island's Island's western high ground, known locally as as the the Thumb. Thumb. AAwell-developed well-developedsystem systemof ofstream streamgullies gullieshas has dissected dissected the the eastern eastern hillsides hillsides of of the the main lobe of the island, as well as much of the hillsides on on the the Thumb. Thumb. These These narrow, narrow, deep deep incised valleys end abruptly at the Nipissing I shoreline, indicating that they formed in preabruptly shoreline, Nipissing, Houghton Low times Nipissing, times when stream stream base levels were extremely extremely low. Cuspate Cuspate barriers barriers grading grading from the Nipissing I bluffs to about 186 186 meters are are also also visible visible on Grand Island. The Cuspate Bather, Barrier,which which isis located located Themost most obvious obvious of of these is the Duck DuckLake Lake Cuspate on the east side of the main lobe of the island. ItIt isis composed composed of of a number number of large ridges ridges that trend east to west on the south side, and north to south on the east east side of of the the barrier. barrier. Duck Duck Lake, Lake, a small inland lake, lake, is is aa lagoon lagoon remnant remnant associated associated with the the barrier. The The Muskrat Muskrat Point Point Cuspate Cuspate Bather, Barrier, formed formedoff off the the southwestern southwestern end end of of the the Thumb, also contains a lagoon remnant, now a small swampy pond. Wave Waveaction actionfrom fromLake Lake Superior Superiorhas has eroded the southeastern southeastern tip of the the Duck Lake Cuspate Cuspate Barrier, the the southern southern limb limb of the the Muskrat Muskrat Point Point Cuspate Cuspate Barrier, Barrier, and and the the southeastern southeastern tip tip of of the the Williams WilliamsLanding Landing Spit, Spit, exposing exposing imbricated imbricated gravel gravel and and cobble cobble beds beds in in both cases. These Theseeroded erodedareas areasshow showup upas ashigh, high, sandy sandy bluffs bluffs along along the modern shoreline. The Grand Island Beach Ridge Complex, a complex of at least 25 beach ridges ranging ranging in tombolo between the Thumb Thumb and and the the main main part part elevation between 186 186 and 183.5 183.5 meters, meters, forms a tombolo of the island. 1i Inplaces placeson onthe thesouthern southernedge edgeof of the the complex, complex, beach beach ridges are submerged by 152 1 52 �Stops 3 & 4 Stop 5 153 �Lake Superior, Superior, while while the the northern northern edge edge is is currently currently being eroded eroded by the modern modem lake, lake, creating creating small coastal foredunes foredunes along along Trout Trout Bay. of Grand Island Island presents presents an an enigma. enigma. Some A steep cliff visible high on the west side of Some workers (Don and Eschman, 1971) have suggested it is a wave-cut bluff from Lake Algonquin. (Dorr and Eschman, 1971) have suggested it is a However, such such aa feature feature would would have have been been destroyed destroyed during during the the Marquette Marquette Advance. Advance. Alternatively, the escarpment may be a remnant of an ice marginal stream channel Alternatively, escarpment may stream channel created created during during the retreat of Marquette Marquette Advance Advance ice ice or or itit may may have been created created by headward headward erosion erosion and and retreat retreat of a caprock on the the highest highest portions portions of of Grand Grand Island. Island. Stop 4. Munising Munising Falls Falls At Munising falls, the Au Train Formation (see (see stop stop 11for for a more complete complete description) description) meters thick. Conformably forms a resistant resistant caprock caprock of of dolomitic dolomitic sandstone sandstoneabout about 55 meters Conformably below is the weaker Miners Castle member of the Munising Formation, which has has been been undercut undercut to to form form a steep high-walled valley. Munising MunisingCreek Creek plunges plunges 10 10meters meters over over the the falls falls in in its its short short journey to to Lake Superior. At plunge pools. pools. They were At the the base base of of the the falls falls are are several potholes and plunge abraded into the sandstone sandstone by by hard cutting cutting tools tools carried from from the overlying overlying caprock caprock and and from from glacial drift. Visitors Visitorsused usedtotowalk walkbehind behindthe thefalls, falls,underneath underneath the the overhanging overhanging caprock, caprock, but but aa recent collapse collapse of aa section section onto onto the the walkway walkway prompted prompted park officials officials to to close close that that part part from from the the general general public. public. The Munising Munising formation formation represents represents aa transgression transgression of of the the shallow shallow Sauk Sauk sea sea onto ontothe themidmidcontinent region in Cambrian Cambrian time. The Theupper upper Miners MinersCastle Castle Member Member isis aa light light gray gray to to white white colored, poorly poorly sorted, sorted, cross-bedded sandstone sandstone that comprises comprises the the upper upper 30 30 meters meters of of the the Munising Formation. In the lower part of the member, thin thin lenses lenses of of blue blue shale shale are are common, common, but but become scarce scarce in the the upper upper portions. portions. Quartz Quartz grains grains dominate dominate the the lithology lithology (>95%) (>95%) of of the the Miners Miners Castle member, member, with feldspar comprising most of the remainder. Most Most quartz quartz grains grains exhibit exhibit straight extinction and are likely of igneous origin. origin. ItIt is is not not uncommon to find find 1-3 1-3 cm cm thick thick beds beds of shale alternating with 10cm 10 cmthick thickbeds bedsof of coarse coarsesandstone sandstoneand and even even conglomerate! conglomerate! Especially Especially in the lower parts of the Miners Castle member. Higher Higher up in the member, member, fewer beds of shale and conglomerate conglomerate are are found, found, and and beds beds consist consist mostly mostly of well-sorted, well-sorted, cross-bedded sandstones sandstones with a greater degree of mineralogical and textural textural maturity. maturity. Some Some individual individual beds are are quartz quartz arenites, but in sum the formation formation is poorly sorted. Quartz Quartzisis also also the the dominant dominant cementing cementing agent, agent, but with only only slight slight secondary secondary enlargement of the detrital detrital grains, grains, it is porous porous and and friable. friable. Authigenic Authigenic pyrite pyrite is is common common enough enough in in some some of the middle middle beds that it is is megascopically megascopically discernable. Discussion Discussionof ofthe theMiners MinersCastle Castlemember member continues continuesat at the the next next stop. stop. Stop Stop 5. 5. Miners Miners Castle This stop stop examines examines the the type locality locality of the Miners Castle member of the Munising Munising formation (see description in stop 4). Sedimentary structures such as mud cracks (mostly Sedimentary structures as (mostly in the shale beds), ripple marks marks and cross cross bedding bedding (as seen at this stop) suggest an alternating alternating fluvialllacustrine environment of deposition. Significantly, fluvial/lacustrine Significantly,the ripple marks and cross bedding in the Miners Castle Castle member member indicate indicate aa transport transport direction direction from the east-northeast, east-northeast, as as opposed opposed to to the northwesterly transport direction direction measured in the older Chapel Rock member (see (see figure figure illustrating cross-bedding directions). The The abrupt abrupt change change in in transport transport directions directions in the two members provides provides further further evidence evidence of an unconformity that separates separates them. The change change in transport direction also also suggests suggests that that the the Wisconsin Arch and the the Northern Michigan Michigan highlands, highlands, 1544 15 �Miners Castle Castle Member Member of the Munising Formation Au Train Train Formation Formation dolomitic, yellow-brown, coarse-and coarse-and medium medium grained with much 148 'Sandstone, very very dolomitic, 148 ' -152' 152' Sandstone, very coarse and little fine, fine, scattered scattered very veryfine fineand andfine finequartz quartzpebbles. pebbles. Some irregularly bedded. bedded. Some large zones conglomeritic. Massive Massive bedded and irregularly sandstone sandstone pebbles. pebbles. Munising Formation, Miners Munising Formation. Miners Castle Castle Member Member 144' - 148' 148' Sandstone, 144' Sandstone, light light yellow gray, medium grained grained with much fine fine and and aa little little fine, fine, even bedded and thin-medium thin-medium beds. Another bed as above above 140' - 144' haccessible 122' - 140' Inaccessible Light yellow-gray sandstone, coarse and very coarse grained with a trace of 121'- 120' granules. Cross-bedded Cross-beddedin inmedium-thin medium-thin beds. beds. Light yellow-gray sandstone medium to fine grained with traces traces of granules. granules. 115'- 121' bedding. Poorly sorted with much fine Medium - thick bedded with cross bedding. material in lower foot foot of bed. 112' - 115' coarse to to medium medium grains. grains. Trace Light yellow gray sandstone, coarse Trace of granules. Massive, cross cross bedded. 111' -112' Light yellow gray sandstone, poorly sorted with sizes ranging from silt silt to to granules. Abundant Abundant limonite limonite staining. Appears Appears to to be be burrowed. Narrow Narrow ledge. ledge. 108' - 111' Light brown gray sandstone. Medium to coarse grained grained with much much fines. fines. Massive. Trace Traceof of granules. granules. Light yellow gray sandstone. Poorly Poorly sorted sorted with grains grains ranging from silt silt to to 106' - 108' granules. Abundant Abundantburrows burrowsbest bestseen seenfrom from overhangs. overhangs. 103' - 106' Light yellow brown sandstone. Medium Medium to to coarse coarse grained grained with with few few granules. granules. Massive bedded. Massive bedded. Same as above above except except more silty and abundant abundant burrows. 99' - 103' 95' - 99' gray sandstone. sandstone. Silty Light yellow gray to gray Silty medium to fine grained with thin beds of red, blue and green shale. Poorly Poorly sorted. sorted. 40' - 95' gray sandstone. sandstone. Poorly sorted to well well sorted beds. beds. The Light yellow gray The upper upper part, part, of medium to fine grained beginning at the top of Miners Castle pinnacle, consists of wed wee1sorted sortedbeds beds of of sandstone, sandstone,interbedded interbedded with with poorly poorly sorted sorted beds beds of of sandstone sandstone containing abundant silt and thin beds of silty shale, and conglomeritic beds with silty shale pebbles. The The upper upper 66 feet contains burrowed beds. At At 10-12 10-12feet feet below the top, are prominent poorly sorted, shaly, conglomeritic and cross are prominent conglomeritic and cross bedded bedded sandstones. sandstones. 20' - 40' Gray sandstone. Poorly Poorlysorted, sorted,medium medium grained grained with with abundant abundant thin thin blue blue shale shale partings. Some conglomerate. Cross bedded. Some conglomerate. Cross bedded. 10' - 20' Light yellow gray sandstone, coarse coarse grained, grained, well well sorted. sorted. Contains Contains clay pebbles. pebbles. Formation, Chapel Munising Formation, Chapel Rock Member Light yellow gray sandstone. Medium 0' 0' -- 10' 10' Medium to to fine fine grained grained with with aa trace trace of of coarse, coarse, wellwellsorted sandstaone. Cross Cross bedded. bedded. Lake Level 183 m (602') Level == 183 (602') 155 �+ Inland—0Prairie du du Chlen Chien inland PJI members arise to to the the east east so that that JacobsvllIe All members Jacobsville is above lake Is above lakelevel levelat atGrand GrandMarais Maraisand andthe theAu AuTrain Train fornialion formationIsismissing missingfrom fromThe the top top of ofcliffs, cliffs. — 7 a —— —— - - Unconformity - -I- —- —— Light brown, hard, dolomilic sandstone. Giauconillc. Au Train Formation Resistant Resistant A Upper 5-12 5-12 meters meters Upper Moderate Moderateto tovery vewdoiomitlc doiommcwttti with O L O gronJies ~ on0 pebDie5. qUarlz granuies and pebbles. Burrowed br the ELnowea "for tnebirdC Diros" i Soft riable ,,poorly pooW sorted sorted Soft, ffriable silty silly, shaM shov, sandstone, often often cross-bedded. cross-bedded, Light yellow-gray color Light yellow-gray color imparted importedby bylimonite. llmontte.(In (In varying varying amounts amounts Miners Castle Member C 0 About 3Dm to lake 0 U- 0) C Cl, C 0' A ——— _Uo9rmjy_ —— Pink. light Pink, Ughtbuff buffto to brown, brown, medium medium omoquommcsandstone. sandstone. grainedorthoquartzWc grained Thin blue shale shale beds beds 2-3 2-3cm Thin blue cmthick. thick. Mudcracks Mudcrocksininshale shalebeds. beds. ""bdsôh"é'(°h€ri Uórtz quartzite, and chert w/minor amounts of siate, BiF, basalt and granite) Chapel Rock Memberô a —————a—— c b a Jacobsville Jacobsville Formation Formation I - —a——— a I Nigular unconformity Nkosic to Arkosic quartz quartz sandstone. sandstone. Red Redto red-brown abundant mottles red-brownwith abundant mottles and where on0sireaks, s ~ ~ o < sespecially es~ecioirv . wnere permeable. Th cmessvaries vanesgrecztts greatly, Denneooie.Thickness from > 1m to 500 m, from>lmtoSOOm. �____________________________________________________________________________________ Ga rat Zircon looter, 5.çtton Dcecflptioaotltthotogy ntis 0 I DeIsmilic ttnd.tae. light brown, Very resistant 3ssso1 kU TRAIN formation tencanlormity • • ISO ''.•.' Top of MUNISINC t.rmatlea Miner's C..tj. nwmb.r teStIsa. .Mte, m.dlwn-grasn.4, friable, ma.!,. badtsg (I' tot thick), fonti vertical di/l. — Details of ..dimtntsry strvcttr.s ob•c,and hyw.ath.riag; ataytadte appnrt be cr*tt.b.dd*d 120 Sandstone wMt. mSwm.praintd. ..U coned, masal,. bedding (I' tel thick). email cavee and arch... friable N'&marc'aa tat;. tcrsdeaa along bedding pta. Smelt—scale crass bedding to,. 11.4 stains ales; certain hastens .... b6. i" bed. very resistant. contains abtaadaat n.atris Sandstone. pr.tn,iaaatly poorly sorted ttt. is gray. tniaor streak. .1 red, blee and grssn, 5... of Mint's Castle piradle 55 Coarse .and.sene conc.atrat.d along cantata bedding p1.... Abundant day pail.;. deposited parallel to the cro.* bedding cbann*I. and Ian... shine cflgtOrnhrstO iO Small ceagiarat. lens.. So. Coarse eand and conglomerate I..... S Slut, grita, red, and yells'. colorado. foflo.tn bedding ,a.'... S.ndst.. gray to grayteh'.bl.a., m.tum,grain.d, pearly .on.d amall_.caIa crosa bedding 4".,i" thick ..parat.d by thin blue hal. I.n.e. l14"-t" thick '4 3° (approalmaisly 2030 percent .hal*), torn, coarse and fin. coagloanarat. / 20 ''i L'&3c 10 , & ¶cat.r t*v.l of bk. r / y I, ( 1 pa.' of Itt.,'0 tail. m..r unonntor Top of Chapel Rock rna,.bor 5aad.tots, pink, coors.-grainsd, nil sorted, rounded, abundant clay pellet. Mud cracks 4"-S' In tonnetar dontloped in beds of bIn. shale ines than I' thick. Clay pellet. sandseont light brown to buff well carted large •cale cross bedding It thick j - Superior Columnar Columnarsection sectionof ofthe theMiners Miners Castle Castle member memberof ofthe theMunising MunisingFormation Formation at atMiners MinersCastle Castle(after (afterHamblin, Hamblin,1958) 1958) 157 157 �Paleogeography member of Paleogeographyduring duringdeposition depositionof of the the Miners Miners Castle member of the the Munising Munising Formation Formation(after (afterHamblin, Hamblin, 1958) 1958) £IPLSNAtION bSSJ V tsuSe ndI.* d— - — •_N_ •m Caib — — fl4 —*• lö? I— I*aj •f — t* un—*. _*._ cni .4 * t tS3a, La - is 0 iG it sai—. t— '0 •0S.iii Cross bedding bedding directions MinersCastle Castlemember member of the the directions in the Miners Munising (after Hamblin, Homblin, 1958) Munising FormatHon Formatiion (after 1958) 158 158 �which which provided providedthe thesource sourcefor forsediments sedimentsduring duringthe the Jacobsville Jacobsvilleand and Chapel Chapel Rock Rock deposition, deposition,had had eroded erodedenough enoughthat thatthe thetransgressing transgressingSauk SaukSea Seasubmerged submerged most most of of the the Upper Upper Peninsula peninsula and and Wisconsin. Wisconsin. Stop6. 6. Kingston Kingston Plain Plain Stop Stop Stop66 isison onthe theKingston KingstonPlain, Plain,an an extensive extensiveoutwash outwashplain plain that that isislocated locatedbetween betweenthe the towns towns of of Munising Munising and and Grand Grand Marais. Marais. The ThePlain Plainpresents presentsaaunique, unique,prairie-like prairie-likesetting setting compared compared to to much much of of the the more more heavily heavily forested forested areas of the Upper Peninsula. The The multitude multitude of of pine pine stumps stumps preserved presemed on on the the Kingston Kingston Plain Plain serve serveas as testimony testimony to to the the intensity intensity of of historic historic clear-cut clear-cut logging. logging. A (Leverett,1911, 1911, A number numberof of workers workershave havestudied studiedthe the geology geology of of the the Kingston Kingston Plain Plain (Leverett, 1929; 1929;Bergquist, Bergquist, 1936; 1936;Martin, Martin, 1957; 1957;Hughes, Hughes, 1968; 1968;Drexler, Drexler, 1981, 1981, Drexler Drexler et et al., al., 1981; 1981;Blewett Blewett and and Rieck, Rieck,1987; 1987;Blewett, Blewett,1994), 1994),which which has has resulted resulted in in aa wide wide range range of of theories theories concerning concerningits its formation formationhistory. history.Largely, Largely,the thecontroversy controversyhas hasfocused focusedon onthe theinterpretation interpretationof ofthe theMunising Munising Moraine, which the Kingston Plain is part of (Blewett, 1994). According to Hughes Moraine, which the Kingston Plain is part (Blewett, 1994). According to Hughes (1968 (1968and and unpublished unpublishedwork), work),and andlater laterby by Blewett Blewett (1994), (19941,whom whom has has done done the the most most current currentQuaternary Quaternary geology geology research research in in the the area, area,the the Plain Plain initially initially formed formed when when Marquette Marquette Advance Advance ice ice probably probably reached reached an an equilibrium equilibriumand andsouthward southwardflowing flowingmeltwater meltwater streams streamsbuilt built the the Upper Upper Kingston Kingston Outwash I). Ice Outwash Plain Plain surface surface at at about about 10,000 10,000 BP (Phase 0. Ice retreated retreated somewhat somewhat from this position, opening opening up drainage drainage to to the the east east between between the the ice ice front front and higher ground to the south, south, creating creating aa channel M-77. The channel at at 283 283 m m that that currently currently parallels state highway M-77. The upper upper portions portions of of the the Kingston Kingston Lake Lake Kettle KettleChain Chainformed formedatatthis thistime. time. Next Next (Phase (PhaseII), lI), the the ice ice margin margin retreated to a new position along along the Lower Kingston Kingston Plain, opening even lower drainage outlets from the west. Consequently, water flowing to the Plain, opening even lower west. Consequently, water east east between between the the ice ice front front and and the the now now abandoned abandoned Upper Upper Kingston ice-contact ice-contact slope, slope, formed formed aa broad, broad, kame kame terrace terraceatatabout about285 285m, m,which whichslopes slopestotothe theeast. east. Marginal Marginal retreat retreat of of the the ice ice from from highlands highlands south south of Grand Grand Marais Marais allowed allowed still still lower lower outlets outlets to to open open (Phase (PhaseIII), I Q ,which which resulted resulted in in the the incision incision of a channel channel at 250-253 m, into the the Lower Lower Kingston Plain Plain surface. surface. The TheHurricane Humcane River River currently currently follows this channel. Also Alsoatatthis this time, time, some some meitwater meltwaterspilled spilledsouthward southward from from the the Lower Lower Kingston Kingston ice-contact ice-contact slope slope south south of of Beaver Beaver Lake, Lake, forming forming the the Long Long Lake Channel. The Thelower lowerportions portionsof ofthe theKingston KingstonLake LakeKettle Kettle Chain, Chain, including includingKingston KingstonLake Lakebasin basinmust musthave haveformed formedduring duringthis thisphase. phase. IV,and and55 of of Blewett, 1994), 1994), the ice withdrew to a position position several several Eventually(Phase (PhaseIV, Eventually kilometers kilometers north north of of the the Lower Lower Kingston Kingston ice-contact ice-contact slope, slope, allowing allowing meltwater meltwater drainage drainage across across aa broad terrace heading at 230 m, known as the Beaver Basin surface. Further retreat of ice broad terrace heading at 230 m, known as the Beaver Further retreat of ice allowed allowed even even lower lower channels channelsat at 225 225 and and 215 215 m m to to be be incised incised into into the the Beaver Basin surface. surface. Finally, the glacier retreated to a position just south of Portal Point, but eventually Finally, glacier eventually further retreat retreat allowed allowedlake lake water water in in the the western western Superior Superiorbasin basin to to flow flow eastward, eastward, abandoning abandoning the the Au Au Train-Whitefish Channel, into the eastern basin, forming an early version of Lake Minong. Train-Whitefish Channel, into the eastern basin, forming an early of Lake Continual Continual retreat retreat allowed allowed Lake Lake Minong Minong to expand, expand, eventually eventually filling the entire Superior Superior basin. 159 �- :'-——".. T't"- -: J. i r- P B - Phdse I Surface —'P. s5QfcEIev.: go RE -. - / "<k, -\' ;. 41t' -<k - Y - I Stops Stops66&&77 160 160 *An �a' — 'I', GoS 90 930 Pr-e dank7 k" //ey 'P. Pre C/ezcjaf L'a//ey? Grand Sa6/ Lke 1' '9 The Kingston Outwash Plain and meltwater channels near Grand Marais, Michigan Ti, '7 C 4 Ml g5 "V.. �ice 5 cc' a'icsA .rr lace 0 a-s tn1 art ordj-/o,a4y Chaewst2ng O7 eat La r i' 0 ,C7Ma,/ack.. I A '4 - - C /aives eat teverd . .noph-ig cc' tciiorh .ntrt.ct - Pi-erent level lake So,ntyor ,,v—*_5- rect;oAt vieai ea..rt ,s,i-tA end 07C sc (a SorjCacej 'lope ecjt'ora - .c4,,tt.n fan .&9nt5' iwein) -Present lake 4/fC 0 -I- 2 -.1. -A. 162 - 3 -I-- �0' Mosaic Mosaic of of digital digital elevation elevationmodels models(DEM) (DEM)processed processedtotoshow showrelief relief(illumination (illuminationfrom fromSE) SE) �; .—.I 0 / I,I) Stop 7.7.Turtle Lake (actually an unnamed pond, soso called stop lbrtle Lake (actually an unnamed pond, calledononthis thistrip tripbecause becauseon on previous previous visits itit was observed observed that many many turtles turtles make make itit their their home) home) occupies occupies aa deep deep kettle kettle in in the the Kingston KingstonOutwash Outwash Plain. The kettle kettle is is the the deepest deepest (though (though not not the the largest) largest) in in aa south-southeast/north-northwest south-southeasthorth-northwesttrending trending chain of kettles that (presumably) were formed as ice stagnated in aa now-buried now-buried bedrock bedrock valley. valley. A from bedrock bedrock and a minimum minimum seismic study conducted by Regis in the 1980's revealed no reflection from sediment thickness of 60 meters. The kettle is several hundred meters in diameter diameter and and is is at at least least 40 40 meters deep. deep. Because Because the the kettle kettle chain chain extends extends across across (cuts) (cuts) each each of of the the outwash outwash and and drainage drainagesurfaces, surfaces, the stagnant Marais) ice was was building building stagnant ice must have been in place from &om the time the Marquette (Grand Marais) surface, and was buried by sediments sediments as the main ice ice mass mass retreated. retreated. the upper Kingston outwash surface, 00 m m hike hike through through the the woods, woods, and and ifif descending descending into into the the kettle, kettle, aa strenuous strenuous This stop requires a 2-3 2-300 return hike. 164 164 �Stop 8. Log Log Slide Slide From the to the the east. east. Two the Log Slide, the Grand Sable complex is visible to Two geomorphic geomorphic features, in this this view: view: The features, the "Banks" "Banks" and the "Dunes" are prominent in The Grand Sable Sable Banks consist of a steep, north-facing exposure of glaciofluvial sediments ranging in thickness consist of a steep, north-facing exposure of glaciofluvial sediments ranging in thickness from from 30 30 to to 100 100 meters, meters, rising rising directly directly above above the the shoreline shoreline of Lake Superior. Superior. To Tothe thesouth southaway awayfrom fromLake Lake Superior, Superior, the Banks form form aa high high terrace terrace surface, which is overlain by the Grand Sable Dunes, a dune dune field field "perched" "perched"up up to to 100 100meters meters above above the the lake lake and and covering covering about about 10 10square square kilometers. kilometers. The The deposit deposit that that underlies underlies the the dune duneplateau, plateau, exposed exposed in in the the Grand Grand Sable Sable Banks, Banks, has has been been variously variously interpreted interpreted as as aa crevasse crevasse filling filling or or kame kame terrace terrace that incorporated incorporated heterogeneous heterogeneous glaciofluvial glaciofluvialdebris debris transported transported by by rivers rivers flowing flowing west to east east along along an ice marginal channel channel (Drexler, (Drexler, 1981; 1981;John D. D. Hughes, Hughes, personal communication). Within Within the the central central portion portion of of the the Banks, Banks, stratigraphy stratigraphy of the the lower lower third third of of the the section section is obscured by colluvial and aeolian aeolian sand; sand; at at the the east and and west ends ends of the banks, the section is better exposed. Upper Upper portions portions of of the the banks banks are several thin thin gravel gravel beds. beds. thterbedded are dominated dominated by coarse, coarse, cross-bedded cross-bedded sand and include several Interbedded silt silt and and sand sand comprise comprise the the middle middle third of the deposit. The Thelower lower third third is is dominated dominated by by fine fine textured textured material, material, primarily primarily silt. silt. AAsurface surfacegravel gravel layer layer is is presently partially exposed in a "stripped "stripped plain" in the central plateau. This This layer layer is is often iron-stained and contributes contributesto toaalag lag that that periodically periodically armors armors the the bluff bluff crest crest as as the the slope slope retreats retreats southward southward (Farrell and Hughes, Hughes, 1985). 1985). The The Grand Grand Sable SableDunes Dunescontain contain evidence evidence of of buried buried soils, soils, which which record record episodes episodes of of geomorphic geomorphic change change consisting consistingof of soil soil profile profile development development followed followed by soil profile profile burial burial (Anderton (Anderton and Loope, Loope, 1995). 1995). In Inmost mostcases, cases,an an entire entire episode episode is is preserved presewed as a buried soil profile or or organic organic accumulation, accumulation,capped capped by by relatively relatively finer sediments, sediments, such as silt and very fine to fine sand, which is capped by medium to coarse eolian cross-bedded sand. The contact between the sand, which is capped cross-bedded sand. upper upper soil soil horizon, horizon, usually usually an an 0/A OIAhorizon, horizon,isisoften oftenvery verysharp, sharp,suggesting suggestingrelatively relativelyrapid rapidburial. burial. Such Such sedimentary sedimentaryand andpedological pedologicalevidence evidencestrongly stronglysuggests suggeststhat that periods periodsof ofstability stabilityare are represented represented by by forest forest vegetation vegetation colonizing colonizing landscape landscape surfaces surfaces within the Dunes, while while periods periods of of instability instabilityare are characterized characterizedby by the the burial burial of trees and associated soil profiles and organic organic accumulations. accumulations. A A soil soil catena, catena, consisting consistingof of aa sequence sequenceof of buried Spodosols, Spodosols, may be found found outcropping outcropping in in various various places places throughout throughoutthe the Dunes, Dunes, especially especially at at the Log Slide Slide locality. The Thecatena, catena,referred referredto to as as the the Sable Sable Creek Creek Soil Soil(Anderton (Anderton and and Loope, Loope, 1995), 1995),is is traceable traceable across across much of the the Bluff top top and and outcrops outcrops sporadically sporadicallywithin within the the Dunes Dunes reflecting reflecting the preservation presemation of a past soilscape soilscape which began forming forming immediately immediatelyafter after deglaciation deglaciation about about 10,000 10,000 years ago, but was isolated from further further surface surface weathering weatheringunder under eolian eolian sediments sediments beginning about 5000 5000 years ago. The Theburial burial event event seems seems to to have have been been initiated initiatedby by the the massive massive destabilization destabilization of the the Bank Front Front during during the the high lake levels of the Nipissing Great Lakes. high lake levels of the Nipissing Great Lakes. While While there there may may have have been been some some eolian eolian activity activity immediately following deglaciation, deglaciation, the evidence tends to support the hypotheses of Farrell and Hughes (1985) who suggest evidence tends to support the hypotheses of (1985) suggest that the Grand Grand Sable Sable Dunes Dunes are are no no older older than 5500 5500 BP. This Thisisisin in contrast contrast to to Marsh Marsh and and Marsh Marsh (1990) (1990) who who argue arguethat that the the Grand GrandSable SableDunes Dunes began began forming forming as as lake lake levels levels rose from from the pre-Nipissing pre-Nipissing lows lows sometime sometimearound around 9000 9000 BP. BP. Marsh Marshand andMarsh Marsh(1990) (1990)maintain maintain that that sand sand nourishment nourishment to to the the Dunes until around around 3500 3500 BP. BP. However, Dunes increased increased from from 9000 9000 BP BP to to 5500 5500 BP and remained high until However, the the presence presenceof of the theSable SableCreek CreekSoil, Soil,which which isis developed developed into into glaciofluvial glaciofluvialsediments, sediments,suggests suggests that that the the Bluff Bluff top topwas wasaastable, stable,forested forestedenvironment environment from from deglaciation deglaciationuntil about about 5000 5000BP BP when when eolian eoliansand sandbegan began to to cover coverthe the upper upper surface. surface. Rising Risingpost-Houghton post-Houghtonlevels levelsapparently apparentlyhad hadlittle little 165 165 �a. t 0 0 2 0) 0) 0 D C 0 0 KN 0' a. 166 �effect on the Banks until well into into the the mid-Holocene, mid-Holocene, suggesting that wave action did not begin to modify the bluff front until lake levels were relatively high during the Nipissing Great Lakes. Stop 9. Ghost Forest Subsequent, Subsequent, post-Nipissing post-Nipissing fluctuations fluctuations in lake level also also seem to have influenced influenced the the Bank front, causing changes in the sediment available for eolian transport on the upper surfaces causing upper surfaces of the Grand Sables, Sables, resulting in a discontinuous discontinuous occurrence occurrence of buried soils soils and organic organic layers layers of various ages within the Dunes. In In addition addition to to the the major major burial event event that covered the Sable Creek Soil at least as early early as around 4500 BP, radiocarbon dates from the Ghost Forest profile also more recent recent burial burial at at about about 100 100years yearsago. ago. Also a record a burial event at about 3500 BP and a more radiocarbon date from other localities localities in the Dunes suggest that eolian activity also took place at about 1500 1500BP, BP, and and at at about about 700 700years years ago. ago. While, these these data data may not be conclusive, an analysis of radiocarbon dates from the Grand Sable Dunes strengthens strengthens interpretations. Beginning Beginning with the investigations investigations of Bach (1978), (1978), researchers working in the Grand Sable Dunes have been collecting and radiocarbon dating Sable collecting the study study area. area. In general, the dates seem to preserved wood, bulk soil, and charcoal from the roughly delineate delineate major times of increased eolian activity, documenting burial events within the Grand Sable Sable Dunes, and likely likely recording fluctuations in the lake levels of the Lake Superior Superior basin. Based on the available available data, data, episodes of increased eolian activity occurred at about about 5300, 5300, 2100, 1500, 500, and 4600, and 3500 3500 RCYBP, RCYBP, and and may also also have occurred at about 2500, 2500,2100, 1500, 1000, 1000,500, and RCYBP. The 100 RCYBP. The first first three three episodes episodesseem seem to to coincide coincide well well with with rising rising Nipissing, Nipissing, Nipissing NipissingI,I, and Nipissing II II phases, which are recognized throughout the southern Great Lakes (Larsen, 1985). The other, The other,later laterepisodes episodesalso alsocompare compare favorably favorably to to previous research research which which indicates indicates fluctuating fluctuating lake levels levels in in the the Lake Lake Michigan basin during the last 3000 years (Larsen, 1985). 1985). Larsen (1985) (1985) has suggested suggested that Holocene lake level fluctuations are linked to climatic climatic changes changes that affected the the temperature temperature and moisture moisture patterns influencing the water balance of the lakes. lakes. Holocene climate of proxy proxy indicators suggest climate changes changes in the the Great Great Lakes, as revealed by a varity of alternating alternating episodes episodes of cool, cool, moist moist and and warm, dry conditions (Swain, 1978; 1978; Bernabo, Bemabo, 1981). 1981). Comparison of burial burial events events within within Grand Grand Sable Sable system system with lake level and climate climate data data from from the the Great In general, general, Great Lakes Lakes region for for the the last last 3000 3000 years indicate a general correlation of events. In of cool, wet climatic increased eolian activity in the dunes appears to correlate with periods of conditions, conditions, while while periods periods of of relative relative stability stability and soil development development are are associated associated with times times of of of shore-zone warm, dry climatic conditions. These These findings findings do not fit Larsen's (1985) model of changes during rising and falling lake levels. In the Larsen model, increased precipitation In the Larsen model, increased precipitation and and lowered temperature result in high lake levels that cause tributary stream aggradation, marsh establishment, and soil profile development in in eolian eolian sands. sands. Decreased precipitation and raised establishment, temperatures cause temperatures cause low lake levels that result in tributary stream erosion, marsh extinction, and soil profiles becoming buried by eolian sands. While While Larsen's model seems to work for most coastal areas, perched dunes, dunes, such as the Grand Sable Sable system, appear to be reacting differently to climatically-induced climatically-induced changes changes in in lake lake level. level. been a nearly nearly constant constant rain rain of of eolian eolian sediments sediments with with In general, there seems to have been relatively short-lived periods of soil development and forest colonization within the Dunes since about 3000 BP. The Thedistinct, distinct,buried buried soil soil profiles profiles of different ages within the Dunes argues for the Bank Bank front. front. Otherwise, the fact that only relatively high lake levels are influencing the Otherwise,ifif the the of stability, but rather a Bank front was continually being undercut, there would be no evidence of 157 �homogeneous deposit of eolian sands. Thus, Thus,the the evidence evidence of of geomorphic geomorphic changes changes from from the the Grand Sable Dunes seems shore of seems to to be be an an indicator indicator of lake lake level changes changes along along the the south southshore of Lake Lake Superior. Th In sum, the buried soil profiles reflect fluctuations fluctuations in the amount amount of sediment sediment available available Hughes, 1985). The for eolian transport within the Dunes (Farrell and Hughes, The availability availability of sediment sediment Bank face face (Marsh (Marshand andMarsh, Marsh,1987) 1987).. High depends on the condition of the Bank High lake levels result in increased wave action, which undercuts the bank toe slope, slope, causing mass mass wasting, wasting, destabilizing destabilizing for wind wind deflation. deflation, If enough sediment is available the Bank face and presenting a fresh surface for on the the high high terraces. terraces. Low lake for a long enough period of time the result is dune development on lake levels allow the Bank face to stabilize stabilize and and perhaps perhaps become become vegetated, vegetated, resulting resulting in in aa reduction reduction or or near elimination of available sediment. Thus, Thus, dune dune building building on the the high high terraces is retarded, retarded, - on - terraces allowing stabilization stabilization and surface surface weathering to begin, as well as forest vegetation vegetation to to colonize colonize the fresh landscape surfaces. Thus, Thus, soil soil profiles profiles formed formed in in the the Grand Grand Sable Sable Dunes during during periods periods basin. These of low lake levels in the Lake Superior basin. These soil soil profiles profiles and in many cases the forests themselves were, however, buried by eolian sediments, sediments, eliminating further soil development development and and forest growth, the result of high lake levels destabilizing the Bank front. result lake destabilizing Stop Stop 10. 10. Sable Falls At Sable Sable Falls, Falls, the the Jacobsville Jacobsville Sandstone Sandstone forms forms the the base of the the section section exposed exposed in in the the gorge. The The Jacobsville Jacobsvillesandstone sandstoneisisaa redbed redbed deposit deposit of of questionable questionable late Proterozoic-early Proterozoic-early Cambrian age named by Lane and Seaman (1907) after the Keweenaw Peninsula town of Jacobsville. There, There,the the"Portage "PortageSandstone" Sandstone"that thatwas was used used as as ornamental ornamental and and construction construction stone stone was quarried. ItIt isisexposed exposedall all along alongthe the southern southern shoreline shoreline of Lake Superior Superior from the Keweenaw Peninsula to Munising. However, However, from from Munising Munising to Beaver Bay, it is below lake level, spare for a few occurrences slightly above above water. water. At Sable Falls and south of Grand Marais, good exposures are found. Thickness Thicknessof of the the Jacobsville Jacobsville appears appears to be extremely extremely variable variable and largely controlled by the underlying Precambrian topography, upon upon which which the Jacobsville unconformably for the most part. For example, rests unconformably example, Hamblin (1958) (1958) cites an instance instance of aa 22 wells, one of which drilled loot of of Jacobsville Sandstone, and the other well drilled drilled through 11100' through only 46' 46 of and the wells are only of the the same same rock rock before before reaching Precambrian quartzite, and 10 miles apart (T47N, (T47N, R1E). RlE). The Jacobsville can be easily recognized recognized by by its its striking striking red redto to red-brown red-browncolor. color. Much of the Jacobsville is mottled with white reduction splotches and streaks. The The color color change change is is abrupt abrupt and distinct. Most of the mottles are related to variations in permeability of the beds. That is, Most of the mottles are permeability of the beds. is. where the beds have the greatest permeability, leaching and white coloration is the greatest. greatest. Most fine grained beds and shale lenses in the Jacobsville are are not not leached leached at at all. all. Leaching most joints, and and cross-bedding. cross-bedding. Spherical often ffollows o l l o k bedding planes, fractures such as joints, Spherical spots spotiofof leaching appear to be controlled controlled by a dark grain or pebble at occurs at the center of the spots. The grains are probably of some some lithology that have a composition sufficient to produce a reducing reducing environment. environment. Texturally, Texturally, the the Jacobsville Jacobsville Formation Formation ranges from conglomerate conglomerate to a fine grained grained siltstone. The by Hamblin Hamblin (1958). (1958). The Theformation formationhas has 44 different different facies, as described by conglomerate conglomerate facies facies occurs occurs mostly at the base of the formation, formation, especially especially where it lies unconformably unconformably on Precambrian rocks (Presque Isle near Marquette, for example), but may also be found found scattered scatteredthroughout throughoutthe theyounger younger beds. beds. Thickness of these beds can be as great as 5 meters. The Themost mostcommon commonof of the the44 facies facies(laterally (laterally and vertically) is a red to reddish brown, medium-grained, medium-grained, lenticular lenticular bedded sandstone. In In some some places, places, lenticular lenticular bedded sandstones sandstones are are 168 �over meters in thickness. Trough over 100 100 meters Troughcross cross bedding bedding and and ripple marks are are common in this this facies. facies. bedding in in the the formation formation accentuate accentuatethe thestructures. structures. The Selective leaching along cross bedding occurrence environment of occurrence of ripple marks, mud cracks cracks and clay pebbles clearly indicate a fluvial environment deposition. AAmassive deposition. massivefacies faciesof of the theJacobsville Jacobsville is is characterized characterized by persistent, thick beds of relatively structureless structureless sandstone, sandstone, many over 3 meters in thickness. At Victoria Falls, a measured measured section of 200 meters of Jacobsville Jacobsville consists consists almost almost entirely entirely of 3 meter thick beds of sandstone. sandstone. Some laterally persistent oscillation ripple marks are found in the beds and support support a lacustrine lacustrine environment of of deposition. deposition. Finally, Hamblin Hamblin recognized recognizedaared redsiltstone siltstonefacies. fades. Though not not common (except (except at Laughing Fish Point and Agate Falls), beds of siltstone siltstone and shale occur occur interfingered with other facies and is interpreted as a quiet-water lacustrine environment facies environment of deposition. deposition. Paleogeographically, the Jacobsville Sandstone represents a continental red bed sandstone sandstone from the the Northern NorthernMichigan Michiganhighlands. highlands. As shown in the deposited by streams flowing northward from paleocurrent (cross (cross bedding and ripple marks) map produced by Hamblin (1958) there is very little deviation in trend (of indicators) indicators) from the mean. An unconformity, in some some places a disconformity, but as on Grand Island, an angular unconformity, separates separates the Jacobsville Jacobsville from the overlying Chapel Rock Member of the Munising Formation. At At Grand Grand Island Island the the Jacobsville Jacobsville dips a few degrees northward, and the Chapel Rock member of the Munising Munising Formation dips a few degrees southward, but at this stop, stop, bedding appears appears to to be be parallel parallel or or nearly nearly parallel parallel at at the the contact. contact. The lower two to fifteen foot section of the Chapel Rock member is a basal conglomerate, fifteen foot conglomerate, formation 90% vein quartz, quartzite quartzite and chert with lesser amounts of slate, basalt, granite, iron formation and sandstone. The Theupper upper 49 49to to 60 60feet feet isis pink pink to to light bluff to brown, medium grained orthoquartzitic sandstone blue-clay and and silty siltyshale shalebeds. beds. The beds in the top 20 orthoquartzitic sandstone with several thin, blue-clay very dolomitic dolomitic and andfrequently frequently"burrowed." "burrowed." Limonite imparts a light or 40 feet are moderately or very yellow-gray color to the member member and occasionally occasionally red to some some thin beds. beds. Northern Michigan The (lower) Chapel Rock member represents a period when the Northern Highlands (to the south) were eroding and shedding their sediments into a shallow empeiric sea south) to the north (see page). The (see the figures on the next page). The Chapel Chapel Rock member is composed composed almost entirely of quartz (mostly of igneous origin; Hamblin, 1958) with minor amounts of feldspar. (mostly minor of tourmaline, and abundant zircon Heavy minerals in the member include well-rounded grains of (20-50% of the total heavies, both altered and unaltered), magnetite, hematite, and ilmenite. Silica is the predominant cement in most places and occurs as secondary overgrowths of varying degrees. Farther Farthereast, east,near nearTahquamenon TahquamenonFalls, Falls, porosity porosity in in the the Chapel Chapel Rock Rock member member isis reduced reduced to almost zero due to the silica cement. Texturally, Texturally, the Chapel Rock member is well-sorted, medium-grained sandstone. Most Most grains grainsare are 1/4 114to 1/2 112 mm diameter. Color Colorgradually graduallyranges ranges sedimentary from white to buff to red. Large Large scale scale trough cross bedding is the most abundant sedimentary The size size of these troughs range from I1 to to nearly nearly 200 200 structure in the Chapel Rock member. member. The meters in width (mean about about 10 10 meters). Megascopically, Megascopically,they they are are useful useful for for differentiating differentiatingthe the Miners Chapel Rock Member Member from the underlying Jacobsville Formation and the overlying Miners Castle member. At At Miners MinersCastle, Castle, they they are are abundant. abundant. They Theyrepresent represent deep deep erosional erosional channels channels that were cut into the older units. Near Near the the base base of the Chapel Rock member, pebbles become abundant in the cross-beds that fill the troughs. Hamblin cross-beds Hamblin(1958) (1958)suggests suggeststhat thatthey theyare areindicative indicative along aa cuspate cuspate shore. shore. Ripples marks are less abundant and of marine deposition in embayments along are both current-formed and oscillatory. Where Wherecurrent-formed, current-formed,they they indicate indicate aa mean mean transport transport direction to the northwest with little little standard standard deviation about that mean (see figure illustrating illustrating cross-bedding directions directions in the the U.P.). This Thisindicates indicatesaafairly fairlysteep steepgradient gradientwith with little little cross-bedding 169 �11 UPLI6*TION S V •t•*d O$Iø *1 — bs#' an a4 — biSS d.ttli. 4 A'SM I.l.. s4 I 474 t1 isa— ii—.— ii I——— iii ii. *i• tsis. 0 G••t_ — .9 0 •? to Cross bedding bedding directions directions in in the the Jacobsville Jacobsville Sandstone Sandstone (after (after Hamblin, Hamblin, 1958) 1958) Paleogeographyduring during deposition depositionof of the theJccobsville JacobsvilleSandstone Sandstone(after (afterHamblin, Hamblin, 1958) 19581 Paleogeography 170 170 �1 Cflt*N*?IO V — •Iadad — ..d at d.(i.IIa I tetIa .1 n. - g*.• •.n k..—.' - • ••—' I— 4, t%St fr.at If SpI —a. Tnqt.....q P•fIi t — — Mtt • ft !a.f •— If so I-. Is ma'.. Cross Crossbedding beddingdirections directionsininthe theChapel ChapelRock Rockmember member ofofthe theMunising MunisingFormation Formation(affer (afterRamblin, Hamblin,1958) 1958) Paleogeography Paleogeographyof ofNorthern NorthernMichigan Michiganduring during deposition deposition of the the Chapel ChapelRock Rockmember member 958) ofthe theMunising MunisingFormation Formation(after (afterHamblin, Hamblin, 1958) of 171 171 �meandering. meandering.InInthe theupper upperpart partofofthe theChapel ChapelRock Rockmember, member,mudcracks mudcracksare arefound foundininthe thefinefinetextured cm in in diameter diameterand and the theintervening intervening textured sandstone sandstoneand andthe theshale shalebeds. beds. They Theyare areabout about55cm cracks cracksare arefilled filled with with sand. sand. Paleogeographically Paleogeographicallyand andenvironmentally, environmentally,they theyindicate indicatedeposition depositionin in aa shallow shallowwater, water, subaerial subaerialenvironment environmentwith with the the sea sea regressing regressing northward. These Thesebeds bedsgrade grade directly into the Miners Castle Member and suggest a minor regression of the Chapel Rock directly into the Miners Castle Member and suggest a minor regression of the Chapel Rocksea. sea. Compact Compact till till isis found found overlying overlying the the bedrock in this valley. The Thetill tillisisreddish reddishin incolor, color,and and texturally ranges from clay to cobbles. It is likely Marquette age (about 10,000 YBP) and was texturally ranges from clay to cobbles. It is likely Marquette age (about 10,000 YBP) and was deposited deposited as as the the Munising Munisingmoraine moraineand and Kingston Kingston outwash outwash plain were being deposited (Phase I1of of thi previous previousdiagrams). diagrams). the Grand Marais Marais Harbor Harbor Stop 11. Grand Grand Grand Marais Marais Harbor Harborisisthe theonly only Harbor Harbor of of Refuge Refuge between between Marquette Marquetteand and Sault SaultSt. St. Marie. Native Americans. Americans. Later, Marie. Originally, Originally,the theprotected protectedbay bay was was aa summer summer camping place for Native French voyageurs used the bay as stopping place to either prepare for, or recuperate French voyageurs used the bay as stopping place to either prepare for, or recuperate from, from, the the dangerous dangerouspaddle paddle along alongthe thecliffs cliffsof of the the Pictured Pictured Rocks Rocksduring during their their travels travelsalong alongthe thesouth southshore shore of of Lake Lake Superior. Superior. The Thetown townitself itselfwas wasestablished establishedininthe the1860's 1860'sby by the the fishing fishing and and lumber lumber industries industriesas as aa boom boom town. town. However, However,by by1910, 1910,the thelumber lumberindustry industrydeclined declinedand and Grand Grand Marais Marais became became mainly mainly a commercial commercial fishing fishing port. Eventually, Eventually,this thisindustry i n d u s e also also declined declined and and the the community community became became all all but aa ghost ghost town. Today, Today,Grand Grand Marais Maraisis is seeing seeing aa renaissance renaissance as as aa summer and and winter winterrecreation recreation town. town. summer Recent, Recent, soon-to-be-published soon-to-be-publishedresearch research at at the the Drexler-Carter Drexler-Carter(D-C) (D-C)site site(Anderton, (Anderton,in in progress), fill section section exposed exposed along along the the front front of of the the eastern eastern portion portion of of the theGrand Grand progress), aa paleo-valley paleo-valleyfill Sable Banks, suggests that prior to the Nipissing transgression, the Grand Marais area may Sable Banks, suggests that prior to the Nipissing transgression, the Grand Marais area may have have consisted consisted of of extensive extensive lagoon. lagoon. Evidence Evidencefor forthe thelagoon lagoonconsists consistsof of extremely extremelythick. thick. Compressed Compressed peat peat deposits, deposits,dated datedatatbetween betweenapproximately approximately7000-6000 7000-6000BP, BP, which which have have been been found foundatatthe theD-C D-C site, site, on on the the floor floor of of Grand Grand Marais Marais Harbor Harbor by by divers, divers, and and during during drilling drilling of wells wells to to the the east east of of the the Harbor. Harbor. The Thepre-Nipissing pre-Nipissinglagoon lagoonwas waslikely likelyprotected protectedbehind behindananextremely extremelylarge largebay baybarrier, barrier, which which may have have extended extended from from as as far far west west as as the the ancestral ancestral Grand Sable Sable Banks Banks or or Au Au Sable Sable Point. Point. The The high high ground groundand andassociated associateddune duneforms, forms,which which begin begin at at Lonesome LonesomePoint Point and andextend extendto tothe the east for for several several kilometers, kilometers, may may be be remnants remnants of of this this older older barrier, bamer, which was was apparently apparently breached breached during rising Nipissing levels. Much Muchfurther furtherwork work isis needed needed to to verify verify these these interpretations. interpretations. The The Nipissing Nipissing transgression transgressioninundated inundated the the Grand Grand Marais Marais area, area, flooding flooding the the mouth mouth of of the the Sucker Sucker River River and and extending extending inland inland for for several several kilometers kilometers south south of of the the high high ground ground that that begins begins at at Lonesome Point. Steep, Nipissing-age, wave-cut bluffs at an elevation of about 195 m (640 ft) Lonesome Steep, Nipissing-age, wave-cut bluffs at an elevation of about I95 m (640 ft) rim the the southern southern edges edges of the town and harbor. Much Much of of the the town town appears appears to to have have been been built built on on aa Nipissing wave-cut wave-cut platform. platform. Nipissing Recently, Recently, Grand Grand Marais Marais Harbor Harbor has has been been the the focus focus of a great great deal of concern by local local residents West Bay. Bay. From residents in regard to the condition of West Fromthe thetime time of of the the earliest earliest written written records and and maps maps of of Grand Grand Marais, Marais,the the bay bay was was originally originally portrayed as relatively relatively deep water lagoon, protected protected behind behind aa low, low,sandy sandybaymouth baymouth barrier barrier that that extended extended from from the the west west side side of of the the current current town, town, east east to to Lonsome Lonsome Point. Point. AAsmall smallchannel, channel,which whichallowed allowedwater waterto to pass pass from from the the bay bay into into the to the harbor. harbor. This the waters waters of of lake lake Superior, Superior, provided provided the only navigable entrance to This natural natural channel, channel, adequate adequate for for several several centuries centuries for for Native Americans Americans and Voyageurs in canoes, was was prone to sand sand bar development, development, which which interfered interfered with commercial shipping shipping associated associated with with the the lumber 800ts. Consequently, various harbor lumber and and fishing fishing industries industries that that began began in in the the late late 11800's. protection protection structures, structures, including includingeventually eventually aa large large breakwater, were built beginning beginning as as early early as as 172 17 2 �L Stop 1 — jt/ioravel Pita - et; Grav4f+t I -. - 'a $k — 3__'_ RM868 - — r -. 3 87O •1 lIlT H V-- -. — Eastward-slopingmeliwater meltwaterdischarge dischargechannels channels southofofGrand Grand Marais Easiword-sloping south Morals 17 3 �1883 1883 to stop sand bars from from blocking blocking the the entrance entrance to the bay (USCOE, (USCOE, 1980). 1980). , Over Over the the years, years, the the harbor harbor protection protection structures structureshave have effectively effectively blocked blocked coastallycoastallytransported transported sand, sand, that that would would have have otherwise otherwisebeen been conveyed conveyed by by littoral littoral drift drift processes, processes,from from replenishing the eastern portion of the original bamer. Consequently,this this part part of of the the barrier barrier has has replenishing barrier. Consequently, been removed removed by by wave wave erosion, erosion, exposing exposing nearly nearly the the entire entire east east end end of the the bay bay to to Lake Lake Superior. Superior. On the west side side of of the the structures, structures,sand sand eroded erodedfrom from the the Grand Grand Sable Sable Banks Banks and and transported transportedto to the the east east has has been been deposited. deposited. Since Since 1961 1961the the beach beach in this area has been growing at a rate of 38,000 cubic m per year (USCOE, 1980). According (1990),the the beach beach has has widened widened by by 1980). Accordingto to Marsh Marsh (1990), 2500-3000 2500-3000 m, m, and, and,ifif left leftunchecked, unchecked,will willeventually eventuallywiden widen to to the thepoint pointwhere wherethe thebeach beach effectively cuts off wave-contact wave-contact with the Grand Sable Banks. ifIf this thishappens, happens,the thesand sandsupply supplyto to effectively the the Grand Grand Sable SableDunes, Dunes,which which isisultimately ultimately tied tied to to lake lakelevels levelsand andbluff bluff recession, recession,will willbe be artificially reduce reduce dune dune nourishment nourishment rates. In Ineffect, effect,the theDunes Dunesmay may cease cease to to exist. exist. artificially Stop stop 12 12 Stop Stop 12 12is is not not really really aa stop, stop, but but an an overview ovewiew of of channels channels as as we we leave leave Grand Grand Marais Marais southward southward on on M-77. M-77. Eastward Eastwarddischarging dischargingstreams streamscut cutchannels channelsatatsuccessively successivelylower lower elevations elevations as the the Marquette Marquette (Grand (Grand Marais) Marais) ice ice retreated retreated into the Lake Superior basin. At least least 88channels channels as basin. At are are recognized recognized from from 207 207 meters meters to 271 meters. Leverett Leverett(1929) (1929)and andothers othersmistakenly mistakenlyinterpreted interpreted these these surfaces surfaces as as Lake Lake Algonquin wave-cut platforms. Hughes Hughes (1968), (19681,through through use use of of aneroid aneroid barometers and and topographic topographicmaps, maps,determined determined they they slope slopeeastward eastward and and asserted assertedthat that they theyare are barometers glacial glacial spillways. spillways. Further, Further,Hughes Hughesrecognized recognizedthe thefact factthat, that, in in profile, profile, the the surfaces surfacesactually actually slope slope southward southward toward toward the the next next escarpment escarpment(characterized (characterized by by poorly poorly drained drained swampy swampyregions regions at at the the south theywere werewave-cut wave-cutterraces, terraces,the the slope slope in in profile profile would would be be in in the the south edge edge of of the the surfaces). surfaces). ifIfthey opposite direction. opposite direction. 174 �REFERENCES Bach, Bach, D.P. 1978. 1978.Plant Plant Communities, Communities,Habitats Habitatsand and Soil Soil Conditions Conditionsof of Grand Grand Sable SableDunes, Dunes, Pictured Rocks National Lakeshore, Michigan. Unpublished Masters Thesis, Michigan Pictured Rocks Lakeshore, Unpublished Master's Thesis, Michigan Technological Technological University, University, 180 180p. p. Bergquist, Bergquist, S.C. S.C. 1936. 1936.The The Pleistocene Pleistocenehistory history of of the the Tahquamenon Tahquamenon and and Manistique Manistique drainage drainage region of hblication 40, 40, of the the northern northern peninsula peninsula of of Michigan. Michigan. Michigan Michigan Geological Geological Survey Survey Publication Geological GeologicalSeries Series34, 34,part part11pp.7-148. pp.7-148. Blewett, Blewett, W.L. W.L. and and R.L. R.L. Rieck. Rieck. 1987. 1987. Reinterpretation Reinterpretationof aa portion of the the Munising Munising Moraine Moraine in in northern northern Michigan. Michigan.Geological GeologicalSociety Societyof ofAmerica AmericaBulletin Bulletin98:169-175 98: 169-175 Blewett, Blewett, W.L. 1994, 1994,Late Late Wisconsin Wisconsin History History of Pictured Rocks Rocks National Lakeshore Lakeshore and Vicinity. Vicinity. National Park Park Service Service PIRO P R O 94-01, 94-01,8 p. National 8 p. Carey, L. 1993. 1993. Interim Interimsoil soilsurvey surveyof ofPictured PicturedRocks RocksNational NationalLakeshore, Lakeshore,Alger AlgerCo., Co.,Michigan. Michigan. USDA, USDA, Soil Soil Conservation ConservationService, Service,Marquette, Marquette,MI. MI. Drexler, Drexler, C.W. C.W. 1981. 1981.Outlet Outletchannels channelsfor for the the post-Duluth post-Duluth lakes lakes of of the the Upper Upper Peninsula Peninsula of of Michigan. PhD PhD dissertation, dissertation, University University of of Michigan, Michigan, Ann Ann Arbor. Arbor. 295 295 p. p. Michigan. Ells, Ells, G.D., G.D., 1967, 1967,Correlation Correlationof of Cambro-Ordovician Cambro-Ordovician Rocks Rocks in in Michigan. Michigan. in in Correlation CorrelationProblems Problems of the Cambrian and Ordovician Outcrop Areas, Northern Peninsula of Michigan, Michigan Cambrian and Ordovician Outcrop Peninsula Basin Geological } pp. Geological Society SocietyAnnual Annual Field FieldExcursion, Excursion,M.E. M.E. Ogstrom Ogstromand andA.E. A.E.Slaughter, Slaughter,{eds. {eds.] pp. 42-57. Farrell, Farrell, J.P. and and J.D. J.D. Hughes Hughes 1985. 1985. Long Long Term Implications, Implications, From a Geomorphological Geomorphological Standpoint, Location at at Grand Grand Sable SableLake. Lake. Contract Report Standpoint, of Maintaining Maintaining H-58 in its Present Location PX60000-4-0839, PX60000-4-0839, submitted submittedto tothe theNational NationalPark ParkService, Service,78 78p.p. Hamblin, Hamblin, W.K., 1958, 1958,Cambrian Cambrian Sandstones Sandstonesof of Northern Michigan. Michigan Michigan Dept. of Natural Natural Resources Pub. 51, 51, 146 146p. p. Resources Larsen, Larsen, C.E. 1985. 1985.Lake Lake Level, Uplift, Uplift, and Outlet Incision, The Nipissing and Algoma Great Lakes. In Quaternary Calkin. Quaternary Evolution Evolution of of the the Great GreatLakes, Lakes, edited edited by by P.F. P.F. Karrow Karrow and and P.E. P.E. Calkin. Geological GeologicalAssociation Associationof of Canada CanadaSpecial SpecialPaper Paper30. 30. Leverett, U.S. Geological Survey Leverett, F. 1929. 1929.Moraines Moraines and and shorelines shorelines of the Lake Superior region. U.S. Prof. Paper Paper 154-A. 154-A.72 72 p. p. Levin, H.L., H.L., 1996, 1996, Earth Earth Through Through Time. Time. 5th 5~ ed., Saunders, Saunders, 568 568 p. Marsh, W.M. 1990. 1990.Nourishment of Perched Sand Sand Dunes and the Issue of Erosion Control in the Great Lakes. Environ. Environ.Geol.Water GeoLWaterSci. Sci.16(2): 16(2):155-164. 155-164. 175 �Marsh, W.M. and B.D. Marsh 1988. 1988. Wind Erosion and Sand Dune Formation Formation orj on High Lake Superior Bluffs. Geografiska GeografiskaAnnaler Annaler 69A 69A (3-4):379-391. (3-4):379-391. Schaetzl, R.J. and D.L. Mokma 1988. 1988. A Numerical Index of Podzol and Podzolic Soil Development. Development. Physical Physical Geography Geography 9(3):232-246. 9(3):232-246. USCOE, 1980, 1980, Final Detailed Detailed Project Project Report on Shore Shore Damage of Grand Grand Marais Harbor, Harbor, Section ifi, in, Detroit, Detroit, MI MI Detroit Detroit District. Michigan, Section 176 � Dublin Core The Dublin Core metadata element set is common to all Omeka records, including items, files, and collections. For more information see, http://dublincore.org/documents/dces/. Title A name given to the resource Institute on Lake Superior Geology Dublin Core The Dublin Core metadata element set is common to all Omeka records, including items, files, and collections. For more information see, http://dublincore.org/documents/dces/. Title A name given to the resource Institute on Lake Superior Geology: Proceedings, 1999 Description An account of the resource Institute on Lake Superior Geology. Marquette, Michigan. May 4-8, 1999. Creator An entity primarily responsible for making the resource Institute on Lake Superior Geology Date A point or period of time associated with an event in the lifecycle of the resource 1999 Format The file format, physical medium, or dimensions of the resource PDF Language A language of the resource English https://digitalcollections.lakeheadu.ca/files/original/c95bde6817524fac0b7a49791755d404.pdf 8b20a8aef357cb8f905e7b7c0b74dba7 PDF Text Text 4 FORTY-SIXTH ANNUAL MEETING St ON LAKE SUPERIOR : SINSTITUTEGEOLOG S — Si h1*r Bay,Ontario — S May. 08-13,2000 44 '1 44 . 4. ••r :4 .tssi.:. S S S S PROCEEDINGS VOLUME 46 45 /4 4 /4 /4 4/4 PARfl: PROGRAMAND ABSTRACTS �46th I.L.S.G. rogram & Abstracts 2000 May 8-13, 8-13,2000 Hosted at at Lakehead University Universi by the Geology Department Thunder Bay, Ontario Canada �46thAnnual Annual Meeting Meeting 46th 1 II INSTITUTE ON LAKE SUPERIOR GEOLOGY U Volume 46 contains the following parts: parts: Part 1: 1: Program and Abstracts Part 2: Field Trip Guidebook — Geology of the Mesoproterozoic Sibley Group 1 -Geology 22 — PGE-Cu-Ni Mine - Geology Geology of the Lac Lac des des Ties Iles PGE-Cu-Ni Mine 33 — Geoarcheology and deglaciation history the Thunder Thunder Bay Bay area - Geoarcheology history of the 44 — - Geology Geology of the Paleoproterozoic Gunflint Formation 55 — - Glacial Glacial history and regional till sampling sampling in the Archean Shebandowan Shebandowan Greenstone Greenstone Belt 6— Finlayson Lake Greenstone Greenstone Geology of of the Archean Archean Steep Steep Rock Rock Lake Lake - Finlayson 6 -Geology Belt - Reference ce to the material material in in this this volume volume should should follow follow the the example examplebelow: below: A., 2000. Chemistry and mineralogy of Lower Chowlay Chocolay G roup rocks, Dickinson Dickinson Argast, A,, County, Michigan, Michigan, [abstract]: [abstract]: Institute Institute on on Lake Lake Superior SuperiorGeology GeologyProceedings, Proceedings,46th 46* Annual Meeting, Meeting, Thunder Thunder Bay, Bay, ON, ON, 2000; 2000; v.46, v.46, Part Part 1, 1, p. p. 1-2. 1-2. Volume 46 is published by the Institute on Lake Superior Geology and distributed by the Institute Institute Secretary-Treasurer. Secretary-Treasurer. Jirsa (term (term 1994-2000) 1994-2000) Mark Jirsa Minnesota Minnesota Geological Geological Survey Survey 2642 University Avenue St. Paul, MN USA 55114-1057 55 114-1057 (612)-627-4780 (6 12)-627-4780 email: jirsaOO iirsa00liätc.umn.edu 1(Sitc.umn.edu http://www.ilsgeology.org ILSG website: website: htto://www.ilsgeologv.org All volumes are are available available at at the the cost costofphotocopying ofphotocopyingfrom from Michigan Michigan Technical TechnicalUniversity UniversityArchives. TSSN 1042-9964 1042-9964 ISSN �INSTITUTE LAKE SUPERIOR SUPERIOR GEOLOGY GEOLOGY INSTITUTE ON ON LAKE CONTENTS Proceedings Proceedings Volume Volume 46 46 Part Part 1—Program I-Program and Abstracts Abstracts Editor: Stephen Editor: StephenA. A. Kissin Kissin Institutes on Institutes on Lake Lake Superior Superior Geology, Geology, 1955-2000 1955-2000 ..... . ...... iii ... By-Laws of the Institute Lake Superior Geology .... By-Laws of the Institute on on Lake Superior Geology . . . .v Constitution of Constitution of the the Institute Institute on on Lake Lake Superior Superior Geology Geology Goldich Goldich Medal Guidelines Guidelines Past Goldich Medallists Medallists ................... ..... . . . vivi ... ..... viii Vlll Goldich Medal Committee ............... ... viii ..... Vlll Citation Recipient....... Citation for 2000 2000 Goldieh Goldich Medal Recipient ...... ix . ................. . . . xi ... .............. . . . . . . xii ... xiii . . . . . . Xlll Student Paper Student Paper Awards Awards Committee Committee ..... ... . . . . . . Xxiii lll Student Travel Travel Awards Awards Student Travel Travel Award Application Application Form Form Student Paper Student Paper Awards Awards Board of Directors Directors ............. Xiv . . . . . . xiv Local Committees Committees ..... . . . . . . xiv ................................. Report of the the Chair Chair of of the the 45th 45th Annual Annual Institute Institute Meeting ...... Program ........................................ Banquet Speaker Banquetspeaker Abstracts Abstracts .... xv .......XV ...... xvi ...... Xix xix ... 1 . 1 �ON LAKE LAKE SUPERIOR SUPERIOR GEOLOGY, GEOLOGY, 1955-2000 1955-2000 INSTITUTES ON # DATE PLACE CHAIRS 1 1955 1 1955 Minneapolis, Minneapolis, Minnesota Minnesota Floughton, Michigan 1956 1956 Houghton, 3 1957 1957 East Lansing, Lansing, Michigan Michigan 44 1958 1958 Duluth, Duluth, Minnesota Minnesota 5 1959 1959 Minneapolis, Minneapolis, Minnesota Minnesota C.E. Dutton Dutton A.K. Sneigrove Snelgrove B.T. Sandefür Sandefiir R.W. Marsden Marsden G.M. Schwartz & C. Craddock Craddock (note (note Schwartz & 2 2 66 77 88 9 9 10 10 11 11 12 12 13 13 14 14 15 15 16 16 17 17 18 18 19 19 20 20 21 21 22 22 23 23 24 24 25 25 26 27 28 29 30 30 31 31 32 32 33 33 34 34 35 35 36 37 38 1960 1960 Madison, Madison, Wisconsin 1961 1961 1962 1962 1963 1963 1964 1964 1965 1965 1966 1966 1967 1967 1968 1968 1969 1969 1970 1970 1971 1971 1972 1972 1973 1973 1974 1974 1975 1975 1976 1976 1977 1977 1978 1978 1979 1979 1980 1980 1981 1981 1982 1982 1983 1983 1984 1984 1985 1985 1986 1986 1987 1988 1988 1989 1989 1990 1990 1991 1991 1992 1992 Port Arthur, Arthur, Ontario Ontario Houghton, Michigan Houghton, Michigan Duluth, Duluth, Minnesota Minnesota Ishpcming, Ishpeming, Michigan St. Paul, Minnesota Minnesota Sault Ste. Marie, Michigan Michigan East Lansing, Michigan Superior, Superior, Wisconsin Oshkosh, Wisconsin Thunder Bay, Ontario Ontario Duluth, Minnesota Houghton, Michigan Madison, Wisconsin Sault Ste. Marie, Ontario Marquette, Marquette, Michigan Michigan Minnesota St. Paul, Minnesota Thunder Thunder Bay, Ontario Ontario Wisconsin Milwaukee, Wisconsin Minnesota Duluth, Minnesota Eau Claire, Wisconsin East Lansing, Michigan International Falls, Minnesota Houghton, Michigan Wausau, Wisconsin Kenora, Ontario Ontario Wisconsin Rapids, Wisconsin Wisconsin Wawa, Ontario Ontario Marquette, Michigan Marquette, Duluth, Minnesota Minnesota Thunder Bay, Ontario Ontario Eau Claire, Claire, Wisconsin Wisconsin Hurley, Wisconsin I correction) correction) E.N. Cameron Cameron E.G. Pye Pye A.K. Snelgrove Snelgrove H. Lepp Lepp A.T. Broderick Broderick P.K. Sims & R.K. Hogberg R.W. White W.J. Hinze H i e A.B. Dickas A.B. G.L. LaBerge LaBerge M.W. Bartley & E. Mercy M.W. D.M. Davidson Davidson Kalliokoski J. Kalliokoski M.E. Ostrom Ostrom P.E. Giblin Giblin J.D. Hughes Hughes M. Walton Walton M.M. Kehienbeck Kehlenbeck U. Mursky G. D.M. Davidson Davidson P.E. Myers Myers W.C. Cambray W.C. D.L. Southwick Southwick D.L. Bomhorst T.J. Bornhorst LaBerge G.L. LaBerge Blackburn C.E. Blackburn J.K. Greenberg J.K. Greenberg Sage E.D. Frey & R.P. Sage J. S. Klasner J.C. Green Green M.M. Kehlenbeck Kehlenbeck P.E. Myers Myers A.B. Dickas Dickas �39 40 41 42 43 44 45 1993 1994 1995 1996 1997 1998 1999 46 2000 D.L. Southwick Southwick T.J. Borithorst Bornhorst M.C. Smyk L.CI.Woodruff Woodruff L.G. R.P. Sage, W. Meyer J.D. Miller, M.A. Jirsa T.J. Bornhorst, R.S. Regis S.A. Kissin, P. Fralick Eveleth, Minnesota Minnesota Houghton, Houghton, Michigan Michigan Marathon, Ontario Ontario Cable, Wisconsin Wisconsin Sudbury, Ontario Ontario Minneapolis, Minnesota Marquette, Marquette, Michigan Michigan Thunder Bay, Ontario Ontario 11 �CONSTITUTION CONSTITUTION LAKE SUPERIOR SUPERIOR GEOLOGY GEOLOGY OF THE INSTITUTE ON LAKE (Last amended by the the Board—May Board-May 8, 1997) 1997) Article II Article Name The name of the organization organization shall be the "Institute on Lake Superior Geology". Geology". Article II Article I1 Objectives Objectives The objectives objectivesof of this this organization organizationare: are: A. To Toprovide provideaameans meanswhereby whereby geologists geologists in in the the Great Great Lakes Lakes region region may exchange ideas and scientific scientific data. B. To Topromote promotebetter better understanding understanding of of the geology of the Lake Superior Superior region. region. C. To Toplan plan and and conduct conduct geological geological field field trips. Article III Article 111 Status && No part of of the income income of the organization organization shall shall insure insure to the benefit benefit of of any any member or individual. In the event of dissolution, the assets of the organization shall organization shall be distributed distributed to to _________(some free (some tax free organization). organization). (To avoid Federal and State income taxes, the organization should be not educational, but only "scientific" or "educational, but also also "non-profit") "non-profit") Anno. 290.01, 290.01, subd. subd. 44 Minn. Stat. Stat. Anna. Minn. Stat. Stat. Anno. 290.05(9) 290.05(9) 1954 1954 Internal Revenue Revenue Code Code s.501(c)(3) s.501(~)(3) Article IV Article Membership Membershir The membership of the organization shall consist of persons who have registered for an annual meeting within the past three three years, and those who indicate interest in being a member according to guidelines approved by the Board of Directors. Directors. Article V Article Meetings Meetings The organization shall meet once aa year. year. The The place and exact date of each meeting will will be be designated designated by by the the Board Board of of Directors. Directors. Article VI Directors Directors The Board of Directors shall consist of the Chair, Secretary-Treasurer, and the last three past Chairs; but if the board should at at any any time time consist consist of of ... I"I ll �fewer than five persons, by reason of unwillingness or inability of any of the above persons to serve as directors, the vacancies on the board may be be filled by the Chair so as to bring the membership of the board to five members. members. Article ArticleVII VII Officers Officers The The officers officers of of this this organization organization shall shall be be aa Chair Chair and and Secretary-Treasurer. Secretary-Treasurer. A. A. The TheChair Chairshall shallbe beelected electedeach eachyear year by by the the Board Board of of Directors, Directors, who shall give due consideration to the wishes of any group that shall give due consideration to the wishes of any group that may may be be promoting the next annual His/her term of office as Chair will promoting the meeting. Hisher term of office as Chair will terminate terminate at at the the close close of of the the annual annual meeting over over which which he/she helshe presides, or or when when his/her hisiher successor shall have been appointed. He/she Helshe will then then serve serve for for aa period period of of three three years years as as aa member member of of the the Board Boardof ofDirectors. Directors. B. The Secretary-Treasurer shall be elected at the annual B. The Secretary-Treasurer shall be elected at the annualmeeting. meeting. His/her Hisiher term term of of office office shall shall be four four years, or until his/her hisher successor successor shall shall have been appointed. have been appointed. Article ArticleVIII VIII Amendments Amendments This This constitution constitutionmay may be be amended amended by by aa majority majority vote vote (majority (majority of of those those voting) voting)of of the the membership membershipof ofthe theorganization. organization. iv �BY-LAWS OF THE INSTITUTE ON LAKE LAKE SUPERIOR GEOLOGY I. Duties Dutiesof of the the Officers Officers and Directors A. ItItshall shallbe bethe theduty dutyof ofthe the Annual Annual Chairman Chairman to: 1. Preside Preside at at the the annual annual meeting. meeting. 2. Appoint Appointall allcommittees committeesneeded needed for for the the organization organizationof of the the annual annual meeting. meeting. 3. Assume Assumecomplete completeresponsibility responsibility for forthe the organization organizationand and financing financing of of the the annual meeting over which he/she presides. helshe B. ItItshall shallbe bethe theduty dutyof ofthe theSecretary-Treasurer Secretary-Treasurerto: 1. Keep Keep accurate accurateattendance attendance records records of of all all annual annual meetings. meetings. 2. Keep Keepaccurate accuraterecords records of of all all meetings meetings of, and correspondence correspondence between, the Board of Directors. Directors. 3. Hold Holdall allfunds fundsthat that may may accrue accrue as as profits profits from from annual meetings meetings or field field organization and operation trips and to make these funds available available for the organization operation of future future meetings meetings as as required. required. C. ItItshall shallbe bethe theduty dutyof ofthe the Board Board of of Directors Directorsto to plan locations locations of of annual annual meetings meetings and to advise advise on the organization organization and financing financing of all meetings. II. Duties 11. Duties and and Expenses Expenses A. Regular $5.00or or less less on on an an annual annual basis basis shall shall be assessed assessed Regularmembership membershipdues duesof of $5.00 each each member member as as determined determined by by the the Board Boardof of Directors.. Directors.. B. Registration Registrationfees feesfor forthe the annual annual meetings meetings shall shall be determined by the Chair in Directors. The consultation with the Board of Directors. The registration registration fees fees can include include determined by expenses to cover operations outside of the annual meeting as determined the Board of Directors. ItItisisstrongly recommended that registration strongly recommended that registration fees fees be be kept at a minimum minimum to to encourage encourage attendance attendance of of students. students. III. Rules 111. Rules of of Order The rules contained contained in Robert's Rules of Order shall govern this organization organization in in all all cases cases to which which they they are are applicable. applicable. IV. Amendments Amendments by aa majority majorityvote vote (majority (majorityof ofthose thosevoting) voting)of of These by-laws may be amended by the membership membership of of the organization; organization; provided provided that such such modifications modifications shall shall not not conflict with the constitution as presently adopted or subsequently amended. constitution v �GOLDICH GOLDICH MEDAL MEDAL GUIDELINES GUIDELINES (Adopted (Adopted by the the Board Board of of Directors, 1981; 1981;amended amended 1999) 1999) Preamble Preamble The The Institute Institute on on Lake Lake Superior Superior Geology Geology was born in 1955, 1955, as documented documented by the fact fact that that the 27th annual meeting was held in 1981. The Institute's continuing objectives are to 27th annual The Institute's continuing objectives are deal with those those aspects aspects of of geology that are related geographically geographically to Lake Superior; Superior; to encourage encourage the discussion discussion of of subjects subjects and sponsoring sponsoring field trips that will bring bring together together geologists geologists from from academia, academia, government surveys, surveys, and industry; and to maintain an an informal informal but but highly highly effective effectivemode modeof ofoperation. operation. During During the the course course of of its its existence, existence, the the membership membershipof of the the Institute Institute (that (that is, is, those those geologists who indicate an interest in the objectives of the ILSG by attending) geologists indicate an interest objectives attending) has has become become aware aware of of the the fact fact that that certain certain of of their their colleagues colleagues have made particularly noteworthy noteworthy and and meritorious meritoriouscontributions contributionsto to the the understanding understanding of of Lake Lake Superior Superiorgeology geology and and mineral mineral deposits. deposits. The The first first award awardwas was made made by by ILSG ILSG to to Sam SamGoldich Goldich in in 1979 1979for for his his many many contributions contributionsto to the the geology geologyof of the the region regionextending extendingover over about about 50 50 years. years. Subsequent Subsequent medalists medalists and and this this year's year's recipient recipientare arelisted listedin inthe thetable tablebelow. below. Award Award Guidelines Guidelines 1) 1) The Themedal medalshall shallbe beawarded awardedannually annuallyby bythe theILSG ILSGBoard Boardof ofDirectors Directorsto toaageologist geologist whose whose name name is is associated associated with a substantial substantial interest in, and contribution contributionto, to, the the geology geology of the Lake Superior region. of the Lake Superior region. 2) The TheBoard Boardof ofDirectors Directorsshall shall appoint appoint the Goldich Medal Committee. The The initial initial appointment appointment will will be be of of three three members, members, one one to to serve serve for for three three years, one one for for two two years, years, and and one one for for one one year. year. The Themember memberwith withthe thebriefest briefestincumbency incumbencyshall shallbe be chair chair of of the the Nominating Committee. After the first year, the Board of Directors shall appoint Nominating Committee. After the first year, the Board of Directors shall appoint at at each each spring years. In histher third third year year this this spring meeting meeting one one new new member member who will serve for three years. In his/her member member shall shall be be the the chair. chair. The TheCommittee Committeemembership membershipshould shouldreflect reflect the the main main fields fieldsof of interest interestand andgeographic geographicdistribution distributionofofILSG ILSGmembership. membership. 3) 3) By Bythe theend endofofNovember, November,the theGoldich GoldichMedal Medal Committee Committeeshall shall make make its its recommendation recommendationto to the theChair Chairof ofthe the Board Board of of Directors, Directors, who who will will then then inform inform the the Board Board of the nominee. of the nominee. 4) 4) The TheBoard BoardofofDirectors Directorsnormally normallywill willaccept acceptthe thenominee nomineeof ofthe theCommittee, Committee,inform inform the the medallist, medallist,and andhave haveone onemedal medalengraved engravedappropriately appropriatelyfor for presentation presentation at at the the next next meeting meetingof ofthe theInstitute. Institute. vi �I sources, such 5) ItIt isisrecommended recommendedthat that the the Institute Institute set set aside aside annually from whatever sources. funds as will be required to support the continuing continuing costs of this award. award. Nominating Nominatine Procedures Procedures 1) The The deadline deadline for for nominations nominations is November 1. Nominations shall be taken at any time by the Goldich Medal Committee. Committee Committee members members may themselves themselves nominate nominate candidates; however, Board members may not solicit for or support individual candidates; individual nominees. 2) Nominations Nominationsmust mustbe bein inwriting writing and and supported supported by by appropriate appropriate documentation documentation such such as as letters of recommendation, lists of publications, curriculum vita's, and evidence of lists curriculum evidence contributions contributions to Lake Superior Superior geology and to the Institute. Institute. 3) Nominations Nominationsare arenot notrestricted restricted to to Institute Instituteattendees, attendees, but are open to anyone anyone who has worked on and contributed to the understanding of Lake Superior Superior geology. Selection Selection Guidelines Guidelines 1) Nominees Nominees are are to to be be evaluated evaluated on on the the basis of their contributions contributions to Lake Superior geology (sensu (sensu lato) lato) including: including: geology a) importance importanceof ofrelevant relevantpublications; publications; b) promotion promotionof ofdiscovery discoveryand andutilization utilizationof of natural natural resources; resources; c) contributions contributionsto tounderstanding understandingof of the the natural natural history history and and environment environmentof of the the region; region; d) generation generationof ofnew new ideas ideas and and concepts; and e) contributions contributionsto to the the training training and and education education of geoscientists geoscientists and the public. 2) Nominees Nomineesare areto tobe beevaluated evaluatedon ontheir their contributions contributionsto to the the Institute Institute as as demonstrated demonstrated by attendance at Institute meetings, presentation of talks and posters, and service attendance at Institute of talks service on on Institute Institute boards, committees, committees, and and field field trips. trips. 3) The Therelative relativeweights weightsgiven givento to each each of of the foregoing foregoing criteria must remain flexible and at the discretion discretion of of the the Committee Committee members. members. 4) There Thereare areseveral severalpoints pointsto tobe beconsidered consideredby by the the Goldich Goldich Medal Medal Committee: Committee: a) An attempt should be made to maintain a balance of medal recipients from An attempt should be made to maintain a balance of from each each of the the three three estates—industry, estates-industry, academia, and government. government. b) ItItmust mustbe benoted notedthat thatindustry industrygeoscientists geoscientistsare are at at aa disadvantage disadvantage in that much of of their work in not published. 5) Lake Canada. This LakeSuperior Superiorhas has two two sides, sides, one one the U.S., U.S., and the other Canada. This is is undoubtedly undoubtedly one of the Institute's great strengths and should be be nurtured nurtured by by equitable equitable recognition recognition of of excellence excellence in in both both countries. countries. vii �GOLDICH MEDALISTS MEDALISTS 1979 Samuel Samuel5. S.Goldich Goldich 1990 Kenneth C. Card Card KennethC. 1980 not not awarded awarded 1980 1991 William Hinze 1991 1981 1981 Carl E. Dutton, Jr. 1992 William William F. F. Cannon 1982 Ralph RalphW. W. Marsden Marsden 1993 Donald Donald W. W. Davis Davis 1983 Burton BurtonBoyum Boyum 1994 Cedric CedricIverson Iverson 1984 Richard RichardW. W. Ojakangas Ojakangas 1995 Gene GeneLaBerge LaBerge K. Sims Sims 1985 Paul Paul K. 1996 David David L. L. Southwick Southwick 1986 G.B. G.B.Morey Morey 1997 Ronald P. Sage Sage Ronald P. 1987 Henry HenryH. H. Halls Halls Petennan 1998 1998 Zell Peterman 1988 Walter WalterS. S.White White 1999 Tsu-Ming Tsu-Ming Han 1989 Kalliokoski 1989 Jorma Jorma}Calliokoski 2000 John 2000 John C C. Green Green GOLDICH MEDAL COMMITTEE COMMITTEE1999-2000 1999-2000 members (Committee (Committeemembership membershipextends extendsthrough throughthe the meeting meeting year year shown; shown; replacement replacement members that year. year. Note will be selected during the Board of Directors' annual meeting of that Note that that the the 1999 Board of Directors) Directors) term of each each committee committee member was extended 11 year by the 1999 John Klasner John Klasner(2000) (2000) Western Illinois Illinois University, Macomb, Illinois Illinois Mark Mark Smyk Smyk(2001) (2001) Ontario Ontario Geological Geological Survey, Survey, Thunder Thunder Bay Bay Johnson (2002) Rod Johnson (2002) Rod Johnson and Associates, Associates, Negaunee, Michigan viii viii �CITATION John C C.Green, Green, Medal Recipient 2000 Goldich Medal John C. C. Green, Green, Professor Professor Emeritus Emeritus of of the the Department Department of ofGeological GeologicalSciences, Sciences, University of Minnesota-Duluth, has had a long, distinguished, and on-going career has distinguished, and on-going careerin in the the Lake Superior Superior region. He received his B.A. B.A. Degree Degree in in Geology Geology from from Dartmouth DartmouthCollege Collegeinin 1953. 1953. He at the the University University of of Oslo Osloon onaaFulbright FulbrightFellowship. Fellowship. He then spent a year amid Norskies at Ph.D. in 1960, both both from from Harvard Harvard University. University. With received his M.A. in 1956 1956 and his Ph.D. With his his dissertation on Appalachian geology of an area in New Hampshire/Maine not quite dissertation on Appalachian geology of in New Hampshire/Maine not quite finished, New Englanders Englanders John and Jan moved to Duluth in 1958 1958 when John accepted the position at UMD. position UMD. Most Mostofofhis hissubsequent subsequentsummers summers were were spent spent mapping mapping in in northern northern He did the Archean portion of the Minnesota for the Minnesota Geological Survey. the the Minnesota Geological Survey. the Archean Gabbro 1966), the first first detailed map map Gabbro Lake 15' 15' Quadrangle Quadrangle(Green, (Green, Phinney, Phinney, and Weiblen, 1966), in the that was undertaken by the MGS the remapping remapping of the the Precambrian Precambrian that undertaken by MGS under under the the leadership of Paul Sims. Whereas Minnesota has been his primary working domain, Whereas Minnesota has been his primary working domain, he he has taught at the Wasatch-Uinta Wasatch-Uinta Geology Field Camp in Utah for six summers, has spent a year year as as aaNASA-NRC NASA-NRC Senior Senior Research Research Associate Associate at the the Johnson Johnson Space Space Center Center in in including study Houston, and has traveled widely — Japan, Iceland, and Namibia — to Iceland, and Namibia - to study and has traveled widely - including volcanic volcanic rocks. rocks. John has served as Head of UMD's Department Department of Geology, has served served on on dozens dozens of university committees, and has chaired several of them. them. He Hewas wason onthe theAll-University All-University Council has chaired chaired the the Board of of Directors Council on Environmental Environmental Quality for eight years. He He has of the Lake Superior Basin Studies Center. He has taught 20 different courses, including Superior Studies He has taught 20 different courses,including several that that deal with geology, one one of of his many He has several with environmental environmental geology, many interests. interests. He has supervised 13 supervised 13 M.S. theses theses and has served served on on 61 61 M.S. and and 55 Ph.D. examining examining committees. committees. He has has authored authored or or co-authored co-authored more more than than 100 100publications, publications, maps, maps, field field guides, guides, and and abstracts. abstracts. John's has been been the theNorth NorthShore ShoreVolcanic VolcanicGroup Group—John's main main scientific scientific interest interest has physical volcanology, stratigraphy, physical volcanology, structure, structure, petrology, petrology, and and chemistry chemistry—- and and the the in general. general. Indeed, the name of John C. Green is synonymous Midcontinent Rift System in with with the NSVG. NSVG. He is a most careflil geologist. Today, careful and observant field geologist. Today, at the the age age of of 68, 68, long long would have have hung hung up up their field boots after many geologists would boots and settled for writing the paper about about their their glory glory days, he is still out their leading field trips, umpteenth summary paper beating the bush and the bugs, and hunting for the outcrops that that will will bring bring him him a little beating John doesn't just look at the rocks! He is the rare "complete closer is the rare "complete closer to the the truth. truth. John doesn't just look at the rocks! naturalist", for he knows every species of flora and and fauna fauna as as well. well. And, And, he he isis very very active active in preservation preservation ooff nature for the enjoyment enjoyment of all. His foresight, initiative, and drive resulted in in the the preservation preservation of of Sugarloaf Sugarloaf Cove/Point CoveIPoint near Schroeder on the North Shore, Shore, with its unique geology, geology, flora, flora, and cultural cultural history, as aa protected protected Natural and and Scientific Scientific ix �Site. Site. He was was instrumental instrumental in the the founding founding and and continuance continuance of SICA, SICA, the Sugarloaf Sugarloaf Interpretative Center Association. Interpretative Center Association. One of his his more more recent recent accomplishments accomplishments is his book on on the the geology geology and and natural natural history of the state parks of the North Shore, entitled "Geology on Display". history state parks of the North Shore, entitled "Geology on Display". It was was published by the 1996. published the Minnesota MinnesotaDNR DNR in in 1996. John has been one one of of the the strongest strongest supporters supporters of the the Institute Institute on on Lake Lake Superior Superior Geology over the last several decades. decades. He presented his first talk there in 1959, 1959, and has added 28 abstracts abstracts since since then. then. It is because of the dedication and support of people people like like John, that the ILSG has remained such a viable and healthy organization for nearly half remained such a viable and healthy organization for nearly half aa century. century. geologist, the the laboratory John C. Green Green—- the the tireless tireless field field geologist, laboratory scientist, scientist, the John C. demanding teacher, teacher, the knowledgeable and and cooperative colleague, the educator of the cooperative colleague, the the most deserving deserving of the public, the complete complete naturalist, naturalist, and and the the advocate advocateof ofILSG ILSG—- is is most Goldich Medal! Medal! All of us us assembled assembled here, as well well as as wife wife Jan, Jan, daughters daughters Martha Martha and and Sarah, sons-in-law Joe and Richard, and five grandchildren, are proud of you! and five grandchildren, are proud of you! Congratulations, J.C.! Congratulations, J.C.! x �4 EISENBREY EISENBREYSTUDENT STUDENTTRAVEL TRAVELAWARDS AWARDS The The 1986 1986Board Board of ofDirectors Directorsestablished established the the ILSU ILSG Student Student Travel Travel Awards Awards to to support support student Institute. The student participation at the annual meeting meeting of the Institute. Thename name "Eisenbrey" "Eisenbrey" was was added Eisenbrey(1926-1985) (1926-1985)and andutilize utilize added to to the theaward awardinin1998 1998totohonor honorEdward EdwardH.H.Eisenbrey contributions contributions made made to to the the 1996 1996Institute Institutemeeting meetingininhis hisname. name. "Ned' "Ned"isiscredited creditedwith with discovery of significant massive sulfide sulfide deposits deposits in in Wisconsin, significant volcanogenic volcanogenic massive Wisconsin, but his his talents as scopewas was much muchbroader—he broader-he has been described as having unique talents as an an ore ore finder, finder, scope geologist, geologist, and and teacher. teacher. These Theseawards awardsare areintended intendedtotohelp helpdefray defraysome someof ofthe thedirect directtravel travel costs costs of of attending attending Institute Institute meetings, meetings, and include include a waiver waiver of of registration registration fees, fees, but but exclude exclude expenses expenses for for meals, meals, lodging, lodging, and and field field trip registration. registration. The Thenumber numberofofawards awards and and value value are aredetermined determined by by the theannual annualChair Chairininconsultation consultationwith withthe theSecretarySecretaryTreasurer. Treasurer.Recipients Recipientswill willbe beannounced announcedatatthe theannual annualbanquet. banquet. The The following followinggeneral general criteria criteria will will be be considered considered by the annual annual Chair, Chair, who who is is responsible responsible for forthe theselection: selection: 1) 1) The Theapplicants applicantsmust musthave haveactive activeresident resident(undergraduate (undergraduate or or graduate) graduate)student studentstatus statusatai the thetime timeof ofthe theannual annualmeeting meetingof ofthe theInstitute, Institute,certified certifiedby by the thedepartment departmenthead. head. who are the senior author author on on either either an oral or poster 2) Students who poster paper paper will be be given given 2) favored favoredconsideration. consideration. 3) 3) ItItisisdesirable desirablefor fortwo twoorormore morestudents studentsto tojointly jointly request requesttravel travel assistance. assistance. 4) 4) InIngeneral, general,priority prioritywill willbebegiven giventotothose thoseininthe theInstitute Instituteregion regionwho whoare arefarthest farthestaway away from from the the meeting meetinglocation. location. 5) Each Eachtravel travelaward awardrequest requestshall shallbe bemade madeininwriting writingtotothe theannual annualChair, Chair,arid andshould should explain need, student and author status, and other significant significant details. details. The The form form below is is optional. optional. Students Students can can use use the the form form below, below, or or consult consultthe the Institute's Institute's web webpage page(ilsgeology.org) (ilsgeology.org) to to apply. apply. Successful Successful applicants should contact the meeting chair to receive receive their their awards awards during during the the meeting. meeting. xi �- p INSTITUTE SUPERIOR GEOLOGY INSTITUTE ONLAKE ONLAKE SUPERIOR GEOLOGY flTenbrey Eisenbrey Student Student Travel Travel Award Award Application Application Student StudentName: Name: Date: Date: Address: email: _____________________ Department DepartmentHead-Typed Head-Typed Department DepartmentHead-Signature Head-Signature Educational Educational Status: Status:________________________ Are the senior seniorauthor authorofofanan oral or poster paper? NO_._ oral or poster paper? Y YES— E S NOAre you the Will Will any any other otherstudents studentsbe betraveling travelingwith withyou? you? Who? Who? ________________ Statement Statementof of need need (use (useadditional additionalpage pageififnecessaiy) necessary) to: Pleasereturn returnto: Please xl' xii �STUDENT PAPER AWARDS ., Each year, the Institute selects the best of the student presentations and honors presenters Funding for for the award registrations of the with aa monetary monetary award. award. Funding award is generated from registrations annual meeting. The TheStudent StudentPaper Paper Committee Committeeis is appointed appointed by by the the annual annual meeting meeting Chair Chair in such a manner as to represent a broad range of professional and geologic expertise. manner as to represent a broad range of professional and geologic expertise. Criteria for Criteria for best best student studentpaper—last paper-last modified by the Board Board in in 1997—follow: 1997-follow: 1) The contribution contribution must be demonstrably demonstrably the work of the student. student. 2) The student student must present the contribution contribution in-person. 3) The Student Student Paper Committee Committee shall shall decide decide how many awards to grant, and whether or not to give give separate separate awards awards for for poster poster vs. vs. oral oral presentations. presentations. 4) In cases of multiple senior author, author, or or multiple student student authors, the award will be made to the senior * the award will be shared equally by all authors authors of the contribution. contribution. 5) The The total amount of the awards is left to the discretion of the meeting Chair and typically is about Secretary-Treasurer, but typically about $300 $300 US. US. 6) The Secretary-Treasurer Secretary-Treasurer maintains, and will supply supply to the Committee, Committee, a form form for for the the numerical ranking of presentations. This This form form was was created created and modified modified by Student Student Paper Committees Committees over several several years in an effort to reduce the difficulties difficulties that may arise from selection background. The selection by raters of diverse background. The use of the form is not required, but is required, is left left to the the discretion discretion of the Committee. Committee. 7) The names of award recipients shall Chair's report report shall be included as part of the annual Chair's that appears appears in in the the next volume of the Institute. Institute. Student Student papers papers will will be be noted noted (*) (*)on onthe the Program. Program. STUDENTPAPER PAPER AWARDS AWARDS COMMITTEE COMMITTEE 2000 STUDENT Manfred M. Kehlenbeck, Chair Chair Manfred Lakehead Univers University, Thunder Bay, Ontario Terrence TerrenceS. J. Boerboom Boerboom Minnesota Geological Survey, St. Paul, Minnesota Graham C. Wilson son Turnstone urnstone Geological Geological Ltd., Campbellford, Campbellford, Ontario Ontario ... xiii Xlll �2000 BOARD 2000 BOARD OF DIRECTORS meeting year shown in parentheses) parentheses) (Board membership extends through the meeting Stephen Stephen A. Kissin, Chair Chair(2003) (2003) Lakehead University, Thunder Thunder Bay, Ontario Ontario Theodore J. Bornhorst Bornhorst(2002) (2002) Michigan Technological Technological University, University, Houghton, Houghton, Michigan Michigan James James D. D. Miller Miller (2001) (2001) Minnesota Geological Geological Survey, Survey, St. St. Paul, Paul, Minnesota Minnesota Ronald Ronald P. P.Sage Sage(2000) (2000) Ontario Geological Geological Survey Survey Mark Mark Jirsa Jirsa(2000) (2000) Institute Institute Secretary-Treasurer Secretary-Treasurer Minnesota Geological Survey, St. Paul, Minnesota LOCAL COMMITTEES LOCAL COMMITTEES 2000 GENERAL GENERAL CO-CHAIRS: CO-CHAIRS:Stephen StephenA.A.Kissin Kissinand andPhilip PhilipW. W. Fralick Fralick PROGRAM PROGRAMAND AND ABSTRACTS ABSTRACTS EDITORS: EDITORS:Stephen StephenA. A. Kissin Kissin FIELD FIELD TRIP TRIPCOORDINATOR COORDINATORAND AND GUIDEBOOK GUIDEBOOKEDITOR: EDITOR:Philip PhilipW. W. Fralick Fralick Assistance to Assistance to the thelocal localcommittee committeewas wasprovided by by the thefollowing individuals: individuals: Karen Karen Farther Farrier - Lakehead Lakehead University Manuscript preparation, accounting accounting and communications Sam Lakehead University Sam Spivak Spivak -- Lakehead Graphics Graphics Becky Rogala Lakehead University Rogala - Lakehead Manuscript preparation Manuscript preparation and and audio-visual audio-visual Mark Smyk Northern Development Developmentand arid Mines Mines Smyk -- Ministry of Northern Organization Organization xiv �SESSION CHAIRS (in order order of appearance): appearance): Wed. AM Manfred Kehlenbeck Lakehead Lakehead University University— - Thunder Thunder Bay Dick Ojakangas University University of of Minnesota Minnesota— -Duluth Duluth Wed. PM Bornhorst Ted Bornhorst Houghton Michigan Technological TechnologicalUniversity University— - Houghton Mike Mudrey Wisconsin Geological Wisconsin Geologicaland and Natural NaturalHistory HistorySurvey Survey— -Madison Madison Thurs. Thurs. AM AM Andrew Mitchell Andrew Mitchell Thunder Bay DST DST Consulting ConsultingEngineers Engineers— - Thunder Bay Tony Naldrett Naldrett Consultant — Toronto Consultant - Toronto Thurs. Thurs. PM PM Mark Mark Smyk Smyk Bay Ontario Ontario Geological GeologicalSurvey Survey— - Thunder Thunder Bay Jim Jim Miller Miller Minnesota Minnesota Geological GeologicalSurvey Survey— - Duluth BANQUET SPEAKER SPEAKER 2000 2000 Bruce Bruce Simonson Simonson Oberlin Oberlin College College "Depositional "Depositional settings settings and and Early Diagenesis Diagenesis of Large Precambrian Precambrian Iron Formations" Formations" xv �REPORT MEETING OF REPORTOF OF TilE THE45"' 4SthANNUAL ANNUAL MEETING OF THE THE INSTITUTE INSTITUTE ON LAKE SUPERIOR SUPERIOR GEOLOGY GEOLOGY Marquette, Marquette, Michigan Michigan REPORT ON MEETING OF THE INSTITUTE INSTITUTE REPORT ON THE THE 45TH 45TH ANNUAL MEETING SUPERIOR GEOLOGY, MARQUETTE, ON LAKE SUPERIOR MARQUETTE, MICHIGAN MICHIGAN The 45th Annual Annual Meeting Meeting of the Institute Institute on on Lake Lake Superior Superior Geology Geology was held in in Marquette, Marquette, Michigan May 4-8, 1999 at the Ramada Inn. The meeting was co-sponsored by Michigan May 4-8, 1999 at the Ramada Inn. was co-sponsored by Northern Northern Michigan University Michigan Technological Technological University. University. Robert S. Regis and Theodore J. University and Michigan Bornhorst co-chaired the annual meeting. meeting. The The meeting was well attended with 120 geoscientists registering from 10 provinces, and and Switzerland. Switzerland. The registering from 10 different states, states, three Canadian Canadian provinces, The meeting meeting consisted of two pre-technical session and two post-technical session field trips, two days of of consisted pre-technical session and two post-technical session field hips, two days technical sessions, sessions, and and an an evening evening banquet. banquet. The Proceedings Volume 45 was published 1- Program Program and and Abstracts Abstracts was was Proceedings Volume published in two two parts. parts. Part 1Theodore J. J. Bornhorst. Bornhorst. There edited by Robert S. Regis and Theodore There were were 33 published abstracts for the 22 oral Part 22 -- Field Trip Trip 22 oral and and 11 11poster posterpresentations presentations given given in in the the technical technical sessions. sessions. Part Guidebook, was Guidebook, was edited edited by by Theodore Theodore J. Bornhorst. There There were were 44 field field trips hips and and for for two two of ofthem them there were were separate separate papers papers with with supplementary supplementary information. information. The Theguidebook guidebookcontained contained several several colored maps and cross-sections. Field hips trips continue to be an important component component of of the the annual annual meeting meeting of ILSG ILSG evidenced evidenced by by 76% of attendees participating in 11 or more field hips. trips. The Theguidebook guidebook contains contains44field fieldtrips: hips: Field trip 11 was titled titled "Early "Early Proterozoic Proterozoic strata of the Marquette iron range, Michigan" and was lead W.F. Cannon. Cannon. This one-day one-day field field trip hip had had 30 30 participants participants who visited classic classic lead by by W.F. geologic localities in in the Marquette Marquette area. area. Field trip "ArcheanIshpeming Ishpeming greenstone greenstone belt belt and and gold goldmineralization, mineralization, Field trio 22 was wastitled titled"Archean Michigan" and and was was lead by T.O. Michigan" T.O. Quigley, Quigley, R.A. R.A. Mahin, Mahin, D.J. D.J. Duskin, Duskin, R.C. Johnson, Johnson, T.J. Bornhorst, and G.W. Scott. This two-day field trip had 28 participants and visited localities This two-day field hip had localities focused on lithology, New data focused lithology, structure, structure, and and gold goldmineralization. mineralization. New data on on several several gold gold prospects were presented. Field trip 3 was Field was titled titled "Tilden "Tilden and and Empire Empire Mines of the the Marquette Marquette iron iron range, range, Michgian" Michgian" and was lead by G.W. Scott, P.M. Nordstrom, Nordstrom, and H.M. H.M. Lukey. Lukey. This This one-day one-day trip trip was was very very well attended with 45 participants. We Wethank thank the the Tilden Tilden Mining Mining Company Company and and the the Empire Empire Partnership for for allowing allowingaccess accesstotothese thesetwo twoiron ironmines. mines. Participants of this Iron Mining Mining Partnership Participants of one-day field trip visited localities within the open-pit mines. This was the first time trip visited localities This was the first timeILSG ILSG has visited either of these two mines. mines. The The last last time time aa Michigan Michigan iron iron mine mine was visited by an ILSG field trip hip was was 27 27 years years ago ago in in 1972. 1972. Field Field trip 44 was wastitled titled"Paleozoic "Paleozoic and and glacial glacial strata shata from from Au Au Train Train totoGrand Grand Marais, Marais, field trip Michigan" and was lead by R.S. Michigan" and R.S. Regis Regis and and J.J. Anderton. Anderton. This one-day one-day field hip had 16 16 This is the first participants. This first time time ILSG ILSG has had had a field field trip hip in in the the Munising Munising area area and and participants were able to see participants were see and and learn learn about about the the geology geology of ofthe thePictured Pictured Rocks RocksNational National Lakeshore. xvi �by 99 out of of the the 120 participants participants at at the the annual annual meeting. meeting. Nelson Ham The banquet was attended by along the the southern edge of the of St. St. Norbert College gave an excellent talk on glacial processes along Laurentide ice sheet. A Ahighlight highlight of of the the banquet banquet was was the awarding of the 1999 1999 Goldich medal to Tsu-Ming Han for his contributions contributions to the North American iron ore industry. It is is interesting interesting to note that Tsu-Ming delivered a paper at the first ILSG annual meeting in in 1955 1955and and another another at at this this meeting some 45 years later. meeting some years later. The technical sessions sessions included two invited papers: "Cross "Cross Margin Transport Transport in in Lake Lake Superior" Superior" presented by by Sarah presented Sarah Green Green and and 'A "ANew NewApproach ApproachtotoHistorical HistoricalReconstruction: Reconstruction: Combining Combining Descriptive and Experimental Paleolimnology" presented presented by by Charlie Charlie Kerfoot. Kerfoot. We We are are grateful grateful to to associated with Cliffs Mining Services, the solicited presentations made by industry industry personnel associated Services, Company and and Empire Iron Iron Mining Mining Partnership. Partnership. Two students were selected Tilden Mining Company selected for Ulrich Puschner (Basel, Switzerland) was awarded awarded $150 for his outstanding presentations. presentations. Ulrich Puschner (Basel, Switzerland) was his paper on metamorphism of the the Portage Portage Lake Lake Volcanics Volcanics in in Michigan Michigan and and Joy Loughry poster paper metamorphism of (Univ. Minnesota-Moms) Minnesota-Morris) was was awarded awarded $150 $150 for for her oral presentation presentation on the Crowduck Crowduck Lake David Ams (Kent State Univ., Group, Kenora, Kenora, Ontario. Ontario. Three students, David Univ., Ohio), Ohio), Dyana Dyana Czeck Czeck (Univ. Minnesota), and Ulrich Puschner were awarded Eisenbrey Eisenbrey Student Travel Travel Awards Awards for a total of $800. All Allof ofthese thesestudents studentspresented presented papers papers at at the meeting. The Institute's Board of Directors met on May 6, 1999 1999 and the following is an overview overview of the meeting. meeting. 1. 1. Accepted the Report Report of of the the Chairs Chairs for for the the 44th 44th ILSG. ILSG. 2. 2. Accepted the 1998-99 1998-99 ILSG financial report. There was discussion on methods to encourage student attendance through monetary and other means. A lower cost for encourage students students to attend field field trips, just like like meeting registration, was acceptable. acceptable. 3. 3. Discussed guidelines guidelinesfor for the the Goldich Goldich Award. Award. Committee for one year. 4. 4. Maintained the composition composition of the Goldich Medal Committee 5. Discussed Discussed recasting of the Goldich Goldich Medal. 6. Discussed and approved 2000 meeting location in Thunder Bay with Kissin and Fralick 6. Fralick as co-chairs. co-chairs. 7. Discussed the possibility of a 2001 meeting in Sault 7. Sault Ste Marie, Michigan. Michigan. 8. 8. Discussed defraying defraying the meeting meeting expenses expenses for the secretary-treasurer. secretary-treasurer. The The Board Board (registration, field trips, and approved waiving registration for all meeting events (registration, banquet). 9. Approved a Corporate Resolution for the secretary-treasurer to conduct investments. 9. 10. Reaffirmed Reaffirmed Board commitment to the ILSG Newsletter Newsletter and Web Web page. page. The The Web Web page page Bomhorst. will be reorganized reorganized by Laurel Laurel Woodruff Woodruff and and Ted Ted Bornhorst. 11. Agreed that only one of the two co-chairs co-chairs would continue continue as as primary primary board boardmember. member. Ted Bornhorst will will be be the the representative representative from from the the 1999 1999meeting. meeting. We wish to thank all of the people the field trips and made people who lead and prepared materials for the presentations. While field trips continue continue as as the the traditional traditional strength strength of of ILSG, ILSG, the the presentations presentations provide a forum for discussion of Lake Superior geology. Of Of course, course, there there are are many many others others who who to the success of aa meeting we acknowledge for contributing to meeting including including the session session chairs, chairs, best best student paper paper award award committee, committee, ILSG ILSG Board Boardmembers, members,and andthe the staff staff of of the the Ramada Ramada Inn. Inn. We We volunteer help help with with registration. registration. Last we thank all of especially thank Suki Smaglik for all of her volunteer those who attended attended the the 45th 45th annual annual ILSG ILSG meeting, meeting, for for without without them there there would would not not be be an an JLSG. ILSG. Our "break pre-meetinginterest. interest. As a result "break even" even" budget budget model was based based on indicated indicated pre-meeting result of of xvii �than expected expected and and some some unexpected unexpected additional additional monies, monies, the meeting generated higher attendance attendance than generated cash flow flow of a few thousands of dollars dollars for for ILSG. !LSG. aa positive cash thousands of personally satisfied satisfied with the overall We are personally overall outcome outcome of of the the meeting meeting and and feel feel ititwas was aa success. success. waswell well worth worth the the effort. effort. We While itit is is aa lot lot of of work work to toput put on on the the ILSG ILSG annual annual meeting, meeting, itit was We encourage others to consider being chair or co-chairs of the ILSG annual meeting. encourage others to consider being chair or co-chairs of the ILSG Regis Ted Bornhorst Bornhorst and and Bob Bob Regis Co-Chairs of the 45th Co-Chairs 45th Annual ILSG xviii �CALENDAR PROGRAM CALENDAR OF OF EVENTS EVENTS AND PROGRAM MONDAY, 2000 MONDAY. MAY MAY 8. 8.2000 I I I 0800-1800 0800-1800 PRE-MEETING FIELD FIELDTRIPS TRIPS PRE-MEETING All field trips trips leave leave and and return returneach eachevening eveningto to Lakehead Lakehead University University Alifleld 1) 1) MESOPROTEROZOIC MEsoPRoTERozoIc SIBLEY SIBLEYGROUP GROUP(Day (DayOne) One) Leaders: Philip Philip Fralick, Fralick, Mark Smyk Smyk TUESDAY. 2000 TUESDAY. MAY MAY 9. 9.2000 I 0800-1800 0800-1800 PRE-MEETING PRE-MEETING FIELD FIELDTRIPS TRIPS 1) MESOPROTEROZOIC MESOPROTEROZOIC SIBLEY SIBLEYGROUP GROUP(Day (DayTwo) Two) Leaders: Leaders: Philip Philip Fralick, Fralick, Mark Mark Smyk Smyk 2) LAC LAC DES DES ILES ILES MINE MINE (I) (I) Leader: Moe Lavigne Moe Lavigne 3) 3) GEOARCHEOLOGY GEOARCHEOLOGY OF OF THE THUNDER THUNDER BAY AREA Leaders: Brian Phillips, Phillips, Scott Scott Hamilton, Hamilton, Joe Stewart, Stewart, Pat Julig, Julig, Bill Bill Ross Ross I 1700-2200 1700-2200 REGISTRATION AT LAKEHEAD UNIVERSITY POSTER POSTER SESSION/CASH SESSIONICASH BAR MIXER Agora/Faculty AgoraPaculty Lounge Lounge xix xix �WEDNESDAY. 2000 WEDNESDAY. MAY MAY 10. 10.2000 0800-1200 0800-1200 REOISTRATION/PRE-REGISTRATION REGISTRATION/PRE-REGISTRATIONPACKET PACKETPICK-UP PICK-UP I: GEOLOGICAL PROVINCE Session I: GEOLOGICAL OVERVIEW OF THE WESTERN SUPERIOR PROVINCE University Centre Theatre Theatre 0900-0915 0900-0915 WELCOME AND OPENING OPENING REMARKS REMARKS 0915-0945 091 5-0945 Kehlenbeck, Kehlenbeck, M.M. M.M. Rocks of ofthe theQuetico QueticoSubprovince Subprovinceand andAdjacent AdjacentTerranes Tenanes A Review of Structures in Rocks 0945-10155 0945-101 Davis, Davis, D.W. D.W. Western Superior Province: Geochronologic GeochronologicAspects Aspects 1015-1040 1015-1040 COFFEE COFFEE BREAK AND AND POSTER POSTER SESSION SESSION 1040-1110 1040-1 110 Tomlinson, Tomlinson, K. K. Western Superior Superior Province: Province: Volcanological Volcanological Aspects Aspects 1110-1140 1110-1140 Fralick, P.W. P.W. Fralick, Western Superior Superior Province: Province: Sedimentological Sedimentological Aspects Aspects 1140-1200 1140-1200 Czeck, D.M.* and Hudleston, P.J. P.J. A Sequence Transpression in the the Seine River River Conglomerates Conglomerates Sequence of Folding and Dextral Transpression 1200-13 1200-1310 10 LUNCH BREAK 1310-1330 1310-1330 R.R. Davis, D.W., Amelin, Y., V., Nowell, Nowell,G.M. G.M. and and Parrish, Parrish, R.R. Hf Isotope Study Study on on Zircons Zircons from from the the Western Western Superior SuperiorProvince Province 1330-1350 1330-1350 Pettigrew, N.T.*, Hattori, Hattori, K.H. and and Percival, Percival, J.A. Intrusion: a POE-bearing Samuels Lake Intrusion: PGE-bearing Quetico-type Quetico-type Intrusion Intrusion in in the the Central, Central, Western Quetico Subprovince, Subprovince, Northwestern Ontario 1350-1410 1350-1410 Wilson, A.C. Archean Diamond Exploration Targets in the Michipicoten Greenstone Greenstone Belt, Wawa, Ontario Ontario 1410-1430 1410-1430 R.P. and and Crabtree, Crabtree, D.C. Morris, T.F., Sage, R.P. Kimberlite, Base Metal, Gold and Carbonatite Exploration Targets, Derived from Overburden Heavy Mineral Data, Killala Lake Area, Northwestern Northwestern Ontario Ontario xx �1430-1450 Karkkäinen, N. and Bornhorst, Bornhorst, T.J. Karkkainen, Small Mafic Intrusions of the Lake Superior Region: Targets for Titanium Titanium Exploration 1450-15 10 COFFEE BREAK AND POSTER SESSION 1510-1530 Bajc,A.F. Bajc, A.F. Results of Regional Till Sampling Sampling in the Western Part of the Shebandowan Shebandowan Greenstone Belt, Northwestern Ontario Greenstone Northwestern Ontario 1530-1550 Cannon, W.F. and Cannon, and Woodruff, Woodruff, L.G. Some Some Factors That Control the Distribution of Mercury in the Near-surface Environment of Isle Royale National Park, Michigan-earth, Wind and Fire 1550-1610 Larson, P.C. Larson, P.C. and andMooers, Mooers, H.D. H.D. Commination Commination and Dilution of Glacial Indicators: Rate Estimates Estimates from from Field Field Data Data 1610-1630 Peterson, D.M. Peterson, D.M. Geometry Between Gold-rich Gold-rich Subsidiary Subsidiary Shear Shear Zones Zones and Major Geometry Between Major Structures: Structures: Implicationsfor Archean Lode-Gold Mineral Exploration Implicationsfor 1630 ILSG Business Business Meeting Meeting 1800-1930 MIXER (Residence Cafeteria) Cafeteria) MIXER Cash Bar 1930-2130 ANNUAL BANQUET BANQUET AND AWARDS PRESENTATION Residence Cafeteria Cafeteria • Announcement Announcementofof47th 4T11 Annual Meeting location location • Banquet BanquetSpeaker: Speaker: Dr. Dr. Bruce BruceSimonson, Simonson,Oberlin Oberlin College College "Depositional Settings Settings and Early Diagenesis Diagenesis of Large Precambrian Iron Formation" xxi �THURSDAY. MAY 11.2000 GEOLOGICAL OVERVIEW OF THE WESTERN SUPERIOR PROVINCE II; Session 1 1: University Centre Theatre Theatre 0900-0930 0900-0930 Lavigne, M.J. The Lac Mine, Northwestern Ontario Lac des des Ties lies Mine, Ontario 0930-1000 0930-1000 Fralick, Fralick, P.W. Western Western Superior Superior Province: Province: Proterozoic Proterozoic Sediments Sediments 1000-1030 1000-1030 Kissin, Kissin, S.A. S.A. Vein-type Deposits of the Thunder Bay Area 1030-1050 1030-1050 COFFEE BREAK AND POSTER POSTER SESSION SESSION 1050-1110 Pueschner, U.* and Schmidt, Pueschner, U.* and Schmidt,S.T. S.T. the Keweenawan Keweenawan Portage Portage Lake Lake Volcanics Volcanics on Low-grade Metamorphic Zonation of the the Keweenaw Keweenaw Peninsula, Peninsula, Michigan Michigan 1110-1130 Rampe, .LS.* Rampe, J.S.* and Holm, Holm, D.K. Modelling the Effect of Intermediate Intermediate Temperature Temperature (350°-500°C) (350'-500°C Mazatzal-Age Mazatzal-Age Thermal Overprinting Superior Region Thermal Overprinting on Argon Diffusion from the Southern Lake Superior 1130-1150 Hudak, G.J., Hudak, G.J., Morton, Morton, R.L. RL. and and Dahlberg, H. Preliminary Volcanology and PreliminaryVolcanology and Hydrothermal HydrothermalAlteration AlterationStudies Studiesat at the the Five Five Mile Lake, Eagles Nest, and Quartz Hill Hill Prospects: Prospects: Implications Implications for forVMS-Style VMS-StyleMineralization Mineralization Eagles in Northeastern Northeastern Minnesota Minnesota 1150-1300 LUNCH LUNCH 1300-1320 Green, Green, J.C. J.C. Mystery Faults Faults of the Cascade River, North Shore, or What Is this Granite Doing Doing Here? Here? 1320-1340 K.J. and Schulz, KJ. and Nicholson, Nicholson, S.W. Lithogeochemistry Lithogeochemistry and and Paleotectonic Paleotectonic Setting Setting of the Bend Massive Massive Sulfide Sulfide Deposit, Deposit, Northern Wisconsin 1340-1400 Van Schmus, Schmus, W.R., W.R, MacNeill, MacNeill, L.C., Holm, and HoIm, D.K., D.K., Boerboom, Boerboom, T.J. and xxii �Jirsa, M.A. Jirsa, M.A. The 1787-1772 1787-1772 Ma Ma East-Central East-Central Minnesota Minnesota Batholith: Batholith: Precursor Precursor to to Crustal Crustal Stabilization in the Lake Superior Region Superior Region 1400-1420 Schweitzer, D.J.*, Schnieder, D.A., and Schweitzer, D.A., Boerboom, Boerboom,T.J., T.J., Holm, Hoim, D.K. BK. and Van Schmus, Schmus,W.R. Assessing the Extent of Assessing the of Early Early Proterozoic Proterozoic Penokean Penokean Versus Versus -A770-1760 -1770-1760 Ma Ma Metamorphism Metamorphism in East-Central East-Central Minnesota Minnesota 1420-1440 HoIm, D.K.. D.K., Hodees. Hodges, K.V. K.V.and and Hurtado, Hurtado, J. Holm. Results of40Ar/39Ar Laser Microprobe Mapping of of~Muscovite from Precambrian ~ e s u l tof s40k~9i~& ~ iec r o ~ r o~~e bAge e Mapping u s c o v i t from e ~recambrian Bedrock of the Southern Lake Superior Region 1440-1500 Kissin, S.A., Okamoto, RG. Okamoto, M., Addison, W.D. W.D. and and Brumpton, Brumpton, R.G. A Possible Sudbury Ejecta Layer in the Gunflint Formation, Northwestern Ontario Sudbury Ontario 1500-1520 COFFEE BREAK AND POSTER POSTER SESSION SESSION 1520-1530 STUDENT AWARDS STUDENT AWARDS 1530-1550 North, J. North,J. Nature of Logan Nature and Distribution Distribution of Logan Diabase Diabase Sills and Gabbro Gabbro Channels in the the near Thunder Thunder Bay, Bay, Ontario: Ontario: Brief BriefComparison Comparisonto toNoril'sk Noril'sk Keweenawan Rift near 1550-1610 Jr. Medaris, L.G. Jr. The Barren Barron Saprolite: Confirmation Confinnation of of Mature Mature Chemical Chemical Weathering Weathering in the Source Source Paleoproterozoic Quartz Arenites in the Lake Superior Region for Paleoproterozoic 1610-1630 Argust,A. Argust, A. Chemistry Chemistry and Mineralogy of Lower Chocolay Group Rocks, Dickinson Dickinson County, County, Michigan Michigan 1630-1650 Simonson, B.M. Simonson, Conglomerates and Intraformational Intraformational Breccias The Distinction Between Flat Pebble Conglomerates Breccias in Precambrian Precambrian Iron Formations Iron Formations xxiii �POSTER PRESENTATIONS POSTER PRESENTATIONS B.R.* and Saini-Eidukat, Saini-Fidukat, B. Bandli, B.R* B. Nomarski DIC Microscopy Analysis of of Plagioclases Plagioclases from from the Duluth Microscopy and Structural State Analysis Complex, Minnesota .J andHavholm, H~VUUIII!, K.G. Beaster, K.F.*, Kohn, J.D.* J.D.t and K.G. Wind or Water? Water? Paleoenvironment of the Proterozoic oterozoic Hinckley Sandstone, Sandstone, Northeastern Minnesota Minnesota Harris, Harris, E.C.A.* E.C.A.* and Wirth, Wirth, K.R. K.R region, eastern eastern Mesabi Mesabi Range, Range, Minnesota Petrogenesis of granitic rocks of the Dunka River region, Hauck, S.A., S.A., Bite, A. and Severson, M. Hauck, and Severson, Copper Pyroxene Homfelsed Homfelsed Archean Archean Giants Giants Range RangeBatholith Batholith Footwall Footwall of of opper Mineralization of Pyroxene thee Keweenanwan South Kawishwi Intrusion, Duluth Complex, NE Minnesota -- Archean Archean orr Keweenawan Mineralization? Mineralization? Jerde, E.A. Jerde, E.A. Magmatic for Nathan's Series: An Initial of the Magmatic Origins Origins for Nathan's Layered Layered Series: Initial Reassessment Reassessment of the or Plutonic Materials Midcontinent Rift's First FirstMaj Major Materials Kean, Kean. W.F. and Luther, Luther. F. F. Additional Paleomagnetic PaleoniagneticStudies Studiesofof aa Proterozoic Proterozoic Diabase DiabaseDike, Dike, in in Pifher Pifher and Irwin Irwin Townships,,Lake Nipigon District, District, Ontario Wirth, K.R. Kennedy, B.C.*, Wirth, K.R and and Vervoort, Vewoort, J.D. Petrogenesis Petrogenesis of the Midcontinent Midcontinent Rift Granophyric Granophyric Complexes Complexes of Northern Minnesota Minnesota Luther, Luther, F.R. Low-grade Metamorphismofofan an Archean Archean Debris Debris Flow, Flow, Irwin, Irwin, Pither Low-grade Metamorphism Pifher and and Meader Meader Townships, Lake Nipigon Region, Ontario Jr. and Medaris, L.G. Jr. and Fournelle, Fournelle, J.H. Tourmaline-bearing QuartzVeins Veinsin in the the Baraboo Baraboo Quartzite: Quartzite: A A New New Occurrence Tourmaline-bearing Quartz Occurrence of the Alkali-deficient Tourmaline, Foitite Morris, R.P. and Crabtree, Morris, T.F., Sage, Sage, RP. Crabtree,D.C. D.C. Kimberlite, Base Metal, Gold and Kimberlite, and Carbonatite Carbonatite Exploration Exploration Targets, Targets, Derived Derived from from Heavy Heavy Mineral Data, Killala Killala Lake Lake Area, Northwestern Ontario Ontario Peterson, Peterson, D.M. Geologic and GIS-based Geologic GIS-based Lode-gold Lode-gold and Volcanogenic Volcanogenic Massive Sulfide Sulfide (VMS) (VMS) Mineral Mineral xxiv xxiv �Potential Maps Maps of aa Portion Potential Portion ofofthe theArchean ArcheanVermillion VermillionGreenstone GreenstoneBelt, Belt,Northeastern Northeastern Minnesota Minnesota E.H.*, Wirth, Wirth, K.R. and Phillips, EX.*, and Morey, Morey, G.B. G.B. Petrogenesis of the Enigmatic Aurora Sill, Mesabi Range, Minnesota Petrogenesis Enigmatic Minnesota Sage, Sage, R.P. The "Sandor" Diamond Diamond Occurrence, Occurrence, Michipicoten Michipicoten Greenstone Greenstone Belt, Belt, Wawa, Wawa, Ontario Ontario Stott, Stott, G. and and Berdusco, Berdusco, B. B. Precambrian Features under the James Bay and Hudson Bay Lowlands Vervoort, Vewoort, J.D., Wirth, Wirth, K.R. and andKennedy, Kennedy, B.C. Isotopic Constraints Constraints on on the Origin of Granophyre in the Midcontinent Isotopic Granophyre Complexes Complexes in Midcontinent Rift Ritt of nNortheastern or the astern Minnesota Wilson, Wilson, A. A. Archean Diamond Exploration Targets in the Michipicoten Greenstone Belt Wolbers, Wolbers, J.A.* and and Seifert, Seifert, K.E. K.E. Petrogenesis of the Silver Creek Midcontinent Rift Petrogenesis Creek Dike: a 1.1 Ga Intrusion in the Midcontinent L.G., Attig, Attig,J.W. J.W.and andCannon, Cannon,W.F. WI. Woodruff, L.G., Geochemical Impacts of an Undisturbed Mineral Deposit -- Results from the Bend Deposit, Chequamegon Chequamegon National Forest, Forest, Wisconsin xxv XXV �FRIDAY. 2000 FRIDAY. MAY 12. 12.2000 0800-1800 0800- 1800 POST-MEETING FIELD TRIPS TRIPS All field field trips leave and and return returneach eachevening eveningto to Lakehead Lakehead University, University,except exceptfor Field an overnight stay in Field Tr4p Trip 6, which will involve an in Atikokan on May 12 (at (at the the participant's expense). participant's expense). 4) PALEOPROTEROZOIC PALEOPROTEROZOIC GUNFLINT GUNFLINTFORMATION FORMATION Leaders: Pier Pufahi and Philip Fralick Pier Pufahl and Philip 5) 5) QUATERNARY QUATERNARYGEOLOGY, GEOLOGY,SHEBANDOWAN SHEBANDOWANBELT BELT Leader: Andy Andy Bajc Bajc - - 6) 6) STEEP STEEPROCK ROCK - FINLAYSON FINLAYSON - LUMBY LUMBY BELTS BELTS (Day (Day One) One) Leaders: Denver Stone, Kirsty Tomlinson, Ray Bernatchez Denver Stone, Kirsty Tomlinson, Ray Bematchez and Philip Philip Fralick Fralick 7) 7) LAC LAC DES DES ILES ILES MINE MINE(II) (11) Leader: Moe Lavigne Moe Lavigne SATURDAY. 2000 SATURDAY. MAY MAY 13. 13.2000 0800-1800 0800- 1800 FIELD FIELD TRJP TRIP66(Day (DayTwo) Two) xxvi xxvi �Chemistry Group Rocks, Chemistry and and Mineralogy Mineralogy of Lower Chocolay Group Dickinson County, Michigan Michigan ARGAST, Anne, Department of Geosciences, Geosciences, Indiana-Purdue Indiana-Purdue University University Fort Fort Wayne, Wayne, Fort Wayne, Wayne,IN IN46805-1499, 46805-1499,argast(%ipfw.edu argastipfw.edu Fort Rocks of the Chocolay Dickinson County, County, Michigan. Michigan. Most Most Chocolay Group rest on Archean basement in Dickinson likely accumulated accumulated in the interval 1.9-2.1 Ga. ago, the Group consists of the basal, partly 1.9-2.1 consists partly conglomeratic, Fern Creek Formation, overlain conglomeratic, overlain by Sturgeon River Quartzite Quartzite and and Randville Randville Dolomite. Chocolay Group likely represents deposition terrigenous and shallow deposition in temgenous shallowmarine marine environments with later environments later units of the Marquette Range Supergroup Supergroup (Menominee (Menominee and and Baraga Baraga Groups) transitioning upwards into deeper water, more active and isolated environments. environments. There are two alternate alternate views for the origin origin of the Fern Creek Creek Formation. Some Some interpret interpret the the Fern Creek (or its putative equivalents of Reany Creek and Enchantment Lake Formations putative equivalents Lake Formations farther north in Michigan) as examples examples of glaciogenic glaciogenic sediments, possibly synchronous synchronous with with Gowganda glaciation (e.g., Pettijohn, 1943; Gair, 1981; Young, 1983; Ojakangas, 1984). Gowganda glaciation Pettijohn, 1943; 1981; 1983; 1984).Others Others interpret the Fern Creek as originating, originating, for for example, in fluviatile, fluviatile, occasionally occasionally torrential torrential environments (e.g., environments (e.g., Bayley et al., 1966; 1966; Larue, 1981; 1981; Mattson Mattson and Cambray, Cambray, 1983). 1983). This This is is an an important determination, determination, affecting affecting aspects aspects of regional and interregional interregional correlation correlation on on aa significant scale (e.g. Ojakangas, 1988). 1988). This study focuses focuses on on the bulk and and mineral chemistries chemistries of the Fern Fern Creek Creek Formation Formation and and Sturgeon Sturgeon River Quartzite Quartzite exposed exposed along an an access access road road to aa hydroelectric hydroelectric dam dam located located about about33 km northeast of Loretto, Loretto, Michigan. The purpose is to further further evaluate evaluate the glaciogenic glaciogenic vs. vs. fluviatile origins fluviatile origins of the Fern Fern Creek Formation, Formation, and to characterize characterize the materials materials to to constrain constrain possible source source areas. Fern Creek rocks are dominated by quartz, sodic sodic plagioclase, K-feldspar, antiperthite, antiperthite, and and micas micas of di- and trioctahedral trioctahedral composition. Sturgeon River is predominantly quartz with minor illite. composition. Sturgeon River quartz with minor illite. Zircon, tourmaline, tourmaline, fluor-hydroxy fluor-hydroxy apatite, apatite, pyrite, rutile, mtile, fluorite, fluorite, monazite, huttonite huttonite and and aa fluorfluorREF mineral occur Zircon and tourmaline tourmaline dominate in the hydroxy REE occur in the Fern Creek Formation. Zircon Sturgeon Sturgeon River River Quartzite. Quartzite. The tourmaline compositions compositionsvary systematically systematically with with vertical vertical position position throughout throughout the the Fern Fern Creek/Sturgeon CreekBturgeon River River sequence. sequence. This This suggests suggests a gradual gradual denudation denudationof of the the source source area areaover over an an extended length of time. extended length Bulk chemistries chemistries for for the the Sturgeon SturgeonRiver River Quartzite Quartzite are are consistent consistent with with an an origin origin as as aa well well sorted sorted sediment in a nearshore marine environment. Fern Creek chemistries are typical of unsorted chemistries unsorted materials materials that have have not undergone undergone hydraulic hydraulic differentiation, differentiation,and and are are similar similarto to chemistries chemistriesfrom from the underlying Carney Lake Gneiss. underlying Carney Lake Gneiss. I �REE distributions distributions are highly highly variable in the Fern Creek Formation, ranging from nearly flat (normalized to PAAS) to extremely steep (e.g. chondrite normalized LdYb La/Yb of 101.5). (normalized 101.5). These These distributions result from enrichment in LREEand Tb-rich minerals. distributions Th-rich The bulk chemistry and presence of REE minerals are consistent with proximal derivation derivation from the underlying (pegmatite-rich) Carney Lake Gneiss. The trends in tourmaline composition composition suggest association association with a process capable of deep erosion over an extended period of time. The similarity similarity of the Fern Creek to stratigraphically equivalent rocks at some distance north suggests suggests a process of significant significant areal extent. Taken together, these results strongly support support the origin origin of the Fern Creek Formation as a proximal till derived from the underlying gneiss. References References iron-bearing Bayley, R.W, Dutton, C.E., and Lamey, C.A., 1966, Geology of the Menominee iron-bearing Counties, Wisconsin: district Dickinson County, Michigan and Florence and Marinette Counties, 96 pp. U.S. Geological Survey Professional Professional Paper Paper 513, 513,96 Gair, J.E., 1981, Lower Proterozoic Proterozoic glacial deposits deposits of Northern Michigan, in Hambrey, M.J., University and Harland, W.B., eds., Earth's pre-Pleistocene glacial record: Cambridge University 803-806. Press, p. 803-806. Lame, D.K., 1981, 1981, The The Chocolay Chocolay Group, Group, Lake Superior Superior region, U.S.A.: Sedimentologic Sedimentologic evidence for deposition deposition in basinal and platform settings settings on an Early Proterozoic Proterozoic craton: Geological v. 92, 92,p. p. 417-435. 417-435. Geological Society Society of of America America Bulletin, Bulletin, Part Part 1,1, v. F.W., 1983, The The Reany Reany Creek Creek Formation: Formation: aa mass-flow mass-flowdeposit deposit of of Mattson, S.R. and Cambray, F.W., possible post Menominee possible Menominee age age [abs.], [abs.], in in Proceedings, Proceedings,29th 29' Annual Institute Institute on Lake Lake Superior Superior Geology, p. 27. 27. Ojakangas, R.W., 1984, 1984, Basal Lower Proterozoic glaciogenic formations, formations, Marquette Marquette Range Annual Supergroup, Upper Peninsula, Michigan [abs.]: in Proceedings, 30th Institute Upper Peninsula, Michigan [abs.]: in Proceedings, 30' Institute on Lake Superior Superior Geology, Geology, Wausau, Wausau,WI, WI,p.p. 43. 43. Ojakangas, R.W., 1988, 1988, Glaciation: Glaciation: An uncommon "mega-event" "mega-event" as a key to intracontinental intracontinentaland and intercontinental intercontinental correlation correlation of Early Proterozoic basin fill, North American and Baltic Baltic New perspectives in basin analysis: Cratons, in Kleinspehn, K.L., and Paola, C., eds., New Springer-Verlag, p. 431-444. 43 1-444. Pettijohn, F.J., 1943, 1943, Basal Basal Huronian Huronian conglomerates conglomerates of Menominee and Calumet Calumet districts, districts, Michigan: Journal of. Geology, v. 51, p. 387-397. Michigan: Geology, 51, 387-397. Young, G.M., 1983, Tectono-sedimentary history of Early Proterozoic Proterozoic rocks of the northern Proterozoic geology of the Great Lakes Great Lakes region, in Medaris, L.G., Jr., ed., Early Proterozoic Lakes region: Geological Society of America Memoir 160, p.15-32. 2 �RESULTS OF REGIONAL TILL TILL SAMPLING IN THE WESTERN PART OF THE SHEBANDOWAN GREENSTONE BELT, NORTHWESTERN NORTHWESTERN ONTARIO ONTARIO THE GREENSTONE BELT, Bajc, A.F., Sedimentary Geoscience Section, Ontario Geological Geological Survey, Survey, Ministry Northern Development and Mines, 933 Ramsey Lake Lake Road, Road, Sudbury, ON of Northern P3E 6B5 6B5 A project of Quaternary Quaternary geological geological mapping mapping and regional till sampling sampling was was undertaken undertaken over the western part of of the Shebandowan Shebandowan greenstone greenstone belt during during the the 1999 1999field field season. season. Quaternary Quaternary mapping helped to characterize characterize the surficial surficial materials materials present within within the the study area and to reconstruct the ice flow history associated with with these these deposits. deposits. This This information information provided a framework framework by which which the regional materials materials compositional compositional datasets could be interpreted. interpreted. The Theregional regional sampling sampling program program provided provided information informationon on the background concentrations concentrations of various elements elements in in till as as well as as on on the the number number and and character character of gold grains grains and base metal indicators indicators in in till. The study area contains a relatively simple record of Quaternary events. events. Most Most deposits deposits were laid down during the final retreat of ice from the the area. Ice flow indicators Ice flow indicatorssuggest suggest aa consistent consistent pattern of flow flow towards towards the south south across across the eastern eastern half half of of the the study study area, area, becoming more westerly towards the west. Till cover is generally thin and discontinuous Till cover is generally thin and discontinuous over most parts of the study area. Thicker, Thicker, more more extensive extensive till till is is present present within within Hagey, Hagey, Conacher Conacher and Blackwell townships. Till Tillsamples samplescollected collected from from these these townships townships are are less less representative representative of local local geology geology than are are samples samples collected collected from from areas areas of of very very thin thin till. till. Geochemical Geochemical and mineralogical mineralogical interpretations interpretations should should consider consider these these local local variations variationsin in till character. character. The till sampling sampling program program has has clearly clearly identified identified aa number number of of precious precious and and base base metal metal exploration belt. Higher exploration targets within the western Shebandowan greenstone belt. Higher density density follow-up follow-up sampling sampling surveys surveys are are recommended recommended for for these these areas areas to to determine determinethe the the anomalies and more more precisely precisely define define potential potential source sourcerocks. rocks. The significance of the regional character character of this this survey survey will assist assist with with the the interpretation interpretationof of local, local, property-scale property-scale geochemical datasets by placing results results into into context context with with respect respect to to regional regional background. background. geochemical datasets The results of this survey survey clearly clearly support support the the use use of of till compositional compositional surveys surveysfor for mineral mineral exploration. exploration. The Theapproach approachfor forfollow-up follow-upsampling samplingprograms programs will will be be dictated dictated by by the the type type of mineralization mineralization sought sought and and the the local local conditions conditionswithin within aa given given property. property. 3 �NOMARSKIIDIC DICMICROSCOPY MICROSCOPY AND AND STRUCTURAL STRUCTURAL STATE ANALYSIS ANALYSIS OF NOMARSKI OF PLAGIOCLASES FROM THE PLAGIOCLASES THE DULUTH COMPLEX, MINNESOTA MINNESOTA BANDLI, Bryan R., Department of Geosciences, Geosciences, North Dakota Dakota State Statc University, University,Fargo, Fargo, ND 58105-5517 USA. (Bryan_Bandli@ndsu.nodak.edu). (Bryan.Bandli@ndsu.nodak.edu). SAINI-BIDUKAT, SAINI-EIDUKAT, Bemhardt, Department Bernhardt, Department of Geosciences, North Dakota State University, Fargo, ND 58105-5517 58 105-5517 USA. (sainieid@badlands.nodak.edu) (sainieid@badlands.nodak.edu) Nomarski Differential Differential Interference Interference Contrast Contrast (DIC) (DIC) and and structural structural state state XRD XRD analyses analyseswere were carried out on samples of Duluth Complex Anorthositic Series rocks. rocks. Nomarski DIC is a reflected light technique technique which uses aa double-crystal double-crystal prism prism to to split split plane-polarized plane-polarizedlight lightto to produce a dark-light shading that highlights microrelief. To use the method on mineral in acid to to produce produce microtopography. microtopography. Anderson Anderson specimens, polished sections are etched in (1983), Pearce and Kolisnik (1990), (1990), and Pearce Pearce (1994) (1994) discuss the the importance importance of of interference interference imaging in showing that high-resolution high-resolution mineral mineral zonation patterns, patterns, that that are are correlatable correlatable with with varying An content, record complicated complicated dissolution dissolution and reaction reaction events events that that occurred occurredduring during crystal growth. growth. Polished block and thin sections sections were prepared from three three samples samples of of the the anorthositic anorthositic series taken near its contact with the Duluth Layered Series, Series, along along Skyline Skyline Parkway Parkway in in Duluth above Oneota Cemetary (Stop 1-5 of Miller, 1995). Sample 1 is an inclusion containing more than 95% plagioclase; plagioclase; sample sample 22 is the the host host gabbroic gabbroic anorthosite, anorthosite, and and sample sample three is from the outcrop used for zircon zircon age age dating dating (Paces (Paces and and Miller, Miller, 1993). 1993).Polished Polishedthin thin sections were prepared on orthogonal orthogonal axes axes to expose expose a variety variety of of crystallographic crystallographic orientations, etched in 48-50% HBF4 HBF4 for approximately seven minutes (adapted from the method of Anderson, 1983), 1983), and then imaged imaged using aa Nomarski Nomarski mirror mirror cube cube and and prism prism slider slider on an Olympus Olyrnpus BX-60 petrographic petrographic microscope. Although some some oscillatory oscillatory zoning was was observed, observed, the the most most common common zoning zoning observed observed was was patchy. This type of zoning zoning could be considered considered a hiatus hiatus type type of of discontinuity discontinuityas as defined definedby by Castro and de la Rosa (1994). Irregular Irregular zoning zoning of of plagioclase plagioclase is is common common in in the the Anorthositic Anorthositic Weiblen, 1990) 1990)and and could could indicate indicate significant significant disruptions disruptions of of the the Series (Miller and Weiblen, crystallizing surface surface due to dissolution dissolution and and reaction events events as as the the crystal crystal mush mush moved moved from from deep to shallow chambers. chambers. Plagioclase Plagioclase structural structural analyses analyses were were carried carried out out on on the the three three samples samples plus plus one one additional additional plagioclase separate separate from from the the Duluth Duluth Anorthositic AnorthositicSeries Series (Sample (SampleD-12) D-12) and and one onefrom from the the plagioclase Gabbro Lake area area (sample (sample BL-27). BL-27). Samples Samples were were crushed crushed and and plagioclase plagioclasewas was hand-picked, hand-picked, powdered, and diffraction patterns collected on a Philips Automatic Vertical Diffractometer Characterization Laboratory at the Materials Characterization Laboratory at NDSU. Scans Scans were were made made from from 6.0 6.0 to to 65 65 degrees 20 using using a step step of of 0.02° 0.02' 28, 20, Cu Ka Karadiation radiation (X= (\= 1.54184 1.54184 angstroms), angstroms), a diffracted diffracted 4 �beam beam monochrometer, monochrometer, and and aa sealed sealed proportional proportional counter. counter. Patterns were were matched matched to to aa plagioclase in the PDF reference file and refined using Garvey's Gamey's (1986) (1986) implementation implementation of the program of Appleman and Evans (1973). Refined A131 and yvalues yvalues were used to determine (1983). Despite determinethe the structural structuralstate state based based on on figures figures from from Kroll Kroll(1983). Despite the the potential potential difficulties difficultieswith with refining refining zoned zoned minerals, minerals, the the results results (with (with the the exception exception of of sample sample 3-99, 3-99, for for which are in in "low" "low' (lowwhich An An content content is yet to be measured) indicate that all the samples are (lowtemperature, temperature,or orordered) ordered)structural structuralstate state(Table (Table1). 1). samnie 1-99 90.180 (-i-I- An 65* 0.084) 2-99 90.247 (+1- 0.204) 62* 3-99 90.299 BL-27 89.843 D-12 90.213 (+1- 0.130) (+1- 0.190) (÷1- 0.218) n.m. 55 63 Table Refinedgamma gamma and values plagioclase separates of Duluth Complex Anorthositic Series rocks. Table 1. Refined and AnAn values for for plagioclase separates of Duluth Complex Anorthositic Series rocks. *from *from Miller Miller (1995); (1995);n.m. n.m. not not measured. measured. Errors Errors reported reported as two standard standard deviations, deviations, because no internal standard wasused. used. standardwas References Referencescited: cited: Anderson, Anderson, A.T., A.T., Jr., Jr., 1983, 1983,Oscillatory Oscillatoryzoning zoning of of plagoclase: plagoclase: Nomarski Nomarski interference interferencecontrast contrast microscopy microscopy of of etched etched polished polished sections: sections: American AmericanMineralogist, Mineralogist,v. v. 68, 68, p. p. 125-129. 125-129. Appleman, Appleman,D.E. D.E. and andEvans, Evans, H.T., H.T., Jr., Jr., 1973, 1973,Job Job 9214: 9214: indexing indexingand and least-squares least-squaresrefinement refinement of 67 pp. 20,67 pp. (NTIS (NTIS of powder powder diffraction diffraction data. data. U.S. U.S. Geological GeologicalSurvey, Survey, Computer Computer Contrib. Contrib. 20, Doc. Doc. PB2-16188) PB2-16188) Castro, A,,and and de dela laRosa, Rosa,J., J., 1994, 1994,Nomarksi Nomarksi study study of of zoned zoned plagioclases plagioclasesfrom from granitoids granitoidsof of Castro,A., the the Seville SevilleRange Range batholith, batholith, SW SW Spain. Spain. Petrogenetic Petrogenetic implications: European European Journal Journalof of Mineralogy, Mineralogy,v.v.6,6,p.p.647-656. 647-656. Garvey, Garvey,R.G., R.G., 1986, 1986,LSUCRIPC LSUCRIPCLeast Leastsquares squaresunit unitcell cellrefmement refinementwith with indexing indexingon onthe the personal personalcomputer. computer.Powder PowderDiffraction, Diffraction,v. v.I1no. no.1., I.,p.p.114. 114. Kroll, Kroll,H., H.,1983, 1983,Lattice Latticeparameters parameters and anddeterminative determinativemethods methods for for plagioclase plagioclaseand andternary ternary feldspars, ed., Reviews Reviews in in Mineralogy, Mineralogy,v.v.2, 2 ed., feldspars, in in Ribbe, P.H., P.H., ed., 2, 2nd ed., p. p. 101-119. 101-119. Miller,J.D., J.D., Jr., Jr.,1995, Duluth Complex Complex at at Duluth, Duluth, in in Miller, Miller, J.D. J.D. Jr., Jr., ed., ed., Field FieldTrip Trip Miller, 1995, The Duluth Guidebook Guidebookfor forthe theGeology Geologyand andOre OreDeposits Depositsof of the theMidcontinent MidcontinentRift Riftin in the the Lake Lake Superior SuperiorRegion. Region.Minnesota MinnesotaGeological GeologicalSurvey SurveyGuidebook GuidebookSeries, Series,no. no. 20, 20,p.p.123-169. 123-169. Miller,J.D., J.D., Jr., Jr., and andWeiblen, Weiblen, P.W., P.W., 1990, 1990,Anorthositic Anorthositic rocks rocks of of the the Duluth DuluthComplex: Complex: Miller, Examples Examplesof of rocks rocks formed formed from from plagioclase plagioclase crystal mush: Journal Journalof of Petrology, Petrology,v.v.31, 31,p.p. 295-339. 295-339. Paces,J.B., J.B., and andMiller, Miller,J.D., J.D., Jr., Jr., 1993, 1993,Precise PreciseU-Pb U-Pb ages agesof of Duluth DuluthComplex Complexand andrelated related Paces, maficintrusions, intrusions,northeastern northeasternMinnesota: Minnesota:Geochronological Geochronologicalinsights insightsto tophysical, physical, mafic petrogenetic,paleomagnetic paleomagneticand andtectono-magmatic tectono-magmaticprocesses processesassociated associatedwith withthe the1.1 1.1Ga Ga petrogenetic, Midcontinent Midcontinentrift rift system: system: Journal JournalofofGeophysical GeophysicalResearch, Research,v.v. 98, 98,p. p. 13,997-14,013. 13,997-14,013. Pearce, Pearce,T.H., T.H., 1994, 1994,Recent Recentwork workon onoscillatory oscillatoryzoning zoningin in plagioclase, plagioclase,in inParson, Parson,I., I.,eds., eds., Feldsparsand andTheft TheirReactions: Reactions:Dordrecht, Dordrecht,Kluwer, Kluwer,p.p.3313-349. Feldspars 13-349. Pearce,T.H., T.H., and andKolisnilc, Kolisnik, A.M., A.M., 1990, 1990,Observations Observationsof of plagioclase plagioclasezoning zoningusing using Pearce, interference EarthScience ScienceReviews, Reviews,v.v.29, 29,p.p.9-26. 9-26. interferenceimaging: imaging:Earth Grierguided guidedus usinincarrying carryingout outthe theplagioclase plagioclasestructural structuralanalyses. analyses.BSE BSE Acknowledgements:Dean DeanGrier Acknowledgements: gratefully NDEPSCoR EPSCoRthrough throughNSF NSFgrant grant#OSR-9452892. #OSR-9452892. gratefullyacknowledges acknowledgesfinancial financialsupport supportfrom fromND 5 �Wind or Water? Paleoenvironment Paleoenvironmentof the Proterozoic Proterozoic Hinckley Sandstone, Sandstone, Northeastern Minnesota Northeastern Beaster, K.F., Geology K.F., Kohn, Kohn,J.D., J.D.,and andHavholm, flavholm,K.G., K.G.,havholke@uwec.edu, havhoIkwuwcc.edu, Geology Department, University of Claire, Eau Claire, WI 54702-4004 o f Wisconsin-Eau Wisconsin-Eau Claire, The Proterozoic Hinckley Sandstone is a mineralogically mature, fine-grained quartz (Tryhorn & arenite representing late stage Keweenawan rift fill sedimentation. Previous work (Tryhom Ojakangas, 1972) interpreted the Hinckley Sandstone as a shallow-water lacustrine deposit. 1972) shallow-water Recent recognition of adhesion structures, formed by sand blown onto a damp surface, suggest be partially partially eolian eolian (wind-deposited). (wind-deposited). The purpose of this project was to that this formation may he reevaluate the environment(s) of deposition environmentfs) of deposition of of the the Hinckley Hinckley Sandstone. Sandstone. The study area is located in Pine County, MN, near the town town of Sandstone, where five sections along the Kettle River were measured and described in detail. Four major facies were identified: planar-bedded sandstone (PS), cross-stratified sandstone (CSS), trough crossstratified sandstone sandstone (TCS), and pebbly trough cross-stratified sandstone (PTS). The planarbedded facies comprises a complexly interbedded sequence of crinkly and mottled strata, preserved ripple forms, and packages of thin (2-6 mm.), planar, inversely graded laminae. Crinkly and mottled strata are interpreted as adhesion structures (Hunter, 1973, 1980). 1980). Ripples have low ripple indices (<10) ( 4 0 ) and steep, normally graded foresets, indicating a subaqueous origin (Hunter, 1977). Planar (Hunter, Planar laminae laminae are are identified identified as as climbing wind-ripple laminations (Hunter, 1977). Therefore, the planar-bedded facies represents an environment where where conditions conditions alternated from wet to damp to to dry. Fine nature of Fine grain grain size, large set size, and the compound nature large sets suggest a large-scale eolian dune dune origin origin for for the the cross-stratified cross-stratifiedsandstone sandstonefacies. facies. In addition, wind-ripple and adhesion lamination were identified in tangential dune apron toe-sets. Trough cross-strata cross-strata and pebbly trough cross-strata facies contain predominantly medium-grained sandstone; pebbles cm.are arecommon commonininthe thepebbly pebbly trough trough cross-stratified cross-stratified facies. facies. pebblesup uptoto44cm. Adhesion and wind-ripple laminae are absent in these relatively small (up to 2 m. wide and 20 cm. thick), simple trough cross-strata. cross-strata. Coarse Coarse grain grain size and nature of strata suggest a subaqueous subaqueous origin origin for for these these facies. facies. Exposures of the Hinckley Sandstone are incomplete and widely separated, limiting detailed correlation of sections. The m. for The thickest thickest exposure exposure measures measures 30 m., whereas a thickness of 150 m. this formation is reported from a well in the the area area (Morey, (Morey, 1977). 1977). However, using a regional regional structural dip of 50 (Tryhorn and Ojakangas, Ojakangas, 1972) the the measured measured sections sections stack stack to to give a 5' or less, (Tryhom sediment sequence sequence that alternates alternates from depositon in subaqueous to subaerial and back to subaqueous conditions several times. Small Small (mm.(mm.- to cm-scale) cm.-scale)extensional extensional faults faultsand andcm.cm.-to to dm.-scale fluid-escape structures are associated associated with with the the subaqueous subaqueousto tosubaerial subaerialtransition. transition. This vertical sequence sequence suggests suggests a rift setting setting with a shifting mosaic of eolian and fluvial, and possibly lacustrine, environments. lacustrmne, environments. Reference Reference cited: cited: by climbing climbing adhesion adhesionripples. ripples. Journal of Sedimentary Sedimentary Hunter, R.E., 1973, Pseudo-crosslamination formed by Petrology, v. v.43, p. 1125-1127. 43, p. 1125-1 127. R.E., 1977, Basic types types of of stratification stratificationininsmall smalleolian eoliandunes. dunes.Sedimentology, Sedimentology,v.v.24, p.361-387. Hunter, R.E., 24, p. 361-387. 6 �- I I I - Hunter, — an Hunter,R.E., R.E., 1980, 1980,Quasi-planar Quasi-planaradhesion adhesionstratification stratification an eolian eolian structure structure formed in wet sand. Journal Journal of of Sedimentary SedimentaryPetrology, Petrology, v. v. 50, 50, p. p. 263-266. 263-266. Morey, Morey, G.B., G.B., 1977, 1977,Revised Revised Keweenawan Keweenawan subsurface subsurface stratigraphy, southeastern Minnesota. Minnesota Minnesota Geological 2lpp. Geological Survey SurveyReport Report of of Investigations Investigations 16, 16,27pp. Tryhorn, Tryhorn, A.D. A.D. and and Ojakangas, Ojakangas, R.W., R.W., 1972, 1972,Sedimentation Sedimentation and petrology of the Upper Precambrian Hinckley Hinckley Sandstone Sandstoneof of east-central east-central Minnesota. In, In,P.K. P.K. Sims Simsand andG.B. G.B. Morey, Morey,eds., eds., Geology Geologyof of Minnesota: Minnesota: AACentennial CentennialVolume, Volume,Minneapolis, Minneapolis,Minnesota MinnesotaGeological GeologicalSurvey, Survey,p. p. 431-435. 431-435. 7 �Some factors factors that control the distribution of mercury in the near-surface environment National Park, Park, Michigan-earth, Michigan—earth, wind, and fire environment of Isle Royale National W.F. W.F. Cannon, Cannon,U.S. U.S. Geological GeologicalSurvey, Survey,Reston, Reston,VA VA L.G. U.S.Geological GeologicalSurvey, Survey,St. St.Paul, Paul,MN MN L.G. Woodruff, Woodruff,U.S. The The concentration concentrationof of mercury mercury in in soils soils on on Isle Isle Royale Royale is is highly variable variable in in response response to to many understood. Our Our studIes studies during during the many factors factors whose affects and interplay are poorly understood. past them. Interest past three three years years have helped to clarify some of them. Interest in in mercury mercury distribution distribution on on the island was heightened in the mid 1990's when potentially dangerous mercury levels the island was heightened in the 1990's when potentially dangerous mercury levels were were discovered discovered in in game game fish fish from from six six of of the island's island'sinland inlandlakes. lakes.Because Becausethese thesesix six lakes were clustered in the north central part of the island, whereas lakes on other parts lakes were clustered in of the whereas lakes on other parts of of the the island island showed showed lower lower mercury mercury levels levels in in game game fish, fish, we initially initially suspected suspected that that previously previously unrecognized unrecognized bedrock bedrock mercury concentrations concentrationswithin within the the watersheds watersheds could could be be aa cause. cause. Small Smallnative nativecopper copperdeposits depositswith withsignificant significantmercury mercury content content are are distributed distributed throughout throughout the the island. island. To Totest testthis thishypothesis hypothesiswe we sampled sampledsoils soilsaround around the the Minong Minong Copper 19&century century mining mining operations, operations, and and within within the the watershed watershed CopperMine, Mine,the thelargest largestofofthe the19th of of Sargent SargentLake, Lake, one one of of the the mercury mercury impacted impacted lakes. lakes. Results Results presented presented last last year year (Cannon (Cannon and and Woodruff, Woodruff, 1999) 1999)showed showed that that aa bedrock bedrock source source for for mercury mercury to to the the impacted impactedlakes lakesisis unlikely. The TheMinong Minongcopper copperdeposit depositproduces produces aa very very pronounced pronounced copper copper anomaly anomaly in in soils, Lake watershed. watershed. We soils, but a comparable comparable anomaly anomaly is absent within the Sargent Lake We did did find, find, however, however, that that a-horizon a-horizon soils soilsin in the the Sargent Sargent Lake Lake watershed watershed contain contain very very high high mercury mercury concentrations. concentrations. Because Because aa bedrock bedrock source source is is unlikely unlikely we we concluded concludedthat that mercury mercury concentrations concentrationswere were largely largelyfrom fromairborne airbornedeposition. deposition. Additional Additional sampling samplingand and analyses analyses have have been been conducted conducted in in the the past past year year to to address address the the question ~uestionof of why whv mercury mercurv concentrations concentrationsare are so so variable variable in in soils soils ifif the the source sourceof of mercury mercurv is atmospheric atmospheric pollution. pollution. There There isis aa very very high high correlation correlationbetween between organic organiccarbon carbonin in soils soils and total mercury content (R=0.9). Thus, it appears that factors that control carbon and total mercury content Thus, it appears that factors that control carbon sequestration sequestrationin in soils soils also also control mercury sequestration. One One factor factorthat that could could influence influence both bothisis the the history history of of forest forest fires. fires. During Duringaafire firemuch muchof ofthe thecarbon carbonon onthe theforest forestfloor floorand and in in surface surface soil soil layers layers may may be be burned, burned, thus thus liberating liberating adsorbed adsorbed mercury mercury as as aa gas gas or or fine fine particles that would be transported out of the area. After a fire, the gradual accumulation particles that would be transported After a fire, the gradual accumulation of of organic organic carbon carbon and and mercury mercury can can require require decades decades or or longer longer to to reestablish reestablish pre-fire pre-fire concentrations. A large portion of Isle Royale burned in 1936, including part concentrations. A large portion of Isle Royale burned in 1936, including partof ofour ourstudy study area, burned in in historic historic times. times. Soils area, whereas the remainder of our study area has not burned Soils within within the the 1936 1936burn burn area area invariably invariably have low carbon and mercury content. All Allsamples samples are are below the mean concentration concentration for the island. Some Somesoils soilsoutside outside of of the the bum burn have have comparably comparably low low values values but most are significantly higher. Further Further sampling samplingis is being being conducted fire to to conducted to to seek seek additional additionalconfirmation confirmationof of the the importance importance of of this this 64-year-old 64-year-old fire current currentmercury mercurydistribution. distribution. is Finally, Finally,the thedistribution distributionof ofmercury mercuryin ingeological geologicalmaterials materialsas asaa possible possiblefactor factorinin controlling controllinemercury mercurv accumulation accumulation in in the aquatic aauatic food web needs to be addressed. High Hi& mercury mercuryconcentrations concentrationsin ingame gamefish fishare arethe theend endresult result of ofsuccessive successiveaccumulations accumulations through various steps in the food web. Mercury concentrations inngame gamefish fishtissue tissuemay maybe be - - .. 8 �as lake water. water. Furthermore, as much as one one million times higher than in the ambient lake Furthermore, mercury mercury enters enters the food food web web as as an an organic organic compound, compound, mostly mostly dimethyl dimethyl mercury, mercury, rather rather than the more common inorganic forms. As a result, may researchers discount the than As a result, may researchers discount the concentrations concentrationsof of mercury mercury in in the the terrestrial terrestrial environment environment as as aa factor factor controlling controllingmercury mercuryin in fish. Rather, the efficiency of methylation processes within a lake and its watershed and fish. Rather. the efficiency of methvlation orocesses within a lake and its watershed and complexities complexitiesin in the the food food web web are are commonly commonly cited cited as as causes causes for for widely widely variable variablemercury mercury content Ourresults resultsnow now show showthat that there there are aremuch much higher higher content of of fish fish between nearby lakes. Our mercury mercury concentrations concentrationsin in soils soilsin in the the watersheds watershedsof of Sargent SargentLake Lake (high (highmercury mercury in in fish) fish) than than in in soils soils around around nearby Lake Richie (low mercury in fish). Although Althoughthese theseresults results address address only only two two lakes, lakes, we we suggest suggestthat that itit would would be be premature prematureto to discount discountvariations variationsin in mercury mercury in in watershed watershed soils soilsas as aa factor factorin in determining determiningthe the intensity intensityof of mercury mercury accumulation accumulationin in related related aquatic aquaticecosystems. ecosystems. . < 4. SARGENT LAKE4J MINONG MINE .:•—. LAKE RICHIE 6 6 0 l2MiIes East half of soil thickness) thickness)in inaaof Isle Isle Royale. Royale. Relative Relative mass mass of of mercury mercury (concentration (concentrationxx soil horizon shown fire. Native Native shown by black squares. White White area areawas was burned burned in in 1936 1936forest forest fire. copper copper mines mines and and prospects prospects shown shown by pick and and hammer hammer symbol. symbol. '. a 7 3 Reference Reference Cannon, W.F., W.F., and and Woodruff, Woodruff, L.G., 1999, 1999,Mercury Mercury distribution distribution in in bedrock, bedrock, native native copper copper Cannon, ore and soils—Isle soils-Isle Royale National Park, Michigan (abs): Institute on Lake Superior Superior Geology Proceedings, 45, p.9-10. p.9-10. Geology Proceedings, v. v. 45, 9 �A SEQUENCE OF FOLDING AND DEXTRAL TRANSPRESSION IN THE SEINE RIVER CONGLOMERATES. Peter J., J., Department Department of of Geology Geology and and Geophysics, Geophysics, University University of of CZECK, Dyanna M. and HUDLESTON, Peter Minnesota, 310 3 10 Pillsbury Drive SE, Minneapolis MN, 55455, 55455, czecO019@tc.umn.edu czec0019@tc.umn.edu GEOLOGICAL INTRODUCTION The Superior Province is subprovinces that that are are is comprised of of approximately approximately east east -- west trending subprovinces defined by lithological contrasts, metamorphic grade, and structural boundaries (Card and Ciesielski, 1986). A A popular popular tectonic tectonic model for for this this province province is is the the successive successive accretion accretion of of island island arcs arcs and and their their associated sediments sediments(Floffluan, (Hoffman, 1989). 1989). metavolcanic Wabigoon Wabigoon and the This study focuses on the boundary between the metavolcanic metasedimentary Quetico subprovinces near Mine Centre, Ontario. The Quetico contains mostly amphibolite facies metasediments, and the Wabigoon contains greenschist facies metavolcanics. Distinctive rocks found along this boundary are the Seine River Metasedimentary Metasedimentary Group including the conglomerates. From River conglomerates polymictic Seine River conglomerates. From stratigraphic evidence, the Seine River deposition of of the the volcanic volcanic sequences sequences(Poulsen (Poulsenetetal., at., 1980). 1980). Preliminary formed late following the deposition attempts at absolute absolute dating dating have have confirmed confirmed this this (Davis (Daviset et al., al., 1989). 1989). Previous structural work along this boundary described a dominant subvertical foliation (Poulsen, 1986; Tabor Tabor and and Hudleston, Hudleston, 1991). 1991). These features are interpreted interpreted to to transecting large folds (Poulsen, have formed during dextral transpression. STRUCTURAL INTRODUCTION The term "transpression" was first introduced by Harland (1971) to describe motion that is obliquely convergent, or motion motion partitioned partitioned into into both both convergent convergentand andstrike-slip. strike-slip. In In Harland's original obliquely convergent, described the development development of of folds folds and and strike-slip strike-slip structures structuresdue duetotooblique obliqueconvergence. convergence. A A paper, he described Marchini (1984). This specialized case of transpression was introduced by Sanderson and Marchini This idealized idealized definition of transpression has been used to describe homogeneous deformation consisting of orthogonal simple shear and pure shear components with constant volume and confined deformation deformation boundaries, possibly corresponding to the strain in deep ductile shear zones that accommodate oblique convergence. Quetico boundary seems to be related to this more specific The dominant foliation along the Wabigoon - Quetico type of transpression transpression based based on on the flattening flattening fabrics fabrics and asymmetric features indicating simple simple shear shear in in subhorizontal plane. the subhorizontal One of the questions addressed by this study is the relationship between the folds and the dominant foliation. Clearly, Clearly,itithas hasbeen beendemonstrated demonstratedthat that folds foldscan canform formin intranspression transpression Flarland Harland transpression fabric, or are they an (1971). Are Are the the folds folds at at this this boundary boundary consistent consistent with the rest of the transpression earlier structural feature? FOLIATION/ BEDDING INTERSECTIONS The Seine Group has well defined bedding indicated by fine grained layers interbedded with the recognized pebble conglomerates. conglomerates. In In this this analysis, analysis, the the major major fold fold in in the Seine River conglomerates was recognized on the basis of of structural structural facing facing between between bedding bedding and and the the dominant dominant foliation foliation(Shackleton's (Shackleton'srule rule—- see Borradaile (1976)). This Thisfold foldisisconsistent consistent with with the the observed observed 'way "wayup" up" indicators indicators in in the the conglomerates conglomerates based on graded bedding. bedding. 10 �If this fold were to have formed as a result of the transpression, transpression, the foliation! foliation1 bedding throughout the the field field area. area. In fact, the plunge of the intersection varies intersections should be consistent throughout throughout the field area. The The intersection intersection angle angle is is generally small because both foliation and bedding throughout are steep; steep; however, however, locally the the angle angle is is quite quite large large nearing nearing 75" 75°atatthe thehinge. hinge. This suggests a more history, and that the folding occurred prior to the major transpressive event. complex history, TECTONIC IMPLICATIONS As described elsewhere in the Superior province, the sequence of initial folding followed by homogeneous transpression (and possibly later stage amplification of the strike- slip slip shear shear component component reasonable for for the the WabigoonWabigoon-Quetico Queticoboundary. boundary. It remains an along discrete shear zones) seems reasonable interesting question whether the folds and the homogeneous transpression were two entirely abrupt, separate events or rather an evolution of structural styles during different stages of the same same oblique oblique collisional event. The fact that the initial folding folding is seen in the Seine Group has important implications for for the the relative timing between this change in in structural structural style style and and Seine Seinedeposition. deposition. Some researchers have pull-apart basins formed as suggested that the Seine Group could have been syntectonically deposited in pull-apart as (Poulsen, 1986). The a result of wrenching (Poulsen, The early folding folding of the Seine seems to indicate that it was deposited earlier in the deformation sequence, prior prior to to at at least least some some of ofthe thefolding. folding. Additionally, the overall geometry of the interconnected faults faults seems seems to indicate that during dextral wrenching, the the Seine Seine Group's "basin" "basin" would would have have been been in in aa compressive compressive rather rather than than an an extensional extensional regime regime required required of ofaapullpullbasin. This apart basin. Thissuggests suggests that that aa different different sedimentation/ sedimentation,tectonic model for the Seine Group is needed. J., 1976. the Palaeozoic Palaeozoic rocks rocks of of the the Malaguide Malaguide Complex Complex Borradaile, G. J., 1976. "Structural "Structural facing" (Shackleton's rule) and the nederlandse akademie akademie van van wetenschappen wetenschappen 79B, 798, near Velez Rubis, SE Spain. Proceedings, Koninklijke nederlandse 330330336. 336. A., 1986. the Superior Province Province of of the the Canadian Canadian Shield. Shield. Geoscience Geoscience Card, K. D., Ciesielski, A,, 1986. DNAG Subdivisions of the Canada 13, 5-13. 13,5-13. Davis, D. W., Poulsen, Poulsen, K. H., Kamo, Kamo, S. S. L., L., 1989. 1989.New New insights insightsinto into Archean Archean crustal crustaldevelopment developmentfrom from geochronology 97, 379-398. geochronology in the Rainy Lake area, area. Superior Superior Province, Canada. Journal of Geology 97,379-398. 8., 1971. 27-42. Harland, W. B., 1971.Tectonic Tectonictranspression transpressionin in Caledonian Caledonian Spitsbergen. Spitsbergen. Geological Magazine 108, 108,27-42. Hoffman, P. F., 1989. America. In: In: Bally, Bally, A. A. W., W., Palmer, A. A. R R. ( Hoflinan, 1989. Precambrian geology geology and tectonic history of North America. Eds.), The geology geology of of North America; an overview. The geology of North America A, pp. 447-512. Poulsen, K. Fl., example of of an an Archean Archean Subprovince Subprovinceboundary boundary in inNorthwestern Northwestern H., 1986. 1986. Rainy Lake Lake Wrench Zone: An example Ontario. (Eds.), Tectonic evolution of greenstone greenstone belts belts Technical Report Ontario. In: de Wit, M. J., Ashwal, L. D. (Eds.), 86-10, pp. 177-179. 177-179. Poulsen, K. H., Borradaile, Archean succession succession at at Ramy Rainy Lake, Lake, Borradaile, G. J., Kehlenbeck, M. M., 1980. An inverted Archean Ontario. Canadian Journal of Earth Sciences 17, 17,1358-1369. 1358-1369. D., 1984. Transpression. Transpression. Journal Journal of of Structural Structural Geology Geology 6,449-458. 6,449-458. Sanderson, D. J., Marchini, W. R. D., Tabor, J. R., Hudleston, P. J., 1991. Deformation at an Archean subprovince boundary, northern Minnesota. 1991. Tabor, Hudleston, Canadian Journal of E Earth Sciences 28,292-307. arth 28,292-307. 11 �A A Hf Hf isotopic isotopic study study on zircons from from the the western western Superior Superiorprovince province D.W. D.W.Davis, Davis,Y. Y.Amelin, Amelin,Earth EarthScience ScienceDept., Dept.,Royal RoyalOntario OntarioMuseum, Museum,100 100 Queen's Queen's Park, dond(drom.on.ca, G.M. G.M. Nowell Nowelland andR.R. R.R. Parrish Parrish Park. Toronto, Toronto. ON, ON. M5S 2C6 dond@,rom.on.ca. NERC NERC Isotope Isotope Geoscience GeoscienceLaboratory, Laboratory,Kingsley Kingsley Dunham Dunham Centre, Centre, Keyworth, Keyworth, Nottingham, Nottingham, NG12 NG12 5GG 5GGUK UK U-Pb U-Pb dating datingof of zircon zirconhas hasprovided provided some someof of the the most most important importantconstraints constraintson on geological geological interpretations interpretationsininthe theSuperior Superiorprovince. province.Zircon Zirconalso alsocontains containsHf, Hf,whose whose176Hf "'Hf isotope isotopecan can be beused used to toinfer inferolder oldercrustal crustal provenance provenance of of the magma from which it crystallized. crystallized. Early Hf studies by Corth and Stott (1993, 1996) in the Uchi subprovince show a distribution studies by Corfu and Stott (1993, 1996) in the distribution of EHf EHf values valuesthat thatrange rangebetween betweendepleted depletedmantle mantleand and aa3.0 3.0Ga Gacrustal crustalgrowth growth curve, curve, reflecting reflecting contamination contaminationfrom fromthe theNorth NorthCaribou Caribouterrane terraneand andsupporting supportingthe themodel modelof ofan anAndean-type Andean-type tectonic tectonicsetting. setting.These Thesestudies studiesused usedthermal thermalionization ionizationmass massspectrometry, spectrometry,which whichisis laborious laboriousand andrequires requireslarge largequantities quantitiesof ofzircon. zircon.The Therecent recentdevelopment developmentof ofmulti-collector multi-collector inductively inductivelycoupled coupledmass massspectrometry spectrometrynow nowpermits permitsprecise precisemeasurement measurementof ofHf Hfisotopic isotopic analyses analyseson onsingle singlezircon zircongrains grainsas assmall smallas as22micrograms microgramswith withanalysis analysistimes timeson onthe the order order of 10 minutes per sample. of 10 minutes per sample. Using Usingthe thePlasmaS4 Plasma54instrument instrumentatatthe the NERC NERC lab, lab,Hf Hf isotopes isotopeswere weremeasured measured on on dated datedzircons zirconsfrom from62 62separate separaterock rockunits unitsin inthe thewestern westernSuperior Superiorregion regionplus plus25 25detrital detrital zircon zircongrains grainsfrom fromthe theca. ca.2700 2700Ga GaQuetico Queticometasediments metasedimentsand andpre-2800 pre-2800Ma Maquartz quartz arenites. arenites.The Themass massspectrometer spectrometeranalyses analyseswere weredone doneover overaafour fourday dayperiod. period.This Thisexpands expands the available Hf database in the transect area by a factor of four. the available Hf database in the transect area by a factor of four. Most Mostdata datafrom fromthe theSW SWWabigoon Wabigoonsubprovince subprovincecluster clustertightly tightlyaround aroundaadepleted depleted mantle value of +6S. +6.5. This confirms that assemblages south of the Wiimipeg mantleEHf Enfvalue Winnipeg River River subprovince subprovincewere weremagmatically magmaticallyemplaced emplacedininan anoceanic oceanicenvironment. environment.Analyzed Analyzedzircons zircons from fromthe theSturgeon-Savant Sturgeon-Savantarea areashow showaatrend trendof ofincreasing increasingcontamination contaminationby byolder oldercrust crust with younger age (decreasing Eflf down to +2). with younger age (decreasing Ein-down to +2). Younger Youngerplutons plutonsand andvolcanics volcanicsfrom fromthe thecentral centralWabigoon Wabigoonsubprovince subprovince(2693-2750 (2693-2750 Ma) mostly scatter around values of +4 ± 1, showing the possibility of slight Ma) mostly scatter around values of +4 1, showing the possibility of slight contamination contaminationby byolder oldercrust. crust.Zircons Zirconsfrom fromthe theolder older3000 3000Ma Maold oldrocks rocksininthe theLumby Lumby Lake Lakebelt beltcluster clustertightly tightlyaround aroundaadepleted depletedmantle mantlevalue value(at (at3.0 3.0Ga) Ga)ofof+5.5. +5.5.Zircons Zirconsfrom from ca. ca.2.9 2.9Ga Gaplume-derived plume-derivedrocks rocksgive giveslightly slightlymore moreenriched enrichedvalues valuesdown downtoto+4. +4.The Theresults results from fromLumby LumbyLake Lakeoverlap overlapwith withthose thosefrom fromsimilar similaraged agedrocks rocksininthe theNorth NorthCaribou CaribouLake Lake area of the Sachigo subprovince, supporting the suggestion that the Lumby Lake and area of the Sachigo subprovince, supporting the suggestion that the Lumby Lake andNorth North Caribou Caribouterranes terranesare arecorrelative. correlative. The TheHf Hfdata datafield fieldfrom fromthe theWabigoon Wabigoonand andSachigo Sachigosubprovinces subprovincesoverlaps overlapsclosely closely with withthat thatofofCorfu Corfuand andStott Stott(1996) (1996)from fromthe theUchi Uchisubprovince. subprovince.InIncontrast contrastzircons zirconsfrom fromthe the Winnipeg WinnipegRiver Riversubprovince subprovinceare arenoticably noticablymore moreenriched, enriched,with withEHf EHfvalues valuesof ofabout about00toto -2 over an age range of 2721 Ma to 3225 Ma. An EHf value of—2 value found on 3.2 Ga Ga -2 over an age range of 2721 Ma to 3225 Ma. An Eufvalue of -2 value found on3.2 zircons zirconsfrom fromthe theCedar CedarLake Lakegneiss gneissimplies impliesaaca. ca.3.5 3.5Ga Gacrustal crustalprotolith, protolith,ininagreement agreement with withresults resultsofofNd Ndwhole wholerock rockisotopes isotopes(Henry (Henryetetal. al.1997). 1997). AAsingle singleanalysis analysisfrom fromthe thewidespread widespread2722 2722Ma Mavolcanics volcanicsininthe theShebandowan Shebandowanbelt belt shows showsaadepleted depletedsignature, signature,asasdoes doesaa2726 2726Ma Mavolcanic volcanicfrom fromthe theMelchett MelchettLake Lakebelt, belt,ininthe the middle middleofofthe theEnglish EnglishRiver Riversubprovince. subprovince.However, However,2723 2723Ma Mavolcanic volcaniczircons zirconsfrom fromthe the Separation SeparationLake Lakegreenstone greenstonebelt, belt,which whichmay mayunderlie underlieEnglish EnglishRiver Rivermetasediments, metasediments,show showaa * 12 �more enriched enriched value value of of -2, -2, suggesting suggesting that that itit is is contaminated contaminatedby by much much older olderWinnipeg Winnipeg River-type River-type crust. crust. Results Results on on detrital detrital zircons zirconsfrom from quartz quartz arenites arenites in in the the North North Caribou Caribouterrane terranegenerally generally overlap An analysis analysis from from 3250 3250 Ma Ma old old zircon zirconin inthe the overlap the the data data field field from from rocks rocks in in this this area. area. An Jutten Jutten quartz quartz arenite arenitein in the the northern northern Wabigoon Wabigoon subprovince subprovinceshows shows still still older oldercontamination contamination (E1 ( h fof of 0), 0), suggesting suggestingthat that 3.0 3.0 to to 3.3 3.3 Ga Ga detrital detrital zircons zircons in this unit were derived derived from from the adjacent adjacent Winnipeg Winnipeg River River subprovince. subprovince.Ca. Ca. 3.2 3.2 Ga Ga zircons zircons from from the the Quetico Quetico metasediments metasediments also show enriched values down to —3, while the youngest zircons at ea. 2.7 also show enriched values down to -3, while the youngest zircons at ca. 2.7 Ga show variable variableenrichments enrichmentsfrom from+5 +5 to to +0, +0, again againsuggesting suggestingaa source sourcepartially partiallyin inthe theWinnipeg Winnipeg River subprovince. River subprovince. The values at at ca. ca. 2.7 2.7 Ga Ga and and 3.0 Ga provides The general general coherence coherenceof ofthe thehighest highestEHf Enfvalues reasonable reasonable constraints constraintson onthe theevolution evolutionof ofthe thedepleted depletedmantle mantlereservoir reservoirduring duringthe thelate late Archean. These results agree with the linear growth trend defined by other Hf Archean. These results agree with the linear growth trend defined other Hf measurements measurements from from younger younger rocks rocks and and from from early early Archean Archean rocks rocks in in Greenland Greenland (Vervoort (Vervoort and Blichert-Toft 1999). They give evidence for a major depletion of the mantle or and Blichert-Toft 1999). They give evidence for a major depletion of the mantle atator before 4.0Ga. Ga.IfIfcontinental continentalcrust crustwas wasthe thecomplimentary complimentaryenriched enrichedreservoir, reservoir,this thisimplies implies before 4.0 that that such suchcrust crustwas wasof ofan anextent extentcomparable comparableto to the thepresent present during duringthe theearly earlyArchean. Archean. Otherwise, Otherwise, the the enriched enriched reservoir reservoir may may have have been been oceanic oceanic crust crust that that was was subducted subductedand and stored Archean. stored in in the the deep deep mantle mantle until until the the end end of of the the Archean. Continuing Hf isotopic studies on precisely Continuing Hf isotopic studies on precisely dated dated zircons zirconspromise promiseto to be beaapowerifil powerful tool tool for forresolving resolvinglocal localand andglobal globalproblems problemsininEarth Earthhistory. history. REFERENCES REFERENCES Corfu, Corfu, F. F. and and Stott, Stott,G. G. 1996. 1996. Hf Hf isotopic isotopic composition composition and and age age constraints on the evolution evolution of of the the Archean Archean central central Uchi subprovince, subprovince, Ontario, Canada. Precamb. Res. 78: 535363. 63. Corfli, Corfu,F. F. and and Stott, Stott,G. G.1993. 1993.Age Ageand andpetrogenesis petrogenesisof oftwo twolate lateArchean Archeanmagmatic magmaticsuites, suites, northwestern northwesternSuperior Superiorprovince, province,Canada: Canada:Zircon ZirconU-Pb U-Pb and andLu-Hf Lu-Hf isotopic isotopicrelations. relations. Jour. Petrol. 34: 8 17-838. Jour. Petrol. 34: 817-838. Henry, Henry,P., P., Stevensen, Stevensen,R., R., Larbi, Larbi,Y., Y.,and andGariepy, Gariepy,C. C.1997. 1997.Use Useof ofNd Ndisotopes isotopestotoquantify quantify 700 in the 700 Ma Maof ofcrustal crustalgrowth growthfrom from3.4 3.4to to2.7 2.7Ga Gain thewestern westernSuperior Superiorprovince province (Ontario, (Ontario,Canada). Canada).Western WesternSuperior SuperiorTransect TransectWorkshop WorkshopReport Report#63: #63:27-36. 27-36. Vervoort, Vervoort,J.D. J.D. and andBlichert-Toft, Blichert-Toft,J.J.1999. 1999.Evolution Evolutionof ofthe thedepleted depletedmantle: mantle:Hf Hfisotope isotope evidence from juvenile rocks through time. Geochim. Cosmochim. Acta evidence from juvenile rocks through time. Geochim. Cosmochim. Acta63: 63:533533556. 556. 13 �MYSTERY FAULTS FAULTSOF OFTHE THE CASCADE RIVER, RIVER, NORTH NORTH SHORE, MYSTERY SHORE, OR, OR,WHAT WHATIS IS THIS THIS GRANITE DOING HERE? HERE? GREEN, GREEN,John JohnC., C., Department DepartmentofofGeological GeologicalSciences, Sciences, University University of Minnesota Duluth, Duluth, MN 55812, jgreen@d.umn.edu jpreen@d.umn.edu Duluth, MN 55812, The The Cascade Cascade River in Cook County, MN, exposes exposes a homoclinal section section about about 13 13km km long longacross across normal-polarity rocks rocks of of the the North North Shore Volcanic Volcanic Group. Group. With normal-polarity With an an average dip of about 12 degrees, this this amounts amounts to a thickness of about 2.4 km. In degrees, Inits itslowest lowest mile mile and and aa major major tributary, tributary, it cuts across several faults faults that that involve the the great, great, cuesta-forming cuesta-forming Terrace Terrace Point Point basalt flow and the thick, underlying Good Good Harbor Harbor Bay Bay sandstone. sandstone. red sandstone and the At the top of of the the cascades, cascades, the conformable contact between the big red also visible visiblefour four miles miles to to the the east at the big Good overlying flood basalt flow, also GoodHarbor HarborBay Bayhighway highway fault. As the the river river starts starts cut, is dropped down to to the the north northaafew fewfeet feetalong alongaa high-angle, hii-angle, east-west fault. cascades,the the top top of of the sandstone can be seen under the to enter enter the the gorge and plunge down the cascades, 100m m into intothe thegorge, gorge,the thebasalt basaltisis interrupted interruptedby byaaremarkable remarkablebreccia brecciaof ofpink, pink, basalt. But Butless less than than 100 apparent fault contact medium-grained granite that occurs in apparent contact with the the volcanic volcanic rocks. rocks. Locally, Locally, fragments of of basalt basalt and and perhaps perhaps sandstone are caught up up in the breccia, but but most of it is granite. On uncontaminated granite. Onthe thedownstream downstreamside, side,abundant abundantjoints joints in in the the adjacent adjacent basalt imply aa upstream, but but itit isis covered. covered. On steep fault contact dipping upstream, On the the upstream upstream side, side, the bounding bounding fault apparently dips much apparently much more more gently gently downstream, downstream,implying implying aa wedge of of granite granite emplaced emplaced mechanically mechanically flows. A fault contact a kilometer or or so to to the northeast between the sandstone into the lava lava. flows. sandstone and aa rhyolite may be related to this event. event. There are two conceivable sources for this granite, granite, which which must must be be far far from from its original original site siteof of There crystallization. related to to the roof zone zone of crystallization. If itit is Keweenawan, and related of the the Duluth Duluth Complex Complexthat thatisis Eagle Mountain, Mountain, ititwould would have havemoved movedupward upward at at least least2.4 2.4km. km. Otherwise exposed up-dip (inland) at Eagle it could be part of the the Archean Archean basement, basement, in in which case it would have come up much farther, perhaps 10 km. ItItisismedium-grained, medium-grained,hypidiomorphic hypidiomorphicwith with minor minor micrographic micrographic patches patches and and its its ferromagnesian silicate is is Fe-rich biotite, which is rare in Keweenawan granites. Petrographically Petrographically itit rocks of of is not a good match for for either either the the Eagle Eagle Mountain Mountain granophyre granophyre or or typical typical Archean granitic rocks the region. Its from, but but not not how it Itsabundant abundantzircons zircons should should solve solve the problem of where it came from, got to to its its present present position. position. x---- ----- Geologic sketch map from from Green, Green, 1996, Geolom Diswlav: Geology Geology Geology on Display: Minnesota's North and Scenery of Minnesota's Shore State Parks, MN Dept. of of Nat. Nat. Resources, Resources. St. St. Paul Paul . .. . ............... ............... .... - Fault 880 Sandstone I 14 �PETROGENESIS OF RiVER REGION, PETROGENESIS OF GRANITIC GRANITIC ROCKS ROCKS OF OF THE THE DUNKA RIVER REGION, EASTERN EASTERNMESAI3I MESABI RANGE, MINNESOTA MINNESOTA HARRIS, Emily HARRIS, Emily C. C. A., A,, Macalester Macalester College, College, St. St. Paul, Paul, MN 55105, 55105, eharris@macalester.edu; eharris@macalester.edu; Wirth, Wirth, Karl Karl R., R., Geology Geology Department, Department, Macalester Macalester College, College, St. St. Paul, Paul, MN MN 55105, 55105, wirth@macalester.edu throughout the the Midcontinent Midcontinent Rift (MCR) Middle Proterozoic felsic igneous rocks are exposed throughout and the eastern Mesabi Range of northern northern Minnesota. Minnesota. Many of these are considered to be Keweenawan (1,100 Ma) in age. However, However,recent recent studies studies suggest suggest that some some early Middle Proterozoic felsic magmatism may have have occurred occuned in the region region as as well well (Phillips (Phillipset. et.al., al.,this thisvolume). volume). To better understand understand the history of felsic magmatism in northern Minnesota, samples from the Dunka River Region, which is situated along the base of the Duluth Complex, have been collected and studied. Felsic Felsicrocks rocksthat thatintrude intrudegabbros gabbrosof of the the Dunka Dunka River River Region Region have have coarse coarse graphic graphic textures, textures, chemically distinct complexes in the Midcontinent Midcontinent Rift. and are chemically distinct from granophyre complexes Granitic rocks were were collected collected from from along along the the eastern eastern Mesabi Mesabi Range Range between between Babbitt Babbitt and and Aurora, Minnesota. Granite with coarse graphic texture was collected from stockpiles within the Granite with coarse graphic within the Biwabik Iron Iron Formation Fonnation and gabbro mining operations operations along the contact between metamorphosed Biwabik gabbro withingabbro gabbroand andiron ironformation formation(Strandlie, (Strandlie,pers. pers. of the MCR. These Thesegranites granitesoccur occuras assmall smalldikes dikeswithin conimunication). They communication). Theyare arecommonly commonly pegmatitie, pegmatitic, and are composed of potassium feldspar or sodic %), and biotite biotite (5-10 (5-10 %). %). Feldspars Feldspars are variably altered altered to plagioclase (40-50 %), quartz (35-45 %), clay minerals and biotite is altered to chlorite. These Thesegraphic graphic granites granites are are mineralogically mineralogically and and texturally comparable comparable to some some felsic felsic granophyres of the Midcontinent Rift (Kennedy (Kennedy et al., this vol.). Other vol.). Othergranitic graniticrocks rocks were were collected collected from ____________________________________ IS 15 nearby outcrops of the eastern eastern margin of of the the Archean Aurora Sill Archean Giants Giants Range Range batholith batholith for for comparison. comparison. MCi felt The Archean granites are finefine- to to mediummediumgnnophyres 10 s 10 grained, and consist consist of of plagioclase plagioclase (20-40%), (20-40%), amphibole amphibole (<15%), (<15%), quartz quartz (10-40%), (10-40%), potassium potassium S. C feldspar feldspar (5-20%), (5-20%), biotite biotite (5-10%), (5-lo%),and andFe-Ti Fe-Tioxox- % ides ides (<5%), (<5%), and and commonly commonlyexhibit exhibitstrained strainedquartz quartz C+ Giants Range bathofith and weakly foliated textures. These These granites granites are are 9a MCRmalIc texturally texturally and and compositionally compositionallysimilar similarto to grangrangnnophyrs gra=ophy= ites of the western Giants Range batholith (e.g., Boerboom and Zartman, 1993). 1993). 60 70 80 o 40~ " " " " 50 SO" " " " " (50 ' 70 80 The graphic graphic granite granite dikes dikes from from the the Dunka Dunka SiO.* drt. %). o) St02(wt. . characterized by a greater Pit are characterized greater silica silica content Figure Figure 1. Plot of Na20+K20 Na 20+1(20 (total (totalalkalis) versus (Si02=70.8-78.7 wt. (Si02=70.8-78.7 wt. %) %) than than isis observed observed in in MCR MCR SiO2 comparing Dunka granites (open Dunks graphic granites (open gi02 wt. %; Kennedy et al., this this ggranophyres r a n o ~ h ~ r(66-76 es circles) with rocks from the Giants Range Giants Ranee vol.) and and the Aurora Aurora Sill Sfflsyenites syenites (54.6-60.7 (54.6-60.7 wt.%; W.%; batholith (Boerboom and Zartman,1993), Zartman,l993), the the Potassium,sodium, sodium,and and Phillips et al., this vol.). Potassium, Aurora Silt Sill (Phillips et at., al., this vol.), and granogranocalcium concentrations of the granite phyre complexes of the MCR (Kennedy granite dikes dikes (Kennedy et et al., al., (K20=2.98-5.16 wt. wt.%; %; Na2O=3.20-6.48 Na20=3.20-6.48wt, wt, %; %; this vol.). this vol.). (1(20=2.98-5.16 * 1 - - - I - - ~~~ ~ 15 �CaO=O.28-1 .09wt. wt.%) %)are aresimilar similar to to those those of of Ca0=0.28-1.09 the MCR granophyres and the Aurora Sill (Figgranophyres ure 1). 1). However, However,most mostof ofthe thegraphic graphic granites granites have high high A1203 Al203 concentrations concentrations and are are have peraluminous, similar to those of the Aurora Sill; MCR granophyres are peraluminous to metaluminous. The metaluminous. Thegraphic graphicgranites granites also have Ti02than than rocks rocks of of the the MCR MCR and and the the AuAuless Ti02 ron Sill. The graphic granites are compositionS i l l . The graphic granites are compositionrora ally similar to those of of the the Giants Giants Range Range batholith, although although they have slightly slightly higher higher 59 Si02 concentrations Si02 valSi02 concentrations (Giants (Giants Range Si02 ppm) ues %). ues range from 52.9-73.6 wt. %). 2. Plot PlotofofNb Nbversus versusY Y comparing comparing Dunka On On trace element element diagrams diagrams (e.g. ZrITiO2 Zr/Ti02 Figure 2. circles) with other graphic granites (open circles) other felsic felsic Nb/Y) the graphic graphic granites granites are are distinct distinct from from vs. Nb/Y) Minnesota; Figure 1 for data rocks of northern Minnesota; see 1 Aurora Sill syenites syenites (Phillips (Phillips et al., al., this this vol.), references. and references. but plot with the Duluth Complex Complex granophyres granophyres ((Kennedy ~ e k e et d al., ~ this vol.). However, However, whereas whereas major element concentrations of Dunka graphic granites are similar similar to those of felsic rocks of the MCR granophyre granophyre complexes, complexes, their trace trace element element compositions are more similar to those of mafic rocks of the MCR granophyres. A plot of Nb vs. Y compositions similar mafic rocks of the MCR granophyres. of (Figure 2) reveals the depletion in graphic granites of both Nb and Y with respect to MCR granogranoY/Nb and and ThfNb ThINb ratios ratios of of the the graphic graphic phyres and Aurora Sill Sill syenites. syenites. Furthermore, Furthermore, the the greater greater Y/Nb batholith and and suggest suggest that that these these rocks rocks contain contain granites are most similar similar to those of the Giants Range batholith a more significant crustal crustal component component than do the MCR granophyres and Aurora syenites. similar in mineral and major element element composicomposiGraphic granites of the Dunka River Area are similar lions to felsic granophyres associated with with the the Midcontinent MidcontinentRift. Rift. However, the low trace element tions concentrations of the concentrations the Dunka Dunka graphic graphic granites granites are are more more similar similar to the the mafic mafic rocks rocks of of the the granophyre granophyre complexes. Therefore, Therefore,we weconclude concludethat thatthe thegraphic graphicgranites granites of of the the Dunka Dunka Region Regionare areunrelated unrelatedto to Midcontinent Rift Rift and and to to the theAurora Aurora Sill. Sill. Alternatively, they the other felsic granophyres of the Midcontinent sirnimight be partial melts of country rock along the base of the Duluth Complex. The The chemical chemicalsimilarity between the Dunka graphic granites and the Giants Range Range batholith batholith granite granite suggests suggests that have produced produced the themelts meltsfor forthe thegraphic graphicgranite. granite. Alternapartial melting of Archean granites could have tively, the graphic graphic granites might be the melting products of nearby argillite, argillaceous siltstone, (e.g., Morey, Morey, 1972). 1972). and fme-grained fine-grained feldspathic feldspathic graywacke graywackeof of the the Virginia Virginia Formation Formation (e.g., j References Zartman, Robert E., E., 1993. Geology, geochemistry, and and geochronology geochronology of the central Boerboom, Terrence J. and Zartman, Giants Range batholith, batholith, northeastern Minnesota. Minnesota. Canadian Canadian Journal Journal Earth Earth Science, Science,v. 30, 30, p. p. 2510-2522. 2510-2522. Kennedy, Bryan Bryan C. wirth, Wirth,K., K., and andVervoort, Vervoort,J,J,this thisvolume. volume.Petrogenesis Petrogenesisof ofthe theMidcontinent MidcontinentRift Riftgranophyric granopbyriccomcomplexes of northern Minnesota. P.K. and and Morey, Morey, G.B., GB., Morey, GB., G.B., 1972. 1972.Mesabi MesabiRange. Range.A A Centennial CentennialVolume, Volume, Minnesota Geological Survey, Sims, P.K. editors, Minnesota Minnesota Geological Geological Survey, Survey,p. 204-217. 204-217. Phillips, Phillips, Erin Erin H. and and Wirth, Wirth, K., K., this this volume. volume. Petrogenesis Petrogenesisof of the the Enigmatic EnigmaticAurora AuroraSill, Sill,Mesabi MesabiRange, Range,Minnesota. Minnesota. 16 �Pyroxene Homfelsed Copper Mineralization in the Pyroxene Hornfelsed Archean Giants RangeBatholith Range Batholith Footwall Keweenawan Footwall of the Keweenawan Intrusion, Duluth South Kawishiwi NE Minnesota - Archean or Keweenawan Mineralization? South Intrusion, Dnlnth Complex, Complex, NE - Steven Miller Trunk Trunk Steven A. A. Hauck, Hauck, Natural Resources Resources Research Research Institute, Institute, University University of of Minnesota, Duluth, Duluth, 5013 Miller Andy Wallbridge Mining Company Fielding Road, Hwy., Duluth, MN, 5581 1, Bite, Wallbridge Mining Company Ltd., 129 129Fieldiing Road, Lively, Ontario, 55811, 5013 P3Y 1L7, 1L7, and Mark Severson, Natural Resources Research Institute, University of Minnesota, Duluth, Duluth, 5013 55811. Hwy., Duluth, MN, 1. Miller Trunk Hwy., MN, 5581 Copper sulfide mineralization mineralization in Ga)Giants GiantsRange RangeBatholith Batholith(GRB) (GRE)footwall footwallofthe of theSouth SouthKawishiwi Kawishiwi Copper sulfide in the the Archean Archean (—2.7 (-2.7 Ga) intrusion the Keweenawan intrusion (SKI) (SKI) of ofthe Keweenawan (1.1 Ga) Ga) Duluth Duluth Complex Complex (DC) (DC) of of northeastern northeastern Minnesota Minnesotawas was first first discovered discoveredby by exploration companies 960s and 1970s, exploration companiesdrilling drillingin in the the I1960s 1970s, and and was was recently reported reported in in outcrop outcropin in the the Spruce SpruceRoad Roadarea area E.. H.. H.. Dahlberg, 1998). The firstdescribed (pers. corn., E.. The Cu mineralization was first described by by Bonnichsen Bonnichsen et et al. al. (1980) and and further further described Severson (1994). According occurs as disseminatedsulfides disseminated sulfides described by Severson Accordingto to Severson Severson (1994), the copper mineralization occurs within the uppermost 330 ft. of the ORB, GRB, although in some some drill drill holes holesthe thefirst first 100 100ft. ft.may maybe bebarren. barren. Chalcopyrite Chalcopyrite is the dominant sulfide. However, pynhotite is However, in in the the overlying overlying SKI rocks pyrrhotite is the dominant dominant sulfide. Also, Also, at at or or just just above above the basal contact contact of of the SKI SKI and within the upper 100 100 ft. of the GRB, semi-massive to massive sulfides sulfides can occur, occur, e.g., drill holes BL-95-1, BL-95- I, K-1. K-I. These Thesesulfides sulfidesare aregenerally generallypyrrhotite-rich, pyrrhotite-rich, and andmay may have have Ni>Cu N i X u values values exceeding exceeding1% 1%Ni Ni and/or contain sulfides GRE, that these andlor Cu. Cu. Severson Severson(1994) (1994)suggests, suggests,based basedon onthe thelinearity linearityof ofthe the drill drill holes holes that contain sulfides in the GRB, drill northeast-trending belts drill holes define define two northeast-trending belts or or faults. Also Alsocoincident coincidentwith withthese theselinear linearzones zonesare areelevated elevatedplatinumplatinummineralizationin inthe theoverlying overlyingSKI. SKI. Bonnichsen Bonnichsen et et al. al. (p. (p. 563,1980) 563,1980) state state these Cugroup element (PGE) and Cr mineralization enriched enriched zones zones in the the GRE ORB "probably "probably resulted resulted because because fractional fractional crystallization crystallizationcaused caused Cu Cu enrichment enrichmentin in the the melts melts as as they trickled downward through a decreasing decreasing thermal thermal gradient beneath the complex". AAsimilar similarmodel modelfor forCu-PGE Cu-PGE mineralization has been proposed for the footwall mineralization in the Sudbury Complex Complex (Naldrett, (Naldrett, et et al., al., 1999) mineralization In 1997, Nickel,began beganaa new new exploration explorationprogram programon ontheir theirSpruce SpruceRoad Road INCO's U.S. U.S. subsidiary, subsidiary,American AmericanCopper Copper&&Nickel, 1997, INCO's Cu-Ni deposit east of Ely, MN. Based copper intercepts Based on on their previous drilling, drilling, INCO identified fifteen s 1% 1% copper interceptsin in the footwall, footwall, which suggested suggested footwall footwall copper copper exploration potential. Recently Recentlyat at Spruce SpruceRoad, Road, several several 1960-era 1960-eradrill drill holes holes geophysical surveys. surveys. Two drill holes (13648,34889) (13648,34889) were probed using a 3D Borehole Borehole Pulse were found to be open for geophysical geophysical survey, was identified identified at at 375131 375m (1,230 (1,230 ft.;Ravenhurst, ft.;Ravenhurst, 1997). EM geophysical survey, and in hole 13648, 13648, a footwall conductor was In 1999, injoint drilled DDH WM-lto WM- ito 1,754 ft. ft. At 183 1999, Wallbridge Mining Mining Company, in joint venture venture with INCO, drilledDDH 183 ft. and 330 footwall copper mineralization was intersected, ft. beneath the basal contact contact of the Duluth Complex Complex (919 ft.), footwall intersected,i.e., i.e., 79.5 79.5 ft. of 1.91% Cu and and 10.5 10.5 ft. ft. of of 0.55% 0.55% Cu. Cu. Nickel, PGEs, and Au ft. of 0.17% Cu, which includes includes 1.1 1.1 ft. 1.91% Cu Au are are minor minor constituents. constituents. The footwall to the DC DC is is generally generally composed composed of of felsic, felsic,intermediate, intermediate, mafic, hybrid hybrid rocks, and and scattered scattered homfelsed homfelsed inclusions of which which may maybe berelated relatedtotothe theGRB. GEE. In the Spruce Road area, Green (1970) inclusions (Severson, (Severson, 1994), 1994), some or all of of granitic rocks, rocks,i.e., i.e.,porphyritic porphyriticandnon-porphyritic. andnon-porphyritic. Both types types are are composed composed ofhomblende-biotite ofhornblende-biotite reports two types ofgranitic adamellite, monzonite, gabbroic adamellite, monzonite,granodiorite, granodiorite,and andseveral severalmafic maficrocks. rocks. All Allrock rocktypes typesare arecut cut by a variety of dioritic and gabbroic dikes, which may have been metamorphosed by the SKI. In In the the vicinity vicinity of of the the Spruce Spruce Road Cu-Ni Cu-Ni deposit, deposit, the the GRB ORB metamorphosed (Green, (Green, 1970). 1970). The has been contact metamorphosed The GRE ORB rocks rocks intersected intersected in WM-linclude WM-Iinclude several several of of these these rock rock types, e.g., porphyritic porphyritic quartz quartz monzonite, monzonite, quartz quartz monzonite, monzonite, granodiorite, granodiorite, monzonite, monzonite, possible Archean Archean Knife Knife Lake Lake Group homfels inclusions, norites, which which are are less lesscertain certainin inorigin. origin. All of these rock types inclusions, as well as melanorites and norites, have undergone pyroxene homfels hornfels (opx+cpx+amphibole) (opx+cpx+amphibole)contact contactmetamorphism. metamorphism. Of primary interest, however, is mineralization within itself. mineralization within the the footwall footwallmelanorites/norites, melanorites/norites, and and the the footwall footwallGRB GRB itself. The melanorites with the the granitoid granitoid rocks, rocks, and and include include rounded rounded fragments fragments of of melanorites and norites have sharp intrusive contacts with them. Petrographically, the melanorites are composed of opx and cpx (30-60%), amphibole (—1-80%), zoned and Petrographically, the melanorites are composed of opx and cpx (30-60%), amphibole ( -1-SO%), uuzonedplagioclase (10-60%),biotite biotite(4-8%), minorquartz(1-3%), oxides(<1-2%), (4-2%), unzoned plagioclase (10-60%), minor quartz (1-3%), apatite(<!%), apatite (<1%), muscovite muscovite (4-3%), (<1-3%), oxides (<1-3%). Opx early. Amphibole and sulfides (4-3%). Opx and and cpx cpx are are subhedral subhedral to euhedral and crystallized early. Amphibole generally rims the pyroxenes, Anhedralto to subhedral, subhedral,zoned zoned pyroxenes, and in some some instances instances corrodes corrodes the pyroxenes producing anhedral crystals. Anhedral 17 �and unzoned plagioclase may show show undulose extinction, extinction, occur occur as equant grains, and are often altered altered to clay clay minerals. Anhedral to subhedral flakes of biotite follow the crystallization of plagioclase and can be porphyroblastic. suhhedral flakes porphyroblastic. Quartz Quartzisis the last silicate to crystallize. Apatite occurs as euhedral rods, both very early and late in the sequence. last silicate to crystallize. Apatite occurs as euhedral rods, both very early and late in the sequence. Oxides (magnetite> ilmenite) and and sulfides sulfides are are last last to crystallize. The The oxides oxides and and sulfides sulfides are are often associated with alteration (magnetite >ilmenite) of the pyroxenes pyroxenes to to biotite, biotite, muscovite, muscovite,talc talc(?), (?),and andchlorite chlorite(?) (?)along alongfractures fracturesand andalong alongthe therims rimsininthe theopx. opx. The sulfides, in order of appearance, appearance, are are millerite, millerite, sphalerite, sphalerite,and andhomite bomiteandlor and/orchalcopyrite. chalcopyrite. The The sulfides sulfides also also occur occur as as interstitial to net-textured net-textured grains that surround surround opx. opx. The melanorites also contain net-textured magnetite. The A similar sulfide and silicate mineralogy occurs in the footwall footwall host host rocks. rocks. These These rocks rocks can can have have feldspar feldspar phenocrysts phenocrysts with a plagioclase plagioclase matrix matrix and minor minor quartz quartz ((5%), amphibole, opx, biotite, oxides (magnetite, ilmenite), ~ 5 % )amphibole, , opx, biotite, oxides (magnetite, ilmenite), and andsulfides sulfides (chalcopyrite, hornite, bomite, millerite, pentlandite, sphalerite). The blebs and anddiscontinuous discontinuous veins, veins, generally generally The sulfides occur as blebs associated with biotite, plagioclase, opx, ±amphibole ±amphibole, ±quartz ±quartz, and oxides. The The plagioclase plagioclase in in these these zones zones is equant and equigranular, and exhibits sutured contacts with the larger plagioclase. The copper mineralization in the granitoid and noritic rocks have Cu:Ni ratios of 8-32:l, 8-32:1, compared to the 3.3:1 3.3: 1 in the overlying DC. The Pd:Pt ratio is these rocks is 1-15:1, compared to the 3:1 in the overlying DC. Data from The Pd:Pt ratio is these rocks is 1-15:1, compared 3: 1 Data fromSeverson Severson (1994) on other footwall intercepts give Cu:Ni and Pd:Pt ratios of 2-9:1 and 2-7:1, respectively, indicating footwall intercepts give Cu:Ni and Pd:Pt of 2-9:1 and 2-7:1, respectively, indicating that thatCu Cuisis enriched, and Ni and PGEs are depleted in WM-1 when compared to other footwall samples. Comparison Comparisonof ofCu:Ni Cu:Niinin all GRB samples indicates a tendency for Cu enrichment and Ni depletion with depth beneath the the basal contact. contact. geology. Possible The origin of this this mineralization mineralization opens opens new and and exciting exciting aspects in Duluth Complex geology. Possible emplacement scenarios scenarios include: include: I) A relict of Archean emplacement. The 1) Themodel model isis supported supported by both sharp contacts contacts and net-textured sulfides sulfides and oxides in the mafic rocks rocks of the footwall. Duluth Complex Complex sulfide. sulfide. The observed depletion of nickel and enrichment enrichment 2) Keweenawan fractionation of Duluth depth below below the the footwall-Duluth footwall-Duluth Complex Complex contact, contact, and andthe theassociation associationof ofnet-textured net-texturedand anddiscontinuous discontinuous of copper with depth biotite-muscovite-talc(?)-chlorite(?) alteration support this possibility. vein sulfide with biotite-muscovite-talc(?)-chlorite(?) feeder-dike' totothe 3) Proximity to a "feeder-dike" theDuluth DuluthComplex. Comvlex.This Thiscase caseisissupported supportedby bythe thepresence presence of ofmagmaticmagmatichigh-grade sulfide intersections intersections not not unlike unlike those those from from Voisey's Voisey's Bay and Sudbury. These looking high-grade Theseintersections intersections are are associated with mafic assemblages not normally part of granitoid intrusions. Regardless ofpreferred genetic model, developments indicate significant new exploration exploration potential Regardless ofpreferredgenetic model, these recent developments potential for the Duluth Complex. Y., 1980, Geologic setting, mineralogy, mineralogy, and geochemistry of magmatic Bonnichsen, B., Fukui, L. M., and Chang, L. L. Y., magmatic D., ed., ed., Proceedings Proceedings ofthe of the fifth fifth quadrennial quadrennial IAGOD IAOOD symposium, symposium, sulfide deposits, Duluth Complex, U.S.A, in Ridge, J. D., Alta, Utah, 1978: Stuttgart, Schweizerbart'sche Schweizerbart'sche Verlagsbuchhandlung, Verlagsbuchhandlung, v. v. 1, p. p. 545-565. Snowbird, Aka, 3. C., C., 1970, Lower Precambrian rocks of the Gabbro Green, J. Gabhro Lake Quadrangle, Quadrangle, northeastern northeastern Minnesota: Minnesota: Minnesota Minnesota Geological Survey, Special Special Publication Series, Series, SP-13, SP-13, 96 96 p. Naldrett, A. J., Asif, M., Schandl, E., Searcy, T., Morrison, G G.. G., Binney, Binney, W. P., P., and and Moore, Moore, C., C., 1999, Platinum-group Platinum-group to the the origin origin of of different different ore ore zones zones and and to to the the exploration exploration for for elements in the Sudbury ores: Significance with respect to orebodies: Economic Economic Geology, Geology, v.v.94, footwall orehodies: 94, no.2, no. 2, p. p. 185-210. 185-210. Ravenhurst, B., 1997, 1997, Geophysical Geophysical survey survey report report for for American American Copper Copper & & Nickel Nickel Inc., Inc., Spruce SpruceRoad Road project: project: Division Division of Lands and Minerals, Minnesota Minnesota Department Department of of Natural Resources, Resources, Open-File Report, 26 26 p. p. of the South South Kawishiwi Kawishiwi Intrusion, Intrusion,Duluth DuluthComplex, Complex,northeastern northeastern Minnesota: Minnesota: Severson, M. J., 1994, Igneous stratigraphy ofthe 210 Duluth, Natural Resources Research Research Institute, Institute, Univ. Minnesota, Minnesota, Duluth, Duluth, Technical Technical Report NRRI/TR-93/34, NRRIITR-93/34,2 10p. p. 18 �An Archean age argument is supported by by::I)1)sharp sharpintrusive intrusivecontacts contactswith with xenoliths xenolithsof ofhost host rock rock in in the the melanorites; melanorites; and 2) magmatic-looking net-textured sulfides and oxides in the melanorites. A Keweenawan argument magmatic-looking sulfides the A Keweenawan argument includes includesthe the previous examples and is also supported by: 1) depletion ofNi and enrichment of copper with depth beneath 1) ofNi and enrichment of copper with depth beneath the the basal basal previous examples and is contact of the DC (as might be expected of a downward differentiating differentiating sulfide sulfidemelt meltthrough through fractures fractures and and faults); faults); 2) 2) association of net-textured and discontinuous vein sulfides with biotite-muscovite-talc (?)-chlorite (?) alteration; and (?) net-textured discontinuous sulfides 3) possible emplacement Keweenawan"feeder "feeder dike" dike" to the DC. Evidence Evidencewould wouldinclude includethe thepresence presenceof ofmagmatic magmatic emplacementof of aa Keweenawan pyrrhotite-pentlandite-chalcopyrite mineralization not unlike that of the Sudbury and Voisey's Bay, as well as the pyrrhotite-pentlandite-chalcopyritemineralization not unlike that of the Sudbury and Voisey's Bay, as well association of mafic assemblages not normally part of the granitoid intrusions. In In any any event, event, the the presence presenceof of Cu-rich Cu-rich well below the basal contact of the SKI (300-425 ft.) ft.) is interesting and suggests a new exploration mineralization well potential for potential for the the DC. DC. Table I. WM-l 1. Footwall Footwall Copper Copper Intersections in WM-1 Interval Ni Interval Feet Cu Cu Ni Co Ag Au Pt Pd ppm ppm ppb ppb ppm ppm (ft.) (ft.) (ft.) (ft4 P P ~P P ~P P ~P P ~P P ~P P ~ppb P P ~ 1102.0-1 107.3 15 2.7 54 152 1102.0-1107.3 5.3 5.3 4872 237 15 2.7 54 59 152 1251.6-1252.7 1.1 19100 592 23 5.7 154 1251.6-1252.7 1.1 19100 592 23 5.7 99 69 69 154 1251.6-1262.1 1251.6-1262.1 10.5 10.5 5496 5496 1249.0-1328.2 1249.0-1328.2 79.2 79.2 1655 1655 421 421 144 144 19 22 22 12 12 2.7 2.7 0.9 0.9 43 43 21 21 23 23 99 69 37 �Results of ^ArP9Ar 40ArP9Ar laser laser microprobe microprobe grain-scale grain-scale age mapping Results of mapping of of muscovite muscovite from from Precambrian bedrock Precambrian bedrock of the southern Lake Superior Superior region HOLM, Daniel Daniel K., K., Department of Geology, HOLM, Department of Geology, Kent State University, University, Kent. Kent, OH OH 44242; 44242; V., and HURTADO, Jose, both at Department of Earth, Atmospheric, and HODGES, Kip V., Cambridge, MA, 01239 Planetary Sciences, Massachusetts Institute of Technology, Cambridge, 01239 step-heating mineral mineral ages collected collected in the 4OArP9Ar step-heating the The results results of of over over 100 100conventional conventional40Ar/39Ar 1990's 1990's from the southern Lake Superior region have greatly increased our understanding of the thermal and deformational deformational history of the crust crust following following the the Paleoproterozoic PaleoproterozoicPenokean Penokean Step-heating experiments, experiments,however, however,may may not not effectively effectively reveal reveal the internal orogeny. Step-heating distribution of radiogenic radiogenic argon within crystals, distribution crystals, but instead can mask mask important importantdetails details of of the the GCA). samples thermal history (Hodges (Hodges et al., 1994, 1994, Geology; Geology; Hodges Hodges and and Bowring, Bowring, 1995, 1995,GCA). step-heating experiments experiments on four We compare results of of previous previous conventional conventional 40Ar/39Ar 40ArP9Ar step-heating muscovite grains grains with with new new results results from from in in situ spot analyses analyses using using the Ar-ion Ar-ion laser laser muscovite microprobe (see table below; age in Ma, uncertainties at two sigma). Samnle s ?A!u2k 97CM7 97CM7 97CM13 97CM 13 96DR8 96DR8 97DR7 97DR7 Location LQ&Qll Republic, MI Dunbar, inb bar, WI Little Falls, WI Neillsville, WI Step-heating ae stemheathe .@g 1716±5 171 6 s plateau olateau 1366±6 iear-plateau near-plateau 1366&6 plateau 11614±5 6 1 4 s plateau 1518 total gas Age gradient 1707-1660 1373-1327 1373-1327 1652-1563 1652-1563 1923-1414 1923-1414 The form 97CM7suggests suggestsincorporation incorporationof ofexcess excess40Ar ^Ar form of of the the age agegradient gradient of of sample sample97CM7 along the grain boundaries. boundaries. Core Core spot spot ages ages of of 1660-1680 1660-1680 Ma Ma are are consistent consistent with a nearby nearby biotite plateau spectrum age (Schneider (Schneider et et al., al., 1996, CJES). CJES). Laser Laser microprobe microprobe results results from the other three samples samples reveal varying degrees degrees of age gradients gradients (see (see Figure Figure 11for forexamples). examples). Sample 96DR8, which yielded an excellent plateau age of 1614±5 1 6 1 4 s Ma, revealed a >90 m.y. my. age gradient. gradient. The The weighted weighted mean mean of the the 10 10 spot spot fusion fusion ages ages is is close close to to the the plateau plateau age. age. Step-heating therefore appears to have homogenized age gradients present in in this this sample. sample. 97CM13 gives gives aa near plateau plateau age of 1366±6 The spectrum of sample 97CM13 1 3 6 6 s Ma, but shows age increasing from from 1334 Ma Ma to to 1383 Ma. Ma. In increments generally increasing I n situ spot spot laser analyses analyses allow us to verify the existence of an age gradient (from at least 1373±12 1373k12 Ma to to 1327±9 1327BMa) Ma) with with significant clarity. Sample Sample97DR7 97DR7yielded yielded aa saddle-shaped saddle-shapedage age spectra spectra with with aa minimum minimum age age increment of 1484±2 Ma (Fig. I). increment of 1484zk2 Ma (Fig. 1). Ar-ion Ar-ion laser microprobe data reveals a spectacular 500 500 m.y. age gradient from core (oldest) to to rim. rim. The my. The youngest youngest ages ages preserved (down to 1414±21 1414±2 Ma) are are obtained from what what is probably a real grain boundary. A difficult problem in in interpreting interpreting 40ArP9Ar 4OArP9Ar age gradients is whether they formed formed during during slow cooling or resulted resulted from from superimposed, superimposed, episodic episodic reheating. reheating. If the entire core to to rim rim south transect, transect, Fig. Fig. 1) 1)reflects reflectssimple simpleslow slow gradient of sample 97DR7 (along the center to south then the implied implied cooling cooling rate rate is is about about 0.3 0.3 K1m.y. K/m.y. This cooling with volume diffusion, then This rate rate is is remarkably similar to the integrated cooling rate estimated for the Proterozoic terrain of the southwest United United States (Hodges et al., southwest a]., 1994). 1994). However, However, consideration consideration of the overall overall geologic context within which these dated samples exist suggests suggests aa more more complex complex episodic episodic thermal history. Case studies studies (i.e., (i.e., Hames Hames and and Cheney, 1996, 1996, Los) Bos) suggest that the form of history. Case grain-scale 'chrontour' 'chrontour' maps maps should should help help to distinguish between between simple and more detailed grain-scale complex thermal histories. histories. Whatever Whatever their their mechanism mechanism of of formation, formation, the the documentation documentation of large and quantifiable quantifiable age gradients gradients in this this study study indicates indicates promise promise for forobtaining obtaining more more detailed information about the Proterozoic thermal evolution of the the southern southern Lake Lake Superior Superior region. 20 �97DR7 Muscovite Muscovite 10000 C-) C, 0 '5 1550 C 0) 1500 1450 0 20 60 40 80 100 % Ar cumulative O h ^Ar cumulativereleased released , - , r , I . I 1 . , , , s 10000 10000 9GDRBMuscovite Muscovite 96DR8 100 100 10 10 I - , I I , , , . 1 , , , , I I . , , 8 , , , I I 96-DR-8 96-DR-8 Muscovite Muscovite - 1650 1 6~0 1600 1600 , I * s - I1, = 1614±5 Ma 1550 t91615Ma 1500 I 0 20 40 60 80 lao % cumulative released released % 30Ar ^Ar cumulative Figure 1. Figure 1.Spot Spotfusion, fusion,single singlecrystal crystalage agedata data(this (thisstudy) study)and andcorresponding corresponding conventional conventional incremental-release data (after Romano, Kent State M.S. thesis, incremental-release data Romano, thesis, 1999) 1999) for fortwo twomuscovite muscovite 97DR7 is coarse samples samples from from the southern southern Lake Lake Superior Superior region. region. 97DR7 coarse muscovite muscovite from from a muscovite gneiss of probable Archean age collected at Sylvan Lake west of Neillsville, muscovite gneiss of probable Archean collected Sylvan Lake west of Neillsville, Wisconsin. 96DR8 Wisconsin. 96DR8 isis muscovite muscovite from from aa late late pegmatite pegmatite dike dike collected collected at at Little Little Falls Falls south of Eau Claire, Wisconsin. Wisconsin. Grain images are video stills of individual (001) cleavage fragments Grain images are video stills of individual Ar-ion laser fusion micron-diameter (outlined), and the dots indicate the position of ca. 100 (outlined), and position 100 fusion pits, each labeled with its measured age (age uncertainties are variable but generally less age (age uncertainties are variable but generally lessthan than Unlabeled pits pits in in 96DR8 too little gas 10 Ma at two two sigma). sigma). Unlabeled 96DR8 produced produced too gas for for effective effective measurement. 21 �PRELIMINARY HYDROTHERMAL ALTERATION PRELIMINARY VOLCANOLOGY VOLCANOLOGY AND HYDROTHERMAL ALTERATION STUDIES STUDIESAT AT THE THE AND QUARTZ QUARTZHILL HILL PROSPECTS: PROSPECTS: FIVE MILE LAKE, EAGLES NEST, AND IMPLICATIONS IMPLICATIONS FOR FOR VMS-STYLE VMS-STYLE MINERALIZATION MINERALIZATION IN NORTHEASTERN MINNESOTA GEORGE .1. HUDAK GEORGE J. HUDAK Department 54901 Departmentof of Geology, University iversityof of Wisconsin Wisconsin Oshkosh, Oshkosh, Oshlcosh, Oshkosh, WI WI 54901 RONALD L. MORTON MORTON Geology Duluth, MA' MN 55812 55812 Geology Department, Department, University Universityof of Minnesota Minnesota—Duluth, -Duluth, Duluth, HENK DAHLBERG Minnesota Department MN Department of of Natural Natural Resources, Resources, Minerals MineralsDivision, Division, Hibbing, Hibbing, MN The Five The Five Mile Mile Lake, Lake, Eagles Eagles Nest, Nest, and and Quartz Quartz Hill Hill prospects prospects occur occur ininArchean Archean metavolcanic metavolcanic and and metasedimentary rocks rocks the the western western half half of the Vermilion District District of northeastern northeastern Minnesota. Minnesota. The metasedimentary TheFive FiveMile MileLake Lake prospects occur within the lower member of the Ely Greenstone Sequence, whereas the Quartz and the Eagles Nest prospects Hill prospect Detailed diamond relogging, Hill prospect occurs within the the Bass Bass Lake LakeSequence Sequence (Peterson, (Peterson, 1999). 1999). Detailed diamond drill core core relogging, petrography, and lithogeochemistry lithogeochemistry have have been been recently recently completed completed at at these these prospects prospects (Hudak (Hudak and and Morton, Morton, 1999) to: petrography, a) better understand the geology (in particular, particular, the physical physical volcanology) volcanology) associated associated with with these these prospects; prospects; b) b) identify identi& and evaluate the metamorphosed hydrothermal alteration mineral assemblages that occur at each of of these these prospects; prospects; and c) evaluate the potential for volcanogenic massive sulfide (VMS) and/or gold mineralization in in these these areas. areas. During our investigation, investigation, a total of eight eight diamond diamond drill drill holes holes from from the the three threeprospects prospects listed listedabove abovewere were and sampled sampled for petrographic petrographic and and lithogeochemical lithogeochemicalanalysis. analysis. Four diamond drill holes from the Five Mile relogged and Lake prospect prospect (SXL-1, (SXL-l, SXL-2, SXL-4), two two diamond diamond drill drill holes holes from from the the Eagle's Eagle'sNest Nestprospect prospect(EN-4 (EN4 SXL-2, SXL-3, SXL-3, and and SXL-4), EN-7), and two diamond diamond drill holes from the Quartz Hill prospect (QH-84-2 and QH-85-4) were relogged with and EN-7), an emphasis emphasis on identi'ing identifyinglithology, lithology,volcanic volcanicfeatures featuresand andtextures, textures,metamorphosed metamorphosedhydrothermal hydrothermal alteration alteration mineral assemblages, assemblages, and syn-volcanic thin sections (33 from Five syn-volcanic and post-volcanic post-volcanic fault zones. Sixty-four thin Five Mile Mile Lake, 18 from Eagles Nest, Nest, and 13 Lake, 13 from from Quartz Quartz Hill) Hill) were were evaluated evaluated for lithology, lithology, alteration alteration types, primary primary and textures, mineral modal analysis, and fragment secondary textures, fragment modal analysis. In In addition, addition, thirty-eight thirty-eight lithogeochernical lithogeochemical (both major and trace element) were were also also performed performed (22 (22 from from Five Five Mile Mile Lake, Lake, 10 from Eagles Nest, and 6 analyses (both from Quartz Hill). Hill). andesite/basalt lava flows and scoriaThe Five Mile Lake region is composed of massive to amygdaloidal andesitehasalt rich volcaniclastic deposits, locally quartz-phyric dacitic to rhyolitic lavas and flow breccias, and and volcaniclastic volcaniclastic and and chemical sedimentary sedimentary rocks. rocks. Quartz-feldspar Quartz-feldspar porphyry porphyry and and diahase diabase dikes are also present throughout chemical throughout the the volcanic volcanic and sedimentary sequence. textures indicate indicate that that these these rocks rocks likely sequence. Volcanic Volcanic textures likely were formed within a deep deep water water Hydrothermal alteration alteration minerals minerals include include epidote, epidote, iron-rich chlorite, magnesium-rich (>500meters) environment. Hydrothermal magnesium-rich Stringer and and semi-massive sulfide mineralization mineralization are are associated associated with with two chlorite, and quartz quartz (silicification). (silicification). Stringer semi-massive sulfide chlorite, assemblage, and and b) an epidote - iron distinct alteration assemblages: a) an early early iron-rich iron-rich chlorite chlorite - sericite sericite - quartz assemblage, iron carbonate assemblage assemblage associated associatedwith with late late sulfide sulfide remobilization. remobilization.The TheFive FiveMile Mile Lake Lake prospect prospect appears appears to to be be a carbonate "Noranda-type" VMS system based on on the criteria discussed by Morton and Franklin (1987). (1987). Two diamond drill holes in the Two diamond drill holes investigated investigated in the Eagles Eagles Nest Nest region region comprise comprise massive massive to toamygdaloidal amygdaloidal andesite/basalt lava flows and associated flow andesiteibasalt flow breccias/hyaloclastite, breccias/hyaloclastite, mafic mafic to to intermediate intermediatevolcaniclastic volcaniclasticsediments, sediments, Algoma-type mixed mixed facies facies (sulfide, (sulfide, oxide, oxide, silicate) silicate) iron iron formations Algoma-type formations and associated associated chert horizons, horizons, interbedded interhedded semi-massive to massive sulfide deposits, deposits, and rhyodacite rhyodacite to rhyolite tuffs and/or siltstone and debris flow deposits, semi-massive tuffaceous volcaniclastic porphyry intrusions intrusions and and diabase diabase dikes dikes are also volcaniclastic sediments. sediments. Quartz Quartz feldspar feldspar porphyry also present. present. textures suggest that the rocks in the area were also formed in a deep water Volcanic textures water (>500 (>500 meters) meters) environment. environment. A A massive sulfide is overlain overlain by by approximately approximately 2 meters (6 feet) of sulfide four meter thick intersection of pyrite-rich massive approximately 22 22 meters meters (73 (73 feet) feet) of of mixed mixedfacies faciesAlgoma-type Algoma-typeiron iron (py)-chert exhalite, which is overlain in turn by approximately formation. The The host host and and footwall footwall rocks rocks to to the sulfide sulfide mineralization mineralization comprise sericite-, iron-rich chlorite-, kaolinitecarbonate- (dolomite (dolomite andlor and/or ankerite) ankerite) and and locally chlorite-alteredfelsic felsic ash ash tuffs tuffs or tuffaceous carbonatelocally magnesium-rich magnesium-rich chlorite-altered tuffaceous volcaniclastic sediments. sediments. Based Based on on the volcanology alteration present, present, the Eagles Nest prospect volcaniclastic volcanology and hydrothermal hydrothermal alteration prospect represent aa "Noranda-type" also appears to represent "Noranda-type" VMS VMS system. system. - 22 - �The two diamond diamond drill holes investigated investigated at the Quartz Quartz Hill Hill prospect prospect comprise comprise amygdaloidal amygdaloidal to massive massive basalt/andesitelava lava flows, flows, mixed mixed volcaniclastic and chemical (including chert, chert, silicate-fades basaltlandesite volcaniclastic and chemical sediments sediments (including silicate-facies iron iron formation, oxide-facies iron formation), and felsic tuffs and/or andlor tuffaceous volcaniclastic sediments. sediments. Massive Massiveto tosemisemimassive sulfide sulfide mineralization mineralization occurs occurs between between 89 89 and and 150 feet feet in exploration diamond drill drill hole QH-84-2, exploration diamond QH-84-2, and is hosted within felsic felsic ash tuff or tuffaceous tuffaceous sedimentary sedimentary rocks. rocks. The relative abundance of felsic tuffs and The and tuffaceous tuffaceous material, coupled with hydrothermal alteration assemblages comprising andalusite, chloritoid, and hon-rich iron-rich chlorite, chlorite, suggests that that the the Quartz Hill mineralization suggests mineralization may represent represent either either a) aa "Mattabi-type" "Mattabi-type" VMS VMS system system (Morton (Morton and and Franklin, 1987); or or b) an ancient shallow subaqueous or subaerial high-sulfidation high-sulfidation system (White and Hedenquist, Franklin, Mattabi-type VMS VMS systems systems are characteristic 1990, Sillitoe et al., al., 1996). 1996). Mattabi-type characteristic of shallow shallow water water 1990, 1995; 1995; Sillitoe, Sillitoe, 1995; Sillitoe meters water water depth) depth) hydrothermal hydrothermal systems, systems, reflect reflect extreme extreme acid acid leaching leaching of the rocks by ((<500 6 0 0 meters by the the hydrothermal hydrothermal fluids, and and may he be analogous to "high fluids, "high sulfidation" sulfidation" epithermal epithermal systems within shallow water environments. environments. Such Such hydrothermal systems may produce gold-rich massive sulfide deposits (Hannington et et al., 1997). 1997). The results of this study indicate that the Vermilion region of northeastern Minnesota contains at least least two examples (Five (Five Mile Lake and Eagles examples Eagles Nest) Nest) of ofdeep deepwater, water,flow-dominated flow-dominated VMS VMSsystems systems(Noranda-type). (Noranda-type). The The Quartz Hill prospect may represent either a volcaniclastic dominated, shallow water "Mattabi-type" VMS system, or Continued re-evaluation re-evaluation of of a shallow subaqueous subaqueous or possibly possibly subaerial subaerial high high sulfidation-type sulfidation-type epithermal epithermal system. system. Continued mapping, diamond these these prospects prospects via detailed detailed field mapping, diamond drill core core relogging, petrographic analysis, analysis, and lithogeochemical studieswill willbe be performed performedduring duringthe the next next year year to further evaluate lithogeochemical studies evaluate and better better understand understand these potentially ore-forming hydrothermal systems. References References Hannington, M., Poulson, K. H., Thompson, J., & Sillitoe, R. H., (1997): Volcanogenic gold gold and and epithermal-style epithermal-style environment. In In Barrie, Barrie, C. C. T., T.,and Hannington, M. D. (Eds.), (Eds.), Volcanic mineralization in the VMS environment. Associated Massive Sulfide Deposits: Processes and Examples in Modern Modem and and Ancient Settings: Settings: GACGACMDD-SED Short Course Volume, 183-214. 183-214. J., & Morton, R. L., (1999): Bedrock and glacial drift Hudak, G. J., drift mapping for for VMS VMS and and lode lode gold gold alteration alteration in in the the Vermilion — Big Fork Greenstone Belt: Part A: Discussion of Vermilion -Big of lithology, lithology, alteration, alteration, and and geochemistry geochemistry atatthe the Five Mile Lake, Eagles Nest, Nest, and Quartz Hill Hill Prospects. Prospects. Minnesota Department of Natural Resources Project 326 Open File Report, 136 136 pages. L., & & Franklin, Franklin, J. J. M., M., (1987): (1987): Two-fold Two-fold classification of Archean volcanic-associated massive sulfide Morton, R. L., Geol., 82, 1057-1063. 1057-1063. deposits. Econ. Geol., D. M., (1999): Economic geology and lode gold and volcanogenic massive sulfide Peterson, D. sulfide prospects prospects of ofthe the western Vermilion District, St. Louis and Lake Counties, northeastern Minnesota. Minnesota Minnesota Exploration Exploration Conference 1999, Lode Gold and Massive Sulfide Sulfide Prospects Prospects in in the the Archean Archean Western Western Vermilion Vermilion District District of of Northeastern Minnesota, Abstracts Abstracts Volume, Volume, 3-5. 3-5. Fl., (1995): (1995): The influence of magmatic-hydrothermal models on exploration strategies Sillitoe, R. H., strategies for volcanoSillitoe, Deposits, Mineralogical In Thompson, Thompson, 3. J. F. H., H., (Ed.), Magmas, Mamas. Fluids, Fluids. and Ore Deoosits, Mineralogical Association Association plutonic arcs. In of Canada Short Course Volume 23,511-525. Sillitoe, R. H., H., Hannington, Hannington, M. M.D., & Thompson, Thompson, J.J. F. F. H., H.,(1996): (1996): High High sulfidation deposits in the volcanogenic D., & massive sulfide environment. Econ. 204-2 12. Econ.GeoL, Geol.,91, 91,204-212. White, N. C., &Hedenquist, 3. W., (1990): Epithermal environments and styles of mineralization: variations and J. W., and their causes, and guidelines for exploration. Jour. 445-474. Jour.Geochein. Geochem.Res., Res., 36, 36,445-474. N. C., & Hedenquist, J. 3. W., W., (1995): Epithermal gold deposits: deposits: styles, characteristics, and Exploration. SEG White, N. Newsletter, 23,9-13. Newsletter, 23, 9-13. 23 �MAGMATIC ORIGINS ORIGINS FOR FOR NATHAN'S NATHAN'S LAYERED SERIES: AN INITIAL REASSESSMENT REASSESSMENT OF OF MAGMATIC THE MIDCONTINENT RIFT'S FIRST FIRST MAJOR PLUTONIC MATERIALS JERDE, Eric JERDE, Eric A. (e.jerde@morehead-st.edu), (e.jerde@morehead-st.edu),Dept. Dept. of ofPhysical Physical Sciences, Sciences, Morehead MoreheadState State University, Morehead, KY 40351 Morehead, 4035 1 In recent years, great greatstrides strideshave havebeen beenmade madein indeciphering decipheringdetails detailsof ofthe the evolution of of the the Midcontinent MidcontinentRift Rift (MCR.),and andthe theemplacement emplacementof ofthe theDuluth DuluthComplex Complexintrusions intrusionsand andassociated associatedlavas. lavas. The The vast vast majority majority of of System (MCR), Ripley, 1996), material produced by the MCR was between 1099 1099and 1095 1095Ma Ma (Miller (Miller and Smyk, 1995; 1995; Miller and Ripley, an indication of how vigorous the system was. The Theearliest earliestmaterials, materials,however, however, were wereproduced producedininexcess excessofof88 years previously, previously, and and because because of their relative rarity are incompletely understood. understood. million years One of the most interesting period of rifting is is known known informally informallyas asNathan's Nathan's Layered Layered interesting intrusions of this early period Series after after the the work of Nathan (1969). HIs still stands as the most intensive study of the rocks, comprising His still stands as the most intensive study of the rocks,comprisingfield field descriptions, petrographic petrographic analysis, and some microprobe and optical determinations of m mineral compositions. No ineral compositions. No work has has been been performed performedon on any anyrocks rocksof ofthis thisseries. series. A U-Pb zircon date of 1106.9  ± .6 .6 Ma has been geochemical work obtained for one (Paces and Miller, 1993), confirming its antiquity in in the the MCR MCR. Nathan one of of the the units units of this series series (Paces Nathan (1969) identified 27 separate the letter designations A-Z and AA in their inferred separate units, which are given the the discordancies discordancies observed. observed. Nathan's chronological order based on the Nathan'sown owninterpretation, interpretation,plus plus those thoseof ofsubsequent subsequent observers, gradational variations, whBe while others others may be sparse dikes or observers,offers that many of the separate separate units may be gradational "sport" varieties, Nathan (1969). varieties, to to use use the theterminology terminology of ofNathan (1969). In terms of major magma bodies, bodies, the the series seriescomprises comprisesfour fourprincipal principalunits: units:A-B A-B(troctolites (troctolitestotogabbronorites), gabbronorites),G0 (oxide-rich olivinegabbro), gabbro),M M (gabbronorite), (gabbronorite), and andP-Q P-Q((troctolites troctolites to to gabbros). gabbros), These (oxide-rich olivine These units units are are present present in in amounts amounts great enough great enough to to permit permit their their being assigned as the principal events in the evolution of the series. Typical Typicalmodal modal abundances and m mineral compositionsfor forthese thesegroups groupsare aregiven givenininTable Table1.1. One One of of the the more more interesting interestingaspects aspects of of ineral compositions the presence of large amounts of of Fe-Ti oxides in many many of of the the units. units. There Thereare areseveral severalunits units that that this series is the occasionally have have in in excess excess of of 30% 30% Fe-Ti Fe-Ti oxides. oxides. Among Among the the major major units, only only Unit 0Gisisnotable notablefor foraahigh high abundance of oxide phases, in some locations exceeding 60%. 60%. This abundance Thisoccurs occursin in aa fairly fairly primitive magma (forming abundant olivine of of Fo.io.50 Fo,0 and andlittle littlequartz quartzororgranophyre), granophyre),resembling resemblingthe theother othermajor majormagmas magmasin inother otheraspects. aspects. 1. TyDical Tvoical Mineral Abundances Abundancesfor for NLS NLS and and Model ModelResults. Results. Table 1. Model g ! Q l & g Q e & & g fl IEli Q! AizQn&Qa Eiz Li! u A-B P-Q 42 42 53 53 Fo AAn6.e lien,; FRY? 58 58 33 An,4 Fo Feat 3 Mg9 Mg*4,9 -—- ~ % 4 3 M 59 --- 62 An555 32 Mg71 M&wl 13 _ 77 24--- Mg53 Mg An55.43 G 22 3 5 8 Fo 11 —- -_ 6kb 6kb 47 io, 10% An Afl63 .. — 46 Fo62 FO(Q 22 6kb 6kb 49 49 14 14 Fo F06o 4 An62 &2 51 6 5 1kb i 14 Mg3 !izAnQ -15% 6kb 2 Q Qi l An Fo 48 6 An54 Fo45 55 Mg, M ~È-~ 33 33 Mg --- M~ Mg5g 343 --2816 Mg.57 Petrographic data data from Nathan (1969). Petrographic (1969). Modelling of magma crystallization was was made made to to explore possible possible scenarios scenarios for for the the unusual unusual abundance abundance of of oxide oxide in the the material material comprising comprisingUnit UnitG. 0. This Thismodelling modelling was was done donewith with the the MAGFOX MAGFOX program program(J. (1.Longhi, Longhi, pers. pa. minerals in comm.). AAtypical typicalcomposition compositionof ofaa Logan Logansill sill (Table (Table 2) 2) was was used used as as aa parent parentsince sinceitit represents representsthe theonly onlycommon common composition in the region that is even remotely remotely coeval coeval(the (theLogan Loganssills havebeen beendated datedatat1108 1108-1./.2 composition that is ills have ; by Davis and and Sutcliffe, 1985). 1985). constraints are poor Nathan's series, series,some someinteresting interesting Although the constraints poor since since no liquid compositions are known for Nathan's features features of of the the modelling are present. Using Usingthe theLogan Logancomposition compositionofofTable Table2,2,materials materialsresembling resemblingthose thoseof ofunits units P-Q, can to 6 kb. In A-B, can be generated generated through through crystallization crystallization at depths depthscorresponding corresponding to Inthis, this, A-B A-B and and P-Q A-B, M, and P-Q, P-Q 24 �I I I   I M after crystallizatiow These shown in can can be be formed fanned after after 10-15% 10-15% crystallization, crystallization, and and M after —25% -25% crystallization Theseresults results are are shown in Table Table I1 adjacent to the the petrographic petrographic observations of Nathan Nathan (1969). (1969). In adjacent to observations of Inthis thismodel, model,the theoxide oxidephases phasesappear appear after after28% 28% crystallization, are moderately moderately abundant abundantthereafter, thereafter,consistent consistentwith withthe thefe few percentofofoxides oxidespresent presentininP-Q P-Q.ItIt crystallization, and and are w percent is interesting interesting to to note existed at at 66 kb, kb, then then the the P-Q P-Q magma must mustbe beolder olderthan thanM, M, in in that ififonly onlyone onemagma magma chamber chamber existed is note that contradiction to the or that that contradiction to the original original mapping. mapping. IfIfNathan Nathan(1969) (1969)isiscorrect, correct,ititimplies impliesthat thatmultiple multiplechambers chambers existed, existed, or recharge was was taking taking place, place, both both of of course course plausible. plausible. At recharge At 66kb, kb,oxides oxidesdo donot notform formininabundances abundancesakin akintotothose thoseseen seen in in >50% crystallization, that point, the 0 until until >SO% crystallization,and and at at that point, the the liquid liquid isis far far more moreevolved evolved than than could could have have produced produced the Unit G responsible for for the the smaller intrusive dikes to other other minerals other minerals seen. seen. Such Such liquids may be be responsible smaller intrusive dikes and and sills sills assigned assigned to other units units enlarge the stability field for and modelling at I kb showed oxide phases, by Nathan. However, lower pressures by However, lower pressures enlarge stability field for oxide and modelling at 1 suggested by by the model 0 are ilmenite appearing appearing after afterless less than than 20% 20% crystallization. crystallization. Materials Materials akin akin to those of Unit G are suggested ilmenite crystallization, Thus 0 may evolution in shallower magma chamber. after after approximately 40% crystallization Thus Unit G may reflect evolution in aa shallower chamber. The tremendous variation and the the gradational gradational nature nature of the rocks is The tremendous variation in in cumulate cumulate textures on on aa small small scale, and rocks is of (and presage) the the later later Anorthositic Anorthositic Series Duluth Complex reminiscent reminiscent of (and in in this this case case may presage) Series rocks rocks of the the Dulutb Complex suggested suggested to to have formed formed as asinjections injectionsof of plagioclase plagioclasecrystal crystalmushes mushes(Miller (Millerand andWeiblen, Weiblen,1990). 1990). Thus, Thus, the the rocks rocksof of Nathan's Nathan's have Layered Series representmaterial material (of (of Logan Logan composition?) in the Layered Series may represent composition?) that that was was emplaced emplaced at at several several levels levels in the crust crust in in the initial phases of rifting. Evolution in these disparate chambers would lead to some magmas having unusual the initial phases of rifting. Evolution in these disparate chambers would lead to some magmas having unusual amounts amount's of nxidm ..--- of -.oxides. -.----. It composition similar It isis interesting interestingto to note note that that the the models models produced produced a liquid composition similar to to the the Grand Grand Portage Portage dikes (composition given Green al., 1987) after after35-40% 3540% crystallization 0. (composition given by G reen etetal., crystallization at at 1kb, lkb, roughly roughly equivalent equivalent to that of Unit G. Perhaps theGrand Grand Portage PortageDikes Dikes are arethe thehypabyssal hypabyssalsibling siblingofofthe theplutonic plutonicUnit Unit G 0 seen further inland. Perhaps the seen farther inland. may - F Table 2. Paren t ('am nnsitinn IIwit in M odelling and one result I wt nerrenti MnO MaO Na,O !c22 un!! 1Q2 1122 A1223 1Q fzQs Logan Login 49.0 49.0 3.40 3.40 13.1 13.1 15.6 15.6 0.22 0.22 5.60 7.45 2.52 2.52 1.16 1.16 0.38 40% 53.9 2.49 13.3 15.1 0.25 2.11 7.07 2.96 1.82 0.62 Grand 52.5 Grand 52.5 Portage Portage 2.48 13.4 13.4 13.3 '13.3 0.19 0.19 3.68 3.68 6.72 6.72 3.17 1.79 1.79 0.48 0.48 @1kb Logan composition from from Geul Logan composition Ged (1970). (1970). Grand of 17 Grand Portage Portage isis an average of 17dikes dikes (Green (Greenet al., 1987). 1987). Citedi References Cited: ItH.,1985, U-Pb Davis, D.W. and Sutclift'e, Sutcliffe, RH.,1985, U-Pb ages ages from the Nipigon Plate and and northern northern Lake Lake Superior: Superior: Geological Geological Society of Davis, AmericaBulletin, 96,1572-1579. 1572-1579. America Bulletin, v. 96, of Mines, Mines, Geological Geological of Devon Location: Ontario Geul, J.J.C., J.J.C., 1970, 1970, Geology of Devonand and Pardee Panfee Townships and Stuart Location: Ontario Department of Geul, Report 52p. Rewrt 87, 87.520. RE., Pesonen, and Wilband, Green,k., Bomhocst, Ti., T.J.,Chandler, Chandler, V.W., Mudrey, Mudrey, MJ., Mya-s, P.E., PisaKtt.LJ., Wilband,J .T., 1987, 1987, Mi., Jr., Myers, Li,, aud iC., Bomhorst IT., Region: Evidence Evidencefor forevolution evolutionof of the the Middle Middle Proterozoic Proterozoic Midcontinent Mideontinent Rift Rift in Keweenawan Keweenawan Dykes of the Lake Superior Region: in 289-302. North America, in Halls, North Halls, H.C. KC.and and Fahrig, Fahrig,W.F., W.F., eds., cds., Mafic MaficDyke DykeSwarms: Swarms:Geol. Geol.Soc. Soc. Canada Camda Spec. Spec. Paper Paper 34, 34,289-302. examples of Wieblen, P P.W., Anorthositic rocks of the D Duluth Miller, J.D., Jr. and Wieblen, .W.,1990, Anorthositic ulufliComplex: Complex: examples of rocks rocks formed formed from &omplagioclase plagioclase Miller, 3D., Jr. Petrology, v. v. 31.295-339. 31,295-339. crystal crvstalmush: mush: Journal of Prtrolotv. Trip Guidebook for in Field Tnp Miller, M.,,1995, Gabbroic intrusions M ~ I IJ.D., ~D. JJrJr. and Smyk, St& M 1995,Gabbroic mmisioiis of the the international mieniatid boundary area, in forthe die region: Minnesota Geoloacal Geological Survev Swvey Guidebook geology deposits of of the Midcontinent emloev and ore dcoosits Mdcooement Rift Rift in m the Lake Lake Superior Suoenorrefflon, ~Series e r iNo. e ~20,171-181. 20, ~ o171-181 . USA, In 1996, Layered intrusions Miller, J.D., J.D., Jr. and bley, intmions in in the Duluth Duluth Complex, Complex,Minnesota, Minnesota, USA, in Cawthorn, Cawthoin, KG., ed., Miller, Ripley,EM., EM., 19%. ItO., ed., Layered Intrusions: Amsterdam. Amsterdam, Elsevier, Uvered Intrusions: Elsevier, 257-301. 257-301. Cook County, The geology geology of a portion portion of the the Duluth Duluth Complex, Cook County,Minnesota: Minnesota: Ph.D. Ph.D. dissertation, dissertation.University University ~ a t h a H.D., n . - ~1969, . ~ . , The Nathan, Minneapolis, l9Sp. of Minnesota, Minnesota. Minueawlls. 1980. related mafic mafic intrusions, northeastern J,D., U-Pb ages Paces,J.B. and ~Miller, i e rJ.D.: , Jr., 1993, 1993"Precise Precise U-Pb ages of ofDuluth Dulufli Complex and related intrusions, northeastern Paces, Minnesota: Minnesota:Geochronological Geochronologicalinsights insightstotophysical, physical,petrogenetic, petrogenetic,paleomagnetic paleomagncticand andtectono-magmatic tectono-magmaticprocesses processes associated associated Midcontinent Rift System: of Geophysical GeophysicalResearch, Research,v.v,98,l3,997-14,013. withthe with the 1.1 1.1Ga MidcontinentRift System:Journal of 98,13,997-14,013. . I . - 25 - �INTRUSIONS OF OF THE THE LAKE LAKE SUPERIOR SUPERIOR REGION: REGION: TARGETS TARGETS FOR FOR SMALL MAFIC INTRUSIONS TITANIUM EXPLORATION KARKKAINEN, Nub, Geological -E N, Niilo, Geological Survey Survey of Finland, 02150 Espoo, Espoo, Finland; Finland; BORNHORST, BORNHORST, Theodore, J., Department of Geological Engineering and Sciences, Michigan Technological University, University, Houghton, oughto on, MI MI 49931 4993 1 - magmatic ilmenite deposits are often in or closely associated with Globally, high-grade magmati anorthosite complexes. Large layered mafic intrusions host Ti-rich magnetite in Fe-Ti oxide anorthosite rocks. There There are are many mafic intrusions intrusions throughout throughout the Lake Superior Superior region that range in in age age from Archean to Proterozoic. However, most of these intrusions are not associated with However, many are are relatively relatively small. small. Despite these characteristics, small mafic anorthosite complexes and many amounts of Ti, based intrusions of the Lake Superior Superior region have the potential to host significant amounts on analogy with a recently documented documented occurrence occurrence in in Finland. Finland. The Finnish Koivusaarenneva Koivusaarenneva gabbro is a small mafic intrusion, not associated with an anorthosite complex, that contains inferred resources of 44 Mt with 15 % ilmenite and 5% V-rich magnetite 50m (an (an additional additional 44 44 Mt Mt are arepossible possible to to aa depth depth of of magnetite (0.7 (0.7 wt. wt. % % V) V) to aa depth depth of of 1150m 300m). The Thefeasibility feasibilityof of mining mining this this ore ore body body is is currently currently being investigated by a Finnish mining mining company. company. Koivusaarenneva gabbro is an elongated sill-like intrusion, 0.5 to 1 km thick and 3 The Koivusaarenneva km long long parallel to strike. strike. The Theintrusion intrusionproduces produces aa 44 mGal mGal gravity gravity anomaly anomaly and a clear clear NE-SWNE-S oriented aeromagnetic anomaly anomaly in the low-intensity low-intensity background. The intrusion was emplaced at 1881 Ma Ma into tonalitic bedrock and is part of a gabbro province province interpreted to to have formed in tensional zones zones in in the the vicinity vicinity of of or or marginal to to convergent convergent plate boundaries. boundaries. The The Koivusaarenneva gabbro is part of a 12 km long chain of intrusions that were emplaced along along a Koivusaarenneva 12 krn NE-SW oriented oriented fault fault zone. The The intrusion intrusion is is mostly composed composed of of modally modally layered layered mediummediumgrained and metamorphosed metamorphosed gabbro and gabbronorite. The magmatic layers have been tilted to a subvertical orientation and faults faults segment segment the intrusion. The intrusion is divided into into three three zones zones on the basis of geochemistry geochemistry and petrography. Fe-Ti oxide-rich layers are common in the lower middle zones. ratioisisconstant constantfor forall allrock rocktypes types in in the the lower zone at and middle zones. The TheTi02/Fe2O3TOT Ti02/FezOsToT ratio about 0.2. The Themiddle middlezone zonecontains containsthe the 22 km km long long ilmenite ilmenite ore body that grades between 8 and an ratioofofthe themiddle middlezone zoneisisbetween between0.25 0.25and and0.50. 0.50. The The upper upper 48% ilmenite. ilmenite. The TheTiO2/Fe2O3TOT Ti02/Fe203ToT ratio zone consists consists of P-rich gabbro and leucogabbro. gabbro The genetic genetic model model of the intrusion intrusion and ore body begins with primary tholeiitic tholeiitic mafic mafic magma emplaced emplaced in a deep deep magma chamber at or near the base of the crust. In the deep chamber, crystal-liquid crystal-liquid fractionation, fractionation,under under conditions conditionsof ofvery verylow lowf02, fm, generated Ti-enriched parent magma averaging about 3.3% TiOz. Ti02. This parental magma was was successively successively injected injected into into each each of of the three zones zones of the the intrusion. intrusion. Variation Variation within the lower lower and upper zones is consistent consistent with with closed-system closed-system crystal-liquid crystal-liquid fractionation fractionation of two separate separate batches of magma magma from the deep deep chamber. chamber. The middle zone contains the voluminous voluminous ilmenite ore. The overall composition of nonnon non-mineralized gabbro mineralized gabbro from the middle zone is compositionally compositionally similar to non-mineralized gabbro 26 �from the lower zone, however, the weighted average composition composition of the middle zone is Fe than than the the weighted weighted average averagecomposition compositionof ofthe thelower lowerzone. zone. The considerably higher in Ti and Fe volume of magma magma in the the middle middle zone zone is is far far too small small to yield the the large large mass mass of of ilmenite ilmeniteunless unless the parent magma had extreme extreme Ti and Fe. Instead, the extreme excess excess of Ti and Fe Fe in in the the middle middle zone can be explained explained by a parent magma with elevated, but rather normal Ti and Fe Fe (like (like the the lower and upper zones) that flowed through the partly crystallized magma chamber. After an zones) crystallized chamber. After an oxide-rich immiscible immiscible liquid was was extracted from the magma this this dense dense material material sank sank to to the the floor floor of the shallow magma chamber to form a Fe-Ti oxide rich matrix between a silicate framework. shallow magma chamber form oxide silicate framework. The Ti and Fe depleted depleted magma magma was then replaced by a new batch of parent magma magma and and so so on. on. . The middle middle zone zone represents represents a channel channel for for magma flow with multiple multiple episodes episodes required required for for accumulation accumulation of the large mass mass of of oxides. A similar similar magma magma flow flow through through model model has has been been proposed to generate generate gabbro-hosted gabbro-hosted Ni-POE Ni-PGE sulfide sulfide mineralization mineralization at Norilsk, Norilsk, Russia Russia (Naldrett (Naldrettet et al., 1996) 1996) and Voisey's Bay, Canada Canada (Evan-Lamswood (Evan-Lamswood et al., 1998). 1998). an For Ti-deposits in small mafic intrusions, an open magma flow through system system is is an essential essential genetic genetic component component to produce produce economic economic size size deposits. Continuity Continuity of of gabbro gabbro intrusions intrusions as a chain or along a fault zone is a favorable geologic geologic setting. setting. An An overall overall elevated elevated Ti Ti content content of of non-mineralized non-mineralized gabbros gabbros is is another another favorable favorable characteristic characteristic indicating elevated elevated Ti in in the the parent parent magma. Small mafic intrusions of the Lake Superior region can be tested for potential to Small mafic intrusions of the Lake Superior can tested for potential to host host Ti Ti resources using an an exploration exploration model based on the Finnish Koivusaarenneva Koivusaarenneva gabbro gabbro intrusion. intrusion. 27 �ADDITIONAL PALEOMAGNETIC STUDIES OF OF A A PROTEROZOIC PROTEROZOIC DIABASE DIABASE DIKE, PIFTIER AND ANDIRWIN IRWINTOWNSHIPS, TOWNSHIPS,LAKE LAKE NIPIGON NIPIGON DISTRICT, DISTRICT, ONTARIO IN PIFHER Kean, W. F., Department Department of of Geosciences, Gwsciences, University University of of Wisconsin-Milwaukee, Wisconsin-Milwaukee, Milwaukee, Milwaukee, WI WI 53201, and Luther, F., Geology Geology Department, UW UW Whitewater, Whitewater, Whitewater, Whitewater, WI WI 53190 53190 An approximately 50 m wide porphyritic diabase dike outcrops outcrops in and Pither in western westernIrwin Irwinand Pier Townships in the Nipigon district and is locally known as greenspar. The dike has a characteristic Townships the Niigon district and is locally known as greenspar. characteristic outcrop as a result of saussaritized greenish mottled appearance in outcrop saussaritizedplagioclase glomerophenocrysts in in aadiabase diabasegroundmass groundmass(Luther, (Luther, 1997). 1997). The dike strikes due north and dips dips vertically, and is is found foundas assegments, segments,off-set off-setby byeast-west east-westfaulting faulting(Mackasey, (Mackasey,1975). 1975). There There are are no radiometric this rock or radiometric dates dates on this or associated associated rocks, rocks,although, although,itit isiscut cutby by aalarge largemiddle middle or or late late Proterozoic sill Proterozoic sill in Irwin Township (Mackasey, 1975). 1975). We previously reported reported palco magnetic studies on on four sites f from (Thomas and paleomagnetic rom this area (Thomas others 1998). Five additional sites were collected in the summer of 1999, primarily others 1998). Five additional sites were collected in the summer of 1999, primarily from from locations locations Pither Township. The The nine nine sites sites span span approximately approximately27km. 27km.of ofthe thedike. dike. Samples Samples from each in Piflier location were subjected suljected to (A.F.) and thermal demagnetization demagnetization. The to both both alternating alternating field (A.F.) The samples samples demagnetization temperatures show one one primary magnetic direction which is removed at demagnetization temperaturesof of 5100 570 C. A.F. A.F. demagnetization demagnetizationof ofsamples samplesup up to to60 60mT, mT,also alsogives givesonly onlyone onedirection directionof ofmagnetization.. magnetization the magnetometer the samples are quite viscous and require a long wait time in the However, the between measurements. All All but two two locations locationsshow shownormal normal polarity polarity with with northwesterly northwesterly declinations (200°-300°) and inclinations of 40° to 80°. One site in southern declinations (200"-300") and inclinations 40" to 80'. One site in southernPifher PifterTownship Township appears 100°, and appears to to be be reversally reversallymagnetized magnetizedwith withdeclinations declinationsof of90° 90"totolOOo, andinclinations inclinationsof of -75°. -75'. The The southern southern most location near Beardmore produces producesinconsistent inconsistentresults. results. Overall, the themagnetic magnetic directions directions are are consistent with Keweenawan paleomagnetic paleomagnetic directions directions in the Lake Superior SuperiorRegion. Region. References References Luther, F., 1997, Pither. 1997,The The Petrology Petrology of of Greenspar: Greenspar: A A Proterozoic Proterozoic Porphyritic Diabase Dike; Pifher and Irwin Townships, Lake Nipigon Nipigon District, District, Ontario., Ontario., [abstract]: [abstracti: Institute on Lake Superior Geology Proceedings, Proceedings,v.v.43, Part l,p. 43, 1,p. Macjçasey, W.O., 1975, Gwlogy Geology of of Dorothea, Dorothea, Sandra, and Irwin Townships, District of Thunder Mackasey, W.O., Bay; Ontario division of Mines, rpt rpt 122 2294, 83 p. 122 with map 2294,83 Kean, W., W.,and and Luther, Luther, F., F., 1998, 1998,Paleomagnetic Paleomagnetic Studies Studiesof ofaaProterozoic ProterozoicPorphyritic Porphyritic Thomas, C., Kean, Diabase Dike, Pifher Nipigon District, District, Ontario.,[abstract]: Ontario.,[abstractj: Institute P i i and Irwin Townships, Lake Nipigon Institute on on Lake Superior Part 1 l,p. ,p. 119. 119. Superior Geology Proceedings,v.44, Part 28 �PETROGENESIS PETROGENESIS OF OF THE THE MIDCONTINENT MIDCONTINENTRIFT RIFTGRANOPHYRIC GRANOPHYRICCOMPLEXES COMPLEXESOF OF NORTHERN NORTHERNMINNESOTA MINNESOTA ---- - - Kennedy, & Wirth, Kennedy,Bryan Bryan C., C., (bkennedy@macalester.edu) (bkennedy@macalester.edu) & Wirth,Karl Karl R., R., Geology Department, Macalester College, St. Jeff D., St. Paul, MN (wirth@macalester.edu); Vervoort, Vervoort,Jeff D., Department Department of Geosciences, University (vervoort@geo.Arizona.edu) University of of Arizona, Arizona, Tucson, Tucson, AZ AZ (vervoort@geo.Arizona.edu) The The hypabyssal hypabyssal granitic granitic rocks rocks of northeastern Minnesota, Minnesota, commonly commonly referred referred to to as as granophyres, granophyres, are are an an important important component component of of the the Midcontinent Midcontinent Rift Rift (MCR) (MCR)of of northeastern northeastern Minnesota. Minnesota. InInthis thisstudy study we we examine examine eight eight intrusive intrusive complexes complexes associated associated with the the rift, rift, including including detailed detailedtransects transects across across the the Misquah Misquah Hills Hills and and Greenwood Greenwood Lake Lake granophyres. Evidence Evidence from petrographic, major and trace element element data data suggest suggest a combination of of magma magma mixing, chemical differentiation, and partial melting melting of of MCR MCR and and older granophyrecomplexes. complexes. older crust crust to to form form the thegranophyre The in 30to to150 150km km in The granophyre granophyre complexes complexes are generally concordant intrusions intrusions that thatrange rangefrom from 30 surface area and are up up to to 1000 meters metersthick. thick. The The complexes basaldiorite, diorite, monzodiorite, monzodiorite, complexes typically consist of basal and quartz monzodiorite monzodiorite and and upper uppergranite graniteand andgranodiorite. granodiorite. The The contact contact zones zones between the mafic and felsic rocks are are compositionally compositionally and and structurally structurally heterogeneous; heterogeneous; evidence evidence of ofmutual mutual intrusive intrusive relationships relationships between between the mafic mafic and and felsic felsic rocks can often be found within the the same same outcrop. outcrop. Porphyritic Porphyriticrhyolire rhyolite overlies granitic of the the complexes complexes (e.g., (e.g., Misquah Misquah Hills, Hills,Greenwood Greenwood Lake, Lake, Eagle EagleMountain, Mountain, granitic rocks rocks of several of and Lima Lima Mountain). Mountain). Thus Thusfar, far,only onlyone oneof ofthe thecomplexes complexeshas has been been dated dated (Swamper (SwamperLake=Greenwood Lake=Greenwood Lake granophyre, granophyre, 1107 1107 Ma Ma ±Â1.1, reversed magnetic polarity; Davis and Green, 1.1, reversed magnetic polarity; Davis Green, 1997); 1997);the the other othercomcomplexes are undated but are generally considered considered to to have have normal normal magnetic magnetic polarity, polarity,with withthe the exception exception of of the the Misquah MisquahHills Hillsbody bodywhich whichisispossibly possibly reversed. reversed. The monzodiorite, monzodiorite, monzodiorite, and diorite) diorite) are The mafic maficrocks rocks of the complexes complexes (e.g., quartz monzodiorite, are distindistinguished by by abundant (15-35 vol.%) significant (1 (1-3 vol.%) apatite. apatite. The -3 vol.%) Thefelsic felsic vol.%) interstitial pyroxene and significant rocks sodic plagioclase plagioclase (30-40 (30-40 vol.%), vol.%), orthoclase orthoclase (25-35 vol.%), and quartz (20-30 (20-30 vol.%). rocks are composed of sodic vol.%). Plagioclase Plagioclase commonly exhibits exhibits normal normal and andoscillatory oscillatorycompositional compositionalzoning; zoning;many manyplagioclase plagioclasegrains grainsare are mantled mantled by by thin thinrims rimsof ofsodic sodicplagioclase. plagioclase. Anhedral Anhedral pyroxene pyroxene and andsmall smallFe-Ti Fe-Ti oxides oxides make make up up less less than than 10% 10% of the rock. All All of of the the rocks rocks in in the the complexes complexes are characterized characterized by granophyric intergrowths of alkalifeldspar feldspar and and quartz. quartz. Intergrowths Intergrowths are are interinter_________________________________________________ 10.0 stitial or more commonly .. stitial between between plagioclase plagioclase or more commonly radiate radiate from from euhedral euhedral plagioclase phenocrysts. phenocrysts. -quartz monzodiorite, monzodiortie, and diorite n monzodiorite, diorite • 8 0 lntergrown quartz ranges from coarse and Intergrown quartz ranges from coarse and mimioo -granophyric -granophyricgranite graniteand and granodiorite granodiorite 7.0 crographic crographiccuneiforms cuneiformsto to fine fine and andradially radiallygragranophyric $ 6.0 6.0 o O nophyricshapes. shapes. The granophyre complexes Thegranophyre complexesdisplay displayaa wide wide 5.0 5Q5.0 0 S silica ino 0 o b $ ' % As %). As inSiO2 (47-76 wt range of range of Si02 (47-76 wt %). cc$°°o 4Z 4.0 4.0 creases, TiOz, MnO, MgO, CaO, and creases, 1107, Fe203, CaO, and 33.0 0 2 0 increases. There P20sdecrease, whereas K P205 K20 There 20 2.0 • m • hare notable compositional "gaps" in lincompositional "gaps" in the lin• .^ ~ ~ 10 l . •~ % ear trends on Harker variation variation diagrams diagrams be0.0 tween the the mafic mafic and and felsic felsic portions portions of each each of of 65,0 55.0 60.0 55.0 60.0 65.0 70.0 75.0 50.0 the complexes (Figure 1). Although rocks in (Figure 1). Although rocks S (w - .i n- 7 (wt,%) .. r... % .,l Si02 the lower complexes have have relalower portions of the complexes relaFig. II - K20 K 2 0(wt. (wt.%) %) versus versusSi02 (wt.%) %)diagramfor diagramforall allsamples Si02 (wt. samples tively low Si02 (47-62 wt. /o) most are tively Si02 (47-62 wt.%) are silica silica illustrating the compositional compositional from the granophyre ganophyre complexes, complexes, illustrating over-saturated over-saturated and all but two two samples samples congap between the rocks of ofthe the intrusions. intrusions. Note the mafic and felsic felsicrocks Note tam normative quartz. The granitic rocks tain The granitic rocks in trend of the major element element variation variation with increasing the linear trend the the upper portions of the complexes are SiO the upper portions of the complexes are SiO z2SiOz.Full Fulldata dataset setin inKennedy Kennedy (2000) (2000) Si02. 1 - ~ Za?aj o & +',PQJ .-• •• ~ - - \ . . . 29 �rich (66-76 wt.%), and and are are slightly to metaluminous metaluminous to slightly 2.0 2.0 1.8 0 1,8 peraluminous. peraluminous. The The mafic mafic and and felsic felsic 1.6 0 - rocks plot along linear — linear trends trends on on most most —— F 1.4 incompatible incompatible trace trace element elementdiagrams diagrams .975 0 0 (e.g., U, U, Nb, Ce, (e.g., Ce, and and Zr Zr vs. vs. SiO SiO2); 2); Q 1.2 0 LZ .950 compositional compositional"gaps" "gaps" between between the the mamaI.0 • -quartz -quartz monzodiorite, monzodiorite,monzomonzofic evident in fie and and felsic felsic rocks rocks are also evident in 0.8 diorite, and diorite these these plots. plots. The Themafic maficand andfelsic felsicrocks rocks o granophyric granite and 0.6 0-6 from from all of the granophyre granophyre complexes complexes granodiorite exhibit -mixing 0.4 trend; exhibit negative negative Nb-anomalies Nb-anomalies on on 0.4 mixing trend; values values at at tick tick ,— marks indicate the fraction of multi-element variation variation diagrams. diagrams. o,7 marks indicate the fraction of 0.2 felsic component component The Th/Nb and The small small variation variation in in the the Th/Nb and ______________ 0.0 M 50.0 £00.0 150.0 200.0 250.0 M 50.0 100.0 150.0 200.0 250.0 Ce/Nb ratios between the the mafic mafic and Ce/Nb felsic rocks suggests that the source of S iO 2/C aO felsic rocks that the source SiOzICaO the hyperbolic Fig. Fig. 22 - KzO/Fe203* KzO/FeaO3* versus versus SiO2/CaO SiOdCaO diagram showing the hyperbolic the the Nb Nb depletion depletionisis common common for both mixing trend for all samples from the granophyre concordant mixing trend for all from the granophyre complexes, concordant the mafic and felsic rocks. the mafic and felsic rocks. withhmixing mixing model. The Themixing mixingmodel model isis based based on on two two end endmember member Although , ~ ~ the the~major ~ ~ ~with majorh element parental compositions (triangles), Sonju Lake (M) and parental compositions (triangles), the intrusion (M) and an an variation variation might mightbe beexplained explainedby bycryscrysaverage of the three most felsic granitic samples (F). (F). The dashed line isis The dashed line average three most tal tal fractionation fractionationofofaatypical typicalMCR MCRmamathe the NSVG the mixing model with the NSVG olivine olivinetholeiite tholeiiteasasthe themafic maficcompowmpofic fie component, component, itit seems seems unlikely that nent, nent,which which isis not not concordant concordantwith with the the data. data. fractionation fractionationofofmafic maficmelts meltscould couldacaccount 10.15% of the intrusive rocks countfor for the theformation formationof of this this large large volume of granitic rock (approximately 10-15% of SiO 27(e.g., (e.g., of the the MCR MCR exposed exposed in northeast northeast Minnesota). Minnesota). Furthermore, Furthermore,on onplots plotsof ofmajor major elements elements versus versus SiO K20; change during during thetrend trendof ofthe thedata datashould shouldchange changein inslope slope as as the the fractionating fractionatingassemblages assemblages change K20;Figure Figure 1) 1) the crystallization. of SiO SiO 22 concentrations concentrations which crystallization. Instead, Instead, the thedata dataplot plotalong alonglinear lineartrends trends over over aa wide range of may may indicate mechanical mixing. mixing. On Ondiagrams diagrams of of major element ratios, the themafic maficand andfelsic felsic rocks rocks plot along vs.SiOz/CaO, SiO2/CaO,Figure Figure2). 2). These These trends trends can be modeled modeled by along hyperbolic hyperbolic trends trends (e.g., (e.g., K2O/Fe2O3* K2O/FezOj* vs. mixing of a mafic mafic (Miller (Miller &Chandler'scomposite & Chandler's composite Sonju Sonju Lake intrusion intrusion parental parental magma (1997)) (1997)) and and felsic felsic (average (average of the the most most evolved evolved samples samples from the granophyre complexes) end-members. IfIf aa more more primitive primitive olivine olivinetholeiite tholeiitefrom fromthe theNSVG NSVGisisused usedas asthe themafic mafic end end member, member, the the resulting resulting model does not fit fit the the data data for for the the granophyre granophyre complexes. complexes. Samples Samplesthat thatdo donot notplot plotalong alongthis thismixing mixingline linelikely likely evolved evolved from mixing products SiO2/CaO z/CaOand andK1O/Fe2O3. K20/Fe203. productsby by fractional fractionalcrystallization, crystallization,which whichwould wouldincrease increaseSiO An A n origin origin for for the the granophyre granophyre complexes complexes by mixing is consistent with the field relationships relationships and and linear trends trends on on major major element elementdiagrams. diagrams. However, However,although although aa combination combinationof ofmagma magma mixing mixing and and fracfractionation tionationmay may explain explainthe theorigin originof ofthe thegranophyre granophyrecomplexes, complexes,itit does does not not explain explainthe thesource sourceof of the thelarge large volume of felsic end-member necessary for mixing. Nd isotope data from the granophyre complexes volume of Nd isotope data from the granophyre complexessugsuggest that that the thefelsic felsic component component may may be be the the result result of of fractionation fractionation or or melting melting of of contemporaneous crustal materials (Vervoort, (Vewoort, this volume). Further Further examination examinationisisneeded neededto todetermine determinean anultimate ultimatesource sourcefor for the the felsic material material and and it's it's relationship relationshiptotothe thegenesis genesisof ofthe thegranophyres. granophyres. * ,-- - References References Davis, Green, J. C. 1997. North American 1997. Geochronology Geochronology of the North American Midcontinent MidwntinentRift Riftininwestern westernLake LakeSu Su Davis, D. W. & Green, perior perior and andimplications implicationsfor forits itsgeodynamic geodynamicevolution, evolution,Can. Can.J.J. Earth EarthSci. Sci.34: 34:476-488 476-488 Kennedy, Kennedy, B.C. 2000. 2000. Petrogenesis Petrogenesisofofmidcontinent midcontinentrift riftgranophyres: granophyres:evidence evidencefrom fromgeochemistry geochemistryof ofKeweenawan Keweenawan granitic northern Minnesota. MacalesterCollege, College, graniticigneous igneous complexes complexes of northern Minnesota. Senior SeniorHonors HonorsThesis, Thesis,Macalester Saint SaintPaul, Paul,MN. MN. Miller, J.D. & Chandler, V.W. Miller,J.D. &Chandler, V.W. 1997. 1997.Geology, Geology,petrology, petrology,and andtectonic tectonicsignificance significanceofofthe theBeaver BeaverBay BayComplex, Complex, northeastern, 3 12. northeastern,Minnesota. Minnesota.Geological GeologicalSociety SocietyofofAmerica AmericaSpecial SpecialPaper Paper312. 30 �A A POSSIBLE POSSIBLESUDBURY SUDBURY EJECTA EJECTA LAYER LAYER IN IN THE THEGUNFLINT GUNFLINT FORMATION, FORMATION,NORTHWESTERN NORTHWESTERNONTARIO ONTARIO Stephen Thunder Bay, Ontario, Stephen A. A. Kissin, Kissin,Department Departmentof ofGeology, Geology, Lakehead University, Thunder Ontario, Makoto International University, Makoto Okamoto, Okamoto,Faculty Facultyof ofEconomical Economical Sciences, Sciences, Kyushu International University, Kitakyushu, Kitakyushu, Japan, Japan,William William 0. D.Addison, Addison,Thunder ThunderBay, Bay,Ontario Ontarioand andGreg GregR. R.Brumpton, Brumpton, Thunder ThunderBay, Bay, Ontario Ontario Previous Previous studies studiesrevealed revealed that that the the Gunflint Gunflint lapilli lapilli tuff tuffunit, unit, located located in in the the Kamistiquia KamistiquiaGorge Gorgenear near Thunder Bay, Ontario, is unlikely to represent an ejecta layer from the Sudbury impact event. Thunder Bay, Ontario, is unlikely to represent an ejecta layer from the Sudbury impact event. Euhedral unit have 878±2Ma (Fralick tuffunit haveyielded yieldedaadate dateof of11878i2Ma (Fralicket et al., al., Euhedralzircons zirconsextracted extractedfrom fromthe thelapilli lapillituff 1998) 1998) presumed presumed to to be be the the age age of of sedimentation sedimentation based based on on aa volcanic volcanic source source for for the the zircons, zircons,too tooold old to 4Ma (Krogh to be be associated associatedwith withthe theSudbury Sudburyevent eventatat1836±1 1836il4Ma (Kroghet et al., a1.J1984) 984) However, However,aadistinct distinctash ash layer higher in section has been layer approximately approximately lOOm loom stratigraphically higher been recently recently discovered discovered and and investigated. investigated. A A grey greyash ashlayer layer11.5 11.5cm cm thick thick isis exposed exposed in in two two locations locationson on the southern southernside side of of the the Kaministiquia Kaministiquia Gorge. Gorge. The Thelayer layerisiscomprised comprisedmostly mostlyofoffriable fiableillite illiteand andmontmorillonite, montmorillonite, but but separation separation of of particulate mudball lapilli, lapilli, crystal crystal fragments fragmentsand and particulatefractions fractionsrevealed revealedthe thepresence presenceof of lithic lithic fragments, fragments, mudball green spherules spherules with a glassy appearance. The The latter latter were were found to be glauconite, glauconite, which also has has been described The crystal crystalfragments fragments described in in the the Gunflint Gunflint lapilli tuff unit (Hassler & Simonson, 1989). The are are mostly mostly pure pure potassium potassium feldspar, feldspar, with with minor minor quartz, quartz, calcite calcite and and various various other other minerals. minerals. The proximal The glauconite glauconitepellets pelletsand andpotassium potassiumfeldspar feldsparclasts clasts have have been been interpreted interpreted as as indicative indicativeof of aaproximal submarine submarine volcanic vent (Hassler & Simonson, 1989). In Inparticular, particular, the the sodium-free sodium-free potassium potassium feldspar feldspar clasts have have been bee; interpreted interpreted as as the theproduct productofofmetasomatic ietasomatic replacement replacement of i f igneous igneous plagioclase. Also present are quench-textured basaltic clasts and occasional devitrified vesicular plagioclase. Also present are quench-textured basaltic clasts and occasional devitrified vesicular glass glass fragments. fragments. However, However,large, large,unstrained unstrainedquartz quartzclasts clastsand and fresh fresh plagioclase plagioclase clasts clasts suggest suggest that aa somewhat somewhat more more felsic felsicvolcanic volcanic source sourcehas has also alsocontributed contributedto to the the particulate particulateassemblage. assemblage. Analyses enclosing shales Analysesof of samples samplestaken taken at at various variousintervals intervals in in the the layer, layer, as as well as as of the enclosing shales at one of of the locations, locations,revealed revealed the the presence presenceof of anomalous anomalousJr Ir (1.9 ppb) ppb) as well as other other PGEs PGEs and and Au. Au. On On the Ni are in the the ash ash layer layer as as compared compared the other other hand, hand, the the chalcophiles chalcophilesCo, Co,Cr Crand andNi are significantly significantly depleted depletedin to which have to the enclosing enclosing shales. AAstrong strongenrichment enrichmentin in Zr Zr indicates indicates the presence of zircons, which have opportunitiesfor for dating dating of of the the material been been separated separated and and should should again again provide provide opportunities material as well well investigation for shock features. features. Shock Shock features features in in the the particulate particulate fraction have not so far far been been identified, and the depletion depletion of of chalcophiles chalcophiles is contrary contrary to expectations expectations in an an ejecta ejecta layer layer(e.g. (e.g. Hildebrand, 1993). However, However, Simonson Simonson et et al. al. (1998) (1998) noted noted that that the the Acraman Acraman impact impact layer layer in in Australia Australia lacks lacks this this enrichment. enrichment.This Thislayer layeras aswell well as as aa layer layer seen in the Hammersley Basin can be explained explained as as the result of submarine impact. As As the the Sudbury Sudbury Structure Structureis is believed to have formed formed in in aa marine marine shelf shelf environment, environment, the the possibility possibilityof of an an impact impact origin origin for for the the Gunflint Gunflintash ash layer layer remains remains open. open. To To date, date, however, however, the evidence evidence is in favor favor of of aa volcanic volcanic source source for for the the ash ashlayer, layer,but but geochronology geochronology will will be be needed neededin inorder orderto to exclude excludethe the possible possible impact impact origin originof of the the layer. layer. 31 �References References Kissin, S.A. Fralick, P.W., Kissin, S.A. and Davis, D.W. (1998) (1998) The age and provenance of the Gunflint Gunflint lapilli lapilli Inst. tuff. Program and Abstracts, 44th Lake Superior Geol, Minneapolis, 66-67. Program and Abstracts, 441hInst. Minneapolis, 66-67. vocaniclastic strata in two Hassler, S.W. and Simonson, B.M. (1989) Deposition and alteration of vocaniclastic Proterozoic iron-formations in Canada. Can. J. Earth Sci. 26, 1574-1585. 1574-1585. lare, early Proterozoic Cretaceous/Tertiary boundary boundary impact impact (or (or the the dinosaurs dinosaurs didn't didn't have a Hildebrand, A.R. (1993) The CretaceousITertiary Roy. Astronom. Astronom.SOC. Soc.Can. Can.g, $, 77-118. chance). J.J. Roy. 77-1 18. Krogh, T.E., T.E., Davis, D.W. and Corfu, F. (1984) Precise U-pb U-pb zircon and baddeleyite ages for the Sudbury area, -446 in The Deposits ofthe of the Sudbury Sudbury Structure, Sudbury area, p.431 p. 43 1-446 The Geology Geology and Ore Deposits Structure,edited editedby by E.G. E.G. Pye, A.J. Naldrett and P.E. Giblin, Ont. Geol. Surv. Spec. Vol. 1, 6O3p. and P.E. Giblin, Ont. Geol. Surv. Spec. Vol. 1 , 6 0 3 ~ . Reeves, S. S. and Hassler, S.W. (1998) anomalybut but Simonson, B.M., Davies, Davies, D., Wallace, Wallace,M., Reeves, Simonson, B.M., Hassler, S.W. (1998) Iridium Iridium anomaly nor shocked quartz quartz from fromLate LateArchean Archeanmicrokrystic microkrysticlayer: layer:Oceanic Oceanicimpact impact ejecta? Geology , ejecta? Geology 2 , 1 19595198. 198. 32 �COMMINUTION COMMINUTION AND AND DILUTION DILUTION OF GLACIAL GLACIAL INDICATORS: INDICATORS: RATE ESTIMATES ESTIMATES FROM FROM FIELD FIELD DATA DATA LARSON, LARSON, Phillip Phillip C., C., and and MOOERS, MOOERS, Howard D., Department D e p m e n t of Geological Sciences, University of Minnesota,Duluth, Duluth,MN MN55812, 55812,plarson2@d.umn.edu plarson2@d.umn.edu Minnesota, Introduction: Introduction: Tracing Tracing glacial glacial indicator indicator trains has long long been been recognized recognized as as being being fundamentally fundamentally a problem problem of of interpreting of an an indicator indicator with with increasing increasingtransport transportdistance distancefrom fromits itssource, source. The interpreting the diminishing diminishing concentrations concentrations of dispersal dispersal pattern of of an an indicator indicator is is aa function function of of the the processes processes of dilution dilution and comminution acting on that indicator indicator during during transport. transport, Numerous Numerousstudies studieshave haveestablished establishedempirically empiricallythat thatdispersal dispersalpatterns patternstypically typicallytake a ethe theform formofofan an exponential exponential decay curve. However, However,while while an anindicator indicator ideally ideally comprises comprises all debris debris with with aa particular particular lithologic lithologic or or geochemical geochemical signature signature derived from a unique source, source, in practice most indicator studies examine only a portion portion of of the the size sizefractions fractionsof ofaatill. till. This This approach approach precludes precludes precise precise quantification quantification of the the systematics systematics of of indicator indicator transport, transport, ininparticular particular quantification quantification of dilution dilution and and comminution comminution rates. This Tbis is due due to to aanumber numberofoffactors; factors;previous previousindicator indicatortracing tracing studies studies have have often often been been limited limited to to examination examination of of only only aa portion of the size size fractions containing containiig an indicator, and in in many many cases cases recognition recognition of of aa unique unique indicator indicator derived derived from from aa specific specific bedrock bedrock source source has has proven proven difficult. dificult. The Thelack lack of due to to dilution (largely a function of specific specific data data relating relating the the relative relative changes changes in in indicator indicator concentrations concentrations due dilution (largely function of interaction interaction with the bed) bed) and and comminution comminution (largely (largely a function function of the the material material properties properties of of the tbe indicator) indicator) have have precluded precludedsatisfactory satisfactoryquantitative quantitativemodeling modelingofofglacial glacialdebris debristransport. transport. The The present present study study attempts attempts to address address these these questions questions by examining examining dispersal dispersal of clasts derived from from aa quartz-epidote District, Minnesota. Minnesota. Bedrock qum-epidote altered basalt unit in the Vermilion District, Bedrock within the study area consists consists of of aa metavolcanic-dominated E-W. Glacial Glacial drift in the area area isis thin thin (0-10 (0-10 m), m), and and metavolcanic-dominated greenstone belt belt striking striking roughly roughly E-W. records advance moving moving from from the the W NNE. records aa single single advance advance of the Rainy Rainy Lobe, with the last glacial advance E . Samples Samples were were collected from basal basal tills, tills, and screened to separate separate ibree three adjacent adjacent size size fractions fractions(1-2, (1-2,2-4, 2-4, and and 4-16 4-16 mm). mm). The collected from screened to The quartz-epidote altered basalt basalt indicator indicator is is visually quartz-epidote altered visually distinct distinct and was was easily easily separated separated from from each eachsize sizefraction; fraction; concentrations represent mass proportions, proportions. A A transport transport distance distance for each each sample sample was was calculated calculated by measuring measuring the the distance distance from from each eachsample samplelocation locationalong alongthe theflow flowpath pathto tothe thesource sourcearea. area. Dispersal: Dispersal: The The concentration concentration of an an indicator indicator in in aa particular particular size size fraction fraction of of till till is is aa function function of of the the change change in in concentration due due to to dilution, dilution, and and the the change change inin concentration concentration due due to to comminution. comminution. The The relationship relationship concentration between dispersal, dispersal, dilution, dilution, and and comminution comminution can can be be between expressed expressedas: as: CD1SJ = (I) Grs~ = CDm CDTLCCOM ' CCOM (1) C Dispersal Dispersal curves cuwes for for the the indicator indicator inineach eachparticle particle 0 size size fraction fraction in in the the study study area areawere weregenerated generatedby byplotting plotting C indicator indicator concentration concentrationagainst againsttransport transportdistance distance(T, (T,inin1cm) !an) 5 of the largest (Fig, 1). I). Concentrations Concentrations of largest clasts clasts (4-16 (4-16 mm) mm) C (Fig. 0 decreased with transport transport distance distance at the the fastest fastest rate, rate, while while 0 decreased medium-sized (2-4 (2-4 mm) mm) clast clast concentrations concentrations decreased decreased at aa medium-sized rate. Dispersal Dispersal of of the the smallest smallest clasts clasts (1-2 (1-2 mm) mm) has has aa lower rate. curious km curious form; form;concentrations concentrationsincrease increaseduring duringthe thefirst fust—5 -5 km transport, then then decrease decrease with with increasing increasing transport transport of transport, 0 4 12 distance. distance. 3 Dilution: Dilution Dilution reduces reduces indicator indicator concentration concentration by by Tmnsporl Distance Distance(km) (km) Dilution: eroding erodiig and incorporating incorporating material from from the the bed bed downflow downflow Figure I . Dispersal Dispersal Curves Cuwes Figure 1. from the mdicator indicator source. source, AAdilution dilutioncurve curveshould should ideally ideally QE doler Allered Basalts Quarlz-Epidote Altered Basalts take a e the form fonn of of aapower power function, function, with with the the exact exact slope slope of of the dilution dilution curve curve at any any given given point point in in space space and and time time aa the function function of of distance distance from from the the source source and and the instantaneous instantaneous rate of erosion and entrainment. These 'hese are aredependent dependent on on a number and the the basal basal thermal thermal regime. regime. Deviations number of of variables, variables, including including bed bed roughness, roughness, bed composition, composition, and Deviations of of aa Trans - 33 �dilution curve from from a power function of represent deviations deviations from from uniform uniform conditions. conditions. However, over relatively short distances on a bed of uniform composition it is short distances on a bed of uniform composition it is , 0.04 reasonabletoto assume assume aa uniform rate of erosion reasonable uniform rate erosion and and S incorporation. incorporation. An estimate of the in the An estimate of the dilution dilution rate rate in 0.03 Vermilion District was obtained by calculating calculating the the total total =05 S proportion of indicator Ct indicator material in the the 1-16 1-16mm nun fraction fraction 5 (Fig. 1). of the total sample pig. I). Regression Regression analysis analysisof of these these E0,02 a> C, S C data results in the following equation equation for dilution: 0 C) CD = O.O348e)2T (2) S S too Clearly, this dilution rate represents non-ideal 2 conditions. This Thisisisdominantly dominantlyan anartifact artifactof of not not Transport Distance Qan) TrawxtDi&nce (km) the—I mm and and +I6 +16mm including the -I nun mm size size fractions in the Figure 2. Dilution Curve Figure 2.Dilution Curve calculations, calculations, however however itit represents represents aa reasonable reasonable Quartz-Epidote Altered Altered Basalts Quartz-Epidote Basalts estimate. estimate. Comminution: Comminution:Comminution Comminutionalters altersthe theconcentration concentrationofofan anindicator indicatorwithin wifimaaparticular particularsize sizefraction hction as asparticles particlesare are than broken down by by clast-on-clast clast-on-clast and andclast-on-bed clast-on-bed interactions. interactions. Larger clasts tend to comminute comminute more more rapidly rapidly than smaller clasts. Larger Largerclasts clastsare arenot notlost lost to to the the system system as as they break down, but are transferred to smaller smaller size size classes. classes. The concentration of an indicator in a particular size fraction hction at a given transport distance is thus a function of of the the of larger larger clasts, clasts, and the rate at rate at which particles are being Kmg added to the size size class class by comminution comminution of at which which particles are leaving the size particles size class class by by comminution comminution to $asmaller smaller clasts. clam. + Comminution rates for indicator Comminution rates indicator clasts in the the OM' I j4no • 1-zm + by rearranging Vermilion Dislxict District were were calculated calculated by Vermilion rearranging • 2-4mm 2-4equation (I) CCOM equation (1)and andsolving solvingforfor CcoM at at each sample sample m' • 4-18mm 4.16location using the 3). CCoM the model modelCDIL CDL (Fig. 3). CCOM for the largest particles showed poor poor correlation correlation with with transport transport F EM,4 e + distance; this is is probably probably aa result result of of significant significantvariation variation 0 S in indicator boulder concentrations in indicator concentrations along along individual individual flow lines resulting from variable rates of addition addition by boulder comminution to this size size class. class. Medium-sized particles showed increase in in CCOM CcoMwith particles showedaarelatively relativelysharp sharp increase om transport distance, reflecting the higher rate transport rate of Transport TtansprlDistance D i m(km) (h) comminution of the comminution the coarsest coarsest particles. particles. The smallest smallest Figure 3. Comminution ComminutionCurves Cu~es particles showed a lower rate of of increase increase reflecting reflecting the Quartz-Epidote Altered Basalts Quartz-Epidote Altered Basalts lower rate at which coarser comminuted to coarser particles are comminuted this size size class. class. Conclusions: Conclusions: Results of indicator indicator tracing in in the the Vermilion Vermilion District District illustrate illustrate the importance importance of segregating sepgating the effects of dilution and comminution comminution to modeling the concentration of an indicator at a particular transport distance. Dilution affects affects the concentration Dilution concentration of each each particle particle size s i z equally, equally, however however comminution comminution rates rates strongly strongly and and differentially influence influence indicator indicator concentrations concentrationsin in differing d i f f e ~size g sizeclasses. classes. Since clast comminution is controlled controlled by by grain size and and material material properties, the the concentration concentration of an indicator indicator at aa particular particular transport transport distance distance can can be be seen seento to be dominantly dominantly aa function function of of the the initial initialparticle particle size sizedistribution distribution and and the the material material properties properties of of the the indicator. indicator. basalts. However, This study focused on dispersal of quartz-epidote qnartz-epidote aaltered l t e d hasalts. However, several severalother otherdispersal dispersaltrains trains were recognized in the the Vermilion Vermilion District Dislxict during during the course course of of the thestudy, study,including includingankerite-sericite ankerite-sericite lode lode goldgoldassociated alteration, and iron formation, associated formation, each each displaying displaying aa unique unique dispersal dispersalpattern. pattern. Given an identical identical glacial glacial of the the differing material material properties properties of of the the indicator. These environment, these differences must be a reflection of Thesedata data underscore that may accompany application of of a general underscore the potential potential problems problems that accompany application general regional regional dispersal dispersal model model to to interpreting particular localized interpreting localized glacial glacial indicator indicator trains. 6 4 0 . 12 10 + + 0A4 + !03it !! Em' :: 2 34 4 6 $ 10 12 �1 Low-grade Low-grademetamorphism metamorphismof of an anArchean Archeandebris debrisflow, flow, Irwin, Irwin, Pifher, Pifher, and and Meader Meader Townships, Lake LakeNipigon NipigonRegion, Region,Ontario Ontario 1 I I Frank FrankR. R.Luther, Luther,Geography Geographyand andGeology GeologyDepartment, Department, UW-Whitewater, hitewater, Whitewater, Whitewater, WI 53190 lutherf@mail.uww.edu lutherf@mail.uww.edu This hisextensive extensivebody bodyof of volcanic volcanic breccia brecciaisislocated locatedeast eastof of Lake LakeNipigon Nipigoninin northern northernIrwin, Irwin, southeastern southeasternMeader, Meader, and and aa large largepart partof of southern southernand andeastern eastern Pifher PiiherTownships. Townships. ItItisis10-25 10-25km kmeast eastof ofLake LakeNipigon Nipigonand and17-28 17-28km kmnorthnorthnortheast northeastofofBeardmore. Beardmore. Mapping Mappingby byMackasey Mackasey(1975), (19751,Kresz Kreszand andZayachivsky Zayachivsky (1989), (1989),and andas as aapart partof of this thisstudy studyshows showsthis thisrock rockto tobe beenclosed enclosedininaathick thick sequence sequenceof of typical typicalgreenstone greenstoneassemblage assemblagerocks. rocks. Metamorphism, Metamorphism,probably probably caused causedby by large large granitic granitic intrusives intrusivesin in Pifher Piiher Twp, increases thenortheast. northeast. increases totothe The Thebreccia brecciawas was thoroughly thoroughly described described and andan anorigin originas asaasubaqueous subaqueous debris debrisflow flowwas wasdocumented documentedby byLuther Luther(1998). (1998). In Inbrief, brief,the the breccia brecciaconsists consistsof of rounded roundedrock rock fragments fragments ranging rangingfrom from <1 e l mm mmto toover over11mmininaavery veryfine-grained finegrained matrix. matrix. Larger Larger fragments fragments tend tend to to be besimilar similar to tothe thematrix matrixinincomposition compositionwhile while smaller smaller fragments fragmentsvary vary in incomposition compositionfrom from that that of of the thematrix matrixto tomafic maficto toultramafic ultramafic to tocarbonate-rich. carbonate-rich. The The matrix matrixof of the thebreccia brecciawas wascomposed composedof of quartz quartzgrains, grains, euhedral euhedral and and broken brokencrystals crystals of of plagioclase, plagioclase, aa glass glassshard/pelitic shardlpelitic fraction fraction (now (now replaced below), and replaced by by the the greenschist greenschist metamorphic assemblage described below), and pyroxene pyroxene and/or andlor hornblende hornblende (now (now chlorite) chlorite) up up to to 0.5 0.5 mm. mm. Representative Representativewhole whole rock rock analyses analyses of of the the portion portionof of the thebreccia brecciaaffected affectedby bylow-grade low-grademetamorphism metamorphism are are presented presented in in Table Table 1; 1;these these analyses analyses show show the the average average (igneous (igneous rock rock equivalent) equivalent) composition compositionof of the thebreccia brecciato tobe bedacitic. dacitic. A A metamorphic metamorphic assemblage assemblage of of Mg-Fe Mg-Fechlorite, chlorite, high-Al high-A1to to high-Fe high-Feepidote, epidote, aluminous aluminous actinolite, actinolite, phengitic-paragonitic phengitic-paragoniticsericite, albite, albite, high-Fe high-Fe biotite, biotite, and and minor minor KK feldspar feldspar over-prints over-printsthe the primary primarytexture textureand andreplaces replacesthe the glass/pelitic glasslpelitic fraction; fraction; EMPA EMPAanalyses analysesof of the themore morevoluminous voluminousmetamorphic-origin metamorphic-originminerals mineralsare are given givenininTable Table2. 2. Most Most of of the the metamorphic metamorphic minerals, minerals, as as isisto to be beexpected expectedinin greenschist greenschist facies faciesrocks, rocks, show showminor minorvariation variationininindividual individualminoral mineralcompositions; compositions; two two minerals, minerals,plagioclase plagioclaseand andepidote, epidote, show showmajor majorcompositional compositionalvariation. variation. Plagioclase varieties: — an5 an5and and— an40. a m . The Thelarge largeplagioclase plagioclase Plagioclaseisispresent presentinintwo two varieties: crystals an40and and are are partially partially sausuritized; saussuritized; these these grains grains crystalshave haveaacomposition compositionofof— anw are are interpreted interpretedas as relict relictigneous igneousplagioclase. plagioclase. The The small small matrix matrix grains grains of of plagioplagioclase an5;these thesegrains grains are are interpreted interpreted as metamorphic metamorphic plagioclase plagioclase generatgeneratclase are are —ans; ed of the the breccia brecciamatrix. matrix. The The variation variation in inepidote epidotecomposition composition ed by by recrystallization recrystallizationof probably probably represents represents crystallization crystallization of of epidote epidote over over aa range rangeof of temperatures; temperatures;high-Al high-A1 epidote epidote usually usually crystallizes crystallizes at at aahigher highertemperature temperaturethan thanthe thehigh-Fe high-Feepidote. epidote. - - - 35 - �In Insummary: summary: aa classic classic greenschist greenschistfacies faciesmineralogy mineralogyof of albite, albite,epidote, epidote, muscovite, muscovite, biotite, biotite, actinolite, actinolite, and and chlorite chlorite overprints overprints the the primary primarymineralogy mineralogyof of the the debris debris flow flow which whichincluded includedfinely-crystalline finely-crystallinequartz, quartz,glass glassand andaltered alteredglass glass(pelite), (pelite), and anddetrital detrital quartz, quartz, plagioclase, plagioclase, and and mafic mafic minerals minerals grains. grains. Table Table1.1. Whole Whole rock rock analyses analyses of of the the samples samples of of the thevolcanic volcanicbreccia brecciawhich whichwere were affected by low-grade metamorphism. Analyses by XRAL. affected by low-grade metamorphism. Analyses by XRAL. S102 AL203 CAO NA2O K20 K20 FE203 T102 P205 P205 LOl S102 AL203 CAO MOO MGO NA20 FE203 FEO FEO MNO MNO TI02 LO1 SUM SUM 0.58 0.15 3.20100.3 3.40 1.72 6.25 4.30 0.08 16.0 3.84 4.00 LN97-3-1A 61.0 61.0 16.0 3.84 4.00 3.40 1.72 6.25 4.30 0.08 0.58 0.15 3.20100.3 LN97-3-1A LN97-6-1B LN97-6-19 63.2 63.2 16.5 16.5 6.03 99.8 6.03 2.15 2.15 3.53 3.53 1.49 1.49 5.30 5.30 3.10 3.10 0.07 0.07 0.51 0.51 0.11 0.11 0.85 0.85 99.8 Table Table2.2. Chemical Chemical analyses analyses of major major greenschist-facies greenschist-facies minerals minerals in in the the volcanic volcanic breccia. breccia. Analyses Analysesby byelectron electronmicroprobe microprobeat atUW-Madison. UW-Madison. hi-Al epidote biotite chlorite 37.9 35.2 25.3 0.3 1.7 0.1 23.9 23.9 28.0 16.8 20.9 10.6 10.6 10.9 10.9 5.6 20.2 23.2 MnO MnO 0.2 0.2 0.2 0.2 0.2 0.3 MgO MgO 13.4 13.4 10.3 16.3 CaO CaO 11.3 11.3 actinohte actinolite b-Al lo-AIeDidote eoidote 5102 Si02 55.5 55.5 37.0 37.0 1102 Ti02 0.0 0.0 ----- A1203 A1203 5.1 5.1 FeO FeO Na20 Na20 K20 K20 TOTAL TOTAL 1.6 1.6 0.1 23.1 23.I 24.3 ----- 0.2 0.2 = 97.9 97.9 96.2 95.1 95.1 0.1 0.1 0.4 9.9 0.1 94.4 86.7 REFERENCES REFERENCES Kresz, D.U. and Zayachivsky, B., 1989, Precambrian geology, Barbara, Meader and Rfher Pifher Townships; 2536-2537,91 p. Townships; Ontario Ontario Geological Geological Survey, Survey, rpt 270 with maps 2536-2537,91 Mackasey, Mackasey, W.O., 1975, 1975, Geology of Dorothea, Sandra, and Irwin Townships, District of Thunder 2294,83 p. Thunder Bay; Bay; Ontario Ontario Division Division of Mines, rpt 122 with map 2294,83 1998,An An Archean Archean subaqueous subaqueous heterolithic heterolithic debris debris flow, flow, Irwin, Irwin, Pifher, and Meader _______ ,1998, Townships, 44thAnnual Annual Institute Instituteon on Townships,Lake Lake Nipigon Nipigon Region, Region, Ontario Ontario(extended (extendedabstract): abstract):44th Lake 44. Lake Superior Superior Geology Geology meeting, meeting, Minneapolis, Minneapolis,Minnesota, Minnesota,v. v. 44. 36 �ThE THEBARRON BARRONSAPROLITE: SAPROLITE:CONFIRMATION CONFIRMATIONOF OF MATURE MATURE CHEMICAL WEATHERING IN IN THE THE SOURCE SOURCE FOR FOR PALEOPROTEROZOIC PALEOPROTEROZOIC QUARTZ QUARTZ AREMTES ARENITESIN INTHE THELAKE LAKE SUPERIOR REGION SUPERIOR REGION MEDAMS, MEDARIS,L.G., L.G., Jr., Jr.,Dept. Dept.ofofGeology Geology&&Geophysics, Geophysics,Univ. Univ. of ofWisconsin-Madison, Wisconsin-Madison, 1215 W. W. Dayton Dayton Street, Street,Madison, Madison,WI, WI,53706, 53706,medaris@geology.wisc.edu medarisgeology.wisc.edu It It has has long long been been inferred inferred that that the the post-1760 post-1760 Ma Ma supermature supennature Baraboo, Bamboo, Sioux, Sioux,Barron Barren and and related related quartz arenites were derived from sources that experienced mature chemical weathering, due quartz arenites were derived from sources that experienced mature chemical weathering, dueto to the in the the near near absence absence of of feldspar feldsparin in the the arenites arenites and and predominance predominance of of kaolinite kaolinite and and pyrophyllite pyrophyllite in the -- - argillaceous 1983; Ojakangas Weber, al., 1986). Paleosols argillaceous strata strata (Don, (~ott,1983; Ojakangas and ~ e b e r1984; , Southwick et al., Paleosols have been recognized recognized beneath beneath the the Baraboo, Baraboo, Sioux, Sioux, and and Barron Barren quartzites quartzites (Medaris (Medaris et et al., al., 1997; 1997; Southwick of aa continuing continuing investigation investigationto to Southwick and and Mosler, 1984), 1984), and and the the present present report report is is part of determine determine the chemical chemical maturity maturity of such such paleosols paleosols and to evaluate evaluate the climatic climatic conditions conditions associated associated with genesis genesis and and deposition deposition of the supermature supennature sedimentary sedimentary rocks. rd- ,xL ------rA-A large large outcrop outcrop of of red saprolite saprolite occurs occurs beneath beneath the A Barton Ban-on Quartzite Quartzite on on the the south southbank bank of of Weirgor Weirgor Creek, Creek, —lOOm east of Reichel Road, in Rusk County (NWI/4, -100m east of Reichel Road, in Rusk County (NW114, R7W). The closest basement Sec 9, 9, T36N, R7W). basement exposure exposure SWll4,Sec SWI/4, is milesouth, south,where wheremetatonalite metatonalite crops out on is —J/2 -% mile on both both sides of Reichel Road. Although Althoughthe the saprolite saprolite and and metametamile apart, tonalite tonaliteoutcrops outcropsare areV2 %mile apart, the the close close similarity similarityin in their textures textures (Fig. 1) 1) makes the metatonalite metatonalite a reasonable reasonable protolith orotolith candidate. The Themetatonalite metatonalitehas has inequigranular ineauimular - texture, texture, in in which which large large quartz quartz grains grains are are surrounded surrounded by aa medium- to fine-grained fine-grained granoblastic granoblastic assemblage assemblage of quartz, Figure 1. Polished Barron polishedslabs slabsof ofBarron plagioclase, hornblende, homblende, epidote, and opaques. opaques. The texture of metatonalite metatonalite protolith protolith and and saprolite; saprolite; metatonalite has has been preserved preserved in in saprolite, saprolite, in which which large large light light grains grainsare are quartz. quartz. the metatonalite relict quartz grains are surrounded by a matrix of finer-grained quartz grains are surrounded finer-grained Table 1. 1. Chemical Chemical Analyses Analyses quartz, quartz, kaolinite-rich kaolinite-rich domains domains (after (after feldspar), feldspar), hematite-rich hematite-rich domains domains % (2) (3) (2) (3) (1) 70.25 67.85 -10 Si02 (after (after hornblende), hornblende), traces traces of of sericite sericiteand tiny, euhedral euhedral crystals of Sioz ~i02 67." 0.24 70.25 0.29 -10 0 crandallite-florencite(aluminophosphate (aluminophosphateminerals). minerals). A1203 14.00 16.15 o crandallite-florencite AIQs 7.05 +9 5.63 Fe203 The The most striking strikingfeature featureof of the the saprolite saprolite chemical chemical composition composition $;FMnO 0.00 0.07 -100 0.09 -97 Mgo 2.41 is the virtual absence absence of of MnO, MnO, MgO, MgO, CaO CaOand andNa2O Na20 and the low MOO 2.41 0.09 -97 concentration concentration of K20 K20 (Table 1). 1). The Thechemical chemicalindex indexof ofalteration alteration o3 -100 -lE 0:58 57 1.17 (CIA) for the saprolite is 95.7, illustrating the high degree x2o (CIA) for the saprolite is 95.7, illustrating the degree of of KSJ 1.17 0.58 -57 ',05 m5 maturity maturity attained attained by by chemical chemical weathering weathering of of the saprolite saprolite [CIA [CIA == I'% LO1 0.70 5.53 100.06 99,91 100*A1203/(AI2O3+CaO+Na2O+K2O) on a molar basis]. The isocon Sum lOO*Al203/(Al203+CaO+Na~0+K20) on a molar basis]. The isocon sum 99.91 1m.w method (Grant, 1986) 1986) has been used to evaluate evaluate the magnitude magnitude of ppm ..à 14 8 -52 8 -52 Rb 14 chemical changes associated with weathering, taking metatonalite chemical changes associated mitatonalite as Sr 321 90 -76 Sr protolith for for the saprolite. saprolite. When Whenoxides oxidesand andelements elementsin insaprolite saprolite Ba 251 31 -89 Ba 91 00 80 91 Zr 80 and and protolith protolith are areplotted plottedagainst againsteach eachother other(Fig. (Fig.2), 2),A1203, A1203,TiO2 Ti02 and and Barron metatonaliie metatonalite protolith (1) Barren pmtoli Zr lie on a straight straight line, line, an an isocon, isocon, along along which the relative concenBarron sapmliie saprolite (2) Barren trations of trations of the defining defining constituents constituents remained remained constant constant dunng during % change relative (3) %change relativeto to isocon isocon r ,. 37 : ;5 7: ;3 4: i:: �weathering. The Therelatively relativelysmall smalldeviation deviationof ofFe203 Fe203 40 40 / from the isocon may be he due to an unrepresentative unrepresentative concentration of Fe203 in the the assumed assumed protolith, rather o 5*SiO: concentration Fez03 in < / O.5'5i02 30 than than its mobility. The The isocon slope of 1.15 1.15 <D 30 + .corresponds corresponds to a 13% 13% mass mass decrease decrease during during 0. weathering, weathering, when MnO, MnO, MgO, MgO, CaO CaO and and Na20 Na20were were 20 2o effectively effectively completely completely removed, removed, and and K20, K20, P205, P20s, Rb, Rh, Sr Sr g and Ba were substantially substantially removed from from metatonalite metatonalite 5 m (Table 1). 1). 0 . m (Table 10 -Fe2%'".2oow2o5 •OPSr The Baraboo Barahoo Quartzite Quartzite is is also also underlain underlain by by aa 7 •SOl'Rb saprolite saprolite on Baxter Baxter Hollow Hollow granite granite (Medaris (Medaris et et al., al., e° • ,'lo*T102 I!•• 00 1997), and application application of the the isocon isocon technique technique to to the the 1997), 00 10 20 30 40 10 20 30 40 Baraboo saprolite yields Barahoo saprolite yields an an isocon isocondefined definedby byAl203 A1203 Barron protolith protolith and Ti02 Ti02with a slope of 1.14, 1.14,corresponding corresponding to to aa 12% 12% diagram for Barron Figure 2. Isocon mass decrease, similar similar to to that that for for the the Barron Barron saprolite. saprolite. protolith saprohte; oxides in wt%, protolith and saprolite; oxides m Chemical maturity matunty of of Baraboo Barahoo saprolite saprolite is comparable comparable to that elements elements in ppm. of Barron saprolite, as as indicated indicated by the "" levels of depletion in in MnO, MnO, MgO, M ~ O CaO, :C~O, 6 60 60 - A % Na20, Sr Sr and and Ba Ba (Fig. (Fig. 3). Depletion Depletion of Si02 Si02 ".. % 40 both saprolites, is --'10% -10% in both saprolites,and and—'30% -30% Fe203 Fe203 § 40 : A A - 20 20 Baraboo. Following was removed at Barahoo. Following 9 weathering of the the Baraboo Barahoo saprolite, saprolite, K20 £2 2-rn 00 Rb were reintroduced by hydrothermal -20 and Rh hydrothermal -20 fluids, which were channeled channeled along along the the §' sub-Baraboo unconforrnity unconformity during suh-Barahoo 60 metamorphism. metamorphism. -80 The Barron and other other contemporaneous contemporaneous b00 . " m " m . n saprolites exhibit a high degree of &  ¡ & m0 Q0 ' &a ' 0S , Q Q Q Q ° mineralogical mineralogical and and chemical chemical maturity, maturity, x g ~ us s a ~ + similar Figure 3. Comparison of similar to that found found in in present-day o f chemical changes changes in in Bàrron Barren and Baraboo saprolites; s~prolites;elements and oxides arranged arranged weathering zones zones in in humid, humid, warm warm climates, climates, in order order of decreasing ionic ionic radius. radius. where intense chemical chemical leaching leaching is is characteristic, characteristic, in demonstrating the existence of a tropical environment in the Lake Superior region at thereby demonstrating -4750-1650 Ma. -1750-1650 Ma. Such Suchaaclimate, climate,combined combinedwith withaastable stabletectonic tectonicsetting, setting,was wasessential essentialfor for supermature features of the Baraboo, Barron and Sioux quartzites. generating the supennature Acknowledgments Acknowledmzents I'm indebted to Mike Mudrey, who drew my attention to the Barron saprolite saprolite and provided a locality map, and to Jim Grant, who enlightened me regarding the isocon method. References Dott, Don, R.H. Jr. (1983) (1983) Geol. Soc. Soc. Amer. Memoir 160, 160, 129-141; 129-141; Grant, J.A. (1986) (1986) Econ. Econ. Geol., Geol., v. 81, 1976-1982; 1976-1982; Medaris, L.G. Jr. eta!. et al. (1997) (1997)43rd 43rd Inst. Inst. Lake Lake Superior Superior Geol., Geol., 39-40; 39-40; Ojakangas, R.W. and Weber, R.W. (1984) Minn. Geol. Sun'., Surv., Rept. Rept. Inv. Inv. 32, 32, 1-15; 1-15;Southwick, Southwick, Mossler, J.H. D.L. et al. (1986) Geol. Soc. Amer. Bull., v. 97, 1432-1441; 1432-1441; Southwick, D.L. and Mossier, (1984) Minn. Geol. Sun'., Surv.,Rept. Rept.Inv. Inv. 32, 32, 17-44. 17-44. - - / - - 7 - - I • • . . . . . 0 - 38 - �TOURMALINE-BEARING VEiNS IN THE BARABOO QUARTZITE: A NEW TOURMALINE-BEARING QUARTZ VEINS OCCURRENCE OCCURRENCE OF THE ALKALI-DEFICIENT TOURMALINE, TOURMALINE, FOITITE FOITITE MEDA1US, L.G., Jr.and FOURNELLE, J.H., Department of Geology & Geophysics, Geophysics, MEDARIS, L.G., Jr.and FOURNELLE, J.H., Department University University of Wisconsin-Madison, 1215 1215 W. Dayton Street, Madison, WI, 53706; 53706; medarisgeology.wisc.edu; johnfgeology.wisc.edu medaris@geology.wisc.edu; johnf@geology.wisc.edu Tourmaline Tourmaline has long long been known to occur in quartz veins in the Baraboo Baraboo Quartzite, Quartzite, but its its chemical composition and geological significance have have never neverbeen been assessed. assessed. The present investigation was undertaken to characterize this tourmaline, as part of an ongoing project to establish the mineralogical and chemical composition of Proterozoic rocks in the Baraboo Bamboo Range. Three samples of tourmaline-bearing tourmaline-bearing quartz quartz veins from low in the Bamboo Baraboo stratigraphic stratigraphic section section on the south limb limb of the Baraboo Baraboo syncline syncline were were selected for investigation: investigation: sample I) 1)aa folded, folded, 1.5 1.5 cm thick quartz quartz vein in in the the regolith regolith of of the the Baraboo Baraboo paleosol from drill core 613 in Baxter Hollow; sample 2) a 3 cm thick quartz vein in quartzite in the SE ¼ 'A Sec. 29, Baxter Hollow; and sample 3) 3) a 3 mm nun thick, tourmaline-rich tourmaline-rich quartz vein in quartzite and metapelite in the NW ¼ 'A Sec. 35, Pine Hollow. All All three samples samples are mineralogically mineralogically simple, consisting of quartz, quartz, specular specular hematite hematite and and tourmaline. tourmaline. Tourmaline Tourmaline occurs in clusters clusters of small, randomly Figure 1. Photomicrograph tourmaline, Photomicrograp~of oftourmaline, oriented oriented pleochroic pleochroic crystals crystals (Fig. (Fig. 1), l), in in which which sample 3, plane polarized light = pale o= 0 pale to medium medium grayish grayish blue blue and and EE == colorless. colorless. Tourmaline analyses Tourmaline analyses were obtained obtained by wavelength Table Electron microprobe Table 1. Electron microprobe analyses analyses 5X50 instrument, quartz veins dispersive tournialine from quartz of tourmaline veins in in dispersive spectrometry on a Cameca SX50 using instrument, using Baraboo Quartzite Barabw Quartzite a 15 kV accelerating voltage, a 10 nA beam current, a beam 15 accelerating voltage, a 10 nA beam current, a beam 2 3 sample 1 2 3 sample p.m.the the(bpZ pZ reduction diameter of 1 pm, reductionsoftware, software, and a wt% combination of natural and synthetic combination synthetic minerals minerals as as standards. standards. 35.14 Si02 35.14 35.23 35.18 35.18 tourmalme by electron Analysis of tourmaline Analysis electron microprobe microprobe presents presents aa 34.86 2O3 35.05 A ~ O S 34.00 34.00 35.05 34.86 14.59 challenge because 13.98 FeO 13.98 12.35 12.35 14.59 to measure measure Li Li and and H H directly, directly, FeO challenge because of of the inability inability to 1.11 0.00 MgO 0.49 0.49 1.11 0.00 MgO the difficulty in determining B and 0 0 precisely, and the Na20 0.62 0.55 0.47 uncertainty in valency of transition elements. Nevertheless, Nevertheless, 8 Sum 84.23 84.29 85.09 results are achieved by normalizing acceptable acceptable results achieved normalizing cations cations to to 24.5 cations p.fu. cationsp.~u. 5.96 6.00 5.96 Si 6.00 5.96 5.96' Si oxygens HzO- and and B203-free B203-free basis and assuming assumingaa oxygens on an H206.85 6.98 6.96 Al 6.96 6.85 6.98 A1 B atoms atoms and and 331 0 atoms stoichiometric formula containing 33 B 10 1.75 2.07 Fe 2.00 2.07 Fe 2.00 1.75 ofF). (in the absence of F). Tourmaline Tourmalinewas wasanalyzed analyzed for for Si, Si, Ti, Al, Mg 0.12 0.28 0.00 Fe, Mn, Mg, Ca, Na, K, F, and Cl, but only Si, Al, Fe, Mg, and Na 0.20 0118 ohs N~ 0.20 0.18 0.15 occupancy are Fe-rich, Fe-rich, site occupancy TheBamboo Baraboo samples samplesare Na were detected (Table 1). The 5.96 6.00 5.96 T(6) 6.00 5.96 5.96 T(6) the Y-site is effectively effectively filled filled with Fe and Al A1 (means (means and 6.00 &00 6.00 Z(6) z(6) 6.00 6.00 6.00 standard deviations are 2.96±0.05, 2.96±0.08 and 2.98±0.06 2.96+0.05,2.96+0.08 2.98L0.06 3.01 3.03 y(3, 2.97 for the three samples), samples), indicating indicating the absence of Li, and the o.is 0120 0.18 0.18 0.15 X(O-1) 0.20 x(0-1) X-site is largely vacant, containing containing subordinate subordinate amounts of Na. ,. 1 r° 39 �Thus, Thus, the the composition composition of of Baraboo Barabootourmaline tourmalineisis close close to type foitite and lies in a field near the foitite corner type foitite and lies in comer of a plane defmed definedby by the the tourmaline tourmaline end-members, end-members, , foitite foitite [O(Fe2+2A~)Aksi60~~(Bo3)3(oH)3(oH)], foitite[D(Fe22Al)Al6SioOia(BO3)3(OH)3(OH)J, schorl 8(B03)3(OH)3(OH)J, schorl[Na(Fe2s)AloSisOj paCFe2+~)A&O~s@O~)3(0I^OH)], and and their their Mg Mg counterparts counterparts(Fig. (Fig. 2). 2). >c All three Baraboo Baraboosamples samplesare arealkali-deficient, alkali-deficient,with with All three A cores 0.5<X0c0.9, 0.5<X60.9, although althoughthey theyeach eachoccupy occupyaadifferent different field field in Fig. 2. The TheFe Fe##ininsample sample33isis99-100 99-100 and and in in sample is 90-95, 90-95, but but sample sample22isismore moremagnesian, magnesian, sample 22 is with the Fe# of rims being 70-85 and of cores, the Fe# of rims being 70-85 and of cores, 35-55. 35-55. The The effective effectiveoperation operationof of the thecoupled coupledexchange, exchange, 90 100 60 70 60 50 40 30 X(D) Fe# Y(A1) ==X(Na) X(Na) + + Y(Fe+Mg), Y(Fe+Mg), is is illustrated illustrated by by X(D) ++Y(Al) F& 4 schorl schorl the linear linear covariance covariance of of Al A1 and and Fe+Mg Fe+Mg (Fig. (Fig. 3). 3). Figure 2. Fipe 2-Compositional variation of Most analyses extend from the theoretical composition of analyses extend from theoretical composition Baraboo tourmaline Bamboo tourmalineininterms termsof ofX-site X-site foitite (6 Al, foitite (7 Al, Al, 22 Fe+Mg) Fe+Mg) toward toward that that for forschorl schorl(6 Al, 33 vacancy, 0, and Fe#, I 0O*Fe/(Fe+Mg) vacancy, 0, and Fe#, 100*Fe/(Fe+Mg) Fe+Mg), although although the the cores cores of of tourmaline tourmaline in in sample sample33 are are 3.C more more aluminous, aluminous,extending extendingtoward toward88Al Aland and11Fe+Mg, Fe+Mg, * type fofte \.... 0 sanplel which, which, in in the the absence ofF of Fand andLi, Li, suggests suggeststhe the presence presence of of A sample2 \.. 4 . an [D(Fe2Al2)Al6Si6O13(BO3)3(OH)3O]. anoxy-foitite oxy-foititecomponent component [D(Fe2+A12)A16S&O18(B03)3(OH)30]. • b. 2.5 25 Foitite Foititeisis aa relatively relativelyuncommon uncommonvariety varietyof oftourmaline tourmaline %Nq : t that has been described from late-stage hydrothermal veins that has been described from late-stage hydrothennal veins ? ?jk associated associatedwith with granitic granitic pegmatites pegmatites and and from from metasomatized metasomatized If wall wall rocks rocks in in areas areas of of Pb-Zn mineralization. Such Suchfoitite foitite "- 2.0 2o : differs differs from from that that at at Baraboo Barabooin incontaining containingappreciable appreciable quantities quantities of of Ti, Ti, Mn, Mn,Ca, Ca, Li Li and and F, F, depending dependingon onlocality, locality, A and andin in being beingassociated associatedwith withaavariety varietyof ofsilicate silicateminerals, minerals, 1.5 6.0 6.5 7.0 7.5 6o 65 7o 75 includingalbite, albite,adularia, adularia,micas micasand andzeolites, zeolites,among amongothers. others. including Al, A aptu am In In contrast, contrast,the theBaraboo Baraboofoitite foititeisischemically chemicallysimple, simple, 3.0 30 1Vs8mp183 containing containingonly onlySi, Si,Al, Al,Fe, Fe,Mg Mgand andNa Na(+ (+B+O+H), B+O+H),and andisis •\\ accompanied accompanied solely solely by quartz quartz and hematite. The Thechemical chemical . \ 2.5 25 constitution constitutionand andalkali alkalideficiency deficiencyof ofBaraboo Barabootourmaline tourmalineare are •.•.c,,v "\..v %.. V V, consistent consistentwith with its its environment environmentof of formation formationin in hydrohydroÈ. a t 2.0 thermal thermal veins veinswithin withinBaraboo Baraboometasedimentary metasedimentaryrocks. rocks. a, & 20 + During post-Penokean folding and low-grade metaDuring post-Penokean folding and low-grade metae U. LL. 3%. morphism, morphism, hydrothermal hydrothermalfluids fluids migrated migrated through through the the 15 -\\ 1.5 v chemically chemicallymature mature Baraboo Baraboo sequence, sequence, which which consists consists almost almost +... V\ B entirely entirelyof of5i02, SiOa,Al203 A1203and andFe203, Fe203, where where they theyscavenged scavengedBB % .1 1.0 10 and and the the few fewother otherelements elementsnecessary necessaryto toprecipitate precipitatequartz, quartz, 60 65 7o 75 8o 6.0 6.5 7.0 8.0 7.5 Al, apfu am hematite, hematite, and and alkali-deficient alkali-deficient tourmaline. Thus, Thus,the the Figure 3. Covariance Covarianceof ofFe+Mg Fe+Mg Figure3. chemical chemicaland and mineralogical mineralogicalcompositions compositionsof ofhydrothermal hydrothermal (Y-and and Z-sites) Z-sites) (Y-site) and and Al A1(Y('V-site) quartz quartzveins veins in in the the Bamboo Baraboo range range are are inherited inherited in in part part from from in Bamboo tourmaline; scale in in Baraboo tourmaline; scale in Proterozoic Proterozoicweathering weatheringand andsedimentation sedimentationprocesses. processes. . & I . , . '%. . t\;\\ \\ .  % ¥. ! atomsper performula formulaunit unit atoms 40 �Metal, Gold Gold and and Carbonatite Carbonatite Exploration Kimberlite, Base Metal, Exploration Targets, Derived From Overburden Overburden Heavy Mineral Data, Killala Lake Area, Northwestern Ontario. MORRIS, MORRIS, T.F., SAGE, SAGE, R.P., Ontario Ontario Geological Geological Survey, 933 933 Ramsey Ramsey Lake Lake Road, Road, Sudbury, ON. P3E tom.morris(ändm.gov.on.ca; CRABTREE, D.C., D.C., Ontario Geoscience Sudbury, ON. P3E 6B5, tom.morrisfaindm.gov.on.ca; P3E 6B5. Laboratories, 933 Ramsey Lake Road, Sudbury, Sudbury, ON., P3E ABSTRACT Since Since 1993, 1993, the Ontario Ontario Geological Geological Survey Survey (OGS) (OGS) has has conducted conducted aa series series of of Quaternary Quaternary mapping mapping and overburden overburden sampling sampling programs programs to assess assess the diamond potential of the the Kapuskasing Kapuskasing Structural Structural A suite suiteof of heavy heavy Zone (KSZ). Kimberlite Kimberlite is is recognized as as the primary host host rock for for diamond. diamond. A minerals (Cr-pyrope minerals (Cr-pyrope garnet, garnet, chromite, cbromite, Mg-rich ilmenite, ilmenite, Cr-diopside Cr-diopside and and forsteritic forsteriticolivine) olivine)are are commonly KIMs). commonlv associated associated with kimberlite kimberlite and and are are referred referred to to as as kimberlite kimberlite indicator indicator minerals minerals(KIMs). The typeiand types and distribution distribution of of KIMs KIMs recovered recovered from from these these programs programs clearly clearly demonstrate demonstratethat that the the KSZ has excellent potential for hosting diamond-bearing kimberlite. kimberlite. To To date, date, 22 occurrences occurrences of of diamond-bearing rock and diamond-bearing and kimberlite kimberlite have have been been discovered discovered in in the the Wawa Wawa area area (KWG (KWG Resources Resources 1nc.ISpider Resources Resources Inc., Inc., Press Press Release, Release, 20/08/97; 20108197; Canabrava Canabrava Diamond Corporation, Corporation, Press Press Inc./Spider Band-Ore Resources Release, 09/12/97; 09/12/97; Band-Ore Resources Ltd., Press Press Release Release 10/02/00; 10102100;Pele Pele Mountain Resources Resources Release, Inc., Press Release, Release, 10/02/00). 10/02/00). Following the success success of the KSZ Quaternary Quaternary mapping mapping and overburden overburden sampling sampling programs, programs, plans to assess similar structures in other parts of Ontario were made. One such assess similar structures in other parts of Ontario were made. One sucharea, area, the the TransTransfrom Michigan Michigan north-northeast north-northeast into intoOntario, Ontario,west west of of Superior Tectonic Zone (TSTZ), extends from Marathon. Marathon. Kimberlites Kiberlites straddle straddlethe the structure structurewithin within Michigan Michigan and and ultramafic ultramafic lamprophyres, lamprophyres, which may belong "clan", are recognized in association with the TSTZ in belong to the kimberlite "clan", Ontario. Ontario. The The TSTZ TSTZ represents represents aa fault fault system system that that has has accommodated accommodated emplacement emplacementof of upper upper mantle derived derived material. material. To To evaluate evaluate the the kimberlite kimberlitepotential potential of of the the TSTZ TSTZ in in Ontario, Ontario,an an area area between the towns of Marathon and Terrace Terrace Bay was chosen for Quatemary Quaternary mapping mapping and and stream stream sediment and till sampling. Collected overburden samples were processed to determine KIM sampling. Collected overburden samples determine KIM signatures. signatures. In addition addition to KIMs, KIMs, overburden overburden samples samples were were processed for for metamorphic metamorphic or or magmatic magmatic gold grains and carbonatite indicator massive sulphide indicator minerals (MMSIM ), ), gold indicator minerals. minerals. The MMSIMs MMSIMs are are associated associated with with 33 main types types of of base base metal deposits: deposits: 1) 1)volcanosedimentary volcanosedimentary massive sulphides sulphides in in high grade grade regional regional metamorphic metamorphic terrain; terrain; 2) skarn skarn and and greisen greisen deposits; deposits; and and 3) magmatic Ni-Cu sulphides. The composition of gahnite, a rare and important MMSIM magmatic sulphides. The composition of gahnite, a rare and important MMSIM associated with metamorphosed associated metamorphosedvolcanosedimentary volcanosedimentarymassive massive sulphide sulphide deposits, deposits, can can also also be used used to indicate indicate the presence presence of of rare-element rare-element pegmatite. pegmatite. The The presence presence and and distribution distribution of of MMSIMs MMSIMs and gold grains grains recovered recovered from from overburden overburden sampling samplingprograms programs completed completed over over the the KSZ KSZ defined defined several several important important base base metal, metal, rare-element rare-element pegmatite pegmatite and and gold gold exploration exploration targets. targets. This presentation presentation provides provides data data and preliminary preliminary interpretations interpretations on the types types and and distribution distribution of kimberlite kimberliteheavy heavy mineral mineral indicators indicators(KIMs), (KIMs), metamorphic metamorphicor or magmatic magmatic massive massive sulphide sulphide indicator minerals (MMSIMs), gold grains grains and carbonatite carbonatite indicator indicator minerals minerals from from modern modem Registered Trademark, Trademark, Overburden Overburden Drilling Drilling Management Management Drilling Drilling Limited Limited 41 �alluvium and till samples collected in the Killala Lake area, northwestern Ontario. This data can be used to focus exploration efforts for kimberlite (diamonds), base metal, gold and carbonatite (rare earth )) deposits. A total of 230 modern alluvium and 82 till samples were collected from across the study area. modern alluvium and till samples, 8 bedrock samples were collected In addition to the modem and processed to characterize their heavy mineral composition. Orientation surveys surveys were were completed over the Prairie Lake Lake Carbonatite, Carbonatite,Major MajorGeneral GeneralResources ResourcesLtd.'s Ltd's Spider Spider Lake Lake base base metal deposit and Cameco Gold Inc.'s Inc.'s Empress EmpressHill Hill gold gold deposit. deposit. These Thesesurveys surveysdefined defined overburden heavy mineral signatures signatures associated with each deposit type. Bedrock and overburden overburden data obtained from the orientation surveys surveys were used to help interpret heavy mineral signatures signatures derived from the regional overburden sampling program. From the overburden samples, samples, a number of kimberlite indicator minerals, base metal indicator minerals, carbonatite iiidicator minerals, carbonatite indicator minerals and a few gold grains were recovered. This data will be released in number 6013, 6013,April April2000. an Ontario Geological Survey Open File Report, number 2000. 42 �Nature and distribution distribution of ofLogan Logandiabase diabase sills sills and and gabbro gabbro channels channelsin inthe the Keweenawan Rift near Thunder Thunder Bay, Bay,Ontario: Ontario: Brief Brief comparison comparison to to Noril'sk Noril'sk - Jon NorthAtlantic AtlanticNickel NickelCorp. Corp. Jon North North- North Flat-lying Flat-lyingLogan Logandiabase diabasesills, sills, vertical verticaldiabase diabasedikes, dikes, and andlayered layeredgabbro gabbrocomplexes complexes intrude intrudelower lowerProterozoic Proterozoicand andArchean Archean rocks rocksin inthe thenorthwest northwestcorner cornerof ofthe theKeweenawan Keweenawan Rift. These 1108 Ma plutonic and hypabyssal rocks are broadly contemporaneous Rift. These 1108 Ma plutonic and hypabyssal rocks are broadly contemporaneouswith with thick thick sequences sequences of of flood flood basalt basaltof of the the North NorthShore ShoreVolcanic VolcanicGroup Groupand andOsler OsierGroup Groupinin northern northernLake LakeSuperior Superiorand andthey they ostensibly ostensibly represent representthe themagma magmapathways pathwaysfor forthe theflood flood basalts. basalts. South Southof of Thunder ThunderBay, Bay,aarugged, rugged,upland uplandarea areaof ofdiabase-capped diabase-cappedcuestas cuestas occupies occupies aa 70 70 km km by by30 30km kmnortheast-trending northeast-trendingtopographic topographicfeature feature--the the"Logan "LoganBasin" Basin"-between betweenThunder ThunderBay Bayand andthe theMinnesota Minnesotaborder. border. The The Keweenawan Keweenawan diabase diabase caps caps of of the above valleys valleys and and canyons canyons thecuestas cuestas(i.e. (i.e. the theLogan LoganSills) Sills) commonly commonly rise rise 15Cm 150 mabove underlain underlainby by deeply deeply eroded erodedflat-lying flat-lying sedimentary sedimentaryrocks rocksof of the the lower lowerProterozoic ProterozoicRove Rove Formation Formation of of the the Animikie Animikie Group. Group. Northwest Northwestof ofthe theLogan LoganBasin BasinArchean Archeangranitoid granitoidrocks rocks of of the the southern southernSuperior SuperiorProvince Provinceform form low low rolling rolling hills. Southeast Southeastofofthe theLogan LoganBasin Basin the thetopography topographyisisaarugged ruggedupland uplandarea areaof ofnortheast-trending, northeast-trending,linear linearridges ridgesformed formedby by vertical verticaldiabase diabaseand andgabbro gabbrodikes dikesintruded intrudeddiscordantly discordantlythrough throughthe theflat-lying flat-lyingstratigraphy stratigraphy of ofthe the Animikie AnimikieGroup. Group. Geological Geologicalmaps mapsofofthe thearea area(e.g. (e.g.Smith Smithand andSutcliffe Sutcliffe1987;1989, 1987;1989, Pye and Fenwick 1963) tentatively illustrate NE-trending faults on the NW and Pye and Fenwick 1963) tentatively illustrate NE-trending faults on the NW andSE SEsides sides of the Logan Basin. of the Logan Basin. The I), high TheLogan LoganBasin Basinhas hasrelatively relativelyhigh hightotal totalmagnetic magneticintensity intensity(TM (TMI), highmagnetic magneticrelief, relief, and andlong longwavelength wavelengthmagnetic magneticanomalies anomaliescaused causedby bythe theflat-lying, flat-lying,magnetic magneticdiabasediabasecapped cappedcuestas. cuestas. North Northofofthe theLogan LoganBasin Basinaadomain domainofoflow lowTMI TMIand andlow lowrelief reliefcoincides coincides with Archeancrust crustand andsoutheast southeastof ofthe theLogan LoganBasin Basinhigh highTMI, TMI,high highrelief, relief,and andhigh high with Archean frequency magnetic anomalies coincide with the area of northeast-trending diabase frequency magnetic anomalies coincide with the area of northeast-trending diabase dikes. dikes.Northeast Northeastand andeast-trending east-trendingfaults faultscan canbe beinterpreted interpretedas asthe theboundaries boundariesofofthe the Logan LoganBasin. Basin. The Thejuxtaposition juxtapositionofofthe thedomain domainofofsills sillsofofthe theLogan LoganBasin Basinagainst againstthe thedomain domainofofdikes dikestoto the thesoutheast southeastcan canbe bereconciled reconciledininan anhypothetical hypotheticalcross crosssection sectionififthe theLogan LoganBasin Basinisis interpreted interpretedas asaagraben grabenwhere wherethe thetransition transitionfrom fromvertical verticaldikes dikesto tohorizontal horizontalsills sillsisis preserved preservedat atdepth. depth.The Thenortheast-trending northeast-trendingdikes dikestotothe thesoutheast southeastare arevertical verticalconduits conduits to tothe theLogan Logansills sillsunroofed unroofedby byerosion erosionininaahorst-like horst-likefeature. feature. In In1995 1995aalocal localprospector prospectordrilled drilledaa499 499mmvertical verticalhole holeinto intothe theLogan LoganBasin BasinininBlake Blake Township Townshipand anddiscovered discoveredan anunusual, unusual,131 131m-thick m-thicksulphide-bearing sulphide-bearinggabbro gabbrobelow belowthe the Logan Sills. Lighifoot and Lavigne (1995) compared the geology and texture of the Logan Sills. Lightfoot and Lavigne (1995) compared the geology and texture of the gabbro gabbroto tothe thefertile fertileNi-Cu-PGE Ni-Cu-PGEbearing bearingsub-horizontal sub-horizontalgabbro gabbrochannels channelsbelow belowthe theflood flood basalt basaltsequence sequenceatatNoril'sk, Noril'sk, Siberia, Siberia,the theworld's world'slargest largestnickel nickeldeposit. deposit. North NorthAtlantic AtlanticNickel Nickelsubsequently subsequentlydetermined determinedthat thatthe thegabbro gabbrowas wasaaflat-lying, flat-lying, northeast-trending, northeast-trending,taxitic-textured taxitic-texturedintrusion intrusionup upto to130 130mmthick thickwhich whichpinches pinchesdown downtotoaa normal-looking normal-lookingLogan Logandiabase diabasesill sillless lessthan than20 20mmthick thickwithin within300 300mmofofthe thecentre centreofofthe the intrusion. intrusion.An Aninterpretation interpretationisisthat thatthe thetransition transitionfrom fromvertical verticaldikes dikestotohorizontal horizontalsills sillsinin the theLogan LoganBasin Basinisisaccompanied accompaniedby byhorizontal horizontalmagma magmachannelling. channelling.This Thisdiscovery discovery underscores underscoresthe thepotential potentialfor forNoril'sk-type Noril'sk-typeNi-Cu-PGE Ni-Cu-PGEconcentrations concentrationsininthe thebasal basalpart partofof the Rift theflood floodbasalt basaltsequence sequenceofofthe theKeweenawan Keweenawan anidea ideathat thathas hasbeen beendeveloped developed Rift—-an and andadvanced advancedby byseveral severalworkers workersininthe thepast pastdecade. decade. 43 �References Lightfoot, P.C., and Lavigne, M.J., M.J., 1995. Nickel, Nickel, copper, and platinum group element mineralization in Keweenawan intrusive rocks: new targets in the Keweenawan mineralization Keweenawan intrusive Keweenawan of the Thunder Bay Bay region, northwestern Ontario. Ontario Ontario Geological Geological Survey Survey Open Open File File Report Report 5928, 32 32 p. p. Fenwick, K.G., KG., 1963. Pye, E.G., and Fenwick, 1963. Atikokan-Lakehead Atikokan-Lakehead Sheet, Map Map 2065, Ontario Department of Mines, Geological Compilation Series, scale 1:253,440. Smith, A.R., and Sutcliffe, R.H., Smith. A.R., R.H., 1987. Keweenawan Keweenawanintrusive intrusive rocks rocks of the Thunder Bay Bav area, in in Summary of Fieldwork, 1987. Ontario OntarioGeological Geological Survey Survey Miscellaneous Miscellaneous Paper paper 137, p. 248-255. A.R., and Sutcliffe, R.H., R.H., 1989. Precambrian Smith, A.R., Precambrian geology of Keweenawan Keweenawan intrusive intrusive River area; area; Ontario rocks in the Crystal Lake-Pigeon River Ontario Geological Survey, Map P. 3139, Geological Series - Preliminary Preliminary Map, Map, scale scale 1:50,000. 1:50,000. Geology 1987. 44 �GEOMETRY BETWEEN GEOMETRY BETWEEN GOLD-RICH GOLD-RICHSUBSIDARY SUBSIDARY SHEAR SHEAR ZONES ZONES AND MAJOR MAJOR STRUCTURES: STRUCTURES: IMPLICATIONS IMPLICATIONS FOR FOR ARCHEAN ARCHEAN LODE-GOLD LODE-GOLD MINERAL MINERAL EXPLORATION EXPLORATION DEAN M. PETERSON Department of Geology, University Minnesota -- Duluth University of Minnesota Detailed GIS-based spatial spatial analysis analysis of of the three Detailed GIs-based three largest largest Archean Archean lode-gold lode-gold mining mining camps camps in in Canada Canada has led led to to the thedevelopment developmentof ofsome someseemingly seeminglyfundamental fundamentalgeometric geometric relationships relationships between major structures, subsidiary subsidiary structures, structures, and and gold gold mineralization. mineralization. The lode-gold between lode-gold mining camps included in the Lake, and Hemlo Hemlo the analysis analysis are arethe theTimmins, Timmins,Kirkland KirklandLake Lake—- Larder Lake, districts, which together have produced approximately 115 million ounces of gold. Additional analysis of the Noranda, Cadillac, and Malarctic analysis Malarctic gold camps camps of northwestern northwestern Quebec Quebec corroborate corroborate the original original findings, and add strength to the implications implications of the model. The relationships relationships link the location and and size size of gold location gold mines mines with with the the sense sense of ofshear, shear,stress stressregime regime(compression (compression verses verses extension verses parallel), and and distance to to the the major major structures structures in in each each camp. camp. Additional analysis doduments the the relationship relationship between between the the location location and size of gold gold mines mines to to the the orientation orientation and and distance distance to subsidiary subsidiary shear zones in the the camps. camps. These relationships allow the the exploration exploration geologist to quickly develop specific lode-gold lode-gold structural structural targets targets based based on on the the simple simple analysis anaiysis of of geologic maps. geologic maps. For this study, study, the major major shear shear zones zones were were divided divided into into compressional, compressional, extensional, and shear parallel segments based on regional maps and and literature literature review review (see (see inset map of parallel segments based regional geological geological maps Figure 1). GIS GIs analysis analysis has has shown shown that that essentially essentially all all of of the the gold gold in in the the camps camps has has been been mined mined a). In within 6 kilometers of major major shear shear zones zones (Table (Table 1la). In addition, addition, greater greaterthan than 98% 98%of of the the gold gold in in the three camps has been mined from zones of regional compression (Table (Table lb). ib). Together, these facts lead to the conclusion conclusion that lode-gold lode-gold mineral exploration programs should be targeted upon areas areas within 6 kilometers kilometers of compressional compressional zones zones of of major major shear shearzones. zones. Inset H .4P N\ 1St Order Shear Shear Zone Zone. 1st Order '\\ yP&IeI 212T 21.27' - \' \ 163.670 163.67' Figure 11 Figure , 59.700 \_ * — -- \ Order Shear Compression Compression Zone 1st Order Zone 7 Regional shear shear zone zone classification classification(inset (insetmap) map)and androles rulesfor forclassifying classiing the geometry of Regional geometry of associated with with major major structures. Angles subsidiary shear zones spatially associated Angles are are measured measured along along arcs from points, in the same direction as the major structures ares Son) inferred intersection points, structures sense of shear. shear. 45 �Proximity (A) (A) and and structural structural (B) (B) relationships Table I1 Proximity relationships between between lode-gold lode-gold mines mines and and major major structures structuresfor for Timunins, Kirkland Lake-Larder Lake, and Hemlo gold the T iins,K i a n d Lake-Larder gold camps, camps, Ontario. Ontario. - A) Proximity Proximity Analysis A) Analysis Distance to Major Structure <3 < 3Kilometers Kilometers 33—6 - 6 Kilometers Kilometers >6 > 6Kilometers Kilometers B) Structural Structural Analysis Analvsis Mined Gold (million Oz) (million Oz) Structural Structural Setting Selling Mined Mined Gold Gold Gold (million Oz) (million Oz) Gold Gold 83.108 83.108 32.100 32.100 0.235 0.235 72.0% 72.0% 27.8% 27.8% 0.2% Compressional Extensional Extensional Parallel 113.539 113.539 1.877 1.877 0.027 98.35% 1.63% 1.63% 0.02% 0.02% ((%) %) Table Table 22 Proximity Proximity (A) and structural structural (B) relationships relationships between lode-gold mines and subsidiary subsidiary structures for the T Timmins, structures i i n s , Kirkland LakeLarder Lake, Lake, and Hemlo Hemlo gold gold camps camps A) Proximity Analysis A) Proximity Analvsis Distance to Subsidiary Shear <200 < 200meters meters 200—250 - 250 meters meters 200 Mined Gold 1%) ('%) (millionOz) Oz) (million Gold 108.417 108.417 5.869 5.869 0.5 10 0.510 1.157 93.91% 93.91% 5.08% 5.08% 0.44% 0.44% 1.00% 250—300 250 - 300 meters > 300 meters Bl Structural Analvsis (250 m Buffer1 Subsidiary Shear Mined Gold t%> (%) Gold Angle ~ n & (million Oz) (million Oz) 106.252 106.252 160° - 180 180° 160¡ 140°- 160° 120°- 140° 1.398 100° - 120° 80° - 100° 0.000 0.400 0.000 60° - 80° 400 - 60° 20° - 40° 0° - 20° 0.006 0.860 4.170 1.200 92.97% 92.97% 1.22% 0.00% 0.35% 0.00% 1.05% 0.01% 0.75% 3.65% (%) 1%) - For this study, the relationship between the major and has been defined and subsidiary subsidiary structures structures has defined by by measurements along an arc in the same same direction as the the dominant dominant sense sense of shear shear of the the major major structure (Figure (Figure 1). 1). Each structure Each subsidiary subsidiary shear zone segment has has an an associated angle to the major segment associated angle major structure stored in its associated GIS database. structure stored its associated GIs database. The location of gold mines and their production records in each camp were spatially records spatially linked linked with shear zone. zone. The the nearest subsidiary subsidiary shear The outcome outcome spatial analysis analysis isis given 2. of this this spatial given in in Table Table 2. Approximately 99% of the gold in the camps has Approximately been mined been mined within within 250 meters meters of of aa subsidiary subsidiary In addition, (Table 2a). 2a). addition, subsidiary subsidiary shear zone (Table high-angle (160°-180°, Figure 1) 1) structures structures in the (1600-180°Figure compressional zones of of the major compressional zones major structures structures account for ofall all gold gold mined mined in the camps -93% of for —93% (Table 2b). Table 33 display the Area calculations in Table usefulness of this analysis usefulness analysis for gold gold exploration. exploration. Programs that that would would be targeted upon the highhighPrograms subsidiary in in regional regional compresangle (160°-l80°) (160"-1800) subsidiary sional zones would would reduce reduce the the total total area to be sional zones be Similar targeting criteria in explored by 99%. explored by 99%. lode-gold exploration programs would greatly lode-gold exploration programs greatly lower lower cost, cost, reduce reduce time, time, and and would would quickly quickly vector the program vector program into areas areas of of high high lode-gold lode-gold mineral potential. - Table 33 Tabulation Table Tabulation of of the the total total GIS GIS map map area, area,areas areaswithin withm 250 250meters metersof ofhigh-angle high-anglesubsidiary subsidiaryshears, shears, and explorationwould wouldbe be targeted targetedonly onlyinin and percentage percentage of of the the map map area area reduced reduced ifif exploration the most favorable favorable areas areas of of the the three three mining mining -camps. . ~Mining Camp Camp Hemlo Hemlo Timmins Timmins Kirkland GIS Map 2 Area ( ~ m ) Area (Km2) 2280.00 4106.00 2414.00 ~~ 5 Buffer Around Hi-angle0 Percentage Reduced from ~ Area (Km2) of2SOm Total Map Area Area (> 1607 Subsidiary Shears Shears Total Map 160°) Subsidiary " 5.55 5.55 19.04 19.04 24.94 24.94 46 99.70% 99.70% 99.42% 99.42% 98.70% 98.70% �GEOLOGIC GEOLOGICAND AND GIS-BASED GIs-BASED LODE-GOLD LODE-GOLD & & VOLCANOGENIC VOLCANOGENICMASSIVE MASSIVE SULFIDE SULFIDE(VMS) (VMS) MINERAL MINERAL POTENTIAL POTENTIALMAPS MAPS OF OFA A PORTION PORTION OF OFTHE THEARCHEAN ARCHEAN VERMILION VERMILIONGREENSTONE GREENSTONEBELT, BELT, NORTHEASTERN NORTHEASTERNMINNESOTA MINNESOTA DEAN M. PETERSON Department Departmentof ofGeology, Geology,University Universityof of Minnesota Minnesota -- Duluth Duluth Lode-gold Lode-gold and VMS VMS mineral mineral potential potential maps maps of of aaportion portionofofthe theArchean ArcheanVermilion Vermiliongreenstone greenstone belt belt in in northeastern northeastern Minnesota Minnesota have have been been developed developed from from the the digital digitalincorporation incorporationof ofthe thelodelodegold and VMS ore deposit models into spatial analysis of a new 1:100,000 1:100,000 scale geologic map of the the study study area. area. The TheGIS-based GIs-basedmineral mineralpotential potentialmodels modelsincorporated incorporatedfuzzy-logic fuzzy-logic techniques techniques of of map map combination combination using using variations variations of of knowledge-driven knowledge-driven (ore deposit deposit model) model) and and data-driven data-driven (analog (analog mining camp analysis) techniques. Inference Inferencenets nets depicting depictingthe the mineral mineral potential potential models models are presented in Figure 1 (lode-gold model) and Figure 2 (VMS model). are presented in Figure 1 (lode-gold model) and Figure 2 (VMS model). .a STEP I Weld Spatial STEP 2 Dab Ptocasmg a Collect Spatial Date and Input into GIS GEOLOGIC GEOLOGIC STRUCTURES STOUCTURES Extraction of GIS Features Relevant to the VMS Ore 2. Cetass burg — I. Recteifr —— ladoeda I.tOtder Prolimhiaiy Maptof Selected GIS Peanuts PoId 3rd Ott Aalt Shass l.ExwtRoekTypa 2. Crate baea I. Babies mapped eats 2. Qeeiy Database 3. C* 3. Ct.att Baits —I S Aakarile SandIa SadISt —I— ASisli' QFP Pynte Afida — Sa GOLD GOLD ANOMALIES ANOMALIES COMPETENCY COMPETENCY CONThASTS CONTRASTS LthSse I. Emct C-to 2. Reclassify Types LCeateBaff froesG ____________________ Tails —— tabs. .a S0 ALTERATION ALTERATION ASSOCIATED ASSOCIATED HOST ROCKS HOSTROCKS it Soils !ssa)cael s_ — Wth_ of Evidence Fany tut(O.lI Map Overlay %Overlay STEP STEP33 to Peedsice = * Intenuedisee Factor Maps STRUCTURAL STRUCTURAL F- Integration i i HOSTROCK HOSTROCK ALTERATION ALTERATION Factor F- Factor 1 GEOChEMICAL GEOCHEWCAL Factor Facto' i ROCK RHEOLOGY ROCKRHEOLOGY Factor Factor Modelling UwkOsss Overlay of Intermediate Factor Maps to Pyodece the Final Predictive Map 04 Map Weightings Map Woifligs - LODE MAY LODEGOLD GOLDMINERAL MINERALPOTENTIAL POTBtTTUU. MAP Figure Figure1.1. Inference Inference net for for the the three-step three-step GIS GIs model model of ofthe thelode-gold lode-gold mineral mineral potential potential of of the theArchean Archean Vermilion Minnesota. The Vermilion greenstone belt, Northeastern, Minnesota. The three three steps stepsare: are:1)1)Detailed Detailedgeologic geologic mapping Conversion of all all data datainto intoprimary primary mapping and compilation compilation of of all all available available geologic geologic data. data. Conversion GIS datasets;2) 2) Extracting Extractingand and enhancing enhancingthe the features featuresof ofthe theprimary primarydatasets datasetsthat thatare areimportant important GIs datasets; for predicting deposits; and and 3) Integration predicting lode-gold lode-gold deposits; Integration of the the preliminary preliminary maps maps using using GIS GIS modeling modeling techniques techniques that that predict predict mineral mineralpotential. potential. 47 �Build Build Collect Collect Spatial Spatial Inpul Data and Input Data Spatial Spatial into into GIS GIs Database Extraction Extractionof of GIS GIS Features Features Relevant Relevan to to ±e theVMS VMS Ore Ore Deposit Deposit Model Model . . sTEP 1 • S MAPPED BEDROCK 13EDROCK GEOLOGY GEOLOUY ALTERATION Al.Tf-RATION ZONES ZONES ROCK, ROCK.CORE, CORE.SOIL SOIL REGIONAL REGIONAL & LAKE MAGNETICS A LAKk SEDIMENT SEDIMENT MAGNI-IlCS GEOCHEMISTRY GEOCHEMISTRY . AIRBORNE & GROUND EM GROUNDFM CONDUCTORS CONDUCTORS ————t——t——±—H— , II . ~Reclaatij e~la~~ify 2 Extract 2. EM contacts con3. Create Cteate buffers buflrs I. I. ~Classi . ~ExtractAitTypes x t r a c t A l ~1~classifyinterval~ ~ ~ intervals 2. Create buffers 2. Grid soil & lakes 3. Buffer rock Ctassifr 3. Classify rock & & core core II. .CompileTF C . & T FMae M ~ ~1.IExtractEM .E~~~~~~EM 2. Reduce pole Claaai' Reduce to topole 2. Classify 3. Calculate Calculate 2VD 2VD 4. Extract Polygona ExtractPolygons STEP 22 STEP Data Data Processing roccssiog Preliminary Preliminary Maps Maps of of Selected GIs GIS Selected Features Features contacts contacts 1 Quattz- contacts contacts Epedote Volcanic-Sedsment contacts Greenstone Subvolcanic Sequences Inmiatotia Msnerattzed Intxut,ves * -Na20 ChIotite Pyrite Cu Zn Soila Cu Zn Lake Cu Zn Rocks Core 2"VD Ground Aithonse Mag EM EM Assign Weights Weights Assign Evidence of Evidence Fair weights to - I) Fuzzyweighs(0-1) Map Overlay MapOverlay STEP 3 STEP Integration itegration Modelling toddling to Produce Produce to Intermediate Intermediate Factor Maps 1 Overlay of Intermediate Intermediate Factor Maps to Produce Produce the Final Predictive Predictive Map 1 1 STRATIGRAPHY STRATIGRAPHY HEAT HEAT Factor Factor Factor Factor 1 ALTERATION ALTERATION Factor Factor rILiTt 1 GEOCHEMICAL GEOCHEMICAL Factor Factor VVMS M S MINERAL POTENTIAL MAP 1 MAGNETIC Factor Factor  EM Factor 0.20 VMSTARGETSI TARGETS !____rIVMS GIS modeling of the VMS potential of the mineral mineral potential of of Figure 22 Inference network for the 3-step GIs the Archean Vermilion greenstone belt. belt, Northeastern, Northeastern, Minnesota. Minnesota. The The three three steps steps in in the thestudy study are: 1) 1) Detailed Detailed geologic geologic mapping mapping and compilation compilation of of all all available available geological, geological,geochemical, geochemical,and and geophysical data. data. Conversion Conversion of of all all data data into into primary GIS GIs datasets; datasets; 2) Extracting and enhancing the features of the primary VMS deposits; and 3) the primary datasets that are important important for predicting predicting VMS Integration of of the preliminary Integration preliminary maps maps using GIS GIs modeling modeling techniques techniques that predict predict mineral mineral potential. Unlike similar greenstone belts of the Canadian Shield in Canada, the Vermilion greenstone belt Minnesota remains remainsunder-explored. under-explored. One One of the main reasons reasons that the area has of northeastern northeastern Minnesota seen little mineral exploration was was due due to to the the discovery of of the the great great iron iron deposits in in the the 1870's. Iron companies acquired great tracks of land and essentially prevented precious and base land and essentially prevented precious and base metal metal exploration for over a century. Recent Recentmapping mappinghas hasshown shownthe thepresence presenceof ofvery verylarge-scale large-scaleVMS VMS alteration systems (> 19 19km km strike strikelength lengthofofsemi-conformable semi-conformable quartz-epidote quartz-epidote alteration) alteration) and and gold-mineralized shear systems analogous to Archean gold camps camps in Canada. The mineral potential potential maps maps integrate integrateimportant important geological, geological, geochemical, geochemical, and and geophysical geophysical data data mapped and compiled by the author with ore deposit models. The Theore oredeposit depositmodels modelshave havebeen been largely developed developed from from the the study study of mines within the Canadian Shield and western Austrailia. largely Areas on the the maps maps with with high high modeled modeled VMS VMS and and lode-gold lode-gold mineral mineral potential potential should shouldbe beexamined examined in detail by or in by exploration exploration geologists geologists because because they they possess possess geologic geologic features features indicative indicative of ofmaj major districts. mining districts. 48 �Samuels Lake Intrusion: Intrusion: A PGE-bearing Quetico-type Intrusion Intrusion in the Central, Western Western Quetico Quetico Central, Subprovince, Northwestern Ontario Ontario •I 2 Keiko H. ~ Hattori Neil T. Pettigrew pettigrewl,, Kbiko a t t o r iand and ' John John A. Percival perciva12 I I. Ont Canada, 1. Dept Dept.of ofEarth EarthSciences, Sciences, University University of Ottawa, Ont. Canada,KIN KIN 6N5 6N5 Survey of of Canada, Canada, Ont. Canada, Canada, KIA 0E8 2. Geological Survey OE8 An array of mafic-ultramafic mafic-ultramafic bodies known as the Quetico Quetico intrusions intrusions occur occur along alongthe the northern boundary of the Quetico Quetico subprovince subprovince adjacent adjacent to the Wabigoon Wabigoon belt (Fig. (Fig. 1). 1). This This study study identified two previously has identified previously unrecognised unrecognised Quetico-type Quetico-type intrusions, intrusions, the Samuels SamuelsLake Lake and and Redhorse Lake intrusions, intrusions, in the central central western Quetico Quetico subprovince subprovince (Fig. (Fig. 1). 1). The The Redhorse Redhorse the westernmost westernmost identified identified example example of of this this type type of of Lake intrusion near the US-Canada border is the intrusion. intrusion. The Quetico Quetico intrusions intrusions characteristically characteristically contain contain hornblendite, hornblendite, clinopyroxenite, clinopyroxenite, minor minor appinite and are accompanied appinite accompanied by Cu-Ni-PGE mineralization. mineralization. Larger intrusions intrusionsalso also contain contain wherlite, gabbro, diorite diorite and syenite. syenite. They are distinguished distinguished from from the mafic-ultramafic mafic-ultramafic intrusions intrusions in the Wabigoon Wabigoon and Wawa Wawa greenstone greenstone belts, such such as as the Bad Vermilion Vermilion Lake, Lake, Grassy Grassy Portage, Portage, and Shebandowan Shebandowan complexes, complexes, by their their lack lack of of associated associated komatiities komatiities and and anorthosites. anorthosites. The 1999 1999 field field season season consisted consisted of reconnaissance reconnaissance work on on the Quetico Quetico intrusions intrusionsalong along the subprovince subprovince boundary boundary and alkaline alkaline intrusions intrusions surrounding surrounding the Samuels SamuelsLake Lake intrusion. intrusion. Grid Grid mapping and sampling were conducted on the Samuels Lake intrusion which was chosen for sampling conducted Samuels Lake intrusion which was chosen for detailed work due to recent recent exploration exploration activity activity and a lack of previous previous work. The Samuels Lake intrusion has an NE-SW elliptical form, displaying Samuels Lake intrusion an elliptical displaying weak weak concentric concentric zoning with a wehrlite wehrlite core core partially surrounded surrounded by hornblendite hornblendite and and completely completely surrounded surrounded by by marginal clinopyroxenite. clinopyroxenite. These These units units are are cut cut by small small dikes dikes and and plugs plugs of of diorite. diorite. The The wehrlite wehrlite and clinopyroxenite clinopyroxenite phases show show aa gradational gradational change change in modal modal abundance abundance of of constituent constituent and clinopyroxene clinopyroxene (Mg# (Mg# =0.83) =0.83) with with minerals. The wehrlite is composed primarily of olivine and minor phlogopite. Sulphides % Sulphides(pyrrhotite, (pyrrhotite,chalcopyrite chalcopyriteand and pentlandite) pentlandite) constitute constitute up up to to 30 30 vol vol % with olivine olivineand andclinopyroxne clinopyroxne suggest suggest the the separation separation of of . The intergrowth textures of sulphides with inuniscible (<0.06 immisciblesulphide sulphide melt melt from fromthe the parental parental silicate silicate magma m a m a .. Low Ni f< 0.06 wt%) wt%)in in olivine suggests suggests sulphide sulphide saturation saturation prior prior or or during during olivine olivine crystallization. crystallization. The The clinopyroxenite clinopyroxenite contains contains clinopyroxene (Mg#= 0.84) variable amounts of olivine (Fo76) and minor phlogopite with clinopyroxene (Mg#= variable amounts of olivine (Fojyj) and minor phlogopite with trace trace sulphides. sulphides. Homblendite Hornblendite isis composed composedof of euhedral euhedralpargasite pargasite to to magnesio-hornblende, magnesio-hornblende,phlogopitic phlogopitic biotite, and plagioclase plagioclase with with trace trace titanite, titanite, pyrrhotite, pyrrhotite, chalcopyrite, chalcopyrite, and and ilmenite. ilmenite. Diorite Dioriteconsists consists of plagioclase, magnesio-hornblende, biotite, quartz, and microcline with trace pyrrhotite, magnesia-hornblende, biotite, quartz, and microcline with trace pyrrhotite, chalcopyrite, ilmenite, magnetite, ilmenite, magnetite, titanite, titanite, and and zircon. zircon. .. intrusion has undergone The Samuels Samuels Lake ~akeintrusion undergone high temperature, deuteric deuteric processes processes and and lowlowtemperature temnerature retrograde retrograde alteration. alteration. The The deuteric deuteric phase chase resulted resulted in in the the formation formation of of hornblende hornblende after clinopyroxene, clinopyroxene, and andthe theformation formationof oflow-Ti low-Timagnetite. magnetite.ItIt may may have have been been accompanied accompanied by by serpentinization of olivine. temperature alteration Low temperature alteration produced tremolite-actinolite tremolite-actinolite alteration of homblende, hornblende, chlorite after hornblende homblende and biotite, and carbonate alteration. Alteration style and biotite, and carbonate alteration. Alteration style and and intensity intensity vary vary between between phases phases and and appear appear to to partially partially control control Cu-PGE Cu-PGE mineralization. mineralization.In In the the clinopyroxenite clinopyroxenite - . - 49 �phase, Cu-POE Cu-PGE mineralization mineralization occurs occurs in areas areas of intense intense alteration alteration of the border border phase phase with with associated associated chalcopyrite-rich chalcopyrite-rich blebs, inter-fingered with actinolite actinolite and calcite. In wehrlite, wehrlite, high high levels of POE mineralization occur in chalcopyrite-rich zones instead of pentlandite-pyrrhotite levels PGE mineralization occur chalcopyrite-rich pentlandite-pyrrhotite rich zones. Small veinlets in wehrlite wehrlite may contain significant significant amounts amounts of of apatite apatite and and Small chalcopyrite chalcopyrite veinlets with elevated POE contents. POE mineralization in the wehrlite phase is associated with the elevated PGE contents. PGE mineralization associated with the immiscible immiscible sulphide sulphide liquid, liquid, indicating indicating a magmatic origin. In the clinopyroxenite clinopyroxenite border border phase, phase, POE mineralization PGE mineralization is is associated associated with apatite, carbonate carbonate and Cu enrichment enrichment suggesting suggestingthat that volatile-rich PGEs. volatile-rich fluid, fluid, most most likely likely deuteric deuteric in origin, origin, were responsible responsible for for concentration concentration of of PGEs. The The Quetico-type Quetico-type intrusions intrusions may not be restricted restricted to the Quetico Quetico belt. The The east-west east-west trending array array of of intrusions intrusions may be extended extended eastward into the Wabigoon Wabigoon subprovince subprovince to to include include Lac Des Milles Lac, Demar Lake, Lake, Taman Taman Lake, Legris Legris Lake, Lac Des Iles, Iles, and and Tip Tip Oabbro Gabbro mafic-ultramafic 1). These These intrusions intrusions have similar similar lithological lithological assemblages assemblages to to the the mafic-ultramafic intrusions intrusions (Fig. (Fig. 1). Quetico Quetico intrusions. intrusions. The The mineralization mineralization observed in Samuels Samuels Lake and other other Quetico Quetico intrusions intrusions are also also similar similar to to that that in in the the clinopyroxenite clinopyroxenitephase phaseof ofthe theRoby Robyzone zoneininthe the2692 2692+41-2 +4/-2 Ma Ma Lac Lac Des Ties mafic-ultramafic complex. If this correlation is supported by geochronology lies mafic-ultramafic geochronology in in progress, progress, it will establish 2692 Ma. establish that that the the Quetico Quetico and and Wabigoon Wabigoon subprovinces subprovinces were proximal proximal by 2692 Figure Figure1.1.Simplified Simplifiedgeological geologicalmap mapof ofWestern WesternWabigoon, Wabigoon, Quetico, Quetico, and Wawa subprovinces. Solid, finely dashed line outlines the distribution of similar subprovinces. Solid, finely dashed line outlines distribution similar mafic-ultramafic mafic-ultramafic intrusions intrusions across across the the Quetico-Wabigoon Quetico-Wabigoonsubprovince subprovince boundary. 50 �PETROGENESIS PETROGENESISOF OFTHE THEENIGMATIC ENIGMATICAURORA AURORASILL, SILL, MESABI MESABI RANGE, RANGE, MINNESOTA MINNESOTA PHILLIPS, PHILLIPS,Erin ErinH. H.(ephillips@macalestetedu); (ephillips@macalester.edu);Wirth, Wirth,Karl KarlR., R.,Geology GeologyDepartment, Department, Macalester Macalester St. Paul, Paul, MN MN 55105 and Morey, G.B., Minnesota Geological 55105 (wirth@macalesteiiedu); (wirth@macalester.edu); and College, St. 2642 University Ave., Ave., St. St. Paul, Paul, MN MN 55114 Survey, 2642 syenitic Aurora Sill intrudes the Biwabii Biwabik Iron-formation Iron-formation of ofthe the Mesabi Mesabi Range Range in in northern northern MmMinThe syenitic nesota. Since the work of White (1954), (1954), the sill sill has has commonly commonly been assigned assigned aa Mesoproterozoic Mesoproterozoic (Keweenawan) because of its resemblance to "red rocks" associated associated with the Midcontinent Midcontinent Rift in the (Keweenawan) age because Duluth region. The Theage ageof ofthe thesill sillisisimportant important to to understanding understanding the the timing timing of of ore ore formation formation in in the Mesabi Mesabi Range. In In1999, 1999,Morey Moreyproposed proposedaaconceptual conceptualmodel model in in which which the the high-grade high-grade ores ores formed formed in in aa regional regional ground-water Strandlie (1999) argued that ground-water system system during during Paleoproterozoic Paleoproterozoic time. Subsequently, Subsequently,Graber Graber and Strandlie nearby appears nearby high high grade grade ores ores must must have have formed formed in Mesoproterozoic Mesoproterozoic or or later later time, because the the Aurora Sill appears to have controlled controlledore-forming ore-forming processes processes in nearby mines. New New data datafrom from this this study study imply imply that that the the Aurora Aurora mineralogically and Sill is quite different, both mineralogically and geochemically, geochemically,from from known known felsic felsic rocks rocks in in the Midcontinent Midcontinent Rift. Thus, Thus,the the age ageof of the the sill sillremains remains uncertain uncertain and the possibility exists that it was intruded soon after deposition of the Biwabik deposition Biwabik Iron-formation Iron-formation in in the the Paleoproterozoic Paleoproterozoic(ca (ca 1878 1878Ma; Ma; Fralick, Fralick,1998). 1998). The Aurora The Aurora Sill Sill extends extends approximately approximately 5.6 5.6 km km along along the the Mesabi Mesabi Range Rangenorth northof ofthe thetown townof ofAurora and ranges in thickness thickness from 6 to 37 m m (White, (White, 1954). The sill was recently exposed exposed during during mining operaoperations in the NW 1/4, NE 1/4, T58N, R15W. RISW. Due to the inaccessibility inaccessibility of the exposures 114,NE 114, sec 3, T58N, ofthe exposuresalong along vertical vertical walls in the mine, samples were collected collected from from large largeblocks blocksalong alongaabench benchimmediately immediatelyabove abovethe thesill. sill. In In all, ten samples samples were studied from this locality along with seven samples from core (16.4-38.1 m in depth) studied locality in see 2, T58N, R15W. R15W. Fine-grained, porphyritic porphyritic syenite syenite from from the the margin margin of of 114, NE 1/4, 114, sec drilled in the NW 1/4, the sill exhibits exhibits trachytic trachytic texture; texture; mediummedium- to to coarse-grained coarse-grained syenite syenite in in the the interior interior of of the sill sill lacks lacks aligned aligned microcrysts (0.2-1.0 (0.2-1.0 mm) mm) plagioclase. Sodic Sodicplagioclase plagioclase(albite) (albite)occurs occurs as as phenoerysts phenocrysts (3.0-7.0 (3.0-7.0 mm) and microciysts Maiic minerals minerals in in finefineand is extensively altered. Mafic ' ' ' ' # ' ' ' ' # ' ' ' ' ' ' ' ' ' I15s grained samples include grained include small small (0.1-0.3 (0.1-0.3 mm) mm) and and euhedral aegirine; euhedral aegirine;fibrous fibrousamphibole amphiboleand andchlorite chloriteare are common in the coarse-grained samples. Other Otherminminerals oxides, Fe sulfide, sulfide, and zirerals are are K-feldspar, K-feldspar, Fe-Ti oxides, 3 ,oI0 con. con. The presence presence of two two feldspars feldspars indicates indicates $ 1 w subsolvus crystallization at at high highPH2@ H2Q 0 Coarse-grained Coarse-grained samples samplescontain contain50 50 modal modal per- S Mideontinent Rift sodic plagioclase plagioclase and modal percent cent sodic and 5-20 5-20 modal percent K-feldK-feld1 Granophyre Complexes Complexes 4: 5 Graaopbyre spar and are classified as syenite syenite and alkali-feldspar alkali-feldspar a? Lester Lester River Sill Sill these rocks insyenite. CIPW CIPW norm norm compositions compositions of ofthese clude 68-82 percent alkali alkali feldspar feldspar (Or (Or ++ Ab), 5-10 Endion Sill sill o 4o , , , , , , , , , , I , , , , percent plagioclase (An), and as much as 5 percent 50 60 70 SO 60 70 80 nepheline; they are are classified classified as as nepheline-bearing nepheline-bearing Si02 %) Sio, (wt. %) alkali syenite or or nepheline-bearing nepheline-bearing syenite. syenite. FineFinegrained samples from along the margin ofthe sill congrained from margin ofthe con- Figure Figure1. 1 Na20+K20 NaO+K20(total (totalalkalis) alkalis) versus Si02 SiO comparwmpartain 74-84 percent normative alkali feldspar (Or + + ing Aurora Sill rocks rocks with with those ofthe of the Endion Endion Sill, Lester Lester (<4%) normative quartz quartz and River Sill (Green, 1972; JJerde, Ab) with small amounts (<40h)n0rmative 1991), Midwntinent Midcontinent Rift d e , 1991), are classified classified as alkali alkali feldspar feldspar syenite. granophyre complexes complexes (Kennedy (Kennedy et al., this volume), volume), and granophyre Samples from from the Aurora Sill exhibit granophyric dikes of the Dunka River region (Harris exhibit little little granophyric (Harris and and percent; Wirth, this this volume). volume). Symbols: inverted geochemical inverted triangles triangles == drill geochemicalvariation variation(SiO2 (SO2= = 54.6-60.7 wt. percent; (open = = fine-grained; Y= = 9-19 Mg# mine (open fine-grained;half-filled half-filled== core; diamonds diamonds == mine 9-19 ppm) suggesting suggesting that that the core; Mg# == 0.40-0.75; Y filled = coarse-grained). = warse-grained). medium-grained; filled medium-grained; intrusion has undergone relatively little intrusion little internal frac- 1.0 6 , 51 �tionation. Al 203 con159 so tionation.All Allofofthe thesamples samplesexhibit exhibithigh highA120i concentrations centrations and andare areperalurninous peraluminous to tometaluminous. metaluminous. There There appears appears to tobe beno nocorrelation correlationbetween betweenstrucstructural tural position position in in the the sill silland andcomposition. com~osition.Marked Marked 00 0 differences differencesexist existininthe theconcentrations concentrationsofofsome someeleelements drillcore coreand and I (e.g., K20 K 2 0and and Si02) SO2) between between drill ments(e.g., mine minesamples samples.Such Suchdifferences differencescould couldreflect reflectdifferdiffer- S-S ent entdegrees degreesof ofalteration alterationororfractionation fractionationalong alongthe the & I length the sill. lengthof ofthe sill.Alternatively, Alternatively,the thedifferences differencesmight might reflect reflectthe thepresence presence of oftwo twoseparate separateintrusions, intrusions, but but this thisisisconsidered consideredunlikely unlikelybecause becausethese thesesample sampletolocalities are well within the 5.6 km expanse of the sill calities are well within the 5.6 km expanse ofthe sill o 0 as 10 15 asdefined definedby by'White White(1954). 0954). "(}"') yhmm) The Aurora Sill is distinct from the felsic com~ h e ~ & o sillis r a distinct from the felsic comFigure2.2.Nb Nbversus v a ~Yplot Yplot s comparing comparingAurora AuroraSill Sillsamples samples plexes plexesofofthe theMidcontinent MidcontinentRift Riftininseveral severalrespects. respects. Figure withanalyses analysesofofMidcontinent MidcontinentRift Riftgranophyre granophyrecomplexes complexes The andquartz with Thesill silllacks lacksthe thegranophyric granophec textures texturesand (Kennedyetetal.5 flmvolume). volume).Symbols SymbolsasasininFigure Figure1.1. al., this that thatare an.typical typicalofoffelsic f&iC rocks r o c kofofthe theMidcontinent Midcontinat (Kennedy $ I - I I Rift. Rift.The Thesill sillisisweakly weaklysaturated saturatedtotoundersaturated undersaturated ininsilica silicaand andcontrasts contrastssharply sharplywith withthe thesilica-saturated silica-saturatedrift-related rift-relatedgranophyres. granophyres. Furthermore Furthermorethe theAurora Aurora Sill Sillisischaracterized characterizedby byhigh hightotal totalalkalis alkalis(Figure (Figure1),I),Nb/Y NbN(Figure (Figure2), 2).and andCe/Zr CeIZrcompared comparedwith withfelsic felsicrocks rocks of ofthe theMidcontinent MidcontinentRift. Rift. The Thesill sillalso alsolacks lacksthe thenegative negativeNb Nbanomalies anomaliesthat that are arecharacteristic characteristicof ofthe the MidcontinentRift Riftgranophyres. granophyres.This Thisproperty propertysuggests suggeststhat thatthe thesill sillwas wasderived derivedfrom fromaamantle mantlemelt meltthat thatdid did Midcontinent Nband andRb, Rb,low-Y low-Ycomposition compositionof ofthe thesill sillisis notinteract interactsignificantly significantly with withcrustal crustalmaterials. materials. The Thehigh highNb not theAnimikie Animildeforelandbasin. foreland basin. typicalofofwithin plategranites m i t e s(Pearce, (Pearce,1984), 1984).consistent consistentwith withemplacement emplacementininthe typical within plate Nd Ndisotope isotopeand andU-Pb U-Pbzircon zirconstudies studiesare areininprogress progressand should provide additional constraints on the petrogenesis genesisand andage ageofofthe theAurora AuroraSill Sill(Phillips, (Phillips,ininprep). prep References ReferencesCited Cited D.W.Davis, Davis,1998, 1998,The TheAge Ageand andProvenance Provenanceofofthe theGunflint Gunflimt LapilliTuff. Tuff.Institute Instituteonon Fralick.P.W., P.W.,S.A. SA.Kissin, Kissin,and and11W. Fralick, Lapilli Lake LakeSuperior SuperiorGeology, Geology,Proceedings Proceedingsand andAbstracts, Abstracts,p.p.66-67. 66-67. Strandlie,1999, 1999,Where Whereace arethe theMetamorphosed MetamorphosedNatural NaturalOrebodies Orebodiesofofthe theMesabi Mesabi Graber,Ronald RonaldG. G.and andAlan AlanI.J.Strandlie, Graber, Range? ononLake 17-19. Range?Institute Institute LakeSuperior SuperiorGeology, Geology,Proceedings Proceedingsand andAbstracts, Abstracts,p.p.17-19. Green,J.C., J.C.,1972, 1972,North NorthShore ShoreVolcanic VolcanicGroup: Group:ininAACentennial CentennialVolume, Volume,Minnesota MinnesotaGeological GeologicalSurvey, Survey,Sims, Sims,P.K. P.K. Green, and andG.B. G.B.Morey, Morey,editors, editors,p.p.294-332. 294-332. andK.R. K.R.Wirth, Wirth,this thisvolume, volume,Petrogeneis Petrogeneisofofgranitic graniticrocks rocksofofthe theDunka DunkaRiver Riverregion, region,eastern easternMesabi Mesabi Harris,E.E.and Harris, Range, Range,Minnesota. Minnesota. Jerde,Eric EricA., A,,1991, 1991,Geochemistry Geochemistry andPetrology PetrologyofofHyuabyssal RocksAssociated Associatedwith withthe theMidcontinent MidcontinentRift, Rift,NorthNorthJerde, and 1-lypabyssal Rocks easternMinnesota. Minnesota.Unpublished Unpublished Ph.D.Thesis, Thesis, UniversityofofCalifornia, California,Los LosAngelas. Augelas. eastern Ph.D. University W i d ,and andJ.J.Vervoort, Vervoort,this thisvolume, volume,Petrogenesis PetrogenesisofofMidcontinent MidcontinentRift RiftGranophyres: Granophyres:EviEviKennedy,Bryan BryanC., C.,K.K.Wirth, Kennedy, dence dencefrom fromgeochemistry geochemistryofofKeweenawan Keweenawangranitic graniticigneous igneouscomplexes complexesofofnorthern northernMinnesota. Minnesota. — Product Morey,G.E., G.B.,1999, 1999.High-Grade High-GradeIron IronOre OreDeposits Depositsofofthe theMesabi MesabiRange, Range,Minnesota MinnesotaProductofofaaContinental-Scale Continental-Scale Morey, Proterozoic 133-142. ProterozoicGround-Water Ground-WaterSystem. System.Economic EconomicGeology, Geology,VV94, 94,p.p.133-142. Pearce,l.A., J.A.,NEW. N.B.W. Harris, Ymdle, 1984, Trace element discrimination diagrams tectonic intetprePearce, Harris, and8ndA.G. AG. Tindle, 1984, Trace element discrimination diagrams forfor thethe tectonic interpretation rocks. Journal of Petrology, V 25, p. 956-983. tationofofgranitic granitic rocks. Journal of Petroloev. V 25. D. 956-983. . , Phillips, Aurora Phillips,Erin ErinH., Hi,ininprep, prep,Petrogenesis Petrogenesisofofthe theEnigmatic Enigmatic AuroraSill, Sill,Mesabi MesabiRange, Range,Minnesota, Minnesota,Unpublished Unpublishedhonors honors thesis, MN. thesis,Macalester MacalesterCollege, College,St.St.Paul, Paul.MN. White, Geological White,David DavidA., A.,1954, 1954,The Stratigraphy Stratigraphyand andStructure Structureofofthe theMesabi MesahiRange, Range,Minnesota. Minnesota.Minnesota Minnesota Geological Survey University ofofMinnesota SurveyBulletin Bulletin38. 38.Minneapolis: Minneapolis:The The University MinnesotaPress, Press.p.n.63-66. 63-66. -. . 52 �I I I Low-grade metamorphic o the Keweenawan Portage Low-grade metamorphic zonation zonation of Lake Lake Volcanics Volcanics on on the the Keweenaw Keweenaw Peninsula, Peninsula, Michigan Michigan U. U. PUESCHNER* PUESCHNER* and and S. S. Th. Th. SCHMIDT SCHMIDT Mineralogisch-Petrographisches Mineralogisch-PetrographischesInstitut Institut Universitaet Universitaet Basel/Switzerland BaseWSwitzerland *UPUESCITNER@l1njbch *U.PUESCHNER@unibas.ch The The metamorphic-hydrothermal metamorphic-hydrothermal alteration and mineral assemblages assemblages of the the Portage Portage Lake Lake Volcanics Volcanics (PLV) (PLV) on onthe theKeweenaw KeweenawPeninsula Peninsulain in Michigan Michigan have been been studied studiedover overthe thelast last - have ten decades due to the occurrence of native copper deposits. Jolly & Smith (1972) ten decades due to the occurrence of native copper deposits. Jolly & Smith (1972) illustrated illustrated for for the the first firsttime timethe theexistence existenceofofa asystematic systematiczeolite-prehnite-pumpellyite zeolite-prehnite-pumpellyite sequence in the PLY. In their Eagle Harbor drill core profile sequence the PLV. In their Eagle Harbor drill core profilethey theyidentified identifiedaazonation zonation from from zeolite zeolite facies facies in in the the upper upper part part of of the thesection sectiontotoaaprehnite-pumpellyite prehnite-pumpellyite facies facies in in stratigraphically lower parts. In this study, three diamond-drill core profiles (Fig. A) A) stratigraphically lower parts. In study, three diamond-drill through through the the PLY PLV were were re-examined re-examined using using aa combination combination of of different different techniques techniques such such as as electron electronmicroprobe microprobeanalysis analysisand and special specialX-ray X-ray powder powder diffraction diffraction techniques. techniques. The Theprofile profile include the Ahmeek, the Copper Harbor, and the Eagle Harbor profile and penetrate penetrate 5000 5000 include the Ahmeek, the Copper Harbor, and the Eagle Harbor m m of of vertical vertical section section in in the the PLY, PLV, and and are are spaced spaced over over aa distance distance of of 50 50kin. km. The Theprofiles profiles were were correlated correlatedusing usingcharacteristic characteristicinterfiow interflowsediments sedimentsand and selected selectedlava lavaflows flowsas asmarker marker horizons. horizons. Macroscopic of 614 samples indicate at least three Macroscopic and microscopic microscopic examination examination of samples indicate three and and possibly possibly up upto tofive fivedifferent differentstages stagesofofalteration alterationbased based on onthe thevarious variousamygdule amygduleinfilling infilling sequences sequences that that can canbe bedifferentiated differentiatedduring duringthe thedeposition depositionand andsubsequent subsequenttilting tiltinghistory history of of the the PLY. PLV. AA vertical vertical as as well well as aslateral lateral zonation zonation is observed observed in the PLY PLV on on the the Keweenaw Keweenaw Peninsula. Peninsula. From From the the approximately approximately southwest southwest to to the the northeast, northeast, three three different different low-grade metamorphic zones can be observed. In the vicinity of the former low-grade metamorphic zones can be observed. In vicinity the former copper copper mining mining region region and andadjacent adjacenttotothe theKeweenaw KeweenawFault, Fault,aapumpellyite-prehnite pumpellyite-prehnitefacies, facies,also also with abundant epidote is observed. Further to the north and stratigraphically below the with abundant epidote is observed. Further to the north and stratigraphically below the Greenstone Greenstone Flow Flow aapumpellyite-prehnite pumpellyite-prehnite facies facies isis present. present. The The flows flows above above the the Greenstone to the the northeast northeast toward toward the the Keweenaw Keweenaw Tip Tip show show aa zeolite zeolite Greenstone Flow and and thrther further to facies facieswith with laumontite, laumontite,phyllosilicates phyllosilicates(mainly (mainlyclinochlore) clinochlore)and andcalcite. calcite. I I I I I I The The alteration alterationof of the the PLY PLV starts startswith withthe thefilling fillingof ofsmall small(<3 (<3 mm) mm) vesicles vesicles and and the the lining lining of 1). During During deposition deposition and and of larger largervesicles vesicleswith withphyllosilicates phyllosilicates(alteration (alterationstage stage 1). subsequent subsequent burial burial metamorphism metamorphism of the the sequence sequence (alteration (alteration stage 2), 2), Section Section CC and andDD (Fig.: A ++ B) B) experienced experienced conditions conditions of ofthe thepumpellyite-prelmite pumpellyite-prehnitefacies facies(assemblage (assemblage (Fig.: A pumpellyite-prehnite-epidote-albite) which the sequence. sequence. The The pumpellyite-prehnite-epidote-albite) which is the highest observed in the beginning beginning thrusting-event thrusting-event of of the the PLY PLV combined combined with with the theformation formationof ofthe theKeweenaw Keweenaw Fault Fault tilts tilts the thePLV. PLV. AAnew newalteration alterationstage stage33with withaafluid fluidprobably probablyoriginating originatingfrom fromthe the Lake LakeSuperior Superiorsyncline synclinenow nowcrosscuts crosscutsand andoverprints overprintsthe the earlier earlierburial burialmetamorphic metamorphicstage stage 53 �2, especially especially in in the the Section SectionAAand andB.B.Afterwards Afterwardsa anew newNINW-SSE NNW-SSE directed directed fracture fracture system was set up on the Keweenaw Peninsula. Along these fracture zones a hyper salinar ore containing containing fluid deposited deposited in open open pore pore space space quartz, quartz, native native copper copper and and calcite calcite conditions similar to the the temperature temperature conditions conditions of of alteration alteration (alteration stage 4) under conditions stage 3. The low-grade history of of the the Keweenaw Peninsula ends ends with with a low-grade metamorphic metamorphic history Keweenaw Peninsula meteoric, cold and low salinity fluid that precipitates the final calcite and late zeolites in veins veins and and still still open open amygdules amygdules(alteration (alterationstage stage5). 5). Differentiation of of Jolly, W. T. a. a. S., S., Raymond Raymond E., E., 1972, 1972, Degradation Degradation and Metamorphic Metamorphic Differentiation the Keweenawan Journal of the Keweenawan Tholeiitie Tholeiitie Lavas Lavas of of Northern Northern Michigan, Michigan, U.S.A.: U.S.A.: Journal Petrology, v. 13, 13, p. p. 273-309. 273-309. Paces, 1988, Magmatic Magmatic processes, processes, evolution and and mantle mantle source characteristics characteristics Paces, contributing to the petrogenesis contributing to petrogenesis of the the Midcontinent Midcontinent Rift basalts: basalts: Portage Portage Lake Lake Volcanics, Keweenaw Peninsula, Michigan [Ph.D. thesis]: Michigan Michigan Technological Technological University, 413p. 4l3p. 54 �A: SW NE [m] -o Top of Portage Lake Volcanics -1000 Hancock Congi. Calumet & Hecla Congl. - 2000 3000 Bohemia Congi. - 4000 Keweenaw Fault - 5000 0 n n. Portage Portage Lake Lake Volcanics Volcanics b q 1- 1 I—-i [ 1 1 1 D57 1 I D57I bigger single flows in in the the PLV PLV Interflow sediments used as marker horizons Interflow horizons other interfiow interflow sediments sediments with with in inthe the PLV PLV sampled drill cores Figure: A: :Back ~ ~ a rotated c k stratigraphic cross-section cross-sectionof of the the Portage PortageLake LakeVolcanics Volcanics (PLV) (PLV) along along strike strike from from Houghton in the southwest to the Keweenaw Point in the the northeast. With With the the sampled sampled drill cores Houghton appropriate marker and appropriate marker horizons. horizons. (Modified (Modifiedfrom from Paces Paces1988) 1988) Simplified sketch of cross-section B: Simplified cross-sectionfor easy easy reference. reference. 55 55 �Modeling Modeling the effect of intermediate intermediate temperature temperature(350°-500°C) (350'-500°C Mazatzal-age Mazatzal-age thermal thermal overprinting on on argon argon diffusion in hornblende from the southern Lake Superior Superior region. region. RAMPE, RAMPE, J.S., and and HOLM, HOLM, D.K., D.K., Dept. Dept. of of Geology, Geology, Kent Kent State State University, University,Kent, Kent,OH OH44242 44242 Mica Ar/Ar ArIAr ages from the southern Lake Superior region leave little question that that much much of of the the Penokean Penokean orogenic belt was thermally and deformationalty deformationally overprinted by Mazatzal (ca. (ca. 1650 1650 Ma) orogenic activity to the south (Holm et al., 1998; 1998; Romano et al., 2000; Loofboro Loofboro and and HoIm, Holm, 1998). Complete Complete resetting resetting of of mica mica argon argon systematics systematics from from bedrock bedrock samples samples beneath beneath 1750-1630 1750-1630 Ma deformed heating to temperatures deformed quartzites quartzites suggests suggests widespread widespread heating temperatures above 350°C 350° during during Mazatzal-related metamorphism. Hornblende Ar/Ar ages ages from within the Mazatzal-related metamorphism. Hornblende ArIAr the deformed deformed region region (Romano, 2000) are predominantly (Romano, 1999; Mancuso, Mancuso, 2000) predominantly younger younger than the the Penokean Penokean Orogeny, Orogeny, scattering from 1800-1638 1800-1638 Ma (Fig. (Fig. 1). 1). Three of of the the hornblende hornblende separates separates analyzed analyzed were were completely completely reset, probably by localized localized hydrothermal fluid-related activity associated with the the Mazatzal postRomano et et al. al. (2000) (2000) have have postulated postulated that the the scatter scatter of of the the other other postMazatzal Orogeny. Orogeny. Romano Penokean Penokean hornblende hornblende ages ages (over (over aa 70 70 m.y. m y . interval) interval) reflect reflect variable variable retention retention of of radiogenic radiogenic argon argon associated associated with episodic episodic loss loss after after initial initial closure closure during during Penokean Penokean time. time. In In order order to to test test this this hypothesis, hypothesis, we we have have modeled modeled various various thermal thermal histories histories by by imposing imposing peak peak temperature temperature excursions excursions from over orogenic orogenic timescales timescales (20-80 (20-80 my.). m.y.). The from 350°-600°C 350'-600° over The effectiveness effectiveness of diffusion diffusion in in resetting ArIAr ages is primarily a function of the the peak peak temperature temperature and its its duration; duration; the the model model resetting Ar/Ar results results are are fairly insensitive insensitive to choice of initial and final conditions (Lootboro (Loofboro and and Holm, Holm, 1998). 1998). The suggests that the distribution of hornblende Ar/Ar ArIAr ages ages (Fig. (Fig. The results of modeling modeling (Fig. (Fig. 2) suggests 1) 1) is consistent with the the partial partial resetting resetting of of argon argon systematics systematics at at ca. ca. 1650 1650Ma Maby bythermal thermalpulses pulses reaching temperatures between between 350' 350° and and 460°C 460°C. A recent petrologic investigation of reaching maximum temperatures the the deformed deformed Baraboo Baraboo quartzite quartzite indicates indicates metamorphic metamorphic temperatures temperatures of of 320°-390°C 320'-39O0C (Medaris (Medarisetet al., 1998). 1998). We Wedo donot notconsider considerititimprobable, improbable, therefore, therefore, that that bedrock bedrock regions regions underlying underlying the the deformed deformed quartzites quartzites reached reached even higher higher temperatures temperatures (between (between 400° 400' and and 460°C) 460°Cduring during Mazatzal-age Mazatzal-age overprinting. overprinting. The Themodeling modelingsuggests suggeststhat thataacombination combinationofofelevated elevatedtemperatures temperatures (350°-460°C (350'-460° with with gradients gradients in inTmax) Tmax)and and localized localized fluid-activity fluid-activity associated associated with withMazatzal Mazatzal deformation deformation provide provide the simplist simplist explanation explanation for preservation preservation of of the the scattered scatteredPenokean, Penokean, intermediate, intermediate, and and Mazatzal Mazatzal hornblende hornblende age agedata data(Fig. (Fig.1). 1). We We present present aa conceptual conceptual model model for for Mazatzal Mazatzal orogenic orogenic overprinting overprinting of of the thesouthern southernLake Lake Superior Superior region (Fig. 3). The Thegeometry geometrywe wedepict depictfor forcollision collisionof ofthe theMazatzal Mazatzalprovince province isisinin concert concert with with that that recently recently proposed proposed for for Mazatzal Mazatzal collision collision in in the thesouthwest southwestU.S.A. U.S.A. (Selverstone (Selverstone et al., 1999) 1999)and and accounts accounts for for southward southward vergence vergence of of folds folds in in the the Baraboo Baraboo quartzite quartzite (Dalziel (Dalziel and and et al., Dott, 1970). 1970). Our Ourresults resultscorroborate corroboratethe thehypothesis hypothesisproposed proposed nearly nearly 20 20years years ago agoby by Dott Dott(1983) (1983) Dott, that that the the severity severity of of quartzite quartzite deformation deformation in in Wisconsin Wisconsin was was related related to tocollision collisionfrom fromthe thesouth southatat —1630 -1630 Ma. Ma. References References Dalziel, Wisc.Geol. Geol.and andNat. Nat.Hist. Hist.Surv. Surv.Inf. Inf.Circ. Circ.14, 14,164 164p.p. Dalziel, I.W.D., I.W.D., and and Dott, Dott, R.H. R.H.,Jr., Jr.,1970, 1970,Wisc. Dott, Dott, R.H., R.H., Jr., Jr., 1983, 1983,Geo. Geo.Soc. Soc.Am. Am. Mem. Mem. 160, 160,129-141. 129-141. Holm, D.K., D.K., Schneider, Schneider,D., D., and and Coath, Coath,C.D., C.D., 1998, 1998,Geology Geology 26, 26,907-910. 907-910. Hoim, Loofboro, 1-82. Loofboro, J.J. and andHolm, Holm,D.K., D.K.,1998, 1998,Inst. Inst.Lake LakeSuper. Super.Geo. Geo.44, 44,881-82. Mancuso, C., 2000, 2000, Kent Kent State StateUniversity University MS MS thesis, thesis,97 97p. p. Mancuso, C., Medaris, L.G., L.G., Jr., Jr., Brown, Brown, PB., P.B.,and andBunge, Bunge,R.J., R.J.,1998, 1998,Inst. Inst.Lake LakeSuper. Super.Geo. Geo.44, 44,89-90. 89-90. Medaris, Romano, Romano, D., D., 1999, 1999,Kent KentState StateUniversity University MS MSthesis, thesis,92 92p.p. K.A., 2000, 2000, Precambrian Precambrian Geology Geology(in (inpress). press). Romano, D., D., HoIm, Holm, D.K., D.K., and and Foland, Poland, K.A., Romano, Selverstone, J., J., Pun, Pun, A., A,, and and Condie, Condie, K.C., K.C., 1999, 1999, Geol. Geol. Soc. Soc. Am. Bull. 111,590-606. I l l , 590-606. Selverstone, 56 �Partial resetting Partial resetting associated associated with with Mazatzal Mazatzal deformation deformation A> i 0'/ dBiW3-0 a Y 7 -'9Q Inu Li Penokean metamorphism /\ Penokean metamorphism (not reset) reset) (not \ c' 500 500 6- complete resetting Locally complete resetting associated associated with with Mazatzal Mazatzal deformation deformation 'S \ Age of Age of metamorphism metamorphism \ \ 2 \ \ a E C) H 4 /1 v 100• 100 25 25 -- 'L \ 300 0 and deformation of quartzites Toward localized localized younger — — D Toward resetting associated associated resetting with with 1100 1100Ma Ma rifting rifting 9 I , 1850 1850 I I P P 1550 1650 1650 1550 Age Age (Ma) (Ma) south of of the the Mazatzal-age Figure 1. Summary Summary of from bedrock bedrock south Figure 1. of hornblende hornblendeAr/Ar ArIAr dates dates from Mazatzal-agethermal thermal front front Romano et al. (after Flomano, Romano, 1999, 1999, and and Mancuso, Mancuso,2000). 2000).Temperature-time Temperature-timepath pathmodified modifiedafter after Romano eta\. (after (2000). Note gap gap in spread of ofhornblende hornblendedates datesbetween between 1733 1733 and and 1646 1646 Ma. (2000). Note in spread Ma. 1850 1750 1750 0 Hornblende — .5 (C S 1750 20 Ma excursion intervals C) 0) S (0 0 PC 0) 1650 80 Ma excursion intervals C S S 5'—— mica ages 2 PC C. C. araooo — < 1550 metamorphism metamorphism I I I I I I I I I I 600 400 500 200 300 200 300 400 500 600 Maximum thermal excursion excursion Maximum temperature reached during thermal (°C) PC) Figure 2. Results Resultsof of modeling modelingaa Mazatzal-age Mazatzal-age (1650-1600 (1650-1600 Ma) thermal overprinting on minerals which the Penokean orogeny orogeny (1850-1830 (1850-1830Ma). Ma). Dashed Dashed curves show effect on initially cooled shortly after the apparent age data for for 20 m.y. m.y. temperature temperature excursions excursionsat atvarious variouspeak peaktemperatures. temperatures. Solid lines for 80 m.y. m.y. excursions. Squares Squaresrepresent represent hornblende hornblende age age data data as in figure 1. Stippled Stippledregion regiondepicts depictsthe thetemperature temperature range necessary to thermally reset reset hornblende hornblende to the degree degree indicated indicated by the the hornblende hornblendeage age data. data. N undeformed Barron undeformed Barren quartzite \ quartzite deformed quartzites sS 1650-1630 0 Ma Ma Mazatzal Orogeny Orogeny C Figure 3. Conceptual Conceptualmodel model(no (no scale) scale) for the Mazatzal orogeny and andits its effects effectsin inthe the southern southernLake Lake Superior region. Modified Modifiedafter after Romano Romano et al., 2000. Collision Collisioncauses causescrustal-scale crustal-scaledeformation, deformation, south-verging of the the Penokean orogenic orogenic belt. belt. CM is continental south-vergingfolds, and heating of much of continental margin, MT is Marshfield Marshfield terrane, MP is Mazatzal Mazatzai province, NFZ is Niagara Niagara fault zone, WMT WMT is is Wisconsin Wisconsin magmatic terrane. magmatic 57 �THE 'SANDOR' 'SANDOR' DIAMOND DIAMOND OCCURRENCE, OCCURRENCE, MICHIPICOTEN MICHIPICOTEN GREENSTONE GREENSTONEBELT, BELT, WAWA, WAWA, preliminary study) ONTARIO study) ONTARIO ( a preliminary SAGE, R.P., R.P., Ontario Geological Survey, Survey, 933 933 Ramsey Lake Road, Sudbury, Sudbury, Ontario, P3E 6B5 (705-670SAGE, 5949; ron.sage@ndm.gov.on.ca) ron.sagendm.gov.on.ca) The "Sandor" diamond occurrence is is the first discovery of a bedrock diamond source in the Michipicoten region since since veteran prospector "Mickey" "Mickey" Clement reported in 1993 1993 the presence of alluvial diamond diamond in the the Michipicoten River to the Ontario Geological Survey. River to the Ontario Geological Survey. A xenolith-bearing lamprophyre dike Surmacz and and Geologist Geologist dike was observed by veteran prospector Sandor Sumiacz Marcefle Marcelle Hauseux along highway 17 17 in Lalibert Township north of Wawa, Ontario on June 22, 1993 1993 (S. ( S. Surmacz, Prospector, personal communication, 1997). area 1997). Exploratory work was being conducted in the area under an Ontario Prospector Assistance Program (OPAP) grant. Diamond indicators were not found but a sample for geochemical analysis returned results interpreted as unfavorable for the presence of diamond diamond (S. Prospector, personal personal communication, communication,1997). 1997). Surmacz, Prospector, Surmacz resampled the the Wawa Wawa dike dike in in 1995. The The sample was was sent to the Saskatchewan Surmacz and and 1-lauseux Hauseux resampled Research Council's diamond recovery laboratory and 6 gem diamonds recovered (press release, KWG Resources Inc., June 6, 1996; 1996; S. S. Surmacz, Sunnacz, Prospector, personal communication, 1997). 1997). The ground was claimed from the Algoma Central Railroad and optioned to Spider Resources Inc. (S. Surmacz, Prospector, 1997). personal communication, 1997). The occurrence represents a unique discovery  42 Ma, L. Heaman, discovery of diamond in Archean (2703 ± University of Alberta, unpublished data) rocks of non-kimberlite composition. The dikes are commonly data) non-kiiberlite of characterized by rounded mafic xenoliths up to 11 metre in size set in a fme fine grained groundmass. The The xenoliths are commonly widely spaced spaced throughout the lamprophyre dike but hut in some dikes the xenoliths may be densely packed. The The xenoliths weather in in positive relief and commonly are enveloped in a dark biotite-rich reaction rim up up to to several several centimeters centimeters in in width. The dikes have been subjected to regional metamorphism and tectonism and actinolite-talc-carbonateassemblage. Primary and the xenoliths altered altered to an actinolite-talc-carbonate mineralogy and texture are are not preserved in in the matrix or xenoliths. Geochemically the dikes dikes approximate aa basalt or or mildly alkalic basalt magma and the xenoliths pyroxenite. These diamoniferous dikes dikes are are concentrated concentrated in in the northwest-central region of the Michipicoten Greenstone Belt largely restricted to to aa synformal anticline anticline centered in Lalibert Township. The dikes are concentrated near and east of of the Dickenson Dickenson Lake Lake syenite syenite stock, but a genetic relationship between the stock and dikes dikes remains to be firmly firmly established. established. The The dikes are are both conformable and crosscutting to the deformed supracrustal supracmstal stratigraphy. The The lamprophyre lamprophyre dikes are are up to 5 m in width and cannot be traced any great great distance in the bush % of of the bush covered terrain. Diamond Diamond is is distributed erratically in the dikes and only 10 10 % dikes have yielded diamond. diamond. The dikes likely source source for for dikes do do not contain contain mineral mineral compositions compositions characteristic of kimberlite and are not a likely the kimberlite kiiberlite indicator indicator minerals found found in in the region. Geophysical Geophysical methods have proven ineffective in in locating the dikes. The presence of actinolite and anomlous Cr and Ni contents in the soils are the most effective prospecting techniques. 58 �Lithogeochemistry Lithogeochemistry and and Paleotectonic Paleotectonic Setting Setting of the Bend Northern Wisconsin Massive Sulfide Deposit, Northern Klaus J. Schulz Nicholson Schulz and Suzanne W. Nicholsov U.S. Geological Geological Survey Survey 954 National National Center Center Reston, VA 20192 20192 The Bend massive sulfide sulfide deposit deposit is is located located in in Taylor Taylor County, County, Wisconsin, Wisconsin, approximately approximately miles north-northwest north-northwest of Medford, Medford, in in the the Chequamegon ChequamegonNational NationalForest. Forest. Exploration 19 miles conducted between 1985 1985and and 1994 1994by by the the former former Jump Jump River River Venture, Venture, and and more more recently recently by by Sharpe Sharpe Energy Energy and and Resources, Resources, identified identified 3.9 3.9 million million short short tons tons of of ore ore grading grading 1.87% 1.87% copper, copper, 0.09 0.09 opt gold, and 0.39 opt silver (DeMatties and Rowell, RowelI, 1996). We conducted a geochemical study conducted of the volcanic section section hosting hosting the the massive massive sulfide sulfidedeposit deposit using using 90 90 samples samplescollected collected from from drill drill core. The (e.g., REE, REE, Zr, Hf, Ta, Ti) to Thestudy studyemphasized emphasizedinterpretation interpretationof ofstable stabletrace traceelements elements(e.g., help determine determine primary primary magmatic magmaticaffinities affinitiesand and the the tectonic tectonic setting settingof of the the volcanic volcanic section section hosting the Bend deposit. deposit. massive sulfide The Bend massive sulfide deposit deposit occurs occurs in a felsic felsic volcanic-dominated volcanic-dominatedsequence, sequence,located located along the southern flank of a mafic volcanic succession (DeMatties, 1994). The felsic volcanic (TDeMatties. 19941. alone sequence is up to 2000 feet thick, steeply dipping, south facing, andlow&greenschist and lower greenschist facies. facies. The stratigraphic footwall consists of bedded felsic tuffs tiffs (sericite stratieraohic (sericite schist) schist) with with interbedded interbedded quartztiffs (quartz-sericite crystal tuffs (quartz-sericiteschist) schist)overlain overlain(stratigraphic (stratigraphichangingwall) hangingwall)by mafic rnafic to felsic feisic fine tuffs tiffs and sediments. feldspar-phyric lava flows, felsic volcaniclastic layers, and associated fine sediments. Alteration, consisting sericitization, and and sulfidation, sulfidation, is is most most intense intense near near the the Alteration, consisting of of silicification, silicification,sericitization, massive sulfide, particularly in the footwall sericite and quartz-sericite schist. Mafic Mafic to to intermediate dikes intermediate dikes and and sills sills (?) (?) are are present present locally. locally. The Bend volcanic sequence volcanic sequence ranges ranges from from basalt basalt through through andesite andesite to to dacite-rhyodacite dacite-rhyodacite with dacite-rhyodacite most abundant. Both Boththe the mafic mafic and and felsic felsic rocks rocks are are calc-alkaline calc-alkaline in FeOt and and high high La/Yb LdYb (>15) (>IS) and and Th/Yb Th/Yb (>0.65) ratios (i.e., Barrett and character with decreasing decreasingFeOt MacLean, 1999). 1999). Mafic Maficrocks, rocks,mostly mostlyandesite andesitewith with minor minor basalt, basalt, are are characterized characterized by enriched enriched 6), relatively flat heavy-REE, prominent depletion of Ta, Zr, Hf, and Ti, ([La/Yb]n 6), relatively flat prominent depletion light-REE light-REE ([LaIYb]n and enriched Th on a primitive primitive mantle mantle normalized normalizedplot plot(Fig. (Fig.la). la). Relatively unaltered Relatively hangingwall felsic hangingwall felsic volcanic volcanic rocks rocks partly partly overlap overlapcompositionally compositionallywith with the the most most evolved evolved andesites andesites 3-4 vs -2-3 --2-3 for the andesites) light-REE(i.e., (i.e.,[La/Sm}n [LaISmln— 3-4 andesites) but have have slightly slightlygreater greaterenrichment enrichmentininlight-REE and no to small negative negative Eu anomalies. On Onaaprimitive primitive mantle mantle normalized normalized plot the the hangingwall patterns similar Nb,Ta, and Ti, felsic rocks show patterns similar to the the andesites andesiteswith with prominent prominent depletions depletions in Nb, lesser lesser depletion depletion of Zr-Hf, and enriched Th (Fig. la). la). The Thehangingwall hangingwalldacite-rhyodacite dacite-rhyodacitewas was plagioclase+pyroxene+Fe-Ti oxide oxide from from the the andesite. andesite. probably derived derived through throughfractionation fractionationof of plagioclase+pyroxene+Fe-Ti Footwall sericite sericite and and quartz-sericite quartz-sericite schist schist show show compositional compositional effects effects of of alteration alteration with with more variable Si02,higher higher K20/K20+Na20, K20/K20+Na20,and andhigher higherSScontent contentthan thanmost mosthangingwall hangingwallfelsic felsic variable Si02, rocks; footwall footwallsamples samplesalso alsoshow showincreasingly increasinglypositive positive Eu Eu anomalies anomalieswith with increasing increasingSScontent. content. felsic rocks rocks mostly mostly have have depleted depleted heavy-PEE heavy-REEand and generally generallylower lowertrace traceelement element The footwall felsic abundances than hangingwall felsic rocks (Fig. ib). lb). Although Althoughthe theheavy-REE heavy-REEdepletion depletionin in the the footwall samples samples could could be be aa result result of of alteration, alteration,some some samples samples with with depleted depleted heavy-PEE heavy-REEshow showno no compositional evidence of significant alteration (e.g., no high S content and/or high K20/K20+ compositional evidence of significant alteration (e.g., no high S content andlor high K20/K20+ Na2Oratio). ratio). Also, studies Na20 studies of of PEE REE mobility mobility associated associated with alteration below massive sulfide deposits have identified deposits identified mobility mobility of of lightlight- and and middle-PEE middle-REE but but general general stability stability of the heavy-PEE heavy-REE (Barrett and MacLean, 1999). (Barren 1999). Thus, Thus,the thecompositional compositionaldifference difference between footwall and hangingwall felsic hangingwall felsic rocks rocks may may reflect reflect primary primary differences. differences. ~ - -~ - - 59 �''JIlT Roc4P.imwve RoWPrirnitiveMantle Mantle 1000 1000 RocWPrlmiffve Mantle Rock/Primit!ve Mantle 1000 1000 b. 100 100 100 Hangingwall Felsic Rocks Hangingwall Felsic Rocks 10 10 10 1 1 Footwall Felsic Rocks .1 .1 I .1 II,, ThNbTsLaCeNdZr HfSmTiGdTbDy Y HoErTmYbLu Figure I.1. Primitive Primitivemantle mantlenormalized normalized(Kerrich (Kemchand andWyman, Wyman,1997) 1997)trace traceelement element plots plots for for Bend a) a) basalt-andesite basalt-andesite and hangingwall b) hangingwall hangingwalland and footwall footwallfelsic felsicrocks. rocks. hangingwall felsic felsic rocks rocks and and b) The Bend volcanic rocks plot as as a typical orogenic caic-alkaline calc-alkaline basalt-andesite-daciterhyodacite suite suite on on various various compositional compositionaldiscrimination discriminationdiagrams diagrams(e.g., (ex., Th-Hf-Ta; Th-Th-Ta; Th-Tb-Ta: . - . Th-FIf-Ta; Th/Yb-TaIYb). the T l k - T ~ I Y ~Further, Further, ). theenriched enrichedlight-REE light-REEand andhigh highTh T bof o fthe theBend Bend suite suiteare arecharacteristic characteristic Acontinental continental setting setting of orogenic sequences in continental settings settings (Barrett (Barren; and MacLean, 1999). 1999). A volcanic rocks rocks in in the the Bend Bend sequence. sequence. In is also supported by the abundance of felsic calc-alkaline volcanic addition, the volcanic rocks hosting the Bend massive sulfide deposit are similar compositionally to those in the Monico Monico area area in in north-central Wisconsin Wisconsin that that host the Pelican deposit (Sims (Sims and and have others, 1989). Neodymium Neodymium isotope isotope data data for for felsic felsic volcanic volcanic rocks in the Monico area have contribution from from an an enriched enriched crustal crustal source. source. The negative epsilon Nd indicating a contribution lithogeochemistry suggests that the Bend deposit deposit and probably other massive sulfide deposits associated with felsic centers in northern Wisconsin (e.g., (e.g., Flambeau, Pelican, Crandon) evolved in an extensional continental setting, possibly a continental back-arc back-arc basin in a southwarddirected subduction system. References cited: lithogeochemistry, and and hydrothermal hydrothennal Barrett, T.J. and MacLean, W.H., 1999, 1999, Volcanic sequences, lithogeochemishy, alteration in some bimodal volcanic-associated massive sulfide sulfide systems: systems: in in Bame, Bathe, C.T. C.T. and alteration Hannington, M.D., editors, Hannington, editors, Volcanic-Associated Volcanic-AssociatedMassive Massive Sulfide SulfideDeposits: Proceeses Proceeses and and Examples in Modem v.8, 8, p. p. 101-131. 101-131. Examples Modem and and Ancient Ancient Settings: Settings: Reviews in Economic Geology, v. DeMatties, T.A., 1994, 1994,Early Early Proterozoic Proterozoicvolcanogenic volcanogenicmassive massive sulfide sulfide deposits depositsin in Wisconsin: Wisconsin:an an overview: Economic Economic Geology, Geology, v. 89, 89, p. 1122-1151. 1122-1151. DeMatties, T.A. and Rowell, W.F., Wi., 1996, 1996,The TheBend Benddeposit: deposit:an an Early Early Proterozoic Proterozoic copper-gold VMS deposit: in LaBerge, LaBerge, G.L., G.L., editor, editor,Volcanogenic Volcanogenicmassive massive sulfide sulfidedeposits depositsof of northern northern Wisconsin: Wisconsin; aa commemorative volume: commemorative volume: Institute Institute on onLake LakeSuporior SuperiorGeology Geology Proceedings, Proceedings,v. v. 42, 42, Part Part 2, 2, p. p. 143143159. 159. Kenich, R. Kemch, R. and andWyman, Wyman,D.A., D.A., 1997, 1997,Review Reviewof of developments developmentsin in trace-element trace-element fmgerprinting fingerprinting of geodynamic geodynamic settings settingsand and their theirimplications implicationsfor formineral mineralresources: resources: Australian AustralianJournal Journalof of Earth Earth 465-487. Sciences, v. 44, p. 465-487. inthe theevolution evolutionof ofthe thePenokean Penokeanorgogen: orgogen:isotopic isotopic Schuiz, K.J. and and Ayuso, Ayuso, R. R. A., A,,1998, 1998,Crustal Crustalrecycling recyclingin Schulz, evidence evidence for for Archean Archean contributions contributionsto tocrustal crustalgrowth growthin inthe the Pembine-Wausau Pembine-Wausau terrane, terrane,northern northern Wisconsin Wisconsin [abstracti: [abstract]: Institute Instituteon onLake LakeSuperior SuperiorGeology GeologyProceedings, Proceedings,44th 44&Annual Annual Meeting, Meeting, Minneapolis, MN, 1998; v. 44, p. p. 113-114. 113-114. v.44, Sims, P.K., Schmus, W.R., Schulz, Schulz, K.J., and and Peterman, Z.E., 1989, 1989,Tecton-stratigraphic Tecton-stratigraphicevolution evolution of P.K., Van Schmus, the Early Proterozoic ProterozoicWisconsin Wisconsin magmatic magmatic terranes terranes of of the the Penokean Penokean Orogen: Orogen: Canadian Canadian Journal Journal of of Earth Sciences, Sciences, v. 26, 26, p. 2145-2158. 2145-2158. 60 �Assessing the extent of Early Proterozoic Mametamorphism metamorphism Proterozoic Penokean Penokeanversus versus—1770-1760 -1770-1760Ma in east-central east-central Minnesota Schweitzer, Kent, OH; OH; Schneider, Schneider, D.A., Schweitzer, D.J., DJ., Dept. Dept. of of Geology, Geology, Kent State University, Kent, DA., Dept. of Earth and Environmental Sciences, Lehigh Lehigh University, University,Bethlehem, Bethlehem,PA, PA;Boerboom, Boerboom, TJ., T.J., Minnesota Geological Survey, Survey, 2642 2642University UniversityAvenue, Avenue,St. St.Paul, Paul,MN, MN;Holm, iloIm,D.K., D.K.,Dept Dept of Geology, Kent State University, Kent, Kent, OH; OH; and and Van Van Schmus, W.R., W.R., Dept. Dept. of of Geology, Geology, University of Kansas, Lawrence, KS. Combined field, field, geophysical, geophysical, and and drill drill core core data from the internal zone Combined zone of of the the Penokean Penokean orogen in Minnesota Minnesota have have greatly greatly increased increased our our knowledge knowledge of of this this orogen's orogen's architecture, architecture,allowing allowing new correlations with the Wisconsin Wisconsin magmatic magmaticterranes terranesto to the the east east (Jirsa (Jirsa et et a]., al., 1995). Lowcorrelations with Lowgrade, greenschist structural panels panels have been identified as greenschist metamorphic, metamorphic, structural as arcuate, arcuate, imbricate imbricate thrust sheets in the poorly exposed, southeast portion of of the zone (Jirsa and Chandler, 1997). To To the west and and north, north, these these structural structural panels panels have have been been intruded intruded by bv abundant abundant post-tectonic vost-tectonic granitoids granitoids that make up aa physically physically continuous continuous mass of bedrock bedrock over over 7000 7000 km2 k d (Figure (Figure 1). 1). Holm et al. al. (1998) (1998) have have documented documentedwidespread widespread post-Penokean post-Penokean (1770-1760 (1770-1760 Ma) Ma) amphibolite amphibolite metamorphism in in the the plutonic plutonic region. region. Our goal is facies metamorphism Ourgoal is to to determine determine the the extent extent of of Penokean Penokean and/or —1760 Mametamorphism metamorphismwithin withinthe the lower-grade lower-grade terranes terranes to the southeast. andlor -1760 Ma We have have dated dated five five mineral mineral separates separates from from recently recently obtained obtained drill core housed housed at at the the Minnesota Geological Geological Survey. Survey. Sample Minnesota Sample localities localities and and associated associated dates dates are are plotted plotted on on figure figure11 (Southwick, 1994; Holm Holm and Lux, together with results from prior thermochronologic thennochronologic studies (Southwick, HoIm et et al., a!., 1998). 1998). Biotite from a biotite-hornblende 1996; Holm biotite.-hornblende granodiorite (EC-8) intruded by the post-tectonic Foley batholith batholith yielded yielded aa plateau plateau age age of 1846±6 post-tectonic Foley 1846k6 Ma Ma (four (four age age increments increments 75% of of the gas released). released). In constituting over 75% In spite spite of of its its proximity proximity to to the the Foley Foley intrusion, intrusion, this this unaffected by by it thermally. thermally. Biotite rock was apparently unaffected Biotite from from aa biotite biotite schist schist(EC-22) (EC-22)sampled sampled east of the Foley batholith yielded a plateau age of 1863±7 1863k7 Ma (eight age increments constituting over 72% of the gas released). Biotite Biotitefrom from aa tonalitic tonalitic orthogneiss orthogneiss (EC-27) yielded a plateau age increments, 81% 81% of of total total gas gas released). released). A 1820± Ma (seven increments, A hornblende hornblende separate separate from the of 1820±7 same drill core sample of orthogneiss yielded a plateau age of 1831±6 1831k6 Ma (seven (seven increments; from a meta-quartzdiorite (EC-l6) yielded 64% of total gas gas released). released). Lastly, hornblende hornblende from meta-quartzdiorite (EC-16) yielded aa 81% of of total total gas gas released). Only plateau hornblende date of 1838±5 1838k5 Ma (seven increments, 81% Only one one other Penokean Penokean Ar/Ar ArIAr age age on hornblende hornblende has been reported from east-central Minnesota Minnesota (1854±5 (1854s Ma plateau plateau date date on on the thePhilbrook Philbrook pluton; pluton; Southwick, Southwick, 1994). 1994). Five previously previously published published hornblende Ar/Ar ArIAr dates dates from from the theplutonic plutonicterrane terreneall allyielded yieldedpost-Penokean post-Penokeandates datesofof—1760 -1760 Ma Ma (Holm et al., 1998). 1998). This is the ArIAr cooling cooling ages ages in in east-central east-central the first first study study totodocument document biotite biotite Penokean Penokean Ar/Ar Minnesota. These Thesedata datafirmly firmlyestablish establishaaPenokean Penokean age age of ofmetamorphism metamorphism for for the the lower lower grade grade structural panels panels described described by by Jirsa and Chandler Chandler (1997). (1997). While While preliminary, preliminary, these these data data also also indicate thermal overprinting overprinting atat either either ca. ca. 1760 Ma Ma (as documented indicate no significant significant thermal documented to the northwest in the plutonic terrane) or at ca. 1630 1630 Ma (as (as long documented documented in adjacent adjacent parts of the the orogen in Wisconsin). ItItappears appearsthe the1770-1760 1770-1760Ma Ma barrovian barrovian amphibolite amphibolite metamorphism metamorphism in in the the internal zone of east-central east-central Minnesota may be restricted restricted to to the the deepest deepest exposed exposed region region which which also contains contains abundant abundant post-tectonic post-tectonic plutons. plutons. If so, so, this this would would be be consistent consistent with with the the interpretation of Holm et al. (1998) (1998) that the deepest deepest exposed region was probably the thickest thickest portion portion of the the Penokean Penokean orogenic orogenic belt belt which which became became unstable unstable and and rapidly rapidly collapsed collapsed (i.e., (i.e., unroofed) at —1760 Ma. The temporal and spatial association of post-tectonic plutons, barrovian -1760 Ma. —1760 Mametamorphism, metamorphism,and andmidcrustal midcrustal unroofing unroofing suggest suggest aa genetic link between -1760 Ma between thermal thermal softening of the overthickened overthickened crust and post-orogenic collapse in the hinterland of the Penokean Penokean orogen. 61 �QiDKeweenawan Supergroup Paleoproterozoic C:) LIWe Falls Fonnation Mixed supraaustai rot and shearS granitic rocks. Mets.plutomc rocks may be Archean an part 0 HilIman tonalite (may be Archean in part) c1 Archean/Proterozoic? Undiffetentiated — Minnesota. Filled Figure 1. 1.Generalized Generalized bedrock bedrockgeology geology map map of of east-central Minnesota. Filled circles circles represent localities Lux, 1996; HoIm etal., (after HoIm Holm and Lux. 1996;Holm etal.. 1998) 1998)which reoresent localities of of prior crior results results (after yielded ca. 1760-1750 Ma dates onmica on mica and hornblende. Also plotted the 1854 1854Ma M a Ar/Ar Arlk clotted is is the vikded 1760-1756% plateau age on hornblende from the Penokean Philbrook Philbrook pluton pluton (southwick, (Southwick, 1 1994). Open 994). Open circles from study. LF circles represent localities localities and results f rom this study. LF is is Little Little Falls, SC SC is St S tCloud. Cloud . ~ ~ ~ - ~ ~ - ~ ~~~~ References References HoIm, D.K.,and D.K.,and Lux, Lux, D.R., DR., 19%, 1996,Core Corecomplex complexmodel model proposed for gneiss dome development Holm, Paleoproterozoic Penokean Penokean omgen, orogen, Minnesota: Minnesota Geology, 24,343-346. 24,343-346. during collapse of the Paleopmteromic D.K., Darrah, K.S., K.S., and Lux, Lux, D.R., DR., 1998, -1760 Ma Holm, D.K., 1998,Evidence for widespread -1760 Ma metamorphism and 870-1820 Ma) morphism and rapid rapid crustal crustal stabilization stabilizationof ofthe theEarly EarlyProterozoic Proterozoic(1 (1870-1820 Ma) Penokean Penokean Orogen, Minnesota: Minnesota American 60-81. 298,60-81. Omgen, AmericanJournal Journalof ofScience, Science,298, M. and Jirsa, M., andChandler, Chandler,V., V,1997, 1997,Scientific Scientifictest testdrilling drillingand andmapping mappingin ineast-central east-centralMinnesota, Minnesota, 1994-1995: Sununary Summaryof oflithologic lithologicresults: results:M~M. Mlnn.Geol. Geol.Smv. Suit Info. Circular 105 pp. 1994-1995: Circular42, 42,105 .,Chandler, Chandler, V, V, and andBoerboom, Boerboom,11, T., 1995, 1995,Extension Extension of of the the Wisconsin Wisconsin magmatic terranes Jim, M Jirsa, lvi, into the Minnesota Minnesota segment of the Penokean omgen: orogen: Institute Institute on on Lake Lake Superior Superior Geology, 4 1st Annual Meeting, 41st Meeting, Marathon, ON, 42.25-26. 42,25-26. D.L., 1994, geochronologic studies studies of of Precambrian Precambrianterranes terranes in inMinnesota: Minnesott Southwick, D.L., 1994,Assorted geochronologic A potpourri of timely information: information: in in Short Short Contributions Contributions to the the Geology Geology of of Minnesota, Minnesota, 1994, 1994, Investigations 43, 1-19. edited by D.L. Southwick, Minnesota Geological Survey Report of Investigations 43,l-19. 62 �THE THE DISTINCTION DISTINCTION BETWEEN BETWEEN FLAT FLAT PEBBLE PEBBLECONGLOMERATES CONGLOMERATES AND AND INTRAFORMATIONAL INTRAFORMATIONALBRECCIAS BRECCIASIN INPRECAMBRIAN PRECAMBRIANIRON IRONFORMATIONS FORMATIONS Bruce BruceM. M.Simonson Simonson Geology GeologyDepartment Department Oberlin OberlinCollege College Oberlin, USA Oberlin,01144074-1044 OH 44074-1044USA Iron Ironformation, formation,aa distinctive distinctivetype type of of rock rock restricted restricted largely to the Precambrian, Precambrian, consists consists mainly of oi silica (in the form of ehert) and such iron-rich minerals as hematite, magnetite, siderite, andlor silica (in the form of chert) and such iron-rich minerals as hematite, magnetite, siderite, and/or greenalite. greenalite. Lamination Laminationand andthin thinbedding beddingare arecommonplace commonplacein inthese theserocks rocksas asevidenced evidencedby by the the near-universal use of the term BIF (for "Banded Iron Formation"), but a substantial minority near-universal use of the term BIF (for "Banded substantial minority of of iron iron formations formations(particularly (particularlythose thosein inNorth North America) America)are are actually actually GIF GIF(for (for "Granular "GranularIron Iron Formation"). Formation"). Such Suchunits unitshave havecoarsely coarselyclastic clastictextures textures(analogous (analogousto tothose thoseof ofcarbonate carbonate grainstones and oolites) and display structures such as cross-bedding rather than grainstones and oolites) and display structures such as cross-beddmg rather thanbanding. banding. CentimeterCentimeter-to todecimeter-scale decimeter-scalelayers layersrich richin insiliceous, siliceous,flat, flat,pebble-size pebble-size fragments fragmentsare areminor minor constituents of both BIF and GIF. The fragments are clearly intraformational in origin constituents of both BIF and GIF. The fragments are clearly intraformational in originand andare are frequently bothsettings, settings, frequentlycited citedas asevidence evidenceof ofdeposition depositionin inshallow, shallow,high-energy high-energyenvironments environmentsininboth but but they they have have very very different differentorigins. origins.The Thefragments fragmentsin in GIF GIFoccur occurin in flat flatpebble pebbleconglomerates conglomerates where where they they generally generally have havewell-rounded well-roundedends, ends, form formaa grain-supported grain-supported framework, framework,and andoriginated originated via via erosion erosionand and reworking reworkingatatthe the sediment-water sediment-waterinterface. interface.In In contrast, contrast,the the fragments fragmentsin inBIF BIF occur in breccias where they are generally much more angular, isolated in a matrix of less occur in breccias where they are generally much more angular, isolated in a matrix of less siliceous siliceousmaterial, material,and andoriginated originatedafter afterdeposition depositionand andatatleast leastshallow shallowburial burialvia viapartial partial liquefaction. liquefaction.The Thedominance dominanceof ofeherty chertyfragments fragmentsin inboth bothbreccias brecciasand andconglomerates conglomeratesindicates indicates that thansilica-poor silica-poorones onesin inboth bothBIF BIFand and that silica-rich silica-richlayers layerswere weresignificantly significantlymore morecohesive cohesivethan GIF. GIF. Many Manv of of the the flat flat pebbles nebbles in in GIF GIF are are identical identical to to nodular nodular masses masses known known as aschert chertpods in -podsin underlying sediments, suggesting they are exhumed nodules. Petrographic evidence such as underlying sediments, suggesting they are exhumed Petrographic evidence such as large differences in minus-cement porosity inside large differences vorositv vs. outside the pods and dramatic thinning- of . individual individuallayers layersas as they they exit exitpods podsindicates indicatesthe the pods podsformed formedvia via early earlysilica silicacementation. cementation.This This widespread widespread early early cementation cementationisis probably probably due dueto to high high silica silicaconcentrations concentrationsin inPrecambrian Precambrian seawater seawater which, which, unlike unlike today, today, caused caused silica silicato to difftise diffuse into into (rather (rather than than out out of) of) sediment sedimentpore pore waters (Siever, 1992, Geochimica et Cosmochiiica Acta 56,3265-3272). waters (Siever, 1992, Geochimica et Cosmochimica Acta 56, 3265-3272). . 63 �PRECAMBRIAN FEATURES UNDER THE THE JAMES JAMES BAY BAY AND HUDSON BAY BAY LOWLANDS LOWLANDS PRECAMBRIAN Geological Survey, Ontario Geological Lake Rd, Rd, Sudbury, Sudbury, ONP3E ON F3E 6B5 Greg Stott, Brian Survey, 933 Ramsey Lake Brian Berdusco, Ontario stottg(ägov.on.ca ;brian.berdusco)ndm.gov.on.ca stottgf%~ov.on.ca brian.berdusco@ndm.eov.on.ca Large cover of of both both the James Bay and and Hudson Large parts parts of the the Superior Superior Province Province underlie underlie the Phanerozoic Phanerozoic cover James Bay Hudson Bay lowlands. This, This, plus plus the the poor poorbedrock bedrockexposure exposureininthe theeastern easternand and northernmost northernmostexposed exposed Sachigo Sachigo Subprovince, Subprovince,has has permitted only limited with permitted limitedsuccess success to date date in correlating correlating the regional geology of of the the Uchi-Sachigo Uchi-Sachigo superterrane superterrane with parts project is planned number of geological the Superior Superior Province Province in in northwestern northwestern Quebec. Quebec. AA project planned to examine examine aa number parts of the problems in addition addition totoregional regionalcorrelations correlations by byreprocessing reprocessing the the ODMJGSC ODMIGSC aeromagnetic aeromagnetic data the 1960s 1960s problems data of of the covering the region mainly north of of Latitude Latitude 510. 51'. This will willbe be done done in in co-operation co-operation with with Regional Regional Geophysics Geophysics staff of under the the lowland cover of the the GSC. GSC. This This poster poster isis intended intended to to outline outlinesome some of of the the Precambrian Precambrian features under cover that might might be he enhanced when the reprocessing is completed. Features and Interpretive Interpretiveissues: issues: the substrate substrateof of the the northern northern Hudson Hudson Bay 1) The complex, broad high magnetic magnetic susceptibility susceptibility that that characterizes characterizes the I) [HBL] isissimilar Lowlands [HBL] similartotothat thatofofthe thePikwitonei Pikwitoneigranulite granulitedomain domainand and adjacent adjacent domains domains in Manitoba. We suspect that that this this region region of old broad range range of of Archean Archean ages ages including includingpre-3.8 pre-3.8 Cia Ga crust crust (cf. (cf. suspect old crust, crust, containing containingaa broad B6hm Geology, JanIOO), JanIOO), continues and underlies underlies the early early BOhm et et al., Geology, continuesinto intothe the northernmost northernmostpart partof of Ontario Ontario and Inlier. Proterozoic Sutton Inlier. Orogen [THO] [THO] are in parts parts of of Manitoba and the the HBL. Re-interpretation 2) Elements of the Trans-Hudson Orogen are exposed exposed in Re-interpretation of the aeromagnetic aeromagnetic patterns patterns that that characterize characterize this this region region suggests suggests several points to to consider: consider: 3) 3) River Belt BeltofofManitoba Manitobadoes doesnot notappear appeartotocontinue continueeastwards eastwards across across the northern northern a) The Proterozoic Fox River HBL but border and and probably probably links links to the hut continues continues north north to to Hudson Hudson Bay Bay near near the the Manitoba-Ontario Manitoba-Ontario border the Internides of the main THO linear gravity gravity anomaly just just offshore, north north of Ontario. Strata seem to reappear reappear as of Strata from from the Trans-Hudson Orogen Orogen offshore offshore in Hudson Bay seem asfolded folded units units north of b) h) the Sutton Inlier the Inlier and anddiscontinuously discontinuouslyextend extend southwards southwards towards the inlier. inlier.These These features features need need further further discrimination to to establish establish their full extent. discrimination full extent. as aa single, single, continuous continuous package packageof of rock rock as as currently c) The Sutton Sutton Inlier Inlier has has for formany manyyears years been been treated treated as c) portrayed on on geological maps maps (compiled (compiled from from the the original original work by H. Bostock GSC Paper Paper 70-42). But a portrayed Bostock -- GSC closer examination of patterns in in its its vicinity vicinity suggests the Sutton Inlier Inlier is of the the aeromagnetic patterns suggests the is not not aa single single large large domain but aa set set of ofsouthward-convex-shaped southward-convex-shaped inliers resemble "klippe-like" domain inliers strung strung along along aa line. They resemble features comprising shallow shallow water platform sedimentary depositsincluding including iron iron formation, and features comprising sedimentary deposits and gabbroic gahhroic sills that southwardsonto ontothe theArchean Archeancraton cratonfrom from the the main main THO belt that might might have have been been transported transported southwards belt offshore. Smaller of the currently defined aeromagneticallyapparent apparent to the north and east east of defined Smaller "klippe" "klippe"are arealso alsoaeromagnetically Sutton Inlier. The the Nastapoka NastapokaFormation Formationon onthe the eastern easternshore shoreofof Hudson HudsonBay Bay (cf. (cf. Sutton The strata strata resemble resemble the Chandler Res.1989) 1989)and andpart partofofthe thePovungnituk PovungnitukGroup Group of of Cape Cape Smith Smith Belt. Chandler and and Parrish, Prec. Res. Beneath the James JamesBay BayLowlands Lowlands [JBL], [JBLJ,there thereisis aa strong strong likelihood likelihood that that the Beneath the the English English River River and and Quetico Quetico metasedimentarysuhprovinces subprovincesconverge converge underthetheJames JamesBay BayLowland Lowlandcover cover and and that that the metasedimentary under the Wabigoon Wabigoon Subprovince pinches pinches out out eastwards. eastwards.Discrimination Discriminationof of this this has hasimportant importanttectonic tectonic implications implications for the original Subprovince original that the converging nature of these these subprovinces. subprovinces. It is compelling compelling to to suggest suggest that converging English English River River and and Quetico Quetico nature resemble telescoped telescoped inter-arc inter-arc basins basins that that wrap wrap around the the east eastend endof of aa Wabigoon Wabigoon microcontinent microcontinent and and continue continue 'basins in Quebec. The merged merged English English R R - Quetico R. and and Opinaca Opinaca R. R. "basins" Quebec. The Quetico isis on-line with with the the Nemiscau Nemiscau R. on-line conceptually conceptually analogous analogous to to the the modern modem basins basins of of the the Solomon Solomon and and Coral Coral seas seas respectively north north and and south south of of east east Papua-New Papua-New Guinea. Guinea. The Sachigo and Uchi Uchi subprovinces to merge merge under under the the eastern easternHBL HBL and and JBL JBL suhprovinces of northwestern Ontario appear appear to and continue as aa single single domain domain and and emerging emerging as asthe theMinto Minto domain domain of northern Quebec. continue eastwards eastwards as Quehec. the eastern easternHBL, HBL,flanked flankedto tothe thewest westby byaafault faultsimilar similar in orientation A major major indenter-like indenter-likefeature feature occurs occurs under the to the the Miniss Miniss Fault. Fault. This Thisfeature, feature, like likeother other"indenters" "indenters"ininnorthwestern northwestern Ontario Ontario (e.g., (e.g., at Savant Savant Lake, Lake, Shebandowan and Manitouwadge), Manitouwadge), closes closesnorthwards northwardsand andborders bordersaa"bow-tie" "bow-tie" aermagnetic aermagneticpattern patternon on its its north Shehandowan and flank, which flank, whichappears appears to to reflect reflectshortening shorteningand andexhumation exhumationofofdeeper deepercrust. crust. - 4) 4) 5) 5) 64 �THE THE 1787-1772 1787-1772MA MAEAST-CENTRAL EAST-CENTRAL MINNESOTA MINNESOTA BATHOLITH: BATHOLITH: PRECURSOR TO TOCRUSTAL CRUSTALSTABILIZATION STABILIZATION IN IN THE THEL.L.SUPERIOR SUPERIOR PRECURSOR REGION REGION - - VAN both bothatatDept. Dept.of ofGeology, Geology,Univ. Univ.ofof VAN SCHMUS, SCHMUS, W.R., W.R.. and andMacNEILL, MacNEILL,L.L.C.,C., ofofGeology, Kansas,Lawrence, Lawrence,KS, KS,55045 55045(rvschmus@ukans.edu); (rvschmus@ukans.edu);HOLM, HOLM.D.K., D.K.,Dept. Dept. Geology,Kent Kent Kansas, both at Minnesota BOERBOOM, JIRSA. M.A, M.A. both at Minnesota State Univ., State Univ.,Kent, Kent,OH; OH; BOERBOOM,T.J. T.J.and and JIRSA, Geological MN GeologicalSurvey, Survey,2642 2642University UniversityAvenue, Avenue,St. St.Paul, Paul,MN The Thecause causeofof—1760 -1760 Ma magmatism in the the southern southernL. L.Superior Superiorregion regionhas hasbeen beenconsidered considered considerable amagmatic enigmatic because of its apparently abrupt nature and the enigmatic because of its apparently abrupt nature and the considerable amagmatichiatus hiatus(—60 (-60 m.y.) m.y.) that that separates separates itit from from Penokean Penokean orogenesis. orogenesis. The Theage age of of post-Penokean post-Penokeanmagmatism magmatisminin Wisconsin, Wisconsin,commonly commonlyreferred referredtotoasas"1760 "1760Ma", Ma",was wasobtained obtainedby by dating datingmg-sized mg-sizedfractions fractionsfrom from here new U-Pb data rhyolites and and epizonal epizonal granites granites (Van (Van Schmus, Schmus, 1980). 1980). We Wereport report here new U-Pb datafrom fromthe the rhyolites recently recentlycharacterized characterizedmidcrustal midcrustalplutonic plutonicterrane terraneinineast-central east-centralMinnesota. Minnesota. This Thisportion portionofofthe the exposed exposed Penokean Penokean orogen orogencontains containsnumerous numerouspost-tectonic post-tectonicplutons plutonsof ofvarying varyingcomposition compositionand and Based on field, drill-core, geometry(Jirsa (Jirsaetetal., al.,1995; 1995;Boerboom Boerboometetal., al.,1995; 1995;1998). 1998). Based on field, drill-core,petrologic, petrologic, geometry and andgeophysical geophysicalstudies, studies,about about20 20separate separateintrusive intrusivebodies bodieshave havebeen been identified identifiedand andcategorized categorized granites; into 1)granodioritic granodioritic to todioritic dioriticrocks; rocks;2)2)gray gray granites; 3) 3)red redgranite granite into four four separate separate groups: groups: 1) quartzofeldspathic dikes. plutons, plutons,dikes dikesand andsills; sills;and and4)4)late laternafic maficplugs plugsand anddiabasic diabasictoto quartzofeldspathic dikes. 0.34 Richmond Granite Intercepts at 4 grains 'N f?2- 0±0&1772.3±1.OMaI MSWD= 1.6; P = a16J 0.32 1 grain 1720 0.30 0.28 600 TV" .1 grains 0.26 0.24 3.5 3.7 3.9 4.3 4.1 201 207 4.5 4.7 4.9 p y 235 U(J Pb!235 Fiyure 1.1. Plot Plotof ofzircon zircondata datafrom fromthe theyounger youngerand andolder olderends endsof ofthe theage agespectrum spectrumfor forthe theEastEastFigure Central CentralMinnesota Minnesotabatholith. batholith.Data Datafor forother otherunits unitsfall fallininbetween betweenthese thesetwo twopopulations. populations. 65 �Our new results are mostly U-Pb isotope dilution analyses from single zircons zircons weighing weighing 11 to to 5 micrograms, with with several several hand-picked, hand-picked,air-abraded air-abradedgrains grainsselected selectedfor foreach eachrock rockunit. unit. For the most part the analyses are not influenced by by xenocrystic cores, cores, although in a few cases they may be present. All units of the post-tectonic suite, the "East-Central All units of the post-tectonic suite, the "East-Central Minnesota Minnesota batholith" (ECMB), (ECMB), yield ages within the range 1772±1 Ma (Richmond Granite) to 1787±3 1772i1 to 1787i3 Ma (Warman (Wannan Granite). The relative relative ages within this range correlate with relative relative ages based based on on field fieldrelationships relationships known). Thus, (where known). Thus, all all units units of of the the ECMB ECMB (St. Cloud Cloud Red Granite, Granite, Reformatory Reformatory Granodiorite; Granodiorite; Rockville Granite, Freedham Tonalite, Anne Lake Lake Granite, Granite, plus plus others) others) were emplaced within 15 15 m.y. are determining determining ages from from surrounding surrounding basement rocks, using using m.y. In Inaddition additionto to the the ECMB, ECMB, we we are outcrop and and drill core samples; preliminary results resultsyield yield an an age age of of 1800±8 Ma for a foliated samples; preliminary 1800± Ma foliated tonaiite tonalite within the Hillman migmatitecomplex. We are are also also redetermining redetermining U-Pb U-Pb ages ages of of several several units of the "1760 Ma" suite in Wisconsin using using single-crystal single-crystal analyses, analyses, but but at at this this time our data definitive. are not definitive. Our results suggest that the "1760 Ma" magmatic event is only only the the last last stage stageof ofaa—25 -25 m.y. m.y. episode of post-tectonic magmatism. These post-tectonic magmatism. These data data significantly significantlyreduce reduce the the time-lag time-lagbetween between the the end of Penokean orogenesis and the onset of post-tectonic plutonism, bringing it into into line line with with thermal and physical physical models which which predict predict characteristic characteristic time-lags time-lags of of only only 20-40 m.y. m.y. (England thermal Thompson, 1984; and Thompson, 1984;Turner Turneret et aL, al., 1992). 1992). Intrusion of the Intrusion of the ECMB ECMB was was associated associated with withwidespread widespread midcrustal midcrustal amphibolite amphibolite and directly preceeded preceeded rapid rapid exhumation exhumation (i.e., (i.e., collapse?) collapse?) and and crustal crustal stabilization metamorphism and In some (Holm al., 1998). 1998). In some regions regions of incipient incipient collapse collapse (i.e., (i.e., India-Asia India-Asia today), today), the the (Holm et al., overthickened crust crust contains contains aa partially partially molten molten layer layer ponded ponded in in its mid-section (Nelson et al., overthickened al., 1996). manner we suggest the overthickened overthickened Penokean crust was was invaded invaded by by 1996). In analagous manner midcrustal melts melts which which probably probably affected affected its its rheological rheologicalbehavior. behavior. Vast magma midcrustal magma intrusion intrusion may may dramatically decreased crustal viscosity and and promoted promoted collapse (as recently proposed for have dramatically the Canadian Cordillera; Cordillera; Vanderhaeghe Vanderhaeghe et et aL, al., 1999). 1999). References Boerboom, T., T., Jirsa, Jirsa, M., M., and Holm, Hoim, D.K., D.K., 1998, Early Early Proterozoic Proterozoic Intrusive Intrusive Rocks of EastBoerboom, Superior Gwl. Geol. Fieldtrip Fieldtrip Guidebook, Central Minnesota: Institute on L. Superior Guidebook, v. 44, 44, p. 3-30. 3-30. Boerboom, T.J., T.J., Setterholm, D.R., D.R., and Chandler, V.W., V.W., 1995, Bedrock geologic map, plate 2 G.N., Project Project Manager, Manager,Geologic Geologicatlas atlasofofSteams SteamsCounty, County,Minnesota: Minnesota: Minnesota of Meyer, G.N., SurveyCounty CountyAtlas AtlasSeries, Series,C-10, C-b, Part A, Geological Survey scales 1:200,000 and l:lOO,000.England, P.C., and and Thompson, A.B., 1984, scales 1:200,000 and l:lOO,OOO.England, P.C., Thompson, A.B., 1984, PressurePressuretemperature-time paths paths of of regional regional metamorphism metamorphism I.I. Heat Heat transfer transfer during during the evolution of temperature-time regions of thickened continental crust: Journal of Petrology, v. 25, p. 894-928. 894-928. Holm, Darrah, K., K., and and Lux, Lux, D.R., D.R., 1998, 1998,Evidence Evidence for forwidespread widespread—1760 -1760 Ma Ma Holm, D.K., D.K., Darrah, metamorphism and and rapid crustal stabilization of the Early metamorphism Early Proterozoic Proterozoic (1870-1820 (1870-1820 Ma) Ma) Penokean orogen, Minnesota: American American Journal Journal of Science, Science, v. 298, p. 60-81. 60-81. Jirsa, M.A., 1995, Bedrock geologic map of easteastM.A., Chandler, V., V., Cleland, J., J., and Meints, J., J., 1995, central Minnesota: Minnesota Minnesota Geological Geological Survey Survey Open-File Open-File Report Report 95-1. Nelson, K.D., K.D., and 27 others, 1996, Nelson, 1996, Partially molten middle crust beneath beneath southern southern Tibet: Tibet: Synthesis of project INDEPTH results: Science, v. 274, p. 1684-1688. 1684-1688. and Foden, Foden, J., J., 1992, 1992,Some Some geodynamic geodynamic and and compositional compositional Turner, Sandiford, M., Turner, S., S., Sandiford, M., and constraints on "postorogenic" magmatism: 1-934. constraints magmatism:Geology, Gwlogy,v.v.20, 20,p.p.93 931-934. Vanderhaeghe, O., 0., Teyssier, Vanderhaeghe, Teyssier, C., and and Wysoczanski, Wysoczanski, R., 1999, 1999, Structural Structural and and geochronologic geochronologic constraints on the role of partial melting during during the formation formation of the the Shuswap Shuswapmetamorphic metamorphic Thor-Odin dome, British Columbia: Columbia: Can. J. Earth Sci., core complex at the latitude of the Thor-Odin 17-943. v. 36, 36, p. p. 9917-943. W.R., 1980, Van Schmus, W.R., 1980, Chronology of igneous rocks associated with the Penokean orogeny orogeny in Wisconsin: Geol. Geol. Soc. Soc.America AmericaSpec. Spec. Paper Paper 182, 182,p. p. 159-168. 159-168. 66 �ISOTOPIC CONSTRAINTS CONSTRAINTS ON THE ORIGIN ORIGIN OF GRANOPHYRE GRANOPHYRE COMPLEXES COMPLEXES IN IN THE THE MIDCONTINENT RIFT OF NORTHEASTERN MINNESOTA. MIDCONTINENT OF NORTHEASTERN MINNESOTA. Vervoort, Jeff D., Department Department of of Geosciences, Geosciences, University of of Arizona, Tucson, Tucson, AZ AZ Vewoort, JeffD., (ve~oor@,geo.arizona.edu); Wirth,K.R., K.R.,(wirth@macalester.edu) (wirth@macalester.edu) & & Kennedy, Kennedy,B.C., B.C., (vervoort(geo.arizona.edu); Wirth, (bkennedy@macalester.edu). Macalester College, St. Paul, MN (bkennedy@macalester.edu). The magmatism of the Midcontinent Midcontinent Rift (MCR) (MCR) is dominantly dominantly mafic in composition compositionin in both both the volcanic In some someportions portionsof of the the MCR, MCR, volcanic sequences sequences as well as the underlying intrusive rocks. In however, the magmatism magmatism is strongly strongly bimodal with significant significant volumes of rhyolite rhyolite and and granite granite in in [1]. This This is is particularly true true for for the northeast northeast limb of the North association with basalt and gabbro [I]. km thick thick volcanic volcanic stratigraphy stratigraphy Shore Volcanic Group Group (NSVG) (NSVG) where where approximately approximately 25% 25% of of its its 6.4 6.4 km other evolved evolved lavas lavas 121. [2]. Evolved intrusive rocks rocks are also also prominent prominent in in is composed of rhyolite and other the northwest flank of the MCR and occur in compositionally stratified complexes. Although these stratified complexes. Although northwest flank are dominantly granitic (granite-granodiorite) (granite-granodiorite) in composition, composition, intermediate intermediate rocks rocks (monzodiorite(monzodioritein the the lower lower portions portions of ofthese thesecomplexes. complexes. Collectively these quartz monzodiorite) predominate in granophyres because of their their characteristic characteristic gmophy& granophyrictextures. textures. The field relahave been termed graniphyres tions, petrography, and geochemistry of these complexes are described by Kennedy petrography, and geochemistry of these complexes are described by Kennedyet et al. al.[3]. [3]. similarities to to the the overlying overlying volcanic volcanic rocks. rocks. Both The granophyres granophyres have striking geochemical similarities 8-67% SiO2 S i O (Fig. 1). 1). have a strong bimodal character illustrated by the compositional gap at 558-67% The chemistry of the rhyolites and the granites are similar in many many respects (e.g., (e.g., major and trace elements, REE patterns) which begs the interpretation elements, interpretation that the granophyric granophyric complexes complexes represent represent the magma chambers chambers that supplied supplied the large rhyolitic rhyolitic eruptions. eruptions. The NSVG lavas are isotopihe NSVG i&topi7 (Fig. 2). 2). Most cally heterogeneous (Fig. Granophyre ~ r a u ~ p ~Complexes Complexes qm values close close basalts e.,, values basaltshave haveinitial initial£Nd • Greenwood 6 1 &wood Lake Lake [4, 5]. 51. to zero or slightly negative negative [4, A A Misquali MiquahHills Hilh The rhyolites, <)Eagle The rhyolites, in in contrast, contrast, typically typically 5 @ EagleMountain Mountain • Pine 0 PineMountain Mountain eNd have strongly strongly negative negativeinitial initial8Nd 4 o Finland values (down values (down to -15) - 15)indicating indicatingthey they were formed formed in in large large part by the the par- 1(20 4 t 3 a NSVG Rhyolites melting and tial melting and assimilation assimilation of of older (most Archean) crustal crustalrocks. rocks. (most likely likely Archean) C> 2 In contrast contrast to to the the NSVG lavas, lavas, the granophyres are more isotopi1I NSVG transitional baaalia b:alts cally homogenous both individually cally homogenous individually 0 and and collectively collectively (Fig. 2). With one one 60 65 75 80 exception hiexception all all granophyres granophyres have have iniSi02 similar to most values 0 tiale., 0 to to -5, -5, similar tial aNd values Figure 1. Si02 S i Ovs. vs. 1(20 K,0 plot illustrating illustrating the linear array basalts in the MCR [7]. [7]. The The isotoisotoand bimodal distribution of of and bimodal distribution of the the granophyre granophyre pic homogeneity of individual gracompositions. Also shown are data for NSVG tholeiitic Also shown are data for tholeiitic nophyres is demonstrated by the and and transitional basalts [5] rhyolites [6]. Few samples Few samples transitional [5] and compositions of two granophyre (4 of 5 are from the Finland granophyre) plot in the SiO2 from Finland granophyre) plot in the Si02 complexes (Misquah complexes (Misquah Hills and and gap (58% to 67%). (58% to 67%). Greenwood Lake) Greenwood Lake) located located in in central central - n .I - 455055 67 �Cook County. The The Greenwood Greenwood Lake Lake granophyre granophyre ranges from monzodiorite to granite ((Si02 S i O 52% to 72%) but has initialENd values of-0.7 of -0.7to to -1.9 -1.9 (Fig. (Fig. initial 2), an extremely extremely small small range considerconsidering analytical analytical reproducibility reproducibility (±0.3 (±0.to to 0.4&Nd G units). The Greenwood Lake ENd 0.4 NSVG Rhplites granophyre was emplaced emplaced during during the the early stage stage of the MCR MCR (1107 (1 107Ma; Ma; [8]). [8]). A Misquah Hilb granophyre The Misquah Hills granophyre has not Misquah granophyre been dated but is likely of similar age because it intrudes because intrudes a sequence sequence of older, 45 50 55 60 65 70 75 reversed polarity lavas. These new isotopic data, in in conconFigure 2. 2. Si02 Figure S i O vs. vs. initial initial EENd of the granophyre junction with major and trace-element chemistry and previously published Nd complexes. Also Also shown shownare are data data for for NSVG NSVG tholeiitic tholeiitic results from 6 other granophyres [6], basalts [5] and rhyolites [6]. Note the Nd isotopic basalts and rhyolites [6]. Note the isotopic [6], homogeneity of the Misquah Hills and Greenwood provide important constraints on the origin of the granophyre Lake granophyres granophyres over over a wide wide range range of of Si02. SiO. granophyre complexes. complexes. First, the granophyres graniphges are isotopically i~ot6~icall~ distinct from the rhyolites. Although Althoughtwo twoof ofthe theCook Cook County County rhyolites rhyolites(Kimball (KimballCreek, Creek,Red Red Rock) Rock) about -5, this is more negative (Eagle have initial G~ values than all but one of the granophyres ENd genetically related to Q = = -7.7). -7.7). This indicates that the granophyres are probably not genetically Mtn., initialENd Mm., initial the rhyolite flows and do not represent the the magma magma chambers chambersfrom fromwhich whichthe therhyolites rhyoliteswere werefed. fed. It is important to note, however, that the granophyres most thoroughly studied thus far (Misquah likely older older(-1 (l 107 Hills, Greenwood Lake) are likely 107Ma). Ma). ItItisisnot notuntil untilthe themain mainstage stageof of the the rift rift (<1100 ( 4 100 &Nd values were erupted erupted in in the the NSVG. NSVG. Ma, [9]) [9]) that thatthe thelarge largerhyolites rhyoliteswith withthe thehighly highlynegative negative Secondly, homogeneity. This Secondly, the two granophyres granophyres examined thus far show remarkable isotopic homogeneity. This implies that these complexes have been derived from a single parental parental magma magma or or from from magmas magmas that are isotopically similar. In In the the case case of of the the granophyre granophyre complexes, complexes, the high silica portions could not have been derived to a significant significant extent from melting or assimilation of older crust. Rather, Rather,ititisis complexes were were produced more probable that the limited isotopic variations within the granophyre complexes minor assimilation. assimilation. It remains by fractionation and mixing processes with only minor remains possible possible that that the the granitic rocks have been derived by partial melting and cannibalization cannibalization of crystallized crystallized MRS magmas lower in the crust, but this seems unlikely considering the refractory nature of such rocks and the availability of less refractory older crust present in the lower crust, especially during early stages stages of of rifling. rifting. sd - sd References: References: [I] [1] J.C.Green, 1982, Geol. Soc. Soc. Am. Am. Mem., Mem., 156,47. 156, 47. [2] J.C.Green and T.J.Fitz, J. Volcan. Geotherm. Geothenn. Res., 54, 177 177 (1993). [3] [3] B.C.Kennedy, B.C.Kennedy, K.R.Wirth, K.R.Wirth, and and J.D.Vervoort, J.D.Vervoort, this this vol[4]J.C.Brannon, J.C.Brannon, Ph.D. Ph.D. thesis, thesis, St. St. Louis Univ. (1984). [5] L.Dosso, L.Dosso, Ph.D. thesis, Univ. ume. [4] (1984). [5] (1984). [6] [6]J.D.Vervoort J.D.Vervoortand andJ.C.Green, J.C.Green, Can. Can. J. Earth Earth Sci.,34, Sci.,34,521 [7]S.W.Nicholson, S.W.Nicholson, Minn. (1984). 521 (1997). [7] K.J.Schulz, and and J.C.Green, J.C.Green,Can. Can.J.J.Earth EarthSci., Sci.,34,504 34, 504(1997). (1997). [8] D.W.Davis and S.B.Shirey, K.J.Schulz, J.C.Green, Can. J. Earth Sci., Sci., 34,476 [9] J.D.Miller J.D.Millerand andJ.D.Vervoort, J.D.Vervoort,ILSG ILSG abstr, abstr, (1996). (1996). J.C.Green, 34, 476 (1997). [9] 68 �ARCHEAN DIAMOND EXPLORATION EXPLORATION TARGETS IN IN THE THE MICHIPICOTEN MICHIPICOTEN GREENSTONE GREENSTONE BELT, BELT, WAWA, ONTARIO WILSON, A. A. C., C., Ministry Ministryof ofNorthern NorthernDevelopment Development and and Mines, Mines, Ontario Ontario Government Government Complex, Complex, Highway 101 101 East, East. WILSON, Porcupine, Ontario, P0N 0. Bag IHO (705-235-1614; (705-235-1614;ann.wilsonfiindm.gov.on.ca ann.wilson(ndm.gov.on.ca Bag 3060, 3060, South South Porcupine, PON 1HO P. 0. Traditionally, diamond exploration Traditionally, exploration in Ontario Ontario has focussed focussed on following following KIM dispersion dispersion trails trails and and on on examining geophysical targets believed to be related related to to kiiberlite kimberlite pipes. pipes. However, the 1993 announcement 1993 announcement of the discovery of three three alluvial alluvial diamonds diamonds recovered recovered from the the Michipicoten Michipicoten River River area area south south of of Wawa Wawa has has led led to tothe the search for much different diamond diamond sources. sources. Surmacz and the frst first discovery discovery of of Archean-aged Archean-agedbedrock bedrock occurrence occurrence of of In 1995, 1995, S. Sunnacz and M. Hauseux made the diamonds in Ontario kilometers north of the town of Wawa. Following diamonds Ontario in Lalibert Lalibert Township, Township, approximately approximately 20 kilometers Following this this discovered nine the same geographic geographic region region in announcement, Spider announcement, Spider Resources Resources discovered nine more diamondiferous dikes in the 1997. Early Earlythis this year, year, Ban-Ore Resources Ltd. announced the discovery of at least one more diamondiferous diamondiferous dike dike Township. To date, commercial stones, 42 macrodiamonds (the GQ Occurrence), macrodiamonds and in Musquash Musquash Township. date, 55 commercial and 338 338 Occurrence), this this time time in microdiamonds have microdiamonds have been recovered recovered from from bedrock bedrock in in an an area area approximately approximately30 30 square square kilometers in size. size. Presently, bedrock in in the the area. The Presently, there there appear appear to to be two two types types of Archean diamond-bearing bedrock The "Sandor"Sandoractinolite+talc+carbonatexenoliths xenolithsranging ranging type" dikes dikes are are mafic mafic in in composition compositionand and contain contain up up to to 35% 35% spectacular spectacular actinolite+talc+carbonate up to 11 metre in size. The fine-grained matrix is foliated. These These cocks rocks have been classified as lamprophyres. These These dikes are detailed P. Sage Sage of of the the Ontario Ontario Geological GeologicalSurvey Surveyin in Sudbury. Sudbury. detailed in in another another featured featured poster poster by by R. R. P. The second type of dike, the GQ-type, is more strongly strongly foliated than the first frst type and and very very closely closely resembles the intennediate intermediate to to felsic felsic tuffs tuffs that host them. The Thematrix matrixisisfute-grained, fme-grained,actinolite-rich actinolite-richand andup up to to 60% 60% subangular, supracrustal xenoliths have been observed in the the dikes. dikes. These rocks have yet to be classified. These Both maximum length length is is unknown. unknown. The 10 m wide) and their maximum Both types typesof ofdikes dikesare aretypically typicallynarrow narrow(0.1 (0.1— 10 dikes trend both northeast northeast and and northwest northwest and, and, as as yet, seem seem to to display display no no readily readily recognizable recognizablegeophysical geophysicalsignature. signature. Both types types of of dikes dikes are are metamorphosed metamorphosedand and are are presumed presumed to to be be slightly slightlyolder older than than the the supracrustal supracrustalrocks rocksthat thatthey they diopsides or KIM signature signatureassociated associatedwith with these these occurrences occurrences is unusual in that there are no chrome diopsides intrude. The TheKIM chrome chrome pyrope gamets garnets related related to the dikes. Chromite Chromiteand andilmenite ilmeniteare are the the only only two two indicator indicator minerals minerals presently presently thought to be associated associated with with these these occurrences. occurrences. These dikes are concentrated concentrated in the central part of the Michipicoten Michipicoten greenstone greenstone belt and and are are related related to to aa synfonnal anticliiie centred on Leclaire Township. These dikes appear to be related to a nappe structure lying synformal anticline centred These dikes appear to be related to a nappe structure lying on on the the northwest shoulder of the Kapuskasing Structural Zone. northwest shoulder of the Kapuskasing Structural Zone. The recent discovery discovery of Archean-aged diamondiferous diamondiferousdikes dikes within the Kapuskasing Kapuskasing Structure Structurein in Ontario Ontario has significantly significantlyinfluenced influenced diamond diamond exploration explorationin in the the province. province. - 69 �DIAMONDS AND AND DIAMOND DIAMOND EXPLORATION EXPLORATION IN IN NORTHERN NORTHERN ONTARIO ONTARIO WITH WITH A FOCUS ON THE MICHIPICOTEN MICHIPICOTENGREENSTONE GREENSTONE BELT, BELT, WAWA, WAWA, ONTARIO WILSON, C., Ministiy Ministryof ofNorthern NorthernDevelopment Development and and Mines, Mines, Ontario Ontario Government Complex, Highway 101 101 East, East. WILSON, A. A. C., P. 0. 0.Bag Bag3060, 3060,South SouthPorcupine, Porcupine,Ontario, Ontario,PON PON1HO 1HO(705-235-1614; (705-235-1614;ann.wilson(1iindm.gov.on.ca) ann.wilson@,ndm.eov.on.ca) Since 1899, it has been postulated that the source of the alluvial diamonds found south of Lake Superior originated east or west of James Bay. Blue Blue (1899) (1899) made this suggestion based on the fact that many of the gravels and boulders found in the glacial drift of Wisconsin, Michigan and Ohio, for example, are identical in composition and structure to the materials north of the Great Lakes. The first in hedrock, bedrock, in in Ontario, Ontario,was wasin in 1914. 1914. Microscopic diamonds were f i r t reported occurrence of diamond in reported by the Ontario Department of Mines in a sample collected from the claims of D. O'Connor in inReaume Reaume Township, located approximately 32 kilometers north of Porcupine. Exploration for diamonds in Ontario began in earnest in about 1960 1960 when the presence of of diamond indicator minerals (KIMs) (KIM5) was was discovered discovered by by Selco SelcoExploration Explorationininthe theMoose MooseRiver Riverdrainage drainagebasin. basin. The first confirmed kimberlite kimherlite was discovered in Hogg Township by Aquitaine Company of Canada iii in 1974. 1974. The James Bay Lowlands have been a diamond exploration hotspot since the late 1980's 1980's and andhas hascontinued continued up to to the the present. present. Exploration has involved companies such as KWG Resources, Resources, to be a favourite exploration target up Spider Resources, Ashton Mining of Canada, Continental Precious Metals, Garde Mining Exploration, B. B. P. Ltd. Exploration kimberlite clusters, the Resources Canada Ltd. and Monopos Ltd. Exploration has led to the discovery of several kiiherlite most notable being the cluster situated in the the Attawapiskat Attawapiskat River Riverarea. area. During the winter winter of 1999-2000, Monopros Monopros Ltd. has been in the process of extracting a 10,000 10,000 tonne bulk hulk sample from the Victor kimberlite kimherlite pipe. Traditionally, diamond exploration has focussed on following KIM dispersion trails and on examining examining related to kimberlite kimberlite pipes. pipes. However, the 1993 announcement announcement of the discovery of geophysical targets believed to be related three alluvial diamonds recovered from the Michipicoten River area south of Wawa has led to the search for for much much different diamond sources. In 1995 Surmacz and M. Hauseux made the first discovery of Archean-aged bedrock occurrence of of 1995 S. Surmacz diamonds in Ontario in Lalibert Township, approximately approximately 20 20 kilometers kilometersnorth northof ofthe thetown townof ofWawa. Wawa. Following this announcement, Spider Resources discovered nine more diamondiferous dikes in the same geographic geographic region in in 1997. Early Early this this year, year, Ban-Ore Ban-OreResources ResourcesLtd. Ltd.announced announcedthe the discovery discovery of of at at least leastone onemore more diamondiferous diamondiferous dike dike Township. To (the GQ Occurrence), this time in Musquash Township. To date, 5 commercial commercial stones, 42 macrodiamonds and 338 from bedrock hedrock in an area area approximately 30 square kilometers in in size. microdiamonds have been recovered from Archean diamond-bearing diamond-bearingbedrock bedrockin inthe thearea. area. The "SandorPresently, there appear to be two types of Archean actinolite+talc+carhonate xenoliths ranging ranging type" dikes are are mafic in in composition composition and and contain contain up to 35% 35% spectacular actinolite+talc+carbonate fme-grained matrix matrix is foliated. foliated. These rocks have been classified as lamprophyres. lamprophyres. up to 11 metre in size. The fine-grained The second type of dike, the GQ-type, is more strongly foliated than the first type and very closely tuffs that that host host them. them. The matrix is fine-grained, actinolite-rich actinolite-rich and up up to 60% resembles the intermediate to felsic tuffs been observed observed in in the the dikes. dikes. These rocks have yet to be classified. classified. subangular, supracrustal xenoliths have been their maximum maximum length length is is unknown. unknown. The 10 m wide) and their The Both types types of ofdikes dikesare aretypically typicallynarrow narrow(0.1 (0.1—- 10 dikes trend both northeast and northwest and, as yet, seem to display no readily recognizable geophysical signature. Both types of dikes are metamorphosed and are presumed to be he slightly older than the supracrustal rocks rocks that they they intrude. The TheKIM KIMsignature signatureassociated associated with with these these occurrences occurrences is unusual in that there are no chrome diopsides or chrome pyrope garnets related to the dikes. Chromite presently ilmenite are the only two indicator minerals presently Chromite and and ilmenite thought to be associated with these these occurrences. occurrences. The recent discovery of of Archean-aged Archean-aged diamondiferous dikes within the Kapuskasing Structure Structure in in Ontario Ontario will significantly influence influence the way that future future diamond exploration is conducted in the province. 19-124. in Report of the Ontario Ontario Bureau Bureau of of Mines Mines 1900, 1900,p.1 p.119-124 Blue, A. 1899. 1899. Are Arethere there diamonds diamondsin inOntario?; Ontario?; in Gibson, T. W. 1914. 1914. Statistical StatisticalReview Review of of the the Mineral Mineral Industry Industry of Ontario for 1913; 1913; in Ontario Bureau of Mines Annual Report 1913, v. v.23, p.47. 23, pt. pi. 1, 1, p. 47. 70 �PETROGENESIS OF THE SILVER SILVER CREEK DIKE: A 1.1 1.1 Ga INTRUSION IN THE MIDCONTINENT MIDCONTINENT RIFT RIFT SEIFERT, Karl Karl E., E., Department Departmentof ofGeological Geological& &Atmospheric Atmospheric WOLBERS, Jennifer A., and SEIFERT, State University, Ames, Iowa 50011 50011 Sciences, Iowa State The Lake Superior at Silver The Silver Creek dike is a mafic intrusion exposed along Lake Silver Creek cliff north of Duluth, Minnesota. Silver Creek cliff is comprised of several lava flows of the North Shore Silver Creek cliff is comprised Volcanic Group, which the the dike dike intrudes, intrudes,and andaathin thinoverlying overlyingsill. sill. Previous Previous misinterpretations misinterpretations of of the result result of of an an unseen unseen upper upper contact, a contact that is Silver Cliff as a single sill were the is now clearly exposed as the result of of aa tunneling tunneling project project in in the the early early 1990s. 1990s. Samples from field work and drill cores taken during the tunneling project have been analyzed for both maior major and trace trace elements. elements. Major Maior element data from both XRF analysis analvsis and microprobe work indicate that that the Silver Creek dike is is aa diabase consisting predominantly of of labradorite, augite, olivine, and Fe-Ti oxides. The The rare rare earth earth element (REE) pattern of the dike's upper chill zone mimics that that of the the overlying flows flows suggesting suggestingcontam&tion contamination inthe theupper upperpart part of of be aa primitive primitive olivine olivine tholeiite the dike. REE REEpatterns patternsofofthe thelower lowerchill chillzone, zone, however, however, show show itit to to be dataindicates indicatesthat that the theSilver SilverCreek Creekdike dikeformed formed from from with no significant contamination. Isotope Isotopedata a relatively primitive and uncontaminated 0. uncontaminated mantle magma with eNd values near near 0. in 71 �Geochemical Impacts of An An Undisturbed Undisturbed Mineral MineralDeposit Deposit— - Results From the Bend Deposit, Chequamegon National Forest, Wisconsin Laurel G. Woodruff, Woodruff, USGS, USGS,St. St.Paul, Paul,MN MN55112 55112(woodruff@usgs.gov), (woodruffusgs.gov), John John W. W. Attig, Attig, Wisconsin Geological and Natural History Survey, Madison, WI 53705, 53705, and William F. F. Cannon, USGS, Reston, VA 22092 The Bend copper-gold massive sulfide deposit in the Medford District District of of the Chequamegon National Forest, Taylor County, Wisconsin, is hosted by Early Proterozoic volcanic rocks. Pre-Pleistocene Pre-Pleistocene saprolite and 100-120 100-120 feet of Quatemary Quaternary materials materials cap cap the mineralized horizon. Ore Oreconsists consists of of massive massive pyrite with varying amounts amounts of bornite, arsenopyrite, chalcocite, and rare gold-silver chalcopyrite, tetrahedrite-tenantite, bornite, tellurides. The ore zone at Bend contains significant concentrations of arsenic, significant concentrations arsenic, bismuth, bismuth, mercury, tellurium, thallium, and antimony antimony in addition to the principal ore metals, metals, copper copper and gold. Because Because these these elements elements are atypical of surrounding bedrock, the Bend deposit was selected selected to examine examine natural elemental dispersion from a buried massive massive sulfide sulfide in in aa glaciated region. The The influence influence of the Bend mineralization on its environment is characterized using a geochemical characterized geochemical database database that that includes: includes: 1) bedrock, sulfide bedrock, massive sulfide provided by Sharpe Energy and Resources and saprolite obtained from diamond drill core provided and the Jump River Joint Venture; 2) regional samples samples of Quaternary Quaternary materials materials from from Taylor County (Attig, subsurface Quaternary Quaternary material and weathered weathered (Attig, 1993); 1993); and 3) subsurface bedrock from the area of the Bend deposit obtained by rotasonic drilling. The USGS drilled five rotasonic rotasonic drill holes through the Quaternary deposits deposits along along aa 0.5 0.5 mile the strike strike of of the the Bend Bendmineralized mineralizedzone. zone. Nearly mile linear transect that crossed the Nearlv continuous core was recovered from every borehole, including up to several feet of weathered weathered bedrock. The core reveals a complex Quatemary Quaternary section section that that consists consistsof of two two till sheets, several intervals of gray, clay-rich lake sediments, and several several areas areas of of outwash. The older till is gray, carbonate-rich carbonate-rich till of the Marathon Marathon Formation Formation and and the the younger is reddish brown till of the Copper Falls Falls Formation. Formation. The Marathon Marathon Formation Formation both underlies and overlies lake sediments and and outwash. outwash. Bedrock Bedrock in the area area of the Bend deposit is directly overlain by the lowermost outwash outwash unit, whereas the Marathon Marathon Formation Formation is draped over metagabbro metagabbro that forms a bedrock high to the south south of of the the deposit. Detailed Detailed geochemical geochemical analyses analyses of the different units show that in addition to obvious color and grain size distinctions, higher average Ca content also distinguishes the Marathon Marathon Formation Formation from from the the Copper Copper Falls Falls Formation. Formation. As much as 20 meters of saprolite saprolite is preserved over massive sulfide sulfide at the Bend Bend deposit. deposit. Saprolite is leached of most metals that are concentrated in unweathered massive sulfide. Cu, Zn, Au, As, Se, and Te concentrations all decline sharply across the transition from massive sulfide sulfide to saprolite, saprolite, whereas whereas Ba, Mn, Ti, Cr, Ni, and V increase increase markedly. Anomalous Anomalous concentrations concentrations of those elements elements within the massive sulfide sulfide are are mostly mostlv lacking in overlying glacial deposits suggesting that the saprolite saprolite cap prevented physical rock by by glacial glacial movement. movement. However, in the glacial deposits directly dispersal of sulfide rock relatively high high values valuesof ofHg Hgand andxAu arefound. found. This over the Bend mineralization, relatively u are of these these elements elements from frommassive massivesulfide. sulfide. In the downsuggests hydromorphic dispersion of 72 �ice direction from the Bend deposit, gold concentrations are found increasingly increasingly higher in the Quaternary section (Figure 1). The The overall pattern for Hg is less distinct, although Hg values found in both Marathon Formation and Copper Falls Formation tills from rotasonic core are markedly higher than Hg values measured in regional subsurface subsurface samples from the same formations. same formations. This study shows that although regional background geochemical values in glacial glacial deposits can be influenced by anomalous concentrations of elements in bedrock, the nature of both the sources and the sinks for various elements controls the dispersion dispersion subcrop of a massive patterns. ItIt also alsoshows showsthat that understanding understanding the character character of the subcrop sulfide and the intervening surficial stratigraphy is critical in geochemical exploration exploration in In the the case caseof of the the Bend Bend deposit, deposit, metal-depleted saprolite caps the deposit this terrane. In and has protected massive sulfide from glacial dispersion, so sulfide-bearing boulders boulders and traditional metal (such as Cu and Zn) anomalies have not developed even in till near the bedrock surface. However, However, more more subtle subtle dispersion dispersion patterns of other elements elements may indicate the presence of sulfide mineralization. sulfide mineralization. North Ta-4 Ta-4 Ta-3 1350 South South Ta-5 I—...—- Ta-2 1330 Ta-i rr L.r CF 1310 . — •• 1290 — —— C I 'S — A I 0 'U — - C) C — Ow . 1270 ow a) w 1250 1230 •-- -. ailay S.----- ls. t Bedrock surface - OH. . , - —___ - -S d deposit 1210 Figure 1: Cross-section of Bend Bend deposit. deposit. CF = Cross-section of of the the surficial surficial section in the area of = Copper = outwash, Falls Formation, MA = = Marathon Marathon Formation, ow = outwash, ls Is == lake lake sediments, sediments, Ta drill hole. hole. Striped designates each rotosonic drill Striped areas areas show locations locations of samples with greater than .01 .O1 ppm Au. Vertical Verticaland andhorizontal horizontaldimensions dimensionsare are not not to to scale. scale. Reference: Attig, Attig,J.1.W., W., 1993, 1993, Pleistocene Pleistocene geology of Taylor County, Wisconsin: Wisconsin Wisconsin Geological Geological 27 p. and Natural History History Survey Survey Information InformationCircular Circular65, 65,27 p. 73 � https://digitalcollections.lakeheadu.ca/files/original/632fe39ce4815072b1d96ab2bd49fbae.pdf 99b9247da40b34d2229b67c16bf62343 PDF Text Text FORTY-SIXTH ANNUAL MEETING INSTITUTE ON LAKE SUPERIOR .GEOLOGY. thunder Bay, Ontario May 08-13; 2000 * 4 1 PROCEEDINGS VOLUME 46 4 PART 2: FIELD TRIP GUIDE BOOKS S �46th I.L.S.G. 46th I.L.S.G. ield Guide May 8-13, 2000 �46thANNUAL ANNUAL MEETING MEETING INSTITUTE INSTITUTE ON LAKE SUPERIOR GEOLOGY GEOLOGY Volume 46 consists of Part Part 1:1:Program Programand and Abstracts Abstracts Part Part 2: 2: Field FieldTrip Trip Guidebook Guidebook References References to to material material in in this this volume volume should shouldfollow follow the the example examplebelow: below: Ams, Holm, D., 2000, Characterization Characterization and timing constraints of Arns, D. and Hoim, post-Penokean meso-scale structures structures in the Watersmeet and Republic gneiss Institute on Lake Superior gneiss domes domes of northern Michigan (abst.): Institute Superior, Geology 46"' Annual Annual Meeting, Meeting, Thunder Bay, Ontario, Ontario, GeologyProceedings, Proceedings,46th v.46, p.2. part 1, 1, p. 2. v. 46, part Volume Volume 46 46 Published Published and and distributed distributedby by Institute Institute on on Lake Lake Superior Superior Geology Geology Mark Jirsa, Jirsa, Secretary-Treasurer, Secretary-Treasurer, I.L.S.G. I.L.S.G. Minnesota Minnesota Geological Survey Survey 2642 University Avenue Avenue St.Paul,MN USA 55114-1057 551 14-1057 St. Paul, MN USA (612) 627-4780 627-4780 (612) email: jirsa00ltc.unm.edu email:jirsaOOl0,tc.urnn.edu ILSG ://www.Qeo.mtu.edulgreat lakes/ilsg/ ILSG website: website:httn httw://www.geo.mtu.edu/great lakedilsd ISBN ISBN 1042-9964 1042-9964 All volumes are available availablefor photocopying photocopying costs costs from Michigan Michigan Technological TechnologicalUniversity UniversityLibrary Library Archives �INSTITUTE INSTITUTE ON LAKE SUPERIOR GEOLOGY PROCEEDINGS PROCEEDINGS Volume 46 Field Trip Guidebook Compiled by: Philip Fralick �TABLE OF TABLE OF CONTENTS CONTENTS The trip description coded to to aid aid The first first page page of of each each field field trip description is is colour colour coded finding it finding it in in the the book. book. Field Trip Field Trip 1) 1) Mesoproterozoic Sibley Sibley Group Group (yellow) Mesoproterozoic (yellow) Field Trip Field Trip 2) 2) Lac des des Iles Iles Mine Mine (purple) (purple) Lac Field Trip Field Trip 3) 3) Geoarcheology of of the the Thunder Thunder Bay Bay Area Area (red) (red) Geoarcheology Field Trip Field Trip 4) 4) Paleoproterozoic Gunflint Gunflint Formation Formation (blue) (blue) Paleoproterozoic Field Trip Field Trip 5) 5) Quaternary Geology Shebandowan Belt Belt (orange) (orange) Quaternary Geology Shebandowan Field Trip Field Trip 6) 6) Steep Rock-Lumby Belts Belts (green) (green) Steep Rock-Lumby �GEOLOGY OF THE MESOPROTEROZOIC SIBLEY SIBLEY GROUP GROUP Philip Fralick, Lakehead University Mark Smyk, Ontario Geological Survey This of a This trip trip will will examine examine the depositional depositional architecture architec playa-alluvial playa-alZuvialsuccession successiondeveloped developed in in an an intracratonic intra basin. The pristine sequence records the effects basin. The pristine sequence records the effectsof ofboth both climate climateand andtectonics tectonicson onsediment sediment character. character. �Geology and and Stratigraphy Stratigraphy of the Mesoproterozoic Sibley Group Group by Philip Mark Smyk2 and Mariah Mariah Mailman' Philip Fralick1, ~ralick',Mark smyk2 and ail man' 1 a Amethystine stromatolite, Rossport Rossport Formation, Formation, Dorion, Dorion, Ontario Ontario Amethystine stromatolite, 1 'Department of '~e~artrnent of Geology, Geology, Lakehead LakeheadUniversity, University,Thunder ThunderBay Bay ON ON P7B P7B 5E1 5E1 2Ontwio '0ntario Geological Survey, Survey, Resident Resident Geologists Geologist'sProgram, Program,Ministry Ministryof ofNorthern NorthernDevelopment Development and 435 S. and Mines, Mines, Suite SuiteB002, B002,435 S. James James St., St., Thunder Thunder Bay ON ON P7E P7E 657 6S7 �FOREWORD FORE WORD This field of the This field guide guide is is intended intended to to provide provide aacomprehensive comprehensive overview overview of the Sibley Sibley Group Group Trip stops have been sedimentary rocks, their stratigraphy and associated mineral deposits. sedimentary rocks, deposits. Trip selected on on the basis of representivity many other key and noteworthy sites selected representivity and accessibility; accessibility; many cannot be easily accessed but are described in the text. This guide follows in the footsteps of a number of previous field trips that have focused on the Proterozoic geology geology of the Thunder Bay area. Field stop descriptions have incorporated Proterozoic incorporated and built upon and Kustra Kustra et et al. (1972), Kustra built upon those found in guide guide books written written by Franklin Franklin and Kustra (1972), aL (1982) and Kissin (1990), as as well as other, unpublished unpublished reports. (1977), Franklin ci et al. contact the staff of the Please contact the Resident Resident Geologist's Geologist's Office, Thunder Bay South District, (807) 475-1331, 475-133 1, for current information regarding regarding permitted permitted access access to private and staked properties. A CKNO WLEDGEMENTS ACKNOWLEDGEMENTS The authors would like like to thank Scott for for assistance in the the scanning of The authors would thank J. J. Scott assistance in scanning 1I digitization digitization of K. Farrier Farrier and and S. Warren photographs and maps. S. Spivak drafted some of the the diagrams. diagrams. K. Warren photographs the Ruby Lake quarry was permitted permitted by Ruby Lake provided word processing support. Access to the Marble Ltd. Ltd. Discussions with J. Franklin, Marble Discussions with Franklin, H. Poulsen, Poulsen, other other geologists geologists and prospectors prospectors are appreciated. appreciated. �INTRODUC HON INTRODUCTION Sedimentaryrocks rocksof of the the Sibley discontinuouslyoutcrop outcropon on the the north north shore shore of Lake Sedimentary Sibley Group Group discontinuously Lake Superior and around Lake Nipigon (Figure 1). The flat-lying to gently dipping, elastic-carbonate Superior and around Lake Nipigon (Figure 1). The flat-lying to gently dipping, clastic-carbonate succession oval area disconfonnably overlying succession occupies occupies aa broad broad oval disconformably to unconformably unconformably overlying Mesoproterozoic, Paleoproterozoic and Neoarchean rocks. Mesoproterozoic, Paleoproterozoic and Neoarchean rocks. Sibley Group rocks are located located in in the the Southern Southern Province Province of of northwestern northwestern Ontario. Ontario. The first first documentation of these red beds was by Logan (1863). Hunt (1873) divided Logan's Upper documentation of these red beds was (1863). Hunt divided Logan's "Upper Copper-Bearing Series" into the Animikie and Keweenaw groups; the Sibley was assigned to the latter. descriptions of of the the Sibley Group were were provided provided by by Bell (1870), Parks (1901) and latter. Other descriptions Wilson (1910) who compared the Sibley Sibley (then called "Nipigon "Nipigon Series") Series") to to similar similarKeweenawan Keweenawan and Paleozoic rocks rocks elsewhere. elsewhere. Despite similarities to these younger rocks, the Sibley Sibley Group Group rocks were different enough to preclude assigning them a definite Precambrian age. Subsequently, they were were given given the the name name "Sibley by Tanton Subsequently, they "Sibley Group" Group" by Tanton (1931) (1931) after after the the Sibley Sibley Peninsula on on which which they they are are well-exposed. well-exposed. The Peninsula The Sibley Sibley Group Group rocks were studied studied by Hawley Hawley (1930) and Moorhouse (1960), but they were not mapped comprehensively comprehensively until Coates Coates (1972). (1972). Mcllwaine (1971a,b; (1971a,b; 1975) 1975) also also studied studied the the Sibley Group Mcllwaine Group rocks. Franklin Franklin (1970) pursued pursued a doctoral thesis thesis regarding regarding the the metallogeny of Proterozoic rocks in the doctoral metallogeny of Proterozoic rocks the Thunder Thunder Bay Bay District, District, including the Sibley Group. Thereafter, he described the stratigraphy and depositional setting of the Sibley Group (Franklin et al. 1980). 1980). The Thetectonic tectonic setting, setting, source source areas, areas, and and environments environments of deposition Keweenawan strata strata in in the the Lake Lake Superior region were were published published by by Morey Morey and deposition of Keweenawan Superior region and A doctoral thesis by Cheadle (1985) was executed on the "lower Ojakangas (1982). the "lower Ojakangas (1982). A doctoral thesis by Cheadle (1985) was executed Keweenawan" Sibley Sibley Group. Group. In all of of these these studies studies the Sibley Sibley Group Group rocks are presented as Rift. ift. This Thisnotion notionwas was refuted refuted by by Fralick Fralick and and Kissin Kissin being genetically related to the Keweenawan R (1995). (1995). Outcrop exposure and drill core lithologies provide evidence that the Sibley Sibley Group Group sedimentary sedimentary rocks are continuous, near-horizontal strata there were deposited in an an extensive, extensive, low-lying low-lying area. area. For this reason, the structure structure in in which which the the sediments sedimentsaccumulated accumulated will will be be called called the the Sibley SibleyBasin. Basin. The Sibley Basin is elongate elongate in a northwesterly northwesterly direction, extending extending from from the north north shore shore of of Lake Lake It Superior in the south, along the western mar margin of Lake Nipigon, to Armstrong in the north. in Nipigon, It discontinuouslywithin withinaa15 15000 000km km area area (Franklin et eta?. crops out discontinuously al. 1980). 1980). The Theexposed exposed basin basin is now 175 175 km wide and and 400 400 km km long. long. 5 The fluvial fluvial and and lacustrine lacustrine strata strata of of the the Sibley SibleyGroup Groupare aredivided dividedinto intothree threesubhorizontal subhorizontal formations: 1) the the lowermost is the Pass Lake Formation; 2) the Rossport Formation overlies it, formations: followed by 3) 3)the the Kama KamaHill Hill Formation. Formation. The Pass Lake Formation varies from 0 to 50 50 m in in thickness thickness and and consists consists of of basal basal conglomerate conglomerate It was and beds of quartz arenite. arenite. It was deposited deposited in in aashallow shallowlacustrine lacustrine and upward-thinning upward-thinning beds of quartz 135 m thick Rossport Formation is composed The 135 thick Rossport composed of a a!. 1980). environment (Franklin et a!. 1980). lower, arenaceous, red red dolomite unit, a central and stromatolitic unit, and an lower, arenaceous, dolomite unit, central chert-carbonate chert-carbonate and stromatolitic unit, upper, argillaceous, argillaceous, red red dolomite dolomite unit. unit. These These beds were were laid down in aa shallow, shallow, saline saline basin basin of of Fifty metres of purple shale constitute the Kama Hill fluctuating size (Franklin et a!. fluctuating a!. 1980). constitute Kama Hill 1980). Fifty metres �Formation. Formation. Desiccation Desiccationcracks, cracks,evaporite evaporiteclasts, clasts,and and mud mud chip chip conglomerates conglomerates in this purple purple shale were formed on mudflats that were subaerially exposed and dried out periodically (ibid). formed on mudflats that were subaerially exposed dried periodically (ibid). The The lack lack of of fossils fossils in in the the Precambrian Precambrian presents problems in age determination and in interpreting that are are present present in in the Sibley Group rocks the environment environment of of deposition. deposition. The stromatolites stromatolites that (Hoffman (Hoffinan 1969) 1969) can can occur occur in in both marine and fresh water, but the red beds are characteristic of a continental setting (Morey (Morey and Ojakangas Ojakangas 1982). 1982). The thick dolomite and gypsum gypsum sequences sequences formed formed during during intermittent, intermittent, arid arid periods. 33 Ma, to 1537 Historically, has been been postulated postulated that that the the Sibley SibleyBasin Basin(1339 (1339+1+/- 33 1537 Ma; Franklin Historically, itit has 1978a; Davis and Sutcliffe 1985, respectively) developed because of crustal attenuation Sutcliffe 1985, attenuation caused caused described itit as a failed by the Keweenawan Rift System. System. Franklin Franklin et et aL al. (1980) described Keweenawan Midcontinent Rift arm, radial radial to aa paloplume palasoplumeininrelation relationthe theKeweenawan Keweenawan Rift. Rift. Morey Morey and Ojakangas (1982) described a sedimentary-tectonic framework for the Sibley Basin that is is related related temporally temporally and and sedimentary-tectonic framework for the Basin that spatially Rift; the Sibley subsidence of of the Sibley Basin developed developed as renewed renewed subsidence spatially to the Keweenawan Keweenawan Rift; Conversely, Cheadle (1986) described Animikie Animikie Fault Block Block Basin Basin (2200-2000 (2200-2000 Ma). Ma). Conversely, Cheadle (1986) described the tectonic framework of the Sibley Basin as broad, subsiding sag where significant fault control is lacking at the Sibley Group red beds are representative of the the margins. margins. It was thought that the Sibley earliest evidence Event. However, evidence of the Keweenawan Rift Event. However, this this interpretation interpretation is problematic. The oldest igneous activity that that isis related relatedtoto rifting riflingisisdated datedatat-1l 109 igneous activity 109 Ma Ma (Davis (Davis and and Sutcliffe Sutcliffe 1985) aa minimum minimum of of -230 230 My Myafter afterthe theSibley SibleyGroup Groupwas was deposited. deposited. Conceptually, Conceptually, aa thermal thermal dome precedes rifting, rifling, and erosion will will occur. occur. It is reasonable to presume that volcanism can be be that volcanism can is preceded by sedimentation on this this time time scale, scale,but butthe thepalasodrainage palodrainage system sedimentation on system will will develop develop away away from the dome. This palocurrent work This conflicts conflicts with the palasocurrent workdone doneby by Cheadle Cheadle (1986) (1986) in which the palodrainage palasodrainagesystem systemflowed flowedtoward towardthe thethermal thermal welt. welt. It is unreasonable to hypothesize that the pre-rifi pre-rift basin was was overlying overlying the the thermal thermal welt. welt. Thus, the presumed presumed relationship relationship of the Sibley Sibley Basin with the Keweenawan Rift must must be be reappraised. reappraised. The two events are not related directly Keweenawan Rift the Sibley Sibley Basin Basin may may be be genetically linked to the Kissin 1995). 1995). Alternatively, Alternatively, the genetically linked (Fralick and Kissin heating event represented by the igneous complex formed at Redstone Point, Lake Nipigon heating represented igneous complex formed Redstone Point, (1537 Ma; Davis SibleyGroup Group Davis and and Sutcliffe Sutcliffe 1984) 1984)as as these these igneous igneous rocks rocks lay lay directly directly under under the the Sibley Basin (Fralick (Fralick and Kissin 1995). 1995). In Inthis thisscenario, scenario,mantle mantle upwelling upwelling would cause partial melting of the lower crust, forming the Redstone Point Point felsic felsic magmas. magmas. The higher heat heat flow flow would would cause cause thermal doming the dome. dome. Upon relaxation of the crust an infracratonic infracratonic doming with erosive stripping of the This basin basin, basin, the Sibley Sibley Basin, Basin, would would be be created. created. This basin would would be be saucer-shaped saucer-shaped without without pronounced pronounced boundary boundary faults. faults. This Thiscorresponds correspondsto to the theactual actual basin basin geometry. geometry. REGIONAL REGIONAL GEOLOGY GEOLOGY The Sibley Group rocks rest unconformably on the Paleoproterozoic Animikie Animikie Group Group (Rove (Rove and and Gunflint Formations) and Ojakangas 1982). Formations) and Neoarchean granitic and volcanic rocks (Morey and The Sibley Formation, a series of trough crossSibley Group Group possibly correlates correlates with the Puckwunge Formation, crossstratified, medium-grained, lensoid sandstones occurring in northeastern Minnesota (Mattis medium-grained, lensoid sandstones occurring northeastern Minnesota (Mattis overlies Paleoproterozoic Rove Formation Formation shales shales and 1972). This formation formation unconformably unwnformably overlies Paleoproterozoic Rove 1972). �represents braided fluvial fluvial channel channel deposition, deposition, exhibiting exhibiting strong, strong, represents South South Saskatchewan Saskatchewan River-type, River-type, braided unimodal flow to the southeast. unimodal flow to the southeast. The and sandstone unit, the the Pass The Sibley Sibley Group Group consists consists of of aa lower lower basal basal conglomerate conglomerate and sandstone unit, Pass Lake Lake Formation, and an Formation, aa middle middle unit unit of of red red and and buff buff dolomitic dolomitic mudstone, mudstone, the the Rossport Rossport Formation, Formation, and an upper unit, unit, the to siltstone to upper the Kama Kama Hill Hill Formation, Formation, consisting consisting of of purple purple shale shale and and buff-coloured buff-coloured siltstone fine has subdivided the Sibley to the fine sandstone. sandstone. Cheadle Cheadle (1986) (1986) has subdivided the Sibley Group Group according according to the different different sedimentary facies. From sedimentary facies. Frombottom bottom to to top: top: Pass Lake Lake Formation Formation Pass Loon Loon Member Member (basal (basal conglomerate conglomerate facies) facies) Fork Bay Member (plane-bedded Fork Bay Member (plane-bedded facies facies and and cross-bedded cross-beddedfacies) facies) Rossport Formation Rossport Formation Channel facies and Channel Island Island Member Member (cyclic (cyclic facies and mudstone mudstone facies) facies) Middlebrun Bay Bay Member Middlebnm Member (stromatolite (stromatolite facies) facies) Fire Hill Hill Member Fire Member (chalcedonic (chalcedonic mudstone mudstone facies) facies) Kama is constituted wholly by by aa laminated shale facies facies and and thus, Kama Hill Hill Formation Formation is constituted wholly laminated shale thus, is is not not subdivided. subdivided. PASS FORMATION PASS LAKE LAKE FORMA TION The Loon Lake Member Member is is best best exposed exposed at at Pass Pass Lake Lake in in aa cliff, The Loon Lake cliff, consisting consisting of of the the Pass PassLake Lake At the Formation, which which runs runs parallel parallel to to the the Canadian Canadian National National Railway. Railway. At the north north end end of of the the Formation, outcrop, the the Paleoproterozoic Rove Formation Formation is is visible visible where where the the lowermost lowermost beds beds of of the the Pass outcrop, Paleoproterowic Rove Pass Lake Formation disconformably overlie overlie it. it. The The Pass Pass Lake Lake Formation Formation ranges ranges in in thickness thickness from from Lake Formation disconformably The Loon facies, consists consists of of thin, 18 thin, lensoid lensoid 18 to to 50 50 m. m. The Loon Member, Member, the the basal basal conglomerate conglomerate facies, conglomeratic sediment. sediment. ItItisisthickest near the the basin basin margin margin and and it it thins thins down to conglomeratic thickest(-'-15 (-15 m) near to about about Animikie taconite, taconite, jasper, jasper, and and shale one metre in the the basin basincenter center(Cheadle (Cheadle 1986). 1986). Animiie shale clasts clasts one metre in predominate in in the over Animikie rocks whereas predominate the conglomerate conglomerate deposited deposited over Animikie rocks whereas vein vein quartz quartz vein, vein, granite, and metavolcanic rock clasts dominate where an Archean basement is present clasts dominate an Archean is present (Cheadle (Cheadle and are are < 5 30 30 cm cm in in diameter diameter (Morey (Morey and and Ojakangas Ojakangas 1982) 1982) and are in in matrixmatrix1986). The The clasts clasts are 1986). The polymictic polymictic matrix matrix isis brick-red brick-red (Franklin (Franklinetet aal. and it support (Cheadle 1986). 1986). The t. 1980) 1980) and it is is composed of of medium medium to to coarse coarse grains grains of of quartz, quartz, hematite, hematite, and and mudstone mudstone(Cheadle (Cheadle1986). 1986). The The composed conglomerate has has calcareous calcareous cement. cement. The with deeper and conglomerate The lenses lenses have have scour scour and and fill fill structures structures with deeper and They are narrower channels channels cut proximal narrower proximal to the the source. source. They are cross-bedded cross-bedded with with rare rare dolomite dolomite mudstone layers. layers. At with the the lower lower half half of of the the bed bed in in clast clast mudstone At Silver Silver Islet, Islet, the the lensoids lensoids are are graded graded with support that changes into matrix support in the upper half (Cheadle 1986). support that changes into matrix support in the upper half (Cheadle 1986). The Fork Fork Bay Bay Member Member is is dominated dominated by by medium-grained medium-grained sandstones sandstones which which are are subdivided subdivided into into aa The lower plane-bedded plane-bedded facies facies and an an upper cross-bedded facies. ItItoverlies overliesthe theLoon LoonMember. Member. Plane Bedded Facies: 20 Plane Bedded Fades: 20 to to 80 80m mofofplaneplane-totocross-bedded cross-bedded quartz quartz arenite arenite overlie overlie the the basal basal conglomerate (Cheadle 1986). This buff-coloured sandstone consists of well-sorted, rounded to This buff-coloured well-sorted, �well-rounded, coarse-grained, mature subarkose to sublitharenite sublitharenite well-rounded, finefine- to to coarse-grained, mature quartz quartz arenite arenite to to subarkose and Ojakangas Ojakangas 1982). Minor quartzfragments fragmentsare arepresent. present. As (Morey and Mmor chert and polycrystalline quartz layers that that separate the 5 cm well, there are thinly interbedded dolomitic mudstone and siltstone layers to 11 m thick thick sandstone sandstone beds. The Theupper upper 55to to 10 10cm cmof ofsome somesandstone sandstonebeds beds contain contain mud mud chips. chips. The plane-bedded facies hosts an array of sedimentary structures plane-bedded facies hosts an array of sedimentary structures including including horizontal laminations and and parting laminations parting lineations, lineations, isolated isolated planar planar cross-beds, cross-beds, straightstraight- to to sinuous-crested sinuous-crested oscillation ripples, rare current ripple laminations, rare sand volcanoes and dewatering tubes, and and oscillation volcanoes and dewatering tubes, desiccation desiccation cracks cracks and halite halite clasts clasts in thinly interbedded mudstone (Cheadle 1986). Cross Bedded Fades: Facies: The Thecross-bedded cross-bedded facies facies is is 55 to to 10 10m m thick, thick, with with mediummedium- to large-scale, large-scale, cross-bedded arenite intercalated beds at cross-bedded intercalated with with 1 m thick thick planar, planar, cross-stratified cross-stratified sandstone sandstone beds Rossport, Red Rock, Channel Island, contains scoured scoured bases and Rossport, Island, and Pass Lake. Lake. This facies contains The ripple-marked ripple-marked and and mud-cracked mud-crackedquartz quartz arenite arenite beds beds have have pebbly (Cheadle 1986). 1986). The pebbly infill (Cheadle horizontal to to wavy wavy stratification stratificationwith withminor minortrough troughcross-beds. cross-beds.The Thepalaeocurrents palocurrents of the crosshorizontal beds at Pass Lake and the Enterprise Mine are scattered, with predominantly south-southeast and east-southeast directions, east-southeast directions, respectively (Morey and Ojakangas 1982). aL (1980) logged the 50 m m cliff cliff exposure exposure at at Pass PassLake. Lake. Twenty metres of of buff arenite Franklin et al. rest on the basal lensoid conglomerate. This This buff buff arenite arenite thins upward from 1 m thick beds at the base to to 1 to 22 cm The sequence alternates alternates upwards upwards from from dolomite dolomite to cm thick thick beds beds at at the the top. top. The base arenite. They recorded 1 m of red dolomitic arenite to 13 m of buff arenite; 1 m of thinly bedded They recorded 1 m of red buff arenite; 1 m of thinly bedded m of of buff buff arenite; arenite; 1 m m of ofred reddolomitic dolomiticarenite; arenite;and and 77m mof of red dolomite and dolomitic arenite; 10 m thickly bedded buff arenite. arenite. AAsharp sharpincrease increase in inthe thedolomite dolomite content, content, aa pigmentation pigmentation change, and a gradual decrease in clastic content mark the upper boundary of the Pass Pass Lake Lake Formation Formation et aL al. 1980). 1980). (Franklin (Franklin et At Redstone Point, along the At the Lake Lake Nipigon Nipigon shoreline, shoreline, the Pass Pass Lake Lake Formation Formation overlies an anorogenic, felsic intrusive-extrusive granitoid suite (Fralick and Kissin 1996, unpublished data) dated at 1537 One metre below the dated 1537 Ma Ma (Davis (Davis and and Sutcliffe Sutcliffe 1985). 1985). One the volcanic-sedimentary volcanic-sedimentary contact, the the igneous rocks rocks are weathered weathered and and the the feldspar feldspar exhibits exhibits aa chalky, chalky, cream cream to to salmon contact, colouration. There There is aa 30 colouration. 30cm cmthick thickvolcanic volcanic breccia breccia with with caliche caliche overlying overlying the the weathered weathered rocks. The igneous rocks. ThePass PassLake LakeFormation Formation isis lacking lacking the the basal basal conglomerate conglomerate at Redstone Redstone Point. Point. Instead, there are fine-grained, red sublithareniite to subarkosic sandstones with massive or Instead, fine-grained, sublitharenite to subarkosic sandstones with massive or parallel-laminated beds. beds. Trough These strata contain very angular, Trough cross-stratification cross-stratification is rare. These volcanic clasts clasts with with oxidized oxidizedrims rimsand andweathered weathered granular to pebble to small cobble-sized, felsic volcanic pebbles. feldspars. There Thereare arealso alsoless lessabundant abundant clasts clasts of of hematitic hematitic mudstone, chert, and caliche pebbles. The basal pebble sandstone sandstone is poorly sorted with subrounded to rounded sand and small angular grains. The hascarbonate carbonatecement cement with with clay filling between the grains. The beds range from from 11 to pebbles. ItIt has 80 cm thick, with a mean thickness of 15 cm. They They are are laterally laterally continuous continuous over several metres with rare, 1 m wide channels. Tightly Tightlypacked packed quartz quartzarenite arenite overlies the basal pebbly sandstone. contains minor minor clay clay in the matrix, The quartz arenite is well-sorted, well-sorted, subangular to subrounded, contains and has quartz cement. The Thearenites arenitesare are folded folded slightly slightly and and plunge at <15° <15' to the east east (Fralick (Fralick and Kissin 1996, 1996, unpublished data). �ROSSPORT FORMA FORMATION ROSSPORT TION The The Rossport Rossport Formation Formation consists consists of of red, red, fine-grained, fine-grained, arenaceous arenaceous and and clayey clayey dolomite. dolomite. It It lies lies disconformably on the the Pass Pass Lake Lake arenite arenite (Franklin (Franklin et et at. al. 1980) disconformably on 1980) and and it it has has aamaximum maximum vertical vertical outcrop of 134 m at marker bed bed (Morey and outcrop of 134 m at its its type type locality locality where where it it is is lacking lacking the the stromatolite stromatolite marker (Morey and Ojakangas 1982). North Ojakangas 1982). North of of Nipigon Nipigon and and north north of of Dorion Dorion there there have have been been 300 300 m m and and 180 180 m m of of the et aL al. (1980) (1980) logged logged and and subdivided subdivided the the the Rossport Rossport Formation Formation drilled, drilled, respectively. respectively. Franklin Franklin et Rossport Formation, Formation, starting starting with with aa lower, lower, argillaceous argillaceousred reddolomite dolomiteunit. unit. They recorded 11 m m of Rossport red through the the sequence, there is red conglomerate conglomerate at at the the base. base. Upwards Upwards through sequence, there is 96 96 m mof ofwell-bedded, well-bedded, brick and arenaceous dolomite intercalated intercalatedwith withbuff buff to to white white arenite, arenite, 11 to to 22 m m of brick red red dolomite dolomite and arenaceous dolomite of black chert, gray chert, and buff calcite that alternate from 0.5 to I cm thick laminae with a lowblack chert, gray chert, and buff calcite that alternate from 0.5 to 1 cm thick laminae with a lowamplitude is topped amplitude crinkle crinkle structure. structure. The The sequence sequence is topped with with 37 37 m m of ofmassive massive red reddolomite dolomite and and arenaceous and irregular arenaceous dolomite dolomite that that fractures fracturesconchoidally. conchoidally. Spherical Spherical and irregular reduction reduction spots spots are are noted throughout the the upper upper and and lower lower units. units. The noted throughout The top top of of the the Rossport Rossport Formation Formation is is marked marked by by aa change as it gradually to to zero. zero. The change in in the the dolomite dolomite content content as it decreases decreases gradually TheRossport Rossport Formation Formation rests rests unconformably on Archean Archean rocks rocks at at Kama Kama Bay. Bay. At unconformably on At this this location, location, as as well well as as at atPass PassLake, Lake, Red Red Rock, and Moseau Mountain, the Rossport's basal, basal, red red conglomerate conglomerateis is not not present. present. Cheadle has divided Cheadle (1986) (1986) has divided the the Rossport Rossport Formation Formation into into four four facies facies from from base base to to top: top: Channel Island Member (cyclic and mudstone facies) Channel Island Member (cyclic and mudstone facies) Middlebrun Middlebrun Bay Bay Member Member (stromatolitefacies) facies) (stromatolite Fire Fire Hill Hill Member Member (chalcedonic (chalcedonic mudstone mudstone facies) facies) Cyclic of the Member isis 77 to It has has Cyclic Facies: Fades: The The cyclic cyclic facies facies of the Channel Channel Island Island Member to 30 30 m m thick. thick. It rhythmic layering of mudstone and dolomite couplets or mudstone and sandstone sandstone couplets. The The couplets couplets range range from from 5 5 to to 160 160 cm cm in in thickness. thickness. The Thesandstone sandstoneand anddolomite dolomiteare areend endmembers members that that have throughout the the sequence. sequence. The have various various degrees degrees of of mud mud interlayering interlaye~g throughout The dolomitic dolomitic mudstone mudstone is is red, massive, friable, and tabular. ItIt isis common common to to both both cycles. cycles. The Themudstone mudstoneoften oftencontains containssilt silt or or sand sand and and rounded, rounded, reworked reworked pebble-sized pebble-sized carbonate carbonate clasts clasts (Cheadle (Cheadle 1986). 1986). Red Red Rossport Rossport Formation Formationmudstones mudstones with with diagenetic diagenetic evaporite evaporite minerals minerals formed by by precipitation precipitation in in aa clastic-dominated, clastic-dominated, sabkha sabkha setting setting Mudstone The Mudstone Facies: Fades: The mudstone mudstone facies facies has has �red red and and buff, buff, dolomicritic dolomicritic mudstone mudstone and and claystone claystone that that are are dominantly dominantly massive massive and and friable, friable, but but have local desiccation cracks and adhesion ripples, and small, scattered gypsum and anhydrite have local desiccation cracks and adhesion ripples, and small, scattered gypsum and anhydrite nodules. One to nodules. One to two two metre metre thick thickfinefine-totomedium-grained, medium-grained, poorly poorly sorted, sorted, subarkose subarkose and and sublitharenite with 10% matrix are sporadically introduced into the dolomicritic mudstone. matrix are sporadically introduced into the dolomicritic mudstone. sublitharenite with These subarkose and sublitharenite beds have powering-down powering-down sequences: scoured scoured bases, bases, planeplanebedded laminations, ripple cross-laminations, and horizontal, suspended load laminations bedded laminations, ripple cross-laminations, and horizontal, suspended load laminations (Cheadle 1986). (Cheadle 1986). Stromatolite Facies: Fades: The Stromatolite Thestromatolite stromatolitefacies, facies,or or the the Middlebrun Middlebrun Bay Member, which is located in the middle of the Rossport Formation, is 80 to 140 cm thick. The Thegray graychert-carbonate, chert-carbonate,cryptcryptalgal laminate is laterally laterally extensive, extensive, but but commonly commonly brecciated. brecciated. The base of this this marker marker bed bed has has alternating layers of light gray dolomite, dark gray chert, and crinkly laminae. Moving upwards, Moving upwards, there is a thin thin chert-carbonate chert-carbonate breccia, a layer layer of of laterally laterally linked linked and and domical domical single single parabolic - parabolic stromatolites, and a dark gray chert band (Cheadle 1986). stromatolites, gray chert band (~headle1986). I 1 I I I I Plan Plan view view section of stromatolitic marble garganicus), (Conophyton garganicus), Wolatko Lake Mudsione Facies:. Facies:. The upper Rossport Rossport Formation is is composed composed of of the the chalcedonic chalcedonic Chalcedonic Mudstone mudstone facies. At the base, there are local lenticular, intraformational, paraconglomerate mudstone facies. the base, there are local lenticular, intraformational, paraconglomerate wedges that that contain contain subangluar subangluar mudstone mudstoneclasts clastsup uptoto22 m m in in diameter. diameter. Reduction Reduction spheres spheres are wedges comnon. Red of common. Redand andbuff, buff,dolomicritic dolomicriticmudstone mudstone and and claystone claystone are the dominant constituents constituents of this sequence. They lack the coarse silt and sand that is present in the Channel island mudstone They lack the coarse silt and sand that is present in the Channel Island mudstone and claystone. Dolomite Dolomitepartially partially replaces replaces 22 cm cm diameter diameter chalcedony chalcedony nodules that are are found found in in weathering horizons. resistant weathering horizons. I �KAJVL4 HILLFORMATION FORMATION KAMA HILL The The Kama Kama Hill Hill Formation Formation consists consists of of aa single single (laminated (laminated shale) shale) facies, facies, and and thus thus is is not not subdivided subdivided into constituent members. The original thickness of the Kama Hill Formation is unknown into constituent members. The original thickness of the Kama Hill Formation is unknown as as the the top top is is truncated truncated by by the the Logan Logan diabase diabase sills. sills. The The Kama Kama Hill Hill laminated laminated shale shale has has aa minimum minimum thickness of 46 46 m m (exposed at Kama Kama Hill), Hill), and and this this varies, varies, depending dependingon onthe the location. location. At thickness of (exposed at At Red Red Rock, Island, and and Stewart StewartLake Lakeititisis 20 20 m m thick, thick, and and at at Albert Albert Lake Lake itit is is 45 Rock, Channel Channel Island, 45 m m thick thick (Franklin et a!. (Franklin et al. 1980). 1980). The Thehorizontally horizontallylaminated, laminated, buff buff arkosic arkosicsiltstone siltstoneto to fine finesandstone sandstoneare are exposed in aa cliff exposed in cliff face face along along the the shore shore of of Kama Kama Bay, Bay, east east of of Nipigon Nipigon (Franklin (Franklin et et aL al. 1980; 1980; Cheadle 1986). The base base is istransitional transitional over over 11 to to 22 mmand andcontains containsvery verylittle littlecarbonate. carbonate. 1986). The Reduction spots are common, as are mud cracks and ripple marks on bedding surfaces Reduction spots are common, as are mud cracks and ripple marks on bedding surfaces(Franklin (Franklin et et al. al. 1980). 1980). Breccia Brecciadikes dikesare arepresent presentand andmud-chip mud-chipconglomerates conglomeratesare are associated associated with with the the siltsiltdominated layers (Morey and Ojakangas 1982; Cheadle 1986). The siltstone layers contain dominated layers (Morey and Ojakangas 1982; Cheadle 1986). The siltstone layers containthe the following ripple cross-laminations, low amplitude ripple following sedimentary sedimentary structures: structures: erosional erosional bases, bases, ripple cross-laminations, low amplitude ripple marks, normal grading, marks, centimetre centimetre to to decimetre decimetre fining-upward fining-upward sequences, sequences, normal grading, and and suspensate suspensate caps caps (Cheadle This formation formation locally locally contains contains (Cheadle 1986) 1986) evaporite evaporite casts casts and andraindrop raindropimpressions. impressions. This carbonate algal stromatolites stromatolites at at the the base base of of the carbonate algal the facies facies in in the the north north half half the the basin basin (Morey (Morey and and Ojakangas Ojakangas 1982; 1982; Cheadle Cheadle 1986). 1986). Enigmatic mudcracks(?) in distal bar Formation bar sequences sequences of of the Kama Hill Formation �.1 I I I I LEGEND L EGEND Conglomerate Basal Conglomerate Dolomite lolomite Sandstone Sandstone Gypsum Siltstone __jshale p Mud Chip Conglomerate Mud 1 Stromatolites , Diabase Magnetic Granite Granite Magnetic Gneiss �DEPOSITIONAL SYSTEM DEPOSITIONAL SYSTEM The Sibley were laid The Sibley Group Group sediments sediments were laid down down in in aa broadly broadly subsiding, subsiding, ovoid ovoid basin basin during during the the Mesoproterozoic. There is no evidence of high relief along any exposed segments of Mesoproterozoic. There is no evidence of high relief along any exposed segments of the the basin basin margin. At the margin. At the time time of of deposition, deposition, the the Sibley Sibley Basin Basin was was situated situated very very close close to to the theequator equator (unpublished paleomagnetic paleomagnetic results, results, Dr Dr G. G. Borradaile) Borradaile) and and was was subjected subjected to to an an arid arid to (unpublished to semiarid semiarid climatic regime. These These factors factors combined combined to to dictate dictate the the types climatic regime. types of of depositional depositional systems systems which which developed the basin's developed during during the basin's active activelifetime. lifetime. The large-scale The large-scale depositional depositional patterns patterns are are quite quite clear clear and and will will be be discussed discussed in in the the following followingpages. pages. However, superimposed on this are complex, and sometimes conflicting, data provided smallHowever, superimposed on this are complex, and sometimes conflicting, data provided by by smallscale structures. This complexity scale structures. This complexity is is aa result result of of the the excellent excellent preservation preservation on on minute minute structures structures in in both outcrop outcrop and and core. the field trip we we will will investigate possible solutions solutions to to some some of of the the both core. During During the field trip investigate possible conflicting data, data, and and hopefully conflicting hopefully gain gain further further insight insight into into how how aaMesoproterozoic, Mesoproterozoic, low-relief, low-relief, interior drainage interior drainage depositional depositional system system operated. operated. Pass Lake Formation Disagreement exists exists as as to to the the depositional depositional setting setting of of the the Pass Pass Lake Formation Disagreement Pass Lake Lake Formation. Franklin et al. Formation. Franklin al. (1980) (1980) believed believed that that the the sandstones sandstones and and conglomerates conglomerates were were deposited deposited in a shallow shallow lacustrine lacustrine environment, environment, whereas Cheadle (1986) put forward an alluvial fan-fluvial fan-fluvial model. This controversy model. This controversy may may be be due due to to different differentdepositional depositional processes processes operating operating in in different different places. The The sequences of powering-down beds,such such as as at at Pass places. sequences of powering-down beds, Pass Lake, Lake, appear appear to to represent represent lacustrine sheet sheet sandstones sandstones laid laid down down during during the the waning waningphases phases of of storm storm events events in in aa shallow lacustrine shallow lacustrine environment. environment. The The lensoid, planar and lacustrine lensoid, large-scale large-scale planar and trough trough cross-stratified cross-stratified sandstones, sandstones, present on present on Channel Channel Island Island and and neighbouring neighbouring islands, islands, probably probably represent represent transverse transverse bar bar sand sand flats flats in aa braided they may may be be aeolian. in braided fluvial fluvial system. system. However, However, they aeolian. The The rapid rapid lateral lateral variations variations in in thickness of of the the unit, thickness unit, not not related related to to position position relative relative to to the the basin basin margin, margin, reflect reflect infilling infilling of of basement depressions depressionsrather rather than than clastic clastic wedges wedges advancing advancing from from sediment sediment entry points. points. A A picture picture arises than sands sands evening evening the the topography topography arises of of the the Pass Pass Lake Lake Formation Formation representing representing first first gravels gravels than by by infilling infilling basement basement valleys valleys through through braided braided stream stream transport transport to to a a shallow shallow lacustrine lacustrine environment. environment. In with In the the upper upper portion portion of of the the Pass Pass Lake Lake Formation, Formation, the the sheet sheet sandstones sandstones become become interbedded interbedded with red, red, silty silty shales. shales. This This represents represents aa more moreoffshore offshoredepositional depositional setting setting where where muds muds deposited deposited between storm events events are are not not eroded by the the next as is between storm eroded by next storm, storm, as is the the case case in in the the nearshore nearshore multimultistorey sandstones. The upward decrease in the sand-to-mud ratio indicates deepening sand-to-mud deepening water water and and culminates in the siltculminates silt- and and mud-dominated mud-dominated Rossport Rossport Formation. Formation. The the Pass The contact contact between between the Pass Lake Lake Formation Formation and and the the Rossport Rossport Formation is is gradational, with the the name Formation gradational, with name change change occurring occurring where where the the mudstone mudstone begins begins to to dominate. Upward Upward through through the the sequence, indicationsofof dessication dessicationbegin begin to to appear dominate. sequence, indications appear (eg. (e.g. mudcracks and and early, authigenic gypsum growth). at this point, growth). Commonly at point, interlayering, interlayering, with with mudcracks millimetre- to to centimetre-scale dolomite laminae, laminae, begins begins to to occur. In drill millimetrecentimetre-scale dolomite occur. In drill cores cores from from areas areas closer to to the of dolomite closer the basin basin center, center, an aninterlaminated, interlaminated, decametres decametres thick, thick, succession succession of dolomite and and gypsum occurs gypsum occurs at at this this stratigraphic stratigraphic position. position. The The dessicated dessicated mudstones mudstones probably probably represent represent periodically exposed exposed mudflats mudflats surrounding surrounding the the lake. lake. This This necessitates necessitates aa regressive regressive phase phase in in the the periodically lower Rossport Rossport Formation, Formation, for for which there is friable siltstone lower which there is some some evidence evidence (e.g. (e.g. brick-red, brick-red, friable siltstone at at Rossport Formation �The dolomite-mudstone horizon). horizon). The dolomite-mudstone interlayered interlayered sequence represents represents aa shallow shallow offshore offshore environment. Muds Muds were were washed washed in during rainy periods and dolomite environment. dolomite precipitated during dry periods as the saline lake shrank. The deeper offshore only received clastic elastic input during the latter stages off this depositional episode. It was probably dominated by chemical depositional was probably dominated chemical precipitation precipitation of dolomite during the wetter periods when the lake salinity decreased, and by rainout of of gypsum gypsum crystals on the bottom during dry intervals with increasing salinity. Alternatively, both may have precipitated during dry intervals with hiatuses representing wet periods. The control in this model is the MgICa Ca2 inhibits dolomite precipitation and a period of removal MgKa ratio. The presence of ca2+ of Ca2 ca2+via viagypsum gypsumprecipitation precipitationisisneeded needed before before dolomite dolomite will will begin begin to precipitate. precipitate. Thus, first gypsum then dolomite would precipitate during the dry intervals in this scenario. gypsum then dolomite would precipitate during the scenario. Oxygen Oxygen and and carbon stable isotope analysis is needed to choose between the two alternatives. Sandstone beds beds appear interbedded with the upper dolomite-mudstone sequence or overlie it. Sandstone interbedded with dolomite-mudstone sequence These are interbedded with red mudstone and the unit is laterally extensive is laterally extensive throughout throughout the the basin. basin. Closer to to the southern Closer southern edge edge of of the thebasin, basin,repetitive repetitivesandstone sandstone assemblages assemblages occur occur (metre(metre- to to decametre-scale thicknesses) with intervening intervening decametre-scale, decametre-scale, dolomite-mudstone dolomite-mudstoneassemblages. assemblages. Here, trough trough cross-stratification and channelling channellingare are much much more more evident evident in the Here, cross-stratification and the sandstones. sandstones. in this unit show higher variability than in the Pass Lake Formation. They appear Paleocurrents in to have a southern southern source as opposed to the northern source for the Pass Lake. Lake. The The sandstones sandstones appear to represent renewed renewed tectonism tectonism and basin tilting, resulting resulting in sediment influx from the south, with sand dunes migrating through scour scour channels channels during duringhigh-discharge high-dischargeevents. events.Whether Whether this was was subaerial subaerial or or shallow shallow subaqueous subaqueous deposition deposition is difficult difficult to determine determine as as strandline strandline position is position is obscure. obscure. Metres to decametres of mud-chip mud-chip conglomerates conglomerates overly the sandstones, sandstones, either interbedded interbedded with Mudstone the upper sandstones sandstones or interbedded interbedded with with siltstones siltstones overlying overlying the upper upper sandstones. sandstones. Mudstone fragments are up to metres in diameter, although this is rare, and have variable compositions. metres in diameter, although is rare, and have variable compositions. This unit appears appears to thicken thicken towards towards the the basin basin center centerand and may mayrepresent representupraising upraisingand andrecycling recycling (cannibalization) of basin margin lithofacies; perhaps a further stage of the north-down (cannibalization) of basin margin lithofacies; perhaps the north-down basin basin tilting, represented by the sandstone sandstone wedges, upraising upraising the southern southern basin margin. The mudblock conglomerate is succeeded in some areas by red mudstones mudstones with mudcracks mudcracks and abundant gypsum veins veins and nodules nodules representing representing clastic clastic sabkhas. sabkhas. In In other otherareas, areas, aabrecciated brecciated and and stromatolitic stromatolitic carbonate occurs at this this horizon. horizon. This Thisrepresents representssubaqueous, subaqueous,shallow shallowlacustrine lacustrine deposition, with teepee teepee structures reflecting reflecting periodic periodic drying. drying.These These units units are are overlain overlain by by the deposition, with Kama Hill Formation. Formation. The Kama Hill Formation consists of red to Kama Hill Formation: to purple purplemudstones mudstones with with Formation: sandstones. The ripple-laminated, coarse-grained siltstones to fine-grained interlayered, coarse-grained siltstones fine-grained sandstones. The interlayered, ripple-laminated, abundance of rippled units increases upward until they are replaced by sandstones, which abundance of rippled increases upward are replaced by sandstones, which continue the coarsening- and thickening-upward trend. The sandstones sandstones and and all all stratigraphically stratigraphically higher units are only present in core. The Kama Hill mudstones represent subaqueous in core. The Kama Hill mudstones represent subaqueousdeposition deposition in a non-saline lake. The coarseningcoarsening- and and thickening-upward sequence sequence reflects reflects delta delta progradation progradation and eventual establishmentof of aa fluvial delta delta top environment, forming the the base base of the next environment, forming next and eventual establishment formation. formation. �This is This is a a new new unit unit which which has has not not been been formally formally named. named. It It is is present present only in drill core from under Nipigon Bay. At some localities, the coarsening-upward only in drill core from under Nipigon Bay. At some localities, the coarsening-upward delta delta Nipigon Bay Bay Formation: Formation: Nipigon sequence of planar cross-stratified, sequence of the the Kama Kama Hill HillFormation Formationisisoverlain overlainby bylarge—scale, large-scale, planar cross-stratified, mediummediumgrained sandstones of the Nipigon Bay Formation. These reach approximately 500 m m in grained sandstones of the Nipigon Bay Formation. These reach approximately 500 in thickness. Mudstone Mudstone and and siltstone siltstone interlayers interlayersare are almost almost totally totally absent absent with with the thickness. the entire entire unit unit consisting of of multi-storey multi-storey sandstones. sandstones. Colour Colour varies varies from red to consisting from red to white, white, with with the the white white sandstones sandstones containing gypsum gypsum grains grains and containing and aa gypsum gypsum cement. cement. Research Research continues continues on on this this formation, formation,with with the the present data data indicating indicating an an aeolian aeolian origin origin with with possibly possibly some some braided braided fluvial fluvial reworking. reworking. present At other other locations, locations, aa different different assemblage the one one described described above the Kama At assemblage separates separates the above from from the Kama Hill Hill Formation. This assemblage overlies the coarsening-upward sequence of the delta and is Formation. This assemblage overlies the coarsening-upward sequence of the delta and is composed of of finingcomposed fining- and and thinning-upward, thinning-upward, multi-storey multi-storey sandstones, sandstones, metres metres to to decametres decametres thick, thick, separated by by friable red mudstones In some some places, places, minor minorcarbonate carbonate separated friable red mudstones and and fissile fissile green green mudstones. mudstones. In layers are layers are associated associated with with the the green green mudstones. mudstones. The The sandstones sandstones are are fluvial fluvial channels; channels; the the intervening mudstones mudstonesrepresent representaa rare intervening rare example example of of a apreserved preservedPrecambrian Precambrianfloodplain floodplain succession with with sun-baked, poorly developed succession sun-baked, poorly developed soils, soils, friable friable units, units, and and small, small, open-water open-water ponds. ponds. The possibly possibly aeolian The aeolian sandstones sandstones lie lie sharply sharply on on top top of of this this unit. unit. �FIELD TRIPROAD TRIP ROAD LOG Stop Number Locality Road Lop Loe (kin) (km) DAY DAY ONE STOPS 1-1 1-1 Remote Drill Core Storage Facility (Generalized (GeneralizedStratigraphy) Stratigraphy) 1-2 1-2 Thunder North (Downtown) Thunder Bay Bay North (Downtown) (Architectural Stone) (Architectural Stone) Junction JunctionHighways Highways 11-17 11-17 and and 587 587 0.0 km (Reset) (Reset) 1-3 Pass Pass Lake Lake (Railway) (Railway) (Animikie/Sibley disconformity; disconformity; Pass PassLake Lake Fm. Fm. Type Type section) section) 5.9 to 6.1 km 1-4 Pass Pass Lake Lake (Highway) (Highway) (Lacustrine (LacustrineSheet Sandstones, Sandstones, Rossport Rossport Fm.) 8.6 km 1-5 Pass Pass Lake Lake (Highway) (Highway) (Lacustrine (LacustrineChannel ChannelSandstones, Sandstones,Rossport Rossport Fm.) Fm.) 9.9 km Pass Pass Lake Lake Crossroad Crossroad 10.3 km Pass Pass Lake Lake (Highway) (Highway) (Subaerial (SubaerialSiltstone-Caliche, Siltstone-Caliche,Rossport RossportFm.) Fm.) 10.7 km Junction JunctionHighways Highways11-17 1 1 - 17and and587 587 0.0 0.0 km km (Reset) (Reset) Turn-off Turn-off(Pipeline (Pipelineroad) road) to to Enterprise Enterprise Pb-Zn Pb-Zn Mine Mine 14.5 14.5 km km 1-6 1-7 �DAY TWO TWO STOPS STOPS DAY Stop Number Stop Number Locality Road Lou Road Loe (kin) (km) Junction of Junction of Highways Highways 11 11 and and 17, 17, east of Nipigon east of Nipigon 0.0 km km (Reset) 0.0 (Reset) 2-1 Gurney (Highway) Gurney (Highway) (Archean-Sibley (Archean-Sibley Unconformity, Unconformity, Debris Debris Flows, Flows, Pass Pass Lake Lake Fm.) Fm.) 39.9 km km (east of 39.9 (east of junction) junction) 2-2 Kama Kama Hill Hill (Highway) (Highway) junction) junction) (Interbedded (Interbedded Dolostone-Siltstone, Dolostone-Siltstone, Rossport Fm.) Fm.) 21.4 km (east of (east of 21.4 km 2-3 Ruby Ruby Lake Lake Marble Marble Quarry Quarry (Turn-off from Highway Highway 17; 17; (Turn-off from 4.1 4.1km km into into site) site) 6.8 km (east of (east of 6.8 km junction) junction) 2-4 2-5 2-6 Junction Junction of of Highways Highways 11 11and and 17, 17, east of Nipigon east of Nipigon 0.0 km (Reset) (Reset) Junction Junction of of Highways Highways 11-17 11-17and and 585 585 4.0 km Turn-off Turn-off to to Moseau Moseau Mountain Mountain 5.0 5.0 km km 17.5 17.5-- 18.5 18.5 km Moseau Moseau Mountain Mountain (Pass Lake Fm. & Evaporite Breccias, Rossport Fm) (Pass Lake Fm.& Evaporite Rossport Fm) Junction Junction of of Highways Highways11-17 11-17and and 628 628 0.0 km km (Reset) (Reset) Pull-off Pull-off parking parking lot; lot; start start of of hiking hiking trail trail 6.3 6.3 km km Lloyds Lloyd's Lookout Lookout q'Shales &Rippled RippledSiltstones, Siltstones, Kama Kama Hill Hill Fm.) Fm) (Shales & (walk (walk trail trail 0.8 0.8 km) km) Junction Junction of of Highways Highways 11-17 11-17 and and 628 628 0.0 km (Reset) (Reset) Big Big Squaw Squaw Creek Creek Road Road Cut Cut (Hornfelsed Rossport Fm.) Fm.) (Hornfelsed 10.2 10.2 km km �(JAY (((UNDER I Rossport Fm 0 0: 12 LAKE Map 2232 NIPIGON-SCHREIBER SHEET, MNDM Miles I P (CO (V 2-5 Lloyd's — (IV4 /.k fACQ,' r Thunder Bay, Ontario a a C I Ic-i -t 1. CD -a. ij 0 CD c-) C/D 0 0 0 0 C/D I-I I ILSG 2000 Sibley Group Field Trip �FIELD FIELD TRIP TRIP STOP STOP DESCRIPTIONS DESCRIPTIONS STOP Y REMOTE GE SITE, SITE, CONMEE STOP 1-1: 1-1: THUNDER THUNDERBA BAY REMOTE DRILL DRILL CORE CORESTORA STORAGE CONMEE TOWNSHIP TO WNSHZP This This stop stop presents presents an an opportunity opportunity to to view view stratigraphic stratigraphic sections sections of of the the Sibley Sibley Group Group in in diamond diamond drill drill core core donated donated to, to, or or collected collected by, by, the the MINDM from private MNDM from private sector sector mineral mineral exploration exploration projects. projects. Core Core from from three three drill drill holes holes has has been been selected selected from from different of different parts parts of the the Sibley Sibley depositional basin to provide depositional basin to provide geographically and stratigraphically geographically and stratigraphically distinct of the distinct sections sections of the constituent constituent formations formations and and their their characteristic characteristic lithologies. lithologies. The The latest latest drilling drilling was was completed completed by by Falconbridge Falconbridge Limited Limited and and joint-venture joint-venture partners, partners,Canmine Canmine Resources Corporation and and Red Red Engine Engine Resources, Resources, in in 1997 1997 from from the the ice ice of of Nipigon Nipigon Bay Bay as as part part Resources Corporation of an exploration program designed to evaluate the area's nickel potential (Assessment files, of an exploration program designed to evaluate the area's nickel potential (Assessment files, Thunder Thunder Bay Bay South South District, District, Thunder Thunder Bay). Bay). Falconbridge Falconbridgebecame becameinterested interestedin inthe thearea areainin1991 1991 and started a compilation and regional reconnaissance program which delineated a 23 km k m long long and started a compilation and regional reconnaissance program which delineated a 23 magnetic anomaly adjacent adjacent to to the the North Airborne and and ground ground magnetic anomaly North Shore Shore fault fault (see (see map map below). below). Airbome geophysical geophysical surveys, surveys, geological geological mapping, mapping, soil soil sampling sampling ensued, ensued, culminating culminatingin in the thedeep deepdrilling drilling program program (ibid). (ibid). No Nosignificant significantnickel nickelnor norcopper coppervalues values were were returned returned from fromthe thedrilling drillingand andthe the Exploration Licence of of Occupation on Lake was allowed allowed to to lapse lapse in Exploration Licence Occupation on Lake Superior Superior was in 1999. 1999. Despite Despite the the disappointing results, the the drilling disappointing results, drilling provided provided aa plethora plethora of of new new stratigraphic stratigraphic information information on on the the Sibley Sibley Group Group in an an area area where where no no drilling drillinghad had previously previously taken taken place. place. Most Most remarkable remarkable of of these these results were the unexpectedly thick sections (up to 850 m) that dwarfed previously measured results were the unexpectedly thick sections (up to 850 m) that dwarfed previously measured sections total thickness thickness on on the the mainland, mainland, as well well as as the the presence presence of of upper upper units units of of sections and and estimated estimated total the the Sibley Sibley Group Group which which had had not notpreviously previously been been recognized recognized (i.e. (i.e. proposed proposed Nipigon Nipigon Bay Bay Formation). Formation). Drill Drill Hole Hole CYP 96-01 CYP 96-01 NB NB 97-02 97-02 NB NB 97-03 97-03 NB NB 97-04 97-04 NB NB 97-05 97-05 (m) Overburden (m) Overburden Sibley Group (m) Sibley Group (m) 2.0 2.0 22.7 22.7 30.0 28.6 28.6 73.2 73.2 62.56 62.56 452.5 452.5 75.0* 75.0* 858.2 858.2 635.1* 635.1* Total Length (m) Total Length (m) 464.5 464.5 677.8 677.8 105.0 105.0 1015.6 1015.6 744.2 744.2 Table showing thicknesses of Sibley Sibley Group Group intersected intersected by Falconbridge Falconbridge Limited's Limited'sdrilling. drilling. (*hole did not reach reach Archean Archean basement) basement) �Vert Island Black Bay Peninsula Osler Osier Group Group FZ1 0 5 km LI Loqari Logandiabase diabase / North Shore / North ShoreFault Fault 1 Archean Archean I 'High" 1 Magnetic 'High" r] Sibley Group Group D -Sibley I/ Map of of Nip Nipigon drilling Map igon Bay, Bay, showing showing location location of Falconbridge Falconbridge Limited's drilling The sedimentary rocks unconformably overlieaa red red granite which has been sedimentary rocks unconformably overlie granite which been subjected subjected to to Mesoproterozoic, equatorial equatorial weathering. weathering. Mesoproterozoic, Two drill holes, completed Noranda Inc., Inc., will also be examined at this stop. completed by Noranda stop. These holes were drilled drilled north of of Dorion Dorion on on aa north-south north-south line, line, with with one one lying lying approximately approximately 15 15 km km closer closer to to Thus, the three holes examined will show basin margin basin center center than than the the other. other. Thus, three holes examined will show basin margin the basin (Falconbridge), (Falconbridge), medial medial (Noranda) (Noranda) and and basin basin center center (Noranda) (Noranda) lithofacies lithofacies assemblages. assemblages. The basin-center drill hole bottoms out in diabase which is overlain by millimetre- to centimetrescale layers layers of dolomite and gypsum. This This assemblage assemblage is is approximately approximately 40 m thick and contains pink to to red, red, clay-rich clay-rich interlayers interlayers near near its its top. top. This is overlain overlain by by aashale-siltstone shale-siltstone sequence sequence containing containing abundant abundant layers layers of of intraformational intrafonnationalconglomerate conglomerate(mud-chip (mud-chipconglomerates). conglomerates). �The The medial medial drill drill hole holeoverlies overliesa agneissic gneissicbasement. basement. An An upward-fining, upward-fining, conglomerate conglomerate to to sandstone sandstone to to siltstone, siltstone, trend trend is is well well developed developed in in the the Pass Pass Lake LakeFormation Formation present present in inthis thishole. hole. Approximately 50 m m of and red Approximately 50 of inter-laminated inter-laminated dolomite dolomite and red mudstone mudstone overlie overlie the the Pass Pass Lake Lake siltstone containing layers of mud-block succeeded by a Formation. in is turn, This, Formation. This, in turn, is succeeded by a siltstone containing layers of mud-block conglomerate. conglomerate. AAbrecciated brecciatedand andstromatolitic, stromatolitic,white whitecarbonate carbonateunit unitoverlies overliesthe theclastic clasticrocks rocksand and this this is is succeeded succeededupwards upwards by by siltstones siltstonesof of the the Kama Kama Hill Hill Formation. Formation. The drill hole hole is is similar The basin-marginal basin-marginal drill similar to to the the medial medial hole hole except: except: 1) 1) the the basal basal Pass Pass Lake Lake is is almost entirely missing; 2) the upper carbonate unit is not present; 3) it contains approximately almost entirely missing; 2) the upper carbonate unit is not present; 3) it contains approximately 550m Sibley strata strata not not previously previously discovered discovered elsewhere elsewhere in in the thebasin. basin. The The upper upper 550m of of overlying overlying Sibley strata consist of a coarsening-upward, deltaic sequence at the top of the Kama Hill Formation. strata consist of a coarsening-upward, deltaic sequence at the top of the Kama Hill Formation. This This is is overlain overlain by by aawell-developed well-developedfluvial fluvialsystem systemwith withmulti-storey, multi-storey, powering-down, powering-down, channel channel sandstone sandstone assemblages assemblagesimbedded imbedded with with floodplain floodplain fines. fines. Overlying Overlyingthis thisisisaasandstone sandstonesuccession succession hundreds dry aeolian aeoliansystem. system. hundreds of of metres metres thick thick which which was was probably probably deposited deposited in in aa dry We We will will spend spend the the morning morning in in the the core coreyard yardexamining examining the the various variouslithofacies lithofacieswhich whichare arepresent present in in each each of of these these lithofacies lithofacies assemblages. assemblages. For Foraa more more detailed detailed description descriptionof of the the sequence sequence see see the the section section on on "Depositional "Depositional Environment". Environment". STOP(S) STOP(.) 1-2A,B,C: 1-2 A,B.C: THUNDER THUNDERBAYNORTH(DOWNTOWN) BAY NORTH (DOWNTOWN) This This series series of of stops stops is is designed designed to to show showexamples examples of of rough rough and and cut cutdimension dimensionstone stonethat thatwas was quarried quarried from three different different sites sites around around the turn turn of of the the century. century. Sibley Sibley Group Group stone stone quarries quarries are are listed listed below below (summarized (summarized from from Hinz Hinz et et al. al.1994): 1994): Quarry Rock Type Cooke Point George George Point Point La Grange Island Nipigon River Quarry Ouarrv Island Island Ruby ~ u bLake ~ yake Simpson SimpsonIsland Island Vert Vert Island Island Wolf Wolf River River Marble Gray Gray sandstone sandstone Red sandstone Variegated marble White White sandstone sandstone Variegated Variegated marble marble Buff Buff sandstone sandstone Red Red sandstone sandstone Buff Buff sandstone sandstone . - Years of Operation 1931-1 940(?) Late 800s(?) Late 118001s(?) 1882-1 1882-1883(?) 883(?) 1883-1910(?) 1883-l910(?) Late 800's(?) Late11800's(?) 1998-present 1998-present 1904-1912 1904-1912 1881-1912 1881-1912 1913-15; 1913-15;1921-31 1921-31 �These three three architectural stops along along one one of Thunder These architectural stops Thunder Bay's major arteries provide an opportunity see aa Bay's major arteries provide an opportunity toto see variety of of Sibley Sibley Group Group stones stonesand and note note the the effects effects of of variety The architectural of exposure. almost a century of exposure. The are taken website descriptions are taken from from aa walking walking tour tour website developed and and maintained by the developed maintained by the Local Local Architecural Architecural Conservation Advisory Committee conservation Advisory Committee (L.A.C.A.C.) (L.A.C.A.C.) (http://www.city.thunder-bay.on.caltbwalkingtourf). (http://www.city .thunder-bay.on.ca/tbwalkingtour/). STOP 1-2A: 432 432 RED RED RIVER RIVER ROAD retaining wall wall is constructed with distinctive, brickThis retaining red Vert red Vert Island Island sandstone sandstone (Nipigon (Nipigon Bay Bay Formation?). Formation?). was aa popular stone used in the construction of many many This was grand homes and other buildings in Fort William grand homes and other buildings in Fort William (now (now Thunder Bay South). PORT ARTHUR STOP 1-2B: PORT ARTHUR INSTITUTE (401 INSTITUTE (401 Red Red River Road) COLLEGIATE COLLEGIATE This building, building, constructed constructedin in 1909 1909of ofSimpson SimpsonIsland Island buff buff sandstone (Nipigon Bay Formation?), is an example of the Queen Anne Anne style that that was was in in common common use use from from the the 1880s l880s I to the 191 Os.wWhen the school school board board made made the initial to 1910s. h e n the initial planning for the building, it was decided that it should be "erected for posterity, and and not not be be of the 'shack' order", resulted in the shack' order", so so they they chose chose the the stately stately Queen Queen Anne style. style. Alterations in 1925 resulted addition of four more classrooms, and more renovations to the north and south in 1953 south 1953 and 1962 1962 created other other rooms. rooms. These These alterations alterationsused usedstone stoneinin an an attempt attempt to to blend created blend into the original original building, but a gynmasium gymnasium planned in 1964 1964 and completed in 1974, 1974, provoked controversy as its design was incompatible incompatible with the rest of the school. school. ' �Port Arthur after its Port Arthur Collegiate _. ..sgiate Institute, Institute, shortly rtly after its construction co ..-.. ~ c t i o n STOP J-2C: South) STOP 1-2C:TRINITY TRINITYUNITED UNITEDCHURCH CHURCH(30 (30Algoma Algoma Street Street South) This building, building, constructed constructed in in 1906, was formerly known as as the This 1906, was formerly known the Trinity Trinity Methodist Methodist Church, Church, and and became the Trinity United Church after the United Church of Canada was formed became the Trinity United Church after the United Church of Canada was formed in in 1925. 1925. Constructed of of rough rough cut, Constructed cut, Simpson Simpson Island Island buff buff sandstone sandstone (Nipigon (Nipigon Bay Bay Formation?), Formation?), this this structure is is an an example 890s to to the the that was was popular popular from from the the 11890s structure example of of the the Late Late Gothic Gothic Revival Revival style style that 1 940s.The Theunusual unusualtower tower features featuresvery very narrow narrow windows, windows, four four buttresses, buttresses, each each capped capped with with aa 1940s. pyramid shaped shaped finial, finial, and and an an extremely extremely sharp sharp hexagonal hexagonalspire. spire.The The rest rest of of the the building also pyramid building also features very very steeply pitched roofs, features steeply pitched roofs, and and arched arched windows windows in in the the Gothic Gothic style. style. �TrinityUnited UnitedChurch Church Trinity STOPI-2D: I-2D:MASONIC MASONICHALL HALL(262-270 (262-270Red RedRiver RiverRoad) Road) STOP Builtinin1910 1910and andalso alsoknown knownas asShuniah ShuniahLodge, Lodge,this thisstone, stone,brick brickand andconcrete concretebuilding buildingreplaced replaced Built the 1909.The Thefirst firstfloor floorisismade madeof ofcut cutNipigon Nipigon theold oldMasonic Masonictemple templethat thatwas wasdestroyed destroyedby byfire fireinin1909. River Rivermarble marble(Rossport (RossportFormation) Formation)and andthe theentrance entrancefeatures featurescarved carvedmarble marblepilasters pilastersand and decorative decorativepanels. panels.Originally Originallythere therewas wasaadome domeon onthe theroof roofover overthe theentrance, entrance,which whichhas hassince since been been removed. removed.The Thecentral centralportion portionof ofthe thebuilding buildinghas hasaaMansard Mansardroof roofof ofFrench Frenchdesign. design.The The building's building'swindows windowsare aredecorated decoratedwith withalternating alternatinground roundand andtriangular triangularpediments pediments above above them. them. Conmercial Commercialspace spaceoccupies occupiesthe theground groundfloor, floor,while whilethe thelodge lodgeisislocated locatedabove. above. �STOP STOP 1-3: 1-3:PASS PASS LAKE LAKE (RAILROAD (RAILROADCUT) CUT) j ' Ill 4 I A A cliff cliff on on the the far far side side of ofthe therailroad railroad tracks tracks contains the type type section of the contains the section of the Pass Pass Lake Lake A Formation. disconformity Formation. A low-angle low-angle disconformity separates the the basal separates basal conglomerates conglomerates of of the the Pass Pass lake Formation from the underlying, —1.9 Ga lake Formation from the underlvin~. -, -1.9 Ga Rove Formation shales (lower photo). The Rove Formation shales (lower r>hoto\. The maroon maroon and and green green shales shales exhibit exhibit extensive extensive weathering. evidence of Mesoproterozoic weathering. evidence of Mesooroterozoic The The basal basal conglomerate conglomerate thins thins and and thickens thickens laterally, laterally, pinching pinching down down to to pebbly pebbly sandstone sandstone in in places. places. Clasts Clastsare are generally generally surrounded surrounded and and by dominated local Gunflint dominated by local Gunflint formation formation lithologies. lithologies. The The matrix matrix is is poorly poorly sorted. sorted. The The conglomerates are overlain by a conglomerates are overlain by a thinningthinningupward of sandstone (ohoto at at uoward sequence seauence of sandstone beds beds (photo laterally left). left). Individual ~ndividualbeds beds are are reasonably reasonablylaterally continuous though sometimes sometimes lens lensout. out. They continuous thoueh They are by upper are dominated dominated bv uover flow flow regime regime parallel oarallel lamination with occasional lamination with occasional ripples ripples and and smallsmallscale scale dunes dunes on on their their tops. tops. . - ~ - A - ~ - of this this depositional environment of depositional environment Both alluvial fansequence is continuous. atuuence is continuous. Both alluvial fanThe braided fluvial and and shallow shallow lacustrine lacustrine (Cheadle (Cheadle 1986; 1986; Franklin Franklin 1980; 1980; respectively) respectively) While examining examining the the lithofacies lithofacies in in the the field depositional environments ments have have been been proposed. proposed. While field we we depositional em will discuss the merits incuts of of each each interpretation. interpretation. between the the Disconformity between Disconformity conglomerate basal basal conglomerate of of the the Pass Pass Lake Lake Formation Formation (cgl) (cgl) Rove and weathered and weathered Formation shales at Pass Pass Formation shales (reg) (reg) at Lake. A Lake. A concretion concretion (con) (con) is is shown at lower right. right. �STOP 1-4: (HIGHWA!) 1-4: PASS LAKE (HIGHWAY) This This is aa roadside roadside exposure exposure of of the the transition transition zone zone between between the Pass Pass Lake Lake and and Rossport Rossport Formations. Laterally Laterally continuous continuoussandstone sandstone beds interlayer in a red silty mudstone assemblage. The sandstones are often massive, though though one bed at this this location location contains contains low angle, angle. wispy, wisvv. trough trough cross-stratification. cross-stratification. Here again, two two possibilities possibilities exist exist for for the theenvironment environment of of deposition. deposition. The sandstones could represent crevasse fines during during flood-stage flood-stage failure failure crevasse splay sand sheets spread out on the floodplain fines of fluvial levee systems. Alternatively, Alternatively, the the sand sand sheets sheets may may represent represent shallow lacustrine storm deposits caused by rainfall event-driven fluvial sand delivery delivery to to a lacustrine system and storm event-driven fluvial surge ebb plus river river mouth mouth density density current current transport of sand offshore into a fair fair weather weather siltsiltdominated area. The merits of both interpretations will be discussed in the field. The merits of both interpretations will be discussed in I �STOP 1-5: WA 17 STOP 1-5:PASS PASSLAKE LAKE(HIGH (HIGHWAT) This This stop stop contains contains aa variety variety of of lithofacies. lithofacies. Large Largesandstone sandstonelenses lensescap capthe the outcrop, outcrop, overlying overlying siltstones, siltstones, a fairly continuous, continuous, non-silty, non-silty, purple purple shale shale and and aa massive, massive, lensoid lensoid dolomite. dolomite. tQ — .1 .: C :- :-A' - r1.a ff !$ ... . S . — ,. . . ',r - -. .1 .. ., Layer geometry geometry and and contact contact relations relations in in this this exposure exposure are are perplexing perplexingat at first first glance. glance. Take Layer Take some some time to to trace time trace out out the the geometries geometries of of the the various various lithologies. lithologies. Hopefully Hopefully we we will will be be able able to to answer answer the the following following questions questionswhile whileat at this thisstop: stop: Is the dolomite dolomite really lensoid? Is the lensoid? Is this this caused by structural disturbance? disturbance? How does does the the dolomite How dolomite correlate across across the road? Are any intraformational intraformational conglomerates present? What is their geometry? geometry? How could have this small small sequence sequence of various lithologies have formed? • STOP 1-6: WA 17 STOP 1-6:PASS PASSLAKE LAKE(HIGH (HIGHWAY) This is is aa small, small, crumbly crumbly outcrop outcrop of of red, red, friable friable silty-mudstone. silty-mudstone. Although Although it it is is not not impressive, impressive, its its This brick-red colour and friable nature are important. important. Commonly, outcrops such as this this one are brick-red interpreted as highly highly sunbaked that is is probably probably what what this this outcrop outcrop represents. represents. interpreted sunbaked soils soils / caliche, and that �1-7: ENTERPRISE STOP 1-7: ENTERPRISE MINE Peter MeKellar discovered aa lead-copper-mineralized veinatatthis thislocation locationinin 1865 1865 that that was was Peter McKellar discovered lead-copper-mineralized vein subsequently developed as as the the Enterprise Enterprise Mine Mine (Tanton (Tanton 1931). 1931). Between 1870 and 1876, subsequently developed 1876, two two shafts were sunk. No. 1 shaft reached a depth of 180 feet (55m); levels were run easterly 76 feet No. 1 shaft reached a depth of 180 feet and westerly westerly 66 feet feet at at aa depth depth of of 60 60 feet. feet. A A stope stope was made in the west drift and a winze was sunk in the east drift about 50 feet from the the shaft. shaft. A crosscut was driven from the the bottom bottom of the the shaft 115feet 5feetsouth. south. Shaft No. 2 was sunk 60 feet at a point approximately 300 feet west of No. 11 of shaft (ibid). The total total recorded productionfrom fromthe themine minewas wasaa single single shipment shipmentofof 167 167 tons tons made made to to The recorded production Swansea, Wales, in in 1875 (ibid) (ibid) that that averaged averaged37.4% 37.4%Pb. Pb. Although no no other metal metal credits credits are Swansea, Wales, listed, appreciable copper, copper, silver silver and and gold gold were were reported reportedin in some somesamples. samples. Analyses conducted by Dr. E.J. Chapman Chapman in in 1874 1874include include one of a large, large, average average sample sample of the vein near surface surface that that returned 41.84% Pb, 5.40% Cu, 3.2 ounce Ag per ton and 0.33 0.33 ounce Au per ton (Tanton 1931). Hawley (1930) reported Chapman's Chapman's estimate estimate of of part part of of the ore body near surface as 47.5% Pb, Hawley Pb, 10.0% Cu, 17 17 dwt. 12 12 grammes grarnrnes (sic) Au and 2 ounces ounces 22 dwt. Ag per ton. ton. Mining operations ceased ceased in in 1876; fire destroyed destroyed the the mine mine buildings buildings aa few few years years later (Tanton (Tanton Mining 1931). New owners dewatered and sampled the workings in 1884 but no ore was produced. 1931). New owners dewatered workings in but produced. 927(ibid). Dewatering, examination and subsequent suspension took place between between 1926 1926and and11927(ibid). The mine site was initially rehabilitated in 1926 and 1927 and is now monitored and maintained by the Canadian CanadianNational ~ a t i o n Railway. al~ailwa~. have described describedthe thelocal localgeology. geology. Ore-bearing Ore-bearingveins veinsoccupy occupyaa Hawley (1930) and Tanton (1931) have breccia breccia zone in in dolomitic dolomitic siltstones siltstones of the the Rossport Rossport Formation Formation that extends extends down into into the the has basement. This Archean granitic basement. This breccia breccia zone strikes 065° 065' and dips 70° 70' SE to vertically. ItIt has been traced traced over over 60 m and has an average width width of 1.2 m. Fracture-controlled offshoots and and been Fracture-controlled offshoots branch veinlets may occur in a metre-wide envelope envelope or or "shatter "shatter zone" zone" around aroundthe themain mainvein. vein. The veins tend to pinch-and-swell; pinch-and-swell; mineralized zones over 4 m wide have been noted (ibid). The veins consist consist of the the ore oreminerals minerals galena, galena, low-Fe low-Fe sphalerite sphalerite pyrite pyrite and chalcopyrite chalcopyrite in a Malachite has gangue assemblage of of quartz / amethystine gangue assemblage amethystine quartz, quartz, calcite calcite and and pink pink barite. barite. Malachite precipitated on chalcopyrite-rich, chalcopyrite-rich, weathered dump material. First synopsized by Hawley Hawley (1930) (1930) and and further further described described by Tanton Tanton (1931), (1931), "lead-zinc-barite "lead-zinc-barite termed, were were reported reportedas asearly earlyas as1866. 1866. Of Of the the approximately approximately veins" (LZBV), as they are locally termed, only the Dorion, Ogema and and Enterprise Enterprisedeposits depositswere weremined minedtotoany anydegree. degree. As 30 deposits, only Dorion, Ogema noted by Franklin Franklin and and Mitchell Mitchell (1977), (1977), these these small small deposits deposits comprise comprise a distinct distinct metallogenetic metallogenetic and is is spatially spatially confined confined to to the the group that has a consistent, simple vein mineralogy and structure, and basin. Although Sibley Group depositional basin. Although temporally temporally similar, similar, they are are clearly clearly distinguishable distinguishable from silver-bearing veins that occur near Thunder Animikie Group Group from silver-bearing veins Thunder Bay in in Paleoproterozoic Paleoproterozoic Animikie sedimentary rocks and Logan diabase. �Franklin Franklinand andMitchell Mitchell(1977) (1977)subdivided subdividedthese theseLZBV LZBVdeposits depositsinto intothree threeclasses: classes: (1) those that have the Sibley Group as at least one wall rock (1) those that have the Sibley Group as at least one wall rock(e.g. (e.g.Dorion DorionMine); Mine); (2) those that are entirely enclosed within Sibley Group rocks (e.g. Enterprise (2) those that are entirely enclosed within Sibley Group rocks (e.g. EnterpriseMine); Mine);and and lie within the Archean basement but near the unconformity with (3) those (3) those lie within the Archean basement but near the unconformity withbasal basal sandstones sandstonesof ofthe theSibley SibleyGroup Group(e.g. (e.g.Ogema OgemaMine). Mine). Wall Wall rock rockalteration, alteration,typically typicallybest best manifested manifested in in dolomitic dolomiticrocks, rocks, isistan tanto togrey greyinincolour colourand andisis characterized characterized by by enrichment enrichmentin in 5i02 Si02and andCaO, CaO,slight slightenrichment enrichmentin inFeO FeOand andMnO MnOand anddepletion depletion of ofMgO, MgO,CO2 CO2and andA1203. A1203.(ibid). (ibid). This This indicates indicates silicification, silicification, the the conversion conversion /I replacement replacement of of dolomite dolomite by by calcite, calcite, removal removal of of feldspar feldspar and and mica mica and and pyritization. pyritization. Metal Metalenrichment enrichmentis is noted noted in in altered alteredwall wallrock. rock. Archean K-Arages, ages,indicating indicatingthat thatvein-forming vein-formingfluids fluidswere were Archean wall wall rocks rockshave havereturned returnedArchean ArcheanK-Ar Sulphur-isotopic data not hot enough to re-equilibrate the argon in the analysed mica. not hot enough to re-equilibrate the argon in the analysed mica. Sulphur-isotopic dataindicate indicate equilibrium equilibrium between between galena galena and and sphalerite sphalerite yielding yielding aa depositional depositional range range of of35°-135°C, 35O-l35OC, and and disequilibrium disequilibriumbetween between sulphide-sulphate sulphide-sulphate pairs pairs (ibid). (ibid). Haynes Haynes(1988) (1988)noted notedthat thatfluid fluidinclusions inclusions in wt.%NaCI NaCl±+ in quartz quartzand andsphalerite sphaleriteindicate indicatedeposition depositionfrom fromNa-Ca Na-Cachloride chloridebrines brines(26-33 (26-33wt.% CaCl2 equiv. equiv. salinity) salinity)atattemperatures temperaturesofof90°-200°C. 9O0-20O0C. He He also alsosuggested suggestedthat thattwo twoisotopically isotopically CaCl2 distinct CaCl2 >> >> Theinclusion inclusionfluids fluidscontain containNaC1 NaCl>>CaCl2 distinctbrines brines were were involved involvedin invein veinformation. formation.The brines and Mississippi Valley-type present-day basinal to KC1, compositionally compositionally similar similar to present-day basinal brines and Mississippi Valley-type KCl, mineralizing mineralizingsolutions. solutions. High ratios 30.7) from from vein vein galena galena (Franklin (Franklin and and Mitchell Mitchell 1977) 1977)likely likelyreflect reflect 2 0 6 ~ b / 2 wratios ~ b ((s 30.7) High206Pb/2°4Pb radiogenic lead associated with the radioactive, Archean, Bowker granite. As noted radiogenic lead associated with the radioactive, Archean, Bowker granite. As notedby byFranklin Franklin (l978b), (1978b),the theEnterprise Enterprise Mine Mine has hasthe thedistinction distinction of ofbeing being the theonly onlyLZBV LZBVdeposit deposittotocontain contain appreciable U)portions portionsof ofthe theEnterprise Enterpriseveins veins appreciable amounts amounts of of uranium. uranium. U-enriched U-enriched(up (upto to540 540ppm ppmU) (Ruzicka (Ruzicka1976) 1976)are areapparently apparentlyspatially spatially associated associated with with galena galena and and likely likely reflect reflectproximity proximityto toaa uraniferous, uraniferous, basement basement source source rock. rock. Lead Leadisotopes isotopesare arehighly highlyanomalous, anomalous,yielding yieldingaa secondary secondary isochron isochron that that likely likely indicates indicatesaamixed mixedArchean-Paleoproterozoic Archean-Paleoproterozoic lead lead source source (Franklin (Franklin and and Mitchell Mitchell 1977). 1977). These These anomalous anomalous and and very very radiogenic radiogenic leads leads are are more more uranogenic uranogenic and and less less thorogenic thorogenic than than leads leads found found in insilver-bearing silver-bearing veins veins near near Thunder Thunder Bay Bay (Franklin (Franklinet et al. al. 1986) 1986)to to which they are temporally and tectonically similar. The LZBV mineralization is most which they are temporally and tectonically similar. The LZBV mineralization is mostlikely likely related 110 Ma). related to to dewatering dewateringof of the the Sibley Sibleybasin basin during during Keweenawan Keweenawanrifting rifting(ca.1090-l (ca.1090-1110 Ma). Franklin Franklin and and Mitchell Mitchell (1977) (1977) suggested suggested that that the the vein vein metals metals were were either either leached leached from from basement basement rocks rocks anchor andlor the breakdown breakdown of of Sibley Sibleysandstone sandstonematrix. matrix. Metals Metals and and sulphate sulphatemoved moved through through permeable permeable Pass Pass Lake Lake Formation Formation sandstone sandstoneas as chloride chloride complexes complexes (Haynes (Haynes 1988) 1988)in in aa very very saline saline brine, brine, and and precipitated precipitated in in veins veins at at the thesandstone sandstone pinch-out, pinch-out, at at or or near near the the Archean Archean unconformity. unconformity. Isotopically Isotopically light light sulphur, sulphur,perhaps perhapsof oforganic organicderivation, derivation,may mayhave havebeen beenlocked lockedinina aH2S-bearing His-bearing gas gas trap trap at the the pinch-out, pinch-out, and and caused caused the the metals metals to to precipitate. precipitate. �- - -s-- -:-ccc: H . . .. - .1.1.II.__•t ,'.' • - • - - • • . - . - . . , 1' .;•.'•• - - —- — — - KAMA HILL-FM-L-.. — I— H S accumulates ROSSPORT FM. pinch-out trap • ' • PASSLAKE FM : , f :.:c:::::::::I.:4;. Tt0Itso •,e.:,.f_.e_•._ . -,.•s• 4—BASEMENT '_.,—,-,—;.-; — 4-t4t'+ + + . + + - • + t + + + • • _ __ — — — Schematic formation of LZBVdeposits from Franklin Franklin and and Mitchell Mitchell (1977); fl977); scale is Schematic model model of of the formation ofLZBV depositsfrom is variable. variable. Amethyst The The largest largest deposits depositsof of amethyst, amethyst,Ontario's Ontario's provincial provincial mineral mineral emblem, emblem, occur occur in in the the Thunder Thunder Bay Bay area. area. Nearly Nearlyall allof ofthe themost mostextensive extensiveand andrichest richestdeposits depositsoccur occur in in aa 10 10km-long, km-long, northeastnortheasttrending trending belt belt near near the the margin margin of of the the Sibley SibleyGroup Group outcrop outcrop where where itit is is underlain underlain by by Hilma Hilma Lake Lake granite granite (Kissin (Kissin 1990; 1990; Garland 1994; 1994; Vos 1976). 1976). Other Otheroccurrences, occurrences,mainly mainly hosted hosted in in granite, granite, are also also spatially spatially related related to to Sibley Sibley outcrop. outcrop. These amethystine quartz, quartz, with minor calcite, calcite, barite and sulphide sulphide These deposits depositsconsist consist of of quartz quartz ++ amethystine minerals minerals (e.g. (e.g. pyrite, pyrite, chalcopyrite, chalcopyrite, bomite). They Theytypically typicallyoccupy occupyfaults faultsand and related related fracture fracture zones zones where where brecciation brecciation and open-space-filling open-space-filling are common (ibid). The The similarities similarities in in geologic geologic setting setting between between amethyst amethyst and and LZBV LZBV led led Kissin Kissin (1990) (1990) to to suggest suggest that that these these two two types types of of vein vein deposits in McArthur McArthur and deposits are are cogenetic. cogenetic. Fluid Fluidinclusion inclusionstudies studiesby by McArthur McArthur (1988), (1988), reported reported in Kissin Kissin (1988), (1988), indicate indicate that that most most amethyst amethyst formed formed near near the the surface, surface, at at temperatures temperatures ranging ranging from from 60' to 90' C. Kissin (1990) suggested that they may be low-temperature derivatives of LZBV, 60" to 90" C. Kissin (1990) suggested that they may be low-temperature derivatives of LZBV, poorer in in sulphides sulphidesand and richer richer in in quartz. quartz. The The presence presence of of aa uraniferous uraniferous basement granite granite (Franklin 1978) was probably crucial in the formation of local amethyst deposits (Kissin 1990), (Franklin 1978) was probably crucial in the formation of local amethyst deposits (Kissin1990), because radioactivity radioactivity is is essential essential in in causing causingelemental elemental substitution substitutionand and defects defectsin in the the quartz quartz crystal crystal that that impart impart the the purple purple colour colour (Garland (Garland1994 1994and and references referencestherein). therein). In In the vicinity vicinity of of the the Enterprise Enterprise Mine, Mine, amethyst amethyst veins veins and and breccia breccia zones zones occur occur in in basement basement granitoids granitoids and and in in overlying overlyingclastic clastic and and stromatolitic stromatoliticSibley Sibley Group Group rocks rocks at at or or near near the the unconformity. paper) basemetal-mineralized metal-mineralizedstromatolites stromatolites(see (seefrontispiece, this this paper) unconformity. Amethyst Amethyst± base the Ontario Gem Welch's Farm occurrence occurrence (C. Anderson, Anderson, pers. comm., 1999), 1999), at occur at the Welch's Company Company Amethyst Amethyst Mine Mine (Garland (Garland 1994) 1994)and in other other places places east east of of Ancliff Ancliff station station (Tanton (Tanton + �1931; J. Scott, Scott, pers. pers. comm., comm., 1999; Mcllwaine 1971 a,b). They They typically typically occur occur on on top top of of 1931; J. 1999; Mcllwaine 1971a,b). prominent granite granite knobs knobs which which may mayreflect reflectpaleotopographic paleotopographic"highs". 'highs. prominent The nearby nearby rockcut rockcut produced produced by the railway railway exposes exposes the the basal basal contact contact of the Sibley The by the of the Sibley Group Group with with underlying Archean Archean granitoids. A regolith regolith makes makes identification identification of of the the contact contact difficult difficult in places. underlvine eranitoids. A in vlaces. Unconformity betweenArchean Archeangranite granite (Gr) (Gr) and and trough Unconformity between trough crossbedded, crossbedded, Pass Pass Lake Lake Formation Formation quartz arenite (s.s.), Enterprise Mine quartz arenite ( i s . ) , Enterprise Mine Medium-grained,trough trough cross-stratified cross-stratifiedsandstones sandstoneslie lie directly directly on on the Medium-grained, the regolith. regolith. The The lensoid, lensoid, cross-cutting bed bed geometry the sandstone discernable. Flow cross-cutting geometry of of the sandstone units units is is easily easily discernable. Flow was was to to the the southeast southeast (Cheadlel986). Again the the exact these units units were were laid laid down (Cheadlel986). Again exact depositional depositional environment environment these down in in is is difficult to to ascertain. difficult ascertain. Without Without fossil fossil evidence evidence to to rely relyon onnear-shore, near-shore,trough troughcross-stratified, cross-stratified, sandstone sandstone sequences sequencesare aredifficult difficultto to differentiate differentiate from from South South Saskatchewan-type, Saskatchewan-type, braided braided fluvial, fluvial, channel channel sandstones. sandstones. Overall Overall unit unit geometry geometry can can give give some some clues, clues, as as can can variability variability of of paleocurrent paleocurrent directions and directions and associated associated minor minor lithofacies, lithofacies, but, but, thick, thick, laterally laterally persistent, persistent, monolithic monolithic successions successions assigning a depositional in serious problems of trough cross-stratified sandstone pose of trough cross-stratified sandstone pose serious problems in assigning a depositional environment. Are Are there there any any clues which would would help help in environment. clues in in this this assemblage assemblage which in deciding deciding between between the the two aforementioned two aforementioned environments? environments? �STOP GH WA 17 STOP2-1: 2-1:GURNEY GURNEY(HI (HIGHWAY) The basal unconformity between the Sibley Group and underlying granitoids is exposed at at this this location. A channel is eroded into basement, and containing matrix-supported visible, eroded into basement, and containing matrix-supported location. A channel is visible, conglomerates overlain by by cross-stratified sandstones. This This sequence sequence differs differs from the conglomerates overlain cross-stratified sandstones. the other other coarse-grained, basal sediments we have examined, as itit represents episodes of subaerial debris represents episodes of subaerial debris flow flow activity activity interspersed intersversed with with normal normal flash flashflood flood runoff. runoff. Unconformity between betweenweatheredArchean weatheredArchean granite (Gr) flows (Gr) and and Pass Pass Lake Lake Formation Formationdebris debrisjlows and Highway 17 17 at at Gurney Gurney and sandstones, sandstones,Highway Archean granitic granitic rocks are altered altered at the unconformity and likely represent a pre-Sibley weathered regolith. This weathered weathered regolith. This weathered paleosol, noted noted by Gill Gill (1926) (1926) and and Moorhouse Moorhouse(1960), (1960),was was locally described by Scott (1987). Friable, locally described Friable,blotchy, blotchy,red redand andgreen greengranite granitehosts hostsquartz-carbonate quartz-carbonate veins between exfoliation exfoliation blocks. Feldspars Feldsnarshave havebeen beenhematitized hematitizedand/or and/ordestroyed; destroyed:. ferromagnesian ferromagnesian minerals minerals have have been been chloritized chlohtized(ibid). (ibid). Limited sampling sampling of of drill drill core core from from the the Black Sturgeon Lake area area cited by Scott (1987) (1987) suggests suggests that this alteration may typically involve marked increases H20 and decreases in NazO, Na20, CaO and perhaps KiO. K20. increases in Fe203, MgO, H2O Paleomagnetic data suggest suggest that this weathering was equatorial (G. Borradaille, unpublished data, 1999). 1999). data, . As (1987) number of As noted noted by by Franklin Franklin(1 (1 978b), Scott (1 987) and Tanton (1948), (1 948), a number of uranium uranium occurrences occurrences are rocks within within the Sibley Sibley are associated associated with with altered altered Archean Archean granitoids granitoids and and overlying overlying sedimentary sedimentary rocks basin, basin, prompting prompting comparisons comparisonswith with the the Athabasca Athabasca basin basin in in Saskatchewan. Saskatchewan. Favourable Favourablelocal local parameters parameters for for supergene supergeneuranium uranium deposits depositsinclude: include: (i) (i) uranium-enriched uranium-enriched basement rocks rocks (quartz monzonites, (ii) onlaps onlapsof ofbasal basal Sibley Sibleysandstones sandstoneson onArchean Archeanpaleotopographic paleotopographic monzonites, pegmatites); pegmatites); (ii) "highs'; "highs";and and(iii) (iii)Keweenawan(?) Keweenawan(?)faults faultsthat thatextend extendto tothe thebasement basement(ibid). (ibid). �STOP 2-2: HILL STOP 2-2:KAIMA KAMA HILL Diabase-capped Kama Hill Hill provides Diabase-capped Kama provides an an excellent excellent roadside roadside exposure exposure of of the theRossport RossportFormation. Formation. The sequence is dominated by interlaminated dolostone and red shale with The sequence is dominated by interlaminated dolostone and red shale with layer layer thicknesses thicknesses ranging from from millimeters millimeters to to ten ten centimeters. There is is some ranging centimeters. There some cyclicity cyclicity in in layer layer thickness thickness variation variation up through the sequence, but it is not a strong trend. Some carbonate layers up through the sequence, but it is not a strong trend. Some carbonate layers contain contain coarsecoarse- to to medium-grained sand sand grains. grains. Dessication medium-grained Dessication cracks cracks are are present, present, but but not not common. common.Synsedimentary Synsedientary deformation manifests manifests itself itself as deformation as small small to to large large slump slump folds folds and and brecciation brecciation of of units unitsin inplaces. places.The The sequence is is intruded sequence intruded by by diabase diabase dykes dykes which which bake bake immediately immediately adjacent adjacent sediments. sediments. Some Some evidence has been been put put forward evidence has forward that that the the diabase diabase intruded intruded watery watery sediment, sediment, but but we we have have not not seen seen clear indications of of this. this. Structural clear indications Structural controls controls on on the the emplacement emplacement of of local local sills sills were were suggested suggested by by Antonellini and and Cambray Cambray (1992). (1992). AAchert-carbonate Antonellini chert-carbonate unit unit (Middlebrun (Middlebmn Bay Bay Member; Member; Cheadle Cheadle 1986) locally hosts hosts stromatolites 1986) locally stromatolites and and hydrocarbons. hydrocarbons. The Kama below the the upper The Kama Hill Hill sequence, sequence, exposed exposed below upper diabase diabase sill, sill, was was laid laid down down in in the theshoreshoreproximal region of a playa lake. Pieces accessible in a pile of excavated talus display proximal region of a playa lake. Pieces accessible in a pile of excavated talus display ripple ripple rainy periods, periods, water marks, mudcracks influx into into the the marks, mudcracks and and rare rare raindrop raindrop impressions. impressions. During During rainy water influx lake lake brought brought and and deposited deposited hematite-rich hematite-rich clays. clays. In In dry dry periods, periods, evaporation evaporation from from the the internal internal drainage system system resulted resulted in in lake contraction, hypersalinity hypersalinity and and the the precipitation drainage lake contraction, precipitation of of dolomite. dolomite. This This requires aa high high MgICa Mg/Ca ratio ratio in in the the lake lake water water and and may may have have been been the the result result of of the the precipitation precipitation of of requires gypsum in in the the central this is is unlikely are expected in the the gypsum central lake. lake. However, However, this unlikely as as higher higher salinities salinities are expected in shallower, marginal marginal areas areas then then the shallower, the lake lake center, center, and and thus, thus, gypsum gypsum precipitation precipitation should shouldbe be initiated initiated in triplets. The The lack in the the shallows, shallows, producing producing shale-gypsum-dolomite shale-gypsum-dolomite triplets. lack of of these these means means that that gypsum gypsum precipitation was was not not necessary necessary to to increase increase the the MgKa Mg/Ca ratio. ratio. The The ambient ambient ratio ratio in in the the lake lake water water precipitation itself must have been high enough for the precipitation of dolomite. itself must have been high enough for the precipitation of dolomite. Interlaminated red formed Interlaminated red shales shales and and dolostone, dolostone, formed by climatic cycling cycling in in aa semi-arid, semi-arid, playa playa lake by climatic lake environment, Rossport Rossport Formation, Formation, Kama environment, Kama Hill. Hill. I Reduction spheres in Reduction suheres in hematitic hematitic siltstone, siltstone. Kama Kama Hill, with black, carbonaceous, locally "",z,.-"*;.," """*""" radioactive centers. �STOP STOP2-3: 2-3:RUBYLAKEMARBLELTD. RUBY LAKE MARBLE LTD.QUARRY QUARRY The The Ruby Ruby Lake Lake Marble Marble Ltd. quany quarry isis owned owned and and operated operated by by Don DonMacAlpine MacAlpine and Gerald Gerald Landry. Landry. Variegated, Variegated, multimulticoloured, coloured, banded banded marble marble is is quarried quarried for for landscaping landscaping stone. stone. Approximately Approximately 175 175 tonnes tonnes of of marble marble were were quarried quarried and and shipped shipped in in 1998 1998(D. (D. MacAlpine, MacAlpine, personal personal communication,1999). 1999). The dimensions dimensions communication, of of the the largest, largest, transported transported block block was was 1.8 1.8 by by 0.50 0.50mm(= ( 1.8 1.8 tonnes) tonnes) (ibid). (ibid). by 0.75 0.75 by Approximately 398 tonnes Approximately 398 tonnes of of marble marble were were quarried quarried and and shipped shipped in in 1999 1999(D. (D. MacAlpine, MacAlpine, pers. pers. comm., comm., 2000). 2000). Additional Additional information information is provided orovided on on their their World World Wide Wide Website Website(http://www.rubylakemarble.com). (http://www.mbylakemarble.com). . This This marble marble consists consistsofofcontact contactmetamorphosed, metamorphosed,Mesoproterozoic, Mesoproterozoic, Rossport Rossport Formation Formation contact sedimentary rocks in the (Sibley (Sibley Group) Group) dolostone dolostone and and other, other, calcareous calcareous sedimentary rocks in metamorphic metamorphic aureole aureole of of Keweenawan Keweenawan diabase diabase sills. sills. It has previously been termed termed Nipigon Nipigon River from 1883 1883 to to ca. ca. 1910 at at a site on the River marble and was quarried quarried from the eastern eastern side side of of the the cxl. 1994). A Nipigon River, approximately km west west of the Ruby approximately 66 km Ruby Lake Lake quarry quarry (Hinz (Hinz et et al. similar, similar, hornfelsed homfelsed unit is is described described in more detail detail at Stop Stop 2-6. all Calcite, and opaque minerals were were noted noted in in thin section by Hinz Him et et al. Calcite, dolomite, epidote epidote and opaque minerals (1994) from the Nipigon Nipigon River River quarry. quarry. The The following following chemical analyses analyses for for Nipigon Nipigon River River (1994) - chemical marble also provided (wt.%)were werialso provided (ibid): (ibid): marble (wt.%) Sample Sample S102 SiO; 89MCK 35.21 35.21 89MCK 1 MgO MgO Ti02 A1203 A1203 Ti02 0.20 0.20 8.20 8.20 Fe203 Fe203 FeO FeO MnO MnO 2.04 2.04 0.05 0.05 23.56 23.56 CaO 26.74 Na20 0.00 1(20 2.38 P205 1.53 1.53 0.10 2.04 0.00 0.03 27.63 35.32 0.00 0.41 0.07 0.09 -09 -09 89MCK 29.19 5.20 -10 Shallow Shallow exploration explorationtrenches trenches on on the side side of the road leading to the top of Ruby Mountain (i.e. (i.e. top of marble. Fine-grained, of the the upper upper sill) sill)have have exposed exposed copper-mineralized copper-mineralized marble. Fine-grained, disseminated disseminated blebs blebs of of native native copper copper (0.1 (0.1 to to 1.0 1.0 mm mm occur occur along along calcite-coated, hairline fractures parallel to fractures are are most easily planes. Mineralized Mineralized fractures easily recognized recognized where where secondary secondary bedding planes. just formed. The top of the the adjacent adjacent (middle?) sill is exposed just (supergene) malachite has formed. Polygonal cooling coolingjoints joints (seen (seen in in plan plan view) view) and and the chilled, upper upper farther along along the the road. road. Polygonal are evident. evident. margin are Similar, calcareous units units have have been been noted noted near near a diabase sill contact at Similar, copper-mineralized, calcareous all Hughes Point, 2.5 km krn to the south-southwest south-southwest by Schnieders et al. (1996). At At this this location, location, 2 to 55 cm cm wide wide calcite calciteveins veinscontain containdisseminated disseminated covellite covellite (after (after chalcocite?) chalcocite?) and and malachite. malachite. �The Theorientation orientationof ofthe theveins veinsare areroughly roughlyparallel parallelto tojoints joints developed developedin inthe theadjacent adjacentsill. sill.Grab Grab samples have returned up to 3.065% Cu, nil Au and nil Ag (ibid). samples have returned up to 3.065% Cu, nil Au and nil Ag (ibid). Franklin Franklin (1970) (1970)described describedcopper-mineralized copper-mineralized stromatolitic stromatolitic units units near nearDisraeli DisraeliLake. Lake. AA variety varietyof ofcopper copperminerals, minerals,including includingdigenite, digenite,cuprite, cuprite,covellite, covellite,chalcopyrite, chalcopyrite,native nativecopper copper and and malachite, malachite, were were identified identified as as open-space open-space fillings fillings in in the the vuggy vuggy host hostrock. rock. Franklin Franklin (1970) (1970)suggested suggestedthat thatthe thecopper copperwas wasintroduced introducedepigenetically epigenetically from fromaagabbro gabbrototoperidotite peridotite The close spatial association plug plug that thatintruded intrudedthese theseSibley SibleyGroup Grouprocks. rocks. The close spatial associationofofcoppercoppermineralized mineralizedrocks rockswith withdiabase diabasesill sillcontacts contactsininthe thevicinity vicinityof ofRuby RubyLake Lakesupports supportsthis thistheory. theory. The Themarble marble isisstromatolitic, stromatolitic, though though this this is is difficult difficult to to ascertain ascertain in in most most places places due due to tothe the alteration. The stromatolites are best seen on the tops of beds where they protrude, causing alteration. The stromatolites are best seen on the tops of beds where they protrude, causing the thecontact contactto tobecome becomewavy. wavy. Hints Hintsof ofthe thepresence presenceofofstromatotactis stromatotactisare arevisible, visible,giving givingthe the impression impression that that aa large largeamount amount ofofthe thehorizontal horizontallayering layeringisisstromatolitic stromatoliticS-mat. S-mat. This This sequence sequence was was deposited deposited in inaastrandline strandlineproximal proximalposition positioninin the the playa, playa, as asdenoted denotedby bythe the horizon at other locations. This infers that lake size presence presenceof ofteepee teepeestructures structuresininthis this horizon at other locations. This infers that lake sizehad had stabilized stabilizedduring during this thisinterval, interval,eliminating eliminatingthe theseasonal, seasonal,large-scale large-scalefluctuations fluctuationsin inshoreline shoreline positioning. positioning. r . - - - - .— t - - — 4T : TI - - - -- Lz.L .. . Parallel-laminated ininpossible Parallel-laminatedcarbonate carbonatewith withvariable variableamounts amountsofofhematitic hematiticclays ...~, 'a possibleS-mat stromatolite, Ruby Lake Quarry �U MOUNTAIN MOUNTAIN STOP 2-4: 2-4: MOSEA MOSEAU The Moseau stop consists consists of of a number Moseau Mountain Mountain stop number of of small small outcrops outcrops extending extending from from the the granitic basement basement to to the middle granitic middle portion portion of ofthe theRossport RossportFormation. Formation. Cross-stratified sandstones of the Pass Lake multiLake Formation Formation overlie basement. The lower lower sandstones sandstones are multistorey, but as we proceed upwards mudstone mudstoneinterbeds interbedsbegin begin to to appear. appear. Above Above this thiszone zonethe the sandstones are replaced by siltstones, continuing the general upward-fining trend. trend. Higher Higher in the siltstone mudblock conglomerates conglomeratesbegin begintoto appear. appear. These, These, in in turn, turn, are are the siltstone succession succession mudblock upwardly transitional into evaporite block conglomerates, with gypsum and dolomite clasts. and dolomite clasts. Diabase intrusions intrusions occur occur above above this this zone. zone. The lower portion of of the sequence is similar to the one observed The lower portion sequence is similar to observed at Pass Pass Lake, Lake, where where a and conglomerates to to the the siltstones thinning and fining trend exists from the basal sandstones and of the basal Rossport Formation. This again represents expansion expansion of a playa playa lake lake system. system. The The intraformational conglomerates which which overly overly this this sequence may may have have been produced by two intrafonnational mechanisms. Dissolution Dissolution of of an evaporitic layer causing collapse of the overlying mechanisms. overlying units, units, or or tectonic raising of the basin margin margin resulting resulting in inthe theerosion erosionand and resedimentation resedimentation in in aa more more basin-center environment of the upper marginal sediments. The latter explanation explanation is preferred as this unit is regional in extent, occurring where it is unlikely that underlying evaporites ever existed. existed. STOP 2-5: S LOOKOUT 2-5: LLOYD LLOYD'S LOOKOUT This stop, located on the Nipigon-Red Rock hiking trail, features exposures of Kama Hill Formation shales and siltstones siltstones underneath a Logan diabase sill which caps the prominent mesa and provides the vantage point over Nipigon Nipigon Bay Bay known known as as Lloyd's Lloyd'sLookout. Lookout. From one can can view view the themouth mouthof ofthe theNipigon NipigonRiver Riverand andNipigon NipigonBay. Bay. The this vantage point, one locations of the quarries 1-2 are shown in the photograph photograph below. quarries mentioned in STOP 1-2 Viewfrom fromLloyd's Lloyd's Lookout, Lookout, looking looking east east over Nipigon Bay View I �This This is is one oneof ofthe thefew fewaccessible accessibleexposures exposuresof ofthe theKama KamaHill HillFormation. Formation.This ThisFormation Formationisis homogeneous, consisting of brick-red mudstones with interlayered, current-rippled, homogeneous, consisting of brick-red mudstones with interlayered, current-rippled,coarsecoarsegrained grained siltstones siltstones and and very veryfine-grained fine-grained sandstones. sandstones. The The rippled rippled layers layers are are usually usually centimeters centimetersto to aa few fewdecimeters decimetersthick. thick.The Themudstones mudstonesare arecommonly commonlymudcracked. mudcracked. Cheadle believed that that this this unit unit was was deposited deposited as as subaerial subaerialmudflats, mudflats, representing representing the the Cheadle (1986) (1986) believed final final stage stageof of infilling infilling of of the the lake lake basin. basin. However, However, new new drill drill core core data dataindicate indicate that that the the Kama Kama Hill Hill Formation Formation is is overlain overlain by by aaprograding, prograding,deltaic deltaicsequence. sequence. This Thisinfers infersa asubaqueous subaqueous position position for for the the Kama KamaHill HillFormation Formationwith withthe thesediments sedimentsrepresenting representingprodelta prodeltato todistal distalbar bar sequences. In core, core, these these are are overlain overlain by by distributary distributary mouth mouth bar bar and andfluvial fluvialchannel channel sequences. In sandstones. The mudcracks are problematic. They may be syneresis cracks, sandstones. The mudcracks are problematic. They may be syneresis cracks, formed formed subaqueously subaqueously through through differential differential swelling swelling of of clays, clays, or or they they may mayrepresent representlarge-scale, large-scale,water water level level fluctuations. fluctuations.Neither Neither of ofthese theseexplanations explanationsappears appearsadequate. adequate. The The view view over over Nipigon Nipigon Bay Bay isistowards towardswhere wherethe thedrillcore drillcoreexamined examinedthe theprevious previousday daywas was drilled. 20 m m of ofwater, water, drilled. During During Kama Kama Hill Hill time time we we would would be be standing standing in in approximately approximately 20 looking looking towards towards aa horizon horizon where where aa delta delta system system would would be be located, located, building building towards towards us. us. STOP STOP 2-6: 2-6:BIG BIGSQUAW SQUAWCREEK CREEKROAD ROAD CUT CUT This This stop stop presents presents the the opportunity opportunity to to view view stoped stoped blocks blocks of of Rossport Rossport Formation Formation dolostone dolostone in in aa diabase diabase sill, sill, as as well well as asthe theattendant attendantmetamorphic metamorphic and andmetasomatic metasomaticeffects. effects. Pale Pale green green to to buff, buff, thinly thinly bedded bedded dolostones dolostonesare are preserved preserved as as rafted rafted xenoliths xenolithsup up to to several severalmetres metres thick. thick. Rafied Formation in Rafted xenoliths of hornfelsed Rossport Formation in Logan diabase diabase sill, sill, Highway Highway 11-17 11-1 7 at at Big Squaw Creek Creek I I I I �Thin section Thin section petrography petrography reveals aa recrystallized, recrystallized, granoblastic granoblastic texture texture predominated predominated by epidote. Subhedral to euhedral, epidote porphyroblasts are typically 0.05 to 0.10mm size, mm in size, Subhedral porphyroblasts are typically 0.05 to 0.10 but they may reach 0.25 mm, in a fine-grained matrix of vermicularly intergrown quartz and feldspar. Large Large (<0.75 (<0.75 cm), cm), optically optically continuous, continuous, decussate, decussate, acicular biotite porphyroblasts Radiating, sheaf-like sheaf-like aggregates aggregates have have been are also overgrown are overgrown by by epidote. epidote. Radiating, been tentatively tentatively Minor sericite sericite and and calcite were were also noted. Epidote persists into the identified as chlorite. chlorite. Minor margin of of the the diabase. diabase. Joints fine-grained, chilled margin Joints and and fractures fractures surfaces may be coated coated with Large, consp conspicuous, lime-green clots of prehnite occur in epidote-calcite veins muscovite. Large, within the diabase. Little work has been done done on on contact contact metamorphic metamorphic effects in vicinity of the diabase diabase sills. sills. (1986) noted noted that that such metamorphism occurs in in calcareous calcareous rocks rocks over over a zone Sutcliffe (1986) Sutcliffe metamorphism occurs zone several metres metres thick, thick, where where bleaching bleaching is is its its most obvious manifestation. manifestation. Fine-grained, Fine-grained, calcmineral-bearing assemblages assemblages identified identified by by Sutcliffe Sutcliffe (1986) (1986) include include calcite, plus (in silicate mineral-bearing (in order of increasing metamorphic grade): talc, tremolite, serpentine (after forsterite) and increasing metamorphic grade): tremolite, serpentine (after forsterite) and Calculations by by Sutcliffe Sutcliffe (1986) (1986) suggest suggest that that the diabase sills were emplaced at diopside. diopside. Calculations shallow crustal crustal levels, levels, near near the the Archean-Proterozoic Archean-Proterozoicunconformity, unconformity,atataalithostatic lithostaticload loadof of shallow <0.4 adjacent 88OSC,while adjacent 0 . 4 kbars. The Thesills sillscrystallized crystallizedover over aa temperature temperature range of 1100° 1100" to 880°C, wall rocks may have experienced 665°C (ibid). experienced temperatures temperatures ranging ranging from 540° 540' to 665'C hornfels at Big Squaw Creek may may reflect simple The mineral assemblage in the calc-silicate hornfels significant recrystallization of sedimentary units without of the impure, impure, calcareous sedimentary units without significant compositional or compositional or volumetric volumetric changes changes (ci'. (cf. Hall and and MacKevitt MacKevitt 1962). 1962). �REFERENCES REFERENCES Antonellini, Antonellini, M.A. M.A. and and Cambray, Cambray, F.W. F.W. 1992. 1992. 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McTavish McTavish Township Township (West of north north halt), half), District District of ofThunder ThunderBay; Bay; Ontario Ontario Department Department of of Mines Mines and and Northern Northern Affairs, Affairs, Preliminary Preliminary Map Map P.720, P.720, scale scale 1:15 1:15 840. 840. . 1975. 1975. McTavish McTavish Township Township (south (south half), half), District District of of Thunder Thunder Bay; Bay; Ontario Ontario Department Department of of Mines Mines and and Northern Northern Affairs, Affairs, Preliminary Preliminary Map Map P.990, P.990, scale scale 1:15 1:I5 840. 840. Moorhouse, W.W. 1960. The Gunflint Moorhouse, W.W. Gunflint iron range in the the vicinity vicinity of ofPort PortArthur; Arthur;Ontario Ontario Department Department of of Mines, Mines, Annual AnnualReport, Report,v.69, v.69, pt.7, pt.7, p.1-40. p.1-40. Morey, Morey, GB. G.B. and andOjakangas, Ojakangas, R.W. R.W.1982. 1982.Keweenawan Keweenawan sedimentary sedimentary rocks rocks of ofeastern eastern Minnesota and northwestern northwestern Wisconsin; Wisconsin; in Tectonic Tectonic history of of the the Lake LakeSuperior Superior basin, Geological Geological Society Society of of America, America, Memoir Memoir 156, 156, p.135-146. p.135-146. Parks, W.A. 1901. 1901. Report of 1901 1901 on on the the geology geology and and natural natural resources resourcesof ofthe thesoutheastern southeastern Nipigon district; Geological Survey of Canada, Report. Nipigon district; Geological Survey of Canada, Report. Ruzicka, V. 1976. in Report 1976. Assessment Assessment of some some Canadian Canadian uranium uranium occurrences; occurrences; in Report of Ruzicka, V. Activities, Part A, Geological Survey of Canada, Canada, Paper Paper 76-IA, 76-lA, p.341-342, p.341-342. �Scott, J.F. J.F. 1987. Uranium occurrences of the Thunder Bay-Nipigon-Marathon area; Ontario Ontario Bay-Nipigon-Marathon area; l58p. Geological Survey, Open File Report 5634, 158p. Sutcliffe, R.H. R.H. 1986. The The petrology, mineral chemistry chemistry and and tectonics tectonics of Proterozoic Sutcliffe, petrology, mineral Proterozoic riftrelated igneous rocks at Lake Nipigon, Ontario; unpublished Ph.D. related igneous rocks Lake Nipigon, Ontario; unpublished Ph.D. thesis, thesis, The The University of Western Ontario, London, 325p. Tanton, T.L. T.L. 1931. Fort William and Port Arthur, and Thunder Cape map-areas, Thunder Tanton, map-areas, Thunder 222p. Bay District, Ontario; Geological Survey of Canada, Memoir 167, 167,222~. Radioactive nodules nodules in in sediments sediments of of the Sibley series, Nipigon, Ontario; 1948. Radioactive . 1948. Ontario; III, section IV, p.69-75. Transactions of the Royal Society of Canada, v.XLII, series 111, Wilson, A.W.G. 1910. 1910. Geology of the Nipigon Basin, Ontario; Canada Department of Mines, Geological Survey Branch, Memoir Memoir No. No. 1, 152p. l52p. 1 �GEOLOGY GEOLOGY OF OF THE THE LAC LAC DES DES ILES ILES PGE-Cu-Ni PGE-Cu-Ni MINE MINE Moe Lavigne, Lavigne, Matawin Matawin Mineral Mineral Exploration, Exploration, and and Moe Staff, Lac Lac des des lies lies Mines Mines Ltd. Ltd. Staff, North American American Palladium Palladium Limited's pit Lac Iles North Limited's open open pit Lac des des lies Mine Archean Lac Lac des des lies Iles mafic-ultramafic mafic-ultrama/Ic Mine is is hosted hosted by by the the Archean intrusive complex. This trip on PGE intrusive complex. This trip willfocus will focus on PGE mineralization mineralization as structure and and alteration. as it it relates relates to to intrusive intrusive lithology, lithology, structure alteration. �PaHadurn Geology Geology of the the Lac Lac des lies lles Palladium Deposit Regional Regional Geology Geology The age rocks rocks (2.6 (2.6 ttoo 3.0 The Lac Lac des des lies lles area is underlain by the Archean age 3.0 billion billionyears) years) of ofthe theCanadian CanadianShield.These Shield.These rocks are overlain and and intruded intruded by by Proterozoic Proterozoic age agerocks rocks(0.9 (0.9t o to 2.2 2.2billion billionyears) years)that thatformed formedduring duringrifting riftingof of the mafictto or have the continent, continent,centered centeredon onLake LakeSuperior.Archean Superior.Archean age. age. mafic o ultramafic intrusions that host, host. or have the potenpoten- tial are dispersed dispersedthroughout throughoutNorthwestern Northwestern 0ntario.These Ontario.These intrusions are are concentratconcentrattial to t ohost hostPGE PGE mineralization, mineralization,are ed malor faults.The 20km km south south of Lac Lac ed within within granite-greenstone granite-greenstone terrain, terrain, and and along major faults.The Quetico Quetico Fault, Fault, which passes passes 20 des lles, lies, is is coincident coincident with with a 180km southwesterly trend trend of PGE bearing intrusi0ns.A intrusions.A particular particular high high concentraconcentral80km southwesterly PGE bearing tion circular feature feature with with a 30 km tion of ofintrusions intrusionsoccur occurininthe theLac Lacdes des lies llesarea, area,aa number of intrusions define a circular diameter.These major crustal sutures are are important important as that can can only only originate originate from diameter.These major as they allow allow PGE PGE rich magma magma that the the earths earths mantle, mantle, ttoo move move upwards upwards into into the the crust. crust Proterozoic mineralization isis not not as as common common in northwestern northwestern Ontario. Ontario.However, However,potential potentialPGE PGE hosting hosting Proterozoicage age PGE PGE mineralization Proterozoic mafic tto voluminous.Gabbro Gabbrocovers coversor or intrudes intrudes most most of the Proterozoic age mafic o ultramafic intrusions are much more voluminous. Lake Superior Superior area, area, no no less lessthan than 20,000 20,000km2.A km2.A recent 8 g/t lies at Wolf Wolf g/t Pd+Pt Pd+Pt discovery discovery made made east of Lac Lac des lles Mountain in a Proterozoic ultramafic intrusion intrusion is testament testament tto o its its potential. potential. Proterozoic age age ultramafic The known knownmafic mafic to t oultramafic ultramaficintrusions intrusionsininthe theLac Lacdes deslIes llesarea area consists consists of of the the following; following; . • Lac des lles lies Complex Complex (—30km2) (-30km2) (Company ownership; ownership;100%) 100%) • Tib TibLake LakeIntrusion Intrusion(—25km2) (-25km2) (Company (Company ownership; ownership;65%) 65%) ..,~ ~, ~:~ ,. • Legris 2km2) (Company ownership; LegrisLake LakeIntrusion Intrusion(—.1 (-1 2km2) ownership; 0%) 0%) • Demars DemarsLake LakeIntrusion Intrusion(-.(-1I km2) km2)(Company (Companyownership; ownership;100%) 100%) . . • Taman Taman Lake Lake Intrusion Intrusion (CI (C Ikm2 km2 (Company (Company ownership; ownership;0%) 0%) DogRiver RiverIntrusions Intrusions(<I (< lkm2) km2) • Dog (Company (Company ownership; ownership;0%) • Buck BuckLake LakeIntrusion Intrusion(—Skm2) (-5km2) (Company (Company ownership; ownership;90%) 90%) • Wakinoo WakinooLake LakeIntrusion Intrusion(--II (-1 kni2) lkm2)(Company (Companyownership; ownership;100%) 100%) w) These intrusion intrusion are are similar similar in in that that they theyare arelate latetectonic tectonicand andintrude intrudetonalite tonalitegneiss, gneiss,have have tholeHtic tholeiitic affinity and contain rangingfrom from ultramafic ultramafic peridotitic contain phases phases ranging peridotiticand andpyroxenitic pyroxeniticcummulates cummulatestot omagnesian magnesiangabbro-norite gabbro-noriteand and iron-rich Taman and Dog Dog River intrusions. is found found in in all all except except the theTaman intrusions. iron-rich gabbro. gabbro. PGE PGE mineralization mineralization is des lles lies Complex consist of three The Lac des three distinct distinct lithological lithologicalpackages; packages; tto o the north, north, ultramafic ultramafic intrusions intrusionscencentered gabbroic intrusions intrusions immediately south of the lake and a horntered on on Lac Lac des des lies, lles, complex gabbroic lake (Mine Complex), Complex),and blende gabbro southwest southwest of of Camp Camp Lake Lake (Camp (Camp Lake Lake lntrusion).These three threesegments segments are are partially partiallyseparated separated by by tonalite of which consist of several septums.The ultramafic ultramafic intrusions intrusions consist consist of of two twocoalescing coalescingcentres, centres, each each of tonalite septums.The It conconintrusive phases.The northern ultramafic centre is nearly circular in plan with a diameter of nearly 4 km. It phases.The northern sist of interlayered interlayered dunite dunite and and wehrlite, wehrlite,olivine-clinopyroxenite olivine-clinopyroxeniteand andclinopyroxenite. clinopyroxenite.and and websterite websteritewhich whichdefine define aa �Palladium concentric concentric inward inward dipping dipping pattern.These pattern.These lithologies lithologies occur occurininseveral several cycles cycles which which probably probably represents represents fractional fractional crystallization of pulses.ItItalso alsorepresents representsrepeated repeatedopportunities opportunities tto concentrate PGE's. This crystallization of separate separate magma magma pulses. o concentrate PGE's. This part of sulphide rich rich horizons, occurrences (>1 part of the thecomplex complexdoes doeshave haveseveral several PGE's PGE's bearing bearing sulphide horizons, and and 55 PGE PGE occurrences (>I g/t g/t Pd+Pt) were discovered 999.The elliptical elliptical southern southern ultramafic wehrlite core Pd+Pt) were discovered in in I1999.The ultramafic centre centre consist consist of of aamassive massive wehrlite coresursur- rounded websterite.These two gabbronorite wedge on the the east side of of the the rounded by by websterite.These two centres centres are are partially partiallyseparated separated by by aa gabbronorite wedge on east side complex..This area PGE occurrences, occurrences,S 5 discovered discovered in in 1999. 1999. complex..This area contains contains 77 PGE The had been been considered considered tto a relatively homogenous hornblende hornblende be a relatively homogenous The Camp Camp Lake Lake Intrusion, Intrusion, south south of of Camp Camp Lake, Lake, had o be gabbro and barren barren of of PGE mineralization. Historically, Historically, itit had had been been subjected subjected tto minimal exploration. exploration. Stripping gabbro and PGE mineralization. o minimal Stripping along its northern northernmargin margininin1999 1999revealed revealedunexpected unexpectedcomplexity complexityand andsampling samplinggenerated generatedlow lowgrade gradePGE PGEassays. assays. along its The mineralcompositionally, texturally texturallyand and structurally structurallycomplex, complex,contains contains abundant abundant PGE PGE mineralThe Mine Mine Complex, Complex, which which isis compositionally, ization. Its Its composition composition ranges rangesfrom from anorthosite anorthosite to ization. t o clinopyroxenite, clinopyroxenite,gabbronorite gabbronoriteto t omelanonorite melanonoriteand andincludes includes magnetite rich rich gabbro.Textures gabbro.Textures include include equigranular equigranularfine fine to to coarse coarse grain, grain, porphyrytic, porphyrytic, pegmatitic. pegmatitic, varitextured varitextured magnetite units three textural units and and heterolithic-gabbro-breccia.These heterolithic-gabbro-breccia.Theselast last three texturaltypes typescoincide coincidewith withallallmineralized mineralizedzones. zones. Fragments in in these these breccias, breccias,which whichvary varyfrom fromaafew few centimeters centimeters tto Fragments o tens tens of of meters metersininsize, size, are are representative representative of of most most of of the the lithologies lithologiesininthe thearea.The area.Thebreccias breccias were were created created as as the result result of of an an energetic energetic influx influxof of aa volatile volatile charged, PGEbearing bearing magma, magma,which whichassimilated assimilatedofofaalarge largevolume volumeof of rock rock and disrupted Iayering.The charged. PGE and disrupted layering.The PGE PGE bearing bearing magma, typically aa melanogabbro, melanogabbro,isisthe the matrix matrix to magma, typically t o the thebreccia brecciaand andcontains containshigh highgrade gradePGE PGEvalues.The values.The accompanyaccompany- ing volatiles, volatiles, migrating migrating through through the altered the the chamber, chamber, produced varitextured varitexturedand andpegmatitic pegmatiticgabbro, gabbro,altered thesilicates, silicates, mobilized produced sulphide poor poor mineralization.The mineralization.The varitextured varitexturedgabbro gabbrothat thatdefines definesthe theoval ovalshape shape mobilized metals and produced of the to the the Roby Roby Zone.The Zone.The occurrence occurrenceof ofthese these key key rock rock types types and and mineralization mineralization the Mine Mine Complex, Complex, is host to throughout the it in throughout the Mine MineComplex Complexisisevidence evidence that thatthe themineralizing mineralizingprocess process affected it in its its entirety. entirety. POE Mineralization of PGE Mineralization of the the Mine Mine Complex Complex Zones of PGE PGE mineralization with delineated resources in the Mine Complex Complex consists consists of the Roby Roby Zone,Twilight Zone, Moore Zone. from 0.7 0.7 e/t g/t to Zone. Baker Zone and Moore Zone. Other Othermineralized mineralizedareas, areas, with values values from to 23 23 g/t g/t Pd Pd have have had limited amounts of surface sampling and anddiamond diamond drilling drilling and and require require follow-up. follow-up. Roby Zone Roby Zone The Roby Zone is is a bulk bulk mineable deposit with aa minimum minimum strike strike length length of of 850 850 meters, meters, width width achieving achieving 365 meters and aa depth depth of 500 meters.The zone and tto and potential exist for zone remains remains open at depth, and o the southeast and for new mineralization mineralization ttoo the the west. west. Ore (7.6% North Roby The Roby Zone contains three three distinct distinctore oretypes; types; Shear Shear Ore (7.6% of volume), North Roby Ore Ore(5.3% (5.3%of ofvolume) volume) and Breccia 1% % of volume). volume). Breccia Ore Ore(87. (87.1 Shear Ore Ore Shear Ore is is confined confinedtto portion of a IS Shear Ore o aa portion 15 to t o25 25meter meterthick thicklayer layerof ofpyroxenite pyroxenitethat thatisisthe thehanging hanging wall in the central portion Only aa 400 400 metre metre portion portion of portionof ofthe theRoby RobyZone, Zone,inincontact contactwith withaabarren barrengabbro gabbrohangingwall. hangingwall. Only of the the �Palladium mineralized, the the strike pyroxenite pyroxenite is is mineralized, strike extensions extensionsare are barren.The barren.Thepyroxenite pyroxeniteisisplanar, planar,trends trendsatat3410, 3 ~ ,is sis subvertical subvertical to t o aa depth depth of of 250 250metres metresand and shallows shallows to to the theeast eastat at greater greaterdepth. depth Higher grades(6 (6tto g/t Pd) are achieved achievedin inthose thoseportions portions o off the Higher PGE PGE grades o 12 12 g/t Pd) are the pyroxenite pyroxenite that that are arealtered alteredto t oaaschisschistose assemblage of actinolite-talc-chlorite (Shear Ore).The sulphide content of the pyroxenite, including the conconlose assemblage of actinolite-talc-chlorite (Shear Ore).The sulphide content of the pyroxenite, including the tained shears, shears,isis 1% 1%t oto3% 3%with with local localpatches patchesofofnet nettexture texture with with up tenor is tained up to to10% 10% sulphide. sulphide. The The PGE PGE tenor is not notproproportional to the sulphide content.The dominant sulphides are pyrrhotite, chalcopyrite and pentlandite. PGM are portional t o the sulphide content.The dominant sulphides are pyrrhotite, chalcopyrite and pentlandite. PGM are vysotskite (Pd,Ni)S Sb2As2 , kotulskite sperrylite PtAs2 ,and aa vysoiskite (Pd.Ni)S , isomerticite isomerticitePd PdIII ISb2As2 kotulskitePd(Te,Bi), Pd(Te.Bi). sperrylite PtAs2 , Merenskyite Merenskyite PdTe2 PdTe2 .and Pd arsenide,either either Stillwaterice Stillwaterite or segment of of the the pyroxenite pyroxenite is is juxtaposed juxtaposed Pd arsenide, o r Palladoarsenide. Palladoarsenide. The The higher-grade higher-grade segment with the higher grades found in the adjacent breccia ore.The PGE tenor of the pyroxenite declines with the higher grades found in the adjacent breccia ore.The PGE tenor of the pyroxenite declines dramatically dramatically ttoo the the south southwhere wherethe thedegree degreeof oftalc talcalteration alterationisisdiminished. diminished.ItI talso alsodeclines declines in in the theadjacent adjacent breccia breccia ore.The ore.The pyroxenite and and iits contained shears shears pinch pinch out out tto to pyroxenite t s contained o the the northwest.The northwest.TheShear Shear Ore Orehas has been been drilled drilledsystematically systematically rn a depth of 500 mecers.The pyroxenite separates the two other major ore types. a depth of 500 meters.The pyroxenice separates the two other major ore types. . . . North Roby Ore Ore N o r t h Roby North ofofthe Roby Ore is a zone whose gradual boundaries are It North thepyroxenite, pyroxenite,the theNorth North Roby Ore is tabular a tabular zone whose gradual boundaries aredefined definedby byassay. assay. It is 20 20 to to 40 The zone zone strikes strikes aatt 20' 20° with with its is 40 meters meters thick, thick, and and 200 200 meters meters long. long.The its footwall footwalldipping dippingto t othe theeast eastat at45° 45wall steeper. steeper.ItIt isishosted hostedby byaawide wide variety variety of of lithologies.At lithologies.At surface, it is is dominated dominated by by surface, it tto o 60° 60Âand and the the hanging hanging wall coarse grain Ieucogabbro containing irregular irregular masses massesof ofvari-textured van-textured gabbro gabbro and and medium medium tto gabbrocoarse grain leucogabbro containing o coarse coarse grain grain gabbronorite.The proportion with depth.The content of of this this norite.The proportionof ofnoritic noriticrock, rock,and andheterolithic heterolithicbreccia brecciaincreases increases with depth.The suiphide sulphide content mineralization ranges from trace amounts to 4%, and typically is less than 0.25%.The sulphide poor mineralization mineralization ranges from trace amounts t o 4%. and typically is less than 0.25%.The sulphide poor mineralization cannot visually visually be be distinguished distinguished from from the the barren cannot barren wallrock.The wallrock.The dominant dominantsulphides sulphides are are pyrrhotite, pyrrhotite.pentlandite. pentlandite,chalchalcopyrite and distribution isis erratic 1616 g/teft Pd) and weakens copyrite and pyrite.The Pd) and weakensininaaNE N Edirection. direction.Systematic Systematic pyrite.The PGE PGE distribution erratic(I( Itot o drilling of a maximum maximum depth depth of of 250 drilling of this this zone zone has has only only attained attained a 250 metres. metres. Breccia Ore Breccia O re Southwest of the Southwest of the Shear Shear Ore, Ore, Breccia Breccia Ore Ore isis contained containedwithin withinaamineralized mineralizedcomplex complexthat thatmeasures measures550 550by by350 350 meters.This complex complex contains contains intrusive intrusive lithologies lithologies that that range range in in composition composition from from clinopyroxenite clinopyroxenite tto meters.This o anorthosite anorthosite van-textured and tto o norite.Textures norite.Texturesinclude includeequigranular equigranular fine fine to t ocoarse coarsegrain, grain, porphyrytic, porphyrytic.pegmatitic. pegmatitic.vari-textured and heterolithheterolithic-gabbroic-breccia. Mineralization is concentrated in these last three textural types, but it is also commonly ic-gabbroic-breccia. Mineralization is concentrated in these last three textural types, but it is also commonlyfound found in medium grain grain norite norite and coarse grain grain gabbro-norite.All gabbro-norite.All of in clinopyroxenite, clinopyroxenite.melanogabbro, melanogabbro, medium and medium medium and and coarse ofthese these rocks types rocks types occur occur as as discontinuous, discontinuous, irregularly irregularlyshaped shaped pods pods with with rnaxiryium maximum dimensions dimensions of of 60 60 meters metersthat, that,when when viewed are in viewed on on aa map, map, are in fact fact aa larger largerscale scale of ofbreccia. breccia. The boundary tto the central portion of the sub-vertical contact with with the the The east east boundary o the central portion of the theBreccia Breccia Ore Ore is is defined defined by by the sub-vertical contact pyroxenite.The southeast extension of of the pyroxenite.The southeast extension the Breccia Breccia Ore Ore remains remains open.The open.The southern southern and and western western boundaries boundaries of of the Breccia Ore are all defined by a gradual decline in PGE content.As defined by the 0.7 g/t Pd assay cutoff, the the Breccia Ore are all defined by a gradual decline in PGE content.As defined by the 0.7 g/t Pd assay cutoff, the western and the the southern southern boundary boundary dips dips steeply steeplyt to the north. north. Due Due tto nature is sub-vertical sub-vertical and o the o the the gradual gradual nature western boundary boundary is distribution, these assaycutoff.The cutoffThe greatest potential of the PGE PGE distribution, these boundaries boundaries are subject to t o changes changes in assay potential for forexpanexpansion of of resources assuming similar similar continuity continuity of the extent extent of sion resources at at the the Roby Roby Zone, Zone.assuming of grade, grade, is is deepening deepening the of the the Breccia Breccia Ore. Ore. �Palladium The The most mostdefinitive definitive lithological lithologicalcontrol controlon onPGE PGEgrade gradewithin withinthe theRoby RobyZone Zoneisisthe thepresence presenceoro rabsence absenceof ofhetheterolithic-gabbro-breccia erolithic-gabbro-breccia and andaccompanying accompanying varitextured varitexturedgabbro.The gabbro.Thebreccia brecciaisisalways always ore, ore, and and other otherlithologies lithologies are are only only ore oregrade gradewhen when in inproximity proximitytot obreccia. breccia.However, However,mineralized mineralized breccia breccia on o n the the margin margin of of the theRoby RobyZone Zone can contain less than 0.7 g/t Pd.Also, with the exception of post mineralization dykes. every lithology can either can contain less than 0.7 g/t Pd.Also. with the exception of post mineralization dykes, every lithology can either be orwaste. waste.I-Ieterolithic-gabbro-breccia Heterolithic-gabbro-brecciaisiscomposed composedof offragments fragmentsaafew fewcentimetres centimetrestotoseveral severalmetres metresinin be ore oreor size area, size that that are are representative representative of ofmost mostof o fthe thelithologies lithologiesininthe the area.as aswell wellas asaafew fewexotic exoticclast.This clast.Thisbreccia brecciahas hasaa wide spectrum of characteristics. It can consist of sub-angular fragments crowded together with very little matrix wide spectrum of characteristics. It can consist of sub-angular fragments crowded together with very little matrix and to aa breccia of 10% sub-rounded fragments fragments (digested (digestedxenoliths) xenoliths) and and 90% 90%matrix. matrix. A A trantranbreccia consisting consisting of 10% sub-rounded and can can grade grade to sition matrix rich breccia is is observed in in the southern Breccia Ore. Melanogabbro matrix rich breccia observed the southern Breccia Ore. Melanogabbroisisthe the sition from frommatrix matrixpoor poortoto matrix Observed gabbroic gabbroic composition composition for for the matrixand andthe theintrusive intrusivemagma magma creating creating the the breccia. breccia. Observed the matrix matrixin inmany many localocations selectively assayed, tions isisinterpreted interpretedas asaacomposition compositionchange changedue dueto t odigestion digestionofofless lessmafic maficxenolithsWhere xenoliths.Where selectively assayed, the gltPd, Pd,and andthe thefragments fragments0.08 0.08 g/t g/t Pd.This Pd.This explains explains the the observation observation that that matrix matrixpoor poor the matrix matrixwill willcontain contain8 8g/t breccia is usually low grade. Pegmatitic gabbro occurs on the rims of the fragments, as irregular patches and breccia is usually low grade. Pegmatitic gabbro occurs on the rims of the fragments,as irregular patches andveinveinlets lets throughout. throughout. Breccia is transitional transitional into Breccia is into varitextured varitextured gabbro gabbroand and lacks lacks distinct distinct xenoliths.Varitextured xenoliths.Varitextured gabbroic gabbroic rock rock range range in in composition from leucocratic to melanocratic, and some varieties are fine grain with medium grain patches and composition from leucocratic t o melanocratic, and some varieties are fine grain with medium grain patches and veinlets, grain with with pegmatitic veinlets, medium medium grain grain with withcoarse coarseand andpegmatitic pegmatiticpatches patchesand and veinlets, veinlets. and and coarse coarse grain pegmatitic patches patches and Pegmatitic rock rock is occursas asconvex convexmultiple multiplelaylayand veinlets. veinlets. Pegmatitic is more more abundant abundant in in the the central central Breccia Breccia Ore. Ore.Here Hereititoccurs ers, and lenses lensesup upto to several severalmetres metresin inwidth width but but not not laterally ers, dykes dykes and laterally continuous.The continuous.The common common pairing pairing of of the the brecbreccia pegmatitic gabbro gabbro nnot cia and and varitextured varitextured gabbro, gabbro, and and its its associated associated pegmatitic o t only only key key to t o interpreting interpretingthe theprocess processthat that created the the ore, ore. but butalso alsoserves serves as as an important importantassociation association that that guides guides exploration. exploration. The 5%chalcopyrite. chalcopyrite.pentlandite. pentlandite,pyrrhotite pyrrhotiteand andpyrite. pyrite.ItItoccurs occursas asfine fine grain grain The Central CentralBreccia BrecciaOre O r econtain containup uptoto5% disseminations throughout. and as coarse blebs interstitial to pegmatitic clinopyroxene and plagioclase.The fine disseminations throughout, and as coarse blebs interstitial t o pegmatitic clinopyroxene and plagioclase.The fine sulphides are contained contained as asstreaks streakswithin within the the clinopyroxene clinopyroxene pseudomorph pseudomorph that that are are now now composed composed of of actinolite, actinolite, sulphides are chlorite chlorite and and talc.This talc.This late late introduction introductionof ofsulphide sulphideisis synchronous synchronous with with the the alteration alteration of ofpyroxene pyroxene to t oactinolite. actinolite. Twilight TwilightZone Zone The Twilight Zone TheTwilight Zone is is aa new new zone zone in inthe theprocess processof ofbeing beingdelineated delineated by by diamond diamond drilling.This drilling.This zone zone isisseparated separated from the Roby Zone on its western boundary by a 50 to 70 metre thick unit of massive homogenous from the Roby Zone on its western boundary by a 50 t o 70 metre thick unit of massive homogenousbarren barrengabgabbro from the broand and separated separated from the southeastern southeastern extension extension of of the theRoby RobyZone Zoneby byaa50 50metre metrethick thickbarren barrendyke.Twentydyke.Twentytwo t w odiamond diamonddrill drillholes holestotodate datehave havedelineated delineatedaazone zone 100 100 metre metrewide. wide, 200 200 metre metredeep deep and and 200 200 metre metrelong.The long.The zone remains open to the east, and south.This area has the same style of lithological complexity as the Roby zone remains open t o the east,and south.This area has the same style of lithological complexity as the Roby Zone, pegZone, but but isis dominated dominatedby byaaless less heterolithic heterolithicgabbronorite-breccia, gabbronorite-breccia,and and does does not notcontain containvaritextured varitexturedand andpegmatitic matitic gabbro.The gabbro.The most mostsignificant significant mineralization mineralization discovered discovered in in this this area area to t odate datewas was intersected intersectedby byholes holes99-040 99-040 and 99-I 71 This mineralization, containing 0.25% to 0.5 % pyrrhotite and chalcopyrite. assayed 2.38 g/t Pd over and 99-1 71 .This mineralization,containing 0.25% to 0.5 % pyrrhotite and chalcopyrite,assayed 2.38 g/t Pd over I I II 6 metres. metres. �North American America:Palladium Palladium Ltd Baker Z Zone Baker one The Baker surface is one one kilometer kilometereast eastofofthe theRoby RobyZone. Zone.Detailed Detailed surfacesampling samplinghas has defined defined aa mineralized mineralized The Baker Zone Zone is zone that that is wide and traced continuously continuously for for 250 meters. This defined by by is 100 100 meters meters wide and traced 250 meters. This northeast-striking northeast-strikingzone zone is is defined zone assaysgreater greaterthan than0.68 0.68g/t g/t Pd Pdand andgenerally generallycontains containsless lessthan than 11% sulphides.The Themineralized mineralizedrock rockconsists consistsof of assays % sulphides. gabbro, varitexcured varitextured gabbro. and heterolithic-gabbro-breccia.To heterolithic-gabbro-breccia.To date, date, the the highest highest grades are associated gabbro, gabbro, pyroxenite, and with aa pyrrhotite-chalcopyrite samplesover overaa 115 meter length with pyrrhotite-chalcopyriterich richarea areaat ataabreccia/gabbro breccWgabbro contact. contact. Channel samples 5 meter assayed4.69 4.69g/t g/tPd, Pd,0.27 0.27g/t g/tAu. 0.48g/t g/tPC. Pt.0.43% 0.43%Cu Cuand and0.39% 0.39% Ni.A3500 3500metres metres(20 (20holes) holes)diamond diamonddrilling drilling Au, 0.48 Ni.A assayed program conducted conducted during during the the winter winter of program of 1998-99 1998-99 tested tested the the zone zone over over aa 250 250 metre metre strike strikelength, length, tto o aa maximum maximum 200 metres, metres, at 50 50 metre metrespacing. spacing. depth of of 200 Moore Moore Zone Zone area 600 600 metres metres south south of of the the Roby Zone poorlyexposed exposedmineralized mineralized area area in in aa swampy area The Moore Moore Zone Zoneisis aapoorly Mineralization has hasbeen beenuncovered uncoveredin inan anarea area 100 100by by200 200meters metersand andappears appearstotohave havea aNW NW strike strike boundary. Mineralization basedon on the the alignment alignmentof of aa sulphide sulphiderich rich zone. zone. Where Where best exposed the the mineralization consist of of heterolithicheterolithicbased best exposed mineralization consist with less less than than 1% 1%disseminated disseminatedpyrrhotite pyrrhotiteand andchalcopyrite.An chalcopyrite.Aninterval intervalofofnorice norite within within the the gabbro-norite-breccia with breccia contains contains 22 to to 5% 5% pyrrhotite pyrrhotite and interval generated generatedfrom from diamond diamond drilling drilling is is and chalcopyrite.The chalcopyrite.The best best assay assay interval 24.3 meters meters grading I .39 g/t g/t Pd+PC+Au, Pd±Pt+Au, 0.29 0.291% Ni, and and 0 0.3 I 2%Cu. Cu.On Onthe the basis basisof of 17 diamond diamond drill drill holes, 24.3 grading 1.39 1% Ni, .3 12% holes, itit is is interpreted that interpreted that the theMoore MooreZone Zoneisisrod rodshaped, shaped,and and has has maximum maximum dimensions of 22m x 45m x 90m 90m deep. deep. �LH r Palladium Pafladium Ltd Northi American Geology of of the the Lake Lake Superior Superior Region Region , _ r -' • BuKkflr pN a 'i . Tc' ,\&wt3 çfra q Wi 80 km radius "( tii2f' t 'fl (Ii. 1 . . . . . . . . . . . METAL> FOR CLEAN AIR PAGE 7 . . ... . . . . .. .. . . . . .. .. . .. : �.. .,.. . . .. . . .. . . . . . C) cf 3 F EL SO D n (D -J .. Ct- North American . . PalladiumLt / .... Geology and mining claims of the Lac des lies area . .. ... . . . . . PAGE:a . . . . . .. . . . . . . . , ... . . . . .. ... . . . . .... . . . . . . . . . . . E T A L S F O R CLEAN A m . .. ... . ,,. . �. .. .. . . . North American Ltd. North ~ m e r i c Pallad:ium aPalladium ~ Ltd., Geology of the Lac des lies complex ...... ... . .. . �. . . Geology of the mine complex . . . ...... . North American Palladium Ltd. 1 �r a N Geology of the Roby Zone ......... 9 .. .. . it r Th / North American Palladium Ltd. �P Norite; equigranular Gabbro-norite; equigranular Meianogabbro-norite (10-35% plag) Ilelerolithic gabbro-norite breccia Gabbro; varitexiured Gabbro;equigranular Incipient heterolithic gabbro breccia Heterolithic qabbro breccia Leucogabbro/East Gabbro Anorthosite (<10% matics) Leucogabbro; porphyrltic Leucogabbro; varitextured Mine Sequence Felsic Dyke Folsic Plutonic Rocks U 025 U 04 Pyroxen lie Heterolithic melanogabbro breccia Melanogabbro Breccia Dykes •I Matic dykes (minor, narrow) lJ LI n 9 EEl lCd •J_ Archean LI Diabase Diabase Breccia Prot€iozolc 0 meters 12.5 Detailed geology, South Roby Zone 25 tit E 2 01 a In -J > if 7 North American Palladium Ltd. �I Surface South Roby RobyZone Zone (overlay (overlay on on "Detailed "Detailed geology, South Roby Zone") SurfacePd Pdassay, assay, South geology, South Roby Zone") Pd Grade 5 >5.0 g/tonne 5 2.50 to 5.0 g/tonne 5 0.70 to 2.50 g/tonne 5 0.35 to 0.70 g/tonne S <0.35 g/tonne z 0-5 > 0 12.5 meters w S mi U 0 00 25 SOUTH ROBY PIT (0 -5 n CM C, 31750 N 1) B �a F as -Q > 7 2 -J c3j fl 3 1 Roby Pit Level Plan Grade Model 0 North American Palladium Ltd 1' . . . PAGE'1.4 . . . .. . . . . . . ' . . . . .... ... . . . . .., .. + O K CLEAN A I R . .METALS . .... .. ..... . . . . .... . . . ., �-r Oeet burden ODD-i collar with driltitole taco downhote 0 25 SC. metera 15 . . . . . '---ft Oetirie 01 Proposed Pit Oetbne ot Current Pit and SurDace Pd Grade - 035 Do 0.70 gltortne Pd Grade - 0.70 to 2.50 g'tonne Pd Grade - 2.50 to 5.0 ylronne Pd Grade >5.0 gilcoine ' LEGEND ' e 0 0 . 20Dm 0 2 z 0 1 . . . .. . . . . 30Dm 400,0 A Roby Zone Grade Model Cross Section 509 N > IT North AmericanPallad:i.umLtd. F n (D 3 -I . . . . . . . . .. . . . .. . . . . �GEOARCHAEOLOGY AND DEGLACIATION GEOARCHAEOLOGY HISTORY OF AREA HISTORY OF THE THE THUNDER THUNDER BAY BAY AREA Brian Phillips, Lakehead University Scott Hamilton, Hamilton, Lakehead Lakehead University Joe Stewart, Lakehead University University Joe Stewart, Lakehead Pat Julig, Larentian University Pat Julig, Larentian University Bill Ross, Ross, Ontario Ontario Ministry Ministry of of Citizenship, Citizenship, Culture and Culture and Recreation Recreation Soon after after deglaciation, deglaciation, native nativepeoples peoples established established habitation habitation Soon examine how how the the local local geomorphology geomorphology will examine sites. This trip will these sites sites and and the the nature nature of of controlled the location of these human activities. activities. �Forty-Sixth Annual Meeting Forty-Sixth Meeting Institute on Lake Superior Geology Thunder Bay, Ontario, May 8-13th, 2000 PRE-MEETING FIELD TRIP 3 PRE-MEETING - Geoarchaeology of the Thunder Bay area - Field Guide Dr. Brian Phillips, Department Department of Geography, Geography, Lakehead Lakehead University. with Dr. Joe Joe Stewart, Stewart, Department of Anthropology, Anthropology, Lakehead University. Hamilton, DeDartment Department of Anthro~oloav, Anthropology, Lakehead Dr. Scott Hamilton. Lakehead University Universitv Dr. Pat Julig, Julig, ~ Department of Anthropology, Laurentian University e ~ a r t m e n t~ n t h r o ~ o lLurentian o~~, Mr. Bill Ross, Regional Archaeologist, Ministry Ministry of Culture Culture and and Recreation. Recreation. - Objectives: Objectives: field trip tripwill willfocus focuson onthe thedeglaciation deglaciationand and lake lake level level history history of of Thunder The field Bay and the area immediately to the west of of the thecity city -the the Kaministiquia Kaministiquia river river valley, Kakabeka Falls Falls and and the Marks Moraine. evidence of of Paleoindian Kakabeka Moraine. In particular, particular, evidence presence associated with the abandoned shorelines, river mouths and deltas associated with shorelines, river deltas of the 9.5 ka ka B.P.) will be examined examined (Figure (Figure 1). 1). Lake Minong stage of Lake Superior Superior (circa (circa 9.5 The trip trip will will start startby byaa visit visit to to the the former former mouth mouth of of the the Current Current River River at at the the north north end of the city, where the Simmonds and McDaid McDaid sites, both surface sites, are located. Then Then the trip will head head west, west, up valley, to the more famous Cummins site, a site,part partofof which which is is preserved preserved within aa fenced area. area. The third area to be be stratified site, the western extent of Lake visited will be the Rosslyn delta, on the Kam river, visited Rosslyn delta, the Kam river, the western extent of there the the trip trip will will travel travel west west to toKakabeka, Kakabeka,where whereearlier earlierLake Lake Beaver Beaver Minong. From there Bay features will be examined. Finally, the trip will mount the Marks moraine, features examined. Finally, trip will mount the Marks moraine, that will place the days observations in context with pre pre and post providing a view that Marquette ice marginal events and Paleoindian Paleoindian presence. - Introduction strongthough though not notexclusive exclusiverelationship relationshipofof Paleoindian Paleoindian habitation habitation There is aa strong in the Thunder Bay area areawith with the the shoreline shoreline features features of of the the post-glacial post-glacial lakes of of the Superior basin, particularly those those of of Lake Minong, established about 9.5 ka ka B.P. B.P. This is perhaps illusory in that they they occupied occupied aa number number of of habitats, habitats, some some far far from from aa lakeshore, but but in geomorphological mapping of of these these shorelines, it is these sites lakeshore, which have been most commonly found and reported. have been most commonly since early early excavations excavations by by MacNeish MacNeish (1952) (1952) by by both Evidence accumulated since amateur and professional archaeologists (Fox 1975, 1980: amateur archaeologists (Fox 1980; Dawson 1983; Julig, Julig, PIano Indians migrated north eastwards from from the the area area of of Dakota Dakota 1984) suggest that Piano cul-de-sac formed formed between between Lake Lake Agassiz, Agassiz, which which covered and Minnesota into the cul-de-sac of Manitoba and parts of Northwestern Ontario at at its maximum Northwestern Ontario maximum extent, extent, the most of lakes of of the Superior basin and the retreating margin of of the Laurentide ice sheet. These people, people, derived derived from from plains plains cultures cultures characterised characterisedby byaa fluted fluted point point lithic These �Sturgeon Pt u4ittgleton I _ p. uneII 1: Keeter T hn,e,r 250,000 tIIand .- B atne .t--- Li CT 1.tAdcKeIIAr Greenetone Pt T ARTHUR r 165 are Pt - S ç1\, - �technology, probablyfollowed followedgame gameinto intothe the area area as as hunters, technology, probably hunters, but but in in staying, staying, to form and in their diversified diversified in in their economic economic activities activities and their tool-kit tool-kit design, design, to form a a recognisable "Interlakes Composite" Composite"(Ross, (Ross,1994) 1994)characterised characterisedby byaa parallel recognisable "Interlakes flaked making particular particular use use of of the flaked point point lithic lithic technology, technology, making the red red (jasper) (jasper) taconite taconite material material found in the siliceous Gunflint Gunflint formation that outcrops in the Thunder Bay Bay area. area. Deglaclation Deglaclatlon HIstory History The broad details of of the the deglaciation of the the Superior Superior basin basin are are shown shown in deglaciation of Figure 2. As ice central of the the Rainy Rainy River River and and Superior Superior lobes lobes withdrew withdrew from from central Figure 2. ice of Minnesota, series of of recessional moraines were were left left in in place. recessional moraines place. The The Vermilion Vermilion Minnesota, aa series moraine, trending northwest northwest to southeast, southeast, across northeastern northeastern Minnesota, Minnesota, was was followed on the Canadian Canadian side of the border, and and the followed by by the Steep Steep Rock Rock moraine on Brule moraine (Figure (Figure 3). 3). Guided Guided by by these these ice Brule moraine ice marginal marginal positions, positions, Lake Lake Agassiz Agassiz found found an an early early eastern eastern outlet outlet through through the Arrow/Whitefish ArrowiWhitefish lakes corridor (circa (circa 11 11 ka and, shortly after, after,through throughthe theShebandowan Shebandowan lake corridor, corridor, ultimately ultimately using ka B.P.) B.P.) and, the Lake Lake Nipigon Nipigon spillways spillways around around 10.4 10.4 ka ka B.P. B.P. (Figure (Figure 2a) to enter enter Early Early Lake Lake Minong Minong (Teller, 1985) which occupied occupied the Superior Superior basin. basin. There is no to believe did not There is no reason reason to believe that that the the warming warming climate climate did not permit permit environmental conditions conditions to to become become suitable suitable for for the the immigration immigration of of animal animal herds and prehistoric peoples into the Thunder Bay region at this time. Only tenuous prehistoric peoples into the Thunder Bay region at time. evidence of such early occupation has been reported (Phillips, 1993: Ross, occupation reported (Phillips, 1993: Ross, 1994), 1994), evidence though corridor has has confirmed confirmed aa number of sites though recent recent work in in the Arrow/Whitefish ArrowIWhitefish corridor sites that most likely represent earlier Paleoindian presence. (McLeod and Phillips, represent an earlier Phillips, 1999). pers. communication, 1999). A major event in the the deglaciation deglaciation history of ofthe the Lake Lake Superior Superior basin basin was the the Marquette readvance readvance (9.9 (9.9ka ka B.P.), B.P.),during duringwhich whichthe the basin basin and and its margins were briefly reoccupied by ice (Figure 2b). Recessional of the Brule Recessional moraines northeast of moraine formed in in their their place. This event moraine were destroyed destroyed and and more more recent features formed of archaeological implications, implications, since since any also also has has considerable considerable archaeological any evidence evidence of occupation prior to to the the Marquette Marquettereadvance readvanceisislikely likelytoto have have been been buried buried or or occupation prior destroyed destroyed completely completely by by the the new new ice ice cover. cover. Hudson Bay ice pushed southwestward southwestward into into the the Lake LakeSuperior Superior basin, basin, to to halt on its southern shore (Drexler, (Drexler, Farrand Farrand and and Hughes, Hughes, 1983). 1983). Only in in aa small small portion of Whitefish Bay near near Sault Sault Ste. Ste. Marie, corner of of the basin, did Whitefish Bay Marie, in the southeast corner did Early an open 1985). The Early Lake Lake Minong Minong remain remain an open lake lake (Farrand (Farrand and andDrexler, Drexler, 1985). Marquette lobe pushed westward against against the the steep steep Minnesota shore shore and, and, where flowed northwest up up the the Kaministiquia Kaministiquia valley valley to the Marks moraine less obstructed, flowed moraine (Figure (Figure 3). This Thisprominent prominentridge, ridge,rising risingto to over over 470 470 m m (1550') (1550') in in places, places, curves curves from Lappe through and around around the the northwest of Kakabeka towards the the through Mokomon Mokomon and northwest of Kakabeka towards Pigeon River (Zoltai, l965b; Burwasser, 1977, 1980; Burwasser and and Pigeon (Zoltai, 1963, 1963, l965a, 1965a, 1965b; Ferguson, 1980). Contemporaneously, to the the west west of of the the Lake Lake Superior Superior basin, the Patricia ice lobe pushed district and and halted to to deposit the pushed towards the Rainy Rainy River district Dog Dog Lake moraine. This This runs runs northwest northwest from Lappe and holds up Hazlewood, One of Lappe, Lappe, where where the two moraines meet, a Hawkeye and and Dog Doglakes. lakes. East of Island, Hawkeye line of glacial debris known as the Mackenzie interlobate moraine can be known Mackenzie be traced traced �Figure Figure 22 The TheGlacial GlacialPeriod Periodand andEarly EarlyPeoples Peoples d) km Figure 1: The retreat of the glaciers in the Superior region nbetween between10,400 10,400and and9,500 9,500year yearago. ago.(from (from Phillips, Phillips, 1993, p. 95) �Figure Figure33 - -.... o0 • to . .-..- . . .. . .. . .. . . . .-... .... ....- . -. . . . - ... . . ... 4 0ma.. mile 40 I area showing moraines moraines and Mapof ofthe theQuetico—Nipigon Quetico-Nipigon area and direction direction of of ice ice movement movement FIG.5.5. Map Fm. duringvarious variousphases. phases. during - from from ZoItal, Zoltai, 11965a) 965a) �through Pearl and and on to through Pearl to the the Black Black Bay Baypeninsula. peninsula. A glacial glacial lake, lake, Lake Kaministiquia, was formed formed between between the the two two ice margins 1985) and, and, at Kaministiquia, was margins (Teller, (Teller, 1985) Lappe, off the the Lappe, a huge sand sand and gravel gravel delta delta was was built built by bysediment sediment pouring pouring off interlobate of debate, however, and and there there interlobate moraine. moraine. This Thisscenario scenarioisisstill stillthe the subject subject of is some the Marks and Dog may be older some field field evidence evidence that that the Marks and Dog Lake Lake moraines moraines may older features that that were were simply reoccupied reoccupied by ice ice ofofthe theMarquette Marquetteadvance advance(Jul19, (Julig, Lake McAndrews and Mahaney, Mahaney, 1990; 1990; Tickle, Tickle, 1996; 1996;Noble, Noble,pers.comm.1999). pers.comm.1999). Lake Agassiz, deprived advance of of the the ice, ice, expanded expanded in area area deprived of its its eastern outlets by the advance and depth (the Emerson phase), and flooded catastrophically through depth Emerson phase), and flooded catastrophically through the the Clearwater Saskatchewan and the Clearwater and and Athabasca Athabasca valleys valleys in in Saskatchewan and Alberta into the Mackenzie Mackenzieriver river and and the the Arctic Arctic ocean ocean (Smith (Smithand andFisher, Fisher,1993). 1993). The of Lake Lake The Marquette readvance obliterated evidence of the earlier phase phase of Superior's shoreline history in most of the basin. Shoreline sites that prehistoric basin. Shoreline sites that prehistoric most people people might might have have occupied in in the area of Thunder Bay before 9.9 ka B.P. B.P. may lie lie buried beneath Marquette deposits. In the four hundred years between 9.9 and 9.5 buried beneath Marquette deposits. the four ka B.P., about which which much more is known, B.P., aa period about known, ice withdrew from from the Lake Lake Superior basin (Figure 2c/2d). Then, again, Paleoindian people followed game up 2cl2d). Then, again, Paleoindian up Superior basin the Interlakes this time time to to settle, settle, in in part at Interlakes corridor and into the Thunder Bay region, this least, on the shores shores of of Lake Beaver Bay (Stuart, 1993) and Lake Minong Minong (Phillips, (Phillips, 1988). 1988). Shoreline Shoreline History History At At the peak peak of of Wisconsinan Wisconsinan glaciation, glaciation, the the northeastern northeastern margin of the the Lake Lake Superior was depressed by the the weight to a ice (isostatic (isostatic depression) depression) to Superior basin was depressed by weight of ice greater degree than the less heavily ice-loaded southwestern side. As a result, than the less heavily ice-loaded southwestern side. result, "rebound" (isostatic (isostatic recovery) since that time has been greater on the north north shore shore of the Lake Lake Superior Superior basin basin than than on on the the south south shore. shore. Lake shorelines which had had been originally originally horizontal horizontal became became progressively progressively tilted tilted along along an an approximate approximate northeast such that that aa shoreline shoreline of of the the same same chronological age increases in northeast axis, axis, such altitude northeast along along the western western shore shore of of Lake Lake Superior. Superior. AA altitude from from southwest to northeast theoretical archaeological site at Grand Marais, Marais, Minnesota, found at 184 184 metres, metres, just theoretical site just above abovethe the present present storm beach, will be of similar age to another theoretical site in contour (1 (117 in Terrace Terrace Bay, Bay, Ontario, Ontario, at the 300 metre contour 17 metres above the the present present lake), lake), with with both both sites sites lying lying on on the the same tilted tilted shoreline shoreline (Figure (Figure 4). As As the the Marquette Marquette ice ice lobe lobe wasted wasted back, the eastern and western sides sides of of the the basin (Figure 2c). 2c). On basin were exposed as separate entities (Figure On the eastern eastern side, a fairly fairly stable Mary's River outlet at Sault stable Lake Lake Minong, controlled by the height of the St. Mary's Ste. Marie, extended northwards up the Ontario shore and westwards along the the Michigan (Farrand and and Drexler, Drexler, 1985). 1985). Michiganshore shore as as they were exposed by by melting melting ice ice (Farrand In succession of of ever ever larger but In the enclosed western end of the basin, a distinct succession progressively lower level progressively lower level lakes lakes formed formed (Lakes (Lakes Duluth, Duluth, Highbridge, Highbridge, Moquah, Moquah, Washburn, Manitou, and and Beaver Beaver Bay), each extending Washburn, Manitou, Bay), each extending further further northeast northeast up the the Minnesota Minnesota - Ontario Ontario shore shore and east east along along the the Wisconsin Wisconsin shore shore (Farrand (Farrand and and Drexler, of these these water bodies bodies were formed Drexler, 1985). Along Along the the land-based land-based margins margins of various features, such as bluffs and beaches, by which the shorelines can various coastal features, can be ice vacated vacated the basin, basin, the the eastern eastern and and western western lakes lakes were were be traced tracedtoday. today. As ice �Figure Figure44 Shoreline ShorelineDiagram Diagramfor forthe thePigeon PigeonRiverlThunder RiverKhunderBay BayArea Area 1400 a; S I H (fromFarrand, Farrand,1960) 1860) (from FIgure Figure 55 ofpotential Figure pre-Nipissing transgression Figure10: 10:The Thepre-Nipissing transgressionand andthe theresulting resulting loss loss ofpotential archaeological archaeologicalsites sitesalong alongthe theshores shoresof ofLake Lake Superior Superior,(from (fromPhillips, Phillips, 1993, 1993, p. P. 100) 100) �united and the single shoreline of Lake Minong was formed around around the the basin basin about about (Figure2d). 2d). For the the next next 1,500 1,500years, years,water-levels water-levelsininthe the Lake Lake Superior Superior 9.5 ka B.P. (Figure basin declined as the St. St. Mary's Mary's sill sill was was eroded eroded down down to to bedrock. bedrock. A staircase of of Post-Minongshorelines shorelineswere wereformed, formed,the thelast lastand and lowest lowest ofof which which was was Lake Post-Minong Lake Houghton, about 8.0 ka B.P. Houghton, about 8.0 ka B.P. By 8.0 8.0 ka B.P., due to isostatic uplift, the the rising levels of of Lake Huron Huron had had By B.P., due isostatic uplift, flooded into the St. St. Mary's Mary's River River and and reversed reversed the the flow flow (Larsen, (Larsen, 1987). 1987). This backThis backflooding led Lake Superior Superior basin basin and and culminated culminated flooding led to slowly rising water-levels in the Lake in the Nipissing lake stage around 5,000 years years B.P.. B.P.. Known as the pre-Nipissing pre-Nipissing transgression, this rise in in water-level water-level was was imposed imposedupon uponaastill-tilting still-tiltingbasin. basin. On On the the north shore, shore, east east of of Dorion, Dorion,the therate rateofofisostatic isostaticuplift upliftremained remained more more rapid rapid than than the waters of of the the pre-Nipissing pre-Nipissing period, period, with with the the result result being being that that the the shoreline rising waters marking the Nipissing lies at at a lower all older older marking Nipissing maximum maximum level level lies lower altitude altitude than than all shorelines, including that of of Lake Lake Houghton. Houghton. On the south shore the pre-Nipissing pre-Nipissing transgression was more rapid than isostatic recovery, and wave action "inherited" rapid isostatic "inherited" the features of older older shorelines, shorelines, modifying modifying and and destroying destroying portions portions of them, them, the features of including pre-existing pre-existing shoreline shoreline archaeological archaeological sites sites(Phillips, (Phillips,1977). 1977). This This causes causes a chronological discontinuity which which is at its its greatest greatest near Duluth Duluth and and decreases decreases towards Dorion where the Houghton shoreline shoreline appears appears above above the the present waterlevel (Figure (Figure 5). 5). Thunder Bay, Bay, evidence evidence of of Paleoindian would normaliy Paleoindian activities activities would normally have have In Thunder been traced as aa continuum continuum from the high high Minong Minong shoreline shoreline to to the the Houghton Houghton (which lies just (which just below below present present water-level), water-level), but but the the pre-Nipissing pre-Nipissing transgression transgression reoccupied the the lower lower and and later later part part of of that that record record and and cut cut a prominent reoccupied prominent bluff on on which the General St. Joseph's Joseph's Hospital, Hospital, and Lakehead General Hospital, the Court House, St. Lakehead University are are built. built. The Nipissing shoreline can be traced traced up up the valley valley towards University Thus, the the later later part part of of the Mapleward road and across across towards towards Mount Mount McKay. McKay. Thus, record, the the important important transition transition into into the the Archaic Archaic period, period, and and aa good Paleoindian record, portion of the early Archaic is is missing missing in in Thunder Thunder Bay. Bay. portion Local HIstory History an interpretation of of the the detailed detailed history of of the the withdrawal withdrawal Figure 6 represents an of Superior (Marquette) ice from from the Thunder Thunder Bay area, area, based on currently known information, though though subject to As ice wasted information, to revision. revision. As wasted back back from from the Marks Marks Moraine, shorelines shorelineson onthe thesouth southside sideofof the the moraine moraine show show that that aa body body of of water water Moraine, between the the moraine moraineand andthe theice icefront front(Figure (Figure6a). 6a).This This proglacial proglacial lake lake collected between and there there is is tenuous tenuous evidence evidence has been named Lake Cedar Creek (Jahnke, 1993), and that with high high level level lakes Lake Duluth Duluth that it connected connected with lakes to the the south, south, perhaps perhaps of Lake Kaministiquia embayment embayment aa small equivalence. As ice equivalence. As ice withdrew withdrew from from the the Kaministiquia small The higher higher levels of of lake readvance to the Intola Moraine occurred (Figure (Figure 6b). The been traced traced into into this this moraine moraine (Stuart, (Stuart,1993), 1993),and andititisis likely likely that that Beaver Bay have been Paleoindian time, probably using the Marks Paleoindian peoples peoples entered entered the area at about this time, Marks causeway. As As ice ice withdrew withdrew further further and and water water level level declined declined to to the moraine as a causeway. of lake Beaver Bay (Figure 6c), the possibility of Paleoindian lower lower levels levels of lake Beaver Bay (Figure 6c), the possibility Paleoindian in the the occupation increases, increases,and and by by the the time Lake occupation Lake Minong Minong was was established established in Kaministiquia embayment, embayment,there thereisisplenty plentyofof evidence evidenceto to prove prove their their presence presence Kaministiquia �Figure Figure 66 An history in in the Bay area. area. An interpretation Interpretation of of post-Marquette post-Marquette history the Thunder Thunder Bay (a) Marquette toe and Proglaciat Lakes area 9,800 years 8.P (b) Intola Moraine Moraine and Upper Upper Lake Beaver Bey Bay circa circa ( bl irrtola 9,700 years years B,P. 9.700 B.P. Hudson Bay t.obe - KaWA7 M s—ar S.—, * — ;8.s'.a.yr — Uporlor Lobe'. 1= ,1-..t22i (c) Lower Cc) LowerLake LakeBeaver BeaverBay Baycirca circa9.600 9.600years yearsB.P. 89. Cd) Lake Minong, 9,500 years B.P. (from Phillips, Hill, Fralick Fralick and Ross, Ross, 1994) 1994) I �(Figure 6d). 6d). The withdrew from The shoreline shoreline diagram diagram (Figure (Figure 4) shows that only as ice withdrew sequence of post-glacial the Thunder Bay region did the sequence post-glacial takes lakes extend into the area. Beaver Bay shorelines shorelines can can be be found found at at Kakabeka, Kakabeka,but butonly onty the the lower tower levels levels extend eastwards eastwards through through the the city towards the Mackenzie Mackenzie River. River. A few notable sites associated with the Minong shorelineare arethe the Simmonds Simmonds A few notable sites associated with the Minona shoreline sites at at the the mouth mouth of of the the Current Current ~ River, Catherine and and McDaid sites i v e r the ,the Biloski, Biloski, Catherine Cummins sites sites along along the north side side of of the Kam embayment, embayment, and and the the collection of on the the Rosslyn Rosslyndelta deltaat atthe themouth mouthof ofthe the Kaminsitiquia Kaminsitiquia River, River,though though here here the the sites on association is less simple and deserved more analysis (Hamilton, 1996). Some association analysis (Hamilton, Paleoindian sites unrelated to to shorelines shorelines occur occur at at High High Falls Falls on on the the Pigeon river, 1982), at at Harstone Harstone Hill, Hill, near near the the junction junction of of the Whitefish on Dog Lake (McLeod, (McLeod, 1982), rivers and and near near Kakabeka Falls where where the the Kaministiquia Kaministiquia river river and Kaministiquia Kaministiquia rivers Kakabeka Falls might have been most logically logically crossed. crossed. The Crane site near Kakabeka, found The Crane found in a garden, provides providesaa rich richcache cacheofofbeautifully beautifullycrafted crafted10 10cm cmbiiaces bifacesin in aa vegetable garden, location apparently unrelated unrelated to to any any topographic topographic feature, feature, though though on on the the surface of of Beaver Bay Bay terraces. one of the higher Beaver Because of their antiquity and the acidic Because of their acidic nature nature of of the the Boreat Boreal forest forest soils, soils, (Figure 7), 7), though though itit is is very very only the lithic materials remain to be found at these sites (Figure likely that many other natural materials would have been been used used by these peoples. Field Excursion Stops - Stop 11 - Hillcrest Stop Hillcrest Park Park Lookout. from the the University will will be down Oliver Road and, and, just just below betow the The route from bluff, left left on on High High Street Streetand and up upthe thehill hill for for aa brief visit to Hillcrest Nipissing bluff, Hillcrest Park Park from where where the the city city can can be seen and Lake from seen in in context context with with local local topography topography and Superior. Superior. - Boulevard Park, Park, the the Bluffs Bluffs and and CentennIal Centennial Park Park Rd. Rd. Stop 2 and 3 - Boulevard will head northeast on on High High St., St., over overthe theSt.Joseph/Hillcrest St.Joseph/Hillcrest island island The route will lefton on Balsam BalsamSt, St,right righton onHudson HudsonAve Aveand and onto onto Arundel Arundel St. from from of Minong times, left which a left turn before Black which Black Bay bridge will lead lead to to the the Bluffs Bluffs Scenic Scenic Lookout. Lookout. Walk down to Simmonds site. Then board to cross Black Black Bay Bay bridge bridge and and turn turn left left on on Walk Centennial Park roadway. Centennial Park Rd Rd to visit the McDaid McDaid site, adjacent adjacent to the roadway. Simmonds (DcJh-4) and arid McDaid McDaid (DcJh-16) (DcJh-16) Sites Sites The Simmonds present Current Current river riverruns runsin in aa channel channel incised incised into into a gently lakeward The present formationthat thatfronts frontsaa bounding bounding rock rock wall, wall, a structural dipping shelf shelf of of Gunflint Gunflint formation structural feature, which now forms the 'bluffs' In the Minong feature, which 'bluffs' scenic scenic lookout lookout (Figure (Figure 8). 8). In Minong river carried carried much muchwater waterand andsediment sedimentfrom frominland inlandproglacial proglaciallake lake flows flows period, the river of coastal coastal history, a series and here evidence evidence supports supports a major 'bar building' building' phase phase of spits or or bars being being formed formed on on both both sides sides of of the the river riveras as water water level of river mouth spits generally declined. generally The highest lay against the bounding at The highest Minong Minong shoreline shoreline lay against the bounding rock rock wall at approximately the the 252 252 m m (827') (827') level level but but between between 240 240 and and 236 236 m (787-774') (787-774') a approximately of sand sand bars bars formed formedparallel parallel to to the the wall wall on on the the west west bank bank of of the the river river and and a series of matching series seriesofofbars barson on the the east east side side curve curve sharply sharply into into the the then then river mouth matching �Figure Figure 7 7 Paleolndlan bifaces from the Paleoindian blfaces the Thunder Thunder Bay Bay region. region. THE LAKEHEAD LAKEHEAOCOMPLEX COMPLEX —REFINED -REFINED BTFACES BIFACES — - DaJn—7 DfJg—1 Quetico Park Oliver O l t v e rLake Lake DeJj-6 DcJi—1 4% I'" OdJf—I tT;.rJTH:::i;:::tc:: OdJn— 7 DdJn—7 1995) (from Ross, 1995) �Figure 88 MOUTh Figure 9: The The changing changing geography geography and and present present characteristics characteristics of Figure of the and sites. (fivm Phillips,1988, 1988, p. p. 135) ~Simmonds i k n d and s ~McDaid c ~ asite; i d (from~hillips, LATER 4O RE LINE A. UPPER MINONG 250fl!m F .SLAOOO\ R.POSTMINONG SERIES OF MAJOR •ARS + FLAT SWALE • EASTERN 'US FORMEDPOST MINONG 217215n, 'F ALLUVIUM .&rMARSH C —Cr— CREST Pr CUFF u,4. DIRECTION OF SLOPE MODIFIED �from aa source source on on the thesame same rock rockwall wall east east of of the the point point where where itit is It from is cut cut by by the the river. river. It appears that the river entered Lake Minong along the rock wall, forming offshore appears that the river entered Lake Minong along the rock wall, forming offshore and beach and beach bars bars which which extend extend south south eastwards eastwards across across the the shallow shallow McVickers McVickers embayment to the southwest. Simultaneously, longshore transport embayment to the southwest. Simultaneously, longshore transport from from the the east east built bars partially across the river mouth at times, only to be later truncated by built bars partially across the river mouth at times, only to be later truncated by fluvial fluvial action. action. The Simmonds site site on on the the west west side, side,occurring occurringon on the the parallel parallel bars bars at at about about The Simmonds 236 m is matched in elevation and position position by by the the McDaid site on on the 236 m (774') (774') is matched in elevation and McDaid site the eastern curving bars bars (Figure (Figure 9). 9). Neither Neither site site is is aa long long term term habitation habitation site site but but show show eastern curving evidence of activity typical typical of of aa river river mouth mouth camping evidence of activity camping and and fishing fishingsite. site. Interestingly, Interestingly, the to have to the the the major major bar bar building building episode episode appears appears to have been been just just subsequent subsequent to occupation of these these two two sites, sites,two twolarge largecurving curvingbars bars being being formed formed at at 231 231 and and 227 227 occupation of m (758-745') flat topped one largely m (758-745') on on the the east east bank, bank, the the latter latter flat topped one largely aa subaqueous subaqueous feature that that was was probably probably contemporaneous contemporaneous with with the the supra-aqueous supra-aqueous ridge ridge form form of of feature the first. On the west bank a very long bar, now unfortunately truncated at its river the first. On the west bank a very long bar, now unfortunately truncated at its river mouth In south west, west, in in places places broadening broadening to over 100 (328') in end, runs mouth end, runs south to over 100 m m (328') in width. width. In almost text-like manner, the mean grain size and sorting characteristics along its almost text-like manner, the mean grain size and sorting characteristics along its length out from from the length confirm confirm that that itit prograded prograded out the mouth mouth across across the the McVickers McVickers embayment, probably mostly in subaqueous form. Some evidence of Paleoindian embayment, probably mostly in subaqueous form. Some evidence of Paleoindian activity has has been been found found on on the the crests crestsofofthese thesenewer newerbars barsbut butno no sites sites equivalent equivalent to to activity those those named. named. - Stop 4 Stop 4 - Mapleward Mapieward Road, Road, the the Cummlns Cummins Site. Site. The route to Balsam The route will will retrace retrace to Balsam and and join join the the Expressway Expressway heading heading southwest. Just Just beyond beyond the the John John St. St. traffic lights the the route southwest. traffic lights route crosses crosses the the Mcintyre Mclntyre River. On On the the north north side side the the low bluff will will be River. low Minong Minong bluff be seen, seen, with with aa housing housing development on on top. top. The The Biloski Biloski site siteoccupies occupiesthis thissurface surfaceand andaa small small sand sand bar bar at at development the bluff bluff foot, foot, where where a a small small embayment embayment and the and secondary secondary river river channel channel once once existed. existed. As the the Expressway Expressway curves curves to to the the south, south,the thearea areaon on the the right right holds holds a As a lengthy lengthy baymouth bar on the end of which lies the Catherine site, unseen from the baymouth of the road. On the summit summit of of Rabbit RabbitMMt (275m, 902'), 902'), which which rises t. (275m, rises behind behind the the embayment, embayment, lies lies the the the Irene site, a lookout lookout site. site. The route route turns turnswest weston on Oliver Oliver Road Road and and within within 22 km km rises The rises up up the the distinct distinct Minong bluff. A left turn on Mapleward Road sees a gentle descent to the Minong bluff. left turn on Mapleward Road sees a gentle descent to the Minong Minong shore again, and and the the Cummins Cummins site. site. Cummins Site 1) The Curnmins Site(DCJi(DCJi-l) By far far the Paleoindiansite site isis that that of of the By the most most significant significant Paleoindian the Cummins Cummins site site (Figure 10). Reported the site site has has been been excavated excavated and and Reported by by a local local collector collector in in 1962, 1962, the considered a has been the focus of thorough thorough examination. examination. Initially Initially considered a typical typical surface surface site, Julig Julig et et al. al. (1986) (1986) concluded concluded that that itit is is a a rare deeply stratified site, stratified Paleoindian Paleoindiansite, site, under use over over a under continued continued use a long long period periodof ofchanging changingenvironmental environmentalconditions. conditions. Though the the basic basic tool tool kit Though kit is is that that of of Plains PlainsPiano Pianoculture culture(Dawson, (Dawson, 1983; 1983; Julig, Julig, 1984), the the wide wide range range of of artefacts artefacts imply imply a a diversification diversification into into woodworking, woodworking, fishing fishing 1984), and beaver trapping in in addition addition to to the and beaver trapping the regular regular hunting hunting of of caribou caribou and and perhaps perhaps bison (McAndrews, (McAndrews, 1982). 1982). The The Cummins Cummins Site Site was was a major regional tool tool making making �Figure 9 tHE MCDAID SITE — geamorphologicl basis and archaeological test and transect locations PT — Pathway V metres • — Shovel • - Excavation in path U — Feature 'Ill' — Culling leil I sites — ((napping 'lotion - Spot height (in metre,) S Beach ridge axis —— — — Swale axis 236.6 236 6? baseline conlrol pabst — Elevation 0236 .7 transect A a I (from Stewart, Ross and Phillips, 1984) �and the the presence of of exotic exotic lithic components components implies implies aa broad geographical centre and interaction interaction with other groups in in the region region (Julig, 1984). 1984). While the the archaeological archaeological value value of of the Cummins Site was being While being revealed, revealed, broader questions questions remained remainedconcerning concerningthe thechoice choiceofofthis this and and other other sites sites for broader habitation, habitation, especially especially in in relation relationto to lake lake margin margin history. history. The Cummins CumminsSite Site occurs occurs across across the the surface surface of of several several large large sand sand and The which trend trend northeastwards from from the the then then Neebing river mouth across gravel bars which southerly gentle gentledip dip slope slopeof oflocal localGunflint Gunflintshales, shales,overlain overlain by by aa thin thin water water a broad southerly washed silty these shales shales occurs occurs jasper jasper taconite, taconite, the the major major source source of of tool till. In these silty till. making material. Figure I10 of the the site and and the the material. Figure 0 shows shows the the fenced fenced area of morphological details (Julig et al., 1990). Figure I 11 1990). Figure I shows the paleogeographic reconstructionofof events events believed believed to to have have formed formed the the area area (Phillips, (Phillips, 1982). reconstruction 1962). Longshore transport from from the the Neebing Neebing rivermouth rivermouth built built aa series series of of progressive bars bars Longshore across the shallow shallow water water rock rock shelf, shelf, recurving recurving into into aa minor across the minor river river valley valley which which sheltered embayrnent embaymentto tothe thewest westofofa arock rockisland. island. AA further further bar bar was was built built formed a sheltered front of of existing existing ones eventually crossed along the front crossed the the embayment embayment in in tombolo-Jike tombolo-tike form to to enclose enclose a small lagoon, the Cummins Pond, after after which which lower lower and and later later form Cummins Pond, the established established plan plan shape. shape. A pollen shoreline features mimicked the pollen core taken in the pond suggests etal., al., 1986). 1986). pond suggests this enclosure enclosure took place place before before 8.1 8.1 ka ka B.P. B.P. (Julig et of the the bars bars is not compatible with with a declining The plan shape and structure of water level indeed the the accumulation and building building up up of of these water level margin, margin, indeed accumulation and these large large features shelf slope slope is unlikely unlikely without without transgressive transgressivewave waveaction. action. Even features on a gentle shelf so, such action across across aa gentle gentle shore shoreslope slopewould would not notordinarily ordinarilybuild build up up a large so, large supra-aqueous bar without some initial encouragement to accumulate sediments supra-aqueous bar without some initial encouragement to accumulate sediments sheet. The along a line line rather rather than disperse them in a sheet. The key key to the existence of these bedrock control. control. While Julig (1984) determined bars in this location is underlying bedrock and ground ground radar studies that that variation variation in sediment through resistivity resistivity and sediment character character irregularities could could be be traced, traced, aa more of the and bedrock bedrock irregularities more simple reconstruction reconstruction of possible. By surveying surveying down downthe theexposed exposed bedrock bedrock dip dip slope bedrock profile is also possible. of the the site, site, the the trend trend (see inset, Figure showed that that beneath beneath the site must north of Figure111) I ) showed must typical of of many that that occur occur in in the the present present topography topography of of these these lie a marked marked rock step, typical flat-lying shales, and often sharpened by wave action. Accumulation of of sediments took place place firstly firstly against against this this rock rock step step and and subsequently subsequently over over the the top top of of it. ItIt is took possible that some till till remained remained in the the angle angle of ofthe thestep. step. To To the the west west of of Mapleward possible Road an an exposure exposure of of coarse coarse sand sand and and gravel gravel with with angular angular shale inclusions at the rear of the bar bar in contact contact with with bedrock bedrock suggests suggestsoverwash overwashof ofthe thetype typethat thatwould would be expected in this scenario (Figure 12). Once the linear feature was established, scenario (Figure 12). Once the established, longshore sediment supply would extend its length and add add to to the the lakeward lakeward face. face. overwash and and building building in elevation is characteristic characteristicof of wave wave action action either either However, overwash storm event eventor or aa transgressive transgressivelake lakemargin. margin. Again, Again,aa 'bar 'bar building' building' in an extreme storm evident at at Cummins. Cummins. Julig Julig (1984) (1984) found found confirmatory evidence of of period seems seems evident confirmatory evidence of these these bars bars during during the the process process of of their their accumulation, accumulation, aa buried buried layer of habitation of water worn being associated associated with with aa period of water worn taconite taconite artefacts artefacts being of overwash overwash and and construction. construction. While occupation of of the site when a lakeshore location offered advantages While of longshore of longshore access, access, lagoon fishing and perhaps perhaps water water transport, transport, a cremation cremation �(1982) Phillips by mapping morphological on based (1990), Mahaney and McAndrews, Julig, scions. sod aandarsi of Figure Onurio Superior. Lake nartbwzern size, UChSeCIOiS Cummins 5. 1don sad Quarry nct'ottons edge 3-Bog acovah1s Minwtg Z.Lower section DI & excavations Main I. pit Growl % cliff — Govt Ontero by purchased site of gortion Fenced ponns undisturbed Sot',. ridges beach Mong tower and middle at grawl-remoct) s.c destnjction site totol to severe of Areas ,-. — ridge beach Minong middle of limits Aggrazimate —— viSit7. the in elevatton Spot pit Gravel xe' zidg bcb and r.n*4 'ccc terrace wove or Bluff —.-, ridge beach Removed ridge Beach — Ouzailo, Supeñor, Lake oorthwzern she, Cummins 4. Fsguzt 500 9 NCThCS PMPOOSIGC1 OF TWP eat TIC$OCR OF CITY 10 Figure �Figure 11 Figure 11 + FLAT SWAtS '1 ALUWIUM MARSH CREST CUFF S ...d. DIRECTI ON OF 5LOFE MOCIFIED C. MAJOI •AR FORMATION FIIOFILE ACROSS CUMMINS Sits EAST OF MAPLEWARD ROSS ri,cit 0. POST MINONsMIN0R EARS FORMED MIMICKING PLANE SHAPE OF MAIN EAR 0—n.. Nh Figure 8: p. Fisure 8:The Thechanging changinggeography geographyand andpresent presentcharacteristics characteristicsofofthe theCummins Cummimsite. site. (from (from Phillips, PhiZlips, 1988, p. 133) 133) �Figure 12 12 Schematic representation representationofofthe the cliff cliff face at the the Cummins site. Schematic site W Wind wi nd Deflation -flation Lag Lag Fbviai Deposits 0—I 00 - Rich Berm Berm Gravel —Rich Magnetite — Rich Magnetita -Rich Foreshore Beach Foreshwe 8each Sands Sands .. . Foreshore Beach cc! Talus Slope Sands Backbeach Backbeach I—.zkl Bioturbated Sands Sands Massive, Heavily Massive, Bioturbated Dune Dune Sands Sands + +.. • 4+ + Bedrock Bedrvk Sedimentology Sediment010 y A wellwell-developed, exposed at the Cummins site. site. Figure30 30shows shows a eveloped, beach deposit is exposed schematicrepresentation representationofofthe thesandy sandy dii cliffface face where where the the strandline strandlinedeposits deposits are are visible. schematic cross-stratified sands sands of of the the foreshore foreshore dominate dominatethe the exposure. exposure. individual Low-angle, planar cross-stratified Individual Iarninae dipping 3' 3° to 12° 12' lakeward lakeward (original swash-backwash surfaces) are arranged atranged into into laminae dipping one another anotheratatvery verylow low angles. angles. The packets which erosively truncate one Theplanar planarcross-stratified moss-stratified both laterally laterally and and vertically vertically into massive sands through a bioturbated sands are transitional both bioturbated zone. the zone. thebioturbated bioturbatedarea area represents represents a sparsely sparsely vegetated vegetatedbackshore backshore environment environment while while massive sands the massive sands were were deposited depositedas asaeoliari aeolian dunes. foreshore sands sands are areerosively erosivelytruncated truncatedininthe theeastem easternportion portionofofthe the dii cliff by by The foreshore magnetite-richsands. sands. Internal internalstructures structuresindicate indicatethat thatthey theyare arealso alsoforeshore foreshoredeposits. deposits. The The magnetite-rich magnetite-richforeshore foreshorelaminae laminaewere wereformed formedduring duringregression regressionwhen whenstorm stormwave wave activiv activity magnetite-rich During the the lower portion of the beach, erosively erosivelytruncating truncating the older older deposits. During reworked the intervening periods periods of fair events sand was removed storm events removed and stored in offshore bars. In inte~ening weather, sand sand moved fmm fromthe theoffshore offshorebars barsback backonto ontothe thebeach beachand andwas waswinnowing winnowing by by weather, waves, producing small waves, produangthe themagnetite-rich magnetite-richlag lag deposits depositsfilling fillingscour scour truncations. truncations. The beach assemblage is is overlain overlainby by erosively erosively based, trough cross stratified stratified sands. sands. Major rainfall rainfallevents events caused after subaereal subaereal exposure exposure of of the area. fomed after area. Major These were formed to flow flow off the adjacent rock knoll knot!dissecting dissectingand and reworking reworkingthe theupper upper layer of beach streams to beach deposits. deposits. 3 Phillips, Fralick Fralick and and Ross, Ross, 1987. Phillips, C-12, From INQUA Field Guide GI 2, Eds. Geddes, Geddes, Kristjansson Kristjansson and and Teller. Teller. Eds. �burial site on on the the rock rock island (Dawson, (Dawson, 1983) was was dated to to 8,480 8,480 + 390 years BP. both just just below below the the aeolian aeolian sands sands that that characteristically characteristically Julig (1984) found artefacts both modified the topography of the the shoreline shoreline features features once once the offshore offshore shelf shelf was modified the topography of exposed by by lower exposed lower lake lake levels levels (circa (circa 8.0 8.0 ka ka BP) BP) and and in in peat peat that that accumulated accumulated in in Cummins Pond, Indications are are that that long longafter afterthe the lake lake ceased ceased to to lap the beach Cummins Pond. Indications beach face, the site remained remained used, used, at at least least until until 7.5 7.5 ka ka BP BP (Julig (Julig et et al., 1986). 1986). - Stop 5 Stop 5 (several) (several) - The The Rosslyn Rosslyn Delta Delta will retrace to to Oliver Oliver Road Roadand and continue continue west, west, turning turning south at the The route will towards Twin Twin City City Crossroads. Crossroads. Immediately Immediatelysouth south of of the the driving driving range, Golf Course towards the road road descends descends aa gentle gentle bluff bluff around around the the 268m 268m (880') (880') contour contour that that is is aa Beaver Beaver the Bay shoreline, shoreline, and and then, then, beyond beyond two two turns turns in in the the road, the descent down the the Bay road, the descent down shoreline arrives flat surface of the offshore shelf and offshore shelf Minong shoreline arrives on the extensive, extensive, flat surface of the Kaministiquia Kaministiquia River River where where it entered Lake Minong. This surface, 222m delta of the (729') at the mainly of sandy with boggy sandy silts, silts, with boggy areas (729') the crossroad, crossroad, is composed composed mainly the crossroads crossroads the the route route will will turn turn west west along underlain by more clayey silts. From the Hwy 11-17, Minong bluff, forming an abrupt rise at 11-17, where, within 2 kms, is again the Minong Hwy at the Weighscales. Weighscales. Turning Turning left, left,once once on on the the terrace, terrace, the the road leads south to several several fields in which the Dairy fields which lithic lithic material material has has been been found. found. These These sites, sites, the Dairy Farm, Farm, Breukelman Evergreen and and Halow A, A, B B and andC, C,will willbe beviewed viewed (Figure (Figure 15) 15) and and then of the Kaministiquia River River towards towards Stanley. Stanley. En the route will follow the north side of route the upper and lower Drezecky sites sites will will be seen (Figure (Figure 17), 17), as as well well as the Pawlick site site which whichcan canbe be seen seen on on the the south south side side of of the river. From Stanley Stanley the the river. From Pawlick Stanley delta and return return to Hwy 11-17. 11-17. route will climb the terraces of the Stanley The following extract extractofof text textand and figures figuresderives derivesfrom fromaa paper paper by by Scoff The following Scott Hamilton, that that has has been been submitted submitted for forpublication publication review review to to the theCanadian Canadian Journal Journal Archaeology. Entitled Entitled"Archaeological "ArchaeologicalPredictive PredictiveModelling Modellingininthe theBoreal BorealForest: Forest of Archaeology. No Easy the paper paper addresses addresses the the difficult difficult problem problem of of developing No Easy Answers", Answers", the developing archaeological predictive models to aid in Forest Class Class environmental environmental assessment. assessment archaeological Among the many many challenges challenges is is the issue of development sensitive Among development of temporally temporally sensitive palaeo-environmental reconstructions, and also models of land use that are are palaeo-environmental reconstructions, and also models of land use that relevant to the political economy and social organization of the ancient peoples relevant political economy and social organization of the ancient peoples under consideration. consideration. "The apparent apparent correlation correlation between between relict relict shorelines shorelines and Piano archaeological archaeological well known in the Thunder Bay area where landscape evolution has been sites is well been of some somestudy study(Figure (Figure 13). 13).While While many many Piano Piano shoreline shoreline archaeological archaeological the subject of documented,the thebest best known known ones ones are are lithic quarry and workshop sites sites are documented, such as the and McDaid Sites (Julig 1984, the Cummins, Cummins, Biloski, Simmonds, Simmonds, and 1984, 1994; 1994; MacNeish 1952; 1952; Hinchelwood Hinchelwood 1990; 1990; Phillips 1988, These large large sites sites are MacNeish 1988, 1993). 1993). These well removed shorelines, but but are are associated associated with with the the late late Pleistocene removed from modern shorelines, shorelines of Glacial Lake Minong Minong and and Gunflint Gunflint Formation Formation bedrock exposures that are suitable suitable for lithic lithic tool tool production production (Figure (Figure 13) 13) (see (see Julig, Julig, McAndrews McAndrews and and Mahaney 1990; Phillips Phillips 1988, 1988, 1993). 1993). However, However, these these special-purpose special-purpose sites sites do do not not characterize the full Paleo-Indian settlement pattern. Rather, the dense recoveries Paleo-Indian Rather, the dense recoveries �from, and ready visibility visibility of, of, these these sites has resulted in their over-representation over-representation in in the published literature. Archaeological Archaeological reconnaissance reconnaissance upon the published archaeological archaeological literature. agricultural fields fields within within the Kaministiquia River River delta delta has has revealed revealed a number number of PIano or or probable probable Plano Piano sites sites in a wide of landscape landscape contexts contexts (Hamilton Plano wide range range of 1996) (Figure (Figure 14). 14). Many Manyofofthese thesesites sitesare arefound foundatatorornear nearLake LakeMinong Minong shoreline shoreline elevations (i.e. 750 750 feet feet or or 228.6 A.S.L). When elevations (i.e. 228.6 metres metres A.S.L.). When placed in aa hypothetical hypothetical Minong- environmental Lake Minong environmentalcontext, they are found associated with: flowing into into sheltered sheltered coves coves of Lake Minong (Figure 15: 1) springs flowing 15: Breukelman Breukelman Evergreen); Evergreen); 2) on points of land that protruded protruded out out into Lake Minong to the the northeast northeast and and southeast of the Breukelman Evergreen site cluster (Figure 15); Breukelman Evergreen site cluster (Figure 15); well-drained sandy knolls surrounded surrounded by by poorly drained 3) upon low, low, well-drained sandy knolls poorly drained 3) upon floodplain/deltaic sediments floodplainldeltaic sediments (Figure (Figure 15: 15: Halow Halow C); 4) along deltaic deltaic backwater backwater channels (Figure 16: DbJi-8, DbJi-7, DcJi-28, DcJi32); 32); or 5) on sandy storm storm beaches beaches developed upon relict deltas (Figure (Figure 16: 16: DcJi-30, DcJi-30, DcJi-31). DcJi-31). Other sites were found upon: upon: 6) raised raised Pleistocene Pleistocene terraces terraces overlooking overlooking the the present present Kaministiquia Kaministiquia River River channel (Figure channel (Figure 17: 17: Pawlick); Pawlick); 7) on high high valley valley rims rims that offer panoramic views (Figure 17: Drezecky E); the Lake Minong shores shores (Figure (Figure 16: 16: Halow Halow A A 8) along draws leading down to the and B); and B); well removed from from late Pleistocene shorelines (Figure 9) along upland upland streams well (Figure 17: DcJj-12, DcJj-13); and 10) upon well-drained upland knolls knolls on what likely were formerly discontinuous permafrost uplands permafrost uplands (Figure (Figure 18: 18: Breukelman BreukelmanField: Field:lithic lithicscatters scatters AA to to E). E). Probable Plano Piano lithic lithic scatters scatters have have also also been been found found upon isolated bedrock Probable controlled knolls knolls offering offering panoramic panoramicviews viewsofof floodplains floodpiainsadjacent adjacenttoto the the Lake controlled Thisrange range of of landscape landscape characteristics Minong shoreline (Figure 19: 19: BeIluz Belluz Farm). This is certainly not exhaustive, but is sufficient to demonstrate demonstrate the the diverse diverse microhabitats microhabitats frequented by frequented by Piano Piano people. people. Lakehead Complex sites in terms of of a very These sites are consistent with other Lakehead preference for Gunflint Gunflint Formation Formation lithic lithic materials materials (Hamilton 1996). However, strong preference virtually all all of of these are well well removed are virtually these sites sites are removed from from bedrock bedrock exposures, exposures, are �Figure Figure 13 13 Late Rolocene watere Cuminins Site Bioski Site Brohn. Site .r Julig, MscAndr..,s nit Maimmy (l900tfl) Figure Figure66The The Correlation Correlationbetween betweenLakehead Lakfcu-u Complex bxinplexsites, sites, Minong Minong beaches beachesand andGunflint GunflintFormation Formationoutcrops outcrops(Hamilton (Hamilton1996:34) 1996:34) �Figure 14 Figure 14 Some Archaeological Sites associated with the Kaministiquia River Delta • Modern Hydrological System U Lake Minong water levels * Lakehead Complex Site SModern Community ..-M fl f Lake Superior distribution of confirmed confirmed or Figure 7 The distribution or probable probable Lakehead LakeheadComplex Complex sites sites on on the the Kaministiquia River (Hamilton1996: 1996:36) 36) Kaministiquia Riverdelta delta(Hamilton �Figure Figure 15 15 Figure or probable welldrained drained sediment sediment near near Figure 88 Confirmed or probable Piano Piano sites on well (750feet feetASL) ASL)(Hamilton (Hamilton 1996:59) 1996:59) LakeMinong Minongshorelines shorelines(750 Lake �1996:65). (Hamilton channels backwater deltaic along and beaches, storm Minong on Sites Piano probable and Confirmed 9 Figure 16 Figure �1). 1996:5 (Hamilton terraces river Holocene early and Pleistocene late along sites Piano possible and Confirmed 10 Figure 17 Figure �Figure 18 18 3ntour Interval = 10 metres AN 1 Figure PIano sites located located upon upon well-drained well-drained knolls knolls in in upland upland Figure11 11 Possible Piano regions (Hamilton1996:47). 199647). regions well well removed removedfrom fromLake LakeMinong Minong(Hamilton �Figure Figure 19 19 Figure Figure12 12Probable ProbablePiano Pianosites siteson on aa bedrock bedrock controlled controlledknoll knoll overlooking overlookingPleistocene Pleistocenefloodplain floodplainzone zone(Hamilton (Hamilton1996:57). 1996:57). �significantly smaller smaller than than the the quarry-workshop quarry-workshop sites sites (such (such as as the the Cummins Site), When compared compared to to the the quarry/workshop quarry/workshop sites, sites, these these and yield many fewer artifacts. When small sites also yield a much higher relative frequency of tools, preforms tools, preforms and small sites also a much higher relative frequency to debitage debitage (Hamilton (Hamilton 1996). This indicates that the small utilized flakes compared to sites represent represent encampments, encampments,hunting hunting stands stands and and food procurement procurement sites, rather than lithic extraction extraction and reduction stations. Such Such observations than lithic reduction stations. observations are hardly surprising, but they do serve as cautionary tales regarding surprising, but they do serve as cautionary tales regarding the dangers dangers of of predicting site distribution on the basis of our current incomplete heritage heritage inventory. inventory. predicting in that that they theydemonstrate demonstratethat thatmodelling modelling ancient ancient These examples are also important in human behaviour requires ongoing ongoing refinement, an understanding of human human human behaviour requires refinement, an understanding of forager behaviour, and a well-developed sense sense of of the the nature nature and and structure structure of of the forager behaviour, ancient landscape landscape and and its its microhabitats." microhabitats." As one leaves delta (Minong, (Minong, 9.5 9.5 ka ka B.P.) B.P.) and and moves As leaves the Rosslyn Rosslyn delta moves up the the present Kaministiquia valley, valley,one one is is in in effect effect travelling travelling back back in time. time. The Stanley delta was built into Lake Beaver Bay (9.7 ka ka B.P.), B.P.), the the first first Superior Superior lake to occupy occupy the area recently recently vacated vacated by Marquette Marquette ice ice retreating retreating from from the the Marks Marks moraine. moraine. Though perhaps less less conspicuous, conspicuous,Paleoindian Paleoindiansites sitesofofthis this period period are are also also Though perhaps present. present. The larger step back in paleogeography paleogeography is is to consider consider the area that lies lies to to the the west of the maximum of the Marks maximum position position of Marks moraine, moraine, an area area which which remained remained west of unglaciated by the Marquette readvance and and which which was was freed freed from from ice icearound around 11.0 unglaciated B.P. Figure Figure 20 20 shows shows the the projected projected maximum maximum position position of ofthe the Marquette Marquettelobe lobe and and ka B.P. the large area covered of aa pre-Marquette pre-Marquette lake lake (Early (Early Lake Lake Minong) , covered by the waters of by the the 1400' contour. contour. On Onthe thebasis basis of of some some long known sites, now approximated by both in the interior Phillips and and Hill (1995) both interior and and on on the the Minnesota Minnesota northshore, northshore, Phillips proposed that a Paleoindian Paleoindian routeway routeway along the Minnesota Minnesota shore turned inland of Judge Judge C. C. Magney MagneyState StatePark, Park,towards towardsNorth Northand andSouth South Fowl Fowl lakes lakes and and just east of in the the Whitefish number of more more recently recently discovered discovered sites in Whitefish Lake region. region. A number Whitefish -- Arrow Arrow Lake Lake corridor corridor supports supports the the contention contention that that Paleoindian peoples peoples Whitefish the Marquette advance, and were present in the area perhaps before and during the Marquette advance, that corridor continued continued to to be used into periods of of Lake that the corridor into the the post-Marquette post-Marquette periods Though conjectural, conjectural, there there is is the possibility that after Beaver Bay and Lake Minong. Though the retreat of of Marquette Marquetteice ice had hadbegun, begun,the the Marks Marks moraine moraine itself itself provided provided aa high ground from the the Whitefish Whitefish Lake Lake area area along along the north of the ground routeway routeway from north side side of Kaministiquia valley of Thunder Thunder Bay. Bay. Kaministiquia valley and andinto intothe the area areato to the the north northand andeast eastof - Stop 6 - Kakabeka Falls Just west west of of the the junction junction of of Hwy Hwy 11-17 and the Stanley turn off, off, the the huge Just structure of the Stanley delta is seen (Figure 21). This delta was formed as the structure of the Stanley delta seen (Figure 21). This delta was formed as Kaministiquia River Beaver Bay. Bay. A A well welt formed formed bluff representing a River entered Lake Beaver lower Beaver Bay phase of 260m (853'), runs along the north north side side of of the main main lower Beaver Bay phase of 260m (853'), runs along the highway, and the surface below below itit (250-2401% (250-240m;820-787') 820-787')is is heavily heavily exploited exploited by the sand and gravel industry. The present Kaministiquia river river has has incised incised deeply into into the delta, creating a terraced valley side. �Figure 2200 Figure -- 1 Kaminisliqili R. Valley 2 Whilefish Lake 4 N & S Fowl Lake 5 Pigeon R.Valley 6 Silver Mountain km SW99 (Alter Phillips and Hill Hamilton 1996) (After Phillips and Hill 1995:22-24, 1995:22-24, HuDUton 1996 Figure 13 Siteson onthe theUplands Uplands west westof ofThunder Thunder Bay Bay Figure 13 Some Piano Archaeological Sites �-4 ( Shorelines - Terraces - -1 r (from Grootenboer, 1972) — -C - Lower Beaver -4 cirumlinoid -r Upp, N N Beaver 88y N ( Figure 21 �Kakabeka Kakabeka village village is is built built on on the the floor (277m; (277m; 909') 909') of of an an old old distributary distributaryof of the the Kaministiquia Kaministiquia river which cut through a higher terrace still (Figure 21). Remnants of this at around around 300m 3Com(984') (984')overlook overlookthe the village. village. They They represent represent the this terrace surface at highest Lake and highest level level of of the Stanley delta, as asitit formed into Upper ~ a k eBeaver ~ e a v e Bay, r and on on the of the the Kaministiquia KaministiquiaRiver, River, the Crane Crane site was found. the one one on on the the west west side side of Kakabeka Falls is aa major major scenic scenic attraction. attraction. ItIt is is formed formed as as aa result of of a very was just just this sort of resistant chert bed that caps the the underlying, underlying, softer softer shales. shales. It was rock material material that was desired desired for tool making. Today, a fairly spectacular gorge lies lies below the falls (Figure 22). There has been some debate concerning the age of the below the falls (Figure gorge, since unless inherited and exhumed from from a previous stage of of river river incision to prior to there is only post to the the Marquette Marquette readvance, readvance, there post Beaver Beaver Bay Bay time time for it to develop its current grandeur. grandeur. An An interesting interestingabandoned abandonedfalls falls and and plunge plunge pool on the west side of the gorge lies lies aa short short walk walk from from the the Park Park Information Information Centre, and represents 'horseshoe' fall that would have been more spectacular than the represents a wide 'horseshoe' present present falls. falls. - Stop 7 (several) (several) - The The Marks Marks Moraine. Moraine. The route will turn on Hwy 590 just just west of of Kakabeka, Kakabeka, run run across across the the High Beaver Bay terrace terrace remnant remnant (look (lookfor forthe thecemetery cemeteryon onthe the right) right) and and due due west west until turning Moraine. As Asthe thedirt dirtroad road rises rises up up the the outer outer face face of of turning north north towards the Marks Moraine. the Marks (1400') and 442m Marks moraine it crosses crosses two distinct distinct benches at 42Gm 426m (1400') (1450'). These shorelines shorelines of of pro-glacial pro-glacial Lake Lake Cedar Cedar Creek Creek have been traced all (1450'). These along of the theMarks Marksmoraine moraine (Jahnke, (Jahnke, 1993) 1993) and and represent represent along the outer outer slope slope of stillstands in a lake earlier than and isolated of the the Superior Superior basin. isolated from the lakes of The Marks Marks Moraine. Moraine. Stopping on the 46Cm (1510'), (1510'),the the view view south south over over the Stopping on the crest crest around around 460m Whitefish valley and the the rugged rugged borderland borderland country country of of the mesa-like NorWesters Norwesters is spectacular. It is not hard hard to to envisage envisage ice ice pushing pushing its its way way up to the Marks Marks moraine, moraine, nor is it hard to imagine pro-glacial Lake Cedar Creek occupying the narrow strip hard imagine pro-glacial Lake Cedar between between the the moraine moraine and and the the retreating retreatingice icemargin. margin. The moraine is not a simple structure. structure. Although Although characterised characterised by by aa till which contains diagnostic pieces of Sibley red red sedimentary sedimentary rocks, along much its length the Marks joins and Marks moraine moraine joins and smothers smothers isolated isolated rock rock outcrops outcrops which which probably probably greatly top of of the the moraine greatly influenced influencedthe the extent to which the ice pushed inland. The top kettles. Spillway remarkable flat flat in many many places places and and is pockmarked pockmarked with with kettles. is remarkable Lake at one channels channels cross cross the the feature feature in in places suggesting suggesting that at one point point Lake Kaministiquia to the north was a few metres higher than Lake Cedar Creek to the south. The moraine moraine appears appears to to have have briefly briefly existed existedas as aa narrow south. The narrow ridge between between these two water bodies, and a possible post-Marquette routeway for animals routeway for animals and water Paleo-lndian Arrow/Whitefish region region and and Paleo-Indian people, from the unglaciated unglaciated (Marquette) ArrowIWhitefish Interlakes corridor. corridor. Interlakes The Conmee Pit and and spiliway. spillway. Conmee Pit Continuing north across across the the moraine and then turning east brings Continuing north moraine and brings the the excursion to to a distinct south across across the moraine excursion distinct channel cutting from from north to south surface. Here Conmee Township has has several several gravel gravel pits. from the huge surface. Here Conmee Township pits. Apart Apart from huge boulder beds that that suggest suggest high high discharges discharges down down this this spillway spillway at at times, times, the the pit boulder beds �Figure 22 (from Grootenboer, 1972) �reveals another another key key fact fact in in understanding local deglaciation. deglaciation. Figure Figure 23 23 shows shows a understanding local rare occasion occasion when when the the western western pit pit face rare face was cleanly cleanly exposed. exposed. Tickle Tickle (1996) (1996) interpreted the the sequence sequence as as consisting consisting of of two two tills separated interpreted separated by by fluvioglacial fluvioglacial sediments. However, However,while while one one till till was was of of diagnostic diagnostic Sibley Sibley origin, origin, the the underlying sediments. lobes. one was of a northern provenance typical of the Patricia or Rainy River lobes. Elsewhere, at several several places places along along the the Marks Marks moraine moraine aa thin thin Sibley till Elsewhere, at till is p'astered over over fluvioglacial fluvioglacial sediments. sediments.The The observation observationsuggests suggeststhat thatthe thebulk bulk of of plastered the Marks moraine may may in in fact fact be be pre-Marquette pro-Marquettein inorigin, origin,with with thin thin Marquette Marquette ice the moraine. moraine.This Thishas hasbeen beenthe the growing growing opinion opinion of another local field field reoccupying the Figure 3, 1999) and and looking the worker (T. (T. Noble, Noble, pers.communication, pers.communication, 1999) looking at Figure worker 3, the possibility of the Marks moraine moraine being being the the result result of of pushing pushing the the eastward eastward part part of of the the possibility former Brule moraine till contorted till former moraine is not not unreasonable. unreasonable. Several exposures exposures of contorted structures also support this idea. idea. Moraine scenic Marks Moraine scenic lookout. lookout. outofofthe thepit pitand andagain againatatthe thecrossroad crossroadbrings bringsone oneto toaa point point in in Turning left out the road from from which which a view east over the Kaministiquia Kaministiquia valley, valley, Thunder Thunder Bay city the distant distant Sleeping Sleeping Giant Giant is is obtained. obtained. The The stop stop is useful only to to impress impress and the of things. It is easy to imagine ice viewers with scale of ice grinding grinding past past Mt. Mt. McKay McKay and and flowing up to imagine imagine that that aa slight slight tilt tilt of of the the present lake flowing up the valley, just as it is easy to would bring the margin of the lake lake right right up up into into the the Kaministiquia Kaministiquia and and Whitefish Whitefish valleys. valleys. 1I I I ii I to the the crossroad, crossroad, the the route routewill will turn turn left leftdown down the the face face of of the Marks Marks Returning to road is is straight, straight,save savefor foraajog jogaround aroundaakettle kettlehole, hole, and, and, lower lower down, down, moraine. The road fields and along the stream stream beds. beds. Turning Turning right rightat at Hwy Hwy 11 11-17 rock is exposed in the fields -17 back to to Kakabeka Kakabeka Falls. Falls. From Fromhere herethe theroute routewill will take take Oliver Oliver brings the excursion back Road back back to to the the University. University.The The road road climbs climbs out out of of Kakabeka over the the Upper Kakabeka over Beaver Bay terrace remnant and then runs due east to Lakehead University. University. One landform of of note note on on the theway wayisis aa crag crag and and tail tail feature, feature, showing the flow up the the Kaministiquia Kaministiquiavalley. valley.The The'Old 'Old Barn' Barn' restaurant restaurantlies lieson on the thetail tail and and on on of ice up farmhouse, open open for for bed bed and and breakfast breakfast (another (another time, time, eh!). ehl). Just east the crag is the farmhouse, the north north of of Oliver Oliver Road Roadisisthe theMurillo Murillodrumlin drumlinfield, field, aa series series of of long of Murillo but to the narrow forms parallel to the the strike strike of ofthe theGunflint Gunflintshales, shales,suggesting suggestingaagood good deal deal of bedrock control. bedrock The The excursion excursion is over. over. We We hope that that participants participants obtained obtained an informed informed glimpse of of the the deglaciation deglaciation history history and and Paleoindian presence in in the area, and glimpse Paleoindian presence and enjoyed enjoyed doing doing so. so. I �Figure Figure23 23 . , Figure Figure1.1 1.1 The TheStudy StudySite Site--Conmee Cn-mee Township Townshipgravel gravelpit pi SOUTH Note: Note: Vertical Vertical sections sectionstaken takenatatnumbered numberedlocations. locations. (from Tickle, 1996) �References and and Bibliography Bibliography References Arthurs, D. 1979. 1979. An Archaic Archaicsite siteon onthe thewestern westernLake LakeSuperior Superiorshore. shore.Report Reporton onfile filewith withthe the Planning and Research Historic Planning Research Branch, Ontario Ministry of of Culture Culture and and Histonc Branch, Ontario Communication, Toronto, Toronto, 35 pp. pp. S. 1985 1985 Deglaciationchronology chronology and and revegetation revegetation in in northwestern northwestern Ontario. Bjorck, S. Ontario. Canadian Canadian Journal of of Earth EarthScience Science 22,850-871. 22, 850-871. G.J. 1977 1977 Quaternary Geology of the City of Thunder Bay Ministry of of Bay and and Vicinity. Ministry Burwasser, G.J. Natural Resources, Resources, Ontario Ontario Geological Survey Report 164. Geological Survey Report OR GR164. Burwasser, G.J. G.J. 1980 1980 Quaternary Quaternarygeology geology of of the the Onion Lake of Burwasser, Lake and Sunshine Sunshine area, area, District of Thunder Bay. Ministry of of Natural Resources, Ontario Ontario Geological Geological Survey Survey Report Report Bay. Ministry Natural Resources, MP94. MP94, Burwasser, G.J. G.J.and andFerguson, Ferguson,A. A.1980 1980Quaternary Quaternarygeology geologyof ofthe theOnion Onion Lake Lakeand andSunshine Sunshine Burwasser, area, District of of Thunder Bay. Ministry of of Natural area, District Bay. Ministry Natural Resources, Resources, Ontario Geological Geological MapP.2203, P.2203, Geological GeologicalSeries, Series, 11:50,000. :50,000. Survey Preliminary Map Clayton, L. L. 1983 1983 Chronology Chronologyof ofLake LakeAgassiz AgassizDrainage Drainage Lake Superior: jTeller, J.T., J.T., and and totoLake Superior: in.Teller, Clayton, Lee, Agassiz, Geological Geological Association of Canada Lee, eds., eds., Glacial Glacial Lake Agassiz, Canada Special Special 26, 291-307. Paper 26,291 -307. Clayton, L L. 1984 Pleistocene Pleistocenegeology geologyof of the theSuperior Superiorregion, region, Wisconsin, Wisconsin, Information InformationCircular No. 46, Wisconsin Geological Geological and Natural History HistorySurvey, Survey, Madison, Madison, Wisconsin. Wisconsin. N O. 46, Clayton, 5. 1982 Clayton, L. and Moran, Moran, S. 1982 Chronology Chronology of of Late LateWisconsin Wisconsin glaciation glaciation in middle North North America, Quaternary Science Science Reviews, vol. vol. 1, pp. pp. 55-82. 55-82. Dawson, K.C.A. K.C.A. 1983a Prehistory of Northern Bay Historical Historical Museum Museum Dawson, Northern Ontario. Ontario. Thunder Bay Society. Society. ite at Thunder Bay, Bay, Dawson, K.C.A. K.C.A. 1983b Cummins Site: A Late Palaeo-lndian (Piano) Site Dawson, Archaeology 39,3-31. 39, 3-31. Ontario. Ontario Archaeology Drexler, C.W., C.W., Farrand, Farrand,W.R. WA. and and Hughes, J.D. .J.D. 1983 1983 Correlation of Glacial Lakes in the Drexler, Correlation of Glacial Lakes the with Eastward EastwardDischarge DischargeEvents Eventsfrom fromLake LakeAgassiz AgassizjnTeller, j. Teller,J.T., J.T.,and and Superior Basin with Agassiz, Geological Geological Association Association of Canada Clayton, Lee, eds., Glacial Glacial Lake Agassiz, Canada Special Special 26, 309-329, Paper 26,309-329. Dudzik, M.J. M.J. 1993 1993 The State Archaeology Archaeology The Paieoindian Paleoindian tradition in northwestern northwestern Wisconsin, Wisconsin, State Regional Program, Siren, Siren, Wisconsin. 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ProteinResidues Residuesin inLithic Liihic Artifacts Artiactsfrom a Stratified Boreal Forest Forest Site. Site. Canadian CanadianJournal JournalofofArchaeology Archaeology 13, 119-132. 119-132. Nordeng, S.C., S.C., A.P. A.P. Ruotsala, Ruotsala,S.A. S.A.Nordeng Nordeng1987 1987Buried Buriedbog bogdates datesthe the time time of of the Nordeng, establishment of postglacial post-glacial Lakes Lakes Houghton Houghton and Nipissing in inthe the western western arm armof of the the Section Geological Society of America Lake Superior basin, North-central Section America Abstracts Abstracts with Program,vol. vol. 19, 19, no. no.4, 4, p. 237. Phillips, B.A. BA. M. Science 195, 11-16. 11-16. Coastal Histories, Science M.1977 1977Shoreline ShorelineInheritance Inheritancein in Coastal Phillips, B.A.M. B.A.M. 1982 Morphological Mapping and and Palaeogeographic Reconstruction of of Phillips, Morphological Mapping Palaeogeographic Reconstruction Former Shorelines Shorelines between between Current Current River Riverand and Rosslyn, Rosslyn, Thunder Thunder Bay, Former Bay, Ontario, Ontario, Including Cummins CumminsSite SiteDcJi-1. DcJi-1. Report Report on file with Historical Historical Planning and Research Research of Citizenship Citizenship and Culture, Culture, Toronto, Toronto, Ontario. Branch, Ontario Ministry of Ontario. Phillips, B.A.M. Phillips, B.A.M. 1988 1988 Palaeogeographic Palaeogeographic reconstruction of shoreline shoreline archaeological archaeological sites sites around Thunder Bay, Ontario. Geoarchaeology: An International Journal, 3, 2, 127138. Phillips, 3A.M. 1993 A Time-Space Model for the Distribution of Shoreline Archaeological the Lake Superior Superior Basin. Basin, Geoarchaeology: An International Journal, 8, 8, 2, 2, 87Sites in the InternationalJournal, 107. 107. Phillips, B.A.M. 3A.M. and C. 1994 History and Glacial and and Shoreline and 1994 The The Geology, Geology, Glacial Shoreline History Phillips, and Hill, Hill, C. Archaeological Potential Potential of of the Lake Superior: Superior: a Archaeological the Minnesota Minnesota North North Shore Shore of Lake background paper paper for for Geomorphologial and Archaeological ArchaeologicalStudies Studies of of Individual background Gwmorphologial and Individual State Parks Report for for Minnesota State Parks on the North North Shore. Shore. Report Minnesota Department Department of Natural Natural and Recreation, Recreation, St. St. Paul, MN. MN. Resources, Division Division of Parks and SAM. and P.W. 1994. 1994. A Transgressive Event on Lake Minong, Northshore Northshore Phillips, B.A.M. andFraiick, Fralick, P.W. of Lake Superior Superior -- Possible Possible Evidence Evidence of of Lake Agassiz Inflow,circa circa9.5 9.5 KA KA BP. BP. Agassiz Inflow, of Journalof ofEarth EarthScience, Science,v.v.31, pp. 1638-1 1638-1641. Canadian Journal 31, pp. 641. Phillips, B.A.M., B.A.M., Hill, Hill, C.L., CL., Fralick, P.W. and and W.A. WA. Ross Shorelines and Ross 1994 1994 Post-Glacial Post-Glacial Shorelines Phillips, Fralick, P.W. alongthe the Northwestern Northwestern Shore Shoreof of Lake LakeSuperior, Superior,Guidebook Guidebookfor for Paleoindian Migration along Fieldtrip E, E, 13th Biennial Meeting Meeting of AMQUA, AMQUA, Minneapolis, Mn. . : 8A.M. and Hill, C.L. CL. 1995 The Phillips, B.A.M. Thedeglaciation deglaciation history history and and geomorphological character a partof ofthe the region region of ofthe the 'Interlakes 'InterlakesComposite' Composite' -some - somenew newevidence. evidence. Symposium Symposium of apart Paleoindian Occupations Occupations of of on 'Archaeology, geomorphology and Paleoenvironmet: Paleoindian Great Lakes, Lakes, 60th 60th Annual of the the Western Western Great Annual Meeting Meeting of the Sociaety Sociaety for for American American Archaeology, Minneapolis, Archaeology, Minneapolis,MN. MN. May May 3-7. W. 1980 AAPalaeo-lndian Oliver Lake Lake Area. Area. Wanikan, 80, 33. Ross, W. Palaeo-Indian Refined Refined Biface Biiace from the Oliver Wanikan, 80, Society. Thunder Bay Bay Chapter, Ontario Archaeological Society. �Ross, Composite:aa re-definition re-definitionofof the the initial settlement of of the Ross, W. W. 1995 The Interlakes Interlakes Composite: initial settlement Agassiz-Minong 76, 3-4. 3-4. Agassiz-Minong Peninsula. Wisconsin Wisconsin Archaeologist, 76, Sharp, Sharp, R.R R.P. 1953 1953 Shorelines Shorelines of the the glacial glacial Great Great Lakes Lakes in in Cook Cook County, County, Minnesota: Minnesota: American Science,251, 251,109-139. 109-139. AmericanJournal JournalofofScience, Smith, TO. 1993 Lake Agassiz: The northwestern outlet and Smith, D.G. D.G. and Fisher, Fisher, T.G. 1993 Glacial Glacial Lake Agassiz: The northwestern outlet and paleoflood, 9-12. 21,9-12. paleoflood, Geology 21, Stewart, Ross, W.A. W.A.and and B.A.M. SAM. Phillips Stewart, J.D., Ross, Phillips1984 1984Investigations Investigationsatatthe theMcoaid McDaidSite Site(DcJh(DcJh16), 16), Thunder Thunder Bay, Bay, Report Reportto to the theOntario OntarioHeritage HeritageFoundation. Foundation. Stewart, A.S. Kissin 1989 1989 Two Isolated Isolated Biface Biace Finds Finds from the the Stewart, JO., J.D., Ross, Ross, W.A. W.A. Faykes, Faykes, A and AS. . Thunder Thunder Bay Bay Area, Area, Wanikan, Wanikan, 89, 89, 3, 3, 4-6, 4-6, Thunder Ontario Thunder Bay Bay Chapter, Chapter, Ontario Archaeological ArchaeologicalSociety. Society. Stuart, 1993 Paleogeographical Paleogeographical reconstruction reconstruction of of Lake LakeBeaver BeaverBay Bayraised raisedshorelines shorelines Stuart, A.J, A.J. 1993 with correlation correlation to possible possible Paleoindian Paleoindian settlement, settlement. Thunder Bay Bay region, region, Ontario. Ontario. HBSc. HBSc. dissertation, dissertation,Dept. Dept.of of Geography, Geography,Lakehead LakeheadUniversity, University,Thunder ThunderBay, Bay,Ontario. Ontario. Taylor, on the the north north Superior shore, American Geologist, vol. Taylor, F.B. 1895 The Nipissing beach on 15, 304-314. 15, p. 304-314. Teller, Agassiz and its fts Influence Influence on on the the Great Great Lakes. Lakes. fi Karrow, Teller, J.T. J.T. 1985 1985Glacial Glacial Lake Agassiz Karrow, P.F., P.F., and Calkin, Calkin, P.E. P.E. eds., eds., Quatemary Quaternary Evolution Evolution of the Great Great Lakes, Lakes, Geological Geological Association Associationof of Canada CanadaSpecial Special Paper Paper 30, 30, 1-16. 1-16. Teller, Thorleifson, L.H. 1983. The - LakeSuperior Superiorconnection. connection. In Teller, J.T. and Thofieifson, The Lake Lake Agassiz -Lake In J.T. Teller and LakeAgassiz, Agassiz,pp. pp.261-290, 261-290, Geological Geological Association Association and L. Clayton, eds., Glacial Glacial Lake of 26. of Canada, Canada, Special Special Paper Paper26. Tickle, Tickle, R. R. 1996. 1996. Depositional Depositional Systems Systems developed developed during during Deglaciation:Evidence D8glaciation:Evidence from from aa portion of the Mats ON., NBA. Dept. of MarksMoraine, Moraine, Conmee Conmee Township, Township, ON., HBA. dissertation, dissertation, Dept. Geography, Geography, Lakehead LakeheadUniversity, University, Thunder Thunder Bay, Bay, Ontario. Ontario. Van Rise, CR. and C.K. Leith 1911 of the the Lake Lake Superior Superior Region, Region, United States States 1911 The Geology of Hise, C.R. Geological Survey, Washington. Washington. Geological 1901, Glacial Glacial Lakes America Bulletin, Bulletin, vol. vol. Winchell, N.H. 1901, Lakes of of Minnesota, Geological Society of America 12, 12, p. p. 108-128. 108-128. Wright, H.E., F-I.E.,1972a 1972aPhysiography PhysiographyofofMinnesota, Minnesota,ininSims, Sims,P.K. P.K.and andG.B. GB.Morey, Morey,eds. eds.Geology Geology of Minnesota: aCentennial volume, 561- 578. Minnesota: acentennial volume, Minnesota MinnesotaGeological Geological Survey, p. 561- Wright, history of of Minnesota, in Sims, Sims, P.K. P.K. and and G.B. GB. Morey, Wright, H.E. H.E. 1972b Quaternary Quaternary history Minnesota, in Morey, eds. eds. Geology of Minnesota: Centennial volume, Minnesota Survey, p. 515515Minnesota: aacentennial Minnesota Geological Survey, 547. 547. Wright, HE. HE. Tunnel hydrology of of the Superior Tunnelvalleys, valleys, glacial glacial surges and subglacial subglacial hydrology Superior lobe, lobe, Minnesota, 136, p. 251-276. 251-276. Minnesota, Geological Geological Society Society of America Memoir 136, �Wright, J.V. 1963 Survey along alongthe the North North Shore Shore of of Lake Wright, J.V. 1963 An An Archaeological Archaeological Survey Lake Superior. Superior. Anthropology Papers, of Canada3, Canada 3,Department Departmentof of Northern Northern Affairs Affairs Anthropology Papers, National National Museum of pp. and National National Resources, Ottawa, 99 pp. Wright, HE., Cushing 1973 Moines Lobe, Geological H.E., C.L. C.L. Matsch, Matsch, and and E.J. Gushing 1973 Superior Superior and and Des DesMoines Geological Society 136, p. 153-1 153-185 Society of America Memoir 136, 85 Wright, Wright, HE. H.E. WA. W.A.Watts Watts1968 1968Glacial Glacialand andvegetational vegetational history of northeastern Minnesota, Minnesota Minnesota Geological Society Survey Survey Special Special Publication Publication11. 11. - Zoltai, S.C. 1963. Glacial features of the Canadian Lakehead, Canadian Geographer Geographer 7, 7, 101 101ead, Canadian 115 Zoltai, S.C. 1 965a. Glacial features of the Quetico-Nipigon area, area, Ontario. Ontario. Canadian CanadianJournal Journal of of Earth Science Science 2, 247-269. 2,247-269. - Zoitai, Thunder Bay Surficial Geology, Geology, 1:506,880, 1:506,880, Map S265, Ontario Zoltai, S.C. S.C. 1965b. 1965b. Thunder Bay - Surticial Ontario Department of Lands and Forests. ! �TIlE PALEOPROTEROZOIC GEOLOGY OF THE GUNFLINT FORMATION Peir Pufahi, Pufahl, University University of British Columbia Fralick, Lakehead Philip Fralick, Lakehead University John Scott, John Scott, Ministry Ministry of of Northern Northern Development Development & Mines Formation records records a chemically dominated shelf shelf The Gunflint Formation silica- and iron-rich iron-rich precipitates precipitates predominate. predominate. sequence in which silicathe role role that both physical physical and and chemical chemical This frzp trip will examine the This processes played in invarious variousshelf shelf environments. environments. �FIELDTRIP 4 DEPOSITIONAL ENVIRONMENTS OF THE PALEOPROTEROZOIC GUNFLINT FORMATION Pier Pufahl and Philip Fralick INTRODUCTION INTRODUCTION Paleoproterozoic many other other important important Paleoproterozoiciron ironformations formationshost host most mostof of the the world's iron ore and many Consequentlythey theyhave havebeen beenthe the focus focus of of hundreds hundreds of of mineral deposits deposits (Simonson, (Simonson, 1985). 1985). Consequently mineralogical, geochemical investigations. However, in in spite spiteof ofthis immense mineralogical, geochemical and sedimentological investigations. this immense amount of data no consensus has ever ever been been reached reachedas asto totheir theirorigins. origins. Some Some of of this this controversy controversy stems accumulated stems from a poor understanding of the sedimentological environments in which they accumulated (Simonson, 1985). They were deposited during a unique interval of earth history when grossly They were deposited during a unique interval different prevailed (Cloud, 1973), and therefore therefore lack lack precise precise different atmospheric atmosphericand and hydrologic hydrologic conditions conditions prevailed modem analogues (Simonson, 1985; Fralick and Barrett, Barrett, 1995). Modem subaqueous hot-spring Modem subaqueous hot-spring activity has provided sediments, but but the provided clues to understanding understanding the precipitation precipitation of iron-rich sediments, mineralogy and deposits is not not comparable comparable to tothe thelarge largePaleoproterozoic Paleoproterozoic iron iron mineralogy and areal areal extent extent of modem deposits formations deposited during during the the Earths Barren, 1995). 1995). Detailed formations deposited Earth's early early history history (Fralick (Fralick and and Barrett, petrographic to interpreting the the paragenesis paragenesis of of petrographic investigations investigations of iron formations formations have contributed to syndepositional, diagenetic and metamorphic mineral mineral assemblages, assemblages, but but they they have done little to provide detailed, reliable information information regarding regarding iron iron formation formationdepositional depositionalprocesses. processes. Minerals Minerals and and provide detailed, textures are are commonly commonly altered altered to to secondary secondary assemblages, and when primary minerals minerals are are present present theoretical has been been limited in in its its ability to explain explain their genesis genesis (Fralick (Fralick and and theoretical chemical chemical modelling modelling has Barrett, Barren, 1995). 1995). Paleoenvironmental Paleoenvironmentalinferences inferencesfrom fromgrain-size grain-sizedistributions distributionsin in iron iron formations formationsare are also plagued with with uncertainty uncertainty because because they they are are commonly commonly indurated, indurated, diagenetically &genetically altered, altered, and and frequently fine-grained fine-grained (Simonson, (Simonson, 1985). 1985). Fortunately, these problems can be overcome by combining a regional basin analysis analysis of clastic clastic and and volcanic volcanicrocks rocks surrounding surroundingiron iron formations formations with detailed detailed examination examination of vertical and lateral facies trends within chemical sedimentary successions (Fralick and Barrett,1995). 1995).Associated Associated lateral faciestrends withinchemical sedimentary successions(Fralick and Barren, sedimentary settings. Sedimentary structures sedimentary and volcanic rocks provide data on depositional settings. structures and lithic processes, and lithic associations associationswithin within iron iron formations formationsgive give information on physical sedimentary processes, regional basin analysis analysis provides a framework framework within which to to view view iron ironformation formationgenesis. genesis. Combining these techniques techniques makes makes paleogeographic paleogeographic reconstruction reconstruction and depositional depositional modelling modelling Barrett, 1995). 1995). This is the same same approach approach used by sedimentologists sedimentologists and possible (Fralick and Barrett, stratigraphers to reconstruct clastic depositional systems. stratigraphers reconstruct clastic depositional systems. Location Location The United States, The main main portion portionofthe of theGunflint Gunflintiron ironrange rangeextends extends170 170km km northeast northeast from from the United States, at Gunflint Lake, to Loon Lake, Ontario (Figure 1). In Minnesota the Gunflint forms a narrow belt Gunflint 1). In narrow belt �Figure 1. Distribution Figure Distributionof ofPaleoproterozoic Paleoproterozoic iron iron formations in the Lake Superior region. Ontario f GUNFLINT — —— — -S. — — 1 4+( 41-4 i2H-' •4.* 4+4+444443+ +4. A . —. MESABI Cf 'of MARQUETTE t,++ •+ 4j 4+4+ 4 + 4 : 444 +44 CUYUNA F rocks younger than early Proterozoic Proterozoic early _____ Penokean plutonics L and volcanics early Proterozoic early ____ rocks, BIF in black Archean greenstone -::.:;:; Archean granite terrane .: +'4" + ... +44 . . . 444+ •831 •44 GOGEBIC .... .... . ..... . __ A . 44+ 44 4.44 4+ L5r '; I, Ii II.— / i/pt/li/I p/il, '1/ LEGEND — I, Archean Archean gneiss gneiss terrane terrane I / t t - . - Minnesota I- ON R1VE - Wisconsin. C. L100km I . �20 the southwest southwest by bythe theDuluth DuluthComplex. Complex. Erosional remnants 98 km 20 km long which is truncated to the northeast Ontario, suggest suggest apre-erosional apre-erosional continuation continuation of the the chemical chemical northeast of of Thunder Thunder Bay at Schreiber, Ontario, sedimentary rocks to the east. sedimentary rocks to the east. Previous Previous Work Work The Gunflint was discovered discovered in in 1850. 1850. The Gunflint iron formation was The earliest earliest recorded recorded geological investigation of the Gunflint by E. D. Ingall in 1887 (Ingall, 1888), who briefly briefly Gunflint was conducted by described the iron-bearing and Whitefish Whitefish Lake. Lake. Other early accounts iron-bearing strata near Silver Mountain and accounts were made by general by Smith Smith (1905) (1905) and Silver Silver (1906). (1906). Van VanHise Hiseand and Leith Leith in in 1911 1911presented presented aa general overview of the iron bearing rocks rocks in in the the Thunder ThunderBay Baydistrict. district. In 1924 J. E. Gill was was the the first to to describe its stratigraphy stratigraphynortheast northeastof ofSilver SilverMountain. Mountain. In 1927 describe the Gunflint in detail, and in 1926, its Gill published the chemical chemical sediments. sediments. T. L. Tanton described the published again, this this time on the origin of the iron prospects at at Mink Mink Mountain Mountain in in 1923, 1923, and in 1931 1931 gave an overview of the general geology in the vicinity vicinity of of Thunder Thunder Bay. Bay. In 1956 formation was divided by Goodwin Goodwin (1956) (1956) into six major sedimentary sedimentary facies 1956the iron formation facies representing Conglomerate Member, Member, 2) Lower Lower representingtwo twodepositional depositionalcycles cyclesand and four four members, members, a 1) 1)Basal Conglomerate Gunflint Member, 3) Upper Gunflint Member and 4) Upper Limestone Member; which are largely Gunflint Member, 3) Gunflint Member correlative with Broderick's (1920) four-fold division of of the Gunflint Gunflint iron iron range range in northeastern Minnesota and Wolff Wolffss (1917) subdivision of the the Biwabik Biwabii iron iron range range in in east-central east-central Minnesota Minnesota (Figure 2). He He also alsodrew drewattention attentionto to evidence evidence of widespread volcanism associated with deposition of the chemical sediments and suggested the iron iron and and silica. silica. In 1960 Goodwin of the chemical sediments and suggested a volcanic source for the 1960Goodwin and Moorehouse published the first detailed geological maps of the region (scale 1:31 1:31 680) 680) and and reported on the economic potential, mineralogy and chemistry of the iron bearing strata, and reported the economic potential, mineralogy and chemistry of the bearing modified modified Gunflint Gunflintstratigraphy stratigraphyinto intoaaLower Lowerand and Upper Upper Gunflint Gunflint depositional depositionalcycle cycle composed composedof of 10 10 members; a Basal Lower Taconite, Taconite, Local Local Lava Lava Basal Conglomerate, Conglomerate, Lower Algal Chert, Lower Shale, Lower Flows, Upper Algal Chert, Chert, Upper Jasper, Upper Shale, Shale, Upper Upper Taconite and an an Upper Limestone Limestone member. Fralick and Barrett Barrett (1995) (1995) have have recently recently redefined redefined Gunflint Gunflint stratigraphy stratigraphy as as simply simply member. consisting oncolitric cherts, cherts, and and cherty cherty consisting of of 22 members; members; aa lower lower member member comprised comprised of of basal algal and oncolitric They grainstones, and an upper member similar in stratigraphy to the lower member. grainstones, upper member similar in stratigraphy to the lower member. They have interpreted interpreted this this succession successionas as representing representing aa wave- and and tide-dominated inner shelf shelf sequence. Floran Lougheed (1983) (1983) and and Simonson Simonson Papike (1975), (1975), Randazzo Floran and and Papike Randazzo and Markun (1980), Lougheed (1987) mineral assemblages comprising comprising the the ~Gunflint (1987) have have given givendetailed detkled petrographic ietro&aphicdescriptions descriptionsof ofmineral unflint iron formation. The iron formation. TheGunflint Gunflintvolcanics volcanics(Goodwin, (Goodwin,1956,1960) 1956,1960)have havebeen been petrographically petrographically described described by Hassler and Simonson by Kissin and REE geochemistry geochemistry has been determined by Simonson (1989). Their TheirREE Fralick exhalative origin Fralick (1994). (1994). Carbon Carbonand andsulfur sulfurisotopic isotopicstudies studieshave have indicated a hydrothermal exhalative geochemical source for for the the iron iron (Cameron, (Cameron, 1983; 1983; Carrigan Camgan and as the source and Cameron, Cameron, 1991). 1991). Other geochemical investigations investigations(Kronberg (Kronbergand and Fralick, Fralick,1992) 1992)have have attributed attributedthe the alteration alteration of the Archean basement to the penetration penetration of Gunflint-derived fluids diagenetic or low-grade metamorphic metamorphic conditions. conditions. of Gunflint-derived fluids under under diagenetic Detailed accounts accounts of of The overlying Rove Formation Formation was was described described by Morey Morey (1967, (1967, 1969). 1969). Detailed microfossils preserved and Barghoorn (1 (1954), Barghoorn microfossils preservedwithin withinGunflint Gunflintchert chertare arerecorded recordedby Tyler andBarghoom 954), Barghoom and Tyler (1965a,b), Awramik (1976). (1976). (1965a,b), Edhom Edhom(1973) (1973) and and Awramik �S. I .... Basal con glomeraté Iron Formation Gunflint . . Formatin Pokagama Quartzite Biwabik Iron Formation 0 a = Dunham Formation Glen Township Formation lJttie Falls Formation Trout Lake Formation Mahnomen Formation Trommaid Formation Formation Rabbit Lake Virginia Formation Rove Morey, 1978 White, 1954 Goodwin, 1958 Cuna range Mesath range Gunflirite Northwest segment S a a Sunday Quartzite Bad River Dolomite Palms Formation Formation Iron- Ironwood Formation Tyler Aldrich, 1929 Blair / Ajibik Quartzite Siamo Slate Negaunee Iron Formation Goodrich Quartzite Michigamme Formation Cannon, 1986 Marquette range Archean rocks, undivided Bad River Dolomite Palms Formation Creek Formation Emperor Volcanic Compl Formation copp NFormation N Michigamrne GogeLNcrage For mation Reany Creek Enchantment Lake Formation Mesnard Quartzite Kona Dolomite Wewe Slate Quartz ite Ajibik Siamo Slate Formation Iron- Negaunee Goodrich Quartz ite Thaden, 1968 Marquette range Saunders Hemlock Formation Amasa and Fence River Formations Michigamme Slate Green stone Badwater Cannon, 1986 A7uPhft - Southeast segment Hemlock Formation Amasa and Fence River Formations Mithigamme Slate Dunn Creek Slate Badwater Greenstone Riverton Iron Formation Fortune Lakes Slate Stambaugh Formation Hiawatha Graywacke Cannon, 1986 ta Figure 2. Proposed correlations ofAnimikie Group sediments in the Lake Superior region. Fern Creek Formation Qua rtzite Sturgeon Randville Dolomite Fetch Formation Formation Iron- Vulcan Michigamme Slate Badwater Greenstone ratttn 2 j a a 0 0 C E a 0 0. = I! a d. 0 a = I 0 0, = 0 a = 2 2' 0 a = �Figure 3. Gunflint sediments sediments outcropping outcropping at at the spiiway Photographs of of Gunflint spillway section section near Figure 3. Photographs Kakabeka Falls. A) Trough Kakabeka Troughcross-stratified cross-stratified"lapihi" 'Tap(Â¥//i"tuff'(reworke volcaniclastic tuff (reworked rip-ups). rip-ups). ofseqAence. B) Large Largealgal algalbioherm biohermdraped drapedby by shales shales at at the the base of sequence. I A C! __ - -— , -: r' a -a / - - / - ;1 '. , - 2 - - I — _----1-_ - ft /; - I .-;C f �Several isotopic investigations investigations have have constrained constrainedthe the depositional depositionalage ageof of the the Gunflint Several isotopic Formation between between 1.6 1.6 and and 2.0 2.0Ga. Ga. Hurley Hurley et et al. at (1962) minimum age age of of deposition depositionof of (1962) obtained aa minimum about K-Ar methods, methods, to to which which they theyapplied appliedan anempirical empiricalcorrection correction factor, factor, about 1.6 1.6 Ga Ga by both Rb-Sr and K-Ar which allowed age of ofapproximately approximately 1.9 1.9Ga Ga(Stille and Clauer, Clauer, 1986). 1986). Faure and which allowed them to propose an age (Stille and approximately 1.6 1.6 Ga. Ga. More Kovach (1969) also obtained a Rb-Sr isochron age of approximately More recently, recently, Stille Stille Clauer (1986) obtained about 2.08 2.08 Ga Ga for forvolcanic volcanicslates slatesinterbedded interbedded and Clauer obtained a Sm-Nd isochron age of about with iron-bearing iron-bearing strata strata of the Guntlint Gunflint Formation. The absolute age age of of the the Gunflint Formation Formationwas wasdetermined determinedby byFralick Fralicketetal. a. (1998) by conducting U-Pb, single zircon geochronology on a sample population from reworked tuffs conducting U-Pb, single zircon geochronology on a population from reworked tuffs outcropping near Kakabeka Kakabeka Falls Falls (Figure (Figure3), 3),aaeuhedral euhedralzircon zircongave gaveaaconcordant concordantage ageof of1878 1878zE2 ± outcropping (Figure 4) which Fralick et al. at (1998) (Figure (1998)argue argueis is the the depositional depositional age of this unit. I KB-TUFF Brown euhedral zircons .34 .338 .336 .334 .332 5.2 5.25 5.3 5.35 5.4 5.45 fromthe theupper upperGunflint GunflintFormation Formation (Fralick, (Fralick,etetal, at 1998) 1998) Figure 4. Concordia Concordiadiagram diagramfor zirconsfrom Animikie Basin Paleoproterozoic sedimentary Animikie Basin Basin form a southwardsouthwardThe Paleoproterozoic sedimentaryrocks rocks deposited deposited in in the Animikie thickening wedge province, which truncated in in eastthickening wedge covering coveringthe the southern southernmargin marginof of the the Superior Superiorprovince, which is truncated central Minnesota and northern Wisconsin by the 'Penokean" magmatic terranes". Sedimentation Minnesota by the "Penokean" terranes". Sedimentation began approximately prior to to or during during approximately 2.1 2.1 Ga Ga ago ago and and ceased ceased roughly 1.85 1.85 Ga ago (Morey, 1983), prior the Penokean orogeny of Goldich et al. at (1961). The nature of the sediment varies considerably, The nature of the sediment varies considerably, (1961). ranging the thick thick successions successions of of ranging from from volcanic volcanic and and clastic to the chemical precipitates which form the iron formation. The Thetermination terminationof ofthe thePenokean Penokeanorogeny orogeny marked marked the onset onset of an intrusive igneous phase plutons into into the theAnimikie Animikiesediments sediments emplaced subduction subductionrelated related tonalitic tonalitic and granitic plutons phase which which emplaced related volcanics volcanics of the the Wisconsin Wisconsin magmatic magmatic terranes. terranes. The the basin basin was was The present form of the and the arc related �achieved around1.1 1.1 Ga Gaago achieved around ago (Silver (Silver and Green, 1972; 1972; Hanson, Hanson, 1975;Wanless Wanless and and Lovebridge, Lovebridge, 1978) 1978) System (King (King and Zietz, 1971) when a north-northwest trending trending branch of the Midcontinental Rift System Zietz, 1971) separated the Animikie Animikie sediments southeastern segment (Morey, 1983). separated sediments into a northwestern and southeastern 1983). of the Animikie Animikie Group unconformably unconformably overlays overlays the the Superior The northwestern segment of Province Malinomen Formation), Province and and consists consistsof a basal sandstone-siltstone (Pokegama (Pokegama Quartzite, Mahnomen Formation), (Gunflint, Biwabik, Biwabii, Trommald iron formations), and a thick, upper, formation (Gunflint, iron formation upper, shale-siltstone shale-siltstone sequence (Rove, Virginia and Rabbit Rabbit Lake Lake Formations). Formations). In east-central Minnesota the the Thomson Formation Rove, Virginia Virginia and and Rabbit Rabbit Lake Lake Formations, Formations, has has also also Formation which has similar similar lithology to the Rove, considered correlative and Ojakangas, Ojakangas, 1970). However, been considered correlativeto the Animikie Group (Morey and However, recent recent structural interpretations have complicated complicated the the correlation interpretations have correlation of these units units (Ojakangas, (Ojakangas, 1995); 1995); northward Penokean Orogeny Orogenyhas hasjuxtaposed units of ofdiffering differingEarly EarlyProterowic Proterozoic juxtaposedunits northward thrusting thrustingduring during the Penokean ages in east-central Minnesota (Southwick et al., 1991; Hemming, Hemming, Minnesota at, 1988; Southwick and Morey, 1991; 1994). Similar within the the southeastern southeastern segment segment in in Similarstructural structuralcomplexities complexities also hinder correlation within northern Wisconsin 1991 ; Gregg 1993). northern Wisconsin and and the the Upper Upper Peninsula Peninsula of Michigan (Klasner et al., at, 1991; 1993). The were deformed deformed during during the the Penokean Penokean orogeny, orogeny, The sedimentary sedimentary rocks rocks of the Animikie Basin were and Archean Archean rocks rocks along along the the forming a zone zone of of deformed deformed and and metamorphosed metamorphosed Paleoproterozoic and southern margin of the Superior Province Province (Sims, (Sims. 1991). It is thought to to have have occurred occurred between between 1.9 1.9 southern margin and Bickford, Bickford, 1985). In the Great Lakes region it and 1.76 Ga (Van Schmus, 1976; Van Schmus and forms the Late Archean crust crust of the the Superior Superior Province Province and and the the forms the transition transition between between the Late Archean Paleoproterozoic Paleoproterowic continental crust of the Mazatzal Mazatzal and Yavapai Yavapai provinces of the southwestern southwestern Deformation along United United States States(Sims (Simsand and Petennan, Peterman,1986; 1986;Hoffman, Hofflnan, 1989; 1989;Barovich Barovich et al., at, 1989). Deformation this thrusting and development of basement basement gneiss gneissdomes domes(Southwick (Southwicket etal., this tectonic tectonic front front involved involved thrusting at, Minnesota, northern northern Wisconsin Wisconsin and and the the 1988). Rocks of the orogeny are exposed in east-central Minnesota, 1988). Upper Peninsula Peninsulaof of Michigan. Michigan. The orogeny Animikie strata strata and and a southern orogeny consists consists of a northern northern zone of deformed deformed Animikie southern assemblage plutonic rocks rocks of of the the Wisconsin Wisconsin assemblageof of arc-related arc-related volcanics volcanics and synorogenic, calc-alkaline plutonic magmatic terranes, separated by by the Niagra Fault Zone Zone in in northern northern Wisconsin Wisconsin and the the Upper Upper Peninsula 1989) and by the Malmo Discontinuity in east-central Minnesota 1989) and by the Malmo Discontinuity in east-central Minnesota Peninsulaof of Michigan Michigan(Sims (Sims et al., at, (Southwick and and Morey, Morey, 1991). 1991). (Southwick The earliest sedimentological for the the Animikie Animikie Basin Basin relied relied on on the the work work of of James James sedimentological models for (1954) successions evolved from from aa "miogeosynclinal" "miogeosynclinal" sequence sequence (1954) who concluded concluded that iron formation successions to a "eugeosynclinal" during Paleoproterowic Paleoproterozoictime. time. James' James original ideas were then "eugeosynclinal" assemblage during discarded in the mid sediments in in aa rift-like rift-like basin basin discarded mid 1970's 1970's in in favour favour of of deposition deposition of Animikie Animikie sediments (Cambray, 1978). 1978). In Inthis thismodel modelrifling riftingwas wasfollowed followedby by the theultimate ultimateclosure closureof of the the basin basin with with the the and Penokean orogeny. orogeny. In the early early 1980's 1980's Young Young (1983), (1983), by analogy analogy with other Phanerozoic and Proterozoic tectonic and sedimentary history history of ofProterozoic Proterozoicdepositional depositionalbasins, basins, interpreted interpretedthe the tectonic Proterozoic rocks in the northern Great Lakes region in terms of an aulacogen model. model. Unfortunately, Unfortunately, there was no general consensus on the driving force which which caused caused the the basin basin to to form and the characteristic characteristic sediments analogous to rift/aulacogen depositional systems are absent. In In the mid 1980's 1980's continued sediments analogousto rifVaulacogen depositional systems research lead to to significant significant advancements advancements in understanding understanding the tectonics associated with basin development. These Thesestrides strideslead leadHoffman Hofflnan(1987) (1987)to tosuggest suggestdeposition depositionof ofchemical-sediments chemical-sediments �Icr\, member 2 member member!1 member member 4 member 3 member member S member 5 , I. p..) : I 20m C ra'< I I C) t ININ coarsening upwards sequence transgression basal transgression middle transgression upper transgression Stratigraphk section from holes Figure 5. Stratigraphic sectionthrough throughthe theGunflint GunflintFormation Formationbased basedon on drill drill core corefrom Figure is aafew few kilometres kilometres north north of the the US US border. barrfcr.A A detailed detailed discussion discusshn of the lithofacies is - - L (sen/o/In the tort 'ft Up vorlion graillsizg changes in water 4 tR1 In4n-nt clianees trends.,, L [_Z L L �occurred crustal loading occurredin inaamigrating migratingperipheral peripheralforeland forelandbasin basinwhich whichformed formedin in response response to crustal loading during during the thePenokean Penokeanorogeny. orogeny.Southwick Southwicketetatal.(1988) (1988)and andSouthwick Southwickand andMorey Morey(1991) (1991)then thenreinterpreted reinterpreted the at, 1960) 1960)in in Minnesota. Like LikeHoffman, Hoffinan,(1987) (1987) thesegment segmentof ofthe thePenokean Penokean orogeny orogeny (Goldich, et al., they peripheral foreland theyalso alsoconcluded concludedthat thatthe theAnimikie AnimikieGroup Groupaccumulated accumulatedin inaaperipheral forelandbasin basinand andthat thatiron iron formation formationdeposition depositionoccurred occurredin inthree threedistinct distincttectonic tectonic settings settings as as the orogeny evolved. evolved. Recently, Recently, Pufahl (1995, 1996) 1995) have Pufahl(1995, 1996)and andHemming Hemming(1994, (1994,1995) have demonstrated demonstrated that this tectonic tectonic model model is is no no longer 1995) contends longervalid. valid. Hemming Hemming(1994, (1994,1995) contendsthat thatnedodimium nedodimiumand and lead lead isotopic isotopic evidence evidence for for the provenance provenanceof ofthe theAnimikie AnimikieGroup Groupis isconsistent consistentwith with the the tectonic tectonic evolution evolution of of the Animikie Animikie Basin Basin beginning telescoped back arc basin basin that that beginningas asaapassive passivemargin marginwithin withinaaback backarc arc basin, basin, and and ending ending as a telescoped closed closedas asaa result resultof ofaa change change in in relative relative plate convergence convergence direction. Nevertheless, Nevertheless,in in recent recentyears years the theforeland forelandmodel modelhas hasreached reachedwidespread widespreadacceptance acceptancebased basedon on high high resolution resolution aeromagnetic data, aeromagneticdata, exploratory exploratory drilling drillingthrough through structurally structurally complex complex regions, and sedimentological sedientological investigations investigations of clastic (Hoffman, 1987; 1987;Southwick Southwicketal. etat,,1988; 1988; Southwick clasticunits unitsabove aboveand and below below iron-bearing strata (Hoffman, Southwick and andMorey, Morey,1991; 1991;Ojakangas, Ojakangas,1995). 1995). GUNFLINT GUNFLINTIRON IRONFORMATION FORMATION PALEOGEOGRAPHIC PALEOGEOGRAPHICRECONSTRUCTION RECONSTRUCTION Interpretations Interpretations presented presented here here are are based based on on the the study study of of core core drilled drilled through through the the Gunflint Guntlint Formation. Formation. The The Formation Formation has has been been divided divided into into five five members members based based on on distinct distinct lithofacies lithofacies associations associationsand andcontrolled controlledby bytransgressive-regressive transgressive-regressivecycles cycles(Figure (Figure5). 5). The The strand strand proximal proximal succession fine-grained, chemical chemical sediments sediments successionpresent presentin inNorthwestern NorthwesternOntario Ontarioofflaps offlapsto to the south as fine-grained, of 6 and and 7). 7). This of the the slope slopeare are approached approachedin in the the Cuyuna Cuyuna Iron Iron Range Range (Figures (Figures 6 Thischapter chapterwill will give give detailed detailed interpretations interpretations of the the depositional depositional environment environment of each each of of these these members; members; but but first first an an overview overviewof ofnearshore nearshoresedimentation sedimentationisispresented. presented. Lateral Lateral and and vertical vertical facies facies changes changes within within the the Gunflint Gunflint Formation Formation indicate indicate deposition deposition occurred on a shallow, non-barred, microtidal, storm-enhanced shelf with little influx. occurred on a shallow, non-barred, microtidal, storm-enhanced shelf with little clastic clasticinflux. Bedforms Bedformsand andinternal internalsedimentary sedimentarystructures structurescomposing composingGunflint Guntlintstrata strataare are directly directly comparable comparable to to those found in modern nearshore-to-shallow marine clastic and carbonate depositional those found in modern nearshore-to-shallow marine clastic and carbonate depositionalsystems. systems. These These facies facies trends trendsrecord recordenergy energytransformations transformationsfrom fromdeep deep water, water, offshore offshorewaves waves to to nearshore, nearshore, shoaling conditions. Minor shoaling waves waves under under fairweather fairweather and storm conditions. Minor mafic mafic flows (Goodwin, 1960) 1960) and extensive extensivetuffaceous tuffaceoushorizons horizons(Hassler (Hassler and and Simonson, Simonson,1989) 1989)within within the the Gunflint Gunflint indicate indicate that that the the region region was was volcanically volcanicallyactive activeat at the the time time of of basin basin formation formationand and subsidence subsidence (Fralick (Fralick and Barrett, Barren, 1995). 1995). The Themain mainmorphological morphologicalelements, elements,bedforms bedformsand andinternal internal sedimentary sedimentary structures structures along along aa typical typical beach-shoreface-offshore beach-shoreface-offshore profile profile are are shown shown in in Figure Figure 8. 8. The Thefollowing followingsummary summary of of these these features and Clifton Clifton et. et. al. at (1971). features is is taken taken from from Walker and Plint (1992), Einsele (1992) and (1971). The foreshore, also portion above above the the low low tide tide line line alsosynonymous synonymouswith with beach, beach, consists consistsof of the the portion Theforeshore, In the the foreshore foreshore zone zone the the most most and and is is dominated dominatedby by the theswash swashand andbackwash backwash of of breaking breakingwaves. waves. In high characteristic dipping seaward. seaward. On characteristicfeature featureis is parallel parallel to to low-angle low-angle cross-bedding cross-bedding dipping On non-barred non-barred high inner (upper foreshore), planar zone and energy an energyshorelines, shorelines,two twoplanar planarlaminated laminatedzones zonesoccur, occur,an an inner (upper foreshore), planar zone and an outer (lower foreshore) planar zone within the zone of breaking waves. waves. In between these outer (lower foreshore) planar zone within these two two zones zones depositional features. the the bedding beddingsurface surfacebecomes becomesrough roughdue dueto to dotted dotted and andirregular irregularerosional erosionaland and depositional features. �Figure 6. Figure 6. Location of driliholes depicted on Figure 7. �G-1 MGS-8 Mahnomen Fm (Cs) 18290 Rabbit Lake Fm (Vs) SW Is. • -.4 MGS-7 MGS-2 20m Figure 7. 30f TB0642 4 Gp,GIICS TB0218 Rove Fm (Vs) NE slope. The green units are fine-grained volcaniclastics. Other units are described in the text. sections are from logged driliholes (for locations see Figure 6). Sc and Si arc fine-graincd chemical sediments of the Lithofacies distribution across the Gunflint, Mesabi and Cuyuna shelf to slope depositional system. Stratigraphic Kakabeka Conglomerate (Cp) GF-3 ftp Pokegama Quartzite (Cs) MGS-5 Virginia Fm (Vs) �Morphological elements, and internal Figure & elements, bedforms bedforms and internal sedimentary sedimentary structures structures along along aa Figure 8. Morphological typical beach-shoreface-offs bore profile. @pica1beach-shoreface-offshoreprofile. - ZONE ZONE OF OF SHOALING SHOALING WAVES SURF ZONE fairweather wave base !Sn'9 P2 stormwave wave storm basebase S SHOREFACE SHOREFACE SHELF INNER SHELF (subtidal) (subtidal) Beciforms Bedforms Grain Grain size size - parallel - laminated laminated mud facies fades silt and and clay clay —I I lunate lunate outer assymetric HCS HCS assYmetric dune planar dune planar fades facies facies rippled facies facies fades facies facies fine sand sand - silt silt - - fine fine medium medium sand sand FORE FORE BACK BACK SHORE SHORE SHORE SHORE (supratidal) (intertidal) (supratidal) (intertidal) inner inner rough rough facies facies inner inner planar planar fades facies coarse coarse fine sand sand - fine mediurr fine fine mediur sand gravel sand gravel - - �In tidally tidally dominated dominated systems systems the the foreshore foreshore and and upper upper shoreface shoreface is is comprised comprised of of flaser, wavy, and In lenticular lenticular bedded bedded sands sands and and muds muds typical typical of of sedimentation sedimentation on inter- and subtidal, sand-mud subtidal, mixed sand-mud flats. The shorefacelies liesbelow belowlow lowtide tidelevel leveland andisischaracterized characterized by by day-to-day day-to-day sand transport transport Theshoreface above fairweather fairweather wave wave base. base. The above Theshoreface shoreface normally normally has has a concave-upward profile, which is is in in equilibrium with with the the waves waves that that shape On the the lower at depths equilibrium shape it. it. On lower shoreface, shoreface, at depths near near or or below below produced by storm fairweather wave base (10 (10 to 20 m), are long crested symmetrical symmetrical wave ripples, produced storm waves. Landward, Landward, on onthe themiddle middleshoreface, shoreface,these these inactive inactive ripples ripples pass into into active active ripples ripples which which become increasingly increasingly asymmetric, trough cross become asymmetric, irregular, and short-crested. Larger, trough cross stratified, stratified, lunate lunate zone. All dunes are frequently observed on the upper shoreface in the breaker zone. All these these bedforms bedforms are are associated with small-scale or larger-scale cross bedding which is is predominantly oriented oriented toward toward continuous agitation, the deposition of mud the land. Because Becausethe thesediments sedimentsof of this this zone zone are are under continuous base and has a lower istypically typically below below fairweather wave base is prevented. The The mud-dominated mud-dominated shelf is depositional slope foreshore and shoreface. Muds typicallyparallel parallel laminated laminated and and highly highly thanthe foreshore Muds are typically depositional slope than bioturbated bioturbated in in modem modem shallow-marine shallow-marinedepositional depositionalsystems. systems. In storm In storm enhanced enhanced shallow shallow marine marine non-barred, non-barred, environments environments the the shoreface shoreface processes processes described thus described thus far, far, as as well well as as processes processes in in deeper deeper regions regions of of the the inner inner and and outer outer shelves shelvesare are strongly strongly affected and and modified modified by by storm storm events events (Davis, (Davis, 1992; 1992; Einsele, Einsele, 1992). 1992). Storms affected Storms can can deposit deposit sandy sandy material in in the material the supra supra tidal tidal zone, zone, as aswell well as asgenerate generatespecial specialnon-channelized non-channelized flow flow conditions conditions in in deeper water. water. These deeper Thesehigh highenergy energyevents eventsfrequently frequently produce produce characteristic characteristic sheet-like sheet-like sand sand and and mud mud beds, called tempestites, of considerable lateral extent (Johnson and Baldwin, Baldwin, 1986; Morton, 1988; Nummedal, 1991; Einsele, 1992). Storm-generated bed forms show a the beach beach Nummedal, 1991; E i e l e , 1992). Storm-generated bed forms show adistinct distincttrend trend from fromthe into deeper water. The upper shoreface (surf zone) displays dunes oriented parallel to the shoreline. into deeper water. The upper shoreface (surf zone) displays dunes oriented parallel to the shoreline. When flow becomes channelized longshore erosively scour scour fairweather fairweather sediments, sediments, longshore and rip currents erosively depositing mediumand coarse-grained, trough and planar, cross stratified sands. The middle depositing medium- and coarse-grained, trough and planar, cross stratified sands. The middle shoreface is dominated dominated by both bedfonns with horizontal or shoreface both flat and swaley bedforms with nearly horizontal or low-angle low-angle swaley swaley cross cross stratification. stratification. Because Becauseof ofthe thecontinual continual agitation agitation of of sediments sediments through through wave wave action action on on the the upper middle shoreface record of of heavy heavy storms storms is isusually usuallydestroyed. destroyed. On the lower lower shoreface shoreface upper and and middle shorefacethe the record On the (5 to 20 20 m m water water depth), depth), the ebb currents currents reaches reaches about about the the same same magnitude magnitude as (5 to the stress stress of of storm storm surge surge ebb as the oppositely oppositely directed the directed storm-wave storm-waveinduced induced oscillatory oscillatory flow flow (Einsele, ( E i e l e , 1992). 1992). Thus, Thus,for foraashort shorttime, time, both currents both currents may stir stir up up sand sand and and mud, mud, which which are are redeposited redeposited as as parallel parallel and and hummocky hummocky crosscrossstratified fine-grained,graded gradedbeds bedsatat the the same same location location or or nearby nearby (Einsele, (Einsele, 1992; 1992; Dott Doll and stratified fine-grained, and Bourgeois, 1982). On inhigh-energy high-energy Bourgeois, 1982). Onthe theinner innershelf shelfand andparts partsof ofthe theouter outershelf, shelf,particularly particularly in environments, environments, storm-induced combined flow may still still generate HCS or thin, graded, graded, sandy sandy beds beds resulting from If the the suspension suspension originates originates from from storms storms and and resulting from laterally laterally flowing flowing suspension suspension currents. currents. If the sandy the sandy layers layers alternate alternate with with shelf shelfmuds, muds, the thestorm storminduced inducedbeds bedsrepresent represent distal distaltempestites tempestites (Aigner, Einsele, the current current component component of of the the (Aigner, 1985; 1985; E i e l e , 1992). 1992). At At greater greater water water depths depths on on the the shelf, shelf, the combined storm beds combined storm flow flow becomes becomes dominant, dominant,leading leadingto to current currentrippled, rippled, offshore, offshore, fine fine sand sand and and silt silt beds and graded graded rhythmites rhythmites (Aigner, and (Aigner, 1985; 1985;Einsele, Eisele, 1992). 1992). Since Sinceonly onlythe thelargest largeststorms stormscan canaffect affectthe the mud deposition. quiescence and mud deposition. storm events events are are followed followed by long long periods of quiescence sea floor in this zone, storm Paleogeographic interpretation interpretation Paleogeographic The following following discussion discussion has divided into into three three sections. sections. Each The has been been divided Eachdeals deals with with interpreting interpreting the vertical and lateral facies trends comprising the basal transgressive, middle regressive and upper upper the vertical and lateral facies trends comprising the basal transgressive, middle regressive and transgressive depositional cycles of the Gunflint Formation in detail. transgressive depositional cycles of the Gunflit Formation in detail. �Kakaheka Conglomerate Conglomerate ,tidal roB Figure 9. Figure 9. Paleogeographic reconstruction reconstruction of of the thedepositional depositional system system which which produced produced the Gunflint Formation. Formation. AAdetailed attributes of this this system system isispresented presented detaileddiscussion discussionof of the the attributes Gunflint -in &the iB &L text. - ?UOPtE �Basal transgression Basal transgression extends from from the the base base of ofthe theAnimikie Animikie Group Group to to the the This 20 m thick, upward fining cycle extends middle of base of the cycle a middle of member member 2. 2. The base cycle is is characterized characterized by the Kakabeka Conglomerate, a backshore, pebbly pebbly beach beach deposit deposit preserved preserved as as aa transgressive pebble lag lag (Figure This backshore, transgressive pebble (Figure 9). 9). This intraformational conglomerate conglomeratewas was formed formedby bythe the localized localizedweathering weatheringof ofthe thepeneplain. peneplain. Then, intraformational tirough subsequent intraclasts were reworked reworked (swash/backwash) these these intraclasts through subsequentstorm-generated storm-generatedwave waveaction action(swashlbackwash) crudely stratified, tidal, beach beach deposits. deposits. Ojakangas into crudely stratified, matrix supported, supported, pebbly, supra tidal, Ojakangas (1983) (1983) has similar interpretation conglomeratic unit forming the the base base of of the the Pokegama Pokegama quartzite quartzite made a similar interpretation of the conglomeratic Mesabi iron range in the Mesabi range in east-central Minnesota. Minnesota. As the basal transgression progressed these coarse beachface beachface sediments sediments were were on-lapped on-lapped by by the fineparallel laminated laminated grainstones grainstones(GP (GP facies) facies) of of member member 1. The the fine- and and medium-grained, medium-grained, parallel 1. The hematite-enriched transition from member I may indicate a change in the redox state of of the hematite-enriched transition from member 1 may indicate a change in the redox state the depositional system level or, or, more more simply, simply,ititmay mayrepresent representoxidation oxidationof of depositional system accompanying accompanying a rise in sea level iron-bearing sediments by late phase oxygen-rich meteoric waters percolating along this lithologic sediments meteoric waters percolating along this lithologic boundary. Deposition boundary. Deposition of of this this thin, thin, parallel parallel bedded bedded grainstone unit marks the onset of intertidal intertidal sedimentation on the the foreshore foreshore (Figure (Figure 9). 9). Member Member l's m) and and apparent apparent lack lack of of sedimentation 1'srelative relative thinness thinness (5 m) desiccation features features suggests suggests that that the the intertidal zone was was not well developed Animikie desiccation intertidal zone developed on the Animikie (tidal range range <2 <2 m) m) (Reineck (Reineck and and shoreline, a situation typical of modem, microtidal environments (tidal Singh, may have have developed developed LLHstromatolitic stromatoliticbioherms bioherms(Ad (Ad facies) facies)at at the base of member 1 may Singh, 1975). 1975). LLH modem, colunmar in much the same way modem, columnarstromatolites stromatolitesand and crypt crypt algal algal knolls knolls form form in the low energy Here columnar intertidal flats flats of intertidal of Shark Shark Bay, Bay, Australia Australia (Hoffman, (Hoffinan, 1976; 1976; Schreiber, Schreiber, 1986). 1986). Here columnar stromatolites develop in the lower intertidal zone in response response to to strong strong wave wave action. action. An oncolitic stromatolites oncolitic mats marks the the transition transition into into the the subtidal subtidal (Figure (Figure horizon (Ao facies) facies) above these intertidal, algal mats Ginsburg (1960) (1960) compared compared modem modern 9) (1 (Logan al.,1964; 1964; Ginsburg, Ginsburg, 1960, 1960, Sellwood, Sellwood, 1986). 1986). Ginsburg ogan et aT, oncolites from Devonian, Permian and Precambrian Precambrian examples examples and oncolites from the the Florida Florida and and Bahama Bahama Banks to Devonian, found they formed I1 to or near near the the subtidal subtidaltransition. transition. Oncolites to 88 feet below mean water level at or from the Paris Paris Basin, Basin, aa non-barred, non-barred, shallow shallow epeiric epeiric sea sea covering covering much much of of northwestern northwestern Europe Europe during the Middle Jurassic, were also determined to characterize this transition (Seliwood, Middle Jurassic, were also determined (Sellwood, 1986). 1986). The overlying flaser and wavy bedded grainstones(Gf, (Gf, Gw Gw facies) of bedded chert-carbonate chert-carbonate grainstones member 2 represents represents subtidal deposition on a shallow, shallow, storm stormenhanced, enhanced,non-barred non-barred shoreline shoreline (Figure (Figure member subtidal deposition 9). 9). Similar Similar Middle Middle and and Upper Upper Cambrian, Cambrian, cyclic, cyclic, peritidal, peritidal, carbonate, carbonate, tempestites tempestites compose compose the the Elbrook Virginia Appalachians Appalachians (Demicco, (Demicco, 1985, 1985, Koerschner Koerschner Elbrook and Conococheague ConococheagueFormations Formations in the Virginia This 1.6 and Read, 1989). krn thick thick carbonate carbonate sequence sequence formed formed on on the the Cambro-Ordivician Cambro-Ordivician 1989). This 1.6 km continental shelf; aggraded, rimmed, mature, passive passive continental continental margin margin (Koerschner (Koerschner and and Read, Read, continental shelf; an aggraded, 1989). Cycles thickness, possess possess aa sharp sharp basal basal transgressive transgressive 1989). Cyclestypically typically range range between between 11 and and 7 7m m in in thickness, surface, are overlain overlain by aa subtidal subtidal unit unit passing passing into into aa tidal tidal flat flat cap, and record regional changes changes in time (Koerschner and and Read, Read, 1989). 1989). Three types of cycles are sea level over very short intervals of time recognized, thin-based cycles. The been recognized, thin-basedcycles, cycles,thrombolitic-based thrombolitic-basedcycles, cycles,and and thick thick based based cycles. The latter latter has has been divided into three grainstone-based and and digitate-algal-bioherm-based,grainstone-based three subcycles, subcycles, those which are digitate-algal-bioherm-based, Ribbon-carbonate-basedcycles cyclesmost most closely closely resemble resemble member member 33 and ribbon-carbonate-based. and ribbon-carbonate-based. Ribbon-carbonate-based therefore will will be be the the only only cycle cycle fully fully reviewed reviewedin inthe thefollowing followingdiscussion. discussion. For Foraafull fulltreatment treatmentof of these cyclic, peritidal carbonates carbonates the reader is referred to Koerschner and Read (1989). �Ribbon-carbonate-based cycles are composed Ribbon-carbonate-based cycles composed of 11 to to 55 m m thick thick fining fining and andcoarsening coarsening upwards upwards sequences sequencesof of flaser flaserbedded beddedcoarse-grained coarse-grainedcarbonate carbonate grainstones/packstones grainstonedpackstones which are are comprised of wavy and lenticular bedded finer-grained pelletal carbonates and rare lime comprised wavy and lenticular bedded finer-grained pelletal carbonates rare lime conglomerates dolomitic mudstones. The conglomeratesintimately intimately interbedded interbedded with with parallel laminated dolomitic The term term comes comes from the field appearance ofthe alternating thin-beds (ribbons) of differentially weathered limestone from the field appearanceofthe alternatingthin-beds (ribbons) of differentially weathered limestone and are and dolostone dolostone (Demicco, (Demicco, 1983). 1983). The Thecoarse-grained coarse-grainedribbon ribboncarbonates carbonatesand and pellet pellet packstones packstones are most similar to the flaser bedded, chert-carbonate grainstones (Of facies) of member 3 in the similar to the flaser bedded, chert-carbonate grainstones (Gf facies) of member 3 Gunflint Gunflintchemical chemicalsedimentary sedimentarysuccession. succession.Coarse-grained Coarse-grainedribbon ribboncarbonates carbonatesare areunlayered unlayered or or have have low-angle cross bedding with weakly graded foreset laminae. Pellet packstones have horizontal low-angle cross laminae. Pellet packstones horizontal laminations, ripple cross-lamination. cross-lamination. Mud-poor pelletlaminations,climbing climbingwave-ripple wave-ripple lamination and wave ripple rich ribbon ribbon carbonates carbonates and and mud-and-pellet mud-and-pellet rich ribbon ribbon sequences sequences most most closely closely resemble resemble wavy wavy bedded, bedded, chert-carbonate chert-carbonategrainstones grainstones(Gw (Gwfacies). facies). Mud-poor, Mud-poor, pellet-rich pellet-rich ribbon ribbon carbonates carbonatesare are planar laminated; pellet laminated;mud-and-pellet-rich mud-and-pellet-richribbon ribbonsequences sequencesare arecomprised comprisedofwavy of wavyand andlenticular lenticular bedded pellet layers interbedded interbedded with with form-discordant form-discordant wave ripples, ripples, starved ripples and and parallel parallel laminated laminated dolomite mudstones mudstones(Koerschner (Koerschnerand and Read, Read, 1989). 1989). dolomite Demicco Demicco (1983) (1983) and Koerschner Koerschner and Read (1989) (1989) interpret these ribbon sequences as recording storm-influenced subtidal settings floored floored by byinterlayered interlayered recordingshallowing shallowingby by aggradation aggradationfrom from storm-influenced Coarsening-upward lime muds muds and and sands, sands, to to subtidal subtidal sand sand flats flats on on aa mature, mature, rimmed rimmed shelf shelf. Coarsening-upward sequences sequencesrecord record low lowenergy, energy, subtidal subtidalconditions, conditions,followed followedby upward-shallowing upward-shallowinginto into high high energy energy shallow zone). Koerschner contend these these shallowwater water settings settings (ie. surf zone and breaker zone). Koerschner and Read (1989) contend coarse-grained coarse-grained ribbon ribbon carbonates carbonatesformed formed on on sand sand flats, flats, where coarse layers were reworked during storms and stormitidalenergy energy waned. waned. The rare lime lime and less less common common fine fine layers layerssettled settledout outasasstorm/tidal conglomerate conglomerate interbeds interbeds were deposited deposited during storms storms which swept semi-lithified, peloidal sands from transgressive from shallow shallowsubtidal subtidaland and intertidal intertidal settings. settings. Fining Finingupwards upwards ribbon ribbon sequences sequences record transgressive high-energy conditions that gave way way to low energy energy conditions conditionsas asthe theplatform platform shallowed. shallowed. Finegrained response grained peletal, peletal, ribbon ribbon carbonates carbonatesformed formed on lower energy, subtidal, mixed sand flats in response to wave wave action action and and grade gradelandward landward into into mixed mixed sand-mud sand-mud flats flats (Koerschner (Koerschner and Read, 1989). 1989). Fairweather with deposition of of thick thick storm layers of Fairweather reworking of wave rippled beds alternated with pelletal pelletal sediment sedimentwith withamalgamated amalgamatedhurnmocky hummocky cross cross stratification, stratification, and wave and current ripples (Koerschner (Koerschnerand and Read, Read, 1989). 1989).Similar Similarclastic, clastic,shallow, shallow,tidal tidal marine marine sequences sequences occur occur in the modem North Sea (Demicco, 1983). North Sea (Demicco, 1983). Unlike wavy Unlike the the Cambrian Cambrian ribbon ribbon carbonates carbonatesof the Virginia Appalachians these flaser and wavy bedded bedded chemical chemicalsediments sedimentsdid didnot notform formby by aggradation aggradationof of upward upward shoaling shoaling grainstone grainstonesequences. sequences. Instead, vertical changes reflect a rate of relative sea level level rise which which changes in iron formation facies reflect consistently consistently outpaced outpaced that that of of sedimentation. sedimentation. Middle regression regression Middle This extends to This minor, minor, 20 20 m m thick, regressive regressive phase begins in the middle of member 2 and extends 3. It records the gradual onset of shallowing from the middle shoreface to the the top top of of member member 3. the lower lower foreshore. foreshore. The Thesubtidal subtidalmixed mixedgrainstone-chemical grainstone-chemicalmud mud flats flats of member 2 coarsen upwards to packages) of flaser bedded chert-carbonate grainstones. grainstones. These to 33 m thick packages) These coarse coarse packages packages formed formed during duringregressive regressiveofflap offlapof oflower-middle lower-middleshoreface shorefacefacies faciesand, and,like likethe theflaser flaser bedded bedded package packageat atthe the base base of of this this member, member, represent represent dune dunedevelopment development in in the the surf surf zone zone of of the upper shoreface. shoreface. �As level continued continued to these flaser flaser and and wavy wavy bedded bedded chert-carbonate chert-carbonate grainstones As sea sea level to fall fall these grainstoneswere were transgressed by the coarser, higher energy, stromatolitic and oncolitic, chert-carbonate, transgressed by the coarser, higher energy, stromatolitic and oncolitic, chert-carbonate,grainstones grainstones of member member 3. 3. These Thesestorm stormenhanced, enhanced,crypt cryptalgal, algal, lower lower foreshore foreshoredeposits depositsmark mark the the regressive regressivepeak peak of of this middle cycle. Like the Gf facies chert-carbonate grainstones of member 2, those of this middle cycle. Like the Gf facies chert-carbonate grainstones of member 2, those comprising comprising member 3 3 also member also record record lunate lunate dune dunedevelopment developmenton onaasubtidal/lower subtidal/lowerintertidal intertidalchert-carbonate chert-carbonate grainstone flat. grainstone flat. The 6 6 cm cm thick, thick, Gi Gi facies grainstone bed bed at at the the base base of of member member 33 in in O'Connor O'Connor township township is is facies grainstone The interpreted as being a proximal tempestite deposited in this shallow, high energy environment. This interpreted as being a proximal tempestite deposited in this shallow, high energy environment. This coarse, storm storm generated lag is coarse, generated lag is thin, thin, possesses possesses aa base base which which appears appears to to erosively erosively scour scour the the flaser flaser bedded chert-carbonate 2, contains contains abundant abundant magnetitemagnetite- and and hematite-rich hematite-rich bedded chert-carbonate grainstones grainstones of of member member 2, rip ups ups and and pinches pinches laterally laterally towards rip towards Blake Blake township; township;all all are are characteristics characteristicsof of nearshore nearshoresheet sheetstorm storm deposits (Einsele, deposits (Einsele, 1992). 1992). With Withaareturn returnto tofairweather fairweatherconditions conditionsthis this storm stormbed bed provided provided an an ideal ideal substrate for stromatolites to colonize. ItIt was not easily easily reworked reworked by by normal normal shelf shelf currents currents substrate for stromatolites to colonize. was firm firm and and not (Fralick, 1988). was however however not not (Fralick, 1988). Development Developmentof of crypt crypt algal algal knolls knolls on on this this intraformational intraformational lag lag was widespread as they they colonized colonized only only the the most most stable stableregions regions sheltered shelteredfrom from fairweather fairweatherreworking. reworking. widespread as The thin, thin, discontinuous, discontinuous, stromatolitic which developed developed above above this this basal, basal, crypt crypt The stromatoliticand and oncolitic oncolitichorizons horizons which algal layer layer suggests suggests subtidal, on aa substrate substrate that that underwent underwent periodic, periodic, algal subtidal, stromatolitic stromatolitic growth growth occurred occurred on fairweather reworking. reworking. The LLH and and SS SS fairweather The development development of of these these poorly poorly formed, formed, discontinuous discontinuous LLH stromatolitic on shallow, shallow, high high energy, energy, subtidal subtidal sand sand sheets sheets stromatolitic bioherms biohermsis is typical typical of of crypt crypt algal algal growth growth on of the the upper upper shoreface (Pratt et et a al., of shoreface and and lower lower foreshore foreshore (Pratt !., 1992). 1992). Upper transgression transgression possibly The upper transgressive member 3, through through member member 5, The upper transgressivecycle cycleextends extendsfrom fromthe thetop top of of member 5, possibly to the top of the Rove Formation; Formation; a vertical distance of almost 700 m. m. Its onset is rapid and Its onset is rapid and records records the those of of the the lower lower shoreface. shoreface. The the progressive progressive onlap onlap of of offshore offshore facies facies over over those The thin thin package package of of hummocky cross stratified chertand hematite-rich grainstones (GHCS facies) at the base of of hummocky cross stratified chert- and hematite-rich grainstones (GHCS facies) at the base member 4 in O'Connor township marks this transition. Modern hummocky-cross-stratified sands member 4 in O'Connor township marks this transition. Modem hummocky-cross-stratified sands occur below wave base base on of storm dominated, shallow shallow marine marine occur below fairweather fairweather wave on the the lower lower shoreface shoreface of storm dominated, depositional systems transition to the the inner inner shelf shelf (Hamblin (Hamblin and and Walker, Walker, 1979; Dott and depositional systemsat ator or near near the the transition 1979; Dott and Binsele, 1992; Davis, Davis, 1992). The Bourgeois, 1982; 1982; Aigner, Aigner, 1985; 1985; Walker and Plint, 1992; Emsele, The parallel parallel bedded, hematite-rich, (Gp facies grainstone) to to which which this this basal basal bedded, hematite-rich,slaty slatyand and cherty chertyiron iron formation formationbeds beds (Gp facies grainstone) hummocky-cross-stratified unit of storm storm deposition deposition near near this this change change hummocky-cross-stratified unit grades grades are are also also characteristic characteristic of They are (Figure 9). 9). They are identical identical to to modern, modem, proximal proximal offshore, offshore, storm-sand storm-sand layers layers (proximal (proximal tempestites) and their their more distal equivalents, rhythmites (distal (distal tempestites) tempestites) (Reinick (Reinick and and tempestites) equivalents, graded rhythmites Singh, Aigner, 1985). these storm 1985). Like Likethe theparallel parallel bedded bedded chemical chemical sediments sediments these storm beds beds also also Singh, 1972; 1972; Aigner, posses a sharp instances may may grade grade upward upward into into plane planelaminated laminatedmud mud layers. layers. In In posses sharp base, and in some instances modern tempestites laminated rhythmites, rhythmites, in modem tempestitesthe the sand sandlayers layersare are either either evenly evenly laminated laminated or or are laminated in which which the lower lower laminae grade upwards upwards into into thinner thinner and and finer-grained finer-grained the laminae are thicker thicker and coarser-grained coarser-grainedand grade laminae (Reinick (Reinick and and Singh, 1972). marine, storm storm laminae 1972). They They are are the the result result of of deposition deposition from shallow marine, generated turbidity currents Finsele, 1992; generated currents (Reinick (Reinick and Singh, 1972; 1972; Walker, 1984; Einsele, 1992; Davis, 1992). 1992). The fine- and medium-grained chert- and hematite-rich hematite-rich grainstone grainstone beds beds comprising comprising this this member member represent episodic development of storm-generated, chemical sedimentary beds. Thicker, episodic development Thicker,graded, graded, coarser beds developed during the most severe storms. The hematite-rich slaty The hematite-rich slaty iron iron formation formation packages between fairweather sedimentation sedimentation on lower packages between storm-grainstones storm-grainstonesrepresents representsthe the return return to fairweather on the lower �Figure precipitation of iron-rich iron-rich sediments on ontheAnimikie theAnimikie shelf. shelf Figure10. 10. Depositional modelfor modelfor the theprecipitation The model is based on data from the Gunflint and Gogebic data collected collectedfrom Gogebic iron ranges. Samples from these areas were Samples from were examined examined in thin section section under under a petrographic petroeraphic - microscope and using aa scanning scanningelectron electronmicroscope microscope with an an energy dispersive dispersive systent rock analysis was also performed performed using an system. Whole Whole rock an inductively inductively coupled plasma. plasma. During Duringthe thePaleoproterozoic Paleoproterozoicthe theworld world ocean ocean contained much less oxygen than enabledFeu FC and thanatatpresent present(Cloud, (Cloud,1973). 1973). This enabled and MC Mnutotostay stayininsolution. solution. Oxygen present in appreciable quantities in the Oxygen would only be present the shallow, near shore environment environmentwhere wherereasonable reasonablelevels levelsof of light light penetration penetrationtotothe thebottom bottomwould would allow allow the cyanobacteria colonies in this area to thrive, and thus release oxygen (1). During the cyanobacteriacolonies in this area to and oxygen (1). During storm pressure system system over overthe the area area storm events events the the combined combined effects of an extreme low pressure and forcing caused the buildup of water in in aa strand-proximalposition. strand-proximal position. Upon and wave waveforcing Upon waning this water would be returned returned to the mid and and outer outer shelfvia shelf via waning of of the the storm storm event event this aa storm storm surge surgeebb ebbflow. flow. The Thedeliverance deliveranceof ofmore morehighly highlyoxygenated oxygenated waters waters to to the the deeper deeper shelf would would cause the the rapid rapid precipitation of iron iron oxide oxide (probably (probably as as iron iron hydroxyoxide) (2). At high high Fe/Mg FdWg ratios ratios itit isis likely likely that that precipitation precipitation of iron iron hydroxyoxide)(2). compounds during this rapid precipitation phase. phase. As oxygen and/or compoundswould would dominate dominate during this rapidprecipitation and/or iron iron is/are Mare depleted depleted precipitation precipitation rate slows slows and silica silica gel, gel, which which isis slowly slowly but but constantly from seawater, seawater, increases increases in in importance importance as as aa constituent constituent of of constantlyprecipitating from the phase due the layer. layer. Finally, Finally,with withdepletion depletionof of iron iron in in the the aqueous aqueousphase due to to precipitation, and a resu king decrease in Fe/Mg ratio, manganese anda resultingdecrease in the the FdWgratio, manganesebegins beginsto to effectively effectivelyscavenge oxygen forming MnO-rich Mn 0-rich tops some layers. layers. If another another storm occurs before oxygenforming tops to some storm event occurs the the Fe/Mg F e w ratio ratioof of seawater seawater has hasdecreased decreased to to the thepoint point manganese manganeseprecipitation precipitation becomes sign jficant the the upper upperportion portion of of the thelayer layer will willnot notform. form. Smaller Smaller storms storms are are becomes significant able precesses to operate in the mid-shelfarea, mid-shelf area, whereas ableto to cause causethe theabove aboveprecesses whereasonly only large large storms shelf Thus, storms effect effect the outer shelf. Thus,manganese manganeseconcentrations concentrationsare are much much higher higherin in rocksformed environment A) sequencefound rocksformed in inthe theouter outershelf-slope shelf-slope environment. A) Typical Typicalsequence found in in the mid-shelf (1cm) cm) chemical chemical sediment sediment laminae laminae directly directly overlay overlay storm mid-shelf where where thick thick (1 generated from the outer mid-shelf. mid-shelf C) B)Typical Typical laminae from C)Thin, Thin, generated granule granule lenses. lenses. B) complete laminae deposited in the outer helf complete laminae deposited helf. �- 1. Fairweather FairweatherPeriod Period - Stratified Stratified Water Water Body Body 02 02 020202 F' 02 — PC' — Mn PC' PC' PC' PC' Mn" -I- FC' 2. Storm - Destratitied Water Body 4 ÷+ PC' Fe' Fe" cmC cm 20 C.mm - mm -5 Ca fl • 'e3'•4 + 5102 Massive Fe304 Granular -o 1e304 2MnO Fe304 + Si02 Massive Fe304 0 Trough Trough Cross-Stratified Fine to Medium Grained Sand Grained - Ripple Laminated d and Massive Very FineS Fine Grained Sand to Coarse - Grained Grained Silt Silt Coarse - - Thinly to Thickly Laminated Mud �shoreface. storm layers lay directly shoreface. In In Blake Blake township township these chemical sedimentary storm directly on the the grainstones grainstonesof ofmember member2. 2. The The pulse pulse of of volcanism volcanism preserved preserved in in the the middle middle of member member 4 as a 6m thick volcaniclastic volcaniclastic horizon deposition. Its (Vsfacies) facies) occurred occurred swiftly, swiftly, outpacing iron formation deposition. Its sharp sharp bottom bottom contact contact horizon(Vs indicates indicatesrapid rapid influx influxof of volcaniclastic volcaniclasticmaterial material into into the depositional depositional system. Its Its gradational gradational upper contact waned gradually gradually over overtime. tuff contactsuggests suggestsdelivery delivery of of volcaniclastics volcaniclastics to the basin waned time. The The lapilli lapillituff (Vt reworked and deposited deposited (Vtfacies) facies)which whichcharacterizes characterizesthe thebase baseof ofmember member 55 is is interpreted interpreted as being reworked by by storms stormsfrom from more more proximal, proximal, nearshore nearshore settings. settings. The Themassive, massive,mediummedium-to tocoarse-grained coarse-grainedchertchertcarbonate grainstone bed (Gi facies) characterizing its base is similar to the (Gi facies) characterizing stromatolitic,storm storm carbonate grainstone stromatolitic, generated itslower lowerbounding boundingsurface surfaceisiserosive erosiveinto intothe thetop topof of member member44 and and itit also also generatedlag lagin inmember member3;3;its pinches laterally towards Blake Township. beds within the Gunflint pinches laterally towards Blake Township. Similar Similar volcaniclastic volcaniclastic beds Gunflint Formation Formation have have also alsobeen been interpreted interpreted by by Hassler Hassler and and Simonson Simonson(1989) (1989) as being being reworked reworked and and redeposited by turbidity currents. redeposited by turbidity currents. The The coarsening coarsening upwards, upwards, massive massive and andcross-stratified, cross-stratified, chert-carbonate, chert-carbonate, grainstone grainstone successions onlapof ofinner innershelf shelffacies facies over those of successions(Gc (Gcfacies) facies)of ofmember member55mark markthe theprogressive progressiveonlap the GHCS thelower lowershoreface shorefaceparallel parallel laminated laminated and and hummocky cross-stratified grainstones (Gp and GHCS facies) facies)(Figure (Figure9). 9).Similar Similarsuccessions successionsdeposited depositedinincoastal coastaland andopen openmarine marineenvironments environmentscomprise comprise the Sussex and and Shannon Shannon sandstones sandstones of the Powder Powder River River Basin Basin in in northern northern the Upper Upper Cretaceous, Cretaceous, Sussex Wyoming. Wyoming.InInWyoming Wyomingcycles cyclescoarsen coarsenfrom fromsilty siltyoffshore offshoremudstones, mudstones,through throughthin thin bedded, bedded, stormstormand and tide-generated tide-generated sandstones sandstones to to cross cross stratified stratified sandstones sandstones with with abundant abundant clay clay rip-ups. rip-ups. The The depositional depositionalmodel modelproposed proposedfor forthe theShannon Shannonand andSussex Sussexsandstones sandstonesconsists consistsof ofmigrating, migrating,offshore offshore bar Hobson barcomplexes complexesthat thathave havetheir theirsurfaces surfacescovered coveredby bysand sandwaves waves(Berg, (Berg,1975; 1975;Brenner, Brenner,1978; 1978;Hobson etetal., al.,1982; 1982;Davis, Davis, 1992). 1992).With Withsome somemodification modificationthis thismodel modelmay may also also be be applied applied to to the the coarsercoarsergrained, grained,shoaling shoalingupwards upwardssequences sequencescomprising comprisingmember member55 of of the the Gunflint GunflintFormation. Formation. Like Like bar bardevelopment development in inclastic clasticsystems systemsgenesis genesisof ofchemical chemicalsedimentary, sedimentary, offshore offshorebar bar complexes 2)the the complexesdepends dependson, on,1)1)the theavailability availabilityof ofcoarse coarsesediment sedimentto to offshore offshore environments environments and and 2) presence presenceof ofcurrents currentscapable capableof ofshaping shapingthis thissand sandinto intowell well defined, defined, migrating, migrating, sand sandbodies. bodies. In In elastic, clastic,shallow shallowmarine marinedepositional depositionalsystems systemscoarse coarsedetritus detritusisissupplied suppliedtotooffshore offshoreareas areasby bystorm storm Tillmanand andMartinson, Martinson,1984) 1984)and andtide tide(Spearing, (Spearing,1976; 1976;Brenner, Brenner,1978; 1978; (Berg,1975; 1975;Walker, Walker,1984; 1984;Tillman (Berg, Seeling, 1978) generated currents. However, unlike their clastic counterparts, bar genesis Seeling, 1978) generated currents. However, unlike their clastic counterparts, genesis in in chemical chemicalsedimentary sedimentarysystems systemsrelies relieson onoffshore offshoreprecipitation precipitation of of iron iron oxides oxides and and silica silica gel gel from from upwelled 1993),and andsubsequent subsequent upwelledenriched enrichedbottom bottomwaters waters(Borchert, (Borchert,1950; 1950;Drever, Drever,1974; 1974;Morris, Moms,1993), current currentreworking reworkingof ofthe thesubstrate substrateinto intorip-up rip-upgrains grains(Simonson (Simonsonand andGoode, Goode,1989) 1989)(Figure (Figure10). 10). Consequently this process does not depend on systems tracts capable of delivering coarse detritus Consequently this process does not depend on systems tracts capable of delivering coarse detritus to development in in a chemical sedimentary, tothe theshelf shelf.Bar Bar development a chemical sedimentary,shallow-marine shallow-marinedepositional depositionalsystem systemisis therefore governed by the position of areas on the shelf with high, primary chertlcarbonate therefore governed by the position of areas on the shelf with high, primary chert/carbonategrain grain production production and and the the presence presence of ofcurrents currentsable abletotorework reworkthese thesechemical chemical precipitates precipitates into into bar bar complexes. The relative stratigraphic position of member 5, over facies characteristic of the lower complexes. The relative stratigraphic position of member 5, over facies characteristic of the lower shoreface graingenesis genesis were were below below shoreface(Gp (Gpand andGHCS GHCSfacies), facies),suggests suggeststhat thatregions regionsofofprimary primarygrain fairweather wave base and that storm-generated, oscillatory flow was responsible for reworking fairweather wave base and that storm-generated,oscillatory flow was responsible for reworkingthe the substrate substrateinto intorip-up rip-upgrains. grains. Finer-grained, Finer-grained,shoaling shoalingupwards, upwards,chemical chemicalsedimentary sedimentarysuccessions successionsfrom fromthe theGogebic GogebicIron Iron Range in Wisconsin (Figure 11) (Pufahl, 1994) are identical to the coarsening upwards successions Range in Wisconsin (Figure 11) (Pufahl, 1994) are identical to the coarsening upwards successions �comprising comprising the Sussex Sussex and Shannon Shannon sandstones in Wyoming. They They are regarded regarded as as being being the distal equivalents equivalentsto to the the coarse coarse offshore offshore bars bars of of the the Gunflint Gunflint(Pufahl, (Pufahl, 1994). 1994). Cycles in Wisconsin Wisconsin coarsen from parallel laminated, magnetite-rich slaty iron formation in much much the the same same way way the the Cretaceous Cretaceous upwards shoaling shoaling cycles coarsen from shelf mudstones. 4 Sm.g 0*4. Dunes 400, 'S 4% 44. ) O4 Figure 11. Figure 11. Development Development oof f coarsening- and thickeningcoarseningthickening- upwards sequences in sequences in Wisconsin Wisconsinwere were related related to progradation of lunate dune offshoreprogradation dominated sand sand sheets. sheets. In a broad sense these offshore In offshore regions of primary grain genesis are similar to the "subtidal carbonate factories" factories" responsible responsible for for grain grain production production on on modem modem and some carbonate some ancient ancient carbonate carbonate platforms (James and Kendall, 1992). The upwards cycles cycles The coarse coarse nature of the Gunflint shoaling upwards suggests bar bar development developmentoccurred occurredatator or near near aa "grainstone "grainstone in Blake and O'Coimor O'Connor townships suggests factory. As with shoreline shoreline retreat retreat factory". Asthe thetransgression transgressionprogressed progressedthese thesefactories factoriesmigrated migrated in step with resulting in the deposition complexes further ftrther from regions of primary deposition of slightly finer-grained bar complexes production. The absence of of aa mud mud grain production. Theexistence existenceof of these these offshore offshore factories factories would account for the absence dominated offshore, offshore, which is so clastic shallow-marine shallow-marine depositional systems dominated so characteristic characteristic of of clastic (Walker and Plint, 1992). 1992). Alternatively, these coarsening upwards, upwards, GGc fades grainstone c facies grainstone successions successions may represent paracycle development (Vail et al., aL, 1977) in regions regions of high high primary primary grain grain genesis genesis during during relative relative sea level rise. Paracycles form in response to a punctuated rise in overall sea level. They record a Paracycles form in response sea level. period of rapid, relative sea level rise rise and still stand, followed by another another relative relative rise rise with with no no period followed by �significant that accumulates accumulates is is coarsening coarsening upwards, upwards, significantfall fall intervening intervening (Vail (Vail et aL, al.,1977). 1977). The sequence that suggestive of mediumsuggestive of continued continued shoaliñg shoaling as sediments sediments accumulate accumulate to sea level. In In this this scenario scenario the the medium-- as grained, chert-carbonate grainstonesatat the the base base of coarsening upward cycles would represent chert-carbonate grainstones grainstone deposition deposition during during rapid rapid sea level level rise as regions of primary primary grain grain genesis genesis migrated migrated shoreward. The coarse-grained tops of cycles would represent accumulation of grainstones shoreward. The coarse-grained tops of cycles would represent accumulation of grainstonesnear near to to base level where breaking waves were able to winnow the substrate during an interval of relative calm. At Atthe thepresent presenttime timedata dataisisinsufficient insufficient to to choose choose whether whether an autocyclic autocyclic (depositional) or allocyclic allocyclic (sea (sea level) level) mechanism mechanism governed governed cycle cycle genesis. - The transitional facies into the the The Gi Gi facies facies chert-carbonate chert-carbonategrainstone erainstonebeds which characterize transitional overlying Rove in Blake township are interpreted as representing deposition from suspension clouds overlying Rove in Blake township are interpreted representing suspension generated generated by either either storms storms or or tectonism tectonism during during basin subsidence. subsidence. OVERVIEW OVERVIEW OF OF THE THEANIMIKIE ANIMIKIEBASIN BASIN The iron-bearing iron-bearing rocks in Ontario and Minnesota Minnesota form form aachemical chemicalsedimentary sedimentary wedge wedge which which fines fines and and thickens thickens from from coarse, coarse, wave wave reworked, reworked, nearshore deposits of the Gunflint Formation to offshore, offshore, parallel-laminated, chemical mudstones of the Trommald iron formation in east-central Minnesota. to those those observed observed in in Minnesota. Lateral Lateral and and vertical vertical facies facies transitions transitions are directly comparable to modem They record modem shallow shallow marine marine clastic clastic and and carbonate carbonate depositional depositional systems. systems. They record energy energy transformations nearshore, shoaling shoaling waves waves under under fairweather fairweather and transformationsfrom fromdeep deepwater, water, offshore offshorewaves waves to nearshore, storm storm conditions. conditions.Paleocurrent Paleocurrentdata datasuggests suggestsdeposition depositionof of chemical chemical sedimentary sedimentaryrocks rocks occurred occurred on on a southward southward facing facing paleoslope. paleoslope. Nearshore rocks consist Nearshore chemical chemical sedimentary sedimentary rocks consist of of successions successions of ofstrand-proximal strand-proximal stromatolites, flaser and wavy and parallel parallel bedded stromatolites, flaser wavy bedded bedded chert-carbonate chert-carbonate grainstones, grainstones, and bedded and hummocky non-barred, microtidal, microtidal, hummocky cross cross stratified stratified hematite-rich cherty grainstones deposited on aa non-barred, storm-enhanced storm-enhancedshoreline shorelinewith with little little clastic clastic influx. Deposition Depositionon on the the inner shelf was dominated by accumulation accumulationof of coarse-grained, coarse-grained,shoaling shoalingupwards, upwards, chert-carbonate chert-carbonategrainstone grainstone successions, successions,possibly possibly associated with offshore bar development. development. Their Their genesis is believed to have been the result of a unique physiological conditions Animikie unique interplay interplaybetween betweenthe the chemical chemicaland and physiological conditionswhich which prevailed prevailed in in the Animikie Basin Basin during during iron iron formation formation deposition. deposition. They Theyformed formedin in proximal proximal offshore offshore areas areas where iron oxide and precipitating, and precipitates into and silica silicagel gel were actively precipitating, and where currents could rework chemical precipitates into rip-up grains grains and redistribute redistribute them. The Theshoaling shoalingupwards upwards successions successions replace replace a mud dominated offshore, offshore, which which is is so so characteristic characteristicof of modern modem shallow-marine shallow-marine depositional depositional systems. systems. Distally, finer-grained and less lesswell welldeveloped. developed. They They Distally, coarsening coarsening upwards upwards sequences sequencesbecome become finer-grained coarsen medium-grained, massive massive and and coarsen from from parallel parallel laminated, laminated, magnetite-rich chemical slates to medium-grained, cross offshore crossstratified, stratified,chert-carbonate chert-carbonategrainstones, grainstones,and andare areinterpreted interpretedas as recording recording progradation of offshore bar complexes of high high primary primary complexeson on the the middle middle shelf shelf below below fairweather fairweather wave base, away from areas of grain paracycledevelopment developmentduring during an an overall overall rise rise grain genesis. genesis. These Thesesuccessions successionsmay mayalso alsorepresent representparacycle in in relative relative sea sealevel. level. Monotonously parallel and slatescharacterize characterizedeposition deposition Monotonouslyinterbedded interbeddedparallel and wavy wavy bedded chemical slates of of iron iron formation formation on on the the outer outer shelf shelfand and slope-break. slope-break. The Thepresence presence of ofrare, rare, massive massive and and cross cross �stratified, magnetite-rich slaty slaty laminations laminations indicates indicates that that stratified, chert-carbonate chert-carbonate grainstones grainstones and graded, magnetite-rich storm-generated storm-generatedturbidity turbiditycurrents currentsoriginating originatingon onthe theinner innershelf, shelf,where where grain grain production productiontook tookplace, place, were for moving moving sediment sediment onto ontothe thedistal distalshelf. shelf The were an an important important mechanism for The existence existenceof of iron iron formation 1963) in in the the Cuyuna Cuyunanorth north range suggests that mass mass flow flow processes processes formation breccia breccia (Schmidt, (Schmidt, 1963) generated the distal distal shelf shelf were important generatedby by large-scale large-scalerotational rotationalslumping slumpingand and sliding sliding on the important in moving sediment sediment from from the the slope slope to to the the rise. rise. Sedimentological Sedimentologicaland andstratigraphic stratigraphicdata datado do not not provide provide definitive definitiveanswers answers to to the the question question of of plate plate tectonic tectonic setting settingof of the the Animikie Animikie Basin. However, However,paleogeographic paleogeographicreconstructions reconstructionsbased based on vertical vertical and and lateral lateral facies facies transitions transitions present within the Gunflint, Gunflint, Biwabik, and Trommald iron formations, and clastic units above and below strata indicate indicate that that it is is doubtful doubtful formations, and below iron-bearing iron-bearing strata deposition migrating peripheral depositionof ofthe theAnimikie AnimikieGroup Groupoccurred occurredwithin withinaamigrating peripheral foreland foreland basin basin (Figure (Figure 12). 12). There There is is an an apparent apparentlack lackof ofcoarse coarseturbiditic, turbiditic, deltaic, deltaic, and and fluvial fluvial sediments, adjacent to the fold thrust thrustbelt, belt, and and paleocurrent paleocurrentdata data from from clastic clastic and chemical sedimentary rocks are are opposite opposite to what should formation was shouldbe be observed observed if if deposition deposition took took place in a foreland basin. Also, Also, if if iron iron formation was to have accumulated accumulated in aa foreland foreland setting setting it it should should be be restricted restricted to the distal distal shelf shelf as as weathering weathering of the peripheral peripheralbulge bulgewould wouldshed shedclastics clasticsinto intonearshore nearshoreregions regionseffectively effectivelypreventing preventingdeposition depositionof ofiron iron formation. formation. Facies Faciestransitions transitionswithin withiniron-bearing iron-bearingmembers membersindicate indicatethe the contrary, contrary, a complete complete shelf shelf sequence, sequence, not not just just the the distal distalportion portionis ispresent. present. Although Animikie Basin Basin in Although data datais is insufficient insufficient to to reconstruct reconstruct the the tectonic tectonic evolution evolution of the Animikie detail, detail,some somegeneral generalinferences inferencesregarding regarding the the depositional depositionalhistory history of of the the Paleoproterozoic Paleoproterowic strata stratain in Ontario Ontarioand and Minnesota Minnesotacan canbe be made. made. Sedimentation Sedimentationwithin withinthe thebasin basinbegan beganwith withan anoverall overallmarine marine transgression the transgressiononto ontothe thesouthern southernmargin marginof ofthe the peneplained peneplainedSuperior Superior province province and deposition deposition of the Pokegama Mahnomen Formation. Formation. The PokegamaQuartzite Quartzite and and Mahnomen ThePokegama PokegamaQuartzite Quartziteaccumulated accumulated in in nearshore, tidally tidally influenced influencedsettings settingswhile whilethe theMahnomen Mahnomen Formation Formation was deposited deposited simultaneously in more distal shelf regions by pelagic settling and waning turbidity currents. This clastic deposition deposition distal shelf regions by pelagic settling turbidity This phase of clastic was probably associated with the early history of basin development. Through time, the continuing was probably associated with the Through continuing erosion erosionof of the the source sourceterrain terrainresulted resultedin in aa reduction reduction of of clastic clastic supply supply to to the the basin, basin, to to aa point pointwhere where iron iron formation formation began to accumulate accumulate on the the shelf, shelf, away away from from the the land-derived land-derived clastics clastics still still accumulating iron formation formation was accumulatingin inthe thenearshore. nearshore.Once Oncethe thehighland highlandwas wasreduced reducedto to near near base base level level iron then then able ableto to accumulate accumulatein inthe thenearshore, nearshore, and anddirectly directlyonlap onlapthe the Superior Superiorprovince. province. Deposition Deposition of of iron ironformation formation occurred occurred during during an anoverall overalltransgressive transgressive marine marine event event punctuated punctuatedby by two twominor minorregressions. regressions.Lateral Lateralfacies faciestransitions transitionswithin withiniron-bearing iron-bearingunits unitsrecord recordaa complete reworked nearshore nearshore deposits deposits completeshelf shelfsequence sequencewhich which fines finesand and thickens thickens from from coarse, coarse, wave wave reworked to the distal distal shelf. shelf. The to parallel-laminated parallel-laminated chemical chemical mudstones mudstones of of the The existence existence of of minor minor mafic mafic flows flows and three volcaniclastic volcaniclastic horizons horizons in in the the and tuffaceous tuffaceous horizons horizons in in the the Gunflint, Gunflint, and andthe thepresence presence of of three Ounflint Gunflintand andMesabi Mesabiiron ironranges rangesindicate indicatethat that the the region region was was volcanically active active during during subsidence subsidence in in this this phase phaseof of basin basin development. development.The Thethickest thickestvolcaniclastic volcaniclastichorizon horizonforms formsthe thebase baseof ofthe theRove, Rove, Virginia, Virginia, and and Rabbit Rabbit Lake Lake Formations, Formations, and and marks marks the the transition transition from from chemical chemical to to clastic clastic sedimentation. sedimentation.This Thisvolcanic volcanicepisode episodestopped stoppediron ironformation formationgenesis genesisby bychoking chokingthe thedepositional depositional system with volcaniclastics. As relative sea level continued to rise deposition within system with volcaniclastics. As relative sea level continued to rise deposition within the the Animikie Animikie Basin Basin was wasdominated dominatedby byaccumulation accumulationof of clastics clasticsderived derived from from the the north north by by southward southward flowing flowing turbidity turbiditycurrents. currents. �Figure asaamigrating migratingperipheral peripheralforeland basin. Arguments Figure 12. 12. The TheAnimikie Animikie Basin Basin modelled modelled as foreland basin. against this tectonic interpretation are presented in the text. SOUTH SOUTH NORTH - - FOLD THRUST BELT FOLD - AND AND - THRUST BELT I FORELAND FORELAND BASIN I migrating to north PERIPHERAL PERIPHERAL BULGE • •iiui sediment sediment eroded eroded from from fold fold -- and and thrust thrust belt belt mmmm — ---- Â¥I - fluvio deltaic flu I sedts .N sediment eroded eroded from sediment from peripheral bulge N SUPERIOR PRO VINCE nearshore clastics ff011 formation and coarse turbidites 0 20km 10 I I I �FIELD TRIP FIELD T R I P STOPS STOPS ITINERARY ITINERARY Stop 11 Stop Stop 22 Stop Stop 33 Stop Stop 44 Stop Stop S5 Stop Stop Stop 66 Stop 77 Stop Stop 88 stop Stop 99 Stop Stop 10 Stop 10 Stop Stop11 11 Stop 12 Stop 12 V V V V V V V V V V V V V V V V V V V V VV V V V V V Basal stromatolites; Nolalu Nolalu turnoff turnoff Basal unconformity, unconformity, stromatolites; Basal unconformity, unconformity, stromatolites; stromatolites; Kaministikwia Kaministikwia Riven Riverr Basal TufTs,volcaniclastic volcaniclastic sediments; sediments; Kakabeka Kakabeka Falls Tuffs, Falls Ribbon chert-carbonate; chert-carbonate; Kakabeka Kakabeka Falls Falls Ribbon Basal Basal pebbly pebbly sandstone; sandstone; Oliver Oliver Road Road Stromatolites, beachrock; beachrock; Rupert Rupert Street Stmmatolites, Collapse breccia; breccia; base basc of High Street Park Collapse of High Street Park Grainstones, stromatolites; Current River Slumped ribbon ribbon chert-carbonate; chert-carbonate; road road to to Pass Pass Lake Lake Slumped Rippled Rippled siltstones; siltstones; Transcanada Transcanada Highway Highway Grainstones with volcanic volcanic sherds; sherds; Terry Teriy Fox Fox Lookout Lookout Grainstones with Grainstones; Transcanada Transcanada Highway Highway near near Current Cunent River Grainstones; River V V V V pa Thunder V o 00 V Bay 000 0 hwy. 1h17 ÷ g —- Lake Superior LEGEND ARCHEAN PROTER OZOIC PROTEROZOIC km km V V 111 0 0 V V V 'I ++ V V V 5 5 Rove Rove Formation Formation Eorniation Gunflint Formation 10 0021 Gunflint Figure 13. Geology Geology of the Thunder ThunderBay Bay area. area Figure 13. Rocks ~ ~ +1 ~ Granitic a ? i Rocks + i c I ~olcanics IV V VJ Volcanics �STOP STOP 11 Proceed west weston onHighway Highway 11/17 11/17(the (the Transcanada) Transcanada) (Figure 13)past Kakabeka Falls and over the Kaministikwia Kaministikwia River. A A few few hundred metres metres past this bridge there is a turn off to Nolalu. Take outcrop Takeitit and and proceed proceed approximately approximately100 100metres, the main outcrop is is on on the the right. right. Chemical Archean granitoids granitoids at Chemical sediments sedimentsof of the Gunflint Gunflint Formation rest directly on Archean this location. This thin conglomeratic conglomeratic Thishighlights highlightsthe the sporadic sporadicdevelopment development ooff the the thin veneer comprising the Kakabeka Conglomerate Conglomerate in inthis thisarea. area. Stromatolites, Stromatolites, including including veneer comprising some these basal basal cherty cherty carbonates. carbonates. The some large forms, are developed in these The stromatolitic stromatoliti; ribbon carbonates carbonates are are abruptly abruptly overlain overlain by aa grainstone grainstone succession. succession. STOP STOP22 Proceed Proceed back to to the the Transcanada Transcanada Highway turn right and cross the Kaministiquia Bridge. Turn park to to end end of Turnleft lefton onroad road immediately immediately after after bridge bridge and drive through park road. road .AApath pathleads leadstotothe thefirst firstset setofofrapids rapidsabove abovethe the bridge. bridge. The The rapids rapids are are formed by Archean granitoids. The The slow-water slow-waterarea area to to the the south southisis underlain Gunflint Formation. Formation. River Riverlevel level will will govern govern what can can be observed observed underlain by the Gunflint at at this this stop. stop. The Kakabeka Kakabeka Conglomerate Conglomerate is patchily developed overlying the Archean Archean at at this stop. stop. Silicified Silicifiedstromatolites stromatolitesare aredeveloped developedon on the the Conglomerate Conglomerateor or directly directly on on the granitic granitic basement. This Thisisis the the location location from from which samples collected in cyanobacteria described in in the theliterature. literature. The in the 1950's 1950's yielded the first Gunflint cyanobacteriadescribed samples samples were were from from the the silicified silicified stromatolites stromatolites and were described by Tyler and and Barghoom (1954). (1954). Barghoorn STOP STOP33 Proceed back to the Transcanada Highway Highway and andturn turn left. left. Turn Turn right right into into the the main main park entrance entrance and and park in in the parking lot. Walk Walkto tothe theobservation observationplatform. platform. The The river river gorge gorge is is composed composed of of aa sequence sequence of of volcaniclastic volcaniclastic shales shales (less (less resistant, darker darker units) units) and and tuffs tuffs (more (moreresistant, resistant, lighter lighter coloured coloured units). units). This sequence sequence represents the ma] or volcaniclastic horizon present in the upper Gunflint Formation represents the major volcaniclastic horizon present the upper Formation and and is is traceable traceable to to the thesouth souththrough throughthe theMesabi MesabiRange. Range. Basalts outcropping outcropping approximately probably correlatable this unit. approximately30 30kilometres kilometresto tothe the southwest southwestare are probably correlatablewith withthisunit. Unpublished Unpublishedgeochemistry geochemistry(major, (major,trace, trace, REE REEanalysis) analysis)performed performedon onsamples samplesof of the the basalt basalt indicate indicate aa tholeiitic tholeiiticcomposition composition with a deep deep mantle source source (plume). STOP STOP44 Walk Walk back back to to the the southeast southeastside sideof ofthe the parking parking lot. lot. An forms this this cut. cut. Folds An outcrop outcrop of of ribbon ribbon chert-carbonate (ankerite) forms Folds and faults faults are present deformation. Commonly, present and and probably probably represent soft sediment deformation. Commonly, past studies studies of of the the Gunflint GunflintFormation Formationhave havedescribed describedthis thistype typeof ofsediment sedimentas asforming formingin inaadeep, deep, quiet quiet water water environment environment and and this this may may be becorrect. correct. However, similar carbonate carbonate sequences intertidal or or lagoonal lagoonal subtidal subtidal sequences are often often attributed attributed to deposition deposition in intertidal environments. environments.The Theevidence evidencesupporting supportingaadeep deepor or aa shallow shallow setting setting will be discussed at at this thisstop. stop. �a tS-s -:. - 4 ., - . -A ..r!'efl j _ Figure wave rip-up rip-up Figure 14. 14. Stop Ston6. 6.A) A)Intraformational Intraformationalbeachrock beachrockconglomerate conglomerateformed by by storm wave of partially partially cemented cementedsurficial surficial layers layers of of medium-grained medium-grainedsand sandin in the the upper upper beach beach of environment B) stromatolites with withmedium-grained medium-grainedan and B)Plan-view Plan-viewof of cabbage-sized cabbage-sizedstromatolites environment. granule sand sand layers layers banked bankedup upagainst againstthem. thea granule 1 �STOP STOP 55 Turn right onto the Transcanada and turn left onto Oliver Road. Turn Turn left on Turn Transcanada and Road and and right right on on Dawson DawsonRoad. Road. Drive 7.4 km km to to aa small small dirt dirt pull pull off off Mapleward Road on the left and park. Walk down the path for a few minutes until you see a small, Walk down rounded outcrop. belonging to to the the Kakabeka Kakabeka Conglomerate. Conglomerate. It This is an outcrop of pebbly sandstone belonging overlies Archean granitic rocks and represents gris (angular, granitic debris), probably probably @tic debris), overlies Archean granitic rocks and represents surrounding basement. weathered from surroundiig STOP 66 STOP Turn left left on Dawson Turn right right on the Turn Dawson Road Road and and proceed proceed to to Thunder Thunder Bay. Bay. Turn onthe Oliver Road. Road. Continue down Oliver Road Turn right right at at Hill Hill Transcanada and left on Oliver the comer corner with with Queen Queen Street. Street. This Street and stop at the This is private property so stay on the outcrop. outcrop. the base base of of the the This is a no hammer stop. The The middle middle stromatolitic stromatolitic unit forming the the Gunflint Gunflint Formation Formationoutcrops outcropsatatthis thislocation. location. The carbonate upper member of the stromatolites are excellently preserved and are visible visible in in both both cross-section cross-section and and plan plan stromatolites forms Carbonate sands sands are are banked up against the cabbage-sized forms view (Figure 14). Carbonate and eventually eventually overwhelm overwhelmthem. them. The stromatolites established themselves themselveson on aa and stromatolites established silicified horizon horizon which at other other locations locationsshows showsevidence evidenceof ofsubaerial subaerialexuosure. exposure.This This silicified provided the necessary hard substrate substrate to to allow allowthe thestromatolites stromatolitesto todevelop. develop. The unit providedthe maj or stromatolitic horizon is overlain by beachrock which has been disrupted by a major stromatolites have been been ripped ripped up up along along with with storm event. Pieces Pieces of of the underlying stromatolites overlying partially cemented carbonate sands. The beachrock formed in inthe theupper upper the overlying beach environment beach environment due to salt salt spray spray from from breaking breaking waves waves depositing depositing meniscus meniscus cements at grain grain contacts contacts of the sand. This partially cemented cements This partially cemented sand sand layer layer on the upper disrupted into slabs when when a large storm caused waves waves to to break in this tbis beach was dismpted environment. environment. STOP STOP 77 Proceed back back to to Oliver Oliver Road. Road. Turn right. Turn the Turn left left on Crown Street (at the junction with near where where it bends bends right right and and &s turns into into Dixon Dixon junction with John John Street) Street)and and drive drive to ;ear Street. Drive one block northwest on a small lane to the base of the High Street Park Drive one block northwest to the base of the High Street Park hill. outcrop forming forming the base of the hill bill is composed composed of carbonate carbonate breccia breccia with with some The outcrop chert clasts. Wavy laminated dripstone forms discontinuous layers blanketing some Wavy laminated dripstone discontinuous of the the roof roof of a of the breccia piles. This Thisisisaacollapse collapse breccia breccia formed by failure of cavern in the ankerite. A number of failures occurred as denoted by the the ankerite. A number of failures occurred as denoted by cavern which were were deposited depositedon ondebris debrispiles pileson onthe thecavern cavernfloor floor interlaminated dripstones, which by roof leakage. This Thisunit unit forms forms the the upper layer of the Gunflint Formation's lower correlatable with with STOP STOP 6. 6. Maximum Maximum member and is often overlain by stromatolites comelatable regression of the Animikie sea occurs at this internal interval leading to to subaerial subaerial exposure exposure Gunflint sediments sediments in the the Thunder ThunderBay Bayregion. region.Evidence Evidenceof ofsubaerial subaerialexposure exposurehas has of Gunflint not been obserned observed in drill core examined from south of the U.S. border. �A) Sills jfied stromatolitic stromatolitic reef reef overlain ales Figure 8.8. A) Siliszjied overlain by by black blackvolcaniclastic volcanicIasticsit shales Figure I15. S . Stop Sto~ (background). plane of ankeritic grainstones. grainstones. -' B) -' Hummocky Hummoc'- bedding ' ?ddingplane of ankeritic �STOP 8 Drive turn left. left. Proceed to its end and andturn turnleft leftonto onto Cumberland. Cumberland. Drive to Oliver Road and turn Continue River. Turn Continue driving driving on on Cumberland Cumberland to to Current Current Ever. Turnleft left onto onto Arundel Arundel Street Streetand and proceed to the cement bridge across the Current Rver. River. Immediately Immediately before crossing crossing the onto Lyon Blvd. Pull to the right into one of the the parking parking m the bridge bridge turn turnleft onto Pull off offto as. areas. Walk to the river then then down down river river to to the the end end of of the the outcrop. outcrop. You are standing on the Paleoproterowic Paleoproterozoic sea sea floor. floor. The The uneven topography of the ankerite ankerite grainstones grainstones reflects reflects the presence of dunes and hummocks produced by the storm which moved moved thi the carbonate sands over over the the bottom 15). carbonate sands bottok (Figure (~igure-15). storm events events which Silicified dot this this irregular irregularseascape. seascape. This forms forms the the lower lower Silicified colonies of stromatolites dot unit of of a tripartite assemblage. Large Large silicified silicifiedstromatolites stmmatolites occur occur on the other side of directly overlying overlying these is aavolcaniclastic volcaniclastic silty silty shale. shale. A description description of the the bridge and directly of this this sequence sequence and and its itsinferred inferreddepositional depositional environment environment follows (taken from Fralick, 1989). Fralick, 1989). Major Major Subdivisions Subdivisions Coalesced domal stromatolites form the microbial bioherms bioherms present present in the outcrops outcrops on on Current underlain by by parallel parallel CurrentRiver. River. They Theyrepresent representaaportion portionof ofthe the upper upper stromatolitic stromatoliticzone and are underlain laminated complicated laminatedand and hummocky hummocky cross-stratified cross-stratified carbonate carbonate grainstone which has undergone a complicated history and dolomitizition-ankeritizition. dolomitization-ankeritization. The bioherms history of of silicification, silicification, neomorphic neomorphic spar growth and are are draped draped by by graded, graded, centimetre-scale centime&-scale beds beds of of dark grey siltstone siltstone and shale shale (Figure (Figure 16). 16). Carbonate Carbonate Grainstone Grainstone The grainstone grainstone is divisible divisible into into three three types: types: 1)1)hummocky hummocky cross-stratified; cross-stratifie4 2) parallel parallel laminated; 3) massive, massive, highly highly silicified. silicified.Flummocky Hummockycross-stratification cross-stratificationgenerally generally has has wavewavelaminated; and and 3) lengths, lengths,between between0.5 0.5 and and 11m. ItItcommonly commonlycontains containsoval oval and and rectangular rectangular rip-up rip-up clasts clasts which, which, when when abundant, abundant,fine fineupwards upwards in in individual individualbeds. beds. Often Oftensilicified silicifiedrip-ups rip-upsor or mixtures mixtures of of silicified silicified and and nonsilicified silicified rip-ups rip-ups are arepresent present in in non-silicified non-silicified beds. beds. Parallel they are less less abundant. The The Parallellaminated laminated grainstone grainstone also also contains rip-up clasts, but they appearance of these units is nodules. The is complicated complicated by the presence of silicified nodnles. Thegrainstone grainstone develops bend around around silicified silicified areas. areas. The compaction compaction developsaa wavy wavy lamination laminationwhere where the the parallel laminae bend deformed but can be deformed laminae laminae are similar similar in inappearance appearance to tohummocky hummocky cross-silicification, cross-silicification, but be distinguished distinguishedby by the thepresence presence of of low-angle low-angleerosive erosive truncations truncationsin in the latter. Silicification is very verycommon. common. One bed bed near near the the base base of of Silicificationof of layers layers and patches within layers is the silicification, culminating, culminating, at at its its top top in the measured measured section section exhibits exhibitsaa marked upward increase in silicification, aa layer layer of of massive massive chert. chert. Another Anotherhighly highlysilicified silicifiedzone zonedirectly directlyunderlies underlies the the stromatolite stromatolitebearing bearing horizon. horizon. Silicified Silicifiedlaminae laminaepresent presentin inother other beds beds have have sharp, sharp, flat top surfaces and sharp irregular bottom bottomsurfaces. surfaces.Water Waterescape escapestructures, structures,common commonthroughout thoughout the the hummocky hummocky cross-stratified cross-stratifiedunits, units, sometimes brittlelydeform deformthese thesesilicifled silicifiedlayers, layers, forming forming cross-cutting cross-cutting carbonate carbonate dikes dikes which rotate sometimesbrittlely plug-like, plug-like,angular angularchert chertblocks blocksto toone oneside. side. �Figure 16. of1 the stromatolitic sequence on Current Current Figure 16. Stratigraphic Stratigraphic sections sections at at varying vafying scales scales 0 the stromatolztzc sequence on River. LEGEND L EGEND I: m Limestone I 90 - Dolomite Dolomite ____ wavy Lamination Hum mocky Cross Cross -Hummocky Stratification Stratification El V / 1 I F / F F / I F F / F so - II, __________ Section A Intrabasinal lntrabasinal Rip—up Clasts Rip-up Clasts Escape Fluid Escape Fluid Structures structures 0 ARCHEAN BASEMENT SECTION B SECTION SECTION A SECTION m I F F Pyrite Lenses % Lenses ___ Pyrite .tr I / / / I / 1' / / 1 I I 1 / / II / I / / I F Hemispherical Hemispherical ___ .Stromatdi+es Stromatolites :° I I 60 - Chert Light/Dark Chert LightIDark e0 I / Parallel to rj Parallel Wavy Lamination Co I F = Interbedded flTInterbedded Siltstone and Siltstone and Shale Shale t1 ''I'll - — — — -JROVE FORMATION -- m m 12 — I--- . -- - - -- - - -I - 7' i/i .9 — 6 17 / ., '.-1 //I ,—. / •6 3 .3 0 0 A PAP SpA P A p PAPA PA P A P A ASASASSA AS P �Microbial Bioherms Bioherm The base of of the thebioherm biohem bearing bearing layers layers isiscomposed composed of ofparallel parallellaminated laminated carbonate carbonate containing isolated isolated centimetre centimetre to todecimetre-scale decimetre-scale (maximum (maximum grainstone, wavy silicified in patches, containiig 20cm 20 cmhigh high xx 50 50 cm cm wide) wide) domal domal stromatolites. stromatolites. They They represent represent the the SH-C/LLH-C SH-CLLH-C type of Logan et aL mounds. Some 01. (1964). Grainstone Grainstonelaminae laminae are are banked banked up against the sides of the microbial mounds. Some mounds are buried by the grainstone while others, after being partially covered, re-established by the grainstone while others, after being p d a l l y covered, re-established themselves. stromatolites begin themselves. The Theamount amountof ofgrainstone grainstonedecreases decreasesupward upward and and the cabbage sized stromatolites laterally merging. This trend resulted in the development of up to 1 m high, sometimes overlapping, This trend resulted in the development of up to 1mhigh, sometimes overlapping, microbial mounds scattered oover bottom. In v e ~the bottom. In areas areas where where early stromatolites stromatolites flourished raised platforms were built (up to 0.5 m above the surrounding bottom) on which large, coalescing. coalescing, domal domal platforms were built (up mounds grew, grew, giving giving aa total total relief reliefabove abovethe the adjacent adjacentarea area of of well well over over1I m. m. All stromatolites stromatolites have internal structures poorly preserved. presewed. have been extensively silicified silicified and internal structuresare are poorly Lamination in the strornatolites, when visible, is caused by the alternation of light and dark stromatolites, caused by the alternation of light and dark chert chert bands. bands. Pyrite layers and irregular blobs are present in the mounds, in places forming up to 20% of the rock. A A stratiform, stratifom,discontinuous discontinuouspyrite pyritelayer layeralso also drapes drapes some some mounds; the larger ones. Lenses Lenses in this unit attain attain thicknesses thicknesses up to to 10 I0 cm. Siliciclastics Siliciclastic, microbial biohems. bioherms. Centimetre-scale beds Siliciclastic, fine f i e grained Centimetre-scale graded graded beds -grained rocks drape the microbial comprising this comprising this unit unit are are internally internally composed composed of of alternating altemating matrix-rich and and matrix-poor, millimetremillimetrescale laminae. The angular qtmtz quartz Thematrix-rich matrix-richlayers layerscontain containfine fine grained, grained, sand-sized sand-sized clasts clasts of very angular and orthoclase containing orthoclase floating floating in aa matrix m&ix composed composed of 02very very fine finegrained graineddark darkmaterial mat-erial-cont&ng disseminated pyrite and 1I to 2% non-carbonate carbon. Matrix-poor layers are composed 2% non-carbonate Matrix-poor layers are composedof of very very (maximum size size 0.1 0.1 mm). mm). The The angular quartz, orthoclase, biotite and muscovite in clast support (maximum thinly bedded rocks are overlain by an indistinctly laminated unit which fills in hollows between thinly bedded rocks are overlain by an indistinctly laminated unit which fills in hollows between the the stromatolite stromatolite mounds. mounds. It is aapoorly poorly sorted, sorted,matrix matrix supported supported silty silty shale shale with bedding bedding parallel muscovite flakes muscovite flakes up up to to 55 mm in length. Shallow, Shallow,saucer saucershaped shapedscours scoursoccur occur in in its its upper upper portion. portion. The scours carbonate grainstone laminae thick. The scours are overlain overlain by carbonate laminae up to 1 cm thick. The grainstone grainstone unit unit is is 10 10 cm in thickness and is interbedded with and overlain by well laminated silty shale similar to the silty similar to thickness and is interbedded lower lower unit. unit. DEPOSITIONAL ENVIRONMENT DEPOSITIONAL ENVIRONMENT AND HISTORY HISTORY Sta2e A -- Storm Dominated Sheq Stage Shelf The presence presence of hummocky hummocky cross-stratified cross-stratifiedcarbonate carbonate grainstone grainstone with with the the absence absence of of wavewaveripple weather wave-base wave-base ripple reworked reworkedtops topsindicates indicatesthat thatthe thesand sandblankets blankets were were deposited depositedbetween between fair fair weather and stom storm wave-base in arelatively a relatively silicicIastic-free siliciclastic-free environment environment (Figwe (Figure 17). The The carbonate, carbonate,or or its its precursor was likely precipitated, eroded and abraded in shallow water areas and transported into deeper water during storm events. Silicified Silicifiedrip-up rip-up clasts clasts and and crusts cmstsdenote denote that that silicification silicificationwas was syndepositional (as degree of silicification increasing towards the syndepositional (asproposed proposed by by Simonson, Simonson,1986); 1986);the the degree bed indicates indicates that that seawater seawater(sensu (sensulato) lato)was wasprobably probablythe thesilicieing siliciing agent. top of the bed �/ - ...: . , .. D. sediments present at Stop 8. Figure Figure17. 17. Developmentalphases DeveIopmentaIphasesofofthe theenvironment environmentrepresented represented by by sedimentspresent atS-. Each text. Each stage stage is is discussed discussed in in the the text. I �- Stare B - Stabilization Siii4fication of Stabilization and Siliczfication Stase of the Substrate If seawater seawater was the the agent agent causing causing alteration alteration of of the the carbonates carbonatesthen then silicification silicification should should increase with length of time the unit was positioned close to the water-sediment interface. increase with length of time the unit was positioned close to the water-sediment interface. This This scenario implies implies that that the the stromatolites formed by by alteration of scenario the massive massive chert chert underlying underlying the stromatolites formed alteration of carbonates during an interval of lowered deposition rate. This is best explained by increasing the carbonates during an interval of lowered deposition rate. This is best explained by increasing the water depth depth so so that that the the bottom bottom sinks sinks below below storm storm wave-base wave-base and and slower slower deposition deposition rates rates ensue. ensue. - Stage C Stase C - Stromatolite Stromatolite Development Development Stromatolites grew on the silicified, silicified, stabilized stabilized substrate, substrate, forming forming inverted-bowl shaped mounds on the Some mounds the bottom. bottom. The lack of of wave wave agitation agitation and and firm firm substrate substrate proved proved ideal. ideal. Some stromatolites were occasionally buried by grainstone laminae brought in by seaward flowing bottom stromatoliteswere occasionally buried grainstone laminae seaward bottom currents generated during storm events. storm Stage D D --Large Large Microbial Bioherm Stase Bwherm Growth Growth Individual stromatolite Individual stromatolitecolonies coloniescoalesced coalesced upwards, upwards, forming forminglarge large mound mound shaped shapedstructures structures irregular bottom bottom topography. topography. Little and creating an irregular Little sediment sediment accumulated accumulated between between the stromatolite stromatolite mounds mounds as as storm storm events events became became less less capable capableof of supplying supplyingdetritus detritusto to the the area. area. - State E - Volcaniclastic VolcaniclasticBurial Growth of of the bioherms was abruptly terminatedby bythe the deposition depositionofof aa series Growth bioherms was abruptly terminated series of volcaniclastic sediment blankets. The Thedraping drapingof of these these blankets blankets over the mounds rather than their than sedimentation from bottom ponding in intermound intermound areas indicates indicates rain out from above rather than currents. currents. feldspars) and and sorting sorting (large The composition (fresh detrital biotite), angularity (subhedral feldspars) well formed crystals floating in a dark fine grained groundmass) all point to little or no reworking floating a dark fine grained of pyroclastic pyroclastic material. asrain rainout outfrom fromash ash landing landingon on material. The Thelayers layersmay mayhave havebeen beendeposited depositeddirectly directlyas the water's surface or as storm deposited layers. The latter is preferred, as the microlaminations can surface or as storm The latter is microlaminations can then be explained explained by fluctuations fluctuationsin in the the energy energy level. level. The Thepresence presenceof of significant significantquantities quantitiesof ofnonnoncarbonate carbon in the groundmass of these rapidly deposited units units may may reflect reflect the the settling settling of of the the volcaniclastics a composition similar siinilarto vegetable soup. soup. The occasional occasional volcaniclasticsthrough throughaa sea sea with acomposition to microbial vegetable large storm event eroded saucer shaped scours into the the fine fine grained grained material material and andtransported transported minor minor amounts of carbonate amounts carbonate in in from from the the shore-proximal shore-proximal zone. zone. Lateral Implications As water depth depth increased, increased, the bottom changed changed from from a wave dominated dominated condition condition to to aa zone zone sedimentation and of slow sedimentation and thus pervasive silicification. silicification.This Thisled ledto to stabilization stabilizationof of the the sediment sedimentand and stromatolites began to develop. With time (increasing water depth) large domal structures grew. With time (increasing water depth) domal structures stromatolites stromatolitic zone of the Gunflint Formation by This succession succession was was brought brought to an end in the upper stromatolitic pyroclastic eruptions eruptionsand and volcaniclastic volcaniclasticdeposition depositiondrastically drastically altering altering bottom bottom conditions. conditions. STOP 99 STOP Turn left on Lyon Blvd. Blvd. Then Arundel. Turn nodder Ave Then right on Anmdel. Turn left on Hodder Ave and and drive drive Transcanada. Turn to the Transcanada. Turnright righton onthe theTranscanada Transcanadaand anddrive driveto to the the Pass Pass Lake Laketurnoff. turnoff. Turn right here and proceed till you encounter encounter a large outcrop of contorted contorted ribbon ribbon chert-carbonate on chert-carbonate on your your left. left. �Figure 18. ribbon chedearbonate chert-carbonate layers. B) SStop Chert-carbonate silt to1 ~11. 1. Chert-carbonate A)-.Ston 9. Disrupted ribbon Figure 18. A) to pebbly pebbly grainstone grainstone with rip-ups of volcaniclastic sediment and fingernail-sized volcaniclastic sediment and fingernail-sized, shards. shards. 1 ____ - :' F&: . 1; _ �a- Jrrce —— _____ w L a: r Ia r TTTT 'a — , -a / 't* ;c •- 5'4 '1r * J * a a : s A .1-1 — at' Efl C_ - \ ' - — — * — a- a- I a -, Figure 19. A) internal laminations medium-grained sandstone stormlayer. layer. The Figure A)Close-up Close-upof internal laminations in a medium-grainedsandstonestorm one third third of of the thelayer layercontains containsupperflow upperfiowregime regimeparallel parallellaminations. laminations. The bottom one two thirds thirds Ic hummockycross-stratified cross-stratjfiedwith withlow lowangle angletruncation truncationsurfaces surfaces upper two is hummocky B) Outcrops Outcropsat at Stop Ston 12. 12. clearly visible. B) �Laterally chert and and ankerite ankerite layers layers occur occur in Laterally continuous continuous interlaminated interlaminated chert in this this outcrop outcrop (Figure 1 8A). These layers are intensely folded and disrupted in places. The outcrop outcrop (Figure 18A). These layers are intensely folded and disrupted in places. The provides an excellent opportunity to discuss if the deformation is synsedimentary, provides an excellent opportunity to discuss if the deformation is synsedimentary, why the the ribbon ribbon chert-carbonates preferentially exhibit exhibit this this type type of of deformation deformation and and why chert-carbonates preferentially what type type of depositional environment what of depositional environment is is represented represented by by these these sediments. sediments. STOP 10 STOP 10 Proceed back back to Bay. Drive Proceed to the the Transcanada Transcanada and and turn turn left, left, towards towards Thunder Thunder Bay. Drive approximately 1.8km road on on the the right. right. Turn approximately 1.8km until until you you reach reach the the small small side side road Turn right right onto onto the the dirt dirt road road and and park. park. Volcaniclastic, Volcaniclastic, very very fine-grained fine-grained sandstones, sandstones, siltstones siltstones and and mudstones mudstones occur occur at at this this location. These location. Theseare areprobably probably correlatable the gorge gorge at correlatablewith with the the interval interval examined examined in the Kakabeka Kakabeka Falls. Falls. The Thevery veryfine-grained fine-grainedsandstones sandstonesand and coarse-grained coarse-grained siltstones siltstonesare are ripple ripple laminated laminated with with well well preserved preserved internal internal structure structure (see (see polished polished hand hand samples). samples). Again possible depositional Again the the possible depositionalprocesses processes which which may may have have operated operated to to form form this this unit unit will be discussed in the field. will be discussed in the field. STOP STOP11 11 Turn right onto onto the the Transcanada Transcanada and and proceed proceed towards towards Thunder Thunder Bay. Bay. Turn Turn right Turn right right at at the the access road to the Terry Fox lookout. Park in the parking lot and walk to the large access road to the Terry Fox lookout. Park in the parking lot and walk to the large outcrop outcrop on on the the highway; highway; watch watch out outfor forcars. cars. A the Gunflint Gunflint Formation Formation at at this this location. location. The A large large diabase diabase sill sill overlies overlies the The Gunflint Gunflint grainstones present here contain large rip-up fragments and both small grainstones present here contain large rip-up fragments and both small and and large large sherds of of volcanogenic volcanogenic origin origin(Figure (Figure 18B). l8B). Volcaniclastic present near near Volcaniclastic shales shales are are present sherds the top of the sedimentary this has has been been described described by by some some workers workers as as the top of the sedimentary sequence sequence and and this However, interbedding interbedding of of volcaniclastic the the Gunflint-Rove Gunflint-Rove contact. contact. However, volcaniclastic shales shales and and chemical sediment the upper upper portions portions of of the the Gunflint Gunflint Formation, Formation, and chemical sediment is is common common in in the and if more sediment occurs occurs at at aa higher higher level level this this cannot cannot be be defined defined as as the the if more chemical chemical sediment contact. contact. STOP STOP 12 12 Turn Turn right right on on the the Transcanada Transcanada and and drive drive across across the the bridge bridge over over the the Current CurrentRiver. River. Proceed up hill on the other Proceed up the the hill on the other side. side. A Arock rock cut cutoccurs occursat at the the top top of of the the hill hill and and there there is a dirt dirt pull-in. pull-in. Park is a Park here. here. This grainstone those examined on the the Current Current River This grainstone sequence sequence is is similar similar to to those examined on River (Figure (Figure 19). There may be metre-scale thinning-upwards cycles present here 19). There may be metre-scale thinning-upwards cycles present here hut but they they are are indistinct. indistinct.Thin, Thin, discontinuous discontinuouschert chertlayers layersoccur occurat at the the tops tops of of these these possible possible cycles. cycles. In places this this chert very carbon-rich, carbon-rich, possibly possibly denoting denoting aa slowing slowing of of the the deposition deposition In places chert is is very rate allowing accumulation of organic carbon. This outcrop provides an opportunity rate allowing accumulation of organic carbon. This outcrop provides an opportunity to discuss to discuss some some of of the the possible possible process process which which could could drive drive deposition deposition of of this this type type of of assymetric cycle (Figure 20). assymetric cycle (Figure 20). Turn right Turn left left on on Turn right on on the the Transcanada Transcanada and and proceed proceed to to Oliver Oliver Road. Road. Turn Oliver Road Road and and turn turn right right at at the the road road leading leading to to the the main main entrance entrance of of Lakehead Lakehead Oliver University. University. �Figure modelfor for nonbarred nonbarred portions portions of Figure 20. 20. Generalized Generalized depositional depositional model of the the strand-proximal strand-proximal Gunflint shelf during deposition of upper Gunflint chemical sediments. Gunjlint shelf during deposition of upper Gunflint chemical sediments. 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G , cd , Early Proterozoic ProteroxoicGeology Gcolog) of ofthe thc Great Great Lakes Lakes Region: Region Geological Geological Society Socicty of of America America Memoir Memoir160, 160,p.p 15-32. 15-32 �GLACIAL GLACIAL HISTORY AND REGIONAL TILL SAMPLING SAMPLING IN THE THE ARCHEAN SHEBANDO WANGREENSTONE GREENSTONE BE BELT SHEBANDOWAN I Andy Bajc, Ontario Geological Survey , Shebandowan Greenstone Belt, Belt, host host to to aa variety variety of of The Shebandowan precious and andbase basemetal metal deposits, deposits, is is aa bedrock-dominated bedrock-dominated terrain, terrain, typically typically having having thin thin till cover. Till Till sampling sampling techniques and resultant grain and resultant gold grain and other other heayy heavy mineral results will be examined in an exploration context context. �INTRODUCTION INTRODUCTION The Shebandowan Shebandowan greenstone greenstone belt, which is located located immediately north and west of the city of Thunder exploration and mining spanning well over 100 Thunder Bay, has a rich history of mineral exploration 100 years. The belt is host to a variety of precious and base metal mineral deposit types. Past producers The mineral deposit types. include the Inco Inco Limited Shebandowan Shebandowan Ni-Cu-PGE mine, the the North Coldstream Coldstream Cu-Au-Ag Cu-Au-Ag mine mine include and the Ardeen Au mine which which was was northern northernOntario's Ontario's first first gold gold producer. producer. Exploration activity activity within response to the depressed prices of precious precious and within the belt has has currently currently subsided, subsided, largely largely in response base metals and the inability ofjunior mining companies to raise hinds for exploration. metals of junior mining companies to raise funds for exploration. In response to this this recent decline decline in mining mining and mineral mineral exploration exploration activity activity within the belt, the Ontario and drift drift geochemistry geochemistry Ontario Geological Geological Survey Survey initiated a 2 year program of Quaternary geology and to further evaluate potential of of the the Shebandowan belt. belt. This was accomplished evaluate the mineral resource potential by detailed (1:50 (1 :50 000 000 scale) scale) Quaternary geology mapping and regional humus and c-horizon till sampling. sampling. Quaternary Quaternarymapping mapping was was undertaken undertaken to to document document the the distribution distribution and character of the various Quaternary deposits within the study area and to reconstruct various Quaternary deposits within the study area and to reconstruct the the ice ice flow flow history history associated associated with with these these deposits. deposits. This Thisinformation informationisis essential essentialfor forthe thesuccessful successfulimplementation implementationof ofmineral mineral exploration drift prospecting prospectingtechniques techniquesand and surficial surficialgeochemistry. geochemistry. explorationprograms programsutilizing utilizing drift During During the the 1998 1998field field season, season, Quaternary Quaternary mapping mapping and and regional regional humus humus and and c-horizon c-horizon till till sampling sampling were conducted conducted over the eastern half of the belt within within the area area covered by the Sunshine Sunshine (52A/l2) (52N12)and andKakabeka KakabekaFalls Falls (52A/5) (52N5) 1:50 1:50000 000scale scaleNational NationalTopographic Topographic System System (NTS) map sheets sheets (Figure (Figure 1). 1). The Theresults resultsof ofthis thiswork workare aresummarized summarizedin in Ontario OntarioGeological Geological Survey Survey Open File Report (Bajc 1999a). 1999a). Mapping Mappingand andsampling samplingwas wasextended extendedwestward westward into into the the Shebandowan Shebandowan Report 5993 5993 (Bajc (52B/9) (52B19) and and Burchell Lake (52B/10) (52B110) 1:50000 1:50 000scale scaleNTS NTS map map areas areas during during the 1999 1999 field season. An OGS OGS preliminary preliminary map map containing containing information information on on the the regional regional distribution distribution of of gold gold grains grains in in till till within was released during the fall of 1999 1999 (Bajc 1999b). The The complete complete mineralogical mineralogical and within this this area area was geochemical geochemicaldatasets datasetsfor for the the western western half half of of the the belt belt were were released released in in the the spring spring of of 2000 2000 (Bajc (Bajc 2000). 2000). BEDROCK BEDROCK GEOLOGY GEOLOGY A A comprehensive comprehensivesummary summaryof of the the bedrock bedrock geology geology of of the the study study area area is is contained contained in papers by Sutcliffe Sutcliffe (1991), (1991), Williams Williams (1991) (1991) and Williams Williams aetall al.(1991) (1991)as aswell wellas asininnumerous numerousOntario Ontario Geological Geological Survey Survey maps maps and reports. The Thestudy studyarea areacontains contains33 distinct distinct bedrock domains domains (Figure (Figure 2). 2). The Thecentrally-located centrally-locatedWawa WawaSubprovince, Subprovince,within withinwhich whichthe the Shebandowan Shebandowan greenstone greenstone belt occurs, occurs, is is fault-bounded fault-boundedto to the the north north by by metasedimentary metasedimentaryand and felsic felsic intrusive intrusive rocks rocks of of the the Quetico Quetico Subprovince Subprovinceand and unconformably unconformably overlain overlain to to the the south southby by Paleoproterozoic Paleoproterozoicmetasedimentary metasedimentaryrocks rocks of Animikie Group Group(Gunflint (Gunflintand and Rove Roveformations). formations). of the the Animikie Metasedimentary Metasedimentaryrocks rocks of of the the Quetico QueticoSubprovince Subprovinceconsist consistprimarily primarily of of turbiditic turbiditic wackes, wackes, arkoses migmatites. PostQuartzarenites arenites and and their their associated associated paragneisses varaeneisses and miematites. Post- to to arkoses and and quartz - syndepositional syn&msitiorkl felsic felsicplutons plutonsconsisting consistingof offeldspar-megacrystic feldspar-megacrysticgranite, granite, granodiorite granodiorite to to tonalite tonalite and and monzonite monzonite comprise comprise aa notable notable proportion proportion of this domain. Narrow, Narrow, elongate elongatelenses lensesof of tholeiitic, tholeiitic, �PROTEROZOIC Jacobsville Gp.- sandstone, shale, wnglomerate [_\j Keweenawan mafic intrusive rocks Sibley Gp.-conglomerate,sandstone,shale I Animikie Gp.-wacke, shale, iron formation, limestone, minor volcanics Oskr Gp.- basalt, wn@omerate, a h s e a ARCHEAN Fekic lntmsbe ro& 0 Queliw Subpvinm mtasedimnta~yrocks UI tig goon Subpvince supracrustal rocks Wawa Subprovince supramstat rocks [S3 1998 Survey Area 19gg suwey Area Figure 1. Figure 1.Location Locationmap mapofofstudy studyarea areaincluding includingregional regionalbedrock bedrockgeology. geology. mafic metavolcanic the Quetico metavolcanic rocks and associated gabbroic rocks occur locally within the Subprovince (Brown 1995, 1995, Osmani Osmani 1997). 1997). Metasedimentary rocks of the Gunflint Gunflint and Rove formations (Animikie Group) were deposited Metasedimentary Minnesota, Wisconsin Wisconsin and and Michigan Michigan(Sutcliffe (Suteliffe 1991). 1991). The within a large basin that extends into Minnesota, Gunflint Formation unconformably on the Archean Formation contains a basal unit of conglomerates conglomerates that rest unconfommbly jasper, basement and are overlain by interbedded argillites, argillite tuffs, cherts, algal cherts, jasper, carbonates, hematite, hematite, magnetite magnetitetaconite taconiteand andsilicate silicate(aconite. taconite. The carbonates, ferruginous carbonates, consists of black, locally pyritic shales and grades upward upward into into overlying Rove Formation consists interbedded black shale and arkosic greywackes. greywackes. Mesoproterozoic "Logan" diabase sills intrude the the Mesoproterowic diabase sills intrude resistant cap rocks of large mesas in the southern part of the map Rove Formation Formation and form the resistant area. Silver Silvermineralization mineralizationoccurs occurslocally locally along along normal normal faults faults that intersect the contact between Rove Formation shales and Logan diabase diabase sills. sills. Notable silver silver deposits deposits occur in the southeastern corner of the Kakabeka Falls NTS map area, in the vicinity of Badger and Beaver mountains mountains comer Mountain group group of of deposits) deposits) and and Silver SilverMountain. Mountain. Accessory minerals minerals in in these these (Creswel or Rabbit Mountain calcite; quartz; quartz; barite; barite; and and fluorite fluorite deposits include: acanthite; pyrite; sphalerite; marcasite; galena; calcite; (Franklin eta/. 1986). et at 1986). �Figure 2. Bedrock geology of the study area, Archean metasedimentary rocks (Wawa Subprovince) Aichean mafic intruswe rocks Archean felsic4ntennediate intrusive rocks Archean meta volcanic rocks * CmsweuRabbit Mtn. Ag deposits Snodgrass Lake Au deposit Shebandowan Ni-Cu-POE mine North Coidsiream Cu-Au mine Animikie Op. Metasedimentaiy rocks Archean metasedirnentary rocks (Quetici, Subprovince) Ardeen Au mine Keweenawan malic intrusive rocks �can be be subdivided into into 2 contrasting Supracrustal rocks of the Shebandowan greenstone belt can packages of metavolcanic metasedimentary rocks: 1) metavolcanic and metasedimentary 1) an older suite of mafic to felsic metavolcanic metavolcanic rocks rocks belonging to the Greenwater Greenwater assemblage; and 2) a younger suite of metasedimentary to the the Shebandowan Shebandowan assemblage. assemblage. The metasedimentary and metavolcanic rocks belonging to Greenwater assemblage consists primarily of tholeiitic basalts with intercalated intermediate to Greenwater assemblage felsic and Stott 1998). Mineralization felsic metavolcanic metavolcanic rocks and minor komatiites (Corfu and Mineralization at the Shebandowan, North Coldstream and Ardeen mines are all contained within Greenwater assemblage Ni-Cu-Pt-Co mineralization mineralizationatatthe theShebandowan Shebandowanmine mineisishosted hosted by by aa gabbrogabbroassemblage rocks. Ni-Cu-N-Co peridotite sill. Cu-Au-Ag mineralization at the North Coldstream mine is hosted by a highly peridotite Cu-Au-Ag mineralization at the North Coldstream mine is hosted silicified silicified gabbro. Gold Goldmineralization mineralizationatatthe the Ardeen Ardeen mine mine occurs occurs in in composite composite quartz veins developed along the Pete and Ardeen fault systems. Advanced exploration developed Pele exploration in the form of a decline ramp ramp and and bulk sample sample was was undertaken undertaken at the Snodgrass Snodgrass Lake Au prospect in central Moss Township mid-i 980s. Gold Township during the mid-1980s. Gold mineralization mineralizationoccurs occurs in in sheared sheared felsic felsic metavoicanic metavolcanic rocks and in sheared and fractured diorite, gabbro and and quartz-feldspar quartz-feldsparporphyries. porphyries. The Haines gabbroanothosite within the the belt. belt. The intrusion, anothosite complex complex represents one of the larger mafic intrusions within which occurrences. which is is crudely layered, is host to a number of Ni-Cu-PGE occurrences. The overlies (i.e., (i.e., fault contact) and The younger, Shebandowan Shebandowan assemblage assemblage both unconformably overlies intrudes intrudes the Greenwater Greenwater assemblage. ItIt consists consists of of alkalic alkalic metavolcanic metavolcanic and intrusive rocks (tuff, breccia, breccia, syenite, syenite, lamprophyre, lamprophyre, quartz quartz and and feldspar feldspar porphyry, granodiorite and diorite) as well as metasedimentary metasedimentaryrocks rocks (arkoses, (arkoses, wackes, conglomerates conglomeratesand oxide-facies oxide-facies iron iron formation) formation) at 1998). This assemblage is interpreted as representing an intracratonic (Schneiders ci' This assemblage is interpreted as representing an intracratonicbasin basin (Schneiders et al. assemblage assemblagesimilar similarto to the the Timiskaming Timiskamingassemblage assemblageof of the the Abitibi Abitibi subprovince. subprovince. Most Most gold gold occurences occurencesin in the the eastern eastern portion portion of of the the Shebandowan Shebandowangreenstone greenstone belt display display a close close spatial association with rocks of the Shebandowan assemblage. The style of gold mineralization is spatial association The style of not unlike and Kirkland Lake. Lake. Gold i m m i nand i I&kland unlike that which occurs in such such prolific mining camps as ~Tinimins mineralization mineralizationisiscommonly commonly associated associatedwith with both both large large scale scale and and subsidiary subsidiarystructures structures and structurally-controlled en echelon echelon quartz veins, structurally-controlledintrusions. intrusions. Mineralization Mineralizationoccurs occursin in sheeted sheetedand and en stockwork stockworkzones zones and and vein vein breccias breccias as as well well as as in in stocks, stocks,dikes dikes and and sills sillsof of felsic felsicto to mafic mafic composition. composition. Gold Goldisisalso alsocommonly commonlyassociated associatedwith: with: sulphide-rich, sulphide-rich,quartz-veined quartz-veined replacement replacement zones zonesin in oxide oxidefacies faciesiron iron formation; formation;silica-flooded, silica-flooded,hydrothermally-altered hydrothermally-altered zones; and and ironcarbonate with shear shear and and permeable permeablezones. zones. Associated carbonate and and pyrite-rich zones commonly associated with alteration alteration and and accessory accessory minerals minerals thclude: include: iron iron carbonate; carbonate; silica; silica; potassic potassic feldspar; feldspar; sericite; sericite; arsenopyrite; tourmaline; tourmaline; and and green green mica (Schneiders (Schneiders et aL al. 1998). 1998). hematite; chlorite; chlorite; calcite; calcite; pyrite; pyrite; arsenopyrite; hematite; Notable Notable exploration explorationprograms programs within within the the current currentstudy study area area are are highlighted highlighted in the last 55 annual annual volumes volumes of of the Resident Resident Geologist's Geologist's Report Report of of Activities. Activities. as GLACIAL GLACIALGEOLOGY GEOLOGY The The study study area area isis characterized characterizedby by several several contrasting contrasting physiographic physiographic regions, each defined by a unique unique suite suite of of overburden overburden conditions. Most Mostof ofthe theBurchell BurchellLake Lakeand and Shebandowan Shebandowan NTS map areas areas as as well well as as parts parts of of the the Sunshine Sunshineand and Kakabeka Kakabeka Falls Falls NTS NTS map map areas areas are are characterized characterized as as bedrock-dominated drift occur occur in in morainic morainic belts, bedrock-dominated terrains. Local Localaccumulations accumulationsof of thick thick drift glaciofluvial glaciofluvial complexes complexesand and narrow, narrow, structurally-controlled structurally-controlleddepressions depressions within within these these uplands. �Thicker within g. Thicker deposits deposits of of till and/or andlor glaciofluvial glaciofluvial and glaciolacustrine sediments occur within#? isolated isolatedbasins basins(Figure (Figure3). 3). AAnorthern northernlowland, lowland,here herereferred referredtotoasasthe the"Kaministikwia "Kaministikwiabasin", basin", occupies Kaministikwia rivers. AA occupies the the valleys valleys of of the the Oskondaga, Oskondaga, Matawin, Shebandowan and Kaministikwia southern In the the northern northern southern basin is centred centred on the valleys of the Whitefish and Kaministikwia rivers. In basin, basin, thick thick deposits deposits(several (several tens tens of of metres) of of glaciofluvial glaciofluvial and glaciolacustrine glaciolacustrine sediments sediments drape a rugged surface rolling landscape landscapewith with sporadic sporadicbedrock bedrock rugged Archean ~ r c h e bedrock bedrock k surface producing producing aa gently rolling outcrops. The low relief observed within the southern basin is a reflection of not only outcrops. The low relief observed within the southern basin is a reflection of not onlythe theflat-lying flat-lying Proterozoic glaciolacustrine deposits that ~roterizoicsediments sedimentsthat that underlie underlie the the region, but the extremely extremely thick glaciolacustrine have have infilled infilled deep deep valleys valleys along the Whitefish Whitefish and Kaministikwia Kaministikwia rivers. Overburden Overburdenthicknesses thicknesses along along these these valleys valleysexceed exceed 60 60m m in in places. places. The The erosional erosionaland and depositional depositionalfeatures features preserved within the study area record a complex history history of of ice ice flow flow events events associated associated with the Wisconsinan glaciation ( T i m 44).1 The Theentire entirestudy study -daciation (Figure area area was was initially initially affected affected by southward flowing "northern" "northern" ice. Striae striaeassociated associatedwith with this thisevent event generally 220° Az. In In the the southern southernhalf half of of the the Sunshine Sunshinemap map area, area, there there is is generally range between 190° 190Âand 220' widespread evidence for an older ice flow event towards 160° Az. The age and significance of this widespread evidence for an older ice flow event 160" significance event event is is not not known. known. Pauses Pauses in in the the general general retreat retreat of of the the "northern" "northern" ice ice lobe lobe resulted resulted in in the the formation formationof oflarge, large, which traverses arcuate, arcuate, recessional recessional moraines moraines in northwestern Ontario. The TheBrule Brule Creek CreekMoraine, Moraine, Aldina A l d i and Marks Marks townships townships in the west-central portion of the Kakabeka Falls NTS map area, represents represents one one of these stilistand stillstand positions (Figure 4). This Thismoraine morainehas hasbeen beentraced tracedwestward westward into the Shebandowan by aa discontinuous discontinuous belt belt of Shebandowan and and Burchell Lake map areas where it is defined by morainic associated ice-contact ice-contact stratified stratifieddeposits. deposits. West of the stud study morainic ridges composed of till and associated with the Eagle Finlayson Moraine (Zoltai area, the Brule Creek Moraine has been correlated area, the Brule Creek Moraine has been correlated with the Eagle Finlayson Moraine (Zoltai 1965). 1965). A A large large ice-contact delta delta built off of this moraine along the south shore of Burchell Lake is graded to to an an upper upper level level of of glacial Lake Agassiz. The Theupper uppertopset topsetsurface surfaceof of the the delta deltaoccurs occursat at an an elevation as1 (1500-1550 feet aasl). s h To To the east of Marks Township, the Brule elevation of 457 to 472 m asl Creek Creek Moraine Moraine has has been been overridden overridden and obscured obscured by by aayounger younger glacial glacial advance advance (Figure (Figure 4). Isolated deposits of northern provenance and Isolated buried deposits denosits of of ice-contact ice-contact stratified stratified glaciofluvial elaciofluvial dewsits possibly associated and associated with with the the Brule Creek Moraine occur in south-central Conmee A d west-central Oliver Olivertownships. townships. - A second major moraine of northern affinity (Dog Lake Lake Moraine) Moraine) is is situated situated in in the the northeastern northeastern corner 4). Unlike comer of of the Sunshine Sunshine map map area area in the vicinity of Dog Lake (Figure 4). Unlike the Brule Creek Moraine, this moraine was constructed following a minor readvance of the "northern" ice lobe. Moraine, this moraine was following Glaciolacustrine readvance. In In the the vicinity vicinity Glaciolacustrine sediments sediments underlying till north of the moraine support aa readvance. of Dog Lake, the moraine is fronted by a lobate, flat-topped, flat-topped, glaciofluvial glaciofluvial plain plain believed believed to to be be deltaic deltaic in origin. The Theelevation elevationof ofthis thisplain plain(460 (460m masl) as]) defines definesthe the level level of of Glacial GlacialLake Lake Kaministikwia, a large large glacial lake which occupied the Kaministikwia basin. Distinctive Distinctivered red clays, clays, associated with this to, but not above, this this glacial lake can be found throughout the basin up to, elevation. �IA r— I' - - r- — C— Figure 3. Digital elevation model of the Shebandowan greenstone belt and surrounding region. ,1 c— r-— C —- — - — -- r - �f(i ij Figure4.4. Ice Ice flow flowpatterns, patterns, major major moraines moraines and and surface surface tills tills of of the the study study area. area. Onlapping Onlappingpattern pattern of ofarrows arrowsindicates indicates age age relationships relationships Figure of ice flow events. Light grey zone indicates area where older, northern till exposed on surface. Dark grey zone indicates of ice flow events. Light grey zone indicates area where older, northern till exposed on surface. Dark grey zone indicates area affected by Marquette readvance (southern area by Superior lobe; northern area by northern lobe). area affected by Marquette readvance (southern area by Superior lobe; northern area by northern lobe). �Kaministikwia was was topographically-supported topographically-supportedon on its its southern southernflanks flanksby by an anupland upland Glacial Lake Kaministikwia in the northwestern corner of the Kakabeka Falls NTS area area (Figure (Figure 3) 3) as as well as as by glacial glacial ice ice advancing out of the Superior basin and whose terminal position is defined by the Marks moraine TheMarks Marksand andDog DogLake Lake moraines moraines are are correlative correlative and and merge merge east east of of the the study study area area (Figure 4). The Striaeassociated associatedwith withthe theadvance advanceof of the the Superior Superiorlobe lobe along the McKenzie interlobate Moraine. Striae range from from 3400 340ÂAz in the northeast to 240 240° Az in the southwest attesting to the lobate nature of the Thisadvance advanceisiscorrelated correlatedwith withthe theMarquette Marquettestadial, stadial,aalate-glacial late-glacial surge surgeevent event that that Superior lobe. This resulted in much of the Superior basin being reoccupied by glacial ice about 9.9 ka With the the ka BP. BP. With corner of the Kakabeka Falls area, the Superior lobe advanced into a exception of the northeast comer glacial lake, referred to as "Glacial Lake OtConnortt Numerous sections sectionsalong along the the O'Connor" (Zoltai (Zoltai 1963). Numerous Whitefish River expose thick sequences of glaciolacustrine rhythmites beneath a fine-textured Superior lobe till. Shorelines Shorelinesof ofthis thisglacial glaciallake lakehave havenot notbeen beenidentified. identified. Superior (Patrician) provenance has been observed throughout the the entire study area. area. On Till of northern (Patrician) On less than than aa few metres metres Archean terrane, beyond the limits of the Superior lobe, the till is generally less thick and has a silty sand texture with low to to moderate moderate stone-content. stone-content. Till cover is significantly more extensive thicknesses of 5 extensive over over the east-central part of the Shebandowan Shebandowan NTS map area where thicknesses to 10 m m are are not not uncommon. uncommon. Unoxidized till generally has an olive-grey olive-grey to to buff-grey buff-greycolour. colour. The contains a high proportion of clasts clasts that are locally-derived. Faceted Faceted and andstriated striatedclasts clasts till often contains within the till indicate deposition by ice flowing towards towards the the south-southwest. south-southwest. Many exposures of this northern till contain remnant clasts Sibley Group metasediments. These Thesedistinctive, distinctive,reddishreddishclasts of Sibley coloured siltstones occur most commonly east of Thunder Bay on the Sibley Peninsula and on the Peninsula and to to aa Nipigon basin. basin. Sibley Sibley Group Group clasts clasts in in northern northern lesser extent, northeast of the study area in the Lake Nipigon till are likely derived from the Nipigon basin, 70 km to the northeast. The Thenon-magnetic non-magneticheavy heavy mineral concentrates concentrates of northern tills are rich in clinopyroxenes derived from Nipigon diabase within this same same area. area. Northern till is buried beneath variable thicknesses of glaciolacustrine deposits deposits and Superior Superior lobe till within the Whitefish-Kaministikwia Whitefish-Kaministikwia lowland. lowland. InInthis thisarea, area,the thetill tillisissignificantly significantlyfinerfinertextured owing owing its fineness fineness to the underlying shales shales and argillites argillites of the Rove and Gunflint formations. formations. Stony Stonytill, till,of ofpresumed presumednorthern northernprovenance, provenance,exposed exposedatatwater waterlevel levelalong alongWhitewood Whitewood Creek in east-central O'Connor Township, contains abundant striated and faceted boulders boulders indicating ice ice flow flow toward toward the the southwest. southwest. Superior Lobe till is easily recognized recognized by its fine-texture fine-texture and and high high proportion proportion of of Animikie Animikie Group Group metasedimentary clasts in the pebble fraction. Even Evenin inareas areasunderlain underlainby by Archean Archean terrane, terrane, as occur in the northeast corner comer of the Kakabeka Falls area, Superior lobe till contains only a small proportion of the underlying rock rock types types in in the the pebble pebble fraction. fraction. This has important implications for programs of mineral exploration utilizing till as a sample medium. medium. The The colour of the unweathered till ranges from dark grey, to brown to reddish-brown. Sections Sectionsof oftill, till,containing containinglayers layerswith with all all 33 reflect the the melting melting out out of of colours have been observed in Oliver and Gillies townships and probably reflect debris bands derived from different bedrock sources. Superior Superiorlobe lobetill till also alsovaries varies markedly markedly in in texture. In InOliver OliverTownship, Township,near nearthe thecommunity communityof ofMurillo, Murillo,Superior Superiorlobe lobetill tillisissilty siltyand andcharged charged with shales shales of the Gunflint Formation. The The till till in in this this region region is is fluted fluted and has been observed to reach thicknesses thicknesses of 7 to 8 m. Similarly, Similarly,to to the the south south in in Scoble Scoble and Gillies Gillies townships, Superior �Lobe till is silty and charged with clasts of Rove Formation shale and Logan diabase. diabase. Along Along the the Whitefish contains less less than than 5% 5% clasts. clasts. This Whitefish River valley, the till is silty to clayey and contains This is is primarily primarily due due to to the the thick thick deposits depositsof ofglaciolacustrine glaciolacustrinesilts siltsand andclays claysthat that were overridden overridden and and incorporated incorporated into the basal debris layers of the advancing Superior lobe. into the basal debris layers of the advancing Superior lobe. OVERVIEW OVERVIEWOF OFFIELDTRIP FIELDTRIPAGENDA AGENDA The landforms, landforms, deposits depositsand and features featureswe we will will be be visiting visitingtoday today will will provide provide an an overview overviewof of the the The important belt. An important elements elements of of the Quaternary Quaternary geology of the Shebandowan greenstone belt. An attempt attempt will willbe be made madeto toillustrate illustratehow howthe thevarious variousQuaternary Quaternarydeposits depositscan canbe beutilized utilizedfor forprograms programs of of mineral mineral exploration. Figure Figure55 shows showsthe the locations locations of of the the fieldtrip fieldtrip stops. The Thefieldtrip fieldtripwill willbegin begin in in the anderosional erosional thecentral centralpart part of ofthe thebelt beltwhere wherewe wewill willhave havean anopportunity opportunitytotoview viewdeposits depositsand features features associated associated with the advance and retreat of northern ice. Some Sometime timewill willbe be spent spent demonstrating demonstratingsampling samplingtechniques, techniques,discussing discussingthe thepros prosand andcons consof ofvarious varioussample samplemedia, media,and and finally, reviewing strategies for property-scale surficial geochemical surveys. We will proceed finally, reviewing strategies for property-scale We will proceed easterly easterlyinto intothe the centre centreof ofthe thenorthern, northern,Kaministikwia Kaministikwiabasin basinwhere wherewe wewill willhave havean anopportunity opportunitytoto view deposits of glacial Lake Kaministikwia and discuss the glacial lake history of this view deposits of glacial Lake Kaministikwia and discuss the glacial lake history of thisand andother other proglacial proglacial water water bodies bodies within within the the region. region. From Fromhere, here,we wewill willproceed proceedsouth southand andwest westwhere wherewe we will have an opportunity to view deposits and landforms associated with the advancing Superior will have an opportunity to view deposits and landforms associated with the advancing Superior lobe. lobe. Stops Stopswill willinclude: include:1)1)aasection sectioncut cutinto intoice-marginal, ice-marginal,subaquatic subaquaticdebris debrisflows flowsdeposited depositednear near the the outer outer limit limitof of the the Superior Superiorlobe; lobe; 2) 2) aa Superior Superiorlobe lobe ice-contact ice-contact delta delta which which has has been overridden overridden by by the the advancing advancingSuperior Superiorlobe; lobe;3) 3) an anexposure exposureof ofSuperior Superiorlobe lobetill tilloverlying overlyingnorthern northerntill; till;4) 4)aa panoramic panoramicview viewof ofthe thelowland lowlandinto intowhich whichthe theSuperior Superiorlobe lobeadvanced; advanced;and and5)5 )aastop stoptotoview viewthe the morphology morphologyof of the the Marks Marks Moraine. Moraine. At Atseveral severalofofthese thesestops, stops,we wewill willhave havean anopportunity opportunityto to discuss discussthe thesuitability suitabilityof ofSuperior Superiordrift driftas asaasample samplemedium mediumfor forprograms programsofofmineral mineralexploration. exploration. The The trip trip will will conclude concludeby by travelling travellingsouthward southwardinto intothe theWhitefish WhitefishRiver Riverlowland lowlandwhere wherewe wewill willlook look at ataa couple coupleof ofexposures exposuresthat thatillustrate illustratethe thedrastic drasticfacies facieschanges changesthat thatoccur occurininboth boththe theSuperior Superiorand and northern northernlobe lobetills tillsas asyou youproceed proceedinto intothe thelowland. lowland.The Thesignificance significanceofofglaciolacustrine glaciolacustrinedeposits deposits exposed exposedatateach eachof ofthe thesites siteswill willbe bediscussed discussedasaswell. well. The proceed westward The bus bus will will depart depart the the Lakehead Lakehead University Universitycampus campus and andproceed westwardalong alongHighway Highway 102 102 towards Kaministikwia where it will meet Highway 11/17 at Sistonens Corners. Turn right onto towards Kaministikwia where it will meet Corners. Turn right onto Highway Highway 11/17 11/17and andproceed proceed west west 16.0 16.0k,ns. kms. Turn Turnleft left on on aasmall small sideroad sideroadsituated situatedapproximately approximately 150 m before before (east (eastof) of)aa sign sign on on the the north northside side of of the the highway highway marking marking "Bylund "BylundPit Pit Road". Road". 150to to 200 200 m Follow Follow the the main mainroute route on on this this sideroad sideroadfor approximately approximately 300 to 400 m. Park Park vehicle vehicle at aa large large area areaofofstripped strippedoutcrop. outcrop.This Thisisisthe theBylundAu Bylund Auoccurrence. occurrence. �Figure 5. Location map of fieldtrip stops. S- C S r r— C - S——-- 5-- - - �Stop 1: Bylund Trenches 1: Property-Scale Sampling Programs: Programs: Bylund Regional and property-scale property-scale surficial sampling sampling programs programs have been been widely used in in the the mineral mineral Unfortunately, aa significant significant proportion of of the surveys exploration sector for many years. Unfortunately, surveys Clearly, many many of of the failures failures undertaken within glaciated terrain have met with mixed results. Clearly, some effort been put forth forth in in understanding understanding the the nature nature of of the the could have been avoided had some development of of sampling sampling strategies strategiesand and Quaternary deposits present within a given area prior to the development At this thisstop, stop,discussion discussionwill will focus focuson on the the various various sampling sampling implementation of sampling programs. At media that are available to the explorationist explorationist for for aa surficial surficial geochemical geochemical perspective, perspective, how how they they are are collected and at what density and finally, the analytical techniques employed for their analysis. Trenches exposed adjacent to the Bylund Au occurrence occurrence will be used to demonstrate demonstrate the the various various media and sampling techniques. The Bylund Au property is located at the west end of the Dawson Road Lots and is is jointly operated by Freewest Resources Resources & & Co. Co. Inc. Inc. and and Greater Greater Lenora LenoraResources ResourcesCorp. Corp. Mineralization is contained within a 125 125 m wide, east-trending east-trending zone zone of of carbonate-altered, carbonate-altered, mafic mafic to to ultramafic ultramafic metavolcanic rocks transected by a stockwork stockwork of northeast-trending northeast-trending quartz-carbonate quartz-carbonate veins veins (Schneiders et al. 1998). 1998). Finely Finelydisseminated disseminatedarsenopyrite arsenopyriteis is commonly commonly associated associated with with Theauriferous auriferousdeformation deformationzone zoneoccurs occursatator ornear near the theunconformable unconformablecontact contact mineralization. The between Greenwater assemblage metavolcanics metavolcanics to the south south and and Shebandowan Shebandowanassemblage assemblage metasedimentary rocks to Channel sampling sampling over over the the main main Bylund occurrence occurrence has to the north. north. Channel 14 m. Outcrops Outcropsexposed exposedin intrenches trenchessituated situatedboth both east eastand and returned values of up to 4.1 g/t Au over 14 showing have have returned returned values values typically typically in in the the range range of of 11 to to 22 g/t g/t Au Au over over several several west of the main showing metres. Notable Notableintersections intersectionsinclude includeaa 0.54 0.54m m section, section,just west west of of the the main main showing, showing, assaying assaying 123 123 g/t Au (C. Bishop, Freewest Resources, personal communication, communication, 1998). 1998). The trenches west of the main Bylund occurrence occurrence were opened to investigate investigate Au and As anomalies in soil. They They expose expose aa variety of material types. Two Two facies facies of till have been recognized; buff-grey, stone-poor, silty sand till till of of semi-local semi-local composition composition and and aa stony, stony, silty siltysand sandtill tillof of a light, buff-grey, local composition. The Thelower, lower,local localtill till contains containsabundant abundantclasts clastsof of mineralized, mineralized, iron-carbonate iron-carbonate altered sericite schist. ItIt isis restricted restricted to to the the up-ice up-ice side side of of aa prominent prominent bedrock bedrock ridge ridge where erosive erosive forces beneath the advancing ice were greatest. Compressive Compressive subglacial subglacial forces forces resulted in the the till till section. This lower, local till being sheared up into the upper parts of the This till till contains contains anomalous concentrations concentrations of gold gold grains grains and appears appears to reflect reflect local local mineralization mineralization along along aa major major break. The Thebuff-grey buff-grey till till reflects reflects semi-local semi-local bedrock bedrock sources sources and and was was probably derived from the melting out of debris bands in the basal portions of the glacier. Red Red glaciolacustrine glaciolacustrine clays clays overlie overlie the till in low-lying ground to the north. Drift Drift thickness thickness diminishes diminishes to to less less than than aa metre metre at at the the crest crest of the hill consists of deeply deeply weathered weathered till. till. Soil samples collected for mineral exploration exploration bill and consists from this area returned anomalous Au and As values. The The bedrock bedrock surface surface drops drops off off abruptly abruptly to the south and is overlain by deposits of different character. Stratified Stratified deposits depositsare are intimately intimately associated associated with the till and were probably deposited in a leeside cavity beneath beneath the the glacier. glacier. These deposits deposits have been modified by glaciolacustrine processes. A A thin thin layer layer of of red clay overlies overlies the till package gravel. This and is capped by nearshore deposits of sand and gravel. This example example clearly clearly demonstrates the variabilty that that can can occur occurover oversuch suchaashort shortdistance. distance. Clearly, Clearly, an understanding of complexity and variabilty the origin of samples samples collected is required required for for the the successful successful interpretation interpretation of of geochemical geochemicaldatasets. datasets. �Sample Media Four distinct media types are commonly sampled for programs of mineral exploration utilizing These include: include: 1) 1) vegetation; 3) b-horizon b-horizon soil; and 4) surficial geochemistry. These vegetation; 2) 4) c-horizon c-horizon humus; 3) 2) humus; till. till. Vegetation Vegetation consists of the leaves, needles, twigs, twigs, cones cones or or bark bark of ofplants. plants. The premise behind behind sampling plant tissue for mineral exploration exploration is that the root systems of the plants will absorb metals contained in groundwater, overburden and bedrock at a given sample site. The The geochemical geochemical response of the plant tissue will therefore provide information on the chemistry of the the substrate on which the plant is growing. Vegetation Vegetationsampling samplingisisbest best utilized utilized in interrains terrainswhere where overburden overburdencover cover is thin (less than 3-4 m) and locally locally derived derived and and where where root root systems systems are are able able to to penetrate penetrate fractures fractures and joints Inareas areasof of thick, thick, exotic exoticoverburden, overburden,vegetation vegetation sampling samplingmay may fail fail to to evaluate evaluate joints in bedrock. In local mineral potential. For Foraaregional regionalor orproperty-scale property-scale sampling sampling program, program, itit is is important important to to collect collect samples of the same organ from plants plants of of the the same same species, species, size size and and outer outer appearance. appearance. Humus is a black to brownish-black, organic-rich material derived from the decomposition of forest lifter. litter. It consists of unidentifiable remains of leaves, roots, needles, bark, etc. that that have have been been Humus sampling sampling broken down into a fine-grained, amorphous material by by organisms and and bacteria. bacteria. Humus is, in many respects, similar to that of vegetation sampling. Being Being aa first first derivative derivative of of vegetation, vegetation, geochemical results geochemical The same same basic basic rules apply to humus resultsshould shouldmimick mimick those of vegetation. The sampling as well. Drastic changes changes in vegetation type could different well. Drastic could produce humus with different Bothhumus humusand andvegetation vegetationare aresusceptible susceptibleto tocontamination contaminationfrom fromanthropogenic anthropogenic compositions. Both 11117 between between the the Shebandowan Shebandowan Nisources of metal. Humus Humussamples samplescollected collectedalong alongHighway Highway 11/17 Cu-PGE mine and the hamlet of Sunshine are strongly contaminated. Hauling Hauling of of Ni-Cu concentrate concentrate in aa corridor corridor aa few few hundered hundered metres metres on on either eitherside sideof of the the highway highway within within along the highway resulted in values are enriched in humus. The Thec-horizon c-horizontill tilldata datawithin withinthis thiscorridor corridorhighlights highlights which metal values the true geochemical geochemical signature signature for for this this area. area. B-horizon soil soil is usually usually the the dark, dark, orange-brown orange-brown material material encountered encounteredat at aa depth depth of of 5-10 5-10 cm cmin in immediately below the humus layer. Often Oftenthere therewill willbe be aathin thinhorizon horizon of ofgreyishgreyishthe soil profile immediately Thislayer layer(Ae) (Ae)has has been been coloured mineral matter (Ae horizon) between the humus and B-horizon. This leached of most metals by the downward percolation of groundwaters rich in humic and fulvic downward percolation of groundwaters rich in humic and fulvicacids acids derived from the decomposition of the overlying organic organic debris. debris. The B-horizon is the the zone of of accumulation accumulation of of clays clays and and iron iron and and manganese manganese oxides oxidesderived derivedfrom fromthe theweathering weatheringof ofunstable unstable mineral grains. They Theyare are excellent excellentscavengers scavengers of metals. B-horizon B-horizonsoils soilscan can be be developed developed on on parent materials of local to non-local composition. For For the successful successful implementation of b-horizon soil sampling surveys, surveys, it is critical that the the parent parent materials materials be be composed composed of of till, till, that that they they have have characteristics and that they be of a local provenance. provenance. ItIt is similar grain size characteristics is also also important important that the till cover not exceed 2 to 3 m in thickness. C-horizon till is the relatively unaltered sediment that underlies the B-horizon. In In well-drained well-drained upland environments, oxidation can extend down several meters meters into into the theprofile. profile. Metals contained within sulphide sulphide minerals in this zone zone of of weathering weathering are generally liberated by oxidation and �hydromorphically dispersed downwards The upper part of the c-horizon will often often be downwards in in the the profile. profile. The enriched in metals compared surveys are compared to to the the b-horizon. b-horizon. C-horizon till sampling surveys are best best undertaken undertaken in areas where till thicknesses are less than The till till will will often often exhibit exhibit aa local local than aa few metres. metres. The signature under these In areas areas where where till cover is thicker, more more expensive expensive sampling sampling these conditions. In methods, such as reverse circulation drilling, are required to obtain till samples from the bedrockloverburdeninterface. interface. bedrock/overburden Analytical Methods explorationutilizing utilizing drift drift prospecting prospecting Analytical methods employed for programs of mineral exploration techniques and surficial geochemistry geochemistry vary depending upon the commodity commodity sought sought and and the sample sample media collected. collected. For the Shebandowan Shebandowan regional sampling sampling survey, 2 samples samples of of screened screened c-horizon c-horizon mm) were collected for analysis. A A 10 10kg kg sample sample was was collected collected for for heavy mineral till (-5 mm) concentration and subsequent subsequent gold grain, kimberlite indicator indicator mineral mineral (KIM) (KIM) and and metamorphic/magmatic massive sulphide indicator mineral Heavy mineral (MMSIM) determinations. determinations. Heavy minerals were separated from the -2 mm fraction of these these samples samples by wet gravity gravity tabling, producing producing a "table concentrate", then further concentrated to >3.2 B3.2 S.G. using density-dependent density-dependent settling settling in in methylene iodide. Magnetic Magneticminerals minerals were were removed removed from from the the methylene iodide heavy mineral concentrate (HMC) using an automagnet. automagnet. At the tabling stage, a preliminary count of gold grains, including size size and shape shape determinations determinations Thegold goldgrain graincontent contentof ofthe thetable tableconcentrates concentrateswas was further further refined refined using using aa was undertaken. The secondary panning samples containing greater panning procedure procedure to to obtain obtain more more exact exact grain grain counts. counts. Only samples 10 gold grains at the tabling stage were panned. The Thesize sizeand and shape shape of of the the panned panned gold gold grains grains than 10 table concentrate. concentrate. were recorded before they were returned to the table A second 2 to 3 kg sample of screened screened c-horizon till was was also also collected collected for for -63 -63 micron micron fraction fraction geochemical determinations. A A 30 30gg split split of of the the -63 -63 micron micron (silt (silt and and clay) clay) size size fraction fraction of this till (1NAA). The neutron activation activation matrix was sent for instrumental neutron activation analysis (INAA). dataset provides excellent information information on on the the Au, As, As, Sb Sb and and REE REE content of the samples. A second 20 to 25 g split was sent for Pt-Pd-Au determinations by by Pb Pb fire fire assay1ICP-MS assay/ICP-MS finish. finish. A third split was sent for geochemical geochemical determinations determinations by ICP-OES and ICP-MS following following aa standard standard aqua regia digestion. These Thesemethods methods produce produce high high quality quality data data on on the the base metal content of the samples. Similar Similaranalytical analyticalmethods methodsshould shouldbe be employed employedfor for vegetation, vegetation, humus humus and and b-horizon b-horizon sampling sampling programs programs as as well. well. For Forhumus, humus,the the—177 -1 77 im pmfraction fractionisisanalyzed analyzedrather ratherthan thanthe the—63 -63 .tm pm fraction. Humus Humussamples samples are are briquetted briquetted prior to neutron activation analysis. Vegetation Vegetation samples are either macerated and briquetted or ashed prior to analysis. analysis. Sampling Strategies The density at which samples samples are collected collected is dependent dependent upon the the style style of of mineralization mineralization sought. sought. Dispersal trains originating from lode gold type mineralization are significantly smaller than those originating from mineralization are significantly smaller than those originating from volcanogenic massive sulphide-type mineralization. mineralization. The The surface surface area area of mineralized rock available for erosion is probably the the most most important factor that that effects effects the the scale scale of of the dispersal train produced. The Theorientation orientationof ofthe themineralized mineralizedstructure structureor or horizon horizon with with respect respect to to �regional ice ice flow flow is is parallel parallel to to regional ice flow also effects the geometry of the the dispersal trains. trains. IfIf regional the strike of mineralization, the resulting dispersal train will be long, narrow and difficult to identify. IfIf regional regional ice ice flow flowisis perpendicular perpendicular to to the the strike strikeof of mineralization, mineralization, then then the the resulting resulting Theposition positionof ofmineralization mineralizationwith withrespect respectto toregional regionalice iceflow flowisisalso also dispersal train will be wider. The important. For For example, example, ifif the the mineralized mineralized horizon is shear-hosted and situated within a deep ravine perpendicular to ice flow, the advancing glacier may not not actively actively erode erode the the mineralized mineralized rock rock and therefore not produce a dispersal plume from mineralization. Dispersal trains originating from lode gold deposits of northern Ontario are typically less than than 200 to 300 m in length. Sampling Samplingprograms programs aimed aimed at at locating locating these types of deposits should Asample samplespacing spacingof of200 200m mand and therefore be designed to be able to identify a train of this length. A 100 m, staggered on 100 100 m lines, is recommended to recognize a potential target of this preferable 100 Onceaadispersal dispersaltrain trainisisidentified, identified,the thedensity densityatatwhich whichsamples samplesare arecollected collectedshould shouldbe be type. Once increased to to 25 25 m or 50 m spacing to more clearly define the source of the Dispersal increased the gold gold anomaly. anomaly. Dispersal arising from base metal targets can reach several kilometres in length. AAsampling samplingprogram program trains arising aimed at identifying this type of dispersal train could involve collecting samples initially at 500 m spacing then increasing the density to to 100 m in anomalous areas to to further refine refine exploration exploration targets. targets. Bylund Case Case Study High density, property-scale property-scale soil soil sampling sampling was was undertaken undertaken over over and and adjacent adjacentto to the theBylund Bylund Au Au occurrence at the west end of Dawson Road Lots. Fifty-three Fifty-threeb-horizon b-horizon soil soilsamples sampleswere were collected collected at 100 100 m centres centres on 6 grid lines spaced 100 100 m apart. The Theproperty propertyisischaracterized characterizedas asaa bedrockbedrockaccumulations of drift drift (till and stratified deposits) deposits) in low-lying areas. dominated upland with local accumulations Most soils soils are developed in till, however, a small small proportion have stratified sands sands and pebbly sands as their parent material. These These samples sampleswere were included included in in the geochemical dataset since most of them were derived from the washing and sorting of of the the underlying underlyingtill. till. Soil samples were not collected from a poorly drained drained wetland wetland that that occurs occurs along along the the west-central west-centraledge edgeof ofthe the property. property. The sample grid is oriented at 150° 150' Az and extends extends approximately 500 m south of the mineralized zone into unaltered Keewatin mafic metavolcanics. The Thesilt siltand andclay clayfraction fractionof ofthe thesoil soilsamples samples were extracted extracted and and geochemically geochemically analyzed analyzed by instrumental instrumental neutron neutron activation activation analysis analysisand and ICPICPfollowing a standard aqua OES following aqua regia digestion. digestion. Contoured plots of Au and As content derived by neutron activation analysis are presented in Figures 6. Other Otherelements elementsdid did not not show show aa close close spatial spatial association with mineralization. The The patterns depicted by Au and As clearly delineate the position of mineralization with little or no evidence for down-ice down-icedispersal dispersalbeyond beyond aa few few hundred metres. Similar Similarscales scalesof of glacial glacial dispersal dispersal have been previously documented at the Matachewan Consolidated Mine in northeastern Ontario (Bajc 1997) as well as at numerous other gold properties within the province. Gold Gold values values quickly quickly 100 to 200 metres down-ice (south-southwest) decline to below detection limit (<2 ppb) within 100 from the Bylund occurrence. Arsenic Arsenic values values display display aa slightly slightly more more diffuse diffuse pattern. L1W west of of the the documented documented Au Au W and L2W, immediately west Elevated Au and As values along L1 zones suggests a possible possible westerly westerly extension extension of ofmineralization. mineralization. A sample on L1 L1W that returned W that returned aa �1280 ppb and an As value of of 88.4 88.4 ppm was was collected collected from from the the fringes fringesof of aa poorly poorly gold value of 1280 This anomaly anomaly may have been drained wetland and contained significant amounts of organic matter. matter. This A produced by hydromorphic dispersion from from mineralized mineralized till till and and rock rock on on the the upland upland to to the the north. north. A anomalous Au and As response response was was obtained, obtained, however, however, from from an an upland upland soil soil 100 100metres metresto to similar anomalous the east. These These22anomalies anomaliesmay may suggest suggest aa second second auriferous auriferous structure structure is is present to the south; south; this warrants further investigation. A A strong strong Au Au and and As As anomaly anomaly along along the the central portions of lines lines 2E and 3E suggest suggestthe the potential potential for for another, another, as as yet yet undiscovered, undiscovered, zone zone of of mineralization. mineralization. recommendations can be drawn drawn from from the the Bylund Bylund soil soil sampling sampling Several conclusions and recommendations orientation survey. orientation survey. 1. Soil geochemistry is a viable exploration tool for shear-hosted 1. shear-hosted gold gold in in the the eastern eastern portion of the Shebandowan Shebandowan greenstone belt. The Thetechnique techniqueisisbest best suited suitedto to upland upland properties with thin till cover and abundant abundant outcrop. outcrop. 2. AAsample samplespacing spacingofof100 100mmstaggered staggeredon onadjacent adjacentlines linesappears appearsto to be be sufficient sufficient for for the the delineation delineation of potential potential mineralized mineralized zones. zones. 3. Gold and arsenic appear to be the elements elements best suited suited for for target delineation delineation at at the the Bylund occurrence. Neutron fraction (-63pm) (-63tm) of Neutron activation activation analysis of the silt and clay fraction of soil provides excellent contrast between background and anomalies. anomalies. 4. 4. There is very little little evidence evidence in in support support of of down-ice down-ice dispersal dispersal of of gold gold greater greater than than 100 100to to 200 m from mineralization. Ultra-high Ultra-highdensity densitysampling sampling(i.e. (i.e.20 20to to 25 25 m m spacing) spacing)would would be required to more more clearly clearly define define glacial glacial dispersal dispersal patterns. patterns. Turn vehicles vehicles around around and proceed proceed back out to the highway. highway. Turn Turn right, right, drive 3.1 km km east along Highway 11/17 and stop at aa rockcut rockcut along alongthe the sides sidesof of the the highway. highway. �A *C) • <2 • <2 Auu mineralization mineralization 5' •<2 • <2 Au (ppb) • <2 • <2 .3 • <2 .3 100 m .3 • • <2 .3 13 • <2 B .1.8 / .2.9 100 m •2O .19 4.6 S /.12 Figure Figure6. 6.Geochemical Geochemicalresponse responseofofb-horizon b-horizonsoils soilsover overand andadjacent adjacentto to the the Bylund Au contoured Au data: B: contoured occurrence, Dawson Road Lots. A: occurrence, Lots. A: data: B: contoured As As data. data. �Stop 2: Crossing Crossing Striation Striation Site Site At this stop, we will have an opportunity to look at an outcrop outcrop of of Shebandowan Shebandowanassemblage assemblage The striation striation metasediments that are well striated and flanked by red, glaciolacustrine clay clay and and till. till. The displays a consistent consistent pattern pattern of of flow flow towards towards the the south south record for the western half of the belt displays There is, is, however, however, evidence evidence for an older becoming progressively more westerly westerly towards towards the the west. west. There ice flow event towards the the southeast in the the southwestern comer corner of of the the Sunshine Sunshine map map area. area. The significance of this event is There are are several several examples examples of of southeasterly-oriented southeasterly-oriented (160° (160' is not not known. known. There Az) striae striae crossed by south-southwesterly south-southwesterly (200-210° (200-2 10' Az) striae striae on on the the outcrop outcrop surface surface (Figure (Figure 7). 7). This older older event event is is In most cases, the older striae are preserved on faceted, protected protected surfaces. surfaces. This krn since it has been observed observed at many sites sites spanning spanning aa 30 30 km recognized as regionally significant since The till till overlying overlying the bedrock surface is distance and is not apparently related to topography. The deposited by ice flowing flowing towards towards the the south-southwest south-southwest (latest (latest ice ice fow fow direction). direction). believed to be deposited on the the southeast southeast end end of of the the roadcut roadcut have have striated striated upper upper surfaces surfaces Faceted boulders within the till on indicating flow towards the south-southwest. This Thisinformation informationisis critical critical for for the the successful successful followfollowanomalies obtained obtained from from this this area. area. up of till anomalies Figure Figure7. 7. Crossing Crossingglacial glacialstriae striaewere werefrequently frequentlyencountered encounteredin in the the Dawson Dawson Road Lots area. In In this example, example, an an older older set set of of striae striaeoriented oriented at at 160° 160' Az Az are are crossed crossed by by aa main main set set oriented oriented at 210° Az. 210' Az. Proceed 11/17 to to Sunshine Sunshine Cross Cross Rd. Rd. Turn left left (north) onto onto sideroad sideroad and Proceed 9.8 9.8km krn east on Highway 11/17 stop by the railway railway tracks. tracks. �Stop 3: Contamination and and Implications for Mineral Exploration 3: Humus Contamination At this stop, we will have an opportunity to discuss humus sampling and potential problems that may arise with contamination. This This site site was chosen for the stop because it is located adjacent to to aa railway siding that was used by 1NCO INCO for for loading loading Ni-Cu Ni-Cu concentrate from the Shebandowan mine onto railway cars. During Duringthe the early early days days of of production production at at the the Shebandowan Shebandowanmine mine site, site, Ni-Cu Ni-Cu concentrate was hauled by dump truck from the mill to the railroad siding at Sunshine, a distance of Thedispersal dispersalof offine fineparticulate particulate suiphides sulphidesby by wind wind from from these these trucks trucks approximately 50 km. The resulted in a strong Ni-Cu geochemical anomaly in humus following the Highway 1117 corridor Highway 111/17 corridor and extending several hundred metres in from the highway. The The Ni-Cu Ni-Cu geochemical geochemical datasets datasetsfor for Sunshine and Kakabeka Kakabeka Falls Falls map areas areas clearly illustrate illustrate this contamination (Figure 8). The The the Sunshine geochemical datasets c-horizon till are are drastically drastically different different from from those those portrayed portrayed by by the the humus humus datasets for c-horizon and reflect the primary geochemical geochemical signature signature associated associated with with local local variations variationsin in bedrock bedrock source source and 7). 7). It would appear appear that there is no signal of contamination within c-horizon rocks (Figures (Figures 66 and rocks till. till. All humus sampling programs should consider the potential for problems associated with contamination. Contamination Contaminationcould couldarise arisefrom fromaavariety varietyof ofsources sourcesincluding including road road dust dust from from local local logging operations, wind-blown tailings dust and airborne fallout from smelters. In In the the Sudbury Sudbury area, there is a strong geochemical signature in humus associated with the smelting operations. The The element associations associations closley mimmick those of the ore mined in Sudbury. Fine Finecolloidal colloidalsulphide sulphide element particles particles are dispersed by wind and quickly oxidize in the surficial environment where they are available for adsorption by humic and falvic fulvic acids acids present present within withinthe thehumus. humus. Should a potential source of contamination be identified within a given area, it is recommended that the explorationist avoid sampling humus and that c-horizon till be considered considered as the preferred sampling medium for surficial geochemical geochemical surveys. surveys. Proceed back back out out to to Highway 11/17. Turn Turnleft left (east) (east)and anddrive drive 3.0 3.0km krn to the intersection intersection of Proceed Highways 11/17 and and 102 102 (Sistonens (Sistonens Corners). Corners).Turn Turnleft leftonto ontoHighway Highway102 102and andproceed proceed7.0 7.0kms krns before turning left into a sand sand and and gravel gravel pit pit owned owned and andoperated operatedby byTowland-Hewitson Towland-Hewitson Construction Ltd. Construction Ltd. �Figure 8. Comparison of humus and c-horizon till geochemical datasets for nickel, Note the strong anthropogenic signature in humus along the Highway 11/17 corridor. This anomaly is attributed to the haulage of Ni-Cu concentrate from the Shebandowan mine to a railway siding near the village of Sunshine. �Stop 4: Glacial Lakes of the Shebandowan Shebandowan Area Portions of of the the Shebandowan Shebandowan study study area were inundated by glacial lakes. These Theseinclude: include:1) 1) Portions glacial Lake Agassiz Agassiz in in the the extreme extreme western western part part of of the the study study area; area; 2) glacial glacial Lake Kaministikwia Kaministikwia glacial and high high level level Superior Superiorbasin basin lakes lakes within the Sunshine Sunshine map area; area; and 3) glacial lakes O'Connor and within Thedeposits depositsof ofthese theseglacial glaciallakes lakes are are considered considered aa Kakabeka Falls map area (Figure 9). The within the Kakabeka hinderance to to programs programs of ofmineral mineralexploration explorationutilizing utilizingsurficial surficialgeochemistry geochemistryininthat thatthey theyconceal conceal hinderance and prevent access to deposits of till till and the the underlying underlying bedrock. bedrock. The composition of glaciolacustrine deposits deposits does does not not closely closely reflect reflect the the composition compositionof ofthe theunderlying underlyingbedrock bedrockand and glaciolacustrine should should therefore not be sampled for mineral exploration purposes. Expensive Expensiveoverburden overburdendrilling drilling techniques must must be be utilized utilized to to sample sample the the glacial glacial tills tills that that underlie underlie these these deposits. deposits. techniques Glacial Glacial Lake Lake Agassiz Agassiz was was the the largest largestof ofseveral severalwater waterbodies bodieswhich whichbordered borderedthe thesouthern southern margin margin of of the the Laurentide Laurentide Ice Sheet Sheet during Late Wisconsinan glaciation. ItItinundated inundatedan anarea areaof of approximately11million million square squarekilometres, kilometres,although althoughatatno noparticular particulartime timedid didititoccupy occupythis thisentire entire approximately area. The Thelake lakeformed formedapproximately approximately12.0 12.0ka kaBP BPwhen whenice iceof ofthe theDes DesMoines MoinesLobe Loberetreated retreatednorth north area. of the the continental continental drainage drainage divide divide in in eastern eastern North Dakota Dakota and northwestern northwestern Minnesota ponding of water water within within the the Red Red River River valley. valley. Progressive Progressiveexpansion expansionofofthe thelake lakeinto intoManitoba, Manitoba,Ontario Ontarioand and parts of of Saskatchewan Saskatchewan occurred occurred with with further further retreat of the ice margin. Glacial GlacialLake LakeAgassiz Agassiz parts extended into into northwestern northwestern Ontario, Ontario, fronting fronting the the retreating retreating ice margin in low-lying areas. Deposits Deposits extended of glacial glacial Lake Lake Agassiz Agassiz occur occur in in the the southwestern southwesterncorner cornerof ofthe theBurchell BurchellLake Lakearea areaalong alongthe the of Obadinaw Obadinaw River River valley. The Thedeposits depositsare aremainly mainlycoarse-textured coarse-texturedwithin withinthis thisregion, region,however, however, varved clays clays have been reported from the banks of Tilly Creek. An Anice-contact ice-contactdelta deltabuilt built off off of ofthe the Brule Creek Creek Moraine Moraine south southof ofBurchell BurchellLake Lakegrades gradesto to an anupper upper level levelof ofLake LakeAgassiz Agassiz(Herman (Herman Brule level) at at 457 457 to 472 m m asl. asl. All Allareas areassouth southofofthis thismoraine moraineand andbelow belowthis thiselevation elevationwould wouldhave have level) been been inundated inundatedby by Lake LakeAgassiz. Agassiz. Glacial Glacial Lake Lake Kaministikwia Kaministikwiaoccupied occupiedthe thevalleys valleysof ofthe theOskondaga, Oskondaga,Matawin, Matawin,Shebandowan Shebandowan and Kaministikwia Kaministikwiarivers riverswithin within the the Sunshine SunshineNTS NTS map maparea. area. The Thelake lakewas wasbordered borderedon onits its and northeastern northeasternand andsoutheastern southeasternflanks flanksby byglacial glacialice iceof ofthe thenorthern northernand andSuperior Superiorlobes, lobes,respectively. respectively. High High ground ground bordered bordered the the lake lake to to the the north, north, west west and and southwest. southwest. The TheDog DogLake Lakeand andMarks Marks moraines morainesmark mark the thepositions positionsofofthe thenorthern northernand andSuperior Superiorlobes, lobes,respectively respectivelywhile whileLake Lake Kaministikwia Anice-contact ice-contactdelta deltaconstructed constructedoff offofofthe theDog DogLake LakeMoraine Morainejust just Kaministikwiawas was in in existence. existence. An south of Dog Lake and whose upper surface occurs at 460 m as! defines the glacial Lake south of Dog Lake and whose upper surface occurs at 460 m as1 defines the glacial Lake Kaministikwia Kaministikwiawater water plane. plane. The Thelake lakeformed formedwithin withinthe thestudy studyarea areaapproximately approximately10.0 10.0ka kaBP BPwhen when the northern and Superior lobes readvanced into the study area during a late-glacial surge event the northern and Superior lobes readvanced into the study area during a late-glacial surge event (Marquette (Marquetteadvance). advance). The Theextent extenttotowhich whichnorthern northernand andSuperior Superiorice iceretreated retreatedprior priortotothis thisevent eventisis not not known. known. Meltwaters Meltwatersinitially initiallydrained drainedfreely freelysouthward southwardoff offofofthe theretreating retreatingnorthern northernice icemargin margin depositing depositingthick thicksequences sequencesof ofglaciofluvial glaciofluvialsands sandsand andgravels gravelswithin withinthe thevalleys valleysofofthe the Kaministikwia Kaministikwiaand and Oskondaga Oskondagarivers. rivers. Progressive Progressiveincision incisionofofthe thefluvial fluvialdeposits depositsoccurred occurredasasbase base levels levelsdropped dropped within within the the lower lowerreaches reaches of of the the valleys. valleys. Thick Thicksections sectionsofofglaciofluvial glaciofluvialsand sandand and gravel gravelare areclearly clearly visible visible from from Highway Highway 102 102within within the the Kaministikwia Kaministikwia river valley. These Thesedeposits deposits are are terraced terraced and and draped draped by by distinctive, distinctive,red red clays clays associated associated with with glacial glacial Lake Kaministikwia. The The red red clays clayswhich whichcan canreach reachthicknesses thicknessesof ofseveral severaltens tensofofmetres, metres,are aretypically typicallyfaintly faintlylaminated laminatednear near the the base base and and become become progressively progressively more more massive massive upwards. upwards. The Thered redpigmentation pigmentationofofthe theclay clayisis �showing the locations of the major moraines and glacial lake basins. Figure 9. Digital elevation model of the Thunder Bay area �derived from Sibley Group metasedimentary source source rocks rocks eroded eroded by bythe the Superior SuperiorLobe. Lobe. Glacial Lake Kaministikwia probably probably lasted no no more more than than aa few few hundred hundred years. years. The lake overflowed westward into the Glacial Lake Agassiz basin via a narrow lowland lowland through through Shebandowan ShebandowanLake. Lake. Red clays within the eastern Lake Agassiz basin attest to this influx influx of of sediment sediment from from Lake Lake GlacialLake LakeAgassiz Agassizmust musthave havefallen fallenfrom fromaa Herman Herman to to aa lower lower level level prior prior to to the the Kaministikwia. Glacial development Kaministikwia. development of Lake Kaministikwia. occupied the the valleys valleys of the Whitefish Whitefish and Kaministikwia Kaministikwia rivers within Glacial Lake 0'Connor O'Connor occupied the Kakabeka Falls map area. The Thelake lakefronted frontedthe the advancing advancingSuperior Superiorlobe lobe during during the the Marquette Marquette the Whitefish Lake Lake basin. basin. Shorelines advance and probably drained westward through the Shorelines associated associated with this glacial lake have not been identified. Fine Finetextured textured glaciolacustrine glaciolacustrinedeposits depositshave have 0'Connor occur both however been observed beneath till up to 350 350 m asl. Deposits Deposits of of glacial glacial Lake O'Connor above and below till of the Superior lobe. This Thissequence sequenceisistypical typical of of an an ice ice advance-retreat advance-retreat cycle cycle within a glacial lake basin. Thick Thicksequences sequencesof ofsilty siltyto to clayey clayey grey grey rhythmites, in places exceeding 30 m in thickness, occur beneath fine-textured Superior lobe till within the Whitefish River lowland. Excellent Excellentexposures exposuresof ofthese thesedeposits depositsoccur occurin inlarge largesections sectionsalong along the the Whitefish Whitefish River River valley and its tributaries. Grey, Grey, rhythmically rhythmically laminated laminated clays clays associated with Lake O'Connor overlie Superior lobe till. These Thesedeposits depositshave havebeen been observed observedto to exceed exceed several several metres metres in in thickness. thickness. As the Superior lobe continued to withdraw from the Whitefish-Kaministikwia lowland, low-level outlets to the Superior Superior basin were uncovered resulting in the termination of glacial Lake Lake O'Connor. O'Connor. Superior basin waters inundated low-lying areas up to This represents represents the the to approximately 260 260 m m asl. asl. This approximate level of glacial Lake Minong, the highest water water body body to to occupy occupy the the entire entire perimeter perimeterof of the Lake Superior basin. Very Verylittle littleisisknown knownabout aboutthe thelate-glacial late-glacialhistory history of of glacial glacial lakes lakes within within Clearly,additional additional studies studiesare are required. this southern basin. Clearly, At this fieldtrip stop, we will look at a section of glaciolacustrine deposits associated with glacial Lake Kaministikwia. These Thesered, red, clay clay rich rich deposits depositsare are unusual unusual in in that that they were deposited in the ice ice margin. margin. The approximately 100 m of water less than a few kilometres from the The clays clays are rhythmically rhythmically laminated laminated at at their their base, where where they they overlie overlie glaciofluvial glaciofluvial deposits depositsof of sand sandand and gravel, gravel, and quickly become massive upwards. There Thereisis very very little little indication indication of of aa proximal proximal ice ice margin. margin. That is, there are very few dropstones and few few indications indications of of seasonal seasonal variability variability in in sediment sediment load. load. Proceed Proceed back back to to Highway 11/17 (Sistonens Corners) and turn left (south). Travel Travel 5.2 5.2km south along along Highway 11/17 and turn turn left on Teitto Road. The The next stop consists of aa road cut on the southeast ofthis this intersection. intersection. southeast corner cornerof Subaquatic Flow Till and Stop 5: Subaquatic and Glaciolacustrine Glaciolacustrine Sediment Sediment of the Superior Superior Lobe Lobe lobe. This At this site, we begin to see the first direct evidence of the advancing Superior lobe. This 22 m m well exposure is located less than a few kilometres from the Marks Moraine and consists of well overlying massive massive dark dark grey grey silty siltytill. till. These sediments were laminated, gritty, pebbly silt and clay overlying likely deposited at the bottom of of Lake Lake Kaministikwia Kaministikwia as as bottom-hugging bottom-hugging density density currents currents and and as as ice-rafted debris (rainout) in water depths of about 50 m. Red Red Sibley SibleyGroup Group siltstones siltstonesand and dark dark grey shales derived from the Gunflint Formation Formation are are clearly clearly recognizable recognizable in in the pebble pebble fraction fraction and and provide direct evidence for a Superior lobe provenance. Red, Red, massive massive clays clays associated associated with with glacial glacial �Lake Kaministikwja Kaministikwia occur less less than a few few kilometres kilometres to Clearly, the to the the north north of of this this site. site. Clearly, the composition of the Superior Superior lobe lobe flow flow tills tills and and glaciolacustrine glaciolacustrine deposits do not reflect the composition deposits do not reflect the This material material should should not not be be sampled sampled for for mineral mineral composition of the underlying Archean bedrock. bedrock. This exploration purposes. purposes. exploration Turn vehicles around and and turn turnleft left onto onto Highway Highway 11/17. 11/17. Proceed south 5.3 5.3 km krn to Proceed south to Briggs Briggs Drive Drive and and turn right (east) (east) into into Conmee Township sand and gravel pit. Park vehicle at gate i f locked. sand and gravel pit. Park vehicle at gate j/locked. OverriddenSuperior SuperiorLobe LobeDelta Delta and and Conmee Conmee Base Stop 6: Overridden Base Metal Metal Float Float exposed sequence sequence At this stop, we will be looking at aa section of of Superior Superior lobe lobe drift. drift. The exposed consists of approximately 6 to 7 m of well sorted, steeply-dipping sand and gravel of Superior consists Clastsin in the the lower lower provenance overlain by 2 to 3 m of silty Superior lobe till till (Figure 10). Clasts glaciofluvial unit consist primarily of Proterozoic Proterozoic metasedimentary metasedimentaryrocks. rocks. Numerous cobbles and Numerous cobbles and Gunflint Formation Formation and and Sibley Sibley Group Group are are recognizable. Foreset beds dip boulders belonging to the Gunflint recognizable. Foreset beds dip The delta delta was steeply to the north and are likely of deltaic origin. origin. The was probably probably built built proglacially proglacially into into an early phase of glacial Lake Kaministikwia. The feature therefore represents a location at which Lake Kaministikwia. The feature advancing Superior Superior Lobe Lobe stalled stalled prior prior to to reaching reaching its its maximum maximumposition positionatatthe theMarks MarksMoraine. Moraine. the advancing The delta is actually located within only 3 km krn of the Superior Superior lobe limit limit and and occurs at an elevation was of about 375 m asl, asi, 85 m below below the the maximum maximum elevation elevation of of Lake LakeKaministikwia. Kaministikwia. The delta was overridden by the Superior lobe resulting in the truncation of the foreset unit and removal of the overridden Superior resulting in the truncation of the foreset unit and removal of the Severalmetres metresof ofsilty, silty,Superior SuperiorLobe Lobe subglacial subglacialtill till was was deposited deposited on on top top of of the the sands sands topset beds. Several and gravels. gravels. of large large angular angular to rounded boulders boulders on on the the pit pit floor. floor. significanceis the occurrence occurrence of Of particular significance from the lower lower glaciofluvial glaciofluvial unit unit and, and, in in some some cases, do not appear to The boulders were extracted from have been transported very far. Some Someof of the the larger larger boulders boulders measure measure several several metres across and still still display striated surfaces. The The boulders boulders are are derived derived from from both both Archean Archean and and Proterozoic Proterozoic source source rocks. Several Severalboulders bouldersof ofsuiphidized sulphidizediron ironformation formationand andmassive massivepyrite pyriteof ofArchean Archeanage agewere were discovered in the boulder piles. One Oneof ofthe theboulders bouldersmeasured measuredover over11m min indiameter diameterand and consisted consisted of massive pyrite and magnetite with 10 to 15% sphalerite disseminated in pyrite-rich sections. 10 15% sphalerite disseminated in pyrite-rich sections. throughout the Sphalerite was also concentrated concentrated along along fractures fractures and and adjacent adjacent to to quartz quartz veinlets veinlets throughout the rock. rock. 18 pprn ppm Cu, Cu, 19 ppm Two samples samples from from the pyrite-rich pyrite-rich zones zones returned returned values values of: of: 1) 1)5.13% 5.13% Zn, Zn, 18 19 pprn 16 ppm Cu, 20 ppm Pb, 245 ppb Au and Pb, 260 ppb Au and 0.5 pprn ppm Ag; and 2) 2)2.85% 2.85% Zn, Zn, 16 pprn Cu, 20 pprn Pb, 245 ppb Au and 0.5 0.5 magnetite-rich zone returned values of 850 ppm Zn, 25 ppm Cu, ppm Ag. A sample from the pprn A sample from magnetite-rich zone returned values of 850 pprn Zn, 25 pprn Cu, 55 ppm <0.2 pprn ppm Ag. Ag. A second second sulphidized sulphidized iron iron formation formation boulder boulder measuring measuring pprn Pb, 25 ppb Au and <0.2 pyrite, returned of pyrite, returned values approximately 0.5 m in diameter and consisting almost exclusively of values of of 140 140 ppb Au Au and ppm Zn, 8 pprn ppm Cu, 11 ppm Pb, 710 ppb 1 1 pprn and <0.2 <0.2 ppm pprn Ag. Ag. pprn There are two possible source source areas areas for for the the boulders. boulders. Superior Superior lobe lobe striae striae in in the the immediate immediate eroded and transported vicinity of the pit are oriented at 320 to 330' 330° Az. IfIf the the boulders boulderswere were eroded and transported by by from they could have been Superior ice, then there is a 5 km window towards the southeast from which which they could have been beyond the the 55 krn km limit. limit. Alternatively, derived. Proterozoic derived. Proterozoic metasedimentary metasedimentary rocks rocks outcrop outcrop beyond Alternatively, the the �Figure 10. Figure 10. Steeply-dipping Steeply-dippingforeset foresetbeds beds of of aa delta delta constructed constructed along the margin of the advancing Township). Silty Superior lobe (Conmee Township). Silty Superior Superior lobe lobe till caps the sequence. boulders could have initially been eroded by northern ice from a source source to the north-northeast north-northeast of of the the pit then remobilized by the Superior lobe. remobilized Superior Exploration work during 900s along the lower reaches of Brule Creek, 4 to 5 km during the early 11900 Sulphur Company and General General north-northeast of the gravel pit, by B.L. Morrison, the Davis Sulphur Chemical Company resulted in the discovery discovery of "seven "seven lenticular masses of brecciated, brecciated, banded iron iron formation, in which pyrite has replaced replaced aa considerable considerable part part of of the the rock" rock" (Carter (Carter 1990b). 1990b). The largest of these masses has a maximum width of 23 m and is 244 m long. Other Other discoveries discoveriesinclude includeaa 21 21 magnetite and and pyrrhotite pyrrhotite and andaa99m mwide wideby by 15 15m mlong longzone zoneof of m wide body of pyrite containing magnetite magnetite-pyrite-jasper ironstone. ItIt is is possible possible that that the the boulders boulders found found within the gravel pit were derived from this area and that sphalerite was was not not recognized recognized in in the the rock. rock. It is is not yet clear whether sulphides indicate proximity to to a VMS style zone zone of of mineralization. mineralization. Further the sulphides Further work is is required required to assess the mineral potential of this area. assess south on onHighway Highway111/I 0.5km. k,n. Turn Turn left leftatatHolland HollandRoad Roadand andproceed proceedeastward eastwardfor for Continue south 1 4 77for for 0.5 roadcut at 2.6 km to a roadcut at the the top top of of aa steep steep decline. decline. �7: Superior Northern Till Stop 7: SuperiorLobe Lobe Till Overlying Northern The purpose of this stop is to compare and contrast contrast tills tills of Superior and and northern northern provenance provenance programs. Exposed with respect to drift prospecting programs. Exposed in in the the road cut cut on on the the south south side side of of the the road road is is approximately fairly high approximately 2 to 3 m of brown, blocky, silty Superior lobe till containing aa fairly from the the Gunflint Gunflint Formation, Formation, 2.5 2.5 km km to to the the southeast. southeast. Despite concentration of platy clasts derived from Despite its apparent subglacial origin, this this till till contains few clasts clasts of of Archean Archean supracrustal supracrustal or or intrusive intrusive composition. An olive grey, silty sand till of northern provenance is exposed in a few An olive grey, silty sand of northern provenance few places beneath the the Superior Superior lobe lobetill. till. Most of the clasts in this this lower till till are are of of an an Archean Archean directly beneath affinity. A quartz-feldspar porphyry is exposed in outcrop further down the slope and probably A quartz-feldspar porphyry is exposed in outcrop underlies the northern till in this exposure. exposure. lobe till till as as aa sample medium medium for for mineral mineral Under discussion is the suitability of Superior lobe exploration programs over Archean terrain terrain in in the the eastern eastern portion portion of of the the belt. belt. Compositionally, Compositionally, lobe till till overlying overlying Archean Archean bedrock bedrockdoes doesnot notreflect reflectlocal localbedrock bedrocksources. sources. This is likely Superior lobe attributed to the fact that the Superior lobe was was surging into into aa glacial glacial lake, lake, overriding overriding fine-grained fine-grained glaciolacustrine deposits and shales. The fine-grained substrates and proglacial lakes faciltated The fine-grained substrates proglacial lakes faciltated the process. Subglacial erosion close to the the ice ice margin margin was wasreduced reduceddue dueto toaafloating floatingice iceshelf shelf surging process. and reduced subglacial pressures caused by buoyancy. subglacial pressures caused by buoyancy. The background concentrations of gold grains grains and and elements elements in in Superior Superior lobe lobe till till are are different from those of northern tills. It is therefore advisable to treat datasets significantly different containing information from both tills as separate populations populations for anomaly anomaly recognition. recognition. Even more more importantly, it is recommended that only the the lower lower northern northern till till be be sampled sampled in in Archean Archean areas areas affected by the the Superior lobe. In In areas areas of of thick thick overburden, overburden, it may be necessary to employ expensive drilling techniques to sample the the lower till. till. Alternatively, Alternatively, itit may may be be possible possible to access access by backhoe backhoe trenching trenching off offof ofoutcrops outcropsininthe thearea. area. To To the the south south of of the the Whitefish Whitefish River River the lower till by lowland, Superior lobe till till is exposed exposed on on the the flanks flanksof ofthe theLogan Logandiabase diabasesills. sills. The The till till in in this this area area appears to reflect local variations in bedrock geology geology and and may maybe be suitable suitablefor for exploration exploration programs programs for such commodities commodities as as silver silver or or the platinum group group elements. elements. the vehicles vehiclesaround around andproceed and proceed back to to Highway Highway 11/17. 11/17. Drive Drive straight through Turn the through Highway down Holland Holland Road Roadfor for 3.2 Ion. kin. Stop at top of hill adjacent to aa microwave 11/17 down microwave tower on on the side of of the the road. road. Proceed pit adjacent adjacent to the south side Proceed to to the the north north edge edge of the sand and gravel pit microwave tower. microwave tower. 8: Scenic Brule Creek Moraine Stop 8: Scenic Lookout and Extension of the Brule this site provides provides the the fieldtrip fieldtrip participant participant an an excellent excellent view view of of the the lowland lowland The view afforded at this advanced during during the the Marquette MarquetteAdvance. Advance. Thunder Bay is located into which the Superior Lobe advanced km to to the the east east and and the the Logan Logandiabase diabasesills sillstotothe thesouth southare areapproximately approximately12 12km kmaway. away. Our over 30 km point is is situated situated approximately approximately 120 120mm above the Whitefish Whitefish River River lowland lowland to tothe the south southand and vantage point the east. east. The 230 m above Lake Superior to the The upland upland on which we stand stand clearly clearly affected the Superior Lobe causing it to halt less than 3 km to the northeast of this advancing Superior this location. location. �-s- —— — -- - - - — - _ - - ____________ -- - _ — — _ - --- - ---j -- -c 1--: -t.... -: _ r— -- - C *S- - — Cr----: I Ic- - ___ - 1- - ____ T_i_± - —- - C --S-- 2__ _ - Figure 11. Figure 11.Oblique Obliqueaerial aerialview viewofofthe theWhitefish-Kaministikwia Whitefish-Kaministikwialowland lowlandinto intowhich whichthe theSuperior Superior the Marquette Marquette stadial. stadial. Mesas of Proterozoic diabase are visible lobe advanced during the in the distance. distance. Exposed in the sand and gravel pit before us is a sequence of glaciofluvial sand and gravel of northern provenance which is in turn overlain by a unit of glaciolacustrine sand and finally by m of silty silty Superior Superior Lobe Lobetill. till. Paleocurrents in the lower glaciofluvial unit suggest approximately 3 m flow towards the the south-southwest. south-southwest. This is consistent with with aa northward northward retreating retreatingice icemargin. margin. The The glaciolacustrine sands glaciolacustrine sands are likely associated associated with with an an early early phase phase of of glacial glacial Lake Lake Kaministikwia. Kaministikwia. A number of buried sand and gravel deposits of northern provenance occur in southern and and adjoining adjoining Oliver Oliver Township. Township. It is possible that these deposits southeastern Conmee Township and Brule Creek Moraine, a significant ice-marginal feature represent the eastern extension of the Bmle the retreating northern northern ice ice lobe. lobe. The eastern extension of the Brule Creek Moraine associated with the beyond the Marks Moraine was obscured by Moraine obscured the the advancing advancing Superior Superiorlobe. lobe. The next next stop stop is is optional optional depending depending upon upon the the condition conditionof ofthe theroad road intothe intothe site. site. Continue Continue west kmdown downHolland HollandRoad RoadtotoSovereign SovereignRoad. Road Turn Turn right right and and drive drive north north 800 800 m. m. Turn another 1. 1.77 km logging road road and follow follow ititfor for approximately approximately600 600m. m. Turn right right at at vv in in road road and andfollow follow road road left on logging (-1 kin,). km). Park Parkvehicle vehicleatatcrest crestofofhilL hill. to the north until you reach reach aa clearcut clearcut('-4 �9: Marks Moraine Stop 9: This fieldtrip stop is located on on the the crest crestof ofthe theMarks MarksMoraine, Moraine,aaterminal terminalmoraine moraineassociated assoiated 9.9 to 10.0 10.0ka ka BP, BP, with the advancing Superior lobe. The The moraine moraine was was constructed constructed approximately approximately 9.9 during the Marquette Stadial. ItIt has has been been traced traced across across the study study area area from the southwestern southwestern corner comer of Marks Township to the southeastern comer corner of of Ware Ware Township. Township. Mapping is required toward Mapping is required toward the the its position. position. Where it is best developed, the moraine consists consists of of multiple multiple till till southwest to determine its ridges within a zone 11 to 2 km wide (Figure 12). It is composed primarily of fine-textured till and 12). It is composed primarily of fine-textured till and relatively low low profile. profile. In other areas, the moraine consists of a stacked therefore displays a relatively sequence of flow tills tills and glaciolacustrine deposits deposits with with no no apparent apparent geomorphic geomorphic expression. expression. The moraine here is assymetrical in cross-section, displaying a steeper slope on the ice-contact side. side. Fine-textured glaciolacustrine sediments sediments interbedded interbeddedwith with Superior Superior southeastern, ice-contact tills occur bevone beyong themoraine morainetotothe thenorthwest. northwest. To To the the southwest southwest are areaa series seriesof of lobe flow tills . the that follow follow the the ice ice margin margin and and terminate terminate in in the the Kaministikwia Kaministikwia basin basin to to northeast-trending channels that the northeast. Paleocurrents flow towards towards the the Paleocurrentsof of cross-bedded cross-bedded sands within these channels indicate flow Kaministikwia basin. Kaministikwia basin. - Drive back out to the intersection of of Sovereign SovereignRoad Roadand andHolland HollandRoad Roadand andproceed proceedsouth south on on Sovereign Road for for 4.9 km km till tillyou youreach reach Highway Highway 590. 590. You have have now now descended descended into into the the Whitefish-Kaministikwialowland, lowland,aavertical verticaldrop dropof ofover over100 100in. m. Sovereign SovereignRoad Roadchanges changes into into Whitefish-Kaministikwia Highway 595 595 beyond beyond Highway Highway590. 590. Continue south on Highway 595 595for for an an additional 4.9 Highway 4.9 km. km. Smith Road Road and and drive drivefor for 3.0 km km till tillyou you reach reach a bridge crossing Turn left on Smith crossing Whitewood Whitewood Creek. Creek. Park the far side Park the vehicle vehicle on the right on on the far side of of the bridge. bridge. Stop 10: 10: Whitewood Creek Section At this stop, we will be looking at a section along the banks of Whitewood Creek that exposes 2 glaciolacustrinedeposits. deposits. The section has has not not been been studied studied tills with intervening and superimposed glaciolacustrine in detail. however, demonstrate demonstrate the the drastic drastic changes changes that that occur occur in in till till character character as as one one detail. It does, however, Archean upland upland to tothe thenorth northinto intothe theWhitefish-Kaministikwia Whitefish-Kaministikwialowland. lowland. At At this this proceeds off of the Archean stop, we will concentrate on on the the lower lower till till unit. unit. The steepness of the section makes makes itit difficult difficult to to units. These units will be viewed at the next fieldstop. view the upper stratigraphic units. At river level is exposed a dark grey, sandy silty silty subglacial subglacial till till presumed presumed to to be be of of northern northern its subglacial subglacial origin. origin. A affinity. The The till till contains contains numerous numerous faceted and striated clasts supporting its stone line or boulder pavement is clearly visible visible aa few metres metres above above water water level level when when the the section section is is towards the the well exposed. Striations Striationson on the the upper upper surfaces surfaces of the boulders indicate ice flow towards southwest. Most Shales, wackes, wackes, ironstones ironstones Mostof of the the clasts clasts are are derived from the Gunflint Formation. Shales, jaspers are commonly seen in the the river river bed. bed. Only and oolitic jaspers Only aa small small proportion proportion of of the clasts clasts are are derived from Archean terrain terrain to to the the north. north. Oxidation of sulphide minerals contained contained within within Gunflint Formation shales has caused a rusty appearance appearance to to the the till till up up to to the the high high water water line line in in the the section. The that which which is is observed observed over over Thecharacter character of of this this lower lower northern till is quite different from that to the the north. north. The owing its its fineness fineness to to the the texture texture Archean terrain to The till is significantly finer textured, owing displays aa much much darker darker colour. colour. It is similar of the underlying source rocks and displays similar in that it appears appears to �:Jw •w&w • fl LjflMj f'? 2 Figure 12. Figure 12. Aerial Aerialphoto photoof ofthe thearea areasurrounding surrounding Stop Stop 9. 9. The Themorainie morainicridges ridgesform form part part of of the the Marks Moraine. Moraine. The Theesker eskerridge ridgewas wasdeposited depositedby bysouthward southwardflowing flowingnorthern northernice. ice. Superior lobe till flanks flanks the eastern eastern margin of of the the esker. esker. �reflect local bedrock sources sources and and therefore is is aa suitable suitable sampling samplingmedium medium for for programs programs of of mineral mineral exploration exploration within within this thisarea. area. The The lower, lower, northern northern till till is is overlain overlainby by aa sequence sequence of of silty silty glaciolacustrine glaciolacustrinesediments sedimentswhich which were were likely deposited within glacial Lake O'Connor. These sediments have likely deposited within glacial Lake O'Connor. These sediments have not not been been looked lookedat at in in any any detail. There Thereare arenumerous numeroussections sectionsalong alongthe thevalley valleyof ofthe theWhitefish WhitefishRiver Riverand andtributaries tributariesthat that expose Lake O'Connor sediments. These sections require detailed examination to expose Lake O'Connor sediments. These sections require detailed examination to assist assist with with unravelling unravelling the the history history of of this this glacial glacial lake. lake. Higher toclayey clayey Higher up up in in the the section, section, immediately immediatelyabove abovethese these stratified stratifieddeposits depositsisisaamassive massivesilty siltyto diamicton pebbles. This diamicton with with aa few few grits grits and and pebbles. Thisunit unitisisinterpreted interpretedto tobe beaatill tillderived derivedfrom fromthe the Superior Superior lobe. lobe. The Thetill till owes owesits itsfine fine texture texture to to the the incorporation incorporation of of large large volumes volumes of of glaciolacustrine deposits into the base of the advancing Superior lobe. This till barely glaciolacustrine deposits into the base of the advancing Superior lobe. This till barelyresembles resembles other other examples examples of of Superior Superior lobe lobe till which we we have have seen seen earlier earlier in this fieldtrip. fieldtrip. The Thepebbles pebbleswithin within this till are easily recognized as derived from the Animikie and Sibley Group metasediments to the this till are easily recognized as derived from the Animikie and Sibley Group metasediments to the northeast and east. This till does not carry a signature of local geology because the ice that northeast and east. This till does not cany a signature of local geology because the ice that deposited deposited it it did did not not have have access access to to the the bedrock bedrock surface. surface. The The upper, upper, Superior Superior lobe lobe till till is is overlain overlainby by aa second secondsequence sequenceof ofglaciolacustrine glaciolacustrinedeposits. deposits. These These sediments sedimentswere were probably probably also also deposited deposited within within glacial glacial Lake O'Coimor O'Connor as as the the Superior Superiorlobe lobe ice ice margin margin retreated retreated eastward eastwardout out of ofthe thelowland. lowland. Turn vehicles around around and and go go back back to to Highway Highway595. 595 Turn for 3.3 km. Turn Turn the the vehicles Turnleft left and and drive drive south southfor 3.3 km. Turn left on Blaikie Rd and Bluikie Rd. anddrive drive east eastfor for 1.8 1.8kin. km.The Theexposure exposurewe wewill will be belooking lookingat atisiscut cutinto intothe the River valley valley and and is is located located on on the southwest southwest side side of the the road. road walls of the the Whitefish Whitefish River Stop Stop 11: 11: Whitefish WhitefishRiver RiverSection. Section. At At this this stop, stop, we we will will have have an an opportunity opportunityto to look look at, at, in in detail, detail, aa section section through through glacial glacial lake lake O'Connor anupper upper sequence sequenceof of glaciolacustrine glaciolacustrineand and fluvial fluvial O'Connor sediments, sediments,Superior SuperiorLobe Lobetill till and and an deposits. deposits. The Thelower lower33toto44mmconsists consistsofofdark darkgrey, grey,well welllaminated laminatedsilt siltand andclay claylikely likelydeposited deposited with are the the Rove Rove and and with glacial glacial Lake Lake O'Connor. O'Connor. The Theclays claysare areclark dark grey grey because because their their source source rocks rocks are Gunflint Gunflint Formations. Formations. Glacial GlacialLake LakeO'Connor O'Connorformed formedproglacially proglaciallywhen when the the Superior Superiorlobe lobe advanced advanced into intothe the Whitefish WhitefishRiver Rivervalley valleyproducing producingaaclosed closedbasin basinsupported supportedon onits itsnorthern northernand andsouthern southern flanks flanksby by high high ground. ground. The Thelake lakemust musthave havedrained drainedwestward westwardout outthrough throughthe theWhitefish WhitefishLake Lakebasin. basin. Eventually Eventually the the advancing advancingSuperior Superiorlobe lobeoverrode overrodethese thesedeposits depositsproducing producingaafine-textured, fine-textured, clayey silt till with few pebbles. This till is very similar to that exposed clayey silt till with few pebbles. This till is very similar to that exposedatatnear nearthe thetop topof ofthe the section at Stop 10. The till is massive, dense, compact and was probably deposited subglacially section at Stop 10. The till is massive, dense, compact and was probably deposited subglacially under of under active active ice. ice. The Thefineness finenessof ofthe theunderlying underlying deposits deposits would would have have prevented prevented the the infiltration infiltration of subglacial meltwater into the substrate. This would help to promote the development of a thin layer subglacial meltwater into the substrate. This would help to promote the development of a thin layer of of water water at at the the glacier glacier sole sole which which would would have have facilitated facilitated the the rapid rapid advance advance of of ice ice into into the the basin. basin. As As mentioned earlier, the base of the advancing Superior lobe was isolated from the bedrock surface by mentioned earlier, the base of the advancing Superior lobe was isolated from the bedrock surfaceby �several tens tens of of metres metres of of intervening intervening sediment. sediment. As this ice not several As aa result, result, the the till till deposited deposited by by this ice does does not display a signature of local bedrock within the Whitefish River valley. display a signature of local bedrock within the Whitefish River valley. Superior Superior lobe lobe till till is is abruptly abruptlyoverlain overlainby by approximately approximately22m mof ofdark darkgrey greyclay clayand andsilty siltyclay. clay. This sediment was deposited proglacially beyond the retreating margin of the Superior lobe. The This sediment was deposited proglacially beyond the retreating margin of the Superior lobe. The dark grey grey colour colour of of this this sediment sediment suggests deposition within dark suggests deposition within aa closed closed basin basin (i.e. (i.e. aa basin basin not not linked linked with Lake with Lake Superior). Superior). This overlain by by approximately approximately 11 m m of of pebble pebble gravel. gravel. The This unit unit is is abruptly abruptly overlain The gravel gravel is is wellwellmoderately sorted and probably of fluvial character. A low-water phase is implied by this unit. unit. moderately sorted and probably of fluvial character. A low-water phase is implied by this Perhaps the the eastward eastward retreat retreat of of Superior Perhaps Superior ice ice beyon beyon d d Stanley Stanley Hill Hill in in southwestern southwestern Paipoonge Paipoonge Township resulted resulted in in the the drop drop of of glacial glacial Lake Lake O'Connor O'Connor to to aa lower Township lower level. level. This Thiswould wouldhave have resulted resulted in the influx of coarse sediments from uplands east of the site (Little Pig and Badger Mountains) in the influx of coarse sediments from uplands east of the site (Little Pig and Badger Mountains) resulting resulting in in the the superposition superposition of of fluvial fluvial sands sands and and gravels gravelsover over clay. clay. The fluvial fluvial unit unit is abruptly overlain overlain by reddish-coloured glaciolacustrine The is abruptly by reddish-coloured glaciolacustrine deposits deposits of of silt, silt, very very fine minor clay. clay. The fine sand sand and and minor Theupper upper surface surfaceof of this thisglaciolacustrine glaciolacustrineplain plain occurs occurs at at approximately approximately 275 275 m m asl, as], well well above above the the highest highest elevations elevations reported reported for for Superior Superiorbasin basin lakes lakesin in the theThunder ThunderBay Bay area. area. These Thesedeposits depositswere werelikely likelylaid laiddown downwithin withinaa confined confined basin basin with with aa configuration configurationsimilar similarto to that of of glacial glacial Lake Lake O'Connor. O'Connor. The of the the sediment sediment that Thesignificance significanceof of the the colour colour and and textural textural change change of is is unclear. unclear. Clearly, Clearly,additional additionalwork work is isrequired requiredto to obtain obtainaa better better understanding understanding of of the the glaciolacustrine history glaciolacustrine history of of this this region. region. �REFERENCES REFERENCES Baje, Bajc, A.F. A.F. 1997. 1997. A Aregional regionalevaluation evaluationof ofgold goldpotential potentialalong alongthe the western western extension extensionof of the the Larder Larder Lake-Cadillac Break, Matachewan area: results of regional till sampling; Ontario Lake-Cadillac Break, Matachewan area: results of regional till sampling; OntarioGeological Geological Survey, Open Open File File Report Report 5957,50 5957, Sop. Survey, p. Bajc, A.F. 1999a. 1999a.Results Resultsof ofregional regionalhumus humusand andtill tillsampling samplingin inthe theeastern easternpart part of of the the Bajc, A.F. Shebandowan greenstone greenstone belt, belt, northwestern northwestern Ontario; Ontario; Ontario Shebandowan Ontario Geological Geological Survey, Survey, Open Open File File Report W2p. Report5993, 5993,92p. Baje, Ak'. 1999b. Bajc, A.F. 1999b. Gold Goldgrains grainsin intill, till,western western Shebandowan Shebandowan greenstone greenstone belt, belt, northwestern northwestern Ontario; Ontario; Ontario Geological Geological Survey, Survey, Preliminary Preliminary Map Map 341 3417, 000. Ontario 7, scale scale 1:100 1:100 000. Bajc, A.F. 2000. Bajc, A.F. 2000. Results Resultsof ofregional regionaltill tillsampling samplingin inthe thewestern westernpart part of ofthe the Shebandowan Shebandowan greenstone northwestern Ontario; Ontario; Ontario greenstone belt, belt, northwestern OntarioGeological GeologicalSurvey, Survey, Open Open File File Report Report 6012, 6012, 82p. 82p. Brown, Brown, G.H. G.H. 1995. 1995. Precambrian Precambriangeology, geology, Oliver Oliverand and Ware Ware townships; townships;Ontario Ontario Geological GeologicalSurvey, Survey, Report 294, 'tSp. Report 294,48p. Carter, Carter, M.W. M.W. 1990b. 1990b. Geology Geologyof ofForbes Forbesand and Conmee Conmeetownships; townships;Ontario OntarioGeological Geological Survey, Survey, Open Open File Report 5726, 158p. File Report 5726, 188p. Corfu, F. and and Stott, Stott, G.M. G.M. 1998. 1998.Shebandowan Shebandowangreenstone greenstonebelt, belt,western westernSuperior SuperiorProvince: Province: U-Pb U-Pb Corfu, F. ages, tectonic implications, and correlations; Geological Society of America, ages, tectonic implications, and correlations; Geological Society of America, v.110, v.110, no.11, no. 11, p. 1467-1484. p.1467-1484. Franiclin,J.M., J.M.,Kissin, Kissin,S.A., S.A.,Smyk, Smyk,M.C. M.C.and andScott, Scott,S.D. S.D. 1986. 1986. Silver Silver deposits deposits associated associated with with Franklin, Proterozoic rocks rocks of of the the Thunder Thunder Bay Bay District, District, Ontario; Ontario; Canadian Proterozoic Canadian Journal Journal of of Earth Earth Sciences, v.23, No. No.10, 10, p.1576-1591. p. 1576-1591. Osmani, LA. l.A. 1997. Osmani, 1997. Geology Geologyand andmineral mineral potential: potential:Greenwater GreenwaterLake Lake area, area, West-Central West-Central Shebandowan Greenstone Greenstone Belt; Belt; Ontario Ontario Geological Geological Survey, Survey, Report Report 296, 296, 135p. l35p. Shebandowan Schneiders, B.R., Scott, Scott, J.F. J.F. and and Smyk, M.C. 1998. Schneiders, B.R., Smyk, M.C. 1998. Report Report of ofActivities, Activities,1997, 1997,Resident ResidentGeologist Geologist Program, Thunder Thunder Bay Bay South South Regional Regional Resident Resident Geologist's Geologist's Report: Program, Report: Thunder Thunder Bay Bay South South District; Ontario District; Ontario Geological Geological Survey, Survey, Open Open File File Report Report 5971, 5971, 56p. 56p. Sutcliffe, R.H. 1991. Sutcliffe, R.H. 1991. Proterozoic Proterozoicgeology geologyof ofthe the Lake Lake Superior Superiorarea; area; in in Geology Geology of of Ontario, Ontario, Ontario Ontario Geological Geological Survey, Survey, Special Special Volume Volume 4, Part Part 1, 1, p.627-660. Williams, H.R. H.R. 1991. Quetico in Geology Geology of of Ontario, Ontario, Ontario Ontario Geological Geological Survey, Survey, QueticoSubprovince; Subprovince;in Special Special Volume Volume 4, Part Part 1, 1, p.383-404. p.383-404. �Williams, T.L. and and Sage, Sage, R.P. R.P. 1991. Wawa Subprovihce; Williams, H.R., H.R., Stott, Stott, G.M., Heather, K.B., K.B., Muir, T.L. in in Geology Geology of of Ontario, Ontario, Ontario OntarioGeological Geological Survey, Survey, Special Special Volume Volume 4, Part Part 1, 1, p.485-542. Zoltai, Zoltai, S.C. S.C. 1963. 1963.Glacial Glacialfeatures featuresof ofthe theCanadian CanadianLakehead Lakeheadarea; area; Canadian Canadian Geographer, Geographer, v.7, p.101-115. p.101-115. Zoltai, Zoltai, S.C. S.C. 1965. 1965.Glacial Glacial features featuresof of the the Quetico-Nipigon Quetico-Nipigonarea, area, Ontario; Ontario; Canadian Canadian Journal Journal of of Earth Earth Sciences,v.2, v.2, p.247-269. p.247-269. Sciences, �GEOLOGY OF STEEP GEOLOGY OF THE THE ARCHEAN ARCHEAN STEEP ROCK LAKE FINLAYSON LAKE LAKE ROCK LAKE - FINLAYSON GREENSTONE BELT GREENSTONE BELT Denver Denver Stone, Stone, Ontario Ontario Geological Geological Survey Survey Kirsty Tomlinson, Survey of of Canada Canada Kirsty Tomlinson, Geological Geological Survey Ray Ray Bernatchez, Bernatchez, Atikokan Atikokan Resources Resources Inc. Inc. Philip Fralick, Fralick, Lakehead Philip Lakehead University University 3.0 Ga Ga assemblage qfIc tofelsic fr/sic This 3.0 assemblageconsists consistsof ofu/tram ultramaflc metavolcanic rocks and metavolcanic and chemical-clastic chemical-clasticsedimentary sedimentaryrocks. rocks. This trip will will examine examine the the structural, structural, petrographic, petrographic, sedimentaological sedimentaologicaland andeconomic economicaspects aspectsof ofthese theserocks. rocks. �FIELDTRIP 2B FIELDTRIP 2B MESOARCHEAN GEOLOGY GEOLOGY OF OF THE THE STEEP STEEP ROCK ROCK MESOARCHEAN LUMI3Y LAKE LAKE TERRAINS TERRAINS LUMBY INTRODUCTION INTRODUCTION The various Mesoarchean Mesoarchean sequences sequencesin in the Canadian Canadian Shield are remarkably similar, being composed metabasalt-quarta areniate-iron areniate-iron formation formation association association or a 2) 2) metavolcanicmetavolcanic:1) a metabasalt-quartz composedof of either either :1) shallow water carbonate association (Thurston and Chivers, 1990; Erikisson et al, 1994). Worldwide shallow water carbonate association (Thurstonand Chivers, 1990;Erikisson Worldwide examples of these associations associations typically overlie overlie granitoids granitoids or volcanic volcanic successions successions intruded by granitoids and include theoleiitic basalt and komatiite, quartz arenite, iron formation, pelite and/or include theoleiitic quartz andlor stromatolitic carbonate. carbonate.Conglomeratic Conglomeraticintervals intervalstypically typicallyare arepresent presentatat the the base base of stromatolitic of these these successions. Included in this association successions. association are the Manjeri Formation at the base of the Ngezi Group in Zimbabwe, the Paddy Market in the the Pilbara Zimbabwe, Paddy Market Supersequence Supersequence in Pilbara Block, Block, and and numerous numerous local local occurrences in in Superior Province Province (Erikisson (Erikissonetet al, al, 1994; 1994; Erikisson Erikisson et et al, al, 1996). Of the various occurrences various examples examplesof of this this association associationthe the carbonate carbonatedominated dominatedSteep SteepRock Rock assemblage assemblagehas has received receivedthe the most most detailed analysis. Thurston and Chivers (1990) and Erikisson et al (1994, (1994, 1996) 1996)concluded concluded that that associations associations of of this this type type are areformed formedas asaa stable stableplatform platform undergoes undergoesrifting. rifting. Data amassed in recent years on these Mesoarchean sequences Data amassed in recent years on these Mesoarchean sequenceshas, has, in in some some cases, cases, led led to to an an elaboration of of preexisting preexisting tectonic tectonic models, models, while while in in other other cases cases has has caused new models to be elaboration be proposed. This new data on the Steep Rock-Lumby Lake Terrains is briefly reviewed at the end of proposed. This new data on the Steep Rock-Lumby Lake Terrains this article, with the the new article, with with the aim aim of of familiarizing familiarizing the field field trip participants participants with new ideas on Mesoarchean tectonics being developed in this area. First we will stan with an introduction to and Mesoarchean tectonics developed First we will start with an description of the the belt. belt. General Geology General Geology The Steep Steep RockRock- Lumby Lumby Lake within the the District District of of Rainy Rainy River, River, extending extending Lake Terrain Terrain is located within Atikokan to the northeast, northeast, and approximately 200km Thunder Bay, Ontario 200km to the west of Thunder from Atikokan and lying approximately TheSteep SteepRock RockGreenstone GreenstoneBelt Beltlies liesimmediately immediatelyto tothe thenorth north of of Atikokan, near the (Figure 1). The (Figure 2). 2). It was first described by Smyth (1891) as a Quetico-Wabigoon subprovince boundary (Figure vertical succession ferruginous strata strata and and volcanics. volcanics. The The belt vertical succession of conglomerate, conglomerate, limestone, limestone, ferruginous belt unconformably overlies the 3003-+5Ma (Davis and Jackson, 1988) tonalitic Mannion Marmion batholith (Wilks, 1986; Stone et al., 1992). 1992). The The greenstone greenstone Belt comprises comprises the following following five Formations defined (1959),Wilks Wilksand andNisbet Nisbet(1986) (1986)(Figure (Figure3) 3)and andStone Stoneetetal. al.(1992). (1992). defined by Jolliffe Jolliffe (1959), 1. quartzo-feldspathic conglomerates 1. Basal quartzo-feldspathic conglomeratesand andsandstones sandstonesof ofthe theWagita WagitaFormation Formation(up (upto to 150 150 m thick) thick) representing representing alluvial alluvial fan fan deposits deposits on on fault fault scarps scarps (Wilks, 1986); 2. Stromatolitic limestones of the Mosher Carbonate Formation(up (uptoto 500 2. Stromatolitic limestones of the Mosher Carbonate Formation 500 m m thick) thick) representing deposition deposition in in aa shallow shallowsea; sea; 3. Iron formation formation and carbonate-Mn-Fe-rich carbonate-Mn-Fe-rich mudstones mudstones of the the Jolliffe Ore Ore zone zone Formation Formation (up to 400 m thick) representing representing deposition deposition in a subsiding subsiding basin (Wilks, 1986); 1986); 4. an unusual high-Mg, predominately pyroclastic komatiitic unit named the Dismal Ashrock 4. predominately pyroclastic komatiitic Formation (50-400 m thick) representing Formation representing shallow water volcanism; and �n -.4 I n t —. —. Location (if nit itihohan /Steep Ruck area in relation to the belt structure of Superior Province. �p.. * N e Geology of the Steep Rock (a and south-east of A), Finlayson Lake (B) and Lumby Lake (C,S, E) areas. t :!lj Figure 2. �5. . aa sequence the Witch Witch Bay Bay Formation Formation (ca. (ea. 55 sequence of mafic and minor felsic metavolcanics called the km km thick) thick) representing representingsubaqueous subaqueousvolcanism. volcanism. T 200 nil] 200 m .1. B. B. Metosedirnents Metosediments WITCH WITCH BAY BAY FORMATION FORMATION (( rnetavolcanics metavolconics , metasedirnents) metosediments I Possible Possible Tectonic break Tectonic break Lovas LOWS ? DISMAL DISMAL ASHROCK ASHROCK JOLLIFFE JOLLIFFE ORE ORE ZONE ZONE Pyrite Pyrite lenses lenses Buckshot Buckshot ore ore Mammil lose Mommillose St ro m a to ites Stromatolites ./ / / Fault MOSHER CARBONATE 1 WAGrTA FORMATION i clostics I unconformity MARMtON COMPLEX MOSHER MOSHER CARBONATE CARBONATE WAGITA WAGITA FORMATION FORMATION clastics ( ctostics) I MARMION MARMION COMPLEX COMPLEX Giant Columnar Columnar Stromalolites Oncolites Strotiform Stromatolites Pseudomorphs otter Gypsum (Atikokania) Branching & Hemispherical Stromotolites Xenoliths Xenoliths Eorly Early Mofic Mafic Dykes Dykes Figure Rock area. area. The sedimenta,y units Figure3.3. A) A) Geology Geology of the Steep Rock Thewhite white area area south south of of the the sedimentary unitsisis mostly mafic volcanics. B) Stratigraphy of the Steep Rock succession. (Mod j/ied mostly B) Stratigraphy of the Steep Rock (Modified afterWllks Wilksand andNisbet, Nisbet,1986).. 1986).. after The The age ageof ofthe theSteep SteepRock Rock Group Group isis fairly fairly well well constrained. constrained. Six Sixdetrital detritalzircons zirconsfrom fromthe the basal basal sandstones sandstonesare areca. ca. 2999 2999 Ma Ma (reported (reported by by Fralick Fralick and and King, King, 1996 1996 as as D. D. Davis, Davis, personal personal communication). The Dismal Ashrock Formation contains zircons which are 2997 Ma, and these communication). The Dismal Ashrock Formation contains zircons which are 2997 Ma, and these may Davis, personal personal communication, communication,1998). 1998). Sphenes Sphenes in in the the Marmion Mannion (D. Davis, may also alsototobe bedetrital detrital(D. batholith batholithhave havebeen beendated datedatatca. ca.2950 2950Ma, Ma,possibly possiblyreflecting reflectingthe theage ageof of hydrothermal hydrothermalactivity activity that that generated JolliffeOre Orezone zoneFormation Formation(D. generatedthe theJolliffe (D. Davis, Davis,persona personacommunication, communication, 1998). 1998). The TheFinlayson FinlaysonLake LakeGreenstone GreenstoneBelt Beltajoins ajoinsthe theSteep SteepRock RockBelt Belttotothe thenorthwest northwestand and extends extendstotothe thenortheast. northeast.ItItisisapparently apparentlyan anextension extensionof ofthe theSteep SteepRock Rock sequence, sequence, but with with the the sedimentary sedimentaryassemblage assemblageon ontop topofofthe thevolcanic volcanicpile pilerather ratherthan thanbelow belowit, it,as asisisthe the case case with with Steep Steep Rock. Rock. The thanthe theSteep SteepRock Rockgreenstone greenstonebelt belt and andthe therocks rocks are are atat The belt belt isismore moredeformed deformedthan greenschist greenschistto toamphibolite amphibolitefacies. facies.The Thebelt beltisisthought thoughttotooverlie overliethe theMarmion Marmionbatholith batholith(Stone (Stone et., et., 1992) 1992)but butthe thecontact contacthas hasbeen beenintruded intrudedby bysynsyn-to to post-volcanic post-volcanic tonalite tonaliteand and granodiorite granodiorite(Stone (Stoneand and Kamineni,1989). 1989).The Thebelt beltisisdominated dominatedbybysheared, sheared,pillowed pillowedand andmassive massivemafic maficlava lavaflows flowsand and Kamineni, banded bandedamphibolites. amphibolites.Thin Thinunits unitsofoffelsic felsictuff tuffand andmetasedimentary metasedimentarvrocks rocksare are intercalated intercalatedwith with the the mafic maficvolcanics volcanicsapproximately approximatelyhalfway half waythrough throughand andatatthe thetop topofofthe thesequence sequence(Fralick (Fralickand andKing, King, 1996). Six detrital zircons from the upper sedimentary sequence give an age range of 3002 to 2997 1996). Six detrital zircons from the upper sedimentary sequence give an age range of 3002 to 2997 �Ma Ma (Fralick (Fralick and and King, King, 1996) 1996)and and aa rhyolite rhyolite near near the the top top of of the the volcanic volcanic sequence sequencehas has been beendated datedat at 2932± 2 Ma (Davis, 1993). 2932  2 Ma (Davis, 1993). The The Luinby LumbyLake LakeGreenstone GreenstoneBelt Beltextends extendseastwards eastwardsfrom fromthe thenorth northend endof of the the Finlayson Finlayson belt (Jackson. (Jackson, l985a, belt 1985a,b). b). The Thesouthern southernmargin margin of ofthe the belt belt is is in in faulted faulted contact contact with with the the Marmion Marmion batholith (Sage (Sage et et al., al., 1974). pillow batholith 1974). The Thebelt beltisisdominated dominated by by mafic mafic volcanic volcanic rocks, rocks, particularly particularly pillow lavas, but but also of komatiite komatiite flows flows and and pyroclastics, pyroclastics, felsic felsic volcanic volcanic units units and and lavas, also contains contains sequences sequences of chemical the chemical and and clastic clastic sediments. sediments. The Thenorthern northernhalf half of of the the belt belt generally generally youngs youngs to to the the south south and and the southern the belt belt dipping dipping steeply. steeply. Jackson a,b) suggested southernhalf half to to the the north, north, with with both both halves halves of of the Jackson(1985 (1985a,b) suggested that represented aa syncline along the the sedimentary sedimentary units units at the centre centre of of the the that the the belt belt represented syncline with with the the fold fold axis axis along at the belt. This model model appears to be belt. This appears to be oversimplified oversimplified as as there there are are reversals reversals in in younging younging direction direction and and because the the stratigraphy stratigraphy in in the the two two halves halves of of the the belt belt is is rather rather different. different. We because We suggest suggest that that these these opposing tectonic boundary simple synclinal synclinal axis, opposing sequences sequencesmay may be be separated separatedby by aa tectonic boundary rather rather than than aa simple axis, but but do not not discount do discount that that the the two two halves halves of of the the belt belt are are related. related. A felsic of the the southern southern half half of of the the belt belt contains contains 2999 2999 Ma Ma tuff unit unit low low in in the the stratigraphy stratigraphy of A felsic tuff zircons and and aa felsic felsic tuff tuff slightly slightly higher higher in the stratigraphy stratigraphy contains range 2999 zircons in the contains zircons zircons in in the the range 2999 to to 2903 2903 Ma (Davis (Davis and and Jackson, Jackson, 1988). 1988). However the 2999 2999 Ma Ma component component in in each eachof ofthese these felsic felsic units units is is Ma However the thought to be be detrital detrital (D. (D. Davis, 1998). This higher felsic felsic unit unit is thought to Davis, personal personal communication, communication, 1998). This higher is also also along 1 50-m-thickunit unit(Jackson, (Jackson, 1985a) 1 985a)ofofsandstones, sandstones,carbonates carbonatesand and chert chert along strike strike from from aa ca. ca. 150-m-thick thought to thought to have have formed formed in in aa shallow shallowwater water environment environment (lower (lower sedimentary sedimentary sequence; sequence; Fralick Fralick and and King, 1996). 1996). A thick thick felsic the belt belt contains contains zircons zircons that that give give aa maximum maximum felsic tuff unit in the northern northern half of the U-Pb age age of of 2973 2973 ma ma (D. (D. Davis, An upper upper sedimentary sedimentary sequence sequence U-Pb Davis, personal communication, communication, 1997). 1997). An described by Fralick and King (1996) m of chert-rich chert-rich iron formation formation and elastic described (1 996) comprises comprises 500-700 500-700 m clastic sedimentary rocks rocks that that occur The upper part of sedimentary occur along along the the centre centre of of the the greenstone greenstone belt. belt. The upper part of the the upper upper sedimentary sequence sedimentary sequence comprises comprises elastic clastic turbidites turbidites with conglomeratic conglomeratic intervals intervals (Fralick (Fralick and King, 1996). 1996). The mafic rocks of of the belt are The mafic and and ultramafic ultramafic volcanic volcanic rocks the Lumby Lurnby Lake Lake greenstone greenstone belt are at at amphibolite the northen northen margin margin of of the the greenstone greenstone amphibolitegrade grade close close to to the the Norway Lake Lake pluton and along along the belt, but but otherwise otherwise they they are are generally generally at at greenschist greenschist facies. facies. They belt, They are, are, in places, places, well well exposed exposed and, and, although original stratigraphic stratigraphic and textural features features are frequently frequently very well preserved, preserved, although often often sheared, sheared, original and textural particularly in particularly in the the northern northern half half of of the the belt. belt. Steep Rock Rock Group Group Steep Smyth (1891) was the the first first to to describe describe the the Steep Steep Rock Rock succession succession which which he he interpreted interpreted as as aa Smyth (1891) was monoclinal assemblage monoclinal assemblageof ofnine nineformations formationsthat that unconformably unconformablyoverlie overlieaa granitic graniticbasement basementcomplex. complex. The unconformable basal (1912), though he reduced reduced Smyth's Smyth's nine 912), though Lawson (1 The unconformable basal contact contactwas was confirmed confirmedby Lawson formations formationsto to four four by eliminating eliminatingthe the dubious dubious upper upper units. units. Moore Moore (1939), (1939), Jolliffe Jolliffe (1966), (1966), Shklanka Shklanka (1972) and Wilks Wilks and Nisbet (1988) (1972) andNisbet (1988)all all redefined redefined the constituents constituents of of the Steep Steep Rock Rock Group, Group, with with the the presently accepted presently accepted definition definitionbeing being the thelatter. latter. Intrusive Igneous Atikokan area Intrusive IgneousRocks. Rocks.The The Atikokan areastraddles straddlesan anelongate elongatebelt beltof ofmetasediments metasedimentsto to the the (Quetico Subprovince) south (Quetico Subprovince)and andmixed mixedmetavolcanic, metavolcanic,gneissic, gneissic,and andfelsic felsicplutonic plutonicrocks rocksto tothe the north north tonalite and and "old" 'old" tonalite (Wabigoon Subprovince). PrePre- to to synvolcanic synvolcanic intrusions intrusions include mafic tonalite tonalite �(which predate the the Marmion Marmion batholith batholith and and Lefteye Lefteye stock stock as as well wellas astonalite tonalite (which predate the Steep Steep Rock Rock Group) Group) in in the and Syn-to postvolcanic postvolcanic intrusions and mafic mafic tonalite tonalite gneisses gneisses of of the the Dashwa Dashwa gneiss gneiss complex. complex. Syn-to intrusions encompass a broad range of felsic to mafic magmas. "Young" tonalite, which postdates postdates some some encompass a broad range of felsic to mafic magmas. "Young" tonalite, which supracrustal the Nevison, Nevison, Righteye, Righteye, Wasp, Wasp, Bow, Bow,and andHardtack Hardtackintrusions. intrusions. The TheLittle Little supracrustal rocks, rocks, occupies occupies the Eye stock is composed of homblendite and diorite. Granodiorite and granite occur in the Diversion, Eye stock is composed of hornblendite and diorite. Granodiorite and granite occur in the Diversion, Margaret, Margaret, Bewag, Bewag, Eye-Dashwa, Eye-Dashwa, and and White White Otter Otterfelsic felsic intrusive intrusive centres. centres. 'Old" tonalite is so-named because it is the dominant " O l d tonalite is so-named because it is the dominant lithology lithology of of the the basement basement complex complex upon which rocks of the Steep Rock Group were deposited. Along northeastern margins upon which rocks ofthe Steep Rock Group were deposited. Along northeastern marginsof of the the Steep Steep Rock of several metres to to metasandstone metasandstone and and Rock belt, belt, the the "old" "old" tonalite tonalite is is gradational gradational over over distances distances of several metres meaconglomerate at the base of the Steep Rock Group. Here the plutonic basement is tan-brown in meaconglomerate at the base of the Steep Rock Group. Here the plutonic basement is tan-brown in colour, shear zones zones and and abundant abundant metagabbro metagabbro dykes. dykes. colour, schistose, schistose, highly highly fractured, fractured, and and transected transected by by shear The dykes are are fewer fewer and and the the "old" in the The metagabbro metagabbro dykes " o l d tonalite tonalite is is less less intensely intensely foliated foliated in the central central Marmion this tonalite, tonalite, collected collected near the Ontario Ontario Hydro Marmionbatholith batholith(Marmion (MarmionLake Lakearea). area).A Asample sampleof ofthis generating station, has has aa U/Pb generating station, Ma (Don (Don Davis, Davis, Royal Royal Ontario Ontario Museum, Museum, U/Pb titanite titanite age age of of 2953 2953 Ma pers.comm., 1987). Granodiorite of the Margaret and Diversion stocks intrudes the northern northern and and pers.comm., 1987). Granodiorite of the Margaret and Diversion stocks intrudes the southern southern margins margins of of the the Marmion Marmion batholith. batholith. "Old" "Old" tonalite tonalite is is typically typically mediummedium- to to coarse-grained, coarse-grained, foliated, foliated, and and inequigranular inequigranular to to porhpyritic. quartz (25%), (25%), and andbiotite biotite(20%). (20%). Plagioclase Plagioclase and porhpyritic. It is composed composed of plagioclase (40%), quartz biotite are extensively altered to epidote, sericite, and chlorite in shear zones and biotite are extensively altered to epidote, sericite, and chlorite in shear zones and adjacent adjacent to to the the Steep Steep Rock Rock belt. belt. Sedimentary SedimentaryRocks Rocks The Rock Group Group and and consists consists of of pebble pebble and and cobble cobble The Wagita Wagita Formation Formation forms forms the the base base of of the the Steep Steep Rock conglomerates interbedded with with poorly poorly sorted sorted sandstones sandstones conglomerateswith withangular angularto to subrounded subrounded igneous igneous clasts clasts interbedded and fine-grained chioritic in thickness thickness from from 0 0 to to 150 chloritic layers. The clastic clastic sequence varies in 150 m and and is is overlain overlain by by carbonates. carbonates. The by dark dark kerogen The Mosher Mosher Carbonates Carbonates are are well well banded banded with with the the layering layering accentuated accentuated by kerogen streaks silica-rich ridges ridges at at some some locations. locations. The The laminated laminated carbonates carbonates streaks or millimetre-scale elevated silica-rich are are commonly commonly brecciated brecciated where where they they are are spatially spatially associated associated with with fault fault zones zones and and mafic mafic dykes. dykes. Calcite, and brecciated brecciated units, units, although although the the ankerite and dolomite dolomite are are present in both the laminated and Calcite, ankerite breccias Stromatolites are breccias often often have have an anadditional, additional,late-stage late-stagedolomitic dolomiticpore-filling pore-filling cement. cement. Stromatolites common forms dominating dominating in in the the lower lower portions portions and common throughout the carbonate carbonate unit, with smaller forms larger mounds, 33 m m in in diameter, diameter, becoming becoming abundant abundant near the upper contact (Wilks and Nesbit, 1988). very irregular irregular upper upper contact contact 1988).The Theentire entirecarbonate carbonateassemble assembleisisup upto to 500 500 m m in thickness with a very which which may may be be karstified. karstified. A rock" overlies the A 100 100to to 300 300 m m thick thick succession successionof of manganiferous manganiferous strata strata termed termed "paint "paint rock" overlies the Mosher Jolliffe Ore Zone, Zone, consists Mosher Carbonates. Carbonates. This Thissuccession, succession,which whichforms formsthe thelower lower unit of the Jolliffe consists of of an an of of an earthy, earthy, poorly poorly consolidated consolidated mixture mixture of of goethite, goethite, hematite, hematite, chert, chert, kaolinite, kaolinite, illite, illite,calcite, calcite, gibbsite gibbsite and and pyrolusite pyrolusite (Huston (Huston 1956). 1956). The Thepaint paintrock rockisisoverlain overlainby by the the upper upper unit unit of of the the Jolliffe Jolliffe Ore Ore Zone, Zone, the the Goethite GoethiteMember, Member, which, like like the paint rock, is composed of of goethite goethiteand and hematite, hematite, but versus 5%, 5%, respectively). respectively). The Goethite Goethite Member, Member, which which but has has aa lower lower manganese manganesecontent content(3.8% (3.8%versus is is 50 50 to to 100 100m m thick, thick,occurs occursboth bothas asbrecciated brecciatedmasses masses and and alternating alternating layers layers of goethite goethite and and chert chert (McIntosh mafic to ultramafic pyroclastics and minor (Mclntosh 1972). 1972).The The Goethite Goethite Member is is overlain by mafic thin thin flows flows of of the the Dismal Dismal Ashrock. Ashrock. �and Nisbet Nisbet (1 (1988) suggest the the depositional depositional environment environment of ofthe small Wilks and 988) suggest the basal basal clastics elasticsis is a small alluvial fan fan with alluvial with aa fluvial fluvial system system that that has has incised incised and and backfilled backfilled channels channels into into the the underlaying underlaying Marmion Complex. Complex. As Marmion As clastic clastic deposition deposition in in the the area area ended, ended, carbonate carbonate began to accumulate in a shallow marine setting. setting. The depth is indicated indicated by byprobable probablegypsumpseudomorphs, gypsum pseudomorphs,possible possible shallow The shallow shallow depth desiccated ripples, ripples, and and polygonal polygonal cracks cracks on on large (Wilks and and Nisbet, desiccated large stromatolites stromatolites (Wilks Nisbet, 1988). 1988). Stromatolite sabkha to Stromatolite morphology may reflect adaptations to various water depths ranging from sabkha subtidal (Wilks (Wilks and and Nisbet Nisbet 1988). 1988). The of the the carbonate carbonate assemblage assemblage suggests suggests an an subtidal The karstified karstified surface surface of interval of subaerial exposure that caused dissolution of the upper units. It is also possible that acidic interval subaerial exposure dissolution upper units. It is also possible that acidic pile and and dissolved dissolved the the carbonates. carbonates. In solutions moved downward through the sediment pile In either either case case the manganiferous manganiferous paint represent residual residual deposits deposits left leftbehind behindafter after carbonate carbonate dissolution. dissolution. paint rock may represent published concerning concerning the the origins origins of ofthe theoverlying overlyingJolliffe JolliffeOre OreZone. Zone. The The alternating alternating layers layers Little is published unit is a classic classic iron iron formation; formation; modified modified through through dissolution dissolution or or as as of chert and Goethe suggest this unit paleosol. aa paleosol. Volcanic Rocks Formation has has been been Volcanic Rocks The Thestratigraphy stratigraphyand andpetrography petrography of of the the Dismal Dismal Ashrock Ashrock Formation Komatiiticlapilli lapillituff tuff makes makesup up over over 80% 80% of of the the described by by Schaefer described Schaefer and Morton Morton (1991). (1991). Komatiitic formation, the remainder comprising comprising lenses lenses of komatiitic komatiitic volcanic volcanic breccia, breccia,komatiitic komatiiticvolcaniclastic volcaniclastic formation, sandstone and siltstone, and mafic to to ultrarnafic ultramafic lava lava flows. flows. The rocks are classified classified as as komatiites komatiites as defined defined by by Arndt Arndt and and Nisbet Nisbet (1 (1982) although spinifex spinifex texture texture is is rare. rare. Wilks (1986) recognized recognized as 982) although possible pseudomorphs after spinifex layering layering' in in one one lava lava flow, flow, and and Schaefer Schaefer and Morton Morton (1991) (1991) possible described lapilli fragments. The nvroclastic pyroclastic rocks of of the the Dismal DismalAshrock Ashrock described micro-spinifex micro-sninifex texture in lanilli Formation thought to have formed by explosive explosive volcanism volcanism caused causedby byultramafic ultramaficmagma magmaentering entering Formationare are thought water-saturated sediments Formations (Schaefer water-saturated sedimentsof of the the Mosher Mosher Carbonate Carbonateand and Jolliffe Ore Zone Formations (Schaeferand Morton, 1991). 1991). The Thetop topof ofthe the Dismal Dismal Ashrock Ashrock Formation Formation is in most places tectonised or invaded original stratigraphic stratigraphic relation-ship relation-ship occurs between between the the Dismal Dismal Ashrock Ashrock Formation-and Formation-and by sills but an original al., 1992; Tomlinson Tomlinson ct ct al., al., 1996% 1996a; TomlinTomlinthe Witch Bay Formation near Strawhat Strawhat Lake (Stone et al., son, 1996). 1996). The Witch Witch Bay Formation dominates Rock greenstone greenstone belt belt and and is is aa sequence sequence of of The dominates the Steep Rock mainly mafic mafic lavas lavas comprising comprising up up to to 80% pillow pillow lavas. lavas. Flyaloclastite and massive massive lava lava flows flows also also mainly Hyaloclastite and beds of of felsic felsic pyroclastic pyroclastic volcanics. volcanics. The occur along with rare beds The volcanics volcanics have have in places been highly suggested that the original thickness thickness was was likely likely to to approach approach 55km kmbased based folded. Stone et al. (1992) suggested of pillow pillow lavas lavas at at the the south south end end of of Steep SteepRock RockLake. Lake. The Witch Bay on a homoclinal sequence of Formation is is overlain by by intermediate to felsic felsic volcanics volcanics whose whose age age and and contact contact relationship relationship with with Formation intermediate to the underlying predominantly mafic mafic sequence sequence is unknown. - A. Finlayson and and Lumby Lake Greenstone Belts Finlayson Early reconnaissance surveys surveys were were conducted conducted in in the the Lumby Lumby Lake Lake area area by by the the Geological Geological Early Canada in the late andthe thearea areareceived receivedconsiderable considerableattention attentionfrom fromprospectors prospectors Survey of Canada late 18001s, 1800's, and 890ts.L. L.F.F.Kindle Kindletraversed traversedthe thearea areain in 1937 1937for forthe theG.S.C. G.S.C.and andthe therocks rocksof ofthe thebelt belt were were in the 11890's. by Jackson (1985). mapped for the Ontario Ontario Geological survey by Woolverton (1960) and again by Volcanic Rocks Volcanic mafic lava lavaflows flowspredominating. predominating. These These Volcanicrocks rocks dominate dominate the belts, with mafic commonly have massive lower portions and pillowed upper portions and are rarely capped by commonly have massive portions and pillowed upper portions and are rarely capped by brecciated flow flow tops. tops. Individual flows (ca. (ca. 44 m ni thick) by thin thin units thick) are are often often separated separated by units of of iron iron brecciated Individual flows �formation and and iron iron rich rich material material is is also also common commonbetween betweenpillows. pillows. Variolitic Variolitic lavas lavas are are found found in in the the formation upper portion of the stratigraphy. upper portion of the stratigraphy. Two komatiite komatiite horizons horizons occur occur in in the the northern northern half half of ofthe thebelt. belt. The The main main komatiitic komatiitic sequence sequence Two is 120 m thick and includes numerous komatiite flows, pillowed and hyaloclastite portions of flows, flows, is 120 m thick and includes numerous komatiite flows, pillowed and hyaloclastiteportions of variolitic intervals, subordinate mafic flows and inter-flow sediment comprising chert and iron variolitic intervals, subordinate mafic flows and inter-flow sediment comprising chert and iron formation (Tomlinson et al., 196b). Komatiite flows are 4 to 13 m thick with cumulate bases and formation (Tomlinson et aL, 196b). Komatiite flows are 4 to 13 m thick with cumulate bases and spinifex-textured tops. tops. This can be be traced traced for for ca. ca. 13 13 krn km along along spinifex-textured This predominantly predominantly ultramafic ultramafic sequence sequence can strike and and occurs occurs on pluton but but itit thins thins to to the This main main strike on either either side side of of the the Van Van Nostrand Nostrand pluton the east. east. This komatiite overlain by by further further mafic maficflows flowsand andiron ironformation. formation. An An upper upperkomatiitic komatiitic unit unit komatiite sequence sequence is is overlain is present east east of of the the Van Van Nostrand Nostrandpluton, pluton, near near the the top top of of the the stratigraphy. stratigraphy. This upper komatiitic komatiitic is present This upper unit varies varies along along strike. 20 m m thick thick bedded beddedpyroclastic pyroclasticunit unit(similar (similar unit strike. To Tothe the east east itit comprises comprises aa Ca. ca. 20 to the the Dismal Dismal Ashrock Ashrock Formation) Formation) interbedded interbedded with with thin thincarbonates carbonatesand andiron ironformation. formation. West West of ofthis this to is ca.20 20m mthick thickcoarse-grained, coarse-grained,unsorted unsortedand andmassive massiveultramafic ultramaficpyroclastic-flow pyroclastic-flowunit. unit. Both Both units units is aa ca. overlie a prominent prominent ca. l0-m-thick, chert-rich chert-rich iron iron formation formation and and are are themselves themselves overlain overlain by by further further overlie a ca. 10-m-thick, amygdaloidal amygdaloidal mafic mafic lavas. lavas. The main sequence in the the southern southern half half of of the the belt belt isis less lesswell wellknown. known. Fine-grained Fine-grained pillow pillow The main sequence in lavas are common but the exposure is not good enough to establish flow thickness or lavas are common but the exposure is not good enough to establish flow thickness or flow flow stratigraphy. phenocrysts up upto to22cm cmacross. across. Poorly Poorly exposed exposed stratigraphy. Some Somelava lava units units contain contain plagioclase plagioclase phenocrysts komatiite flows unknown extent near the the top top of ofthe thestratigraphy stratigraphy(which (whichwere werefirst firstrecorded recorded komatiite flows of of unknown extent occur occur near by Jackson, I 985a). Thin felsic tuff units (10-20 m) occur intermittently in the southern stratigraphic by Jackson, 1985a). Thin felsic tuff units (10-20 occur intermittently in the southern stratigraphic sequence. sequence. Sedimentary Rocks Sedimentary RocksAAthin thinsuccession successionofoffelsic felsicmetavolcanic metavolcanicunits units and and matasediments matasediments occurs occurs approximately halfway halfway through through the the volcanic volcanic sequence sequenceand and aa thicker thicker assemblage assemblage of of elastics clastics and and approximately chemical sediments caps the In the the Finlayson Finlayson Lake Lake area area the the lower chemical sediments caps the assemblage. assemblage. In lower clastic clastic wedge wedge thickens and and coarsens coarsens to to the the southwest, and is is gradational in this this direction to aa felsic thickens southwest, and gradational in direction to felsic volcanic volcanic assemblage (Figure (Figure 4). Beds vary in thickness assemblage 4). Beds vary from from centimetre-to centimetre-to metre-scale metre-scale in thickness averaging averaging approximately 70 Coarse-grainedsand sand with with felsic felsic volcanic-clast pebble bands bands approximately 70 centimetres. centimetres. Coarse-grained volcanic-clast pebble dominates, except except in in volcanic volcanic proximal proximal areas areas where units gain gain in in importance. importance. dominates, where the the conglomeratic conglomeratic units Clastic mud drapes drapes and and mafic centimetre-scaleinterbeds. interbeds. The The sandstones sandstones are are Clastic mud mafic tuffs tuffs rarely rarely form form centimetre-scale massive and and nongraded. nongraded. Bed the metasedimentary massive Bed thicknesses thicknesses decrease decrease to to the the northeast northeast where where the metasedimentary succession thin and sporatically present. succession is thin �Little Falls! Little Falls 1Finlayson Finlayson Lumby Lumby i V A . . "V V v v Oo:,.. . V " "V V v v V oO...... A . VV . VV V V v v v v v + ++ + +±± + 500 m V V V V V V V V V v V v VV v v V v ; .. v v V V V V vV vV v V V V v Scale V V V V V V V vV V v ±±+ V vV vV ±± ± ± ++± + + + V V IV V V ~ v v v v l'V " V " V v Vv Vv v v I V vV I , 61 Iv V V v Vv V v v V V V V v v .....:::...: .... ...-.... V V V v V V v V V V V V v v v vv v v. v v vV vV "V v V " V v V v V v V vV "V "V vV v V vV v V v V v V v V v vv v v v v v v v vV vV vV vV vV vV vV vV vV vV v v V v K\"+";;v:v V v v V v v v v + + v + + + + + v v v v v v + + + + + + + V V V + + + + + + + v+ v + + + + + Figure Figure 4. 4. V ~ I" vV vV vV vV vV vV vV vV vV vV vV vV vV vV vV v ~ v V v V v V v V v V v V v V v V v V v V vV vV vV vV vV v ~ lv vv vv vV vV vV vV vV vV vV vV vV vV vV vV vV v l v v v v v v v v v v v v v v v v I lYlafic Volcanic Volcanic Mafic Rocks Rocks AA Felsic Volcanic Faisic Volcanic Rocks Rocks 1+ +1 Intrusive lntruslveRocks Rocks IV V '' v IV ±1 4 km Iron Iron Formation Formation Carbonate 11111111111 Carbonate Lo0oal Conglomerate Conglomerate Pf1 Sandstone/Siltstone Sandstonepiltstone A J Agglomerate Agnlomerate .. l;".;,vvy .:,.v V + + - " - V V V v A V V v + V " " v + v+ + Reconstruction of Finlayson andLumby -.sect;anal Reconstruction of the the units unitsin in the Finlayson andLumbyLakes Lakesarea areain incross trim-sectional view. view. The The stratigraphy stratigraphyisIs discussed discussedin in the thetext. text. These sediments sediments represent represent aa clastic clastic debris apron formed adjacent to, and deriving sediment These sediment Sedimenttransport transport was was via via subaqueous subaqueous sediment-water sediment-water dispersions dispersions from, a felsic volcanic centre. Sediment with to keep keep material material in in suspension. suspension. This with dispersive dispersivepressure pressure probably acting acting as an important force to This requires a high slope, slope, possibly higher higher than 10 in the the area areathe theflows flowswere weregenerated. generated. Subarial Subarial requires 10 degrees, in mafic mafic volcanism volcanism was was also also active activeduring during this this depositional depositional interval. interval. The Lake area area is is also also laterally laterally transitional transitional metasedimentary belt belt present present in the Lumby Lake The lower lower metasedimentary to felsic centimetres, and felsic volcanics. volcanics. Sandstones Sandstonespresent presenthere hereare are more more thinly bedded, averaging 15 centimetres, do mafic ash interbeds. They nongraded varieties exist. do not contain containmafic ashinterbeds. Theyare aremassive, massive,and and both both graded graded and andnongradedvarieties exist. The elastic with cherts cherts and and carbonates. carbonates. The cherts are laminated laminated on on the the clastic sequence is intercalated with centimetrerecrystallized with with fractures, fractures, which may centimetre-and and subcentimeter-scale subcentimeter-scaleand and the the carbonates carbonates are recrystallized represent represent original original bedding, bedding, spaced spaced on on the the decimeter-scale. decimeter-scale. This provides very little information information on ondepositional depositionalenvironment. environment. The sandstones sandstones This sequence sequence provides suggest imply aa water water suggest deposition depositionby by grain grainflows flows and and high-density turbidity turbidity currents, currents, but this does not imply depth. Personal Personalexperience experienceindicates indicatesthat thatArchean Archean carbonates carbonates associated with cherts usually form in shallow shallow water water environments, environments, though though this this remains remains speculative. speculative. The capping cappingsedimentary sedimentarysequence sequencepresent present at Finlayson The Finlayson Lake conformably conformably overlies overlies pillowed and massive mafic volcanic pile in the volcanic rocks in the the southern and central area and an agglomeratic pile north. Basal by centimetre centimetre thick thick DE DE Basalcherts chertsand andoxide oxidefacies faciesiron iron formation formation are are succeeded upwards by turbidites. turbidites. These gradually gradually thicken and coarsen coarsen up sequence sequence to decimeter decimeter thick, graded graded beds beds Above this this zone zone internal, internal, scallop-shaped scours, composed of medium-grained sand. Above scours, filled filled with coarse-grained sand, appear in the beds. These Theseare areoverlain overlainby by pebble pebble and and cobble cobble conglomerates conglomerates with sandstone sandstone interbeds interbeds and lenses lenses (Figure (Figure 5). 5). The coarsening coarsening upward upward trend trend in in this this zone is interrupted grainsize to medium-grained medium-grained turbidites, turbidites, which again gradationally gradationally interruptedby by abrupt abruptdecreases decreasesin grainsize coarsen coarsen upwards upwards to to conglomerates. conglomerates. + + v �m. F-6 200 S. s. graphite graphite sulfides sulfides C. C. ch e ii chert 9. 9. 150 F-5 1I-I- +H Diabase Diabase 1 Conglomerate Conglomerate Sandstone with with lil Sandstone L°o°o°S! I.E I.F. Iron IronFormation Formation ________ [i.cJ j1 - ________ L: fl—El :1 L _______ H 1 bc?ed ________ 100 Al I scours scours Sandstone Sandstone ( turbidites ) (turbidites) Siltstone Siltstone Slate SlateCouplets Couplets Slate Slate MaficVolcanic Volcanic Mafic Rocks Rocks Agglomerate Agglomerate F-4 F-2 F-i c.Is. ___ oJ c..,g.js. 0 FigureS. sections through Figure 5. Stratigraphic Stratigraphicsections throughthe theuppersedimentary uppersedimentaryunit unitononFinlayson FinlaysonLake. Lake.Section Section F-i logged other F-1was was loggednear nearthe thenorth-east north-eastend endofofthe thelake. lake.The The othersections sectionsare arespaced spaced along approximately iO10 km alonga aline linerunning running approximately krntotothe thesouth-west south-westand andending endingwith withF-6 F-6inin the lake. system braidedfault systemlongitudinally longitudinallycutting cuttingthe thebelt belt thesouthern southernportion portionofthe of the lake.AAbraidedfault inintwo twonear nearitsitscenter centerdownsteps downstepsthe thestratigraphy stratigraphyininaanorth-east north-eastdirection. direction. 1 I < 1 I �3,000 Ma 2,925 Ma ?7 A v V V v Vv v V v " V V .—C?\ 1 Little LittleFalls FallsI1Finla Finlayson yson V I? I? — —— r fle?.o.o.c?1o.? OOoooo C v ?1 ? I V v V v V v Lumby Lumby vV / Iron Iron Formation Formation IJJJfflJJCarbonate Carbonate J'I Conglomerate Conglomerate Sandstone Slate % H I Agglomerate Siltstone I/Slate Agglomerate ..... Sandstone ____ ____ Siltstone IAAI Felsic F e M cVolcanic VolcanicRocks Rocks Mafic VolcanicRocks Rocks l"I Mafic Volcanic Figure for the Figure6.6. Sequential Sequential environmental environmental reconstruction reconstruction of of the the depositional depositional environments environments for the lower sedimentary units of the the Finlayson Finlayson and lower sedimentary sedimentary units units(A) (A) and and upper uppersedimentary units (B, C) of and Lumby Lumby Lake greenstone greenstone belts. Processes Processes are arediscussed discussedin in the the text. text. Il �This After cessation cessation of of mafic This succession succession represents represents shoreline shoreline progradation progradation (Figure (Figure 6). 6). After mafic volcanism a starved succession of chemical sediments was deposited. The first clastics delivered volcanism a starved succession of chemical sediments was deposited. The first clastics delivered to silts transported transported by by low-density low-density turbidity turbidity flows. flows. This This probably probably represents represents to the the area area were were clays clays and and silts prodelta debris, though sediment transport via storm currents is possible. Shoreline progradation prodelta debris, though sediment transport via storm currents is possible. Shoreline progradation caused caused the the coarsening coarseningupwards upwardssuccession successionto to form, form, culminating culminatingin in deposition depositionin in depths depthseffected effectedby by wave induced scour. Delta top sands and gravels cap the sediment pile and show the effects lobe wave induced scour. Delta top sands and gravels cap the sediment pile and show the effects of of lobe outbuilding outbuildingand andabandonment, abandonment,with withsubsequent subsequentsubsidence subsidenceinduced induced flooding floodingand and aa return return to to deeper deeper water water conditions. conditions. This Thisisisfollowed followedby byaaminor minorcoarsening coarseningupward upward sequence sequenceformed formedby by another anotherstage stage of is capped capped by by aa final final flooding flooding event. event. of delta delta lobe lobe outbuilding outbuildingin in the the area area and and the the entire entire sequence sequence is The The sedimentary sedimentary sequence sequence capping capping the the assemblage assemblage of of mafic mafic volcanic volcanic rocks rocks in in the the Lumby Lumby Lake thick sequences sequences ofboth ofboth clastic and chemical chemical units units (Figures (Figures 5). 5). WayLake greenstone greenstonebelt belt consists consistsof of thick clastic and up up directions directionsare are ambiguous ambiguous though though itit is is more more likely likely that that the the iron iron formation formation and and chert chert assemblage assemblage overlies overlies the the elastic clastic assemblage. assemblage. AAthin thinzone zoneof ofchert chertand andiron ironformation formationseparates separates the the volcanic volcanic sequence sequence from from the the clastic clastic sediments. sediments. The Theclastics clasticsconsist consistof of decimeter-scale decimeter-scaleturbidites turbiditeswith with metremetrescale the map map area. area. Structural scale conglomeratic conglomeratic interbeds interbeds in in the the western western portion portion of of the Structural complexities complexitiesand and scarcity if aa coarsening coarsening upwards upwards trend trend exists. exists. In scarcity of of outcrops outcrops prohibited prohibited ascertaining ascertaining if In the the west west the the elastic clasticsuccession successionis isoverlain overlainby by thinly thinly laminated laminatedcarbonates carbonates with with submillimeter-scale submillimeter-scale clay clay drapes drapes commonly commonly developed developed between between laminations. A Avery very chert-rich chert-rich iron formation formation assemblage assemblage overlies the carbonates in the west, lies on clastics in the central area and directly overlies the carbonates in the west, lies on clastics in the central area and directly overlies the the volcanic volcanic succession successionin inthe theeastern easternoutcrop outcroparea area(Figure (Figure4). 4). Scarcity of outcrop Scarcity of outcrop in in this this belt belt inhibits inhibits aa detailed detailed reconstruction reconstruction of of depositional depositional environments. environments.After Aftercessation cessationof ofvolcanic volcanicactivity activityaaclastic clasticsediment sedimentstarved starved interval interval was was followed followed by by deposition depositionvia via high high and and low low density density turbidity turbidity currents. currents. Conglomeratic Conglomeraticunits unitsprobably probably represent represent the the most most strand-proximal strand-proximaldepositional depositional events. events. This Thisisisfollowed followedby bythe thesequence sequencebecoming becomingrapidly rapidly sediment sedimentstarved starvedwith withcarbonates carbonatesdeposited deposited in in the the shallower shallower areas, areas, in in the the west west where where the the strandstrandproximal and cherty cherty iron iron formation formation in in deeper deeper areas. areas. With proximal conglomerates conglomerates are are located, located, and With increasing increasing water migrated westward westward until until iron iron formation formation diachronouscontact contactwith with the the iron iron formation formation migrated water depth depththe the diachronous was was being being deposited depositedthroughout throughoutthe theentire entirearea. area. Structure Structure The from mainly mainly The east-trending east-trending Quetico-Wabigoon Quetico-Wabigoonboundary boundary separates separatesturbidites turbiditesto the south from volcanic rocks to the north and is a first order lithostrnctural feature in the area. Regional volcanic rocks to the north and is a first order lithostructural feature in the area. Regional juxtaposition subduction-related accretion accretion of ofthe juxtapositionof ofthe thecontrasting contrastinglithologies lithologieshas has been been attributed attributed to subduction-related the Quetico sedimentary prism against the Wabigoon volcanic arc about 2695 Quetico sedimentary prism against the Wabigoon volcanic arc about 2695 Ma Ma ago. ago. Quetico Quetico metasediments metasedientshave have pervasive pervasive easterly easterly structural structural trends trends and and isoclinal, isoclinal, mainly mainly easteast- facing facing folds folds possibly possibly generated generated by by strong strongdextral dextraltranspression transpression after after accretion. accretion. In contrast, contrast, Wabigoon WabigoonSubprovince Subprovinceshows showsmegascopic megascopicoval ovalstructures structuresdefined definedby by concentrically concentricallyzoned zoned structural structural trends trends in in gneisses gneissesand and supracrustal supracrustal rocks rocks that that envelope envelope felsic felsic plutons. plutons. Metavolcanic belts are are situated situatedbetween between some someoval oval structures. structures. This Thisstructural structuralpattern pattern may may have have originated originated due to rise of granites overlying granitesand and gneisses gneissesin incentral centralparts parts of of oval oval structures structures attendant attendant with slumping of dense overlying supracrustal supracrustalrocks rocksinto intomarginal marginaltroughs troughs(metavolcanic (metavolcanicbelts). belts). The Theaxes axesof ofsix sixmajor majorfolds foldsextend extendalong alongthe the central central Finlayson Finlayson belt belt whereas whereas the the Steep SteepRock Rock belt belt shows showsfewer fewerfolds foldsand andaa thick thick east-younging east-youngingsequence sequenceof of pillow pillow lavas lavas that that may may be be aa deformed deformed lava lavacone. cone. �A complex system system of of oblique-slip and and normal normal faults faults and and metagabbro metagabbro dykes dykes transect transect the the A Marmion batholith. batholith. The Samuel fault fault appears appears to to have have The dip-slip, dip-slip, probably probably reverse reverse displacement displacement Samuel uplifted a segment segment of the batholith batholith into into the the central central Steep SteepRock Rockbelt. belt. Displacements Displacements of of reverse reverse sense sense uplifted are also likely to have occurred on the Atikokan fault, which is conformable conformable with the the upper upper ashrock ashrock transcurrent fault fault in in the the vicinity vicinity of of contact in the Steep Rock Mine area. Clear Clear evidence evidence of a major transcurrent the Quetico-Wabigoon Quetico-Wabigoon boundary has not been found. Metamorphism Metamorphism Supracrustal belts of Metavolcanic belts belts have Supracrustal belts of the the Atikokan Atikokan area areaare aremetamorphically metamorphically zoned. zoned. Metavolcanic greenschist assemblages (chlorite-epidote-plagioclase-calcite+actinolite) and and greenschist assemblages at their cores (chlorite-epidote-plagioclase-calcit&actinolite) amphibolite assemblages assemblages at the margins margins (hornblende-plagioclase-biotite-ilmenite-sphene). (hornblende-plagioclase-biotite-ilmenite-sphene). amphibolite Metamorphic grade grade does does not not change but increases Metamorphic change abruptly abruptly at at the the Quetico-Wabigoon Quetico-Wabigoon boundary boundary but increases garnet, and and staurolite staurolite isograds. isograds. Pressuresteadily southward as defined by biotite, Ca-amphibole, garnet, Presswetemperature conditions conditions in in the the garnet garnet zone zone of of Quetico Quetico metasediments metasediments fall fall in in the the upper upper greenschist greenschist temperature facies facies (P-230-430 (P230-43O MPa, MPa,T-419-577T). T4l9-577°C). Except for greenschist greenschist assemblages assemblages in the Marmion Marmion batholithadjacent batholith adjacent to to the the Steep Steep Rock Rock belt, belt, Except tonalites and gneisses show amphibolite conditions (P=560 (P=560 MPa, MPa, T=7OO0C). T=700°C). tondites The high metamorphic grade of of gneisses gneisses within within oval oval structures structures is is attributed attributedto totheir theirhaving having risen from deeper crustal levels, as well as proximity to felsic plutons. Thermal anomalies risen from deeper cmstal levels, as well as proximity to felsic plutons. Thermal associated with oval structures associated structures and and plutons, plutons, superimposed superimposed on regional burial metamorphism, metamorphism, may may be responsible responsible for the metamorphic zonation of these supracrustal belts. metamorphic zonation supracrustal Tectonic Environment Environment Tectonic Nisbet (1988) were were the the first first to to attempt attempt to to define definethe the tectonic tectonic environment environment that that Wilks and Nisbet Mesoarchean Mesoarchean strata strata in the Atikokan Atikokan area area formed in. They believed that a rift, formed by extension extension of the Marmion Marmion block, is the most most probable probable tectonic setting for the the Steep Steep Rock Rock Group. Group. This explains explains the outcrop outcrop patterns patternsof of the the Steep SteepRock Rock and and nearby nearby Lumby Lumby Lake Lake successions successionsas as having having formed formed on on two two adjacent tilted tilted blocks. blocks. Alternatively, may have have taken taken place place on on aa stable stable divergent divergent adjacent Alternatively, sedimentation sedimentation may continental margin with all or only the lower lower part of of the the Wagita Wagita Formation Formation representing synrift symift deposits and the remainder of the succession up to and including the Joliffe Ore Zone reflecting deposition on a post-fift post-rift stable shelf. shelf. If the overlying Witch Bay Bay volcanics volcanics are areautochthonous, autochthonous,they they deposition record renewed extension. extension. A study by Thurston and Chivers (1990) put the Steep Rock and Lumby Lake Belts into a A * group they they termed sequences. These These consist, consist,from frombase basetoto top, top, of of quartz group termed platform platform sequences. quartz arenite arenite ± carbonate, oxide facies iron formation and komatiitic to tholeiitic volcanic rocks. They strornatolitic strornatoliticcarbonate, oxide facies formation komatiitic to tholeiitic volcanic rocks. They compare these with plateform sequences at modern passive margins. compare sequences at modem at the the base base of of the the Steep Rock Fralick and King (1995) correlate the sedimentary sequence at Group with sediments at the top of the Finlayson-Lumby Lake Lakevolcanic volcanicsuccession. succession. This implies chronologicallyseparated separatedby byaasedimentation sedimentationevent. event. They They also also two periods of mafic volcanism chronologically record subsidence of of an an oceanic oceanic plateau plateauand andthe thelong longperiod period stress that the sedimentary sequences record plume driven volcanism is consistent consistent with with coupling coupling of ofthe thearsenosphere arsenosphereand andlithosphere. lithosphere. If If they they of plume are correct this would plate tectonics during the the early are would negate negate the the operation operation of of modern-style modem-style plate tectonics during Mesoarchean. Mesoarchean. �Hollings et a1 a! (1998) agree with Fralick and and King's King's (1995) stratigraphic interpretation but advance a more elaborate model model to to explain explainthe thegeochemistry geochemistryof ofvolcanic volcanicand andintrusive intrusiveunits. units. They They which is mainly mainly represented represented by by the the believe that an arc arc developed, developed, due to subducting lithosphere, which deformed and eroded remnants of the intrusive tonalites. tonalites. Failed subduction of an ocean plateauridge complex al, 1998). complex juxtaposed the the arc arc intrusives intrusives with the metavolcanics (Hollings et a], 1998). Kusky and Hudleston (1999) agree with with Hollings Hollings et et d al (1998) (1998)that thatthe thetonalites tonalitesrepresent representan an sedimentary succession formed formed aa shallow shallow water water carbonate carbonate eroded arc remnant, but suggest that the sedimenw platform during arc rifling and the Dismal Ashrock is an allochthonous melange overridden by rifting Dismal allochthonous ovemdden by structurally structurally emplaced emplaced arc arc volcanics volcanics of of the the Witch Witch Bay Bay Formation. Formation. Based on extensive geochemical analysis of volcanic units Tomlinson et al(1999) al (1999) propose that the unfractionated high-Mg basalts basalts represent represent high unfractionated basaltic basaltic komatiites and spinifex-textured spinifex-textured high-Mg degree partial melts of the upper mantle. These are geochemically similar to lavas erupted forming empted forming degree These the modem Ontong-Java Ontong-Java oceanic plateau. Enriched Enriched basaltic basaltic komatiites represent a deep mantle plume source that has not been mixed with depleted Volcanism in in the the Steep Rock, has not been mixed with depleted mantle. mantle. Volcanism Rock, Finlayson and Lumby Lake belts most likely occurred in a continental setting and was probably proceeded by rifling rifting of of the continental continental crust. The Thestratigraphy stratigraphyof of the greenstone greenstone belts and evidence of magmatism may 70 Ma) Ma) indicates indicates that more than one pulse of plume magmatism of protracted protracted volcanism volcanism (ca. (ca. 70 have been involved (Tomlinson et a!, 1999). have been involved (Tomlinson et al, 1999). Obviously opinions tectonic setting the the succession succession developed developed in. The fieldtrip Obviously opinionsdiffer differas as to the tectonic will provide a form where these ideas can be discussed on the outcrop. provide a form where these �REFERENCES: REFERENCES: - Antevs, E.,l951, E.,l951, Glacial Glacialclays claysininSteep SteepRock RockLake, Lake, Ontario, Ontario,Canada; Canada; Geological Society Sooiety of America Bulletin, Bulletin,v. v.62, 62,nono.ID, 10,p. p. 1223-1262 1223-1262 Brain, Canadian Mining JJournal, v. 61, 61, p. p. 573.574. 573-574. 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Lithopmk Secretarm, Unwcrs8ty Rrilish Columbia. Colurnbi&PP. pp 29-35 . Hardy, R.M., R.M.. and R.F.,1960, Boulder in vvarved at Steep SteepRock RockLake, Lake,Ontario, Ontario,Canada; Canada;Geological GeologicalSociety SocietyofofAmerica AmericaBulletin, Bulletin,v. v. m c d clay at Hmdy, and Legget, L e ~ e tR.F.,1960, , Boulder 71,no. 71, no. I,1,p. p. 93-94. 93-94. of Steep RockImn Iron Mines Mines Limited; Limited; The kPrecambrian, 8-tO. Steep Rock m b r i a n , v.v.23, 23, P. p. 8-10. Hicks, H.S., 1950, 1950, Geology of the iron deposits of Huston, WI., Queen's University, Kii@ton, Kingston, Ontario. H u s t o ~W.J., ~ , 1956, 1956,The TheSteeprock St-pmck Manganiferous Manganifmus Foot-wall Foot-wall Paint; Paint; M.Sc. MSc. thesis. thesis. Q m e d s University, Indares. A, and Martignole, J.,1985, J..l985, Biotite-garnet geothermometryininthe thegranulite granulitefacie: fades: the the influence influenceof of Ti Ti and and Ai Al in Indares. A, and Martignole. 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Jolliffe, A,W,, Rock Lake, Lake, Ontario: Ontario: in in The The relatiomhip relationship of of rnineralimion mineralization to ofthe the Steep Sleep Rock Rock Group, Group, Steep Steep Rock lo Precambrian Prccmb"an Jolliffe, A.W., 1966, 1966,Stratigraphy Stratigraphy of stratigraphy in certain m mining ofOntario and Quebec, PrecambrianSymposium, Symposium,edited editedby byA.M. A.M.Goodwin, Goodwin,Geological Geological Association Association smtigraphy i n i n gareas m m of Ontarioand Qmebeo, Precambrian Paper No. No. 3, 3, p. p. 75-98. 75-98. of Canada, Special Paper Jolliffe, A.,W., oresof ofSteep Steep Rock Rock Lake: Lake: Economic Economic Geology, G d o g y , v.50, v. 50,no.4, "0.4. p.373-398. p.373-398. Jolliffe, A..W., 1955, 1955,Geology Geologyand andiron imnores c h e a n granitic updm K m i n m i , D.C.. D.C., Thivierge. Thivierge, R.H., RH.. and and Stone, Stone, D., Kaminent. D., 1988, Development Developmentof of aa camlwtic cataclasticfault faultmne zoneininan ankArchean graniticplulm pluton of of the the SSuperior structural, geochemical geochemical and andgeophysical geophysicalcharacte"stics: characteristics:AAmerican JournalofofScience, Science, v.v.288, 288, p.p.458.494. 458494. Province: smclural, mdJournal Lakespluton, ploton, Atikokan, Alikokan,northwestern norlhwestern Ontario, Canada; Canada; Kmineni, D.C., 1982,AAstudy sNdyofofrock mckalteration alterationininthe theEye-Dashwa Eye-Dmhwa Lakes Kansineni, D.C.. and and Dugal, Dugal, J.J.B., JIB., 1982, ('heroical Geology, v. 36, 36, p. p. 35-57. 35-57. Chemical Geology, v. Kmineni, D.C., and andStone, Stone, D.,1983, D.,1983, The The ages ages of fmcturos in tlse the Eye-Dmhwa o Mineralogy Kamineni, D.C., of fractures Eye-DashwaLakes Lakespluton. pluton.Atikokan, Atikokan, Canada; Canada;Contribuliom Contributionstto Mineralogy and Petrology, Petrology, v. v. 83, p. 237-246. and D., 1983, granite kKamineni, i n m i , D., 1983, Sulphur-isotope Sulphur-isolop~geochemistry gco~hemistryof fracture-filling xiacNre-filling gypsum mpaum in in an an-'Archean --A~chean granitenear near Atikokan, Atikokan,Ontario. Ontario.Canada: Canada: Chemical Geology Geology v.39.p.263-272. Chemical v.39.p.263-272. Kimberley, M.M.,and andSorbara, Sorbma,J.P., J.P..1976, Post-Archean weathering of pmceedings of of the the 1976 1976Geotraverse Geomve-=Kimberley, MM., 1976, Post-Arehean of Steep Steep Rock Rock Gmup GroupIron Iron Fornation: Formation: proceedings Conference, University University of Conference, of Toronto, Tomnto, Toronto, Toronto, Ontario, Ontario, p. p. 128-136. 128-136. �Lawson, AC., Lake, Ontario Canada, Canada, Memoir28, Memoir 28, P. P 7-15. A.C., Geological GeologicalSunYey SunYey011912, of 1912,The TheGeology Geologyof of Steeprock SteepmckLake, 7-15 Legget, MW., 1953, Ontario, Canada: Canada: Economic Economic Geology, Geology, v.v. ha% R.F., R.F., and and Bartley, B d e y , M.W., 1953,An An engineering engineering study study of of glacial glacialdeposits dewsits at at Steep Steep Rock Rock Lake, Lake, Ontario, 13-540. 48, 48. p. p. 5513-540. Miller, v. I2,p. 12,p. 304-317. 304-317 Miller, Wa., W.G.,1903, 1903.Iron lmnranges rangesofofnorthern northernOntario; Ontario;Ontario OntarioBureau Bureauof ofMines, Mines, v. Moore, Mcare, ES., E X , 1939, 1939,Geology Geologyand and ore oredeposits depositsof ofthe theAtikokan Atikokan area: area: Ontario Ontario Department Department of Mines, Mines, v. 48, 48, Pt. pt. 2, 2, P.p. 1-34 1-34(published (pblished 1940). 1940). Accompanied 48a, scale scale 1I inch inch to to II mile. Accompanied by by Map Map 48% mile. Moore, ES., Canada, Transaction Section 4,3rd 4,3rd series, v.32, E X ,1938, 1938,The TheSteeprock SteepmckSeries: Series: Royal Royal Society Society of ofcanada, series, v. 32,p. p. 11-23. 11-23, Morris, M.V., 1986, Geochemistry and tectonic seuing setting of the Steep Rock Rock greenstone greenstone belt, belt,Atikokan, Atikokan,Canada; Canada;BSc. B.Sc.thesis, thesis,Carleton CarletonUniversity, University, 1986, Geochemistry Ottawa, Oltawa,Ontario, Ontario,162p. l62p. Roberts, T,L. and Bartley, replacement in in deep deep seated seated iron iron ore deposits Lake Superior Superior region; Economic hnomic B d q . M.V, M.V, 1943, 1943. Hydrothermal Hydmthennal replacement dewsits of the Lake Geology, v' 38. Geology, v 38. p. p. 1-24. 1-24, their geology, geology, ppetrography, Schaefer, 5.J., S.J.. Morton, Morton, P., P., 1991, 1991. Two Two komatiitic komatiiticpyroclastic pymclastic units, units, Superior Superior Province, Fmvince, northwestern northwestern Ontario: their e m p p h y , and correlation. Canadian CanadianJournal Journal of of Earth EatthScience Science 28, 1455-1470. 1455-1470. Schaefer, Schaefer, S.J., 1989, 1989, AAcomparison comparisonofoftwo twoultramafic ultramaticpyroclastic pyroclasticrock rock units, units, northwestern northwestem Ontario: Ontario: Institute Institute of of Lake Lake Superior SuperiorGeology Geology Proceedings, v. 35, p. 77. Proceedings, Shklanka, Shklanka, R., 1972, 1972, Geology Geology of of the the Steep SteepRock RockLake Lakearea, area,District DistrictofofRainy RainyRiver; River;Ontario OntarioDepartment Department of ofMines Minesand andNorthern NorthernAffairs, Affiirs, Geological Report93, Report 93, I l4p. Smith, Sheet. Geological Survey of Canada, sscale Smith, W.H.C., W.H.C., and Mclnnes, W., 1897, Seine River Sheet. Suwey ofcanada, a l e I1:253 12.53440. 440, of America Bulletin, v. v.4, Smith, 4, p. p. 333-348. 333-348 Smith, W.H.C., 1893, 1893, The Archean Archean rocks rocks west of of Lake Superior; Geological Geologicd Society Society ofAmerica Smith, Smith, F.G., 1942, 1942, Notes Notes on on the the iron iron ores ores of of Steeprock Steepmck Lake, Lake, Ontario; Ontario; University Universityof of Toronto Toronto Studies, SNdies, Geological Geologid Series, Series, No. 47, Contributions Contributions to 1-75. to Canadian CanadianMineralogy, Mineralogy,p.p.771-75, Sniyth, Lake, Ontario; Ontario;American AmericanJournal JournalofofScience, Science,v.v.42, 42, p.p.317-331. 3 17-331 Smyth, H.L., H.L., 1891, 1891, Structural Structural geology of Steep Rock Lake, Stone, Stone, D., Kamineni, Kamineni, D.C., D.C., Brown, Brow, A., A., and and Everitt, Eveflit R.A., R.A., 1989, 1989. A A comparison comparisonof of fracture h t u r e styles stylesin in two two granitic graniticbodies bodiesof ofthe theSuperior Superiorprovince; province; Canadian Journal of Earth Sciences. Sciences. v. 26, p. 387-403, 387403. Canadian Stone, 1982, Fractures and fracmre fracture in in fillings fillings of of the the Eye-Dashwa Fye-Dashwa Lakes Lakes pluton, pluton, Atikokan, Atikokan, Ontario; Ontario; Canadian Canadian Journal Journal of of Stone, U.. D., and and Kamineni, Kamineni,D.C., D.C.,1982, Earth Sciences, Sciences, v 19, 19, p. 789-803. Stone, the Atikokan Canada, Map 1666A, Stone, D., Kamineni, Kamineni, D.C., D.C., 1989, 1989,Geology Geologyof ofthe Atikokan area, area, Ontario Ontario Geological Geological Survey Suwey of ofCanada, 1666A, scale 1:50,000. 1:50,000, Precambrian geology geology of of the Atikokan m area, Ontario. Geological Survey of Stone, Stone. D., D., Karnineni, Kamineni. D.C., D.C., Jackson, Jackson,M.C., M.C., 1992, 1992, Precambrian a, northwestern northwestern Ontario. Bulletin 405, 106 Canada, Bulletin I06 pp. 35, p.p. 131-141, 1941,Origin Tanton,T.L., 1941, Origin to the hematite deposits at Steep Rock Rock Lake, Lake, Ontario; Ontario;Royal RoyalSociety Societyof ofCan* Canada,Transactions, Transactions,v.v.35, 131-141. Tanton,T.L., Lake, Ontario; Ontario; Royal Royal Society Society of of Canada, Canada,Transactions, Transactions,Section Section4,4,v.v.20, Tanmn,T.L., 1926, 1926, Recognition Recognition of the Coutchiching near Steep Rock Lake, 20, p. 39-49. 3949. Tanton,T.L., of Canada, Canada,Transactions, Transactions,v.v.40. p. 103-112 103-112. Steep Rock Lake; Royal Society of 40. p. Tant0n.T.L.. 1946, 1946. The iron iron ore at Steep Tanton,T.L., 1927, 1927, Mineral Mineral deposits deposits of of Steep Steep Rock Rock Lake Lake map-area, maparea, Ontario; Ontario; Geological Survey Swwey of of Canada, Canada, Summary Summay Report, 1925, 1925,Pt. pt. C, C, p. p. Tanton,T.L., IC-lIC, IC-IIC. Secular variation variation in greenstone Canada. P.C., Chivers, Chivers, K.M., K.M., 1990, 1990, Secular Thurston, P.C., greenstone sequence development development emphasizing Superior Province. Province. Canada. Research 46,2148. 46,21-58. Precambrian Research and Chivers, Chivers, K.M., K.M., 1990, 1990,Secular Secular variation variation inin greenstone greenstone sequence sequence development development emphasizing cmphmizing Superior Province, Canada: Canadc Thurston, P.C., and Research:v.v.46, p.21 Precambrian Research: 46, p. 21 -58. -58. 'Tomlinson, K.Y., Thurston, P.C., P.C., Hughes, Hughes, D.J., D.J., Keays, R.R., 1996%The central Wabigoon Wabigom region: pemgenesis of mafic-ultramafic matic-ultram&k rocks Tomlinson, KY.. Thurston, R.R., l996a, region: petrogenesis rocks in in the Steep Rock, Lumby Lake and O h n g a Lake greenstone In: Harrap, Harap, R.M., RM., Obonga greenstone belts belts (continental (continental rifIing rifting and drifIing drifting in in the Archean). Archean). In: Helmstaedc e p m #53. Helmstaedt, H. Fds.), (Eds.), Western Superior Transect Transect Second SecondAnnual AnnualWorkshop Workshop(Oci (Oct.20-2l,l995), 20-21,1995),Lithoprobe LithoprobeRReport #53.Lithoprobe Lithoprobe Secretariat, University of British Secretariat British Columbia, pp. 65-73. �Tonilinson, KY., 1996,The belts, northem northern Ontario, Ontario, Canada: Canada: unpublished Tom1ins.m. K.Y., 1996,megeochemistry geochemisryand andtectonic tectonicsetting sewingofofearly earlyPrecambrian Precambriangreenstone greenstone belts, unpubliihd PhD thesis. University University of PhD thesis, of Portsmouth, P o ~ m o u t hUK, U& , pp.287. pp.287. Tomlinson, K.Y., KY., Hughes, I) the Hughes, Di., D.J.,Thurston, 'Ibumton,P.C., P.C., 1996b, 1996b,Metavoleanic Metavolcanic rocks rocks of of the the central c e n d Wabigoon Wabigmn Subprovince: Subprovince: 1) the Lurnby Lumby Lake Lake Tomlinson, greenstonebelt. belt.1": In: Summary Summas'yofofFicidwork other Activities, 1996. Geological Survey pp. 60-63. 60'63. greenstone Fieldwork and and otherAdvities. 1996. Ontario OntarioGeological SurveyMiscellaneous MiscellaneomPaper Paper 166. 166, pp. tJgIow, vicinity of Rook No. No. 8, 12th IInternational I, 12th n t m d o n a l Geological GeologicalCongress, Congress,issued iswed Uglow, W.L., W.L.. 1913, 1913, Geology Geology of of the the vioinity ofSteep Steep Rock Rock Lake: Lake: in in Guide Guide Rook 8, Pt. pt. I, by the Canada, p. by the Geological Geological Survey S w e yof ofCanada p. 46.53. 46-53. Walcott, Ontario. CanadCanada;Geological GeologicalSurvey Surveyof ofCCanada. Memoir 28, 28, p. p. 16onfossils fos?.ils from tiomlimestone limestoneof o fSteeprock Steeprock Series, Series, Ontario, d a . Memoir 16W d w C CD,, C.D.,1912, 1912,Notes Noteson 23. 23. Wilks, ME., NorthwesternOntario: Ontario:aaMajor Major Archean ArcheanUmwfonnity Unconformity an an Archean Archean Swomatolites, Stromatolites, TheGeology Geologyof ofthe theSteep Steep Rock Rock Group Group Norrhwestem Wilks, M.E..1936, 1986,The MSc thesis. Saskatchewan, MSG thesis. University University Saskatchewan.Saskatoon, Saskmon,Saskatchewan, Saskatchewan, 206 206 pp. pp. Wilks, unconformity and Wilb. ME,, M.E.,and andNisbet, N i s ME.G., E.G.,1988, 1988,Stratigraphy Stratigraphyofofthe theSteep SteepRock Rock Group, Group, northwestern northwestern Ontario: Ontario: aa major major Archean Amhean unwnfomity and Archean Amhem stromatolites: smmatolites: Canadian Canadian iournal l o ~ aofoflEarth EaOhSciences. Sciences,v.v.25, 25,P. p. 370-391. 370-391. Wilka, ME., major Archean Wilks, M.E., 1986, 1986,The Thegeology geologyofofthe theSteep SteepRock RockGroup, &up, northwestern mxthwestem Ontario: Ontario: a a major Archem unconformity unwnfomity and and Archean Archean stromatolites; smmmliies; M.Sc. thesis, MSe. thesis,University UnivmityofofSaskatchewan, Saskatchewan,Saskatoon, Stskmon,Saskatchewan, Saskatchewan,206 206P. p. Wilks, ME,, ofofthe Wilb, M.E.,Nisbct, Nisbet,E.G., E.G.,198$, 1988,Stratigraphy Shati-hy theSteep SteepRock RockGroup, Group,northwestern norrhwestmn Ontario Ontario major major Archean Archean unconformity unwnfomity and and Archean Archean stromatolites. 370-391, smmatoliies. Canadian Canadian iournal JournalofofEarth EarthScience:25, Scimce:25,370-391. Wright, CM,, the Steeprock Queen'sUniversity, University,Kingston, Kingston, Ontario. Ontario. zonesininthe thehangingwall hangingwallofofthe Steeprock Ore %Zone; Zone; M.Sc. M.SG thesis, thesis, Queeds Wright, C.M.,1959. 1959,Pyrite Pyritezones I I �Day 1 Field Field Trip Tnp Stops Stops Field stops in the Lumby Lake Lake greenstone greenstone belt. From Thunder Bay travel NW to to Upsala Upsala on onTrans-Canada Trans-Canada Highway Highway 17. 17.Approximately Approximately 15-16 km further west of Upsala at the Graham road, turn left (west) onto the Graham logging logging road, gravel road to Sapawe. This road initially follows the Firesteel Sapawe. follows Firesteel River (Provincial Series Pakashkan Lake sheet). After approx. approx. 24-25 24-25 km you come to aa junction junction map 52G15E, 52G/SE, Pakashkan where the main gravel Sapawe-Upsala road turns south (left), continue ahead (right gravel Sapawe-Upsala south (right hand hand fork) and after km you you come come to to aabridge bridgecrossing crossingBrush Brush Creek Creek (Provincial (Provincial Series Series map map after 22 km 520/SW, Gulliver River sheet). You are at the eastern extent of the greenstone belt and 52G/SW, Gulliver eastern within the northern half of the stratigraphy (Figure 1). 1). This generally east-west bush road runs across most of the length of the Lumby Lumby Lake Lake greenstone greenstone belt (at a low low angle angle to to the the strike) before turning turning south near Lumby Lake and joining the gravel north-south Premiere south joining Lake road (near km 33), main Sapawe-Upsala Sapawe-Upsala road (between km 33), which which later later rejoins rejoins the main 12 and 13). 13). Stop 643340E 5435920N: 5435920N:BIF, BIF,ultramafic ultramafic fragmentals, fragmentals, mafic Stov 1: 1: UTM UTM zone zone 15, 15,643340E maficlavas. lavas. reachthe thefirst firststop stop(Figure (Figure 1). 1).ItIt is is on the From Brush Creek Creek continue continue another another —2km -2km totoreach left side of the road next next to to aa clearing clearing for for parking, parking, and opposite opposite aa road road heading heading off off on on the the right hand side. The area area was was burnt burnt over over in in 1995 1995but but new new trees have been planted and are are growing Om thick growing fast. fast. A A large largeoutcrop outcropofofbanded-iron banded-ironformation formationisisclose closetotothe theroad road(—4 (-10m unit) and then further from the road (south) is an ultramafic fragmental sequence then further from the road (south) is an ultramafic fragmental sequence(—20m (-20m thick). South of this are are mafic mafic amygdaloidal amygdaloidal flows, followed by mafic pillow lavas. The ultramafic fragmental ultramafic fragmental sequence sequence is unusual unusual and and ofofdebatable debatable origin. origin. It comprises comprises predominantly ultramalic ultramafic lithic, lithic, lapilli-sized lapilli-sized fragments fragments within an an ultramafic ultramafic matrix matrix (bulk (bulk composition 12 to 21 wt. % MgO, 38-45 wt. % Si02). a ranges from ungraded to graded 12 21 wt. % MgO, % Si02). It ranges from ungraded to graded and would be breccia. In places it shows be classified classified un-genetically un-genetically as aa volcaniclastic volcaniclastic breccia. shows evidence and quenched but was was itit generated evidence of hyaloclatite hyaloclatite textures textures and quenched fragments fragments but generated by by predominantly pyroclastic or autoclastic processes and has it been resedimented? predominantly pyroclastic or autoclastic processes and has it been resedimented? in high-field strength strength Geochemically these are Al-depleted komatiites komatiites which are enriched in elements and light rare earth earth elements elements (REE) (WE) but depleted depleted in in heavy heavy REE. See See Tomlinson Tomliison (l999a) for et al. (1999a) foraadetailed detaileddescription descriptionof of the the chemistry chemistry and and petrogenesis. petrogenesis. Stop 2: UTM 637750E 5437300N: 5437300N: komatiite komatiite flows, interflow interfiow BIF BIF and and chefl. Stov UTM zone zone 15, 15,637750E chert. From stop I continue a further —6 km west along the road to a small turn off on the right. stop 1 continue a further -6 km west Follow Follow this thistrail trailfor for—200 -200 m then then turn turn left leftonto ontoanother anotherfrail trailand andafter after—300 -300 m you you come cometo to the outcrop or a large, flat, flat, glacially glacially polished polished outcrop. outcrop. ItIt may may be be possible possible to drive drive right right to outcrop the trails may be too too muddy. muddy. At this this stop stop (Stop (Stop 2, Figure Figure 1) 1) there there are are several several large large �mapof ofthe theLumby LumbyLake Lake greenstone greenstone belt belt showing showing trip trip localities Figure 1: GeoLogical Geological map Jackson, 1985 (geochronology from Davis and Jackson, 1985 and and Tomlinson Tomlmson et et a!., al., 1999b). 1999b). -t Norway Lake Pluton Ma 3014 Ma A Red Paint /3014 -t , /, Irene-Eltruit me-Eltruit Lakes ikes Complex Complex Lake -s - — .1 Gargoyle Lake 4' Norway A Lake V 'Bar 1 2 Divers ion W 1 T 1 -- L - 2997 r'---a 0,-1c,11', Jefferson Lake !U..::A - Stnç * Sapawe4 Post-tectonic granite Post-tectonic granite Pre-tectonic tonalite-gabbro intrusive complex Pre-tectonic granodioritegranodioritetonalite gneiss I . ) - r. Marmion Batholith 3003. Ma Sedimentary edimentary rocks - Brush Brush Creek I Lake -1 .4 - <2963 ~ 2 9 6 3Ma 6 kilometers h/f. ' Sapawç * Komatiitic ir Komatiiticrocks rocks Intermediate felsic ..a. ~termediateto felsic A pillow ~nging Pillow p younging volcanic rocks direction direction * volcanicrocks rocks * U-Pb U-Pbage age Mafic volcanic --f-i— 4 4- 1 Faults Faults Fold axis: Fold . axis: . syncline anticline, anticline, Q Trip @ Triplocality locality Roads Roads ala �komatiite outcrops that have been stripped by a prospector (Ray Bernatchez) and hence the rocks are well exposed with beautifully preserved textures and field relationships visible. The first large outcrop contains komatiite flows, some are thin (<lm thick) with thin pillowed flow tops (sequence youngs to the SW\ Spinifex texture is rare on this outcrop. Spherules are common as are ancient cracks that facilitated devitrification. Walk through the bush towards the NW and several outcrops occur along the way, the first on a small scarp shows wonderful spinifex texture. Several small outcrops show banded iron formation (BIF) and evidence of komatiite lava flowing into water-laden sediment. Peperite textures, evidence of autobrecciation, ultramafic pillows etc. are all beautifully preserved. Continue to the NW and a large outcrop of spinifex textured komatiite occurs. Flows are separated by thin units of cherty BIF. A 9m thick flow contains randomly orientated pyroxene crystals (altered to actinolite) which in the top 3m of the flow are spinifex textured with branching acicular blades. Generalized log of these outcrops shown in Figure 2 (from Tomlinson et al., 1996 and 1999b). Compositionally many of these flows are basaltic komatiites (18-13 wt. % MgO) and spinifex textured high-Mg basalts (9-12 wt. % MgO). Chemically they differ from the ultramafic fragmental units and are Al-undepleted with REE profiles that are generally unfractionated (Tomlinson et al., 1999a). Stons 3 and 4: UTM zone 15, 0637345E 5437130N, and further along the road: Mafic lava flows. Return to the east-west road that runs across the greenstone belt, reset the odometer and continue driving west. Many outcrops along the road between the komatiite locality and the culverts at Pinecone and Cryderman Lakes (2 large lakes either side of the road after a -7.5 km stretch) show well preserved mafic lava flows. This lithology (having undergone various states of strain) makes up the majority of the greenstone belt stratigraphy. We will stop at a couple of localities before Pinecone and Crydennan Lakes. In the first (just -300 m from where we rejoined the road, Stop 3, Figure I), flow top breccia is overlain by a massive flow base, which is in turn overlain by pillowed lava, which is capped by thin hyaloclastite. The complete flow is 3.8 m thick with 80 cm of pillowed flow. Further along the road several outcrops show undefonned pillows where younging direction is easy identified (any of these outcrops are suitable for stop 4). Pillows are small with convex upward tops and bases that project downwards into the interstices between the underlying pillows. 4 S t o 5: ~ UTM zone 15,633266E 5435600N: view. Continue along the "main" road until reaching the culverts at Pinecone and Cryderman Lakes (Stop 5, Figure 1, -7-7.5 km from Stop 3), reset the odometer again. These lakes occur at the central east-west axis of the belt within sedimentary units that separate the northern and southern halves of the belt. Unfortunately the sedimentary units are poorly exposed but the view is nice and so is the water if its warm enough for swimming! �Figure 2. Lower komatiite unit, northern assemblage, Lumby Lake greenstone belt (after Tomlinson et al., 1999a). Metres SW Pyroxene cumulate Pillowed and spherultitc flows Komatiite flow Ultramafic hyaloclastite Komatiite flow Ultramafic hyatoclastite Interbedded komatiite flows, iron formation and chert Komatiite flow Komatiite flow Gabbro with increasing proportion of tremolite needles towards the top �Stoo 6 (if time allows): UTM zone 15,628130E S433850N: mafic lavas. Continue following the road through the belt. The road heads predominantly west and is now cutting the southern stratigraphy at a low angle to the strike. Unlike the northern half of the belt (which youngs southwards), the southern half youngs predominantly to the north. Mafic pillow lavas again make up the majority of the stratigraphy and an outcrop 6 km further on shows good younging to the north (Stop 6, Figure 1). - Stoo 7: UTM zone 15,624000E 54323SON: felsic volcanics a t S margin of the belt. Continue on this "main" road for a further -6 lan as the road eventually turns south into the felsic volcanic sequence at the base of the greenstone belt. Close to Lumby Lake itself a large property has been cleared by Ray Bernatchez and the felsic sequence is well exposed (Stop 7, Figure 1). Felsic volcanic rocks make up a relatively thick sequence here. They have been dated at 3 localities along the southern margin of the belt (including this site) and range from 3001 to 2997 Ma which is within error of the age of the Marmion tonalite. The felsic volcanics are quartz porphyritic and range from fragmental units to massive rhyolite flows. Continue south and this road rejoins the main gravel logging road down to Sapawe (Provincial Series map 52B/NW, Marmion Lake sheet). A few km south of Sapawe the road rejoins Trans-Canada Highway 11. To the right is Atikokan and to the left is Thunder Bay. References Davis, D.W. and Jackson, M.C., 1988. Geochronology of the Lumby Lake greenstone belt: a 3 Ga complex within the Wabigoon Subprovince, northwest Ontario. Geol. Soc. Am. Bull., 100, 818-824. Tomlinson, K.Y., Hughes, D.J., Thurston, P.C. and Hall, R.P. 1999a. Plume magmatism and crustal growth at 2.9 to 3.0 Ga in the Steep Rock and Lumby Lake area, western Superior Province. Lithos, 4611, 103-136. Tornlinson, K.Y., Davis, D.W., Thurston, P.C., Hughes, D.J. and Sasseville, C. 1999b. Geochemistry, Nd isotopes and geochronology from the Central Wabigoon Subprovince and North Caribou Terrane: regional correlations leading towards a Mesoarchean reconstruction; in Harrap, R.M. and Helmstaedt, H. (eds.). Western Superior Transect 1999 Annual Meeting, Lithoprobe Report #70. Lithoprobe Secretariat, University of British Columbia, p 136-146. Tomlinson, K.Y., Hughes, D.J. and Thurston, P.C. 1996. Metavolcanic rocks of the central Wabigoon subprovince: 1) the Lumby Lake greenstone belt. Summary of Fieldwork and Other Activities, 1996. Ontario Geological Survey Misc. Paper 166: 6063. �Day 2. Atikokan area Day 2 features several unique geologic features spanning 300 My of Archean crustal evolution in the southern Wabigoon and adjacent Quetico Subprovinces. Stops include the early Mannion tonalite batholith, a rare Archean unconformity, the Steep Rock Group (a platform sequence) and contiguous metavolcanic and metasedimentary rocks (Figure 1). An attempt is made to examine the structural relation between these rocks. Most stops are in vicinity of the abandoned Steep Rock Iron Mine from which approximately 100 Mt of ore were removed from 1944 to 1979. Starting from the junction of Highways 622 and 11B in Atikokan, proceed west on Highway 11B turning north on Mercury or O'Brien Streets. Continue past the Atikokan airport in the direction of the abandoned Steep Rock Iron Mine. After passing under the Canadian National Railway overpass, follow the paved perimeter road along the west side of the mine area. The perimeter road curves around the north end of the mine area and crosses back and forth beneath a power line. Stop where the road crosses the power line for the second time approximately 1 1 km from the start and walk west to low, rounded outcrops interspersed with grassy areas. The Marmion batholith -The Marmion batholith is a large oval tonalitic intrusion extending at least 50 km east of Atikokan. Dated at 3003+5 Ma (Davis and Jackson 1988) it is among oldest felsic intrusions in the western Superior Province and together with the pre 2900 Ma Dashwa Gneiss Complex and Finlayson and Lumby greenstone belts (Davis and Jackson 1988) is part of the enigmatic older volcanoplutonic terrane in the central Wabigoon Subprovince. The Marmion batholithformed a mature erosional surface on which the Steep Rock Group was unconformably deposited at an unknown but probably early stage in tectonic evolution of the area. Although rare in central parts of the Marmion batholith, metagabbro dikes are voluminous near the Steep Rock belt; some dikes seem topredate whereas others postdate the Steep Rock Group. Although the tectonic environment at the time of Steep Rock Group deposition is speculative, the dikes imply extensional conditions, possibly in a rifted continental margin setting (Wilks and Nisbet 1988). Felsic and mafic varieties of tonalite are mapped in the Marmion batholith near the Steep Rock belt. These are typically medium-grained, weaklyfoliated and inequigranular to porphyritic rocks composed of essentially plagioclase, quartz and biotite and up to 20% hornblende in the mafic variety. The Marmion batholith is cut by ductile-brittlefaults and primary minerals are extensively converted to sericite, carbonate, chlorite and actinolite within a few kilometers of the Steep Rock belt. Stop 6-1 The Marmion batholith adjacent to the Steep Rockgreenstone belt Exposures in the power line right-of-way are somewhat poor due to an intense brown weathering rind but consist of tonalite interspersed with about 30% metagabbro dikes. Dikes are irregular in shape and are mainly north-northeast trending. All rocks are well foliated to friable and intensely altered to greenschist minerals. A few hundred meters south of this locality the Marrnion tonalite is overlain by the Steep Rock Group. �Figure 6-1 : Geologic map of the Atikokan area shown field-trip stops 6-8 and 6-9. See Figure 63 for other stops. �From the power line, follow the perimeter road south for a distance of about 1 km where the pavement ends at an abandoned railway crossing. Park in the grassy area near the end of the paved perimeter road and walk west along the tom-up railway roadbed. Unconformity at the base of the Steep Rock Group - Greenstone belts are interspersed with voluminousfelsic plutonic rocks throughout the Superior Province and in the majority ofplaces the boundaries between the two are marked by sharp contacts where plutonic rocks intrude and contact metamorphose greenstone belts. Rarely is the base of an Archean greenstone belt preserved although in recent years, an increasing number of localities have been identified where the bases of greenstone successions lie unconformably on felsic plutonic rocks. Most arc: found in remote northwestern parts of the Superior Province. The Steep Rock Lake locality represents an extremely rare, well-preserved and accessible example of an Archean unconformity and is featured in several stops on this trip. Stop 6-2 Unconformity at the base of the Steep Rock Group Outcrops at this locality illustrate the gradational nature of the unconformity at the base of the Steep Rock Group. After walking about 200 m along the tom-up railway line past outcrops of mainly tonalite, you will see a large vertical rock-cut on the east side. Foliated, relatively fine-grained dark metagabbro makes up most of the vertical rock-cut and, at the north end of the vertical rock-cut, is transitional to friable, buff, gritty metasandstone (Wagita Formation). The metasandstone is poorly bedded, but locally shows clasts, and is well foliated, possibly indicating enhanced shearing at the unconformity. The metasandstone can be traced north from the large vertical rock-cut through a series of small exposures to a rounded outcrop of metaconglomerate that lies opposite piles of mine-waste placed on the railway line. Boulders of the conglomerate are mainly tonalite and a dark rock that is probably metagabbro. Beyond the metaconglomerate, rock-cuts show carbonate breccia, tonalite and metagabbro. Outcrops at the obstructed tunnel entrance are metamorphosed pelite and sandstone. The section along the railway line passes back and forth through the unconformity at the base of the Steep Rock Group. Rarely is the unconformity sharply defined as the transition from tonalite to sandstone takes place gradually over distances of a few meters. Return to the vehicle and drive .9 km south along the gravel perimeter road past remains of the head frame of the Hogarth shaft and a branch road (east) to the former concentrator plant area. Turn right and proceed .2 krn down the pit access ramp. Turn right at the first side-road and proceed .15 km and park at the outside of a sharp bend overlooking the pit. Walk down the gravel slope following an erosional channel past several rusty, jagged outcrops of tonalite and gabbro. Follow a flagged trail from the base of the gravel slope about 100 m westerly through a wooded area and emerge onto a north-facing slope interspersed with outcrops, boulders and �Mafic Metavolcanii rocks Dismal Ashroch Jolliffe Ore Zone Mosher Carbonate Wagita Formation (elastics) Stromatolites Unconforrnity Marrnion Batholith Early Mafic Dikes Figure 6-2: Schematic diagram (after Wilks and Nisbet 1988) showing the Steep Rock Group and contiguous supracrustal rocks of the Steep Rock belt. See legend of Figure 6-1.The upper ashrock contact is locally faulted and may represent a depositional time-gap. �small trees. The Steep Rock Group -The Steep Rock Group was extensively studied over the past century (see reviews in Stone et at. 1992) and although early workers offered diverse structural and stratigraphic interpretations, later studies showed the Group to be a homoclinal succession of 4 formations totalling about 1000 m thickness. These include,from the base up, the Wagita Formation (conglomerate, sandstone), Mosher Carbonate Formation (limestone, dolostone), Jolliffe Ore Zone Formation (goethitic ironformation) and Dismal Ashrock Formation (ultramafic pyroclastic rocks) as shown in Figures 6-2 and 6-3. The lower boundary of the Steep Rock Group is defined by an unconformity at the base of the Wagitaformation. Although sheared locally (e.g. Stops 6-2, 6-3) other exposures of the unconformity (e.g. Stop 6-5) show little deformation and preclude tectonicjuxtaposition of the Steep Rock Group onto the Marmion batholith. The upper contact of the Dismal Ashrock Formation is highly deformed in the Steep Rock Mine area and is widely cited as the upper boundary of the Steep Rock Group (e.g. Jolliffe 1955). The Steep Rock Group is cited as a prime example of a platform sequence (Thurston and Chivers 1990); platform sequences typically comprise a succession of quartz arenite and conglomerate, stromatolitic carbonates, iron formation and komatiitic rocks unconformably overlyingfelsic plutonic rocks. Most are concentrated in the Sachigo Subprovince and arepre 2.8 Ga in age having preceded the mafic, mafic tofelsic and "Timiskaming-type" volcanic sequences that make up many greenstone belts. Geologic evidence suggests platform sequences developed in shallow water in a tectonically stable environment, involving initial erosion of widespread older sial followed by rift-related volcanism (Thurston and Chivers 1990). Stop 6-3 Marmion tonalite; Wagita Formation; Mosher Carbonate Formation; stromatolites The outcrop at the end of the trail is made up of buff, gntty, poorly bedded Wagita Formation and altered friable tonalite that gives way westerly over a distance of about 10 m to grey, bedded Mosher Carbonate Formation. Note that the contact between clastic metasedimentary rocks and Mosher Carbonate Formation is sharp; rocks are strongly foliated possibly due to shearing at this locality. About 10 m north at the low end of the outcrop, spherical and pseudocolumnar stromatolites, typically .1 m in diameter are exposed in bedded Mosher Carbonate Formation. A west-sloping face of the outcrop provides a lateral section showing the concentric domical shape of stromatolites. Apexes of the stromatolite domes indicate a westerly younging direction. Continue down the slope to a level area and turn west toward the edge of the Hogarth open pit. Observe large domical stromatolites exposed on the west-facing wall of the upper bench. Rather than returning to the vehicles by the way in which you came, proceed northerly from the level area along a steep access ramp to the perimeter road. Walk along the perimeter road to the vehicles and drive .1 km up the hill and park in a level place at the observation area. Walk to the west side of the observation area. Stop 6-4 Scenic lookout and overview of the Steep Rock Group The partly flooded Hogarth pit can be seen to the north and the Roberts pit to the extreme �Figure 6-3: Detailed geologic map of the Steep Rock Mine area showing l o c a t i o n s o f field-trip stops 6-1 to 6-7. Dlsmel Ashrook Formatton Pyrite Zones JoIHffe Ore Zone Formati Moaher Carbonate Format! Wagita Formation ~onai~te - ./--ROÈ -Railway, ..... - ' abandoned railws Water lavç*l1 9 8 8 ) Geological contact / Fault ^%/Aautt + zone synctirr outcrop �south. Looking west, the west arm of Steep Rock Lake can be seen beyond a concrete retaining dam. This stop provides an overview of the west-facing Steep Rock Group and adjacent, eastfacing mafic metavolcanic sequences in the Mine area (Figure 6-3). The scenic lookout is situated on Marmion tonalite at the base of the Steep Rock Group. The Wagita Formation is not well exposed and can be either absent or else thin at this locality. In either case, the base of the Steep Rock Group extends along the foot of the slope immediately in front of you. Grey outcrops underlying the tree-covered hill 200 to 300 m west, and the rusty jagged bluff to the northwest are Mosher Carbonate Formation. The Jolliffe Ore Zone Formation is almost completely flooded; a few reddish outcrops at the northwest end of the Hogarth pit may be remnants of the ore-zone. Dark grey-greenish outcrops on the west side of the pit near the centre of the mine area are Dismal Ashrock Formation. The sides of large heaps of waste rock on the west side of the mine area also appear to be mainly ashrock. The upper bench road that runs nearly fill1 length of the west side of the mine area approximately marks the contact between Dismal Ashrock Formation and adjacent mafic metavolcanic rocks. East-facing pillow lavas and metagabbro dikes underlie most of the tree-covered ridge beyond the upper bench road. The failed slope at the northwest end of the Hogarth pit is in metagabbro and tonalite. Proceed back down the side-road, turn right and continue 1 km down the main access ramp. Park at the junction with the first bench road to the left and walk about 300 m south along the bench road. Stop 6-5: Unconformity; Wagita Formation; Mosher Carbonate Formation The large bluff east of the bench road is composed of tonalite cut by thick, inclined metagabbro dikes. Near the top and at the south end of a small talus slope about 300 m from the parking area, steep-westerly dipping beds of rusty Mosher Carbonate Formation lie in unconformable contact with tonalite along the face of the bluff. Normally grey crystalline tonalite becomes buff, friable and altered possibly reflecting development of a regolith at the unconformity. Mafic minerals and plagioclase are altered to chlorite, sericite and carbonate however, the rock retains a relict igneous texture shown by unaltered quartz grains dispersed throughout the medium. The unconformity is marked by a transition over a distance of 1 to 2 m from altered tonalite through gritty sandstone (Wagita Formation) to bedded Mosher Carbonate Formation. Quartz content increases up-section in the sandstone; quartz grains are nresent in the lower carbonate beds. The unconformitv is relatively unfaulted at this locality. Proceed back up the main ace of Dismal Ashrock in the west wall of the Hogarth pit Stop 6-6:Dismal Ashrock Formation mine to exposures �The soft, dull, dark green rock is representative of Dismal Ashrock Formation. The ashrock is composed of dark, poorly sorted, subrounded lapilli and is essentially a lapilli tuff that rarely shows stratification. Some lapilli are zoned possibly due to accretionary growth under subaerial conditions. Although Jolliffe (1955) noted thin lava flows in this unit, the ashrock is dominantly pyroclastic and in this regard is rare among Archean komatiites. Continue north on the upper bench road along the west side of the mine area. Turn right and proceed .3 km down a pit-access ramp turning right at an ensuing junction and continue .2 km down toward the flooded Hogarth pit. Park by two power poles mounted in cement-filled tires. Walk north along the access road curving up-hill to the west. From the end of the road follow a flagged trail north over heaps of mine waste to the edge of the pit. Supracrustal assemblages and the structure of greenstone belts - Although originally interpreted as homoclinal successions, geochronology has shown in recent years that many greenstone belts are composites of supracrustal assemblages differing in age by up to 300 Ma (e.g. Corfu and Andrews 1986; Ayres and Corfu 1991). Although assemblages are major structural components of greenstone belts, mapping of assemblages has proven difficult because many contain similar types of volcanic and sedimentary rocks and all have been affected by late metamorphism and deformation. Boundaries between assemblages tend to be poorly exposed and can be either depositional time gaps orfaults with large possible displacements. In certain well-studied areas such as the Favourable Lake greenstone belt, assemblage boundaries appear to be mainly thrust faults (Ayres and Corfu 1991). At the present locality, the boundary between the Dismal Ashrock Formation and contiguous mafic metavolcanic rocks could possibly be an assemblage boundary. Favourable evidence includes the major lithologic and structural transition from the west-facing Steep Rock Group to a thick sequence of east-facing mafic lava flows and gabbro. The boundary isfaulted in the mine area (Figure 6-3; Stop 6-7),which implies that the mafic sequence could have been tectonically juxtaposed with the Steep Rock Group. Since neither the Steep Rock Group or metavolcanic rocks of the Steep Rock belt are dated, the depositional time gap at their mutual contact is unknown. Stop 6-7: Deformation at the contact between the Dismal Ashrock Formation and mafic metavolcanic rocks The pale green to white outcrops west of the upper bench road are pillowed mafic flows. East of the flooded Hogarth pit are bluffs of rusty Mosher Carbonate Formation. Approximately where the trail ends, the Steep Rock Group curves abruptly west and is cut off by a large metagabbro dike and the Bartley fault at the northwest end of the Hogarth pit. Metagabbro and tonalite make up most of the large bluff beyond the northwest end of the pit; a large rock slide in this area forced the mine to close prematurely in 1979. Provided that the slope of waste rock to the north is not flooded, carefully move down the �slope. Observe the pale-green to white friable rock that shows good pencil structure in the bench wall to your left. The pale green rock is probably a deformed mafic metavolcanic flow. Moving farther down the slope you pass beside soft, crumbled and crenulated, variably rusty to dark green rock of uncertain type. Upon reaching the lower bench level, go west along the bench to apoint where it is overrun with talus. The darkgreen deformed rocks in the pit wall behind the bench are Dismal Ashrock Formation and metagabbro. A rusty zone, which is possibly a pyrite lense, can be seen high on the pit wall. Several subvertical, north-trending mesoscopic faults cut up through the ashrock and are eroded back into the pit wall. The area illustrates severe deformation at the upper ashrock contact in the mine area, Mineral lineations plunge down-dip westerly implying a dominant component of dip-slip faulting. Proceed back up the ramps to the upper bench road and go south on to the paved perimeter road in the direction of Atikokan. Turn right on the road leading to the seaplane base on Steep Rock Lake and continue up a steep hill and around several curves for .4 km. Park in a turn-out on the left side of the road and walk east about 50 m through small trees to low outcrops in an abandoned gravel pit. Stop 6-8 (optional) Pillowed mafic metavolcanic flows This outcrop lies within the Canadian Charelston Gravel Pit that was strip-mined for ironore gravel in 1960 to 1965. Pillowed mafic metavolcanic flows that underlie the western half of the Steep ~ o c belt k are represented in this outcrop. Pillows typically have a pale-green, homogeneous interior and very-fine-grained, dark-green rims. Several varieties of pillows ranging from large "mattress" to small spherical types occur together. The younging direction derived from pillow shapes in this outcrop and elsewhere in the western Steep Rock belt is east. A massive flow occurs at the extreme west end of the outcrop. The rock is calc-alkaline basalt. Proceed back to Atikokan and south to the junction of Highway 11B and Highway 11. Turn west on Highway 11 and continue for 1.2 kilometers turning north on a forest access road just before Kemuel Lake. Drive about 200 m into a clear-cut and reforested area, park at the first turn-out and walk to a low outcrop on the east side of the road. Stop 6-9 (optional) Quetico metasedimentary rocks This outcrop shows several types of bedding and sedimentary features. Thick beds (up to 1. m) of fairly homogeneous metawacke occur at the north side of the outcrop. Bed thickness is generally .05 to .2 m; many beds are graded from a coarse sandy base to a grey, laminated, silty top. Truncated beds and crescentic scour channels filled with coarse material are present. Clasts (up to .2 m) of fine-grained, white chert or possibly �felsic volcanic material fill some scoured channels. Grainsize gradation and scour channels indicate that the local younging direction is south. The outcrop is cut by quartz veins, fractures and small-displacement faults. The mafic mineral is mainly biotite. Metamorphic grade increases south with the appearance of amphibole and garnet about 1. krn distant. End of Day 2. Return to Atikokan or Thunder Bay. �References Ayres, L.D. and Corfu, F. 1991. Stacking of disparate volcanic and sedimentary units by thrusting in the Archean Favourable Lake greenstone belt, central Canada; Precambrian Research, v. 50, p. 221-238. Corfu, F. and Andrews, A.J. 1987. Geochronological constraints on the timing of magmatism, deformation, and gold mineralization in the Red Lake greenstone belt, northwestern Ontario; Canadian Journal of Earth Sciences, v. 24, p. 1302-1320. Davis, D.W. and Jackson, M.C. 1988. Geochronology of the Lumby Lake greenstone belt: a 3 Ga complex within the Wabigoon Subprovince, northwest Ontario; Geological Society of America, Bulletin, v. 100, p. 818-824. Jolliffe, A.W. 1955. Geology and iron ores of Steep Rock Lake; Economic Geology, v. 50, p.373-398. Stone, D., Kamineni, D.C. and Jackson, M.C. 1992. Precambrian geology of the Atikokan area, northwestern Ontario; Geological Survey of Canada, Bulletin 405, 106p. Thurston, P.C. and Chivers, K.M. 1990. Secular variation in greenstone sequence development emphasizing Superior Province, Canada; Precambriari Research, v. 46, p. 21-58. Wilks, M.E. and Nisbet, E.G. 1988. Stratigraphy of the Steep Rock Group, northwestern Ontario: a major Archean unconformity and Archean stromatolites; Canadian Journal of Earth Sciences, v. 25, p. 370-391. � Dublin Core The Dublin Core metadata element set is common to all Omeka records, including items, files, and collections. For more information see, http://dublincore.org/documents/dces/. Title A name given to the resource Institute on Lake Superior Geology Dublin Core The Dublin Core metadata element set is common to all Omeka records, including items, files, and collections. For more information see, http://dublincore.org/documents/dces/. Title A name given to the resource Institute on Lake Superior Geology: Proceedings, 2000 Description An account of the resource Institute on Lake Superior Geology. Thunder Bay, Ontario. May 8-13, 2000. Creator An entity primarily responsible for making the resource Institute on Lake Superior Geology Date A point or period of time associated with an event in the lifecycle of the resource 2000 Format The file format, physical medium, or dimensions of the resource PDF Language A language of the resource English https://digitalcollections.lakeheadu.ca/files/original/6069db93fb592ecdd4a76f58a9bae2c9.pdf 47805a815831581565df2436ab456bb3 PDF Text Text 47th Annual Meeting Institute on Lake Superior Geology Proceedings Volume 47 Part 1—Program and Abstracts Madison, Wisconsin • May 9—12, 2001 �INSTITUTE ON LAKE SUPERIOR GEOLOGY U 47th Annual Meeting May 9-12, 2001 Madison, Wisconsin Hosted by: University of Wisconsin-Extension Wisconsin Geological and Natural History Survey University of Wisconsin-Madison Department of Geology and Geophysics Proceedings Volume 47 Part 1 - Program and Abstracts �47th Annual Meeting Institute on Lake Superior Geology Volume 47 contains the following parts: Part 1: Program and Abstracts Part 2: Field Trip Guidebook 1- Sedimentologic, Tectonic and Metamorphic History of the Baraboo Interval: New Evidence from Investigations in the Baraboo Range, Wisconsin 2 - Geology, Ore Deposits, and Cultural History of the Upper Mississippi Valley Zinc-Lead District 3 - Economic Geology of the Baraboo and Waterloo Quartzites of Southern Wisconsin Reference to the material in this volume should follow the example below: Medaris, L.G., Jr., 2001, Precambrian geology of S. Wisconsin: A panorama from the Baraboo Range, [abstract]: Institute on Lake Superior Geology Proceedings, 47th Annual Meeting, Madison, WI, 2001, v. 47, Part 1, p. 51. Volume 47 is published by the Institute on Lake Superior Geology and distributed by the Institute Secretary-Treasurer: Mark Jirsa Minnesota Geological Survey 2642 University Avenue St. Paul, MN USA 55114-1057 (612) 627-4780 email: jirsa001tc.umn.edu ILSG webstite http://www.ilsgeology.org/ ISSN 1042-9964 Cover Illustration: Van Hise Rock, Abelmans Gorge, SW1/4, sec. 28, T21N, R5E, Sauk County, Wisconsin from Salisbury, R.D., and W. W Atwood, 1900, The Geography of the Region About Devil's Lake and the Dalles of the Wisconsin: Wisconsin Geological and Natural History Survey Bulletin V. Plate IX. Charles R. Van Hise and Charles K. Leith used this outcrop as a laboratory to demonstrate the fundamental geometric relationship between slaty cleavage and bedding at an outcrop-scale for inferring larger-scale structures. See Field Trip Stop 4, this meeting, Part 2, p. 17. �CONTENTS Proceedings Volume 47 Part 1—Program and Abstracts Editor: Michael G. Mudrey, Jr. iv Institutes on Lake Superior Geology, 1955-2001 Constitution of the Institute on Lake Superior Geology v By-Laws of the Institute on Lake Superior Geology vi An Obituary for Samuel S. Goldich by Bruce R. Doe vii Goldich Medal Guidelines xiv Goldich Medalists XV Goldich Medal Committee xvi Citation for 2001 Goldich Medal Recipient by Gene L. Laberge xvii Eisenbrey Student Travel Awards xviii Student Travel Award Application Form xviii Student Paper Awards xix Student Paper Awards Committee xix xx Membership Criteria Board of Directors Xxi Local Committee XXi Session Chairs XXU Banquet Speaker Xxii Report of the Chair of the 46th Annual Institute Meeting xxiii Program XXiV Xxiv Xxiv Wednesday May 9 Thursday Morning May 10 Thursday Afternoon and Evening May 11 xxv xxvi xxvii Friday Morning May 11 Friday Afternoon May 11 Saturday May 12 XXVfl xxviii List of Poster Presentations Abstracts 1 111 �INSTITUTES ON LAKE SUPERIOR GEOLOGY, 1955-2001 # 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 DATE PLACE 1955 Minneapolis, Minnesota 1956 Houghton, Michigan 1957 East Lansing, Michigan 1958 Duluth, Minnesota 1959 Minneapolis, Minnesota 1960 Madison, Wisconsin 1961 Port Arthur, Ontario 1962 Houghton, Michigan 1963 Duluth, Minnesota 1964 Ishpeming, Michigan 1965 St. Paul, Minnesota 1966 Sault Ste. Marie, Michigan 1967 East Lansing, Michigan 1968 Superior, Wisconsin 1969 Oshkosh, Wisconsin 1970 Thunder Bay, Ontario 1971 Duluth, Minnesota 1972 Houghton, Michigan 1973 Madison, Wisconsin 1974 Sault Ste. Marie, Ontario 1975 Marquette, Michigan 1976 St. Paul, Minnesota 1977 Thunder Bay, Ontario 1978 Milwaukee, Wisconsin 1979 Duluth, Minnesota 1980 Eau Claire, Wisconsin 1981 East Lansing, Michigan 1982 International Falls, Minnesota 1983 Houghton, Michigan 1984 Wausau, Wisconsin 1985 Kenora, Ontario 1986 Wisconsin Rapids, Wisconsin 1987 Wawa, Ontario 1988 Marquette, Michigan 1989 Duluth, Minnesota 1990 Thunder Bay, Ontario 1991 Eau Claire, Wisconsin 1992 Hurley, Wisconsin 1993 Eveleth, Minnesota 1994 Houghton, Michigan 1995 Marathon, Ontario 1996 Cable, Wisconsin 1997 Sudbury, Ontario 1998 Minneapolis, Minnesota 1999 Marquette, Michigan 2000 2001 CHAIRS C.E. Dutton A.K. Sneigrove B.T. Sandefur R.W. Marsden G.M. Schwartz & C. Craddock E.N. Cameron E.G. Pye A.K. Sneigrove H. Lepp A.T. Broderick P.K. Sims & R.K. Hogberg R.W. White W.J. Hinze A.B. Dickas G.L. LaBerge M.W. Bartley & E. Mercy D.M. Davidson J. Kalliokoski M.E. Ostrom P.E. Giblin J.D. Hughes M. Walton M.M. Kehienbeck G. Mursky D.M. Davidson P.E. Myers W.C. Cambray D.L. Southwick T.J. Bornhorst G.L. LaBerge C.E. Blackburn J.K. Greenberg E.D. Frey & R.P. Sage J. S. Kiasner J.C. Green M.M. Kehienbeck P.E. Myers A.B. Dickas D.L. Southwick T.J. Bornhorst M.C. Smyk L.G. Woodruff R.P. Sage, W. Meyer J.D. Miller, M.A. ursa T.J. Bomhorst, R.S. Regis S.A. Kissin, P. Fralick M.G. Mudrey, Jr., B.A. Brown Thunder Bay, Ontario Madison, Wisconsin iv �__________ CONSTITUTION OF THE INSTITUTE ON LAKE SUPERIOR GEOLOGY (Last amended by the Board—May 8, 1997) Article I Name The name of the organization shall be the "Institute on Lake Superior Geology'. Article II Objectives The objectives of this organization are: A. To provide a means whereby geologists in the Great Lakes region may exchange ideas and scientific data. B. To promote better understanding of the geology of the Lake Superior region. C. To plan and conduct geological field trips. Article III Status No part of the income of the organization shall insure to the benefit of any member or individual. In the event of dissolution, the assets of the organization shall be distributed (some tax free organization). to (To avoid Federal and State income taxes, the organization should be not only scientific" or "educational, but also "non-profit") Minn. Stat. Anno. 290.01, subd. 4 Minn. Stat. Anno. 290.05(9) 1954 Internal Revenue Code s.501(c)(3) Article IV Membership The membership of the organization shall consist of persons who have registered for an annual meeting within the past three years, and those who indicate interest in being a member according to guidelines approved by the Board of Directors. Article V Meetings The organization shall meet once a year. The place and exact date of each meeting will be designated by the Board of Directors. Article VI Directors The Board of Directors shall consist of the Chair, Secretary-Treasurer, and the last three past Chairs; but if the board should at any time consist of fewer than five persons, by reason of unwillingness or inability of any of the above persons to serve as directors, the vacancies on the board may be filled by the Chair so as to bring the membership of the board to five members. Article VII Officers The officers of this organization shall be a Chair and Secretary-Treasurer. A. The Chair shall be elected each year by the Board of Directors, who shall give due consideration to the wishes of any group that may be promoting the next annual meeting. His/her term of office as Chair will terminate at the close of the annual meeting over which he/she presides, or when his/her successor shall have been appointed. He/she will then serve for a period of three years as a member of the Board of Directors. B. The Secretary-Treasurer shall be elected at the annual meeting. His/her term of office shall be four years, or until his/her successor shall have been appointed. Article VIII Amendments This constitution may be amended by a majority vote (majority of those voting) of the membership of the organization. V �BY-LAWS OF THE INSTITUTE ON LAKE SUPERIOR GEOLOGY I. Duties of the Officers and Directors A. It shall be the duty of the Annual Chairman to: 1. Preside at the annual meeting. 2. Appoint all committees needed for the organization of the annual meeting. 3. Assume complete responsibility for the organization and financing of the annual meeting over which he/she presides. B. It shall be the duty of the Secretary-Treasurer to: 1. Keep accurate attendance records of all annual meetings. 2. Keep accurate records of all meetings of, and correspondence between, the Board of Directors. 3. Hold all funds that may accrue as profits from annual meetings or field trips and to make these funds available for the organization and operation of future meetings as required. C. It shall be the duty of the Board of Directors to plan locations of annual meetings and to advise on the organization and financing of all meetings. II. Duties and Extenses A. Regular membership dues of $5.00 or less on an annual basis shall be assessed each member as determined by the Board of Directors.. B. Registration fees for the annual meetings shall be determined by the Chair in consultation with the Board of Directors. The registration fees can include expenses to cover operations outside of the annual meeting as determined by the Board of Directors. It is strongly recommended that registration fees be kept at a minimum to encourage attendance of students. III. Rules of Order The rules contained in Robert's Rules of Order shall govern this organization in all cases to which they are applicable. IV. Amendments These by-laws may be amended by a majority vote (majority of those voting) of the membership of the organization; provided that such modifications shall not conflict with the constitution as presently adopted or subsequently amended. vi �AN OBITUARY FOR SAMUEL S. GOLDICH By Bruce R. Doe Goldschmidt Medal winner in 1983, Samuel Stephen Goldich died 20 December 2000 at his apartment in Applewood, Colorado (a suburb of system in granites. In brief, the theory says that as the Denver), less than a month before his 92nd birthday. Sam, as he was widely known, received early fame with his 1938 paper in the Journal of Geology on rock weathering based on his Ph.D. thesis, an amazing paper that continued to receive citations into the 1990s, more than 50 years later. In short, he deter- mined that the resistance of igneous minerals to weathering was the inverse of the Bowen Reaction Series, that is minerals crystallized at lower temperatures were more resistant to weathering than those crystallized at high temperatures (and pressures). In other words the last minerals to crystallize (e.g., the most resistant was quartz followed by orthoclase, etc.) from a melt were the most resistant to weathering, a sequence that became known as the Goldich Stability Series (for a short discussion of this on the web see the 1996 web site of Pamela Gore at http://www.dc.peachnet.edu/_pgore/ge0logY/geo 10 1/weáther.htm. A few years later in 1941, a second, two-part widely utilized paper was published by pressure on minerals and rocks is released through uplift and erosion, they expand and make lead that is not in the structure accessible to removal by crustal fluids. No biography of Goldich would be complete without mention of Sam's interest in the 3 ,500-myr.-old rocks of the Minnesota River Valley Sandell and Goldich on the trace-element concentrations in igneous rocks, also in the Journal of Geology. This pioneering paper introduced the dithizone colorimetric analytical technique for trace-element determination to earth science and resulted in some of the most precise trace-element data in extent at the time and for decades thereafter. Sam got into an argument with the late Paul Gast which originally appeared to be 3,800 myr. old in his collaborations with Ed Catanzaro and later Tom Stern (see Goldich, Hedge and Stern, 1970). This discovery over which radiometric dating system on biotite led to the search of other areas in the U.S. for would be more susceptible to alteration by weathering -- the K-Ar system or the Rb-Sr system -- and a bet ensued. Paul thought that K-Ar would be more affected by weathering which would open the structure of biotite and let the argon escape which was not bound in the structure. Sam, however, thought that Rb-Sr would be more affected because the Sr that did perancient rocks with the discovery by others of these sorts of rocks in Michigan and Wyoming. He ended his research career with a very important paper on the air abrasion method ofpreparing zircons for U-Th-Pb dating (Goldich and Fischer, 1986) that has become not fit in the structure would be subject to ion exchange. Thus a paper resulted (Goldich and Gast 1966). Incidentally, Goldich won the bet. A very important paper with Mudrey (first presented in abstract form at the Geological Society of America Interior Distinguished Service Award in 1965, and he much used for Pb isotope tracer work as well as zircon dating. Sam received the Department of was a founder of the Institute of Lake superior Geology and received its first Goldich Award in 1980. S.S. Goldich received an AB from the University meeting as Goldich and Mudrey, 1969, with the paper appearing in 1972) using dilatancy to help explain the ofMinnesotain 1929 andeventuallyaPh.D. in 1936. In between, he earned an M.A. from Syracuse University in 1930 (and was to receive their Alexander Winchell Award in Geology in 1977), spent two years as an assistant in geology at the then Missouri discordance of the U-Th-Pb ages in zircons never received the acclaim it deserved because of its original publication in a Russian book, but Doe was later to make use of it in explain the U-Th-Pb whole-rock vii �School of Mines, 1930-1932 (now, University of Missouri at Rolla) where his association with Garrett Muilenburg resulted in his first paper (Muilenberg and Goldich, 1933), and was a fellow at Washington University in St. Louis where he published a paper with Carl Tolman (Tolman and Goldich, 1935). While a graduate student at the University of Minnesota, he was a chemist in the famous Rock Analysis Laboratory. In the period 1936- 1941, Sam rose from instructor to Associate Professor at the Texas Agricultural and Mechanical College which resulted in a number of papers on Texas geology and developed his research interest in iron ore in a paper with Barnes, Goldich, and Romberg (1949) that resulted in the milestone papers with Henry Lepp (Lepp and Goldich, 1959, 1964). He served World War II in the U.S. Geological Survey in exploration and study of laterite and bauxite in a number of unusual locations that eventually resulted in a series of papers during a second tour with the U.S. Geological Survey in 1947 and 1948. There were papers with Hendricks and Nelson in 1946 on a portable differential thermal analysis unit for bauxite exploration, with Bergquist on aluminous latentic soil ofthe Dominican Republic in 1947, and with Bridge in 1948 on the bauxite of Babelthuap Island in the Palau Group of islands. time and became the founding Branch Chief of the famous Branch of Isotope Geology in 1960, now defunct. Initially, the Branch was located at the old National Bureau of Standards site on Connecticut Avenue and Van Ness in Washington. D.C. (Now the site of the University of the District of Columbia). This location also allowed Goldich to make a close association with Bill Shields of the National Bureau of Standards (NBS, now called the National Institute of Standards and Technology) who was involved in using mass spectrometry for redeterniining atomic weights. This association resulted in much upgrading of the instrumentation in the Branch plus the building of new equipment known as Shields Mass Spectrometers and led the late Paul Gast to say that Shields was the most valuable employee in the Branch of Isotope Geology and the U.S. Geological Survey didn't even have to pay him. The core of this Branch came from the old Nucleonics Group that had been headed by Frank Senftle. In addition to Senftle, there were Irving Friedman, Henry Faul, Lorin Stieff, Thomas Stern, and Meyer Rubin, among others. Stieff shortly left to pursue his interest in world peace. Faul and Goldich had a falling out and Faul eventually left for the University of Pennsylvania. Quickly added were Ron Kistler (who was soon to return to the U.S. Geological Survey in Menlo Park, Sam rejoined the University of Minnesota in California), Carl Hedge, Edward Catanzaro, and 1948 and became Professor and Director of the Rock Analysis Laboratory the following year, a position he became a professor at the University of Alberta, Bruce Doe. Catanzaro soon left to join Shields at the NBS. The NBS site had to be abandoned because of their move to Gaithersburg and the Assistant Chief Geology for the Central Region came up with a small building (Bldg. 21) at the former WW II munitions plant in Lakewood, Colorado, known as the Denver Federal Center. John Rosholt was already there, and Irving Friedman in 1963 was the first to move. John Stacey and Mitsunobu Tatsumoto were soon added Harry Gehman who went to work in the oil industry, and Bruce Doe moved there in 1963 followed by and Richard B. Taylor who became Chief of the Branch of Central Mineral Resources in the U.S. Geological Survey. Master's candidates included most of the others in 1964, including Robert Zartman and John Obradovich. During a period of years after this move, Senftle and Stern stayed in Washington, D.C., and joined other groups. Meyer Rubin was to remain there in the Branch with his carbon- 14 operation. A popular way for the Branch of Isotope Geology to acquire researchers was from other branches. was to hold until his departure in 1959 (and was to receive the Minnesota Outstanding Achievement Award in 1985). Notable among his Ph.D. graduate students were Ralph Erickson who was the founding Branch Chief of the U.S. Geological Survey's Geochemical Exploration Branch, Ronald Burwash who Gary Ernst, currently a Professor at Stanford Univer- sity, and Zell Peterman a former Chief of the late Branch of Isotope Geology, U.S. Geological Survey, and a pioneer in strontium isotope geochemistry. During this period and in collaboration with Alfred Zell Peterman, for example, came from a branch Nier of the University of Minnesota, Sam organized called Geochemical Census (and, for example, later in Menlo Park, Marvin Lanphere from the Branch of a potassium-argon facilty in the Department of Alaskan Geology, and Brent Dalrymple from the Geology with Halfdon Baadsgaard (who also later became a professor at the University of Alberta). A Branch of Theoretical Geophysics) [History of the Branch of Isotope Geology after Sam ceased being Branch Chief in 1964 is not covered here.] . number of important papers resulted from this collaboration. Upon leaving the University of Minnesota, Doe, a Post-doctoral Fellow at the Geophysical Laboratory, was hired under an agreement that the Goldich joined the U.S. Geological Survey a third viii �U.S. Geological Survey would acquire a 12-inch Shields solid-source mass spectrometer. After that, however, most equipment was obtained as a result of cooperation with other organizations. Stieff, for example, arranged an investigation of uranium series disequilibrium in soils that freed up money for a second 12-inch Shields mass spectrometer and the stayed on for a fifth year to get a bachelors degree in geological engineering but decided to go on and get a master's degree somewhere else as well. I went in to Sam to tell him this and I was going to ask him not to prejudice others that I would ask to write letters of reference for me. I only got out that I was thinking of going somewhere for a master degree when he interrupted that he thought that was a great idea and he could get me a good deal at Missouri School of Mines. He added that I would never regret it. So I decided to leave it at that, and he was right, I never did regret it. Later when I mentioned I wanted to go on for a Ph.D., he suggested I apply to Caltech and that he would have a place for me in the isotope lab when I flunked out. Well, I did apply and was accepted, but, fortunately, never flunked out. Once I told Dick Taylor about my confusion concerning the unexpected result over the master's degree proposal, and he replied, that Sam was hard on me because he thought I had potential. I had noticed that with certain students of little accomplishment he would talk about building of a clean laboratory for isotopic investigations in Denver. A program with Saudi Arabia freed up money for a 6-inch Shields solid-source mass spectrometer. Money was obtained from the Japan-U.S. Scientific Cooperation Program for an argon mass-spectrometer (for an entertaining account of the argon mass spectrometer, you are referred to Glynu's book "The Road to Jaramillo"). After his tour as Chief of the Branch of Isotope Geology, Goldich was to leave the U.S. Geological Survey again and from 1964-1965 joined Pennsylvania State University as Professor of Geology and Geochemistry and Director of the Mineral Constitution Laboratories, for which he was to hire his former associate Oliver Ingamells. The State University of New York began upgrading their faculty and Sam moved to the State University of New York at Stony Brook as Professor of Geology from 1965 to 1968 at which he oversaw the building of another isotope fishing, hunting, movies, and the like, but that he eventually even wrote papers with some of the people he was hardest on. However, he left an ill will with many which probably accounts for this remarkable scientist not winning more honors than he did. But there were a lot of us that learned to overcome Sam's laboratory and hired Gil Hanson who became a professor there. Restless, he moved to Northern outbursts and to regard him as a friend and wonderful scientist. Illinois University in 1968 as Professor of Geology until his retirement in 1977 as emeritus and where he organized yet a fourth isotope geology laboratory. He was to move to Denver in his retirement and became emeritus at the Colorado School of Mines. Sam was a fellow of the American Geophysical Union, Mineralogical Society of America, and Geological Society of America. Selected Bibliography of Samuel Stephen Goldich Bridge, Josiah, Goldich, Samuel S., Preliminary report on the bauxite deposits of Babeithuap island, Palau group, p. 46, 1948. Cameron, R.L., Goldich, S.S., Hoffman, J.H., Radioactivity age ofrocks from the Windmill islands, Budd coast, Antarctica, Stockholm Contributions in Geology, 6, p. 1-6, 1960. No discussion of Sam would be complete with- out some mention of his famous personality. Although Sam could be very generous, he was prone to giving unsolicited good advice or opinions. This Goldich, Samuel S., A study of rock-weathering, 97 p., 1936. Thesis Doctoral from University of Minnesota, Minneapolis, Minneapolis, MN, United States advice or opinions was often given in a tone that the recipient would take as criticism or, even, condemnation. Perhaps all those who were close to Sam, and even many more distant, experienced this at some time or other. He was prone to allergies which did not improve his disposition. I recall once in a class when he repeatedly asked some question in an increasingly agitated and loud voice punctuated by his blowing his Goldich, Samuel S., Authigenic feldspar in sandstones of southeastern Minnesota, Journal of Sedi- nose as one student after another he called upon Goldich, Samuel S., A study in rock weathering, couldn't answer it. He finally said with a cute smile, "This class sure is stupid when I don't feel good." I Journal of Geology, 46(1), p. 17-58, 1938. recall thinking he didn't like me when I was an Goldich, Samuel Stephen, Bergquist, Harlan Richard, undergraduate at the University of Minnesota. I had Aluminous latentic soil of the Sierra de Bahoruco mentary Petrology, 4 (2), p. 89-95, 1934. ix �area, Dominican Republic, West Indies, U. S. Geological Survey Bulletin, B 0953-C, p. 53-84, 1947. Goldich, Samuel S., Lidiak, Edward G., Hedge, Carl Goldich, Samuel Stephen, Origin and development of aluminous latente and bauxite, Geological Society of America Bulletin, 59 (12, Part 2), p. 1326, 1948. area, Journal of Geophysical Research, 71(22), p. E., Walthall, Frank G., Geochronology of the midcontinent region, United States; [Part] 2, Northern 5389-5408, 1966. Goldich, Samuel S., Muehlberger, William R., Goldich, Samuel Stephen, Bergquist, Harlan Richard, Lidiak, Edward G., Hedge, Carl E., Geochronology of the midcontinent region, United States; [Part] 1, Scope, methods, and principles, Journal ofGeophysical Research, 71(22), p. 5375-5388, 1966. Aluminous lateritic soil of the Republic of Haiti, West Indies, U. S. Geological Survey Bulletin, B 0954-C, p. 63-111, 1948. Goldich, Samuel Stephen, Oslund, Eileen H., Composition of Westerly granite G- 1 and Centerville diabase W-l, Geological Society of America Bulletin, 67(6), p. 811-815, 1956. Goldich, S.S., Geochronology in the Lake Superior region, Inst. Lake Superior Geology, 13th Ann., East Lansing, Mich., 1967, p. 13, 1967. Goldich, S.S., Ingamells, CO., Suhr, N. H., Anderson, D. H., Analyses of silicate rock and mineral standards, Canadian Journal of Earth Sciences, 4(5), p. 747-755, 1967. Goldich, Samuel Stephen, Nier, Alfred Otto C., Problems of the division of Precambrian time, Institute on Lake Superior geology, April 21-22, 1958., p. 11, 1958. Goldich, S.S., Mudrey, M.G., Jr., Dilatancy model Goldich, Samuel Stephen, Nier, Alfred Otto C., for discordant U-Pb zircon ages, Abstracts with Baadsgaard, Halfdon, Three-fold division ofPrecam- Programs - Geological Society of America, Part 7, p. 80, 1969. brian in the Lake Superior region, Transactions American Geophysical Union, 39 (3), p. 516, 1958. Goldich, S.S., Nier, A.O., Washburn, A.L., A (super Goldich, S.S., Hanson, G.N., Geology of the Saganaga-Northern Light Lakes area, Minne- 40) /K (super 40) age of gneiss from McMurdo sota-Ontario, Inst. Lake Superior Geology, 15th Sound, Antarctica, Transactions - American Geophysical Union, 39 (5), p. 956-958, 1958. Ann., 1969, Tech. Sess. Abs., p. 16, 1969. Goldich, S.S., Geochronology in the Lake Superior region, Geochronology of Precambrian stratified rocks--Internat. Conf., Edmonton, Alberta, 1967, Papers, Canadian Journal of Earth Sciences, 5 (3, Part 2), p. 7 15-724, 1968. Goldich, Samuel S., Nier, Alfred 0., Baadsgaard, Halfdon, Hoffman, John H., Krueger, Harold W., The Precambrian geology and geochronology of Minnesota, Bulletin - Minnesota Geological Survey, 193 p., 1961. Goldich, S.S., Geochronology of the Minnesota-Ontario border region, Summary of fieldwork, 1969, Information Circular - Minnesota Geological Survey, 7, p. 30, 1969. Goldich, S.S., Hedge, C.E., Dating of the Precambrian of the Minnesota River valley, Minnesota, Journal of Geophysical Research, 67 (9), p. 3561-3562, 1962. Goldich, S.S., Ages of rocks assigned to the Penokean orogeny in Minnesota, Summary of fieldwork, 1969, Information Circular - Minnesota Geological Survey, 7, p. 31, 1969. Goldich, S.S., Hedge, C.E., Investigations in Rb-Sr dating, Journal of Geophysical Research, 67 (4), p. 1638, 1962. Goldich, S.S., Age of the Precambrian rocks of southwestern Minnesota, Summary of fieldwork, Goldich, S.S., Ingamells, C.O., Comparative determi- nations of potassium and rubidium, Transactions American Geophysical Union, 44(1), p. 109, 1963. 1969, Information Circular - Minnesota Geological Survey, 7, p. 31, 1969. Goldich, S.S., Gast, P. W., Effects of weathering on the Rb-Sr and K-Ar ages of biotite from the Morton Goldich, S.S., Hanson, G.N., Hailford, C.R., Mudrey, Gneiss, Minnesota, Earth and Planetary Science M.G., Jr., Re-interpretation of the structure of the Letters, 1(6), p. 372-375, 1966. Saganaga-Northern Light Lakes area, x �Minnesota-Ontario, Special Paper Society of America, p. 114, 1969. - Goldich, Samuel S., Ages of Precambrian Banded Geological Iron-Formations, Precambrian iron-formations of the world, Economic Geology and the Bulletin of the the Morton and Montevideo gneisses and related Society of Economic 1126-1134, 1973. rocks, southwestern Minnesota: Geological Society of Amenca Bulletin, 81, p. 367 1-3696, 1970. Goldich, S.S., Hedge, C.E., 3 ,800-Myr granitic gneiss Goldich, S.S., Hedge, C.E., and Stern, T.W., Age of Geologists, 68 (7), p. in south-western Minnesota, Nature (London), 252. (5483), p. 467-468, 1974. Goldich, Samuel S., Turek, Andrew, Hanson, Gilbert N., Peterman, Zell E., Correlation of early Precam- brian basins of the Canadian shield, Geological Goldich, S.S., Hedge, C.E., Interpretation ages in Association of Canada-Mineralogical Association of Canada, Joint Annual Meetings, Abstracts of Papers, p. 27, 1970. Minnesota — Reply: Nature, 257 (5528), p. 722-722, 1975. Goldich, S.S., Bodkin, J.L., Fluorine in Cenozoic Goldich, S.S., Lunar and terrestrial ilmenite basalt, Science, 171 (3977), p. 1245-1246, 1971. volcanic rocks of Ross Island and vicinity, Antarctica; a progress report, Bulletin - Dry Valley Drilling Project (DVDP) (6), p. 6-7, 1975. Goldich, S.S., Geochronology in Minnesota, Geology of Minnesota; A Centennial Volume, p. 27-37, 1972. Goldich, S.S., Doe, Bruce R., Delevaux, M.H., Possible further evidence for 3.8 b.y.-old rocks in the Minnesota River valley of southwestern Minnesota, Goldich, S.S., The Penokean orogeny [abstr.], Proceedings and Abstracts - Institute on Lake Superior Geology, Annual Meeting, 1972. Open-File Report - U. S. Geological Survey, OF 75-0065, p. Il, 1975. Goldich, S.S., Treves, S.B., Suhr, N.H., et al., Geochemistry of Cenozoic volcanic-rocks of Ross-Island and vicinity, Antarctica: Journal of Geology, 83 (4), p. 415-435, 1975 Goldich, S.S., Ages of Precambrian iron-formations, Precambrian iron-formation symposium, Abstracts and Field Guides, p. [19], 1972. Goldich, Samuel S., Geochronology and geochemistry, Field Trip Guide Book for Precambrian Migmatitic Terrane of the Minnesota River Valley, Guidebook Series - Minnesota Geological Survey, 5, p. 17-41, 1972. Goldich, S.S., Precision and accuracy in silicate analysis, National Bureau of Standards Special Publication (422), p. 79-89, 1976. Goldich, S.S., Problems in dating old Precambrian rocks, Program with Abstracts - Geological Associa- Goldich, Samuel S., Fallacious isochrons and wrong numbers, North-Central Section, 6th Annual Meeting, tion of Canada; Mineralogical Association of Canada; Canadian Geophysical Union, Joint Annual Meeting, 1, p. 71, 1976. Meeting: Geological Association of Canada, 29th annual meeting; Mineralogical Association of Canada, 21st annual meeting, Edmonton, Alberta, Canada, May 19-21, 1976. Abstracts with Programs - Geological Society of America, 4 (5), p. 322, 1972. Goldich, S.S., Mudrey, M.G.,Jr., Model' rasshireniya dlya ob"yasneniya nesoglasnykh urano-svintsovykh vozrastov v tsirkonakh; Dilatancy model for explain- Goldich,. S.S., Peterman, Z. E., Geology and geochemistry of the Rainy Lake area, Gorton, M. P. (editor), Archean geochemistry, Precambrian Research, 11(3-4), p. 307-327, 1980. Meeting: Archean geochemistry field conference, Ontario and Minnesota, Canada, Aug. 2-17, 1978. ing discordant uranium-lead zircon ages, Ocherki sovremennoy geokhimii i analiticheskoy khimii, p. 415-418, 1972. Goldich, S.S., Hanson, G.N., Hallford, C.R., and Mudrey, M.G., Jr., Early Precambrian rocks in the Saganaga Lake-Northern Light Lake area, Minnesota-Ontario. Part II. Petrogenesis, Doe. B.R. (edi- Goldich, S.S., Wooden, J.L., Geochemistry of the tor) and Smith, D.K. (editor), Studies in Mineralogy Archean rocks in the Morton and Granite Falls areas, and Precambrian Geology, Memoir - Geological southwestern Minnesota, Gorton, M. P. (editor), Archean geochemistry, Precambrian Research, 11 Society of America, l3S,p. 151-178, 1972. (3-4), p. 267-296, 1980. Meeting: Archean geochemxi �istry field conference, Ontario and Minnesota, brian iron formations, Economic Geology and the Bulletin of the Society of Economic Geologists, 59 Canada, Aug. 2-17, 1978. (6), p. 1025-1060, 1964. Goldich, S.S., Wooden, J.L., Origin of the Morton Gneiss, southwestern Minnesota; Part 3, Geochronol- Lepp, Henry, Goldich, Samuel S., Kistler, Ronald W., A Grenville cross section from Port Cartier to Mount Reed, Quebec, Canada, American Journal of ogy, More, G. B. (editor), Hanson, Gilbert N. (editor), Selected studies of Archean gneisses and lower Proterozoic rocks, southern Canadian Shield, Special Paper - Geological Society of America (182), p. 77-94, 1980. ISBN: 0-8137-2182-2. Science, 261 (8), p. 693-7 12, 1963. Lepp, Henry, Goldich, Samuel S., Origin of Precambrian iron formations, Kvenvolden, Keith A. (editor), Goldich, S.S., Wooden, J.L., Ankenbauer, G.A., Jr., Geochemistry and the origin of life, Benchmark Levy, T.M., Suda, R.U., Origin of the Morton Papers in Geology, 14, p. 195-209, 1974. (reprint) Gneiss, southwestern Minnesota; Part 1, Lithology, More, G. B. (editor), Hanson, Gilbert N. (editor), Ludwig, K.R., Zartman, R.E., Goldich, S.S., Gentry, Robert V., Lead retention in zircons; discussion and reply, Science, 223 (4638), p. 835, 1984. Selected studies of Archean gneisses and lower Proterozoic rocks, southern Canadian Shield, Special Paper - Geological Society of America (182), p. 45-56, 1980. ISBN: 0-8137-2182-2. Peterman, Z.E., Goldich, S.S., Hedge, CE., and Yardley, D.H., Geochronology of the Rainy Lake Goldich, S.S., Hedge, C.E., Stern, T.W., Wooden, Region, Minnesota-Ontario, Doe, B.R. (editor) and J.L., Bodkin, J.B., North, R.M., Archean rocks of the Granite Falls area, southwestern Minnesota, More, G. Smith, D.K. (editor), Studies in Mineralogy and Precambrian Geology, Memoir - Geological Society of America, l35,p. 193-215, 1972. B. (editor), Hanson, Gilbert N. (editor), Selected studies of Archean gneisses and lower Proterozoic rocks, southern Canadian Shield, Special Paper - Sandell, Ernest Birger, Goldich, Samuel S., The rarer Geological Society of America (182), p. 19-43, 1980. metallic constituents of some American igneous ISBN: 0-8137-2182-2. rocks, American Mineralogist, 24(12, Part 2), p. 12, 1939. Goldich, Samuel S., Determination of ferrous iron in silicate rocks, Chemical Geology, 42 (1-4), p. Sandell, Ernest Birger, Goldich, Samuel Stephen, The rarer metallic constituents of some American igneous 343-347, 1984. rocks; Part 1, Journal of Geology, 51. (Part 1), p. 99-115, (Part 2), 167-189, 1943. Goldich, S.S., and Fisher, L.B., Air-Abrasion experiments in U-Pb dating of zircon: Chemical Geology, v. 58: (3), p. 195-215, 1986 Shields, W.R., Garner, E.L., Hedge, C.E., Goldich, S.S., Survey of Rb (super 85)/Rb (super 87) ratios in minerals, Journal of Geophysical Research, 68 (8), p. Hanson, G.N., Goldich, S.S., Early Precambrian Rocks in the Saganaga Lake-Northern Light Lake 233 1-2334, 1963. Area, Minnesota-Ontario; Part II, Petrogenesis, Doe. B.R. (editor) and Smith, D.K. (editor), Studies in Mineralogy and Precambrian Geology, Memoir Geological Society of America, 135, p. 179-192, 1972. Shields, W.R., Goldich, S.S., Garner, E.L., Murphy, T. J, Natural variations in the abundance ratio and the atomic weight of copper, Journal of Geophysical Research, 70 (2), p. 479-49 1, 1965. Jenks, William F., Goldich, S.S., Ignimbrites in Stern, T.W., Goldich, S.S., Newell, M.F., Effects of southern Peru, Geological Society of America Bulletin, 65 (12, Part 2), p. 1271, 1954. weathering on the U-Pb ages of zircon from the Morton Gneiss, Minnesota, Earth and Planetary Science Letters, 1(6), p. 369-371, 1966. Lepp, Henry, Goldich, Samuel Stephen, The chemistry and origin of iron formations, Economic Geology and the Bulletin of the Society of Economic Geologists, 54 (7), p. 1348-1349, 1959. Stuckless, John S., Weiblen, Paul W., Goldich, Samuel S., A petrogenetic model for the alkalic rocks from the Ross Island area, Antarctica, Dry Valley Drilling Project (DVDP) Seminar-i, Bulletin - Dry Valley Drilling Project (DVDP), 4, p. 52-53, 1974. Lepp, Henry, Goldich, Samuel S., Origin of Precamxii �Stuckless, J. S., Miesch, A.T., Goldich, S.S., Weiblen, P. W., A Q-mode factor for the petrogen- esis of the volcanic rocks from Ross Island and vicinity, Antarctica, McGinnis, Lyle D. (editor), Dry Valley Drilling Project, Antarctic Research Series, 33, p. 257-280, 1981. ISBN: 0-87590-177-8. Wooden. J.L., Goldich, S.S., Suhr, N.H., Origin of the Morton Gneiss, southwestern Minnesota; Part 2, Geochemistry, More, G. B. (editor), Hanson, Gilbert N. (editor), Selected studies of Archean gneisses and lower Proterozoic rocks, southern Canadian Shield, Special Paper - Geological Society of America (182), p. 57-75, 1980. ISBN: 0-8137-2182-2. Yardley, D.H., Goldich, S.S., Preliminary review of Precambrian shield rocks for potential waste repository, YIOWIISUB-436712, p. (unpaginated), 1975. xlii �G0LDICH MEDAL GUIDELINES (Adopted by the Board of Directors, 1981; amended 1999) Preamble The Institute on Lake Superior Geology was born in 1955, as documented by the fact that the 27th annual meeting was held in 1981. The Institute's continuing objectives are to deal with those aspects of geology that are related geographically to Lake Superior; to encourage the discussion of subjects and sponsoring field trips that will bring together geologists from academia, government surveys, and industry; and to maintain an informal but highly effective mode of operation. During the course of its existence, the membership of the Institute (that is, those geologists who indicate an interest in the objectives of the ILSG by attending) has become aware of the fact that certain of their colleagues have made particularly noteworthy and meritorious contributions to the understanding of Lake Superior geology and mineral deposits. The first award was made by ILSG to Sam Goldich in 1979 for his many contributions to the geology of the region extending over about 50 years. Subsequent medalists and this year's recipient are listed in the table below. Award Guidelines 1) The medal shall be awarded annually by the ILSG Board of Directors to a geologist whose name is associated with a substantial interest in, and contribution to, the geology of the Lake Superior region. 2) The Board of Directors shall appoint the Goldich Medal Committee. The initial appointment will be of three members, one to serve for three years, one for two years, and one for one year. The member with the briefest incumbency shall be chair of the Nominating Committee. After the first year, the Board of Directors shall appoint at each spring meeting one new member who will serve for three years. In his/her third year this member shall be the chair. The Committee membership should reflect the main fields of interest and geographic distribution of ILSG membership. The out-going, senior member of the Board of Directors shall act as liaison between the Board and the Committee for a period of one year. 3) By the end of November, the Goldich Medal Committee shall make its recommendation to the Chair of the Board of Directors, who will then inform the Board of the nominee. 4) The Board of Directors normally will accept the nominee of the Committee, inform the medalist, and have one medal engraved appropriately for presentation at the next meeting of the Institute. 5) It is recommended that the Institute set aside annually from whatever sources, such funds as will be required to support the continuing costs of this award. Nominating Procedures 1) The deadline for nominations is November 1. Nominations shall be taken at any time by the Goldich Medal Committee. Committee members may themselves nominate candidates; however, Board members may not solicit for or support individual nominees. 2) Nominations must be in writing and supported by appropriate documentation such as letters of recommendation, lists of publications, curriculum vita's, and evidence of contributions to Lake Superior geology and to the Institute. 3) Nominations are not restricted to Institute attendees, but are open to anyone who has worked on and contributed to the understanding of Lake Superior geology. xiv �Selection Guidelines 1) Nominees are to be evaluated on the basis of their contributions to Lake Superior geology (sensu lato) including: a) importance of relevant publications; b) promotion of discovery and utilization of natural resources; c) contributions to understanding of the natural history and environment of the region; d) generation of new ideas and concepts; and e) contributions to the training and education of geoscientists and the public. 2) Nominees are to be evaluated on their contributions to the Institute as demonstrated by attendance at Institute meetings, presentation of talks and posters, and service on Institute boards, committees, and field trips. 3) The relative weights given to each of the foregoing criteria must remain flexible and at the discretion of the Committee members. 4) There are several points to be considered by the Goldich Medal Committee: a) An attempt should be made to maintain a balance of medal recipients from each of the three estates—industry, academia, and government. b) It must be noted that industry geoscientists are at a disadvantage in that much of their work in not published. 5) Lake Superior has two sides, one the U.S., and the other Canada. This is undoubtedly one of the Institute's great strengths and should be nurtured by equitable recognition of excellence in both countries. xv �GOLDICH MEDALISTS 1979 Samuel S. Goldich 1990 Kenneth C. Card 1980 not awarded 1991 1981 Carl E. Dutton, Jr. William Hinze 1992 William F. Cannon 1982 Ralph W. Marsden 1993 Donald W. Davis 1983 Burton Boyum 1994 Cedric Iverson 1984 Richard W. Ojakangas 1995 Gene LaBerge 1985 Paul K. Sims 1996 David L. Southwick 1986 G.B.Morey 1997 RonaldP.Sage 1987 Henry H. Halls 1998 Zell Peterman 1988 Walter S. White 1999 Tsu-Ming Han 1989 Jorma Kalliokoski 2000 John C. Green 2001 John S. Kiasner GOLDICH MEDAL COMMITTEE Mark Smyk (2001) Ontario Geological Survey, Thunder Bay Rod Johnson (2002) Rod Johnson and Associates, Negaunee, Michigan Frank Luther (2003) University of Wisconsin, Whitewater James D. Miller, Jr., as out-going senior member of Institute Board of Directors, is liaison between Goldich Medal Committee and the Board through the 2001 meeting. xvi �CITATION FOR JOHN S. KLASNER 2001 G0LDICH AWARD RECIPIENT It is my distinct honor and privilege to present this citation for John Klasner, the 22 recipient of the Goldich Award. John was born and raised in the Upper Peninsula. He received his Bachelor's degree in 1957 from Michigan State. His first professional job was with [NCO in the bush of northern Ontario in the summer of 1957. From 1958 to 1962, John worked for Geophysical Services International reducing seismic data for petroleum exploration in New Mexico, Texas, Wyoming, and then overseas in Libya and Muscat. He returned to Michigan State in 1962 and earned a Master's degree in geophysics in 1964. His thesis, mapping a bedrock valley by gravity methods was sponsored by the Groundwater Branch of the U.S.G.S. For the next five years, John worked for the Standard Oil Company of California as an exploration geophysicist stationed mainly in Anchorage, Alaska. He worked in the Cook Inlet area, and while in Anchorage, he met and married his wife, Gretchen, who also happens to be from the U.P. of Michigan. He worked in California from 1967 to 1969, and was then transferred back to Alaska in 1969 to work on the North Slope oil project. In the fall of 1969, he left Standard Oil to work on a Ph.D. at Michigan Tech., under Jo Kalliokoski. His dissertation was on the structure and metamorphism in the western Marquette range. I believe that John's thesis was the first study to show that the Early Proteozoic rocks are detached from the Archean in the area, suggesting large-scale horizontal tectonics. Upon completion of his Ph.D. in 1972, John joined the faculty at Western Illinois University, where he taught for 27 years. He resumed his contact with the U.S.G.S. spending summers mapping in northern Michigan. John as applied his knowledge of geophysic and structural geology to solving problems in the Precambrian of a number of areas including he Marquette range, the Gogebic range, the Feich trough, several areas in Wisconsin and in the Trans-Hudson Orogeny. He has done a broader range of structural studies in the Lake Superior region than anyone I know. He has a long list of publications (49) resulting from his work, in addition to the teaching and administrative load at an undergraduate university. He received the highest awards offered by Western Illinois University for his teaching and research. An indication of the esteem with which he was held at Western is shown by his being named Director of their Honors Program from 1994-1998. He introduced many students to the mysteries of he Precambrian by leading a field trip to the area every year. Especially important, I think, has been his role of introducing undergraduate students to professional activities by supervising fourteen Senior theses and six Honors theses during his years of teaching at Western. I have had the privilege of working directly with John since the mid-i 980s, doing field work in Wisconsin and northern Michigan. During this time John has been the mentor for a number of NAGGED/USES Summer trainees and volunteers. I have found John to be an exceptionally dedicated teacher of young geologists, as well as being a very competent geologist himself, a very good woodsman, and a pleasant fellow to work with. Therefore, it is with great pleasure that I present the 2001 recipient of the Goldich Award for "Outstanding Contributions To The Geology Of The Lake Superior Region", John S. Klasner. Gene L. LaBerge xvii �_______________________________ _____________ ___________ EISENBREY STUDENT TRAVEL AWARDS The 1986 Board of Directors established the ILSG Student Travel Awards to support student participation at the annual meeting of the Institute. The name "Eisenbrey" was added to the award in 1998 to honor Edward H. Eisenbrey (1926-1985) and utilize substantial contributions made to the 1996 Institute meeting in his name. 'Ned" Eisenbrey is credited with discovery of significant volcanogenic massive sulfide deposits in Wisconsin, but his scope as much broader—he has been described as having unique talents as an ore finder, geologist, and teacher. These awards are intended to help defray some of the direct travel costs of attending Institute meetings, and include a waiver of registration fees, but exclude expenses for meals, lodging, and field trip registration. The number of awards and value are determined by the annual Chair in consultation with the Secretary-Treasurer. Recipients will be announced at the annual banquet. The following general criteria will be considered by the annual Chair, who is responsible for the selection: 1) The applicants must have active resident (undergraduate or graduate) student status at the time of the annual meeting of the Institute, certified by the department head. 2) Students who are the senior author on either an oral or poster paper will be given favored consideration. 3) It is desirable for two or more students to jointly request travel assistance. 4) In general, priority will be given to those in the Institute region who are farthest away from the meeting location. 5) Each travel award request shall be made in writing to the annual Chair, and should explain need, student and author status, and other significant details. The form below is optional. Successful applicants will receive their awards during the meeting. enbrey INSTITUTE ONLAIE SUPERIOR GEOLOGY Student Travel Award Application Student Name: Date. Address: DpartmentHead-Tjped EducationalStatns:__________________ Department Head-Si gnature Are you the senior author of an oral or poster paper? YES_ NO___ Will any other students be traveling with you? Who? Statement of need (use additi onal page Efnecessary) Please xviii rdurn to: �STUDENT PAPER AWARDS Each year, the Institute selects the best of the student presentations and honors presenters with a monetary award. Funding for the award is generated from registrations of the annual meeting. The Student Paper Committee is appointed by the annual meeting Chair in such a manner as to represent a broad range of professional and geologic expertise. Criteria for best student paper—last modified by the Board in 1997—follow: 1) The contribution must be demonstrably the work of the student. 2) The student must present the contribution in-person. 3) The Student Paper Committee shall decide how many awards to grant, and whether or not to give separate awards for poster vs. oral presentations. 4) In cases of multiple student authors, the award will be made to the senior author, or the award will be shared equally by all authors of the contribution. 5) The total amount of the awards is left to the discretion of the meeting Chair and Secretary-Treasurer, but typically is in the amount of about $300 US. 6) The Secretary-Treasurer maintains, and will supply to the Committee, a form for the numerical ranking of presentations. This form was created and modified by Student Paper Committees over several years in an effort to reduce the difficulties that may arise from selection by raters of diverse background. The use of the form is not required, but is left to the discretion of the Committee. 7) The names of award recipients shall be included as part of the annual Chair's report that appears in the next volume of the Institute. Student papers will be noted on the Program. STUDENT PAPER AWARDS COMMITTEE Dave Meineke - Committee Chair Menden Engineering LLC Anne Argast Indiana University - Purdue University Fort Wayne Thomas J. Evans Wisconsin Geological and Natural History Survey Steve Kircher Nicolet Minerals xix �MEMBERSHIP CRITERIA FOR THE INSTITUTE ON LAKE SUPERIOR GEOLOGY Approved May 8, 1997 A. Membership in the Institute on Lake Superior Geology requires either participation in Institute activities, or an indication on a regular basis of interest in the Institute. Those individuals registering for an annual meeting will remain as members for 4 years unless: 1) they indicate no further interest in the Institute by responding negatively to the statement on meeting circulars "Remove my name from the mailing list"; or 2) two successive mailings in different years are returned by the postal service as address unknown. B. Those individuals who have not registered for an annual meeting in the past 4 years must indicate an interest in the Institute by postal, electronic , or verbal correspondence with the Secretary-Treasurer at least once every two years. Such individuals will be removed from the membership if they indicate no further interest in the Institute or two successive mailing in different years are returned by the postal service as address unknown. C. The Secretary-Treasurer will maintain a list of current members. The list will include the date of the beginning of continuous membership, dates of returned mail, dates of last contact (expression of interest), and the date membership expires, barring a change of status initiated by the member. Those individuals who have become members of ILSG by Section B will have an expiration date listed at 2 years from the upcoming meeting. For example, a member who expresses interest in September of 1997 (the next annual meeting is May, 1998) will have an expiration date of May, 2000, unless the member contacts the Secretary-Treasurer or attends an annual meeting. D. "Member for Life" status is granted to individuals who have been (nearly) continuous participants of the ILSG meetings for 15 years, Goldich Medal recipients, or those who have served as meeting chairs. This status will be further maintained unless the individuals indicate no further interest in the Institute, or 4 mailings in different years are returned by the postal service as address unknown, or they are deceased. E. All members will be mailed the First Circular for the Annual Meeting and the ILSG Newsletter. The Chair of the annual meeting may opt to send the first circular to additional individuals. All returned mail should be reported to the Secretary-Treasurer. F. The Secretary-Treasurer can designate any individual who is on the ILSG membership list (mailing list) as of January 1, 1997 as a member for life based on participation in ILSG activities. G: Members are strongly encourage to send address corrections to the Secretary-Treasurer to avoid unintentional lapse of membership. xx �2001 BOARD OF DIRECTORS (Board membership through the close of the meeting year shown) Michael G. Mudrey, Jr., General Chairman (2004) Bruce A. Brown, Co-chair Wisconsin Geological and Natural History Survey Stephen A. Kissin (2003) Lakehead University Theodore J.Bornhorst (2002) Michigan Technological Univensty James D. Miller, Jr. (2001) Goldich Liaison Minnesota Geological Survey Mark A. Jirsa - Executive Secretary (2002) Minnesota Geological Survey 2001 LOCAL PLANNING COMMITTEE Michael G. Mudrey, Jr. - Co-chair Bruce A. Brown - Co-chair Robert H. Dott, Jr. - Program Co-chair L. Gordon Medaris, Jr. - Program Co-chair Kathleen M. Zwettler - Meeting Coordinator Assistance to the local committee was provided by the following individuals from the Wisconsin Geological and Natural History Survey: James M. Robertson Director and State Geologist - Wisconsin Geological and Natural History Survey Virginia Trapino Office Support Mindy James Publication Preparation Susan Hunt Graphic Arts Michael L. Czechanski Program and Technical Assistance xxi �2001 SEssioN CHAIRS (In order of appearance) James M. Robertson - Geologic Overview of Southern Wisconsin Wisconsin Geological and Natural History Survey D.L. Daniels - Geophysical Overview and Earliest Archean Evolution U.S. Geological Survey William F. Cannon - Geology and Hydrogeology ofArsenic in Domestic and Public Water Supplies U.S. Geological Survey Michael D. Lemcke - Geology and Hydrogeology of Arsenic in Domestic and Public Water Supplies Wisconsin Department of Natural Resources Suzanne W. Nicholson - General Geology U.S. Geological Survey Dean Rossell - Developments in Understanding Keweenawan Geology Kennecott Exploration Company D.K. HoIm - Thermo-Tectonic History of 1800 to 1200 Ma post-Penokean to Pre-Keweenawan Rocks Bowling Green State University D.A. Schneider - Thermo- Tectonic History of 1800 to 1200 Ma post-Penokean to Pre-Keweenawan Rocks Syracuse University Eric Jerde - Developments in Understanding Archean Geology and Ore Depo.its Morehead State University 2001 BANQUET SPEAKER Thomas C. Hunt University of Wisconsin - Platteville A Practical Exercise in Metallic Mine Reclamation - Ladysmith, Wisconsin xxii �REPORT ON THE 46TH ANNUAL MEETING OF THE INSTITUTE ON LAKE SUPERIOR GEOLOGY Thunder Bay, Ontario The 46tl Annual Meeting ofthe Institute on Lake Superior Geology was held in Thunder Bay, Ontario, May 8-13, 2000, at Lakehead University. The meeting was sponsored by the Department of Geology, Lakehead University, with the assistance of the Ministry of Northern Development and Mines, Thunder Bay office. The meeting was co-chaired by Stephen A. Kissin and Philip W. Fralick. The meeting was attended by approximately 200 geoscientists from the United States and Canada. The meeting consisted of two days of technical sessions, with welcoming reception and annual banquet, and after six field trips before and after the technical sessions. The Proceedings Volume 46 was published in two parts. Part 1 - Program and Abstracts was edited by Stephen A. Kissin. There were 41 published abstracts for the 23 oral and 18 poster presentations given in the technical sessions. Part 2 - Field Trips was edited by Philip W. Fralick. There were six field trips, one before and after the technical sessions; all were described by the respective leaders in Part 2 of the Proceedings. The field trips were as follows: Mesoproterozoic Sibley Group was lead by Philip Fralick and Mark Smyk. This was a two day trip. 1) Lac des Iles Mine was lead by Moe Lavigne. The trip was run before and after the technical sessions. 2) Geoarcheology of the Thunder Bay Area was lead by Brian Phillips, Scott Hamilton, Joe Stewart, Pat 3) Julig, and Bill Ross. Paleoproterozoic Gunflint Formation was lead by Peir Pufahl and Philip Fralick. 4) Quaternaiy Geology, Shebandowan Belt was lead by Andy Bajc. 5) Steeprock-Finlayson-Lumby Belts, a two day trip was lead by Denver Stone, Kirsty Tomlinson, Ray 6) Bernatchez and Philip Fralick. The annual banquet was held in the Residence Dining Room at Lakehead University. The dinner speaker was Bruce Simonson of Oberlin College whose talk "Depositional Settings and Early Diagenesis of Large Precambrian Iron-Formations" was enthusiastically received. The 2000 Goldich Medal was awarded to John C. Green for his contributions to the geology of the North Shore Volcanic Group. The technical sessions included seven invited papers on the Canadian side of Lake Superior: M.M. Kehlenbeck "A Review of Structures in Rocks of Quetico Subprovence and Adjacent Terranes", D.W. Davis "Western Superior Province: Geochronologic Aspects", K. Tomlinson "Western Superior Provence: Sedimentological Aspects", M.J. Lavigne "The Lac des Ties Mine, Northwestern Ontario", P.W. Fralick "Western Superior Province: Proterozoic Sediments", and S.A. Kissin "Vein-type Deposits of the Thunder Bay Area". Student awards were given to Neil Pettigrew (University of Ottawa) for his oral presentation on the Samuels Lake intrusion, Ontario and to K.F. Beaster and J.D. Kohn (University of Wisconsin-Eau Claire) for their poster presentation on the Hinckley Sandstone of Minnesota. The Eisenbrey Student Travel Award was distributed among eight student presenters of oral and poster papers. The Board of Directors of the Institute met for a brief business meeting on May 10. Michael Mudrey of the Wisconsin Geological and Natural History Survey agreed to host the 2001 meeting at Madison, Wisconsin. The term of the Secretary-Treasurer, Mark Jirsa, expired at this meeting. He was nominated for an additional term as Secretary-Treasurer. There being no further nominations, he was acclaimed for an additional term. We wish to thank all those who contributed to the success of the meeting. The field trip leaders who contributed to the guidebook in Part 2 and devoted time and energy to field trips merit our special thanks. The session chairs are thanked for their services as well as the awards committee. We are especially grateful to Mark Smyk and staff of the Ministry of Northern Development and Mines, Sam Spivak, Karen Farrier, Becky Rogola and France Lagroix of the Department of Geology for invaluable assistance. Finally we would like to thank all participants whose attendance made the meeting a financial success. Stephen A. Kissin and Philip W. Fralick Co-Chairs of the 46th Annual ILSG xxiii �CALENDAR OF EVENTS AND PROGRAM WEDNESDAY MAY 9 8:00 am. FIELD TRIP 1: Sedimenlology, Tectonic and Metamorphic History of the Baraboo Interval: New Evidence from Investigations in the Baraboo Range, Wisconsin L.Gordon Medans, Jr. and Robert. H. Dott, Jr. University of Wisconsin - Madison Return of Trip 1 6:00 p.m. 5:00 p.m. - 8:00 p.m. Registration 7:00 p.m. - 10:00 p.m. Welcoming Reception, Cash bar and Poster Setup THURSDAY MAY 10 7:00 a.m. - 9:00 a.m. REGISTRATION 8:10 a.m. INTRODUCTORYREMARKS M.G. Mudrey, Jr. Chairman Wisconsin Geological and Natural History Survey SESSION I: GEOLOGIC OVERVIEW OF SOUTHERN WISCONSIN Session Chair: J.M. Robertson, Director and State Geologist, Wisconsin Geological and Natural History Survey 8:20 a.m. MICKELSON, D.M. and Clayton, L., (University of Wisconsin - Madison; Wisconsin Geological & Natural History Survey) Recent Advances in Understanding the Glacial Record of Wisconsin 9:05 a.m. BYERS, C.E. (University of Wisconsin - Madison) Overview of Paleozoic Geology in Southern Wisconsin 9:50 a.m. MEDARIS, L.G., Jr. (University of Wisconsin - Madison) Precambrian Geology of S. Wisconsin: A Panorama from the Baraboo Range 10:35 a.m. COFFEEBREAK AND POSTER SESSION SESSION II: GEOPHYSICAL OVERVIEW AND EARLIEST ARCHEAN EVOLUTION Session Chair: D. Daniels, US. Geological Survey 10:55 a.m. CHANDLER, Val W. and MUDREY, M.G., JR. Overview of Aeromagnetic Mapping: Minnesota (Chandler) and Wisconsin (Mudrey) 11:20 a.m. CANNON, W.F., Daniels, David L., Snyder, Stephen L., and Nicholson, Suzanne W. A Preliminary Interpretation of New Aeromagnetic and Gravity Data in Wisconsin 11:40 a.m. VALLEY, J.W., Peck, W.H., King, E.M, Graham, C.M., and Wilde, S.A. The Cool Early Earth: Oxygen isotope Evidence for Continental Crust and Oceans on Earth at 4.4 Ga NOON LUNCH BREAK ILSG BOARD MEETING (by invitation) POSTER SESSION xxiv �SESSION III: GEOLOGY AND HYDROGEOLOGY OF ARSENIC IN DOMESTIC AND PUBLIC WATER SUPPLIES Session Chairs: W.F. Cannon (U.S. Geological Survey) M.D. Lemcke (Wisconsin Department of Natural Resources) 1:30 p.m. NORDSTROM, D. Kirk (US. Geological Survey) Overview of Arsenic Occurrences and Processes in Controlling Mobility in Groundwater 2:30 p.m. MUDREY, M.G., Jr., Brown, B.A., Freiberg P.G., and Simo, J.A. Mississippi Valley-Type Mineralization in the Fox River Valley, Eastern Wisconsin 2:45 p.m. GOTKOWITZ, M.B., Schreiber, M.E., and Simo, J.A. Contrasts in the Geologic and Hydrochemical Occurrences of Arsenic contamination of Groundwater in Eastern Wisconsin 3:05 p.m. KANIVETSKY, Roman ilydrogeochemical Modeling of Arsenic in Minnesota Ground Water 3:25 p.m. KOLKER, Allan, Cannon, W.F., Haack, S.K., Westjohn, D.B. and Woodruff, L.G. Hydrogeologic Setting of Elevated Arsenic in Southeastern Michigan 3:45 p.m. COFFEE BREAK AND POSTER SESSION SESSION IV: GENERAL GEOLOGY Session Chair: Suzanne W. Nicholson, US. Geological Survey 4:05 p.m. WOODRUFF, L.G., Attig, J.W., and Cannon, W.F. Geochemistry of Quaternary Deposits in North-central Wisconsin: Geochemical Exploration and Provenance Analysis 4:25 p.m. FAUBLE, Philip, and Lien, Jennifer Some Observations from the Williams Quarry Exposure: Evidence of Debris Flow Deposits in the Parfeys Glen Formation? 4:45 p.m. BOERBOOM, Terrence J. and Jirsa, Mark A. Stratigraphy of the Paleoproterozoic Denham Formation Basalt, Arkose, and Dolomite 6:00 p.m. a Continental Margin Assemblage of ICE BREAKER - MIXER Cash Bar 7:00 p.m. • • • • ANNUAL BANQUET AND AWARD PRESENTATION Announcement of 48th Annual Meeting Location Memorial on Samuel Stephen Goldich 1909 - 2000 2001 Goldich Award Presentation to John Kiasner Banquet Speaker: Thomas Hunt, University of Wisconsin Platteville A Practical Exercise in Metallic Mine Reclamation - Ladysmith, Wisconsin Participants who are not registered for the banquet are welcome to join for the speaker xxv �FRIDAY MAY 11 8:10 a.m. INTRODUCTORYREMARKS M.G. Mudrey, Jr. Chairman Wisconsin Geological and Natural History Survey V: DEVELOPMENTS IN UNDERSTANDING KEWEENA WAN GEOLOGY Session Chair: Dean Rossell, Ken necott Exploration Company SESSION 8:20 a.m. MILLER, James D., Jr. The Duluth Complex: What it Is, What it Ain't, and What We Still Don't Know 8:50 a.m. GREEN, J.C., Davis, D.W., and Schmitz, M.D. Three New Zircon Dates for the Midcontinent Rift, North Shore, Minnesota: More Data, More Questions 9:10 a.m. ROGALA, B., and Fralick, P.W. A Metamorphosed Evaponte Sequence from the Sibley Basin SESSIoN VI: THERMO-TECTONIC HISTORY OF 1800 TO 1200 MA POST-PENOKEAN TO PRE-KEWEENA WAN ROCKS IN THE MIDWEST Session Chairs: D.K. Holm, Kent State University D.A. Schneider, Syracuse University 9:30 a.m. HOLM, D.K., Van Schmus, W.R. and MacNeill, L.C. Age of the Humboldt granite, northern Michigan: Implications for the origin of the Republic metamorphic node 9:50 a.m. VAN SCHMUS, W.R., MacNeill, L.C., Hoim, D.K., and Boerboom, T.J. New U-Pb Ages from Minnesota, Michigan, and Wisconsin: Implications for Late Paleoproterozoic Crustal Stabilization 10:10 a.m. COFFEEBREAK AND POSTER SESSION 10:30 a.m. SCHWEITZER, D., Hoim, D., Van Schmus, W.R. and Boerboom, T. Results of Igneous Thermometry and Barometry on the East-central Minnesota Batholith: Evidence for Post-emplacement Exhumation and Cooling 10:50 a.m. NAYMARK, Alissa, Singer, Brad, and Medaris, L.G., Jr., Recognition of Post-1630 Ma Fluiddriven Metamorphism in Baraboo Interval Quartzites by Means of Laser Probe 40Ar/39Ar Geochronology 11:10 am. DAVIS, Peter B., Williams, Michael L., Bownng, Samuel A. and Ramezani, Jahan Middle Proterozoic Tectonic History of the Central Tusas Mountains, Northern New Mexico, and Comparison with the Baraboo Interval, Southern Lake Superior Region 11:30 a.m. WILLIAMS, M.L., Jercinovic, M.J., and Karlstrom, K.E. Proterozoic Tectonic History of Southwestern North America: Insight from Microprobe Monazite Geochronology 11:50 a.m. HOLM, D., Jercinovic, M.M., and Williams, M. Initial Results of In Situ electron Microprobe (EMP) Age Dating of Monazite from the Southern Lake Superior Region: Confirmation of Widespread Geon 17 Metamorphism xxvi �_____ 12:10 p.m. SCHNEIDER, D.A., Hoim, D.K., and Hamilton, M.A. Directing Timing Constraints of Paleoproterozoic Metamorphism, Southern Lake Superior Region: Results from Shrimp U-Pb Dating of Metamorphic Monazites 12:30 LUNcH BREAK POSTERS removed after Lunch SESSION VII: DEVELOPMENTS IN UNDERSTANDING ARCHEAN GEOLOGYAND ORE DEPOSITS Session Chair: 2:00 p.m. Eric Jerde, Morehead State University HUDAK, George J., Peterson, Dean M., and Morton, Ronald L. New Volume Calculations for the Pyroclastic Eruptions Associated with the Sturgeon Lake Caldera Complex, Northwestern Ontario: Implications for the Scale of Archean Volcanic Processes 2:20 p.m. PETERSON, D.M., Gallup, C., Jirsa, M.A. and Davis. D.W. Correlation of Archean Assemblages Across the U.S.-Canadian Border: Phase I Geochronology 2:40 p.m. JIRSA, Mark A. and Chandler, Val W. Geophysical Answers to Geologic Queries in the Superior Province of Northern Minnesota C., Mason, John K., Schnieders, Bernie R., and Stott, Greg M. A Synopsis of Archean and Proterozoic Platinum Group Element Mineralization in the Thunder Bay District, Ontario 3:00 p.m. SMYK, Mark 3:20 p.m. COFFEEBREAK SESSION VIII: GEOLOGIC SETTINGS OF WEEKEND FIELD TRIPS 3:40 p.m. MUDREY, M.G., Jr., Hunt, T.C., and Czechanski, M.L. Overview of Field Trip 2: 4:00 p.m. Upper Mississippi Valley Zinc-Lead District BROWN, B.A., Luther, F.R., Courter, S.M., Schmitt, J.W., and Lien, 3. Field Trip 3: Economic Geology of the Baraboo and Waterloo Quartzites 5:00 p.m. SINGER, Brad (Department of Geology and Geophysics) Tour of Weeks Hall, University of Wisconsin (Transportation provided) SATURDAY 8:00 a.m. and Weeks End Refreshment Seminar MAY 12 FIELD TRIP 2: Upper Mississippi Valley Zinc-Lead District M.G. Mudrey, Jr. and Thomas C. Hunt Wisconsin Geological and Natural History Survey and University of Wisconsin - Platteville 8:00 a.m. 6:00 p.m. TRIP 3: Industrial Mineral and Aggregate Resources of the Baraboo Interval Quartzites Brown, B.A., Luther, F.R., Courter, S.M., Schmitt, J.W., and Lien, 3. Wisconsin Geological and Natural History Survey, University of Wisconsin - Whitewater, Mathy Construction, Kraemer Company FIELD Return of Field Trips xxvii �POSTER PRESENTATIONS BESKAR, Shawn The Blake Gabbro: A taxitic-tectured gabbro sill south of Thunder Bay, Ontario BIHARI, D.B. and Kissin, S.A. Alteration and Pge-au Mineralization in the North Roby Zone, Lac Des lies Mine, Northwestern Ontario BOERBOOM, Terrence J. Redefined Volcanic and Sedimentary Stratigraphy of the Northern St. Croix Horst in Pine County, Minnesota, and the Application of Arcview to Geologic Mapping BROWN, B.A. and Czechanski, M.L. GIS Applications for Resource Inventory and Land-use Planning in Wisconsin BUCHHOLZ, Thomas W., Faister, Alexander U., and Simmons, Wm. B. Recent Developments in the Mineralogy of the Nine Mile Piuton, Wausau Complex CANNON, W.F. and Woodruff, L.G. Regional Arsenic Anomalies Shown by NURE Stream Sediment and Hydrogeochemical Data in Northern Wisconsin and Michigan CHANDLER, Val W. and Morey, G.B. Paleomagnetic Study of Paleoproterozoic Rocks in the Animikie Group, Northern Minnesota DAHL, D. Structure, Stratigraphy and Punctuated Evolution of Minnesota's Mineral Exploration Archives DANIELS, David L., Nicholson, Suzanne W., Cannon, William F., and Kucks, Robert P. New Aeromagnetic Map of Wisconsin Examined by Regional Context Jerde, Eric A., SAL VATO, DanielJ., Thole, Jeff and Wirth, Karl R. The Early Gabbroic Series of the Midcontinent Rift System: Continued Assessment of Magmatic Origins JOHNSON, Dave Distribution of Arsenic in Wisconsin Groundwater JOHNSON, J.R. and Kissin, S.A. Fluid Inclusion Evidence for a Role for Hydrothermal Activity in the Roby Zone, Lac Des lies Mine, Northwestern Ontario KELLY, Colleen, and Kean, William F. Rock Magnetic Studies of Phyllitic Zones from the Baraboo Syncline, Wisconsin KNOBELOCH, Lynda, Warzecha, Charles. and Nelson, Shelli Health Surveillance in a Community Affected by Arsenic-Contaminated Water LARSON, Phillip C. Potential for Copper Mineralization in the Animikie Group, Minnesota LIVELY, Richard and Morey, G.B. Contributions to the Cultural Geography of the West Mesabi Range, Northern Minnesota xxviii �MILLER, J.D., Jr., Wahi, T.E., Green, J.C.,Chandler, V.W., Severson, M.A., and Peterson, D.E. Digital Geologic Map of Northeastern Minnesota and Associated Databases in GEMS - a Modified Arcview Format MUDREY, M.G., Jr., and Brown, B.A. Structure of the Buried Precambrian Basement in Southwest Wisconsin and Its Influence on Regional Paleozoic Geology and Zinc-Lead Mineralization MUDREY, M.G., Jr., Brown, B.A. and Daniels, Daniels L. Preliminary Analysis of Aeromagnetic Data in Southern Wisconsin: The Role of Precambrian Basement in Paleozoic Evolution NEMITZ, Michael B. and Larson, Phillip C. Mineralogical Variations in Iron-formation in the Thermal Metamorphic Aureole of a Diabase Dike NEWKIRK, Trent T., Hudak, George J., and Hauck, Steven A. Preliminary Lava Flow Morphology Studies at the Five Mile Lake Vms Prospect, Archean Vermilion District, Ne Minnesota: Implications for Volcanic Processes, Volcanic Paleoenvironments, and VMS Exploration NICHOLSON, S.,W., Boerboom, T., Cannon, W.F., Wirth, K., and Isachsen, C.E. A New Look at the 1.1. Ga Chengwatana Volcanics in the St. Croix Horst, Minnesota and Wisconsin ODETTE, Jason D., Hudak, George J., Suszek, Thomas, and Hauck, Steven A. Preliminary Evaluation of Hydrothermal Alteration Mineral Assemblages and Their Relationship to VMS-style Mineralization in the Five Mile Lake Area of the Archean Vermilion Greenstone Belt, Northeastern Minnesota PETERSON, Dean M., Gallup, Christina, Jirsa, Mark A. and Davis. Donald W. Correlation of Archean Assemblages Across the U.S.-Canadian Border: Phase I Geochronology PEYCHAL, C., Kean, W.F., and Schaper, D. Magnetic Survey Near Waterloo Wisconsin PHILLIPS, Erin H., Wirth, Karl R., Veroort, J.D. Gehrels, G.E. Nd and U-Pb Isotope Studies of the Syenitic Aurora Sill, Mesabi Range, Minnesota REID, Daniel D. Freeze/Thaw Testing of Carbonate Aggregate Sources in Wisconsin - a Status Report SANDLAND, Travis 0., Wirth, Karl R., Vervoort, Jeff D., Gehrels, George E., Kennedy, Bryan C. and Harpp, Karen S. Roles of Fractional Crystallization and Assimilation in the Production of Midcontinent Rift Granophyres SMYK, Mark C., Stewart, Jennifer and O'Brien, Mark S. Platinum Group Element Exploration in Northwestern Ontario SNYDER, Stephen L., Ervin, C.Patrick, Geister, Daniel W., and Daniels, David L. A New Gravity Map of Wisconsin SOOFI, M.A. and King, S.D. Post-rift Evolution of the Midcontinent Rift System: Some Numerical Experiments Weissbach, Annette E., HEINEN Elizabeth M., and Lauridsen, Keld B. A Study of Well Construction for Arsenic Contamination in Northeast Wisconsin xxix �Industry and Informational Displays CRONK, William J. Layne Northwest, W229 N5005 DuPlainville Rd, Pewaukee, WI 53072. Phone (262)-246-4646 KIRCHER, Steve Crandon Mine Development, Nicolet Minerals, 7 N. Brown St, 3rd Floor, Rhinelander, WI 54501. Phone (715)365-1450 (Rhinelander office), (715)478-1516 (Crandon office) STEWART, Jennifer Ontario Geological Survey Resident Geologist Program, Northwestern Ontario District, Suite B002, 475 South James Street, Thunder Bay ON, P7E 6E3. Phone (807) 475-1108 SUNDEEN, S. Paul Michigan Department of Environmental Quality, Geological Survey Division, 735 E. Hazel Street, P.O. Box 30256, Lansing, MI 48909. Phone(517) 334-6959. xxx �The Blake Gabbro: A taxitic-textured gabbro sill south of Thunder Bay, Ontario. Shawn Beskar - University of St. Thomas South of Thunder Bay, Ontario, plutonic and hypabyssal rocks associated with the Keweenawan Rift (1109 Ma to 1086 Ma) intrude sedimentary rocks of the Lower Proterozoic (1.9 Ga) Animikie Group. Prior to the discovery of the Blake Gabbro, the igneous terrane south of Thunder Bay was thought to have been comprised of five distinct intrusions (Lightfoot and Lavigne, 1995): (1) Logan Sills; (2) Arrow River Dikes; (3) Pigeon River Dikes; (4) Crystal Lake Gabbro; (5) Pine River - Mount Molly Intrusion. Discovered in 1995, the Blake Gabbro is situated south of Thunder Bay within Blake Township, some 60 km north of the Duluth Complex. The region is characterized by northeast trending diabase-capped ridges and deeply eroded valleys. Positioned beneath a sequence of flat lying Logan Sills, the Blake Gabbro intrudes the argillites of the Rove Formation (Animikie Group). Since 1995, diamond drill cores that intersect the Blake Gabbro have been recovered and logged. From these cores it has been determined that the Blake Gabbro is a northeast trending, sub-horizontal sill of limited plan width but unknown strike length. The maximum thickness intersected by holes drilled thus far is 131 m. The sill thins to less than 20 mat its margins, some 300 m from the center of the body. Samples of the Blake Gabbro have been taken from the diamond drill cores for petrologic study. Initial studies indicate that the Blake Gabbro is a taxitic-textured sulphide-bearing sill. Plagioclase and pyroxene are present in roughly equal quantities. Elongate, cumulus plagioclase grains of variable size are enclosed by optically continuous intercumulus pyroxene. Initial analyses of plagioclase yield compositions ranging from An72 to An83. Minor amounts of olivine and biotite are present. Sulphide minerals consist of pyrrhotite and chalcopyrite. Preliminary whole-rock geochemical data obtained through XRF spectroscopy is presented in Table 1. The significance of the Blake Gabbro is realized upon comparison with the igneous terrane of Noril'sk, Siberia. The region south of Thunder Bay is thought to be equivalent in many respects to the geologic setting of the Noril'sk region and as such, may host large magmatic sulphide deposits (Lightfoot and Lavigne, 1995). The Keweenawan Osler Group Volcanic rocks are similar in composition to the Nadezhdinsky Formation lavas at Noril'sk. Both exhibit large degrees of crustal contamination (as evidenced by their high silica content and LaJSm ratio) and are depleted in nickel and copper. At Noril'sk, chonoliths (subvolcanic tube-like magma channels) containing mineralized picrites and gabbros served as feeders to the overlying sequence of flood basalt. It is thought that the Blake Gabbro may represent such a conduit. Chalcophile elements (nickel, copper and platinum group metals) missing from the associated Osler Group Volcanic sequence may reside within the Blake Gabbro, although the preliminary geochemical data presented seems to suggest otherwise. REFRENCES Lightfoot, P.C. and Lavigne, Jr., M.J. 1995. Nickel, copper, and platinum group element mineralization in Keweenawan intrusive rocks: new targets in the Keweenawan of the Thunder Bay region, northwestern Ontario: Ontario Geological Survey, Open File Report 5928, 32p. 1 �Table 1. Preliminary whole-rock geochemistry Major element data presented as weight per cent Trace element data presented as parts per million BP98.1-1 BP99.1-2 BP99.2-1 BP99.3-2 BP99.3-3 Si02 Ti02 51.42 49.29 48.54 52.00 51.18 3.38 1.43 1.27 2.95 3.48 A1203 13.84 18.52 15.18 13.65 13.97 Fe203 MnO MgO CaO Na20 1(20 P205 17.09 10.91 11.14 16.15 16.54 0.17 0.14 0.14 0.15 0.16 4.44 6.72 10.16 4.62 4.92 6.76 10.85 9.11 6.68 6.99 2.97 2.81 1.58 2.67 2.70 1.35 0.66 0.61 1.38 1.33 0.59 0.25 0.18 0.44 0.48 Total 102.01 101.58 97.91 100.69 101.75 Sc 23.5 25.6 25.2 25.8 26 V 337.5 224 200.9 343.9 396.8 Cr 51.8 157.1 104.8 63.1 48.9 Co 46.1 46.7 58 47.5 45.9 Ni 67 121.1 207 79.2 74.5 Zn Ga Rb Sr 162.5 82.9 90.6 172.9 144.9 25.6 20.9 19.5 23.9 24.1 54.9 23.2 29.3 61.3 60.8 425 306.6 348.8 447.4 501.8 Y 42.4 23.5 20.4 36.2 36 Zr 277.8 101.7 87.3 243.6 233.5 Nb 30.8 9.7 9.5 27.4 28.9 Ba 337.7 167.4 189.3 390.9 442.8 La Ce Pb 32.4 6.6 4.2 32.3 24.8 79.5 26.6 25.6 77.3 68.7 7.5 3.9 3 10.1 6.7 2 �ALTERATION AND PGE-AU MINERALIZATION IN THE NORTH ROBY ZONE, LAC DES ILES MINE, NORTHWESTERN ONTARIO BIHARI, D.B. and KISS1N, S.A., Department of Geology, Lakehead University, Thunder Bay, ON, P7B 5E 1, stephen.kissin(Z)lakeheadu.ca The Lac des Ties Complex appears as a linear zone of mafic plutons that trend east to northeast and extends from Lake Nipigon to Atikokan in northwestern Ontario (Sutcliffe, 1986). The complex is situated in Archean granitoids that consist of gneissic tonalites, medium-grained hornblende diorites and quartz diorites. The Lac des lies Complex occurs in a circular outcrop fashion that is approximately 30 km in diameter and is the largest of a series of mafic to ultramafic intrusions (Sutcliffe, 1986). The Roby Zone was the initial site of mining at the Lac des Iles Mine. The North Roby Zone is its narrow northward extension. The North Roby Zone contains a narrow strip (<50 m) of anomalously high PGE and Au values associated with sparse sulfides called "noseeum ore". Five stripped outcrops approximately 50 x 10 m were studied in the North Roby Zone. Alteration of primary pyroxene to talc and pink coloration of recessively weathered plagioclase is strongly suggestive of hydrothermal alteration. The five stripped outcrops reveal a northeasterly striking, steeply dipping sequence of leucogabbro, varitextured gabbro, pyroxenite and east gabbro. A total of 32 hand samples were collected and studied in thin section. From these 21 were selected for whole-rock and trace element analysis in order to compare chemistry of altered and unaltered samples. Hydrothermal alteration appears to have affected the primary ortho- and clinopyroxenes of the host rocks, progressively converting them to talc. Other petrographic indications are obscure, as regional metamorphism has overprinted the Lac des Iles Complex and its mineralized rocks. The grade of metamorphism is the albite-epidote subfacies of greenschist facies as evidence by incipient breakdown of plagioclase to sericite and clinozoisite, chioritization of pyroxenes and formation of tremolite-actinolite, as well as minor metamorphic albite. Chlorite coronas surround mafic minerals, and develops decussate assemblages of chlorite and tremolite-actinolite. Minor penetrative deformation is evident in undulatory extinction in plagioclase and development of weak schistosity. The development chlorite coronas and general overprinting ofmafic minerals by chlorite and sericitization ofplagioclase are significant in distinguishing hydrothermal alteration from subsequent regional metamorphism. Analysis did not generally reveal striking compositional variations in the host rocks; however, more detailed analysis did show chemical effects of alteration. Chondrite-normalized REE plots revealed that all REEs were depleted relative to unaltered rocks; however, in most altered leucogabbro and varitextured gabbro, minor to insignificant depletion of Eu relative to other REEs produced an apparent positive Eu anomaly in the plots. Other chemical changes, because of their subtle expression and obscurity owing the problem of closure, were examined by use of Pearce Element Ratios. Most notable was Na-depletion due to alteration, which can be distinguished from igneous fractionation effects in plagioclase. Sutcliffe, R.H., 1989. Magma Mixing in Late Archean Tonalitic and Mafic Rocks of the Lac des lies Area, Western Superior Province. Precambrian Research, vol. 44, pp.81-101. 3 �________________ REDEFINED VOLCANIC AND SEDIMENTARY STRATIGRAPHY OF THE NORTHERN ST. CROIX HORST IN PINE COUNTY, MINNESOTA, AND THE APPLICATION OF ARC VIEW TO GEOLOGIC MAPPING BOERBOOM, Terrence J. (Minnesota Geological Survey, boerb001@unm.edu) Pine County, Minnesota, located on the northwestern margin of the St. Croix horst (Fig. 1), contains bedrock that ranges from Archean to Pale ozoic in age; however, most of the county is underlain by rocks of the Midcontinent rift (Fig. 2). The southeastern half of the county is underlain by mafic volcanic rocks ofthe St. Croix horst, late rift-filling sedimentary rocks (Hinckley Sandstone and Fond du Lac Formation) underlie the central part of the county, and the far northwestern corner is made up of Archean and Paleoproterozoic rocks (see Boerboom, this volume). This county was recently remapped by the Minnesota Geological Survey (MGS)', but due to generally poor outcrop, the mapping relied heavily on geophysical and drill hole data. ArcView GIS software proved useful in manipulating and integrating these data, particularly the 4000 water wells contained in the MGS County Well Index database. This presentation is intended to demonstrate the usefulness of Arc View software in map construction, and also to show the results of our mapping efforts in T Pine County. Other Arc files to be demonstrated /1 — Pine include maps of depth to bedrock, bedrock topography, and surficial geology. Craddock (1972) provides a review of the history I — St. — -) Croix horst of investigations in Pine County and environs, but some of the notable early accounts of the bedrock geology in Pine County are by Upham (1888) and Hall (1901); Grout (1910) described the occurrence of copper mineralization in Pine County. The most recent published geologic map to cover Pine County is 1:250,000scale(Moreyandothers, 1981). Ourlatest mapping coincides with other mapping projects in — N / Sedimentary rocks Intrusive rocks Volcanic rocks \ I Figure 1. Location of Pine County relative to the St. Croix horst and the Mid-continent rift system. adjacent Wisconsin (Wirth and others, 1998, Cannon and others, 2001; Nicholson and others, 2001). Geologists on both sides of the border benefited greatly from the recent acquisition of high-resolution aeromagnetic data in Wisconsin by the U.S.G.S., as summarized by Cannon and others (2001). The St. Croix horst, part of the Mesoproterozoic Midcontinent rift system, is comprised of subaerial mafic volcanic rocks that have traditionally been lumped together as the Chengwatana volcanic group. Based on our work and that of the U.S.G.S., the term "Chengwatana" is now restricted only to those volcanic rocks that lie between the Douglas and Pine Faults (Fig. 2). The demarcation of Keweenawan sedimentary vs. volcanic rocks (i.e. the Douglas Fault) is welldefined on the basis of water well information. The Pine Fault (Fig. 2) lies inboard of and parallel to the Douglas Fault, and as summarized by Cannon and others (2001), may have been a bounding fault that controlled the distribution of graben-fill volcanic rocks. Hall (1901) first applied the term "Chengwatana Series" to a series of steeply dipping basalt flows and interfiow conglomerates exposed along the Snake River near Pine City, Minnesota. According to Hall: "Thefloodofl898, which tore away the dam at the foot of Cross Lake and poured down the [Snake] river a vast volume of water, cleaned out in an admirable manner for examination the channel of the stream for several miles." In this stretch of outcrop, Hall recognized 65 steeply dipping lava flows and five interfiow conglomerates. Our remapping of this now less wellexposed sequence identified 37 basalt flows that range from 10 to 300 feet thick, and six interfiow conglomerates that range from 10 to 100 feet thick, although a more careful examination might reveal more flows. The interfiow conglomerates contain abundant round boulders of Keweenawan-type granophyric granite and porphyritic basalt from an unknown source. This sequence, the type locality for the Chengwatana volcanic group, dips about 65 degrees east, and starts within a few hundred feet of the Douglas Fault. Other outcrops of the redefined Chengwatana group that are adjacent to the Douglas Fault dip 40 to 70 degrees east, and those near the Pine Fault dip 10 degrees west. This change in dip is consistent with aeromagnetic patterns that indicate the presence of a southward-plunging syncline that merges 4 �into an unnamed fault (Fig. 2). Hall (190 l)recognized this syncline on the basis of the change in dip direction. Sedimentary rocks similar to the Fond du Lac Formation are present on top of the horst at the south edge of the county. The Minong volcanics (approximately 1094 Ma; Nicholson and others, 2001), part of the northeast-plunging Ashland Syncline, lie to the east of the Chengwatana group, and are interpreted to be younger. The Minong volcanics are distinguished from an unnamed central pile of volcanic rocks to the north by divergent linear aeromagnetic patterns. Aeromagnetic lineaments imply that the rocks in this central panel are folded into a doubly-plunging anticline (Fig. 2). Several aeromagnetically-inferred, reverse-polarized diabase dikes cut all three of the volcanic packages in Pine County. The Hinckley fault (Fig. 2) is proposed as a splay from the Douglas Fault that has displaced the contact between the Hinckley Sandstone and Fond du Lac Formation slightly upward, based on outcrop and geophysical data. North of this fault, the Hinckley Sandstone is typical cliff-forming, uniform and fine-grained quartz arenite, whereas south of the fault the sandstone forms subdued outcrops, is slightly more feldspathic, and contains scattered cobbles of quartzite and minor agate. Locally, tributary streams have cut through Sandstone similar to Fond du Lac Formation Figure 2. Simplified geologic map of Pine County, Minnesota. this feldspathic sandstone and exposed conglomeratic sandstone, typified by trough cross-beds with trough bases lined by small basalt cobbles, which is assigned to the underlying Fond du Lac Formation. Although the major distribution of rock types has not changed significantly as a result of this mapping effort, we have been able to refine the volcanic stratigraphy of the St. Croix horst. Pronounced linear trends on aeromagnetic maps, essentially parallel to the strike of bedding in volcanic rocks, outline the different volcanic basins, and the measured orientations of volcanic flows in outcrops match those aeromagnetic trends. 'This work was done as part of the Pine County Geologic Atlas (Minnesota Geological Survey, County Atlas Series, in prep.), which includes data base, bedrock geology, surficial geology, Quaternary stratigraphy, depth to bedrock and bedrock topography, and mineral resource plates. References: Cannon, W.F., Daniels, D.L., Nicholson, S.W., Phillips, J., Woodruff, L.G., Chandler, V.W., Morey, G.B., Boerboom, T.J., Wirth, K., and Mudrey, M.G., Jr., 2001, New map reveals origin and geology of North American Mid-continent rift: Eos, v. 82, no. 8, p. 97. Craddock, C., 1972, Keweenawan geology of east-central and southeastern Minnesota, in Sims, P.K., and Morey, G.B., eds., Geology of Minnesota—A centennial volume: Minnesota Geological Survey, p. 4 16-424. Grout, F.F., 1910, Keweenawan copper deposits: Economic Geology, v. 5, p. 471-476. Hall, C.W., 1901, Keweenawan area of eastern Minnesota: Bulletin of the Geological Society ofAmerica, v. 12, p. 312342. Morey, G.B., Olson, B.M., and Southwick, D.L., 1981, East-central Minnesota, bedrock geology: Minnesota Geological Survey, scale 1:250,000. S.W., Boerboom, T.J., Cannon, W.F., and Wirth, K., 2001, Reinterpretation of the Chengwatana volcanics in Nicholson, the St. Croix horst, Minnesota and Wisconsin: Geological Society ofAmerica, North-Central Section Abstracts, 35" Annual Meeting. Upham, W., 1888, The geology of Pine County, in Winchell, N.H., and Upham, W., eds., The geology of Minnesota: Minnesota Geological Survey Final Report 1, v. 2, p. 629-645. Wirth, K., Cordua, W.S., Kean, W.F., Middleton, M., and Naiman, Z.J., 1998, Field guide to the geology of the southeastern portion of the Midcontinent rift system, eastern Minnesota and western Wisconsin: Institute on Lake Superior Geology 44" Annual Meeting, Minneapolis, Minn., Proceedings, v. 44, Pt. 2, Field trip guidebook, P. 33-75. 5 �STRATIGRAPHY OF THE PALEOPROTEROZOIC DENHAM FORMATION-A CONTINENTAL MARGIN ASSEMBLAGE OF BASALT, ARKOSE, AND DOLOMITE BOERBOOM, Terrence J., and JIRSA, Mark A. (Minnesota Geological Survey, boerb001@umn.edu andjirsa001@umn.edu) The Paleoproterozoic Denham Formation, as originally defined, consists of metamorphosed quartz-rich sedimentary rocks, dolomite, and mafic volcanic rocks (Morey, 1978). The type locality of the Denham Formation, in northwestern Pine County, Minnesota (see figure 2 in Boerboom, this volume), consists of a series of outcrops in and near an abandoned glacial outwash channel. The Denham Formation forms a pronounced linear, positive aeromagnetic anomaly that can be traced from the exposures for 40 miles to the west, to Mille Lacs Lake (Boerboom and others, 1999). This anomaly follows the northern margin of the Archean McGrath Gneiss (2550±14 Ma, Van Schmus and others, this volume). The anomaly is produced by scattered chert-magnetite clasts within fragmental volcanic rocks. The Denham area was mapped as part of the Pine County Geologic Atlas (see Boerboom, this volume). In addition to the outcrops, 15 exploratory drill cores and cuttings holes were utilized in the map interpretation, as was information from water wells contained in the Minnesota Geological Survey County Well Index. The results will be published on the forthcoming 1:100,000 scale geologic map of Pine County, which will include a 1:12,000 scale inset map of the type locality. The rocks of the Denham Formation have undergone regional, amphibolite-grade metamorphism and at least two periods of deformation. The mafic volcanic rocks are amphibolitic, but contain well-preserved primary features. The granular sedimentary rocks are recrystallized, but retain much of their primary grain size, shape, and composition. In contrast, layers interpreted as pelitic sedimentary rocks are recrystallized to garnet-staurolite-sericite schist. Dolomite is completely recrystallized to marble, with local relict bedding features. The first of two deformation events was synchronous with metamorphism to the garnet zone of the amphibolite facies (Holm, 1986). It produced Si foliation that typically is parallel to bedding, and a locally strong, shallowly plunging, stretching lineation. The second deformation folded Si and bedding along steeply dipping axes, and was concurrent with or followed by peak metamorphism that produced staurolite. In the Denham valley, the stratigraphic sequence dips variably to the north, having local F2 folds with overturned limbs. North of the valley, bedding and SI in graywacke are nearly horizontal, and are deformed into open F2 folds with local crenulation features. North of these graywacke outcrops, the bedding dips to the south, defining a broad, regional-scale, F2 syncline. Despite deformation and metamorphism, the stratigraphy of the Denham Formation forms a coherent package that is shown schematically on Figures 1 and 2. In this discussion, metamorphic rock names, and the prefix "meta" are omitted for clarity. The base of the Denham consists of interbedded siltstone and cross-stratified pebble conglomerate. This is overlain by coarse-grained and locally conglomeratic arkose that apparently pinches out laterally. The arkose is interbedded 3-10 Graphitic argillite with amygdaloidal basalt flows that grade stratigraphically upward (northward) from Dolomite >500 massive, to pillowed, to fragmental. The volcanic rocks are thickest at the eastern limit of outcrop, where at least four flows of nearly 1000 feet total thickness were c Fragmental mafic ol anic rocks 700 recognized and thin westward to two flows of 300 feet total thickness This distribution implies that the eastern exposures are nearest to the vent, which may lie beneath the DOIOiIC ad arkose Fond du Lac Formation (Fig 2) The overlying arkosic and pelitic strata apparently Shale 350 pinch out to the east where the volcanic package thickens, and are not present in drill holes to the north and east of the Denham valley. The northern-most outcrops in the Pillowed basalt valley consist of very pure dolomite, now marble, having ptygmatically folded and 3001000 strongly lineated quartz veins. Drill cores show that the dolomite is at least 500 feet Dolomiticarkose 200 thick, and is overlain by graywacke that is exposed discontinuously to the north for some distance. The contact between dolomite and overlying graywacke is marked by Siltstone 1100 a thin layer of graphitic argillite. Field and petrographic observations imply that clastic detritus in the Denham Formation was derived in large part from a weathering residuum on the subjacent McGth McGrath Gneiss. Near the contact with the Denham Formation, the McGrath grades Gneiss : abruptly from granite gneiss containing quartz, orthoclase, plagioclase, and biotite; to Figure 1. Stratigraphic column of strongly foliated, quartz- and sericite-rich schist that contains orthoclase, but no Denham Formation; thicknesses plagioclase. The arkosic parts of the Denham Formation similarly lack plagioclase, in feet. Ok 6 �Fraacvolc Dolomitic mble —----- — I r' -— t. t_ L - - Lva_3. Explanation Metagraywactse (Palnoproterozotc) Strike and dip of inclined bedding showing younging dtrection Direction and plunge of lineations inctnding Outcrop — elongate metamohic mineeds, fold axes. on McOuath Ofleiss Strike and dip of Fl cleavage Map urea — Fond On Lac Formation _ Conlacl between basalt flows and elongate pillows -r-10 Strike and dip of inclined bedding, youngiug direclion unknown —r_ Strike and dip of overturned bedding. in this example beds top to northeast but dip southwest Geologic contact Figure 2. Simplified geologic map of the Denham Formation and adjacent McGrath Gneiss. and are composed of quartz and orthoclase grains, together with scattered clasts of granitic gneiss. Studies of saprolite developed beneath Cretaceous sedimentary rocks on Precambrian crystalline rocks in southwestern Minnesota may provide an analog (Setterholm and others, 1989). These studies demonstrate that plagioclase is one of the first minerals to alter to kaolinitic clay during the weathering process, and that orthoclase and quartz are the most resistant to weathering. The basal Cretaceous strata locally consists of reworked saprolite, including beds of cross-stratified sandstone and nearly pure kaolinitic shale, Exposures of basal Cretaceous sedimentary rocks locally contain detrital orthoclase and quartz derived by slight reworking of grus-textured, weathered granite. We infer that the same process occurred in the Paleoproterozoic by erosion and reworking of weathered McGrath Gneiss into beds of arkose and kaolinitic shale. These were subsequently metamorphosed to produce recrystallized arkose and staurolite-garnet- sericite schist. Weathering of orthoclase may have liberated potassium for the inferred conversion of kaolinite to sericite during metamorphism. The Denham Formation is interpreted to represent a rift-margin assemblage deposited during the Paleoproterozoic, genetically similar to, and perhaps temporally equivalent with, the Chocolay Group in Michigan. In this setting, the McGrath Gneiss was part of the continental margin that was weathered and eroded to provide detritus to an evolving rift basin undergoing active, shallow water volcanism. Interbedded arkose and dolomite higher in the stratigraphic section represent foundering of the shelf and deepening water, possibly by subsidence of localized grabens. The lack of arkose in the upper, dolomite-dominated part of the sequence indicates that deposition of coarse detritus was restricted to the shallow, nearshore environment adjacent to the McGrath. The sedimentological gradation of dolomite to graywacke stratigraphically upward indicates further deepening water and associated turbidite deposition. The deformation of the Denham Formation is inferred to be the product of basin closure during the Penokean orogeny. References: Boerboom, T.J., Severson, M.J., and Southwick, DL., 1999, Bedrock geology of the Mule Lacs 30 x 60-minute quadrangle, eastcentral Minnesota: Minnesota Geological Survey Miscellaneous Map Series M-l00, scale 1:100,000. Holm, D.K., 1986, A structural investigation and tectonic interpretation of the Penokean Orogeny: east-central Minnesota: Unpubi. M.S. thesis, University of Minnesota, Duluth, 114 p. Morey, GB., 1978, Lower and Middle Precambrian stratigraphic nomenclature for east-central Minnesota: Minnesota Geological Survey Report of Investigations 21,52 p. Setterhoim, DR., Morey, GB., Boerboom, T.J., and Lamons, R.C, 1989, Minnesota kaolin clay deposits—A subsurface study in selected areas of southwestern and east-central Minnesota: Minnesota Geological Survey Information Circular 27, 99 p. 7 �GIS Applications for Resource Inventory and Land-use Planning in Wisconsin B. A. Brown and M. L. Czechanski Wisconsin Geological and Natural History Survey Madison, Wi Wisconsin has recently enacted comprehensive "smart growth"land-use planning legislation that specifically requires counties and local units of government to consider metallic and nonmetallic mineral resources as they develop and adopt a comprehensive plan by 2010. Wisconsin's nonmetallic mine reclamation rules take effect in 2001. These rules contain provisions to protect undeveloped aggregate deposits from zoning changes, and designate end uses for reclaimed sites, both of which link reclamation into the planning process. Implementation of mandatory reclamation and planning for future supplies both require an inventory of active production sites. In addition, planning requires analysis of geologic data to identify location, extent, and quality of undeveloped resources. Wisconsin Geological and Natural History Survey (WGNHS) is working in cooperation with the U.S. Geological Survey and several state agencies to compile a spatial database of active operations and historic mineral production sites. This database will ultimately link existing state and federal databases containing a variety of information on location, lithology, formation, engineering testing, permit status etc., through a common identification number. WGNIHS is also working with county and local governments to inventory active sites and to assemble and assess the quality of geologic data available for comprehensive planning. Computerized geographic information system (GIS) technology provides powerful new tools for inventory and analysis of mineral resource information. Digital coverages showing the locations of mines, pits, and quarries, and spatial databases documenting the character and extent of deposits can now be easily incorporated with bedrock and surficial geology, soils maps, water resource maps and an ever increasing variety of other environmental, cultural, and political coverages to feed directly into the land-use planning process. We will present an interactive demonstration of statewide and county geologic and mineral resource coverages recently produced by WGNHS and discuss some of the land-use planning methodologies and applications currently under development. 8 �Field Trip 3:Economic Geology of the Baraboo and Waterloo Quartzites Bruce A. Brown (1), Frank R. Luther (2), Susan M. Courter (3), James W. Schmitt (4), and Jennifer Lien (5) Field trip 3 will examine the aggregate and industrial mineral resources of the Proterozoic Baraboo and Waterloo Quartzites of southern Wisconsin. In the Waterloo area twenty miles east of Madison, we will visit a large quarry that produces construction aggregate, breakwater stone, and railroad ballast. We will travel from waterloo to the Baraboo area, where we will visit five operations that produce a variety of aggregate products. The Proterozoic quartzites of southern Wisconsin have long been recognized for their unique hardness and durability, refractory properties, and resistence to weathering. Quarries have operated in both areas for more than a century, producing a variety of industrial mineral products and aggregates. Today the major uses for this hard and durable rock are railroad ballast, riprap and breakwater stone, and crushed stone base material. A variety of specialty aggregates ranging from seal coat chips to leachate collection and filter bed material are produced as well. Stop 1 will be the Michels Materials Waterloo quarry. This operation was opened in 1988 as a source of large stones with high resistance to freeze-thaw loss, for use in constructing breakwaters and erosion control structures on the great lakes. Bedding in the Waterloo Quartzite is up to 2 meters thick and joints are widely spaced, allowing blocks up to 10 tons or larger to be quarried. Crushed material was first produced only as a means of disposing of undersize waste rock. Michels continues to produce breakwater stone that exceeds all Corps of Engineers specifications, but much of the current output is crushed for ballast and construction aggregate. We will not have time to visit the historical quarries located to the south of the Michels Quarry which were operated in the early 1900s for refractory blocks, but the geology of the Michels quarry and the old quarry area is described in previous guidebooks by Luther(1992, 1997). From Stop 1 we will travel northwest across the glaciated landscape of Dane and Colombia counties to the Baraboo Range. This drive will provide a look at a classic drumlin landscape. Stop 2 will be the Williams quarry, operated by the Kraemer Company. This quarry is located on the north limb of the Baraboo syncline and utilizes the Parfreys Glen Formation, a time-transgressive, near-shore deposit that accumulated around the Baraboo bluffs during Cambro-Ordovician submergence. This quarry produces aggregate that is essentially a quartzite gravel. As the quarry goes deeper into the hillside, more solid quartzite is being quarried. The sedimentary structures in the coarse basal conglomerates and overlying sandstones are spectacular. Stop 3 will briefly examine the 1760 Ma. Rhyolite that underlies the quartzite, 9 — �exposed in a road cut on STH 33. Stop 4 will be Milestone Materials Jesse Pit a combination gravel pit/quartzite quarry on top of the south range. Lunch will be in Devils Lake State Park, near the site of a former refractory and abrasive quarry. After lunch we will visit Milestone's Fox Ridge pit and asphalt plant where a variety of quartzite aggregate products are produced, sold, and made into asphalt paving materials. We will next visit the Martin-Marietta Rock Springs Quarry, a historic operation now a major producer of ballast. We will finish at the Kraemer Co, LaRue Quarry on the south range near the site of the historic Sauk and Illinois iron mines. LaRue Quarry contains many examples of sedimentary and tectonic structures as well as examples of quartzite weathering. The trip will return to the Sheraton by 6:00 PM. Luther, F.R., (1992 ), The Waterloo Quartzite at the old Portland Quarry: in The 56th Annual TriState Geology Field conference Guidebook to the Geological setting of whitewater, Wisconsin and surrounding Area, Jack Travis, ed. P51-61. Luther, F.R. (1997), The Precambrian Waterloo Quartzite, Dodge and Jefferson Counties, Wisconsin—Petrology, Structure, and Industrial Use: in Mudrey, M.G., Jr., ed. Guide to Field Trips in Wisconsin and Adjacent areas of Minnesota., 31st Meeting Northcentral Section, Geol. Soc. Am., Madison, WI, p.31-35. 1) Wisconsin Geological Survey, Madison, WI 2 )UW-Whitewater, Whitewater, Wi 3) Michels Materials, Inc., Brownsville, WI 4) D.L.Gasser Construction, Baraboo, WI 5) The Kraemer Company, Plain, WI 10 �RECENT DEVELOPMENTS IN THE MINERALOGY OF THE NINE MILE PLUTON, WAUSAU COMPLEX BUCHHOLZ, Thomas W., 1140 12th Street North, Wisconsin Rapids, Wisconsin 54494; FALSTER, Alexander. U., and SIMMONS, Wm. B., Department of Geology and Geophysics, University of New Orleans, New Orleans, Louisiana 70148 The mid-Proterozoic Wausau Complex is composed of four intrusive centers; from north to south the Stettin, Wausau, Rib Mountain and Nine Mile plutons (Meyers eta!, 1984). The Stettrn intrusion is the oldest and most ailcalic, and the three other plutons are progressively younger and more siicic. The youngest and most silicic intrusion, the Nine Mile Pluton, is an epizonal anorogenic and heterogeneous granitic intrusion, with locally abundant pegmatites, aplites and miarolitic zones. Miarolitic cavities in the pegmatites as well as miaroles within some phases of the granite attest to shallow levels of emplacement of the pluton. At the surface the granite is altered to a friable disaggregated material called "grus" that is extensively quarried for use as road gravel. The Nine Mile pluton's pegmatites and aplites contain a wealth of mineral species (Faister, 1981, 1987, Hanson et a!., 1998. Buchholz eta!., 1999, 2000), which show heterogeneous distribution for many species across the pluton. Titanium oxide species, such as anatase, brookite, and rutile are abundant in pegmatites of the northern part of the pluton and are far less conspicuous in the central and southern portions. Anatase is by far the most abundant polymorph in the Nine Mile pluton. Niobium and tantalum mineralization is sparse in the northern part of the pluton but becomes more abundant in the central and southern parts. As in most other anorogenic pegmatites, Nb> Ta in Nb-Ta oxides such as ferrocolumbite, uranopyrochlore, liandratite/petschekite, and ilmenorutile. However, in some small-scale, restricted environments late-stage Ta-enrichment is manifest as tapiolite, manganotantalite, strueverite and microlite. In Ta-rich areas there is also a dramatic increase in the abundance of fluorite (Buchholz et al., 1999, 2000). In these areas fluorite becomes a significant mineral phase in some of the pegmatites and even in the adjacent granite. Beryllium mineralization is dominated by phenakite and bertrandite. Rare beiyl, bavenite, and euclase tend to be more common in the northern segment of the pluton. Lithium mineralization is absent but elevated contents of Li are found in micas (lithian biotite and zinnwaldite) in the central and northern parts of the pluton, typically associated with more fractionated mineral species of the Nb-Ta oxides. LREE-mineralizalion in the Wausau complex is dominated by phosphates of the monazite group, rhabdophane, and by carbonates of the bastnaesite group. HREE-minerals are essentially restricted to xenotime-group minerals. Both LREE and HREE minerals are found throughout the pluton. Unlike the REEminerals in the South Platte district in Colorado (Simmons Ct a!., 1987), REE-minerals in the Nine Mile pluton occur as small crystals and grains throughout the pegmatites (Hanson et a!., 1998), whereas in the South Platte pegmatites, they form large masses in the core margin and in the replacement units. Zirconium mineralization is restricted to zircon, which occurs as an accessory mineral throughout the complex, but more HI-enriched examples are restricted to the high-F environments. Tin is exceedingly rare but it has been found as cassiterite in the central and western portions of the pluton. Some Nb-Ta-oxide minerals from this area contain elevated Sn-content, as well. Manganese mineralization tends to increase from north to south throughout the pluton. The mineralogy of the Nine Mile pluton exhibits some unusual geochemical trends which are not commonly seen in other anorogenic intrusive systems (which are typical NYF-type environments, i.e. Nb, Y, and F-enriched): The strong Ta-, HI- and minor Li-, and Sn-enrichment, if only in localized environments, are far more characteristic of LCT-type pegmatites (Li, Cs, and Ta-enriched). REFERENCES: Buchholz, T. W., Falster, A. U. & Simmons, Wm. B. 1999. Ta, Nb, U, Y, and REF Minerals of the Koss Quariy, Marathon County, Wisconsin: The 26th Rochester Mineralogical Symposium, Abstracts of Contributed Papers. p.6. Buchholz, T. W., Falster, A. U. & Simmons, Wm. B. 2000. Additional Mineralogy of the Koss Quarry, Miarathon County, Wisconsin: The 27" itochester Mineralogical Symposium, Abstracts of Contributed Papers. P.S. 11 �Falster, A. U. 1981. Minerals of the Wausau Pluton: The Mineralogical Record, 12, P. 93-97. Faister, A. U. 1987. Minerals of the Pegmatitic Bodies in the Wausau Pluton, Marathon Co., Wisconsin: Rocks and Minerals, 62, p. 188-193. Faister, A. U., Simmons, Wm. B., Webber, K. L., & Buchholz, T.W. (in press). Peginatites and Pegmatite Minerals of the Wausau Complex, Marathon C., Wisconsin: Special volume published by the Societa Italiana di Scienze Naturali Hanson, S.L., Faister, A.U., Simmons, W.B., Webber, K.L., Buchholz, T. 1998. Rare-Earth-Element (REE) Mineralization of Pegmatites in the Wausau Complex, Marathon County, Wisconsin: The 25th Rochester Mineralogical Symposium, Abstracts of Contributed Papers. p. 12. Myers, P.E., Sood, M.H., Berlin, L.A. & Faister, A.U. 1984. The Wausau Syenite Complex, Central Wisconsin: Thirtieth Annual Inst. On Lake Superior Geology, Field Trip Guidebook 3. Simmons, W. B., M. T. Lee, and R. H. Brewster 1987. Geochemistry and evolution of the South Platte granitepegmatite system, Jefferson Co., Colorado. Geochimica et Cosmochimica Ada, 51, 455-471. 12 �CAMBRO-ORDOVICIAN STRATIGRAPHY OF SOUTHERN WISCONSIN: SEQUENCE STRATIGRAPHY RULES Byers, C.W., Dept. of Geology and Geophysics, University of Wisconsin, Madison, WI 53706 cwbyers(i).geology.wisc .edu During the past decade, the series of sandstone and carbonate formations that range from Late Cambrian through Late Ordovician have been reinterpreted n terms of the tenets of sequence stratigraphy. Older interpretations relied heavily on the facies concept; while some facies changes are still accepted, others have been superceded by the recognition of subtle unconformities, both at formation contacts and within formations. The new approach breaks the stratigraphic column into numerous unconformity-bounded units, indicating many short-term sea level fluctuations. These cycles are shorter by more than an order of magnitude than the major cratonic sequences originally defined by Sloss. Rarely do they local sequences show the full range of features expected in a complete cycle: subaerial weathering, lowstand sediments, marine transgressive surface, zone of maximum flooding, offlapping deposits. More typically, the sequences are asymmetric and truncated, with their thicknesses dominated by only one phase of the transgressive-regressive cycle. For example, the Cambrian Jordan Sandstone consists of two shaling-upward marine packages (offlaps) separated by a surface of transgression; lowstand and transgressive deposits are lacking. In contrast, the Ordovician St. Peter Sandstone is composed mostly of eolian lowstand and transgressive marine strata, with a thin cap of Glenwood Shale representing the zone of maximum flooding. Offlapping strata are thin or absent. Because southern Wisconsin lies on the flank of a cratonic dome, minor unconformities might be expected to grade into comformable sections downdip into the surrounding basins but reappear on other cratonic highs, if the cycles are eustatic in origin. 13 �A preliminary interpretation of new aeromagnetic and gravity data in Wisconsin W. F. Cannon, David L. Daniels, Stephen L. Snyder, Suzanne W. Nicholson, USGS, Reston, VA This geologic sketch map showing Precambrian basement terranes of Wisconsin is an early interpretation of newly acquired and compiled gravity and aeromagnetic data. Geophysical data are supplemented by bedrock mapping in the north and by limited drill hole information and erosional windows through Paleozoic cover in the south. The map presents a new picture of parts of the Precambrian basement in the southern and western parts of the state where it is largely concealed by a thin cover of Paleozoic strata. The map allows inferences on the mineral resources of shallowly buried basement rocks. NOKEAN FOLD AND THu rfI'?* • Most of the basement of Wisconsin is composed of rocks formed or modified during the Penokean orogeny, roughly 1850 m.y. ago. Isotopic evidence indicates that Penokean crust extends throughout the southern part of the state where younger granite, rhyolite, 14 �and quartzite lie unconformably on it. All were folded and metamorphosed in the foreland of the Mazatzal orogen sometime after 1760 Ma. Archean crust can be confidently traced as far south as the Trempealeau fault, but there is no geologic or isotopic evidence for it south of that structure. The southern Penokean Province appears to be entirely juvenile crust formed during the Penokean orogeny and composes the continental basement for the slightly younger Mazatzal orogeny. Large anorogenic granite plutons were intruded at about 1450 Ma and mafic plutons of unknown age also are widespread. Finally, dikes of diabase, probably related to the Midcontinent rift, cut all other Precambrian units. Diabase dikes Midcontinent Rift- sandstone in flanking basins. I. I Midcontinent Rift- basalt flows and conglomerate in central horst (1100 Ma). Anorogenic granite plutons and related rhyolite. Roughly 1 450 m.y. old. Mafic plutons of unknown age. Identified by circular to ovoid corresponding magnetic and gravity anomalies. Quartzite, lesser argillite and schist, minor iron-formation. Unconformable on 1 760 Ma rhyolite and granite. Strongly folded and variably metamorphosed. Granite plutons (1 760 Ma). Post -orogenic plutons with respect to Penokean orogeny. Rhyolite and epizonal granite (1760 Ma). Contains undifferentiated areas of younger quartzite. Strongly folded in Mazatzal orogeny. ROCKS OF PENOKEAN OROGEN Fold and thrust belt- Early Proterozoic metasedimentary and metavolcanic rocks and Archean basement gneisses. 1' . VV v I V V• Y Pembine-Wausau terrane- Early Proterozoic metavolcanic rocks, syntectonic granite. Archean basement lacking or discontinuous. Marshfield terrane- Archean gneiss and infolded Early Proterozoic metavolcanic and granitic rocks. Mostly granitic gneisses based on low gravity values. Ia—I V V V V V K V V *VXXXX V V V 1.' Marshfield terrane- Archean gneiss and infolded Early Proterozoic metavolcanic and granitic rocks. Mostly mafic gneiss based on high gravity values. Southern Penokean terrane- poorly known unit with high gravity and magnetic anomalies. Probably mostly mafic metavolcanic rocks. Contains undifferentiated areas of quartzite and 1 760 Ma rhyolite and granite. Southern Penokean terrane- poorly known unit with low gravity and magnetic anomalies. Probably mostly felsic rocks. Contains undifferentiated areas of quartzite and 1 760 Ma rhyolite and granite. Northern limit of Paleozoic strata. 15 �REGIONAL ARSENIC ANOMALIES SHOWN BY NURE STREAM SEDIMENT AND HYDROGEOCHEMICAL DATA IN NORTHERN WISCONSIN AND MICHIGAN W. F. Cannon, USGS, Reston, VA L. G. Woodruff, USGS, Mounds View, MN A regional arsenic anomaly in northeastern Wisconsin and the upper peninsula of Michigan is identified in the NURE (National Uranium Resource Evaluation) surveys of stream sediments and ground water. The anomalous region is about 250 miles long in north-south direction and as much as 75 miles wide. Examination of the anomaly with regard to bedrock and glacial geologic features suggests that it is a composite anomaly caused by two different bedrock sources of arsenic and variations in glacial dispersal of arsenic-rich bedrock. The two sources differ in their expression. One, the Michigamme anomaly is expressed mostly in stream sediments and to a lesser degree in well water. The other, the Fox River Valley anomaly is expressed strongly in well water, but has almost no stream sediment signature. Figure 1. Composite arsenic anomaly map of northern Wisconsin and Michigan. Base is map of glacial lobes. The shaded semi-transparent surface shows a combined anomaly from both NURE stream sediment and well water data. The surface shows the more anomalous of the two data sets relative to the regional mean values of 2 ppm As for stream sediments and 0.65 ppb As for well water. Only areas with arsenic above regional mean values are shown in the 3-D surface. The surface is defined by about 3200 stream sediment analyses and 3500 well water analyses. Black unit is arsenic-bearing Michigamme Formation and heavy line is the outcrop trace of arsenic-bearing Ordovician sandstone. 16 �Figure 2. A. The Fox River Valley anomaly shown by well water. Anomaly lies mostly west of arsenic-rich sandstone. B. The Michigamme anomaly shown by stream sediments. Anomaly location is controlled by location of Michigamme Formation and glacial features. Base map as in Figure 1. Arrows show direction of ice movement. The Fox River Valley Anomaly The Fox River Valley arsenic anomaly is best shown by NURE well water data and is only weakly expressed in stream sediment data (see Figure 2A). Arsenic values range up to a maximum of 60 ppb in well water. Interestingly, a great majority of the wells that show high arsenic in the NURE data lie west of the outcrop trace of the gently eastdipping arsenic-bearing sandstone and also west of the area where more recent data has identified an arsenic problem in wells. Bedrock in the western area of the anomaly is mostly Cambrian sandstone and Precambrian crystalline rocks, mostly granite. No arsenic source is known in these rock units. The anomaly is mostly within the area once occupied by the Green Bay glacial lobe and lies in a down-ice direction from the Ordovician sandstone. Glacial transport of arsenic-rich bedrock into the anomalous area appears to be a significant factor, suggesting that the immediate source of arsenic in well water west of the outcrop of the arsenic-rich sandstone is the unconsolidated glacial deposits. The Michigamme Anomaly The Michigamme anomaly is most strongly expressed in stream sediment date, but also occurs in well water data (Figure 2). It is geographically restricted by a combination of bedrock and glacial geology. The northern extent of the anomaly in stream sediments coincides very closely with the northern extent of the outcrop belt of black slate within the Precambrian Michigamme Formation. The eastern extent of the anomaly in northern Michigan is defined by the western margin of the Green Bay glacial lobe, which did not cross arsenic-rich bedrock. To the south, there appears to be glacial dispersal of arsenicrich bedrock in both the Green Bay lobe and Langlade sublobe in northern Wisconsin where high arsenic values in stream sediments and well water extend more than 50 km south of the outcrop belt of the Michigamme black slates. 17 �PALEOMAGNETIC STUDY OF PALEOPROTEROZOIC ROCKS IN THE ANIMIKIE GROUP, NORTHERN MINNESOTA CHANDLER, Va! W. and MOREY, G.B. (Minnesota Geological Survey, chand004@umii.edu and moreyOol @urnn.edu) A pilot study was conducted to investigate paleomagnetism in the Pokegama Quartzite and Biwabik Iron Formation of the Paleoproterozoic Animikie Group. The quartzite was sampled at six sites along the northern margin of the central and western parts of the Mesabi Iron Range, with three to six oriented samples collected per site. The iron-formation was sampled at four sites at a small outlier located to the north of the range near Pike Mountain; one to five oriented samples were collected per site. All samples are fresh and unoxidized. Core and cube specimens were cut from the field samples, and selected specimens were subjected to stepwise alternating-field and thermal demagnetization. Observed directions of magnetization have considerable scatter, and some specimens, especially those of magnetite-rich ironformation, were highly unstable during stepwise demagnetization. Nonetheless, several samples of each unit yielded stable, well-clustered magnetizations which appear to be associated with the early history of the rocks. With regard to thermal demagnetization, high blocking temperatures (greater than 600°C) are consistent with hematite as the primary carrier of stable magnetizations in the iron-formation. Hematite is an original or very early diagenetic phase in the iron-formation, whereas magnetite is a diagenetic phase that may have formed much later in the paragenetic scheme. Unstable or nulled magnetizations above thermal levels of 550°C in Pokegama specimens imply that magnetic minerals other than hematite may be present. Correcting for a bedding dip average of 100 to the south, the stable magnetizations of the Biwabik and Pokegama formations are directed at declinations/inclinations averaging 242°/65° and 289°/85°, respectively. The Pokegama (alpha=13.3°) and Biwabik (alpha=21.9°) directions cannot be discriminated from each other, or from a direction derived previously for the stratigraphically equivalent Gunflint Iron Formation in Canada (Symons, 1966) within 95 percent confidence. Our Animikie directions also overlap with those of a secondary imprint recognized to the north in the pre-Animikie Kenora-Kabetogama dikes by Halls (1986), who attributed it to a regional episode of hydrous alteration that tended to be more pronounced southwards, towards the Animikie basin. A working model that is consistent with present observations proposes that the diagenesis and subsequent magnetization of the Animikie rocks were accompanied by a regional groundwater flow system that may have been concentrated near the base of the Animikie sequence. The results of this study indicate that further paleomagnetic work on the Animikie Group rocks will be valuable, although the selection of sites that will produce useful results may pose some problems. Remaining tasks include determining if the Pokegama and Biwabik directions are truly indiscriminate from each other as well as from other Paleoproterozoic directions reported in the area. Ultimately, tightly constrained paleopole(s) can be combined with high-resolution radiometric dating to significantly improve the Paleoproterozoic apparent polar wander path for North America. References Cited: Halls, H. C., 1986, Paleomagnetism, structure, and longitudinal correlation of middle Precambrian dykes from northwestern Ontario and Minnesota: Canadian Journal of Earth Sciences, v. 23, p. 142-157. Symons, D. T. A., 1966, A paleomagnetic study of the Gunflint, Mesabi, and Cuyuna Iron Ranges in the Lake Superior Region: Economic Geology, v.61, p. 1336-1361. 18 �AN OVERVIEW OF AEROMGANETIC MAPPING IN MINNESOTA CHANDLER, Val W., Minnesota Geological Survey,2642 University Avenue, St. Paul, MN 55114, chand004@tc.umn.edu AN OVERVIEW OF AEROMAGNETIC MAPPING IN WISCONSIN MUDREY, M.G. Jr., Wisconsin Geological and Natural History Survey, 3817 Mineral Point Rd., Madison, WI 53705, mgmudreyfacstaff.wisc.edu MINNESOTA Magnetic methods have long been used by geologists in Minnesota to help investigate poorly exposed Precambrian bedrock. In fact, the Cuyuna iron range, which was discovered in 1904 by dip needle, was the first mining district in the United States that was discovered wholly by a geophysical method. The first large-scale magnetic project in Minnesota occurred after WWII, when George M. Schwartz, then-director of the Minnesota Geological Survey (MGS), made a cooperative arrangement with the U.S. Geological Survey (USGS) for surveying in Minnesota using the newly developed aeromagnetic method. Although the priority of this early work was locating new iron ore resources, the usefulness of the new method in mapping Precambrian geology was quickly realized, and by 1950 over 40,000 square miles of northern Minnesota had been covered by this method. During the 1960s while P.K. Sims was director of the MGS, the USGS aeromagnetic coverage over the entire state was completed, and an integrated program of geologic mapping using aeromagnetic and gravity data began. These efforts culminated in 1970 with the publication of a state geologic map, the first since 1932. By the mid-1970s, the potential of the USGS aeromagnetic data had been realized, and newer, higher resolution data were needed. Through the efforts of Matt Walton, thendirector of the MGS, and Robert Hansen, then-executive director of the Legislative Commission on Minnesota Resources (LCMR), a new state-wide program of high-resolution aeromagnetic surveying began in 1979. Funding came primarily from the LCMR, with additional contributions of data from the USGS, the U.S. Steel Corporation and the Geological Survey of Canada. The data obtained earlier was flown at one mile line spacing with 1000 feet terrain clearance, and much of the new flying was conducted at ¼ mile spacing with 500 feet terrain clearance. In addition, the new data were digital and could be readily subjected to a variety of computer-based processing and enhancement schemes to assist in geologic interpretation and mapping. State-wide coverage was completed in 1991, and the new aeromagnetic data, used in conjunction with an improved gravity database, have dramatically improved Precambrian geologic mapping in Minnesota. Virtually all Precambrian bedrock in the state has been re-mapped at a scale of 1:1,000,000 or larger. The new geologic maps, as well as the geophysical data used to help make them, will be useful to a variety of scientific and economic investigations for many years to come. WISCONSIN T.C. Chamberlin's geologic staff began mapping in northern Wisconsin in 1 870s as a continuation of mapping in southern Wisconsin. It was recognized that conventional geological techniques did not provide sufficient information in the glacially covered, 19 �geologically complex areas of the Gogebic Range. C.E. Wright of the Chamberlin's Wisconsin Geological Survey sent a sketch to instrument maker Gurley in Troy, New York, of a "dipping needle" based on a design he had seen from Sweden. The determination of the inclination and declination of the magnetic field had been well established by R.D. Irving and C.R. Van Hise of the U.S. Geological Survey by the late nineteenth century. Beginning in 1913, W.O. Hotchkiss and colleagues of the Wisconsin Geological and Natural History Survey (WGNHS) mapped large areas of northern Wisconsin by conventional and magnetic methods to assess mineral value for taxation. In 1935, C.K. Leith, R.J. Lund and A. Leith of the U.S. Geological Survey were able to produce a reasonable regional geologic map of the Lake Superior Precambrian that was based on conventional geology, mineral mapping, and extensive magnetic surveys. Using fluxgate magnetometers developed during World War II, G.P. Wollard and his students undertook regional magnetic surveying in Wisconsin in the early 1 960s. Of note is the regional aeromagnetic map of Wisconsin in 1964 by R.W. Patenaude and colleagues, who mapped Wisconsin on a 1 0-km line spacing at 1 000-m elevation. Prior to 1972, more detailed surveys were limited to small areas in support of geologic programs in southwestern and central Wisconsin. In 1972, the WGNHS received a small grant from industry to initiate surveys in central Wisconsin. With this seed and grants from Upper Great Lakes Regional Commission, the WGNHS and University of WisconsinOshkosh professor John Karl conducted a survey of a large area in northern Wisconsin. That survey was completed in 1977 with a "fill in the holes" grant from U.S. Geological Survey. These and subsequent public surveys were flown on lines spaced at 805 m, and oriented in a north-south direction. The altitude was draped to topography at 305 m above ground level. Interest in massive sulfide exploration in the 1 980s resulted in many private surveys, some of which were released to the public through the WGNHS. More recently (1997-1999) the U.S. Geological Survey completed surveying the remaining land areas of Wisconsin. The release of these data on CD-ROM is stimulating a reevaluation of the regional geologic fabric of the upper Midwest. Remaining activities include an adjustment of the surveys to a common base and preliminary analysis of the newly acquired data by W.F. Cannon and others. The statewide coverage, used in conjunction with an improved gravity database, will dramatically improve subsurface geologic mapping. The new geologic maps as well as the geophysical data used to help make them will be useful to a variety of scientific and economic investigations for many years to come. 20 �STRUCTURE, STRATIGRAPHY AND PUNCTUATED EVOLUTION OF MINNESOTA'S MINERAL EXPLORATION ARCHIVES David Dahi, Minnesota Department of Natural Resources, Hibbing, Mn 55746 A project to catalog the content of Minnesota DNR's mineral exploration archives for remote digital access has provided a substantial "opportunity" to better understand the structure and relationships among some 15,000 unpublished mineral exploration documents, and the 100+ exploration programs they came from. Together, the documents provide a mosaic of evolving mineral exploration methods and exploration models, and reflect changing exploration focus over time. In the past, archive users have often had a sense of déjà vu when researching Minnesota's archives. Indeed, during the process of cataloguing the content, some 25% of the archive documents were found to be duplicates of existing information. In some cases, more than a dozen copies of a document existed in the files. The lineage of that duplication, and the reasonable geographic motif that led to that duplication offer several lessons about the geographic nature of mineral exploration programs and storage of mineral exploration data for future geologic research. Within government activities, remote access to the mineral exploration archive provides a needed input for more responsive local and regional planning, and offers a historical background for mineral resource management decisions. In conjunction with online comparison to other data sets such as DOQ's, DRG's, DEM's, Public Land Survey, aeromagnetic data, published geologic maps, land use, landsat, soils and other baseline information, the exploration data archives can now be used to more quickly glean unique insights about previous exploration efforts and to develop insights for new geologic and geophysical exploration and research. 21 �NEW AEROMAGNETIC MAP OF WISCONSIN EXAMINED IN A REGIONAL CONTEXT DANIELS, David L., daveusgs.gov, NICHOLSON, Suzanne W., swnichusgs.gov, CANNON, William F., wcannonusgs.gov, U.S. Geological Survey, MS 954 National Center, Reston, VA 20192, and KUCKS, Robert P., rkucksusgs.gov, U.S. Geological Survey, MS964 DFC Box 25046, Denver, CO 80225 The new aeromagnetic map of Wisconsin portrayed in color at a scale of 1:500,000, is the result of digitally blending grids of 22 surveys flown between 1948 and 1999. The composite grid features 1) a resolution of 250m, and 2) a common elevation; all surveys were either flown at, or digitally continued to, an elevation of 1000 ft (305m) above mean terrain, prior to assembling into a state grid. The U.S. Geological Survey acquired all recent data in the state (1988 to 1999) amounting to about 77,000 line-miles. The digital flightline data for three of these surveys have recently been released on CD-ROMs. These data were added to earlier USGS surveys and 4 surveys acquired by Wisconsin Geological and Natural History Survey. Flight lines are V2-mile apart or less for 95% of the state, giving the aeromagnetic map nearly uniform specifications, and making the map an excellent tool for USGS mineral resource investigations. The Wisconsin grid has also been digitally blended with data from surrounding areas (Chandler, 1991; Hildenbrand and Kucks 1984, 1991) to form a preliminary regional aeromagnetic map of the North-Central US that reflects the structure of Precambrian basement rocks (see gray-scale index map). The regional map will be shown in color at a scale of 1:2,000,000. The aeromagnetic data of the region include some surveys of widely spaced flight lines (3 to 6 miles), particularly in northwestern and central Illinois, Lake Michigan, and the lower-peninsula of Michigan. These are areas where higher resolution data would be helpful to better define basement geology. Aeromagnetic features observed within Wisconsin can be traced into surrounding states. These features include: 1) high-amplitude linear anomalies that record the upturned edges of Keweenawan basaltic lava flows of the Midcontinent Rift System, and the smooth magnetic field of the flanking sedimentary basins; 2) abundant, narrow, linear magnetic anomalies probably generated by diabase dikes show a variety of trends across the region. (These anomalies are prominent only in areas of high-resolution surveys); 3) a strong ENE directed aeromagnetic fabric in areas of exposed Precambrian rocks in northern Wisconsin, Minnesota, Michigan's northern Peninsula, and Canada that records highly-deformed basement rocks, and 4) an aeromagnetic fabric with no preferred trend and abundant circular to arcuate anomalies, that characterizes much of the area to the south. This undirected fabric may reflect large areas of anorogenic igneous rocks, although part of the undirected fabric could also be due to greater depth to basement and lower survey resolutions. In SE Wisconsin a belt of high overall magnetic intensity lies within this area of undirected fabric, and is characterized by a series of high-amplitude, oval to circular anomalies. The belt continues SW through Illinois and Iowa into Missouri and eastward across Lake Michigan (A-A' on figure). The circular to oval anomalies suggest plutonic complexes in the basement. References Chandler, V. W., 1991, Shaded-relief aeromagnetic anomaly maps of Minnesota: Minnesota Geological Survey, one sheet, Scale 1:1,000,000 Hildenbrand, T.G., and Kucks, R.P., 1984, Residual total intensity magnetic map of Ohio: U.S. Geological Survey Geophysical Investigations Map GP-096 1, 1 sheet, scale 1:500,000. Hildenbrand, T.G., and Kucks, R.P., 1991, Total intensity magnetic anomaly map of Missouri: U.S. Geological Survey Open-File Report 9 1-0573, 1 sheet, scale 1:500,000. 22 �Aeromagnetic Anomaly Map of Wisconsin and North-Central US 0 0 _950 9O0 100 0 100 kilometres NAD27/LCC9O 23 200 -85° �MIDDLE PROTEROZOIC TECTONIIC HISTORY OF THE CENTRAL TUSAS MOUNTAINS, NORTHERN NEW MEXICO, AND COMPARISON WiTH THE BARABOO INTERVAL, SOUTHERN LAKE SUPERIOR REGION DAVIS, Peter B 1, WILLIAMS, Michael L. 1, BOWRING, Samuel A 2, and RAMEZANI, Jahan 2. (1) Department of Geosciences, Univ of Massachusetts, Amherst, MA 01003, davis@geo.umass.edu, (2) Earth, Atmospheric & Planetary Sciences, Massachusetts Institute of Technology The similarity between mid-Proterozoic quartzite units of the Baraboo interval, and the Ortega quartzite of northern New Mexico, has been recognized for decades. (Dott 1993) These similarities are based on sedimentary characteristics and the general timing of deposition, deformation and metamorphism of these supermature quartzite units. Plate tectonic reconstruction models also show a trend in the bedrock's mantle separation age extending from southwest to northeast that conned these units (Hoffman 1988)(Figure#1). However, drawing a meaningful correlation between them across a 1000-mile separation is extremely difficult because of the sparse nature of intervening exposure, and the uncertainty in the absolute timing of events. Recent work in the Tusas Mountains of northern New Mexico has further constrained the tectonic history that affected the Ortega quartzite among other units, and therefore might shed light on this tentative correlation. Recent field mapping, geochronology, and petrologic analysis in the Tusas Mountains has focused on a northwest-southeast striking enigmatic discontinuity that is suspected to be a late mesoproterozoic ductile fault. This fault juxtaposes higher-grade complexly deformed supracrustal immature to mature metasediments (which includes the Ortega Quartzite) and felsic metavolcarncs found to the south against lower grade immature metasediments and mafic to felsic metavolcanics and intrusives found to the north (Figure#2). Ductile deformational features present in these rocks can be grouped into three generations. A strong bedding parallel Si foliation is ubiquitous, however there are few Fl folds. D2 features include reclined tight to isoclinal folds with a strong SW dipping S2 foliation, and SW plunging stretching lineations (L2), sub-parallel to fold axes. Kinematic indicators suggest transport on this lineation was to the northeast. These structures are more pronounced south of the discontinuity. D3 produced east-west trending open folds, and either a newer crenulation clevage, or reactivated S2. In some localities D3 has reoriented F2 folds into F3 folds. Metamorphic conditions can also be grouped into three generations. Ml conditions reached lower greenschist facies. M2 reached greenschist facies conditions. M3 is discontinuous across the NW-SE discontinuity from upper greenschist to the north, to sub-amphibolite to the south (550°C -4.5kb). Timing of all three of these deformational events were traditionally correlated with the 1.67-1.65Ga. Mazatzal orogeny. New geochronologic data of 1.67-1.69 Ga. for the wealdy deformed Tusas granite suggests that the strong fabric in the Moppin group host rock was produced before 1.69Ga., possibly during the Yavapai Orogeny. A refined age for the Tres Piedras Granite, and a syn-Di dike, is now 1.67-1.69 Ga. is interpreted to suggest that the first two fabrics in the granite, directly correlative to regional fabrics, are indeed the result of 1.68-1.65Ga. Mazatzal tectonism. These data also further constrain the age of deposition of the Hondo group, which includes the 24 �______ Ortega Quartzite, to older than 1.69 -Ga., but younger than the underlying 1.70-1.7lGa. Burned Mountain rhyolite. D3, which increases in strength from north to south across the Tusas Mountains, was recently constrained in the southern Tusas Mountains to 1.45-1.4OGa. (Bishop et al 1996). Island-Arc Related Mafic to Felsic Volcanic sediments and Intrusives Moppin Group > 1.775 The earliest tectonic event represents an Tusas Granite early phase of thrusting with syn-orogenic - 1.69 Ga plutonism, and is primarly preserved to the SuDracrustal northern portion of the Tusas Mountains. The Sediments Tres second event, thought to be the result of additional and Volcanics thrusting with folding, is preserved throughout the Granite —1.68 Ga Tusas Mountain range. The third event significantly overprinted much of the range both Vadito Group tectonically and thermally. Its effects are thought to -1 .7OGa. be the result of the burial of the range to the midcrust leaving the region to eventually cool isobarically, erasing much of the evidence for earlier events. The effects of this overprint however 5 Miles strong in the southern half of the tusas, diminish at the discontinuity, and are poorly preserved to the Figure#2 - Tectonic Map of north. the Tusas Mountains, NM This refined model for the central Tusas Mountains of northern New Mexico provides a better framework with which to compare the Baraboo Interval in future regional models. Both regions contain a generalized supracrustal sequence of rhyolite followed by laminated to massive supermature quartzites. Constraint on the timing of deposition of both quartzite units is between approximately 1.71 — 1.65 Ga. Deformation is constrained between deposition and respective thermal event around 1.45 Ga. (Medaris 1996). Some have suggested that folding of the Baraboo Interval occured around approximately 1.63 Ga., during which whole-rock Rb-Sr systems were reset over the region. The 1.45 Ga. thermal and tectonic event that affected both the southern Lake Superior Region and the Tusas Mountains is thought to be related to the anorogenic magmatic event (Anderson / 1992). Proterozoic rocks of northern New Mexico and the Baraboo Interval of the southern Lake Superior region are windows into important tectonic processes. These widely separated windows reveal different structural levels and foreland proximities along a general orogenic trend across the Laurentian margin as it grew through mid-Proterozoic time. Hoffman, Paul F. United plates of America, the birth of a craton; early Proterozoic assembly and growth of Laurentia, Annual Review of Earth and Planetary Sciences. 16; P 543-603. 1988. Bishop, Jennifer L. Williams, Michael L. Lanzirotti Antonio. A doubly-looping P-T-t-D history for Proterozoic rocks of northern New Mexico and implications for the tectonothermal behavior of the mid-crust. Abstracts with Programs, Geological Society of America. 28; 7, P 495. 1996. Medaris, Gordon L. The Baraboo Quartzite, Wisconsin; Proterozoic deposition and deformation in the Lake Superior region. Abstracts with Programs, Geological Society of America. 28; 7, P376. 1996. Dott, Robert H. The Proterozoic red quartzite enigma in the north-central United States; resolved by plate collision?. In: Early Proterozoic geology of the Great Lakes region. Memoir Geological Society of America. 160; Pages 129-141. 1983. 25 �SOME OBSERVATIONS FROM THE WILLIAMS QUARRY EXPOSURE: EVIDENCE OF DEBRIS FLOW DEPOSITS IN THE PARFEYS GLEN FORMATION? PHILIP FAUBLE, Wisconsin Department of Natural Resources, P.O. Box 7921, Madison, WI 53707-7921; faub1p@dnr.ta.wi.us JENNIFER LIEN, Kraemer Company, P.O. Box 235, Plain, WI 53577; jen1@mhtc.net A quarry located on the north side of the North Range of the Baraboo Syncline, originally developed to mine sand and gravel from a quartzite conglomerate of the Parfeys Glen Formation, has recently expanded into insitu Baraboo Quartzite. This provides a unique opportunity to observe the Precambrian/Cambrian unconformity and its relationship to the overlying conglomeratic deposits. The undifferentiated quartzite conglomerate and conglomeratic sandstones, found in a broad band on both sides of the North and South Ranges of the Baraboo Hills, were first described in detail by Dalziel and Doll (1970). They inferred that these deposits were the result of wave action eroding and transporting quartzite from the ancestral Baraboo Hills during the transgression of the late Cambrian seas. These deposits were later named the Parfeys Glen Formation by Clayton and Attig (1990), who split the formation into three componants: a talus conglomerate directly adjacent to the quartzite, a conglomeratic sandstone and a sandstone unit that may or may not contain quartzite pebbles. Although the causes of the lithologic differences between individual units within the Parfreys Glen Formation were unclear, they considered it likely that the talus conglomerate was considerably older than the adjacent sandstone. At present, the quarry exposure is approximately 15 meters high, 200 meters long, north facing, and generally oriented east to west, parallel to the axis of the North Range. There are three distinct lithologies exposed along the quarry wall consisting of the following, from the base of the exposure to the top: in-situ quartzite, a very coarse quartzite conglomerate, and a finer-grained conglomeritic sandstone that gradually transitions to a quartz sandstone. In-situ Quartzite: An irregular, rounded outcrop of Precambrian Baraboo Formation quartzite is exposed at the base of the quarry wall. The quartzite is slightly overturned and dips steeply to the north. The main quarry face roughly parallels the strike of the quartzite beds. The largest exposure of quartzite is located just west of the center of the quarry wall and seems to represent a subdued topographic high prior to deposition of the upper units. The most striking feature of the in-situ quartzite is the presence of a smooth, rounded, gently undulating erosional surface along the unconformity between the quartzite and the overlying conglomerate. This smooth surface is present on both vertical and near horizontal exposures. While smooth, this surface is not varnished and does not possess striations, gouges or percussion marks. There are no obvious potholes developed in this surface, but shallow features that resemble small chutes are common. Quartzite Conglomerate: Overlying the smooth erosional unconformity developed on the quartzite is a quartzite conglomerate of varying thickness. This deposit is thinnest on the top of the quartzite knob, thickest within two low areas that flank the western and eastern sides of the knob, and gradually thins to the east. An exposure along the western wall of the quarry indicates that the coarse conglomerate gently dips northward. The conglomerate is composed of large rounded boulders of quartzite suspended in an unsorted, massive matrix of sand, rounded pebbles and cobbles. The conglomerate is poorly cemented and seems to lack any materials smaller than fme sand. All lithic fragments larger than sand are composed of quartzite or quartzite breccia likely derived from the nearby outcrops of Baraboo quartzite. Depending on quarry development, exposed quartzite boulders can range in size from 1 to over 3 meters in diameter along their longest visible axis. The largest boulders appear to be concentrated along the quartzite unconformity and the upper margins of the deposit. As first noted by Dalziel and Dott (1970), boulders larger than 2 meters in diameter tend to be angular or posses smooth rounded features on only one or two faces. Boulders smaller than about 2 meters are almost always completely rounded. There does not appear to be any clear fabric or preferred orientation to the larger clasts within the deposit. Con glomeratic Sandstone: Above and to the north of the quartzite conglomerate is a conglomeratic sandstone that thickens dramatically from less than 3 meters directly above the quartzite knob to over 10 meters at the northern edge of the quarry. It is composed of horizontally bedded strata consisting of alternating layers of sand and pebble conglomerate. This deposit is likely marine in origin, with abundant glauconite, sometimes occurring in thin, discrete beds, and abundant Scolithus burrows in the sand layers. The sandstone is visibly finer grained and much better cemented than the quartzite conglomerate directly below it. In contrast to the large boulders found in the conglomerate, an informal, random sampling of 50 of 26 �the largest pebbles visible in the sandstone exposed along the eastern wall of the quarry indicated a long axis diameter no greater than 20 cm. On the eastern wall of the quarry, the horizontally bedded conglomeratic sandstone can be seen to neatly onlap the north-dipping conglomerate. Above the conglomerate/sandstone unconformity, sandstone drapes the larger boulders projecting above the surface of the conglomerate deposit. Along the southern wall of the quarry, the conglomeratic sandstone extends from above the quartzite conglomerate to within about 3 meters of the top of the exposure where it abruptly transitions into a well cemented quartz aremte. This transition does not appear to be an unconformable surface, but likely reflects the drowning of the pebble source as the transgressing Cambrian seas covered the crest of the North Range. Conclusions: The exposure at the Williams Quarry clearly preserves and records three distinct events that occurred on the North Range of the ancestral Baraboo Hills sometime from the late Precambrian to the late Cambrian. First, topographically prominent exposures of the Baraboo quartzite were eroded into a series of smoothly rounded features. Second, conditions changed and a deposit of unsorted quartzite debris (conglomerate) covered the erosional surface, filling in swales and blanketing hillslopes. Lastly, a marine deposit of sand and locally derived pebbles covered the conglomerate. The exact processes and conditions that produced the smooth weathering/erosional surface on the insitu quartzite are unknown. However, the nature of the unsorted quartzite conglomerate indicates that it is likely the result of subaerial mass movements of material eroded from the crest of the North Range. We suggest that these movements took place in the form of large debris flows that generally followed drainages developed in the ancestral Baraboo Hills. Similar coarse conglomeritic deposits adjacent to Precambrian erosional surfaces have been noted in other regions. The lowest facies of the Upper Cambrian Lamotte Sandstone in southeast Missouri contain locally-derived rhyolite boulder conglomerates that have been interpreted as small alluvial fans formed, in part, by debris flows adjacent to the incised Precambrian bedrock of the ancestral St. Francois Mountains (Houseknecht, 1978). The wide grain size distribution of the conglomerate, ranging from fine sands to boulders several meters in diameter, the larger clasts suspended within in an unsorted mass, and the lack of clear grading or internal structures, closely matches the description of debris flow deposits in Coussot (1996). Debris flow deposits result from the rapid transport and mass emplacement of a highly viscous slurry of water and debris. Evidence that the quartzite debris within the conglomerate was transported and not merely weathered in place can be seen at the unconformable boundary between the in-situ quartzite and the conglomerate, just east of the bedrock knob. The in-situ quartzite at this location contains an extensive quartzite breccia, very similar to the Rock Springs (Abelman's Gorge) breccia (Dalziel and Dott, 1970). Directly above the smooth, truncated surface of the eroded breccia lie large boulders and cobbles that contain no evidence of breccia. Conversely, large grains of breccia-bearing material can be seen in the conglomerate mass above other areas that lack insitu breccia. Many other questions concerning this conglomerate deposit remain unanswered. The source area and the processes that produced the rounded boulders, cobbles and sand that make up the conglomerate remain enigmatic. Thick deposits of Paleozoic and glacial sediments obscure the most likely quartzite source areas near the crest of the North Range, south of the quarry. If the top of the conglomeratic sandstone represents the drowning of the uppermost quartzite outcrop, then the source area for the conglomerate may be no more than a few meters higher in elevation than the top of the quartzite knob exposed in the quarry wall. This doesn't preclude the formation of a debris flow because, once a flow is initiated, it may continue to move over slopes as low as a few degrees. Debris flows are also very poor rounding agents, so it is likely that the quartzite clasts in the deposit were already rounded smooth prior to transport. Features visible in a few of the conglomerate boulders suggest that at least some of the rounding occurred in situ, possibly in response to intense chemical weathering. REFERENCES CITED Clayton, L. and Attig, J., 1990, Geology of Sauk County, Wisconsin, Wisconsin Geological and Natural History Survey Information Circular No. 67, 68p. Coussot, P. and Meunier, M., 1996, Recognition, classification and mechanical description of debris flows, Earth Science Reviews, 40, 209-2TJp. Dalziel, I.W. and Dott, R.H., 1970, Geology of the Baraboo District, Wisconsin, Wisconsin Geological and Natural History Survey Information Circular No. 14, l64p. Houseknecht, D. and Etheridge, F., 1978, Depositional history of the Lamotte Sandstone of southeast Missouri, Journal of Sedimentary Petrology, v.48, 5'75-586p. 27 �Contrasts in the Geologic and Hydrochemical Occurrences of Arsenic Contamination of Groundwater in Eastern Wisconsin Gotkowitz, M.B., Wisconsin Geological and Natural History Survey, 3817 Mineral Point Road, Madison, WI 53705 mbgotkow(facstaffvisc .edu Schreiber, M.E., Department of Geological Sciences, Virginia Tech, Derring Hall, Blacksburg, VA 24061 mschreib@vt.edu Simo, J.A., Department of Geology and Geophysics, University of Wisconsin-Madison, 1215 W. Dayton St, Madison, WI 53706 simo@geology.wisc.edu Clusters of arsenic-impacted wells are found in two areas of eastern Wisconsin: the Fox River valley (east-central Wisconsin) and the Lake Geneva (southeastern Wisconsin) areas. In the Fox River valley area, arsenic concentrations up to 12,000 ppb have been measured in groundwater from a CambrianOrdovician sandstone aquifer. An arsenic-rich, sulfide-bearing, secondary cement horizon (SCH) is commonly present at the top of the Ordovician St. Peter Formation. Within the SCH, arsenic occurs in pyrite and marcasite and in iron oxyhydroxides, but not as a separate arsenopyrite phase. Whole rock concentrations of arsenic within the SCH range from about 15 to 675 ppm. Core samples show that arsenic-bearing minerals are also present in the St. Peter below the SCH. Several pieces of evidence support the hypothesis that oxidation of sulfides is the cause of high (>100 ppb) concentrations of arsenic in well water, including 1) the presence of arsenic-bearing sulfides in the aquifer, 2) water-chemistry data that show a positive correlation between arsenic, iron, and sulfate and negative correlation between arsenic and pH; and 3) nearly identical sulfur isotopic signatures in pyrite and dissolved sulfate. There is a strong correlation between high arsenic concentrations and the occurrence of intersecting elevations of the SCH and water levels within wells. This relationship provides the basis for our conclusion that atmospheric oxygen, introduced to the SCH through well boreholes, provides an oxidant to the system. However, the cause of more commonly encountered, moderate (less than 100 ppb) arsenic concentrations found in wells in the Fox River valley is not well understood. The variability of the thickness of the SCH and the associated mass of arsenic within the sulfides, as well as the local availability of an oxidant to fuel the oxidation of the SCH, may contribute to the spatial variability in arsenic concentrations in well water. The available water quality data are not sufficient to determine if other geochemical mechanisms, such as desorption or reductive dissolution of arsenic-bearing iron oxyhydroxides, control the moderate arsenic concentrations measured in well water. Our preliminary work in the Lake Geneva area indicates that geologic and hydrogeologic conditions leading to a cluster of arsenic-impacted wells in this part of the state are not similar to those in the Fox River valley. Arsenic has been detected in wells open to the Quaternary deposits, Silurian dolomite, and the Cambrian-Ordovician sandstone. Arsenic concentrations in rock samples from these aquifers range from 1.4 to 18 ppm; aqueous concentrations in well water range up to 80 ppb. Water chemistry in arsenic-contaminated wells is not consistent with sulfide oxidation, and sulfide mineralization has not been observed in rock samples collected from the area. These results indicate that other geochemical mechanisms of arsenic release, such as the reduction of arsenic-bearing iron-oxides, may also affect Wisconsin groundwater supplies. 28 �THREE NEW ZIRCON DATES FOR THE MIDCONTINENT RIFT, NORTH SHORE, MINNESOTA: MORE DATA, MORE QUESTIONS GREEN,J. C., Geological Sciences, U. of MN Duluth, Duluth, MN 55812; DAVIS, D. W., Royal Ontario Museum, 100 Queen's Park, Toronto, ON M5S 2C6; and SCHMITZ, M. D., Earth and Planetary Sciences, MIT, 77 Mass. Ave., Cambridge, MA 02139 U/Pb zircon dates have been obtained for three significant localities on the North Shore, with some intriguing results. Skeletal zircons from the residual monzodiorite at the top of the Duluth Complex Layered Series in Duluth give an age of 1098.5 +7-1.3 Ma (DWD). This agrees with the 1099.3 +1- 0.3 Ma age determined by Paces and Miller (1993) from a segregation within the upper part of the Layered Series. The skeletal crystal habit assures that the new date represents the magma crystallization age, not inherited crystals. A rhyolite flow exposed below the quarry in the southeast flank of Canton Peak near Tofte gives an age of 1092.6 +7- 2.0 Ma (DWD). This is the youngest date yet found on the North Shore. This local volcanic sequence is apparently isolated by faults from the rest of the North Shore Volcanic Group, including its uppermost sequence, the Schroeder-Lutsen basalts (SLB), and it is clearly younger than the 1096.6 +7- 1.9 Ma Palisade thyolite (Davis and Green, 1997) which unconformably underlies the SLB. Since it has been suested (Miller et al., 1995) that the SLB is an outlier or fringe of the Portage Lake Volcanics (dated at 1096-1094 Ma, Davis and Paces, 1990), this new date implies either that the SLB is actually considerably younger that the PLy, or that the Canton Quarry sequence is an isolated remnant of heretofore unrecognized late volcanic activity on the Minnesota flank of the MRS. Furthermore, the dated quarry sequence is intruded by the anorthosite-xenolith-bearing Carlton Peak diabase, making that still younger and not coeval with dated units of the Beaver Bay Complex (—1096 Ma, Paces and Miller, 1993). Finally, a granite xenolith in the Terrace Point basalt flow southwest of Grand Marais (Green, 2000) is dated at 1096.7 +7- 1.4 Ma (MDS). Since this medium-grained, upper mesozone-looking biotite granite must have crystallized slowly at many kilometers' depth before being broken off and carried to the surface in the basalt magma, this implies that the Terrace Point flow (basal flow of the SLB) is significantly younger than the granite. A coarse-grained segregation vein within the Schroeder basalts was collected and processed, but no zircons or baddelyite were found, leaving the SLB still undated. Davis, D.W. and Green,J.C., 1997, Geochronology of the North American Midcontinent rift in western Lake Superior and implications for its geodynamic evolution: Can. Jour. Earth Sci., v. 34, p. 476-488 Davis, D.W. and Paces,J.B., 1990, Time resolution of geologic events on the Keweenaw Peninsula and implications for development of the Midcontinent Rift system: Earth and Planet. Sci. Lett., v. 97, p. 54-64 Green, J .C., 2000, Mystery faults of the Cascade River, North Shore, or, What is this granite doing here? (abs.): Proceedings Vol. 46, Part 1: Abstracts and Programs, Forty-Sixth Ann. Institute on Lake Superior Geology, Thunder Bay, ON, p. 14 Miller,J.D.,Jr., Chandler, V.W., Green,J.C. and Witthun, K., 1995, The Finland Tectonomagmatic Discontinuity - a growth fault marking the western margin of the Portage Lake volcanic basin of the Midcontinent Rift System: Basement Tectonics 10, R.W. Ojakangas, A.B. Dickas, andJ.C. Green, Eds, Kiuwer Acad. Publ, p. 35-40 Paces,J.B. and Miller,J.D.,Jr., 1993, Precise U-Pb ages of Duluth Complex and related mafic intrusions, northeastern Minnesota: Geochnonological insights to physical, petrogenetic, paleomagnetic, and tectonomagmatic processes associated with the 1.1 Ga Midcontinent Rift System: Jour. Geophys. Res., v. 98, No. B8, p. 13,997-14,013. 29 �INITIAL RESULTS OF IN SITU ELECTRON MICROPROBE (EMP) AGE DATING OF MONAZITE FROM THE SOUTHERN LAKE SUPERIOR REGION: CONFIRMATION OF WIDESPREAD GEON 17 METAMORPHISM IIOLM, D., dhohnkentedu, Dept of Geology, Kent State University, 44242; JERCINOVIC, MJ., and WILLIAMS, M., both at Dept of Geosciences, University of Massachusetts, Amherst MA 01002. Introduction. Like most orogens the pattern and degree of Proterozoic metamorphism preserved across the 1870-1830 Ma Penokean orogemc belt is highly variable. Widespread 1630 Ma metamorphism of much of the Penokean arc terrane in Wisconsin is well documented (see Table 4 of Peterman et aL, 1985, CMP; Romano Ct al., 2000, PreC. Res.) and intrusion of the 1470 Ma Wolf River batholith certainly produced thermal overprinting in central and southern Wisconsin (Hohn et aL, 1998, GSAA; Naymark et al., 2001, GSAA). Until recently, intermediate pressure and higher temperature metamorphism both north and west of the arc terrane (northernmost Wisconsin, northern Michigan and east-central Minnesota) has been attributed to the geon 18 Penokean orogeny (see overview by Geiger and Guidotti, 1989, Geoscience Wise.). Three separate studies published in the late 1990's however (Schneider Ct al., 19%, CJES; Marshak et al., 1997, Geology; Hohu et al, 1998, AJS) proposed the presence of a widespread geon 17 amphibolite facies overprinting metamorphism. In order to better establish the timing of intermediate grade metamorphism in the southern Lake Superior region we have started a microprobe monazite geochronology study of selected metamorphic samples from east-central Minnesota and northern Wisconsin. EMP dating of monazite is currently emerging as a rapid and accurate means of geochronology, and is most easily applied to the Precambrian where the Pb concentration often allows greater analytical precision (Williams et al., 1999, Geology). Results from East-Central Minnesota. We dated monazite from a staurolite-garnet schist outcrop (sample MN-29) of the metamorphosed Little Falls Formation collected on the Mississippi River (Blanchard Dam). Thermobarometric, thermochronologic, and textural analysis of this and other metamorphosed samples led Hoim et al. (1998) to suggest two episodes of aniphibolite facies metamorphism (a geon 18 Penokean Ml and a younger geon 17 M2 associated with emplacement of abundant post-tectonic plutons). Eight EMP spot analyses on three separate monazite grains yielded U-Th-P ages ranging from 1755 Ma down to 1667 Ma (mean age of 1719±21 Ma). The oldest ages are concordant with abundant Ar/Ar mica and hornblende ages obtained throughout the region (Holm and Lux, 19%, Geology; Holin et al., 1998). Results from northern Wisconsin. We have obtained preliminaiy data from two drill core samples of garnet-biotite-sillimanite schist located near Park Falls, Wisconsin. These samples occur within the recently identified fault-bounded, sillimanite-bearing panel just north of the Niagara Fault zone (Park Falls subterrane of Cannon et al., 1998, ILSG). Sample PF-2-311 yielded a mean age of 1710 ± 43 Ma from 3 spots analyzed on 3 separate monazite grains. Sample BL-2-252 (located nearby the first sample) revealed a distinctly chemically zoned grain which produced distinct core and rim ages of 1805 Ma and 1695 Ma, respectively. Finally, we sampled the well known kyanite bearing outcrop located near the town of Powell. This sample is located within the higher pressure fault-bounded panel identified as the Powell subterrane (Cannon et at., 1998). Ten EMP spot analyses on three separate grains yielded U-Th-Pb ages ranging from 1780 Ma to 1747 Ma(meanageofl765±7Ma). Implications and Conclusions. These data, although preliminary, appear to support other independent evidence for a widespread, post-Penokean, geon 17 intermediate grade metamorphic event in the southern Lake Superior region. In Minnesota, geon 17 metamorphism appears concentrated within the internal zone of the orogen where abundant post-tectonic pistons exist To the north in the medial zone earlier geon 18 metamorphic ages are preserved in garnet grade rocks (Schneider et aL, 2001, ILSG). In northern Wisconsin the age of metamorphism in stmctural panels preserving contrasting metamorphic conditions (sillimarnte versus kyanite) appears to be dominantly geon 17 although a hint of earlier Penokean metamorphism is apparently preserved (see also Schneider et at., 2001, for Penokean metamorphic ages preserved north of the Niagara Fault zone in northern Michigan). These metamorphic age constraints suggest that the fault-bounded subterranes may have been juxtaposed after the Penokean orogeny during a period of widespread metamorphism followed by rapid unrooflng (as suggested by geon 17 cooling ages). We conclude that microprobe monazite geochronology holds promise for unraveling the timing of multiple metamorphic and tectonic events in the Lake Superior region as it has for other portions of the southern maigin of Laurentia (Williams et at, 2001, ILSG). 30 �AGE OF THE HUMBOLDT GRANITE, NORThERN MICHIGAN: IMPLICATIONS FOR THE ORIGIN OF THE REPUBLIC METAMORPHIC NODE. HOLM, D., dholni(ã)Jentedu, Dept of Geology, Kent State University, 44242; VAN SCLIMUS, W.R.. and MacNEILL, LC., both at Dept of Geology, Univ. of Kansas, Lawrence, KS, 55045. The alkali-feldspar granite near Humboldt lies on the northeastern edge of a large negative gravity anomaly that is roughly coincident with the Republic metamorphic node. Hornblende, muscovite, and biotite Ar/Ar ages obtained from country rock across the node are 1720-1670 Ma (Schneider et al., 1996). A whole-rock Rb/Sr minimum age of 1733±25 Ma on the granite was reported by Schulz et a!. (1988). The concordance of the whole-rock age with the thermochronologic data led Schneider Ct a!. (1996) to infer that post-tectonic plutonism caused the metamorphic nodal pattern. In order to test this hypothesis we obtained both U-Pb and Ar/Ar mineral age data on the Humboldt granite. U-Pb zircon results. Six single-grain analyses of somewhat tuibid grains separated from a sample of the Humboldt granite (AGR-1, collected by Holin) yielded a linear array on a conventional U-Pb concordia diagram. All six analyses yield an upper intercept age of 1806±21 Ma, although one analysis is clearly off the line. Elimination of this analysis yields an age of 1805 ±7 Ma with a lower intercept of 181 ±64 Ma. One analysis is nearly concordant and has a 201Pb/206Pb age of 1802±6 Ma. Thus it is clear that the ciystallization age is significantly older than the Ar retention age or the Rb/Sr age, which is a common situation in the Lake Superior region. Ar/Ar mica results. We dated three separate mica fractions obtained from a coarse phase of the granite. In order to test for possible intraciystalline age gradients we furnace step-heated the rim and core portion of a coarse muscovite grain. Both analyses yielded essentially concordant plateau dates of 1712±6 Ma (core) and 1703±6 Ma (rim). Step-heating of biotite did not produce a reliable plateau age. Incremental ages increased monotonically with the three highest temperature fractions giving ages between 1670 and 1700 Ma (amounting to 45% of the gas released). These Ar/Ar results are comparable to mica Ar/Ar ages from older bedrock of the Republic region and are concordant within error with the whole-rock Rb/Sr age of the Humboldt granite. The crystallization age of the granite indicates that it could not have provided the heat source needed to form the Republic metamorphic node at ca. 1720 Ma. We cannot rule out the possibility of a younger geon 17 intrusive body existing in the Republic subsurface, although thus far geon 17 plutons have been documented predominantly south of the Niagara fault zone (the sole exception being the 1781 Ma Parlc Falls granite, Van Schmus et a!., 2001). A combination of anomalously high basement heat production rates (Attob, 2000) together with basement remobilization (i.e., Marshak et al., 1997) might better explain geon 17 low P/high T metamorphism in the Republic region of northern Michigan. Attob, K, 2000, Contrasting Metamorphic Record of Heat Production Anomalies in the Penokean Orogen of Northern Michigan: Journal of Geology, v. 108, p. 353-36 1. Marshak, S., Tinkham, D., Allcmim, F., Bruekner, H., and Bornhorst, T., 1997, Dome-and-keel provinces formed during Paleoproterozoic orogenic collapse — core complexes, diapirs, or neither?: Examples from the Quadrilatero Ferrifero and the Penokean orogen: Geology, v. 25, p. 415-418. Schneider, D., Holin, D., and Lux, D., 1996, On the origin of Early Proterozoic gneiss domes and metamorphic nodes, northern Michigan: Canadian Journal of Earth Sciences, v. 33, p. 1053-1063. Schulz, K.J., Sims, P.K., and Peterman, Z.E., 1988, A post-tectonic rare-metal-rich granite in the Southern 34th Ann. Inst. on L. Superior Geology, Marquette, Michigan, Complex, Upper Peninsula, Michigan: p. 95-96. Van Schmus, W.R, MacNeill, L.C., Holm, D.K, and Boerboom, T.J., 2001, New U-Pb ages from Minnesota, Michigan, and Wisconsin: Implications for Late Paleoproterozoic Crustal Stabilization: 47th Ann. Inst. on L. Superior Geology, Madison, Wisconsin, May (this volume). 31 I �206PbI 0.20 0.22 0.24 0.26 0.28 0.30 0.32 0.34 3.0 3.4 3.8 207Pb/235U 4.2 4.6 5.0 5.4 �NEW VOLUME CALCULATIONS FOR THE PYROCLASTIC ERUPTIONS ASSOCIATED WITH THE STURGEON LAKE CALDERA COMPLEX, NORTHWESTERN ONTARIO: IMPLICATIONS FOR THE SCALE OF ARCHEAN VOLCANIC PROCESSES GEORGE J. HUDAK Department of Geology, University of Wisconsin Oshkosh, Oshkosh, WI 54901 DEAN M. PETERSON and RONALD L. MORTON Department of Geology, University of Minnesota — Duluth, Duluth, MN 55812 The Archean Sturgeon Lake Caldera Complex (SLCC) of northwestern Ontario comprises a north-facing, homoclinal, bimodal sequence of caldera-associated, greenschist facies metamorphosed, volcanic, intrusive and sedimentary strata with a composite thickness of nearly 4500 meters and a strike length of at least 25 km (Morton et al., 1991). At least three volcanic-associated massive sulfide (VMS) orebodies were formed as sub-seafloor replacement deposits within quartz-phyric, pumice-rich vitric tuff within the caldera complex (F-Group, Mattabi, and Sturgeon Lake); the other three orebodies in the region (Sub-Creek Zone, Creek Zone, and Lyon Lake) were probably formed from structural deformation of the Sturgeon Lake Mine (Hudak, 1996). Hudak et al. (2000) have divided the caldera complex into three stratigraphic sequences. The Pre-Caldera Sequence (PCS) is composed of a 200-2100 meter thick succession comprising subaerial basalt lavas, scoria-rich volcaniclastic rocks, and very minor rhyolite lavas that formed prior to the development of the caldera complex. The Early Caldera Sequence (ECS) comprises a 650-1300 meter thick succession of subaerial rhyolite ash tuff formed immediately prior to the formation of the caldera edifice, and subaqueous coarse heterolithic breccias, syneruptive aphyric and quartz-phyric pumice-rich vitric tuffs, and andesitic to rhyolitic lava flows formed prior to, or simultaneously with, the Mattabi VMS orebody. The Late Caldera Sequence (LCS) is composed of a complex, 500-1500 meter thick succession of subaqueous quartz- and quartz-plagioclase-phyric vitric tuffs, andesitic to dacitic lava flows, lava domes, and cryptodomes, resedimented syn-eruptive ash-rich mudstones, ash-rich sandstones, and lithic lapillistones, as well as post-eruptive tuffaceous mudstones, tuffaceous sandstones, tuffaceous breccias, and Algoma-type iron formations. Hudak (1996) and Morton et a!. (1998) have shown that the stratigraphic relationships indicate that the SLCC developed in a manner similar to the well-known caldera cycle of Smith and Bailey (1968). The presence of exceptionally well-preserved, often delicate primary lithological textures within the volcaniclastic and volcanic rocks in the south Sturgeon Lake region has allowed individual rock units and their facies equivalent deposits to be distinguished and correlated. These features indicate that only minor amounts of structural deformation, and probably only minor amounts of diagenetic compaction, have occurred within the intracaldera volcaniclastic rocks that are present. This, along with the steeply dipping nature of the strata in the region, allows us to make very accurate areal calculations of the volcaniclastic strata by means of geographic information system (GIS) analysis. Although arguably speculative, volumes of individual pyroclastic eruptions have been calculated using the average thicknesses of each of the major pyrociastic units within the caldera, the strike lengths of the pyroclastic units, and the assumption that these units were deposited within a circular caldera. The results of our eruption volume calculations are contained in Table 1. These calculations indicate that, although Archean in age, the SLCC eruptions were similar in scale to eruptions associated with Cenozoic arc-associated caldera systems. Thus, it appears that not only was the caldera cycle (Smith and Bailey, 1968) established by Late Archean time, but that pyroclastic eruptions occurring in Archean arc-associated caldera complexes were similar in scale to pyroclastic eruptions occurring in more recent arc-associated caldera systems. Although more detailed studies on the evolutionary processes and eruptive volumes need to be completed at other well-preserved Archean caldera complexes, these results may provide us with clues to Late Archean tectonic and petrological processes. 33 �Table 1. Volume Estimates of Sturgeon Lake Caldera Complex Eruptions Eruption Caldera Sequence - Estimated Jackpot Lake High Level Lake Bell River Mattabi Lower "L" Middle "L" Upper "L" Eruption Pre-Caldera Early Caldera Early Caldera Early Caldera Late Caldera Late Caldera Late Caldera VoIu(J 8.8 16.6 1.9 28.7 3.0 6.9 3.5 Table 2. Volume Estimates of Historic Caldera Eruptions Estimated Volume (km3) Source Pinatubo (1991) Krakatau(1883) Santorini (3.6 ka) Tambora (1815) Vandever Mtn Tuff(T-J) Taupo (1.8 Ka) Kuwai (—1450) 4-5 10 25-30 25 13-26 30-35 32-39 Lipman, 2000 Lipman, 2000 Lipman, 2000; Cas and Wright, 1987 Cas and Wright, 1987 Kokelaar and Busby, 1992 Lipman, 2000: Cas and Wright, 1987 Monzier et al., 1994 References Cas, R. A., and Wright, J. V., 1987. Volcanic Succession Modern and Ancient: Allen and Unwin, London, 528 pp. Hudak, G. J., 1996. The physical volcanology and hydrothermal alteration associated with late caldera volcanic and volcaniclastic rocks and volcanogenic massive sulfide deposits in the Sturgeon Lake region of northwestern Ontario: unpublished Ph. D. dissertation, University of Minnesota, Minneapolis, MN, 463 pages. Hudak, G. J., Morton, R. L., Peterson, D.M., and Franklin, J. M., 2000. The Sturgeon Lake Caldera Complex, northwestern Ontario: volcanological evolution of an Archean shallow water VHMS belt: Volcanic Environments and Massive Sulfide Deposits, CODES Special Publication 3, p. 8991. Kokelaar, P., and Busby, C., 1992. Subaqueous explosive eruptions and welding of pyroclastic deposits: Science, v. 257, p. 196-201. Lipman, P. W., 2000. Calderas, in Sigurdsson, H., 2000, Encyclopedia of Volcanoes: Academic Press, San Diego, CA, p. 643-662. Monzier, M., Robin, C., and Eissen, J.-P., 1994. Kuwae (—1425 A. D.): the forgotten caldera: Journal of Volcanology and Geothermal Research, v. 59, p. 207-218. Morton, R. L., Walker, J. S., Hudak, G. J., and Franklin, J. M., 1991. The early development of an Archean submarine caldera complex with emphasis on the Mattabi ash-flow tuff and its relationship to the Mattabi massive sulfide deposit: Economic Geology, v. 86, p. 1002-1011. Morton, R. L., Hudak, G. J., Walker, J. S., Jongewaard, P. K., and Murphy, C. M., 1998. The stratigraphy and physical volcanology of the Archean south Sturgeon Lake Caldera Complex, northwestern Ontario: Geological Association of Canada / Mineralogical Association of Canada Annual Meeting Abstract Volume 23, p. A-128. Smith, R. L., and Bailey, R. A., 1968. Resurgent Cauldrons, in Coats, R. R., Hay, R. L., and Anderson, C. A. (eds), Studies in Volcanology (Howell Williams Volume), Geological Society of America Memoir ll6,p. 153-210. 34 - �A PRACTICAL EXERCISE IN METALLIC MINE RECLAMATION LADYSMITH, WISCONSIN T.C. HUNT, Director of the Reclamation Program, School of Agriculture, University of Wisconsin - Platteville, Platteville, WI 53818 hi November 1968, Great Lakes Exploration, a subsidiary of Kennecott, intersected copper mineralization along the Flambeau River south of Ladysmith, Rusk County, Wisconsin. This discovery and the rising environmental consciousness in Wisconsin lead to nearly 25 years of legislation, engineering evaluation, and environmental regulation. The Flambeau Mine was officially opened on July 31, 1993 and by the time the mine closed in 1997, 1.9 million short tons of ore averaging 8.9 percent copper and 0.10 ounces per ton of gold were produced. This mine was unique in that all of the ore was shipped directly to smelters for metal recovery; there was no beneficiation on site. Reclamation of the property was an important part of the entire mine design. Kennecott Minerals' Flambeau Mine reclaimed their open pit copper mine under the jurisdiction of Wisconsin's environmentally sensitive metallic mining laws; viewed by many as the most strict in the nation. It was alleged that Wisconsin's modem mining laws were prohibitive, but the Flambeau Mine provides a case study demonstrating viable mining and reclamation within the constraints of rigorously protective regulatory requirements can happen. The mine site is adjacent to the Flambeau River, one of Wisconsin's premier whitewater canoeing area, and surface water, groundwater, and mine water were important parts of the mining plan. Reclamation was initiated prior to the completion of mining. Flambeau backfilled the open pit mine by layering mine waste and carbonate rock to control acidity, and reclaimed the surface using state-of-the-science ecological restoration methods. The company brought the surface of the former pit to its approximate original contour, rebuilt pre-existing intermittent stream channels, restored native plant communities, and developed a series of biofilters and wetlands to enhance runoff quality. A trail system opens the site to the public for recreational pursuits such as hiking, cross-country skiing, and bird watching. Bald Eagles and black bears are frequent visitors to the site. Visual inspection and statistical analysis of surface water samples present evidence that the site is stabilizing and that the hydrologic system is functioning as designed. Monitoring continues on the site, and the vegetative sampling results indicate the reclaimed mine site is on the desired trajectory for plant community development, diversity, cover, plant frequency, and productivity. This experience of a well designed and implemented mine plan, in conjunction with a well designed and implemented reclamation plan, illustrates that mining and the environment can be compatible. 35 �THE EARLY GABBROIC SERIES OF THE MIDCONTINENT RIFT SYSTEM: CONTINUED ASSESSMENT OF MAGMATIC ORIGINS JERDE, Eric A. (e.jerde@moreheadst.edu) and SAL VATO, Daniel J. (student), Department of Physical Sciences, Morehead State University, Morehead, KY 40351; THOLE, Jeff and WTRTH, Karl R., Geology Department, Macalester College, St. Paul, Minnesota, 55105 The Early Gabbroic Series of the Midcontinent Rift System (MCR), informally known as Nathan's Layered Series (after Nathan, 1969), is comprised of numerous tabular and sheetlike intrusions just south of the Gunflint Trail in the vicinity of Poplar Lake in extreme northeastern Minnesota. A U-Pb zircon date of 1106.9 ± 0.6 Ma has been obtained for one of the units in this series (Paces and Miller, 1993), making it among the oldest materials associated with the MCR. Nathan (1969) identified 27 separate units, given the letter designations A-Z and AA in their inferred chronological order. The chronological sequence was based entirely on cross-cutting relations and discordances observed. Nathan's own interpretation, plus those of subsequent observers, offers that many of the separate units may be gradational variations, while others may be unique dikes or "sport" varieties (to use the terminology of Nathan (1969). In terms of major magma bodies, the series comprises four principal units: A-B (troctolites to gabbronorites), F-G (oxiderich olivine gabbro), M (gabbronorite), and P-Q (troctolites to gabbros). These intrusions can fairly be considered to be the principal events in the evolution of the Early Gabbroic Series. A key aspect of this series of rocks, and one that led to the initial interest by H.D. Nathan in the I 960s, is that several units contain large amounts of Fe-Ti oxides. In places oxides comprise in excess of 30% of the rock (Nathan, 1969). However, among the major units listed above, only unit F-G is notable for high abundances of oxide, exceeding 60% at some locations. Until now, no chemical analyses have been available for rocks of this series. Initial modeling of magma crystallization (Jerde, 2000) indicated that the principal units of the early Gabbroic Series may be the result of polybaric fractionation. In such a scenario, units A-B, and P-Q formed through crystallization at 6kb, with M being more fractionated. Unit F-G could have formed through extensive crystallization at I kb. Oxide phases are favored by fractionation at lower pressures, resulting in the higher amounts seen in unit F-G. Results of initial chemical analyses of bulk rocks (Table I) show that both high-Al, low-Ti magmas and low-Al, high-Ti magmas are present. This is an interesting result since it has long been assumed that the earliest magmatic products of the MCR were all low-Al and high-Ti. The oxide-rich nature of the Early Gabbroic Series was consistent with this assumption. From this data, it is evident that unit F is significantly different from other units. Unit F may not be associated with unit G at all, and chemically resembles unit A. This is in marked contrast to the interpretation of Nathan (1969). The mineral data for some of the units shows variations consistent with multiple magma compositions, particularly among the pyroxenes. Among pyroxenes, Unit C appears to resemble unit P-Q, which was originally thought to be much younger. The variations in pyroxene may be additional evidence for polybaric fractionation since pressure differences plays a pivotal role in the appearance of pyroxene during crystallization. Most plagioclase is of an intermediate An content, showing very little variation among the units. The latest field efforts have focused on individual units, simply to be systematic. These probably represent individual intrusions, and once each one is examined, they can hopefully be placed into a broader context. The first unit examined was P-Q. This unit is present in a single band extending from Poplar Lake for approximately 15 kilometers to the west. It is interesting to note that Unit P is repeated, appearing twice in the magma stack (Fig. 1). In both instances, unit J is present stratigraphically above unit P. Unit J has a very characteristic appearance, with large ophitic pyroxenes (up to 3 cm) and layers of coarse grained material rich in Fe-Ti oxides. In most instances, when the top of unit P is approached, material very much like unit J appears, suggesting a gradational contact. A definitive contact between P and J was not observed at any location. Chemical and mineral data, along with the completely gradational contact between P (a gabbro) and Q (a troctolite), indicate that these are probably a single intrusion that has undergone continuous fractionation. It is possible that J is simply a late stage fractionate, formed after P. The repetition of unit P may reflect a second pulse of magma, or perhaps faulting (a thrust?) There is some indication that the two layers of unit P may have different compositions (compare sample JO-I 4 with the other unit P compositions in Table 1). One sample does not a difference make, however, and a definitive answer awaits further analysis, which will take place in the next few weeks. Recent studies of anorthosite-bearing intrusions such as the Kiglapait, Laramie, and Nain intrusions, has indicated that anorthosites can be produced through fractionation of a high-Al, high-Fe basaltic magma at pressures of 9-14 kb (Scoates and Lindsley, 2000). Such high-Al, high-Fe melts are consistent with low degrees of melting of an Fe-rich, enriched mantle source. Fractionation of these melts at higher pressures (-.14 kb) produces strong Fe enrichment and oxide phases appear early in the crystal assemblage. In such a scenario, the fractionation produces a ferrodiorite which is in equilibrium with anorthosite of an intermediate (An) composition. Enrichment of Si during fractionation is only possible at low pressures due to a thermal divide between cpx and opx at pressures in excess of 5 kb (Scoates and Lindsley, 2000). If such a magma were parental to the Early Gabbroic Series, it suggests that some of the Early Gabbroic Series units may be siblings to the liquids that formed the anorthositic series further to the south. Additional crystallization modeling is definitely needed to explore this new potential source for rocks of the early stages of the Midcontinent Rift development. 36 �! Table 1. Preliminary whole-rock compositions of major units from the Early Gabbroic Series Sample Unit J9-38 J9-35 J9-32 J9-31 J9-2 J9-46 J9-24 J9-23 J9-22 J9-29 A A B B C F G G G SiO2 TiO2 48.26 0.25 49.47 0.25 52.63 52.66 50.02 51.53 45.65 0.55 0.75 0.50 47.31 4.79 3.05 M M M 47.06 51.48 48.09 48.29 47.03 P 48.31 io-io P P jo-il J0-14 J9-26 J0-4 J0-13 J9-48 J9-41 J9-40 J9-37 J9-27 J9-17 1.12 3.73 20.01 17.93 13.84 16.36 16.23 15.08 15.74 12.98 15.14 49.20 49.30 0.41 1.83 1.80 1.72 22.98 18.93 22.28 17.52 15.56 15.40 14.53 p 4743 2.15 15.81 P 49.63 51.70 1.15 J Q Q Q Y 1.61 1.30 2.64 48.17 49.03 0.93 0.17 0.12 16.14 14.68 18.48 19.92 52.76 1.75 18.81 1.28 1.32 1.54 1.11 1.31 1.26 1.99 1.99 2.19 0.92 1.38 1.26 1.62 1.50 1.45 1.50 1.67 1.30 1.21 1.72 1.48 1.70 !P MiiQ M CaO 8.50 8.80 10.24 7.42 8.72 8.38 13.27 13.26 14.60 6.14 9.20 8.41 10.79 9.98 9.68 9.97 11.14 8.63 8.03 11.46 9.85 11.30 0.12 0.14 0.23 0.16 0.15 0.16 0.18 9.40 10.70 8.03 8.99 8.24 4.73 0.21 5.41 0.20 0.08 0.13 0.09 0.15 0.16 0.16 0.17 0.16 0.15 0.17 0.16 0.14 0.10 4.88 8.75 1.76 7.43 1.76 10.25 7.23 7.15 7.84 6.46 7.25 7.64 8.16 7.12 4.38 8.92 9.05 8.38 11.08 11.68 12.05 9.60 9.39 7.36 9.58 9.74 10.15 7.71 12.81 12.09 12.60 11.80 12.94 12.79 7.12 7.66 3.07 2.94 2.75 2.13 2.65 2.46 2.34 2.87 2.68 3.13 3.80 2.85 3.78 2.63 2.40 2.44 2.32 2.45 2.32 2.58 3.14 3.38 2.92 0.25 0.23 0.22 0.42 0.25 0.33 0.61 0.81 0.93 0.98 0.29 0.48 0.29 0.23 0.37 0.21 0.29 0.19 0.47 0.35 0.35 2.15 !Qs 0.04 0.03 0.02 0.13 0.03 0.10 0.57 0.31 0.76 0.07 0.03 0.11 0.07 0.02 0.13 0.06 0.03 0.02 0.11 0.07 0.06 0.22 99.33 99.39 100.51 100.83 100.37 100.64 98.96 99.14 99.32 99.44 99.40 99.26 98.47 100.07 99.90 100.22 99.39 99.72 100.32 99.00 99.11 99.19 61.8 62.6 62.1 63.0 61.8 60.7 35.9 39.0 34.4 31.0 55.9 24.7 59.9 53.2 53.7 55.3 47.7 56.9 59.9 52.8 53.2 37.8 Analyses performed by XRF in the Department of Geology, Macalester College, St. Paul. Fig. 1. North-South cross section of the Early Gabbroic Series. Note the P-J-Q-P-J sequence in the center of the figure. (from Nathan, 1969). 0 I,,,, References Cited: Jerde, E.A., 2000, Magmatic origins for Nathan's Layered Series: An initial reassessment of the Midcontinent Rift's first major plutonic materials: Institute on Lake Superior Geology Proceedings, 46th Annual Meeting, Thunder Bay, ON, May, v.46, part 1, p. 24-25. Nathan, H.D., 1969, The geology of a portion of the Duluth Complex, Cook County, Minnesota: Ph.D. dissertation, University of Minnesota, Minneapolis, i98p. Paces, J.B. and Miller, J.D., Jr., 1993, Precise U-Pb ages of Duluth Complex and related mafic intrusions, northeastern Minnesota: Geochronological insights to physical, petrogenetic, paleomagnetic and tectono-magmatic processes associated with the 1.1 Ga Midcontinent Rift System: Journal of Geophysical Research, v.9 8, 13,997-14013. Scoates, J.S. and Lindsley, D.H., 2000, New insights from experiments on the origin of anorthosite: EOS Transactions American Geophysical Union, v.81, no.48, Fall meeting Supplement. 37 �GEOPHYSICAL ANSWERS TO GEOLOGIC QUERIES IN THE SUPERIOR PROVINCE OF NORTHERN MINNESOTA JIRSA, Mark A., and CHANDLER, Va! W. (Minnesota Geological Survey, jirsa001@umn.edu, and chand004@umn.edu) Geophysical investigations play a vital role in geologic mapping in Minnesota. As an example, we present here some highlights from mapping the Archean Superior Province in parts of Minnesota where the bedrock is covered by glacial sediment as thick as one hundred meters. Mapping of the well-exposed Archean rocks, restricted largely to the Vermilion district of northeastern Minnesota (Fig. 1), was completed in the 1960s and 1970s. Although significant, this outcrop mapping suffered from two shortcomings: 1) the area constitutes less than 5 percent of the state's bedrock crust; and 2) the Vermilion district may not be representative of the remainder of the state's Archean terranes that comprise two-thirds of Minnesota's first crystalline bedrock beneath glacial materials. These shortcomings were recognized in the late-1970s by Dr. Matt Walton, then-director of the Minnesota Geological Survey (MGS). He lobbied the State Legislature and received funding (from 1979 to 1991) to collect high-resolution, state-wide, aeromagnetic data. Additional aeromagnetic data were contributed by the U.S. Geological Survey and U.S. Steel Corporation. This was coupled with efforts to map areas having poorly exposed bedrock, acquire gravity and corresponding rock properties data, and drill test-borings in locations determined by the new geophysical data and geologic models. After two decades, the results include aeromagnetic coverage of the entire state, a grid containing more than 56,000 gravity stations (averaging 1 station per 2 square kilometers, state-wide), 2,500 determinations of density and magnetic susceptibility from nearly every major rock type, and drill cores representing many of Minnesota's Archean rocks. Armed with these data, the MGS has produced variably detailed geologic maps, and in the process raised important questions about the nature of the Archean crust. Some of those questions are described below. International VERMILION DISTRICT Falls 9o COOK- ,-' >GRB NIA HORN LIJthb2 SIDE LAKE // Archean rocks Mafic to felsic stocks Granitoid batholiths Schist of sedimentary protolith Gneiss and schist I L_ 0 (JJ Layered mafic complexes 6Omi 0 I I 80km MAP AREA Metavolcanic and metasedimentary rocks Figure 1. Simplified geologic map of the Superior Province in Minnesota showing the location of various map areas discussed in the text (LLSD—Leech Lake structural discontinuity, GRB—Giants Range batholith). 38 �Early thrust nappes Mapping in the Cook-Side Lake area (Fig. 1) was directed toward understanding the geological relationships between well exposed strata of the Vermilion district on the east, and the less well exposed rocks of the Side Lake area on the west. The volcanic sequences in each district are lithologically similar, and form broad anticlines that face stratigraphically toward one another. The intervening area, covering some 600 square kilometers, is marked by scattered exposures composed of turbiditic graywacke and slate of the Lake Vermilion Formation. These strata are complexly deformed, and their interpretation required detailed structural and sedimentological analysis. The model that evolved requires that much of the Lake Vermilion Formation has been exhumed to a level that exposes the bottom of a very large thrust nappe. Geophysical data are consistent with this interpretation, as they show graywacke as a relatively thin, geophysically translucent package overlying a "floor" of denser and variably magnetic volcanic strata. Leech Lake structural discontinuity The broadly folded volcanic and turbiditic strata of the Lake Vermilion Formation are part of what is known as the Soudan belt. The Soudan belt is structurally contrasted with the adjacent Newton belt to the north; the latter forms a series of fault-bounded, mostly north-facing, homoclinal panels. The Newton belt differs further in containing komatiitic flows and abundant mafic to ultramafic sills that are not present in rocks of the Soudan belt. In the well-exposed Vermilion district, the belts are dissected by late faults to such an extent that the relationships between the belts, and even the exact position of the boundary, are unclear. Extending the belts westward away from the zone of coinciding faults using a combination of geophysical, outcrop, and drilling data identified a major state-wide discontinuity between the two contrasting structural panels. Although its origin is not well understood, the informally named Leech Lake structural discontinuity (LLSD on Fig. 1) is considered a significant Archean crustal suture. Mud Lake syncline Because Archean bedrock in the area known as the Virginia horn (Fig. 1) is mantled by magnetic iron-formation of Paleoproterozoic age, recent mapping in the area relied almost exclusively on gravity modeling. The Archean bedrock is marked by a large fold, thought by earlier geologists to be an anticline, having graywacke in the core and volcanic strata on the limbs. The graywacke is complexly folded, and detailed structural analyses of cleavage/bedding relationships produced a contrasting model of an early-formed, west-facing, upright syncline. The model was tested by a series of gravity profiles that outlined a broad synform that is cored by relatively low-density graywacke, and flanked by inwardfacing limbs of dense basaltic crust. Gravity modeling indicates that graywacke along the syncline axis is I to 2 kilometers thick and underlain by dense basaltic rocks. Geophysical boundary at 5 kilometers Constrained by physical property data, gravity and magnetic model studies of Superior Province rocks in Minnesota indicate that density and magnetization contrasts associated with the Archean greenstone-granite belts do not appear to extend to depths much greater than about 5 kilometers. This depth is surprisingly shallow, given the width and near-vertical geometry of most of these belts. The belts could be cut off by low-angle thrusting, which would be consistent with the convergent-margin, accretionary models advanced by the Canadian Lithoprobe project. On the other hand, the limited depth extent of the greenstone-granite belts could represent enhanced assimilation and mixing of magmatic and supracrustal components at depth. Support for the latter model exists along the southern boundary of the Giants Range batholith with adjacent supracrustal sequences that are complexly invaded and locally migmatized by granodiorite. In either interpretation (low-angle thrust or assimilation at depth), gravity and magnetic model studies indicate the observed anomaly signatures associated with Superior Province rocks in Minnesota are largely the result of sources within the uppermost crust, and that relatively little anomaly signature is apparently produced by middle or lower crustal rocks. In summary, aeromagnetic data, supplemented by gravity and rock property data, have had tremendous impact on mapping Superior Province rocks in Minnesota. These geophysical data provide an essential framework and continuity that is not typically available from existing drill holes and outcrops. During the last 20 years, much of the Archean bedrock outside of the Vermilion district has been remapped at scales of 1:1,000,000 or greater. This ongoing mapping provides a valuable base for launching mineral exploration programs, and has revolutionized our understanding of early crustal evolution in Minnesota. 39 �DISTRIBUTION OF ARSENIC IN WISCONSIN GROUNDWATER DAVE JOITThSON, Drinking Water & Groundwater Bureau, Wisconsin Department of Natural Resources, PU Box 7921, Madison, WI 53707-7921, johnsdmmail0.dnr.state.wi.us Iii the past ten years, with the recognition of elevated arsenic is drinking water supplies, the Wisconsin Department of Natural Resources has analyzed over 15,000 individual samples statewide. Ten percent of the statewide samples exceed the 10 ppb proposed Arsenic standard by the US Environmental Protection Agency; in some large areas over 25 percent of the samples exceed this level. The objectives of the sampling program were to (1) identify the distribution of elevated arsenic in water supplies, (2) identify concentration ranges and causes for the elevated arsenic, and (3) determine construction guidelines to minimize the problem. The arsenic appears in many settings, the most common presently recognized being a northeast trending belt in east-central Wisconsin, west of the Fox River. The highest concentration in Wisconsin, 15,000 ppb, occurs in this belt. Numerous studies (Burkel, 1993; Pelczar, 1996; Simo and others, 1996,1997; and Gotkowitz, 2001) have identified a sulfide-rich horizon recognized near the top of the St. Peter sandstone. This appears to be the principal source for As in this area. However, there are some elevated levels west of the western-most subcrop extent of the sandstone unit. Other areas of elevated As have been identified. These include relatively shallow domestic water wells in Silurian dolomite in southeast Wisconsin and in association with the Upper Mississippi Valley Zinc-Lead District in southwestern Wisconsin. Elevated concentrations are also noted in isolated areas in central and northeastern Wisconsin associated with unique Precambrian units. Township-based surveys of private wells in east central Wisconsin are continuing and may permit greater delineation of the As problem and possible solutions. Burkel, R.S., 1993, Arsenic as a Naturally Elevated Parameter in Water Wells in Winnebago and Outagamie Counties, Wisconsin: unpub. MS thesis, University of Wisconsin -Green Bay, 111 p. Pelczar, J.S., 1996, Groundwater Chemistry of Wells Existing Natural Arsenic Contamination in East-central Wisconsin: unpub. MS thesis, University of Wisconsin - Green Bay, 206 p. Simo, J.A., Freiberg, P.G., and Freiberg, KS., 1996, Geologic Constraints on Arsenic in Groundwater with Applications to Groundwater Modeling: Wisconsin Water Resources Center GRR 96-01, 57 p. Simo, J.A., Freiberg, P.G., and Schreiber, M.E., 1997, Stratigraphic and Geochemical Controls on the Mobilization and Transport of Naturally Occurring Arsenic in Groundwater: Implications for Water Supply Protection in Northeastern Wisconsin: Wisconsin Water Resources Center GRR 97-05, 56 p. Gotkowitz, M.B., Scbrieber, M.E., and Simo, J.A., 2001, Contrasts in the geologic and hydrochemical Occurrences of Arsenic contamination of Groundwater in Eastern Wisconsin: thstitute on Lake Superior Geology, this meeting. 40 �FLUID INCLUSION EVIDENCE FOR A ROLE FOR HYDROTHERMAL ACTIVITY IN THE ROBY ZONE, LAC DES ILES MINE, NORTHWESTERN ONTARIO JOHNSON, J.R. and KISSIN, S.A., Department of Geology, Lakehead University, Thunder Bay, ON, P7B 5E 1, stephen.kissin@lakeheadu.ca The Roby Zone of the Lac des lies Pd-Pt-Ni-Cu-Au mine, located 90 km north-northwest of Thunder Bay, Ontario, was the initial locus of mining activity in the deposit. A striking aspect of the deposit in the early stages of mining was the coincidence of the ore zone with an envelope of taicose hydrothermal alteration (Michaud, 1998). Based on evidence of hydrothermal activity in off-set and deep, copper-rich deposits at Sudbury (Molnar et al., 1997) and observations of felsic veins and pods in the Roby Zone, an investigation of fluid inclusions was undertaken. From a suite of samples collected during pre- and early-mining stages at the Roby Zone by Michaud (1998), hand specimen were selected. The hand samples used in the study were selected based on the presence and abundance of transparent minerals. From three hand samples (Lac-3 18, Lac-304 and Lac-46) taken from the heterolithic gabbro located in the middle of the Roby Zone, a number of doubly polished sections 100 tim-thick were prepared. Sample Lac-3 18 is composed of pegmatitic gabbro that contain minor veins of plagioclase and epidote. Sample Lac-304 consists of a quartz vein that is emplaced within a medium-grained gabbro. The last sample used, Lac-46, is a mediumgrained gabbro crosscut by a felsic vein network. Four distinct types of fluid inclusions were observed occurring in plagioclase and quartz: Type I - Single-phase liquid inclusions. These were extremely numerous in quartz but less common in plagioclase. Type II- Two-phase inclusions (liquid + vapour). The most numerous type of inclusion that was found in plagioclase. The majority had a vapour content of 10-20% by volume. Type III - Polyphase inclusions (liquid + vapour + one or more solid phases). These were fairly abundant but of a small size, occurring only only in plagioclase. Numerous inclusions contained a single crystal, but only a few were found to contain more than one solid. Type IV - CO2-rich polyphase inclusions. These were found only in plagioclase, containg two solids, two liquids and vapour. The fluid inclusion studies revealed the following results: Type II and Type III inclusions - All but one inclusion homogenized to vapour in the range of 540.1-352.4°C, but the majority were in the range 460-420°C. Eutectic temperatures generally clustered about -52°C or -49.8°C, the eutectics 41 �for NaC1-CaC12-H20 and CaCl2-H20, respectively. Some lower eutectic temperatures observed may be the result of the small size of the inclusions and difficulty in detecting the first melting. Some eutectic temperatures were near -21.2°C, the NaCl-H20 eutectic temperature. These may be attributed to lower concentrations of CaC12, such that its effects on melting behaviour were difficult to observe. Most inclusions in this group had final melting temperature of about -20°C, indicating moderate to high salinity. Type IV inclusion - Only one inclusion containing liquid CO2 and two daughter crystals was observed. The eutectic temperature was -54.2°C with a final melting temperature of -15.5°C, consistent with data from Type II and II inclusions. Liquid CO2 homogenized to vapour at 26.8°C, and the remaining vapour homogenized to liquid at 160.8°C. However, the daughter crystals melted at 230°C and >412°C, the decrepetation temperature. Type I - Liquid only inclusions exhibited eutectic temperatures of--34°C and final melting temperatures of-15°C. These inclusions, although saline, were clearly formed at low temperature. The study has shown that high-temperature saline fluids are intimately associated with the ore zone of the Roby Zone. It is suggested that the present distribution of the ore is the result of hydrothermal activity associated with these fluids, possible of late magmatic origin. Similarity to fluids active in the Sudbury Igneous Complex is striking. Michaud, M.J., 1998. The Geology, Petrology, Geochemistry and Platinum-Group ElementGold-Copper-Nickel Ore Assemblage of the Roby Zone, Lac des Iles Mafic-Ultramafic Comples, Northwestern Ontario. M.Sc. thesis, Lakehead University, Thunder Bay, Ontario. Molnar, F., Watkinson, D.H., Jones, P.C. and Gatter, I., 1997. Fluid inclusion Evidence for Hydrothermal Enrichment of Magmatic Ore at the Contact Zone of the Ni-Cu-PlatinumGroup Element 4b Deposit, Lindsley Mine, Sudbury, Canada. Economic Geology, vol. 92, pp. 674-685. 42 �HYDROGEOCHEMICAL MODELING OF ARSENIC IN MINNESOTA GROUND WAT1R KANTVTSKY, Roman, Minnesota Geological Survey, 2642 University Avenue, St. Paul, MN 55114, kaniv001@umn.edu Concentrations of dissolved arsenic in Minnesota ground water commonly exceed 3pJL (micrograms per liter) and are as much as 157 piL. The highest regional concentration of arsenic in ground water (0.06—91 WL, mean 6 iJL) is documented in the western part of the state where the aquifers are buried bodies of sand, gravel, and silty sand that form discontinuous lenses beneath lake deposits and within till. Because of this, the hydrogeochemical modeling was performed for ground water systems in this part of the state. A surface complexation two-layer sorption model was used to assess the mechanisms controlling arsenic distribution in the Quaternary buried artesian aquifer and Cretaceous aquifer systems. The release of sorbed arsenic from iron hydroxides into ground water was estimated by this model. The test data consisted of concentrations of total arsenic and iron in solution; this was derived from the arsenic and iron concentrations in the geological materials. The result of this model is the distribution of arsenic—either adsorbed to the surface of iron hydroxides, or into the aqueous phase. These results suggest that mobility of arsenic is promoted by the onset of suboxic conditions in aquifer systems where iron hydroxides have sorbed arsenic. The reduction of ferric oxides and hydroxides, together with the reduction of As(V) to the less-strongly adsorbed and more mobile As(III), can release adsorbed arsenic into ground water. This reduction may be driven by microbial degradation of natural organic matter in aquifer systems. The source of the arsenic in the Quaternary buried artesian system is presumed to be iron oxides and iron hydroxides that have sorbed arsenic, and form amorphous coatings on mineral grains within the silty-clayey till. Despite the fact that the arsenic concentrations in the ground water and the geological materials used for the modeling were far apart, the modeling illustrates that the process is probably generic and not limited by geography. Based on the sorption model and the classification of aqueous environments, the working model that explains the mech anisms controlling distribution of arsenic in ground water can be applied to five hydrogeochemical systems in Minnesota: the Quatemary buried artesian aquifer system, the Quaternary water-table aquifer system, the Cretaceous aquifer system, the Paleozoic- Mesoproterozoic artesian basin aquifer system, and the Precambrian crystalline rock aquifer system. The thick, silty-clayey, glacial and lacustrine sediments that cover the aquifers of the Quatemary buried artesian aquifer system in west-central Minnesota serve as a geochemical transition zone associated with the transformation from oxic to suboxic conditions. In areas where the tifi is more sandy, suboxic conditions may not exist. Variability in arsenic concentrations in water of the Quaternary buried artesian aquifer system can thus be explained by changes in geochemical conditions, the variability of the arsenic content in the sediments, or by variability in Waters within other distribution of chemical reductants (e.g. buried organic matter). hydrogeochemical systems typically have low concentrations of arsenic, possibly because they are associated with oxic conditions. High arsenic concentrations associated with sulfide mineralization or iron-formation may be present locally within any system, but are not a regional feature of any of these hydrogeochemical systems. Reference: Kanivetsky, R., 2000, Arsenic in Minnesota ground water: hydrogeochemical modeling of the Quaternary buried artesian aquifer and Cretaceous aquifer systems: Minnesota Geological Survey Report of Investigation 55, 23 p. 43 �ROCK MAGNETIC STUDIES OF PHYLLITIC ZONES FROM THE BARABOO SYNCLINE, WISCONSIN. KELLY*, COLLEEN, AND KEAN, WILLIAM F., Department of Geosciences, University of Wisconsin —Milwaukee, P.O. Box 413, Milwaukee, WI 53201 wkean@uwm.edu. (* student) Preliminary paleomagnetic results based on limited sampling from a variety of rock types, suggested that the magnetism of the metamorphic rocks associated with the Baraboo Syncline was pre-folding (Kean and Mercer,1986). The detailed work by Mercer (1984) based on data from two quartzite sites on the southern limb and one site on the northern limb shows the magnetism is carried by hematite, and is prefolding. The unfolded magnetic direction is Dec=201°, Inc.66.4°, Alpha 95=10.7°, which gives a paleopole at 257°E, 4.67°N. This is consistent with 1.75Ga. paleopole positions for North American. However, the sites with phyllites were notably inconclusive (Mercer, 1984). Possible causes are; incomplete structural information, synfolding magnetization that was not recorded by the quartzite, or anisotropy of magnetization caused during the folding. Nonetheless magnetic results from these strata could provide important clues about the actual age of folding of the syncline. The phyllites result from metamorphism of clay rich layers within the original sandstone sequence, which could also contain hematite, magnetite or maghemite. It is likely that the magnetic mineralogy, and/or the magnetic direction in these layers will change during metamorphism and folding, and therefore provide information on the deformation history. A suite of oriented hand samples, collected from phyllitic zones on both sides of the Baraboo Syncline, were subjected to a variety of magnetic measurements to determine the magnetic mineralogy and remanent directions. The measurements included stepwise alternating field (AF) and thermal demagnetization to either 1 OOmT or 750° C respectively, magnetic susceptibility, saturation isothermal remanent magnetization (SIRM), and hysteresis properties. A.F. demagnetization was mostly ineffective. However, the thermal demagnetization results show that the majority of samples have a single magnetic direction that reduced to zero intensity between 650-750° C. The SIRM plots never reach saturation by 300mT, and the coercivity of remanence (Hcr) values derived from the hysteresis ioops are in the range of 140-180 mT. These results are indicative of hematite with an effective grain size of 15-20 tm, that probably developed during metamorphism. However, additional studies are required to exclude the possibility that the differences in the magnetic directions for these sites are not due to local structural conditions, or anisotropy of remanent magnetization. References: Mercer, D.,1984, Paleomagnetism of the Baraboo Quartzite, Unpublished MS thesis, UWMilwaukee, 294 pp. Kean, W.F. and Mercer, D., 1986, Preliminary Paleomagnetic Study of the Baraboo Quartzite, Wisconsin, Geoscience Wisconsin, Vol. 10, p 46-53. 44 �HEALTH SURVEILLANCE IN A COMMUNITY AFFECTED BY ARSENICCONTAMINATED WATER Lynda Knobeloch and Charles Warzecha, Wisconsin Department of Health and Family Services Shelli Nelson, University of Wisconsin-Madison, Environmental Toxicology Center Many private drinking water wells in Wisconsin's Fox River Valley contain naturally occurring arsenic at levels of health concern (Riewe et al., 2000). In 1993, the Department of Health and Family Services surveyed water use and health status among families living in the affected region. Data from this initiative indicated that residents whose daily arsenic intakes exceeded 50 were approximately three times more likely to report skin cancer than residents with lower arsenic intakes (Haupert et al, 1996). The Department is currently re-evaluating arsenic exposure and health status in this region. Three factors make this re-evaluation timely. In January, the U.S. EPA lowered the safe drinking water standard for arsenic from 50 ug/L to 10 ugIL, increasing the number of wells that will be deemed "unsafe." Since the previous study, the number of families that use private wells in this region has increased dramatically. In addition, repeated sampling of several wells in this region seems to indicate that arsenic concentrations are increasing over time, possibly due to regional drawdown of the aquifer. The current study covers a much broader geographic region than the 1993 study. Each township within Outagamie and Winnebago Counties has been encouraged to participate. To date, nearly 2000 families have submitted well water samples for arsenic analysis and completed a 4-page health questionnaire. This larger study population, combined with a more extensive list of health outcomes, is expected to provide us with a better understanding of arsenic exposure and its impact on the health of families that consume water from private wells in these counties. References: Riewe T, Weissbach A, Heinen L, and R Stoll, 2000. Naturally occurring arsenic in well water in Wisconsin. Water Well J; (June 2000): 24-31. Haupert TA, Wiersma JH, and JM Goldring, 1996. Health effects of ingesting arseniccontaminated groundwater. Wisc Med J; 95(2):100-104. 45 �HYDROGEOLOGIC SETTING OF ELEVATED ARSENIC IN SOUTHEASTERN MICHIGAN KOLKER, Allan, and CANNON, W. F., U.S. Geological Survey, Reston, VA, 20192, HAACK, S. K., and WESTJOHN, D. B., U.S. Geological Survey, Lansing, Ml, 48911, and WOODRUFF, L. G., U.S. Geological Survey, Saint Paul, MN 55112. High levels of arsenic, up to nearly 40 times the EPA standard of 10 tg/L, are present in southeastern Michigan, primarily in private supply wells. To investigate the problem, the USGS, in collaboration with the University of Michigan, sampled more than 100 wells, including public, private and monitoring wells, and examined aquifer materials in the region for possible sources of arsenic. The study area includes nearly all of Genesee, Huron, Lapeer, Livingston, Oakland, Sanilac, Shiawassee, Tuscola, and Washtenaw counties, which have a combined population of more than 2 million. Of the wells sampled by the USGS, more than 50% exceed the current EPA drinking water standard [1,2]. Most of the affected wells are completed in the Marshall Sandstone (Mississippian), the principal bedrock aquifer in the region, but in some cases, water in overlying glacial aquifers, or in the Saginaw (Pennsylvanian) aquifer is also affected. Problem wells are concentrated in the eastern and southeastern parts of the Marshall Sandstone subcrop belt, where Marshall Sandstone is in direct hydrologic contact with permeable Pleistocene glacial deposits [3]. To investigate the possible relation between the composition of aquifer materials and the arsenic content of well water, test wells were drilled by the USGS in Huron County (H-i 5D) and Lapeer County (LP-1), in areas known to contain wells with high arsenic contents. Both of the USGS wells show a gradual decrease in total arsenic of well water with depth, but redox conditions (Eh = 29 to 68 mV; [1]) and the fraction of As III (88 — 100% of total arsenic), measured for H-15D, are essentially uniform with depth (Figure). There is no distinct correlation between arsenic contents of aquifer materials, sampled in 4.5 ft. (1.37 m) intervals (0 to —300 ppm), and waters, sampled largely in 50-ft. (15.7 m) intervals (Figure). Likewise, there is no correlation between As concentration and total Fe or SO4 contents of waters in the region, even for samples having the highest (>50 p.g/L) As contents. These findings suggest that in-situ pyrite oxidation in the Marshall aquifer is very limited. In the Marshall Sandstone and in portions of the overlying Michigan Formation, pyrite is locally present as a cement whose texture indicates growth that has displaced framework sand grains. This pyrite locally contains highly arsenic-enriched domains (up to 8.5 wt. %) occurring as overgrowths on pyrite framboids having much lower arsenic contents, that are in turn incorporated into pyrite having low arsenic contents [4,5]. Well cuttings containing arsenic-rich pyrite have arsenic contents as high as 1020 ppm. Investigation of till samples containing iron oxy-hydroxides, probably derived from weathering of arsenian pyrite, shows arsenic contents up to about 0.7 weight percent. This indicates that a portion of the arsenic is retained during the weathering/oxidation process, or that arsenic is concentrated on oxide surfaces by adsorption of aqueous arsenic. Because there are multiple sources of arsenic in glacial and bedrock aquifers that are in hydrologic continuity, no single process may explain the overall distribution of arsenic in southeastern Michigan wells. Reduction of iron-oxyhydroxides in glacial aquifers by exposure to suboxic ground water, is one possible source. In-situ pyrite oxidation, while limited, may locally be enhanced by high concentrations of bicarbonate [6]. Because of the extreme arsenic contents of some Marshall Sandstone pyrite, small amounts of in-situ oxidation could result in contamination of bedrock aquifers. Likewise, we cannot rule out sporadic paleo-oxidation of pyrite in the bedrock aquifer, resulting from lower water table levels that existed following the last glaciation. All of these processes have likely contributed to the widespread but sporadic nature of arsenic enrichment in southeastern Michigan ground water. 46 �Compilation of analytical results for arsenic in USGS test cores H-15D (A), and LP-1 (C) and waters in corresponding packed intervals (B and D). Data represent bedrock intervals only, with the exception of glacial drift recovered from LP-i. Brackets on water data indicate size of packed intervals represented. Results for arsenic speciation in H-i 5D waters are from M.-J. E a C 0 10 Kim [21. 20 30 Sandstone! 40 Siltstone 60 70 Mudstone 80 90 100 Shale 110 120 As (ppb) As (ppm) Carbonate References and selected geochemical characteristics of [1] Haack, S. K., and Trecanni, S. L., 2000, Arsenic concentration U.S. Geological Survey Water Resources in southeastern Michigan: ground water and aquifer materials Investigations Report 00-4171, 38 p. groundwater of southeast Michigan: Ph.D. dissertation, [2] Kim., M.-J., 1999, Arsenic dissolution and speciation in University of Michigan, Ann Arbor, Ml, 201 p. framework of the Michigan Basin Regional Aquifer [3] Westjohn, 0. B., and Weaver, T. L., 1998, HydrogeologiC Professional Paper 1418, 47 p. System: U.S. Geological Survey pyrite in the Mississippian 0. B., Woodruff, L. G., 1998, Arsenic-rich [4] Kolker, Allan, Cannon, W. F., Westjohn, Michigan ground water: Geological Society anomalous arsenic in southeastern Marshall Sandstone: Source of of America, Abstracts with Programs, v. 30, no. 7, p. A-59. D. B., Haack, S. K., and Kim, M.-J., 1999, Arsenic in [5] Kolker, Allan, Cannon, W. F., Woodruff, L. G., Westjohn, EOS, American Geophysical Union southeastern Michigan ground water: Results of USGS test drilling: S147. Transactions, v.80, no.17, p. S146ions and arsenic dissolution by ground water: [6] Kim, M.-J., Nriagu, Jerome, and Haack, S. K., 2000, Carbonate 34, p. 3094-3100. Environmental Science and Technology, v. 47 �POTENTIAL FOR COPPER MINERALIZATION IN THE ANIMIKIE GROUP, MINNESOTA LARSON, Phillip C., Department of Geological Sciences, University of Minnesota, Duluth, MN 55812, plarson2@d.umn.edu Numerous lines of evidence have recently been identified suggesting the potential occurrence of Keewenawanstyle native copper or White Pine-style sediment-hosted copper mineralization in Animikie Group sediments in northeastern Minnesota. Native copper has been reported in quartz veins in the Wanless Mine near Buhi (Gruner, 1946). Copperstained rocks have been observed in the Butler Taconite mine (D. Ridgeway, pers. comm.). Hydrothermally altered diabase dikes in the National Steel Pellet Company (NPSC) Mine have elevated copper values (up to 950 ppm) associated with a chlorite-quartz alteration assemblage (Larson et a!., 1999). In addition, diagenetic pyrite from the NSPC mine frequently displays a secondary coating of chalcopyrite on bedding and fracture surfaces. Finds of float native copper in glacial drift have occasionally been reported in the Nashwauk-Keewatin area of the Mesabi Range (L. Mattson, pers. comm.). It is improbable that this float copper is derived from the Lake Superior basin, as surficial drift on the Mesabi has either a northwest or northeast provenance; this strongly suggests a local provenance. These occurrences suggest the northern flank of the Animikie Basin has hosted a regional-scale mineralizing event by an oxidized cupriferous fluid. The timing of copper mineralization is constrained by cross-cutting relationships. A series of diabase dikes intrude iron formation in the NSPC mine area; these dikes are tentatively dated at —1 100 Ma. Overprinting of alteration on well-developed cooling structures and post-emplacement shears in the dikes suggests that the copper mineralizing event significantly post-dated dike emplacement — similar to native copper mineralization on the Keewenaw peninsula. In contrast, in the South Stevenson Mine a diabase dike intruded the natural iron-ore body, indicating dike emplacement post-dates natural iron-ore formation. These relationships demonstrate that the natural iron-ore forming hydrothermal event is distinct from, and preceded the copper mineralizing event. Morey (1999) has presented a model for formation of natural iron ore deposits on the Mesabi by alteration of Biwabik iron-formation by a hydrothermal fluid generated deep in the Animikie basin. A topographically-driven regional hydraulic flow system was induced by recharge in a highland area bounding the southern end of the basin. Fluids evolved deep in the basin were driven through relatively permeable strata at the base of the Animikie Group (Pokegama Quartzite). These fluids leaked upward along fractures through the overlying iron-formation toward the margins of the basin. Concentration of iron oxides in natural iron-ore deposits is chiefly a function of silica removal from unaltered iron-formation. Evidence suggests that this process extended down into the underlying Pokegama Quartzite as well. Holway (1956) reported that at the Auburn Mine, quartzite underlying the natural iron-ore was composed of friable sand from which the silica cement had been leached. In most exposures, the Pokegama Quartzite is a well-cemented low permeability rock. However, local desilicification associated with natural iron-ore formation has enhanced permeability along numerous fault- and fracture-hosted fluid pathways. During formation of the Midcontinent Rift System, rift-filling volcanics, intrusives, and sediments truncated the southern margin of the Animikie basin. The base of the Animikie Group is thus presumably in contact with volcanic rocks in the deeper portions of the rift — the likely source of oxidized cupriferous brines associated with Keewenawan native copper mineralization. These same fluids may have been driven from the western flank of the rift into the basal portion of the Animikie Group (Fig. 1). Fluid flow would have been focused through the basal clastic units, and in particular along the preexisting desilicified faults and fractures. Overlying iron-formation and shale units would have served as effective aquitards. Two scenarios for concentration of significant copper mineralization by cupriferous brines discharging along the northern margin of the basin present themselves (Fig. 2). High-porosity, high-permeability desilicified clastic sediments within the Pokegama Quartzite may be the host for native copper mineralization similar to that observed in brecciated flow-tops and conglomerate beds on the Keewenaw Peninsula. Interaction of the brines with the iron-sulfide-rich base of the Virginia Formation may have produced stratiform copper sulfide mineralization similar to that observed at the White Pine and Presque Isle deposits. 48 �Midconfinent Rift Mesabi Range Animikie Basin NW OronfoIBaieId Group Sec mentsJSE Figure 1. Schematic cross-section of post-Midcontinent Rift flow system through the Animikie Basin. k\ \ White Pine-Style Copper Sulfide \Tirginia Formation Figure 2. Schematic cross-section of copper mineralization, showing relationship between faults/fractures, desilicification, and Animikie Group sediments. References Gruner, J.W., 1946, Mineralogy and Geology of the Mesabi Range: Office of the Commissioner of the Iron Range Resources and Rehabilitation, St. Paul, 127 p. Hoiway, W., 1956, Auburn Mine, in Schwartz, G.M., ed., Geol. Soc. America Annual Meeting Field Trip 1 Guidebook, p.160-167. Larson, P. C., Hanttula, J. E. and Price, J. 5., 1999, Proterozoic mafic dikes, western Mesabi Range, Minnesota. GSA Abstracts with Programs, Vol. 31, No. 7: 106. Morey, G. B., 1999, High-grade iron ore deposits of the Mesabi Range, Minnesota — product of a continental-scale Proterozoic ground-water flow system. Economic Geology 94: 133-142. 49 �CONTRIBUTIONS TO THE CULTURAL GEOGRAPHY OF THE WEST MESABI RANGE, NORTHERN MINNESOTA LIVELY, Richard and MOREY, G. B. (Minnesota Geological Survey, lively@umn.edu and morey001@umn.edu) The Mesabi Iron Range in northern Minnesota has produced more than 4 billion tons of iron ore and taconite from more than 500 mines since ore was first shipped from that area in 1892. Mining, confined to an east-northeast trending strip of land some 100 miles long and 4 miles wide, has greatly modified both the original landscapes and associated cultural features. In this discussion, we assess some of those changes utilizing modern data and topographic maps prepared during the summer of 1899 and 1900 by E.C. Bebb and his assistants D.L. Fairchild and Louis B. Weed, all topographers with the U.S. Geological Survey. The original data were compiled at a scale of 1:16,000 with a contour interval of 20 feet, and ultimately were published at a scale of 1:50,000 in 1903 (Leith, 1903). The original field maps were obtained from the Cuyler Adams estate in the early 1 980s and were subsequently digitized by Emily Bauer of the Minnesota Geological Survey to produce a pre-mining topographic rendition of the western half of the Mesabi range. The digitized maps were prepared as part of a larger study of the hydrologic character of the western Mesabi range sponsored by the Legislative Commission on Minnesota Resources (LCMR). We compare here the 1899-1900 data with topographic data obtained in 1999 by the Minnesota Department of Natural Resources as part of the Mesabi Elevation Project (DNR, 1999). As one would expect, open-pit mining has considerably changed the topographic expression along the range, mainly by increasing the relative abundance and depth of topographically low areas and redistributing topographically high areas. In general, the overall spread in elevation has increased by over 100 feet due to excavation, while over the same period the maximum elevations on the range have not changed substantially. When comparing data from the 1999 high-resolution digital surface with data from the 1899-1900 survey in undisturbed areas, the resulting correlations are virtually identical. This implies a high degree of accuracy among the early topographers mapping the Mesabi range. In 1899-1900, the western half of the range contained 11 mines and 17 mine dumps totaling about 0.7 square miles, or about 0.3 percent of the 230 square miles originally mapped. In 1986, mining activity accounted for about 140 square miles of pits and dumps, or about 60 percent of the study area. Mining also significantly affected drainage patterns along the range. In 1899-1900, mapped streams totaled over 400 miles in length, whereas only about 220 miles could be found compiled from topographic maps between 1970 and 1990, a reduction of about 45 percent. Much of that loss involved the removal of headwaters for many southward flowing streams along the south side of the Laurentian drainage divide. The transportation features mapped on the range in 1899-1900 were primarily limited to about 170 miles of roads or trails and about 125 miles of railroad track. Most of these extended along the strike of the range, with relatively little development crossing the range. By 1990, railroad mileage had doubled to about 250 miles and road length had increased to over 1000 miles. In addition to the increased transportation network, mining created and destroyed many towns as it progressed. For example, the entire town of Hibbing was moved several miles after a rich deposit was discovered under its streets. The Leith (1903) report also included a geologic map that was designed to aid exploration by delineating the boundaries of the Biwabik Iron Formation. That map, compiled during the spring of 1900 and the summers of 1900 and 1901, relied heavily on the support and geologic information, especially test pit and drill hole data, provided by J.U. Sebenius of the Lake Superior Consolidated Iron Mines (now owned by the U.S. Steel Corporation). Although the geologic data base was limited to relatively few, sparsely distributed data points, the resulting geologic map read very much as it does today, even with more complete data now available. The only significant difference involves a better understanding of faults and related structures which became apparent as extensive test drilling and mining progressed. References Cited: Leith, C.K., 1903, The Mesabi iron-bearing district of Minnesota: United States Geological Survey Monographs, v. 43, 316 p., 1 plate. Minnesota Department of Natural Resources, 1999, Mesabi Elevation Project: St. Paul, Minnesota. 50 �PRECAMBRIAN GEOLOGY OF S. WISCONSIN: A PANORAMA FROM THE BARABOO RANGE MEDARIS, L.G., Jr., Dept. of Geology & Geophysics, Univ. of Wisconsin-Madison, 1215 W. Dayton Street, Madison, WI, 53706, medarisgeology.wisc.edu Red, supermature quartzites, most notably the Baraboo, Barron, and Sioux Quartzites, have long been recognized as a distinctive Proterbzoic feature in the southern Lake Superior region, signifying depositionon a stable craton under conditions of intense chemical weathering in the presence of significant free atmospheric oxygen (Dalziel & Dott, 1970; Ojakangas & Weber, 1984; Southwick et al., 1986). The quartzites were inferred to be post-1750 Ma in age, to have been folded and metamorphosed at —4630 Ma, and locally intruded by granitic rocks at —1450 Ma. The term, Baraboo interval, was introduced by Dott (1983) for this succession of sedimentation, deformation, metamorphism, and intrusion in the time span of 1750 to 1450 Ma. In the last six years investigators at Wisconsin and Dan Holm at Ball State and coworkers have taken a renewed interest in the Baraboo interval, and their results substantiate the original concept and framework of the Baraboo interval and provide a more detailed understanding of the disparate geological processes that shaped the southern Lake Superior region in mid-Proterozoic time. Igneous Basement of the Baraboo Range The Baraboo Quartzite is underlain by diorite, granite, and rhyolitic lavas and pyroclastic rocks (Dalziel and Doff, 1970). U-Pb zircon ages of the Baxter Hollow granite and rhyolite are indistinguishable, and taken together, yield an age of 1749±12 Ma (Van Wyck, 1995). Chronologically and petrologically, the Baraboo basement is correlative with the subalkalic granite and rhyolite suite of the Fox River Valley (Smith, 1978; Anderson et a!., 1980). Igneous textures are well preserved in all units of the Baraboo basement, although igneous minerals are partly to completely replaced by a variety of greenschist facies minerals. Typically, biotite is replaced by chlorite, plagioclase is transformed to albite and fine-grained epidote (saussurite), and intermediate alkali feldspar is recrystallized to a fine-grained mixture of near end-member microcline and albite. Hornblende in diorite is partly replaced by chlorite and intergrown actinolite and cummingtonite. Paleosols beneath the Quartzites Mature paleosols have been recognized beneath the Sioux, Baraboo, and Barron quartzites (Southwick & Mosler, 1984; Medaris et al., 1997; Medaris, 2000). Among these paleosols, the Barron represents the best standard for comparison, because it has not been affected by later hydrothermal alteration, as have the other two. The Barron paleosol is a saprolite, derived from Penokean metatonalite and consisting of quartz, kaolinite, hematite, traces of sericite, and crandallite-florencite. During weathering of the metatonalite protolith, A12O3, TiO2 and Zr remained immobile, Na20, CaO, MgO, and MnO were effectively removed, Ba, Sr, K2O, and Rb were substantially reduced, and SiO2 decreased by 10%. The extreme chemical maturity of the Barron saprolite is reflected in a high value, 95.7, for its Chemical Index of Alteration. The Baraboo Quartzite is underlain by saprolite, which varies in thickness from 30 to 50 feet and was derived from granite and rhyolite. Chemical changes in the Baraboo saprolite relative to protolith are similar to those in the Barron, except for subsequent hydrothermal addition of K20 and Rb. Common features of the Barron, Baraboo, and Sioux paleosols are the absence of feldspar and a high degree of mineralogical and chemical maturity, similar to present-day weathering profiles in warm, humid climates, where intense chemical leaching is characteristic. Such a climate and a stable tectonic setting were essential for generating the supermature features of the Baraboo interval quartzites. Depositional Age and Composition of Baraboo Interval Sedimentary Rocks A post-Pen okean depositional age for the Baraboo interval quartzites was long recognized, and recent analyses of detrital zircon grains in the Baraboo, Barron, Flambeau, McCaslin, and Sioux quartzites have yielded numerous U-Pb ages from 1782 to 1712 Ma (Van Wyck, 1995; Doff et a!., 1997; Holm Ct al, 1998), demonstrating that the quartzites were deposited no earlier than —1710 Ma. The chemical maturity of the Baraboo 51 �interval sediments was previously inferred from the near absence of detrital feldspar, the abundance of pyrophyllite or kaolinite, and the predominance of zircon, magnetite, rutile, and apatite among heavy minerals. Recent analyses of Barron, Baraboo, and Sioux siltstone, pelite, and their metamorphosed equivalents, yield compositions consisting essentially of Si02, Al203, Fe203, hO2, and H20, with a Chemical Index of Alteration ranging from 96.8 to 98.6. The extreme chemical maturity of the Baraboo interval sediments reflects a source region that experienced extensive chemical leaching and produced detritus consisting largely of quartz, kaolinite, and hematite. 1630 Ma Folding and Metamorphism There was widespread Rb-Sr isotopic resetting at 1635±33 Ma in Fox River Valley granite and rhyolite, Baxter Hollow granite, and Baraboo rhyolite (Dott & Dalziel, 1972; Van Schmus et al., 1975; X = 1.42*1011 yr'), and it was suggested that such isotopic resetting was coincident with folding of the quartzites, which might represent an eastern expression of the Mazatzal deformation in the southwestern U.S. (Dott, 1983; Van Schmus et al., 1993). The extent of foreland deformation is marked by a 1630 Ma tectonic and thermal front in northern Wisconsin, which was located on the basis of 40ArP9Ar cooling ages of mica and hornblende in basement rocks and the distribution of folding in quartzites (Holm et al., 1998; Romano et al., 2000). The Barron Quartzite is unfolded and unmetamorphosed, consisting of quartz, kaolinite, and hematite. In contrast, the Baraboo Quartzite and underlying basement have been folded and recrystallized under low grade conditions (Medaris et al., 1998). The coexistence of quartz and pyrophyllite in the metasedimentary rocks requires a temperature between 285°C and 360°C, at 1 kbar and unit activity of H20. Post-i 630 Ma HydrothermalActivitv Muscovite grains from sub-Baraboo metasaprolite and from muscovite-pyrophyllite-diaspore veins near the base of the Baraboo quartzite yield discordant 39Ar release spectra, with well-defined plateaux ages at 1456±11 and 1467±11 Ma, respectively (Naymark et al., 2001a). An apparent whole-rock Rb-Sr isochron age for saprolite and pedogene is 1336±75 Ma. These data provide the first substantial evidence for a Wolf River-age imprint on the Baraboo Range, due to the effects of hydrothermal fluids that probably were driven along the sub-Baraboo nonconformity by heat from regionally extensive Wolf River magmatism. Muscovite grains from two samples of Sioux pipestone, which contain the assemblage muscovitepyrophyllite-diaspore, also yield discordant 39Ar release spectra, but with significantly younger plateaux ages of 1370±10 and 1268±11 Ma (Naymark et al., 2001b). The geological significance of such ages is unclear at present, and the —100 m.y. difference in ages of the two samples, which occur at the same stratigraphic level, deserves further investigation. Nevertheless, these recent 40ArP9Ar results reveal the existence of important, and possibly widespread, post-1630 Ma hydrothermal activity in the southern Lake Superior region. References Anderson, J.L. et al. (1980) Contrib. Mineral. Petrol., v. 74, 3 11-328; Dalziel I.W.D. & Dott R.H., Jr. (1970) Wis. Geol. Nat. History Survey, Inf. Circ. 14, 164 pp; Dott, RH. Jr. (1983) Geol. Soc. Amer. Memoir 160, 129-141; Dott, R.H., Jr. & Daiziel, I.W.D. (1972) Jour. Geol., v. 80, 552-568; Dott, R.H., Jr. et al. (1997) Geol Soc. Amer. Abstr. with Progr., v. 29, No. 4, 13; HoIm, D. et at. (1998) Geology, v. 26, 907-910; Medaris, L.G. Jr. et al. (1997) 43rd Inst. Lake Superior Geol., 39-40; Medaris, L.G., Jr. et al. (1998) 44th Inst. Lake Superior Geol., 89-90; Medaris, L.G., Jr. (2000) 46th Inst. Lake Superior Geol., 37-38; Naymark, A. et at. (2001a) Geol. Soc. Amer. Abstr. with Progr., v. 33, No. 4, in press; Naymark. A. et al. (2001b) 47th Inst. Lake Superior Geol., in press; Ojakangas, R.W. & Weber, R.W. (1984) Minn. Geol. Surv., Rept. mv. 32, 1-15; Romano, D. et at. (2000) Precambr. Res., v. 104, 25-46; Smith, E.I. (1978) Geol. Soc. Amer. Bull., v. 89, 875-890; Southwick, D.L. et at. (1986) Geol. Soc. Amer. Bull., v.97, 1432-1441; Southwick, D.L. & Mossler,J.H. (1984) Minn. Geol. Surv., Rept. mv. 32, 17-44; Van Schmus, W.R. et at. (1975) Geol. Soc. Amer. Bull., v. 86, 1255-1265; Van Schmus, W.R. et al. (1993) Precambrian: Conterminous U. S., Geol. North America, v. C-2, 270-28 1, Geol. Soc. Amer.; Van Wyck, N. (1995) Ph.D. thesis, Univ. Wis.-Madison, 280 pp. 52 �RECENT ADVANCES IN UNDERSTANDING THE GLACIAL RECORD OF WISCONSIN MICKELSON, D.M., Department of Geology and Geophysics, University of Wisconsin, Madison, WI 53706. Micke1son(dgeology.wiscedu and CLAYTON, LEE, Wisconsin Geological and Natural History Survey, 3817 Mineral Point Rd., Madison, WI 53706. Several glacier advances reached Wisconsin, but the record of early ice advances is sparse, probably because of their age (some >800 ka) and the intense erosion that took place during the subsequent glaciations (Alden, 1918; Bleuer, 1970; Baker, etal., 1983; Miller, 2000). Thin, discontinuous till occurs on the uplands in west central and central Wisconsin and south of the late Wisconsin deposits in southern Wisconsin. Most have been classified into the lithostratigraphic system adopted by the Wisconsin Geological and Natural History Survey, as have younger 1987; Clayton, 1991). More detailed mapping of 1984; Attig, glacial deposits (Mickelson, Quaternary deposits at 1:100,00 scale has been published for about 18 counties, and several more are in preparation. South and west of late Wisconsin and older glacial deposits lies the Dnftless Area. Recognized as driftless since before 1850 because of its higher relief and lack of erratics, the Driftless Area has Paleozoic bedrock close to the surface with only a cover of bess less than lOm thick. The landscape has been produced by fluvial erosion since at least sometime in the Tertiary. Although Black (1960) suggested that it was glaciated, there is no evidence that it was (Mickelson etal., 1982). In all likelihood, the Driftiess Area remained unglaciated because it had to cross the deep, east-west Lake Superior basin. Much ice was diverted into the Green Bay Lobe and into the Superior Lobe, which extended westward into Minnesota. The Driftless Are a is surrounded by glacial deposits of different ages, but was never surrounded by ice as portrayed by early workers and many textbooks. Late Wisconsin ice advanced into the northeast Wisconsin by about 24,000 radiocarbon years ago based on model results and radiocarbon dates in Illinois. There is a relative lack of radiocarbon dates from this time period in Wisconsin, probably because permafrost was thick and tundra vegetation covered the landscape. Also, ice was particularly erosive behind the ice margin compared to further south in Illinois. Although there is no radiocarbon record of the advance, model results indicate that the Lake Michigan Lobe advanced more quickly than lobes that had to traverse the deep, east-west oriented Lake Superior basin (Cutler, j., 2000a) because extensive calving slowed their advance. Ice of the Green Bay, Langlade, Chippewa, and Superior Lobes clearly advanced onto permafrost. This argument is based field observation of ice wedge casts (Clayton, etal., 1997), the lack of buried wood, (Attig, etal., 1989) evidence of tundra vegetation (Maher and Mickelson, 1996), and model results (Cutler, etal., 2000b). Landforms near the maximum ice extent appear to reflect subglacial conditions at the time they were deposited. Relief within end moraines increases from about 10 m in southern Wisconsin to more that 60 m in northern Wisconsin, reflecting the wider, longer lasting frozen-bed zone near the margin. Drumlins are extensive, probably because slow melt out of subglacial permafrost caused inhomogenities in the bed and differential streamlining. Tunnel channels left by large, probably catastrophic, flows of water from beneath the ice sheet are common along the outer margins in press). Tunnel channels and drumlins appear to be absent farther south in (Clayton,., 1999; Cutler, Illinois where buried wood and model results indicate there were warmer temperatures during the advance to the maximum ice advance position. The length of time that ice remained at or near the maximum position in the Green Bay lobe is debated. Maher and Mickelson (1996) have argued that ice remained near its maximum extent until about 15, 000 years ago and that subsquent deglaciation was rapid based on radiocarbon dates from Devils Lake and northeastern Wisconsin. Colgan submitted) argue that deglaciation was slower based on cosmogenic dates and time needed for (1999; Colgan glacial landform development. References Cited Attig, J.W., Clayton, Lee, and Mickelson, D.M., (Eds.), 1988, Pleistocene stratigraphic units of Wisconsin 198487: Wisconsin Geological and Natural History Survey, Information Circular 62, 61 pp. Attig, J.W., Mickelson, D.M., and Clayton, Lee, 1989, Late Wisconsin landform distribution and glacier-bed conditions in Wisconsin, Sedimentary Geology, v. 62, p. 399-405. Baker, R.W., Biehl, J.F., Simpson, T.W., Zelazny, L.W., and Beske-Deihl, S., 1983, Pre-Wisconsinan glacial 53 �stratigraphy, chronology, and paleomagnetics of west-central Wisconsin: Geological Society of America Bulletin, v. 94, p. 1442-1449. Clayton, Lee, Attig, J.W., and Mickelson, D.M., and Johnson, M.D., 1991, Glaciation of Wisconsin: Wisconsin Geological and Natural History Survey, Educational Series 36, 4 p. Clayton, Lee, Attig, J.W., Mickelson, D.M., 1997, Conditions around the margin of the Green Bay lobe during the height of the Wisconsin glaciation: j: Mudrey, M.G., Jr., Guide to Field Trips in Wisconsin and adjacent areas of Minnesota, 31st Annual meeting of the North-central section, Geological Society of America: Wisconsin Geological and Natural History Survey, p. 23-30. Clayton, L, Attig, J.W., and Mickelson, D.M., 1999, Tunnel channels formed in Wisconsin during the last glaciation: In Mickelson, D.M. and Attig, J.A., (Eds.), Glacial Processes Past and Present: Geological Society of America Special Paper 337, p. 69-82. Colgan, P.M. and Mickelson, D.M., 1997, Genesis of streamlined landforms and flow history of the Green Bay lobe, Wisconsin, USA: Sedimentary Geology, v. 111, p. 7-25. Colgan, P.M., 1999, Reconstruction of the Green Bay Lobe, Wisconsin, United States, from 26,000 to 13,000 radiocarbon years B.P. :In Mickelson, D.M. and Attig, J.A., (Eds.), Glacial Processes Past and Present: Geological Society of America Special Paper 337, p. 137-150. Colgan, P.M., Bierman, P.R., Mickelson, and Caffee, Marc, submitted, Variation in glacial erosion near the southern margin of the Laurentide Ice Sheet, south central Wisconsin: implications for cosmogenic dating of glacial terrains: Geological Society of America Bulletin, Cutler, P.M., Colgan, P.M., Mickelson, D.M., and MacAyeal, 2000a, Influence of the Great Lakes on the advance of the southern Laurentide Ice Sheet at the last glacial maximum: Geological Society of America, 2000 Abstracts with Programs, v. 32, no. 7, p. A-330 Cutler, P.M., MacAyeal, D.R., Mickelson. D.M., Parizek, B.R., and Colgan, P.M., 2000b, A numerical investigation of ice-lobe-permafrost interaction around the southern Laurentide Ice Sheet: Journal of Glaciology, v. 46, no. 153, p.311-325. Cutler, P. M. Clayton, Lee, Mickelson, D.M., Colgan, P.M., and Attig, J.W., in press, Tunnel Channels and Associated Fan Deposits in Wisconsin, U.S.A.: Insights into the Plumbing of the Southern Laurentide Ice Sheet: Quaternary International. Maher, L.J. Jr., and Mickelson, D.M., 1996, Palynological and radiocarbon evidence for deglaciation events in the Green Bay lobe, Wisconsin: Quaternary Research, v. 46, p. 251-259. Mickelson, D.M., 1997, Wisconsin's glacial landscapes: In Ostergren, R.C. and Vale, T.R., Wisconsin Land and Life: Madison, University of Wisconsin Press, p. 35-48. Mickelson, D.M., Clayton, Lee, Baker, R.W., Mode, W.N., and Schneider, A.F., 1984, Pleistocene stratigraphic units of Wisconsin: Wisconsin Geological and Natural History Survey, Miscellaneous Paper, 84-1, 199 pp. Miller, J.W., 2000, Glacial stratigraphy and chronology of central southern Wisconsin, west of the Rock River, Wisconsin: Madison, Wisconsin, M.S. Thesis, University of Wisconsin, 147 pp. Mickelson, D.M.,Knox, J.C. and Clayton, Lee, 1982, Glaciation of the Driftless Area: An evaluation of the evidence, In: Quaternary history of the Driftless Area , Knox, J.C., Clayton, Lee, and Mickelson, D.M. (Eds.), Wisconsin Geological and Natural History Survey, Field Trip Guidebook 5, p. 155-169. 54 �THE DULUTH COMPLEX: WHAT IT IS, WHAT IT AIN'T, AND WHAT WE STILL DON'T KNOW p Miller, James D., Jr. (Minnesota Geological Survey, do Natural Resources Research Institute, 5103 Miller Trunk Highway, Duluth, MN 55811 mille066@tc.umn.edu) Since the time of the first Minnesota state geological survey over 100 years ago (1.), several generations of geologists have worked to unravel the mysteries of the igneous rocks of northeastern Minnesota: the aptly named Duluth Complex. Each new level of understanding was brought about by new data or concepts about geological processes. With early survey studies recognizing the general distribution of igneous rock types, Grout's (2-5) work in the Duluth area established many of the broader geologic relationships of the Complex and developed fundamental concepts about how layered mafic intrusions form, many of which are still held today. However, one of his principle ideas, that the Duluth Complex is a large singular lopolithic intrusion (2), was proven to be an oversimplification by a flurry of geologic mapping conducted throughout the complex in the 1950s to 1970s (6-13). These studies were spurred by efforts to establish a geological framework within which to understand the Cu-Ni sulfide deposits first discovered in the late-1940s. Despite the fact that these deposits have yet to prove of economic importance, this intense period of geologic mapping served to formalize the general intrusive stratigraphy of the Duluth Complex and showed it to be a multiply intruded igneous system. In the early-70s, acceptance of the plate tectonic theory and recognition that the Duluth Complex was part of an intracontinental rift system created a new paradigm within which to evaluate the magmatic and tectonic history of the Duluth Complex (14). The current generation of Duluth Complex studies have focused on five major objectives: 1) 2) 3) 4) 5) to interpret the geologic picture of the vast, poorly exposed central part of the Duluth Complex using high-resolution aeromagnetic data acquired in the early-1980s (15, 16); to unravel the intrusive history of the complex with high resolution U-Pb dating of its gabbroic, anorthositic and felsic rocks (17, 18); to delineate the internal igneous stratigraphy of the various layered intrusions of the Duluth Complex with core logging, detailed mapping, and petrologic studies (19-22); to map the intrusive components of the hypabyssal Beaver Bay Complex and distinguish these from intrusions of the deeper Duluth Complex (23); and to evaluate the potential for economic base- and precious-metal deposits in areas of known mineralization and in other unexplored areas of the Duluth Complex (25). This presentation will highlight some of the new ideas that have emerged from this generation of studies and that are currently being summarized in a new 1:200,000-scale digital geologic map of northeastern Minnesota (see Miller and others, this volume) and in a companion report to be published in summer, 2001. It will also attempt to clarify some misconceptions about the Duluth Complex and point out where more study is needed. Keweenawan intrusive igneous rocks compose more than 60 percent of the bedrock geology of northeastern Minnesota, but only about half of them constitute the Duluth Complex. The Duluth Complex refers to those intrusions that were emplaced into the base of the comagmatic volcanic edifice of the North Shore Volcanic Group. Intrusions emplaced higher within the volcanic pile are not considered part of the Duluth Complex, but rather belong to the Beaver Bay Complex or, where isolated, are identified as individual subvolcanic bodies. Other than scattered, isolated masses of strongly hornfelsed mafic volcanic rock, the Duluth Complex is virtually a continuous mass of intrusive igneous rock. Within that mass, four general rock series are distinguished on the basis of age, dominant lithology, internal structure, and structural position within the complex. Each rock series was multiply emplaced and, where possible, individual intrusion names are assigned. 55 �Early Gabbroic Series—layered sequences of dominantly gabbroic cumulates occurring along the northeastern contact of the Duluth Complex. With their reversed magnetic polarity and 1108 Ma U-Pb zircon age (17), these rocks were evidently emplaced during the early magmatic stage of rifting. Two intrusive units are currently recognized: Nathan's Layered Series and the Cucumber Lake gabbro, though the latter has not been mapped in detail (10). Felsic Series—massive granophyric granite with lesser intermediate rocks occur in a semicontinuous string of elliptical bodies along the eastern and central roof zone of the complex. Ongoing age dating and isotopic studies of these various bodies by Vervoort (26, 18) suggest that most were emplaced during early magmatic activity between 1109 to 1102 Ma and came from Paleoproterozoic to Mesoproterozoic crustal sources. The position of major mafic and anorthositic intrusions beneath these granophyre bodies suggests that the felsic rocks acted as density barriers to mafic magmas, thus causing their plutonic emplacement. Anorthositic Series—a structurally complex suite of foliated, but rarely layered plagioclase-rich gabbroic cumulates that evidently formed by multiple emplacement of plagioclase crystal mushes (27). The erratic internal structure of these rocks typically precludes distinguishing individual intrusive bodies. Although commonly intruded by and included in layered series rocks, U-Pb dating indicates comparable ages of 1099 Ma for both rock series (17). Layered Series—previously referred to as the troctolitic series (9-12, 14), this suite is composed of troctolitic to ferrogabbroic cumulates that constitute at least 11 major mafic layered intrusions. These intrusions display a range of internal differentiation from poorly differentiated troctolitic bodies, such as the Partridge River and South Kawishiwi intrusions, to the well-differentiated Duluth Layered Series and Greenwood Lake intrusion (21). Interpretations of geophysical data over the unexposed central and southern parts of the complex (15, 16; Miller and others, this volume) have led to the recognition of several previously unidentified layered intrusions: the Boulder Lake, Western Margin, Greenwood Lake, and Osier Lake intrusions. Aeromagnetic data also imply that emplacement of the thick sheet-like intrusions of the layered series occurred by sequential overplating of previous intrusions beginning in the northwestern part of the complex and progressing southeastward. Although much has been learned about this enormous and complex igneous system in the past 20 years, much more remains to be done before a complete picture of the Duluth Complex is developed. Vast areas of the Duluth Complex and associated subvolcanic intrusions are unmapped in detail (especially in the BWCA). Age dating studies have only begun to unravel the emplacement history of Duluth Complex intrusions and their possible relationship to higher subvolcanic intrusions and volcanic rocks. Determining the igneous stratigraphy of the newly recognized, but poorly exposed layered intrusions (and their potential for stratiform POE deposits) will require systematic drilling and geochemical studies. These and other challenges await the next generation of geologists who dare to tackle the mysteries of the Duluth Complex. References: 1) Winchell, 1899, MGS Final Rpt IV; 2) Grout, 1918a, Am J Sci 46, p.516; 3) Grout, l9l8b, J Geol 26, p.626; 4) Grout, 1918c, J Geol 26, p.481; 5) Grout, 9l8d; J Geol 26, p.439; 6) Grout, Sharp, & Schwartz, 1959, MGS Bull 39; 7) Taylor, 1964, MGS Bull 44; 8) Green, Phinney & Weiblen, 1966, MGS Misc Map M-2; 9) Phinney, 1972, Geol of Mimi: Cent Vol, p.335; 10) Phinney, 1972, Geol of Minn: Cent Vol, p.346; II) Davidson, 1972, Geol of Minn: Cent Vol, p.354; 12) Bonnichsen, 1972, Geol of Minn: Cent Vol, p.361; 13) Green, 1982, MGS Geologic Map of Minn—Two Harbors sheet; 14) Weiblen & Morey, 1980, Am J Sci 280-A, p. 88; 15) Chandler, 1990, Econ Geol 85, p.816; 16) Miller & Chandler, 1999, MGS Misc Map M-l0l; 17) Paces & Miller, 1993, J Geophys Res 98, p.13997; 18) Vervoort & others, this volume; 19) Severson & Hauck, 1990, NRRIJGMIN-TR-89-1l; 3) Severson, 1994, NRRI/TR-93/34; 21) Miller & Ripley, 1996, Layered intrusions, Elsevier, p.257; 22) Severson & Miller, 1999, MGS Misc Map M-91; 23) Miller & Chandler, 1997, GSA Spec Paper 312, p.73; 24) Hauck et a!., 1997, GSA Spec Paper 312, p.137; 25) Miller, 1999, MGS Inf Circ 44; ) Vervoort & Green, 1997, Can J Earth Sci 34, p.521; 27) Miller & Weiblen, 1990, J Pet 31, p.295. 56 �DIGITAL GEOLOGIC MAP OF NORTHEASTERN MINNESOTA AND ASSOCIATED DATABASES IN GeMS—A MODIFIED ARCVIEW FORMAT Miller, J.D., Jr.', WahI, T.E.', Green, J.C.2, Chandler, V.W.', Severson, MA.3, and Peterson, D.E.23 1) Minnesota Geological Survey, 2642 University Ave., St. Paul, MN 55114; 2) Department of Geological Sciences, University of Minnesota—Duluth, Duluth, MN 55812; 3) Natural Resources Research Institute, 5013 Miller Trunk Highway, Duluth, MN 55811 The Minnesota Geological Survey (MGS), in collaboration with the Natural Resources Research Institute and the Department of Geological Sciences at the University of Minnesota—Duluth, is currently compiling geologic, structural, drill hole, geophysical and geochemical data from northeastern Minnesota into an ArcViewbased GIS called GeMS (Geologic Mapping System). The main focus of this project, which is being funded by the Minnesota State Legislature through the Minerals Coordinating Committee, is to develop a new 1:200,000-scale geologic map of the Duluth Complex and related Keweenawan igneous rocks. The map will be available in summer, 2001 either as a 1:200,000-scale paper map, as a downloadable image from the MGS website, or as part of a CD-ROM that will also include all related data compiled for the study in an ArcView format. A companion report addressing the geology and mineral potential of the Duluth Complex will also be published in summer, 2001. This presentation will give an overview of the basic components of GeMS and will describe the types and attributes of database themes included in the compilation. GeMS was initially conceived to be a user-friendly interface to the UNIX workstation-based Arclnfo software for the purpose of digitally storing, retrieving and imaging geologic, geophysical and geochemical data (WahI and others, 1995, 1997). GeMS was recently converted to ArcView 3.2 for this and other MGS mapping projects because of ArcView's common usage as GIS software on the PC platform, its expanded data management capabilities, and its more flexible and easy-to-use graphical user interface. ArcView manages geographical data as point, line and polygon themes and links them to attribute tables containing related information. ArcView is particularly well-suited to making geologic maps because of its ability to sort data and interpretive themes by various attributes, to graphically portray the sorted data in a variety of ways, and to accommodate various types of base images (DRGS, geophysical images, orthophotos, etc.). The types of data and information themes that are part of the current version of GeMS are listed in Table 1. Table 1. Data and interpretive themes included in GeMS Data type Theme type Attributes outcrop polygon field station ID, geologist, date visited, data source, observational detail, exposure, outcrop types, # of photos taken, # of samples taken, rock type, field description, map unit sample point field station ID, geologist, date sampled, data source, form of sample, rock type, map unit, field description, # of thin sections, petrographic description, related data available (probe, whole rock, isotope, assay, geochron, rock properties) structure point field station ID, geologist, date measured, data source, structure type, attitude, confidence level, # of averaged measurements, display scale drill hole point drill hole ID, date drilled, logged by, date logged, lessee, elevation, azimuth, plunge, depth, depth to bedrock, first bedrock, last rock type, present core location, core diameter map lines line geologist, date, basis 1, basis 2, line type (e.g., fault, contact, dike, fold axis, etc.) map unit polygon geologist, date, basis I, basis 2, map label, unit description miscellaneous varied gossan zones, test pit locations, etc. 57 �The advantages of moving from the old cartographic methods of making geologic maps to a GIS-based approach are numerous: GIS maps are easily updated as new data become available; several types of geologic data can be viewed at the same time; and different bases can be used. In addition to these advantages common to all GIS map systems, GeMS incorporates some other unique and useful features. These include source identification data (who, when and where). This is especially important for the compilation of the 1:200,000-scale geologic map of northeastern Minnesota, which compiles data and interpretations from various sources. Another important feature is the identification of the basis for geologic interpretations (map lines and units). For example, possible options for the basis for a fault interpretation are: topographic expression, inference from aeromagnetic data, geologic unit offset, air photo lineament, or local observation in outcrop. The database for northeastern Minnesota available on CD-ROM will not be a complete compilation. The amount of detailed outcrop data alone that could potentially be compiled totals more than 100,000 polygons. This project is concentrating on data from areas that are open to mineral exploration. The completeness of the database at present is shown in Table 2. In addition to continuing to fill out this database, some other elements that will be added to GeMS include 1) compiling all geochemical data and linking that database to outcrop and drill hole samples, 2) allowing for drill core logs to be added to the database, and 3) exporting portions of the system to handheld devices to allow direct data capture in the field. As new mapping is conducted and new data are acquired, updated versions of the regional geologic map and its associated database will be published—a task made easier having moved our map-making into the digital age. Table 2. Current Status of Data Compilation for the Northeastern Minnesota Geologic Map Area Data Type Outcrop Areas where compilation nearly complete Areas yet to be compiled —23,000 Duluth area, southern and central Duluth complex, Allen and Babbitt quadrangles, Beaver Bay Complex' Northern Duluth Complex (map areas of Phinney, Davidson, Foose, and Nathan), North Shore (Green) Units compiled Total units to be compiled to date >100,000 Samples2 —5000 —3600 Duluth area, central Duluth Complex, Allen quadrangle, Beaver Bay Complex Samples of Green and misc. uncatalogued samples and thin sections stored at the MGS Structure —8000 >5000 All published geologic maps Unpublished mapping by Phinney and Green —600 All drill hole data are compiled Drill Holes —600 ')only about 30% of outcrop polygons in the Beaver Bay Complex have their attributes compiled, the unattributed polygons thus mark only outcrop location. 2) includes well-located samples for which geochemical, petrographic, or rock property data exist and/or for which a preserved sample or thin section exists. References: 1995 ESRI International User Conference Proceedings, http://www.esri.comllibrary/userconf/proc95/to200/p I 67.html Wahl, T.E., Miller, J.D., Jr., Bauer, E.J., 1995, Bedrock geologic mapping using Arclnfo: Wahi, T.E., Miller, J.D., Jr., Jirsa, M.A., Boerboom, T.J., Chandler, V.W., Runkel, A.C., Dahl, D., Severson, M.J., 1997, Geologic mapping System (GeMS): a digital approach to bedrock geologic mapping: Institute on Lake Superior Geology, Proceedings v. 43, part 1, p. 59-60. 58 �STRUCTURE OF THE BURIED PRECAMBRIAN BASEMENT IN SOUTHWEST WISCONSIN AND ITS INFLUENCE ON REGIONAL PALEOZOIC GEOLOGY AND ZINC-LEAD MINERALIZATION MUDREY, M.G. Jr., Wisconsin Geological and Natural History Survey, 3817 Mineral Point Rd., Madison, WI 53705, mgmudreyfacstaff.wisc.edu BROWN, B.A., Wisconsin Geological and Natural History Survey, 3817 Mineral Point Rd., Madison, WI 53705, babrown1@facstaff.wisc.edu Our recent geologic mapping in southwestern Wisconsin has focused on pre-Sinnipee Group formations in the area north of the historic upper Mississippi Valley Zinc-Lead Mining District and south of the Wisconsin River. The regional stratigraphy can be clearly defined from outcrop exposures and mineral exploration boreholes in the Tunnel City Group, Trempealeau Group, Prairie du Chien Formation, and Ancell Group. The relatively easy recognition of the various units, in some cases to within 3 meters of a member or formation boundary, permits recognition of repeated sections and offset. This and previous mapping permits delineation of regionally significant anticlines, synclines, and faults, some which of have throws of more than 30 meters. Our analysis of recent aeromagnetic data (Bracken and Nicholson, 2000) leads to a better understanding of folds and faults recognized in outcrop and permits extrapolation of some of the faults to the east at least 60 km. The large, broad folds mapped by previous workers were based on detailed examination of mineral exploration boreholes and outcrops. Many of the structures correlate with basement linear features defined from the aeromagnetic data. Some of the folds, such as the Allamakee Anticline, may be related to readjustments along Keweenawan and older structural features (such as the Belle Plaine Fault and equivalent structures). Other east-west features, notably the Meekers Grove Anticline, are coincident with aeromagnetic linears at depth. These linear features are probably faults or faults with coincident dikes and probably define the north tectonic edge of the Illinois Basin. Regional map analysis suggests a steepening of dip of the Paleozoic rock units southward into the Illinois Basin along these regional deep basement trends, from a regional dip of less than 10 feet per mile to over 20 feet per mile. The large, quiet magnetic areas in western Grant County and else where in southern Wisconsin may reflect Wolf River-age plutons within the basement because the signatures are circular and apparently undeformed. Wolf River-aged material has been drilled along the state line between Wisconsin and Illinois (Coates, and others, 1983). Some of the linear anomalies defined from aeromagnetic data are coincident with positive linear gravity anomalies (Geister and Ervin, this meeting) and are probably wide, mafic dikes. The location of the plutons and faults probably influenced sedimentation patterns during the early Paleozoic by localizing the large reef/carbonate bank deposits of Middle Ordovician (Ludvigson and others, 1983). It is commonly thought that deep brines from the Illinois Basin gave rise to the hydrothermal solutions responsible for mineralization (Bethke, 1986). Localization of the 59 �zinc-lead mineralization along small faults and folds in mine workings is well documented from detailed mine mapping; however, this mineralization does not appear to be related to the deeper, more extensive basement structures. Heyl and others (1970) concluded that the broad-scale folds and faults were responsible for the tectonic framework, but the structures controlling ore deposition were developed by solution and slumping during the mineralization stages. We propose that the broader tectonic elements at the periphery of the Illinois Basin controlled ascent of the hydrothermal brines and therefore distribution of regional mineralization. The rapid cooling of those ascending brines along fractures resulted in the mineral concentrations. In this model it is the details of depth of burial of individual geologic units, their uplift and cooling history, and timing of transit of the hydrothermal brines, that are important in mineralization rather than host-rock lithology and local structure. Bethke, C.M., 1986, Hydrologic constraints on the genesis of the Upper Mississippi Valley mineral district from Illinois Basin brines: Economic Geology, v. 81, p. 233-249. Bracken, R.E., and Nicholson, S.W., 2000, Aeromagnetic Surveying in Wisconsn 1998-99: Digital Data Files: U.S. Geological Survey Open-File Report 99-527. Coates, M.S., Haimson, B.C., Hinze, W.J., and Van-Schmus, W.R., 1983, Introduction to the Illinois Deep Hole Project: Journal of Geophysical Research. B, v 88, no. 9, p. 7267-7285. Heyl, A.V., Broughton, W.A., and West, W.S., 1970 (1st edition), Geology of the Upper Mississippi Valley Base-Metal District, Wisconsin Geological and Natural History Survey [3Td Information Circular 16, 45 p. (some sections revised by M.G. Mudrey, Jr. in 1978 edition]). Ludvigson, G.A., Bunker, B.J., Witzke, B.J., and Garvin, P.L, 1983, A burial diagenetic model for the emplacement of zinc-lead sulfide ores in the Upper Mississippi Valley, USA: in Kisvarsanyi, G., Grant, S.K., Pratt, W.P., and Koenig, J.W., eds. International conference on mississippi valley type lead-zinc deposits (proceedings volume): University of Missouri Rolla, Rolla, MO, p. 497-5 15. 60 �___ PRELIMINARY ANALYSIS OF AEROMAGNETIC DATA IN SOUTHERN WISCONSIN: THE ROLE OF PRECA1'LBRIAN BASEMENT IN PALEOZOIC EVOLUTION MUDREY, M.G. Jr., Wisconsin Geological and Natural History Survey, 3817 Mineral Point Rd., Madison, WI 53705, mgmudreyfacstaff.wisc.edu BROWN, B.A., Wisconsin Geological and Natural History Survey, 3817 Mineral Point Rd., Madison, WI 53705, babrown1@facstaff.wisc.edu DANIELS, David L., U.S. Geological Survey, MS954 National Center, Reston, VA 20192, dave@usgs.gov The new aeromagnetic map of Wisconsin was the result of digitally blending the data from 22 surveys flown between 1948 and 1999. The most recent survey (74,000 line-kilometers), acquired by the U.S. Geological Survey, covers much of southern Wisconsin. The flight line data for four surveys acquired by the U.S.Geological Survey during the past 12 years have been released on CD-ROMs. These data were added to earlier U.S.Geological Survey surveys and 4 surveys acquired by Wisconsin Geological and Natural History Survey. Flight lines are 800m apart or less for 95% of the state, giving the aeromagnetic map nearly uniform specifications. All surveys were either flown at or continued to an elevation of 305m above terrain prior to assembling into a state grid. The data interval of the grid is 250 m. In this presentation, we show a preliminary analysis of the aeromagnetic data south of 4350, for which there is little Precambrian information either from outcrop or cuttings from deep boreholes. The resulting aeromagnetic map of southern Wisconsin illustrates the structure of the Precambrian rock underlying Paleozoic and Pleistocene cover. The pattern generally represents a complex Precambrian terrane that may include middle Proterozoic granite-green stone terrace containing small, circular anomalies related to the Wolf River batholith. The dominant Precambrian bedrock in eastern Wisconsin is quartzite of the Baraboo type. This unit is generally magnetically transparent; as a result, the magnetic signature originates from rock of the basement to the quartzite. In places, notably Fond du Lac County, folding within some units in the quartzite sequence is evident and suggests interbedded slate and iron formation. Other basement features include well defined faults in the Precambrian, some of which are clearly of Paleozoic age. In eastern Wisconsin the Waukesha and related faults define a basement terrace boundary, and in southern Wisconsin the Beloit and other faults define the northern edge of the Illinois Basin. The lack of relationship between the Upper Mississippi Valley Zinc-Lead District mineralization and Precambrian basement suggests a minor role for pre-Paleozoic elements during localization of the zinc-lead mineralization. 61 �MISSISSIPPI VALLEY-TYPE MINERALIZATION IN THE FOX RIVER VALLEY, EASTERN WISCONSIN (Modified from 42nd ILSG - Cable, Wisconsin, 1996) MUDREY, M.G. Jr., Wisconsin Geological and Natural History Survey, 3817 Mineral Point Rd., Madison, WI 53705, mgmudrey@facstaff.wisc.edu BROWN, B.A., Wisconsin Geological and Natural History Survey, 3817 Mineral Point Rd., Madison, WI 53705, babrownl@facstaff.wisc.edu FREIBERG, P.G., Department of Geology and Geophysics 1215 W. Dayton St., Madison, WI 53706-1692, SIMO, J.A., Department of Geology and Geophysics 1215 W. Dayton St., Madison, WI 53706-1692, simo@geology.wisc.edu Regional NURE (National Uranium Resource Evaluation Program) geochemical data suggest that anomalous concentrations of arsenic and other mineral exploration path-finder elements are present in the area southwest of Green Bay, Wisconsin where the Sinnipee, Ancell and Prairie du Chien Groups are the uppermost bedrock units. In addition, fluorine levels in groundwater have been known to be high in the Fox River valley between Green Bay and Appleton, where fluorite and other Mississippi Valley-type minerals are reported to be present in well cutting from the Sinnipee Group. Areas of significantly elevated values occupy northwestern Outagamie County and adjacent areas. A clearly defined nickel province that spatially corresponds to the arsenic province suggests that a polymetallic (As, Co, Mo, Ni, Th, V) hydrogeochemical province exists in eastern Wisconsin and may relate to documented faults (Mudrey and Bradbury, 1992). The geology differs from the better documentd five-element (Ni-Co-As-Ag-Bi) veins (Kissin, 1993) by being carbonate hosted rather than shale or volcanic hosted, but are similar in essential mineralogy and elements. Economic concentrations of Mississippi Valley-type mineralization have not been found in Wisconsin outside of Grant, Iowa, and Lafayette Counties, but geologic logs of 16 mineral exploration holes and more than 600 water wells in eastern Wisconsin contain reports of minor mineralization. In addition, more than 100 occurrences of sulfide minerals have been reported from outcrops and quarries throughout southern and eastern Wisconsin (Brown and Maass, 1992). A fairly continuous horizon of sulfide mineralization has been observed in quarries and drill core from Kenosha to Green Bay. Mineralization within this horizon consists of sulfide-cemented sandstone and sulfide infills of vugs and molds of fossil. The principal concentration of mineralization has been observed at or near the top of the St. Peter sandstone, but scattered mineralization is known throughout the Paleozoic section in this region. References: Brown, B.A. and Maass, R.S.. 1992, A reconnaissance survey of wells in eastern Wisconsin for indications of Mississippi Valley type mineralization: Wisconsin Geological and Natural History Survey Open-file Report WOFR 1992-3, 31 p. 62 �Kissin, S.A., 1993, Five-element Ni-Co-As-Ag-Bi) Veins: in P.A. Sheahan and M.E. Cheny, Ore Deposit Models, Volume II, Geoscience Canada Reprint Series,V. 6, p. 87-98. Mudrey, M.G., Jr., and Bradbury, K.R., 1992, Evaluation of NURE hydrogeochemical data for use in Wisconsin groundwater studies: Wisconsin Geological and Natural Histoly Survey Open-file Report WOFR 93-2, 61 p., 1 computer diskette. Mudrey, M.G., Jr., Brown, B.A., Freibeg, P.O., and Simo, J.A, 19%, Mississippi ValleyType Mineralization in the Fox River Valley, Eastern Wisconsin (abs.): Institute on Lake Superior Geology Proceedings, 42nd Aimual Meeting, Cable, WI, 1996, v. 42, part 1, p. 38-39 63 �OVERVIEW OF FIELD TRIP 2: UPPER MISSISSIPPI VALLEY - ZINC-LEAD DISTRICT, WISCONSIN MUDREY, M.G., Jr., Wisconsin Geological and Natural History Survey, 3817 Mineral Point Road, Madison WI 535705, mgmudreyfacstaff.wisc.edu HUNT, T.C., Director of the Reclamation Program, School of Agriculture, University of Wisconsin - Platteville, Platteville, WI 53818, huntt@am.uwplatt.edu CZECHANSKI, M.L., Wisconsin Geological and Natural History Survey, 3817 Mineral Point Road, Madison WI 535705, mlczecha@facstaff.wisc.edu First recovery of galena in the Driftless Region of Wisconsin, Illinois, Iowa and Minnesota was by native Americans for ornamentation about 1000 C.E. By 1690 Europeans recognized the lead deposits and began mining in what is now known as the Upper Mississippi Valley Zinc-Lead District. In the early 19th century, this was the premier lead mining district in North America. Numerous immigrant groups and developers were attracted to the area and the resulting population in flux played a major role in the eventual formation of the states of Illinois, Iowa, and Wisconsin. Initial mineral development (late 1 8111 and early 1 9t11 centuries) consisted of collecting surface occunences of galena and digging down until the excavations became unstable (badger holes). Deeper mining techniques were initiated, but were hampered by inadequate dewatering techniques below the water table. By 1850 lead production had peaked. Metallurgical developments and techniques to dewater mines led to significant zinc production (zinc ore became abundant with depth), initially from smithsonite (dry bone) and since 1900 from spha!erite. Peak production years were 1917 and 1952. The last mine, Eagle-Picher's Shullsburg Mine, ceased production in 1978. Since 1900, the U.S. Bureau of Mines, the U.S. Geological Survey, and the Wisconsin Geological and Natural History Survey have collected large amounts of information from the area including, detailed mine maps, drillhole locations, assay data, and geologic logs. This information is summarized in detailed geologic maps. Al Hey! and others (1959) summarized information up to 1950s in U.S. Geo!ogica! Survey Professiona! Paper 309. Hey! and others (1970) prepared a shorter summary of Professional Paper 309 for the Geological Society of America Meeting in Milwaukee in 1970. In addition, a large number of detailed geologic maps were prepared for southwestern Wisconsin and adjoining Illinois and Iowa. This area is the type-locality of the Upper Mississippi Valley Zinc-Lead mineralization. Warm (135 to 180 °C) mineral-bearing saline bnnes from the south (Illinois Basin) and southwest (Iowa Basin) are responsible for the mineralization. The bulk of the mineralization occuned in Middle Ordovician strata during the PermianlPennsylvania. Dominant mineralization occurred in the Decorah shaly dolomite, with significant quantities of mineralization in the over- and under-lying dolomite strata. Deeper mineralization has not been significantly tested. Local ore controls include minor folds and faults. Mineralization occurs as replacement and breccia filling in vertical fractures and crevices (gash veins), 64 �dipping fracture planes (pitches) and horizontal bedding planes (flats). Gash veins not uncommonly occur directly over the pitch and flat structures. There is a general vertical ore zonation with lead in the vertical veins and zinc concentrated in pitches and flats. Replacement and solution breccia are common, leading to some bonanza-type mineralization. Wall rock alteration is minimal, suggesting no widespread thermal events, but rather joint and fracture localization. The field trip will examine the Potosi Hill Ordovician geologic exposure, where the entire section from the Ancell Group through the Sinnipee Group is exposed; the Platteville Mining Museum and Bevan Mine which illustrates the regional geology and historical mineral development techniques; Pendarvis State Historical Site which captures the 1 830s spirit of mining;; and modem reclamation at the Shullsburg site, location of the last producing zinc mine in Wisconsin (1978). Heyl, A.V., Agnew, A.F., Lyons, E.J., and Behre, C.H., Jr., 1959, The Geology of the Upper Mississippi Valley Zinc-Lead District: U.S. Geological Survey Professional Paper 309, 310 p. Heyl, A.V., Broughton, W.A., and West, W.S., 1970 (1st edition), Geology of the Upper Mississippi Valley Base-Metal District, Wisconsin Geological and Natural History Survey Circular 16, 45 p. (some sections revised by M.G. Mudrey, Jr. in 1978 (3"' edition)) 65 �RECOGNITION OF POST-1630 MA FLUID-DRIVEN METAMORPHISM IN BARABOO INTERVAL QUARTZITES BY MEANS OF LASER PROBE 40Ar/39Ar GEOCHRONOLOGY NAYMARK, ALISSA, SINGER, BRAD and MEDARIS, L.G., Jr., Deptartment of Geology and Geophysics, Univ. of Wisconsin-Madison, 53706, anaymark@students.wisc.edu, bsinger@geology.wisc.edu, medaris @geology.wisc.edu. The southern Lake Superior region experienced many transformations during Proterozoic time Quartzites of the Baraboo interval, most notably the Baraboo, Barron, and Sioux, are known to have been deposited between —1710 Ma and 1630 Ma on 1750 Ma and older igneous and metamorphic basement. Quartzites south of Hoim et al.'s (1998) tectonic front were folded at —1630 Ma and, presumably, subjected to low-grade metamorphism at the same time. The present investigation, using CO2 laser probe 40Ar/39Ar incremental-heating methods, was undertaken to evaluate the timing and extent of low-grade metamorphism in Baraboo interval sedimentary rocks. Surprisingly, little evidence for 1630 Ma metamorphism was found in the analyzed samples; instead, a strong signature of post-1630 Ma hydrothermal activity was discovered in the Baraboo and Sioux quartzites. The Baraboo Ranke: Age spectra for three muscovite samples are discordant in the low temperature gas steps, but gave similar plateau ages. The initial 30% of gas released typically gave apparent ages beginning at —900 Ma in the vein material, and —1200 Ma in the samples from Baxter Hollow, rising to concordant plateau ages for the last 70% of the gas released. Muscovite from hydrothermal muscovite-pyrophyllite-diaspore veins in the base of the Baraboo Quartzite yielded a plateau age of 1467±10 Ma (±2) [Figure 1A]. Samples of muscovite from metasaprolite at Baxter Hollow yielded plateau ages of 1456± 11 and 1461± 12 Ma [Figure 1B]. These data provide the first evidence that hydrothermal metamorphism coeval with the Wolf River Batholith affected rocks in the Baraboo Range. We propose that this hydrothermal activity was due to large-scale movement of fluids through the crust, driven by heat provided by Wolf River granitic magmatism. The Denzer diorite is a member of the —1750 Ma igneous suite underlying the Baraboo Quartzite. It preserves an igneous texture, but was weakly recrystallized, presumably at 1630 Ma, with plagioclase partly replaced by albite and epidote, biotite altered to chlorite, and hornblende altered to actinolite, cumrningtonite, and chlorite. Biotite from the Denzer diorite yielded a plateau age of 1746±12 Ma [Figure 1D] that may reflect time since crystallization. In contrast, two samples of hornblende with intergrowths of actinolite, cummingtonite, and chlorite, yielded ages of 1596±16 and 1427± 15 Ma, which represent partial and complete Ar resetting of what may have been a 1630 Ma metamorphic assemblage. Sioux Ouartzite: Numerous samples of fine-grained metasedimentary rocks (pipestone) were collected from Pipestone National Monument, SE Minnesota. They were analyzed optically and via electron microprobe, X-ray diffraction, and X-ray fluorescence to determine their mineralogical and chemical compositions. Most samples contain the assemblage: muscovite-pyrophyllite-diaspore, similar to pipestone and hydrothermal veins at Baraboo. Owing to the fine grain size (—20 pm), less than 0.0 1mg whole rock samples were prepared from the SiOux pipestone based on X-ray diffraction patterns indicating that muscovite was the only potassium bearing phase present. The samples with K20 greater than 4.0 wt. % and more than 35% modal muscovite were chosen for the whole rock 40Ar/39Ar experiments. The plateau ages are slightly discordant at low and high temperature. However, 80% of the gas gave plateau ages of 1370±10 and 1268±10 Ma [Figure 1C], suggesting that post-1460 Ma hydrothermal activity affected the Sioux Quartzite. The geological significance of these ages from Sioux pipestone remains unclear, and the 100 million year difference in age between two samples from the same stratigraphic level is problematic. A possible explanation is differential loss of argon via diffusion from multiple small domains within the submicroscopic mica. The Barron Quartzite: The Barron Quartzite, which is located north of Holm et al.'s (1998) inferred tectonic front, was unaffected by 1630 Ma folding and metamorphism, and consists 66 �. predominately of quartz, kaolinite, and hematite. Although muscovite is rare in the Barron sedimentary rocks, t was found immediately beitw the Barron Quartzite in a vein, which cuts metatonalite basement. Both the vein and metatonalite are now saprolites, having been weathered in Proterozoic time, and the muscovite is partly replaced by kaolinite. The muscovite yields a plateau age of 1808±14 Ma, demonstrating that the Barron Quartzite and underlying basement were not affected by 1630 Ma folding and metamorphism, or by 1460 Ma hydrothermal activity. Conclusions: "°Ar/39Ar analyses of Baraboo and Sioux samples that were affected by Kmetasomatism, including Baraboo metasaprolite and hydrothermal veins and Sioux pipestone, revealed post-1630 Ma hydrothermal activity in the southern Lake Superior region. Hydrothermal fluids attending Wolf River magmatism exploited the nonconformity separating quartzites from underlying plutonic and metamorphic rocks. The muscovite 40Ar/39Ar plateau ages most likely record low temperature crystallization (—300CC) assemblages in metasaprolite, hydrothermal veins, and pipestone. Further investigation will be necessary to delineate the scale of this potentially regional fluid flow in the crust. Reference: HoIm, D., D. Schneider, and C. D. Coath. (1998) Age and deformation of Early Proterozoic quartzites in the southern Lake Superior region: Implications for extent of foreland deformation during final assembly of Laurentia. Geology, v. 26, p. 907-9 10. A 2000- B I I I I 2000 OOBOWIa muscovite vein 1467.14 ± 10.55 Ma . 96BHIA Baxter Hollow muscovite 1461.23 ± 11.79 Ma and 1455.93± 11.45 Ma • 1600 : 1600: 4 120O- 1200 , 8O0 800- 400- 400- I I I 20 40 60 C I 80 , 0 iC 0 I 0 uuu. D I OOPNMOI muscovite whole rock 1370.42± 10.30 Ma 20 40 I 60 I 80 10 0 • 1600- 1600- ,1200- OODDOI Denzer Diorite biotite 1742.02±11.91 Ma 1200 I: OOPNMO3 muscovite whole rock 1268.10± 10.63 Ma 800- 400 0 I I I I 20 40 60 80 100 0 20 40 60 80 100 Cumulative 39Ar released % Cumulative 39Ar released % Figure 1: Age spectra discussed in text. Weighted mean plateau ages are reported with 2 errors. 67 �MINERALOGICAL VARIATIONS IN IRON-FORMATION IN THE THERMAL METAMORPHIC AUREOLE OF A DIABASE DIKE NEMITZ, Michael B., and LARSON, Phillip C., Department of Geological Sciences, University of Minnesota, Duluth, MN 55812 The Biwabik Iron-formation in the National Steel Pellet Company Mine near Keewatin, Minnesota is cut by a series of diabase dikes. It has previously been empirically observed that iron-formation adjacent to these dikes is characterized by enhanced magnetite weight recovery, increased silica liberation indices, and increased oxidation reflected as elevated Fe3!Fe2 ratios. Granular cherty iron-formation samples were collected in two transects perpendicular to the contact of a 5-rn thick diabase dike. The transects extended 25-rn along the strike of the ironWhole-rock geochemical analyses, x-ray diffractometry, and reflected- and formation. transmitted-light polarizing microscopy were used to assess the geochemical, mineralogical, and textural variations in iron-formation adjacent to the dikes. Microscopy indicates an increase in the total amount of primary, euhedral magnetite, hematite, and total Fe-oxide proximal to the dike. The total Fe-oxide content appears to increase in an exponential fashion. This trend is reflected in the whole-rock Fe content. Magnetite occurs in all samples as primary euhedral crystals. Hematite occurs in a number of forms: euhedral to subhedral pseudomorphs after magnetite (martite), as inclusions in the lattice of euhedral magnetite, or as fine grained aggregates. Previous to iron-formation oxidation, a hydrothermal alteration event was focused along the dike margins. Alteration leached Mg, Ca, and Na from both diabase and iron-formation. This event is reflected in the iron-formation whole-rock Mg content, which show that Mg has essentially been removed in the 5-m zone proximal to the contact. Carbonate, and to a lesser extent Fe-silicate minerals have essentially been removed in the 10-rn zone proximal to the dike contact. Conversely, void space is most abundant in this same zone. This suggests void space has been created at the expense of carbonate and silicate phases. The increase in void space also correlates with the increase in hematite proximal to the This suggests that the oxidation of Fe-oxides to hematite may be related to increased porosity and permeability of iron-formation due to void space. Increased porosity allowed dike. oxidizing meteoric waters to circulate deeper along the dike margins. This study demonstrates that thermal metamorphism of iron-formation by diabase dikes has caused an increase in Fe-oxide content, both magnetite and hematite, thus resulting in increased magnetite weight recovery. However, the increase in void space due to alteration has allowed increased circulation of meteoric waters, resulting in oxidation of iron-formation and elevated hematite content relative to magnetite. 68 �PRELIMINARY LAVA FLOW MORPHOLOGY STUDIES AT THE FIVE MILE LAKE VMS PROSPECT, ARCHEAN VERMILION DISTRICT, NE MINNESOTA: IMPLICATIONS FOR VOLCANIC PROCESSES, VOLCANIC PALEOENVIRONMENTS, AND VMS EXPLORATION TRENT T. NEWKIRK, GEORGE J. HUDAK Department of Geology, University of Wisconsin Oshkosh, Oshkosh, WI 54901 STEVEN A. HAUCK Natural Resources Research Institute, University of Minnesota-Duluth, Duluth, MN 55811 As part of a two-year grant from the Minerals Coordinating Committee (MCC, State of Minnesota), we have undertaken a field-based, detailed investigation of the pillow lava morphology at the Five Mile Lake volcanic-associated massive sulfide (VMS) prospect, which is located approximately 15 miles southwest of Ely, Minnesota. This prospect is situated within a greenschist facies metamorphosed assemblage of Archean subaqueous, primarily mafic metavolcanic and metasedimentary rocks. These rocks lie within the Lower Member of the Late Archean Ely Greenstone (Peterson and ursa, 1999). Historically, several mineral exploration programs have been conducted in the Lower Member of the Ely Greenstone to evaluate its potential for VMS-style base metal mineralization. One of the most significant exploration programs to date was completed in 1995, when Teck Exploration Ltd. intersected stringer Zn-Cu mineralization in several diamond drill holes at the Five Mile Lake prospect. Cas (1992) and Gibson et al. (1999) and have emphasized the importance to mineral exploration programs of determining the volcanic environments associated with VMS mineralization. Gibson et al. (1999) have noted that mapping the orientation of synvolcanic dikes and sills is perhaps one of the most effective means to identify synvolcanic fault zones in lava flow dominated volcanic settings. This mapping is important because these structures not only dictate the location of volcanic vent sites, but also commonly control the locations of hydrothermal discharge sites responsible for making VMS deposits. Unfortunately, the generally small size of synvolcanic dikes and sills relative to their volcanic products commonly makes them difficult to recognize, especially in ancient volcanic sequences that are often plagued by a general lack of outcrop. Thus, detailed facies mapping in volcanic sequences is also an essential part of determining vent proximal volcanic environments. Studies of modern subaqueous mafic lava flows indicate that flow morphology has a direct relationship to effusion rate, cooling rate, and the slope upon which the lavas are erupted (Kennish and Lutz, 1998). In areas with relative fast effusion rates, sheet flows commonly occur in vent proximal environments, and grade laterally into pillow lavas farther from the volcanic vent. Slow effusion rates favor the immediate development of pillow lavas. It is interesting to note that several studies (Ballard and Moore, 1977; Ballard et al., 1981; Hekininan, 1984; Hekinian et al., 1989) have found that the glassy margins on vent proximal sheet flows tend to be thicker than the glassy margins on more distal, pillow lavas formed from the same eruption. This occurs because pillow lavas generally contain more crystals or crystal nuclei that inhibit the formation of their glassy outer margins (Kennish and Lutz, 1998). Therefore, the thickness of the glassy margins on these lava flows is also a general indicator of proximity to the volcanic vent. We have undertaken detailed mapping (1:120 scale to 1:5000 scale) of the physical characteristics of the extremely well-preserved, relatively undefonned pillow lavas at the Five Mile Lake prospect. We have measured various features of these pillows, including pillow shape, pillow horizontal dimensions, pillow vertical dimensions, pillow vesicularity, pillow selvedge characteristics, and the thicknesses of chlorite-rich, formerly glassy pillow margins. The relatively high vesicularity of these 69 �pillows (commonly between 10% and 15%), as well as the local presence of multiple pillow selvedges suggests that these flows were formed in a relatively shallow (<1 km) subaqueous environment. Our detailed mapping has also allowed us to identify several shallow mafic dikes that can be seen undergoing a vertical, then lateral transformation into pillow lavas. These regions represent the volcanic vent sites from which these pillow lavas issued. In several vent-proximal locations, chert-rich exhalite horizons (up to 1 meter thick) containing traces to several percent pyrite, sphalerite, and chalcopyrite are also present. Thus, our results support the relationships between proximal volcanic environments and mineralization in lava flow dominated sequences indicated by Gibson et al. (1999). Of particular interest are the results of our measurements of the thickness of the formerly glassy margins surrounding the pillows at the prospect. We have found that the formerly glassy pillow margins are clearly thicker (>4.5 cm thick) at these vent proximal locations than they are at locations that appear to be more distal to volcanic vents (where they are generally 2cm or less in thickness). Our results suggest that in pillow-dominated sequences, the thickness of the glassy margin surrounding pillow margins may be an accurate indicator of proximity to volcanic vents. This has significant implications for mineral exploration, as this measurement can be easily and quickly completed during field mapping, and may provide an effective means to identify regions within monotonous pillow sequences that are more likely to contain VMS mineralization. References Ballard, R. D., and Moore, J. G., 1977. Photographic Atlas of the Mid-Atlantic Ridge Rift Valley: Springer-Verlag, Berlin, 114 p. Ballard, R. D., Francheteau, J., Juteau, T., Rangin, C., and Normark, W.,1981. East Pacific Rise at 21°N: the volcanic, tectonic and hydrothermal processes of the central axis: Earth and Planetary Science Letters, v. 55, p. 1-10. Cas, R. A. F., 1992. Submarine volcanism: eruptions styles, products, and relevance to understanding the host rock successions to volcanic-hosted massive sulphide deposits: Economic Geology, v. 87., p. 5 11-541. Gibson, H. L., Morton, R. L., and Hudak, G. J., 1999. Submarine volcanic processes, deposits, and environments favorable for the location of volcanic-associated massive sulfide deposits: Reviews in Economic Geology, v. 8, p. 13-5 1. Hekinian, R., 1984. Undersea Volcanoes: Scientific American, v. 251, p. 46-55. Hekinian, R., Thompson, G., and Bideau, D., 1989. Axial and off-axial heterogeneity of basaltic rocks from the East Pacific Rise at 12°35'N — 12°5 1 'N and 1 1°26'N — I l°30'N: Journal of Geophysical Research, v. 94, p. 17437-17463. Kennish, M. J., and Lutz, R. A., 1998. Morphology and distribution of lava flows on mid-ocean ridges: a review: Earth Science Reviews, v. 43, p. 63-90. Peterson, D. M., and Jirsa, M. A., 1999. Bedrock Geological Map and Mineral Exploration Data, Western Vermilion District, St. Louis and Lake Counties, Northeastern Minnesota. 70 �A NEW LOOK AT THE 1.1 GA CHENGWATANA VOLCANICS IN THE ST. CROIX HORST, MINNESOTA AND WISCONSIN Nicholson, S.W., U.S.Geological Survey, MS 954, Reston, VA 20192; Boerboom, T., Minnesota Geological Survey, St. Paul, MN 55114; Cannon, W.F., U.S.Geological Survey, MS 954, Reston, VA 20192; Wirth, K., Macalester College, St. Paul, MN 55105; and Isachsen, C.E., University of Arizona, Tucson, AZ 85721 The 1.1 Ga Midcontinent rift system (MRS) hosts several classes of hydrothermal and magmatic mineral deposits (Nicholson et al, 1992). Recent speculation about the presence of additional magmatic mineral deposits (e.g., "Voisey's Bay"-type Ni-Cu: Schulz et al., 1998) has focused attention on the chemical compositions of rift-related basalts and the identification of central volcanic complexes as exploration tools. The St. Croix horst contains the most southerly exposure of volcanic and sedimentary rocks related to the MRS, but until now, sufficient chemical, age, and geophysical data have not been available to characterize adequately the nature of the volcanic rocks (Nicholson et al., 1997) and their relationship to the regional chemical stratigraphy established for the MRS. North of the St. Croix horst rift-related rocks are exposed around the margins of Lake Superior and detailed stratigraphic sections are well established. Outcrops within the St. Croix horst are sparse: the volcanic rocks are nearly all subaerial basalt flows and were previously assigned to the Chengwatana Volcanics. Recently Cannon et al. (2001) used new detailed aeromagnetic imaging and age determinations to subdivide the former Chengwatana Volcanics into three units, the Minong Volcanics, the Clam Falls Volcanics, and a newly redefined Chengwatana Volcanics (Fig. 1). More than 200 chemical analyses are now available for volcanic rocks in the St. Croix horst. When compared to the regional chemical stratigraphy recognized previously around western Lake Superior (Nicholson et al., 1997), the three new volcanic units appear to be related as follows. The youngest unit, the Minong Volcanics, is most similar to the Portage Lake Volcanics (1096-1094 Ma). Both are dominated by low- TiO2 (less than about 2.0 wt. % Ti02 ) basalts with low abundances of incompatible trace elements. Like the Portage Lake Volcanics, the Minong Volcanics contain few rhyolites, but a rhyolite flow near the base of the section has been dated at about 1094 Ma (Lake Nelson rhyolite; Zartman et al., 1997), an age comparable to the upper Portage Lake Volcanics. Basalts with depleted compositions similar to N-MORB occur as flows near the top of the Minong Volcanics and as dikes in the upper Portage Lake Volcanics. The Clam Falls Volcanics unconformably underlie the Minong Volcanics. It is also dominantly lowTi02 basalts, but high-Ti02 basalts (more than about 2.5 wt % Ti02; increased abundances of incompatible trace elements) are more common in this unit than in the overlying unit. The high- TiO2 basalts are similar in composition to high- Ti02 basalts in the Portage Lake Volcanics and the underlying upper Kallander Creek Volcanics (dated at 1098 Ma) to the northeast. Although chemically similar, the metamorphic grade of the Clam Falls Volcanics is considerably higher than the Minong, Portage Lake, or Kallander Creek Volcanics, suggesting that this unit represents exhumation of a more deeply buried portion of the rift (Wirth et al., 1997). A rhyolite flow at the base of the Clam Falls Volcanics yields ages between 1100 and 1102 Ma (unpub. data: K.R. Wirth). The oldest unit, the newly redefined Chengwatana Volcanics now confined to the volcanic rocks between the Pine and Douglas faults, is dominated by high- Ti02 basalts with accompanying intermediate and felsic volcanic rocks. This association of high-hO2 basalts with intermediate and felsic volcanic rocks has been postulated elsewhere in the rift to be related to central volcanic complexes, sites of prolonged shallow magma chamber development and accompanying volcanism. The Amnicon gabbroic and granophyric intrusive complex southeast of Duluth cuts the base of the redefined Chengwatana Volcanics and most likely represents the magma chamber for a central volcanic complex. The extensive granophyre in the Amnicon pluton is identical chemically to an overlying rhyolite flow. This rhyolite flow has a preliminary date of about 1106 Ma (unpub. data: C.E. Isachsen). Southwest of the Amnicon pluton the Chengwatana Volcanics include more low- hO2 basalts as the influence of the localized Amnicon magmatic system diminishes. In conclusion, the high- Ti02 basalts and related intermediate and felsic rocks of the redefined Chengwatana Volcanics in the St. Croix horst were probably erupted from localized magmatic sources from about 1107 to about 1102 Ma. This was followed by outpourings of voluminous low-Ti02 flood basalts characteristic of the main stage of nfting of the MRS after about 1102 Ma, now represented in the St. Croix 71 �horst by the Clam Falls and Minong Volcanics. Central volcanic complexes in the St. Croix horst, such as the Amnicon complex, may be potential exploration targets for Cu-Ni sulfide mineralization, if further study can show the availability of a source of sufficient sulfur to produce segregation of Cu-Ni+PGE metals. References: Cannon, W.F., Daniels, D.L., Nicholson, S.W., Phillips, J., Woodruff, L.G., Chandler, Va!, Morey, G.B., Wirth, K.R., and Mudrey, MG., Jr., 2001, New map reveals origin and geology of North America Midcontinent rift: EOS, v. 82, no.8, pp. 97-101. Davis, D.W., and Green, J.C., 1997, Geochronology of the North American Midcontment rift in western Lake Superior and implications for its geodynamic evolution: Canadian Journal of Earth Sciences, v. 34, pp. 476-488. Davis, D.W., and Paces, J.B., 1990, Time resolution of geologic events on the Keweenawan Peninsula and implications for development of the Midcontinent rift system: Earth and Planetary Science Letters, v. 97, pp. 54-64. Nicholson, S.W., Cannon, W.F., and Schulz, K.J., 1992, Metallogeny of the Midcontinent rift system of North America: Precambrian Research, v., 58, pp. 355-386. Nicholson, SW., Shirey, S.B., Schulz, K.J., and Green, J.C., 1997, Rift-wide correlation of 1.1 Ga Midcontinent rift system basalts: implications for multiple mantle sources during rift development: Canadian Journal of Earth Sciences, v. 34, pp. 504-520. Schulz, K.J., Cannon, W.F., Nicholson, S.W., and Woodruff, L.G., 1998, Is there a "Voisey's Bay" —type Ni-Cu sulfide deposit in the Midcontinent rift system in the Lake Superior region?: Mining Engineering, v. 50, pp. 57-62. Wirth, K.R., Vervoort, J.D., and Naiman, Z. J., 1997, The Chengwatana Volcanics, Wisconsin and Minnesota: petrogenesis of the southernmost volcanic rocks exposed in the Midcontinent rift: Canadian Journal of Earth Sciences, v. 34, pp. 536-548. Zartman, R.E., Nicholson, SW., Cannon, W.F., and Morey, G.B., 1997, U-Th-Pb zircon ages of some Keweenawan Supergroup rocks from the south shore of Lake Superior: Canadian Journal of Earth Sciences, v. 34, pp. 549-561. Upper Michigan and North-Central Wisconsin Northwest Wisconsin Eastern Minnesota Fig.!: Stratigraphic column for Keweenawan volcanic rocks on the south shore of western Lake Superior. The U-Pb age dates are from the following sources: a, Davis and Green, 1997; b, Zartman et a!., 1977; c, Davis and Paces, 1990; d, unpublished data, K.R. Wirth; e, unpublished data, C.E. Isachsen 72 �OVERVIEW OF ARSENIC OCCURRENCES AND PROCESSES CONTROLLING ARSENIC MOBILITY IN GROUND WATER D. Kirk Nordstrom U.S. Geological Survey Boulder, CO Introduction Arsenic concentrations in ground waters can range from less than a few jtg/L to tens or even hundreds of mg/L in locally contaminated environments. Both anthropogenic and natural sources for arsenic in ground waters occur in many locations world-wide. Natural sources are causing or have caused poisoning of populations in India, Bangladesh, Chile, Argentina, Mexico, Taiwan, Mongolia, Japan, and China. Mining activities are responsible for arsenic poisoning in Thailand. Arsenic mass poisoning in Bangladesh is the largest known, affecting nearly 30 million people. The processes that enrich arsenic in minerals and in ground waters are complex but apprehensible. Sources The geochemical cycle of arsenic from magmatic-hydrothermal processes through weathering, sedimentation, and diagenesis transforms the element in a number of ways that produces an array of present-day natural sources. Probably the single most abundant mineral source of arsenic is arsenian pyrite. Pyrite is ubiquitous in the earth's crust, occurring in sedimentary, metamorphic, and igneous rocks. Arsenic has a strong affinity for the sulfur site in pyrite, substituting up to about 10 wt. % regardless of whether the origin is sedimentary or hydrothermal (Kolkar, Nordstrom, and Goldhaber, 2001). Arsenopyrite contains higher concentrations of arsenic (39-53%) but it is a much rarer mineral. Arsenopyrite and arsenian pyrite are commonly found in association with gold mineralization so that gold mining frequently releases arsenic to the environment. Other arsenic-rich minerals include orpiment, realgar, and enargite. Weathering of these minerals in oxidizing environments solubilizes arsenic as As(III) and ultimately as As(V). Arsenate, or As(V), has a strong adsorption affinity for hydrated iron oxides (Pierce and Moore, 1982) and in oxidized sediments iron oxides can be a source of soluble arsenic if they undergo reductive dissolution during early diagenesis. Geothermal springs are commonly enriched in arsenic, containing 0.1-5 mgIL dissolved arsenic (as both As(llI) and As(V)). Geothermal power plants often have to deal with proper disposal of arsenic-enriched waste waters. Anthropogenic sources of arsenic are numerous. The primary source of industrial and commercial arsenic was arsenic trioxide that was produced as a by-product of metal mining and processing, primarily from copper smelting. More than 300,000 tons of flue dust containing an average of 6.5% arsenic were piled at Anaconda, Montana before removal and disposal. Stockpiles of arsenic trioxide still exist without proper containment and are releasing soluble arsenic to ground waters. Several arsenic insecticides (copper, lead, calcium, magnesium, zinc, and sodium arsenites and arsenates), herbicides (sodium arsenite and methanearsonate, disodium methanearsonate, and cacodylic acid), dessicants (arsenic acid), wood preservatives, animal feed additives, drugs, chemical weapons, and alloys were produced for many years. Roxarsone, an organic arsenical, is still widely used today to 73 �clean parasites out from the stomachs of pigs and poultry (Garbarino et al., 2001). Transformations and Processes Arsenic in surface and ground waters occur dominantly as either arsenite, As(III), or arsenate, As(V). Reduction of arsenic occurs with the possible formation of several methylated species, the most prevalent being monomethly- and dimethylarsenic acid. Several microorganisms including species of fungi, algae, and bacteria catalyze the reduction of arsenic. Methylated arsenic is volatile and is released to the atmosphere in open systems. Oxidation of arsenic is also catalyzed by microbes and it has been demonstrated that soluble As(III) and arsenic sulfide minerals such as arsenopyrite and orpiment can be catalytically oxidized to soluble As(V). More than 25 species of arsenic-oxidizing bacteria have been identified and many more are believed to exist. In geothermal waters, the dominant form of dissolved arsenic is As(ffl) at the source of the discharge but this can be oxidized rapidly to As(V) by microbes that survive at temperatures of 50-95°C. Little is known about the breakdown of feed additives such as roxarsone. Although there has been research on the transformations of arsenic within humans and some other organisms, the pathways are very complicated and much remains to be learned. Water quality environments that encourage solubilization and mobility of arsenic are high pH and oxic conditions, anoxic or moderately reducing conditions with no sulfate reduction, anoxic with strongly reducing conditions with little to no sulfate present, or strongly acidic oxidizing conditions (below the normal solubility of hydrated iron oxides). Environments that encourage low arsenic mobility are moderately acidic to neutral and oxidizing conditions, or organic rich sulfate-reducing environments. References Garbarino, J.R., Rutherford, D.W., and Wershaw, R.L. (2001) Degradation of roxarsone in poultry litter. USGS Workshop on Arsenic in the Environment, Feb. 21-22, 2001, website: wwwbrr.cr.usgs.gov/Arsenic Kolkar, A., Nordstrom, D.K., and Goidhaber, Mi. (2001) Occurrence and micro-distribution of arsenic in pyrite. USGS Workshop on Arsenic in the Environment, Feb. 21-22, 2001, website: wwwbrr.cr.usgs.gov/Arsenic Pierce, M.L. and Moore, C.B. (1982) Adsorption of arsenite and arsenate on amorphous iron hydroxide. Water Res. 16, 1247-1253. 74 �PRELIMINARY EVALUATION OF HYDROTHERMAL ALTERATION MINERAL ASSEMBLAGES AND THEIR RELATIONSHIP TO VMS-STYLE MINERALIZATION IN THE FIVE MILE LAKE AREA OF THE ARCHEAN VERMILION GREENSTONE BELT, NORTHEASTERN MINNESOTA JASON D. ODETTE, GEORGE J. HUDAK, THOMAS SUSZEK Department of Geology, University of Wisconsin Oshkosh, Oshkosh, WI 54901 STEVEN A. HAUCK Natural Resources Research Institute, University of Minnesota Duluth, Duluth, MN 55811 The Minerals Coordinating Committee (MCC, State of Minnesota) recently awarded a two year grant to geologists from the Natural Resources Research Institute (NRRI), University of Minnesota — Duluth (UMD), and the University of Wisconsin Oshkosh to further characterize the geology, volcanology and metamorphosed hydrothermal alteration mineral assemblages associated with several volcanic-associated massive sulfide (VMS) prospects in the Vermilion District of northeastern Minnesota. This investigation includes detailed outcrop mapping, diamond drill core relogging, petrography, lithogeochemistry, and geophysical rock property evaluations. The Five Mile Lake prospect occurs approximately 15 miles southwest of Ely, Minnesota, and is situated within greenschist facies metamorphosed, primarily mafic Archean metavolcanic and metasedimentary rocks within the Lower Member of the Ely Greenstone Sequence of the Vermilion District. In 1994, Teck Exploration Ltd. intersected volcanic-associated massive sulfide (VMS) — style stringer Zn-Cu mineralization in three of four diamond drill holes completed at this prospect. Subsequent studies by the Minnesota Department of Natural Resources (Hudak and Morton, 1999) have suggested that mineralization at Five Mile Lake may be representative of that associated with "Noranda-type" (Morton and Franklin, 1987) Archean VMS We are currently completing a detailed investigation of the mineralogical, chemical, and spatial characteristics of the metamorphosed synvolcanic hydrothermal alteration that occurs at the Five Mile Lake VMS prospect. Our two-month long field program was completed during the summer, 2000, and consisted of two investigative phases. The first phase comprised GPS-assisted geological mapping of the entire prospect at 1:5000 scale, with more detailed mapping of surface-mineralized zones at 1:120 scale. During our mapping, special attention was paid to alteration mineral assemblages present, and their apparent relationships to locally extremely well-preserved volcanic and volcaniclastic textures. Hand samples were collected from each outcrop. When appropriate, a portable, hand-held diamond drill was used to collect samples of adjacent alteration mineral assemblages. During the second phase of our investigation, Teck Exploration Ltd.'s four diamond drill holes (SXL-1, SXL-2, SXL-3 and SXL-4) were relogged, with particular emphasis being paid to the alteration mineral assemblages and textures present. Laboratory investigations are currently being conducted. All outcrop and drill core samples have been slabbed and investigated using a binocular microscope for alteration mineral assemblages, alteration textures, and alteration paragenesis. Prepartion of one hundred ninety-seven thin sections is currently being completed, and petrographic analyses on the available thin sections are being performed. Fiftythree samples have been analyzed for major and trace elements by ALS Chemex Labs, Inc. (Sparks, NV). At the present time, we have concentrated our alteration studies on the mafic pillow lava flows and the diabase dikes that occur at the prospect. Based on our preliminary field and laboratory investigations, all pillow lavas at the prospect have undergone varying degrees of hydrothermal alteration. This is consistent with the findings of Peterson (personal communication, 2001), who indicates that the prospect resides within a semiconformable alteration zone comprising at least 3 0km2 of rocks. Three distinct hydrothermal alteration mineral assemblages occur within the pillow lavas at the prospect. The 75 �least altered assemblage (LA) comprises pillow lavas containing a mineral assemblage composed of albite + epidote + chlorite in proportions which are consistent with greenschist facies metamorphism of an original basalt or basaltic andesite lava composition. A quartz + albite + epidote ± actinolite assemblage (QAE) occurs within pillow cores, whereas a chlorite + actinolite ± epidote assemblage (CA) occurs in pillow selvedges and within the matrix to pillow breccia and pillow hyaloclastite. Locally, CA assemblage filled amygdules occur within the QAE assemblage pillow cores, and these rocks seem to have a close spatial relationship to thin (<Im thick) mineralized exhalite horizons at the prospect. Textural relationships indicate that the paragenesis of these alteration mineral assemblages is early QAE followed by later CA. Mass balance analysis of least altered pillow lavas, QAE assemblage, and CA assemblage rocks have been performed using constant Al203 and best fit (based on Al203, Ti02, Zr, Nb) isocons (Grant, 1986). Relative to least altered rocks, QAE assemblage rocks illustrate gains in Si02 and Na20 and decreases in CaO, Fe203, FeO, MgO, MnO, K20, H20, Cu and Zn. These trends may be indicative of regional silicification and spilitization from rapidly heated, downwelling, silica-saturated hydrothermal fluid. Relative to least altered rocks, CA assemblage pillows are enriched in MgO, Fe203, FeO, Zn and H20 and are depleted in Si02, K20, and CaO. These results may represent an alteration assemblage formed from the mixing of cooler, downwelling Mg-rich seawater and hotter, upwelling Fe- and Zn-rich evolved hydrothermal solutions within permeable pillow selvedges and hyaloclastite. Locally, diabase dikes are altered to epidosite. The epidosite zones comprise rounded to oval, 0.1-1.5 meter diameter patches composed of pale green epidote (locally up to 40%) + quartz ± actinolite. Preliminary x-ray diffraction analyses indicate that the major epidote mineral in these epidosite zones is clinozoisite. Least altered diabase is composed of a mineral assemblage containing quartz-clinochloreferroactinolite and albite with only minor (<5%) epidote and clinozoisite being present. Mass balance analysis of the least altered diabase and the epidosite alteration patches have also been performed using constant A1203 and best fit isocons. These analyses indicate that the epidosite zones are enriched in CaO, and simultaneously depleted in Na20, K20, MnO, Fe203, FeO, 5, Zn, and Cu relative to the least altered diabase. We initially interpret these epidosite patches as areas of locally high water:rock ratio alteration within lower semi-conformable alteration zones associated with high temperature base metal leaching. At the present time we are in the process of further characterizing the alteration mineral assemblages by means of our laboratory studies. Petrographic and x-ray analyses to further characterize the mineralogy and paragenetic sequences of the alteration mineral assemblages is just beginning, and further geochemical classification of the alteration mineral assemblages will be performed. It is believed that in the long term, further characterization of the alteration mineral assemblages at the Five Mile Lake VMS prospect will provide exploration companies with additional data that is needed to conduct efficient and effective mineral exploration programs for VMS deposits in the Vermilion District. References Grant, J. A., 1986. The isocon diagram — a simple solution to Gresen's equation for metasomatic alteration: Economic Geology, v. 81, p. 1976-1982. Hudak, G. J., and Morton, R. L., 1999. Bedrock and Glacial Drift Mapping for VMS and Lode Gold Alteration in the Vermilion — Big Fork Greenstone Belt, Part A, Discussion of Lithology, Alteration, and Geochemistry at the Five Mile Lake, Eagles Nest, and Quartz Hill Prospects: Minnesota Department of Natural Resources Project 326, 136 pages. Morton, R. L., and Franklin, J. M., 1987. Two-fold classification of Archean volcanic-associated massive sulfide deposits: Economic Geology, v. 82, p. 1057-1063. 76 �CORRELATION OF ARCHEAN ASSEMBLAGES ACROSS THE U.S.-CANADIAN BORDER: PHASE I GEOCHRONOLOGY PETERSON, Dean M. (Natural Resources Research Institute, Duluth, MN, dpetersl@nrri.umn.edu); GALLUP, Christina (University of Minnesota-Duluth, cgallupd.umn.edu); uRSA, Mark A. (Minnesota GeologicalSurvey,jirsa OOl@umn.edu); and DAVIS, Donald W. (Royal Ontario Museum, Toronto, ON, dond@rom.on.ca) Past attempts at temporal correlation of Archean stratigraphic assemblages between rocks of the geochronologically well constrained Shebandowan district of Ontario, and the Vermilion district of northeastern Minnesota (Figure 1), have invariably suffered because: I) at some scale, one greenstone belt looks pretty much like another; 2) rocks of both districts are dissected by faults having poorly known displacements; and 3) little geochronologic data exists for the Minnesota rocks. Nevertheless, detailed analyses reveal that there are significant stratigraphic and lithologic relationships in each assemblage that can be compared and contrasted. Recent U-Pb geochronology is beginning to shed light on similarities and differences between assemb1aes in the two areas. Here we report the results of two sets of U-Pb dates on zircons from the Vermilion district. - Locatkrn of dated samples A 2683±1.4 Ma Porphyry B 2722±0.9 Ma Rhyohte - '11'" S ,',S - ''/, .'.''.." '.Northern Light Gneiss Saganaga piuton" ,t,A,,, 'l Western SupedoProvtce Vermilion " wgoo, District A R B j IIIIlIU4Soudari 'Btgfork ' Shebandowan 's.Stratigraphic faong p'Lake \,.... ,E!y',' , ;)" 'SSS, ,-,5555 s'Gmnitnd truss S.ipeno r Twnisiiameg lype conglomeratic sequences - ''" 'S" Wawa Subprovlnce Vermilion Ouetico Subprovlnce Wabigoon Subprovince Graywactra Metasvcanic rocks J1111 Graywacke -KomatutcTholeidic NEWTON BELT Shebandowan GREETCHELL Cak-akaiic/thoIeitic/komatiitic Migmatite. schist. and j granite TIf1 Graywacke SOUDAN BELT SAGANAGONS ASSEMBLAGE LI Cac-aalcflhoeiiiic Figure 1. Preliminary correlation of Late Archean stratigraphic assemblages and belts through the Vermilion district, showing the location of dated samples. Inset shows the map location within the western Superior Province. Rocks of the Vermilion district are subdivided on the basis of stratigraphic and structural contrast into two distinct domains, known as the Soudan and Newton belts (Figure 1). The Soudan belt contains large, broad folds involving caic-alkalic and tholeiitic volcanic strata overlain by, and locally interdigitates with, turbiditic rocks. In contrast, the Newton belt consists of elongate, northeast trending, and mostly northward-younging volcanic and volcaniclastic sequences. Volcanic rocks of the Newton belt differ from those of the Soudan in containing locally abundant komatiitic flows and peridotitic sills (eg. the Newton Lake Formation and Deer Lake sequence). The belts are fault-bounded, and the relationship between stratigraphic units within each belt is largely conformable, though faults obscure contacts locally. In its eastern extension, the Soudan belt is continuous with the Saganagons assemblage that terminates against the Saganaga pluton and Northern Light Gneiss (Figure 1). The Newton belt extends discontinuously eastward into the Shebandowan district, and broadens to form the approximately 2720 Ma-old Greenwater and Burchell assemblages2. The Greenwater assemblage is similar to the Newton Lake Formation in younging predominantly to the north, and in containing komatiitic and tholeiitic flows, mafic and ultramafic sills, and local intermediate to felsic flows and pyroclastic rocks. The Burchell is lithologically similar and temporally identical, but youngs to the south. Intrusions in both districts vary from felsic porphyries demonstrably related to volcanism, to large plutons emplaced posttectonically. Both districts contain unconformable, Timiskaming-type sequences composed of caic-alkalic volcanic rocks, conglomerates, and finer grained sedimentary rocks. These Timiskaming-type rocks include the roughly 2690 Ma-old Shebandowan assemblage2 and some lithologic components of the Knife Lake Group in Minnesota5. Periods of generally N-S-directed compression resulted in three major deformation events that are recognized in rocks of both districts. The earliest, D1, produced broad, locally recumbent folds within the Soudan belt and major fault zones throughout the region. The affect of D1 on rocks of the Newton belt and much of the Greenwater assemblage appears to have been thrust imbrication of large crustal blocks, resulting in mainly northward stratigraphic facing. Field relationships indicate that uplift, faulting, and the deposition of Timiskaming-type sequences in local fault-bounded basins occurred late in D1 deformation. The 77 �second deformation event, D2, produced synchronous regional metamorphism, foliation development, and structures having largely dextral asymmetry. D2 has been constrained in the Vermilion district to the time period 2674 Ma to 2685 Ma', and between about 2680 and 2685 Ma in the Shebandowan2. The abundant NE- and NW-trending faults that dissect the stratigraphic assemblages are assigned to D3. The two samples from the Vermilion district were selected mainly because they had the potential to produce zircons, and their ages would constrain the timing of volcanism and D2 deformation. Zircons were separated and isotopic compositions were measured at the Royal Ontario Museum in Toronto, using methods developed by Krogh4. The samples include: A) Newton belt a weakly deformed, irregularly shaped quartz-feldspar porphyry (QFP) body intruded discordantly along a basalt - iron-formation contact within the Pac Man Pond gold prospect. Field relationships indicate that the QFP was emplaced late in D2, because it (and similar intrusions) cuts D2 shear zones but is itself weakly deformed. B) Soudan belt — quartz-phyric rhyolite lava flow in the Fivemile Lake VMS prospect. Zircons from the Newton belt sample were very light brown, small (—lig after abrasion), subhedral, prismatic, and typically cracked. The zircons from the Soudan belt sample were colorless to light brown or pink, larger (—2-3 jig after abrasion), euhedral to subhedral, prismatic, and except for rare grains having a clear core, lacked observable internal cracks. After abrasion, three zircons from each sample were chosen for dating: the results are shown in Figure 2, plotted as 2 sigma error ellipses relative to concordia. Regression and age calculation follow the method of Davis (1982). Only one zircon without cracks could be found in the Newton belt sample. This produced the datum that is closest to concordia (Figure 2). It defines a line with the other data, giving an upper concordia intercept age of 2681 +1-4 Ma. All data have 207Pb/206Pb ages that are indistinguishable within error. Under the assumption that Pb loss was recent, the average 207Pb/206Pb age of 2683.0 +1- 1.4 Ma gives a more precise value for the age of intrusion. The age of this late-syn D2 porphyry constrains the maximum age of D2 in the Vermilion district, and is similar in age to parts of the Giants Range batholith, which forms the southern margin of the Vermilion greenstone belt. Data from the Fivemile Lake rhyolite zircons plot very near concordia and have indistinguishable 207Pb/206Pb ages that average to 2722.6 ± 0.9 Ma. This is the first age ever reported for the Ely Greenstone, and is similar in age to rhyolites in the Greenwater assemblage in Shebandowan district. .528 .526 D .524 .522 .520 .518 13.4 13.5 13.6 11.6 13.7 12 12.4 12.8 207Pb/235LJ 207Pb/235u Figure 2. U-Pb isotopic compositions for A) Porphyry in the Newton Belt, and B) Rhyolite in the Soudan Belt. 7 The ca 2720 Ma volcanic rocks in the Vermilion and Shebandowan districts, as well the Manitouwadge area6' farther to the east, together with the bracketed ages for D2 deformation that are nearly identical in all three districts, implies that this terrane defines a major orogen extending more than 600 kilometers. The individual belts have been strongly attenuated by deformation and pluton emplacement, but further U-Pb dates will continue to explore the Vermilion district in this broader orogenic context. Boerboom, T.J., and Zartman, R.E., 1993, Geology, geochemistry, and geochronology of the central Giants Range batholith, northeastern Minnesota: Can. J. Earth Sci. 30:25 10-2522. 2Corfu, F., and Stott, G.M., 1998, Shebandowan greenstone belt, western Superior Province: U-Pb ages, tectonic implications, and correlations: GSA Bulletin 110:1467-1484. 3Davis, D.W., 1982. Optimum linear regression and error estimation applied to U-Pb data. Can. J. Earth Sci. 19: 2141-2149. 4Krogh, T.E., 1982, Improved accuracy of U-Pb ages by the creation of more concordant systems using an air abrasion technique. Geoch. et Cosmochim. Acta, 46: 637-649. 5iirsa, M.A., 2000, The Midway sequence: a Timiskaming-type pull-apart basin deposit in the western Wawa subprovince, Minnesota: Can J. Earth Sci., 37: 1-15. 6Zaleski, E., van Breemen, 0., and Peterson, V.L., 1999, Geological evolution of the Manitouwadge greenstone belt and WawaQuetico subprovince boundary, Superior Province, Ontario, constrained by U-Pb zircon dates of supracrustal and plutonic rocks: Can. J. Earth Sci., 36: 945-966. 7Davis, D.W., Schandi, E.S., and Wasteneys, H.A. 1994. U-Pb dating of minerals in alteration halos of Superior Province massive sulfide deposits: syngenesis vs. metamorphism. Contrib. Mineral. Petrol. 115: 427-437. 78 �MAGNETIC SURVEY NEAR WATERLOO WISCONSIN PEYCHALI*, C., KEAN', W. F., and SCHAPER2*, D., Department of Geosciences, University of Wisconsin -Milwaukee'4 Department of Geological Engineering, University of Wisconsin-Madison2. wkean@uwm.edu. (* student) The Waterloo Wisconsin area continues to provide geologic puzzles because of its diverse bedrock. The Waterloo Quartzite is considered by most as cotemporaneous with the Baraboo Quartzite. A mafic dike is known from two quarries about I mile apart along a north-south strike, and a course feldspar rich pegmatite appears within 200 meters north of the quartzite quarry in which the mafic dike is found ( Luther, 1977). The age relationship of these three rock types is still uncertain. Although, the two igneous rock types intrude the quartzite, and both are dated in the range of 1.45 -1.5 Ga.(Van Schmus Ct al. 1978, Brown, 1986), which is not necessarily the primary age. Paleomagnetic studies on the mafic dike provide a well defmed magnetic direction of Dec.=299°, Inc.-43°, N=26, Alpha 95= 13.7°, giving a paleopole at 323° E, 2° S which is interpreted as a 1 .7Ga. pole position ( Schaper and Kean, 1999). The object of this study is to better define the magnetic basement in this region in an attempt to clarify the relationship of these known rocks. A proton precession magnetometer survey covered most of the roads in the vicinity of the old Portland Quarry and the Michels Materials Quarry. A first survey covered the region at 0.1 mile spacing. Selected locations were resurveyed at 50 meter spacing , and also with a continuously reading rubidium vapor magnetometer. Finally one road section was covered at 2 meter spacing. Well construction reports, and the aeromagnetic maps of the region were examined for additional insight into the bedrock. The aeromagnetic maps show a general decreasing trend from west to east, with a 200 nT. anomaly northeast of the Michels Materials quarry, where well construction reports indicate granite. The ground magnetic survey shows a 1000 nT. negative anomaly along Highway 19 that appears to be in line with the known outcrops of the mafic dike. The negative value is consistent with the negative remanent magnetism of the mafic dike. Similar anomalies are found on the south-north section of Hubbleton Rd. which passes in front of the active quarry. We interpret these as the extension of the dike to the north east of its known outcrop. References: Brown, B.A., 1986, The Baraboo Interval in Wisconsin, Geoscience Wisconsin, vol.10, p.1-15. Luther, F. R., 1997, the Precambrian Waterloo Quartzite, Dodge and Jefferson Counties, WisconsinPetrology, structure and Industrial Use. In "Guide to Field Trips in Wisconsin and Adjacent Areas of Minnesota". M.G. Mudrey Jr. Field Trip Coordinator, Wisconsin Geological Survey, 114 pp. Schaper, D., and Kean, W., 1999, Multiple Magnetic Directions in a Proterozoic Dike near Waterloo, Wisconsin. Fall Meeting AGU, abstracts. Van Schmus, W.R., 1978, Geochronology of the Southern Wisconsin Rhyolites and Granites, Geoscience Wisconsin, vol.2, p.1 9-24. 79 �Nd and U-Pb Isotope Studies of the Syenitic Aurora Sill, Mesabi Range, Minnesota Phillips, Erin H., Macalester College, St. Paul, MN 55105; Wirth, Karl R., Geology Department, Macalester College, St. Paul, MN 55105, wirth@macalester.edu; Vervoort, J.D., and Gehrels, G.E., Dept. of Geosciences, University of Arizona, Tucson, Arizona 85721 The Aurora sill is a concordant tabular intrusion approximately 5.6 km long and 6 to 37 meters thick that occurs in the Mesabi Range north of the town of Aurora, Minnesota. The age of the sill is unknown, but it has commonly been assigned a Mesoproterozoic (Keweenawan) age because it intrudes the 1.88 Ga Biwabik Iron-Formation and also because of its resemblance to granitic complexes, or "granophyres", of the Midcontinent Rift (White, 1954). The geochemistry and petrography of the Aurora sill, however, are quite different from the Midcontinent Rift (MCR) granophyres (Phillips et al., 2000). The isotopic data presened ho indicate that the Aurora sill has a Keweenawan age and represents a unique occurrence of this rock type in this portion of the MCR. Mineralogically, the Aurora sill is composed of albite, potassium-feldspar, aegerine, fibrous amphibole, chlorite, Fe-Ti oxides, Fe sulfide, and zircon and is classified as a syenite (< 5% normative quartz or nepheline) based on both modal and normative compositions. The presence of two feldspars indicates subsolvus crystallization and high P1120. Albite is the predominant mineral in the sill and is aligned in fine-grained samples to produce a trachytic texture. Samples from the Aurora sill exhibit limited geochemical variation (Si02=54.6-60.7 wt. percent; Mg#=0.4-0.75; Y=9-19 ppm) suggesting that the intrusion has undergone relatively minor internal fractionation. A large sample from the Aurora sill yielded only a few small (60-80 jim) anhedral zircons. No crystal faces were present on any of the zircon grains but it is unknown whether this is due to fracturing during processing or resorption of the grains. Four U-Pb zircon analyses (each consisting of 3 small zircons) yield a highly discordant regression with an upper intercept of 2970 ± 257 (2; Figure 1). It is improbable that this date represents the age of the sill because it intrudes the Biwabik Iron-Formation that was deposited about 1.88 Ga(Fralick et al., 1998). Our interpretation is that the zircons grew in the Mesoproterozoic with significant inheritance from Archean basement rocks in the region. The lower intercept of 1190 ± 466 Ma indicates either zircon growth or a Pb loss event in the Mesoproterozoic that may have coincided with intrusion of the sill. Nd isotopes provide further evidence of a Keweenawan age for the Aurora sill. A slightly negative epsilon Nd value of -1.4 results when an age of 1,100 Ma is assumed for the Aurora sill (Figure 2). If older ages are used, they result in unrealistically high ENd values (ENd = +9 @ 1,800 Ma; ENd +23 @ 2,900 Ma). The Nd isotopic results corroborate a Keweenawan age (1 .1 Ga) for the sill and are consistent with the lower U-Pb zircon intercept. If the Aurora sill is Keweenawan in age, the sill would represent a relatively rare type of alkaline 0.6 magmatism in this part of the MCR. The sill is distinct from the granophyric complexes of the northwestern limb of the MCR in several respects. The granophyric 0.5 textures and modal quartz that are typical of felsic rocks of the MCR are not present in the Aurora sill. The sill is saturated to weakly undersaturated in silica and 0.4 contrasts sharply with the silica saturated granophyres of the MCR. Furthermore the Aurora sill is characterized by high total alkalis, Nb/Y, and Ce/Zr compared with felsic rocks of the MCR. The Aurora 0.3 sill also lacks the negative Nb anomalies that are 0.2 characteristic of the MCR granophyres. Although there are no known Keweenawan syenites in the vicinity of the Aurora sill, there are several alkaline intrusions in 01 the northern portion of the MCR. The Coldwell Complex and Killala Lake Complex both contain 7Pb* 1235U syenites that have been dated at 1108 ± I Ma, near the Figure 1 80 �beginning of continental rifting (Heaman and Machado, 1992). Preliminary examination of the geochemistry of these syenites displays similarities to the Aurora sill. For example, they exhibit high Nb/Y ratios and follow similar trends on many geochemical plots (e.g., Na20+K20 versus Si02) and have broadly similar ENd values to the early E Nd (T) gabbro phases from the Coldwell complex (Heaman and Machado, 1992). Unlike the Coldwell and Killala Lake complexes, the Aurora sill is not known to be associated with carbonitites. The Nd isotopic and trace-element signatures of the Aurora sill suggest that it was derived from a mantle melt that did not interact with older, evolved crustal materials. However, this Age (Ga) Figure 2 . interpretation is not fully consistent with the U-Pb zircon data which clearly indicate inheritance of older zircons. It is difficult to imagine a process whereby zircons are inherited from the extant Archean crust without that crust contributing a highly unradiogenic Nd isotopic signature (negative ENd values) to the sill. This could occur if the assimilant was of low concentration and/or near-chondritic Sm/Nd ratios, but neither is a common characteristic of zircon bearing lithologies. One possibility is that the zircons in the Aurora sill have been derived from small degrees of assimilation of Biwabik Iron-Formation or related Animikie sediments. These sediments have variable but generally less negative E values in the Mesoproterozoic (Hemming et al., 1995) and also contain Archean detrital zircons. The age of the Aurora sill is important to understanding the timing of ore formation in the Mesabi Range. In 1999, Morey proposed a conceptual model in which the high-grade ores formed in a regional ground-water system during Paleoproterozoic time (1.6-2.5 Ga). Subsequently, Graber and Strandlie (1999) argued that nearby high grade ores must have formed in Mesoproterozoic or later time, because the Aurora sill appears to have controlled ore-forming processes in nearby mines. Since a Keweenawan Aurora sill could not have had an effect on ore-formation in the Paleoproterozoic, it is not possible at this time to confirm the model described by Morey (1999). References Cited Fralick, P.W., S.A. Kissin, and D.W. Davis, 1998, The Age and Provenance of the Gunflint Lapilli Tuff. Institute on Lake Superior Geology, Proceedings and Abstracts, p. 66-67. Graber, Ronald G. and Alan J. Strandlie, 1999, Where are the Metamorphosed Natural Orebodies of the Mesabi Range? Institute on Lake Superior Geology, Proceedings and Abstracts, p. 17-19. Heaman, L.M. and Machado, N., 1992, Timing and origin of the Midcontinent rift alkaline magmatism, North America: Evidence from the CoIdwell complex. Contributions to Mineralogy and Petrology, V 110, p. 289-303. Hemming, S.R., S.M. McLennan, and G.N. Hanson, 1995, Geochemical and Nd/Pb isotopic evidence for the provenance of the Early Proterozoic Virginia Formation, Minnesota. Implications for the tectonic setting of the Animikie basin, Journal of Geology, V 103, p. 147-168. Morey, G.B., 1999, High-Grade Iron Ore Deposits of the Mesabi Range, Minnesota Product of a Continental-Scale Proterozoic Ground-Water System. Economic Geology, V 94, p. 133-142. Phillips, E.H., 2000, Petrogenesis of the Enigmatic Aurora Sill, Mesabi Range, Minnesota, Unpublished honors thesis, Macalester College, St. Paul, MN. Phillips, E.H., K.R. Wirth, and G.B. Morey, 2000, Petrogenesis of the Enigmatic Aurora Sill, Mesabi Range, Minnesota. Institute on Lake Superior Geology, Proceedings and Abstracts, p. 51-52. White, David A., 1954, The Stratigraphy and Structure of the Mesabi Range, Minnesota. Minnesota Geological Survey Bulletin 38. Minneapolis: The University of Minnesota Press, p. 63-66. 81 �Freeze/Thaw Testing of Carbonate Aggregate Sources in Wisconsin — A Status Report Daniel D. Reid, Wisconsin Department of Transportation, 3502 Kinsman BlvcL, Madison, Wisconsin 53704-2507 Delamination and deterioration of exposed pavement aggregates has been a common occurrence on highways in southern and northeastern Wisconsin, and has lead to highway maintenance problems in some areas. The principal cause of these problems is crushed stone aggregate produced from Sinnipee Group (Galena, Decorah and Platteville Formations) rock. Prior to 1999, the Wisconsin Department of Transportation (WisDOT) excluded entire formations and members of the Sinnipee Group as a way of mitigating pavement problems. A study of carbonate aggregate resources in Wisconsin, conducted jointly by WisDOT and the Wisconsin Geologic and Natural History Survey (WGNHS), provided a comprehensive analysis of the stratigraphy and geologic properties of Sinnipee Group aggregate resources. This study identified significant regional variability in Sinnipee Group rock, and concluded that the laboratory freeze/thaw test was the most effective method of identifying problem aggregate sources. Based on this data, WisDOT concluded that specifications excluding certain formations and members were not appropriate for uniform application across the entire state. As a result of the WisDOT/WGNHS carbonate aggregate study, WisDOT developed and implemented specifications for freeze/thaw testing of carbonate aggregate sources used in pavements and bridge decks in October 1999. These specifications mandated freeze/thaw testing in counties where Sinnipee Group rock outcrops, and set the threshold for loss at 18% by weight. Included in the specifications was a clause that allows WisDOT to waive freeze/thaw testing for existing aggregate sources determined to be in the Silurian System or Prairie du Chien Group of carbonate rocks. WisDOT has now completed over 230 independent freeze/thaw tests on carbonate aggregate source material throughout Wisconsin. To date, the results indicate that freeze/thaw testing is performing it's intended function. A decrease in pavement problems has been reported and WisDOT now has an effective method of controlling aggregates that produce excessive delamination. As an added benefit, aggregate producers are now permitted to use aggregate sources that were excluded prior to establishment of the freeze/thaw testing specification, so long as material from these sources tests under the 18% threshold. References: - AASHTO, 1996, Standard Specification for Soundness of Aggregates by Freezing and Thawing, American Association of State Highway and Transportation Officials (AASHTO) Designation T 103-91. Brown, Bruce A., 1999, Aggregate Resources of the Sinnipee Group in Eastern and Southern Wisconsin, Wisconsin Geologic and Natural History Survey Open-File Report 1999-07. Ostrom, M.E., 1967, Paleozoic Stratigraphic Nomenclature for Wisconsin, Wisconsin Geological and Natural History Survey Information Circular No. 8. 82 �___ A Metamorphosed Evaporite Sequence from the Sibley Basin Rogala, B. and Fralick, P.W., Department of Geology, Lakehead University, Thunder Bay, Ontario The Sibley Group sediments were deposited in a subsiding infracratonic basin (Fralick and Kissin, 1995), between 1339 ± 33 Ma (Franklin et aL, 1980) and 1537 +10-2 (Davis and Sutcliffe, 1984). The Group is divided into three main Formations: Pass Lake, Rossport, and Kama Hill, representing deposition in a braided fluvial-mudflatplaya environment (Cheadle, 1986). This study concentrates on a section through a lateral correlative of the cyclic facies contained in the Rossport Formation present in the Noranda drill core NI-92-5. The location of this drill hole is north f iier cored sections and outcrops of the cyclic facies and represents a more basin center environment. The cyclic facies to the south consists of alternating layers of dolomite and red shale with individual layers, in the approximately 40 m thick assemblage, varying from mm- to dm- In drill hole NI-92-5 the layering is at a similar scale, but is composed of alternations between what was first thought to be dolomite-rich and gypsum-rich scale. intervals, reflecting wet and dry seasonality in the central playa environment. SEM and XRD analysis indicate that the sequence was metamorphosed. The progression of metamorphic facies, from lower to higher T towards the diabase sill, is represented by the following reactions: 3CaMg(C03)2 + 4SiO2 +1H20 —' lMg3Si4Oio(OH)2 + 3CaCO3 + 3CO2 and 5Mg3Si4O10(OH)2 + 6CaCO3 + 45i02 —. 3Ca2Mg5Si8O22(OH)2 + 6C02 + 2H20 or 2Mg3Si4Oio(OH)2 +3CaCO3 - lCa2Mg5Si8O22(OH)2+ lCaMg(CO3)2 + 1CO2 +1H20 or 5CaMg(C03)2 + 8SiO2 + 1H2O — lCa2Mg5Si8O22(OH)2 + 3CaCO3 + 7CO2 (Winkler, 1974) Near the diabase sill pargasite, a hornblende with the composition (Na,K)01Ca2Mg4A13Si6O22(OH), is the dominant mineral. Clinochlore, a chlorite mineral with a composition of Mg5Al5Si3Oio(OH), is found throughout the metamorphic series. Both of these minerals are common in magnesian carbonate metamorphism (Pattison and Tracy, 1991). Primary layering has been masked in places by metamorphism. However, S.E.M. analysis clearly shows the mineralogical layering, reflecting variations in primary geochemical constituents between individual laminae. ICP-AES analysis also highlights the varying compositions of the sequence. CafMg ratios indicate the precipitation of gypsum in many layers. This is supported by the observation of gypsum using S.E.M.. The pargasite tends to exist in layers with differing K and Na proportions. The K and Na ions may reflect the incorporation of KCI and NaC1. Both of the minerals are found in S.E.M. sections taken near the middle of the sequence. 83 �Clastic input is variable between individual layers, but shows an increase at the top of the section. This increase is related to the appearance of sand sheets, which typically mark the end of the cyclic facies in the Sibley Group sediments. Clastic material becomes slightly enriched in elements denoting a mafic rock source up-section. The source material is distinctly alkalic. Alkalic material may be associated with plume activity, which would fit the infracratonic theory for the formation of the Sibley Basin. However, suitably alkalic rocks have not been found in the area. References Cheadle, B.A. 1986. Alluvial-playa sedimentation in the lower Keweenawan Sibley Group, Thunder Bay District, Ontario. Canadian Journal of Earth Sciences, 23, 527-542. Davis, D.W. and Sutcliffe, R.H. 1984. U-Pb ages from the Nipigon Plate and Northern Lake Superior. Geological Society of America Bulletin, 96, 1572-1579. Fralick, P. and Kissin, S. 1995. Mesoproterozoic basin development in central North America: implications of Sibley Group volcanism and sedimentation at Redstone Point. in: Petrology and metallogeny if volcanic and intrusive rocks of the midcontinent rift system, Proceedings of the International Geological Correlation Program, Project 336. Franklin, J.M., Mcllwaine, W.H., Poulsen, K.H. and Wanless, R.K. 1980. Stratigraphy and depositional setting of the Sibley Group, Thunder Bay District, Ontario, Canada. Canadian Journal of Earth Sciences, 17, 633-651. Pattison, D.R.M. and Tracy, R.J. 1991. Phase equilibria and thermobarometry of calcareous, ultramafic, and mafic rocks, and iron formations. In: Kerrick, D.M. (ed.), Contact Metamorphism. Reviews in Mineralogy, 26, Mineralogical Society of America. Winkler, H.G.F. 1974. Petrogenesis of Metamorphic Rocks. Springer-Verlag: New York Inc., 320 p. 84 �Roles of Fractional Crystallization and Assimilation in the Production of Midcontinent Rift Granophyres. Sandland, Travis 0., (tsandland@Macalester.edu) & Wirth, Karl R., Geology Department, Macalester College, St. Paul, MN, 55105; Vervoort, Jeff D. & Gehrels, George E., Department of Geosciences, University of Arizona, Tucson, AZ, 85721; Kennedy, Bryan C., Geology Department, Macalester College, St. Paul, MN, 55105; Harpp, Karen S., Department of Geology, Colgate University, Hamilton, N 13346 The granitic complexes of the Midcontinent Rift (MCR), commonly termed granophyres, comprise a significant portion of the Duluth Complex in northern Minnesota. They range in size from 30 to 150 km2 in surface area and are ito 2 km in thickness. They consist of basal diorite and monzodiorite and progress upward to quartz monzodiorite, granodiorite, and granite. This study focuses on the petrogenesis of four of these complexes: the Greenwood Lake, Misquah Hills, Eagle Mountain, and Pine Mountain granophyres. Miller and Vervoort (1996) identified two magmatic stages in this part of the MCR. An "early stage" from 1108-1105 Ma, and a "main stage" from 1100-1094 Ma. The four granophyre complexes addressed in this study have U-Pb zircon ages consonant with this chronology. The older granophyres include the Misquah Hills and Greenwood Lake complexes with ages of 1106±6 Ma and 1106±3 Ma (±2 sigma), respectively, and were emplaced during the early stage of the rift. The Eagle Mountain and Pine Mountain granophyres have ages of 1098±4 and 1095±4 Ma, respectively, and were emplaced during the main magmatic stage. The granophyre complexes vary widely in composition (47-76 wt. % Si02) and plot as linear Figure 1 trends on many Harker variation diagrams. The two granophyre groups (early and main stage) are indistinguishable on such plots and appear to have ci very similar major element chemistry. Incompatible trace elements (including REEs) are enriched in both groups (Fig. 1) although the early stage granophyres generally have higher concentrations than the late stage granophyres. Incompatible trace element ratios (e.g., LaISm, Gd! Yb) are similar for both groups. The early stage granophyres have initial epsilon Nd values between 20 0 and -2. In contrast, the main stage granophyres are isotopically enriched, with initial epsilon Nd Ce values between -3 and -8. The isotopic and incompatible element data suggest both fractional crystallization (FC) and La Pr Tb Ho Tm Lu Nd Sm Gd Dy Er Yb Eu assimilation fractional crystallization (AFC) processes were involved in the evolution of the granophyres. The large negative epsilon Nd values associated with the main stage granophyres indicate AFC processes and suggest contamination by an isotopically enriched source, possibly felsic Archean crustal rocks. This trend can be seen on a graph of epsilon Nd vs. La/Yb (Fig. 2). The main stage granophyres also 85 �have low Nb/Y ratios, a signature of contamination by crustal materials, whereas the Nb/Y ratios of the early stage granophyres are positively correlated with La/Sm (Fig. 3). If AFC processes were active during the formation of the early stage granophyres, the assimilant was likely limited to juvenile mafic rocks with little or no isotopic enrichment. Alternatively, the enrichment of incompatible elements in the early stage granophyres could be the result of fractional crystallization. Figure 2 Figure 3 20 2 FC AFC 10 - Early Stage. Main Stages 0 I -8 -7 I I I -6 -5 -4 I -3 -2 0 I -l La/Sm Epsilon Nd These data support the model of rift evolution as presented by Vervoort and Green (1997). The early stage granophyres were formed either by fractional crystallization, or by AFC processes with contamination from a high Sm/Nd mafic crust. During this stage of rift evolution, the middle to upper crust was probably relatively cold, so assimilation likely occurred in the lower crust due to local heating as a result of plume initiation. The main stage granophyres are isotopically contaminated and suggest AFC processes at work. During this time period, renewed rifling resulted in higher ambient temperatures in the crust, and allowed melting of older, low Sm/Nd, negative epsilon Nd sources, possibly at middle to upper crustal levels. References: Miller, J.D., Vervoort, J.D., 1996, The latent magmatic stage of the Midcontinent rift: a period of magmatic underplating and melting of the lower crust. in 42" Annual Meeting of the Institute on Lake Superior Geology, Cable, Wis., May 1996, Proceedings volume 42, pp 33-35. Vervoort, J.D., and Green, J.C., 1997, Origin of evolved magmas in the Midcontinent rift system, northeast Minnesota: Nd-isotope evidence for melting of Archean crust: Canadian Journal of Earth Sciences, v. 34. p. 52 1-535. 86 �DIRECT TIMING CONSTRAINTS ON PALEOPROTEROZOIC METAMORPHISM, SOUTHERN LAKE SuPERIOR REGION: RESULTS FROM SHRIMP U-PB DATING OF METAMORPHIC MONAZITES Schneider, D.A., Syracuse University, Syracuse, NY, 13244; Hoim, D.K., Kent State University, Kent,OH, 44242; Hamilton, M.A., Geological Survey of Canada, Ottawa, ONT, K1A 0E8 The age of the Penokean Orogeny has been firmly established for decades by U-Pb pluton age data. The timing of post-orogenic cooling and lower temperature overprinting has only been established more recently by thermochronologic investigations. Little information exists however on the timing of the initial higher-grade metamorphism which affected the southern Lake Superior region during the Paleoproterozoic. Such information represents a critical missing link in our understanding of the tectonothermal evolution of the crust during and after Penokean orogenesis. Monazite, a REEphosphate accessory mineral, grows as a common metamorphic phase under amphibolite and higher-grade conditions. Monazite U-Pb ages typically yield reliable estimates for the timing of peak metamorphism, although post-metamorphic deformation and fluid flux can cause lower-temperature monazite dissolution and reprecipitation. We utilized the SHRIMP at the GSC in Ottawa to obtain geochronologic information on distinct mineral domains (e.g., core vs. rim) which may have resulted from particular tectonothermal events. Through BSE imaging prior to analyses, we found rim textures spatially distinct from interior replacement textures. Age data are indistinguishable from each domain and replacement probably resulted from the same thermal event as the rim neogrowth. Age data summarized below include only concordant or near concordant analyses and are reported as weighted average 207Pb/206Pb ages. In this pilot study we separated monazite from an amphibolite grade Paleoproterozoic metasedimentary unit in east-central Minnesota (Kettle River locality) and from an Archean gneiss unit within the Peavy district, northern Michigan (Foster City locality). From Kettle River, a sample of garnet schist, which attained peak metamorphic conditions of 470-520°C at 5-6 kbar, yielded distinct populations of core and rim U-Pb ages from 5 monazite grains. Eight analyses of core domains yielded a U-Pb monazite crystallization age of 1834.0 ± 6.1 Ma, reflecting primary metamorphic growth. A population of monazite rimlreplacement spot analyses, characterized by a higher Th content, yielded an age of 1792.9 ± 4.3 Ma. This latter age is similar to the --1799 Ma U-Pb crystallization age of the deformed Hillman tonalite (Van Schmus et aL, 2000, ILSG and this volume). From Foster city (>500°C and -4 kbar), an Archean muscovitebiotite quartzofeldspathic gneiss yielded a monazite core age of 1834.4 ± 6.0 Ma from 10 spots on 11 grains. Rimlreplacement domain analyses from 9 spots yielded a younger age of 1809.8 ± 6.3 Ma, consistent with high-temperature cooling in the region (1800 and 1785 Ma Ar-Ar hornblende ages; Mancuso et al., ILSG, 1997). 87 �These metamorphic U-Pb ages are the first reliable metamorphic dates from this Paleoproterozoic orogen and indicate a widespread thermal pulse at 1835 Ma in response to accretion-induced crustal thickening. Albeit preliminary, the age of metamorphism is remarkably consistent across the orogen. High temperature Ar-Ar cooling ages on hornblende (—500°C) from north of the Watersmeet dome (—1822 Ma; Schneider et a!., 1996, CJES) and biotite Ar-Ar dates from low-grade structural panels from east-central Minnesota (1840-1830 Ma; Schweitzer et al., 2000, ILSG) are compatible with an —1835 Ma orogenwide metamorphic episode. Further accessory mineral geochronology holds promise for better elucidating the timing of syn-orogenic metamorphism, as well as overprinting post-orogenic events throughout the southern Lake Superior region. Foster City Archean mu-bi quartzofeldspathic schist 0.35 -a a. (p 0 0.33 1: 0.31 0.29 0.27 4.2 4.4 0.33 0.31 0.29 0.27 4.2 4.4 4.6 88 4.8 5.0 5.2 5.4 5.6 �RESULTS OF IGNEOUS THERMOMETRY AND BAROMETRY ON THE EAST-CENTRAL MINNESOTA BATIIOL1TH: EVIDENCE FOR POST-EMPLACEMENT EXHUMATION AND COOLING SCHWEiTZER, D., and HOLM, D., both at Dept of Geology, Kent State University, Kent; OH, 44242; VAN SCHMUS, W.R., Dept. of Geology, Univ. of Kansas, Lawrence, KS, 55045; BOERBOOM, T., Minnesota Geological Survey, 2642 University Avenue, St Paul, MN The internal zone of the Penokean orogen in east-central Minnesota was invaded by abundant plutonism associated with emplacement of the East-Central Minnesota Batholith (ECMB) from 1787 to 1772 Ma (Van Schmus et al., 2000). Previous application of the Aluminum-in-Hornblende (AH) igneous barometer on phases of the ECMB indicate paleodepth estimates that increase from -13 km in the north (Ka-F, K-4; Fig 1) to —18 km in the southeast near St Cloud (SC, Fig 1). HoIm aed others (1998) inferred the depth differences to reflect intrusion of different magma bodies into a rapidly unroofing terrane. This interpretation predicts that progressively younger intrusions would have been emplaced into progressively shallower crustal levels. At the time, their hypothesis was limited by the lack of any precise age data on the intrusions analyzed. The new ECMB U-Pb age data provides the framework to directly test this hypothesis of syn-emplacement exhumation. We selected six new samples for further All barometric work (starred localities, Fig 1). Anderson and Smith (1995) outlined the important role that temperature plays in the Al concentration in homblende rims and proposed a temperature correcting calibration for the application of the All barometer. For this reason, the Hornblende-Plagioclase (HB-PL) thermometer (Blundy and Holland, 1992) was applied to these samples in order to derive a crystallization temperature estimate for each sample. The Schmidt (1992) pressure calibration is presented in order to compare the effects of the temperature correction. The electron microprobe at the University of Maine, Orono was used to obtain compositional data used for both the All barometer and HB-PL thermometer. The results of these analyses are summarized in the following table. Table 1: Summary of igneous thermometry and barnmetry results Schmidt, 1992 A and S, 1995 An Content B and H, 1990 kbar kbar Temperature (°C) (%) Sample ID Rock Unit EC-31 EC-15 DS-99-17 EC-1 EC-35 RFG-7 Granodiorite Mafic Plug Anne Lake Granite Watab Quartz Dionte Granodiorite Reformatory Granodiorite 789 ± 38 49.99 59.35 31.29 40.01 43.77 51.31 884±38 745 ± 38 6% *38 746±38 783 ± 38 9.1 ± 0.6 13.4 ± 0.6 6.0 ± 0.6 5.2 ± 0.6 8.5 ± 0.6 6.4 ± 0.6 <6.5 ± 0.6 <6.2 ± 0.6 4.9 ± 0.6 5.0 ± 0.6 <7.2 ± 0.6 4.4 ± 0.6 Assuming an average overburden density of 2.7 g/cc, the pressures recorded by EC-31, EC-15, and EC-35 correspond to maximum emplacement depths of 23-27km. These appear to be anomalously high when compared to other rocks in the area and probably reflect artificial Al enrichment of hornblende crystal rims due to high An content. Samples RFG-7 (17 lan), EC-1(18 km), and DS-99-17(18 km) when corrected for temperature effects appear to preserve viable estimates since they are consistent with prior barometric results. In the north, samples Ka-F and K-4 (Fig. 1) both preserve emplacement depths of 13 km but their UPb ages are 15m.y. apart. To the south, all samples near St Cloud record —17-18 km depths regardless of age. This implies that very little uplift occurred during emplacement of the ECMB. The bulk of post-tectonic exhumation appears to have occurred after the emplacement of the ECMB. Preserved pressure differences probably reflect deeper emplacement depths (from N to 5) across the batholith. Post-emplacement exhumation is consistent with cooling ages being 10-20 m.y. younger than ciystallization ages from the batholith (Holm et al, 1998; Hohn and Lux, 19%). The ECMB was likely completely exhumed prior to deposition of the Early Proterozoic (1750-1650 Ma) red quartzites. 89 �MSD: \ ,.- H It Is MN-29 :-::•::-: 18±2km I— A l P16 (MSD) ,c—I___ -. ', / -, — _s. \ I_,>. — — -%.— •5_ , / 5—— '11787* ' I<23*2km s. ,,-I, ' 5. Is ; '___-\ I_/'-'/ — I S —' — I -. Is * I <24t2kI — c-i J , — ;, _, __'_l 10 km F/ /' , _s— -, I, / — .,- —. — I / \ 'I'—'' ' — —' - Figure 1: Simplified map of the internal zone of the Pekonean orogen. Localities marked with filled circles represent samples analyzed by Hotm et at (1998). Starred localities denote samples analyzed in this study. MSD = Malmo Structural Discontinuity; SC = St. Cloud; LF = Little Falls. U-Pb ages after Van Schmus et at (2000). References Anderson, J.L, and Smith, D.R, 1 995,The effects of temperature and oxygen fugacity on the Al-in -hornblende barometer: American Mineralogist, v.80, p.549-559. Blundy, J.D., and Holland,TJ.B, 1990, Calcic amphibole equilibria and a new amphibole-plagiodase geothermometer: Contributions to Mineralogy and Petrology, v.104, p.208-224. HoIm, D.K.and Lux, D.R, 1996, Core complex model proposed for gneiss dome development during collapse of the Paleoproterozoic Penokean orogen, MN: Geology, v.24, p.343-346. Holm, D.K., Darrah, KS., and Lux, D.R., 1998, Evidence for widespread —.1760 Ma metamorphism and rapid stabilization of the Early-Proterozoic (1870-1820 Ma) Penokean orogen, MN: Am. J. of Science, v.298, p.60-81. Schmidt, M.W., 1992, Amphibole compoisition in tonalite as a function of pressure: an experimental calibration of the Al-in-hornblende barometer: Contributions to Mineralogy and Petrology, v.1 10, p. 304-310. Van Schmus,W.R., MacNeill, LC., Holm, D.K, Boerboom,TJ., and isa, M.A., 2000,The 1787-1772 Ma east-central Minnesota batholith: Precursor to crustal stabilization in the Lake Superior region: ILSG proceedings, 46th annual meeting, Marquette, Ml, v.46, p.65-66. 90 �A SYNOPSIS OF ARCHEAN AND PROTEROZOIC PLATINUM GROUP ELEMENT MINERALIZATION IN THE THUNDER BAY DISTRICT, ONTARIO SMYK, Mark C., MASON, John K. and SCHNIEDERS, Bernie R., Ontario Geological Survey, Ministry of Northern Development and Mines, Suite B002, 435 James St. South, Thunder Bay, ON P7E 6S7, and STOTT, Greg M. Ontario Geological Survey, Ministry of Northern Development and Mines, Willet Green Miller Centre, 933 Ramsey Lake Road, Sudbury, ON P3E 6B5 Platinum group element (PGE) occurrences and deposils are in both Neoarchean and Mesoproterozoic mafic to ultramafic intrusive rocks in the Thunder Bay District. Recent, dramatic increases in platinum group metal prices have prompted renewed interest in PGE exploration, resulting in the discovery of hitherto unknown hosts and styles of mineralization. Archean There are four broad, temporally diverse settings for Neoarchean PGE mineralization: (1) Pre-tectonic, mafic to ultramafic, subvolcanic(?) intrusions intimately associated with greenstone belts of various ages in the Wawa and Wabigoon subprovinces; (e.g. Haines Gabbro (Shebandowan belt / Wawa; 2722 Ma); Core Zone gabbro (Obonga Lake belt / Wabigoon; 2733 Ma); (2) Post-tectonic, mafic to ultramafic intrusions (Ca. 2692 Ma), related to late plutonism in the Wabigoon Subprovince, hosted by gneissic tonalite-granodiorite (e.g. Lac des Iles and Tib Lake complexes; Buck Lake, Legris Lake, etc.); (3) Syn- to post-tectonic, mafic to ultramafic intrusions (a.k.a. "Quetico-type"; Ca. 2680 to 2688 Ma) hosted by Quetico subprovince metasedimentary rocks (e.g. Samuels Lake, Kawene, Nym Lake, Chief Peter Lake, North Elbow Lake, etc.); and (4) Mafic intrusive rocks occurring within syn- to post-tectonic, diorite-monzodiorite-monzonite suites with sanukitoid affinity (ca. 2680 to 2685 Ma), within the Wabigoon, Quetico and Wawa subprovinces (cf Stern eta!. 1989) (e.g. Roaring River Complex; Entwine Lake). Disseminated to locally net-textured chalcopyrite, Fe-sulphides, pentlandite and magnetite typically characterize PGE-mineralized zones, which are commonly associated with intrusive contacts, polyphase intrusive breccias, as well as sheared and hydrothermally altered zones. Proterozoic Mesoproterozoic intrusive rocks associated with the Midcontinent Rift locally range in age from Ca. 1108 Ma (e.g. reversely polarized Coldwell alkaline complex; Logan diabase) to ages younger than the magnetic polarity reversal that occurred between 1105 and 1102 Ma (Davis and Green 1997). A tabulated synopsis is provided below: 91 �Intrusion I Lithology Mineralization Style Local Examples (Associated PGE-Miizeralized Areas) Disseminated sulphides and native metals in lherzolite, dunite, peridotite,_etc. Disseminated and blebby sulphides in medium- to coarsegrained, varied-textured (a.k.a._'taxitic')_gabbro Disseminated sulphides in Crspinel-bearing cumulate layers Disseminated, intergranular sulphides, fracture fillings Disseminated sulphides in medium- to coarse-grained Leckie Lake (Wolf Mountain); Hele Township; Eva-Kitto townships Normal Magnetic Polarity <(1005-1102 Ma): U Layered(?) picritic ultramafic intrusions Layered gabbro-anorthositic intrusions: Crystal Lake Gabbro Pine Point - Mount Mollie Gabbro Pigeon River and Arrow River diabase dykes Crystal Lake Gabbro (Great Lakes Nickel deposit) (Cr-spinel-bearing, anorthositic gabbro above Cu-Ni deposit) (Mount Mollie; Pine River) (Wallenius; Naomi Island; Jarvis Point) gabbro_and_diabase Reversed Magnetic Polarity (ca. 1108 Ma): Logan diabase sills, cone sheets Tholeiitic to alkaline complexes: CoIdwell alkaline complex Killala Lake alkaline complex I Sparse, disseminated sulphides Disseminated sulphides in medium- to coarse-grained, van-textured (a.k.a. taxitic) gabbro Disseminated sulphides in massive Fe-Ti-oxide cumulate layers (Numerous) Coldwell Two Duck Lake gabbro (Marathon deposit); Geordie Lake gabbro Eastern Border gabbro (Skipper Lake zone) Killala Lake Border gabbro (Sandspit Killala) (Unknown) The development of tectono-magmatic models for these various suites of intrusions is the focus of ongoing research as part of the Ontario Geological Survey's Operation Treasure Hunt. These new data will provide new insights into late Archean subprovince accretion in the Superior Province, as well as the development of the Midcontinent Rift. They will help to elucidate possible links between the age, geochemistry and setting of these intrusive rocks and PGE mineralization processes in order to generate new exploration targets. References Davis, D.W. and Green, J.C. 1997. Geochronology of the North American Midcontinent rift in western Lake Superior and implications for its geodynamic evolution; Canadian Journal of Earth Sciences, V.34, p.476-488. Stern, R.A., Hanson, G.N. and Shirey, S.B. 1989. Petrogenesis of mantle-derived, LILE-enriched Archean monzodiorites and trachyandesites (sanukitoids) in southwestern Superior Province; Canadian Journal of Earth Sciences, v.26, p.1688-1712. 92 �PLATINUM GROUP ELEMENT EXPLORATION IN NORTHWESTERN ONTARIO SMYK, Mark C., S11IWART, Jennifer and O'BRIEN, Mark S. Ontario Geological Survey, Ministry of Northern Development and Mines, Suite B002, 435 James St. South, Thunder Bay, ONP7EÔS7 During the past two years there has been a marked increase in exploration for the platinum-group elements (PGE) In iiorthwestern Ontario. This interest has been driven by a dramatic rise in the prices of platinum and palladwm. Renewed PGE exploration in northwestern Ontario has also been significantly influenced by the sticcess of North American Palladium Ltd.'s Lac des Ties Mine which produced 95 116 ounces of -palladium at àcash cost of US$142 per ounce in 2000. Recent exploration efforts at Lac des lies have increased 'the measured and indicated resource to 145 600 000 tonnes at an average grade of 1.57 glt Pd, 0.17 g/t Pt, 0.12 g/t Au, 0.06% Cu and 0.05 % Ni. There were over 100 PGE exploration programs in northwestern Ontario in 2000, accounting for more than half of all mineral exploration in the region. These exploration efforts have focused on both Archean and Proterozoic mafic to ultramafic intrusions, leading to the discovery of many occurrences in areas andlor intrusions not previously known to host PGE mineralization. PGE occur in two main geological settings: (1) In Archean pre- to post-tectonic, mafic to ultramafic intrusions. Mineralization may be associated with: • Disseminated "sparse" sulphides in gabbro and ultramafic rocks (e.g. Lac des Ties complex and satellite intrusive complexes), and localized by: • Zones of hydrothermal alteration • Heterolithic, igneous breccia zones Contact zones and tectonic structures • • (Semi-) massive, sheared, copper-nickel sulphide deposits (e.g. Shebandowan and Thierry mines) in ultramafic rocks • Sheared ultramafic rocks with copper-nickel sulphides intruding banded iron formation (e.g. Trout Bay) • Chromitite within layered ultramafic complexes (e.g. Big Trout Lake, Chrome Lake?) (2) In Mesoproterozoic, Midcontinent Rift-related (ca. 1108-1102 Ma), mafic to ultramafic intrusions near Lake Superior and Lake Nipigon. Mineralization may be associated with: • Disseminated suiphides in coarse-grained to pegmatitic, van-textured ("taxitic") gabbro (e.g. Great Lakes Nickel; Marathon deposits) • Massive oxide (± sulphide) units in layered gabbro (e.g. Coidwell Eastern Gabbro (Ti-Fe-oxides); Great Lakes Nickel (Cr-spinel) • Disseminated sulphide ± native metals in olivine-rich, layered ultramafic rocks (e.g. Wolf Mountain) 93 �A NEW GRAVITY MAP OF WISCONSIN SNYDER, Stephen L., U.S. Geological Survey, MS 954 National Center, Reston, VA 20192, ssnyder@usgs.gov; ERVIN, C. Patrick, Dept. of Geology and Environmental Geosciences, Northern Illinois University, DeKalb, IL 60115, pervin@niu.edu; GEISTER, Daniel W., Dept. of Geology and Environmental Geosciences, Northern Illinois University, DeKalb, IL 60115, z011561@students.niu.edu and DANIELS, David L., U.S. Geological Survey, dave(usgs.gov. A new Bouguer anomaly gravity map of Wisconsin has been created from more than 37,000 gravity measurements collected between 1948 and 2000. North of latitude 44° N., more than 28,000 stations were compiled by C.P. Ervin and M.E. Thompson. These data include stations from the Wisconsin Geological and Natural History Survey (WGNHS), the National Geophysical Data Center (NGDC), the Defense Mapping Agency (DMA), the U.S. Geological Survey (USGS), and Northern Illinois University. An approximate station interval of 1 mile (1.6 km) was established where possible, but limited access in some areas necessitated a greater spacing. Prior to 1999, the data south of latitude 44° N. totaled approximately 3800 stations from NGDC and from G. Randy Keller (University of Texas-El Paso). The current USGS effort, begun in 1999, is directed at upgrading the gravity coverage of the state south of latitude 44° N. with a station density comparable to that north of 44° N. To date we have added measurements at more than 6800 stations to achieve a nominal spacing of one to two miles. These new data replace the older data from the NGDC, which had a nominal station spacing ranging from 3 to 10 miles. Nearly all of the data are tied to the Wisconsin First-order Gravity Base Station Network, which is in turn tied to the International Gravity Standardization Network-1971 (IGSN-71). The 37,000 measurements were then gridded at an interval of 500 m. The map will be presented at a scale of 1:500,000. The rationale for upgrading the gravity coverage has been to provide higher resolution data to assist in the interpretation of the basement geology of southern Wisconsin, much of which is hidden by glacial and Paleozoic cover. The gravity data, along with aeromagnetic data, give clues to the structural evolution of the Precambrian crust, making the map an excellent tool for USGS mineral resource studies. Some notable features shown on this map include 1) the Midcontinent gravity high, which has one of the steepest gravity gradients in the conterminous US, 2) the flanking gravity lows corresponding to Keweenawan sedimentary basins, 3) gravity highs over inferred mafic plutons in southeastern Wisconsin, 4) a low centered on the Precambrian Wolf River batholith, but much larger in area, 5) gravity lows associated with granitic intrusives just south of latitude 46° N., and 6) several northwest trending linear features of unknown origin. The accompanying figure shows a shaded relief image of the gravity map. 94 �92° -89 -91 880 -87° .5 .15 H 21 .— .55 — 27 .— 30 .— 33 — 35— 35 I 42 * 45 — -45 * 51 54 * 50 53 -55 72 -51 500 milhigals 50 50 0 klometres NA027/ LGC-90 95 �POST-RIFT EVOLUTION OF THE MIDCONTINENT RIFT SYSTEM: SOME NUMERICAL EXPERIMENTS Soofi, M. A., and King, S. D., Department of Earth and Atmospheric Sciences, Purdue University, West Lafayette, Indiana 47907 The Midcontinent Rift system (MCR) is a major geological and geophysical feature of North America. This 1.1 b.y. old feature (Nicholson and Shirey, 1990; Klewin and Shirey, 1992) is believe to have evolved first through the tensile forces of a rift origin and then through the compressive forces from the intraplate collision between North America and Grenville Tectonic Zone (GTZ) (Van Schmus and Hinze, 1985). The support for interaction between the MCR and GTZ come from the geophysical studies which reveal thrust faults and folds along the length of the MCR (e.g., Zhu and Brown, 1986; Chandler et al., 1989; Mariano and Hinze, 1994; Allen et al., 1997). Also, the time of thrusting along the MCR is constrain to be 1060 Ma (Bornhorst et al., 1988; Cannon et al., 1993) which is comparable to 1100-1060 Ma (Easton, 1992) as the duration of collision in Grenville Tectonic Zone. A quantitative study of the late-stage deformation of the MCR under the Grenville tectonism has been performed by Soofi and King (1999). They showed that the distance between the MCR and Grenville Tectonic Zone is appropriate for the two geologic provinces to interact. We expand on their findings and investigate the contribution of various factors involved in the collision between North America and the Grenville terranes, including: the size of colliding terranes of Grenville Tectonic Zone; the location of collision along the eastern and southern boundaries of North America; and the angle of convergence between North America and the Grenville terranes. We use a 2D, viscous, finite element model that treats lithosphere as a thin sheet with stresses averaged over its thickness (for computational method see Houseman and England (1986); for program location see the web site http : / /www.earth.monash.edu.au/Research/Basil). The model boundaries coincide with pre-Grenville collision boundary of North America. In the model, the MCR is considered as a low-strength block. We consider the present shape of the MCR as the shape at the time of collision with the Grenville terranes. The models are run to represent 21 Ma of convergence at the rate of 50 mm/yr. To constrain the model results we use geophysically observed uplifts along the reverse faults of the MCR (e.g., Zhu and Brown, 1986; Mariano and Hinze, 1994; Allen et al., 1997). These uplifts are compared with crustal thickening along the MCR in the model. Based on our results we conclude that the 3 to 8 km variation in uplift along the thrust faults of the western arm of the MCR is the consequence of size of the colliding terranes and location of the collision. The model results also suggest that deformation along the eastern arm of the MCR was comparable to that along the western arm. The reason we do not observe such deformation in geophysical studies (e.g., Zhu and Brown, 1986) is, perhaps, due to later surficial and/or tectonic processes. We also conclude that collision with Crenville Tectonic Zone was active along both the eastern and southern boundaries of North America. This resulted in the non-linear shape of the western arm of the MCR and may also played a role in the formation of the Belle Plaine fault. We do not observe any significant difference in the model results for different angles of convergence between North America and Grenville terranes. Consideration of other constraints in addition to the uplift along the MCR may help to determine the dominant angle of convergence between North America and Grenville Tectonic Zone. 96 �REFERENCES CITED Allen,D.J., Hinze, W.J., Dickas, A.B., and Mudrey, M.G.Jr., 1997, tnterMedgeophysical modeling of the North American midcontineñt rift system: New thterpretations for western Lake Superior, northwestern Wisconsin, and eastern Minnesota: Geological Society of America Special Paper 312, p. 47-71. Bornhorst, T J, Paces, J B, Grant, N K, Obradich D, and Thiber, NkK 1988, Ae f native copper mineralization, Ke-weenaw Peninula, Michigan: conmi (eiogy, v 83, p. 41,19-625 Cannon, W.F., Petermn, Z.E., and Sims, P.K., 193, Crustal- sca1ethrtisting and origin of the Montreal river monocline - A 35 km thick cross-section of the midcontinent rift in northern Michigan and Wisconsin: Tectonics, v. 12, p. 728-744. Chandler, V.W., McSwiggen, P.L., Morey, G.B., Hinze, W.J,, and Anderson, R.R., 1989, Interpretation of seismic reflection, gravity, and magnetic data across middle Proterozoic mid-continent rift system, northwestern Wisconsin, eastern Minnesota, and central Iowa: American Association of Petroleum Geologists Bulletin, v. 73, p. 261-275. Easton, R.M., 1992, The Grenville Province and the Proterozoic history of central and southern Ontario, in Thurston, P.C. Williams, H.R., Sutcliffe, R.H., and Stott, G.M., eds., Geology of Ontario, Ontario Geological Survey, Special volume 4, Part 2, p. 715-904. Houseman, G., and England, P., 1986, Finite strain calculations of continental deformation 1. Method and General results for Convergent zone: Journal of Geophysical Research, v. 91, p. 3651-3663. Klewin, K.W., and Shirey, S.B., 1992, The igneous petrology and magmatic evolution of the midcontinent rift system: Tectonophysics, v. 213, p. 33-40. Mariano, J., and Hinze, W.J., 1994, Structural interpretation of the Midcontinent Rift in eastern Lake Superior from seismic reflection and potential-field studies: Canadian Journal of Earth Sciences, v. 31, p. 619-628. Nicholson, S.W., and Shirey, S.B., 1990, Midcontinent rift volcanism in the Lake Supe- rior region: Sr, Nd, and Pb isotopic evidence for a mantle plume origin: Journal of Geophysical Research, v. 95, p. 10851-10868. Soofi, M.A., and King, S.D., 1999. A modified beam analysis effect of lateral forces on lithospheric flexure and its implication for post-rift evolution of the Midcontinent Rift System, Tectonophysics, v. 306, p. 149-162. Van Schmus, W.R., and Hinze, W.J., 1985, The midcontinent rift system: Annual Reviews of Earth and Planetary Science, v. 13, p. 345-383. Zhu, T., and Brown, L.D., 1986, Consortium for continental reflection profiling Michigan surveys: Reprocessing and results: Journal of Geophysical Research, v. 91, p. 11477-11495. 97 �THE COOL EARLY EARTH: OXYGEN ISOTOPE EVIDENCE FOR CONTINENTAL CRUST AND OCEANS ON EARTH AT 4.4 Ga VALLEY, JW*, PECK, WH, KING, EM, Dept. of Geology + Geophysics, Univ. of Wisconsin-Madison; GRAHAM, CM, Dept. of Geology + Geophysics, Edinburgh Univ., Scotland; and WILDE, SA, School of Applied Geology, Curtin Univ., Bentley, Western Australia, * valley@geology.wisc.edu Zircons preserve the best record of U-Pb crystallization age and oxygen isotope ratios of igneous rocks. The I8O of non-metamict zircon is unaffected even by hydrothermal alteration and high-grade metamorphism. Ion microprobe analysis of detrital zircons from the —3 Ga Jack Hills metaconglomerate (Narryer Gneiss Terrane, Yilgarn Craton, Western Australia) yield UPb ages from 3.1 to 4.4 Ga (Fig. 1, SHRIMP II, ref 1) and I8O from 5 to 8 %c (Cameca 4f, ref 2). The 18O of these zircons averages 6.3, and is 1 per mil higher than that in equilibrium with the mantle and that of normal Archean granitic zircons (Fig. 2; 5.3±0.3 %o, 5.5±0.4 %, respectively; ref 3). The distribution of mantle-like vs. mildly elevated 18O values for magmas is constant from 2.7 to 4.4 Ga, and on 4 continents (Fig. 2). The age of 4.404 ±0.008 Ga from one 200 im zircon is >99% concordant and represents the oldest recognized terrestrial material. This crystal is zoned in ö'80 (5.0±0.7% vs. 7.4±0.7%o) and REEs (La=0.3 to 13.6 ppm), and contains inclusions of Si02. REE patterns are HREE enriched with positive Ce and negative Eu anomalies; calculated melts are LREE enriched. Taken together, these results suggest crystallization from a quartz-saturated granitic magma and thus the existence of continental crust, possibly in a setting like Iceland. The high 6180 portion of the crystal would be in equilibrium with a magma at 6'80(WR)= 8.5-9.5%. There is no known mantle reservoir with such high values. '8O(WR) values above 8.5 are typical of "S-type" granites that have melted or assimilated material that was altered by low temperature interaction with water at the surface of the Earth (i.e., weathering, diagenesis, low T hydrothermal alteration). Thus the high 18O value of the 4.4 Ga zircon suggests that surface temperatures were cool enough for liquid water suggesting that the early steam-rich atmosphere condensed to form oceans at that time. The evidence for liquid water and oceans at 4.4 Ga suggests a Cool Early Earth. This contrasts with the Hot Early Earth and global magma oceans envisioned at 4.5-4.3 Ga based on: an impact origin of the Moon (4.45-4.50 Ga), core formation, higher Hadean radioactive heat production, and intense early meteorite bombardment (4). The surface of the Earth cools quickly to form a crust by radiation, but a magma ocean caused by these processes would persist beneath the initially thin crust for up to 400 m.y. (5) and might erupt as massive flood basalts in response to major meteorite impacts, boiling surface waters. The thermal contrasts presented by these lines of evidence are minimized if the Moon and core formed earlier (-.4.5 Ga), if the Moon formed by a process not involving a Mars-size impactor, or if the early meteorite bombardment was less intense or irregular in timing. It is possible that periods of Cool vs. Hot Early Earth alternated, with 98 �boiling of early oceans after major impact events followed by periods of cooler surface conditions. If life evolved in these seas, multiple extinctions before 3.9 Ga are suggested. 1.20 Detrital Zircon from Jack Hills Metaconglomerate W74 1.10 1 .00 0.90 0.80 206Pb 238 U 0.70 0.60 0.50 0.40 0.30 0.20 0.10. 207 Pb/ 235U -I- 7 A + 6 dD A AAA £ V A 5.3±0.3%c A V A a mantle zircon A A £ V A 0 V A Jack Hills Australia V Barberton + Superior Province 4, Scotland ® Manitouwadge Miscellaneous 2 2600 , 2800 3000 3200 3400 3600 3800 4000 4200 4400 U-Pb Zircon age (Ma) (1) SA Wilde, JW Valley, WFI Peck and CM Graham (2001) Evidence from Detrital Zircons for the Existence of Continental Crust and Oceans on the Earth 4.4 Gyr Ago. Nature. 409: 175-178. (2) WH Peck, JW Valley, SA Wilde, and CM Graham (2001) Oxygen Isotope Ratios and Rare Earth elements in 3.3 to 4.4 Ga zircons: Ion Microprobe Evidence for Early Archean high ö'80 Continental Crust. Geochim Cosmochim Acta, in press (3) WH Peck, EM King, JW Valley (2000) An Oxygen Isotope Perspective on Precambrian Crustal Growth and Maturation. Geology 28: 363-366; EM King, JW Valley, DW Davis, GR Edwards (1998) Oxygen isotope ratios of Archean plutonic zircons from granite-greenstone belts of the Superior Province. Precam, Res 92: 365-387. (4) HN Pollack (1997) Thermal Characteristics of the Archaean, in: de Wit and Ashwal (eds), Greenstone Belts, 223-232 (5) Y Abe (1993) Physical State of the Very Early Earth. Lithos 30:223-235 99 �NW U.PB AGES FROM MINNESOTA, MICHIGAN, AND WISCONSIN: IMPLICATIONS FOR LATE PALEOPROTEROZOIC CRUSTAL STABILIZATION. Van Schmus, W.R. (rvschmus@ku.edu) and MacNeil!, L.C., both at Dept. of Geology, Univ. of Kansas, Lawrence, KS 66045, HoIm, D.K., Dept. of Geology, Kent State University, Kent, OH 44242; and Boerboom, T. J., Minnesota Geological Survey, 2642 University Avenue, St. Paul, MN 55114. As part of a comprehensive study of the East-Central Minnesota Batholith (ECMB: Boerboom and HoIm, 2000; Van Schmus et al., 2000), we have also determined the U-Pb ages of several rock units spatially and (or) temporally related to it. The samples fall into several categories (Table 1): (a) the McGrath Gneiss to the NE of the ECMB in Minnesota; (b) Penokean basement east of the ECMB in Minnesota; (c) post-Penokean, preECMB rocks in Michigan and Minnesota, and (d) units coeval with or slightly younger than the ECMB in Minnesota and Wisconsin. Table 1. New U-Pb Results from Minnesota, Michigan, and Wisconsin. Sample Description MNOO-07 McGrath Gneiss, 2 mi. west of McGrath, MN 2550 ± MNOO-0 1 Bradbury Creek granodiorite, 4 mi. south of Onamia, MN Tonalitic gn., Hillman migmatite?, 3 mi. south of Onamia, MN 1877±15 Ma MNOO-02 MN99-09 MNOO-03 MNOO-04 AGR-1 Late tonalite in Hiliman migmatite, 3 mi. SE of Lastrup, MN Late tonalite in Hilhnan migmatite, 9 mi. west of Onamia, MN Late tonalite in Hilhnan migmatite, 13 mi. west of Onamia, MN Humboldt granite, Humboldt, MI (Hoim et aL, 2001) Multiple East Central Minnesota Batholith Van Schmus et al. (2000); Boerboom and HoIm (2000) Includes EC-2, -4, -5, -15, and -25 of Jima and Chandler (1997) 1787 to 1772 Ma PF-99 VS73-37 Two-mica granite, Park Falls, Wisconsin Radisson Granite, Radisson, Wisconsin 1781 ± 14 Ma 1776 ± 08 Ma V573-08 VS77-251 VS79-85 Amberg granite, 1 mi. north of Amberg, WI Lugerville granite, 1.5 mi. SW Lugerville, WI Lugerville granite, Rock Carry Rapids, 1 mi. E Lugerville, WI 1754±llMa VS74-13 VS73-02 Observatory Hill rhyolite, 6 mi. south of Montello, WI Montello granite, Montello, WI Age 14 Ma 1853 ± 10 Ma 1798 ± 03 Ma (composite of 3 samples) 1805 ± 07 Ma all 1749 ± 04 Ma (pooled; all near) concordia) 1759 ± 02 Ma 1746 ± 03 Ma The oldest sample is from the McGrath Gneiss and confirms the late Archean age of that unit. Two samples yielded Penokean ages. The Bradbury Creek granodiorite was dated by Goldich and Fischer (1986) at 1869 ± 5 Ma, and our date of 1877 ± 15 Ma is fully consistent with this. A tonalitic gneiss (MNOO-02) about one mile to the north-northwest and mapped as Hillman migmatite yields a slightly younger, but statistically indistinct, age of 1853 ± 10 Ma. We are investigating the possibility that the Bradbury Creek unit is more extensive than originally defmed from aeromagnetic data. In any case, normal Penokean ages occur in eastern Minnesota, and Penokean basement forms the host crust for the ECMB. Several samples yielded U-Pb ages close to 1800 Ma. The main units in Minnesota are late, undeformed (or less deformed) tonalite phases within the Hillman migmatite complex. Samples from three separate localities yield a mean age of 1798 ± 3 Ma for the tonalite. For one of these samples (MNOO-03), the tonalite dated intrudes deformed tonalitic gneiss similar to that of MNOO-02. At this time it appears that the protolith for the Hillman migmatite may be Penokean, but that it was extensively injected by younger tonalite about 1800 Ma. 100 �Further detailed sampling and geochronology will need to be done to test this option. In Upper Michigan an alkali-feldspar granite near Humboldt yielded an upper intercept age of 1805 ± 7 Ma (HoIm et al., 2001). These rocks define a distinct post-Penokean, pre-ECMB phase of magmatism in or near the southern part of the Superior Province. As reported previously (Van Schmus et al., 2000), the East-Central Minnesota Batholith was emplaced within a relatively short span of time 1787 to 1772 Ma. We analysed zircons from several drill core samples to the east (ursa and Chandler, 1997), and the results (Table 1: EC-2, EC-4, EC-5, EC-1 5, EC-25) extend the known area of the ECMB. In order to determine whether units of the so-called "1760 Ma" suite of rocks in Wisconsin are coeval with the ECMB, we reanalysed several samples from the senior author's collection, plus one new sample (PF-99) using single-grain analyses and more precise techniques. The westernmost samples (PF-99 and VS7337) yield ages indistinguishable from those of the ECMB, suggesting that magmatism of that episode extended into northwestern Wisconsin. In contrast, samples of the "1760 Ma suite" farther east (Amberg and Lugerville granite) or farther south (Montello granite, Observatory Hill rhyolite) are distinctly younger, with ages of 1746 to 1759 Ma. These ages are similar to Ar-Ar ages reported for the ECMB and indicate that the last major magmatic pulse occurred about 1750 Ma. Our new data now suggest three main post-Penokean pulses of magmatism about 25 m.y. apart in the southern Lake Superior region: ca. 1800, 1775, and 1750 Ma. The origin of the thermal energy in each case is presently unknown. These ages fall within the time span of magmatism in the Yavapai province-northern Central Plains orogen (inner accretionary belt; Van Schmus et al., 1993) and could correlate with pulses of northward directed subduction associated with southward growth of the continent. Interestingly, the two older and deeper-seated igneous bodies currently reside in Paleoproterozoic crust unaffected by younger Mazatzal deformation and reheating (Holm Ct al., 1998). It appears that localization of the earlier pulses in the west (Minnesota) and north (northwesternmost Wisconsin) may have contributed to the overall greater exhumation of these areas (compared to most of Wisconsin) and that this in turn may have dramatically strengthened the crust in those regions. We note that crustal remelting and thinning after orogenesis can both contribute to an overall stronger continental lithosphere. One fmal note: reference to a "1760 Ma" suite in Wisconsin should probably now be discontinued, since those rocks formed in two pulses at about 1775 and 1750 Ma. Boerboom, TJ., and Holm, D.K., 2000, Paleoproterozoic intrusive igneous rocks of southeastern Stearns County, central Minnesota. Minn. Geol. Survey, Rept. mv. 56, 36p + 1 map. Goldich, S.S., and Fischer, L.B., 1986, Air-abrasion experiments in U-Pb dating of zircon. Chemical Geology, v. 58, p. 195-215. Holm, D., Schneider, D., and Coath, C., 1998, Age and deformation of Early Proterozoic quartzites in the southern Lake Superior region: Implications for extent of foreland deformation during final assembly of Laurentia: Geology, v. 26, p. 907-910. Holm, D., Van Schmus, R., Boerboom, T., and Jirsa, M., 1999, Role of post-Penokean granite genesis in crustal stabilization in the Lake Superior region, north-central United States. Geol. Soc. America Abstracts with Programs, v. 31, no. 7, p. A-259. Hoim, D.K., Van Schmus, W.R., and MacNeill, L.C., 2001, Age of the Humboldt granite, northern Michigan: Implications for the origin of the Republic metamorphic node. 47th Ann. Inst. on L. Superior Geology, Madison, Wisconsin, May (this volume). Jirsa, M.A., and Chandler, V.W., 1997, Scientific test drilling and mapping in east-central Minnesota, 19941995: summary of lithologic results. Minn. Geol. Survey, Inf. Circular 42, lO5p. Schweitzer, D.J., Schneider, D.A., Boerboom, T.J., HoIm, D.K., and Van Schmus, W.R., 2000, Assessing the extent of Early Proterozoic Penokean versus 1770-1760 Ma metamorphism in east-central Minnesota. Abstracts, 46th Ann. Inst. on L. Superior Geology, Lakehead University, Thunder Bay, Ontario, May Van Schmus, W.R., Bickford, M.E., and Condie, K.C., 1993, Early Proterozoic crustal evolution, in Reed, J.C., Jr., Bickford, M.E., Houston, R.S., Link, P.K., Rankin, D.W., Sims, P.K., and Van Schmus, W.R., editors, Precambrian: Conterminous U.S. Geological Society of America, The Geology of North America, v. C-2, p.270-281. Van Schmus, W.R., MacNeill, L. C., Holm, D.K., Boerboom, T.J. and Jima, M.A., 2000, The 1787-1772 Eastcentral Minnesota batholith: precursor to crustal stabilization in the L. Superior region. Abstracts, 46th Ann. Inst. on L. Superior Geology, Lakehead University, Thunder Bay, Ontario, May 101 �A STUDY OF WELL CONSTRUCTION FOR ARSENIC CONTAMINATION IN NORTHEAST WISCONSIN ANNETTE E. WEISSBACH, Wisconsin Department of Natural Resources, DNRNortheast Region, Waste Management, Remediation, and Redevelopment, 1125 N Military Aye, P0 Box 10448, Green Bay WI 54307-0448 ELIZABETH M. HEINEN, Wisconsin Department of Natural Resources, DNRManitowoc Field Station, 2220 E CTH V, Mishicot WI 54228, and KELD B. LAURIDSEN, Wisconsin Department of Natural Resources, DNR-Northeast Region, Waste Management, Remediation, and Redevelopment, 1125 N Military Aye, P0 Box 10448, Green Bay WI 54307-0448 Arsenic has been detected in approximately one third of the private drinking water wells in the Fox River valley of Northeast Wisconsin. Concentrations detected are some of the highest found naturally occurring in the world. Research has indicated that presently 3.5% of the wells in Outagamie and Winnebago counties exceed the current drinking water standard of 50 ppb, whereas close to a quarter of the wells may exceed the proposed standard of 10 ppb. Department of Natural Resources study results indicate the geochemical phenomenon causing the elevated levels of arsenic in groundwater of this region is associated with oxidation of a sulfide-mineralized zone located at the top of the deep sandstone aquifer system. A regional decline in water levels may have exposed this sulfide rich zone to oxidation from air within the open boreholes of water wells extending through this zone. This oxidation process can initiate a chemical reaction similar to acid mine drainage. Recommendations have been developed for constructing wells within a delineated advisory area. This guidance recommends constructing wells with well casing pipe to extend through the sulfide rich zone. This study compared arsenic concentrations of wells constructed according to the guidance, with wells constructed to traditional construction standards. Additionally, this study examined data to determine if it was better to replace a contaminated well with a new one, or to reconstruct the existing well with a liner. The results of this study indicate that the guidance gives adequate protection for wells constructed in the arsenic advisory area and that liners are successful at reducing arsenic concentrations, although not as successful eliminating arsenic contamination. 102 �holes from which the samples were collected, and so may be from near the base of the Quaternary section. Low ppm Th I wt.% K ratios, which is the case for most of these high K tills, in general are indicators of potassic alteration. Because there is no apparent process that would create this type of alteration pattern following till deposition, it is proposed that tills with high K contents may have a local bedrock source area characterized by potassic alteration. This alteration may indicate pre-Marathon Foration paleoweathering of bedrock or may indicate local or regional hydrothermal alterat4on. Because potassic alteration can indicate precious metal and sulfide mineralization, high-K tills in the lower part of the Marathon Formation, characterized by some high Zn values, may aid in mineral exploration. Provenance Discrimination Samples of Quatemary deposits collected from closely spaced rotasonic boreholes in the area of the Bend massive sulfide deposit in Taylor County proved to have unique geochemical characteristics that could be xpiained by differences in source areas and sedimentological processes (Woodruff and others, 2000). The classification of till samples in the field was successfully duplicated by discriminate analysis of the geochemical data set using the statistical software package 5+. Based on geochemistry and grain size, samples from the Bend area were statistically grouped into either Copper and a Lake Falls or Marathon Formations, easily distinguishing a carbonate provenance Superior provenance. The same type of discriminate analysis was run on the regional data set using identical element and grain size input. When compared to field classifications, results gave an error of 17% (correctly predicting 38 of 46 samples) for a carbonate provenance and an error of 5% (correctly predicting 51 of 54 samples) for a Lake Superior provenance. However, the utility of this statistical approach for the regional Quaternary data set is questionable. Geochemical fingerprints of correlated Mg Cu and Ti for and Ca values for samples from the Marathon Formation and correlated samples from the Copper Falls Formation identified in the Bend section are less distinct compared to the in the regional data set. Several factors inherent to the regional data, as These Bend area data, may complicate correlations and discrimination of provenance. factors include differences in the method of sample collection (rotasonic core vs. auger glaciofluivial or sampling), which could influence sample identification (e.g., till vs. glaciogenic debris samples), and the existence of geochemical outliers, such as the high larger geographic area K tills, in the regional data set that may reflect sampling from a with many diverse bedrock sources of material. References Wisconsin Attig, J. W., 1993, Pleistocene geology of Taylor County, Wisconsin: Geological and Natural History Survey Bulletin 90, 35 p. Woodruff, L.G., Attig, J.W., and Cannon, W.F., 2000, Geochemical impacts of an undisturbed mineral deposit — results from the Bend deposit, Wisconsin [abs]: Institute on Lake Superior Geology Proceedings, v. 46, p. 72-73. 105 � https://digitalcollections.lakeheadu.ca/files/original/0274839d2a0a8f7d05473aabb3bc01b8.pdf c44648cb3e8f8088276e886956c5658f PDF Text Text ���CONTENTS CONTENTS Proceedings Volume 47 Part 22 -— Field Trips Interval: New TripI: Tripi: Sedimentologic, Tectonic and Metamorphic Metamorphic History of the Baraboo Interval: 11 Evidence from Investigations in the Baraboo Range,Wisconsin Investigations Locality 1: Baxter Hollow 10 10 Locality 2: Hydrothennal Veins, Hwy 12 14 14 Hydrothermal 15 Locality 3: Quartzite and Metapelite, Hwy 12 15 Locality 4: Abelman's Gorge 17 17 Leaders: L. Gordon Medaris, University of Wisconsin -- Madison Madison Robert H. Dott, Jf., Madison Jr., University of Wisconsin -- Madison Trip Trip 2: Geology, Ore Deposits, and Cultural History ofthe of the Upper Mississippi Valley Zinc-Lead District Stop 1: Platteville Mining Museum and Rollo Jamison Museum Stop 2: Potosi Hill - Ordovician Sinnipee Group Stop 3: New Diggings Lead Digs Stop 4: Shullsburg Mine Site - Metallic Mine Reclamation Reclamation Stop 5: Pendarvis State Historical Site (Mineral Point) Historical 23 30 30 36 36 39 Leaders: M.G. M.G. Mudrey, Mudrey, Jf., Jr., Wisconsin Geological and Natural History Survey Thomas C. Hunt, University of Wisconsin - Platteville of the Baraboo and Waterloo Quartzites Trip Trip 3: Economic Geology Geology of Quartzites of Southern Southern Wisconsin Stop Stop 1: Michels Michels Materials Waterloo Quarry Stop 2: The Kraemer Co. Williams Quarry Stop Stop 3: 1,760 1,760 MaRhyolite Ma Rhyolite Stop Stop 4: Milestone Materials Jesse Pit and Quarry Stop Stop 5: Milestone Materials Fox Ridge Asphalt Plant and Sales Yard 6: Martin Marietta Aggregates Aggregates Rock Springs Quarry Stop 6: Stop 7: Kraemer Company LaRue Quarry Leaders: Leaders: Brown, Wisconsin Geological and Natural History HistOlY Survey Bruce A. Brown, Survey University of Wisconsin - Whitewater Frank R. Luther, University Whitewater Susan M. M. Courter, Michels Materials Susan Materials James W. Schmitt, D.L. Gasser Construction Construction Company Jennifer Lien, The Kraemer Company 111 43 46 47 49 50 50 51 52 �This page intentionally left blank �Field Trip 11 Sedimentologic, Tectonic and Metamorphic History of the Baraboo Interval: Interval: New Evidence from Investigations in the Baraboo Range, Range, Wisconsin Wisconsin by H. Dott, Dort, Jr. Ir. L. Gordon Medaris, Ir. Jr. and Robert H. Department of Geology and Geophysics Geophysics of Wisconsin Wisconsin -- Madison Madison University University of Devil's Lake State Park View to the west along the East Bluff, Devil's State Park (foreground), Devil's Lake (background) Baraboo Quartzite (foreground), (background) �This page intentionally left blank �FOREWORD Baraboo Range began began in 1852 and and culminated in in 1970 with with Geological investigations of the Baraboo Dott. publication of the monograph, "Geology of the Baraboo District, Wisconsin", by Dalziel and Dott. Despite its publication 30 years ago, this monograph (with accompanying accompanying detailed geological map) Despite remains today the most comprehensive Baraboo Range. comprehensive treatise on the Baraboo In 1996 a paleosol at the base of the Baraboo Baraboo Quartzite Quartzite was discovered in a drill core taken in in Baxter Hollow (Medaris et al., 1996). Recognition of ofthe paleosol, which was developed at the expense the developed expense of granite underlying the quartzite, resolved any remaining question about the relative ages of the Baraboo Quartzite and Baxter Hollow Granite. This discovery subsequently inspired aa new look at the Baraboo techniques that that were unavailable unavailable 30 years ago, and led led to Baraboo Range, using a variety of analytical techniques depositional age of the quartzite, paleoclimatic environment, elaboration of a number of topics, including depositional data substantiate substantiate the sedimentary geochemistry, and conditions and age of metamorphism. The new data Dott and provide additional insight into into the processes conclusions originally drawn by Dalziel and Don discovery is is responsible for producing the Baraboo Range. An especially exciting and unexpected unexpected new discovery the occurrence of 1,460 Ma hydrothermal activity along the base base of the Baraboo Quartzite, presumably driven by heat from Wolf River-type magmatism. Proterozoic evolution of of the Baraboo This field guide provides an updated overview overview of the Proterozoic and describes several key outcrops, from which Range, based on the results of our recent investigations, investigations, many of the new data were obtained. INTRODUCTION Red, supermature quartzites, most notably the the Baraboo, Barron, and Sioux Quartzites, Quartzites, have long long been recognized as distinctive and important Precambrian Precambrian features in the southern Lake Superior Superior region. region. The physical and chemical characteristics of the quartzites signify deposition in a stable cratonic setting under conditions of intense chemical weathering in the presence of significant free oxygen in the post-1,750 1997; FloIm Holm et a!., al., atmosphere. These quartzites are now known to be post-I, 750 Ma in age (Dott et al., 1997; ~ 1,630 Ma (Romano eta!., et al., 2000), and locally intruded 1998), to have been folded folded and metamorphosed at 1,630 I,450 Ma (Dott and Dalziel, 1972). by granitic rocks at ~—l,450 1972). The term, Baraboo interval, was introduced by Dott DoU (1983) for this distinctive sequence of sedimentation, deformation, and metamorphism in the time span of 1,450 to 1,750 Ma. Our recent investigations not only validate the concept ofthe of the Baraboo interval, but also provide greater insight into the disparate geological events that shaped shaped the southern Lake Superior region in mid-Proterozoic time. REGIONAL SETTING Baraboo interval sedimentary rocks are widely distributed in the southern Lake Superior region metamorphic rocks. The (Fig. 1), where they lie nonconformably on 1,750 Ma and older igneous and metamorphic the general southerly direction paleocurrents, the increase in sediment thickness from north to south. south, direction of paleocurrents, suggest that chemical maturity of the sedimentary rocks, and the occurrence of mature paleosols suggest deposition occurred occurred on a stable, passive continental margin on the southern edge of a Proto-North American craton (Dott, (Dort, 1983). All of the quartzites in Figure 1, 1, except for the Waterloo, have yielded detrital zircon grains with V-Pb ages in the range, 1,712 to 1,778 et aL, 1997; Holm et al., U-Pb 1,778 Ma (Dott (Dort eta!., 1998; Van Wyck, 1995), and these data, combined with the inferred time offolding of folding and deformation at —1,630 Ma, established from 4°ArP9Ar 40Ar/39Ar cooling ages of basement amphibole and mica (Romano ~1,630 (Romano et al., (Dort and Dalziel, Dalziel, 1972; Van Schmus et al., 1975), 2000) and Rb-Sr resetting of granite and rhyolite (Dott eta!., 3 3 �constrain deposition to between between 1,710 and 1,630 Ma. Subsequently, constrain deposition of of the the Baraboo Baraboo interval interval sediments sediments to 1,710 and 1,630 Ma. Subsequently, the easternmost quartzites at McCaslin and Waterloo were intruded by granitic rocks of Wolf Wolf River River age age the easternmost quartzites at McCaslin and Waterloo were intruded by granitic rocks of Dalziel, 1972; 1972; Van Wyck, Wyck, 1995). 1995). (Dott and Daiziel, 200 km NO (, ~-S~D~--~ MN Barron (300 m) • • 1630Ma McCaslin \ A ,. Flambeau ­ ~..t f~-Water - - ­ '~ to ­ B"abOO(~ml ~I ~_MI NE , )~ IA I IN Figure Figure 1. 1. Distribution Distribution of of Baraboo Baraboo and and correlative correlative quartzites quartzites in in the the southern southern Lake Lake Superior Superior region, with meters, and region, with average average paleocurrent paleocurrent directions, directions, thicknesses thicknesses in in meters, and paleosol paleosol localities localities quartzites have (*). Heavy (*). Heavyline lineisisthe theinferred inferred1,630 1,630Ma Matectonic tectonic front, front, south south of of which which quartzites have been folded (Hoim been (Holm et al., aI., 1998) 1998) IGNEOUS IGNEOUS BASEMENT BASEMENT OF OF THE THEBARABOO BARABOO RANGE RANGE The Baraboo Baraboo Quartzite Quartzite is diorite near the town town of of Denzer, Denzer, by The is underlain underlain by by diorite near the by granite granite in in Baxter Baxter both limbs of the syncline in its Hollow, and and by rhyolitic lavas and pyroclastic rocks beneath both limbs of the syncline in its eastern eastern part part Hollow, granite and rhyolite are (Daiziel and Dott, 1970). U-Pb zircon ages of the Baxter Hollow (Dalziel and Dott, 1970). U-Pb zircon ages of the Baxter Hollow granite and rhyolite are indistinguishable, and indistinguishable, and taken taken together, together, yield yield an an age age of of1,749±12 1,749±12 Ma Ma (Van (Van Wyck, Wyck, 1995). 1995). Chronologically Chronologically subalkalic granite and rhyolite rhyolite suite suite of of and petrologically, petrologically, the the subalkalic granite and is correlative correlative with with the and the Baraboo Baraboo basement basement is Fox River River Valley Valley igneous igneous suite suite contains the Fox Fox River River Valley Valley (Smith, (Smith, 1978; Anderson etet al.. a!.. 1980). 1980). The The Fox the 1978; Anderson contains analyses demonstrate that both metaluminous and peraluminous types, and recent chemical both metaluminous and peraluminous types, and recent chemical analyses demonstrate that Denzer Denzer diorite is peraluminous. peraluminous. and and rhvolite rhyolite is is both both peraluminous peraluminous and and diorite is is metaluminous, metaluminous, Baxter Baxter Hollow Hollow granite granite is the Baxter Hollow metaluminous (Fig. (Fig. 2A). 2A). Among Ma silicic silicic lithologies. lithologies. the Baxter Hollow granite granite is is the the metaluminous Amongall allthe the1,750 1,750 Ma Fe-number and least differentiated differentiated in as measured by fe-number in terms terms of of major major elements, elements, as measured by and Ca-number Ca-number (Fig. (fig. 2B). 2B). least of Figure 2. containing 625-700 The Denzer diorite is metaluminous and plots outside the scales The Denzer diorite is metaluminous and plots outside the scales of Figure 2. containing 625-700 ppm ppm Sr. Sr, 0.62-0.68. of 0.70-0.82, Fe-number of 0.46-0.48. and Ca-number of an A1203/(K20+Na20+CaO) AbO)(K20+Na20+CaO) value of 0.70-0.82, fe-number of0.46-0.-l8. and Ca-number of 0.62-0.68. 44 �• 1000 1000 G Baxter Hollow granite rhyolite booBara R granite Hollow Baxter G R Baraboo rhyolite GG C C G cC G G G E P P 100 100 R P 0. 0 .3 R E P R en P C/) R R R R R P granites peraluminous ~~ P P '--- peraluminous granites A M1 MJi'l.MM;P ~ ~ metaluminous granites A graniteS metaluminous PP I"" I"" I"" j_.IPH 1.0 1.1 10 0.9 1.0 I 1.2 I"" 1.3 I",.;"" 10 0.9 1.1 1.2 1.3 1.0 1.0 * + 0.9 + R + C G ~ ".).. R 0 ~~, G a) 0.7 ~...,,~. <$)~ G G a) 0.6 0.61 G 0 E rhyolite boo Bara R granite Ho/low Baxter G B G Baxter Hollow granite B R Baraboo rhyolite t! , o ! , I, ,! I I !! I!!!, I , ! ! ! I, ! I I I CaO/(CaO+Na20) molecular 0.3 0.2 0.1 0.5 0.1 0.2 03 molecular CaO/(CaO+Na20) ! !! !,!! 0.4 ('3 0 " G Li:::J u E G G ~ 07 ~ 0 G ~ G 0+ U- "'' 'oj>. G 0.8 0.8 R 0 ~ * ~ ++ R +,. 0OJ u. R + ++ * + OJ u. metaluminous granites R 6" Cl :2: + 0 granifes meta/uminous J. / + / 0.4 0.5 0 impublished) Medaris, 1980; al., et Anderson 1978; Smith, from (data suite Valley River Fox the of granites (F) peraluminous and (M) metaluminous with (R) rhyolite Baraboo and (G) granite Hollow Baxter of comparison Chemical 2. Figure Figure 2. Chemical comparison of Baxter Hollow granite (G) and Baraboo rhyolite (R) with metaluminous (M) and peraluminous (P) granites of the Fox River Valley suite (data from Smith, 1978; Anderson et aI., 1980; Medaris, unpublished) quartz. q, saussurite; and albite mostly plagioclase, p, hornblende; h, biotite; after chlorite c, biotite; b, feldspar; alkali a, Abbreviations: polarizers). crossed matrix, aphanitic m microphenocrists (plagioclase rhyolite Baraboo and light), polarized plane (micrographic, granite Hollow Baxter light), polarized plane granular, (subhedral diorite Denzer in textures typical of Photomicrographs 3. Figure Figure 3. Photomicrographs of typical textures in Denzer diorite (subhedral granular, plane polarized light), Baxter Hollow granite (micrographic, plane polarized light), and Baraboo rhyolite (plagioclase microphenocrysts in aphanitic matrix, crossed polarizers). Abbreviations: a, alkali feldspar; b, biotite; c, chlorite after biotite; h, hornblende; p, plagioclase, mostly albite and saussurite; q, quartz. 5). (Fig. cummingtonite and actinolite intergrown and chlorite by replaced partly is hornblende diorite. Denzer In 4). (Fig. albite and microcline end-member near of mixture fine-grained extremely an into exsolves feldspar alkali intermediate and (saussurite), epidote fine-grained and albite to transformed is plagioclase chlorite, by replaced is biotite Typically, minerals. facies greenschist of variety a by replaced completely to partly being minerals igneous with extensive, is lization recrystal- although 3), (Fig. basement Baraboo the of units all in preserved well are textures Igneous Igneous textures are well preserved in all units of the Baraboo basement (Fig. 3), although recrystal­ lization is extensive, with igneous minerals being partly to completely replaced by a variety of greenschist facies minerals. Typically, biotite is replaced by chlorite, plagioclase is transformed to albite and fine-grained epidote (saussurite), and intermediate alkali feldspar exsolves into an extremely fine-grained mixture of near end-member microcline and albite (Fig. 4). In Denzer diorite, hornblende is partly replaced by chlorite and intergrown actinolite and cummingtonite (Fig. 5). 5 5 �Figure image, showing Figure 4. 4. Back-scattered electron image, partial of relict igneous alkali feldspar, partial replacement of af (Or 54-70) 54-70) by by K-feldspar, K-feldspar, k (Or 98.5) and albite, af(Or ab p, epidote epidote and and albite albite after plagioclase; ab (Ab (Ab 96.4). 96.4). p, q, q, quartz. of amphibole in Denzer Denzer Figure 5. 5. Ca Ka X-ray map of diorite. Relict igneous hornblende, hb, partly partly chI, and an intergrowth of replaced by chlorite, chl. actinolite, act, and cummingtonite, cum. cum. BARABOO QUARTZITE QUARTZITE BARABOO The 1,500 m thick and is overlain conformably by by the black black Seeley Seeley Slate Slate The Baraboo Quartzite is 1,500 (100 (100 m), m), Freedom Freedom Dolomite Dolomite with with iron formation formation (300 m), Dake Quartzite (65 m), and Rowley Creek Slate The Baraboo Baraboo Quartzite Quartzite consists consists of of 85-90% 85-90% of of quartz quartz arenite and subordinate subordinate quartz wacke, wacke, Slate (45m). (45m). The which are characterized by prominent cross bedding bedding (Fig. (Fig. 6) 6) and and ripple ripple marks, marks, 5-10% 5-10% of ofconglomerate, conglomerate, and Although all of of these rock types have experienced low and 5-10% 5-10% of of siltstone siltstone (Fig. (Fig. 7) 7) and and pelite pelite (Fig. (Fig. 8). 8). Although grade 9) and grade metamorphism, metamorphism, the the original original clastic elastic textures are remarkably well-preserved in quartzite (Fig. 9) Figure 6. 6. Typical Typical quartzite quartzite with with prominent prominent Figure cross bedding. metasiltstone with with refracted refracted Figure 7. Typical metasiltstone Coin isis 2.5 2.5 cm in in cleavage, Field cleavage, Field Locality Locality 2. 2. Coin diameter. 6 6 �fL. Figure 9. Photomicrograph of typical quartzite with relict clastic texture (partly crossed polarizers). polarizers). crossed (partly texture elastic relict with quartzite typical of Photomicrograph 9. Figure __j cleavage. crenulation and folds chevron with Larue, near Metapelite 8. Figure Figure 8. Metapelite near Larue, with chevron folds and crenulation cleavage. polarizers). crossed (partly texture elastic relict with metasiltstone of Photomicrograph 10. Figure Figure 10. Photomicrograph of metasiltstone with relict clastic texture (partly crossed polarizers). intense experienced that region source a implies sediments interval Baraboo the of maturity chemical ages average to compared and shale average to normalized extreme The 11). (Fig. different of shale are compositions rock the when apparent readily (Al:O±K2O+Na2O+CaO) is maturity chemical of degree remarkable The Al203/ 100*molar = CIA radius. ionic decreasing 98.6. to 96.8 from ranging high, exceptionally of order in arranged Elements ages. the over shale average to compared and 1985) McLeiman, and (Taylor is Alteration of Index Chemical The MnO. and MgO, CaO, Na20, K20, of concentrations shale average to normalized rocks, metasedimentary interval Baraboo fine-grained of Compositions 11. Figure low extremely with H20, and Ti02, Fe203, A1203, Si Al Fe Mg Ca Na K Si02, of entirely almost consist chemically 0.001 quartzites Barron and Sioux, Baraboo, the Cenozoic & from metapelite and Metasiltstone minerals. Mesozoic heavy among apatite and rutile, magnetite, 0.01 Paleozoic zircon, of predominance the and pyrophyllite, x of abundance the feldspar, detrital of absence Proterozoic near the from inferred been long has Quartzite x 0.1 Archean Baraboo the of maturity chemical The -9-Sioux metasiltstone. and quartzite in domains interstitial in and 8), (Fig. cleavage crenulation Barron of development by accompanied is it where Baraboo layers, metapelite in only occurred has lization recrystal- Complete 10). (Fig. metasiltstone metasiltstone (Fig. 10). Complete recrystal­ 10 F r - - - - - - - - - - - - - - - - - - _ lization has occurred only in metapelite layers, Baraboo -.­ CIA 50.4 - 65.4 where it is accompanied by development of Barron crenulation cleavage (Fig. 8), and in interstitial .. < SIOUX domains in quartzite and metasiltstone. ".ii x -; The chemical maturity of the Baraboo ~ Archean f 0< Quartzite has long been inferred from the near ~ 0.1f~ ProterozOic absence of detrital feldspar, the abundance of x ii PaleOZOIC pyrophyllite, and the predominance of zircon, E CIA 96.8 - 98.6 magnetite, rutile, and apatite among heavy "' MeSOZOIc & CenozoIc minerals. Metasiltstone and metapelite from the Baraboo, Sioux, and Barron quartzites 0.001 I~-----'---~--~-----'---~--'---' K Na Ca Mg Fe AI Si chemically consist almost entirely of SiOl, Ah03, Fe 203, Ti0 2, and H 20, with extremely low Figure I 1. Compositions of fine-grained Baraboo interval metasedimentary rocks. normalized to average shale concentrations of KlO, Na 20, CaO, MgO, and (Taylor and McLennan, 1985) and compared to average MnO. The Chemical Index of Alteration is shale over the ages. Elements arranged in order of exceptionally high, ranging from 96.8 to 98.6. decreasing ionic radius. CIA = 100*molar AbO/ The remarkable degree of chemical maturity is (AbOJ+K20+N a20+CaO) readily apparent when the rock compositions are normalized to average shale and compared to average shale of different ages (Fig. 11). The extreme chemical maturity of the Baraboo interval sediments implies a source region that experienced intense 10 ~ 1i~ ; ~ : ~I ~ , .. ~ . ' 7 7 �chemical leaching leaching and and produced produced detritus detritus consisting consisting largely largely of of quartz, quartz, kaolinite, kaolinite, and and hematite. hematite. chemical The persistent question about the about the grains of of the Baraboo Quartzite and relative ages of I Individual Individual grains of detrital detrital zircon zircon 0.34 ft from basal Baraboo Quartzite 0.34 from basal Baraboo Quartzite Baxter Hollow granite was was resolved resolved with with the the 1800 Ma UW Radio genic Isotope Lab ! UW Radiogenic Isotope Lab 1800 Ma discovery of the sub-Baraboo paleosol in drill of paleosol in drill Analyst: Analyst: Ron Ron Schott Schott 0.30 0.30 core from Baxter Hollow (Medaris (Medaris et et al., aI., 1996) 1996) 1600 and subsequent recognition of 1600 Ma _ _ 1761 (3) I of saprolite saprolite in in b ,i712(4) •1866 (3) outcrop in Baxter Hollow granite granite and and in in 0.26 1715(12) 6 rhyolite beneath the east end 1400 MaZ °.'222 1691(2) -1866 (3) end of of the syncline syncline 1400 Ma - 1691 (2) al., 1997). (Medaris et aI., 1997). Further Further confirmation confirmation i< •17793 . 0 0.22 -1779 (3) post-1,750 Ma depositional age of of the post-l,750 of the 0- ° CD o quartzite was provided by U-Pb analyses of N M. detrital zircon from near the base of of the the 0.18 1000 Ma quartzite, using the single-grain evaporation quartzite, 1740 (6) -1740 (6) technique. Among Among the the seven seven grains grains analyzed, analyzed, _~I --'---'----'I_ _ J 0.14 0.14 six are slightly discordant and and one one is is more more so, so, 5.0 4.0 3.0 2.0 1.0 1.0 2.0 3.0 4.0 5.0 age of with one onegrain grainyielding yieldinga 207Pb/206Pb a 207Pbpo6Pb age 2O7pb* 207 * / 235 pb U 1,691 1,866 Ma, and the other other six six ranging rangingfrom from 1,691 12. V-Pb U-Pb concordia concordia diagram diagram for Figure 12. Figure for detrital detrital zircon zireon to 1,779 Ma (Fig. (Fig. 12; Dott et al., 1997). Although a1., 1997). Although grains from the Baraboo Quartzite. 207Pb/206Pb ages are grains from the Baraboo Quartzite. 207Pbfo6 Pb ages are of 1,691 1,691 and 1,715 1,715 Ma are the two grains with ages of given for for individual individualgrains; grains;2cr 2 standard given standard deviations deviations are are shown in parentheses. highly radiogenic and may not be reliable, the the in parentheses. shown other grains are "well behaved" and indicate indicate that + hematite deposition may ~ 1,710 Ma. may have have begun begunas aslate lateasas—4,710 qtz :!: hematite diorite, qtz diorite, rutile rutile silt stone granite svanbergite siltstone 5vanbergite granite METAMORPHISM & petite pelite albite & rhyolite & & rhyolite albite r ' I ~ ,I / - ­ 01.1- ;;~; ~i~) "" II 1 chlorite chlorite pale osol pri actinolite paleosol Although the structure of of the Baraboo Range actinolite cummingtonite has been been well well studied, studied, little attention has has been cummingtonite has been mc epidote epidote devoted to metamorphism, other than identifying identifying titanite titanite pyrophyllite in metapelite. ItItisis now (kaolinite, now known known that that all all (kaolinite, retrograde) lithologic units in the Baraboo Baraboo Range Range have have been been retrograde) recrystallized to varying hydrothermal varying degrees degrees by by low-grade low-grade veins metamorphism (Medaris et at., 1998). Because of veins metamorphism (Medaris et aI., 1998). Because Si02 the extreme chemical maturity maturity of ofmany many rock rock types, types, the critical mineral assemblages can be adequately represented in in the the system, system, K20-Al203-Si02K 20-Ab03-SiOz- H20 H20 (KASH) (Fig. 13). Baraboo quartzite. metasiltstone, (KASH) (Fig. 13). Baraboo quartzite. metasiltstone, and metapelite metapelite contain contain quartz and pyrophyllite plus plus and svanbergite (a hematite, rutile, and svanbergite accessory hematite, (a strontian strontian aluminophosphate-sulfate diagenetic diagenetic mineral); mineral); of quartz, quartz, muscovite, muscovite, hematite, hematite, metapaleosol consists of usp and rutile; rutile; hydrothermal hydrothermal veins veins near of the the and near the the base base of A1203 K20 quartzite contain pyrophyllite, muscovite, and Figure compositions and diaspore; and the metaigneous basement is Figure 13. 13. Rock Rock compositions and mineral mineral assemblages assemblages in in the Baraboo Range, projected into the system, the Baraboo Range, projected into the system, KASH. KASH. characterized by quartz, microcline, microcIine, and and albite albite Abbreviations: dsp, diaspore; mc, microcline; ms, mus+/- muscovite, hematite, chlorite, epidote, epidote, titanite, titanite, Abbreviations: dsp, diaspore; me, microeline: ms, mus­ covite; qtz, covite; qtz, quartz: quartz: pri. prl. pyrophyllite. pyrophylJite. actinolite, and cummingtonite, depending depending on on 8 8 ,I �2. and I Localities Field on sections following the in further discussed are results new significant These magmatism. River Wolf from pulse thermal a by driven fluids hydrothermal of activity the to related presumably found, was Ma —1,460 at overprint strong a metamorphism, Ma 1,630 for evidence obtaining than rather However, 2001). eta!., (Naymark Ma 1,630 of age metamorphic a confirm to effort an in taken under- recently was Range Baraboo the in muscovite (1975). and hornblende of investigation 40Ar/39Ar A eta!. Schnius Van and (1972) Dalziel and Dott north. the to ages older and Penokean from south the in of data from recalculated intercept and Age ages post-Penokean separates front tectonic the 2000); Valley. River Fox the and Baraboo from rhyolite and granite for isochron Rb-Sr 15. Figure a!., et Romano 1998; al., et (Holm rocks basement in biotite and hornblende of analyses 40Ar/39Ar 6 S I Ri.r by established was 1) Fig. (see Wisconsin central 40 30 20 10 0 0.6 and northern in deformation foreland of extent 0.70254 the marking front tectonic a of position The 8.1 = MSWD 0.8 time. this at occurred also Range Baraboo the of metamorphism and folding that implication 1.0 5 the with 1993), Schmusetal., Van 1983; (Dott, U.S. southwest the in orogeny Mazatzal 1.2 w Ma -—1,650 the with associated deformation foreland to related metamorphism low-grade 1.4 regional by caused was resetting Rb-Sr granite Valley River Fox V such that suggested was it Subsequently, ). yr rhyohte Valley River Fox = Ma(X 33 ± 1,635 of age isochron BaxterHollowgranite 1.42*10.11 1.6 rhyolite Baraboo A Rb-Sr whole-rock apparent an yielded Valley River Fox the and Baraboo from rocks igneous that and Ma —l,650 at region Superior Lake southern the in systems Rb-Sr of resetting widespread was there that recognized Schmus Van 1975 in However, Range. Baraboo the from available were ages mineral metamorphic meaningful no recently, Until metamorphism. Baraboo of conditions the precisely more establish to effort an in underway are studies inclusion Fluid respectively. C, 335 1. = a(H20) for calculated and 290 and 50°C, 3 and 275 to lowered be would KASH, system, the in reactions Stable 14. Figure limits temperature these example for 0.9 0C T activity, H20 reduced At 345°C. and 305°C 450 400 350 300 250 to further temperature the restrict between 0 Quartzite Baraboo the of base the at veins hydrothermal in diaspore and pyrophyllite of coexistence The kbar. 1 at 60°C 3 and 285°C 2 between to metamorphism of temperature the constrains kyanite) or (andalusite phase 4 aluminosilicate an or kaolinite of absence the in pyrophyllite and quartz of association stable The 14. Figure in shown topology 6 the in resulting 1989), al., et (Brown base data thermodynamic GeoCaic the of means by activity H20 unit at calculated been have 8 KASH, system, the in equilibria Phase product. retrograde a is it that indicate relations textural occurs, kaolinite Where composition. bulk specific specific bulk composition. Where kaolinite occurs, textural relations indicate that it is a retrograde product. Phase equilibria in the system, KASH, 8I I \ , , have been calculated at unit H 20 activity by means of the GeoCalc thermodynamic data base (Brown et al., 1989), resulting in the 6 topology shown in Figure 14. The stable association of quartz and pyrophyllite in the .... (IJ absence of kaolinite or an aluminosilicate ~ 4 phase (andalusite or kyanite) constrains the 0: temperature of metamorphism to between 2 285°C and 360°C at 1 kbar. The coexistence of pyrophyllite and diaspore in hydrothermal veins at the base of the Baraboo Quartzite oI V /1 <1 /' I I I I restrict the temperature further to between 250 300 350 400 450 305°C and 345°C. At reduced H 20 activity, T,oC 0.9 for example, these temperature limits Figure 14. Stable reactions in the system, KASH, would be lowered to 275 and 350°C, and 290 and calculated for a(HzO) = I. 335°C, respectively. Fluid inclusion studies are underway in an effort to establish more precisely the conditions of Baraboo metamorphism. Until recently, no meaningful metamorphic mineral ages were available from the Baraboo Range. However, in 1975 Van Schmus recognized that there was widespread resetting of Rb-Sr systems in the southern Lake Superior region at ~ 1,650 Ma and that igneous rocks from Baraboo and the Fox River Valley yielded an apparent whole-rock Rb-Sr I l. Baraboo rhyolite 1.6 Y Baxter Hollow granite isochron age of 1,635 ± 33 Ma (A = 1.42*10. 11 n Fox River Valley rhyolite yr· l ). Subsequently, it was suggested that such 'V Fox River Valley granite 1.4 Rb-Sr resetting was caused by regional <0 low-grade metamorphism related to foreland ~ (f) 1.2 deformation associated with the ~ 1,650 Ma !'--­ Mazatzal orogeny in the southwest U.S. (Dott, <Xl (jj 1.0 1983; Van Schmus et aL, 1993), with the implication that folding and metamorphism of 0.8 the Baraboo Range also occurred at this time. MSWD = 8.1 The position of a tectonic front marking the 0.6 I I I I I I I I extent of foreland deformation in northern and o 10 20 30 40 central Wisconsin (see Fig. 1) was established by Rrfl7j sr8 6 40 ArP9 Ar analyses of hornblende and biotite in basement rocks (Holm et al., 1998; Romano et aL, Figure 15. Rb-Sr isochron for granite and 2000); the tectonic front separates post-Penokean ages rhyolite from Baraboo and the Fox River Valley. in the south from Penokean and older ages to the north. Age and intercept recalculated from data of A 40ArP9 Ar investigation of hornblende and Dott and Dalziel (1972) and Van Schmus et al. muscovite in the Baraboo Range was recently under(1975). taken in an effort to confirm a metamorphic age of 1,630 Ma (Naymark et al., 2001). However, rather than obtaining evidence for 1,630 Ma metamorphism, a strong overprint at -1,460 Ma was found, presumably related to the activity of hydrothermal fluids driven by a thermal pulse from Wolf River magmatism. These significant new results are discussed further in the following sections on Field Localities 1 and 2. i . . . I — 9 9 ! I �DESCRIPTIONS OF FIELD TRIP LOCALITIES LOCALITIES Figure 16. Figure 16. Perspective Perspective sketch sketch map map of of the the Baraboo Baraboo Range, Range, showthg showing Field Field Trip Trip Localities Localities 1-4, 1-4, of quartzite in in the Baraboo syncline syncline (light stipple), extent extent of of glacial glacial drift drift (parallel (parallel distribution of lines), and and important from map map by by L.J. LJ. Maher). Maher). lines), important geographic geographic features features (modified (modified from Locality 1: Locality 1: Baxter Baxter Hollow Hollow 1 (SW¼, Sec 33, 33, T1IN, TI iN, R6E; (SW i4, Sec R6E; Figure Figure 17) 17) Relation Baxter Hollow Hollow granite granite and and Baraboo Relation between between Baxter Baraboo Quartzite; sub-Baraboo paleosol Quartzite: sub-Baraboo paleosol Note that the are on Note that the outcrops outcrops in in Baxter Baxter Hollow Holloware 0!l private private property, and and pennission permission is is required required for for access. access. property, Although the contact contact between Although the between Baxter Baxter Hollow Hollow granite and Baraboo Quartzite is not exposed, granite and Baraboo Quartzite is not exposed, the the closest outcrops of the two rock types being 20 closest outcrops of the two rock types being 20 feet feet apart, (1970) concluded and Doff Dott (1970) concluded that that quartzite quartzite apart, Daiziel Dalziel and is nonconformable on on granite, granite, because is nonconformable because of of the the absence absence of granitic granitic dikes dikes in quartzite, quartzite of in quartzite, quartzite xenoliths xenoliths in in granite, and contact metamorphic effects in quartzite. granite, and contact metamorphic effects in quartzite. The uppermost uppermost outcrops outcrops of of granite granite in The in Baxter Baxter Hollow Hollow are commonly commonly sheared, sheared, most most likely are likely due due to to concenconcen­ tration along the tration of of deformation deformation along the quartzite-granite quartzite-granite Figure 17. Locality 1, 1, Baxter Baxter Hollow. Hollow. Symbols: Symbols: PEg, PEg, contact by differential slip between two competent contact by differential slip between two competent Baxter Hollow Hollow granite; granite P€b, Quartzite Baxter PEb, Baraboo Quartzite; lithologic units units during during folding. folding. lithologic €, Upper Cambrian quartzite conglomerate and E, and conglomeratic sandstone. This and other locality locality maps from from Dalziel and Dott, 1970. maps 1970. 10 10 �i; I :1 W rrIiiI I . ' c: 11: 18. Composite figure figure of Baraboo Baraboo paleosol paleosol in Drill Drill Core 613. Left: boxed drill core with recovered Figure 18. quartzite. regolith, and saprolite; saprolite; center: enlargements of selected selected intervals; right: photomicrographs of quartzite (note (note Si0 Si022 overgrowths on on detrital detrital quartz quartz grains). grains). regolith (pedogene). and saprolite. quartzite saprolite. 11 11 �The lower lower 100-200 The 100-200 meters meters of of quartzite quartzite exposed exposed uphill uphill to to the the north north are are characterized characterized by by red, red, Pebbles average 30 sand-sized strata strata with with pebble mm in in sand-sized pebble beds beds and and lenses. lenses. Metapelite Metapelite layers layers are are rare. rare. Pebbles average 30 mm formation, milky vein quartz pebbles diameter, but range up to 68 mm near the base. Throughout the diameter, but range up to 68 mm near the base. Throughout the formation, milky vein quartz pebbles The latter probably predominate, predominate, but but red red cherty cherty granules granules and and pebbles pebbles form form aa persistent persistent lesser lesser component. component. The latter probably Stratification here here consists include include clasts clasts of of devitrified devitrified groundmass groundmass from from the the 1,750 1,750 Ma Ma rhyolites. rhyolites. Stratification consists mostly mostly 50 cm thick. Several these of long, low-angle oflong, low-angle cross cross bedding bedding in in both both tabular tabular and and wedge wedge sets sets up up to to 50 cm thick. Several sets sets of ofthese overturning beneath beneath their their upper upper truncation truncation surfaces. surfaces. A cross laminae show syndepositional overturning A sudden sudden and disturbed pore fluid and grain increase of shear velocity scoured grains from the bed increase of shear velocity scoured grains from the bed and disturbed pore fluid and grain packing, packing, causing incipient of the the cross cross bed bed set set deformed deformed as as ififentirely entirely causing incipient liquefaction liquefaction during during which which the the upper upper part part of characteristic of fluvial and liquid. Such Such distorted distorted cross liquid. cross bedding bedding in in low-angle low-angle sets sets is is most most characteristic of fluvial and tidal tidal sands, sands, which experience large fluctuations of current velocity. which experience large fluctuations of current velocity. holes drilled drilled in The quartzite-granite quartzite-granite contact The contact was was penetrated penetrated by by eight eight holes in 1959 1959 by by the the U.S. U.S. Army Army the contact was recovered in only one drill core, this this Corps of Engineers, and although material from the contact was recovered in only one drill core, single recovery was fortuitous, because it demonstrates the the existence existence of of aa paleosol paleosol beneath beneath the the quartzite quartzite pebbly quartzite is separated from underlying (Medaris et et al., al., 1997). 18) overlying overlying pebbly quartzite is separated from underlying (Medaris 1997). In In drill drill core core 613 613 (Fig. (Fig. 18) pedogenic zone, zone, consisting consisting of of fine-grained foot-thick, reddish-purple pedogenic granitic saprolite saprolite by byaa2Y2 2\12 foot-thick, fine-grained hematite, hematite, largely Granitic texture is preserved in saprolite, but biotite quartz, and muscovite (± (± kaolinite). kaolinite). Granitic texture is preserved in saprolite, but biotite is is largely replaced by by muscovite. muscovite. The replaced by hematite, and and feldspar feldspar isis completely completely replaced The first first feldspar feldspar to to appear appear in in of the saprolite drill core is feet below below quartzite. quartzite. Note that is —30 ~30 feet that the the uppermost uppermost part part ofthe saprolite (2" (2" thick) thick) has has aa not in to that pronounced pronounced planar planar fabric fabric (Fig. (Fig. 18), 18), which which is is similar similar in in style, style, if if not in scale, scale, to that in in the the sheared sheared granite granite outcrops. change in oxides, has been calculated by Chemical weathering weathering in as % Chemical in the the paleosol, paleosol, expressed expressed as % change in oxides, has been calculated by unweathered granites from outcrops —30 and 40 feet comparing paleosol paleosol samples comparing samples to to the the average average of of two two unweathered granites from outcrops ~30 and 40 feet (Fig. to be be immobile during weathering below the contact, contact,and andnormalizing normalizingtotoA1203, Al z0 3, which which is is assumed assumed to immobile during weathering (Fig. in K. effective removal of Mg, Ca, and Na, and enrichment 19). 19). The The most most notable notable chemical chemical changes changes are effective removal of Mg, Ca, and Na, and enrichment in K. o ,.-----~-o-r~ 0 o 1 ,--------,---___, 0.1 o ~ .::."....;~. ,.~..... :. " :.......'::..1­ 0 a ~ I s s ss ~ 10 {g :.~ 10 10 ••••••••••••••••••••• •••• ••••••• J••••• GG .. ..... 100 ~--'-'---'--'-~~...L.......l.-o-~ 20 -20 -40 -60 -60 -40 -20 00 20 01 — ~ ..~ s 10 :~ L ..; 100 -100 -100 100 0 0 100 300 200 200 300 % change Fe203 % change Fe203 L . 50 25 0 100-100......--e~-'-'-'-'~~~.L........J -50 -25 -75 -100 -75 -50 -25 MgO 0 25 50 % change Lot % change MgO 0.1 ,------,-~-___, 0 0 0 III ~ 0.1 01 01 b 10 I r i G % % change change S102 5i02 01 ~ 0 0 I peciogenic pedogenic zone z one, 0 0 0 i,: ~(·········t·:~ i·····:::,;::··l···:~·····r·1· 1 I 0) -c 0 1 0 .- s saprO1!t 10 10 is athered ,·················,1; ·········,··;;=:,:;;;;····;1'· ·················'···1·;·'· I_t_II• GIG 100 100 -100 -100 -80 -80 -60 -60 ' -40 -40 -20 -20 % change % change CaO CaO 00 1 0 -60 ' -1000-60 -100 -80 -60 -40 -40 -20 -20 % change Na20 % change Na20 ' 0 0 100-80 -60 -40 -20 0 ' 20 . -80 -60 -40 -20 0 K20 20 % change % change K20 19. Depth Depth variation variation in in % % change change of of selected selected oxides Figure Figure 19. oxides in in the the Baraboo Baraboo paleosol. paleosol. 0, O. pedigene; pedigene; S, S, saprolite; saprolite; G, G, granite. granite. 12 12 40 60 40 60 �___________________________________________ occurred, but that K K was We believe that all feldspar was altered during weathering weathering and that K leaching occurred, reintroduced during later metasomatism 80 " - - - - - - - - - - - - - - - - - - - - - - - , 80 associated with fluid flow along the sub­ subsaprolite comparison comparison 60 Baraboo nonconformity. Note that detrital E 0 ]i feldspar is rare in quartzite, and interlayered, interlayered, 0 ec. 40 0. fine-grained metasedimentary metasedimentary rocks are are 20 .S for impoverished in K, Na, and Ca. A model for ~ \ ,c .... t.:: / .s0 01 Baraboo saprolite, prior to K metasomatism, metasomatism, ~ is is provided by the Barron saprolite, saprolite, which is ~ -20 a) ~ unmetamorphosed and located located north of the the • asa) -40 0) g> inferred 1,630 Ma tectonic front (Fig. 1; 1; 0 ~ -60 -c Medaris, 2000). A comparison comparison of the two ':!< o -80 saprolites (Fig. 20) reveals a close similarity similarity in most elements, except for the enrichment of -100 ! ¥ ! '.~! ! -100 p AI Si Rb Al Rb KK Ba Sr Na Ca Ca Mg Mn Fe Fe Ti K and Rb in Baraboo saprolite. The chemical features of the Baraboo and Barron paleosols Figure Figure 20. Chemical Chemical comparison of are similar to those of modern-day, modem-day, mature weathering weathering Baraboo and Barron saprolites. Baraboo profiles developed in warm, humid climates. profiles - (,l C.) 1 I 1 An apparent whole-rock Rb-Sr isochron age of the paleosol is 1336 ± ± 75 Ma (Fig. 21), and 39 Ar release spectrum, with a well-defined plateau plateau at at metasaprolite yields a discordant 39Ar muscovite from metasaprolite evidence for 1,456 ± 11 (Fig. Naymark et aI., These data provide the substantial evidence a 1,456 11 Ma 22; al., 2001). These data provide first substantial ± Wolf River imprint on the Baraboo Range, due most likely to the the effects of hydrothermal hydrothermal fluids that were channeled along the sub-Baraboo nonconformity and driven by a thermal pulse generated by regionally sub-Baraboo nonconformity extensive magmatism of Wolf River age. 0.85 j ~ 0.80 (jj r-:- co (jj 075 0.75 z 7 I a0 I I 1 I I 1500 ro 1500 1)3 ~ 1250 1250 OJ 'E ~ « 0. c. 0. c. I I I I I 55 I ! L1J~ 1456 t 11 ± Ma (2o) Ma (20") 1000 1000 750 muscovite, metasapralite, metasaprolite, Baxter Hollow muscovite. Hallow 500 500 250 250 o 0 I 6 ThnJI IF=!' C) Cl «0 MSWD = 19.4 194 2 4 2 3 3 4 TI- - - - - - - - - - - - - - - - - - - - , 1750 1750 UW Radiogenic Radio genic Isotope Lab Lab Analyst: Ron Schott — 0.70817 0.70817 ~ 0.70 0.70 \ 2000 I Baraboo paleosol paleosol R regolith (pedogene) (pedogene R S s saprolite saprolite UW Rare Gas Geochronology UWRare Geochronoiogy Lab Lab Analyst: A!,ssa Alissa Naymark Naymark 4naIySf: +-I---~--~---~-------< 40 60 80 20 40 60 80 100 o 0 7 Cumulative 39Ar Released (%) 87; Sr 86 Rb87! Sr86 Rb Figure 21. Rb-Sr whole-rock isochron for the paleoso!. metamorphosed Baraboo paleosol. 39Ar Figure 22. 22. 39 Ar release spectrum for muscovite from the the metamorphosed Baraboo saprolite. 13 13 �Locality 2: 2: Hydrothermal Hydrothermal Veins. Locality Veins, Hwy Hwy 12 12 (SW1/4, NE1/4, Sec Sec 34, 34, TIIN, Ti iN, R6E; (SWl/4, NEl/4, R6E; Figure Figure 23) 23) Diaspore.-muscovite-pyrophyllite veins in in Baraboo Baraboo Diaspore-muscovite-pyrophyllite veins Quartzite, near the base of the section Quartzite, near the base ofthe section Figure 24. 24. Diaspore-muscovite-pyrOPhyllite Figure Diaspore-muscovite-pyrophyllite veins veins in quartzite. in quartzite. Figure 23. Locality 2, 2, hydrothermal hydrothennal vems veins in in quartzite. Symbols as in in Fig. Fig. 17. 17. of Baraboo Quartzite, which contains a A few few meters meters east east of dark red A of Highway Highway 12 12 is is aa dark red outcrop outcrop of Baraboo Quartzite, which contains a consisting of of diaspore, diaspore, muscovite, muscovite, and network ofthin, of thin, white network white hydrothermal hydrothermal veins veins (Fig. (Fig. 24), 24), consisting and pyrophyllite. pyrophyllite. occurring in the center and intergrown muscovite The veins veins are are commonly zoned, with The with diaspore occurring in the center and intergrown muscovite and and pyrophyllite along the margins (Fig. 25). Kaolinite pyrophyllite along the margins (Fig. 25). Kaolinite of pyrophyllite. occurs as a retrograde replacement of pyrophyllite. Locally, fine-grained fine-grained sedimentary Locally, sedimentary rocks, rocks, originally quartz-bearing, near the base of the originally quartz-bearing, near the base of the quartzite have quartzite have been been pervasively pervasively replaced replaced by by diaspore, diaspore, muscovite, pyrophyllite, pyrophyllite, and muscovite, and hematite, hematite, resulting resulting in in aa soft, purple-red stone that was quarried by Native soft, purple-red stone that was quarried by Native Americans for for the the production production of of pipes. pipes. This Americans This mineral mineral assemblage is the same assemblage is the same as as that that in in the the classic classic pipestone (catlinite) (catlinite) from pipestone from the the Sioux Sioux Quartzite Quartzite (Medaris et al., 1999). The formation (Medaris et a!., 1999). The formation of of diaspore diaspore at at 300-350°C in in the the Si0 Si02-rich 300-350°C environment of of the the 2-rich environment Baraboo and and Sioux Baraboo Sioux quartzites quartzites is is surprising, surprising, and and requires the influence of a fluid phase with an requires the influence of a fluid phase with an 0.01. extremely extremely low low activity activity of of Si02, Si0 2, on on the the order order of of 0.0 I. 14 14 05mm Figure 25. Photomicrograph of hydrothermal vein in Figure 25. Photomicrograph ofhydrothennal vein in quartzite (plane (plane polarized polarized light). quartzite light). Abbreviations: Abbreviations: dsp, dsp. diaspore; ms, muscovite: prl, pyrophyllite. diaspore; ms. muscovite: prl. pyrophyllite. �Muscovite in a sample discordant 39Ar 39Ar release release spectrum with with a Locality 2 yields a discordant sample of vein from Locality " --------------------, 2000 plateau age of 1,467 ± 11 Ma, which is within ± 11 error of the 1,456 Ma plateau age for muscovite muscovite 1750 1750 from metasaprolite. Thus, the age of fluid 1500 1500 ..... ro activity responsible for K-metasomatism in the 1250 Baraboo 1,460 Ma. J1250j ~ -1,460 Baraboo Range is well established at ~ 1467 ±± 11 Ma Ma (2o) (20-) 1467 Although migration was C woo 1000 Although large-scale fluid migration !!! probably probably driven by heat from Wolf River fr 750 muscovite, ms-pu-dsp ms-prl-dsp vein, vein, Hwy Hwy 12 12 muscovite, c( magmatism, magmatism, the source and composition of such 500 500 fluid fluid remains remains unknown unknown and deserves UW Rare Gas Gas Geocivoao!ogy GeochronologyLab Lab 250 250 UWRare investigation. Analyst: Alissa Nayma,* Naymarl< AaaIyst I f 11 AhSSa Figure 26. Ar release spectrum for muscovite from ~ 26. 39 Ar hydrothermal vein in quartzite, Highway 12. o 0 I o 0 I 20 20 40 40 60 60 80 80 100 100 CumulatIve 39Ar Released (%) (%) Cumulative Ar Released Locality 3: Quartzite Quartzite and and Metapelite, Metapelite, Hwy 12 12 (NWI/4, IS, Ti TlIN, Figure 27) 27) (NW 1/4, Sec 15, iN, R6E; Figure Sedimentary and metamorphic metamorphic features of Baraboo Baraboo Sedimentwy quartzite and metapelite metapelite "~:Ji£b Qal 27. Locality 3. 3, Baraboo quartzite and meta­ metaFigure 27. Symbols: Qal. Qal, Quaternary alluvium; other pelite. Symbols: as in in Fig. Fig. 17. 17. symbols as outcrop at Locality Locality 3, illustrating illustrating aa Figure 28. Quartzite outcrop cross sets reactivation surface (left arrow) and contorted cross (right arrow). DO NOT HAMMER HAMMER THIS OUTCROP! OUTCROP! The upper stratigraphic stratigraphic portion portion of the Baraboo quartzite differs in several ways ways from the lower part part at at The Baxter Hollow. Pebbly layers are rare, metapelite layers are Baxter are more more common common (the thickest known zone zone isis exposed here), here), and the style style of stratification is different. Cross bedding exposed bedding is higher angle and occurs occurs in in sets sets mostly 10 10 to 20 em cm thick. thick. Master Master bedding surfaces are commonly defined by by thin metapelite. metapelite. Individual mostly are slightly slightly concave upward; sets of cross laminae are mostly tabular, but some cross laminae are some troughtrough­ shaped sets occur in this roadcut. Excellent asymmetric. sinous-crested sinous-crested ripple ripple marks marks visible visible on one of the exposure indicate the dominant dominant south-flowing surface in the middle ofthe south-flowing paleocurrent direction typical typical the entire foonation. formation. for the On the south-facing south-facing cliff, several reactivation surfaces and some some contorted cross cross sets sets are are exposed exposed in cross section section (Fig. 28). Reactivation surfaces are convex-up in convex-up truncations truncations of of cross bed sets. They They spasmodic activation of of dune forms that produce cross bedding, and are most most characteristic characteristic of indicate spasmodic 15 15 �tidal systems. The dominant migrate to to form form cross cross laminations, laminations, then tidal systems. The dominant tidal tidal flow flow activates activates dunes, dunes, which which migrate then the subordinate flow partially erodes the dunes to form the convex-up surface. When the tide the subordinate flow partially erodes the dunes to form the convex-up surface. When the tide turns turns again, again, the dominant of cross cross laminae, which bury the reactivation laminae, which bury the reactivation the dominant flow flow reactivates reactivates the the dunes dunes to to form form aa new new set set of surface. In this cliff, the the dominant dominant currenf current'ss bed bed shear occasionally disturbed disturbed the the grain grain packing packing and and caused deformation of cross laminae as described for Locality 1. Reactivation surfaces suggest that the the caused deformation of cross laminae as described for Locality I. Reactivation surfaces suggest that origin, indicating a gradual northward of the Baraboo Quartzite is of of shallow marine origin, indicating a gradual northward upper half of transgression during formations are are all all considered considered to to be transgression during its its deposition; deposition; the the overlying overlying Precambrian Precambrian formations be normal normal marine. manne. of the A the north end of of the the roadcut roadcut and and at at the the top A prominent prominent metapelite metapelite layer layer is is exposed exposed at at the north end top of the hill, hill, metapelite (Fig. where one one can can see see excellent exposures of and crenulation crenulation cleavage cleavage in in metapelite (Fig. 29). of chevron folds folds and 29). where Red quartzite quartzite boudins are common Red common in in metapelite, metapelite, as as are are folded folded white white quartz quartz veins, veins, which which appear appear to to inferred to to have have originally originally been emanate from from the the quartzite quartzite boudins. boudins. The metapelite is inferred been aa kaolinite-rich kaolinite-rich in metapelite, which shale, based on its bulk chemical composition. composition. The which is is shale, The present present mineral mineral assemblage assemblage in metapelite, with subordinate typical for metapelite metapelite throughout throughout the the Baraboo Baraboo Range, Range, consists consists mostly mostly of ofpyrophyilite pyrophyllite with subordinate small grains grains of of rutile, and minor tablets of of black black hematite, hematite, small rutile, and minor amounts of recrystallized quartz, thin tablets retrograde kaolinite (Fig. 30). Trace of retrograde kaolinite (Fig. 30). Trace amounts amounts of Ce-bearing svanbergite, SrAl3(P04)(S04)(OH)6, Ce-bearing svanbergite, SrAb(P0 4 )(S04)(OH)6, 10 to 20 20 !-lm tm in 10 to in diameter, diameter, are are scattered scattered through through the the metapelite (Medaris and Fournelle, 1998). The metapelite (Medaris and Fournelle, 1998). The occurrence of this this diagenetic diagenetic aluminophosphatealuminophosphate­ occurrence of sulfate mineral is significant because itit bears bears on on sulfate mineral is significant because the phosphorus flux in the oceans. the phosphorus flux in the oceans. Figure 30. Back-scattered Back-scattered electron electron image image of of Figure 30. metapelite. Locality 3. Abbreviations: h, hematite; metapelite, Locality 3. Abbreviations: h, hematite; k, k, kaolinite; kaolinite; p, p, pyrophyllite; pyrophyllite; q, q, quartz. quartz. Figure 29. Chevron folds folds and and crenulation crenulation cleavage cleavage in metapelite, Locality 3. The scale The scale coin, coin, enhanced enhanced by a black circle, is is 2.5 cm em in in diameter. diameter. DO NOT HAMMER THIS THIS OUTCROP! OUTCROP! 16 16 �Gorge Ableman's 4: Locality Locality 4: Ableman's Gorge dunes eolian Cambrian Upper Rock; Hise Van zone; breccia quartzite quartzite; in layers metasiltstone and ripples Quartzite; Baraboo and conglomerate Cambrian Upper between unconformity Angular 31) Figure R5E; T12N, 28/29, Sec (SW1/4, (SW1I4, Sec 28/29, T12N, R5E; Figure 31) Angular unconformity between Upper Cambrian conglomerate and Baraboo Quartzite; ripples and metasiltstone layers in quartzite; quartzite breccia zone; Van Hise Rock; Upper Cambrian eolian dunes 17. Fig. in as symbols other Group; City Tunnel Cambrian Upper €tc, Sandstone; Galesville Cambrian Upper Eg Symbols: dunes. eolian Cambrian and unconformity angular 4D, Rock; Hise Van 4C, breccia; quartzite 4B, Quartzite; Baraboo and conglomerate Cambrian Upper between unconformity angular 4A: Gorge. Ableman's 4, Locality 31. Figure Figure 31. Locality 4, Ableman's Gorge. 4A: angular unconformity between Upper Cambrian conglomerate and Baraboo Quartzite; 4B, quartzite breccia; 4C, Van Hise Rock; 4D, angular unconformity and Cambrian eolian dunes. Symbols: €g Upper Cambrian Galesville Sandstone; Etc, Upper Cambrian Tunnel City Group; other symbols as in Fig. 17. N 8r,,",,- Zon. ­ 1100 1000 .11m:['p'f~~ ~11.EJ51in ",?,.iH I~~~900 D B C 1 ? ? A t 'kh~s;;~.. 5'/0 iOcx ~:;;:;r~I']1'l' ~'fq 'Opo Feel o Feel (1970). Dott and Daiziel from Modified gorge. the of ends both at cliffs quartzite buried against butting strata Cambrian of symmetiy the Note D. - A letters by indicated Localities Field with west), (lookmg Gorge Ableman's through section Cross 32. Figure Figure 32. Cross section through Ableman's Gorge (looking west), with Field Localities indicated by letters A-D. Note the symmetry of Cambrian strata butting against buried quartzite cliffs at both ends of the gorge. Modified from Dalziel and Dott (1970). features guartzite unconformity; angular Precambrian - Cambrian Upper 4A: 4A: Upper Cambrian - Precambrian angular unconformity; quartzite features Baraboo. the of part upper marine, the in be must exposures These waves. by formation indicate which symmetric, and straight relatively are these of crests the 3, Locality at ripples the Unlike bed. overlying the of bottom the on ripples the of casts are see we What board. wash great-grandmother's resembling face marked ripple spectacular a is quarry the of end south The help). (binoculars boulders quartzite coarse with conglomerate Cambrian Upper brown-weathering and quartzite red between unconformity angular the see can one cliff, the of top the At face. quarry old the in visible layers metasiltstone thin and sets bed cross with quartzite vertical exposes 32) (Fig. Gorge Ableman's of side west the on quarry abandoned The The abandoned quarry on the west side of Ableman's Gorge (Fig. 32) exposes vertical quartzite with cross bed sets and thin metasiltstone layers visible in the old quarry face. At the top of the cliff, one can see the angular unconformity between red quartzite and brown-weathering Upper Cambrian conglomerate with coarse quartzite boulders (binoculars help). The south end of the quarry is a spectacular ripple marked face resembling great-grandmother's wash board. What we see are casts of the ripples on the bOllom of the overlying bed. Unlike the ripples at Locality 3, the crests of these are relatively straight and symmetric, which indicate formation by waves. These exposures must be in the marine, upper part of the Baraboo. 17 17 �4B:Qjiartzite 4B: Quartzite Breccia Breccia Zone Exposed on on the the west west wall wall of the gorge Exposed of the gorge is is aa quartzite breccia zone, consisting of angular red quartzite breccia zone, consisting blocks cemented cemented by a stockwork of of white quartz blocks generally massive, veins (Fig. (Fig. 33). 33). The vein quartz is generally massive, veins of which but locally euhedral quartz crystals, some crystals, some of which (a member member of are coated by dickite (a of the the kaolinite kaolinite are The mineral group), group), occur occur in mineral in vugs vugs (Fig. (Fig. 34). 34). The growth euhedral quartz crystals commonly show growth euhedral indicates that zoning, and and preliminary investigation indicates that zoning, isotopes quartz is is zoned zoned with with respect to oxygen isotopes as as quartz 18 from 9.33 to 18.95 %o ranging well, with 18O from 9.33 to 18.95 %0 well, with 8 0 in one one crystal crystal (Fig. (Fig. 35). 35). S. (VSMOW) in (VSMOW) S. W. W. Bailey Bailey for fluid reported a temperature of of 105-107°C 105-1 07°C for fluid reported inclusions in in the the quartz, quartz, which which is inclusions is consistent consistent with with the the (cited in in Daiziel Dalziel and and Doft, Dott, 1970). 1970). presence of dickite (cited In some some places places in in the the breccia breccia zone, zone, the the In slightly separated quartzite fragments fragments appear quartzite appear to to be be slightly separated the impression pieces of a jigsaw jigsaw puzzle, giving the impression that that fragmented by some the quartzite might have been fragmented by the some Perhaps brecciation type of explosive activity. Perhaps brecciation was was type (sub critical caused by passage of a low-temperature caused by passage of a low-temperature (sub critical fluid to to the the vapor vapor point) hydrothermal hydrothermal fluid point) fluid from from the the fluid shallower levels field as it migrated from deeper to shallower levels field Figure 33. Quartzite breccia, Martm-Marietta Quarry, north limb limb of of the the along the the quartzite strata in the north along Figure 33. Quartzite breccia, Martin-Marietta Quarry, along strike and 1 km east of Field Locality 4B. hydrothermal activity activity is syncline. The The age age of such hydrothermal along strike and ­ I km east of Field Locality 4B. is syncline. Precambrian, because unknown, other other than than being being Precambrian, unknown, because Cambrian conglomerate. breccia boulders and cobbles of quartzite occur in in the the overlying overlying Upper Upper Cambrian conglomerate. boulders and cobbles of quartzite breccia occur 1 mm 1 mm UW Stable Isotope Lab Analyst: Mike Spicuzza UW Stable Isotope Lab Analyst Mike Spicu2Za Sample Sample 98BB20 986820 breccia, Figure 34. 34. Polished Polished slab Figure slab of of quartzite quartzite breccia, crystals. showing aa vug vug lined lined by by euhedral euhedral quartz showing quartz crystals. VSMOW) in a zoned Figure 35. Variation of ö'°O 180 (%o, of8 (%0, VSMOW) in a zoned Figure 35. Variation breccia. euhedral quartz crystal from the quartzite euhedral quartz crystal from the quartzite breccia. 18 18 �here. quartzite the in seen be also can cleavage widely-spaced a and bedding Cross idea. better a have not do We surface. unusual this produced probably time Pleistocene during silt and sand by blasting wind that suggested Twenhofel W.H. 1930s, the In polish. exceptional an has quartzite of outcrop an highway, the of west just and north meters 100 32). (Fig. gorge the of end south the at spring artesian the behind seen is as quartzite the in joints and bedding along weathering by produced fissures down filtered that sand Cambrian as it interpret We saw? just we that unconformity the below feet 200 least at here doing this is What quartzite. vertical of outcrop an within quartzite of fragments angular enclosing sandstone quartz Cambrian-type tan-colored, has exposure subtle a zone, breccia the of north meters 100 About alteration. hydrothermal of episodes unrelated and different two by affected was Range Baraboo the whether or 2), and 1 (Localities quartzite the of base the modified that fluids River-age Wolf the of variants shallower and cooler are brecciation with associated fluids thermal hydro- the whether seen be to remains It Range. Baraboo the in feature widespread a thus is breccia quartzite of development The syncline. the throughout scattered are vertical, and east-west oriented also features, breccia incipient with veins quartz thin and kilometers, of-20 distance a over syncline Baraboo the of limb north the along occur breccia quartzite of Outcrops dip. vertical and strike east-west an with layers, quartzite adjoining the to parallel oriented and thick meters -400 is zone breccia The The breccia zone is ~ 100 meters thick and oriented parallel to the adjoining quartzite layers, with an east-west strike and vertical dip. Outcrops of quartzite breccia occur along the north limb of the Baraboo syncline over a distance of ~20 kilometers, and thin quartz veins with incipient breccia features, also oriented east-west and vertical, are scattered throughout the syncline. The development of quartzite breccia is thus a widespread feature in the Baraboo Range. It remains to be seen whether the hydro­ thermal fluids associated with brecciation are cooler and shallower variants of the Wolf River-age fluids that modified the base of the quartzite (Localities 1 and 2), or whether the Baraboo Range was affected by two different and unrelated episodes of hydrothermal alteration. About 100 meters north of the breccia zone, a subtle exposure has tan-colored, Cambrian-type quartz sandstone enclosing angular fragments of quartzite within an outcrop of vertical quartzite. What is this doing here at least 200 feet below the unconformity that we just saw? We interpret it as Cambrian sand that filtered down fissures produced by weathering along bedding and joints in the quartzite as is seen behind the artesian spring at the south end of the gorge (Fig. 32). 100 meters north and just west of the highway, an outcrop of quartzite has an exceptional polish. In the 1930s, W.H. Twenhofel suggested that wind blasting by sand and silt during Pleistocene time probably produced this unusual surface. We do not have a better idea. Cross bedding and a widely-spaced cleavage can also be seen in the quartzite here. Rock Hise Van 4C: 4C: Van Hise Rock wall). washboard ripple-cast the did (as south the to be also must up' 'way the that shows geometry its for this, with consistent is bedding cross truncated The Gorge. Ableman's of south the to axis its with syncline a be must structure that that infer then We fold. large a surface axial the parallels roughly cleavage the that assume we part, a is Rock Hise Van which of structure larger the see not can we Although beds. quartzite two these of each in visible is bedding cross addition, In side. either on quartzite pink coarser the into (flattens) refracts cleavage this that note degrees; 20 about northward dipping cleavage slaty shows it Today Quartzite. Baraboo the of part upper the mudstone silty a as deposited was rock the of center the in band dark vertical The within Landmark. Historical National a declared was Rock the 1999, May, In annually. visit professionals and students of hundreds century; a for trips field for stop essential an this made has Rock Hise Van of clarity and accessibility The 'way-up.' or direction facing structural determining for marks ripple and bedding cross folds, drag cleavage, of use the perfected team Their region. Superior Lake the of geology Precambrian the study to side. either on quartzite cross-bedded by bounded layer central Leith later and Hise Van by headed Madison slaty the with east, the from viewed Rock Hise Van 36. Figure at office district a 1882 in established had Survey Geological U.S. the mining, iron of commencement the by Stimulated country. vegetated in clear not typically are which structures, larger-scale inferring for clue scale outcrop- an as bedding and cleavage slaty between relationship geometric fundamental the demonstrate to laboratory a as this used Leith, K. Charles protégé, his and Hise Van R. Charles sign. historic 1999 a and plaque metal 1923 a by described as geologists, for interest historic special of is 36) (Fig. highway the of side east the on Rock Hise Van Van Hise Rock on the east side of the highway (Fig. 36) is of special historic interest for geologists, as described by a 1923 metal plaque and a 1999 historic sign. Charles R. Van Hise and his protege, Charles K. Leith, used this as a laboratory to demonstrate the fundamental geometric relationship between slaty cleavage and bedding as an outcrop­ scale clue for inferring larger-scale structures, which are typically not clear in vegetated country. Stimulated by the commencement of iron mining, the U.S. Geological Survey had established in 1882 a district office at Figure 36. Van Hise Rock viewed from the east, with the slaty Madison headed by Van Hise and later Leith central layer bounded by cross-bedded quartzite on either side. to study the Precambrian geology of the Lake Superior region. Their team perfected the use of cleavage, drag folds, cross bedding and ripple marks for determining structural facing direction or 'way-up.' The accessibility and clarity of Van Hise Rock has made this an essential stop for field trips for a century; hundreds of students and professionals visit annually. In May, 1999, the Rock was declared a National Historical Landmark. The vertical dark band in the center of the rock was deposited as a silty mudstone within the upper part of the Baraboo Quartzite. Today it shows slaty cleavage dipping northward about 20 degrees; note that this cleavage refracts (flattens) into the coarser pink quartzite on either side. In addition, cross bedding is visible in each of these two quartzite beds. Although we can not see the larger structure of which Van Hise Rock is a part, we assume that the cleavage roughly parallels the axial surface a large fold. We then infer that that structure must be a syncline with its axis to the south of Ableman's Gorge. The truncated cross bedding is consistent with this, for its geometry shows that the 'way up' must also be to the south (as did the ripple-cast washboard wall). 19 19 �and Eolian 4D: Basal Basal Cambrian Cambrian Unconformity and 4D: Eolian Dunes Dunes basal Cambrian unconformity again to the northeast (Fig. From Van Van Hise Hise Rock, From Rock, we we can can see see the the basal Cambrian unconformity again to the northeast (Fig. Cambrian conglomerates. high on on the the wall wall at the top 32, right right end). end). The flat-lying strata high 32, at the top of of the the Gorge Gorge are are Cambrian conglomerates. against buried cliffs of sandstones underlie As shown shown in in Figure 32, Cambrian sandstones As underlie these these and and terminate terminate against buried cliffs of eolian dunes blown up these sandstones quartzite. Large, Large, sweeping cross beds in these quartzite. sandstones were were formed formed within within eolian dunes blown up fell from the cliffs to be angular blocks blocks of of quartzite quartzite occasionally against those those cliffs. cliffs. Rare, Rare, scattered angular against occasionally fell from the cliffs to be Late Cambrian sea is sand. The The arrival the encroaching buried, but but not abraded, abraded, by by the the eolian sand. buried, arrival here here of ofthe encroaching Late Cambrian sea is quartzite conglomerate, which is underlain by a recorded by by aa sharp boundary with overlying rounded recorded rounded quartzite conglomerate, which isparallel underlain by a vertical called Skolithos (closely spaced, straight, sandstone layer with marine worm burrows called sandstone Skolithos (closely spaced, straight, parallel vertical 20 mm from 33 -- 20 tubes about 1 mm in diameter and from mm long). long). pocket sample of most of the important features of the Ableman's Gorge provides a geologic vest of the Ableman's Gorge provides a geologic vest pocket sample of most of the important within afeatures mountain deposited, then then folded folded and Baraboo Hills. Baraboo Quartzite was deposited, and metamorphosed metamorphosed within a mountain Ma ago), an elliptical ring of quartzite hills eroded. In range, which was then eroded. In Late Late Cambrian Cambrian time time (500 (500 Ma ago), an elliptical ring of quartzite hills range, encroached, those hills were converted deposits. Then, began to be buried by wind deposits. began Then, as as the the Cambrian Cambrian sea sea encroached, those hills were converted tropics at about 15 degrees south latitude, so islands. North North America America lay to an an atoll-like atoll-like ring ring of of islands. lay in in the the tropics at about 15 degrees south latitude, so to cliffs and tore away quartzite huge waves, waves, which the sea passing tropical storms generated huge which broke broke upon upon the sea cliffs and tore away quartzite and occasionally swept rounded boulders blocks. Repetition of this scenario rounded boulders up up to to 1.5 1.5 m m in in diameter, diameter, and occasionally swept blocks. the islands became buried by sediment, for half haifaa kilometer some of them them offshore for kilometer or or so. so. Gradually Gradually the islands becameisland burieddisappeared by sediment, some by the clearly revealed than here. The Abieman testimony of which is nowhere more clearly revealed than here. The Ableman island disappeared by the buried until the end of the Ordovician highest islands end of Cambrian time, but the highest islands were were not not finally finally buried until the end ofthe Ordovician end Period (ca 440 Ma). Acknowledgments departmental Weare are indebted indebted to to many of our departmental We many ofour encouragement, and and colleagues for for their interest, encouragement, colleagues John Fournelle technical expertise. These include technical expertise. These include John Fournelle (rare gas (electron microprobe,1, Brad Singer Singer (rare (electron microprobe), Brad gas isotopes), isotopes), John Valley (stable Clark Johnson (radiogenic isotopes), Clark Johnson isotopes), John Valley (stable inclusions), who isotopes), and and Phil Phil Brown Brown ('fluid (fluid inelusiam), who isotopes), made possible possible provided analytical analytical facilities facilities that that made provided Baraboo data. data. Several acquisition ofmany of man of the new ofthe new Baraboo Several acquisition analyses that that are are students and technicians pe/formed performed analyses students Alissa Nayniark, reported here, reported here, including ineluding Robb Robb Bunge, Bunge, Alissa Naymark. Brian Hess Hess prepared prepared Ron Schott, Schott, and and Mike Mike Spicuzza. Spicuzza. Brian Ron thin sections, sections, and and Mary various types of high-quality thin ofhigh-quality Mmy composite diagram of the Diman created created the Diman the marvelous marvelous composite diagram ofthe Baraboo paleosol. Geological and and Natural Natural From the From the Wisconsin Wisconsin Geological provided access to the History Survey. Histor.v Survey. Bruce Bruce Brown Brown provided access to the examination which Baxter Hollow Hollow drill drill core. core, the Baxter the examination of ofwhich take aa new look at at the to take prompted us to new look the Baraboo Baraboo Range, Range, the Barron and Mike Mudrey informed us of paleosol, and Mike Mudrey informed us of the Barron paleosol. unmnodJIedBaraboo Baraboo which serves serves as as aa model for unmodified which model for paleosol. 20 20 Cleopatra's Needle, overlooking Devil's Lake Cleopatra's Needle, overlooking Devil's Lake �REFERENCES Anderson, J.L., Cullers, RL. Anorogenic metaluniinous metaluminous and peraluminous peraluminous granite R.L. and Van Schmus. Sciunus. W.R W.R. (1980) Anorogenic plutonism Wisconsin, USA: Contrib. Mineral. PetroL, 311- 328. plutomsm in the Mid-Proterozoic of Wisconsin, Petrol., v. 74, p. 311PTA-system: a Geo-Calc Geo-Calc software software package package for the Brown, T.H., Berman, RG. and Perkins, E.H. (1989) PTA-system: Mineral., v. 74, 74, p. p. 485-487. 485-487. calculation and display of activity-temperature-pressure phase diagrams: Amer. Mineral., Jr. (1970) Geology of the Baraboo Wisconsin: Wisconsin Geol. GeoL Nat. Dalziel, I.W.D. and Dott, RH. Jr. Baraboo district, Wisconsin: History Survey ml. Inf. Circ. 14. 164 pp. 164 pp. in the the north-central north-central United States: States: Resolved Resolved by by plate plate Dott, RH., R.H., Jr. (1983) The Proterozoic red quartzite enigma in collision?: GeoL p. 129-141. Geol. Soc. Amer. Memoir 160. p. 129-141. Dott, R.H., Jr. and Dalziel, I.W.D. (1972) Age and correlation of of the Precambrian Baraboo Baraboo Quartzite of Wisconsin: 552-568. Jour. Geol., v. 80, p. p. Dott, R.H., Jr., Medaris, L.G., Jr. and Schott. RC. (1997) Doll, Schott, R.C. (1997) Post-1760-Ma deposition of the Baraboo Quartzite: Confinnation Soc. Amer. Abstracts with Programs, Programs. v. Confirmation from detrital zircon ages and new field evidence: Geol. Soc. 29, No.4, No. 4, p.13. p.13. of Early Proterozoic Proterozoic quartzites in in the Holm, Hoim. D.K., Schneider, C.D. (1998) Age and deformation of Schneider, D. and Coath, C.D assembly of southern Lake Superior region: Implications Implications for extent of foreland defonnation deformation during final assembly Laurentia: Geology, V. p. 907-910. v. 26, p. 907-9 10. Dott, R.H.. Jr.. J.H.. Johnson, C.M., Schott, R.C. R.e. and and Baumgartner, L.P. (1996) Age Age Medaris, L.G., Jr., Dolt, Jr., Fournelle, J.H.. CM., Schott, Inst. Lake Superior Geol., Abstracts with and geological significance Superior Geol., significance of the Baraboo Quartzite Quartzite: 42nd 1nst. Programs, v. 42, p. p. 31-32. Dott, R.H.. RH.. Jr. Jr. and McSweeney, K. (1997) (1997) The sub-Baraboo paleosol, Medaris, L.G., Jr., Baumgartner, Bau.mgartner, L.P.. Dolt weathering and metasomatism: metasomatism: 43rd 43rd Inst. Lake Lake Superior Superior Wisconsin: Geochemical Geochemical evidence for Proterozoic weathering 43. p. 3 9-40. p. 39-4U. Geol., Abstracts with Programs, v. 43, R.J. (1998) Post-1.76 Ga low-grade metamorphism of Medaris, L.G., Jr., Brown, Brown. P.B. and Bunge. Rl of the the Baraboo Baraboo v. 44, p.89-90. p.89-90. Quartzite: 44th Inst. Lake Superior Geol.. Abstracts with with Programs, v. Medaris, L.G., Jr., and Foumelk Svanbergite in the Baraboo Baraboo Quartzite: Quartzite: Significance Significance for diagenetic Fournelle. lH J.H. (1998) Svanbergite Geol., Abstracts with processes and phosphorous flux in Precambrian oceans: 44th Inst. Lake Superior GeoL Programs, V. v. 44, p.91-92. p.91-92. Medaris, L.G., Jr., Fournelle, 1.H., Broihan, J.H. (1999) Chemical and mineralogical J.H., Boszhardt, R.F. and Broihan. comparison of Baraboo, Barron. and Sioux argillite. metapelite and pipestone: 45th Inst. Lake Superior Geol., Abstracts with Programs. Programs, v. 45. p.35-36. p.35-36. Medaris, L.G., L.G.. lr. Jr. (2000) The Barron saprolite Confirmation of mature chemical weathering in the the source for Mcdaris, saprolite: Confirmation Paleoproterozoic Paleoproterozoic quartz arenites aremtes in the Lake Superior Superior region: 46th Inst. Lake Superior Geol., Abstracts with Programs, v. 46, p. p. 37-38. Naymark, A., Singer, B.S. and Medaris, L. G.. Jr I) Recognition of Wolf River-age metamorphism in the L.G.. Jr. (200 (2001) Baraboo Ar thermochronology: thermochronology: Geol. Soc. Amer. Abstracts with Programs, v. V. 33, Baraboo Range by means of 4°ArP~ 40Ax/39Ar no. 4, in press. Romano, D., Holm, D.K. and Foland. K.A. (2UOO) (2000) Determining the extent and nature of Mazatzal-related overprinting of the Penokean orogenic belt in the southern Lake Superior region, north-central USA: Res.. v. 104, p. Precambrian Res., p. 25-46 Smith, E.I. El. (1978) Precambrian rhyolites and granites in south-central Wisconsin: Field relations and Smith, 875-890. geochemistry: GeoL Geol. Soc. Amer. Bull Bull.... v 89. p. 875-890. SR. and McLennan, Crust: Its Composition and Evolution: Blackwell, BlackwelL Taylor. S.R McLeiman. S.M. SM. (1985) (1985) The ContlI1ental Continental Crust: Oxford, 312 pp. pp. Van Schmus, W.R., Thurman. E.M. and Peterman. Z.E. ZE (1975) Geology and Rb-Sr chronology chronology of Middle Wisconsin: Geol. Soc. Amer. Bull., v. 86. Precambrian rocks in eastern and central Wisconsin BulL, V. 86, p. p. 1255-1265. K.C. (1993) Early Proterozoic Jr. Proterozoic crustal evolution, in Reed, J.C. J.e. Jr Van Schmus, W.R., Bickford. M.E. and Condie. K.c. U.S.. Geology of North America, America. V. v. C-2, GeoL Geol. Soc. Amer., Boulder, et al., eds., Precambrian: Conterminous US. Boulder, p. 270-281. 21 �This page intentionally left blank �Field Trip 2 Geology, Ore Deposits, and Cultural History of the Upper Mississippi Valley Zinc-Lead District M.G. Mudrey, Jr. Wisconsin Geological and Natural History Survey 3817 Mineral Point Road Madison, Wisconsin 53705-5100 T.C. Hunt University of Wisconsin–Platteville Platteville, Wisconsin 53818 Headframe of a southwestern Wisconsin zinc-lead mine circa 1930 (photograph courtesy of Platteville Mining Museum). �This page intentionally left blank �BACKGROUND The Upper Mississippi Valley Zinc-Lead District of southwestern Wisconsin was one of the oldest continuously producing mining districts in the United States. The largest and most productive parts of the district extended across five Wisconsin counties and into small areas in Illinois and Iowa (fig. 1). Over 1.2 million tons of zinc and nearly 100,000 tons of lead were recovered from the Wisconsin part of the Upper Mississippi Valley District from 1910 to 1974. Heyl and others (1959) suggested that an additional 250,000 tons of zinc and 350,000 tons of lead were produced in the Wisconsin part of the district from 1800 to 1910. This field trip provides a geologic, mineral deposit, and cultural overview of the area. Numerous detailed geologic reports about the area have been prepared; the most significant by Heyl and others (1959) documents ____ R5W. 4 5, 8Z0p8 5 3 4 (lW. 2 ShE. 3 2 N. 5.3* - %J 98 AL CR A N FORD E H 111151(1150 So..0411. , 04 WyLodfl CL 20. Elk.d.,° :: a F/\ PlO1( PlO / 20. Pb ,-51k90R00 'I 90 DE L A W 0th_I:. 08 -: J P1.5*—rn. J3UQU( \ sal 0 U B UO 80* Yb..t a S —- S. RSW '4.zo MADISON — I M(H..b smo LA F A 3 4 1 Y 0AV A S / 084101118(0 — E TT E I N A 4W O \J0 •s I I Pb O L.m (0.o V*-. PSZ.o13 c1( I oa.,...jus. ! CX,I2 SM_S ON 08_i —— b.l W110 P111th do. 5u a—. L F'-—— 94 1*, 0 Ce,18 Mi Pt1 -+44 ,1L58 FL A M A K 97 ° / E Pd - ESS 6 RAE INDEX TO MINES AND DIGGINGS 25 . M0.,.IC,.d01.I08 2 LO&1(jIfld000000 3. Cop,., 0111 ,.io. 4 R1500IO0 00.4 O!W1080 5. 3.01410118011*44401(1 7 24 N 6. AlI leAd Clj1(11884101111t 51(101 C 0100W Il1llI• 9 W800$AORId(OIOOdd00lII*l ID 11111. IIIC5*ff11 0* dIgolliR II W00dlO.4I..d10040 8. f( 12. 0It11Cnl*0p IS. D.195W1111110141 IS. 5101. 811ff SWOOP - IS $o!dgqOfl q00.0, IN 05.100111. 4IWIP II 0(1.10 dIRgIIOP IS St*d(01(&IOSddMO. IS. 1010 C SSZAOP 20. M4*0..A9W14( 2!. *40041.444111(1 22. ML C41011 4089040 250808* 0 EXPLANATION 081.180. .1.5840.4110.110. dSIII.404 e1 — Ml.,, 01 5.1858010 1R Geltilt 0.00,89, and P1110.4111. MIt. II 0410 II• P00.1, dli CA.,, 410115 — 41.0800 Pb.Z0,Co.d 16.4. 8AO0 (005011.01 II Figure 1. Map of the main part of the Upper Mississippi Valley district and mineral deposits in outlying parts of the district (from Heyl and others, 1959). 25 �hundreds of mineral properties in Illinois, Iowa, and Wisconsin. A good summary of the geology and economic geology of the district is given by Heyl and others (1970). In addition, more than 1,000 square miles have been mapped and published on standard 1:24000, 7.5-minute topographic maps. The zinc and lead mines of southwestern Wisconsin are part of the earliest producing zinc-lead mining districts in the United States—the Upper Mississippi Valley District. There was a small amount of production in Minnesota. Production prior to 1800 was very small. Use of galena and mining were reported by explorers Jean Nicolet in 1634 and by Nicolas Perrot in 1692. In 1788 Julien Dubuque obtained permission from the Sauk and Fox to work lead mines in the area.. Dubuque mined, with these Native Americans as his labor force; on the west bank of the Mississippi River in the vicinity of what is now Dubuque, Iowa. This was the principal mining center in the region from 1788 until Dubuque’s death in 1810. Early white miners worked the properties during the summer, returning south in the winter. The arrival of permanent settlers in 1825, the Winnebago Peace Treaty, and “lead rush of 1827” established the Upper Mississippi District as a major mineral producer and resulted in the states of Illinois, Iowa, and Wisconsin. The Mexican War of 1847, the California Gold Rush of 1849, and the cholera epidemic of 1854 brought the district into decline, but by 1859 and the Civil War, production of lead increased, and eventually zinc production began. The District remained in production until 1978 with the close of the Eagle–Picher mine in Shullsburg. Around 1906, systematic mine mapping was begun by students and faculty at the Wisconsin School of Mines, now University of Wisconsin–Platteville. In 1946 systematic geologic mapping was initiated by the U.S. Geological Survey. This mapping program was built on the foundation of mine maps and mineral reserve studies initiated during World War II. Thecooperation of the former U.S. Bureau of Mines, U.S. Geological Survey, University of Wisconsin–Platteville, and the Wisconsin Geological and Natural History Survey led to the development of the Wisconsin Mineral Development Atlas (Heyl and Broughton, 1980). In a series of atlas plates at 1:2400-scale, mine workings, drillhole location and number, and selected surface features (roads, lead digs) are shown. The details of the 30,000 drillholes are kept in approximately two dozen large binders covering Grant, Iowa, and Lafayette Counties. Supplemental data include Green County. From this information Broughton (1991) estimated 12.5 million tons of ore averaging 4.94 percent zinc and 0.47 percent lead remain in place. There are large areas for which there is no modern (post-1900) mineral exploration, and little exploration data below the base of the Sinnipee Group. The field trip begins in Madison, Wisconsin, proceeds to Platteville (Stop 1) for an overview of the district at the Bevan Mine and Rollo Jamison Museum. The Bevan Mine is an 1845 lead mine that produced more than two million pounds of lead ore in one year. The underground workings include two dioramas, one of an 1840 crevice lead mine, and the other a 1935 zinc mine. The Mining Museum includes numerous dioramas about the regional geology and mineral deposits and how miners in the 19th century went about their business. The geologic stop will be west of Dickeyville on Potosi Hill (Stop 2). This road cut contains St. Peter sandstone (Ancell Group) at the base to Galena Dolomite (Sinnipee Group) at the top. Two stops will be made to address mine reclamation: west of New Diggings (Stop 3), where one of the few remaining area of lead digs is preserved (natural reclamation from 1840), and Shullsburg at the former Eagle–Picher mine (Stop 4). The trip ends with a tour of Pendarvis State Historical Site (Stop 5), which recreates the cultural–historical setting of the 1840s mine district. 26 �Geology and Ore Deposits The zinc-lead deposits of southwestern Wisconsin are a classic example of the stratabound Mississippi Valley-type zinc–lead deposits. Although deposits are known to occur in most of the lower Paleozoic dolomite and sandstone units of the district (fig. 2), all important ore bodies are in the Middle Ordovician Sinnipee Group (Platteville, Decorah, and Galena Formations). The most common type of deposits (fig. 3) are (1) those associated with vertical or steeply inclined joints or fractures, called gash-vein or crevice deposits (dominantly galena with gangue); j E ZINC ' z I/ i/z / / 2 A/,/ / I a % k Average Maquoketa shale 200 - Dolomite, buff, cherty; argillaceous near base 110 108—240 // Dolomite, yellowish-buff, thin-bedded, shaly 40 Dolomite, yellowish-buff, thick-bedded;.Receptacuhtes in middle 80 / - ,, 7 /7 1" Dolomite, drab to buff; cherty; Receptac-uhies near base Platteville formation Limestone and dolomite, brown and grayish; green, sandy shale and phosphatic nodules at base St. Peter sandstone Sandstone. quartz, coarse, rounded - 105 35—40 . DISCONFORMITY -DISCONFORMITY— -r-±7 225 - Dolomite, limestone, and shale, green and brown; phosphatic nodules and bentonite near base Decorah formation —— 90 // "/ / 1 0 Dolomite, buff, cherty; Pentamerizs at top, Shale, blue, dolomitic; phosphatic depauperate fauna at base Galena dolomite > — thickn:ss, Description 40+ — — ----- -- Prairie du Chien group (undifferentiated) Trempealeau formation 280- Dolomite, light-buff, cherty; sandy near base and in upper part; shaly in upper part .: - 0— 320 240 .____________ — Sandstone, siltstone, and dolomite 120-150 Franconia sandstone Sandstone and siltstone, glauconitic 110—140 Dresbach sandstone Sandstone •I- -/- - a z a, 0. 0. Eau Claire sandstone 60-- 140 Siltstone and sandstone Mount Simon :.' . -- - -. -: sandstone ---:-:-:•:•:-: Sandstone 700— 1050 440— 780 Figure 2. Simplified stratigraphic section showing relative quantitative stratigarphic distribution of lead and zinc in the Upper Mississippi Valley district (from Heyl and others, 1978). 27 �(2) those associated with inclined and horizontal fractures, called pitch-and-flat deposits (sphalerite with minor galena and gangue); (3) those consisting of fine galena and sphalerite scattered through the country rock, called disseminated deposits; and (4) those consisting of angular breccia or country rock fragments cemented with ore and associated minerals, called breccia deposits. The most abundant gangue minerals with the ore minerals sphalerite and galena are calcite, pyrite, marcasite, barite, and rarely, chalcopyrite. The ore deposits are contained within weak structures produced by gentle folds in the dolomite strata. The ore deposits show vertical and regional zoning. Copper, barium, nickel, and arsenic are abundant in the east-central part of the district. Vertically, lead is greater in the higher part of a mineralized area; zinc, iron sulfides, nickel, and secondary dolomite are more abundant in the deeper deposits, generally conforming to structural control. Details of the district and individual properties are given in Heyl and others (1959). The paragenetic sequence generally involves early deposition of quartz, dolomite, pyrite, marcasite, with several generations of sphalerite and galena. Mineralization of cobaltite, chalcopyrite, chalcocite, millerite, and enargite are reported. Late gangue minerals include most of the calcite. It should be emphasized that the paragenetic sequence is generalized. Deposition Figure 3. Diagrammatic plans and sections illustrating typical patterns of gash-vein lead deposits and underlying pitch-and-flat deposits of the arcuate and linear types and their stratigraphic position to one another (from Heyl and others, 1978). 28 �throughout the general sulfide period took place under conditions of rhythmic oscillations in composition and temperature; such oscillations formed the hundreds of minute color bands characteristic of all the main minerals. McLimans and Barnes (1975) argued that most, if not all, of the distinct color-banding in sphalerite from mine to mine and area to area are coeval. McLimans and Barnes (1975) also argued for warmer temperatures (up to 220°C) for the deposits; most other workers suggest 150°C is a maximum. The high temperature seems to be supported by Rowan and Goldhaber (1996) and Zimmerman (1986), but their interpretations differ. Rowan and Goldhaber argued for a relatively thin Paleozoic cover (less than 3,000 ft) and higher heat flow; Zimmerman argued for normal geothermal gradients, but deeper burial (up to 9,000 ft). Outside of ore deposits, regional maximum temperatures were quite low (50 to 90°C, Blabaum, 1995). I interpret these data to suggest that the region was not deeply buried, but that high temperature mineral solutions were restricted to faults and fracture channels, and hence ore deposits were hotter than country rock. Extensive lead isotope data clearly identify disconformable lead that varies regionally; lead isotope ratios are lowest to the west and south. It is generally thought that mineralization of the district occurred during the Permian–Pennsylvanian by long-distance transport of metalbearing brine from the adjacent Illinois basin. FIELD TRIP The field trip (fig. 4) will visit the Platteville Mining Museum and Bevan Mine (Stop 1), examine Ordovician geologic exposures at Potosi Hill (Stop 2), an historic unreclaimed area of 1830 lead digs near New Diggings (Stop 3), modern metallic mine reclamation at the former Shullsburg zinc–lead mine/mill site (Stop 4), and the Pendarvis State Historical Site (Stop 5). 1 Platteville Museum 2 Potosi Hill 3 New Diggings 4 Shullsburg Reclamation 5 Pendarvis Miles Figure 4. Map showing field trip stops. 29 �Stop 1: Platteville Mining Museum and Rollo Jamison Museum Location: SW¼NE¼ sec. 15, T3N, R1W, Grant County, Wisconsin (Platteville 7.5-minute topographic quadrangle, 1952). Authors: Modified from <http://platteville.wi.us/visitors/mining.html>. Description: The Platteville Mining Museum traces the development of lead and zinc mining in the Upper Mississippi Valley through models, dioramas, artifacts, and photographs. The surface part of the museum includes dioramas of mining and a mosaic of maps showing at 1:24,000scale the geology and structure of the district. The underground part of the Museum, the Bevan Lead Mine, is an 1845 lead mine which produced over two millions pounds of lead ore in one year and is accessed via a walk down decline. The diorama in the mine shows how mining was accomplished in the 1840s (crevice deposits of lead), and in the 1930s (pneumatic jackleg drill and mine carts). Ceiling bolting is extensive in the underground mine; this was a demonstration area in the the past on how to install mine bolts. A small, reconstructed headframe and hoist and a track with a 1931 locomotive and ore cars complement the underground mine. For more information contact: City of Platteville Museum Department, 405 East Main Street, P.O. Box 780, Platteville, Wisconsin 53818; telephone (608) 348-3301. Stop 2: Potosi Hill—Ordovician Sinnipee Group Location: Roadcut at east side of U.S. Highway 61 in the SW¼NW¼ sec. 7, T2N, R2W, Grant County (Potosi 7.5-minute topographic quadrangle, 1972; fig. 5). Author: M.G. Mudrey, Jr. (modified from Ostrom, 1987). Description: This is an excellent and easily accessible exposure of the upper part of the Ancell Group (St. Peter and Glenwood Formations), and the Sinnipee Group (Platteville, Decorah, and Galena Formations). The exposure consists of a lengthy roadcut on the north side of U.S. Highway 61 (Whitlow and West, 1966). At least two east–west faults are recognized in the outcrop, the most significant (about 10 ft of throw) is in the valley between the upper and lower exposures. On the southeast wall of the quarry at the north end of the roadcut can be seen an example of the pitch and flat structure that hosts the zinc–lead mineralization in the district. The Sinnipee Group is the principal host of zinc and lead mineralization in the Upper Mississippi Valley Base-Metal District. This locality has been well studied over the past 50 years. The lithologic description given is that of Agnew (1956) with modifications by Ostrom (1978, 1987), and Mudrey (field reviews from 1976 to 2001). Agnew’s descriptions are the most comprehensive; however, slumping and outcrop deterioration and road construction have changed the ease with which individual parts of the exposure may be examined. The description given here is a composite of Agnew, Ostrom, and Mudrey. Figure 6 shows the geologic section exposed at the Potosi Hill roadcut. The base of the section consists of Ordovician sandstone of the St. Peter Formation, Ancell Group. The Tonti Member is the thickest of the three members in the formation, and consists dominantly of friable fine- to coarse-grained sandstone. Thickness can vary considerably, from absent to over 100 m thick. This variation is attributed to deposition on an erosional surface; deep channels are recognized elsewhere, particularly in La Crosse County. The basal unit of the St. Peter is the clay-rich Readstown Member, which may be a reworked residual regolith. The upper unit of the St. Peter seen in this exposure is a bluish-gray silt to shale, which can be locally absent in the region. Bioturbation in this unit is common. The St. Peter appears to be a near-shore deposit (Dott and others, 1986). In the area of the type locality, St. Paul, Minnesota, it appears to be entirely ma30 �rine; in the Madison and southern Wisconsin area, it is entirely nonmarine (Winfree and Dott, 1983). Locally the St. Peter is well cemented, ranging from silica to hematite. Habermann (1978) interpreted most of the cementation as the result of duricrust development during the Ordovician; however, in places, notably in area of known zinc-lead sulfide mineralization, some of the hematite cementation appears to be the result of weathering of minor sulfide ore bodies. The overlying Ordovician Sinnipee Group consists of a basal Figure 5. Topographic map showing location of field trip stop 2. Platteville Formation of several dolomitic limestone to dolomite members; the Decorah Formation, a shaly dolomite; and the uppermost Galena Formation, a vuggy weathering cherty dolomite. The lowermost member of the Platteville Formation, the Pecatonica Member, was formerly quarried in the district for building stone. The Quimbeys Mill Member, the uppermost member of the Platteville, is a sublithographic dolomite. This less than 1-m thick bed is very distinctive and is used through the district as a marker to the base of the mining horizon (termed glass rock because of the conchoidal fracture). The overlying Decorah Formation has been defined in many ways over the years, but is generally mapped as the shaly, dolomite part of the Sinnipee Group. Members in the Decorah are easily recognized. The basal Spechts Ferry Member is overlain by the Guttenberg (pronounced GUT-ten-berg), which contains brown petroliferous shale partings. This unit recognized in the mining district as “oil rock” and is a source bed for petroleum in Iowa and Michigan, where it is deeply buried. The Ion Member overlies the Guttenberg and consists of a blue unit and a gray unit, both very shaly dolomite with minimal structural strength. Most of the zinc–lead mineralization in the area is hosted by the Ion. Thickly bedded Galena Dolomite overlies the Decorah Formation. In the absence of fossils, field mapping has relied on the abundance of chert to divide the unit into a lower cherty unit and an upper relatively non-cherty unit that is less dolomitized. Weathering of the unit results in a mosaic outcrop pattern (locally termed honey-comb), where the less dolomitic parts of the rock are dissolved in preference to the harder, more indurated well-dolomitzed parts. Receptaculites is abundant in the upper, non-cherty part of the section. 31 �120GALENA FORMATION 110- Potosi Hill Section SE ¼NW ¼ sec, 7, T2N, R2W Grant County, Wisconsin 100OECORAH FORMATION Ion Member 90- 80Guttenberg Member 70 60- 50McGregor Member 40- 30- 20Pecotonice Member 10- 0- Figure 6. Potosi Hill section; explanation on following pages. (Modified from Ostrom, 1987.) 32 �Thickness (ft) Unit Member thickness (ft) Sinnipee Group Galena Dolomite Formation Prosser Member (upper cherty) Dolomite, olive drab to light brown, thick- to thin-bedded; medium to coarse grained, vuggy, abundant white chert; Receptaculties near top 4.0 44+ (lower Receptacultities Zone) Lower Receptaculities Zone; dolomite, olive drab to light brown, thickbedded, medium-to-coarse-grained, abundant chert, abundant Receptaculities 16.0 (lower cherty) Lower Cherty Zone; dolomite, olive drab to light brown, thick- to mediumbedded, medium to coarse grained, bands of chert nodules 14.5 (buff) Lower Buff Zone; dolomite, light brown, slight green mottling; thickbedded 9.5 Decorah Formation Ion Dolomite Member (Gray Unit) Dolomite, olive to gray, medium- to thick-bedded, vuggy, green shale partings throughout, sparry calcite present 13.5 (Blue Unit) Blue unit; dolomite, purplish gray, medium grained, slightly fossiliferous. Green shale present as partings, and as 0.5-ft bed, 0.8 ft below the top of the Interval, calcite present 5.1 Shale, green dolomitic shale in middle of interval 0.9 33 19.5 �Guttenberg Limestone Member (Oil Rock) Limestone, pinkish to purplish brown, fine grained to sublithographic, fossiliferous, upper 1 ft fine- to medium-grained, red-brown shale present as parting, calcite and limonite and iron sulfide present in small amounts 4.6 Shale metabentonite, brownish orange, crumbly, sticky when wet 0.1 Limestone, purplish brown, sublithographic, thin wavy bedding, fossiliferous, brown carbonaceous shale present as thin beds and partings, calcite and limonite present. Thin metabentonite bed at base 9.6 Limestone, brown gray, fine grained, thick-bedded 1.0 15.3 Spechts Ferry Shale Member (Clay Bed) Shale, orange gray, calcareous, and limestone, tan gray, fine grained, limestone 0.4 to 0.7 ft from base of unit 0.8 Limestone, gray, fine-grained, thin bedded 0.6 Shale, gray, green, brown, fissile, some beds fossiliferous, limestone present as thin lenses near middle of the interval 3.2 Limestone, tan with iron oxide mottling, fine grained, thin bedded 0.8 Shale, gray-green-brown. Fissle with thin lenses of gray fine-grained limestone 1.7 Limestone, dark to light gray, thin-bedded fossiliferous 0.7 Shale, brown-green-orange-gray, brown carbonaceous shale parting at top 0.5 Limestone, purplish brown, fine grained, thin-bedded, very fossiliferous, fucoids at base 0.5 Metabentonite, orange, sticky when wet, with brown shale partings 0.2 8.8 Platteville Formation Quimbys Mill Member (Glass Rock) Limestone, dark purplish gray, sublithographic, thick-bedded, conchoidal fracture, irregular upper surface, shale at base 0.8 0.8 14.5 29.5 MacGregor Member (Magnolia) Limestone, light grayish tan, fine grained, dense, partings of yellowish platy shale, very fossiliferous, thin 2 in. to 10 in. beds, upper 5 ft generally thicker bedded 34 �Mifflin Sub-member Limestone, light grayish brown, fine-grained, dense, medium-to thickbedded, discontinuous partings of bluish-green shale, fossiliferous 15.0 Pecatonica Member (Quarry Beds) Dolomite, brownish gray, fine to medium crystalline, sugary texture, thinto medium-bedded, even-bedded, beds 0.1 to 18 in. thick. Weathered surface shows distinct but discontinuous thinner beds 3.0 Dolomite, bluish, medium-grained, granular, sugary textured, argillite 1.0 Dolomite, brownish gray, fine to medium grained, crystalline, sugary texture, thin- to medium-bedded, even-bedded, beds about 1in. thick 8.0 Dolomite, bluish, medium grained, granular, sugary textured, argillite 1.0 Dolomite, brownish gray, fine to medium grained, crystalline, sugary texture, medium-bedded, even-bedded, beds thicker than 1 ft 6.0 Dolomite, brownish gray, fine to medium grained crystalline, sugary texture, medium-bedded, even-bedded, beds about 1 ft thick 4.6 23.6 Ancell Group Glenwood Formation Hennepin Member (Shale) Very silty, sandy dolomite, yellowish brown, abundant phosphatic pellets up to 2 mm in diameter, scattered round medium quartz sand grains, poorly sorted, iron-oxide cemented 0.5 0.5 1.5 1.5 Harmony Hill Member Silty shale, brown and bluish green grading downward to bluish green with some redish brown, little rounded medium grained quartz sand, abundant pale green clay in matrix, reworked/bioturbated texture St. Peter Formation Tonti Member (Sandrock) Sandstone, light yellowish gray, very fine to medium grained, Some light brown stains cross-bedded Base of exposure in drainage ditch 35 �Stop 3: New Diggings Lead Digs Location: Intersection of County Highways J and W, NW¼NW¼SW¼ sec. 22, T1N, R1E, Lafayette County, Wisconsin (New Diggings, 7.5- minute quadrangle, 1952). Author: M.G. Mudrey, Jr. (2001). Description: The area south of the intersection was extensively mined for residual lead in the early part of the nineteenth century. Miners would dig down over surface occurrences of galena, collecting residual galena in the soil. At some depth, depending principally on the competency of the soil profile, the dig was abandoned, and another started adjacent to the first dig. Once the area had been mined, miners would move on to another area. There was no attempt at active reclamation or deeper mining at that time. The area north of the intersection was also heavily mined; however, leveling of the surface in the 1950 for agriculture effectively removed the topographic evidence of mining. The high alkalinity of the soil derived from the Sinnipee Group dolomite neutralizes any acid mine drainage from oxidation of sulfide minerals and allows native plant communities to rapidly recover. Stop 4: Shullsburg Mine Site—Metallic Mine Reclamation Location: East side of Lafayette County O, 2 miles south of Shullsburg, sec. 22, T1N, R1E, Lafayette County (Shullsburg 7.5-minute topographic quadrangle, 1972; fig. 7). Authors: T.C. Hunt (University of Wisconsin–Platteville) and M.G. Mudrey, Jr., 2001. Figure 7. Topographic map showing location of field trip stop 4. 36 Description: The Shullsburg/Blackstone mining unit, known as the Calumet and Hecla Mine, was discovered by Calumet and Hecla Consolidated Copper Company about 1947 in a systematic exploration drilling program. In 1949 a 360-ft shaft was sunk on the property. Typically in the Upper Mississippi Valley Base Metal District, small ore bodies were identified from surface drilling exploration, and cross-cuts and drifts were driven from existing areas of mining to the newly discovered ore. Mining was by room and pillar methods. Within the mine, many of the drifts converged to make this complex one of the largest producers in the district. Galena and sphalerite were the principal ores mined. The most abundant minerals associated with the ore minerals were calcite, pyrite, marcasite, barite, and more rarely, chalcopyrite. Some individual intersections of ore over a 10-ft vertical interval assayed at more than 14 percent zinc. The ore was processed by �an on-site 1,000 ton per day flotation mill. The mill feed ranged between 4 to 6 percent zinc (Heyl and others, 1959; Heyl and others, 1970). The ore was hosted in the Decorah Formation, about 280 ft below the pre-mine groundwater surface. Groundwater pumping to dewater the mine ranged from 4 to 17 million gallons per day, and the cone of depression extended over 12 square miles (Evans and Cieslik, 1985). Eagle Picher Company (EP) acquired the properties in 1954. EP operated this site continuously from 1954 until 1979. The zinc and lead ore body was accessed via a decline that was built to replace the shaft that had succumbed to fire. EP extracted about 1,000 tons per day using a modified room and pillar mining method and processed about 1,500 tons of ore per day in the flotation mill on-site. Ore was also received from the nearby Bear Hole mine (Reinke, 1977). In the 1970s Wisconsin changed its mining laws to require a reclamation plan and financial bonding in conjunction with a mining permit. On April 18, 1978, Eagle-Picher received a permit from the Wisconsin Department of Natural Resources to mine zinc and lead at the site. The permit to mine was secured with only an approved reclamation plan; no bond was required because the operation was permitted as a nonconforming project site (Wisconsin Department of Natural Resources, April 18, 1978). The permitted mining site covered 72 acres at the Shullsburg mine and mill and an additional acre at the Blackstone pump site. In 1981, Inspiration Development Company gained ownership of four nonconforming mining units in southwestern Wisconsin that were under permit with the Wisconsin Department of Natural Resources; the Shullsburg site was among them. Most of these sites had been developed decades earlier, but were not permitted until mid to late 1970s. Only the Bear Hole (a nearby ore deposit) and Shullsburg units produced ore after they were permitted. The mining units in southwestern Wisconsin were shut down permanently during the period of 1978 and 1979. IDC never produced ore after its purchase, but IDC assumed responsibility for the reclamation of the site which is currently in different phases of reclamation. The primary environmental concerns were groundwater and surface water pollution, dusting from waste piles, stockpiles, and roads, aesthetics, and safety concerns. Following the closure of the Shullsburg Mine water quality in some nearby private watersupply wells deteriorated. Affected wells were located within the cone of depression created by pumping to keep the underground mine dewatered (fig. 8). Following mine closure, groundwater from these wells showed increased levels of sulfate, iron, calcium, magnesium, and total dissolved solids. The mechanism of contamination was postulated to be the following sequence: (1) oxidation of sulfide minerals, (2) formation of soluble sulfate mineral phases, (3) breakdown of carbonate host rock by acid produced during sulfide oxidation, and (4) dissolution of soluble materials by groundwater with rock strata that was previously dewatered during active mining (Evans and others, 1983; Evans and Cieslik, 1985). The impacted wells were reconstructed or abandoned and new wells constructed into the underlying sandstone aquifer. Numerous relic mine waste piles exist nearby this site including flotation tailings, jig tailings, waste-rock piles, and junk piles. Waste materials were trucked off-site as merchantable by-product for purposes of construction or agriculture. The decline portal has been backfilled, graded, top dressed, and stabilized with vegetation. Surface drainage has been restored so that runoff water is discharged from the sites without significant erosion. Observable subsidence or caving has not occurred at this site. This site predates topsoil salvage requirements. Generally, no topsoil remained for redistribution during reclamation activities, but where it was available in the form of dikes and berms, it was used to topdress the site. IDC has routinely used cow manure as a substitute for topsoil to 37 �Figure 8. Areal extent of cone of depression developed around the Bear Hole and Shullsburg Mines, Lafayette County, Wisconsin (from Evans and others, 1983). \- 38 �effect the establishment of vegetation. Most of the site is reasonably well stabilized with vegetation. Introduced pasture grasses and legumes were approved by the Wisconsin Department of Natural Resources for the last phase of final reclamation at this site. During the first phase of final revegetation in the mid-1980s, native trees, grasses, and shrubs were installed (Hunt, 1989). The area is not sited in wetland habitat. Proximity to a perennial stream may have impacted the riparian area, but baseline data are scarce. Presently, the impacts appear minimal. The existence of on-site settling ponds have created wetland habitat, albeit small and of marginal value. The designated post-mining land use for the nonconforming Shullsburg mining unit is a designated wildlife area, which is compatible with the adjacent land-use pattern. The current management level of this site is low, but there are plans to conduct a prescribed fire to help revitalize the native vegetation. The topography of this site is modified by waste piles, steepsided settling ponds, and relic mine openings and artifacts. The existing vegetation is a mixture of introduced agronomic pasture grasses and native vegetation. The existing oak groves present on these sites represent pre-settlement vegetation. Stop 5: Pendarvis State Historical Site (Mineral Point) Location: NE¼SE¼ sec. 31, T4N., R3E., Iowa County, Wisconsin (Mineral Point 7.5-minute topographic quadrangle, 1980). Author: Modified from <http://www.shsw.wisc.edu/sites/pend/>. Description: The museum consists of a series of stone buildings salvaged in the 1930s by Robert Neal and Edgar Hellum, who formed a partnership to acquire, restore and rebuild the few remaining cottages built by Cornish miners in the early 19th century. Their venture, called Pendarvis after an estate in Cornwall, preserves the regional cultural legacy of the early history of mining in southwest Wisconsin. Early miners extended their search for lead from northwestern Illinois into Wisconsin around 1820. Much of this early mining was seasonal, with the miners returning south to Illinois in the winter. With the arrival of Cornish miners and their families in the late 1830s, small villages were developed in proximity to the lead mines. In the hill south of Pendaris is the Merry Christmas Mine. Originally lead was mined by recovering residual galena from the soil (the hill side is extensively pockmarked with lead digs). Once the residual lead was recovered, the early miners sunk shallow shafts (above the water table) to recover galena from bedrock. For more information: Pendarvis State Historical Site, 114 Shake Rag Street, Mineral Point, Wisconsin 53565; telephone (608) 987-2122. REFERENCES Agnew, A.F., 1956, in Agnew, A.F. and Sloan, R.E., The Ordovician Rocks of Southwestern Wisconsin and Northeastern Iowa: Second Day, October 29, 1956: in G.M. Schwartz, ed., Guidebook for Field Trips, Minneapolis Meeting, 1956, Geological Society of America, p. 86. Blabaum, J.M., 1995, Origin and maturation of the organic matter in the Middle Ordovician Guttenberg Member of the Decorah Formation of southwestern Wisconsin: Geoscience Wisconsin, v. 15, p. 71–76. 39 �Broughton, W.A., 1991, Zinc and lead reserves of southwest Wisconsin: The undrilled lead digs of southwest Wisconsin: Wisconsin Geological and Natural History Survey Open-File Report 1991-5, 11 p. Dott, R.H., Jr., Byers, C.W., Fielder, G.W., Stenzel, S.R., Winfree, K.E., 1986, Aeolian to marine transition in Cambro-Ordovician cratonic sheet sandstones of the northern Mississippi Valley, USA: Sedimentology, v. 33, no. 3, p. 345–367. Evans, T. J., and Cieslik, M.J., 1985, Impact of groundwater from closure of an underground zinc–lead mine in southwest Wisconsin: Wisconsin Geological and Natural History Survey Miscellaneous Paper 81-01, 16 p. Evans, T.J., Cieslik, M.J., and Hennings, R.G., 1983, Investigation of the effects of recent mine closings on ground-water quality and quantity in the Shullsburg area: Wisconsin Geological and Natural History Survey Open-File Report 1983-1, 36 p. Habermann, G.M., 1978, Mineralogic and textural variations of the duricrust in southwestern Wisconsin: Ph.D. thesis, University of Wisconsin–Madison, 153 p. Heyl, A.V., Jr., Agnew, A.F., Lyons, E.J., Behre, C.H., Jr., and Flint, A.E., 1959, The Geology of the Upper Mississippi Valley Zinc-Lead District: U.S. Geological Survey Professional Paper 309, 310 p. Heyl, A.V. (and Broughton, W.A.), 1980, A very brief history of the Wisconsin mineral development atlas; general information and procedures concerning zinc-lead atlas: Wisconsin Geological and Natural History Survey Open-File Report 1980-4, 6 p. Heyl, A.V., Broughton, W.A., and West, W.S., 1970 (revised 1978), Geology of the Upper Mississippi Valley Base-Metal District: Wisconsin Geological and Natural History Survey Information Circular 16, 45 p. Hunt, T.C. 1989. Mined land reclamation in Wisconsin since 1973: Ph.D. Thesis. University of Wisconsin–Madison. 194 p. McLimans, R.K. and Barnes, H.L., 1975, Sphalerite stratigraphy in the upper Mississippi Valley Pb-Zn deposits: Economic Geology, v. 70, no. 7, p. 1324–1325. Ostrom, M.E., 1978, Potosi Hill Exposure, in Geology of Wisconsin: Outcrop descriptions: Wisconsin Geological and Natural History Survey, Gr-7/2N2W, 4 p. Ostrom, M.E., 1987, Middle Ordovician rocks at Potosi Hill, Wisconsin: in Geological Society of America Centennial Field Guide–North-Central Section, 1987, p. 201–204. Reinke, G. H., December 2, 1977, Eagle-Picher Industries, Shullsburg Mine and Mill Unit Environmental Impact Assessment Worksheet, Bureau of Solid Waste Management: Wisconsin Department of Natural Resources. 40 �Rowan, E.L. and Goldhaber, M.B., 1996, Fluid inclusions and biomarkers in the Upper Mississippi Valley zinc-lead district; implications for the fluid-flow and thermal history of the Illinois: U.S. Geological Survey Bulletin B 2094-F, 34 p. Whitlow, J.W., and West, W.S., 1966, Geology of the Potosi Quadrangle, Grant County Wisconsin, and Dubuque Country, Iowa: U.S. Geological Survey Bulletin 1123-I, p. 533–571. Winfree, Keith, and Dott, R.H., Jr., Progress on the St. Peter Sandstone of the Upper Midwest, in M.G. Mudrey, Jr., Field Trip chairman, Sedimentology of Ordovician Carbonates and Sandstones in Southwestern Wisconsin: Field Trip Guide Book, 17th Annual Meeting, North-Central Section, Geological Society of America, 1983, p. 4–13. Wisconsin Department of Natural Resources. April 18, 1978, Order Number EX-78-32B. Eagle Picher Industries, Shullsburg Mine and Mill Unit Permit to Mine: Wisconsin Department of Natural Resources, 3 p. Zimmerman, R.A., 1986, Fission-track dating of samples of the Illinois drill-hole core: U.S. Geological Survey Bulletin 1622-J, p. 99–108. 41 �This page intentionally left blank �Field Trip 3 Economic Geology of the Baraboo and Waterloo Quartzites of Southern Wisconsin Bruce A. Brown Wisconsin Geological and Natural History Survey 3817 Mineral Point Road Madison, Wisconsin 53705-5100 Frank R. Luther Department of Geology University of Wisconsin–Whitewater Whitewater, Wisconsin 53190 James W. Schmitt D.L. Gasser Construction Box 441 Baraboo, Wisconsin 53913 Susan M. Courter Michels Materials Box 128 Brownsville, Wisconsin 53006 Jennifer Lien The Kraemer Company Box 235 Plain, Wisconsin 53577 Stockpiles of Baraboo quartzite aggregate, LaRue Quarry. �This page intentionally left blank �INTRODUCTION The Proterozoic quartzites of the Baraboo Range and the Waterloo area of south-central Wisconsin have been quarried for a variety of industrial mineral products since the late nineteenth century. The extreme hardness and refractory properties of the quartzite were recognized early, and both areas were important producers of refractory blocks, mill liners, grinding pebbles, and several types of abrasives. Grinding pebbles were used in place of steel balls in mills that ground clay and feldspar for the ceramic industry, talc and other materials for the cosmetic industry, and in grinding some types of metallic ores. The most commonly used pebbles were flint beach pebbles, of 3 to 4 inch size, hand picked from beaches in northern Europe. Wisconsin State Geologist William O. Hotchkiss was instrumental in promoting Wisconsin quartzite for this use when European sources were cut off during World War I. The early operations used pebbles from gravels derived from the Paleozoic conglomerates formed adjacent to the quartzite, such as we will see at Stop 2. Later, grinding balls were manufactured by crushing quartzite, sorting for size and shape, and tumbling to achieve rounding. The last grinding ball producer, the Baraboo Quartzite Co., ceased operations in the 1980s. Today the primary uses for southern Wisconsin quartzite are crushed stone aggregates, riprap, and breakwater stone. For many years, the hard, abrasive nature of the quartzites, which average 98 percent silica, made crushed quartzite aggregates prohibitively expensive due to excessive wear on crushing and screening equipment. Crusher jaws quickly wore out, and steel wire screens commonly had to be replaced daily to maintain tight gradation specifications. Modern alloys, combined with the use of plastic and rubber-faced screens, have increased efficiency and reduced the cost of producing railroad ballast and a variety of quartzite aggregates. This guide is intended to provide the locations of stops and a brief outline of the geology and industrial process and products at each site that we intend to visit. Additional handouts relating to products, testing, specifications, and history will be provided on the day of the trip. We have not provided lengthy detailed descriptions of each stop because the geologic features we will see will likely change with the next round of production blasting. Wherever possible, we have tried to cite appropriate published field guides that explain the geology of nearby or relevant exposures regularly accessible to the public. We will visit six active quarrying operations on Trip 3. Company personnel will be available to describe the geology, mining, and processing methods, and the products made at each site. Because these are active operations, we will need to sign releases and MSHA Part 46 site-specific hazard training forms. Please remember to observe all safety rules and use common sense at all times. Especially stay away from highwalls and unstable slopes. GEOLOGY OF THE QUARTZITES Because the primary focus of this trip is on economic geology, only a brief discussion of the geologic history of the Baraboo Interval rocks of southern Wisconsin is included. The reader is referred to general discussions of tectonic setting (Greenberg and Brown, 1984) and previous guides to the Waterloo area (Luther, 1992, 1997), and the Baraboo area, (Dalziel and Dott, 1970; Malone and others, 1997; Medaris and Dott, 2001). The Baraboo and Waterloo quartzites belong to a group of sedimentary rocks that include the McCaslin, Rib Mountain, Necedah, Hamilton Mound, Flambeau, Barron quartzites of Wisconsin and probably the Sioux Quartzite of Minnesota that were deposited on continental crust formed during the 1850 Ma Penokean Orogeny (Greenberg and Brown, 1984). For many years the exact age of the quartzites and the timing of deformation and metamorphism were hotly debated. Recent work summarized by Medaris and Dott (2001) suggested that the Baraboo quartzite was deposited on a basement of 1,760 Ma. Granite and rhyolite, and that most of the 45 �metamorphism and alteration at Baraboo resulted from hydrothermal activity accompanying emplacement of the Wolf River Batholith at around 1,460 Ma. The Waterloo quartzite is intruded by pegmatite of Wolf river age, suggesting that recrystallization and metamorphism may also be related to this regional thermal event. Both the Baraboo and Waterloo quartzites have been deformed. The Baraboo Range is an isolated doubly plunging syncline, slightly overturned to the south. The Waterloo outcrop area is in the nose of a broad eastward-plunging synclinal structure. Several possible models for deposition and subsequent deformation of the quartzites have been proposed (Greenberg and Brown, 1984), but the timing of deformation is still debated, possibly related to a regional 1,630 Ma thermal event, but certainly after about 1,720 Ma and prior to the 1,460 hydrothermal event. Quartzite, presumably equivalent to the Baraboo and Waterloo quartzites, is the most common basement lithology found in deep wells throughout southeastern Wisconsin. The stratigraphic sequence at Baraboo consists of 1,500 m of red to purple quartzite, overlain by 100 m of Seeley slate, 300 m of Freedom Formation (dolomite and carbonate iron formation), 65 m of pebbly Dake quartzite and 45m of Rowley Creek slate (Dalziel and Dott, 1970). The quartzite is well exposed, but the overlying formations, except for the Dake, are known from drill core. All of the operations that we will visit are located in or adjacent to the lower quartzite sequence. The upper formations are rarely exposed, being covered by Paleozoic sandstone and Quarternary glacial deposits in the interior of the syncline. At Stop 5 we will be near the site of two of the three historic iron mines that, before closing in the early 1920s, briefly mined the iron-rich carbonates of the Freedom Formation. The stratigraphic sequence at Waterloo is poorly known because of very limited exposure. Most of the known outcrop is in the area of the Michels Quarry, and consists of gray pebbly quartzite interbedded with argillite beds that have been metamorphosed to andalusite schist (Luther, 1992, 1997). Outlying exposures that show less evidence of metamorphism tend to have the more typical reddish-purple color and hydrothermal quartz veins and breccias seen in other Baraboo Interval quartzites. Stop 1: Michels Materials Waterloo Quarry Location: NE¼ sec. 33 and NW¼ sec. 34, T 9N, R13E, 1.5 miles east of Portland, Wisconsin, on Highway 19 (Waterloo 7.5-minute topographic quadrangle, 1976; fig. 1). Leaders: Frank Luther, Sue Courter, and Bruce A. Brown. Description: The Michels Waterloo Quarry was opened in 1988 by the Edward E. Gillen Co., a Milwaukee marine contractor involved in harbor and breakwater construction on the Great Lakes. Exploratory core drilling indicated massive bedding up to 2 to 3 m thick that would allow for quarrying of individual blocks up to 20 tons in size. The rock was tested and proved to exceed all Corps of Engineers specifications for breakwater stone, particularly resistant to freezethaw. The quarry site is also conveniently located for transport of blocks to Milwaukee by rail or truck. The Gillen Co. soon began to accumulate a large pile of waste blocks too small for breakwater stone and brought in crushing equipment to convert this material into railroad ballast and other aggregate. A rail loading facility was built 1 mile south of the quarry and ballast is moved to the site by truck. The rock is gray to reddish gray in color and consists of thoroughly recrystallized sandsized quartz grains, with interlayered pebbly beds containing pebbles of quartz, chert, jasper, and iron formation up to 1.5 cm. The massive beds of quartzite are separated by 10 to 20 cm argillite beds that are metamorphosed to andalusite schist. The thick east-dipping beds facilitate quarrying of large blocks, but make maintaining a flat quarry floor difficult. Glacial till overburden thickens to the east, and contains abundant quartzite boulders. Paleozoic sandstone conglomerate similar to the Parfreys Glen Formation of the Baraboo area locally occurs above the quartzite. 46 �- _S - 55 ± -_S— — _ 44' S -. -S — __-44-44.'44— 44—7895 .- - -44- -44-44- z 7 Figure 1. Topographic map showing location of Stop 1. We will examine the quarry geology, mining and crushing methods, and products. From Waterloo we will proceed northwestward across the glaciated terrane of eastern Dane County to Stop 2, located at the east end of the Baraboo Range. On the way we will have the opportunity to see some classic examples of drumlins and other glacial landforms. Stop 2: The Kraemer Co. Williams Quarry Location: SE¼, NE¼ sec. 19, T 12 N, R 8,E, Columbia County, south side of Highway 33, about 3 miles west of I-90-94 (Pine Island 7.5-minute topographic quadrangle, 1975; fig. 2). Leaders: Jennifer Lien, Phil Fauble, and Bruce A. Brown. Description: The Williams Quarry and another operation 0.5 mile to the west were opened in the Parfreys Glen Formation (Clayton and Attig, 1990), a time-transgressive, proximal conglomeratic facies formed by wave and storm action around the Baraboo Range as it was slowly buried by advancing seas during Cambrian and Ordovician time. The face at Williams has now advanced far enough into the hillside to expose three distinct lithologic units. At the base of the highwall, steeply dipping quartzite of the Baraboo north range is exposed. The quartzite is cut by numerous white quartz veins, and is locally brecciated and recemented by white hydrothermal quartz. Vugs and cavities in the breccia zone are filled with white clay and lined with quartz crystals up to 20 cm in length. Overlying the quartzite is a poorly sorted deposit consisting of clasts ranging from sand sized up to rocks 2 to 3 m in diameter (fig. 3). Fauble and Lien (2001) suggested that this unit may have originated as a debris flow because of the lack of sorting and evidence of reworking by wave action. Overlying and lapping onto the debris flow are beds of pebble conglomerate and sandstone typical of the Parfreys Glen Formation. These beds contain sedimentary structures and trace fossils typical of near-shore marine deposits. Abundant glauconite suggests equivalence to 47 �Figure 2. Topographic map showing location of Stop 2. Figure 3. South face at Williams Quarry showing Parfreys Glen conglomerate over coarse debris flow deposit overlying quartzite with white veins and clay pockets. the Tunnel City Group away from the Baraboo Range. The Williams Quarry produces base course and a small amount of riprap. Crushing and screening are done intermittently as needed, using portable equipment, typical of smaller quarry operations throughout rural Wisconsin. 48 �Stop 3: 1,760 Ma Rhyolite Location: SW¼ NE¼ sec. 33, T12N, R7E, south side of Highway 33, 0.3 mile east of the Lower Narrows of the Baraboo River (Lewiston 7.5-minute topographic quadrangle, 1975; fig. 4). Leader: Bruce A. Brown. Description: We will stop at this old road cut to examine the rhyolite that underlies the Baraboo quartzite. This rock is typical of the 1,760 Ma metarhyolites exposed along the northern and southern edges of the Baraboo syncline and to the northeast in the Fox Valley (Smith, 1978). The rock is a dark reddish brown color, and contains quartz and feldspar phenocrysts in a fine-grained matrix. A tuffaceous texture is visible in thin section and hand specimen. Flattened shards and pumice fragments can commonly be seen on weathered outcrop surfaces. The rhyolites have never been commercially quarried in the Baraboo area, but were extensively quarried for paving blocks in the Fox Valley at Berlin and Utley (Buckley, 1898). As you return to the van, notice the shoulder stone along Highway 33, and the aggregate used in the asphalt pavement. The shoulder stone was likely from the Williams Quarry. The asphalt contains a high percentage of quartzite aggregate. Wisconsin Department of Transportation has been slow to embrace quartzite as an aggregate for asphalt mixes because the dense quartzite does not absorb asphalt readily. This pavement seems to be performing well with no sign of deterioration after several years of use. Quartzite has performed well as a concrete aggregate in Wisconsin, outlasting the cement and fine aggregate matrix in many older pavements and sidewalks. In the city of Madison, examples of concrete with quartzite aggregate poured in the 1920s are still in use. We will drive through the Lower Narrows, where the Baraboo River cuts through the North Range on our way to the next stop. The quarry at the southwest end of the narrows was formerly operated by the Baraboo Quartzite Co., a producer of mill linings and grinding balls for many years. This was the last active producer of grinding media in the district, closing in the early 1980s. 15 Figure 4. Topographic map showing location of Stop 3. 49 �Figure 5. Topographic map showing location of Stop 4. Stop 4: Milestone Materials Jesse Pit and Quarry Location: NW¼SW¼ sec. 15, T11N, R7E, 2 miles east of Highway 113 on south side of Tower Road, Sauk County (Baraboo 7.5-minute topographic quadrangle, 1994; fig. 5). Leader: Jim Schmitt. Description: The Jesse Pit began as a sand and gravel operation along the terminal glacial moraine. As the pit was deepened, quartzite was exposed and quarrying began (fig. 6). We are now on the south limb of the Baraboo syncline, and the exposed quartzite dips to the north at a low angle. The dip surface is a bedding plane, and in many areas excellent examples of ripple marks can be seen. The Jesse Pit is an example of a growing number of sand and gravel operations that have encountered bedrock and begun to produce crushed stone as well. Gravel is in demand for concrete aggregate, but many gravel deposits lack sufficient coarse crushing material needed to achieve the percentage of fractured surfaces required to meet modern asphalt mix design standards. Operations such as Jesse Pit have the advantage of being able to furnish concrete and asphalt aggregate plus a variety of other products ranging from sand to landscape boulders. We will examine the quartzite exposures and look at some of the glacial material as well as discuss some of the reclamation activities currently in progress at this site. Stop 5: Milestone Materials Fox Ridge Asphalt Plant and Sales Yard Location: SE¼ sec. 22, T12N, R6E, 2 miles north of Baraboo on Fox Hill Road. Leader: Jim Schmitt. Description: At this stop we will examine some of the 27 products produced at or marketed from the Fox Ridge Pit. The list includes seven quartzite products ranging from base course to washed sand and seal coat chips. The quartzite is hauled in to this site from quarries such as Jesse and Rock Springs. We will discuss the uses of quartzite for asphalt aggregate as well as a variety of construction uses. 50 �Figure 6. View of Jesse Pit looking north. Working face in quartzite in foreground; sand and gravel face behind. Slope in background near tree line is reclaimed pit area ready to be seeded. Stop 6: Martin Marietta Aggregates Rock Springs Quarry Location: SW¼ sec. 28, T11N, R5E, 0.5 miles north of Rock Springs (Rock Springs 7.5-minute topographic quadrangle, 1975; fig. 7). Leader: Bruce A. Brown (Joe Michels). Description: This large quarry was opened in 1958 by the C&NW Railroad and operated exclusively as a source of railroad track ballast for many years. At the time it was opened, the large-scale production of quartzite ballast was not considered cost effective because of the hard abrasive nature of the rock and the resulting equipment maintenance costs. The C&NW ultimately proved that the superior performance of quartzite under heavy, high-speed train traffic was worth the cost in the long run. The angular quartzite interlocked to form a stable, welldrained track base, and did not break down under heavy traffic, as did limestone. Today the quarry is operated by Martin Marietta and it remains one of the largest ballast producers in Wisconsin. We are directly across the Upper Narrows of the Baraboo River from Van Hise rock, and several historic quarries. The old quarries are now part of a Wisconsin Department of Natural Resources Natural Area; originally they were operated for refractory and grinding media, with some early limited production of crushed stone. The bedding in this area is nearly vertical as at Williams Quarry (Stop 2). Hydrothermal breccias cemented with white quartz are also common in this area. The geology of the Narrows area is described in detail by Medaris and Dott (2001) as Locality 4 of Field Trip 1 for this meeting. We will tour the quarry and examine the large modern crushing and screening plant. As we drove up the hill to the quarry office, we passed a large pile of fines created by years of ballast production. This material at one time was eroding and washing into the Baraboo River 51 �below. It has since been stabilized and vegetation is beginning to take hold. Does anyone have any good ideas for marketing this stuff? Stop 7: Kraemer Company LaRue Quarry Location: NW¼ sec. 22, T11N, R5E (Rock Springs 7.5-minute topographic quadrangle, 1975; fig. 8). Leaders: Jennifer Lien and Bruce A. Brown. Description: The LaRue Quarry is a historic operation Figure 7. Topographic map showing location of Stop 6. in the Baraboo region. At one time this quarry produced ballast and was connected to the C&NW at North Freedom by the track now used by the Midcontinent Railway Museum. We may be in time to see the steam train pull into the quarry on one of its runs. Foundations of the old permanent crushing and screening plant and a few ruined buildings remain from the earlier operation. As we drive into LaRue Quarry, the leaders will point out the sites of two historic iron mines also served by this branch line from 1900 to around 1922. The quarry is now operated on an as-needed basis with portable crushing and screening equipment. The principal product is construction aggregate, primarily base course. Rue Figure 8. Topographic map showing location of Stop 7. 52 �Figure 9. East face of LaRue Quarry, showing unconformity of Paleozoic sandstones overlying Baraboo quartzite. LaRue is on the south range and, as at Jesse Pit, beds dip at a low angle to the north. Thin argillite beds are present and cross-bedding can be seen on joint surfaces. Ripple marks are common on bedding surfaces. LaRue provides some excellent views of the unconformity between the quartzite and the onlapping Cambrian-Ordovician sandstones (fig. 9). Alteration along joint surfaces has produced a weathering pattern similar to spheroidal weathering in granite. Rounded boulders can be found in which the interior is fresh purple quartzite surrounded by a rind of bleached sandstone resembling the overlying sediments. REFERENCES Buckley, E.R., 1898, On the Building and Ornamental Stones of Wisconsin: Wisconsin Geological and Natural History Survey Bulletin 4, 544 p. Clayton, L., and Attig, J.W., 1990, Geology of Sauk County, Wisconsin: Wisconsin Geological and Natural History Survey Information Circular 67, 68 p. Dalziel, I.W.D., and Dott, R.H., Jr., 1970, Geology of the Baraboo District, Wisconsin: Wisconsin Geological and Natural History Survey Information Circular 14, 164 p. Fauble, Philip, and Lien, Jennifer, 2001, Some Observations from the Williams Quarry Exposure: Evidence of Debris Flow Deposits in the Parfreys Glen Formation: Abstracts, 47th Annual Institute on Lake Superior Geology, Madison, Wisconsin, p. 26–27. 53 �Greenberg, J.K., and Brown, B.A., 1984, Cratonic sedimentation during the Proterozoic: An anorogenic connection in Wisconsin and the upper Midwest: Journal of Geology, v. 92, p. 159–171. Luther, F., 1992, The Waterloo Quartzite at the old Portland Quarry, in Travis, J., ed., the 56th Annual Tri-State Geology Field Conference, Whitewater, Wisconsin, p. 51–61. Luther, F., 1997, The Precambrian Waterloo Quartzite, Dodge and Jefferson Counties, Wisconsin—Petrology, Structure, and Industrial Use: Field Trip 5, in Guide to Field trips in Wisconsin and Adjacent Areas of Minnesota: Wisconsin Geological and Natural History Survey, Madison, Wisconsin, p. 31–35. Malone, D.H., Van Wyck, N., and Nelson, R., 1997, Field guide for field trip leaders to the Baraboo district, Wisconsin: Field Trip 3 in Guide to Field Trips in Wisconsin and Adjacent Areas of Minnesota: Wisconsin Geological and Natural History Survey, Madison, Wisconsin, p.13–22. Medaris, L.G. Jr., and Dott, R.H., Jr., 2001, Field Trip 1:Sedimentologic, Tectonic, and Metamorphic History of the Baraboo Interval: New Evidence from investigations in the Baraboo range, Wisconsin: 47th Annual Institute on Lake Superior Geology, Madison, Wisconsin, p. 1–21 (this volume). Smith, E.I., 1978, Introduction to Precambrian rocks of south-central Wisconsin: Geoscience Wisconsin, v. 2, p. 1–15. 54 � Dublin Core The Dublin Core metadata element set is common to all Omeka records, including items, files, and collections. For more information see, http://dublincore.org/documents/dces/. Title A name given to the resource Institute on Lake Superior Geology Dublin Core The Dublin Core metadata element set is common to all Omeka records, including items, files, and collections. For more information see, http://dublincore.org/documents/dces/. Title A name given to the resource Institute on Lake Superior Geology: Proceedings, 2001 Description An account of the resource Institute on Lake Superior Geology. Madison, Wisconsin. May 9-12, 2001. Creator An entity primarily responsible for making the resource Institute on Lake Superior Geology Date A point or period of time associated with an event in the lifecycle of the resource 2001 Format The file format, physical medium, or dimensions of the resource PDF Language A language of the resource English https://digitalcollections.lakeheadu.ca/files/original/2456791f0692913e884f16bfdc1fc9dd.pdf b199c02ed01d1fc8083e26b36a355f3f PDF Text Text INSTITUTE ON LAKE SUPERIOR GEOLOGY 48TH ANNUAL MEETING PROCEEDINGS VOLUME 48 PART 1 –PROGRAM AND ABSTRACTS Kenora, Ontario – May 12-16, 2002 �INSTITUTE ON LAKE SUPERIOR GEOLOGY 48TH ANNUAL MEETING PROCEEDINGS VOLUME 48 PART 1 –PROGRAM AND ABSTRACTS �CONTENTS Proceedings Volume 48 Part 1—Program and Abstracts Editors: K. O’Flaherty, C. Storey Institutes on Lake Superior Geology, 1955-2002.............................................................. iii Constitution of the Institute on Lake Superior Geology......................................................v By-Laws of the Institute on Lake Superior Geology........................................................ vii Membership Criteria for the Institute on Lake Superior Geology................................... viii Goldich Medal Guidelines ................................................................................................. ix Past Goldich Medalists ...................................................................................................... xi Goldich Medal Committee................................................................................................. xi Citation for 2002 Goldich Medal Recipient ..................................................................... xii Eisenbrey Student Travel Awards .....................................................................................xv Student Travel Award Application Form ........................................................................ xvi Student Paper Awards..................................................................................................... xvii Student Paper Awards Committee .................................................................................. xvii Board of Directors ......................................................................................................... xviii Local Committees .......................................................................................................... xviii Session Chairs.................................................................................................................. xix Banquet Speaker ................................................................................................................xx Report of the Chair of the 47th Annual Institute Meeting.................................................xx Program............................................................................................................................xxv Abstracts ..............................................................................................................................1 Cover Photo: Regina Mine, 1918. The Regina Mine produced intermittently from 1895 to 1943, yielding over 8,000 ounces gold and 1,460 ounces silver. The Regina was the first mine in North America to use cyanide for gold recovery. ii �INSTITUTES ON LAKE SUPERIOR GEOLOGY, 1955-2002 # 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 DATE 1955 1956 1957 1958 1959 1960 1961 1962 1963 1964 1965 1966 1967 1968 1969 1970 1971 1972 1973 1974 1975 1976 1977 1978 1979 1980 1981 1982 1983 1984 1985 1986 1987 1988 1989 1990 1991 1992 1993 1994 1995 1996 PLACE Minneapolis, Minnesota Houghton, Michigan East Lansing, Michigan Duluth, Minnesota Minneapolis, Minnesota Madison, Wisconsin Port Arthur, Ontario Houghton, Michigan Duluth, Minnesota Ishpeming, Michigan St. Paul, Minnesota Sault Ste. Marie, Michigan East Lansing, Michigan Superior, Wisconsin Oshkosh, Wisconsin Thunder Bay, Ontario Duluth, Minnesota Houghton, Michigan Madison, Wisconsin Sault Ste. Marie, Ontario Marquette, Michigan St. Paul, Minnesota Thunder Bay, Ontario Milwaukee, Wisconsin Duluth, Minnesota Eau Claire, Wisconsin East Lansing, Michigan International Falls, Minnesota Houghton, Michigan Wausau, Wisconsin Kenora, Ontario Wisconsin Rapids, Wisconsin Wawa, Ontario Marquette, Michigan Duluth, Minnesota Thunder Bay, Ontario Eau Claire, Wisconsin Hurley, Wisconsin Eveleth, Minnesota Houghton, Michigan Marathon, Ontario Cable, Wisconsin CHAIRS C.E. Dutton A.K. Snelgrove B.T. Sandefur R.W. Marsden G.M. Schwartz & C. Craddock E.N. Cameron E.G. Pye A.K. Snelgrove H. Lepp A.T. Broderick P.K. Sims & R.K. Hogberg R.W. White W.J. Hinze A.B. Dickas G.L. LaBerge M.W. Bartley & E. Mercy D.M. Davidson J. Kalliokoski M.E. Ostrom P.E. Giblin J.D. Hughes M. Walton M.M. Kehlenbeck G. Mursky D.M. Davidson P.E. Myers W.C. Cambray D.L. Southwick T.J. Bornhorst G.L. LaBerge C.E. Blackburn J.K. Greenberg E.D. Frey & R.P. Sage J. S. Klasner J.C. Green M.M. Kehlenbeck P.E. Myers A.B. Dickas D.L. Southwick T.J. Bornhorst M.C. Smyk L.G. Woodruff iii �43 44 45 46 47 48 1997 1998 1999 2000 2001 2002 Sudbury, Ontario Minneapolis, Minnesota Marquette, Michigan Thunder Bay, Ontario Madison, Wisconsin Kenora, Ontario R.P. Sage, W. Meyer J.D. Miller, M.A. Jirsa T.J. Bornhorst, R.S. Regis S.A. Kissin, P. Fralick M.G. Mudrey, Jr., B.A. Brown P. Hinz, R.C. Beard iv �CONSTITUTION OF THE INSTITUTE ON LAKE SUPERIOR GEOLOGY (Last amended by the Board—May 8, 1997) Article I Name The name of the organization shall be the "Institute on Lake Superior Geology". Article II Objectives The objectives of this organization are: A. To provide a means whereby geologists in the Great Lakes region may exchange ideas and scientific data. B. To promote better understanding of the geology of the Lake Superior region. C. To plan and conduct geological field trips. Article III Status No part of the income of the organization shall insure to the benefit of any member or individual. In the event of dissolution, the assets of the organization shall be distributed to _________ (some tax free organization). (To avoid Federal and State income taxes, the organization should be not only "scientific" or "educational, but also "non-profit") Minn. Stat. Anno. 290.01, subd. 4 Minn. Stat. Anno. 290.05(9) 1954 Internal Revenue Code s.501(c)(3) Article IV Membership The membership of the organization shall consist of persons who have registered for an annual meeting within the past three years, and those who indicate interest in being a member according to guidelines approved by the Board of Directors. Article V Meetings The organization shall meet once a year. The place and exact date of each meeting will be designated by the Board of Directors. Article VI Directors The Board of Directors shall consist of the Chair, Secretary-Treasurer, and the last three past Chairs; but if the board should at any time consist of fewer than five persons, by reason of unwillingness or inability of any of the above persons to serve as directors, the vacancies on the board may be filled by the Chair so as to bring the membership of the board to five members. Article VII Officers v �The officers of this organization shall be a Chair and Secretary-Treasurer. A. The Chair shall be elected each year by the Board of Directors, who shall give due consideration to the wishes of any group that may be promoting the next annual meeting. His/her term of office as Chair will terminate at the close of the annual meeting over which he/she presides, or when his/her successor shall have been appointed. He/she will then serve for a period of three years as a member of the Board of Directors. B. The Secretary-Treasurer shall be elected at the annual meeting. His/her term of office shall be four years, or until his/her successor shall have been appointed. Article VIII Amendments This constitution may be amended by a majority vote (majority of those voting) of the membership of the organization. vi �BY-LAWS OF THE INSTITUTE ON LAKE SUPERIOR GEOLOGY I. Duties of the Officers and Directors A. It shall be the duty of the Annual Chairman to: 1. Preside at the annual meeting. 2. Appoint all committees needed for the organization of the annual meeting. 3. Assume complete responsibility for the organization and financing of the annual meeting over which he/she presides. B. It shall be the duty of the Secretary-Treasurer to: 1. Keep accurate attendance records of all annual meetings. 2. Keep accurate records of all meetings of, and correspondence between, the Board of Directors. 3. Hold all funds that may accrue as profits from annual meetings or field trips and to make these funds available for the organization and operation of future meetings as required. C. It shall be the duty of the Board of Directors to plan locations of annual meetings and to advise on the organization and financing of all meetings. II. Duties and Expenses A. Regular membership dues of $5.00 or less on an annual basis shall be assessed each member as determined by the Board of Directors.. B. Registration fees for the annual meetings shall be determined by the Chair in consultation with the Board of Directors. The registration fees can include expenses to cover operations outside of the annual meeting as determined by the Board of Directors. It is strongly recommended that registration fees be kept at a minimum to encourage attendance of students. III. Rules of Order The rules contained in Robert's Rules of Order shall govern this organization in all cases to which they are applicable. IV. Amendments These by-laws may be amended by a majority vote (majority of those voting) of the membership of the organization; provided that such modifications shall not conflict with the constitution as presently adopted or subsequently amended. vii �MEMBERSHIP CRITERIA FOR THE INSTITUTE ON LAKE SUPERIOR GEOLOGY Approved May 8, 1997 A. Membership in the Institute on Lake Superior Geology requires either participation in Institute activities, or an indication on a regular basis of interest in the Institute. Those individuals registering for an annual meeting will remain as members for 4 years unless: 1) they indicate no further interest in the Institute by responding negatively to the statement on meeting circulars "Remove my name from the mailing list"; or 2) two successive mailings in different years are returned by the postal service as address unknown. B. Those individuals who have not registered for an annual meeting in the past 4 years must indicate an interest in the Institute by postal, electronic , or verbal correspondence with the Secretary-Treasurer at least once every two years. Such individuals will be removed from the membership if they indicate no further interest in the Institute or two successive mailing in different years are returned by the postal service as address unknown. C. The Secretary-Treasurer will maintain a list of current members. The list will include the date of the beginning of continuous membership, dates of returned mail, dates of last contact (expression of interest), and the date membership expires, barring a change of status initiated by the member. Those individuals who have become members of ILSG by Section B will have an expiration date listed at 2 years from the upcoming meeting. For example, a member who expresses interest in September of 1997 (the next annual meeting is May, 1998) will have an expiration date of May, 2000, unless the member contacts the Secretary-Treasurer or attends an annual meeting. D. "Member for Life" status is granted to individuals who have been (nearly) continuous participants of the ILSG meetings for 15 years, Goldich Medal recipients, or those who have served as meeting chairs. This status will be further maintained unless the individuals indicate no further interest in the Institute, or 4 mailings in different years are returned by the postal service as address unknown, or they are deceased. E. All members will be mailed the First Circular for the Annual Meeting and the ILSG Newsletter. The Chair of the annual meeting may opt to send the first circular to additional individuals. All returned mail should be reported to the Secretary-Treasurer. F. The Secretary-Treasurer can designate any individual who is on the ILSG membership list (mailing list) as of January 1, 1997 as a member for life based on participation in ILSG activities. G. Members are strongly encourage to send address corrections to the Secretary-Treasurer to avoid unintentional lapse of membership. viii �GOLDICH MEDAL GUIDELINES (Adopted by the Board of Directors, 1981; amended 1999) Preamble The Institute on Lake Superior Geology was born in 1955, as documented by the fact that the 27th annual meeting was held in 1981. The Institute's continuing objectives are to deal with those aspects of geology that are related geographically to Lake Superior; to encourage the discussion of subjects and sponsoring field trips that will bring together geologists from academia, government surveys, and industry; and to maintain an informal but highly effective mode of operation. During the course of its existence, the membership of the Institute (that is, those geologists who indicate an interest in the objectives of the ILSG by attending) has become aware of the fact that certain of their colleagues have made particularly noteworthy and meritorious contributions to the understanding of Lake Superior geology and mineral deposits. The first award was made by ILSG to Sam Goldich in 1979 for his many contributions to the geology of the region extending over about 50 years. Subsequent medalists and this year's recipient are listed in the table below. Award Guidelines 1) The medal shall be awarded annually by the ILSG Board of Directors to a geologist whose name is associated with a substantial interest in, and contribution to, the geology of the Lake Superior region. 2) The Board of Directors shall appoint the Goldich Medal Committee. The initial appointment will be of three members, one to serve for three years, one for two years, and one for one year. The member with the briefest incumbency shall be chair of the Nominating Committee. After the first year, the Board of Directors shall appoint at each spring meeting one new member who will serve for three years. In his/her third year this member shall be the chair. The Committee membership should reflect the main fields of interest and geographic distribution of ILSG membership. The out-going, senior member of the Board of Directors shall act as liaison between the Board and the Committee for a period of one year. 3) By the end of November, the Goldich Medal Committee shall make its recommendation to the Chair of the Board of Directors, who will then inform the Board of the nominee. 4) The Board of Directors normally will accept the nominee of the Committee, inform the medalist, and have one medal engraved appropriately for presentation at the next meeting of the Institute. 5) It is recommended that the Institute set aside annually from whatever sources, such funds as will be required to support the continuing costs of this award. ix �Nominating Procedures 1) The deadline for nominations is November 1. Nominations shall be taken at any time by the Goldich Medal Committee. Committee members may themselves nominate candidates; however, Board members may not solicit for or support individual nominees. 2) Nominations must be in writing and supported by appropriate documentation such as letters of recommendation, lists of publications, curriculum vita's, and evidence of contributions to Lake Superior geology and to the Institute. 3) Nominations are not restricted to Institute attendees, but are open to anyone who has worked on and contributed to the understanding of Lake Superior geology. Selection Guidelines 1) Nominees are to be evaluated on the basis of their contributions to Lake Superior geology (sensu lato) including: a) importance of relevant publications; b) promotion of discovery and utilization of natural resources; c) contributions to understanding of the natural history and environment of the region; d) generation of new ideas and concepts; and e) contributions to the training and education of geoscientists and the public. 2) Nominees are to be evaluated on their contributions to the Institute as demonstrated by attendance at Institute meetings, presentation of talks and posters, and service on Institute boards, committees, and field trips. 3) The relative weights given to each of the foregoing criteria must remain flexible and at the discretion of the Committee members. 4) There are several points to be considered by the Goldich Medal Committee: a) An attempt should be made to maintain a balance of medal recipients from each of the three estates—industry, academia, and government. b) It must be noted that industry geoscientists are at a disadvantage in that much of their work in not published. 5) Lake Superior has two sides, one the U.S., and the other Canada. This is undoubtedly one of the Institute's great strengths and should be nurtured by equitable recognition of excellence in both countries. x �PAST GOLDICH MEDALISTS 1979 Samuel S. Goldich 1991 William Hinze 1980 not awarded 1992 William F. Cannon 1981 Carl E. Dutton, Jr. 1993 Donald W. Davis 1982 Ralph W. Marsden 1994 Cedric Iverson 1983 Burton Boyum 1995 Gene LaBerge 1984 Richard W. Ojakangas 1996 David L. Southwick 1985 Paul K. Sims 1997 Ronald P. Sage 1986 G.B. Morey 1998 Zell Peterman 1987 Henry H. Halls 1999 Tsu-Ming Han 1988 Walter S. White 2000 John C. Green 1989 Jorma Kalliokoski 2001 John S. Klasner 1990 Kenneth C. Card 2002 Ernest K. Lehmann GOLDICH MEDAL COMMITTEE Ron Sage (2002) Ontario Geological Survey, Thunder Bay Rod Johnson (2002) Rod Johnson and Associates, Negaunee, Michigan Frank Luther (2003) University of Wisconsin, Whitewater James D. Miller, Jr., as out-going senior member of Institute Board of Directors, is liaison between Goldich Medal Committee and the Board through 2001 meeting. xi �Citation Ernest K. Lehmann 2002 Goldich Medal Recipient Ladies and Gentlemen: Thank you for being here tonight for this presentation of the 2002 Sam Goldich Medal Award. I don’t know if any of you remember the late Ben Dickerson. He was one of the premier exploration geologists of his time and wrote a column in Skillings Magazine. The column was called “ News and Rumor” from the Bush”. It described current exploration activity particularly in the U.S. during those golden years of the 70’s and 80’s. At that time the exploration community was quite small and Ben seemed to know everyone. His column was cryptic in that he would commonly refer to people in coded names. For example there was the “Great Buawa” and the “Shallow”. Ernie was referred to as the “Bearded Sphinx of the North”. I’m not sure where that came from, but know the “Sphinx” was “good copy” because he was so active in minerals exploration particularly in the Great Lakes region in those days as he certainly is today. I had the good fortune and privilege of working with Ernie for nearly two decades. Over the years, his list of accomplishments in the field of economic geology and mineral exploration are many. It would take hours to go through them all. So I will focus on those related to the Lake Superior area. First some background. Ernie was born in 1929 in Heidelberg, Germany. He was educated in the public schools of New Rochelle, N.Y., attended Williams College, in Williamstown, Massachusetts, where he graduated cum laude in geology in 1951. He attended graduate school in geology at Brown University, Providence, Rhode Island, and completed the Owners and Presidents Management Program of the Harvard Business School in 1984. He is married to Sally Willius Lehmann (his better half) and resides in Minneapolis, Minnesota. Prior to founding Ernest K. Lehmann & Associates, Inc. in 1967, Ernie was an independent consultant and partner in a Minneapolis based geological consulting firm from 1958 to 1967. In 1950, he began his career by working first as a miner and then as geologist for the Signal Mining Company at Bannack, Montana. From 1951 to 1958, Ernie worked for Kennecott Copper Corporation and its exploration arm, Bear Creek Mining Company. Ernie served on active duty as a Terrain Intelligence Analyst in the U.S. Army Corps of Engineers from 1953 to 1955 and was awarded the Commendation Ribbon for his service. As many of you know, Ernie is the founder and CEO of North Central Mineral Ventures Inc. and of Ernest K. Lehmann & Associates, Inc. Under his leadership, the firms have engaged in the planning, management and execution of mineral exploration programs, mineral deposit development, mine appraisal and mineral economic studies particularly in the Great Lakes region. These activities have spanned most important hard mineral commodities including ferrous, non-ferrous, precious and strategic metals, industrial minerals and fertilizer raw materials. In the course of their activities, he and his firms have been active in staffing and managing exploration and mine development projects and acquiring private and public mineral xii �lands in both the U.S. and abroad. The latter activities have included claim staking, mineral leasing of private, state and federal lands, and the creation and management of mineral joint ventures. In addition to extensive work in the US and Canada, he has conducted and managed exploration and consulted on mine development and evaluation Central and South America, Africa and Europe. In the course of his activities, Ernie has specialized in exploration management and in mineral deposit appraisal evaluation. He has appeared extensively as an expert witness on mineral property appraisal and taxation and on mining claim related issues. He has served on advisory committees to the Office of Technology Assessment of the U.S. Congress on strategic and critical minerals and to the state of Minnesota on direct reduction of iron ores. On behalf of the American Institute of Professional Geologists, he has testified before Congress on strategic minerals issues and on the 1872 mining law. He has also testified before Congress on issues related to the Federal Land Management Policy Act. Before state legislative committees, he has testified on mineral property appraisal, mineral taxation, mineral leasing and mine permitting. In 1985, he became president of the American Institute of Professional Geologists, also serving the Institute in various other capacities on a state and national level. In 1987, he was awarded the Ben H. Parker Medal, the Institute’s highest award for service to the geological profession, and has been awarded Honorary Membership in the Institute in 1997. He currently serves as Chairman of the AIPG Foundation and is a member of numerous other technical and professional bodies including the Society of Economic Geologists, The Mining and Metallurgical Society of America, the Society of Mining Engineers, the Society for Geology Applied to Mineral Deposits, and the Northwest Mining Association. He is a registered geologist in Minnesota, California, Georgia, Delaware and Alaska and is accredited by the European Federation of Geologists. He is currently a director and president of the Minnesota Exploration Association and serves on various committees in Minnesota in this capacity, including the Blue Ribbon Committee on Minnesota Minerals, the advisory board to the Natural Resources Research Institute and the State Mapping Advisory Committee. Ernie has also been actively involved in mining related environmental issues again particularly in the Great Lakes area. He was instrumental in initiating and executing the Minnesota Mining Permit Simulation Project, a joint state agency, environmental community and industry effort to examine the mine permitting process and problems for non-ferrous metal mining. He helped organize a workshop on financial assurance in the mining industry in cooperation with the Minnesota DNR, MPCA, and the Audubon Society. Ernie and the firm were consultants to the state of Maine charged with developing metal mining regulations, spanning activities from exploration through operation and closure. The firms were also involved in mine permitting activities in Wisconsin. To this I would like to mention some of the major projects Ernie has initiated in the Great Lakes area. These include: 1) Exploration programs for Bear Creek in 1952, 1956 through 1957 for copper and copper nickel in the Duluth and Mellon Gabbro Complexes and Nonesuch Shale. xiii �2) Copper and copper-nickel exploration projects carried out for Cerro Corp. from 1967-1969 in Wisconsin, Minnesota, Michigan and Ontario. He was one of the first explorationists to recognize the Wisconsin greenstone belts as an important VMS target . 3) VMS exploration joint ventures in Wisconsin that spanned from 1975 through 1993. Such notables as Getty, Chevron, Denison Mines and Asarco were involved with these projects. Under the supervision of the late Ned Eisenbrey, these programs resulted in three discoveries. Of these one, the Bend copper-gold deposit, is and remains potentially economic. The huge amount of geologic and geophysical data generated from these exploration projects also resulted in establishing a more detailed “geologic framework” that was previously lacking for the Wisconsin greenstone belts. This work culminated in several papers published in “Economic Geology” in 1990 and 1994. 4) At the same time Ernie was managing a major VMS program in Archean of northern Minnesota from 1979 through 1985 for Getty and Billiton. 5) From 1980 to 1982, Ernie was one of the first to seriously begin exploring the interior of the Duluth Complex for copper-nickel and PGMs through a joint venture with Billiton. His exploration efforts continue today with a focus on the Birch Lake PGM project that involves Impala. I believe Ernie’s past and present exploration and political efforts in Minnesota today has resulted in the current brisk activity within the Duluth Complex and transformed the state to an attractive part of the world to conduct environmentally responsible mining projects. Finally, with deep gratitude and respect, I would like to present this year’s Sam Goldich medal recipient, my mentor and friend, Ernest K. Lehmann. Theodore A. DeMatties xiv �EISENBREY STUDENT TRAVEL AWARDS The 1986 Board of Directors established the ILSG Student Travel Awards to support student participation at the annual meeting of the Institute. The name "Eisenbrey" was added to the award in 1998 to honor Edward H. Eisenbrey (1926-1985) and utilize substantial contributions made to the 1996 Institute meeting in his name. "Ned" Eisenbrey is credited with discovery of significant volcanogenic massive sulfide deposits in Wisconsin, but his scope was much broader—he has been described as having unique talents as an ore finder, geologist, and teacher. These awards are intended to help defray some of the direct travel costs of attending Institute meetings, and include a waiver of registration fees, but exclude expenses for meals, lodging, and field trip registration. The number of awards and value are determined by the annual Chair in consultation with the Secretary-Treasurer. Recipients will be announced at the annual banquet. The following general criteria will be considered by the annual Chair, who is responsible for the selection: 1) The applicants must have active resident (undergraduate or graduate) student status at the time of the annual meeting of the Institute, certified by the department head. 2) Students who are the senior author on either an oral or poster paper will be given favored consideration. 3) It is desirable for two or more students to jointly request travel assistance. 4) In general, priority will be given to those in the Institute region who are farthest away from the meeting location. 5) Each travel award request shall be made in writing to the annual Chair, and should explain need, student and author status, and other significant details. The form below is optional. Successful applicants will receive their awards during the meeting. xv �INSTITUTE ON LAKE SUPERIOR GEOLOGY Eisenbrey Student Travel Award Application Student Name: Date: Address: email: Department Head-Typed Department Head-Signature Educational Status: Are you the senior author of an oral or poster paper? YES Will any other students be traveling with you? NO Who? Statement of need (use additional page if necessary) Please return to: xvi �STUDENT PAPER AWARDS Each year, the Institute selects the best of the student presentations and honors presenters with a monetary award. Funding for the award is generated from registrations of the annual meeting. The Student Paper Committee is appointed by the annual meeting Chair in such a manner as to represent a broad range of professional and geologic expertise. Criteria for best student paper— last modified by the Board in 1997—follow: 1) The contribution must be demonstrably the work of the student. 2) The student must present the contribution in-person. 3) The Student Paper Committee shall decide how many awards to grant, and whether or not to give separate awards for poster vs. oral presentations. 4) In cases of multiple student authors, the award will be made to the senior author, or the award will be shared equally by all authors of the contribution. 5) The total amount of the awards is left to the discretion of the meeting Chair and SecretaryTreasurer, but typically is in the amount of about $300 US. 6) The Secretary-Treasurer maintains, and will supply to the Committee, a form for the numerical ranking of presentations. This form was created and modified by Student Paper Committees over several years in an effort to reduce the difficulties that may arise from selection by raters of diverse background. The use of the form is not required, but is left to the discretion of the Committee. 7) The names of award recipients shall be included as part of the annual Chair's report that appears in the next volume of the Institute. Student papers will be noted on the Program. STUDENT PAPER AWARDS COMMITTEE Peter Hollings Lakehead University, Thunder Bay Neil Pettigrew Avalon Ventures Ltd., Thunder Bay Connie Dickens U.S. Geological Survey, Reston, Virginia xvii �BOARD OF DIRECTORS Mike Mudrey, Chair Wisconsin Geological and National History Survey, Madison, Wisconsin 2000-2003 Steve Kissin, Department of Geology, Lakehead University, Thunder Bay, Ontario 1999-2002 Ted Bornhorst, Department of Geological Engineering and Sciences, Michigan Tech UniversityHoughton, Michigan 1998-2001 Jim Miller, Minnesota Geological Survey, St. Paul, Minnesota Secretary-Treasurer Mark A. Jirsa, Minnesota Geological Survey St. Paul, Minnesota LOCAL COMMITTEE Peter Hinz, Ontario Geological Survey, Resident Geologist Program, Kenora, ON Richard C. Beard, Northwest Mineral Development Services, Kenora, ON Charles E. Blackburn, Blackburn Geological Services, Kenora, ON Christine Blackburn, Blackburn Geological Services, Kenora, ON Kevin O’Flaherty, Kenora, ON Carmen Storey, Ontario Geological Survey, Resident Geologist Program, Red Lake, ON Kathleen McGowan-Hinz, Kenora, ON SESSION CHAIRS xviii �Alasdair Mowat Emerald Fields Resource Corp., Kenora Philip Fralick Lakehead University, Thunder Bay Mark Smyk Ontario Geological Survey, Thunder Bay 2002 BANQUET SPEAKER L. Harvey Thorleifson Geological Survey of Canada Ottawa, Ontario The Search for Diamonds in Canada xix �REPORT OF THE CHAIR OF THE 47TH ANNUAL MEETING Michael G. Mudrey, Jr. Chair ILSG 2001 The 47th Annual Institute on Lake Superior Geology was jointly hosted by the University of Wisconsin-Extension Geological and Natural History Survey and the University of WisconsinMadison, Department of Geology and Geophysics , in Madison, Wisconsin on May 9-12, 2001. Principal local committee members were M.G. Mudrey, Jr . and B.A. Brown, co-chairs, Robert H. Dott, Jr, and L.Gordon Medaris, Jr., Program-cochairs, and Kathleen M. Zwettler, Meeting Coordinator. Other principal individuals are listed in the Proceedings Volume. Attendance at ILSG 2001 A total of 172 professionals and student professionals attended the meeting, 82 of whom preregistered by the April 2, 2001 deadline. A total of 26 students were registered, ten of whom requested and received travel assistance and had registration fees for the meeting waived. Eisenbrey Student Travel Awards 2001 Ten students requested and received travel assistance form the Eisenbrey Student Travel Award Fund established to support student participation at the Annual Institute. Details, including criteria and application forms are available at the Eisenbrey website. Justin Johnson- Lakehead University-Thunder Bay, Ontario - Fluid Inclusion Evidence for a Role for Hydrothermal Activity in the Roby Zone, Lac Des Iles Mine, Northwestern Ontario; Becky RogalaLakehead University-Thunder Bay, Ontario - A Metamorphosed Evaporite Sequence from the Sibley Basin ; Dan BihariLakehead University-Thunder Bay, Ontario - Alteration and Pge-au Mineralization in the North Roby Zone, Lac Des Iles Mine, Northwestern Ontario; Phillip LarsonUniversity of Minnesota-Duluth - Potential for Copper Mineralization in the Animikie Group, Minnesota; Michael NemitzUniversity of Minnesota-Duluth - Mineralogical Variations in Iron-formation in the Thermal Metamorphic Aureole of a Diabase Dike; Lisa LarsonUniversity of Minnesota-Duluth - ; Muhammad Asif Soofi- Purdue University, West Lafayette, Indiana - Post-rift Evolution of the Midcontinent Rift System: Some Numerical Experiments; Jason OdetteUniversity of Wisconsin-Oskosh - Preliminary Evaluation of Hydrothermal Alteration Mineral Assemblages and Their Relationship to VMS-style Mineralization in the Five Mile Lake Area of the Archean Vermilion Greenstone Belt, Northeastern Minnesota ; xx �Trent Newkirk- Dan Schweitzer- University of Wisconsin-Oskosh - Preliminary Lava Flow Morphology Studies at the Five Mile Lake Vms Prospect, Archean Vermilion District, Ne Minnesota: Implications for Volcanic Processes, Volcanic Paleoenvironments, and VMS Exploration ; and Kent State University-Kent Ohio - Results of Igneous Thermometry and Barometry on the East-central Minnesota Batholith: Evidence for Post-emplacement Exhumation and Cooling . Meeting Summary The 47th Annual Institute on Lake Superior Geology Annual Meeting was held at the Sheraton Madison Hotel, the same location as the 1973 meeting. The 2001 meeting focused on hydrogeologic aspects of arsenic in groundwater, completion of acquisition of detailed regional geophysical data; the evolution of the post-Penokean--pre-Keweenawan crystal terrane of North American in 36 poster displays and 32 oral presentations . The two days of technical sessions were preceded by Field Trip 1 - Sedimentologic, Tectonic and Metamorphic History of the Baraboo Interval led by L. Gordon Medaris, Jr. , and Robert H. Dott, Jr. (University of Wisconsin-Madison) , and followed by Field Trip 2 - Upper Mississippi Valley Zinc-Lead District led by M.G. Mudrey, Jr. (Wisconsin Geological and Natural History Survey) and Thomas C. Hunt (University of Wisconsin-Platteville) and Field Trip 3- Industrial Mineral and Aggregate Resources of the Baraboo Interval Quartzites lead by Bruce A. Brown (Wisconsin Geological and Natural History Survey), Frank R. Luther (University of Wisconsin Whitewater), James W. Schmitt (D.L. Gasser Construction), Susan M. Courter (Michels Materials) and Jennifer Lien (The Kraemer Company) The meeting began with regional geologic summaries of the Pleistocene of Southern Wisconsin by D.M. Mickelson (University of Wisconsin-Madison) and Lee Clayton (Wisconsin Geological and Natural History Survey), Sequence Stratigraphic Analysis of the Paleozoic by Charles E. Byers (University of Wisconsin-Madison), and Stratigraphic Metamorphic Analysis of the Baraboo Supracrustal Rocks of the Midcontinent by L. Gordon Medaris, Jr. , (University of Wisconsin-Madison). A series of invited presentations completed the morning of the first technical sessions three presentations on Aeromagnetic Investigations in the Midwest. An invited presentation on an Overview of Arsenic Occurrences and Processes Controlling Arsenic Moblity in Ground Water by D. Kirk Nordstrom (U.S. Geological Survey) kicked off a special session of four papers on the Hydrogeologic Setting of Elevated Arsenic and Heavy Metals in Public and Private Water Supplies. General geologic topics completed the first day. Three papers on the Midcontinent Rift started Friday morning, followed an invited symposium of eight papers on the Thermo-Thermo-Tectonic History of 1800 to 1200 Ma post-Penokean to pre-Keweenawan. The remaining significant presentations dealt with Archean and platinumgroup element geology. The technical program was completed by 3:30 p.m. Proceeding including Pat 1 (Programs and Abstracts) and Part 2 (Field Trip Guidebook) are available from the Institute . xxi �Best Student Paper Awards for 2001 were presented to Alissa Naymark-University of Wisconsin-Madison (oral) Cash award plus chrome-plated drill bit donated by Layne Northwest Travis Sandland-Macalester College (poster) and Erin H. Phillips-Macalester College (poster) Jason D. Odette-University of Wisconsin-Oshkosh (poster) Trent T. Newkirk-University of Wisconsin-Oshkosh (poster) After the break, Mike Mudrey and Bruce Brown regaled the remaining participants with previews of their field trips (Field Trip 3 was eventful in that a flat tire delayed the trip ( How many ILSGers does it take to change a tire? Three! Frank Luther, Mark Jirsa and Bob Reszka), and Brad Singer and John Valley lead the group on an impressive tour of the isotope laboratories in the Department of Geology and Geophysics. The entire group of ILSG participants remaining in Madison joined the Department of Geology and Geophysics Geology Club for the annual Departmental Picnic courtesy of contributions from Steve Kircher, Crandon Mine Development, Nicolet Minerals, and William J. Cronk, Layne Northwest, directly to the Institute. Annual Banquet and Goldich Award At the Annual Banquet Bruce R. Doe prepared, and Michael G. Mudrey, Jr. delivered a biographic history of Samuel S. Goldich who passed away on 20 December 2000 in Applewood, Colorado. After the introduction of 6 of the surviving Goldich recipients, an upbeat Gene LaBerge presented John S. Klasner with the Goldich Medal for 2001 for his contributions to the Institute and Lake Superior Geology. Tom Hunt illustrated the successful reclamation of the Ladysmith Mine of Kennecott Mining for the after dinner address, and Peter Hinz of the Ontario Geological Survey invited participants to the 48 th Annual Meeting in Kenora . Best Student Paper Awards for 2001 Alissa Naymark-University of Wisconsin-Madison (oral) Cash award plus chrome-plated drill bit donated by Layne Northwest Travis Sandland-Macalester College (poster) Erin H. Phillips-Macalester College (poster) Jason D. Odette-University of Wisconsin-Oshkosh (poster) Trent T. Newkirk-University of Wisconsin-Oshkosh (poster) Details of presentations are found in the Proceedings and Abstracts for the 47 th Annual Meeting . After the break, Mike Mudrey and Bruce Brown regaled the remaining participants with previews of their field trips (Field Trip 3 was eventful in that a flat tire delayed the trip ( How many ILSGers does it take to change a tire? Three! Frank Luther, Mark Jirsa and Bob Reszka), and Brad Singer and John Valley lead the group on an impressive tour of the isotope laboratories in the Department of Geology and Geophysics. The entire group of ILSG participants remaining in Madison joined the Department of Geology and Geophysics Geology Club for the annual Departmental Picnic courtesy of contributions from Steve Kircher, Crandon Mine Development, Nicolet Minerals, and William J. Cronk, Layne Northwest, directly to the Institute. xxii �Proceedings including Part 1 (Programs and Abstracts) and Part 2 (Field Trip Guidebook) are available from the Institute . Institute on Lake Superior Geology c/o Mark Jirsa, Executive Secretary 2642 University Avenue St. Paul MN 55114-1057 Phone: (612)-627-4539 Fax: 612-627-4778 e-mail: jirsa001@maroon.tc.umn.edu xxiii �48th ANNUAL MEETING INSTITUTE ON LAKE SUPERIOR GEOLOGY Program xxiv �Program of Events Sunday, May 12 06:00 - 18:00 Field Trip 1: Tanco Rare-Element Pegmatite, Southeastern Manitoba Monday, May 13 08:00 - 18:00 Field Trip 2: Quaternary Geology of Southeastern Manitoba 08:00 - 16:00 Field Trip 3: Structure and Sedimentology of the Seine Conglomerate, Mine Centre Area, Ontario 17:00 – 20:00 Registration – Best Western Lakeside Inn, Kenora, Ontario 19:00 – 21:00 Ice-Breaker Social and cash bar in Best Western Lakeside Inn (Authors at poster from 19:30 to 21:00) xxv �TUESDAY MAY 14 8:00 a.m. - 9:00 a.m. REGISTRATION 9:00 a.m. INTRODUCTORY REMARKS P. Hinz Co-Chairman, Ontario Geological Survey, Kenora, ON TECHNICAL SESSION I: Session Chair: Mark Smyk, District Geologist, Ontario Geological Survey, Thunder Bay, ON 9:15 a.m. K. O’Flaherty, (Consulting Geologist, Kenora, ON) A Brief History of Mining in Northwestern Ontario 9:40 a.m. M. Sanborn-Barrie*, T. Skulski, N. Rayner, (Geological Survey of Canada, Continental Geoscience Division, Ottawa, ON) and J.R. Parker (Ontario Geological Survey, Precambrian Section, Sudbury, ON) 300 my evolution of the Red Lake greenstone belt, western Superior Province, Ontario: A synthesis of current constraints on volcanism, sedimentation, deformation, metamorphism and gold mineralization 10:05 a.m. COFFEE BREAK AND POSTER SESSION 10:30 a.m. B. Nitescu*, A. R. Cruden, A. R. Bailey, (University of Toronto, Toronto, ON) Crustal Models of the Western Superior Province from gravity and Lithoprobe seismic data. 10:55 a.m. P. Fralick* and King, (Department of Geology, Lakehead University, Thunder Bay ON) Mesoarchean evolution of Western Superior Province: evidence from metasedimentary sequences near Atikokan 11:20 a.m. M.A. Jirsa, (Secretary-Treasurer, ILSG, St. Paul, MN) A Report on the Secretary-Treasurer's Position LUNCH BREAK ILSG BOARD MEETING (by invitation) POSTERS xxvi �TECHNICAL SESSION II: Session Chair: Alasdair Mowat, Emerald Fields Resource Corp., Kenora, ON 1:30 p.m. D. Peterson, (Natural Resources Research Institute, University of Minnesota-Duluth, Duluth, MN) Cu-Ni-PGE Mineralization in the South Kawishiwi intrusion; North Western Minnesota. Variation due to magmatic processes. 1:55 p.m. B. Rogala*, P.W. Fralick, and G. Borradaile, (Department of Geology, Lakehead University, Thunder Bay, Ontario) New Information from the Sibley Group 2:20 p.m. M.A. Jirsa, (Minnesota Geological Survey, St. Paul, MN) Archean and Paleoproterozoic mafic intrusions in Minnesota 2:45 p.m. COFFEE BREAK AND POSTER SESSION 3:15 p.m. C. Sturm, (Geology Department, Oberlin College, Oberlin, OH) Petrographic study of the Otter Tail Pluton, Superior Province, Northwestern Ontario 3:40 p.m. G. Ferguson* and A. Woodbury, (Department of Civil Engineering, University of Manitoba, Winnipeg, MB) Ground water and heat flow in an interlobate moraine in southwestern Manitoba. 6:00 p.m. SOCIAL - Cash Bar 7:00 p.m. Annual Banquet and Award Presentation • Announcement of 49th Annual Meeting Location • 2002 Goldich Award Presentation to Mr. Ernie Lehmann, Citation by Ted Dematties • Banquet Speaker: Dr. L. Harvey Thorleifson, Geological Survey of Canada The Search for Diamonds in Canada xxvii �WEDNESDAY MAY 15 8:00 a.m. - 9:00 a.m. REGISTRATION 9:00 a.m. INTRODUCTORY REMARKS R.C. Beard Co-Chairman, Northwest Mineral Development Services, Kenora, ON TECHNICAL SESSION III: Session Chair: Philip Fralick, Lakehead University, Thunder Bay, ON 9:15 a.m. H.H. Woodard, (Department of Geology, Beloit College, Beloit, WI) Internal structures within crustal structural slabs, Quetico-Wawa subprovince junction, Quetico Provincial Park, Ontario 9:40 a.m. R. Bernatchez, (Atikokan Resources Ltd., Atikokan, ON) Mesoarchean Base Metal Systems in the Atikokan Area, NW Ontario, Canada 10:05 a.m. COFFEEBREAK AND POSTER SESSION 10:30 a.m. L.G. Medaris*, B.S. Singer, P.E. Brown, B.R. Jiccha, M.E. Smith, (University of Minnesota-Duluth, Duluth, MN) Wolf River age brecciation in the Baraboo quartzite, Wisconsin: implications for Proterozoic tectonics in the Lake Superior Region. 10:55 a.m. D.L. Southwick, (Minnesota Geological Survey Ret’d, Pacitas, NM) Inferences from the Hattemberger deep drill hole, Carlton County, Minnesota, pertinent to regional stratigraphy and mineral potential of the western segment of the Penokean Orogen 11:20 a.m. J.C. Pedersen* and D. Bubar, (Avalon Ventures Ltd., Toronto, ON) Mineralogy and zonation of the Big Whopper Pegmatite, Separation Rapids, Kenora area, Ontario 11:45 a.m. M.A. Jirsa (Secretary-Treasurer, ILSG, St. Paul, MN) Discussion on the Secretary-Treasurer’s Position 12:00 Presentation of Student Paper Awards LUNCH BREAK 3:00 p.m. FIELD TRIP 6: Departs for Red Lake. xxviii �Thursday, May 16 08:00 - 18:00 Field Trip 4: Industrial Minerals and Paleozoic Geology of Southeastern Manitoba 08:00 - 16:00 Field Trip 5: Separation Rapids Rare-Element Pegmatite Field, Ontario 08:00 - 18:00 Field Trip 6: Geology of the Red Lake Camp, Ontario xxix �POSTER PRESENTATIONS Boerboom, T. (Minnesota Geological Survey, St. Paul, MN) The influence of Archean crustal structures on the margin of the Penokean orogen near Pope County, west central Minnesota. Buchholz, T.W. (Wisconsin Rapids, WI); Falster, A.U. and Simmons, Wm. B. (University of New Orleans, New Orleans, LO). Heterogeneity in the nine mile pluton, wausau complex, in terms of high field strength element (hfse) and rare earth element (ree) bearing minerals Cannon, W.F., (USGS, Reston, VA), Laberge, G.L. (Oshkosh, WI), Klasner, J. S., (Macomb, IL), Dicken, C., (USGS, Reston, VA) Geology of the western Gogebic Iron Range, northwest Wisconsin—a record of sedimentation and deformation across the northern margin of the Penokean orogen Fein, E., (Oberlin College, Oberlin, OH) Anisotropy of magnetic susceptibility in the Otter Tail Pluton, Northwestern Ontario Hubin, J. and Cordua, Wm. (University of Wisconsin, River Falls, WI) SEM imaging of fossil nannobacteria from the supergene zone, Flambeau copper mine, Ladysmith Wisconsin. Johnson, J.R., Kissin, S.A. and Hollings, P. (Lakehead University, Thunder Bay, ON) VHMS mineralization and alteration within the Lumby Lake Greenstone Belt, Northwestern Ontario Kelso, I.S. and Kissin, S.A. (Lakehead University, Thunder Bay, ON) Geology and fluid inclusion studies of the Thunder Bay Agate Mine, Northwestern Ontario Miller, J.D. Jr.1, Green2, J.C., Severson3, M.J., Chandler1, V.W., Peterson3, D.M., Hauck3, S.A., and Wahl1 T.E, (1Minnesota Geological Survey, St. Paul, MN, 2University of Minnesota–Duluth, Duluth, MN, 3Natural Resources Research Institute, Duluth, MN) New geologic map and report of the Duluth Complex and related rocks, Northeastern Minnesota. R.L. Patelke, (Natural Resources Research Institute, University of Minnesota-Duluth, Duluth, MN) Digital Drill Logs for the Duluth Complex - Lithology and Assays Peterson, D.M. (Natural Resources Research Institute, University of Minnesota-Duluth, Duluth, MN) xxx �3-Dimensional View Through a Mineralized System: the South Kawishiwi Intrusion, Duluth Complex Severson, M.J. (Natural Resources Research Institute, University of Minnesota-Duluth, Duluth, MN) The Mine Permitting Process in Minnesota - Who, What, Where, and When. Sikkila, K. (Wisconsin Department of Transportation, Superior, WI) Description of a pegmatite occurrence on the eastern margin of the Mellen Granite, State Highway 13, Ashland County, Wisconsin Woodruff, L.G. (U.S. Geological Survey, Mounds View, MN), W. F. Cannon, and C. Dicken, (U.S. Geological Survey, Reston, VA) Impact of fire on the forest floor and mineral soils, Snowbank Lake, Minnesota COMPANY POSTERS Avalon Ventures Ltd., 111 Richmond Street West, Suite 1116 Toronto, ON M5H 2G4 Emerald Fields Resource Corp., 1546 Pine Portage Road Kenora, ON P9N 2K2 Goldcorp Inc., Balmertown, ON P0V 1C0 Nuinsco Resources Ltd., 940 The East Mall, Suite 110 Toronto, ON M9B 6J7 xxxi �48th ANNUAL MEETING INSTITUTE ON LAKE SUPERIOR GEOLOGY Abstracts ��Mesoarchean Base Metal Systems in the Atikokan Area, NW Ontario, Canada Bernatchez, R. (Atikokan Resources Ltd., Atikokan, ON) A high grade silver-lead-zinc showing was discovered in the Lumby Lake Metavolcanic Belt in 1995 between Lumby and Herontrack Lake 100 meters north of the creek. Three grab samples taken from this showing returned an impressive 109, 189 and 416 oz Ag/ton with other samples assaying up to 25% lead and 8% zinc. Since 1995, Atikokan Resources has carried out an extensive exploration program consisting of detailed geological mapping, a 2292 sample soil survey, a 150 whole rock geochemical survey, ground geophysical magnetic, electromagnetic and IP surveys ( dipole-dipole and Gradient array) and seven diamond drill holes over a grided area 6.6 km E-W x 2 km N-S from the west end of Lumby Lake to Hutt Lake. All but one diamond drill hole was drilled on the main high grade silver discovery area located between Lumby and Herontrack Lake. This work has been successful in defining a world class size VMS system. This VMS system is located near the base of the southern limb of the Lumby Lake Mesoarchean Syncline. The detailed geological mapping has identified at least three major eruptive cycles of predominantly intermediate to felsic pyroclastic and tuffaceous rocks. Each eruptive cycle has been terminated with the deposition of exhalative chert and sulphides. These three horizons have been identified as the Lumby-Spoon Lake (southern), Delos Lake and Pond Lake (northern) Horizon. Most of the mechanical stripping has been focused on the Lumby-Spoon Lake Horizon. The rocks along the top portion of the Delos and Pond Lake Horizon are poorly exposed. Limited portions of these two horizons were exposed by mechanical stripping near the west end of each lake. The main high grade silver-lead-zinc discovery is located at the top of the Lumby-Spoon Lake Horizon. This horizon has now been traced from outcrop exposure and drilling for a distance of about 3 kilometers. This east-west striking horizon consists of four or more repeated sub-cycles of quartz-phyric rich tuff, lapilli tuffs (coarse and fine) and chert mineralized with sulphides. The mineralization is contained within the chert, tuff, lapilli tuff in the form of dissemination, stringers and semi-massive sulphide beds. The sulphide mineralization consists of sphalerite, galena, native silver, acanthite, pyrite, chalcopyrite and pyrrhotite. Each felsic cycle vary in thickness from a few meters up to 20-25 meters. The upper cherty portion of each cycle contains is usually mineralized with sphalerite, galena and acanthite and/or native silver. The tuff lapilli tuff section generally contains stringer mineralization of chalcopyrite, pyrite with minor sphalerite, galena acanthite and pyrrhotite. The main high-grade silver showing within the Lumby-Spoon Lake has been drill-tested with six diamond drill holes along an east-west strike length of 450 meters and down to a depth of about 400 meters. Mineralization has been intersected in drill holes over core length from 13 metres and up to 82 metres. Native silver was observed in all six holes drilled on the Lumby-Spoon Lake Horizon. The zone is still open at depth and on strike east and west. In total, the four or five sub-cycles forms a mineralized horizon measuring over 200 meters wide in the main showing area. 1 �The geology, mineralogy and alteration of the mapped area have shown strong similarity with other VMS deposits found in the Archean, Properozoic, and Mesozoic Eras. The drilling and litho geochemical rock sampling have shown the classic footwall chloritic and/or talc alteration, sericitic hanging wall alteration, zinc-lead-silver capping and footwall stringer mineralization. The litho geochemical rock sampling has shown areas of sodium depletion and potassium enrichment within the felsic rocks and magnesium enrichment within the footwall. This alteration appears to be parallel to sub-parallel to the stratigraphy. The felsic volcaniclastic rocks appear to have been derived from a highly fractionated sub-volcanic magma and have been classified as F2 and F3a type rhyolites. A new exploration program of detailed geological mapping, litho geochemical sampling and ground geophysical magnetic and electromagnetic surveys carried out in the Richardson Lake area, 12 km east and on strike with the main high grade silver-lead-zinc showing, has identified similar thick felsic bi-modal volcaniclastic rock sequence. It appears to be the easterly extension of the island arc at Lumby Lake. Several new base metal occurrences have been discovered and are contained within similar quartz- spheric felsic volcaniclastic rocks similar to those found in the Lumby Lake felsic rocks. K. Tomlinson of the GSC (2000) has identified island arc volcanism in both the southern and northern limb and at the base of the Lumby Lake Meta-volcanic Belt. The work carried out to date by ARI has shown that at least two island arc systems may exist within the lower portion of the southern limb of the Lumby Lake Meta-volcanic Belt. It is however, conceivable, that more that two island arc systems exist in this part of the belt. Recent work by ARI in the upper portion of the belt, north of the synclinal fold axis in the northern limb, has identified a different style of mineralization contained within sulphide facies IF. It is unknown at this time if thses two styles of mineralization are related to the same volcanic event of island arc building. It is possible that the Lumby Lake Meta-volcanic Belt may contain world class size VMS deposits yet undiscovered. The results obtained to date by Atikokan Resources Inc. shows that potential. ARI continues to explore and find previously identified and unidentified VMS base metal style mineralization in the Lumby and Finlayson Lake Meta-volcanic Belts. 2 �The influence of Archean crustal structures on the margin of the Penokean Orogen near Pope County, West-central Minnesota Boerboom, T. J., (Minnesota Geological Survey, St. Paul, MN (boerb001@umn.edu)) The western margin of the Paleoproterozoic Penokean Orogen in Minnesota is marked by a series of northwest-trending, sawtooth-like fault offsets, or tear faults, that correspond in space but not in orientation to major northeast-oriented block-bounding shear zones within the adjacent Archean Minnesota River Valley subprovince (Figs. 1A and 1B). The origin of these tear faults, whether reactivated Archean structures or structures formed strictly during the Penokean orogenic cycle is not clear, but they may be the result of scissors faulting focused on preexisting weaknesses in the crust during pre-orogenic extension. Pope County was mapped as part of the Minnesota Geological Survey County Atlas geologic mapping program, supported by the Minnesota Department of Natural Resources, Division of Waters. The bedrock there is deeply buried beneath glacial drift, and there are only six drill cores available for the 720 square mile (1900 square kilometer) county. Considering this, it is obvious that any geological interpretation of the bedrock geology is more accurately described as an interpretation of geophysical characteristics; nevertheless, several prominent structural features can be recognized from the geophysical data. The Minnesota River Valley subprovince has been subdivided into four blocks⎯the Benson, Montevideo, Morton, and Jeffers blocks, from north to south (Fig. 1B). Each of these crustal blocks is separated by straight and narrow east-northeast-trending geophysical lineaments that have been shown to be north-dipping shear zones (Southwick and Chandler, 1996; Southwick, 2002). In Minnesota, the western margin of the Paleoproterozoic Penokean Orogen changes from a northeast orientation that is roughly parallel to the Wawa-Minnesota River Valley subprovince boundary, to a north-south orientation that is perpendicular to the regional fabric of the adjacent Minnesota River Valley subprovince (Figs. 1A and 1B). The major sawtooth-notched offsets, or tear faults, are most prominent in the north-south stretch, where they coincide spatially with the major block-bounding faults in the adjacent Minnesota River Valley subprovince. The most prominent of these tear faults, which crosses southern Pope County, separates the Archean Montevideo block from Paleoproterozoic rocks on the east, but to the west is contained wholly within the Archean Benson block (Fig. 1B). The eastern extent of this fault is occupied by a continuous string of late- to post-tectonic, mafic to felsic intrusions (Fig. 1B) that have been verified by drilling to consist of intrusive rocks similar to those exposed in outcrops to the northeast, near St. Cloud. The concentration of these late, ovoid intrusions along the fault plane implies that the fault extends to deep crustal depths. The tear faults may have formed strictly during Paleoproterozoic time, or they may be reactivated Archean structures that were oriented parallel to the direction of maximum extension and shortening of the Penokean deformational belt. In either case, the coincidence of the orogen-bounding tear faults with major northeast-trending shear zones in the adjacent Minnesota River Valley subprovince 3 �implies that preexisting structures in the Archean crust provided zones of weakness which ultimately controlled the location of the tear faults. Boerboom, T.J., in prep., Bedrock geology of Pope County, Minnesota, plate 2 of Harris, K.L., project manager, Geologic atlas of Pope County, Minnesota: Minnesota Geological Survey County Atlas C-15, Part A, scale 1:200,000. Southwick, D.L., 2002, Geologic map of pre-Cretaceous bedrock in southwest Minnesota: Minnesota Geological Survey Miscellaneous Map M-121, scale 1:250,000. Southwick, D.L., and Chandler, V.W., 1996, Block and shear-zone architecture of the Minnesota River Valley subprovinces: Implications for late Archean accretionary tectonics: Canadian Journal of Earth Sciences, v. 33, no. 6, p. 831–847. 4 �Heterogeneity in the Nine Mile Pluton, Wausau Complex, in terms of high field strength element (hfse) and rare earth element (ree) bearing minerals. Buchholz, T.W., (1140 12th Street North, Wisconsin Rapids, Wisconsin 54494); Falster, A. U., and Simmons, Wm. B., (Department of Geology and Geophysics, University of New Orleans, New Orleans, Louisiana 70148). The Nine Mile pluton is the youngest and most silica-rich of the four intrusive centers of the Wausau complex which is exposed in Marathon County, Wisconsin. The complex is approximately 1.5 Ga in age and locally abounds in pegmatitic veins, aplites, and miarolitic granite. Mineralization in these environments is commonly varied and complex, though in many cases restricted to small localized environments. Notable variation exists in minerals of HFSE (high-field strength elements such as Nb, Ta, Zr, Th, etc) and to a lesser extent in REE (rare earth elements). The type and size of these mineral-rich bodies varies throughout the pluton. In the northern portion of the pluton, large and well-defined pegmatitic bodies with sizeable miarolitic cavities containing a wealth of accessory phases are abundant. The size of pegmatitic veins and the size of miarolitic cavities are smaller in the central and southern parts of the pluton. Small miarolitic cavities in dikes and in granite typically host the accessory minerals in the northern area of the pluton. Significant variation also exists with respect to Nb, Ta, Ti and REE+Y mineralization. In the northern part of the pluton, titanium oxides such as anatase, brookite, and rutile are widespread but they are rare in the central and southern portions. Columbite-tantalite group minerals are most abundant in the central part of the pluton, but less abundant in the south and rare in the northern part. Conversely, Nb-dominant euxenite-group minerals which are rare to absent in the central portion of the pluton are more abundant in the southern and western parts. REE+Y mineralization appears to be more evenly distributed but may be slightly more abundant in the central part. Zircons are widespread in small amounts throughout the pluton and show Hf-enrichment, particularly in close proximity with fluorite. This enrichment occurs mainly in the central portion of the pluton, although isolated instances have been noted in the south and west. Cassiterite is exceedingly rare but has been noted in the central, western, and northern parts of the pluton. Fluorite is most abundant in the central portions of the pluton where it is commonly intimately associated with the Nb-Ta-oxide minerals microlite, manganotantalite and tapiolite. The link of high fluorine activity and more highly evolved geochemical fractionation of Nb-Ta oxides is obvious. Such highly fractionated oxides generally do not occur in NYF-type (NYF = Nb-Y-F enriched pegmatites typical of anorogenic origin) pegmatitic environments. The localized niches of high F activity are where these uncommon HFSE and REE phases occur. In all cases of exotic mineralogy, the central portion of the Nine Mile pluton differs from the rest of the pluton; it is also only here that several high-Sc phases have been found. These observations may indicate that the central portion of the Nine Mile pluton may actually be a fifth intrusive center. Buchholz, T. W., Falster, A. U. & Simmons, Wm. B. 1999. Ta, Nb, U, Y, and REE Minerals of the Koss Quarry, Marathon County, Wisconsin: The 26th Rochester Mineralogical Symposium, Abstracts of Contributed Papers. p. 6. 5 �Buchholz, T. W., Falster, A. U. & Simmons, Wm. B. 2000. Additional Mineralogy of the Koss Quarry, Marathon County, Wisconsin: The 27th Rochester Mineralogical Symposium, Abstracts of Contributed Papers. p. 5. Buchholz, T. W., Falster, A. U. & Simmons, Wm. B. 2001. Minerals of the Ladick East Quarry, Marathon County, WI: The 28th Rochester Mineralogical Symposium, Abstracts of Contributed Papers. p. 7. Falster, A. U., Simmons, Wm. B., Webber, K. L., & Buchholz, T.W. 2000. Pegmatites and Pegmatite Minerals of the Wausau Complex, Marathon C., Wisconsin: Memorie della Societa Naturali e del Museo di Storia Naturale di Milano, V. 30, p. 13-28. Hanson, S.L., Falster, A.U., Simmons, W.B., Webber, K.L., Buchholz, T. 1998. Rare-EarthElement (REE) Mineralization of Pegmatites in the Wausau Complex, Marathon County, Wisconsin: The 25th Rochester Mineralogical Symposium, Abstracts of Contributed Papers. p. 12. Keppler, Hans. 1993. Influence of fluorine on the enrichment of high field strength trace elements in granitic rocks: Contributions to Mineralogy and Petrology, V. 114, p. 479-488. Myers, P.E., Sood, M.H., Berlin, L.A. & Falster, A.U. 1984. The Wausau Syenite Complex, Central Wisconsin: Thirtieth Annual Institute On Lake Superior Geology, Field Trip Guidebook 3. 6 �Geology of the western Gogebic Iron Range, northwest Wisconsin—a record of sedimentation and deformation across the northern margin of the Penokean orogen Cannon, W. F., (USGS, Reston, VA), Laberge, G. L. (Oshkosh, WI), Klasner, J. S., (Macomb, IL), Dicken, C., (USGS, Reston, VA) Between 1991 and 1994 we examined most bedrock exposures of the iron-bearing strata and adjacent units of the western Gogebic Iron Range. We also compiled previously mapped features from both published and unpublished sources, including very detailed but unpublished mapping performed by iron mining companies in the 1950’s. The Gogebic Iron Range is a steeply north-dipping monocline of Early Proterozoic strata. The monocline formed at about 1.1 Ga (Cannon and others, 1993) by crustal-scale thrusting on faults such as the Atkins Lake-Marenisco fault that tilted gently south-dipping rocks formed during the Penokean orogenic cycle at approximately 1.9-1.8 Ga. The map pattern therefore is a cross section of the Penokean features that passes from a weakly deformed depositional and deformational foreland in the east to parts of the Penokean orogen toward the west that were more tectonically active both during deposition and deformation. Early Proterozoic strata lie unconformably on Late Archean granitic and metavolcanic rocks. The Bad River Dolomite, the oldest of the Early Proterozoic strata, is thin and discontinuous in the east but forms a continuous unit several hundred meters thick in the Grandview area in the west. Eastward from the Mt. Whittlesey area the basal unit of the Palms Formation commonly is a chert breccia composed of a residuum of chert fragments formed by dissolution of the cherty dolomite of the Bad River. Elsewhere, basal argillite beds of the Palms lie directly on the Bad River or Archean basement. The Palms Formation maintains uniform character and thickness 7 �across the mapped area. It consists of thin-bedded argillite and argillaceous quartzite in the lower part and thick-bedded quartzite in the upper part. The Ironwood Iron-formation lies conformably on the Palms. Near Upson and eastward the Ironwood displays a five-fold internal stratigraphy (Huber, 1959) of wavy-bedded jaspillitic iron-formation interlayered with even-bedded carbonate and silicate iron-formation. This stratigraphy cannot be traced far west from Upson. Jaspillitic and hematitic units are rare from Mt. Whittlesey to the west where the iron-formation has more reduced mineral assemblages and scarcer cherty units. The westernmost exposures in the Grandview area are banded gruneritemagnetite iron-formation, which becomes progressively leaner and more argillaceous to the west. The iron-formation in the Grandview area is roughly 2,000 feet thick as opposed to 5001000 feet farther east. In the westernmost part of the Grandview area drill holes show that the iron-formation becomes interbedded with black shale. The Tyler Formation overlies the Ironwood, probably with low angle unconformity, and is predominantly a thick sequence of graded-bedded turbidites. Most Early Proterozoic rocks were variably metamorphosed at about 1.1 Ga in the broad contact aureole of the Mellen intrusive complex. The Early Proterozoic stratigraphic section records deposition in a relatively shallow stable basin through the time of deposition of the Palms Formation. Beginning with deposition of the Ironwood, there are indications of tectonic instability and variations of depositional setting across the area. In the east iron-formation appears to have accumulated under tectonically quiescent conditions allowing widespread deposition of similar lithologies and thicknesses. To the west, deposition appears to have been in progressively deeper water and to have had a greater input of fine-grained clastic material. Also, in the Grandview area, sills of diabase as much as 1,000 feet thick occur in the iron-formation and enigmatic beds of breccia, possibly of volcanic derivation, suggest a proximity to tectonically and volcanically active parts of the Penokean orogen. The situation may be similar to the eastern end of the Gogebic Range where sills and volcanic rocks interfinger with the Ironwood. Finally, deposition of the turbidites of the Tyler Formation marks the transgression of a deep-water foreland basin in advance of accreting volcanic arcs of the Wisconsin magmatic terranes to the south. Penokean structures are much more intensely developed in the west than the east. Near Upson, structures are limited to rare outcrop-scale folds in the iron-formation and to moderately to weakly developed cleavage in more argillaceous units of the Tyler Formation. From near Mt. Whittlesey to the Mineral Lake area folding and faulting are much more intense. Folds with wavelengths of hundreds of meters are discernable in the iron-formation. Bedding plane faults and other originally low angle faults are also common including a basal decollement that separates the Early Proterozoic strata from Archean basement. Folds appear to have been mostly assymetrical to recumbent and north-verging, but Middle Proterozoic tilting has rotated these so that they are now mostly overturned structures. Likewise, original low angle thrusts are now tilted toward the north and have the appearance of down-to-the-north normal faults. Cannon, W.F., Peterman, Z.E., and Sims. P.K., 1993, Crustal-scale thrusting and origin of the Montreal River monocline—a 35-km-thick cross section of the Midcontinent rift in northern Michigan and Wisconsin: Tectonics, v.12, p. 728-744. Huber, N.K., 1959, Some aspects of the origin of the Ironwood Iron-formation of Michigan and Wisconsin: Econ. Geology, v. 54, p. 82-118. 8 �Anisotropy of magnetic susceptibility in the Ottertail pluton, Northern Ontario. Fein, E. M., Sturm, C. L., and Czeck, D. M., (Department of Geology, Oberlin College, Oberlin OH, 44074, Elizabeth.Fein@oberlin.edu.) INTRODUCTION In this project, we studied the structural and magnetic fabrics of the Ottertail Pluton, a small, granitic body within the Superior Province of Northern Ontario. The Ottertail, part of the Algoman suite of quartz monzonites and granodiorites, intruded surrounding rocks along the Wabigoon- Quetico subprovince boundary around 2.7 Ga (Davis et. al, 1989). From field observation, the emplacement of the Ottertail Pluton has been considered to be postdeformational due to the lack of obvious deformation fabrics evident in other types of rocks at the subprovince boundary (e. g. Davis et. al, 1989; Poulsen, 2000) . This interpretation has been used to constrain the timing of final deformation along the Wabigoon- Quetico boundary associated with microplate collision. PROBLEM On a much smaller scale, within deformed conglomerates, such as the nearby Seine River conglomerates, rigid clasts often display evidence of much less deformation than do more yielding clasts. Could a similar situation have occurred on a much larger scale in the case of the Ottertail Pluton? The relatively rigid granite body could appear to be relatively undeformed in the field, even if the timing of its emplacement was pre- or syn- tectonic. This situation, where a pluton appears undeformed despite being present during deformation, has been shown to occur in some modern tectonic regimes (e. g. Paterson & Tobisch, 1988). A more detailed study of plutonic fabrics and relationships is needed to conclusively determine whether a pluton is truly “post deformational.” METHOD In August of last year, we sampled an E-W (and a shorter N-S) transect across the Ottertail Pluton traveling along Highway 11, west of Mine Centre, Ontario. Thirty-one sites were sampled resulting in a total of 218 oriented cores. The anisotropy of magnetic susceptibility (AMS) of these granitic cores was measured to learn about the history of pluton emplacement. The measurements were conducted at the Institute of Rock Magnetism at the University of Minnesota in Minneapolis in January of this year. In general, the samples have a significant AMS signal contributed by multi-domain magnetite. The AMS data has been complied to describe the attitude of the variations in magnetic fabric within the Ottertail Pluton. To determine the relative timing of pluton emplacement with respect to the deformation, we need to show whether the magnetic fabric is concordant with preserved, regional patterns of strain. The AMS study will be combined with our field observations and a detailed petrographic study. 9 �RESULTS Regional deformation fabrics have already been well documented in the literature (e. g. Poulsen, 1986; Poulsen, 2000; Czeck, 2001). Preliminary results of our study suggest that the magnetic fabrics preserved in the Ottertail are related to the pattern of regional strain fabrics in the surrounding rocks. Further work will be conducted to analyze the magnetic fabrics to determine if, indeed, the Ottertail Pluton is pre- or syn- tectonic. If it can be shown to be pre- or syntectonic, this will have major implications for the relative timing of larger, regional, tectonic events. In particular, if the Ottertail is representative of other Algoman plutons and the deformation is truly regional, it may not be possible to constrain the end of regional deformation using the date of the intrusion of Algoman granites. Czeck, D. M., 2001. Strain analysis, rheological constraints, and tectonic model for an Archean polymictic conglomerate: Superior province, Ontario, Canada. Unpublished Ph. D. Thesis, University of Minnesota, 245 p. Davis, D. W., Poulsen, K. H., Kamo, S. L., 1989. New insights into Archean crustal development from geochronology in the Rainy Lake area, Superior Province, Canada. Journal of Geology 97, 379-398. Paterson, S. R., Tobisch, O. T., 1988. Using pluton ages to date regional deformations: problems with commonly used criteria. Geology 16, 1108-1111. Poulsen, K. H., 1986. Rainy Lake Wrench Zone: An example of an Archean Subprovince boundary in Northwestern Ontario. In: de Wit, M. J., Ashwal, L. D. (Eds.), Tectonic evolution of greenstone belts Technical Report 86-10, pp. 177-179. Poulsen, K. H., 2000. Archean metallogeny of the Mine Centre - Fort Frances area. Ontario Geological Survey Report 266, 121. 10 �Groundwater and Heat Flow in an Interlobate Moraine in Southeastern Manitoba. Ferguson, G. A. G. and Woodbury, A. D., (Department of Civil Engineering, University of Manitoba) Significant deviations from conductive heat flow occur in the Sandilands area of southeastern Manitoba as a result of groundwater flow. The main geological feature of this area is an interlobate moraine that coincides with the subcrop belt of the Ordovician Winnipeg Formation, which is composed primarily of sandstone and shale. The sandstone of the Winnipeg Formation acts as a regional aquifer and regional hydraulic head distribution and hydrogeochemistry suggest that the Sandilands area is an important source of recharge to this aquifer. The sandstone aquifer of the Winnipeg Formation is hydraulically separated from overlying hydrostratigraphic units west of the subcrop belt by a layer of low permeability shale that is thought to be continuous [Betcher, Third Canadian Hydrogeological Conference (1986)]. Overlying the Winnipeg Formation is the Ordovician Red River Formation, consisting of dolomitic limestone in the study area. The Red River Formation contains an aquifer in its upper extent, and previous studies have suggested that the Sandilands is an important recharge area for this aquifer as well. However, Sandilands recharge is likely less important as this carbonate aquifer is also recharged through the tills between the moraine and the Red River [Render, Cdn. Geotech. Journal, v.7, 243-274 (1970)]. Till is also present at the base of the moraine and acts as a semi-confining layer. Deviations from conductive heat flow provide a means of determining the direction and magnitude of groundwater flow, and are an efficient method of investigating the interaction between the groundwater in the surficial glaciofluvial sediments and the underlying bedrock aquifers. The geothermal gradient in the Superior Province of southeastern Manitoba is approximately 0.01 OC/m, which corresponds to a heat flow of approximately 40 w/m2. Temperature profiles through the moraine in the Sandilands area show geothermal gradient as low as 0.006 OC/m below the depth of penetration for seasonal variations. One-dimensional analytical models indicate that downward flow of groundwater must be occurring at a rate of approximately 10-8 m/s to produce the observed curvature seen in the temperature profiles. Analysis of temperature profiles in areas adjacent to the moraine has also aided in interpreting the hydrostratigraphy of the area. Temperature profiles through the upper shale unit of the Winnipeg Formation are linear, indicating that this layer is does act as an effective confining layer for the underlying sandstone aquifer. Discharge areas and areas of predominantly horizontal flow are present in the area surrounding the moraine, suggesting that not all of the water infiltrating into the moraine reaches the underlying bedrock aquifers. 11 �Mesoarchean Evolution of Western Superior Province: Evidence from Metasedimentary Sequences near Atikokan P. Fralick and D. King, (Department of Geology, Lakehead University, Thunder Bay, Ontario, P7B 5E1. (pfralick@mercury.lakeheadu.ca)) Paleogeographic reconstructions based on data supplied by metasedimentary sequences provide a basis for understanding plate movements which create sedimentary basins. This combined with geochronology allows sequential developmental stages of a craton to be deciphered. Thus, by interpreting environment of deposition from outcrop data, inferring provenance from composition of the metasedimentary units, and determining the age of detrital zircons and zircons in interstratified or intrusive igneous rocks insight will be gained on the plate movements which caused a basin to subside. The above was applied to a Mesoarchean sequence of metasedimentary and metavolcanic rocks to evaluate the degree basin subsidence could be explained by lateral plate motions similar to those of today. The succession is on the southern margin of Wabigoon Subprovince in the Atikokan area. It consists of, along an eighty kilometre belt from southwest to northeast,: 1) the Steep Rock Group, 2) the Little Falls assemblage, 3) the Finlayson Lake greenstone belt, and 4) the Lumby Lake greenstone belt. The oldest rocks exposed in the sequence are pre 3014 Ma tholeiitic basalts (Figure 1), the dominant rock type in the entire assemblage. The lowermost sedimentary units at Little Falls and Finlayson consist of felsic agglomerates and tuffs laterally transitional into resedimented sandstones and conglomerates. Transport was via high density mass flows, though some beds are possibly traction current deposits. Mafic ash layers are present throughout. Age determinations of the resedimented, pyroclastic zircon population gave 2996.9+-0.8 Ma, almost identical to the compositionally similar (Stone et al, 1992) Marmion Batholith which intrudes the area. Felsic volcanism also occurs in the Lumby Lake belt at this time. Plume derived (Hollings et al, 1999; Hollings and Wyman, 1999; Tomlinson et al, 1999) mafic and ultramafic volcanism continued in these belts until some time after 2828 Ma (age determination of Tomlinson et al, 2001) when eruptions ceased and a coarsening upward sedimentary sequence of iron formation, DE turbidites, classic turbidites, wave reworked coarse sandstones, and conglomerates was deposited at Finlayson The geochemistry and detrital zircon population (2997 to 3002 Ma) of the Finlayson sandstones is similar to Wagita Formation sandstones, a fluvial unit deposited in incised paleovalleys at the base of the Steep Rock Group (Wilks and Nisbet, 1988). Eroded basalt and tonalite detritus moved through Steep Rock paleochannels building out the shoreline in the Finlayson area. The sequence at Lumby consists of classic turbidites interbedded with lenses of mass flow conglomerates near the top, overlain by carbonate and finally iron formation. Although sedimentation was probably sinchronous in the Lumby area, geochemistry indicates komatiites were important source material here. Clastic sedimentation in the entire area was ended by transgression causing backfilling of Wagita fluvial channels followed by rapid drowning of the entire source area. Stromatolitic carbonates were deposited in the shallow ocean, but as subsidence continued the carbonate was replaced by iron formation. At 2780 Ma (Tomlinson et al, in press) the next volcanic cycle began with eruption of the komatiitic Ashrock Formation. 12 �The mafic and ultramafic volcanic units which dominate the sequence have been ascribed to plume generated melts erupting in an ocean plateau environment (Tomlinson et al, 1999; Hollings and Wyman, 1999; Hollings et al, 1999); the presence of the tonalites being ascribed to slab melting in a proximal subduction zone (Hollings et al, 1999). Though this model is elegant the new age determinations render it unworkable. Generation of felsic melts by plume induced heating at the base of the overthickened basaltic plateau is compatible with tonalite geochemistry (Smithies, 2000). The sedimentary sequence is consistent with an ocean plateau environment, but definitely not representative of a continental rift or cover sequence as previously suggested (Thurston and Chivers, 1990). Partial melts generated in the lower basaltic crust formed magma chambers 2 to 4 km below surface. This magma fed felsic eruptions which, in turn, supplied most of the material for clastic layers lower in the volcanic pile. Eruption of the enclosing basalts was probably sporadic, as the area was effected by pulses of plume activity (Tomlinson et al, 1999). These events lasted for over 185 Ma, into the Neoarchean, until finally terminated by a hiatus in volcanic activity. With the end of plume driven crustal heating, thermal decay induced subsidence lead to subareal to shallow water clastic sedimentation and shallow to deep water chemical sedimentation. The existence of an ocean plateau for over 185 Ma, and possibly over 235 Ma, calls into question the operation of plate tectonics in the Mesoarchean, and especially fast spreading, multiple ridge-subduction zone configurations proposed for this time period. If the plateau was undergoing lateral plate motion subduction zones must have been well spaced and movement slow to allow for its activity over such a long time period. This is difficult to reconcile with a hotter earth requiring greater heat dissipation capacity than today. The other alternative: conventional plate tectonics did not operate in the Mesoarchean, but rather heat loss was achieved through vigorous plume activity, possibly similar to the early history of Mars, needs to be explored further. Hollings, P. and Wyman, D., 1999. Lithos, 46, 189-213. Hollings, P., Wyman, D. and Kerrich, R., 1999. Lithos, 46, 137-161. Smithies, R.H., 2000. Earth and Planetary Science Letters, 182, 115-125. Stone, D., Kamineni, D.C. and Jackson, M.C., 1992. Geological Survey of Canada, Bulletin 405. Thurston, P.C. and Chivers, K.M., 1990. Precambrian Research, 46, 21-58. Tomlinson, K., Davis, D.W., Hughes, D.J. and Thurston, P.C., 1998. Lithoprobe Report 65, 35-47. Tomlinson, K., Hughes, D.J., Thurston, P.C. and Hall, R.P., 1999. Lithos, 46, 103-136. Tomlinson, K., Davis, D.W., Stone, D. and Hart, T., 2001. Lithoprobe Report, Western Superior. Tomlinson, K., Davis, D.W., Stone, D. and Hart, T., in press, Precambrian Geology. Wilks, M.E. and Nisbet, E.G., 1988. Canadian Journal of Earth Sciences, 25, 370-391. 13 �EEl Felsic Volcanic Rocks LUMBY SOUTH Mafic Volcanic ______________ 2997 Ages in Million years 2828 WALLACE I AVP Grarntic Rocks —e .— —C U— —U U— FINLAYSON LITTLE PAT T c Fig. 1. Stratigraphic sections of Mesoarchean rocks in the Atikokan area, and Wallace Lake in the Uchi Belt for comparison. Geochronology mainly from Tomlinson et al and Stone et al. 14 �SEM Imaging of fossil nannobacteria from the supergene zone, Flambeau Copper Mine, Ladysmith, Wisconsin Hubin, J. and Cordua, Wm., (Department of Planet and Earth Science, Univeristy of Wisconsin-River Falls, 410 South Third Street, River Falls, WI 54022 william.s.cordua@uwrf.edu) The discovery of nannobacteria fossils in Eocene supergene zones in Chilean copper deposits (Sillitoe et. al. 1996) suggested that similar, but older, nannobacteria may be found in the Cambrian to Precambrian supergene zone of the Flambeau Copper Mine in Rusk County, Wisconsin. A scanning electron microscope study of samples from the Flambeau Mine focused on the interface between pyrite and replacing chalcocite. Images revealed several sites where spherical clusters 0.1 to 0.3 microns in diameter are present (fig. 1). Through visual comparison with existing studies and elimination of other possible explanations, these clusters are interpreted as being nannobacteria. The age of supergene mineralization at the Flambeau Mine predates the 525 million year old Mt. Simons sandstone (May and Dinkowitz, 1996), and may pre-date the deposition of the Barron quartzite (1750 - 1650 m.y.) (Medaris, 2000). If these are fossil nannobacteria rather than recent contaminants, it suggests that the involvement of nannobacteria in the supergene enrichment processes spans a considerable proportion of geologic time. Acknowledgements: We are indebted to Jeff Thole and his assistants for their help in using the SEM facilities at Macalester College for this study. REFERENCES: May, E.R., and Dinkowitz, S., 1996. An overview of the Flambeau supergene enriched massive sulphide deposit: geology and mineralogy, Rusk County, Wisconsin, in LaBerge, G., edited, Volcanic massive sulphide deposits of northern Wisconsin: A commemorative volume: Insitute on Lake Superior Geology Proceedings, 42nd Annual Meeting, Cable, WI, v.42, part 2, p. 67-93 Medaris, G. 2000, The Barron saprolite: confirmation of mature chemical weathering in the source for Paleoproterozoic quartz arenites in the Lake Superior region [abstract] Institute on Lake Superior Geology Proceedings, 46th Annual Meeting. Thunder Bay, ON, 2000, Part 1, p.37-38. Sillitoe, R.H., Folk, R.L. and Saric, N. 1996, Bacteria as mediators of copper sulphide enrichment during weathering, Science, vol. 272, p. 1153-1155. 15 �Figure 1. Suspected nannobacteria (arrows) at pyrite-chalcocite interfaces, Flambeau Mine, Ladysmith, Rusk County, Wisconsin. 20,000x. White bar = 5 microns. 16 �Archean and paleoproterozoic mafic intrusions in Minnesota Jirsa, M. A., (Minnesota Geological Survey, St. Paul, MN (jirsa001@umn.edu)) Exploration for platinum group elements (PGEs) in Minnesota has been restricted largely to mafic intrusions of the Mesoproterozoic Duluth Complex for obvious reasons—the complex contains known PGE occurrences associated with previously outlined coppernickel deposits. A new study by the Minnesota Geological Survey and the Natural Resources Research Institute is looking beyond the Duluth Complex to describe and analyze the varied mafic, ultramafic, and alkalic intrusions in the northern, western, and east-central parts of the state. Although geochronologic data are sparse, field and geophysical evidence implies that most of these intrusions are Archean and Paleoproterozoic in age. Figure 1 shows some of the major mafic intrusions and intrusive complexes for which some “ground truth” (drill core or outcrop) exists. They have been identified by surface and geophysical mapping and drilling; however, few have been thoroughly described and analyzed, and almost none have been analyzed for PGE content. Some of the intrusions are lithologically similar to the so-called “Quetico” and “Atikokan” intrusions that are the targets of exploration in Canada. The geologic settings of significant PGE deposits worldwide include mafic to ultramafic plutons associated with volcanic arc terranes in linear orogenic belts (Ural-type), differentiated sill complexes, ophiolitic complexes, syn- to late-orogenic layered complexes (Bushveld and Stillwater), and alkalic to subalkalic composite plutons. This study is designed to characterize the various types of mafic intrusions in Minnesota and perhaps broaden the exploration horizon to similarly diverse terranes throughout the state. At present, an inventory containing the pertinent facts from more than 150 individual intrusions and thousands of diabasic dikes has been compiled and sampling work has begun. As an initial classification, the known intrusions are grouped below first according to the age of host rocks into which they were emplaced, and secondly on the basis of perceived temporal, mineralogic, and geometric attributes. ARCHEAN HOST ROCKS Layered mafic-ultramafic complexes—Pre-tectonic with respect to the main metamorphic and foliation-forming deformation event. The rocks are variably metamorphosed and have tholeiitic to komatiitic compositions. The presence of layering and cumulate textures indicates differentiation. Rock types include peridotite, pyroxenite, gabbro, anorthositic gabbro, and diorite. Examples: Deer Lake Complex and Newton Lake Formation. Subvolcanic mafic sills—Pre-tectonic, variably metamorphosed, presumably hypabyssal intrusions associated with greenstone sequences. They typically are tholeiitic in composition. Rock types include gabbro, pyroxenite, and diorite. Example: Thistledew Lake sequence. Amphibolitic sills and dikes—Typically schistose, metamorphosed, and folded, narrow sills emplaced into schists and granitic intrusions of the Quetico subprovince. Example: Ash River amphibolite. 17 �Grygla p/Won ( Ash River amphibo/ite N - I Dever P'U(UT' *,'/ N.anLn. Thistledow Lake, Duluth Complex and related rocks sills 1• r, p EXPLANATION anomaly / Aeromagnetic interred lobe diaba&c dike iiiiuuiij,ipuui or containing, matic phases '\\\- &Y Drill hole Figure 1. Generalized map of Minnesota showing the distribution of mafic intrusions and drill holes that intersect mafic intrusive rocks. Many of the drill holes encountered intrusions too small to be depicted. Intrusions discussed in the text are labeled. 18 �Lamprophyric, pyroxenitic, peridotitic, and hornblendic intrusions—Syn- to post-tectonic dikes and small, irregular bodies. They typically are coarse-grained, oxide-rich, and strongly magnetic. Example: Dead River pluton. Sanukitoid composite stocks—Discrete, post-tectonic intrusions of the dioritemonzodiorite-monzonite-syenite suite. They typically are quartz-poor to quartzabsent. Most contain intrusive phases and enclaves of amphibole-pyroxene-micabearing diorite, locally of lamprophyric affinity. Example: Gheen pluton. Tonalite-diorite intrusions—Discrete, probably post-tectonic intrusions that contain magmatic phases varying from tonalite to diorite and gabbro. Example: Grygla pluton and associated intrusions. PALEOPROTEROZOIC AND ARCHEAN HOST ROCKS Gabbroic intrusions—Discrete, typically semicircular intrusions containing gabbro, troctolite, anorthositic gabbro, and pyroxenite. Typically show as magnetic and gravity highs. Example: Lake Washington intrusion. Pyroxenite and peridotite plugs and stocks—Small, circular to irregularly shaped bodies having strong magnetic signatures. Commonly occur along linear geophysical discontinuities. Examples include many of the small intrusions in central Minnesota shown on Figure 1 by drill hole locations. Age is uncertain, but one is known to intrude ~1780 Ma granite. Diabasic to gabbroic dikes—Northwest-trending dikes are part of the Kenora– Kabetogama swarm of Paleoproterozoic age, other dike orientations are both Paleoproterozoic and Mesoproterozoic in age. Outcrop mapping indicates dike widths between 30 and 100 meters. Larger dikes commonly are composite and have central zones composed of granodiorite and leucogabbro. This classification will undoubtedly be modified with the addition of new petrographic and geochemical data. This study is funded by the Minnesota Legislature on recommendation of the Minnesota Minerals Coordinating Committee. 19 �VHMS mineralization and alteration within the Lumby Lake Greenstone Belt, Northwestern Ontario Johnson, J.R., Kissin, S.A. and Hollings, P., (Department of Geology, Lakehead University, Thunder Bay, ON, P7B 5E1, jrjohnsonca@yahoo.ca) The Lumby Lake greenstone belt, located approximately 40 km northeast of Atikokan, Ontario or 165 km northwest of Thunder Bay, Ontario, has been a focus of exploration activity for the past one hundred years. The belt is located within the Wabigoon Subprovince of the Superior Province. The Wabigoon Subprovince is interpreted as a collage of 3 – 2.7 Ga plutonic and volcanic terranes (Blackburn et al, 1991), where as Tomlinson et al. (1999) have shown that the Lumby Lake belt ranges in age from 28983001 Ma. Mapping done by Jackson (1985a, b) showed the belt to be dominated by mafic metavolcanic units that occur as massive to pillowed flows. Thin felsic volcanics and clastic sedimentary units were found throughout the belt along with less common ultramafic flows, located only towards the top of the stratigraphic sequence. The Marmion Lake Batholith intrudes the southern portion of the belt. In the past the belt has been discounted as a possible base metal camp due to the relative absence of felsic material. Hollings and Wyman (1999) documented that the mafic volcanic rocks of the belt are similar to those of modern ocean plateau tholeiites (associated with plume related volcanism), consistent with the presence of komatiites. These authors invoked a complex model of plume arc interaction to account for the presence of arc related felsic volcanics within the plateau related mafic pile. Hollings and Wyman (1999) reported the presence of two distinct types of felsic volcanic rock, and comparable plutonic phases, within the Lumby Lake belt. One suite characterized by fractionated heavy rare earth elements (HREE) are comparable to the nonprospective F1 of Lesher et al (1996), the second suite with unfractionated HREE are similar to the variably prospective F2 of Lesher. The F2 felsic horizons are found within the Lumby Lake-Spoon Lake area and further to the south within the Marmion Lake Batholith. Tomlinson et al. (1999) found that the felsic volcanics of belt, in general, give the oldest ages, ~3 Ga. Additional exploration, by Atikokan Resources Inc. (ARI) in the last decade, and mapping done, in conjunction with ARI, in the last year has identified the presence of additional extensive felsic flows, tuffs and breccias, predominately in the southern portion of the belt. Areas of base metal mineralization, such as the stratabound pyrite, sphalerite, galena, chalcopyrite, native silver and silver sulphides found in the Lumby Lake-Spoon Lake area (0.2 to 9.2% Zn, #0.25% Cu, 1.0% Zn and 37 – 60 g Ag/t) and the pyrite, sphalerite, galena, pyrrhotite and chalcopyrite located near Richardson Lake, have been revealed. It should be noted that there is a scarcity of volcanic hosted massive sulphide deposits of 3 Ga or older 20 �Examination of the area near Richardson Lake indicates that silicification and chloritization of the rocks is common with sericite alteration less prominent. This alteration is consistent with that found in the footwalls of volcanogenic massive sulphide deposits (Franklin, 1993). Additional mapping and geochemical work, involving the classification of newly located felsic horizons and the relative enrichment and depletion of elements, will lead to further defining these zones of alteration and enable the location of additional base metal targets. In addition geochemical analyses will be utilized to further define the tectonic setting of the Lumby Lake belt. Blackburn, C. E., Johns, G. W., Ayer, J. A., Davis, D. W., 1991, Wabigoon Subprovince, Geology of Ontario. Ontario Geological Survey, p. 303-382. Davis, D. W., and Jackson, M. C., 1988, Geochronology of the Lumby Lake greenstone belt: A 3 Ga complex within the Wabigoon Suprovince northwestern Ontario: Geological Society of America Bulletin, v. 100, p. 818-824. Franklin, J. M., 1993, Volcanic-associated massive sulphide deposits, in Kirkham, R. C., Sinclair, W. D., Thorpe, R. I. And Duke, J. M., eds, Mineral Deposit Modeling: Geological Association of Canada, Special Paper 40, p. 315-334. Hollings, P. and Wyman, D., 1999, Trace element and Sm-Nd systematics of volcanic and intrusive rocks from the 3 Ga Lumby Lake Greenstone belt, Superior Province: evidence for Archean plume-arc interaction. Lithos, v. 46, p. 189-213. Jackson, M. C., 1985a, Geology of the Lumby Lake area, eastern part, districts of Kenora and Rainy River: Ontario Geological Survey Open-File Report 5535, 122 p. Jackson, M. C., 1985b, Geology of the Lumby Lake area, western part, districts of Kenora and Rainy River: Ontario Geological Survey Open-File Report 5534, 151 p. Lesher, C. M., Goodwin, A. M., Campbell, I. H. and Gorton, M. P., 1986, Trace-element geochemistry of ore associated and barren, felsic metavolcanic rocks in the Superior Province, Canada; Canadian Journal of Earth Sciences, v. 23, p. 222-237. Tomlinson, K. Y., Davis, D. W., Thurston, P. C., Hughes, D. J., and Sassevile, C., 1999, Geochemistry, Nd isotopes and geochronology from the Central Wabigoon Subprovince and North Caribou Terrane: regional correlations leading towards a Mesoarchean reconstruction. Lithoprobe Report #70, p. 136-152. 21 �Geology and fluid inclusion studies of the Thunder Bay Agate Mine, Northwestern Ontario Kelso, I.S. and Kissin, S.A., (Department of Geology, Lakehead University, Thunder Bay, ON, P7B 5E1 stephen.kissin@lakeheadu.ca.) The Thunder Bay Agate deposit, located northeast of Thunder Bay at the junction of Highway 11/17 and Highway 527, was discovered in 1989 and developed into the presently operating Thunder Bay Agate Mine in 1996. The deposit is hosted by carbonate units of the Gunflint Formation and is 50m NE of the contact with olivine diabase of a Logan sill. The deposit has a surface exposure of approximately 160 x 200m. Throughout the area of the deposit, intermittent open spaces within the host-rock are filled by agate. Where the agate-filled spaces are larger than ~50cm high and 1m wide, there is evidence of collapse brecciation of the host-rock. The largest agate-filled space observable is 2m wide and 0.8m high. Thunder Bay agate consists of three mineral phases: chalcedony, quartz, and graphitic carbon. The chalcedony can be subdivided into three varieties: dark amorphous silica (opal-A?), light amorphous silica (opal-CT?), and translucent chalcedony. A consistent sequence of mineralization is observed throughout the deposit. From nucleation against the host-rock, the sequence is rhythmic bands of dark amorphous silica, light amorphous silica, translucent chalcedony, and quartz-encased, carbon-filled vugs. As mineralization radiates from several points of nucleation, interference patterns generate complex, sinuous structures in the sequence. Although graphitic carbon is not always present, where it does occur it is never observed to be in direct contact with the host-rock or chalcedony. Quartz is often the final stage of mineralization and is rarely observed to be in direct contact with the host-rock. The rhythmic bands of each stage vary from <1mm to >1cm in width. Three types of fluid inclusions, according to the terminology of Roeder (1984), were found: Type I: Single-phase inclusions containing liquid or vapour only. A number of Type I inclusions in quartz were examined; however, no change on freezing was observed. Type II: Two-phase liquid + vapour inclusions. These are the most common type of inclusion in quartz. Eutectic, final melting and homogenization temperatures were obtained. Type III: Three-phase liquid + vapour + solid(s) inclusion. Not observed in this study. Type IV: CO2-rich inclusions. These homogenized at <31°C and decrepitated when heated above homogenization. Type II Two-phase inclusions (liquid and vapour) are the most numerous type of primary inclusion within the quartz. These inclusions range in size from 4 to 50µm along their greater axis and have a vapour content of 2% to 7% by volume. All Type II inclusions in the quartz homogenized to liquid in the range of 70 - 190°C with the majority homogenizing within the range of 100-130°C. The eutectic and final melt temperatures of the inclusions clustered around two ranges. Inclusions with eutectic temperatures of 22 �approximately -52°C exhibited final melt temperatures of -34 to -27°C; inclusions with eutectic temperatures of approximately -25°C exhibited final melt temperatures of -7 to 2°C. The higher temperature cluster corresponds to the NaCl-H2O eutectic temperature of -22°C. The lower temperature cluster of inclusions likely contain minor amounts of CaCl in solution with NaCl. The chalcedony is almost exclusively devoid of inclusions; however, one cluster of about 10 Type IV inclusions containing liquid CO2 were observed in translucent chalcedony. In these inclusions the frozen CO2 displays visible melting at -45°C and homogenized at 30.2°C. Fluid inclusion studies indicate the quartz was emplaced in a low-temperature, lowpressure hydrothermal environment. The timing of deposition is delimited between the age of the Gunflint Formation (1878 ma; Fralick et al., in press) and the Logan sills (1109 ma, Davis and Sutcliffe, 1985) which have been seen to contain xenoliths of typical agate (J. Scott, pers. com., 2001). The deposition of agate appears to be related pervasive, early silicification of the Gunflint and other Lake Superior-type iron formations, as summarized by Simonson (1987). He proposed that silicification most likely could be attributed to siliceous thermal springs located nearer the axis of the depositional basin. Compaction could expel the siliceous solutions to the margins of the basin. Rimstidt and Barnes (1980) showed that silica precipitation in response to declining is most effective in a decrease from 300 to 100°C, the approximate mean homogenization temperature observed in quartz-hosted inclusions. Silica solubility also decreases sharply with a drop in pH. Organic matter producing CO2 at the site of agate deposition would both cause silica precipitation and dissolution of carbonate host rocks through lowering of pH. Evidence of such CO2 production is seen in the presence of Type IV CO2-rich inclusions. Organic matter also is believed to provide a favourable nucleation site for silica (Knoll, 1985). Thus, the occurrence of the agate deposit in carbon-rich carbonate rocks can be explained. Fralick, P., Davis, D.W., and Kissin, S.A. in press. The Age of the Gunflint Formation, Ontario, Canada: Single zircon U-Pb age determinations from reworked volcanic ash. Canadian Journal of Earth Science. Davis, D.W., and Sutcliffe, R.H. 1985. U-Pb ages from the Nipigon Plate and northern Lake Superior. Geological Society of America Bulletin 96: 1572-1579. Knoll, A.H. 1985. Exceptional preservation of photosynthetic organisms in silicified carbonates and silicified peats. Philosophical Transactions of the Royal Society of London B311: 111-122. Rimstidt, J.D., and Barnes, H.L. 1980. The kinetics of silica-water reactions. Geochimica of Cosmochimica Acta 44: 1683-1699. Roedder, E. 1984. Fluid Inclusions. Mineralogical Society of America, Reviews in Mineralogy 12. Simonson, B.M. 1987. Early silica cementation and subsequent diagenesis in arenites from four Early Proterozoic iron formations of North America. Journal of Sedimentary Petrology 57: 499-511. 23 �WOLF RIVER-AGE BRECCIATION IN THE BARABOO QUARTZITE, WISCONSIN: IMPLICATIONS FOR PROTEROZOIC TECTONICS IN THE LAKE SUPERIOR REGION Medaris, L.G., Jr., Singer, B.S., Brown, P.E., Jicha, B.R., and Smith, M.E., (Dept. of Geology and Geophysics, Univ. of Wisconsin-Madison, 1215 W. Dayton St., Madison, WI, 53706; medaris@geology.wisc.edu) Breccia zones in Baraboo Quartzite, consisting of angular red quartzite fragments cemented by a stockwork of white quartz veins (Fig. 1), are distributed sporadically throughout much of the Baraboo Range. Larger breccia zones tend to be parallel with associated bedding, although thin quartz veins with incipient breccia features are commonly crosscutting. The most prominent breccia zone, which is well exposed in Ableman's Gorge, is ~100 meters thick and can be traced for ~20 kilometers along the north limb of the Baraboo syncline. Figure 1. Quartzite breccia, Martin-Marietta Quarry, north limb, Baraboo syncline Figure 2. Back-scattered electron image of muscovite (light gray), kaolinite (dark gray), and quartz (medium gray) in breccia cement The breccia cement is composed predominantly of massive vein quartz, which is occasionally accompanied by small amounts of specular hematite. Locally, euhedral quartz crystals occur in vugs, some of which are partly to completely filled by kaolinite. Muscovite is rare in the breccia cement, but muscovite was recently discovered by Phil Fauble in an outcrop of breccia in the bluffs east of Devil's Lake on the south limb of the syncline. At this locality, prominent flakes of muscovite appear to be in textural equilibrium with kaolinite and quartz (Fig. 2). 24 �The stable coexistence of quartz, kaolinite, and muscovite is limited to temperatures below ~300oC by the reaction, kaolinite + quartz = pyrophyllite + H2O (Fig. 3). Quartz in the muscovite bearing sample contains abundant H2O-rich fluid inclusions, which yield homogenization temperatures from 160 to 186oC and freezing point depressions from 1.2 to -6oC, corresponding to maximum salt contents of ~6.8 wt%. The fluid inclusion isochores, combined with phase equilibrium constraints, indicate that brecciation occurred in the range, 200 to 280oC and 500 to 2000 bars (depths of 2 to 8 kms). Such a temperature range is lower than that for the predominant quartz + pyrophyllite assemblage in the Baraboo Quartzite, which is stable between about 300 and 375oC at 2000 bars. Step-heating, using a defocused CO2 laser, of a single muscovite grain (ca. 0.01 mg) from the breccia cement yielded a discordant 40Ar/39Ar age spectrum with a well-defined plateau at 1,459  3 Ma (Fig. 4), representing ~75% of the gas released during the heating experiment. This result is concordant with 40Ar/39Ar plateau ages of 1,456  11 and 1,467  11 Ma for muscovite from metasaprolite and muscovite-pyrophyllite-diaspore hydrothermal veins in the Baraboo Quartzite (Naymark et al., 2001). Results of this investigation provide additional evidence for post-1,630 Ma hydrothermal activity in the Baraboo Range, which was first recognized by Naymark et al. (2001) and attributed to the influence of 1,465 Ma Wolf River magmatism (Medaris, 2001). We suggest that emplacement of the 1.5-1.4 Ga transcontinental belt of A-type granites, of which the Wolf River batholith is part, provided the heat flux necessary for promoting regionally extensive fluid flow and accompanying hydrothermal alteration along permeable channels. It now appears that such hydrothermal activity extended far beyond the Baraboo Range, including the Sioux Quartzite in Minnesota (Naymark, et al., 2001) and the Athabasca Basin in northern Canada (Kotzer, et al., 1992). Further research may reveal that much of the Paleo- and Mesoproterozoic crust of the Lake Superior region was affected by areally extensive, but stratigraphically restricted, hydro- thermal alteration at 1.5-1.4 Ga. REFERENCES Kotzer, T.G., et al. (1992) Can. Jour. Earth Sci., v. 29, p. 1474-1491; Medaris, L.G., Jr. (2001) 47th Inst. Lake Superior Geol., p. 51-52; Naymark, A., et al. (2001) 47th Inst. Lake Superior Geol., p. 66-67. 25 �New geologic map and report of the Duluth Complex and related rocks, Northeastern Minnesota. Miller, J. D. Jr.1, Green2, J. C., Severson3, M. J., Chandler1, V. W., Peterson3, D. M., Hauck3, S. A., and Wahl1 T. E, (1Minnesota Geological Survey, 2642 University Avenue, St. Paul, MN 55114, 2Department of Geological Sciences, University of Minnesota–Duluth, Duluth, MN 55812, 3Natural Resources Research Institute, 5013 Miller Trunk Hwy., Duluth, MN 55811) The Minnesota Geological Survey (MGS), in collaboration with the Natural Resources Research Institute, recently published a 1:200,000-scale map of the Duluth Complex and related rocks of northeastern Minnesota (Miller and others, 2001). A companion report (Miller and others, 2002) describes the geology and mineral potential of the map area; a CD-ROM included in the report contains the digital map and related field data. This ambitious project was funded by a grant from the Minnesota State Legislature on the recommendation of the Minerals Coordinating Committee. The two products constitute the largest and most complete summary of the Duluth Complex ever produced and, undoubtedly, will serve as a benchmark for future exploration and research. Several developments in the last 20 years led to the regional compilation. Gravity and high-resolution aeromagnetic data were used in conjunction with test drilling to map the vast, poorly exposed central part of the Duluth Complex. Detailed mapping in the better exposed part of the complex, as well as core logging along the its base, led to a greater understanding of the petrologic, structural, and stratigraphic relationships in the intrusive sequence. High-resolution radiometric dating aided the unraveling of the intrusive history of the complex, and advances in Geographic Information Systems (GIS) greatly enhanced our ability to produce complicated geologic maps. Finally, and perhaps most importantly, the sharp upturn in PGE exploration in the Duluth Complex created an urgent need for an improved geologic framework. The new geologic map (Miller and others, 2001) has two major components: a 1:200,000-scale geologic map that delineates over 270 rock units, and a more generalized 1:500,000-scale geologic map that classifies the rock units into 72 time–stratigraphic entities. Additional information on the two sheets include (1) a map that shows the relative density of outcrops and drill-out locations; (2) a 1:500,000 gray-scale image of the first vertical derivative of the aeromagnetic data; (3) an index to 64 published and unpublished mapping projects used in the present compilation; (4) a correlation diagram for the 72 generalized time–stratigraphic units; (5) brief descriptions of rock units; and (6) a list of references. Because of the importance of gravity and magnetic data to this compilation, a related map that presents the second vertical derivative of gravity data (color) superimposed on reduced-to-pole, first vertical derivative of magnetic data (black and white) is available at a scale of 1:200,000 (Chandler, 2001). The maps can be purchased from the Minnesota Geological Survey in paper form; they are also available 26 �as PDF files from the Minnesota Geological Survey web site (http://www.geo.umn.edu/mgs). The new 1:200,000-scale geologic map is a greatly improved representation of the Duluth Complex and related rocks; for example, the southern and northwestern parts of the complex are depicted as a composite of several intrusions consisting of troctolitic and gabbroic cumulates. Much of the PGE exploration has focused along the base of the complex in two cumulate bodies, the South Kawishiwi and Partridge River intrusions, but several similar bodies defined by the new map may become exploration targets. The map refines our understanding of the geology of the upper part of the complex, which consists of a partially disrupted cap of anorthositic rocks and several felsic intrusions. Improvements have also been made in mapping the Beaver Bay Complex and other hypabyssal intrusions in the volcanic roof of the complex. One of the bodies, the Sonju Lake intrusion, is being explored for PGE potential, and the new map identifies other mafic cumulate and gabbroic bodies in the roof zone that may be worthy exploration targets. Finally, the North Shore Volcanic Group, which forms the roof (and locally the footwall) of the complex, has for the first time has been subdivided into informal formational entities on a geologic map. The companion report (Miller and others, 2002) provides a general description of the Duluth Complex and related rocks as portrayed on the map and assesses the potential for nonferrous mineral deposits. The following is a summary of each of the 8 chapters and appendix: 1, Formal definition of nomenclature and stratigraphic and rock-type classifications used to describe the Mesoproterozoic (Keweenawan) rocks of northeastern Minnesota; 2, History of geologic mapping and mineral exploration of the complex; 3, Geophysical attributes of the complex and related rocks; discussion of how data aid interpretation of the buried bedrock geology and deeper geologic structure of northeastern Minnesota; 4, Geology and structure of the Archean and Paleoproterozoic rocks that form the footwall of the complex; 5, Volcanic stratigraphy and structure of the comagmatic North Shore Volcanic Group, into which the Duluth Complex and related intrusions were emplaced; 6, Geologic, structural, and stratigraphic relationships of various intrusions of the complex; 7, Geology of the Beaver Bay Complex and related hypabyssal intrusions; 8, Types of mineralization that are known to occur or may occur in the complex and related Keweenawan rocks; identification of new exploration target areas; and Appendix, Description of digital image and data layers included in the CDROM (back pocket) and an explanation of how to access the GIS layers within the ArcView program. The CD-ROM accompanying the report contains ArcView -based digital compilations of the geologic map and related field data, as well as base maps and geophysical images. Attribute tables identify the source and character of data that accompany the geology layers (map units, geologic faults, and contacts) and the related field data layers (outcrops, structure measurements, drill holes, and field samples). An MGS-created 27 �extension, GeMS (Geologic Mapping System) allows the abbreviated attribute data to be decoded. Compilation of all pertinent field data was not possible under the time constraints of the two-year project. Priority was given to data from explorable areas of the Keweenawan in northeastern Minnesota. Updated versions of this digital compilation will be produced as warranted by new mapping and additional archiving of older field data. Chandler, V.W., 2001, Superimposed magnetic on gravity anomaly map of the central Duluth Complex and western part of the Beaver Bay Complex, Lake and St. Louis Counties, Minnesota: Minnesota Geological Survey Miscellaneous Map Series M-120, scale 1:200,000. Miller, J.D., Jr., Green J.C., Severson, M.J., Chandler, V.W., Hauck, S.A., Peterson, D.M., and Wahl, T.E., 2002, Geology and mineral potential of the Duluth Complex and related rocks of northeastern Minnesota: Minnesota Geological Survey Report of Investigations 58, 207 p. + compact disc in back pocket. Available by the end of March 2002. Miller, J.D., Jr., Green J.C., Severson, M.J., Chandler, V.W., and Peterson, D.M., 2001, Geologic map of the Duluth Complex and related rocks, northeastern Minnesota: Minnesota Geological Survey Miscellaneous Map Series M-119, 2 sheets, scales 1:500,000 and 1:200,000. 28 �Crustal models of the Western Superior Province from gravity and Lithoprobe seismic data Nitescu, B., Cruden, A.R., Bailey, R.C., (Department of Geology, University of Toronto, Toronto, ON M5S 3B1, bnitescu@geology.utoronto.ca) The western part of the Superior Province (WS) is characterised by a regional pattern of linear, EW-trending, fault-bounded belts containing distinctive rock types, structures, ages, metamorphic conditions, and geophysical attributes. Detailed geological, geochemical and geochronological studies in the past two decades have led to the formulation of the “accretion hypothesis” in which the WS is interpreted to have assembled progressively from north to south by collisions with various arc, oceanic and continental fragments. To test this hypothesis at depth a Lithoprobe transect was established in the WS, and acquisition of seismic refraction and reflection data, as well as detailed gravity observations were made along several profiles crossing the WS subprovinces. The refraction/wide-angle reflection data indicate a crustal thickness of 4043 km and relatively high average crustal velocities of 6.6-6.7 km/s (White et al. 1997). A high velocity basal crustal layer (7.5-7.7 km/s) was imaged west of Lake Nipigon in the southern WS beneath the Wawa, Quetico and central Wabigoon subprovinces (White et al. 2001). In general, on the seismic reflection sections the lower crust is homogeneously reflective, the middle crust is heterogeneous and strongly reflective, and the upper crust is heterogeneous and often weakly reflective. The Moho is well imaged and shows a flat or slightly dipping geometry below the Berens River Subprovince, a crustal root below the Uchi Subprovince and an upwarp beneath the metasedimentary English River Subprovince (ERS) and its along strike continuation in the Wabigoon indentor. The Bouguer gravity data in the WS show variations between -10 and -90 mgal, gravity highs occurring over the metavolcanic belts, and gravity lows in most of the areas underlain by felsic intrusions. An exception is represented by the metaplutonic Berens River Subprovince, which is characterised by a regional gravity high. The most outstanding gravity feature observed in the WS is a prominent Bouguer gravity high (>20 mgal) coincident with the length of the metasedimentary ERS. The lack of detailed correspondence between this anomaly and the surface distribution of the metasediments suggests a deep linear source (Nitescu and Cruden 2001). A significant positive anomaly also occurs in the Winnipeg River Subprovince east of Kenora, and broadly parallels the surface distribution of the Lount Lake batholith. It is not clear whether this anomaly is related to the ERS gravity anomaly, or some other deep-crustal feature. The aim of the present study is to investigate the crustal structure of the WS based on gravity models constrained by seismic information and to infer the processes responsible for its present-day configuration. We present results obtained from a gravity inversion algorithm (Pilkington and Crossley 1986) employed for the determination of the Moho topography in the WS, and 2.5-D gravity forward models of the WS crust obtained along N-S seismic lines 1 and 2b. The inversion model of the Moho topography reveals the existence of EW-trending crustal roots below the Uchi and Wabigoon subprovinces (Moho depths of 43-44 km) separated by a parallel rise of the Moho to depths of 37-39 km below the ERS. In the 29 �region underlain by the high velocity basal slab the Moho deepens from 41 km below central Wabigoon Subprovince to 47 km below the northern Quetico Subprovince. These results generally agree with the Moho geometry observed along the seismic profiles, although in detail there are differences. For instance, the N-S extent of the Moho upwarp below the ERS is overestimated in the inversion model, which clearly demonstrates that the ERS gravity anomaly cannot be accounted for only by the Moho rise as observed on the reflection sections. The 2.5D gravity forward model along reflection line 2b extends from the Winnipeg River Subprovince to the Berens Subprovince along the Red Lake road. The model indicates that north of the ERS the observed Bouguer gravity field combines the effects of the Moho topography and upper crustal structures (greenstone belts and various intrusive bodies), with no major density variations occurring at the mid- and lower crustal levels in this segment of the crust. Due to poor reflectivity below the ERS, the seismic data does not constrain well the location at depth of the ERS anomaly source, which may correspond to a transparent region observed between 2-4 s TWT, above a zone of weak mid-crustal reflectivity. The lower density of the rocks exposed at surface in the region of the Winnipeg River Subprovince anomaly indicates that its source is also buried. This anomaly could be caused either by a dense body, which may be related to the source of the ERS anomaly, or by uplifted mid-crustal rocks as suggested by the seismic fabric at the southern end of line 2b. In the latter case the modelling results show that the uplifted Winnipeg River Subprovince mid-crustal rocks should extend to the south below the northern Wabigoon Subprovince. The 2.5D forward gravity model of the WS crust along reflection corridor 1 extends for 500 km from the northern Wawa Subprovince to the Sachigo Subprovince. In the model, Moho topography and the interface relief between major crustal layers (as revealed by the refraction data) cause long wavelength gravity anomalies. Short wavelength anomalies are generated by upper crustal metavolcanics and granitoids. The high-density (3.1-3.2 g/cc), high-velocity basal slab imaged in the southern half of the corridor is not reflected in the long wavelength gravity field as a maximum, since the effect of the positive density contrast created in the lower crust is cancelled by the combined effects of the southward deepening of the Moho and the downward depression of the intra-crustal interfaces above the slab. The present study shows that the gravity field in the WS can be successfully modelled in accord with seismic reflection/refraction data by upper crustal density variations and undulations of the Moho and the interfaces between major crustal layers. The structural grain of the subprovincial configuration is not paralleled by density variations in the middle and lower crust, but is reflected in the Moho undulations. The cause of the crustal roots beneath the granite-greenstone subprovinces is not clear. They may be related to greenstone belt loading, but this depends on whether the lower crust was strong enough after the formation of the greenstone belts to prevent the relaxation of the initial Moho depressions through flow. The Moho upwarp below the ERS may be preserved from a ca. 2710-Ma-old extensional episode in the WS which led to the uplift of the Winnipeg River Subprovince and the formation of sedimentary basins on its flanks (Nitescu and Cruden 30 �2001). The deepening trend of the Moho towards the Quetico and Wawa subprovinces is probably related to the load imposed at the lower crustal level by the observed highvelocity/high density basal slab. This slab was previously interpreted as a remnant of a subducted Archean oceanic plate (White et al. 2001), but it could alternatively represent a Proterozoic igneous underplating episode related to Mid-continental rift magmatism. It is likely that the crustal structure of the WS contains not only elements preserved from Kenoran tectonism, but also younger post-orogenic effects. Therefore caution should be used when interpreting the features revealed by the seismic data solely in terms of processes responsible for the accretionary stage of the Superior Province. Nitescu, B., and Cruden, A.R. 2001. Gravity models of the English River Subprovince: implications for its deep structure and tectonic origin. In 2001 Western Superior Transect Seventh Annual Workshop, University of British Columbia (in press). Pilkington, M., and Crossley, D.J. 1986. Determination of crustal interface topography from potential fields. Geophysics, 51, p.1277-1284. White, D., Asudeh, I., Kay, I., Forsyth, D., and Roberts, B. 1997. Preliminary results of the 1996 Lithoprobe Western Superior seismic refraction survey. In 1997 Western Superior Transect Third Annual Workshop, University of British Columbia, Lithoprobe Report #63, p.106. White, D., Musacchio, G., Helmstaedt, H.H., Harrap, R., Thomson, C., Sol, S. 2001. Remnants of Archean subduction in the Western Superior Province: Results from combined Lithoprobe deep seismic studies. In 2001 Western Superior Transect Seventh Annual Workshop, University of British Columbia (in press). 31 �Digital Drill Logs for the Duluth Complex - Lithology and Assays Patelke, R. L., (Natural Resources Research Institute, University of Minnesota Duluth, 5013 Miller Trunk Highway, Duluth, MN 55811-1442) Since 1988 the Natural Resources Research Institute (NRRI) staff has logged 950 Duluth Complex drill holes of the about 1,500 holes with core available (of the approximately 2,200 holes recorded as penetrating the Complex). This project involves transcribing all of the NRRI logs, plus our interpretation of company logs for drill holes with no core remaining, into a consistent digital format. This downhole “from-to” interval format includes logged rock type, map unit (reconciled from cross-sections and geologic maps where available), and the interval distance up from footwall. This is combined with other data tables, being consolidated from older reporting and projects, which will include: all drill hole specific information (location, company, year drilled, etc.); down hole survey data; all original assays (usually copper-nickel +/sulfur); secondary assays on selected intervals; all available PGE plus gold assays; and eventually all whole rock geochemistry and microprobe data. The format will allow this data to be sorted and filtered geographically, by deposit, by company, by depth or distance from footwall, or other criteria. This data format is intended primarily for use in 3-D mining software and is available on CD-ROM as Excel spreadsheet files, ASCII text files, and as a Gemcom for Windows (Microsoft Access) database. NRRI staff will also format this database to the users needs if practical. The database will also be posted on the NRRI Economic Geology Group website at: http://www.nrri.umn.edu/egg/. The ultimate purpose of this work is to improve the ability to do statistical and spatial analysis of Duluth Complex geology by rapidly combining lithological and assay data for both scientific study and deposit evaluation. This analysis breaks down into two broad categories. Simple 2-D comparisons, such as: comparisons between intrusions or deposit areas; rock type versus grade; ratio of a particular rock type which is mineralized versus part not mineralized; assay grade of a particular unit; or grade as a function of distance from footwall (see Table 1 for examples from Babbitt and Serpentine deposits). More complex 3-D analysis can also be done by using this data to create lithological and grade surfaces, solids, or block models, then intersecting these models; compositing grade by rock type, map unit, level, or distance from a particular point or surface; assessing linear and 3-D variography; contouring by level or distance from a point; and other manipulations of the raw data. Most mining software is very flexible, and the overall data layout will allow NRRI or others to add distance or point data (distance from collar, such as a thin section location) or from-to interval data (such as alteration, grain size, or other assayed elements) as separate tables that can then be compared to the existing data set. The utility in this is the time savings in answering the numerous small questions that arise as well as easing modeling efforts on the Duluth Complex Cu-Ni sulfide and Fe-Ti oxide deposits 32 �Table 1: Consolidated Rock type versus Copper, Nickel, Sulfur, and Copper:Nickel ratio, for Babbit and Serpentine Deposits, St Louis County Minnesota. Surface drill holes only. “Consolidated Rocktypes” are condensed from over 1,000 individual rock types over about 25,000 lithological intervals. “Percent Mineralized” assumes that company sampled all mineralized zones. This is essentially true at Babbitt-Serpentine, but not always true for other deposit areas. Grades are only for the mineralized portions, no unsampled footage (zero value?) was included in the average. "Consolidated Rocktype" Overburden (glacial drift) OUI (Oxide Ultramafic Intrusions) Anorthositic rocks Augite Troctolites Contaminated Rocks Total footage of rock type Percent of rock type in deposit Total mineralized footage of rock type Total unmineralized footage of rock type Percent mineralized of rock type Average copper grade of rock type Average nickel grade Average sulfur grade Average Cu:Ni of rock type of rock type ratio 10,122 2,824 1.8 0.5 447 2,377 0 16 0.31 0.10 1.92 3.29 63,510 63,210 30,792 11.3 11.2 5.5 18,151 28,443 18,248 45,359 34,767 12,544 29 45 59 0.31 0.42 0.44 0.09 0.10 0.11 0.66 1.14 2.25 3.32 4.02 4.06 Gabbroic Rocks Mixed Duluth Complex (not logged) Pegmatitic Rocks Ultramafic Rocks Troctolitic Rocks Dikes, Basaltic Veins, Granitic Massive Sulfides Semi-Massive Sulfides Virginia Formation 3,022 166,344 0.5 29.5 1,348 70,695 1,674 95,649 45 42 0.33 0.39 0.08 0.10 0.85 1.03 4.32 3.74 710 24,473 143,059 698 2,428 415 343 24,760 0.1 4.3 25.4 0.1 0.4 0.1 0.1 4.4 139 7,732 63,929 181 870 413 341 6,279 571 16,741 79,130 517 1,558 2 2 18,481 20 32 45 26 36 100 99 25 0.36 0.36 0.38 0.08 0.29 2.02 1.45 0.38 0.10 0.11 0.10 0.02 0.08 0.57 0.43 0.10 0.71 0.74 0.90 0.35 1.04 12.68 9.69 2.43 3.53 3.17 3.62 2.58 3.51 3.86 4.17 3.04 Bedded Pyrrhotite Unit Virginia Sill MG Sill Sill in Biwabik Iron Formation Biwabik Iron Formation Pokegama Quartzite Giants Range Granites Basalts Massive Chlorite Faults Massive Graphites Hybrids (Hornblendite, etc.) Orthopyroxenites Massive Oxides (not in OIUs) Serpentinites deposit total: deposit averages: 3,834 1,686 9,537 284 6,976 20 420 2,951 12 630 10 505 111 49 76 563,811 0.7 0.3 1.7 0.1 1.2 0.0 0.1 0.5 0.0 0.1 0.0 0.1 0.0 0.0 0.0 100 2,928 311 1,129 4 507 906 1,375 8,408 281 6,469 20 301 2,404 4 443 5 412 20 23 57 330,500 76 18 12 1 7 0 28 19 67 30 60 18 82 55 25 40 0.13 0.09 0.10 0.03 0.11 0 0.14 0.20 0.19 0.36 0.41 0.31 0.44 0.52 0.47 0.04 0.05 0.03 0.01 0.03 0 0.05 0.08 0.06 0.10 0.08 0.12 0.14 0.13 0.11 4.25 0.35 0.49 0.14 0.44 0 0.29 0.85 0.34 1.15 1.31 1.67 2.29 0.56 1.62 2.50 1.58 2.45 2.67 3.05 0 2.34 2.65 2.75 3.66 4.58 2.86 3.79 4.40 4.72 0.39 0.10 1.29 3.66 24.40 34,742 25,445 60,187 5.20 34,314 25,873 60,187 37.10 34,532 25,655 60,187 47.00 34,414 25,773 60,187 119 547 8 187 6 93 91 27 19 223,192 maximums: number of assayed intervals: number of unassayed intervals: total number of intervals: 33 �Mineralogy and Zonation of the Big Whopper Pegmatite, Separation Rapids area, Kenora, Ontario Pedersen, J. C. P.Geo., (Consulting Geologist, Avalon Ventures Ltd.) and Bubar, D. S. (President and CEO, Avalon Ventures Ltd.) The Big Whopper pegmatite is the largest in a field of rare metal pegmatites occurring in the Separation Lake metavolcanic belt, situated approximately 60 km north of Kenora, Ontario. This greenstone belt occurs at the boundary of the English River and Winnipeg River sub-provinces of the Superior structural province. It is interpreted to be the eastern continuation of the Bird River Greenstone belt in Manitoba, which hosts the Cat Lake rare metal pegmatite field and the famous Tanco pegmatite. The Big Whopper pegmatite is 100% owned by Avalon Ventures Ltd. Exploration work to date has defined indicated and inferred resources totalling 11.6 million tonnes grading 1.34% Li2O, 0.30% Rb2O and 0.007% Ta2O5. The deposit is now at the feasibility study stage as a potential producer of lithium-rich feldspars, tantalum and mica. The Big Whopper is a vertically-oriented pegmatite dyke hosted by deformed metavolcanic rocks of lower to middle amphibolite facies metamorphism (amphibolite). A north-directed compressional tectonic event produced flattening and a strong vertically oriented regional schistosity striking WNW at the Big Whopper. This schistosity is folded about a sub-vertical axis. The Big Whopper itself exhibits high-strain features and a tight S-fold geometry, with the thickened central portion of the pegmatite coinciding with the hinge zone, and attenuated limbs extending to the east and west. The pegmatite has been traced over a strikelength of 1.5 km and ranges from 10 to 80 m in width. The dominant economic minerals in the deposit are petalite and columbite-tantalite, the principal ore mineral of tantalum. Petalite is a rare lithium aluminosilicate mineral used in certain specialty glass and ceramics applications, such as thermal shock resistant cookware. Tantalum finds its major use (approximately 60%) in the manufacture of miniature tantalum capacitors, which are currently in high demand for use in popular electronics products such as computers and cell phones. The deposit also contains significant quantities of rubidium potash (Rb-K) feldspar and albite, (both used in the glass and ceramic industries); lepidolite, an important source of rubidium in the chemicals industry, as well as the tin mineral cassiterite. Other potentially valuable industrial minerals include muscovite mica (some with elevated lithium) which may comprise up to 15% of the ore, spodumene averaging 3-5% occurring as SQUI (spodumene-quartz intergrowth) replacement rims on petalite, cassiterite, pale pink spessartine garnet and high-purity quartz. Minor accessory minerals include apatite, zircon, gahnite, monazite, xenotime, rare sulphides, sulphosalts, and thorite. Mineralogical zoning observed in the Big Whopper is characteristic of highly evolved rare metal pegmatites, with well-developed wall zones and internal intermediate zones classified according to their dominant constituent minerals (Figure 1). The mineralogical zones of the Big Whopper identified to date are Wall Zone (predominantly albitite), Megacrystic Feldspar and Quartz-Mica marginal Zones and Petalite (intermediate) Zone. The Petalite Zone is the largest zone defined to date, comprising approximately 80% of the volume of the Big Whopper. Its essential mineralogy consists of petalite, Rb-K-feldspar, albite, quartz and mica. Sub-zones are defined based on subtle textural and mineralogical variations such as the presence of lepidolite mica. 34 �Lepidolite-rich zones tend to occur on the periphery of the deposit and are typically enriched in tantalum. THE BIG W-IOPPER PEGMATITE Detailed Geology lro 700W N I 600W 300W ( EngIMi River .— IiaseIine—* PETALITE ZONE Ato D: A - petalte (white) k-feldspar quartz a lb te B - petalte (pink) k-feldspar albite I C- petalite (blue-grey and pink) albite mica 0 - peta lite lepido lite a lb te (ta ntalum-rich zone >0.01 % Ta 0) I:.: I interdigitated PSLL ZONE (albitite) and FE LDSFR, QUARtZ-MICA ZON ES 100 amphibolite host rocks metre stripped outcrop Fie I: BiWhcwer Geology 35 / �Cu-Ni-PGE Mineralization in the South Kawishiwi Intrusion, Northeastern Minnesota Variation due to Magmatic Processes Peterson, D. M., (Economic Geology Group, Natural Resources Research Institute, University of Minnesota, Duluth email: dpeters1@nrri.umn.edu) INTRODUCTION The Mesoproterozoic South Kawishiwi intrusion (SKI), which is exposed in a 32 x 8-kilometer arcuate band along the northwestern margin of the Duluth Complex, is composed dominantly of troctolitic cumulates. Footwall rocks to the intrusion include, from north to south, the Paleoproterozoic Virginia and Biwabik Iron Formations, and the Late Archean Giants Range batholith. Regional crosscutting features and remnant pillars and xenoliths indicate that the SKI intruded along the boundary between Mesoproterozoic volcanic and Anorthositic Series rocks and the older footwall strata. The SKI abuts the troctolitic Partridge River intrusion on the southwest, is inferred to be semi-conformable to the later Bald Eagle intrusion to the east, and abuts and cuts older Anorthositic Series rocks to the northeast. The basal mineralization within the SKI occurs dominantly in heterogeneous zones of troctolitic, gabbroic, noritic, and ultramafic rocks. This heterogeneity is a function of many factors, including footwall assimilation, dehydration and volatile fluxing from the footwall strata into the overlying magmas, chilling, and repeated magma injection. Miller and Severson (2002) subdivide the intrusion into five major map units from the base upwards: 1) a heterogeneous basal contact zone of sulfide-bearing troctolitic, gabbroic, and noritic rocks; 2) ophitic augite-troctolite; 3) poikilitic leucotroctolite; 4) ophitic troctolite; and 5) homogeneous troctolite. Severson (1994) and Zanko et al. (1994) have further subdivided the marginal zone of the intrusion into 17 different units, with sulfide mineralization dominantly confined to four units: the Basal Augite-Norite (BAN), Basal Heterogeneous (BH), Updip Wedge (UW), and Ultramafic 3 (U3) units. Minor mineralization higher up in the igneous stratigraphy of the intrusion occurs locally in the Ultramafic 1 (U1) and Ultramafic 2 (U2) units. Recent research has identified two dominant styles of mineralization (“Open” and “Confined”) within the intrusion that have distinctive differences in their igneous stratigraphy, metal contents, timing, and mode of origin. Simplified regional geologic and mineralization style maps for the SKI are presented in Figure 1. 36 �Figure 1. Simplified regional geologic (left) and basal mineralization style (right) maps of the South Kawishiwi intrusion. Disseminated basal mineralization within the SKI has traditionally been divided into five distinct deposits: 1) Serpentine, 2) Dunka Pit, 3) Birch Lake, 4) Maturi, and 5) Spruce Road. The disseminated sulfides occur as interstitial grains that average about 1-5% (visual estimation) and range from trace amounts to 10%, with local zones of massive sulfide at the basal contact. Major sulfides are pyrrhotite, chalcopyrite, cubanite, and pentlandite. Pyrrhotite is generally the dominant sulfide, especially closer to the basal contact. Recent work by Wallbridge Mining Company and the author have defined a potential additional deposit area east of the Maturi deposit, informally named the Maturi Extension deposit. Although the style of mineralization in all of the deposits is dominated by disseminated Cu-Ni sulfides, differences occur between the deposits in igneous stratigraphy, Cu-Ni and PGE grade, mineralization thickness, and contained tonnes. Regional analysis of the drill hole assay data for all of the deposits of the South Kawishiwi intrusion has led to the identification of two main styles of mineralization associated with the base of the intrusion (Fig.1). These mineralization types include: 1. “Open” – vertically extensive (> 450 meters) mineralization with low - moderate Cu-Ni grade and low Au+PGE grades. Cu-Ni grades typically increase towards the basal contact although the mineralized zones are typically erratic in their spatial extent and grade and commonly interfinger in a random pattern with zones that are barren of sulfides. Restricted zones of massive sulfide occur locally at the basal contact. This erratic pattern of mineralization, in part, mirrors the lithologic heterogeneity of the basal units. Examples of this open style include the Spruce Road, Serpentine, and Dunka Pit deposits. 2. “Confined” – vertically restricted (< 150 meters) mineralization with moderate - high Cu-Ni grades and moderate to very high (locally) Au+PGE grades. Cu-Ni grades typically are the highest near the top of the mineralized zone (units U3 and BH) and gradually decrease with 37 �depth toward the basal contact, and no zones of massive sulfide at the basal contact have been identified. For example, the upper portion of the mineralized zone within the Maturi deposit consistently exhibits copper values in excess of 1.0% that decrease to ~0.25% at the basal contact. Examples of the confined style include the Maturi, Maturi Extension, and the Birch Lake deposits. The differences between the styles of mineralization reflect the different histories for the rocks hosting the mineralization. It is hypothesized that the early Open-style of mineralization reflects repeated small injections of sulfur-saturated, highly contaminated magma. In contrast, the Confined-style of mineralization reflects much larger batches of more primitive magma that may have incorporated much of its sulfur by assimilation of Open-style mineralized rocks (or remnant magma). Miller, J.D., Green, J.C., Severson, M.J., Chandler, V.W., Hauck, S.A., Peterson, D.M., and Wahl, T.E., 2002, Geology and mineral potential of the Duluth Complex and related rocks of northeastern Minnesota: Minnesota Geologic Survey, Report of Investigations 58, 200 p. Miller, J.D., Jr., Green, J.C., Severson, M.J., Chandler, V.W., and Peterson, D.M., 2001, Geologic map of the Duluth Complex and related rocks, northeastern Minnesota: Minnesota Geological Survey Miscellaneous Map Series M-119, nominal scale 1:200,000. Peterson, D.M., 2002, Copper-Nickel grade maps for the Spruce Road deposit, South Kawishiwi Intrusion, Duluth Complex: Natural Resources Research Institute, University of Minnesota, Duluth, Report of Investigations, NRRI/RI-2002/03, 99 p. Severson, M.J., 1994, Igneous stratigraphy of the South Kawishiwi intrusion, Duluth Complex, northeastern Minnesota: Natural Resources Research Institute, University of Minnesota, Duluth, Technical Report NRRI/TR 93/34, 210 p. (with plates) Zanko, L.M., Severson, M.J., and Ripley, E.M., 1994, Geology and mineralization of the Serpentine copper-nickel deposit, Duluth Complex, Minnesota. Natural Resources Research Institute, University of Minnesota, Duluth, Technical Report, NRRI/GMIN-TR-93-52, 90p. 38 �3-Dimensional View Through a Mineralized System: the South Kawishiwi Intrusion, Duluth Complex Peterson D. M., (Economic Geology Group, Natural Resources Research Institute, University of Minnesota, Duluth email: dpeters1@nrri.umn.edu) A 35x8x2 km three-dimensional AutoCAD™ model of the basal contact surface of the South Kawishiwi intrusion (SKI) has recently been completed. The model is based on the location of ~ 800 drill hole piercing points into footwall strata and geophysical data (Figure 1). Integration of regional geological, geophysical, and geochemical features with the 3-D model has led to new ideas on possible feeder channels for magmas of the northern SKI. The interpreted master magmatic feeder channel of the northern SKI is fed from the central Mid Continent Rift through the Bald Eagle Intrusion gravity high, into a dike-like body of troctolitic rocks (herein termed the BEI Trough) cutting older Anorthositic Series rocks (Fig. 1). The 3-D model has been instrumental in the development of new ideas on the location and origin of the Cu-Ni-PGE mineralization within the SKI. Integration of the magmatic feeder channel concept with lineament analysis and recent PGE assays has led to the development of conceptual models for the formation of the Spruce Road (Peterson, 2002) and Maturi (Peterson, 2001) deposit areas. Early, contaminated magmas that formed the Spruce Road deposit were deflected to the north by a pillar of older Anorthositic Series rocks (Fig. 1) that is located at depth within the northern portion of the SKI (Fig. 2). Moreover, PGE-enriched Cu-Ni mineralization of the Maturi Extension deposit is located beneath the pillar, and a conceptual model for the formation of this deposit area is given in Figure 3. Figure 1. Regional shaded relief 3-D model of the SKI 39 �. Figure 2. Conceptual magma flow model for the Spruce Road area. Figure 5. Conceptual model for the formation of the Cu-Ni deposits of the northern SKI. Sheet-like mineralization of Maturi located to the left of the diagram, and the PGE-enriched Maturi Extension located under the Anorthositic Series block. Peterson, D.M., 2001, Development of a conceptual model of Cu-Ni-PGE mineralization in a portion of the South Kawishiwi Intrusion, Duluth Complex, Minnesota: Laurentian University – Society of Economic Geologists, Second Annual PGE Workshop, Sudbury, Ontario. Peterson, D.M., 2002, Copper-Nickel grade maps for the Spruce Road deposit, South Kawishiwi Intrusion, Duluth Complex: Natural Resources Research Institute, University of Minnesota, Duluth, Report of Investigations, NRRI/RI-2002/03, 99 p. 40 �New Information from the Sibley Group Rogala, B., Fralick, P.W., and Borradaile, G. (Department of Geology, Lakehead University, Thunder Bay, Ontario) The Sibley Group sediments were deposited in a subsiding intracratonic basin (Fralick and Kissin, 1995) between 1537 +10-2 Ma (Davis and Sutcliffe, 1984) and 1339 ± 33 Ma (Franklin et al., 1980). It is presently thought that these sediments were deposited closer to 1537 Ma. The Group was previously divided into three main Formations: Pass Lake, Rossport, and Kama Hill. The Pass Lake Formation consists of the conglomeratic Fork Bay Member and the sheeted sandstones of the Loon Lake Member, representing a braided fluvial environment (Cheadle, 1986). The Rossport Formation is separated into the Channel Island, Middlebrun Bay, and Fire Hill Members. The Channel Island Member is a cyclic dolomite-shale unit interpreted to be playa lake sediments (Cheadle, 1986). The Middlebrun Bay Member is a stromatolitic unit, considered a marker bed for the Sibley Group. It represents a period of relatively stable water and salinity levels. The Fire Hill Member consists of mudcracked red silt with mudchip conglomerates and sand sheet incursions. It signifies a time of tectonic tilting of the basin. The Kama Hill Formation is not subdivided, and is composed of purple shales and siltstones interpreted as mud flat deposits (Cheadle, 1986). The Nipigon Bay Formation is a new addition to the Sibley Group, overlying the Kama Hill Formation. The exposure of this unit is quite limited. It has only been found to crop out on some of the islands in Nipigon Bay, in particular Quarry Island and Vert Island. The Nipigon Bay Formation has also been found in several holes drilled by Falconbridge Limited in 1997. These holes intersected approximately 500 m of well-sorted medium sandstone. The colour of the sandstone can be buff, red, orange, or purple. The sandstone has cross-stratification, which varies from low- to high-angle. The thickness of cross-stratification sets is also variable, ranging from 20 cm to 300 cm, with an average thickness of 100 cm. Figure 1 SiO2 content varies through the Sibley stratigraphy. The upper 500 m is the Nipigon Bay Formation. Si O 2 C o n t e n t 50. 00 55. 00 60. 00 65. 00 70. 00 75. 00 80. 00 85. 00 90. 00 95. 00 1 00. 00 0 1 00 200 300 400 500 600 700 800 900 1 000 Extensive geochemistry was conducted on the sandstones throughout the Sibley stratigraphy, from the Pass Lake Formation to the Nipigon Bay Formation. The geochemistry shows an 41 �interesting series of element peaks within the Pass Lake Formation, indicating sharp, contrasting influxes of source material. However, source-rock modeling has not proven conclusive at this point. The geochemistry indicates an abrupt change at the base of the Nipigon Bay Formation. This Formation is much less variable and shows a different source-rock character than that of the Pass Lake Formation. This is portrayed in Figure 1, using SiO2 content, although the same pattern is repeated in all of the elements that were used for this analysis. The Channel Island Member of the Rossport Formation has also produced some interesting information. Paleomagnetic analysis was conducted on a 50 cm section of core from Noranda’s NI-92-7 drill hole. The inclinations were calculated and graphed to show the variations. The result was the chart in Figure 2 (left), which defines a curve that is believed to represent secular variation. This work will be followed up with isotope geochemistry and scanning electron microscopy for further interpretations. Figure 2 Paleomagnetic inclinations measured at 1 cm intervals along a 50 cm length of core. Inclination (degrees) -50 -40 -30 -20 -10 0 10 20 30 40 0 5 10 15 20 25 30 35 40 45 References Cheadle, B.A. 1986. Alluvial-playa sedimentation in the lower Keweenawan Sibley Group, Thunder Bay District, Ontario. Canadian Journal of Earth Sciences, 23, 527-542. Davis, D.W. and Sutcliffe, R.H. 1984. U-Pb ages from the Nipigon Plate and Northern Lake Superior. Geological Society of America Bulletin, 96, 1572-1579. Fralick, P. and Kissin, S. 1995. Mesoproterozoic basin development in central North America: implications of Sibley Group volcanism and sedimentation at Redstone Point. in: Petrology and metallogeny if volcanic and intrusive rocks of the mid-continent rift system, Proceedings of the International Geological Correlation Program, Project 336. Franklin, J.M., McIlwaine, W.H., Poulsen, K.H. and Wanless, R.K. 1980. Stratigraphy and depositional setting of the Sibley Group, Thunder Bay District, Ontario, Canada. Canadian Journal of Earth Sciences, 17, 633651. 42 �300 my evolution of the Red Lake greenstone belt, western Superior Province, Ontario: A synthesis of current constraints on volcanism, sedimentation, deformation, metamorphism and gold mineralization. Sanborn-Barrie, M.1, Skulski, T.1, Rayner, N.1 and Parker, J.R.2 (1Geological Survey of Canada, Continental Geoscience Division, 601 Booth Street, Ottawa, ON, K1A 0E8; 2Ontario Geological Survey, Willet Green Miller Centre, Sudbury, ON, P3E 6B5) msanborn@NRCan.gc.ca The Red Lake gold camp preserves an extensive record of magmatic and sedimentary activity from 3.0-2.7 Ga, and evidence of multiple episodes of deformation, hydrothermal alteration and metamorphism. The oldest volcanic rocks, which host its major lode gold deposits, are komatiite and tholeiitic basalt of the Balmer assemblage which includes minor 2.99-2.96 Ga intermediate to felsic volcanics and chemical metasedimentary rocks. Some of these basaltic rocks have trace element compositions (Th/Nb) reflecting local interaction with a differentiated crust, however, continental basement has not yet been observed in the belt. A thick sequence of 2.94-2.91 Ga intermediate to felsic calc-alkaline flows and pyroclastic rocks, interbedded with basalt, komatiite and stromatolitic carbonate comprise the overlying Ball assemblage. Ball volcanic rocks show trace element variations (e.g. Th/Nb) in mafic to felsic volcanic rocks that are also consistent with contamination by differentiated crust. Relatively juvenile εNd values of +0.8 to +1 in these felsic rocks suggest that the contaminant was relatively young (~3 Ga) crust. Ball ultramafic rocks have depleted εNd values of +2.2 and may reflect intra-arc extension and upwelling of depleted mantle-derived magma. Quartz-rich fuchsite-bearing clastic rocks of the c. 2.9 Ga Slate Bay assemblage have detrital zircon profiles (GSC SHRIMP, n=140 grains; and Corfu et al., 1998) that indicate derivation from predominantly Ball (with lesser Balmer) sources. This clastic sequence, which extends the length of the belt, overlaps the Ball/Balmer contact, however, north of Red Lake (McInnes Lake), Ball-age volcanic rocks and iron formation are in depositional contact with the Balmer assemblage (Corfu et al. 1998). Ball volcanism was followed by the deposition on Balmer substrate of the 2.894 Ga Bruce Channel assemblage comprising calc-alkaline intermediate pyroclastic rocks overlain by an upward-fining sequence of clastic sediments and chert-magnetite iron formation. Felsic tuff has depleted εNd values of +2 (Henry et al. 1999), reflecting a change between 2.99 and 2.89 Ga toward isotopically depleted magmatism that may reflect crustal growth at a juvenile continental margin (cf. Henry et al. 2000). The overlying Trout Bay assemblage comprises a lower sequence of basalt, 2.85 Ga intermediate pyroclastic and epiclastic rocks, iron formation and an upper sequence of pillowed tholeiitic basalt. The upper basalt sequence has depleted, MORB-like trace element profiles reflected in positive εNd values of +2, similar to model Archean depleted mantle. The Trout Bay and Ball assemblages face toward each other across an interpreted tectonic contact that may reflect telescoping across the continental-oceanic interface. Following a hiatus of some 100 my, the onset of extensive calc-alkaline volcanism is recorded by the Confederation assemblage with c. 2.75-2.74 Ga shallow marine to subaerial calc-alkaline mafic to felsic volcanic rocks of the McNeely sequence, overlain and interstratified by c. 2.74 Ga submarine, mixed calc-alkaline and tholeiitic basalts and FIII-type rhyolite of the Heyson assemblage. McNeely volcanic rocks have an εNd value of +1 to +0.8, whereas Heyson volcanic rocks have depleted εNd values of +2.9. These geochemical and isotopic data are consistent with establishment of a Neoarchean shallow marine arc (McNeely) on the existing Mesoarchean 43 �continental margin sequence, with local intra-arc extension and eruption of high temperature F3 rhyolite and submarine tholeiitic basalt (Heyson). A depositional relationship between the Confederation and Mesoarchean assemblages is supported by a c. 2.75 Ga felsic dyke that cuts the Balmer assemblage, and by Mesoarchean inheritance in c. 2.74 Ga volcanic rocks (Corfu et al., 1998). An angular unconformity is indicated by opposing facing of Balmer and Confederation strata in the Madsen area, consistent with overturning of the Balmer (D0) prior to Confederation volcanism. Local occurrences of coarse clastic rocks, such as ironstone-derived conglomerate on Wolfe Bay, may represent basal conglomerate marking this unconformity. Typically, however, the interface between Neoarchean and Mesoarchean volcanic rocks is covered by a c. 2.735 Ga clastic sequence, the Huston assemblage. Detrital zircon populations from conglomerate samples of the Huston assemblage from the Balmertown and Madsen areas show single, prominent (50-60 grains), c. 2.74 Ga detrital age peaks that indicate derivation from the Confederation assemblage. Undated conglomeratic rocks that underlie the youngest volcanic assemblage in the belt (c. 2.733 Ga Graves) are correlated with the Huston assemblage, as are argillaceous to turbiditic rocks that conformably overlie c. 2.744 Ga McNeely volcanic rocks in central Red Lake. Shallow marine to subaerial, 2.73 Ga calc-alkaline, intermediate to felsic volcanic rocks and synvolcanic plutons of the Graves assemblage reflect Andean-style arc magmatism that culminated in the c. 2.72-2.70 Ga Kenoran orogeny. The youngest supracrustal rock in the belt is a pebble conglomerate, once thought to correlate with the “Austin tuff” ore horizon. This garnetiferous metasedimentary rock yielded a diverse detrital zircon population profile (n=56 grains), with ages that correspond to the Balmer, Ball, Trout Bay and Confederation assemblages, and younger. The maximum depositional age of this sample is 2700 ±6 Ma, the upper intercept of a 5-spot regression for the youngest detrital zircon analysed. This young supracrustal sequence provides a new maximum age for penetrative deformation and amphibolite-facies metamorphism in the Red Lake area. Its relationship to gold mineralization is no longer certain. The Red Lake greenstone belt displays evidence of several episodes of deformation, interpreted to be closely linked with extensive hydrothermal activity and gold mineralization. Nonpenetrative deformation (D0) appears to have involved overturning of the c. 2.99 Ga Balmer assemblage, possibly related to recumbent folding, prior to Neoarchean volcanism. The main stages of penetrative deformation were imposed after ca. 2.74 Ga volcanism. These resulted in northerly trending, south-plunging F1 folds and associated S1/L1 fabrics, superimposed by eastto northeast-trending D2 structures (F2/S2/L2) in western and central Red Lake, and by southeasttrending folds and fabrics (the “mine trend”) in eastern Red Lake. D1 may be bracketed between 2.744 Ga, the age of Confederation volcanic rocks in central Red Lake that contain F1 structures, and c. 2.733 Ga, the age of the Graves volcanic sequence that does not appear to have been affected by D1. It seems probable that deposition of the Huston assemblage took place synchronous with, and as a response to deformation (D1) and that D1 is linked to a change in plate dynamics that took place between Confederation and Graves volcanism. An important constraint on the timing of D2 is provided by the relationship of regionally extensive D2 fabrics to the 2718 ±1 Ma Dome Stock. Supracrustal rocks adjacent to the stock, and occurring as xenoliths within the stock, contain a penetrative S2 fabric. The stock itself contains a weak throughgoing NE-striking foliation coplanar to S2 observed elsewhere. These fabric relationships suggest that the main cleavage-forming stage of D2 predated intrusion of the Dome stock at 2718 Ma, but that shortening was sustained beyond its emplacement. Penetrative strain 44 �appears to have outlasted c. 2700 ±6 Ma, the maximum age of young unconformably overlying conglomeratic rocks that display a penetrative tectonic foliation coplanar to D2 fabrics throughout central Red Lake. Metamorphic mineral assemblages within this sample and surrounding rocks include staurolite-cordierite-garnet-bioite from pelitic compositions and orthoamphibole-garnet from mafic compositions, indicating that amphibolite facies metamorphism also outlasted ca. 2700 ±6 Ma. We interpret tectonometamorphism of the Red Lake belt between c. 2.718 and 2.7 Ga to be the result of orogenic activity related to collision between the c. 3 Ga North Caribou terrane and the c. 3.6-3.0 Ga Winnipeg River terrane, to the north and south of the Red Lake belt, respectively. If the dated “Austin tuff” sample represents an intact relict of the gold ore horizon mined from the Madson area, these new data would suggest gold mineralization of young, unconformably overlying clastic rocks after ca. 2.7 Ga. However, this is in contrast to the timing of gold mineralization in the Balmertown area, which has been shown to predate 2714 ±4 Ma, the age of a post-ore porphyritic dyke from the New Red Lake (formerly A.W. White) mine (Corfu and Andrews, 1987). Corfu, F. and Andrews, A.J., 1987. Geochronological constraints on the timing of magmatism, deformation and gold mineralization in the Red Lake greenstone belt, northwestern Ontario. Can. J. Earth Sci. 24, 13021320. Corfu, F., Davis, D. W., Stone, D. and Moore, M., 1998. Chronostratigraphic constraints on the genesis of Archean greenstone belts, northwestern Superior Province, Ontario, Canada. Precam. Res. 92, 277-295. Henry, P., Stevenson, R.K., Larbi, Y. and Gariepy, C., 2000. Nd isotopic evidence for Early to Late Archean (3.4-2.7 Ga) crustal growth in the western Superior Province (Ontario, Canada). Tectonophysics, v.322, p.135-151. 45 �The Mine Permitting Process in Minnesota - Who, What, Where, and When. Severson, M. J., (Natural Resources Research Institute, University of Minnesota Duluth, 5013 Miller Trunk Highway, Duluth, MN 55811-1442 e-mail: mseverso@nrri.umn.edu) Interest in the Cu-Ni-PGE deposits of the Duluth Complex has been recently renewed due to advances in hyrometallurgical processes and increased PGE metal prices. Economic evaluations are currently being conducted for several of the deposits, and in some cases, initial steps have also been taken in order to obtain the various permits to mine. In Minnesota, the permitting process for a non-ferrous, metallic mine is complicated; involves dealing with numerous different federal, state, and local agencies; and as yet, has not been carried through to completion for establishment of either an open pit or underground mine. This project outlines each of the necessary permitting steps that are needed to develop a metallic mine, and provides time lines, or length of the various determination processes, for each type of permit that would be required. Also included are lists of agencies, contact persons, phone numbers, and e-mail addresses. All of the data generated in this project will be used to produce a report, and supplemental pamphlet, that fully describes what each permit entails. At the forefront of the mine permitting process in Minnesota is an environmental review process consisting of preparation of an Environmental Impact Statement (EIS), and because an EIS is mandatory, it must be preceded by preparation of a scoping Environmental Assessment Worksheet (EAW). Many of the permits that are mining-related require this process to be completed (Table 1). The scoping EAW is designed to identify potentially significant issues (including possible environmental, sociological, economic, and health risk impacts) that will be associated with a proposed mine and will need further study in the EIS. Thus, the EAW is a “blueprint” for the EIS because it sets limits on what will be discussed further and at what level of detail. It is a standardized six-page questionnaire (31 questions), accompanied by numerous supplemental pages to fully answer the questions, and “typically” takes 90-120 days to complete. The EIS, which typically takes 280 days to complete (legally mandated time), is a thorough study of the issues defined in the EAW and provides information regarding environmental impacts and how they can be avoided/minimized. It considers and sets forth a series of “reasonable” alternatives (including the “no-build” alternative), possible permit conditions, and possible mitigation measures. The EIS does not approve or disapprove of a project; rather, it provides information and alternatives. A determination on the adequacy of the information provided in the EIS must be made before it can be used in determining whether to grant or deny any mine-related permit applications. The Minnesota Department of Natural Resources (DNR) is the Responsible Government Unit (RGU) for both the scoping EAW and EIS. The EAW/EIS process should begin as soon as possible because the entire process could take around 1.5 years before a final adequacy decision can be made. Furthermore, no decisions on most mine-related permits can be made until after the EIS process has been completed (actually 25-90 days after the adequacy decision). It is extremely important to make early contact with all of the agencies that are responsible for granting permits for several reasons that include: 1. to insure that all issues relating to the various permits are included for study in the EIS; 2. to begin preparation on some of the permits so they can be issued as quickly as possible after the EIS is complete (some permits can take up to 1.5 years (or more) before decisions to grant or deny can be made); 3. to avoid duplication of efforts 46 �for the various permits and establish cooperation between the agencies; and 4. to get the public informed and involved to hopefully minimize later delays in the permitting process. Table 1: List of potential permits required to establish a non-ferrous, metallic mine in Minnesota. Permit Agency Approximate Application determination time* Permit to Mine** DNR Minerals 7-8 months WCA-Wetlands Replacement Plan** DNR Minerals 4-6 months Water Appropriation Permit** DNR Waters < 2 months Public Waters Work Permit** DNR Waters < 2 months Dam Safety Permit** DNR Waters < 2 months Part 70 - Air Quality Permit** MPCA 1.5 years NPDES/SDS Stormwater Permits (two - for Construction and Industrial Activity) NPDES/SDS Wastewater Permits** ( two - for industrial process wastewater and sewage) Hazardous Waste Permit** MPCA < 2 months? MPCA 1.5 years MPCA 1-3 years Section 404 Permit (discharges to wetlands)** ACOE Section 10 Permit ? (Affects to “navigable” waters of the US) Section 401 Certification (wetland certification needed before 404 permit can be issued) Water Treatment Plant Permits ACOE 120 days (unless Fed. EIS required?) ? MPCA 60-120 days ? MPCA ? Local Permits - zoning, construction, bonding, etc varies “short” period * = Minimum time to complete (assuming optimal conditions) after all data that are required to be submitted for the permit are complete ** = Permit that by itself may require a mandatory EAW and/or EIS. Abbreviations: DNR = Department of Natural Resources; MPCA = Minnesota Pollution Control Agency; ACOE = Army Corps of Engineers; NPDES = National Pollutant Discharge Elimination System; SDS = State Disposal System; WCA = Wetland Conservation Act. 47 �Description of a pegmatite occurrence on the eastern margin of the Mellen Granite, State Highway 13, Ashland County, Wisconsin. Sikkila, K., (Wisconsin Department of Transportation, District 8, Superior, Wisconsin) A highway construction project supervised by the Wisconsin Department of Transportation, District 8 office took place during the 2001 field season on State Highway 13 immediately north of the City of Mellen in central Ashland County. Construction activity began at the intersection with State Highway 169, extending northward for 3480 meters. The project consisted of a realignment within the existing right-of-way and necessitated the blasting, excavation and removal of approximately 33000 cubic meters of rock. Bedrock geology in the project area consists of intrusive rocks of the Lower Keweenawan (approximately 1.1 Ga) Mellen Complex. The highway right-of-way is positioned over the contact between two discrete rock bodies within the Complex: the gabbroic rocks of the Potato River Intrusion (to the east); and the younger Mellen Granite (to the west). A previously existing roadcut along the right-of-way indicated the presence of an intrusive breccia at this intrusive contact. The primary lithology of the breccia matrix in this previously existing roadcut appears to be granodiorite, with xenoliths of gabbro, lesser amounts of mafic volcanic rocks, and minor amounts of metasediments of probable Lower Proterozoic age. New exposures resulting from construction activity indicate an additional complexity to this brecciated contact margin, culminating in the presence of a small pegmatite body approximately 520 meters to the north of the original intrusive breccia exposure. The petrography of the pegmatite itself appears to consist primarily of coarse-grained potassium feldspar (perthite), quartz and biotite, with accessory epidote, apatite and other currently unidentified minerals. An irregular central “core” contains abundant quantities of myrmekite, various unidentified phosphates(?), and an unidentified pale lilac-colored mineral. Analyses will be performed on these minerals in the near future. The intrusive breccia in the areas proximal to the pegmatite displays moderate to strong potassium metasomatism, with plagioclase altered to potassium feldspar/perthite/myrmekite and the generation of epidote as a residual by-product, the alteration of mafic minerals in gabbroic xenoliths to biotite and/or phlogopite and hornblende, etc. Anastomosing swarms of small irregular felsite (aplite?) dikes also occur in this zone. Evidence for later-stage cataclasis and a retrograde chlorite event is represented by occurrences of chloritized mafic fault gouge and the presence of books of chlorite replacing biotite phenocrysts in areas proximal to these gouge zones. Irregular localized bodies of intrusive rocks of intermediate composition (syenite, monzonite, monzonite porphyry, monzogabbro, quartz diorite, etc.) also occur along the perimeter of this breccia/pegmatite zone. Widely disseminated sulfides (pyrite/chalcopyrite) are also noted. 48 �Inferences from the Hattenberger deep drill hole, Carlton County, Minnesota, pertinent to regional stratigraphy and mineral potential of the western segment of the Penokean Orogen Southwick, D.L., (Minnesota Geological Survey (retired); davidsouthwick@earthlink.net) The Hattenberger core hole, drilled vertically to a depth of 7,440 feet (2,268,3 meters) near Kettle River in Carlton County, Minnesota, penetrates a sequence of metamorphosed and deformed sedimentary and volcanic strata of Paleoproterozoic age within the fold and thrust belt of the Penokean orogen. Continuous core recovered from the depth interval 803 to 7,440 feet (244.8 to 2,268.3 meters) provides a rare depth-dimensional view of the lithostratigraphy and structures in rocks that are not well exposed at the surface. The cored interval below depth 4,780 feet (1,457.3 meters) consists predominantly of quartz-rich mica schist, calcareous mica schist, and dolomitic marble that are interstratified on coarse to fine scales. Relatively minor amounts of mafic volcanic rock (both flows and fragmental types) and recrystallized cherty iron-formation are interstratified with the dominant quartzose, micaceous, and calcareous metasedimentary rocks in the upper part of this lowermost major division of the core. In the upper major division of the core, above depth 4,780 feet, the predominant rock types are (1) dark-colored, thinly bedded graphitic mica schist and phyllite; (2) non-magnetic, graphitic, silicate-carbonate-sulfide iron-formation, parts of which are characterized by prominent porphyroblasts of Fe-rich garnet and amphibole; and (3) an assortment of mafic volcanic rock types that in general form thin stratigraphic units interbedded with the metasedimentary components. Sills of metadiabase chemically identical to the volcanic rocks occur throughout the whole core, in both the lower sequence of quartzose and calcareous schists and the upper sequence of graphitic and iron-rich rocks. Altogether, the sills and allied metavolcanic rocks amount to about half of the total footage drilled, with the greater part being sills. The lithologic and structural attributes of the lower sequence of rocks in the Hattenberger core match well with those of the Denham Formation at its type locality (Morey, 1978; Boerboom and Jirsa, 2001). Likewise, the attributes of the upper sequence match well with those of the Glen Township Formation, the type section for which is contained in several cores drilled about 23 miles (37 kilometers) along regional strike to the west of the Hattenberger locality (Morey, 1978). The assumed Denham–Glen Township contact in the Hattenberger core is occupied by a thick sill of metadiabase, the margins of which are strongly sheared. This leaves the nature of the formational contact open to question. It could be a conformable contact invaded by the sill, with the shearing at sill margins due to mechanical contrasts during complex, multi-stage regional deformation, or it could be a tectonic contact invaded by the sill that was later reactivated. 49 �Highly deformed, variably metamorphosed stratotectonic complexes of calcareous metasedimentary rocks, carbonate-silicate-sulfide iron-formation, and mafic metavolcanic rocks are the regional hosts for economic mineral deposits in several important mining camps, including the Homestake district in South Dakota (Caddey and others, 1991) and the Broken Hill and Mount Isa districts in Australia (Ashley and others, 1998; Painter and others, 1999). The mechanical contrasts among the various rock types in these complexes, together with the geochemical reactivity of the calcareous and iron-rich strata, provide fertile ground for mineral deposition from spatially associated hydrothermal systems. Clearly, the geological attributes revealed in the Hattenberger core are not of themselves meaningful indicators of mineral-deposit probability. However, those attributes taken in conjunction with mineralogical evidence of hydrothermal activity in the Cuyuna mining district (McSwiggen and others, 1995; Melcher and others, 1996) and the presence of barren massive sulfide deposits in the Glen Township area (Han, 1968) suggest that broad areas of east-central Minnesota are intrinsically prospective for a variety of ore-deposit types. Ashley, P.M., Lottermoser, B.G., and Westaway, J.M., 1998, Iron-formations and epigenetic ironstones in the Palaeoproterozoic Willyama Supergroup, Olary domain, South Australia: Mineralogy and Petrology, v. 64, p. 187-218. Boerboom, T.J., and Jirsa, M.A., 2001, Stratigraphy of the Paleoproterozoic Denham Formation—a continental margin assemblage of basalt, arkose, and dolomite [abs.]: Institute on Lake Superior Geology, 47th Annual Meeting, Proceedings, v. 47, Program and Abstracts, pt. 1, p. 6-7. Caddey, S.W., Bachman, R.L., Campbell, T.J., Reid, R.R., and Otto, R.P., 1991, The Homestake gold mine, an Early Proterozoic iron-formation-hosted gold deposit, Lawrence County, South Dakota: U.S. Geological Survey Bulletin 1857-J, p. J1-J67. Han, T.M., 1968, Ore mineral relations in the Cuyuna sulfide deposit, Minnesota: Mineralium Deposita, v. 3, no. 2, p. 109-134. McSwiggen, P.L., Morey, G.B., and Cleland, J.M., 1995, Iron-formation protolith and genesis, Cuyuna range, Minnesota: Minnesota Geological Survey Report of Investigations 45, 54 p. Melcher, F., Morey, G.B., McSwiggen, P.L., Cleland, J.M., and Brink, S.E., 1996, Hydrothermal systems in manganese-rich iron-formation of the Cuyuna North range, Minnesota: Geochemical and mineralogical study of the Gloria drill core: Minnesota Geological Survey Report of Investigations 46, 59 p. Morey, G.B., 1978, Lower and Middle Precambrian stratigraphic nomenclature for east-central Minnesota: Minnesota Geological Survey Report of Investigations 21, 52 p. Painter, M.G.M., Golding, S.D., Hannan, K.W., and Neudert, M.K., 1999, Sedimentologic, petrographic, and sulfur isotope constraints on fine-grained pyrite formation at Mount Isa Mine and environs, northwest Queensland, Australia: Economic Geology, v. 94, no. 6, p. 883-912. 50 �Petrographic Study of the Ottertail Pluton, Superior Province, Northwestern Ontario Sturm, C. L., Czeck, D. M and Fein, E., (Oberlin College Geology Department, Oberlin Ohio 44074. Claire.sturm@oberlin.edu) INTRODUCTION This study concentrates on the Ottertail Pluton at the Wabigoon-Quetico subprovince boundary in the western Superior Province near Mine Centre, Ontario. The Ottertail is one of the Algoman plutons dated at 2686 Ma (Davis et. al, 1989), which have been used to constrain the termination of deformation at the subprovince boundary (e. g. Davis et. al, 1989; Poulsen, 2000). Our goal is to study the mineralogy and microstructures of the pluton in thin section. At the macroscopic level the pluton seems largely undeformed because of the general lack of macroscopic deformation fabrics. This has led many researchers to interpret the Ottertail Pluton to be posttectonic. However, it has been shown that determining the relationship between pluton emplacement and deformation requires more detailed analysis (Paterson and Tobisch 1988). We are using petrographic analysis combined with a magnetic fabric study to better determine the relationship between the pluton emplacement and deformation at the Wabigoon-Quetico boundary. ANALYSIS Using optical petrography and a vibrating sample magnetometer (VSM), we determined the mineralogy and magnetic mineralogy of the pluton. In general, the pluton ranges from quartz monzonite to granite to granodiorite. Mineralogy consists of: quartz, plagioclase, microcline, microcline perthite, hornblende, myrmekite, and some zircon. There are also minor amounts of sericite, clinozoisite, magnetite (and other opaque minerals) in some portions of the pluton. The grain sizes vary. Many quartz crystals have undulose extinction and some have subgrains, which suggest slight deformation by dislocation processes. Minor metamorphism is indicated by sericite in plagioclase crystals, and microcline perthite. At the macroscopic level, the pluton seems largely undeformed, but our study of anisotropy of magnetic susceptibility (AMS) and microstructures show that there is some evidence for deformation. Davis, D. W., Poulsen, K. H., Kamo, S. L., 1989. New insights into Archean crustal development from geochronology in the Rainy Lake area, Superior Province, Canada. Journal of Geology 97, 379-398. Paterson, S. R., Tobisch, O. T., 1988. Using pluton ages to date regional deformations: problems with commonly used criteria. Geology 16, 1108-1111. Poulsen, K. H., 2000. Archean metallogeny of the Mine Centre - Fort Frances area. Ontario Geological Survey Report 266, 121. 51 �Internal structures within crustal structural slabs, Quetico-Wawa subprovince junction, Quetico Provincial Park, Ontario Woodard, H.H. (Department of Geology, Beloit College, Beloit, Wisconsin 53511) The rocks of the Wawa subprovince, adjacent to the Quetico-Wawa subprovince junction, in the region between Agnes Lake and McKenzie Lake in Quetico Provincial Park, Ontario can be grouped into two discrete structural slabs. Detailed mapping of the ductile borders of these slabs indicates that the slabs are approximately 2 km thick and probably form the limbs of major recumbent folds. The base of each slab is defined by a ductile structural discontinuity, possibly representing the lower limb of a nappe or thrust surface. The northeastern McKenzie Lake slab rests upon the underlying Agnes Lake slab. The rocks which make up these structural slabs are amphibolite-grade, migmatitic, mica-quartz-feldspar-garnet schists, amphibolite, and tonalitegranodiorite. All of these rocks contain major deformational structures which were formed before, during and after the emplacement of the enclosing crustal slabs. The earliest recognizable structures are found only in the tonalite-granodiorites. These structures are layers of centimeter-scale thickness, and most are only recognized on outcrop surfaces where the layers are accentuated by superficial weathering. These layers are probably caused by centimeter-scale shearing within the tonalites. Both field measurements and aerial photo interpretation demonstrate that these centermeter-scale layers occur in “structural packages” which often have thicknesses on a scale of hundreds of meters. Hundreds of strike and dip measurements made on these layers, in conjunction with interpretation of large-scale, detailed, aerial photographs, demonstrate that the layers are deformed into a complex series of folds with typical wave lengths ranging from one to two kilometers. Many of the folds appear overturned, but some are upright, and most plunge northeastward, with occasional reversal of plunge. Interlayered and infolded with the tonalites are schists and amphibolites, and primary structures in these meta-sedimentary and metavolcanic rocks sometimes allow determination of stratigraphic top. All of the internal layers and folds are cut and smeared by the last recognizable ductile deformation along the subprovince junction. The internally folded rocks are later broken into individual kilometer-scale structural blocks which are bounded by steeply dipping faults. These faults are rarely exposed in outcrop, but some cut and offset the Quetico-Wawa subprovince ductile junction. Thus, a brittle phase of deformation followed the last ductile deformation at the subprovince junction and the emplacement of the crustal slabs. These faults, which cut the internal folds of the McKenzie Lake crustal slab, appear unrelated to the Burntside Lake brittle fault zone. This fault has been traced in outcrop about 100 km northeastward from its type locality on Burntside Lake, Minnesota and is mapped as terminating against the Quetico-Wawa junction in the vicinity of McKenzie Lake. The internal faults typically lack the intense centimeter-scale brecciation and the intense hydrothermal oxidation so characteristic of the Burntside Lake fault zone. Further, the strike orientation of seventy-five mapped internal faults appear geometrically related to the ductile folding of the Quetico-Wawa junction (and crustal slab development) rather than to the northeast-striking Burntside Lake fault. 52 �Thus, the internal structures within the McKenzie Lake crustal slab initially appear to record intense centimeter-scale shearing within all the rocks. This shearing is followed by ductile folding and complete recrystallization and then by recumbent overfolding of the sheared and folded sequence to produce the crustal slab. Following slab emplacement, the rocks are broken into kilometer-scale fault blocks, the strikes of which suggest a relationship to a later stage of compression across the subprovince junction. The latest ductile deformation along the QueticoWawa subprovince junction cuts the crustal slabs, and all their rocks and internal structures. The Agnes Lake structural slab, which underlies the McKenzie Lake slab, contains a similar suite of rocks and has similar internal structures to the above-described McKenzie Lake slab. However, within the Agnes Lake slab the internal structures are dominated by a series of northeast-striking, gently northwest-dipping, ductile shear zones chiefly at the contacts with tonalite and schistose rock units. These ductile shears are themselves recumbently folded and overturned toward the southeast. Although fieldwork continues on the Agnes Lake slab, the current interpretation of these internal ductile shears is that they represent folded sections of an earlier Quetico-Wawa subprovince junction, which have been sheared and folded into the Agnes Lake slab. 53 �Impact of fire on the forest floor and mineral soils, Snowbank Lake, Minnesota Woodruff, L.G., (U.S. Geological Survey, Mounds View, MN, 55112 (woodruff@usgs.gov)), Cannon, W.F., and Dicken, C., (U.S. Geological Survey, Reston, VA 20192) We are investigating the geochemical effects of fire on the forest floor and mineral soils in an area of the Superior National Forest near Snowbank Lake that was burned in a fuel reduction prescribed fire by the USDA Forest Service on October 11, 2000. The forest around Snowbank Lake, in northern Minnesota, is a mixed stand of older-aged balsam fir, spruce, aspen, red pine and jack pine. Many trees, particularly mature balsam and spruce, were blown down by a severe storm in July 1999. The scheduled Snowbank Lake fire gave us the opportunity to establish 10 study sites in the proposed burn area. At each site we described and collected soils prior to the fire, immediately after the fire, and seven months after the fire to quantify physical and chemical changes in the forest floor as a result of the burning. Initial sampling was in July 2000. At each site, forest floor material (living moss, forest litter, and/or humic layers) and mineral soil horizons (A-, E-, B- and C-horizons as available) were collected for analysis. The thickness of each layer was measured, and representative samples were collected for density calculations. The fire burned much of the fine fuel at the surface and affected 8 of the 10 sample sites. On October 12, prior to any post-fire rainfall, we resampled the sites. Burn severity (a qualitative assessment of the heat pulse directed towards the ground during a fire) was estimated and where possible samples comparable to pre-burn samples were collected. The sites were resampled seven months later in May 2001, following a winter of moderate snow cover. The fuel load at the surface and the moisture content of the forest surface controlled the major impact of the fire on the forest floor. Fire severity was high (100% of organic forest floor material consumed, mineral soil exposed) at 4 sites, moderate at 1 site (some forest floor material burned, mineral soil not exposed), and light at 3 sites (surface material charred with minimal loss at the forest floor). Two sites were untouched by fire. One of the elements of interest in this study was mercury. Gaseous elemental mercury in the atmosphere is transferred into a forest environment by wet and dry deposition onto the forest floor, creating a repository of mercury that is bound to organic carbon compounds. Recent studies show that smoke plumes from forest fires carry substantial mercury, but the origin of that mercury was in question (Friedli et al., 2001). Our preburn sampling shows that much of the mercury at the forest surface is bound to organic material on the forest floor and in organic mineral soils. Severe fire can vaporize much of this mercury as the organic compounds are combusted. Based on pre-burn analyses and measured thickness and density of organic material and assuming that all mercury in the organic layer is emitted during high severity burns when the forest floor is burned down to the mineral soil, average mercury emissions from the Snowbank Lake burn were about 2 mg/m2 of burned surface. This estimate only takes into account mercury bound to organic material on the forest floor and does not include burned foliage or woody fuels. Mercury bound to organic material in A-horizon mineral soils was not lost, even at sites of high burn severity, indicating that the fire’s thermal pulse did not heat soils above the 357oC vaporization temperature of mercury. Because the footprint of an historic fire was apparent in our study of soil geochemistry in Isle Royale National Park (Woodruff and Cannon, 2001) we anticipated that exposure of mineral 54 �soils by fire would lead to loss of both mercury and carbon over time. Loss of organic matter should be accelerated by solar heating of previously shaded soils and by lower input rates of organic matter because of loss of forest canopy. Interestingly, analyses of A-horizon soils collected at Snowbank Lake in May 2001 show no carbon loss and marked increases in mercury rather than decreases (Figure 1A). The reasons for this increase are unknown, although we speculate that it may be the result of leaching of mercury from the overlying ash layer or possibly from enhanced sorption of mercury by exposed organic material in mineral soils. The fact that carbon does not increase concomitant with mercury suggests that physical incorporation of ash and adsorbed mercury is not the cause of higher mercury concentrations. Lead, which much like mercury has an atmospheric source and is enriched in the forest floor and organic mineral soils, is enriched in the uppermost mineral soil samples collected in October after the fire compared to preburn values (Figure 1B), but comparable soil samples collected the following May show a slight decrease in lead, although most values are still higher than July 2000 levels. The increase of lead in soils immediately following the fire may be the result of the concentration of residual lead remaining after the burning of forest vegetation. Lead sorbed onto organic material may not volatilize in the fire, but could collect on surface soils. Additional sampling is planned for May 2002 to monitor the evolving geochemistry of the forest surface. This research shows that there are both immediate and long-term impact from fire, including loss of volatile elements and profound element movement at the forest surface. Figure 1. Mercury and lead versus carbon in A-horizon soil samples from the area of the Snowbank Lake prescribed fire. Friedli, H., L. Radke and J. Lu, 2001, Mercury in smoke from biomass fires: Geophysical Research Letters, v. 28, p. 3223-3226. Woodruff, L.G. and Cannon, W.F., 2001, The effect of fire on mercury and carbon in forest soils: results from northern Michigan and Minnesota: Geological Society of America Abstracts with Programs, v.33, p. A186. 55 � https://digitalcollections.lakeheadu.ca/files/original/9e1527ceb6b24c1bb2230ab8c4120149.pdf 125fa414cc8aa8747725d63da098aa94 PDF Text Text INSTITUTE ON LAKE SUPERIOR GEOLOGY 48th Annual Meeting Proceedings Volume 48 Part 2 - Field Trip Guidebook Kenora, Ontario – May 12-16, 2002 �INSTITUTE ON LAKE SUPERIOR GEOLOGY 48th Annual Meeting May 12-16, 2002 Kenora, Ontario Hosted by: Peter Hinz and Richard C. Beard Co-Chairs Sponsored by the Ontario Geological Survey Proceedings Volume 48 Part 2 - Field Trip Guidebook (Compiled by Blackburn Geological Services) �48th Annual Meeting Institute on Lake Superior Geology Volume 48 contains the following parts: Part 1: Program and Abstracts Part 2: Field Trip Guidebook 1 - Tanco Rare-Element Pegmatite, Southeastern Manitoba 2 - Quaternary Geology of Southeastern Manitoba 3 - Structure and Sedimentology of the Seine Conglomerate, Mine Centre Area, Ontario 4 - Industrial Minerals and Paleozoic Geology of Southeastern Manitoba 5 - Separation Rapids Rare-Element Pegmatite Field, Ontario 6 - Geology of the Red Lake Camp, Ontario Reference to the material in this volume should follow the example below: Lichtblau, A. and Storey, C.C. 2002. Geology of the Red Lake Camp, Ontario: Institute on Lake Superior Geology Proceedings, 48th Annual Meeting, Kenora, Ontario, 2002, v. 48, Part 2, p. 121-138. Volume 48 is published by the Institute on Lake Superior Geology and distributed by the Institute Secretary-Treasurer: Mark Jirsa Minnesota Geological Survey 2642 University Avenue St. Paul, MN USA 55114-1057 (612) 627-4780 email: jirsa001@tc.umn.edu ILSG webstite http://www.ilsgeology.org/ ISSN 1042-9964 Cover Illustration: Geologists examining a dump at the Gold Hill mine, Kirkup Township, 13 km southeast of Kenora, in 1914. Between 1886 and 1893 this mine produced 1090 ounces of gold from 220 tons milled. Four shallow shafts were sunk to a combined depth of 258 feet: the headframe for one of them is seen in the picture. The winning of gold from narrow discontinuous quartz veins was typical of the numerous small-scale mines of the Kenora goldfields in the latter part of the 19th and the early 20th century. ii �CONTENTS Proceedings Volume 48 Part 2 – Field Trips Trip1: The Tanco Rare-Element Pegmatite, Southeastern Manitoba ....................................1 Leaders: Staff, Tantalum Mining Corporation of Canada, Ltd. Trip 2: Quaternary Geology of Southeastern Manitoba..........................................................23 Stop 1: Striated outcrop, West Hawk Lake ................................................................26 Stop 2: West Hawk Lake, Till Section .......................................................................27 Stop 3: West Hawk Lake, Meteorite Impact Structure ..............................................28 Stop 4: Sapping Channels (Upper Cambell Beach) ...................................................30 Stop 5: Upper Campbell Beach of Lake Agassiz .......................................................31 Stop 6: Interglacial Site at Grunthal...........................................................................32 Leaders: E. Nielsen, Manitoba Geological Survey G. Matile, Manitoba Geological Survey Trip 3: Structure and Sedimentology of the Seine Conglomerate, Mine Centre Area, Ontario ........................................................................................................................37 Stop 1: Basal facies, low deformation, Shoal Lake road............................................60 Stop 2: 2D view, sandy lenses, dextral shear, Forest Tour road ................................61 Stop 3: 3D view, moderate deformation, Horsecollar Junction, Hwy 11 ..................61 Stop 4: Ultra deformed conglomerate, Hwy 11 .........................................................61 Stop 5: Small fold, Seine River bridge, Hwy 11 ........................................................62 Leaders: D. Czeck, Oberlin College P. Fralick, Lakehead University Trip 4: Industrial Minerals and Paleozoic Geology of Southeastern Manitoba ....................69 Stop 1: Sungro horticultural shagnum peat bog and plant .........................................90 Stop 2: Cold Spring Granite dimension stone quarry and plant.................................90 Stop 3: Gillis Tyndall Stone quarry and plant............................................................91 Leaders: J. Bamburak, Manitoba Geological Survey R. Bezys, Manitoba Geological Survey iii �Trip 5: Separation Rapids Rare-Element Pegmatite Field, Ontario ......................................95 Stop 1: Big Mack pegmatite.....................................................................................107 Stop 2: Separation Rapids pluton .............................................................................109 Stop 3: Big Whopper pegmatite ...............................................................................110 Stop 4: Marko's pegmatite........................................................................................115 Stop 5: James' pegmatite ..........................................................................................116 Leaders: C. Blackburn, Blackburn Geological Services D. Bubar, C. Pedersen, K. Rees, Avalon Ventures Ltd. C. Galeschuk, Tantalum Mining Corporation of Canada, Ltd. A. Mowatt, Emerald Fields Resource Corp. T. Pryslak, A..P. Pryslak Geological Services Trip 6: Geology of the Red Lake Camp, Ontario ...................................................................121 Stop 1: Meso-neoarchean contact, Woodland Cemetery road .................................130 Stop 2: Calcite carbonatized pillowed flows, Sandy Bay road ................................130 Stop 3: Cofederation/Balmer assemblages contact, Suffel Lake road .....................130 Stop 4: Madsen deposit, power line outcrops ..........................................................131 Stop 5: Buffalo deposit.............................................................................................133 Stop 6: Howey mine .................................................................................................134 Stop 7: Howey Bay-Flat Lake deformation zone.....................................................134 Stop 8: Redcon carbonate zone, Nungesser road .....................................................135 Leaders: A. Lichtblau, Ontario Geological Survey C. Storey, Ontario Geological Survey Staff, Goldcorp Inc. - Red Lake Mine Staff, Placer Dome North America - Campbell Mine iv �Field Trip 1 The Tanco Rare-Element Pegmatite, Southeastern Manitoba Peter Vanstone Chief Geologist Steven Young Mill Superintendent Roland Simard Mine Superintendent Carey Galeschuk Project Geologist Alistair Gibb Chemical Plant Superintendent Tantalum Mining Corporation of Canada Limited P.O. Box 2000 Lac du Bonnet, Manitoba R0E 1A0 "Giraffe" underground at the Tanco mine. �INTRODUCTION Pegmatites throughout the world range in age from late Archean (2,500-2,800 million years) to Miocene (5-23 million years) (Cerny 1989a). Within Canada, there are noticeable concentrations of rare-element pegmatites associated with the following orogenic events: 1. the Kenoran Orogeny (2,750-2,550 million years) in the Archean Superior Province; 2. the Hudsonian Orogeny (1,800 – 1,600 million years) in the Churchill Province; and, 3. the Grenville Orogeny (1,200 – 900 million years) in the Grenville Province. The pegmatite being commercially exploited by Tantalum Mining Corporation of Canada Limited (Tanco) is an example of an extremely fractionated, pollucite-bearing pegmatite which was emplaced during the Kenoran Orogeny. The Tanco pegmatite is located at Bernic Lake in the Canadian Shield of southeastern Manitoba, approximately 180 kilometres by paved and all-weather gravel road northeast of Winnipeg (Figure 1). The nearest communities, Lac du Bonnet and Pinawa, are located approximately 60 kilometres and 75 kilometres, respectively, from the minesite. Tanco has been a significant producer of tantalum concentrates, ceramic-grade spodumene concentrates, pollucite and other materials since the late 1960’s. More recently cesium N (icY ii Winnipeg IdIlUVI du Bois Lac PiIqIM if I Seauj ic o 20 ——— 10 Figure 1. Location of Tanco 2 20 30 40 40 30 50 �chemicals have been produced at the minesite. During this time, the pegmatite has been the subject of numerous studies because of its very limited low temperature alteration, lack of postemplacement, structural deformation and its absence of weathering effects. The geographic location of the pegmatite and the willingness of Tanco to allow access to its extensive diamond drill core library, as well as, the underground workings have also been contributing factors. For more information on the Tanco pegmatite and pegmatites in general, the reader is referred to the Canadian Mineralogist issues by Berry (1972), Cerny (1982), Martin and Cerny (1992), and Anderson et al (1998). Also, Brown and Ewing (1986) edited an issue of the American Mineralogist focused on pegmatites and granitic rocks, and Moller et al (1989) edited the proceedings of a workshop on the lanthanides, tantalum and niobium. Brisbin (1986) discusses pegmatite intrusion mechanisms and Ercit (1986) discusses tantalum mineralogy. An overview of the Tanco pegmatite and the mining/milling operations was published by Crouse, et al (1979) and Thomas (1984) completed a fluid inclusion study of the Tanco pegmatite. Tanco is 100% owned by Cabot Corporation of Boston, Massachusetts and is operated by the Cabot Specialty Fluids division headquartered in Houston, Texas. TANCO HISTORY In 1928, Jack Nutt Mines staked and explored the Bernic Lake area pegmatites for tin. During the following two years, shaft sinking began and a small tin concentrator was established on what is now the Tanco minesite. Feed for this mill came from the nearby exposed pegmatites. At this same time, a four hole drill program was underway to explore the pegmatites at depth. It was during this program that the Tanco pegmatite was intersected in Hole #3. Work on the property continued through 1930, but poor economic conditions forced the company to abandon the property. The claims subsequently reverted back to the Crown. In 1955, Montgary Petroleum Corporation Limited acquired the property and completed an extensive surface drill program. Over the next couple of years, a power transmission line from Pointe du Bois and a mine access road were constructed. Also, the sinking of a threecompartment shaft began and some surface facilities were built. In 1957, American Metals Company, Limited optioned the property from Montgary and completed a surface drill program. It was during this work that the internal zonation of the pegmatite was recognized and documented (Hutchinson 1959), and pollucite was identified. During 1959 and 1960, Chemalloy Minerals Limited (formerly Montgary) completed both surface and underground drill programs, and extracted small quantities of pollucite and quartz. In 1961, the mine was placed on care and maintenance and then allowed to flood in 1962. In 1966, Chemalloy started to evaluate the tantalum potential of the pegmatite. Extensive diamond drilling was carried out from surface and underground over the subsequent three years. The initial result of this activity was the formation in 1967, of Tantalum Mining Corporation of Canada Limited (Tanco), a joint venture between Chemalloy and Northern Goldfield Limited. In 1969, construction of a 500 ton per day tantalum gravity concentrator was completed and Tanco began commercial production. Production of ceramic grade spodumene concentrates began on a pilot scale in 1984, and went commercial in 1986 when the new spodumene concentrator was completed. Although the lithium potential of the pegmatite had been investigated over the years for the production of 3 �ceramic grade spodumene concentrates and lithium carbonate, none of these investigations proceeded beyond the feasibility stage. The Tanco joint venture remained in place until 1993 when Cabot Corporation acquired 100% of the operation. Up to 1993, different companies, in addition to the original two companies, were involved in the joint venture. These include: Manitoba Development Corporation (1972-1993), Kawecki Berylco Industries/Cabot (1974-1993) and Hudson Bay Mining and Smelting Co. Ltd. (1978-1993). In 1996, Cabot formed the Cabot Specialty Fluids division and started construction of the cesium brine plant. In 2001, the plant was expanded to allow for the manufacture of conventional cesium chemicals. RARE-ELEMENT PEGMATITE FORMATION Rare-element pegmatites, like the Tanco pegmatite, occur in synclinoria of metavolcanicmetasedimentary sequences that separate granitoid batholiths from gneissic tonalities. The pegmatites evolve from late orogenic, peraluminous (A/[C+N+K]>1), S-type granites. The resultant pegmatite fields are situated on the lower portions of relatively steep geothermal gradients (±40°-50°C/km.). The complex type pegmatites are commonly emplaced in low pressure/high temperature facies (upper greenschist to lower amphibolite) metamorphic terrains with emplacement generally at a depth of four to six kilometers (Cerny 1989a). The parental, fertile granite is late- to post-tectonic and post-dates the peak of regional metamorphism. These granites are leucocratic and although commonly equigranular, may be porphyritic. At depth, they are biotite bearing and grade upward or laterally into a two-mica granite or a muscovite granite which is capped by a coarse grained to pegmatitic, megacrystic Kfeldspar, graphic leucogranite (Cerny and Meintzer 1988). This pegmatitic granite stage is an integral step in the formation of rare-element pegmatites. The pegmatitic melt forms within the parental, fertile granite through the process of magmatic differentiation. This melt collects in the upper portion of the fertile granite pluton, with the volatiles and other liquidus-depressing constituents such as H2O, F, Li, B and P increasing outward from the parental granite. These constituents, plus even small amounts of exsolved supercritical fluid, reduce the viscosity of the melt. The lower the liquidus temperature and the less viscous the melt, the more mobile the melt becomes and the further out it will migrate. Melt migration occurs when there is sufficient internal pressure and the magma reservoir is tapped by a tectonic disturbance of the outermost solidified shell of the pegmatitic granite. Pegmatite groups form a regional zonation around the parental granite with the complexity of the pegmatites increasing away from the parental granite (Cerny 1991b) (Figure 2). Rare-Element Pegmatite Classification Pegmatites can be divided into two types, the lithium-cesium-tantalum (LCT) type and the niobium-yttrium-fluorine (NYF) type. Over the years, the LCT type pegmatites have been well studied because of their economic significance. These pegmatites have been an economic source of lithium, tantalum, tin, cesium and rubidium minerals with mica, quartz and feldspathic sand by-products. The LCT type of pegmatites can be subdivided into classes based on mineralogy/chemistry and complexity (Table 1). 4 �I I I I / / / / / / / / / 1 / / ' Li,Be,Ta,Sn (Rb,Cs) I \ . Figure 2. Schematic section of a zoned fertile granite-pegmatite system. 1. fertile granite; 2. pegmatitic granite; 3. barren to beryl bearing pegmatites; 4. beryl-type, columbite- to phosphate-bearing pegmatites; 5. complex spodumene (or petalite) bearing pegmatites with Sn, Ta, ±Cs; 6. faults. (modified from Cerny 1989b) LCT type pegmatites have a number of chemical characteristics that distinguish them from the NYF type pegmatites. Some of these features include the following: • the tantalum content exceeds the niobium content; • the tin content can equal tantalum content; • they contain low levels of the light and heavy rare earths; • the pegmatites are enriched in boron and alkali elements; and, • they have low levels of uranium and thorium. Mineralogical characteristics can also be used to distinguish between LCT type and NYF type pegmatites. Some of the characteristics of the LCT type pegmatites include: • a general absence of fluorite (fluorine is tied up in minerals such as topaz, lepidolite, amblygonite); • a common occurrence of lithium and phosphate minerals; • the presence of tourmaline; 5 �• • simpler oxides of tantalum and niobium ±tin with essentially no rare earth element (REE) content; and, beryl can be present. The Tanco pegmatite is a good example of the complex type-petalite subtype of LCT pegmatite and is probably the most studied pegmatite of its type. Pegmatite Types Subtypes Characteristics Examples Beryl (i) (ii) beryl-columbite beryl-columbite-phosphate • relatively simple Greer Lake, MB PEG Group, NWT Complex (iii) spodumene petalite complex internal zonation lithium rich diverse mineralogy primary crystallization is greater than secondary replacement bodies Hugo, SD; Harding, NM (iv) • • • • Complex (v) amblygonite Lepidolite AlbiteSpodumene Albite • high fluorine activity Tanco, MB; Bikita, ZM, Peerless, SD Brown Derby #1, CO Kings Mountain, NC • least common • generally small Hengshan Field, P.R.C. Table 1. Classification of LCT type pegmatites. (modified from Cerny 1991a) GEOLOGIC SETTING The Bernic Lake pegmatite group, of which the Tanco pegmatite is a member, is one of a number of such groups comprising the Winnipeg River Pegmatite Field located in the Archean Bird River Greenstone Belt of the western Superior Province in the Canadian Shield (Figure 3). The Bird River Greenstone Belt is bounded on the north by the English River Subprovince, a belt of highly metamorphosed metasediments and metavolcanics rocks, and mafic to felsic batholiths and plutons (Beakhouse 1991a). To the south, this belt is bounded by the pluton-dominant Winnipeg River Subprovince (Beakhouse 1991b). The Bird River Greenstone Belt is comprised of six formations of the Rice Lake Group. In general terms, the belt consists of mafic to felsic metavolcanic and derived metasedimentary rocks all of which have been intruded by synvolcanic to late tectonic mafic to felsic intrusives. Of these formations, the Eaglenest Formation is the oldest and the Booster Lake Formation is the youngest (Trueman 1980). The six formations are listed below in chronological order. 1) Booster Lake Formation: metapelite and metagreywacke - unconformity 2) Flanders Lake Formation: lithic meta-arenites and metaconglomerate - unconformity 3) Bernic Lake Formation: felsic to mafic metavolcanic and metasedimentary units, felsic and mafic intrusive with porphyry units 6 �- unconformity4) Peterson Creek Formation: metarhyolites and clastic components 5) Lamprey Falls Formation: metabasalts, Bird River Sill, metagabbro 6) Eaglenest Lake Formation: metamorphosed volcanic wacke IVIdflROUd / / / JIILdFIU Sachigo Subprovince Bird River greenstclne belt Berens River SubDrovince --- 250 kflometres _________ Superior Province Southern Province and Nipigon Plate Phanerozoic basin sequence .___— Subprovince boundary Figure 3. Regional geological setting of the Tanco pegmatite (modified from Beakhouse 1991b). 7 �Trueman (1980) defined four major structural events in the area. The first two events were episodes of east-west folding, the second event being associated with the emplacement of large regional batholiths. These events led to associated prograde, low pressure/high temperature metamorphism (Abukuma type) in the Bernic Lake Formation. The third event was major eastwest faulting, with associated retrograde metamorphism. The last major event was a second faulting episode that propagated a series of northwest trending faults. With this event there was localized retrograde metamorphism. Overall the metamorphic grade throughout the Bernic Lake Formation is upper greenschist to lower amphibolite facies (Cerny, et al 1981). Numerous synvolcanic intrusive units intrude the Bird River Greenstone Belt. They range in size from a kilometre up to about 25 kilometres and generally display an elongated east-west shape. The compositions of these intrusives vary from body to body and even within an individual intrusive, and include gabbro, anorthositic gabbro, diorite, quartz monzonite, granodiorite and granite. Quartz and quartz-feldspar porphyries are also found throughout the belt. The Bernic Lake Formation, which is in fault contact with the Booster Lake Formation to the north and the Peterson Creek Formation to the south, consists of a complex array of layers of metamorphosed basalt, andesite, dacite, rhyolite, iron formation, conglomerates, volcanic wackes and sandstone. Lateral continuity is not common among most of the rock types and is only persistent in the mafic to intermediate metavolcanics and, in part, the iron formations. Other volcanic units in the area seem to be composed of flows of limited lateral extent. Syn- to post-tectonic emplacement of granite and pegmatitic granite stocks throughout the Bird River Greenstone Belt provided the source for a number of rare-element pegmatite groups found within the belt. Of all the pegmatites identified in the area, the largest and most economically significant ones occur within the Bernic Lake pegmatite group situated within the Bernic Lake Formation. The major pegmatites of this group include the Tanco, Dibs, Buck, Coe, and Pegli. All of these pegmatites have an east-west elongation, are horizontal to sub-horizontal in orientation and are hosted by either mafic intrusives or associated mafic metavolcanic units. TANCO PEGMATITE GEOLOGY The Tanco pegmatite, situated at the western end of Bernic Lake, is an extremely fractionated, rare-metal, complex type-petalite subtype, LCT pegmatite and is hosted by a late-stage, subvolcanic, metagrabbro (Tanco amphibolite) intrusive. The age of the Tanco pegmatite is 2,650 – 2,550 million years (Cerny 1989a). The pegmatite is completely blind or buried, and only sub-crops in a limited area in the bottom of Bernic Lake. Based on hundreds of diamond drill hole intercepts, the pegmatite has a maximum length of approximately 1,990 metres and a maximum width of 1,060 metres (Figure 4), and is up to 100 metres thick. The total tonnage of the pegmatite has been calculated to be approximately 25 million tonnes (Stilling, 1998). Emplacement is hypothesized to be within the pressure shadow of an easterly trending, dual plunging, anticlinal axis (Cerny, et al 1981). More recent data has given rise to the possibility that dilation may have been aided by a number of pre-existing faults that could have freed up the overlying block of metagabbro, thus allowing the intruding pegmatitic fluid to “hydraulically” lift the overlying host rock. Initial intrusion of this fluid appears to be into a sub-horizontal joint 8 �set that is ubiquitous throughout the Bernic Lake area. The bi-lobate shape of the pegmatite may also be influenced by a possible sinistral offset of the host anticline. OS 1.0 0.6 Tanco Mineral OS 1.0 NI kIIon,41n LI I cd7a-'----T—--—7 I - C' -' 7)-i 0 LI '—-' L7 f Lake Figure 4. Plan view of the Tanco Pegmatite Pegmatite Zonation Internally, the pegmatite is composed of nine discrete mineralogical zones with the different ores of economic interest – those of tantalum, spodumene, cesium and rubidium – each essentially occurring in different zones. Characteristic textures and mineralogical assemblages distinguish each zone. The pegmatite is the host to approximately 100 different minerals (Cerny, et al 1998). A coloured longitudinal section of the Tanco pegmatite is appended and a brief description of each of the internal zones is given below. A more complete description of the pegmatite zonation and mineralogy can be found in Cerny, et al (1998). Of the nine zones comprising the pegmatite, only the Border and Wall Zones occur as concentric shells enveloping the entire pegmatite. When combined, however, the Lower and Upper Intermediate Zones also form a concentric shell within the pegmatite. The Central Intermediate and Lepidolite Zones have both been subjected to late stage micaceous alteration. Unlike the stereotypical zoned pegmatite, the location of the Quartz Zone or core is in the upper portion of the dike for most of the mine and in its more traditional, central location only in the western portion. Border Zone (Zone 10) This is a very thin zone (a few to 30 centimetres) that envelops the pegmatite and is composed of fine-grained, saccharoidal assemblage of albite and quartz with lesser to rare tourmaline, apatite, biotite, beryl and triphylite. In places it may have a layered appearance. 9 �Wall Zone (Zone 20) The Wall Zone consists of very coarse grained, brick-red perthite, quartz, fine to coarse-grained tourmaline, albite, brown to greenish muscovite books and accessory white beryl. In general, the hanging-wall Wall Zone is thinner and coarser grained than the footwall Wall Zone. Increased albite (cleavelandite) content and bands of “footwall” aplite characterize this latter Wall Zone. The tin content of the zone generally exceeds the tantalum content. Aplitic Albite Zone (Zone 30) This zone is one of the main tantalum ore zones and is most prominent in the eastern portion of the pegmatite. The dominant mineral is a pale blue to white, fine-grained, saccharoidal albite. Quartz is a common constituent with subordinate to rare minerals including muscovite, Taoxides (predominantly wodginite), beryl and apatite. Texturally, undulating layers of the saccharoidal albite distinguish the zone. Where the Aplitic Albite Zone is in contact with the Quartz Zone, the contact is generally characterized by increased tantalum along the contact and within the albite in very close proximity to the contact (“nugget effect”). In some places, white beryl crystals that have grown off the albite into the quartz mark this contact. Lower Intermediate Zone (Zone 40) The locally known Mixed Zone is characterized by both its diversity of minerals and grain size. The mineral assemblage that distinguishes this zone is comprised of coarser grained microclineperthite and SQUI pseudomorphs (Spodumene-QUartz Intergrowth after primary petalite) in a finer grained matrix of albite, quartz and micas. Assemblages consisting of quartz pods containing amblygonite and/or spodumene, and radial rims of cleavelandite and lithianmuscovite around feldspar rich assemblages are less common. Common subordinate to rare minerals include lithian-muscovite, lithiophilite, lepidolite, petalite and Ta-oxides. The generally gradational contacts with the tantalum and spodumene zones allow for the selective mining of this zone for both tantalum and spodumene, but only under strict grade control. Upper Intermediate Zone (Zone 50) The Spodumene Zone as it is referred to, has evolved from the Lower Intermediate Zone and is comprised of very coarse-grained microcline-perthite and SQUI with lesser spodumene blades, quartz and amblygonite. Subordinate to rare mineralogy consists of pollucite, lithiophilite, albite, lithian-muscovite, petalite, eucryptite and Ta-oxides (predominantly tantalite). The SQUI, which is an oriented intergrowth of cogenetic spodumene and quartz, has resulted from the isochemical breakdown of the primary petalite. This process occurs under decreasing pressure conditions during the cooling of the intrusion (London (1986). This zone displays the largest crystals in the pegmatite with the petalite pseudomorphs (SQUI) attaining lengths up to approximately seven metres and the microcline-perthite reaching up to ten metres in length. Central Intermediate Zone (Zone 60): The MQM (Muscovite and Quartz after Microcline) Zone is another of the main tantalum ore zones. The zone is comprised of microcline-perthite, quartz, albite and muscovite with 10 �subordinate to rare beryl, Ta-oxides (predominantly wodginite), spodumene, sulphides, and apatite. The minerals are medium to coarse grained. Quartz Zone (Zone 70) This is a massive, monomineralic zone with accessory spodumene (SQUI) and amblygonite. When in contact with the tantalum zones, the contact is commonly characterized by increased tantalum concentration (“nugget effect”) Pollucite Zone (Zone 80) The Pollucite Zone is a sub-zone of the Upper Intermediate Zone with a gradational contact occurring between the two, and consists of a monomineralic core of pollucite enveloped by an assemblage of SQUI, microcline-perthite, amblygonite, petalite and interstitial pollucite. Polygonal fracturing with lithian-muscovite and/or quartz filling is not uncommon within the core. Accessory minerals include apatite and albite. This is the zone from which the cesium ore is mined. Lepidolite Zone (Zone 90) This zone forms two flat lying, east-west elongated sheets within, (at least in part) the Central Intermediate Zone and in contact with the Upper Intermediate Zone. The mineral assemblage consists of fine-grained, purple lithian-muscovite and lepidolite with lesser microcline-perthite, and subordinate to accessory albite, quartz, beryl and Ta-oxides (predominantly microlite). The zone is mined for tantalum and has been mined, on a limited scale, for rubidium. MINING The heart of the Tanco pegmatite is situated some 60 metres (~200 feet) below Bernic Lake, and is accessible from surface either via a shaft or via a 400 metre (~1,300 foot), 20 percent decline. Mining is carried out using the “room and pillar” method. The mine’s shallow depth contributes to lower inherent ground stresses and generally stable ground conditions. After weighing these factors, and considering the diverse mineralogy encountered at Tanco, it was decided that the Room and Pillar mining method would provide the optimum approach for economic extraction at Tanco. The first pillar design saw pillars 16 metres square (50 ft. x 50 ft.), with mining rooms also at 16 metres wide. As mining progressed over the years, ongoing rock mechanics studies showed that the rooms could be increased to 22 metres or 72 feet, without excessively loading the pillars. Pillar reduction has now been done successfully throughout the mine and continues as an integral part of the mining plan. Two-boom hydraulic jumbos perform all drilling for drifts, slashes, benches and arches. During the initial top slice development, the roof is carefully arched, utilizing smooth blasting techniques. The roof arches allow residual ground stresses to be redirected to the post pillars. Ground stress in the Tanco mine is considered low, relative to other hard rock mines, and as such, rock bolting is rarely required. At Tanco, the roof of mature mine workings may often average 20 metres (~65 feet) above the working levels below, and in places, may reach 30 metres (~95 feet). These high backs are 11 �carefully monitored throughout mining operations, utilizing custom designed aerial lift devices (referred to as Giraffes). Where suited, mining is carried out, utilizing a single boom Simba longhole drill. In particular, the longhole method has been the primary approach to pillar reduction. The broken ore is transported utilizing 5 yd3, 6 yd3 and 7 yd3, load-haul-dumps (LHD’s) – mobile, front-end loader units - and a 20 ton truck to various ore-passes, which are located throughout the mine. The ore is broken on grizzlies (metal grates at the top of the ore pass), utilizing either mobile or stationary hydraulic rock breakers. The ore is then passed to an underlying tramming level where it is transported to the shaft by a train of 4 ton, Granby style, side dump ore cars, and hoisted to surface coarse ore bins via 4 ton Kimberly style skips. Tantalum and spodumene ores are stored in one of two loading pockets and skipped on a daily basis up the two-compartment shaft, into dedicated surface coarse ore bins. The mine however, must produce and provide three distinct ores to the mill. To overcome the limitation of the system, one loading pocket and associated coarse ore bin is emptied weekly and an appropriate tonnage of pollucite ore is batched through. Mine ventilation air is downcast from surface through one of two vent raises, one being, in part, the Jack Nutt shaft from 1929/30 and the other, a 1.8-m (6 foot) diameter bore-hole raise. The exhaust mine air up-casts through the access decline. Total fresh air volume exceeds 5300 m3 per minute (190,000 ft3 per minute) and is appropriate for the operation of Tanco’s fleet of diesel mining equipment. A fleet of personnel carriers and service trucks supports mining operations. Tanco maintains all of its mine equipment at its own on-site facilities. MINERAL PROCESSING Due to land constraints, the concentrator is constructed on a peninsula formed by two bays on Bernic Lake. The building is multi-floored, with equipment on a total of six levels. The major items of concentration equipment are on two levels, with feed preparation equipment, filters and driers, on the upper levels, with pumps on the lower levels. The first stage of processing, common to all four mineral products, is crushing, where the coarse ore from underground (-300 mm in size) is broken down to –12 mm. in size. The tantalum, spodumene and pollucite ores are crushed into separate fine-ore, storage bins. The new dry grinding plant supplies ground pollucite for the cesium formate plant. Different processes concentrate each ore. Tantalum is processed by gravity concentration, a process that makes use of the fact that tantalum minerals are much heavier than the waste minerals. Spodumene, on the other hand, is primarily processed by flotation, which makes use of the different physical and chemical characteristics of the surfaces of the various minerals. Pollucite is ground and then subjected to acid leaching and other chemical processing to produce cesium chemicals. Tantalum Processing (Figure 5.) There are three main elements in the gravity concentration of Tanco’s minerals: liberation of the values from the gangue or waste rock; feed preparation of the ground product into different size fractions; and concentration of the different fractions. At Tanco, the plant is split effectively into four fractions – grinding/spiral circuit, coarse sand circuit, fine sand circuit and slime circuit. 12 �Fine ore is first ground to pass 2 mm. The –2 mm. product passes to the spirals, which recover the coarse, free, tantalum minerals, which may otherwise have been ground too fine for effective recovery. The spiral tailing is sized at 0.30 mm. by a Linatex hydrosizer with the underflow recirculating to the main grinding mill. Figure 5. Tanco’s tantalum gravity separation flowsheet. Effective feed preparation is essential for satisfactory separation on shaking tables, and this is carried out with cyclones, followed by Bartles-Stokes hydrosizers. The hydrosizers contain four spigots and an overflow. The spigot products, or sand fractions, are distributed to further banks of spirals. These spirals each produce a low-grade concentrate, a recirculated middling, and a 13 �tailings product. Falcon concentrators scavenge the fine sand tailings products. This centrifugal separator is one of the newest concentration devices, confirming Tanco’s commitment to “leading edge technology” in the pursuit of performance. Rougher concentrates from all sections are collected in a storage tank from which the cleaner section is fed at constant flowrate and density. Classification in cyclones and a hydrosizer sizes feed to four cleaner tables, which produce a fine, 35% Ta2O5 concentrate, a recirculated middling, and a tailing. Overflows from the various cylcones along with the Stokes hydrosizer overflow constitute the feed to the ultrafines circuit. These are thickened in another bank of cyclones and treated on a Mozley MultiGravity Separator (MGS). The MGS produces a rougher concentrate, upgraded on Bartles CrossBelts. Overall recovery of tantalum ranges from 69-72%. During the summer months accumulated tailings can be processed along with the ore; the same flowsheet being used. Recovery from the tailing portion of the feed is of the order of 30%, upgrading the feed from 0.05% to 30% Ta2O5. The specifications of a typical tantalum concentrate produced at Tanco is given in Table 2. Element Typical Concentrate (wt. %) Ta2O5 35% - 38% SnO2 14% - 18% Nb2O5 5% - 8% TiO2 2% - 4% Table 2. Typical tantalum concentrate Tantalum Markets Tanco’s tantalum concentrates are shipped to the Cabot Performance Materials facility in Boyertown, Pennsylvania for conversion to the metal or tantalum compounds. The major uses for tantalum are in the electronics industry and for cutting tools. High quality capacitors are the major single use for tantalum. Europe is the major consumer of tantalum carbide used in production of hardmetal alloys for cutting tools. Other tantalum alloys are important constituents of aero engines, and for acid resistant pipes and tanks used in the chemical industry. One minor but important use of tantalum is in the medical industry, for “spare-part” surgery – tantalum “pins” are used for such areas as hip-joint replacements, as it is the only metal that is not rejected by body fluids. Spodumene Processing (Figure 6) After crushing to –12 mm., the heavy medium Triflo circuit rejects the feldspar from the –12 mm. +0.5 mm. range. Ferrosilicon and magnetite as a 70:30 mixture are used with a feed density of 2.74 kg/l. and effective density of separation of 2.65 kg/l. The –0.5 mm. fraction continues to the grinding circuit. The sink product and the –0.5 mm. fraction are ground in closed circuit with a 2 mm. primary screen and a Linatex hydrosizer with an approximate cut point of 150 micron. Rougher and cleaner spirals recover coarse free tantalum within the grinding circuit. A 5 foot, low intensity drum magnet removes ground steel produced during the grinding process. The grinding circuit product is scavenged for tantalum by two Falcon concentrators. Tantalum from the Falcon concentrators is upgraded on a Double Deck Holman Table with the tailings and middlings returning to the grinding circuit. Coarse tantalum from the cleaner spiral is also 14 �upgraded on a single Holman Table. The tantalum recovered from the spodumene circuit is a valuable by-product. Figure 6. Schematic flowsheet of the spodumene circuit Prior to the amblygonite flotation stage, in order to control phosphate levels, the pulp is deslimed by single stage cycloning. Due to the nugget-like appearance of the amblygonite, close control of this flotation stage must be maintained. Starvation quantities of collector are used based on 15 �feed tonnage and previous tails assays. Starch is used as a depressant for spodumene at pH 9.2. A spodumene-phosphate by-product called Montebrasite is produced to meet market requirements. This concentrate is subjected to wet high intensity magnetic separation to remove weakly magnetic iron materials. This concentrate is pumped to a belt filter and propane fired rotary drier. The dried concentrate goes to a storage bin prior to bagging or bulk shipping to meet the customers’ requirements. Mica is then removed with a single flotation stage. This step assists in the removal of K2O from the final concentrate product. The mica flotation tailings are two stage cycloned to remove starch. Two conditioning stages for automatic pH control and collector addition are carried out prior to rougher flotation. The rougher concentrate goes on to two or three stages of cleaning to The Wet High Intensity Magnetic Separator (WHIMS) non-magnetic fraction is thickened by two stages of cycloning and stored in a holding tank prior to tonnage controlled feeding to the belt filter and propane fired rotary drier. Final product handling is carried out utilizing air slides and dense phase pneumatic pumping to storage bins. The final product can be shipped to the customer in 25 kg, 1,000-kg bags, or bulk, via road or rail. The concentrate is sold to markets worldwide. Water used within the circuits is either fresh (from Bernic Lake) or re-cycled pond overflow depending on the section of the plant. Spodumene Product Specifications Clients can accept different levels of impurities, depending on their specific use of the material. Specifications of Tanco’s 7.25%, -200 Mesh, 6.8%, and Spodulite grade concentrates are shown in Table 3. Spodumene Markets Customers specify tight impurity levels for the use of spodumene concentrates in the glass and ceramics industries, and the process for the production of these concentrates is based on removal of contaminant minerals. Spodumene can be used either as a feedstock for the production of lithium carbonate and metal, or directly, in its mineral form, in the glass and ceramics industries. Since the development of the “salars” in the USA and Chile, most lithium carbonate is recovered from these sources, and little spodumene is now used for chemical production. Lithia is a very powerful flux, especially when used in conjunction with potash and soda feldspars. In ceramics, lithium lowers thermal expansion and decreases the firing temperature. Glasses containing lithia are much more fluid in the molten state than those containing proportionate amounts of sodium or potassium. Lower viscosity and faster melting can be utilized to improve glass quality in terms of fewer defects such an unmelted or partially melted raw material grains, and more rapid removal of small bubbles. Lower viscosity can permit the glassmaker to run a forming machinery at a higher rate, or create more elaborate products such as some perfume bottles. In frits and glazes, lithia is used to reduce the viscosity and thereby increase the fluidity of the coatings. This reduces maturing times and lowers firing temperatures. Small amounts of lithia also increase gloss. 16 �Element/Sizing 7.25% Grade -200 Mesh 6.8% Mesh Spodulite Li2O 7.25 ± -0.1% 7.10% ± -0.2% 6.80% min. 5.00% min. 0.15% max. 0.08% max. 0.10% max. 0.06% ± -0.01% Fe2O3 Na2O 0.35% max. 0.30% max. 0.45% max. 0.75% max. K2O 0.30% max. 0.60% max. 0.40% max. 0.75% max. P2O5 0.27% max. 0.40% 0.27% max. 0.20% max. MnO2 0.04% max. 0.06% max. 0.04% max. 0.05% max. Al2O3 24.0% min. 25.0% min. 23.0% min. 20.0% typ. Tyler 20 Mesh 0.0% max. Tyler 28 Mesh Trace max. Tyler 48 Mesh 1.0% max. Tyler 200 Mesh 50.0% min. 10.0% max. 55.0% min. 80.0% typ. Table 3. Tanco’s spodumene products specifications. CESIUM FORMATE Cesium formate is a clear, water soluble fluid with a specific gravity of 2.3 g/cm3 (i.e. it is two and one third times heavier than water) and a viscosity similar to water. It is used in the oil drilling industry as a drilling fluid, where the properties of low viscosity, high specific gravity and complete solution confer significant benefits over traditional mud (bentonite) based drilling fluids in deep wells greater than 4,575 metres (15,000 ft.). Use of cesium formate eliminates formation damage, particularly skin formation while drilling through the reservoir (oil bearing) rock. This results in improved hydrocarbon flows to the well giving better daily production from the well, in addition to enhanced recoveries from the reservoir in the long term - that is more hydrocarbons may be extracted from the well before well stimulation techniques become necessary. From an occupational health and safety perspective, there are considerable benefits to the use of cesium formate. The pH is between 10 - 11, and skin contact, although undesirable, has no immediate consequences. Low mammalian toxicity is an added benefit. The low environmental toxicity of cesium formate makes it the fluid of choice in areas where environmental sensitivities are particularly acute. Cesium Formate Plant The cesium formate pilot plant was designed, built and commissioned in 1996/97 in response to a potential market for formate brines. The focus of plant production was aimed at the oil and gas industries’ demand for a high-density, solids free drilling fluids. The plant was designed to 17 �readily incorporate process changes and modifications enabling it to produce a wide variety of cesium-based products, thus allowing Tanco and Cabot to rapidly respond to these future markets. The original plant was designed to produce 500 barrels/month of 2.3 g/cm3 specific gravity cesium formate. In 1999, expansion of the plant allowed for the production of 700 bbl/month. In 2001, the plant underwent a further expansion in order to accommodate the manufacturing of conventional cesium chemicals. Since Bernic Lake is a headwater lake and therefore very susceptible to environmental damage, the plant design minimizes environmental impacts on the surrounding area. All areas of the plant are contained to capture any spilled material, and wastes are stored in a lined disposal cell, which eliminates the discharges to the lake. Cesium Formate Manufacture Pollucite ore is mined from the Tanco mine along with the spodumene and tantalum ores. The mine contains approximately 75% of the worlds proven reserves of pollucite. The ore is crushed to –12 mm., and then dry ground in a ball mill to a powder form. Utilizing a series of acid/base reactions, the cesium is extracted from the pollucite ore and converted to a high-density, cesium formate solution. The final product is shipped by container to Aberdeen, Scotland and Bergen, Norway for use by the drilling industry in the North Sea, and to Houston, Texas for use in the Gulf of Mexico. Markets Cesium chemicals are currently used primarily in catalyst and chemical synthesis applications. While current worldwide demand for fine cesium chemicals is approximately 700,000 pounds a year, it is expected that new applications in the oil, gas and chemical industries for these products will increase in demand by more than ten-fold. TANCO UNDERGROUND TOUR STOPS Due to the constant changes underground as a result of on-going mining activities, the stops for the tour will not be determined until closer to the date of the tour. The tour participants will receive a tour stop handout upon arrival at the minesite. 18 �REFERENCES Anderson, A.J., Groat, L.A. and Simmons, W.B.Jr. (eds.) (1998): Granitic Pegmatites: The Cerny – Foord Volume. The Canadian Mineralogist, vol. 36, pt. 2. Beakhouse, G.P. (1991a): Winnipeg River Subprovince, in Thurston, P.C., Williams, H.R., Sutcliff, R.H. and Stott, G.M., (eds.), Geology of Ontario: Ministry of Northern Development and Mines, Special Volume 4, Part 1, pp.239-278. Beakhouse, G.P. (1991b): Winnipeg River Subprovince, in Thurston, P.C., Williams, H.R., Sutcliff, R.H. and Stott, G.M., (eds.), Geology of Ontario: Ministry of Northern Development and Mines, Special Volume 4, Part 1, pp.279-302. Berry, L.G. (ed.) (1972): The Tanco Pegmatite at Bernic Lake, Manitoba. The Canadian Mineralogist, vol. 11, pt. 3. Brisbin, W.C. (1986): Mechanics of pegmatite intrusion. The American Mineralogist, vol. 71. N°s. 3 and 4, pp. 644-651. Brown, G.E., Jr., and Ewing, R.C. (eds.) (1986): R. H. Jahns Memorial Issue: The mineralogy, petrology, and geochemistry of granitic pegmatites and related granitic rocks. The American Mineralogist, vol. 71, N°.’s 3 and 4. Cerny, P. (ed.) (1982): Granitic Pegmatites in Science and Industry. Mineralogical Association of Canada Short Course Handbook 8. Cerny, P. (1989a): Characteristics of pegmatite deposits of tantalum, in Moller, P., Cerny, P. and Saupe, F., (eds.), Lanthanides, Tantalum and Niobium: Society for Geology Applied to Mineral Deposits, Special Publication 7, Springer-Verlag, pp.195-239. Cerny, P. (1989b): Exploration strategy and methods for pegmatite deposits of tantalum, in Moller, P., Cerny, P. and Saupe, F., (eds.), Lanthanides, Tantalum and Niobium: Society for Geology Applied to Mineral Deposits, Special Publication 7, Springer-Verlag, pp.274-302. Cerny, P. (1991a): Rare-element Granitic Pegmatites. Part II: Regional to Global Environments and Petrogenesis. Geoscience Canada, vol. 18, pp. 49-67. Cerny, P. (1991b): Rare-element Granitic Pegmatites. Part 1: Anatomy and Internal Evolution of Pegmatite Deposits. Geoscience Canada, vol. 18, pp.68-81. Cerny, P., Ercit, T.S. and Vanstone, P.J. (1998): Mineralogy and Petrology of the Tanco Rareelement Pegmatite Deposit, Southeastern Manitoba. International Mineralogical Association, Field Trip Guidebook B6, 17th General Meeting, Toronto, Ontario, Canada. Cerny, P. and Meintzer, R.E. (1988): Fertile granites in the Archean and Proterozoic fields of rare-element pegmatites: crustal environment, geochemistry, and petrogenetic relationships, in Taylor, R.P. and Strong, D.F. (eds.), Recent advances in the geology of granite related mineral deposits: Canadian Institute of Mining and Metallurgy, Special Volume 39, pp. 170-207. Cerny, P., Trueman, D.L., Ziehlke, D.V., Goad, B.E., and Paul, B.J. (1981): The Cat LakeWinnipeg River and Wekusko Lake Pegmatite Fields, Manitoba. Manitoba Department of Energy and Mines, Mineral Resources Division, Economic Geology Report ER80-1. Crouse, R.A., Cerny, P., Trueman, D.L. and Burt, R.O. (1979): The Tanco Pegmatite, Southeastern Manitoba. The Canadian Mining and Metallurgy Bulletin, Feb. 1979, pp.142-151. 19 �Ercit, T.S. (1986): The simpsonite paragenesis: the crystal chemistry and geochemistry of extreme Ta fractionation. Ph.D. thesis, University of Manitoba, Winnipeg, Manitoba, Canada. Hutchinson, R.W. (1959): Geology of the Montgary Pegmatite. Economic Geology, vol. 54, pp. 1525-1542.. London, David (1984): Experimental phase equilibria in the system LiAlSiO4-SiO2-H2O: a petrogenetic grid for lithium rich pegmatites. American Mineralogist, vol. 69, pp. 995-1004. Martin, R.F. and Cerny, P. (eds.) (1992): Granitic Pegmatites. The Canadian Mineralogist, vol. 30, part 3. Moller, P., Cerny, P. and Saupe, F. (eds.) (1989): Lanthanides, Tantalum and Niobium. Society for Geology Applied to Mineral Deposits, Special Publication N°. 7, Springer-Verlag, New York, NY. Stilling, A. (1998): Bulk composition of the Tanco Pegmatite at Bernic Lake, Manitoba, Canada. M.Sc. thesis, University of Manitoba, Winnipeg, Manitoba, Canada. Thomas, A.V. (1984): A petrological and fluid inclusion study of the Tanco pegmatite, S.E. Manitoba. M.Sc. thesis, University of Toronto, Toronto, Ontario, Canada. Trueman, D.L. (1980): Stratigraphy, structure, and metamorphic petrology of the Archean greenstone belt at Bird River, Manitoba. Ph.D. thesis, University of Manitoba, Winnipeg, Manitoba, Canada. 20 �21 �22 �Field Trip 2 Quaternary Geology of Southeastern Manitoba Erik Nielsen and Gaywood Matile Quaternary Geologists Manitoba Geological Survey Industry, Trade and Mines 360-1395 Ellice Avenue Winnipeg, Manitoba R3G 3P2 Canada Extensive wetlands that started to form in response to mid-Holocene climate change, are a common feature of the southeastern Manitoba landscape. The photo was taken approximately 25 km east of Sandilands. �INTRODUCTION The climatic, geomorphic and ecological changes that have occurred in northwestern Ontario, southeastern Manitoba and Canada in general, over the last 100 000 years have been nothing short of spectacular. The Sangamonian Interglacial, which was not unlike the present interglacial, lasted from approximately 125 000 to 75 000 years ago, and ended with the advance of the Laurentide Ice Sheet in what was the greatest ecological catastrophe to befall Canada in recent geological time. The Laurentide Ice Sheet flowed southward out of Quebec and Nunavut and covered most of Canada and the northern parts of the United States as far south as New York City and De Moines, Iowa. The southern ice margin fluctuated periodically throughout the Wisconsinan, but northwestern Ontario and southeastern Manitoba and most of the rest of Canada were locked in the icy grip of the continental ice sheet until almost 10 000 years ago. For an estimated 65 000 years, northwestern Ontario and southeastern Manitoba lay devoid of trees, grasses and all living things, under a one kilometre thick ice mass! Ameliorating climate in the late Pleistocene saw the rapid northward and northeastward retreat of the ice margin and the establishment of glacial Lake Agassiz between the retreating ice margin and the high ground to the south, east and west. Lake Agassiz, at times over 200 m deep persisted for about 4 000 years from approximately 11 700 to 7 700 years BP and occupied all of Manitoba below the Cretaceous Escarpment, as well as much of northwestern Ontario. The flat fertile plains of the Red River valley and parts of northwestern Ontario, such as the Fort Francis area, resulted from the deposition of thick deposits of deepwater glaciolacustrine sediments. The numerous beach deposits in northwestern Ontario, southeastern Manitoba and elsewhere, record successive lake levels. Water levels recorded by the beaches relate to differential isostatic rebound and stepwise drainage of Lake Agassiz into the Gulf of Mexico, the Great Lakes and the Arctic Ocean before the lake finally drained into Hudson Bay. POSTGLACIAL VEGETATION AND CLIMATE Little is know of the postglacial vegetation of southeastern Manitoba despite the extensive and detailed work in the region by the Geological Survey of Canada and the Manitoba Geological Survey over the last fifteen years. Information on the postglacial climate and vegetational history of the region is inferred form a single pollen diagram from Hayes Lake near Kenora (McAndrews, 1982). The vegetational history of Hayes Lake suggests that the area was invaded by spruce forest immediately upon deglaciation and regression of Lake Agassiz. The early spruce forest changed to pine, birch, poplar and alder forest after 10 000 years BP. Based on the available data from Hayes Lake, open, mixed woodland existed in the northwestern Ontario and southeastern Manitoba during the early to mid-Holocene. Spruce and fir increased at the expense of alder after about 3 600 years BP, in response to a cooling climate. The present vegetation has remained relatively stable for the past 3 600 years. QUATERNARY GEOLOGY OF SOUTHEASTERN MANITOBA Twelve thousand years ago all of Manitoba, except possibly isolated areas above the Manitoba Escarpment, was completely covered by glacial ice, which at it's maximum extended as far south 24 �as Des Moine, Iowa. Rapid glacial retreat, caused by the rapid amelioration of climate, was enhanced by a proglacial lake environment, which promoted accelerated ice beak-up by means of iceberg calving along the glacier margin. By ten thousand years ago the ice margin was at the south end of Lake Winnipeg, and southeastern Manitoba was ice-free. As ice retreated into southeastern Manitoba it divided into two glacial lobes, the Rainy Lobe which advanced from the northeast and the Red River Lobe which advanced from the northwest. Sediments deposited by the Rainy Lobe typically have a sand-rich matrix and Precambrian-rich clast lithology, whereas sediments carried by the Red River Lobe are typically silt-rich and predominantly Paleozoic carbonate clasts, reflecting the lithologies of the bedrock that the glacier was advancing over. The interlobate position between these two ice-lobes is defined by large, sorted sand deposits in the south, the Sandilands Moraine, and sand and gravel deposits further north (Figure 1). Retreat was rapid, commonly followed by minor glacial readvances that eroded or destroyed previously deposited recessional moraines. Figure 1. Field trip stops plotted on a Digital Elevation Model of a portion of southeastern Manitoba Glaciation in Manitoba blocks the natural northward drainage and consequently a proglacial lake, glacial Lake Agassiz, formed as the ice front retreated north of the continental divide in South Dakota. Lake Agassiz existed for about four thousand years, from about 11 700 years before present (BP) until about 7 700 years BP when it finally drained into Hudson Bay (Thorleifson, 1996). Paleostrandlines and associated radiocarbon dates from southeastern 25 �Manitoba document much of Lake Agassiz history (Figure 1). The initial phase of Lake Agassiz, the Lockhart Phase, during which time the lake drained southward into the Gulf of Mexico, and encompasses the highest levels of the lake lasted until about 11 000 years BP. The Lockhart Phase in southeastern Manitoba is represented by numerous, but poorly defined strandlines along the higher parts of Sandilands Moraine and by most of the clay deposited in the Red River valley to the west. The Lockhart Phase was followed by the Moorhead Phase which ended about 9 900 years BP. The Moorhead Phase is characterized by relatively low water levels, due to glacial retreat in the Lake Nipigon area of northwestern Ontario, which allowed drainage through lower outlets to Lake Superior and the Atlantic Ocean. Several, well-developed beaches and wave-cut escarpments and at least one in-filled abandoned river channel represent the Moorhead Phase north and west of the Sandilands Moraine. The following Emerson Phase, spanned the interval from about 9 900 to 9 300 years BP. A glacial readvance in northern Ontario blocked the eastern outlets. This caused the level of Lake Agassiz to rise to approximately the level it was at the end of the Lockhart Phase. The elevation difference was the result of about 1 000 years of isostatic rebound. Lake Agassiz again drained south into the Gulf of Mexico via the Mississippi River. Four prominent lake levels formed during the Emerson Phase, the Norcross, Tintah, Upper Campbell and the Lower Campbell. The Upper and Lower Campbell levels are the bestdeveloped strandlines in Lake Agassiz and can be traced in this region around the Sandilands Moraine and eastward almost to the Ontario border. A great deal of erosion occurred along the Sandilands Moraine at this time as a result of the prevailing winds coming from the northwest, across the open expanse of the lake. The final phase of Lake Agassiz, the Morris Phase, is represented by a series of regularly spaced, moderately well developed strandlines (Figure 1). The final drainage of the lake, occurred as successively lower eastern outlets opened, first draining through Lake Superior and then through more northerly outlets to the north Atlantic, until the final drainage into Hudson Bay about 7 700 years BP. During the rise and fall of Lake Agassiz water levels, the Sandiland Moraine, a large generally unconfined sand aquifer, rapidly became saturated and de-watered. The rapid de-watering caused the formation of sapping channels throughout the moraine, one of which is truncated by the Upper Campbell, and is therefore clearly related to the final drainage of Lake Agassiz from the area. FIELD TRIP STOPS STOP 1 - STRIATED OUTCROP, WEST HAWK LAKE Northwestern Ontario and the adjacent parts of southeastern Manitoba have been glaciated numerous times throughout the Pleistocene. Each successive glaciation in large part removes the evidence of previous glaciation. Previously deposited sediments are stripped away and bedrock outcrops are molded and striated such that they record only the most recent events. Consequently, the terrestrial glacial record is largely incomplete. The outcrop of pillow basalt at this stop was striated and polished by the last ice flow to affect this area (Figure 2). The striations, orientated towards 230º, are common throughout the area and 26 �record glacier movement out of Hudson Bay towards the southwest. Striations are typically fine scratches on the gentle stoss sides of this outcrop. The plucking and steep sides at the down glacier side of the outcrop, indicates that the ice flow was towards the southwest and not the northeast. Minor variations in striation direction across the outcrop is due to topographic deflection at the glacier sole and is not related to different glacial events. In addition to striations, numerous p-forms, areas that have been eroded by subglacial meltwater under hydraulic head imposed by the glacier, are found on the outcrop. Figure 2. Striated outcrop at West Hawk Lake showing ice flow towards 230º. Striations are best preserved under till or glaciolacustrine sediments. Once glacial polish and striations have been exposed to weathering they don’t usually last very long. STOP 2 – WEST HAWK LAKE, TILL SECTION Till is the material that is directly deposited by the action of glacier ice although there may be considerable influence of subglacial meltwater. It consists of a wide variety of grain sizes from clay to boulders and may be considered as being generally unsorted (Figure 3). Till is generally derived primarily by the comminution of the immediately underlying bedrock with only very small components originating from various up glacial sources. This is the case with the till in the West Hawk Lake area, which is sandy in texture and was derived primarily by the comminution of the underlying volcanic rocks. A small proportion of the till was derived from granitic rocks that outcrop approximately 5 km to the northeast. The till is generally not calcareous, but in places Paleozoic carbonate erratics derived from the Hudson Bay Lowland, 650 kilometres to the 27 �northeast, can be found testifying to long distance glacial transport. Carbonate erratics are however rare, both because of the long glacial transport and the low survival rate of these soft lithologies, but also because of dissolution by near surface weathering in the time since the area was deglaciated. Carbonate erratics, which may be found in the scree were probably ice rafted and subsequently deposited in the glaciolacustrine sediments, which are common in the area. Carbonate erratics are probably not derived from the till at this site. Figure 3. Section at West Hawk Lake exposing sandy till of northeast provenance. STOP 3 - WEST HAWK LAKE, METEORITE IMPACT STRUCTURE West Hawk Lake is almost 4 km wide and nearly circular in shape. It was drilled in the 1960s by the Dominion Observatory and found to be approximately 100 m deep and contain approximately 100 m of sediment overlying the Precambrian basement. The circular shape and great depth of the lake, as well as the presence of shock-metamorphosed quartz and other features indicates the lake was formed by a meteor impact. The oldest sediments in the crater are of Cretaceous age indicating the impact occurred prior to that time, possibly in the Paleozoic. Because the lake is so deep compared to its diameter, it has been believed for many years that sediment deposited in the lake would be protected from erosion during glaciation. Glacier ice moving over the lake would shear over the top of the lake and not penetrate to the bottom. Previously deposited sediment would therefore be unaffected by glaciation. In addition, the great depth and the fact that there are no major rivers draining the lake means that sediments entering the lake would not be eroded or flushed through the lake. Consequently, the possibility exists that a complete Holocene, glacial and pre-glacial record spanning perhaps millions of years 28 �might be preserved in the sediment in-fill at the bottom of the lake. Jim Teller from the Department of Geology, University of Manitoba, has undertaken coring of the upper 15 m of the sediment in-fill and is planning to core the remaining 75-85 m to elucidate the glacial history, the history of glacial Lake Agassiz and climate variability of the mid continent over possibly the last million years or more. En route to Stop 4 we drive west on the Trans Canada Highway. Approximately 12 km west of Falcon Lake we leave the area affected by glaciation from Hudson Bay and northwestern Ontario. The ice flow direction changes to southeasterly (145º) and the associated till becomes fine textured and highly calcareous, having been derived by the comminution of Paleozoic carbonate bedrock in the Manitoba Interlake, northwest of Winnipeg. We will have an opportunity to observe diamicton, similar to this till, in the Grunthal pit at Stop 6. Point of Interest In some sections of the low boreal forest, the construction of the Trans-Canada Highway had a considerable effect on drainage and the height of the water table. Where the Trans-Canada Highway becomes divided, just west of Falcon Lake, a small stand of eastern white cedars (Thuja occidentalis) in the median illustrates the impact of hydrological change on the local vegetation. The growth of these trees began to be affected following highway construction in 1981. Although most of these trees had been growing since the early 1800s, the elevated water table caused their ringwidth and wood density to decline by 50 percent within two to three years. While some cedars were able to survive under the raised water table for several years, the last tree had succumbed to flooding by 1993. Although most are still standing upright, these trees have been dead for 10 to 20 years. Figure 4. Composite tree-ring density curves for eastern white cedar (Thuja occidentalis) from Falcon Lake and East Braintree. 29 �In other areas of southeastern Manitoba, which marks the western limit of cedars, trees growing around undisturbed wetlands can live up to 350 years and possibly longer as is the case around East Braintree. These long-lived cedar trees can potentially provide records of changes in environmental conditions since the mid-17th century and may greatly improve our understanding of the natural variability of climate, forest fire frequency and insect infestations in this region (Figure 4). STOP 4 - SAPPING CHANNELS (UPPER CAMPBELL BEACH) The Upper Campbell beach is Lake Agassiz's most prominent strandline and defines the Sandilands Moraine as an island about 9 500 years BP (Figure 1). This phase of Lake Agassiz relates to the final drainage of the lake as progressively lower eastern outlet were opened by glacial retreat until the lake finally completely drained into Hudson Bay. The lunch spot is located on the back or landward side of the Upper Campbell beach, on the shore of a small lake. This small lake is located at the down slope end of what is believed to be a sapping channel. The head of this channel is 5 km to the southeast (Figure 5). This site clearly indicates that the sapping channel is truncated by the Upper Campbell beach, making it older than the beach. k Peat r%%Upper Cajnpbell WavecuffScarp 'I C SaLing els '1 ciofluvial Norcross Sand . Navecut $carp 5km Figure 5. Surficial geological map draped on a Digital Elevation Model of a portion of southeastern Manitoba. Stop 4 is located at the lower end of the sapping channels. The sapping channels are typically infilled with peat. Conical depressions are found above and below the Norcross wavecut scarp. Sapping channels have only been recognized in the Sandilands area, and are only found above the Upper Campbell beach, in areas where silty sands and fine sands are the predominant 30 �sediments. During times of high lake levels in Lake Agassiz, prior to the formation of the Upper Campbell beach, a high water table would have existed in the Sandilands. With the drop in lake level to the Upper Campbell beach, the water table would have dropped accordingly. This reequilibration of the water table would have taken place rapidly, perhaps in a decade or less, resulting in high gradients in the local hydrogeologic system. These high gradients made it possible to mobilize silt and transport it from the hydrogeologic system. The surficial expressions of this transport are the sapping channels, created where groundwater discharge occurred. Numerous conical depressions occur in the Sandilands that are also likely the result of groundwater movement and are believed to be contemporaneous with the sapping channels. These conical depressions occur almost exclusively in silty sands, above and below the Norcross escarpment, 5 km to the southeast. Although the term piping is commonly used to refer to flushing of sediment from beneath a dam in civil engineering terms, piping can occur in natural settings when there is upward movement of groundwater under high gradients in silts and silty sands (Higgins, 1982). The high gradients enable silt to be removed from the sediment matrix and depressions were formed as the remaining sediment collapses under the influence of gravity. Following a drop in the level of Lake Agassiz, groundwater flowing from higher elevations to lower elevations may have become semi-confined as overlying sediments became finer. The resulting upward gradient combined with presence of overlying silty sands suggests that piping is a viable mechanism for forming these conical depressions. STOP 5 - UPPER CAMPBELL BEACH OF LAKE AGASSIZ During the Emerson phase of Lake Agassiz the Sandilands Moraine was subjected to a tremendous amount of shoreline erosion. The prevailing winds were from the northwest and Sandilands was an island in the southeast part of the Lake Agassiz basin. As a consequence, the Sandilands Moraine was subjected to waves with a fetch in access of 300 km. Evidence of this erosion are two 20 m high wave-cut scarps, the Upper Campbell and Norcross scarps, on the northwest flank of the moraine. Large well-developed spits are situated on both ends of these scarps. The largest of these spits is found south of the lower of the two scarps, the Upper Campbell scarp. Figure 6. Ground penetrating radar profile across the Upper Campbell spit. This west to east profile is 150 metres wide with 30 metre thick foreset beds and several metre thick topsets. There is fine-grained glaciolacustrine sediment at the base of the foresets. 31 �This stop is located on the crest of the southern spit. The spit is approximately 15 k long, 8 k wide and 30 m thick and composed predominantly of sand with minor amounts of gravel. Ground penetrating radar surveys carried out by the Geological Survey of Canada and the Manitoba Geological Survey show the structure of the spit to be large foreset beds which prograde southward in the core and westward on the west flank (Figure 6). Topset beds are several metres thick. STOP 6 - INTERGLACIAL SITE AT GRUNTHAL Although the exposure at the Grunthal pit is poor, it is interesting because musk ox (Ovibos moschatus), extinct bison, (possibly Bison antiquus) and wooly mammoth (Mammuthus primigenius) (Figure 7) bones have been dredged from below the water table. Wood and a variety of organic-rich, fine-textured silt and silty-clay sediments have also been recovered during gravel extraction, but the stratigraphy of the site is speculative. Figure 7. Lower M1 molar of Mammuthus primigenius (V2554) from the Grunthal pit. (A) Lateral aspect. (B) Occlusal aspect. The sediment above the water table and the sand and gravel extracted by the dredge is interpreted to be late Wisconsinan, ice-proximal, glaciofluvial sediment deposited 11-12 000 years ago, when the last glacier ice to affect the area was waning. These sand and gravel deposits are in part capped by diamicton that may have been deposited as debris flows in a proximal glaciofluvial environment. 32 �Little is known about the sediments underlying the late Pleistocene sediments below the water table. The various bones, wood and the organic-rich sediments dredged from the bottom of the pit suggest the underlying deposits are of mid-Wisconsinan interstadial or possibly Sangamonian Interglacial age. Radiocarbon dating of a wood sample gave a finite age of 44 020 ± 1 030 years BP (GX-27643) suggesting an interstadial age, although dates in this range are close to the limit of the radiocarbon technique and must be accepted with some trepidation. The presence of bones of Mammuthus primigenius and Bison antiquus strongly suggest an interglacial age. In addition, a lophar index of 9 (number of lophs per 100 mm of mesiodistal crown length) of an M1 mammoth molar from the deposit (Graham Young and Ed Dobrzanski, per com 2002) is similar to an M1 or M2 molar of Sangamonian age from Bird, Manitoba, (Nielsen et al. 1988) further suggesting an interglacial age for the deposit. Two samples of organic-rich mud, dredged from below the water table, were submitted to Paleotec Services in Ottawa for macrofossil analysis. The plant macrofossil evidence suggests a forested environment dominated by spruce trees and the presence of sedges, buckbean and mosses further indicates the area was poorly drained. The presence of bark beetles (Scolytidae) agrees with the plant fossil evidence of a forested environment. The insect fossils, specifically rove beetles are in agreement with the plant macrofossil data suggesting a stream or slowly moving water in a poorly drained area possibly a pond or wet depression. The absence of aquatic submergent plants and other typical aquatic faunal elements suggest the pond was temporary rather than permanent. The water-worn bones in association with finer textured organic-rich silt and silty clay suggest the deposit may be in part a point bar. Alternatively, the bones became abraded when they were incorporated into the overlying glaciofluvial sediments. Interpretation of the floral and faunal macrofossil assemblage indicates the climate at the time of deposition was probably warm. This conclusion is based on the abundant macrofossil remains of spruce along with bark beetles suggesting the climate was at least warm enough for the growth of boreal forest. However, the absence of fossil evidence of other boreal taxa, specifically pine and deciduous trees such as birches and alders is puzzling. The forest, being composed of only spruce, resembles the boreal forests in northern regions. This, along with the presence of fossil rove beetles (Eucnecosum) which have distributions restricted to northern boreal, arctic, or alpine areas suggests the climate may have been cooler than today. The macrofossil evidence and the presence of M. primigenius, Bison antiquus and Ovibos moschatus at the site are taken to indicate a northern or boreal steppe or steppe-tundra environment. All the taxa from the site except the Pleistocene megafauna can be found living in southern Manitoba today, with the rove beetle being at its southern limit. It is therefore concluded from the macrofossil evidence that the deposit at Grunthal is probably of interglacial age, and it is tentatively assigned to the Sangamonian. Point of interest If time permits a small detour will be made to the Dawson Trail, which was the first ‘road’ linking Fort Garry to eastern Canada. 33 �Simon James Dawson, an engineer and land surveyor, was given the task in 1857 of surveying the country between Lake Superior and the Red River valley in Manitoba. Dawson subsequently proposed a route from Port Arthur’s Landing, which later became Port Arthur and then Thunder Bay, that would use waterways and roads, to prepare the way for the railroad and thereby forestall northward expansion by aggressive American interests. Figure 8. Map showing the Dawson Trail between Port Arthur’s Landing (Thunder Bay) and Fort Garry (Winnipeg). Construction of the Dawson Trail in Manitoba was started in 1868 under the direction of John Allan Snow, as a make-work project after several years of repeated crop failure in the Red River valley, but was then hastened because of potential trouble with the métis. The 1200 man army of Colonel Garnet Joseph Wolseley, which was sent west from Upper Canada in 1870 to quell the métis uprising led by Louis Riel, was in part employed to help finish the construction of the Dawson Trail (Figure 8). The army worked on the road to the point where it was passable and arrived in the Red River settlement in August of 1870. Interestingly the army traveled from Fort Francis to Fort Garry via Lake of the Woods and the Winnipeg River and did not use the Dawson Trail from the Northwest Angle, and across Sandilands. The trip from Port Arthur’s Landing to 34 �Fort Garry lasted approximately one month and was made by approximately 1600 travelers in 1873. With the completion of the Canadian pacific Railroad in 1885, the Dawson Trail was quickly forgotten after having being used for only a few years and never really being finished as Dawson originally envisioned it. However, much of the trail is still in use either as bush roads or snowmobile trails. Parts of the Trans-Canada Highway between Richer and Winnipeg also follow the original road. The road is especially well preserved in sections of Sandilands where in some boggy areas the original corduroy can still be found. ACKNOWLEDGEMENTS We would like to thank Graham Young and Ed Dobrzanski of the Manitoba Museum of Man and Nature for their analysis of the vertebrate bones from the Grunthal pit and their help in making the Sangamonian age assignment of the deposit. We would also like to thank David Riddle of Manitoba Historic Resources Branch for supplying the Dawson Trail map. Grant Ferguson of the Department of Engineering, University of Manitoba wrote the very eloquent description of the formation of the sapping channels for us. REFERENCES Higgins, Charles G. 1982. Piping and sapping: development of landforms by groundwater outflow. pp. 18-59. In: Groundwater as a Geomorphic Agent. R.G. LaFleur (ed.) 1982. Allen and Unwin, Inc. London, U.K. Kerr, D.G.G. 1975. Historical Atlas of Canada. Third revised edition. Thomas Nelson & Sons (Canada) Ltd. McAndrews, J.H. 1982. Holocene environment of a fossil bison from Kenora, Ontario. Ontario Archaeology, vol. 37, pp.41-51. Nielsen E., Churcher, C.S., and Lammers, G.E. 1988. A wolly mammoth (Proboscidea, Mammuthus primigenius) molar from the Hudson Bay Lowland of Manitoba. Canadian Journal of Earth Sciences, vol. 25, pp. 933-938. Thorleifson H. 1996. Review of Lake Agassiz History. In, Teller, J.T., Thorleifson, L.H., Matile, G. and Brisbin, W.C. eds. Sedimentology, geomorphology and history of the central Lake Agassiz basin. Geological Association of Canada Field Trip B2, 101p. 35 �36 �Field Trip 3 Structure and Sedimentology of the Seine Conglomerate, Mine Centre Area, Ontario Dyanna Czeck Department of Geology Oberlin College 52 W. Lorain Street Oberlin, OH 44074 Philip Fralick Department of Geology Lakehead University Thunder Bay, ON P7B 5E1 Moderately deformed Seine conglomerate containing metavolcanic and granitoid clasts, with clast tiling due to dextral deformation. Hwy 11, 1 km east of Horsecollar Junction. �FOREWORD This trip will examine sites related to the development and deformational history of a synorogenic sedimentary unit, the Seine Conglomerate. The unit extends across the Canada/ United States border in the Rainy Lake region, an area that has sparked interest and controversy for American and Canadian geologists for over a century. The Seine is of significant interest because it preserves important structural and sedimentological clues that may lead us to a better understanding of the tectonic history of the Archean Wabigoon-Quetico subprovincial boundary. REGIONAL SETTING Introduction and Tectonic Setting The central portion of the Superior province is characterized by alternating subprovinces of metavolcanic-plutonic and metasedimentary natures (Fig. 1). Figure 1. The Superior Province. From Card and Ciesielski (1986). One popular tectonic interpretation for the central portion of the Superior Province is of repeated island arc, microcontinent collisions. The collisions are evidenced by rocks that can be interpreted as arc sequence subprovinces (metavolcanics) and their corresponding accretionary prism subprovinces (metasediments) (Langford and Morin, 1976; Hoffman, 1989; Percival and 38 �39 Figure 2. Simplified Geologic Map of Mine Centre area showing the extent of the Seine. Geology compiled from Wood, 1980a & b, Stone, 1998a & b, and Czeck, 2001. �Williams, 1989; Card, 1990; Hoffman, 1990). In general, the ages in the greenstone belts are similar along strike, but differ systematically across strike (Hoffman, 1989). This is consistent with the island-arc accretion model. A history of southward accretion has been proposed to explain the juxtaposition of Superior Province terranes (Langford and Morin, 1976; Percival and Williams, 1989; Card, 1990). The Seine Conglomerate, located in the Rainy Lake region of the western Superior Province, was deposited along the boundary between the Wabigoon metavolcanic/plutonic subprovince and the Quetico metasedimentary subprovince (Fig. 2). The structural observations along the Wabigoon–Quetico boundary are consistent with an oblique island-arc microplate collision circa 2.7 Ga. In this part of the Superior Province, it seems likely that first the Quetico acted as a subduction prism during accretion of the Wawa to Wabigoon. Then, it was effectively shifted from the subduction prism setting to a back-arc setting, as subduction shifted (Percival and Williams, 1989). In the Rainy Lake region, a series of lithostratigraphic terranes were assembled together along structurally controlled, stratigraphically discordant boundaries during the collisions. The boundary between the Wabigoon and Quetico Subprovinces in this region is divided into three primary blocks by dextral wrench faults (Poulsen, 1986). Each of the small terranes and subterranes may have undergone a somewhat unique history of formation and deformation. The Quetico Fault forms the northern boundary, separating the granite-greenstone terrain of Wabigoon Subprovince from the Coutchiching Group argillites and the Seine Conglomerate. The Seine River-Rainy Lake Fault forms the southern boundary of these sedimentary sequences with the Quetico turbiditic metasediments to the south. The wedge-shaped area lying between the two major fault systems is itself dissected by splays off the major east-west faults, which isolate the lithic units, destroying stratigraphic integrity. This problem has resulted in historical speculation on the lateral equivalency of the Seine and Coutchiching sediments (Merritt, 1934) and the Coutchiching and Quetico (Lawson, 1913). Geochronology Davis et al (1989) used U-Pb, single zircon geochronology to bracket the ages of the Coutchiching and Seine between 2704+-3 to 2692+-2 and 2696+5-3 to 2686+2-1 respectively. Even though an overlap in age existed, Davis et al (1989) believed that structural considerations indicated that the Coutchiching is slightly older than the Seine. Further detrital zircon geochronology of the Seine was conducted by Davis and reported in Fralick and Davis (1999). Of the two samples analysed one was from the sandstone dominated lithofacies (collected near the Seine River bridge) and the other was from the conglomerate dominated lithofacies (collected near Horsecollar Junction on Highway 17). The detrital zircons in both samples give very consistent ages with the sandstone lithofacies clustering at 2693+-1 (Fig. 3) and the conglomerate lithofacies clustering at 2692+-1 (Fig. 4). These detrital zircon ages are similar to the Bear Pass pluton, a granitic mass which outcrops near the Seine 40 �Conglomerate (Fralick and Davis, 1999). Metamorphic titanite from the pluton gave an age of 2684+-5. Figure 3. Isochron showing U-Pb detrital zircon ages from the upper Seine Group (supplied by D. Davis). Figure 4. Isochron showing U-Pb detrital zircon ages from the lower Seine Group (supplied by D. Davis). Detrital zircons from the nearby Quetico and Coutchiching metasediments have an age distribution that is very different than that from the Seine Conglomerate. Their youngest ages are 2699+-1 for the Quetico and 2704+-3 for the Coutchiching with the population in both rock units extending back past 3000Ma. This is in sharp contrast to the Seine zircons which indicate 41 �dominance of a single source. This source may have evolved slightly through time as the age for the upper sandstone is slightly older than the lower conglomerate, though within error. This inverse age stratigraphy may reflect erosive unroofing of slightly older segments of the source igneous body. In any case, the Seine must be 2692 Ma, or younger, and its detritus was derived from a different source than the Quetico and Coutchiching (Fralick and Davis, 1999). The Bear Pass pluton is a good candidate for the source of the sediment except its zircons have lower Th/U ratios than the Seine. The Seine’s Th/U ratios of 0.74 to 1.07 are more typical of alkaline igneous rocks (Fralick and Davis, 1999). Alkaline igneous rocks 2692 Ma in age are present to the east of the area in the Shebandowan region. Metamorphic titanite in the Rice Bay Dome has given an age of 2693-+3 Ma , coeval with or predating the Seine (Davis et al,1989). The Bear Pass intrusion also predates the Seine and is late-tectonic, probably emplaced into the Rice Bay Dome after the Coutchiching turbidites had been overturned (Fralick and Davis, 1999). Thus, the Seine was deposited after an early period of folding and metamorphism. What can we learn from the Seine? The Rainy Lake region has been metamorphosed, generally to greenschist grade, and deformed in response to the Archean microplate collisions. Most of the preserved deformation is of a ductile nature, and thus occurred at significant depth. The Seine itself is metamorphosed and significantly deformed. From the geochronology and sedimentological evidence (to be described below), we know that the Seine was deposited in a dynamic convergent plate setting. From the significant flattening fabrics and structural evidence, we know that the Seine was subsequently buried and deformed at mid-crustal levels. Therefore, the Seine preserves a record of a conglomerate’s journey through the crust within a dynamic convergent zone. We can hope to interpret from the Seine a relatively late stage record of the microplate collision history at the Wabigoon- Quetico tectonic boundary through a history of syn-deformational deposition, burial, and deformation. Through analysis of the sedimentology, early structures, and late structures, we can hope to interpret various portions of the conglomerate’s path through the crust. SEDIMENTOLOGY OF THE SEINE The Seine Conglomerate was interpreted to have been deposited in a fluvial system by Wood (1980). This system undergoes a gradual transition from conglomerate dominated near its base to sandstone dominated near its top. Channels in the lower portion of the section are Scott type (Miall, 1978), with gravel and cobbles forming both longitudinal bars and interbar channels. Through cross-stratified, medium-grained sandstones, representing chute channels, commonly form small lenses in these sequences. The coarse-grained lithofacies association is transitional upwards into successions which contain thicker layers of trough cross-stratified sandstone. This represents a transition from gravelly main channels to channels dominated by the migration of sand dunes. With further fining upwards, the Formation becomes sandstone dominated. The sandstones are organized into stacked, trough cross-stratified lenses, with rarer large-scale, planar cross-stratified layers and conglomeratic horizons. This reflects development of a South Saskatchewan type braided river (Miall, 1978) with dune migration prevalent in the channels and only minor development of sandy transverse and gravelly longitudinal bars. To further clarify the 42 �relationship between the lithofacies present in the rocks and the environments in which the sediment was deposited, the remainder of this section will discuss the types of sediment deposited in the differing sub-environments of gravelly to sandy braided streams. Braided rivers are multichannel streams with large width to depth ratios that commonly develop in high slope areas, such as alluvial fans and proglacial outwash plains. This type of channel pattern is generally caused by a combination of factors which include: large diurnal and seasonal fluctuations in discharge; high slope, or a rapid increase in slope; high discharge velocities; the dominance of bedload sediment (sand and gravel) in transport; and, meagre vegetation on the floodplain. These factors result in the stream being easily able to erode its banks, spread out laterally and choke its channel with coarse sediment building midchannel islands. The channel morphology of braided rivers is characterised by a series of channels and bars which are occupied at various levels of discharge (Williams and Rust, 1969). During most of the year, with normal to low discharge, one, two or more channels will snake through the assemblage of bars. However, during peak discharge all the previously dry bars and minor channels will be overtopped and the river will develop only one large channel. Flood events, such as this, are the intervals when the coarsest sediment, generally composing the bars, but also flooring the channels in high energy systems, will move. Hammer and Smith (1983) found that bedload sediment transport increases at an exponential rate with river discharge. As the majority of coarse sediments are transported in bedload during high discharge events, with reduction in discharge the ability of the river to continue transporting this material down gradient is also reduced (Burton, 1989). At this point the largest material in transport stops moving. This produces a low velocity shadow downstream from the sedimented material where more detritus accumulates. This process leads to the formation of gravel bars, termed longitudinal bars, within the river channel. If the channel is in a relatively high slope area, the sand and finer material in transport will only be deposited if it is trapped or carried into the pores between the gravel and sedimented as matrix. Here, the main channel is pebble, cobble or boulder dominated with this detritus arranged into a stacked sequence of commonly irregular lenses. These lenses represent areas of scour and deposition on the bottom of a larger channel. Some gravel lenses may be formed by either migration of coarse-grained dunes or lateral fill into scour pits producing cross-stratification. In less energetic systems trough cross-stratified sand lenses will interbed with the gravel. This represents sand in bedload tractive transport as dunes being deposited and not re-eroded. Further reduction in energy levels of the system will eventually cause the main channel deposits to become a series of stacked, trough cross-stratified sandstone lenses. In braided streams carrying gravel, longitudinal bars will develop, splitting the flow at low stage (Figs. 5 & 6). These bars are lozenge-shaped mounds of pebbles, cobbles or boulders in clast support with a coarse-grained matrix. They are usually internally massive and nongraded, though occasionally parallel lamination is present. While the bars are submerged during maximum discharge events they are subjected to extremely turbulent flow, during which time they are modified by both erosion and deposition. Such processes result in the head of the bar being continually reworked producing a well sorted and coarser grained deposit (Burton, 1989). A significant decrease in velocity over the length of the bar results in a corresponding decrease in the size of material being deposited. 43 �Figure 5. Photograph of the North Saskatchewan River in Alberta. The main channel (A) is cutting around a longitudinal bar which grades from a coarse head (B) to a finer pebble tail with a veneer of darker coloured sand (C). The bar tail in the foreground also has darker sandy areas mantling it (C) and is cut by chute channels (D); one of which is building a chute delta (E). If main channel erosion was not occurring at F this would be the site of a bar edge sand wedge supplied by the nonconfined overbar flow. During waning flow, the bar tail will be shielded from the main current in the river as the bar top, in the center of the bar, begins to become emergent. This may cause a thin sand sheet, or patches of sand in lower areas, to be deposited over the bar tail. As the flow stage continues to drop small channels will sporadically develop cutting across the upper surface of the bar, from a main channel upstream to another main channel downstream. These are chute channels which commonly fill with trough cross-stratified sand produced by dunes migrating down the channels. They form sand lenses in the gravelly longitudinal bar. Where chute channels rejoin the main channel sediment may accumulate as a large avalanche face building out into the deeper main channel (chute delta). This produces a large-scale, planar cross-stratified sand or gravel deposit banked up against the side of the longitudinal bar. Similar, but laterally extensive, deposits can also be formed by unconfined sheet flow over the only slightly submerged surface of the bar. Again, where this flow enters the deeper main channel a large-scale, planar cross-stratified wedge of sediment will be banked up against the bar. This is called a bar edge sand wedge (Figs. 5 & 6). All of the above may be present in sand dominated braided systems, but the longitudinal bars will be subordinate and may be absent. The main bar forms in these systems are transverse bars. These are large sand waves, features similar to continuous crested, long wavelength dunes. 44 �Figure 6. Block diagram of a coarse-grained braided stream schematically showing: coarse bar head (A); finer bar trail with thin sand patches which accumulate in areas shielded from the current during waning flow (B); chute channel with dunes (C); chute delta (D); bar edge sand wedge (E); and main channel with dunes (F). Gravelly braided stream deposits similar to these dominate the lower Seine Conglomerate. Figure 7. Block diagram of a sand dominated braided stream schematically showing: the main channel with dune migration producing trough cross-stratification (A); transverse bar migration and stacking producing sandflats which are internally planar cross-stratified (B); minor (to no) development of gravelly longitudinal bars (C). Sandy braided stream deposits, and especially the main channel facies, dominate the upper Seine Conglomerate. Where they are abundant they will pile up next to one another clogging the channel with sand and producing large areas of sand flats (Smith, 1970; Miall, 1985) (Fig. 7). Internally, they are composed of large-scale (commonly>1m thick sets), planar cross-stratification. Transverse bars are quite laterally continuous and are interbedded with other large-scale, planar cross-stratified sand units, in sand flats (downstream accretion macroforms of Miall, 1988), or successions of smaller lenses of trough cross-stratified sand, representing dune migration on the channel floor 45 �(Fig. 7). The transverse bars are mostly active during higher discharge. During low discharge, their tops may become emergent and eroded, and dunes mantle their surface. The next flood event will often result in the bar building in a somewhat different direction. This will result in an apparent change in the angle of the cross-stratification (a reactivation surface). This sloping surface may also show evidence of erosion and contain small lenses of trough crossstratification. This completes the general overview of sediment deposits associated with channel sequences in braided streams. Floodplain lithofacies are usually minor to nonexistent in these successions as the fine grained deposits have little preservation potential. Braided streams commonly avulse, changing the position of their channel and combing the floodplain, eroding the fine-grained deposits and forming stacked channel sequences. The Seine Conglomerate contains lithofacies corresponding to all of the channel subenvironments discussed above. Conglomerate dominated longitudinal bar-channel sequences are the most common in outcrop. However, sandier channel sequences are not rare and gain importance higher in the Formation. STRUCTURAL GEOLOGY Deformed primary fabrics Bedding is often difficult to discern in the Seine. Where it can be identified, it is displayed by variations in grain sizes, often indicated by fine-grained layers interbedded with pebble conglomerates. In some cases, cross bedding can be seen within larger sandy layers. In general, bedding strikes approximately east – west, and is subvertical (Fig. 8). This orientation is similar to bedding attitudes measured throughout much of the Superior Province (Poulsen, 1986; Hudleston et al., 1988; Bauer and Bidwell, 1990; Tabor and Hudleston, 1991; Bauer et al., 1992; Jirsa et al., 1992; Bauer and Hudleston, 1995; Hudleston and Bauer, 1995). Bedding is generally subvertical and subparallel regardless of lithology. However, this fact does not necessarily indicate deformation of a continuous stratigraphic sequence. Based on opposing stratigraphic facing in adjacent rocks, an unconformity between the volcanic units and the base of the Seine conglomerate can be identified (Stop 1) (Lawson, 1913; Poulsen et al., 1980; Poulsen, 2000). There are some exceptions to the general EW, vertical bedding orientation. In the area along Shoal Lake (Stop 1), the bedding strikes more NE/ SW with a shallower (~65°) southeasterly dip. The orientations of the bedding within the Shoal Lake area and adjacent rocks to the north and south combine to create a large, gentle S structure, with shallower dips on the middle section of the S. Several folds on the scale of hundreds of meters have been identified within the Seine metasediments based on stratigraphic facing (scour beds and cross-beds) and lithologic similarity (Hsu, 1971; Wood et al., 1980a; Wood et al., 1980b; Poulsen, 2000). These folds have vertical limbs and are typically upright and isoclinal. The trends of the hinges are roughly parallel to the foliation (EW). The plunges of the hinges are unknown, and cannot be constructed due to the subparallelism of the limbs. In a few locations (see Stop 5), one can see small scale folds that may display horizontal bedding at the hinges. 46 �Figure 8. Equal area stereonets showing structural fabric data near Mine Centre, Ontario. A) Poles to bedding. 46 measurements. B) Poles to foliation. 142 measurements. C) Mineral lineations. 123 measurements. D) Intersections between foliation (cleavage) and bedding. 44 measurements. From Czeck (2001). Ductile deformation Ductile deformation (as evidenced by rocks with pronounced foliations and mineral lineations) is pervasive throughout the entire Wabigoon–Quetico boundary zone. The overall dominance of the foliation over the lineation creates an S-L type fabric. However, strain is also localized into an anastomosing network of more discrete shear zones, including two main zones of localized shear and displacement. These are the Seine River - Rainy Lake Fault and the Quetico Fault, which diverge to the west and merge to the east (Fig. 2). An anastomosing pattern of smaller shear zones links the major shear zones shown in anastomosing, gentle S-like shapes (Fig. 9). The locations of these smaller shear zones have been determined by linear features observed on electromagnetic anomaly maps or are identified as the discordant boundaries of apparently independent lithostratigraphic terranes (Poulsen, 1986; Poulsen, 2000). Direct observation of these smaller shear zones is difficult because they are typically under water or buried beneath recent sedimentary deposits and not exposed, presumably because they are highly erodable. The presence of discrete shear zones implies some strain partitioning between shortening and wrench components of ductile deformation along the Wabigoon–Quetico boundary. It is probable that the discrete shear zones are zones with relatively high wrench influence. Conversely, it is probable that the wide zones of deformation between the shear zones have undergone deformation with a stronger shortening influence. In some instances, small (on the order of a few meters), secondary shear zones may be seen. 47 �Figure 9. Schematic diagram illustrating structural features of Rainy Lake Wrench Zone. Short solid arrows identify downward facing units. From Poulsen (1986). Foliation is moderately to well developed in all rocks of the region, with the exception of some late stage plutons. It is especially well developed along the major shear zones and the Seine River – Rainy Lake and Quetico Faults. The foliations are largely subvertical and at a low angle both to bedding (except in the hinge of folds) and to the subprovince boundary (Fig. 8). An exception to the subvertical foliation is in the area along Shoal Lake (Stop 1). Here, like the bedding, the foliation strikes more NE/ SW with a shallower dip (~65°). Like the bedding, the combined orientations of the foliations within this Shoal Lake area and adjacent rocks to the north and south create a large, gentle S structure, with shallower dips on the middle section of the S. Unlike the bedding, the cleavage is not folded by the major upright folds. It is, however, affected locally by crenulations. In general, there is no consistently oriented intersection lineation between bedding and foliation throughout the Seine. Instead, this lineation defines a great circle corresponding roughly to the planes of foliation and bedding. This is to be expected in the situation in which bedding and foliation are subparallel because slight variations in orientation of the two planar features will have a significant effect on the orientation of the intersection lineation. Typically, chlorite or amphibole forms a mineral lineation, which varies in intensity from weak to strong depending on location. The lineation plunge is highly variable across the Wabigoon– Quetico boundary without any clear systematic change from east to west or from north to south, although there are local domains of similar lineation plunge (Czeck, 2001). The highest concentrations of lineation orientations plunge steeply to the east, and their mean orientation is 66°/076. However, there are also significant numbers of westward and shallowly plunging lineations. The range of lineation orientations is great enough that the “average lineation” may have little geologic meaning. 48 �The lineation referred to thus far is the mineral lineation, a lineation due to the preferred alignment of mineral grains or clusters of grains. This lineation is present in most rock types along the Wabigoon–Quetico boundary. Within the Seine conglomerate, there are, in fact, two distinct linear elements that can be measured independently: the mineral lineation and that defined by the long axes of the conglomerate clasts. Both can be considered penetrative features of the rock fabric. The long axes of clasts within the conglomerate are generally coincident with the mineral lineation as would be expected if the conglomerate clasts were an accurate recorder of strain and the mineral lineation reflects the stretching direction Relatively late-stage sinistral and dextral crenulations locally affect the cleavage. These crenulations are fairly small (usually cm scale). They are most abundant in the most highly sheared rocks. This correlation and the relative timing of the crenulations makes it seem likely that they formed during the latest stage of a continuing saga of transpression. Features of deformed conglomerates The Seine Group provides an excellent opportunity to observe the effects of competency contrasts on deformation. These natural competency contrasts allow us to obtain structural information that is unavailable in more homogeneous rocks, making the conglomerates are excellent tools for structural analysis and tectonic interpretations. Within the conglomerates, asymmetric shear sense indicators are prevalent. In general, these are either in the form of asymmetric pressure shadows at the ends of clasts, wrapped foliation indicating rotation of the most rigid clasts, and clast tiling. All of these shear-sense indicators are most evident on the subhorizontal plane, regardless of lineation orientation. They indicate dextral sense of shear. In general, the conglomerate clasts have been strongly flattened, although the degree of flattening is strongly dependent on lithology. The intensity of flattening strain varies greatly through the field area. We will be viewing several degrees of deformation on the various stops of the fieldtrip. TECTONIC STORY OF THE SEINE METASEDIMENTARY SEQUENCE AND SURROUNDING ROCKS Plate Collisions and Sediment Deposition Comparing the zircon populations of sedimentary units in the Rainy River area with other rock groups in the region generates some interesting trends. The zircon populations of turbidites and conglomerates on the northern margin of Wabigoon Subprovince ( Savant Group and Ament Bay Formation) exhibit similarities with the Coutchiching metasediments (Davis, 1997). The conglomeratic units near the northern margin of Wabigoon Subprovince represent braided fluvial systems (Turner and Walker, 1973; Devaney, 1999). The sediments they were transporting were deposited in the same time bracket (Davis et al, 1988) as some of the sedimentary units near Rainy Lake. If the sedimentary units in the Rainy Lake area represent detritus shed off of upraised blocks during collision-orogeny, as appears to be the case (Davis et al, 1989), 49 �Figure 10. Interpretive sketches showing subduction and plate convergence along the southern margin of Wabigoon Subprovince. The accretionary prism built at 2700 Ma of trench turbidites is represented by the Quetico. Northward subduction in the Schreiber and Shebandowan areas ceased at approximately 2720 Ma, but restarted in the Shebandowan area at 2692 as immanent collision ceased subduction in the Quetico trench. After collision of the Wawa-Abitibi terrain with the Quetico-Wabigoon assemblage, orogenic uplift affected the area. During this interval small basins opened on both sides of the suture zone and accumulated coarse fluvial deposits including the Seine Conglomerate. understanding the sequencing of sedimentary pulses is key to deciphering the tectonic forces which formed the Seine Basin and uplifted its source area. To understand this sequencing, it is necessary to outline the tectonic history of the region, and the sedimentary response to tectonism, from 2720 Ma to 2685 Ma. Sedimentary sequences deposited between 2720 and 2685 Ma in, and adjacent to, Wabigoon Subprovince record the final phases of subduction and collision of this area with landmasses to the north and south. Examined basin fill sequences are divisible into three depositional systems tracts. Sediments in the Beardmore-Geraldton area record progradation of braided streams and fan/braid delta complexes from a volcanically active area to the north (Devaney and Fralick, 1985; Devaney, 1987; Devaney and Williams, 1989). The outbuilding sequence fed detritus to a poorly structured, turbidite ramp/fan assemblage in the forearc basin (Barrett and Fralick, 1989), from which it was rerouted into the Quetico trench, via multiple channel systems (Fralick et al., 1992) (Fig. 10). Sediment geochemistry confirms that the calc-alkaline volcanic rocks present in the Onaman-Tashota area, to the immediate north of the forearc basin, were the source of the sediment (Fralick and Kronberg, 1997). Lower Zr and Y values in sandstones from this area compared to analyses of rocks from the western trench (data from Sawyer, 1986) indicate less involvement of older felsic crust as a sediment source. Zircon geochronology (data from D. Davis) demonstrates that the northern Quetico trench received sediment between approximately 50 �2705-2699 Ma, whereas the forearc basic continued to accumulate sediment until at least 2696 Ma. No zircons older that 2828 were found in these sequences. In contrast the zircon population of samples from the western Quetico (Davis et al., 1990) (Fig. 10) contains both 2900 and 3000 Ma zircons, indicating the erosion of older tonalites in this area. A sedimentary assemblage present to the east of Terrace Bay, in Wawa Subprovince, contains a poorly structured turbidite succession which correlates as the distal equivalent of the Quetico trench deposits (Purdon, 1995) (Fig. 10). The geochemistry of these rocks is very similar to the trench and forearc assemblages to their north, with lower Zr and Y than the trench sandstones to the west. Their geochemistry does not match local sources in the Hemlo and Winston Lake areas. Detrital zircon geochronology matches the Quetico trench sediments to the north, with the exceptions that the main zircon population, which probably reflects age of deposition, is 3 Ma younger, and the sandstones contain a 2900 Ma population. Similar turbidites are present in two other areas of the northern Wawa Subprovince; Shebandowan and Manitouwadge. At the former they are younger than 2700 Ma (F. Corfu, pers. comm.), and at the latter they are younger than 2692 Ma (E. Zaleski, pers. comm.). In the Shebandowan belt, the turbidites are succeeded by a 2692 Ma (Corfu and Stott, 1986), high-Na volcanic assemblage interlayered with near-shore, moderate-to high-slope marine deposits. These are in turn succeeded by <2686 Ma (Corfu and Stott, 1998) braided stream conglomerates eroding crystalline basement. This depositional system tract records 2709-2693 calc-alkaline arc volcanism on the southern margin of Wabigoon Subprovince and its erosion and transport to the Beardmore-Geraldton forearc basin and Quetico trench at approximately 2700 Ma. A trench-full state developed at approximately 2696 Ma and the sediment apron expanded to the south covering tholeiitic basalts and a starved clastic-chemical sequence in the area east of Terrace Bay. Similar sequences in Shebandowan and Manitouwadge probably represent overflow in these areas as well. Diachronous overflow younging to the east suggests oblique closure of the arcs comprising northern Wawa Subprovince with the Quetico trench. Deep-marine sediments and volcanic assemblages in the Shebandowan area were upraised at 2692 Ma to surface levels, while deepmarine sedimentation continued in the Manitouwadge area, further indicating west-side-first scissor closure. The second tract encompasses the English River Subprovince and Warclub Group, on the northern margin of Wabigoon Subprovince. The depositional systems which formed these two units were very similar. They are both primarily composed of unstructured medial to distal turbidite assemblages. The Warclub Group thickens and coarsens upward from a 10m thick basal zone composed of a starved slate-chert assemblage that overlies mafic volcanics. Near its top, minor interbedding with ashes of the Berry River Volcanics occurs. It is sharply overlain by the volcanic unit, which is mostly composed of grainflows of felsic volcanic detritus. The Warclub Group is laterally continuous to the east of Dryden, but does not lithically correlate with sediments in the Minnitaki Lake area. Zircon geochronological patterns (Davis, 1995) for the Warclub Group and English River sediments exhibit a variety of ages. This is in contrast to patterns for sediments on the southern margin of Wabigoon Subprovince, which show a clustering of young ages, and indicates that syndepositional volcanism was not an important sediment source. The youngest detrital zircon age determination for the Warclub Group is 2716 Ma (Davis, 1995), which is in agreement with its stratigraphic position below the 2712 Ma Berry 51 �River Volcanics (Davis, 1995). Volcanics interbedded with the Warclub Group near Vermilion Bay give an age of 2716 Ma (Davis, 1995). The youngest detrital zircon present in the English River assemblage is 2705 Ma (Davis, 1995). Turbidites of the English River Subprovince and the Warclub Group accumulated in a deep water setting; in the case of the latter, accumulation occurred directly on a mafic assemblage. The turbidites fed from the erosion of local rocks which were upraised, probably tectonically. Deposition of the Warclub Group ceased at 2712 Ma when a felsic volcanic episode effected its basin. English River sediments continued to accumulate until at least 2705 Ma (Davis, 1995). The Warclub Group was most likely deposited in a remnant ocean basin between the Wabigoon and Winnipeg River landmasses. The English River sediments may represent either a remnant ocean basin or a classical trench. The third depositional systems tract includes the Abram, Minnitaki, Savant, Sturgeon and Conglomerate Lake Groups, and possibly the Crowduck and White Partridge Bay Groups. These sedimentary sequences represent high-slope, fan delta deposits fed into an east-west linear trough which developed south of the north margin of Wabigoon Subprovince. Basal units are dominated by erosion products from the immediately adjacent, underlying lithologies. There is a rapid upward increase in the amount of felsic volcanic detritus, with some sequences almost entirely composed of this material. Reworked sedimentary clasts, representing all fan delta lithofacies, are important constituents of some sequences. Ages of youngest zircons are variable, ranging from post 2707 Ma (Stott and Davis, 1999) for Conglomerate Lake (probably depositional age) to 2699 Ma for Crowduck Lake (D. Davis, pers. comm.). Zircon populations are varied, indicating erosion of older units rather than penecontemporaneous volcanism. The basin system represents proximal foreland basin deposits which were overridden by thrust sheets. Multiple periods of thrusting are indicated by cannibalism, and variation in youngest zircon ages. The Conglomerate Lake assemblage was deposited between 2703 and 2709 Ma; the basal Savant Group at 2704 Ma (Davis, 1995). These ages are similar to ages for cessation of sedimentation in the English River assemblage, and indicate foreland thrusting may be linked to closure of the English River oceanic system. The three depositional systems tracts are interrelated due to the controlling tectonic processes. Closure of the Warclub remnant ocean initiated development of a foreland thrust belt on the northern margin of Wabigoon Subprovince. During the same period, extensive calc-alkaline volcanism commenced on the southern margin of the subprovince, with commencement of north directed subduction, and fed a systems tract which delivered sediment to two other subprovinces. Probably oblique closure of Wawa arc systems terminated the southern depositional system at 2692 Ma in the west, and resulted in upraising of deep-water environments to shallow depths. By 2686 Ma oceanic deposits, which had formed only 14Ma previously, were being eroded by streams draining the Wawa-Quetico-Wabigoon collision zone. The depositional environment of the Coutchiching turbidites is consistent with a source-distal, off fan or braid delta setting. Its sedimentology is also consistent with a distal Quetico ramp setting but its position on the northern, source-proximal basin margin makes this scenario unlikely. The Coutchiching most likely was deposited as a submarine apron to the south of fandeltas fed by thrust-faulting on the northern margin of the Wabigoon subprovince. The age 52 �distribution of zircons from the Coutchiching Group (Davis et al., 1989) is similar to that of coarse-grained metasedimentary sequences present on the northern boundary of the Wabigoon subprovince, all of which have youngest detrital zircons of 2704 Ma, a few m.y. earlier than the Quetico (Davis 1995, Davis 1990). None of these metasediments show the concentration of ages less than 2710 Ma that is characteristic of the Quetico metasediments, suggesting that they are slightly earlier. The Seine Conglomerate represents the youngest pulse of sedimentation in the evolving collision zone between the Wawa-Abitibi oceanic volcanics, the Quetico trench sediments and the Wabigoon craton. The west side first, scissor closure of the Wawa-Abitibi terrain with the Wabigoon resulted in compression and metamorphism in the Rainy Lake area at 2692 Ma while the Shebandowan area 200 km to the east was just starting to be uplifted and the Manitouwadge area 500km to the east still had an active trench system and subducting ocean floor. Scissor closures such as this denote oblique collision or collision of a promontory. In either circumstance, transpression, or partitioning of oblique deformation into boundary-parallel (wrench) and boundary-perpendicular components (folding or thrust faulting) is likely to result (e. g. Harland, 1971). As blocks slide past one another in wrench settings, strike-slip basins can form as dilation zones open at fault curves, terminations with stepovers, or extensional duplexes. Small rifts can also open due to lateral terrain escape from the compression zone. There are several late-stage conglomerates similar to the Seine in the Superior Province, many bearing a striking resemblance to one another. They are known as Timiskaming type conglomerates (e. g. Pettijohn, 1943). Based on sedimentological evidence, including the large clast size, relative rarity of cross-bedding in quartzites, and the predominance of relatively immature graywackes interbedded with the conglomerates, Timiskaming type conglomerates have long been recognized as forming in a dynamic, tectonic environment (Pettijohn, 1943). Specifically, researchers have concluded that the conglomerates may have formed synkinematically, possibly in wrench related basins (Poulsen, 1986; Poulsen, 2000). This conclusion is based on the fact that, like the Seine Group conglomerates, other Timiskaming type conglomerates are often found along major wrench zones within the Superior Province. Detailed provenance studies of Timiskaming-type conglomerates have supported the wrench basin interpretation, in that source areas have been located both north and south of the deposition area (Legault and Hattori, 1994). Thus, due to the scissor-closure interpreted from the Seine clasts’ provenance and the association of the Seine and other Timiskaming type conglomerates with major wrench zones, it may be appropriate to compare the early structures and stratigraphy in the Seine group to those of more modern strike-slip basins. The aerially limited basin into which the Seine was deposited most likely opened due to some wrench-related process, while the general compression in the area upthrust a possibly yoked source terrain. Plate collisions and Deformation In general, the rocks at this boundary show a history of upper crustal stacking and wrenching followed by ductile transpression. The stacking is evidenced by significant amounts of upright bedding and early folds. As deformation continued and rock units became buried, ductile deformation became dominant. This part of the deformation sequence created the dominant S-L 53 �fabrics and was responsible for most of the strain in the rocks. Continued ductile transpression resulted in late-stage crenulations and kinks in the foliation fabric. There is some evidence for minor, brittle structures that formed during the waning moments of deformation. Along the Wabigoon- Quetico boundary, there are two general deformational phases of collision evidenced by the structural field observations. Note that the distinction of two deformational phases is NOT meant to imply that there were two stages of collision, but only that the structural style evolved during the collisional history. The first phase can be interpreted to have included shortening or stacking of strata, frequently coinciding with boundary-parallel motion, in the upper crust. After the first phase and corresponding crustal thickening, the second phase of deformation that created the dominant structural fabric is interpreted to have involved deeper, ductile transpression. The structures preserved in the Seine and surrounding rocks are a result of both their upper-crustal and deeper level deformation. Structural Evidence of the Tectonic Nature of the Seine Basin The sedimentological evidence supports the interpretation that the Seine Group was deposited in a dynamic, tectonic environment. The structural evidence supports this conclusion as well. The Seine is the latest of supracrustal rocks to have been deposited at the Wabigoon–Quetico boundary (Poulsen et al., 1980; Davis et al., 1989; Fralick and Davis, 1999). Despite not containing as many folds as its neighboring rock units, the Seine has also undergone deformation that caused the bedding to become vertical. Even though both the Seine and its neighboring rock units are vertically oriented, the reversal in stratigraphic facing between the base of the Seine and the directly adjacent volcanic units (Lawson, 1913; Poulsen et al., 1980; Poulsen, 2000) implies that the earlier strata were tilted, at least in part, prior to Seine group deposition. Therefore, it can be interpreted that the early stacking deformation began before and endured during deposition of the Seine. Thus the Seine group was deposited in a dynamic, tectonic environment, most likely in a basin formed through strike-slip faulting processes that would be expected at an obliquely convergent margin. The specific type of strike-slip basin (pull-apart, duplex related, fault splay, …) in which the Seine was deposited remains unclear. However, the geometries of the structures within the Seine Group may provide clues as to the nature of this basin. The dominant vertical nature of the bedding implies that the bedding was probably tilted during the first, upper-crustal stage of deformation by some means (folding, faulting, or both). The few relict folds within the Seine suggest that at least part of the basin was undergoing shortening during basin evolution. This observation leads to the conclusion that the basin was most likely not a simple extensional pullapart basin (Poulsen, 1986), but rather some other type of wrench-related basin that contained significant areas undergoing shortening during its formation. If we assume that shear zones form in relatively weaker zones of rocks, the present–day location and orientations of the bounding ductile shear zones may be indicative of the earlier brittle faults. If we follow this logic, the gentle S-shapes of the bounding faults suggest a restraining bend rather than a releasing bend in a dextral strike-slip regime (Fig. 11). This type of restraining bend would likely be associated with thrusting, overturned folding, and localized areas of subsidence and sediment accumulation (Christie-Blick and Biddle, 1985). This scenario seems 54 �Figure 11. A) Bends in dextral strike-slip fault resulting in either a restraining bend and corresponding thrust faults, overturned folds, and sediment accumulation or a releasing bend and the corresponding normal faulting and pull apart basin. Based on Christie-Blick and Biddle, 1985. B) Possible basin that may have formed if Quetico Fault to the north had relatively more displacement than the Seine River - Rainy Lake Fault to the south. likely for the Seine basin. Alternatively, one could imagine that both the southern Seine RiverRainy Lake Fault and the northern Quetico Fault were active master-faults and the secondary features (now seen as secondary shear zones) were insignificant in the early history (Fig. 11b). In this scenario, one might expect a basin to form at the fault intersection if the displacement on the Quetico Fault was significantly more than the displacement along the Seine River-Rainy Lake Fault. Alternatively, it is possible, given the scarcity of folds within the Seine, that the Seine could have been deposited in a pull-apart basin; however, this would require that the sense of motion along the faults was sinistral rather than dextral during this early history. There is no evidence for such a change in sense of fault motion, but a switch in motion sense would be possible given that such evidence would likely have been later obliterated by the dominant ductile fabrics. A change in fault sense would require a change in plate motion or the geometry of the boundary. Given the above three scenarios, it may not be possible to prove any one of them, but it seems that the first scenario, that of a basin forming at a restraining bend, is most likely. The original nappe-like nature of the folds and the likelihood of thrusting (see below) support this scenario. Evidence of Upper Crustal (Brittle) Deformation: Upright bedding as a result of “Stacking” The major piece of evidence for the first phase of deformation is the ubiquitous steep bedding. One might consider two structural end-members, folding and faulting, that could cause the subvertical tilting of strata. After folding, one would expect to see repetition of stratigraphy and opposing stratigraphic facing directions in adjacent strata. Even in areas with upright, isoclinal folds, one might also expect to see some areas with horizontal bedding corresponding to the fold hinges. After faulting, one would also expect to see repetition of stratigraphy, but not necessarily reversals in stratigraphic facing directions. Within the Seine and surrounding regions, it seems likely that the tilting of bedding was achieved, to some degree, through both faulting and folding, a combination referred to here as “stacking” (Czeck, 2001). 55 �There is significant evidence for folding throughout the Superior Province in general and the Wabigoon–Quetico boundary in particular. Evidence for folding includes visible hinges of some folds and opposing directions of stratigraphic facing (Hooper and Ojakangas, 1971; Bauer, 1985; Poulsen, 1986; Hudleston et al., 1988; Bauer and Bidwell, 1990; Tabor and Hudleston, 1991; Bauer et al., 1992; Jirsa et al., 1992; Bauer and Hudleston, 1995; Hudleston and Bauer, 1995). Several large, upright and isoclinal folds have been identified within the Seine metasediments based on stratigraphic facing (scour beds and cross-beds) and lithologic similarity (Hsu, 1971; Wood et al., 1980a; Wood et al., 1980b; Poulsen, 2000). The present–day upright orientation of folds is consistent with either originally nappe-like or more upright folds. In either case, the second phase of deformation, bulk ductile transpression, would have the effect of rotating the fold limbs from steep to subvertical orientations. However, the combination of several observations including the present-day juxtaposition of adjacent right-way-up and overturned folds (Poulsen et al., 1980; Borradaile, 1982; Poulsen, 2000), suggest that the original orientations of many of the folds were nappe-like. There is less direct evidence for thrusting, due to a general lack of sedimentary markers that would enable one to recognize duplicated sequences of rock. Instead, the most convincing pieces of evidence for the existence of faults are observations that suggest that all of the vertical bedding could not be a consequence of folding alone. First, within the Seine metasedimentary sequence, folds are much less evident than those reported in other areas, but the dominance of vertical bedding is still the rule. Second, unlike in rocks faulted by brittle mechanisms, folded rocks often leave a record of strain. It has been shown in some areas within the Superior Province that after “unstraining” the folded component of the preserved strain, the strata are still dipping vertically (Schultz-Ela, 1988). Thus, folding alone is insufficient to account for the vertical bedding. The lack of evidence for faults may indicate that stacking occurred entirely by folding. However, it is also true that if thrust faults were originally present, one would not expect to see evidence of them, other than tilted bedding, after the major fabric-forming deformation (phase 2) took place. Thus, it may be impossible to conclusively determine to what degree the initial stacking event consisted of folds or thrusts. If modern arcs are a suitable analogy to describe the tectonics of the Wabigoon–Quetico boundary, we may consider that while both folding and faulting play a role, faulting appears to be the dominant process at modern arcs (Karig et al., 1979; Karig et al., 1980). Thus, in all likelihood, both thrusts and folds were operational during the stacking phase of deformation at the Wabigoon–Quetico boundary, and it is possible that faulting, although not directly evident, was the dominant process. The relative contributions of faulting and folding to the overall structure may not be equivalent across granite-greenstone terranes, nor even across different portions of the same boundary, such as the Wabigoon–Quetico subprovince boundary. Lack of key exposures and a detailed stratigraphic framework, allied with obfuscation caused by overprinting fabrics from the second phase of deformation, may make it difficult to ascertain the relative contributions of folding and faulting. The term “transpression” was first introduced by Harland (1971) to describe obliquely convergent motion between two crustal blocks, or motion partitioned into convergent and strikeslip components. Harland, in his original analogue experiments, demonstrated this type of partitioning by generating folds within a deforming medium bounded by two rigid obliquely 56 �convergent plates. In an analogous region of deforming rocks, oblique plate collision may partition motion into strike-slip zones parallel to the boundary and folds and thrusts whose strikes rotate during deformation. The probable contemporaneous history of convergence and strike-slip motions along the Wabigoon–Quetico boundary, as manifested by both faulting/folding (stacking) and wrenching, suggests that Harland-type transpression may have been occurring during the stacking phase of deformation. At least this is likely during the stacking phase that occurred contemporaneously with Seine Group deposition. It should be noted that the “stacking” in the Seine may or may not be contemporaneous with any of the “stacking” record within adjacent lithologic domains, even within the Quetico and Seine River - Rainy Lake fault-bounded wedge. In fact, the opposite facing directions found between the Seine and a directly adjacent volcanic unit within the wedge reinforces the idea that at least some of the stacking in adjacent units occurred prior to Seine deposition. Deeper Ductile deformation: Homogeneous Transpression with Variable Extrusion The second phase of deformation formed the dominant structural fabric in the Seine. It formed the penetrative foliation and lineation fabrics, as well as most of the recorded strain. Figure 12. Idealized transpression model according to Sanderson and Marchini (1984) In general, the foliation is subvertical, and the individual clasts within the Seine conglomerates display a flattening fabric with a subvertical plane of flattening. On subhorizontal planes, the clasts commonly form dextral shear sense indicators, regardless of lineation orientation. Most of these fabric features along the boundary are consistent with a type of ductile transpression first described by Sanderson and Marchini (1984). Sanderson and Marchini (1984) provided a mathematical description of a specialized case of transpression: homogeneous deformation consisting of orthogonal simple shear and pure shear components (Fig. 12). In addition to these two components, their model involves constant volume and confines deformation to a vertically bounded zone. Such an idealized scenario is, perhaps, most likely to correspond to strain in deep, vertical ductile shear zones during oblique convergence. The structural fabrics for this model were predicted by Fossen and Tikoff (1993) and are summarized in Fig. 13. The consistencies of fabrics observed along the Wabigoon–Quetico boundary with the homogeneous transpression model suggest that at least the Wabigoon–Quetico boundary as a whole has undergone quasi homogeneous transpression. 57 �Fig. 13. Generalized transpression. Strain (simple shear and pure shear components) and fabrics (foliation, lineation, conglomerate clast asymmetry) based on Sanderson and Marchini (1984) and Fossen and Tikoff (1993). The front and back sides of the boxes are parallel to the deformation zone boundaries. The mineral fabrics are shown in the general case with fabric oblique to the deformation zone boundaries. As strain accumulates, the foliation becomes progressively closer to subparallel with the deformation zone boundaries. Ellipses (some with “tails”) represent schematic clast traces on each plane. Based on Czeck (2001). Significantly, the mineral lineations along the Wabigoon–Quetico boundary are neither vertical nor horizontal, as predicted by the Sanderson and Marchini (1984) transpression model; they plunge between 0-90° in both east and west directions (Fig. 8). The most likely way to create variable obliquely plunging lineations of this type is through a combination of Sanderson and Marchini style transpression with nonvertical extrusion (Fig. 14) (Czeck, 2001). In the original Fig. 14. Schematic view of strain and deformation fabrics for monoclinic transpression with nonvertical extrusion. Light colored ellipses represent schematic clast traces on each plane. (a) Simple view of transpression with nonvertical extrusion. (b) Schematic view of transpression with overall bulk vertical extrusion and localized zones of nonvertical extrusion. Dark colored ellipses represent schematic "hard" zones that influence local extrusion directions. The relative location of Fig. 8a is indicated. Based on Czeck (2001). 58 �Sanderson and Marchini style transpression and subsequent models (Sanderson and Marchini, 1984; Fossen and Tikoff, 1993; Robin and Cruden, 1994; Dutton, 1997; Jones and Holdsworth, 1998; Lin et al., 1998), extrusion of material was assumed to be vertically upwards. This assumption is logical because, in general, one would expect the direction towards the earth’s surface to provide the least resistance for material movement. However, rocks at depth may have other boundary conditions that cause local pressure gradients to deviate from this first-order assumption. For many reasons, such as the anastomosing of shear zones and influences of large lithologically diverse bodies, the local pressure gradients at depth may cause rocks to extrude in nonvertical directions. Given this model, the large range of lineation orientations in the Seine is not surprising considering the lithologically diverse nature of the subprovince boundary and the intricately anastomosing shear zones. As noted by some authors (e. g. Bauer et al., 1992), there may be a final stage of deformation involving amplification of strike-slip motion along wrench zones. This late stage of deformation has often been described as brittle in nature, and thus represents rock exhumation. The presence of brittle faulting of dextral strike-slip motion without contemporaneous thrusting (Kennedy, 1984), may suggest that the latest stage of deformation was almost entirely strike-slip. However, some late-stage brittle faults associated with N-S shortening have been observed (Tabor and Hudleston, 1991). There may also have been an amplification of shortening between the major strike-slip faults, thus creating a more discretely partitioned deformation toward the end of the tectonic history (Tabor and Hudleston, 1991). Evolution of tectonic styles The stacking and the homogeneous transpression most likely developed as an evolution of structural styles during different stages of the same oblique collisional event. The presently exposed rocks undoubtedly underwent a voyage through different zones in the crust as evidenced by their deposition at the surface and ductile deformation at some depth. This gradual change in position within the crust is probably responsible for the observed evolution in deformation styles. It is important to note that the two phases of deformation described here are similar to the commonly discussed “D1” and “D2” described throughout the Superior Province. While specific structural details are different, the general trend of folds overprinted by intense ductile flattening fabrics is common (Poulsen, 1986; Hudleston et al., 1988; Bauer and Bidwell, 1990; Tabor and Hudleston, 1991; Bauer et al., 1992; Jirsa et al., 1992; Bauer and Hudleston, 1995; Hudleston and Bauer, 1995). Locally, rocks at all the Superior Province microplate boundaries may have undergone the same general story of tectonic stacking and wrenching in the upper crust followed by crustal thickening and ductile transpressive flattening as the rocks were deformed at deeper levels. While this general story may be similar, it is important to consider that the regional or even local correlation of these “D1” and “D2” events is probably inappropriate. While the Seine metasedimentary group was forming in a wrench-related basin and surrounding rocks were being stacked, other rocks- even those located along the same microplate boundary or even within the same fault-bounded wedge- may have already reached a deeper level of the crust and began a more ductile, homogeneous phase of transpression. Thus, it is dangerous to correlate exact styles of deformation (e.g. folds) in the Seine with those in either of the adjacent Wabigoon or Quetico subprovinces. 59 �FIELD TRIP STOPS (Stops are located by UTM co-ordinates based on NAD 83, UTM Zone 15) Drive to outcrops located on the west side of Shoal Lake Road, south of Mine Centre. (0526600E 5394850N) STOP 1 - BASAL FACIES OF THE SEINE CONGLOMERATE, EXAMPLE OF LOW DEFORMATION At this location, we are near the basal contact of the Seine. Based on opposing stratigraphic facing in adjacent rocks, an unconformity between the volcanic units and the base of the Seine conglomerate can be identified (Lawson, 1913; Poulsen et al., 1980; Poulsen, 2000). The clasts within the Seine include more tonalite than is typical further up in the section. A possible saprolite may be observed between the volcanics and the Seine (C. Hemstad, pers. comm.). Strain at this location is unusually low. Foliation and bedding attitudes are atypical, subparallel with a more NE/SW strike and shallower (~65°) southeasterly dip than is typical for the rest of the Seine’s area. In addition, the clasts appear to be much more angular and irregularly shaped than the rest of the Seine. This is a highly unusual outcrop of Seine that poses several interesting questions that are open for discussion. We pose some here with the hope of encouraging some reflection and discussion at the outcrop. The orientations of the bedding and foliation within the Shoal Lake area and adjacent rocks to the north and south combine to create a large, gentle S structure, with shallower dips here on the middle section of the S. There are several different ways to interpret this sigmoidal map pattern. The various interpretations have bearing on the timing of the geometrical arrangement of structures with respect to the phases of deformation, and therefore will also influence our interpretations of the nature of the Seine basin. Five interpretations are suggested here: 1) The variation in orientation of foliation around the Shoal Lake area may be due to a late stage, gentle folding event. This is suggested by the similar changes in strike and dip of both foliation and bedding. The fold axis of this structure is approximately 55°/077. 2) As suggested by Poulsen (2000), the faults and small-scale shear zones could be equivalent to those created in fault models of strike-slip systems such as those of Tchalenko (1970), Lowell (1972), and Wilcox et al. (1973). If this were the case, since these models involve Mohr-Coulomb failure, the orientations of the faults would have been determined relatively early in the deformation history, during Harland-type transpression, when the rock would have behaved in Mohr-Coulomb fashion. In this scenario, the Rainy Lake – Seine River fault was the “master fault,” and the Quetico and smaller shear zones formed later as second order conjugate shears. Since there is significant, deeper level, ductile deformation recorded along these same faults, they must have been reactivated during ductile deformation because they were zones of weakness. 3) Alternatively, the orientation of the faults may have been determined during the later ductile transpressive stage of deformation. In this case, the orientation of the major faults and the minor 60 �shear zones would constitute a mega-scale S-C feature creating the sigmoidal pattern seen on the map (Fig. 9). 4) It is also possible that the largest faults were formed by brittle processes, buried and then reactivated as ductile shear zones, with the smaller shear zones being formed later purely by ductile means. 5) Yet another interpretation is possible. It could be that the sigmoidal shape of the foliation is related to lithological contrasts, with foliation wrapping around more rigid bodies. In such a scenario, the rocks to the east of the Bad Vermilion intrusive complex (the large plutonic unit in the west-central portion of Fig. 2) were caught in a large strain shadow region (Borradaile and Dehls, 1993). This hypothesis is consistent with the lower strain found in this area. The apparent “wrapping” of the fabrics around this intrusion seems analogous to the “wrapping” of foliations and lineations around relatively rigid conglomerate clasts at a smaller scale. Not surprisingly, there exists a similar asymmetry in shape between the rigid conglomerate clasts and large rigid units such as the Bad Vermilion intrusive complex. In addition, the shapes of the clasts here are much more angular than the rest of the Seine clasts. If one were to consider studies that model nonspherical clasts in deformation, we would expect more deformed outcrops of Seine to have barrel or bone shaped deformed clasts (Treagus et. al, 1996; Treagus and Lan, 2000). As we will see at the next outcrops, this is not the case. Why? Drive East along Hwy 11, right onto Forest Tour Road. (0536650E 5398850N) STOP 2 - TWO-DIMENSIONAL HORIZONTAL VIEW OF SEINE CONGLOMERATE, SANDY LENS AND DEXTRAL SHEAR INDICATORS This outcrop allows us to see a large 2D view of the Seine. The deformation here is typical of much of the field area, the granitoid clasts being fairly undeformed while the volcanic clasts reflect significant flattening. Minor amounts of quartzite, BIFs, and other lithologic clast types are also observable. Dextral shear sense indicators are prominent including asymmetric pressure shadows and clast tilings. Many sandy beds and channels, often with graded bedding, can be located within this outcrop. Is it possible to determine stratigraphic facing here? Drive East along Hwy 11 to Horsecollar Junction. (0542150E 5398500N) STOP 3 - THREE-DIMENSIONAL VIEW OF MODERATELY DEFORMED SEINE CONGLOMERATE This outcrop allows us to see a 3D view of the Seine. The deformation here, as at the last stop, is typical of much of the field area with average strain and dominant flattening fabrics. Here we can observe the subparallel, undulatory nature of bedding and foliation. The lineation plunge here is relatively steep (~78°E). The dextral asymmetric indicators are most prominent on the subhorizontal plane. 61 �Drive East along Hwy 11. (0559500E 5398900N) STOP 4 - ULTRA DEFORMED SEINE CONGLOMERATE WITH ALTERATION The conglomerates here are extremely deformed. Both volcanic and plutonic clast types are extremely flattened. Many clasts are flattened beyond recognition, giving the rock a striped appearance. Is it possible to estimate strain in a rock that is this deformed? The lineation plunge here is typical of the field area (~44°E). While this lineation is “average” stretching lineation for the Seine, it is in no ways representative of the typical deformation due to the wide variance in lineation orientation. The lineation orientation does not vary systematically across the field area and is not directly related to the amount of strain (Czeck, 2001). Again, the dextral asymmetric indicators are most prominent on the subhorizontal plane. This is the case throughout the field area, regardless of lineation orientation, a result that one would not expect in either an ideal strike-slip shear zone or homogeneous transpression. The combination of subhorizontal asymmetric shear indicators and variable lineation orientations makes a deformation model of quasi homogeneous transpression with a variable extrusion direction most likely (Czeck, 2001). The extensive carbonate alteration in this rock suggests that fluid flow was an important factor during deformation. This implies the possibility of volume loss in these ultra deformed rocks. There was probably a symbiotic relationship between fluid localization and enhanced deformation. Drive back West along Hwy 11, stop just east of Seine River bridge. (0551850E 5398700N) STOP 5 - SMALL FOLD IN SEINE At this stop, we can observe the sandier facies more typical of the upper part of the Seine sequence. Cross beds and localized deposits of gravel can be observed. The cross beds allow us to recognize stratigraphic facing. The cross beds are deformed, and a good example of a meter-scale fold evident. This fold is asymmetric and upright with its axis oriented 6°/S83W. This subhorizontal fold axis orientation is similar to fold axes orientations described in the Quetico Subprovince and contrasts with the subvertical fold axes described in the Wabigoon subprovince (Borradaile, 1982). Localized prolate strain, atypical of the field area, is evident in the fold hinge. Down the road, just east of this outcrop, another small fold can be observed in the sandy facies. Does this fold have the same subhorizontal fold axis? 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Ontario Geological Survey Preliminary Map P. 2201, scale 1:15840. 67 �68 �Field Trip 4 Industrial Minerals and Paleozoic Geology of Southeastern Manitoba James D. Bamburak and Ruth K. Bezys Manitoba Geological Survey 360-1395 Ellice Avenue Winnipeg, Manitoba R3G 3P2 Interior of the Manitoba Legislative Building, Winnipeg, built in the early 1900s. Decorative dolomitic limestone, the world famous "tapestry stone" with its unique mottled appearance, is still being quarried from the Selkirk Member, Red River Formation in the Garson area. �FOREWORD Currently, the Province of Manitoba has 18 industrial mineral processing plants and quarries, excluding the production of aggregate (Fig. 1 and Table 1). The 2001 estimated value of industrial mineral production in the province is $78.1 million, including aggregate production that forms slightly less than half of the total. The $78.1 million represents 7% of the province’s mineral production. Fourteen of Manitoba’s industrial mineral processing plants and quarries are situated in southeastern portion of the province. Figure 1. Industrial mineral producing plants and quarries in southern Manitoba Industrial minerals produced in southeastern Manitoba include lithium, cesium, tantalum, sand, aggregate, dimension stone and peat. Peat is considered as a quarry mineral under the Manitoba Mines and Minerals Act. Lithium, cesium, and tantalum are produced for export from the Tanco mine in the Bernic Lake pegmatite (Field Trip No. 1, this volume). Sand and aggregate are quarried for use in local construction. Dimension stone and peat are quarried for local consumption and export. Two companies, Sun Gro Horticulture Canada Ltd., and Premier Horticulture Ltd. extract horticultural quality sphagnum peat. The locations of the peat operations are shown on Figure 1 and listed in Table 1. Five companies, Cold Spring Granite (Canada) Ltd., Gillis Quarries Limited, Carrieres Polycor Inc., Manex Granit Ltd. and Canital Granite Ltd. quarry dimension 70 �Table 1 INDUSTRIAL MINERAL PROCESSING PLANTS AND QUARRIES 2002* No. 1 2 Location Elma (P&Q) Whitemouth (Q) Company Sun Gro Horticulture Canada Ltd. Carrieres Polycor Inc. 3 Bernic Lake (P&Q) Tantalum Mining Corporation of Canada Ltd. 4 Winnipeg (P) Westroc Inc. 5 6 Brandon Winnipeg (P) Nexen Inc. Canital Granite Ltd. 7 Moss Spur (Q) 8 Lac du Bonnet (P&Q) dimension stone 9 Garson (P&Q) 10 Medika (Q) Sun Gro Horticulture Canada Ltd. Cold Spring Granite (Canada) Ltd. Gillis Quarries Limited Manex Granit Ltd. 11 Meditation Lake (Q) Manex Granit Ltd. 12 PR 307&309 (Q) Manex Granit Ltd. 13 14 15 16 17 18 Julius North (P&Q) Caribou Cluster (Q) Giroux (P&Q) Harcus (Q) Faulkner (P&Q) Flin Flon (P) Sun Gro Horticulture Canada Ltd. Premier Horticulture Ltd. PremierHorticulture Ltd. Westroc Inc. Graymont Western Canada Ltd. Hudson Bay Mining and Smelting Co., Limited Product Peat moss Granite, dimension stone Tantalum oxide, spodumene and amblygonite concentrates, cesium and rubidium ores and cesium formate Gypsum wallboard Sodium Chlorate Granite, dimension stone Peat moss Granite, Tyndall stone Granite, dimension stone Granite, dimension stone Granite, dimension stone Peat moss Peat moss Peat moss Gypsum Lime, limestone Sulphur (P) Plant (Q) Quarry * excludes aggregate producers stone. Gillis quarries a dolomitic limestone, the renowned "Tyndall Stone", and the other companies quarry granite. Locations of the stone quarries are shown on Figure 2. INTRODUCTION This one day field trip is designed to visit three industrial mineral sites, including one Lower Paleozoic site. The sites that will be visited include: • the sphagnum peat bog harvesting operation and plant of SunGro Horticulture Canada Ltd. near Elma (Stop 1); 71 �• the granite dimension stone quarry and plant of Cold Spring Granite (Canada) Ltd. near Lac du Bonnet (Stop 2); and, • the Ordovician Tyndall Stone quarry and plant of Gillis Quarries Limited at Garson (Stop 3). Figure 2. Granitic dimension stone quarries in southeastern Manitoba. Sphagnum Peat Canada holds more than a third of the world’s peat resources with 1 223 834 km2 of peatlands, or 12 percent of the total land mass (Tarnocai et al., 1995). Approximately 40% of Manitoba's surface is covered with peat deposits, many of which are inaccessible and/or of uneconomic thickness and quality to be harvested (Dixon and Stewart, 1988). Nevertheless, Manitoba holds vast reserves of peat suitable for horticultural or energy peat production. Two companies, Sun Gro Horticulture Canada Inc. (Stop 1) and Premier Horticulture Inc. harvest 6 bogs in southeastern Manitoba (Fig. 1) for horticultural quality peat. An aerial view of a typical peat extraction area is shown in Figure 3. Peat companies hold almost 4000 hectares of leases in good standing, and 5500 hectares of pending leases in the Interlake and southeastern Manitoba. Peat production in Manitoba 72 �in 2001 was estimated to be worth over $25 million, and this figure is sure to increase as new companies bring their bogs into production. Figure 3. Caribou cluster peat extraction area of Premier Horticulture Inc. Horticultural quality sphagnum is the preserved, but undecomposed, remains of sphagnum moss plants. Sphagnum deposits accumulate in areas of poor drainage where the rate of atmospheric precipitation exceeds the rate of evapotranspiration, i.e. the low boreal forest climatic zone. The accumulation of sphagnum occurs within an acidic, nutrient poor environment, above the level of the local water table. The characteristics of sphagnum that allow it to survive in this environment are the same characteristics that make it valuable to the horticultural industry as a growing medium and soil conditioner (Schmidtke and Bamburak, 1996). These characteristics are: 1. the ability to absorb approximately 20 times its weight in water; 2. a high capacity for cation exchange; 3. a fibrous structure that introduces volume and pore space to a soil mix; 4. compressibility; and, 5. the ability to resume its precompression volume after compression is released. Sphagnum moss is composed largely of rigid walled hyaline cells. The function of these cells is to absorb and hold water. Since the sphagnum must get all its nutrients from the 73 �nutrient poor atmospheric precipitation, it is able to absorb approximately 20 times its weight in water and has a high cation exchange capacity. These properties make it a valuable growing medium in places like Texas where the native soil is fine and does not retain moisture. The hyaline cells are compressible and will resume their shape even after being compressed to a 10:1 ratio. The sphagnum moss can be compressed into bales for efficient transport. These properties are retained after the plant has died and even when it is slightly humified. Since the sphagnum accumulation takes place in an acidic, oxygen poor environment, it is possible for several metres of relatively undecomposed sphagnum to develop. The high quality bogs in southeastern Manitoba accumulated sphagnum to a maximum depth of approximately 2.5 m over a period of 4000 years. A bog must be prepared before peat extraction occurs. First the trees and roots are removed, ditches are dug, and the bog is drained. It may take two years to prepare a bog for harvesting. Sun dries the surface of the bog, which is then raked using a harrower (or cultivator) to loosen the surface peat. This loose, dry sphagnum peat is lifted from the surface with vacuum harvesters (Fig. 4). The harvesters empty the peat into stock piles, or winrows. The stock piled peat is either moved into the plant for processing or is stored in plastic "silage" tubes for future processing when unfavourable weather prohibits harvesting. (Peat can't be extracted if the weather is too wet or too dry, because quarrying equipment can't operate on a bog that has been saturated by rain or melt water and sparks from equipment can ignite peat dust in hot, dry weather). Figure 4. Conga line of peat vacuum harvesters on Elma bog of Sun Gro Horticulture Canada Inc. Once in the plant, the peat is dried (if necessary). Popped perlite is added as a volumizer. The peat is treated with surfactants, which increase absorptive capacity, and fertilizers. 74 �The type and quantity of the chemicals added to the peat are dependent on the intended end use. Specialized mixes are available for several applications, i.e. soil mix for violet plants. The peat is baled, shrink-wrapped on pallets and stored in the warehouse before being loaded onto semi trailers. Some of the peat is sold in local markets, but most goes to nurseries and greenhouses in the southern United States. The peat companies take advantage of backhaul rates by shipping the peat south in trucks that bring produce to Manitoba from the southern United States. Ninety percent of the peat from Sun Gro's Manitoba quarries is exported to Texas. If the Sun Gro operations in Alberta or New Brunswick are unable to produce because of bad weather or labour problems, Manitoba peat is diverted to markets west or east of Texas to cover the shortfall. Both Sun Gro Horticulture and Premier Horticulture operate harvesting operations and plants across Canada (Schmidktke and Bamburak, 1996). Granitic Dimension Stone Four companies quarry Precambrian granitic dimension stone at 5 sites in southeastern Manitoba (Fig. 2). They include: Cold Spring Granite (Canada) Ltd., Carrieres Polycor Inc., Manex Granit Ltd. and Canital Granite Ltd. At all sites, the granitic outcrops possess unique physical features that permit the quarrying of large blocks of stone Schmidtke (1993). They include: 1. widely spaced, preferably orthogonal fractures that will allow removal of blocks with a minimum trimmed size of 2.0 m by 1.25 m by 1.25 m; 2. widely spaced, or preferably the absence of, veining; 3. homogeneous, attractive and fashionable colours and textures; 4. the absence of minerals that pluck when polished, or oxidize and cause unsightly rust spots when exposed to the elements; 5. road access; 6. proximity to transportation routes, finishing facilities and markets; and, 7. acceptable strength values that meet ASTM standards (as per Annual Book of ASTM Standards). Two of the granitic dimension stone cutting and polishing plants are located in southeastern Manitoba (Fig. 1 and Table 1). One plant (Stop 2) is adjacent to the quarry near Lac du Bonnet (Cold Spring Granite), and the other plant is situated in Transcona, on the east side of Winnipeg (Canital Granite). Tyndall Stone 75 �At Garson, Tyndall Stone is quarried by Gillis Quarrries Ltd. (Fig. 1 and Table 1), east of the plant. This famous dimension stone, sometimes called “tapestry stone”, occurs in the lower half of the 43 m thick Selkirk Member of the Ordovician Red River Formation. Its unique appearance comes from a matrix of light-coloured limestone, with mottled areas of dark dolomitic limestone distributed uniformly throughout. The horizontal beds are approximately 60 to 100 cm thick, beneath 1 to 6 m of overburden consisting of soil, lake clays and stony glacial till. The upper four beds in the quarry (total thickness 2 to 4 m) have either a buff and golden-brown buff matrix. The fifth layer down has a matrix, which is transitional into the underlying beds that have a steel-gray matrix (Wilkins, 1986; Coniglio, 1999). After the overburden is stripped, the stone is extracted using two 2.5 m diameter circular saws, drilling and wedging. The 6 to 8 tonne stone blocks are taken into the plant where they are cut and finished using diamond tipped saws or are ground, sheared or split into a variety of products. Finishes available are rubbed (machine smoothed), bushhammered, pointed face, rough cut, sandblasted, split and rustic. Stone is usually marketed as dimension stone, which is cut and shaped to specification or as random ashlar, which are pre-cut into standard or random shapes to be set into mortar (Wilkins, 1986; Coniglio, 1999). 76 �REGIONAL GEOLOGICAL SETTING The Province of Manitoba is completely underlain by 3.0 to 1.7 billion year old Precambrian rock, which is overlain in the southwest and northeast by younger (less than 570 million years old) Phanerozoic sedimentary rocks (Fig. 5). Pleistocene and Holocene deposits, younger than 2 million years in age cover most of these earlier rocks. Industrial minerals in Manitoba range, in age and form, from Precambrian dimension stone to Holocene peat deposits. Figure 5. Principal geological domains of Manitoba Within southeastern Manitoba, the Precambrian surface is exposed in the east half of the area and is known as the Precambrian Shield. The surface dips to the west (Fig. 6), where it is covered by an increasing thickness of Lower Paleozoic strata which also dip gently to the southwest at approximately 2.8 m per km (Fig. 7). The eastern edge of the Paleozoic outcrop belt represents the Manitoba Lowland or First Prairie Level, which is 77 �bounded on the east by the Precambrian Shield, and on the west by the Manitoba Escarpment. Figure 6. Precambrian structure contour map. The Manitoba Escarpment forms the eastern edge of the Second Prairie Level, which is underlain by Cretaceous strata dipping gently to the southwest at 1.5 to 1.9 m per km. The actual Escarpment is composed of soft, easily eroded sands and shales in the lower part of the Cretaceous, underlying a resistant shale cap (Odanah Member of the Pierre Shale). In southeastern Manitoba, industrial minerals are mined from Precambrian, Lower Paleozoic and Holocene localities. Granite quarries (Fig. 2) are situated within late tectonic granitic batholiths and plutons on the western edge of the Archean Superior Province. The Ordovician Tyndall Stone quarry (Gillis Quarry, Fig. 1) occurs within the eastern edge of the Paleozoic outcrop belt. The harvested spahagnum peat bogs (Fig.1) 78 �are located in areas of thick glacio-lacustrine sediments that overlie Archean terrane or Ordovician strata. Figure 7. Structure cross section, southern Manitoba. Precambrian Basement The Precambrian of southeastern Manitoba is comprised of younger Archean granitic batholiths or plutons that have intruded the older greenstone, sedimentary and gneissic formations of the Wabigoon, Winnipeg River, Bird River and English River domains of the Superior Province (Fig. 5). The structure contours on the buried Precambrian surface are shown in Figure 6. All granitic dimension stone production to date has been derived from the Winnipeg River and Bird River domains. The Medika and Betula Lake plutons are situated within the Winnipeg River Domain. The Lac du Bonnet Batholith (LDBB), located to the northwest, lies within the Bird River Domain. For the purpose of the visit to Cold Spring’s Lac du Bonnet Quarry (Stop 1), the following will focus on the latter. The LDBB (outlined on Fig. 2) is the youngest intrusion in the Winnipeg River area (Tammemagi et al., 1980). The batholith is a predominantly pink granite that extends over approximately 1000 km2 from Pointe du Bois southwestward beneath Paleozoic cover. The largest exposures of the batholith occur east of the town of Lac du Bonnet, but isolated outcrops are found as far west as the farmlands directly north of Beausejour. Many of the outcrops of Lac du Bonnet granite have widely spaced fractures, which makes them potential sources of dimension stone (Schmidtke, 1993). 79 �The geology of the Lac du Bonnet Batholith (LDBB) has been the subject of intensive study by Atomic Energy of Canada Ltd. (AECL) as a research site for geological, geotechnical and hydrogeological studies to determine the potential for storing nuclear waste at depth in granite. The regional geology has been described, in detail, by Tammemagi et al. (1980) and McCrank (1985). Lower Paleozoic Stratigraphy The Lower Paleozoic beds (Table. 2) exposed in southeastern Manitoba form part of the Manitoba outcrop belt that is located on the northeastern edge of the Western CanadaSedimentary Basin (WCSB). The WCSB is a composite feature which includes both the Elk Point Basin (Fig. 8), centered in south-central Saskatchewan (which controlled Devonian deposition), and the Williston Basin, centered in northwestern North Dakota (which controlled the depositional patterns throughout the remainder of postCambrian time). Since the Manitoba outcrop belt appears to be situated on the northeastern edge of the sedimentary basin, and roughly parallels the regional structure contours, one might surmise that the strata comprising the outcrop belt would be relatively uniform in lithology. The outcrop would also represent marginal shelf-type deposits relative to the thicker, more basinal sedimentary sequence found to the southwest in the subsurface. However, this is not the case for most Paleozoic formation in southwest Manitoba. The outcrop belts, particularly the Ordovician and Devonian, show marked changes in both thickness and lithology, indicating a complex and varied tectonic and depositional framework (Bezys and McCabe, 1996). The outcrop succession is not marginal to the depositional basin, but rather exposes a series of dip sections of the basin, which show the maximum possible isopach and lithofacies variation. As well, the directions of the dip sections are opposite: basinal Ordovician outcrops occur at the southern end of the outcrop belt, whereas basinal Devonian outcrops occur at the northern (or northwestern) end of the outcrop belt. Regional strike of the Paleozoic strata is approximately north-south, and regional dip increases gradually and uniformly from about 2.6 m/km in the eastern part of southeastern Manitoba to 4.2 m/km in the western part. Despite the regional structural dip to the southwest, isopachs of the Winnipeg and Red River formations all trend eastwest and thicken to the south at up to 0.3 m/km (Fig. 9B and 10B, respectively). This indicates a major change in tectonic framework subsequent to early Paleozoic time, as mentioned previously. The present north-south structural trend probably developed during late Paleozoic to early Mesozoic, due to uplift with associated erosion and eventual exposure of Precambrian bedrock in southeastern Manitoba. A detailed discussion outlining: the evolution of the complex pattern of structural trends in the Lower Paleozoic; a regional tectonic control for apparent anomalies in facies trends; and other related structural and stratigraphic anomalies are described in Bezys and McCabe (1996). 80 �Table 2. Geological formations in Manitoba. 81 �Figure 8. Major structural features of the Elk Point and Williston basins. Ordovician Winnipeg Formation The Winnipeg Formation, a quartzose sandstone interbedded by green, waxy shale with sand and silt interbeds, is exposed in outcrop east at the northeast end of the southeastern Manitoba area, on Black Island and near Seymourville. Structure contours and isopachs 82 �Figure 9A. Winnipeg Formation structure contour map. 83 �Figure 9B. Winnipeg Formation isopach map. 84 �Figure 10A. Red River Formation structure contour map. 85 �I * I •1 Red River Formation IsopachMap - Sm —— Churchill Superior :---- BoundaryZone Outcrop belt suborop I LTt1,1OJW zk Figure 10B. Red River Formation isopach map. 86 I N _______ kilonwtres �for the Winnipeg Formation are shown in Figures 9A and B, respectively. The formation was described, in detail, by McCabe (1978). Red River Formation The Red River Formation consists of two principal subunits, the lower Red River and upper Red River strata (Table 2). In the vicinity of the south basin of Lake Winnipeg, the lower Red River (Baillie, 1952) can be subdivided into three mappable members: a lower Dog Head Member, a medial Cat Head Member, and an upper Selkirk Member (=Tyndall Stone). Lower Red River strata consist of light grey to yellowish- and brownish-buff, prominently mottled, fossiliferous, commonly cherty, dolomitic limestones. The upper Red River strata consist of dolomite and argillaceous cherty dolomite, designated as the Fort Garry Member. A thin, high calcium limestone bed occurs locally at the top of the Fort Garry Member. Stucture contours and isopachs for the Red River Formation are shown in Figures 10A and B, respectively. At Garson, Gillis Quarries Limited (Stop 3) is actively quarrying the Red River Formation (Selkirk Member) for its dimension stone (Tyndall Stone). Stony Mountain Formation The Stony Mountain Formation is subdivided into three members, in ascending order: the Gunn, Penitentiary, and Gunton (Table 2). The Williams Member was once included within the Stony Mountain Formation; however, standardized correlations established for the new Atlas of the Western Canada Sedimentary Basin (Norford et al., 1994) have placed the Williams into the overlying Stonewall Formation (Bezys and McCabe, 1996). The Gunn Member consists of greyish-red to purplish-grey, fossiliferous, calcareous shale with interbeds of relatively clean, fossiliferous limestone. The Penitentiary Member consists of yellowish- to reddish-grey, fossiliferous, argillaceous dolomite. These two members together comprise the lower Stony Mountain. The upper Stony Mountain (Gunton Member) consists of a buff, finely crystalline, sparsely fossiliferous, nodular-bedded dolomite that is relatively uniform in thickness and lithology. All three members are exposed in the Mariash Quarry and abandoned City of Winnipeg quarries at Stony Mountain, an erosional outlier of the Stony Mountain Formation, located 7 km southwest of the Town of Stonewall, near the western edge of the southeastern Manitoba area. The Gunton Member acts as a cap rock for a shallowly buried, east-facing, north-trending escarpment (Gunton Escarpment), 4 km east of the Town of Stonewall. The Gunton Member is extensively used for crushed stone, extracted from quarries in the Stony Mountain and Stonewall areas. The stone has also been used to construct buildings in Winnipeg, Stony Mountain (including the Federal Penitentiary) and in Stonewall. 87 �Ordovician/Silurian Stonewall Formation The Williams Member, is the basal unit of the Stonewall Formation (Bezys and McCabe, 1996). It represents the oldest of a series of so-called “para-time-stratigraphic” markers; thin sandy and/or argillaceous beds that can be traced for many hundreds of kilometres throughout most of the Williston Basin (Table 2, Fig. 8). These marker beds provide the primary means for stratigraphic subdivison of Upper Ordovician and Silurian strata and probably represent deposits related to brief periods of shoaling or even slight uplift and erosion (i.e. non-sequences) (Porter and Fuller, 1959). The Williams Member consists of buff to grey to red, sublithographic dolomudstone. The lower Stonewall beds, above the Williams Member, consist of pale yellowish-grey to yellowish-brown, faintly mottled, medium- to thin-bedded, finely crystalline dolomite with sparse, poorly preserved fossils. A sandy argillaceous marker bed, the “t-marker” or “t-zone”, separates the lower Stonewall Formation from the upper Stonewall Formation. The upper Stonewall Formation consists of light brown to grey, laminated to thin-bedded, sparsely fossiliferous microcrystalline dolomite, which is capped by a grey to buff dolomudstone marker bed, the Upper Stonewall Marker. According to Bezys and McCabe (1996), the t-marker within the upper part of the Stonewall Formation, also marks the position of the Ordovician-Silurian boundary in the Williston Basin. This was confirmed in biostratigraphic studies, based upon outcrop and subsurface investigations. The formation was previously quarried in the Town of Stonewall for lime and aggregate production. Silurian Interlake Group The Interlake Group, consisting of the Fisher Branch, Moose Lake, Atikameg, East Arm and Cedar Lake formations (in ascending stratigraphic sequence), is exposed near the western margin of southeastern Manitoba area. In the subsurface, the group consists of yellow-orange to grey, fossiliferous, oolitic, stromatolitic dolomite, interrupted by sandy, argillaceous marker beds. Jurassic and Cretaceous South of the City of Winnipeg, within the Manitoba Lowland, a large area of Jurassic sediment infills a major pre-Mesozoic channel in the Paleozoic erosion surface. Also, many small Cretaceous outliers have been noted in karst features penetrated by water wells (Bannatyne, 1988). Recent Six peat quarries (Fig.1) are located in areas of thick glacio-lacustrine sediments that overlie Archean terrane or Ordovician strata. Over the past 4000 years, sphagnum plants have contributed organic matter that has accumulated to a maximum depth of approximately 2.5 m. 88 �Near Elma, Sun Gro Horticulture Ltd. (Stop 1) harvests sphagnum peat from spring to fall from a drained bog. Sphagnum peat is also produced on a seasonal basis at 5 other sites, on a seasonal basis, by Sun Gro Horticulture Canada Inc. and Premier Horticulture Inc. 89 �FIELD TRIP STOPS Leave Kenora, on Trans Canada Hwy, travel west for 110 km to Prawda, at junction of Trans Canada Hwy and PR 506. Continue on Trans Canada Hwy (west) to Hwy 11 (11 km), turn right (north) to Sun Gro Horticulture entrance road (12 km), turn left (west), park in visitor’s parking area. STOP 1 – SUNGRO HORTICULTURE SPHAGNUM PEAT BOG AND PLANT The Elma bog (Fig. 1 and Table 1), quarried by Sun Gro Horticulture Canada Ltd., is approximately 3000 acres (12.14 km2) in area and has been in production since 1969. The on site plant was completed in 1972. Peat is quarried using the vacuum harvesting method described above. The bales are loaded at the plant into semitrailers and shipped to the southern United States. A small percentage of the peat is sold for local consumption at retail stores in Manitoba. Reserve estimates have not been published by the company. Leave Sun Gro parking area, travel east on exit road back to Hwy 11, turn left (north) for 50 km to Cold Spring Granite entrance road, turn left (west), park in visitor’s parking area. STOP 2 – COLD SPRING GRANITE DIMENSION STONE QUARRY AND PLANT The quarry and plant of Cold Spring Granite (Canada) Ltd. (Fig. 2) are located in the south central area of the LDBB on a 1220 m long 6 to 8 m high ridge approximately 10 km south of the Town of Lac du Bonnet (Fig. 2). The quarry is accessed via Highway 11. The Precambrian monadnock (Bezys et al., 2001) was first quarried from 1933 to 1949 by a local, Ivor Peterson, for tombstones. An American company, Cold Spring Granite Ltd., reopened the quarry in 1959 and has produced stone from the ridge to the present time. The product is a fine grained pale rose granite sold under a variety of trade names including Lac du Bonnet, Canyon Rose, Colonial Rose and Canadian Mist. Even grained rock is used for monuments and building stone, textured or variegated rock is used for tiles and countertops. The plant at Lac du Bonnet is equipped to make grave markers, countertops, paving and landscaping material and structural panels. Blocks are shipped to the Minnesota plant for finishing into headstones, mausoleums, monuments, columbariums, structural panels, tiles, custom design industrial work, paving and landscaping material. Fine grained, even textured Lac du Bonnet granite is prized for grave markers, monuments and headstones, because sandblasted letters and designs stand out well. It is also a preferred rock for precision industrial applications because it takes a very tight smooth polish, i.e. precision milling surfaces. Rock is sold locally from the Lac du Bonnet quarry, and internationally through Cold Spring Granite's office in Cold Spring, Minnesota. 90 �Figure 11. Granite dimension stone blocks being removed from Cold Spring Quarry in 1982. Prior to 1987, rock was removed from the quarry with wire saws and moved into the plant using hoists (Fig. 11). Since 1987, blocks have been removed by drilling and blasting. Sections of the outcrop are drilled off with portable, track-mounted, hydraulic drills. The drilled sections are then separated from the outcrop by blasting. The blast must move the section of rock without shattering it or inducing microfractures. The sections of rock are then drilled and wedged into smaller blocks that are moved to the plant with a 988 Cat loader. The plant has a 10 wire slab saw, a Salvatore 16 head polishing machine, a JB 110 granite milling machine, a 24" diamond saw and 6', 2', and 1' hydraulic splitters. Blocks are cut into slabs with the wire saw. The slabs are cut and polished with the diamond saw and the polishing machine for use as structural stone. Polished slabs are also manufactured into paving stone and grave markers with the hydraulic splitters and into countertops and furniture with the milling machine. Raw blocks are shipped to plants in Montreal for manufacture into granite tile and to the plant in Cold Spring, Minnesota to be processed for all other applications. Leave Cold Spring parking area, travel east on exit road back to Hwy 11, turn right (south) to PTH 44, turn right (west) to Garson (total 55 km) arrive Gillis Quarries, park in visitor’s parking area. STOP 3 – GILLIS TYNDALL STONE QUARRY AND PLANT Gillis Quarries Limited quarries an 8 m thick section of pale yellowish brown, dolomite mottled, burrowed, fossiliferous micrite of the Selkirk Member of the Ordovician Red River Formation at Garson (Fig. 1 and Table 1). In the quarry, the well known “Tyndall Stone”, is extracted using two 2.5 m diameter tungsten carbide-toothed circular saws, 91 �(Fig. 12), followed by wedging of the blocks along the bedding planes. The stone is finished in the plant, as described earlier. Three colours of stone are produced from various parts of the quarry – buff (a light creamy beige with pastel brown mottles) and golden buff (possibly due to ground water) from the upper beds. And, gray (a pale bluish grey with gray-brown mottles) from the lower beds (Wilkins, 1986; Coniglio, 1999). Figure 12. Carbide toothed circular saw in Gillis Tyndall Stone Quarry. The quarry is noted for its well-preserved fauna of large cephalopods, gastropods, corals, stromatoporoids, bryozoans, crinoids, trilobites, brachiopods, bivalves and calcareous algae, etc. A waste pile is available to hunt for fossils. Gillis Quarries Limited has been a family-owned business since 1915 when August Gillis and his son, Charles, acquired a quarry property in Garson. The stone was finished in Winnipeg, until 1968 when the Garson plant was built. Gillis Quarries has owned all the quarry property in Garson since 1973. The company estimated that based on the 1986 production rate, it had at least 100 to 125 years of stone in reserve (Garson and District History Book Committee, 1990). References: Corehole M-3-69 (internal government core logs) (Garson Quarry, 15-3-136EPM). Go east on Hwy 44, 7 km to Hwy 12, turn right (south) and continue 38 km to the Trans Canada Hwy. Turn left (east) and continue to Kenora (175 km). 92 �REFERENCES Baillie, A. D. 1952. Ordovician geology of Lake Winnipeg and adjacent areas, Manitoba. Manitoba Mines Branch Publication 51-6, 64 p. Bannatyne, B.B., 1980. Sphagnum bogs in southern Manitoba and their identification by remote sensing; Manitoba Energy and Mines, Economic Geology Report ER79-7, 103p. Bannatyne, B.B., 1988. Dolomite resources of southern Manitoba; Manitoba Energy and Mines, Economic Geology Report ER85-1, 4 maps, 39p. Betcher, R. N., McCabe, H. R., and Render, F. W. 1993. The Fort Garry aquifer in Manitoba. Manitoba Energy and Mines, Geological Report GR93-1, 15 p. Bezys, R.K. and McCabe, H.R. 1996. Lower to Middle Paleozoic stratigraphy of southwestern Manitoba – Field Trip Guidebook B4: Geological Association of Canada/Mineralogical Association of Canada Annual Meeting, Winnipeg, Manitoba, May 27-29, 1996. Bezys, R.K., Matile, G.L.D. and Keller, G.R. 2001. Investigation of Precambrian monadnocks (NTS 62I/1 and 62/8); in Report of Activities 2001, Manitoba Industry, Trade and Mines, Manitoba Geological Survey, p. 133-137. Coniglio, M. 1999. Manitoba’s Tyndall Stone; in Wat on Earth; University of Waterloo, Department of Earth Sciences, Spring 1999, pp. 15-18. Dixon R.J. and Stewart, J., 1988. Peatland inventory of Manitoba: III- Interlake region using LANDSAT thematic mapper; Manitoba Department of Mines and Natural Resources, Surveys and Mapping Branch, 21p. Garson and District History Book Committee 1990. Garson, then and now 1890-1990; Derksen Printers Ltd., pp. 14-26. McCabe, H.R., 1978. Reservoir potential of the Deadwood and Winnipeg Formations, southwestern Manitoba, Manitoba Energy and Mines, Geological Paper GP 78-3, 54p. McCrank, G.F.D., 1985. A geological survey of the Lac du Bonnet Batholith, Manitoba; Atomic Energy of Canada Limited, Report AECL-7816, 63p. Norford, B.S., Haidl, F.M., Bezys, R.K., Cecile, M.P., McCabe, H.R., and Paterson, D.F. 1994. Middle Ordovician to Lower Devonian strata of the Western Canada Sedimentary Basin, in Geological Atlas of the Western Canada Sedimentary Basin, G.D. Mossop and I. Shetson (compilers), Calgary, Canadian Society of Petroleum Geologists and Alberta Research Council, p. 109-127. Porter, J.W. and Fuller, J.G.C.M. 1959. Lower Paleozoic rocks of the northern Williston Basin and adjacent areas. American Association of Petroleum Geologists Bulletin, Vol. 43, No. 1, pp. 124-189. Schmidtke, B.E., 1993. Granitic dimension stone potential of southeast Manitoba; Manitoba Energy and Mines Economic Geology Report ER93-1, 52p. 93 �Schmidtke, B.E. and Bamburak, J.D., 1996. Industrial minerals of southeast Manitoba – Field Trip Guidebook B7, Geological Association of Canada/Mineralogical Association of Canada Annual Meeting, Winnipeg, Manitoba, May 27-29. 1996. Tammemagi, H.Y., Kerford, P.S., Requeima, J. and Temple, C.A., 1980. A geological reconnaissance of the Lac du Bonnet Batholith; Atomic Energy of Canada Limited, Report 6439, 68p. Tarnocai, C., Kettles, I.M., Ballard, M., 1995. Peatlands of Canada; Geological Survey of Canada, Open File 3152. 1:6 000 000 map with marginal notes. Wilkins, C., 1986. Manitoba’s magnificent limestone graces Canada’s finest buildings; Canadian Geographic, v. 106, no. 1, pp. 28-37. 94 �Field Trip 5 Separation Rapids Rare-Element Pegmatite Field, Ontario Charles Blackburn Blackburn Geological Services Site 130, Comp. 21 Kenora, Ontario P9N 3W Don Bubar President and CEO Avalon Ventures Ltd. 1116-1111 Richmond Street West Toronto, Ontario M5H 2G4 Carey Galeschuck Project Geologist Tantalum Mining Corporation of Canada Limited Box 2000 Lac du Bonnet, Manitoba R0E 1A0 Alasdair Mowatt President Emerald Fields Resources Corporation 1546 Pine Portage Road Kenora, Ontario P9N 2K2 Chris Pederson Consulting Geologist Karen Rees General Manager Avalon Ventures Ltd. 777 Red River Road Thunder Bay, Ontario P7B 1J9 Tony Pryslak A.P. Pryslak Geological Services 15 Hunterspoint Rd. Winnipeg, Manitoba R3R 3B6 Aerial view of the Big Whopper pegmatite, from the southeast �FOREWORD Separation Lake and surrounding area has in recent years emerged as, if not the most, certainly among the most, important host to rare-element pegmatites in Ontario. The Separation Rapids pegmatite field (Figure 1), located where the English River forest access road crosses the English River near Separation Rapids, was first discovered in the 1993 field season by Fred Breaks of the Ontario Geological Survey (OGS). However, the presence of beryl-bearing pegmatites had been known long before roads were pushed into this region, since at least the 1930s, when a Geological Survey of Canada field crew working its way along the lakes and waterways of the English River noted beryl "in a large pegmatite dyke cutting volcanics on the east shore of English River 2 miles northwest of Separation rapids" (Stockwell 1932). Access in those days was difficult, and so possibilities of exploitation lay dormant for 50 years. Separation Lake and the surrounding area was included in a 37 000 km² reconnaissance survey of the present English River and Winnipeg River subprovinces in the 1970s (Breaks and Bond 1993), and although other previously known rare-metal pegmatites were examined in some detail, little attention was paid to the pegmatites at Separation Lake. Then, in the 1980s, Carmen Storey of the OGS, as part of a broad evaluation of the industrial mineral potential of a large part of northwest Ontario, sampled what was possibly the same dike as Stockwell had examined and noted accessory red garnet and apatite. He also found lithium and berylium assay values in other pegmatites recently exposed along the newly opened right-of-way for the English River road (Storey 1990). It was not until late in the field season of 1993, when Fred Breaks, following a long summer of investigation of the Raleigh lake pegmatites, and taking the opportunity to visit the OGS field camp of Charlie Blackburn at Separation Rapids, knowing of the beryl mineralization and suspecting that the pegmatites there might show some further characteristics of the prized rare-element group, that the real potential began to emerge (Breaks 1993). Blackburn was completing the second year of a broad geological survey of the never-before-mapped Separation Lake greenstone belt. He and Jeff Young (Blackburn and Young 1993) had become involved in the possibilities of base metal potential in the belt, at that time being explored by Champion Bear Resources Ltd., and had not realised that other more exciting and exotic metals lay beneath their feet. Tony Pryslak, working for Champion Bear, had also encountered beryl-bearing pegmatites in their base metal exploration program. A half-day of fieldwork convinced Breaks that he was on to something, and in the next few days he laid the foundation for what was to eventually develop over the next 5 field seasons into the discovery of the Big Whopper and Big Mac pegmatites and numerous other bodies. Breaks (1993) was quick to realise that the Separation Rapids pluton, exposed on islands and along the shoreline of the English River, bears striking similarity in size, constituent granitic units and mineral content to the peraluminous Greer Lake pluton of the Winnipeg River Pegmatite District in Manitoba, the location of the Tanco Mine. He related the pegmatites, that had up to that time only been discovered on the 96 �97 Figure 1. General geology and distribution of rare-element groups in the Bird River-Separation Lake metasedimentary-metavolcanic belt, southeast Manitoba and northwest Ontario. Orthopyroxene-in isograd outlines the Umfreville-Conifer lakes granulite zone. Figure taken from Figure 1 in Breaks and Tindle (2002). �east side of the river, to the pluton, and called the complete package the Separation Rapids Pegmatite Field. In the following field season Breaks began what was to become a detailed investigation of the area around Separation Rapids, in partnership with colleagues Andy Tindle (Breaks and Tindle 1994) and Yuanming Pan (Breaks and Pan 1995). Thanks to painstaking work, discovery of the Big Whopper pegmatite was made by Breaks and Tindle in 1996 on the west side of the English River (Breaks and Tindle 1996, 1997). Following announcement in 1996 of the discovery, the Big Whopper was staked by local prospectors Bob Fairservice and Jim Willis. Further expansion of the Separation Rapids pegmatite field was made to the west. Discovery of the Big Mack was made in 1998 by two other local prospectors, Al Mowatt and Phil Thorgrimson. Meanwhile, Tantalum Mining Corporation of Canada Ltd. (Tanco) geologists Carey Galeschuk and Peter Vanstone were further exploring the numerous pegmatites on ground earlier investigated by Champion Bear to the east of the river. Tanco continues to explore under a joint venture agreement with Gossan Resources Ltd. Other companies that became major stakeholders included Avalon Ventures Ltd. (Big Whopper), Emerald Fields Resources Corp. (Big Mack) and Champion Bear Resources Ltd. (Marko's Pegmatite). Most recently Tony Pryslak and Seymour Sears, working for Champion Bear Resources, enabled further expansion of the field to a minimum 6.5 km strike length, with their discovery of a number of rare metal pegmatites (e.g. the Glitter Zone) further to the west. INTRODUCTION Breaks and Tindle (1997) have pointed out that: "Rare-metal class pegmatites of the complex-type and petalite-subtype represent the most desirable target for tantalum, cesium, rubidium and ceramic quality petalite in Archean terrain settings......Current economic interest is focussed upon the petalite potential.......The widest part of the Big Whopper Pegmatite averages 37% petalite over 60 m which is comparable to the world's premiere petalite deposit at the Bikita Pegmatite of southern Zimbabwe. The tantalum potential is also considerd significant as wodginite, the chief ore mineral for Ta at the Tanco Mine of southeastern Manitoba, is not only widespread in the Separation Lake area, but also exhibits compositional variation unlike any other pegmatite group on a global scale. Cesium.....also has high exploration potential as pollucite, the only ore mineral for the metal, has ...been verified in the area." So-called "fertile" granite/pegmatite systems are typically peraluminous and of an S-type heritage (Breaks and Tindle 1997). The 4 km² Separation Rapids pluton represents a classic example of a fertile granite. It has generated a rare-element pegmatite field with a minimum presently known east-west dimension of 12 km that is 3 km at its widest. The pluton compares in size and constituent granitic units with the Greer Lake pluton (Cerny et al 1981) 55 km to the northwest in the Winnipeg River Pegmatite District of southeast Manitoba (Figure 1). Similarities include presence of cordierite, beryl, cassiterite and the common presence of primary layering between pegmatitic leucogranite, sodic aplite, 98 �99 Figure 2. Distribution of rare-element pegmatite mineralization in the Separation Rapids pegmatite group, and location of field trip stops 1 through 5. Modified from Figure 3 in Breaks and Tindle (2002). �potassic pegmatite and coarse grained granite. Beryl has been found at numerous places that constitute a zone in the southern portion of the pluton, either as a primary phase, or secondary with garnet, muscovite and biotite after cordierite. The pegmatites have recently (Breaks and Tindle 2002) been grouped into an eastern and a western subgroup, based on their position relative to the Separation Rapids pluton. However, both subgroups exhibit a beryl zone and a complex, petalite-bearing zone. The Big Whopper, Big Mack and Glitter Zone pegmatites are located within the petalite subzone in the western subgroup, and the Marko's and James' pegmatites are in the complementary subzone in the eastern subgroup. Audrey's pegmatite lies within the beryl zone, just outside the petalite zone. REGIONAL GEOLOGICAL SETTING The Separation Rapids pegmatite field is set in the heart of the Separation Lake greenstone belt (Figures 1 and 2). Metavolcanic and subordinate metasedimentary rocks occur discontinuously along the English River-Winnipeg River subprovincial boundary from the Ontario-Manitoba border in the west to western Lac Seul in the east, a distance of about 100 km. They represent the eastern extension of the Bird River greenstone belt in Manitoba (Cerny et al. 1981) (Figure 1). The Separation Lake greenstone belt (Figure 1 and 2; Blackburn and Young 2000; Blackburn et al 1994a,b) is the largest segment, extending from the east shore of Umfreville Lake to Helder Lake, a distance of 45 km, and with a maximum width of 5 km. It consists predominantly of a lower sequence of mafic metavolcanic rocks, with intercalated magnetite-bearing iron formations, a single discontinuous clastic metasedimentary unit, and overlying subordinate felsic metavolcanic rocks. Gabbro sills intrude the mafic metavolcanic sequence. A thin unit of polymictic conglomerate and sandstone lies along the northern margin of the belt. Along the length of the belt the volcanosedimentary assemblage faces predominantly to the north. However, the lower sequence is folded about the westerly plunging Separation Narrows anticline, while in the west folding has been about the easterly plunging Paterson Lake antiform. Metamorphic grade is amphibolite throughout the belt. Breaks and Tindle (2002) suggest on the basis of geochronology done in the Bird River portion in Manitoba that the belt has an age range of >2844 Ma to 2740 Ma, while the Separation Rapids pluton has been dated at 2646 +/- 2 Ma (Larbi et al 1999). The English River Subprovince, extending north from the Separation Lake belt to the Uchi Subprovince, is comprised of metasedimentary migmatites (50%), and felsic to intermediate plutonic rocks comprised of a tonalitic suite in the west and a granodiorite to granite suite in the east (Breaks 1991). Metamorphic grade varies from amphibolite to granulite, and has affected all rocks except 100 �those of a peraluminous suite (Breaks 1991). The Winnipeg River Subprovince, south of the Separation Lake belt, is comprised of felsic to intermediate plutonic rocks ascribed to two suites, an early tonalitic suite in the north and a later granitic suite in the south by Beakhouse (1991). Rocks of the tonalitic suite in the subprovince are metamorphosed to medium to high grade, while granitic suite rocks were either synchronous with or postdated regional metamorphism (Beakhouse 1991). GEOLOGY OF THE PEGMATITE FIELD The Separation Rapids pluton and the Separation Rapids rare-element pegmatite field lie entirely within the greenstone belt (Figure 2). There appears to be little direct relationship between the pegmatite field and the stratigraphy of the greenstone belt. However, deformation events could have provided convenient structural traps into which the pluton and the pegmatites were emplaced. A major folding event, represented by folding about the Separation Narrows anticline, preceded emplacement of the cross cutting Separation narrows pluton, dated at 2646 +/- 2 Ma, as noted above. De la Fuente (1998), in a study done for Tanco, interpreted three deformation phases, such that D1 and D2 predated emplacement of the Separation Narrows pluton. He interprets the pluton to therefore be parent to pegmatites that are only weakly deformed, such as the Marko's pegmatite. In his interpretation, the Separation Narrows pluton cannot be parental to the Big Whopper and Big Mack pegmatites, both of which are complexly folded. He suggests that the source of the Separation Narrows pluton may be at depth either within the greenstone belt or "within the mainly undeformed Winnipeg River subprovincelate granites outcropping to the south" (de la Fuente 1998). His analysis that the Treelined Lake granite was involved in D2 and D3 deformation is consistent with this granite being a possible source of the Big Whopper, Big Mack, James and other complexly deformed pegmatites. These structurally based interpretations of relative timing of emplacement of various pegmatites and granitic bodies differ from the interpretation of Fred Breaks and colleagues (eg. Breaks and Pan 1995; Tindle and Breaks 2000: Breaks and Tindle 2002), made on mineralogical and geochemical arguments, that there is a consistent evolutionary trend from the Treelined Lake granite complex through the Separation Narrows pluton, to the various pegmatite groups. Detailed discussion of all other aspects of the Precambrian geology of the Separation Lake area, such as lithology, stratigraphy, metamorphism and mineral deposits, other than those associated with the rare metal pegmatites, has been made by Blackburn and Young (2000). Breaks and Tindle (2002) have recently presented a detailed account of the Separation Narrows pegmatite field, from which much of the rest of this section is paraphrased or quoted in parentheses. 101 �Treelined Lake Granite Complex The Treelined Lake granite complex is a "peraluminous granite mass situated in the adjacent English River subprovince. This granite mass is an irregular-shaped, 3 to 23 by 63 kilometer mass situated mostly in the core of the Umfreville-Conifer lakes granulite centre." (Figure 1). There is an abrupt regional metamorphic discontinuity at the boundary between the English River subprovince and the Separation Lake greenstone belt, jumping from upper amphibolite in the greenstones to granulite in the migmatized clastic metasedimentary rocks to the north. Although not a field trip stop in the present guide, the boundary is described in detail as Stop 1-6 in the Western Superior Province Fieldtrip Guidebook for Precambrian '95 (Beakhouse et al 1995). Rocks of the Treelined Lake granite complex characteristically contain the metamorphic minerals garnet, orthopyroxene, cordierite, while the "southwestern apophysis consists mainly of garnetbiotite and muscovite-biotite granite with local, in situ pegmatite zones that contain rareelement-enriched mineralogy." Breaks and Tindle (2002) discuss such a pegmatite that occurs very close to the boundary adjacent to the Umfreville Road that contains "tourmaline, topaz, cassiterite, gahnite, fluorapatite,....microlite, manganocolumbite and manganotantalite." Separation Rapids Pluton The Separation Rapids pluton (Figures 2) has a "core of coarse-grained, potassiumfeldspar-porphyritic, garnet-biotite-muscovute granite that is enveloped by a larger area composed of various pegmatitic granite units." Variable textural and mineralogical features include: wide range in grain size, from aplite to potassic pegmatite and pegmatitic leucogranite (with potassic megacrysts up to one meter in diameter); graphic, plumose, radial, and unidirectional solidification textures; layering among units; a peraluminous mineralogy of cordierite, primary muscovite, biotite, garnet and schorl tourmaline; and metasomatic rare-element-rich biotite and muscovite along contacts with mafic metavolcanic host-rocks and enclaves. "Rare-element minerals.....are largely confined to...the southeastern part of the pluton. These comprise occurrences of green and white beryl, columbite-tantalite group minerals and cassiterite in potassic pegmatite, various sodium-rare-element-enriched pods and layers (albitite, albite trondhjemite and muscovite-quartz-cleavelandite pods) and more rarely in fine-grained leucogranite." Rocks of the pluton are conveniently exposed on the shore-lines and islands of the English River. Eastern Subgroup Pegmatites The eastern subgroup of pegmatites (Figure 2) covers a 7.5 km² area to the east of the English River. It "comprises a narrow, 0.5 by 5 kilometre, central axis of 11 complex type, petalite subtype pegmatites that is almost completely enveloped by zones of beryltype pegmatites." "The beryl zone contains dikes of pegmatitic leucogranite, potassic pegmatite and minor sodic aplite.....Green and white beryl....is the most widespread rareelement mineral. Cassiterite, ferrocolumbite and gahnite represent widespread accessory 102 �minerals. (In the beryl zone) Wodginite.....has only been documented in Audrey's pegmatite." Topaz has been found in four dikes in the beryl zone. The petalite zone pegmatites characteristically, in addition to petalite, contain a diverse population of oxide minerals, in particular wodginite. The 8 by 130 metre Marko's pegmatite in particular contains a diversity of wodginite species (viz. titanowodginite, ferrowodginite, ferrotitanowodginite, and tungsten-rich wodginite). Marko's pegmatite is notable also for its zonation, containing four primary zones and two replacement units. Features of the primary zones are dominated by megacrysts of petalite and of potassium feldspar. In the replacement zones: spodumene-quartz intergrowths (the SQUI so common at Tanco) occur within petalite megacrysts; lepidolite replaces muscovite; and oxide minerals are especially conspicuous. Southwestern Subgroup Pegmatites The southwestern pegmatite subgroup of pegmatites (Figure 2) occupies a 0.3 to 0.8 by 6.5 kilometre area to the west of the English River. It is divisible into two zones, a beryl type and a petalite subtype zone. The beryl zone contains numerous small and large pegmatites with major mineralogy similar to those of the eastern subgroup. The petalite zone contains nine relatively larger, deformed pegmatite lenses, the largest of which in surface outcrop are the 56 by 650 metre Big Whopper and the 30 by 100 metre Big Mack. "The initial resource estimate of Avalon Ventures Limited....revealed the Big Whopper pegmatite to contain 7.1 million tonnes with an average of 1.285% Li2O, 0.346%Rb2O and 0.007% Ta2O5 over a strike-length of 600 metres and to a depth of 200 metres." At the Big Mack, "a preliminary estimate of 300 000 tonnes averaging 30.5% petalite to a 65 metre depth has been indicated by the initial diamond drilling program." "Petalite content of the core of the Big Whopper and Big Mack pegmatites ranges from 30 - 60%.....Petalite is of optimum quality for use as a direct feedstock in the lithium glass and ceramic industry." Extremely low iron contents, a deleterious metal in the glass-making industry, are indicated in samples taken by Breaks and Tindle that analyzed at <5 to 123 ppm Fe. "Furthermore, Li2O contents (4.6 - 4.7 %) are somewhat higher than the 4.3% average of six Li2O analyses compiled from the literature." "Other phases in the petalite zone pegmatites include garnet...., cordierite, lepidolite, cookeite, spodumene, eucryptite, bikitaite, holmquistite, topaz and chrysoberyl. Oxide phases include cassiterite, gahnite, ferrowadginite, ferrotapiolite, ferrocolumbite, manganocolumbite, ferrotantalite, struverite, and yttro- and yttrian pyrochlore (Tindle and Breaks 2000). Potassium and sodium feldspar minerals, of high purity, represent potential valuable byproducts of the exploitation of petalite pegmatites in the area. Potassium feldspar from the southwestern subgroup also reveals a significant variation in Rb content.....(Those) from the Big Whopper pegmatite indicate a rubidium content mainly in the 1.5 to 2.0 wt. % range with a maximum value of 3.0 wt %." 103 �FRACTIONATION TRENDS IN RARE ELEMENT PEGMATITES Oxide "minerals of the columbite-tantalite group are the most common Nb-Ta species in rare element pegmatites" (Tindle and Breaks 2000). Following Cerny and Ercit (1985), Tindle and Breaks (2000) have used the columbite-tantalite quadrilateral (Fig. 3) to Figure 3. Columbite-tantalite quadrilateral. Vectors describe variation trends in beryltype and complex-type pegmatites. From Fig. 9, Tindle and Breaks (2000). analyse fractionation trends in both beryl-type and complex-type pegmatites of the Separation Narrows rare element pegmatite field. Fractionation trend may be strongly influenced by the activity of fluorine, as indicated in the evolution paths shown in the quadrilateral (Fig. 3). Changes in bulk chemistry, increase in temperature and decrease in pressure result in the formation of petalite, lepidolite and amblygonite subtype pegmatites, all noted for their high fluorine activity. Tindle and Breaks (2000) have subdivided the Separation Rapids pegmatites into Fesuites and Mn-suites on the basis of columbite-tantalite (oxide mineral) compositions. Figures 4, 5,and 6 demonstrate the use of this classification for the four pegmatites to be visited on the field trip. Data for those of the southwest sub-group complex-type pegmatites are shown on Fig. 4, and for the eastern sub-group complex-type pegmatites on Figs. 5 and 6. Data for a number of other pegmatites are also included on the diagrams, taken from Tindle and Breaks (2000). For clarity, envelopes have been added around the data for the Big Mack, Big Whopper and lepidolite unit of the Big Whopper (Fig. 4), Marko's pegmatite petalite core and outer layer (Fig. 5) and James' pegmatite (Fig. 6). 104 �Figure 4. Columbite-tantalite quadrilateral: major SW subgroup petalite pegmatites. Modified from Fig. 13a, Tindle and Breaks (2000). In Fig. 4, the Big Mack pegmatite data clearly fall in the Fe-suite, as do most of the pegmatites of the southwest sub-group. However, data for the Big Whopper pegmatite are spread over a large area of the quadrilateral, while data for the lepidolite unit show extreme fractionation along the high Mn side of the quadrilateral. It is suggested that the apparent randomness of Big Whopper data reflect the complex folding this pegmatite has undergone. The Marko's pegmatite (Fig. 5) is the only Mn-suite petalite-subtype in the eastern subgroup. According to Tindle and Breaks (2000), the fractionation trend is from the outer, earlier crystallizing, layered pegmatite-aplite unit toward the late crystallizing petalite rich core. In Fig. 6, the James' pegmatite data fall in the Fe-suite. The differentiation trend is subvertical in the diagram, indicating fluorine-poor conditions. However, the pegmatite is more evolved than the primitive dikes #9 and #10 (same diagram) and equivalent to approximately 50% of the samples from the Big Whopper (Fig. 4). 105 �Figure 5. Columbite-tantalite quadrilateral: eastern subgroup, manganese suite petalite pegmatite. Modified from Fig. 12b, Tindle and Breaks (2000). Figure 6. Columbite-tantalite quadrilateral: eastern subgroup Fe suite petalite pegmatites. Modified from Fig. 12a, Tindle and Breaks (2000). 106 �THE FIELD TRIP The trip commences in Kenora. Proceed north on Highway 659 to the turn-off on to English River Road, just south of Redditt. Take the English River Road to the turn-off on to the Sand Lake Road, about 7 km south of the Separation Narrows bridge. Proceed along the Sand Lake Road to the Emerald Fields Resources access road, to the Big Mack pegmatite (Fig. 2). STOP 1 - BIG MACK PEGMATITE The Big Mack pegmatite (Fig. 7) is complexly folded and compressed into a 35 m x 100 m lens with several prominent apophyses tapering to the south, southeast and west. These apophyses consist of non-petalite bearing sodic aplites, blocky potassic pegmatite and holmquistite bearing granitic units. Several units will be observed within the Big Mack: A) Wall zone of medium blocky quartz+plagioclase+muscovite+garnet+biotite. Cordierite is common in this unit and in the apohyses. It is generally altered to garnet+mica+holmquistite rich simplectites that give the unit and several metres of the interior petalite zone a spotted appearance. B) Petalite rich, medium to coarse blocky phase of quartz+plagioclase+Kspar+muscovite+petalite. The petalite varies up to 60% in this unit and is identified by light brown weathering. C) Chrysoberyl bearing petalite pegmatite. This unit is restricted to a lens at the south end of the trench. It is grey due to the dominance of biotite over muscovite. Petalite content is generally lower than in unit B (15-20%), and it is generally finer grained but still blocky in nature and contains sporadic lime green 1-15 m chrysoberyl crystals. D) Primary aplite layered with petalite pegmatite. Folds are defined by this unit. E) Replacement albitic unit seen as white weathering layers and pods of muscovite+garnet+albite+quartz+K-spar. This unit is best observed enveloping the mafic metavolcanic screens. F) Post deformation, fracture controlled to vein like features include bikitaite, holmquistite and eucryptite. The eucryptite can be recognized by its grey, recessive weathering, capped by a lacy network of quartz veining. Massive to pillowed mafic flows can be observed on the hill north of the parking area. 107 �108 Figure 7. The Big Mack pegmatite, showing location of units discussed in the text. �Return to the Sand Lake Road, and then to the Separation Narrows bridge. Board boats and travel down stream, passing through Separation Rapids, to Heart Island on the Separation River (Fig. 2). STOP 2 - SEPARATION RAPIDS PLUTON The Separation Rapids Pluton is interpreted by Tanco geologists to be a flat lying, sheetlike, layered, very fractionated pegmatitic granite. The interpretation of the pluton being a sheet rather than a stock-like body is based on an aeromagnetic survey flown for Tanco (Assessment Files, Ministry of Northern Development and Mines, Kenora) that shows a magnetic pattern of similar continuity, amplitude and intensity as in the surrounding volcanic rocks extending beneath the Separation Rapids Pluton. Figure 8. Location of Heart Island in the Separation Rapids pluton. Heart Island (Fig. 8) displays classic pegmatitic granite features such as “bird’s-foot mica”, megacrystic potash feldspars, pegmatitic vugs, and aplite banding. If time permits, Red Handed Island, the larger island to the west of Heart island, will be visited. This island features a flat lying lepidolite-bearing pegmatitic granite that postdates D1 and D2 deformation phases. It is affected by D3 phase open folds with E-W 109 �axes gently plunging to the west. It may represent an external facies of the Separation Rapids pluton. Proceed by boat from Heart Island to Avalon Ventures Ltd.'s boat landing on the west shore of the river. A short walk inland leads to the Big Whopper pegmatite (Fig. 2). STOP 3 - BIG WHOPPER PEGMATITE Introduction Following staking of ground over the Big Whopper by local prospectors Bob Fairservice and James Willis in 1996, the 560 acre property (since expanded to 4480 acres) was optioned to Avalon Ventures Ltd. which has earned a 100% interest, subject to a 2% NSR royalty interest retained by the vendors. Figure 9. Big Whopper pegmatite. Areas 1 and 2 of the field trip stop are indicated. In 1997 and 1998, Avalon Ventures Ltd. began exploring the property by conducting linecutting, ground magnetic, geological and geochemical surveys, overburden stripping, trenching, mineralogical studies and diamond drilling totalling 8,751 metres in 57 holes. This work delineated the Big Whopper (Fig. 9) over a strike length of 1.5 km with widths 110 �ranging from 10 m to 80 m and to a vertical depth of 250 metres where it remains open. Total indicated and inferred petalite resources are estimated at 11.6 million tonnes grading 1.34% Li2O, 0.30% Rb2O and 0.007% Ta2O5. In 1999, a pre-feasibility study was completed on the deposit by Micon International Ltd. which concluded that development of the deposit as a producer of petalite plus feldspars, mica and tantalum, was economically viable and recommended proceeding with a bulk sampling program and full feasibility study. This work has not yet begun. In 2001, in response to higher tantalum prices, Avalon conducted a program of 1,401 metres of diamond drilling in 12 holes, channel sampling, mineralogical and metallurgical studies to better define tantalum distribution within the Big Whopper pegmatite system. The dominant economic minerals in the deposit are petalite and columbite-tantalite, the ore mineral of tantalum. The deposit also contains significant quantities of rubidiumpotash feldspar, albite, lepidolite, and cassiterite. At the Big Whopper, which is hosted entirely within amphibolites, a north-directed compressional tectonic event produced flattening and a strong vertically oriented regional schistosity striking west-northwest. This schistosity is folded about a sub-vertical axis, with minor folds commonly observed both in the pegmatite and the amphibolite host rocks. The Big Whopper itself exhibits tight s-fold geometry, with the thickened central portion of the pegmatite coinciding with the hinge zone, and attenuated limbs extending to the east and west. Fold axes exhibit vertical to sub-vertical orientations. Parallel mineral lineations indicate a strong vertical stretching component, with aspect ratios in the order of 5:1 to 10:1. Small pegmatites flanking the Big Whopper commonly exhibit boudinage structures indicative of a high-strain environment. Mineralogy and Zonation Mineralogical zoning observed in the Big Whopper is characteristic of highly evolved rare metal pegmatites, with well-developed wall zones and internal intermediate zones classified according to their dominant constituent minerals (Figure X). Metallogenic zoning is closely related to mineralogic zoning. The predominant mineralogical zones of the Big Whopper are as follows: 1. Wall Zone (predominantly albitite) 2. Megacrystic Feldspar and Quartz-Mica marginal Zones 3. Petalite (intermediate) Zone 1. The Wall Zone is a narrow 1 to 10 metre wide endocontact zone of albitite consisting essentially of saccharoidal to aplitic albite with accessory K-feldspar, muscovite, quartz, and Mn-rich garnet (spessartine). Proximal dykes and stringers exhibit the same mineralogy as the Wall Zone albitite. Cassiterite and tantalum oxides are commonly associated with the albitite, along with rare gahnite (a zinc spinel). Albitite characteristic of the Wall Zone commonly occurs in intimate association with the Megacrystic Feldspar Zone and these zones together with the Quartz Mica Zone, likely reflect early, more primary phases of pegmatite development. 111 �2. The Megacrystic Feldspar Zone is confined to the eastern and western internal margins of the Big Whopper pegmatite and resembles pegmatitic granite. It consists predominantly of orange-pink to grey-white, coarse to megacrystic K-feldspar and coarse silvery mica aggregates in an albitic matrix. Highly elevated whole rock rubidium values averaging in excess of 0.3% Rb2O are attributed to Rb-K-feldspar as an essential mineral in the pegmatite. The Quartz Mica Zone occurs in intimate association with the Megacrystic Feldspar Zone, and is generally enveloped by or interdigitated with it. It contains 50% quartz, 30% muscovite, and 20% K-feldspar. Elevated whole rock lithium values in this zone (up to 0.5% Li2O) are attributed to the presence of micas of the lithian muscovite to lepidolite series. 3. The Petalite Zone is an intermediate zone of the Big Whopper pegmatite and is the largest defined to date, comprising approximately 80% of its volume. The essential mineralogy consists of petalite, Rb-K-feldspar, albite, quartz and mica. A crude but distinct petalite zoning can be identified within the Big Whopper pegmatite as tightly folded layers with progressive fractionation increasing eastward. Ribbon-like, white petalite displaying schlieren-like habit (Type A) grades to coarse pink and pink-white petalite (Type B), and to blue-grey to pink-grey petalite (Type C). A fourth sub-zone (Type D) is recognized based on the presence of the purple mica lepidolite and occurs peripheral to Types A-C, mainly to the south and east. This zone is enriched in tantalum, typically assaying greater than 0.01% Ta2O5. Type C is a very fine-grained, equivalent of Types B and A, which is very highly foliated, mica-rich unit and commonly occurs interlayered as coarse-grained bands and lenses within Types B and A. Petalite in this unit tends to be partially altered to spodumene-quartz intergrowth (“SQUI”) exhibiting a net texture. Mineralization The main economic minerals of the Big Whopper deposit are petalite, Rb-K-feldspar, albite, lepidolite and columbite-tantalite. The Big Whopper pegmatite system is characterized by unusually high purity end-member compositions of the constituent minerals, a feature reflecting the highly evolved chemistry of the system. Petalite (LiAlSi4O10) is almost stoichiometrically pure, averaging close to the theoretical maximum lithium content of 4.8% Li2O, with only traces of soda, potash, and iron. It averages about 25% of the ore, and varies from white to pale pink in colour. Albite averages 11% soda, 0.10% potash, 0.35% lime, 0.01% iron oxide (Fe2O3). It makes up 40% of the ore, and on average ranges from white to bluish-white in colour. Rb-K-feldspar constitutes 10 to 15% of the ore. Although known in other pegmatites where it generally exhibits perthitic intergrowth, the Big Whopper variety carries only 0.3-0.4% Na2O along with 2.8% Rb2O, 15-16% K2O and. It is generally grey-white in colour and typically occurs as large megacrysts in the petalite ore. Lepidolite (K Rb(Li,Al)2-3(AlSi3O10)(O,OH,F)2) is a distinct purple-coloured mica that occurs in marginal zones of the Big Whopper and in separate flanking dykes. The mineral is an ore of rubidium, containing up to 4% Rb2O, and can comprise up to 15% of the ore. 112 �Columbite-tantalite (Mn,Fe)(Nb,Ta)O6 Manganocolumbite and manganotantalite predominate with rare microlite and ferrocolumbite, all occurring as fine-grained dark brown opaques. Tantalum is well distributed through the deposit but is typically enriched to levels exceeding 0.01% Ta2O5 in marginal lepidolite-rich petalite zones and albitite dykes. Other potentially valuable industrial minerals include muscovite mica (some with elevated lithia) which may comprise up to 15% of the ore, spodumene averaging 3-5% occurring as SQUI replacement rims on petalite, cassiterite, pale pink spessartine garnet and high-purity quartz. Minor accessory minerals include apatite, zircon, gahnite, monazite, xenotime, rare sulphides, sulphosalts, and thorite. Field Stop Descriptions Area #1: Big Whopper Petalite Deposit Main Mass The large stripped exposure of the Big Whopper main mass reveals all of its major mineralogical zones and sub-zones. The Wall Zone and feldspathic zones are exposed on the northwest side of the outcrop. The coarse white and pink petalite zone (Type B) is well exposed in the trench in the central part of the outcrop. It is flanked by Type A and C petalite mineralization with Type D (lepidolite rich) occurring on the south side and in a separate exposure to the east. The surface trench along the top of the Whopper averages 1.58% Li2O, 0.33% Rb2O and 0.007% Ta2O5 across 58.90 metres. Amphibolite screens occur within and at the margins of the Big Whopper. These screens are commonly disjointed with mullioned terminations, but are continuous to depth. Narrow 2 to 5 cm wide albitic haloes characteristically rim most of these screens, and show remarkably little variation in width regardless of the size of the amphibolite screen. These rims are interpreted as reaction fronts or depletion haloes, in which are concentrated lithophile elements (specifically Li, Rb, and Cs) forming mica-rich (glimmerite) selvedges to the amphibolite screens. The white albitic rims are depleted in these elements, but commonly exhibit elevated tantalum values of up to 0.049% Ta2O5. Area #2: Lepidolite Dike Lepidolite-rich petalite pegmatite dikes occur flanking the Main Mass of the Big Whopper pegmatite system mainly to the east. These dikes tend to be enriched in tantalum relative to the Main Mass of the Big Whopper reflecting the greater abundance of more high-evolved tantalum minerals such as microlite and wodginite in the Lepidolite Dyke. Channel sampling of this outcrop has produced an average of 0.023% Ta2O5 over 3.15 metres, with individual assays up to 0.031% Ta2O5. Dark blue fluor-apatite is a common accessory mineral Return to Avalon's landing on the Winnipeg River, and by boat to the Separation Narrows bridge. Proceed north on the English River Road about 3 km to the Umfreville 113 �114 Figure 10. Marko's pegmatite, showing location of zones discussed in the text. �Road turn off. A skidder trail leads from the Umfreville Road to Marko's pegmatite (Fig. 2). STOP 4 - MARKO'S PEGMATITE Marko's pegmatite (Fig. 10) extends along strike for a distance of 190 m in an east-west direction. It has a shallow dip to the south and is discordant to the near vertical dip of the iron formation that is its host rock. The pegmatite has a maximum thickness of 15 m and a maximum down dip extension of 30 m. Drill intersections indicate in cross section that Marko's pegmatite occupies a tension fracture that extends from the gabbro/iron formation contact at surface and progresses south across the iron formation at a relatively shallow angle but near normal to the primary layering in the iron formation. In longitudinal section Marko's pegmatite plunges 5-10º to the west. A second pegmatite, the North Marko's pegmatite, lies along the gabbro/mafic metavolcanic contact at surface, 20 m to the north of marko's pegmatite. Diamond drilling shows that the pegmatite extends to a depth of 40 m as a single, near vertically dipping sheet and then splits into north and south dipping sections. The south limb increases in size and degree of differentiation in the down dip and easterly directions. The North Marko's pegmatite is essentially barren at surface, but drill results show that mineralogy and geochemistry changes abruptly with depth and association with either a roll or flattening of the dike. This is likely due to the entrapment of fluorine rich fluids along these structural features. Both pegmatites are pristine and undeformed by the folding events that affected the Big Mack and Big Whopper pegmatites. Marko's pegmatite is exposed as two lenses at surface (Fig. 10). This is due to a sigmoidal roll in the moderate dip of the intrusion to the south. The internal zones can be readily traced and differentiation trends established with confidence along the surface exposures and in drill core. Zones of Marko's pegmatite to be examined are as follows: A) Wall zone comprised of quartz+albite+muscovite+beryl. Accessory minerals include black oxides (cassiterite, wodginite), green tourmaline and apatite. B) Petalite rich core zone, containing up to 95% petalite. The amount of petalite is locally variable, as seen in the westernmost part of the outcrop which consists essentially of coarse blocks of K-spar up to 2 m across, with interstitial petalite. This represents the crest of the pegmatite. C) Layered pegmatite-aplite. Quartz+garnet+biotite aplite is interlayered with a coarser muscovite+beryl granite. Fine grained black oxide minerals are common in the albite rich unit. A 1.6 m channel sample assayed 0.165% Ta2O5 and 0.10% Sn. D) Grey, fine grained granite withj minor muscovite and fine grained black oxides. 115 �E) Muscovite replacement unit of K-spar. F) Albitization of the petalite core. North Marko's pegmatite will also be examined. It has a simple assemblage at surface of quartz+K-spar+albite+mica with minor bands of aplite. Return to the Umfreville Road/English River Road intersection. Proceed north on the English River Road to a 75 m trail on the left leading to James' pegmatite (Fig. 2). STOP 5 - JAMES' PEGMATITE This highly fractionated pegmatite (Fig. 11), intruded into mafic metavolcanics, is strongly deformed and folded. De la Fuente (1998) has described it as an example of pre D2 deformation phase pegmatite. The Treelined Lake Granite, which shows the same deformation, is suggested (de la Fuente 1998) to be source granite for pre D2 pegmatites and pegmatitic granites Figure 11. Location of James' pegmatite In addition to quartz and feldspars, minerals present include green beryl, lithiophilite, petalite, spodumene blades, abundant black tourmaline, curviplanar mica (“ballpeen 116 �mica”), which is assumed to be lithium rich, and possibly zinnwaldite. Ferrowodginite has been identified in this pegmatite (Fred Breaks, personal communication). This zoned pegmatite is approximately 30 metres by 2 metres. The joint venture of Tanco and Gossan Resources Ltd. drilled the dike in 1996. The best Ta205 grades obtained were 0.035% in drill core and 0.026% at surface. The pegmatite dips to the southwest at about 60° and appears to widen at depth. End of field trip stops. 117 �REFERENCES Beakhouse, G.P. 1991. Winnipeg River Subprovince; in Geology of Ontario, Ontario Geological Survey, Special Volume 4, Part 1, p.279-301. Beakhouse, G.P., Blackburn, C.E., Breaks, F.W., Ayer, J., Stone, D. and Stott, G.M. 1995. Western Superior Province Fieldtrip Guidebook, Precambrian '95; Ontario Geological Survey, Open File Report 5924, XXp. Blackburn, C.E. and Young, J.B. 1993. Geology of the Separation Lake greenstone belt; in Summary of Field Work and Other Activities 1993, Ontario Geological Survey, Miscellaneous Paper 162, p.68-73. Blackburn, C.E. and Young, J.B. 2000. Precambrian geology of the Separation Lake area, northwestern Ontario; Ontario Geological Survey, Open File Report 6001, 94 p. Blackburn, C.E., Young, J.B., Searcy, T.O. and Donohue, K. 1994a. Precambrian geology of the Separation Lake greenstone belt, west part; Ontario Geological Survey, Open File Map 241, scale 1:20 000. Blackburn, C.E., Young, J.B., Searcy, T.O. and Donohue, K. 1994b. Precambrian geology of the Separation Lake greenstone belt, east part; Ontario Geological Survey, Open File Map 242, scale 1:20 000. Breaks, F.W. 1991. English River Subprovince; in Geology of Ontario, Ontario Geological Survey, Special Volume 4, Part 1, p.239-277. Breaks, F.W. 1993. Granite-related mineralization in northwestern Ontario: I. Raleigh Lake and Separation Rapids (English River) rare-element pegmatite fields; in Summary of Field Work and Other Activities 1993, Ontario Geological Survey, Miscellaneous Paper 162, p.104-110. Breaks, F.W. and Bond, W.D. 1993. The English River Subprovince – an Archean gneiss belt: geology, geochemistry and associated mineralization; Ontario Geological Survey, Open File Report 5846, v. 1 and 2, 884 p. Breaks, F.W. and Pan, Y. 1995. Granite-related mineralization in northwestern Ontario: III. Relationship of granulite metamorphism to rare-element mineralization in the Separation Lake area of the English River Subprovince in Summary of Field Work and Other Activities 1995, Ontario Geological Survey, Miscellaneous Paper 164, p. 79-81. Breaks, F.W. and Tindle, A.G. 1994. Granite-related mineralization in northwestern Ontario: II. Detailed examination of the Separation Narrows (English River) rare-element group in Summary of Field Work and Other 118 �Activities 1994, Ontario Geological Survey, Miscellaneous Paper 163, p. 109-112. Breaks, F.W, and Tindle, A.G. 1996. New discovery of rare-element pegmatite mineralization, Separation Lake area, northwestern Ontario; Ontario Geological Survey, Open File Report 5946, 9p. Breaks, F.W. and Tindle, A.G. 1997. Rare-metal exploration potential of the Separation Lake area: an emerging target for Bikita-type mineralization in the Superior Province of NW Ontario; Ontario Geological Survey, Open File Report 5966, 27p. Breaks, F.W. and Tindle, A.G. 2002. Rare-metal mineralization of the Separation Lake area, northwest Ontario: characteristics of a new discovery of complex-type, petalitesubtype, Li-Rb-Cs-Ta pegmatite in Industrial Minerals in Canada, CIM Special Volume 53, p. 159-178. Cerny, P. and Ercit, T.S. 1985. Some recent advances in the mineralogy and geochemistry of Nb and Ta in rare-element granitic pegmatites; Bulletin Mineralogie, v. 108, p. 499-532. Cerny, P., Trueman, D.L., Ziehlke, D.V., Goad, B.E. and Paul, B.J. 1981. The Cat Lake-Winnipeg River and the Wekusko Lake pegmatite fields, Manitoba; Manitoba Department of Energy and Mines, Economic Geology Report ER80-1, 216p. de la Fuente, F. 1998. Structural analysis of the Tanco's Separation Lake property, western Ontario, Canada; report for Tantalum Mining Corporation of Canada Limited, 29 p. Larbi, Y., Stevenson, R., Breaks, F.W., Machado, N. and Gariepy, C. 1999. Age and isotopic composition of Late Archean leucogranites: implications for continental collision in the western Superior Province; Canadian Journal of earth Sciences, Vol. 36, p. 495-510. Stockwell, C.H. 1932. Beryllium deposits; p.126 in Geology and mineral deposits of a part of southeastern Manitoba, by J.F. Wright; Geological Survey of Canada. Memoir 169, 150p. Storey, C.C. 1990. An evaluation of the industrial mineral potential of parts of the districts of Kenora and Rainy River; Ontario Geological Survey, Open File Report 5718, 259p. Tindle, A.G. and Breaks, F.W. 2000. Tantalum mineralogy of rare-element granitic pegmatites from the Separation Lake area, northwestern Ontario; Ontario Geological Survey, Open File Report 6022, 387p. 119 �120 �Field Trip 6 Geology of the Red Lake Camp, Ontario Andreas Lichtblau and Carmen Storey Ontario Geological Survey Ministry of Northern Development and Mines 227 Howey Street, Box 324 Red Lake, Ontario P0V 2M0 Example of late gold vein stockwork forming part of the High Grade Zone, 32 Level, Red Lake Mine. Estimated contained gold in sample: 298 ounces (at 7,284 ounces gold per ton). Photo courtesy of Goldcorp Inc. �REGIONAL GEOLOGY The Red Lake District (Fig. 1) is underlain by Archean rocks of the Superior Province of the Canadian Shield. Rocks of four subprovinces are found in the Red Lake District: 1. Uchi Subprovince rocks in the Red Lake District comprise the Red Lake and BirchConfederation Lake greenstone belts in which the bulk of exploration and mining activity has taken place. The supracrustal rocks of the Red Lake greenstone belt can be subdivided into several assemblages with ages ranging from ca. 2990 Ma to ca. 2700 Ma (Table 1). Major granitoid intrusions show a range from ca. 2734 Ma to 2699 Ma (Table 2). 2. English River Subprovince rocks, south of the Uchi Subprovince, are predominantly metasedimentary and host minor intrusive rocks similar to those in the Quetico Subprovince. 3. To the north, the Berens River Subprovince formed the core of a microcontinent. This area is underlain by ca. 2750-2690 Ma felsic plutonic rocks interpreted as a magmatic arc formed at an Andean-style margin that culminated in the Kenoran orogeny. These plutonic rocks intruded an older subtratum (North Caribou terrane) on which Mesoarchean volcanic rocks of the Red Lake belt are also interpreted to have formed. 4. The Sachigo Subprovince comprises crustal blocks ranging from Paleoarchean (>3.4 Ga) to Neoarchean (ca. 2.7 Ga) in age. Figure 1. Western Uchi Subprovince (modified from Percival et al. 2000) 122 �123 Figure 2. General geology of the Red Lake greenstone belt (after Parker 2000). Tour stops as indicated. �GEOLOGY OF THE RED LAKE BELT (adapted from Sanborn-Barrie et al. 2001) The Red Lake greenstone belt (Fig. 2) is dominated by the (ca. 2990 Ma) maficultramafic Balmer assemblage, an oceanic plain sequence; minor calc-alkalic volcanic rocks of arc-like affinity terminate the assemblage. The majority of lode gold deposits in the camp are hosted by the basal mafic-ultramafic sequence. A later diverse lithologic association, the Ball assemblage, appears to represent a shallow marine, volcanic edifice built upon the Balmer substrate. Table 1. Summary of supracrustal lithologies and radiometric ages in the Red Lake greenstone belt (modified from Parker 2000; with new ages from Sanborn-Barrie et al. 2001 and Skulski et al. 2001; final error estimates are not cited for the new unpublished ages of T. Skulski). Supracrustal assemblage English River ? U-Pb Age (Ma) <2700±6 Rock types and descriptions References Polymictic pebble conglomerate. Thought to correlate with the Austin tuff, host to the Madsen gold deposit. Strongly calc-akaline rocks. Andesitic to dacitic pyroclastic rocks SanbornBarrie et al. 2001 Corfu and Andrews 1987 ConfederationGraves (north Red Lake) 2733±1.5 Huston (Cemetery) ConfederationHeyson (southeast Red Lake) ≤2743 Well-bedded argillite and turbiditic wacke; polymictic conglomerate. Basal sequence is commonly tholeiitic to calcalkaline with lobe-hyaloclastite rhyolite flows; intermediate pyroclastic rocks; basalt; and feldspar-phyric andesite. Calc-alkaline rocks are more abundant at higher stratigraphic levels. Skulski et al. 2001 Corfu and Wallace 1986 ConfederationMcNeely (central and SE Red Lake) Trout Bay 2742; 2748+10/-5 Dominated by calc-alkaline, intermediate lapilli-tuff breccia and lapilli tuff SanbornBarrie et al. 2001 2853 Lower tholeiitic basalt sequence with associated gabbroic rocks overlain by finegrained clastic metasedimentary rocks (wacke, argillite) interlayered with subordinate intermediate pyroclastic rocks and chertmagnetite iron formation. Overlain by tholeiitic, pillowed basalts. Strongly calc-alkaline intermediate pyroclastic rocks overlain by pebble conglomerate, thinly bedded wacke and capped by chert-magnetite iron formation Interlayered, feldspathic wacke, lithic wacke and argillite; lenses of pebble and cobble conglomerates and quartz-rich pebble conglomerate and quartz arenite. Typically calc-alkaline intermediate pyroclastic rocks and rhyolite flows; komatiitic to tholeiitic SanbornBarrie et al. 2001 2748+10/-5 to 2739±3 Bruce Channel 2894±1.5; 2894±2 Slate Bay ≤2916 Ball 2940±2; 2925±3 124 Corfu and Wallace 1986; Corfu and Andrews 1987 Corfu et al. 1998 Corfu and Wallace 1986 �Balmer 2992+20/-9; 2989±3; 2964+5/-1 basalt; overlain by chert-magnetite iron formation and dolomitic marble which contains stromatolites. Tholeiitic basalt, basaltic komatiite and komatiite interlayered with subordinate chertmagnetite iron formation; minor clastic metasedimentary rocks; minor intermediate to felsic pyroclastic rocks; and rhyolite. Corfu and Andrews 1987 Table 2. Summary of lithologies and radiometric ages for major granitoid intrusions in the Red Lake greenstone belt (modified from Parker 2000; new ages cited in Sanborn-Barrie et al. 2001 and elsewhere do not have final error estimates assigned, as this U-Pb data is not yet published). Granitoid intrusion Cat Island pluton U-Pb Age (Ma) 2699 Rock types and descriptions References Potassium feldspar granodiorite SanbornBarrie et al. 2001 Noble 1989 Walsh Lake pluton 2699 Killala-Baird batholith 2704±1.5 Hammel Lake batholith Dome stock 2717±2 2718±1 McKenzie stock 2720±2 Red Crest stock 2729±1.5 Potassium feldspar- and quartz-phyric monzogranite; xenolith-rich, diorite or granodiorite; possible oxidized phase at Ranger Lake with broad magnetic anomaly Potassium feldspar- and quartz-phyric monzogranite; xenolith-rich, diorite or granodiorite, diorite or granodiorite; oxidized, magnetite-bearing marginal phase. Potassium feldspar and quartz porphyritic monzogranite; associated anorthositic intrusion. Granodiorite and augite porphyritic diorite/gabbro. Augite porphyritic diorite-gabbro; some ultramafic rocks; granodiorite Augite porphyritic diorite-gabbro Little Vermilion batholith Douglas Lake pluton 2731±3 Hornblende tonalite-granodiorite 2734±2 Biotite tonalite Corfu and Andrews 1987 McMaster 1987 Corfu and Andrews 1987 Corfu and Andrews 1987 Corfu and Andrews 1987 Corfu and Andrews 1987 Corfu and Stone 1998 Widespread ca. 2894 Ma calc-alkaline volcanism is represented in Red Lake by the Bruce Channel assemblage. Overlying this is the ca. 2850 Ma Trout Bay assemblage which includes substantial basaltic and gabbroic rocks in western Red Lake which are prospective for PGE mineralization, and which includes minor intermediate pyroclastic rocks throughout central Red Lake. The Trout Bay assemblage may correlate with Woman assemblage rocks of the Confederation Lake belt. A regional angular unconformity is interpreted to separate the Mesoarchean assemblages from the Neoarchean Confederation assemblages. Volcanogenic massive sulphide mineralization is associated with the younger sequence. A significant number of felsic 125 �units are classed as FII and FIII type rhyolites, considered highly prospective for large (Kidd Creek/Noranda type) massive sulphide deposits (Parker 1999). A newly recognized component of the Neoarchean supracrustal package is the Huston sedimentary assemblage that includes polymictic cobble- to pebble-conglomerate and argillite; clasts include jasperoidal chert iron formation, massive sulfide pebbles, and mafic flow (?) rocks, as well as well-bedded, graded turbiditic wacke and argillite. The U-Pb age of detrital zircons give single age peaks of 2743 and 2746 Ma at the cemetery and Madsen sites respectively (Skulski et al. 2001), indicating erosion of pre-existing Confederation age rocks, and deposition after ca. 2743 Ma. Recent age dating (Skulski et al. 2001) has also yielded multiple ages of detrital zircons from a fragmental unit thought to correlate with the Austin "tuff" ore zone at the former Madsen mine. Most of the Meso- and Neoarchean assemblages exposed in Red Lake are represented in this unit. Maximum age of deposition is consequently ≤2700±6 Ma. DEFORMATION (adapted from Sanborn-Barrie et al. 2001) The Red Lake greenstone belt has undergone at least three phases of deformation: 1) D0, a non-penetrative, early (pre-2748 Ma) event involving overturning of the Balmer assemblage; 2) D1, (bracketed between 2733-2742 Ma) resulted in a north trending foliation that is axial planar to F1 folds and involved east-west shortening; and 3) D2, (ca. 2720-2700 Ma) resulted in a dominantly east- to northeast-striking foliation that refolds F1 folds. A local 'deflection' of S2 around the McKenzie stock created an east-southeast striking corridor of heterogenous strain forming the "Mine Trend", from Cochenour through the Balmertown area, hosting the major gold deposits of the camp. HYDROTHERMAL ALTERATION (adapted from Parker 2000) The Red Lake greenstone belt has been affected by a large-scale (10's of kilometres) hydrothermal alteration system, resulting in approximately contemporaneous a) strong to intense, distal calcite carbonatization that affects rocks of all ages; and b) less extensive (kilometres), proximal, strong to intense ferroan-dolomite and potassic alteration, found in almost all areas hosting gold mineralization. Carbonate alteration affects both the Dome (2718±1 Ma) and McKenzie (2720±2 Ma) stocks and is overprinted by calcsilicate, skarn-like alteration formed during the intrusion of the Killala–Baird batholith (2704±1.5 Ma) and the Walsh Lake pluton (2699 Ma). The significant carbonate alteration event is therefore bracketed between 2718 and 2704 Ma, during D2. The main macroscopic features of carbonate alteration are pervasive replacement of rock matrix, open-space filling/replacement of primary porosity (vesicles, pillow selvages, hyaloclastite matrix), filling of extension veins with massive, colloform, crustiform and cockade breccia textures, networks of variably oriented veins and "jigsaw puzzle" breccia veins. 126 �Multiple stages of carbonate alteration and veining have been recognized, indicating continuous carbonatization during D2 deformation. Potassic metasomatism takes the form of sericite/muscovite alteration in greenschistfacies rocks; in ferroan-dolomite altered ultramafic rocks fuchsite occurs instead of sericite. Potassic alteration in amphibolite-facies mafic and ultramafic rocks takes the form of pervasive biotite ± muscovite. Centimetre- to metre-wide, strong to intense, biotite ± calcite ± ferroan-dolomite ± disseminated pyrite alteration halos often enclose ferroan-dolomite veins in amphibolite-facies mafic rocks. Biotite altered zones in amphibolite-facies rocks are characterized by a diverse assemblage of aluminosilicate minerals such as andalusite, staurolite and cordierite, with garnet, chloritoid, cummingtonite and anthophylite. Barren, pervasive silicification within proximal alteration zones may be due to release and remobilization of silica during periods of pervasive carbonatization. The majority of gold deposits in the Red Lake belt are quartz and arsenopyrite rich selective replacement zones of colloform-crustiform ferroan-dolomite veins and breccia. GEOLOGY OF THE CAMPBELL-RED LAKE GOLD DEPOSIT (adapted from Dubé et al. 2002) Gold has been continuously produced from the Campbell-Red Lake (formerly known as the Campbell-Dickenson) deposit since 1948: current production levels and reserves are given in Table 3. Historical production figures for the Red Lake greenstone belt are shown in Table 4. Table 3. Current gold production and reserves, Red Lake greenstone belt Mine Production to end of 2000 Production in 2001 Tonnage Grade Tonnage @ Grade @ Total Commodity Reserves at end of 2001 Total Commodity Tonnage Grade Goldcorp Inc. Red Lake Mine 74 148 tons @ 1.57 ounces per ton 85 115 ounces Au 246 618 tons @ 2.26 opt Au (223 728 tonnes @77.50 g/t) 503 385 ounces Au 3 208 000 tons (2 910 000 tonnes) (1) 1.34 opt Au (46.04 g/t ) Placer Dome (CLA) Ltd. Campbell Mine 473 000 tonnes @ 15.7 g/t Au 229 408 ounces Au 438 000 tonnes @13.3 g/t 178 139 ounces Au 1 941 000 tonnes (2 139 600 tons) (2) 16.7 g/t Au (482 800 tons @ 0.388 opt Au) (1) News release, Goldcorp Inc. February 7, 2002 (2) News release, Placer Dome (CLA) Ltd. February 14, 2002 127 (0.487 opt Au) �Table 4. Historical gold production, Red Lake greenstone belt GOLD PRODUCTION IN THE RED LAKE GREENSTONE BELT to December 31, 2001 MINE YEARS PRODUCTION OF CAMPBELL RED LAKE GOLDCORP (DICKENSON) MADSEN COCHENOUR-WILLANS MCKENZIE RED LAKE HOWEY HASAGA STARRATT OLSEN H.G. YOUNG MCMARMAC GOLD EAGLE RED LAKE GOLD SHORE BUFFALO ABINO LAKE ROWAN RED SUMMIT MOUNT JAMIE 1949 - PRESENT(1) 1948 - PRESENT(1,2) 1938 - 1976, 1997(4) - 1999 1939 - 1971 1935 - 1966 1930 - 1941, 1957(7) 1938 - 1952 1948 - 1956 1960 - 1963 1940 - 1948 1937 - 1941 1936 - 1938 1981 - 1982 1985 - 1986 1986 - 1988 1935 - 1936 1976 TOTAL ORE MILLED (SHORT TONS) GOLD PRODUCED TROY OUNCES OUNCES PER TON 17,979,851 8,619,008 8,678,143 2,311,165 2,353,833 4,630,779 1,515,282 907,813 288,179 152,978 180,095 86,333 31,986 2,733 13,023 591 552 10,335,248 3,736,704 2,452,388 1,244,279 651,156 421,592 218,213 163,990 55,244 45,246 40,204 21,100 1,656 1,397 1,298 277 265 0.575 0.434(3) 0.283(5) 0.538(6) 0.277 0.091(8) 0.144 0.181 0.192 0.296 0.223 0.244 0.052 0.511 0.100 0.469 0.480 47,752,344 19,390,257 0.406 NOTES: (1) Includes final production figures for 2001. (2) For 1997, 1998 and 1999 no production due to strike by unionised employees. (3) From 1970, includes production from Robin Red Lake. (4) Includes clean up ore and materials from the mine site. (5) Historic grade, actual grade for 1999 was 0.14 ounce per ton gold. (6) Includes production from Annco and Wilmar properties. (7) Continuous production 1930 to 1941; includes 268 ounces recovered from clean up in 1957. (8) The ore mined at Howey, before sorting totalled 5,158,376 tons. The average production from run-of-mine ore was therefore 0.0817 ounce per ton gold. Alteration facies in the High Grade Zone at Goldcorp Inc.'s Red Lake Mine have been described by Dubé et al. 2002: 1. an outer, metre-wide, garnet-chlorite-magnetite alteration with chlorite-amphibole-andalusite and locally associated centimetre- to metre-wide 'bleached zone' containing andalusitemuscovite-quartz-ilmenite ...; 2. a proximal, centimetre- to metre-wide, massive to laminated, reddish-brown, biotite-carbonate alteration with disseminated pyrite (3-5%) and carbonate veinlets in well foliated basalt; and 3. a gold-rich, strongly foliated, silicified zone with abundant fine-grained arsenopyrite, sericite, and rutile, and lesser amounts of pyrite, pyrrhotite, magnetite, and stibnite (≤15%). This third alteration facies is adjacent to the silicified auriferous carbonate veins and replaces the biotite-carbonate-rich alteration. 128 �The chronology of gold-rich replacement textures suggests a syn-D2 mineralizing event, dominated by silicification of carbonate veins, contemporaneous with boudinage of the veins. The silicified carbonate veins are hosted mainly by basalt; areas of high-grade gold mineralization are controlled by F2 fold hinges deforming the basalt-ultramafic contact. Multiple periods of silicification and gold deposition overprint and replace the carbonatization in these lower pressure hinge zones. The extremely high grade ore (>2.0 oz/t Au) currently mined at Goldcorp Inc.'s Red Lake Mine, is possibly due to a combination of factors, including the presence of a lowpermeability ultramafic cap, allowing the build-up of very high fluid pressure in the footwall basalt; the high iron content of the tholeiitic basalt, creating a chemical, as well as structural, trap for the auriferous fluids; multiple D2 strain events; repeated episodes of gold deposition and remobilization into a low pressure F2 fold hinge hosting the High Grade Zone. SUMMARY OF STOPS, SURFACE FIELD TRIP, RED LAKE BELT The first outcrops after the underground tours will traverse both the proximal-distal alteration facies and the Neo–Mesoarchean boundary. ¾ The tour then continues to the south-central portion of the Red Lake greenstone belt, within the metamorphic aureole of the Killala-Baird batholith. ¾ Outcrops at the interface of Meso- and Neoarchean assemblages expose rock units similar to those mined at the past producing Madsen mine, a high temperature, disseminated, stratabound gold deposit, quite dissimilar to deposits in the 'Mine Trend'; ¾ this is followed by a visit to the Dome stock, a mineralized granodiorite intruded into the volcanics in the central portion of the belt; ¾ followed by stops in the town of Red Lake to view the site of the Howey mine, and to examine intensely deformed rocks within the purported Howey Bay – Flat Lake deformation zone; ¾ the last stops will be within strongly altered and veined Balmer rocks in the northeast portion of the belt. 129 �STOP 1 - MESO-NEOARCHEAN CONTACT Woodland Cemetery Road and Hwy. 125 (Fig. 2) These outcrops show altered relatively low-strain pillowed basaltic komatiite flows of the Balmer Assemblage unconformably overlain by polymictic conglomerate of the Huston assemblage. The exposures are in the transition from calcite carbonatization (distal alteration) to ferroan-dolomite (proximal) alteration. The pillowed and minor massive flows show extensive iron carbonate alteration as well as iron carbonate and quartz veins. Fuchsite is present in the central part of the outcrops on the west side of the highway (cemetery side). The Campbell Mine is approximately 1.5 km to the north While the mafic flows have not been directly dated at this locality, they are typically variolitic, and show a geochemical similarity with known Balmer age rocks elsewhere; the massive and pillowed flows here can be traced to Balmertown, where an intercalated rhyolite at the Campbell mine was dated at 2989 ± 3 (Corfu and Andrews 1987). Variolitic flows occur in the northern part of the outcrops on the east side of the highway. However, they are unconformably overlain by Huston polymictic conglomerate further south along the outcrop. The conglomerate contains a large proportion of rounded cherty, jasperoidal and pyritic fragments. It represents an apron of Confederation assemblage (McNeely age-2743 Ma) detritus deposited at the break in the paleoslope between the Confederation volcanic centre and its Balmer age substrate. STOP 2 - CALCITE CARBONATIZED PILLOWED FLOWS: DISTAL CARBONATE ALTERATION FACIES Outcrops on west side of Hwy. 125 and Sandy Bay Road (Fig. 2) Slightly deformed pillows of the Balmer assemblage show pervasive calcite carbonatization, calcite veins and pods. Amygdules are also filled (replaced?) with calcite. Jig-saw puzzle breccias (created by fluid overpressure at depth) are cemented by calcite. This represents the distal, outer halo of carbonate alteration. STOP 3 - CONTACT BETWEEN CONFEDERATION AND BALMER ASSEMBLAGES Suffel Lake Road and Hwy. 618 (Figs. 2 and 3) Exposures on the south side of the highway are part of the lowermost units of the Neoarchean Confederation assemblage. The outcrops here are amphibolite-facies 130 �tholeiitic, quartz-feldspar-porphyritic lapilli-crystal tuff, with thin, dark grey, collapsed pumice fragments; occasional lapilli sized lithic clasts are also observed. Strike of the rocks is generally northeast, facing and dipping steeply southeast. A sample from this unit, 800 m northeast of the intersection, gave an age of 2744 ± 1 Ma (Corfu and Andrews 1987). The north side of the road exposes highly altered tholeiitic, mafic volcaniclastic rocks of the Balmer assemblage. Abundant garnet and biotite rims clasts; minor andalusite is present. This outcrop, barren at this locality, forms part of the Austin "tuff" ore zone, described further below. STOP 4 - MADSEN DEPOSIT, POWER LINE OUTCROPS (Figs. 2 and 3) Time limitations of the tour do not permit a complete visit of the Madsen deposit; a brief description of the deposit follows: Geology of the Madsen Deposit (adapted from Dubé et al. 2000) Madsen is a stratabound, replacement-style, disseminated gold deposit, exhibiting two alteration facies, the mineralogy of which is now represented by two amphibolite-facies zones: 1) a pervasive aluminous, metre- to tens-of-metres-wide, low-strain, outer zone, containing andalusite-garnet-biotite-staurolite-amphibole; metre-wide stockwork amphibole veins and veinlets alternate with the pervasive alteration. Timing of this alteration is pre- to syn-D1, but its relationship to gold mineralization is not yet known; indeed, it could be classified as the amphibolite-facies equivalent of volcanogenic massive sulfide (VMS) type alteration, related to a Confederation age syn-volcanic hydrothermal alteration system; 2) an inner zone comprising a banded-laminated texture, characterized by bands of actinolite-hornblende-microcline-calcite-tourmaline, alternating with biotiterich bands. The amphibole is commonly randomly oriented. Diopside locally forms disseminated crystals up to 7-8 cm long, or veinlets. Ore zones occur within the inner alteration zone, and comprise finely layered, sulfide-rich lenses up to a few metres wide. Sulfides (8-10%) comprise pyrrhotite, pyrite and/or arsenopyrite with trace chalcopyrite, and are found as disseminations or veinlets parallel to lamination/foliation. Gold occurs in the native state as inclusions in silicate minerals and locally as coatings on sulfide minerals. Highest grade is found in areas of most intense alteration, represented by quartz-biotite-muscovite-microcline assemblage in mm-cm bands or layers. Crenulation of alteration bands, sulfides and calcite veinlets by S2 as well as the large-scale deformation and folding of Austin ore lenses by F2 folds are consistent with pre- to early D2 timing of gold mineralization. A minimum age on the deposit is 2699 ± 4 Ma (Corfu and Andrews 1987), the age of a cross-cutting post-ore granodiorite dyke. 131 �1/ I 400m / // J // //// d//// oO// / Figure 3. Geology of the Madsen mine area (modified from Dubé et al. 2000) 132 �Proximal alteration and style of mineralization may indicate the Madsen deposit to be related to higher temperature (400º-600ºC) gold deposits and gold-skarn deposits hosted by mafic volcanics (Parker 2000). South Austin Zone – Powerline Section The base of this series of poorly exposed outcrops is a well banded/layered example of Austin "tuff", from which the bulk of the 2.5 million ounces gold of the Madsen deposit were mined between 1938-1976 (Table 4). At this locality the Austin is a strongly altered (biotite, amphibole, garnet) mafic volcaniclastic/epiclastic rock, with wacke and conglomerate clasts, occupying the position of the unconformity between Balmer and Confederation assemblages. Further up the hill the Confederation age quartz-feldspar porphyritic lapilli tuff unit from Stop 1 forms the structural and stratigraphic hangingwall of the deposit and marks the beginning of Confederation time. Overlying this unit is an altered (biotite, garnet) polymictic conglomerate outcrop, part of the Huston assemblage, that yielded a single peak in detrital U-Pb zircon ages of ≤ 2746 Ma (Sanborn et al. 2001a). At the top of the hill, feldspar phyric tuff of the Confederation assemblage is exposed. STOP 5 - BUFFALO DEPOSIT - DOME STOCK MINERALIZATION (Fig. 2) The approximately 7 km diameter hornblende-biotite granodiorite stock (Table 2) has been dated at 2718 ± 1 Ma (Corfu and Andrews 1987) and is interpreted to have been emplaced during D2 (Sanborn-Barrie et al. 2001). The stock is variably iron-carbonate, sericite, and chlorite altered and deformed. Exposures to be visited (Figure 4) are at its southern contact; here it intrudes, and contains xenoliths of, foliated Balmer assemblage mafic volcanic rocks (Figure 4). The stock hosts several gold occurrences and two past-producing mines: the Red Lake Gold Shore produced 21,100 ounces gold, and the Buffalo Mine produced 1656 ounces gold. The Buffalo prospect was discovered in 1925 and explored several times since then. Note the adit reopened by Claude Resources Ltd. in October 1998 to further explore the Buffalo deposit. Gold is hosted within two sets of quartz-tourmaline-pyrite-calcite veins in conjugate orientation (centimetre-wide NE veins: 239°/73° N, and decimetre-wide NW veins: 119°/76° S; Pettigrew 1999). Their orientation may be as a result of the intersection of two previously interpreted (Durocher and Hugon 1983) deformation zones (St. Paul BayMartin Bay and Flat Lake-Howey Bay Deformation Zones). The dominant vein set strikes NW; primary quartz vein fill was replaced by tourmaline, concomitant with bleached pink metasomatic halos developing around tourmaline-rich portions of the veins. Gold is concentrated in the calcite-albite-sulfide halos, in particular at its outer fringe, where chalcopyrite and tellurides were deposited. A second stage of gold 133 �mineralization is associated with Bi-tellurides in fractures and cavity fillings in quartz and late fracture-filling pyrite, hosted within the qtz-tourmaline-pyrite-calcite veins. mafic volcanics granodiorite '---1 vein / shear Figure 4. Detailed geology of south side of Buffalo Pit (from Lavigne et al. 1986) STOP 6 - HOWEY MINE (Fenced in pit - drive by: Fig. 2) On the north side of Hammell Road a cement foundation marks the site the former Howey mine. Behind the fenced off area is the site of the crown pillar mined out in the final stages of the mine. The Howey Mine was the first producer (1930-1941) in the Red Lake camp and remains the lowest grade profitable gold mine in Canadian mining history (final average grade 0.08 opt Au, having produced 422 000 ounces gold). The Howey (and adjacent Hasaga) ore bodies occur in a boudinaged, variably sericitized and silicified quartz-feldspar porphyry dyke trending approximately 065°/80°S. Centimetre-wide, auriferous quartz veinlets trend 080°, making an angle of 15° with the contacts of the dyke and dip 80°S. Gold-bearing quartz veinlets formed as the last of three episodes of quartz veining. Gold is associated with pyrite-sphalerite-galena-tourmaline ± tellurides. Small flat outcrops between the highway and the fence are highly deformed intermediate rocks of the Howey Mine hanging wall. This site lies within the northeast trending Howey Bay – Flat Lake deformation zone and comprises Confederation age rocks. STOP 7 - HOWEY BAY-FLAT LAKE DEFORMATION ZONE (Fig. 2) The Howey Bay – Flat Lake deformation zone was defined by Durocher and Hugon (1983), and was interpreted to be part of a belt-wide system of transcurrent shear zones hosting most of the major gold deposits. Recent detailed work has led to a reevaluation of this concept (Sanborn-Barrie et al. 2000). 134 �This stop is approximately 750 m southwest of the Howey mine. Intense deformation at this stop has destroyed most primary textures that might be used to identify the rocks. The dominant rock type is mylonitized intermediate tuff. Pink felsic dikes that cut the intermediate rock are also mylonitized. Iron-carbonate veins are boudinaged and transposed into the shear direction. The far western extremity of the outcrops exposes deformed quartz-feldspar dyke (similar in appearance to the Dome stock) containing mafic xenoliths and quartz-tourmaline veinlets. STOP 8 - REDCON CARBONATE ZONE: Proximal ferroan-carbonate alteration; carbonate veining West and east sides of Nungessor Road (Fig. 2) This area is approximately 4 km north of the Campbell–Red Lake deposit, still within the proximal, ferroan-carbonate alteration facies. The outcrops are weakly foliated (145°), dominantly massive to pillowed Balmer assemblage basalts, occurring within the amphibolite-facies metamorphic aureole of the Walsh Lake pluton. The stripped area on the east side of the Nungesser road was mapped in detail (Figure 5) by Redcon Gold Mines in 1981 (assessment files) and now forms part of Goldcorp Inc.'s holdings. Here, a 1-2 m wide carbonate vein is exposed near its southeastern termination. The vein can be traced in outcrop and drilling for approximately 750 m to the west-northwest and will be seen at the next stop on the west side of the road. Gold occurs in north-northwest trending, irregular, centimetre-thick quartz-actinolite stringers within the carbonate vein. After an initial, pervasive biotite alteration event, cross-cutting relationships suggest the following sequence of formation (from Lavigne et al. 1986): 1. amphibole-quartz-calcite cross-fractures 2. quartz-calcite veins 3. ferroan-dolomite veins 4. mafic dyke 5. auriferous quartz veins Silicification evident in the pillowed flow on the northern half of the outcrop is barren and apparently not related to the gold-rich silicification event, rather, it may be due to local silica dumping following pervasive carbonate metasomatism. A "black line" fault occurs in the northern wall rocks of the main carbonate vein. A mafic (or lamprophyre) dyke (unit 4, above) cuts the vein, but is itself cut by late quartzactinolite-gold stringers. 135 �TYPE A VEINS TYPE C VEINS I \\\\\\\ss\\1 hb+q+pI+blo 1i2:J Pillow basalt Type A veins re aorom,e (type ci veine EI Matic dike (D) II Quartz ±Au (tvoe E) veina Fault Prominent Joints Figure 5. Detailed geology of the Redcon prospect (modified from Lavigne et al. 1986) The western outcrops are approximately 300 m west-northwest of the previous exposures. Things to note on the western series of outcrops: • differing colours of cross-cutting carbonate veins • colloform/crustiform textures in carbonate veins • andalusite-garnet-biotite alteration of pillows cut by calc-silicate veins (diopside ± calcite, quartz, tourmaline; retrograding to epidote, tremolite, actinolite/hornblende, magnetite) • calc-silicate veins cross-cut by carbonate veins • folding of carbonate veins by the "Mine trend" S2 136 �REFERENCES AND BIBLIOGRAPHY OF RECENT RESEARCH Chi, G., Dubé, B. and Williamson, K. 2002. Preliminary fluid-inclusion microthermometry study of fluid evolution and temperature-pressure conditions in the Goldcorp High-Grade zone, Red Lake mine, Ontario, in Current Research 2002C27, geological Survey of Canada, 14p. Dubé, B., Balmer, W., Sanborn-Barrie, M., Skulski, T. and Parker, J. 2000. A preliminary report on amphibolite-facies, disseminated-replacement-style mineralization at the Madsen gold mine, Red Lake, Ontario; in Current Research 2000-C17, Geological Survey of Canada, 12p. Dubé, B., Williamson, K., and Malo, M. 2001. Preliminary Report on the Geology and Controlling Parameters of the Goldcorp Inc. High Grade Zone, Red Lake Mine, Ontario; Geological Survey of Canada, Current Research 2001-C18, 13 p. Dubé, B., Williamson, K., and Malo, M. 2002. Geology of the Goldcorp Inc. High Grade zone, Red Lake mine, Ontario: an update, in Current Research 2002-C26, Geological Survey of Canada, 15p. Durocher, M.E. and Hugon, H., 1983. Structural geology and hydrothermal alteration in the Flat Lake-Howey Bay deformation zone, Red Lake area, in Summary of Field Work, 1983, Ontario Geological Survey, Miscellaneous Paper 116, p. 216 to p. 219. Gulson, B.L., Mizon, K.J. and Atkinson, B.T. 1993. Source and timing of gold and other mineralization in the Red Lake area, northwestern Ontario, based on lead-isotope investigations, Canadian Journal of Earth Science v. 30, pp. 2366-2379. Horwood, H.C., 1940. Geology and mineral deposits of the Red Lake area, in Fortyninth Annual Report of the Ontario Dept. of Mines, vol. XLIX, Pt. II, 231p. Lavigne Jr., M.J., Hugon, H., Andrews, A.J. and Durocher, M.E. 1986. Gold deposits of the Red Lake District, Relationships of gold mineralization to regional deformation and alteration in the Red Lake greenstone belt, Ontario, in Gold '86, Excursion Guidebook, ed. Pirie, J. and Downes, M.J., p.167 to p.211. Parker, J.R. 1999. Exploration potential for volcanogenic massive sulphide (VMS) mineralization in the Red Lake greenstone belt; in Summary of Field Work and Other Activities 1999, Ontario Geological Survey, Open File Report 6000, p.19-1 to 22-26. Parker, J.R. 2000. Gold mineralization and wall rock alteration in the Red Lake greenstone belt: a regional perspective; in Summary of Field Work and Other Activities 2000, Ontario Geological Survey, Open File Report 6032, p.22-1 to 22-27. 137 �Parker, J.R. 2001. Intermediate to Felsic Plutons in the Red Lake Greenstone Belt: Relationship to Deformation and Gold Mineralization; in Summary of Field Work and Other Activities 2001, Ontario Geological Survey, Open File Report 6070, p. 191 to 19-10. Penczak, R.S., and Mason, R. 1999. Characteristics and origin of Archean premetamorphic hydrothermal alteration at the Campbell Gold Mine, Northwestern Ontario, Canada, Economic Geology, v. 94. pp. 507-528. Penczak, R.S., and Mason, R. 1997. Metamorphosed Archean epithermal Au-As-Sb-Zn(Hg) vein mineralization at the Campbell Mine, Northwestern Ontario, Economic Geology, v.92, pp 696-719. Percival, J.A., Bailes, A.H., Corkery, M.T., Dubé, B., Harris, J.R., McNicoll, V., Panagapko, D., Parker, J.R., Rogers, N., Sanborn-Barrie, M., Skulski, T., Stone, D., Stott, G.M., Thurston, P.C., Tomlinson, K.Y., Whalen, J.B., and Young, M.D. 2000. An integrated view of Western Superior crustal evolution: highlights of 2000 NATMAP studies, in Summary of Field Work and Other Activities 2000, Ontario Geological Survey, Open File Report 6032, p.13-1 to p.13-17. Pettigrew, N., 1999. Structural and alteration history of the Buffalo Gold Deposit, Red Lake, Ontario; B.Sc. Thesis, University of New Brunswick, 154p. Pirie, J. and Downes, M.J., eds., 1986. Gold '86 Excursion Guidebook. Sanborn-Barrie, M., Skulski, T., and Parker, J. 2001. Three hundred million years of tectonic history recorded by the Red Lake greenstone belt, Ontario, in Current Research 2001-C19, Geological Survey of Canada, 32p. Sanborn-Barrie, M., Skulski, T., Parker, J. and Dubé, B., 2000. Integrated regional analysis of the Red Lake greenstone belt and its mineral deposits, western Superior Province, Ontario, in Current Research 2000-C18, Geological Survey of Canada, 16p. Skulski, T., Sanborn-Barrie, M. and Sanborn, N., 2001. New U-Pb geochronology in the Red Lake greenstone belt, Western Superior NATMAP, unpublished poster. Stone, D. and Hallé, J. 2000. Geology of the Blackbear, Yelling and Stull Lake areas, Northern Superior Province, Ontario, in Summary of Field Work and Other Activities 2000, Ontario Geological Survey, Open File Report 6032, p. 15-1 to 15-9. 138 � Dublin Core The Dublin Core metadata element set is common to all Omeka records, including items, files, and collections. For more information see, http://dublincore.org/documents/dces/. Title A name given to the resource Institute on Lake Superior Geology Dublin Core The Dublin Core metadata element set is common to all Omeka records, including items, files, and collections. For more information see, http://dublincore.org/documents/dces/. Title A name given to the resource Institute on Lake Superior Geology: Proceedings, 2002 Description An account of the resource Institute on Lake Superior Geology. Kenora, Ontario. May 12-16, 2002. Creator An entity primarily responsible for making the resource Institute on Lake Superior Geology Date A point or period of time associated with an event in the lifecycle of the resource 2002 Format The file format, physical medium, or dimensions of the resource PDF Language A language of the resource English https://digitalcollections.lakeheadu.ca/files/original/144f6c8afe6c22b14b0587341cb54d7e.pdf c67d0082182c4da907410c829b7469e8 PDF Text Text 49TH ANNUAL INSTITUTE ON LAKE SUPERIOR GEOLOGY IRON MOUNTAIN, MICHIGAN MAY 7 — 11, 2003 Proceedings 49- a- Volume - ------PART -PROGRAMS PROGRAMS AND ABSTRACTS ABSTRACTS PART 11— AND �INSTITUTE INSTITUTE ON ON LAKE LAKESUPERIOR SUPERIOR GEOLOGY GEOLOGY 49TH ANNUAL MEETING MAY 7-11, 2003 IRON MOUNTAIN, MICHIGAN HOSTED HOSTEDBY: BY: LAUREL G. LAUREL G.WOODRUFF WOODRUFFAND AND WILLIAM WILLIAMF. F.CANNON CANNON Co-Chairs Co-Chairs U.S.GEOLOGICAL GEOLOGICAL SURVEY U.S. SURVEY With With assistance assistance from from Michigan MichiganTechnological TechnologicalUniversity University and and John JohnGartner, Gartner,Coleman ColemanEngineering EngineeringCompany Company Volume Volume 49 49 Part Proceedings and Abstracts Abstracts Part 11 — - Proceedings Compiled Compiledand and edited edited by byLaurel LaurelWoodruff, Woodruff,U.S. U.S. Geological GeologicalSurvey Surveyand and Theodore Theodore Bornhorst, Bornhorst, Michigan Michigan Technological University University Cover CoverPhoto: Photo:Berkshire BerkshireShaft, Shaft,Menominee MenomineeRange, Range,Michigan. Michigan.Photo Photofrom fromthe theMichigan Michigan Technological University Mining Engineering Department Collection. Technological University Mining Engineering Department Collection. �49TH 4gTHINSTITUTE INSTITUTE ON LAKE LAKE SUPERIOR SUPERIOR GEOLOGY GEOLOGY VOLUME VOLUME 49 49CONSISTS CONSISTSOF: OF: PART PART1: 1:PROGRAM PROGRAMAND ANDABSTRACTS ABSTRACTS PART2: 2: FIELD FIELDTRIP TRIPGUIDEBOOK GUIDEBOOK PART OVERVIEW: OVERVIEW: PALEOZOIC PALEOZOICSTRATIGRAPHY STRATIGRAPHYAND ANDTECTONICS TECTONICSALONG ALONG THE THE NIAGRA NIAGRA SUTURE SUTURE ZONE, MICHIGAN MICHIGANAND AND WISCONSIN WISCONSIN TRIP MAGMATIC 1:PEMBINE-WAUSAU PEMBINE-WAUSAU MAGMATICTERRANE TERRANE TRIP 1: TRIP 2: MENOMINEE MENOMINEEIRON IRONDISTRICT DISTRICT TRIP 2: TRIP 3:STRATRIGRAPHY STRATRIGRAPHYAND ANDSTRUCTURE STRUCTUREOF OFTHE THEIRON IRONRIVER RIVER—TRIP3: CRYSTAL CRYSTALFALLS FALLSBASIN BASIN TRIP - THE THE REPUBLIC REPUBLICMINE MINE TRIP4: 4: LIFE LIFECYCLE CYCLEOF OFAN ANIRON IRONDEPOST DEPORT— FROM FROM ORE ORE GENESIS GENESIS TO TO MINE MINERESTORATION RESTORATION Reference to to material in Part 1 1 should should follow the t h e example below: Rogala, Rogala, B., B., Fralick, Fralick,P., P., and and Borradaile, Borradaile,G., G., 2003, 2003, AA magnetostratigraphic magnetostratigraphicand andsecular secularvariation vari$ion 4gth study study of of the the Sibley Sibley Group Group [abstract]; [abstract];Institute Instituteon onLake LakeSuperior SuperiorGeology GeologyProceedings, Proceedings, 49 Annual Ml, v. v.49, Annual Meeting, Meeting, Iron Iron Mountain, MI, 49, part part 1, 1,p.65-66. p. 65-66. and distributed by Publishedby bythe the 49th 4gth Institute Instituteon on Lake Lake Superior Geology Geology a n d distributed bythe the Published ILSG Secretary-Treasurer: ILSG MarkJirsa Jirsa(through (through2003) 2003) Mark Minnesota Minnesota Geological GeologicalSurvey Survey 2642 University UniversityAvenue Avenue 2642 Paul, MN MN55114-1 55114-1057 St. Paul, 057 In In 2004 2004 contact: contact: USA USA JirsaOOl @tc.urnn.edu @tc.umn.edu JirsaOOl Peter Peter Hollings Hollings Lakehead Lakehead University University Department of of Geology Geology Department Thunder Thunder Bay, Bay, ON ON P7B P7B5E1 5E1 CANADA CANADA peter.hollinas@lakeheadu.ca Deter.hollinps@lakeheadu.ca ILSG website: http://www.ilscieolopy.orp htt~://www.ilsaeoloav.org ILSG ISSN 1042-9964 �CONTENTS CONTENTS PROCEEDINGS PROCEEDINGS VOLUME VOLUME 49 49 PART PART1—PROGRAM 1-PROGRAM AND AND ABSTRACTS ABSTRACTS Institutes Instituteson on Lake LakeSuperior SuperiorGeology, Geology,1955-2003 1955-2003............................................................ iviv Constitution Constitutionof of the the Institute Instituteon onLake LakeSuperior Superior Geology Geology ................................................... vivi vii By-Laws of of the the Institute Instituteon onLake LakeSuperior Superior Geology Geology ....................................................... vii By-Laws ... MembershipCriteria Criteria ...................................................................................................... Membership viH VIII GoldichMedal MedalGuidelines Guidelines............................................................................................... Goldich ix ix Goldich GoldichMedal MedalCommittee Committee ............................................................................................... xx Past Goldich GoldichMedallists Medallists ..................................................................................................xi Past xi Citation Citation for for 2003 2003Goldich GoldichMedal MedalRecipient Recipient..................................................................... xD xii Eisenbrey EisenbreyStudent StudentTravel TravelAwards Awards................................................................................. xiv xiv xiiv Student Travel Travel Award Award Application ApplicationForm Form ....................................................................... xHv Student Student Student Paper PaperAwards Awards................................................................................................... xv xv Student Paper Paper Awards Awards Committee Committee ................................................................................ xv xv Student SessionChairs Chairs .............................................................................................................. Session xv xv Board of of Directors Directors ........................................................................................................ Board xvi xvi Local Committees Committees......................................................................................................... Local xvi xvi BanquetSpeaker Speaker.......................................................................................................... Banquet xvi xvi xvii Report of the the Chair Chair of of the the 48th 48thAnnual AnnualMeeting Meeting............................................................ xvii Report Program ....................................................................................................................... Program )O(i List of of Contributors Contributors ....................................................................................................... List X)(iI xxii Abstracts ................................................................................................................... Abstracts iii III xxi ... )O(VItI xxvm �INSTITUTES LAKE SUPERIOR INSTITUTESON LAKE SUPERIOR GEOLOGY GEOLOGY # YEAR YEAR CHAIRS CHAIRS PLACE PLACE 1 1955 Minneapolis, Minneapolis,Minnesota Minnesota C.E. Dutton C.E. Dufton 2 1956 Houghton, Houghton,Michigan Michigan A.K. A.K. Snelgrove Snelgrove 3 1957 East EastLansing, Lansing,Michigan Michigan B.T. B.T. Sandefur Sandefur 4 1958 Duluth, Duluth,Minnesota Minnesota R.W. Marsden R.W.Marsden 5 1959 Minneapolis, Minneapolis,Minnesota Minnesota G.M. G.M. Schwartz Schwartz && C. C. Craddock Craddock 6 1960 Madison, Madison,Wisconsin Wisconsin Eli. E.N.Cameron Cameron 7 1961 Port Port Arthur, Arthur, Ontario Ontario E.G. E.G. Pye Pye 8 1962 Houghton, Houghton,Michigan Michigan A.K. A.K. Snelgrove Snelgrove 9 1963 Duluth, Duluth, Minnesota Minnesota H. H.Lepp Lepp 10 1964 lshpeming, Ishpeming,Michigan Michigan A.T. A.T. Broderick Broderick 11 1965 St. St. Paul, Paul,Minnesota Minnesota P.K. P.K. Sims Sims && R.K. R.K. Hogberg Hogberg 12 1966 Sault SaultSte. Ste.Marie, Marie,Michigan Michigan R.W. R.W. White White 13 1967 East EastLansing, Lansing,Michigan Michigan W.J. W.J.Hinze Hinze 14 1968 Superior, Superior,Wisconsin Wisconsin A.B. A.B. Dickas Dickas 15 1969 Oshkosh, Oshkosh,Wisconsin Wisconsin G.L. G.L. LaBerge LaBerge 16 1970 Thunder ThunderBay, Bay,Ontario Ontario M.W. E.Mercy Mercy M.W. Bartley& Bartley &E. 17 1971 Duluth, Duluth,Minnesota Minnesota D.M. D.M. Davidson Davidson 18 1972 Houghton, Houghton,Michigan Michigan J. J. Kalliokoski Kalliokoski 19 1973 Madison, Madison,Wisconsin Wisconsin M.E. M.E. Ostrom Ostrom 20 1974 Sault SaultSte. Ste.Marie, Marie,Ontario Ontario P.E. P.E.Giblin Giblin 21 1975 Marquette, Marquette,Michigan Michigan J.D. J.D. Hughes Hughes 22 1976 St. St.Paul, Paul,Minnesota Minnesota M. M.Walton Walton 23 1977 Thunder ThunderBay, Bay,Ontario Ontario M.M. M.M.Kehlenbeck Kehlenbeck 24 1978 Milwaukee, Milwaukee,Wisconsin Wisconsin G. G.Mursky Mursky 25 1979 Duluth, Duluth,Minnesota Minnesota D.M. D.M.Davidson Davidson 26 1980 Eau EauClaire, Claire,Wisconsin Wisconsin P.E. P.E.Myers Myers 27 1981 East EastLansing, Lansing,Michigan Michigan W.C. W.C.Cambray Cambray 28 1982 International InternationalFalls, Falls,Minnesota Minnesota D.L. D.L.Southwick Southwick 29 1983 Houghton, Houghton,Michigan Michigan T.J. T.J.Bornhorst Bornhorst iv �30 1984 Wausau, Wisconsin Wisconsin G.L. LaBerge G.L. LaBerge 31 1 985 Kenora, Ontario Ontario C.E. C.E. Blackburn Blackburn 32 1986 Wisconsin Rapids, Wisconsin Rapids, Wisconsin Wisconsin J.K. Greenberg Greenberg 33 1987 Wawa, Wawa,Ontario Ontario 34 1988 Marquette, Michigan Michigan J. S. Klasner Klasner 35 1989 Duluth, Minnesota Minnesota J.C. J.C. Green Green 36 1990 Thunder Bay, Bay, Ontario Ontario M.M. Kehlenbeck M.M. 37 1991 Eau Claire, Wisconsin P.E. Myers Myers 38 1992 Wisconsin Hurley, Wisconsin A.B. A.B. Dickas Dickas 39 1993 Eveleth, Minnesota Minnesota D.L. Southwick 40 1994 Houghton, Michigan Michigan T.J. Bornhorst Bornhorst 41 1995 Marathon, Ontario Ontario M.C. Smyk M.C. Smyk 42 1996 Cable, Wisconsin Wisconsin L.G. Woodruff 43 1997 Sudbury, Ontario Ontario Meyer R.P. Sage & W. Meyer 44 1998 Minneapolis, Minnesota Minnesota J.D. Miller & M.A. J.D. M.A. Jirsa Jirsa 45 1999 Marquette, Michigan Michigan Regis T.J. Bornhorst Bornhorst & R.S. Regis 46 2000 Thunder Bay, Ontario Ontario S.A. Kissin & P. Fralick S.A. Fralick 47 2001 Madison, Wisconsin Wisconsin M.G. Mudrey, Jr. & & B.A. B.A. Brown Brown 48 2002 Kenora, Ontario Ontario P. Hinz Beard Hinz & R.C. Beard 49 2003 Iron Mountain, Michigan Michigan L.G. L.G. Woodruff & W.F. Cannon Cannon E.D. Frey & R.P. Sage Sage E.D. V �__________(some CONSTITUTION OF THE INSTITUTE ON LAKE SUPERIOR GEOLOGY (Lastamended amendedby bythe theBoard—May Board-May 8,8,1997) (Last 1997) ArticleII Article Name The The name nameof of the the organization organizationshall shall be bethe the "Institute "Instituteon onLake Lake SuperiorGeology". Geology". Superior ArticleIII1 Article Obiectives Obiectives Theobjectives objectivesof of this thisorganization organizationare: are: The A. A. To Toprovide provideaameans meanswhereby wherebygeologists geologistsininthe theGreat GreatLakes Lakesregion regionmay may exchangeideas ideasand andscientific scientificdata. data. exchange B. B. To Topromote promotebetter betterunderstanding understandingofofthe thegeology geologyofofthe theLake LakeSuperior Superiorregion. region. C. field C. To Toplan planand andconduct conductgeological geological fieldtrips. trips. . Status No No part part of of the the income income of of the the organization organizationshall shallinsure insureto to the the benefit benefitof ofany any member memberor or individual. individual.In Inthe the event eventof of dissolution, dissolution,the theassets assetsof ofthe theorganization organization (sometax tax free freeorganization). organization). shall shallbe bedistributed distributedto to Article IllIll Article a (To (To avoid avoid Federal Federal and and State State income incometaxes, taxes, the the organization organizationshould shouldbe benot notonly only "scientific" "scientific"or or "educational, "educational, but but also also "non-profit") "non-profit") ArticleIV IV Article Article VV Article ArticleVI Vl Article Article VII Vll Article ArticleVIII Vlll Article Minn. Minn. Stat. Stat. Anno. Anno. 290.01, 290.01, subd. subd.44 Minn. Minn. Stat. Stat. Anno. Anno. 290.05(9) 290.05(9) 1954 1954 Internal InternalRevenue RevenueCode Codes.501 s.501(c)(3) (c)(3) Membership Membership The The membership membership of of the the organization organizationshall shall consist consist of of persons persons who who have have registered registeredfor for an an annual annualmeeting meetingwithin withinthe thepast pastthree threeyears, years, and andthose thosewho who indicate a member according to guidelines approved by the indicate interest interestin in being being a member according to guidelines approved by the Board Board of of Directors. Directors. Meetinas Meetings The The organization organization shall meet once a year. The Theplace placeand and exact exact date date of of each each meeting meeting will will be be designated designated by by the the Board Boardof of Directors. Directors. Directors Directors The The Board Boardof of Directors Directorsshall shall consist consist of of the the Chair, Chair, Secretary-Treasurer, Secretary-Treasurer,and andthe the last last three three past past Chairs; Chairs; but if the the board board should should at at any any time time consist consist of of fewer fewer than than five five persons, persons, by by reason reasonof of unwillingness unwillingnessor or inability inabilityof of any any of of the the above above persons persons to to serve serve as as directors, directors, the the vacancies vacancieson on the the board boardmay may be be filled filled by by the the Chair Chairso so as as to members hi^ of of the the board boardto to five five members. members. to bring brina the the membership 0fficeA Officers The officers officers of this organization organization shall shall be be aa Chair Chair and and Secretary-Treasurer. Secretary-Treasurer. A. The TheChair Chairshall shallbe beelected electedeach each year year by by the the Board Board of of Directors, Directors, who who shall shall give give due consideration consideration to the wishes of any group group that may may be be promoting promoting the the next next annual meeting. His/her Hislherterm term of of office officeas asChair Chairwill will terminate terminate at at the the close close of of the the annual annual meeting meeting over which which he/she helshe presides, presides, or when his/her hislher successor successor shall shall have been appointed. He/she Helshe will will then serve serve for aa period period of three years as a member member of the Board Board of Directors. Directors. B. The meeting. His/her TheSecretary-Treasurer Secretary-Treasurershall be be elected at the annual meeting. Hislher term of office shall be four years, or until his/her successor shall have term of office shall be four years, or until hislher successor shall havebeen been appointed. appointed. ~mendments Amendments This This constitution constitution may may be be amended amended by by aa majority majorityvote vote (majority (majorityof of those thosevoting) voting) of of the the membership membership of of the the organization. organization. vi �BY-LAWS OF BY-LAWS OFTHE THE INSTITUTE INSTITUTE ON LAKE LAKE SUPERIOR SUPERIOR GEOLOGY GEOLOGY I. Duties of the Officers and Directors I. Directors A. It shall be the duty of the Annual Annual Chairman Chairman to: to: I1.. Preside Presideat at the the annual annualmeeting. meeting. 2. Appoint Appointall allcommittees committeesneeded neededfor for the theorganization organizationof of the theannual annualmeeting. meeting. 3. Assume Assume complete completeresponsibility responsibility for for the the organization organization and and financing financing of of the the meeting over which annual meeting which he/she hershe presides. presides. B. It shall be the duty of the Secretary-Treasurer B. Secretary-Treasurer to: 1. Keep I. Keepaccurate accurateattendance attendance records recordsof of all all annual annual meetings. meetings. 2. Keep Keepaccurate accurate records recordsof of all all meetings meetings of, of, and and correspondence correspondence between, the Board of Directors. Directors. 3. Hold all funds Hold all funds that that may may accrue accrue as as profits profits from from annual annual meetings meetings or field trips for the organization and operation of of and to make these funds available for future future meetings meetings as as required. required. of the the Board of Directors to plan locations of annual C. It shall be the duty of C. organization and meetings and to advise on the organization and financing financing of of all all meetings. meetings. II. Duties 11. Dutiesand and Expenses Expenses $5.00 or or less less on on an an annual basis shall be A. Regular Regularmembership membershipdues dues of of $5.00 assessed each member as determined by the Board of Directors.. B. Registration Registrationfees fees for for the the annual annual meetings meetings shall shall be be determined determined by by the Chair in the Board Board of of Directors. Directors. The consultation with the The registration registration fees fees can can include include expenses to cover operations outside of the annual meeting as determined determined by recommended that registration the Board Board of Directors. Directors. It is strongly recommended registration fees be be attendance of students. kept at a minimum to encourage attendance Ill. Rules Ill. Rules of of Order Order The rules contained in Robert's Rules of Order shall govern this organization organization in in all cases cases to which which they they are are applicable. applicable. IV. IV. Amendments Amendments These by-laws by-laws may be amended by a majority majority vote (majority (majority of those those voting) voting) of of the the membership of the organization; provided that such modifications modifications shall shall not conflict conflict with the constitution constitution as presently presently adopted adopted or subsequently subsequently amended. amended. - Last 996 May, 11996 Last Amended Amended— May, vii vii �MEMBERSHIP MEMBERSHIPCRITERIA CRITERIA FOR FOR THE THE INSTITUTE ON LAKE LAKE SUPERIOR INSTITUTE SUPERIOR GEOLOGY GEOLOGY Approved May 8, 1997 8,1997 A. Membership Membershipin inthe theInstitute lnstituteon onLake LakeSuperior Superior Geology Geology requires requires either either participation participationin in Institute activities, activities, or an indication on aa regular basis of of interest interest in in the the lnstitute, Institute. Those Those individuals registering for an annual annual meeting meeting will remain remain as members members for for 44 years years unless: unless: 1) they indicate no further interest interest in in the Institute Institute by by responding respondingnegatively negatively to to the the statement on meeting meeting circulars circulars "Remove "Remove my my name name from from the the mailing mailinglist"; list";or or 2) 2)two two different years are successive mailings in different are returned returned by by the the postal postal service service as as address address unknown. unknown. B. Those individuals individuals who have have not not registered registered for an an annual annual meeting meeting in in the thepast past44years years must indicate indicate an interest interest in the Institute by postal, electronic, or verbal correspondence lnstitute by or verbal correspondence with the Secretary-Treasurer Secretary-Treasurer at least once every two two years. years. Such Suchindividuals individualswill will be be removed from the membership membership if they indicate indicate no no further further interest interestin in the the Institute lnstituteor ortwo two different years are successive mailing in different are returned returned by by the postal postal service service as as address address unknown, unknown. C. The The Secretary-Treasurer Secretary-Treasurer will maintain a list of current members. The The list listwill will include include the date of the beginning beginning of continuous continuous membership, membership, dates of returned returned mail, dates dates of last contact (expression of interest), and the date membership expires, barring a change of status initiated by by the the member. member. Those Those individuals individuals who have have become become members membersof of ILSG ILSG by by Section B will will have have an an expiration expiration date date listed listed at at 22 years years from from the the upcoming upcoming meeting. For For example, a member who expresses interest interest in in September of 1997 1997 (the (the next nextannual annual 2000, unless meeting is May, 1998) will have an expiration date of May, 2000, unless the the member member contacts contacts the Secretary-Treasurer Secretary-Treasureror or attends attends an an annual annual meeting. meeting. 0. "Member D. "Memberfor forLife" Life"status statusisisgranted grantedto to individuals individualswho who have have been been (nearly) (nearly) continuous participants of the ILSG meetings meetings for 15 years, Goldich Medal recipients, or those who have sewed served as as meeting meeting chairs. chairs. This maintained unless the This status will be further maintained individuals indicate no further further interest in the the lnstitute, Institute, or 4 mailings in different years are returned by the postal service as address unknown, or they are are deceased. deceased. E. All All members memberswill will be be mailed mailedthe the First FirstCircular Circularfor for the the Annual Annual Meeting Meetingand andthe theILSO ILSG Newsletter. The Chair of the annual meeting may opt to to send the the first first circular to Newsletter. additional individuals. All All returned returnedmail mail should shouldbe be reported reported to to the the Secretary-Treasurer. Secretary-Treasurer. F. The TheSecretary-Treasurer Secretary-Treasurercan candesignate designateany any individual individualwho who is is on on the the ILSG ILSGmembership membership list (mailing list) as of January 1, 1997 as a member for life based on participation participation in in ILSG ILSG activities. activities. corrections to the SecretaryG. Members Membersare are strongly strongly encouraged encouraged to send address corrections Secretay Treasurer to avoid unintentional unintentional lapse lapse of membership. membership. viii viii �GOLDICH GOLDICHMEDAL MEDALGUIDELINES GUIDELINES (Adopted by the the Board Board of Directors, (Adopted Directors, 1981; 1981; amended amended1999) 1999) Preamble Preamble documented by the fact that the 27th The Institute lnstitute on Lake Lake Superior Superior Geology Geology was born in 1955, as documented meeting was held in 1981. The annual meetino TheInstitute's Institute'scontinuing continuina objectives obiectivesare are to to deal dealwith with those those aspects of geiogy geology that are related geographically to to Lake Lake .&p&ior; Superior; to to encourage encourage the the discussion discussion of of ispects subjects and geologists from and sponsoring sponsoring field trips that will bring bring together geologists from academia, academia, government government surveys, and industry; maintain an informal industty; and to maintain informal but highly effective mode of operation. the course of its existence, the membership membership of the Institute During the lnstitute (that (that is, those geologists who indicate an interest in the the objectives of the ILSG ILSO by attending) attending) has has become aware of the fact fact that certain of their colleagues meritorious contributions to the colleagues have have made made particularly parlicularly noteworthy and meritorious understanding of Lake understanding Lake Superior Superior geology geology and and mineral mineraldeposits. deposits. The first award award was made made by by ILSO ILSG to Sam Goldich Goldich in in 1979 1979 for his his many many contributions contributions to to the the geology of the region region extending over about 50 years. Subsequent Subsequentmedallists medallistsand andthis thisyear's year'srecipient recipientare are table below. listed in the table below. Award Guidelines 1) The Themedal medalshall shallbe beawarded awardedannually annuallyby bythe the ILSG ILSGBoard Boardof of Directors Directorsto toaageologist geologistwhose whosename name is associated with a substantial interest in, and contribution contribution to, to, the the geology geologyof of the the Lake LakeSuperior Superior region. region. 2) The TheBoard Boardof of Directors Directorsshall shall appoint appoint the the Goldich Goldich Medal Medal Committee. The Theinitial initialappointment appointmentwill will of three three members, one one to to serve serve for for three three years, years, one onefor fortwo twoyears, years,and andone onefor forone oneyear. year. The The be of member with the the briefest incumbency incumbency shall shall be be chair chair of ofthe the Nominating Nominating Committee. Committee. After the first the Board of of Directors shall appoint at each spring meeting meeting one new member year, the member who will serve for three years. In the chair. chair. The Committee In his/her hisher third year this member shall be the Committee membership the main main fields fields of of interest interest and and geographic geographic distribution distributionof of ILSG ILSG membership. membership. The outshould reflect the going, senior senior member of the Board of Directors going, Directors shall act as liaison liaison between between the the Board Board and and the Committee for aa period Committee period of of one one year. year. 3) By Bythe the end end of of November, November, the Goldich Goldich Medal Medal Committee Committee shall make make its its recommendation recommendation to the of the Board of of Directors, who will then inform the Board of the nominee. Chair of 4) The The Board Boardof of Directors Directors normally normallywill will accept the nominee nominee of the Committee, Committee, inform inform the medallist, and have one medal engraved appropriately appropriately for presentation medal engraved presentation at the next next meeting meetingof of the the Institute. lnstitute. 5) recommended that the Institute lnstitute set set aside aside annually annually from from whatever whatever sources, sources, such such funds funds as as will will 5) It is recommended support the continuing continuing costs be required to supporl costs of of this this award. award. Nominating Procedures Nominatina Procedures shall take 1) The The deadline deadline for nominations is November 1. The The Goldich Goldich Medal Medal Committee shail at any anytime. nominations at time. Committee Committeemembers membersmay maythemselves themselves nominate nominate candidates; however, for or supporl support individual Board members may not solicit for individual nominees. nominees. 2) Nominations Nominationsmust mustbe bein inwriting writingand andsupported supportedby by appropriate appropriatedocumentation documentationsuch such as as letters letters of recommendation, publications, curriculum curriculum vita's, and recommendation. lists of ~ublications. and evidence evidenceof of contributions contributionsto to Lake Lake Superior geologiand geology and to the Institute. superior lnstitute. 3) Nominations Nominationsare are not not restricted restricted to Institute lnstitute attendees, but but are are open open to anyone who has worked on contributed to to the the understanding of Lake Superior geology. and contributed ix �Selection Guidelines Guidelines Selection 1) Nominees Nomineesare aretotobe beevaluated evaluatedon onthe thebasis basisofoftheir theircontributions contributionsto toLake LakeSuperior Superiorgeology geology 1) (sensulato) lato)including: including: (sensu a) importance importanceofofrelevant relevantpublications; publications; a) b)promotion promotionofofdiscovery discoveryand andutilization utilizationofofnatural naturalresources; resources; b) c) c) contributions contributionstotounderstanding understandingofofthe thenatural naturalhistory historyand andenvironment environmentof ofthe theregion; region; d') generation generat'onofofnew newideas ideasand andconcepts; concepts;and and d) e) and e) contributions contributionstotothe thetraining tra~ning andeducation educationof ofgeoscientists geoscientistsand andthe thepublic. public, 2) 2) Nominees Nomineesare aretotobe beevaluated evaluatedon ontheir theircontributions contributionsto tothe theInstitute lnstituteas asdemonstrated demonstratedby by attendance attendanceat at Institute lnstitutemeetings, meetings,presentation presentationof oftalks talksand andposters, posters,and andservice sewiceon onInstitute lnstituteboards, boards, committees, committees,and andfield fieldtrips. trips. 3) 3) The Therelative relativeweights weightsgiven giventotoeach eachofofthe theforegoing foregoingcriteria criteriamust mustremain remainflexible flexibleand andatatthe the discretionof of the the Committee Committeemembers. members. discretion 4) There Thereare areseveral severalpoints pointstotobe beconsidered consideredby bythe theGoldich GoldichMedal MedalCommittee: Committee: 4) a) a)' An Anattempt attemptshould shouldbe bemade madetotomaintain maintainaabalance balanceofofmedal medalrecipients recipientsfrom fromeach eachofofthe the three threeestates—industry, eslales-inoustry, academia, academia,and andgovernment. government. b) ItIt must mustbe benoted notedthat that industry industrygeoscientists geoscientislsare are at ataadisadvantage disadvantageininthat thatmuch muchofoftheir the.r b) work work ininnot notpublished. published. 5) 5) Lake LakeSuperior Superiorhas hastwo twosides, sides,one onethe the U.S., U.S.,and and the the other other Canada. Canada. This Thisisisundoubtedly undoubtedlyone oneof of the the Institute's Institute'sgreat greatstrengths strengthsand andshould shouldbe benurtured nurturedby byequitable equitablerecognition recognitionofofexcellence excellenceininboth both countries. countries. GOLDICH GOLDICH MEDAL MEDALCOMMITTEE COMMITTEE Serving Sewing through through the the meeting meeting year year shown shown in inparentheses parentheses Frank Frank Luther Luther(2003) (2003) University University of Wisconsin, Whitewater Ron Sage Sage(2004) (2004) Ron Ontario Ontario Geological Geological Survey Survey (retired) (retired) David DavidMeineke Meineke(2005) (2005) Meriden Meriden Engineering, Engineering, Hibbing, Hibbing, Minnesota Minnesota Steve Kissin,as asout-going out-goingsenior seniormember memberof ofInstitute lnstituteBoard Boardof ofDirectors, Directors,isisliaison liaison Steve Kissin, between Goldich Medal Committee and the Board through the 2004 meeting between meeting x �2003 2003GOLDICH GOLDICHMEDAL MEDALRECIPIENT RECIPIENT Klaus Klaus J. Schulz Schuiz U.S. Geological Geological Survey Survey Reston, Virginia Reston, Virginia GOLDICH GOLDICHMEDALISTS MEDALISTS 1979 1979 Samuel SamuelS. S. Goldich Goldich 1991 William WilliamHinze Hinze 1991 1980 1980 not notawarded awarded 1992 William WilliamF.F.Cannon Cannon 1981 1981 Carl Carl E. E. Dutton, Dutton, Jr. Jr. 1993 Donald DonaldW. W. Davis Davis 1982 1982 Ralph RalphW. W.Marsden Marsden 1994 Cedric CedricIverson Iverson 1983 I983 Burton BurtonBoyum Boyurn 1995 Gene GeneLaBerge LaBerge 1984 1984 Richard RichardW. W.Ojakangas Ojakangas 1996 I996 David DavidL.L.Southwick Southwick 1985 1985 Paul PaulK. K.Sims Sims 1997 1997 Ronald RonaldP. P.Sage Sage 1986 1986 G.B. G.B.Morey Morey 1998 Zell ZellPeterman Peterman 1998 1987 I987 Henry HenryH. H.HaIls Halls 1999 1999 Tsu-Ming Tsu-MingHan Han 1988 1988 Walter WalterS. S.White White 2000 2000 John JohnC. C.Green Green 1989 1989 Jorma JormaKalliokoski Kalliokoski 2001 2001 John John S. S. Klasner Klasner 1990 1990 Kenneth KennethC. C.Card Card 2002 2002 Ernest Ernest K. K. Lehmann Lehmann xi �CITATION KlausJ. J. Schulz Schulz Klaus 2003 Goldich Goldich Medal Medal Recipient Recipient 2003 Klaus Klaus Schulz Schulz has has had had aa long long and and productive productivecareer career spanning spanning more morethan than30 30years years as asaa geologist geologistininthe theLake LakeSuperior Superiorregion. region.He Hewas wasintroduced introducedto tothe thegeology geologythrough throughhis his educationin inthe thearea, area,he hecompleted completedgraduate graduatestudies studiesininthe theregion, region,performed performedseveral several education summers summers of of field field work work for for mining miningcompanies companies in in aa number number of different different areas, areas, and and has has conducted conductedextensive extensiveresearch researchas as aa scientist scientistwith withthe theU.S. US. Geological GeologicalSurvey. Survey.This This extensive extensiveand anddiverse diverse experience experiencehas hasmade madehim himaa real realauthority authorityon onthe thegeology geologyof ofthe the Lake Superior Superiorregion. region. Lake Klaus Klaus received receivedhis his B.S. B.S. degree degree in in geology geology from from the the University Universityof of WisconsinWisconsinOshkosh Oshkoshinin1971. 1971.He Hecompleted completedhis hisMasters Mastersdegree degreeatatthe theUniversity UniversityofofMinnesotaMinnesotaDuluth Duluthin in 1974, 1974,with with aa thesis thesis project project in in the the Vermilion Vermilion district districtof of northern northernMinnesota. Minnesota.He He received receivedhis his Ph.D. Ph.D. from from the the University Universityof of Minnesota Minnesotain in1977 1977with withaadissertation dissertationon onthe the petrology petrology of volcanic rocks rocks in the Vermilion district. Klaus spent the next two years as a National NationalResearch Research Council Council Research ResearchAssociate Associate with with NASA NASA at at the the Johnson JohnsonSpace SpaceCenter Center in in Houston, Houston, where he he studied Archean basaltic and ultramafic magma types as analogs analogs of early early planetary planetary crust. In In 1982, 1982, after three years as a faculty member member at Washington Washington University University in in St. St. Louis, Louis, Klaus Klaus resigned resigned his his teaching teachingposition positionand andjoined joinedthe theU.S. U.S.Geological Geological Survey Survey in in Reston, Reston, VA, fulfilling a long-standing long-standing dream dream of his. his. During During the next next twenty twenty years with with the the USGS USGSKlaus Klaus was was aa research research scientist scientist and and administrator administrator with with a strong strong interest interestin in the the geology geologyof of the theLake LakeSuperior Superiorregion. region. The The traits traits that that have have made made Klaus Klaus a success success were evident early early in his his career. In In his his undergraduate undergraduate days days at Oshkosh, Oshkosh, Klaus Klaus distinguished distinguished himself as as an an avid avid reader reader of the the geological geological literature. literature. As a junior in 1970, 1970, he wrote an outstanding outstanding research research paper paper discussing greenstone belts and modern modern island island arcs. He He discussing the similarities similarities between Archean greenstone worked worked several summers doing fieldwork for Bear Creek Mining Mining Company Company in in central central Wisconsin Wisconsin and and northern northern Michigan, Michigan, and for U.S. Steel Steel Corp. Corp. in in the the Vermilion Vermilion district district of of northern northern Minnesota. Minnesota. This combination of field work and and a thorough thorough knowledge knowledge of of the the literature literature has has continued continued to be a hallmark hallmark of his his professional professional career, career, and and has has led led to to aa number number of of significant significant contributions contributions to the geology geology of of the the Lake LakeSuperior Superior region. region. In William Spence In the summer of 1971, Klaus and William Spence discovered discovered the Lake Lake Ellen Ellen kimberlite working as exploration geologists in the kimberlite near Crystal Falls, Michigan, while working area. area. Klaus Klaus was very much involved involved in the recognition recognition of the rock rock as as aa kimberlite. kimberlite. This This the first first kimberlite kimberlitediscovered discovered in in the the Lake LakeSuperior Superiorregion. region. was the xii xv �His Masters thesis involved considerable mapping in the Ely greenstone greenstonebelt belt in in Minnesota, and and geochemical geochemical studies studies for his his Ph.D. Ph.D. dissertation dissertationshowed showedthat thatthe theNewton Newton Lake to komatiites. komatfltes. This was the first Lake Formation Formation was a high-magnesium high-magnesium basalt, similar to documented occurrence rocks in in the the Lake Superior region. documented occurrence of komatHtic komatiitic rocks 1980's, his field mapping and and geochemistry geochemistry of of rocks in the Pembine Pembine In the early 1980's, area of the Wisconsin Wisconsin magmatic magmatic terranes demonstrated demonstrated the presence presence of ophiolitic ophiolitic rocks. rocks. the Lake Superior region, Again, this was the first documented ophiolite in the region, and and showed that the Wisconsin magmatic magmatic terranes were, at least in part, an oceanic oceanic island island arc. arc. His His subsequent model model for the evolution of the Marquette Range Range Supergoup Supergoup on on the the continental continental margin during familiarity with the rocks during the Penokean Penokean orogeny is an extension of his familiarity rocks in in the region of the the geologic literature region combined combined with his encyclopedic knowledge of literature on the evolution of continental continental margins. margins. the GLIMPCE program, program, which which ultimately provided provided Klaus also contributed to the significant insight insight into the structure and origin of the Mid-continent Mid-continent rift, rift, and and into into its its magmatic origin origin and metallogeny. metallogeny. He has authored and co-authored more than than 120 publications, maps, maps, abstracts abstracts and field guides, including 1992, including field guides for the 1984, 1984, -1 992, and and 2003 2003 Institute Institutemeetings. meetings. Klaus' contributions have provided aa better better understanding understanding of the Archean, the the the Middle Proterozoic, and and the the Phanerozoic history of the Lake Early Proterozoic, the Lake Superior region. And he continues to be an active contributor on a global global stage, stage, taking takingthe the knowledge knowledge and experience experience that he has gained in the Lake Lake Superior region region and and applying applying itit to international international projects. projects. Therefore, itit is Schulzas as is my my distinct pleasure pleasure and honor honor to present present Klaus KlausJuergen JuergenSchulz the 2003 recipient recipient of the Goldich Medal Medal "For Outstanding Outstanding Contributions ContributionsTo To The The Lake Lake Superior Superior Region". Region". Submitted by Submitted by Gene Gene L. L. LaBerge LaBerge xui xiii �__________________________________________ __________________________ EISENBREY STUDENT TRAVEL AWARDS The The 1986 1986Board BoardofofDirectors Directorsestablished establishedthe theILSO ILSGStudent StudentTravel TravelAwards Awardstotosupport supportstudent student participation of the the Institute. Institute. The participation at the annual meeting of The name name Eisenbrey" "Eisenbrey"was was added added to to the the awardin in1998 1998totohonor honorEdward EdwardH.H.Eisenbrey award Eisenbrey(1(1926-1985) 926-1 985) and and utilize utilize substantial substantialcontributions contributions made madeto to the the 1996 1996Institute Institutemeeting meetingin in his his name. name. "Ned" "Ned"Eisenbrey Eisenbreyisiscredited creditedwith withdiscovery discoveryofof significant massive sulfide sulfide deposits deposits in in Wisconsin, significant volcanogenic volcanogenic massive Wisconsin, but his his scope scope was was much much broader—he broader-he has has been been described described as as having having unique unique talents talents as as an anore orefinder, finder,geologist, geologist,and and These awards are intended help defray some of the direct travel costs ofof teacher. These awards intended to help defray some of the direct travel costs teacher. attending Institute meetings, and include a waiver of registration fees, but exclude expenses attending Institute meetings, and include a waiver of registration fees, but exclude expenses for meals, meals, lodging, lodging, and andfield fieldtrip tripregistration. registration. The The annual annual Chair Chair ininconsultation consultation with with the the for Recipients Secretary-Treasurer determinesthe the number number of of awards be Secretary-Treasurer determines awards and andvalue. value. Recipients will be announcedat at the the annual annualbanquet. banquet. announced The The annual annual Chair, Chair, who who isisresponsible responsible for for the theselection, selection, will will consider consider the thefollowing followinggeneral general criteria: criteria: 1) 1) The Theapplicants applicantsmust musthave haveactive activeresident resident(undergraduate (undergraduateor or graduate) graduate)student studentstatus statusat at the the time time of of the the annual annual meeting meeting of of the the Institute, Institute, certified certified by by the department departmenthead. head. 2) 2) Students Studentswho whoare arethe thesenior seniorauthor authoron oneither eitheran anoral oralor orposter posterpaper paperwill willbe begiven givenfavored favored consideration. consideration. 3) ItIt is is desirable desirablefor for two two or or more morestudents studentsto to jointly jointly request requesttravel travelassistance. assistance. 3) 4) 4) InIngeneral, general,priority prioritywill willbe begiven giventotothose thoseininthe theInstitute Instituteregion regionwho whoare arefarthest farthestaway awayfrom from the the meeting meetinglocation. location. 5) 5) Each Eachtravel travelaward awardrequest requestshall shallbe bemade madeininwriting writingto to the the annual annualChair, Chair,and andshould shouldexplain explain need, need, student and author status, and other significant details. The Theform formbelow belowisisoptional. optional. Successful Successful applicants applicants will will receive receive their their awards awards during during the the meeting. meeting. - NSTITUTE ONLAKUPERIORGEOLOGY ONLAKESUPERIORGEOLOGY INSTITUTE EisenbreyStudent Student Travel Travel Award Application Application Date: Date: StudentName: Name: student Address: Address: email: Department Head-Typed Department DepartmentHead-Signature Head-Signature Educationalstatus: Status: Educational Are you author of anoforal poster paper? paper? YESNO-NO_ Are youthe thesenior senior author anororal or poster YES_ who? Who? Willany anyother other students studentsbe betraveling travelingwith withyou? you? Will statement Statementofofneed need(use (useadditional additionalpage pageififnecessary) necessary) Please Pleasereturn returnto: to: xiv �STUDENTPAPER PAPERAWARDS AWARDS STUDENT Each year, year, the the Institute Instituteselects selects the the best best of of the the student student presentations presentations and and honors honors Each presenterswith with aa monetary monetary award. Funding Fundingfor for the theaward awardisis generated generated from from registrations registrations presenters of the theannual annualmeeting. meeting.The TheStudent StudentPaper PaperCommittee Committeeisisappointed appointedby bythe theannual annualmeeting meeting of Chairin insuch suchaamanner manneras asto to represent representaabroad broadrange rangeof of professional professionaland andgeologic geologic Chair expertise. Criteria Criteriafor forbest beststudent studentpaper—last paper-last modified modifiedby bythe theBoard Boardinin2001—follow; 2001-follow: expertise. 1) The Thecontribution contributionmust mustbe bedemonstrably demonstrablythe thework workofofthe thestudent. student. 1) 2) 2) The Thestudent studentmust mustpresent presentthe thecontribution contributionin-person. in-person. 3) The TheStudent StudentPaper PaperCommittee Committeeshall shalldecide decidehow howmany many awards awards to to grant, grant, and and whether whether or or 3) not to to give give separate separate awards awards for for poster postervs. vs.oral oralpresentations. presentations. not 4) 4) InIncases casesofofmultiple multiplestudent studentauthors, authors,the theaward awardwill willbe bemade made to to the the senior senior author, author, or or the award awardwill willbe beshared sharedequally equallyby byall allauthors authorsof ofthe thecontribution. contribution. the 5) The Thetotal totalamount amountofofthe theawards awardsisisleft leftto tothe thediscretion discretionof of the themeeting meetingChair Chairand and 5) Secretary-Treasurer, but typically is in the amount of about $500 US (increase approved Secretary-Treasurer, but typically is in the amount of about $500 US (increase approved by Board, Board,10/01). 10101). by 6) 6 )The TheSecretary-Treasurer Secretary-Treasurermaintains, maintains,and andwill willsupply supplyto to the the Committee, Committee, aa form form for for the the numerical numerical ranking ranking of presentations. This Thisform form was was created createdand and modified modifiedby by Student Student Paper Paper Committees Committees over over several several years years in in an an effort to to reduce reduce the the difficulties difficultiesthat that may mayarise arise from from selection selectionby by raters raters of diverse background. The Theuse useof of the theform formisisnot notrequired, required,but butisis left to to the the discretion discretionof of the the Committee. Committee. left 7) The Thenames namesofofaward awardrecipients recipientsshall shallbe beincluded includedas as part partof of the the annual annualChair's Chair'sreport report 7) that that appears appearsininthe thenext nextvolume volumeof ofthe theInstitute. Institute. Student Student papers papers will will be be noted noted on on the the Program. Program. 2003STUDENT STUDENTPAPER PAPERAWARDS AWARDSCOMMITTEE COMMITTEE 2003 Theodore - Michigan TheodoreBornhorst Bornhorst - MichiganTechnological TechnologicalUniversity, University,Houghton, Houghton, Ml MI --- Chair Chair Kevin KevinSikkila Sikkila—-Wisconsin Wisconsin Department Department of of Transportation, Transportation,Superior, Superior,WI Wl Anne Purdue University University Fort Fort Wayne, Wayne, Fort Wayne, IN AnneArgast Argast—-Indiana IndianaUniversity University — - Purdue IN Tim St. Norbert TimFlood Flood— -St. Norbert College, College, De De Pere, Pere,WI Wl 2003 2003SESSION SESSIONCHAIRS CHAIRS Peter Geological Survey, Kenora, PeterHinz Hinz— - Ontario Geological Kenora,ON ON Eric Jerde Morehead State University, Morehead, Eric Jerde - Morehead State University, Morehead, KY KY James Miller Miller -- Minnesota Minnesota Geological GeologicalSurvey, Survey, Duluth, Duluth, MN MN James Mike MikeMudrey, Mudrey,Jr. Jr.— - Wisconsin Geological Geological and and Natural Natural History History Survey, Survey, Madison, Madison,WI Wl xv �2003BOARD BOARDOF OFDIRECTORS DIRECTORS 2003 Board Boardappointment appointmentcontinues continuesthrough throughthe theclose closeofofthe themeeting meetingyear yearshown shownininparentheses, parentheses,ororuntil untilaa successor successorisisselected selected Laurel Laurel Woodruff Woodruff Co-Chair Co-Chair2003 2003meeting meeting(2006) (2006) U.S. U.S. Geological GeologicalSurvey, Survey,St. St.Paul, Paul,MN MN Peter Hinz Hinz(2005) (2005) Peter Ontario OntarioGeological GeologicalSurvey, Survey,Kenora, Kenora,ON ON Jr. (2004) (2004) Michael C. G. Mudrey, Mudrey,Jr. Michael Wisconsin WisconsinGeological Geologicaland andNatural NaturalHistory HistorySurvey, Survey,Madison, Madison,WI Wl Stephen A. Kissin Kissin(2003) (2003) Stephen A. Lakehead LakeheadUniversity, University,Thunder ThunderBay, Bay,ON ON Hollings-Secretary-Treasurer(2006) (2006) Peter Hollings-Secretary-Treasurer Peter Lakehead LakeheadUniversity, University,Thunder ThunderBay, Bay,ON ON Mark A. A. Jirsa-Secretary-Treasurer-"emeritus" Mark Jirsa-Secretary-Treasurer-"emeritus" (in transition) transition) Minnesota MinnesotaGeological GeologicalSurvey, Survey,St. St.Paul, Paul,MN MN 2003LOCAL LOCALCOMMITTEES COMMITTEES 2003 General General Co-Chairs Co-Chairs Laurel LaurelC. G. Woodruff Woodruff—-U.S. U.S.Geological GeologicalSurvey, Survey,St. St. Paul, Paul, MN MN WilliamF.F.Cannon Cannon—-U.S. U.S. Geological GeologicalSurvey, Survey,Reston, Reston,VA VA William Program Program and Abstracts Abstracts Editors Editors Laurel U.S. LaurelG. G. Woodruff Woodruff-- -US.Geological GeologicalSurvey, Survey,St. St.Paul, Paul,MN MN Theodore J. Bornhorst — Michigan Technological University, Houghton,MI MI Theodore J. Bornhorst - Michigan Technological University,Houghton, Field Field Trip Trip Guidebook Guidebook Editor Editor WilliamF.F.Cannon Cannon— U.S. U.S.Geological GeologicalSurvey, Survey,Reston, Reston,VA VA William - Acting Acting Local LocalCommittee, Committee, Iron IronMountain Mountain John Coleman Engineering, Engineering, Iron IronMountain, Mountain, Ml MI JohnGartner Gartner—- Coleman Connie ConnieDicken Dicken— - U.S. U.S. Geological GeologicalSurvey, Survey, Reston, Reston, VA VA Sally - Oshkosh, WI Wl SallyLaBerge LaBerge— 2003 BANQUET SPEAKER Susan Susan Martin Martin Department Department of of Social Social Sciences Sciences Michigan Michigan Technological Technological University University Houghton, Houghton, Michigan Michigan The indigenous indigenous people of the Lake Superior Superior Basin: Basin: Understanding Understandingthe the links links among among environment, geology and religious belief belief xvi xvi �48TH Report Reportof of the theChair Chair of of the the 48'" Annual Annual Meeting Meeting 2002 Peter Hinz, Hinz, Co-Chair Co-ChairILSG ILSG2002 Peter The 48thAnnual AnnualInstitute Instituteon onLake LakeSuperior SuperiorGeology Geologywas was hosted hostedby by the the Ontario Ontario Geological Geological The Survey 2001. Principal Surveyon on May May9-12, 9-12,2001. Principallocal localcommittee committeemembers memberswere werePeter PeterHinz Hinzand and Richard C. C. Beard, Beard, co-chairs, co-chairs,Carmen CarmenC. C.Storey, Storey, and andKevin KevinO'Flaherty O'FlahertyProgram Programco-chairs, co-chairs, Richard CharlesE. E. Blackburn, Blackburn,Field FieldTrip TripCo-ordinator, Co-ordinator,M. M.Kathleen KathleenMcGowan-Hinz, McGowan-Hinz,Treasurer, Treasurer, Charles and Christine ChristineC. C. Blackburn, Blackburn,Secretary. Secretary.Other Other principal principalindividuals individuals are are listed listed in in the the and Proceedings ProceedingsVolume. Volume. 2001 AttendanceatatILSG ILSG2001 Attendance A A total total of of 97 97 professionals professionalsand andstudent student professionals professionalsattended attendedthe the meeting, meeting, 39 39 of of whom whom pre-registered pre-registeredby by the the April April 2, 2, 2001 2001 deadline. deadline. A A total total of of 88 students studentswere were registered, registered, 77of of whom whom requested requestedand andreceived receivedtravel travelassistance. assistance. Eisenbrey Student StudentTravel TravelAwards Awards2001 2001 Eisenbrey Seven Seven students students requested requested and and received received travel assistance assistance from the Eisenbrey Eisenbrey Student Student Travel Travel Award Award Fund Fundestablished establishedto to support support student student participation participationat at the the Annual Annual Institute. Institute. Details, website. Details, including includingcriteria criteria and andapplication applicationforms, forms, are areavailable availableat atthe theILSG ILSGwebsite. BogdanNitescu Nitescu Bogdan Claire Sturm Sturm Claire ElizabethFein Fein Elizabeth Justin Johnson Johnson Justin Becky Rogala Rogala Becky WilliamJahn Jahn William DanielaVallini Vallini Daniela University of Toronto, Toronto, Toronto, Toronto, ON ON University Oberlin OberlinCollege, College, Oberlin, Oberlin,OH OH Oberlin Oberlin College, College, Oberlin, Oberlin,OH OH Lakehead University, University, Thunder Thunder Bay, Bay, ON ON Lakehead Lakehead Lakehead University, University, Thunder Thunder Bay, Bay, ON ON University University of Minnesota Minnesota-- Duluth, Duluth, Duluth, Duluth, MN MN University University of Western Western Australia, Nedlands, Nedlands, WA WA MeetingSummary Summary Meetin The 48 Annual AnnualInstitute Instituteon onLake LakeSuperior SuperiorGeology GeologyAnnual AnnualMeeting Meetingwas washeld heldat atthe theBest Best Western Western Lakeside Lakeside Inn Inn and and Convention Convention Centre, Centre, the the same same location locationas as the the 1985 1985meeting. meeting. The The one-and-a-half one-and-a-halfdays days of of technical technicalsessions sessionswere werepreceded precededby: by:Field FieldTrip Trip11— - Tanco Rare-Element Rare-Element Pegmatite, Peamatite. Southeastern Southeastern Manitoba Manitoba led led by bv staff of the the Tantalum Tantalum Mining Mining Corporation by Quaternary Geology corporation of of Canada ~ a n a dLtd.; a~ t d .followed followed ; byField FieldTrip Trip22—-Quaternary Geologyofof Southeastern Southeastern Manitoba Manitoba led ledby by E. E. Nielsen Nielsenand and Gaywood GaywoodMatile Matile(Manitoba (ManitobaGeological Geological Survey); Survey); and and Field Field Trip 33- Structure structure and and Sedimentology Sedimentologyof the the Seine Seine Conglomerate, Conglomerate, Mine Mine Centre Centre Area, Ontario Ontario lead lead by by Dyanna Dyanna Czeck (Department (Department of Geology, Geology, Oberlin Oberlin College) College) and Philip Fralick (Department (Department of Geology, Geology, Lakehead Lakehead University) University) Due Due to the small number number of talks talks submitted, submitted, the the Technical Technical Session Session Chairs Chairs were were unable unableto to group group talks into into session session themes. The The meeting meeting began began with with an an anecdotal anecdotal history historyof of mining mininginin northwestern northwestern Ontario Ontario presented presented by by Kevin Kevin O'Flaherty, followed followed by by regional regional scale scale talks talks on on the Western Superior Province. The ~uperior~rovince. Theremainder remainderof of the the technical technicalsessions sessionsincluded includedaa broad broad range range of talks talks focusing focusing on on ground ground water, water, petrography, petrography, sedimentology, sedimentology, mineralogy mineralogyand and structural structural topics. The The final final session session ended ended at noon, noon, allowing allowing for for an an early early departure departureof of Field Field Trip 66 to Red Red Lake. Lake. Post Post meeting meeting trips trips included: included: Field Field Trip Trip 4— 4 - Industrial Industrial Minerals and and Paleozoic Separation Rapids Paleozoic Geology Geology of of Southeastern SoutheasternManitoba; Manitoba;Field FieldTrip Trip55— -Separation RapidsRareRareElement Pegmatite Geology of of the the Red Lake Camp. All Pegmatite Field, Ontario; and Field Field Trip 6— 6 - Geology field field trips ran ran smoothly smoothly considering considering the the frigid frigid conditions conditions of of early early May May in in northwestern northwestern Ontario. ILSG Secretary -Treasurer, Mark Jirsa was the lone participant Ontario. 1LSG Secretary -Treasurer, Mark Jirsa was the lone participantof of Field FieldTrip Trip66 successful in obtaining samples from Goldcorp's Red Lake Mine in Red Lake. He successful in obtaining samples from Goldcorp's Red Lake Mine in Red Lake. Hewas was able to do this by cunningly cunningly embedding embedding the samples samples in in the the back back of of his his neck. neck. Upon Upon returning to Kenora the samples were proudly displayed in a baggy kindly supplied supplied by by the staff of Red Red Lake's Lake's Margaret MargaretCochenour Cochenour Memorial MemorialHospital Hospitalemergency emergencyroom. room. - - - ~ xvii �Annual Banquet and Goldich Goldich Award At the Annual Annual Banquet Banquet Ted Ted DeMatties DeMatties presented presented the the citation citation for Ernest Ernest K. K. Lehmann, Lehmann, recipient recipient of the the Goldich Goldich Medal Medal for 2002 2002 for for his his contributions contributionsto to the the Institute Instituteand andLake Lake Superior Superior Geology. Geology. L. L. Harvey Harvey Thorliefson, Thorliefson, Geological GeologicalSurvey Survey of Canada, Canada, provided provided aa scintillating scintillating discussion discussion on The Search Search for Diamonds Diamondsin in Canada Canada for the the after after dinner dinner address. Laurel Laurel Woodruff Woodruff and and Bill Bill Cannon Cannon of of the the U.S. U.S. Geological GeologicalSurvey Survey invited invited 49th Annual in participants participants to the the 49Ih~ n n u aMeeting Meeting l in Iron Iron Mountain, Mountain, Michigan. Michigan. 2002 Best Student Paper Awards 1) Becky BeckyRogala Rogala--Lakehead LakeheadUniversity,Thunder University,ThunderBay, Bay, Ontario Ontario ($400, ($400, oral oral presentation) presentation) New in formation from from the Sibley New information Sibley Group Group OberlinCollege, College, Oberlin, Oberlin, Ohio Ohio ($50, ($50, poster; poster; Co-authors Co-authorsC.L. C.L. Sturm Sturm 2) Elizabeth ElizabethFein Fein--Oberlin Anisotropy of magnetic magnetic susceptibility susceptibility in in the the Ottertail Ottertailpiuton, and D.M. Czeck) Anisotropy pluton, Northern NorthernOntario Ontario 3) Claire ClaireSturm Sturm--Oberlin OberlinCollege, College,Ohio Ohio($50, ($50, oral; oral; Co-authors Co-authors D.M. D.M. Czeck Czeck and and E. E. Fein) Fein) Petro graphicstudy studyof of the the Offertail Ottertailpluton, pluton, Superior Superior Province, Province, Northwestern Northwestern Ontario Petrographic 2002 Eisenbrey Student Student Travel Awards Awards University of of Toronto, Toronto, Toronto, Toronto, ON ON ($250) ($250) 1) Bogdan BogdanNitescu Nitescu-- University 2) Claire ClaireSturm Sturm--Oberlin Oberlin College, College, Oberlin, Oberlin, Ohio Ohio ($200) 3) Elizabeth ElizabethFein Fein-- Oberlin OberlinCollege, College,Oberlin, Oberlin, Ohio Ohio($200) ($200) 4) Justin JustinJohnson Johnson--Lakehead LakeheadUniversity, University,Thunder Thunder Bay, Bay, ON ON($150) ($150) LakeheadUniversity, University,Thunder Thunder Bay, Bay, ON ON ($150) ($150) 5) Becky BeckyRogala Rogala--Lakehead 6) William WilliamJahn Jahn--University Universityof of Minnesota, Minnesota, Duluth, Duluth,MN MN($150) ($150) 7) Daniela DanielaVallini Vallini -- University University of Western Western Australia, Nedlands, WA ($400) 2002 Goldich Goldich Medal Recipient 2002 Recipient Lehmann Ernest K. Lehmann MTII MTU Archives Donation Donation A check for $100 Technological University Archives, as required $100 was sent to Michigan Technological required by Board agreement ($1 per participant per meeting), for maintenance of ILSG proceedings proceedings archives. Proceedings including Part 1 (Programs and Abstracts) Abstracts) and Part 2 (Field Trip Guidebook) Guidebook) are available from the Institute: Institute: Institute on Lake Superior Geology do c/oMark MarkJirsa, Jirsa, Secretary Secretary -- Treasurer Treasurer Minnesota Geological Survey Survey 2642 University 2642 University Avenue St. Paul MN 55114-1057 551 14-1057 Phone: 612.627.4539 612.627.4539 Fax: Fax: 612.627.4778 612.627.4778 jirsaool @tc.umn.edu e-mail: jirsa001 @tc.umn.edu xvhi xviii �4&h1 ANNUAL INSTITUTE LAKE SUPERIOR GEOLOGY BOARD 4dhANNUAL INSTITUTE ON LAKE BOARD OF DIRECTOR'S DIRECTOR'S MEETING MEETING Board of Directors Directors Peter Hinz (2002 (2002General GeneralChair) Chair) Michael Mudrey Mudrey (2001 (2001 Co-chair) Co-chair) Steve Kissin Kissin (2000 (2000 Co-chair) Co-chair) Laurel Woodruff: Proxy Proxy for Ted Ted Bornhorst Bornhorst (1999 (1999 Co-chair Co-chair and and liaison liaison with Goldich Goldich committee) committee) Mark Jirsa (Institute (InstituteSecretary-Treasurer) Secretary-Treasurer) Guests Guests Phil Fralick Fralick (2000 (2000 Co-chair) Co-chair) Carmen Storey storey (2003 Program program Chair) Kevin O'Flaherty (2003 (2003 Program Program Chair) Chair) Bill Cannon Cannon (proposed (proposed 2003 2003 Co-chairs) Co-chairs) Rod Johnson (Goldich Rod Johnson (Goldich Committee) Committee) Frank Luther Luther (Goldich (Goldich Committee) Committee) based on the secretaries' notes and recollection; recollection; any omissions or The following is based misstatements unintentionaL Motions by the the Board Boardof of Directors Directors are generally generally misstatements are unintentional. Motions by paraphrased—"approved" paraphrasedÑ'approve or or "accepted" "accepted implying implyingthat that aa motion motionwas was made, made, seconded, and passed unanimously. The and passed The expression expression "generally "generally agreed" carries carries less formality, be pursued. pursued. Some formality, but but indicates indicates a directive that will be Some issues issues that that were were resolved resolved after after the Board Boardmeeting, but but during during the conference conference are are included includedhere here for for closure. closure. MINUTES MINUTES 1. Accepted Acceptedreport reportof of the the Chairs Chairs for for the the 47th 47th ILSG, ILSG, Madison, Madison, Wisconsin; Wisconsin; as as printed printed in in the the Proceeding Proceeding Volume (Mudrey), and minutes of last Board meeting, meeting. May 10, 2001 (Jirsa) (Jirsa) 2. 2, Received, Received,discussed, discussed, and andaccepted accepted2001-2002 2001-2002 ILSG ILSG Financial FinancialSummary Summary (Jirsa). (Jirsa). (4gth 3. Discussed location—Iron Mountain, Discussedand andapproved approved2003 2003 ( 4 9 annual) meeting location-Iron Mountain, Michigan, and tentative co-chairs Laurel Woodruff and Bill Cannon, Cannon, USGS. As currently currently envisioned, envisioned, Ted Bornhorst Bornhorst will handle handle logistics logistics of field trips. 4. Approved ApprovedPeter PeterHinz Hinzas as on-going on-goingILSG ILSG Board Boardmember. member. 5. Discussed Discussedreplacing replacingRod RodJohnson Johnson as as the the "member "member from from industry" industry" on on Goldich Goldich Committee Committee (end (end of term term 2002) 2002) with several several candidates candidates including including Dave Dave Meineke Meineke of of Meriden Meriden Engineering, Hibbing, Minnesota. Dave later accepted the position and was welcomed, and Rod was thanked for for his service to to the the Institute, during during the the annual annual banquet. banquet. Dave's Dave's term will end after Goldich Goldich selection for the the meeting meeting of of 2005. 6. Discussed Discussedreplacement replacementof of Mark MarkJirsa Jirsa as as ILSG ILSGSecretary-Treasurer Secretary-Treasurer(end (endof of 4-year 4-year term term 2002). A new member to the Institute, Peter Hoflings, Lakehead University in Thunder Institute, Peter Hollings, Lakehead University in Thunder Bay, was installed installed as "Secretary-Treasurer in-training," pending pending a vote vote by by the the general general membership membership (as required required in in By-Laws). By-Laws). Because Because of his his newness newness to the the Institute, Institute,the the board board generally agreed that Peter Peter would serve serve 2 years of the the 4-year 4-year term term concurrently concurrentlywith with Mark Mark in a period of transition. At the end end of the the 22 years years (following (following the the 2004 2004 meeting), meeting),the the finances and records finances records of the institute, institute, and and responsibilities responsibilities of the the position positionwould would fall fall to to Peter. Peter. This was presented to to the membership after after the the Board meeting, and and was was generally accepted. accepted. 7. Other Otherbusiness: business: a) Discussed Discussed the offer by by Mike Mike Mudrey Mudrey to take take over over as as ILSG ILSG webmaster—It webmaster-lt was was generally agreed that Mike Mike could could do that, assuming assuming Ted Ted was was busy busy with with other other obligations and probably probably would not mind the relief. relief. Subsequent Subsequent discussions discussionsindicate indicate xix �that Ted Ted would like like to to continue continue in in this this endeavor, endeavor, and and has has already already paid paid in in advance advance for for 5 years of web service service to to continue. continue. ItIt remains remains in in Ted's Ted's hands. hands. b) Discussed efforts by Graham Wilson to list ILSG publications as part of his —Steve Kissin MINLIB project and website (www.turnstone.ca) (www.turnstone.ca)ÑStev Kissin volunteered volunteered to contact Graham and see if there is anything that the ILSG can and should do to assist, assist. c) Discussed Discussed the prospect prospect of extending extending aa "free "free ride" ride" to to annual annualGoldich GoldichMedal Medal recipients. It was generally generally agreed agreed that registration registration costs costs should should be be paid paid by by the the annual meeting annual meeting committee, and and that that lodging, lodging, meals, meals, and and travel travel costs costscould couldbe bepaid, paid, at the discretion discretion of the the annual annual meeting meeting chairs. chairs. d) Discussed Discussed the the ILSG ILSG Newsletter—Peter NewsletterÑPete Hinz Hinz has has offered offered to to write write itit beginning beginningin in that transition. The topic of of 2004 or so. He can coordinate with Ted Bornhorst about that whether the Newsletter Newsletter should should remain remain paper, or be be changed changedto to aa wholly wholly electronic electronic format was discussed discussed and and tabled. tabled. Most Most seemed seemed to to think think we we should shouldeventually eventuallyswitch switch with email notification. This This raised a further further to a web-based newsletter, perhaps with issue issue that members must be encouraged to notify the secretary-treasurer of changes in email email address address or or other other status. status. sampling—An issue was raised that that at at least one group of regular e) Questionable sampling-An meeting meeting participants participantshas has a tradition tradition of using using guidebooks guidebooksto to locate locateplaces placesfor formassive massive sampling programs. In this one case, samples are sold to Wards or other rock rock and mineral mineral specimen specimen dealers. The The problems problems are are 1) 1) some some of of the the localities localitiesdiscussed discussedinin guidebooks guidebooks are on private land (and therefore trespassing is likely), and 2) taking large amounts of sample from some localities limits the use of these sites sites to future generations. It was generally agreed that ILSG would print in their guidebooks a Policy Statement that warns of this "questionable "questionable sampling sampling practice." practice." Mark Mark Jirsa Jirsa will will create such language create language for inclusion inclusion in in future future guidebooks. guidebooks. abstracts—Peter f) Discussed Discussed digital submission of a b s t r a c t e e t e r Hinz warns from experience that for preparers, particularly this practice can easily turn into a nightmare for particularly if the submitters don't follow (or the host organization doesn't specify) rigid rigid guidelines guidelines for submission formats. This includes both text and illustration formats. Adjournment submission formats. both text and illustration formats. Adjournment Respectfully Respectfully submitted on January 27, 2003 to Peter Peter Hinz, Hinz, Chair Chair of of the the 48th 48thannual annual meeting, for incorporation into the Report of the Chair to appear in Proceedings Proceedings Volume 49. Mark Jirsa, Secretary-Treasurer, Institute on Lake Superior Geology xx �PROGRAM xxi �49th The following companies made made generous generous contributions contributions to to the the 49"' Annual Annual Meeting. Meeting. We thank them and and John John Gartner Gartner of the the Local Local Committee Committee for their commitment to the the Institute Institute on on Lake Lake Superior Superior Geology. Geology. For For almost almost 50 years this this organization organization has has thrived thrived through through the the sustained sustained interests interests of of individuals, and government agencies in the individuals, corporations, corporations, universities, universities, and government agencies the international geologic community. community.This Thisdedication dedicationtoto an an exchange of international geologic exchange of scientific ideas and aa passion passion for for field field trips trips (even (even in in driving driving rain rain or or snow) snow) has enabled enabled the ILSG ILSG to to fulfill fulfill one one of of its its primary primary objectives: objectives: to to promote promote better better understanding understandingof of the thegeology geology in in the the Lake Lake Superior Superiorregion. region. Kleiman Well Drilling, Kleiman Pump Pump &&Well Drilling,Inc. Inc. P.O. 704 P.O. Box 704 Iron Mountain, Michigan 49801-0704 49801-0704 Prime Prime Meridian Meridian Resources ResourcesLtd. Ltd. N7478 N7478 Niagara Niagara Lane Lane Lac, WI Wl 54935 54935 Fond du Lac, Coleman Coleman Engineering Engineering Company Company Circle Drive Drive 635 Circle Iron Mountain, MI Ml 49801 49801 xxii �WEDNESDAY MAY 7,2003 WEDNESDAY 7, 2003 8:00 TRIP 1: 1: WISCONSIN MAGMATIC TERRANE 8:00a.m. a.m.FIELD FIELD TRIP WISCONSIN MAGMATIC TERRANE(#1 (#1ININGUIDEBOOK) GUIDEBOOK) Klaus Klaus Schulz, Schulz, U.S. U.S. Geological GeologicalSurvey Survey Gene Oshkosh,emeritus emeritus GeneLaBerge, LaBerge,University UniversityofofWisconsin Wisconsin—- Oshkosh, - OF FIELD TRIP TRIP 2: 2:THE THEREPUBLIC REPUBLICMINE MINE— LIFE LIFECYCLE CYCLE OFAN ANIRON IRONORE ORE 8:00 a.m. a.m. FIELD 8:00 DEPOSIT (#4 IN INGUIDEBOOK) GUIDEBOOK) DEPOSIT FROM FROMGENESIS GENESIS TO RECLAMATION RECLAMATION(#4 William WilliamCannon, Cannon,U.S. U.S.Geological GeologicalSurvey Survey John John Meler, Meier,Cleveland ClevelandCliffs Cliffs Iron Iron Company Company 6:00 Return of 6:00 p.m. Return of Trips Trips11 and and22 4:00 p.m. p.m. - 8:00 Registration 4:00 8:00 p.m. p.m. Registration 7:00 p.m. p.m. -- 9:00 and Poster Poster Setup Setup 7:00 9:00 p.m. p.m. Ice Breaker Social and THURSDAYMAY 8,2003 THURSDAY 8, 2003 - 8:00 8:00 a.m. a.m.- 9:00 9:00a.m. a.m.REGISTRATION REGISTRATION Note: Note: Technical TechnicalSessions Sessionsare arein inWhite White spruce, Spruce,Pine PineMountain MountainResort Resort 4• *: Denotes Denotes Student Student Presentation Presentation 8:15 a.m. a.m.INTRODUCTORY INTRODUCTORYREMARKS REMARKS 8:15 Laurel G. G. Woodruff and and William WilliamF. F. Cannon, Cannon,Co-Chairs Co-Chairs TECHNICAL TECHNICALSESSION SESSIONII Session Session Chair: Chair: Jim Jim Miller, Miller, Minnesota Minnesota Geological Geological Survey, Survey,Duluth, Duluth,MN MN - 8:30 - Menominee Range 8:30 a.m. a.m. Harold HaroldBernhardt Bernhardt Menominee RangeHistorical HistoricalFoundation FoundationMuseum Museum A A brief brief history historyof of iron ironmining mining on on the theUpper UpperPeninsula's Peninsula'sMenominee MenomineeIron IronRange Range 9:00 9:00 a.m. Cannon, W.F., W.F., LaBerge, G.L. G.L. and Klasner, Klasner, J.S. J.S. Niagara Niagara suture suture zone, northern Michigan Michigan and and Wisconsin—tectonics Wisconsin-tectonics in in the the 1.85 1.85 Ma Ma arc-continent arc-continent collisional collisional boundary boundary K. 9:30 a.m. Schulz, K. A A Paleoproterozoic Paleoproterozoic suprasubduction suprasubductionzone ophiolite-island ophiolite-island arc complex complex in northeastern northeasternWisconsin Wisconsin 10:00 10:OO a.m. a.m.COFFEE COFFEEBREAK BREAKAND ANDPOSTER POSTER SESSION SESSION 10:40 a.m. am. Schneider, D.A., HoIm, D.K., D.K., O'Boyle, O'Boyle, C. C., Hamilton, M. and Jercinovic, Jercinovic, M. D.A., Holm, , Hamilton, M. Paleoproterozoic development of a gneiss dome corridor in the southern Lake Paleoproterozoic development gneiss dome corridor in the southern Lake Superior Superior region, region,USA USA 11:00 a.m. Holm, HoIm, D.K., D.K., Van Van Schmus, Schmus, W.R., W.R., MacNeill, MacNeill, L.C., L.C., Boerboom, Boerboom, T.J., 11:OO a.m. T.J., Schweitzer, D. and Schneider, D.A. Schweitzer, D. and Schneider, D.A. Late Paleoproterozoic Paleoproterozoic (1900-1600 (1900-1600 Ma) Ma) tectonic tectonic history history of of the the northern northernmidmidcontinent, continent, U.S.A.: Implications Implicationsfor for crustal crustalstabilization stabilization 11:20a.m. 11:20 a.m. Medaris, L.G., L.G., Jr. and and Dofl, Dott,R.H., R.H., Jr. Jr. The sedimentology, metamorphism, The Sioux Sioux Quartzite Quartzite revisited: sedimentology, metamorphism,geochemistry geochemistryand and the the origin origin of of pipestone pipestone 11:40p.m. 11:40 p.m. Smyk, Smyk, M.C. M.C. The planned activities activities and objectives objectives The Lake Lake Nipigon Nipigon Geoscience Geoscience Initiative Initiative— - planned xxiii �12:00 Meeting (by invitation) 12:OO p.m. p.m. Lunch LunchBreak— Break -Poster PosterSession Sessionand andILSG ILSGBoard Board Meeting (by invitation) TECHNICAL TECHNICALSESSION SESSIONIIII Session SessionChair: Chair:Mike MikeMudrey, Mudrey,Jr., Jr.,Wisconsin WisconsinGeological GeologicalSurvey, Survey,Madison, Madison,WI Wl 1:30 1:30 p.m.4 p.m. +Heggie, Heggie,C. G. and and Hollings, Hollings,P. P. Geochemistry Geochemistry.and and mineralization mineralizationof of the the Seagull Seagull Intrusion, Intrusion, Northern Northern Ontario Ontario +:. 1:50 Johnson, J.R., 1:50 p.m. p.m. + Johnson, J.R., Hollings, Hollings,P. P.and andKissin, Kissin,S.A. S.A. Mineralization Mineralizationof of the theNorton NortonLake LakeCu-Ni-POE Cu-Ni-PGEdeposit deposit 2:10 2 3 0 p.m. p.m. Miller, Miller,J.J.D., D., Jr. Jr. Petrology Petrologyand and POE PGE potential potential of of the theGreenwood GreenwoodLake Lake Intrusion, Intrusion,central centralDuluth Duluth Complex, Complex,Lake LakeCounty, County,Minnesota Minnesota 2:30 2:30 p.m. p.m. + + Joslin, Joslin,G.D., G.D., Miller, Miller,J.D., J.D., Jr. Jr. and andRowell, Rowell,W.F. W.F. Stratiform StratiformPd-Pt-Au Pd-Pt-Aumineralization mineralizationininthe theSonju SonjuLake LakeIntrusion, Intrusion,Lake LakeCounty, County, Minnesota Minnesota 2:50 2:50 p.m. p.m. + + Marma, Marma, J., Brown, Brown,P. P.and andHauch, Hauch,S. S. Magmatic Magmaticand and hydrothermal hydrothermalPOE PGE mineralization mineralizationof of the the Birch Birch Lake LakeCu-Ni-POE Cu-Ni-PGE Deposit Depositin in the theSouth South Kawishiwi, Kawishiwi,Duluth Duluth Complex, Complex, northeast northeast Minnesota Minnesota 3:10 3:10p.m. p.m.COFFEE COFFEEBREAK BREAKAND ANDPOSTER POSTERSESSION SESSION 3:30 3:30 p.m. p.m. Waggoner, Waggoner,1. T. AAhydrothermal hydrothermalcomponent componentofofIron IronFormations Formations—A -A Marquette Marquette Range Rangeperspective perspective 3:50 3:50 p.m. p.m. Tsu-Ming Tsu-MingHan Han Mode of occurrence Mode of occurrence of of trona trona and and thermonatrite thermonatriteand andtheir theirpossible possibleorigin originininthe the Negaunee Iron-Formation of the Marquette Range, Lake Superior District, Negaunee Iron-Formation of the Marquette Range, Lake Superior District,USA USA 4:10 4:10 p.m. p.m. Blaske, Blaske,A.R. A.R. Geology of Valley type mineralization mineralization at Bellevue, Geology of the the MississippiMississippi-Valley Bellevue, Michigan Michigan 4:20 4:20 p.m. p.m. +ç Larson, Larson,P. P. Mean Mean transport transport length length in in tills tills of of the the southern southernportion portion of of the theLaurentide Laurentideice icesheet: sheet: implications implications for for drift drift exploration explorationin in the the Lake LakeSuperior Superiorregion region .:. 4:50 4:50 p.m. p.m. + Marlow, Marlow, L., L., Mooers, Mooers,H. H. and andLarson, Larson,P. P. Glacial Glacial Lakes Aitkin and Upham: Upham: their their origin origin and and environmental environmentalhistory history 5:10 530 p.m. p.m. Trow, Trow,J. J. Five wan copper copper sulfides sulfides in in Ontario and Five gold gold possibilities in some Keweena Keweenawan Michigan Michigan xxiv �- - ICEBREAKER BREAKER— MIXER MIXER— CASH BAR CASH BAR 6:00 p.m. p.m. ICE 6:00 BANQUET 7:00 p.m. p.m. ANNUAL ANNUAL BANQUETAND ANDAWARD AWARDPRESENTATION PRESENTATION 7:00 Announcement of of 50th 50"'Annual Annual Meeting Meeting Location Location • Announcement Presentationto Klaus Klaus Schulz Schulz 2003 Goldich Award Presentation • Banquet Address Address • 2003 Banquet Dr. Technological University Dr. Susan Martin, Michigan Technological University The indigenous indigenous people people of of the the Lake Lake Superior Superior Basin: Understanding links among geology Understanding the links among environment, geology and and religious religious belief belief . Ing participants Meeting participantswho who are arenot notregistered registeredfor forthe thebanquet banquetare arewelcome welcometo tothe thebanquet banquetaddress address Meet FRIDAY 9, 2003 FRIDAY MAY 9,2003 TECHNICAL TECHNICAL SESSION SESSION Ill Ill Session Chair: Chair: Eric Jerde, Jerde, Morehead State State University, University,Morehead, Morehead, Kentucky Kentucky 8:20 8:20 a.m. a.m. INTRODUCTORY INTRODUCTORYREMARKS REMARKS Laurel 0. G.Woodruff Woodruffand andWilliam WilliamF. F.Cannon, Cannon,Co-chairs Co-chairs 8:30 a.m. a.m. Hollings, Hollings, P., P., Fralick, Fralick, P. P. and and Kissin, Kissin, S. S. Geochemista'y andgeodynamic geodynamic implications implications of of the the 1537 1537 Ma Redstone Redstone Point Geochemistry and Point anorogenic anorogenic granite, granite, Ontario, Ontario, Canada Canada 8:50 a.m. a.m. 8:50 Buttram, R.M. P.M. and Bjornerud, Bjornerud, M. M. Textural constraints on holith Textural constraints on the the origin of rapakivi rapakivi textures textures in in the theWolf WolfRiver RiverBat Batholith 930 a.m. 9:10 am. -:Sequence .Sandin, NA. N.A. and and Bornhorst, Bornhorst, T.J. T.J. Marquette County, Sequence of Precambrian Precambrian mafic dikes in Marquelte County, Michigan, with +: - emphasis emphasis on on the the Sugarloaf Sugarloaf Mountain Mountain and and Republic Republic areas areas 9:30 a.m. a.m. Jerde, Jerde, E.A. E.A. Gabbro/granophyre relations relations of of the the Crocodile CrocodileLake Lake Intrusion: Intrusion: a possible vent for the Hovland Hovland Lavas? Lavas? 9:50 a.m. < + Vislova, T. T. Evaluation of initial magma compositions for the Bald Eagle Intrusion Intrusion and associated rocks associated rocks 10:10 COFFEEBREAK BREAKAND AND POSTER POSTER SESSION SESSION 10:lOa.m. a.m.COFFEE 10:30a.m..:• Charkoudian, K., 10:30 a.m. +: Charkoudian, K., Tikoff, B. 6. and and Bauer, Bauer, R. R. Stike -slipseparation separation of of the the Burntside Burntside trondhjemite trondhjemite and and the Wakemup Stike-slip WakemupBay Bay tonatlite, tonatlite, Northern Northern Minnesota Minnesota -:. 10:50 a.m. a.m. + Garbowicz, Garbowicz, A. A. and Bjornerud, Bjornerud,M. M. Paleostress eastern part of the Paleostress inferences from slip vectors in the eastern the Wisconsin Wisconsin segment of the the Midcontinent rift rift 11:10 am.. :+e Potter, E.G. and Mitchell, Ri-I. 1 1 :10 a.m. E.G. and R.H. The rare and exotic mineralogy mineralogy of of the Western Subcomplex of the Deadhorse Deadhorse Creek Diatreme, Northwestern Northwestern Ontario Ontario xxv �11:30 a.m. a.m. Brown, Brown, B.A., Jr., Czechanski, M.L., 11:30 B.A., Mudrey, M.G., M.G., Jr., M.L., Reid, Reid, D.D. D.D. and and Hunt, Hunt, T.C. T.C. Highway construction, construction, mine reclamation, and land-use planning challenges in the the historic historic Upper Upper Mississippi Mississippi Valley Valley lead-zinc lead-zinc district district of of southwest southwestWisconsin Wisconsin 11:50a.m. 1 1:50 a.m. Wattrus, N. N. High-resolution High-resolution multibeam bathymetry in Lake Superior 12:10 p.m. p.m. LUNCH LUNCHBREAK— BREAK -POSTERS POSTERSREMOVED REMOVED AFTER LUNCH LUNCH TECHNICAL TECHNICAL SESSION SESSIONIV Chair: Peter Session Chair: Peter Hinz, Hinz,Ontario OntarioGeologicai GeologicalSurvey, Survey,Kenora, Kenora,ON ON 1:40 a.m. a.m. 1:40 Vatlini, D.A., N.J., Rasmussen, Rasmussen, B., B., Fletcher, I. + Vallini, D.A., McNaughton, N.J., I. and Griffin, B.J. B.J. xenotime U-Pb geochronology geochronology to to unravel unravel the the history history of of Proterozoic Using xenotime sedimentary basins: aa study study in in Western WesternAustralia Australia and and the the Lake Lake Superior Superior region 2:00 p.m. p.m. Kissin, Kissin, S.A., S.A., Vallini, Vallini, D.A., Addison, W.D. W.D. and and Brumpton, Brumpton, G.R. 2:00 D.A., Addison, G.R. zircon ages from the flint and and Rove Rove Formations, Formations, northwestern northwestern Ontario New zircon the Gun Gunflint Ontario 2:20 p.m. p.m. +Richardson, • Richardson, A., 2:20 A., Fralick, P. and Hollings, P. Sibley zircon and whole rock geochemical Sibley Basin sediment provenance using zircon methods: Possible Possiblesource source areas areas of of the the Pass Pass Lake Lake Formation Formation + 2:40 p.m. p.m. + Rogala, Rogala, B., B., Fralick, Fralick, P. P. and and Borradaile, G. 2:40 magnetostratigraphic and secular variation study of the A magnetostratigraphic the Sibley Sibley Group Group 3:00 p.m. COFFEE COFFEE BREAK BREAK p.m. Argast, Argast, A. 3:20 p.m. What does sediment chemistry tell us about rocks like those those from the the Fern Fern Creek Formation? 3:40 p.m. p.m. Bartnik, Bartnik, P. J. and 3:40 and Evans, B. W. Geology and hydro geology in in the the Kingsford, Michigan Geology hydrogeology Michigan area area 4:00 p.m. p.m. Presentation Presentation of Student Student Paper Paper Awards Ted Bornhorst, Michigan Technological University: University: Student Student Paper Paper Committee Committee SATURDAYMAY MAY10,2003 10, 2003 SATURDAY (#2 IN 8:00 a.m. a.m.FIELD FIELDTRIP TRIP 3: 3: MENOMINEE MENOMINEE IRON IRON RANGE (#2 IN GUIDEBOOK) Gene Oshkosh, emeritus Gene LaBerge, LaBerge, University University of of Wisconsin Wisconsin— - Oshkosh, John Kiasner, Klasner, University University of Western Western Illinois, Illinois, emeritus emeritus William Cannon, William Cannon, U.S. US. Geological GeologicalSurvey Survey 6:00 p.m. p.m. Return Return of Trip Trip 3 6:00 SUNDAYMAY MAY11, 2003 SUNDAY 11,2003 8:00 a.m. FIELD TRIP4:4:Iron Iron River River —Crystal Crystal Falls Falls Iron Iron District 8:00 FIELD TRIP District(#3 (#3ININGUIDEBOOK) GUIDEBOOK) LaBerge, University Oshkosh, emeritus emeritus Gene LaBerge, University of Wisconsin Wisconsin— - Oshkosh, John Klasner, Klasner, University of Western Western llllnois, Illinois, emeritus emeritus William Cannon, William Cannon, U.S. U.S. Geological Geological Survey Survey 6:00 p.m. p.m. Return Return of Trip Trip 4 6:00 EM �POSTER PRESENTATIONS PRESENTATIONS Brown, B.A., Brown, B.A., Czechanski, Czechanski, M.L., M.L., Mudrey, Mudrey,M.G., M.G., Jr. Jr. and and Reid, Reid,D.D. D.D. Wisconsin Wisconsin mineral resource resource GIS GIs and and related related digital digital map map and anddatabase databaseproducts products— -a progress report Boerboom, T. Boerboom, Bedrock geologic maps of Keweenawan Bedrock geologic Keweenawan volcanic volcanic and intrusive intrusive rocks rocks in in the the Lake wood, French French River, River, and and Knife Knife River 7.5' quadrangles, North Lakewood, 7.5'quadrangles, North Shore Shore of of Lake Lake Superior, Superior, Minnesota Minnesota Easton, P.M. Easton, P.M. Geology and mineral potential of Proterozoic intrusions in the Geology Proterozoic mafic intrusions the northern northern Grenville Province of Ontario Grenville Ontario Hart, T.R. Hart, rocks of of the Lake Nipigon and Crystal Keweena wan mafic and ultramafic intrusive rocks Keweenawan and . northwestern Ontario Lake areas, northwestern Ontario S.A., Oreskovich, Oreskovich, J.A. and Hauch, S.A., and Severson, Severson, M.J. M.J. Geology, drill holes, mineral leases, and geophysics in the andgeophysics the Duluth Duluth and and Beaver Beaver Bay Bay Compexes, northeastern Minnesota: Integration Integration of of various various GIS G I sdatabases databasesto totell tellaa story of the history of past and current current Cu-Ni-PGE Cu-Ni-PGE mineral mineral exploration exploration • Heiling, 4Heiling,C.D. C.D. Oaf vertLake Lake Volcanic VolcanicComplex, Complex,St. St Louis Louis County, Minnesota Peperites of the Gafvert •4. Hooker, Hocker,S.M., S.M., Hudak, Hudak, G.J., G.J., Odette, Odette,J.D. J.D. and andNewkirk, Newkirk,T.T. T.T. Chemistry of alteration mineral phases phases at at the Five Five Mile Mile Lake Lake volcanic-hosted prospect, NE Minnesota massive sulfide prospect, Minnesota Jirsa, M. .+:.Keatts, Keatts, M.J., Jirsa, M. and and Hoim, Holm,D. D. 40ArPArsingle-grain single-grainanalyses analyses of of Precambrian Precambrian mafic intrusions intrusions in Results of 4oArf'Ar in northern northern north-central Minnesota and north-central Minnesota • McKenzie, Â¥: McKenzie, M.A., M.A., Hoim, D.K., D.A. and and Jercinovic, Jercinovic, M. Holm, D.K., Schneider, D.A. I . of EMP monazite monazite geochronology geochronology in in E-C E-C Minnesota: Minnesota: Evidence Results of Evidence for for largelargescale geon 17 post-tectonic plutonism 17 metamorphism associated with post-tectonic •:-Metsaranta, Metsaranta,R., R.,Fralich, Fralich, P. P.and and Hollings, Hollings, P. P. investigation of Mesoarchean volcanic and and rnetasedimentary metasedimentary A geochemical investigation Mesoarchean meta metavolcanic Uchigreenstone greenstone belt belt rocks from the the Birch Birch — - Uchi . :+ Nicholson, and Cannon, Nicholson,S. S. W. W. and Cannon, W.F. W.F. and structure structure of Keweenawan Keweena wan rocks rocks of of the the St. St. Croix horst, northwestern northwestern Stratigraphy and Wisconsin Wisconsin W.,Parker, Parker,J.R., JR.,Straub, Straub, K.J. K.J. and and Tomllnson, Y. Stott, G.M., G.M., Davis, 13. D. W., Tomlinson, K. K.Y. goon Subprovince, Archean tectonostratigraphic tectonostratigraphicassemblages assemblages of of eastern eastern Waba Wabagoon Subprovince, northwestern north western Ontario Ontario xxvii �ABSTRACTS Xxviii �WHAT DOES SEDIMENT SEDIMENT CHEMISTRY TELL US ABOUT ROCKS FORMATION? LIKE THOSE FROM THE FERN CREEK FORMATION? Argast, Anne, Department of Geosciences, Geosciences, Indiana Indiana University Purdue Purdue University University Fort Wayne, Fort Wayne, IN 46805-1499, 46805-1499, Argast@ipfw.edu Argast@ipfw.edu Bulk chemical analyses are accepted and powerful tools for the the study of of metamorphic and igneous rocks. Bulk chemical chemical analyses analyses are are less accepted accepted and and less less widely widely used used for for the the study studyof of sedimentary rocks. This is at least partly the result of a widely-held view that chemical data result a widely-held view that chemical dataare are unreliable unreliable indicators indicators of sedimentary sedimentary events events due due to to the the post-burial post-burial diagenetic diageneticalteration alterationof of the the sediment. sediment. In recent years, this view has been reinforced reinforced with with studies studies indicating indicatingthe thepotential potential for for extreme diagenetic diagenetic alteration alteration of sediments, sediments, with with km-scale km-scale transport transportproposed proposedin insome somesystems systems (e.g., Wintsch and and Kvale, Kvale, 1994). 1994). Potassium is often singled-out as an especially mobile component in diagenetic systems. For example, Awwiller (1993), working in the Gulf Coast Tertiary, postulates an increase from 2.0 to 3.8 wt. percent K20 in mudrocks, due significantly to to the the transport transport of of K K as aspart part of of 1UJ0 pore volumes of fluid passing through the system in the depth range from 1500 to 4000 m below the surface. surface. Donnelly, 1987) maintains maintains KzO K20 is a generally conservative An alternate view (Argast and Donnelly, that observed variations in KzO K20 content preserve element in diagenetic settings, and that preserve compositional characteristics present at and before accumulation. Depending on your point-ofdiagenetically and metamorphically metamorphicaily altered view, the chemistry of diagenetically altered sedimentary sedimentaryrocks rocks may may (or (or not) provide provide useful information information about about provenance, provenance, weathering and other qualities of the may not) sedimentary system. system. Unconsolidated Unconsolidated sediments, sediments, delivered as turbiditic pulses of siliciclastic siliciclastic debris debris eroded eroded from from the the Himalaya Mountains, accumulated on the Bengal Pan Fan (DSDP 218) and now at subbottom subbottom depths from 12 12 to 729 m, produce chemical trends very similar to those previously noted in lithified lithified sedimentary rocks. rocks. The The similarity similarity in in chemical chemical trends trends across this broad (and metamorphosed) sedimentary range of conditions and environments suggests sedimentary chemical trends arise from fundamental conditions imposed upon the system before burial, and are are not necessarily necessarily the the result of extensive extensive diagenetic alteration alteration at depth. depth. Proterozoic, Lower Chocolay Group) is well exposed along the The Fern Creek Formation (Early Proterozoic, Sturgeon River near the dam northeast of Loretto, Michigan. These rocks have been interpreted interpreted as glaciogenic in origin, and the diamictites they contain used as evidence for glacially-derived dropstone units. Others have interpreted the Fern Creek Formation as nonglaciogenic nonglaciogenic in in origin origin lagoonal or or with the sediments accumulated in fluviatile environments grading upward into into lagoonal estuarine environments. Field and textural qualities (to be discussed discussed as as part part of of aa post-meeting post-meeting hon Range) fieldtrip in the Menominee Iron Range) support support aa glaciogenic glaciogenicorigin. origin. 1 �Bulk rock chemistry chemistry also also supports supports aa glaciogenic origin (Argast, (Argast, 2002) . The The chemical chemical data, data, including sediments from including the the absence absenceof of aacorrelation correlationbetween between K20 K2Oand andA1203, A1203show sediments from the Fern Creek Formation Formation were were deposited deposited without without extensive extensivesorting sorting or or demixing demixing of of hydraulically hydraulically coarsercoarserNa20/K20 and atomic + K)/Al K)/A1 atomic and (2Ca (2Ca ++ Na + and finer-grained fractions. Other data, including the NazO/K^O ratio ratio suggest suggest sediment sediment accumulated accumulated with with abundant abundant original original feldspar. feldspar. The The chemical chemical index index of of alteration (CIA) Gowganda diamictite diamictite (CIA) ranges ranges from from 50 50 to 61, 61, similar similar to the average average CIA of 57 in Gowganda matrices. The accessory accessory suite suite is complex complex and includes includes poorly rounded zircons. zircons. These These attributes attributes are consistent consistent with an an origin origin as as aa glacial glacial till. till. . and/or thorium were identified identified in the Several minerals enriched in rare earth elements (REE) andlor Fern Creek Creek Formation. Formation.These Theseinclude includemonazite, monazite,huttonite huttonite(monoclinic (monoclinicThS1O4) ThSi04) and a fluorfluorhydroxy-REE mineral. Th concentrations concentrations as high as 53 53 ppm were noted in one one bulk bulk analysis. analysis. Efforts to obtain obtain aa chemical chemical date date on these minerals minerals have so so far far been unsuccessful. unsuccessful. The Camey Carney Lake Lake Gneiss Gneiss is is aa chemically-compatible chemically-compatiblepossible possible source source for for the the Fern Fern Creek Creek Formation. Formation. REFERENCES REFERENCES Argast, A., A,, 2002, 2002, The The lower lower Proterozoic Proterozoic Fern Creek Creek Formation, Formation,northern northern Michigan: Michigan:mineral mineral and and J. Earth Earth Sci., Sci., v. v. 39, 39,p. p. 481481bulk geochemical geochemical evidence evidence for for its glaciogenic glaciogenic origin: origin: Can. Can. J. 492. 492. Argast, S. and Donnelly, Donnelly, T.W., T.W., 1987, 1987, The chemical chemical discrimination discrimination of of clastic clastic sedimentary sedimentary components: components: J. J. Sed. Sed. Pet., Pet., v. v. 57, 57, p. p. 813-823. 813-823. Awwiller, D.N., 1993, 1993, Illite/smectite Illitelsmectite formation formation and and potassium potassium mass mass transfer transfer during duringburial burial diagenesis of mudrocks: a study from the Texas Gulf Coast Paleocene-Eocene: Sed, diagenesis mudrocks: study Texas Coast Paleocene-Eocene:J.J. Sed. 501-512. Pet., v. 63, 63, p. 501-512. of Wintsch, R. P. and Kvale, C. M., 1994, 1994, Differential mobility of elements in burial diagenesis of siliciclastic J. Sed. Sed. Res., Res., v. v. 64A, 64A, p. p. 349-361. 349-361. siliciclasticrocks: rocks: 3. 2 �GEOLOGY AND HYDROGEOLOGY IN THE KINGSFORD, MICHIGAN MICHIGAN AREA BARTNTK, PATRICK PATRICK J., J., pbartnik0arcadis-us.com, pbartnik@)arcadis-us.com, ARCADIS ARCADIS G&M, (I&M, Inc., BARTNIK, Inc., Kingsford, Kingsford, Michigan, 49802; and bevans@arcadis-us.com, ARCADIS EVANS, BRUCE W., bevans@arcadis-u.s.com, ARCADIS G&M, G&M, Inc., Inc., Milwaukee, Milwaukee, Wisconsin, 53202 Wisconsin, 53202 Investigations have been undertaken in a portion of the City Investigations City of Kingsford, Kingsford, Michigan Michiganand and Michigan (the Breitung Township, Michigan (the study study area) area) to determine determine the the geologic geologic and and hydrogeologic of glacial sediments and and bedrock. bedrock. The hydroeeologic characteristics of The study study area area is is located located Dickinson in ~ i c k i n s oCounty County i in the south-central south-central Upper Upper Peninsula Peninsula of of Michigan. Michigan. 1EPA)t ffpT I 7 .' '. I . . / IUNGSEOkD .. ,*-. 4 C&y md L v". ] """ l—% Cit;ofKingsford 1. f.I if, P'1 \ — — Study Area * ty 1ownship Kinysford City Supply Well The ARCADIS investigations were largely completed between April 1997 1997 and January January 2001, but are continuing. During During the the investigations, investigations, over 300 300 soil borings were were completed, along with with 47 47 test test pits pits and and 9.5 9.5 miles miles of of geophysical geophysical study. study. The topography is by three three distinct distinct landform terraces (Upper, Lower, and Riverside), which characterized by range in elevation from approximately 1,120 feet above mean sea level (ft msl) to 1,045ftftmsl. msl. The Upper Terrace contains several isolated glacial kettles. approximately 1,045 elevation of of the the Menominee Menominee River River is is approximately approximately 1,037 1,037 ftft msl. msl. The The geology geology is The elevation 3 �comprised of unconsolidated glaciofluvial and glaciolacustrine deposits of clay, silt, sand, that exhibit complex horizontal horizontal and and vertical vertical spatial spatialvariability. variability. These and gravel that Michigamme Slate and the Lower sediments overlie the Middle Precambrian Michigarnme Formation. Depth to groundwater in the Precambrian metavolcanic Quinnesec Formation. unconsolidated deposits ranges from about 10 feet below land surface (bis) near the to more more than than 50 feet feet bls bis in in the theUpper UpperTerrace. Terrace. Groundwater flow Menominee River to follows irregular pathways toward the Menominee River, but generally flows from northeast to southwest. Vertical Vertical hydraulic hydraulic gradients range from +0.863 ft/ft in upland —0.012ft/ft ftlftnear nearthe theMenominee MenomineeRiver. River. Hydraulic Hydraulic conductivities conductivities range from iO3 areas to -0.012 10'~ per second (cdsec) (cm/see) to to 10" 10' cm/sec material to to 1.03 xx 1i03 centimeters per c d s e c for coarser-grain material 0'~ i05 0 "cm/sec c d s e c for for the the very very fine-grain sand and sandy silt. The Thebedrock bedrockisis ccm/sec d s e c to 3.94 x 1 considered impermeable. impermeable. Groundwater generally considered Groundwater flow velocities range from approximately 3 ft/day to 280 ft/day in coarser-grain units, units, and and from from approximately approximately0.1 0.1 fine-grain sand and sandy silt. ft/day to 3 ft/day in the very fine-grain To aid in the understanding of the complex complex geology within the study study area, area, threethreetopographic surface, dimentional modeling of the geology was undertaken using the topographic surface, and glacial glacial sediments. sediments. Thirteen geologic units identified from the bedrock surface, and borehole data were categorized in to 3 units, based on permeability and anticipated anticipated effects on groundwater flow. flow. The modeling and visualization of the geology were The Geostatistical Software Library (GSUB), (GSLIB), developed at Stanford completed using a Geostatistical FORTRAN programs, and Environmental Visualization System University, FORTRAN System (EVS) Development Corporation. Corporation. software developed by the C Tech Development 4 �GEOLOGY GEOLOGY OF OF THE THE MISSISSIPPI-VALLEY MISSISSIPPI-VALLEYTYPE TYPE MINERALIZATION MINERALIZATIONAT MICHIGAN BELLEVUE, MICHIGAN BLASKE, Allan R., Blaske Geoscience, BLASKE, Allan R., Blaske Geoscience, 8313 8313 Hartel, Hartel, Grand Grand Ledge, Ledge, Ml MI48837 48837 The Bayport Bayport Limestone is exposed exposed in in quarrying quarrying operations operations at at Bellevue, Bellevue, in in southwestern southwestern Eaton Baton County, Michigan. Mining has active around around Bellevue County, Michigan. Mining has been been active Bellevue since since the mid-1800's. Approximately 25 25 feet of the Bayport is exposed in the quarrying Approximately quarrying operations, and consists of a buff colored thin-bedded limestone. gray to buff limestone. The Bayport Bayport limestone limestone is is late Mississippian in age, age, and comprises the upper portions of the The Mississippian in the Grand Rapids Group. Grand Group. It is underlain underlain by the the Michigan Michigan Formation, Formation, also of of the the Grand Grand Rapids Rapids below the Grand Group. The The early earlyMississippian Mississippian Marshall Marshall Sandstone and Coldwater Shale lie below Rapids Group. The TheBayport Bayportisisoverlain overlainby bythe theearly earlyPennsylvanian PennsylvanianSaginaw SaginawFormation Formation(within (within the Michigan Basin), but covered only by glacial sand and gravel at the quarry site. gravel at the quarry site. Mineralogy of the deposit is simple, Mineralogy of simple, consisting consisting predominantly of pyrite, marcasite, and calcite. Pyrite is most commonly found as encrustations of cubic crystals, formed directly on limestone. limestone. Mamasite Marcasite is generally generally lighter in color than the pyrite, and often in iridescent, iridescent, platy crystal groups. Marcasite is by by far the dominant iron sulfide. sulfide. Two observed. Early Marcasite is dominant iron Two generations generations of calcite are observed. Early calcite is found as calcite as small small crystals crystals lining lining cavities cavities as as drusy drusycoatings. coatings. The second generation of calcite is found in large, large, euhedral euhedral crystals and cleavable masses. Trace Traceamounts amountsof ofsphalerite, sphalerite, barite, and fluorite are present. Fluorite Fluorite was was the the earliest earliest to to form, form, as as small small brown brown crystals crystals directly directly on the Pyrite was was formed on the limestone. limestone. Pyrite formed in association association with the the early early calcite. calcite. Marcasite and and sphalerite pyrite. Second sphalerite are later than the early calcite and pyrite. Second generation generationcalcite calcitebegan began slightly slightlyafter after the marcasite. Tiny Tiny crystals crystals of of marcasite marcasite can also also be be found found on on the the large large calcite, calcite, indicating indicating that that formation of of marcasite continued to to the end of formation marcasite continued of mineralization. mineralization. Barite Barite appears appears later than the sulfides, but before the end of the calcite formation. sulfides, calcite formation. Mineralizationisis present present predominantly predominantlyinin brecciated brecciated zones zones and and vein structures Mineralization structures within within the the The most Bayport Limestone. Limestone. The most common common type type of breccia breccia consists consists of of small, small, angular angular clasts clasts surrounded by by open-space open-spacefilling fillingofofsulfides sulfidesand andcalcite. calcite. A second type of breccia consists consists of of surrounded type of larger, rounded rounded clasts, clasts, with with the the interstitial larger, interstitial spaces spaces filled filled with aa muddy muddy limestone limestone and and pyrite. pyrite. Orientation and and size size of of the mineralized mineralized zones zones within within the the limestone limestone is is not not known, due to lack of Orientation within the the quarry quarry and and insufficient insufficienthistorical historicalmapping. mapping. Fine-grained iron sulfide is also exposure within observed as replacement structures, along apparent solution fronts within the massive massive limestone. limestone. The geochemistry of the the sulfides indicates indicates the the simplicity simplicity of of the the mineralization. mineralization. 36-element ICP geochemistry of analysis of of pyrite pyrite and and marcasite marcasite separates, separates, as as well well as a composite breccia sample, indicate very analysis concentrations of of trace trace elements. elements. Copper, lead and low concentrations and zinc zinc are are found found at at concentrations concentrations of of less less than 60 ppm; ppm; nickel nickel is is less less than than 30 30 ppm; ppm; and and cadmium cadmium and and cobalt cobalt less lessthan than 55ppm. ppm. Barium is generally less less than than 20 20 ppm. ppm. Manganese is high in the also low, generally the breccia breccia (385 (385 ppm), ppm), and and lower lower in the sulfide separates (64 to 109 ppm), while chromium is high in the sulfides (150 ppm) and low 5 �ppm). Arsenic in the breccia (31 ppm). Arsenic isis present present in in the the breccia breccia (7 (7 ppm), ppm), but but low low in in the the iron iron sulfides sulfides at at less than 5 ppm. ppm. Sulfur isotopic were analyzed analyzed on on separated samples of Sulfur isotopic compositions compositions were of pyrite, pyrite, marcasite, marcasite, and and sphalerite. Sulfur (6S) ofofthe Sulfur isotopic compositions (S^S) thesulfide sulfidephases phasesfrom fromthe theBayport BayportLimestone Limestone are for These are 14.5°/ 14S0Ioofor forthe the pyrite, pyrite, 12.8°/ 12.8°/o forthe themarcasite, marcasite, and and 19.8°/ 19.8'loofor forthe thesphalerite. sphalerite. These compositionsindicate indicatethat that the the mineralizing mineralizingfluids fluids were were basinal basinal brines brines from from within compositions within the the Unpublished data obtained from the surrounding Mississippian and Pennsylvanian Pennsylvanian formations. formations. Unpublished USGS (Westjohn, I). B., pets. pers. comm.) comm.) as part part of the the RASA RASA program program indicate indicate aa large large range range of of (Westjohn, D. 34 . 8SSSininsamples samplescollected collectedfrom fromthe theunderlying underlyingMarshal! MarshallSandstone Sandstone and and Michigan Michigan Formation, Formation, as well as the overlying Saginaw Formation Formationand andthe theJurassic Jurassic Red Red Beds. Beds. Pore well overlying Saginaw Pore water, water, whole-rock, whole-rock, sulfide, and sulfate sulfur isotope isotope compositions compositions for the the underlying underlying formations formations exhibit exhibitaverage average o/ 20°/c,, while the average 634S withinthe the overlying overlying formations formations is near 17 S^S within 17 'loo. S^S near 20°/oo Temperature Temperature of the mineralization has been determined using fluid inclusions in calcite (Panter, (Panter, K. 5., S., 2001). 2001). Calcite afforded afforded the only mineral phase with with inclusions inclusions for formicrothermometric microthermometric study. Temperatures Temperaturesof of homogenization homogenization indicate a bimodal distribution, with aa low low temperature temperature mean of approximately 5g°C 58°C, and and a high high temperature mean mean of of approximately 138OC. 138°C. The The mean mean temperature of all inclusions These temperatures are similar to those temperature of inclusions analyzed analyzed was was 107°C. 107OC. These temperatures are those compositions in authigenic minerals the Mississippian observed observed using using isotopic isotopic compositions authigenic minerals in Mississippian and and Pennsylvanian sandstones (Westjohn, (Westjohn, D. B., 1994). 1994). Fluid salinities salinities based based on on freezing freezing point point Pennsylvanian sandstones equivalent weight percent depression range from 2.6 to 9.5 equivalent percent NaCI. NaCl. The quarries quarries at at Bellevue Bellevue are are located located within within55 to to 66 miles miles to the north The north and and west west of of the the known known northwest end of the northwest the Albion-Scipio Albion-Scipio Oil Oil Field Field Trend. Trend. This oil oil field field (dolomitized (dolomitized fracture fracture and and solution cavities) structure is located within the Trenton-Black River (Middle (Middle Ordovician) Ordovician)rocks, rocks, 4,000 feet feet deeper deeper than than the the Bayport Bayport Limestone. Limestone. The structure structure is related related to to faulting faulting within within some 4,000 basement rocks. rocks. Evidence the basement Evidence of of the the structure, structure, however, however, is is present present in in the the lower lowerMississippian Mississippian Sunbury Shale Shale Formation, Formation, (approximately (approximately 3,000 3,000 feet feet higher higher than than the Middle Ordovician rocks), the Coldwater the Sunbury), and the the Coldwater Shale Shale (overlying (overlying the Sunbury), and the Marshall Marshall Sandstone Sandstone (overlying (overlying the If movements associated with this are evident Coidwater). Coldwater). If movements associated with this structure structure are evident in in the theformations formations immediately below the Bayport Limestone, it seems likely that the Bayport Bayport Formation Formation would would also also be affected by faulting associated with with the structure. Faulting Faulting associated associatedwith with the theTrend Trendisislikely likely responsible for small in the Bayport, allowing allowing for for brecciation, brecciation, subsequent subsequent fluid fluid responsible for small structures structures in the Bayport, precipitation of the mineralization. migration, and precipitation mineralization. REFERENCES REFERENCES Panter, K. 5., S., 2001. 2001. A Preliminary Preliminary Microtermometric Study of Fluid Inclusions in Calcite Calcite from data, Bowling Bowling Green Green State University, OH Bellevue, Michigan, unpublished data, of Westjohn, D. B., 1994, Michigan Basin RASA Solid-Phase Investigation, in Geohydogeology of Carboniferous Aquifers of the Michigan Basin, Great Lakes Section-SEPM, 1994 Fall Carboniferous Aquifers of the Michigan Section-SEPM, 1994 Fall Field Conference, September 23-24, 1994, 1994, Lansing, MI 6 �GEOLOGIC MAPS MAPS OF OFKEWEENAWAN KEWEENAWAN VOLCANIC AND INTRUSIVE ROCKS BEDROCK GEOLOGIC IN THE LAKEWOOD, FRENCH FRENCH RIVER, RIVER, AND KNIFE RIVER 7.5' QUADRANGLES, NORTH SHORE OF OF LAKE LAKE SUPERIOR, SUPERIOR,MINNESOTA MINNESOTA f., Minnesota Geological Survey, St. Paul, Paul, MN, MN, boerbOOI@umn.edu boerb001@umn.edu BOERBOOM, Terrence J., Geological Survey, Survey, with with partial partial funding funding by by the U.S. The Minnesota Minnesota Geological U.S. Geological Geological Survey Survey STATEMAP STATEMAP geologic mapping program, has recently published detailed bedrock geologic geologic maps maps of of three threequadrangles quadrangles located along the North North Shore of Lake Superior northeast of Duluth, Minnesota Minnesota (Fig. 1; located 1; Boerboom and others, 2002a, b). Field Field mapping mapping was was completed completedatat aa scale of 1:12,000, others, 1:12,000, and compiled compiled at a scale scale of of has shown that some some flow flow sequences sequences can can he be traced traced inland inland as as far as 10 1:24,000. This mapping 10 to 12 12 1:24,000. mapping has shown that of individual individual flows flows within within the thelarger larger flow flow units. units. Several kilometers, and has identified hundreds of Several mafic to felsic, subcordant to discordant discordant sills sills and and intrusions intrusions have have also also been been mapped. mapped. Prior to this mapping, bedrock geologic geologic maps maps for for this this area were at aa scale mapping, the only only published published bedrock scale of of (for example example Miller Miller and others, 2001). 2001), and other work was concentrated concentrated along the shoreline 1:200,000 (for shoreline of Lake Superior. Superior. Brannon Brannon(1984) (1984)sampled sampled160 160successive successivevolcanic volcanic flows, flows, starting startingabove abovethe theLester LesterRiver River geochemical study. study. Green sill and ending in Two Harbors, as part of an exhaustive geochemical Green and and others others (1977) (1977) included this this area area as part of aa more included more broad broad coastal coastal zone zone management management study. study. Schwartz and Sandberg Sandberg published a paper on the diabase sills near Duluth that included some of the (1940) published the sills sills mapped mapped during during this study. Sandberg Sandberg(1938) (1938) mapped mapped the the stratigraphy stratigraphy of the flows exposed exposed at the the shoreline shorelinefrom from Duluth Duluth to to Two Harbors, identifying some 180 180 lava lava flows. flows. Although all of these these studies studies made made some someincursions incursions inland from the shore, none of them provided systematic mapping away from the shoreline shoreline proper. Bedrock exposure in the map area varies greatly, from nearly continuous outcrop along the shoreline shoreline and many of the short short streams streams along along the the slope slope into into Lake Lake Superior, Superior, to to variably variablyabundant abundant outcrop outcropin in the the hills inland from the lakeshore. Throughout Throughout the the map map area, area, there there are are many many closely closelyspaced spacedstreams streams that that bedrock perpendicular perpendicular to to the the strike strike of of the the volcanic volcanic stratigraphy. stratigraphy. Hence, have eroded into the bedrock Hence, many of the individual flows could could be be traced traced for for a great individual flows great distance distance along along strike strike by tying tying them them together together from from one one streamcut to the next, in combination combination with with the the shoreline outcrops. outcrops. In In contrast, contrast,the the more more resistant resistantintrusive intrusive typically exposed exposedon onthe thetops topsand andslopes slopesofofhigh highhills. hills. The northeast northeast part part of of the map area is rocks are typically aeromagnetic poorly exposed and thus much of the bedrock geology in that area is constrained constrainedlargely largelyby by aeromagnetic data. data. Green (2002) has proposed a subdivision of the North Shore Volcanic Group into a series series of informal informal sequences and formations formations that that are are separated by major lithological breaks or by sequences and separated by lithological and and geochemical geochemical breaks by Within the the area of the maps shown here, these include the Larsmont basalts, Sucker River intrusions. Within intrusions. Lakewood lavas, lavas, and and the the Lakeside Lakeside lavas lavas (Fig. (Fig. 2). 2). The detailed detailed bedrock geologic geologic maps maps shown basalts, the Lakewood here subdivide these informal informal formations formationsinto into multiple multiple layers layers comprised comprisedof of lava lava flows of here subdivide these of similar similar documented. composition and texture in which multiple flow contacts have been documented. REFERENCES Boerboom, T.J., T.J., Green, J.C., J.C., and Jirsa, Jirsa, M.A., M.A., 2002a, 2002a, Bedrock Bedrock geology geology of of the French French River and Lakewood quadrangles, St. Louis County, Minnesota: Minnesota Geological Survey quadrangles, St. Louis County, Minnesota: Minnesota Geological Survey Miscellaneous Miscellaneous Map M128, scale 1:24,000. 1:24,000. Bedrock geology geology of of the Knife River quadrangle, St. Louis and Lake Counties, -2002b, 2002b, Bedrock Counties, Minnesota: Survey Miscellaneous Miscellaneous Map Map M-129, scale 1:24,000. Minnesota Geological Survey Brannon, J.C. J.C. 1984, Geochemistry Geochemistry of of successive successive lava lava flows flows of of the Keweenawan North Shore Volcanic Group: St. dissertation,312 312p. p. Group: St. Louis, Louis, Washington Washington University, University, Ph.D. dissertation, 7 �Green, Green, J.C., J.C., 2002, 2002,Volcanic Volcanicand andsedimentary sedimentary rocks rocksofofthe theKeweenawan KeweenawanSupergroup Supergroupininnortheastern northeastern Minnesota, Minnesota,Chapter Chapter55of of Miller, Miller,J.D., J.D., Jr., Jr., Green, Green,J.C., J.C.,Severson, Severson,M.J., M.J., Chandler, Chandler,V.W., V.W.,Hauck, Hauck,S.A., S.A., Peterson, T.E.,Geology Geologyand and mineral mineralpotential potentialof ofthe theDuluth DuluthComplex Complexand andrelated related Peterson,D.M., D.M., and andWahl, Wahl,T.E., rocks rocksof of northeastern northeasternMinnesota: Minnesota: Minnesota MinnesotaGeological GeologicalSurvey Survey Report Report of of Investigations Investigations 58, 58, p. p. 9494105. 105. Green, Green, J.C., J.C., Jirsa, Jirsa, MA., M.A.,and andMoss, Moss,C.M., C.M., 1977, 1977,Environmental Environmental geology of the North North Shore Shore of of Lake Lake Superior:Minnesota MinnesotaGeological GeologicalSurvey, Survey,99 99p.p. Superior: Miller, J.C.,Severson, Severson,M.J., M.J., Chandler, Chandler,V.W., V.W., and andPeterson, Peterson,D.M., D.M., 2001, 2001,Geologic Geologicmap map Miller, J.D., J.D., Jr., Jr.,Green, Green,J.C., of of the the Duluth Duluth Complex Complex and and related related rocks, northeastern Minnesota: Minnesota Minnesota Geological Geological Survey Survey MiscellaneousMap MapM-119, M-119,scale scale1:200,000. 1:200,000. Miscellaneous Sandberg, Sandberg, A.E., 1938, 1938, Section Section across across Keweenawan Keweenawan lava lava flows flowsatatDuluth, Duluth,Minnesota: Minnesota: Geological Geological Society of of America America Bulletin, Bulletin,v. v. 49, 49, p. p. 795-830. 795-830. Society Schwartz, Schwartz, G.M., G.M., and and Sandberg, Sandberg, A.E., A.E., 1940, 1940, Rock series series in in diabase diabase sills sillsatatDuluth, Duluth,Minnesota: Minnesota: Geological Society of America Bulletin, v.51, v. 51,p. p. 1135-1172. 1135-1172. Geological AmericaBulletin, 92' 47 47' map showing showing location location of of Figure 1.1. Index map Figure mapped quadrangles. quadrangles. Work Work is is currently currently in in progress on the the Two Two Harbors Harbors and and Castle Castle progress Dangerquadrangles. quadrangles. Danger Index map map showing showing the the Figure 2.2. Index relative positions positions of the the informal informal volcanic units of Green (2002). volcanic Green (2002). Intrusive rocks Volcanic rocks Boundary of informal volcanic units units volcanic 88 �MINERAL RESOURCE WISCONSIN MINERAL RESOURCEGIS CISAND AND RELATED RELATED DIGITAL DIGITALMAP MAP AND AND DATABASE PRODUCTS -A PROGRESS REPORT REPORT B:A.1,CZECHANSKI, CZECHANSKI,M.L.', Mi.', MUDREY, BROWN, B.A.', MUDREY,M.G., M.G., Jr.', ~ r . and ' ,andREID, REID,Daniel DanielD.2 D.' (1) (1) Wisconsin Geological and Natural History Survey, Univ. of Wisconsin-Extension, 3817 Survey, Wisconsin-Extension, 3817Mineral Mineral Point Road, Madison, Madison, WI 53705, 53705, babrownl@facstaff.wisc.edu, babrownl @facstaff.wisc.edu, (2) (2) Wisconsin Dept of Transportation, 3502 Transportation, 3502 Kinsman Blvd, Madison, Madison, WI WI 53704-2507 53704-2507 information on 1,302 A new Mines, Pits and Quarries (MPQ) database containing information throughout Wisconsin Wisconsin has has been been completed by the Wisconsin significant nonmetallic mining sites throughout Geological and Natural History Survey (WGNHS) in cooperation cooperation with the the U.S U.S Geological Geological Survey (USGS). Locations were digitized from county-based digital orthophotography orthophotographywherever wherever (MASIMIIILS available and by site site visits. visits. Data Datatables tableswere werelinked linkedtotoexisting existingUSGS USGSdatabases databases (MAS/MILS and MRDS) and to Wisconsin Department of of Transportation Transportation (WDOT) (WDOT) aggregate test data; this linkage of all previous digital and analog analog databases is the first updated updated inventory inventory since since1980. 1980. Future versions will be augmented with current site information, collected under the nonmetallic nonmetallic reclamation program of Wisconsin Department of Natural Natural Resources, and additional historic sets such as the Road Material Survey WGNHSIWDOT. Survey sites sites of of the the WGNHSIWDOT. orthophotography, soil, Georeferenced maps layered with digital geology, topography, orthophotography, soil, and so forth provide a valuable land-use planning resource. Concern Concernfor forsafety safetyand andconstruction construction reconstruction of U.S. Highway 151 through the historic Upper Mississippi problems in the reconstmction District, southwest Wisconsin, Wisconsin, made possible the scanning and Valley Base-Metal Mining District, georeferencihg of the the Wisconsin Wisconsin Mineral MineralDevelopment DevelopmentAtlas. Atlas. The Mineral Development Atlas georeferencing of is a detailed set of of 1,450 section-scale maps (1 (I inch equal inch equal 200 200 feet) feet) of of mine mine workings, workings, drill-hole drill-hole dating from 1900 until until mining ceased ceased in 1979. These maps were location and ancillary data dating maintained by the WONTIS and the the University University of Wisconsin-Platteville Wisconsin-Platteville and WGNHS and and were were scanned scannedby by the the WDOT. WDOT. All Wisconsin water well construction reports for 1936-1988 are now available available on CDRom. They provide an extensive data set for geologic mapping as well as environmental environmental and and water resource analysis. New WGNHS map products are being produced in digital digital form and a variety of analog maps including the 1:24,000 1:24,000 USGS geologic quadrangle maps of the lead-zinc lead-zinc district are being converted to digital as resources allow. digital as resources allow. This presentation will provide an interactive demonstration demonstration of these these data data sets sets and and GIS GIs layers, a review of available map data such as regional geophysics, and an update on the status of geologic geologic mapping mapping at at the the WGNHS. WGNHS. 9 �HIGHWAY CONSTRUCTION, CONSTRUCTION,MINE MINERECLAMATION, RECLAMATION,AND AND LAND-USE LAND-USEPLANNING PLANNING CHALLENGES CHALLENGES IN THE THE HISTORIC HISTORICUPPER UPPER MISSISSIPPI MISSISSIPPI VALLEY VALLEY LEAD-ZINC LEAD-ZINC DISTRICT OF OF SOUTHWEST SOUTHWEST WISCONSIN BROWN, B.A.1, M.L.', REID, B.A.', MUDREY, M.G., Jr.1, ~ r . ' CZECHANSKI, , M.L.', REID, Daniel Daniel D.2, D.', and HUNT, T.C.3, Wisconsin Geological Geological and T.c.~,(1) Wisconsin and Natural History Survey, Univ. of Wisconsin-Extension, Wisconsin-Extension, babrown1@facstaff.wisc.edu, 3817 Mineral Point Road, Madison, WI 53705, babrownl@facstaff.wisc.edu, mgmudrey@wisc.edu, (2) Wisconsin Dept. of of Transportation, 3502 Kinsman Blvd, Madison, WI mgmudrey@wisc.edu, 53704-2507, (3) Reclamation Program, Univ. of Wisconsin-Platteville, 712 Pioneer Tower, Platteville, Platteville, WI WI 53818 53818 The Upper Mississippi Valley Valley Lead-Zinc District of Wisconsin, Illinois, Iowa, and Minnesota produced nearly 10 10 million tons of lead-zinc ore from the 1820s 1820s until the last last mine mine closed closed in 1978. The district will probably never be mined again, but but problems problems related to mineralization and past mining activity pose significant problems for highway construction and post-mining land use. Specific hazards and engineering problems problems include include (1) Highly altered and unstable rock and construction, (2) leachate from shallow abandoned mine workings encountered during highway construction, roaster-pile waste and (3) locally degraded degraded groundwater groundwaterfrom fromlead-zinc lead-zincsulfide sulfidemines. mines. As rural residential development increases, increases, the abandoned workings, particularly poorly sealed sealed shafts, can be a hazard. Most low-sulfide low-sulfide waste rock has been recycled as aggregate, and carbonate-rich tailings overgrown with vegetation vegetation make it difficult to find any surface evidence of small, small, older mine sites sites that may cause cause problems. problems. High sulfate in groundwater samples was noted in 1978 following closure 1978 following closure and and flooding flooding in an an area where large mines had operated for more than 50 years and a drawdown cone had bad developed developed over a 20-square mile area. A well-replacement program near Shullsburg Shullsburg restored potable water supplies. Onsite reclamation consisted consisted of establishing establishing vegetation vegetation on the tailings tailings and and crushing crushing the the coarse waste rock for aggregate. Leachate from zinc roaster waste piles produced over 100 100 years Mineral Point. The roaster piles were resulted in highly acidic and metal-rich surface water near Mineral successfully reclaimed by surface grading and contouring contouring along along with neutralization and fertilization to allow vegetation to establish. This was accomplished accomplished at aa fraction fraction of of the the cost cost of of removal of the roaster waste waste piles. piles. Previously undiscovered sulfide sulfide mineralization mineralization and and associated associated rock rock alteration alterationexposed exposedduring during construction along U.S. Highway 151 near Mineral Mineral Point Point resulted in the unanticipated highway construction unanticipated structures. The need to identify identify areas areas of need for engineering redesign of major roadcuts and structures. potentially unstable slopes led to scanning of the Wisconsin Mineral Development Development Atlas, Atlas, which which has proven to be invaluable in identifying areas of mineralization, alteration, alteration, and and abandoned abandoned workings in the path of construction. These detailed maps (1 inch to 200 200 feet) feet) of of mine mine workings workings and exploration drillhole locations are now being used by county and regional planners planners and and zoning authorities to identify and incorporate potential mining related hazards hazards into into land-use land-use planning. planning. 10 �TEXTURAL CONSTRAINTS TEXTURES IN IN THE THE WOLF WOLF RIVER TEXTURAL CONSTRAINTSON ON THE THE ORIGIN ORIGIN OF RAPAKIVI TEXTURES RIVER BATHOLITH BATHOLITH R. Michele Buttram Buttrarn and and Marcia Marcia Bjornerud Bjomemd Geology Department, Department, Lawrence University, Appleton, WI 54912 The Wolf River Batholith of north-central Wisconsin, a 1.47 Ga composite anorogenic pluton, includes some of the world's finest examples of 'rapakivi' granite, granite,in in which which large large plagioclase. Although potassium feldspar crystals are mantled by plagioclase. Although rapakivi rapakivi granites graniteshave have origin of of this this distinctive distinctive texture, texture, both both in the been described for more than a century, the origin elsewhere, remains remains controversial. controversial. Some workers argue that Wolf River complex and elsewhere, point under equilibrium rapakivi mantles are coronae formed at a peritectic or eutectic point crystallization conditions. Others Others maintain that rapakivi rapaldvi textures record disequilibrium associated with magma mixing mixing and and or or sudden sudden changes changes in in pressure. pressure. While most previous investigations investigations have focused on the chemistry of rapakivi granites, this study study examined examinedthe thephysical physicalcharacter characterofofthe theWolf WolfRiver Riverrocks rocks—- specifically, specifically, the size, shape, orientation and distribution rapakivi-type feldspar crystals. Among distribution of the rapahvi-type Amongthe the most striking characteristics of these rocks is the large size of the feldspars (up to 7 cm in length). Statistical Statisticalanalyses analyses show show that there is no significant significant difference in size or aspect with and and without without the therapakivi rapakivimantle. mantle. However, the K-feldspar ratio between crystals with tend to be be rounder rounder (less euhedral) euhedral) than than non-rapakivi non-rapakivi cores of the rapakivi-type crystals tend grains, suggesting prior to to the growth of the suggesting that they experienced significant resorption prior plagioclase mantle. A Aweak weak grain grain shape shape fabric fabric and and random random juxtaposition of rapakivi rapaldvi and non-rapakivi grains must also be explained by any viable model for the origin of the grains also explained texture. Our Our data data appear appearto to be be most most consistent consistent with the magma mixing model, which is compatible with earlier geochemical studies of the Wolf River complex. compatible complex. 11 �Niagara suture suture zone, zone, northern northernMichigan Michiganand andWisconsin—tectonics Wisconsin-tectonics in Ma arc-continent arc-continent collisional boundary the 1.85 Ma W.F. G.L. LaBerge, W.F. Cannon, Cannon,(U.S. (U.S.Geological GeologicalSurvey, Survey,Reston, Reston,VA VA20192, 20192, wcannon@usgs.Rov) wcannon(Susss.sov) G.L. LaBerge, (University of of Wisconsin-Oshkosh Wisconsin- Oshkosh(retired) (retired)and andU.S. U.S.Geological GeologicalSurvey), Survey),John JohnS.S.Klasner Kiasner (Western Illinois University (retired) (retired)and and U.S. U.S.Geological Geological Survey) Survey) The Niagara suture suture zone, zone, as as used used here, here, is is aa belt belt varying varying in in width width from fromabout about66 km krnto to40 40km kmlying lying north of the Niagara fault. It separates the accreted accreted volcanic volcanic arcs arcs of the the Wisconsin Wisconsinmagmatic magmatic terranes (WMT) on the south from the autocthonous and parautochtonous continental margin metavolcanic rocks rocks of of rocks on the north. ItIt consists consists of of Paleoproterozoic Paleoproterozoic metasedimentary and metavolcanic upon which they they were the epicratonic Marquette Range Supergroup Supergroup and Archean basement rocks upon deposited. The TheArchean Archean rocks rocks constitiute constitiute the the southern southern margin of the Superior craton, which was rifted and eventually separated during extensional eventually separated during extensional phases of the Penokean orogenic orogenic cycle, and then thrust northward northward during Penokean convergence. The suture zone is marked by very high strain and widespread multiple steeply to vertically plunging folds. folds. The suture zone is one of whose hierarchy hierarchy of of component component parts parts is is shown numerous subdivisions of the Penokean orogen whose below. Michigamme subterrane subterrane Michigamme Foreland fold Foreland fold and thrust "Niagara \ Niagarasuture suture zone Park Falls panel /, I Watersmeet Watersmeet panel Beechwood Beechwood panel Iron River River panel Menominee panel cianel /1 north north PENOKEAN OROGEN\ — - Niagara Niagara fault --PENOKEAN OROGEN --ioihh — — \\ south\ Pembine-Wausau (northern ~ e m b i n e - ~ a u s terrane aterrane u (northernpart part of ofWMT) WMT) - --- Mars hfleld terrane (southern (southern part Marshfield part of ofWMT) WMT) The The map pattern shown here was derived from published detailed maps in the east east (Bayley and and others, 1966; Dutton, 1971; others, 1961) others. 1971: James and others 1968; and James and others. 1961) and from our recent work in the west, where outcrops are scarce but access to recent exploration recentwork exploration drill electromagnetic data have aided in information as well as proprietary detailed aeromagnetic and electromametic clarifying the geologic>el~tionships geologic relationships (Cannon clarifying (Cannon and and others, others,1998). 1998). Each of the five fault panels of the Niagara suture suture zone has a unique unique set set of characteristics. characteristics. Watersmeet panel- Paleoproterozoic Paleoproterozoic strata are mostly pelitic schists schists and and gneisses gneisses containing containing ferruginous near the the base. base. They ferruginous strata and locally dolomite near They were were deposited deposited on on aa basement basement of Archean gneiss. gneiss. Both basement and cover were deformed deformed into into gneiss gneiss domes. domes. High-pressure metamorphism metamorphism produced kyanite-bearing assemblages. assemblages. Park Falls panel- Generally similar to Watersmeet panel except that metamorphism metamorphismwas lower lower pressure and sillimanite-bearing sillimanite-bearing assemblages assemblagesare arepredominant. predominant. Beechwood panel- Consists of Paleoproterozoic Paleoproterozoic graywacke graywacke and shale and mafic volcanic rocks rocks in in equal parts. parts. Archean basement is not exposed. exposed. Folds are roughly equal are ENE-trending and have subhorizontal axes. Rocks are are in greenschist greenschistfacies. facies. hon Iron River River panel- Rocks are the Paint River Group, including the Badwater Greenstone. Archean basement is not exposed. Strata are multiply folded creating a complex complex fold fold interference interference map map pattern. Most Most fold fold plunge steeply. Metamorphosed Metamorphosedto to greenschist greenschist or or sub-greenschist sub-greenschist facies. 12 �_____________________________ 89' 90' 88' t 4, '4— 46'- 3i •"'$ — ., S, 1' nt titer-i' V '7 A•S 50 0 I I I 7 AL-) L nt nit n-i' rlLp,1reflorniflee A 7 7 ,a 7 50 L'/AtvAkva 7 AS 7 A•3 7 , CL, L LVA tY' tvA tvA C. 7 7 L KM - 7,,. 7 7 89' 88' Maoshowing showingthe thefive fivestructural structuralpanels panels(Park (ParkFalls, Falls.Watersmeet, Watersmeet, Beechwood. IronRiver, River. Map Beech wood, Iron and that the Niagara andMenominee) ~enominee) thatconstitute constitutethe ~ i a ~ asuture suture r a zone. zone.Faults Faultsthat thatbound boundthe thepanels panelsare are Flambeau FlambeauFlowage Flowagefault fault(FFF), (FFF),Powell Powellfault fault(PF), (PF),Elmwood Elmwoodfault fault(EF), (EF),Paint PaintRiver Riverfault faull(PRF), (PRF), Badwater Badwaterfault fault(SF), (BF),North NorthRange Rangefault fault(NRF), (NRF),and andSouth SouthRange Rangefault fault(SRF). (SRF). 9'l' Menomineejanelpanel-Rocks Rocksare areentirely entirelyof ofPaleoproterozoic Paleoproterozoic age. age.No NoArchean Archeanbasement basementisisexposed. exposed. Menominee Strain Strainwas wasextreme. extreme. Commonly Commonlyallallstructural structuralelements, elements,including includingfold foldaxes, axes,are aresubvertical. subvertical. Metamorphism Metamorphismisislower lowertotoupper uppergreenschist greenschistfacies faciesand andlargely largelypost-tectonic. post-tectonic. These Thesepanels, panels,and andthe theNiagara Niagarasuture suturezone zone that that they they constitute, constitute,differ differfrom fromthe theMichigamme Michigamme subterrane subterraneto tothe thenorth. north.There Therewas waslittle littlepenetrative penetrativedeformation deformationofofArchean Archeanbasement basementisisininthe the Michigamme Michigamme subterrane. subterrane. Paleoproterozoic Paleoproterozoicstrata stratawere weremoderately moderately to toweakly weakly deformed. deformed. Folds, Folds, for postforthe themost mostpart, part,are aresimple simpleand andgently gentlyplunging. plunging.Metamorphic Metamorphicgrade gradeisisvariable variableand andmostly mostlyposttectonic. Thus, the Niagara suture zone documents a range of tectonic styles unique to the very tectonic. Thus, the Niagara suture zone documents a range of tectonic styles unique to the very high strains strainsin inaabelt beltno nomore morethan than aa few few tens tens of of kilometers kilometerswide, wide, along alongwhich which differential differential high movement craton margin margin on on the the north north was was movement between between the the accreting accreting arcs arcs on on the the south south and and the the craton concentrated. concentrated. References References Bayley, Bayley,R.W., R.W.,Dutton, Dutton,CE., C.E.,and andLamey, Lamey,C.A., C.A.,1966, 1966,Geology Geologyofofthe theMenominee Menomineeiron-bearing iron-bearingdistrict, district, Dickinson DickinsonCounty, County,Michigan Michiganand and florence Florenceand andMarinette MarinetteCounty, County,Wisconsin: Wisconsin:U.S. U.S.Geological GeologicalSurvey Survey Professional 96p. ProfessionalPaper Paper513, 513.96~. Cannon, Cannon,WE., W.F.,LaBerge, LaBerge,G.L. G.L.Kiasner, Klasner,J.S., J.S.,and andSchulz, Schulz,K.J., K.J.,1998, 1998,Reinterpretation Reinterpretationof of the the Penokean Penokean 44th continental part of ofnorthern northern Wisconsin Wisconsin and Michigan Michigan (abs.): (abs.):Proceedings Proceedingsof of 44' Annual AnnualInstitute Institute continentalmargin margin in in part on onLake LakeSuperior SuperiorGeology, Geology,v.v.44, 44,p.p.52-53. 52-53. Dutton. Dutton,CE., C.E.,1971, 1971,Geology Geologyofofthe theFlorence Florencearea, area,Wisconsin Wisconsinand andMichigan: Michigan:U.S. US. Geological GeologicalSurvey Survey Professional 54 p.p. ProfessionalPaper Paper633, 633,54 James, James,H.L., H.L.,Clark, Clark,L.D., L.D.,Lamey. Lamey,C.A., C.A.,and andPettijohn, Pettijohn,EU., F.J.,1961, 1961,Geology GeologyofofCentral CentralDickinson DickinsonCounty, County, Michigan: Michigan:U.S. US. geological geological Survey Survey Professional ProfessionalPaper Paper 310, 310,176 176p.p. James, James, H.L., H.L., Dutton, Dutton, CE., C.E.,Pettijohn, Pettijohn,F.J., F.J., and and Weir, Weir,K.L., K.L.,1968, 1968,Geology Geologyand andore oredeposits depositsof ofthe theIron IronRiver River US. Geological Crystal Falls Falls district, district,Iron Iron County, County, Michigan: US. GeologicalSurvey SurveyProfessional Professional Paper Paper 570, 570,134 134p. p. -- Crystal 13 �Strike-slip separation Strike-slip separation of the Burntside Burntside trondhjemite and and the the Wakemup Wakemup Bay Bay tonalite, Northern Minnesota Karoun Charkoudian, Basil Tikoff Department of Geology and Geophysics, Wisconsin. Madison WI, WI, 53706 53706 Geophysics, University of Wisconsin, Robert Bauer Department of Geological GeologicalSciences, Sciences,University University of of Missouri, Missouri,Columbia, Columbia,MO, MO, 65211 65211 INTRODUCTION The INTRODUCTION TheVermilion Vermilionfault faultisisaalocal localtectonic tectonicboundary boundary in in the the southern southern Canadian Canadian Shield juxtaposing the Quetico subprovince (granites and schists) with the Wawa greenstones. Quetico subprovince greenstones. Burntside trondhjeniite The Bumtside trondhjemite and the Wakemup Bay tonalite are small, elliptical, Archean granites granites separated by 35 k km of right right lateral offset offset on on the the Vermilion Vermilionfault faultin innorthern northernMinnesota. Minnesota. The m of Vermilion fault is interpreted interpreted as initially initially active as a normal fault, juxtaposing the shallow shallow Wawa the north (figure 1, greenstone to the south with the deeper granites and migmatized schists to the 1, reactivated as a strike-slip trondhjemite from stage stage 1). 1). It was later reactivated strike-slip fault, separating the Burntside trondhjemite from the Wakemun Wakemup Bay tonalite (figure 1, stage 2). Although the Vermilion fault is the regional Although the Vermilion fault is the regional 1. . Bav, . boundary between between the the Quetico Quetico and Wawa Wawa subprovinces, the Haley fault lies to the south south of of the the Vermilion fault and contains contains Quetico schists schists that belong- [ Stage N s t a x II Queticp gnttanaschsts on the north side side of of the Vermilion vermilion fault fault (figure 1) 1). The purpose of this study is to compare pluton setting fabrics, fabrics composition, of emplacement setting, composition, and shape of the two plutons to to determine determine if they constitute constitute a piercing point on the Vermilion fault. In In addition, addition, we have 20km determined din on on the the Vermilion Vermilion fault, fault. constrained constrained ..---~ the dip I emplacement history of the Wakemup tonalite. tonalite, and the emplacement the determined determined a potential potential cause cause for the the isolated isolated fault fault block block Queticp Sge 2 granites and schists that now contains contains the the Wakemup WakemupBay Bay pluton pluton (figure (figure11, 44 Bumtslde stage 2). stage Wakenup 110 The Burntside Bumtside trondhjeimte trondhjemite is is aa small small lenticular lenticular s pluton that intruded intruded the schist schist that lies lies to to the the north north of of the the ShaawaLake Bumtside continuation of the Vermilion Burntside Lake fault, a continuation fault at its eastern end. The TheWakemup Wakemup Bay Bay pluton pluton is is aa biotite-bearing tonalite that intruded biotite-bearing intruded the schist schist that lies lies Figure Figure 11 just to to the the north north of of the the Haley Haley fault. fault. - - -çffr ~ ~ tr ~ n'" The Anisotropy of Magnetic Susceptibility (AMS) is a rapid, nonAMS ANALYSIS ANALYSIS used in in granitic granitic studies studies to to obtain obtain magnetic magnetic fabrics. fabrics. Principle destructive technique, commonly used Principle magneticfoliation foliationisisdefined definedasas k-k1 kmx-k,,,, AMS ellipsoid axes are defined as km>kht>k,nin. The magnetic thethe is defined defined as as the the orientation orientation of of km,. plane, and the magnetic lineation is Wakemup Bay Bay tonalite tonalite (500-8500pSI) (500-8500pSI) The bulk susceptibility varies widely in both the Wakemup Burntside trondhjemite (SOO-3500pSI). This range range of of susceptibility susceptibility is attributed to the and the Bumtside (500-3500pSI). This content throughout throughout these these bodies. bodies. The large variation in magnetite content The AMS foliations foliations parallel parallel the the in both both plutons. plutons. Lineations measured field foliation in Lineations in in the the Wakemup Wakemup Bay tonalite tonalite dip dip shallowly shallowly to the E and W, and lineations lineations in the Burntside Bumtside trondhjemite trondhjemite dip dip shallowly shallowlyto to the the ENE ENEand andWSW. WSW. consistently parallel Magnetic lineations consistently parallel the long long axis axis of of the the plutons. plutons. The Bumtside and Wakemup plutons were selected selected for a gravity gravity study study GRAVITY STUDY lithology (biotite (biotite schist) with with a significant and because they both contain aa single surrounding lithology gicc). In consistent density contrast (Adensity (Adensity == -0.08 -0.08 to -0.1 glcc). In addition, addition, the gravity gravity data allows allows us to model the dip of the Vermilion Vermilion fault. fault. 14 �Lacoste and Romberg Romberg gravity gravity meter meter model modelGGwas wasused usedfor forboth bothareas. areas. After A Lacoste Burntside pluton and corrections, a forward model approach was used to interpret the depth of the Bumtside Vermilion fault geometry using WinGLink, WinGLink, a geophysical geophysical interpretation interpretation software software program. program. The Burntside pluton pluton is a thick body body between between 2-3 2-3 km km in inthickness. thickness. The Vermilion fault is a steeplyBumtside dipping to to vertically vertically oriented orientedfeature. feature. Using a gravimetric gravimetric three-dimensional thee-dimensional iterative north dipping technique on on the the Wakemup Wakemup Bay Bay pluton pluton resulted resulted in in aa good goodfirst-order first-orderpicture pictureof ofthe thepluton. pluton. Most technique thin, less less than than 0.5km 0.5km thick. thick. There are two root zones of up to 4 km krn depth, of the pluton is very thin, both of which lie on the southern portion of the Wakemup pluton, furthest away away from from the the Vermilion fault. fault. INTERPRETATION We interpret the Burntside Bumtside and Wakemup plutons as as part part of of the the same same granitic complex complex prior prior to to strike-slip strike-slip faulting faulting on on the theVermilion Vermilionfault. fault. These igneous bodies are granitic composition and both both have undergone solid-state deformation. deformation. The The plutons have similar similar in composition settings. The structural settings. The Wakemup Wakemup Bay pluton intrudes an F3 fold hinge and the Burntside pluton has refolded F2 folds at its southern end. Given Given the the separation, separation, the the folding folding episodes episodes may may or or may may not correlate correlate exactly. exactly. The gravity inversion and AMS study on the Wakemup pluton provide constraints constraints on on pluton emplacement. The The pluton pluton has has an an average average thickness thickness of of 0.5 km. Because the pluton reflects the true thickness thickness of the pluton. pluton. The TheAMS AMS contains a roof of wallrock, this estimate reflects F3fold. fold. foliation and lineation parallel the the fold fold limbs limbs and and fold fold hinge, hinge, respectively, respectively, of of aa km-scale km-scale F3 Therefore we interpret the Wakemup F3 fold fold hinge. hinge. Wakemup as syntectonically intruding intruding an an F3 We use a forward gravity model to estimate the dip on the Vermilion fault, which dips 70° N N and and vertical. vertical. This interpretation requires that the section of the Vermilion fault between 70' Bumtside pluton was not active as a south-side down normal fault. south of the Burntside We propose the following tectonic tectonic model model (figure (figure 1). The Burntside Bumtside pluton and the Bay pluton pluton were were initially initially part part of of the the same same granitic granitic complex. complex. The Wakemup Bay The Vermilion Vermilion fault fault was was 1, stage 1), l), which which juxtaposed the the aznphibolite amphibolite facies facies Quetico Quetico initiated as a normal fault (figure 1, sub-province with with the the greenschist greenschist facies facies Wawa Wawa belt. belt. The The Wakemup Wakemup tonalite, tonalite, with with aa thick thick root root on on promontory in the the fault system. The its south side, acted as a promontory The Vermilion Vermilion fault fault was was then then reactivated as a strike-slip fault (figure 1, stage 2), cutting through the thinnest (NW) section of the Wakemup Bay pluton. This This created created the the fault-bounded fault-bounded block block that that contains containsthe theWakemup WakemupBay Bay pluton. Therefore, Therefore, itit isis evident evident that that the the pluton pluton shape shape has played a crucial role in controlling Vermilion fault orientation, both for the early normal faulting and later strike-slip faulting. REFERENCES REFERENCES Bauer, R.L., 1985. 1985, Norwegian Bay Quadrangle, St. Louis County, Minnesota. Minnesota MinnesotaGeological Geological Survey, Miscellaneous Map series. 1:24,000. Survey, Miscellaneous series, Map Map M-59, M-59, 1:24,000. Bauer, R.L., 1986, 1986, Multiple folding and pluton emplacement in Archean migmatites of the southern Vermilion granitic complex, complex,northeastern northeasternMinnesota. Minnesota.Can. Can.1. J.Earth EarthSci., Sci.,v.v.23, 23, p. 1753-1764. 1753-1764. R.L., and Bidwell, Bidwell, M.E., ME., 1990, Bauer, R.L., 1990,Contrasts Contrasts in the response to dextral transpression across the Queticoboundary in innortheastern northeasternMinnesota. Minnesota. Can. J. Earth Sci., v. v.27, Wawa subprovince boundary 27, p. p. 1521-1535. 1521-1535. Sims, MG., 1972, Sims, P.K., and Mudrey, M.G., 1972,Burntside Burntsidegranite granitegneiss, gneiss,Vermilion Vermiliondistrict, district,ininSims, Sims,P.K., P.K.,etetal., al.,eds., eds., Geology of Minnesota: A Centennial Centennial Volume: Volume: St. Paul, Minnesota Minnesota Geological Survey, p. 98-101. Vigneresse, emplacement by regional deformation: Tectonophyiscs, Tectonophyiscs, v. 249, p. 1995, Control of granite emplacement Vigneresse, J.L., 1995, 17 3-186. 173-186. 15 �MINERAL POTENTIAL POTENTIAL OF PROTEROZOIC PROTEROZOIC MAFIC GEOLOGY AND MINERAL MAFICINTRUSIONS INTRUSIONS IN THE THE NORTHERN PROVINCE OF ONTARIO NORTHERN GRENVILLE GRENVILLE PROVINCE ONTARIO R.M. EASTON, EASTON, Ontario OntarioGeological GeologicalSurvey, Survey,933 933 Ramsey Ramsey Lake Lake Road, Road, Sudbury, Sudbury,Ontario OntarioP3E P3E6B5, 6B5, mjke.easton@ndm.gov.on.ca imke.easton@ndm.eov.on.ca Since 1998, 1998, mafic intrusions near the Grenville Front in Ontario have been prime exploration targets targets for for Cu-Ni-PGE Cu-Ni-PGE mineralization. mineralization. To To assist assist in this this effort, effort, the the Ontario Ontario Geological Geological has conducted detailed mapping in in high high potential areas of of the Grenville Province between between Survey has and 2002. This poster summarizes 1999 and summarizes the results results of these these mapping mapping efforts. efforts. East Bull Lake East Lake intrusive intrusivesuite, suite,including includingthe theRiver RiverValley Valleyintrusion: intrusion:Country Countryrocks rocksto to East Bull Lake intrusive intrusive (EBU) (EBU)suite suiterocks rocks in in the thearea area are areinferred inferredto to be be mainly mainlyArchean Archean in in age, age, and and are grouped into 4 gneiss associations. Metamorphic grade is upper amphibolite associations. Metamorphic amphibolite facies; facies; country country rocks to the mafic mafic intrusions intrusions are are commonly commonlymigmatitic. migmatitic. The Paleoproterozoic Paleoproterozoic EBLI intrusions emplaced EBU suite consists of several mafic layered intrusions emplaced between 2490 and kin, roughly and 2468 2468 Ma Ma (James (Jameset et al. al. 2002) 2002)that that occur occurover overaadistance distanceofof—250 -250 km, centered on the present site site of Sudbury. Sudbury. The largest of these bodies in the Grenville Grenville is the River Valley intrusion, intrusion, which underlies underlies roughly roughly 100 100kin2 km2 of Dana and Crerar Crerar townships. townships. Previous Previousmaps maps correlated correlated mafic rocks west of Crerar Township with the River Valley intrusion. intrusion. This This study indicates that at least 3 separate separate intrusions are present, each emplaced emplaced into into different different country country rocks, and with different different stratigraphy stratigraphyand and mineral mineral potential. potential. EBU EBU suite suiterock rock types types range range in composition composition from anorthosite anorthosite to melanorite, troctolite and rarely peridotite; leucogabbronorite leucogabbronorite and gabbronorite dominante. The crystallization crystallization order order of primocryst phases is most commonly plagioclase (An80.62), olivine (Fo7659), orthopyroxene primocryst phases is most commonly plagioclase (An80.62), olivine (Fo76-59), orthopyroxene (En7558), titanomagnetite,and and clinopyroxene. clinopyroxene. In In Dana Dana Township, Township, the (En75.58),titanomagnetite, the River River Valley Valley intrusion intrusion locally exhibits primary mineralogy and well preserved igneous textures. textures. Phase Phase layering varies from cm- to m-scale, which is discernable discemable in outcrop, outcrop, and dm or or larger, larger, which which is is identified identified by by detailed mapping. Isomodal layering is most common; mineral and size graded graded layers are less common. Cryptic layering is well documented for the River Valley intrusion. Pearce-element Pearce-element chondrite-normalized REE diagrams illustrate illustrate that each ratio and chondrite-normalized each body formed formed from from one one or or more more cogenetic magmas (James et al. 2002). A high-Al, low-Ti tholeiite tholeiite composition composition can can explain explain the the dominant leucocratic rock compositions in in the the EBU EBU suite suite (James (James et et al. al. 2002). 2002). EBLI suite, contact-type Cu-Pd-Pt mineralization (1 Within the EBU (1 to 10 10g/t g/t Pd+Pt+Au) Pd+Pt+Au) occurs in the matrix of an inclusion and/or fragment-bearing gabbronorite to leucogabbronorite andlor fragment-bearing gabbronorite to leucogabbronoriteat at the base or side of the intrusions where the primary igneous contact contact is preserved. preserved. A A second, second, similar, zone of mineralization may occur 100-200 100-200 m above above the contact. contact. Examples Examples occur occur throughout the EBLI EBU suite, suite, however, the most consistent grades grades have been reported from the River Valley intrusion in Dana Township. Chalcopyrite and lesser lesser pyrrhotite pyrrhotite form form 1-3 1-3 % % sulfide, sulfide, either finely disseminated or as local cm-sized patches. PGE mineralization mineralization is is commonly commonly associated with suiphide. sulphide. Study of the East Bull Lake intrusion indicates indicates that that mineralization mineralization originates from the intrusion and subsequent subsequent dynamic dynamic mixing of S-saturated, S-saturated, inclusion-bearing, inclusion-bearing, second-stage second-stage (PGE enriched, i.e. 20-100 ppb PGE) magmas magmas that that entered enteredthe the magma magma chamber chamber carrying liquid sulfide droplets (James et al. 2002). Reef-style mineralization mineralization has has yet yet to to be be documented within the EBLI suite. suite. 16 �GeologicaJ history history between Sudbury Geological Sudburyand andRiver RiverValley: Valley:Archean Archeanrocks rocksininthis thisarea arearecord record aa sequence of events similar to that observed observed in the Levack Gneiss complex complex and and high-grade high-grade portions of the Quetico subprovince, subprovince, but unlike the Pontiac subprovince. The following geological history is inferred. After deposition of greywackes south of the Temagami Temagami greenstone greenstone belt, invasion by tonalitic to granodioritic plutons, probably accompanied accompanied by burial, burial, formed formed the the migmatitic migmatitic gneisses gneisses now represented represented by the Pardo Pardo and Red Cedar Cedar Lake Lake gneiss gneiss associations, associations,likely likely between 2685 and 2675 2675 Ma. This This was was followed followed by by a second second period period of of tonalitic tonaliticto togranodioritic granodioritic magmatism, deformation deformation and metamorphism metamorphism at at mid-crustal mid-crustal levels levels between between 2670 2670and and2660 2660Ma. Ma. products of of this this latter activity. activity. Subsequent felsic The Crerar gneiss association represents the products magmatism at roughly 2640 Ma was accompanied accompanied by emplacement emplacement of pegmatite pegmatiteveins. veins. A logical extension of this work is to interpret the gneiss associations as a southwarddeepening deepening section of the crust. As interpreted, interpreted, Archean metawackes metawackes exposed exposed immediately immediatelynorth north of the Grenville Front Front represent high-levels high-levels of of the the crust. crust. The The Pardo Pardo gneiss, gneiss, immediately immediately south of of the Grenville represents the middle part of aa 10-15 Grenville Front, represents 10-15 km km thick thick upper upper crustal crustallayer layerdominated dominated by supracrustal and intrusive rocks. The Red Cedar Cedar Lake gneiss and the the Street Street gneiss gneissassociation association represent the basal portion of this upper crustal layer, with with the the former former derived derived from from a sequence and the latter metasedimentary rock sequence latter from a greenstone greenstone sequence. sequence.Intrusive Intrusiverocks rocks of of the the Crerar gneiss association are part of aa 10-15 km thick thick middle middle crustal crustallayer. layer.This Thiscrustal crustalsection sectionisis 10-15 km roughly equivalent to that observed across the Wawa gneiss gneiss domain. domain. Emplacement Emplacementof ofEBLI EBLIsuite suite bodies occurs at several levels within this this crustal crustal section. section. Flett Township Townshipmafie maficIntrusions: Intrusions:Evidence Evidencefor foraamafic maficand andA-type A-typegranite granite magmatic magmatic province in the northern Grenville Province was discovered while examining mafic intrusions near Temagami that that occur in in Tomiko Tomiko domain, near near its contact with with the Grenville Front tectonic zone. rocks consist consist of of gneissic gneissic granite, granite, with with minor minor mafic mafic and quarztose gneiss and Proterozoic country rocks The Fall Fall Lake Lake intrusion intrusion consists consists of of little little metamorphosed metamorphosed gabbro and metaconglomerate. The Fanny Lake Lake intrusion intrusion consists consists of of olivinite olivinite and and troctolite. troctolite. Igneous texture is leucotroctolite. The Fanny well preserved, but metamorphic coronas occur occur around around primary olivine olivine and and clinopyroxene. clinopyroxene. indicates that that both both bodies bodies are are slightly slightly alkalic, alkalic, compositionally compositionally similar to the Geochemistry indicates diabase dike dike swarm swarm dated dated at at 1238  ± 44 Ma, Ma, and and have have affinities affinities to to within-plate within-plate basalts. Sudbury diabase intrusion yielded pristine baddeleyite, with with 3 concordant or just just slightly The Fall Lake intrusion slightly discordant 1235±22Ma. Ma.The TheFanny Fanny Lake Lake sample discordant grains grains giving givingan an average average207Pb/206Pb 2 0 7 ~ b / 2 0age 6age ~ bofof1235 yielded baddeleyite, baddeleyite, with with some some grains grains having thin thin zircon zircon overgrowths, consistent with the presence of corona textures in the body. Two concordant grains without overgrowths overgrowths gave an 1238  ± 2 Ma. Ma. average average 2207Pb/2°6Pb 0 7 ~ b / 2 fage fage i ~ of bof1238 Both intrusions are spatially associated with the A-type Mulock granite, granite, dated previously at 12444L3 Ma. Intrusions Intrusions of of similar similar age include include the the Sudbury dike dike swarm, Mercer anorthosite, 1244+4/.3Ma. the West West Bay Bay and and Powassan Powassan granitoid granitoid plutons. plutons. The The new new age age data data provides provides further evidence and the of aa bimodal bimodal magmatic province active from 1270-1235 for the presence of 1270-1235 Ma in the Laurentian margin of the Grenville Province. Province. The The tectonic setting is interpreted as an extensional extensional rift that of a continental continental arc active on on the southern margin of North America formed inboard of America between 1450-1300 Ma. Ma. This This setting setting resembles resembles that that of of the the Cenozoic Cenozoic Columbia River Basalt Group. Group. R.S., Easton, Easton, R.M., R.M., Peck, Peck. D.C. D.C. and Hrominchuk, Hrominchuk, J.L. J.L. 2002. 2002. The East Bull Lake intrusive James, R.S., intrusive suite: suite: remnants of a —2.48Ga Galarge largeigneous igneousand andmetallogenic metallogenicprovince provinceininthe theSudbury Sudburyarea areaof of the the Canadian Canadian Shield; Economic -2.48 v.97, p.1577-1606. Geology, v.97, 17 �PAIEOSmES5 INFERENCES FROM FAULT PALEOSTRESS INFERENCES FROM FAULTSLIP SLIPVECTORS VECTORSIN INTHE THEEASTERN EASTERNPART PARTOF OFTHE THE WIscoNSIN SEGMENT MIDCONTINENT Rwr WISCONSIN SEGMENTOF OF THE MIDCONTINENT Amy Garbowicz, Marcia Marcia Bjomerud, Bjomerud, 54912 Geology Department, Lawrence Lawrence University, Appleton, WI 54912 Building accurate models models for for both Building accurate both the opening opening and closing of of the the Midcontinent Midcontinent Rift Rift requires an understanding of the the evolution of regional stresses over over time. This study requires an understanding of evolution of regional stresses study paleostress indicators indicators in in the the portion portion of of the Rift exposed near focused on slickenfibers as paleostress northeasternmost Wisconsin. Wisconsin. The the southern shore of Lake Superior in northeastemmost The orientations orientations of slickenfibers were were used used to determine slickenfibers determine slip vectors vectors on outcrop-scale outcrop-scale faults faults within within riftriftrelated igneous and sedimentary rocks. Rocks sampled span the entire range of related and sedimentary rocks. Rocks sampled span the range the the Keweenawan Supergroup, from the Tyler Formation to the Freda Sandstone, with most of the sampling in the Porcupine Volcanics, the Kallander Creek Volcanics, and the Mellen Gabbro. for their their age, age, Gabbro. . The mineral composition of the slickenfibers was used as a proxy for based on the based the known known regional regional sequence sequence of of secondary secondary mineralization mineralization within within the the Rfit. Rfit. Chlorite and epidote slickenfibers slickenfibers were grouped together and considered considered older older since since these these were among were among the first first minerals minerals precipitated precipitated by by hydrothermal hydrothermal fluids following following the the main main of calcite and zeolite were considered to be magmatic interval. interval. Slickenfibers of be younger. younger. Some individual faults were observed to have multiple generations of slickenfibers slickenfibers with reactivation or or continuous continuous slip over aa protracted protracted different compositions, indicating either reactivation Data from the period of time. period time. Data the field field were were analyzed analyzed using using Fault Fault Kinematics Kinematics (by (by R. R. Allmendinger, Cornell Unviersity), a program that calculates best-fit paleostress tensors Allmendinger, Cornell Unviersity), a program that from fault slip slip information. information. The calculated tensors all indicate indicate normal normal stress stress regimes regimes (maximum principal stress subvertical), even even for the latest (maximum principal latest generations generations of of slickenfibers. slickenfibers. This contrasts with the the results This contrasts with results of studies studies on on the the Keweenaw Keweenaw Peninsula, Peninsula, which which have have documented two distinct stress documented two stress regimes. regimes. There, There, early early normal normal faulting faulting gives way to to far-field stresses associated with the Grenville reverse faulting, possibly as a response to far-field Orogeny. Orogeny. The The absence absence of of reverse-slip reverse-slip vectors vectors in in the the northeastern northeastern Wisconsin Wisconsin segment segment of of the Midcontinent Rift may reflect the misorientation of this part of of the the rift rift with withrespect respectto to those far-field stresses. stresses. . 18 �Mode of Occurrence their Possible Possible Origin in in the the Negaunee Occurrence of Trona and Thermonatrite and their Iron-Formation of the Marquette Range, Range, Lake Superior District, USA Tsu-Ming Han (Retired) (Retired) Research Research Laboratory, Cleveland-Cliffs Cleveland-CliffsInc. Inc. A white colored substance Negaunee Ironsubstance is often seen on the surface of the silicate-bearing Negaunee Formation of low metamorphic grade on the Marquette Range, Michigan. This substance is mostly of a mixture containing hydrous hydrous sodium sodium carbonates carbonates(trona (tronaand andthermonatrite) thermonatrite) It occurs as thin coatings coatings coatings along bedding (Figure 1-A), and in fractures cutting across the bedding; as coatings and colloform colloform clusters on bedding planes (Figure 1-B); and as contour patterns distributed between the fractures fractures of bedding surfaces. Furthermore, nearly pure trona was developed quickly as as dendrites dendrites and minute minute dots dots on on the the cut cut surfaces surfaces of of some somehand hand specimens specimensin instorage storage(Figure (FigureC). C). To To the writer's writer's knowledge, knowledge, these these minerals minerals have have not not been been previously previously reported reportedfrom from Precambrian Precambrian BIF BIF of of the the equivalent equivalentmetamorphic metamorphicgrade gradein in other otherdistricts. districts. 4' 4fr.! Figures Mode of of occurrence occurrence of of trona trona and and thermonatrite. thermonatrite. Figures1 1—- Mode A-As white B-As colloform bedding plane. plane A—As whitecoatings coatings along along bedding. bedding. B—As colloform clusters clusters on a bedding C- As specimenin in storage. storage. C— Asdendrites dendriteson onthe the cut cut surface surface of a hand specimen The iron-formation is composed of magnetite, siderite, siderite, ankerite, ankerite, and stilpnomelane.. stilpnomelane.. The Minnesotaite more than Na in in these these minerals minerals Minnesotaite is also locally present in noticeable quantities. quantities. K is more as is the case in nearly all of the As aa as the Precambrian iron-formations iron-formations of of low low metamorphic metamorphic grade. grade. As 19 �_____________________ general general rule, rule, stilpnomelane stilpnomelanecontains containsmore moreKK and and Na Na than than the theminnesotaite. minnesotaite. However, However, the the K20:Na20 ratio these minerals and K20:Na20 ratioinin these minerals andin..the in theiron ironformation& formationsmay may vary vary substantially.. substantially. . Based Basedon onthe theresults resultsfrom fromthe thehighly highlypurified purifiedwater waterleaching leachingtests testson onmore morethan thantwenty twentydifferent different samples, practicallyinsoluble insoluble samples, the theNa Nain inthe theiron-formation iron-formationisiswater-soluble water-solublewhereas whereasthe theKKisispractically (Figures 2A and and B). B).The TheXRD XRDand and analytical analyticaldata datashow showaagood goodcorrelation correlationbetween between the theamount amount (Figures2A of Na20, K20 and the the amounts amounts of ofNa20, K 2 0and andA1203 A1203(Figures (Figures3A 3Ato to C). C). of stilpnomelane stilpnornelaneand 1L40 0.35 0.30 0.25 0.20 0.15 0.34 p.06 0.04 0.30 y25.66x+2.1167 = 0.7495 25, 0.9 20. 15 0.7 ar. I In .BTst':T 5 0 0 0.05 0 0.10 0.15 0.1 0.2 0.3 20 0.4 0.5 0.6 0.7 0.8 0.20 - Figure Figure 22-AAand andBB Solubility Solubilityof ofK20 K 2 0and and Na20 Na20 in the the silicate-bearing silicate-bearingiron-formation iron-formationwith with high high in and low K20:Na20 K20:Na20ratios. ratios. and - 0.9 Figure33- A A to to CC Relationship Relationshipofofstilpnomelane stilpnomelane Figure to K20, K20,Na20 Na20and andA1203. A1203. to 5 . 5 0. 0. c/ 00 % #4203 Y m A1203 0.5 0.5 1.0 1.0 1.5 1.5 2.0 2.0 2.5 2.5 It It may be logically concluded concluded that most of the sodium was was derived derived from from the stilpnomelane, stilpnomelane, which which was leached leached out by meteoric water. The mixture mixture of of the the hydrous sodium sodium carbonates carbonates was then developed through evaporation under the atmospheric conditions. developed through evaporation under the atmospheric conditions. 20 I1 3.0 3.0 �and Ultramafic Ultrainafic Intrusive Intrusive Rocks of the Lake Nipigon and Keweenawan Mafic and Ontario Crystal Lake areas, northwestern Ontario 933Ramsey RamseyLake LakeRoad, Road, Sudbury, Sudbury,Ontario Ontario P3E R.,Ontario OntarioGeological GeologicalSurvey, Survey,933 Hart,Thomas ThomasR., Hart, 6B5; tom.hart@ndm.gov.on.ca tom.hart@ndm.gov.on.ca 6B5; The Keweenawan diabase sills in the the Lake Lake Nipigon and and Crystal Crystal Lake Lake areas, areas, northwest of Lake Lake Superior, Superior, consist of two two distinct distinct geochemical geochemical and and geographical geographicalgroups groups with each area also hosting a number of unique intrusions intrusions that suggest suggest different different tectonic tectonic processes. Mapping by Smith and Sutcliffe (1987) in in the the Crystal Crystal Lake Lake area area identified identified a processes. series of 6 Logan diabase sills >5 m thick that gently dip dip to to the the southwest, and intrude into the early Proterozoic Rove Formation. Formation. Northeast Northeast trending dykes of of the the Pigeon Pigeon River swarm range from olivine to quartz diabase in composition, and include dykes that crosscut the Logan sills and dykes that appear to merge with the sills. crosscut sills. The The layered layered gabbro gabbro — anorthosite anorthosite -- troctolite Crystal Lake Gabbro crosscuts and contains inclusions of Pigeon of the Logan sills can can be be subdivided into into a low Ti02 Ti02 -Th/Yb - ZrN Zr/Y River dykes. Samples of group and group (OGS (OGS2002). 2002). The high Ti02 group group and aa high high Ti02 Ti02-ThJYb -Th/Yb - ZrIY group The high Ti02 group waswas asbeing beingquartz quartz normative, comparable theLogan type sills Logan by Sutcliffe identified as normative, andand comparable to the to type by sills Sutcliffe (1991). Samples identified as Pigeon River dykes exhibit high degree of variability (1991). Samples identified as Pigeon River dykes exhibit a highadegree of variability suggestingthat thatthey they represent at least unrelated intrusions. Oneofsubset suggesting represent at least three three unrelated intrusions. One subset the of the Pigeon TiOz group of Logan sills, and and another another Pigeon River River dykes dykes is is comparable comparable to the the low low TiO2 subset is comparable to the Crystal Lake Lake Gabbro. Gabbro. Most Most of of aa third third subset subset of of dyke dykesamples samples are located along Highway 61 61 close close to to the the Pigeon Pigeon River, River, and and contain contain lower lower trace element than the the other other intrusions intrusions in the area. Gabbro samples from the abundances and ratios than Crystal Lake Gabbro intrusion display some overlap with the low Ti02 hO2 group groupof of Logan Logan Zr/Y, Th/Yb, and Th/Ta ThITa ratios. ratios. The Logan sills but also includes samples with higher ZrIY, diabase diabase sills sills are confined to the area to the south of Thunder Bay, with the Nipigon diabase diabase sills sills located locatedto to the the north. north. intrusive event in the the Lake Nipigon Nipigon area is probably The initial Keweenawan intrusive flat lying lying to to shallowly shallowly dipping dipping peridotites peridotites located located in the represented by the relatively flat Disraeli, Leckie Seagull -- Fox Leckie— - Seagull Fox Mountain, Mountain, Hele, and Kitto areas that form intrusions a Disraeli, few kilometres in diameter. The peridotites are composed of orthocumulate orthocumulate to mesocumulate mesocumulate textured wehrlite to lherzolite, containing containing 11 to 2% reddish brown mica mica and and commonly a discontinuous olivine gabbro border phase (e.g. Sutcliffe 1987; 1987; Hart et al. 2002). The Disraeli, Seagull and Hele Hele peridotites are characterized characterized by higher MgO and Zr/Y ThiTa ratios than the Nipigon diabase series of of ZrIY and Th/Yb values but lower Th/Ta diabase sills. sills. A series stratigraphically below the Nipigon sills, as exposed 0.5 to 3.0 3.0 m thick sills are located stratigraphically exposed along Highway 17 at Kama Kama Hill. Hill. These These sills have MgO, Th/Yb ThIYb and Th/Ta Itt/Ta values values intermediate intermediate between the peridotites and Nipigon sills, and subdivided subdivided into into higher higher Th/Ta Th/Ta and lower ThITa may be be possible possible with with additional sampling. These sills have Th/Ta subgroups may ThITa and LdYb La/Yb ratios comparable to the high TiO2 Th/Ta Ti02 group of Logan sills, but generally generally have lower trace element abundances. The The Kitto peridotite also has Th/Yb, Th/Ta and and Zr/Y ratios that overlap with these sills rather than the other peridotites. The olivine ZrIY these peridotites. The olivine tholelite m thick, thick, and are chilled against the peridotite peridotite tholeiite Nipigon diabase sills are up to 200 200 in work indicates indicatesthat that some some sills sills were were formed formed by bymultiple multiple pulses pulses of of intrusions. Previous work Hart et et al. al. 2002), but the chemistry of the sills over the magma (e.g. Sutcliffe, 1987; Hart 21 �entire Lake Nipigon area area displays displays little little variation. Geochemical Geochemical differences differencesbetween between the the peridotites and Nipigon diabase sills the variations observed in the sills are comparable to the Osler Ti02 values Osier Group volcanic rocks (e.g. Sutcliffe, Sutcliffe, 1991). The Nipigon sills have Ti02 values comparable but higher ThTa ThiTa and lower LaNb La/Yb Ti02 group of Logan sills but comparable to the low Ti02 ratios. The differences differences in the the geochemistry geochemistry of the diabase diabase sills sills between between the the Lake LakeNipigon Nipigon and Crystal Lake areas is similar to the differences observed observed in in the the volcanic volcanic rocks of of a number of flood basalt provinces (e.g., Mantovani et al. 1985). The regional extent of the geochemical groups within the Keweenawan Keweenawan intrusions intrusionsisisnot notknown. known. An initial examination Complex (Ripley examination of troctolites troctolites from from the Babbit deposit of the Duluth Complex (Ripley et al. ThITa, ThlYb, ThIYb, and ZrN Zr/Y ratios comparable comparable to to the Nipigon peridotites 1999) indicates Th/Ta, peridotites rather than the intrusions intrusions of the the Crystal Crystal Lake area. area. References Hart, T.R., terMeer, M., and Jolette, C. C. 2002. 2002. Precambrian Precambrian geology of Kitto, Eva, Summers, Summers, Dorothea Dorothea and andSandra Sandra Townships, 206 Townships, Beardmore Beardmore area, area, northwestern northwesternOntario; Ontario; Ontario Ontario Geological Geological Survey, Survey, Open OpenFile FileReport Report6095, 6095,206 p. P. L.S., de Sousa, M.A., MA., Civetta, Innocenti, F., 1985. Mantovani, M.S.M., Marques, L.S., Civetta, L., L.,Atalla, L., and Innocenti, 1985.Trace Trace element and strontium isotopic constraints constraints on the origin and evolution evolution of of Parana Paranacontinental continental flood flood basalts basalts of of Santa Santa strontium Catarina State (southern Brazil); Journal of of Petrology. Petrology, v.v.26, 26, p. 187-209. 187-209. Ontario Geological Survey. Survey, 2002 2002. Proterozoic Volcanic volcanic and Intrusive Data associated associated wilh with Oniano fntrusive Whole Rock Geochemical Daia the Keweenawan Kewcenawan Midcontinent Midconunent Rift, Rift.Lake Lake Superior Suoenor Area, Area. Ontario; Onlano. Ontario Onlano Geological Geological SurveyMiscellaneous Miscellaneous . Survey Release—Data 114. Release-Data 114. Ripley, EM., Sm-Nd, and Pb isotonic isotopic consl~aints constraints on mantle Rinlev. Larnbert. D.D., D.D.. and and Frick, Frick. L.R., L.R.. 1999. 1999. Re-Os, Re-0s. Sm-Nd. mantle and crustal ..r.., , E.M.. - ,Lambert, contributions to magmatic contributions magmatic sulfide sulfide mineralization in the Duluth Complex; complex; Geochimica Geochimica et et Cosmochimica Cosmochimica Acta, Acta, v. 62, p.3349-3365. p.3349-3365. v. Smith, AR. and 7987. andSutcliffe, Sutcliffe.RH. R.H. 1987.lCeweenawan Keweenawanintrusive intrusive rocks of the Thunder TTiunder Bay area; in Summary Summary of Field Smith. A.R. Work and Other 137, p. Other Activities, Activities. Ontario Ontano Geological Geological Survey Miscellaneous Paper paper-137. p.248-255. 248-255. Sutcliffe, LakeNipigon, Nioigon. Canada;Contributions Conmbuiions Sutclifie. R.H., R.H.. 1987. 1987.Petrology Pctrolow Middle Proterozoic Proterozoic diabase diabase and and picrites niintes from from Lake -.ofof Middle . - Canada; to Mineralogy p.201-211. Mineralogy and Petrology, v.96, p. 201-211. Sutcliffe, R.H., RH., 1991. 1991.Proterozoic Proterozoicgeology geologyof of the theLake Lake Superior Superior area; area; in Geology of Ontario, Ontario, Ontario Ontario Geological Geological Survey Special Volume Volume4, 4,Part Part!, 1,p.627-658. p. 627-658. 22 �DRILL HOLES, HOLES, MINERAL MJNERALLEASES, LEASES,AND ANDGEOPHYSICS GEOPHYSICSIN GEOLOGY, DRILL NTHE DULUTH AND BEAVER BAY COMPLEXES, NORTHEASTERN NORTHEASTERN MINNESOTA: MINNESOTA: INTEGRATION INTEGRATION OF GIS DATABASES DATABASES TO TELL A STORY OF THE HISTORY OF PAST AND VARIOUS GIs CURRENT CU-NT-PGE MINERAL EXPLORATION CURRENT CU-NI-PGE MINERAL EXPLORATION Steven Hauck, Julie Julie A. A. Oreskovich, Oreskovich, and and Mark J. J. Severson, Severson,Economic EconomicGeology GeologyGroup, Group, Steven A. Hauck, Natural Resources Resources Research Research Institute Institute (NRRI), (NRRI), University University of Minnesota, Minnesota, Duluth, Duluth, 5013 5013 shauck@nni.umn.edu Miller Trunk Highway, Duluth, MN 55811-1442, shauck@nrri.umn.edu Mineral exploration in the Duluth Complex began in 1948 on Spruce Road when two prospectors found sulfide mineralization. mineralization. Subsequent Subsequentcore coredrilling, drilling,geological geologicalmapping, mapping,and and airborne airborneand and ground geophysics by more than 28 exploration companies (including (including the NRRI, MGS MGS Dept. of Natural Resources, Minnesota Geological Survey, Minnesota Survey, and the DNR - Dept. Resources, Division Division of Lands Lands and Minerals), over the next 52 copper-nickeltplatinum-groupelement element 52 years years led led to to the the discovery discovery of copper-nickel±platinum-group mineralization along the basal contact of of the the Duluth Duluth Complex Complex (Fig. 1). Ten (PGE) mineralization Ten Cu-Ni-PGE Cu-Ni-PGE orPGE-Cu-Ni years. Over or PGE-Cu-Ni deposits depositswere were defined defined by by drilling drilling during these years. Over 2,142 2,142 drill drill holes holes have have with 1,666 of of these holes being drilled been drilled into the Duluth and Beaver Bay complexes with the basal basal contact. Over along the Over 954,000 954,000 ft. ft. of of drill drill core from the the basal basal contact contact has has been relogged by NRRI, and their results are discussed in many publications. publications. Geophysical Geophysical exploration exploration began began as as early as 1956, by Bear Bear Creek Creek Mining Mining Company, and and continues continues today. today. The State of Minnesota State Minnesota (MGS), with funding from the Legislative Commission on Minnesota Minnesota Resources, Resources, flew flew high high this area area as as well well as asthe therest restof ofthe thestate. state. The MGS has also resolution aeromagnetics over this collected and produced a gravity map covering both both complexes. complexes. Peak Peak exploration exploration(1966-1978) (1966-1978) began with the the leasing leasing of of State State of of Minnesota Minnesotamineral mineralrights rightsinin 1966 1966(Fig. (Fig. 1). 1). Exploration and began resource calculations) continued through development (drilling, bulk sampling, shaft sinking, resource In 1998, 1998, State State and and Federal Federal mineral mineral leasing and exploration exploration drilling drilling began to to increase increase with with 1978. In rise in price price of PGEs; PGEs; 2) possible use of new new hydrometallurgical hydrometallurgical techniques to more the: 1) rise recover copper copper and nickel; nickel; and and 3) 3) introduction introduction of of new new PGE PGE exploration exploration models efficiently recover (sulfide saturation; Miller et al., 2002) for intrusions in in the Beaver Bay Complex, i.e., at Sonju and the the Duluth Duluth Complex, i.e., Greenwood Lake Lake and and Layered Layered Series Series at at Duluth). Duluth). The Lake, and The maps maps poster illustrate the relationship between geology, geophysics, geophysics, drilling, drilling, and and mineral in this poster were produced produced in ArcView (GIs). (GIS). The The maps were were also also compiled compiled by by using using leasing and were the DNR's online information from: 1) the online (minarchive.dnr.state.mn.us) (minarchive.dnr.state.rnn.us)attributeattribute- and and GIS-based GIs-based database of non-ferrous minerals' information information and and State State mineral mineral rights rights holdings; holdings; 2) 2)U.S. U.S.Forest Forest leases, permits, permits, and applications database; database; and and 3) 3) NRRI NRRI in-house GIS data on the history Service leases, of Cu-Ni-PGE Cu-Ni-PGE mineralization. mineralization. Using the resulting GIs GIS database, the spatial relationships in the of in drilling, leasing, leasing, etc. with with time and place place were were then then combined combined with geological changes in information from Miller et al. (2002) to better understand the past and present exploration exploration areas areas to assist in in defining new new areas in in which to to explore explore for for non-ferrous non-ferrous minerals. and to References References Miller, J. D., Jr., Green, J.C., Severson, Severson, M.J., Chandler, V.W., V.W., Hauck, Hauck, S.A., S.A., Peterson, Peterson, D.M., D.M., and and Wahl, T.E., T.E., 2002, Geology and mineral potential of of the Duluth Complex and related rocks rocks of of 207 p. northeastern Minnesota: Minnesota Geological Survey Report of Investigations 58, 58,207 23 �s-ale so Deposit/Area as as as as as as N1i •ChiIL,LSSdJOeSideLHGLOi •1u0b14/HGs SPRUCE RD INCO & t '0 0 0 CU 0 as as t as 50 as as !essk;L Ij_ Rod & Mstsse-i R Spiace - Ieoo MATURI CU as Leek - Spease Rood —1— —f-—I— Il—eorCoeekHII BABBITT (M in no ma x) o(E9e! III AMAX (Mesabo) USS DUNKA ROAD I oeeoo (NorthMel) PolyNeti I I -— Ceeeo WYMAN CREEK USSIITa .1.1 11111 Ii: DUNKA PIT ; Begs yi,—os—foeesotios dells og 11 ErIch WETLEGS <ii AMAX * Duval Duval — fl"II WATER HEN(OUI) • Bear B e a rCreek Creek i_- - SOFILSONCRECK WESTERN MARGIN II It • : Exxon Exxon heIst Dodge! I I I • t/Des o,-e/Aoeecoe Seed • Other O t h e r Companies Companies I —— — LOCCOOS BIRCH LAKE 11 II hee,icoo She d/N(COR LONCNOSE (Out) -ii INCO•. SCATTERED Reosceek.. BeoCeeek••I OR I - • Neeost RECONNAISSANCE Ducol DRILLING SCATTERED DRILLING I USS toXXp • •Ul — / Si * so OS 0 5 Beg, Cooed o sO Si so I o ! '0 so C - Stereos S Ctsfffft ! GUNFLINT TRAIL = CONCENTRATED DRILLING St SI-il 0 320koJg-WhItesIde JJjOekJoyfl as 0 fl I-os--s-so Si LEGEND LEGEND • INCO INCO uss uss 0 0 Si 0 0 '0 0 0 0 0 0' 0 Ot 5 as 2 Figure 1. History Historyof of Cu-Ni-PGE Cu-Ni-PGEexploration explorationin in the the Duluth DuluthComplex Complex (after (afterMiller Milleret etal., al., 2002). 2002). as 0 - as Si �Geochemistry and Mineralization of the Seagull Intrusion, Northern Ontario Heggie, G., P., P., (Depanment of Geology, Lakehead Heggie, G.,and andHollings, Hollings, (Department of Geology, LakeheadUniversity, University,955 955Oliver Oliver Road, Thunder Bay, On, P7B 5E1, gheggie@mail.lakeheadu.ca) gheggie@mail.lakeheadu.ca) Platinum Group Group Elements Elements (POE-Platinum, (PGE-Platinum, Palladium, Osmium Osmium and and Iridium) Indium) have have seen seen substantial increases in demand over the last 30 years, as industrial and and commercial commercial users users have increased their consumption. consumption. Canadian Canadian production of these metals has until until recently recently been limited to by-products from from nickel Sudbury). Opening Opening of of the the copper mines (e.g., Sudbury). lies mine in Ontario Ontario demonstrated demonstrated the the Lac des fles economic PGE deposits potential for economic deposits in in Canada. Further work on deposit deposit and and exploration models is essential essential to to identifying identifying new targets and prospective prospective host rocks. rocks. 4 Lake N(pfgono 1'> •z SeaguU I Quetico Subprovrnce I Lake Superhr • • bIeyGro The Seagull Lake intrusion is found found within the n's Osler Grp Nipigon Embayment, approximately 70km 1). north east east of Thunder ThunderBay, Bay,Ontario Ontario(Fig. (Fig.1). Relative age dating places the age of the intrusion to be younger Seagull Lake intrusion younger than than Figure 1. Map Map showing location of Seagull Intrusion Intrusion Figure the Sibley Group sedimentary sedimentary sequence, sequence, (1339±33 (1339±3Ma) (Franklin et et al., al., 1980), 1980), and regional regionalgeology. geology. as part of the intrusion has been seen to cross cut Sibley Sibley stratigraphy. stratigraphy.A A chilled chilledmargin margin has has been been Intrusion and and the the younger younger Nipigon Nipigon Sills defining defining an upper age of of observed between the Seagull Intrusion approximately 1.1 Ga (Davis (Davis and and Sutcliffe, Sutcliffe,1985). 1985).This This falls falls within within the the time time of of mid-continental mid-continental region. Volcanic Volcanic activity activity was was responsible responsible for for production production of of thick thick rifting in the Lake Superior region. al., 1989) beneath beneath and around the shores of Lake Superior and the basaltic sequences (Cannon et al., mafic to ultramafic complexes complexes (e.g., Duluth complex). emplacement of numerous mafic C The Seagull Intrusion Intrusion is is currently currently under under exploration exploration by by East East West West Resource Resource Corporation, It is a ultramafic intrusion intrusion consisting consisting of of cumulate cumulate olivine, olivine, and oxide minerals with pyroxene layered ultramafic oikocrysts and interstitial feldspar. feldspar. Lithological Lithological phases phases include include dunites, lherzolites, olivine gabbronorites, gabbros, and and pryoxenites. pryoxenites. A A distinctive distinctive olivine gabbronorite is found within the but this exhibits chilled margins and is thought to post date the formation of the rest of intrusion but intrusion. the intrusion. 25 �Ni (ppm) Interval (m) Cu (ppm) 1160 269 4.0 375.0 WMOO-01 1413 501 408.0 4.5 1565 12.0 779 572.0 987 6.0 1180 546.0 WM98-02 1647 112 379.0 8.0 WM98-05 1841 1843 569.0 6.0 1455 1220 6.0 579.0 Figure2.2.Table Tableofofmetal metalcontents contentsfrom fromassay assay(Caven, (Caven,It,R.,2000) 2000) Figure DDH Depth (m) Pt (ppb) 307 336 363 535 336 693 458 Pd (ppb) 383 418 438 566 393 847 537 Mineralization Mineralizationoccurs occursininthe theform formofofPGE PGEminerals mineralsassociated associatedwith withdisseminated disseminatedFeNi FeNisulfides sulfides (pentlandite).Pentlandite Pentlanditeisisfound foundininhigher higherabundances abundancesatatdiscrete discreteintervals intervalsthroughout throughoutthe the (pentlandite). intrusion,with witha ageneral generalincrease increasetowards towardsthe thebase baseofofthe theintrusion. intrusion. intrusion, Work Workisiscurrently currentlybeing beingundertaken undertakentotounderstand understandthe thestratigraphy stratigraphyofofthe theintrusion, intrusion,the thenature natureofof the theplatinum platinumgroup groupmineralization, mineralization,and andformational formationalcontrols controlsononthe themineralized mineralizedzones, zones,which whichare are present presentininthe theintrusion intrusionininorder ordertotoaid aidininthe thedevelopment developmentand andrefinement refinementofofexploration exploration techniques,and anddeposit depositmodels. models. techniques, Cannon, J.C., Cannon,W.F., W.F.,Green, Green,A.G., A.G.,Hutchinson, Hutchinson,D.R., D.R.,Lee, Lee,M., M..Milkereit, Milkereit,B., B.,Behrendt, Behrendt,J.C., J.C.,Halls, Halls,H.C., H.C.,Green, Green, J.C., Dickas, Dickas,A.B., A.B.,Morey, Morey,GB., G.B.,Sutcliffe, Sutcliffe,R., R.,and andSpencer, Spencer,C., C.,1989, 1989,The TheNorth NorthAmerican AmericanMidcontinent Midcontinentrift rift beneath beneathLake LakeSuperior Superiorfrom fromGLIMPCE GLIMPCESeismic SeismicReflection Reflectionprofiling. profiling.Tectonics, Tectonics,v.v.8,8,p.p.305-332. 305-332. Caven, R.J., R.J., 2000, 2000,Progress ProgressReport Reporton onthe theWolf WolfMountain Mountainand andDisraeli DisraeliProperties Propertiesfor forEast EastWest WestResource Resource Caven, Corporation, Ltd. Corporation,Canadian CanadianGolden GoldenDragon DragonResources ResourcesLtd. Ltd.and andAvalon AvalonVentures VenturesLtd. Davis, Davis, D.W., D.W., and and Sutcliffe, Sutcliffe, R.H., R.H., 1985, 1985, U-Pb U-Pb ages agesfrom fromthe theNipigon Nipigonplate plateand andNorthern NorthernLake LakeSuperior. Superior. GeologicalSociety SocietyofofAmerican AmericanBulletin, Bulletin,v.96, v.96,p.p.1572-1579. 1572-1579. Geological Franklin, Franklin,J.M, J.M.McJlwaine, Mcllwaine,WIT., W.H., Poulsen, Poulsen,K.H., K.H., and and Wanless, Wanless,R.K., R.K., 1980, 1980,Stratigraphy Stratigraphyand anddepositional depositionalsetting settingofof the theSibley SibleyGroup, Group,Thunder ThunderBay Baydistrict, district,Ontario, Ontario,Canada. Canada.Canadian CanadianJournal JournalofofEarth Earth Sciences, Sciences,v.17, v.17,p.p. 633-65 1. 633-651. 26 �PEPERITES OF PEPERITES OF THE THE GAFVERT GAFVERTLAKE LAKE VOLCANIC VOLCANIC COMPLEX, COMPLEX, ST. LOUIS MINNESOTA COUNTY, MINNESOTA Heiling, Carrie Came D., Department Geological Sciences, Sciences, University of Minnesota Minnesota Duluth, Duluth, Department of Geological 1114 Kirby Drive, Drive, Duluth, Duluth, MN, 55812; cheiling@d.umn.edu cheiling@d.umn.edu The Gafvert Lake area, located within the Upper Ely member of the Ely Greenstone Greenstone of forms part of of aa the Vermilion District in Northeastern Minnesota (Figure 1) (Card, 1990), forms Morton (personal (personal communication) communication)has has large, Archean, felsic volcanic complex. Morton late stage caldera interpreted the complex to be a composite volcano that underwent late collapse. This Thisstudy studyhas has focused focused on on aa two two square square mile area in the central part of the complex. Here Herethe the complex, complex,from from the the oldest oldest to to the the youngest rocks, is composed of a) coarse, heterolithic breccias (interpreted (interpreted to represent meso-and mega breccias) breccias) (Morton, (Morton, personal communication), b) more than 3000 feet of massive to bedded pumice-rich communication), and beds beds of of chert chert and and massive to lapilli tuff, c) dacitic lavas and domes, and d) lenses and pyrite (Figure 2). The The breccias breccias and and lapilli lapilli tuffs tuffs have have been been intruded intruded by by aa semi-massive pynte swarm of feldspar porphyry dacite dikes that represent feeders to the domes domes and/or andlor flows. flows. Peperites are rocks formed by the in situ disintegration of magma intruding and mixing unconsolidated sediment sediment or or ash ash (Skilling (Skillingetetal., al., 2002). 2002). At Gafvert Lake the with wet unconsolidated dikes intruded and peperites formed near the top of the complex where dacite porphyry dikes mixed with wet, unconsolidated pumice-rich pumice-rich lapilli lapilli tuff. tuff. This mixing led to quenching quenching of the the dacitic magma magma and disruption disruption and and vesiculation vesiculation of the lapilli and fragmentation of tuffs. The Thepeperites peperites occur occur within within 100 100 feet feet of dike contacts though they form much more extensive areas where where several several dikes dikes occur occur close close together. together. Angular and finger-like blocks of dike material occur within the peperite, peperite, locally locally these these are are connected connectedto toaanearby nearbydike. dike. Macrotextures in outcrop and microtextures in thin section helped identify and classify classify the following fragment types and internal structures within the peperites: a) blocky juvenile juvenile fragments fragments with chilled chilled rims rims and and occasional occasional jig-saw fit fit textures, textures, b) b) platy platyto to ragged ragged juvenile juvenile fragments fragments with curviplanar curviplanar surfaces surfaces and and broken gas gas bubbles, bubbles, c) c) ameboid ameboidto to juvenile fragments, fragments, d) abundant pumice which exhibits variable vesicularity. vesicularity. globular juvenile Most of this pumice is juvenile to the lapilli lapilli tuffs tuffs but a small small percentage percentage contains contains feldspar feldspar to those those found found in in the the dikes possibly indicating local, rapid vesiculation crystals identical to of dike material. Close Close to to dike dike margins margins feldspar feldspar crystals are broken and internally with fractures fracturesfilled filledby bylapilli lapillituff. tuft Pumice, fractured with Pumice, close close to to dike dike contacts, may be broken or disaggregated into into several several small small jigsaw-fit jigsaw-fitpieces. pieces. Locally the ash matrix to radiating away from from dike margins. the lapilli tuffs is amygdaloidal with amygdules radiating References References K.D., 1990, A A review review of of the the Superior Superior Province Province of of the the Canadian Canadian Shield, a product of Card, K.D., Archean accretion: Precambrian Precambrian Research, Research,v.v. 48, 48,pp. pp. 99-156. 99-156. Ely, Minnesota, 2003, Mapquest, www.mapquest.com. Mapquest, www.mapquest.com. Morton, R.L., communication, University of Minnesota-Duluth. R.L.,2003, personal communication, White, J., J., McPhie, McPhie, J., J., 2002, 2002, Peperite: Peperite: a review of magma-sediment mingling, Journal Skilling, I., White, of Volcanology Volcanology and Geothermal GeothermalResearch, Research,xc v. 114, 114,pp pp 1-17. 1-17. 27 �___ \ 01 crane Lake Agnes Lake St. Lóujc Buyck--. 0% - !L h__c1tQ/iF 6urrit'i'1 : - For. . it Trout Lake I RObIF1SOr'' Forestcenter0 lear island st,L120K -—22 .••' -- ,Babbitt — — ;Emlrarrass Erit :-°_V S Virgirii&.J_c.Auroja 11001 9 1 L4SAbCIIA — . r Murphy Cit HoYt Lakes IToirñi . .0Yihyte Fifllaç_fl — (Mapqucst, 2003). Location of Gafvert Lake complex 1: Location Figure Figure 1: complex (Mapquest, 2003). Exp I a n at io fl Explanation - -? ' Tuft II - • Peperite samples samples Fault Zone '" ''Contacts Contacts / \" /\/ Railroad ' R a i l r o a dgrade grade Mud Road 4, "Mud Creek Road / -Â¥ 7 ) - p '*__ -ç. \ .'f -,Qg __DE" I 'S-- ,' , "- " N UI Tuff Qac / /A/ . Diab " Zrtc c'_ Bx N ,. - - - -. I Mbas -- Metabasalt Metabasalt Q Qfp-QtzfeldPorphyry - Qtzfeld Porphyry Cht - Black Chert Cht Diab -- Diabase Diabase Dikes Dikes Dior -- Diorite Dior Diorite Dac -- Dacite Dac Dacite Dikes Dikes luff Tuft Tuff - Lapilli Lapilli Tuff Bx -- Breccia Breccia Bx -- Siltstone &&Iron IronFm Fm 81st SIst - - I 01p , Sisi It METERS Wa to O 0 of Gafvert Lake Lake volcanic complex. Figure 2: Generalized map of a portion of 28 28 �CHEMISTRY CHEMISTRY OF OF ALTERATION ALTERATION MINERAL MINERAL PHASES PHASES AT THE FIVE MILE MILE LAKE LAKE VOLCANIC-HOSTED MASSIVE SULFIDE PROSPECT, NE MINNESOTA VOLCANIC-HOSTED MINNESOTA Hocker, J., Odette, Odette, J.J. D., D.,and andNewkirk, Newkirk, T. T.T., T.,Department DepartmentofofGeology, Geology, Hocker, S. M., Hudak, Hudak, G. J., University of Wisconsin Blvd., Oshkosh, WI 54901, hudak@uwosh.edu Wisconsin Oshkosh, Oshkosh, 800 800 Algoma Blvd., Alteration mineral assemblage assemblage mapping mapping at at the Five Mile Lake Alteration mineral Lake Prospect Prospect in in the the Vermilion Vermilion District of northeastern Minnesota has identified two distinct types of alteration alteration zones zones within within 2.7 2.7 billion year-old billion year-old volcanic volcanic and and volcaniclastic volcaniclastic rocks rocks associated associated with withvolcanic-hosted volcanic-hosted massive massive sulfide (VHMS) (VHMS) mineralization mineralization (Hudak (Hudak etet al., al., in press; al., 2001a, 2001a, 2001b; 2001b; Peterson, Peterson, press; Odette et al., alterationzones zones are are composed composed of of various 2001). 2001). Regional Regional semi-conformable semi-conformable alteration various proportions of ± amphibole ± chlorite + epidote quartz epidote 5 amphibole 5 chlorite ± quartz + i plagioclase plagioclase feldspar. feldspar. These regional, semiconformable alteration alteration zones zones are locally cross-cut by several relatively narrow, northeastsemiconformable northeasttrending disconformable alteration alteration zones composed composed of fine-grained fine-grained chlorite and/or sericite that are closely associated with synvolcanic synvolcanic fault fault zones. zones. Electron microprobe microprobe analyses analyses of of the various Electron various alteration alteration mineral mineral phases phases (epidote (epidote group group minerals, chlorite, chlorite, amphibole, amphibole, white white mica, mica, and and feldspar) feldspar) have have been been conducted conducted in an effort minerals, effort to to associated with the better understand hydrothermal processes processes associated the development development of the the semiconformableand and disconformable disconformablealteration alterationzones zonesatat the the Five Five Mile Lake prospect. semiconformable prospect. These These that: a) epidote group minerals range in composition from zoisite/clinozoisite zoisite/clinozoisite to analyses indicate that: pistacite; pistacite; b) chlorite chlorite is dominantly dominantly ripidolite; ripidolite; c) amphibole amphibole is is primarily primarily actinolite actinolite and and ferroferroactinolite, with magnesio-homblende and ferro-hornblende ferro-hornblendealso alsopresent; present;d)d) sericite sericite is fineactinolite, with magnesia-hornblende and finegrained muscovite; and e) e) plagioclase plagioclase feldspar feldsparisisdominantly dominantlyalbite. albite. Alteration mineral chemistry chemistry at at the the Five Mile Lake Alteration mineral Lake Prospect Prospect is remarkably remarkably similar similar to to that that from the the Noranda Noranda VHMS VHMS mining mining camp camp of of Canada, Canada, as as well well as as other other VHMS VHMS mining mining camps around the world. world. This alteration mineral chemistry chemistry suggests the presence of of aa complex, complex,long-lived long-lived hydrothermal system that that evolved (hundreds of of meters) hydrothermal system evolved from seafloor-proximal seafloor-proximal (hundreds meters) to to deeper deeper subseafloor environments (-1-3 (—4-3kilometers) kilometers)asasthe the volcanic volcanic rocks rocks were buried subseafloor environments buried by by apparently apparently mafic to intermediate volcanism and associated sedimentation. This rapid, dominantly effusive mafic suggests that in addition to the Five Mile Mile Lake Lake Prospect, Prospect, the the uppermost uppermost several several hundred hundred meters meters of the Lower Member of the Ely Greenstone also has excellent exploration potential for VHMS mineral deposits. deposits. References References Galley, A,, A., Bailes, A., Hannington, M., Hollc, G., Katsube, 1, Paquette, S., Bailes, A., Hannington, M., Holk, G., Katsube, J., Paquette, F., F., Paradis, Paradis, S., Galley, Santaguida, F., Database for Santaguida, F., and Taylor, Taylor, B., 2002, Database for CAMIRO CAMIRO Project Project 94E07: 94E07: Interrelationships between subvolcanic subvolcanic intrusions, intrusions, large-scale large-scale alteration alteration zones, zones, and VMS Interrelationships between VMS of Canada Open File Report 4431 (CD-ROM). deposits: Geological Survey of Hudak, G. J., Heine, J., J., Newkirk, Newkirk, T., T., Odette, Odette, J., J., and Hauck, S., S., in press. press. Comparative Comparativegeology, geology, stratigraphy, and lithogeochemistry lithogeochemistryof of the the Five Five Mile Mile Lake, Lake, Quartz Hill, and Skeleton stratigraphy, and Skeleton Lake Lake Vermilion District, District,NE NE Minnesota: Minnesota: A report to the Minerals Coordinating VMS occurrences, Vermilion Coordinating Committee, DNR Minerals Division, State State of Minnesota. 29 �Kranidiotis, Kranidiotis,P. P.and andMacLean, MacLean,W. W.H., H.,1987, 1987,Systematics Systematicsofofchlorite chloritealteration alterationatatthe thePhelps PhelpsDodge Dodge Massive MassiveSulfide SulfideDeposit, Deposit,Matagami, Matagami,Quebec: Quebec:Economic EconomicGeology, Geology,v.v.82, 82,p.p.1898-1911. 1898-1911. Odette, Odette, J. D., D., Hudak, Hudak, G. G. J., J., Suszek, Suszek, T., T.,and andHauck, Hauck, S. S.A., A,,2001a, 2001a,Preliminary Preliminary evaluation evaluation of hydrothermal alteration alteration mineral mineral assemblages assemblages and and their their relationship relationship to to VMS-style VMS-style hydrothermal mineralization mineralization in the Five Mile Mile Lake Lake area areaof ofthe theArchean ArcheanVermilion VermilionGreenstone GreenstoneBelt, Belt, NE NE 47th Minnesota: Institute Institute on on Lake Lake Superior SuperiorGeology, Geology, 47thAnnual Annual Meeting, Meeting, Proceedings ProceedingsVolume Volume Minnesota: 47, Part Part 1-Program 1-Programand and Abstracts, Abstracts,p. p. 75-76. 75-76. 47, Odette, Odette, J. D., D., Hudak, Hudak, G. G. J., J., Suszek, Suszek,T., T.,and andHauck, Hauck,S.S.A., A.,2001b, 2001b,Preliminary Preliminaryevaluation evaluation of of hydrothermal alteration alteration mineral mineral assemblages assemblages and and their their relationship relationship to to VMS-style VMS-style hydrothermal Archean Vennilion Vermilion Greenstone Greenstone Belt, Belt, NE NE mineralization in the Five Mile Lake Lake area area of of the the Archean mineralization Minnesota: Minnesota: Geological Society Society of of America America Abstracts Abstracts and and Programs Programs Volume Volume 33, 33, No. No. 6, 6,p. p. AA420. 420. Peterson, Peterson, D. M., M., 2001, 2001, Development Development of of Archean Archean lode-gold lode-gold and and massive massive sulfide sulfidedeposit deposit exploration exploration models using geographic geographic information information system system applications: applications: targeting targeting mineral mineral exploration exploration in northeastern northeastern Minnesota from analysis analysis of of analog analogCanadian Canadianmining miningcamps: camps: unpublished unpublished Ph. Ph. D. D. dissertation, dissertation,University Universityof of Minnesota, Minnesota,Duluth, Duluth, Minnesota, Minnesota,503 503p.p. 18-cm 16 14 H —I P 1111111 0.0 O4'.B 0.2 0.8 0.0 PSEUOOThUNPNGOT CQRVNOOflILIT! -J "ffiff. 12 10 — C— •FM.CnICaC!*I AU. o'A•*TPff C ow—5—o'.w TALC .C1tGTh 00 \ TOk..S. 6- 'RI 10 20 0.D 30 1.0 tM. — 3.0 2.0 4.0 5.0 6.0 A WTIG ON EPIDOTE NA C0RUIUM 1.0 0.9 0,8 0.7 0.6 ft. :? 0.5 0.4 0.3 0.2 0.1 ThCCLASE 0.0 K&A 6.0 analyses for for epidote-group epidote-group minerals minerals (A), (A),chlorites chlorites Figure 1.1. Summary of electron microprobe analyses Figure (B), amphiboles (C), and white white micas (D) from the Five Mile Mile Lake Lake Prospect Prospect and andselected selectedVHMS VHMS mines. Compositional fields for Noranda minerals determined from Galley et al. (2002). (2002). 30 �GEOCHEMISTRYAND AND GEODYNAMIC GEODYNAMICIMPLICATIONS IMPLICATIONS THE 1537 1537 MA GEOCHEMISTRY OFOFTHE MA POINT ANOROGENIC REDSTONE POINT ANOROGENICGRANITE, GRANITE,ONTARIO, ONTARIO,CANADA CANADA Hollings, Fralick, P.P.and andKissin, Kissin,S.S.(Department (DepartmentofofGeology, Geology,Lakehead LakeheadUniversity, University, 955 955 Hollings, P., P., Fralick, Rd., Thunder Thunder Bay, Bay, Ontario, P7B 5E1, 5E1, Canada; Canada; Peter.HollinRs@lakeheadu.ca) Oliver Rd., Peter.Hollings@lakeheadu.ca) The The Redstone Redstone Point granite granite is is a Mesoproterozoic felsic igneous Mesoproterozoic felsic igneous complex (1537+101-2 Ma; Davis Davis and complex (1537+10/-2 Ma; Sutcliffe, 1984) located in the the northern northern portion of the Sibley Sibley Basin on the west shore of Lake 1). It It is is shore Lake Nipigon Nipigon (Fig. (Fig. 1). unconformably overlain overlain by by arenites of unconfonnably the Pass Lake Sibley Lake Formation Formation of of the the Sibley Group. These sediments are in turn Group. These sediments are turn intruded and overlain overlain by by an an extensively extensively developed sills developed Sequence sequence of diabase diabase sills related to an early related to early stage stage of of the the MidMidevent. The Continent Rifting event. The entire entire sequence has been gently folded into aa shallowly, easterly plunging plunging succession succession of open synclines and anticlines, open synclines and anticlines, with with Figure 1. Map Map showing Figure showing the the location location of the the Redstone Redstone Point Point dips not usually usually exceeding exceeding 15°. 15". Outcrop Outcrop granite in relation relation to Proterozoic granite Proterozoic anorogenic anorogenic granite granite complexes of ofNorth North America. America. Modified after after Anderson complexes Anderson (1983) (1983) density density of of igneous igneous units units is very very good good along the shoreline of Lake Nipigon, in contrast contrast to to sedimentary sedimentary sequences, sequences,which which only only provide provide small, scattered scattered outcrops. outcrops. The igneous rocks of Redstone Point have been briefly described by Davis and and Sutcliffe Sutcliffe (1985), (1985), wherein they emphasised that the rocks are wherein they emphasised that are anorogenic anorogenic granites granites gradational gradational to rhyolites rhyolites and and fragmental rhyolites and and dacites. In fact, fragmental rhyolites fact, presently presently accessible accessible outcrop outcrop indicates indicates that that extrusive extrusive members dominate the the magmatic magmatic rocks rocks of of the area. Porphyritic texture with members dominate with volcanic volcanic features features including vesicles, flow flow structures, agglomeratic units, units, rubbly rubbly flow flow tops including vesicles, structures, agglomeratic tops and and segregation segregation cylinders differentiate extrusive extrusiverocks rocks from from more more limited cylinders differentiate limited exposures exposures of of uniformly uniformly textured textured intrusive rocks. As As contacts between between units units are are generally unexposed unexposed and the base base of of the section is nowhere exposed, thicknesses thicknesses of of units units and and of the nowhere exposed, the entire entire succession succession are areunknown; unknown;however, however, continuous outcrop outcrop in in cliff-forming cliff-formingunits unitsindicates indicatesthat that aa minimum of lOOm continuous minimum thickness thickness of 100m of volcanic rock is present in in the the area. area. The igneous rocks are distinctively brick red, red, suggesting suggesting the the dominace dominace of of ferric ferric iron iron in the The igneous rocks distinctively brick the various mineral hosts but especially in trace amounts in feldspars. feldspars. The The intrusive intrusivemember memberdisplays displays equigranular phaneritictexture texturewith withmost mostmineral mineralgrains grains11 to to 5 mm in diameter. equigranular phaneritic diameter. The volcanic rocks are true porphyries with phaneritic phenocrysts of alkali feldspar, quartz and hornblende hornblende in an aphanitic matrix of of the the same minerals. minerals. Quartz Quartz phenocrysts phenocrystsare areeuhedral euhedraland and 11 to to 33 mm in aphanitic matrix diameter associated with alkali feldspar phenocrysts occasionally exhibiting exhibiting synneusis synneusis twinning twinning of microcline. Homblende and magnetite are less as well as as albite-pericline albite-pencline twins indicative indicative of microcline. Hornblende less 31 �_________________________________________________ abundant and finer grained than in the intrusive rocks. Near flow tops the porphyries grade into textured aphanitic uniformly textured aphanitic rhyolites with sparse phenocrysts. The samples samples from the the Redstone Redstone Point Point intrusive intrusive complex complex are all all characterised characterised by high high Si02 SiO, contents (73-83 (73-83 wt%) wt%) and and elevated elevatedK,0 1(20and andNN;0 contents q 0 abundances abundances (2-7 (2-7 wt% wt% and and 0.2-3.5 0.2-3.5 wt% wt% respectively). respectively). They They are are typically typically LREE relatively LREE enriched enriched with with relatively unfractionated HREE HREE (La/Sm, (La/Smn = = unfractionated 2.8-5.1; Gd/Yb,, GdIYb == 1.1-1.6; 1.1-1.6; Fig. 2) characterised by elevated elevated and are characterised and Nb Nb contents. contents. Samples Samples Zr, Y and from the Redstone Redstone Point Point igneous igneous 02.13 complex fulfil fulfil the detailed complex detailed trace trace 02-H element criteria of of Whelan element criteria Whelan et al. al. y (1987) (1987) for anorogenic anorogenic granites. granites. o . I 1 . . . . Rb Tli Rb Ra BaTh Pr S SrNd U HISmEu, fl GdThOy Er YbLu U NbLa Nb La Cc Cc Fr t hid Zr Hf Sin Eu ll Gd 7% D! Tile Y ifc Er Yb Lu Al A1 U V V Sc SP Figure Representative primitive mantle normalised diagram diagram for Figure 2. Representative for samples from from the the Redstone RedstonePoint Pointigneous igneous complex Similarities Similarities between between Proterozoic Proterozoic basin sequences basin sequences (e.g., (e.g., Athabaska, Athabaska, Thelon, Hornby Bay and Sibley basin fill sequences) imply that basin genesis and developmental developmental controls were similar. The setting, setting, architecture, depositional systems and deformational deforrnational histories of all four basins strongly infer that they are intracratonic, forming as a result of heating cratonic lithosphere. The heating event is represented represented in in northern northern Canada by by numerous 1790 to 1730 Ma anorogenic, syenogranite batholiths and and comagmatic ash-flow tuffs occurring syenogranite batholiths occurring west of of Hudson Hudson Bay. In the western Great Lakes region a heating event produced the 1537 Ma Redstone western Great the 1537 Ma Redstone Point Point assemblage and and other 1500 records a assemblage 1500 Ma Ma anorogenic anorogenic batholiths. The southern southern mid-continent mid-continent records lithospheric heating event with anorogenic granite production production from from approximately approximately 1480 1480to to 1320 1320 Ma (Fig. 1). 1). These These events events outline outline aa progressive progressive southward southward displacement displacement of lithospheric heating from a maximum age of approximately 1750 ma in northern Canada to aa minimum minimum age age of of 1310 1310 Ma in the As heat transfer Ma the southwestern southwestern United United States. States. As transfer from from the the asthenosphere asthenosphere is the the only only heating, drift of North America over hotter than mechanism for producing extensive lithospheric heating, regional ages of of heating, drift rates of approximately 1.1 average asthenosphere is implied. Using regional 1.1 cm/year are necessary, and agree in magnitude with present to 1.4 cmlyear present rates. rates. REFERENCES Anderson, J., J., 1983. Proterozoic anorogenic anorogenic granite granite plutonism plutonism of of North North America. In: Medaris et Anderson, al., (Eds), Proterozoic Proterozoic geology. Geological Society Society of America America Memoir Memoir 161, 161,133-154. 133-154. Davis, D., D., and Davis, and Sutcliffe, Sutcliffe, R., R., 1985. 1985. U-Pb ages ages from from the the Nipigon Nipigon Plate Plate and and Northern Northern Lake Lake Superior. Bulletin, 96, Superior. Geological Geological Society of America Bulletin, 96, 1572-1579. 1572-1579. Whelan, J., Currie, Currie, K., K., and andChappeli, Chappell, B., B.,1987. 1987.A-type A-typegranites: granites:geochemical geochemicalcharacteristics, characteristics, discrimination Contributions to 407-419. discrimination and petrogenesis. Contributions to Mineralogy Mineralogy and and Petrology, Petrology, 95, 95,407-419. 32 �PALEOPROTEROZOIC (1900-1600 Ma) TECTONIC HISTORY OF LATE PALEOPROTEROZOIC OF THE THE NORTHERN NORTHERN FOR CRUSTAL STABILIZATION STABIUZATION MID-CONTINENT, U.S.A: IMPLICATIONS FOR HOLM, D.K., Dept. of Geology, Geology, Kent Kent State StateUniversity, University, Kent, Kent, OH OH44242; 44242;VAN VANSCHMIUS, SCHMUS, MacNEILL, L.C., Dept. of Geology, University of of Kansas, Lawrence, KS 66045; W.R., and MacNELL, Minnesota Geological BOERBOOM, T.J., Minnesota Geological Survey, 2642 University Avenue, St. St. Paul, Paul, MN MN SCHWEiTZER, D., Dept. of Geology, 55114; SCHWEITZER, Geology, Kent State State University, University, Kent, OH OH 44242; 44242; SCHNEIDER, D.A., Dept. of Geological Geological Sciences, University, Athens, SCHNEJDER, Sciences, Ohio University, Athens, OH OH 45701 45701 We propose that the the late late Paleoproterozoic Paleoproterozoic igneous and and deformational deformational history history preserved preserved in in the the southern Lake Lake Superior region is the southern Superior region the result resultofofnorthwest-directed northwest-directed convergence convergence during during and and New U-Pb zircon ages indicate indicate that that late to post-Penokean following geon 18 Penokean accretion. New magmatism began ca. 1800 1800 Ma and and generally generally migrated migrated southeastward southeastward across across the thenewly newlyaccreted accreted terrane. Magmatic Magmaticpulses pulses atatca. ca.1800, 1800,1775, 1775,and and1750 1750Ma Mamay maycorrelate correlatewith withnorthwest-directed northwest-directed growth of of the North North American mid-continent. We suggest subduction associated with southward growth suggest that geon 17 Yavapai-age slab rollback caused continental arc magmatism to step step southeastward southeastward between 1800 and 1750 Ma (Fig. (Fig. 1A). As As the the slab slab steepened, steepened, the reduced compressional compressional stresses thermal input allowed for collapse of the overthickened and increased thermal overthickened portions of of the thePenokean Penokean In northern collapse involved involved the the formation formation of of gneiss crust. cmst. In northern Wisconsin, Wisconsin, collapse gneiss domes domes and and their their exhumation panels brought brought up up from depth via exhumation within discrete fault-bounded panels via tectonic tectonic extrusion extmsion (Schneider (Schneider et al., al., ILSG, ILSG, 2003). 2003). Collapse of the thePenokean Penokeanorogen orogen—- and possibly temporary temporary cessation of crustal stabilization and deposition of Baraboo Interval cessation of slab slabsubduction subduction—- resulted in cmstal quartzites between between 1750 and 1650 in aa long-lived quartzites 1650 Ma. Ma. However, However, in long-lived orogen orogen model, model,renewed renewed tectonism to the the south south resulted resulted in in the the eventual accretionofof aa Mazatzal Mazatzal arc arc (Fig. tectonism to eventual accretion (Fig. IB) 1B) with with widespread deformation deformationand andmild mild reheating reheatingof of Penokean Penokean crust crust to to the north. The age of of this this widespread Ar/Ar step-heating studies on basement rock deformation is inferred from conventional ArIAr rock beneath beneath undeformed Baraboo BarabooInterval Intervalquartzites. quartzites. The 1900 to 1600 deformed and undeformed 1600 Ma tectonic history of the north-central United States, States, not not surprisingly, records the the southward growth and the north-central United surprisingly, records and tectonic tectonic development of the southern Laurentian margin. New and published 40Arf39Ar mineral agesdelineate delineatethe thenorthern northern and and western western extent of geon New 4 0 ~ r / 3 9mineral ~r ages geon crustal deformation. deformation. Interestingly, 16 crustal Interestingly, only lower-grade crust intruded by the the shallower-level shallower-level ca. 1750 Ma Ma plutons (and associated associated rhyolites) rhyolites) were weredeformed deformedsignificantly significantlyduring duringgeon geon 16. 16. Deeper level collapsed crust and crust pervasively invaded by the older magmatic pulses are level collapsed cmst and cmst pervasively invaded by magmatic pulses arelargely largely unaffected by Mazatzal deformation deformation and and reheating. reheating. We suggest suggest that post-orogenic post-orogenic intrusions intrusions and and crustal thinning was an important step in strengthening strengthening and stabilizing the the crust crust in inthe thesouthern southern Lake Superior Superior region. region. O'Boyle, Hamilton, and Jercinovic, 2003, 2003, Paleoproterozoic Paleoproterozoic development of of a Schneider, Holm, O'Boyle, gneiss dome corridor corridor in in the the southern southern Lake LakeSuperior Superiorregion, region,USA: USA: Institute on Lake Superior Geology Abstracts (this (this volume). volume). 33 �avapai subduction (ca. 1750 Ma) w -southward propagation of magmatism from 1775 Ma ECMB to 1750 Ma granites and rhyolites in Wl Mazatzal orogeny (1650-1630 Ma) deformation of during ost-Penokean" quartzites 8azatzal accretion " age Figure 11:: A) A) Subduction Subduction rollback model model proposed to explain magmatic magmatic age progression the Penokean convergence, preprogressionacross across the Penokean orogen, orogen, ca.Yavapai convergence, accretion. Mazatzal ECMB East-centralMinnesota Minnesota batholith. batholith. B) Mazatzal ECMB ==East-central B) Mazatzal Mazatzal accretion model (modified aL,2000) to to explain explain deformation deformation accretion model (modifiedafter after Romano Romano et al.,2000) of Baraboo Interval Interval quartzites quartzites and and southward southward growth growth of of Laurentia. Laurentia. 34 �GABBRO/GRANOPHYRE OF THE THE CROCODILE CROCODILELAKE LAKEINTRUSION: INTRUSION: A GABBROIGRANOPHYRERELATIONS OF POSSIBLE VENT FOR THE HOVLAND LAVAS? (e.jerde@morehead-st.edu), Department of Physical Sciences, Morehead State JERDE, Eric A. (e.jerde@morehead-st.edu). State University, Morehead, KY 40351 40351 One of the notable notable characteristics characteristics of the Midcontinent Midcontinent Rift Rift is the presence of large large amounts amounts of of felsic felsicmaterial. material. Indeed, the nature and origins of this abundant abundant silicious silicious material material has been the source source of numerous numerous studies studies(e.g., (e.g., Nelson, 1991; Green and and Fitz, Fitz, 1993; 1993; Vervoort Vervoort and andGreen, Green, 1997; 1997;Kennedy Kennedyeteta!., 2000;Sandland Sandlandetetal., al.,2001). 2001). To the Nelson. al., 2000, Series is a pronounced ridge south of the Early Gabbro Series ridge composed composed of of this this felsic felsic material, material, properly properlytermed termedaa Series layers are granophyre. The Early Gabbro Series are inc!ined inclined to the south, south, thus are below the granophyre granophyre stratigraphically. This This felsic felsic rock rock was was noted and and described described by Nathan (1969) (1969) as a very late-stage material, and has presumed to to have have formed formed significantly significantlyafter afterthe the gabbros gabbrosin inthe theregion. region. However, several severa! generally been presumed observations !ater than than the the granophyres. granophyres. These observationsindicate indicate that the gabbro was emplaced later These include include gradational gradational contacts, contacts, with some chilling of the gabbro. Another described as Another observation observation is is the the abundance abundance of material described as "intermediate "intermediate rock" by various investigators aL, 1959). This This materia! material is always found between the investigators in the past (e.g., Grout et al., gabbro gabbro and granophyre, granophyre,and is is presumably presumably the the result of of assimilation assimilationof of granophyre granophyreby by an an intruding, intruding,hot hotgabbro. gabbro. Investigations Investigations into into possible origins of the the granophyres granophyres(Sandland (Sandlandet et al., al., 2001; 2001; Karl Karl Wirth, Wirth,pers. pers.comm.) comm.) included included radiometric radiometric age age determinations, determinations, and and revealed revealed that that the the granophyres granophyresadjacent adjacentto to the theEarly EarlyCiabbro Gabbro Series Seriesare, are, like the gabbros, Ga),and andessentially essentiallycontemporaneous. contemporaneous. Because gabbros, among among the earliest earliest rocks of the the rift rift (—1107 (-1 107 Ga), Because silicious silicious materia! material generally is a late-stage product of magma evolution, evolution, the surprising antiquity of the the granophyres granophyres adds to questions thheir origin. questionssurrounding their The early age for the grar granophyres however, suggest suggest an an origin origin fifor the layered layered nature nature of of the the Early Early Gabbro Gabbro 3r the 1013hyres does, however, Series stratigraphically. Senes located below them stri :ti;graphically. Due granophyric material would have created created aa Due to to their their low low density, density, the granophyric . that .. . reiaraea . ~ ~ > - > . . . - -. ~ ~.~material . . coming ~~. up "from below. barrier retarded the buoyant. gamroic gabbroic up rrom below. These harrier mat me rise of buuyani These rising rising !iquids liquids would would have have beeni forced to spread !aterally, resulting in the the ;aP apparent layering that isis obserl observed, andproviding providing aa cap, cap, blocking blocking any any laterally, resultingin bee] red, and parent layeringthat further ler rise of gabbroic gabbroic material. material. furti east of of the the layered layered Earl: EarlyY (Gabbro Series of of Nathan Nathan (19 (1969) is another another occurrence occurrence of Immediately to the east 69) is Jabbro Series ~ . ~ ~ > & - L . c. . . , (i.e., . —1107 < granophyre, also determined Ga;Karl Kar!Wirth, Wirth,pers. pers. comm.). comm.). This 01 an early early origin origin n.e., -1 I U I Ga; This granopnyre, aeiermmea to be ne among among those mose of termed the the Crocodile Crocodile Lake Lake Intrusion by by Miller Miller et et al. al. (2001). (2001), and and the rocks are interpreted to be rock group has been termed geophysica! evidence, evidence, and and aa few few sample sample examinations examinations(Babcock, (Babcock, 1959). 1959). Work gabbroic based on geophysical Work done done between between 1913 edges of of this this intrusion, intrusion, and and indicates indicates that that they they are are basalt basalt lavas lavas and gabbroic 1913 and 1948 1948 included the very edges intrusions, along with "red "red rock" (Grout et al., 1959) 1959) that is now known to refer to granophyre. (1969), there is a body of gabbroic material stratigraphically stratigraphica!ly below below the Like the series mapped by Nathan (1969). granophyre. granophyre. During the past year, a reconnaissance reconnaissance was was made made into into the the Crocodile Crocodile Lake Lake Intrusion Intrusion to to examine examine some of the rock rock re!ations (Fig. 1). Traverses by forest forest blowdown, blowdown,but butthe theoutcrops outcropsare arenumerous. numerous. Several relations Traverses were greatly hampered by gabbro units are present, as well we!l as as aa band band of of "intermediate "intermediate material" materiaP' at at the the very very top top of of the the gabbro, below the granophyre. Within Withinthe thegranophyre granophyreitself, itself, several several bodies bodies of of gabbro gabbrowere were found found to to have have actually actuallyintruded intrudedthe the granophyre. In Inthe thecoarse-grained coarse-grainedinteriors interiors of of these these bodies, bodies,the thegabbro gabbroisisindistinguishable indistinguishablefrom fromthe thegabbros gabbros (i.e., below the granophyre granophyre stratigraphically). stratigraphically). observed further further north (i.e., south of of the the granophyre granophyre are are prominent prominent knobs knobs and and ridges ridges that that are are composed composed of basalt. These Immediately to the south These part of the Hovland Lavas, which are are reversely reversely polarized, polarized, and were extruded extruded during the earliest earliest are mapped as pan discontinuous bodies (and other stringers stringers and local dikes) period of the the rifting. rifting. It is perhaps possible that the discontinuous dikes) within within feeder conduits for the eruptive eruptive basalts basa!ts immediately immediately to to the the south south (shown (shown schematically schematically the granophyre represent the feeder are basaltic basaltic stringers stringers and and small small dikes. dikes. Surrounding in Fig. 2). In In several several other other places within the granophyre, there are Surrounding !arger gabbroic bodies bodiesare areobvious obviousreaction reactionzones zoneswhere wheregranophyre granophyrehas hasbeen beenassimilated assimilatedinto intothe thegabbro. gabbro. In In the larger to the the south, south,numerous numerous inclusions inclusions are arepresent present that that are are pinkish pinkish in in color, color. along with with one of the flows immediately to felsic stringers stringers and irregular masses of felsic felsic material. to assess assess the the relation relation between between the the gabbros gabbros within within the the granophyre granophyre and the lavas to the Further work is planned to south. IfIf this thisisisindeed indeed aa feeder feeder system, system, itit might provide provide insight insight into into the the mechanism mechanism of magma magma emplacement emplacement and and the the eventual "breakthrough" "breakthrough" to the surface, during during the the onset onset of of rifling. rifting. h he earl^ ~ .~~~ . ~ . ~ ~ ~ . ~ . ~. ~~~ ~ ~ ~~ ~~ . . ~ .~ ~ ~ . 35 P-. �ReferencesCited: Cited: References (1959)MS. M.S.thesis, thesis.University UniversityofofWisconsin, Wisconsin.Madison, Madison,4747p.p. Babcock,R.C., R.C..Jr. Jr.(1959) Babcock, Geothermal Research, Journal of Volcanological and Green. J.C. and Fitz. T.J., 1993. Journal of Volcanological and Geothermal Research,54, 54,177-196. 177.196. Green, J.C. and Fitz, T.J., 1993, Bulletin 39, 163p. G.M. 1959 Minnesota Geologica Survey Grout, F.F., Sharp, R.P., and Schwm, G.M. 1959 Minnesota Geologica Survey Bulletin 39, 163p. Grout, F.F., Sharp, R.P., and Schwartz, Union Jerde,BA. E.A.and andKennedy, Kennedy.B.C., B.C.,2000, 2000.American AmericanGeophysical Geophysical Union2000 2000Fall FallMeeting, Meeting,San SanFrancisco. Francisco. Jerde, and Wirth, KR. 2001, ILSG 47, 36-37. Jerde, E.A., Salvato. D.J. Thole. J., and Wirth, K.R. 2001. ILSG 47.36-37. Jerde, BA., Salvato, D.J, Thole, S., 29-30. Kennedy,B.C., B.C.,Wirth, Wirth,K.R., K.R.,and andVervoort, Vervoort,J.D., J.D.,2000, 2000,ILSG ILSG46, 46.29-30. Kennedy, M.J., Chandler, V.W., and Miller,J.D., J.D..Jr., Jr.,Green, Green,J.C., J.C.,Severson, Severson, M.J., Chandler, V.W., andPeterson, Peterson,D.M., D.M.,2001, 2001,Minnesota MinnesotaGeological Geological Miller, M119. SurveyMiscellaneous MiscellaneousMap MapSeries Series M-119. Survey 198p. University Nathan.HI)., H.D..1969, 1969. Ph.D.dissertation, dissertation. UniversityofofMinnesota, Minnesota.Minneapolis, Minneapolis, 198p. Nathan, Ph.D. University of Minnesota. Duluth. Nelson. N. 1991. M S . Thesis. University of Minnesota. Duluth. Nelson, N. 1991, MS. Thesis, K.S. 2001, LSG 47, 85-86. Gehrels, G.E., Kennedy, B.C., Sandland,TO., T.O.,Wirth, Wirth,KR., K.R.,Vervoort, Vervoort,J.D., J.D., Gehiels, G.E., Kennedy, B.C.,and andHarpp, H q p , K.S. 2001, ILSG 47,8546. Sandland, Vervoort,3D. J.D.and andGreen, Green.J.C., J.C.,1997, 1997.Canadian CanadianJournal JournalofofEarth EarthSciences, Sciences,34,521-535. 34.521-535. Vervoort, Lake, showing location of Fig.i.1. Reconnaissancegeologic geologicmap mapofofthe theregion regionjust justsouth southofofCrocodile Crocodile Lake, showing location of Fig. Reconnaissance Lake Intrusion gabbros sabhrobodies bodiesininthe thegranophyre granophyre thatforms formsthe thecap capabove abovethe theCrocodile Crocodile Lake Intrusion gabbros gabbro that andintermediate intermediaterocks. rocks. and '4 possible feeder for the Hoviand Lavas. Schematic N-Scross crosssection sectionofofFig. Fig.1 1showing showingthe the possible feeder for the Hovland Lavas. Fig.2.2.Schematic Fig. N-S 36 �East West Resource ResourceCorporation Corporation(EWR) (EWR) has has undertaken undertakenaa detailed detailedexploration explorationprogram program in the vicinity of Norton Lake, including an extensive drilling program. Detailed Detailed examination examination of of being paid paid to to the the mineralized mineralized 'main' zone drill core has been undertaken with special attention being zone to to determine the exact nature of the mineralization. Preliminary Preliminaryresults results indicate indicate the the deposit denosit consists consists of massive pyrrhotite with pentlandite, magnetite, chalcopyrite and pyrite. pyrite. The The platinum group element's element's (PGE's) (PGE's)are arefound foundforming formingdiscrete discreteplatinum platinumgroup groupminerals mineralsand andare arealso alsobelieved believedto to form a solid solution with the sulphides. sulphides. Results ~ e s u i tshow sshowthat that in inaddition additionto toprimary primarymineralization mineralization a secondary, hydrothermal, enrichment enrichment of PGE's PGE's has has taken takenplace. place. Mineral Mineral Pyrrhotite Pyrrhotite Pentlandite Pentlandite Pyrite Chalcopyrite Chalcopyrite Manganoan fllmenite Illmenite 1 Magnetite Michenerite Hessite Hessite Formula Fe,.$ Fei.S (Fe,Ni)9S8 (Fe,NihSs FeS2 CuFeS2 CuFeSi (Fe,Mn)Ti03 (Fe,Mn)Ti03 Fe304 1 Fe304 1 PdBiTe Ag2Te 1 Ag2Te Elements Minor Elements Ni Co Co Co Co Ni Notes Notes Main mineral mineral Secondary Secondary Trace Trace, also also veins More common common than magnetite, magnetite, easily mistaken for magnetite in polished section section 1 Sb, Pt Table 1: Table 1:Summary Summaryof of the mineralogy mineralogy of Norton Lake Lake deposit. deposit. Corfu F. and Stott G.M. 1996. 1996. Hf isotopic composition and age constraints constraints on on the evolution evolution of of the Archean Central Uchi Subprovince, Ontario, Canada. Precambrian Research, v. 78, p 53-63 East West Resources Resources Corporation, Corporation, 2001. 2001. Annual Annual Report. Report. PGM Ventures, Ventures, 2003. 2003. www.pgm-ventures.com Stott 0. G.M. M.and andCorfu Corfu F. F. 1991, 1991,Uchi Uchi Subprovince, Subprovince, in Geology of Ontario, Ontario, Ontario Geological Survey Survey Special Special Volume Volume 4, 4, Part Part1.1. 38 �STRATIFORM STRATIFORM Pd-Pt-Au Pd-Pt-AUMINERALIZATION MINERALIZATION IN IN THE THE SONJU SONJU LAKE LAKE INTRUSION, INTRUSION, LAKE COUNTY, MINNESOTA JOSLIN, 1114 Kirby JOSLIN,Gregory GregoryD. D.Department Departmentof ofGeological Geological Sciences, Sciences, University of Minnesota-Duluth, 11 14 Kirby Drive, MILLER, James D., Jr., Drive, Duluth, Duluth, MN MN 55812, 55812,email: email:ioslOOl3@d.umn.edu; josl0013@d.urnn.edu;MILLER, Jr., Minnesota Minnesota do NRRI, 5013 Miller Trunk TrunkHwy, Hwy,Duluth, Duluth,MN MN 5581 55811; and ROWELL, ROWELL, Geological Survey, c/o 1; and 6th William, St., Minneapolis, MN 55402. 55402. William, F., Franconia Minerals MineralsCorp., Corp.,12 12S. S. 6 St., The Sonju Lake intrusion intrusion (SLI) is a 1200 1200 m thick, closed-system, well-differentiated, tholeiitic, layered intrusion located within the Mesoproterozoic Midcontinent Rift-related Beaver Bay Complex of northeastern Minnesota (Miller and and Chandler, Chandler, 1997). 1997). In the late 1990's, 1990's. outcrop outcrop sampling by Miller (1999) indicated indicated the presence of meter-scale stratiform Pd-Pt-Au mineralized POE reef) within the oxide gabbro interval (or PGE gabbro unit of the SLI, located about 2/3 of the way up intrusion. In from the basal contact of the intrusion. In June of 2002 Franconia Minerals Corp. conducted exploratory drilling exploratory drilling through through the the Pd-Pt-Au Pd-Pt-An enriched enriched zone. zone. In hand sample, the mineralized interval appears as a homogeneous oxide gabbro, with no enrichment. However, geochemically the location of the visible indication of precious metals enrichment. mineralization is distinct. Three Three drill drill cores, cores, spanning spanning aa strike strike length of approximately 800 m, define define and are are correlated correlated on the the basis basis of of aa distinctive distinctive Cu-Au Cu-Au break datum (Fig. 1). 1). With the exception exception of localized Pt enrichment enrichment associated with an interval interval enriched in olivine olivine about about 110 110m m below the Cu-Au horizon, all Pd-Pt-Au enrichment occurs over an interval of 0 to 90 m below the defined datum (Fig. 2). In In general general precious precious metals metals peaks are stratigraphically stratigraphically offset from one another, progressing upward upward in in the the succession successionPd->Pt->Au. Pd-*Pt-)Au. Maximum Maximumgrades gradesin in 0.3m 0.3m long long core core samples are 410 ppb Pd, 275 ppb Pt, and 1080 ppb ppb Au. Au. Above the Cu-Au break, all precious metals are very strongly depleted. Strong Strong correlation correlation between Fe. Fe, Al A1 and modal olivine with precious metals peaks indicates indicates a possible possible connection connection between subtle subtle modal layering layering of of plagioclase, plagioclase, oxide, oxide, and and olivine olivine with withmineralization. mineralization. The oxide oxide gabbro-hosted POE PGE reef in the Sonju Sonju Lake intrusion intrusion shows shows marked similarities, similarities, with some differences, Skaergaard intrusion intrusion of of East East differences, to stratiform stratiform POE PGE mineralization in the Skaergaard Greenland (Andersen et al., 1998), 1998). the Rincon del Tigre Complex of Bolivia (Prendergast, (Prendergast, 2000), 2000). intrusions throughout throughoutthe the world. world. Whole rock and many other tholeiitic mafic layered intrusions geochemistry, clinopyroxene clinopyroxene and olivine compositions, compositions, and petrographic data are are consistent consistent with with an orthomagmatic origin for the mineralization related to the fractional fractional segregation segregation of of sulfide sulfide magma. The melt from silicate magma. The homogeneity homogeneity of the host rock, the thickness of the mineralized interval, and the offset of metal concentrations concentrations imply that sulfide sulfide saturation saturation was was passively passively thggered by fractional crystallization of the Sonju magma. Mungall (2002) recently triggered Mungall(2002) recently argued argued that that stratigraphic POE reefs can be satisfactorily stratigraphic offsets of Pd, Pt, Au and Cu peaks common to many PGE satisfactorily model of of sulfide liquation liquation and and settling. settling. The model shows explained by a kinetic model shows that that the the degree degree will be be controlled controlled by by kinetic kinetic factors, factors, such such as as the the diffusivity diffusivity of of of offset and metal enrichment will of sulfide supersaturation, sulfide sulfide droplet droplet size, and its its settling chalcophile elements, the degree of result in in variability of of the apparent apparent silicate/sulfide silicate/sulfide melt melt ratio ratio (R (R factor). factor). The velocity, which result The correlation correlation of multiple multiple peaks peaks of POE PGE with with subtle, subtle, broad broad modal modal variations variations may may be be related related to to repeated convective overturn caused by the crystallization of of magnetite magnetite in in an environment environment of of sulfide over-saturation, over-saturation, as suggested by Prendergast (2000) (2000) to explain a similar similar correlation correlation in in the the Rincon del Tigre Complex. Some Some evidence evidence of late-stage sulfide dissolution and remobilization remobilization exists, but it appears to have little to no effect effect upon upon the the distribution distribution of of precious precious metals. metals. 39 �SLO2-3 SLO2-2 5L02-1 mno,3 ibo,e Co'Aob,,ak rlTrm,T +70.0 — +70.0 +80.0 — +600 —+000 4105 — +40.0 +300 — +35.0 +10.0 — +20.0 .300,0 +30,0 — lddk!4- Fig. Fig.1:1:Correlation Correlationofofdrill drill cores 1, 5L02-2, coresSLO2SL02-1, SL02-2,and and SLO2-3 SL02-3showing showingdistinctive distinctive 00 1=11— .10.0 — ''0.0 -10.0 — '20.0 — 30,0 WWIII— — .40.3 -40.0 Cu-Au Cu-Aubreak. break.The TheCu-Au Cu-Au break breakisisused usedtotoprovide provideaa datum datumtotowhich whichall all stratigraphic stratigraphicplots plotsare are correlated, correlated,and andposition positioninin stratigraphy stratigraphyisismeasured measuredasas meters metersabove aboveororbelow belowCu-Au Cu-Au break. break. '50.0 -10,0 — '00.0 11214- — '70.0 -700 — '00+ 11414- Will- — '90,0 ._,I000 —-lion -100.0 112111— -110.0 —'120.0 -l 00.0 — -000,0 [It'i—' Cu'Au break 8 • Au(ppb) Cu ppm) mete's above Cu-Au break 5L02-3 SLO2-2 SL02-1 — +700 — +700 — +700 t00.0 — +600 — -+600 +50,0 —*500 —+50,0 +400 — 5400 — +400 300 — +30.0 — +30.0 200 — +20.0 — 420.0 — +100 — +10.0 +10.0 — -10.0 — -100 — -20,0 — - 00i 20,0 — -500 — -30,0 — 420 — '400 — .000 — -50.0 '600 — -00.0 -700 — -700 — .70.2 000 — .800 — -00.0 — 900 — -00.0 — -00.0 1000 __..,1000 —100.0 7100 —110.0 —-110.0 —-1200 —010.0 —'120.0 300 — '132.5 — -130.0 —00 -400 888 Fig. Fig.2: 2:Correlation Correlationof of Pd Pd and Pt in drill holes SLO2and Pt in drill holes SL021,1,SLO2-2, SL02-2,and andSLO2-3. SL02-3. Notice Noticemultiplicity multiplicityof of spikes spikesand andoffset offsetbetween between Pt Ptand andPd Pdpeaks. peaks. I 2 § § U Pd)ppb) W Po(ppb) References: References: Andersen, Rasmussen, Andersen. J.J. C. C. 0., O., Rasmussen,H., H.,Nielsen, Nielsen,T. T. F. F.D., D., Ronsbo, Ronsbo,J.J. G., G., 1998, 1998,The The Triple TripleGroup Groupand andthe the Platinova PlatinovaGold Goldand andPalladium PalladiumReefs Reefsininthe theSkaergaard SkaergaardIntrusion: Intrusion:Stratigraphic Stratigraphicand andPetrographic Petrographic Relations. 488-509. Relations.Economic EconomicGeology. Geology.Vol. Vol.93, 93,pp. pp.488-509. Miller, Miller,J.J. D. D. Jr., Jr.,1999, 1999,Geochemical GeochemicalEvaluation Evaluationof ofPlatinum PlatinumGroup GroupElement Element(PGE) (PGE)Mineralization Mineralizationininthe the Sonju 44,31 3 1p. p. SonjuLake Lake Intrusion, Intrusion, Finland, Finland,Minnesota: Minnesota: Minnesota Minnesota Geological Geological Surv. SUN.Information InformationCircular Circular44, of the Beaver Miller, J. D., Jr., and Chandler, V. W., 1997, Geology, petrology, and tectonic significance Miller, J. D.. Jr., and Chandler, V. W.. 1997, Geology, petrology. and tectonic significance of the Beaver Bay Bay Complex, Complex,northeastern northeasternMinnesota, Minnesota,inin Ojakangas, Ojakangas,R. R.W., W., Dickas, Dickas,A. A.B., B., Green, Green,J.J.C., C.,eds., eds.,Middle Middle Proterozoic Proterozoicto toCambrian CambrianRifting, Rifting, Central CentralNorth North America: America:Geological GeologicalSociety Societyof of America AmericaSpecial SpecialPaper Paper 312, p. 73-96. 312, p.73-96. Mungall, E.,2002, 2002,Kinetic KineticControls Controlson onthe thePartitioning Partitioningof ofTrace TraceElements ElementsBetween BetweenSilicate Silicateand andSulfide Sulfide Mungall,J.J. E.. Liquids. Liquids. Journal Journal of of Petrology. Petrology. Vol.43, Vol. 43, pp.749-768 pp. 749-768 Prendergast, Tire Complex, D., 2000,Layering 2000,Layering and Precious Metals Mineralization in the Rincon del Tigre Complex, Prendergast, M. M. D.. Eastern Bolivia. Economic Geology. Vol. 95, pp. 113-130. Eastern Bolivia. Economic Geology. Vol. 95, pp. 113-130. 40 �RESULTS OF SINGLE-GRAINANALYSES ANALYSESOF OFPRECAMBRIAN PRECAMBRIAN MAFIC MAFIC RESULTS OF40Ar/39Ar '")~r/^'>~r SINGLE-GRAIN INTRUSIONS IN IN NORTHERN NORTHERN ANI) AND EAST-CENTRAL EAST-CENTRALMINNESOTA MINNESOTA INTRUSIONS KEA'ITS, M.J., Kent, OH OH44242; 44242;JIRSA, uRSA, M., KEATTS, MJ., Dept. of Geology, Kent State University, Kent, St. Paul, MN 551 14-1057; Minnesota Geological Geological Survey, Survey, 2642 University University Avenue West, St. Minnesota 55114-1057; HOLM, HOLM, D., Dept. Dept. of of Geology, Geology, Kent Kent State StateUniversity, University, Kent, Kent,OH OH44242 44242 Age information from mafic mafic intrusive intrusive suites suites is critical Age information from critical for for proper proper interpretation interpretation of the the geologic history and for mineral deposit models in the Lake Superior region. region. As As part of an effort to evaluate evaluate PGE potential potential in mafic mafic intrusions intrusions in Minnesota, Minnesota, several several plutons plutons have been dated dated using the CO2 Ar/Ar incremental heating technique at the University of of Wisconsin-Madison Wisconsin-Madison COi laser ArIAr Rare Rare Gas Gas Geochronology Geochronology Laboratory. Laboratory. For late-stage late-stage shallow shallow plutons plutons containing containing primary primary magmatic homblende, Ar/Ar ArIAr mineral mineral ages are likely likely to to closely closely approximate approximate the crystallization crystallization magmatic hornblende, age. In regions regions with with aamore moreprotracted protractedthermal thermalhistory history(i.e., (i.e.,low-grade low-grademetamorphism, metamorphism, slowslowcooling, etc.), the Ar/Ar intrusions from ArIAr data provide minimum ages for the mafic plutons. Mafic intmsions Minnesota selected for for this study study represent aa broad range range of of geologic geologic settings, settings, including including1) 1)small small mafic supracrustal and and intrusive intrusive rocks rocks within mafic plutons plutons emplaced emplaced into Paleoproterozoic Paleoproterozoic supracrustal within the Penokean orogen (samples 264, R17); and 2) varied, varied, primarily latelate- to post-tectonic post-tectonic intrusions intrusions in in supracrustal rocks of the Archean Archean Wabigoon Wabigoon (samples Al, Al, B21, UBD) and Wawa (samples K15, LP, ANA) subprovinces of Superior Province. We We report report here here the initial results from LP, subprovinces of Superior Province. from eight eight separate intrusions (Fig. 1). separate intrusions (Pig. 1). A homblende East-central Minnesota. (R17) from East-central Minnesota. A hornblende grain grain (R17) from aa sample sampleofofmedium-grained medium-grained hornblendite from the Tibbett's Brook intrusion cutting the homblendite the East-central East-central Minnesota Minnesota batholith batholith in in Morrison Co. yields yields aa plateau date of 0.006 Ga from contiguous increments from 44 contiguous increments Momson Co. plateau date of 1.770 1.770 ±Â 0.006 constituting 74% of of the gas released. constituting 74% released. AAbiotite biotitegrain grain(264) (264)from fromaasample sampleofofcoarse-grained coarse-grained biotitic olivine gabbronorite gabbronorite cutting the Little Falls Formation in Morrison Momson Co. yields yields aa plateau plateau constituting 68% of the gas released. date of 1.791 ± Â0.008 0.008 Ga from 5 contiguous increments constituting Wawa Subprovince. A hornblende grain (ANA) from a sample sample of of prismatic prismatic homblende hornblendediorite diorite collected near Red Lake in Beltrami Co. yields a near-plateau date of 2.587 ±0.012 a . 0 1 2 Ga Ga in in 55 nonnoncontiguous incrementsconstituting constituting50% 50%ofofthe thegas. gas. A A biotite biotite grain grain (K15) (K15) from from a sample contiguous increments sample of biotite granodiorite porphyry collected in Norman Co. yields aa plateau date date of 2.639 2.639±Â 0.007 Ga 0.007 Ga from 6 contiguous increments constituting 79% 79% of of the gas released. A biotite grain (LP) from a sample of porphyritic syenite collected at the the Wawa-Quetico Wawa-Quetico subprovince subprovinceboundary boundary in in St. St.Louis Louis Co., 0.006 Ga from from 77contiguous contiguous Co., in the the Linden Linden Pluton, Pluton, yields yields aa plateau plateau date date of 2.666 2.666 ±Â 0.006 increments constituting constituting 88% of the gas released. grain (£321 (B21) from the Oaks intrusion leucodiorite sampled Wabigoon Subprovince. A hornblende grain near Fault in in Roseau 1 ±Â 0.008 0.008 Ga from 88 near the Vermilion Vermilion Fault Roseau Co. yields yields aa plateau plateau date date of of 2.67 2.671 contiguous increments increments constituting constituting75% 75%ofofthe thetotal totalgas gasreleased. released. A A hornblende homblende grain grain (Al) (Al) from the Black River gabbro, collected in Roseau Co., yields a plateau date of 2.685 ± 0.011 Ga from from 2.685  0.011 11 contiguous increments increments constituting constituting90% 90%of of the the total total gas gas released. released. A hornblende hornblende (UBD) (UBD) from a sample collected in Koochiching Co. north of the sample of homblende-biotite hornblende-biotite gabbro collected the Rainy Rainy LakeLakeSeine River Fault Fault yields yields aa plateau plateau date date of of 2.695 Seine River 2.695 ±  0.007 0.007 Ga from 66 contiguous contiguous increments increments constituting 49% of the gas released. released. 41 �_____________ __________________________ ___ The mineral age data data from mafic mafic plutons plutons from from the the Wabigoon Wabigoon subprovince subprovince are are synchronous synchronous Mafic plutons plutons from from the the with the last deformation event (D2) dated in the range 2.685-2.674 Ga. Ga. Mafic Wawa subprovince give an 80 m.y. Interestingly, the Linden m.y. age age range range from from 2.58 2.58 to to 2.66 2.66 Ga. Ga. Interestingly, Linden Pluton gives a biotite Pluton biotite date date concordant concordant (within (within error) with the youngest youngest mafic pluton from the Wabigoon subprovince. subprovince.The Theyounger youngerspread spreadofof ages ages from from the Wawa Wabigoon Wawa are are consistent consistent with with southward growth of the Superior Province Province during the the latest latest Archean. Archean. Mafic plugs plugs evident evident from aeromagnetic maps in in east-central Minnesota are comagmatic with the circa 1.775 aeromagnetic maps east-central Minnesota comagmatic with 1.775 Ga Ga EastEastcentral Minnesota batholith. batholith. Further constraining the temporal framework of mafic mafic intrusions intrusions may contribute to mineral deposit models models for for PGE may contribute to mineral deposit PGE in these these intrusions intrusions and and their their analogs analogs in in adjacent states states and and provinces. provinces. Fig.1 °Ar/"Ar age Fig.l "ArPAr age spectra: spectra: t, = plateau age, age, çt, == total total gas gas age. age. 2.0 2.0 2.0 R17 I 264 1.5 o t_.._1 :. e 1.8 1.0 0.5 3.0 Btite MSWD Biotite MSWD2.57 2.57 Amphibole MSWD 1.78 1.770±0.006 t, = 1.770  0.006 Ga Ga t9 = 1.653 1.653  ± 0.005 0.005 Ga p Ga [.1 t==1.791 t, 1.791±0.008 t 0.008 Ga Ga 1.782  ± 0.007 Ga t,t9 == 1.782 1.5 3° ANA .. o H- — 2 25 Amphibole MSWD MSWD 0.30 = 2.671 ± 0.008 Ga t9 = 2.705 ± 0.013 Ga Amphibole MSWD Amphibole MSWD 0.71 0.71 = 2.587 ± 0.012 Ga = 2.550 ± 0.009 Ga 2.0 3.0 2.0 3.0 K15 — t: 2.5 TTL..c.H 2.5 . 2 Amphibole Amphibole MSWD MSWD1.81 1.El Biotite MSWD MSWD 2.48 2.46 t, = 2.639 ±Â 0.007 Ga Ga 2.685 ± t, = 2.685 Â0.011 0.011 Ga Ga = 2.640 ± 0.007 Ga t = 2.700 ± 0.010 Ga 2.0 — LP % Ir11 — m —LI 2.5 2.5 2 Amphibole MSWD MSWD 1.03 1.03 ± 0.007 Ga t, = 2.695  = 2.730 ± 0.006 Ga Biotite MSWD 1.11 = 2.666 ± 0.006 Ga = 2.657 ± 0.006 2.0 - 0 0 2.0 100 0 $00 0 —. . 100 $ 20 20 30 30 40 50 SO 60 60 700 7 80 Cumulative "Ar "Ar released (%) 90 SO 42 10 10 20 20 30 40 S O 50 60 60 7 700 80 "Ar released Cumulative "Ar released (%) 90 90 300 100 �Ontario New zircon ages from from the the Gunflint and Rove Formations, Formations, northwestern northwestern Ontario Kissin, Kissin, S.A., Department Departmentof of Geology, Geology,Lakehead Lakehead University, University,Thunder ThunderBay, Bay,ON, ON,P7B P7B5E1 5E1Canada, Canada, stephen.kissin@lakeheadu.ca stephen.kissin@lakeheadu.ca ;;Vallini, Vallini, D.A., D.A., University University of Western Australia, Australia, 35 35 Stirling Stirling Hwy, Crawley, 6009, W.A., iWO, Canada; W.A., Australia; Australia; Addison, Addison, W.D., RR 2, Kakabeka Kakabeka Falls, Falls, ON, ON, POT 1W0, Canada; Brumpton, Brumpton, G.R.., 211 21 1 Henry Henry St, St, Thunder Thunder Bay, ON, P7E 4Y7, Canada. Canada. Previous work based on U-Pb U-Pb geochronology geochronology from presumed volcanogenic volcanogenic zircons zircons obtained obtained from a tuff layer at the lower/upper ± 2Ma, lowerlupper Gunflint Formation boundary yielded an age of 1878 1878  2Ma, believed to approximate the age of deposition of of the the unit unit (Fralick et et al., al., 2002). This This age age corresponds closely with the age of the correlative Hemlock Formation of Michigan (1874 ±  corresponds closely Schneider et al., 9Ma; Schneider a]., 2002). 2002). 9Ma; We report here preliminary age determinations determinations based on SHRIMP SHRIMP analyses of zircons extracted from three volcanic ash layers; one lying in the Gunflint Gunflint Formation, Formation, and and two within the overlying Rove Formation. The The Gunflint-Rove Gunflint-Rovecontact contact is an an important important reference reference point. Pufahl and Fralick (2000) placed it at the top of a sequence sequence of chert-carbonate chert-carbonate grainstones grainstones which which is overlain by carbonaceous shales of of the the Rove Rove Formation. Formation. The Gunflint Gunflint exposure exposure outcrops at Little Falls, on lOm (topographically) (topographically) below the -10m Little on the the south southside sideof of the theKakabeka KakabekaFalls FallsGorge, Gorge,— Gunflint lapilli tuff dated by Fralick et al. (2002). A Rove volcanic ash ash exposure exposure at at Oliver Oliver Creek Creek is estimated (stratigraphically)above abovethe theGunflint-Rove Gunflint-Rove contact. contact. Zircons were also estimated to be —70m -70m (stratigraphically) extracted from an ash layer within Falconbridge Pine River (PR98-1) (PR98-1) drilicore drillcore (688.24m (688.24m down down contact. hole), located -Am -4m above the Rove-Gunflint contact. The Oliver a mean 207Pb/206Pb age of of 1821 1821 ± ""~b/^Pbage  16 single The OliverCreek Creekzircons zirconsrecorded recorded a mean 16 Ma while a single age of 1840Ma 1840Ma was obtained from the drillcore PR98-1 sample. sample. The The errors errors cited cited are are at at the the one one standard deviation (10) ( l a ) and and 95% 95% confidence confidence level level and and the the analyses analysesare are less lessthan than5% 5%discordant. discordant. There recordedfrom from each each locality locality which are assumed to There are are also also two two younger younger ages ages of of —1786Ma -1786Ma recorded outliers. be outliers. The Little Falls zircons, zircons, which are are somewhat somewhat rounded rounded and and fractured, fractured,yielded yielded various various than 2000Ma. 2000Ma. Most Most of of the the ages ages are more more than 10% 10% discordant, discordant,and and these these samples samples ages, all older than may have suffered lead loss. As As well, well, there there are are some some indications indicationsof of admixture admixtureof of shalely shalelymaterial material in the ash layer at this locality. Older Older zircons zircons from from the the lapilli lapilli tuff tuff layer layer at at the the lower/upper lowerlupper Gunflint Gunflint contact (Fralick (Fralick et al., a]., 2002) 2002) were also found found to be admixed admixedwith with Paleoproterozoic Paleoproterozoic zircons. zircons. Using the stratigraphic column of of Pufahl and Fralick (2000), we estimate that the drillhole (PR9S-i) Gunflint lapilli (PR98-1)samples samplesare—i are -1 lOm 10m above the Gunflint lapilli tuff tuff layer layer containing containingthe the zircons zircons dated dated by Fralick et al. (2002), (2002),while while we we estimate estimatethe theOliver OliverCreek Creeksamples samplestotobebe—iSOm -150m above this same layer. The ages reported here indicate that a slow sedimentation sedimentationrate ratemust must have havebeen been required in order to account for the age difference difference between between the the lapilli lapilli tuff tuff of Pufahl and Fralick Fralick and the two sets of Rove dates reported here. here. This This slow Rove Rove sedimentation sedimentation rate is comparable that reported in banded iron formations formations of the early early Proterozoic Proterozoic Campbell CampbellGroup, Group,Griqualand, Griqualand, West Sequence, Sequence, South Africa (Barton et al., 1994). 1994). 43 �Oliver Creek reasonable agreement The Oliver Creek ages ages reported here are are in reasonable agreement with the the 1833 1833±Â 6Ma age reported by Schneider Schneider et a!. al. (2002) for the Tobin Lake Pluton, which is undeforined undeformed by Penokean deformation and intrudes presumed Hemlock Volcanic equivalents. However, However,the the with the the Penokean Penokean zircons from the Rove Formation suggest that volcanic activity associated with continued for for at at least least 40 40 m.y. m.y. Further Orogeny continued Furtherstudies studiesare are underway underway to clarify some of the questions raised by our results. results. Barton, E.S., Altermann, Smith, C.B. 1994. U-Pb Altermann, W., William, 1.5., I.S., amd Smith, U-Pb zircon zirconage agefor foraatuff tuff in in the Campbell Group, Griqualand West Sequence, South Africa: Implications for Early Proterozoic Proterozoic rock rock accumulation accumulation rates. rates. Geology Geology 22: 22:343-346. 343-346. Fralick, P., Davis, D.W., and Kissin, S.A. 2002. 2002. The Ontario, The age age of the Gunflint Formation, Ontario, reworked volcanic ash. Canadian Canada: single zircon U-Pb age determinations from reworked Journal of Earth Earth Science Science39: 39:1089-1091. 1089-1091. Pufahl, P. and Fralick, P. 2000. Fieldtrip 4: Depositional environments environments of the Paleoproterozoic Paleoproterozoic Gunflint Formation. Proceedings of the Institute Institute on on Lake Lake Superior SuperiorGeology, Geology, 46, 46, pt.2. D.A., Bickford, Bickford, M.E., M.E., Cannon, Cannon, W.F., W.F.,Schulz, Schulz,K.J., K.J.,and andHamilton, Hamilton,M.A. M.A.2002. 2002. Age of of Schneider, D.A., formations, Marquette volcanic rocks and syndepositional iron formations, Marquette Range Range Supergroup: Supergroup: implications Paleoproterozoic iron formations implications for for the tectonic tectonic setting setting of Paleoproterozoic formations of the Lake Lake Superior Superior Region. Canadian Canadian Journal Journal of of Earth Science Science 39: 39:999-1012. 999-1012. 44 �OF THE THE SOUTHERN SOUTHERN PORTION OF O FTHE THELAURENTIDE LAURENTIDE ICE ICE MEAN TRANSPORT TRANSPORT LENGTH LENGTH IN TILLS OF SHEET: IMPLICATIONS FOR DRIFT EXPLORATION EXPLORATION IN THE THE LAKE LAKE SUPERIOR SUPERIOR REGION REGION LARSON, Phillip Phillip C., C., Department of Minnesota, MN 55812, 55812, LARSON, Department of Geological Geological Sciences, University University of Minnesota, Duluth, Duluth, MN plarson2@'d.umn.edu plarson2@d.umn.edu Introduction Bedrock - till, till, Bedrock in the the Lake is typically typically covered covered by by aamantle mantleofofglacigenic glacigenicsediments sediments— Lake Superior region is outwash, that presents significant challenge challenge to successful successful application application of of surficial surficial outwash, and lacustrine lacustrinesediments sediments—- that presents a significant geochemical techniques techniques widely widely used used to help targets. The glacial glacial environment environment is is very very complex, complex, geochemical help generate generate drilling drillingtargets. with sediments produced produced by by a range of processes. with sediments processes. Till represents the ideal sampling sampling media media in in these theseenvironments, environments, direction) is attached to since a vector (ice flow direction) to the the composition composition at any location location indicating indicatingthe thedirection directiontotothe thesource source of any defined anomaly. anomaly. However, recent work has led to recognition that both the the magnitude magnitude of of aa till till geochemical geochemical anomaly andthe the potential potential transport transportdistance distancetotoits itssource sourcemay mayhave haveaawide widerange rangeofofvalues. values. This is a reflection of anomaly and transport distance of till-forming material, material, and is related the mean transport related to the the fundamental fundamental sediment sediment transport transport process process responsible for forming forming the till. responsible till. Theory The concentration concentration of an indicator (a distinct distinct lithologic or geochemical component derived from a discreet in till till is the direct product of the physical processes processes of of glacial glacial erosion, erosion, transport, transport, and and deposition. Indicator source) in Indicator concentrationisis controlled controlledby by aa number number of of variables, including substrate substrate hardness hardness and and the the efficacy of the glacial concentration variables, including erosional regime. ice flow indicator mass regime. Under Under steady steady state state ice flow conditions conditions and and uniform uniform bed bed erosion erosion rates, rates, indicator mass concentration c in (1) down-ice down-ice of of an an indicator indicator source sourceof of finite finiteflow-line flow-linelength lengthLL(1) (1) is: is: concentration ci intill till atatany anytransport transportlength lengthTT(1) — L (1) where X X isis the the erosion erosion length length scale scale (I). (1).For Fortills tills down-ice down-ice of of the the indicator indicator source, under steady state state conditions, conditions, the decrease &/ST assumes assumes aa quasi-exponential quasi-exponential form. form. decrease in indicator indicator concentration concentration with with increasing increasing transport transport length length bc/8T Erosion length length scale, scale, \X,isisrelated relatedto to the the spatial spatial bed bed erosion erosion rate rate E E ((mL3) and the thickness of the debris layer in Erosion m r ) and (m-1.): transport md 1d (mV2): (2) increases, so so does the mean transport XXis is closely related to the mean transport distance distance of till-forming material; as X X increases, distance. distance. vs. Long-Distance Long-Distance Transport: Transport: Examples Short- vs. Tills in the Lake Superior Superior region can be broadly broadly grouped grouped into two two categories categories based based on onthe themean meantransport transport length of the till forming material. mean transport length Tills characterized characterized by short-distance short-distance mean length are commonly commonly composed composed of of coarse-grained coarse-grained material containing abundant abundant angular angular clasts, clasts, and and display rapid rapid decrease in indicator material containing indicator concentration concentration with with transport transport length. This This isis exemplified exemplified by by tills tills overlying overlying the the Vermilion Vermilion greenstone greenstone belt of of northern northern Minnesota, Minnesota, which which displays displays rapid decrease decrease in in concentration concentrationofofnumerous numerousindicator indicatorlithologies; lithologies; X for range from 2.Oi0m. m. A ?for . thisthis tilltill range from 1.01.0 to to 2.0-103 rapid dispersal train composed composedofof clasts clasts of of Nipigon Nipigon diahase diabase in in till east dispersal train east of of Lake Lake Nipigon. Nipigon, Ontario Ontario displays displays similar similar characteristics. Dispersal in indicator indicatorconcentration; concentration;calculated calculated?\for forthis this Dispersal isis characterized characterizedby by aa similar similar rapid rapid decrease decrease in till range 102 m over relatively relatively soft greenstone greenstone to to 2.4-lo4 2.4 i04 m m over over hard hard diabase. diabase. Both range from from5.5 5.5-10' Both tills tills are are interpreted interpreted to to have formed by by erosion of of hard hard bed bed by quarrying and abrasion, and englacial transport. transport. Tills characterized by long-distance Tills characterized by long-distance mean mean transport transport length are are commonly commonly composed composed ofoffine-grained fine-grained material with aa relatively low abundance of rounded material with relatively low abundance of rounded clasts, and display display little little apparent apparent decrease decrease in inindicator indicator with transport transport length. length. Cretaceous shale grains in Des Moines Lobe tills of the Minnesota concentration with Minnesota River valley show relatively relatively little little decrease decrease in in concentration concentration along along the the flow flow axis axis extending extending down down the the valley valley (Matsch, 1972); the calculated X Xfor for this this till till is is 5.0-lo5 5.01 5 m. m. Carbonate-bearing Carbonate-bearing tills overlying the Canadian Shield north of Lake Lake Superior Superior (Thorleifson and and Kristjansson, Kristjansson, 1993) show similar long-distance transport of Paleozoic Paleozoic carbonate carbonateand andProterozoic Proterozoic greywacke clastswith withlittle little decrease decrease in in concentration; concentration;the thecalculated calculated1.Xfor forthis thistill till is is o.oio5 6.0-10m. m. Both tills are are greywacke clasts have deposited deposited from deforming subglacial sediment layers (deformation (deformation tills). interpreted to have 45 �Discussion Discussion tills are are characterized characterizedby by1).that that are 10 to to 100 times The data indicate deformation tills times higher than those of of thin, thin, coarse-grained tills. Tills characterized by intermediate intermediate values of the erosion erosion length length scale scale X 1. have not as as yet yet been been recognized in the Lake Superior region, and perhaps perhaps do do not not exist. This Thisgap gapininrecognized recognized values values suggest suggest there there are are two main processes by which which bed bed material material is is eroded eroded and and entrained, entrained,transported, transported, and anddeposited deposited— - entrainment entrainment and and transport by a deforming subglacial subglacial layer, and erosion by quarrying and abrasion and transport transport as as an an englacial englacial debris debris load with deposition deposition by lodgement or meltout. Deformation tills form with with little little accompanying accompanying erosion of underlying underlying hard hard bedrock. bedrock. Their formation is is consistent with with redistribution of unconsolidated regolithoror sediment derived from consistent redistribution of unconsolidated regolith sediment derived from aa preglacial preglacial reservoir. reservoir. Consequently,till till composition composition reflects reflectsthat that of of distant distant (>100 Consequently, (>lo0 km) km)bedrock. bedrock. Tills characterized characterized by short short mean mean restricted erosion erosion and and entrainment and and transport of hard bedrock. transport length indicate spatially and temporally restricted Their formation is consistent consistent with erosion erosion by quarrying quarrying and abrasion abrasion of of hard hard bedrock bedrockwith withsubsequent subsequentextensive extensive textural Till composition km) bedrock. bedrock. textural modification during during transport. transport. Till composition closely reflects reflects that thatofofnearby nearby(—10 (-10 1cm) Consequently, these tills have enormous potential value as geochemical sampling sampling media. Recognition of the process process responsible responsible for till till formation formation in in aa given given area areaisiscritical criticalfor forsuccessful successfulapplication application of surficial geochemical and boulder tracing exploration techniques techniques in the Lake Lake Superior Superior region. region. Limited scope scope orientation surveys surveys aimed aimed at at characterizing characterizingthe theerosion erosionlength lengthscale scale 1?. provide provide a means orientation means of of quickly quickly assessing assessing the potential for successful application of drift exploration techniques on both both regional and property scales. 46 �Glacial Glacial Lakes Lakes Aitkin and Upham: their origin origin and and environmental environmental history history PhillipLarson Larson LisaMarlow, Marlow,Howard HowardMooers, Mooers,&&Phillip Lisa Department Departmentof ofGeological GeologicalSciences, Sciences,University Universityof of Minnesota, Minnesota, Duluth, Duluth, Minnesota Minnesota55812 55812 Glacial Minnesota bounded Glacial Lakes Lakes Aitkin Aitkin and and Upham Upham occupied a basin in north-central Minnesota bounded on on the the north northby by the the Giants GiantsRange Range and and to to the the east, east, south, south,and and west west by by hummocky hummocky moraines moraines of of the the Rainy Rainy lobe, lobe, Superior Superior lobe, lobe, and St. Louis sublobe. The The lakes lakescaine came into into existence existence with the the retreat retreat of of the the Rainy Rainy lobe lobefrom fromthe theSt. St.Croix Croix phase phase sometime sometimeafter after15,000 15,000yr yr BP BP (Clayton (Clayton and and Moran, Moran,1982; 1982; Mooers Mooersand andLehr, Lehr, 1997). 1997).The Thebasin basinwas waslater lateroveridden overiddenby by the the St. St. Louis Louis sublobe sublobe from from the the northwest. northwest.With Withthe thewastage wastageofofthe theice iceof ofthe theSt. St.Louis Louissublobe, sublobe,the the basin basin was was again againoccupied occupiedby by lakes; as Lake Lake AitkinAJpham I and the later phase as lakes; the the earlier earlierphase phase is is referred referred to as as Lake AitkinlUpham Aitkin/Upham II.Sediment Sedimentof ofthe theearly earlylake lakephase phaseisispreserved preserved at at aa few localities. localities. One Onesuch such AitkinAJphamII. locality locality preserves preserves aa sequence sequence that helps redefine the glacial glacial chronology. AAsedimentary sedimentarysequence sequence located locatedin in the thenortheast northeastcorner comerof of the the Upham Upham basin basin reveals reveals sub-aqueously sub-aqueously deposited depositedRainy RainyLobe Lobe outwash outwashbeneath beneathglaciotectonically glaciotectonically deformed deformedfine-grained fine-grained lake lake sediments sediments deposited depositedby by the theSt. St. Louis Louis sublobe. sublobe. This, This,along alongwith withother othergeomorphic geomorphicrelationships relationships(P.C. (P.C.Larson, Larson,unpublished unpublisheddata) data) indicates indicatesthat thatthe theRainy RainyLobe Lobe ice ice margin margin was was coincident coincidentwith with the the Giants Giants Range Range when when the theSt. St. Louis Louissublobe sublobeadvanced advancedacross acrossthe thelake lakebasin. basin. Using @EM) the the elevation elevationof of lake lakebasin basin was was adjusted adjustedfor forisostatic isostatic Using aa Digital DigitalElevation Elevation Model Model (DEM) rebound based on the highest lake level, then tilted incrementally through several stages rebound based on the highest lake level, then tilted incrementally through several stagesto toassess assess beaches, beaches, inlets, inlets, and and outlets outlets over time. AAseries seriesof ofsuccessively successivelylower lower outlets outletsdraining drainingto tothe theSt. St. Louis Louis River Riverserved servedas as outlets outlets for for Glacial Glacial Lakes Lakes Aitkin Aitkin and and Upham Upham (Hobbs, (Hobbs,1983; 1983;Farnum, Farnum,1964; 1964; Wright, Norwood through through the the Embarrass Embarrass Wright, 1972). 1972).Meltwater Meltwaterentered enteredthe thelakes lakesfrom fromGlacial GlacialLake LakeNorwood gap, gap,and and later laterfrom fromGlacial GlacialLake LakeKoochiching Koochichingalong alongthe thePrairie PrairieRiver. River. During During this this time time Aitkin Aitkin and and Upham Upham were were confluent, confluent,and and the the outlet outlet was was established establisheddown down the the modern modem St. St.Louis LouisRiver. River. The The lakes lakes were were separated separated by by aa sill sill ca ca 11,500-10,100 11,500-10,100yr yr BP, BP, after after inflow inflow from from Koochiching Koochichingwas was divertedto to Glacial GlacialLake LakeAgassiz. Agassiz. diverted Extensive Extensive dune dune fields fields formed following initiation initiation of drainage drainage of the lakes. Granulometry Granulometry indicates throughout the thebasin. basin. Maximum indicates a 4p 4(pgrain grain size size signature characterizes dunes throughout Maximum dune dune amplitude metersand anddune dunemorphologies morphologiesrecord recordprominent prominentnorthwesterly northwesterlywinds. winds. Dunes amplitude is is —3 -3 meters overly overly source source areas, areas, which include include an underfiow underflow fan fan deposited deposited by by the the Prairie Prairie River Riverinlet inletand andthe the western margin marginof of Lake Lake Upham. Upham. western A sediment sediment core core collected collected from Hay Lake (93°W, (93'W, 52°N), 52ON), located located within aa dunefield dunefieldat atthe theedge edge of Glacial Glacial Lake Lake Upham, records three prominent peaks in whole-core whole-core magnetic magnetic susceptibility susceptibility between No clastic clasticinput inputisisevident evidentafter after6,600 6,600yr yrB.P., B.P.,suggesting suggestingdune dune between 10,100 10,100and and 6,600 6,600 yr BP. No stability. The timing of dunes within the basin has important implications for other dunes throughout Minnesota. Eolian Eolianevents eventsrecorded recordedin in the the core coreare areinterpreted interpreted as as the the result resultof of lake lake drainage drainage and exposure exposure of abundant abundant source material material during during Late Late Glacial Glacial and and Early Early Holocene Holocene rather rather than than landscape landscape destabilization destabilization because of mid-Holocene aridity (Keen et al., 1990; 1990; Grigal Grigal et et al., al., 1976; 1976;Dean Dean et et al., 1996; 1996; Dean, 1997). 1997). Additionally, Additionally,this thissediment sedimentcore core places places aa minimum minimum age on the drainage of of Glacial Lakes Lakes Aitkin Aitkin and and Upham Upham II. II. Lake Upham must have drained drained after 47 �age on the drainage of Glacial Lakes Aitkin and Upham IiT. I. Lake Upham must have drained drained after 11,500 B.P. and Lake Aitkin may have persisted until ca. 7,000 10,100 yr B.P. 7,000 yr 11,500 yr BP and before 10,100 BR BP. Clayton, L. and Moran, S.R. 1982, 1982, Chronology Chronology of late Wisconsinan glaciation glaciation in in middle middle North North America. Quaternary Quaternary Science ScienceReviews Reviews11(1), (I),55-82. 55-82. Ahlbrandt, T.S., Dean, W.E., Ahlbrandt, T.S., Anderson, Anderson, R.Y., R.Y., Bradbury, Bradbury, J.P., 1996. 1996.Regional Regional aridity aridityin in North North America during the middle Holocene. Holocene. The The Holocene Holocene 6 (2), 145-155. 145-155. Dean, W.E., 1997. 1997. Rates, Rates, timing, timing, and and cyclity cyclity of Holocene eolian activity activity in in north-central United United States: 1-334. States: Evidence Evidence from from varved varvedlake lakesediments. sediments.Geology Geology25 25(4), (4),33 331-334. H.E., Jr. Jr. 1964. A Late-Wisconsin Late-Wisconsin buried soil near Farnham, R.S., McAndrews, J.H., and Wright, H.E., Minnesota, and its paleobotanical setting. 393-412. Aitkin, Minnesota, setting. American American Journal Journal of of Science Science262, 262,393-412. Drexier, 1985. 1985. Late-Wisconsinan and Holocene Holocene History History of of the the Lake Lake Superior Superior Farrand, W.R. & Drexler, In Karrow, Karrow,Quaternary Quaternary evolution evolution of of the the Great Great Lakes, Lakes, Geological Geological Association Association of of Canada Canada Basin. In Special Paper 30, 30, 17-32. 17-32. D.F., Severson, R.C., R.C., Golz, G.E., 1976. Evidence Evidence of of eolian eolian activity activity in north-central Grigal, D.F., Geological Society Society of America America Bulletin Bulletin 87, 87, 1251-1254. 1251-1254. Minnesota 8,000 to 5,000 yr. ago. Geological Aitkin, Upham, and early Lake Hobbs, H.C. 1982, 1982, Drainage relationships of Glacial Lakes Aitkin, Agassiz in northeastern Minnesota. In In Teller, Teller,J.T., J.T., and and Clayton, Clayton,Lee, Lee,eds., eds.,Glacial GlacialLake LakeAgassiz: Agassiz: Geological Association of Canada Special Paper 26, 245-259. Canada Special Paper 26,245-259. K.L., Shane, L.C.K, L.C.K, 1990. A continuous record record of of Holocene Holocene eolian eolian activity and Keen, K.L., Lake Ann, east-central east-central Minnesota. Minnesota. Geological vegetation change at Lake Geological Society Societyof of America America Bulletin Bulletin 102, 1646-1657. 102,1646-1657. Mooers, Mooers, H.D., H.D., Lehr, J.D., 1997. 1997. Terrestrial record of Laurentide ice sheet reorganization reorganization during Heinrich events. events. Geology Geology 25 25 (11), (ll), 987-990. 987-990. H.E. 1972, Quaternary Quaternary history historyof ofMinnesota. Minnesota In In Sims, P.K., and Morey, G.B., GB., eds., Wright, H.E. eds., Geology of of Minnesota: A 15-578. A Centennial Centennial Volume: Volume: Minnesota MinnesotaGeological GeologicalSurvey, Survey,5515-578. 48 �and Hydrothermal HydrothermalPGE PGEMineralization Mineralizationof ofthe theBirch BirchLake LakeCu-Ni-PGE Cu-Ni-PGEDeposit Deposit Magmatic and in the South northeast Minnesota South Kawishiwi Intrusion, Duluth Complex, northeast Minnesota John Marma, Mama, Phil Brown and Steve Steve Hauck* Hauck* University of of Wisconsin, Wisconsin, Madison, Madison, Wisconsin Wisconsin 53706, USA Department of Geology Geology and Geophysics, University *Natat Resources Research *Natural Resources ResearchInstitute, Institute,University Universityof ofMinnesota, Minnesota, Duluth, Duluth, Minnesota 55811, 55811, USA USA The The Birch Birch Lake Lake Cu-Ni-POE Cu-Ni-PGE Deposit is located 12 12 miles south south of Ely, MN in the the South South Kawishiwi Intrusion (SM) (SKI) of of the the Duluth Duluth Complex (DC). The TheSKI SKIisisone oneof of two twolayered layered mafic mafic intrusions intrusions along along the the basal contact contact of the the DC to host sub-economic Cu-Ni-POE Cu-Ni-PGE deposits. deposits. Mineralization is is dominantly dominantly hosted by the U3 layer, the lower-most of three ultramaficultramafictroctolite packages characterized characterized as a zone of alternating ultramafic (picrite-peridotite) (picrite-peridotite) and troctolite troctolite horizons horizons with with lenses lenses and and pods of oxide-bearing oxide-bearing (>5%) (>5%) ultramafic ultramafic and/or and/or massive massive oxide. oxide. The purpose of this study study was to locate, describe, describe, and characterize the textural relationships relationships among platinum group group minerals minerals (POM), (PGM), sulfides, sulfides, and silicate silicate phases to help help delineate delineate the the relative significance significanceof primary and remobilized platinum group group element element (POE) (PGE) concentrations. concentrations. Samples Samples from from 4 drill drill holes transecting the Birch Lake Deposit were obtained obtained from from the the (NRRI) located located in in Duluth, Duluth, MN. MN. EMPA and Natural Resource Research Institute (NRRI) and detailed detailed c15.tm in petrography were used to locate POE PGE bearing minerals, averaging <l5yan in diameter, diameter,and andto to geochemistry. Identifying POM textural relationships with characterize the host mineral geochemistry. Identifying the PGM other phases is critical to understanding the mechanism mechanism by by which which PGMs POMs were were deposited. deposited. Data from this study study will aid exploration exploration in locating other other deposits deposits and and guide guide metallurgists metallurgists in in improving recovery recovery techniques. techniques. POEs occur most often as various Pd minerals with associated PGEs associated Pt, Pt, Os, Os, Ir, Ir, Ru, Ru, Au, Au, Ag, Ag, Te, Te, Bi minerals categories of silicate-sulfide-PGM silicate-sulfide-PGMtextural textural minerals and and were were grouped grouped into into the following following 4 categories relations: PGMs that occur in "halos" "halos" residing most commonly commonly in anorthite-enriched anorthite-enriched zones zones in• in relations: 1) PGMs primary plagioclase around either interstitial sulfide sulfide (dominantly (dominantly chalcopyrite), chalcopyrite), interstitial interstitial sulfide sulfide and silicate silicate (dominantly (dominantly chalcopyrite, chalcopyrite, clinopyroxene, clinopyroxene, and hydrous silicates silicates (amphibole (amphibole and and biotite)), or silicate or hydrous hydrous silicate) silicate) (Figure (Figure 1). This This style style of silicate (dominantly clinopyroxene or POMs identified. 2) 2) Remobilized RemobilizedPOMs PGMsthat thatoccur occurin in mineralization hosted 58% of the total PGMs chlorite, serpentine, or secondary magnetite. magnetite. This chlorite, This style style of of mineralization mineralization hosted hosted 21% 21% of of the the total total PGMs identified. 3) 3)Random RandomPOMs PGMsthat that occur occur in in poikilitic poikilitic anorthite-rich anorthite-richplagioclase plagioclase(An (An75-An 75-An POEs sometimes residing in disseminated 95) and clinopyroxene (Wo 30-Wo 50) with PGEs chalccipyriteor orhydrous hydroussilicate silicate pockets, pockets,but butno no association association with with "halos". "halos". This style of chalcopyrite POMs identified. 4) 4)In In interstitial interstitialsulfides sulfidesor orsilicates silicatesthat that mineralization hosted 11% 11% of the total PGMs include (?) textures, or include hydrous silicates, silicates, chalcopyrite, chalcopyrite, clinopyroxene, clinopyroxene, sulfides sulfides with symplectite symplectite ('1) calcite. This style calcite. style of mineralization mineralization hosted 10% 10% of the total total POMs PGMs identified. identified. POM concentrations in The following following is a summarized summarized model for the formation of high PGM the Birch Lake deposit. The SKI begins as a magma body that is replenished The SKI begins as a magma that is replenished with with multiple multiple saturated. The injections of magma, which becomes sulfur saturated. The magma magma body body is is relatively relatively POE PGE poor, poor, the conduits with a PGE POE enriched due to partial loss of sulfides during emplacement leaving the segregation of the total sulfide. The The sulfides sulfides in in the the magma magma body body scavenge scavenge available availablePOEs PGEs and and grains. Primary crystallize as disseminated, interstitial sulfide grains. Primary hydrous hydrous phases phases form form at at this this time time 49 �from a fluorine-rich, deuteric fluid. fluid. A Cu-, PGE-rich, sulfide-poor fluid A Cl-, Cu-, fluid enters enters the the magma magma chamber at its base via the original magma conduit(s) and/or faults. faults. The The fluid fluidmigrates migrates along along grain boundaries, and interacts with the larger interstitial sulfides. A A dynamic dynamicenvironment environmentisis created created in which the fluid, fluid, containing containing aa significant significantconcentration concentration of of dissolved dissolvedmetals, metals,begins beginsto to consume and use sulfur from the larger grains to produce more more sulfides. At At the the same sametime, time, the the fluid is reacting with neighboring neighboring grains, grains, specifically specifically plagioclase, plagioclase, and and through through aa cation cation exchange exchange reaction, alters the plagioclase rims, enriching them in calcium. This This reaction reaction causes causesaa volume volume loss that is filled with precipitated (±chlorite) producing the disseminated precipitated sulfides and POMs PGMs (±chlorite "halos" Finally, another anotherfluid fluid migrated migrated through through "halos" around the larger interstitial grains (Figure 1). Finally, the intrusion that remobilized POMs on a small scale. intrusion remobilized PGMs on a small scale. Based on evidence evidence solely from the Birch Lake deposit, deposit, POM PGM mineralization mineralizationappears appears "compartmentalized". This concentrated or "compartmentalized. This could could be the result of two possible mechanisms: 1) Areas of high PGM POM concentrations are dependent on on their proximal proximal distance to "feeder" "feeder" zones (i.e. conduits or faults) where fluids can be introduced; introduced; and/or 2) High POM PGM concentrations concentrationsare are that localize fluid movement. due to structural controls within these heterogeneous rocks that of primary primary vs. vs. remobilized remobilized This study contributes to the current debate on the roles of (deuteric?) PGE PGE mineralization mineralization in in layered mafic mafic intrusions. intrusions. For the Birch fdeuteric?) Birch Lake Lake deposit, deposit, the the data data suggest both mechanisms played important roles in the origin of the ore minerals. Figure Figure 11 a.) Photomicrograph Photomicrograph in in plane-polarized plane-polarizedlight lightof ofthin thinsection sectionBL BL89-2 89-22516.4 2516.4—- locations locations A-L. chalcopyrite and and pyroxene pyroxene cross-cut cross-cut by by vertical verticalchlorite chlorite veins, veins, all all of of which which are Large interstitial chalcopyrite by a disseminated, dominantly dominantly chalcopyrite chalcopyrite halo halo that that is is in in An-enriched An-enriched plagioclase surrounded by rims. Notice Notice all all PGMs, PGMs, except except one, either occur in the halo; in chlorite veins; in interstitial biotite; or in clinopyroxene. The The altered altered plagioclase plagioclase and altered pyroxene on the left side of the occurrences -this —thisincludes includesareas areaswithin withinthe theoriginal originalhalo. halo. This image are devoid of any PGM occurrences fluid event that that removed PGMs and altered the minerals, which it suggests a second alteration fluid passed through. Dashed line represents the extent of halo and An-enrichment in the adjacent plagioclase grains. grains. White stars represent PGM POM occurrences. occurrences. Cpx=Clinopyroxene, plagioclase Opx=Orthopyroxene, Bi=Biotite, Bi=Biotite, Chl=Chlorite, Chl=Chlorite, Cpy=Chalcopyrite, Plag=Plagioclase Plag=Plagioclase 50 �EMP MONAZITE RESULTS OF EMP MONAZITEGEOCHRONOLOGY GEOCHRONOLOGYIN IN B-C E-C MINNESOTA: MINNESOTA: EVIDENCE EVIDENCE FOR LARGE-SCALE GEON 17 17 METAMORPHISM ASSOCIATED WITH POSTPLUTONISM TECTONIC PLUTOMSM MCKENZIE, M.A., and HOLM, D.K., both at Dept. of Geology, Kent State University, Kent, OH; SCHNEIDER, D.A., Dept. of Geological Sciences, Ohio University, Athens, OH; OH, SCHNEIDER, JERCII4OVIC, M., M., Dept. of Geosciences, Geosciences, University of Massachusetts, Massachusetts, Amherst, JERCINOVIC, Amherst, MA MA Determination of the Determination the timing timing and and extent extent of of poly-phase metamorphism metamorphism is is essential essential in in unraveling the the tectonic tectonic history history of of a region. region. The The pattern and degree of metamorphism preserved across the Penokean orogenic belt in the southern Lake Superior region is highly variable. dates fromeast-central east-centralMinnesota Minnesotaindicate indicatewidespread widespread cooling cooling at -1760 0~r/3Q dates ~ r from Abundant 440Ar/39Ar 1760 Ma shortly after the emplacement emplacementof ofthe theeast-central east-centralMinnesota Minnesotabatholith batholith(ECMIB) (ECMB)atat—1775 -1775 Ma Ma (Hoim (Holm et al., 1998; in review). Yet YetU-Pb U-PbSHRIIvIP SHRIMP monazite ages from three localities localities across the northern MI, region (e-c MN, northern MI,and andnorthern northernWI) WI)record recordonly onlyaauniform uniform—1830 -1830 Ma metamorphic metamorphic episode and episode and aa secondary secondaryyounger younger—1800 -1800 Ma thermal pulse linked linkedto toaarecently recentlyidentified identified—1800 -1800 Ma magmatic event event (Schneider et al., in in review). review). This study utilizes the total Pb electron (EMP) monazite age dating technique to better constrain the extent of thermal thermal microprobe (EMP) overprinting surrounding the batholith. overprinting surrounding batholith. in situ situ metamorphic metamorphic monazite monazite ages ages from from three three For this study we obtained obtained in Paleoproterozoic metasedimentary garnet-staurolite schist samples and one garnet-cordierite garnet-cordierite from the the plutonic plutonic zone of of east-central east-centralMinnesota Minnesota (Figure (Figure 1). 1). Schist gneiss sample from Schist sample sample AMpredominantly elongate monazite grains displaying a mottled chemical variation in 016 contains predominantly Th content. content. This ± 33 Ma from 79 79 spots spots on on seven seven Y and Th This sample sample yielded yielded aa mean age of 1746 1746  Maand and 1760 1760Ma. Ma. A third grains. Two Two age age domains domainswere were recognized recognizedatat—1738 -1738 Ma third less less prominent —1780Ma Maage agedomain domainwas wasobtained obtainedon onsome somehigh highYYregions. regions. Schist Schist sample -1780 sample MN-29 MN-29 contains contains sub-euhedral monazite monazite displaying prominent prominent regions regions of of high highTh Th content. content. This This sample sample yielded a 10 Ma from 92 spots 1764±Â 10 spots on five grains. A A single singleprominent prominent age agedomain domain was was mean age of 1764 recognized atat— 1772 1772 Ma. Schist Schistsample sampleP-16 P-16contains containsmonazite monazitewith with very very irregular irregular grain grain recognized numerous inclusions, inclusions, and variable Th Th content. content. This sample sample yielded yielded aa mean age age of boundaries, numerous grains. Two 1772 1772±Â 33 Ma from 92 spots on seven grains. Two age domains are identified: aaprominent prominent age age domain at —1770 Maand andaasmaller smaller population population age domain at —1800 Ma. Lastly, the Sartell -1770 Ma -1800 Ma. Sartell euhedral monazite gneiss, sample S-2, contains euhedral monazite grains displaying displaying distinctive distinctive core/rim corelrim textures. textures.  3 Ma from 102 spots on seven grains. Three Three age age This sample yielded a mean age of 1756 1756 ± domains are identified: two 1750 Ma and 1770 1770Ma Ma and and aa third third less less twoprominent prominentdomains domainsatat— 1750 Ma on high U cores. cores. prominent domain domain at at —1800 -1800 Ma Mathermal thermalimprint imprint associated associated with intrusion reveal aa profound profound —1770 -1770 Ma Our EMP results reveal of the 1775 Ma Ma ECMB. ECMB. The The considerable considerable distance distance of of some some of these these samples samplesfrom from the the western western edge of of the exposed exposed batholith (30-40 km) and the absence of Penokean metamorphic ages absence metamorphic ages suggests that that the the thermal thermal pulse pulse must have been been dramatic. dramatic. However, KHowever, the the garnet-schist garnet-schist sample sample KR (east of Mille Lacs) that records only geon 18 18 SHRIMP ages lies north of the the region of of thermal thermal of the the batholith. batholith. We influence of We note note that that sample sample K-R K-R is is located located just north north of of the the Malmo MaimoStructural Structural Discontinuity (MSD) (MSD) and and sample sample AM-016 is is located located south south of of it. it. Our Discontinuity Our data data reveal reveal that that the the MSD MSD juxtaposes rocks of different metamorphic metamorphic age (geon 18 18 metamorphism to the north from from geon - - 51 �ba' C) CD . '° <o ,__._ toaaa C') Epp CD .-,. 0 •L rQ5o o ECDCD -t r> to u — — " Un J•fl1 tr4 0 t nfl ni C)g <'o— rM -t. flH hU >E;•<'z g :h UH 17 metamorphism to the south). We propose, therefore, that the MSD is a geon 17 structure that exhumed the plutonic terrane of east-central Minnesota. West of Mille Lacs, a significant portion of the MSD juxtaposes post-Penokean plutons to the south against older metamorphic rocks to the north. This clearly supports our interpretation that this structure was active well after Penokean orogenesis. z __c_ C C S S a a I Frequncy P-16 Composite - AllSamples All Ages Histogram F) 01 52 CD 0 0, 'C to 0 I Figure 1: Histograms of BMP Th-U-total Pb in situ monazite spot ages. . ¶. a 0 ) .:po S. H 0 a Frequency 5 5 Frequency a —— I, •1 0 C 0, a C, 0 3 <'c C, .. C) MN-29 Conposte AM-016 Composite t o C,, pp —— Holm, D.K., Dan-ah, K., andLux, D., 1998, American Journal of Science, 298,60-81. Holm. D.K., Van Schmus, W.R., MacNeill, L., Boerboom, T., Schweitzer, D., and Schneider, D.A., in review, Geological Society of America Bulletin. Schneider, D.A., Holm, D.K., O'Boyle, C.,Hamilton, M., Jercinovic, M., in review, Geological Society of America Special Volume "Gneiss Domes and Orogeny." �THE SIOUX QUARTZITE REVISITED: SEDIMENTOLOGY, METAMORPHISM, GEOCHEMISTRY AND THE ORIGIN OF PIPESTONE GEOCHEMISTRY MEDARIS, L.G., L.G., Jr., Jr., and DOTT, R.H., Jr., Dept. of Geology & Geophysics, University University of Wisconsin-Madison, Madison, medaris@geology.wisc.edu; Wisconsin-Madison, Madison,WI, WI,53706; 53706; medarisgeology.wisc.edu;rdott@geology.wisc.edu rdottgeoIogy.wisc.edu Red, supermature supermature quartzites of the Baraboo Interval were deposited after 1.75 1.75 Ga on a stable craton craton in in the presence of free atmospheric oxygen under under conditions conditions of of intense intense chemical chemical weathering. weathering. Some atmospheric oxygen Some quartzites quartzites (Baraboo and and Flambeau) Flambeau) were were folded folded and and recrystallized recrystallizedatat 1.63 1.63 Ga Ga (HoIm ci aT, al., 1998), 1998), and and many many (Baraboo (Holm et quartzites were hydrothemally hydrothermallyaltered alteredatat1.46 1.46 Ga Ga (Medaris (Medaris etci al., 2002, quartzites were 2002, in in press), press), presumably presumably in in response promoted by by continental continental scale scale A-type A-type magmatism. magmatism. These discoveries response to brine migration migration promoted discoveries have prompted us to reevaluate the sedimentology, metamorphism, and geochemistry of the Sioux Quartzite. Sedimentolozy The Sedimentolo.eg TheSioux SiouxQuartzite, Quartzite, which which isisseveral several hundred hundred meters meters thick, thick, is is composed composed mostly mostly of quartz sandstone with interstratified ci al., 1986). 1986). Heterogeneous Heterogeneous interstratified lenses of red mudstone (Southwick et cobble conglomerate occurs at the base and finer pebbly layers are scattered throughout the lower half half or so, whereas mudstones Sedimentary structures in the sandstones mudstones occur chiefly chiefly within the upper upper half. half. Sedimentary sandstones include predominant - 15 15 cm in in thickness, thickness, rare rare predominant festoon-style, festoon-style, nested trough cross cross beds beds averaging averaging 10 10— zones sets, a few examples zones of planar-tabular planar-tabular sets, examples of herring herring bone bone cross cross bedding, bedding, and and both both asymmetric asymmetric and and symmetric ripple marks. The mudstones are mostly massive, massive, but but parallelparallel- laminated laminated and andripple-laminated ripple-laminated varieties are also also present. present. In In most most cases, cases, quartz quartz silt silt and and fine fine sand in a finer varieties are sand grains grains are disseminated disseminated in rare graded graded laminations laminations are arealso alsopresent. present. Some mudstones mudstones show polygonal polygonal 'mud' 'mud' cracks, matrix, but rare cracks, and and the overlying sandstones commonly contain intraclasts ripped up from such cracked beds Interpretations of the Sioux depositional environment include shallow marine and braided fluvial Interpretations (Doff, 1983; 1986). In In the the latter scenario, the cross bedded et a!., a!., 1986). bedded sandstones sandstones represent represent river river (Dott, 1983; Southwick Southwick ci' channel deposits, and the mudstones, channel deposits, mudstones, slack water deposits in in ponds ponds between between active active channels. channels. However, However, this interpretation is inconsistent with the the rarity of scoured channel bases bases and and tabular sets of planar cross inconsistent with laminations, which would would have have formed formed by by laterally laterally migrating migrating bars, bars, and and the existence of wave laminations, which wave ripples, ripples, which expected in in the the sands sands of of aa braid braid plain. plain. Ojakangas (1984) suggested which are not expected Ojakangas and Weber (1984) suggested that that the the one-third of the Sioux formation formation was was deposited deposited in a shoreline marine setting with tidal influences, upper one-third accounting for the polygonal desiccation desiccation cracks, cracks, and the herringbone herringbone cross bedding, wave ripples, polygonal and thickness and extent of certain certain mudstone mudstone layers layers (now (now pipestone). pipestone). Interpretation Interpretation of of the the Sioux Sioux as asaa fluvial-to-marine fluvial-to-marine transgressive succession successionwould wouldconform conformtoto the present transgressive present interpretation interpretation of of the thecorrelative correlativeBaraboo Baraboo Quartzite, which has wave ripples ripples and and reactivation reactivation surfaces surfaces in in its upper upper half half (Medaris (Medaris et et al., al., in press). Metamorphism Metamorvhism Mineral Mineralassemblages assemblages in in finefine5 grained grained Sioux sedimentary rocks can be 5 expressed in the expressed in the system, system, KASH, KASH, as as portrayed portrayed in in a:4 0:4 Figure 1, where rock compositions are projected compositions projected onto the anhydrous onto anhydrous plane, plane, K-Al-Si, K-Al-Si, and and two two 3 critical dehydration reactions reactions are plotted. Additional phases include abundant hematite and Additional 22 a Ti02 TiO; phase, phase, either either anatase anatase in in the theCottonwood Cottonwood 1989), or rutile in Basin (CB) Basin (CB) (Stelz, (Stelz, 1989), in the Pipestone Basin (PB). The stable of 11 Pipestone (PB). The stable existence existence of the CB kaolinite in the CB (Stelz, (Stelz, 1989) 1989) requires temperatures below -300°C -100°C, whereas temoeratures whereas pyronvro250 350 T, 300 phyllite in in the the PB PB is is stable stable above above-300°C -100°C. The T, 0C OC phyilite 250 300 53 �quartz-pyrophyllite assemblageininthe the PB PB (0, (0, Fig. quartz-pyrophyllite assemblage Fig. 1), I), ininwhich which vermicular vermicular kaolinite kaolinite has has been been replaced replacedby bypyrophyllite pyrophyllite(Fig. (Fig.2A), 2A), most likely likely represents represents higher highertemperature, temperature, largely largelyisochemical isochemical most recrystallization of ofaaquartz-kaolinite quartz-kaolinite protolith, protolith, like likethat thatininthe theCB CB recrystallization The occurrence occurrence of muscovite muscovite in both both basins basins isis (0, Fig. Fig. 1). 1). The (C>, attributed to to K-metasomatism K-metasomatism related related to to 1.46 1.46Ga Gahydrothermal hydrothermal attributed (+,Fig. Fig.1)1)isisaametasomatic metasomaticrock rock composed composed of of activity. Pipestone Pipestone(+, activity. pyrophyllite, muscovite, diaspore, diaspore, hematite, hematite, and and rutile, rutile, ininwhich which pyrophyllite, former quartz quartz grains grains have have been been completely completely replaced replaced by bydiaspore, diaspore, former Because the Sioux 2B). Because the Sioux pyrophyllite, and muscovite (Fig. pyrophyllite, muscovite (Fig. 2B). Quartzite Quartzite is is largely largely undeformed undeformed and and lies lies north north of of the the extrapolated extrapolated trend et al., al.,1998), 1998), trend of of the the 1.63 1.63 Ga GaMazatzal Mazatzal tectonic tectonic front front (HoIm (Holm et we we suggest suggest that that all all metamorphic metamorphic features features of of the theSioux SiouxQuartzite Quartzite are are due due to to 1.46 1.46Ga Gahydrothermal hydrothermal activity, activity, rather rather than than aaMazatzal Mazatzal event. event. Geochemistry Geochemistq Where Whereunmodified unmodifiedby byK-metasomatism, K-metasomatism, finefinegrained grained sedimentary sedimentary rocks rocks of of the theBaraboo BarabooInterval Intewalare areremarkably remarkably mature, mature, being being practically devoid devoid of of K, K, Na, Na, Ca, Ca, Mg, Mg, and and Mn Mn (Fig. (Fig. 3), values of 97 to 99. 31, and and having Critical Index of Alteration Alteration values 99.InIn such 3) and and such rocks rocks the the wide wide range range ininproportion proportion of of Si Si to to Al A1(Fig. (Fig. 3) of quartz quartz to to kaolinite kaolinite in inthe the I), reflects the original original proportion proportion of quartz to to kaolinite, kaolinite, or orpyrophyllite pyrophyllite(Fig. (Fig. 1), quartz protolith sediments. protolith sediments. has stabilized stabilized K-metasomatism has muscovite muscovite in both the CB and and PB, PB, but but the muscovite-bearing muscovite-bearing rocks in the the CB CB 0 150 2 record aa lower lower temperature temperature and and higher higher record C ratio ratio of of Si/Al SiIAl compared compared to to pipestone pipestone in in 1uJ (Fig. 1). 1). The Theclassic classicpipestone, pipestone, the PB (Fig. o in addition addition to to substantial substantial KK contents, contents, in contains contains lower lower Si and and higher higher Al A1than than pyrophyllite in associated associated quartz quartz ++pyrophyllite that in samples (Figs. (Figs. 1 & 3). Assuming Assuming Zr Zr to to samples be an an immobile immobile element, element, isocon isocon be calculations indicate indicate that that the the mean mean calculations -50 pipestone pipestone composition composition was produced by by 65% Si02, S O 2 ,45 45 to to 55% 55% removal of 20 to 65% -100 Al Si Mn Fe 11 K Na Ca Mg Ti02, Ti02,35 35 to to 65% 65% Fe203, Fe203, and addition of 15 to 45% 45% Al203 A1203and and—800% -800% K20, K20, 15 pyrophyllite samples. samples. compared to the average average compositions compositions of of the two Si-rich Si-rich and and two two Al-rich Al-rich quartz quartz ++pyrophyllite compared The composition of of one one pipestone pipestone sample sample(*, (*, Fig. Fig. 1) 1) requires requires removal removal of of 68% 68% Si02 Si02 and and The reconstructed reconstructed composition addition addition of of50% 50%A1203 A1203during during metasomatism. metasomatism. Further investigation investigation is underway to provide a more more detailed detailed evaluation evaluation of of brine brinecompositions compositions and and metasomatic processes involved in this important, regional scale, 1.46 Ga hydrothermal event. metasomatic 1.46 Ga hydrothemal event. References Geol. Amer. References Dott, Dott,RH. R.H.Jr.Jr.(1983) (1983) Geol.Soc. SOC. h e r .Memoir Memoir160, 160,129-141; 129-141;HoIm, Holm,U. D. etetatal.(1998) (1998)Geology, Geology,v.v.26, 26, 907-910; Medaris, L.G., Jr. et at (2002) 48th Inst. Lake Superior Geol., 24-25; Medaris. L.G., Jr. eta!. L.G., Jr. et 01.(in (inpress) press) 907-910; Medaris, L.G., Jr. et aL (2002) 48th Inst. Lake Superior Geol., Jour. Ojakangas, R.W. Geol. Jour. Geol.; Ojakangas, RW. & & Weber, Weber,R.W. R.W.(1984) (1984)Minn. Mi. Geol. Sun'., S w . ,Rept. Rept.mv. Inv.32, 32,1-15; 1-15;Soutkwick, Southwick,D.L. D.L. etet at Amer. al.(1986) (1986)Geol. Geol,Soc. SOC. Amer.Bull., Bull.,v.v.97, 97,1432-1441; 1432-1441;Stelz, Stelz,D.E. D.E.(1989) (1989)M.S. MS.Thesis, Thesis,Wichita WichitaState StateUniv., Univ.,140 I40pp. pp. 850 54 �_____________ A geochemical investigation investigation of of Mesoarchean Mesoarchean metavoIcanic metavolcanic and and metasedirnentary metasedimentary rocks from from the the Rirch-Uchi Birch-Uchi greenstone greenstone belt Metsaranta, R., Hollings, P.P(Department of of Geology, Lakehead Metsaranta, R.,Fralick, Fralick,P.P.and and Hollings, . (Department Geology, LakeheadUniversity, Universio,Thunder ThunderBay Bay ON CAN, CAN, P7B 5 SE)) EI) Most Mesoarchean greenstonebelts belts in in the Western Most Mesoarchean grtGlfibL"fifie Western Superior Province are comprised comprised primarily of komatiite-tholeiite komatiite-tholeiite sequences and associated associated sedimentary sedimentary rocks (Thurston (Thurston and Chivers 1990). 1990). These These—2.9-3.0 -2.9-3.0 Ga Ga assemblages assemblages have have been been interpreted interpretedto to represent represent plume generated volcanism in oceanic plateau settings (for example, Hollings et al. al. 1999, 1999, Tomlinson et aL1999). a1.1999). This study is aa preliminary preliminary investigation investigation of metavolcanic metavolcanic and metasedimentary strata strata from from the Mesoarchean metasedimentary Mesoarchean Balmer assemblage assemblage of the the Birch-Uchi Birch-Uchi Rogers et et al. greenstone belt. belt. Rogers al. (2000) (2000) have have suggested suggested that, that, given given their theirgeochemical geochemical affinities and Nd isotopic evidence for contamination by older crust, volcanic rocks of the may represent represent aa continental continentalarc arcsetting. setting. This implies that the Balmer Balmer assemblage may Assemblage may represent a distinct tectonic setting from those proposed Assemblage may represent a distinct tectonic setting from proposed for other other B Mesoarchean rocks in the the Superior Superior Province. F'rovince. Sediment geochemistry geochemistry and and depositional depositional environment studies studies along along ¶C — / :t ...,/ with igneous igneous geochemistry will will be ..-:?;_ applied to provide further further constraint constraint on on applied / -, - — the possible tectonic setting of these the possible tectonic setting these — rocks. rocks. — r* '— •M ç' The The Birch-Uchi Birch-Uchi greenstone greenstone belt is located in the central located in central portion portion of of the the W It is Uchi (Fig.1). is Uchi Subprovince Subprovince (Fig.!). comprised comprised of three three volcanic units termed termed the Balmer, Balmer, Nanow Narrow Lake Lake and and spanning Woman assemblages, Woman assemblages, spanning approximately approximately 250 Ma. Ma. The Balmer Balmer assemblage is the assemblage the oldest oldest of these these volcanic units and volcanic units and has has U-Pb U-Pb zircon zircon ages from felsic volcanic horizons that suggest an an age of ca. suggest ca. 2975-2989 2975-2989 Ma Ma (Rogers et al., 2000). The stratigraphy (Rogers et al., The stratigraphy of the the Balmer Balmer assemblage assemblage is is divided divided into four four suites: suites: aalower lowersedimentary sedimentary sequence, aa mafic sequence, mafic volcanic volcanic suite and and petrographically distinct distinct felsic two petrographically felsic volcanic suites suites (Rogers volcanic (Rogers et et a1. al. 2000). 2000). Samples collected for for this study Samples collected study are are located in the the southern southern portion portion of of the the located 1- Location Location and generalized generalized geology geology of of study study Figure 1area and Birch-Uchi Greenstone belt (modified from from assemblage in the Woman Woman Balmer assemblage Stott and Corfu stott Cofi 1991) 1991) River/Bear RiverBear Lake area. These These comprise comprise 16 samples from the lower sedimentary sequence and 34 samples of the mafic mafic volcanic volcanic suite (2000). suite of Rogers Rogersetetal. a1.(2000). , J: - - —— L 144)t,Iun, Lake 55 �Field observations suggest that the the Balmer Balmer assemblage assemblage sedimentary rocks are turbiditic. turbiditic. Sediment geochemistry geochemistrywill will be be applied to constrain the source rocks compositions for Sediment constrain the these sediments. As As no no contact contact with with underlying underlying older rocks has been identified this might provide valuable about the preexisting provide valuable information information about preexisting older older crust. crust. Alternatively, the the may be be derived derived from the Balmer assemblage volcanics volcanics and and this this could support a sediments may hypothesis that that the the Balmer assemblage represents aa continental continental arc arc setting with hypothesis assemblage represents with the the sediments deposited in a fore-arc trench. trench. Volcanic rock samples samples appear The first first is aa Volcanic rock appear to fall fall into intotwo twocompositional compositional trends. trends. The tholeiitic trend trend comprised comprised of of primarily primarily tholeiitic tholeiiticbasalts basaltsand andandesites. andesites. The second tholeiitic second is is aa calc-alkaline trend trend of of andesitic to rhyodacitic The geochemistry of these calc-alkaline rhyodacitic compostion. compostion. The geochemistry of samples will be be applied setting for for these rocks samples will applied to suggest suggest a possible possible tectonic tectonic setting rocks and and implications of this in relation to to other other Mesoarchean Mesoarchean terranes. terranes. 400 C = C C * 300 Rhyolite Tr ac 0.1 N C Rhyodacite/ a >. 200 rachyA Andesite 0.01 N • I SIIJNP1 AndeslQ asa ..I 100 AIk.Bas SubAlkaline Basa t .001 .01 0.1 1 10 0 200 100 300 Zr ZT Nb/Y N bN Lithology Figure 3- Lithology Discrimination diagram for Assemblage Balmer Assemblage volcanics. Circles volcanics. Circles are q w e s are Tholeiitic trend ssquares caic-alkaline trend. calc-alkaline Figure 3-A plot of V vs Zr showing compostional compostional groups groups in Balmer Assemblage Assemblage volcanics. volca~cs. Circles are Tholeiitic trend squares are calc-alkaline calc-alkaline trend. trend. References: References: Hollings, P., Wyman, Wyman, D. D. and and Kerrich, Kerrich, R. R. 1999. Komathte-basalt-rhyolite Hollings. P,, Komatiite-basalt-rhyolite associations northern Superior Province greenstone belts: belts: significance of plume-arc volcanic associations interaction in the the generation generationof ofthe theproto protocontinental continentalSuperior SuperiorProvince. Province.Lithos Lithos 46: 137-162. interaction in 137-162. Rogers, N., McNicoll, V., V., van van Stall, C.R., C.R., and and Todinson, Tomlinson, K.Y. K.Y.2000. 2000. Lithogeochemical Lithogeochemical in the the Uchi-Confederation lJchi-Confederation greenstone greenstone belt, northwestern O Ontario: implications for studies in n h o : implications for Archean Archean Tectonics. Geological 16: 1lip. lp. GeologicalSurvey Surveyof of Canada, Canada,Current Current Research 2000-C 2000-C16: G.M., and andCorfu, Corfu,F. F. 1991. 1991. Uchi Subprovince. Tn: of Ontario, Ontario, special Stott, G.M., In: Geology of volume 4, 4, part part 1. Ontario OntarioGeological GeologicalSurvey, Sumey,pp pp 145-238. 145-238. P.C. and and Chivers, Chivers,K.M. K.M. 1990. 1990. Secular Thurston, P.C. Secular variations in greenstone sequence development emphasizing Superior Superior Province, Province,Canada. Canada. Precambrian Research. 46: 21-58 emphasizing Tomlinson, K.Y., K.Y.,Hughes, Hughes,D.J., D.J., Thurston, Thurston,PP.C., andHall, Hall,R.P. R.P. 1999. 1999. Plume Todinson, C , and magmatism and and cmstal crustal growth at 2.9 2.9 to 3.0 Gain Ga in the Steeprock and Lumby Lake Lake area, area, Western Western Superior Province. Province. Lithos 46: Superior 46: 103-136. 103-136, 56 �PETROLOGYAN1I ANJl PGE POTENTIAL GREENWOODLAKE LA= INTRUSION, INTRUSION, PETROLOGY POTENTIAL OF THE THE GREENWOOD CENTRAL CENTFULDULUTH DULUTH COMPLEX, COMPLEX,LAKE LAKECOUNTY, COUNTY,MINNESOTA MINNFSOTA MILLER, MILLER,James, James,D., D., Jr., Jr., Minnesota MinnesotaGeological GeologicalSurvey, Survey,mille066@tc.umn.edu milleO66@tc.umn.edu This This report report summarizes summarizes the results results of of aa petrologic petrologic and and metallogenic metallogenic study study of of drill drill core coreand and outcrop outcrop samples samples that that profile profile the the Greenwood Greenwood Lake Lake intrusion intrusion (GLI) (GLI) of of the the central centralDuluth Duluth Complex Complex (Fig. 1). The Thelittle littlethat thatwas wasknown knownabout aboutthis thisvery very poorly poorly exposed exposedlayered layeredmafic maficintrusion intrusionprior priorto to (Fig. 1). this this study study came came from from interpretation interpretation of of its itsaeromagnetic aeromagneticsignature, signature,seven sevendrill drillcores, cores,and andsparse, sparse, localized localized outcrop. outcrop. The Thepurpose purposeofofthis thisstudy studywas wastotoestablish establishthe theigneous igneousstratigraphy stratigraphyofofthe theGLI GLI and and to to evaluate evaluate its itspotential potentialfor forPGE PGEreef reefmineralization. mineralization. The The GLI GLI isis an anapproximately approximately two two kilometer-thick, kilometer-thick, sheet-like sheet-like intrusion intrusion that that dips dips gently (approximately (approximately10°) 10")to to the east east and covers an area of about in length) about 300 square square kilometers. For For this this study, study, 19 19bedrock bedrock drill drill cores cores (20 (20 to to 80' 8O'in length) were were acquired acquired in inearly early2002 2002along alongthe thewest—northwest-trending west-northwest-trending Erie/LTV ErieLTV railroad railroad and andpowerline powerline west west of of Lake Lake County County Highway Highway 22(Fig. (Fig. 1). I). Samples from these these cores cores and andfrom fromintermittent intermittent outcrops outcrops along the eastern eastern extent extent of of the the railroad railroad grade grade were weresubjected subjectedtotopetrographic petrographicstudy studyinin transmitted transmitted and reflected light, light, microprobe microprobe analyses of olivine olivine and and pyroxene pyroxene composition, composition, and and whole whole rock rock analyses analyses of of their theirlithogeochemistry, lithogeochemistry, including including platinum, platinum, palladium, palladium, and and gold gold concentrations. concentrations. The The results results of of the the drilling drilling and and petrographic petrographic study study show show that that the the igneous igneousstratigraphy stratigraphy of of the the GLI GLI can can be be grossly grossly subdivided subdivided into into aa lower lower troctolitic troctolitic zone zone(GLtr, (GLtr,0-650 0-650meters), meters),composed composed mostly mostly of of leucotroctolitic leucotroctoliticcumulates, cumulates,aa medial medial gabbroic gabbroiczone zone(GLog, (GLog,650-1800 650-1800meters), meters),composed composed of (GLfg,1800-2130 1800-2130meters), meters), of olivine olivine oxide oxide gabbro gabbro cumulates, cumulates,and and an an upper upper ferrogabbroic ferrogabbroiczone zone(GLfg, composed largely of magnetite magnetite gabbro gabbro (Fig. (Fig. 2). 2). The troctolitic troctolitic zone zone contains contains abundant, abundant, large large anorthositic and oxide gabbroic gabbroic inclusions, inclusions, presumably derived derived from from anorthositic anorthositic series seriescountry country rock. Although Althoughthe theGLI GLIisisaawell-differentiated well-differentiated intrusion intmsion that that formed formedas asan anopen openmagma magma system, system, microprobe data show that cryptic layering trends (such as Fo in in olivine, olivine,Fig. Fig. 2) 2) are are inconsistent inconsistent with formation by in situ crystallization crystallization differentiation. differentiation. This This and and other other evidence evidence (such (such as abrupt abmpt changes in lithology, lithology, leucocratic leucocratic compositions of troctolitic troctolitic rocks, rocks, and and suspect suspectcumulus cumulustextures textures of troctolitic troctolitic rocks) suggest suggest that that the the differentiated differentiated character character of of the theGLI GLIwas wasprobably probablyinherited inherited from from aa deeper deeper crustal crustal magma chamber, chamber, which which was itself itself undergoing undergoingopen opensystem systemdifferentiation. differentiation. The chemostratigraphy chemostratigraphy of chalcophile chalcopbile elements elements through through the the GLI GLI are are difficult difficultto tointerpret interpretinin such such a complex open magma system, but suggest that some potential for PGE reef mineralization may occur in the lower part of the gabbroic zone (Fig. 2). Below Belowthis thislevel, level,recharging rechargingmagmas magmas appear to have been undersaturated in sulfide, and copper copper and and sulfur sulfurconcentrations concentrationshigher higherin inthe the pabbroic zone (above 800 meters) indicate An unexpected unexpected result of this gabbroic indicate intermittent intermittent saturation. saturation. An study was the discovery of aa large, large, sulfide-bearing sulfide-bearing oxide oxide gabbro gabbroinclusion inclusionwithin withinthe thetroctolitic troctolitic zone. Aeromagnetic Aeromagnetic data data suggest suggest that this inclusion is aa conformable conformable tabular mass with a strike length of about 8 kilometers. The magnetic data further suggest The magnetic further suggest that that similar similar rock rock types types form form part of the footwall to the GLI, GLI. The The possibility possibility of of sulfur sulfur contamination contamination in in the the contact contact aureole aureole around this inclusion and along the base of the intrusion intmsion warrants further exploration of these areas for contact-type contact-typeCu-Ni-PGE Cu-Ni-PGE sulfide sulfidemineralization. mineralization. ., Funding for this project was provided to the Minnesota Geological Geological Survey Survey by aa grant grant from from the Minnesota State Legislature Legislature on the recommendation of the Minerals Minerals Coordinating CoordinatingCommittee. Committee. 57 �Generalized Generalized geology geology of of the the Greenwood GreenwoodLake Lake intrusion intrusionand and the the central ceneal Duluth Duluth Complex. Small Small dots denote denote drill d i l l hole hole and and Complex. diamonds denote denote outcrop outcrop locations locations along along diamonds ErieLTV railroad railroad tracks. tracks. Long Long dashed dashed lines lines Erie/LTV denote denote faults. faults.Intrusive Intrusiveunits unitsare: are: Figure 1. 1. Figure GLtr—-GLI GLtr-GLl troctolitic troctoliticzone zone GIog-GLIgabbroic gabbroiczone zone GIog—GLI GLtg—GLI GLfpGLlferrogabbroie ferrogabbroiczone zone MW—Mt. MW-Mt. Weber Weber granophyre granophyre CLLS—Cloquet CLLS-Cloquet Lake Lakelayered layeredseries series BEI-Bald Eagle Eagle intrusion intrusion BEI—Bald SKI—South SKI-South Kawishiwi Kawishiwi intrusion intrusion PAl—Partridge PRI-Partridge River Riverintrusion intrusion WMI—Western WMI-Western Margin Margin intrusion intrusion sew Layered Series Ferrogabbroic Femgatbr& Gabbroic Gabbmic S T-IIrc L____J Trociolluc Fetsc Series ri Morihositic l___J Series Norih Shore a Group Virginia Forniston Biwabik ranFormation Giants Range I,-: Granite o0 10 10 20 20 Kilometers Kilometers Sample locationo I I Au concentrations of Fo Foin in olivine olivine and and of of Cu, Cu, Pt + Figure 2. 2. Chemostratigraphy Chemostratigraphy of + Pd, Pd, and and Au wncentrations through thmugh the the Figure locations of of drill drill core Lake intrusion. intmsion. Stratigraphic Stratigraphic locations core (boxes) (boxes) and and outcrop outcrop (diamonds) (diamonds) Greenwood Lake samples and general are shown shown in in the left columns. g e n e d lithostratigraphy lithostratigraphy are columns. Large Largeinclusions inclusionsofofanorthositic anorthositic (ox gb) gb) are denoted. Abrupt series rocks (AS) and oxide gabbro (ox Abmpt increases increasesin inCu/Pd CuPd(arrows) (mows)may maymark mark sulfide saturation events. The The zone found most favorable favorable to to host host PGE PGE reef reef mineralization mineralizationis is identified. identified. 58 �Stratigraphy and the St. St. Croix Croix horst, horst, northwestern northwestern Stratigraphy andstructure structureof ofKeweenawan Keweenawan rocks of the Wisconsin U.S.Geological Survey, Sun'ey, Reston, VA S.W. Nicholson, and W.F.Cannon, U.S.Geologica1 The St. St. Croix Croix horst horst is is the the partially inverted inverted central graben graben of the the Midcontinent Rift System System (MIRS)that thatextends extendssouthwestward southwestwardfrom from western westernLake Lake Superior. Superior. It It is is bounded by the (MRS) Douglas fault on the the northwest northwest and and the Atkins Lake fault on the the southeast. southeast. Both Both are arenow now reverse faults, but may have been graben-bounding normal faults during rifting and and northern limit of of the the horst horst is is White's White's Ridge, a subsurface basement high volcanism. The northern evident in both seismic seismic and and gravity gravity data, data, which did not subside subside substantially substantiallyduring duringrifting rifting and against which rift volcanic and sedimentary rocks pinch out or become much much thinner. thinner. Lake Superior from the St. Croix White's Ridge Ridge effectively effectively separates separates the MRS in western Lake horst and the volcanic, sedimentary, sedimentary, and structural history of the two rift segments segments differ differ in several aspects. High-resolution aeromagnetic, gravity, and seismic data permit the the tracing of flow sequences for long distances and to great depth. This geometry geometry combined combined with with the the chemistry of the volcanic rocks allows us us to to decipher decipher aa volcanic volcanic stratigraphy stratigraphy in in spite spite of of widespread cover by glacial deposits and Paleozoic sedimentary rocks (Cannon (Cannon et et al., al., 2001). interpretations (Chandler Our interpretation, aided by previous gravity and seismic interpretations (Chandleret et al., al., is that that the original structure of of the St. Croix horst was an asymmetric graben, or 1989), is possibly a half graben, like those of the Lake Superior portion of the MRS. MRS. The The Lake Lake Owen Owen fault was a major growth fault fault on the southeast southeast side side of the the graben graben and and the the volcanic volcanicfill fill fault, The Douglas fault on the thickened toward and terminated against the fault. the northwest northwest side side of of the horst is not clearly a growth feature and may be simply a thrust formed formed during during rift rift inversion. Thrust displacement on the Douglas Douglas fault fault must must be be 20 km or more because it juxtaposes of the base of a thick volcanic sequence sequence over the younger younger Bayfield Bayfield Group. Group. Cannon et al. (2001) (2001) and Nicholson et al. (2001) used chemical chemical and and aeromagnetic aeromagneticdata datato to define the Minong Volcanics, the underlying Clam Clam Falls Falls Volcanics, and the Chengwatana Volcanics as three formations making up the graben-filling graben-filling volcanic volcanic sequence. sequence.The Thethree three have similar chemistry, chemistry, but were defined defined by structure structure and and geochronology. geochronology.The Thethree-part three-part division no longer seems justified justified and the Chengwatana and Clam Falls Volcanics are Volcanics, as earlier earlier defined, were restricted restricted combined into a single unit. The Chengwatana Volcanics, to a fault-bounded belt belt between between the theDouglas Douglasand andPine Pinefaults faultsand andtheir theirstratigra'phic stratigrahic not known known directly. directly. We now believe, based on seismic relationships to other volcanics were not data, that the Pine fault does not extend into the the northern northern part of of the horst, where the previously defined Chengwatana and Clam Falls units units appear to be a continuous depositional sequence of compositionally indistinguishable flows that we propose be called entirely Chengwatana. basalts about Chengwatana. The Minong Volcanics, a sequence sequence of low-Ti02 low-TiOibasalts about 33km kmthick, thick, overlie the Chengwatana, Chengwatana, along an apparent low angle angle disconformity disconforrnitybased based on onaeromagnetic aeromagnetic form lines. These form lines also show a disconfonnity disconformity within the Minong volcanics on the of the the Ashland Ashland syncline. syncline. A A lower lower unit, unit, not not present present on the northwest northwest limb, is southeast limb of mostly high-Ti02 high-Ti02 basalt. basalt. Based Based on on the the presence presence of of abundant abundanthigh-TiO2 high-Ti02 basalts basaltsand andmore more magmatic center center was was active in this area sometime evolved rocks, we infer that a localized magmatic flow in in the the upper upper part of of this sequence. A second, but before 1095 1095 Ma, the age of a rhyolite flow may have have existed existed on on the western margin of the graben near apparently older, volcanic center may 59 �_____ the Amnicon Amnicon Complex Complex where the Chengwatana Volcanics are mostly high-Ti02 high-Ti02basalts, basalts, andesites and rhyolites. rhyolites. Clastic sedimentary sedimentary rocks of the Oronto Group overlie the volcanic rocks. Only the basal unit, the Copper Copper Harbor Conglomerate, Conglomerate, is preserved in most of the St. St. Croix horst where as as much as 2 km of sandstone and conglomerate lie along the axis of the Ashland syncline. The krn sandstone conglomerate Ashland syncline. Copper Harbor thins to only a few tens of meters toward the northern end of the horst in the same areas where the volcanic section also shows substantial thinning. Apparently the area now comprising comprising the northern part of the St. Croix horst did not subside nearly as deeply deeply as parts farther to the southwest. southwest. This relatively positive relief persisted throughout throughout volcanic volcanic activity and deposition deposition of the Copper Harbor Conglomerate. Conglomerate. The overlying overlying Nonesuch Shale Shale maintains a relatively relatively uniform thickness around the northern part of the Ashland syncline, syncline, suggesting suggesting that that the the topographic topographic high high was was buried buried by by that that time. time. 91'00' EXPLANATION EXPLANATION 4V00' Bayfield and BayfieldGroup Group and equivalent sandstones Freda Sandstone Nonesuch Shale copper Harbor Conglomerate Gabbro and granophyre Minong Volcanicslow-Ti basalts Minong volcanicshigh-Ti basalts Chengwatana volcanics Kallander Creek Kallander CreekVolcanics Volcanicl Siemens Creek Volcanics volcanics Siemens Archean and Paleoproterozoic Paleopmterozoic 46'OO,i__ 46'O 92'OO' 92W 0 rocks 91°00 90 30 KM WY., Daniels, Cannon, Cannon, W.F., Daniels, D.L., D.L., Nicholson, Nicholson, S.W., Phillips, J., Woodruff, Woodruff, L.G., Chandler, Chandler, V.W., V.W., Morey, Morey, G.B., G.B., Boerboom, T., Wirth, K.R., and Mudrey, M.G., MG., Jr., Boerboom. Jr., 2001, 2001,New New map mapreveals revealsorigin originand andgeology geologyof ofNorth North American v. 82. 82, no. no. 8, 8, pp. pp. 97-101 97-101 American Midcontinent Midcontinent rift: rift: EOS, EOS, v. V.W., McSwiggen, P.L., P.L., Morey, Morey, G.B., GB., Hinze, W.J., W.J., and Anderson, R.R., R.R., 1989, Interpretation of Chandler, V.W., seismic seismic reflection, gravity, and magnetic data across Middle Proterozoic Mid-continent Rift system, northwestern Wisconsin, eastern Minnesota, and central Iowa: American Association of Petroleum Petroleum Geologists Geologists v. 73, 73, p. p. 261-275. 261-275. Bulletin, v. SW., Boerboom, W.F., Wirth, K. and Isachsen, C.E., C.E., 2001, A new look at the the 1.1 Ga Ga Nicholson, S.W., Boerboom, T., Cannon, W.F., Chengwatana horst, Minnesota Minnesota and Wisconsin, Institute Institute on Lake Superior Superior Geology, Chengwatana Volcanics in the St. Croix horst, 1,p. 71-72. 71-72. v. 47, part 1, 60 �TheRare Rareand andExotic ExoticMineralogy Mineralogyof of the theWestern WesternSubcomplex Subcomplexof of the the Deadhorse DeadhorseCreek Creek The Diatreme,Northwestern NorthwesternOntario. Ontario. Diatreme, G. Potter Potterand andRoger RogerH. H. Mitchell Mitchell EricG. Eric egpotter@mail.lakeheadu.ca egpotter@mail.lakeheadu.ca Dept. Dept.of of Geology, Geology,Lakehead LakeheadUniversity, University,955 955Oliver OliverRoad, Road,Thunder ThunderBay, Bay,ON. ON.P7B P7B5E1 5El The Themain main mineralized mineralizedzone zoneof ofthe thewestern westernsubcomplex subcomplexof ofthe theDeadhorse DeadhorseCreek Creekdiatreme diatreme exhibits complex complexmineralization mineralizationinvolving: involving: first first and and second second order ordertransition transitionmetals metals exhibits (specifically PEE; Be; Th; and U. The (specifically Sc, Ti, V, Cr, Mn, Fe, Zr and Nb); REE; Themineralization mineralization is Nbis manifested manifested by by the the presence presence of of the the following followingminerals: minerals: thortveitiite, thortveitiite,Sc-V-aegirine, Sc-V-aegirine, NbV-rutile, V-mtile, V-crichtonite, V-crichtonite, Ba-Mn-hollandite, Ba-Mn-hollandite, zircon, zircon, monazite-Ce, monazite-Ce, xenotime-Y, xenotime-Y, uraninite, uraninite, thorite, thorogummite, thorogurnmite, barite, barite, barylite, barylite, tyuyamunite, tyuyamunite, phenacite, phenacite, pyrite, pyrite, hematite, hematite, thorite, magnetite magnetite and and several several as as of of yet yet unnamed unnamed mineral mineral species species (Platt and Mitchell, Mitchell, 1996; 1996;Smyk Smyk et al., 1993; this study). Of interest in this presentation are: Nb-V-rutile, crichtonite et al., 1993; this study). Of interest in this presentation are: Nb-V-mtile, crichtoniteand and Sc-V-aegirine. Sc-V-aegirine. The The Nb-V-rutile Nb-V-mtile isis enriched enriched in in Cr2O3, with concentrations concentrations reaching Cr203, with reaching 30 6.49 6.49 wt.%. wt.%. The enrichment enrichment of of - Cr2O3 and Nb205 is similar to that Cr203 and Nb2O5 similar to that of of rutile mtile reported reported in in alkaline alkalineigneous igneous :1 20 rocks, as illustrated in an atomic rocks, as illustrated in an atomic - percent plotofof~Cr percent plot + r 3 4++' Nb5 Nb5+++ Ta5 ~ a ^ 1991). vs. Ti4 (Haggerty, vs. ~ i ^ (Haggerty, 1991). z 10 + However, Nb205 contents contents are are However, the the Nb2O5 - unusually unusually high high compared comparedto toalkaline alkaline M ~ ÑT ~ ~ ~igneous & ~ rocks igneous rocks in in general, general, with with " 00 29.32 concentrations reaching 95 100 80 85 90 50 55 55 60 65 70 75 75 80 85 90 95 100 concentrations reaching 60 65 70 50 Ti4 (Atomic%) Ti4* ( A ~ O ~%)C wt.%. Such such Nb2O5 Nb205 contents contents&re re wt.%. I similar similar to those those reported in in ilmenorutile, ilmenorutile, whiph which is historically found in pegmatites. pegrnatites. Also Also unique to the rutile is the distinct the Deadhorse Deadhorse Creek: Creek futile distinct enrichment enrichment of V2O3 V203 (up to 10.52 10.52 wt.%) and and the the lack lack of of tantalum. tantalum....' wt.%) : The Sc-V-aegirines Sc-V-aegirines present present at at Deadhorse Deadhorse Creek Creek contain contain the the highest highest reported reported The concentrations of Sc2O3 and and V203 V2O3(16.46 (16.46and and11.99 11.99wt.%, wt.%,respectively). respectively). The only only other other have been occurrences of of VV- and andSc-enriched Sc-enriched aegirine aegirine have been reported reported from from alkaline alkaline occurrences metasomatites metasomatites associated with iron-ore deposits in Ukraine (Valter et al., 1994; 1994;Pavlishin Pavlishin et al., presence thortveitiite and al., 2000). 2000). OfOfnote noteisisthethe presenceofofboth both thortveitiite(Sc2Si2Oi) (Sc2Si2O7) andSc-enriched Sc-enriched aegirine within the main mineralized zone. zone. Although Although the the source source of the the Sc Scin inthe theaegirine aegirine remains conjectural,itit appears appears that that the the Sc, V and Na remains somewhat somewhat conjectural, Na was was scavenged scavengedfrom from alteration of the main mineralized mineralized zone zone by Fe-rich fluids. fluids. The V-rich V-rich crichtonites crichtonites are best termed termed vanadium-rich vanadium-rich analogues of crichtonite-(Sr) crichtonite-(Sr) and and senaite-(Pb). The in the the crichtonites crichtonites isis peculiar, peculiar, as as the the presence of of Nb205in The enrichment enrichment in Nb2O5 Nb has has been been aa distinguishing distinguishing feature feature of of the the mantle-derived mantle-derivedend end members memberslindsleyite-(Ba) lindsleyite-(Ba) 61 �the crichtonites plot ininthe Interestingly, the theupper-mantle upper-mantle and mathiasite-(K) mathiasite-(K) (LIMA). (LIMA). Interestingly, and LIMA quadrant of FeO + Fe203 + MgO vs. Ti02 (Haggerty, 1991), near + F e B 3 + MgO vs. Ti02 (Haggerty, 1991), near the the LIMA LIMA LIMA quadrant of compositions compositionsdue dueto tothe thereplacement replacementof of iron ironby by vanadium. vanadium. The mtiles and and The Nb-enriched Nb-enriched rutiles have believed to crichtonite are crichtonite are believed to have formed fonned relatively relatively early early in in aa 30 30 crichtrmite (s$ Crichtnnite(Sr) multistage-alteration Armalcolite Ooadrant • (?EE) multistage-alteration sequence sequence of of the the diatreme — Deadhorse Creek &n,irc am,(Pb) w). Deadhorse Creek diatreme by by O 25 reaction reaction of of stoichiometric stoichiometricrutile mtilewith with Lovamgitc (Ca) + hydrous hydrous alkaline alkaline solutions solutions ennched enriched 20 in Nb Nb and and V. V. These These hydrous hydrous alkaline alkaline solutions solutions likely likely also alsoaltered altered Armalcolite Ouandrant DHC Crichinnite 15 zircon zircon to to an an unnamed unnamed hydrated hydrated awhich is zirconosilicate, calcium zirconosilicate, which is — calcium LIMACrptonites— with the found found in in association association with the 10 72 64 68 56 60 52 52 56 60 64 68 crichtonite and rutile. crichtonite and mtile. Textural Textural and and TtO2çVt. /o) TiO, (Wt.%) suggest that compositional data compositional data suggest that subsequent alteration alteration formed fonned the the Sc-V-aegirines Sc-V-aegirines and and imparted imparted the the pervasive pervasive subsequent hematitization hematitization to to the the main main mineralized mineralizedzone. zone. I I I I I I n - ~ i ~ b Crichtonite ~Crichtooite ~ ~ i t i ~ Non-Kimberlitic - - - p • - — I I I I I ' References References of the upper Oxide Minerals: Minerals: mineralogy of upper mantle. mantle. In: In: Oxide Haggerty, S.E. S.E. (1991): (1991): Oxide mineralogy petrologic and and magnetic magnetic significance. significance. Reviews Reviews in in Mineralogy, Mineralogy, 25, 25,Mineral. Mineral. Soc. Soc. Amer., 335-416. Amer., 335-416. Platt, Platt, R.G. R.G. and and Mitchell, Mitchell, R.H. R.H. (1996): (1996): Transition Transition metal metal rutiles mtiles and andtitanates titanatesfrom fromthe the Miner. Miner. Deadhorse Creek Diatreme complex, northwestern Ontario, Canada. Deadhorse Creek Diatreme complex, northwestern Ontario, Canada. Mag., 403-413. 60,403-413. Mag., 60, Pavlishin, Baldan, F.G., F.G., Bugaenko, V.M., Voznyak, Voznyak, D.K., D.K., Galaburda, Pavlishin, V.1., V.I., Baklan, Bugaenko, V.M., Galaburda, Yu, A., A., G.O., Mel'nikov, Kulchic'ka, Dekhtulins'ky, E.S., Donskey, O.M., Krivdik, S.G., Krivdik, G.O., Mel'nikov, Donskey, V.S., Radzivill, A, Ya. Ya. And And Zimbal, Zimbal, S.M. S.M. (2000): (2000): Science-based Science-based perspectives perspectives of of improvement of mineral mineral resources resourcesor orrare raremetals metalsinin Ukraine. Ukraine. Mineral., Journal, improvement of 22, no.1, no.l,5-20. (in Russian) Russian) 22, 5-20. (in Smyk, M.C., Taylor, R.P., Jones, Smyk, M.C., Taylor, R.P., Jones, P.C. P C . and and Kingston, Kingston, D.M. D.M. (1993): (1993): Geology Geology and and geochemistry geochemistry of the West Dead Horse Horse Creek Creek rare-metal rare-metal occurrence, occurrence,northwestern northwestern Ontario. Explor. Mining. Geol., 2, no. 3, 245-25 1. Ontario. Explor. Mining. Geol., 2, no. 3,245-251. Valter, V.M., Sharkin, O.P. O.P. and Yakolev, Valter, A.A., Khomenko, V.M., Yakolev, V.M. V.M. (1994): (1994): AA vanadian vanadian aegirine in alkaline metasomatites from Zheltye Vody. Vody. Doklady Doklady Akademii Akademii Nauk Nauk Ukrainy, Ukrainy, No. 3, 3, 110-116. 110-116.(in (in Russian) Russian) 62 �Sibley Sibley Basin Basin sediment sediment provenance provenanceusing using zircon zircon and andwhole whole rock rockgeochemical geochemical methods: methods: Possible Possible source sourceareas areasof of the thePass PassLake LakeFormation Formation Richardson, Hollings, P.P. (Department Geology, A.,Fralick, Fralick,P.,P.,and and Hollings, (Departmentofof Geology,Lakehead LakeheadUniversity, University,955 955 Richardson,A., Oliver OliverRd., Rd., Thunder ThunderBay, Bay,Ontario, Ontario,P7B P7B5E1, 5E1,Canada; Canada,ajrichar@mail.lakeheadu.ca) airichar@mail.lakeheadu.ca) The TheSibley SibleyGroup Groupconsists consistsof of Proterozoic Proterozoicsediments sedimentsthat that outcrop outcropdiscontinuously discontinuouslyover overaa 15000 15000sq. sq. km km region region in in the the area area surrounding surrounding central central and and southern southern Lake Lake Nipigon. Nipigon. Its Its age age is is bracketed Redstone Point Point Complex Complex(1537 (1537 bracketedby by the theunderlying underlyingRedstone ++lo/-2 101-2 Ma; +I-33 33Ma Ma Ma;Davis Davisand andSutcliffe, Sutcliffe.1985) 1985)and anda a1339 1339+1Rb-Sr Rb-Srage ageon ondiagenetically diageneticallyaltered alteredSibley Sibleysediments sediments(Franklin, (Franklin, 1978). SibleyGroup Groupwas was divided divided into into three three formations: formations:the the 1978).The The Sibley Kama Kama Hill Hill Formation Formation(top), (top),the theRossport RossportFormation, Formation,and and the the Pass PassLake LakeFormation Formation(bottom), (bottom),by by Franklin, Franklin, et et al. al. (1980). (1980).The The Kama Kama Hill Hill Formation Formationconsists consistsof of aalaminated laminatedshale shalefacies, facies,the the Rossport Rossportof of mudstone mudstoneand and stromatolitic stromatoliticfacies, facies,and and the the Pass Pass Lake Lakeof of aaconglomeratic conglomeraticfacies faciesand andaaplane-bedded plane-beddedor orcrosscrossbedded bedded sandstone sandstonefacies facies(Cheadle, (Cheadle,1986). 1986).This Thisstudy study investigates investigatesthe thesources sourcesthat thatfed fedsediment sedimentto tothe thePass PassLake Lake Formation Formationin in the thesouthern southernportion portion of of the the basin. basin. 30km LEGEND Proterozoic 1097 Ma rn Li_J Oslar Group 1110 Ma DI. base :I. ,1339Ma Regional Regional granitic granitic sources sourcesmay may include: include: the the Mesoproterozoic Mesoproterozoic Redstone Redstone Point Point anorogenic anorogenic intrusion, intrusion, Sample Locations Neoarchean Neoarchean peraluminous peraluminous Quetico Queticogranites, granites, and and Granite •,, Redstone Point Point Granite McKenzie McKenzie granites. granites. Of Ofthese, these,the the Redstone Redstone Point Point isis more more Artisan highly evolved than the others and contains abundant highly evolved than the others and contains abundant • Regional Granites ~ ~ it^^~ l ~ ~ ~ l Granitic Rocks Metasedimentaty zircon zircon and and aa distinct distinctgeochemical geochemical signature signaturewith withvery very elevated PassLakeFm. elevated values values for forthe thehigh highfield field strength strengthelements elements Rocks (HFSE). (HFSE). Samples Sampleswere were collected collectedfrom fromsurface surfaceexposures exposuresatatseveral several Figure 1. 1. Regional Regional geologic geologic map map with with sample sample Figure locations (Fig. 1). Representative samples of the Pass Lake locations (Fig. 1). Representative samples of the Pass Lake locations. locations. Formation Formation of of the the Sibley SiblevGroup Grouowere were taken taken from from aa cliff cliff section section directly directlyacross acrossfrom fromPass PassLake Lakeon on Hwy. Hwy. 587. 587. Individual Individualbeds beds were were grouped grouped into into assemblages assemblages consisting of up to 16 16 beds. Bed Bedthickness thicknessbecame became finer finer and and thinner up section. AAtotal totalof of 26 grained sandstone. sandstone. Two 26hand hand samples sampleswere were obtained from the Pass Lake cliff and consisted of fine to medium grained Two additional Pass Lake Formation samples were obtained from road cuts cuts further furtherup-section up-section that that consisted consistedof of medium medium grained grained sandstone. sandstone. Additional granitic samples were were obtained from road cuts along Hwy 11/17 11/17 and each location. Samples and Hwy. 527 (Fig. 1). One One sample sample was was taken taken from fromeach Samples of of Redstone Point sandstones, and and granite granite samples samples were were previously obtained by by P. P. Fralick from from the the English English Bay Bay region region of of Lake Lake Nipigon Nipigon (Fig. (Fig. 1). 1). S Sibley Graup 1537 Ma Granite and Rhyolite 1900 Ma AnImikle Group • 1 I - Figure x-Ray Figure 2. 2. Backscatter X-Ray SEM-EDS SEM-EDSimage image of of aa zircon zircon AR-01. fromsample sampleAR-Ol. from ICP-AES Plasma -- Atomic Emission ICP-AES (Inductively Coupled Plasma Emission Spectroscopy) Spectroscopy) Samples were cut into approximately 4 x 3 x 0.5 cm sections and crushed to included to aa fine fine powder nowder of <30 microns. Chemical Chemicalpreparation preparation included - hydrofluoric hydrofluoric acid acid digestion digestion to to remove remove all all silica silica and and allow allow complete complete solution solutionof of samples. Prepared samples were analysed at the Lakehead University Prepared samples were analysed at the Instrument Laboratory. Laboratory. 63 �A SEM-EDS SEM-EDS (Scanning (Scanning Electron ElectronMicroscope Microscope- - Energy EnergyDispersive Dispersive X-Ray X-Ray Microanalysis) Microanalysis) Samples Samples were were ground ground to to 30 30micron micron thin thinsections sectionsand andcut cutinto into discs discs suitable suitable for for the the SEM SEM stage. stage. Before Beforeanalysis, analysis,samples samples were carbon coated to prevent charge build- up while being analysed. Samples analysed for with were analysed. carbon Samples coatedwere were to prevent analysed charge for50 build50seconds seconds up while withan being an accelerating voltage of 20 KeV, and a beam current 0.475 accelerating voltage of 20 KeV, and a beam current ofof0.475 t, ..'$?Â¥: . .:. pA using using aa JEOL JEOL 5900 5900 SEM SEMwith withaasystem systemresolution resolutionof of139 139 pA . - .. eV, at at Lakehead Lakehead University Instrument Instrument Laboratory. Laboratory. Images Images eV, . .A* .:.. . . were taken using a backscatter-electron detector. Zircons were were taken using a detector. Zircons were .. analysed Zr,Y, Y,Th, Th,U, U,and andHf. Hf. analysed for for five five elements: elements: Zr, The The use use of of zircons zirconsin insediment sedimentprovenance provenancestudies studieshas hasbeen been 10Y+TKU IO-Y+T~+U WIO Hrlo limited to to work work done done by by Owen Owen(1987) (1987)which whichinvolved involved limited employing employing hafnium hafnium content of of detrital detritalzircons zirconsin indetermining determining zirconsfrom from Figure Figure3.3. SEM-EDS analyses of zircons the upper Jackfork the source source of of the hupper JackforkSandstone Sandstoneand andthe theParkwood Parkwood Pass PassLake LakeFm Fm sandstones sandstones(points), (points)'Redstone Formation. He Hecame cameto tothe theconclusion conclusionthat thathafnium hafniumcontent content Formation. Point Pointsandstones sandstones(squares), (squares),Redstone RedstonePoint Point of of these these zircons zircons agreed agreed with with optical opticaland andcathodoluminescence cathodoluminescence (+),and andregional regionalArchean Archeanand and Granites(+), Granites modal modal analyses, analyses, and and is is aa viable viable method methodfor forprovenance provenance Neoarchean Neoarcheangranites granites(triangles), (triangles). determination. determination. This This study study is is the the first first to touse useSEM-EDS SEM-EDSmethods methodsasaswell wellas as analyses for Y, Th, and U. Fig. 3 shows zircon analysis results. The majority of zircons plot at Zr/Hf ratio analyses for Fig. 3 shows zircon analysis The majority of zircons plot at Zr/Hf ratio of of approximately Y, Th, Th,and and U, U, but but aa significant significantpopulation populationshow showaaY, Y,Th, Th,UU approximately 40 40 with with relatively relatively low low amounts amounts of of Y, enrichment trend. The Thegeochemical geochemical signature signature of zircons from from both sandstones sandstones and and granites granites show show similarity, similarity, and and indicates indicates local local sourcing sourcingof of sediment sediment • £ with Archeanand and with aa possible possible influence influence of of regional regionalArchean Proterozoic Proterozoic felsic felsic igneous igneous intrusives. intmsives. 2000 Whole Whole rock rock interpretation interpretation of ofICP-AES ICP-AES ppmZr/%T02 ppm Zr/%T102 geochemistry geochemistry (Fig. (Fig. 4) 4) trends trends agree agree with with SEM SEM 1000 loGo distribution within samples. Immobile elemental distribution within samples. Immobile elemental element element ratios ratios of of the the Pass Pass Lake Lake sandstones sandstonestend tendto to - A fall on on aa mixing trend between between enriched enrichedand and nonnonfall I 125 75100 25 50 enriched 0 25 wm 75 Nb/%Ti02 ' 150 enriched sources. This Thisstudy studyhighlights highlights the the possible possible usefulness of using SEM-EDS generated data usefulness of using SEM-EDS generated datain in concert concert with with more more traditional traditionalchemical chemicalanalyses analysesin in Figure Figure4. 4. Immobile Immobileelement elementplot plotofofICP-AES ICP-AESanalyses. analyses. provenance provenancestudies. studies, Pass PassLake Lakesandstones sandstones(points) (points)plot plotininsimilar similarfield fieldtoto sandstones derived from, and overlying Redstone Point sandstones derived from, and overlying RedstonePoint granite granite (squares). (squares). Redstone (+), and and other other Redstonepoint point granite granite (+), granites granites (triangles) (triangles)are arealso alsoshown. shown. . I I I , 1 . A I I I 1 References References Cheadle, Alluvial-playasedimentation sedimentationininthe thelower lowerKeweenawan KeweenawanSibley SibleyGroup, Group,Thunder ThunderBay BayDistrict, District, Cheadle, BA. B.A.(1986) (1986)Alluvial-playa Ontario; Journal of of Earth EarthSciences, Sciences,v.v.23, p.527-542. Ontario; Canadian Journal 23, p. 527-542. Davis, Davis, D., and Sutcliffe, Sutcliffe,R., (1985) (1985) U-Pb U-Pb ages ages from from the Nipigon Plate Plate and Northern Lake Lake Superior. Superior.Geological GeologicalSociety Society of of America 1572-1579. America Bulletin, Bulletin, 96, 96, 1572-1579. Franklin, in Rubidium-strontium Rubidium-strontiumisochron isochron age age studies, studies. Report Report2,2, geological geological Franklin, J.M., (1978) (1978)The The Sibley Sibley Group, Group, Ontario; Ontario; in Survey of Canada, Canada, Paper Paper77-14, 77-14,p.p. 31-34. 31-34. Survey Franklin, McIlwaine, W.H., W.H., Poulsen, Poulsen, K.H. K.H. and and Wanless, Wanless. R.K. R.K. (1980) (1980)Stratigraphy Stratigraphyand anddepositional depositionalsetting settingofofthe the Franklin, J.M., Mcllwaine, Sibley 17,p.633-651. p.633-651. Sihley Group, Group, Thunder Thunder bay District District Ontario, Ontario, Canada; Canada; Canadian Canadian Journal Journal of of Earth Earth Sciences, Sciences,v.v. 17, Owen, Sedimentary Petrology, Vol 57, No.5., NO.^., 1987., 1987..p.p.831-838. 831-838. Owen, M. (1987) (1987) Hafnium in Detrital Zircons: Journal of Sedimentary Vol57, 64 �Magnetostratigraphic and Group A Magnetostratigraphic and Secular SecularVariation Variation Study Study of the the Sibley Group Rogala, P. and Borradaile, G. (Department of Geology. Lakehead University, Thunder Rogala,B., B.,Fralick, Fralick, P. and Borradaile, G. (Department of Geology, Lakehead University, ThunderBay, Bay, Ontario, P711 SEI, brogala@lakeheadu.ca) brogala@lakeheadu.ca) P7B 5E1, The Sibley Sibley Group Group is is aa red red bed bed sequence sequence that that was was deposited deposited in in aasubsiding subsidingintracratonic intracratonic basin (Fralick and Kissin, 1995) 1995) overlying, in part, a 1537+10-2 1537+10-2 Ma (Davis (Davis and and Sutcliffe, Sutcliffe, 1984) 1984) anorogenic granite-rhyolite complex. The Group was previously divided into three main anorogenic granite-rhyolite complex. The Group previously divided three main Rossport, and and Kama Kama Hill. Hill. An unnamed Formations: Pass Lake, Rossport, unnamed Formation and the Nipigon Bay Formation have have recently recently been been added. added. The Formation The Pass Pass Lake Lake Formation Formation consists consists of of the the conglomeratic conglomeratic Loon Lake Lake Member of the Loon Member and the the sheet-like sheet-like sandstones sandstones of the Fork Fork Bay Bay Member, Member, representing representing aa braided fluvial environment environment (Cheadle, (Cheadle, 1986). 1986). The Rossport Formation Formation is separated separated into the the braided Channel Island, Island, Middlebrun MiddlebrunBay, Bay,and andFire FireHill HillMembers. Members. The Channel Member is is a Channel Channel Jsland Island Member cyclic dolomite-shale dolomite-shale unit unit interpreted interpretedtoto be be playa cyclic playa lake lake sediments sediments (Cheadle, (Cheadle, 1986). 1986). The Middlebrun Bay Bay Member, considered a marker marker bed bed for for the Sibley Group, is aa stromatolitic Middlebrun stromatolitic unit unit that represents a migrating strandline. The The Fire Fire Hill Hill Member Member consists consistsof of mudcracked mudcrackedred red silt siltwith with mudchip conglomerates and sand sand sheet sheet incursions. incursions. It signifies a time of of tectonic tectonic tilting tilting of the the basin. The Kama basin. Kama Hill Hill Formation Formation is not not subdivided, subdivided, and is is composed composed of of purple purple shales shales and and siltstones interpreted as mud flat flat deposits deposits (Cheadle, (Cheadle, 1986). 1986). The The unnamed Formation is divided divided two unnamed unnamed Members. Members. These into two These represent represent a deltaic deltaic and fluvial fluvial environment. environment. The The Nipigon Nipigon Bay Formation Formation consists of of cross-stratified sandstonebeds, beds, and and is is thought to denote Bay cross-stratified sandstone denote an an acolian aeolian environment. environment. Samples were were taken taken from Samples from the Pass Pass Lake, Lake, Rossport, Rossport, Kama Kama Hill, Hill, and and Nipigon Nipigon Bay Bay Formations for a paleomagnetic study. study. The unnamed Formation was not sampled due to the lack of exposure. of exposure. The ThePass PassLake, Lake,Kama Kama Hill, Hill, and and Nipigon Nipigon Bay Bay Formation Formation were were used to to conduct conduct a preliminary of the the Sibley Sibley Group. Group. The TheRossport RossportFormation Formation was was preliminary study of the magnetostratigraphy of sampled from unoriented drill core, core, thus could only be used to study study secular secular variation. variation. The paleopoles calculated from the Pass Lake, Lake, Kama Kama Hill, Hill, and andNipigon NipigonBay BayFormations Formations have been been plotted along an apparent apparent polar wander path (APWP) defined defined by Elston Elston et et at. al.(2002) (2002) (Figure 1). 1). The samples samples from from the Pass Pass Lake Lake Formation Formation have been divided into into sample sample groups groups corresponding to Quarry Island, Transitional to to the Rossport Formation, and and an an outcrop outcrop atat Pass Pass The paleopole of the with a diagenetic Lake. Lake. The paleopole of the Quarry Quarry Island Island Group Group corresponds corresponds with diagenetic event at at 1978), and and the approximately approximately 1339±33 1339±3 Ma Ma (Franklin, (Franklin, 1978), the latter latter two two groups groups have havepaleopoles paleopoles associated with an The Kama has an older associated with an early earlyKeweenawan Keweenawan overprint. overprint. The Kama Hill Formation Formation has older discordant paleopole and and a younger younger paleopole paleopole that that isis located located within within the 1500 Ma section of the discordant paleopole that the the Sibley Sibley Basin Basin formed formed prior prior to to this, as is apparent polar polar wander path. is apparent path. This This suggests suggests that supported by by the recent discovery of sedimentary xenoliths within the 1537 supported 1537 Ma Ma Redstone Redstone Point Point granite. that lie on the APWP granite. The The Nipigon Nipigon Bay Bay Formation Formation has paleopoles paleopoles that APWP near near 1400 1400 Ma Ma and and 1100 Ma. Ma. The The first first paleopole paleopole may may be primary or related to the diagenetic diagenetic event that affected the Pass Lake samples at 1339 1339 Ma. The Thelatter latter paleopole paleopole correlates correlateswith with the the Osler OsierVolcanics. Volcanics. Formation revealed a The paleomagnetic study on a 90 cm core section from the Rossport Formation When this this curve was compared secular variation curve. curve. When compared to typical typical secular secular variation variation curves curves (Butler, 1998; Tauxe, Tauxe, 1998), the the time-span time-spanfor for Sibley Sibleydeposition depositioncan canbe beestimated. estimated. The 90 cm section was estimated to to represent represent 2500 2500 to to 3000 3000 years. years. This can can be be extrapolated extrapolated to to estimate estimate that that the Rossport Formation could potentially potentially represent represent 75 75 000 000 years years of of deposition. deposition. 65 �210'S — 240'S Figure 4.12 Paths (APWP) is plotted Figure 4.12 AAwell-defined well-defined Proterozoic Proterozoic Apparent Apparent Polar Polar Wander Paths al., 2002). The components are ThePass PassLake LakePCA PCAcomponents are designate designatewith withQI, QI,T, T, (after Elston et at., and 0 0 to the Quany to indicate indicatethe Quarry Island, Island, Transitiona', Transitional, and and Outcrop Groups. The The Kama Kama Hill Hill KH and and the the Nipigon Nipigon Bay Bay Formation Formation isisNB. NB. The PCA, PCB, and Formation is designate KH PCC components are denoted respectively by A, B or C after the Formation short form. form. Note that NB-C is a reversed reversed pole pole on on the the back back side of of the the globe. globe. Elston Blston et al. al. (2002) has provided a lower (Sl) (Si) and provided and upper upper (S2) (S2) Sibley Sibley Group pole based on data from Robertson well as as aa pole pole for for the the Keweenawan Keweenawan Osier Osler Group Group (Kl) (Ki) and lower Powder Mill (1973), as well Volcanics (K2). (K2). 1998. Paleomagnetism: magneticdomains domains to to geological Butler, R.F. R.F. 1998. Paleornagnetism: magnetic geological terranes, terranes, Department Department of of Geosciences Geosciences University of Arizona, (originallypublished published by by Blackwell University Arizona, http://www.geo.arizona.edu/Paleomag/bookl http://www.eeo.arizona.edu/Paleomag/book/ (originally Blackwell Scientific Publications Publications in 1992) 1992) Cheadle, B.A. BA. 1986. Alluvial-playasedimentation sedimentationininthe thelower lowerKeweenawan KeweenawanSibley SibleyGroup, Group,Thunder ThunderBay Bay District, District, 1986.Alluvial-playa 527-542. CanadianJournal Journalof ofEarth EarthSciences, Sciences, 23, 23,527-542. Ontario. Canadian Davis, D.W. and Sutcliffe, Suteliffe,R.H. RH. 1984. 1984.U-Pb U-Phages agesfrom fromthe theNipigon NipigonPlate Plateand and Northern Northern Lake Superior. Geological Geological Society of of America America Bulletin, Bulletin, 96, 1572-1579. 1572.1579. D.P., Enldn, Enkin, R.J., R.J., Baker, Baker, J. J. and Kisilevsky, Kisilevsky, D.K. D.K. (2002). Elston, D.P., (2002). Tightening Tighteningthe theBelt: Belt:paleomagnetic-stratigraphic paleomagnetic-stratigraphic constraints on deposition, correlation, and and deformation of of the Middle Proterozoic (ca. 1.4 1.4 Ga) Ga) Belt-Purcell Belt-Purcell United States States and andCanada. Canada. Geological Society ofAmerica Bulletin, 114, Supergroup, United 114, 619-638. 619-638. basin development development in in central central North North America: of America: implications of Fralick, P. and and Kissin, Kissin, S. S. 1995. 1995. Mesoproterozoic basin Sibley Group volcanism volcanism and sedimentation at Redstone Point. In: Petrology and metallogeny metallogeny of volcanic volcanic and intrusive system, Proceedings Proceedings of of the International International Geological Geological and intrusive rocks rocks of of the themid-continent mid-continent rift system. Correlation Program, Project 336. 336. in: Wanless, Wanless, R.K. R.K. and andLoveridge, Loveridge, W.D., W.D., Rubidium-strontium Rubidium-strontium 1978. The Sibley Group, Group, Ontario, Ontario, in: Franklin, J.M. J.M. 1978. report 2. 2. Geological 3 1-34. isotopic age studies, report Geological Survey Survey of Canada Canada Paper Paper77-14, 77-14.31-34. Robertson, W.A. WA. (1973a). Robertson, (1973a). Pole position position from thermally thermally cleaned cleaned Sibley Group sediments sediments and its its relevance relevance to to Proterozoic magnetic magneticstratigraphy. stratigraphy. Canadian Canadian Journal Journal of Earth Eon/i Sciences, Sciences 10, 10, 180-193. 180-193. Tauxe, L. 1998. 1998.Paleomagnetic Paleomagneticprinciples principlesand andpractice, practice,Kiuwer KluwerAcademic Academic Publishers, Publishers, Netherlands, Netherlands,299 299p.p. 66 �Mafic Dikes in Marquette County, County, Michigan with with Sequence of Precambrian Precambrian Mafic emphasis on the Sugar/oaf Sugarloaf Mountain and and Republic Republic Areas N.A. Sandin and T.J. Bornhorst Engineering and Bomhorst (Department (Department of Geological and Mining Engineering and Sciences, Michigan Technological University, Sciences, University, Houghton, Houghton, MI 49931) 4993 1) Precambrian mafic dikes are very common throughout Marquette County, Michigan. Michigan. These dikes Ga). Past Past studies studies by Kantor dikes have have ages agesfrom fromArchean Archean(—2.7 (-2.7 Ga) to middle Proterozoic Proterozoic (—1.1 (-1.1 Ga). Kantor (1968), Gair (1969), Cannon (1974), and Baxter and Bomhorst Bornhorst (1988) have suggested up to six suggested different mafic dike events in Marquette County. These events were interpreted to consist of (from old to young): 1) Archean mafic dikes post-Archean post-Archean volcanism volcanism and before Archean granitoid intrusions intrusions which cut the Archean volcanic rocks; 2) Archean mafic dikes that cut Archean granitoid intrusions, but are subjected to Archean deformation; 3) Archean mafic dikes sedimentary rocks of the that cut Archean basement rocks, but do not cut Early Proterozoic sedimentary dikes that cut Marquette Range Marquette Range Supergroup; 4) Early Proterozoic mafic dikes Supergroup sedimentary rocks rocks prior to Penokean metamorphism and deformation; 5-6) Supergroup 5-6) N-S and E-W Keweenawan mafic dikes. This study has confirmed much of Baxter and and Bornhorst Bomhorst (1988), (1988), however, new data indicate significant significant modifications. modifications. This study focused on the Sugarloaf Sugarloaf Mountain area near Marquette, Ml MI because because of of the the excellent exposures on shore and adjacent to Lake Superior, and previous work by Kantor exposures adjacent previous work by Kantor (1968), who identified mafic dikes of multiple ages. In the Sugarloaf Mountain area over over 300 mafic dikes intruding Archean tonalitic basement were identified and mapped using using aa GPS GPS and pace pace method. method. Dikes receiver and the compass and Dikes identified identified as as critically critically important important to to understanding the sequence of events were sampled for microscopic and chemical chemical study. study. Bornhorst (1988) interpreted interpreted thin, thin, discontinuous, discontinuous, tabular tabular mafic mafic bodies bodies at Baxter and Bomhorst in the the Sugarloaf Sugarloaf Mt. Mt. area as as being being Archean Archeanpost-plutoniclpre-deformation post-plutonic/pre-defonnation Wetmore Landing in above). While While this this interpretation interpretation is is still still possible, possible, the the favored favored mafic dikes (number 22 above). interpretation here is that these mafic bodies are xenoliths that were deformed deformed during during the the Archean along with the host plutonic rocks. plutonic rocks. In Marquette Marquette County, Baxter and Bornhorst Bomhorst (1988) (1988) as well as as previous previous workers workersrecognized recognized the numerous mafic intrusives intrusives that cut Marquette Marquette Range Supergroup Supergroupsedimentary sedimentaryrocks rocksprior prior to to Penokean metamorphism and deformation. deformation. These These were were presumed presumed to to be be of of generally generallythe the same same that in the Sugarloaf Mt. area, three age separate mafic intrusive age. This study indicates that intrusive events events of this age are present. Based on cross-cutting cross-cutting relationships, the sequence sequenceconsists consistsof of diabase diabase dikes trending N20¡E N20°E, diabase diabase dikes dikes trending trending N60¡E N60°E, and anddiabase diabase dikes dikes trending trending east-west. east-west. In In discriminated from addition to cross-cutting relationships, these groups can be discriminated from each each other otherby by trace trace elements. elements. N20°E diabase diabasedikes dikesare arethe theoldest oldest of ofthe theEarly EarlyProterozoic Proterozoicdikes. dikes. In the Sugarloaf Mt. The N2093 area, these dikes N20°E and range in width from NO593 to N20% from one one to to 25 dikes vary in trend from from N05°E 25 feet. feet. Mafic dikes of this age are are the the most most common common of of the Early Early Proterozoic Proterozoic dikes dikes in the Sugarloaf Mountain area. These These dikes dikes exhibit exhibit aa varying varying texture texture from from porphyritic porphyritic to to phaneritie phaneritic from fromthe the dike interiors interiors to the margins. They consist of hornblende, pyroxenes, pyroxenes, chlorite, chlorite, plagioclase, plagioclase, epidote, and sericite. The The REE REE patterns patterns are are enriched enriched in in light-REE light-REEwith with aa moderate moderateslope. slope. Compared to the REE patterns of the sills sills from from the the Marquette Marquette Range Range Supergroup, Supergroup,the theN20°E N2093 concentration of of light-REE, light-REE, is is less less depleted depleted in in heavy-REE, heavy-REE, and has a series has a higher concentration shallower slope. Thus, Thus, our our initial initial interpretation interpretationis is that that these these dikes dikes are are not not related relatedto tothe thesills. sills. 67 �The TheN60°E N60"Emafic maficdikes dikesare areintermediate intermediateEarly Early Proterozoic Proterozoic age. age. They Theyvary varyinintrend trendfrom from N45°E and N45% to N60t N60"E andrange rangeininwidth widthfrom fromone onetoto6060feet. feet.These Theseare arethe theleast leastcommon commonof ofthe theEarly Early Proterozoic Proterozoicdikes dikesininthe theSugarloaf SugarloafMountain Mountainarea. area.They Theygenerally generallyhave havethinly thinlyfoliated foliatedmargins margins with with aa massive, massive,fine-grained fine-grainedinteriors. interiors. These Thesedikes dikeshave haveaaphaneritic phaneritic texture textureand and consist consist of of hornblende, hornblende,pyroxenes, pyroxenes,chlorite, chlorite,plagioclase, plagioclase,epidote, epidote,sericite, sericite,and andminor minoramounts amountsofofcarbonate. carbonate. These Thesedikes dikescross-cut cross-cutthe theN20°E N20TE diabase diabase dikes. REE REEpatterns patternsare areenriched enrichedininlight-REE light-REEand andhave have aasteep steepslope. slope.Compared Comparedtotothe theN20°E N20%series seriesand andthe thesills sillsof ofthe theMarquette MarquetteRange RangeSupergroup, Supergroup, the theN60°E N60"E dikes dikes are are more more enriched enriched in light-REE light-REE with a steeper slope. slope. The TheN60°E N60"Edikes dikes are are more more depleted depletedin inheavy-REE heavy-REEthan thanthe theN20°E N20"Eseries. series.Our Our initial initialinterpretation interpretationisisthat thatthese thesedikes dikesare areaa distinct distinctmagmatic magmaticevent eventwith withrespect respecttotothe theearlier earlierN20°E N20%dikes dikesand andthe themafic maficsills. sills. The Theeast-east east-eastdiabase diabasedikes dikesare arethe theyoungest youngest series seriesof of the the Early Early Proterozoic Proterozoicdikes. dikes. They Theyvary vary in inwidth widthfrom fromfive fivetoto75 75feet feetwide. wide.These Thesedikes dikesgenerally generallyhave have thinly thinlyfoliated foliatedmargins margins with with aa massive, massive,fine-grained fine-grainedinterior, interior,although althoughtwo two dikes dikeshad had porphyritic porphyritic interiors. interiors. They They have have aa phaneritic phaneritictexture textureand andconsist consistof of homblende, hornblende,pyroxenes, pyroxenes,chlorite, chlorite,plagioclase, plagioclase,epidote, epidote,and and sericite. sericite.These Thesedikes dikescross-cut cross-cutthe theN20°E N20"Ediabase diabasedikes dikesand andthe theN60°E N60"Ediabase diabasedikes. dikes. Compared Compared to tothe theREE REEpatterns patternsof ofthe thesills sillsfrom fromthe theMarquette MarquetteRange RangeSupergroup, Supergroup,the theeast-west east-west dikes dikeshave haveaa higher concentration of light-REE and a steeper slope. The east-west dikes are depleted in the higher concentration of light-REE and a steeper slope. The east-west dikes are depleted in the heavy-REE heavy-REEcompared comparedtotothe theN20°E N20%dikes. dikes. They They are are lower lowerin in light-REE light-REEand andhave haveaashallower shallower slope than the N60°E series. Our initial interpretation is that these dikes are a distinct slope than the N60% series. Our initial interpretation is that these dikes are a distinctmagmatic magmatic event eventfrom fromthe theearlier earlierdikes dikesand andthe themafic maficsills. sills. There Thereare arethree threedistinct distinctmafic maficdike dikeevents eventsin in the theSugarloaf SugarloafMt. Mt.Area. Area.We Wepropose proposethat thatthese these dikes dikesare are not not related related to tothe themafic maficsills sillsthat that cut cut the theMarquette MarquetteRange RangeSupergroup. Supergroup.IfIf true, true, then then there theremust must be be atatleast least4, 4,and andlikely likelymore, more, Early Early Proterozoic Proterozoicmafic mafic magmatic magmaticpulses pulses in in the the Marquettearea. area. Marquette Two Twogroups groupsof of unmetamorphosed unmetamorphoseddiabase diabasedikes dikeswere were identified identifiedin inthe theSugarloaf SugarloafMt. Mt.area, area, consistent consistent with with Baxter Baxter and and Bornhorst Bomhorst (1988). (1988). These Thesedikes dikesare areKeweenawan Keweenawanin inage ageand and consist consist of of north-southtrending trendingseries seriesand andan aneast-west east-westtrending trendingseries. series. Both Both dikes dikeshave haveaadiabasic diabasictexture texture aanorth-south andvary vary from from10 10toto75 75 feet feet wide. wide. and In In the the Republic Republicarea, area,Baxter Baxterand and Bornhorst Bornhorst (1988) (1988) suggested suggestedthat thatsome somemetamorphosed metamorphosed mafic maficdikes dikes with with distinct distinctplagioclase plagioclase phenocrysts phenocrysts are are older older than than the themetamorphosed metamorphosedProterozoic Proterozoic dikes dikesin in the the Sugarloaf Sugarloaf area. area.They They proposed proposed that that these these dikes dikes might might correlate correlatewith withthe theMatechewan Matechewan dike dikeswarm swarmnorth north of of Lake Lake Superior Superiorin in Canada. Canada. We We tested tested this this hypothesis hypothesisby bydoing doingchemical chemical analysis analysis of these these dikes. dikes. The The REE REE data data for for these dikes dikes are are similar similar to to Matechewan Matechewandikes dikesfrom from elsewhere elsewhereand and support supportthe the hypothesis hypothesisproposed proposed by by Baxter Baxter and and Bornhorst Bornhorst(1988). (1988). References References Baxter, Baxter,D.A. D.A. and and Bornhorst, Bornhorst,TI., T.J.,1988, 1988,Multiple MultipleDiscrete DiscreteMafic MaficIntrusions IntrusionsofofArchean ArcheantotoKeweenawan KeweenawanAge, Age, western 2 pp. western Upper Upper Peninsula, Peninsula,Michigan: Michigan:Institute Institute on Lake Lake Superior Superior Geology Geology Proceedings Proceedingsand andAbstracts, Abstracts,v. v. 34, 34.2 pp. Cannon, Cannon, W.F., W.F.,1975, 1975,Bedrock Bedrock Geological Geological Map Mapof of the the Republic Republic Quadrangle, Quadrangle,Marquette MarquetteCounty, County,MI: MI:U.S. U S .Geological Geological Survey, Survey, Miscellaneous MiscellaneousInvestigations InvestigationsSeries SeriesMap, Map,1-862. 1-862. Gair, MI: U.S. US. Gair, J.E. J.E. and and Thaden, Thaden, RE., R.E.,1968, 1968,Geology Geologyof ofthe the Marquette Marquetteand andSands SandsQuadrangles, Quadrangles,Marquette MarquetteCounty, County, MI: Geological 77 pp. Geological Survey SurveyProfessional ProfessionalPaper Paper397, 397,77 pp. Halls, Halls, ll.C. H.C.and andPhinney, Phinney,W.C., W.C.,2001, 2001,Petrogenesis Petrogenesisof ofthe theEarly EarlyProterozoic ProterozoicMatachewan MatachewanDyke DykeSwarm, Swarm,Canada, Canada,and and Implications 22 Implications for for Magma Magma Emplacement Emplacementand Subsequent Subsequent Deformation: Deformation: Canadian CanadianJournal Journal of of Earth Earth Sciences Sciences 38, 38,22 pp. PP. Kantor, Swarms in in the the Sugarloaf Sugarloaf Mountain Mountain Area, Area, Marquette Marquette County, County,MI: MI:M.S MS. Kantor, J.A., J.A., 1969, 1969, Assimilation Assimilation and Dike Swarms Thesis, Thesis, Michigan Michigan Technological Technological University, University, Houghton, Houghton, MI, MI, 83 83 pp. pp. 68 �PALEOPROTEROZOIC DOME CORRIDOR CORRIDOR IN THE THE PALEOPROTEROZOIC DEVELOPMENT OF A GNEISS DOME SOUTHERN SOUTHERN LAKE LAKE SUPERIOR SUPERIOR REGION, REGION, USA USA SCHNEIDER, SCHNEIDER, D.A., Dept. of Geological Geological Sciences, Sciences,Ohio Ohio University, University, Athens, Athens, OH OH 45701; 45701; HOLM, D.K., and O'BOYLE, C., C., Dept. Dept. of of Geology, Geology, Kent State State University, Kent, OH 44242; HAMILTON, HAMILTON, M., M., Continental Continental Geoscience Geoscience Division, Division, Geological Geological Survey Survey of of Canada, Canada, Ottawa, Ottawa,ON ON Canada; and JERCINOVIC, MA 01003 01003 JERCINOVIC, M., Dept. of Geosciences, Geosciences, U-Mass, Amherst, Arnherst, MA Paleo-reconstruction of the Penokean orogen at Ca. Ma reveals reveals the presence of of a Paleo-reconstruction ca. 1750-1700 Ma narrow corridor corridor of Archean cored Paleoproterozoic gneiss domes just north of and parallel Paleoproterozoic gneiss domes of and parallel to to the the main suture Wisconsin, and and northern northern Michigan. Michigan. Penokean suture zone zone in Jvlinnesota, Minnesota, Wisconsin, Penokean (ca. (ca. 1850 1850Ma) Ma) metasedimentary rocks infolded within the domes metasedimentary domes give give predominantly 1750-1700 1750-1700Ma Ma cooling cooling ages and are overlain depositionally depositionally by ca. 1700 1700 Ma Baraboo Baraboo interval interval quartzites. quartzites. We We conducted conducted SHRIMP and total-Pb EMP geochronometry to obtain metamorphic timing constraints on U-Pb SHRIMP distinct monazite monazite mineral domains domains from from amphibolite amphibolite grade grade rocks rocks sampled sampledacross acrossthe the entire entirelength length of the gneiss dome corridor. Based Based on on metamorphic metamorphicmonazite monazite crystallization crystallization ages, ages, midcrustal midcrustal amphibolite facies metamorphism (Ml) (Ml) peaked peaked around around 1830 1830Ma Ma and and was was concurrent concurrent with with late late reliably recorded recorded at at ca. ca. 1800 Ma Ma (M2) and and Penokean plutonism; subsequent thermal pulses are reliably again at ca. 1765 1765 Ma (M3), (M3), both also also coeval coeval with magmatic magmatic activity. activity. The youngest monazite monazite ages overlap overlap with abundant abundant Ar-Ar mineral mineral age age data, data, which which indicate indicate widespread cooling of of the gneiss dome comdor corridor immediately immediately following M3. M3. We We propose propose that that the the lime during structural modification of of the the tectonically tectonically buried buried gneiss domes formed at this time continental margin rocks. In In our ourconceptual conceptual model model (Fig. (Fig. 1), l), northward northward vertical vertical extrusion extrusion of of aa decoupled midcrustal block containing the gneiss dome corridor accommodated gravitational collapse of overthickened crust. Elevated Elevatedcountry countryrock rock temperatures temperaturesaccompanied accompaniedwith with profuse profuse melting (i.e., intrusion of the East-central Minnesota batholith) promoted doming of the lower density Archean basement into the more dense overlying Paleoproterozoic metasedimentary rocks, ultimately enabling its complete decoupling from the remaining lower crust. This Thisprocess, process, primarily driven by buoyancy forces, allows for the redistribution of crustal mass from thick to horizontal crustal crustal extension. extension. Tectonic extrusion and crustal thin regions without significant horizontal thinning at this stage may have been facilitated by a decrease in horizontal compressive compressive stresses acting on the region from the south (i.e., Yavapai slab rollback as proposed by Holm HoIm et al., ILSG, 2003). 2003). In Inour ourmodel model(Fig. (Fig.1), l),the thefaults faultsbounding boundingthe thegneiss gneissdome domecorridor comdorare areca. ca.1765 1765 structures, although some, like the Niagara Fault zone, are am reactivated Penokean structures. Ma structures, We note that in east-central Minnesota, a significant portion of the Malmo Structural Structural discontinuity juxtaposes post-Penokean plutons to the south south against older older metamorphic metamorphic rocks to the north (west of Mille Lacs). This This clearly clearly supports supports our our interpretation that this structure structure (and the Flambeau Flowage fault equivalent in northern Wisconsin) Wisconsin) was active active well after Penokean orogenesis. orogenesis. D.K., Van Schmus, W.R., W.R., MacNeill, L.C., Boerboom, Boerboom, T.J., Schweitzer, Holm, D.K., Schweitzer, D., and and Schneider, D.A., 2003, Late Paleoproterozoic (1900-1600 Ma) tectonic history of the northern U.S.A.: Implications for for crustal crustal stabilization: stabilization: Institute mid-continent, U.S.A.: Institute on Lake Superior Superior Geology abstracts abstracts (this (this volume). volume). 69 �Penokean Penokean orogen, orogen, Ml: MI: 1830 2830 Ma Ma to to M2: M2:1800 1800Ma Ma $S NN warm, warm, Penokean Penokean orogen, orogen, M3: M3: 1765 1765 Ma Ma N N SS GNEISS DOME DOMECORRIDOR COftRlDOR GNEISS ARCHEAN GRANITE-GREENSTONE V.1SONSIN MAGMA11C TERRANE Quvenile island alt) ARCHEAN GNEISS PALEOPROTEROZOC ROCKS (supracwstal} F ~ g ~1. 1. x eSchematic SchemaucN-S N-Scross-sections cross-secttonsat at1830-1800 1830-1800Ma Ma(A) (A)and and Figure 11765 765 Ma Ma (6) (B) dep~cling depicting the [he proposed proposed evolution evoluttonot of the thegneiss gnelssdome 6ome corridor corndor in In northern northern Wisconsin. Wtsconsin. Note Noterelative relativelocations locattons ol of gray gray circles clrcies that represent depth of crustal blocks. that represent depth of crustal blocks. 70 �A Paleoproterozoic suprasubduction suprasubduction zone arc complex zone ophiolite-island ophiolite-island arc in northeastern northeastern Wisconsin Wisconsin Schulz, Klaus Schulz, Klaus J., J., (U.S. (U.S.Geological GeologicalSurvey, Survey,Reston, Reston,VA VA 20192, 20192, kschulz@usgs.gov) kschulz@us~s.~ov) The Paleoproterozoic Paleoproterozoic volcanic volcanic and and associated associated intrusive intmsive rocks rocks exposed exposed in in northeastern northeastern Wisconsin Wisconsin are are the the easternmost easternmost exposures exposures of of the the Pembine-Wausau Pembine-Wausau terrane, terrane, the the northernmost northernmost of of the the two two Wisconsin Wisconsin magmatic magmatic terranes terranes that that were were accreated accreated to to the the southern southern margin of the Archean Atchean Superior SuperiorCraton during during the the Penokean Orogeny Orogeny (Sims (Sims and and others, others, 1989). The The rocks rocks of of the the Pembine-Wausau Pembine-Wausau terrane terrane are are separated separated from the epicratonic sedimentary rocks of the Marquette Range Supergroup to the north in Michigan by the Niagara fault fault zone. zone. The volcanic rocks of the the Pembine-Wausau terrane terrane exposed exposed northeastern northeastern Wisconsin, Wisconsin, formed at about 1,870 1,870Ma Ma and and are are cut cut by a variety variety of intrusive intrusive rocks ranging ranging from from synsynvolcanic gabbros, diorites, and tonalities to syn-and post-tectonic granitoids (i.e., Dunbar Dunbar Oneiss Gneiss and related rocks). The Thevolcanic volcanicrocks rocks are are divided divided into into four four fault-bounded fault-bounded units, units, McAllister, Beecher, and Pemene formations. These the Quinnesec, McAllister, Theseunits units are are interpreted interpreted to record the evolution evolution of of aa Paleoproterozoic Paleoproterozoic suprasubduction suprasubductionzone zoneophiolite-island ophiolite-islandarc arc complex, the Pembine Pembine ophiolite-arc ophiolite-arc complex. complex. of The Quinnesec Formation is the oldest volcanic unit and consists predominantly of lava flows pillowed basalt flows and massive diabase, but includes andesite and rhyolite lava and fragmental rocks locally. Several Several large large gabbro gabbro sills sills are are present, present, particularly particularly near the Niagara fault zone, some with peridotite and pyroxenite layers. In In addition, addition, aa large large serpentinized peridotite-gabbro pendotite-gabbro body that produces a large large positive positive magnetic magnetic anomaly anomaly is is exposed exposed south south of Timms Timms Lake Lake (Morgan (Morgan County County Park) Park) east east of of Pembine, Pembine,Wisconsin. Wisconsin. is locally Serpentinized peridotite is dominant in the western part of this body where it is cut by coarse-grained (1-5 cm) dikes of of pyroxenite. Layered Layered and and massive massive gabbro gabbro and and masses of strongly foliated-lineated gabbro are dominant in the eastern part of the body where they are cut by numerous mafic dikes with cliabasic microdioritic textures; some diabasic to microdioritic some of the dikes dikes appear appear to to be be sheeted. sheeted. The rocks of the Quinnesec Formation appear to record the birth and youth stages of a suprasubduction zone ophiolite (Shervais, 2001). 2001). Rocks Rocks formed formed during during the initial phase of ophiolite evolution evolution typically include include layered layered and and isotropic isotropic plutonic plutonic gabbros, gabbros,sheeted sheeted dikes, and a "lower" "lowe?' volcanic volcanic section consisting consisting of low-K tholeiitic basalt and basaltic andesite with MORB MORE and primitive arc tholeiite tholeiite affinities. Gabbros Gabbros formed formed during during this stage are often ductilely deformed deformed (foliated (foliated or or boudinaged) boudinaged) in in response response to to syn-magmatic syn-magmatic extension. Rocks Rocks formed formed during during the the second second or or youth stage of ophiolite formation include intrusive mafic-ultramafic sills and diabase dikes, and an "upper" volcanic unit unit characterized by basalt and andesite with with highly depleted incompatible trace element compositions (i.e., low-Ti basalt, high-Mg andesite and boninite) (Shervais, (shemais, 2001). basalts and gabbros are tholeiitic, with generally low Compositionally, the Quinnesec basalts Ti02 and other high field strength element abundances, Ti02 other abundances, and and flat to extremely extremely light REE REE 71 �some of of the the basalts, basalts, gabbros, and and depleted patterns (Sims and others, 1989). Tn In addition, some Ti02 and REE REF abundances, abundances, but relatively high Cr and Ni andesites have very low Ti02 contents. The Thetrace traceelement element characteristics characteristicsof of the the mafic mafic rocks rocks overlap overlap those those of of mid-ocean mid-ocean ridge basalts and primitive island-arc tholeiite suites whereas the andesites show with fore-arc-related fore-arc-relatedboninites. boninites. The presence in in the upper upper part part of of compositional affinities with the Quinnesec Quinnesec Formation Formation of mafic mafic rocks rocks derived derivedfrom from highly highlyrefractory refractorymantle mantle isis particularly diagnostic of a relationship to the early stages of of intraoceanic subduction and formation (Shervais, 2001). 2001). This fomation in a forearc setting (Shemais, This also implies that the Quinnesec Formation and associated rocks did not form in a back-arc basin near or on the margin of the Superior Johnson, 1997), Superior Craton, as has recently been proposed (Van Wyck and Johnson, 1997), but rather formed as an intraoceanic ophiolite-arc system above a southward dipping (in present coordinates) coordinates) subduction subduction zone. zone. The McAllister, Beecher and Pemene formations consist of volcanic and volcaniclastic calc-alkaline rocks ranging from andesite (McAllister) to rhyolite (Pemene), all with calc-alkaline compositions characteristic of of mature mature oceanic oceanic arcs, arcs. These volcanic rocks and associated intrusives, such as the Newingham Tonalite and Twelve Foot Falls Quartz Diorite, appear appear compatible with the third or maturity stage of suprasubduction ophiolite evolution compatible suprasubduction zone ophiolite evolution (Shervais, 2001). Characteristic (Shemais, Characteristic of this stage are intrusive rocks, such as hornblende diorite, quartz diorite, and tonalite, as well as volcanic rocks ranging from basalt to diorite, to calc-alkaline caic-alkaline compositions. compositions. Volcanism typically becomes rhyolite, all with transitional to in these sequences. sequences. In many cases, rocks of this stage have not more silicic with time in of the subjacent ophiolite, ophiolite, but rather have been attributed attributed to postbeen considered part of ophiolite arc volcanism (Shervais, ophiolite (Shervais, 2001). 2001). It appears appears likely that growth of the Pembine ophiolite-arc complex was terminated terminated by its its collision with and obduction onto the passive passive southern southern margin margin of the the Superior SuperiorCraton. Craton. Because subduction appears to be largely driven by slab pull, the southward southward subduction subduction of oceanic lithosphere lithosphere attached to the Superior Superior continental continental margin would would have have pulled pulled the the continental lithosphere lithosphere along with it as it descended descended into into the the subduction subduction zone zone below below the the ophiolite-arc system. With With detachment detachment of of the the subducting subducting oceanic oceanic lithosphere, lithosphere, the the buoyancy of the continental lithosphere lithosphere would have led to its rapid uplift along along with with the the leading edge of the the ophiolite-arc ophiolite-arc complex complex ((Shervais, 2001). This S h e ~ a i s2001). , This stage stage is is recorded recorded by by the deformation sequence and by the intrusion of the synSF- to post-tectonic post-tectonic deformation of the ophiolite-arc sequence units of the the Dunbar Dunbar dome. dome. Shervais, J.W., 2001, Birth, death, and resurrection: the life life cycle cycle of suprasubduction suprasubduction zone zone ophiolites: ophiolites: Geochemistry Geophysics Geosystems, Geosystems, v01.2, vol.2, Paper Paper number 2000GC0~080. 2000GC000080. On-line publication publication at at htto://g-cubed.org. hm:I/g-cubed.org. Sims, W.R., Schulz, Schulz,K.J., K.J., and and Petennan, Peterman, Z.E., Z.E., 1989, 1989, Tectono-stratigaphic Tectono-stratigraphic evolution evolution of of Sims, P.K., Van Schmus, W.R., Proterozoic Wisconsin magmatic terranes of the Penokean Orogen: Canadian Canadian Journal the Early F'roterozoic Journal of of Earth Earth Sciences, v. v. 26, 26,p.p.2145-2'58. 2145-2158. Van Wyck, N., N., and Johnson, C.M., C.M., 1997, Common lead, Sm-Nd, and U-Pb constraints constraints on on petrogenesis, petrogenesis, crustal architecture, and tectonic setting of the Penokean orogeny (Paleoproterozoic) cmstal (Paleoproterozoic)in in Wisconsin: Wisconsin: Geological Society of America Bulletin, Bulletin, v, v. 109, p, p. 799-808. 72 �- PLANNW PLANNED ACTIVITIES ACTIVITIES AND THE LAKE LAKB NIPIGON GEOSCIENCE INITIATIVE OBJECTIVES SMYK, Mark C., Ontario Geological Survey, Ministry SMYK, Ministry of Northern Development Development and Mines, Suite 8002, 435 James Suite B002,43S JamesSt. St.South, South,Thunder ThunderBay, Bay,ON ONP7E P7E6S7, 6S7,and andmembers membersof ofthe theScientific Scientificand and Implementation Committees. Committees, Lake Lake Nipigon NipigonGeoscience GeoscienceInitiative, Initiative,c/o do Ontario Prospectors Association, 1000 1000 Alloy Drive, Drive, Thunder Bay, ON P7B 6A5 The Lake Nipigon Geoscience Initiative Initiative (LNGI) (LNGI) was created in 2002 as a $7.0 M Cdn. Cdn. project projectaimed aimed at at attracting mineral investment to the area around Lake Nipigon. The O Ontario Prospectors Association's attracting n t ~ Prospectors o Association's (OPA) portion of the project is funded funded through through an agreement agreement with the Northern Ontario Onmio Heritage Heritage Fund. The partnering with the Ontario Geological Survey (OGS), the Ministry of Northern Development and OPA is partnering Canadian Mining Industry Research Organization (CAMRO), (CAMIRO), Lakehead University, Mines (MNDM), the Canadian partners and communities in the L&e Lake Nipigon area. It will focus focus on four key as well as with private sector pmners objectives: Lake Nipigon Nipigon region region through collection collection of high Maintain and then increase mineral investment in the Lake 1. 1. quality geological data and provision of interpretations that meet the needs and priorities priorities of of the the mineral mineral industry and that maintain maintain or attract attractmineral mineral investment investmentto to Ontario; Ontario; exploration discovery discovery rate by addressing "masking and deep search search challenges challenges 2. Increase the mineral exploration and skill gap" in the area; area; recently recognized 3. Respond to, and evaluate, new and exciting mineral deposit models recently 3. recognized for for nickelnickelcopper, palladium-platinum, and gold-copper mineralization in the region; 4. Reinforce and demonstrate an innovative economic development model based on local local community, community$ partnerships in geoscience that result in mineral resource economic industry, and government partnerships economic development in the local communities, communities, the the region, region, and and Ontario. Ontario. The LNGI predominantly of Emhayment, which consists predominantly LNGI is focused on the Nipigon Basin Basin I1 Embayment, Mesoproterozoic, Midcontinent Midcontinent Rift-related, RiR-related, ultramafic ultramaficto mafic mafic intrusions intrusions that that have have intruded intruded Mesoproterozoic Sibley Sibley Group sedimentary sedimentary rocks and Archean Archean basement basement rocks rocks of of the the Quetico Queticoand and Wabigoon Wabigmn subprovinces. snbprovinces. comprehensive geoscience geoscience database database that that will will assist assist in in mineral mineral exploration. exploration. The The project will develop a comprehensive consultations that helped LNGI evolved through a series of community and industry consultations helped define define the the project project parameters. AAthorough thorough compilation compilationof of previous previous exploration exploratiou and and geological data data provided provided aa baseline baseline for for the project and identify potential potential gaps in the the geoscience database. database. The The main main components componentsof of the the initiative initiative include: • • • • • • • • Precambrian Section, Detailed geological mapping, undertaken by Precambrian Section, OGS OGS Airborne Airborne magnetic survey survey Gravity Gravity survey survey Quaternary (surficial) (surticial) case studies, studies, undertaken undertaken by Sedimentary SedimentaryGeoscience GeoscienceSection, Section,OC)S OGS Geochronology Geochronology Physical property studies studies Geographic Information Systems (GIs) (GIS) compilation Complementary Complementary research at Lakehead University • Sibley Fralick) Sibley Group studies (P. Fmlick) intrusion studies (P. Hollings; G. Borradaile) • Nipigon mafic intmsion Bomadaile) • Sulphide mineralization mineralization studies studies(S. (S. Kissin) Kissin) . 73 �The TheOntario OntarioGeological GeologicalSurvey Surveywill willhelp helpacquire acquireand and publish publish the the results results of of the the geoscience geosciencestudies studies as as maps, maps, reports,and and digital digitaldata datasets. sets.The Theinformation informationwill willthen then be be available available over over the the Internet Internet through though the tbe MNDM's MiWM's reports, ERMES ERMESand andCLAIMap CLAIMapsystems. systems.This Thisvaluable valuableinformation informationwill be be used to to globally globally market market the tbe resource resoutce potentialand andinvestment investmentappeal appealofofthe theLake LakeNipigon Nipigonregion. region. potential 74 �TECTONOSTRATIGRAPHIC ASSEMBLAGES OF EASTERN ARCHEAN TECTONOSTRATIGRAPHIC WABIGOON SUBPROVINCE, NORTHWESTERN ONTARIO ONTARIO STOTT Greg STOTT GregM., M., Ontario OntarioGeological GeologicalSurvey, Survey,Sudbury, Sudbury, ON, ON, P3E P3E 6B5 6B5 (greg.stott@ndm.gov.on.ca), DAVIS, Don. W., Department of Geology, University of of (greg.stott@ndm.gov.on.ca), DAVIS, of ON, PARKER, PARKER, Jack Jack R., R., Ontario Ontario Geological Geological Survey, Survey, Sudbury, ON, Toronto, Toronto, ON, STRAUB, Kristan J., Laurentian University, University,Sudbury, Sudbury,ON ONand andTOMLINSON, TOMLINSON, Kirsty STRAUB, Knstan J., Y., Geological Survey of Canada, Y., Canada, Ottawa, Ottawa, ON ON The Archean Wabigoon Subprovince Subprovince is a complex of volcanic and sedimentary sedimentary of Mesoarchean to Neoarchean age. The supracrustal assemblages and granitoid suites of of this subprovince, which includes the Onaman-Tashota greenstone easternmost part of greenstone belt east of Lake Nipigon, preserves a history of over 250 million years of volcanism. This area has recently recently been been treated treated to to aa regional regional mapping, mapping, geochemical geochemical and and geochronological part of of the the Western Western Superior NATMAP project. A 1:250 000 compilation synthesis as part map (Stott et al. 2002) arising from this project illustrates the subdivision subdivision of of the the OnamanOnamanTashota (0-T) (O-T) greenstone belt belt into into tectonostratigraphic tectonostratigraphic assemblages assemblages (Figure (Figure 1), I), based on stratigraphic geochronological and geochemical similarities similarities and stratigraphic correlations, geochronological and contact contact component of of this this map, map, summarized summarized in in Figure Figure 2, 2, is is the the relationships. A more interpretive component delineation delineation of the assemblages in terms of the environment environment of crystallization of of volcanic volcanic and plutonic rocks and deposition of sedimentary sedimentary rocks. This is based on on lithologic lithologic and and geophysical characteristics, whole-rock geochemical classification, and where available, available, Nd isotopic isotopic signatures. signatures. Onaman-Tashota greenstone belt straddles the width of the eastern The Onaman-Tashota eastern Wabigoon Wabigoon Subprovince between the English River and Quetico metasedimentary subprovinces. Subprovince metasedimentary subprovinces. ItIt isis mainly composed composed of Neoarchean Neoarchean(dominantly (dominantly2.74 2.74— - 2.72 2.72 Ga) basaltic and dacitic dacitic flows, flows, volcanic rocks occur autobreccia and pyroclastic rocks. Mesoarchean (3.05 (3.05 —2.92 - 2.92 Ga) volcanic occur in in the northwest and along the western margin of the belt. Widespread Nd isotopic isotopic evidence evidence in the northern part of the Onaman-Tashota belt suggests that Neoarchean volcanism volcanism erupted thmugh half of the belt through Mesoarchean basement. Basement in the northern half contains an older component component than than that that south of of the Humboldt Humboldt Bay High High Strain Zone. The 2.74 Ga Willet assemblage tholeiitic basalts of ocean floor affinity dominate 2.74 dominate the the northern northern half of the 0-T O-T belt. belt. This This assemblage is flanked to the the north north and and south by calc-alkalic of continental continental margin arc affinity that border metasedimentary subprovinces assemblages of subprovinces composed of of flysch-like wacke wacke derived derived from from the the erosion erosion of of the the 0O-T belt and plutons plutons - T belt during orogenesis at at circa circa 2.7 2.7 Ga. Ga. Most Most sedimentary units units within within the the 0-T O-T belt form the supracrustal assemblages, assemblages, reflecting reflecting erosion of the underlying volcanic and youngest supracrustal and plutonic rocks towards the English English River River and Quetico basins basins to the north and south. Reference Reference Stott, G.M., Davis, D.W., D.W., Parker, Parker, J.R., J.R., Straub, Straub, K.J. ILI. and Tomlinson, K.Y. K.Y. 2002. Geology and Assemblages, eastern eastern Wabigoon Wabigoon Subprovince, Subprovince, Ontario; Ontario; Ontario Ontario Geological Geological Survey, Tectonostratigraphic Assemblages, Preliminary Map P.3449, scale 1:250 1:250 000. KY., Stott, Tomlinson, G.M.and and Davis, D.W. 2000. Nd isotopes in the eastern Wabigoon subprovince: Tomlinson, K.Y., Stott, G.M. for crustal crustalrecycling recyclingand andcorrelations correlationswith withthe thecentral centralWabigoon; Wabigoon;in inHarrap, Harrap, R.M. R.M. and and implications for I-Ielmstaedt,H.H. H.H.(eds.), (eds.),2000, 2000,Western WesternSuperior SuperiorTransect Transect Sixth Sixth Annual Annual Workshop, Workshop, Lithoprobe Report Report #77, #77, Helmstaedt, Lithoprobe Lithoprobe Secretariat, Secretariat, University University of British British Columbia, Columbia, p.119-126. p.119-126. 75 �__________ Figure1.1. Figure Tectonostratigraphic Tectonostratigaphic assemblagesof of the the assemblages Onaman-Tashota Onaman-Tashota greenstone greenstonebelt beltand and Proterozoic Proterozoicdiabase diabasedike dike swarms, swarms,Eastern Eastern Wabigoon WabigoonSubprovince. Subprovince. i o__o 1e o Kilameires Presreetlo = 0' Moos Is mlanreediala nwIarasw ass.eblagos jmeppsdi&, Is aMOOsodeaso asseaamagas Niri5000labauseilIl Ares.., Uas1jsdtstad plusast — CSaO,c rn,100asbnaSaW assamb)aga, C— m 1T!2J EnlolsIlar — Heml MalmUp-Veaus unsabdisidad Nipiger iKasreeasaasl slabs. didps (0100 Ma) and Marathon diahaaa dId. errors 12101 and 2120 Ma) *4,-p .__+ + '-•l- + -_. to. Is-a as eJ it) Wtle thdahth) Oreanar leelsilda) Zi' lhrsaloaandlh.bee Isslaidle) canasru East )thseasr Marshall Shear elena Albad-OlSdhll 4 Z222 ElethasSRlcMly (saJbaOnaas) fl staladnewas dials,, sib, salem )244E hI 247.1 Ma) arId kasadasi tIlt ftaashlisn Uscsrredlled dbMs so andatasal age. possibly ralal,dIo Biac0005Il,a 2170 Ma) UI Malaffoeer (2101 and 2121 Ma) dika swaass Figure2. 2. Tectonic Tectonic Figure affinities affinitiesassigned assignedtoto volcanicand and volcanic sedimentary sedimentary assemblages assemblagesand and plutonic plutonicsuites. suites. + + 1- +.+,+.+ 0Nakina 4 )a rss--'a------C-a't + -a-/ p Lake Nopigon1., Is°—.1 + •4 + + + + + + + + -p 4Th—---rI-n- — + + + + + + + + + + + + + -p 4 •-0- Proterozoic i continental plume related a'nyMyM Ocean floor Oceanic unsubdivided Archean 4 Orogenic plutons I } continental arc conbnental margin arc + 4.4—cc + ::-:;1 Orogenic sediments 1 Unknown tectonic affinity 20 0 Kilomalyas Meaoarcliean continental unsubdivided 76 �FIVE GOLD GOLD POSSIBILITIES SOME KEWEENAWi4N KEWEENAWAN COPPER SULFIDES FIVE POSSIBILITIES IN IN SOME SULFIDES IN IN ONTARIO AND AND MICHIGAN MICHIG?d Prow, Trow, Jim, Jim, Geological Geological Sciences, Sciences, Michigan Michigan State State University, University, emeritus, 540 Lake Avenue *2, HanCock, emeritus, 540 #2, HancoCk, Michigan 49930 49930 Most fire—assayed fire-assayed "invisible" "invisible"gold, gold, from from .12 -12to to 2.50 2.50 oz oz Au/st, Au/st, occurs in "blue "blue chalcocite" chalcocite" (with (with minor covellite) covellite) but not in black black chalcocite chalcocite (with (with no covellite) covellite) on on the the adit, adit, 1st, lst, 2nd, 2nd, and and 3rd levels Mamainse Point, Point, Ontario. Ontario. levels of of the the Coppercorp Coppercorp mine mine at at Mamainse Both Both occur occur with with specular specular hematite. hematite. Copper Copper mineral mineral zoning zoning exextending from from carbonates and oxides through through native native copper, copper, black chaldocite and specularite, chalcocite specularite, "blue "blue chalcocite" chalcocite" and specularite, specularite, to to bornite and chalcopyrite is related to to nearness nearness to the the Keweenaw Keweenaw and related faults faults apparently down which circulated oxidizing solutions The solutions during during an an upward-migrating upward-migrating hydrothermal hydrothermal episode. episode. The former faults electrical anomalies, whereas former faults display positive SP electrical anomalies, whereas nearly perpendicular perpendicular cross faults faults with commercial commercial ores display display negative SP SP anomalies anomalies of this convective convective hydrothermal hydrothermal cell cell (Trow). (Trow). Such progressive hydrothermal fluids Such progressive oxidation of hydrothermal fluids is is suggested suggested for for the Keweenawan of Michigan by the USGS1s USGS's Woodruff, Woodruff, Cannon, Cannon, and and Back. Back. Ontario, Trow For Ontario, Trow deduces thermochemical thermochemical calculations calculations with with standard standard free free energies energies and typical activities activities for for constituents constituents (except (except for for oxygen, oxygen, whose whose activities activities are are the the unknowns). unknowns). These are arrayed on on a logarithmic logarithmic scale scale which mimics the the observed observed copper copper mineral mineral zones, zones, and in that sequence sequence AAuS U S -first ~firstoxidized oxidized to to deposit deposit gold gold at at the the which chalcopyrite chalcopyrite first same oxygen activity at which first oxidized to to covellite covellite and and specularite. specularite. At the the present present it it is is uncertain uncertain if if the the "blue chalcocite" chalcocite" exsolved exsolved ivto into chalcocite chalcodite and covellite from from llblue at low low temperatures, of original covellite digenite at temperatures, or if most of original covellite was was replaced replaced by by late late chalcocite chalcocite at at roughly roughly 2,500 2,500 times times the the oxygen oxygen activity activity at at which which covellite covellite originally originally formed. formed. Essentials Essentials for for gold at Coppercorp include include 1) 1) Keweenawan Keweenawan permeable permeable basaltic vesicular beds and conglomerates, conglomerates, 2) 2) felsite felsite intrusives intrusives with with permeable permeable border border breccias as as conduits conduits for for rising rising hydrohydrothermal solutions, solutions, 3) 3) nearness to the the Keweenaw Keweenaw and and related related faults faults with with positive positive SP SP anomalies, anomalies, 4) 4) mineralized mineralized cross cross faults faults with with ores ores yielding negative negative SP anomalies, anomalies, and 5) 5) "blue ''blue chalcocite". chalcocite". In Michigan, Michigan, field examination examination of ore ore deposits deposits and and structures structures mapped by the the USGS USGS shows shows that that the the major major lodes lodes (Baltic, (Baltic, Ashbed, Ashbed, Isle Royale, Pewabic, Osceola, Calumet Isle Royale, Pewabic, Osceola, Calumet conglomerate, conglomerate, and and Kearsarge) Kearsarge) and the Cliff, Cliff, Central, Central, and and Delaware Delaware fissure fissure deposits deposits all all displayS display negative SP anomalies. anomalies. The Keweenaw, Keweenaw, Hancock, Hancock, Mayflower, Mayflower, and and negative SF Gratiot—Suffolk 5? anomalies, anomalies, approapproGratiot-Suffolk faults faults all display positive SP priate for downward oxidative oxidative contamination contamination of of rising rising hypogene hypogene (not supergene) supergene) mineralization. (not mineralization. the best best matches to Canadian Canadian gold gold in From southwest to northeast the Michigan Michigan , so so far examined, examined, occur 1) 1) from from Mass Mass City City to to the the Indiana Indiana mine adjacent intrusives and the Keweenaw fault fault in adjacent to felsite intrusives in Houghton and and Keweenaw Counties the Allouez Ontonagon County, 2) In Houghton Gap Gap fault fault between Copper City and New Allouez is is near the Copper , 77 �2 City felsite felsite and and the the Keweenaw Keweenaw fault. fault. According to to Bornhorst, Bornhorst, page 132, 132, Randy Weege of C & H H thought thought that that this this fault fault perhaps perhaps was was aa fluid fluid pathway pathway for for 60% 60% of of the the district's district's copper copper production. production. Further, Further, it it replicates replicates and and improves improves upon upon the the best best geophysical geophysical signature signature at Coppercorp, Coppercorp, the the persistent persistent SB SB zone, zone, with with flanking flanking negative SP anomalies negative anomalies in in the the midst midst of of which which is is aa positive positive SP SP anomaly. anomaly. In Michigan, the positive "core" "core" anomaly splinters splinters the northern northern end end of of the the negative negative anomalies anomalies in the westward of offf the vicinity of vicinity of Abmeek. Ahmeek. This This part of the the district district contains contains arsenic, arsenic, which accompanies accompanies gold in in many western western mining mining camps. camps. 3) 3 ) In In 1999 1999 million tonnes tonnes of chalcocite Maki and and Bornhorst Bornhorst reported reported on on the the 4½ 4% million chalcocite amygduloids of the in drilled amygduloids the Gratiot Gratiot deposit deposit in in Keweenaw Keweenaw County, County, This lode where these these beds beds are are intruded intruded by by dacite dacite (felsite). (felsite). This lode appears appears at at the the intersection intersection with with the the southward southward extension extension of of Trow's Trow's negative negative SF SP anomaly anomaly as as observed observed at at the the Central Central mine mine and and 2¼ 2% miles miles 4) In Keweenaw County, County, the the USGS's USGS's Hank Hank Cornwall Cornwall on on the SSE. SSE. 4) to the pages 166—167 166-167 describes describes minor minor traces traces of of gold gold with with mainly mainly chalco— chalcocite and specularite specularite and some some covellite covellite and and chalcopyrite chalcopyrite in in an an amygduloid near near the the top top of of the the Greenstone Greenstone flow. flow. This This is is not not near near the Keweenaw fault, N.4°E. vertical fault fault, but it is is cut by a N.4OE. fault with a negative SF SP anomaly, anomaly, which must be intersected at depth by a a N.4°E., SF anomaly, anomaly, where it N.40~., 35°—45°NW. 350-45oNW. fault fault with a positive SP it is is exposed exposed to to the the east east of of the the vertical vertical fault. fault. There exists exists aa possipossibility for for aa horizontal horizontal ore ore shoot shoot at at these these faults' faults' intersection. intersection. These geologic map These four four possibilities possibilities are plotted on the latest geologic of the the Keweenaw Keweenaw peninsula, Peninsula, by by Cannon Cannon and and Nicholson. Nicholson. Not yet yet reconnoitered reconnoitered possililities possililities may may occur occur to to the the northeast northeast of of these. these. Remember, Remember, from from 1849 1849 to 1961 1961 the the old timers all missed the the Carlin Carlin "invisible" gold. ttinvisible" gold. Nevada is is now now the the biggest gold producing producing state state because of the observations, observations, thinking, thinking, and and Perseverance perseverance of of the the USGS's USGSss Ralph Ralph Roberts Roberts and and Newmont's NewmontlsJohn John Livermore. Livermore. REFERENCES REFERENCES CITED Bornhorst, T. P. J., 3., 1997, Tectonic context of native copper Bornhorst, 1997, Tectonic copper deposits deposits Midcontinent Rift System, System, in Geological of the North American Midcontinent in Geological 127-136. Society of America Special Special Paper Paper 312, 312, p. p. 127—136. Cannon, Nicholson, S. W., 2001, Geologic map of Cannon, W. F. and Nicholson, 2001, Geologic of the the Michigan, USGS USGS Geological Keweenaw Peninsula and adjacent area, area, Michigan, Geological Investigations Investigations Series Series Map Map 1—2696. 1-2696. Cornwall, Differentiation in lavas of the Cornwall, H. R., 1951, 1951, Differentiation the Keweenawan Keweenawan series Michigan, series and the origin of the copper deposits of Michigan, Geological Society no.2, p. p. 159—201. 159-201. v. 62, 62, no.2, Geological Society of of America America Bull. Bull. v. Maki, 3. Gratiot chalcocite Maki, J. C., 1999, 1999, The Gratiot chalcocite deposit, deposit, Keweenaw Keweenaw Peninsula, Michigan, Michigan Technological University, M.S. Peninsula, Technological University, M.S. Thesis, 71 Thesis, 71 p. p. Trow, Trow, 3., J., 1992, 1992, Inductive Inductive electrostatic electrostakic gradiometry gradiometry (IESG) (IESG) deciphers deciphers Keweenawan copper plumbing system, system, Soc. SOC. Mining, Mining, Metall. and and Expl. Phoenix Phoenix Meeting, Meeting, Preprint Preprint 92—32, 92-32, 22 22 p. p. Woodruff, L. G., Cannon, Cannon, W. W. F., and Back, 3. M., M., 1994, Woodruff, Back, J. 1994, Chalcocite Chalcocite Portage Lake volcanics, volcanics, Keweenaw mineralization in the Portage Keweenaw Peninsula, Peninsula, Michigan, Michigan, 40th 40th Ann. Inst. Inst. on on Lake Lake Superior Superior Geology, Geology, Houghton, Houghton, Abstracts, p - 77—78. 77-70. Abstracts, p. 78 �Using xenotime U-Pb geochronology tto unravel the the history of Proterozoic U-Pb geochronology o unravel Proterozoic sedimentary sedimentary basins: a study study in inWestern Western Australia Australia and and the the Lake Superior Region N.J., Rasmussen, B., Fletcher, dvallini@aeol.uwa.edu.au, McNaughton, N.J., Fletcher,I., I., Griffin, Griffin, B.J., B.J., Vallini, D.A., D.A., dvallini@cieol.uwa.edu.au, University of Western Western Australia, 35 University 35 Stirling StirlingHwy, Hwy,Crawley, Crawley, 6009, Australia Diagenetic xenotime ('(P04) (YPOJ is is aa trace trace constituent constituent in in aa wide wide variety variety of of siliciclastic siliciclasticsedimentary sedimentaryrocks. rocks, It typically forms pyramidal crystals of only a few microns in size, rarely exceeding exceeding 10 10 pm, pm, growing on (isostructural] detrital zircons. A recent study by Vallini et al. (2002) [isostructural] detrital (2002) showed showed convincing convincingpetrographic petrographic and age relationships that demonstrate this U-bearing phosphate phosphate could could begin begin forming forming in sediments at or just below the sediment-water sediment-waterinterface, interface, shortly shortly after burial. burial. A few years years ago ago itit was was discovered discoveredthat that itit is possible 0 pm possible to date xenotime crystals 1210 pmininsize, size,using usingthe theSHRIMP SHRIMP (Sensitive (SensitiveHigh HighResolution ResolutionIon Ion Microprobe), providing a robust Microprobe), providing robust isotopic isotopic age age for its its formation, formation, hence an age for for early early diagenesis diagenesisand andaa close proxy for sediment deposition. Xenotime is especially useful in that it has has very high high U U contents contents and remains remains closed to to radiogenic radiogenic parent-daughter parent-daughter mobility, unlike most most other other dateable dateablediagenetic diagenetic mineral. Diagenetic Diageneticxenotime xenotimeU-Pb U-Pbgeochronology geochronology has has the the potential potential to unravel unravel the the chrono-stratigraphy chrono-stratigraphy of unfossiliferous unfossiliferous sedimentary sedimentary basins, especially especially those sequences sequences devoid devoid of of dateable dateableinterlayered interlayered volcanic rocks. basins where where aa lack of aareliable main application application is in Precambrian Precambrian basins reliabletemporal temporal volcanic rocks. Its main framework hinders evolution and framework hinders an an understanding understanding of basin basin evolution and maturation, maturation, tectonic tectonic affiliations, metallogeny metallogeny and and value value as as exploration explorationtargets. targets. Xenotime also forms during post-diagenetic fluid flow events, such as alteration, mineralisation mineralisation and and metamorphism, as well as being metamorphism, as being aa magmatic magmatic mineral mineral and and aadetrital detritalheavy heavymineral. mineral.The Theexceptional exceptional its excellent range excellent properties in situ range of of formation formation conditions conditions of xenotime, xenotime, coupled coupled with with its properties for in situ geochronology, provide many many new new opportunities opportunities in in establishing establishing the the timeframe timeframe of events geochronology, provide events in inmany many hitherto hitherto poorly poorly understood understoodsedimentary sedimentarybasins. basins. Unusually coarse (up to 200 Unusually coarse 200 microns) microns) and and abundant abundant diagenetic diagenetic xenotime xenotime crystals c!ystals in inthe themetametasandstones of the greenschist greenschist facies Mount Mount Barren Barren Group, Group, southwestern southwestern Australia, Australia, allow allowthe thedetailed detailed study of xenotime within a phosphatic phosphatic sandstone interval and and is study xenotime and its host rock. rock. Xenotime occurs within present in multiple different styles styles - as cement present multiple morphologically morphologically different cement overgrowths overgrowths on zircons, zircons, pyramidal pyramidal overgrowths on on zircons, zircons, cement (no zircon) in shale laminations, replacement of shale (?) (7) intraclasts intraclasts overgrowths and as fluid events events from from early diagenetic to low and as xenotime xenotime crystals crystals within within intraclasts. intraclasts, Multiple Multiple fluid diagenetic to low temperature/early temperaturelearly hydrothermal, hydrothermal, prior prior to metamorphism, metamorphism, were recorded recorded within within single singlexenotime xenotimecrystals. crystals. U/Pb geochronology, accompanied by Ob~eNati0nS observations of of petrographic relationships relationships between SHRIMP UlPb of xenotime and other diagenetic the various various generations generations of xenotime and between between xenotime xenotime and diagenetic minerals minerafs and pyrobitumen,allowed allowedfor for the the construction construction of of a temporal for the diagenetic pyrobitumen, temporal framework framework for diagenetic and and early early hydrothermal events that that occurred within these rocks; (1) ca 1700 1700 Ma: deposition deposition of of partly partlyre-worked re-worked phosphatic siliciclasticsediments sedimentson on the the seafloor seafloor was was followed followed by by in-situ of the in-situ phosphatisation phosphatisation of the phosphatic siliciclastic sediments formation (mean (mean age age of of 1697i 1697± 77 Ma), (2) With burial, sediments and an initial period of xenotime formation burial, an an early pore-filling pore-filling carbonate cement was introduced into parts of the interval, i n t e ~ a las , well well as as early early diagenetic diagenetic cuboid pyrite growth, (3) ca 1650 1650Ma: Ma: during during burial burial diageriesis, diagenesis, aa fluidfluid- movement movementevent eventcaused causedthe the dissolution of of primary pore pore space space and formation of of xenotime xenotime (mean age of 1646 Ma),with with partial dissolution 1646 ±t 88 Ma), accompanying phosphate remobilisation, (4) Oil migration event, (5) Several accompanying Several silica silica cement cementgenerations generations introduced around this time, (6) ca ca 1560 1560Ma: Ma: minor minor addition addition of of xenotime xenotime rims rimsto toexisting existingovergrowths, overgrowths, (7) ca ca 1480 1480 Ma: Ma: addition addition of of xenotime xenotime cement cement (no (no zircon) zircon) in in shale shale interlaminations, interlaminations, (8) (8) ca ca1200 1200Ma: Ma: peak peak of metamorphism. metamorphism. Wavelength Dispersive Spectrometer (WDS) microprobe analysis of each type type of of xenotime xenotime showed showed a gradual from LREE enrichment enrichment to to MREE MREE enrichment, enrichment,with withtime. time. Due Due to to this this radational gradual change change from gradational nature, discrete boundaries between generations, based based on on chemistry, chemistry, could could not not be established, established. This study of diagenetic to hydrothermal hydrothermal xenotime dramatically dramatically improved improved the the estimated estimatedage agerange rangeof of the Mount Mount Barren Group, which was was previously previously constrained constrained to 1200 1200 Ma Ma(peak (peakmetamorphism) metamorphism)and and 1790 Ma Ma (youngest (youngest detrital detrital zircon zircon population), population), and and discounted discounted some some previous previous tectonic tectonic models models concerning the the timing of collision between between major major cratons cratons within western Australia Australia and andthese these cratons cratons with East East Antarctica. Antarctica. Using the information gleaned gleaned from the study of xenotime in the Mount Mount Barren Barren Group, Group, aa similar similar study study basin in in the the Lake is currently underway on another Proterozoic sediment-dominated basin Lake Superior Superior Region Region containing the the Marquette Range Supergroup Supergroup and and its its equivalents, equivalents, the the North Range, Mille Marquetle Range Mille Lacs Lacs and and containing The early Proterozoic strata consist of of three unconformity-bounded unconformity-bounded lithostratigraphic Animikie Groups. The lithostratigraphic groups consisting of glaciogenics, quartzites, dolomite, iron iron formation, greywacke greywacke and andshale shaleand andminor minor intercalated volcanics. Sedimentation Sedimentation is is thought thought to to have begun Ma (correlation of Chocolay intercalated volcanics. begun —2240 -2240 Ma Chocolay 79 �Group with with Gowganda Gowganda Fm, Fm, upper upper Huronian Huronian Supergroup, Ontario) (Fairbain (Fairbain et al., 1969) 1969) and and ceased ceased by by Group —1850Ma Ma(coinciding (coincidingwith with orogen-normal orogen-normalarc arc collision collision along along the the Niagara Fault zone and the Malmo -1850 Malmo Discontinuity, during during the the Penoken Penoken Orogeny) Orogeny)(Sims (Simsetetal., al., 1993). 1993).Part Partof of the the study study is is to to determine Discontinuity, determine if xenotime-rich horizons, such such as as that in the Mount xenotime-rich horizons, Mount Barren Barren Group, can be located located in in this this stratigraphy stratigraphy and to to document document the thesedimentological, sedimentological,structural structuralor orstratigraphical stratigraphicalfeatures featuresthat thatthey theyhave haveinincommon. common. Ceflain rock units units from from the the different different sequences sequences over over the whole whole region region were were targeted targeted for for xenotime xenotime Certain analysis using proposed proposed sedimentological sedimentoiogical controls for xenotime formation that were determined from the Mount Mount Barren BarrenGroup Groupstudy. study. One sedimentary feature favourable to xenotime formation may be the presence of large quantities of sedimentary sedimentary apatite apatite within within the the host host rock rock or or adjoining adjoining rocks. rocks. A A field fieid sample sample of of low low greenschist greenschist facies facies phosphatic chert-conglomerate,atat the the base base of the Baraga phosphatic chert-conglomerate, Baraga Group, Group, from from aa documented documented phosphorite phosphorite locality locality in in the Dead Dead River River Basin, Basin, northern norlhern Michigan, contains large quantities of xenotime ranging from <30 <30 pm pm pitted pittedovergrowths overgrowthson on detrital detritalzircons, zircons,to to>100 >I00micron micronxenotime xenotimecements. cements. Other rock units units that that contain contain xenotime xenotime overgrowths overgrowths and cements of appreciable appreciable size and quantity, were; were; (i) (i) quartzite quartzite beds beds ininseveral several drillholes drillholesthrough through the the Mahnomen Mahnomen Formation, Formation, Mille Mille Laos Lacs Group, Group, Cuyuna Range, Range, contain up up to to 50 50 xenotime xenotime crystals crystals per per thin thin section, section, some someofofthese theseup uptoto—60 -60 pm pmin in size, (ii) (ii) aa sandstone sandstone bed bed within drillcore from the base of the Baraga Group in Dead River Basin- its largest was 60 o b s e ~ e dwas 60 pm pm(Di) (iii) aagrit-pebble grit-pebbleconglomerate conglomerate and and very very coarse-grained coarse-grained largest xenotime xenotime observed sandstone sandstone outcrop outcrop at Slate Slate River River Kill Hill locality, locality, Baraga Baraga Basin, Basin, which is is assumed assumed to to lie lie at at the the base base of of the the xenotime grains grains per per thin thin section which are pm in in size, and (iv) Baraga Group, averaged averaged —15 -15 xenotime are up up to to —60 -60 prn conglomerate at Big Eric's Crossing locality, Baraga Basin, contains the basal basal Baraga Baraga Group hematitic conglomerate up to 55 xenotime xenotime grains grains per per thin thin section, section, some some of of these these are are up uptoto—100 -100 pm pm in insize. size. Pokegema Pokegema Quartzite Quartzite samples, samples, West West Mesabi Mesabi Range, Range, showed showed minor <30 pm prn xenotime xenotime overgrowths overgrowths on on zircons. zircons. All of of the therock rocksamples samplesdescribed describedabove aboveare arevery verycoarse-grained coarse-grainedsandstone/conglomerate sandstone/conglomerate beds beds which are either which either located located near near aastratigraphic stratigraphic boundary boundary and/or andlor are are interbedded interbedded with with shale shalebeds. beds. Xenotime Xenotirne from these localities were analysed on the SHRIMP SHRIMP and and revealed revealed several several age age groups; groups; (i) (i) xenotime xenotime in in the the Mahnomen MahnomenFormation Formationdrillcore drillcorerevealed revealedages agesofof—1870 -1870 Ma Maand and—1770 -1770 Ma (1760-1790 (1760-1790 Ma), (U) One large xenotime overgrowth from the Dead drillcore,gave gavean anage ageofof—2600 -2600 (ii) One Dead River RiverBasin Basindtilfcore, Ma, (Di) xenotime contained contained within within the the Slate River Hill outcrop (iii) xenotime outcrop yielded yielded ages ages of of —2500 -2500 Ma, Ma, (iv) the samples from Ma. The The samples from Big Big Eric's Eric's Crossing Crossingcontained containedxenotime xenotimeshowing showingages agesofof—2550 -2550 Ma Ma and and —1750 -1750 Ma. Ouartzite in in the the West West Mesabi Range, Range, contained contained xenotime xenotime with with an an age age of of Pokegem Quartzite sample from the Pokegema -2300 -2300 Ma Maand and—1770 -1770 Ma. Ma. Xenotime yielding yielding ages ages of of ca 2500 Ma Xenotime Ma or or older older may may be befrom fromrecycled recycleddetrital detrital(magmatic) (magmatic) grains. grains. The younger Ma (1760-1790 (1760-1790 Ma), Ma), occurs occurs in in xenotime from widespread localities younger age age of of —1770 -1770 Ma localities across across the Lake Lake Superior Superior Region Region and may may reflect reflect an an epigenetic epigenetic thermal thermal event event across across the the region. region. The The age age Maof of anorogenic anorogenic magmatism, magmatism, pluton pluton emplacement emplacement and and appears to correlate correlate with an an episode episode at at —1760 -1760 Ma gneissic doming gneissic doming recorded recorded throughout throughout Wisconsin, Wisconsin, northern northern Michigan Michigan and and central centralMinnesota. Minnesota. ItIt partial melting of crustal rocks postdates the Penoken Orogeny and involved paflial rocks as as aa result result of of continentcontinentcontinent or continent-arc collision to the south south of the the region region (Sims, (Sims, 1996). 1996). This This event event is is approximately approximately coeval with the development of the Central Plains Plains Orogen (1800-1630 Ma) to the south and may be a consequence consequence of the the accretion accretion of this this terrane terrane to to the the North North American American continent continent(Sims, (Sims, 1996). 1996). This study highlights highlights the sensitivity of in-situ xenotime geochronology to identifying identifying cryptic fluid flow events within within basins. basins. This This study study will be be ongoing ongoing in in 2003-2004. 2003-2004. Fairbafrn H.W., Hurley, P.M., P.M., Card, K.D. K.D. and and Knight, C.J., C.J., 1969, Correlation and radiometric ages of Fairbaim H.W., Nipissing metasediments with Proterozoic Canadian Journal Journal of Nipissing Diabase Diabase and Huronion Huronlon metasedlments Proterozoic events in Ontario: Canadian Earth Sciences, v. 6, p. D. 489-497. Sims, P.K., Proterozoic Penokean eds., Archean and P.K., 1996, 1996,Early Ear1y'~roterozoic PenokeanOrogeny, Orogeny,ininSims SlmsP.K. P.K.and andCarter, Cafier, L.M.I-1., L.M.H., eds., and Late Survey Late Proterozoic Proterozoic Geology Geoloav of the Lake Lake Superior Suoerior Region, Realon. U.S.A.. 1993: 1993:U.S. US.Geological Geoloaical S u ~ eProfessional vProtessional -, of - . U.S.A., u Paper 1556, p.28-60. 1556, p. 28-60. Sims, al., 1993, Region and Trans-Hudson Trans-Hudson Orogen, in J.C., Jr., Jr., and Slms, P.K., P.K., et al., 1993, The Lake Superior Region in Reed, Reed, J.C., and others, eds., eds., Precambrian:Conterminous Society of of America. America, the the Precambrian:Conterminous U.S.: US.: Boulder, Colorado, Geological - Souetv Geology of ~ North v. C-2, p. o r l America, hAmerica, v. p. 11-120. 11-120. Vallini, B.,. Kranez. Krapez, B.,. Fletcher. Fletcher, l.R., Vallini.. D., D...Rasmussen, Rasmussen. 5.. 1.R.. and and McNaughton, McNauahton. N.J.. 2002, 2002.. Obtaining Obtainina diagenetic diaoenetlc , . B.. - . N.J., ages from metamorphosed sedimentary rocks: U-Pb of unusually metamorphosed sedimentary U - ~ dating dating b unusually coarse coarse xenotime xenotirne cement cement in In phosphatic v.30, phosphatic sandstone: Geology, v. 30,p. p.1083-1086. 1083-1086. ~ ~~ 80 . ~-~ ~ �EVALUATION OF INITIAL MAGMA COMPOSITIONS COMPOSITIONS FOR FOR THE THE BALD BALD EAGLE EAGLE INTRUSION INTRUSION AND ASSOCIATED ROCKS VISLOVA, Tatiana, Tatiana, Department Department of of Geology Geology and and Geophysics, Geophysics, University University of of Minnesota Minnesota VISLOVA, funnel-shaped concentrically-zoned concentrically-zoned Bald the Duluth Duluth The funnel-shaped BaldEagle Eagle Intrusion Intrusion in in the Complex is characterized characterized by very very restricted mineral compositions, and consists consists of of only only two units: units: ananolivine—plagioclase olivine-plagioclase cumulate cumulateand andananolivine—plagioclase-clinopyroxene olivine-plagioclase-clinopyroxene cumulate (Weiblen, 1980). In terms terms of of differentiated differentiated units units (Weiblen, 1965; Weiblen Weiblen and Morey, 1980). expected in the Bald to be expected in a typical typical layered layered intrusion, intrusion, the Bald Eagle Eagle Intrusion Intrusion appears appears to be petrologically petrologically incomplete. incomplete. This This has has raised raised the question question whether the four-phase (olivineplagioclase-clinopyroxene-oxide)cumulates, cumulates, assigned assignedto to the the Greenwood Lake Intrusion plagioclase-clinopyroxene-oxide) found to to the south of the Bald Eagle (Miller et al., 2002), and granophyre granophyre found Eagle Intrusion Intrusion are genetically related to the Bald Eagle Intrusion Intrusion (Weiblen (Weiblen and and Morey, Morey, 1980). 1980). New petrographic studies and and microprobe analyses (Vislova, (Vislova, 2003) 2003) make make it New petrographic studies microprobe analyses possible to evaluate for the Bald possible evaluate parent parent magma magma compositions compositions for Bald Eagle Eagle Intrusion, Intrusion, and and quantitatively assess possible petrogenetic relationships between the Bald Bald Eagle Eagle Intrusion Intrusion and spatially associated rocks. Computer programs programs (MELTS, Ghiorso and Sack, Sack, 1995; 1995; Ariskin et et al., al., 1993) were used to investigate and COMAGMAT, COMAGMAT, Ariskin investigate these questions. questions. A A primitive North North Shore Volcanic Group olivine tholeiite tholeiite (P-melt) (P-melt) was used as as an an initial initial composition (Miller magma composition (Miller and and Ripley, Ripley, 1996). 1996). Equilibrium crystallizationofof P-melt, P-melt, calculated calculated by by MELTS Equilibrium crystallization MELTS at at I1 atm total total pressure and oxygen quartz-fayalite-magnetite pressure oxygen fugacity fugacity near near ororbelow belowthethe quartz-fayalite-magnetite buffer, buffer, reproduces the crystallization order and mineral assemblages observed in the Bald Eagle Intrusion. The The calculated calculated composition compositionof ofthe thefirst firstclinopyroxene clinopyroxene(mg (mg— 81) 81) equals the one of the first plagioclase and olivine observed, however calculated compositions of olivine are are much much higher than those This could be ascribed higher those observed. observed. This ascribed to to the the dynamics dynamics of ofcrystal-melt crvstal-melt - than segregation in in a flowing segregation flowing magma system. Until the crystals crystals suspended suspended in magma magma grow grow large enough they might be carried away, erupted, and found as phenocrysts in lavas. lavas. At -—7 At 7 % melt melt remaining remaining MELTS MELTS reproduces reproduces the most most evolved evolved mineral mineral compositions in in the Bald Eagle This suggests that the Bald compositions Eagle Intrusion Intrusion (Fig. (Fig. 1). This suggests that Bald Eagle Eagle Intrusion might might be be a complete sequence with with a few Intrusion complete crystallization crystallization sequence few percent percent remaining remaining melt. the question melt. It leaves leaves unanswered unanswered the question of of the the origin origin of of four-phase four-phase cumulate cumulate and and granophyre. Modelingshows showsthat that aa more more evolved evolved high high Ti Ti and and high high Fe melt Modeling melt (D-melt) (D-melt) is required for crystallization of the evolved evolved units units in in the the Greenwood GreenwoodLake Lake Intrusion Intrusion (Fig. (Fig.1). 1). This melt of P-melt in an melt can can be be produced produced by by fractional fractional crystallization crystallization of an intermediate intermediate magma chamber at 2-3 kbar total total pressure. Equilibrium crystallization of of D-melt D-melt at 1 atm Equilibrium crystallization atm reproduces reproduces the the crystallization crystallization order, the the appearance of Fe-Ti Fe-Ti oxides, oxides, and and the the compositions most of order, appearance of compositions ofof most of the the units units associated with the Bald Eagle Intrusion (Fig. I). 1). However, However, the the most most evolved evolvedrocks rocks in in the the Greenwood LakeIntrusion Intrusion(ferrogabbro (ferrogabbrowith withFoFo<c 50) 50) and Greenwood Lake and granophyre granophyre were were not not reproduced crystallization. These units might require fractional reproduced by equilibrium equilibrium crystallization. require fractional crystallization or assimilation. assimilation. - 81 �. 65 c. C x 0 I- 6•, >1 . ,. I • 4: A -. 265 65 A£As Zig, A • 1 4 .f s0 E , 6060 A 5 A AA - A . 55 55 1 <>Bald EagleIntrusion Intrusion oBald Eagle tGreenwood AGreenwoodLake LakeIntrusion Intrusion +Calculated from P-melt P-melt • Calculated from sCalculated A Calculatedfrom from D-melt D-melt I 30 30 40 40 50 60 50 60 Mg/ (Mg+Fe) (Mg+Fe)in in olivine olivine Atom % % Mgf 70 70 60 80 MgI(Mg+Fe) variations variations in in coexisting olivine and Fig. 1. Mg/(Mg+Fe) and clinopyroxene. clinopyroxene. References: References: Ariskin, A.A., Frenkel, M.Y., MY., Barmina, Barmina,G. G. S., S., and and Nielsen, Nielsen,R. R. L., L.,1993, 1993,COMAGMAT; COMAGMAT;aa differentiation processes. processes, Computers & Geosciences, 19 FORTRAN program to model magma differentiation (8), p. 1155-1170. 1155-1170. Ghiorso, mass transfer transfer in magmatic processes; IV, A Ghiorso, M. S., and Sack, Sack, R.O., 1995, 1995, Chemical mass revised and internally consistent thermodynamic model for the interpolation interpolation and internally consistent and extrapolation extrapolation elevated temperatures and pressures, of liquid-solid equilibria in magmatic systems at elevated Contributions to Contributions to Mineralogy Mineralogvand and Petrology, Petrolopy, 119 119(2-3), (2-3),p. p. 197-212. 197-212. Hauck, S.A., Peterson, Peterson, D.M., D.M., and Miller, J.D., Jr., Green J.C., Severson, Severson, M.J., Chandler, V.W., Hauck, Wahl, T.E., 2001, Geology and mineral potential of the Duluth Complex Complex and related related rocks rocks of Geological Survey SurveyReport Report of of Investigations Investigations 58,207 58, 207pp. pp. + + northeastern Minnesota: Minnesota Geological disc in back pocket, 2002. compact compact pocket, 2002. Miller J.D., Jr. and and EM. E.M.Ripley, Ripley,1996, 1996,Layered Layeredintrusions intrusionsofofthe theDuluth DuluthComplex, Complex,Minnesota, Minnesota, USA. In: In: Cawthorn Cawthom R.G. (ed.) (ed.)Layered Lavered Intrusions, Intrusions, 531 pp. Vislova, T., 2003, Petrology of the Bald Eagle Intrusion and associated rocks rocks and its its relevance relevance to to crystallization in dynamic magma chambers in in the the Midcontinent Midcontinent Rift, Ph.D. Dissertation, crystallization Dissertation, University of Minnesota, Minnesota, 226 226 pp. pp. Weiblen, P.W. and Morey, Ci. B., 1980,AAsummary summaryof ofthe thestratigraphy, stratigraphy, petrology, petrology, and and structure structure G. B., 1980, of the Duluth Complex. In: In: Irving, Irving, A. J., and Dungan, M. A. A. (ed.), (ed.),1980, 1980,The TheJackson Jacksonvolume, volume, p. 88-133. 88-133. American Journal of Science, Science,Vol. Vol. 280-A, 280-A, Part Part 1,1,p. funnel-shaped, gabbro-troctolite gabbro-troctolite intrusion in the Weiblen, P.W., 1965, 1965, A funnel-shaped, the Duluth Duluth Complex, Complex, Lake Lake Ph.D. Dissertation, Dissertation, University County, Minnesota, Ph.D. University of Minnesota, 161 161pp. pp. 82 �A Hydrothermal Component A Component of Iron Formations-A Marquette Range Perspective T.D., 141 141 Chippewa, Chippewa, Negaunee, MI MI 49866 49866 Waggoner, T.D., The origin of of Lake Lake Superior Superior banded banded iron iron formations formations (BIF) (BIF) has has been been aa contentious contentious issue issue for at least aa century century and and aa half. half. Concepts of origin include include weathering, weathering, volcanic and organic activity activity whereby ions are carried Clear organic whereby ions carried in in and andprecipitated precipitated from from solution. solution. Clear definition of of the definition the source, source, mode mode of of transport transport orordepositional depositionalmechanisms mechanisms isis generally generally lacking. This Thispaper paperwill willaddress addressthe the strong strongevidence evidence for for aa hydrothermal hydrothermal source for "hard ores" found in the upper parts of ores" of the the Negaunee Negaunee Iron Formation (NIP) (NIP)and by extension a possible source BIP portion. The source for for the precursor hematite in the BIF TheRange Range was was formed formedin in aa tectonically active area believed to be an extensional rifting environment not unlike those active an extensional rifting environment unlike those found in Fe-Oxide (Cu, U, U,Au, REE) and some VIIMS VHMS deposits deposits The Marquette Range portion of the the Lake Lake Superior SuperiorIron Iron District District displays displays many many features features similar to other large Lake Superior BIFs found around the world and, thus, making it an excellent study subject subject for for the source excellent study source and and role role played played by by igneous igneous and andsedimentary sedimentary processes. The TheNegaunee Negauneeand andbasal basalGoodrich Goodrichunits unitsexhibit exhibitBlIP, BIF, soft soft supergene supergeneenriched enriched concentrationsand and "hard "hard ores" ores" as massive concentrations massive bodies, bodies, banded banded jaspilites jaspilites and and detrital detrital "Hard ores" conglomerates. "Hard conglomerates. ores" are generally generally dense silver gray to black black massive massive metallic metallic magnetite or schistose metallic hematite associated with jaspilite jaspilite and contain in excess of of of the the origin of the 60% iron. iron. Discussion Discussion of the "hard "hard Ores" Ores" on on the theMarquette Marquette Range Range has has metamorphism or revolved revolved around around supergene supergene enrichment enrichment prior to metamorphism or hydrothermal hydrothermal enrichment associated associated with the Penokian Orogeny. Orogeny. of the field field geology geology do donot not support support with with either eitherof ofthese thesepositions. positions. First, the Many features of cobble and pebbles of jasper hematite in the the basal basal Goodrich Goodrich conglomerate conglomerate show show random random orientation of of the 'schistose' orientation 'schistose' hematite hematite indicating indicating the the schistose schistose nature nature of of the the hematite hematite not a result of metamorphism. In existed prior to emplacement and not In addition addition many many of of the the with the "hard rocks associated associated with "hard ores" ores" exhibit exhibit hydrothermal hydrothermal minerals minerals including including sericite, sericite, tourmaline, chlorite, chloritoid, high aluminous silicates, garnet, hematite, magnetite and tourmaline. The lower and Menominee below the the NIP lower Proterozoic Proterozoic Chocolay Chocolay and Menominee sediments sediments below NIF exhibit exhibit Specular, multiple examples examples of of high-grade hematite that that can be interpreted multiple high-grade hematite interpreted as as vents. vents. Specular, microplaty and and bytroidal bytroidalhematite hematiteare arefairly fairlycommon commonininmany manyoutcrop outcropareas. areas. Some Some of of microplaty All the sites these have been described previously in literature while others have not. previously others have not. All sites were subject to exploration for iron ore during century and most exhibit exhibit were exploration for during the the late late 119th9 century shallow shafts. The The major major components components are are chert, chert, jasper and and vein quartz along along with coarse specular, microplaty microplaty and and bytrioidal bytrioidal hematite hematite contained contained in in breccia breccia zones zones that exhibit specular, exhibit episodic reworking. reworking. There episodic There are are alterations alterations to the host host rock rock as as some some occurrences occurrences exhibit exhibit chlorite, silica, silica, k-spar and aluminous alurninous silicates. silicates. A large area in sections sections 21, 22, and and 23, 23, 47-26 47-26 contain contain multiple multiple enriched enriched hematite hematite sites breccia zones adjacent to northwesterly trending faults. that form two northwest trending breccia In addition there is aa In addition to the the silica silica flooding, flooding, brecciation brecciation and and hematite hematite concentration concentration there significant area area of of andalusite cordierite and and chloritoid chloritoid adjacent adjacent to to the eastern significant andalusite cordierite eastern linear linear 83 �breccia zone in section 23. These section 23. Theseminerals minerals are are present present in aa much much broader lower regional chlorite zone of metamorphism metamorphism and most likely are a result of the hydrothermal event that impacted the three square square miles miles referenced referenced above. above. A conglomerate in Sec. 22 and 23, 47-26 has been previously described as "unusual" and 23,47-26 is sandwiched sandwiched between between lower Chocolay Chocolay argillite argillite units. units. Clasts causing dimpling in the underlying argillite were described as rafted elasts clasts from a glacial interlude. interlude. It is unlikely reef growth growth during during the the same period of of that a glacial event coincided with significant algal reef time. The "unusual" is extremely coarse, tightly tightly packed packed and and shows no time. "unusual" conglomerate conglomerate is extremely coarse, sedimentary features, sedimentary features. In addition significant rinds of k-spar have formed on the the granite granite gneiss cobbles. The The cobbles cobbles and and matrix matrix contain contain euhedral euhedral magnetite, martite and specular hematite suggesting suggesting this this area was tectonically active and may well have been been an an active active vent area over a period vent period starting starting at the the earliest earliest extensional extensional period period and continued continued to be active beyond resembles some some of of the breccias beyond the Ajibik Ajibik time. time. The conglomerate conglomerate resembles breccias at Olympic Dam and could well be a hydrothermal breccia. REE chondrite normalized analysis of of the hematite vents match quite closely closely with with both both the hematite, mametite magnetite and combination the hematite. combinationhematite/magnetite hematitelmasnetite "hard ores" found found throughout the the Range. Range. Recent hematite confirms throughout Recent work work on on the the Brockman Brockman microplaty microplaty hematite confirms a hydrothermal hydrothennal origin due to the recognition of surrounding alteration to the host. - - Initially the the vent vent areas areas were were studied studied in in relation relation to to the "hard "hard Ores" Ores" but the fact fact that that the the vents are all hematite suggests they could be the source for the precursor hematite seed hematite the source for the precursor hematite seed cores that Han Han identified identified in low low metamorphic metamorphic grade grade BIF BIF units. units. These seed cores cores have have been been identified identified in in the theNegaunee, Negaunee, Biwabik, Biwabik, Brockman, Brockman, Solcoman, Sokoman, Temiscamie Temiscamie and and Kuruman Iron hon Formations. Formations. that the extensional phase of rifting ceased ceased near near the the end of NIP time It is quite plausible that ofNIF and and aa reverse reverse compressional compressional event event started started causing causing faulting faulting that that produced producederosional erosional material for the basal Goodrich conglomerate. conglomerate. Reference: Reference: Origin of of Magnetite hon Formations Han, T.H., 1988, 1988, Origin Magnetite in Precambrian Precambrian Iron Formations of Low Low Han, T.H., Metamorphic Grade, Grade, Proceedings Proceedings of of the Seventh Metamorphic Seventh Quadrennial Quadrennial IAGOD Symposium, Symposium, p. 641-656. 641-656. 84 �nigh-Resolution High-ResolutionMultibeam Multibeam Bathymetry Bathymetry in in Lake Lake Superior. Superior. N. J. N. J. Wattrus Large Large Lakes Lakes Obsewatory, Obseruotory,University Universityof of Minnesota, Minnesota, Duluth, Duluth,MN MN 55812 55812 Like all large large lakes, lakes, the the composition composition and and shape shapeof ofthe thelake lakefloor floorof of Lake Lake Superior Superior reflects the processes that well as as in in the past. that shape shape its its formation formation today as well Maps of of the the lake floor floor made made with withtraditional traditional echosounders echosounders lack the resolution resolution to these processes preserved preserved in in permit scientists to read the subtle subtle "fingerprint' "fingerprint" of of these the lake-floor. advent of of modem, modem, high-resolution high-resolution multibeam multibeam sonar has has lake-floor. The advent revolutionized the the mapping mappingof of the the sea-floor. sea-floor. In a traditional echosounder, echosounder, the depth depth to to the thelake-floor lake-floor below the ship ship is measured measured by by timing timing how how long long It it takes for an an acoustic acousticping ping to to travel travel to to and back to the ship. the lake-floor and ship. the delay, the deeper The longer the deeper the the lake This type of surveying lake floor floor is. This surveying provides high-resolution bathymetric information along the trackline trackline followed by the the survey survey boat. is followed by boat. Nothing Nothing is about the known about the lake lake floor floor either either side. side. High-resolution multibeams use a fan of acoustic acoustic beams beams (over (over100) 100)to measure the shape of the measure the shape of the lake lake floor floor along a "swath'. "swath".By sailing a series of overlapping swaths, It it is possible to achieve complete complete coverage coverage of the lake lake floor at high resolution. resolution. Backscatter Backscatter information informationcollected collected with with the bathymetric data can can be used to to create psuedo-sidescan images of the create psuedo-sidescan images These can can be used to map lakefloor. These map spatial variations variations in the spatial the composition composition of the the lake lakefloor. floor. from the the catalog catalog of ofmultibeam multibeam surveys surveys conducted conducted by the Examples, drawn from Large Lakes LakesObservatory, Observatory,are arepresented. presented.These Theseillustrate ifiustrate the the potential potential of of this this Large formapping mapping the the subtle subtle signal processes technology for signal of past geologic processes superimposed on superimposed on the the lake lakefloor. floor. 85 � https://digitalcollections.lakeheadu.ca/files/original/8525569c75ccfe6981beac1369d7b7e6.pdf 8131941cb506976ea49cb08392f013c4 PDF Text Text INSTITUTE ON ON LAKE LAKE SUPERIOR SUPERIOR GEOLOGY GEOLOGY INSTITUTE 49t 4 9 'Annual ~ n n u aMeeting Meeting l Proceedings Volume 49 Part 2- Field Trip Guidebook QuinnesecMine, Mine.Menominee MenomineeIron IronDistrict District Quinnesec Wausecapyritic pyriticslate slate Wauseca A' Refoldedfold foldstyle styleof ofIron IronRiver-Crystal River-CrystalFalls Fallsallochthon allochthon Refolded Iron Mountain, Mountain, Michigan Michigan Iron May 7-11, 7- 11,2003 May 2003 �INSTITUTE ON LAKE SUPERIOR GEOLOGY 49TH ANNUAL MEETING MAY 7-12, 2003 IRON MOUNTAIN, MICHIGAN HOSTED BY: HOSTED Laurel Laurel G. Woodruff and William William F. F. Cannon Co-chairs Co-chairs U.S. Geological Geological Survey Survey With assistance from Michigan Technological University University and and John Gartner, John Gartner, Coleman Engineering Engineering Company Company Local committee committee representative representative Proceedings Proceedings Volume Volume 49 49 Part 2 2— Field Trip Trip Guidebook Guidebook - Field Compiled Compiled and and edited editedby byWilliam WilliamF. F.Cannon, Cannon,USGS USGS Illustrations prepared Dickenand andStacy StacySaari, Saari,USGS USGS Illustrations preparedby byConnie ConnieL.L.Dicken �CONTENTS Proceedings Volume Volume 49 49 Proceedings Part 2— 2 - Field Trips Part Trips Overview—Paleoproterozoic stratigraphy and Overview-Paleoproterozoic stratigraphy and tectonics tectonics along along 1 the the Niagara Niagara suture suture zone, Michigan Michigan and Wisconsin Wisconsin. ....... .1 Trip Trip 1. 1. Pembine-Wausau Pembine-Wausau magmatic magmatic terrane Trip Trip 2. Menominee Menominee Iron Iron District District. ................. . 3333 .......................... . 47 47 Trip Trip 3. Stratigraphy Stratigraphyand and structure structureof of the the Iron Iron RiverRiver644 Crystal Crystal Falls Falls basin basin. ................................ . 6 Trip Trip 4. Life Lifecycle cycleof ofan aniron irondeposit—the deposit-the Republic RepublicMine Mine 877 from from ore ore genesis genesis to mine mine restoration restoration ................ . 8 Cover illustrations: illustrations: Wauseca Wauseca Pyritic Pyritic Member Member of Dunn Dunn Creek Creek Slate. AAsulfide sulfidefacies faciesiron-formation iron-formationfrom fromthe the Iron Iron River-Crystal River-Crystal Falls district, Michigan. Original Original photograph photograph appears appears in USGS in USGS Professional ProfessionalPaper Paper 570. 570. Schematic illustration illustration of cross-folding cross-folding in in the the Iron Iron River-Crystal River-CrystalFalls Falls district district as as depicted depicted USGS Professional ProfessionalPaper Paper 570. 570. in USGS Quinessec Mine in the Menominee Iron District at at Quinnesec, Quinnesec, Michigan. Michigan. Photograph by Photograph by Elizabeth Heinen. Heinen. Elizabeth �PALEOPROTEROZOIC STRATIGRAPHY AND TECTONICS ALONG THE PALEOPROTEROZOIC STRATIGRAPHY NIAGARA NIAGARA SUTURE ZONE, MICHIGAN AND WISCONSIN G.L. LaBerge1, ~ a ~ e r g eW.F. ' , cannon2, J.S.Klasne,3, ~lasne?, W,Ojakangas4 0jakangas4 Cannon2, K.J. K.J. Schulz2, Schuli, J.S. R.R.W. U.S. University Wisconsin-Oshkosh(retired) (retired)and and U.S. U.S. Geological GeologicalSurvey, Survey,2* U.S. University of Wisconsin-Oshkosh Geological Survey, Geological Survey, Western Illinois University (retired) and U.S. U.S. Geological GeologicalSurvey, Survey, University (retired) 4 University of Minnesota Minnesota Duluth Duluth (retired) (retired) INTRODUCTION INTRODUCTION The Niagara Niagara suture zone formed during the Penokean Penokean orogeny at about 1875 1875 Ma by collision of island island arcs of the Wisconsin magmatic magmatic terranes with the southern margin of the Superior craton and its epicratonic cover of the Marquette Marquette Range Supergroup. The Niagara Niagara fault, fault, generally generally considered considered the the principal principalsuture suture Supergroup. boundary, has an arcuate trace across northern Wisconsin defined defined primarily from geophysical data, sparse sparse outcrops, outcrops, and and widely widely spaced spaced drill drill core core data data(fig. (fig.1). 1).In In geophysical more detail, the Niagara fault is but one of a family of subparallel anastamosing anastamosing faults that bound bound structural panels of Paleoproterozoic Paleoproterozoic rocks, which together comprise the Niagara suture zone (fig. 2). The rocks within these panels have a distinctive structural style marked marked by by tight tight folds folds with with widely widely varying varying but but commonly commonly steeply plunging axes. These probably formed by refolding of simpler, gently plunging folds, which are widely recorded recorded in in correlative correlative strata strata north north of of the the suture suture zone. A blanket of glacial material material over most of the region, the on-lap of Paleozoic thick cover cover of of Keweenawan Keweenawanrocks rocksof of Paleozoic rocks rocks in northern northern Michigan Michigan and and aa thick the Midcontinent rift system in northwestern Wisconsin and eastern Minnesota Minnesota have obscured the suture zone over most of its length in the southern Lake Superior region. region. The area area described described in in this this guide guide is is the the only only area areawhere where extensive exposures allow direct observations observations of stratigraphic stratigraphic and and structural structural features along features along the collision collision zone. The purpose of these field trips is to examine exposures along and on both sides of the Niagara suture zone. Stops were chosen to illustrate: 1) the Paleoproterozoic Paleoproterozoic sedimentary sedimentary sequence sequence developed developed on on the the continent continent margin; margin;2) 2) magmatic terranes; and 3) igneous rocks that constitute parts of the Wisconsin magmatic some of the structural collision of the island island structural features produced as a result of the collision arcs with the continent margin, and their influence influence on interpretations interpretationsof the stratigraphy. stratigraphy. 1 �92' 84' 88' EXPLANATION 46' Pajeozoic strata- limestone, dolomite, sandstone shale Grenville Province- Middle Proterozoic gneiss and Ed'dáiplutonic rocks fiIi.± Midcontinent Rjft- Middle Proterozoic flood basalt, rhyolite, sandstone, and gabbroic intrusive rocks Anorogenic pluton- Middle Proterozoic granite, " anorthosite Marquette Range Supergroup andAnimikie GroupEarly Proterozoic metasedimentary and meta vol conic rocks. Iron ranges in black Wisconsin Maginatic Terranes- Early Proterozoic metavolcanic, metasedimentary rocks, andplutons Huronian Supergroup- Early Prolerozoic sedimentary rocks, gabbroic intrusions Superior Province- Archean granilic and - ' metavolcanic rocks — — — Gravity gradient, southern edge ofArchean craton MAJOR JR ON RANGES A Gogebic B i'il'arquette ( I \• C Menominee 42' D Iron River Crystal Falls E Cuyuna F Mesabi 2 TGGUnfltit 92' Figure Figure1. 1.Generalized Generalizedgeologic geologicmap mapof ofthe theLake LakeSuperior Superiorregion regionshowing showingthe themajor majoriron iron ranges. ranges. The Thesouthern southernpart partof ofthe theupper upperpeninsula peninsulaofofMichigan Michiganand andadjacent adjacentparts partsofofnortheastern northeastern Wisconsin Wisconsincontain containexposures exposuresofofArchean Archeanrocks rockswith withoverlying overlyingPaleoproterozoic Paleoproterozoic metasedimentary metasedimentaryand and metavolcanic metavolcanicrocks rocksof of the theMarquette MarquetteRange RangeSupergroup, Supergroup,as aswell well as as aa wide wide variety varietyof of volcanic, volcanic, sedimentary, sedimentary,and andintrusive intrusiverocks rocksof ofthe theWisconsin Wisconsin magmatic magmaticterranes. terranes. The The modern moderngeologic geologicframework frameworkofofthe thearea areahas hasbeen beenestablished established largely 1940'sthrough through largely by by mapping mappingby by the the U.S. U.S. Geological GeologicalSurvey Surveyconducted conductedfrom fromthe the1940's the Jamesand andothers, others,1968; 1968;Sims, Sims, the1980's 1980's(Bayley, (Bayley,and andothers, others,1966; 1966;Dutton, Dutton,1971; 1971;James 1990; 1990; Sims Sims and and Schulz, Schulz, 1993). 1993). Beginning Beginningininthe thelate late1970's, 1970's,the theimportance importanceof ofthe the Niagara Niagarafault fault zone zone as as aa suture suturebetween betweenoceanic oceanicterranes terraneson onthe thesouth southand andaacontinental continental assemblage assemblageon onthe thenorth northwas wasdocumented documented(Cambray, (Cambray,1978; 1978;Greenberg Greenbergand andBrown, Brown, 1983; Larue and Sloss, 1980; Larue, 1983). This led to a period of study of the 1983; Larue and Sloss, 1980; Larue, 1983). This led to a period of study of thestructural structural geology geology of of the the region regionin inorder order to todecipher decipherthe thestructural structuralevents eventsconsequent consequentto tosuturing suturing (Larue (Larue and and Ueng, Ueng, 1985; 1985;Sedlock Sedlockand andLarue, Larue,1985; 1985;Ueng Uengand andLarue, Larue,1987). 1987).This This guidebook guidebook draws draws heavily heavily on on these these previous previousstudies, studies,supplemented supplementedin inplaces placesby byour our own own observations. observations. 2 �8900 8800 - 8800' - Diabasedike dike Diabase (Middle (MiddleProterozoic) Proterozoic) of the the Niagara of Niagara fault /\/ Faults set set /Av A/Faults Faults Cambrian Cambrian El Munising MunisingSandstone Sandstone Paleoproterozoic 46 00, 0° Metagabbro Metagabbro Paint Grroup, Paint River Grroup, iron-formation iron-formationin inblack black Baraga Group Group Menominee MenomineeGroup, iron-formation iron-formation in in black black Chocolay Chocolay Group Group Wisconsin MagmaticTerranes MagmaticTerranes Archea n Archean Granite Granite and and gneiss gneiss BF BLF CT FT NF NRF -4530 45¡30PRF PRF SRF 30 0 30 60 Badwater fault fault Badwator Bush Lake Lake fault fault Bush Calumet trough Calumet trough Felch Felchtrough trough Niagara Niagara fault fault North North Range Range fault fault Paint Paint River River fault fault South South Range Range fault fault 90 Kilometers Kilometers Figure 2. Geologic Geologic map map of the Niagara Niagara suture suture zone and surrounding surrounding terranes terranes showing the location of named named features referred to in the text. Figure �CONTINENT CONTINENT MARGIN MARGIN SEQUENCE SEQUENCE A thick succession of dominantly dominantly sedimentary rocks that were deposited deposited on Archean basement is widely distributed in northern Michigan, Wisconsin and Minnesota, and, to a lesser extent, in northern northern Ontario. The succession records a wide variety of geologic iron-formations in environments and includes the extensive and economically important iron-formations the Lake Superior Superior region. region. STRATIGRAPHY Archean Archean Carney Lake Gneiss: The Carnev Theonly onlyextensively extensivelyexposed exposedArchean Archean unit unit in in the the field field trip trip area areais is the Carney 2). The The Carney Carney Lake, Lake, like like other other Archean Archean rocks rocks farther farther Carney Lake Lake Gneiss Gneiss (fig. (fig. 2). north, is exposed in the core of a Penokean bounds the Menominee Penokean structural uplift. It bounds Menominee Range on the north north and and is is the the basement basement on on which which the the Paleoproterozoic Paleoproterozoiciron-bearing iron-bearing sequence sequence of the Menominee Menominee Range Range was deposited. The Carney Lake Lake Gneiss is seen at stops 2-2 and 2-3, where it is exposed beneath the unconformity unconformity at the base of the Paleoproterozoic Fern Creek Formation. According to Treves (1 (1966) 966) granitic gneiss forms forms about 85 85 percent percent of the the unit. unit. Inclusions Inclusionsof of amphibolite, amphibolite, biotite biotite schist schist and and some some quartzite quartzite constitute constitute about about 10 10 percent, the the remainder remainder being being granodiorite granodiorite and and syenite syenite dikes. AmphiboUte inclusions are are more abundant in the northern Amphibolite inclusions northern part part of the the complex, complex, whereas biotite biotite schist is is more more common common in in the southern part. part. According to Davis Davis and and others others (1960) (1960) the Carney Carney Lake Lake Gneiss Gneiss is is about 2,700 million million years old. Foliation Foliation and tabular inclusions inclusions define a complex internal internal folding pattern pattern in the gneiss, which is mostly mostly a result of Archean Archean deformation. deformation. Paleoproterozoic Paleoproterozoic The Paleoproterozoic continent continent margin margin sequence is is comprised comprised of sedimentary and volcanic rocks rocks at at least least several severalkilometers kilometersthick thickininthe theMenominee Menomineeand andIron IronRiver River--Crystal Crystal Falls districts and probably much thicker in much of the area. The stratigraphic relationships are shown in figure 3, which compares the stratigraphy in the field trip area relationships with that in other well-studied well-studied areas to the north north and east. Originally Originally referred referred to as "Huronian" by (1911), and andlater lateras as"Animikie "AnimikieSeries" Series"by byJames James by Van Hise Hise and and Leith Leith (1911), (1958), (1 958), the sequence was renamed renamed the Marquette Range Supergroup, comprised of the Chocolay, Menominee, Menominee, Baraga Baragaand and Paint PaintRiver RiverGroups, Groups,by byCannon Cannonand andGair Gair(1970). (1970). The stratigraphic stratigraphic succession succession of the the first three three groups groups is is well well established. established. However, However, the stratigraphic stratigraphic position position of the Paint Paint River River Group, Group, along along with the Badwater Badwater Greenstone, is is of four less certain. The Paint River Group was originally considered the youngest of stratigraphically stratigraphically superposed superposed groups groups by by James James (1958), (1958), but but more more recent recent interpretations interpretations generally emplaced over the Baraga Group. generally consider consider it to be be an allochthon allochthon structurally structurally emplaced The Paint Paint River Group Group may may be be a distal, deeper water equivalent of the Menominee Menominee and Baraga Groups, which has been thrust onto the continental margin during Penokean compressive compressive deformation. deformation. 4 �Areas north and east of Areas north Menominee MenornineeRange Range Iron River-Crystal River-CrystalFalls Falls Iron field trip trip NortheasternWisconsin Wisconsin Northeastern 1 , allochthon allochthon Amberg Granite I 1833 Ma Diabase and gabbro ] 11 1 Goodrich Quartzite Ne 0.1 unconformity unconfmitY Amasa AmasaIron Iron - formation 1- — Negaunee ic lrontormation5 aj -- unconformity — I Piblk AjibikQuartzite Quartzite - ' -I860 Ma —1860 ...Ma 1 Volcanic Volcanic and and mafic mafic intrusive intrusiverocks rocks —1870 -1870 Ma Ma Ophiolite Dunn Creek Slate I Feich FelchFormation Formation Badwater Greenstone uhconfomiity unconformity Kona KonaDolomite Dolomite Randviile Dolomite Dolomite Randville Mesnard Quartzite Sturgeon SturgeonQuartzite Quartzite Enchantment Lake Formation Fern Fern Creek Creek Formation Formation giaciogenic gladogenicsediments sediments unconformity -- unconformity Granite Graniteand and gnelss gneiss n I unconformity 0n 1 Qieciogenlc sediments Archean Archean 1 Granite Graniteand and gneiss gneiss . Riverton Iron-Formation Riverton Iron-Formation 1874 Ma ISiamo Siamo Slate Slate 1 21 2 Hiawatha Graywcke CD z . Vulcan Vulcan Iron-formation iron-formation Volcanics FortuneLake LakeSlate Slate Fortune I 0. I Stambaugh Stambauah Formation Formation Michigamme Michigamme Formation Formation (0 1835 Ma u Diabase and gabbro 2 Michigamme Formation 0 Spikehom Creek Granite I 'Tobin Lake Granite Diabase and gabbro 1752 Ma 1 detachment detachment surface surface Camey Lake Gneiss —2700 Ma Camey!-$;p I Metasedimentary ro Metasedimentaryrocks Note: The Thestratigraphic stratigraphicrevisions revisions shown shown in in Note: diagram diagram are are not not official official USGS USGS revisions revisions to to stratigraphic stratigraphic usage usageas as of of2003. 2003. Figure 3. Correlation Correlation chart chart of Paleoproterozoic Paleoproterozoic strata strata in in Menominee Menominee and and Iron IronRiverRiverFigure Crystal Crystal Falls Falls and and surrounding surrounding terranes. terranes. Includes Includeschanges changesto to previous previoususage usagenot notyet yet officially officiallyadopted adoptedby bythe the USGS. USGS. Chocolay Chocolay Group Group Fern Creek Creek Formation: Formation: Francis FrancisJ.J.Pettijohn Pettijohn(1943) (1943) described describedand andnamed namedthe the Fern Paleoproterozoic Fern Fern Creek Creek Formation, Formation,verified verified itit as as aa basal basal sedimentary sedimentaryunit unit resting resting Paleoproterozoic unconformablyupon upon Archean Archean granitic granitic basement basement of of the the Carney Carney Lake LakeGneiss, Gneiss,and and unconformably suggested aa glacial glacial origin. origin. Additional Additional descriptions descriptionswere were made made by by Trow Trow (1948), (1948), by by suggested Freedman and and others others (1961) (1961) and and by by Bayley Bayley and and others others (1966). (1966). Prior Prior to to Pettijohn's Pettijohn'swork, work, Freedman the relationships relationships of these these sedimentary sedimentary rocks rocks to the granitic rocks of the region region were the debated debated by by Bayley Bayley (1904), (1904), Lamey Lamey (1937), (1937), and and Dickey Dickey (1936). (1936). Two other other basal basal Paleoproterozoic Paleoproterozoicformations formationsin in the the region, region,the theEnchantment EnchantmentLake Lake Two Formation Formation and and the the Reany Reany Creek Creek Formation, Formation, are are present present in in the the Marquette MarquetteTrough, Trough,50-55 50-55 miles miles north north of the the Fern Fern Creek Creek exposures. exposures. ItIt has has been beensuggested suggestedby byseveral severalworkers workersthat that these rock rock units unitsare arealso alsoglaciogenic glaciogenicand andcorrelative correlativewith with the the Fern FernCreek CreekFormation Formation these (e.g., Gair and and Thaden, 1968; 1968; Puffett, Puffett, 1969; 1969; Gair, 1981; 1981; Ojakangas, 1984). The two exposures of the Fern Creek Formation seen on these the Fern Creek Formation seen on these field field trips trips (stops (stops2-2 2-2and and2-3) 2-3)are are of more morethan than local localsignificance. significance.Correlation Correlationwith with the the Gowganda GowgandaFormation Formationininthe the of Huronian Huronian Supergroup Supergroup ca ca 120 120 miles miles to to the the east east in in Ontario Ontario and and with with the the Snowy Snowy Pass Pass Supergroup 900 900 miles miles to the the WSW in in Wyoming Wyoming has has been been proposed proposed by by various various workers Supergroup (e.g., (e.g., Puffett, Puffett, 1969; 1969; Young, Young, 1970, 1970, 1973, 1973, 1983; 1983; Ojakangas, Ojakangas, 1984, 1984, 1985, 1985, 1988; 1988; Roscoe Roscoe and Card, Card, 1993). 1993). Young Young (1970) (1970) suggested suggestedthat that all allof of these theseunits, units,and andothers othersininQuebec Quebec and 5 �and the NW Territories, Territories, are are remnants remnants of of aa continental-scale continental-scaleglaciation. glaciation. Furthermore, Furthermore, correlation correlation with glaciogenic glaciogenic units units on the Fennoscandian Fennoscandian Shield in Finland Finland and adjacent Karelia, Russia, has also been proposed (Marmo and Ojakangas, 1984; Ojakangas, Ojakangas and others, 2001). 1985, 1988; Ojakangas and others, 1991; 1991; Ojakangas strengthened by the presence of It must be emphasized that the correlations are greatly strengthened similar stratigraphic stratigraphic sequences sequences in in all of the above-named above-named areas and regions. This is is as follows, moving stratigraphically stratigraphically upward: glaciogenic rocks, paleosols paleosols (or remnants thereof), orthoquartzites, orthoquartzites, and and carbonates carbonates (Ojakangas, (Ojakangas,1997; 1997; Ojakangas Ojakangas and and others, others, 2001). Mafic 2.15 Ga cut cut all all the the aforementioned aforementioned sedimentary - 2.1 5 Ga Mafic dike dike swarms swarms dated dated at at 2.2 2.2 — sequences. It is possible possible that the glaciogenic glaciogenic units units of North North America and and the Baltic Baltic region (Marmo and Ojakangas, 1984) were formed on a single supercontinent, Kenorland, at about 2,300 Ma Ma (Ojakangas, (Ojakangas, 1988). 1988). The breakup breakup of Kenorland Kenorland occurred occurred at 2.2 — 2.1Ga Gawith withthe theemplacement emplacementof of the the Nipissing Nipissing mafic mafic sills sills and and dike dike swarms of of the - 2.1 Canadian Canadian Shield and the Jatulian mafic rocks rocks of the Fennoscandian Fennoscandian Shield. The Fern Fern Creek Formation Formation is exposed in only a few small areas adjacent to the Archean Carney Lake Gneiss Gneiss (figs. 2, 4). These These exposures exposures likely likely represent represent erosional erosional remnants remnants of more more widespread widespread glaciogenic glaciogenic deposits depositspreserved preservedin intopographic topographic lows lowson onthe theArchean Archean bedrock bedrock surface. Post-glacial Post-glacial weathering, erosion, and sorting sorting by wind and water resulted stratigraphic sequence of glaciogenic deposits, paleosol resulted in the stratigraphic paleosol (sericitic (sericitic schist), and quartz sand (now the Sturgeon Sturgeon Quartzite) Quartzite) that will be seen at stop 2-2 (Fern Creek locality) Black Creek Creek (sec. (sec. locality) and and stop stop 2-3 2-3 (Sturgeon (SturgeonRiver Riverlocality). locality).Two Twoother otherlocalities localities—- Black 6, T. 39 N., R. 28 W.), and Pine Creek (sec. 32, T. 41 N., N., R. 29 W.) W.) (Freedman (Freedman and and others 1961) are relatively relatively inaccessible inaccessible and and not as well exposed. These others 1961) — - are These four four small small areas of exposure are located along a 17-mile portion of the northwest-trending exposure located 17-mile portion northwest-trendingcontact between the Carney Lake Gneiss and these basal Paleoproterozoic units (fig. 4). The two field stops are within 5 miles of each other. Sturcieon Quartzite: At thick, light light colored, colored, Sturaeon Quartzite: At most most places places in in the the Menominee Menominee district district aa thick, vitreous quartzite forms the basal basal Paleoproterozoic unit on the Carney Lake Gneiss (Bayley and others, 1966). 1966). The type exposures exposures of the Sturgeon Sturgeon Quartzite Quartzite are along the Sturgeon Sturgeon River in the Felch Felch district, about six mites miles north of the Menominee district (see fig 2). In In the Menominee Menominee district the quartzite quartzite forms a continuous continuous belt belt along along the southwest margin of the Carney Lake Gneiss. ItIt is well exposed at stops 2-2 and 2-3. The Sturgeon Sturgeon Quartzite Quartzite ranges ranges from 1,000 1,000 to 2,000 feet thick, thick, is is composed composed primarily primarily of white, gray, green or pink vitreous vitreous quartzite, quartzite, commonly showing ripple marks and crossbedding. It is composed composed almost entirely of quartz. quartz. Trow (1948) (1948) showed that the crossbedding bedding data suggest that the quartz quartz sand sand of the Sturgeon Sturgeon was derived derived from the northwest, and Pettijohn Pettijohn (1957) (1957) showed that many of the Paleoproterozoic quartzites of the Lake Superior Superior region region had had a source source area area to the west or northwest. The Sturgeon Sturgeon Quartzite is considered considered to have formed during a marine marine transgression transgression onto the Archean craton, possibly to the northwest. Bayley and others (1966) interpreted the quartzite to (1966) interpreted be conformable conformable and gradational gradational with the Fern Fern Creek Formation, and to be conformable conformable with the overlying overlying Randville Randville Dolomite. Dolomite. Randville Dolomite: The TheRandville RandvilleDolomite Dolomiteoverlies overliesthe the Sturgeon SturgeonQuartzite Quartzitein in the the Menominee and Felch districts. It takes its name from exposures near Randville, north of of southeast-trending belts belts in the Menominee Menominee Iron Mountain. The dolomite occurs in three southeast-trending 6 �district because because of repetition repetition by by faulting faulting (Bayley (Bayley and others, 1966). 1966). ItIt is estimated to be be thick. Classic Classic exposures exposures of deformed deformed stromatolitic dolomite dolomite are are present present about 2,000 feet thick. at stop stop 2-6. The Randville Randville is composed mainly of massive massive clastic dolomite with thick- and thinbedded sandy dolomite, dolomitic and quartzose slate, and pebbly dolomite 3-12 conglomerate (Bayley (Bayley and others, 1966). 1966). Domal stromatolites 1-3 1-3 inches high and 3-1 2 common and widespread in the formation. They form reefs reefs as inches in diameter are common much much as 50 feet thick and and are are of great great aerial aerial extent. extent. The The stromatolites stromatolites are usually in thinbedded sandy dolomite and conglomeratic dolomite of shallow water origin. The clastic dolomite consists mainly of rounded rounded carbonate fragments that range range in size from sand to cobbles. Internally the fragments consist of fine-grained fine-grained dolomite. dolomite. Bayley and others (1966) (1966) stated stated that the the presence presence of of stromatolites, stromatolites, oscillation oscillationripple ripplemarks, marks,mud mudcracks cracksand and (1981) clastic beds indicates deposition in very shallow water. Larue (1 981) reported that remnants of anhydrite and gypsum gypsum crystals, along with the bedding features, suggest deposition of the Randville Randville Dolomite in a paleo-sabkha environment. Thus, the Chocolay Group may record continuous deposition from a glacial environment (the Fern Creek Formation) Formation) to an an arid arid sub-tropical sub-tropical environment environment(the (theRandville RandvilleDolomite). Dolomite). Menominee Group Menominee Feich Felch Formation: The TheFelch FelchFormation Formationisisaasericitic sericiticslate slateand andquartzite quartzitethat thatoverlies overliesthe the Randville Randville Dolomite. Dolomite. ItIt consists consists of thin-bedded thin-beddedsericitic sericitic slate slateand andphyllite phylliteand andintercalated intercalated thin-bedded thin-bedded quartzite, with the quartzite quartzite layers layers more more prevalent prevalent near near the top of the (Bayley and and others, others, 1966). 1966). ItIt is is about about 100 100 feet feet thick thick in in the the Menominee Menominee district, district, formation (Bayley formation but thickens to about 500 feet in in the Feich Felch district district to the north. Bayley and others (1966) considered the Felch Formation Formation to be correlative with the Ajibik Quartzite and Siamo Slate of the Marquette district and the Palms Palms Formation Formation of the Gogebic district. They state that although the Felch Felch Formation Formation is structurally concordant on the Randville Dolomite, both local and regional relationships suggest that the Felch Formation is unconformable on the Randville Dolomite. However, the Felch Formation is conformable and gradational gradational with the overlying overlying Vulcan Vulcan Iron-formation. Iron-formation. Iron-formation: The Vulcan Iron-formation: The Vulcan Vulcan Iron-formation Iron-formationis is the the major major iron-bearing iron-bearing unit of the iron-formation is divided divided into four units, two composed mainly of of Menominee district. The iron-formation granular iron-formation and two composed of slate and slaty iron-formation. In iron-formation composed In succeeding order the units are the Traders Iron-bearing Iron-bearingMember, the Brier Slate, the Iron-bearing Member, and the Loretto Curry Iron-bearing Loretto Slate. The Traders and Curry Members layers of granular granular jasper alternating alternating with layers layers of magnetite magnetite and and hematite. hematite. The The contain layers Brier and Loretto Members are mainly laminated siliceous iron-rich slate, which locally Loretto Members contains laminae of detrital quartz, feldspar, micas, micas, zircon and tourmaline. According to (1958), 958), the iron-formation iron-formation is about 1,000 feet thick, of which about 730 feet is is Dutton (1 ferruginous 330 feet, Loretto LorettoSlate Slate == 400 400 feet) feet) and and 270 270 feet feet is is ferruginous slate slate (Brier (Brier Slate Slate == 330 iron-formation (Traders granular iron-formation (Traders = 100 100 feet, Curry Curry = = 170 170 feet). The The Vulcan is is seen seen at 2-4 and stops 2-4 and 2-5. 7 �Group Baraga Group In the area of the field trips, rocks rocks of the Baraga Baraga Group Group are are mostly mostly in in the the Menominee Menominee Range, where they consist of a variety of rock types generally combined combined into into the Michigamme Formation. The belts underlain by the Michigamme Michigamme Formation are very poorly exposed, exposed, which accounts, at least in part, for for the lack lack of of detailed detailed mapping mapping of of what what may well be otherwise discernible map units. According to Bayley and others (1966) (1966) the Michigamme Formation consists chiefly of slate, especially quartzose, micaceous, and Michigamme graphitic varieties, subgraywacke, subgraywacke, quartzite, quartzite, conglomerate, conglomerate, dolomite, dolomite, dolomitic dolomitic quartzite, quartzite, iron-formation.More More recent recent exploration exploration drilling drilling also has has identified identified units units of and some iron-formation. rocks. An unconformity unconformity between between the Michigamme Michigamme and and underlying underlying Vulcan mafic volcanic rocks. Iron-formation is indicated indicated by the presence of widespread basal conglomerate, Iron-formation clasts of iron-formation iron-formationand and other other Menominee Menominee and and Chocolay Chocolay Group Group containing clasts lithologies, and by regional truncation truncation of pre-Baraga pre-BaragaGroup Group units units beneath beneath the the basal basal lithologies, Michigamme units. The Michigamme Michigamme Formation Formation is is the youngest youngest Paleoproterozoic Paleoproterozoic unit Michigamme preserved preserved in in the the Menominee MenomineeRange. Range. The Michigamme Michigamme Formation Formation extends extends westward westward and is present widely, although poorly exposed, in fault panels panels lying lying between between the Wisconsin magmatic magmatic terranes terranes and and the the Iron Iron River-Crystal Falls allochthon. has provided providedaa detailed detaileddescription description of of these these River-Crystal allochthon. Dutton Dutton (1971) (1971) has lithologically as their equivalents in the Menominee rocks, which are equally as varied lithologically Range. Farther north, the Michigamme Michigamme Formation is structurally beneath the Iron Iron RiverCrystal Falls allochthon and is widely exposed north and east of the allochthon. This area also has has considerable lithologic diversity, but graded-bedded graded-bedded graywackes, graywackes, pelitic politic schist and slate, and and impure impure quartzite become become more more dominant dominant toward toward the north north and and interlayered interlayered mafic volcanic rocks rocks and iron-formation iron-formationbecome become volumetrically volumetrically minor. minor. Total thickness of the Michigamme Michigamme Formation Formation is is not not known, known, but but itit is is probably probably several several thousand feet or more. Dutton Dutton (1971) (1971) stated stated that that the the Michigamme Michigamme might might be be as as much muchas as 20,000 feet thick in in the Florence, Florence, Wisconsin Wisconsin area. area. Barovich Barovich and and others others (1989) (1989) used used Nd Nd isotope data to show that the Michigamme Michigamme Formation Formation in in the field trip area area was derived derived from a Paleoproterozoic Paleoproterozoic source. Sims and others (1993) (1993) suggest that the source was the Wisconsin Wisconsin magmatic magmatic terranes terranes to to the the south, south, with with deposition deposition in in aa foredeep foredeep environment environment during docking docking of the the Wisconsin Wisconsinmagmatic magmatic terranes terranes with with the the continent continent margin. margin. Paint River Group Group Rocks assigned to the Paint River Group consist of about 6,500 feet of sedimentary sedimentary strata, which overlie as much much as 15,000 volcanic rocks. rocks. They form the of 15,000 feet of volcanic They form the bedrock bedrock of the Iron Iron River-Crystal River-Crystal Falls Falls district district (James (James and and others, 1968). 1968). Five Five formations formations were were assigned assigned originally to the Paint Paint River River Group. Here, Here, we add add a sixth sixth formation, the the Badwater Greenstone, as discussed in more detail below. The stratigraphic position position of the Paint Paint River River Group Group has has been been problematical problematical for more more than than half half aa century. century. The The group group was interpreted (e.g. Leith Leith and and interpreted to be be part part of the the Michigamme MichigammeFormation Formation in in older older reports reports (e.g. others, 1935), 1935), but but was interpreted interpreted to to be be aa separate separate group group (younger (younger than than the the Michigamme) by James and others (1968) Michigamme) (1968) and Cannon and Gair (1970). (1970). However, as discussed discussed below, below, more recent recent studies studies have have suggested suggested that the the Paint Paint River River Group Group may may be a fault-repeated fault-repeated sequence sequence correlative correlative with the Baraga Baraga and/or and/or Menominee Menominee Groups Groups (cf. (cf. Sims Sims and 1993). Below, Below, we provide provide evidence evidence that the Paint Paint River Group Group is an and others, others, 1993). is an 8 �structurally emplaced emplaced over the Michigamme Michigamme Formation Formation and consists of deepallochthon structurally water distal distal equivalents equivalents of the Menominee Menominee and Baraga Baraga Groups. Groups. The 6,500 feet of Paint Paint River River Group Group sedimentary sedimentary strata strata have have some some special special Larue and and Sloss Sloss (1980) (1980) point point out that presence presence of turbidites indicates indicates characterisitics. Larue that they were deposited in a subsiding basin. Likewise, 986) noted Likewise, Cannon Cannon (1 (1986) noted "the group consists of a very unusual unusual sequence sequence of extremely extremely ferruginous ferruginous slate, greywacke, and carbonate carbonate iron-formation. iron-formation.The The abundance abundance of pyritic pyritic and and graphitic graphitic slate, slate, the absence absence of more more oxidized oxidized facies facies of iron-formation, iron-formation, and and the the drastic drastic lateral lateral facies facies changes changes of of some some units suggest that the group was deposited in deep, anaerobic water in a tectonically environment." unstable environment." Badwater Greenstone: The The Badwater Badwater Greenstone Greenstone is is aa thick sequence of massive massive and units (agglomerates) (agglomerates) along with minor pillowed basalt, with the pillows and fragmental units interbedded slate and iron-formation iron-formation(James (James and and others, 1968). 1968). ItIt is is seen seen at stop stop 3-7. 3-7. interbedded The Badwater Badwater is estimated estimated to be be 3,000 3,000 to 8,000 feet feet thick, but but may may be be up up to to 15,000 15,000 feet thick in the Iron relative age of the Badwater Iron River area (James and others, 1968). The The relative Greenstone Greenstone has has been been uncertain uncertain for many many years, but but most most recent recent interpretations interpretations(e.g., 1993) consider consider it to be be correlative correlative with the lithologically and chemically Sims and others, 1993) Hemlock Formation. Formation. As such, itit would be be equivalent to part of the Menominee similar Hemlock Group Group deposited deposited about 1875 1875 Ma. We here here suggest suggest that that the the Badwater Badwater be be placed placed within the Paint Paint River River Group in contrast contrast to its its previous previous assignment assignment to the Menominee Menominee or Baraga Baraga Groups Groups for reasons reasons discussed discussed more more fully fully below. Dunn Creek Slate: The TheDunn DunnCreek Creek Slate Slate is is composed composed of 400 400 to 1,500 1,500 feet of strata strata between the Badwater Badwater Greenstone and the Riverton Riverton Iron-formation Iron-formation(James (James and others, 1968). It is seen at stop stop 3-5. 3-5. The The Dunn Dunn Creek Creek is is aa lithologically lithologically varied varied unit unit comprised comprised of of aa sequence sequence of well-bedded well-bedded to laminated laminated argillite argillite and cherty argillite, argillite, with units units of somewhat coarser impure impure quartzite, and and thin cherty iron-formations. iron-formations. The term "slate" is a misnomer misnomer in that most most of the rock rock has, has, at at best, best, aa moderately moderately developed developed cleavage, cleavage, and true slates are rare. rare. The upper upper part part of the the formation formation is is aa distinctive distinctive highly highly graphitic graphitic argillite and argillite breccia unit, the the Wauseca Wauseca Pyritic Member (stop (stop 3-3), 3-3), which is present throughout the Iron Iron River-Crystal River-Crystal Falls Falls district district and and forms the footwall of the Iron-formation (James and others, 1968). The Wauseca is an example of Riverton Iron-formation sulfide facies iron-formation sulfide iron-formationas as defined defined by by James James (1954). (1954). ItIt contains contains from from 15 15 to to 25% 25% Fe Fe from 10 and from 10 to 30% 30% S. In In the the Iron Iron River River area area parts parts of the the Wauseca Wauseca Member Member contain contain carbon that has has not been been altered altered to graphite, graphite, suggesting suggesting that that the the rocks rocks have have undergone undergone little, if any metamorphism. metamorphism. Tyler and and others others (1957) (1957) showed that some of the carbonaceous carbonaceous material material in the Iron Iron River River area area is, in in fact, coal, coal, and and as such, this is is one one of the oldest known occurrences of coal in the world. The lower part of the Dunn Creek known occurrences coal in The part Dunn Slate Slate is is poorly poorly exposed, but but evidently evidently varies varies considerably considerablyin incharacter characterwithin withinthe thedistrict district (James Badwater (James and others, 1968). 1968). The basal basal contact contact of the the Dunn Dunn Creek Creek with the Badwater Greenstone Greenstone is poorly poorly known, but probably probably conformable. conformable. The great lateral lateral changes changes in thickness of the Dunn thickness Dunn Creek suggest suggest that that itit was was deposited deposited over aa surface surface with considerable relief and that the relief was buried buried before before the later later phases phases of deposition deposition so that thin units units of the Wauseca Wauseca Member Member are are continuous continuous over over the the entire entire district. The The Dunn Dunn Creek is conformable conformable with and and locally locally gradational with the basal basal units of the Riverton Riverton Iron-formation. Iron-formation.This contact contact is is seen seen at at stop stop 3-3. 3-3. The The Riverton Riverton is is also also seen seen at stops stops 3-3 3-3 and 3-4. 3-4. 9 �The 10 10to to 800-foot-thick 800-foot-thickRiverton Riverton Iron-formation Iron-formationis is conformable Riverton Iron-formation: The and gradational with the underlying Dunn Creek Slate, and is the main iron-bearing unit in the Iron River-Crystal Falls district. It is described in detail by James and others (1 968). Where it is is oxidized oxidized it consists consists primarily of thin-bedded chert and iron-rich iron-rich (1968). carbonate, layers of stilpnomelane and disseminated graphite. However, in most areas iron-formationis is altered, altered, with with the the iron iron oxidized oxidized to limonite limonite and and goethite, goethite, and and the the chert chert the iron-formation being variably leached (James and others, 1968). The best natural natural exposure of the unoxidized phase of the Riverton is on the apron of the dam on the Paint River in Crystal Falls, Michigan Michigan (stop (stop 3-6). 3-6). The Hiawatha Hiawatha Graywacke Graywacke ranges in thickness from 0 -- 500 feet Hiawatha Grawacke: Graywacke: The and disconformably overlies the Riverton Iron-formation. Iron-formation.The basal part of the formation formation breccia of chert fragments in is a breccia in a graywacke graywacke matrix, matrix, which is well exposed along the Paint River in Crystal Falls (James and others, 1968). The chert fragments are commonly commonly an inch inch or more more in in size, but but locally locally range range up up to as much much as 2 feet in in length. length. Above the basal basal breccia breccia unit, unit, most most of the the Hiawatha Hiawatha Graywacke Graywacke is is a dark gray gray massive massive medium grained greywacke in which clastic grains are readily visible. In the western part Iron River River area area the graywacke graywacke is is particularly particularlycoarse coarse and and contains contains aa large large amount amount of the Iron of clastic feldspar (James (James and and others, others, 1968). 1968). They They suggested suggested that that the the change change from from chemical ironchemical to clastic deposition deposition was the result result of structural structural disturbance disturbance that halted halted ironformation formation deposition. deposition. Stambaugh Formation: The Stambauoh The Stambaugh Stambaugh Formation Formation is is about 100 100 feet thick and is composed composed of a lower lower laminated laminated cherty unit overlain by massive massive chloritic slate and some graywacke (James and others, 1968). 1968). Much of the unit is moderately moderately to strongly magnetic, a feature that was very helpful in resolving the structure in the district. helpful Fortune Lakes Slate: The The Fortune Fortune Lakes Lakes Slate Slate is is the uppermost uppermost formation of the Paint River Group and the youngest Precambrian Precambrian unit in the district (James and others, 1968). 1968). It also underlies underlies the largest area and, because of poor exposure, is the least known known formation. ItIt is is at at least least 4,000 feet feet thick thick and and is is composed composed dominantly dominantly of of slates slates with with interbedded graywacke and minor iron-formation. Graded-bedded graywacke composes Graded-bedded about 25 percent of the formation. Graded Graded units units range range in in thickness from 1-30 1-30feet (James and others, 1968). 1968). Stratigraphic Synthesis Stratigraphic Synthesisof of the the Marquette MarquetteRange Range Supergroup Supergroup The foundation foundation for modern modern stratigraphic stratigraphic terminology terminology of of the the Paleoproterozoic Paleoproterozoicstrata strata of of the the southern southern Lake Lake Superior Superior region region was established established by James James (1958), (1958), who defined the fourfourfold group group designation designation still still in in use use and and introduced introduced the term term Animikie Animikie Series Series for the the stratigraphically superposed sequence of Chocolay, Menominee, Baraga, presumably stratigraphically and and Paint Paint River River Groups. Groups. The term term "Marquette "Marquette Range Range Supergroup" Supergroup" was introduced introduced by Cannon and Gair (1970) (1970) to to replace replace "Animikie "Animikie Series" Series"in in compliance compliancewith with the the North North American Stratigraphic Stratigraphic Code; an an assemblage assemblage of groups groups is is aa supergroup, supergroup, not not aa series, series, and the name name "Animikie" "Animikie" was already already aa well established established group group name namein inMinnesota Minnesotaand and Ontario. In more recent years, two principal principal changes have been proposed. First is the recognition that the Menominee Group contains thick volcanic formations that are temporal equivalents of the major major iron-formations. iron-formations.This This relationship relationship is is best best documented documented in the eastern Gogebic range where the Emperor Volcanic Complex (Trent, 1976) Emperor 1976) interfingers with the Ironwood interfingers Ironwood Iron-formation Iron-formation and is unequivocally unequivocally part of the Menominee 10 �(Klasner and and others, 1998). 1998). Likewise, Likewise, the Hemlock Hemlock Formation, Formation, aa thick thick Group succession (Klasner rocks long long considered considered aa part part of the the Baraga Baraga Group, Group, was was succession of volcanic rocks reassigned reassigned to the Menominee Menominee Group Group (Cannon, 1986). 1986). Although Although relationships relationships are not not as definitive as in the Gogebic definitive Gogebic Range Range because because of structural structural complications complications and and poor poor exposures, the correlation correlation is supported supported by interbedded interbedded iron-formations iron-formationswithin the Hemlock and an extensive iron-formation (AmasaIFence River) River) overlying the Hemlock, Hemlock, iron-formation (Amasa/Fence which are believed to be the westward continuation continuation of the Negaunee Negaunee Iron-formation Iron-formationfrom the Marquette Marquette Range. Also, the Amasa Formation Formation is is unconformably unconformably overlain overlain by by a conglomerate lithologically lithologically indistinguishable from basal basal conglomerate conglomerate of the Goodrich Goodrich Quartzite of the Marquette Marquette Range. Range. Taken Taken together, together, the the weight weight of of evidence evidence suggests suggests that that Emperor and Hemlock Hemlock volcanic rocks rocks were erupted erupted simultaneously simultaneously with ironboth the Emperor formation deposition and interfinger interfinger with the Ironwood Ironwood and Negaunee Negaunee Iron-formations. Iron-formations. EmperorIIronwood assemblage assemblage and and the Hemlock/Amasa Hemlock/Amasa assemblage assemblage are are Both the Emperor/Ironwood unconformably overlain by a conglomerate marking marking the base base of the Baraga Baraga Group Group and and unconformably thus thus seem seem properly properly assigned assigned to to the the Menominee Menominee Group. Group. second principal principal change change to to stratigraphic stratigraphiccorrelation correlation is is the the recognition recognition that that the the Paint Paint A second River Group is likely an allochthon allochthon structurally emplaced over the Baraga Group and is therefore not necessarily therefore necessarily a younger sequence. sequence. As we propose propose here, certain lithologic similarities between Paint River units and Menominee and Baraga Group units suggest similarities that the Paint Paint River River is equivalent to both both the Menominee Menominee and Baraga Baraga Groups. The five formations originally assigned formations assigned to the Paint Paint River River Group Group lie in their entirety within the Iron Iron River-Crystal River-Crystal Falls basin (referred (referred to as the Iron Iron River-Crystal River-Crystal Falls district by James and others, 1968). 1968). Over the years there have have been been differences differences in in opinion opinion concerning concerning the relative ages of the strata strata within the Iron Iron River-Crystal River-Crystal Falls Falls basin, the underlying underlying Badwater Greenstone, and nearby nearby Baraga Baraga and Menominee Group strata. Leith Leith and others (1935) (1935) interpreted interpreted the sedimentary sedimentary rocks rocks of the district to to be be roughly roughly equivalent equivalent to the Michigamme Michigamme Formation, Formation, but but they they were were uncertain uncertain about about the the stratigraphic stratigraphic position position of of what they called Pentoga belts belts of greenstone greenstone (Badwater (Badwater Greenstone Greenstone called the Paint Paint River River and and Pentoga of current usage). James James (1958), (1958), however, however, proposed strata of the Iron Rivercurrent usage). proposed that the the strata of the Iron RiverCrystal Falls district comprised the uppermost the Paint River Group of four Paint River Group Crystal uppermost stratigraphic groups that make stratigraphic make up up the the Marquette Marquette Range Range Supergroup. Supergroup. The The Badwater Badwater Greenstone Greenstone was considered to be part of the Baraga Baraga Group. Larue Larue and and Sloss Sloss (1980) (1980) discussed sedimentation of the Marquette Marquette Range Range Supergroup Supergroup and and accepted accepted James' James' interpretation, interpretation, whereas others questioned questioned the stratigraphic stratigraphic position position of the Paint Paint River River Group. For example, Cambray Cambray (1978) (1978) suggested suggested that the Paint Paint River River Group Group is is stratigraphically equivalent to the Menominee 1992), stratigraphically Menominee Group. More More recently, Sims (1990, (1990, 1992), and Sims and Schulz (1993) (1993) proposed proposed that the Paint Paint River Group Group is the stratigraphic equivalent of the Baraga Baraga Group Group and and they correlated correlated the Badwater Badwater Greenstone Greenstone with the Hemlock Hemlock Formation Formation in in the the Menominee MenomineeGroup. Group. is some some lithologic lithologic similarity between between units units of the Paint Paint River River As shown in figure 3, there is Group and other nearby nearby successions, successions, the most most obvious obvious being being a thick and and extensive extensive banded iron-formation iron-formation overlain disconformably disconformably by clastic rocks rocks including including ferruginous conglomerate. In In this this regard, regard, the the Riverton Riverton Iron-formation/Hiawatha Iron-formation1HiawathaGraywacke Graywacke VulcanlMichigamme succession succession of succession of the Paint Paint River River Group Group is is similar to the Vulcan/Michigamme the Menominee Menominee Range Range and and the the Negaunee/Goodrich NegauneelGoodrichsuccession successionof of the theMarquette MarquetteRange. Range. We suggest suggest that that the the Riverton/Hiawatha RivertonIHiawathadisconformity disconformity is is equivalent equivalent to to the the Menominee/Baraga formations MenomineelBaraga unconformity unconformity elsewhere elsewhere and that the Riverton Riverton and older formations of the Paint Paint River Group Group are are equivalent equivalent to Menominee Menominee Group Group units, whereas the Hiawatha and younger parts parts are equivalent to the Baraga Baraga Group. Group. Thus, the thick clastic, 11 �units of the upper upper part part of the the Paint Paint River River Group Group are are correlatives correlativesof rocks rocks in part turbiditic, units of similar depositional setting setting in the Baraga Baraga Group. The Badwater Badwater Greenstone Greenstone may may be be the equivalent of the Hemlock Hemlock Formation Formation in the Menominee Menominee Group. We here here suggest suggest Badwater Greenstone should be placed placed in the Paint River Group rather than the that the Badwater Structural evidence presented Menominee Group. Structural presented below indicates that the Badwater is sequence, as indicated indicated by the widespread occurrence of part of the allochthonous sequence, steeply plunging integral part part of the Paint Paint plunging folds characteristic characteristic of the allochthon, and is an integral being the the volcanic volcanic base base on on which which younger younger units unitswere were deposited depositedwith with River succession, succession, being is more more aptly included included with the Paint Paint River Group rather than apparent conformity. ItIt thus is separated and thus has unknown unknown in other groups from which it is structurally separated stratigraphic relations. stratigraphic relations. Structure Structure The area of the field trips spans the Paleoproterozoic Paleoproterozoic suture separating the Archean Superior craton and Paleoproterozoic Paleoproterozoic epicratonic rocks on the north from Paleoproterozoic Paleoproterozoic oceanic and island arc rocks of the Wisconsin magmatic magmatic terranes on the south. The most commonly commonly accepted model model for accretion is is northward northward emplacement emplacement south-directed subducting slab, eventually leading to the of volcanic arcs over a south-directed of Penokean culmination of Penokeandeformation deformation as as the the arcs arcs collided collided with the southern edge of the Superior Superior craton. craton. The Niagara fault zone, a zone of intense intense shearing as much much as several kilometers kilometers wide in some areas, is the feature which most completely separates volcanic rocks on the south from epicratonic sedimentary rocks on the north north and is generally considered to be the surface surface trace trace of the the suture. suture. However, However, itit is is but but one one of of aa series series of of anastamosing anastamosingfaults faults structural panels in which volcanic and sedimentary rocks are intermixed. that bound structural Niagara These panels compose a belt as much much as 25 km wide, which we refer to as the Niagara northward suture zone. Available structural data indicates that these panels were thrust northward during collision and are allochthonous with regard regard to Archean basement rocks and, in some cases with regard regard to lower parts parts of the sedimentary sedimentary succession. succession. The allochthons are characterized by a complex structural structural history in which refolding refolding of early folds has resulted resulted in diversely diversely and and commonly commonly steeply steeply plunging plunging folds. folds. Terminology Terminology Because Because various names have been applied over the years to structural elements composing what we now refer to as the Niagara Niagara suture zone, the following discussion (1966) correlates the terms used used here with previous terminology. Both Bayley and others (1 966) and Dutton Dutton (1971) (1971) defined defined the structural structural panels panels of the region region and and the map map geometry geometry has has remained remained essentially unchanged unchanged since their work. They, however, did not use the term "Niagara fault", although they did recognize and map the fault as a major boundary boundary between between the dominantly volcanic rocks to the south and dominantly sedimentary rocks to the north. They did name name other faults and and also also applied applied names names to various structural structural blocks. We have have retained retained their names names throughout throughout most most of this this report. report. With With recognition recognitionof of and Ueng Ueng (1985) (1985) introduced introducedthe the significance of the Niagara Niagara fault as aa suture, suture, Larue Larue and the fault as term "Florence-Niagara "Florence-Niagara terrane" to encompass encompass the eight structural structural panels panels defined defined by Bayley and others (1966) roughly ten-kilometer-wide zone of (1966) and Dutton (1971) (1971) as a roughly rocks exhibiting internal deformation unique suture exhibiting very intense internal unique to the tectonics of the suture zone. An additional terrane, the Crystal Falls terrane, was proposed by Ueng Ueng and Larue Larue 12 �(1987) (1 987) and considered to be part of the terrane-boundary tectonic assemblage because its complex, although although less less intense intense deformational deformational history. history. In In this report report we have have used used of its the term "Niagara terrane and "Niagara suture zone" to encompass encompass both both the Florence-Niagara Florence-Niagara terrane Crystal Falls Falls terrane. The suture suture zone is is bounded bounded on the south by the Niagara Niagara fault zone. The rocks rocks of the suture suture zone zone all all show show a complexity complexity and intensity of folding much much exhibited by correlative strata strata farther north. north. The northern northern boundary boundary of the greater than exhibited suture zone is the Badwater Badwater fault and and Paint Paint River River fault, both both probably probably originally thrusts, which transported transported Paleoproterozoic RiverPaleoproterozoic strata strata northward. northward. We use use the term term "Iron "Iron RiverFalls allochthon" allochthon" as as an an equivalent equivalent to to the the "Crystal "CrystalFalls Fallsterrane" terrane"of of Ueng Uengand and Crystal Falls Larue Larue (1987) (1987) and and "Iron "Iron River-Crystal River-CrystalFalls Fallsbasin" basin"of of many manyolder older reports. reports. Niagara Niagara Fault Fault Zone Zone The Niagara Niagara fault zone is is a zone of highly highly strained strained rock most most commonly commonly up to a few hundred hundred meters meters wide wide although although there there are arefew few places placeswhere where ititisisexposed exposedand andits itswidth width can be estimated. Its Its location location (see (see fig. 1) 1) is is relatively relatively well defined in the regions regions covered by this field guide, but lack of outcrops outcrops to the west make make its its location location somewhat problematic. In In those regions regions its its location location is is based based largely on interpretation of aeromagnetic maps maps on which the fault is is expressed expressed as a discontinuity of structural structural patterns. On geologic maps maps itit is is generally generally portrayed portrayed as a single line line separating mostly mostly metasedimentary metasedimentary rocks rocks on the north north from metavolcanic metavolcanic rocks rocks on the south, but but itit is is likely likely to have numerous numerous splays extending southward into the volcanic terranes, only some of which have have been been seen seen in in outcrop. outcrop. On the field trips we will examine two of the best-exposed best-exposed areas of the fault zone. Highly sheared rocks of the fault zone are are well exposed exposed in in Piers Piers Gorge Gorge (stop (stop 2-1). Although this locality locality is about a kilometer south of the mapped mapped fault, there is is little little doubt that shearing shearing seen here is a splay of the Niagara Niagara fault. Rocks Rocks within the fault zone are severely flattened and stretched stretched and and foliation foliation strikes strikes generally generally WNW and and dips dips steeply steeply south. High High strain has has resulted resulted in in rotation rotation of fold axes axes to parallelism parallelism with the direction of maximum maximum Larue, 1985). 1985).Based Basedon onstretch stretchlineations, lineations,which whichplunge plunge600 60' elongation (Sedlock (Sedlock and and Larue, SW, Sims Sims and and Schulz (1993) (1993) suggest suggest that tectonic tectonic transport transport was northeastward, northeastward, perpendicular to the trace of the fault, and and onto onto the exposed exposed part part of the continental continental margin margin to the north. north. They They infer inferthat that the thefault faultzone zonedips dipsabout about700 70' to to the the south. south. The The fault fault zone is also seen at stop 3-1 3-1 at the Pine Pine River dam. There, very highly strained rocks rocks of the Michigamme Michigamme Formation Formationare are well well exposed. exposed. Although the Niagara Niagara fault has has been been widely accepted as a paleosuture, gravity studies by Attoh and and Klasner Klasner (1989) (1989) suggest suggest that that the the Archean Archean cratonic cratonicrocks rockscontinue continuesouthward southward at depth to a steep gravity gradient that trends northeastward northeastward across north-central north-central Wisconsin (fig. Wisconsin (fig. 1). 1). By By that that interpretation interpretationthe the Niagara Niagara fault fault is is aa major major thrust, thrust, which which has has transported arc rocks transported rocks for aa least least aa few few tens tens of of kilometers kilometersnorthward northward over over the the southern southern edge of the Superior Superior craton. Based Based on on gravity gravity model model studies, studies, Klasner Klasner and Osterfeld Osterfeld (1984) suggested that magmatic (1984) had had previously suggested magmatic domes, such such as the Dunbar Dunbar Dome, Dome, are allochthonous, detached at depth and thrust northward northward in the hanging hanging wall of the Niagara Niagara fault, which flattens flattens at depth depth toward toward the south. 13 �Niagara Niagara suture suturezone zone Both Both the the Menominee Menominee and and Iron Iron River-Crystal River-Crystal Falls Falls districts districts lie lie near near the the southern southern edge edge of of the exposed continental margin of the Penokean orogen and both lie within the Niagara the exposed continental margin of the Penokean orogen and both lie within the Niagara suture suture zone zone as aswe we define defineitithere. here.The Thecontinental continentalrocks rocksnorth northof ofthe theNiagara Niagarafault faultare are highly highly faulted faulted and and divided divided into into aa series series of of structural structuralblocks. blocks. Sedlock Sedlock and and Larue Larue(1985) (1985) refer refer to to these these blocks blocksas as "fault "faultbounded boundedtectonostratigraphic tectonostratigraphicterranes", terranes", but butwe we prefer preferto to use use the the term term "structural "structuralpanels" panels" because becausethey they do do not not fit fit the the strict strictdefinition definitionof of aa tectonostratigraphic tectonostratigraphic unit, unit,which whichisisdefined definedin inthe the Glossary Glossaryof of Geology Geologyas asaa"mixture "mixtureof of rock faultrock stratigraphic stratigraphicunits unitsresulting resultingfrom from tectonic tectonic deformation." deformation."Rather Ratherthese theseare arefaultbounded boundedslices slices of of rocks rocksor orrock-stratigraphic rock-stratigraphicsequences sequencesthat thathave haveaaunique uniquestructural structural signature. signature. Although Althoughboth bothdistricts districtsare arepart partof ofthe theNiagara Niagarasuture suturezone, zone,they theyare aredistinctly distinctly different differentfrom fromeach eachother otherstructurally. structurally.Thus Thusthey theywill willbe bediscussed discussedindividually individuallybelow. below. Menominee Menominee District District The The Menominee Menomineedistrict districtlies lieswithin within the the Niagara Niagarasuture suture zone zone at at the the southern southern edge edge of of aa series series of of uplifted upliftedblocks blocksof of Archean Archeanbasement basement(figs. (figs.1,1,2). 2).Those Thoserocks rocksnorth northofofthe the Menominee Menomineerange rangecontain contain fault-bounded fault-boundedtroughs troughsof of tightly tightlyappressed appressedPaleoproterozoic Paleoproterozoic strata—the Felch and and Calumet Calumet troughs troughs (fig. 2)-2 ) - down-faulted down-faulted between between blocks blocks of of Archean Archean strata-the Felch rocks. rocks.Studies Studiesby byKlasner Klasnerand andothers others(1989) (1989)and andKlasner Klasnerand andSims Sims(1993) (1993) suggest suggestthat that these Archean blocks were uplifted and thrust northward along Bush Lake fault, a these Archean blocks were uplifted and thrust northward along Bush Lake fault, a master masterfault fault that, that, they theysuggest, suggest,carried carriednow noweroded erodedPaleoroterozoic Paleoroterozoicand andArchean Archean rocks rocks onto onto the the continental continentalhinterland hinterlandto tothe thenorth. north.AAseries seriesof of south-verging south-vergingthrusts thrustsoccurs occursinin the the Felch Felchand andCalumet Calumettrough troughareas. areas. These Thesemay mayhave havedeveloped developedas as back-thrusts back-thrustsduring during the thenorthward northwardthrusting thrustingevent, event,or orthey theymay mayhave havedeveloped developedlater laterduring duringthe theMazatzal Mazatzal orogeny orogeny (HoIm (Holm and and others, others, 1999; 1999;Romano Romanoand and others, others, 2000). 2000). The The general generalstructure structureof of the theMenominee Menomineeiron irondistrict district(fig. (fig.4) 4)isisaasouth-facing south-facinghomocline homocline of of Paleoproterozoic stratain which stratigraphic arecreated createdby Paleoproterozoicstrata inwhich stratigraphicrepetitions repetitionsare bythree three major major faults (Bayleyand andothers, others,1966). 1966).The Thefaults faultscut cutthe the faultsand andby byfolding foldinginternal internalto tofault faultslices slices(Bayley folds foldslongitudinally, longitudinally,approximately approximatelyalong alongthe thefold foldaxes, axes,repeating repeatingthe thePaleoproterozoic Paleoproterozoic sequence sequencethree three times timesand andforming formingthree three"ranges". "ranges".Farthest Farthestnorth, north,the theCarney CarneyLake Lake Gneiss forms the core of a broad anticlinal structure. The Paleoproterozoic Gneiss forms the core of a broad anticlinal structure. The Paleoproterozoicstrata stratalie lie unconformably unconformablyon on the the gneiss gneissand anddip dipsteeply steeplyto to the the south southor orare areoverturned overturned(as (asat atstop stop 2-3) 2-3)and anddip dipsteeply steeplynorth northand andface facesouth. south.Farther Farthersouth, south,the thePaleoproterozoic Paleoproterozoicstrata strataare are repeated repeatedtwice twice by bymajor majorfaults faultsto toform formthe thetwo tworanges rangesof ofthe thedistrict. district.These Thesefaults faultswere were named 4). namedthe theNorth NorthRange Rangefault faultand andSouth SouthRange Rangefault faultby byBayley Bayleyand andothers others(1966) (1966)(fig. (fig.4). The Thefaults faultshave havesteep steepdips dipsatatthe thepresent presentlevel levelofofexposure exposureand andconsistently consistentlyshow showsouthsouthside-up side-updisplacement. displacement.Most Mostrecent recentinterpretations interpretations(e.g., (e.g.,Sims Simsand andSchulz, Schulz,1993) 1993) consider them to have been thrust faults, which were steepened by continued consider them to have been thrust faults, which were steepened by continuedshortening shortening of of the thethrust thrustpanels. panels.The Therocks rocksininthe thehanging hangingwall wall(south (southside) side)ofofthese thesefaults faultshave haveno no indications indicationsof of Archean Archeanbasement basementrocks, rocks,inincontrast contrastto tothe thearea areaimmediately immediatelyto tothe thenorth north where wherethe theCarney CarneyLake LakeGneiss Gneissisisan anintegral integralpart partofofthe thestructure. structure.The Thenorth northrange rangeand and south southrange rangepanels panelsmay maybe beallochthons allochthonsdetached detachedfrom frombasement basementand andthrust thrustnorthward northward over overthe themore moreautochthonous autochthonoussequence sequenceofofthe thenorthern northernpart partofofthe thedistrict. district.The The Menominee range is bounded on the south by the Niagara fault (stop 2-1), along Menominee range is bounded on the south by the Niagara fault (stop 2-I), alongwhich which itit isisinincontact contactwith withvolcanic volcanicrocks rocksof ofthe theWisconsin Wisconsinmagmatic magmaticterranes. terranes. 14 �87 4630' •r •( •( •( • . . a , 4552'3O — I • • '2 —Ferr Cre,!Ic Fm Fern Cr,ck rm 88 730" 87 5700 2 I 90 55 2 4 87 4630 I 00 5 10 ip 8 6 I I 1'O 10 12 12 I 15 15 Miles Miles Kilometers Kilometers EXPLANATION EXPLANATION Cambrian Cambrian MunisingSandstone Sandstone Munising North NorthofofNiagara Niagarafault fault Paleoproterozoic Paleoproterozoic SouthofofNiagara Niagarafault fault South Paleoproterozoic Paleoproterozoic Metadiabase Metadiabase E Michigamme Formation Michigamme Formation -graywacke graywacke LI. Badwater Greenstone Badwater Greenstone Vulcan VulcanIron-formation Iron-formation L HoskinsLake LakeGranite Granite Hoskins MarinetteQuartz QuartzDiorite Diorite ........ Marinette Metagabbro Metagabbro QuinnesecFormation Formation Quinnesec Randville RandvilleDolomite Dolomite Sturgeon SturgeonQuartzite Quartzite Fern FernCreek CreekFormation Formation - — fault fault Archean Archean Granitic Graniticrocks rocksand andgneiss gneiss 0 L:.' Carney Lake Gneiss Carney Lake Gneiss Figure Figure4. 4. Geologic Geologicmap mapof ofpart partofofthe theMenominee MenomineeIron IronRange Rangeshowing showingthe thelocation locationofof field trip stops. Geology is from Bayley and others (1966). field trip stops. Geology is from Bayley and others (1966). Thesefaults faultscontinue continuetotothe thenorthwest northwestinto intothe theFlorence, Florence,Wisconsin Wisconsinarea areaand andalong alongthe the These southside sideof ofthe theIron IronRiver-Crystal River-CrystalFalls Fallsdistrict, district,where whereDutton Dutton(1971) (1971)mapped mappedfour fourfaultfaultsouth boundedstructural structural"blocks". "blocks".He Henamed namedthe theblocks, fromnorth northtotosouth, south,the BruleRiver blocks,from theBrule River bounded block,the theKeyes KeyesLake Lakeblock, block,the thePine PineRiver Riverblock, block,and andthe thePopple PoppleRiver Riverblock. block.The The block, 15 �Menominee Menominee Range Range and contains, in in its its western portions, portions, an an extensive extensive dolomite dolomite (Saunders Formation) Formation) generally generally accepted accepted as the equivalent equivalent of the the Randville Randville Dolomite Dolomite of (Saunders Menominee Range. Range. The The occurrence occurrence of of these these shelf-deposited shelf-depositedrocks rocksin inthe the the Menominee southernmost and and structurally structurally highest highest thrust thrust panel panelof of the the continental continentalforeland forelandindicates indicates southernmost the continental continental shelf shelf originally originally extended extended substantially substantiallysouth south of of the the present presentNiagara Niagara that the fault. fault. - Iron District Iron River - Crystal Falls District 88 1800" EXPLANATION EXPLANATION North North of o f Niagara Niagara fault Tobin TobinLake LakeGranite Granite Metagabbro Metagabbro - Paint Group - undivided Paint River River Group undivided Fortune FortuneLake LakeSlate Slate Riverton Riverton Iron-formation Iron-formation Dunn DunnCreek CreekSlate Slate 463'00" Badwater BadwaterGreenstone Greenstone a Michigamme MichigammeFormation, Formation, graywacke graywackeand andvolcanic volcanicrocks rocks Michigamme MichigammeFormation Formation --quartzite quartzite Michigamme MichigammeFormation Formation --graywacke graywacke Amasa Iron-formation Hemlock Volcanics undivided undivided HemlockVolcanics Randville Dolomite Randville Dolomite :k.j_ Saunders SaundersFormation Formation Dickinson DickinsonGroup Groupundivided undivided ,n South South of of Niagara Niagara fault 4552'30" ,-,!;..:+ Bush Lake Lake granite Bush granite Granite and tonalite Graniteand tonalite Quinnesec Formation Formation Quinnesec EI] Metasedimentary Metasedimentaryrocks rocks - — faults faults • field fieldtrip tripstops stops 88 1800" 22 I I 55 22 00 I I I I 00 I 44 66 I I I F 55 Miles Miles 88 F I I I 10 10 Kilometers Kilometers NF-Niagara fault NF-Niagarafault SRF- South South Range Range fault fault NRF-North Range fault NRF-North Range fault BF-Badwater fault BF-Badwaterfault PRF-Paint River PRF-Palnt River fault fault CS-Commonwealthsyncline svncline CS-Commonwealth MA-Mastodon MA-Mastodonanticline anticline TBS-Tim TBS-TimBowers Bowerssyncline syncline Figure 5. 5. Geologic Geologicmap mapof of the theFlorence Florencearea areaand andeastern easternpart partof ofthe theIron IronRiver-Crystal River-Crystal Figure (1971)and and Falls district district showing showing the the location locationof of field fieldtrip trip stops. stops. Geology Geologyisisfrom fromDutton Dutton(1971) Falls James James and and others others (1968). (1968). 16 �The Iron Iron River-Crystal River-Crystal Falls District (fig. 1, 2, 5) is a triangular-shaped basin of tightly tightly triangular-shaped basin folded strata of the Paint Paint River Group. Structural studies by James and others (1968) (1968) showed that sedimentary strata of the Iron Iron River-Crystal River-Crystal Falls basin are tightly and multiply folded. Dips of less than 60 degrees are rare. For the most part the trends of the parallel or sub-parallel sub-parallel to the principal principal axis of the triangular triangular district. fold axes are parallel Stratigraphically overturned beds are common. There are a dozen or more faults having displacements measured in thousands of feet. In In addition, James and others (1968, (1968, page 87) noted "It is the opinion of one of the authors (FJP) that the folds in in the Michigamme Michigamme Slate are unrelated to those in the Badwater Greenstone and Dunn Creek suggestingthat thatthat thatthe theMichigamme Michigammehas hasaa different different structural structuralsignature signature than than slate...", suggesting Francis J. Peftijohn Pettijohn (FJP) the Badwater Greenstone and overlying Dunn Dunn Creek Creek Slate. Slate. Francis suggested that aa north-trending north-trendingfault fault separates separates the the Michigamme Michigamme from from the the futher suggested Badwater and Paint River Group strata along the eastern edge of the district. More recent structural studies (Ueng and Larue, 1987) identified identified four phases of deformation, including two major folding events that resulted in the extremely complex fold interference pattern characteristic of the district. This refolded interference refolded fold geometry geometry is exceptionally well displayed displayed at stop stop 3-6. 3-6. exceptionally Uncertainty concerning the stratigraphic position of the Paint River Group and Badwater (1990) (1993) to Greenstone, as discussed above, led Sims (1 990) and Sims and Schulz (1 993) to propose that a thrust (detachment) fault (the Badwater thrust fault) lies at the base of the Badwater Greenstone Greenstone and that the Badwater Badwater and and overlying overlying Paint Paint River River Group Groupstrata strataare are allochthonous, allochthonous, tectonically emplaced above Baraga Group strata of the continental margin. Although the Badwater thrust fault was not directly observed, they based their interpretation on unpublished geochemical data by K. J. Schulz, and and the the presence of of interpretation "extensive thrust faulting" faulting" of continental 'extensive continental margin margin strata. strata. To test this this interpretation, interpretation, Klasner Klasner and and others (1999) (1999) compared compared the structural structural signature signature (primarily orientation of fold axes) in the Paint River Group strata and Badwater Greenstone with the structural signature in underlying Baraga Group strata. Based on measurement of 123 measurement 123 fold axes throughout the Iron Iron River-Crystal River-Crystal Falls basin, they found that most most fold fold axes axes plunge plunge steeply steeply (approximately (approximately 85 degrees) north (fig. 6A). There There are are at least least three other trends in in the plot plot of the the fold fold axes, indicating indicating that the rocks rocks in in the the Paint River Group are multiply deformed. In contrast, fold axes in the area north and east of the Iron Iron River-Crystal River-Crystal FaIls Falls basin plunge at low angles to the west-northwest or east-southeast east-southeast (see (see fig. 6B). 6B). These These measurements measurementswere were made made mainly mainly in in Michigamme Michigamme Formation strata of the Baraga Baraga Group. The striking striking difference in in structural structural history history of these two regions separates regions supports the proposal proposal of Sims Sims (1990) (1990) that aa thrust fault separates these two regions. regions. Thus, the Paint Paint River including the Badwater Greenstone, Greenstone, River Group, including appears appears to be allochthonous, allochthonous, having having been thrust onto the autochthonous autochthonous Baraga Baraga Group Group strata. strata. The metamorphic metamorphic grade grade of rocks rocks surrounding surrounding the the Paint Paint River River Group Group ranges ranges from from greenschistto greenschist toamphibolite amphibolite(James (Jamesand andothers, others,1968; 1968;Bayley Bayleyand andothers, others, 1966; 1966;Dutton, Dutton, 1971), but Paint River Group rocks of the Iron Iron River-Crystal Falls district reach only greenschist or lower metamorphic metamorphic grade. This feature, too, suggests suggests that that there there is is aa fault fault with considerable displacement separating the Paint River Group from surrounding considerable displacement Paint surrounding rocks. rocks. 17 �A 0 0 •0 0 0 4 123 fold axes 123 fold axes in in rocks rocks of of the theIron IronRiver-Crystal River-CrystalFalls Falls 0 allochthon allochthon 0 .00 .0 0 f 36 Michigamme 36 fold fold axes axes in Michigamme Formation in footwall of allochthon. allochthon.Black Blackdot dotisis beddingbeddingcleavage cleavage intersection intersection at at stop stop 3-8. 3-8. Figure Figure 6. Stereoplots Stereoplots (lower (lower hemisphere hemisphere equal equal area area projections) projections) showing showing the the orientation orientation of fold fold axes axes within within the the Iron IronRiver-Crystal River-CrystalFalls Falls allochthon allochthon(A) (A)and and in in the the Michigamme Michigamme Formation Formation north north and and east of the the allochthon allochthon (B). (B). north-northeasterly-orientedcross cross section sectionconstructed constructedfrom fromunderground undergroundmapping mappinginin A north-northeasterly-oriented mine mine workings workings (James (James and and others, others, 1968) 1968)in inthe the Iron IronRiver Riverarea areaprovides providesan anexample exampleof of the complexity complexity of folding folding typical typical of of this this district. district. The The structure structureseen seenhere heresuggests suggeststhat thatthe the initial folding folding in in the the Iron Iron River-Crystal River-CrystalFalls Fallsbasin basin may may have have been beenrecumbent recumbent (fig. (fig. 7A). 7A). initial synclinein in Hiawatha Hiawatha Graywacke Graywackeand and overlying overlying The cross cross section section shows shows aa recumbent recumbent syncline The Riverton Iron-formation. Iron-formation.In Inthe the third thirddimension dimensionthis this fold foldplunges plungessteeply steeplyinto intothe thesection section Riverton NW). ItItisisstrongly stronglyoverprinted overprintedby byother otherfolds foldsof of diverse diverseorientations. orientations.The Thesyncline syncline (to the the NW). (to closes toward the southwest and the overturned upper limb in which the stratigraphically closes toward the southwest and the overturned upper limb in which the stratigraphically older Riverton Riverton Iron-formation Iron-formationlies liesabove above Hiawatha HiawathaGraywacke Graywacke suggests suggestsaa northward northward structural structural vergence. vergence. The The orientation orientationof of fold foldaxes axesmeasured measuredin inoutcrops outcropsnear nearthe themine mineare are shown shown in in figures figures 7B 7B and and 7C. 7C. 18 �___ ____ ___ NE A 1500" 1500' 1000' 1000' 1000 1 EXPLANATION deposits 500 500' 500 Metodiabose dike HioessthssGoywoeke Riverton Iron-Formation Dunn Creek Slate Mined ore bodies LEVE SEA LEVEL LEVEL 200 0 200 400 600feet Figure Figure7. 7.AA-Geologic Geologiccross crosssection sectionthrough throughthe theBuck BuckMine MineininIron IronRiver, River,Michigan, Michigan,about about 12 12miles mileswest westof ofCrystal CrystalFalls. Falls.Cross Crosssection sectionisisininsec. sec.1,1,T.T.42 42N., N.,R.R.35 35W., W.,and andsec. sec.6,6, T. T.42 42N., N.,R.R.34 34W. W.Reproduced Reproducedfrom fromJames Jamesand andothers others(1968) (1968)totoshow showlarge largerefolded refolded recumbent recumbentsyncline, syncline,the thevery verytight tightfolding, folding,and andwide widediversity diversityofofaxial axialsurfaces surfacesofoffolds. folds. Lower Lowerhemisphere hemisphereequal equalarea areastereograms stereogramsofoffold foldaxes axesininoutcrops outcropsofofRiverton RivertonIronIronformation formation(B) (B)and andHiawatha HiawathaGraywacke Graywacke(C) (C)near nearthe themine. mine. 19 �History of Iron History Iron Mining Mining the Menominee district district in 1848 by by two two explorers, explorers, J.W. J.W. Foster Iron ore was discovered in the and S.W. Hill, Hill, according according to Winchell Winchell (1895). (1895). However, However, iron iron mining mining did did not not begin begin until until 1870, when when N.P. N.P. Saxton started digging pits and trenches on the site of of the Breene the first first ore being shipped in 1873 (Bayley and and others, others, 1966). All All the the major Mine, with the mines had been located located by 1878. 1878. Production Productioncontinued continued until until 1958, 1958, with with aa total total production production from the district of approximately 85,000,000 tons (Bayley and others, 1966). 1966). Seven mines produced produced nearly 77,000,000 tons of ore, with a majority of the production production from the district coming coming from three three mines, mines, the the Chapin Chapin (27,500,000 tons), the the Penn Penn (21,700,000 tons) and the Aragon (11,200,000 (11,200,000 tons) (Dutton, 1958). 1958). Production Production from the Chapin Mine ended in 1934 1934 with a major collapse of the workings. The subsidence from Chapin this collapse collapse formed the lake lake on the north north side of Iron Iron Mountain. Mountain. A causeway across the district was Highways U.S.-2 and U.S.-141. Ore from the district lake now carries the traffic on Highways hauled hauled by rail to Escanaba, Ml, MI, from where it was carried carried by boat to steel mills mills on the lower Great Lakes. All of the ore shipped shipped from the district was high-grade high-grade natural natural iron iron ore. Although the iron-formation iron-formation in the Menominee Menominee district was studied as a possible source of beneficiating beneficiating ore (a "taconite "taconite ore"), ore"), no no commercial commercial operation operation has has been been undertaken. undertaken. Harvey Mellen, a United States land surveyor, first discovered discovered iron iron ore ore in in the the Iron IronRiverRiverCrystal Falls district in 1851 commenced in 1881 1851 (James (James and others, 1968). Mining commenced I881 and the first ore ore was shipped shipped in in 1882. 1882. Except Except for for the the early early years years of of mining, mining, when when many manymines mines recovered by underground underground were operated as small open pits, nearly all of the ore was recovered mining mining (James (James and others, 1968). 1968). Mine exposures and maps of the numerous mines greatly helped helped resolve the complex structure of the district. A major major hazard hazard to mining mining was caused by the pyritic slate of the Wauseca Pyritic Member of the Dunn Creek Slate, to air in the the mines. During the the 92-year which would burn spontaneously when exposed to period 974, approximately approximately 205,000,000 205,000,000 tons tons of iron ore were shipped from period from 1882-1 1882-1974, the district. district. Although there there were were 121 121 mines mines in in the the district, district, aa majority majorityof of the the ore ore came came from from about a dozen mines. about a dozen mines. In the Florence district, iron iron ore ore was recovered recoveredfrom from six six relatively relativelysmall small mines minesbetween between 1980. Only about about 8,000,000 8,000,000 tons tons of of predominantly soft soft hematite and limonite 1880 and 1960. ore with a high phosphorous produced (Dutton, 1971). The Florence phosphorous content was produced Florence mine was the most productive productive mine in the district with 3,680,000 tons shipped between 1880 and 1931. Nearly Nearly all of the production production from the district district was from the Riverton Riverton IronIronformation (Dutton, formation (Dutton, 1971). 1971). PEMBINE-WAUSAU MAGMATIC PEMBINE-WAUSAU MAGMATIC TERRANE Introduction Introduction northeastern Wisconsin The volcanic and plutonic plutonic rocks rocks that are widely distributed in northeastern south of the Menominee Menominee and Iron Iron River-Crystal River-Crystal Falls iron-bearing iron-bearing districts in Michigan are the easternmost easternmost exposures of a major major east-trending east-trending belt belt of volcanic and plutonic plutonic 20 �Pembine-Wausau terrane, the northernmost of the two Wisconsin Wisconsin rocks known as the Pembine-Wausau magmatic terranes (Sims and others, 1989). 1989). The occurrences in Marinette and Florence represent the best-exposed best-exposed portion of this suite of rocks in the Lake Counties, Wisconsin represent Superior region region and include a dismembered dismembered ophiolite sequence (Schulz, 1987). The magmatic terranes represent represent complex magmatic magmatic arcs accreted accreted to to the Wisconsin magmatic southern margin Paleoproterozoic Penokean Penokean margin of the Archean Superior Craton during the Paleoproterozoic orogeny orogeny (Sims (Sims and and others, others, 1989). 1989). The Pembine-Wausau Pembine-Wausau terrane is is mainly composed composed of tholeiitic and calc-alkaline volcanic and others, others, 1989). A A more rocks that formed between 1860 and 1889 Ma (Sims and restricted calc-alkaline volcanic succession restricted succession was deposited deposited between between 1835 1835 and and 1845 1845Ma Ma on the older rocks rocks along along the southern margin margin of the terrane terrane in in Marathon Marathon County. Granitoid rocks constitute nearly half of the exposed rocks in the terrane and range in age from about 1870 1870 to 1760 1760 Ma. These intrusive rocks are mainly mainly granodiorite and tonalite but include gabbro, diorite and granite (Sims and others, 1993). 1993). An older suite of granitoids ranging ranging in age from about 1870 1870 to 1840 1840 Ma is broadly syn-orogenic whereas post-collsional alkali-feldspar younger post-colisional alkali-feldspar granite suites were emplaced at about 1835 Ma and 1760 1760 Ma. The magmatic magmatic rocks rocks of the Pembine-Wausau Pembine-Wausau terrane terrane are are separated separated from from epicratonic rocks of the Marquette Marquette Range Range Supergroup Supergroup to the north north by the Niagara Niagara fault zone (see Bayley and others, 1966, and Dutton, 1971) and from the Marshfield magmatic terrane to the south along the Eau Eau Plaine Plaine shear zone (Sims (Sims and and others, others, 1989). 1989). General Geology Geology Volcanic rocks are relatively well exposed in the the northern and eastern part of Marinette County and eastern Florence Florence County in northeastern Wisconsin, where they form an arcuate belt around the large Dunbar gneiss-granitoid dome (fig. 8) (Sims (Sims and Schulz the Quinnesec Formation by James 1993). The supracrustal rocks, formally named the (1958), (1958), consist of metamorphosed metamorphosed basalt, andesite, dacite, and rhyolite lava flows and volcaniclastic rocks, and locally, sedimentary rocks including greywacke, graphitic slates, and iron-formation. iron-formation.Pyritic to pyrrhotitic pyrrhotitic massive sulfide bodies are also present Cummings, 1982; 1983). Gabbro Gabbro sills sills are are common, common, locally (Hollister and Cummings, 1982; LaBerge, 1983). particularly in the northern part of the sequence (Bayley and others, 1966). Serpentinite bodies, bodies, commonly with some some associated associated gabbros, gabbros, are are also also present presentlocally. locally. Jenkins (1973) (1973) noted noted that at least four lithologically distinct volcanic units could be defined in northeastern northeastern Wisconsin with three of the units units sufficiently sufficiently different different from the the lithologies (Prinz,1958; 1958;Bayley Bayleyand andothers, others, lithologies of the the type type area area of of the the Quinnesec Quinnesec Formation Formation(Prinz, 1966) to warrant their their separate designation. designation. He proposed proposed the the informal names McAllister formation, Beecher formation, and Pemene Pemene formation, listed listed in the order of progressively progressively (1973) that this this also represents the order of more silicic units, and Jenkins (1 973) suggested that decreasing age. More recently, DePangher (1982) (1982) proposed that the Quinnesec the Quinnesec Group consisting consisting of of five five lithostratigraphic lithostratigraphic units Formation be designated the having formational status. For the purposes of this field guide, the informal nomenclature proposed by by Jenkins Jenkins (1973) (1973) will will be be used used for for the the volcanic volcanic rocks rocksin inthe the area. area. proposed 21 �88" 0845" 87" 5830" 87° 4815" 45" 4100"- 45° 4100" I 88" 0845" 22 I I 87° 4815" 87° 58' 30" 00 ' I ' 22 I 88 , I 00 55 66 44 ' 10 10 55 10 10 'I I I I 15 15 12Miles 12 Miles I Kilometers Kilometers EXPLANATION EXPLANATION Munising MunisingSandstone Sandstone(Cambrian) (Cambrian) Paleoproterozoic rocks rocks north northof of Niagara Niagara fault fault Paleoproterozoic Michigamme MichigammeFormation Formation -graywacke graywacke Vulcan VulcanIron-formation Iron-formation Randville RandvilleDolomite Dolomite Paleoproterozoicrocks rocksof ofWisconsin Wisconsin Magmatic MagmaticTerranes Paleoproterozoic Terranes Intrusive trusiverocks rocks Volcanicrocks rocks Volcanic . Spikehorn SpikehornCreek CreekGranite Granite formation' . . . Rhyolite Rhyoliteand and dacite dacite"Pemene "Pernene formation" Bush BushLake LakeGranite Granite Basaltic andesitic breccia "McAllister "McAllister formation" formation" Basaltic and andesitic r"J Hoskins HoskinsLake LakeGranite Granite , ,,=.*: Rhyolite Beecher formation Rhyolite,felsic felsictuff tuff,graywacke graywackenBeecher formation" TwelveFoot FootFalls FallsQuartz QuartzDiorite Diorite Twelve Marinette MarinetteQuartz QuartzDiorite Diorite Serpentiniteand andgabbro, gabbro, base base of of ophiolite ophiolitecomplex complex Serpentinite NewinghamTonalite NewinghamTonalite QuinnesecFormation Formation Quinnesec ' NewinghamTonalite, NewinghamTonalite, . , Athelstane AthelstaneQuartz QuartzMonzonite Monzonite megacrystic megacrysticfacies facies .. . DunbarGneiss Dunbar Gneiss Metagabbro Metagabbro Volcanic Volcanicand andgranitic graniticrocks rocksundivided undivided - — faults faults •0 field fieldtrip tripstops stops Figure 8. 8. Generalized Generalizedgeologic geologic map map of of part partof of northeastern northeasternWisconsin Wisconsinshowing showingthe the Figure location locationof fieldtrip stops. of field tripstops. The units unitsof of the theDunbar Dunbargneiss-granitoid gneiss-granitoiddome domeintrude intrudethe thevolcanic volcanicrocks rocksininnorthern northern The MarinetteCounty, County, and andthe the Athelstane AthelstaneQuartz QuartzMonzonite Monzoniteintrudes intrudesthem themininthe thesouth. south. Marinette 22 �Small Small intrusive intrusive bodies bodies ranging ranging from hornblendite hornblendite and gabbro to quartz quartz diorite, diorite, granite granite and and calc-alkaline calc-alkalinelamprophyre lamprophyre are are widespread, widespread, particularly particularly in in the southeastern southeastern parts parts of of the the exposed exposedvolcanic volcanic sequence. sequence. To To the the north north and and northeast, northeast, the the volcanic volcanic sequence sequenceis is truncated truncated by by the the Niagara Niagarafault fault (Bayley (Bayley and and others, others, 1966; 1966; Dutton, Dutton, 1971), 1971),which which marks marksaa major major discontinuity discontinuity in in the rocks rocks of the the region. region. North North of this this fault, fault, rocks rocksof of the the Michigamme Michigamme Formation Formation and other units units of the Marquette Marquette Range Range Supergroup Supergroup occur, occur, along Archeangneissic gneissicrocks. rocks. alongwith with basement basementuplifts upliftsof of Archean The The supracrustal supracrustalrocks rocks and and associated associatedsubvolcanic subvolcanic intrusives intrusives are are variably variably altered altered to to greenschist facies mineral assemblages throughout the eastern outcrop area but contain greenschist facies mineral assemblages throughout the eastern outcrop area but contain assemblages assemblages as as high high as as amphibolite amphibolitefacies facies adjacent adjacent to to the the Dunbar Dunbar dome dome and andfurther further to to the the west. west. The The rocks rocksare areregionally regionallyfolded foldedon onnorthwest-trending northwest-trendingaxes, axes,but butthey theycommonly commonly lack lack aa strong strongpenetrative penetrativecleavage cleavage in in the the east. east. As As aa result, result, primary primarytextures textures and and structures structuresare are generally generally well well preserved preservedin in the the eastern eastern outcrop outcrop area. area. Units Units generally generally face face outward Dunbardome dome and and Athelstane Athelstane intrusion. intrusion. outwardfrom from the the margins marginsof of the the Dunbar Contacts Contactsbetween between the the various various volcanic units units are not not exposed, but but are are interpreted interpreted to to be be high-angle high-anglefaults faults (Jenkins, (Jenkins, 1973; 1973; Sims Sims and and Schulz, Schulz, 1993). 1993). Because Because of of uncertainties uncertaintiesin in the the amount amount of of displacement displacement on on these these faults faults and and the the complexity complexity of of folding, folding, detailed detailed correlations correlationsbetween between units units have have not not been been possible. possible. Present Present geologic geologic data data support support the the interpretationof of the the Quinnesec Quinnesec Formation Formation(as (as used used by by Jenkins) Jenkins) as as the the oldest oldest volcanic volcanic interpretation unit. unit. The The relative relativeages agesof ofthe theother otherunits, units,however, however,remain remainuncertain. uncertain.The Theunits unitsmay mayhave have been beenstructurally structurallyemplaced emplaced and and may may not not be be in in their their original original stratigraphic stratigraphic position. position. The The regional McAllisterformation formation may may be be younger younger than than the the regionalstructure structuresuggests suggeststhat that the the McAllister Beecher Beecher formation formation but but older older than than the the Pemene Pemeneformation. formation. Further Furtherwork work isisrequired requiredto to resolve resolvethe the age ageand andstratigraphic stratigraphicrelationships relationshipsof ofthese theseunits. units. Until Until relatively relativelyrecently recently the age age of the the volcanic volcanic rocks rocks in in northeastern northeasternWisconsin Wisconsin was was aa point point of of controversy. controversy.Van VanHise Hiseand andBayley Bayley(1900) (1900)and andBayley Bayley(1904) (1904)originally originally Archeanbecause becauseof ofthe thestriking strikingsimilarity similarityofofthese these interpretedthe the"Quinnesec "Quinnesecschists" schists"as asArchean interpreted rocks rocksto to Archean Archean rocks rockselsewhere elsewhere in in the the Lake Lake Superior Superior region. region. Van Van Hise Hiseand and Leith Leith (1911) subsequentlyassigned assignedthe theQuinnesec Quinnesecto toaapost-Michigamme post-Michigamme(i.e. (i.e. (1911)subsequently Paleoproterozoic) Paleoproterozoic) age age on on the the basis basis of of the the interpretation interpretationof of Hotchkiss Hotchkissand and others others (1915) (1915) that the Michigamme Formation graded upward into volcanic rocks in Florence County, that the Michigamme Formation graded upward into volcanic rocks in Florence County, Wisconsin.Dutton Dutton(1971) (1971)later laterreinterpreted reinterpretedthe therelationship relationshipininthis thisarea areaand andplaced placedaa Wisconsin. faultbetween betweenthe the volcanic volcanic units unitsto to the the south south and andthe the Michigamme MichigammeFormation Formationto to the the fault Bayleyand andothers others(1966) (1966) and andDutton Dutton(1971), (1971), favored favoredan anArchean Archean age, age,although although north.Bayley north. acknowledgingthat thatdefinitive definitivefield fieldevidence evidencewas was lacking lackingto to establish establishthe the age ageof of the the acknowledging Quinnesec QuinnesecFormation. Formation. Banks Rebello(1969) (1969) reported reportedaa U-Pb U-Pbzircon zircon age age of of 1,866±39 1,866±3Ma Mafor for aa felsic felsic Banksand andRebello volcanic sample sample from from south south of of the the Dunbar Dunbardome. dome. This Thisage, age, which which isisnot notresolvable resolvablefrom from volcanic the theages agesofofthe therocks rocksofofthe theDunbar Dunbardome dome(Sims (Simsand andothers, others,1984), 1984),isisnow nowgenerally generally taken takenas asthat thatofofthe thevolcanic volcanicsequence sequenceininnortheastern northeasternWisconsin, Wisconsin,although althoughthis thislocality locality isisisolated 1,870±5Ma Mawas was isolatedfrom fromthe themain mainareas areasof of outcrop. outcrop. More Morerecently, recently,an anage ageof of 1,870±56 obtained for the basalts of the Quinnesec Formation by whole-rock Sm-Nd isotopic obtained for the basalts of the Quinnesec Formation by whole-rock Sm-Nd isotopic systematics(Beck (Beckand andMurthy, Murthy,1991). 1991).Thus, Thus,the theage ageof ofthe thevolcanic volcanicrocks rocksinin systematics Archean as as northeasternWisconsin Wisconsinisisnow nowestablished establishedas as Paleoproterozoic Paleoproterozoicand andnot notArchean northeastern once oncethought. thought.Their Theirage ageisisgenerally generallysimilar similarto tothat thatobtained obtainedfor forthe themassive massivesulfide sulfide depositsnear nearCrandon, Crandon,Monico Monicoand andLadysmith Ladysmithto tothe thewest west (Sims, (Sims,1976) 1976)and andto toages agesof of deposits 23 �magmatic terrane terrane (Sims and other volcanic and and plutonic plutonic rocks rocks of the the Pembine—Wausau Pembine-Wausau magmatic others, 1989). 1989). Volcanic Units Units The four volcanic units that comprise the supracrustal sequence in Marinette and Florence Counties, as well as some of the granitoid bodies that intrude them, are briefly (1989), described below. Further information can be found in Sims and others (1 989), Sims and (1993). 993). Although the rocks are mostly others (1992), (1992), and Sims and Schulz (1 metamorphosed fades, the metamorphosed at greenschist facies, the prefix prefix "meta" "meta"is is generally generally omitted omitted below belowfor for simplicity. simplicity. Quinnesec Formation: The Quinnesec Formation is the dominant volcanic unit exposed in northeastern Wisconsin. Its Its stratigraphic thickness is not known known because because of uncertainties in the degree of folding and faulting but is probably on the order of several thousand meters. The Quinnesec Formation consists predominantly of basalt lava flows fragmental andesite and diabase in the north, but includes includes pillowed pillowed and fragmental andesite in in the the south. south. The The basalt is commonly pillowed, with the pillows locally variolitic. The pillowed flows are in commonly pillowed, pillows locally The pillowed flows are in some areas overlain by thick (tens of meters) sections of pillow breccia and hyaloclastite breccia (N. V2, ½, sec. 11, T. 37 N., A. R. 21 E., E., Faithorn Faithorn 7.5 minute minute quadrangle). quadrangle). Andesite Andesite breccia increases increases in abundance abundance southward southward in in the formation, formation, and and is is generally generally plagioclase plagioclaseand and clinopyroxene-phyric clinopyroxene-phyric and amygdaloidal. amygdaloidal. Fresh, Fresh, glacially glacially polished polished outcrops outcrops around aroundthe the new location location of the Kremlin mine pit east of Pembine (S. V2, ½, sec. 26, T. 37 N., R. 21 E., Faithorn Faithorn 7.5 minute minute quadrangle) quadrangle) provide provide excellent excellent exposures exposures of of andesite andesitebreccia. breccia.Felsic Felsic tuff and breccia breccia are also present locally in the Quinnesec, particularly in the northern Menominee River. Felsic Felsic fragmental fragmental units unitsare are also also present presentin inthe the portion near the Menominee LaSalle LaSalle Falls Falls area along along the Pine Pine River River in in Florence Florence County County (Bayley (Bayley and and others, others, 1966; 1966; Dutton, Dutton, 1971). 1971). tholeiitic, with with generally generally low low Ti02 Ti02 and and other other Compositionally, the Quinnesec basalts are tholeiitic, high-field-strength element abundances, and flat to extremely light rare-earth element high-field-strength rare-earth (REE) depleted patterns (Sims and others, 1989). In addition, some of the basalts basalts and andesites have have very very low low Ti02 Ti02and and REE REEabundances, abundances, but butrelatively relativelyhigh highCr Crand andNi Ni the andesites contents. The trace element characteristics of the mafic volcanic rocks overlap those of mid-ocean ridge basalt mid-ocean basalt (MORB) (MORB) and and primitive primitive island-arc island-arc tholelite tholeiite suites suites whereas whereasthe the with boninites (fig. 9), although none of the andesites show compositional affinities with andesites are as high in MgO as true boninites. The felsic volcanic rocks have low potassium compositions with relatively low REE flEE abundances abundances and flat REE REE patterns. patterns. They are are similar in in composition composition to tholeiitic plagiogranite/rhyolite plagiogranitelrhyolite (Schulz, 1987; Sims and others, 1989). 1989). The compositional data suggest that the original basaltic magmas that gave rise incompatiblerise to the Quinnesec rocks rocks were derived from a variably incompatiblevalue element-depleted mantle source. This is supported by a large positive epsilon Nd value 1991), indicative indicative of of derivation derivation from from aa mantle mantlewith with of 4.2 for the basalts basalts (Beck (Beck and and Murthy, Murthy, 1991), long-term depletion in light rare-earth rare-earthelements. elements. 24 �2.0 ' I -L 1.6 1.2 - Beecher Beecher andesites andesites A A Phanerozoic Phanerozoic boninites 0.8 Pemene Pemene - rhyol ites 0.4 0.0 40 50 60 70 80 S102 (wt. %) 2.0 I I I a I I I I 1.6 0 1.2 Beecher andesites 0.8 Pemene rhyolites Phanerozoic boninites 0.4 .1 L 0.0 0 50 100 150 200 Zr (ppm) Figure 9.Plots Plotsof of Ti02 TiOaversus versusSi02 SiOg(upper) (upper)and andZr Zr (lower) (lower)for forvolcanic volcanicrocks rocks(triangles) (triangles) Figure9. andrelated relatedgabbros gabbrosand anddiabase diabase(circles) (circles)from fromthe theQuinnesec QuinnesecFormation, Formation,northeastern northeastern and Wisconsin.Note Notethat thatseveral severalofofthe thesamples samplesplot plotininthe thefield fieldofofPhanerozoic Phanerozoicboninites. boninites. Wisconsin. Fields Fieldsalso also are areshown shownfor for Beecher Beecherandesites andesitesand andPemene Pemenerhyolites. rhyolites. Sedimentaryrocks rocksappear appeartotobe berare rarewithin withinthe theQuinnesec QuinnesecFormation. Formation.Where Wherepresent, present, Sedimentary they theyconsist consistmostly mostlyofofchert, chert,graywacke, graywacke,slate slateand andiron-formation. iron-formation.Iron-formation Iron-formationoccurs occurs asthin thinunits unitsinterlayered interlayeredwith withvolcaniclastic volcaniclasticsedimentary sedimentaryrocks rocksand andtuffs, tuffs,and andconsists consistsofof as 25 �interlayered interlayered chert and siderite (Cummings, 1978). 1978). A small massive massive sulfide deposit, containing containing pyrrhotite pyrrhotiteand and chalcopyrite, chalcopyrite, in in a felsic tuff, and and in in aa fine-grained fine-grainedblack black slate slate that that occurs occurs between between the the felsic felsic tuff tuff and and aa mafic mafic unit unit is is exposed exposed at at Pine Pine Rapids Rapids (locally (locally known "LaSalle Falls") Falls") on on the the Pine Pine River River (LaBerge, (LaBerge,1983). 1983). known as "LaSalle In In addition to volcanic rocks, the Quinnesec Formation Formation also contains a number of gabbroic gabbroic and and ultramafic ultramafic rocks rocks (Sims (Sims and and Schulz, Schulz, 1993). 1993). Numerous Numerous large large gabbro gabbro bodies bodies are are present, present, particularly particularly near near the Niagara Niagara fault zone. These These bodies bodies are are more more or or less less conformable conformable with with the the basaltic basalticflows flows and andprobably probablyrepresent representsynvolcanic synvolcanicsills, sills,although although Bayley Bayley and and others others (1966) (1966) considered considered the gabbroic gabbroic sills to be be "post-Animikie" "post-Animikie"in in age. age. Gabbro Gabbro and and anorthositic anorthositic gabbro gabbro comprise comprise the the bulk bulk of the the sills. sills. Some Some sills sills also also contain contain peridotite peridotite(serpentinite) (serpentinite) and and pyroxenite pyroxenite layers layers and magnetite-rich magnetite-richgabbro. gabbro. Trace Trace element element and and isotopic isotopic data data for for the the gabbros gabbros show show they are are comagmatic comagmatic with with the the basalts basalts of of the the Quinnesec Quinnesec Formation Formation(Schulz, (Schulz, unpublished unpublisheddata). data). Several Several serpentinized serpentinized peridotite peridotite bodies bodiesof of varying varyingsizes sizesoccur occurwithin withinthe thevolcanic volcanic succession, succession, but but the the largest largest and and best-exposed best-exposed occurs occurs south south of Timms Timms Lake Lake (Morgan (Morgan County County Park) Park) east east of Pembine, Pembine, Wisconsin. Wisconsin. The The body body trends trends east east from from outcrops outcropsin in the the NE. sec.19, 19,T. T. 37 37 N., N., R. R. 21 21 E., for for a distance of about %, sec. about 4.5 km kmto to the theNorth NorthBranch Branch NE. 1/4, Pemebonwon %, sec. 22, T. 37 37 N., N., R. R. 21 21 E. E. The The body body produces produces aa large large Pemebonwon River River in in the NE. ¼, magnetic magnetic anomaly. Serpentinized peridotite is dominant in the western part body anomaly. Serpentinized peridotite is dominant in part of the the body where (1-5 cm) dikes of pyroxenite pyroxenite now now replaced replaced by by where itit is is locally locally cut by by coarse coarse grained grained (1-5 amphibole. amphibole. The textures, although The serpentinite serpentinite generally generally shows few primary primary textures, although primary primary compositional compositional layering layering is is suggested suggested locally locally by differential differential weathering of bands bands in in some some outcrops. outcrops. Veins Veins of of carbonate carbonate and and cross-fiber cross-fiber asbestos asbestos are are common. common. Layered Layered and and massive massive gabbro, gabbro, along along with local local masses masses of strongly strongly foliated-lineated foliated-heated gabbro, gabbro, are are dominant dominant in in the the eastern eastern part part of of the the body. body. The The gabbroic gabbroic rocks rocks are are cut cut by by numerous numerousmafic mafic dikes, some of which appear to be sheeted, with diabasic to microdioritic textures. The dikes, some of which appear to be sheeted, diabasic microdioritic The strongly strongly foliated-lineated foliated-lineatedgabbro gabbro masses masses appear appear as as screens screens between between the the dikes. dikes. The The foliation in in the the gabbro gabbro screens screens is is at at aa high high angle angle to to the the contacts contacts of of the the body body with with the the foliation Quinnesec Quinnesec basalts. basalts. The The strong strong deformational deformationalfabric fabric of of the the gabbro gabbro screens screens is is not not present present in in most most of of the the associated associated rocks rocks of of the the body, body, including including the the dikes. dikes. This This suggests suggeststhat that the the deformation deformation of of the the gabbro gabbro in in the the screens screens occurred occurred prior prior to emplacement emplacement of the dikes dikes and and to to the the regional regionaldeformation. deformation.The Thetrend trendof of the the mafic maficdikes dikesisisabout aboutparallel parallelto tothe thetrend trendof of the serpentinite-gabbro serpentinite-gabbrobody body(—E-W) (-E-W) and generally at a high high angle angle to to the the foliation foliation of of the the the gabbro gabbro screens. screens. The The dikes dikes do do not not appear appear to to extend extend into into the the surrounding surrounding pillow pillow basalts. basalts. These These features features suggest suggest that that the the serpentinite-gabbro serpentinite-gabbro body body may may be be fault-bounded fault-bounded and and tectonically emplacedwithin within the the Quinnesec Quinnesec Formation. Formation. The The compositions compositions of of the the gabbros gabbros tectonically emplaced and and diabasic diabasic dikes dikes within within this this body bodyrange rangefrom fromMORB MORBto todepleted depletedisland-arc island-arctholeiite tholeiiteand and high-magnesiumandesite andesite with with boninitic boninitic affinities; affinities; these these mafic mafic rocks rocks are are similar similar in in high-magnesium composition compositionto to the the basalts basaltsin inthe the Quinnesec QuinnesecFormation Formation(fig. (fig.9). 9). The The lithologies lithologiesand andtheir their arrangement arrangementin inthis this ultramafic-gabbroic ultramafic-gabbroicbody, body, along alongwith with those those of of the the Quinnesec QuinnesecFormation Formationgenerally, generally,are are similar similar to to those those that that characterize characterize Phanerozoic Phanerozoic ophiolite sequences sequences(fig. (fig. 10). 10).This This includes includes(from (frombottom bottomto to top): top): mafic-ultramafic mafic-ultramafic ophiolite plutonic plutonic rocks, rocks, aa dike dike(sheeted?) (sheeted?)complex, complex,extrusive extrusivepillowed pillowedand andmassive massivebasalt basaltlava lava flows, flows, and and overlying overlying arc-related arc-relatedvolcaniclastic volcaniclastic rocks. rocks. Tectonized Tectonized ultramafic ultramafic rocks rocks representing suboceanic suboceanic mantle mantle have have not not been been recognized. recognized. Also, based based on on the present present representing exposure,the the ultramafic-mafic ultramafic-maficcumulates cumulatesand anddike dikecomplex, complex,although although present, present,are aremuch much exposure, less less extensive extensive than than in in the ideal ideal ophiolite sequence sequence (fig. (fig. 10). 10). This This may may be be aa function function of 26 �limited limited exposures exposures in in the region region and/or and/or lack lack of of preservation preservationof of the the lower lowerpart partof of the the ophiolite ophiolite sequence sequenceduring during later later magmatic magmaticand andtectonic tectonicevents, events.Incomplete Incompletesequences sequences are are common commonin in ophiolites ophiolitesfound found ininmany manyorogenic orogenic belts belts(Moores, (Moores,2002). 2002).The Thelithologic lithologic association associationobserved observedin in the the Quinnesec Quinnesec and andthe the compositions compositionsof of rocks, rocks,ranging rangingfrom from MORB MORE3 to depleted depleted island-arc island-arc tholeiite tholeiite and and high-magnesium high-magnesiumandesite andesiteof of boninitic boniniticaffinity, affinity, and plagio-rhyolite, are similar to Cenozoic suprasubduction zone ophiolites like those and plagio-rhyolite, are similar to Cenozoic suprasubduction zone ophiolites like those of of the the Coast Coast Ranges Rangesin inCalifornia California(Shervais (Shervaisand andKimbrough, Kimbrough,1985; 1985;Shervais, Shervais,2001). 2001). J 1 1 , ^ , I, Shallow-water Shallow-water or terrestrial terrestrial sedimentary sedimentaryrocks rocks Unconformity Unconformity Pelagic sediments Pelagic sediments sediments or or abyssal abyssal deep-sea fan sediments or or volcanic volcanicarc arc deposits deposits Mafic pillow breccia, Mafic pillow pillowlava, lava, pillow breccia, and and massive massive flows Mafic Mafic sheeted sheeted dike dike complex complex \( 1/ Massive plagiogranite Massive gabbro, diorite, and plagiogranite Cumulate Cumulatesection: section: ultramafic-mafic ultramafic-maficcumulates cumulatesatatbase, base, more toward top. more felsic toward top. Commonly Commonlycyclic, cyclic,common common contorted contortedlayering layeringand and other other evidence evidence for deformation deformation Petrologic Moho Ultramafic peridotite with Ultramafic tectonite; peridotite with discontinuous discontinuous layers of of dunite dunite (D) and and concentrations concentrations of chromite (Cr) chromite(Cr) Figure 10. 10. Schematic Schematic cross-section cross-section of of aa complete completeophiolite ophiolite(after (afterMoores, Moores,2002). 2002). Figure The Quinnesec Quinnesec Formation Formationis is intruded intruded by by units units of of the the Dunbar Dunbar dome dome including includingthe the Marinette Marinette Quartz Quartz Diorite Diorite and and the the Spikehorn Spikehorn Creek Creek Granite, Granite, as as well well as as by by the the Newingham Newingham Tonalite Tonalite and and Twelve Foot Foot Falls Falls Quartz Quartz Diorite Diorite (Sims (Sims and and Schulz, Schulz, 1993) 1993) and and numerous numerous 27 �To the the southeast the the Quinnesec is in small lamprophyre dikes and plugs locally. To apparent fault contact with the Pemene formation (Sims and Schulz, 1993). McAllister formation: The The McAllister McAllisterformation formationappears appearsto to be be in in fault fault contact contactwith with the the the area (Jenkins, 1973). It occurs in a roughly east-west belt adjoining volcanic units in the between the Pemene formation to the north and the Beecher formation formation to the south (Sims and Schulz, 1993). It ranges in thickness from about 300 meters in the west to W and ~.70-80'W 3,000 meters in the east with units facing north and generally striking N.70-80° consists of of calc-alkaline caic-alkalirie basaltic to to andesitic andesitic dipping near vertical. The McAllister consists volcanic breccia breccia with aa lithic lithic tuff matrix, matrix, and and locally locally pillowed pillowedand and massive massivelavas. lavas. Fragments in the breccia breccia are distinctive distinctive in in that they they generally generally contain contain large largepyroxene pyroxene crystals crystals that are now replaced replaced by hornblende. Amygdules are also common in many gradation in fragment fragments. Vertically, the McAllister formation shows no consistent gradation size. However, laterally, fragment fragment size size increases from from west west to to east east (Jenkins, 1973). Near the Menominee suggesting the Menominee River, blocks more than 15 cm in diameter are common, suggesting source area for this dominantly fragmental fragmental unit may be located located to the east in Michigan. source formation: The Beecher formation: The Beecher Beecher formation formation extends extends in a north-facing, east to southeasttrending belt belt south of the McAllister formation and north north of the Athelstane Quartz Quartz and Schulz, Schulz, 1993). The The formation formation is at at least 3,000 3,000 meters thick thick with aa Monzonite (Sims and thicker (2,000 - 3,000 m) lower unit consists dominantly of of lower and upper unit. The thicker caic-alkaline flows and and lesser calc-alkaline plagioclaseplagioclase- and pyroxene-phyric andesite and dacite lava flows interbedded felsic volcaniclastic rocks. The thinner (up to 300 m) upper unit consists of interbedded rounded ash, crystal tuff, lapilli tuff, and coarser fragmental rocks, some with distinctive rounded pink to white felsite fragments. Some units show grading whereas others are unsorted. Black slates are also present present locally in the upper upper part part of the the formation. formation. The lower part of the Beecher Beecher formation, where intruded intruded by the Athelstane Quartz Monzonite, faces away from the intrusion intrusion and and has has aa well well developed developed foliation foliation and and steeply steeply plunging lineation. Dikes plunging Dikes of Athelstane Quartz Quartz Monzonite Monzonite extend extend only only aa short short distance distance formation. into the Beecher formation. Pemene formation: The The Pemene Pemeneformation formationisisinterpreted interpretedto to be bethe the youngest youngest volcanic volcanic unit in eastern Marinette County. It occupies a broad broad oval oval area area whose whose outline outline is is well well in the the northern part part of of the Miscauno Island 7.5 7.5 minute expressed in the local topography in 2,000 meters thick and consists predominantly predominantly of of quadrangle. The Pemene is at least 2,000 thick (45 300 m) calc-alkaline calc-alkaline rhyolite lava flows typically composed of a flow-top (45 -- 300 hyaloclastite microspheruliticcentral central core. core. hyaloclastite breccia, an underlying flow-banded flow-banded unit, and a microspherulitic The microspherulitic microspherulitic core constitutes the bulk of each flow and contains plagioclase plagioclase phenocrysts, commonly in glomeroporphyritic clusters, clusters, and and locally locally phenocrysts phenocrystsof of blue blue and lower contacts contacts quartz. The flow-banded unit, where present, has gradational upper and and laminar to highly-contorted highly-contorted banding. The The top top of each each flow flow has has aa layer layer of of hyaloclastite hyaloclastite breccia 3 to 75 m thick that probably formed by quench fragmentation as the hot rhyolite flows sec. 13, 13, flows came came in in contact contactwith with cold coldexternal externalwater. water.Exposures Exposuresininthe theNE NE1/4, 14, NW ¼, 14, sec. T. 36 N., R. 21 E., E., (Miscuano (Miscuano Island Island 7.5 minute quadrangle) provide an excellent cross sectional view of one of these rhyolite flows. Here, large open outcrops show a transition from massive massive microspherulitic microspheruliticrhyolite rhyoliteupward upward into into flow-banded flow-banded rhyolite rhyolitebreccia brecciawith with clasts to about 30 cm (a "crackle "crackle breccia"?). breccia"?). This in turn grades grades upward upward into a spectacular fine hyaloclastite hyaloclastite consisting of black rhyolite fragments, some with fine internal banding and white rinds rinds (figs. 11 11 and and 12). 12). Thin Thin sedimentary sedimentary units unitswith with graded graded 28 �bedding are present between some rhyolite flows. The general characteristics characteristics of the Pemene rhyolites is similar to those of other submarine rhyolite lava flow and dome complexes such that on the Island Island of Ponza, Italy (Scutter and others, 1998). Autobrecciated Autobrecciated and and hyaloclastite hyaloclastitecarapace carapace banded and Flow banded and microspherulitic interior Figure 11. Schematic cross-section of of the the upper part of of a subaqueous rhyolite lava flow in the Pemene Pemene formation. formation. Photograph of the rhyolite hyaloclastite in the upper carapace of a Figure 12. Photograph subaqueous Pemene subaqueous Pemene rhyolite rhyolite lava lava flow. 29 �The Pemene Pemene formation shows little evidence of a penetrative structural fabric. The flows show a southward dip in the north and dip nearly vertically in the south. Jenkins (1 (1973) 973) interpreted the structure of the Pemene as an east-trending, asymmetric, doubly interpreted of plunging plunging syncline. syncline. Major Intrusive Intrusive Rocks Rocks A variety of intrusive rocks are present within the supracrustal sequence in northeastern Wisconsin. They range tonalite to range from synvolcanic synvolcanic gabbro, diabase, diorite, and tonalite syntectonic intermediate to felsic granitoids (including those related related to the Dunbar dome), lamprophyric lamprophyric dikes and plugs, and post-tectonic granites and diabase dikes. Twelve Foot Falls Quartz Diorite: The Twelve Foot Falls Quartz Diorite comprises a some 20 20 km km by by 55 km km in size size to to the the west west of of Beecher, Wisconsin Wisconsin large "sill-like" intrusion some of gray, gray, generally medium to to coarse-grained coarse-grained (Sims and Schulz, 1993). It is composed of quartz quartz diorite diorite containing containing subhedral subhedral crystals crystals of of sodic sodic andesine, andesine,subhedral subhedralhornblende, hornblende, and anhedral bluish quartz. In composition it is similar to calc-alkaline calc-alkaline andesites in the McAllister and Beecher formations (Sims (Sims and others, others, 1992). 1992). Atheistane Atheistane Quartz Monzonite intrudes the Beecher Athelstane Quartz Monzonite: The Athelstane formation and extends for an unknown formation and extends for an unknown distance distance to to the the south southand andwest west(Sims (Simsand andSchulz, Schulz, 1993). It consists dominantly of of medium- to to coarse-grained quartz monzonite and locally contains contains numerous numerous metavolcanic metavolcanicinclusions. inclusions. The The Athelstane Athelstane Quartz QuartzMonzonite Monzoniteisisdated dated at 1,836±15 1,836±1Ma Ma (Banks (Banks and and Cain, 1969). 1969). The The Amberg Amberg Granite, Granite,which which intrudes intrudesthe the Athelstane Quartz Monzonite west and north of of Amberg (Sims and Schulz, 1993), 1993), is dated 1,756±1Ma Ma (Van (Van Schmus, Schmus, 1980). 1980). dated at 1,756±19 Dunbar Dunbar Dome Dome Only a brief summary of of the aeoloav geology of of the Dunbar dome is presented presented here for the Note. Onlv purposes of the present trips. More More comprehensive comprehensive accounts accounts are are available available in in aa guidebook auidebook by bv Sims Sims and and others others (1984), (19841, and and in in U.S. U.S. Geological Geoloaical Survey Survey Professional ProfessionalPaper Paper 1517 by Sims and and others others (1992). (1992). 1517 bv The Dunbar dome is one of several granitoid domes in northern Wisconsin that have have cores of gneiss, migmatite migmatite and granitoid rocks rocks and are mantled mantled by metavolcanic metavolcanic and Pembine-Wausau magmatic terrane (Sims and others, metasedimentary rocks in the Pembine-Wausau 1985). Where ages have been determined, both the core of the domes and mantle or cover rocks are of Paleoproterozoic age. The Dunbar dome is a complex antiformal structure consisting of a central core of Dunbar Gneiss, Marinette Quartz Diorite, and from the core composed of Hoskin Lake Granite, and three lateral protuberances (lobes) from the west, west, Spikehorn Creek Granite on on the the east, and Newingham Bush Lake Granite on the Tonalite on the south (Sims and others, 1992). structural evolution of 1992). The intrusive and structural the dome spanned the relatively short time of about 30 Ma, from syn-tectonic syn-tectonic events at about 1865 1865 Ma to post-tectonic post-tectonic at about about 1835 1835 Ma. Ma. Conclusions Conclusions The volcanic and associated intrusive rocks in northeastern Wisconsin south of the fault, the Pembine ophiolite, are are interpreted to to record the the evolution of of a Niagara fault, 30 �Paleoproterozoicsuprasubduction suprasubductionzone zone ophiolite-island ophiolite-islandarc arc sequence. sequence. Shervais Shervais(2001) (2001) Paleoproterozoic has has shown shown that suprasubduction suprasubductionzone zone ophiolites ophiolites tend tend to to display displayaa consistent consistentsequence sequence of events tectonic processes. events during their formation formation and evolution in response response to similar tectonic processes. This This sequence sequence includes includesthe the following following(after (afterShervais, Shervais,2001): 2001): (1) Birth, Birth, which which entails entails the the initiation initiationof ophiolite ophiolite formation formation during during extension extension above above aa (1) reconfigured intraoceanic subduction zone. Rocks formed newly forming or reconfigured during during the the initial initial phase phase of ophiolite ophiolite formation include include layered layered and isotropic isotropic plutonic gabbros, sheeted dikes, and a "lower" volcanic section consisting lowplutonic gabbros, sheeted dikes, and a "lower" volcanic section consistingof oflowK K tholeiitic tholeiitic basalt basalt and and basaltic basaltic andesite andesite with with MORB MORB and and primitive primitive arc arc tholeiite tholeiite affinities. Gabbros Gabbros formed formed during during this this stage stage are are often often ductilely ductilely deformed deformed (foliated (foliated affinities. or or boudinaged) boudinaged)in in response responseto to syn-magmatic syn-magmaticextension. extension. (2) (2) Youth, Youth, during duringwhich which continued continuedmelting meltingof of previously previouslydepleted depletedasthenospheric asthenospheric mantle mantle occurs occurs in in response response to to increased increased fluid flux from from the the subducting subducting slab. Rocks Rocks formed during during the the second second phase phase of ophiolite ophiolite formation formation include include intrusive intrusive maficmaficformed ultramafic ultramafic sills sills and and additional additional dikes, dikes, and andan an"upper" "upper"volcanic volcanicunit unitcharacterized characterizedby by basalt and andesite with highly depleted incompatible trace element basalt and andesite with highly depleted incompatible trace element compositions compositions (i.e., (i.e., low-Ti low-Tibasalt, basalt, high-Mg high-Mgandesite andesiteand andboninite). boninite). (3) Maturity, Maturity,during duringwhich which the the subduction subductionzone zone stabilizes stabilizes and and the the rate rate of of crustal crustal (3) spreading slows. slows. Rocks Rocks formed formed during during this this phase phase include include hornblende hornblende diorite, spreading quartz quartz diorite, diorite, tonalite, and and volcanic volcanic rocks rocks ranging ranging from from basalt basalt to to rhyolite, rhyolite, all all with with transitional transitional to tocalc-alkaline calc-alkalinecompositions. compositions.Volcanism Volcanismtypically typicallybecomes becomesmore more silicic silicic with time. In In many many cases, these rocks rocks have have not been been considered considered part part of the subjacent subjacent ophiolite, ophiolite, but but rather rather have have been been attributed attributed to post-ophiolite post-ophiolitearc volcanism. volcanism. (4) Death, Death,which which results resultsfrom from the the demise demiseof of active activespreading spreadingand andsubduction. subduction.In Inthe the (4) case case where where death death results results from from collision collision with with an an active activeocean oceanspreading spreadingcenter, center, dikes dikes and and lavas lavas with with oceanic oceanic basalt basalt compositions compositionsmay maycrosscut crosscutand andoverlie overliethe the older older ophiolite-arc ophiolite-arcsection. section. (5) Resurrection, Resurrection,which which accompanies accompaniesemplacement emplacementby by obduction obduction onto onto aa passive passive (5) continental margin marginor or accretionary accretionary uplift uplift with with renewed renewedsubduction. subduction. In In the the case case continental where where death death is is the the result result of of collision collision with with aa passive passive margin, margin, death death and and resurrection of of the the ophiolite ophiolite sequence sequencemay mayoccur occuressentially essentiallysimultaneously. simultaneously. resurrection The rocks rocks of of the the Quinnesec Quinnesec Formation Formationappear appear to to record record the the first first two two stages stagesof of The suprasubduction zone zone ophiolite evolution. The presence presence in the upper upper part of the suprasubduction Quinnesec Formation Formation of basalt basalt and and andesite andesite lavas lavas and dikes derived from highly highly Quinnesec refractory mantle mantle is is particularly particularly diagnostic diagnostic of aa relationship relationship to to the the early early stages stages of refractory intraoceanic forearcsetting setting(Shervais (Shervaisand andKimbrough, Kimbrough, intraoceanicsubduction subductionand and formation formationin inaaforearc 1985; Beccaluva Beccaluvaand and Serri, Serri, 1988). 1988).This This further furtherimplies impliesthat that the the Quinnesec QuinnesecFormation Formationand and 1985; associated rocks rocks did did not not form form in in aa back-arc back-arcbasin basin near near the the margin margin of of the the Superior Superior associated Craton, but but probably probablyformed formedas asan anintraoceanic intraoceanicophiolite-arc ophiolite-arcsystem systemabove aboveaasouthward southward Craton, dipping dipping(in (inpresent presentcoordinates) coordinates)subduction subductionzone. zone. McAllister, Beecher Beecherand and Pemene Pemene formations formationsand and The calc-alkaline calc-alkalinevolcanic volcanic rocks rocks of of the the McAllister, The associated associatedintrusives intrusivessuch such as as the the Newingham Newingham Tonalite Tonalite and and Twelve Twelve Foot Foot Falls Falls Quartz Quartz Diorite appear appear compatible compatiblewith with the the third thirdstage stage(maturity) (maturity)of ofsuprasubduction suprasubductionzone zone Diorite ophiolite evolution. evolution. Shervais Shervais (2001) (2001) notes notes that that for for aa suprasubduction suprasubduction zone zone ophiolite ophiolite to to ophiolite reach maturity maturity requires requires that that the the ocean ocean basin basin being being subducted subducted be be large large enough enough to to reach complete completethe the first first two two stages stageswithout without disappearing. disappearing.This This suggests suggests that that the the 31 �Paleoproterozoic significant in size (at Paleoproterozoic ocean basin that was subducted was probably significant least many many hundreds hundreds of kilometers). kilometers). It appears likely that growth of the Pembine Pembine ophiolite-arc system system was terminated terminated by by its its collision obduction onto onto the passive passive margin margin of the the Superior Superior craton. craton. Since Since collision with with and and obduction subduction subduction appears appears to to be be largely largely driven driven by by slab slab pull, pull, the the southward southward subduction subduction of of oceanic oceanic lithosphere lithosphere attached attached to to the the Superior Superior continental continental margin marginwould would have have pulled pulled the the continental lithosphere along with it as it descended into the subduction zone below continental lithosphere along with it as it descended into the subduction zone below the the ophiolite-arc ophiolite-arcsystem. system. With With detachment detachment of of the the subducting subductingoceanic oceanic lithosphere, lithosphere,the the buoyancy buoyancy of the the continental continental lithosphere lithosphere would have have led led to its its rapid rapid uplift uplift along along with with the the leading leading edge edge of of the the ophiolite-arc ophiolite-arc system system (Shervais, (Shervais, 2001). 2001). This This interpretation interpretationsuggests suggests that the the volcanic volcanic and and associated associated rocks rocks of of northeastern northeastern Wisconsin Wisconsinare are allochthonous, allochthonous,as as is is also also suggested suggested by by gravity gravity and and magnetic magnetic data data for for the the region region (Klasner (Klasner and and others, others, 1985; 1985; Attoh Attoh and and Klasner, Klasner, 1989). 1989). This This stage stage is is recorded recorded by by the the deformation deformationof of the the ophiolite-arc ophiolite-arc sequence Dunbardome. dome. ItItisis sequence and and by by the the intrusion intrusionof the the syn-tectonic syn-tectonic units units of of the the Dunbar possible possible that the shallow-water shallow-water sedimentary sedimentary rocks rocks (carbonates) (carbonates) along along the the west west margin margin of of the Dunbar Dunbar dome dome (Sims (Sims and and Schulz, Schulz, 1993) 1993) represent represent Chocolay Chocolay Group Group rocks rocks of of the the Marquette Marquette Range Range Supergroup Supergroup that that were were uplifted upliftedfrom from the the continental continentalmargin marginbasement basement below below during during formation formation of of the the Dunbar Dunbardome. dome. 32 �FIELD FIELDTRIP TRIP1I PEMBINE-WAUSAU PEMBINE-WAUSAU MAGMATIC MAGMATICTERRANE TERRANE Klaus Klaus J. J. Schulz, USGS, Reston, VA VA and and Gene Gene L. LaBerge, University University of of Wisconsin-Oshkosh Wisconsin-Oshkosh (retired), (retired), Oshkosh, WI Wl and andUSGS USGS Pillowed flows of high-Mg high-Mg andesite of the Quinnesec Quinnesec Formation, Formation, part part of the Pillowed Pembine Pembine ophiolite ophiolite complex, complex, Quiver Quiver Falls, Falls, Wisconsin Wisconsin �FIELD FIELDTRIP TRIP1I PEMBINE-WAUSAU MAGMATIC MAGMATIC TERRANE TERRANE PEMBINE-WAUSAU Klaus J. Schulz, Schulz, USGS, Reston, VA and Gene L. LaBerge, University University of WisconsinWisconsinOshkosh Oshkosh (retired), (retired),Oshkosh, Oshkosh,WI Wland andUSGS USGS The Paleoproterozoic Paleoproterozoicvolcanic volcanic and andassociated associatedintrusive intrusiverocks rocksexposed exposedininthe theeastern eastern The part of of Marinette MarinetteCounty County in in northeastern northeastern Wisconsin Wisconsin are are the the easternmost easternmost exposures exposures of of part the Pembine-Wausau Pembine-Wausauterrane, terrane, the northernmost northernmost of the two Wisconsin magmatic magmatic terranes the (Sims (Sims and others 1989). 1989). The volcanic rocks are composed composed of tholeiitic tholeiitic and calc-alkaline volcanic and and volcaniclastic volcaniclastic rocks rocks that formed at about 1870 1870 Ma Ma (Sims (Sims and and others, others, 1989). 1989). volcanic They They are are cut cut by by aa variety variety of intrusive intrusive rocks rocks ranging ranging from from syn-volcanic syn-volcanic gabbros, gabbros, diorites, diorites, and tonalities tonalities to to syn-and syn-andpost-tectonic post-tectonicgranitoids granitoids(i.e., (i.e., Dunbar DunbarGneiss Gneissand andrelated relatedrocks). rocks). and The The magmatic magmatic rocks rocks of of the the Pembine-Wausau Pembine-Wausauterrane terrane are are separated separated from from the the epicratonic epicratonic sedimentary sedimentary rocks rocks of of the the Marquette Marquette Range Range Supergroup Supergroup in in Michigan Michigan by by the Niagara Niagara fault fault zone. The The lithologic lithologic units units present present in in eastern eastern Marinette Marinette County County and and their chemistry chemistry zone. strongly strongly suggest suggest that that these these rocks rocks represent represent aa Paleoproterozoic Paleoproterozoicsuprasubduction suprasubduction zone zone ophiolite, the the Pembine Pembine ophiolite ophiolite (Schulz, 1987; 1987; Sims Sims and others, 1989). 1989). The ophiolite ophiolite, and and associated associated island-arc island-arcrocks rocks were accreted accreted to the southern southern margin margin of the the Archean Archean Superior Superior Craton Craton during during the the Penokean PenokeanOrogeny. Orogeny. On On this this field field trip trip we will examine examine the major major lithologies lithologies that comprise comprise the Pembine Pembine ophiolite. This includes examples of ultramafic rocks (serpentinite), layered ophiolite. This includes ultramafic rocks (serpentinite), layered and and massive massive gabbros cut cut by by mafic mafic dikes, dikes, pillow pillow basalts basalts and and andesites, andesites, and and several overlying calcgabbros alkaline alkaline arc-related arc-relatedvolcanic volcanic and andvolcaniclastic volcaniclasticrocks rocks(fig. (fig.1-1). 1-1). 34 �88 0845' 8T 5830" 88°08'45" 8758'30" 87 4815" 45 41 00 22 t I 0 0 ' 5 ' 2 I 0 0 55 6 6 4 'II 5 5 ' 8748'15" 88 , II 10 10 10 10 •II 15 15 12 Miles Miles 12 II Kilometers Kilometers EXPLANATION EXPLANATION Munising Sandstone Munising Sandstone(Cambrian) (Cambrian) Paleoproterozoic north of Paleoproterozoic rocks north o f Niagara fault Formation-graywacke Michigamme Formation graywacke Iron-formation Vulcan lron-formation Dolomite Randville Dolomite Paleoproterozoic rocks of Terranes Paleoproterozoic of Wisconsin Magmatic MagmaticTerranes Intrusive trusive rocks rocks Volcanic rocks . E Spikehorn Creek Spikehorn CreekGranite Granite and dacite dacite "Pemene formation" formation" . . ...., Rhyolite Rhyoliteand Granite Bush Lake Granite Basaltic and andandesitic andesitic breccia breccia"McAllister "McAllisterformation" formation Hoskuns Lake Lake Granite Granite Hoskins Rhyolute tuff graywacke Beecher formation" formation Rhyolite, felsuc felsic tuff,graywackel'Beecher Athelstane Athelstane Quartz Monzonite Monzonite Twelve Foot FallsQuartz Quartz Diorite Diorite Twelve Marinette Quartz Diorite Diorite Marinette Serpentinite of ophiolite ophiolite complex complex Serpentinite and and gabbro, base of NewinghamTonalite jJ NewinghamTonalite Quinnesec Formation Quinnesec Formation NewinghamTonalite, NewinghamTonalite, megacrystic facies megacrystic .. . Metagabbro Metagabbro Volcanic and rocks undivided undivided and granituc granitic rocks — faults - faults • field field trip trip stops stops Figure 1-1. Generalized geologic map of part of northeastern northeastern Wisconsin Wisconsin showing showing the the location of field trip stops stops 1-1 1-1 through through 11-8. See figure figure 3-2 3-2(p. (p. 67) 67) for for location locationof of stops stops1-9 1-9 location -8. See and 1-10. 1-10. 35 �____ _______ __ ____________ ____ _______ ° '6 / 1' + ET. -r1I k N 32 ' - ' aveH Pt -f •. - --- I && • ./ — c( - - . ./ ;. L 9Xt I - — - N ' . . . \ . / - — * . .. ) - • 2Y -- I . ( T. \ - — Approximatel 10 miles to Dunbar - 26O . . k. . ••• -' - n — . '- iaN . - . .— . - l . IZ I K" w 3 I) 5000 0 — ,_ — 0 10000 METERS I I 10000 20000 30000 — -= 400CR FEET Figure Figure1-2. 1-2.Part Partofofthe theEscanaba Escanaba1:100,000-scale 1:I 00,000-scaletopographic topographicmap mapshowing showingthe thelocation location of of field fieldtrip tripstops stops1-1 1-1through through1-7 1-7and andsupplemental supplementalstops stops1-8 1-8and and1-11. 1-11. Stop side U.S. 141, SW NE Stop1-1. 1-1.Spikehorn SpikehornCreek CreekGranite Granite(west (west side U.S.Highway Highway 141, SW¼,?h, NE1/4 '%sec. Isec. , 36, 36,T. T.38 38N., N.,R. R.20 20E.). E.). The Theoutcrop outcropon onthe thewest westside sideofofU.S. U.S.Highway Highway141 141(fig. (fig.1-2) 1-2)isisrepresentative representativeofofthe the Spikehorn SpikehornCreek CreekGranite, Granite,aagray graytotopinkish pinkishgray, gray,finefine-totomedium-grained medium-grainedmassive massive granite granitewith withscattered scatteredpotassium potassiumfeldspar feldspargrains grainsas asmuch muchas as22cm cminindiameter. diameter.The The granite graniteisiscomposed composedofofplagioclase plagioclase(sodic (sodicoligoclase) oligoclase)with withweak weaknormal normalzoning, zoning, 36 �microclinemicroperthite, microperthite,quartz, quartz,biotite, biotite,sphene, sphene,and andopaque opaqueoxides. oxides.Accessory Accessoryminerals minerals microcline include zircon, allanite, apatite (rare), and fluorite (rare). The granite has sharp intrusive include zircon, allanite, apatite (rare), and fluorite (rare). The granite has sharp intrusive contacts contactswith with the the Quinnesec Quinnesecvolcanic volcanicrocks rocksand andthe theMarinette MarinetteQuartz QuartzDiorite. Diorite. The The Spikehorn SpikehornCreek Creek Granite Granite isis aa post-tectonic post-tectonicdiapiric diapiric intrusion intrusion on on the the northeast northeast side side of of the the Dunbar Dunbar dome dome with with an an age age of of 1,835±6 1,835*6 Ma Ma (Sims (Sims and and others, others, 1992). 1992). ItIt is is similar similar in in composition LittleTobin Lake Lake Granite, Granite, which which intrudes intrudes the the Badwater Badwater composition and and age age to to the the LittleTobin Greenstone Greenstonenorth north of of the the Niagara NiagaraFault Faultzone zone (Schneider (Schneiderand and others, others, 2002; 2002; see see also also field field trip trip 3, 3, stop stop 3-9). 3-9). Both Both the the Spikehorn Spikehornand and Little LittleTobin Tobin Lake Lakegranites granites represent represent"stitching" "stitching" plutons, plutons, emplaced emplaced after after collision collision of of the the Pembine-Wausau Pembine-Wausaumagmatic magmaticterrane terranewith with the the passive passive margin margin of of the the Superior Superior Craton. Craton. As As such, such, the the age age of of these these granites granites provides providesaa minimum minimumage agefor for the thePenokean PenokeanOrogeny. Orogeny. Stop Stop 1-2. 1-2. Exposures Exposuresof of Serpentinite, Serpentinite,Gabbro. Gabbro,and and Mafic Mafic Dikes Dikes(i.e., 0.e.. Ophiolite) Ophiolite)East East of (NW1/4, %, NW ¼, sec. sec. 22, 22ÂT. T. 37 37N., N.?R. R. 21 21E.) Em) ofPembine Pembine(NW % Follow Follow the the red red flags flags and and trail trail north north to to outcrops outcrops of of serpentinite serpentinite on on the the south south side side of of the the North NorthBranch BranchPemebonwon PemebonwonRiver. River.The Theserpentinite serpentiniteininthe thesurrounding surroundingoutcrops outcropsshows shows variable variable features features including includinglayering layering(fig. (fig. 1-3), 1-3),brecciation, brecciation,and andcarbonate carbonateand andserpentine serpentine veining. veining. Chromite Chromiteisisclearly clearly evident evident in insome some samples. samples. Some Some serpentinite serpentinite is is highly highly magnetic magnetic whereas whereas other other samples samples are are not; not; this this may may reflect reflectoriginal original variations variations in in the the proportion proportionof of olivine olivineand andpyroxene pyroxenein in the the ultramafic ultramafic rocks. rocks.Locally, Locally,dikes dikes of of pyroxenite pyroxenite (now (now altered alteredto to talc-serpentine) talc-serpentine)have havebeen beenobserved observedcutting cuttingthe theserpentinite. serpentinite. Figure Figure1-3. 1-3.Photograph Photographof ofnearly nearlyvertical verticallayering layeringininultramafic ultramafic(serpentinite) (serpentinite)rocks rocksat at stop 1-2. stop1-2. 37 �As we walk south we will first first see further exposures of serpentinite followed after a few hundred hundred meters meters by by a series series of of outcrops outcrops with with variable variable proportions proportionsof of layered layeredgabbro, gabbro, foliated-lineated gabbro, massive diabase and quartz diabase (dikes?), all cut by foliated-lineated reddish-brown-weathering reddish-brown-weathering mafic dikes (figs. 1-4 1-4 and 1-5). The foliation in the foliated gabbro is variable in strike between N.15 W. to N.15 E. and dips steeply either E or W. The mafic dikes generally strike about E-W parallel parallel to the overall trend of the serpentinite-gabbro body and dip steeply. The dikes do not appear to extend outside the body into the surrounding pillow basalts. The serpentinite-gabbro body appears to be fault-bounded and and tectonically tectonically emplaced emplaced within within the the Quinnesec Quinnesec Formation. Formation. Figure Figure 1-4. Photograph Photograph of rusty weathering mafic dikes with gabbro screens at stop 1-2 1-2 (Note, dike dike margins margins are are highlighted). highlighted). The lithologies lithologies and their arrangement in this ultramafic-gabbroic ultramafic-gabbroic body along with those of the Quinnesec Quinnesec Formation Formation generally are similar to those that characterize recent ophiolite sequences (Moores, 2002). This includes (from bottom to top): mafic-ultramafic mafic-ultramafic plutonic rocks, rocks, aa dike dike (sheeted?) (sheeted?) complex, complex, extrusive extrusivepillowed pillowedand andmassive massivebasalt basaltlava lava flows, and overlying volcaniclastic sedimentary rocks. The compositions of the gabbros and mafic island-arc tholeiite and MORB to depleted island-arc mafic dikes within this body range from MORB high-magnesium high-magnesium andesite with boninitic affinities; the mafic rocks rocks are similar in composition to the gabbros and basalts basalts in the Quinnesec Formation Formation (Sims and others, 1989; Schulz, 1987 1987 and unpublished unpublished data). The The lithologic lithologic association association and and chemistry chemistry are are similar to recent suprasubduction zone ophiolites like those of the Coast Ranges in California California (Shervais and Kimbrough, 1985; Shervais, 2001). These data, along with the presence of overlying overlying calc-alkaline caic-alkaline island-arc island-arc volcanic and volcaniclastic rocks, suggest formation of the Quinnesec Quinnesec as as a suprasubduction suprasubduction zone ophiolite associated with forearc extension during the early stages of subduction subduction and island arc formation. 38 �Figure Figure 1-5. 1-5. Close-up Close-up photo photo of of rusty rusty weathering weathering mafic mafic dike dike cutting cuttingfoliated foliated gabbro gabbro at at stop stop 1-2. 1-2. Note Note cleavage cleavage development development along along the the upper upper margin margin of of dike dike (dike (dike contacts contactsare are hightlighted). hightlighted). Stopl-3. Stop1-3.Pillow Pillowbasalt basaltofofthe theQuinnesec QuinnesecFormation. Formation,Quiver QuiverFalls Fallson onthe theMenominee Menominee River sec. 24, T. 37 River(NE (NE1/4, %, SW SW 1/4, %, sec. 37 N., N., R. R.21 21E.) E.) - Basalt Basaltand andandesite andesitepillow pillow lavas lavasand and pillow pillow breccias brecciasare are common common in in the the Quinnesec Quinnesec Formation. three-dimensionalview viewofofpillows pillowscan canbe beseen seenininthis thisexposure exposurealong alongthe the Formation.AA three-dimensional banks banksof of the theMenominee MenomineeRiver Riverat at Quiver QuiverFalls Falls(fig.1-6). (fig.l-6). Here, Here,south-facing south-facingelongate elongate closely closely packed packedbasalt basaltpillows pillowscan can be be seen seen with with excellent excellent preservation preservation of of features features due due to to the thelow lowdegree degreeof ofdeformation. deformation.Locally, Locally,the thebasalt basalthere hereisisalso alsohighly highlyvariolitic variolitic(fig. (fig.1-7) 1-7) with with large large(1-2 (1-2cm) cm)round roundpinkish pinkishsiliceous-appearing siliceous-appearingvarioles. varioles. Chemically Chemicallythe the basalt basalt isis characterized (9.8 wt.%), wt.%), and andvery very low low Ti02 Ti02(0.35 (0.35 wt.%), wt.%), Zr Zr (35 (35 characterizedby byrelatively relativelyhigh highMgO MgO(9.8 ppm), ppm),and andREE REE(flat (flatpattern patternatat—6 -6 xx chondrites) chondrites) contents. contents. ItIt is is similar similar in in composition composition to to some someof of the themassive massivediabasic diabasicgabbro gabbroseen seenat atstop stop1-2. 1-2. 39 �Fig1-ire 1-6. Figure 1-6. Photograph Photograph of of pillow pillow basalt basalt in in the the Quinnesec Quinnesec Formation Formation at at Quiver Quiver Falls Falls on oi the the Menominee MenomineeRiver River(stop (stop1-3). 1-3). FigiJre 1-7. 1-7.Photograph Photographof of variolitic variolitic basalt basalt at at Quiver Quiver Falls Falls on on the the Menominee Menominee River River (stop (s1 Figure 1-3). 1-3)I. 40 �Stop 1-4. 1-4. Andesite Andesite Breccia Brecciaat atthe theNew NewKremlin KremlinMine MinePit Pit(5(S½, Vs,sec. sec.26, 26,T.T.37 37N., N.,R. R. Stop 21 21 E.) E.) The fresh fresh glacially glacially polished polished outcrops outcrops around around the the new new Kremlin Kremlin mine mine pit pit at at this this stop stop The provide excellent exposures of andesite breccia breccia in the upper upper part part of the Quinnesec Quinnesec provide Formation. The Kremlin Kremlin mine mine processes processes the Quinnesec rocks rocks for roofing roofing granules. granules. The The Formation. andesite breccia breccia consists consists of of angular angular to to sub-rounded sub-roundedvolcanic volcanic fragments fragments ranging rangingfrom from andesite about 55 cm cm to to at at least least 40 40 cm cm across across in in aa matrix matrixof of 0.5 0.5 to to 2.0 2.0 cm cmhyaloclastite hyaloclastitefragments. fragments. about The sub-rounded sub-roundedfragments fragments and and hyaloclastite hyaloclastitematrix matrix suggest suggest that that the the unit unit may mayrepresent represent The andlor subaqueous subaqueous debris debris flows. flows. Note Note the the black black pyroxene pyroxene phenocrysts phenocrysts in in pillow breccias brecciasand/or pillow some of of the the andesites andesites clasts. clasts. Locally Locallyto to the the west, west, similar similar rocks rocksare are interlayered interlayeredwith with some rhyolite rhyolite flows flows and and tuffs. tuffs. Stop1-5. 1-5.McAllister McAllister Formation Marek Road %,sec. sec.22, 22,T.T.36 36N., N.,R.R.21 21 Stop Formation onon Marek Road (NE(NE 1/4,%, NENE 1/4, E.) The McAllister McAllister formation formation consists consists of of caic-alkaline calc-alkaline basaltic basalticto to andesitic andesitic volcanic volcanic breccia breccia The with aa crystal crystal lithic lithic tuff tuff matrix, matrix, and and locally locally pillowed pillowedand and massive massive lavas. lavas. This outcrop outcrop is is with typical of of the the McAllister McAllister volcanic volcanic breccia. breccia. Fragments Fragments in in the the breccia brecciaare are distinctive distinctive typical because they they generally generally contain contain large large pyroxene pyroxene crystals crystals that that are are now now replaced replaced by by because hornblende. Amygdules Amygdules are are also also common common in in many many fragments. fragments. The The size size of of fragments fragments in in hornblende. the McAllister McAllister formation formation increases increases from from west west to to east. east. Near Near the the Menominee Menominee River, River, blocks blocks the over 15 15 cm cm in in diameter diameter are are common common suggesting suggestingthe the source source area areafor for this this dominantly dominantly over fragmental fragmental unit unit may may be be located locatedto to the the east east in in Michigan. Michigan. Stop onon Marek Road (NW 1/4,%,NW Stop1-6. 1-6.Beecher BeecherFormation Formation Marek Road (NW NW1/4, %, sec. sec. 26, 26,T. T. 36 36N., N.,R. R.21 21 E.) E.1 The Beecher Beecherformation formationconsists consistsof oftwo twounits: units:aathick thick(—2,000-3,000 (-2,000-3,000 m) m) lower lower unit unit The consisting consisting dominantly dominantly of of calc-alkaline calc-alkaline plagioclaseplagioclase- and and pyroxene-phyric pyroxene-phyric andesite andesite and and dacite lava lavaflows flows and andlesser lesserpyroclastic pyroclasticrocks, rocks,and andaathinner thinner(—300 (-300 m) upper upper unit, which which dacite consists consists of of interbedded interbedded felsic felsic ash, ash, tuff tuff and andcoarser coarser fragmental fragmental rocks. rocks.The Theexposures exposuresat at this lapillituff, tuff, and and this stop stop are are in in the the upper upper unit unit and and show show bedded bedded crystal crystal tuff tuff (fig. (fig. 1-8), 1-8),lapilli coarser coarser units, units, some some with with distinctive distinctive rounded rounded pink pink to to white white felsite felsite fragments fragments (fig. (fig. 1-9). 1-9). Some Some units units are are graded graded whereas whereas others others are are unsorted. unsorted. Graded Graded bedding bedding in in some some layers layers indicates tops tops to to the the northeast. northeast. Jenkins Jenkins(1973) (1973) suggested suggestedthat that at at least leastsome someof of the the rocks rocks indicates of of the the Beecher Beecherformation formationwere weredeposited depositedsubaerially. subaerially. 41 �4L - -. — —. - 4 —? S — -;.. —-— :;-— :-— :t_ —. ;:;b -- - ,- —- ,- -. __4 --- . __( . : Figure 1-8. 1-8. Photograph Photograph of bedded bedded crystal crystal tuff in in the the upper upper unit unit of of the the Beecher Beecherformation, formation, Figure stop stop1-6. 1-6. Figure 1-9. 1-9.Photograph Photographof of aa distinctive distinctive fragmental fragmental unit unitwith with rounded roundedpink pinkto to white white felsite felsite Figure 1-6. fragmentsininthe theupper upperpart partof ofthe theBeecher Beecherformation, formation,stop stop1-6. fragments 42 42 �Stop 1-8. 1-8. Pemene Pemene Formation Formationat at Pemene Pemene Falls Fallson onthe theMenominee MenomineeRiver River(NW (NW corner, corner, Stop Sec. sec. 23, T. 37 37 N., N., R. R. 25 25 W.) W.) Exposed along along the bank bank of the the Menominee Menominee River River at Pemene Pemene Falls Falls is is rhyolite rhyolite of the Exposed Pemene Formation. Formation. The The rocks rocks are are dark dark gray gray to to reddish reddish gray, gray, contain contain few few feldspar feldspar Pemene phenocrysts, and are generally microspherulitic. Phenocrysts, many of which are phenocrysts, and are generally microspherulitic. Phenocrysts, many glomeroporphyritic, consist consist mainly mainly of euhedral euhedral to subhedral subhedral albite; however, phenocrysts phenocrysts glomeroporphyritic, blue quartz quartz are are present present locally. locally. The The microspherules microspherules consist consist of radial radial intergrowths intergrowths of of blue quartz quartz and and albite. This phase phase of the the Pemene Pemene probably probably represents represents the devitrified devitrified interior interior portion portion of of aa rhyolite rhyoliteflow. flow. In In areas areas to to the the west, Pemene Pemene rhyolite rhyolite lava lava flows show internal internal gradations gradations from massive massive microspherultic rhyolite rhyolite at their their centers centers to flow-banded flow-banded rhyolite rhyolite and and finally autobreccia autobreccia microspherultic and hyaloclastite hyaloclastite carapaces. carapaces. This suggests suggests the Pemene Pemene rhyolite rhyolite flows were deposited deposited and subaqueously. Locally, Locally, felsic dikes dikes are found found cutting cutting the rhyolite. rhyolite. subaqueously. SupplementalStop Stop 1-8. 1-8. Dunbar Gneiss Dunbar, Wisconsin Supplemental Gneiss West and North of Dunbar, Wisconsin Stop 1-8a. 1-8a. Dunbar Gneiss on the West Side of of County CountyRoad Road U U Stop of the the Intersection Intersection of Y4, SW SW ¼, Y4, sec. sec.26, 26,T. T.37 37N., N.,R. R.18 18E.). E.). withU.S. U.S.Highway Highway8 8(SW (SW1/4, with The low low outcrops outcrops here here are are composed composedmainly mainly of of megacrystic megacrysticgranite granite gneiss gneiss that that contains contains The rafts of layered layered amphibolite amphibolite (fig. (fig. 1-10). 1-10). This This lithology lithology is is similar similar to to that that dated dated from from an an rafts outcrop to to the the north northwith with aa U-Pb U-Pbzircon zircon concordia concordia upper upper intercept intercept age age of of 1,862±5 1,862~5 Ma outcrop Ma N. (Sims and and others, others, 1992). 1992).Lineation Lineationin inthe theamphibolite amphiboliteplunges plungesgenerally generallyabout about20-25° 20-25' N. (Sims 85-90' E. E.Locally, Locally, the the amphibolite amphiboliteisisrefolded refoldedby byfolds foldshaving havingN. N.50° 50' W. W.steep steepaxial axial 85-90° N. 70° 70' W. foliation. foliation. The The granite granitegneiss gneiss surfaces. The The granite granite gneiss gneiss has pervasiveN. hasaa pervasive surfaces. composition, and is interpreted plutonic protolith protolith (Dunbar Gneiss) tonalitic in Gneiss) is is tonalitic in composition, and is interpreted as a plutonic (Dunbar (Sims (Sims and and others, others, 1992). 1992). Stop1-8b. 1-8b.Migmatitic MigmatiticDunbar DunbarGneiss Gneiss (Center sec.15, 15,T.T.3737N., N.,R.R.18 18E.). E.). Stop (Center sec. The exposures exposures on on the the east east side side of of the the road roadare are of of migmatitic migmatiticDunbar DunbarGneiss. Gneiss.The Thegneiss gneiss The here here consists consistsmainly mainly of of compositionally compositionally layered layered rocks, rocks, biotite biotite gneiss, gneiss, and and lesser lesser amphibolite, intruded intrudedby by megacrystic megacrystic biotite biotitegneiss, gneiss, granite granitepegmatite, pegmatite, and and aplite. aplite. All All amphibolite, N. 50-55° 50-55' W. at at 90°. 90'. The The foliation foliation is is defined defined by by rocks are are deformed deformed with with foliation foliation striking striking N. rocks biotiteand andhornblende hornblendealignment alignmentand andisisgenerally generallyparallel paralleltotocompositional compositionallayering. layering. biotite 43 �_ — ..— a.— * it,r * -- qr * - ..._ - ..- ' -. ,—. - •* - - I . -. — .4 T Figure 1-10. 1-10. Photograph Photograph of an an outcrop outcrop of of megacrystic megacrystic Dunbar Dunbar Gneiss Gneiss with with folded folded Figure amphibolite amphiboliterafts raftsat atstop stop1-8a. 1-8a. SupplementalStop Stop1-9. 1-9. Sulfide Sulfide deposit depositat at"LaSalle "LaSalleFalls" Falls"on onthe thePine PineRiver. River.(NW (NW Supplemental %, SE 1/4, SE%, ¼,sec. sec.30, 30,T.39 T.39N., N.,R.18 R.18E.E.See Seefigure figure3-1 3-1and and3-2 3-2for for location.) location.) The Pembine-Wausau Pembine-Wausauterrane terraneisishost hostto to aanumber numberof of volcanogenic volcanogenicmassive massivesulfide sulfide The deposits, deposits, two two of of which whichare areknown knownin innortheastern northeasternWisconsin Wisconsin(Cummings, (Cummings,1978; 1978;LaBerge, LaBerge, 1983). 1983). The The deposit deposit on on the the Pine PineRiver Riverisisthe theonly onlyknown knownnaturally naturallyexposed exposedmassive massive sulfide sulfidedeposit depositin inWisconsin. Wisconsin. LaSalle Falls) Falls) on on the the Pine Pine River River occurs occurs in in The deposit deposit at at Pine Pine Rapids Rapids(locally (locally known known as as LaSalle The 3-2). the Quinnesec Quinnesec Formation Formationabout about one one mile mile south south of of the the Niagara NiagaraFault Faultzone zone (fig. (fig. 3-2). the LaSalleFalls Fallsis is formed formed where where the the Pine Pine River River flows flows over over aa resistant resistant unit unit of of rhyolite rhyolite LaSalle breccia brecciaonto onto an an easily easily eroded eroded unit unit of of sulfide-bearing sulfide-bearing schist schist that that occurs occurs between betweenthe the rhyolite rhyolite and and aa unit unit of of mafic maficvolcanic volcanic rocks. rocks.Removal Removalof of the the easily easily eroded eroded schist schist has has formedaa narrow narrowgorge gorge on on the the Pine PineRiver Riverfor for several severalhundred hundredfeet feet below belowthe the falls. falls. The The formed withaaprominent prominentlineation lineationthat thatplunges plunges rocksstrike strikenearly nearlyeast-west east-westand anddip dip60-70° 60-70' SSwith rocks 50-60°, 50-60, SS40° 40' W. W. The deposit deposit was was discovered discovered during during an an airborne airborne geophysical geophysical survey survey in in the the 1970's, 1970's, and and The has has been beendrilled. drilled. The Themain mainpart partof ofthe thegeophysical geophysicalanomaly anomalyextends extendsdownstream downstreamwithin within theriver riverchannel channelbetween betweenexposures exposuresof of rhyolite rhyoliteon onthe the north northand andbasaltic basalticrocks rockson onthe the the south. Drill Drillcores cores show show that that the the rhyolite rhyolite consists consists of of coarse coarse fragments fragmentsin inaa relatively relatively south. sulfide-richmatrix, matrix, aa typical typical "stringer "stringer ore". ore". Rhyolite Rhyoliteexposed exposed at at the the falls falls is is very very pitted, pitted, sulfide-rich due due to to breakdown breakdownof of the the sulfide-rich sulfide-rich(pyrrhotite-chalcopyrite) (pyrrhotite-chalcopyrite)matrix matrix material. material. Exposures Exposures 44 �immediately below below the falls, at the stratigraphic stratigraphic level level of the the main main EM EM anomaly, consist consist of immediately approximately approximately18 18m m of of sulfide-bearing sulfide-bearingschist schist and and cherty cherty units. units. The Thesedimentary sedimentaryunit unit isis mainly laminated laminated chloritic chloritic and and sericitic sericitic schist with pyritic lenses lenses up to 3 mm mm thick. mainly Garnets Garnets are are common commonin insome some layers. layers. Sprays Sprays of of black black tourmaline tourmaline are are present present in in the the mafic mafic volcanic volcanic rocks rocks on on the the south south side side of of the the river. river. The The structure structure in inthe the area areaisissomewhat somewhat puzzling. puzzling.Based Basedon on regional regional geology, geology, Dutton Dutton (1971) Bayley and and others others (1966) (1966) concluded concluded that that the the Quinnesec Quinnesec Formation Formationfaces faces (1971) and and Bayley north northnear near the the Niagara NiagaraFault. Fault. Sims Simsand andothers others(1984) (1984) also also reported reportedthat that the the Quinnesec Quinnesec faces DunbarDome, Dome, which which lies lies south south of of "LaSalle "LaSalleFalls". Falls". In In faces northward northwardaway away from from the the Dunbar addition, although although deformation deformationhas hasobscured obscuredfacing facingdirection directionindicators, indicators,such suchas as pillows, pillows, addition, %, NE NE ¼, %, sec. sec. 26, 26, T. T. 34 34N., N., A. R. in most mostareas, areas,north-facing north-facingpillows pillowsare areexposed exposedininthe theSW SW1%, in 17 E., about abouttwo two miles mileswest westof of"LaSalle "LaSalleFalls". Falls".However, However,the thelithologic lithologicsequence sequenceand and 17E., pattern patternof of mineralization mineralizationat at "LaSalle "LaSalleFalls" Falls"suggests suggests that that the the rocks rockshosting hostingthe the mineralization mineralization face face southward. southward. The The zone zone of of "stringer "stringerore" ore" isisnorth northof of the the main mainsulfide sulfide zone, zone, and and the the sequence sequence is is "overlain"(?) "overlain1'(?)by by mafic mafic volcanic volcanic rocks rocksto to the the south. south. SupplementalStop Stop1-10. 1-10.Pine PineRiver RiverPegmatite Peqmatite bodies. (NW NE V*.sec. sec.22, 22, TT .39 .39 Supplemental bodies. (NW ¼,%,NE 1/4, N., figures 3-1 and 3-2 for for location.) location.) N., R.17 R.17 E.) See figures - (WARNING: (WARNING: - Because Because this thisexposure exposureisisnear nearthe thePine PineRiver RiverWILD WILDRIVERS RIVERSAREA. AREA, no no collecting collectinuis ispermitted permittedat at this this locality.) locality.) Dutton Dutton (1971) (1971) reported reportedthe the occurrence occurrenceof of pink pinktourmaline tourmalinein inaa pegmatite pegmatitedike dikefrom fromthis this area. area. The Thepegmatites pegmatitesare arelocated locatedapproximately approximately150 150feet feetwest westof ofthe thePine PineRiver Riverand and approximately approximately300 300feet feetsouth southof of Highway Highway101 101in inFlorence FlorenceCounty County(fig. (fig.3-1). 3-1).The Thelocation location is is about about aa mile milesouth southof of the theNiagara NiagaraFault. Fault. The Thepegmatite pegmatitebodies bodiesare areup upto toaafew fewmeters meterswide wideand andcut cutfelsic felsicvolcanic volcanicrocks rocksof ofthe the Quinnesec QuinnesecFormation. Formation.The Thepegmatites pegmatitesare aresub-parallel sub-parallelto tothe thefoliation foliationininthe thevolcanic volcanic rocks, rocks,strike strikenearly nearlynorth-south, north-south,and anddip dipabout about50 50degrees degreeswest. west. AA number numberof of small small lithium-rich lithium-richpegmatite pegmatitebodies bodiesininthe thearea areacontain containspodumene, spodumene,lepidolite, lepidolite,and andelbaite elbaite tourmaline tourmalineas aswell wellas asquartz, quartz,albite albiteand andmicrocline. microcline.Some Somepegmatites pegmatitescontain containabundant abundant pink tourmaline crystals 0.5 1.0 cm wide and 2.5 5.0 cm long, commonly oriented pink tourmaline crystals 0.5 - 1.0 cm wide and 2.5 - 5.0 cm long, commonly oriented roughly roughlyperpendicular perpendicularto to the theupper uppercontact contactof of the thepegmatite. pegmatite.Some Sometourmalines tourmalinesare arecolor color zoned, zoned, with withaapink pinkcore coreand andblue-green blue-greenrind. rind.The Thepegmatites pegmatitesare arecomposed composeddominantly dominantly of of aplitic apliticquartz-feldspar quartz-feldsparwith withsome somelepidolite. lepidolite.The Thepegmatites pegmatitesrepresent representhighly highlyevolved evolved granitic graniticmelts meltsrelated relatedto tothe thenearby nearbyBush BushLake LakeGranite Graniteassociated associatedwith withthe theDunbar Dunbar gneiss-granitoid gneiss-granitoiddome dome(Sims (Simsand andothers, others,1992). 1992). Supplemental SupplementalStop Stop1-11. 1-11. Metasedimentary MetasedimentarvRocks Rockson on the the Northwest NorthwestSide Sideof ofthe the Dunbar DunbarDome Dome(SW (SW1/4 %, SE SE¼, VA, sec. sec.7,7,T.T.37 37N., N.,R.R.18 18E.) E.) Metasedimentary Metasedimentaryrocks rocksare areexposed exposedintermittently intermittentlyon onthe thewest westside sideof of the theDunbar Dunbardome dome and andadjacent adjacentto toand andnorthwest northwestof ofthe theBush BushLake Lakelobe lobe(Sims (Simsand andSchulz, Schulz,1993). 1993).Although Although included includedby byDutton Dutton(1971) (1971)ininthe theQuinnesec QuinnesecFormation, Formation,subsequent subsequentmapping, mapping, geophysical geophysicaldata, data, and andcore coredrilling drillingby byaaprivate privatecompany companyshow showthat that these these strata strataunderlie underlie the theQuinnesec. Quinnesec.The Theexposed exposedmetasedimentary metasedimentaryrocks rocksare aremetamorphosed metamorphosedatatamphibolite amphibolite grade gradeand andare aremainly mainlyquartz-rich quartz-richschist, schist,impure impuremarble, marble,calc-silicate calc-silicaterocks, rocks,and andbiotite biotite schist. schist.Drilling Drillingand andelectromagnetic electromagneticdata dataindicate indicatethat thataagraphitic graphiticschist schistlies liesalong alongthe the 45 �west west side side of of the the Bush Bush Lake Lake lobe lobe stratigraphically stratigraphically below below the the exposed exposed metasedimentary metasedimentary rocks. rocks. The The large large exposure exposure at at this this stop stop on on the the south south side side of of Macintire MacintireCreek Creek consists consistsof of interbedded interbeddedcaic-silicate calc-silicaterocks rocks and and biotite biotite schist schist that that are are cut cut by by granite granite pegmatite pegmatite and and apilite apilite dikes, dikes, identical identical to to those those exposed exposed within within the the western western part part of the the Dunbar Dunbar dome. dome. At At another SW %, A, sec. VA, SW sec. 11, 11, T. T. 38 38 N., N., R. R.17 17E.), E.), aa another outcrop outcrop area areato tothe thenorth north(NW (NW1/4, succession 100m mthick thick of of marble, marble,calc-silicate calc-silicaterocks, rocks,and andthin thininterbeds interbedsofofbiotite biotite succession at at least least 100 schist schist and and ferruginous ferruginous quartzite quartzite is is exposed. exposed. The The marble marble at at this this location locationhas has structures structures suggestive suggestive of of stromatolites. stromatolites. In In many many respects respects the the metasedimentary metasedimentaryrocks rocks exposed exposed on on the the west west side side of of the the Dunbar Dunbar dome dome resemble resemble those those of of the the Chocalay ChocalayGroup Group of of the the Marquette MarquetteRange Range Supergroup, Supergroup,as as exposed exposed in in the the Menominee Menominee iron iron range range to to the the north north (Bayley (Bayley and and others, others, 1966). 1966). These These metasedimentary metasedimentaryrocks rocks may may compose compose aa tectonic tectonic slice slice of of continental-margin continental-margin rocks rocks that that is is interleaved Dunbar dome dome and and volcanic volcanic rocks rocks of the Quinnesec interleaved with with granitoid granitoid rocks rocks of of the the Dunbar Formation. Formation. Alternatively, Alternatively, they they may may have have been been uplifted uplifted from from beneath beneath the the over-thrust over-thrust Quinnesec Formation during the formation of the Dunbar dome. Quinnesec Formation during the formation of the Dunbar dome. 46 �FIELD FIELD TRIP TRIP 22 MENOMINEE MENOMINEE IRON IRON DISTRICT DISTRICT Gene Gene L. L. LaBerge, LaBerge, University Universityof of Wisconsin-Oshkosh Wisconsin-Oshkosh(retired) (retired)and andUSGS; USGS;John JohnS. S. Kiasner, Klasner, Western WesternIllinois IllinoisUniversity University(retired) (retired)and andUSGS; USGS;William WilliamF. F.Cannon, Cannon, USGS; gas, University USGS; Richard Richard W. W.Ojakan Ojakangas, University of Minnesota Minnesota Duluth Duluth (retired) (retired) The Quinnesec Quinnesec Mine Mine near near Quinnesec, Quinnesec, Michigan Michigan produced produced about 500,000 tons of siliceous siliceous iron iron ore between between 1887 1887 and 1935 1935 from open pits pits and stopes in the Vulcan IronIronformation. The Theworkings workingsseen seenhere hereare areon onthe the overturned overturnednorthern northern limb limb of a syncline. The The locality locality is is also also noted notedfor for the the excellent excellentexposures exposuresof of the thebasal basalCambrian Cambrian unconformity. The The roof roof of of the the working working in in the the upper upper right right is is the base base of the Munising Sandstone, Sandstone, which which lies lies with with an an angular angular unconformity unconformityon onthe theoverturned overturnedVulcan VulcanIronIronPhotographby byElizabeth ElizabethHeinen. Heinen. formation. Photograph �FIELD TRIP TRIP 22 FIELD MENOMINEE MENOMINEE IRON IRONDISTRICT DISTRICT Gene L. LaBerge, University University of Wisconsin-Oshkosh Wisconsin-Oshkosh(retired) (retired)and and USGS; USGS;John John S. S. Gene F. Cannon, Cannon,USGS; USGS; Klasner, Western WesternIllinois IllinoisUniversity University(retired) (retired)and and USGS; USGS;William WilliamF. Kiasner, Richard W. Ojakangas, Ojakangas, University University of of Minnesota MinnesotaDuluth Duluth(retired) (retired) Richard W. 88" 730 87 5700 87 46 30" 11 Fern Creek Fe, 'reek Fm 88 730 22 0 I 55 22 44 I 00 66 88 12 12 10 10 I I 55 I 10 10 15 15 Miles Miles Kilometers Kilometers EXPLANATION EXPLANATION Cambrian Cambrian MunisingSandstone Sandstone Munising North Northof ofNiagara Niagarafault fault Paleoproterozoic Paleoproterozoic . South South of of Niagara Niagara fault fault Paleoproterozoic Paleoproterozoic Metadiabase Metadiabase Hoskins HoskinsLake LakeGranite Granite MichigammeFormation Formation.graywacke Michigamme graywacke Marinette MarinetteQuartz QuartzDionte Diorite Badwater Badwater Greenstone Greenstone Metagabbro Metagabbro Vulcan Vulcan Iron-formation Iron-formation Quinnesec QuinnesecFormation Formation Randville Randville Dolomite Dolomite llh1llJ Sturgeon Sturgeon Quartzite Quartzite Fern Fern Creek Formation Formation - — fault fault Archean Archean Granitic Graniticrocks rocksand andgneiss gneiss Carney CarneyLake LakeGneiss Gneiss Figure 2-1. Geologic Geologic map map of of part part of of the the Menominee MenomineeIron-district Iron-districtshowing showingthe thelocation locationof of Figure field trip trip stops. stops. Geology Geologysimplified simplifiedfrom fromBayley Bayleyand andothers others(1966) (1966)and andSims Simsand andSchulz Schulz field (1993). (1993). 48 �0 5000 I I 1 217 10000 t IUt Kmbeyç 5000 I 1 / 20000 — - M ion 2-4rway I I 30000 I / I 10000 T I 0 I 40000 ciP etQp 'L 15 000 I Stfl —=-- NNii 5J L- r I n ci' ( I I I ,— I 70000 FEET 20 000 METERS 288k _— _- _—''2 g3j I ' c—_? — Figure 2-2. Part of the Escanaba 1:100,000-scale topographic map showing the location of field trip stops 2-1 through 2-5. See figure 3-2 for the location of stop 2-6. 0 —— 1000 700 57 - J" �This This trip trip examines examines rocks rocks of of the the Menominee Menomineeiron-bearing iron-bearingdistrict, district, with with emphasis emphasis on on units units of the the Paleoproterozoic PaleoproterozoicMarquette Marquette Range Range Supergroup. Supergroup.Archean Archean rocks rocks of of the the Carney Carney of Lake Lake Gneiss Gneiss are are seen seen at at two two stops stops and and volcanic volcanic rocks rocks of of the the Wisconsin Wisconsinmagmatic magmatic terranes, intensely intensely deformed deformed in in the the Niagara Niagara fault fault zone, zone, are are also also seen. seen. The The geologic geologic map map terranes, of the the field field trip trip area area isis shown shown in in figure figure 2-1 2-1and and aa road roadmap mapof of the the field fieldtrip tripstops stopsisisinin of figure figure2-2. 2-2. Stop River. (SE 1/4, NE 1/4, Stop2-1. 2-1. Piers PiersGorge Gorgeon onthe theMenominee Menominee River. (SE 114, NE %, sec. sec.24, 24,1. T.39 39N., N.,R. R. 30 30W.) W.) Rocks Rocksexposed exposedalong alongthe the Menominee MenomineeRiver Riverat atPiers PiersGorge Gorgeare arealmost almostcertainly certainlyaabranch branch of of the theNiagara Niagarafault faultzone zoneand andrepresent representone oneof of the thefew fewexposures exposuresof ofthe thefault faultzone. zone.This This location location is is about about one one kilometer kilometer south south of of the the mapped mappedtrace trace of of the the Niagara Niagarafault. fault. The Thehill hill lying lying north north of of the the gorge, gorge, but but still still south south of of the the mapped mappedfault, fault, isisunderlain underlainby bymetagabbro metagabbro that that isismuch muchless lessdeformed deformedthan thanthe therocks rocksininthe thegorge. gorge.These Theserelationships relationshipsindicate indicatethat that strain strain along alongthe the fault fault was was distributed distributedvery very heterogeneously heterogeneouslyand andconcentrated concentratedin indiscrete discrete zones zones of of very very high highstrain strainsurrounding surroundingislands islandsof of weakly weakly deformed deformedrocks. rocks.The Therocks rocksininthe the gorge gorgeare arehighly highlyfoliated foliatedand andlineated lineatedquartz-sericite quartz-sericiteschists schistsand andchloritic chloriticschists, schists, probably probablydeveloped developedfrom from felsic felsic and andmafic maficvolcanic volcanicrocks. rocks.Felsic Felsicand andmafic maficvolcanic volcanicrocks rocks with with only only weak weak foliation, foliation, along along with with mafic maficsills sills with with little little internal internaldeformation, deformation, are are exposed exposed on onboth bothsides sides of of this this strongly stronglyfoliated foliatedzone. zone. Metagraywacke Metagraywackeof of the the Marquette MarquetteRange Range Supergroup Supergroupisisexposed exposedin inNorway, Norway,about about 22miles milesnorth northofofthis thislocality, locality,and andvolcanic volcanicand and plutonic plutonicrocks rocksof of the the Wisconsin Wisconsinmagmatic magmaticterranes terranesare areexposed exposedalong alongthe theMenominee Menominee River Riverininthis thisarea. area. The 80'-85' W W and anddips dips 800850 80'-85' N. N. and and has has aa stretch stretch lineation lineation Thefoliation foliationhere herestrikes strikesNN800850 that plunges 600650, N 85° W. that plunges 60'-65', N 85' W. As As the the recognized recognizedboundary boundarybetween between the the dominantly dominantly sedimentary sedimentary rocks rocks of the the Marquette Marquette Range RangeSupergroup Supergroupto tothe thenorth northand andthe theWisconsin Wisconsinmagmatic magmaticterranes terranesto tothe thesouth, south,the the Niagara Niagarafault faultzone zoneisiscommonly commonlyreferred referredto toas asaasuture. suture.However, However,ititlacks lackssome somefeatures features (such (suchas asaamélange) melange)that thatare aretypical typicalof of suture suturezones. zones.Geophysical Geophysicalevidence evidence(Attoh (Attohand and Klasner, LaBergeand andKlasner, Klasner,2001) 2001) suggests suggeststhat thatthinned thinnedcontinental continentalcrust crust Klasner,1989; 1989;and andLaBerge of of the theSuperior Superiorcraton cratonhas hasbeen beenoverridden overriddenby bythe theWisconsin Wisconsinmagmatic magmaticterranes, terranes,and and extends extendsin inthe the subsurface subsurfacefor for 10-50 10-50miles milessouth southof of the theNiagara Niagarafault faultzone. zone.IfIfthis thisisisthe the case, case, the the Niagara Niagarafault faultzone zonemay maybe bethe the frontal frontalthrust thruston onwhich whichoceanic oceanicrocks rocksof of the the Wisconsin Wisconsinmagmatic magmaticterranes terranesoverrode overrodethe thecontinent continentmargin marginassemblage assemblageof ofthe the Marquette MarquetteRange RangeSupergroup. Supergroup.Continued Continuedcompression compressionof of the thesuture suturezone zoneresulted resultedin inthe the steepening of the thrust surfaces into their present, nearly vertical orientation. steepening of the thrust surfaces into their present, nearly vertical orientation. Stop Stop2: 2: Fern FernCreek Creeklocality locality—-Archean Archean basement. basement.Fern FernCreek Creek Formation, Formation,and and Sturgeon SturqeonQuartzite. Quartzite.(N(N½, Vi,sec. sec.34, 34,T.T.40 40N., N.,R. R.29 29W.). W.). Take TakeCounty CountyRoad Road573 573to tothe thenortheast northeastoff offofofU.S. U.S.2,2,about about11mile milenorthwest northwestofofthe thetown town of ofNorway. Proceedabout about22miles milesand andturn justbeyond beyondthe thebridge overPine Pine Norway.Proceed turnnorth north(left) (left)just bridgeover Creek, milesto toFern FernCreek, Creek,which whichcrosses crosses Creek, onto ontoaasecondary secondaryroad. road.Proceed Proceedabout about1½ 1Vz miles the about 1% thesecondary secondaryroad roadatataasharp sharpbend bendininthe theroad. road.Proceed Proceed about 34 mile milefarther farthertotoaasmall small intermittent intermittentcreek creekthat thatalso alsocrosses crossesthe theroad. road.Park Parknear nearhere. here.See Seefigure figure2-3 2-3for foraa detailed 2-4for foraageneralized generalizedrock rockcolumn. column. detailedmap, map,and andFigure Figure2-4 50 �r OuTCffOP M A P Figure2-3. Location Location map map of of stop stop 2-2. 2-2. (from (fromPettijohn, Pettijohn,1943.) 1943.) Figure2-3. FERN FERN CREEK FM FM M (FERN LOCALITY) (FERN CREEK LOCALITY) 150 100 50 -°.o: • DIAMICTITE DIAMICTITE ARGILLITE ARGILLITE DROPSTONES DROPSTONES 0 CONGLOMERATE CONGLOMERATE Figure2-4. 2-4. Generalized Generalizedstratigraphic stratigraphiccolumn columnat at Fern FernCreek Creeklocality. locality.SQ SQat atthe thetop topof ofthe the Figure column column designates designates the the Sturgeon SturgeonQuartzite. Quartzite. 51 �situated in a NW-trending NW-trendingvalley about 175 175 m m wide, between between two Note that the road is situated prominent topographic highs. The Carney Lake Lake Gneiss Gneiss forms the prominent prominent bluff bluff and and prominent Sturgeon Quartzite Quartzite forms aa prominent prominent upland on the northeast side of the road, and the Sturgeon Fern Creek ridge on the southwest side of the road. The valley is situated on the Fern Formation, Formation, of which the the lowest lowest 60 60 to to 70 70 m mare are somewhat somewhatexposed. exposed. Archean-Paleoproterozoic contact, a major unconformity unconformity representing representing a few The Archean-Paleoproterozoic hundred million years of erosion, is now subvertical, as are the Fern Creek Formation Formation substop is is at this this unconformity, unconformity, and and then we will and the Sturgeon Quartzite. Our first substop move up-section up-section through the subunits of the Fern Fern Creek Formation Formation and end in the Sturgeon Sturgeon Quartzite. Quartzite. Substop subs to^ 1. From the road, move about 100 100 m up the small creek bed bed to the subvertical unconformity, unconformity, where we can can observe observe both both the the Carney CarneyLake LakeGneiss Gneissand andthe theoverlying overlying basal gneiss-fragment (i.e., arkosic) conglomerate conglomerate of the Fern Fern Creek Creek Formation. Formation. Note Note basal the angular to subangular nature nature of the clasts, obviously locally derived. Minor beds of red arkosic sandstone are also present. The entire entire sequence has stratigraphic tops toward the south. Interpretation: High-velocity High-velocityfluvial fluvialand andin-situ in-siturubble/debris rubbleldebrisflow flow deposits. deposits. Substop 2. Reverse Reverse direction and head back toward the road, moving up the stratigraphic section. This poorly exposed subunit, 60-75 feet thick, is a laminated laminated finescattered larger stones. Many of these stones show clear evidence grained argillite with scattered fine-grained sediment from above, causing a bowing of having been "dropped" into the fine-grained penetration of the underlying laminae. Others do not show these downward and/or a penetration relationships relationships and are therefore therefore called called "lonestones" "lonestones"rather rather than than "dropstones" "dropstones"(fig. (fig.2-6). 2-6). Note the E-W E-W slatey slatey cleavage cleavage that that crosses crossesthe thebedding, bedding,which whichstrikes strikesabout aboutNN500 50' W. W. S that the stone has Figure 2-5. Thin-bedded argillite and siltstone with dropstone. Note that both both pierced pierced and and bowed bowed down down the the underlying underlying laminae. laminae. 52 �Figure Figure 2-6. 2-6. Large Large (35 (35 cm) cm) lonestone lonestone (beneath (beneath hammer) hammer) in in vertical vertical laminated laminated siltstone/sandstone siltstone/sandstone beds. beds. Some Some smaller smaller lonestones lonestones are are also also present. present. Interpretation: Deposition Depositionof of fine-grained fine-grainedsediment sedimentin in aa body body of of water water (marine?) (marine?) near near a melting melting glacier, glacier, with with the the larger larger clasts clasts dropped dropped in in from from icebergs icebergs and/or and/or aa floating floating ice ice shelf. shelf. Substop Substop 3. The next next subunit subunit is is a diamictite, diamictite, aa matrix-supported matrix-supported conglomerate conglomerate with with rather rather sparse clasts clasts set in in a massive massive graywacke graywacke matrix matrix (fig. (fig. 2-7). 2-7). Note Note the the total total lack lack of of bedding bedding sparse and and the presence presence of aa crude crude schistosity schistosity that causes causes the the rock rock to to break break into into thick thick slabs. slabs. Interpretation: (i.e.tillite) tillite)or orby bythe the"raining "rainingout" out" Interpretation: Deposition Depositiondirectly directlyby byglacial glacialice ice(i.e. of detritus detritus from from icebergs icebergsor or aa floating floating glacier glacier onto onto aa basin basin floor floor lacking lackingcurrents currentsto to generate (i.e., "rainout "rainouttill"). till"). generate lamination lamination (i.e., Substop Cross the road, road, following following the marked marked trail trail about about 100 100m m across across aa low-lying low-lying Substop 4. Cross area area without outcrops, base of the the ridge ridge that that lies southwest of the road. The first outcrops, to the the base lies southwest of the road. The first low-lying low-lying exposure at the base base of the ridge ridge is is poorly poorly exposed exposed and and is is composed composed of argillite/sericite m thick. thick. The The low-lying low-lyingarea areamay maybe be argillite/sericiteschist schist and and sericitic sericiticquartzite, quartzite, about about 55 m totally totally or in part underlain by by this rock, which is softer softer than than the rocksof substops or in part underlain this sericitic sericitic rock, which is the rocks of substops 1-3 1-3 and and the overlying overlying vitreous quartzite. The The prominent prominent ridge ridge is is composed composed of the the Sturgeon Sturgeon Quartzite Quartzite (fig. (fig. 2-8). 2-8). ItIt is is well well cemented cemented with with silica silica and and is is totally totally recrystallized, recrystallized, making making itit aa very resistant resistant rock rock unit. unit. ItIt is is composed composed almost almost totally totally of of well-sorted, well-sorted, finefine- to to 53 �medium-grained quartz sand; few grains are coarser than 1 mm. Original Original grain boundaries are easily seen boundaries seen only only in in the the sericitic sericitic quartzite. quartzite. Diamictite with scattered scattered stones stones and and crude crude schistosity. schistosity. Figure 2-7. Diamictite Interpretation: The The sericite sericite schist schist is is a paleosol and the sericitic quartzite is aa reworked paleosol that that was developed upon the the Fern Creek Creek Formation during during aa long period of extensive weathering in a subtropical or tropical climate. The overlying period Sturgeon Quartzite is is the product product of the reworking reworking and and sorting sorting of the the weathered weathered detritus detritus Sturgeon by wind and water. The quartzite here is about 325 m thick, and elsewhere in the region region it has a maximum thickness of 600 m (Freedman and others, 1961). It obviously represents the transported resistant quartz sand fraction of a very broad, deeply chemically weathered surface that was largely developed upon granitic rock over a long period period of time. There is is no no diagnostic diagnostic evidence evidence within the quartzite itself of a terrestrial terrestrial (fluvial) versus a marine environment environment of deposition. deposition. However, However, an an apparently apparently conformable conformable relationship with the overlying thick Randville Randville Dolomite Dolomite (300-430 (300-430m), m), which which is is stromatolitic and contains detrital detrital quartz grains and thin interbeds interbeds of quartzite, is strongly marine environment environment for the Sturgeon Sturgeon Quartzite. In In addition, suggestive of a shallow marine high in the formation suggests suggests a gradational gradational contact contact with the diopside-rich quartzite high and others, others, 1961). Detrital quartz grains in the the sericitic Randville Dolomite (Freedman and schist show a marked 1966), indicative of marked elongation and alignment (Bayley and others, 1966), shearing shearing along along this this softer softer zone zone beneath beneaththe the quartzite. quartzite. 54 �Figure Figure 2-8. 2-8. Ripples Ripplesin inSturgeon SturgeonQuartzite Quartzite Stop Stop2-3: 2-3: Sturgeon SturqeonRiver RiverDam Damlocality. locality.Archean Archeanbasement, basement,Fern FernCreek CreekFormation, Formation, and andSturgeon SturgeonQuartzite. Quartzite.(E(E½,95sec. ,sec.8,8,T.T.3939N., N.,R.R.29 29W.). W.). From Stop Stop 2, 2, backtrack backtrack about about 1½ 1V2 miles milesto to County CountyRoad Road573. 573. Turn Turn left left (east) (east) and and From proceed proceedabout about3½ 3%miles. miles.Turn Turnleft left(east) (east)on onSwede SwedeSettlement SettlementRoad, Road,which whichleads leadstoward toward the mile.Turn Turnleft left(north) (north)on onaasmaller smallerroad road thepower powerstation/dam stationldamand andproceed proceedfor for about about1½ 1V2 mile. that V2 mile mileto tolocked lockedgate. gate.Park Parkhere. here.IfIf thatleads leadsto to the thepower powerstation/dam. stationldam. Proceed Proceedabout about½ approaching approachingthis stopfrom fromthe thevillage villageof Loretto,take takeCounty CountyRoad Road573 573north outof thisstop of Loretto, northout of Loretto V2 mile. mile.Then Thenturn turnright right(east) (east)on onSwede SwedeSettlement SettlementRoad, Road,which whichleads leads Lorettofor forabout about½ miles.Turn Turnleft left(north) (north)on onaa towardthe the power powerstation/dam, stationldam,and andproceed proceedfor for about about1½ 1V2 miles. toward smaller smallerroad roadthat that leads leadsto to the the power powerstation/dam. stationldam. Proceed Proceedabout about½ V2 mile mileto to locked lockedgate. gate. Park Parkhere. here.As As of of this thiswriting writinginin2003, 2003, the thedam damisisslated slatedfor forremoval removalininthe therelatively relativelynear near future. future. Here Herethe theSturgeon SturgeonRiver Riverhas hascut cutaadeep deepgorge gorgethrough throughthe theSturgeon SturgeonQuartzite; Quartzite;the the formation formationwas wasnamed namedfor forthis thislocality. locality.This Thissmall smallarea areahas hasbeen beenwell wellstudied, studied,especially especially because Archean-Paleoproterozoiccontact contactat at the thedam. dam.The Thearea area becauseof of the thepresence presenceof of the theArchean-Paleoproterozoic has hasbeen beendescribed describedby byCredner Credner(1869), (1869),Brooks Brooks(1873), (1873),Rominger Rominger(1881), (188l), Irving Irving(1890), (1890), Bayley Bayley(1904), (1904),Lamey Lamey(1937), (1937),Pettijohn Pettijohn(1943), (1943),and andTrow Trow(1948). (1948). SubstoD subs to^ 1. 1. Walk Walk past past the the gate gate to to the the end end of of the the road roadat at the the powerhouse powerhouseand and dam. dam. We We will willtraverse traverseback theroad roadto vehicles,thus thusobserving observingthe therock unitsinin backup upthe tothe thevehicles, rockunits stratigraphic stratigraphicsequence. sequence.The Thedam damwas wasconstructed constructedon onSturgeon SturgeonRiver RiverFalls, Falls,which whichwas was held heldup upby byaa thick thick mafic maficdike dikethat thatcan canbe beseen seenininthe thewoods woodsoff offthe theeast eastend endof ofthe thedam. dam. The ArcheanCarney CarneyLake LakeGneiss Gneissand andthe thePaleoproterozoic Paleoproterozoic Theunconformity unconformitybetween betweenthe theArchean Fern FernCreek CreekFormation Formationcan canbe beseen seenininaasmall smallground-level ground-levelexposure exposureadjacent adjacenttotothe thedam dam 55 �(fig. 2-9). The lowest lowest bed bed in in the the Fern Fern Creek Creek is is aa diamictite diamictite at at this this spot, spot, whereas whereas aa short short distance to the west on the river bottom bottom by by the power power station, station, the the lowest lowest unit unit is is arkosic arkosic sandstone with rare oversized oversized stones. Figure Figure 2-9. Unconformity Unconformity at Sturgeon Sturgeon River River dam. dam. Hammer Hammer head head rests rests on on Archean Archean Carney Lake Lake Gneiss Gneiss and and hammer hammer handle handle is is on on basal basal diamictite diamictite of the the Fern Fern Creek Creek Formation. Formation. Nearby Nearby in river bottom, bottom, the the basal basal unit unit is is arkosic arkosic sandstone sandstone with with rare rare dropstones, illustrated 1. dropstones, illustratedininfigure figure2-1 2-11. FERN FERN CREEK FM FM (STURGEON LOCALITY) (STURGEONRIVER RIVER LOCALITY) M - 75 SANDSTONE ARGILLITE 50 ARKOSE • 25 / 25 M 20 CONGLOMERA GcK' SANDSTONE SANDSTONE SANDSTONE SANDSTONE DROPSTONES L 2Fm5nw DIAMITITE DIAMICTITE DIAMICTITE DIAMICTITE DIAMICTITE DIAMICTITE SANDSTONE SANDSTONE ARGILLITE ARGILLITE 10 CONGLOMERATE GRAYWACKE ARGILLITE DIAMICTITE DIAMICTITE SANDSTONE SANDSTONE DROPSTONES DROPSTONES ONFSTONFS DIAMICTITE DIAMICTITE SANDSTONE SANDSTONE DROPSTONES DROPSTONES 2-10. Figure 2-1 0. Stratigraphic column at Sturgeon Sturgeon River River locality. SQ at the the top of the the column column designates the Sturgeon designates Sturgeon Quartzite. Quartzite. 56 �2-10 Figure 2-1 0 is a measured measured column column of of the the Fern FernCreek Creek Formation. Formation.The Thelower lower25 25m mare arewell well exposed when there is no water in the channel. Note that this portion of the formation consists of five beds of diamictite (matrix-supported (matrix-supportedconglomerate) as thick as 2.5 m, arkosic sandstone sandstone beds beds as as thick as as 2.6 m m with rare rare oversized oversized stones, stones, stacked stacked three arkosic sandstone beds beds with minor intercalated intercalated siltstone and argillite argillite laminae, laminae, an argillite argillite arkosic sandstone 15 cmconglomerate. conglomerate.Because Becausethe thewater waterlevel levelisiscommonly commonlyhigh, high, bed 4.5 cm thick, and a 15cm figures 2-11 2-11 and and 2-12 2-12 are are included included here here to illustrate illustrate some important important features. figures 2-11. stratigraphic column. Note Figure 2-1 1. Granitic dropstone in lowest sandstone of the stratigraphic that the stone has pierced and bowed down the underlying laminations. stone has pierced and bowed down the underlying laminations. the river bottom is not found found on the west Interestingly, the well-exposed section seen in the bank mof of conglomeratic conglomeratic rock is present present there. 1%m there. Apparently Apparently the the more more bank of the the river; river;only only11/2 complete section is preserved preserved in a topographic low on the Archean surface. However, faulting may may be a factor factor as as well, for weathered weathered pyrite pyrite is present along a fault between the Archean basement basement and the Fern Fern Creek west of the powerhouse. The middle middle 25 m m of the Fern Fern Creek Creek Formation Formation is is relatively relatively poorly poorly exposed; figure 2-10 2-10 shows this portion portion consisting of conglomerate, conglomerate, graywacke graywacke sandstone sandstone with oversized stones, stones, and and arkosic arkosic sandstone sandstonewith with oversized oversizedstones. stones. 57 �beds of stratigraphic stratigraphic column column of Figure Figure 2-10. View Figure 2-12. Second, third, and fourth beds is to west. Beds 2 and 4 are diamictites below and above arkosic sandstone with rare dropstones. dropstones. Interpretation: This This isisaa glaciogenic glaciogenic sequence. sequence. The The diamictites may be thin tills suggested by deposited beneath glacial ice, but more likely are debris flow deposits as suggested one diamictite bed that grades upward upward into sandstone. Some of the conglomeratic beds beds are difficult to clearly classify classify as either matrix-supported matrix-supported or clast-supported. One 20 cm bed at the 15 15 m level level in the section is graded from medium medium sand to clay, suggestive of a turbidity current mechanism. Several of the oversized stones in the sandstone and greywacke beds show either a bowing down of the underlying laminae or an actual penetration, indicating indicating that the stones were dropped into the basin from above and are indeed dropstones. Other lonestones lonestones may be dropstones, too, but clear evidence is lacking. The likely likely mechanism mechanism for deposition deposition of dropstones dropstones is release from melting melting icebergs icebergs or from from aa floating floatingglacier. glacier. Substop 2: The 50 and and 75 75 m m on Figure Figure 2-9 is intermittently intermittently The25 25m msection section between between 50 exposed on the west bank of the river, but this area is usually inaccessible because of high water. It includes beds of sericitic sericitic quartzite interbedded interbedded with sericite schist. The sericitic nature of this interval is illustrated by sericitic nature of this interval is illustrated by aa small small road-level road-leveloutcrop outcropbetween betweenthe the the river just just north of the quartzite ridge. This is a sericitic quartz pebble road and the conglomerate with sericite clay chips, some reddish rather than yellow-green in color. Interpretation: This Thissericitic sericitic portion portion of of the the column column is is interpreted interpreted as a reworked reworked paleosol that formed on the Fern Fern Creek Formation Formation during a warm climatic period period that followed glaciation. Trow (1948) first suggested suggested that this might might be be a paleosol. paleosol. Substop 3: Sturgeon SturgeonQuartzite Quartzite ridge. ridge. Note Note that that the the bedding bedding is is slightly overturned towards the south, and that cross-bedding cross-bedding indicates that stratigraphic tops are to the 58 �Cross-bedding is is of both both trough trough and and planar planar types. types. According According to to Trow Trow (1948), (1948), the the south. Cross-bedding general cross-bedding cross-bedding indicates indicates aa paleocurrent paleocurrent trend trend from from the the northwest northwest toward toward the the general southeast. southeast. Interpretation: Abundant Abundantasymmetrical asymmetricalripple ripplemarks markshave havelow lowripple rippleindices indices Interpretation: lengthlripple height) height) indicative indicative of deposition deposition by water rather rather than by wind. The (wave length/ripple beds are generally generally of even thickness, indicative indicative of aa shallow shallow marine marine rather rather than than aa fluvial fluvial beds environment of of deposition. deposition. See See text text for for substop substop 44 of of stop stop 2-2 2-2for for additional additionalinterpretation interpretation environment of the the genesis genesis of of the the Sturgeon SturgeonQuartzite. Quartzite.The TheSturgeon Sturgeonhas haslong longbeen beencorrelated correlatedwith with of the the Mesnard Mesnard Quartzite Quartzite of of the the Marquette MarquetteTrough. Trough. Stop 2-4. Brier Brier Slate Member of the Vulcan Iron-formation inNorway, Norway,MI. MI. (Modified (Modified Stop Iron-formation in fromDutton, Dutton,1958). 1958).(E(E1/2, Vz, SE SE ¼, Vn, sec. sec. 5, 5, T. T. 39 39N., N., R. R. 18 18W.) W.) from Three iron iron mines, mines, the the Aragon, Aragon, Cyclops, Cyclops, and and Norway Norway mines mines were were developed developed in in the the Three northern part part of of the the city city of of Norway, Norway, MI, MI, and and subsidence subsidence of of these these abandoned abandonedmines mines has has northern limited development development in in this this part part of of the the city. city. The The Aragon Aragon mine mine was was the the third third largest largest limited producer of of iron iron ore ore in in the the Menominee Menominee district district (Dutton, (Dutton, 1958), 1958), and and the the head headframe frame of of the the producer mine still still stands stands about about 55 blocks blockseast east of of this this stop. stop. Figure Figure2-13 2-13 shows shows the the location locationof of mine several interesting interestinggeological geological features, features, but but the the trip trip will will visit visit only only the the Brier Brier Slate Slate Member Member several type type locality. locality. According to to Dutton Dutton (1958), (1958), outcrops outcrops along along the the ridge ridgenorth northof of Norway Norwayare are Randville Randville According Dolomite with with aa rather rather extensive, extensive, but but incomplete, incomplete, cover cover of breccia breccia composed composed of of dolomite dolomite Dolomite fragments that that are are slightly slightly to to thoroughly thoroughly silicified. silicified. (This (This breccia breccia is is similar to that at the top fragments of the the correlative correlative Bad Bad River River Dolomite Dolomite in in the the Gogebic Gogebic district, district, some some 120 120miles miles westwestof northwest of here.) here.) The Thesilicification silicificationisisbelieved believedto to be bethe the result result of of surficial surficial weathering weathering in in northwest pre-iron-formationtime. time. The The dolomite dolomite dips dips about about 60 60 degrees degrees southward, southward, post-Randville -- pre-iron-formation post-Randville and the the convexity convexity of stromatolites stromatolites in the dolomite face in the dolomite indicate indicate that that the the beds beds also also face and southward. Small Small outliers outliers of of Cambrian Cambrian sandstone sandstone overlying overlying the the Randville Randville Dolomite Dolomite are are southward. also (e.g., at at Rochon RochonSt. St. and and Curry Curry Lane Lane along along the the ridge). ridge). also present present (e.g., The TheRandville Randvilleisisoverlain overlain by by the the Felch FelchFormation, Formation,the the basal basalunit unit of of the the Menominee Menominee Group. Group. One One of of the the few few exposures exposures of of the the Felch FelchFormation Formationis is at at this this locality locality in in Norway Norway (Dutton, 1958). 1958). The The Felch FelchFormation Formationconsists consists of of sericitic sericitic slate slate and and thin thin layers layers of of (Dutton, quartzite. quartzite. The The uppermost uppermostpart part of of the the formation formation isisaa ferruginous ferruginous quartzite quartzitethat that isisaamarker marker bed bed throughout throughout the the district. district. The The quartzite quartziteis is aa transitional transitional unit unit between betweenthe the dominantly dominantly clastic, clastic, non-ferruginous non-ferruginousstrata strataof of the theFelch FelchFormation Formationand andthe theiron-rich iron-richchemical chemical sediments of the Vulcan Iron-formation (Dutton, 1958). sediments of the Vulcan Iron-formation (Dutton, 1958). Three Threemembers membersof of the theVulcan VulcanIron-formation Iron-formationwere wereexposed exposedininNorway Norwayin in1958, 1958, accordingto to Dutton Dutton(1958). (1958).Exposures Exposuresof of the thebasal, basal,thin-bedded thin-beddedoxide oxidefacies faciesTraders Traders according Member are are present present at at the the northeastern northeastern end end of of aa southwesterly southwesterly trending trending area area of of Member outcrops.The TheTraders Tradersisispresently presentlyexposed exposednorth northof of Sixteenth SixteenthAve. Ave. and andMain MainSt., St., in inthe the outcrops. oldCyclops Cyclopsmine mineworkings, workings, which which isisbeing beingused usedas as aa landfill landfillby by the the city city of of Norway. Norway. The The old Brier Brier Slate Slate Member Member (this (this stop) stop) is is exposed exposed on on an an outcrop outcrop knob knob at at Eleventh Eleventh Ave. and and the the Aragonlocation, location,southwest southwestof of the theTraders TradersMember Memberlocation. location.In Infact, fact, the theBrier BrierSlate Slatewas was Aragon named namedfor for exposures exposureshere. here. Several Several small-scale small-scale folds folds that that plunge plunge about about 45 45 degrees degrees easterlyare areexposed exposedalong alongthe the old oldrailroad railroadcut cut on onthe the north northside sideof of the theoutcrop. outcrop. easterly According theoxide oxidefacies, facies,oolitic ooliticand andgranular granulariron-formation iron-formationof ofthe the Accordingto to Dutton Dutton(1958), (1958),the 59 �Curry member member of of the theVulcan Vulcan Iron-formation Iron-formationwas wasexposed exposedat atthe thesouthwest southwestend endof ofthe the Curry outcroparea. area. outcrop The Michigamme MichigammeFormation Formationunconformably unconformablyoverlies overlies the the iron-formation iron-formationand andisisexposed exposedin in The several low low roadcuts roadcutsalong alongU.S. U.S. Hwy-8 Hwy-8on on the the southern southernoutskirts outskirtsof of Norway. Norway. several 00 I 1I2 112 I I 1 1 1 i Miles Miles Figure 2-13. 2-13. Part Partofofthe theNorway Norway7½' 7 %quadrangle quadrangleshowing showingthe thelocation locationof of stop stop2-4 2-4and and Figure some other features of geologic interest. some other features of geologic interest. Stop 2-5. 2-5. Quinnesec Quinnesec mine, mine, just just northwest northwestof of Quinnesec, Quinnesec,Ml, MI, (Modified (Modifiedfrom fromDutton, Dutton, Stop T. 39 39 N., N., R. R. 30 30W.) W.) 1958)(SW (SW1/4 Y4, SE SE 1/4 34, sec. 34, T. 1958) sec. 34, (NOTE: For this property. property. For For (NOTE; For safety safety reasons reasons aa security security fence fence surrounds surrounds this MI, Ph (906-774-4471). permission to enter contact Joe Massie, Quinnesec, permission to enter contact Joe Massie, Quinnesec, MI, Ph (906-774-4471). The abandoned abandonedworkings workingsof of the theQuinnesec Quinnesecmine mineare aremainly mainlyininthe theTraders Tradersiron-bearing iron-bearing The member of the Vulcan Iron-formation. The mine lies on the overturned north, limbofof aa member of the Vulcan Iron-formation. The mine lies on the overturned north, limb 60 second order syncline (fig. 2-1 4). The Precambrian strata at the mine dip about second order syncline (fig. 2-14). The Precambrian strata at the mine dip about 60 degreeshorth, north,but butface facesouthward, southward,inasmuch inasmuchas asthe theBrier Brierslate slatemember memberofofthe theVulcan Vulcanisis degrees 60 �along the south side side of the the excavated excavated approach approach to to the the mine, mine, and and the the Felch FelchFormation Formationisis along the north north wall of the the workings. Note the Cambrian sandstone north side side of the the sandstone overlying the mine workings along the north hill, providing an unusual view of an unconformity unconformity (fig. 2-15). 2-15). The basal basal portion portion of the the sandstone contains contains numerous numerous angular angular slabs slabs of of oxidized oxidized iron-formation, iron-formation,iron iron ore, ore, and and sandstone slate in a sandy matrix. matrix. Clearly, this area area was a small island island as the Cambrian Cambrian sea sea advanced over the area. The clasts clasts of iron iron ore ore in in the the basal basal conglomerate conalomeratealso also indicate indicate the area. that the ore here here was formed formed before before the the Cambrian Cambrian sea sea covered coveredthe area. R. 30W. R. 30 W. I I 1000 feet 0 <") 1 1 I xmj Xm Michigamme MichigammeFormation Formation Vulcan Iron-formation Iron-formation [&c Curry Curry Member Member Iron-bearing Iron-bearing Member Member Xvb Brier Slate Member Xvt Traders Iron-bearing Iron-bearing Member :1;X 1 1 xfXf 1 1IXrI Xr 1 Open pit ..>.Exposed Exposedbedrock bedrock J<^_) Small Small area of exposed exposed bedrock bedrock $j Strikeanddipof Strike and dip ofbeds beds X 50 Strike Strikeand and dip dip of overturned overturned beds beds Beds dip 70°-80° 70'-80' except Felch Formation Formation --*- Randville Dolomite Randville Dolomite as noted 2-14. Figure 2-1 4. Map Map of of the the Quinnesec Quinnesec mine mine and and vicinity vicinity at stop stop 2-5 showing that the workings were developed developed in the overturned overturned northern northern limb limb of aa small small syncline. syncline. Map Map from from Bayley Bayley (1957). (1957). 61 �5. Abandoned workings at Quinnesec mine. Ore bodies were mined from the Figure 2-1 2-15. Iron-bearingmember member of Vulcan Iron-formation. Iron-formation.View View looking looking west west shows shows beds beds Traders Iron-bearing but facing facing south. Roof Roof of workings workings is is base base of of the the Munising Munising Sandstone Sandstone of of dipping north, but of the the basal Cambrian unconformity. Cambrian age and provides an excellent view of Photo Photo by Elizabeth Elizabeth Heinen. Heinen. Stop 2-6. Marqaret St. on Lake Antoine in Iron Mountain. Mountain, 2-6. Randville Randville Dolomite Dolomite alonq along Margaret in Iron (Modified from 1958) (SE 1/4, MI. (Modified fromDutton, Dutton, 1958) (SE %,NE NE1/4, %, sec. 29, 29, T. T. 39 39 N., N., RR30 30 W.) W.) - This exposure exposure of the Randville Randville Dolomite Dolomite on the south shore of Lake Lake Antoine Antoine was formerly the site of a small small quarry quarry for the the production production of of road road material. material. Operation Operation of of the the quarry was halted during the late 1930's through the influence of geologists and other interested people who wanted the the site preserved for for future geologic examination interested (Dutton, 1958). 1958). The glacially scoured scoured outcrop shows a variety of sedimentary sedimentary and structural structural features. The rocks rocks are are dipping dipping nearly nearly vertically, and face southward. southward. Sedimentary Sedimentary features features preserved here include abundant stromatolites (fig. 2-15), typically 3-4 inches high and preserved 2-15), 4-8 inches inches in diameter. The old old quarry quarry face provided provided a vertical vertical view of the stromatolites now largely obscured by graffiti. Thin layers of quartz sand are interbedded interbedded with the dolomite, and and ripple ripple marks marks and and mud mud cracks cracks are are present present in in places. places. These These features features suggest a very shallow water environment of deposition, and several authors (e.g. Larue, 1981) have suggested that the Randville Dolomite may have been deposited in a paleo paleo sabkha sabkha environment. environment. - 62 �Structural Structural features features exposed exposed here here include include deformed deformed stromatolites. stromatolites. Several Several layers layers of stromatolites that are are strongly strongly skewed skewed in in a right-lateral right-lateraldirection direction are are present. present. The The dolomite dolomite evidently evidently recrystallized recrystallized readily, readily, allowing allowing ductile ductile deformation deformationof of the the stromatolites. stromatolites. Possible fracture is nearly nearly "axial planar" to the deformed deformed Possible fracture cleavage is oriented so that it is stromatolites, and and is is roughly roughly parallel parallel with the regional regional structure. Figure interbedded Randville Dolomite at stop 2-6. Laminated Laminated dolomitic layers layers are interbedded Figure 2-16. 2-16. Randville with with stromatolitic stromatolitic dolomite. dolomite. Stromatolite Stromatolite mounds mounds are are deformed deformed and and show show an an asymmetry asymmetry indicating right lateral lateral sense of shear. View is looking looking down at a horizontal surface and indicating a right beds bedsdip dip vertically. vertically. 63 �FIELD TRIP 3 STRATIGRAPHY AND STRUCTURE OF THE IRON RIVERCRYSTAL FALLS BASIN BASIN William F. Cannon, USGS, USGS, Reston, VA; VA; John John S. S, Kiasner, Klasner, Western WesternIllinois Illinois (retired) and USGS; University (retired) USGS; Gene Gene L. LaBerge, LaBerge, University Universityof of WisconsinWisconsinOshkosh Oshkosh (retired) (retired) and and USGS USGS Tightly folded Riverton Iron-formation Michigan. Tight Iron-formation near Stager Lake, Michigan. complex folds such as these are typical of the structural style of the Iron RiverCrystal Falls Crystal Falls allochthon. allochthon. �FIELD TRIP 3 FIELD BASIN STRATIGRAPHY AND STRUCTURE OF THE IRON RIVER-CRYSTAL FALLS FALLS BASIN William F. Cannon, USGS, Reston, VA; John John S. Klasner, Kiasner, Western Illinois University (retired) and USGS; Gene L. LaBerge, University University of Wisconsin-Oshkosh Wisconsin-Oshkosh (retired) (retired) and (retired) USGS USGS The Iron Iron River-Crystal River-Crystal Falls iron district was mined extensively for high-grade high-grade "soft" iron 1882 until the early 1970's 1970's producing producing more more than than 200 200 million million tons of ore. ores from 1882 Because of of the high economic interest in the region, the availability of many underground mine workings, workings, and extensive diamond drilling, drilling, a detailed detailed stratigraphy stratigraphy and and deciphered in in what what otherwise otherwise would would have havebeen beenaa largely largelyunknown unknownterrane, terrane, structure was deciphered mostly concealed by the nearly continuous cover of glacial deposits. The most detailed region was conducted by a large group of USGS USGS and affiliated affiliated geologists geologists study of the region 1943 and continuing 10 years. Surface exposures exposures were mapped mapped beginning in 1943 continuing for about 10 in detail, as were most underground underground mine workings. Ground magnetic surveys helped delineate the surface surface trace trace of of certain certain units unitsand and the the extensive extensivecollection collectionof of exploration explorationdrill drill core was examined. One of the earliest aeromagnetic surveys was conducted here II.The The work of the the USGS USGS when the technique was still classified shortly after World War II. was aided immeasurably immeasurably by the cooperation of the numerous mining companies active The results results of that that painstaking painstakingwork work were weresummarized summarizedininUSGS USGSProfessional Professional in the area. The Paper 570 (James and others, 1968), which remains the the only comprehensive comprehensive account account of of the geology geology of the region. Much Much of the the descriptive descriptive material material in in this this guide guide is is taken taken from from that that work. Additional detailed studies of the Florence area, Wisconsin were done by Dutton 1971) and also were instrumental (Dutton, 1971) instrumental in determining the geological relationships Iron River-Crystal River-Crystal Falls basin, including areas visited in along the southern extent of the Iron the first three stops of this this trip (figs. (figs. 3-1 3-1 and and 3-2). 3-2). The Iron Iron River-Crystal River-Crystal Falls basin is a triangular structure, with an area of about 300 square miles, underlain underlain by strata of the Paint Paint River Group. It is surrounded, except on part of the eastern side, by volcanic rocks of the Badwater Greenstone. Greenstone. Our current current interpretation of the area is that the Paint Paint River Group, as originally defined, and the Badwater northward during the Badwater Greenstone, are an allochthon, and were thrust northward driven by arc arc collision collision south south of of the the Niagara fault. fault. This trip trip traverses traverses Penokean orogeny, driven from the Niagara fault, as seen at Pine River Flowage in northern Wisconsin, northward Niagara Pine River Flowage northward across the complexly deformed deformed fault panels of the Niagara Niagara suture zone, and onto the structurally simpler rocks rocks north of the Iron Iron River-Crystal River-Crystal Falls Falls allochthon. Most stops examine the lithology and structure of rocks of the Paint Paint River River Group. Principal Principal observations are the preponderance preponderance of steeply plunging folds in all panels of the suture particularly in the Iron Riverzone rocks, the extraordinarily complex fold patterns, particularly Crystal Crystal Falls Falls allochthon, and the contrast with the simpler, gently plunging folds north of the suture suture zone. zone. 65 �EXPLANATION EXPLANATION North North of o f Niagara Niagara fault Tobin Tobin Lake Lake Granite Granite Metagabbro Metagabbro El Paint undivided Paint River Group - undivided Fortune FortuneLake LakeSlate Slate Riverton Riverton Iron-formation Iron-formation Dunn DunnCreek CreekSlate Slate X . " El El Badwater Badwater Greenstone Greenstone Michigamme MichigammeFormation. Formation, graywacke and graywacke and volcanic volcanicrocks rocks Michigamme MichigammeFormation Formation --quartzite quartzite Michigamme MichigammeFormation Formation -- graywacke graywacke Iron-formation Amasa Iron-formation Hemlock Volcanics undivided undivided HemlockVolcanics Randville Dolomite Randville Dolomite Saunders Formation Formation Saunders Dickinson undivided Dickinson Group undivided South o off Niagara fault fault Bush Lakegranite Granite and tonalite Quinnesec Formation Formation Qulnnesec El Metasedimentary rocks Metasedimentary rocks — faults - faults 2 I field field trip tripstops stops NE-Niagara fault fault NF-Niagara SRF-South South Range Range fault fault SRF- 0 I 5 5 • I I 2 4 I I 8 6 I I I I 0 0 Miles 5 5 10 10 Kilometers NRF-North Range fault NRF-North Range fault BF-Badwater fault fault BF-Badwater Riverfault fault PRF-Paint River CS-Commonwealth syncline MA-Mastodon anticline anticline MA-Mastodon Bowers syncline syncline TBS-Tim Bowers Figure 3-1. Geologic map of the eastern eastern part part of of the the Iron Iron River-Crystal River-CrystalFalls Falls basin basin showing the location location of stops stops for for field field trip trip 3. 3. 66 �Figure Figure3-2. 3-2. Part Partof of the theIron IronMountain Mountain1:100,000-scale 1:100,000-scaletopographic topographicmap mapshowing showingthe the location locationof of field fieldtrip tripstops stops3-1 3-1through through3-4 3-4and and1-9, 1-9,1-10. 1-10. Stop3-1. 3-1. Michiqamme MichiciammeFormation FormationatatPine PineRiver RiverFlowage Flowaue(NE (NE1/4, 114,SW SW1/4, 114,sec. sec.28, 28,T. T. Stop 39 39N. N.R. R.18 18E.) E.) This Thisoutcrop outcroplies lieswithin withinthe thePine PineRiver Riverstructural structuralblock blockas asdefined definedby byDutton Dutton(1971). (1971). Large Largeexposures exposuresare arealong alongthe thegorge gorgeof ofthe thePine PineRiver Riverjust justdownstream downstreamfrom fromthe thePine Pine River River dam. dam. The The Pine PineRiver Riverblock blockisiscomposed composedalmost almostentirely entirelyof ofthe theMichigamme Michigamme Formation Formationconsisting consistingmostly mostlyof ofgraywacke graywackeand andlesser lesserquartzite quartziteand andconglomerate conglomerate(stop (stop 3-2). 3-2).Although Althoughpenetrative penetrativedeformation deformationisisintense intenseand andthere thereare aremany manysmall-scale small-scalefolds folds well wellexposed exposedat atthis thisstop, stop,the theoverall overallstructure structureofofthe theblock blockseems seemstotobe beaauniformly uniformly south-facing south-facingsuccession successionas asindicated indicatedby bycross crossbeds bedsand andgraded gradedbeds. beds. The Theoutcrops outcropsseen seenhere hereare arevery veryclose closetotothe theNiagara Niagarafault faultwhose whoselocation locationhere hereisiswell well constrained constrainedby byrather ratherabundant abundantoutcrops outcrops(see (seefig. fig.3-3). 3-3).The Therocks rocksexposed exposedbelow belowthe the dam damare areno nomore morethan than500 500feet feetnortheast northeastof of the thevolcanic volcanic rocks rocksof of the theQuinnesec Quinnesec Formation, Formation,part partof of the theWisconsin WisconsinMagmatic MagmaticTerranes. Terranes.The TheMichigamme MichigammeFormation Formationininthis this vicinity vicinitywas waswell welldescribed describedby byDutton Dutton(1971) (1971)and andthe thefollowing followingisisextracted extractedfrom fromhis his report. report."The "Therock rockisisgray grayand andwell-bedded well-beddedininlayers layersone-fourth one-fourthtotoone-half one-halfinch inchthick. thick.The The percentage percentageofofminerals mineralsininthe therocks rocksisisapproximated approximatedas asquartz quartzfrom from20 20toto50; 50;sericite sericiteand and muscovite to 40. 40. Dark Dark muscovitefrom from20 20to to70; 70;biotite biotitefrom from10 10to to25; 25; and andchlorite, chlorite,ifif present, present,from from55 to red redgarnets garnetsare areabundant abundantininthe theschist schistnear nearthe thequartzite; quartzite;they theylocally locallyare areconcentrated concentratedinin layers layersand andlenses, lenses,but butthey theymay maybe beminor minorororabsent. absent.Some Somegarnets garnetshave havebeen beenrotated rotated 67 �formation as as much much as as 25 25 degrees, degrees,as as shown shownby bythe the angular angulardiscordance discordancebetween between after formation general foliation foliation and and the the layers layers of of very very fine fine opaque opaque grains grainswithin within the the garnets. garnets. Deflected Deflected general foliation at at the the boundary boundarysurfaces surfacesof of the thegarnets garnetsalso alsoindicates indicatesdirection directionbut butnot notamount amount foliation of of rotation." rotation." 'so O EXPLANATION 1T S . n Michigamnie Slate qu.rte slate. Locally includes,nleor conglomerate (cQi) 055. agglomerate and tremoiite orhist nsl qC QUuttottlc cungluma,ate. Locally In. g:un,ritic (at) or magnetuLic cludea (m..t Iron-formation a. oes.tnblage of this units. Locally includes graphitic slat. (gal), guotte. mice slate (Cl). quarts grsywaclte (gw), grunerittc achiot (Qru). and amphi bout. (am) If 1000 FEET A L 0 Outcrop Outcrop or orgroup group of of small smalloutcrops outcrops Metaf,lsic cod q5arcz. Uetafelalczocks.toetazhyoiite? rocks-metarhyolll~? andquartzmuscovite m u s c o v i f achier; schist: locally locsltyincludes tncludos in. intertoiiated fsch) t e r t o f l à § tactual ~schlat(schi Strikeand and dip dipof ofbode beds Strike Direction uf of top tv@ detennined detçwaineby bygraded çrçd Direction bedding bedding z Contact L.ong daubed wfl eta .pprox4mately 1*. hott dashed where Inferred; fl rated: dotted where concealed; queried Øzare Strike and dip of beds beddlu Dlrectinh of top detenulned by cross doubtful 0 Iii UJ 0 Probable Probablefault fault aDotted i?otted wh,re whewcOncealed conceiled II.. U. upthcown tiptftrown U. Q. slde;D. d d à §0 downthrawnalde;querlatd downtbtowniildfquer~~d wftwe where doubtful do~bttui d5 Quinnesec Portnation ...... T s - Vertical Inclined Inclined Vertical Strikeand anddip dipof ofbeds beds Strike Strikeand anddip dipof of foliation foliation Strike *t_ Strike and anddip di ofofbed bedand andplunge plunge Strike o&eatiou of lineation SB Abandonedshaft shaft Abandoned x Test Testpit pit Figure3-3. 3-3. Geologic Geologicmap mapof of part partof of the theFlorence Florencearea, area,Wisconsin Wisconsinshowing showingthe thelocation locationof of Figure 3-2.Map Maporiginally originallypublished publishedby byDutton Dutton(1971, (1971,figure figure3). 3). fieldtrip tripstops stops3-1 3-1and and3-2. field 68 �A STOP 3-1 flU dots- stretched concretions diamonds- mineral mi squares- fold axes Figure 3-4. 3-4. Lower Lower hemisphere hemisphereequal equalarea areastereoplots stereoplotsshowing showingorientation orientationof of fold foldaxes axes Figure and andrelated relatedstructures structuresat atvarious variousstops stopsfor forfield fieldtrip trip3.3. 69 �The rocks rocks near near the dam dam are are aa strongly strongly foliated foliated and and lineated lineated chlorite-garnet chlorite-garnetschist. Primary Primary layering is well preserved preserved but but has has been been transposed transposed parallel parallelto to S1 8, foliation. Dextral drag folds in the transposed layering have steeply plunging axes (see fig. fig. 3-4,A) that are parallel parallel to mineral mineral lineations lineations on foliation foliation surfaces. Axes of maximum maximum elongation in deformed clasts and andconcretions concretionsplunge plunge60 60 degrees degrees toward toward the south, parallel parallel to the in mineral mineral lineation. lineation. These These highly highly strained strainedrocks rockshave havean anS1 S1foliation foliation that that dips dips steeply steeply south south as do the elongation elongation (stretching) (stretching) axes. These These steep, steep, south south plunging plunging structures structures seem seem to be be characteristic characteristic of the the Niagara Niagara fault fault zone. Similarly Similarly oriented, steeply south plunging plunging structures structures occur south south of the the Niagara Niagara Fault Fault zone, probably probably in in splays of the Niagara Niagara fault in in volcanic rocks rocks of the Wisconsin Wisconsin magmatic magmatic terrane terrane that that crop crop out out aa few few miles miles south south of of Pine River River Dam (Sims (Sims and others, 1985). 1985). The structural structural fabric in in this region region reflects reflects the Pine overthrusting--with overthrusting-with a right right -lateral -lateral component--of component--of the Wisconsin Wisconsin magmatic magmatic terrane terrane from from the south onto the continental margin margin and and later steepening steepening of the thrusts thrusts to their their present present orientation. orientation. Stop3-2. Conglomerate of the Michigamme Stops-2. Quartzite and Conqlomerate Michiqamme Formation Formationnear near Pine Pine River sec. 28, T. 39 (NE1/4, %, NW 1/4 %, sec. 39 N., N., R. I?.18 18E.) E.) RiverDam. Dam.(NE The quartzite conglomerate conglomerate exposed exposed here (fig. (fig. 3-3) 3-3) is is the most most prominent prominent and and bestbestexposed andothers (1935)considered considered exposed unit in the Pine River Block (Dutton, 1971).Leith Leithand others(1935) (Dutton,1971). it to be be a separate separate formation (the (the "Breakwater "Breakwater Quartzite"). Quartzite1').However, However, according to Dutton Dutton (1971), (1971), it appears appears to be be a lens lens within the Michigamme Formation Formation and he did not give it a separate separate stratigraphic stratigraphic name. name. Figure Figure 3-5. 3-5. Conglomerate ConglomerateininMichigamme MichigammeFormation Formationatatstop stop3-2 3-2showing showingstrongly strongly stretched figure 5. 5. stretched and and aligned aligned pebbles. pebbles. Photograph Photograph from from Dutton Dutton (1971), (1971), figure 70 70 �The quartzite conglomerate conglomerate is about 700 feet thick and extends northwestward northwestward about 3 near the center of sec. 28, T. 39 39 N., N., R. R. 18 18 E., E., to to the the NE NE corner, corner, sec. sec. 24, 24, T. T. 39 39 miles from near R. 17 17 E., E., (Dutton, (Dutton, 1971). 1971). Cross-bedding Cross-bedding indicates indicates that statigraphic statigraphic tops tops are are toward toward N., A. the southwest. Layers and lenses of quartzite with flat (or flattened and stretched) pebbles and cobbles (fig. 3-5) of recrystallized recrystallized chert and iron-formation iron-formation are the dominant lithology. (Note: This locality is is only only about about one one half half mile mile north northof ofthe theNiagara Niagarafault.) fault.) The matrix within the pebbly units is composed of quartz, fine-grained fine-grained hematite or magnetite, 965), who showed that or both. The unit was studied studied in detail by Nilsen (1 (1965), that it consists of of two conglomeratic subunits separated by a quartzite and pebbly quartzite subunit. His paleocurrent analysis indicates a predominant current flow toward the southeast in a shallow, near-shore near-shore basin. basin. Structurally, there appears appears to to be be aa cleavage-parting cleavage-partingparallel parallelwith with bedding. bedding.Bedding Bedding 65' SW. Stretched Stretched N55OW, parallel parallel to the strike of the Niagara Niagara fault, and and dips 65° strikes N55°W, pebbles pebbles plunge plunge steeply steeply southwest. southwest. Iron-formation and Stop 3-3. Riverton Iron-formation and Wauseca Wauseca Pyritic Pvritic Member Member of Dunn Dunn Creek Slate (SW %, SW SW¼, %, sec. sec.34, 34,T. T. 40 40N., N.,R. R. 18 18 E.) E.) Slate (SW¼, - named by Dutton (1971) and This stop is a'ong along the axis of the Commonwealth Commonwealth syncline named is within Dutton's Dutton's Brule Brule River River block, block, now now included includedas as the the southeastern southeasternextension extensionof of the the River-Crystal Falls allochthon. Roadcuts Iron River-Crystal Roadcuts on Highway Highway N N about about 2 miles miles southeast southeast of of Florence, Wisconsin were made made after Dutton's Dutton's mapping mapping of the area, but but reveal reveal geology geology very much as inferred inferred on his maps. The roadcuts consist of alternating units of black, pyritic slate of the Wauseca Pyritic Member, the uppermost uppermost member of the Dunn Creek iron-formation of the overlying Riverton IronSlate, and cherty carbonate and silicate iron-formation formation. Individual Individual lithologic units of slate and iron-formation iron-formation are generally a few tens of feet thick and and the contact between between them is well exposed in many places along the roadcut. roadcut. The interleaving interleaving of the the two two units units is is probably probably aa result result of of repetition repetitionby by tight tight folding, folding, contacts cannot be traced around fold hinges within the limits of the roadcut. although contacts The lithologies lithologies could could be be stratigraphically stratigraphically interlayered, interlayered, but but such such broad-scale broad-scaleinter-bedding inter-bedding is not known elsewhere in the district where a few feet, feet, at most, of transitional beds occur between workings. We think it more between the two units where exposed in many mine workings. likely that folds with amplitudes greater than the height of the roadcut roadcut cause the repetitions with a geometry like those displayed in parts of figure 7 (p. 19) at the Buck mine in which fold amplitudes are many times greater then fold wave-lengths. Smallscale tight folds showing this type of geometry are common within individual lithologic units in this roadcut. The Wauseca consists consists of multiply multiply deformed, black, ferriginous, and and highly pyritic slate with thin - up to a few inches thick - beds of chert. The Wauseca Wauseca was classified as a sulfide fades iron-formation classified sulfide facies iron-formationby (1954) and and was his principal byJames James (1954) was his principal example for defining defining this facies. Foliation is generally parallel to the bedding and axial Foliation planar folds in N55OW,85°NE, 85ONE, and and is is parallel parallelto to the the trend trend in bedding. bedding. ItIt is is roughly roughly oriented oriented N55°W, of the Brule Brule River River block. block. The The rock rock is is folded foldedisodlinally isoclinally with with axes axes that that plunge plungevariably variablybut but most plunge steeply northwest (see stereoplot on fig. 3-4,B). These small folds are most likely likely parasitic to the Commonwealth Commonwealthsyncline. syncline. The Wauseca Wauseca Pyritic Pyritic Member Member has has some anomalous anomalous chemical characteristics. Ongoing studies by the USGS of the geochemistry geochemistry of black slates in the region found that a roadcut contained contained 1230 1230 parts parts per million composite of 30 feet of black black slate in in this roadcut arsenic and 14 14 parts per million selenium, both values being the highest that we have 71 �detected in northern northern Wisconsin Wisconsin and the upper peninsula detected peninsula of Michigan. Michigan. Studies are continuing Wauseca might might contribute contribute to aa regional regional continuing to determine to what degree the Wauseca arsenic anomaly icial materials. surficial materials. arsenic anomaly in insurf 3-4. Riverton Riverton Iron-formation Iron-formation along Stop 3-4. alonq eastern limb limb of of Iron Iron River-Crystal River-CrystalFalls Falls basin (NW basin (NW¼, ?A,sec. sec.31, 31,T.T.42 42N., N., R. R. 32 32 W.). W.). Typical Riverton Riverton Iron-formation Iron-formationis is exposed exposed in in cuts cuts along along two sub-parallel sub-parallel abandoned abandoned railroad single-track road. The exposures railroad spurs, the northern of which is drivable as a single-track are approximately in the middle of the Riverton, which in this area strikes NNE and dips of the area are steeply to the west into the Iron Iron River-Crystal Falls basin. Detailed maps of Professional Paper 570 by James and others (1 (1968) 968) and detailed included in USGS Professional lithologic descriptions of the Riverton are in the same publication. In general, the Riverton, where unaffected unaffectedby by secondary secondary oxidation, oxidation, which which is is widespread widespreadin inthe the district, district,isis thin-bedded and consists mostly of interbedded chert and siderite. Iron silicate minerals, thin-bedded and consists mostly interbedded and Iron silicate minerals, mostly stilpnomelane, are only locally important. Thin partings of argillaceous and carbonaceous carbonaceous material material are common common and and some pyritic pyritic layers layers are also widespread. Iron-formation at stop 3-4. Figure 3-6. Tight folds in the Riverton Iron-formation The rock seen here here is is generally only weakly oxidized so preserves many of the original sedimentary minerals and structures. Like Like all of the Iron Iron River-Crystal River-Crystal Falls allochthon, 72 I..,— �___ metamorphic metamorphicgrade gradeisisextremely extremelylow lowand andno nometamorphic metamorphiceffects effectsare aredetectable detectableininhand hand specimens. specimens.Small-scale Small-scalefolds foldsare arevery verywell welldeveloped. developed.Most Mostplunge plungegently gentlyto tomoderately moderately toward towardthe thenorth northor orsouth south(fig. (fig.3-4,C). 3-4,C). -N ) ' V — 7 Xr (J'-',p / - - - () v4 / - - La M — u3': 1UO1S - - 1650 iom 5000 reek ., ' I \ 4 -— - - 632W 4Q 1DJO METERS 5000 0 I 0 10000 4O FEET 20000 Figure Figure3-7. 3-7.Part Partofofthe theIron IronRiver River1:100,000-scale 1:100,000-scaletopographic topographicmap mapshowing showingthe thelocation location ofoffield trip stops 3-5 through 3-9. field trip stops 3-5 through 3-9. 73 �Stop 3-5. 3-5. Dunn DunnCreek CreekSlate Slatenear nearAlpha, Alpha,MI MI(NW (NW SE1/4, %, sec. sec. 7, 7,T. T. 42 42 N., N., R. R. 32 32 W). Stop ¼,%,SE The Dunn Creek Slate is the lowermost lowermost unit of the Paint River Group as defined by James (1958). (1958). It lies, probably conformably, on the Badwater Greenstone Greenstone and has a gradational upper contact with the Riverton Iron-formation. Iron-formation. It is a unit of greatly varied Iron River-Crystal River-Crystal Falls basin, and is lithology and thickness considering the entire Iron defined more as a stratigraphic interval interval than by a distinctive lithology. James and others (1968) described the variations in lithology and thickness. The area near the village of (1968) Alpha contains the best exposures and probably the greatest stratigraphic thickness of Dunn Creek. The The detailed detailed mapping mapping of the the area area by by the the USGS USGS as as part part of the the Iron Iron the Dunn 968) also produced a series River-Crystal Falls study presented presented in James and others (1 (1968) of more detailed reports published by the Geological Survey of Michigan. The report on area (Pettijohn (Pettijohn and and others, 1969) 1969) subdivided subdivided the Dunn Dunn Creek into into three the Alpha area mappable units based on a unit of distinctive laminated slate that forms the middle part of the formation and separates upper and lower units of gray to black, cherty, in part part sideritic, slate. The mapping of these units units was very useful in tracing the northward northward extension of the Mastodon Mastodon anticline, but for reasons not known to us these internal internal units on maps in in Professional Professional Paper Paper 570. 570. According to Pettijohn and others were not shown on (1969) (1969) the exposures seen at this stop are in the lower unit of the Dunn Creek Slate and lie about 1500 feet west of the trace of the axial plane of the Mastodon Mastodon anticline. This MI (fig. outcrop is located on the north side of Highway N about one mile east of Alpha, Ml 3-7). The outcrop consists of black ferruginous slate with more massive, massive, openly folded, cherty layers. There is a slatey foliation parallel to bedding in places. Elsewhere foliation N40°W is axial planar to the open open folds folds in in the the massive massivelayers layers and and is is generally generallyoriented orientedN40°W, 75ONE. 75°NE. A stereoplot of of fold fold axes from the broader region in this area (fig.3-4,D) shows that the folds plunge plunge steeply steeply to gently gently north-northwest. north-northwest. Fold Fold axes axes reported reported by Pettijohn Pettijohn plunged from 40-80 degrees northwest. and others (1969) (1969) also plunged northwest. It is clear from the relationships mapped in this area that even regional folds like the Mastodon anticline have steep plunges plunges within the allochthon. allochthon. Iron-formation at Stop 3-6. Riverton Iron-formation at the the Paint Paint River River Dam Dam in in Crystal Crystal Falls. Falls. Mt. MI. (Center, sec. (Center, sec. 20, 20, T. T. 43 43 N., N., R. R. 32 W.) 500-800 feet thick in the Crystal Falls area and is mostly The Riverton Iron-formation Iron-formation is 500-800 inter-laminated siderite Exposures inter-laminatedchert and siderite; Exposuresjust just below belowPaint PaintRiver RiverDam Damprovide providethe the of the the Riverton and of of the best example in the district both of the primary Iithology lithology of characteristic of the Iron extraordinary structural complexity of the deformation characteristic Iron RiverCrystal Falls allochthon. A sketch map of the outcrop, published by James and others (1968), (1968), is reproduced reproduced here to provide a view of the entire outcrop, some of which is flooded periodically, depending on the rate of flow of the Paint River. The exposure chert-siderite lithology, which comprises the bulk of of the Riverton IronIronshows the typical chert-siderite formation throughout the district. district. There are are also good good examples examples of a silicate silicate ironironformation, a lithologic type unique to the Crystal Falls area. These were described by "......at at the the apron apron of of the the Paint PaintRiver River dam dam in in Crystal Crystal James and others (1968) (1968) as follows: ".. Falls the chert-siderite chert-siderite iron-formation iron-formation contains layers that consist dominantly of stilpnomelane. These layers, which are from a fraction of an inch inch to several inches thick, distinguished in the outcrop from the chert and siderite by their inferior are readily distinguished inferior hardness hardness and by by their their peculiar peculiar closely closely spaced spaced cross cross fracture fracture that that resembles resemblesthat that of ofsome some coal." Some Somebeds bedsare arealso alsorelatively relativelyrich richin inpyrite. pyrite. 74 �Inclined Vertical Overturned Strike and dip of bedding . ......... ... .......... .... . Bedding plane Trace of selected bedding plane Traced o r r o ~ nm Daubed w h e w u.vproxiwzlely locnted -.... . t k oulcw~ Fault,showing relative movement Dotted where concealed 1010 I L 00 , , I l 1010 I I 20 20 I I 30 30FOCI FEET I SurveyedbybyH.HL. L. Jamesand and Srveyod James W W 5, S Why,, White 948 1948 I Figure3-8. 3-8.Sketch Sketchmap mapofofRiverton RivertonIron-formation Iron-formationatatPaint PaintRiver RiverDam, Dam,Crystal CrystalFalls, Falls, Figure Michigan. Michigan.(James (Jamesand andothers, others,1968, 1968,fig fig21) 21) showsthat thatmost mostfolds foldsplunge plungesteeply steeplyto tothe thewest west(note (notethat thatnorth northisistoward toward Figure3-4, 3-4,EEshows Figure 55degrees degreestotovertical. vertical.But, But, theupper upperright rightininfigure figure3-8). 3-8).Plunges Plungesare aresteep, steep,varying varyingfrom from55 the onthe themost mostnortheasterly northeasterlypart partofofthe theoutcrop outcropfolds foldsplunge plungetoward towardthe thenorth northatatabout aboutright right on angles anglesto tothe theother otherfolds. folds.These Theseabrupt abruptvariations variationsininfold foldgeometry geometryare arecharacteristic characteristicofof the thedistrict districtas asrevealed revealedininthe themany manyunderground undergroundmines minesthat thatwere weremapped mappedduring duringthe the periodof ofmining miningininthe theearly earlytotomid-i mid-1900's. additiontotothe thefold foldaxes axesthat thatwe wehave have period 900's. InInaddition Larue(1987), (1987),who who measured,this thisexposure exposurewas wasstudied studiedinindetail detailby byUeng Uengand andLarue measured, recognized44 phases phasesof of deformation deformationand andprovide provideaadetailed detaileddiscussion discussionof ofthe thestructural structural recognized history.To Togeneralize generalizetheir theirconclusions, conclusions,the thefolds foldsthat thatplunge plungesteeply steeplytotothe thewest westformed formed history. ininan second aninitial initialmajor majorfolding foldingphase phaseand andthose thosethat thatplunge plungesteeply steeplytotothe thenorth northare areaasecond phase. phase. 75 �Stop 3-7. Badwater Greenstone north northof ofCrystal CrystalFalls Falls(sec. (sec.18, 18,T.T.43 43N., N.,RR32 32 W.) W.) Badwater Greenstone Alloutcrops outcropsininthis thisarea areaare areon onprivate privateland landand andshould shouldnot notbe bevisited visitedwithout without NOTE: All prior permission permission of property property owners. owners. The Badwater Greenstone is a thick succession of submarine mafic volcanic rocks that underlies the Dunn Creek Slate, probably conformably, although evidence is scant. As the Paint River Group because discussed above, we propose to include the Badwater in the structural evidence indicates that it is part of the Iron Thus structural Iron River-Crystal Falls allochthon. Thus it has definable stratigraphic stratigraphic relationships relationships to to the the overlying overlying Paint Paint River River strata stratabut but isisin in fault fault contact with all other surrounding units. James and others (1968) (1968) described rocks of the Badwater as .somewhat varied in detail, but in in general general they they are are massive massivefine-grained fine-grained Badwater as ". ...somewhat dark-greenish-gray rocks that consist chiefly of chlorite, actinolite, hornblende, dark-greenish-gray rocks consist chiefly of chlorite, actinolite, hornblende, albite, albite, clinozoisite-epidote, and carbonate. carbonate. Ellipsoidal Ellipsoidal and and agglomeratic agglomeratic structures structuresare are common. common. fragmental volcanics . The rocks rocksalmost almostcertainly certainly originated originatedas as sub-marine sub-marine flows and fragmental entirely, of of primary primary basaltic basaltic composition." composition." The formation and are dominantly, ifif not entirely, carbonate-rich slate and thin ironcontains minor sedimentary rocks consisting of carbonate-rich formation. James James estimated estimated that the the Badwater Badwater is is as as much much as as 15,000 15,000 feet thick thick in in places, places, but its thickness varies varies greatly greatly within within the the district. district. I'. . . At this stop the Badwater Greenstone is a strongly deformed pillow basalt and pillow stretched volcanic clasts and breccia. The basalt is weakly to strongly foliated, and has stretched N80°W85°NE. 85ONE. Stretched Stretched clasts clasts and and pillows pillows pillows. Foliation is generally oriented oriented N80°W, plunge steeply northwest as shown in figure 3-4, F. These steeply plunging structures, similar to those inherently part of the Niagara suture zone rocks from here southward to the Niagara Niagara fault, are are the the principal principal evidence evidence that the Badwater Greenstone Greenstone is is part part of the Iron Iron River-Crystal River-Crystal Falls Falls allochthon allochthon and and is is structurally structurally detached detachedfrom from more moresimply simply deformed rocks to the north that will be seen at stop 3-8. Stop 3-8. 3-8. Michiciamme Michiqamme Formation Formation north northof of Crystal CrystalFalls, Falls,MI MI(SW (SW¼, %, NE NE ¼, %, sec. 12, T.43N., T. 43 N., R.33W.) R. 33 W.) The Michigamme Formation, a thick sequence of clastic rocks, dominantly graded and bedded graywackes and thinner-bedded siltstones, underlies a very large area north and east of the Iron River-Crystal Falls allochthon. Broad, open folds with steeply dipping, Iron River-Crystal Falls more or less less east-west east-west trending, trending, axial axial planes planes and and shallowly-plunging shallowly-plungingfold foldaxes axes scattered outcrops of varicolored slate are characterize deformation. At this locality scattered located on the north side of the Paint River, about six-tenths six-tenths of a mile west from the Highway-141 this characteristic fold fold geometry. Prominent slatey Highway-141 bridge and display well this cleavage cleavage is oriented oriented N75°W, N75¡W80°NE, 80°NEand and intersections intersections of of bedding beddingand andcleavage cleavageindicate indicate that fold axes plunge 15 15 degrees west. Outcrop-scale Outcrop-scale folds with this orientation are also present here. This nearly horizontal, westerly plunge of the fold axes is characteristic characteristic of fold axes found in the Michigamme Formation Formation along the north and east sides of the Iron Iron River-Crystal Falls district, and contrasts contrasts sharply with the steeply plunging orientation of Greenstone and overlying Paint fold axes and stretch stretch lineations lineations found in the Badwater Greenstone the rocks here and those at River Group strata. This contrast in structural style between the all other stops seen to this point indicate that there is a fundamental structural structural boundary boundary between the Badwater Greenstone and other rocks of the allochthon and the Michigamme Michigamme Formation. The outcrops visible south of the River are Badwater Greenstone, Greenstone, indicating indicating that the boundary boundary lies immediately immediately south of these Michigamme Michigamme 76 �probably beneath beneath the river. We have have proposed proposed the name name Paint Paint River River fault for outcrops, probably structure and interpret interpret itit to be be the basal basal detachment of the allochthon. this structure Stop 3-9. Little Tobin Lake Lake Granite Granite (NE (NE 1/4, %, see. Stop Little Tobin sec.21, 21,T. T. 42 42 N., R. 32 32 W.) A dike-like dike-like body of granite, called called the little Tobin Lake Lake dike dike by James and others others (1968), intrudes the Badwater intrudes Badwater Greenstone Greenstone and forms a body about 2 miles long long and a quarter quarter of a mile wide (fig. 3-1). The The rocks rocksare are gray gray to to reddish reddish gray gray and and finefine- to to medium-grained medium-grained and are composed dominantly of microcline microcline microperthite, microperthite, albite, and mica. In In this area the Badwater Badwater is intensely intensely folded on the Mastodon anticline and the adjacent Tim Bowers syncline, syncline, both both of which which are are traversed traversed by by the the dike, dike, which which maintains maintainsaa nearly nearlystraight straighttrace. trace. emplaced after the major major folding of the Paint Paint River River Group. Group. The dike clearly seems to be emplaced It yielded a U-Pb zircon date of 1833+/-6 Ma (Schneider and others, 2002), which places emplacement of the Iron Iron River-Crystal River-CrystalFalls Falls allochthon. a younger limit on the age of emplacement bodies of granite granite lie between here and Crystal Falls, about 5 miles Several other smaller bodies to the north. north. These, too, are apparently apparently post-tectonic post-tectonic and and occur both both within the allochthon and in the structurally lower Michigamme Formation. James and others (1968) (1 968) states "The granitic granitic bodies bodies all all have have been been sheared sheared to to some some extent, extent, and andall allhave have been metamorphosed". Perhaps these granites record a younger, circa 1650 Ma been record circa 1650 deformation as has been been proposed proposed for this area by Romano Romano and others (2000). (2000). deformation 77 �REFERENCES REFERENCES CITED CITED K., and and Klasner, Klasner, J.S., J.S., 1989, 1989,Tectonic Tectonicimplications implicationsof of metamorphism metamorphismand andgravity gravity Attoh, K., field in in the Penokean Penokean orogen of northern northern Michigan: Tectonics, Tectonics,v. v. 8, 8, p. p. 911-933. 91 1-933. 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Shervais, J.W., 2001, Birth, Birth, death, death, and and resurrection: resurrection:the the life life cycle cycle of of suprasubduction suprasubduction zone ophiolites: Geochemistry Geophysics Geosystems, vol.2, Paper ophiolites: Geochemistry Geophysics Geosystems, Paper number number 2000GC000080 http://g2000GC000080 [20,925 [20,925 words, 88 figures, figures, 33 tables]. tables]. On-line On-linepublication publicationat at http:llgcu bed .o rg cubed.org. Shervais, J.W. and and Kimbrough, Kimbrough, D.L., D.L., 1985, 1985, Geochemical Geochemicalevidence evidence for for the the tectonic tectonic setting of the Coast Range Range ophiolite: ophiolite: aa composite composite island island arc-oceanic arc-oceanic crust crust terrane terrane in in western v. 13, 13, p. p. 35-38. 35-38. western California: California: Geology, Geology, v. 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Sims, P.K., P.K., Schulz, K.J., DeWitt, DeWitt, E., E., and and Brasaemle, Brasaemle,B., B., 1993, 1993, Petrography Petrographyand and geochemistry geochemistry of Early Early Proterozoic Proterozoicgranitoid granitoid rocks rocks in in Wisconsin Wisconsin magmatic magmaticterranes terranesof of the the Penokean orogen, northern Penokean northern Wisconsin—a Wisconsin-a reconnaissance reconnaissance study: study: U.S. U.S. Geological Geological Survey Bulletin Bulletin 1904-J, lgO4-J, p. p. J1-J31. J1-J31. Trent, V.A., 1976, 1976, The The Emperor Emperor Volcanic Volcanic Complex Complex of of the the eastern easternGogebic Gogebic Range, Range, G.V., and Wright, Wright, W.B.,eds., Changes Changes in in stratigraphic stratigraphic nomenclature nomenclature Michigan, in Cohee, G.V., by the U.S. Geological Geological Survey, 1975: U.S. Geological Survey Bulletin 1422-A, p. 69-74. 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Great 85 �FIELD FIELD TRIP TRIP 44 LIFE LIFE CYCLE CYCLE OF OF AN AN IRON IRON DEPOSIT—THE DEPOSIT-THE REPUBLIC REPUBLIC MINE MINE FROM ORE GENESIS GENESIS TO MINE MINE RESTORATION RESTORATION William F. Cannon, USGS, Reston, VA; VA; John G. G. Meier, Cleveland Cleveland Cliffs Cliffs Iron Iron Co., Ishpeming, Ishpeming, MI; Thomas Thomas Waggoner, Waggoner,Geologic Geologic Consultant, Consultant, Negaunee, Negaunee, MI MI Republic pit pit in in 1973, 1973, approximately approximatelyat at mid-point mid-pointof of production. production. The Republic The The Republic RepublicWetlands Wetlands Preserve Preserveinin2002, 2002, constructed constructedon onthe theformer formertailings tailings basin basin of of the the Republic Republicmine. mine. �FIELD FIELDTRIP TRIP 44 LIFE LIFE CYCLE CYCLE OF OF AN AN IRON IRONDEPOSIT—THE DEPOSIT-THE REPUBLIC REPUBLICMINE MINEFROM FROMORE OREGENESIS GENESIS TO TO MINE MINERESTORATION RESTORATION William William F. Cannon, Cannon, USGS, USGS, Reston, Reston, VA; VA;John John G. G.Meier, Meier, Cleveland ClevelandCliffs CliffsIron IronCo., Co., lshpeming, Ishpeming, MI; MI; Thomas ThomasWaggoner, Waggoner,Geologic GeologicConsultant, Consultant,Negaunee, Negaunee, MI MI Brief Brief history historyof of mining miningand andgeologic geologicstudies studies Mmmci: M i n i : The The Republic RepublicMine Minein inwestern westernMarquette MarquetteCounty, County,Michigan Michiganproduced produced more more than than 75 75million milliontons tonsof ofiron ironore oreduring duringtwo twogenerations generationsofofmining. mining.The TheRepublic RepublicIron Iron Company was was organized organized in in Marquette, Marquette, Michigan Michigan in in October October 1870 1870 and and mining mining at at what is is Company now now the the site site of of the theclosed closedRepublic RepublicMine Minebegan beganinin1871. 1871.Operated Operatedby bythe theRepublic RepublicIron Iron Company, Company, the the mine mine was was producing producing 235,000 235,000 tons tons of of hard, hard, specular specular hematite hematite by by 1880. 1880. Mining Mining operations operations were were conducted conducted in in open open pits pits and and 14 14 shafts. shafts. The The greatest greatest shaft shaft depth depth was was 2,910 2,910 feet. feet. The TheCleveland-Cliffs Cleveland-CliffsIron IronCompany Companyacquired acquiredthe the mine minein in1914 1914and and operated operateditituntil until1926 1926when whenititclosed. closed.Shipments Shipmentsfrom from the the stockpile stockpilecontinued continueduntil until1937. 1937. The 937 was Thetotal totalore oreshipped shippedfrom from1872-1 1872-1937 was more morethan than 8.5 8.5 million milliontons. tons.After Afterthat, that,the the mine 950s. minesat satidle idleuntil untilthe theearly early11950s. In In 1952, 1952, construction construction of of the the modern-day modern-dayfacilities facilities began began and and the the open open pit pit mine mine was was in in production productionby by1956, 1956,mining mininglow-grade low-gradeiron ironore ore that that was was concentrated concentratedat at the the mine's mine'splant plant and andpelletized pelletizedat at the the former formerEagle EagleMills Millspellet pelletplant plantin inNegaunee NegauneeTownship. Township. In Inthe the early early 1960's 1960'san anexpansion expansionof of the themine, mine,including includingpelletizing pelletizingand andadditional additionalconcentrating concentrating equipment, equipment, took tookplace. place.This Thisexpansion expansionwas was completed completedin in1964, 1964,at at which which time time Republic Republic was was producing producingmore morethan than22 million milliontons tons of of iron ironore orepellets pelletsannually. annually. AA unique uniquepart partof of the the mining miningoperation operationat at Republic Republicwas was the the in-pit in-pitcrushing crushing system, system, which which performed performedcoarse coarse crushing crushingnear nearthe the floor floor of of the thepit pitand andtransported transportedthe thecrushed crushedore orefrom fromthe thepit pitto tothe the plant, plant,aavertical verticallift liftof of 647 647feet, feet,via viaaa2,814-foot 2,814-footconveyor conveyorininan aninclined inclinedtunnel tunnelin inthe the footwall footwallof of the theore orebody. body. In In1981, 1981,with with the the iron ironore oreand andsteel steelindustry industryin inaa deep deep recession, recession,operations operationsat at Republic Republic were were suspended. suspended. When Whenhope hopefaded fadedthat thatmarket marketconditions conditionswould wouldimprove improveto to allow allowpellet pellet production productionto to resume, resume,Republic Republicwas was permanently permanentlyclosed closed in in early early 1996. 1996. More More than than 45 45 million milliontons tonsof of pellets pelletswere wereproduced producedatatthe theRepublic Republicplant plantbetween between1964 1964and and1981. 1981. Including Includingpellets pelletsproduced producedat at the theEagle EagleMills Millsplant plantand andsome someproduced producedat at the the Humboldt Humboldt plant plantwith withRepublic Republicore, ore,Republic Republicaccounted accountedfor formore morethan than63 63million milliontons tonsofofpellets pelletssince since 1956. 1956.When Whenthe themine mineclosed closedinin1981, 1981,Republic Republicemployed employedmore morethan than700 700people. people. In Inaddition additionto to being beingaamajor majoriron-producing iron-producingarea areafor for more morethan thanaacentury, century,the thegeologic geologic relationships relationshipsshown shownininthe themine minearea areaand andother othernearby nearbyexposures exposureshave haveplayed playedan an important importantrole rolein indeveloping developingconcepts conceptsof of the theorigin originof of iron-formations iron-formationsof ofvarious various sedimentary sedimentaryfacies, facies, their theiralteration alterationthrough throughregional regionalmetamorphism, metamorphism,and andaarather rather complex complex history historyof of iron ironconcentration concentrationthat that led ledto tothe theformation formationof of the thehigh-grade high-gradeores oreson on which whichthe theinitial initialmining miningwas wasbased. based.This Thistrip tripvisits visitssome someof of these theseexposures exposuresand andprovides provides aareview reviewof of the the rich richhistory historyof of studies studiesof of the thegeology geologyof of iron irondeposits depositsininthis thispart partof of the the Lake LakeSuperior Superiorregion. region. 87 �Geologic Geoloqic studies: The Thefirst firstrecorded recordedgeologic geologicobservations observationsat at Republic Republic were made by Government Government Land Office surveyors in 1846 1846 while surveying the township and range grid of the area. They clearly recognized recognized the importance importance of the ore that was readily visible on what was then a prominent prominent hill hill along along the the Michigamme MichigammeRiver. River. Five years later the area was visited by J.W. Foster Foster and and J.D. Whitney, Whitney, U.S. U.S. Government Government Geologists, "The 1851): "The Geologists, who provided provided the the following description description (Foster (Foster and and Whitney, Whitney, 1851): largest mass mass observed by us in this region occurs on the left bank of the Machi-gamig, Machi-gamig, in section section 7, of township township 46, range range 29, 29, and and traces traces of of itit are are to to be be observed observedin in several several of of the the adjoining adjoining sections. sections. ItIt here here rises rises in in aa nearly nearly vertical vertical cliff to to the the height height of of one one hundred hundredand and thirteen thirteen feet, and and is is somewhat somewhat variable variable in in purity. purity. For For the the most most part part itit has has aa slaty slaty cleavage, cleavage, and, on on close close inspection, inspection, is is observed observed to be be composed composed of alternating alternatingbands bands of of micaceous micaceous specular iron and quartz, tinged red by the peroxide of iron: but there are occasional occasional belts belts which display display a granular texture, and and apparently apparently possess possess a greater greater degree degree of purity. purity. These These laminae laminae are are nearly nearly vertical, vertical, exhibiting exhibiting few contortions, contortions, and and range range with so much much uniformity, uniformity, that the observer observer would would be be inclined inclined to refer refer both both the the slates slates and and the iron iron to aa common common origin. origin. Interlaminated Interlaminatedwith with itit is is aa band band of of rock rock composed composedmainly mainly of of white, granular granular quartz, quartz, with with traces traces of feldspar, feldspar, through through which which are are disseminated disseminated particles, particles, as as well as rounded rounded masses, of specular specular iron. iron. ItIt is is difficult difficult to to pronounce pronounce whether whether this this is is aa conglomerate conglomerate or or breccia." breccia." During the ensuing 20 years, the wave of exploration and development along the Marquette Marquette Range reached reached Republic. In 1871, shortly before before mining was initiated, the ore was was described described by by Swineford Swineford (1871). (1871). His His description description of Smith Smith Mountain, Mountain, as as itit was then then called, called, was "The "The mountain mountain rises rises to aa height height of nearly, nearly, ifif not not quite, quite, 1,000 1,000 feet feet above above the the waters waters of the the Michigammi Michigammi River, River, which which runs runs near near its its base, base, and and the explorations explorations made made last summer summer reveal reveal the the existence existence of an an immense immense body body of ore, which can be traced over a last mile mile by by outcrops outcrops alone. The The writer writer visited visited this this mountain mountain last last summer summer and and has has no no hesitation hesitation in in saying saying the he he believes believes itit to be be by by far the the most most valuable valuable property property yet discovered. discovered. The The ore ore is is aa very pure pure magnetic, magnetic, similar similar to to that that of of the the Washington Washington and and Champion. Champion. The The elevation elevation is is such such that the ore ore can can be be mined mined at aa comparatively comparatively trifling trifling cost, cost, and and itit would would be be an an easy easy matter matter to to mine mine and and ship ship aa hundred hundred thousand thousand tons tons in in the the first first year after after commencing commencing operations." He Hefurther furtherstates states"It "It was was originally originally discovered discovered by by S.C. Smith, Smith, Esq., Esq., of of Marquette, Marquette, from from whom whom itit takes takes its its name, name, and and who who threw threw away away an an immense immense fortune fortune in its sale at a nominal price." Apparently Apparently Mr. Mr. Swineford Swineford had had a rather optimistic optimistic eye, both both in in estimating estimating topographic topographic relief relief and and ore ore reserves. reserves. In 1873, 1873, T.M. Brooks Brooks published published aa comprehensive comprehensive survey survey of the iron-bearing iron-bearingrocks rocks of of the the In Marquette range range including including both both descriptions descriptionsand and an an atlas. atlas. At Republic Republic he he determined determined the the Marquette detailed detailed internal internal stratigraphy stratigraphy of of the the iron-formation iron-formationand and produced produced the the first first detailed detailedmap map of of the deposit. deposit. He He recognized recognized the synclinal synclinal character character of the host host rocks rocks and and described described the the several several lithologic lithologic types of iron-formation iron-formation and and ores ores exposed exposed in in the area. Like Like Swineford, Swineford, Brooks was was very very impressed impressed by by the the large large ore ore exposure exposure and and wrote wrote "The "The immense immense mass mass of of Brooks pure Va of of the the pure specular specular ore, which which was was naturally naturally exposed exposed near near the center center of the the north north ½ southeast Sec.7, 7,T. 1. 46, 46, R. R. 29, 29, could could leave leave no no reasonable doubt in the mind mind of the southeast 1/4 % ofofSec. experienced experienced observer, observer, that this deposit of ore ore was one of the the largest, this deposit was one largest, ifif not not the the largest, largest, in in the the Marquette Marquette region. region. This This outcrop, outcrop, the the extent extent of of which which is is shown shown on on the the map map of of the the Republic Mountain, Mountain, being being there marked marked "pure "pure specular specular ore", is, is, so so far far as as II know, know, the the Republic largest outcrop outcrop of of any any equally equally rich rich ore, ore, ever ever found found in in the the United United States." States." largest 88 �more detailed detailed and accurate accurate description of the geology geology was published published in 1897 1897 by Henry A more of the classic USGS Monograph 28 by Van Hise and Bayley Lloyd Smyth as Chapter VI of on the geology geology of the "Marquette "Marquette Iron-bearing Iron-bearingDistrict" District" (Van (Van Hise Hise and Bayley,1897). Bayley,1897). By original mines mines were well established and an understanding understanding of the that time, the original processes of ore-formation ore-formation was being being developed developed by Van Hise and Bayley. Smyth's Republic were an important part of that research research and are discussed in observations at Republic more detail below. Among Smyth's contributions were recognition of the detailed sequence of the Early Early Proterozoic Proterozoic strata, which has has not been been significantly stratigraphic sequence modified since, with with the exception exception of some some changes changes in in nomenclature, nomenclature,and anddelineating delineatingthe the modified With regard regard to to the the ore ore deposits, deposits, Smyth's Smyth's maps maps plunging synclinal geometry of the strata. With were the first (and (and only) ones that showed showed a distinct separation between between dominantly hard specularite ores and dominantly magnetite ores. He correctly surmised that the hard ores formed formed by secondary secondary concentrations concentrations within the iron-formation, iron-formation,in part part through leaching of original original siliceous beds, and also recognized recognized the detrital detrital character of iron iron enrichments Goodrich Quartzite. Quartzite. enrichments in the basal basal conglomerates conglomerates of the Goodrich Much later, in the early 1950's, 1950's, Harold Harold James of the USGS USGS published published two fundamental papers papers in which Republic Republic played a major role. His work on zones of regional metamorphism metamorphism (James, 1955) 1955) was strongly influenced influenced by the Republic Republic area, which was at the center of a zone of sillimanite grade grade metamorphism metamorphism of his his Republic Republic metamorphic metamorphic node. node. The The Republic Republic area area was was the the sole sole locality locality where where several severallithologic lithologictypes typesof of ironironformation were within within this this high-grade high-gradezone zone and and was was the the principal principalexample exampleupon uponwhich whichhe he defined the very high-grade high-grade metamorphic metamorphic effects effects on iron-formation. iron-formation. A A fundamental fundamental outcome outcome of that study was that even very intense metamorphism metamorphism does not change change the majority of the iron, iron, an an idea idea contrary contrary to widely held held concepts original oxidation state of a majority at that time. The relationships relationships upon upon which he based based that conclusion are clearly displayed in a glacially polished outcrop at the Kloman Kloman Mine (fig. 4-1, stop 4-1). James's studies of the importance importance of sedimentary sedimentary conditions in determining the mineralogic mineralogic character of iron-formations, published published as his his famous "Sedimentary "Sedimentary facies of iron-formation" iron-formation" (James, 1954), also drew heavily heavily on relationships relationships seen seen in in the the Republic Republicarea, area, and and again again the the exposures exposures at Kloman Kloman mine mine were were instrumental instrumentalin inshowing showingthe therelationship relationshipbetween between bedding bedding characteristics characteristicsand and mineralogy mineralogyof of iron-bearing iron-bearingphases. phases. The most most recent recent comprehensive comprehensive geologic geologic study of the Republic Republic area area was conducted by Cannon (1975) who mapped mapped the geology of the iron-bearing iron-bearingsequence and and surrounding surrounding Cannon (1975) the rocks, including detailed mapping in the open-pit. Because the pit was developed in the same stratigraphic unit unit that contained contained the high-grade high-gradeores ores mined mined previously previously underground, exposures of those high grade ores and their relationships to host rocks rocks were abundant in the pit and were a fundamental component of Cannon's study of the component Cannon's origin of hard hard iron iron ores of the Marquette Marquette Range Range (Cannon, (Cannon, 1976). 1976). Unfortunately Unfortunately those those exposures exposures are are now now flooded flooded in in the the abandoned abandonedpit. pit. Geology of the Republic Republic area The Republic Republic area area has has many many similarities similarities to the Marquette Marquette Iron Iron Range Range to the north north and and east and and is is generally generally considered considered to be be an extension of it. Paleoproterozoic Paleoproterozoic strata strata of the Marquette Range Supergroup are preserved in a syncline, the Republic trough, between uplifted blocks of Archean gneisses. The stratigraphic units defined in the Marquette Iron Range, can be applied in the Republic trough as well, and to some extent can be traced directly into into the Marquette Marquette Range. Range. The The Paleoproterozoic Paleoproterozoic units units in the Republic Republic area area consist of a basal sequence of the Ajibik Ajibik Quartzite Quartzite and and Siamo Siamo Slate Slate which were basal clastic sequence 89 �mapped mapped as as aa single single unit unit by by Cannon Cannon (1975) (1975) because because very limited limited exposure exposure does does not not allow allow accurate accurate mapping mappingof of aa contact contactbetween betweenthem. them.These Theseare areoverlain overlainby bythe theNegaunee Negaunee Iron-formation, Iron-formation,the the principal principaliron-bearing iron-bearingunit. unit.The TheGoodrich GoodrichQuartzite Quartzitelies liesunconformably unconformably on on the the Negaunee. Negaunee. The The unconformity unconformity was was well well exposed exposed in in the Republic Republic pit pit before before flooding. flooding. The Thebasal basalpart partof of the theGoodrich Goodrichisisaaferruginous ferruginousconglomerate, conglomerate,which whichgrades grades upward into quartzite. The youngest strata are biotite-garnet schist with beds of upward into quartzite. The youngest strata are biotite-garnet schist with beds of impure impure quartzite, quartzite, which which make makeup upthe the Michigamme MichigammeFormation. Formation.The The Michigamme Michigammealso also contains contains aa basal unit unit of silicate-magnetite silicate-magnetiteiron-formation. iron-formation. Several Several sills sills of of diabase diabase were were intruded intrudedinto into basal the the strata, strata, mostly mostlyin inthe the iron-formation, iron-formation,and andhave havebeen beenfolded foldedwith with it. it. The synclineof of The fundamental fundamentalstructure structure of of the thearea areaisisaanarrow, narrow,deep, deep,northwest-plunging northwest-plungingsyncline Paleoproterozoic Paleoproterozoicstrata strata of of the the Marquette MarquetteRange Range Supergroup Supergroupflanked flanked by by Archean Archean gneisses. gneisses.Gravity Gravitystudies studiesindicate indicatethat that along along Highway Highway95, 95, where where the the trough trough is is about about 3,000 3,000 feet feet wide, wide, ititisisabout about5,000 5,000 feet feet deep deep(Klasner (Klasnerand andCannon, Cannon,1974). 1974).Axes Axes of of minor minor folds foldsmeasured measuredin inthe the Republic Republicpit, pit, which which follows follows the the iron-bearing iron-bearingbeds beds around around the the keel keel of to the 45'to the northwest. northwest.The The tight tightcompression compressionwithin within the the of the the trough, trough, plunge plungeabout about45° syncline syncline has hasproduced producedintense intensesmall small scale scale folding folding in in some some units, units, such such as as the the schists schists of of the 4-2(fig. (fig.4-1). 4-1).This Thisdeformation deformationapparently apparentlyalso also the Michigamme MichigammeFormation Formationseen seenat at stop stop4-2 has hascaused causedsevere severeattenuation attenuationof of the the iron-formation iron-formationalong alongthe thelimbs limbsof of the thesyncline synclineas as shown shown by by the the drastic drasticthinning thinningseen seen in in traversing traversingfrom from the the Republic Republicpit pitat at the the keel keelof of the the structure structure along alongstrike strikeonto ontothe thenearly nearlyvertical verticallimbs. limbs. The Thecontact contactbetween betweenthe the Paleoproterozoic Archean basement basement gneisses gneisses is is interpreted interpretedto to be be aa fault fault Paleoproterozoicstrata strata and and Archean along along both bothlimbs limbsof of the the syncline. syncline.The Thefault fault on onthe thesouthwestern southwesternlimb limbwas was well well exposed exposedin in the thepit pitand andcompletely completelytruncates truncatesthe the Negaunee Negauneeand andAjibik/Siamo AjibikISiamostrata strataproducing producingthe the fish-hook fish-hook shape shapeof of the thetaconite taconiteorebody. orebody. Bedding Beddingininthe theiron-formation iron-formationnear nearthe thefault, fault,as as well Archeanrocks rocksalong alongthe thefault, fault,generally generallydips dipsfrom from75°-85° 75'-85' totothe the well as asshear shearfoliation foliationininArchean southwest indicating that the fault is a high-angle reverse fault at the present exposure southwest indicating that the fault is a high-angle reverse fault at the present exposure level. level.The The fault fault along alongthe the northeast northeastlimb limbisisnot notas aswell well documented documentedby byexposures, exposures,but but beds bedson on the the northeast northeastlimb limbare arecommonly commonlyoverturned overturnedand anddip dip about about 85° 85' to to the the northeast northeast suggesting suggestingthat that the thenortheast northeastlimb limbfault faultisisalso alsoaahigh highangle anglereverse reversefault. fault.Thus Thusthe the Republic Republictrough troughhas hasan anunusual unusualgeometry geometryininbeing beingaasyncline synclinethat thatwidens widenssomewhat somewhat below belowthe thepresent presentsurface. surface. The Theintense intensePenokean Penokeandeformation deformationrecorded recordedininthe thePaleoproterozoic Paleoproterozoicstrata strataof of the the Republic Archean gneisses gneisseswhere where intense intense Republictrough troughisisnot notpresent presentwithin withinthe the surrounding surroundingArchean multiple multiplefolding foldingevents eventsdocumented documentedby byTaylor Taylor (1967), (1967),Cannon Cannon(1975), (1975),and andHoffman Hoffman (1987) (1987)appear appearto tobe beentirely entirelyaaresult resultof of late lateArchean Archeantectonism. tectonism.Cannon Cannon(1973) (1973)used used metadiabase metadiabasedikes dikesas asstructural structuralmarkers markersto toindicate indicatethe thegeneral generalabsence absenceof of penetrative penetrative Penokean Archeanrocks. rocks.These Thesedikes, dikes,which whichoccur occurinin Penokeandeformation deformationininthe theareas areasof of Archean northeastnortheast-and andnorthwest-trending northwest-trendingswarms, swarms,are aremetamorphosed metamorphosedby byPenokean Penokean metamorphism metamorphismof of the theRepublic Republicnode nodeand, and,ininplaces, places,have havesheared shearedmargins marginscaused causedby by Penokean Penokeandeformation, deformation,but buteverywhere everywheremaintain maintaintheir their vertical, vertical, planar planardike dikegeometry geometryand and have haveessentially essentiallyno nointernal internaltectonic tectonicfabric. fabric.Relict Relictdiabasic diabasictextures texturesare arecommonly commonlywell well preserved preservedeven evenininthe themost mosthighly highlymetamorphosed metamorphoseddikes. dikes.Thus Thusititappears appearsthat thatPenokean Penokean deformation Archeanbasement basementrocks rockswas waslargely largelyconfined confinedto tozones zonesof of deformationwithin withinareas areasof of Archean shearing, shearing,which whichseparate separatelarger largerblocks blocksof of rock rockthat thatremained remainedrigid. rigid.The TheRepublic Republictrough, trough, therefore, therefore,isisaagraben grabenwith withrespect respecttotoArchean Archeanrocks. rocks.The Thesynclinal synclinalform formofofthe thetrough troughofof Paleoproterozoic strata is a result of those strata being molded around the structural Paleoproterozoic strata is a result of those strata being molded around the structural form formcreated createdby bydifferential differentialmovement movementofofindividual individualdiscrete discreteblocks blocksofofArchean Archeanbasement basement rocks. rocks. 90 �____ EXPLANATION EXPLANATION Mesoproterozoic Mesoproterozoic Diabase Diabase Paleoproterozoic Paleoproterozoic Metadia Metadiabase base E Michigamme Fm. Fm. --Michigamme lower lower slate slate member member MichigammeFm. Fm. Michigamme -- banded banded silicate-magnetite silicate-magnetite iron-formation iron-formation Goodrich GoodrichQuartzite Quartzite ::-: Goodrich Qua rtzite Goodrich Quartzite -- basal conglomerate basal conglomerate Negaunee NegauneeIron-Fm Iron-Fm hematite-richoxide oxidefades facies -- hematite-rich Negaunee NegauneeIron-Fm Iron-Fm -- magnetite-rich magnetite-richoxide oxidefacies facies Negaunee NegauneeIron-Fm Iron-Fm -- iron ironsilicate silicatefacies facies Siamo Slate and Ajibik Siamo Ajibik Quartzite, undifferentiated undifferentiated Quartzite, Archean Archean Granitic Graniticgneiss gneiss Mafic gneiss Lii. Mafic gneiss open open pit pit minedumps dumps EJ mine - — faults faults 8800 1/2 0 ,I 1 I miles miles Figure 4-1. Geologic Geologic map map of of the the Republic Republicarea, area, Michigan Michiganshowing showingthe the location locationof of field field Figure trip trip stops. stops. Geology Geologyfrom from Cannon Cannon(1975). (1975). t 91 �Economic geology geology The iron iron ores produced produced at Republic Republic were of two different different types: early production production was of high-grade high-gradeores ores that occur within the upper upper part part of the the Negaunee Negaunee Iron-formation Iron-formationand and lower lower part part of the overlying overlying Goodrich Goodrich Quartzite. Quartzite. These These are are locally locally known known as "hard ores" because because of their their compact, compact, coarse coarse crystalline crystalline nature. nature. The The more more recent recent production productionof iron iron concentrate concentrate and and pellets pellets was was from from lower-grade lower-gradematerial materialtypical typical of of upper upperstratigraphic stratigraphicunits units of the Negaunee Iron-formation. Negaunee Iron-formation. Concentrating-grade Concentratinci-aradeore (taconite): (taconite): The The modern modern open open pit pit of the the Republic Republic mine mine was developed developed to mine mine the uppermost uppermost parts parts of the Negaunee Negaunee Iron-formation Iron-formationconsisting consisting mostly mostly of hematitic hematitic jasper (fig. (fig. 4-2). 4-2). The The ore ore horizon horizon varied varied from from 400-600 400-600 feet feet thick in in the pit. The ore horizons horizons dip approximately approximately vertically along in the northern part of the pit, which which lies lies along along the the northeast northeast limb limb of the the Republic Republic syncline, syncline, but but dips dips flatten flatten to to about about 45 45 degrees degrees in in the the southern southern part part of of the the pit pit near near the the synclinal synclinal axis. axis. Coarse-grained Coarse-grainedspecular specular hematite hematite was the most important important ore mineral mineral but but some some magnetite magnetite was also produced produced from from aa thin thin unit unit of of banded bandedchert-magnetite chert-magnetiteiron-formation iron-formationthat that formed formedaacontinuous continuousunit unit no no more more than a few tens of feet feet thick stratigraphically stratigraphically below below the hematitic hematitic jasper. Some Some iron Goodrich iron production production also came from highly highly ferruginous conglomerate conglomerate of the Goodrich Quartzite, mostly present as a lens lens as much much as several hundred hundred feet thick in in the southwest part part of the pit. Essentially Essentially all of the iron iron was deposited as primary sedimentary sedimentary accumulations. accumulations. The iron iron content content of the ore ore was no no greater than than typical of the Negaunee Negaunee elsewhere in the region. region. The economics economics of the deposit deposit were controlled controlled principally by the structural structural geometry geometry of the ore ore beds beds and and by by the the oxide oxide mineralogy mineralogy and and grain grain size. Lower Lower units units of the Neguanee, grunerite)- magnetite magnetite iron-formation, iron-formation, Neguanee, never mined, consist of silicate silicate (mostly (mostly grunerite)which which was was not not amenable amenable to to concentration concentration by by the the techniques techniques used used at at Republic. Republic. These These rocks, rocks, along along with three diabase diabase sills, underlie underlie the prominent prominent ridge ridge along the northeast northeast and and southeast flanks flanks of the pit pit where they dip dip nearly nearly vertically. The uppermost uppermost diabase diabase sill the orebody orebody (figs. (figs. 4-3, 4-3, 4-5). 4-5). The The unusual unusual strength strength and and stability stability of sill forms forms the the footwall of the this this metadiabase metadiabaseallowed allowed the the development development of of aa high high footwall footwall of of the the pit, pit, which which stood stood several several hundred hundred feet high high as a vertical vertical to slightly overhanging overhanging rock face. This This situation situation was was an an important important economic economic factor factor in in that that itit eliminated eliminated the the need need for for the the large large amount amount of of waste footwall waste rock rock removal removal that that would would have have been been necessary necessary to to maintain maintain aa more more typical typical footwall pit pit slope. slope. In In addition to the occurrence occurrence of the hematite hematite and and magnetite magnetite iron-formation, iron-formation, other other geologic geologic factors factors were critical critical in in enhancing enhancing the economics economics of the Republic Republic mine. The The geometry geometry of the syncline syncline created created the moderately-dipping moderately-dipping and thick sequence sequence of ironironformation formation along along the the keel, keel, which which was was required required to to extract extract ore ore with with an an economically economically permissible permissible amount amount of of removal removalof of underlying underlyingiron-silicate iron-silicateand anddiabase, diabase,and andoverlying overlying Goodrich Goodrich Quartzite Quartzite waste rock. rock. Also, the the high high degree degree of metamorphic metamorphicrecrystallization recrystallization was was vital vital in in enhancing enhancing the the liberation liberationand and concentration concentration of of iron iron minerals, minerals, in in that that grinding grinding to to very-fine very-finegrain grain size size was was not not required required to to allow allow separation separation of of iron-minerals iron-mineralsfrom from chert chert by by the the flotation flotationprocess processused usedat atRepublic. Republic. 92 �:f • • 4- • - • • • .1: • • • •;r. • :-•'.. :•' - • • -- - •.•• - - • . I— - • • -• • • • - :. Ygure 4-2. Wavy-bedded jaspilite typical of the ore zone for the Republic open pit. .ighter layers are specular hematite and darker layers are lenticular beds of ietamorphosed jasper. �Figure Figure 4-3. 4-3. The The Republic Republicopen open pit pit in in 1973. 1973. View View looking lookingSE SE along along the the NE NE limb limb of of the the Republic Republicsyncline. The high wall on the left side of the pit the upper upper contact contact of syncline. The high wall on the left side of the pit is is the of aa metadiabase metadiabasesill, sill,now nowdipping dippingvertically. vertically. Hard Hardores: ores: The Thefirst firstphase phaseofofmining miningatatRepublic Republicwas wasbased basedon onhigh-grade high-grade(60-65% (60-65%Fe) Fe) concentrations concentrationsof of specular specularhematite hematiteand andmagnetite, magnetite,which whichwere were referred referredto toas ashard hardore ore (fig. (fig.4-4), 4-4),inincontrast contrastto tothe theearthy earthymasses massesof ofiron ironoxides oxidesand andhydroxides, hydroxides,the thesoft softores, ores, widely widely mined minedin inthe the eastern easternparts partsof of the theMarquette Marquettedistrict. district. The Theorigin originof ofhard hardores oreshas has been investigated since the geologic studies of Van Hise and Bayley (1897), who were been investigated since the geologic studies of Van Hise and Bayley (1897), who were the thefirst firstto torecognize recognizeaaconnection connectionbetween betweenthe theNegaunee-Goodrich Negaunee-Goodrichunconformity unconformityand and occurrence occurrenceof of hard hardore. ore.They Theyproposed proposedthat thatoxidation oxidationof of siderite sideriteand andleaching leachingof ofsilica silica from fromthe theiron-formation iron-formationby bygroundwater groundwaterformed formedhematite hematiteconcentrations. concentrations.They They envisioned envisionedtectonism tectonism as as important importantin inproducing producingaapermeable permeablecrushed crushedzone zoneat at the the unconformity unconformityto toaccentuate accentuategroundwater groundwaterflow. flow. Later, Later,Van VanHise Hiseand andLeith Leith(1911) (1911) proposed surficialweathering weatheringand and proposedthe theclassic classictheory theorythat thatthe thehard hardores oresformed formedby bysurticial leaching leachingof of the theNegaunee NegauneeIron-formation, Iron-formation,during duringthe theuplift upliftpreceding precedingdepositon depositonofofthe the Goodrich Quartzite, and are paleosupergene concentrations; this weathered and Goodrich Quartzite, and are paleosupergene concentrations; this weathered and leached leachedmaterial materialwas was later laterdeformed deformedand andmetamorphosed metamorphosedto toproduce producethe thepresent presenthard hard ore. ore. This Thistheory theorywas was widely widely accepted acceptedand andmost mostrecently recentlysupported supportedby byGair Gair(1975) (1975) based based largely largelyon onobservations observationsin inthe the Cliffs CliffsShaft Shaftmine mineininlshpeming. Ishpeming.Others Othershave haveproposed proposedthat that the thehard hardores oresare areat atleast leastpartly partlyhydrothermal hydrothermal(Roberts (Robertsand andBartley, Bartley,1943; 1943;Crump, Crump,1948; 1948; Anderson, Anderson,1968; 1968;Marsden, Marsden,1968). 1968). AAcomprehensive comprehensivereexamination reexaminationof of the the hard hardores oresof of the theMarquette MarquetteRange Rangeby byCannon Cannon (1976), (1976),including includingcritical criticalrelationships relationshipsthen thenexposed exposedin inthe the Republic Republicpit, pit, suggested suggestedthat that there thereare aretwo twotypes typesofofhard hardore, ore,each eachformed formedby byaasubstantially substantiallydifferent differentset setofof processes. processes.He Herecognized recognizedaadistinction distinctionbetween betweendominantly dominantlyspecular specularhematite hematiteores, ores, 94 �possessed Penokean Penokean tectonic fabrics, and dominantly magnetite magnetite ores, which commonly possessed massive and appear to post-date which generally are massive post-date tectonism. The hematite ores show geologic relationships relationships that are fully consistent with the original original paleosupergene paleosupergene origin proposed by Van Hise and Leith and are still believed to record an interval interval of oxidative proposed hiatus between between the Negaunee Negaunee IronIronweathering and leaching during the stratigraphic hiatus Goodrich Quartzite. The geologic geologic map map of the Republic Republic area area published published by by formation and Goodrich (in Van Hise and Bayley, 1897) clearly distinguished distinguished hematite hematite and and magnetite Smyth (in separate ore lenses. lenses. Cannon Cannon types of ores, which occurr in distinct and to some extent separate documented that a similar duality of ore types is widespread in the western Marquette documented range, most particularly at the Greenwood and Champion mines. The magnetite ore is invariably post-tectonic, commonly commonly contain contain euhedral euhedral quartz quartz crystals crystals in vugs, vugs, and and occurs occurs Cannon proposed proposed that the magnetite magnetite ores formed formed from from aa within hematitic host rocks. Cannon hydrothermal fluid that was reducing with respect to the hematitic host rock. He suggested that fluids fluids released released by metamorphic metamorphic devolatilization of the iron-formation, iron-formation, suggested which was rich in both hydrous and carbonate minerals in its primary state, was the origin of the hydrothermal hydrothermal fluids. Metamorphism Metamorphism of the Republic Republic node node is is known known to have origin begun begun during the closing phases phases of Penokean Penokean deformation deformation but but to have have outlasted outlasted and reached its peak after deformation. Thus, the magnetite magnetite hard hard ores were interpreted interpreted to have been deposited shortly after formation of the Republic syncline and to be precipitates from reduced metamorphic fluids carrying ferrous iron from stratigraphically precipitates lower parts of the iron-formation iron-formation to the upper parts where reaction with hematite hematitc beds caused caused precipitation precipitationof magnetite. magnetite. Figure 4-4. Former in Republic pit showing onleft leftand Former exposure exposure in Republic pit showing wavy-bedded wavy-beddedjaspilite jaspilite on and magnetite hard ore on right. The hard truncates jaspilite bedding hard ore truncates bedding at a nearly nearly right angle. Within a few centimeters of the contact, much much of the jasper is is converted converted to to milky milky crystals have quartz and partly removed removed from the rock, creating vugs into into which quartz crystals grown. The loss of volume resulted in brecciation brecciation of the iron-formation, which was later healed and largely obliterated by magnetite deposition. Magnet is about 12 cm long. 95 �pit and mill The Republic pit mill metallurgical In 1947 Cleveland Cliffs Iron Co. began research on devising a viable metallurgical concentrating scheme scheme to upgrade upgrade the banded banded specular specular chert iron-formation iron-formationat at Republic Republic to a suitable grade of concentrate. concentrate. The crude crude ore composition composition was 38% 38% Fe, Fe, 42.5% Si02, SiOa, 0.033% P, P, 0.90% 0.90% MgO, MgO, 0.53% 0.53% CaO, CaO, 0.72% 0.72%A1203, A1203,0.03% Na20, NaaO,and and 0.04% 0.04% K20. K20.AA concentration process process was needed needed to produce a product with roughly 65% Fe and 5% Si02. The Company settled on a hot anionic flotation of the specularite after the crude Si02. was ground to 90% passing passing 325 mesh mesh size. After the board board of directors directors approved approved a new new mining operation at Republic, Republic, the company company teamed teamed with with three three partners partnerswho who would would consume & LL Steel Steel Corp., Corp., and and consume the pellet pellet product (i.e. Wheeling Pittsburgh, Pittsburgh, JJ & International Harvester Harvester Co.). Operations International Operations started started with with site site clearing clearingin in1952 1952foUowed followed by construction construction of a concentrator concentrator capable capable of producing producing an initial initial 600,000 long long tons tons (It) of concentrate. concentrate. Pelletization Pelletization (agglomeration) (agglomeration)was was initially initiallyconducted conductedat at the the Eagle EagleMills Millspellet pellet plant located located southwest of the City of Marquette Marquette starting starting in in 1956. 1956. In In 1962, 1962, a pelletizing facility located at the mine was brought on line with production increasing to 2.6 million It of pellets pellets per per year. year. The open pit was developed by a conventional bench-berm system from surface to an of +940 feet. A unique feature of the Republic ultimate depth of Republic Mine was the development of the vertical footwall on the northeast side of the pit that was vertical to slightly overturned overturned footwall referred required steel mesh screen referred to as the highwall (fig. 4-5). This distinctive design required spalled rock from falling into work areas. held in place by rock bolts to prevent spatted the pit crusher was relocated from from the pit crest to an During the middle 1970s the aditkhamber located located in the high high wall on the +1130 +I130 bench (lower left of fig. 4-5). A 28002800adit/chamber grade had had been been driven from surface surface to the chamber chamber to to house house foot-long gallery at 11% 11% grade foot-long the conveyor used to move the ore from the crusher to the plant plant stockpile (upper (upper right right of fig. 4-5). 4-5). Mining was conducted using conventional shovel-truck shovel-truck equipment equipment to to get the the ore to to the crusher. Initial Initial haulage haulage units units were 34 tons Euclid Euclid trucks. However, by the time the mine was idled idled in in 1981, 1981, 80-ton 80-ton units units were were standard. standard. Republic crude was extremely hard hard and and initial initial production production drilling drilling used used the the Linde LindeJet Jet Piercing machine machine in which fuel oil and spa11the the rock rock and oxygen oxygen were combusted combusted to to heat heat and and spall for drilling. During 970s the the mining equipment industry developed During the the 11970s developed rotary rotary machines machines capable of delivering 90,000 lbs. Ibs. of down pressure to the bit, which allowed the mine to change change over to conventional blast hole drilling. Blasting Blasting required required the use of ammonium nitrate and fuel oil (ANFO) at a high usage exceeding one pound per ton whereas other required results for half the powder factor. mines could get the required dewatering wells wells on on the the pit pit perimeter perimeter that that Rock stability at the mine was enhanced by dewatering drew down water keeping keeping it from the pit faces and and further stabilizing stabilizing the pit pit walls. This was especially important on the northwest side of the pit where the Michigamme Michigamme River had been partly diverted to allow pit development. 96 �Figure 4-5. The highwall at Republic. View is looking southeast. The steep rock face is the upper upper contact of a metamorphosed metamorphosed diabase diabase sill, which was emplaced emplaced at the base base of the oxide-facies ore unit. Other rock faces in upper upper left are underlying beds of magnetitegrunerite grunerite iron-formation, iron-formation,which were removed removed as waste. The units units now now dip vertically or are slightly overturned so that, in in places, places, the highwall highwall projects projects slightly outward over the pit. The two portals portals in in lower center are the access access to the primary primary crusher. Crushed Crushed ore ore was moved through an inclined moved to stockpile (on horizon horizon in upper right) by conveyor conveyor through inclined tunnel. The highwall highwall was about 300 feet high high at the time time of this this photograph photograph near near the the end end of pit pit operation. operation. Crude Crude ore underwent underwent three crushing crushing stages stages to provide provide a product product less less than than ½-inch %-inch size, which was fed to the grinding grinding section. Grinding Grinding consisted consisted of a conventional conventional rod rod mill mill with a steel rod rod charge charge to effect effect size size reduction. reduction. The The crude crude was then then sent sent to to aa ball ball mill mill containing containing small steel steel balls balls to complete complete the grinding grinding to aa size size suitable to liberate liberate ore ore minerals from gangue. The crude crude was discharged at 90% passing passing 325 mesh. Flotation Flotation using a fatty acid reagent separated the iron iron from the gangue gangue by by floating floating the iron iron minerals (anionic). The coarse nature of the product required required further grinding grinding to make make itit suitable for pelletizing. Concentrate Concentrate was reground reground in in ball ball mills, heated, heated, and and the pulp pulp was sent hot hot to roughers, roughers, cleaners cleaners and and scavengers. scavengers. The The final final product product was was dewatered, dewatered, balled, balled, and finally sent to the Allis Chalmers Grate Kiln system to be heated to 2440° F to Chalmers Grate Kiln system be heated 2440' F produce a tough pellet capable of withstanding handling and transport to the furnace. The product product was carried carried to Marquette Marquette by by rail rail and and then shipped shipped via lake lake cargo vessels vessels to steel furnaces in in the lower lower Great Great Lakes. Lakes. Scrubber Scrubber and and electrostatic electrostatic precipitators precipitators 97 �removed removed 99% 99% of the the particulate particulatematter matter from from the the discharge discharge air. air. Tailings Tailings from from the the process process settled in in vast settling settling ponds ponds located located southeast southeast of the the plant plant that that have have subsequently subsequently were settled been been converted converted to to viable viable wetlands. wetlands. From 1956 1956 to 1981 1981 the mine mine produced produced 62 62 million million tons tons of pellets pellets recovered recovered from from 145 145 From million million tons tons of of crude crude ore. ore. Considerable resources resources remain remain in in the ground ground at currently currently subeconomic status. The The Considerable resources, as as estimated estimatedby byCleveland ClevelandCliffs CliffsIron IronCo., Co., include includeboth bothspecular specularhematite hematiteore, ore, resources, the traditional traditionalore ore mined minedat at Republic, Republic,and and magnetite-silicate magnetite-silicateiron-formation, iron-formation,which which was was the not amenable amenable to concentration concentration by by the the process process used used at at Republic. Republic. The The estimated estimated not resources in million of long tons (MLT) of ore are: resources in million long tons (MLT) ore are: Ore Resource Grade SiOsininconc. cone. Oretype type Grade Fe Fe Recovery Recovery Fe Feininconcentrate concentrate Si02 Spec. hematite 63 MLT ML T 38% Fe 44% Spec. hematite 38% Fe 44%Wt. Wt.Rec. Rec. 65.0% 65.0%Fe Fe 5.00% 5.00% Mag. 60 MLT 27% Wt. 27%Fe Fe 33% 33% Wt,Rec. Rec. 67.0% 67.0% Fe Fe 5.80% Mag.-Silicate -Silicate 60 MLT 5.80% Talc is is common common in in footwall footwall ore ore in in the the area areaof of the the axial axial keel keelof of the the syncline. syncline. MgO MgO Talc analyses analyses range range from from 1% 1% to 4.7%. Schistose Schistoseconglomerates conglomeratescontain containsericite, sericite, chlorite, chlorite, epidote and and tourmaline. tourmaline. Most Most ore ore in in the the pit pit contained contained 0.20% 0.20% Ti02 TiOpbut but the the southwest southwestPark Park epidote City area area had had elevated elevated values values in in the the .50 .50 to to 1.65% 1.65%Ti02 Ti02as as rutile rutile associated associated with with hematite hematite City Mine Mine closure closureand and restoration restoration From tailings tailinas basin basin to to the the Republic RepublicWetlands Wetlands Preserve: Preserve:The The Republic RepublicMine Mine in in Marquette Marquette From County, Michigan Michiganceased ceasedoperations operationsinin1981, 1981,but butwas wasnot notofficially officiallyclosed closeduntil until1996. 1996. County, Planswere were made madeto to reclaim reclaimaasubstantial substantialportion portionofofthe theRepublic RepublicMine Mineas asaawetland wetland Plans mitigationproject projectto to serve serve the the needs needsof of the the nearby nearbyEmpire Empireand and Tilden Tilden mines minesand and other other mitigation Cliffs-managedproperties. properties. The The Cleveland-Cliffs Cleveland-CliffsIron IronCompany Companyand and its its partners partnersin in the the Cliffs-managed two active active mines mines agreed agreed to to proceed proceedwith with what what is is called called the the Republic Republic Wetlands Wetlands Preserve Preserve two (RWP). The The Michigan MichiganDepartment Departmentof of Environmental EnvironmentalQuality Quality and and the the U.S. U.S. Environmental Environmental (RWP). Protection Agency were involved from the inception of the project. Protection Agency were involved from the inception of the project. NorthernEcological EcologicalServices, Services,Inc. Inc.(NES) (NES)and andCliffs CliffsMining MiningServices ServicesCompany Company(CMSC) (CMSC) Northern formed the the project project team team involved involvedin in the the planning, planning, design, design, construction, construction, and and monitoring monitoring of of formed createdlrestoredon on iron iron the RWP RWPproject. project. Approximately Approximately650 650 acres acres of of wetlands wetlands were were created/restored the tailingsand andreuse reusewater water basins basinsat atthe theRepublic RepublicMine Mine(fig. (fig.4-6). 4-6). Another Another 1,650 1,650acres acresof of tailings wetlands and and uplands uplands were were included included in in the the RWP, RWP, bringing bringingthe the total total acreage acreage'to 2,300 wetlands to 2,300 acres. acres. Water Water levels levelsin in the the tailings tailings basins basins were were managed managedto to create create optimal optimal conditions conditions for for wetlandvegetation, vegetation, with with dormant dormantseeding seedingand andfertilizing fertilizingbeing beingdone, done, as aswell well as as aerial aerial wetland application application of of seed seed and and fertilizer fertilizer on on less less accessible accessible areas. areas. Over Over 250,000 250,000 trees trees were were planted plantedin inthe the wetlands. wetlands. 98 �Figure 4-6. Wildlife trail in a forested and emergent wetland developed on the former tailings basin tailings basin at the Republic Republic Mine, Mine, now now the the Republic RepublicWetlands WetlandsPreserve. Preserve. RWP completed its fifth, and final, year of monitoring monitoring and and the In 2002, phase I of the RWP wetland plant growth and wildlife use is nothing short of spectacular. Peregrine Peregrine falcons, a federal endangered endangered species, have have been been documented documented on a number of occasions using pair of bald bald eagles eagles nests nests there, as as well as as osprey osprey and and common common loons, loons, all the RWP. A pair state-threatened species. There is also a great blue blue heron heron nesting nesting colony, with approximately 60 nests active each year. Over 100 100 species of birds have been documented documented using the site. The land has been transformed from former mined lands to a diverse component component of the landscape landscape in about five years' time. The wetland credits credits that have not been been used to compensate compensate for unavoidable unavoidable wetland impacts at the Empire Empire and Tilden Tilden mines mines are in the process process of being being placed placed in in a wetland mitigation bank to be used for future mine-related mitigation mine-related projects projects in Marquette Marquette County. In summary, the RWP RWP is is a classic classic example example of how how the mining mining industry industry and and government government a valuable natural regulators can work together to reclaim former mine land and create 9 asset that benefits requirements. benefits area area wildlife and satisfies satisfies the mitigation mitigation requirements. FIELD FIELD TRIP TRIP STOPS STOPS Several Several previous previous ILSG ILSG field field trips trips have have visited visitedthe the Republic Republicarea. area. The Thefollowing following descriptions are taken largely from guidebooks guidebooks prepared prepared by by Cannon Cannon and Klasner Klasner (1972) and Cannon Cannon and and others others (1975). (1975). Stop Iron-formation at Stop 4-1. Negaunee Iron-formation at Kloman Klomanmine. mine. Kloman (also (also known known as Columbia) Columbia) Mine was a small, early mine that produced The Kloman about 95,000 tons of hard hard ore between between 1873 1873 and 1883. 1883. The ore body lay along the 99 �Negaunee Iron-formation Iron-formationand and Goodrich Goodrich Quartzite. Quartzite. The The pit pit is is visible visible contact with the Negaunee inside of the fenced area but is not available for examination because of safety concerns. The principal principal interest interest at this this stop stop is is the the 'arge, large, glacially glacially polished polishedoutcrop outcrop of of the the concerns. Negaunee Iron-formation Iron-formation lying just northeast northeast of the fenced fenced area. Here the Negaunee exhibits a small-scale interbedding of several different lithologic types of iron-formation. iron-formation.A A detailed detailed section section is is shown shown here here as as originally originally presented presented by by Cannon and Klasner Klasner (1972) and much much of the description description is is likewise likewise taken taken from that that Cannon earlier field guide. The outcrop outcrop is is on the northeast northeast limb limb of the the Republic Republic syncline. syncline. Beds Beds earlier N 45°W 45OW and anddip dip vertically. vertically. As As aa point pointof of reference referenceto tothe thedetailed detailedsection sectionthe the strike about N 42 feet feet on on the the section. section. The The large eye-bolt set into into the the outcrop outcrop corresponds corresponds to to the the bed bed at at 42 'arge Negaunee as seen here shows a marked lateral facies change from the Republic Republic open Whereas the the ore ore horizon horizon in in the the pit pit is is entirely entirely pit only about 3,000 feet along strike. Whereas with aa few tens tens of of feet feet of of chert-magnetite chert-magnetiteiron-formation iron-formationat at the the base, base,the the same same jaspilite, with ironchert-magnetite and and chert-magnetite-silicate chert-magnetite-silicate ironhorizon here contains many units of chert-magnetite formation interbedded interbedded with with the the jaspilite. jaspilite. correspondence between characteristics and mineralogy A close correspondence between bedding characteristics mineralogy suggests that the present mineralogy, although a product of sillimanite-grade mineralogy, product sillimanite-grade metamorphism, metamorphism, still still differences in the sediments, particularly reflects original differences particularly in oxidation state of the iron. Hematite-bearing units units are are typically typically wavy-bedded wavy-beddedand and contain contain red redor ormaroon maroonjasper, jasper, Hematite-bearing much much of which has abundant bright red red granules, possibly possibly originally oolites. This is in contrast to the magnetite-rich magnetite-richand and silicate-bearing silicate-bearingunits, units, which are are typically evenbedded. Presumably Presumably the wavy-bedded wavy-bedded hematitic rocks were deposited in relatively shallow water, above wave base, where currents were sufficiently intense to produce disturbed bedding and oolites, and the water was sufficiently sufficiently oxygenated to result in a disturbed even-bedded magnetite and silicate rocks, on the thoroughly oxidized sediment. The even-bedded other hand, are presumed presumed to have have formed formed in in deeper deeper water, below wave base, where a combination of quiet bottom bottom conditions and relatively unoxygenated unoxygenated water allowed the accumulation of ferrous ferrous iron this is is so, so, the rocks rocks here here iron minerals minerals in in uniform uniform layers. layers. IfIf this indicate indicate deposition deposition in progressively shallower shallowerwater severalfluctuations eitherinin in progressively water with with several fluctuationseither depth of water or depth of wave action action to produce produce the interlayering interlayering of lithologic types in in the transition zone between the dominantly ferrous sediments at the base of the section transition between sediments base and the ferric sediments sediments at the top of the section. section. The correspondence correspondence between between bedding bedding characteristics characteristics and mineralogy mineralogy is convincing evidence that these rocks represent represent a primary primary oxide facies facies of iron-formation iron-formationand and that the the specularite and magnetite magnetite are metamorphic metamorphic derivatives derivatives of primary primary hematite hematite and magnetite or some precursor minerals with similar oxidation states. Some minerals that are considered formed by diagenetic or early metamorphic considered primary may have formed metamorphic changes; changes; however, the the oxidation oxidation state state of of each bed must reflect the composition of bottom or interstitial interstitial waters, for adjacent beds beds are are commonly commonly of markedly markedly different different oxidation oxidation states. The relationships relationships shown in this outcrop were instrumental instrumental in the recognition recognition that some iron-formation is a primary facies of iron-formation hematitic iron-formation iron-formation (James, 1954). 1954). 100 �____ _______ feet GoodrichQuartzite Quartzite Goodrich meters . 0 unconformity EXPLANATION EXPLANATION massivespecularite specularite with with variable Hard ore: massive magnetite and amounts of magnetite and little little or or no no chert. chert. 5 :-:: yq ,--- Wavy-bedded discontinuous beds Wavy-bedded jaspillite: discontinuous beds jasper or or jasper-mantled jasper-mantled chert, much much with with of jasper interbedded with with specularite granular texture, interbedded layers with minor to moderate amounts of layers with moderate amounts magnetite. to22 inches inchesthick. thick. magnetite.Beds Beds typically typically11to 10 c 50 --H E Even-bedded chert-magnetite chert-magnetite iron-formation: iron-formation: typically in 1/2 to to 11 inch inch thick. thick. Chert Chert is is typically in beds beds 1/2 white or gray and interbedded magnetite is white interbedded magnetite is fine-grained and fine-grained andmassive. massive. 20 — - —1—— -- Even-bedded chert-magnetite-silicate chert-magnetite-silicate iron-formation: similar similar to to chert-magnetite chert-magnetite iron-formation: iron-formation iron-formationbut butwith withaaselvage selvage of of grunerite grunerite at chert-magnetite chert-magnetite contacts. contacts. 25 1±TTIT chert-silicate iron-formation: iron-formation: Even-bedded chert-silicate chert and and grunerite grunerite with with thin thin interlayered chert of magnetite magnetite within within grunerite grunerite laminae of layers layers / —, , iron-formation: grunerite Silicate-magnetite iron-formation: grunerite with magnetite; with laminae laminae and and disseminations of magnetite; non-cherty. non-cherty. 14, b - - 4 -"i.kLi><-!" covered covered Figure 4-7. Detailed stratigraphic section section across across the outcrop outcrop of Negaunee NegauneeIron-formation Iron-formation at the Kloman Kloman mine mine (from (from Cannon Cannon and and Klasner, Klasner, 1972). 1972). The rocks rocks here here were metamorphosed metamorphosedto to sillimanite sillimanite grade grade during during the the Penokean Penokeanorogeny orogeny (James, 1955), as indicated by the coarse grain size of chert and by mineral (James, 1955), as indicated by the coarse grain size of chert and by mineral assemblages assemblages in in nearby nearby pelitic pelitic and and mafic mafic rocks. rocks. Of particular particular interest interest at at this this outcrop outcrop is is the the 101 �lack of equilibration of oxidation states between between adjacent units units in spite of the intense metamorphism. metamorphism. Dominantly Dominantly hematitic units are in sharp contact with dominantly magnetitic units, and although hematitic beds are nowhere in direct contact with silicatebearing beds, they are separated by only thin beds in many places. These relationships bearing attest to the inability of metamorphic metamorphic fluids to induce induce widespread oxidation or reduction of solid phases and are a classic illustration illustration of rocks in which the chemical potential potential of oxygen during metamorphism metamorphism was buffered buffered by the solid phases. 4-2. Michigamme Michigamme Formation Formation garnet-amphibole garnet-amphibole schist. schist. Stop 4-2. roadcut on the east east side side of Highway Highway 95 95 shows shows tightly tightly folded folded schist of the Michigamme Michigamme A roadcut Formation, which here is mostly an iron-rich meta-argillite, meta-argillite, now consisting of biotitegarnet-amphibole (grunerite) (grunerite) schist containing a few inch-thick inch-thick layers layers of impure quartzite. Although the rock is in the sillimanite zone of metamorphism, metamorphism, sillimanite is not present here because of the lack of appropriately aluminous compositions. Blades and rosettes of light-colored rosettes light-colored iron-amphibole iron-amphibole are common and have been mistaken for sillimanite in field examination of this outcrop by many geologists. It is interesting interesting to note Harold James James who defined defined the Republic Republic metamorphic metamorphic node, and the sillimanite zone that Harold its core, in in his his classic classic paper paper on zones of regional regional metamorphism metamorphism (James, (James, 1955) 1955) never never at its observed sillimanite in outcrops. The only occurrence was in a glacial erratic boulder of of Michigamme-type schist, which he presumed was transported only a short distance. The Michigamme-type zone was defined more on the basis of assemblages in mafic rocks than on the distribution of sillimanite. Later, Later, detailed detailed mapping mapping of the region region (Cannon (Cannon and and Klasner, Klasner, distribution (fibrolite) in in one one outcrop outcrop of of the the Michigamme MichigammeFormation Formationseveral several 1976) did find sillimanite (fibrolite) miles northeast of this locality. An additional sillimanite occurrence was reported in drill core about three miles miles northwest northwest of of here here by by Haase Haase(1979). (1979). This outcrop outcrop is is approximately approximately on the axis of the Republic Republic syncline. Minor folds with attenuated limbs are common amplitudes much greater than wavelengths and greatly attenuated and and reflect reflect the gross gross geometry geometry of of the the Republic Republictrough, trough, which which along along the the highway highway is is estimated estimated to be be about about 5,000 feet feet deep deep by by gravity gravity models models (Klasner (Klasner and and Cannon, 1974) 1974) but is only about 3,000 feet wide. The folding is markedly non-cylindrical at outcrop scale, and domains of homogeneous homogeneous strain are very small, being measurable measurable in a few tens tens of square square feet. feet. Although Although most most minor minor folds folds plunge plunge northwest northwest in in accord accord with with the the plunge of the Republic Republic syncline, the plunge of minor folds vary from about 15 15 to 65 degrees. degrees. The The non-cylindrical non-cylindrical nature nature of the folding folding may may be be aa reflection reflectionof an an earlier earlier folding, which has has been been strongly overprinted overprinted by by the development development of the Republic Republic syncline. The style of folding roadcut folding is is especially especially well shown near the north north end of the roadcut (fig. 4-8) where a 13-inch-thick quartzite bed bed is is repeated repeated many many times by folds. Axes 1- to 3-inch-thick of adjacent folds, only a few inches apart, have plunges that diverge by as much as 60 degrees. degrees. At the next next stop stop (stop (stop 4-3) 4-3) we will see a major major contrast contrast between between the high high degree degree of structures seen here and their near absence in nearby Archean penetrative Penokean Penokean structures basement rocks. basement rocks. 102 �Figure 4-8. Vertical face about 1 1 meter high high showing tight folds in Michigamme Michigamme biotitie-garnet Formation at stop 4-2. Folds are shown by a thin quartzite layer (light) in biotitie-garnet schist. Note Note thickened thickened hinge hinge regions regions and and attenuated attenuated limbs. limbs. Fold Fold at right right is is completely completely dismembered, a geometry geometry reflecting reflecting the the Republic Republic syncline syncline itself. itself. 4-3. Archean Archean gneiss gneiss and younger younger dikes. Stop 4-3. This roadcut roadcut on the west side of Highway Highway 95 near near the intersection intersection with Old Old Highway Highway 95 shows a widespread variety of granitic gneiss, which makes makes up part of the southern southern complex, complex, the basement basement on on which Paleoproterozoic Paleoproterozoic strata strata were deposited. The most most abundant abundant rock type in in the southern southern complex complex is is aa coarsely coarsely megacrystic megacrystic granite, granite, named named the Bell Bell Creek Creek Gneiss Gneiss by Cannon Cannon and and Simmons Simmons (1973). (1973). Rock Rock typical typical of this unit unit is is exposed roadcut. The The rocks rocks near near the the center center exposed in the northern northern and and southern southern parts parts of this this roadcut. are finer-grained finer-grained and and somewhat sheared sheared granite. granite. The The relationships relationships in in the southern southern part part of the outcrop outcrop are are sketched sketched in in figure figure 4-9 4-9 and and illustrate illustratetwo two major major periods periods of of orogeny orogeny that that affected Archean rocks; rocks; the the older older being beingan an intense intense Late Late Archean Archean folding folding and and the the affected the Archean younger being being non-penetrative non-penetrative deformation deformation during during the Penokean Penokean orogeny. orogeny. The The oldest oldest rock is the granitic gneiss, which was deformed and metamorphosed metamorphosed in the Archean event. Northwest-trending Northwest-trendingplanar planar structures structures are are shown shown mostly mostly by by preferred preferred orientation orientation of large microcline megacrysts and, in places, by a subtle compositional layering expressed expressed as variations in in abundance abundance of the megacrysts. megacrysts. A northeast-trending northeast-trending truncates the northwest-trending porphyritic dike of metadiabase truncates northwest-trending structures. The dike trends roadcut exaggerating exaggerating its its true true thickness. thickness. Typically, Typically, such such dikes dikes trends subparallel to the roadcut are no no more more than a few tens tens of feet feet thick. thick. This This dike dike truncates truncatesthe the granite granite foliation, foliation, but butisis metamorphosed to a grade typical of this part of the Republic massive, although metamorphosed Republic 103 �metamorphic metamorphic node. Thus, it must must have have been been emplaced emplaced after after the Archean deformation deformation but before the Penokean Penokean metamorphism. metamorphism. Its Its massive massive nature, nature, including including preserved preserved diabasic texture in thin section, and its straight trace indicates indicates that itit was not not deformed deformed during the Penokean Penokean orogeny, even though its its emplacement emplacement must must predate predate the orogeny. orogeny. Such dikes are very common throughout the southern southern complex complex and consistently show these same relationships of retaining retaining planar planar dike dike geometry geometry and relict diabasic textures. Deformation, Deformation, presumably presumably of Penokean Penokean age, is is seen seen in in some dikes as sheared sheared margins, margins, but even in those cases, the planar dike geometry geometry is not not altered. Good Good examples examples of this can be seen in other roadcuts roadcuts north north of here here heading heading toward Humboldt. Humboldt. The occurrence occurrence of such planar metadiabse metadiabse dikes at literally literally hundreds hundreds of localities throughout the southern complex is prime evidence that the complex was not penetratively deformed basement during the Penokean Penokean orogeny. Rather, Penokean Penokean deformation deformation of the Archean basement appears to have been been accomplished by relative movement between discrete, rigid, faultbounded blocks. This indicates indicates that the intense intense deformation deformation of Paleoproterozic Paleoproterozic strata, does not not extend extend into into the basement. The The fault blocks blocks of such as just seen at stop 4-2, does Archean rocks rocks appear to have have provided a rigid rigid form around around which the Paleoproterozoic Paleoproterozoic strata were molded. In In the case of the Republic Republic trough, the structure with respect respect to Archean rocks is a deep, narrow narrow graben graben between between two high-angle high-angle reverse faults. The syncline developed in the Paleoproterozoic rocks as a result of their compression between the two bounding fault uplifts. Estimates Estimates of metamorphic metamorphic pressures pressures by Hasse Hasse (1979) (1979) and Attoh and Klasner Klasner (1989) (1989) indicate indicate that the Republic Republic area was buried buried beneath kilometers of strata during Penokean roughly eight kilometers Penokean deformation and was heated to 550' to 600° metamorphic conditions, conditions, which slightly postdated postdated temperatures temperatures of 5500 600°C at peak metamorphic the major deformation. Under Under those conditions the Archean granitic gneisses gneisses apparently apparently did not deform plastically, but rather retained retained considerable strength strength so that the shape shape of fault-bounded basement the individual fault-bounded basement blocks blockscontrolled controlledthe the geometry geometryof of structures structuresin inthe the overlying overlying strata. strata. roadcut is is a Mesoproterozoic Mesoproterozoic diabase dike related related to the A final feature in this roadcut Midcontinent rift and part of the Baraga dike swarm of reversed magnetic polarity dikes intruded has a chilled chilled contact against both the granitic intruded at roughly roughly 1.1 Ma. The dike has gneiss and and metadiabase metadiabase dike virtually unmetamorphosed. unmetamorphosed. dike and and is is virtually 104 �or 0 0 0 '0 0 ip 10 feet feet 9O M Figure Figure 4-9. Sketch Sketch map map of southern southern part part of of roadcut roadcut showing showing relationships relationshipsbetween between Archean granitic gneiss and diabase dikes of two different ages. Archean granitic gneiss and diabase dikes of two different ages. Ref erences References Anderson, JJ G, G, 1968, 1968, The The Marquette Marquettedistrict, district, in inRidge, Ridge,J. J. D. D.ed., ed., Ore Oredeposits depositsof of the the United United States States 1933-1967 1933-1967 (Graton-Sales (Graton-SalesVol.): Vol.): New New York, York, American American Institute Instituteof of Mining, Mining, Metallurgical, Metallurgical, and Petroleum Petroleum Engineers, Engineers, v. 1, p.508-517. p. 508-517. K, and and Klasner, Klasner, J.S., J.S., 1989, 1989,Tectonic Tectonicimplications implicationsof of metamorphism metamorphismand andgravity gravity Attoh, K, field in in the the Penokean Penokean orogen orogen of of northern northernMichigan: Michigan:Tectonics, Tectonics,v. v. 8, 8, p. p. 911-933. 91 1-933. field Brooks, T.B., 1873, 1873, Iron-bearing Iron-bearingrocks rocks(economic): (economic):Michigan MichiganGeological GeologicalSurvey, Survey,Upper Upper Brooks, Peninsula, Peninsula, v. v. 1, 1,pt. pt. 1, 1,319 319p. p. Cannon, inYoung, Young, G.M., G.M., ed., ed., Cannon, 1973, 1973, The The Penokean Penokean orogeny orogenyin in northern northernMichigan, Michigan, in Huronian stratigraphy stratigraphy and and sedimentation: sedimentation:Geological GeologicalAssociation Associationof of Canada Canada Special Special Huronian Paper Paper 12, 12, p.251-271. p. 251-271. Cannon, Cannon, W.F., 1975, 1975,Bedrock Bedrockgeologic geologic map mapof ofthe theRepublic Republicquadrangle, quadrangle,Marquette Marquette County, Michigan: Michigan: U.S. U.S. Geological Geological Survey Survey Miscellaneous Miscellaneous Investigations InvestigationsSeries Series map map I-I862, 862, scale scale 1:24,000. 1:24,000. 105 �1976, Hard Hard iron iron ore ore of of the the Marquette MarquetteRange, Range, Michigan: Michigan: Economic Economic Cannon, W.F., 1976, Geology, v. 71, P. p. 1012-1028. 1012-1028. and Klasner, Klasner, J.S., 1972, 1972, Guide Guide to to Penokean Penokean deformational deformationalstyle style and and Cannon, W.F., and regional metamorphism metamorphismof the the western western Marquette MarquetteRange, Range,Michigan: Michigan:Proceedings Proceedingsofof18th 18th Institute on Lake Lake Superior Superior Geology, v. 18, 18, p. B1-B38. B1-B38. Annual Institute and Kiasner, Klasner, J.S., 1976, 1976, Geologic Geologic map map and and geophysical geophysical interpretation interpretationof of Cannon, W.F., and the Witch Witch Lake Lake quadrangle. quadrangle. Marquette, Marquette, Iron, Iron, and and Baraga BaragaCounties, Counties, Michigan: Michigan: U.S. U.S. Geological Survey Miscellaneous 1:62,500. Geological Miscellaneous Investigation InvestigationSeries Series Map Map 1-987, 1-987, Scale 1 :62,500. Cannon, W.F., and and Simmons, Simmons, G. G. C., C., 1973, 1973, Geology Geology of of part part of of the the southern southerncomplex, complex, Marquette district, Michigan: Journal of Research of the U.S. Geological Geological Survey, v. 1, p. 165-172. 165-1 72. Gair, J.E., Kiasner, Klasner, J.S., J.S., and and Boyum, Boyum, B.H., B.H., 1975, 1975, Marquette MarquetteIron IronRange: Range: Cannon, W.F., Gair, Proceedings of 21St Proceedings 21'' Annual Institute on Lake Superior Geology, v. 21,p. p.125-1 125-174. v.21, 74. Crump, R.M., 1948, Ph.D. 1948, Origin Origin of hard hard iron iron ores ores of the the Marquette Marquette district: district: unpublished unpublishedPh.D. dissertation, University of Wisconsin-Madison, Madison, Wisconsin, 87 p. dissertation, University Madison, 87 J.W., and Whitney, J.D., 1851, Foster, J.W., 1851, Report Report on on the the geology geology of of the the Lake Lake Superior Superior land land district, part 2, the iron region, together with the general geology: geology: U.S. U.S. 32nd 32'' Congress, Congress, Special Session, Session, Senate Senate Executive Executive Document, Document,v. v. 3, 3, no. no.4, 4, 406 406p. p. Gair, J.E., J.E., 1975, 1975, Bedrock geology and ore deposits deposits of the Palmer quadrangle, Marquette County, Michigan: U.S. Geological Geological Survey Survey Professional ProfessionalPaper Paper769, 769, 159 159p. p. C.S., 1979, Metamorphic petrology of the Negaunee Iron-formation, Haase, C.S., Iron-formation, Marquette Marquette district, northern northern Michigan: Michigan: Ph. Ph. D. D. Dissertation, Dissertation, Indiana Indiana University, University, 246 p. Hoffman, M.A., M.A., 1987, The southern complex: geology, geochemistry, mineralogy mineralogy and mineral chemistry of selected uranium- and thorium-rich granites: unpub. Ph. D. dissertation, dissertation, Michigan Michigan Technological Technological University, Houghton, Houghton, Michigan, 382 p. James, H.L., 1954, 1954, Sedimentry Sedimentry facies facies of iron-formation: iron-formation:Economic Economic Geology, Geology, v. v. 49, 49, p. p. 235-293. 235-293. James, H.L, H.L., 1955, 1955,Zones Zonesof of regional regionalmetamorphism metamorphismin in the the Precambrian Precambrianof of northern northern Michigan: Geological Geological Society Society of America America Bulletin, Bulletin, v. v. 66, 66, p.1455-1488. p.1455-1488. Kiasner, J.S. and Cannon, W.F., W.F., 1974, Klasner, J.S. 1974, Geologic interpretation interpretation of gravity gravity profiles profiles in in the western Marquette Marquette district, district, northern northern Michigan: Michigan: Geological Geological Society Society of America Bulletin, v. 8. 85, p. p. 213-21 213-218. Marsden, R.W., 1968, 1968, Geology Geology of the iron iron ores ores of the the Lake Lake Superior Superior region region in in the the united united in Ridge, J.D., ed., ed., Ore Ore deposits depositsof of the theUnited UnitedStates States1933-1 1933-1967 967 (Graton-Sales (Graton-Sales States, in Vol.): New York, American Institute Vol.): Institute of Mining, Metallurgical Metallurgical and Petroleum Petroleum Engineers, v. 1, p 489-507. 489-507. 106 �M.W., Roberts, H.M., and Bartley, M.W ., 1943, 1943, Hydrothermal replacement in deep seated iron ore deposits deposits of the Lake Lake Superior region: region: Economic Economic Geology, v. 38, p.1-24. p.1-24. Swineford, A.P., 1871, 1871, Swineford's Swineford's history historyof of the the Lake LakeSuperior Superioriron irondistrict-its district-itsmines minesand and furnaces: Marquette, Michigan, Marquette Marquette Mining Mining Journal, 98 p. Taylor, W.E.G., 1967, 1967, The The geology geology of of the the lower lower Precambrian Precambrianrocks rocks of of the the ChampionChampionRepublic area of upper upper Michigan: Michigan: Northwestern NorthwesternUniversity University Report Report 13, 13, 33 33 p. p. Van Hise, Hise, C.R., and and Bayley, Bayley, W.S., W.S., 1897, 1897,The TheMarquette Marquetteiron-bearing iron-bearingdistrict districtof ofMichigan: Michigan: Geological Survey Monograph U.S. Geological Monograph 28, 608 608 p. p. Van Hise, C.R., and and Leith Leith C.K., 1911, 1911, The geology of the Lake Lake Superior Superior region: region: U.S. U.S. Geological Survey Monograph Geological Monograph 52, 641 p. p. 107 ������Proceedings Volume 49 PARTI - PROGRAMS AND ABSTRACTS �INSTITUTE ON LAKE LAKE SUPERIOR GEOLOGY GEOLOGY 49TH ANNUAL MEETING MAY 7-11, 2003 IRON MOUNTAIN, MICHIGAN HOSTED BY: BY: LAUREL G. G. WOODRUFF AND WILLIAM WILLIAM F. LAUREL WOODRUFF F. CANNON CANNON Co-Chairs Co-Chairs U.S. GEOLOGICAL SURVEY U.S. GEOLOGICAL SURVEY With assistance Technological University assistance from Michigan Michigan Technological University and John John Gartner, Gartner, Coleman Coleman Engineering Engineering Company Company Volume Volume 49 49 —Proceedings Proceedingsand and Abstracts Abstracts Part 1 edited by Compiled and edited by Laurel Laurel Woodruff, Woodruff, U.S. U.S. Geological Geological Survey Survey and and Theodore Bornhorst, Bornhorst, Michigan Michigan Technological Technological University University Cover Photo: Cover Photo:Berkshire BerkshireShaft, Shaft,Menominee Menominee Range, Range, Michigan. Michigan. Photo from the Michigan Technological Technological University University Mining Mining Engineering EngineeringDepartment DepartmentCollection. Collection. �49TH INSTITUTE ON LAKE SUPERIOR GEOLOGY 4gTH GEOLOGY VOLUME VOLUME49 49CONSISTS CONSISTS OF: OF: PART 1 1::PROGRAM AND PART PROGRAM AND ABSTRACTS ABSTRACTS PART 2: 2: FIELD TRIP PART FIELD TRIPGUIDEBOOK GUIDEBOOK OVERVIEW: PALEOZOIC PALEOZOICSTRATIGRAPHY STRATIGRAPHYAND AND TECTONICS TECTONICS ALONG THE NIAGRA SUTURE ZONE, ZONE, MICHIGAN AND WISCONSIN 1: PEMBINE-WAUSAU PEMBINE-WAUSAUMAGMATIC MAGMATICTERRANE TERRANE TRIP 1: MENOMINEEIRON IRONDISTRICT DISTRICT TRIP 2: MENOMINEE TRIP TRIP 3: 3:STRATRIGRAPHY STRATRIGRAPHYAND ANDSTRUCTURE STRUCTUREOF OFTHE THEIRON IRONRIVER RIVER—CRYSTAL CRYSTAL FALLS FALLS BASIN BASIN TRIP TRIP 4: 4: LIFE LIFECYCLE CYCLEOF OFAN ANIRON IRONDEPOST DEPOST— - THE THE REPUBLIC REPUBLIC MINE MINE RESTORATION FROM ORE GENESIS TO MINE RESTORATION to material in Part 1 should should follow follow the Reference to the example example below: below: Rogala, B., Fralick, Fralick, P., and Borradaile, G., 2003, A magnetostratigraphic magnetostratigraphicand and secular secular variation varittion 49th study of the Sibley Sibley Group Group [abstract]; [abstract]; Institute Institute on Lake Lake Superior Geology Geology Proceedings, Proceedings, 49 Annual Annual Meeting, Meeting, Iron Iron Mountain, Mountain, Ml, MI, v. v. 49, 49, part part 1, 1, p. p. 65-66. 65-66. 49th Published by the 4gth Institute on Lake Superior Geology and distributed distributed by Published Institute by the Secretary-Treasurer: ILSG Secretary-Treasurer: Mark Jirsa (through (through 2003) 2003) Minnesota Minnesota Geological Geological Survey 2642 University University Avenue Avenue St. Paul, MN 551 55114-1057 14-1057 USA USA @tc.umn.edu JirsaOOl @tc.umn.edu In 2004 contact: contact: Peter Hollings Hollings Lakehead University University Department Department of Geology Geology Thunder Bay, ON P7B P7B5E1 5E1 CANADA peter.hollinas@ lakeheadu.ca Deter.hollincl@lakeheadu.ca I LSGwebsite: website: httr://www.ilscjeolociy.orci htt~://www.ilsaeoloav.org ILSG ISSN 1042-9964 1042-9964 �CONTENTS CONTENTS PROCEEDINGS VOLUME VOLUME 49 PART 1—PROGRAM I-PROGRAM AND AND ABSTRACTS ABSTRACTS Institutes Institutes on Lake Lake Superior Superior Geology, 1955-2003 1955-2003............................................................ iv Constitution of the Institute Constitution Institute on on Lake Lake Superior Superior Geology Geology ...................................................vi vi By-Laws vii By-Laws of the Institute Institute on Lake Lake Superior Geology Geology ....................................................... ... Membership Criteria Criteria ...................................................................................................... VIII viii ix Goldich Medal Medal Guidelines Guidelines............................................................................................... ix Goldich Medal Committee ............................................................................................... xx Past Goldich Medallists Medallists .................................................................................................. xi Citation xii Citation for 2003 2003 Goldich Goldich Medal Medal Recipient Recipient ..................................................................... xii Eisenbrey Student Eisenbrey Student Travel Travel Awards Awards ................................................................................. xiv Student Student Travel Award Application Application Form Form ....................................................................... xiiv Student Student Paper Paper Awards Awards ................................................................................................... xv Student xv Student Paper Paper Awards Committee Committee ................................................................................ Session Session Chairs Chairs .............................................................................................................. xv Board xvi Board of Directors Directors ........................................................................................................ xvi Local xvi xvi Local Committees Committees......................................................................................................... Banquet xvi Banquet Speaker Speaker.......................................................................................................... xvi Report Report of the Chair of the the 48th 48th Annual Annual Meeting Meeting............................................................ xvii Program xxi xxi Program ....................................................................................................................... List of Contributors xxii Contributors ....................................................................................................... ... Abstracts ................................................................................................................... xxviii Abstracts XXVIII III iii �INSTITUTES LAKE SUPERIOR GEOLOGY INSTITUTES ON LAKE SUPERIOR GEOLOGY # YEAR PLACE PLACE CHAIRS CHAIRS 1 1955 Minneapolis, Minnesota Minnesota C.E. Dutton Dutton 2 1956 Houghton, Michigan Houghton, Michigan A.K. Snelgrove Snelgrove 3 1957 East Lansing, Michigan Michigan B.T. Sandefur 4 1958 Duluth, Minnesota Minnesota R.W. Marsden Marsden 5 1959 Minneapolis, Minnesota G.M. Schwartz & C. Craddock Craddock 6 1960 Wisconsin Madison, Wisconsin Cameron E.N. Cameron 7 1961 Port Arthur, Ontario Ontario E.G. Pye Pye 8 1962 Houghton, Michigan Michigan A.K. Snelgrove A.K. Snelgrove 9 1963 Duluth, Minnesota Minnesota H. Lepp Lepp 10 1964 lshpeming, Michigan Ishpeming, Michigan A.T. Broderick Broderick 11 1965 St. Paul, Paul, Minnesota Minnesota P.K. Sims & R.K. Hogberg Hogberg 12 1966 Sault Ste. Marie, Marie, Michigan Michigan R.W. White 13 1967 Lansing, Michigan East Lansing, Michigan W.J. Hinze Hinze 14 1968 Superior, Superior, Wisconsin Wisconsin A.B. Dickas A.B. Dickas 15 1969 Oshkosh, Wisconsin Wisconsin LaBerge G.L. LaBerge 16 1970 Thunder Bay, Ontario Ontario M.W. Bartley E. Mercy Mercy Bartley & E. 17 1971 Duluth, Minnesota Minnesota D.M. Davidson Davidson 18 1972 Houghton, Houghton, Michigan Michigan J. Kalliokoski Kalliokoski 19 1973 Madison, Wisconsin Wisconsin M.E. Ostrom Ostrom 20 1974 Sault Ste. Marie, Ontario P.E. Giblin Giblin 21 1975 Marquette, Marquette, Michigan Michigan J.D. Hughes Hughes 22 1976 St. Paul, Minnesota Minnesota M. Walton 23 1977 Thunder Bay, Ontario Ontario M.M. Kehlenbeck Kehlenbeck 24 1978 Milwaukee, Wisconsin Wisconsin G. Mursky Mursky 25 1979 Duluth, Duluth, Minnesota Minnesota D.M. Davidson Davidson 26 1980 Eau Claire, Wisconsin Wisconsin P.E. Myers Myers 27 1981 East Lansing, Michigan Michigan W.C. Cambray Cambray 28 1982 International International Falls, Falls, Minnesota Minnesota Southwick D.L. Southwick 29 1983 Houghton, Houghton, Michigan Michigan T.J. Bornhorst Bornhorst iv �30 1984 Wausau, Wausau, Wisconsin Wisconsin G.L. LaBerge LaBerge 31 1985 Kenora, Ontario Ontario G.E. C.E. Blackburn Blackburn 32 1986 Wisconsin Wisconsin Rapids, Rapids, Wisconsin Wisconsin J.K. Greenberg Greenberg 33 1987 Wawa, Wawa,Ontario Ontario 34 1988 Marquette, Michigan Marquette, Michigan J. S. Klasner Klasner 35 1989 Duluth, Minnesota Minnesota J.C. Green Green 36 1990 Thunder Bay, Bay, Ontario Ontario M.M. Kehlenbeck Kehlenbeck 37 1991 Wisconsin Eau Claire, Wisconsin P.E. Myers Myers 38 1992 Hurley, Wisconsin A.B. Dickas A.B. Dickas 39 1993 Eveleth, Minnesota Minnesota D.L. Southwick Southwick 40 1994 Houghton, Michigan Michigan T.J. Bornhorst Bornhorst 41 1995 Marathon, Ontario Ontario M.C. Smyk 42 1996 Cable, Wisconsin Wisconsin L.G. Woodruff 43 1997 Sudbury, Ontario Ontario R.P. Sage & W. Meyer Meyer 44 1998 Minneapolis, Minneapolis, Minnesota Minnesota J.D. Miller Miller & M.A. M.A. Jirsa Jirsa 45 1999 Marquette, Marquette, Michigan Michigan T.J. Bornhorst R.S. Regis Regis Bornhorst & R.S. 46 2000 Thunder Bay, Ontario Ontario S.A. Kissin & P. Fralick Fralick 47 2001 Madison, Wisconsin Wisconsin B.A. Brown Brown M.G. Mudrey, Jr. & B.A. 48 2002 Kenora, Ontario Ontario P. Hinz & R.C. Beard Beard 49 2003 Iron Iron Mountain, Mountain, Michigan Michigan L.G. Woodruff & W.F. Cannon Cannon E.D. Frey & R.P. Sage E.D. V �__________(some CONSTITUTION SUPERIOR GEOLOGY CONSTITUTION OF THE INSTITUTE ON ON LAKE LAKE SUPERIOR GEOLOGY (Last 1997) (Last amended amended by by the the Board—May Board-May 8, 8,1997) Article Article II Article Article IIII Article Ill Article III Name Name The name name of the the organization organization shall shall be be the the "Institute "Instituteon on Lake Lake Superior Geology". Geology". Objectives Objectives The objectives objectives of this this organization organization are: are: A. To Toprovide provideaameans meanswhereby wherebygeologists geologistsin inthe the Great GreatLakes Lakesregion regionmay may exchange exchange ideas ideas and and scientific scientificdata. data. B. To Topromote promotebetter betterunderstanding understandingof of the the geology geology of of the the Lake LakeSuperior Superior region. region. C. To plan and conduct geological field trips. To plan and conduct geological field trips. Status Status No part of the income income of the organization organization shall insure insure to the the benefit benefit of of any any member or individual. individual. In the event of dissolution, dissolution, the assets assets of the the organization organization distributed to shall be distributed (some tax free free organization). organization). (To avoid avoid Federal Federal and State State income income taxes, the organization organization should should be be not not only only "scientific" 'scientific" or "educational, "educational, but but also also "non-profit") "non-profit") Article Article IV IV Article V Article Article VI Article VI Article VII Article VII Article Article VIII VIII Minn. Stat. Anno. 290.01, subd. 44 Minn. Stat. Anno. 290.05(9) 1954 Internal 1954 Internal Revenue RevenueCode Codes.501 s.501(c)(3) (c)(3) Membership Membership The membership membership of the the organization organization shall shall consist consist of of persons personswho who have have registered for an annual meeting meeting within the past three years, and and those those who who indicate interest in being a member according to guidelines guidelines approved approved by by the Board of Directors. Directors. Meetings Meetings The organization organization shall meet once a year. The The place placeand andexact exact date dateof of each each meeting meeting will be designated designated by the Board Board of Directors. Directors. Directors Directors The Board Board of Directors Directors shall shall consist consist of the the Chair, Chair, Secretary-Treasurer, Secretary-Treasurer,and andthe the last three past past Chairs; Chairs; but but if the the board board should should at at any any time time consist consist of of fewer fewer than than five persons, persons, by reason reason of unwillingness unwillingness or inability inability of any any of of the the above above persons persons to serve as directors, directors, the vacancies on the board board may may be be filled filled by by the the Chair Chair so so as as to bring bring the membership membership of the the board board to to five five members. members. Officers Officers The officers of this organization organization shall shall be be aa Chair Chair and and Secretary-Treasurer. Secretary-Treasurer. A. The TheChair Chairshall shallbe beelected electedeach each year year by by the the Board Board of of Directors, Directors, who who shall shall give due consideration consideration to the wishes of any group group that may may be be promoting promoting the the next annual meeting. His/her Hislher term term of of office officeas as Chair Chair will will terminate terminate at at the the close close of of helshe presides, presides, or when his/her hislher successor successor shall shall the annual meeting meeting over which he/she have been appointed. He/she Helshe will will then then serve serve for aa period period of of three three years years as as aa member of the Board Board of Directors. Directors. B. The TheSecretary-Treasurer Secretary-Treasurershall shall be elected at the annual meeting. His/her Hislher term of office shall shall be be four years, or until until his/her hislher successor successor shall shall have have been been appointed. appointed. Amendments Amendments This constitution may be amended amended by a majority majority vote (majority (majority of of those those voting) voting) of of the membership membershipof of the the organization. organization. vi �BY-LAWS OFTHE THE INSTITUTE INSTITUTE ON LAKE LAKESUPERIOR SUPERIOR GEOLOGY BY-LAWS OF GEOLOGY I. Duties I. Duties of the Officers Officers and Directors Directors A. A. It shall be the duty of the Annual Chairman to: 1. Preside Presideat at the theannual annualmeeting. meeting. Appointall allcommittees committeesneeded neededfor for the theorganization organizationof of the theannual annualmeeting. meeting. 2. Appoint 3. Assume Assumecomplete completeresponsibility responsibilityfor for the theorganization organizationand andfinancing financing of of the the annual annual meeting meeting over over which which he/she helshepresides. presides. B. It shall be the duty of the Secretary-Treasurer B. Secretary-Treasurer to: 1. Keep Keepaccurate accurateattendance attendancerecords recordsof of all all annual annual meetings. meetings. 2. Keep accurate records of all meetings of, and correspondence Keep accurate records of all meetings of, and correspondencebetween, between,the the Board of Directors. Directors. 3. Hold Holdall allfunds fundsthat thatmay mayaccrue accrueas asprofits profitsfrom fromannual annualmeetings meetingsor or field fieldtrips trips and to make make these these funds funds available available for the the organization organization and and operation operationof of future meetings meetings as as required. required. C. C. It shall be the duty of the Board Board of Directors Directors to plan plan locations locations of of annual annual meetings meetings and and to advise on the organization organization and and financing financing of of all all meetings. meetings. II. Duties Duties and and Exrenses Expenses A. Regular Regularmembership membershipdues duesof of $5.00 $5.00 or or less lesson on an an annual annual basis basis shall shall be be assessed each member member as determined determined by by the Board Board of Directors.. Directors.. B. Registration be determined Registrationfees feesfor forthe theannual annualmeetings meetingsshall shallbe determinedby by the the Chair Chair in in of Directors. The consultation with the Board of The registration registrationfees fees can can include include expenses to cover operations operations outside of the annual annual meeting meeting as as determined determinedby by the Board Board of Directors. Directors. It is strongly recommended recommended that registration registration fees fees be be kept at a minimum minimum to encourage encourage attendance attendance of students. students. III. Ill. Rules Rules of Order Order The rules contained contained in Robert's Robert's Rules Rules of Order Order shall shall govern govern this this organization organizationin in all all cases to which they they are are applicable. applicable. IV. Amendments Amendments amended by a majority These by-laws by-laws may be amended majority vote (majority (majority of those those voting) voting) of of the the membership of the organization; membership organization; provided provided that such modifications modifications shall shall not not conflict conflict with the constitution constitution as as presently presently adopted adopted or or subsequently subsequentlyamended. amended. Last Last Amended Amended— - May, 1996 1996 vii vii �MEMBERSHIP CRITERIA FOR MEMBERSHIP CRITERIA FOR THE THE INSTITUTE LAKE SUPERIOR GEOLOGY INSTITUTE ON LAKE SUPERIOR GEOLOGY Approved May May 8, 8, 1997 1997 A. Membership Membershipininthe theInstitute Instituteon onLake LakeSuperior SuperiorGeology Geologyrequires requireseither either participation participationin in on aa regular regular basis basis of of interest interest in in the the Institute. Institute. Those Institute activities, or an indication on Those individuals years unless: unless: individuals registering registering for an an annual annual meeting meeting will remain remain as as members membersfor for 44 years 1) they indicate no further interest in the Institute Institute by by responding responding negatively negatively to to the the 2) two two statement on meeting meeting circulars circulars "Remove "Removemy my name name from from the the mailing mailinglist"; list";or or 2) statement successive mailings mailings in different different years are are returned returned by by the the postal postal service service as as address address successive unknown. unknown. Those individuals individuals who have have not not registered registered for for an an annual annual meeting meetingin in the the past past44 years years B. Those must indicate indicate an interest interest in in the the Institute Institute by by postal, postal, electronic, electronic, or or verbal verbal correspondence correspondence Secretary-Treasurer at least once every two two years. years. Such with the Secretary-Treasurer Such individuals individuals will be removed from the membership membership ifif they they indicate indicate no no further further interest interest in in the the Institute Instituteor or two two successive mailing mailing in different different years are are returned returned by by the the postal postal service service as as address address successive unknown. unknown. C. The TheSecretary-Treasurer Secretary-Treasurerwill will maintain maintain a list of current members. The The list list will will include include of returned mail, dates of of last the date of the beginning of continuous membership, dates of contact (expression (expression of interest), interest), and and the the date date membership membership expires, expires, barring barringaa change changeof of status initiated by the member. Those individuals who have become members of ILSO Those individuals who have become members ILSG by by Section B will have an expiration date date listed listed at at 22 years years from from the the upcoming upcoming meeting. meeting. For For example, a member who expresses interest interest in September of 1997 1997 (the (the next next annual annual meeting is May, 1998) will have an expiration date of May, 2000, unless unless the member member contacts the Secretary-Treasurer Secretary-Treasurer or attends attends an an annual annual meeting. meeting. D. "Member "Memberfor for Life" Life"status statusisisgranted grantedto to individuals individualswho who have have been been (nearly) (nearly) continuous continuous 15 years, years, Goldich Goldich Medal Medal recipients, recipients, or or those those who who participants of the ILSG ILSG meetings meetings for 15 have served as meeting chairs. This This status status will will be be further further maintained maintained unless unless the the mailings in in different different years years are are individuals indicate no further interest interest in the Institute, Institute, or 4 mailings returned by the postal service as address unknown, unknown, or they are deceased. deceased. E. All All members memberswill will be be mailed mailedthe the First First Circular Circular for for the the Annual Meeting Meeting and and the ILSG ILSG Newsletter. The The Chair Chair of of the the annual annualmeeting meetingmay may opt opt to to send send the the first first circular circular to to additional individuals. All All returned returned mail mail should should be be reported reported to the Secretary-Treasurer. Secretary-Treasurer. F. The TheSecretary-Treasurer Secretary-Treasurercan candesignate designateany any individual individual who is is on the ILSG ILSG membership list (mailing list) as of January January 1, 1, 1997 1997 as a member for life life based based on on participation participationin in ILSG ILSG activities. activities. G. Members Membersare are strongly stronglyencouraged encouragedto to send send address address corrections corrections to to the the SecretarySecretaryTreasurer Treasurer to avoid avoid unintentional unintentional lapse lapse of of membership. membership. VIII viii �GOLDICH MEDAL GUIDELINES (Adopted by the 1981; amended 1999) 1999) the Board of of Directors, 1981; Preamble Preamble Institute on on Lake Lake Superior Superior Geology Geology was was born born in in 1955, 1955, as as documented documentedby bythe the fact fact that thatthe the27th 27th The Institute annual meeting was held in 1981. The TheInstitute's Institute'scontinuing continuingobjectives objectives are are to to deal deal with with those those aspects of geology geology that are are related related geographically geographicallyto Lake Lake Superior; Superior; to to encourage encourage the the discussion discussionof of aspects subjects and sponsoring field trips that will bring together together geologists geologists from from academia, academia, government and industry; industry; and and to maintain maintain an informal informal but but highly highly effective effective mode modeof of operation. operation. surveys, and During the course of its existence, existence, the membership membership of the the Institute Institute (that (that is, is, those thosegeologists geologistswho who indicate an interest interest in in the objectives objectives of the the ILSG ILSG by by attending) has has become become aware awareof of the the fact fact that that indicate colleagues have have made made particularly particularly noteworthy noteworthyand and meritorious meritorious contributions contributionsto to the the certain of their colleagues understanding understanding of Lake Lake Superior Superior geology geology and and mineral mineral deposits. deposits. The first award award was made made by by ILSG ILSG to to Sam Sam Goldich Goldich in in 1979 1979for for his his many manycontributions contributionsto tothe thegeology geology of the region extending over about 50 years. years. Subsequent Subsequent medallists medallists and and this year's recipient recipient are listed listed in the table table below. below. Guidelines Award Guidelines 1) The The medal medalshall shall be beawarded awardedannually annually by by the ILSG Board of Directors to a geologist whose name is associated with a substantial interest in, and contribution contribution to, the geology of the Lake Lake Superior region. region. 2) The TheBoard Boardof of Directors Directorsshall shall appoint appoint the Goldich Medal Committee. The The initial initial appointment appointment will for two two years, years, and and one one for for one one year. year. The be of three members, one to serve for three years, one for The briefest incumbency shall be chair chair of of the the Nominating Committee. Committee. After member with the briefest After the the first first year, the Board Board of Directors Directors shall shall appoint at each each spring spring meeting meeting one one new new member memberwho who will will serve serve years. In the chair. chair. The Committee for three years. In his/her hislher third third year this member shall be the Committee membership membership geographic distribution distribution of of ILSG membership. membership. The should reflect the main fields of interest and geographic The outoutgoing, senior member member of the the Board Board of of Directors Directorsshall shall act act as as liaison liaisonbetween betweenthe the Board Boardand andthe the Committee for a period Committee period of one one year. 3) By Bythe theend endof of November, November,the the Goldich GoldichMedal Medal Committee Committee shall shall make make its its recommendation recommendationto to the the Chair of the Board Board of Directors, Directors, who will then inform inform the the Board Board of the the nominee. nominee. 4) The TheBoard Boardof of Directors Directorsnormally normallywill will accept accept the the nominee nominee of of the the Committee, Committee, inform informthe the medallist, medallist, medal engraved and have one medal engraved appropriately appropriately for presentation presentation at the next next meeting meetingof of the the Institute. Institute. recommended that the Institute 5) It is recommended Institute set aside aside annually from whatever sources, sources, such such funds funds as as will will required to support the continuing be required continuing costs of this award. award. Nominating Procedures Nominatina Procedures 1) The The deadline deadline for nominations nominations is November 1. The The Goldich Goldich Medal Medal Committee Committee shall shall take time. Committee nominations at any time. Committeemembers membersmay maythemselves themselves nominate nominatecandidates; candidates; however, however, Board members may may not not solicit for or or support support individual individual nominees. nominees. 2) Nominations Nominationsmust mustbe beininwriting writingand andsupported supportedby byappropriate appropriatedocumentation documentationsuch such as as letters letters of of recommendation, lists recommendation, lists of publications, publications, curriculum curriculum vita's, vita's, and and evidence evidenceof of contributions contributionsto to Lake Lake Superior geology and and to the the Institute. Institute. 3) Nominations Nominationsare arenot notrestricted restrictedto to Institute Instituteattendees, attendees, but but are are open open to anyone anyone who has worked on and and contributed contributedto the the understanding understandingof of Lake LakeSuperior Superiorgeology. geology. ix �Selection Guidelines Nomineesare areto tobe beevaluated evaluatedon on the the basis basis of of their their contributions contributionsto to Lake Lake Superior Superior geology geology 1) Nominees (sensu (sensu lato) lato) including: including: a) importance importanceof of relevant relevant publications; publications; b) promotion promotionof of discovery discoveryand andutilization utilization of of natural natural resources; resources; c) contributions contributionsto tounderstanding understandingof of the the natural naturalhistory history and and environment environment of the the region; region; d) generation generationof of new newideas ideasand and concepts; concepts; and and e) contributions contributionsto to the thetraining trainingand and education education of of geoscientists geoscientists and and the the public. public. 2) Nominees Nomineesare areto tobe beevaluated evaluatedon ontheir their contributions contributions to to the the Institute Instituteas as demonstrated demonstratedby by attendance attendance at at Institute Institutemeetings, meetings, presentation presentationof of talks talks and andposters, posters,and andservice serviceon onInstitute Instituteboards, boards, committees, committees, and and field field trips. trips. 3) The Therelative relativeweights weightsgiven givento toeach eachof of the theforegoing foregoing criteria criteria must must remain remainflexible flexible and andat at the the discretion discretion of the the Committee Committeemembers. members. 4) There Thereare areseveral severalpoints pointsto tobe beconsidered consideredby bythe the Goldich Goldich Medal Medal Committee: Committee: Anattempt attemptshould shouldbe bemade madeto tomaintain maintainaabalance balanceof of medal medalrecipients recipientsfrom from each eachof of the the a) An three estates—industry, estates-industry, academia, academia, and and government. government. b) It must be noted noted that industry industry geoscientists are are at aa disadvantage disadvantage in in that that much muchof of their their work in in not not published. published. 5) Lake of LakeSuperior Superiorhas hastwo two sides, sides, one one the U.S., and the other Canada. This This is is undoubtedly undoubtedly one of the Institute's Institute's great great strengths strengths and and should should be be nurtured nurturedby by equitable equitable recognition recognition of of excellence excellenceininboth both countries. countries. GOLDICH GOLDICH MEDAL MEDAL COMMITTEE COMMITTEE Serving through the meeting year shown in parentheses Frank Frank Luther Luther(2003) (2003) University of Wisconsin, Whitewater Ron R o n Sage Sage (2004) (2004) Ontario Geological Geological Survey Survey (retired) (retired) David David Meineke Meineke (2005) (2005) Meriden Engineering, Engineering, Hibbing, Hibbing, Minnesota Minnesota Steve Kissin, Kissin,as asout-going out-goingsenior seniormember member of of Institute Institute Board Board of Directors, Directors, is is liaison between Goldich Medal Committee and the Board through the 2004 meeting meeting x �2003 2003GOLDICH GOLDICHMEDAL MEDALRECIPIENT RECIPIENT Klaus Klaus J. Schulz Schulz U.S. Geological Geological Survey U.S. Reston, Virginia Virginia GOLDICH MEDALISTS MEDALISTS 1979 Samuel SamuelS. S.Goldich Goldich 1991 Hinze 1991 William Hinze 1980 not notawarded a warded 1992 William WilliamF. F.Cannon Cannon 1981 1993 1 993 Donald DonaldW. W. Davis Davis Carl E. Dutton, Dutton, Jr. 1982 Ralph RalphW. W. Marsden Marsden 1994 Cedric CedricIverson Iverson 1983 Burton BurtonBoyum Boyum 1995 Gene GeneLaBerge LaBerge 1984 Richard RichardW. W. Ojakangas Ojakangas 1996 David DavidL. L.Southwick Southwick 1985 1997 Ronald RonaldP. P. Sage Sage Paul K. Sims Sims 1986 G.B. G.B. Morey Morey ZelI Peterman 1998 Peterman 1998 Zell 1987 Henry HenryH. H. Halls Halls 1999 Tsu-Ming Tsu-MingHan Han 1988 Walter Walter S. S. White White 2000 John JohnC. C.Green Green 1989 Jorma JormaKalliokoski Kalliokoski 2001 2001 John S. Klasner Klasner 1990 Kenneth KennethC. C. Card Card 2002 Ernest ErnestK. K.Lehmann Lehmann xi �CITATION Klaus J. Schulz 2003 Goldich Medal Recipient Recipient ning more Klaus Schulz has had had a long long and and productive productivecareer careerspan spanning more than than 30 30 years years as a geologist geologist in in the the Lake Lake Superior Superior region. region. He He was was introduced introducedto to the the geology geologythrough throughhis his education education in the area, he he completed completed graduate graduate studies studies in in the the region, region,performed performedseveral several summers of field work for mining mining companies in a number of different areas, and has conducted extensive extensive research research as aa scientist scientist with the U.S. U.S. Geological Geological Survey. Survey. This This conducted extensive extensive and diverse diverse experience experience has has made made him him a real real authority authority on on the the geology geology of of the the Lake Superior region. Klaus Klaus received received his B.S. degree degree in in geology geology from the the University Universityof of WisconsinWisconsinOshkosh Oshkosh in 1971. 1971. He He completed completed his his Masters Masters degree degree at at the the University Universityof of MinnesotaMinnesotaDuluth Duluth in 1974, with a thesis project project in in the the Vermilion district district of northern northern Minnesota. Minnesota. He He received received his Ph.D. from the University University of Minnesota Minnesota in in 1977 1977 with aa dissertation dissertation on on the the petrology petrology of volcanic rocks rocks in in the Vermilion district. district. Klaus Klaus spent spent the the next next two two years years as as aa National National Research Research Council Council Research Research Associate Associate with NASA at the Johnson Johnson Space Space Center Center in Houston, where he studied basaltic and ultramafic ultramafic magma magma types types as as analogs analogs of of studied Archean basaltic early planetary crust. In 1982, after three years as a faculty faculty member at at Washington Washington University University in St. Louis, Louis, Klaus Klaus resigned resigned his his teaching teaching position position and and joined the the U.S. U.S. Geological Geological Survey in Reston, VA, fulfilling a long-standing long-standing dream dream of of his. his. During During the the next nexttwenty twenty years years with the USGS Klaus Klaus was a research research scientist scientist and administrator administrator with a strong strong interest interestin in the geology of the Lake Lake Superior Superior region. region. The traits that have have made made Klaus Klaus a success success were evident early early in in his his career. career. In In his his undergraduate days at Oshkosh, undergraduate Oshkosh, Klaus Klaus distinguished distinguished himself himself as as an an avid avid reader reader of of the the geological literature. literature. As a junior in in 1970, 1970, he he wrote wrote an an outstanding outstanding research research paper paper discussing the similarities similarities between between Archean greenstone greenstone belts belts and and modern modern island island arcs. arcs. He He worked several summers doing fieldwork fieldwork for Bear Bear Creek Creek Mining Mining Company Company in in central central Wisconsin and northern Michigan, and for U.S. U.S. Steel Corp. Corp. in the the Vermilion Vermilion district district of of northern Minnesota. This combination combination of field work and and a thorough thorough knowledge knowledgeof of the the literature has continued continued to be be a hallmark hallmark of his his professional professional career, career, and and has has led led to to aa number of significant significant contributions contributions to the the geology geology of the the Lake Lake Superior Superiorregion. region. In the summer of 1971, 1971, Klaus Klaus and and William William Spence Spence discovered discovered the the Lake LakeEllen Ellen kimberlite near Crystal Falls, Falls, Michigan, while working as exploration exploration geologists geologists in in the the area. Klaus was very much involved involved in the recognition recognition of the rock rock as as aa kimberlite. kimberlite. This This was the first kimberlite kimberlite discovered discovered in in the the Lake Lake Superior Superior region. region. xl' �Masters thesis involved involved considerable mapping in the Ely Ely greenstone greenstone belt belt in in His Masters considerable mapping studies for his his Ph.D. Ph.D. dissertation dissertation showed showed that that the the Newton Newton Minnesota, and geochemical geochemical studies Lake Formation Formation was a high-magnesium high-magnesium basalt, basalt, similar to komatiites. komatiites. This This was was the the first first documented occurrence occurrence of of komatiitic komatiiticrocks rocksin in the the Lake LakeSuperior Superiorregion. region. documented In the early 1980's, his field mapping mapping and geochemistry geochemistry of rocks rocks in in the the Pembine Pembine area area of the the Wisconsin Wisconsin magmatic magmaticterranes terranesdemonstrated demonstratedthe thepresence presenceof ofophiolitic ophioliticrocks. rocks. Again, this was the the first first documented documentedophiolite ophiolite in in the the Lake Lake Superior Superiorregion, region,and andshowed showed magmatic terranes were, at least in part, an oceanic island arc. His that the Wisconsin magmatic model for the the evolution evolution of of the the Marquette MarquetteRange RangeSupergoup Supergoupon onthe thecontinental continental subsequent model margin during during the the Penokean Penokean orogeny orogeny is is an an extension extension of of his his familiarity familiarity with with the the rocks rocksininthe the margin region combined combined with his his encyclopedic knowledge knowledge of the geologic geologic literature literature on on the the region evolution of continental continental margins. margins. Klaus also contributed contributed to the GLIMPCE GLIMPCE program, program, which ultimately ultimately provided provided significant insight into the structure and origin of the Mid-continent rift, and into its magmatic magmatic origin origin and and metallogeny. metallogeny. He has authored authored and and co-authored co-authored more more than 120 120 publications, publications, maps, maps, abstracts abstracts and field guides, including including field field guides guides for the the 1984, 1984, 1992, 1992, and and 2003 2003 Institute Institutemeetings. meetings. Klaus' contributions contributions have provided provided a better understanding understanding of the the Archean, Archean, the the Early Proterozoic, Proterozoic, the Middle Proterozoic, and the Phanerozoic history history of the the Lake Lake Superior region. And he continues continues to be be an active active contributor contributor on on aa global global stage, stage, taking taking the the knowledge experience that he knowledge and experience he has gained gained in the Lake Lake Superior Superior region region and and applying applying itit to international international projects. projects. Therefore, it is my my distinct distinct pleasure pleasure and and honor honor to present present Klaus Klaus Juergen Juergen Schulz Schulz as as the 2003 recipient recipient of the Goldich Medal "For Outstanding Contributions To The Lake Superior Region". Region". Submitted by Gene Submitted Gene L. L. LaBerge LaBerge xiii �____________________________________________ __________________________ EISENBREY STUDENT TRAVEL AWARDS The 1986 1986 Board Board of of Directors Directors established established the the ILSG ILSG Student Student Travel Travel Awards Awards to to support support student student participation at at the annual meeting of of the the lnstitute. Institute. The The name name "Eisenbrey" "Eisenbrey" was added added to the award in 1998 to honor honor Edward Edward H. Eisenbrey Eisenbrey (1926-1985) (1926-1985) and utilize substantial contributions made to the 1996 Eisenbrey 1996 Institute lnstitute meeting meeting in his name. "Ned" "Nedt1 Eisenbreyisiscredited creditedwith withdiscovery discoveryof of significant scope was was much much significant volcanogenic volcanogenic massive massive sulfide sulfide deposits deposits in in Wisconsin, Wisconsin, but but his scope broader—he broader-he has been described as having having unique unique talents as an an ore ore finder, finder,geologist, geologist,and and teacher. These are intended to help defray teacher. These awards awards are intended to defray some some of the the direct direct travel travel costs costs of of attending Institute lnstitute meetings, and include a waiver waiver of registration fees, but but exclude exclude expenses expenses The annual Chair in for meals, meals, lodging, lodging, and and field field trip trip registration. registration. The in consultation consultation with the the Secretary-Treasurerdetermines determinesthe the number number of of awards will be Secretary-Treasurer awards and and value. value. Recipients Recipients will be announced at the annual banquet. banquet. The annual Chair, who is is responsible responsible for the the selection, selection, will will consider consider the the following following general general criteria: criteria: 1) The Theapplicants applicantsmust musthave haveactive activeresident resident (undergraduate (undergraduateor or graduate) graduate) student student status status at at the time of the the annual annual meeting meetingof of the the Institute, lnstitute,certified certifiedby bythe thedepartment departmenthead. head. 2) Students Studentswho who are arethe the senior senior author author on on either either an an oral oral or or poster poster paper paper will will be be given given favored consideration. consideration. 3) It is desirable for two or more more students students to jointly request request travel travel assistance. assistance. 4) InIngeneral, general,priority prioritywill willbe begiven givento tothose thoseininthe the Institute lnstituteregion regionwho who are are farthest farthest away away from from the meeting meeting location. location. 5) Each Eachtravel travel award award request requestshall shall be be made made in in writing writing to to the the annual annual Chair, and and should should explain other significant details. details. The need, student and author status, and other The form form below below is is optional. optional. Successful applicants will receive receive their awards during the meeting. meeting. n INSTITUTE ONLAKUPERIOAGEOLOGY Application Eisenbrey Student Travel Award Application Student Student Name: Name: Date: Date: Address: email: Department Department Head-Typed Head-Typed Department Educational Status: Educational Status: Department Head-Signature Head-S~gnature Areyou youthe the senior author anororal or paper? poster paper? YES_ Are senior author of anof oral poster YESNO- NO_ Will any other other students students be be traveling travelingwith with you? you? Who? Who? Statement Statement of need need (use (use additional additional page page ifif necessary) necessary) Please Please return return to: to: xiv �STUDENT PAPER AWARDS Each year, the lnstitute student presentations presentations and and honors honors Institute selects the best of the student Funding for for the the award award is is generated generated from from registrations registrations presenters with a monetary award. Funding of the annual meeting. The TheStudent StudentPaper PaperCommittee Committeeisis appointed appointedby by the the annual annual meeting meeting Chair in such a manner as to represent represent aa broad broad range range of of professional professionaland andgeologic geologic expertise. Criteria Criteriafor for best beststudent student paper—last paper-last modified modifiedby by the the Board Board in in 2001—follow: 2001-follow: Thecontribution contributionmust mustbe bedemonstrably demonstrably the the work work of of the the student. student. 1) The 2) The student must present the contribution in-person. The student must present the contribution in-person. TheStudent StudentPaper PaperCommittee Committeeshall shalldecide decidehow how many manyawards awards to to grant, grant, and and whether whether or or 3) The not to give separate awards for poster poster vs. oral presentations. presentations. casesofofmultiple multiplestudent studentauthors, authors,the theaward awardwill will be bemade madeto to the the senior senior author, author,or or 4) InIncases award will be be shared shared equally by by all all authors authors of the the contribution. contribution. the award Thetotal totalamount amountof ofthe theawards awardsisisleft leftto tothe thediscretion discretionof of the themeeting meetingChair Chairand and 5) The Secretary-Treasurer,but but typically typically is is in in the the amount amount of of about about $500 $500 US US (increase (increaseapproved approved Secretary-Treasurer, by Board, Board, 10/01). 10101). TheSecretary-Treasurer Secretary-Treasurermaintains, maintains,and andwill will supply supply to to the the Committee, Committee,aa form form for for the the 6) The numerical ranking of presentations. presentations. This Thisform formwas wascreated createdand andmodified modifiedby byStudent Student numerical Paper Committees over several years in an effort to reduce reduce the difficulties difficultiesthat that may may arise arise from selection by raters of of diverse diverse background. background. The use of the form is not required, but is left to the discretion discretion of the the Committee. Committee. Thenames namesof ofaward awardrecipients recipientsshall shall be beincluded includedas as part part of of the the annual annual Chair's Chair's report report 7) The that appears appears in the next next volume of the the Institute. lnstitute. Student papers papers will be noted noted on the Program. Program. 2003 STUDENT PAPER AWARDS COMMITTEE Theodore TheodoreBornhorst Bornhorst- -Michigan MichiganTechnological TechnologicalUniversity, University, Houghton, Houghton, MI MI -- Chair Kevin WI KevinSikkila Sikkila— - Wisconsin Department of Transportation, Superior, Wl Anne Argast PurdueUniversity University Fort FortWayne, Wayne, Fort Wayne, Wayne, IN Anne Argast— - Indiana Indiana University University — - Purdue Tim Tim Flood Flood— - St. Norbert Norbert College, De De Pere, Pere, WI Wl 2003 SESSION CHAIRS Peter Ontario Geological Survey, Survey, Kenora, Peter Hinz Hinz— - Ontario Kenora, ON ON Eric Jerde Eric Jerde--Morehead MoreheadState StateUniversity, University, Morehead, Morehead, KY KY James James Miller Miller- -Minnesota MinnesotaGeological GeologicalSurvey, Survey,Duluth, Duluth, MN MN Mike Mudrey, Wisconsin Geological Mike Mudrey,Jr. Jr.— -Wisconsin Geological and and Natural Natural History History Survey, Survey, Madison, Madison, WI Wl xv �2003 BOARD OF 2003 BOARD OFDIRECTORS DIRECTORS appointment continues continues through through the the close close of of the the meeting meeting year year shown shown in in parentheses, parentheses, or oruntil untilaa Board appointment successor is selected Laurel Woodruff Woodruff Co-Chair Co-Chair2003 2003meeting meeting(2006) (2006) U.S. Geological Geological Survey, Survey, St. St. Paul, Paul, MN MN Peter Hinz Hinz (2005) (2005) Geological Survey, Kenora, ON Ontario Geological Michael G. Mudrey, Jr. (2004) Michael (2004) Wisconsin Wisconsin Geological Geological and and Natural NaturalHistory HistorySurvey, Survey, Madison, Madison, WI Wl Stephen A. A. Kissin Kissin(2003) (2003) Lakehead University, Lakehead University, Thunder Thunder Bay, Bay, ON ON Hollings-Secretary-Treasurer (2006) Peter Hollings-Secretary-Treasurer (2006) Lakehead University, Thunder Lakehead Thunder Bay, Bay, ON ON A. Jirsa-Secretary-Treasurer-"erneritu~~~ Jirsa-Secretary-Treasu rer-"emeritus" (in (in transition) transition) Mark A. Minnesota Geological Geological Survey, Minnesota Survey, St. Paul, Paul, MN MN 2003 COMMITTEES 2003LOCAL LOCAL COMMITTEES General General Co-Chairs Co-Chairs Laurel Laurel G. G. Woodruff Woodruff—-U.S. U.S.Geological GeologicalSurvey, Survey, St. St. Paul, Paul, MN MN William F. Cannon — U.S. Geological Survey, Reston, VA William F. Cannon - U.S. Geological Survey, Reston, VA and Abstracts Abstracts Editors Program and Laurel Laurel G. G. Woodruff Woodruff----U.S. U.S.Geological GeologicalSurvey, Survey,St. St. Paul, Paul, MN MN Theodore J. Theodore J. Bornhorst Bornhorst—-Michigan MichiganTechnological TechnologicalUniversity, University,Houghton, Houghton,MI MI Field Trip Guidebook Editor Editor William F. William F.Cannon Cannon—- U.S. U.S. Geological GeologicalSurvey, Survey, Reston, Reston, VA VA Acting Local Local Committee, Iron lron Mountain John Gartner John Gartner— - Coleman Coleman Engineering, Engineering, Iron lron Mountain, Mountain, MI MI Connie Dicken Connie Dicken— - U.S. Geological Geological Survey, Reston, Reston, VA Sally LaBerge Sally LaBerge— - Oshkosh, Oshkosh, WI WI 2003 BANQUET SPEAKER Susan Martin Martin Department of Social Department Social Sciences Sciences Michigan Technological University University Houghton, Houghton,Michigan Michigan The indigenous indigenous people of the Lake Superior Superior Basin: Basin: Understanding Understanding the links links among environment, geology and religious religious belief xvi xvi �48TH Report of the Chair of the 4aTHAnnual Meeting Meeting Hinz, Co-Chair Co-Chair ILSG ILSG 2002 2002 Peter Hinz, 48th The 4athAnnual Institute lnstitute on Lake Lake Superior Superior Geology Geology was hosted hosted by by the the Ontario Ontario Geological Geological 9-12, Survey on May 9-1 2, 2001. Principal Principal local committee members members were Peter Peter Hinz Hinz and and Richard C. Beard, co-chairs, co-chairs, Carmen C. Storey, and and Kevin Kevin O'Flaherty OrFIahertyProgram Programco-chairs, co-chairs, Richard McGowan-Hinz,Treasurer, Charles E. Blackburn, Blackburn, Field Field Trip Co-ordinator, Co-ordinator, M. Kathleen Kathleen McGowan-Hinz, and Christine C. Blackburn, Blackburn, Secretary. Secretary. Other principal principal individuals individuals are listed listed in in the the Proceedings ProceedingsVolume. Volume. Attendanceat atILSG ILSG2001 2001 Attendance A total of 97 97 professionals professionalsand and student student professionals professionalsattended attendedthe the meeting, meeting,39 39of of whom whom pre-registered by the April 2, 2001 deadline. A total of 8 students pre-registered students were were registered, registered,77 of of whom requested requested and and received received travel travel assistance. Eisenbrey Student Eisenbrey Student Travel Travel Awards Awards2001 2001 Seven students students requested requested and and received received travel travel assistance assistance from from the the Eisenbrey EisenbreyStudent Student Travel Award Fund Fund established established to support student student participation participation at at the the Annual Annual Institute. lnstitute. Details, including criteria and application application forms, are available available at the ILSG ILSG website. Bogdan Nitescu Bogdan Nitescu Claire Claire Sturm Sturm Elizabeth Fein Elizabeth Fein Justin Johnson Johnson Becky Rogala Rogala William Jahn Jahn Daniela Daniela Vallini Vallini University of Toronto, Toronto, Toronto, ON University ON Oberlin Oberlin College, College, Oberlin, Oberlin, OH OH Oberlin Oberlin College, College, Oberlin, Oberlin, OH OH Lakehead University, Thunder Bay, Lakehead Bay, ON ON Lakehead University, Thunder Bay, Lakehead Bay, ON ON University of Minnesota - Duluth, Duluth, Duluth, Duluth, MN MN of Western Australia, Nedlands, University of Nedlands, WA Meetin Meetin Summary Summary tf The 48 Annual AnnualInstitute lnstituteon onLake LakeSuperior SuperiorGeology GeologyAnnual Annual Meeting Meeting was held held at the Best Western Lakeside Lakeside Inn Inn and and Convention Convention Centre, Centre, the the same same location locationas as the the 1985 1985meeting. meeting. The one-and-a-half days of technical sessions were preceded by: Field Trip 1 — Tanco one-and-a-half days of technical sessions were preceded by: Field Trip 1 - Tanco Rare-Element Rare-Element Pegmatite, Pegmatite, Southeastern Southeastern Manitoba Manitoba led led by by staff of of the the Tantalum TantalumMining Mining Corporation of Canada Quaternary Geology of - Quaternary Corporation Canada Ltd.; Ltd.; followed followedby byField FieldTrip Trip22— Southeastern Manitoba Nielsen and Gaywood Matile Matile (Manitoba (Manitoba Geological Geological Southeastern Manitoba led led by E. Nielsen Survey); and Field Field Trip 3- Structure Structure and and Sedimentology Sedimentology of the the Seine Seine Conglomerate, Conglomerate,Mine Mine Centre Area, Ontario Ontario lead lead by by Dyanna Dyanna Czeck (Department (Department of Geology, Geology, Oberlin Oberlin College) College) and Philip Fralick Fralick (Department (Department of Geology, Geology, Lakehead Lakehead University) University) Due to the small number number of talks talks submitted, submitted, the the Technical Technical Session Session Chairs Chairs were were unable unable to to group talks into into session session themes. The The meeting meeting began began with with an an anecdotal anecdotal history historyof of mining miningin in northwestern Ontario presented O7FIaherty,followed followed by by regional regional scale scale talks talks on on northwestern presented by by Kevin Kevin O'Flaherty, the Western Western Superior Superior Province. Province. The Theremainder remainderof ofthe thetechnical technicalsessions sessionsincluded includedaabroad broad range of talks focusing focusing on on ground ground water, water, petrography, petrography,sedimentology, sedimentology,mineralogy mineralogyand and structural topics. The final final session session ended ended at noon, noon, allowing allowing for an an early early departure departure of of Field Field Trip Trip 66 to to Red RedLake. Lake. Post Postmeeting meetingtrips tripsincluded: included:Field FieldTrip Trip44— - Industrial IndustrialMinerals Mineralsand and Paleozoic Geology 5 - Separation SeparationRapids RapidsRareRareGeology of Southeastern SoutheasternManitoba; Manitoba;Field FieldTrip Trip5— Element Pegmatite Geology of of the Red Lake - Geology Lake Camp. Camp. All All Pegmatite Field, Field, Ontario; Ontario;and andField FieldTrip Trip66— field field trips trips ran ran smoothly smoothly considering considering the the frigid frigid conditions conditionsof of early earlyMay Mayin innorthwestern northwestern Ontario. ILSG Secretary Secretary -Treasurer, -Treasurer, Mark Mark Jirsa Jirsa was the the lone lone participant participant of of Field FieldTrip Trip 66 successful in obtaining samples samples from from Goldcorp's Goldcorp's Red Red Lake Lake Mine Mine in in Red Red Lake. Lake.He Hewas was able to do this this by by cunningly cunningly embedding embedding the the samples samples in in the the back back of of his hisneck. neck.Upon Upon returning to Kenora Kenora the samples were proudly proudly displayed displayed in a baggy baggy kindly kindly supplied supplied by by the the staff of Red Red Lake's Lake's Margaret MargaretCochenour CochenourMemorial MemorialHospital Hospitalemergency emergencyroom. room. xvii xvii �Goldich Award Annual Banquet Banquet and Goldich the Annual Annual Banquet Banquet Ted Ted DeMatties DeMatties presented presentedthe the citation citation for for Ernest ErnestK. K.Lehmann, Lehmann, At the Goldich Medal Medal for 2002 for his his contributions contributions to to the the Institute lnstituteand and Lake Lake recipient of the Goldich Superior Geology. L. Harvey Harvey Thorliefson, Geological Survey of Canada, Canada, provided provided aa Thorliefson, Geological scintillating discussion on The Search Search for Diamonds Diamonds in in Canada Canada for the the after after dinner dinner address. Laurel Woodruff and and Bill Bill Cannon Cannon of the the U.S. U.S. Geological Geological Survey Survey invited invited 49th participants the 4gth Meeting in in Iron Iron Mountain, Mountain, Michigan. Michigan. participants to the Annual Meeting 2002 Best Student Student Paper Awards Awards 1) Becky Becky Rogala Rogala-- Lakehead LakeheadUniversity,Thunder University,Thunder Bay, Bay, Ontario Ontario ($400, oral presentation) presentation) formation from the Sibley New in information Sibley Group Group 2) Elizabeth ElizabethFein Fein-- Oberlin OberlinCollege, College, Oberlin, Oberlin, Ohio Ohio ($50, ($50, poster; poster; Co-authors Co-authors C.L. C.L. Sturm Sturm and D.M. Czeck) Anisotropy of magnetic susceptibility in the Ottertail Ottertailpluton, pluton, Northern Ontario Ontario 3) Claire ClaireSturm Sturm-- Oberlin OberlinCollege, College, Ohio Ohio($50, ($50, oral; oral; Co-authors Co-authorsD.M. D.M. Czeck Czeck and and E. E. Fein) Fein) Petrographic study of the Petrographic the Ottertall Ottertail pluton, Superior Superior Province, Province, Northwestern NorthwesternOntario Ontario Student Travel Awards 2002 Eisenbrey Student Awards 1) Bogdan BogdanNitescu Nitescu-- University Universityof of Toronto, Toronto, Toronto, Toronto, ON ON ($250) ($250) 2) Claire OberlinCollege, College,Oberlin, Oberlin,Ohio Ohio($200) ($200) ClaireSturm Sturm--Oberlin 3) Elizabeth ElizabethFein Fein-- Oberlin OberlinCollege, College,Oberlin, Oberlin, Ohio Ohio ($200) ($200) 4) Justin LakeheadUniversity, University,Thunder Thunder Bay, Bay, ON ON ($150) ($150) JustinJohnson Johnson--Lakehead 5) Becky Rogala Lakehead University, Thunder Bay, ON ($150) 5 ) Becky Rogala - Lakehead University, Thunder Bay, ON ($150) 6) William WilliamJahn Jahn--University Universityof of Minnesota, Minnesota, Duluth, Duluth, MN MN ($150) ($150) 7) Daniela Universityof of Western WesternAustralia, Australia,Nedlands, Nedlands, WA WA ($400) ($400) DanielaVallini Vallini--University 2002 Goldich Goldich Medal Recipient 2002 Ernest K. Lehmann Lehmann Archives Donation MTU Archives Donation A check check for for $100 $100 was was sent sent to to Michigan Michigan Technological TechnologicalUniversity UniversityArchives, Archives, as as required requiredby by Board agreement ($1 per per participant participant per per meeting), meeting), for for maintenance maintenanceof of ILSG ILSGproceedings proceedings archives. archives. Proceedings Proceedings including Part Part 11 (Programs (Programs and and Abstracts) and and Part Part 22 (Field (Field Trip Trip Guidebook) Guidebook) are available available from from the the Institute: lnstitute: Institute on Lake Superior Geology lnstitute do c/o Mark Mark Jirsa, Jirsa, Secretary Secretary -- Treasurer Treasurer Minnesota Minnesota Geological Geological Survey 2642 University University Avenue St. Paul Paul MN MN 55114-1 55114-1057 057 612.627.4539 Phone: 61 2.627.4539 Fax: Fax: 612.627.4778 612.627.4778 e-mail: jirsaOO1 jirsaool @tc.umn.edu @tc.umn.edu xviiiii xvi �48th ANNUAL INSTITUTE ON LAKE SUPERIOR GEOLOGY BOARD OF DIRECTOR'S MEETING Board of Directors Directors Peter Hinz (2002 (2002General GeneralChair) Chair) Michael Mudrey Mudrey (2001 (2001 Co-chair) Co-chair) Steve Kissin Kissin (2000 (2000 Co-chair) Co-chair) Laurel Woodruff: Proxy Proxy for Ted Ted Bornhorst Bornhorst (1999 (1999 Co-chair Co-chairand and liaison liaisonwith with Goldich Goldich committee) committee) Mark Jirsa (Institute (Institute Secretary-Treasurer) Secretary-Treasurer) Guests Guests Phil Fralick Fralick (2000 (2000 Co-chair) Co-chair) Carmen Carmen Storey Storey (2003 (2003 Program ProgramChair) Chair) O'Flaherty (2003 Kevin O'Flaherty (2003 Program ProgramChair) Chair) Bill Cannon (proposed 2003 Co-chairs) (proposed 2003 Co-chairs) Rod Johnson (Goldich (Goldich Committee) Committee) Frank Luther (Goldich (Goldich Committee) The The following following is based on the secretaries' notes notes and and recollection; recollection; any any omissions omissions or or unintentionaL Motions misstatements are unintentional. Motions by by the the Board Board of Directors Directors are are generally paraphrased—"approved" paraphrased-"approved" or or "accepted" "accepted"implying implying that that aa motion motionwas wasmade, made, seconded, and passed unanimously. The Theexpression expression"generally "generallyagreed" agreed" carries carriesless less be pursued. pursued. Some formality, but indicates a directive that will be Some issues issues that that were were conference are are included included here here for for resolved after the Board meeting, but during the conference closure. closure. MINUTES MINUTES 1. Accepted Acceptedreport reportof of the the Chairs Chairsfor for the the 47th 47th ILSG, ILSG, Madison, Madison, Wisconsin; Wisconsin; as as printed printed in in the the Proceeding Volume (Mudrey), and minutes of last Board Board meeting, meeting, May May 10, 10, 2001 (Jirsa) (Jirsa) 2. Received, Received,discussed, discussed, and andaccepted accepted2001-2002 2001-2002 ILSG ILSG Financial FinancialSummary Summary (Jirsa). (Jirsa). (4gth 3. Discussed annual) meeting Discussedand and approved approved 2003 2003 (4gth meeting location—Iron location-Iron Mountain, Mountain, Michigan, Michigan, and tentative co-chairs co-chairs Laurel Laurel Woodruff Woodruff and and Bill Bill Cannon, Cannon,USGS. USGS.As As currently currently envisioned, Ted Bornhorst Bornhorst will handle handle logistics logistics of field field trips. 4. Approved ApprovedPeter PeterHinz Hinzas ason-going on-goingILSG ILSGBoard Boardmember. member. 5. Discussed Discussedreplacing replacingRod RodJohnson Johnsonas as the the "member "member from from industry" industry" on on Goldich Goldich Committee Committee (end (end of term term 2002) 2002) with with several several candidates candidates including including Dave Dave Meineke Meinekeof of Meriden Meriden Engineering, Hibbing, Minnesota. Dave later accepted the position and was welcomed, Engineering, Minnesota. Dave later accepted the position and was welcomed, and Rod was thanked for his service to the Institute, during the the annual banquet. Dave's Dave's term will end after Goldich Goldich selection selection for the the meeting meeting of of 2005. 2005. 6. Discussed Discussedreplacement replacementof of Mark MarkJirsa Jirsaas as ILSG ILSGSecretary-Treasurer Secretary-Treasurer(end (endof of 4-year 4-year term term 2002). A new member member to the the Institute, Institute, Peter Peter Hollings, Hollings,Lakehead LakeheadUniversity Universityin in Thunder Thunder Bay, was installed installed as "Secretary-Treasurer "Secretary-Treasurer in-training," pending pending a vote vote by by the the general general membership membership (as (as required required in in By-Laws). By-Laws). Because Because of his his newness newness to to the the Institute, Institute,the the board board generally agreed that Peter Peter would serve 2 years of the the 4-year term term concurrently concurrentlywith with Mark Mark in a period period of transition. At the the end end of the the 22 years years (following (followingthe the 2004 2004 meeting), meeting),the the finances and records records of the the institute, institute, and and responsibilities responsibilitiesof the the position positionwould would fall fall to to Peter. Peter. was generally generally This was presented to the membership after the Board meeting, and was accepted. accepted. 7. Other Other business: business: a) Discussed Discussed the offer by by Mike Mike Mudrey Mudrey to take take over as as ILSG ILSG webmaster—It webmaster-It was was generally agreed that Mike Mike could could do that, assuming assuming Ted Ted was was busy busy with with other other obligations and probably probably would not mind mind the relief. relief. Subsequent Subsequent discussions discussions indicate indicate xix xix �that Ted Ted would would like like to to continue continuein in this this endeavor, endeavor, and and has has already alreadypaid paidin inadvance advancefor for that 55 years years of of web web service service to to continue. continue. ItIt remains remains in in Ted's Ted's hands. hands. b) Discussed Discussedefforts effortsby by Graham GrahamWilson Wilsonto to list listILSG ILSGpublications publicationsas aspart partofofhis his b) MINLIB project and S t e v e Kissin Kissin volunteered volunteered to and website (www.turnstone.ca) -—Steve contact Graham Graham and and see see ifif there there isis anything anythingthat that the the ILSG ILSGcan canand andshould shoulddo doto to contact assist. assist. Discussedthe the prospect prospect of of extending extending aa "free "free ride" ride" to to annual annual Goldich GoldichMedal Medal c) Discussed recipients. ItIt was was generally generally agreed agreed that that registration registrationcosts costs should shouldbe bepaid paidby bythe the recipients. annual meeting meeting committee, committee, and and that that lodging, lodging, meals, meals, and and travel travel costs costscould couldbe bepaid, paid, annual at the the discretion discretion of of the the annual annual meeting meetingchairs. chairs. Discussed the the ILSG ILSG Newsletter—Peter NewsletterÑPete Hinz Hinz has has offered offeredto to write write ititbeginning beginninginin d) Discussed 2004 or or so. so. He Hecan cancoordinate coordinatewith with Ted TedBornhorst Bornhorstabout aboutthat thattransition. transition.The Thetopic topicofof 2004 whether the the Newsletter Newslettershould shouldremain remainpaper, paper, or or be bechanged changedto toaawholly whollyelectronic electronic whether format was was discussed discussedand andtabled. tabled. Most Mostseemed seemedto to think think we weshould shouldeventually eventuallyswitch switch format to to aa web-based web-basednewsletter, newsletter,perhaps perhapswith with email emailnotification. notification.This Thisraised raisedaafurther further issue that members members must must be be encouraged encouraged to to notify notify the the secretary-treasurer secretary-treasurerof of issue changes in email address or other status. changes in email address or other status. e) Questionable Questionablesampling—An sampling~An issuewas was raised raisedthat that at at least leastone onegroup groupof ofregular regular e) issue meeting meeting participants participants has has aa tradition tradition of of using using guidebooks guidebooksto to locate locateplaces placesfor formassive massive sampling programs. programs. In In this this one one case, case, samples samples are sold sold to Wards Wards or other other rock rock and and sampling 1) some some of of the the localities localitiesdiscussed discussedin in mineral specimen specimen dealers. dealers. The The problems problems are are 1) mineral guidebooksare are on on private privateland land(and (andtherefore thereforetrespassing trespassingisislikely), likely),and and2) 2)taking taking guidebooks large amounts amountsof of sample samplefrom fromsome somelocalities localitieslimits limitsthe theuse useof ofthese thesesites sitestotofuture future large generations.ItItwas was generally generallyagreed agreedthat that ILSG ILSGwould would print printinintheir theirguidebooks guidebooksaa generations. Policy Statement Statement that that warns warns of this this "questionable "questionablesampling sampling practice." practice." Mark Mark Jirsa Jirsa will will Policy create create such such language languagefor for inclusion inclusionin infuture futureguidebooks. guidebooks. f)f) Discussed Hinz abstracts~peter Hinzwarns warns from fromexperience experiencethat that Discusseddigital digitalsubmission submission of of abstracts—Peter this practice practice can can easily easilyturn turn into intoaa nightmare nightmarefor for preparers, preparers,particularly particularlyififthe the this submitters don't don't follow follow (or (or the the host host organization organization doesn't specify) specify) rigid rigid guidelines guidelines for submitters submission formats. Adjournment Adjournment submission formats. This This includes includes both both text and illustration formats. Respectfully Respectfullysubmitted submittedon on January January 27, 27, 2003 2003to to Peter PeterHinz, Hinz,Chair Chair of of the the48th 48thannual annual meeting, meeting, for for incorporation incorporationinto intothe theReport Reportof of the theChair Chairto toappear appearininProceedings ProceedingsVolume Volume 49. 49. Mark Mark Jirsa, Jirsa, Secretary-Treasurer, Secretary-Treasurer,Institute Instituteon onLake LakeSuperior SuperiorGeology Geology xx �0 0 -o PROGRAM >< x xxi �49th The following companies made generous contributions to the 4gth Annual Meeting. Meeting. We thank them and and John John Gartner Gartner of of the the Local Local Committee Committee for for their commitment to the Institute on Lake Superior Geology. For almost commitment the Institute on Lake Superior Geology. For almost 50 years this sustained interests interests of this organization organization has thrived through through the sustained individuals, corporations, universities, and government agencies individuals, corporations, universities, and government agencies in the the international geologic community. community. This This dedication dedicationtoto an an exchange of international geologic exchange of scientific ideas and aa passion for for field field trips trips (even (even in in driving driving rain rain or or snow) snow) has enabled the ILSG to to fulfill fulfill one one of of its its primary primary objectives: objectives: to promote better understanding of the geology in the Lake Superior region. Kleiman Pump & Well Drilling, &Well Drilling, Inc. Inc. P.O. Box Box 704 704 Iron Mountain, Michigan 49801-0704 49801-0704 Prime Meridian Meridian Resources Resources Ltd. Ltd. N7478 Niagara Niagara Lane Lane Fond du Lac, Lac, WI Wl 54935 54935 Coleman Engineering Engineering Company Company 635 Circle Drive Drive Iron Mountain, MI 49801 49801 xxii �+ WEDNESDAY MAY 7, 2003 8:00 a.m. TRIP 8:00 a.m.FIELD FIELD TRIP1:1WISCONSIN : WISCONSINMAGMATIC MAGMATICTERRANE TERRANE (#1 (#I IN IN GUIDEBOOK) GUIDEBOOK) Klaus Schulz, U.S. Geological Geological Survey Oshkosh, emeritus Gene LaBerge, LaBerge, University University of of Wisconsin Wisconsin— - Oshkosh, 2: THE ORE 8:00 a.m. FIELD TRIP 2: THEREPUBLIC REPUBLICMINE MINE— - LIFE LIFE CYCLE CYCLEOF OF AN IRON ORE FROM GENESIS GENESIS TO TO RECLAMATION RECLAMATION(#4 (#4 IN GUIDEBOOK) GUIDEBOOK) DEPOSIT FROM William William Cannon, U.S. US. Geological Geological Survey John Meier, Meier, Cleveland Cleveland Cliffs Cliffs Iron Iron Company Company 6:00 p.m. p.m. Return Return of Trips 11 and 6:00 and 2 4:00 p.m. p.m. -- 8:00 8:00p.m. p.m. Registration Registration 7:00 p.m. p.m. -- 9:00 9:00p.m. p.m. Ice Breaker Social and Poster Setup THURSDAY MAY 8, 2003 8:00 a.m. -- 9:00 9:00a.m. a.m.REGISTRATION REGISTRATION Note: Technical Technical Sessions Sessionsare are in inWhite White Spruce, Spruce, Pine Pine Mountain Mountain Resort Resort + Denotes Denotes Student Presentation Presentation 8:15 a.m. 8:15 a.m. INTRODUCTORY INTRODUCTORYREMARKS REMARKS Laurel Laurel G. Woodruff and and William William F. F. Cannon, Cannon, Co-Chairs Co-Chairs TECHNICAL TECHNICAL SESSION SESSION II Session Chair: Jim Miller, Minnesota Minnesota Geological Survey, Duluth, MN MN - 8:30 a.m. Harold HaroldBernhardt Bernhardt- Menominee MenomineeRange RangeHistorical HistoricalFoundation FoundationMuseum Museum A brief history history of iron iron mining mining on on the the Upper Upper Peninsula's Peninsula's Menominee MenomineeIron Iron Range Range 9:00 a.m. a.m. Cannon, Cannon, W.F., W.F., LaBerge, LaBerge, G.L. GL. and Klasner, Klasner, J.S. J.S. Niagara suture suture zone, northern northern Michigan Michigan and and Wisconsin—tectonics Wisconsin-tectonics in in the the 1.85 1.85 Ma arc-continent arc-continent collisional collisional boundary boundary 9:30 a.m. a.m. Schulz, Schulz, K. 9:30 A Paleoproterozoic Paleoproterozoic suprasubduction suprasubduction zone ophiolite-island ophiolite-island arc arc complex complex in northeastern northeastern Wisconsin Wisconsin 10:00 10:OO a.m. a.m. COFFEE COFFEEBREAK BREAKAND ANDPOSTER POSTER SESSION SESSION 10:40 a.m. a.m.Schneider, Schneider, D.A., D.A., Holm, HoIm, D.K., D.K., O'Boyle, O'Boyle, C., C., Hamilton, Hamilton, M. and Jercinovic, Jercinovic, M. 10:40 M. Paleoproterozoic development of a gneiss dome corridor in the the southern southern Lake Lake Superior region, USA USA 11:00 a.m. Holm, Hoim, D.K., D.K, Van 11:OO a.m. Van Schmus, Schmus, W.R., W.R., MacNeill, MacNeill, L.C., L.C., Boerboom, Boerboom, T.J., T.J., Schweitzer, Schweitzer, D. D. and and Schneider, Schneider,D.A. D.A. Late Paleoproterozoic (1900-1600 (1900- 1600 Ma) tectonic history of the the northern northern midmidU.S.A.: Implicationsfor for crustal crustalstabilization stabilization continent, U. S.A. :Implications 11:20 a.m. Medaris, Medaris, L.G., L.G., Jr. Jr. and Dott, 11 :20 a.m. Dott, R.H., R.H., Jr. The Sioux Quartzite metamorphism, geochemistry Quartzite revisited: sedimentology, metamorphism, geochemistry and and the origin of pipestone 11:40 p.m. Smyk, M.C. 1 1:40 p.m. The planned activities activities and The Lake Lake Nipigon Nipigon Geoscience GeoscienceInitiative Initiative— - planned and objectives objectives xxiii xxiii �12:00 p.m. Lunch Poster Session Session and 12:OO p.m. LunchBreak Break— - Poster and ILSG ILSG Board BoardMeeting Meeting(by (byinvitation) invitation) TECHNICAL SESSION SESSION IIII TECHNICAL Session Chair: Mike MikeMudrey, Mudrey, Jr., Jr., Wisconsin Wisconsin Geological Geological Survey, Survey, Madison, Madison, WI Wl 1:30 p.m. •: Heggie, Heggie, G. G. and and Hollings, Hollings, P. 1 :30 p.m. P. Geochemistry and mineralization of the Seagull Intrusion, Northern Ontario Geochemistry Ontario +:+ p.m.++:•:•Johnson, Johnson,J.R., J.R.,Hollings, Hollings, P. P. and and Kissin, Kissin, S.A. 1:50 p.m. Mineralization Mineralization of the Norton Lake Cu-Ni-PGE Cu-Ni-PGE deposit 2:10 p.m. Miller, J. J. D., Jr. 2:lO Petrology and PGE potential of the Greenwood Lake Intrusion, central central Duluth Complex, Lake County, County, Minnesota Minnesota p.m. •: Joslin, Joslin, G.D., Miller, J.D., Jr. and 2:30 p.m. G.D., Miller, and Rowell, Rowell,W.F. W.F. Stratiform Pd-Pt-Au mineralization in the Sonju Lake Intrusion, Lake County, Minnesota Minnesota +:+ 2:50 p.m. p.m. + + Marma, J., J., Brown, Brown, P. 2:50 P. and and Hauck, Hauck, S. S. Magmatic Magmatic and hydrothermal hydrothermal PGE mineralization mineralization of the Birch Birch Lake Lake Cu-Ni-PGE Cu-Ni-PGE Deposit Deposit in the the South South Kawishiwi, Duluth Complex, northeast northeast Minnesota Minnesota 3:10 p.m. 3:lO p.m.COFFEE COFFEEBREAK BREAKAND ANDPOSTER POSTER SESSION SESSION Waggoner, T. 3:30 p.m. Waggoner, T. Marquette Range perspective A hydrothermal hydrothermal component component of of Iron IronFormations Formations—A -A Marquette p.m. Tsu-Ming Tsu-Ming Han 3:50 p.m. Han Mode of occurrence occurrence of trona trona and and thermonatrite thermonatrite and and their their possible possible origin origin in in the the Iron-Formation of the Marquette Negaunee Iron-Formation Marquette Range, Lake Superior District, District, USA USA 4:10 p.m. Blaske, Blaske, A.R. 4:lO A.R. Mississippi-Valley at Bellevue, Michigan Geology of the MississippiValley type mineralization at 4:20 p.m. p.m. + Larson, Larson, P. 4:20 P. Mean transport length in tills of the southern portion of the Laurentide Laurentide ice sheet: implications for drift exploration exploration in the Lake Superior region +:+ 4:50 p.m. p.m. 63+ Marlow, Marlow, L., Mooers, H. and Larson, Larson, P. 4:50 P. environmental history Glacial Lakes Aitkin and Upham: their origin and environmental 5:10p.m. TrowJ. 5:10 p.m. Trow, J. Five gold possibilities in some wan copper copper sulfides sulfides in Ontario some Keweena Keweenawan Ontario and Michigan Michigan xxiv �6:00 p.m. CASH BAR 6:00 p.m. ICE BREAKER BREAKER— - MIXER — - CASH 7:00 p.m. p.m. ANNUAL ANNUALBANQUET BANQUETAND ANDAWARD AWARDPRESENTATION PRESENTATION 50th • Location Announcement of 5oth Annual Meeting Location • 2003 Klaus Schulz Schulz 2003 Goldich Goldich Award Presentation Presentation to Klaus • 2003 Banquet Banquet Address 2003 Dr. Susan Martin, Martin, Michigan Michigan Technological Technological University University The indigenous indigenous people of the Lake Superior Basin: Understanding Understanding the links links among environment, environment, geology geology and religious religious belief Meeti ng participants Meeting participantswho whoare arenot notregistered registeredfor forthe thebanquet banquetare arewelcome welcometo tothe thebanquet banquetaddress address FRIDAY MAY 9, 2003 TECHNICAL SESSION Ill Ill Session Session Chair: Eric Jerde, Morehead Morehead State State University, Morehead, Morehead, Kentucky Kentucky 8:20 8:20 a.m. a.m. INTRODUCTORY INTRODUCTORYREMARKS REMARKS Laurel G. Woodruff Woodruff and and William William F. F. Cannon, Cannon, Co-chairs Co-chairs Laurel 8:30 a.m. a.m. Hollings, Hollings, P., P., Fralick, Fralick, P. P. and and Kissin, Kissin,S. S. Geochemistiy and of the the1537 1537Ma Ma Redstone Redstone Point Geochemistry and geodynamic geodynamicimplications implications of Point anorogenic anorogenic granite, Ontario, Canada Canada 8:50 a.m. a.m. +*.:. Buttram, P.M. R.M. and and Bjornerud, M. : Buttram, M. Textural constraints in in thethe Wolf River BatBatholith ho 11th Textural constraintson onthe theorigin originofofrapakivi rapakivitextures textures Wolf River 9:10 a.m. a.m. + .:.Sandin, Sandin, N.A. N.A. and and Bornhorst, Bornhorst, T.J. Sequence of Precambrian Precambrian mafic dikes in Marquette County, County, Michigan, Michigan, with with emphasis on the Sugar/oaf Sugarloaf Mountain and Republic areas 9:30 a.m. a.m. Jerde, Jerde, E.A. E.A. Gabbro/granophyre theCrocodile CrocodileLake Lake Intrusion: Intrusion: aa possible possible vent vent Gabbro/granophyre relations relations ofofthe for the Hovland Lavas? for the Hovland Lavas? 9:50 Vislova, 9:50 a.m.. :.:• 0 Vislova, T. T. Evaluation of initial initial magma compositions compositions for the Bald Bald Eagle Eagle Intrusion and Evaluation of magma for the Intrusion and associated rocks rocks associated 10:10 a.m. COFFEE 10:10 COFFEEBREAK BREAKAND AND POSTER POSTER SESSION SESSION 10:30 a.m. a.m. + •:•Charkoudian, Charkoudian, K., K., Tikoff, Tikoff, B. and :+ and Bauer, Bauer, R. R. Stike -slipseparation separationofof Burntside trondhjemite Wakemup Bay Bay Stike-slip thethe Burntside trondhjemite andand thethe Wakemup tonatilte,Northern NorthernMinnesota Minnesota tonatlite, 10:50 1O:5O a.m. <+ .:.Garbowicz, Garbowicz, A. A. and Bjornerud, Bjornerud, M. M. Wisconsin Paleostress inferences from slip vectors the eastern eastern part part of the Paleostress inferences from slip vectors in in the the Wisconsin segment rift segmentofofthe theMidcontinent Midcontinent rift 11:10 Potter, E.G. E.G.and and Mitchell, Mitchell, R.H. 11:10 a.m. +*•:• : Potter, R.H. The and exotic exoticmineralogy mineralogyofofthe the WesternSubcomplex Subcomplex of of the theDeadhorse Deadhorse The rare rare and Western Creek Diatreme, Northwestern Ontario Creek Diatreme, Northwestern Ontario xxv XXV �B.A., Mudrey, Mudrey, M.G., M.G., Jr., Jr., Czechanski, Czechanski, M.L., M.L., Reid, Reid,D.D. D.D. and andHunt, Hunt,T.C. T.C. 11:30 a.m. a.m. Brown, Brown, B.A., Highway construction, construction, mine mine reclamation, reclamation, and and land-use land-use planning planning challenges challenges in in the historic historic Upper Upper Mississippi Mississippi Valley Valley lead-zinc district of southwest southwest Wisconsin Wisconsin 11:50a.m. 11:50 a.m. Wattrus, Wattrus, N. N. High-resolution multibeam bathymetry in Lake Lake Superior Superior High-resolution 12:10 p.m. p.m.LUNCH LUNCHBREAK BREAK—-POSTERS POSTERSREMOVED REMOVEDAFTER AFTER LUNCH LUNCH 12:10 \ TECHNICAL SESSION IV IV TECHNICAL Session Chair: Peter PeterHinz, Hinz,Ontario OntarioGeological GeologicalSurvey, Survey, Kenora, Kenora, ON ON 1:40 a.m. a.m. +*:•:•Vallini, Vallini,D.A., D.A.,McNaughton, McNaughton,N.J., N.J.,Rasmussen, Rasmussen,B., B.,Fletcher, Fletcher, I. I. and and Griffin, Griffin, B.J. B.J. U-Pb geochronology to unravel the history history of Proterozoic Proterozoic Using xenotime U-Pb sedimentary basins: basins: aastudy studyininWestern WesternAustralia Australia and andthe theLake LakeSuperior Superiorregion region sedimentary 2:00 p.m. p.m. Kissin, S.A., S.A., Vallini, D.A., D.A., Addison, W.D. W.D. and Brumpton, Brumpton, G.R. G.R. New zircon ages from from the the Gun Gunflint Ontario flint and and Rove Formations, northwestern northwestern Ontario 2:20 p.m. p.m. +%+ Richardson, Richardson, A., A., Fralick, P. and Hollings, Hollings, P. P. Sibley Basin sediment provenance using zircon and whole rock geochemical methods: Possible Possiblesource sourceareas areasof of the thePass Pass Lake Lake Formation Formation G. 2:40 p.m. p.m. ++:•:•Rogala, Rogala,B., B.,Fralick, Fralick, P. P. and and Borradaile, Borradaile, G. A magnetostratigraphic magnetostratigraphic and secular variation study study of of the Sibley Group 3:00 3:00 p.m. p.m. COFFEE COFFEE BREAK BREAK 3:20 p.m. Argast, A. sediment chemistry tell us about rocks like those from the What does sediment the Fern Fern Creek Formation? 3:40 p.m. p.m. Bartnik, Bartnik, P. J. and and Evans, B. B. W. ford, Michigan area Geology and hydrogeology hydrogeology in in the the Kings Kingsford, 4:00 p.m. p.m. Presentation Presentation of Student 4:00 Student Paper Paper Awards Awards Bornhorst, Michigan Michigan Technological University: University: Student Paper Committee Ted Bornhorst, Committee SATURDAYMAY MAY10,2003 10, 2003 SATURDAY 8:00 a.m. a.m. FIELD FIELDTRIP TRIP3: 3:MENOMINEE MENOMINEEIRON IRONRANGE RANGE (#2 (#2 IN IN GUIDEBOOK) GUIDEBOOK) Gene emeritus Gene LaBerge, LaBerge, University Universityof of Wisconsin Wisconsin— - Oshkosh, emeritus John Klasner, University University of of Western WesternIllinois, Illinois,emeritus emeritus William Cannon, U.S. William U.S. Geological Geological Survey 6:00 p.m. p.m. Return Return of Trip 3 6:00 3 SUNDAYMAY MAY11, 2003 SUNDAY 11,2003 TRIP4:4:Iron Iron River River — Crystal Falls Falls Iron ININGUIDEBOOK) 8:00 a.m. FIELD TRIP - Crystal IronDistrict District(#3 (#3 GUIDEBOOK) Gene Oshkosh, emeritus Gene LaBerge, LaBerge, University Universityof of Wisconsin Wisconsin— - Oshkosh, John Klasner, Klasner, University University of of Western WesternIllinois, Illinois, emeritus emeritus William Cannon, Cannon, U.S. Geological Survey 6:00 p.m. p.m. Return Return of of Trip 4 6:00 xxvi xxvi �POSTER PRESENTATIONS Brown, Czechanski, M.L., Mudrey, MG., M.G., Jr. Jr. and andReid, Reid, D.D. D.D. Brown, B.A., Czechanski, Wisconsin mineral resource GIS GIs and related digital map and database database products Wisconsin —a a progress report Boerboom, Boerboom,T. T. Bedrock geologic geologic maps maps of of Keweena Keweenawan intrusive rocks rocks in in the the Bedrock wan volcanic and intrusive North Shore Shoreof of Lake Lake Lakewood, Lake wood, French French River, River, and and Knife River 7.5' quadrangles, quadrangles, North Superior, Minnesota Easton, Easton, R.M. P.M. Geology and mineral potential of Proterozoic Proterozoic mafic intrusions in the the northern northern Grenville Province of Ontario Grenville Ontario Hart, Hart, T.R. Keweena wan mafic ma f/cand andultramafic ultramaficintrusive intrusive rocks rocks of of the Lake Nipigon Nipigon and Keweenawan and Crystal Crystal Lake areas, areas, northwestern Ontario Ontario S.A., Oreskovich, Oreskovich, J.A. and Hauck, S.A., and Severson, Severson, M.J. M.J. and Beaver Bay Geology, drill holes, mineral leases, and geophysics in the Duluth and Integration of of various various GIS GIs databases databases to to tell tell a Compexes, northeastern Minnesota: Integration story story of the the history history of of past past and and current currentCu-Ni-PGE Cu-Ni-PGEmineral mineral exploration exploration •+ Heiling, C.D. Heiling, :+ C.D. Peperites of the Gafvert Gafvert Lake Volcanic Volcanic Complex, Complex, St. Louis County, County, Minnesota Minnesota Hocker, S.M., S.M., Hudak, Hudak, G.J., G.J., Odette, Odette, J.D. J.D. and Newkirk, ++•:. : Hocker, Newkirk,T.T. T.T. alteration mineral phases at the Five Mile Lake volcanic-hosted Chemistry of alteration volcanic-hosted massive massive sulfide sulfide prospect, NE NE Minnesota Minnesota ++•: Keatts, Keatts,M.J., M.J., Jirsa, Jirsa,M. M. and and Hoim, Holm, D. D. single-grainanalyses analyses of of Precambrian Precambrian mafic intrusions intrusions in Results of 40ArI9Ar ^Ar^Ar single-grain in northern northern and north-central north-central Minnesota Minnesota Mckenzie, M.A., and Jercinovic, Jercinovic, M. ++ McKenzie, M.A., Hoim, Holm, O.K., D.K., Schneider, D.A. and M. Evidence for largeResults of EMP monazite geochronology in in E-C E-C Minnesota: Minnesota: Evidence scale geon 17 17 metamorphism metamorphism associated associated with with post-tectonic post-tectonic plutonism plutonism Metsaranta,R., R.,Fralich, Fralich, P. P. and and Hollings, Hollings, P. ++:•:•Metsaranta, geochemical investigation volcanic and metasedimentary A geochemical investigation of of Mesoarchean Mesoarcheanmeta metavolcanic metasedimentary rocks from Uchi greenstone greenstone belt from the theBirch Birch— - Uchi Nicholson, S. Nicholson, S.W. W. and Cannon, Cannon, W.F. W.F. Stratigraphy wan rocks of the St. Stratigraphy and and structure structure of of Keweena Keweenawan St. Croix Croix horst, horst, northwestern northwestern Wisconsin Wisconsin Stott, G.M., G.M., Davis, D. W., K.J. and Tomlinson, Tomlinson,K. K.Y. Y. Stott, W.,Parker, Parker,J.R., JR., Straub, 1(4. Archean tectonostratigraphic assemblages of eastern Waba goon Subprovince, Archean tectonostratigraphicassemblages of eastern Wabagoon Subprovince, northwestern north western Ontario Ontario xxvii ��ABSTRACTS xxvffl ��WHAT DOES SEDIMENT CHEMISTRY TELL US ABOUT ROCKS LIKE THOSE FROM THE FERN CREEK FORMATION? Department of Geosciences, Indiana University Argast, Anne, Department University Purdue Purdue University University Fort Fort Wayne, Fort Wayne, IN 46805-1499, 46805-1499, Argast@ipfw.edu Argast@ipfw.edu Bulk chemical chemical analyses analyses are are accepted accepted and and powerful powerful tools tools for for the the study study of of metamorphic metamorphicand and igneous rocks. rocks. Bulk Bulk chemical chemical analyses analyses are are less less accepted accepted and and less less widely widely used used for for the the study studyof of sedimentary rocks. This is at least partly the result of a widely-held view that chemical chemical data data are are unreliable indicators indicators of of sedimentary sedimentary events events due due to to the the post-burial post-burial diagenetic diageneticalteration alterationof of the the sediment. In recent years, this view has been reinforced with studies sediment. studies indicating indicating the the potential potential for for extreme extreme diagenetic diagenetic alteration alteration of of sediments, sediments,with with km-scale km-scale transport transport proposed proposedin insome somesystems systems (e.g., Wintsch and Kvale, 1994). 1994). Potassium Potassium is often singled-out singled-out as an especially especially mobile component in diagenetic systems. For example, example, Awwiller (1993), (1993), working working in in the the Gulf Gulf Coast Coast Tertiary, Tertiary,postulates postulatesan an increase increasefrom from2.0 2.0to to 3.8 wt. percent K20 1 0 pore K20in mudrocks, mudrocks, due due significantly to the transport of K as part of i03 volumes of fluid fluid passing through through the the system system in in the the depth depth range range from from 1500 1500to to 4000 4000m mbelow below the the surface. surface. An alternate alternate view (Argast (Argast and and Donnelly, Donnelly, 1987) 1987)maintains maintains K20 K20isis aa generally generallyconservative conservative element in diagenetic settings, and that observed variations in K K20 2 0 content preserve compositional compositional characteristics characteristicspresent present at at and and before before accumulation. accumulation.Depending Dependingon on your your point-ofpoint-ofview, the chemistry chemistry of diagenetically diageneticallyand metamorphically metamorphically altered altered sedimentary sedimentaryrocks rocks may may (or (or may not) provide useful information information about about provenance, provenance, weathering weathering and and other other qualities qualitiesof of the the sedimentary sedimentary system. system. Unconsolidated sediments, Unconsolidated sediments, delivered delivered as turbiditic pulses of siliciclastic debris eroded from the Mountains, accumulated Himalaya Mountains, accumulated on the the Bengal Fan (DSDP (DSDP 218) 218) and and now now at at subbottom subbottomdepths depths from 12 noted in lithified 12 to 729 m, produce chemical trends very similar to those previously noted (and metamorphosed) sedimentary sedimentary rocks. The similarity in chemical trends across across this this broad broad range of conditions conditions and and environments environmentssuggests suggests sedimentary sedimentary chemical chemical trends trends arise arisefrom from fundamental conditions conditions imposed imposed upon upon the the system system before before burial, burial, and and are are not not necessarily necessarily the the result result of extensive extensive diagenetic diagenetic alteration alteration at at depth. depth. The Fern Creek Formation Formation (Early (Early Proterozoic, Proterozoic, Lower Lower Chocolay Chocolay Group) Group) is is well well exposed exposedalong along the the Sturgeon Sturgeon River near the dam dam northeast of of Loretto, Loretto, Michigan. Michigan. These These rocks rocks have have been been interpreted interpreted as glaciogenic in origin, origin, and and the diamictites diamictites they they contain contain used as as evidence evidence for for glacially-derived glacially-derived dropstone dropstone units. units. Others Others have have interpreted interpretedthe the Fern Fern Creek Creek Formation Formation as as nonglaciogenic nonglaciogenicin in origin origin with the sediments accumulated environments grading upward into lagoonal or accumulated in fluviatile environments estuarine environments. environments. Field and textural qualities (to be discussed as part of a post-meeting fieldtrip in the Menominee Menominee Iron Range) Range) support support aa glaciogenic glaciogenic origin. origin. 1 �chemistry also also supports supports aa glaciogenic glaciogenic origin origin (Argast, (Argast, 2002) 2002) . The chemical data, Bulk rock chemistry chemical data, including the absence absenceof of aa correlation correlationbetween betweenK20 K 2 0and andA1203, A1203,show sediments sedimentsfrom from the the Fern Fern including deposited without without extensive extensivesorting sortingor or demixing demixingof of hydraulically hydraulicallycoarsercoarserCreek Formation Formation were deposited + Na ++ K)/A1 and finer-grained finer-grained fractions. Other data, including the Na20/K20 Na20/K20 and (2Ca + K)/Al atomic atomic ratio suggest sediment accumulated with abundant original feldspar. The The chemical index of of 61, similar similar to to the average average CIA CIA of 57 57 in in Gowganda Gowganda diamictite diamictite alteration (CIA) ranges from 50 to 61, matrices. The accessory suite suite is complex and and includes includes poorly poorly rounded rounded zircons. zircons. These These attributes attributes are consistent with an origin as as aa glacial glacial till. till. . Several minerals enriched enriched in rare earth elements elements (REE) (REE) and/or andlor thorium thorium were were identified identifiedin in the the Fern Creek Formation. These include include monazite, huttonite huttonite (monoclinic (monoclinic ThSiO4) ThSi04) and a fluorfluorhydroxy-REE mineral. Th concentrations concentrations as high as 53 53 ppm were noted in one bulk analysis. Efforts Efforts to obtain obtain aa chemical chemical date date on on these these minerals minerals have have so sofar far been been unsuccessful. unsuccessful. The Carney Lake Gneiss Gneiss is aa chemically-compatible chemically-compatible possible possible source source for for the the Fern Fern Creek Creek Formation. Formation. REFERENCES Argast, A., 2002, 2002, The The lower lower Proterozoic Proterozoic Fern Fern Creek Creek Formation, Formation,northern northern Michigan: Michigan:mineral mineraland and bulk geochemical evidence J. Earth Earth Sci., Sci.,v. v. 39, 39,p. p.481481evidence for for its its glaciogenic glaciogenic origin: origin: Can. Can. J. 492. 492. Argast, S. and Donnelly, T.W., 1987, of clastic sedimentary 1987, The chemical discrimination of components: J. Sed. Pet., v. 57, p. 813-823. 813-823. components: Awwiller, D.N., 1993, Illite/smectite formation and potassium mass transfer during burial 1993, Illite/smectite diagenesis Sed. diagenesis of mudrocks: aa study study from from the Texas Texas Gulf Coast Coast Paleocene-Eocene: Paleocene-Eocene:J.J. Sed. Pet., v. 63, p. 501-512. 501-512. of 1994, Differential mobility of elements in burial diagenesis of Wintsch, R. P. and Kvale, C. M., 1994, siliciclastic siliciclastic rocks: J. Sed. Sed. Res., Res., v. v. 64A, 64A, p. p. 349-361. 349-361. 2 �GEOLOGY AND HYDROGEOLOGY IN THE KINGSFORD, MICHIGAN MICHIGAN AREA GEOLOGY BARTNIK, PATRICK J., pbartnik@arcadis-us.com, pbartnik@arcadis-us.com,ARCADIS ARCADIS G&M, G&M, Inc., Inc., Kingsford, Kingsford, Michigan, 49802; and EVANS, ARCADIS G&M, G&M,Inc., Inc.,Milwaukee, Milwaukee, EVANS, BRUCE BRUCE W., W., bevans@arcadis-us.com, bevans @ arcadis-us.com,ARCADIS Wisconsin, 53202 Wisconsin, 53202 Investigations have been undertaken in a portion of the City of Kingsford, Investigations Kingsford, Michigan Michigan and and Breitung Township, Michigan (the study study area) to determine determine the geologic geologic and and of glacial sediments sediments and and bedrock. bedrock. The hydrogeologic characteristics of The study study area is located located south-central Upper Peninsula Peninsula of Michigan. Michigan. in Dickinson County in the south-central The ARCADIS investigations investigations were largely largely completed between April April 1997 1997and and January January 2001, but are continuing. During Duringthe theinvestigations, investigations,over over300 300soil soil borings borings were were completed, along with 47 test pits and 9.5 miles of geophysical study. The The topography topography is is characterized by three distinct characterized distinct landform terraces (Upper, (Upper, Lower, and and Riverside), Riverside), which which range in elevation elevation from from approximately approximately 1,120 1,120feet feet above above mean sea sea level level (ft (ft msl) msl) to to approximately approximately 1,045 1,045 ft msl. The The.Upper Upper Terrace Terrace contains contains several several isolated isolated glacial glacial kettles. kettles. The elevation of the Menominee River is approximately 1,037 ft msl. The Thegeology geology is is 3 �comprised of unconsolidated unconsolidated glaciofluvial and and glaciolacustrine glaciolacustrinedeposits deposits of of clay, clay, silt, silt,sand, sand, and gravel that exhibit complex horizontal and vertical spatial variability. These These the Lower sediments overlie the Middle Precambrian Michigamme Slate and the Precambrian metavolcanic Quinnesec Formation. Formation. Depth to groundwater in the unconsolidated unconsolidated deposits deposits ranges from about 10 10 feet below land surface (bls) near the Menominee bis in the Upper Terrace. Groundwater Menominee River to more than 50 feet bls Groundwaterflow flow follows irregular pathways toward the Menominee River, but generally flows from northeast to southwest. +0.863ft/ft ft/ftin in upland upland southwest. Vertical Verticalhydraulic hydraulicgradients gradientsrange range from from +0.863 ft/ftnear nearthe theMenominee Menominee River. River. Hydraulic areas to —0.012 -0.012 ft/ft Hydraulicconductivities conductivitiesrange rangefrom from1 O3 centimeters per second (cdsec) (cm/sec) to to 10.' 101ccm/sec forcoarser-grain coarser-grainmaterial materialtoto1.03 1.03x x1 i0 d s e c for 0'~ cm/sec " c~d s e cfor forthe thevery veryfine-grain fine-grainsand sand and and sandy sandy silt. The Thebedrock bedrock is c d s e c to 3.94 xx 1i00cm/sec generally considered impermeable. Groundwater Groundwaterflow flow velocities velocities range range from from approximately 3 ft/day to 280 ft/day in coarser-grain units, and from approximately approximately0.1 0.1 approximately ft/day ft/day to 33 ft/day ftlday in in the the very very fine-grain fine-grain sand sandand andsandy sandysilt. silt. To aid in the understanding of the complex geology within the study area, threedimentional dimentional modeling of the geology was undertaken using the topographic surface, bedrock surface, and glacial sediments. sediments. Thirteen geologic units identified from the borehole data were categorized in to 3 units, based on permeability and anticipated effects on groundwater flow. The The modeling modeling and visualization of the geology were completed completed using aa Geostatistical GeostatisticalSoftware SoftwareLibrary Library (GSLIB), (GSLEB), developed developed at at Stanford Stanford University, FORTRAN programs, and and Environmental Environmental Visualization VisualizationSystem System(EVS) (EVS) software developed by the C Tech Development Corporation. Corporation. 4 �GEOLOGY GEOLOGY OF OF THE THE MISSISSIPPI-VALLEY MISSISSIPPI-VALLEYTYPE TYPE MINERALIZATION MINERALIZATIONAT BELLE VUE, MICHIGAN MICHIGAN BELLEVUE, BLASKE, Allan Allan R., R., Blaske BlaskeGeoscience, Geoscience,8313 8313Hartel, Hartel,Grand GrandLedge, Ledge,ME MI 48837 48837 BLASKE, The Bayport Limestone is exposed in quarrying quarrying operations at Bellevue, in southwestern southwestern Eaton Eaton County, Mining has County, Michigan. Michigan. Mining has been been active active around around Bellevue Bellevue since since the mid-1800's. Approximately 25 feet of the Bayport is exposed in the the quarrying quarrying operations, and consists of a gray to buff colored thin-bedded thin-bedded limestone. limestone. Bayport limestone Mississippian in comprises the upper portions portions of The Bayport limestone is is late Mississippian in age, age, and comprises the upper of the Grand Rapids Group. Group. It is underlain underlain by by the the Michigan Michigan Formation, Formation, also of the the Grand Grand Rapids Rapids Group. The Theearly earlyMississippian MississippianMarshall Marshall Sandstone Sandstone and and Coldwater Coldwater Shale Shale lie lie below below the the Grand Grand Rapids Group. The TheBayport Bayportisisoverlain overlainby bythe theearly earlyPennsylvanian PennsylvanianSaginaw SaginawFormation Formation(within (within the Michigan Basin), Basin), but but covered covered only only by by glacial glacial sand sand and and gravel gravel at at the the quarry quarry site. site. Mineralogy of the deposit deposit isis simple, simple,consisting consistingpredominantly predominantly of of pyrite, pyrite, marcasite, marcasite, and and calcite. calcite. Pyrite is most commonly commonly found as encrustations encrustations of cubic cubic crystals, crystals, formed directly directly on limestone. limestone. Marcasite is generally generally lighter lighter in in color color than than the the pyrite, pyrite, and and often often in in iridescent, iridescent,platy platycrystal crystalgroups. groups. Marcasite is by by far the dominant iron sulfide. sulfide. Two of calcite calcite are are observed. observed. Early Marcasite is dominant iron Two generations generations of calcite is found as small coatings. The small crystals crystals lining cavities as drusy drusy coatings. The second second generation generation of calcite is found in large, masses. Trace large, euhedral euhedral crystals and cleavable masses. Trace amounts amountsof of sphalerite, sphalerite, barite, and fluorite are present. Fluorite was the earliest to form, as small brown crystals Fluorite was the earliest to form, as small brown crystalsdirectly directly on the Marcasite and Pyrite was was formed formed in association association with with the the early early calcite. calcite. Marcasite and the limestone. limestone. Pyrite sphalerite sphalerite are later than the early calcite and pyrite. Second Second generation generation calcite calcite began slightly slightly after the marcasite. Tiny Tinycrystals crystalsof of marcasite marcasite can can also alsobe befound foundon onthe thelarge largecalcite, calcite,indicating indicatingthat that Barite appears later than formation of marcasite continued to the end of mineralization. formation the end of mineralization. appears than the the sulfides, sulfides, but before the end end of of the the calcite calcite formation. formation. Mineralization present predominantly predominantlyinin brecciated brecciated zones zones and and vein Mineralization isis present vein structures structures within within the Bayport Limestone. Limestone. The The most most common common type type of of breccia breccia consists consists of of small, small,angular angular clasts clasts surrounded by open-space open-space filling filling of of sulfides sulfides and and calcite. calcite. A second surrounded by second type type of of breccia breccia consists consists of larger, rounded clasts, clasts, with with the interstitial larger, rounded interstitial spaces spaces filled with aa muddy muddy limestone limestone and and pyrite. pyrite. Orientation Orientation and size of the mineralized zones within the limestone is not known, known, due due to to lack lack of of mapping. Fine-grained exposure within the quarry and insufficient historical mapping. Fine-grained iron iron sulfide sulfide is is also also observed as replacement structures, structures, along along apparent apparent solution solution fronts fronts within within the the massive massivelimestone. limestone. 36-element ICP of the sulfides indicates the the simplicity simplicity of of the the mineralization. mineralization. 36-element The geochemistry geochemistry of analysis of pyrite and marcasite separates, as well as as aa composite composite breccia breccia sample, sample, indicate indicate very very low concentrations of of trace elements. Copper, Copper, lead lead and andzinc zinc are arefound foundatatconcentrations concentrationsof of less less than 60 ppm; nickel is less than 30 is than 30 ppm; ppm; and and cadmium cadmium and cobalt less than 5 ppm. Barium is also low, generally less than 20 ppm. Manganese is high in the breccia (385 ppm), and lower in Manganese is high in the breccia (385 pprn), and lower in the sulfide separates (64 to 109 109 ppm), pprn), while chromium is high in the sulfides sulfides (150 (150 ppm) and and low 5 �in the breccia (31 ppm). Arsenic Arsenic isis present present in in the the breccia breccia (7 (7 ppm), ppm), but low in the the iron iron sulfides sulfides at less than 5 ppm. Sulfur isotopic were analyzed on separated Sulfur isotopic compositions compositions were analyzed on separated samples samples of pyrite, pyrite, marcasite, marcasite, and and sphalerite. Sulfur Sulfur isotopic isotopic compositions compositions (34S) (S^S) of of the the sulfide sulfide phases phases from from the Bayport Limestone are 14.5°/ for for for are 14.5°/o forthe the pyrite, pyrite, 12.8°/ 12.8°/o forthe themarcasite, marcasite, and and 19.8°/ 19.8°/o forthe thesphalerite. sphalerite. These compositionsindicate indicatethat that the the mineralizing fluids were were basinal basinal brines compositions mineralizing fluids brines from within within the the surrounding Mississippian Mississippian and and Pennsylvanian Pennsylvanian formations. formations. Unpublished surrounding Unpublished data data obtained obtained from from the the USGS (Westjohn, D. D. B., pers. comm.) as part of the RASA program indicate a large range range of of program indicate 6S ininsamples S^S samplescollected collectedfrom fromthe theunderlying underlyingMarshall MarshallSandstone Sandstoneand andMichigan Michigan Formation, Formation, as well as the overlying Formation and and the the Jurassic Jurassic Red Red Beds. Beds. Pore well overlying Saginaw Formation Porewater, water,whole-rock, whole-rock, sulfide, and sulfate sulfur sulfur isotope isotope compositions compositions for the the underlying underlying formations formations exhibit exhibit average average 345 20°/, while S^S near 20°/oo whilethe the average average S^S within the overlying overlying formations formationsisisnear near170/00. 17 Oleo. Temperature of the mineralization has been determined determined using fluid inclusions in in calcite calcite (Panter, (Panter, K. 5., S., 2001). 2001). Calcite afforded the only only mineral mineral phase phase with with inclusions inclusionsfor formicrothermometric microthermometric study. Temperatures Temperaturesof of homogenization homogenization indicate indicate aa bimodal bimodal distribution, distribution, with with aa low low temperature temperature mean of approximately approximately 58°C, 5g°Cand a high temperature mean of approximately approximately 138°C. 138OC. The Themean mean These temperatures are similar to those temperature temperature of all all inclusions inclusions analyzed analyzed was was 107°C. 107OC. These temperatures are those the Mississippian observed using isotopic compositions in authigenic minerals in observed using isotopic compositions authigenic minerals Mississippian and and Pennsylvanian sandstones (Westjohn, (Westjohn, D. B., Pennsylvanian sandstones B., 1994). 1994). Fluid salinities salinities based based on on freezing freezing point point depression range from 2.6 to 9.5 9.5 equivalent equivalentweight weight percent percent NaCI. NaCl. The quarries at Bellevue are located located within within55 to to 66 miles miles to the north and west of the quarries at Bellevue are the known known northwest end of the northwest the Albion-Scipio Albion-Scipio Oil Oil Field Field Trend. Trend. This oil field field (dolomitized (dolomitized fracture fracture and and solution cavities) structure is located within the Trenton-Black River (Middle Ordovician) rocks, cavities) structure is located within the Trenton-Black River (Middle Ordovician) rocks, some 4,000 feet deeper than the Bayport Limestone. The The structure structureisis related relatedto tofaulting faultingwithin within the basement basement rocks. Evidence Evidenceof ofthe thestructure, structure,however, however, isispresent present ininthe thelower lowerMississippian Mississippian Sunbury Shale Formation, (approximately 3,000 feet higher than the Middle Middle Ordovician Ordovician rocks), rocks), the Coldwater the Coldwater Shale (overlying (overlying the Sunbury), Sunbury), and and the the Marshall Marshall Sandstone Sandstone (overlying (overlying the the are evident Coldwater). Coldwater). If movements movements associated associated with this this structure structure are evident in in the theformations formations immediately below the Bayport Limestone, Limestone, itit seems seems likely likely that that the the Bayport Bayport Formation Formationwould would also also with the the structure. structure. Faulting associated with the Trend is likely be affected by faulting associated with responsible for for small structures responsible structures in the the Bayport, Bayport, allowing allowing for for brecciation, brecciation, subsequent subsequent fluid fluid migration, and precipitation of the the mineralization. mineralization. REFERENCES REFERENCES of Fluid Inclusions in Calcite from 2001. A A Preliminary Preliminary Microtermometric Study of Panter, K. S., 2001. Bellevue, Michigan, unpublished data, Bowling Green State University, OH Westjohn, D. B., 1994, of 1994, Michigan Basin RASA Solid-Phase Solid-Phase Investigation, in Geohydogeology of Carboniferous Aquifers Aquifers of of the Michigan Basin, Great Lakes Carboniferous Lakes Section-SEPM, Section-SEPM, 1994 1994 Fall Fall Field Field Conference, Conference, September September23-24, 23-24, 1994, 1994,Lansing, Lansing, MI MI 6 �WAN VOLCANIC AND INTRUSIVE ROCKS BEDROCK GEOLOGIC GEOLOGICMAPS MAPSOF OFKEWEENA KEWEENAWAN IN THE THE LAKE WOOD, FRENCH RIVER, AND KNIFE RIVER 7.5' QUADRANGLES, QUADRANGLES, NORTH LAKEWOOD, FRENCH KNIFE SHORE OF LAKE LAKE SUPERIOR, SUPERIOR, MINNESOTA MINNESOTA BOERBOOM, Terrence Terrence J., Minnesota Minnesota Geological GeologicalSurvey, Survey, St. St. Paul, Paul, MN, MN, boerb001@umn.edu boerb001 @umn.edu The Minnesota Minnesota Geological Geological Survey, with with partial partial funding funding by by the theU.S. U.S.Geological GeologicalSurvey SurveySTATEMAP STATEMAP geologic mapping program, has recently recently published published detailed detailed bedrock bedrock geologic geologic maps maps of of three three quadrangles quadrangles located along the North Shore of Lake Lake Superior Superior northeast northeast of of Duluth, Duluth, Minnesota Minnesota (Fig. (Fig. 1;1;Boerboom Boerboomand and others, 2002a, was completed completed at at a scale of 1:12,000, at a scale 2002a, b). b). Field mapping mapping was 1:12,000, and compiled compiled at scale of 1:24,000. This mapping has shown that some flow sequences can can be traced inland as far as 1:24,000. as 10 10to to 12 12 kilometers, and has identified hundreds of of individual flows flows within within the the larger larger flow flow units. units. Several mafic to felsic, subcordant subcordant to discordant discordant sills sills and and intrusions intrusionshave have also also been been mapped. mapped. Prior to this mapping, bedrock geologic geologic maps maps for for this this area area were were at at a scale of mapping, the only only published published bedrock 1:200,000 (for example Miller and others, 2001), and other work was concentrated along the shoreline of Lake Superior. Brannon Brannon(1984) (1984)sampled sampled160 160successive successivevolcanic volcanic flows, flows, starting starting above above the the Lester Lester River River sill and ending in Two Two Harbors, Harbors, as part part of of an an exhaustive exhaustive geochemical geochemical study. Green Greenand andothers others(1977) (1977) included this area as part included this part of of aamore morebroad broadcoastal coastalzone zonemanagement managementstudy. study. Schwartz and Sandberg Sandberg (1940) published a paper on the diabase sills near Duluth that included some of the the sills sills mapped mapped during during this study. Sandberg Sandberg(1938) (1938)mapped mapped the the stratigraphy stratigraphyof of the the flows flows exposed exposed at the shoreline shoreline from Duluth to Two Harbors, identifying some 180 180 lava lava flows. flows. Although all of these these studies studies made made some some incursions incursions inland from the shore, shore, none none of them them provided systematic systematicmapping mapping away away from fromthe the shoreline shorelineproper. proper. Bedrock exposure in the map area area varies varies greatly, greatly, from from nearly nearly continuous continuous outcrop outcrop along alongthe the shoreline shoreline and many of the short short streams streams along along the the slope slope into into Lake Lake Superior, Superior, to variably variably abundant abundant outcrop outcrop in the hills inland hills inland from the lakeshore. Throughout Throughout the the map map area, area, there there are are many many closely closely spaced spaced streams that have eroded into the bedrock perpendicular to the strike of the volcanic stratigraphy. Hence, Hence,many many of of the the individual flows flows could could be be traced traced for for a great individual great distance distance along along strike by tying tying them them together together from from one one the shoreline shoreline outcrops. outcrops. In contrast, the more resistant intrusive streamcut to the next, in combination with the rocks are typically typically exposed exposed on on the the tops tops and and slopes slopes of of high high hills. hills. The rocks The northeast northeast part of the the map map area area is is poorly exposed and thus much of the bedrock geology in that area is constrained largely by aeromagnetic aeromagnetic data. data. Green (2002) has proposed a subdivision subdivision of of the the North North Shore Shore Volcanic Volcanic Group Group into intoaa series seriesof of informal informal sequences and formations that are separated sequences and formations that separated by major major lithological lithological and and geochemical geochemical breaks breaks or or by by intrusions. Within intrusions. Within the the area area of of the themaps mapsshown shown here, here, these these include include the the Larsmont Larsmont basalts, Sucker River River basalts, the Lakewood lavas, and and the Lakeside Lakeside lavas lavas (Fig. (Fig. 2). The Thedetailed detailedbedrock bedrockgeologic geologicmaps mapsshown shown here subdivide these informal into multiple layers comprised comprised of of lava flows here subdivide these informal formations formations into multiple layers flows of of similar similar composition and texture in which which multiple multiple flow flow contacts contacts have have been been documented. documented. REFERENCES REFERENCES Boerboom, T.J., Green, J.C., and Jirsa, M.A., 2002a, 2002a, Bedrock Bedrock geology geology of the French French River River and and Lakewood quadrangles, St. Louis County, Minnesota: Minnesota quadrangles, MinnesotaGeological Geological Survey Survey Miscellaneous Miscellaneous Map Map MM128, scale 1:24,000. 1:24,000. 2002b, Bedrock geology of the Knife River River quadrangle, quadrangle, St. St. Louis Louis and and Lake Lake Counties, Counties, Minnesota: Minnesota: Minnesota Minnesota Geological Geological Survey Survey Miscellaneous MiscellaneousMap Map M-129, M- 129,scale scale1:24,000. 1:24,OOO. Brannon, J.C. 1984, 1984, Geochemistry Geochemistry of successive successive lava flows of the the Keweenawan Keweenawan North North Shore Shore Volcanic Volcanic Group: St. St.Louis, Louis,Washington WashingtonUniversity, University,Ph.D. Ph.D. dissertation, dissertation,312 312p. p. 7 �Green, J.C., J.C., 2002, 2002, Volcanic Volcanic and and sedimentary sedimentary rocks rocks of of the theKeweenawan Keweenawan Supergroup Supergroup in in northeastern northeastern Green, Minnesota, Minnesota, Chapter Chapter 55 of of Miller, Miller, J.D., J.D.,Jr., Jr.,Green, Green,J.C., J.C.,Severson, Severson,M.J., M.J.,Chandler, Chandler,V.W., V.W.,Hauck, Hauck,S.A., S.A., and Wahi, Wahl, T.E., T.E., Geology Geology and and mineral mineral potential of of the the Duluth Duluth Complex Complex and and related related Peterson, D.M., and rocks of of northeastern northeastern Minnesota: Minnesota MinnesotaGeological GeologicalSurvey SurveyReport Report of of Investigations Investigations 58, 58, p. p. 9494105. 105. Green, Green, J.C., J.C., Jirsa, Jirsa, M.A., M.A., and and Moss, Moss, C.M., C.M., 1977, 1977,Environmental Environmental geology geology of of the the North North Shore Shoreof ofLake Lake Superior: Superior: Minnesota MinnesotaGeological GeologicalSurvey, Survey,99 99 p.p. Miller, J.D., J.D., Jr., Jr., Green, Green, J.C., J.C., Severson, Severson,M.J., M.J.,Chandler, Chandler,V.W., V.W.,and andPeterson, Peterson,D.M., D.M.,2001, 2001,Geologic Geologicmap map Miller, of of the the Duluth Duluth Complex Complex and and related related rocks, rocks, northeastern northeastern Minnesota: Minnesota: Minnesota MinnesotaGeological GeologicalSurvey Survey Miscellaneous MiscellaneousMap MapM-1 M- 119, 19,scale scale1:200,000. 1:200,000. Sandberg, Sandberg, A.E., 1938, 1938, Section Section across across Keweenawan Keweenawan lava flows flows atatDuluth, Duluth,Minnesota: Minnesota: Geological Geological Society Societyof of America AmericaBulletin, Bulletin,v.v.49, 49, p. p. 795-830. 795-830. Schwartz, G.M., G.M., and Sandberg, Sandberg, A.E., 1940, 1940, Rock Rock series series in in diabase diabase sills sills atatDuluth, Duluth,Minnesota: Minnesota: Schwartz, Geological Geological Society Society of of America America Bulletin, Bulletin, v.51, v. 51, p. p. 1135-1172. 1135-1172. Figure Figure 1.1. Index Index map map showing showing location location of of mapped Work isis currently currently inin mapped quadrangles. quadrangles. Work progress progress on on the the Two Two Harbors Harbors and andCastle Castle Danger Dangerquadrangles. quadrangles. diabase Figure Figure 2.2. Index Index map map showing showing the the relative positions positions of of the the informal informal relative volcanicunits unitsof ofGreen Green(2002). (2002). volcanic - LIII Intrusiverocks rocks Intrusive Volcanicrocks rocks Volcanic Boundary of informal volcanic units 8 �WISCONSIN MINERAL RESOURCE RESOURCE GIS GIs AND RELATED DIGITAL DIGITAL MAP MAP AND DATABASE PRODUCTS RELATED PRODUCTS -A REPORT A PROGRESS REPORT BROWN, BA.1, B:A.', CZECHANSKI, CZECHANSKI,M.L.', M.L.',MUDREY, MUDREY,M.G., M.G.,Jr.1, ~ r . 'and ,andREID, REID,Daniel DanielD.2 D .(1) (1) ~ BROWN, Geological and and Natural Natural History History Survey, Survey, Univ. Univ. of of Wisconsin-Extension, Wisconsin-Extension,3817 3817Mineral Mineral Wisconsin Geological Point Road, Madison, Madison, WI 53705, 53705, babrowni babrownl @facstaff.wisc.edu, @facstaff.wisc.edu,(2) Wisconsin Dept of Transportation, Transportation, 3502 3502 Kinsman Kinsman Blvd, Blvd, Madison, Madison,WI WI 53704-2507 53704-2507 A new Mines, Mines, Pits Pits and and Quarries Quarries (MPQ) (MPQ) database database containing containing information information on on 1,302 1,302 significant nonmetallic mining sites sites throughout Wisconsin has has been been completed completedby by the the Wisconsin Wisconsin Geological and Natural History History Survey Survey (WGNHS) (WGNHS) in cooperation cooperation with with the the U.S U.S Geological Geological Survey (USGS). Locations Locations were digitized digitized from from county-based county-based digital digital orthophotography orthophotographywherever wherever available (MASIMILS available and by site visits. Data Datatables tableswere were linked linked to to existing existingUSGS USGS databases databases(MAS/MILS and MRDS) and to Wisconsin Wisconsin Department Department of of Transportation Transportation(WDOT) (WDOT)aggregate aggregatetest testdata; data;this this linkage linkage of all previous digital digital and and analog analog databases databases is is the the first first updated updated inventory inventorysince since1980. 1980. Future versions will be augmented with current site information, collected under the nonmetallic reclamation program of Wisconsin Department of Natural Resources, and additional historic sets such as the Road Material WGNHSJWDOT. Material Survey Survey sites sites of of the the WGNHS/WDOT. Georeferenced maps layered with digital geology, topography, orthophotography, Georeferenced orthophotography,soil, soil, and so forth provide a valuable land-use planning resource. Concern Concern for for safety safety and and construction construction the historic historic Upper Upper Mississippi problems in the reconstruction of U.S. Highway 151 through the possible the scanning and Valley Base-Metal Mining District, southwest Wisconsin, made possible georeferencing of the Wisconsin Mineral Development Atlas. The The Mineral Mineral Development DevelopmentAtlas Atlas of mine workings, drill-hole is a detailed set of 1,450 1,450 section-scale section-scale maps (1 inch equal 200 feet) of location and ancillary ancillary data dating from from 1900 1900 until mining mining ceased ceased in in 1979. 1979.These These maps maps were were maintained by the WGNHS and and the University University of Wisconsin-Platteville Wisconsin-Plattevilleand and were were scanned scannedby by the the WDOT. WDOT. All Wisconsin water well construction reports for 1936-1988 1936-1988 are now available on CDmapping as well well as environmental environmental and Rom. They provide an extensive data set for geologic mapping water resource analysis. analysis. New WGNHS map products are are being produced produced in in digital digital form form and andaa variety of analog maps including including the 1:24,000 1:24,000USGS geologic geologic quadrangle quadrangle maps maps of of the the lead-zinc lead-zinc district are being converted converted to digital as as resources allow. allow. This presentation will will provide provide an an interactive interactivedemonstration demonstrationof of these thesedata datasets setsand andGIS GIs layers, a review of available available map data such as regional geophysics, and and an update update on on the the status status of of geologic mapping at the WGNHS. WGNHS. 9 �HIGHWAY CONSTRUCTION, CONSTRUCTION,MINE MINERECLAMATION, RECLAMATION,AND ANDLAND-USE LAND-USEPLANNING PLANNING HIGHWAY HISTORIC UPPER UPPER MISSISSIPPI MISSISSIPPIVALLEY VALLEY LEAD-ZINC LEAD-ZINC CHALLENGES IN THE HISTORIC DISTRICT DISTRICT OF OF SOUTHWEST SOUTHWEST WISCONSIN BROWN, B.A.1, B.A.~,MUDREY, MUDREY,M.G., M.G.,Jr.1, ~ r . 'CZECHANSKII, ,CZECHANSKI, M.L.1, M.L.', REID, REID, Daniel DanielD.2, D . ~and and , HUNT, HUNT, BROWN, T.C.3, T.c/, (1) Wisconsin Geological and and Natural History Survey, Survey, Univ. Univ. of Wisconsin-Extension, Wisconsin-Extension, Wisconsin Geological 3817 38 17 Mineral Point Road, Madison, Madison, WI 53705, 53705, babrown1@facstaff.wisc.edu, babrown 1@ facstaff.wisc.edu, mgmudrey@wisc.edu,(2) Wisconsin Dept. of Transportation, 3502 Kinsman Blvd, Madison, WI mgmudrey@wisc.edu, 53704-2507, Wisconsin-Platteville,712 712 Pioneer PioneerTower, Tower, 53704-2507, (3) Reclamation Program, Univ. of Wisconsin-Platteville, Platteville, Platteville, WI 53818 538 18 of Wisconsin, Illinois, Illinois, Iowa, Iowa, and and Minnesota Minnesota The Upper Mississippi Valley Lead-Zinc District of produced nearly 10 million tons of lead-zinc ore from the 1820s until the last mine closed in 1978. The district will probably never be mined again, but problems related related to to mineralization mineralization and and past mining activity pose significant significant problems problems for for highway highway construction construction and and post-mining post-miningland land use. Specific hazards and engineering problems include (1) (1) Highly Highly altered altered and and unstable unstable rock rock and and shallow abandoned leachate from from abandoned mine workings workings encountered encountered during during highway highway construction, construction,(2) (2) leachate from lead-zinc lead-zinc sulfide sulfide mines. mines. As roaster-pile waste and (3) locally degraded groundwater from As rural rural residential development increases, increases, the the abandoned abandoned workings, workings, particularly particularlypoorly poorly sealed sealedshafts, shafts,can can be a hazard. Most low-sulfide low-sulfide waste waste rock rock has has been recycled recycled as as aggregate, aggregate, and and carbonate-rich carbonate-rich tailings overgrown with vegetation make make it difficult difficult to to find find any any surface surface evidence evidenceof of small, small,older older mine sites that may cause problems. problems. in an an High sulfate in groundwater samples was noted in 1978 following closure and flooding in area where large mines had operated for more than 50 drawdown cone cone had had developed developed 50 years and a drawdown over a 20-square mile area. area. A well-replacement well-replacement program program near Shullsburg Shullsburg restored restored potable potable water water supplies. supplies. Onsite Onsite reclamation consisted consisted of of establishing establishingvegetation vegetation on on the the tailings tailingsand andcrushing crushingthe the coarse waste rock for aggregate. Leachate from zinc roaster waste piles produced over 100 years over 100 years resulted in highly acidic and metal-rich surface surface water near Mineral Point. Point. The The roaster roaster piles piles were were successfully reclaimed by surface contouring along with neutralization surface grading and contouring neutralization and and of the cost of of fertilization to allow vegetation to establish. This was accomplished at a fraction of removal of the roaster waste piles. piles. rock alteration exposed exposed during Previously undiscovered sulfide mineralization and associated rock highway construction along U.S. Highway 151 near Mineral Point resulted in the 151 resulted in the unanticipated unanticipated engineering redesign of major roadcuts roadcuts and structures. structures. The The need need to to identify identify areas areas of of need for engineering the Wisconsin Wisconsin Mineral Mineral Development Development Atlas, which potentially unstable slopes slopes led to scanning scanning Of of the of mineralization, mineralization, alteration, alteration, and and abandoned has proven to be invaluable in identifying areas of workings in the path of construction. construction. These These detailed detailed maps maps (1 (1 inch inch to to 200 200 feet) feet) of of mine mineworkings workings exploration drillhole and exploration drillhole locations locations are are now now being being used used by by county county and and regional regional planners planners and and potential mining mining related related hazards hazards into into land-use zoning authorities to identify and incorporate potential planning. 10 �TEXTURAL CONSTRAINTSON ONTHE THEORIGIN ORIGINOF OF RAPAKIVI TETURE IN IN THE THEWOLF WOLF RIVER RiVER TEXTURAL CONSTRAINTS RAPAKIVI TEXTURES BATHOLITH BATHOLITH R. Michele Buttram Buttram and and Marcia Marcia Bjornerud Bjornerud Geology Department, Lawrence University, Appleton, WI 54912 549 12 The Wolf River Batholith of north-central Wisconsin, a 1.47 Ga composite anorogenic pluton, includes some of the world's finest examples of 'rapakivi' granite, granite, in in which which large large potassium feldspar crystals are mantled by plagioclase. Although Although rapakivi rapakivi granites granites have have been described for more than a century, the origin of of this distinctive texture, both in the Wolf River complex and elsewhere, remains remains controversial. controversial. Some workers argue that rapakivi mantles are coronae formed at a peritectic or eutectic point under equilibrium crystallization conditions. Others Others maintain maintain that rapakivi textures record disequilibrium associated with magma mixing and or sudden sudden changes in pressure. While most previous previous investigations investigations have have focused focused on on the the chemistry chemistry of of rapakivi rapakivi granites, granites, specifically, this study study examined examinedthe thephysical physicalcharacter characterofofthe theWolf WolfRiver Riverrocks rocks—- specifically, the feldspar crystals. crystals. Among size, shape, orientation and distribution of the rapakivi-type feldspar Among the most striking characteristics of these rocks is the large size of the feldspars (up size feldspars (up to to 77 cm cm in in length). Statistical Statistical analyses analysesshow show that that there there is is no no significant significant difference difference in in size size or or aspect aspect ratio between crystals with and without the rapakivi mantle. However, However, the the K-feldspar K-feldspar cores of the rapakivi-type rapakivi-type crystals crystals tend to be rounder (less (less euhedral) euhedral) than than non-rapakivi non-rapakivi grains, suggesting that they experienced significant resorption prior to the growth growth of of the the plagioclase mantle. AAweak weakgrain grainshape shapefabric fabric and and random random juxtaposition of of rapakivi rapakiviand and non-rapakivi grains must must also also be be explained explained by by any any viable viable model model for for the the origin origin of of the the texture. Our Ourdata data appear appearto to be be most most consistent consistent with with the the magma magma mixing mixing model, model, which which isis compatible with earlier geochemical studies of the Wolf River River complex. complex. 11 �Niagara suture suture zone, zone, northern northernMichigan Michiganand andWisconsin—tectonics Wisconsin-tectonics in Ma arc-continent arc-continent collisional boundary boundary the 1.85 Ma W.F. Cannon, Cannon,(U.S. (U.S. Geological GeologicalSurvey, Survey, Reston, Reston, VA VA 201 92, wcannon @ usgs.gov) G.L. 20192, wcannon@usgs.gov) G.L. LaBerge, LaBerge, (University of of Wisconsin-Oshkosh Wisconsin-Oshkosh(retired) (retired)and andU.S. US.Geological GeologicalSurvey), Survey),John JohnS. S.Klasner Kiasner illinois University (retired) (retired) and (Western Illinois and U.S. U S . Geological Geological Survey) Survey) The Niagara suture suture zone, as used here, is a belt varying varying in width from from about about 6 km to 40 km lying north of the Niagara Niagara fault. fault. It separates the accreted volcanic arcs of the Wisconsin magmatic terranes (WMT) on the south south from from the autocthonous autocthonous and parautochtonous parautochtonous continental continentalmargin margin rocks on the north. ItItconsists consistsof of Paleoproterozoic Paleoproterozoic metasedimentary metasedimentary and and metavolcanic metavolcanic rocks of epicratonic Marquette Marquette Range Range Supergroup Supergroup and and Archean Archean basement basement rocks rocks upon upon which which they they were were the epicratonic deposited. The TheArchean Archeanrocks rocksconstitiute constitiutethe thesouthern southernmargin margin of of the the Superior Superiorcraton, craton, which which was was deposited. rifted and eventually eventually separated separated during during extensional extensional phases phases of of the the Penokean Penokean orogenic orogeniccycle, cycle,and and during Penokean Penokean convergence. convergence. The The suture suture zone zone is is marked marked by by very very high high then thrust northward during strain and widespread multiple steeply to vertically plunging folds. The suture suture zone zone is is one one of of subdivisions of the Penokean Penokean orogen whose hierarchy of component component parts parts is is shown shown numerous subdivisions below. below. Michigamme subterrane Foreland fold fold and thrust i Foreland Niagara suture \~ i a ~ a suture ra zone /, Park Falls panel Watersmeet Watersmeet panel Beechwood Beechwood panel Iron Iron River River panel Menominee panel Menominee oanel j J / I I/ PENOKEAN OROGEN PENOKEANOROGEN,, \\ \ north north - - -south south- - Niagara fault - - - - Pembine-Wausau (northern part ~ e m b i n e - ~ a u s aterrane u (northern part of of WMT) WMT) Mars hfield terrane (southern (southern part Marshfield part of ofWMT) WMT) -- The map pattern shown here was derived from published detailed detailed maps in the east east (Bayley (Bayley and and Dutton, 1971; others, 1966; 1966; Button, 1971; James and others others 1968; 1968; and James and others, others, 1961) 1961)and and from from our our but access access to to recent recent exploration exploration drill drill recent work in the west, where outcrops are scarce but information as well as proprietary detailed aeromagnetic aeromagnetic and electromagnetic electromagneticdata data have have aided aided in in relationships (Cannon clarifying the geologic relationships (Cannon and others, others, 1998). 1998). Each of the the five five fault fault panels panels of of the the Niagara Niagara suture suture zone zone has has aa unique unique set set of of characteristics. characteristics. Watersmeet panel- Paleoproterozoic Paleoproterozoic strata strata are are mostly mostly pelitic pelitic schists schists and and gneisses gneissescontaining containing near the the base. base. They ferruginous strata and locally dolomite near They were were deposited deposited on on a basement of deformed into into gneiss gneissdomes. domes. High-pressure Archean gneiss. Both Both basement and cover were deformed metamorphism produced kyanite-bearing kyanite-bearing assemblages. assemblages. Park Falls panelpanel- Generally Generally similar similar to to Watersmeet Watersmeet panel panel except except that that metamorphism metamorphismwas was lower lower pressure and sillimanite-bearing sillirnanite-bearing assemblages assemblages are are predominant. predominant. Beechwood Beechwood panelpanel- Consists Consists of of Paleoproterozoic Paleoproterozoic graywacke graywacke and shale shale and and mafic mafic volcanic volcanic rocks rocks in in roughly equal parts. Archean Archean basement basement is not exposed. Folds Folds are are ENE-trending ENE-trending and have subhorizontal axes. Rocks are in greenschist facies. facies. Iron River panelvanel- Rocks are the Paint River Group, Group, including including the the Badwater Badwater Greenstone. Greenstone.Archean Archean basement is not exposed. exposed. Strata Strata are are multiply multiply folded folded creating creating aa complex complex fold fold interference interferencemap map pattern. Most Mostfold foldplunge plunge steeply. steeply. Metamorphosed Metamorphosedto togreenschist greenschist or or sub-greenschist sub-greenschist facies. facies. 12 �88' 9•1 46' c-is tic r-,c V A a V - A r-ic a r-tc A ?AA .A vA I I I a LV" I_VA A 0 A a '- A 7 a Lv A A a Fembine— "ausau terrane ,%/AA — -l LV i_L V IL Vi L) 50 A— cv' 1.-V1 c-is) .1 I_V1 v a LVA cv" 1 50 1KM ai ,a , 1a i 91' 89' 88' 0• Map showing showing the the five five structural structuralpanels panels (Park (ParkFalls, Falls,Watersmeet, Watersmeet,Beechwood, Beechwood,Iron IronRiver, River, Map and Menominee) that that constitute constitute the Niagara Niagara suture zone. Faults Faultsthat thatbound boundthe thepanels panelsare are Flambeau Flambeau Flowage Flowage fault fault (FFF), (FFF), Powell Powell fault (PF), Elmwood fault (EF), Paint River fault (PRF), (PRF), Badwater Badwater fault fault (BF), (BF),North NorthRange Rangefault fault(NRF), (NRF),and andSouth SouthRange Rangefault fault(SRF). (SRF). Menominee Menominee panel- Rocks are entirely of Paleoproterozoic age. No No Archean Archean basement basement is is exposed. exposed. Strain Strain was extreme. Commonly Commonlyall allstructural structuralelements, elements,including including fold fold axes, axes, are are subvertical. subvertical. Metamorphism Metamorphism is is lower lower to to upper upper greenschist greenschist facies faciesand and largely largely post-tectonic. post-tectonic. These These panels, panels, and and the the Niagara Niagara suture suturezone zone that that they they constitute, constitute,differ differfrom fromthe theMichigamme Michigamme subterrane Archeanbasement basementisisin in the the subterrane to the north. There Therewas waslittle littlepenetrative penetrativedeformation deformationof of Archean Michigamme subterrane. Paleoproterozoic deformed. Folds, Paleoproterozoic strata strata were moderately to weakly deformed. for for the the most part, are are simple simpleand and gently gently plunging. plunging. Metamorphic Metamorphic grade grade is is variable variableand and mostly mostly postposttectonic. Thus, Thus,the theNiagara Niagarasuture suturezone zonedocuments documentsaarange range of of tectonic tectonic styles styles unique unique to to the the very very high strains strains in in aa belt belt no no more more than than aa few few tens tens of of kilometers kilometers wide, wide, along along which which differential differential movement between the accreting arcs on the south and the craton margin on the accreting arcs on the south and the craton margin on the north north was was concentrated. concentrated. References References Bayley, Bayley, R.W., R.W., Dutton, Dutton, C.E., C.E.,and and Lamey, Lamey, C.A., C.A., 1966, 1966,Geology Geologyof of the the Menominee Menomineeiron-bearing iron-bearingdistrict, district, Dickinson Dickinson County, County, Michigan Michigan and and Florence Florence and and Marinette MarinetteCounty, County,Wisconsin: Wisconsin:U.S. U.S. Geological GeologicalSurvey Survey Professional 96p. Professional Paper 513, 5 13,96p. Cannon, Cannon, W.F., LaBerge, G.L. Klasner, J.S., and Schulz, K.J., 1998, 1998, Reinterpretation of the Penokean 44th continental margin in part of northern Wisconsin and Michigan (abs.): Proceedings Proceedings of 44thAnnual Annual Institute Institute continental on on Lake Lake Superior Superior Geology, Geology,v. v. 44, 44, p. p. 52-53. 52-53. Dutton, Dutton, C.E., 1971, 1971, Geology Geology of the Florence area, Wisconsin and Michigan: U.S. Geological Survey Professional Paper 633, 633,54 p. Professional 54 p. James, James, H.L., H.L., Clark, Clark, L.D., L.D., Lamey, Lamey, C.A., C.A., and and Pettijohn, Pettijohn,F.J., F.J., 1961, 1961,Geology Geologyof ofCentral CentralDickinson DickinsonCounty, County, Michigan: Michigan: U.S. U.S. geological geological Survey SurveyProfessional ProfessionalPaper Paper 310, 3 10,176 176p.p. James, H.L., Dutton, C.E., C.E., Pettijohn, F.J., F.J., and Weir, K.L., 1968, 1968, Geology and ore deposits of the Iron River Professional Paper Paper 570, 134 p. -- Crystal Crystal Falls district, Iron County, Michigan: U.S. Geological Survey Professional 13 �Strike-slip separation separation of the Burntside trondhjemite and and the Wakemup Wakemup Bay tonalite, Northern Minnesota Northern Minnesota Karoun Charkoudian, Basil Tikoff Department of Geology and Geophysics, Geophysics, University of Wisconsin, Wisconsin, Madison Madison WI, WI, 53706 53706 Robert Bauer Department of Geological Geological Sciences, Sciences, University of Missouri, Missouri, Columbia, Columbia, MO, MO, 65211 6521 1 INTRODUCTION The INTRODUCTION TheVermilion Vermilionfault faultisisaalocal localtectonic tectonicboundary boundary in the southern Canadian Shield juxtaposing the Quetico Quetico subprovince subprovince (granites (granites and and schists) schists) with with the the Wawa Wawa greenstones. greenstones. Burntside trondhjemite The Bumtside trondhjemite and and the Wakemup Bay tonalite tonalite are are small, small, elliptical, elliptical, Archean Archeangranites granites separated km of right lateral offset on the Vermilion Vermilion fault fault in in northern northernMinnesota. Minnesota. The separated by 35 35 krn normal fault, fault, juxtaposing juxtaposing the the shallow Wawa Wawa Vermilion fault is interpreted as initially active as a normal greenstone to the south with the deeper deeper granites granites and and migmatized schists schists to to the the north north (figure (figure1,1, stage 1). fault, separating the the Burntside Burntside trondhjemite trondhjemite from from 1). It was later reactivated as a strike-slip fault, stage Bay tonalite (figure 1, stage 2). 2). Although the Vermilion fault is the regional the Wakemup Bay boundary between between the the Quetico Quetico and and Wawa Wawa subprovinces, subprovinces,the th Haley fault lies to the south of the Vermilion fault and contains Quetico Quetico schists schists that belong belong on the north side of the Vermilion Vermilion fault fault (figure (figure 1). 1). The purpose purpose of this this study study is is to to compare compare emplacement setting, fabrics, composition, composition, and shape shape of the two plutons to determine if they constitute constitute a piercing piercing point on the Vermilion fault. In In addition, addition, we have determined the dip on the Vermilion Vermilion fault, constrained constrained the emplacement emplacement history of the the Wakemup Wakemup tonalite, tonalite, and and determined a potential cause for the isolated fault block that now contains contains the the Wakemup Wakemup Bay pluton (figure (figure 1, 1, stage 2). The Burntside trondhjemite trondhjemite is a small lenticular pluton that intruded the schist that lies to the north of the Burntside Bumtside Lake fault, fault, a continuation continuation of of the the Vermilion Vermilion fault at its eastern end. The The Wakemup Wakemup Bay pluton is a biotite-bearing biotite-bearing tonalite tonalite that that intruded intruded the the schist schistthat that lies lies Figure 11 just to to the the north north of of the the Haley Haley fault. fault. Figure g'one The Anisotropy AMS ANALYSIS ANALYSIS Anisotropy of Magnetic Magnetic Susceptibility Susceptibility (AMS) (AMS) is is aa rapid, rapid, nonnondestructive technique, commonly used in granitic studies to obtain obtain magnetic magnetic fabrics. fabrics. Principle Principle The magnetic foliation is defined as the kmx-kint AMS ellipsoid axes axes are are defined defined as as knBx>kint>kmin. plane, and the magnetic lineation is defined as the orientation of kmx. The bulk susceptibility j.tSI) susceptibilityvaries varies widely widelyin inboth boththe theWakemup WakemupBay Baytonalite tonalite(500-8500 (500-8500pS1) and the Burntside trondhjemite (5OO-350OSI). (500-3500pSI). This This range of susceptibility susceptibility is attributed attributed to the large variation in magnetite content throughout these bodies. The The AMS AMS foliations foliations parallel parallel the the measured field foliation in both plutons. Lineations Lineationsin inthe the Wakemup Wakemup Bay Bay tonalite tonalite dip dip shallowly shallowly to the E and W, and lineations in the Burntside trondhjemite dip shallowly to the ENE and WSW. WSW. Magnetic lineations lineations consistently consistently parallel parallel the the long long axis axis of of the the plutons. plutons. The Burntside GRAVITY GRAVITY STUDY STUDY Burntside and Wakemup plutons were selected selected for for aa gravity gravity study study because they both contain a single surrounding lithology (biotite schist) with a significant and g/cc). In consistent density density contrast contrast (Adensity (Mensity = -0.08 to -0.1 glcc). = -0.08 In addition, addition,the the gravity gravitydata data allows allowsus us to model the dip of the Vermilion Vermilion fault. fault. 14 �meter model model G G was was used usedfor forboth both areas. areas. After A Lacoste and Romberg gravity meter corrections, a forward forward model approach approach was used to interpret interpret the depth of the Burntside Burntside pluton pluton and and Vermilion fault geometry using WinGLink, WinGLink, aa geophysical geophysical interpretation interpretation software software program. program. The km in in thickness. thickness. The Vermilion Vermilion fault is a steeplysteeplyBurntside pluton is a thick body between 2-3 km north dipping to vertically oriented feature. Using Using aa gravimetric gravimetric three-dimensional three-dimensional iterative iterative technique on the Wakemup Bay pluton pluton resulted resulted in in aa good good first-order first-order picture picture of of the the pluton. pluton. Most of the pluton is very thin, less than 0.5km thick. There are are two root zones zones of up to to 4 km depth, thick. There both of which lie on the southern southern portion portion of the the Wakemup pluton, pluton, furthest furthest away away from from the the Vermilion fault. INTERPRETATION We interpret interpret the the Burntside Burntside and and Wakemup Wakemup plutons plutons as as part part of of the the same same on the the Vermilion Vermilion fault. fault. These granitic complex prior to strike-slip faulting on These igneous igneous bodies bodies are are similar in composition and both have undergone solid-state deformation. The plutons have similar structural settings. The TheWakemup WakemupBay Bay pluton pluton intrudes intrudes an an F3 F3 fold hinge hinge and the Burntside Burntside pluton Given the the separation, separation, the the folding folding episodes episodes may may or may has refolded F2 folds at its southern end. Given not correlate correlate exactly. exactly. The gravity gravity inversion inversion and and AMS study study on the Wakemup Wakemup pluton provide provide constraints constraints on on pluton emplacement. The km. Because The pluton pluton has has an average thickness of 0.5 km. Because the pluton contains a roof of wallrock, this estimate reflects the true thickness of the pluton. The TheAMS AMS foliation foliation and and lineation lineation parallel parallel the the fold fold limbs limbs and and fold fold hinge, hinge, respectively, respectively,of of aakm-scale km-scale F3 F3fold. fold. Therefore Therefore we interpret interpret the the Wakemup Wakemup as as syntectonically syntectonicallyintruding intruding an an F3 F3 fold fold hinge. hinge. We use a forward forward gravity model to estimate estimate the dip dip on on the the Vermilion Vermilion fault, fault, which whichdips dips between 70° 70' N and vertical. This Thisinterpretation interpretationrequires requiresthat thatthe the section sectionof of the theVermilion Vermilionfault fault south of the Burntside pluton was not active active as a south-side south-side down normal normal fault. fault. We propose the following tectonic model (figure 1). The The Burntside Burntside pluton pluton and and the the granitic complex. complex. The Wakemup Bay pluton were initially part of the same granitic The Vermilion Vermilion fault fault was was initiated as a normal fault (figure 1, juxtaposed the amphibolite facies Quetico 1, stage 1), I), which juxtaposed with the the greenschist greenschist facies facies Wawa Wawa belt. belt. The Wakemup tonalite, with a thick root on sub-province with its south side, acted as a promontory in the fault system. The The Vermilion Vermilion fault fault was was then then reactivated as a strike-slip fault (figure 1, stage 2), cutting through the the thinnest thinnest (NW) section of of the Wakemup Bay pluton. This This created createdthe the fault-bounded fault-bounded block block that that contains contains the the Wakemup Wakemup Bay pluton. Therefore, Therefore,ititisisevident evidentthat thatthe thepluton plutonshape shapehas has played played aa crucial crucialrole role in in controlling controlling Vermilion Vermilion fault orientation, orientation, both both for for the the early early normal normal faulting faulting and and later later strike-slip strike-slipfaulting. faulting. REFERENCES REFERENCES Minnesota. Minnesota Bauer, R.L., 1985, 1985, Norwegian Bay Quadrangle, St. Louis County, Minnesota. Minnesota Geological Geological Survey, Miscellaneous Miscellaneous Map series, series, Map Map M-59, M-59, 1:24,000. 1:24,000. Bauer, R.L., 1986, 1986, Multiple Multiple folding folding and and pluton pluton emplacement emplacementin in Archean Archeanmigmatites migmatitesof of the the southern southern Vermilion granitic 1753-1764. granitic complex, complex, northeastern northeastern Minnesota. Minnesota. Can. Can. J. J. Earth Earth Sci., Sci., v. v. 23, 23, p. p. 1753-1764. Bauer, R.L., and Bidwell, M.E., 1990, 1990, Contrasts in the response to dextral transpression across the QueticoWawa subprovince boundary in northeastern Minnesota. Can. Can. J. J. Earth Earth Sci., Sci., v. v. 27, 27, p. p. 1521-1535. 1521-1535. Sims, P.K., and Mudrey, M.G., 1972, district, in in Sims, P.K., P.K., et et al., eds., eds., 1972, Burntside granite gneiss, Vermilion district, Geology of Minnesota: Centennial Volume: St. St. Paul, Minnesota Minnesota Geological Geological Survey, Survey, p. p. 98-101. 98-101. Minnesota: A Centennial Vigneresse, Vigneresse, J.L., J.L., 1995, 1995,Control Control of of granite graniteemplacement emplacementby by regional regional deformation: deformation:Tectonophyiscs, Tectonophyiscs,v.v.249, 249,p.p. 173-186. 173-186. 15 �GEOLOGY AND MINERAL MINERAL POTENTIAL POTENTIAL OF PROTEROZOIC PROTEROZOIC MAFIC MAFIC INTRUSIONS IN THE NORTHERN GRENVILLE GRENVILLE PROVINCE PROVINCE OF ONTARIO ONTARIO R.M. EASTON, Ontario Geological Survey, Survey, 933 Ramsey Lake Road, Sudbury, Ontario P3E 6B5, mike.easton@ndm.gov.on.ca rnike.easton@ndm.gov.on.ca Since 1998, 1998, mafic intrusions intrusions near the Grenville Grenville Front in Ontario Ontario have have been been prime prime exploration targets for Cu-Ni-PGE Cu-Ni-PGE mineralization. mineralization.To To assist assist in in this this effort, effort, the the Ontario OntarioGeological Geological Survey has conducted detailed mapping in high potential areas of the Grenville Grenville Province Province between between 1999 and 2002. This poster summarizes the results of these mapping efforts. efforts. East Bull Bull Lake Lakeintrusive intrusivesuite, suite,including includingthe theRiver RiverValley Valleyintrusion: intrusion:Country Countryrocks rockstotoEast East East Bull Lake intrusive intrusive (EBLI) (EBLI) suite suite rocks in the area area are inferred to be mainly Archean Archean in in age, age, and and are grouped into 4 gneiss associations. associations. Metamorphic grade is upper amphibolite amphibolite facies; fades; country country rocks to the mafic intrusions intrusions are are commonly commonly migmatitic. migmatitic. The Paleoproterozoic PaleoproterozoicEBLI EBLI suite suite consists consists of several several mafic mafic layered layered intrusions intrusions emplaced emplaced between 2490 krn, roughly roughly 2490 and and 2468 2468 Ma Ma (James (Jamesetetal. al.2002) 2002)that thatoccur occurover overaadistance distanceofof—250 -250 km, site of Sudbury. Sudbury.The The largest largest of these bodies in in the the Grenville Grenvilleisis the the River River centered on the present site Valley intrusion, intrusion, which underlies roughly 100 of Dana Dana and Crerar townships. Previous maps 100 km2 krn2 of correlated correlated mafic rocks west of Crerar Crerar Township Township with with the the River River Valley Valley intrusion. intrusion.This This study study indicates indicates that at least least 3 separate separate intrusions intrusions are are present, present, each each emplaced emplacedinto into different differentcountry country rocks, and with different different stratigraphy stratigraphy and mineral potential. EBLI suite rock types range in composition from anorthosite anorthosite to melanorite, melanorite, troctolite troctolite and and rarely peridotite; leucogabbronorite leucogabbronorite and gabbronorite dominante. dominante. The The crystallization crystallizationorder order of of olivine orthopyroxene (An80-62), olivine (Fo7659), orthopyroxene primocryst phases phases is is most mostcommonly commonlyplagioclase plagioclase(An8062), (En7558), titanomagnetite,and andclinopyroxene. clinopyroxene. In In Dana Dana Township, Township, the the River River Valley intrusion (En75-58),titanomagnetite, locally exhibits primary mineralogy and well preserved igneous textures. textures. Phase Phase layering layering varies from cm- to m-scale, m-scale, which is discernable discernable in outcrop, outcrop, and and dm dm or or larger, larger, which which is is identified identifiedby by detailed mapping. Isomodal layering is most common; common; mineral and and size size graded graded layers layers are are less less common. Cryptic layering is well documented for the River Valley intrusion. intrusion. Pearce-element Pearce-element ratio and chondrite-normalized chondrite-normalizedREE REE diagrams diagrams illustrate illustrate that that each each body formed formed from from one one or or more more tholeiite composition composition can can explain explain the the cogenetic magmas (James et al. 2002). A high-Al, low-Ti tholeiite al. 2002). 2002). dominant leucocratic rock compositions compositions in the the EBLI EBLI suite suite (James (James et al. Within g/t Pd+Pt+Au) Pd+Pt+Au) Within the the EBLI EBLI suite, suite, contact-type contact-type Cu-Pd-Pt Cu-Pd-Pt mineralization mineralization (1 (1 to to 10 10g/t occurs in the matrix of an inclusion and/or fragment-bearing gabbronorite to leucogabbronorite inclusion fragment-bearing gabbronorite to leucogabbronoriteat at the base or side of the intrusions intrusions where the primary igneous contact is preserved. preserved. A A second, second, m above the the contact. contact. Examples Examples occur occur similar, zone of mineralization may occur 100-200 m throughout the EBLI suite, however, the most consistent consistent grades have been reported reported from from the the % sulfide, sulfide, River Valley intrusion in Dana Township. Township. Chalcopyrite and lesser lesser pyrrhotite pyrrhotite form form 1-3 1-3% disseminated or as local cm-sized either finely disseminated cm-sized patches. PGE mineralization mineralizationis is commonly commonly associated with sulphide. sulphide. Study Study of the East Bull Lake intrusion indicates indicates that that mineralization mineralization originates from the intrusion and subsequent subsequent dynamic dynamic mixing of S-saturated, S-saturated,inclusion-bearing, inclusion-bearing, second-stage (PGE enriched, i.e. 20-100 20-100 ppb PGE) magmas that entered entered the the magma magma chamber chamber second-stage carrying liquid sulfide sulfide droplets droplets (James (James et et al. al. 2002). 2002). Reef-style Reef-style mineralization mineralizationhas has yet yet to to be be documented within the the EBLI EBLI suite. suite. 16 �history between Geological history between Sudbury Sudburyand andRiver RiverValley: Valley:Archean Archeanrocks rocksin in this this area area record a sequence of events similar to that observed in the Levack Gneiss Gneiss complex complex and and high-grade high-grade portions of the Quetico subprovince, subprovince, but unlike the Pontiac subprovince. The following geological history is inferred. inferred. After deposition of greywackes greywackes south south of the the Temagami Temagarni greenstone greenstone belt, invasion by tonalitic tonalitic to to granodioritic granodioritic plutons, plutons, probably probably accompanied accompaniedby by burial, burial, formed formed the the migmatitic gneisses gneisses now represented represented by the Pardo Pardo and and Red Red Cedar Cedar Lake Lake gneiss gneiss associations, associations,likely likely between 2685 and 2675 2675 Ma. Ma. This This was was followed followedby by aa second second period period of of tonalitic tonalitic to to granodioritic granodioritic magmatism, deformation deformation and and metamorphism metamorphism at at mid-crustal mid-crustal levels levels between between 2670 2670and and2660 2660Ma. Ma. The Crerar gneiss association association represents represents the the products products of of this this latter latter activity. activity.Subsequent Subsequentfelsic felsic magmatism at roughly 2640 Ma was accompanied accompanied by emplacement of pegmatite pegmatite veins. veins. A logical extension of this work is to interpret the gneiss associations as a southwarddeepening section of the crust. crust. As interpreted, interpreted, Archean Archean metawackes metawackes exposed exposed immediately immediatelynorth north of the Grenville Grenville Front represent high-levels of the crust. crust. The The Pardo Pardo gneiss, gneiss, immediately immediatelysouth south of of the Grenville Grenville Front, represents represents the middle middle part of aa 10-15 10-15 km km thick thick upper upper crustal crustallayer layer dominated dominated supracrustal and intrusive by supracrustal intrusive rocks. rocks. The Red Cedar Cedar Lake gneiss and and the Street Street gneiss gneiss association association represent the basal portion of this upper crustal crustal layer, layer, with the former former derived derived from from aa metasedimentary rock sequence and the latter latter from a greenstone sequence. sequence. Intrusive Intrusive rocks rocks of of the the km thick middle middle crustal crustal layer. layer. This This crustal crustal section section is is Crerar gneiss association are part of a 10-15 10-15 km roughly equivalent to that observed observed across the Wawa gneiss domain. domain. Emplacement Emplacementof of EBLI EBLI suite suite bodies occurs at several levels levels within this this crustal crustal section. section. Flett Evidence forfora amafic Flett Township Townshipmafic maficIntrusions: Intrusions: Evidence maficand andA-type A-typegranite granitemagmatic magmaticprovince province in the northern Grenville Grenville Province Province was discovered while examining mafic intrusions near Temagami that occur occur in Tomiko Tomiko domain, domain,near near its its contact contact with with the the Grenville GrenvilleFront Fronttectonic tectoniczone. zone. Proterozoic Proterozoic country country rocks consist consist of of gneissic gneissic granite, granite, with with minor minor mafic mafic and andquarztose quarztosegneiss gneissand and metaconglomerate. metaconglomerate. The Fall Lake intrusion consists of little metamorphosed gabbro and leucotroctolite. The Fanny Lake intrusion consists of olivinite leucotroctolite. olivinite and and troctolite. troctolite. Igneous Igneous texture texture is is well preserved, but metamorphic coronas coronas occur occur around around primary olivine olivine and and clinopyroxene. clinopyroxene. Geochemistry indicates that both bodies are slightly alkalic, alkalic, compositionally compositionally similar similar to to the the ±44 Ma, Ma, and and have have affinities affinities to to within-plate within-plate basalts. basalts. Sudbury diabase dike swarm dated at 1238  The Fall Lake intrusion intrusion yielded yielded pristine pristine baddeleyite, baddeleyite, with 33 concordant concordantor or just slightly slightly discordant grains 1235±22Ma. Ma. The The Fanny Fanny Lake sample 2 0 7 ~ b / 2 0age 6age ~ bofof1235 sample discordant grainsgiving givingan anaverage average207Pb/206Pb yielded baddeleyite, with some grains having thin zircon overgrowths, overgrowths, consistent consistent with with the the presence of corona corona textures textures in in the the body. body. Two Two concordant concordant grains grains without without overgrowths overgrowthsgave gavean an average 207Pb/206Pb 1238  ± 2 Ma. 2 0 7 ~ b / 2 0age 6age ~ bofof 1238 average Both intrusions intrusions are are spatially spatially associated associatedwith with the the A-type A-type Mulock Mulock granite, granite,dated dated previously previously at 12444L3 1 2 4 4 1 - Ma. ~ Intrusions of similar age include the Sudbury dike swarm, swarm, Mercer Mercer anorthosite, anorthosite, granitoid plutons. The new age data data provides provides further further evidence evidence and the West Bay and Powassan granitoid for the presence of a bimodal magmatic province active from 1270-1235 1270-1235Ma Ma in in the the Laurentian Laurentian margin of the Grenville Province. The tectonic setting is interpreted as an extensional rift nft that formed formed inboard inboard of aa continental continental arc arc active active on on the the southern southern margin margin of of North North America Americabetween between 1450-1300 1450-1300 Ma. This setting setting resembles that of the Cenozoic Cenozoic Columbia ColumbiaRiver River Basalt BasaltGroup. Group. James, R.S., Easton, Easton, R.M., R.M., Peck, Peck, D.C. D.C. and and Hrominchuk, Hrorninchuk, J.L. J.L. 2002. 2002.The TheEast EastBull BullLake Lakeintrusive intrusivesuite: suite:remnants remnantsof ofaa —2.48Ga Galarge largeigneous igneousand andmetallogenic metallogenicprovince province in in the the Sudbury Sudbury area of the Canadian Canadian Shield; -2.48 Shield; Economic Economic p.1577-1606. Geology, v.97, p. 1577-1606. 17 �PALEOSTRESS INFERENCES PALEOSTRESS INFERENCES FROM FROMFAULT FAULT SLIP SLIP VECTORS VECTORS IN IN THE THE EASTERN EASTERNPART PARTOF OFTHE THE WISCONSIN SEGMENT SEGMENTOF OFTHE i'H MIDCONTINENT Rwr WISCONSIN MIDCONTINENT RIFT Amy Garbowicz, Garbowicz, Marcia Marcia Bjornerud, Bjornemd, Geology Department, Department, Lawrence University, Appleton, WI 54912 549 12 Building accurate accurate models models for for both both the opening Building opening and closing closing of the the Midcontinent Midcontinent Rift Rift requires an an understanding of the evolution requires understanding of evolution of regional regional stresses stresses over over time. time. This This study study paleostress indicators indicators in in the the portion portion of of the Rift exposed near focused on slickenfibers as paleostress of Lake Superior in in northeasternmost northeasternmost Wisconsin. Wisconsin. The orientations of the southern shore of slickenfibers were were used used to determine slickenfibers determine slip vectors vectors on on outcrop-scale outcrop-scale faults within riftspan the the entire range of the related igneous and related and sedimentary sedimentary rocks. rocks. Rocks Rocks sampled sampled span the Keweenawan Supergroup, from the Tyler Formation to the Freda Sandstone, with most of the sampling in the Porcupine Porcupine Volcanics, Volcanics, the Kallander Kallander Creek Creek Volcanics, Volcanics, and and the the Mellen Mellen Gabbro. . The The mineral composition of the slickenfibers was used as a proxy for their age, Gabbro. based on the based the known known regional regional sequence sequence of of secondary secondary mineralization mineralization within within the Rfit. Rfit. Chlorite and epidote slickenfibers were grouped together and considered older since these slickenfibers were among the first were first minerals minerals precipitated precipitated by hydrothermal hydrothermal fluids following the main main of calcite and zeolite were magmatic interval. interval. Slickenfibers of were considered considered to to be be younger. younger. Some individual faults were observed to have have multiple multiple generations generations of of slickenfibers slickenfiberswith with different compositions, indicating indicating either either reactivation reactivation or or continuous continuous slip slip over a protracted protracted different period Fault Kinematics Kinematics (by R. period of time. time. Data Data from the the field field were were analyzed analyzed using using Fault Ailmendinger, Cornell Unviersity), a program that calculates Allmendinger, calculates best-fit best-fit paleostress paleostress tensors tensors from fault slip tensors all indicate normal stress slip information. information. The calculated tensors stress regimes regimes (maximum principal principal stress subvertical), even for the (maximum the latest latest generations generationsof ofslickenfibers. slickenfibers. This This contrasts contrasts with with the results results of of studies studies on on the theKeweenaw Keweenaw Peninsula, Peninsula, which which have have documented two two distinct stress documented stress regimes. regimes. There, There, early early normal normal faulting faulting gives gives way way to reverse faulting, possibly as a response to far-field far-field stresses stresses associated associated with the the Grenville Grenville Orogeny. The Orogeny. The absence absenceof of reverse-slip reverse-slipvectors vectors in in the the northeastern northeastern Wisconsin Wisconsin segment segment of of the Midcontinent Midcontinent Rift may reflect the misorientation of this part of the rift with respect to those far-field far-field stresses. stresses. . 18 �Possible Origin in in the the Negaunee Negaunee Mode of Occurrence of Trona and Thermonatrite and their Possible Iron-Formation of the Marquette Range, Lake Superior District, USA Tsu-Ming Han (Retired) (Retired) Research Laboratory, Cleveland-Cliffs Cleveland-Cliffs Inc. the silicate-bearing Negaunee Negaunee IronIronA white colored substance substance is often seen on the surface of the Formation of low metamorphic Range, Michigan. This substance is metamorphic grade grade on the Marquette Marquette Range% thermonatrite) ItIt occurs mostly of a mixture containing hydrous sodium carbonates (trona and thermonatrite) occurs as as thin coatings along bedding (Figure (Figure 1-A), 1-A), and in fractures cutting cutting across the bedding; as coatings patterns distributed distributed and colloform clusters on bedding planes (Figure 1-B); and as contour patterns Furthermore, nearly pure trona trona was developed quickly quickly between the fractures of bedding surfaces. Furthermore> dendrites and minute dots as dendrites dots on the cut cut surfaces surfaces of of some some hand specimens specimens in in storage storage(Figure (FigureC). C). To the writer's knowledge, knowledge, these these minerals minerals have not been previously reported reported from Precambrian Precambrian BIF B E of of the the equivalent equivalent metamorphic metamorphicgrade grade in in other other districts. districts. ILl Figures - Mode Mode of occurrence occurrence of trona and thermonatrite. thermonatrite. Figures 11— A—As whitecoatings coatingsalong along bedding. bedding. B-As B—Ascolloform colloformclusters clusters on on aa bedding bedding plane. A-As white C— Asdendrites dendriteson onthe thecut cut surface surface of of aa hand hand specimen in storage. C- As storage. The iron-formation is composed composed of of magnetite, magnetite, siderite, siderite, ankerite, ankerite, and and stilpnomelane.. stilpnomelane.. Minnesotaite Minnesotaite is also locally present in noticeable quantities. K is more than Na in these minerals as is the case in nearly nearly all all of of the the Precambrian Precambrian iron-formations iron-formationsof oflow lowmetamorphic metamorphicgrade. grade. As As aa 19 . �general generalrule, rule,stilpnomelane stilpnomelanecontains containsmore moreKKand andNa Nathan thanthe theminnesotaite. rninnesotaite.However, However,the the K20:Na.20 K20:NaZOratio ratioininthese theseminerals mineralsand andinthe in theiron ironformationa formationsmay mayvary varysubstantially.. substantially. . Based Basedon onthe theresults resultsfrom fromthe thehighly highlypurified purifiedwater waterleaching leachingtests testson onmore morethan thantwenty twentydifferent different samples, samples,the theNa Naininthe theiron-formation iron-formationisiswater-soluble water-solublewhereas whereasthe theKKisispractically practicallyinsoluble insoluble (Figures 2Aand andB). B).The TheXRD XRDand andanalytical analyticaldata datashow showaagood goodcorrelation correlationbetween betweenthe theamount amount (Figures2A ofofstilpnomelane Na20, K20 ofNa.20, K20and andA1203 A1203(Figures (Figures3A 3AtotoC). C). stdpnomelaneand andthe theamounts amountsof y = 9.9759x- 0645 0.05 0 0.10 0.15 020 - Figure22 AAand andBB Solubility Solubilityof ofK20 K 2 0and andNa20 Na20 Figure in the silicate-bearing iron-formation with high in the silicate-bearing iron-formation with high andlow low K20:Na20 K20:Na20ratios. ratios. and - 25: R 2O 15 15 - Figure33- AAto to C C Relationship Relationship of of stilpnomelane stilpnomelane Figure toK20, K20,Na20 Na20and andA1203. Al203, to 00 0.5 0.5 1.0 1.O 1.5 1.5 2.0 2.0 2.5 2.5 ItItmay may be be logically logicallyconcluded concludedthat thatmost mostof ofthe thesodium sodiumwas wasderived derivedfrom fromthe the stilpnomelane, stilpnomelane, which ofthe thehydrous hydroussodium sodiumcarbonates carbonateswas was whichwas was leached leachedout outby bymeteoric meteoricwater. water.The Themixture mixtureof then thendeveloped developedthrough throughevaporation evaporationunder underthe theatmospheric atmosphericconditions. conditions. 20 3.0 3.0 �Keweenawan Mafic and and Ultramafic Intrusive Intrusive Rocks of the Lake Nipigon and Ontario Crystal Lake areas, northwestern Ontario Hart, Hart, Thomas ThomasR., R.,Ontario OntarioGeological GeologicalSurvey, Survey,933 933Ramsey RamseyLake LakeRoad, Road, Sudbury, Sudbury, Ontario Ontario P3E 6B5; tom.hart@ndm.gov.on.ca tom.hart @ndm.gov.on.ca The Keweenawan diabase diabase sills sills in the Lake Lake Nipigon and and Crystal Crystal Lake Lake areas, areas, northwest of Lake Superior, Superior, consist consist of of two distinct distinct geochemical geochemical and and geographical geographicalgroups groups with each area also hosting hosting aa number number of unique unique intrusions intrusions that that suggest suggest different differenttectonic tectonic processes. Mapping Mapping by Smith Smith and Sutcliffe Sutcliffe (1987) (1987) in the Crystal Crystal Lake Lake area area identified identified aa series of 6 Logan diabase diabase sills sills >5 >5 m thick that gently gently dip dip to the southwest, southwest,and and intrude intrude into the early Proterozoic Proterozoic Rove Rove Formation. Formation. Northeast Northeast trending trending dykes dykes of of the the Pigeon Pigeon River River swarm range from olivine olivine to quartz diabase diabase in composition, composition,and and include includedykes dykes that that crosscut the Logan sills and dykes that appear to merge with the sills. sills. The The layered layered gabbro gabbro — anorthosite anorthosite -- troctolite troctolite Crystal Lake Gabbro crosscuts and contains inclusions of Pigeon -Tb/Yb - ZrIY Zr/Y River dykes. Samples of the Logan sills sills can be subdivided subdivided into into aa low low TiO2 Ti02 -TWYb group and -Tb/Yb - Zr/Y (OGS2002). 2002).The The high Ti02 group ZrIY group group (OGS high Ti02 group waswas and aa high high TiO2 Ti02 -Th/Yb identified as asbeing beingquartz quartz normative, comparable theLogan type Logan by Sutcliffe normative, andand comparable to thetotype sills bysills Sutcliffe (1991). Samplesidentified identified Pigeon River dykes exhibit high degree of variability (1991). Samples as as Pigeon River dykes exhibit a higha degree of variability suggesting that they represent represent at least three three unrelated unrelated intrusions. intrusions. One One subset subset of of the the comparable to the low TiO2 of Logan Logan sills, and another Ti02 group of Pigeon River dykes is comparable Gabbro. Most subset is comparable to the Crystal Lake Gabbro. Most of of aa third third subset subset of of dyke dyke samples samples contain lower lower trace trace element element are located along Highway 61 close to the Pigeon River, and contain abundances and ratios than the other other intrusions intrusions in the area. area. Gabbro Gabbro samples samplesfrom from the the Crystal Lake Gabbro intrusion display some overlap with the low TiO2 group of Logan Ti02 of Tb/Ta ratios. The Th/Yb, and TWTa sills but also includes samples samples with higher Zr/Y, ZrIY, ThIYb, The Logan diabase sills are confined to the area to the south of Thunder Thunder Bay, with the Nipigon Nipigon diabase sills located to the north. north. The initial initial Keweenawan Keweenawan intrusive intrusive event event in in the the Lake Lake Nipigon Nipigon area area isis probably probably represented by the relatively flat lying to shallowly dipping dipping peridotites peridotites located located in in the the Disraeli, Seagull - Fox Mountain, Hele, and Kitto areas that form intrusions a - Seagull Leckie— Disraeli,Leckie few kilometres in diameter. The peridotites are composed of orthocumulate to mesocumulate textured wehrlite to lherzolite, containing 1 to 2% reddish brown mica and commonly a discontinuous (e.g. Sutcliffe Sutcliffe1987; 1987;Hart Hart et et al. al. discontinuous olivine olivine gabbro gabbro border border phase phase (e.g. 2002). The Disraeli, Seagull Seagull and Hele peridotites are characterized characterized by higher higher MgO and and Zr/Y Tb/Yb values but lower ThITa Th/Ta ratios than the Nipigon diabase sills. A series of of ZrIY and TWYb 0.5 to 3.0 m thick sills are located stratigraphically below below the Nipigon sills, as exposed Tb/Yb and Tb/Ta along Highway 17 at Kama Hill. These sills have MgO, TWYb TWTa values values intermediate Tb/Ta intermediate between the peridotites and Nipigon sills, and subdivided into higher Th/Ta and lower Tb/Ta subgroups may be possible with additional sampling. These sills have TWTa subgroups with additional sampling. These sills have Tb/Ta La/Yb ratios comparable to the high Ti02 group of Logan sills, but generally ThITa and LalYb have lower trace element abundances. The Kitto peridotite also has ThIYb, Th/Yb, Th/Ta Tb/Ta and Zr/Y ratios that overlap with these sills rather than the other peridotites. The olivine ZrIY tholeiite Nipigon diabase sills are up to 200 m thick, and are chilled against the peridotite pendotite intrusions. Previous work indicates that some sills were formed by multiple pulses of of magma (e.g. Sutcliffe, Sutcliffe, 1987; 1987; Hart et al. al. 2002), 2002), but the the chemistry chemistry of of the the sills sills over overthe the 21 �entire Lake Nipigon area area displays displays little little variation. variation. Geochemical Geochemical differences differencesbetween between the the entire peridotites and Nipigon diabase diabase sills are comparable comparable to the variations observed in the peridotites Osier values Osler Group volcanic rocks (e.g. Sutcliffe, 1991). The The Nipigon Nipigon sills sills have have Ti02 Ti02 values Ti02group group of of Logan sills sills but higher higher ThITa Th/Ta and and lower lower La/Yb LdYb comparable to the the low low Ti02 comparable differences in the the geochemistry geochemistry of the the diabase diabase sills sills between between the the Lake Lake Nipigon Nipigon ratios. The differences and Crystal Lake areas is similar to the differences observed in the volcanic volcanic rocks of aa flood basalt provinces provinces (e.g., (e.g., Mantovani Mantovani et et al. al. 1985). 1985).The The regional regionalextent extentof of the the number of flood An initial initial geochemical groups within the Keweenawan intrusions is not known. An examination of troctolites troctolites from from the the Babbit Babbit deposit deposit of of the the Duluth Duluth Complex Complex(Ripley (Ripleyetetal. al. examination 1999) Th/Yb, and and Zr/Y Zr/Y ratios ratios comparable to the Nipigon peridotites peridotites ThITa, Th/Yb, 1999) indicates ThTFa, rather than the intrusions intrusions of the the Crystal Crystal Lake area. area. References References Hart, T.R., terMeer, M., and Jolette, C. 2002. Precambrian geology of Kitto, Eva, Summers, Dorothea and Sandra Townships, Beardmore area, northwestern Ontario; Ontario Geological Survey, Open File Report 6095, 206 206 p. PL.S., de de Sousa, Sousa, M.A., MA., Civetta, L., Atalla, L., and Innocenti, Innocenti, F., F., 1985. Trace Trace element element and and Mantovani, M.S.M., Marques, L.S., strontium isotopic constraints on the origin and evolution of Parana continental flood basalts of of Santa Santa Catarina State (southern Brazil); Journal of Petrology, v. 26, p. 187-209. Ontario Geological Survey, 2002. Proterozoic Volcanic and Intrusive Whole Rock Geochemical Data associated with the Keweenawan Midcontinent Rift, Lake Superior Area, Ontario; Ontario Geological Survey Miscellaneous Release—Data 114. Release-Data 114. EM., Lambert, Pb isotopic isotopic constraints constraints on on mantle mantle and and crustal crustal Ripley, E.M., Lambert, D.D., and Frick, L.R., 1999. 1999. Re-Os, Sm-Nd, and Pb to magmatic magmatic sulfide mineralization in the Duluth Complex; Geochimica et Cosmochimica Acta, contributions to v. V. 62, p.3349-3365. Smith, A.R. and Sutcliffe, R.H. 1987. Keweenawan intrusive rocks rocks of of the the Thunder Bay area; in Summary Sunnnary of Field Work and Other Activities, Ontario Geological Survey Miscellaneous Paper 137, 137, p. 248-255. 1987.Petrology Petrology of of Middle Middle Proterozoic Proterozoic diabase diabase and picrites from Lake Nipigon, Sutcliffe, R.H., RH., 1987. Nipigon, Canada; Canada; Contributions Contributions to Mineralogy and Petrology, v.96, p. 201-211. 201-21 1. Sutcliffe, R.H., RH., 1991. 1991.Proterozoic Proterozoic geology geologyof of the the Lake Lake Superior Superior area; area; in in Geology Geology of of Ontario, Ontario, Ontario Ontario Geological Geological Survey Survey Part Special Volume 4, P art 1, 1, p. 627-658. 22 �GEOLOGY, DRILL HOLES, MINERAL MINERAL LEASES, AND GEOPHYSICS GEOPHYSICS IN THE THE DULUTH DULUTH GEOLOGY, INTEGRATIONOF OF AND BEAVER BAY COMPLEXES, NORTHEASTERN MINNESOTA: INTEGRATION VARIOUS GIS GIs DATABASES DATABASES TO TO TELL TELL A A STORY STORYOF OFTHE THE HISTORY HISTORYOF OFPAST PASTAND AND VARIOUS CURRENTCU-NI-PGE CU-NI-PGEMINERAL MINERALEXPLORATION EXPLORATION CURRENT Steven A. Hauck, Hauck, Julie Julie A. A. Oreskovich, Oreskovich,and and Mark Mark J.J. Severson, Severson,Economic EconomicGeology GeologyGroup, Group, Steven Natural Natural Resources ResourcesResearch Research Institute Institute(NRRI), (NRRI),University University of of Minnesota, Minnesota,Duluth, Duluth,5013 5013 MN 55811-1442, 55811-1442,shauck@nrri.umn.edu shauck@nrri.umn.edu Miller Trunk Trunk Highway, Highway, Duluth, Duluth,MN Miller Mineral exploration exploration in the Duluth Duluth Complex Complex began in 1948 1948 on Spruce Spruce Road when two prospectors found found sulfide sulfide mineralization. mineralization. Subsequent Subsequentcore coredrilling, drilling,geological geologicalmapping, mapping,and andairborne airborneand and ground ground geophysics geophysics by more more than than 28 28 exploration explorationcompanies companies (including (includingthe the NRRI, NRRI,MGS MGS-Minnesota Minnesota Geological Survey, Survey, and and the DNR -- Dept. Dept. of Natural Resources, Resources,Division Divisionof of Lands Lands and and Minerals), over the next 52 years led to the discovery of copper-nickel±platinum-group element Minerals), over the next 52 years led to the discovery of copper-nickelkplatinum-group element (PGE) mineralization mineralization along the basal contact of the Duluth Complex (Fig. 1). Ten Ten Cu-Ni-PGE Cu-Ni-PGE or or PGE-Cu-Ni deposits deposits were were defined by drilling during these years. Over Over2,142 2,142drill drill holes holes have have been drilled drilled into into the Duluth Duluth and and Beaver Bay complexes with 1,666 1,666 of these holes being drilled along along the basal contact. contact. Over Over954,000 954,000ft. ft.of ofdrill drillcore corefrom fromthe thebasal basalcontact contacthas hasbeen beenrelogged relogged by NRRJ, publications. Geophysical NRRI, and their results are discussed in many publications. Geophysical exploration exploration began began as as early as 1956, 1956, by Bear Creek Mining Company, and continues today. The The State State of of Minnesota Minnesota (MGS), with funding funding from from the Legislative Legislative Commission Commission on on Minnesota MinnesotaResources, Resources,flew flewhigh high resolution aeromagnetics aeromagnetics over over this area as well as the rest of the state. The TheMGS MGShas hasalso also collected collected and produced a gravity map covering both complexes. Peak Peakexploration exploration(1966-1978) (1966-1978) began with the leasing leasing of State State of Minnesota Minnesota mineral rights in 1966 1966 (Fig. 1). Exploration Explorationand and development (drilling, bulk sampling, shaft sinking, resource calculations) continued through development (drilling, bulk sampling, shaft sinking, resource calculations) continued through 1978. 1978. In In1998, 1998,State Stateand andFederal Federal mineral mineral leasing leasing and and exploration explorationdrilling drilling began began to to increase increase with with the: 1) 1) rise in in price price of of PGEs; PGEs; 2) 2) possible possible use use of of new new hydrometallurgical hydrometallurgicaltechniques techniquesto tomore more efficiently efficiently recover recover copper copper and and nickel; nickel; and and 3) 3) introduction introductionof of new new PGE PGE exploration explorationmodels models (sulfide i.e.,atatSonju Sonju (sulfide saturation; saturation;Miller Miller et et al., al., 2002) 2002) for for intrusions intrusionsin in the the Beaver BeaverBay BayComplex, Complex,i.e., Lake, and the Duluth Complex, Duluth). The Complex, i.e., Greenwood Lake and Layered Series at Duluth). The maps maps in this this poster poster illustrate illustrate the the relationship relationshipbetween between geology, geology,geophysics, geophysics, drilling, drilling,and andmineral mineral leasing leasing and were produced in ArcView (GIS). (GIs). The Themaps maps were were also alsocompiled compiledby by using using information from: 1) (minarchive.dnr.state.mn.us)attributeattribute-and and GIS-based GIs-based DNR's online online(minarchive.dnr.state.mn.us) 1) the DNR's database database of non-ferrous non-ferrous minerals' minerals' information information and and State State mineral mineral rights rights holdings; holdings; 2) 2) U.S. U.S. Forest Forest Service GIs data dataon onthe thehistory history Service leases, leases, permits, permits, and and applications applicationsdatabase; database; and and3) 3) NRRI NRRI in-house in-houseGIS of Cu-Ni-PGE Cu-Ni-PGE mineralization. mineralization. Using Usingthe theresulting resultingGIS GIsdatabase, database,the thespatial spatialrelationships relationshipsin inthe the changes in drilling, drilling, leasing, leasing, etc. etc. with with time time and and place place were were then then combined combinedwith withgeological geological information information from from Miller Miller et et al. al. (2002) (2002)to to better better understand understandthe the past past and andpresent presentexploration explorationareas areas and and to assist assist in in defining definingnew new areas areas in in which which to to explore explorefor fornon-ferrous non-ferrousminerals. minerals. References References Miller, Jr., Green, Green, J.C., J.C., Severson, Severson, M.J., M.J., Chandler, Chandler, V.W., V.W., Hauck, Hauck, S.A., S.A., Peterson, Peterson, D.M., and Miller, J. D., Jr., Wahl, T.E., 2002, 2002, Geology and mineral potential of the Duluth Complex and related rocks of northeastern Minnesota: 207 p. Minnesota: Minnesota MinnesotaGeological Geological Survey SurveyReport Report of of Investigations Investigations58, 58,207 p. 23 �- CU S CU SC INCO 0 CD Creeku Beer Creek I = U (Ii U Ui S Ut S S 0 0 S 0 CU USS S N 1 t S 0 S 0 Dovl Coo Neweori 0 S 10 INCO Beer Creek' I S N 10 S OJ N S 0 N I I I - CU = (S Theel U XX CU 0 CU CU CU CU I CU CU CU a 0' INc0 0' CU 0 S Di 10 I S 0' CU S = 0 - - I PotyMeti 10 0 0 0' CU 0' Xl 0' - CU 0' - - 0 = = CONCENTRATED DRILLING - II IU \felkrdgeU• S 0 Di = SCATTERED DRILL NG Arerieer S/ic d/NICDR CK Lehcerrr I - 0 CU SSS CU 10 N 0 N CU CU S 5555555555555 N !hosorr 1 oxocL1 Cleveerd CliP Fe I • N CD 11111 0 S 55 N Blerkerkerg—Wkiteside U I orrotioc dril eg) I r4 I AMAX - S CU uss •I Devot helps D ooge CD I (costly iroc Beer Creek IIHIIIIHHIII BI I I k/S Moore/A ercerr ShijId Creek I S - sPLie Rood Mokori S ---Beor Ceek •L,L Lrek1 Beer Creeki Bee B Sproce Rood cUr Creek INCO •1US'BM1MGS S CU - Metri = S IIIjIflIII S UCkidere eed Cdhiteeide S CU Figure 1. History of Cu-Ni-PGE exploration in the Duluth Complex (after Miller et at., 2002). GUNFLINT TRAIL DRILLING RECONNAISSANCE OR SCATTERED LONGNOSE (Oul) BIRCH LAKE WATER HEN (OUI) WESTERN MARGIN SO. FILSON CREEK WETLEGS DUNKA PIT WYMAN CREEK (NorthMef) DUNKA ROAD (Minnamax) (Mesaba) BABBITT MATURI SPRUCE RD & Deposit/Area kin.iesolo sow C—Ni nvwol INCO • Duval • Exxon • Other Companies AMAX • Bear Creek !I USS • LEGEND �Geochemistry and Mineralization of the Seagull Seagull Intrusion, Northern Ontario Heggie, P., P., (Department of Geology, Lakehead Heggie,G., G.,and andHollings, Hollings, (Department of Geology, LakeheadUniversity, University,955 955 Oliver Oliver Road, Thunder Bay, On, P7B 5E1, gheggie gheggie@mail.lakeheadu.ca) @ mail.1akeheadu.ca) Platinum Group Elements Elements (PGE-Platinum, (PGE-Platinum, Palladium, Osmium Osmium and Iridium) Indium) have seen seen substantial increases in demand over the last substantial 30 years, as industrial and commercial users have increased their consumption. consumption. Canadian Canadian production of these metals has until recently been limited to by-products from nickel Sudbury). Opening of the copper mines (e.g., Sudbury). Lac des mine in in Ontario demonstrated demonstrated the des Ties Iles mine the potential for economic economic PGE PGE deposits deposits in in Canada. Further work on deposit and exploration exploration models is is essential essential to to identifying identifying new targets and prospective prospective host rocks. rocks. The Seagull Lake intrusion intrusion is found found within within the the Nipigon Embayment, approximately 70km approximately 70km north east of Thunder Thunder Bay, Ontario Ontario (Fig.1). (Fig.1). Relative Relative age dating dating places the age age of the Seagull Lake intrusion to be younger than Map showing location location of Seagull Intrusion Intrusion Figure 1. Map the Sibley Sibley Group sedimentary sedimentary sequence, sequence, and (1339±33 Ma) (Franklin et al., 1980), and regional regionalgeology. geology. (1339k33 1980), as part of the intrusion has been seen to cross cut Sibley Sibley stratigraphy. A chilled chilled margin has been observed between the Seagull Seagull Intrusion and the younger Nipigon Sills defining defining an upper age of approximately 1.1 Ga (Davis (Davis and and Sutcliffe, Sutcliffe,1985). 1985).This This falls falls within within the the time time of of mid-continental mid-continental rifting in the Lake Superior region. Volcanic activity was responsible for production Superior region. Volcanic activity responsible for productionof of thick thick basaltic sequences sequences (Cannon (Cannon et et al., al., 1989) 1989)beneath beneath and and around around the the shores shoresof of Lake LakeSuperior Superiorand andthe the emplacement of numerous mafic to ultramafic complexes (e.g., Duluth complex). complexes (e.g., Duluth complex). The Seagull Seagull Intrusion is currently currently under exploration exploration by East East West West Resource Resource Corporation, Corporation,ItIt isis aa consisting of cumulate layered ultramafic intrusion consisting cumulate olivine, olivine, and oxide oxide minerals minerals with with pyroxene pyroxene oikocrysts and interstitial feldspar. feldspar. Lithological phases include include dunites, dunites, iherzolites, lherzolites, olivine olivine gabbronorites, gabbros, and pryoxenites. A distinctive distinctive olivine olivine gabbronorite gabbronorite is is found found within within the the gabbronorites, intrusion but this exhibits chilled chilled margins and is thought to post date the formation of the rest of the intrusion. intrusion. 25 �DDH WMOO-01 WMOO-01 Depth (m) (m) Depth 375.0 375.0 408.0 572.0 546.0 379.0 Interval Interval (m) (m) 4.0 4.0 4.5 12.0 6.0 8.0 6.0 6.0 6.0 Cu Cu (ppm) (ppm) 269 269 Ni (ppm) Ni ( P P ~ 1160 1160 Pt pt (ppb) (PP~) 1413 1565 779 WM98-02 1180 987 WM98-05 112 1647 569.0 1843 1841 579.0 1220 1455 579.0 1220 1455 Figure Figure 2. Table Table of metal metal contents contents from from assay assay (Caven, (Caven, R., R., 2000) 501 307 307 336 363 535 336 693 458 458 Pd (ppb) pd (PP~) 383 383 418 438 566 393 847 537 Mineralization occurs in the form of PGE minerals associated with disseminated FeNi sulfides (pentlandite). Pentlandite is found in higher abundances at discrete intervals intervals throughout throughout the the intrusion, with a general increase increase towards the base base of of the the intrusion. intrusion. Work is currently being undertaken to understand the the stratigraphy stratigraphy of the the intrusion, intrusion, the the nature nature of of the platinum group mineralization, mineralization, and and formational formational controls controls on on the the mineralized mineralized zones, zones,which whichare are present in the intrusion in order to aid in the development and refinement of exploration techniques, and deposit models. Cannon, W.F., Green, A.G., Hutchinson, D.R., Lee, M., Milkereit, B., B., Behrendt, Behrendt, J.C., J.C., Halls, Halls, H.C., H.C., Green, J.C., Dickas, A.B., Morey, G.B., Sutcliffe, Dickas, Sutcliffe, R., and and Spencer, Spencer, C., C., 1989, 1989,The TheNorth NorthAmerican AmericanMidcontinent Midcontinent rift rift Reflection profiling. profiling. Tectonics, Tectonics, v. 8, p. 305-332. beneath Lake Superior from GLIMPCE Seismic Reflection Caven, R.J., 2000, Progress Caven, R.J., Progress Report Report on on the the Wolf Wolf Mountain Mountain and and Disraeli Disraeli Properties Properties for for East EastWest WestResource Resource Corporation, Corporation, Canadian Canadian Golden Golden Dragon Dragon Resources Resources Ltd. Ltd. and and Avalon Avalon Ventures VenturesLtd. Ltd. Davis, D.W., D.W., and R.H., 1985, Davis, and Sutcliffe, Sutcliffe, R.H., 1985, U-Pb U-Pb ages ages from from the the Nipigon Nipigon plate plate and andNorthern Northern Lake LakeSuperior. Superior. Geological Geological Society Society of American American Bulletin, Bulletin, v.96, v.96, p. 1572-1579. 1572-1579. Franklin, J.M, Mcllwaine, McIlwaine, W.H., Poulsen, K.H., and and Wanless, Wanless, R.K., R.K., 1980, 1980,Stratigraphy Stratigraphy and and depositional depositional setting setting of of the Sibley Group, Thunder Thunder Bay Bay district, district, Ontario, Ontario, Canada. Canada. Canadian Canadian Journal of of Earth Earth Sciences, v.17, p. p. 633-65 633-651. 1. 26 �PEPERITES PEPERITESOF OF THE THEGAFVERT GAFVERTLAKE LAKE VOLCANIC VOLCANIC COMPLEX, COMPLEX,ST. ST. LOUIS COUNTY, MINNESOTA MINNESOTA Heiling, Carrie D., Department of Geological Geological Sciences, Sciences, University University of of Minnesota Minnesota Duluth, Duluth, 1114 1114 Kirby Drive, Duluth, MN, 55812; cheiling@d.umn.edu cheiling@d.umn.edu The Gafvert Lake area, located within the Upper Ely member of the Ely Greenstone Greenstone of the Vermilion District in Northeastern Minnesota (Figure 1) (Card, 1990), forms part part of of a large, Archean, felsic volcanic complex. Morton Morton (personal (personal communication) communication) has has interpreted the complex to be a composite volcano that underwent late stage caldera collapse. This Thisstudy studyhas has focused focused on on aa two two square square mile mile area area in in the the central central part part of of the the complex. Here Herethe thecomplex, complex,from fromthe theoldest oldestto to the the youngest youngest rocks, rocks, is is composed composed of of a) a) coarse, heterolithic breccias (interpreted (interpreted to represent meso-and mega breccias) breccias) (Morton, (Morton, personal communication), b) more than 3000 3000 feet feet of massive massive to to bedded bedded pumice-rich pumice-rich lapilli tuff, c) dacitic lavas and domes, and and d) d) lenses lenses and and beds of of chert chert and and massive massive to to semi-massive pyrite (Figure 2). The The breccias breccias and and lapilli lapilli tuffs tuffs have have been intruded by a swarm of feldspar porphyry dacite dikes that represent feeders to the domes and/or and/or flows. flows. Peperites are rocks formed by the in situ disintegration of magma intruding and and mixing mixing with wet unconsolidated sediment et al., al., 2002). At At Gafvert Gafvert Lake the sediment or or ash (Skilling (Skilling et peperites formed near the top of the complex where dacite dacite porphyry dikes intruded intruded and and unconsolidated pumice-rich pumice-rich lapilli lapillituff. tuff. This mixing led to quenching mixed with wet, unconsolidated and fragmentation of the dacitic magma and disruption and vesiculation vesiculation of of the the lapilli lapilli tuffs. The peperites occur within 100 feet of dike contacts though they form much The peperites occur within 100 feet of dike contacts though they form much more together. Angular and extensive areas where several dikes occur close together. and finger-like blocks of dike material occur within the peperite, locally these are connected to aa nearby nearby dike. dike. Macrotextures in outcrop and and microtextures microtextures in thin thin section section helped helped identify identify and and classify classify the following fragment types and internal structures within the peperites: a) a) blocky blocky jig-saw fit textures, b) platy to ragged juvenile fragments with chilled rims and occasional jig-saw juvenile fragments with curviplanar surfaces and broken gas bubbles, c) ameboid to globular juvenile fragments, d) abundant pumice which exhibits variable variable vesicularity. vesicularity. Most of this pumice is juvenile to the lapilli tuffs but a small percentage contains feldspar crystals identical to those found in the dikes possibly indicating local, local, rapid rapid vesiculation vesiculation of dike material. Close Closeto todike dikemargins marginsfeldspar feldspar crystals crystals are are broken broken and and internally internally fractured with fractures filled by lapilli tuff. Pumice, Pumice, close close to to dike dike contacts, contacts, may may be jigsaw-fit pieces. pieces. Locally the ash matrix to broken or disaggregated into several small jigsaw-fit the lapilli tuffs is amygdaloidal amygdaloidal with amygdules amygdules radiating away from dike margins. margins. References References Card, K.D., 1990, Province of of the the Canadian Canadian Shield, Shield, aa product product of of 1990, A review of the Superior Province Archean accretion: Precambrian Research, v. 48, pp. 99-156. Precambrian Research, v. 48, pp. 99-156. Minnesota, 2003, Mapquest, Ely, Minnesota, Mapquest, www.mapquest.com. www.rnapquest.com. communication, University University of Minnesota-Duluth. Minnesota-Duluth. Morton, R.L., 2003, personal communication, Skilling, Skilling, I., White, J., McPhie, McPhie, J., J., 2002, 2002, Peperite: Peperite: aa review of magma-sediment magma-sediment mingling, mingling, Journal Journal of Volcanology Volcanology and Geothermal Geothermal Research, Research, v. 114, 114, pp 1-17. 1-17. 27 �Figure 1: 1: Location Location of of Gafvert Gafvert Lake Lake complex complex (Mapquest, (Mapquest, 2003). 2003). Explanation Explanation • Peperite samples Fault Zone Contacts / '" ' Railroad grade grade , " Mud Creek Road / Mud Road f' * A/ - Mbas - Metabasalt Metabasalt SIst METERS 200 00 J0 Â¥s 410 400 600 oo 800 Figure Figure 2: Generalized Generalized map of a portion of Gafvert Gafvert Lake volcanic complex. complex. 28 Q Qfo- Qtzfeld - QtzfeldPorphyry Porphyry Black Chert Cht -- Black Cht Diab -- Diabase Diabase Dikes Dikes Dior Dior -- Diorite Diorite Dac -- Dacite Dikes Dikes Dac Tuff -- Lapilli Lapilli Tuff luff Bx Bx -- Breccia Breccia SIst SIst - Siltstone &&Iron Iron Fm Fm �CHEMISTRY OF OF ALTERATION ALTERATION MINERAL MINERAL PHASES PHASES AT THE FIVE MILE MILE LAKE LAKE CHEMISTRY VOLCANIC-HOSTED MASSIVE MASSIVE SULFIDE SULFIDE PROSPECT, PROSPECT,NE NE MINNESOTA MINNESOTA VOLCANIC-HOSTED locker, Hocker, S. S.M., M.,Hudak, Hudak, G. G.J.,J.,Odette, Odette,J.J.D., D.,and andNewkirk, Newkirk,T.T.T., T.,Department Department of ofGeology, Geology, University of Wisconsin Wisconsin Oshkosh, Oshkosh, 800 800 Algoma Algoma Blvd., Oshkosh, WI 54901, hudak@uwosh.edu hudak@uwosh.edu Alteration mineral Lake Prospect Prospect in in the the Vermilion Vermilion Alteration mineral assemblage assemblage mapping mapping at at the the Five Mile Lake identified two distinct types of alteration zones within 2.7 District of northeastern Minnesota has identified year-old volcanic volcanic and and volcaniclastic volcaniclastic rocks rocks associated associated with withvolcanic-hosted volcanic-hosted massive massive billion year-old 2001a,2001b; 2001b;Peterson, Peterson, mineralization (Hudak et a!., al., in in press; press; Odette Odette et et al., al.,2001a, sulfide (VHMS) mineralization 2001). 2001). Regional Regional semi-conformable semi-conformable alteration alterationzones zones are are composed composed of of various various proportions proportions of of quartz quartz ++ epidote epidote ±Â amphibole amphibole ± chlorite chlorite ±Â plagioclase plagioclase feldspar. feldspar. These regional, regional, These are locally locally cross-cut cross-cut by by several severalrelatively relativelynarrow, narrow,northeastnortheastsemiconformable alteration zones are composed of fine-grained fine-grained chlorite chlorite and/or andlor sericite sericite that that trending disconformable alteration zones composed are closely closely associated associated with with synvolcanic synvolcanicfault faultzones. zones. Electron microprobe microprobe analyses the various various alteration alteration mineral mineral phases phases (epidote (epidote group group Electron analyses of of the minerals, chlorite, feldspar) have conducted in an effort effort to to minerals, chlorite, amphibole, amphibole, white white mica, mica, and and feldspar) have been been conducted better understand understand hydrothermal hydrothermal processes processes associated associated with with the the development development of the the semiconformable and Mile Lake Lake prospect. prospect. These These semiconformable and disconformable disconformable alteration alteration zones zones at at the the Five Mile zoisite/clinozoisite to analyses indicate that: a) epidote epidote group group minerals minerals range in composition composition from zoisite/clinozoisite analyses pistacite; b) chlorite chlorite is is dominantly dominantly ripidolite; ripidolite; c) c) amphibole amphibole is is primarily primarily actinolite actinolite and and ferroferropistacite; actinolite, with magnesio-hornblende magnesio-hornblende and is fineheactinolite, and ferro-hornblende ferro-hornblendealso also present; present; d) d) sericite is grained grained muscovite; muscovite; and and e) e) plagioclase plagioclasefeldspar feldsparisisdominantly dominantlyalbite. albite. chemistry at the Five Five Mile Mile Lake Lake Prospect Prospect is is remarkably remarkably similar similar to that that Alteration mineral mineral chemistry VHMS mining mining camp camp of of Canada, Canada,as as well well as as other other VHMS VHMSmining miningcamps campsaround around from the Noranda VHMS the world. world. This alteration alteration mineral mineral chemistry chemistry suggests the presence of aa complex, complex, long-lived long-lived hydrothermal system evolved from from seafloor-proximal seafloor-proximal (hundreds meters) to deeper deeper hydrothermal system that that evolved (hundreds of of meters) subseafloor environments kilometers) as as the the volcanic volcanic rocks rocks were wereburied buriedby byapparently apparently subseafloor environments (-1-3 (1 -3 kilometers) dominantly effusive effusive mafic mafic to to intermediate intermediate volcanism volcanism and and associated associated sedimentation. sedimentation. This This rapid, dominantly addition to the the Five Five Mile Mile Lake Lake Prospect, Prospect, the the uppermost uppermost several several hundred hundred meters meters suggests that in addition Lower Member Member of of the the Ely Ely Greenstone Greenstonealso also has has excellent excellentexploration explorationpotential potential for for VHMS VHMS of the Lower mineral deposits. deposits. References References F., Paradis, Paradis, S., S., Hannington, M., Holk, G., G., Katsube, Katsube, J., J., Paquette, Paquette, F., Galley, A., Bailes, A., Hannington, Galley, A., Bailes, M., Holk, Santaguida, Santaguida, F., F., and and Taylor, Taylor, B., B., 2002, 2002, Database Database for CAMIRO CAMIRO Project Project 94E07: 94E07: Interrelationships between subvolcanic intrusions, intrusions, large-scale large-scale alteration zones, and and VMS VMS Interrelationships between subvolcanic deposits: deposits: Geological Geological Survey Surveyof ofCanada CanadaOpen OpenFile FileReport Report4431 443 1(CD-ROM). (CD-ROM). and Hauck, Hauck, S., S., in in press. press. Comparative Comparativegeology, geology, Newkirk, T., T., Odette, Odette, J., and Heine, J., J., Newkirk, Hudak, G. J., Heine, Mile Lake, Lake, Quartz Quartz Hill, Hill, and and Skeleton SkeletonLake Lake stratigraphy, and lithogeochemistry of the Five Mile VMS VMS occurrences, occurrences, Vermilion Vermilion District, District, NE Minnesota: AAreport reportto tothe theMinerals MineralsCoordinating Coordinating Committee, Minerals Division, State of Minnesota. DNR Minerals Minnesota. Committee, DNIR 29 �Kranidiotis, Kranidiotis, P. P. and and MacLean, MacLean, W. W. H., H., 1987, 1987,Systematics Systematicsof of chlorite chlorite alteration alteration at at the the Phelps Phelps Dodge Dodge Massive Sulfide Sulfide Deposit, Deposit,Matagami, Matagami,Quebec: Quebec:Economic EconomicGeology, Geology,v.v.82, 82, p. p. 1898-1911. 1898-1911. Massive Odette, Odette, J. D., Hudak, Hudak, G. G. J., J., Suszek, Suszek, T., T., and and Hauck, Hauck, S. S.A., A.,2001a, 2001a. Preliminary Preliminary evaluation evaluation of hydrothermal hydrothermal alteration alteration mineral mineral assemblages assemblages and and their their relationship relationship to to VMS-style VMS-style Archean Vermilion Vermilion Greenstone Greenstone Belt, Belt, NE NE mineralization in the Five Mile Mile Lake Lake area area of of the theArchean mineralization 470h Minnesota: Institute Institute on on Lake LakeSuperior SuperiorGeology, Geology, 47thAnnual Meeting, Meeting, Proceedings Proceedings Volume Volume 47, 47, Part Part 1-Program 1-Programand and Abstracts, Abstracts, p. p. 75-76. 75-76. Odette, D., Hudak, Hudak, G. G. J., J., Suszek, Suszek, T., T.,and andHauck, Hauck, S.S.A., A.,2001b, 2001b,Preliminary Preliminary evaluation evaluation of Odette, J. D., hydrothermal hydrothermal alteration alteration mineral mineral assemblages assemblages and and their their relationship relationship to to VMS-style VMS-style mineralization in the Five Five Mile Mile Lake Lake area area of of the theArchean Archean Vermilion Vermilion Greenstone Greenstone Belt, Belt, NE NE mineralization Minnesota: Geological Geological Society Society of of America America Abstracts Abstracts and and Programs Programs Volume Volume 33, 33,No. No. 6,6, p. p. AAMinnesota: 420. 420. Peterson, Peterson, D. M., M., 2001, 2001, Development Development of of Archean Archean lode-gold lode-gold and and massive massive sulfide sulfidedeposit deposit exploration models models using using geographic geographic information information system system applications: applications: targeting targeting mineral mineral exploration exploration in northeastern northeastern Minnesota Minnesota from analysis analysis of of analog analog Canadian Canadian mining mining camps: camps: exploration Duluth, Minnesota, Minnesota, 503 503 p. p. unpublished Ph. Ph. D. D. dissertation, dissertation, University University of of Minnesota, Minnesota, Duluth, unpublished Fe (total) 18 0.2 0.4 0.6 16 14 12 10 0 AlzQ, CORUNDUM CORUNDUM 0.9 0.8 0.7 0.6 La :' 0.5 0.4 0.3 0.2 0.1 I 6.0 6.5  Flm Mite Lake Amphlboto I 7.0 7.0 7.5 8.0 ORTHOCLASE ORTHOCLtSE KAISiiO. KOJSieOe Figure Figure 1.1. Summary Summary of of electron electronmicroprobe microprobeanalyses analysesfor forepidote-group epidote-groupminerals minerals(A), (A),chiorites chlorites (B), (B), amphiboles amphiboles (C), (C), and andwhite whitemicas micas(D) (D)from fromthe theFive FiveMile MileLake LakeProspect Prospectand andselected selectedVHMS VHMS mines. mines.Compositional Compositionalfields fieldsfor forNoranda Norandaminerals mineralsdetermined determinedfrom from Galley Galleyetetal. al.(2002). (2002). 30 30 �GEOCHEMISTRY AND GEODYNAMIC GEODYNAMICIMPLICATIONS IMPLICATIONSOFOFTHE THE 1537 GEOCHEMISTRY AND 1537 MA MA REDSTONE REDSTONE POINT POINT ANOROGENIC ANOROGENICGRANITE, GRANITE,ONTARIO, ONTARIO,CANADA CANADA Hollings, (DepartmentofofGeology, Geology,Lakehead Lakehead University, University, 955 955 Hollings, P., Fralick, Fralick, P.P.and andKissin, Kissin,S.S.(Department Oliver Rd., Rd., Thunder Bay, Bay, Ontario, Ontario, P7B P7B 5E1, 5E1, Canada; Canada; Peter. Peter.Hollines@lakeheadu.ca) Hollinss @ lakeheadu. ca) The Redstone Point Point granite is is aa felsic igneous Mesoproterozoic Mesoproterozoic felsic igneous complex Ma; Davis complex (1537+10/-2 (1537+10/-2 Ma; Davis and and Sutcliffe, 1984) located in the northern northern portion of the Sibley Sibley Basin on the the west west shore of Lake Nipigon (Fig. 1). shore of Lake Nipigon (Fig. 1). It is is unconformably overlain by by arenites unconformably overlain arenites of of the Pass Lake Lake Formation Formation of of the the Sibley Sibley are in turn Group. Group. These These sediments sediments are turn intruded and overlain by an an extensively extensively sills developed developed sequence sequence of diabase diabase sills related to an early stage of the Midrelated to early stage of the Midevent. The entire Continent Continent Rifting Rifting event. entire sequence sequence has been gently folded into aa shallowly, easterly plunging plunging succession succession of open synclines and anticlines, with open synclines and anticlines, with of the the Redstone Point Point Figure 1. Map showing the location of dips usually exceeding 150. Outcrop not usually exceeding 15O. Outcrop granite in relation relation to Proterozoic Proterozoic anorogenic anorogenic granite granite density of of igneous igneous units units is very very good good of North North America. America. Modified after after Anderson (1983) density complexes of Anderson(1983) sedimentary sequences, sequences, which which only only provide provide along the shoreline of Lake Nipigon, in contrast contrast to to sedimentary small, scattered scattered outcrops. outcrops. The igneous rocks of Redstone Point Point have have been been briefly briefly described describedby by Davis Davisand andSutcliffe Sutcliffe(1985), (1985), of Redstone wherein they they emphasised emphasised that that the the rocks are to rhyolites and wherein are anorogenic anorogenic granites gradational gradational to fragmental rhyolites rhyolites and and dacites. dacites. In fact, presently fragmental presently accessible accessible outcrop indicates that extrusive extrusive members dominate dominate the the magmatic magmatic rocks rocks of the area. members area. Porphyritic Porphyritic texture texture with with volcanic volcanic features features including vesicles, vesicles, flow flow structures, units, rubbly rubbly flow tops including structures, agglomeratic agglomeratic units, tops and andsegregation segregation cylinders differentiate differentiate extrusive extrusive rocks rocks from from more limited cylinders limited exposures exposures of of uniformly uniformly textured textured intrusive rocks. As contacts between units are generally unexposed and the base of the section is nowhere exposed, thicknesses thicknesses of of units units and of nowhere exposed, of the the entire entire succession succession are are unknown; unknown; however, however, continuous outcrop in in cliff-forming units indicates indicates that that a minimum continuous outcrop cliff-forming units minimum thickness thickness of of lOOm 100m of of volcanic rock is present in the area. area. The igneous rocks are the dominace of ferric are distinctively distinctively brick brick red, suggesting suggesting the dominace of ferric iron iron in in the the various mineral hosts but especially in trace amounts in feldspars. The intrusive member displays equigranular phaneritic phaneritic texture texture with with most most mineral mineral grains grains 11 to to 5 mm in diameter. equigranular diameter. The The volcanic volcanic rocks are true porphyries porphyries with with phaneritic phaneritic phenocrysts phenocrysts of of alkali alkali feldspar, feldspar,quartz quartzand andhornblende hornblendein in an aphanitic matrix of of the same minerals. Quartz phenocrysts are are euhedral euhedraland and 11 to to 3 mm in an aphanitic matrix Quartz phenocrysts diameter associated with alkali feldspar phenocrysts occasionally exhibiting synneusis twinning as well as as albite-pencline albite-pericline twins twins indicative indicative of of microcline. microcline. Hornblende Hornblende and and magnetite magnetite are are less less 31 �abundant and finer grained than in the the intrusive intrusive rocks. rocks. Near Near flow flow tops tops the the porphyries porphyriesgrade grade into into uniformly textured aphanitic rhyolites with sparse phenocrysts. textured rhyolites with sparse phenocrysts. The samples from the The the Redstone Redstone Point Point intrusive intrusive complex complex are all all characterised characterised by by high high Si02 Si02 contents (73-83 (73-83 wt%) wt%) and elevated contents elevated K20 &O and and Na20 Na,0 abundances abundances (2-7 wt% wt% and and 0.2-3.5 0.2-3.5 wt% wt% respectively). They They are respectively). are typically typically LREE enriched LREE enriched with relatively unfractionated IIREE (La/Sm,, unfractionated HREE (La/Smn = = 2.8-5.1; Gd/Yb,, = = 1.1-1.6; 1.1-1.6; Fig. 2) 2.8-5.1; Gd/Ybn 2) and are are characterised characterised by by elevated elevated Zr, Y Y and and Nb Nbcontents. contents. Samples Samples from the Redstone Redstone Point Point igneous igneous complex fulfil fulfil the complex the detailed detailed trace trace criteria of of Whelan element criteria Whelan et al. al. (1987) for anorogenic anorogenic granites. granites. . f _J Rb BaTii Tb UU Nb La Ce C <b Ba Nb La Pr Pr Sr Nd Sr Nd Zr Ba T La M Zr Hf llf Sn, Sin Eli Ti Gd (a Tb Tb fly W) 7Y Ho 110 P Fr Yb Yb LII 41 V Sc Sc mantle normalised Figure 2. Representative primitive mantle normalised diagram diagram for for samples from the the Redstone Redstone Point Pointigneous igneouscomplex complex Similarities Similarities between between Proterozoic Proterozoic basin sequences sequences (e.g., (e.g., Athabaska, Athabaska, Thelon, Hornby Bay and and Sibley Sibley basin fill fill sequences) sequences) imply that basin genesis genesis and and developmental developmental controls were similar. The setting, architecture, depositional systems and deformational histories of all four basins strongly infer that they are intracratonic, forming as a result of heating cratonic The heating heating event is represented represented in in northern northern Canada by by numerous 1790 to 1730 Ma lithosphere. The anorogenic, syenogranite syenogranite batholiths batholiths and comagmatic ash-flow tuffs occurring west of anorogenic, comagmatic ash-flow of Hudson Hudson Bay. In the the western western Great Great Lakes Lakes region region aa heating heating event event produced produced the the 1537 1537Ma Ma Redstone Redstone Point Point assemblage and and other 1500 records a assemblage 1500 Ma anorogenic anorogenic batholiths. The southern southern mid-continent mid-continent records heating event with anorogenic granite granite production production from from approximately 1480 to to 1320 lithospheric heating Ma (Fig. 1). These events outline a progressive southward displacement of lithospheric heating 1). events outline a progressive southward from a maximum age of approximately 1750 1750 ma in northern Canada to aa minimum minimum age age of of 1310 1310 Ma in the Ma the southwestern southwestern United States. States. As heat heat transfer transfer from from the the asthenosphere asthenosphere is the the only only mechanism for producing extensive lithospheric heating, drift of North America over hotter than average asthenosphere is implied. Using regional ages of heating, drift rates of approximately 1.1 1.1 cm/year are necessary, and agree in magnitude magnitude with present rates. rates. to 1.4 1.4 cmlyear REFERENCES REFERENCES Anderson, J., 1983. Proterozoic anorogenic granite granite plutonism plutonism of of North North America. America. In: In: Medaris Medaris et Anderson, al., (Eds), Proterozoic Proterozoic geology. geology. Geological Society of America Memoir Memoir 161, 161,133-154. 133-154. Davis, and Sutcliffe, Sutcliffe, R., 1985. 1985. U-Pb U-Pb ages ages from from the the Nipigon Nipigon Plate Plate and and Northern Northern Lake Lake Davis, D., and Superior. Superior. Geological Geological Society Society of America Bulletin, Bulletin, 96, 96, 1572-1579. 1572-1579. Whelan, J., Currie, Currie, K., K., and andChappell, Chappell,B., B.,1987. 1987.A-type A-typegranites: granites:geochemical geochemicalcharacteristics, characteristics, Whelan, discrimination and petrogenesis. Contributions to Mineralogy and Petrology, 95, 407-419. discrimination and petrogenesis. Contributions to Mineralogy and Petrology, 95,407-419. 32 �PALEOPROTEROZOIC (1900-1600 (1900-1600 Ma) Ma) TECTONIC TECTONIC HISTORY HISTORY OF OF THE THE NORTHERN NORTHERN LATE PALEOPROTEROZOIC MID-CONTINENT, MID-CONTINENT, U.S.A: IMPLICATIONS IMPLICATIONS FOR CRUSTAL CRUSTAL STABILIZATION STABILIZATION HOLM, D.K., Dept. of Geology, Geology, Kent State State University, Kent, OH OH 44242; 44242; VAN VAN SCHMUS, SCHMUS, W.R., and MacNEILL, L.C., Dept. of Geology, Geology, University of Kansas, Lawrence, Lawrence, KS 66045; 66045; BOERBOOM, T.J., Minnesota Geological Survey, 2642 University University Avenue, Avenue, St. Paul, Paul, MN MN 55114; SCHWEITZER, D., Dept. of Geology, Kent State University, Kent, OH 44242; 551 14; SCHWEITZER, D., Dept. of Geology, State Kent, OH 44242; SCHNEIDER, SCHNEIDER, D.A., Dept. of Geological Geological Sciences, Sciences, Ohio Ohio University, University, Athens, Athens, OH OH 45701 45701 We propose that the late late Paleoproterozoic Paleoproterozoicigneous igneous and and deformational deformationalhistory history preserved preserved in in the the southern Lake Superior southern Lake Superior region region is the the result result ofofnorthwest-directed northwest-directed convergence convergence during during and following geon 18 18 Penokean accretion. accretion. New U-Pb zircon ages indicate that late to post-Penokean magmatism began ca. 1800 1800 Ma Ma and and generally generally migrated migrated southeastward southeastwardacross across the the newly newlyaccreted accreted terrane. Magmatic Magmatic pulses pulses atatca. ca.1800, 1800,1775, 1775,and and1750 1750Ma Mamay maycorrelate correlatewith withnorthwest-directed northwest-directed subduction associated with southward growth of the North American mid-continent. mid-continent. We suggest suggest that geon 17 Yavapai-age slab rollback caused continental arc magmatism to step southeastward 17 continental to step southeastward As the the slab slab steepened, steepened, the reduced compressional compressional stresses between 1800 and 1750 Ma (Fig. 1A). As and increased thermal input allowed allowed for collapse collapse of of the the overthickened overthickenedportions portions of of the the Penokean Penokean In northern collapse involved involved the the formation of gneiss crust. In crust. northern Wisconsin, Wisconsin, collapse formation of gneiss domes domes and and their their within discrete fault-bounded panels panels brought brought up up from depth via tectonic exhumation within tectonic extrusion extrusion (Schneider - and possibly temporary temporary (Schneider et al., al., ILSG, ILSG, 2003). 2003). Collapse of the the Penokean Penokeanorogen orogen— resulted in crustal stabilization stabilization and deposition deposition of of Baraboo Baraboo Interval Interval cessation of of slab slabsubduction subduction—- resulted However, in a long-lived orogen model, renewed quartzites between 1750 and 1650 Ma. quartzites between 1650 Ma. However, in long-lived orogen model, renewed tectonism to to the the south of a Mazatzal tectonism south resulted resulted in the the eventual eventual accretion accretion of Mazatzal arc (Fig. (Fig. 1B) 1B) with with widespread deformation deformation and and mild mild reheating reheating of of Penokean widespread Penokean crust to the the north. north. The age of this this deformation is inferred from conventional Ar/Ar ArIAr step-heating studies on basement rock beneath deformed and undeformed undeformed Baraboo Baraboo Interval Intervalquartzites. quartzites. The 1900 to 1600 Ma tectonic history of of United States, not surprisingly, records the southward the north-central north-central United surprisingly, records southward growth growth and tectonic tectonic development of the southern southern Laurentian margin. New and published mineral agesdelineate delineatethe the northern northern and and western extent of geon ^ ~ r / ^ ~mineral r ages published 40Ar/39Ar 16 crustal deformation. Interestingly, Interestingly, only only lower-grade lower-grade crust intruded by the shallower-level ca. 1750 Ma plutons (and associated rhyolites) were were deformed significantly during during geon geon 16. Deeper Deeper level by the older level collapsed crust and crust crust pervasively pervasively invaded by older magmatic magmatic pulses pulses are are largely largely by Mazatzal deformation and reheating. reheating. We suggest that post-orogenic intrusions and unaffected by crustal thinning was an important step in strengthening strengthening and stabilizing the crust in the the southern southern Lake Superior Superior region. region. Schneider, Holm, O'Boyle, Hamilton, Hamilton, and and Jercinovic, Jercinovic, 2003, 2003, Paleoproterozoic Paleoproterozoic development of a gneiss dome corridor in the southern Lake Superior region, region, USA: USA: Institute Institute on on Lake Lake Superior Superior Geology Abstracts (this (this volume). volume). 33 �subduction (ca' vapai subduction (ca. 1750 1750 Ma) Ma) w —southward pro propagation "Â¥southwar agation of magmatism magmattsm I from to 1750 Ma granites granites and and rhyolites from 1775 1775 Ma Ma ECMB ECMB to 17 0 Ma rhyolites in WI Wl S N NFZ NFZ 2J750-1630 7 5 0 4 6 3 0Ma Maquartzites quartzites /_— ,. ', ,f — — 1...AVRENtIA -I . '- ' '—-— C -' Mazatzal orogen orogeny Mazatzal y (1650-1630 (1650-1630 Ma) Ma) 2 deformation deformation of "post-Penokean ost-Penokean"quartzites quartettes during Mazatzal azatzai accretion accretion A) Subduction Subduction roHback model proposed proposed to to explain magmatic magmatic age Figure 1: 1: A) rollback model progression the Penokean progressionacross across the Penokean orogen, orogen,ca.Yavapai ca.Yavapai convergence, preaccretion. ECMB = East-central East-central Minnesota Minnesota batholith. batholith. B) Mazatzal accretion. ECMB = 6)Mazatzal Mazatzal accretion model (modified after Romano et al , 2000) to explain deformation to explain deformation accretion model (modified after Romano et a]., quartzites and and southward southward growth growth of of Baraboo Interval quartzites of Laurentia, Laurentia, 34 �GABBRO/GRANOPHYRE LAKE INTRUSION: INTRUSION: A GABBROIGRANOPHYRE RELATIONS OF THE CROCODILE LAKE POSSIBLE VENT FOR THE HOVLAND LAVAS? JERDE, Eric A. (e.jerde@morehead-st.edu), (e.jerde@morehead-st.edu),Department Department of Physical Physical Sciences, Sciences,Morehead Morehead State State University, Morehead, KY 40351 4035 1 Morehead, KY One of the notable characteristics characteristics of of the the Midcoritinent Midcontinent Rift is the presence of large large amounts amounts of felsic felsic material. material. Indeed, the nature and origins origins of this this abundant abundant silicious silicious material material has has been been the the source sourceof of numerous numerousstudies studies(e.g., (e.g., Nelson, 1991; a!., 2000; 2000; Sandland et al., 2001). To 1991; Green and Fitz, 1993; 1993; Vervoort and Green, 1997; Kennedy et al., Tothe the south of the Early Gabbro Series is a pronounced ridge composed of of this this felsic felsic material, material, properly properly termed termed aa granophyre. granophyre. The Early Gabbro Gabbro Series Series layers layers are are inclined inclined to to the the south, south,thus thus are are below below the the granophyre granophyre stratigraphically. This This felsic felsic rock rock was was noted noted and and described described by by Nathan Nathan (1969) (1969) as as aa very very late-stage late-stage material, material, and has generally been presumed to have formed significantly after after the the gabbros gabbros in inthe theregion. region. However, several observations indicate that the gabbro was emplaced later than than the the granophyres. granophyres. These These include include gradational gradational contacts, contacts, with some chilling of of the the gabbro. Another Another observation observation is is the the abundance abundance of material described as "intermediate "intermediate rock" by various investigators in the past (e.g., Grout et al., 1959). This This material material isis always always found found between between the gabbro and granophyre, granophyre, and is is presumably presumably the the result result of assimilation assimilationof granophyre granophyre by by an an intruding, intruding,hot hot gabbro. gabbro. Investigations into possible origins origins of the granophyres granophyres (Sandland (Sandland et et al., al., 2001; 2001; Karl Karl Wirth, Wirth,pers. pers.comm.) comm.) included radiometric age determinations, determinations, and revealed revealed that that the the granophyres granophyresadjacent adjacent to to the the Early EarlyGabbro GabbroSeries Seriesare, are, of the rift rift (-1 (-.1107 Ga), and and essentially essentially contemporaneous. contemporaneous. Because like the gabbros, among the earliest rocks of 107 Ga), silicious material generally is a late-stage late-stage product of magma evolution, evolution, the surprising surprising antiquity antiquity of the the granophyres granophyres adds to questions questions surrounding surrounding their their origin. origin. The early age for the granophyres granophyres does, does, however, suggest suggest an origin origin for the the layered layered nature nature of of the the Early Early Gabbro Gabbro Series located below them stratigraphically. Due Due to to their their low low density, density, the granophyric material would have created a barrier that retarded the rise of buoyant gabbroic material coming up up from from below. below. These rising liquids liquids would have layering that that is is observed, observed, and and providing providing aa cap, cap, blocking blocking any any been forced to spread laterally, resulting in the apparent layering further rise of gabbroic gabbroic material. material. of the layered Early Early Gabbro Gabbro Series Series of of Nathan Nathan (1969) (1969) is is another another occurrence occurrence of of Immediately to the east of Ga;Karl KarlWirth, Wirth,pers. pers. comm.). comm.). This granophyre, also determined to be among those those of an early early origin origin (i.e., (i.e., —1107 -1 107 Ga; by Miller Miller et et al. al. (2001), (2001), and and the the rocks rocks are are interpreted interpreted to to be be rock group has been termed the Crocodile Lake Intrusion by sample examinations examinations (Babcock, (Babcock, 1959). Work gabbroic based on geophysical evidence, and a few sample Work done done between between 1913 and 1948 1948 included included the the very very edges edges of of this this intrusion, intrusion, and and indicates indicatesthat that they they are are basalt basalt lavas lavasand andgabbroic gabbroic intrusions, along with "red rock" (Grout (Grout et et al., al., 1959) 1959)that that isis now now known known to to refer refer to to granophyre. granophyre. Like the series mapped by Nathan (1969), there is a body of gabbroic material stratigraphically below the granophyre. granophyre. was made made into into the the Crocodile Crocodile Lake Lake Intrusion Intrusionto to examine examine some someof ofthe therock rock. During the past year, a reconnaissance was relations (Fig. 1). Traverses Traverseswere weregreatly greatly hampered hampered by by forest forest blowdown, blowdown, but the outcrops are are numerous. numerous. Several Several gabbro units are present, as well as a band of "intermediate "intermediate material" material" at the the very very top top of of the the gabbro, below below the the granophyre. Within Within the the granophyre granophyreitself, itself, several several bodies bodies of gabbro gabbro were were found to have actually actually intruded the granophyre. In In the the coarse-grained coarse-grainedinteriors interiorsof of these these bodies, bodies, the the gabbro gabbro is is indistinguishable indistinguishable from from the gabbros gabbros below the granophyre granophyre stratigraphically). stratigraphically). observed further north (i.e., below of the the granophyre granophyre are are prominent prominent knobs knobs and andridges ridgesthat thatare arecomposed composed of ofbasalt. basalt. These Immediately to the south of are mapped as part of the Hovland Hovland Lavas, Lavas, which which are are reversely reversely polarized, polarized, and and were were extruded extrudedduring duringthe theearliest earliest period of the rifting. ItIt isisperhaps perhapspossible possiblethat that the the discontinuous discontinuousbodies bodies (and (and other other stringers stringers and and local local dikes) dikes) within within the granophyre represent the feeder feeder conduits conduits for for the the eruptive eruptive basalts basalts immediately immediatelyto to the the south south (shown (shownschematically schematically in Fig. 2). In In several severalother otherplaces places within within the the granophyre, granophyre,there there are are basaltic basaltic stringers stringers and small dikes. Surrounding Surrounding has been been assimilated assimilated into into the the gabbro. gabbro. In the larger gabbroic bodies are obvious reaction zones where granophyre has immediately to the south, numerous inclusions are present that are pinkish one of the flows immediately pinkish in in color, color, along along with with felsic stringers and irregular masses masses of felsic material. material. Further work is planned to assess assess the relation relation between the gabbros gabbros within within the granophyre granophyre and and the the lavas lavas to to the the south. IfIf this and the the this isis indeed indeedaa feeder feeder system, system, itit might might provide provide insight insight into the mechanism of magma emplacement and "breakthrough" to the eventual "breakthrough" the surface, surface, during during the the onset onset of of rifting. rifting. 35 �References Cited: References Cited: Babcock, R.C., Jr. (1959) M MS. S .thesis, thesis,University Universityof of Wisconsin, Wisconsin,Madison, Madison, 47 47 p. p. Research, 54, 177-196. 177-196. Green, J.C. and Fitz, T.J., 1993, 1993, Journal of Volcanological and Geothermal Research, Grout, SurveyBulletin Bulletin39, 39, 163p. l63p. Grout, F.F., F.F., Sharp, Sharp, R.P., and Schwartz, Schwartz, G.M. 1959 Minnesota Geologica Survey Jerde, E.A. and Kennedy, Kennedy, B.C., B.C., 2000, 2000, American American Geophysical Geophysical Union 2000 2000 Fall Meeting, Meeting, San San Francisco. Francisco. Jerde, Jerde, Salvato, D.J, D.J, Thole, Thole, J., J., and and Wirth, Wirth, K.R. K.R. 2001, 2001, ILSG ILSG 47, 47, 36-37. 36-37. Jerde, E.A., Salvato, Kennedy, B.C., B.C., Wirth, Wirth, K.R., K.R., and and Vervoort, Vervoort,J.D., J.D.,2000, 2000,ILSG ILSG46, 46,29-30. 29-30. Jr., Green, J.C., Severson, Severson, M.J., Chandler, Chandler, V.W., and Peterson, D.M., 2001, Minnesota Minnesota Geological Geological Miller, J.D., Jr., Survey 19. Survey Miscellaneous MiscellaneousMap MapSeries SeriesM-1 M-119. Nathan, H.D., 1969, of Minnesota, Minnesota, Minneapolis, Minneapolis, 198p. l98p. 1969, Ph.D. dissertation, University of Nelson, N. 1991, 1991,M.S. M.S. Thesis, Thesis, University Universityof of Minnesota, Minnesota,Duluth. Duluth. Sandland, TO., Wirth, 47, 85-86. Wirth,K.R., K.R.,Vervoort, Vervoort,J.D., J.D.,Gehrels, Gehrels,G.E., G.E.,Kennedy, Kennedy, B.C., and Harpp, K.S. 2001, ILSG 47,8586. Sandland, T.O., Vervoort, J.D. and Green, J.C., 1997, 34, 521-535. 1997, Canadian Canadian Journal of Earth Sciences, 34,521-535. Fig. 1. Reconnaissance Reconnaissancegeologic geologicmap map of of the the region region just south south of Crocodile Crocodile Lake, Lake, showing showing location location of gabbro bodies in the the granophyre granophyre that forms forms the the cap cap above above the the Crocodile Crocodile Lake LakeIntrusion Intrusiongabbros gabbros and intermediate intermediate rocks. rocks. .4 SchematicN-S N-S cross crosssection sectionof of Fig. Fig. 11showing showing the the possible possible feeder feeder for for the the Hovland Hovland Lavas. Lavas. Fig. 2. Schematic 36 �MINERALIZATION MINERALIZATION OF OF THE THE NORTON NORTON LAKE LAKE Cu-Ni-PGE Cu-Ni-PGEDEPOSIT DEPOSIT JOHNSON, JOHNSON, J.R., J.R.,HOLLINGS, HOLLINGS,P.P.and andKISSIN, KISSIN,S.A. S.A.Department DepartmentofofGeology, Geology,Lakehead Lakehead University, Thunder Bay, ON, P7B 5E1, jrjohnsonca@yahoo.ca 5E1, jrjohnsonca0 yahoo.ca The Norton Lake Cu-Ni-PGE lun northeast northeast of of Fort Fort Cu-Ni-PGE deposit deposit is located located approximately approximately50 50 km Hope, within the Miminiska-Fort Hope Greenstone belt of the Uchi Subprovince, northwest Hope, Miminiska-Fort Hope Greenstone belt of the Uchi Subprovince, northwest Ontario (Figure 1). Only Onlylimited limitedgeological geological investigations investigationshave have been been undertaken undertaken within within the the belt due to both its remote location and sparse outcrop. As As aa result result of of this this the the belt belt has has been been subdivided based on limited structural and regional stratigraphic considerations considerations (Stott (Stott and and Corfu, Corfu, 1991). The The Norton Norton Lake Lake deposit depositis is located located within within an an unnamed assemblage assemblage comprising comprising basaltic flows with magnetite iron formations. formations. ItItisisthought thought that that this this assemblage assemblagecan can be be correlated, correlated, through similar rock types and aeromagnetic trends, with with the the -2900 Ma Northern Pickle Pickle terrane of the Pickle Lake greenstone greenstone belt (Corfu (Corfu and and Stott, Stott, 1996). 1996). Figure Figure1:1:A-Map A-Mapof of Superior SuperiorProvince Provinceshowing showinglocation location of of Uchi Uchi Subprovince. Subprovince. B Simplified Simplified geology geology map of the Miminiska-Fort Miminiska-Fort Hope Hope Greenstone Greenstonebelt belt (after Stott and Corfu, Corfu, 1991). 1991). The Norton Lake area consists consists of massive massive to pillowed pillowed basalts basalts with with rare rare ultramafic ultramaficflows. flows. The deposit itself is hosted within a sheared amphibilite amphibolite with minor gabbroic units. Previous Previous work determined 944 500 500 tonne tonne nickel-copper nickel-copper deposit depositcontaining containing0.72% 0.72%Ni Ni determined the deposit deposit to to be be aa 944 West Resource Resource Corporation, Corporation, 2001). 2001). The and 0.56% Cu with an undefined PGE potential (East West The geological setting, host rock and mineralization of the Norton Lake deposit deposit are are comparable comparableto to that of the Thierry Deposit, Pickle Lake, Ontario. The The Thierry Thierry Mine Mine is is currently currently undergoing renewed exploration exploration to to determine determineits its viability viability as as aa PGE PGE deposit deposit (PGM (PGM Ventures). Ventures). 37 �East West Resource Resource Corporation Corporation (EWR) has undertaken a detailed exploration program of Norton Lake, including an an extensive extensive drilling drilling program. program. Detailed in the vicinity of Detailed examination examination of of being paid paid to to the the mineralized mineralized 'main' zone drill core has been undertaken with special attention being zone to to determine the exact nature of the mineralization. Preliminary Preliminary results results indicate indicate the the deposit deposit consists consists chalcopyrite and and pyrite. pyrite. The platinum group of massive pyrrhotite with pentlandite, magnetite, chalcopyrite element's s) are element's (PGE' (PGE's) are found found forming discrete discrete platinum group minerals and are also believed to form a solid solution solution with the suiphides. sulphides. Results Resultsshow showthat thatin inaddition additionto toprimary primarymineralization mineralization a secondary, hydrothermal, enrichment of PGE's has has taken taken place. place. Mineral Mineral Pyrrhotite Pyrrhotite Pentlandite Pentlandite Pyrite Pyrite Chalcopyrite Chalcopyrite Manganoan Manganoan Illmenite Illmenite Formula Fei-xS FeiS (Fe,Ni)9S8 (Fe,Ni)9S8 FeS2 FeS2 CuFeS2 CuFeS2 (Fe,Mn)Ti03 (Fe,Mn)Ti03 Magnetite Michenerite Michenerite Hessite Hessite Fe304 PdBiTe PdBiTe Ag2Te Ag2Te Minor Elements Elements Ni Co Co Co Ni Notes Main mineral Secondary Secondary Trace Trace, also veins More common common than magnetite, magnetite, easily mistaken for magnetite magnetite in polished section section Sb, Sb, Pt Table Table 1: 1: Summary Summary of the mineralogy mineralogy of Norton Norton Lake Lake deposit. deposit. Corfu F. and Stott G.M. 1996. 1996. Hf isotopic composition and age constraints on the evolution of the Archean Central 78,pp53-63 53-63 Central Uchi Subprovince, Subprovince,Ontario, Ontario,Canada. Canada.Precambrian Precambrian Research, Research,v. v. 78, East West Resources Resources Corporation, Corporation,2001. 2001. Annual Annual Report. Report. PGM Ventures, 2003. 2003. www.pgm-ventures.com www.pgm-ventures.com Stott G. M. and and Corfu Corfu F. F. 1991, 1991,Uchi Uchi Subprovince, Subprovince,in in Geology Geology of of Ontario, Ontario,Ontario OntarioGeological Geological Survey Special Special Volume 4, 4, Part 1. 1. 38 �Pd-Pt-Au MINERALIZATION STRATIFORM Pd-Pt-AU MINERALIZATION IN THE SONJU LAKE INTRUSION, LAKE COUNTY, MINNESOTA JOSLIN, GregoryD. D.Department Departmentof of Geological GeologicalSciences, Sciences,University University of of Minnesota-Duluth, Minnesota-Duluth, 1114 1114 Kirby Kirby JOSLIN, Gregory joslOOl3@d.umn.edu;MILLER, MILLER, James D., Jr., Minnesota Drive, Duluth, MN 55812, email: josl0013@d.umn.edu; Geological Survey, Survey, c/o do NRRI, 5013 Miller Miller Trunk TrunkHwy, Hwy,Duluth, Duluth,MN MN558 55811; andROWELL, ROWELL, 11; and William, F., Franconia Minerals MineralsCorp., Corp.,12 125. S.6th 6"' St., Minneapolis, MN 55402. The Sonju Sonju Lake intrusion intrusion (SLI) (SLI) is a 1200 1200m m thick, closed-system, closed-system, well-differentiated, well-differentiated,tholeiitic, tholeiitic, layered intrusion located within the the Mesoproterozoic Mesoproterozoic Midcontinent Midcontinent Rift-related Rift-relatedBeaver Beaver Bay Bay Complex of of northeastern northeastern Minnesota Minnesota (Miller (Millerand andChandler, Chandler,1997). 1997). In In the the late late 1990's, outcrop sampling by Miller (1999) (1999) indicated the presence of meter-scale meter-scale stratiform stratiformPd-Pt-Au Pd-Pt-Au mineralized mineralized interval (or PGE reef) within the oxide oxide gabbro gabbro unit of the the SLI, SLI, located about about 2/3 213 of of the the way way up up from the basal contact of the intrusion. In In June June of of 2002 2002 Franconia Franconia Minerals Minerals Corp. Corp. conducted conducted exploratory drilling drilling through through the the Pd-Pt-Au Pd-Pt-Au enriched enriched zone. zone. exploratory In hand sample, the mineralized interval appears as a homogeneous oxide gabbro, gabbro, with no visible indication of precious metals enrichment. However, However, geochemically the location location of the mineralization is distinct. Three Threedrill drillcores, cores,spanning spanningaastrike strikelength length of of approximately approximately 800 800m, m, define define and are are correlated correlatedon on the the basis basis of of aa distinctive distinctiveCu-Au Cu-Au break break datum datum(Fig. (Fig.1). 1). With the exception of localized Pt enrichment associated with an interval enriched in olivine about 110 m m below the Cu-Au horizon, horizon, all Pd-Pt-Au enrichment occurs over an interval interval of 0 to to 90 90 m m below the the In general general precious precious metals metals peaks peaks are are stratigraphically stratigraphicallyoffset offset from from one one defined datum (Fig. 2). In Maximumgrades gradesin in 0.3m 0.3m long core another, progressing progressingupward upwardininthe thesuccession successionPd+Pt+Au. Pd-)Pt-Au. Maximum samples are 410 ppb Pd, 275 ppb Pt, and 1080 ppb ppb Au. Au. Above Above the Cu-Au break, all precious metals are very strongly depleted. Strong A1 and and modal modal olivine olivine with Strongcorrelation correlationbetween between Fe, Fe, Al precious metals peaks indicates a possible connection between subtle modal modal layering layering of of plagioclase, plagioclase, oxide, oxide, and olivine olivine with with mineralization. mineralization. The oxide gabbro-hosted gabbro-hosted PGE reef in the Sonju Sonju Lake Lake intrusion intrusion shows shows marked marked similarities, similarities, with some differences, differences, to stratiform stratiformPGE PGE mineralization mineralization in in the the Skaergaard Skaergaard intrusion intrusionof of East East Greenland (Andersen et al., 1998),the the Rincon Rincon del del Tigre Tigre Complex Complex of of Bolivia Bolivia (Prendergast, (Prendergast,2000), 2000), al., 1998), and many other tholeiitic mafic layered intrusions throughout throughout the the world. world. Whole Whole rock rock geochemistry, clinopyroxene clinopyroxene and olivine compositions, and petrographic data data are are consistent consistentwith with an orthomagmatic origin for the mineralization related to the fractional fractional segregation segregation of of sulfide sulfide melt from silicate magma. The The homogeneity homogeneity of the host rock, the thickness of the mineralized interval, interval, and the offset offset of metal metal concentrations concentrationsimply imply that that sulfide sulfide saturation saturationwas was passively passively triggered by fractional crystallization crystallization of the Sonju magma. magma. Mungall (2002) recently argued Mungall(2002) argued that stratigraphic offsets offsets of Pd, Pd, Pt, Pt, Au Au and and Cu Cu peaks common to many PGE reefs can can be satisfactorily satisfactorily explained by a kinetic model of sulfide liquation and settling. The The model model shows shows that that the the degree degree of offset and metal enrichment will be controlled by by kinetic kinetic factors, factors, such as as the the diffusivity diffusivity of of chalcophile elements, the degree of sulfide supersaturation, supersaturation, sulfide droplet size, and its settling chalcophile velocity, which result in variability of the apparent silicatelsulfide silicate/sulfide melt melt ratio ratio (R factor). The The correlation of multiple peaks of PGE with subtle, correlation subtle, broad broad modal variations variations may may be be related related to to by the crystallization crystallization of of magnetite magnetite in in an an environment environment of of repeated convective overturn caused by sulfide over-saturation, as suggested by Prendergast (2000) to explain a similar correlation in sulfide over-saturation, suggested (2000) explain a similar correlation in the the Rincon del Tigre Complex. Some Someevidence evidence of of late-stage late-stage sulfide sulfide dissolution dissolution and remobilization exists, but it appears appears to have little little to to no no effect effect upon upon the the distribution distributionof of precious precious metals. metals. 39 �nrelorl ,bovo *60.0 - - -' Ft!lI1lI—._+50.0 ' +40,0 " *30,0 -. .. +70.0 *70.0 *60.0 *60.0 *50.0 *50.0 *40.0 *40.0 +30.0 *20.0 - -'-' ' ' ';'*. - ,,::-- +10_A 410.0 0.0 -10.0 -10.0 -10.0 .20.0 -20.0 -20.0 -30.0 -30.0 -40.0 .40.0 -500 -50.0 -5 0.0 1AJJ114i1_ -40,0 -70.0 '60,0 -60.0 -70.0 -70.0 -80.0 -60.0 -90.0 -90.0 I—.— " -30.0 1111111— 85000001 5 -40.0 11111111— . , -ao,o 00.0 1+00 -110.0 4 -110.0 '110.0 -120.0 , -120.0 -120.0 -130.0 'break +200 0.0 0.0 Cu-Au *30.0 920.0 *100 5L02-3 SLO2-2 SLO2—1 Cu-Au break +70,0 r -130.0 Fig. 1: Correlation Correlation of of drill cores SLO2-1, SL02-1, SLO2-2, SL02-2, and SLO2-3 showing showing distinctive SL02-3 break. The Cu-Au break. The Cu-Au Cu-Au break is used to provide a datum to which all stratigraphic plots are correlated, and position in stratigraphy is measured as meters above above or or below below Cu-Au Cu-Au break. break. -130.0 0 • Au ppb) Cu (ppm) 5L02-3 SLO2-2 SLO2-1 '*70.0 '+70.0 +60.0 .660.0 —.50.0 *50.0 *40.0 -+40.0 *30.0 +30.0 *20.0 -620.0 *10.0 *10.0 -10.0 -10.0 -20.0 -20.0 -30.0 -30.0 .40.0 '' -40.0 - -50.0 -50.0 -60.0 '60.0 .70.0 -70.0 .80.0 -80.0 -90.0 -90.0 l00.0 -100.0 -510.0 -110.0 '-520.0 -120.0 Fig. 2: Correlation Correlation of Pd Pd and Pt Pt in in drill drillholes holesSLO2SL021, I, SLO2-2, SL02-2, and and SLO2-3. SL02-3. Notice multiplicity of spikes spikes and offset offset between Pt and Pd peaks. -130.0 -130.0 S • Pd)ppb) S Pt(ppb) References: References: 0., Rasmussen, Andersen, J. C. O., Rasmussen, H., H., Nielsen, Nielsen, T. T. F. F. D., Ronsbo, Ronsbo, J. U., G., 1998, 1998, The The Triple Triple Group Group and and the the Platinova Gold and Palladium Reefs in the Skaergaard Intrusion: Stratigraphic and Petrographic Petrographic Relations. Relations. Economic Economic Geology. Geology. Vol. Vol. 93, 93, pp. pp. 488-509. 488-509. Miller, J. D. Jr., 1999, 1999, Geochemical Geochemical Evaluation Evaluation of Platinum Group Element (PGE) Mineralization in the Sonju Lake Intrusion, Finland, Minnesota: Minnesota: Minnesota Minnesota Geological Geological Surv. Surv. Information Information Circular Circular 44, 44, 31 3 1p. p. Miller, J. D., Jr., Jr., and and Chandler, Chandler, V. W., 1997, 1997, Geology, Geology, petrology, and tectonic significance of the Beaver Bay Complex, northeastern Minnesota, in Ojakangas, R. R. W., W., Dickas, A. A. B., B., Green, J. C., eds., Middle Proterozoic Proterozoic to to Cambrian Cambrian Rifling, Rifting, Central CentralNorth North America: America: Geological GeologicalSociety Societyof of America AmericaSpecial SpecialPaper Paper 312, p. 73-96. 73-96. Mungall, Mungall, J. E., 2002, 2002, Kinetic KineticControls Controlson on the thePartitioning Partitioningof of Trace TraceElements ElementsBetween BetweenSilicate Silicateand andSulfide Sulfide Liquids. Journal Journalof of Petrology. Petrology. Vol. Vol. 43, 43, pp. pp. 749-768 749-768 Prendergast, M. D., 2000,Layering 2000,Layering and Precious Metals Mineralization in the Rincon del Tigre Complex, Eastern Bolivia. Bolivia. Economic Economic Geology. Geology.Vol. Vol. 95, 95, pp. pp. 113-130. 113-130. 40 �RESULTS OF OF 40Ar/39Ar 4 0 ~ r / 3 9SINGLE-GRAIN ~r ANALYSES MAFIC RESULTS SINGLE-GRAIN ANALYSESOF OF PRECAMBRIAN PRECAMBRIAN MAFIC INTRUSIONS IN NORTHERN NORTHERN AND EAST-CENTRAL EAST-CENTRAL MINNESOTA MINNESOTA KEAYFS, M.J., Dept. of Geology, Kent State University, Kent, OH 44242; JIRSA, KEATTS, JIRSA, M., Minnesota Geological Geological Survey, 2642 University Avenue West, St. St. Paul, Paul, MN MN 55114-1057; 55114-1057; HOLM, D., Dept. of Geology, Kent State University, Kent, OH 44242 Age information from mafic mafic intrusive intrusive suites suites is is critical of the Age information from critical for proper proper interpretation interpretation of geologic history and for mineral deposit models in the Lake Superior region. As part of an effort to evaluate evaluate PGE potential potential in in mafic mafic intrusions intrusions in in Minnesota, Minnesota, several several plutons plutons have have been been dated dated CO2 laser ArIAr Ar/Ar incremental heating technique at the University University of Wisconsin-Madison using the C 0 2 laser Rare Rare Gas Gas Geochronology Geochronology Laboratory. Laboratory. For late-stage late-stage shallow shallow plutons plutons containing containingprimary primary magmatic hornblende, ArIAr Ar/Ar mineral ages are are likely likely to to closely closely approximate approximate the the crystallization crystallization age. In regions age. regions with with aamore moreprotracted protractedthermal thermalhistory history(i.e., (i.e.,low-grade low-grademetamorphism, metamorphism, slowslowcooling, etc.), the Ar/Ar data provide minimum ages for the mafic plutons. Mafic intrusions ArIAr data minimum ages plutons. intrusions from from Minnesota selected for this study represent a broad range of geologic settings, including 1) small mafic and intrusive mafic plutons plutons emplaced emplaced into into Paleoproterozoic Paleoproterozoic supracrustal supracrustal and intrusive rocks rocks within within the the Penokean orogen (samples 264, R17); and 2) varied, primarily late- to post-tectonic intrusions in rocks of of the Archean Wabigoon Wabigoon (samples (samples Al, Al, B21, UBD) and Wawa (samples K15, supracrustal rocks of Superior Province. Province. We We report report here the initial LP, ANA) subprovinces subprovinces of initial results results from from eight eight separate intrusions (Fig. (Fig. 1). 1). East-central ~Minnesota. A hornblende ~ast-central innesota.A hornblende grain grain (R17) (R17) from from aa sample sampleofofmedium-grained medium-grained homblendite batholith in hornblendite from the Tibbett's Brook intrusion cutting the East-central Minnesota batholith Morrison Co. yields yields aa plateau date of from 44contiguous contiguousincrements increments Morrison Co. plateau date of 1.770 1.770 ±Â 0.006 Ga from constituting 74% of of the the gas released. constituting 74% released. AAbiotite biotitegrain grain(264) (264)from fromaasample sampleofofcoarse-grained coarse-grained biotitic olivine gabbronorite cutting the Little Falls Formation in Morrison Co. Co. yields yields aa plateau plateau date of 1.791 1.791 ± Â0.008 0.008 Ga from 5 contiguous increments constituting constituting 68% of the gas gas released. released. twa Subprovince. A Ahornblende Wawa Subprovince. hornblendegrain grain(ANA) (ANA)from fromaasample sampleofofprismatic prismatichornblende hornblende diorite diorite collected near Red Lake in Beltrami Co. yields a near-plateau date of 2.587 ±0.012 ~ 0 . 0 1Ga 2Ga in in 55 nonnoncontiguous incrementsconstituting constituting50% 50%ofofthe the gas. gas. A A biotite biotite grain grain (K15) (K15) from from a sample contiguous increments sample of collected in in Norman Norman Co. Co. yields yields aa plateau plateau date date of of 2.639  ± 0.007 biotite granodiorite porphyry collected 0.007 Ga from 6 contiguous increments constituting 79% 79% of of the gas released. A biotite grain (LP) from a sample of porphyritic syenite collected at the Wawa-Quetico subprovince boundary in St. Louis Co., from 77contiguous contiguous Co., in the the Linden Linden Pluton, Pluton, yields yields a plateau plateau date date of 2.666 2.666 ±Â 0.006 Ga from increments increments constituting constituting 88% 88% of of the the gas gas released. released. Wabigoon Subprovince. A hornblende grain (B21) from the Oaks intrusion leucodiorite leucodionte sampled 0.008 Ga from 88 near Fault in Roseau 1 ±Â 0.008 near the Vermilion Vermilion Fault Roseau Co. Co. yields yields aa plateau plateau date date of of 2.67 2.671 contiguous increments constituting 75% 75% of of the the total total gas gas released. released. A hornblende grain (Al) (Al)from from 0.0111 Ga from the Black River gabbro, collected in Roseau Co., yields a plateau date from date of of 2.685 2.685 ±Â 0.01 11 contiguous increments increments constituting constituting 90% 90% of of the the total total gas gas released. released. A A hornblende hornblende (UBD) (UBD) from a sample Co. north north of the sample of of hornblende-biotite hornblende-biotite gabbro collected collected in Koochiching Koochiching Co. the Rainy Rainy LakeLakeSeine River Fault Fault yields yields a plateau date of Seine River plateau date of 2.695 2.695 ±  0.007 Ga from from 66 contiguous contiguous increments increments constituting constituting 49% of the gas released. released. 41 �The mineral age data from from mafic mafic plutons plutons from from the the Wabigoon Wabigoon subprovince subprovince are are synchronous synchronous Mafic plutons plutons from from the the with the last deformation event (D2) dated in the range 2.685-2.674 Ga. Mafic Wawa subprovince give give an an 80 m.y. age range from 2.58 to 2.66 Ga. Interestingly, Interestingly,the theLinden Linden Pluton gives a biotite biotite date date concordant concordant (within error) with the youngest youngest mafic pluton from the Pluton Wabigoon subprovince. Wawa are are consistent consistent with with Wabigoon subprovince.The Theyounger youngerspread spreadofof ages ages from from the Wawa southward growth of of the Superior Province Province during during the the latest latest Archean. Archean. Mafic plugs evident from aeromagnetic maps 1.775 Ga Ga EastEastaeromagnetic maps in in east-central Minnesota Minnesota are are comagmatic comagmatic with with the circa 1.775 central Minnesota batholith. Further constraining the mafic intrusions intrusions the temporal framework of mafic may contribute contribute to mineral deposit deposit models these intrusions intrusions and and their their analogs analogs in in may to mineral models for for PGE PGE in these adjacent states states and and provinces. provinces. Fig.i agespectra: spectra:t t, ==plateau plateau age, age, t, tq == total total gas age. Fig.l 40Ar/39Ar "Ar/^Ar age age. 2.0 0 2.0 Ri 7 264 1.5 2:: fl.... 1 1.8 J0.5 3.0 Biotite MSWD MSWD 2.57 2.57 Amphibole MSWD 1.78 Amphibole MSWD 1.78 t, tp== 1.770 1.770±Â0.006 0.006Ga Ga t9= t = 1.653±0.005 1.653 0.005Ga Ga I I 6t ==1.791 1.791±Â0.008 0.008Ga Ga t, = 1.782 1.782±  0.007 0.007Ga Ga 1.5 3.0 ANA B21 —--————ur Ct 0 2.5 1 Amphibole 0.71 Amphibole MSWD MSWD0.71 2.587  ± 0.012 0.012 Ga tp= 2.587 tg 2.550  ± 0.009 0.009 Ga Ga t, == 2.550 2.0 2.0 2.0 3.0 " 3.0 Ki 5 .__.__.__ Ct 0 . Al ti. ...:::.::::::: 2.5 Biotite MSWD Biotite MSWD 2.48 2.48 2.639 ± t, = 2.639  0.007 0.007Ga Ga = 2.640 2.640±Â 0.007 0.007Ga Ga 3.0 3.0 LP t:,Vt:::::::ZV:. : Amphibole MSWD Amphibole MSWD 1.81 1.81 t, = 2.685 2.685 ± tp  0.011 0.011 Ga Ga t9== 2.700 2.700  ± 0.01 0.010 tg 0 Ga Ga 2.0 -. 2.0 UBD —iF :1:2.:, 0 2.5 - Amphibole Amphibole MSWD MSWD 0.30 0.30 t ==2.671 2.671 ±Â0.008 0.008Ga Ga tto==2.705 2.705±Â0.013 0.013Ga Ga 2.5 Biotite MSWD Biotite MSWD1.11 1.I1 t,, = 2.666 2.666±Â 0.006 0.006Ga Ga t9 2.657 ± 6 == 2.657  0.006 0.006 2.0 0 0 10 10 20 20 30 30 40 40 50 50 60 60 700 7 60 80 Cumulative released (%) Cumulative39Ar "Ar released (%) 2.0 900 1100 0 9 00 0 42 , 10 10 Amphibole MSWD MSWD 1.03 1.03 2.695 ± $, = 2.695  0.007 0.007Ga Ga 2.730 ± 6 .= 2.730  0.006 0.006Ga , --"-" *- - , 20 30 30 40 40 50 60 60 700 7 80 80 Cumulative Cumulative 9Ar "Ar released released (%) (%) r-- 90 90 100 100 �New zircon New zircon ages agesfrom fromthe the Gunflint Gunflint and and Rove RoveFormations, Formations,northwestern northwestern Ontario Ontario Kissin, S.A., Department Department of Geology, Geology, Lakehead University, Thunder Thunder Bay, ON, P7B 5E1 5E1 Canada, Canada, stephen.kissin@lakeheadu.ca; stephen.kissin@lakeheadu.ca ;Vallini, Vallini, D.A., D.A.,University University of of Western Western Australia, Australia,35 35 Stirling Hwy, Stirling Hwy, Australia; Addison, W.D., W.D., RR 2, 2, Kakabeka Kakabeka Falls, Falls, ON, ON, POT POT iWO, 1W0,Canada; Canada; Crawley, 6009, W.A., Australia; Brumpton, G.R.., 211 Bmmpton, 21 1 Henry St, Thunder Thunder Bay, ON, P7E 4Y7, Canada. Canada. Previous work based on U-Pb geochronology geochronology from presumed volcanogenic zircons zircons obtained obtained 1878 ±Â 2Ma, from a tuff layer at the lower/upper lowerlupper Gunflint Formation boundary yielded an age of 1878 believed to approximate the age of of deposition of of the unit unit (Fralick et et al., 2002). 2002). This This age age corresponds closely with the age of the correlative correlative Hemlock Formation Formation of Michigan Michigan (1874 (1874 ±: 9Ma; Schneider 9Ma; Schneider et a!., al., 2002). We report report here preliminary preliminary age age determinations determinations based on on SHRIMP SHRIMPanalyses analyses of of zircons zircons Formation, and and two two within within the the extracted from three volcanic ash layers; one lying in the Gunflint Formation, Rove Formation. Formation. The overlying Rove The Gunflint-Rove Gunflint-Rovecontact contact is is an an important important reference reference point. point. Pufahi Pufahl and Fralick (2000) placed it at the top of a sequence sequence of chert-carbonate chert-carbonategrainstones grainstones which which is is of the the Rove Rove Formation. Formation. The Gunflint exposure exposure outcrops outcrops at at overlain by carbonaceous shales of The Gunflint Little Little Falls, Falls, on on the the south southside sideof of the theKakabeka KakabekaFalls FallsGorge, Gorge,--1Om -10m (topographically) (topographically) below below the the Gunflint lapilli tuff dated by Fralick et a!. al. (2002). A Rove volcanic ash exposure exposure at Oliver Oliver Creek Creek is estimated to be -70m (stratigraphically) (stratigraphically) above above the Gunflint-Rove Gunflint-Rove contact. contact. Zircons were also extracted extracted from an ash ash layer layer within within Falconbridge Falconbridge Pine Pine River River (PR98-1) (PR98-1)drillcore drillcore(688.24m (688.24mdown down hole), above the Rove-Gunflint Rove-Gunflint contact. hole), located located —4m -4m above contact. The a mean 207Pb/206Pb of~1821 16 Ma while aa single single ^ ~ b l age ~age~of 1821 ~ b±Â 16 The Oliver OliverCreek Creekzircons zirconsrecorded recorded a mean of 184OMa wasobtained obtained from from the the dnllcore drilicore PR98-1 PR98-1 sample. sample. The The errors errors cited cited are at the one age of 1840Ma was discordant. deviation ((la) standard deviation l o ) and and 95% 95% confidence confidence level and the analyses are less than 5% discordant. There are recorded from from each each locality locality which which are assumed to are also also two two younger younger ages ages of of —1786Ma -1786Ma recorded be outliers. outliers. The Little Falls zircons, zircons, which are are somewhat somewhat rounded rounded and and fractured, fractured, yielded yielded various various ages, all older than 2000Ma. Most Most of of the the ages ages are are more more than 10% 10% discordant, discordant, and and these these samples samples may have suffered lead loss. As As well, well, there thereare are some some indications indicationsof of admixture admixtureof of shalely shalelymaterial material in the ash layer at this locality. Older Olderzircons zirconsfrom from the the lapilli lapilli tuff tuff layer layer at at the the lower/upper lowerlupper Gunflint Gunflint contact contact (Fralick (Fralick et al., al., 2002) 2002) were were also also found found to to be be admixed admixedwith with Paleoproterozoic Paleoproterozoic zircons. zircons. Using the stratigraphic stratigraphic column of Pufahl and Fralick (2000), we estimate that the drillhole lOmabove abovethe theGunflint Gunflint lapilli lapilli tuff layer containing containing the drillhole (PR98-1) (PR98-1)samples samplesare are—1 -1 10m the zircons zircons dated by Fralick Fralick et a!. (2002), while we estimate the Oliver Creek samples to be —150m above al. (2002), while we estimate the Oliver Creek samples to be -150m this same layer. The ages reported reported here indicate indicate that aa slow slow sedimentation sedimentationrate rate must must have have been been required in order to account account for for the age age difference difference between between the lapilli lapilli tuff tuff of of Pufahl Pufahl and andFralick Fralick and the two sets of Rove dates reported here. This slow Rove sedimentation rate is comparable that reported in banded iron iron formations formations of of the the early early Proterozoic Proterozoic Campbell CampbellGroup, Group,Griqualand, Griqualand, West Sequence, Sequence, South South Africa Africa (Barton (Barton et et a!., al., 1994). 1994). 43 �The Oliver Creek ages reported here are in reasonable agreement with the 1833 1833±Â 6Ma undeformed by by age reported by Schneider et al. (2002) for the Tobin Lake Pluton, which is undeformed Penokean deformation and intrudes presumed Hemlock Volcanic However, the the Volcanic equivalents. equivalents. However, zircons from the Rove Formation Formation suggest suggest that volcanic activity activity associated associated with with the the Penokean Penokean continued for for at at least least 40 40 m.y. m.y. Further Orogeny continued Furtherstudies studies are are underway to clarify some of the questions raised questions raised by our our results. results. Barton, E.S., Altermann, W., William, I.S., amd Smith, C.B. 1994. U-Pb U-Pb zircon zircon age age for for aa tuff tuff in in the Campbell Campbell Group, Group, Griqualand GriqualandWest West Sequence, Sequence,South South Africa: Africa: Implications Implicationsfor forEarly Early Proterozoic 22: 343-346. 343-346. Proterozoic rock accumulation accumulation rates. rates. Geology Geology 22: Fralick, P., Davis, D.W., and Kissin, S.A. S.A. 2002. The Theage ageof of the the Gunflint GunflintFormation, Formation,Ontario, Ontario, Canada: single zircon U-Pb age determinations determinations from reworked volcanic ash. ash. Canadian Canadian Journal 1089-1091. Journal of Earth Earth Science Science 39: 39: 1089-1091. Pufahi, Pufahl, P. and and Fralick, Fralick, P. P. 2000. 2000. Fieldtrip Fieldtrip 4: 4: Depositional Depositionalenvironments environmentsof of the thePaleoproterozoic Paleoproterozoic Gunflint 46, pt.2. pt.2. Gunflint Formation. Formation. Proceedings Proceedings of of the the Institute Institute on on Lake Lake Superior Superior Geology, Geology, 46, W.F., Schulz, K.J., K.J., and and Hamilton, Hamilton, M.A. M.A. 2002. Age Schneider, D.A., Bickford, M.E., Cannon, W.F., Age of of volcanic rocks and and syndepositional syndepositional iron iron formations, formations, Marquette Marquette Range Range Supergroup: Supergroup: implications implications for for the the tectonic tectonic setting setting of of Paleoproterozoic Paleoproterozoiciron iron formations formationsof of the theLake Lake Superior Region. Canadian Journal of Earth Science 39: 999-1012. Canadian Journal of Earth Science 39: 999-1012. 44 �THE SOUTHERN PORTION OF OF THE THE LAURENTIDE LAURENTIDE ICE ICE MEAN TRANSPORT LENGTH LENGTH IN TILLS OF THE SHEET: IMPLICATIONS IMPLICATIONS FOR FOR DRIFT DRIFT EXPLORATION EXPLORATION IN THE THE LAKE SUPERIOR SUPERIOR REGION REGION LARSON, Department of Geological Sciences, Sciences, University Minnesota, Duluth, 55812, LARSON, Phillip Phillip C., Department of Geological University of of Minnesota, Duluth, MN MN 55812, plarson2 @d.umn.edu plarson2@d.umn.edu Introduction Introduction Bedrock the Lake Lake Superior Superior region region isistypically typically covered covered by byaamantle mantleofofglacigenic glacigenicsediments sediments—- till, Bedrock in the outwash,and andlacustrine lacustrinesediments sediments — presents presents a significant - that significant challenge to successful successful application application of of surficial surficial outwash, geochemical techniques techniques widely widely used used to help geochemical help generate generate drilling drilling targets. targets. The glacial glacial environment environment is is very very complex, complex, with sediments produced produced by by a range of processes. with processes. Till represents represents the the ideal ideal sampling samplingmedia media ininthese theseenvironments, environments, since a vector (ice flow direction) is attached to the composition composition at any location indicating the direction to the source of any defined anomaly. anomaly. However, recent work work has led led to to recognition recognition that that both both the themagnitude magnitudeof ofaatill tillgeochemical geochemical anomaly and and the the potential potential transport transport distance distance to to its its source source may may have have aa wide wide range range of of values. values. This anomaly This isis aa reflection reflection of of material, and and is related to the the mean mean transport distance of till-forming till-forming material, the fundamental fundamental sediment sediment transport process responsible for forming forming the the till. till. Theory The concentration of an an indicator indicator (a (a distinct distinct lithologic lithologic or or geochemical geochemical component component derived derived from from aa discreet discreet in till till is the direct product of the physical processes processes of of glacial glacial erosion, erosion,transport, transport,and anddeposition. deposition. Indicator Indicator source) in concentration concentration is controlled by a number number of of variables, variables, including including substrate substrate hardness and the the efficacy efficacy of of the theglacial glacial erosional regime. regime. Under Under steady steady state state ice ice flow flow conditions conditions and and uniform uniform bed bed erosion erosion rates, rates, indicator indicator mass mass concentration ci c in till at any transport transport length length TT (1) (1) down-ice of an indicator source source of finite finite flow-line flow-linelength length LL (1) (I) is: cTO — L (1) where For tills down-ice of of the indicator source, under steady state conditions, the where X. is the erosion length length scale scale (1). (1). For decrease decrease in indicator indicator concentration concentration with with increasing increasingtransport transportlength lengthcäc/5T 8c/8T assumes assumes aaquasi-exponential quasi-exponential form. form. Erosion length scale, scale, X, X,isis related related to to the the spatial spatial bed bed erosion erosion rate rate EE (m-1'") (ml3) and and the the thickness thickness of the the debris debris layer layer in in Erosion length transport transportmd md (m12): (m-l'2): (2) E X closely related related to to the the mean transport distance of till-forming material; as ?X increases, X isis closely increases, so so does does the the mean mean transport transport distance. distance. ShortTransport: Examples Short- vs. Long-Distance Transport: Examples Tills in the Lake Superior Superior region region can can be be broadly broadly grouped grouped into into two two categories categories based based on onthe themean meantransport transport length of the till forming forming material. material. Tills characterized by short-distance short-distance mean transport transport length length are are commonly commonly composed composed of of coarse-grained coarse-grained material containing abundant abundant angular angular clasts, and display material containing display rapid decrease decrease in in indicator indicator concentration concentration with with transport transport length. This Thisisisexemplified exemplifiedby bytills tillsoverlying overlyingthe theVermilion Vermiliongreenstone greenstonebelt beltof ofnorthern northernMinnesota, Minnesota,which whichdisplays displays rapid in concentration concentrationof ofnumerous numerousindicator indicatorlithologies; lithologies; range from 2.0 l0m. m. A XX forfor thisthis tilltill range from 1.01.0 to to 2.0-lo3 rapid decrease decrease in dispersal train composed composed of of clasts clasts of of Nipigon dispersal train Nipigon diabase diabase in till till east east of of Lake LakeNipigon, Nipigon, Ontario Ontario displays displays similar similar characteristics. Dispersal for this this Dispersalisischaracterized characterizedby byaasimilar similarrapid rapiddecrease decreaseininindicator indicatorconcentration; concentration;calculated calculatedXX for till range from 5.5-10' 5.5.102 m m over over relatively relatively soft soft greenstone greenstone to to 2.4-lo4 2.4 i04 m m over over hard hard diabase. diabase. Both Both tills tills are areinterpreted interpretedto to have formed by erosion of hard bed by quarrying quarrying and abrasion, abrasion, and and englacial englacial transport. transport. Tills characterized Tills characterized by long-distance long-distance mean transport transport length length are are commonly commonly composed composed of offine-grained fine-grained material with with a relatively material relatively low low abundance abundance of rounded rounded clasts, clasts, and and display display little little apparent apparent decrease decrease in in indicator indicator with transport length. Cretaceous concentration with Cretaceous shale shale grains grains in in Des Moines Lobe tills of the Minnesota Minnesota River valley show relatively little decrease in concentration along the flow axis extending down down the valley valley (Matsch, 1972); the XI.for forthis thistill tillisis5.0-10 5.0 l0 m. m.Carbonate-bearing Carbonate-bearingtills tillsoverlying overlyingthe the Canadian Canadian Shield Shield north of Lake Superior calculated ? (Thorleifson and Kristjansson, 1993) 1993) show show similar similar long-distance long-distance transport transport of of Paleozoic Paleozoic carbonate carbonateand andProterozoic Proterozoic m. Both tills greywacke clasts concentration; the 6.0-10' tills are are greywacke clasts with with little little decrease decrease in in concentration; the calculated calculated XXfor forthis this till till is 6.0 I m. interpreted interpreted to have deposited deposited from from deforming deforming subglacial subglacialsediment sediment layers layers (deformation (deformationtills). tills). 45 �Discussion by A,? that are 10 to 100 The data indicate deformation tills are characterized by 100 times higher than those of thin, by intermediate intermediate values values of of the the erosion erosion length length scale scale 'k? have have not as yet been coarse-grained tills. Tills characterized characterized by recognized in in the Lake Lake Superior Superior region, region, and and perhaps perhaps do do not not exist. exist. This recognized This gap gap in in recognized recognized values values suggest suggest there are entrainment and two main main processes by which bed material two material is is eroded eroded and and entrained, entrained, transported, transported, and and deposited deposited— - entrainment transport by a deforming subglacial layer, and erosion by quarrying and abrasion and transport as an englacial debris load with deposition by lodgement lodgement or meltout. Deformation tills form with little little accompanying accompanying erosion of underlying underlying hard bedrock. bedrock. Their formation formation is is consistent with redistribution of unconsolidated regolith or or sediment derived from consistent with redistribution of unconsolidated regolith sediment derived from aa preglacial preglacial reservoir. reservoir. Consequently, till composition reflects that of distant Consequently, till composition reflects distant (>100 (>I00 km) krn) bedrock. bedrock. Tills characterized characterized by short short mean mean transport length indicate spatially and temporally restricted erosion and entrainment and transport of hard bedrock. Their formation is consistent consistent with with erosion erosion by by quarrying quarrying and and abrasion abrasion of of hard hard bedrock bedrockwith withsubsequent subsequentextensive extensive Till composition closely reflects reflects that textural modification modification during during transport. transport. Till composition closely that of of nearby nearby (—10 (-10 km) krn) bedrock. bedrock. Consequently, Consequently, these tills have enormous enormous potential potential value as geochemical geochemical sampling sampling media. media. Recognition of the process responsible responsible for till till formation formation in aa given given area area is is critical critical for forsuccessful successfulapplication application of surficial surficial geochemical geochemical and boulder tracing tracing exploration exploration techniques in the Lake Lake Superior Superior region. region. Limited scope scope orientation surveys aimed aimed at characterizing the erosion length provide a means orientation surveys characterizing the length scale X A, provide means of of quickly quickly assessing assessing the the potential for successful successful application application of of drift drift exploration explorationtechniques techniqueson on both both regional regionaland andproperty propertyscales. scales. 46 �Glacial Lakes Aitkin Aitkin and and Upham: Upham: their their origin and environmental history Lisa Marlow, Howard Mooers, & Phillip Phillip Larson Geological Sciences, Department of Geological Sciences, University of Minnesota, Minnesota, Duluth, Duluth, Minnesota Minnesota 55812 55812 Aitkin and Upham occupied a basin in north-central Minnesota Glacial Lakes Aitkm Minnesota bounded bounded on on the the north by the Giants Range and to the east, south, south, and west by hummocky moraines moraines of of the the Rainy Rainy The lakes lakes came came into into existence existence with with the the retreat retreat of of the the lobe, Superior lobe, and St. Louis sublobe. The Rainy lobe from the St. St. Croix Croix phase phase sometime sometime after after 15,000 15,000yr yr BP BP (Clayton (Clayton and and Moran, Moran,1982; 1982; Mooers and Lehr, 1997). 1997). The Thebasin basinwas waslater lateroveridden overidden by by the the St. St. Louis Louis sublobe sublobefrom from the the northwest. With sublobe,the the basin basin was was again again occupied occupied by by Withthe thewastage wastageof of the theice iceof of the theSt. St.Louis Louis sublobe, Aitkin/Upham I and the later phase as as Lake Lake lakes; the earlier phase is referred to as Lake AitkinJUpham AitkinflJpham at a few few localities. localities. One Sediment of of the the early early lake phase is preserved at One such AitkinAJpham II. Sediment locality preserves a sequence that helps redefine the glacial chronology. chronology. A sedimentary sedimentary sequence located in the northeast Upharn basin basin reveals reveals sub-aqueously sub-aqueouslydeposited depositedRainy Rainy Lobe Lobe northeast corner comer of the the Upham outwash beneath glaciotectonically glaciotectonicallydeformed deformed fine-grained fine-grained lake lake sediments sediments deposited depositedby by the the St. St. Louis sublobe. This, This,along alongwith with other othergeomorphic geomorphicrelationships relationships(P.C. (P.C. Larson, Larson, unpublished unpublisheddata) data) indicates indicates that the Rainy Lobe ice margin was coincident coincident with the the Giants Giants Range Range when when the the St. St. sublobe advanced across the lake lake basin. Louis sublobe Using a Digital Elevation Elevation Model Model (DEM) (DEM) the elevation elevation of of lake lake basin basin was was adjusted adjustedfor forisostatic isostatic rebound based on the highest lake lake level, level, then then tilted tilted incrementally incrementally through through several severalstages stagesto to assess assess beaches, inlets, and outlets over time. AAseries seriesof of successively successively lower lower outlets outlets draining draining to to the the St. St. and Upham Upham (Hobbs, (Hobbs, 1983; 1983;Farnum, Farnum,1964; 1964; Louis River served as outlets outlets for for Glacial Glacial Lakes Aitkin and Wright, 1972). Meltwater Meltwaterentered enteredthe the lakes lakes from from Glacial Glacial Lake Lake Norwood Norwood through through the the Embarrass Embarrass gap, and later from Glacial Lake Koochiching along the the Prairie Prairie River. River. During During this this time time Aitkin Aitkin and Upham were confluent, confluent, and and the outlet outlet was was established established down down the the modern modem St. St.Louis Louis River. River. The lakes were separated separated by a sill ca 11,500-10,100 11,500-10,100yr BP, after after inflow inflow from from Koochiching Koochiching was was diverted to Glacial Glacial Lake Lake Agassiz. Agassiz. of the lakes. Granulometry Extensive dune fields formed following initiation of drainage of Granulometry 4ip grain grain size size signature signaturecharacterizes characterizesdunes dunesthroughout throughoutthe thebasin. basin. Maximum dune indicates a 4(p amplitude metersand anddune dunemorphologies morphologiesrecord recordprominent prominentnorthwesterly northwesterlywinds. winds. Dunes amplitude is —3 -3 meters overly source areas, which include include an underfiow underflow fan deposited deposited by the Prairie Prairie River River inlet inlet and and the the western margin of Lake Upham. Lake Upham. A sediment core collected collected from from Hay Lake (93°W, (93OW, 52°N), 52ON), located within aa dunefield dunefieldat at the the edge edge of Glacial Lake Upham, records records three prominent peaks in whole-core whole-core magnetic magnetic susceptibility susceptibility between 10,100 10,100 and 6,600 yr BP. No No clastic clasticinput input isis evident evident after after 6,600 6,600 yr yr B.P., B.P., suggesting suggestingdune dune stability. The timing of dunes within the basin has important implications for other dunes throughout Minnesota. Eolian Eolianevents eventsrecorded recorded in in the the core core are are interpreted interpretedas as the the result result of of lake lake drainage and exposure of abundant source material during Late Glacial and Early Holocene exposure source material during Glacial and Early Holocene rather than landscape landscape destabilization destabilization because because of mid-Holocene mid-Holocene aridity aridity (Keen (Keen et et al., al., 1990; 1990;Grigal Grigal et al., 1976; Dean et a!., 1996; Dean, 1997). Additionally, this sediment core places a minimum 1976; al., Additionally, this sediment core places a minimum age on the drainage of of Glacial Lakes Aitkin Aitkin and Upham Upham II. II. Lake Upham must have drained after 47 �Lakes Aitkin Aitkin and and Upham Upham II. II. Lake Upham must have drained after age on the drainage of Glacial Lakes 11,500 yr BP and before 10,100 10,100 yr B.P. and Lake Aitkin may have persisted until ca. 7,000 7,000 yr 11,500 BP. BP. Clayton, L. and Moran, S.R. S.R. 1982, 1982, Chronology Chronology of late late Wisconsinan Wisconsinan glaciation glaciation in in middle middleNorth North America. Quaternary Quaternary Science Science Reviews Reviews 11 (1), (I), 55-82. 55-82. Dean, W.E., Ahlbrandt, Ahlbrandt, T.S., T.S., Anderson, Anderson, R.Y., R.Y., Bradbury, Bradbury, J.P., J.P., 1996. 1996.Regional Regional aridity aridityin in North North America during the middle (2), 145-155. 145-155. middle Holocene. Holocene. The The Holocene Holocene 66 (2), Dean, W.E., 1997. 1997. Rates, Rates, timing, timing, and and cyclity cyclity of Holocene Holocene eolian eolian activity activity in in north-central north-central United United States: States: Evidence from varved lake lake sediments. sediments. Geology Geology 25 25 (4), (4), 331-334. 331-334. Farnham, R.S., McAndrews, J.H., and Wright, H.E., Jr. 1964. 1964. A Late-Wisconsin buried soil near Famham, Aitkin, Minnesota, and 393-4 12. and its its paleobotanical paleobotanical setting. setting. American American Journal Journal of of Science Science262, 262,393-412. History of of the the Lake Lake Superior Superior Farrand, W.R. & Drexler, 1985. 1985. Late-Wisconsinan and Holocene History Basin. In In Karrow, Karrow,Quaternary Quaternaryevolution evolution of of the the Great Great Lakes, Lakes, Geological Geological Association Association of of Canada Canada Special Paper 30, 30, 17-32. 17-32. Grigal, D.F., Severson, Severson, R.C., Golz, Golz, G.E., G.E., 1976. 1976.Evidence Evidence of of eolian eolian activity activity in in north-central north-central 1-1254. Minnesota 8,000 8,000 to 5,000 5,000 yr. ago. ago. Geological GeologicalSociety Societyof ofAmerica AmericaBulletin Bulletin87, 87,125 1251-1254. Upham, and and early early Lake Lake Hobbs, H.C. 1982, 1982, Drainage Drainage relationships relationships of of Glacial Glacial Lakes Lakes Aitkin, Aitlun, Upham, Agassiz in northeastern Minnesota. In Teller, J.T., and Clayton, Lee, eds., Glacial Lake In Teller, J.T., and Clayton, Lee, eds., Glacial Lake Agassiz: Agassiz: 245-259. Geological Association of Canada Canada Special Special Paper Paper 26, 26,245-259. Keen, K.L., Shane, Shane, L.C.K, 1990. 1990. A continuous continuous record of Holocene Holocene eolian eolian activity activity and and vegetation change at Lake Ann, east-central Minnesota. Minnesota. Geological Geological Society Society of America America Bulletin Bulletin 102, 102, 1646-1657. 1646-1657. Mooers, H.D., Lehr, J.D., 1997. 1997.Terrestrial Terrestrial record of Laurentide Laurentide ice ice sheet sheet reorganization reorganization during during Heinrich events. Geology Geology 25 (11), (1 I), 987-990. 987-990. Sims, P.K., P.K., and and Morey, Morey, G.B., G.B.,eds., eds., Wright, H.E. 1972, 1972, Quaternary Quaternary history of Minnesota. Minnesota. In Sims, Geology of of Minnesota: A 15-578. A Centennial CentennialVolume: Volume:Minnesota MinnesotaGeological GeologicalSurvey, Survey,5515-578. 48 �Magmatic and Hydrothermal HydrothermalPGE PGEMineralization Mineralizationof of the the Birch Birch Lake LakeCu-Ni-PGE Cu-Ni-PGEDeposit Intrusion, Duluth Complex, northeast northeast Minnesota in the South Kawishiwi Intrusion, John Marma, Marma, Phil Phil Brown Brown and and Steve Steve Hauck* Hauck* Department Department of Geology Geology and Geophysics, Geophysics, University of Wisconsin, Wisconsin, Madison, Madison, Wisconsin Wisconsin53706, 53706,USA USA *Natural *Natural Resources Research Research Institute, Institute, University of Minnesota, Minnesota, Duluth, Duluth, Minnesota Minnesota 55811, 5581 1,USA USA The Birch Lake Cu-Ni-PGE Cu-Ni-PGE Deposit Deposit is located located 12 12 miles miles south south of of Ely, Ely, MN MN in in the the South South Kawishiwi Intrusion (SKI) of the Duluth Complex (DC). The The SKI SKIis is one one of of two two layered layered mafic mafic intrusions along the basal contact of the DC to host sub-economic Cu-Ni-PGE deposits. intrusions contact of the DC to host sub-economic Cu-Ni-PGE deposits. Mineralization Mineralization is dominantly dominantly hosted hosted by by the the U3 U3 layer, layer, the lower-most lower-most of of three three ultramaficultramafictroctolite troctolite packages characterized characterized as as aa zone zone of alternating alternatingultramafic ultramafic (picrite-peridotite) (picrite-peridotite)and and troctolite (>5%) ultramafic ultramaficand/or andlormassive massiveoxide. oxide. troctolite horizons horizons with lenses lenses and and pods pods of of oxide-bearing oxide-bearing(>5%) The purpose of this study study was to locate, locate, describe, describe, and and characterize characterizethe the textural textural relationships relationships among platinum group group minerals minerals (PUM), (PGM), sulfides, sulfides,and and silicate silicatephases phases to to help help delineate delineatethe the relative significance significance of primary and remobilized remobilized platinum platinum group group element element (PGE) (PGE)concentrations. concentrations. Samples drill holes transecting transecting the the Birch Birch Lake Lake Deposit Deposit were were obtained obtainedfrom fromthe the Samples from 4 drill Natural Resource Research Institute (NRRI) located in in Duluth, Duluth, MN. MN. EMPA EMPA and and detailed detailed petrography were used to locate PGE bearing minerals, minerals, averaging averaging e15pm <15tm in in diameter, diameter,and and to to characterize characterize the host mineral geochemistry. Identifying Identifying the PGM PGM textural textural relationships relationships with with other phases is critical to understanding the mechanism by by which which PGMs PGMs were deposited. Data Data from this study will aid exploration in locating other deposits and guide metallurgists in improving improving recovery techniques. techniques. Ir,Ru, Ru, Au, Au,Ag, Ag, Te, Te, PGEs occur most often often as various various Pd minerals minerals with with associated associatedPt, Pt, Os, Os,Ir, categories of silicate-sulfide-PGM silicate-sulfide-PGMtextural textural Bi minerals and were grouped into into the following following 44 categories relations: 1) PGMs PGMs that occur in "halos" residing most commonly in anorthite-enriched relations: anorthite-enrichedzones zones in in primary plagioclase around either interstitial interstitial sulfide sulfide (dominantly (dominantly chalcopyrite), chalcopyrite),interstitial interstitial sulfide sulfide and silicate silicate (dominantly chalcopyrite, chalcopyrite, clinopyroxene, and hydrous silicates silicates (amphibole (amphiboleand and silicate) (Figure (Figure 1). This This style style of biotite)), or silicate (dominantly clinopyroxene or hydrous silicate) of the the total total PGMs PGMs identified. identified. 2) Remobilized PGMs that occur in mineralization hosted 58% of chlorite, serpentine, or secondary magnetite. This This style style of of mineralization mineralization hosted hosted 21% 21% of of the the total total PGMs identified. 3) 3)Random RandomPGMs PGMsthat thatoccur occurin inpoikilitic poiluliticanorthite-rich anorthite-richplagioclase plagioclase(An (An 75-An 75-An 95) and clinopyroxene clinopyroxene (Wo 30-Wo 50) with PGEs sometimes residing in disseminated but no no association with with "halos". "halos". This style of chalcopyrite or hydrous silicate pockets, but mineralization hosted 11% 4)In In interstitial interstitialsulfides sulfidesor orsilicates silicatesthat that mineralization 11% of the total PGMs identified. 4) include hydrous silicates, (?) textures, textures,or or silicates, chalcopyrite, chalcopyrite, clinopyroxene, sulfides sulfides with symplectite symplectite(?) calcite. This style of mineralization mineralization hosted hosted 10% 10% of the the total total PGMs PGMs identified. identified. of high PGM concentrations in The following is a summarized summarized model for the formation of the Birch Lake deposit. The TheSKI SKIbegins begins as as aa magma magma body body that is replenished replenished with multiple multiple injections of magma, which becomes sulfur saturated. The The magma magma body body is is relatively relatively PGE PGE poor, due to partial loss of sulfides during emplacement leaving the conduits with a PGE enriched segregation of the total sulfide. The Thesulfides sulfidesin in the the magma magma body body scavenge scavengeavailable available PGEs PGEs and and crystallize as disseminated, interstitial sulfide grains. Primary Primary hydrous hydrous phases phases form form at at this this time time 49 �fro:maafluorine-rich, fluorine-rich,deuteric deutenc fluid. fluid. A Cl-, Cu-, PGE-rich, sulfide-poor from sulfide-poor fluid enters the magma faults. The chamber at its base via the original magma conduit(s) and/or faults. The fluid fluid migrates migrates along along grain boundaries, and interacts with the larger interstitial interstitial sulfides. A A dynamic dynamic environment environment is is created in which the fluid, containing a significant concentration of dissolved metals, begins containing significant concentration of dissolved metals, begins to to to produce produce more more sulfides. sulfides. At consume and use sulfur from the larger grains to At the the same same time, time, the the fluid is reacting with neighboring grains, specifically plagioclase, and through aa cation cation exchange exchange them in in calcium. calcium. This reaction, alters the plagioclase rims, enriching them This reaction reaction causes causes aa volume volume (±chlorite) producing producing the the disseminated disseminated loss that is filled with precipitated sulfides and PGMs (±chlorite "halos" around the larger interstitial grains (Figure 1). 1). Finally, Finally, another another fluid fluid migrated migrated through through "halos" the intrusion that remobilized remobilized PGMs on on aa small small scale. scale. Based on evidence evidence solely solely from from the Birch Lake deposit, deposit, PGM PGM mineralization mineralizationappears appears concentrated or "compartmentalized". This Thiscould couldbe be the the result result of of two two possible possiblemechanisms: mechanisms: 1) 1) of high PGM concentrations are dependent on on their their proximal proximal distance distance to to "feeder" "feeder" zones Areas of 2) High PGM PGM concentrations concentrationsare are (i.e. conduits or faults) where fluids can be introduced; introduced; and/or and/or 2) due to structural controls within these these heterogeneous heterogeneous rocks that localize localize fluid fluid movement. movement. This study contributes to the current debate on the roles of of primary vs. remobilized mafic intrusions. intrusions. For (deuteric?) PGE mineralization in layered mafic For the the Birch Lake Lake deposit, deposit, the data data suggest both mechanisms played im of the ore minerals. )ortant roles in the sussest nlaved imiortant orisin ore minerals. Figure Figure 11 locations A-L. A-L. a.) Photomicrograph in a.)~hotomicro~ra~h inplane-polarized plane-polarizedlight lightofofthin thinsection sectionBL BL89-2 89-22516.4 25 16.4—- locations Large interstitial chalcopyrite chalcopynte and pyroxene cross-cut by vertical chlorite veins, all of which are surrounded by a disseminated, disseminated, dominantly chalcopyrite halo that is in An-enriched plagioclase rims. Notice Notice all allPGMs, PGMs,except except one, one, either either occur occur in the halo; in chlorite veins; in interstitial biotite; or in clinopyroxene. clinopyroxene. The Thealtered alteredplagioclase plagioclase and and altered alteredpyroxene pyroxene on on the the left left side side of of the the image are devoid includesareas areaswithin withinthe theoriginal originalhalo. halo. This devoid of any PGM occurrences occurrences —this -this includes suggests a second alteration fluid event that removed PGMs and altered altered the the minerals, minerals,which which itit passed through. Dashed Dashedline linerepresents representsthe theextent extentof of halo halo and andAn-enrichment An-enrichment in in the the adjacent adjacent plagioclase grains. White Cpx=Clinopyroxene, White stars stars represent represent PGM occurrences. occurrences. Cpx=Clinopyroxene, Opx=Orthopyroxene, Bi=Biotite, Bi=Biotite, Chl=Chlorite, Opx=Orthopyroxene, Chl=Chlorite, Cpy=Chalcopyrite, Cpy=Chalcopyrite, Plag=Plagioclase Plag=Plagioclase 50 �RESULTS OF OF EMP EMP MONAZITE MONAZITE GEOCHRONOLOGY GEOCHRONOLOGYIN E-C MINNESOTA: MINNESOTA: EVIDENCE EVIDENCE FOR LARGE-SCALE GEON 17 METAMORPHISM ASSOCIATED WITH POSTLARGE-SCALE GEON 17 METAMORPHISM ASSOCIATED WITH POSTTECTONIC PLUTONISM MCKENZIE, M.A., and HOLM, D.K., D.K., both at at Dept. Dept. of Geology, Geology, Kent State State University, University, Kent, Kent, OH; SCHNEIDER, SCHNEIDER, D.A., D.A., Dept. Dept. of of Geological Geological Sciences, Sciences, Ohio Ohio University, University,Athens, Athens,OH; OH; JERCINOVIC, M., Dept. of Geosciences, Geosciences, University of Massachusetts, Massachusetts,Amherst, Amherst, MA MA Determination of the timing and extent of poly-phase metamorphism is essential in Determination unraveling the tectonic history of a region. The The pattern pattern and and degree degree of of metamorphism metamorphism preserved preserved across the Penokean orogenic belt in the southern Lake Superior Superior region is highly variable. Abundant 40Ar/39Ar dates from east-centralMinnesota Minnesotaindicate indicatewidespread widespread cooling cooling at at -1760 - 1760 Ma ~ r l dates ~ from r east-central shortly after the emplacement emplacementof of the the east-central east-centralMinnesota Minnesotabatholith batholith(ECMB) (ECMB)atat—1775 -1775 Ma (Hoim (Holm et al., 1998; 1998; in review). Yet Yet U-Pb U-PbSHRIMP SHRIMPmonazite monaziteages ages from from three three localities localitiesacross across the the Ma metamorphic MN, northern northern MI, MI, and and northern northern WI) WI)record recordonly onlyaauniform uniform—1830 -1 830 Ma region (e-c MN, episode 1800 Ma thermal thermal pulse pulse linked linkedtotoaarecently recentlyidentified identified—1800 -1800 episode and and aa secondary secondaryyounger younger—1800 Ma magmatic event (Schneider et al., a!., in in review). review). This This study study utilizes utilizes the the total total Pb Pb electron electron microprobe (EMP) monazite age dating technique to better constrain the the extent of of thermal overprinting overprinting surrounding surrounding the batholith. batholith. metamorphic monazite monazite ages ages from from three three For this study study we obtained obtained in situ metamorphic Paleoproterozoic gamet-staurolite schist samples and one garnet-cordierite Paleoproterozoic metasedimentary garnet-staurolite gneiss sample from the plutonic zone of east-central Minnesota (Figure 1). Schist Schistsample sampleAMAM016 contains contains predominantly elongate elongate monazite monazite grains grains displaying displaying aa mottled mottled chemical chemical variation variation in in Y and Th content. This Thissample sampleyielded yieldedaa mean mean age age of of 1746 1746±Â 3 Ma from 79 spots spots on seven grains. Two Maand and1760 1760Ma. Ma. A third less prominent Twoage agedomains domainswere were recognized recognized at at —1738 -1738 Ma —1780 Maage agedomain domainwas wasobtained obtainedon onsome somehigh highYYregions. regions. Schist sample MN-29 contains -1'780 Ma sub-euhedral monazite displaying prominent regions of of high high Th Th content. content. This This sample sampleyielded yielded aa 10 Ma from 92 spots on five grains. A mean age of 1764  10 A single singleprominent prominentage age domain domain was was 1764 ± recognized 1772 Ma. Schist recognizedatat— 1772 Schistsample sampleP-16 P-16contains containsmonazite monazitewith withvery veryirregular irregulargrain grain boundaries, numerous inclusions, and variable Th content. This This sample sampleyielded yielded aa mean mean age age of of 1772 Two age age domains domains are identified: aaprominent prominent age age 1772 ±Â 33 Ma from 92 spots on seven grains. Two domain Maand and aa smaller smaller population population age domain Ma. Lastly, the Sartell domain at at —1770 -1770 Ma domain at at —1800 -1800 Ma. Sartell gneiss, corelrimtextures. textures. gneiss, sample sample S-2, S-2, contains contains euhedral euhedral monazite monazite grains grains displaying displaying distinctive distinctivecore/rim Ma from 102 spots on seven grains. Three This sample yielded a mean age of 1756 ± 3 Three age age sample 1756  3 domains 1750 Ma and 1770 1770 Ma and and aa third third less less domains are are identified: identified:two twoprominent prominentdomains domainsatat— 1750 prominent 1800 Ma on high U U cores. cores. prominent domain domainatat—1800 Our EMP Ma thermal thermal imprint imprint associated with intrusion EMP results results reveal reveal aa profound profound—1770 -1770 Ma intrusion of the 1775 1775 Ma ECMB. The Theconsiderable considerabledistance distanceof of some someof of these thesesamples samplesfrom fromthe the western western edge of the exposed batholith (30-40 km) and the absence of Penokean metamorphic ages exposed batholith (30-40 krn) and the absence of Penokean metamorphic ages suggests that the thermal pulse must have been dramatic. However, However, the the garnet-schist garnet-schistsample sample KKR (east of Mille Mule Lacs) that records only geon 18 SHRIMP SHRiMP ages lies north of the region of thermal influence of the batholith. We Wenote notethat thatsample sampleK-R K-R isislocated locatedjust just north north of of the theMalmo MalmoStructural Structural of it. Our Discontinuity (MSD) and sample AM-016 is located south of Our data datareveal reveal that that the the MSD MSD juxtaposes rocks of different different metamorphic age (geon 18 18 metamorphism to the north from geon - - - - 51 �17 metamorphism to the south). We We propose, propose, therefore, therefore, that the the MSD MSD is is aa geon geon 17 17 structure structure that exhumed the plutonic terrane of east-central Minnesota. West West of of Mille Mille Lacs, Lacs, aa significant significant juxtaposes post-Penokean plutons to the south against older metamorphic portion of the MSD juxtaposes rocks to the north. This Thisclearly clearlysupports supportsour our interpretation interpretationthat that this this structure structurewas was active activewell well after Penokean orogenesis. orogenesis. Hoim, D.K., Darrah, K., and Lux, D., 1998, 60-8 1. 1998,American American Journal Journal of of Science, Science,298, 298,60-8 Holm, T., Schweitzer, D., and Schneider, Holm, D.K., Van Schmus, W.R., MacNeill, L., Boerboom, T., D.A., in review, review, Geological GeologicalSociety Society of of America America Bulletin. Bulletin. Schneider, D.A., Holm, Hoim, D.K., O'Boyle, C., C., Hamilton, Hamilton, M., Jercinovic, Jercinovic, M., in review, review, Geological Society of America Special Volume "Gneiss Domes and Orogeny." Special volume Domes and Orogeny." Composite MN-29 Composite AM-Ol 6 Composite 0 7 0 1700 04 7720 2 1740 7 4 1760 1760 1780 1780 1800 1800 Mo8 More 1700 1700 1720 1720 1740 1740 Age (Ma) AW (Ma) 1760 1760 1780 1780 !do0 1000 More Mo. Age ~ g (Ma) (Ma) e Composite S-2 Composite P-16 Composite 20 - 1520 10- IS U. 5- 1 0 1700 71720 7 4 1740 1760 1760 1780 1780 1800 1000 More Mo,. 1 1 0-' 1700 1700 1720 1720 1740 1740 1760 1760 1780 1780 1800 WOO Mor. More Age (Ma) Ag. (Ma) - Histogram AllSamples Samples - All Ages Histogram All 700 1720 1740 1760 780 1800 1820 Age (Ma) - Figure 1: Histograms Histogramsof of EMP EMP Th-U-total Th-U-total Pb in situ s i t ~monazite spot ages. 52 �THE SIOUX QUARTZITE REVISITED: SEDIMENTOLOGY, SEDIMENTOLOGY, METAMORPHISM, METAMORPHISM, GEOCHEMISTRY GEOCHEMISTRY AND THE THE ORIGIN ORIGIN OF PIPESTONE PIPESTONE Geology & & Geophysics, Geophysics, University University of of MEDARIS, L.G., Jr., and DOTT, R.H., Jr., Dept. of Geology Wisconsin-Madison, Madison,WI, WI,53706; 53706;medaris@geology.wisc.edu; medarisgeology.wisc.edu;rdott@geology.wisc.edu rdottgeoIogy.wisc.edu Wisconsin-Madison, Madison, Red, supermature quartzites of the Baraboo Baraboo Interval were deposited after after 1.75 1.75 Ga Ga on on aa stable stablecraton craton ininthe the presence of free atmospheric oxygen oxygen under under conditions of intense intense chemical chemical weathering. weathering. Some presence Some quartzites quartzites (Baraboo and and Flambeau) Flambeau) were were folded folded and and recrystallized recrystallizedatat 1.63 1.63 Ga Ga (Holm (HoIm et et al., 1998), 1998), and and many many (Baraboo quartzites were were hydrothermally hydrothermallyaltered alteredatat 1.46 1.46 Ga Ga (Medaris (Medaris et et a!., quartzites al., 2002, 2002, in in press), press), presumably presumably in in response to brine migration promoted by by continental continental scale scale A-type A-type magmatism. magmatism. These response migration promoted These discoveries discoveries have have prompted us to reevaluate the sedimentology, metamorphism, and geochemistry of the Sioux Sioux Quartzite. Quartzite. Sedimentolo'y SedimentologvThe TheSioux SiouxQuartzite, Quartzite,which whichisisseveral severalhundred hundredmeters metersthick, thick,isiscomposed composed mostly mostly of quartz sandstone with interstratified interstratified lenses of red red mudstone mudstone (Southwick (Southwick et et al., al., 1986). 1986).Heterogeneous Heterogeneous cobble conglomerate occurs at the base and finer finer pebbly layers layers are are scattered scattered throughout throughout the the lower lower half half or or Sedimentary structures structures in the sandstones so, whereas mudstones mudstones occur chiefly chiefly within within the the upper upper half. half. Sedimentary sandstones include 15 cm in in thickness, thickness, rare rare include predominant predominant festoon-style, festoon-style, nested trough trough cross cross beds bedsaveraging averaging1010—- 15 zones of planar-tabular sets, a few zones planar-tabular sets, few examples examples of of herring herring bone bone cross cross bedding, bedding, and and both bothasymmetric asymmetric and and symmetric ripple marks. The mudstones are mostly massive, but parallel- laminated and ripple-laminated varieties are are also also present. present. In In most cases, quartz quartz silt silt and and fine sand grains are disseminated in a finer varieties most cases, disseminated in finer rare graded graded laminations laminations are are also also present. present. Some mudstones show polygonal polygonal 'mud' cracks, matrix, but rare cracks, and and the overlying sandstones commonly contain intraclasts ripped up from such such cracked cracked beds beds Interpretations of the Sioux depositional environment include shallow marine and and braided fluvial fluvial (Doll, 1983; Southwick et al., a!., 1986). 1986). In the latter latter scenario, scenario, the cross cross bedded bedded sandstones sandstones represent represent river river (Dott, channel deposits, and the mudstones, mudstones, slack slack water water deposits deposits in in ponds ponds between between active activechannels. channels.However, However, this interpretation interpretation is inconsistent with the rarity of scoured channel bases and tabular sets sets of of planar planar cross cross laminations, which would would have have formed formed by laterally bars, and the existence laminations, which laterally migrating migrating bars, existence of of wave wave ripples, ripples, Ojakangas and and Weber Weber (1984) (1984) suggested suggested that that the the which are not expected in the the sands of a braid plain. Ojakangas expected in braid plain. one-third of the Sioux formation was deposited in a shoreline upper one-third shoreline marine marine setting setting with with tidal tidal influences, influences, polygonal desiccation cracks, and accounting for the the herringbone herringbone cross cross bedding, bedding, wave ripples, polygonal and thickness thickness and extent of certain certainmudstone mudstonelayers layers(now (nowpipestone). pipestone). Interpretation Interpretation of of the the Sioux Siouxas asaafluvial-to-marine fluvial-to-marine transgressive succession would conform to the present interpretation of the correlative Baraboo transgressive succession would conform to the present interpretation of the correlative Baraboo Quartzite, which has wave ripples and reactivation surfaces surfaces in in its its upper upper half half (Medaris (Medariseteta!., al.,ininpress). press). Metamorphism Metamorphism Mineral Mineralassemblages assemblages in in finefine55 grained Sioux sedimentary rocks rocks can be 9 expressedininthe the system, system,KASH, KASH,asasportrayed portrayedin inac- 4 _ expressed Figure 1, 1, where rock rock compositions compositions are are projected projected onto the anhydrous onto anhydrous plane, plane, K-Al-Si, K-Al-Si, and and two two 3critical dehydration reactions are plotted. are plotted. Additional phases phases include abundant hematite Additional hematite and 2a Ti02 TiOz phase, phase, either either anatase anatase in in the the Cottonwood Cottonwood (Stelz, 1989), 1989), or rutile in the Basin (CB) Basin (CB) (Stelz, 11 The stable existence Pipestone Basin (PB). Pipestone (PB). The existence of - co~onwood the CB kaolinite in the CB (Stelz, (Stelz, 1989) 1989) requires temperatures —300°C, whereas pyrotemperatures below -300°C pyroI /I I I phyllite ininthe thePB PB isis stable stableabove above-300°C 300°C. The phyllite The 250 300 350 T, OC 53 �quartz-pyrophyllite assemblageininthe thePB PB(0, (0, Fig. 1), quartz-pyrophyllite assemblage I), in in which which vermicular kaolinite has been replaced by by pyrophyllite pyrophyllite (Fig. (Fig. 2A), 2A), most likely most likely represents represents higher higher temperature, temperature, largely largely isochemical isochemical recrystallization of a quartz-kaolinite protolith, like that in the CB CB The occurrence of muscovite in both (0, Fig. 1). 1). The occurrence of muscovite in both basins basins is is attributed to K-metasomatism related to 1.46 attributed K-metasomatism related 1.46 Ga Ga hydrothermal hydrothermal ("I",Fig. Fig. 1)1)isisaametasomatic metasomatic rock composed of activity. Pipestone Pipestone (+, pyrophyllite, muscovite, diaspore, hematite, and and rutile, pyrophyllite, muscovite, diaspore, hematite, rutile, in in which which former quartz grains have been completely former completely replaced by diaspore, diaspore, pyrophyllite, and and muscovite pyrophyllite, muscovite (Fig. (Fig. 2B). 2B). Because Because the Sioux Sioux undeformed and lies north of the extrapolated Quartzite is largely undeformed trend of the 1.63 al., 1998), 1998), 1.63 Ga Ga Mazatzal Mazatzal tectonic tectonic front front (Hoim (Holm et al., we suggest suggest that all all metamorphic metamorphic features features of of the the Sioux Sioux Quartzite Quartzite 1.46Ga Ga hydrothermal hydrothermal activity, activity, rather rather than than aa Mazatzal Mazatzal are due to 1.46 event. event. Geochemistry Where Where unmodified unmodified by by K-metasomatism, K-metasomatism, finegrained grained sedimentary rocks of the Baraboo Interval are remarkably mature, being practically Mg, and and Mn Mn (Fig. (Fig. mature, practically devoid devoid of K, Na, Ca, Mg, 3), and having Critical Critical Index Index of of Alteration Alteration values values of of 97 97 to to 99. 99. In In such rocks rocks the the wide wide range range in in proportion proportion of of Si Si to to A1 Al (Fig. 3) and such quartz to kaolinite, 1), reflects reflects the the original original proportion proportion of quartz to kaolinite in the kaolinite, or or pyrophyllite pyrophyllite (Fig. (Fig. I), protolith sediments. sediments. K-metasomatism has stabilized 200 muscovite in both both the the CB and PB, but but muscovite in .4i the muscovite-bearing rocks in the CB muscovite-bearing rocks CB 150 150 record record a lower lower temperature temperature and and higher higher ratio of Si/Al SiIAl compared to pipestone in the PB (Fig. 1). The Theclassic classicpipestone, pipestone, 5 100 loo .s 8 in addition addition to to substantial substantial KK contents, contents, contains lower Si Si and higher contains lower higher Al A1 than than 8oa.to 50 that in associated associated quartz + + pyrophyllite pyrophyllite fca"!& samples (Figs. 1 & & 3). 3). Assuming samples (Figs. Assuming Zr to ~ g ? be an immobile element, isocon ID calculations indicate the mean indicate that the mean E -50 pipestone composition was produced by 0 removal of 20 to 65% Si02, removal of Si02, 45 to 55% 55% -100 Ti02, Si Fe TI Ti02, 35 to 65% 65% Fe203, Fe203,and addition of K Na Mn Fe Ti Al Si K Na Ca Mg Mg Mn 15 to to 45% 45%A1203 A1203and and—800% -800% 1(20, K20, compared to the average compositions of the two Si-rich Si-rich and two Al-rich Al-rich quartz quartz ++ pyrophyllite samples. samples. The reconstructed composition of of one one pipestone pipestone sample sample (*, (*, Fig. Fig. 1) 1) requires requires removal removal of of 68% 68% Si02 Si02and and reconstructed composition addition during metasomatism. addition of of 50% 50%A1203 A1203during metasomatism. Further Further investigation investigation is underway underway to provide a more more detailed detailed evaluation evaluation of of brine brine compositions compositions and and metasomatic processes involved in this important, important, regional scale, scale, 1.46 1.46 Ga Ga hydrothermal hydrothermal event. event. References Dott, Dott,R.H. R.H.Jr. Jr.(1983) (1983)Geol. Geol.Soc. Soc.Amer. Amer.Memoir Memoir 160, 160,129-141; 129-141;HoIm, Holm, D. eta!. et al.(1998) (1998)Geology, Geology, v. 26, 907-9 10; Medaris, L.G., Jr. eta!. (2002) 48th Inst. Lake Superior Geol., 24-25; Medaris. L.G., Jr. Geol., 24-25; Medaris. L.G., Jr. eta!. et al.(in (in press) press) 907-910; Medaris, L.G., Jr. et al. (2002) 48th Inst. Lake Jour. Geol.; Ojakangas, Ojakangas, R.W. R.W. & & Weber, Weber,R.W. R.W.(1984) (1984)Mimi. Minn. Geol. Geol. Surv., Surv., Rept. Inv. 32, 1-15; 1-15; Southwick, D.L. et a!. al. (1986) (1986) Geol. Soc. Soc. Amer. Bull., v. 97, 1432-1441; 1432-1441;Stelz, Stelz, D.E. D.E. (1989) (1989)M.S. M.S. Thesis, Thesis,Wichita Wichita State StateUniv., Univ.,140 140pp. pp. (, Cd, C.) d . = - r 5 54 �A geochemical investigation investigation of of Mesoarchean Mesoarchean metavolcanic and metasedimentary metasedimentary rocks from the Birch-Uchi Birch-Uchi greenstone belt Metsaranta, Hollings, P.P. (Department of of Geology, Metsaranta,R., R.,Fralick, Fralick,P.P.and and Hollings, (Department Geology,Lakehead LakeheadUniversity, University,Thunder ThunderBay Bay ON CAN, P7B P7B 5E1) 5E1) Most Mesoarchean belts in the Mesoarchean greenstone greenstone belts the Western Western Superior Superior Province Province are are comprised comprised primarily of komatiite-tholeiite komatiite-tholeiite sequences sequences and and associated associated sedimentary sedimentary rocks rocks (Thurston (Thurston and Chivers Chivers 1990). 1990). These These—2.9-3.0 -2.9-3.0 Ga Ga assemblages assemblages have been been interpreted interpreted to to represent represent plume generated generated volcanism volcanism in in oceanic oceanic plateau plateau settings settings(for (forexample, example,Hollings Hollingsetetal. al.1999, 1999, Tomlinson et et al.1999). al.1999). This study study isis aapreliminary preliminary investigation investigation of of metavolcanic metavolcanic and and metasedimentary strata from the metasedimentary strata the Mesoarchean Mesoarchean Balmer Balmer assemblage assemblage of of the theBirch-Uchi Birch-Uchi greenstone belt. belt. Rogers Rogers et al. al.(2000) (2000)have havesuggested suggested that, that,given giventheir theirgeochemical geochemical affinities affinities and and Nd isotopic isotopic evidence evidence for for contamination contamination by by older older crust, crust, volcanic volcanic rocks rocks of of the the Balmer assemblage may represent a continental arc arc setting. This This implies implies that that the the Balmer Balmer Assemblage may represent those proposed proposed for for other other sent aa distinct tectonic tectonic setting from those Mesoarchean Mesoarchean rocks rocks in in the the Superior Superior P \ B,U' Province. Province. Sediment geochemistry geochemistry and and depositional depositional environment environment studies studies along along with igneous igneous geochemistry geochemistry will will be M8 applied to provide provide further further constraint constraint on on the possible tectonic setting of these possible tectonic setting of these — Ss.thviti LSO rocks. rocks. A i:3 I N N The Birch-Uchi Birch-Uchi greenstone greenstone belt belt is is located in the located in the central central portion portion of of the the MNI NM It Uchi (Fig.1). It is is Uchi Subprovince Subprovince (Fig.1). volcanic units three comprised comprised of three volcanic units termed the Balmer, Balmer, Narrow Narrow Lake Lake and and spanning assemblages, Woman Woman assemblages, spanning approximately 250 Ma. Ma. The Balmer Balmer assemblage assemblage is is the the oldest oldest of these these volcanic units and has volcanic units has U-Pb U-Pb zircon zircon ages from felsic felsic volcanic volcanic horizons horizons that that suggest suggest an age age of of ca. ca. 2975-2989 2975-2989 Ma Ma (Rogers et al., 2000). The Thestratigraphy stratigraphy of the the Balmer Balmer assemblage assemblage is is divided divided into four four suites: suites: aalower lowersedimentary sedimentary sequence, sequence, a mafic mafic volcanic volcanic suite suite and and two two petrographically petrographically distinct distinct felsic felsic volcanic volcanic suites suites (Rogers (Rogers et et al. al. 2000). 2000). Samples for this study Samples collected collected for study are are located in the the southern southern portion portion of of the the Figure Figure 11-Location Locationand andgeneralized generalizedgeology geologyof ofstudy study area area and and Birch-Uchi Birch-UchiGreenstone Greenstonebelt belt(modified (modifiedfrom from Balmer assemblage assemblage in in the Woman Woman Stott Stott and and Corfu Corfu 1991) 1991) River/Bear RiverIBear Lake area. These Thesecomprise comprise 16 samples from the 34 samples samplesof of the themafic maficvolcanic volcanic the lower lower sedimentary sedimentary sequence sequence and and 34 suite suite of of Rogers Rogers et et al.(2000). al.(2000). 55 �Field observations suggest that the the Balmer Balmer assemblage assemblage sedimentary sedimentary rocks are are turbiditic. turbiditic. Sediment geochemistry geochemistry will will be be applied applied to constrain the source rocks compositions Sediment compositions for these sediments. As Asno nocontact contactwith with underlying underlying older older rocks rocks has been identified identified this might provide provide valuable valuable information information about about the the preexisting preexisting older older crust. crust. Alternatively, the the sediments may be derived from the Balmer assemblage volcanics and this could support a hypothesis that the Balmer hypothesis that Balmer assemblage assemblage represents represents aa continental continental arc setting setting with with the the sediments deposited in a fore-arc fore-arc trench. Volcanic rock samples appear Volcanic rock appear to fall fall into intotwo twocompositional compositionaltrends. trends. The The first first is aa tholeiitic trend trend comprised comprised of of primarily primarily tholeiitic tholeiitic basalts basalts and and andesites. andesites. The The second second is is aa caic-alkaline trend of andesitic to rhyodacitic compostion. The geochemistry of these calc-alkaline trend of andesitic rhyodacitic geochemistry of samples will will be be applied samples applied to suggest suggest aa possible possible tectonic tectonic setting setting for these these rocks rocks and and implications ten-anes. implications of this this in relation relation to to other other Mesoarchean Mesoarchean terranes. 400 0 300 * 200 0 U II I I 0.01 100 .001 .01 I U 0 0.1 1 0 10 200 100 300 Zr Nb/Y NbN Figure 33- Lithology Lithology Discrimination diagram for Balmer Assemblage volcanics. Circles Circles are Tholeiitic trend squares are calc-alkaline trend. calc-alkaline trend. Figure 3-A plot of V vs Zr showing compostional groups in Balmer Assemblage Assemblage volcanics. volcanics. Circles are Tholeiitic trend squares are calc-alkaline calc-alkaline trend. trend. References: References: Hollings, P., Wyman, D. and Kerrich, R. 1999. Komatiite-basalt-rhyolite Komatiite-basalt-rhyolite volcanic associations associations northern northern Superior Superior Province Province greenstone greenstonebelts: belts: significance significanceof of plume-arc plume-arc interaction in the generation of of the the proto proto continental continentalSuperior SuperiorProvince. Province. Lithos Lithos 46: 137-162. 137-162. Lithogeochernical Rogers, N., McNicoll, V., van Stall, C.R., and Tomlinson, K.Y. 2000. Lithogeochemical studies in the Uchi-Confederation Uchi-Confederation greenstone greenstone belt, belt, northwestern northwestern Ontario: Ontario: implications implicationsfor for Archean Archean Tectonics. Geological 2000-C 16:1lip. GeologicalSurvey Survey of of Canada, Canada, Current Research 2000-C16: lp. Stott, G.M., and Corfu, F. F. 1991. Uchi Uchi Subprovince. Subprovince. In: In:Geology Geology of of Ontario, Ontario, special special volume 4, part 1. 8. 1. Ontario OntarioGeological GeologicalSurvey, Survey,pp pp145-23 145-238. Thurston, P.C. and Chivers, K.M. 1990. 1990. Secular Secularvariations variationsin ingreenstone greenstonesequence sequence development development emphasizing Superior Province, Canada. Precambrian PrecambrianResearch. Research. 46: 46: 21-58 21-58 D.J., Thurston, Thurston,P.C., P.C., and andHall, Hall,R.P. R.P. 1999. 1999. Plume Tomlinson, K.Y., Hughes, D.J., magmatism and crustal growth at 2.9 to 3.0 Ga in the Steeprock Steeprock and and Lumby Lumby Lake Lake area, area, Western Western Superior Province. Province. Lithos 46: 46:103-136. 103-136. 56 �PETROLOGY PETROLOGYAND AND PGE POTENTIAL POTENTIAL OF OF THE THE GREENWOOD GREENWOOD LAKE LAKE INTRUSION, INTRUSION, COMPLEX, LAKE CENTRAL DULUTH COMPLEX, LAKE COUNTY, COUNTY, MINNESOTA MILLER, James, D., Jr., Minnesota Minnesota Geological Geological Survey, Survey, mille066@tc.umn.edu mille066@tc.umn.edu MILLER, This report summarizes the results of a petrologic and metallogenic of drill core and metallogenic study of outcrop samples samples that profile profile the the Greenwood Greenwood Lake Lake intrusion intrusion (GLI) (GLI) of of the the central centralDuluth DuluthComplex Complex (Fig. 1). 1). The Thelittle littlethat thatwas wasknown knownabout aboutthis thisvery verypoorly poorlyexposed exposedlayered layeredmafic maficintrusion intrusionprior priorto to this study came from interpretation interpretation of its its aeromagnetic aeromagnetic signature, seven drill cores, and sparse, sparse, localized outcrop. The Thepurpose purposeof of this thisstudy study was was to to establish establish the the igneous igneous stratigraphy stratigraphy of of the GLI and to evaluate evaluate its its potential potential for for PGE PGEreef reef mineralization. mineralization. The GLI is an an approximately approximately two two kilometer-thick, sheet-like 10') to to the the east east and and covers covers an kilometer-thick, sheet-like intrusion intrusion that that dips dips gently gently (approximately (approximately10°) area of about 300 square kilometers. For For this this study, study,19 19bedrock bedrock drill drill cores cores (20 (20 to to 80' 80'in in length) length) Erie/LTV railroad railroad and powerline were acquired acquired in in early early 2002 2002along alongthe thewest—northwest-trending west-northwest-trending ErieILTV west of Lake 1). Samples Samples from from these these cores and west Lake County County Highway Highway 22 (Fig. (Fig. 1). and from from intermittent intermittent outcrops along the eastern extent of the railroad grade were subjected subjected to petrographic study in transmitted and reflected light, microprobe microprobe analyses analyses of olivine olivine and and pyroxene pyroxene composition, composition, and and whole rock whole rock analyses analyses of of their theirlithogeochemistry, lithogeochemistry, including including platinum, platinum, palladium, palladium, and gold gold concentrations. concentrations. The results of the drilling drilling and and petrographic petrographic study study show show that the the igneous igneous stratigraphy stratigraphy of of the the GLI can be grossly (GLtr, 0-650 0-650meters), meters), composed composed GLI grossly subdivided subdivided into into aa lower lower troctolitic troctolitic zone zone (GLtr, mostly of leucotroctolitic leucotroctolitic cumulates, cumulates, aa medial gabbroic gabbroic zone (GLog, 650-1800 meters), composed of olivine oxide gabbro (GLfg, 1800-2130 1800-2130 meters), gabbro cumulates, cumulates, and and an an upper upper ferrogabbroic ferrogabbroic zone (GLfg, composed largely of magnetite magnetite gabbro gabbro (Fig. (Fig. 2). 2). The troctolitic zone contains contains abundant, abundant, large anorthositic and oxide oxide gabbroic gabbroic inclusions, inclusions, presumably presumably derived derived from from anorthositic anorthositicseries seriescountry country rock. Although Althoughthe theGLI GLIisisaawell-differentiated well-differentiatedintrusion intrusionthat that formed formedas asan anopen openmagma magma system, system, microprobe data show that cryptic cryptic layering layering trends trends (such (such as as Fo Fo in in olivine, olivine, Fig. Fig. 2) 2) are areinconsistent inconsistent with formation by in situ crystallization differentiation. This This and and other other evidence evidence (such as abrupt changes in lithology, lithology, leucocratic leucocratic compositions compositions of of troctolitic troctolitic rocks, rocks, and and suspect suspect cumulus cumulus textures textures of troctolitic rocks) suggest of the GLI was suggest that the the differentiated differentiated character of was probably inherited from a deeper crustal crustal magma magma chamber, chamber, which which was was itself itself undergoing undergoing open opensystem systemdifferentiation. differentiation. The chemostratigraphy of chalcophile chalcophile elements elements through through the GLI GLI are are difficult difficult to to interpret interpretin in such a complex open magma system, system, but suggest that some potential for PGE reef mineralization may occur in the lower part of the gabbroic gabbroic zone (Fig. 2). Below Belowthis thislevel, level,recharging rechargingmagmas magmas appear to have been undersaturated undersaturated in in sulfide, sulfide, and and copper copper and and sulfur sulfur concentrations concentrationshigher higherin inthe the gabbroic zone (above 800 meters) indicate intermittent intermittent saturation. saturation. An unexpected result of this study was the discovery discovery of of aa large, large,sulfide-bearing sulfide-bearingoxide oxide gabbro gabbro inclusion inclusion within within the thetroctolitic troctolitic zone. Aeromagnetic Aeromagneticdata datasuggest suggestthat thatthis thisinclusion inclusionisisaaconformable conformabletabular tabularmass masswith withaastrike strike length of about 8 kilometers. The The magnetic magnetic data data further further suggest suggest that similar similar rock types form part of the footwall to the GLI. The Thepossibility possibilityof of sulfur sulfurcontamination contamination in the contact aureole around this inclusion and along the base of the intrusion of these areas for intrusion warrants further exploration of contact-type contact-type Cu-Ni-PGE Cu-Ni-PGE sulfide sulfide mineralization. mineralization. Funding for this project was provided to the Minnesota Geological Survey by a grant from recommendation of the Minerals Coordinating the Minnesota State Legislature on the recommendation Coordinating Committee. Committee. 57 �Figure 1. 1. Generalized geology of the Greenwood Lake intrusion and the central Duluth Small dots dots denote Complex. Small denote drill drill hole hole and and diamonds diamonds denote outcrop locations locations along ErieILTV ErieILTV railroad tracks. tracks. Long Long dashed dashed lines lines denote denote faults. faults. Intrusive Intrusiveunits units are: are: GLtr—GLI GLtr-GLI troctolitic zone Glog—GLI Glog-GLI gabbroic gabbroic zone zone GLfg—GLI GLfg-GLI ferrogabbroic ferrogabbroic zone MW—Mt. Weber granophyre MW-Mt. granophyre CLLS—Cloquet CLLS-Cloquet Lake Lake layered layered series series BEI—BaId Eagle intrusion BEI-Bald intrusion SKI—South Kawishiwi intrusion SKI-South PRI—Partridge River PRI-Partridge River intrusion intrusion WMI—Western WMI-Western Margin Margin intrusion intrusion Layered Layered Series Series Ferrogabbroic Ferrogabbroic Gabbroic Gabbroic Troclolitlc Troclolillc 3 L: ] Felsic Series k Anorthositic Series North Shore Volcanic Group Group Virginia Formation Biwabik IronFormation Giants Range Granite • • meters 20 Kilometers Kilometers 10 10 0 0 Who rock Whole rockgeochemistry geochemistry OHvine 2000 / 1600 / ,Pt+Pd * re .1 1200 * P. 0 800 400 C -,* I. 0 r— = = • 807060504030 Fo : 0 400 800 1200 Cu (ppm) 0 = •. —— 204060 Pti-Pd PttPd && Au Au (ppb) (ppb) Cu/Pd (xlO Figure Figure 2. Chemostratigraphy Chemostratigraphyof of Fo Fo in in olivine olivine and and of Cu, Pt ++ Pd, and Au concentrations concentrations through through the the Greenwood Lake Stratigraphic locations locationsofof drill drill core (boxes) Lake intrusion. intrusion. Stratigraphic (boxes) and and outcrop outcrop (diamonds) (diamonds) samples and general lithostratigraphy are are shown shown in in the the left columns. columns. Large Large inclusions inclusions of of anorthositic anorthositic series rocks (AS) and oxide gabbro (ox gb) are denoted. Abrupt (arrows) may mark Abrupt increases in Cu/Pd Cu/Pd (arrows) mark increases in sulfide saturation events. The The zone zone found foundmost most favorable favorable to host PGE reef mineralization mineralization is identified. identified. 58 �Stratigraphy and northwestern Stratigraphy andstructure structureof ofKeweenawan Keweenawan rocks rocks of the St. Croix horst, northwestern Wisconsin Wisconsin S.W. Nicholson, and W.F.Cannon, U.S.Geological U.S.Geologica1Survey, Survey, Reston, Reston, VA VA graben of of the Midcontinent Rift System The St. Croix horst is the partially inverted central graben (MRS) that extends southwestward southwestward from western Lake Lake Superior. Superior. ItIt is is bounded bounded by by the the Douglas fault on the northwest and the Atkins Lake fault on the southeast. Both are now reverse faults, but may have been graben-bounding normal faults during rifting and volcanism. The northern northern limit of the horst is White's Ridge, a subsurface basement high volcanism. evident in both seismic and gravity data, which did not subside substantially during rifting and against which rift volcanic and sedimentary rocks pinch out out or or become become much much thinner. thinner. White's Ridge Ridge effectively effectively separates separates the the MRS MRS in in western western Lake Lake Superior Superior from from the the St. St. Croix Croix horst and the volcanic, volcanic, sedimentary, sedimentary, and and structural structural history history of of the the two two rift rift segments segmentsdiffer differin in High-resolution aeromagnetic, gravity, gravity, and and seismic seismic data data permit permit the the tracing tracing of of several aspects. High-resolution flow sequences for long distances and to great depth. This geometry combined with the chemistry of the volcanic rocks allows us to decipher a volcanic volcanic stratigraphy in spite of widespread cover by glacial deposits deposits and and Paleozoic Paleozoic sedimentary sedimentary rocks rocks (Cannon (Cannon etetal., al.,2001). 2001). Our interpretation, interpretation, aided aided by previous gravity gravity and and seismic seismic interpretations interpretations (Chandler (Chandleretetal., al., 1989), is that the original structure of the St. Croix horst was an an asymmetric asymmetric graben, graben, or or possibly a half graben, like like those those of of the the Lake Lake Superior Superior portion portion of of the the MRS. MRS. The TheLake LakeOwen Owen fault was a major growth fault on on the the southeast southeast side side of of the the graben graben and and the the volcanic volcanic fill fill thickened toward and terminated against the fault. The Douglas fault on the northwest side of of the horst is not clearly a growth feature and may be simply a thrust formed during rift rift km or more because it inversion. Thrust displacement on the Douglas fault must be 20 krn juxtaposes of the base of a thick volcanic sequence over the younger Bayfield Group. Cannon et al. (2001) and Nicholson et al. (2001) used chemical and aeromagnetic data to underlying Clam Falls Volcanics, and the Chengwatana define the Minong Volcanics, the underlying Volcanics as three formations making up the graben-filling graben-filling volcanic volcanic sequence. sequence. The The three three three-part have similar chemistry, but were defined by structure and geochronology. The three-part division no longer seems seems justified and and the the Chengwatana Chengwatana and and Clam Clam Falls Falls Volcanics Volcanicsare are combined into a single single unit. The The Chengwatana Chengwatana Volcanics, Volcanics, as as earlier earlier defined, defined, were were restricted restricted to a fault-bounded belt between the Douglas and and Pine Pine faults faults and and their their stratigraphic stratigraphic relationships to other other volcanics were were not known known directly. directly. We We now now believe, believe, based based on on seismic seismic data, that the Pine fault does not extend into the northern northern part of the horst, where the depositional previously defined Chengwatana and Clam Falls units appear to be a continuous depositional sequence of compositionally indistinguishable indistinguishable flows flows that that we we propose propose be be called called entirely entirely Chengwatana. The Minong Volcanics, aa sequence krn thick, thick, low-Ti02basalts basalts about about 33 km sequence of of low-Ti02 overlie the Chengwatana, along along an an apparent apparent low low angle angle disconformity disconfomity based based on on aeromagnetic aeromagnetic disconformity within within the Minong volcanics on the form lines. These form lines also show a disconformity southeast limb of the Ashland syncline. syncline. A A lower lower unit, unit, not not present present on on the the northwest northwestlimb, limb,isis mostly high-Ti02 high-Ti02 basalt. Based on the presence of abundant high-Ti02 basalts and more evolved rocks, we infer infer that aa localized magmatic center center was was active active in in this this area area sometime sometime upper part part of of this sequence. A second, but but before 1095 Ma, the age of a rhyolite flow in the upper apparently older, volcanic center may have existed existed on the the western western margin margin of of the the graben graben near near 59 �______ Volcanics are mostly mostly high-TiOz high-Ti02 basalts, the Amnicon Complex where the Chengwatana Volcanics andesites and rhyolites. rhyolites. Clastic sedimentary rocks of the Oronto Oronto Group overlie overlie the volcanic volcanic rocks. rocks. Only Only the the basal basal unit, the Copper Harbor Conglomerate, Conglomerate, is is preserved in most of of the the St. St. Croix Croix horst horst where where as as krn of sandstone and conglomerate conglomerate lie along along the the axis axis of of the the Ashland Ashland syncline. syncline. The The much as 2 km Copper Harbor thins to only a few tens of meters toward the northern northern end end of of the the horst horst in in the the same areas where the volcanic section also shows substantial substantial thinning. thinning. Apparently Apparently the the area area now comprising the northern part of the St. St. Croix Croix horst did did not not subside subside nearly nearly as as deeply deeply as as parts farther to the southwest. This relatively positive relief persisted throughout throughout volcanic volcanic activity and deposition of the Copper Harbor Conglomerate. Conglomerate. The The overlying overlying Nonesuch Nonesuch Shale Shale Ashland syncline, syncline, maintains a relatively uniform thickness around the northern part of of the the Ashland suggesting that the topographic high was buried by that time. time. 9 I OOO' 92W 47OO 47-00, EXPLANATION EXPLANATION Bayfield Bayfield Group Group and and equivalent sandstones i:: Freda Sandstone Nonesuch Shale Copper Copper Harbor Harbor Conglomerate Conglomerate Gabbro granophyre Gabbro and and granophyre \\\ Minong Volcanicslow-Ti basalts Minong Minong VolcanicsVolcanics- Y11 high.Ti basalts Chengwatana Volcanics Chengwatana Volcanics Kallander Creek Kallander Creek Volcanics Volcanics 1 Siemens Creek Siemens Creek Volcanics Volcanics Archean and Paleoproterozoic Paleoproterozoic rocks 46OO 46'00' 92°OO 0 30 60 90 KM Cannon, W.F., Daniels, D.L., Nicholson, S.W., SW., Phillips, Phillips, J., J., Woodruff, Woodruff, L.G., L.G., Chandler, Chandler, V.W., V.W., Morey, Morey, G.B., G.B., Boerboom, T., Wirth, KR., K.R.,and andMudrey, Mudrey,M.G., M.G., Jr., Jr., 2001, 2001, New New map map reveals reveals origin origin and and geology geology of North American American Midcontinent Midcontinent rift: EOS, EOS, v. v. 82, 82, no. no. 8, 8, pp. pp. 97-101 97-101 Chandler, Chandler, V.W., V.W., McSwiggen, McSwiggen, P.L., P.L., Morey, Morey, G.B., G.B., Hinze, Hinze, W.J., W.J., and and Anderson, Anderson,R.R., R.R.,1989, 1989,Interpretation Interpretationof of seismic seismic reflection, reflection, gravity, gravity, and and magnetic magnetic data data across across Middle Middle Proterozoic Proterozoic Mid-continent Mid-continentRift Rift system, system, northwestern northwestern Wisconsin, Wisconsin, eastern eastern Minnesota, Minnesota, and and central central Iowa: Iowa: American American Association Associationof of Petroleum PetroleumGeologists Geologists Bulletin, Bulletin, v. 73, 73, p. p. 261-275. 261-275. Nicholson, S.W., Boerboom, T., Cannon, Cannon, W.F., W.F., Wirth, Wirth, K. K. and and Isachsen, Isachsen, C.E., C.E., 2001, 2001, A A new new look look at at the the 1.1 1.1Ga Ga Boerboom, T., Chengwatana Chengwatana Volcanics Volcanics in the St. St. Croix Croix horst, horst, Minnesota Minnesota and Wisconsin, Wisconsin, Institute Institute on on Lake Lake Superior Superior Geology, Geology, v. 47, part 1, 1, p. 71-72. 71-72. 60 �of the Western Subcomplex of of the the Deadhorse Deadhorse Creek The Rare and Exotic Mineralogy of Diatreme, Northwestern Ontario. Ontario. Eric G. Potter and Roger Roger H. Mitchell egpotter@mail.lakeheadu.ca egpotter@mail.lakeheadu.ca Dept. of Geology, Lakehead University, 955 Oliver Road, Thunder Bay, ON. P7B 5E1 5E1 The main mineralized zone of the western western subcomplex of the Deadhorse Creek diatreme exhibits complex involving: first first and second exhibits complex mineralization mineralization involving: second order order transition transition metals metals (specifically Sc, Ti, Ti, V, V, Cr, Mn, Mn, Fe, Fe, Zr Zr and and Nb); Nb); REE; REE; Be; Be; Th; Th; and and U. U. The The mineralization mineralization (specifically Sc, is manifested by the presence of of the the following following minerals: minerals: thortveitiite, thortveitiite, Sc-V-aegirine, Sc-V-aegirine,NbNbV-rutile, V-crichtonite, Ba-Mn-hollandite, zircon, monazite-Ce, monazite-Ce, xenotime-Y, uraninite, tyuyamunite, phenacite, thorite, thorogummite, thorite, thorogummite, barite, barite, barylite, tyuyamunite, phenacite, pyrite, pyrite, hematite, magnetite and several as of yet unnamed mineral species (Platt (Platt and and Mitchell, Mitchell, 1996; 1996;Smyk Smyk et a!., al., 1993; 1993; this study). Of Ofinterest interestininthis thispresentation presentation are: are:Nb-V-rutile, Nb-V-rutile, cnchtonite crichtoniteand and Sc-V-aegirine. Sc-V-aegirine. I I The Nb-V-rutile The Nb-V-rutile is enriched in Cr203, Cr203,with concentrations concentrations reaching Alkaline Igneous Suites 30 30 ,--. The 6.49 wt.%. wt.%. The enrichment enrichment of of &: Cr203 and Cr2O3 and Nb2O5 Nb2O5isis similar similar to that 80 A Xenoliths in Kimberlite of rutile reported in alkaline igneous reported alkaline igneous 20 2o rocks, as illustrated in an atomic rocks, illustrated an atomic t-1+ - percent percentplot plotofofcr3+ Cr3 ++ Nb5* Nb5 + ~Ta5a ~ ^ "0 1991). (Haggerty, vs. Ti4i ~ (Haggerty, vs. ~ * 1991). z+ lo However, the Nb205 However, the Nb205 contents contents are are 3 unusually high compared to alkaline compared Lunar Meteorites igneous igneous rocks in general, general, with 0 0 29.32 90 95 50 55 60 65 75 80 85 50 55 60 65 70 75 80 85 90 95 100 100 concentrations concentrations reaching 29.32 , <.a+ Ti 11 (Atomic (Atomic °') o,/o) wt.%. Such such Nb2O5 m205contents contents are are wt.%. which is is historically historicallyfound foundin in pegmatites. pegmatites. Also similar to those reported in ilmenorutile, which unique to the Deadhorse Creek Creek rutile rutile is the distinct of V203 (up to 10.52 unique distinct enrichment enrichment of V203 (up 10.52 wt.%) and the lack of tantalum. tantalum. I I I I I I I !! Deadhorse Creek contain the The Sc-V-aegirines present at Deadhorse The Sc-V-aegirines the highest reported of Sc203 Sc203 and V203 V203 (16.46 (16.46 and and 11.99 wt.%, wt.%, respectively). respectively). The concentrations of The only only other other have been occurrences of occurrences of VV- and andSc-enriched Sc-enriched aegirine aegirine have been reported reported from from alkaline alkaline a!., 1994; metasomatites associated with iron-ore deposits in Ukraine (Valter et al., 1994; Pavlishin presence thortveitiite (Sc2Si2O7) et al., al., 2000). 2000). OfOfnote noteis isthethe presenceofofboth both thortveitiite (Sc2Si207)and andSc-enriched Sc-enriched within the main main mineralized mineralized zone. zone. Although aegirine within Although the the source source of of the the Sc Sc in in the the aegirine aegirine remains somewhat somewhat conjectural, conjectural,itit appears appearsthat thatthe the Sc, Sc, V V and Na was remains was scavenged scavenged from alteration of the main mineralized mineralized zone by Fe-rich fluids. fluids. analogues of of crichtonite-(Sr) and The V-rich crichtonites are best termed vanadium-rich analogues senaite-(Pb). The Nb2O5in the crichtonites is peculiar, as the presence presence of Theenrichment enrichmentin inNb2O5 Nb has been a distinguishing distinguishing feature feature of of the the mantle-derived mantle-derived end end members members lindsleyite-(Ba) lindsleyite-(Ba) 61 �_____________________ ___________________ __________________ and mathiasite-(K) mathiasite-(K) (LIMA). (LIMA). Interestingly, Interestingly, the the crichtonites crichtonites plot plot in the theupper-mantle upper-mantle LIMA quadrant quadrant of of FeO ++ Fe203 LIMA Fe203++ MgO MgO vs. vs. TiO2 Ti02(Haggerty, (Haggerty, 1991), 1991), near the the LIMA LIMA compositions due to the the replacement replacement of of iron iron by vanadium. vanadium. The Nb-enriched rutiles mtiles and crichtonite crichtonite are believed to to have have Non-Kimberlitic Crichtpnite in formed aa formed relatively early in 30 C,,chtornte (Sr). Davthtc (UREB) Armalcolite Ouadrant multistage-alteration sequence of the the Deadhorse Creek diatreme by Senaite (Pb), 25 of stoichiometric rutile with reaction mtile Lovetingite (Ca). hydrous alkaline solutions hydrous solutions enriched enriched 20 1 These hydrous Nb and V. in Nb and V. hydrous Upper-Mantle LIMA Crichtonite alkaline solutions likely also also altered altered Armalcolite Armalcolite Ouand.rant Ouandrant 15 unnamed hydrated zircon to to an unnamed hydrated -DFIC Crichtomtc calcium zirconosilicate, zirconosilicate, which is is JIMA cric(ttonites__Pptle 10 found in association with the 56 52 56 60 64 68 72 60 64 68 crichtonite and rutile. rutile. Textural and and /o) TiO, (Wt.%) 1102 (Wt. compositional data suggest suggest that imparted the pervasive subsequent alteration alteration formed the Sc-V-aegirines Sc-V-aegirines and imparted pervasive hematitization hematitization to the the main main mineralized mineralized zone. zone. 35 I I I — I I References References Haggerty, S.E. (1991): of the upper (1991): Oxide Oxide mineralogy mineralogy of upper mantle. mantle. In: In: Oxide Oxide Minerals: Minerals: petrologic and 25, Mineral. Mineral.Soc. Soc. and magnetic magnetic significance. significance. Reviews Reviewsin inMineralogy, Mineralogy, 25, Amer., 335-416. 335-416. Platt, R.G. and and Mitchell, Mitchell, R.H. R.H. (1996): (1996): Transition Transition metal metal rutiles mtiles and titanates titanates from from the the Miner. Miner. Deadhorse Creek Diatreme complex, northwestern Ontario, Canada. Deadhorse Diatreme complex, northwestern Ontario, Canada. 403-413. Mag., 60, 60,403-413. Pavlishin, V.I., V.1., Baklan, Baklan, F.G., F.G., Bugaenko, V.M., Voznyak, D.K., Galaburda, Pavlishin, Bugaenko, V.M., Voznyak, D.K., Galaburda, Yu, A., A., Dekhtulins'ky, E.S., Donskey, O.M., Krivdik, S.G., Kulchic'ka, G.O., Mel'nikov, V.S., Radzivill, A, Ya. Ya. And And Zimbal, Zimbal, S.M. S.M. (2000): (2000): Science-based Science-basedperspectives perspectives of of improvement of of mineral mineral resources resourcesor orrare raremetals metalsinin Ukraine. Ukraine. Mineral., Journal, improvement 22, no.1, 1, 5-20. 5-20. (in Russian) Russian) 22, no. Smyk, M.C., Taylor, R.P., Jones, Smyk, M.C., Taylor, R.P., Jones, P.C. and and Kingston, Kingston, D.M. D.M. (1993): (1993): Geology Geology and and geochemistry of the West Dead Dead Horse Horse Creek Creek rare-metal rare-metal occurrence, occurrence, northwestern northwestern Ontario. Explor. Mining. Geol., Ontario. Geol., 2, no. 3, 245-251. 245-251. Sharkin, O.P. and and Yakolev, Yakolev, V.M. V.M. (1994): (1994): AAvanadian vanadian Valter, A.A., Khomenko, V.M., Sharkin, aegirine in alkaline alkaline metasomatites from Zheltye Vody. Dokiady DokladyAkademii Akademii Nauk Ukrainy, No. 3, 110-116. 110-116. (in Russian) 62 �methods: Possible Sibley Basin sediment provenance using zircon and and whole whole rock rock geochemical methods: source areas of the Pass Lake Formation Richardson, A., A., Fralick, Fralick,P., P.,and andHollings, Hollings,P.P.(Department (DepartmentofofGeology, Geology,Lakehead LakeheadUniversity, University, 955 Richardson, SE!, Canada; Oliver Rd., Thunder Bay, Ontario, P7B 5E1, Canada; ajrichar@mail.lakeheadu.ca) airichar@mail.lakeheadu.ca) [CANADA A. +4+ - + + 48 $upfls. + +4+1 + + + +1 USA L. Huron 4__u_,r ' —+ 4 4 +++ +4+ 4 30km 4+ ++4 ÷4+ LSGEND II. Proterozoic 4+4. 1097 Ma V Odor Group 1110 Ma *4 1.. 1 / 1537 EJ GranfteMa and Rhyolit. l800Ma Arilmikie Group AnImikle Group Archean Granific anmitic Rocks R W ~ ^] Metasedimentary Metasedlrnentary a MÇ.VOIC;~, .4* 4+ ++ + epa.s ÷+ >1339Ma Sibley Group 9 + Rocks Rocks 1 .1 Lake Superior The Sibley Group consists of Proterozoic Proterozoic sediments sediments that outcrop discontinuously over a 15000 15000 sq. km region in the area surrounding central and southern Lake Nipigon. Its age is bracketed bracketed by the underlying underlying Redstone Redstone Point Point Complex Complex (1537 (1537 +101-2 Ma; Davis and Sutcliffe, +/- 33 33 Ma Ma +lo/-2 Ma; Sutcliffe, 1985) 1985)and andaa1339 1339+1Rb-Sr age on diagenetically diagenetically altered altered Sibley Sibley sediments sediments(Franklin, (Franklin, 1978). The Sibley Group was divided into three formations: the Kama Hill Formation Formation (top), (top), the the Rossport Rossport Formation, Formation, and and the the Pass Lake Formation (bottom), by Franklin, et al. (1980). The The Kama Hill Formation Formation consists consists of aa laminated laminatedshale shale facies, facies,the the Rossport of mudstone mudstone and stromatolitic stromatolitic facies, facies, and and the the Pass Lake of a conglomeratic conglomeratic facies facies and and aa plane-bedded plane-beddedor or crosscrossbedded sandstone sandstone facies (Cheadle, (Cheadle, 1986). 1986).This This study study investigates investigates the sources sources that fed sediment sediment to to the the Pass Pass Lake Lake Formation in the southern portion of the basin. Formation southern portion basin. Regional granitic granitic sources sources may include: include: the the Mesoproterozoic Redstone Point anorogenic intrusion, Redstone Point anorogenic intrusion, mpjjQfions Neoarchean peraluminous Quetico Quetico granites, granites, and and Redstone Point Granite McKenzie granites. Of Of these, these,the theRedstone RedstonePoint Point isis more more highly evolved than the others others and contains contains abundant abundant Regional Granltes Granites R Regional zircon and a distinct distinct geochemical geochemical signature signaturewith with very very • Pass PassLake LakeFm, elevated values for the high field Fm. field strength strength elements elements (HFSE). (HFSE). Samples Samples were collected collected from from surface surface exposures exposuresat at several several locations l o c a t i o n(Fig. s ( ~ i1). ~ . Representative Representativesamples samplesof of the the Pass Pass Lake Lake Formation of the Sibley Group Group were were taken taken from from aa cliff cliff section section directly across from Pass Lake on Hwy. 587. Individual Individual beds beds were grouped into assemblages consisting of of up up to to 16 beds. beds. Bed thickness total of of thickness became finer and thinner up section. AA total 26 hand samples were obtained from the Pass Lake cliff and consisted of of fine fine to to medium medium grained grained sandstone. sandstone. Two additional additional Pass Lake Formation Formation samples samples were were obtained obtained from from road road cuts cuts further further up-section up-sectionthat that consisted consistedof of medium medium grained grained sandstone. sandstone. Figure Fiigure 1. 1. Regional Regionalgeologic geologicmap mapwith withsample sample locations. locations. Additional granitic granitic samples were obtained from from road cuts cuts along along Hwy Hwy 11/17 11/17 Hwy. 527 527 (Fig. (Fig. 1). One sample was was taken taken from from each each location. location. Samples and Hwy. of Redstone Point sandstones, and granite samples were previously obtained obtained by P. Fralick Fralick from the English Bay region of Lake Nipigon (Fig. (Fig. 1). 1). Figure Fiigure 2. 2. Backscatter Backscatter X-Ray X-Ray SEM-EDS image of a zircon from sample AR-Ol. AR-01. ICP-AES (inductively Coupled Plasma -- Atomic Emission Spectroscopy) ICP-AES (Inductively Spectroscopy) Samples were cut into approximately 4 x 3 x 0.5 cm sections sections and crushed to a fine powder of <30 microns. Chemical Chemical preparation preparationincluded included hydrofluoric acid digestion to remove all silica and allow complete complete solution solution of samples. Prepared Prepared samples samples were were analysed analysed at at the the Lakehead University Instrument Laboratory. 63 �SEM-EDS (Scanning (Scanning Electron Microscope -- Energy Dispersive X-Ray Microanalysis) SEM-EDS X-Ray Microanalysis) Samples were ground to 30 micron thin sections and cut into discs suitable for the SEM stage. Before Before analysis, analysis, samples samples were carbon coated to prevent charge build- up while being analysed. Samples analysed. Samples were were analysed analysed for for 50 50 seconds seconds with with an an accelerating voltage of 20 KeV, and a beam current of 0.475 pA using a JEOL 5900 5900 SEM SEM with a system system resolution resolution of of 139 139 University Instrument Instrument Laboratory. Laboratory. Images eV, at Lakehead University taken using using aa backscatter-electron backscatter-electron detector. detector. Zircons were taken Zircons were analysed for five elements: Zr, Y, Th, U, and Hf. The use of zircons in sediment provenance studies has been 1o*Y+Th+U limited to work done by Owen (1987) (1987) which involved employing hafnium content of detrital zircons in determining Figure 3. SEM-EDS SEM-EDS analyses analyses of zircons zircons from from the source of the upper Jackfork Sandstone and the Parkwood Fm sandstones (points), (points) Redstone Pass Lake Fm Formation. He Hecame came to to the the conclusion conclusion that that hafnium hafnium content content Point sandstones (squares), Redstone Point these zircons agreed with optical and cathodoluminescence of optical and cathodoluminescence (ranites (+), Granites (+),and andregional regional Archean Archean and modal analyses, and is a viable method for provenance Neoarchean granites (triangles), (triangles). determination. determination. This study is the first to use SEM-EDS SEM-EDS methods methods as as well well as as analyses for Y, Th, and U. U. Fig. results. The Fig. 33 shows shows zircon analysis results. The majority majority of of zircons zircons plot at Zr/Hf ZdHf ratio of significant population population show show aa Y, Y, Th, Th, U approximately 40 with relatively low amounts of Y, Th, and U, but a significant enrichment trend. The enrichment trend. The geochemical geochemical signature signature of zircons from both sandstones sandstones and granites show show 3000 of sediment similarity, and indicates local sourcing sourcing sediment A with a possible influence influence of of regional regional Archean Archean and and . Proterozoic felsic igneous intrusives. 2000 2000 0 Whole rock interpretation interpretation of of ICP-AES ICP-AES ppm Zr/%Ti02 geochemistry (Fig. 4) trends agree with SEM 11000 ow elemental distribution within samples. Immobile Immobile element ratios of the the Pass Pass Lake Lake sandstones sandstones tend tend to to enriched and nonfall on a mixing trend between J 0 0 25 50 125 150 175 sources. This O 25 50 ppm 75Nb/%Ti02 loo Iz5 150 175 enriched sourc&. This study study highlights highlights the possible ppm Nb/%T02 usefulness of using SEM-EDS generated data in concert with more traditional chemical chemical analyses analyses in Figure 4. Immobile Immobileelement elementplot plot of of ICP-AES ICP-AESanalyses. analyses, provenance studies. Pass Lake Lake sandstones sandstones (points) (points)plot plot in in similar similarfield field to to sandstones derived from, and overlying overlying Redstone Redstone Point granite (squares). Redstone Redstone point granite (+), and other (triangles) are also shown. granites (triangles) shown. . ' I A I References References Cheadle, Cheadle, B.A. (1986) (1986)Alluvial-playa Alluvial-playa sedimentation sedimentationin in the the lower lower Keweenawan Keweenawan Sibley Sibley Group, Group,Thunder ThunderBay BayDistrict, District, Ontario; Ontario; Canadian Canadian Journal Journal of of Earth Earth Sciences, Sciences,v. v. 23, 23, p. p. 527-542. 527-542. Davis, D., and Sutcliffe, of Sutcliffe, R., (1985) (1985) U-Pb ages from the Nipigon Plate and Northern Lake Superior. Geological Society of America Bulletin, Bulletin, 96, 96, 1572-1579. 1572-1579. Franklin, age studies, Report Report 2, geological Franklin, J.M., (1978) (1978) The Sibley Sibley Group, Group, Ontario; Ontario; in Rubidium-strontium isochron age Survey Survey of Canada, Canada,Paper Paper 77-14, 77-14,p.p.331-34. 1-34. Franklin, J.M., J.M., McIlwaine, Mcllwaine, W.H., Franklin, W.H., Poulsen, Poulsen, K.H. and Wanless, R.K. (1980) (1980) Stratigraphy and depositional setting of the Sibley Sibley Group, Thunder bay District Ontario, Ontario, Canada; Canadian Journal of Earth Sciences, v. 17, p.633-651. Owen, M. (1987) 57, No.5., 1-838. (1987)Hafnium Hafnium in in Detrital Detrital Zircons: Zircons: Journal Journal of of Sedimentary SedimentaryPetrology, Petrology,Vol Vol57, NOS.,1987., 1987.,p.p.83 831-838. 64 �A Magnetostratigraphic Magnetostratigraphic and andSecular SecularVariation VariationStudy Studyof of the theSibley Sibley Group Group Rogala, P. and Borradaile, G. (Department of Geology, Lakehead University, Thunder Rogala,B., B.,Fralick, Fralick, P. and Borradaile, G. (Department of Geology, Lakehead University, ThunderBay, Bay, brogala@lakeheadu.ca) Ontario, P7B 5E1, brogala@lakeheadu.ca) The Sibley Group is aa red red bed bed sequence sequence that that was was deposited deposited in in aasubsiding subsidingintracratonic intracratonic basin (Fralick and Kissin, 1995) 1995)overlying, overlying, in part, part, aa 1537+10-2 1537+10-2Ma Ma (Davis (Davisand andSutcliffe, Sutcliffe,1984) 1984) The Group anorogenic anorogenic granite-rhyolite granite-rhyolite complex. complex. The Group was was previously previously divided divided into into three three main main Formations: Pass Lake, Rossport, and Kama Kama Hill. An An unnamed unnamed Formation Formation and and the the Nipigon Nipigon Bay Bay Formation have recently recently been been added. added. The The Pass PassLake LakeFormation Formation consists consists of of the theconglomeratic conglomeratic Formation have Loon of the Fork Loon Lake Member Member and the the sheet-like sheet-like sandstones sandstones of Fork Bay Bay Member, Member, representing representing a The Rossport braided environment (Cheadle, (Cheadle, 1986). 1986). The Rossport Formation Formation is separated separated into the the braided fluvial environment Channel Island, Middlebrun Bay, and Fire Hill Members. The Channel Island Member is Channel Island, Middlebrun Bay, and Fire Hill Members. The Channel Island Member aa The cyclic unit interpreted interpreted to to be playa cyclic dolomite-shale dolomite-shale unit playa lake lakesediments sediments(Cheadle, (Cheadle, 1986). 1986). The Middlebrun Bay Member, considered a marker bed for the Sibley Sibley Group, Group, isis aastromatolitic stromatoliticunit unit that represents a migrating strandline. The The Fire Fire Hill Hill Member Member consists consists of mudcracked mudcracked red silt with mudchip conglomerates and sand of tectonic tectonic tilting tilting of of the the sand sheet sheet incursions. incursions. It signifies a time of The Kama basin. basin. The Kama Hill Formation Formation is not not subdivided, subdivided, and is is composed composed of of purple purple shales shales and and siltstones interpreted as mud flat deposits (Cheadle, (Cheadle, 1986). The Theunnamed unnamed Formation Formation isis divided divided These represent represent aa deltaic deltaic and and fluvial fluvial environment. environment. The TheNipigon Nipigon into two unnamed Members. Members. These Bay Formation consists of cross-stratified sandstone beds, beds, and and is thought to denote denote an an aeolian aeolian environment. environment. Samples were taken taken from Samples were from the the Pass Pass Lake, Lake, Rossport, Rossport, Kama Kama Hill, Hill, and and Nipigon Nipigon Bay Bay Formations for a paleomagnetic paleomagnetic study. study. The unnamed Formation was not sampled due to the lack of exposure. The ThePass PassLake, Lake,Kama KamaHill, Hill,and andNipigon Nipigon Bay Bay Formation Formation were were used used to to conduct conduct aa preliminary study of of the magnetostratigraphy of the the Sibley Group. The TheRossport RossportFormation Formation was was magnetostratigraphy of sampled from unoriented drill drill core, core, thus thus could could only only be be used used to to study study secular secularvariation. variation. The paleopoles calculated from the Pass Lake, Lake, Kama Kama Hill, Hill, and and Nipigon Nipigon Bay Bay Formations Formations have been plotted along an apparent polar wander path (APWP) defined by Elston et al. (2002) (2002) Elston et al. an apparent polar wander (APWP) defined (Figure 1). 1). The samples samples from from the the Pass Pass Lake Lake Formation Formation have have been been divided dividedinto intosample samplegroups groups corresponding to Quarry Island, Transitional to the Rossport Formation, and and an an outcrop outcrop at at Pass Pass The paleopole of the with a diagenetic Lake. Lake. The paleopole of the Quarry Quarry Island Island Group Group corresponds corresponds with diagenetic event event at 1978), and and the latter 1339±3 Ma (Franklin, (Franklin, 1978), latter two two groups groups have havepaleopoles paleopoles approximately 1339±33 approximately The Kama has an older associated with with an an early earlyKeweenawan Keweenawan overprint. overprint. The Kama Hill Formation Formation has older associated discordant paleopole paleopole and a younger paleopole paleopole that that is is located within within the 1500 Ma section of the that the the Sibley Basin formed formed prior prior to to this, this, as is apparent apparent polar wander wander path. path. This This suggests suggests that Sibley Basin supported by the recent discovery discovery of sedimentary sedimentary xenoliths within the 1537 1537 Ma Ma Redstone Redstone Point Point Formation has has paleopoles paleopoles that that lie lie on on the APWP near 1400 granite. granite. The Nipigon Bay Formation 1400 Ma and and 1100 Ma. The Thefirst firstpaleopole paleopolemay maybe beprimary primary or orrelated related to to the thediagenetic diageneticevent eventthat thataffected affectedthe the Pass Lake samples at 1339 OsierVolcanics. Volcanics. 1339 Ma. The Thelatter latterpaleopole paleopole correlates correlateswith with the the Osler The paleomagnetic study on a 90 90 cm cm core core section section from from the the Rossport Rossport Formation Formationrevealed revealed aa When this curve variation curve. curve. When curve was was compared compared to to typical typical secular secular variation variation curves curves secular variation (Butler, 1998; Tauxe, Tauxe, 1998), the the time-span time-span for for Sibley Sibley deposition depositioncan canbe be estimated. estimated. The 90 (Butler, 90 cm cm section was estimated to represent represent 2500 2500 to to 3000 years. years. This This can can be be extrapolated extrapolated to estimate estimate that the Rossport Formation could potentially represent 75 000 years of deposition. Rossport Formation could potentially represent 75 000 years of deposition. 65 �Figure Figure4.12 4.12 AAwell-defined well-definedProterozoic ProterozoicApparent ApparentPolar PolarWander WanderPaths Paths(APWP) (APWP)isisplotted plotted (after Elston et al., al., 2002). 2002). The ThePass PassLake LakePCA PCAcomponents componentsare aredesignate designatewith with QI, QI,T, T, and indicatethe theQuarry QuarryIsland, Island,Transitional, Transitional, and and Outcrop Groups. The TheKama Kama Hill Hill and 00totoindicate Formation is designate KH and the Nipigon Bay Bay Formation Formation is is NB. NB. The The PCA, PCB, and PCC PCC components components are are denoted denoted respectively respectively by A, B or C after the Formation short short form. Note that NB-C is a reversed pole on the back side of of the the globe. globe. Elston Elston et et al. al. (2002) (2002) has has provided a lower (Si) (Sl)and andupper upper (S2) (S2) Sibley Sibley Group Group pole pole based on data from Robertson (1973), as well as a pole for the Keweenawan Keweenawan Osler Osier Group (Ki) (Kl)and and lower lower Powder Powder Mill Mill Volcanics (K2). (K2). magnetic domains domains to to geological Butler, R.F. R.F. 1998. 1998. Paleomagnetism: Butler, Paleomagnetism: magnetic geological terranes, terranes, Department Department of of Geosciences Geosciences University (originally published published by http://www.~eo.arizona.edu/Paleomae/book/ (originally by Blackwell Blackwell University of of Arizona, Arizona,http://www.geo.arizona.edu/Paleomag/book/ Scientific Publications Publications in in 1992) 1992) Scientific Cheadle, B.A. B.A. 1986. Alluvial-playa Cheadle, Sibley Group, Group, Thunder Thunder Bay Bay District, District, Alluvial-playasedimentation sedimentationin inthe thelower lowerKeweenawan Keweenawan Sibley CanadianJournal JournalofofEarth EarthSciences, Sciences,23, 23,527-542. Ontario. Canadian 527-542. Davis, D.W. and Sutcliffe, R.H. R.H. 1984. Geological 1984.U-Pb U-Pbages agesfrom fromthe theNipigon NipigonPlate Plate and and Northern Northern Lake Lake Superior. Superior. Geological 96, 1572-1579. 1572-1579. Society of America America Bulletin, 96, Elston, D.P., Enkin, R.J., Baker, Baker, J.J. and and Kisilevsky, Kisilevsky, D.K. D.K. (2002). (2002).Tightening Tighteningthe theBelt: Belt:paleomagnetic-stratigraphic paleomagnetic-stratigraphic constraints constraints on deposition, deposition, correlation, correlation, and and deformation deformation of of the the Middle Middle Proterozoic Proterozoic (ca. (ca.1.4 1.4Ga) Ga)Belt-Purcell Belt-Purcell GeologicalSociety Society of of America Bulletin, 114, 114,619-638. Supergroup, United States and Canada. Geological 619-638. basin development in central North America: and Kissin, Kissin, S. S. 1995. Fralick, P. and 1995. Mesoproterozoic Mesoproterozoic basin development in America: implications implications of Sibley Group volcanism volcanism and and sedimentation sedimentation at at Redstone Redstone Point. Point. In: Petrology Petrology and and metallogeny metallogeny of of volcanic volcanic Proceedings of of the the International International Geological Geological and intrusive intrusive rocks rocks of of the themid-continent mid-continent rift rift system, system, Proceedings and Correlation Program, 336. Program, Project Project 336. Franklin, J.M. J.M. 1978. Franklin, in: Wanless, Wanless,R.K. R.K.and andLoveridge, Loveridge,W.D., W.D.,Rubidium-strontium Rubidium-strontium 1978. The Sibley Sibley Group, Group, Ontario, Ontario, in: isotopic age studies, report report 2. Geological Geological Survey Survey of Canada Paper Paper 77-14, 77-14, 31-34. 3 1-34. W.A. (1973a). (1973a). Pole position position from from thermally thermally cleaned Sibley Sibley Group Group sediments sediments and and its its relevance relevance to to Robertson, W.A. Proterozoic magnetic stratigraphy. Canadian Canadian Journal Journal of of Earth Earth Sciences Sciences,10, 10,180-193. 180-193. Tauxe, L. 1998. KluwerAcademic Academic Publishers, Publishers, Netherlands, Netherlands, 299 p. 1998.Paleomagnetic Paleomagneticprinciples principlesand andpractice, practice,Kluwer 66 �Mafic Dikes Dikes in in Marquette Marquette County, County,Michigan Michigan with with Sequence of Precambrian Precambrian Mafic Sugarloaf Mountain Mountain and and Republic Republic Areas emphasis on the Sugarloaf Sandin and and T.J. T.J. Bornhorst Bornhorst (Department of Geological and Mining Engineering and N.A. Sandin Sciences, Sciences,Michigan Michigan Technological TechnologicalUniversity, University,Floughton, Houghton,MI MI49931) 49931) Precambrian Precambrian mafic mafic dikes dikes are arevery very common common throughout throughout Marquette MarquetteCounty, County,Michigan. Michigan.These These 1.1 Ga). dikes Archean(—2.7 (-2.7 Ga) Ga)to tomiddle middleProterozoic Proterozoic(— (-1.1 Ga). Past Past studies studiesby by Kantor Kantor dikes have haveages agesfrom fromArchean (1968), (1968), Gair (1969), (1969), Cannon Cannon (1974), (1974),and and Baxter Baxter and and Bornhorst Bornhorst (1988) (1988)have havesuggested suggestedup upto tosix six different of different mafic dike events in Marquette County. These events were interpreted to consist of (from Archean mafic mafic dikes dikes post-Archean post-Archean volcanism volcanism and and before before Archean Archean (from old to young): young): 1) 1) Archean granitoid intrusions intrusions which cut the Archean volcanic rocks; 2) Archean mafic dikes that cut Archean granitoid intrusions, intrusions, but but are are subjected subjectedto to Archean Archean deformation; deformation;3) 3)Archean Archeanmafic maficdikes dikes that cut Archean basement rocks, but do not cut Early Proterozoic sedimentary rocks of the that cut Archean basement rocks, but do not cut Early Proterozoic sedimentary rocks of the Marquette 4) Early Early Proterozoic Proterozoic mafic mafic dikes dikesthat thatcut cutMarquette MarquetteRange Range Marquette Range Range Supergroup; Supergroup;4) Supergroup Supergroup sedimentary sedimentaryrocks prior prior to to Penokean Penokean metamorphism metamorphism and and deformation; deformation;5-6) 5-6)N-S N-Sand and E-W E-W Keweenawan Keweenawan mafic mafic dikes. dikes. This This study study has confirmed confirmed much of Baxter and Bomhorst Bornhorst (1988), however, however, new new data data indicate indicatesignificant significantmodifications. modifications. This This study study focused focusedon on the the Sugarloaf SugarloafMountain Mountain area areanear near Marquette, Marquette,MI MIbecause becauseof ofthe the excellent excellent exposures exposures on on shore shore and and adjacent adjacent to to Lake Superior, Superior, and previous work by Kantor (1968), (1968), who identified identified mafic mafic dikes dikes of of multiple multiple ages. ages. In In the the Sugarloaf Sugarloaf Mountain Mountainarea areaover over300 300 mafic dikes Archean tonalitic tonalitic basement basement were were identified identifiedand andmapped mappedusing usingaaGPS GPS dikes intruding intruding Archean receiver receiver and and the the compass compass and and pace method. Dikes Dikesidentified identifiedas ascritically criticallyimportant importanttoto understanding the the sequence sequence of of events events were were sampled sampled for for microscopic microscopic and andchemical chemicalstudy. study. Baxter Baxter and and Bornhorst Bornhorst (1988) (1988) interpreted interpreted thin, thin, discontinuous, discontinuous, tabular tabular mafic mafic bodies at Wetmore post-plutoniclpre-deformation Wetmore Landing Landingin in the the Sugarloaf SugarloafMt. Mt.area areaas asbeing beingArchean Archeanpost-plutonic/pre-deformation mafic dikes (number (number 2 above). While this interpretation interpretation is still possible, the favored interpretation interpretation here is that these mafic bodies are xenoliths that were deformed during the Archean along with the the host host plutonic plutonic rocks. rocks. In Marquette Marquette County, County, Baxter Baxter and and Bornhorst Bornhorst (1988) (1988)as as well well as asprevious previousworkers workersrecognized recognized the numerous mafic intrusives intrusives that that cut cut Marquette Marquette Range Range Supergroup Supergroupsedimentary sedimentaryrocks rocks prior prior to to Penokean metamorphism metamorphism and and deformation. deformation.These These were were presumed presumed to to be be of of generally generallythe the same same age. This study indicates indicates that in the the Sugarloaf Sugarloaf Mt. Mt. area, area, three three age age separate separatemafic mafic intrusive intrusiveevents events of this age are present. present. Based Based on on cross-cutting cross-cuttingrelationships, relationships,the the sequence sequenceconsists consistsof of diabase diabase dikes trending N20°E, N60°E, and and diabase diabase dikes dikes trending trending east-west. In N20°Ediabase dikes trending N60°E In addition to cross-cutting cross-cuttingrelationships, relationships,these these groups groups can can be be discriminated discriminatedfrom fromeach eachother otherby by trace elements. elements. trace The of the Early Proterozoic Proterozoic dikes. dikes. In The N20°E N20° diabase dikes are the oldest of In the the Sugarloaf SugarloafMt. Mt. area, these these dikes dikes vary vary in in trend trend from fromN05°E N05OE to to N20°E N 2 0 2 and range in width width from from one one to to25 25feet. feet. Mafic dikes of this age are the most common of the Early Proterozoic dikes in the Sugarloaf Mountain area. These Thesedikes dikesexhibit exhibitaavarying varyingtexture texturefrom fromporphyritic porphyritic to to phaneritic phaneritic from fromthe the dike dike interiors interiors to to the the margins. margins. They They consist consist of of hornblende, hornblende, pyroxenes, pyroxenes, chlorite, chlorite,plagioclase, plagioclase, epidote, epidote, and sericite. sericite. The TheREE REEpatterns patternsare areenriched enrichedin inlight-REE light-REEwith withaamoderate moderateslope. slope. Compared to the REE patterns of the sills from the Marquette Range Supergroup, the Compared REE patterns of the sills from the Marquette Range Supergroup, theN20°E N20° series has a higher concentration concentrationof of light-REE, light-REE,is is less less depleted depletedin in heavy-REE, heavy-REE, and andhas hasaa shallower shallower slope. Thus, Thus,our ourinitial initialinterpretation interpretationisisthat thatthese thesedikes dikesare arenot notrelated relatedto tothe thesills. sills. 67 �The N60°E mafic dikes dikes are intermediate intermediate Early Early Proterozoic Proterozoic age. age. They vary in trend from N60° mafic N45°E N60°E and and range range in in width width from from one one to to 60 60 feet. feet. These These are are the the least least common of the Early N45OE to N60° Proterozoic dikes in the Sugarloaf Mountain area. They generally have They generally have thinly thinly foliated foliated margins margins fine-grained interiors. interiors. These dikes have a phaneritic phaneritic texture texture and and consist consist of of with a massive, fine-grained hornblende, pyroxenes, chlorite, chlorite, plagioclase, plagioclase, epidote, epidote, sericite, sericite,and and minor minoramounts amountsof of carbonate. carbonate. diabase dikes. dikes. REE N20°diabase REE patterns are enriched enriched in light-REE light-REE and have These dikes cross-cut the N20°E N20% series and the sills of the Marquette Range Supergroup, Supergroup, a steep slope. Compared Comparedto to the the N20°E the N60°E dikes are more enriched in light-REE with a steeper N60°dikes steeper slope. The TheN60°E N60°dikes dikesare aremore more depleted in heavy-REE interpretation is that these heavy-REE than the N20°E N20° series. Our initial interpretation these dikes dikes are are aa distinct distinct magmatic event event with with respect respect to to the the earlier earlier N20°E N20° dikes and the mafic sills. sills. of the the Early Early Proterozoic Proterozoic dikes. dikes. They The east-east diabase dikes are the youngest series of They vary in width from from five five to to 75 75 feet feet wide. These dikes generally have thinly foliated foliated margins with aa massive, fine-grained fine-grained interior, interior, although although two two dikes dikes had had porphyritic porphyritic interiors. interiors.They They have have aa phaneritic texture and consist of hornblende, pyroxenes, chlorite, plagioclase, epidote, and sericite. sericite. These Thesedikes dikescross-cut cross-cutthe theN20°E N20Z diabase diabasedikes dikesand andthe theN60°E N60Z diabase diabasedikes. dikes.Compared Compared to the REE patterns of the sills from the Marquette Range Supergroup, the east-west dikes have a higher concentration of light-REE and a steeper slope. The The east-west east-westdikes dikes are are depleted depletedin in the the compared to the N20°E N20% dikes. They are lower in light-REE and have a shallower shallower heavy-REE compared slope than the N60°E interpretation is that these dikes are N60° series. Our initial interpretation are a distinct distinct magmatic magmatic event from the earlier earlier dikes dikes and and the mafic mafic sills. sills. Mt. Area. We propose that these There are three distinct mafic dike events in the Sugarloaf Mt. dikes are not related to the mafic mafic sills sills that that cut cut the the Marquette MarquetteRange Range Supergroup. Supergroup.IfIf true, true,then then and likely likely more, more, Early Proterozoic mafic magmatic magmatic pulses pulses in in the the there must be at least 4, and Marquette area. Marquette area. Two groups groups of unmetamorphosed diabase dikes were identified in the Sugarloaf Mt. area, consistent with Baxter and Bornhorst (1988). These Thesedikes dikesare are Keweenawan Keweenawan in in age age and and consist consist of of diabasictexture texture a north-south trending series and an east-west trending series. Both Both dikes dikes have have aa diabasic and vary from 10 10 to 75 75 feet wide. that some some metamorphosed metamorphosed In the Republic area, Baxter and Bornhorst (1988) suggested that mafic dikes with distinct distinct plagioclase plagioclase phenocrysts phenocrysts are are older older than the the metamorphosed metamorphosedProterozoic Proterozoic dikes in the Sugarloaf area. area. They proposed that these dikes dikes might might correlate correlate with with the the Matechewan Matechewan dike swarm north of Lake Superior Superior in Canada. Canada. We We tested tested this this hypothesis hypothesis by by doing doing chemical chemical analysis of these dikes. The REE data data for for these dikes dikes are are similar similar to to Matechewan Matechewan dikes dikesfrom from elsewhere and support support the hypothesis proposed proposed by Baxter Baxter and and Bornhorst Bornhorst (1988). (1988). References References Baxter, D.A. and Bornhorst, T.J., 1988, 1988, Multiple Discrete Mafic Intrusions of Archean to Keweenawan Age, 2 pp. western Upper Peninsula, Michigan: Michigan: Institute Institute on on Lake Lake Superior Superior Geology Geology Proceedings Proceedings and and Abstracts, Abstracts,v.v.34, 34,2 pp. U.S. Cannon, W.F., 1975, 1975, Bedrock Geological Map of the Republic Quadrangle, Marquette County, MI: U S . Geological Miscellaneous Investigations Survey, Miscellaneous InvestigationsSeries SeriesMap, Map,1-862. 1-862. Gair, J.E. and Thaden, R.E., 1968, 1968, Geology Geology of the Marquette and Sands Quadrangles, Marquette County, MI: U.S. 77 pp. Geological Survey Survey Professional Professional Paper Paper 397, 397,77 pp. Hails, H.C. and Phinney, Halls, Phinney, W.C., 2001, 2001, Petrogenesis Petrogenesisof of the the Early Early Proterozoic ProterozoicMatachewan MatachewanDyke DykeSwarm, Swarm,Canada, Canada,and and Implications for Magma Emplacement 22 38,22 Implications Emplacement and Subsequent Subsequent Deformation: Deformation: Canadian Canadian Journal Journal of of Earth Earth Sciences Sciences38, pp. PP. Kantor, J.A., 1969, 1969, Assimilation Assimilation and and Dike Dike Swarms Swarms in in the the Sugarloaf Sugarloaf Mountain Mountain Area, Area, Marquette MarquetteCounty, County,MI: MI:M.S. M.S. Thesis, Michigan Technological Technological University, University, Houghton, Houghton, MI, MI, 83 83 pp. pp. 68 �PALEOPROTEROZOIC DEVELOPMENT OF A GNEISS DOME CORRIDOR IN THE SOUTHERN LAKE SUPERIOR SUPERIOR REGION, REGION, USA SCHNEIDER, D.A., Dept. of Geological Sciences, Sciences, Ohio Ohio University, University, Athens, Athens, OH OH 45701; 45701; HOLM, D.K., and O'BOYLE, O'BOYLE, C., C., Dept. Dept. of of Geology, Geology, Kent Kent State State University, University, Kent, Kent, OH OH 44242; 44242; HAMILTON, M., Continental Continental Geoscience Division, Geological Survey of Canada, Ottawa, ON Canada; M., Dept. Dept. of of Geosciences, Geosciences, U-Mass, U-Mass, Amherst, Amherst,MA MA 01003 01003 Canada; and JERCINOVIC, JERCINOVIC, M., Paleo-reconstruction of a Paleo-reconstruction of the Penokean orogen at ca. 1750-1700 1750-1700 Ma reveals the presence of narrow corridor corridor of Archean Archean cored cored Paleoproterozoic Paleoproterozoic gneiss gneiss domes domes just north north of of and andparallel parallel to tothe the main suture zone in Minnesota, Wisconsin, and northern Michigan. Penokean Penokean (ca. (ca.1850 1850Ma) Ma) metasedimentary rocks infolded within the domes give predominantly 1750-1700 1750-1700 Ma cooling ages and are overlain depositionally depositionally by ca. ca. 1700 1700Ma Ma Baraboo Baraboo interval interval quartzites. quartzites.We Weconducted conducted U-Pb SHRIMP and total-Pb EMP geochronometry to obtain metamorphic timing constraints on distinct distinct monazite mineral domains domains from from amphibolite amphibolitegrade grade rocks rocks sampled sampledacross acrossthe theentire entirelength length of the gneiss dome corridor. Based Basedon onmetamorphic metamorphicmonazite monazite crystallization crystallizationages, ages,midcrustal midcrustal amphibolite amphibolite facies metamorphism (Ml) (Ml) peaked peaked around around 1830 1830Ma Ma and and was was concurrent concurrentwith with late late Penokean plutonism; subsequent thermal pulses are reliably recorded at ca. 1800 Ma (M2) and again at ca. 1765 1765 Ma (M3), (M3), both also also coeval coeval with with magmatic magmatic activity. activity. Ar-Ar mineral mineral age data, data, which which indicate indicate The youngest monazite ages overlap with abundant Ar-Ar widespread cooling cooling of the gneiss gneiss dome dome corridor corridor immediately immediately following followingM3. M3. We We propose propose that that the the of the tectonically buried gneiss domes formed at this time during structural modification of continental margin rocks. In Inour ourconceptual conceptual model model (Fig. (Fig.1), I), northward northward vertical vertical extrusion extrusionof of aa midcrustal block containing decoupled midcrustal containing the the gneiss gneiss dome dome corridor corridor accommodated accommodatedgravitational gravitational collapse of overthickened crust. Elevated Elevatedcountry country rock rock temperatures temperatures accompanied accompaniedwith with profuse profuse promoted doming of the lower melting (i.e., intrusion of the East-central Minnesota batholith) promoted density Archean basement into the more more dense dense overlying overlying Paleoproterozoic Paleoproterozoicmetasedimentary metasedimentary rocks, ultimately enabling its complete decoupling from the remaining lower crust. This This process, process, redistribution of of crustal crustal mass from thick to primarily driven by buoyancy forces, allows for the redistribution thin regions without significant horizontal crustal extension. Tectonic Tectonicextrusion extrusionand andcrustal crustal thinning at this stage stage may have have been facilitated facilitated by aa decrease decrease in in horizontal horizontal compressive compressivestresses stresses acting on the region from from the south south (i.e., (i.e., Yavapai Yavapai slab slab rollback rollback as as proposed proposed by by Hoim Holm et et a!., al., ILSG, 2003). In In our ourmodel model(Fig. (Fig.1), I),the thefaults faultsbounding bounding the the gneiss gneissdome domecorridor corridorare areca. ca. 1765 1765 Ma structures, structures, although some, some, like like the the Niagara Niagara Fault Fault zone, zone, are are reactivated reactivatedPenokean Penokean structures. structures. of the Malmo Structural We note that in east-central Minnesota, a significant portion of discontinuity juxtaposes post-Penokean plutons to the south against older metamorphic rocks to discontinuity of Mille Mule Lacs). This the north (west of This clearly clearly supports supports our interpretation that this structure (and the Flambeau Flowage fault equivalent in northern Wisconsin) was active well after Penokean orogenesis. orogenesis. Holm, D.K., Van Schmus, W.R., MacNeill, L.C., Boerboom, T.J., Schweitzer, D., and Schneider, Schneider, D.A., 2003, 2003, Late Paleoproterozoic Paleoproterozoic(1900-1600 (1900-1600 Ma) Ma) tectonic tectonic history history of of the the northern northern mid-continent, U.S.A.: Implications for crustal stabilization: Institute on Lake Superior mid-continent, Institute on Lake SuperiorGeology Geology abstracts (this abstracts (this volume). volume). 69 �Penokeanorugm, orogen,Ml: Ml: 1830 Ma to M2: Penohan 1830 Ma M2: 1800 1800 Ma Ma N N s$ warm, Penokean orogen, M3: 1768 Ma N ONEISS GNEISS DOME DOME CORRtDOR CORRIDOR WISCONSIN WISCONSIN MAGMATIC MAGMATIC TERRANE TERRAME (uveniIe Quvimiie island iaiad an;) arc) ARCHEAN GRANITE-GREENSTONE GRAWE-GREENSTONE ARCHEAN GNEISS E PALEOPROTEROZOIC ROCKS (supracrustal) Figure Figure 1. 1. Schematic SchematicN-S N-Scross-sections cross-sectionsatat1830-1800 1830-1800Ma Ma (A) and (B) depicting depictingthe the proposed proposed evolution evolution of ofthe the gneiss gneiss dome 1765 1765 Ma Ma (6) northern Wisconsin. Note corridor in northern Note relative relative locations locationsof of gray gray circles circles that represent represent depth depth of of crustal cruslaf blocks. blocks. 70 s$ �suprasubduction zone A Paleoproterozoic suprasubduction zone ophiolite-island ophiolite-island arc arc complex complex northeastern Wisconsin in northeastern Wisconsin Schulz, Klaus Schulz, Klaus J., J., (U.S. (U.S.Geological GeologicalSurvey, Survey,Reston, Reston,VA VA20192, 20192,kschuiz@usRs.Rov) kschulz@usgs.gov) The Paleoproterozoic Paleoproterozoic volcanic and associated associated intrusive rocks exposed in northeastern Wisconsin are the easternmost easternmost exposures exposures of the Pembine-Wausau terrane, the northernmost of the two Wisconsin magmatic terranes that were accreated to the southern margin of the Archean Archean Superior SuperiorCraton Craton during during the the Penokean Penokean Orogeny Orogeny (Sims (Simsand andothers, others, 1989). The The rocks rocks of of the the Pembine-Wausau Pembine-Wausau terrane are separated separated from the epicratonic epicratonic sedimentary rocks of the Marquette Marquette Range Supergroup sedimentary Supergroup to the north in Michigan Michigan by by the the Niagara fault fault zone. zone. The volcanic rocks of the Pembine-Wausau terrane exposed northeastern Wisconsin, formed synformed at about about 1,870 1,870Ma Ma and and are are cut cut by by aa variety variety of intrusive intrusive rocks rocks ranging ranging from from synvolcanic gabbros, diorites, and tonalities to syn-and post-tectonic granitoids (i.e., Dunbar Gneiss and related rocks). The Thevolcanic volcanicrocks rocksare aredivided divided into into four fourfault-bounded fault-boundedunits, units, the Quinnesec, Quinnesec, McAllister, Beecher, and Pemene formations. These Theseunits units are areinterpreted interpreted to record the evolution evolution of of aa Paleoproterozoic Paleoproterozoicsuprasubduction suprasubductionzone zone ophiolite-island ophiolite-islandarc arc complex, complex, the Pembine Pembine ophiolite-arc ophiolite-arccomplex. complex. The Quinnesec Formation is the oldest volcanic unit and consists predominantly of pillowed basalt flows and massive diabase, but includes andesite and rhyolite lava flows and fragmental rocks locally. Several Severallarge largegabbro gabbro sills sills are are present, present, particularly particularly near near the Niagara fault zone, some with peridotite and pyroxenite layers. In In addition, addition,aa large large serpentinized serpentinized peridotite-gabbro peridotite-gabbrobody that produces produces aa large large positive positive magnetic magneticanomaly anomalyisis exposed Timrns Lake Lake (Morgan (Morgan County County Park) Park) east east of of Pembine, Pembine,Wisconsin. Wisconsin. exposed south south of Timms Serpentinized Serpentinized pendotite peridotite is is dominant dominant in in the the western western part of of this this body where it is locally locally cut by coarse-grained coarse-grained (1-5 cm) dikes of pyroxenite. Layered Layered and massive massive gabbro gabbro and and masses of strongly strongly foliated-lineated foliated-lineatedgabbro gabbro are are dominant dominant in in the the eastern eastern part part of of the the body body where they are cut by numerous mafic dikes dikes with diabasic diabasic to to microdioritic microdioritictextures; textures;some some of the dikes dikes appear appear to be sheeted. sheeted. The rocks of the Quinnesec Quinnesec Formation Formation appear appear to to record record the the birth birth and and youth youth stages stagesof of aa zone ophiolite ophiolite (Shervais, (Shervais, 2001). 2001). Rocks formed fonned during the initial phase suprasubduction zone of ophiolite ophiolite evolution evolution typically typically include include layered layered and and isotropic isotropic plutonic plutonic gabbros, gabbros,sheeted sheeted dikes, and a "lower" volcanic section consisting of low-K tholeiitic basalt and basaltic consisting MORB and primitive arc tholeiite affinities. Gabbros Gabbros formed formed during during this this andesite with MORE stage are often ductilely deformed (foliated or boudinaged) in response response to syn-magmatic syn-magmatic extension. extension. Rocks Rocksformed formedduring duringthe thesecond secondor oryouth youth stage stageof of ophiolite ophioliteformation formationinclude include intrusive intrusive mafic-ultramafic mafic-ultramafic sills and diabase dikes, and an "upper" volcanic volcanic unit characterized characterized by basalt and and andesite andesite with highly highly depleted depleted incompatible incompatibletrace trace element element compositions compositions (i.e., low-Ti basalt, high-Mg andesite and boninite) (Shervais, 2001). Compositionally, Compositionally,the Quinnesec Quinnesec basalts basalts and and gabbros gabbros are are tholeiitic, tholeiitic,with with generally generallylow low Ti02 and TiOz and other other high field field strength strength element abundances, and flat to extremely light REE 71 �depleted patterns (Sims and others, 1989). 1989). In In addition, addition,some some of of the the basalts, basalts,gabbros, gabbros, and and andesites REE abundances, abundances, but but relatively relativelyhigh high Cr Cr and andNi Ni andesites have very low Ti02 TiOzand and REE contents. The Thetrace traceelement elementcharacteristics characteristicsof of the the mafic mafic rocks rocks overlap overlapthose those of of mid-ocean mid-ocean ridge basalts and primitive island-arc tholeiite suites whereas the andesites show fore-arc-relatedboninites. boninites. The presence in the upper part part of of compositional affinities with fore-arc-related Quinnesec Formation Formation of mafic rocks derived the Quinnesec derived from from highly highly refractory mantle mantle is is diagnostic of a relationship particularly diagnostic relationship to the early stages of intraoceanic intraoceanic subduction subductionand and This also also implies implies that that the the Quinnesec Quinnesec formation in a forearc setting (Shervais, 2001). This Formation Formation and associated associated rocks did not form in a back-arc basin near or on the margin of the Superior 1997),but but Superior Craton, Craton, as has recently been proposed (Van Wyck and and Johnson, Johnson, 1997), rather formed as an intraoceanic intraoceanic ophiolite-arc ophiolite-arc system system above a southward southward dipping dipping (in (in coordinates) subduction zone. present coordinates) The McAllister, McAllister, Beecher and Pemene formations consist of volcanic and volcaniclastic rocks ranging from from andesite andesite (McAllister) (McAllister)to to rhyolite rhyolite (Pemene), (Pemene), all all with with caic-alkaline calc-alkaline compositions compositions characteristic characteristic of mature oceanic arcs. These Thesevolcanic volcanic rocks rocksand andassociated associated Twelve Foot Foot Falls Falls Quartz Diorite, Diorite, appear intrusives, such as the Newingham Tonalite and Twelve compatible compatible with the third or maturity stage of suprasubduction zone ophiolite evolution (Shervais, 2001). Characteristic Characteristicof of this this stage stageare are intrusive intrusive rocks, rocks, such such as as hornblende hornblende rocks ranging ranging from from basalt basalt to to diorite, quartz diorite, and tonalite, as well as volcanic rocks rhyolite, all with transitional transitional to calc-alkaline calc-alkaline compositions. Volcanism Volcanismtypically typicallybecomes becomes more silicic with time in these sequences. In In many many cases, cases, rocks of of this this stage stage have have not been considered considered part of the subjacent subjacent ophiolite, but rather have been attributed to postophiolite ophiolite arc volcanism volcanism (Shervais, (Shervais,2001). 2001). It appears likely that growth of the Pembine Pembine ophiolite-arc ophiolite-arccomplex complex was was terminated terminatedby by its its collision obduction onto the passive southern margin of the Superior Craton. collision with and obduction Because subduction appears appears to to be be largely largely driven driven by slab slab pull, pull, the the southward southwardsubduction subduction of oceanic lithosphere lithosphere attached attached to the Superior continental margin would have pulled the continental continental lithosphere lithosphere along with it as it descended into the subduction zone below the ophiolite-arc system. With With detachment detachment of of the the subducting subducting oceanic oceanic lithosphere, lithosphere,the the buoyancy of the continental continental lithosphere lithosphere would have have led led to to its its rapid rapid uplift uplift along alongwith withthe the leading edge of the ophiolite-arc ophiolite-arc complex (Shervais, 2001). This Thisstage stageisisrecorded recordedby by the the deformation of the syn-to to post-tectonic post-tectonic the ophiolite-arc ophiolite-arcsequence sequence and and by by the the intrusion intrusion of of the the synunits of the Dunbar Dunbar dome. dome. Shervais, J.W., 2001, Birth, death, and resurrection: resurrection: the life cycle of suprasubduction zone ophiolites: Geochemistry Paper number number 2000GC000080. 2000GC000080. On-line publication publication at Geochemistry Geophysics Geosystems, vol.2, Paper http://g-cubed.org. http://e-cubed.org. P.K., Van Schmus, W.R., W.R., Schulz, K.J., K.J., and and Peterman, Peterman, Z.E., Z.E., 1989, Tectono-stratigraphic Tectono-stratigraphic evolution evolution of of Sims, P.K., the Early Proterozoic Proterozoic Wisconsin Wisconsinmagmatic magmatic terranes terranesof of the the Penokean PenokeanOrogen: Orogen:Canadian CanadianJournal Journalof ofEarth Earth Sciences, v. 26, 158. Sciences, 26, p. p. 2145-2 2145-2158. Van Wyck, N., and and Johnson, Johnson, C.M., C.M., 1997, 1997,Common Common lead, lead,Sm-Nd, Sm-Nd,and and U-Pb U-Pbconstraints constraintson onpetrogenesis, petrogenesis, crustal architecture, and tectonic setting of the Penokean orogeny (Paleoproterozoic) in Wisconsin: crustal architecture, and tectonic setting of the Penokean orogeny (Paleoproterozoic) in Wisconsin: Geological Geological Society Society of America America Bulletin, Bulletin, v. v. 109, 109,p. p. 799-808. 799-808. 72 �THE THE LAKE NIPIGON GEOSCIENCE GEOSCIENCE INITIATIVE INITIATIVE -- PLANNED ACTIVITIES ACTIVITIES AND AND OBJECT! VES OBJECTIVES SMYK, Mark C., C., Ontario Ontario Geological Geological Survey, Survey, Ministry Ministryof ofNorthern NorthernDevelopment Developmentand andMines, Mines, SMYK, Mark Suite B002,435 B002, 435 James James St. St. South, South, Thunder Thunder Bay, Bay, ON ON P7E P7E 6S7, 6S7,and andmembers membersof ofthe theScientific Scientificand and Implementation Committees, Conmiittees, Lake Lake Nipigon Nipigon Geoscience Geoscience Initiative, Initiative,c/o do Ontario Prospectors Association, 1000 Association, 1000 Alloy Drive, Drive, Thunder Thunder Bay, Bay, ON ON P7B P7B 6A5 6A5 was created created in in 2002 2002 as as aa $7.0 $7.0 M M Cdn. Cdn. project project aimed at The Lake Nipigon Geoscience Initiative (LNGI) was the area area around Lake Lake Nipigon. Nipigon. The The Ontario OntarioProspectors Prospectors Association's Association's attracting mineral investment to the (OPA) portion of the project project is is funded funded through through an an agreement agreementwith with the the Northern Northern Ontario OntarioHeritage HeritageFund. Fund.The The OPA is partnering with the Ontario Ontario Geological Geological Survey Survey (OGS), (OGS), the the Ministry Ministry of Northern Northern Development Developmentand and Mines (MNDM), the Canadian Canadian Mining Mining Industry Research Research Organization Organization (CAMIRO), (CAMIRO),Lakehead Lakehead University, University, as well as with private sector partners and communities communities in the Lake Nipigon area. area. It will will focus focus on on four four key key objectives: objectives: 1. Maintain 1. Maintain and then increase increase mineral mineral investment investmentin in the the Lake Lake Nipigon region region through through collection collectionof of high high quality geological data and provision provision of interpretations interpretationsthat meet meet the the needs needs and and priorities priorities of of the the mineral mineral industry and that maintain or attract mineral investment investment to Ontario; 2. 2. Increase the mineral exploration discovery discovery rate by addressing addressing "masking and deep deep search search challenges challenges and skill gap" in the area; area; 3. Respond nickel3. Respond to, and and evaluate, evaluate, new new and and exciting exciting mineral mineral deposit deposit models models recently recently recognized recognizedfor fornickelcopper, copper, palladium-platinum, palladium-platinum,and and gold-copper gold-coppermineralization mineralizationin in the the region; region; 4. 4. Reinforce Reinforce and and demonstrate demonstrate an an innovative innovativeeconomic economic development developmentmodel model based based on on local localcommunity, community, industry, industry, and government government partnerships partnerships in in geoscience geoscience that result result in in mineral mineral resource resource economic economic development development in the the local local communities, communities, the the region, region, and and Ontario. Ontario. The LNGI is Embayment, which which consists consists predominantly predominantly of of is focused focused on on the the Nipigon Nipigon Basin Basin // Embayment, Mesoproterozoic, Mesoproterozoic, Midcontinent MidcontinentRift-related, Rift-related,ultramafic ultramaficto to mafic mafic intrusions intrusionsthat that have haveintruded intruded Mesoproterozoic Mesoproterozoic Sibley Sibley Group Group sedimentary sedimentaryrocks rocks and and Archean Archean basement basementrocks rocks of of the theQuetico Queticoand and Wabigoon Wabigoon subprovinces. subprovinces. The project will develop a comprehensive will assist in in mineral mineral exploration. exploration. The comprehensive geoscience database that will The LNGI evolved evolved through aa series series of of community community and industry industry consultations consultations that helped define define the the project project parameters. AAthorough thoroughcompilation compilationof of previous previousexploration explorationand and geological geological data data provided provided aa baseline baseline for for the project and identify the geoscience database. The identify potential potential gaps gaps .in in the Themain main components componentsof ofthe theinitiative initiative include: include: • • • • • • • • Detailed geological geological mapping, mapping, undertaken undertaken by by Precambrian Precambrian Section, Section, OGS OGS Airborne Airborne magnetic magnetic survey survey Gravity Gravity survey survey Quaternary Quaternary (surficial) (surficial) case case studies, studies, undertaken undertaken by Sedimentary SedimentaryGeoscience Geoscience Section, Section,OGS OGS Geochronology Geochronology Physical property studies studies Geographic (GIs) compilation compilation Geographic Information Information Systems Systems (GIS) Complementary Complementary research at Lakehead Lakehead University • Sibley Group studies studies (P. (P. Fralick) Fralick) • Nipigon mafic intrusion intrusion studies studies (P. (P. Hollings; Hollings; G. G. Borradaile) Borradaile) • Sulphide Sulphide mineralization mineralization studies studies (S. (S. Kissin) 73 �The Ontario Ontario Geological Geological Survey Survey will will help acquire acquire and and publish publish the the results results of of the the geoscience geosciencestudies studiesas asmaps, maps, reports, and digital data sets. The Theinformation informationwill will then then be be available available over over the the Internet Internet through through the the MNDM's MNDM's ERMES and CLAIMap CLAIMap systems. systems. This valuable valuable information information will be used to globally globally market market the the resource resource potential and investment investment appeal appeal of the the Lake Lake Nipigon region. region. 74 �TECTONOSTRATIGRAPHIC ARCHEAN T E C T O N O S T U T I G M P H I C ASSEMBLAGES ASSEMBLAGES OF O F EASTERN EASTERN WABIGOON SUBPROVINCE, NORTHWESTERN ONTARIO STOTT Greg ONyP3E P3E 6B5 6B5 STOTT GregM., M.,Ontario OntarioGeological Geological Survey, Survey, Sudbury, Sudbury, ON, (greg.stott@ndm.gov.on.ca), DAVIS, Don. W., Department of Geology, University of of (greg.stott@ndm.gov.on.ca)y Toronto, Toronto, Toronto, ON, ONyPARKER, PARKER,Jack JackR., R.,Ontario OntarioGeological GeologicalSurvey, Survey,Sudbury, Sudbury,ON, ON, Toronto, STRAUB, Kristan J., Laurentian University, University, Sudbury, Sudbury, ON ON and andTOMLINSONy TOMLINSON, Kirsty Y., Geological Survey of Canada, Ottawa, ON The Archean Wabigoon Subprovince Subprovince is a complex of volcanic and sedimentary supracrustal assemblages supracrustal assemblages and granitoid suites suites of Mesoarchean Mesoarchean to Neoarchean Neoarchean age. age. The The easternmost Onaman-Tashota greenstone belt easternmost part of this subprovince, subprovince, which includes the Onaman-Tashota east of Lake Nipigon, preserves aa history history of over over 250 250 million million years years of of volcanism. volcanism.This This area has recently been treated to a regional mapping, geochemical and geochronological 11250000 000 compilation compilation synthesis as part of the Western Superior Superior NATMAP project. A 1:250 map (Stott et al. 2002) arising arising from this project illustrates the subdivision of the OnamanTashota (O-T) (Figure 1), based (0-T) greenstone greenstone belt into tectonostratigraphic assemblages (Figure based on on stratigraphic correlationsy correlations, geochronological and geochemical similarities stratigraphic similarities and and contact contact relationships. Figure 2, 2,isisthe the relationships. A more interpretive interpretive component of this map, summarized in Figure delineation of the assemblages assemblages in in terms terms of of the the environment environmentof of crystallization crystallizationof of volcanic volcanic and plutonic rocks and deposition deposition of sedimentary rocks. This is based on lithologic and geophysical characteristics, characteristics, whole-rock whole-rock geochemical geochemical classification, classification,and and where where available, available, Nd isotopic isotopic signatures. signatures. The Onaman-Tashota Onaman-Tashotagreenstone greenstone belt straddles straddles the the width width of of the the eastern easternWabigoon Wabigoon Subprovince Subprovince between the English English River River and and Quetico Queticometasedimentary metasedimentarysubprovinces. subprovinces.ItIt isis mainly dacitic flows, flows, mainly composed composedof ofNeoarchean Neoarchean(dominantly (dominantly2.74 2.74—- 2.72 Ga) basaltic and dacitic autobreccia and autobreccia and pyroclastic pyroclasticrocks. rocks.Mesoarchean Mesoarchean(3.05 (3.05—- 2.92 2.92 Ga) volcanic rocks occur occur in the northwest northwest and and along along the the western western margin margin of of the the belt. belt. Widespread Widespread Nd Nd isotopic isotopicevidence evidence in the northern part of of the the Onaman-Tashota Onaman-Tashota belt belt suggests suggests that that Neoarchean Neoarchean volcanism volcanism erupted erupted through Mesoarchean Mesoarchean basement. basement. Basement Basement in in the the northern northern half half of of the the belt belt contains contains an older older component component than than that that south south of of the the Humboldt Humboldt Bay Bay High High Strain StrainZone. Zone.The The 2.74 Ga Willet Willet assemblage assemblagetholeiitic tholeiitic basalts basalts of of ocean ocean floor floor affinity affinity dominate dominatethe thenorthern northern half of the O-T calc-alkalic 0 - T belt. belt. This This assemblage assemblage is is flanked flanked to to the the north north and and south southby by calc-alkalic assemblages assemblages of continental continental margin margin arc arc affinity affinity that border border metasedimentary metasedimentarysubprovinces subprovinces composed of flysch-like wacke derived from the erosion of the O-T belt and composed flysch-like derived from the erosion of the 0 - T belt and plutons plutons during orogenesis orogenesis at circa circa 2.7 2.7 Ga. Ga. Most Most sedimentary sedimentary units units within within the the O-T 0 - T belt belt form formthe the youngest supracrustal supracrustal assemblages, assemblages, reflecting erosion of the the underlying underlying volcanic volcanic and and plutonic rocks towards towards the the English English River River and and Quetico Queticobasins basins to to the the north northand andsouth. south. Reference Reference Stott, G.M., Davis, D.W., Parker, J.R., J.R., Straub, K.J. and Tomlinson, K.Y. 2002. Geology and Tectonostratigraphic Tectonostratigraphic Assemblages, Assemblages,eastern eastern Wabigoon Wabigoon Subprovince, Subprovince,Ontario; Ontario;Ontario OntarioGeological GeologicalSurvey, Survey, 000. Preliminary Map P.3449, scale 1:250 1~250 Tomlinson, K.Y., Stott, G.M. and Davis, D.W. 2000. Nd isotopes in the eastern Wabigoon subprovince: implications for crustal recycling and correlations with with the the central central Wabigoon; Wabigoon; in in Harrap, Harrap, R.M. R.M. and Helmstaedt, H.H. (eds.), 2000, Western Superior Transect Sixth Annual Workshop, Lithoprobe Report #77, Lithoprobe Secretariat, Secretariat, University University of of British British Columbia, Columbia,p.119-126. p. 119-126. 75 �Figure Figure1. 1. Tectonostratigraphic Tectonostratigraphic assemblages assemblages of of the the Onaman-Tashota Onaman-Tashota greenstone greenstone belt and and Proterozoic diabase dike swarms, Eastern Wabigoon Subprovince. Subprovince. , +•t!4+ •-4..:L--•, .....a.4 ++ ++ + +++ •++ +÷++÷ + + + + .4 P + + + + + .4 + 4 + + ++ 4 + + + + .4 + + + + + + + + + 4 + + + .4 + .4 + + 4. + .4 + + + + 4 +ZP+ .4 + F ( + + + .._+ + ++ +4 + + .4 4+ + + + 4 + + + + + .4 + .4 .4 + + .4 + + + .4 + + + + + + + + + .4 + + + 4* + .4 + + + + Figure 2. Tectonic Figure Tectonic affinities assigned to volcanic and sedimentary sedimentary assemblages and assemblages plutonic suites. suites. + + .4 + +4+ + + + .4 + + 4 .4 + + + .4 ++t#4J + 4+4+ +±+ + + + + + •# 4 .4 + + + r++.— + '4.4 + + + + —-,"+ + +_ + + + 4.' + + + + 4 .t(__... (4. + + + +,I. + +1) + / / Lake Nipigon + + + + + + +c--.4+ + + + Proterozoic Proterozoic [ I- ' I I plume Continental p i m e related related m 4-L 11 - Orogenic plutons plutons orogenic orogenic sediments sedimen& Orogenic Continental arc Contmental Continental rnargm margin arc Cont~nsntal unsubdivided Continental unsubdivided 3 Ocean Ocwan floor floor Oceanic Oceanic unsubdivided unsubdivided Archean Archean Unknown Unknown tectonic tecton~caffinity afflnlty I0 10 0 0 7 Mesoarchean .Mesoarchean ..- - - -.-..- - Kilometres Kllometres ?//////A 76 20 20 ÷ �FIVE GOLD POSSIBILITIES IN SOME KEWEENAWAN COPPER SULFIDES SULFIDES IN IN ONTARIO AND MICHIGAN Trow, Jim, Trow! Jiml Geological Sciences, Sciences! Michigan State State University, University! emeritus, emeritusl 540 540 Lake Lake Avenue *2, #Z1 Hancoek, HancoC!kl Michigan Michigan 49930 49930 gold, Most fire—assayed fire-assayed "invisible" ltinvisiblell goldl from from .12 .12 to to 2.50 2.50 oz oz Au/st, Au/str occurs in minor covellite) in "blue I1bluechalcocite" c h a l ~ o c i t e(with (with ~~ covellite) but but not not in in black chalcocite (with (with no no covellite) covellite) on on the the adit, adit! 1st, lstl 2nd, 2nd1 and and 3rd levels of the Pointl Ontario. Ontario. the Coppercorp Coppercorp mine mine at at Mamainse Mamainse Point, Both occur occur with with specular specular hematite. hematite. Copper mineral zoning zoning exextending from carbonates and oxides through native copper, copper! black chaleocite and specularite, chalcocite specularitel "blue Itbluechalcocite" c h a l ~ o c i t eand ~ ~ specularite, specularitel to to bornite and chalcopyrite is related to nearness to the Keweenaw and related faults faults apparently down which circulated oxidizing solutions The solutions during an an upward-migrating upward-migrating hydrothermal hydrothermal episode. episode. The anomalies! whereas whereas former faults display positive SP electrical anomalies, nearly perpendicular cross faults faults with commercial ores ores display negative SP anomalies of this convective hydrothermal cell cell (Trow). (Trow). Such progressive oxidation of hydrothermal fluids fluids is is suggested suggested for for the Keweenawan of Michigan by the USGS's USGSts Woodruff, Woodrufff Cannon, Cannon! and and Back. Ontario, Trow deduces thermochemical calculations For Ontario! calculations with standard standard free energies and typical activities for constituents constituents (except (except for for oxygen, whose activities oxygenl activities are are the the unknowns). unknowns). These are arrayed arrayed on on a logarithmic scale which mimics the the observed copper copper mineral zones, zonesl AuS- first and in that sequence AUS-I first oxidized oxidized to to deposit deposit gold gold at at the the same oxygen activity at which chalcopyrite first first oxidized oxidized to to covellite and and specularite. specularite. At the present it it is is uncertain if if the the "blue chalcocite" iito chalcoCite and covellite from I1blue c h a l ~ o c i t eexsolved ~~ ivto chalcocite digenite at low temperatures, temperatures, or if if most of original covellite covellite was replaced by 2!500 times times the the oxygen oxygen by late late chalcocite chalcocite at at roughly roughly 2,500 activity at which which covellite covellite originally originally formed. formed. Essentials for gold at Coppercorp Coppercorp include include 1) 1) Keweenawan permeable permeable vesicularbeds conglomeratesl 2) 2) felsite felsite intrusives intrusives basaltic vesicular beds and and conglomerates, with permeable permeable border border breccias breccias as as conduits conduits for for rising rising hydrohydrothermal solutions, solutionsl 3) 3) nearness to to the the Keweenaw Keweenaw and and related related faults faults with positive SP anomalies, anomaliesl 4) 4) mineralized cross cross faults faults with with ores ores yielding negative SP anomalies, anomaliesr and 5) 5) "blue 'Iblue chalcocite". chalc~cite~~. In Michigan! Michigan, field examination of ore ore deposits deposits and and structures structures (Balticl Ashbed, Ashbed! mapped by the USGS shows shows that the the major lodes lodes (Baltic, Isle Royale, Royalel Pewabic, Pewabicl Osceola, Osceola, Calumet conglomerate, conglomeratet and and Kearsarge) Kearsarge) and the Cliff, Cliff! Central, Central! and Delaware Delaware fissure fissure deposits deposits all all display display Keweenaw, Hancock, Mayflowerl Mayflower, and negative SP SP anomalies. anomalies. The Keweenaw! Gratiot—Suffolk faults Gratiot-Suffolk faults all all display positive positive SF SP anomalies, anomaliesl approappropriate for downward oxidative contamination hypogene contamination of of rising rising hypogene (not supergene) supergene) mineralization. mineralization. From southwest southwest to northeast the the best matches to to Canadian Canadian gold gold in in Michigan examined, occur 1) from Mass City to the Indiana so far examinedl Michigan so Indiana mine adjacent to felsite felsite intrusives intrusives and and the the Keweenaw Keweenaw fault fault in in Ontonagon County, Countyl 2) 2) In In Houghton Houghton and and Keweenaw Keweenaw Counties Counties the the Allouez Allouez Gap fault between Copper City and and New Allouez Allouez is is near near the the Copper Copper , 77 �2 City felsite felsite and the the Keweenaw Keweenaw fault. fault. According to to Bornhorst, Bornhorstl page 132, 132! Randy Weege of C & H thought thought that this this fault fault perhaps perhaps was a fluid pathway for 60% of the district's districtls copper copper production. production. Further, it replicates replicates and improves Further! improves upon the the best geophysical geophysical signature Coppercorp, the persistent SB signature at Coppercorpl SB zone, zone! with with flanking flanking negative negative SP anomalies anomalies in in the midst of which which is is aa positive positive SP SP anomaly. llcorell splinters anomaly. In Michigan! Michigan, the positive "core" anomaly splinters westward off the northern northern end of the the negative negative anomalies anomalies in in the the vicinity vicinity of of Ahmeek. Ahmeek. This part of the the district district contains contains arsenic, arsenicl which accompanies accompanies gold in in many western western mining camps. camps. 3) In In 1999 1999 Bornhorst reported on the Maki and Bornhorst the 4½ 4% million million tonnes of chalcocite chalcocite in drilled amygduloids of the Gratiot deposit in in Keweenaw Keweenaw County, Countyl where these these beds are intruded intruded by dacite dacite (felsite). (felsite). This lode This lode appears appears at the intersection intersection with the the southward southward extension extension of of Trow's Trowls negative SP anomaly as as observed at at the the Central Central mine mine and and 2¼ 2% miles miles negative to to the the SSE. SSE. 4) 4) In Keweenaw Keweenaw County, Countyt the the USGS's USGS1s Hank Hank Cornwall Cornwall on on 166-167 describes describes minor traces traces of gold with with mainly mainly chalco— chalcopages 166-167 specularite and some some covellite covellite and and chalcopyrite chalcopyrite in in an an cite and specularite amygduloid amygduloid near near the the top top of of the the Greenstone Greenstone flow. flow. This is is not not near near faultl but it it is is cut cut by aa N.4°E. N.dOE. vertical vertical fault fault with with the Keweenaw fault, negative SP anomaly, anomalyl which which must be intersected intersected at at depth depth by by aa a negative N.4°E., 35°-45°NW. N.4OE.! 35O-45O~W.fault fault with a positive positive SP SP anomaly, anomalyt where where it it is is exposed to to the the east east of of the the vertical vertical fault. fault. There exists exists a possibility for a horizontal horizontal ore ore shoot shoot at at these 5 h b e faults' faults4 intersection. intersection. possibilities are plotted on on the the latest latest geologic geologic map map These four possibilities of the the Keweenaw Keweenaw peninsula, peninsulal by by Cannon Cannon and and Nicholson. Nicholson. Not yet yet reconnoitered possililities possililities may occur occur to to the the northeast northeast of of these. these. Remember, Remember! from from 1849 1849 to to 1961 1961 the the old timers timers all all missed the the Carlin Carlin "invisible" gold. llinvisiblell gold. Nevada is is now now the the biggest biggest gold gold producing producing state state because of the observationst observations, thinkingl thinking, and and Perseverance perseverance of of the the USGS's Ralph Roberts USGS1s Roberts and Mewmont's Newmontls John John Livermore. Livermore. REFERENCES CITED Bornhorst, T. J., Bornhorstl J e t1997, 1997! Tectonic Tectonic context context of of native native copper copper deposits deposits of the North A~erican American Midcontinent Midcontinent Rift Rift System, Systeml in in Geological Geological Society of America Special Special Paper Paper 312, 3121 p. 127—136. 127-136. Cannon, Cannon! W. F. and Nicholson, Nicholsonl S. S. W., W e 12001, 2O0lt Geologic Geologic map map of of the the Keweenaw Peninsula Peninsula and adjacent adjacent area, areal Michigan, Michigan! USGS USGS Geological Geological Investigations Investigations Series Series Map Map 1—2696. 1-2696. Cornwall, Cornwalll H. R., R e 1 1951, 19511 Differentiation Differentiation in in lavas lavas of of the the Keweenawan Keweenawan series and the origin Michigan! origin of the the copper copper deposits deposits of of Michigan, Geological Geological Society Society of of America America Bull. Bull. v. v. 62, 62# no.2, no.2# p. p. 159-201. 159-201. Maki, J. C., Makit C.! 1999, 199g1 The The Gratiot Gratiot chalcocite chalcocite deposit, deposit! Keweenaw Keweenaw Peninsulal Technological University, Universityl M.S. M.S. Peninsula, Michigan! Michigan, Michigan Technological Thesisl 71 p. p. Thesis, 71 Trow, J., Trow, J o t 1992, 1992! Inductive Inductive electrostatic electroskakic gradiometry gradiometry (IESG) (IESG) deciphers Keweenawan Keweenawan copper plumbing system, systeml Soc. SOC. Mining, Miningl Metall. and and Expl. Expl. Phoenix Phoenix Meeting, Meetingl Preprint Preprint 92—32, 92-32! 22 22 p. p. Woodruff, Woodrufft L. L. G., G e lCannon, Cannon! W. W. F., F.! and and Back, Back! J. J. M., M.! 1994, 1994# Chalcocite Chalcocite mineralization mineralization in in the the Portage Portage Lake Lake volcanics, volcanicst Keweenaw Keweenaw Peninsula, Peninsulal Michigan, 40th Michiganl 40th Ann. Inst. Inst. on on Lake Lake Superior Superior Geology, Geologyl Houghton, Houghtonl Abstracts, p . 77—78. 77-78. Abstracts! p. 78 �Using xenotime U-Pb geochronology to to unravel the history U-Pb geochronology history of ofProterozoic Proterozoicsedimentary sedimentary basins: a study basins: study in in Western Western Australia Australia and and the the Lake Lake Superior Superior Region Region McNaughton, N.J., N.J., Rasmussen, Rasmussen, B., B., Fletcher, Fletcher, I., I., Griffin, B.J., Vallini, D.A., dvallini@peol.uwa.edu.au, dvallini@aeol.uwa.edu.au, McNaughton, B.J., University of Western Australia, 35 Stirling Hwy, Crawley, 6009, Australia Diagenetic xenotime (YPO4) is aa trace trace constituent in a wide variety of siliciclastic (YPOJ is siliciclastic sedimentary sedimentary rocks. rocks. It typically forms pyramidal crystals of only aa few few microns microns in in size, size, rarely rarelyexceeding exceeding10 10pm, vm,growing growingon on [isostructural] detrital detrital zircons. zircons. A A recent study by Vallini et al. (2002) [isostructural] (2002) showed showed convincing convincing petrographic petrographic and age relationships that demonstrate demonstrate this U-bearing U-bearing phosphate phosphate could begin begin forming forming in in sediments sediments at at or just below below the sediment-water sediment-water interface, interface, shortly shortly after burial. burial. A few years ago itit was discovered discovered that itit 10 pm is possible to date xenotime crystals 210 vmininsize, size,using usingthe theSHRIMP SHRIMP(Sensitive (SensitiveHigh HighResolution ResolutionIon Ion for its formation, hence an age for early diagenesis and a Microprobe), providing aa robust isotopic age for close proxy for sediment deposition. Xenotime especially useful useful in in that that it has very high U contents Xenotime is especially and remains remains closed closed to toradiogenic radiogenicparent-daughter parent-daughter mobility, mobility, unlike unlike most mostother otherdateable dateablediagenetic diagenetic mineral. Diagenetic Diageneticxenotime xenotimeU-Pb U-Pbgeochronology geochronologyhas hasthe thepotential potentialto tounravel unravelthe thechrono-stratigraphy chrono-stratigraphy of unfossiliferous unfossiliferous sedimentary sedimentary basins, especially especially those sequences sequences devoid devoid of of dateable dateable interlayered interlayered volcanic basins where where aa lack lack of aa reliable volcanic rocks. Its Its main main application application isis in Precambrian Precambrian basins reliable temporal temporal affiliations, framework basin evolution evolution and framework hinders hinders an an understanding understanding of basin and maturation, maturation, tectonic affiliations, metallogeny and value as exploration metallogeny exploration targets. targets. Xenotime also forms during post-diagenetic Xenotime post-diagenetic fluid flow events, events, such such as as alteration, alteration,mineralisation mineralisationand and metamorphism, as as well well as being a magmatic metamorphism, magmatic mineral mineral and aa detrital detrital heavy heavy mineral. mineral. The The exceptional exceptional in situ its excellent excellent properties range of of xenotime, range of formation formation conditions conditions of xenotime, coupled coupled with with its properties for in situ geochronology, provide many many new new opportunities opportunities in in establishing establishing the the timeframe timeframe of of events geochronology, provide events in many many hitherto poorly understood understood sedimentary sedimentary basins. basins. Unusually coarse coarse (up (up to 200 crystals in the metametaUnusually 200 microns) microns) and and abundant abundant diagenetic diagenetic xenotime xenotime crystals sandstones of the greenschist greenschist facies facies Mount Mount Barren Barren Group, Group, southwestern Australia, allow the detailed detailed study of xenotime xenotime and its its host host rock. rock. Xenotime Xenotime occurs occurs within within aa phosphatic phosphatic sandstone sandstone interval interval and is is present in multiple different styles styles - as as cement cement overgrowths overgrowths on on zircons, zircons, pyramidal pyramidal present multiple morphologically morphologically different overgrowths on zircons, cement (no (no zircon) zircon) in in shale shale laminations, laminations, replacement replacement of of shale shale (?) (7)intraclasts intraclasts fluid events and as intraclasts. Multiple Multiple fluid events from from early early diagenetic diagenetic to low low as xenotime xenotime crystals crystals within within intraclasts. temperature/early temperaturelearly hydrothermal, hydrothermal,prior prior to to metamorphism, metamorphism,were were recorded recordedwithin withinsingle singlexenotime xenotimecrystals. crystals. U/Pb geochronology, accompanied by observations of petrographic relationships between SHRIMP UlPb between the various various generations generations of xenotime xenotime and and between between xenotime xenotime and other other diagenetic diagenetic minerals minerals and and pyrobitumen,allowed allowedfor for the the construction of a temporal pyrobitumen, construction of temporal framework framework for the the diagenetic diagenetic and and early early events that that occurred within these rocks; (1) ca 1700 hydrothermal events 1700 Ma: Ma: deposition deposition of of partly partly re-worked re-worked phosphatic siliciclastic siliciclastic sediments sedimentson on the the seafloor seafloor was was followed followed by in-situ of the phosphatic in-situ phosphatisation phosphatisation of sediments and an initial period 1697k 7 Ma), Ma), (2) (2) With With burial, burial, an an period of xenotime xenotime formation (mean age of 1697± early pore-filling pore-fillingcarbonate carbonate cement cement was introduced introduced into into parts parts of of the the interval, interval, as as well well as as early earlydiagenetic diagenetic cuboid pyrite ca 1650 1650Ma: Ma:during duringburial burialdiagenesis, diagenesis, aafluidfluid-movement movementevent eventcaused causedthe the pyrite growth, growth, (3) (3) ca Ma), with with partial dissolution of primary pore space and formation of xenotime (mean age of 1646 1646 ± 88 Ma), accompanying phosphate remobilisation, remobilisation, (4) Oil migration migration event, (5) Several Several silica silica cement cement generations generations ca 1560 1560Ma: Ma: minor minor addition addition of of xenotime xenotimerims rimsto toexisting existingovergrowths, overgrowths, introduced around this time, (6) (6) ca (7) ca 1480 1480 Ma: Ma: addition addition of of xenotime xenotime cement cement (no (no zircon) zircon) in in shale shale interlaminations, interlaminations, (8) (8) ca ca 1200 1200Ma: Ma: peak of metamorphism. metamorphism. Wavelength Wavelength Dispersive Dispersive Spectrometer Spectrometer (WDS) (WDS) microprobe microprobe analysis of each each type type of of xenotime xenotimeshowed showed with time, time. Due to this a gradual gradual change from LREE LREE enrichment enrichment to MREE MREE enrichment, enrichment, with this gradational gradational could not be established. nature, discrete boundaries between generations, based on chemistry, could This study study of of diagenetic diagenetic to to hydrothermal hydrothermalxenotime xenotimedramatically dramaticallyimproved improvedthe the estimated estimatedage agerange rangeof of the Mount Mount Barren Barren Group, Group, which which was was previously previously constrained constrained to to 1200 1200Ma Ma(peak (peakmetamorphism) metamorphism)and and 1790 1790 Ma Ma (youngest (youngest detrital detrital zircon zircon population), population), and and discounted discounted some some previous previous tectonic tectonic models models concerning the timing of of collision collision between between major major cratons cratons within within western western Australia Australia and andthese thesecratons cratons with East East Antarctica. Antarctica. Using the information gleaned from the study of xenotime xenotime in the Mount Mount Barren Barren Group, a similar study basin in in the Lake Superior Region is currently underway on another Proterozoic Proterozoic sediment-dominated basin containing and its equivalents, the North Range, containing the Marquette Marquette Range Supergroup Supergroup and equivalents, the Range, MilIe Mille Lacs Lacs and and Animikie Groups. Groups. The early early Proterôzoic Proterozoic strata strata consist consist of of three three unconformity-bounded unconformity-bounded lithostratigraphic groups consisting consisting of glaciogenics, glaciogenics, quartzites, quartzites, dolomite, dolomite, iron iron formation, formation, greywacke greywacke and and shale shale and and minor minor volcanics. Sedimentation is thought intercalated volcanics. thought to to have havebegun begun—2240 -2240 Ma Ma (correlation (correlationof of Chocolay Chocolay * 79 �Group with Gowganda Gowganda Fm, upper Huronian Huronian Supergroup, Ontario) (Fairbain et al., 1969) 1969) and ceased ceased by —1850Ma Ma(coinciding (coincidingwith with orogen-normal orogen-normalarc arccollision collision along along the the Niagara Fault zone and -1850 and the the Malmo Malmo Discontinuity, during during the the Penoken Penoken Orogeny) Orogeny)(Sims (Simsetetal., al., 1993). 1993). Part Partof of the the study study is to determine if Discontinuity, xenotime-rich horizons, such such as as that in the Mount xenotime-rich horizons, Mount Barren Barren Group, can be be located located in in this this stratigraphy stratigraphy and to document the sedimentological, sedimentological, structural structural or or stratigraphical stratigraphical features features that thatthey theyhave haveinincommon. common. Certain rock rock units from the different Certain different sequences sequences over over the whole region region were targeted targeted for xenotime xenotime analysis using proposed proposed sedimentological controls for xenotime formation that were determined determined from the Mount Mount Barren Barren Group Group study. study. feature favourable favourable to to xenotime xenotime formation formation may may be be the the presence of of large quantities One sedimentary feature of sedimentary sedimentary apatite apatite within the host host rock rock or or adjoining adjoining rocks. rocks. A field field sample sample of of low lowgreenschist greenschist facies facies phosphatic chert-conglomerate, chert-conglomerate,atatthe the base base of of the Baraga Group, phosphatic Group, from a documented documented phosphorite phosphorite locality in the Dead Dead River River Basin, Basin, northern northern Michigan, Michigan, contains contains large large quantities quantities of of xenotime xenotimeranging rangingfrom from <30 <30 pm pm pitted pitted overgrowths overgrowthson on detrital detrital zircons, zircons,to to>100 >I00micron micronxenotime xenotimecements. cements. Other rock units units that that contain contain xenotime xenotime overgrowths overgrowths and cements of appreciable size and quantity, were; were; (i) (i) quartzite quartzite beds beds in inseveral several drillholes drillholes through through the the Mahnomen Mahnomen Formation, Formation, Mille Mille Lacs Lacs Group, Group, Cuyuna Range, contain up to 50 50 xenotime xenotime crystals crystals per per thin thin section, section, some some of ofthese theseup uptoto—60 -60 pm pm in in size, (ii) a sandstone sandstone bed bed within within drillcore drillcore from from the the base baseof of the theBaraga BaragaGroup GroupininDead DeadRiver RiverBasinBasin-its its largest was 60 pm (iii) (iii)a agrit-pebble grit-pebbleconglomerate conglomerateand andvery verycoarse-grained coarse-grained largest xenotime xenotime observed observed was 60 pm sandstone outcrop at Slate River Hill Hill locality, Baraga Basin, which is assumed to lie at the base base of the Baraga xenotime grains grains per thin section which are pm in size, and (iv) Baraga Group, averaged averaged —15 -15 xenotime are up up to to —60 -60 pm the basal basal Baraga Baraga Group Group hematitic hematitic conglomerate conglomerate at at Big Big Eric's Eric's Crossing Crossing locality, locality, Baraga BaragaBasin, Basin,contains contains up to 55 xenotime xenotime grains grains per per thin thin section, section, some some of of these these are are up uptoto—100 -100 pm pm in in size. size. Pokegema Pokegema Quartzite samples, West Mesabi Mesabi Range, Range, showed showed minor <30 pm xenotime overgrowths on zircons. All of of the therock rocksamples samplesdescribed describedabove aboveare arevery verycoarse-grained coarse-grainedsandstone/conglomerate sandstone/conglomerate beds beds which are either which either located located near near aastratigraphic stratigraphic boundary boundary and/or and/or are are interbedded interbedded with with shale shale beds. beds. Xenotime from from these localities were were analysed on the SHRIMP Xenotime SHRIMP and revealed revealed several age groups; groups; (i) xenotime in xenotime in the the Mahnomen MahnomenFormation Formationdrillcore drillcorerevealed revealedages agesofof—1870 -1 870Ma Maand and—1770 -1 770Ma Ma(1760-1 (1760-1790 790 Ma), (ii) One One large large xenotime xenotime overgrowth overgrowth from the Dead Dead River River Basin Basin drillcore, drillcore, gave gave an anage ageofof—2600 -2600 Ma, (iii) xenotime xenotime contained contained within the the Slate Slate River River Hill Hilloutcrop outcropyielded yielded ages agesofof—2500 -2500 Ma, Ma, (iv) (iv) the the samples from from Big BigEric's Eric'sCrossing Crossingcontained containedxenotime xenotimeshowing showingages agesofof—2550 -2550Ma Maand and—1750 -1 750 Ma. Ma.The The sample from the Pokegema Quartzite in the West Mesabi Mesabi Range, Range, contained contained xenotime with an an age age of of -2300 -2300 Ma Maand and—1770 -1 770 Ma. Ma. Xenotime yielding yielding ages ages of of ca 2500 Ma Xenotime Ma or or older older may may be be from from recycled recycleddetrital detrital (magmatic) (magmatic) grains. grains. The younger age age of of —1770 -1770 Ma (1760-1790 Ma), occurs in xenotime from from widespread widespread localities localitiesacross across thermal event event across across the region. The age the Lake Superior Superior Region and may reflect reflect an epigenetic epigenetic thermal anorogenic magmatism, appears to correlate correlate with with an anepisode episodeat at—1760 -1760 Ma of anorogenic magmatism, pluton pluton emplacement emplacementand and It gneissic doming gneissic doming recorded recorded throughout throughout Wisconsin, Wisconsin, northern northern Michigan Michigan and and central central Minnesota. Minnesota. It postdates the Penoken Orogeny and involved partial melting of of crustal rocks as a result result of of continentcontinentcontinent-arc collision to the south of the region (Sims, 1996). This event is approximately continent or continent-arc coeval with the development development of the the Central Central Plains Plains Orogen Orogen (1800-1630 (1800-1630 Ma) Ma) to to the the south south and and may may be be aa consequence of the accretion of this terrane to the North American continent (Sims, 1996). 1996). This study highlights highlights the sensitivity sensitivity of of in-situ in-situxenotime xenotime geochronology geochronology to to identifying identifyingcryptic cryptic fluid fluid flow flow events within basins. This study will be be ongoing in 2003-2004. Fairbairn Fairbairn H.W., Hurley, Hurley,P.M., P.M., Card, Card, K.D. K.D. and and Knight, Knight, C.J., C.J., 1969, 1969,Correlation Correlationand and radiometric radiometricages agesof of Nipissing Nipissing Diabase Diabase and and Huronion Huronion metasediments metasedimentswith with Proterozoic Proterozoicevents events in in Ontario: Ontario: Canadian CanadianJournal Journalof of Earth Earth Sciences, Sciences, v. v. 6, 6, P. p. 489-497. 489-497. Sims, P.K., 1996, in Sims Sims P.K. P.K. and and Carter, Carter, L.M.H., L.M.H., eds., eds., Archean Archean and and 1996, Early Early Proterozoic Proterozoic Penokean Penokean Orogeny, Orogeny, in Late Proterozoic Geology Geology of the Lake Lake Superior Superior Region, Region, U.S.A., 1993: U.S. Geological Geological Survey Professional Professional Paper Paper 1556, 1556, p. p. 28-60. 28-60. Sims, P.K., et al., 1993, in Reed, Reed,J.C., J.C., Jr., Jr., and and 1993, The Lake Lake Superior Superior Region Regionand and Trans-Hudson Trans-HudsonOrogen, Orogen, in others, eds., Precambrian:Conterminous Precambrian:ConterminousU.S.: U.S.: Boulder, Boulder, Colorado, Colorado, Geological GeologicalSociety Society of America, the Geology of North America, v. C-2, p. p. 11-120. 11-120. Vallini, D., Rasmussen, Rasmussen, B., B., Krapez, Krapez, B., B., Fletcher, Fletcher,l.R., I.R., and and McNaughton, McNaughton, N.J., N.J., 2002, 2002, Obtaining Obtainingdiagenetic diagenetic ages from metamorphosed metamorphosedsedimentary sedimentary rocks: rocks: U-Pb U-Pbdating dating of of unusually unusuallycoarse coarse xenotime xenotimecement cementinin phosphatic phosphatic sandstone: sandstone: Geology, Geology, v. 30, 30, p. p. 1083-1086. 1083-1086. 80 �EVALUATION OF INITIAL MAGMA COMPOSITIONS FOR THE BALD EAGLE INTRUSION AND ASSOCIATED ROCKS VISLOVA, Tatiana, Department of Geology and Geophysics, University of Minnesota The funnel-shaped concentrically-zoned Bald Eagle Intrusion in the Duluth Complex is characterized by very restricted mineral compositions, and consists of only two units: an olivine—plagioclase cumulate and an olivine—plagioclase-clinopyroxene cumulate (Weiblen, 1965; Weiblen and Morey, 1980). In terms of differentiated units expected in a typical layered intrusion, the Bald Eagle Intrusion appears to be petrologically incomplete. This has raised the question whether the four-phase (olivineplagioclase-clinopyroxene-oxide) cumulates, assigned to the Greenwood Lake Intrusion (Miller et al., 2002), and granophyre found to the south of the Bald Eagle Intrusion are genetically related to the Bald Eagle Intrusion (Weiblen and Morey, 1980). New petrographic studies and microprobe analyses (Vislova, 2003) make it possible to evaluate parent magma compositions for the Bald Eagle Intrusion, and quantitatively assess possible petrogenetic relationships between the Bald Eagle Intrusion and spatially associated rocks. Computer programs (MELTS, Ghiorso and Sack, 1995; and COMAGMAT, Ariskin et al., 1993) were used to investigate these questions. A primitive North Shore Volcanic Group olivine tholeiite (P-melt) was used as an initial magma composition (Miller and Ripley, 1996). Equilibrium crystallization of P-melt, calculated by MELTS at 1 atm total pressure and oxygen fugacity near or below the quartz-fayalite-magnetite buffer, reproduces the crystallization order and mineral assemblages observed in the Bald Eagle Intrusion. The calculated composition of the first clinopyroxene (mg 81) equals the one observed, however calculated compositions of the first plagioclase and olivine are much higher than those observed. This could be ascribed to the dynamics of crystal-melt segregation in a flowing magma system. Until the crystals suspended in magma grow large enough they might be carried away, erupted, and found as phenocrysts in lavas. At -7 % melt remaining MELTS reproduces the most evolved mineral compositions in the Bald Eagle Intrusion (Fig. 1). This suggests that the Bald Eagle Intrusion might be a complete crystallization sequence with a few percent remaining melt. It leaves unanswered the question of the origin of four-phase cumulate and granophyre. Modeling shows that a more evolved high Ti and high Fe melt (D-melt) is required for crystallization of the evolved units in the Greenwood Lake Intrusion (Fig. 1). This melt can be produced by fractional crystallization of P-melt in an intermediate magma chamber at 2-3 kbar total pressure. Equilibrium crystallization of D-melt at 1 atm reproduces the crystallization order, the appearance of Fe-Ti oxides, and the compositions of most of the units associated with the Bald Eagle Intrusion (Fig. 1). However, the most evolved rocks in the Greenwood Lake Intrusion (ferrogabbro with Fo < 50) and granophyre were not reproduced by equilibrium crystallization. These units might require fractional crystallization or assimilation. 81 �85 . ,. *A G. 0 0 x I- 0. 0 .E 75 0 U+ A tL±&& A , --. 0) 6565 1 # E E 0 o <60 60 BaId Eagle Intrusion AGreenwood LakeIntrusion Intrusion Greenwood Lake A • Calculated 4 Calculated from P-melt P-melt Calculated from D-melt Lsf4. 55 55 30 30 40 50 50 60 Atom % % Mg/ (Mg+Fe) in olivine (Mg+Fe) olivine 70 70 80 80 Mg/(Mg+Fe) variations variations in in coexisting olivine and clinopyroxene. Fig. Fig. 1. Mg/(Mg+Fe) References: References: Ariskin, A.A., Frenkel, M.Y., Barmina, Barmina, G. S., and Nielsen, R. L., 1993, 1993, COMAGMAT; COMAGMAT; aa FORTRAN program to model magma differentiation processes, Computers Computers & Geosciences, Geosciences, 19 19 (8), p. 1155-1170. 1155-1170. IV, A Ghiorso, M. S., and Sack, R.O., 1995, 1995, Chemical Chemical mass transfer in magmatic processes; processes; IV, revised and internally internally consistent consistent thermodynamic model for the interpolation interpolation and and extrapolation extrapolation of liquid-solid equilibria equilibria in magmatic systems at elevated elevated temperatures temperatures and and pressures, pressures, Contributions Contributions to Mineralogy Mineralogy and and Petrology, Petrology, 119 119 (2-3), (2-3), p. 197-212. 197-212. Miller, J.D., Jr., Green Green J.C., J.C., Severson, Severson, M.J., M.J., Chandler, Chandler,V.W., V.W., Hauck, Hauck, S.A., S.A., Peterson, Peterson, D.M., D.M., and and mineral potential potential of of the the Duluth Duluth Complex Complex and and related related rocks rocks of of Wahl, T.E., 2001, Geology and mineral Report of of Investigations Investigations 58,207 58. 207 pp. pp. ++ northeastern Minnesota: Minnesota Geological Survey Report compact disc in back pocket, 2002. 2002. Miller J.D., Jr. and andE.M. E.M. Ripley, Ripley,1996, 1996,Layered Layeredintrusions intrusionsof of the the Duluth Duluth Complex, Complex, Minnesota, In: Cawthorn Cawthorn R.G. R.G. (ed.) (ed.)Layered LayeredIntrusions, Intrusions,531 53 1 pp. USA. In: Vislova, T., 2003, Petrology Petrology of the Bald Eagle Intrusion Intrusion and associated associated rocks rocks and and its relevanceto to its relevance crystallization in dynamic Midcontinent Rift, Ph.D. Dissertation, Dissertation, crystallization dynamic magma chambers in the Midcontinent University of Minnesota, 226 pp. Weiblen, Weiblen, P.W. and and Morey, Morey, G. G. B., B., 1980, 1980,A A summary summary of of the the stratigraphy, stratigraphy,petrology, petrology,and and structure structure of the Duluth Complex. In: In: frying, Irving, A. A. J., J., and and Dungan, Dungan, M. A. A.(ed.), (ed.),1980, 1980,The TheJackson Jacksonvolume, volume, American Journal of Science, Science, Vol. 280-A, Part 1, 1, p. 88-133. 88-133. Weiblen, P.W., 1965, 1965, A funnel-shaped, funnel-shaped, gabbro-troctolite gabbro-troctolite intrusion intrusion in in the the Duluth Duluth Complex, Complex,Lake Lake County, Minnesota, Ph.D. Dissertation, University of Minnesota, 161 pp. University of Minnesota, 161 82 �A Hydrothermal Hydrothermal Component Component of Iron Iron Formations-A Formations-A Marquette Marquette Range Range Perspective Perspective Waggoner, T.D., 141 141 Chippewa, Chippewa,Negaunee, Negaunee, MI MI49866 49866 Waggoner, T.D., The origin of Lake Superior Superior banded iron formations (BIF) has been a contentious contentious issue for at least a century century and aa half. half. Concepts of origin origin include include weathering, weathering, volcanic volcanic and and organic activity activity whereby whereby ions ions are are carried in and organic and precipitated precipitated from from solution. solution. Clear definition of of the source, definition source, mode mode of of transport transport or ordepositional depositional mechanisms mechanisms is is generally generally lacking. This Thispaper paperwill willaddress addressthe thestrong strongevidence evidencefor for aa hydrothermal hydrothermal source source for for "hard "hard ores" found in the upper upper parts parts of of the the Negaunee Negaunee Iron Iron Formation Formation (NIF) (NIF) and and by extension extension aa possible source for the precursor hematite in the BIF portion. Range was formed formed in a portion. The Range tectonically active area believed to be an extensional extensional rifting rifting environment environment not not unlike unlike those those REE) and and some some VHMS deposits deposits found in Fe-Oxide (Cu, U, Au, REE) The Marquette Range portion of of the the Lake Lake Superior SuperiorIron Iron District Districtdisplays displaysmany many features features BJFs found around the world and, thus, making it an similar to other large Lake Superior BIFs excellent study subject subject for for the source excellent study source and and role role played played by by igneous igneous and andsedimentary sedimentary processes. The Goodrich units units exhibit exhibit BIF, BIF, soft soft supergene supergene enriched TheNegaunee Negaunee and and basal basal Goodrich concentrations and "hard concentrations and "hard ores" ores" as as massive massive bodies, bodies, banded banded jaspilites jaspilites and and detrital detrital conglomerates. conglomerates. "Hard "Hard ores" are are generally generally dense silver gray gray to to black black massive massive metallic metallic magnetite or schistose metallic hematite associated with jaspilite jaspilite and contain in excess of 60% iron. of the the origin iron. Discussion Discussion of origin of of the the "hard "hard Ores" Ores" on on the the Marquette Marquette Range Range has has revolved revolved around around supergene supergene enrichment enrichment prior prior to metamorphism metamorphism or or hydrothermal hydrothermal enrichment enrichment associated associated with the the Penokian Penoluan Orogeny. Orogeny. of the field geology geology do do not not support support with witheither eitherof ofthese thesepositions. positions. First, the Many features of Goodrich conglomerate conglomerate show show random random cobble and pebbles of jasper hematite hematite in in the the basal basal Goodrich orientation of the 'schistose' orientation of 'schistose' hematite hematite indicating indicating the schistose schistose nature nature of of the the hematite hematite existed prior to emplacement and not a result of metamorphism. In In addition addition many many of of the the rocks associated with the "hard "hard ores" ores" exhibit exhibithydrothermal hydrothermal minerals minerals including including sericite, sericite, chlorite, chloritoid, chloritoid, high aluminous aluminous silicates, silicates,garnet, garnet, hematite, hematite, magnetite magnetiteand and tourmaline. tourmaline. The lower NIF exhibit exhibit lower Proterozoic Proterozoic Chocolay Chocolay and Menominee Menominee sediments sediments below below the NW multiple examples of of high-grade hematite that that can be interpreted multiple examples high-grade hematite interpreted as vents. vents. Specular, Specular, microplaty and bytroidal bytroidal hematite hematite are are fairly fairly common commoninin many many outcrop outcropareas. areas. Some microplaty and Some of of these have been described described previously in literature while others have not. not. All the sites sites were lgth century and most exhibit exhibit were subject to exploration exploration for iron ore during during the late late 19th shallow shafts. The Themajor majorcomponents componentsare arechert, chert,jasper jasper and andvein veinquartz quartzalong alongwith withcoarse coarse specular, microplaty and and bytrioidal hematite contained contained in in breccia zones specula, microplaty bytrioidal hematite zones that that exhibit exhibit episodic reworking. reworking. There There are are alterations alterations to to the the host hostrock rockas assome someoccurrences occurrencesexhibit exhibit chlorite, silica, silica, k-spar k-spar and aluminous aluminous silicates. silicates. A large area in sections sections 21, 21, 22, 22, and 23, 47-26 contain contain multiple multiple enriched enriched hematite hematite sites sites that form two northwest trending trending breccia zones zones adjacent adjacent to to northwesterly northwesterlytrending trending faults. faults. In addition there isis a In addition to the the silica silicaflooding, flooding, brecciation brecciation and hematite hematite concentration concentration there significant area of of andalusite and chloritoid adjacent to the significant area andalusite cordierite cordierite and chloritoid adjacent the eastern eastern linear linear 83 �breccia zone in section 23. These Theseminerals minerals are are present present in in aa much much broader broader lower lower regional chlorite zone of metamorphism and most likely are a result of the hydrothermal event that impacted impacted the three square square miles referenced above. above. A conglomerate in Sec. 22 and 23, 47-26 has been previously described as "unusual" and 23,47-26 is sandwiched sandwiched between lower lower Chocolay Chocolay argillite argillite units. units. Clasts causing dimpling in the the underlying argillite were described as rafted clasts from a glacial glacial interlude. interlude. It is unlikely unlikely reef growth during the the same period period of of that a glacial event coincided with significant algal reef coarse, tightly tightly packed packed and shows no time. The "unusual" "unusual" conglomerate conglomerate is extremely extremely coarse, sedimentary sedimentary features. features. In addition significant rinds of k-spar have formed formed on on the the granite granite gneiss cobbles. The Thecobbles cobblesand andmatrix matrix contain contain euhedral euhedral magnetite, magnetite, martite and specular specula hematite suggesting this area was tectonically tectonically active and may well have been an an active active vent area over a period vent period starting starting at at the the earliest earliest extensional extensional period period and continued to be resembles some some of of the breccias active beyond beyond the Ajibik Ajibik time. time. The conglomerate conglomerate resembles breccias at at Olympic Dam and could well be a hydrothermal breccia. analysis of of the hematite match quite closely with both REE chondrite normalized analysis hematite vents match "hard ores" the hematite, hematite, magnetite magnetite and and combination combination hematite/magnetite hematitelmagnetite "hard ores" found throughout the the Range. Range. Recent throughout Recent work work on onthe theBrockman Brockrnan microplaty microplaty hematite hematite confirms confirms aa hydrothermal origin due to the recognition of surrounding surrounding alteration alteration to the the host. host. Initially the the vent vent areas areas were were studied studied in in relation relation to to the the "hard "hard Ores" Ores" but but the the fact that that the Initially vents are all hematite suggests they could be the source source for the the precursor precursor hematite hematite seed cores have have cores that Han identified in low low metamorphic metamorphic grade BIF units. These seed cores been been identified identified in in the theNegaunee, Negaunee,Biwabik, Biwabik, Brockman, Brockrnan, Sokoman, Sokoman, Temiscamie Temiscamie and and Kuruman Iron Formations. Formations. It is quite NIF time time quite plausible plausible that that the the extensional extensional phase phase of of rifting rifting ceased ceased near the end end of of NIP and aa reverse and reverse compressional compressional event event started started causing causing faulting faulting that that produced produced erosional erosional material for the basal Goodrich conglomerate. Reference: Reference: Han, T.H., T.H., 1988, 1988, Origin Origin of Magnetite Magnetite in in Precambrian Precambrian Iron Iron Formations Formations of of Low Low Metamorphic Grade, Grade, Proceedings Proceedings of of the Seventh Metamorphic Seventh Quadrennial Quadrennial IAGOD IAGOD Symposium, Symposium, p. 641-656. 641-656. 84 �High-Resolution Multibeam Bathymetry Bathymetry in Lake Superior. Superior. N. N. JJ.. Wattrus Large Lakes 558122 Lakes Observatory, Observatory,University Universityof of Minnesota, Minnesota,Duluth, Duluth,MN MN 5581 Like all large large lakes, lakes, the composition and and shape shapeof of the the lake lakefloor floor of of Lake Superior reflects the processes that that shape shape its itsformation formation today as a s well as in the past. Maps of of the the lake floor floor made made with with traditional traditional echosounders echosounders lack the the resolution resolution to to permit scientists scientists to to read read the the subtle subtle"fingerprint" "fingerprint" of these processes preserved in the lake-floor. The The advent advent of of modem, modem, high-resolution high-resolution multibeam sonar sonar has has revolutionized the the mapping mapping of of the the sea-floor. sea-floor. In a traditional echosounder, the the depth depth to to the the lake-floor lake-floor below the ship ship is measured measured by by timing timing how how long long it takes takes for for an a n acoustic acoustic ping ping to to travel travel to to the lake-floor and back to the ship. lake-floor and ship. longer the the delay, the the deeper the The longer lake floor is. This type of of surveying provides high-resolution bathymetric information along the trackline followed by the the survey boat. Nothing is followed by known about the the lake lake floor floor either side. side. High-resolution multibeams use a fan High-resolution multibeams of acoustic beams 100)to beams (over (over 100) measure the the shape shapeof of the the lake lake floor floor along a "swath". By sailing sailing aa series of "swath". By overlapping swaths, swaths, it is is possible possible to to achieve complete coverage coverage of the lake lake floor aatt high resolution. Backscatter information Backscatter information collected collected with the bathymetric data can be used to create psuedo-sidescan psuedo-sidescan images images of of the These can can be be used used to map lakefloor. These spatial variations in in the the composition composition of of the lake floor. lake floor. Examples, drawn from the the catalog of of multibeam multibeam surveys surveys conducted conducted by the Large Lakes Observatory, are presented. These illustrate the potential of Large Lakes Observatory, are presented. These illustrate of this this for mapping mapping the the subtle subtle signal processes technology for signal of past geologic processes superimposed superimposed on on the the lake lakefloor. floor. 85 � Dublin Core The Dublin Core metadata element set is common to all Omeka records, including items, files, and collections. For more information see, http://dublincore.org/documents/dces/. Title A name given to the resource Institute on Lake Superior Geology Dublin Core The Dublin Core metadata element set is common to all Omeka records, including items, files, and collections. For more information see, http://dublincore.org/documents/dces/. Title A name given to the resource Institute on Lake Superior Geology: Proceedings, 2003 Description An account of the resource Institute on Lake Superior Geology. Iron Mountain, Michigan. May 7-11, 2003. Creator An entity primarily responsible for making the resource Institute on Lake Superior Geology Date A point or period of time associated with an event in the lifecycle of the resource 2003 Format The file format, physical medium, or dimensions of the resource PDF Language A language of the resource English https://digitalcollections.lakeheadu.ca/files/original/fbb8f910e05cdd14c47cd729c9a998c9.pdf 7d8d30bac0d37353bfa2cdd70c285dea PDF Text Text 50TH ANNUAL INSTITUTE ON LAKE SUPERIOR GEOLOGY DULUTH, MINNESOTA, MAY 4-9, 2004 �INSTITUTE ON LAKE SUPERIOR GEOLOGY 50TH ANNUAL MEETING MAY 4-9, 2004 DULUTH, MINNESOTA HOSTED BY: STEVEN A. HAUCK AND MARK J. SEVERSON Co-Chairs NATURAL RESOURCES RESEARCH INSTITUTE, UNIVERSITY OF MINNESOTA DULUTH WITH ASSISTANCE FROM THE NRRI ECONOMIC GEOLOGY GROUP, MINNESOTA GEOLOGICAL SURVEY, AND THE DEPARTMENT OF GEOLOGICAL SCIENCES, UMD Volume 50 Part 1 – Proceedings and Abstracts Compiled and edited by Steven A. Hauck, Dean Peterson, and Julie Oreskovich Cover Photos: Upper Left – Soudan Iron Formation, 25th Level West, Soudan Underground Mine State Park, Soudan, MN; Center – ILSG 2003 Quinnesec Mine, WI, Menominee Iron District Field Trip; Lower Left – Natural Ore Auburn Mine, Eveleth MN, Looking Northwest Along the Auburn Fault. 2 �50TH INSTITUTE ON LAKE SUPERIOR GEOLOGY VOLUME 50 CONSISTS OF: PART 1: PROGRAM AND ABSTRACTS PART 2: FIELD TRIP GUIDEBOOK TRIP 1: Volcanic Stratigraphy, Hydrothermal Alteration, and VMS Potential of the Lower Ely Greenstone, Fivemile Lake to Sixmile Lake area. TRIP 2: Geologic Highlights of New Mapping in the Southwestern Sequence of the North Shore Volcanic Group and Beaver Bay Complex. TRIP 3: Late Wisconsinan Superior-lobe Deposits in the Lake Superior Basin Northeast of Duluth. TRIP 4: Geology of the Eastern Mesabi Iron Range, Northeastern Minnesota. TRIP 5: Classic Outcrops of Northeastern Minnesota. TRIP 6: Glacial and Postglacial Landscape Evolution in the Glacial Lake Aitkin and Upham Basin, Northern Minnesota. TRIP 7: Economic Geology of Archean Gold Occurrences in the Vermilion District, Northeast of Soudan, Minnesota. TRIP 8: Geology of the Western Contact of the Duluth Complex, Partridge River and South Kawishiwi Intrusions, Northeastern Minnesota. Reference to material in Part 1 should follow the example below: Holm, D.K., Van Schmus, R.W., and Schneider, D.A., 2004, The Influence of Radiometric Dating for Unraveling the Precambrian Geologic History of the Lake Superior Region [abstract]; Institute on Lake Superior Geology Proceedings, 50th Annual Meeting, Duluth, MN, v. 50, part 1, p. 80-84. Published by the 50th Institute on Lake Superior Geology and distributed by the ILSG Secretary-Treasurer: Peter Hollings Lakehead University Department of Geology Thunder Bay, ON P7B 5E1 CANADA peter.hollings@lakeheadu.ca ILSG website: http://www.lakesuperiorgeology.org ISSN 1042-9964 3 �CONTENTS PROCEEDINGS VOLUME 50 PART 1—PROGRAM AND ABSTRACTS Institutes on Lake Superior Geology, 1955-2004 5 Constitution of the Institute on Lake Superior Geology 7 By-Laws of the Institute on Lake Superior Geology 8 Membership Criteria 9 Goldich Medal Guidelines 10 Goldich Medal Committee 11 Past Goldich Medalists 12 Citation for 2004 Goldich Medal Recipient 13 Eisenbrey Student Travel Awards 14 Student Travel Award Application Form 14 Student Paper Awards 16 Student Paper Awards Committee 16 Session Chairs 16 Board of Directors 17 Local Committees 17 Banquet Speaker 18 Report of the Chair of the 49th Annual Meeting 19 Program 25 List of Contributors 26 Abstracts 37 4 �INSTITUTES ON LAKE SUPERIOR GEOLOGY # YEAR PLACE CHAIRS 1 1955 Minneapolis, Minnesota C.E. Dutton 2 1956 Houghton, Michigan A.K. Snelgrove 3 1957 East Lansing, Michigan B.T. Sandefur 4 1958 Duluth, Minnesota R.W. Marsden 5 1959 Minneapolis, Minnesota G.M. Schwartz & C. Craddock 6 1960 Madison, Wisconsin E.N. Cameron 7 1961 Port Arthur, Ontario E.G. Pye 8 1962 Houghton, Michigan A.K. Snelgrove 9 1963 Duluth, Minnesota H. Lepp 10 1964 Ishpeming, Michigan A.T. Broderick 11 1965 St. Paul, Minnesota P.K. Sims & R.K. Hogberg 12 1966 Sault Ste. Marie, Michigan R.W. White 13 1967 East Lansing, Michigan W.J. Hinze 14 1968 Superior, Wisconsin A.B. Dickas 15 1969 Oshkosh, Wisconsin G.L. LaBerge 16 1970 Thunder Bay, Ontario M.W. Bartley & E. Mercy 17 1971 Duluth, Minnesota D.M. Davidson 18 1972 Houghton, Michigan J. Kalliokoski 19 1973 Madison, Wisconsin M.E. Ostrom 20 1974 Sault Ste. Marie, Ontario P.E. Giblin 21 1975 Marquette, Michigan J.D. Hughes 22 1976 St. Paul, Minnesota M. Walton 23 1977 Thunder Bay, Ontario M.M. Kehlenbeck 24 1978 Milwaukee, Wisconsin G. Mursky 25 1979 Duluth, Minnesota D.M. Davidson 26 1980 Eau Claire, Wisconsin P.E. Myers 27 1981 East Lansing, Michigan W.C. Cambray 28 1982 International Falls, Minnesota D.L. Southwick 5 �29 1983 Houghton, Michigan T.J. Bornhorst 30 1984 Wausau, Wisconsin G.L. LaBerge 31 1985 Kenora, Ontario C.E. Blackburn 32 1986 Wisconsin Rapids, Wisconsin J.K. Greenberg 33 1987 Wawa, Ontario E.D. Frey & R.P. Sage 34 1988 Marquette, Michigan J. S. Klasner 35 1989 Duluth, Minnesota J.C. Green 36 1990 Thunder Bay, Ontario M.M. Kehlenbeck 37 1991 Eau Claire, Wisconsin P.E. Myers 38 1992 Hurley, Wisconsin A.B. Dickas 39 1993 Eveleth, Minnesota D.L. Southwick 40 1994 Houghton, Michigan T.J. Bornhorst 41 1995 Marathon, Ontario M.C. Smyk 42 1996 Cable, Wisconsin L.G. Woodruff 43 1997 Sudbury, Ontario R.P. Sage & W. Meyer 44 1998 Minneapolis, Minnesota J.D. Miller & M.A. Jirsa 45 1999 Marquette, Michigan T.J. Bornhorst & R.S. Regis 46 2000 Thunder Bay, Ontario S.A. Kissin & P. Fralick 47 2001 Madison, Wisconsin M.G. Mudrey, Jr. & B.A. Brown 48 2002 Kenora, Ontario P. Hinz & R.C. Beard 49 2003 Iron Mountain, Michigan L.G. Woodruff & W.F. Cannon 50 2004 Duluth, Minnesota S.A. Hauck & M.J. Severson 6 �CONSTITUTION OF THE INSTITUTE ON LAKE SUPERIOR GEOLOGY (Last amended by the Board—May 8, 1997) Article I Article II Article III Name The name of the organization shall be the "Institute on Lake Superior Geology". Objectives The objectives of this organization are: A. To provide a means whereby geologists in the Great Lakes region may exchange ideas and scientific data. B. To promote better understanding of the geology of the Lake Superior region. C. To plan and conduct geological field trips. Status No part of the income of the organization shall insure to the benefit of any member or individual. In the event of dissolution, the assets of the organization shall be distributed to _________ (some tax free organization). (To avoid Federal and State income taxes, the organization should be not only "scientific" or "educational, but also "non-profit") Article IV Article V Article VI Article VII Article VIII Minn. Stat. Anno. 290.01, subd. 4 Minn. Stat. Anno. 290.05(9) 1954 Internal Revenue Code s.501(c)(3) Membership The membership of the organization shall consist of persons who have registered for an annual meeting within the past three years, and those who indicate interest in being a member according to guidelines approved by the Board of Directors. Meetings The organization shall meet once a year. The place and exact date of each meeting will be designated by the Board of Directors. Directors The Board of Directors shall consist of the Chair, Secretary-Treasurer, and the last three past Chairs; but if the board should at any time consist of fewer than five persons, by reason of unwillingness or inability of any of the above persons to serve as directors, the vacancies on the board may be filled by the Chair so as to bring the membership of the board to five members. Officers The officers of this organization shall be a Chair and Secretary-Treasurer. A. The Chair shall be elected each year by the Board of Directors, who shall give due consideration to the wishes of any group that may be promoting the next annual meeting. His/her term of office as Chair will terminate at the close of the annual meeting over which he/she presides, or when his/her successor shall have been appointed. He/she will then serve for a period of three years as a member of the Board of Directors. B. The Secretary-Treasurer shall be elected at the annual meeting. His/her term of office shall be four years, or until his/her successor shall have been appointed. Amendments This constitution may be amended by a majority vote (majority of those voting) of the membership of the organization. 7 �BY-LAWS OF THE INSTITUTE ON LAKE SUPERIOR GEOLOGY I. Duties of the Officers and Directors A. It shall be the duty of the Annual Chairman to: 1. Preside at the annual meeting. 2. Appoint all committees needed for the organization of the annual meeting. 3. Assume complete responsibility for the organization and financing of the annual meeting over which he/she presides. B. It shall be the duty of the Secretary-Treasurer to: 1. Keep accurate attendance records of all annual meetings. 2. Keep accurate records of all meetings of, and correspondence between, the Board of Directors. 3. Hold all funds that may accrue as profits from annual meetings or field trips and to make these funds available for the organization and operation of future meetings as required. C. It shall be the duty of the Board of Directors to plan locations of annual meetings and to advise on the organization and financing of all meetings. II. Duties and Expenses A. Regular membership dues of $5.00 or less on an annual basis shall be assessed each member as determined by the Board of Directors.. B. Registration fees for the annual meetings shall be determined by the Chair in consultation with the Board of Directors. The registration fees can include expenses to cover operations outside of the annual meeting as determined by the Board of Directors. It is strongly recommended that registration fees be kept at a minimum to encourage attendance of students. III. Rules of Order The rules contained in Robert's Rules of Order shall govern this organization in all cases to which they are applicable. IV. Amendments These by-laws may be amended by a majority vote (majority of those voting) of the membership of the organization; provided that such modifications shall not conflict with the constitution as presently adopted or subsequently amended. Last Amended – May, 1996 8 �MEMBERSHIP CRITERIA FOR THE INSTITUTE ON LAKE SUPERIOR GEOLOGY Approved May 8, 1997 A. Membership in the Institute on Lake Superior Geology requires either participation in Institute activities, or an indication on a regular basis of interest in the Institute. Those individuals registering for an annual meeting will remain as members for 4 years unless: 1) they indicate no further interest in the Institute by responding negatively to the statement on meeting circulars "Remove my name from the mailing list"; or 2) two successive mailings in different years are returned by the postal service as address unknown. B. Those individuals who have not registered for an annual meeting in the past 4 years must indicate an interest in the Institute by postal, electronic, or verbal correspondence with the Secretary-Treasurer at least once every two years. Such individuals will be removed from the membership if they indicate no further interest in the Institute or two successive mailing in different years are returned by the postal service as address unknown. C. The Secretary-Treasurer will maintain a list of current members. The list will include the date of the beginning of continuous membership, dates of returned mail, dates of last contact (expression of interest), and the date membership expires, barring a change of status initiated by the member. Those individuals who have become members of ILSG by Section B will have an expiration date listed at 2 years from the upcoming meeting. For example, a member who expresses interest in September of 1997 (the next annual meeting is May, 1998) will have an expiration date of May, 2000, unless the member contacts the Secretary-Treasurer or attends an annual meeting. D. "Member for Life" status is granted to individuals who have been (nearly) continuous participants of the ILSG meetings for 15 years, Goldich Medal recipients, or those who have served as meeting chairs. This status will be further maintained unless the individuals indicate no further interest in the Institute, or 4 mailings in different years are returned by the postal service as address unknown, or they are deceased. E. All members will be mailed the First Circular for the Annual Meeting and the ILSG Newsletter. The Chair of the annual meeting may opt to send the first circular to additional individuals. All returned mail should be reported to the Secretary-Treasurer. F. The Secretary-Treasurer can designate any individual who is on the ILSG membership list (mailing list) as of January 1, 1997 as a member for life based on participation in ILSG activities. G. Members are strongly encouraged to send address corrections to the Secretary-Treasurer to avoid unintentional lapse of membership. 9 �GOLDICH MEDAL GUIDELINES (Adopted by the Board of Directors, 1981; amended 1999) Preamble The Institute on Lake Superior Geology was born in 1955, as documented by the fact that the 27th annual meeting was held in 1981. The Institute's continuing objectives are to deal with those aspects of geology that are related geographically to Lake Superior; to encourage the discussion of subjects and sponsoring field trips that will bring together geologists from academia, government surveys, and industry; and to maintain an informal but highly effective mode of operation. During the course of its existence, the membership of the Institute (that is, those geologists who indicate an interest in the objectives of the ILSG by attending) has become aware of the fact that certain of their colleagues have made particularly noteworthy and meritorious contributions to the understanding of Lake Superior geology and mineral deposits. The first award was made by ILSG to Sam Goldich in 1979 for his many contributions to the geology of the region extending over about 50 years. Subsequent medallists and this year's recipient are listed in the table below. Award Guidelines 1) The medal shall be awarded annually by the ILSG Board of Directors to a geologist whose name is associated with a substantial interest in, and contribution to, the geology of the Lake Superior region. 2) The Board of Directors shall appoint the Goldich Medal Committee. The initial appointment will be of three members, one to serve for three years, one for two years, and one for one year. The member with the briefest incumbency shall be chair of the Nominating Committee. After the first year, the Board of Directors shall appoint at each spring meeting one new member who will serve for three years. In his/her third year this member shall be the chair. The Committee membership should reflect the main fields of interest and geographic distribution of ILSG membership. The out-going, senior member of the Board of Directors shall act as liaison between the Board and the Committee for a period of one year. 3) By the end of November, the Goldich Medal Committee shall make its recommendation to the Chair of the Board of Directors, who will then inform the Board of the nominee. 4) The Board of Directors normally will accept the nominee of the Committee, inform the medallist, and have one medal engraved appropriately for presentation at the next meeting of the Institute. 5) It is recommended that the Institute set aside annually from whatever sources, such funds as will be required to support the continuing costs of this award. Nominating Procedures 1) The deadline for nominations is November 1. The Goldich Medal Committee shall take nominations at any time. Committee members may themselves nominate candidates; however, Board members may not solicit for or support individual nominees. 2) Nominations must be in writing and supported by appropriate documentation such as letters of recommendation, lists of publications, curriculum vita's, and evidence of contributions to Lake Superior geology and to the Institute. 3) Nominations are not restricted to Institute attendees, but are open to anyone who has worked on and contributed to the understanding of Lake Superior geology. Selection Guidelines 1) Nominees are to be evaluated on the basis of their contributions to Lake Superior geology (sensu lato) including: 10 �a) b) c) d) e) importance of relevant publications; promotion of discovery and utilization of natural resources; contributions to understanding of the natural history and environment of the region; generation of new ideas and concepts; and contributions to the training and education of geoscientists and the public. 2) Nominees are to be evaluated on their contributions to the Institute as demonstrated by attendance at Institute meetings, presentation of talks and posters, and service on Institute boards, committees, and field trips. 3) The relative weights given to each of the foregoing criteria must remain flexible and at the discretion of the Committee members. 4) There are several points to be considered by the Goldich Medal Committee: a) An attempt should be made to maintain a balance of medal recipients from each of the three estates— industry, academia, and government. b) It must be noted that industry geoscientists are at a disadvantage in that much of their work in not published. 5) Lake Superior has two sides, one the U.S., and the other Canada. This is undoubtedly one of the Institute's great strengths and should be nurtured by equitable recognition of excellence in both countries. GOLDICH MEDAL COMMITTEE Serving through the meeting year shown in parentheses George Hudak (2006) University of Wisconsin, Oshkosh Ron Sage (2004) Ontario Geological Survey (retired) David Meineke (2005) Meriden Engineering, Hibbing, Minnesota Steve Kissin, as out-going senior member of Institute Board of Directors, is liaison between Goldich Medal Committee and the Board through the 2004 meeting 11 �2004 GOLDICH MEDAL RECIPIENT Paul W. Weiblen Department of Geology & Geophysics University of Minnesota, Minneapolis GOLDICH MEDALISTS 1979 Samuel S. Goldich 1992 William F. Cannon 1980 not awarded 1993 Donald W. Davis 1981 Carl E. Dutton, Jr. 1994 Cedric Iverson 1982 Ralph W. Marsden 1995 Gene LaBerge 1983 Burton Boyum 1996 David L. Southwick 1984 Richard W. Ojakangas 1997 Ronald P. Sage 1985 Paul K. Sims 1998 Zell Peterman 1986 G.B. Morey 1999 Tsu-Ming Han 1987 Henry H. Halls 2000 John C. Green 1988 Walter S. White 2001 John S. Klasner 1989 Jorma Kalliokoski 2002 Ernest K. Lehmann 1990 Kenneth C. Card 2003 Klaus J. Schultz 1991 William Hinze 2004 Paul W. Weiblen 12 �Citation Paul W. Weiblen 2004 Goldich Medal Recipient Paul W. Weiblen, or P.W., has been a friend and professional colleague for more than 40 years. We have worked together on more projects than I can remember since P.K. Sims selected us to help implement his programs at the Minnesota Geological Survey in the early 1960s. Therefore, it is my distinct honor and privilege to serve as P.W.’s citationist for the 2004 Goldich Medal. P.W. was born and raised in Miller, South Dakota, and after graduation from high school in 1945, he entered the U.S. Army. In the summer of 1945, World War II had ended in Europe, but we were still in combat with Japan. Luckily, before P.W. finished training, the war ended, and he was sent to Germany. After military service P.W. returned to college and earned a B.A. degree at Wartburg College in Waverly, Iowa (1950), and an M.A. in History at the University of Minnesota (1952). P.W. came into geology in sort of a roundabout way. Apparently, he was in Istanbul working as an agent for American Express when he met a geologist who exposed him to the wonders of the profession. Consequently, he returned to the University of Minnesota in 1959, received an M.S. degree (1962) and Ph.D. degree (1965). He stayed at the University in the Geology and Geophysics Department as an Assistant Professor (1965), Associate Professor (1969), Professor (1980), and Professor Emeritus (1997). He was hired specifically to organize and supervise the Department’s Electron Microprobe Laboratory (1965-1980). In the 1960s, electron microprobes were at the cutting edge of modern research, and this facility was one of the first in the country. Along the way he served as Curator of the petrology collection (1970-1997) and supervisor of the scanning electron microscope facility (1970-1997). He took a year off from the University to work at NASA Headquarters in Washington, D.C., and served as Director of the University’s Space Science Center (1985-1990). As an academic, P.W. served on an array of academic, professional, and service committees. That service included the Board of Directors of the Campus Club (1994-1996) and its President (1996-1997). He regularly taught courses in physical geology, igneous and metamorphic petrology, optical mineralogy/electron microprobe techniques, and numerous seminars covering all kinds of geologic topics. He served as mentor for 10 Ph.D. theses—by students including M.G. Mudrey, Jr., K.J. Schulz, R.W. Copper, R. Bauer, W. Day, J.D. Miller, Jr., S.W. Nicholson, and B. Saini-Eidukat—and 13 master’s theses. P.W. was first and foremost an igneous petrologist with eclectic interests, and he could generate ideas faster than anyone I know, which he was always willing to share. Much of the research that I have received credit over the years started out in P.W.’s brain as a throwaway. Unlike many research geologists today who focus on one narrow topic, P.W. concentrated on five separate research topics over much of his career. One subject included activities that focused primarily on the petrogenesis of the Midcontinent Rift System, especially the Duluth Complex. A second subject focused on the origin of copper- and nickel-sulfide mineralization in the Duluth Complex, especially as it relates to metal 13 �recovery from these possible ores. A third topic revolved around the origin of Archean greenstones in northern Minnesota and the high-grade gneisses in the Minnesota River Valley. A fourth subject, which he researched with Ed Roedder of the U.S. Geological Survey, focused on petrologic and geochemical attributes of melt inclusions in lunar samples obtained on various Apollo missions. Lastly, P.W. has been active in research to improve quantitative chemical analyses using electron beam techniques. Lately P.W. has delved into high-voltage electrical pulse methods for disaggregating rocks to produce clean mineral separates. All of these activities produced well over 100 publications including many presented here at the Institute. All are marked by the careful use of data, acquired both in the field and in the laboratory, and a strong intellectual component. Some of his contributions have been controversial, but they have always made us think. That thinking has led us to a better understanding of geologic processes, and for us in the Institute, a better understanding of early earth history in the Lake Superior region. Before I close, I would like to say a few words about P.W. the man. You never really know a person until you have to live with them in a tent camp after five days of rain. P.W. was always an easy-going, personable, considerate guy who was a pleasure to be around. I would go into the bush with him any day. It is my distinct honor to present to the Institute, Paul W. Weiblen as its 2004 recipient of the Goldich Medal for “Outstanding contributions to the geology of the Lake Superior region”. Submitted by G. B. Morey April 2004 14 �EISENBREY STUDENT TRAVEL AWARDS The 1986 Board of Directors established the ILSG Student Travel Awards to support student participation at the annual meeting of the Institute. The name "Eisenbrey" was added to the award in 1998 to honor Edward H. Eisenbrey (1926-1985) and utilize substantial contributions made to the 1996 Institute meeting in his name. "Ned" Eisenbrey is credited with discovery of significant volcanogenic massive sulfide deposits in Wisconsin, but his scope was much broader—he has been described as having unique talents as an ore finder, geologist, and teacher. These awards are intended to help defray some of the direct travel costs of attending Institute meetings, and include a waiver of registration fees, but exclude expenses for meals, lodging, and field trip registration. The annual Chair in consultation with the Secretary-Treasurer determines the number of awards and value. Recipients will be announced at the annual banquet. The annual Chair, who is responsible for the selection, will consider the following general criteria: 1) The applicants must have active resident (undergraduate or graduate) student status at the time of the annual meeting of the Institute, certified by the department head. 2) Students who are the senior author on either an oral or poster paper will be given favored consideration. 3) It is desirable for two or more students to jointly request travel assistance. 4) In general, priority will be given to those in the Institute region who are farthest away from the meeting location. 5) Each travel award request shall be made in writing to the annual Chair, and should explain need, student and author status, and other significant details. The form below is optional. Successful applicants will receive their awards during the meeting. I NSTITUTE ONLAKE SUPERIOR GEOLOGY Eisenbrey Student Travel Award Application Student Name: Date: Address: email: Department Head-Typed Department Head-Signature Educational Status: Are you the senior author of an oral or poster paper? YES Will any other students be traveling with you? NO Who? Statement of need (use additional page if necessary) Please return to: 15 �STUDENT PAPER AWARDS Each year, the Institute selects the best of the student presentations and honors presenters with a monetary award. Funding for the award is generated from registrations of the annual meeting. The Student Paper Committee is appointed by the annual meeting Chair in such a manner as to represent a broad range of professional and geologic expertise. Criteria for best student paper—last modified by the Board in 2001—follow: 1) The contribution must be demonstrably the work of the student. 2) The student must present the contribution in-person. 3) The Student Paper Committee shall decide how many awards to grant, and whether or not to give separate awards for poster vs. oral presentations. 4) In cases of multiple student authors, the award will be made to the senior author, or the award will be shared equally by all authors of the contribution. 5) The total amount of the awards is left to the discretion of the meeting Chair and SecretaryTreasurer, but typically is in the amount of about $500 US (increase approved by Board, 10/01). 6) The Secretary-Treasurer maintains, and will supply to the Committee, a form for the numerical ranking of presentations. This form was created and modified by Student Paper Committees over several years in an effort to reduce the difficulties that may arise from selection by raters of diverse background. The use of the form is not required, but is left to the discretion of the Committee. 7) The names of award recipients shall be included as part of the annual Chair's report that appears in the next volume of the Institute. Student papers will be noted on the Program. 2004 Student Paper Awards Committee Glenn Adams (Chair) – Doe Run Company, Viburnum, MO Angelique Magee – Ontario geological Survey, Thunder Bay, ONT Jim Small – Edward Kraemer and Sons, Burnsville, MN 2004 Session Chairs David Dahl – MN Dept. of Natural Res., Lands & Minerals Div., Hibbing, MN Jayne Englebert – MSA Professional Services, Baraboo, WI Sidney Hemming – Lamont-Doherty Earth Observatory, Palisade, NY Douglas Hunter – Wallbridge Mining Company, Lively, Ont. Jill Peterman – Wisconsin Department of Transportation, Superior, WI Mark Smyk – Ontario Geological Survey, Thunder Bay, Ont. Wanda Taylor – University of Nevada at Las Vegas, Las Vegas, NV Scott Wolter – American Petrographics Service Company, St. Paul, MN 16 �2003 BOARD OF DIRECTORS Board appointment continues through the close of the meeting year shown in parentheses, or until a successor is selected Steven A. Hauck Co-Chair 2004 Meeting (2007) Natural Resources Research Institute, University of Minnesota Duluth, Duluth, MN Laurel Woodruff (2006) U.S. Geological Survey, St. Paul, MN Peter Hinz (2005) Ontario Geological Survey, Kenora, ONT Michael G. Mudrey, Jr. (2004) Wisconsin Geological and Natural History Survey, Madison, WI Peter Hollings-Secretary-Treasurer (2006) Lakehead University, Thunder Bay, ONT 2004 LOCAL COMMITTEES General Co-Chairs Steven A. Hauck – Natural Resources Research Institute, Univ. Minn. Duluth Mark J. Severson – Natural Resources Research Institute, Univ. Minn. Duluth Program and Abstracts Editors Steven A. Hauck -- Natural Resources Research Institute, Univ. Minn. Duluth Dean Peterson -- Natural Resources Research Institute, Univ. Minn. Duluth Julie Oreskovich -- Natural Resources Research Institute, Univ. Minn. Duluth Field Trip Guidebook Editor Mark J. Severson – Natural Resources Research Institute, Univ. Minn. Duluth . Acting Local Committee, Duluth, MN Barbara Hauck – Duluth, MN John Heine – Natural Resources Research Institute, University of Minnesota Duluth Julie Heinz – Natural Resources Research Institute, University of Minnesota Duluth Charles Matsch - Department of Geological Sciences, University of Minnesota Duluth James D. Miller, Jr. – Minnesota Geological Survey, Duluth, MN Penny Morton – Department of Geological Sciences, University of Minnesota Duluth Julie Oreskovich - Natural Resources Research Institute, University of Minnesota Duluth Richard Patelke - Natural Resources Research Institute, University of Minnesota Duluth Dean M. Peterson - Natural Resources Research Institute, University of Minnesota Duluth Lawrence M. Zanko - Natural Resources Research Institute, University of Minnesota Duluth 17 �2004 BANQUET SPEAKER R. H. Dott, Jr. Department of Geology & Geophysics University of Wisconsin, Madison, WI 53706 THE VAN HISE ARMY AND OTHER PIONEERS OF LAKE SUPERIOR GEOLOGY 18 �Report of the Chair of the 49th Annual Meeting REPORT OF THE 49TH ANNUAL MEETING OF THE INSTITUTE ON LAKE SUPERIOR GEOLOGY Iron Mountain, Michigan The U.S. Geological Survey, with assistance from Michigan Technological University, hosted the 49th Annual Institute on Lake Superior Geology on May 7 – 11, 2003 at the Pine Mountain Resort in Iron Mountain, Michigan. The meeting consisted of two days of technical sessions with two pre- and two post-technical session field trips. John Gartner and Ted Bornhorst provided pre-meeting assistance. Sally LaBerge, Gretchen Klasner, and Suzanne Nicholson provided valuable logistical assistance on-site at Pine Mountain. Connie Dicken was media czar for the technical sessions, keeping all presentations on track while ignoring all needless advice. Pre-meeting registration was 104 students and professionals with an additional 61 on-site registrations, for a total of 165 registrants. Proceedings Volume 49 was published in two parts. Part I – Program and Abstracts, edited by Laurel Woodruff and Ted Bornhorst – the volume contains 45 published abstracts, for 33 oral and 12 poster presentations; and Part 2 – Field Trip Guidebook, edited by William Cannon, with assistance from Connie Dicken and Stacy Saari. The 49th meeting marked the first time in its history that an ILSG meeting was held in this part of Michigan. Field trips visited areas new to the ILSG, which may have resulted in the excellent subscription for all the trips. On Wednesday, May 7, Bill Cannon and staff from Cleveland Cliffs Mining lead a field trip to the Republic Mine, where the life cycle of the deposit, from ore genesis to mining and restoration, was covered. Three other field trips were developed to examine exposures along and on both sides of the Niagara suture zone, a major structural and geologic feature that marks the boundary between the Superior craton and the Wisconsin magmatic terranes. Klaus Schulz and Gene LaBerge lead the Wednesday field trip to the Wisconsin magmatic terrane on the southern side of the suture zone. On Saturday and Sunday, May 10 and 11, Bill Cannon, Gene LaBerge, John Klasner, and Dick Ojakangas were co-leaders for successive field trips through the Menominee Iron District (Saturday) and the Iron River – Crystal Falls area (Sunday). The Field Trip Guidebook for these three trips drew on previous studies in the area and the more than 100 cumulative years of Lake Superior geology expertise of the field trip leaders to provide a comprehensive and definitive compilation of the Paleoproterozoic stratigraphy and structure of the Niagara suture zone in this part of Michigan and Wisconsin. One hundred and twenty participants attended the banquet on Thursday night. This year’s banquet speaker was Susan Martin of Michigan Technological University. Dr. Martin is a professor of industrial archeology at Michigan Technological University and the author of the book Wonderful Power: The Story of Ancient Copper Working in the Lake Superior Basin. The title of Dr. Martin’s post-banquet talk was: The indigenous people of the Lake Superior Basin: understanding the links among environment, geology, and religious belief. As always, a highlight of the banquet was the presentation of the 2003 Goldich medal to Klaus Schulz of the U.S. Geological Survey, recognizing his long and productive career as a geologist in the Lake Superior region. 19 �The technical session began with three invited presentations. The first was by Harold Bernhardt of the Menominee Range Historical Foundation Museum on the mining history of the Menominee Iron Range. The following two talks, by Bill Cannon and Klaus Schulz, were on the Paleoproterozic rocks of the Niagara suture zone, established the context for the three field trips on that topic. The student paper committee had a difficult job this year. Twenty of the presentations in the technical sessions were from students – 15 oral and 5 posters. In the end, three awards were given: Best Student Paper ($300) went to Karoun Charkoudian (University of Wisconsin-Madison) for her talk titled: Strike-slip separation of the Burntside trondhjemite and the Wakemup Bay tonalite, Northern Minnesota. In recognition of the large number of excellent student presentations, two additional students were chosen for Honorable Mention ($100 each) - Amy Garbowicz (Lawrence University) and Stephanie Hocker (University of Wisconsin – Oshkosh). The Student Paper Award fund was supplemented by silent auction of an original volume of the classic Butler and Burbank USGS Professional Paper 144 on Copper Deposits of Michigan. Eisenbrey Student Travel Grants were given to 15 students: Greg Joslin and Phillip Larson – University of Minnesota, Duluth; Merida Keatts and Mary McKenzie – Kent State; John Marma and Karoun Charkoudian, – University of Wisconsin, Madison; Amy Garbowicz – Lawrence University; Daniela Vallini – University of Western Australia; Stephanie Hocker – University of Wisconsin-Oshkosh; and Becky Rogola, Geoff Heggie, Justin Johnson, Riku Metsaranta, Eric Potter and Adam Richardson, all from Lakehead University. All awards were presented at the conclusion of the technical sessions. The Institute’s Board of Directors met on May 8, 2003 and a brief overview of the meeting is provided below: 1. Accepted the Report of the Chair for the 48th ILSG from Peter Hinz and minutes of last Board meeting, May 14, 2002 from ILSG secretary-treasurer, Mark Jirsa. 2. Accepted the 2002-2003 ILSG Financial Summary from Mark Jirsa. 3. Approved one co-chair from the 49th meeting, Laurel Woodruff, as on-going board member. 4. Nominated George Hudak of the University of Wisconsin, Oshkosh to replace Frank Luther on the Goldich Committee, a position that George later graciously accepted. 5. Approved Duluth, Minnesota as the location for the 2004 (50th annual) ILSG and cochairs Steve Hauck and Mark Severson. 6. Discussed the transition of the Secretary Treasurer position from Mark Jirsa to Peter Hollings and accepted a proposal that both be appointed co-treasurers during the transition period. 7. Discussed the transition and evolution of the ILSG webpage and procedures required to move the ILSG into the electronic era. th 8. Discussed possible activities related to 50 meeting to commemorate the longevity and impact of the ILSG. The 49th ILSG meeting was a great success and we wish to thank all the people who contributed to that success. The staff of Pine Mountain was professional and responsive to the needs of a large group. Kleiman Pump and Well Drilling, Iron Mountain, MI, Prime Meridian Resources, Ltd., Fond du Lac, WI, and Coleman Engineering Co., Iron Mountain, MI provided generous monetary contributions. The field trips this year had a large number of participants, and thanks are due to field trip leaders, van drivers, and everyone else who stepped up when needed to drive, hand out lunches, unlock gates, or keep the crowds 20 �moving. As always, everyone who attended the 49th ILSG was willing to help as necessary or adapt to any situation that developed. The meeting this year was well attended and we are heartened by the excellent student participation and attendance, a trend we hope continues. Because of the outstanding response to the meeting and field trips, the 49th ILSG generated several thousand dollars for the ILSG general fund. We both are very happy with the outcome of the 49th meeting and hope that others think it was a success. An ILSG meeting requires a lot of work and time for all involved, but the assistance of the larger ILSG community makes the job of the co-chairs almost bearable, and we encourage others to take on the task. Laurel Woodruff and Bill Cannon Co-Chairs, 49 21 �INSTITUTE ON LAKE SUPERIOR GEOLOGY BOARD OF DIRECTORS MEETING 49th Annual Institute Meeting Thursday, May 8, 2003 Iron Mountain, Michigan Board of Directors Laurel Woodruff (2003 General Chair) William Cannon (2003 Co-chair) Peter Hinz (2002 Co-chair) Michael Mudrey (2001 Co-chair) Steve Kissin (2000 Co-chair) Peter Hollings (Institute Secretary-Treasurer) Guests Mark Jirsa (Emeritus Institute Secretary-Treasurer) Steve Hauck (proposed 2004 Co-chair) Mark Severson (proposed 2004 Co-chair) Ted Bornhorst (Communications Coordinator) Ron Sage (Goldich Committee) Frank Luther (Goldich Committee-outgoing member) The following is based on the secretaries' notes and recollection; any omissions or misstatements are unintentional. Motions by the Board of Directors are generally paraphrased—"approved" or "accepted" implying that a motion was made, seconded, and passed unanimously. The expression "generally agreed" carries less formality, but indicates a directive that will be pursued. Some issues that were resolved after the Board meeting, but during the conference are included here for closure. MINUTES 1. Peter Hinz presented his report on the 48th meeting and stressed the importance of ensuring that the audiovisual component of the sessions runs smoothly. Hinz remarked that the folder of advice to meeting chairs has been replaced by an electronic version, which Woodruff agreed to forward to the next Chairs. Jirsa noted that the full minutes of the Board of Directors Meeting is not normally published in the Proceeding Volume. Accepted report of the Chairs for the 48th ILSG, Kenora, Ontario; as printed in the Proceeding Volume (Hinz), and minutes of last Board meeting, May 14, 2002 (Jirsa). 9. Received, discussed, and accepted 2002-2003 ILSG Financial Summary (Jirsa). Bornhorst agreed to close the ILSG Michigan accounts this year. 10. Approved Laurel Woodruff as on-going board member 11. Discussed replacing Frank Luther as “academic member” on Goldich Committee (end of term 2003). George Hudak of the University of Wisconsin, Oshkosh was proposed and accepted by the Board. George later accepted the position and was welcomed. 12. Discussed and approved 2004 (50th annual) meeting location—Duluth, Minnesota, and co-chairs Steve Hauck and Mark Severson. Hauck and Severson presented a list of seven potential field trips proposed for the meeting. Bornhorst advised the co-chairs to keep field trips close to home in order to avoid impacting upon future meetings. 13. Discussed the transition of the Secretary Treasurer position from Jirsa to Hollings. Distribution of publications to be transferred to Hollings this year with transfer of the Archives and funds at the 50th Annual Meeting. Hollings to open Canadian bank accounts and arrange non-profit status for ILSG in Canada. Accepted a proposal that Jirsa and Hollings be appointed co-treasurers during the transition period. 22 �14. Discussed the transition of Webmaster from Bornhorst to Mudrey. It was agreed that the website would be moved from Michigan Tech to a commercial ISP with Mudrey and Bornhorst to coordinate the transition 15. Discussed and accepted transition from a paper to an electronic newsletter. Mudrey suggested establishing an Email list and agreed to moderate this. Woodruff, Jirsa, Mudrey and Hollings to form a committee to investigate the possibility of making the proceedings volumes available online. Committee to report to the board at the 50th annual meeting. 16. Discussed and agreed that long service pins are created for members who have been involved with the Institute for more than 15 years. Woodruff has the attendance lists and will pursue for presentation at the 50th annual meeting. 17. Other business a. Bill Cannon proposed a compilation of 50 years of ILSG photos. This would be prepared as a CD to coincide with the 50th annual meeting. Cannon will be assisted by Gene LaBarge. A request for photographs was presented to the membership at the banquet. b. It was requested by Luther that GPS locations of outcrops be included in future field guides c. Mark Smyk and Pete Hollings offered to organize 51st Annual meeting in Nipigon, Ontario in 2005, to coincide with the culmination of new geoscience initiatives in the region. Adjournment Respectfully submitted on May 13, 2003 to Laurel Woodruff, Co-chair of the 49th annual meeting, for incorporation into the Report of the Chair to appear in Proceedings Volume 50. Pete Hollings and Mark Jirsa Secretary-Treasurer, Institute on Lake Superior Geology 2003 Best Student Paper Awards Best Student Paper ($300): Karoun Charkoudian, University of Wisconsin, Madison; for her presentation co-authored with Basil Tikoff; Strike-slip separation of the Burntside trondhjemite and the Wakemup Bay tonalite, northern Minnesota. Honorable Mentions ($150 each): Amy Garbowicz, Lawrence University, Appleton, Wisconsin; for her presentation co-authored with Marcia Bjornerud; Paleostress inferences from fault slip vectors in the eastern part of the Wisconsin segment of the Midcontinent Rift. Stephanie Hocker, University of Wisconsin, Oshkosh; for her poster co-authored with G. Hudak, J. Odette, and T. Newkirk; Chemistry of alteration mineral phases at the Fivemile Lake volcanic-hosted massive sulfide prospect, northeastern Minnesota. 2003 Eisenbrey Student Travel Awards 1) Geoff Heggie, Lakehead University ($100) 2) Adam Richardson, Lakehead University ($100) 3) Justin Johnson, Lakehead University ($100) 4) Becky Rogala, Lakehead University ($100) 5) Eric Potter, Lakehead University ($100) 6) Riku Metsaranta, Lakehead University ($100) 7) Greg Joslin, University of Minnesota, Duluth ($100) 8) Phillip Larson, University of Minnesota, Duluth ($100) 9) Merida Keatts, Kent State, Ohio ($100) 10) Mary McKenzie, Kent State, Ohio ($100) 11) John Marma, University of Wisconsin, Madison ($100) 12) Karoun Charkoudian, University of Wisconsin, Madison ($100) 23 �13) Amy Garbowicz, Lawrence University, Appleton, Wisconsin ($100) 14) Stephanie Hocker, University of Wisconsin, Oshkosh ($100) 15) Daniela Vallini, University of Western Australia ($200) 2004 Goldich Medal Recipient Paul W. Weiblen, Department of Geology & Geophysics, University of Minnesota MTU Archives Donation Proceedings including Part 1 (Programs and Abstracts) and Part 2 (Field Trip Guidebook) are available from the Institute: Institute on Lake Superior Geology c/o Mark Jirsa, Secretary - Treasurer Minnesota Geological Survey 2642 University Avenue St. Paul MN 55114-1057 Phone: 612.627.4539 Fax: 612.627.4778 e-mail: jirsa001@tc.umn.edu 24 �PROGRAM 25 �The following companies made generous contributions to the 50th Annual Meeting. We thank them for their commitment to the Institute on Lake Superior Geology. For 50 years this organization has thrived through the sustained interests of individuals, corporations, universities, and government agencies in the international geologic community. This dedication to an exchange of scientific ideas and a passion for field trips (even in driving rain or snow) has enabled the ILSG to fulfill one of its primary objectives: to promote better understanding of the geology in the Lake Superior region. Franconia Minerals Corporation, Spokane, WA Idea Drilling Incorporated, Virginia, MN Iron Mining Association, Duluth, MN Lehmann Exploration Management, Minneapolis, MN Meriden Engineering, LLC, Hibbing, MN Minerals Processing Corporation, Duluth, MN Minnesota Exploration Association (MExA), Minneapolis, MN Minnesota Minerals Coordinating Committee, St. Paul, MN Teck Cominco American Incorporated, Spokane, WA Wallbridge Mining Company, Lively, ONT 26 �Tuesday May 4, 2004 7:30 a.m. Field Trip 1: Volcanic stratigraphy, hydrothermal alteration, and VMS potential of the lower Ely Greenstone, Fivemile Lake to Sixmile Lake area. Field Trip Leaders: George Hudak (UWO), John Heine (NRRI), Mark Jirsa (MGS), Dean Peterson (NRRI). 6:00 p.m. Overnight in Tower, MN at Fortune Bay Casino. 8:00 a.m. Field Trip 2: Geologic Highlights of New Mapping in the Southwestern Sequence of the North Shore Volcanic Group and Beaver Bay Complex. Field Trip Leaders: Terry Boerboom (MGS), Jim Miller (MGS), and John Green (UMD – Dept. of Geol. Sci.). 6:00 p.m. Overnight in Duluth on your own. Wednesday May 5, 2004 8:00 a.m. Field Trip 2: Geologic Highlights of New Mapping in the Southwestern Sequence of the North Shore Volcanic Group and Beaver Bay Complex. Field Trip Leaders: Terry Boerboom (MGS), Jim Miller (MGS), and John Green (UMD – Dept. of Geol. Sci.). 8:00 a.m. Field Trip 3: Late Wisconsinan Superior-lobe Deposits in the Lake Superior Basin Northeast of Duluth. Field Trip Leader: H. Hobbs (MGS). 8:00 a.m. Field Trip 4: Geology of the Eastern Mesabi Iron Range, Northeastern Minnesota. Field Trip Leaders: R. Ojakangas (UMD – Dept. of Geol. Sci.), M. Severson (NRRI), P. Jongewaard (United Taconite), D. Halverson (Northshore mining), J. Arola (Inland), J. Evers (Cliffs-Services). 6:00 p.m. - Return of Trips 1, 2, 3, and 4 4:00 p.m. - 8:00 p.m. Registration 7:00 p.m. - 9:00 p.m. Ice Breaker Social and Poster Setup 27 �Thursday May 6, 2004 7:00 a.m. – 4:00 p.m. REGISTRATION 8:00 a.m. – 8:05 a.m. INTRODUCTORY REMARKS Steven A. Hauck and Mark J. Severson, Co-Chairs SPECIAL TECHNICAL SESSION I The History of Geologic Investigations in the Lake Superior Region Session Chairs: Mark Smyk, Ontario Geological Survey, Thunder Bay, ONT Sidney Hemming, Lamont-Doherty Lab., Columbia Univ., NY 8:05 a.m. – Old Prospector “Gold is Where You Find It! So Is Ag and Cu and Fe!” The OLD PROSPECTOR: Gold Rushes and Mineral Prospecting, 1848 to 1900 in Western North America and The Lake Superior Region 8:35 a.m. – Johnson, A.M. Douglass Houghton’s 1840 Field Excursion to Lake Superior 8:55 a.m. – Miller, J.D., Jr. N.H. Winchell's Study of the Keweenawan Supergroup Rocks of Northeastern Minnesota, 1872-1900 9:15 a.m. – Smyk, M.C., and Magee, A. Silver Threads and Golden Needles: Geological Milestones in Northwestern Ontario 9:35 a.m. – Holm, D.K., Van Schmus, R.W., and Schneider, D.A. The Influence of Radiometric Dating for Unraveling the Precambrian Geologic History of the Lake Superior Region 9:55 a.m. - 10:20 a.m. COFFEE BREAK AND POSTER SESSION 10:20 a.m. – Chandler, V.W., Boerboom, T.J., and Jirsa, M.A. Promontory Tectonics of the Penokean Orogen in Minnesota: A Gravity and Magnetic Perspective 10:40 a.m. – Medaris, G., Jr., and Singer, B. Geochronology of Precambrian Rocks in Central Wisconsin: A Review and New 40 Ar/ 39Ar Analyses 11:00 a.m. – Southwick, D.L. Late Paleoproterozoic Rhyolite-Quartzite Sequences in the Southwestern U.S.: Speculative Relationship to Rocks of the Baraboo Interval 11:20 a.m. – Ormand, C.J., and Czeck, D.M. Three-Dimensional Geometry and Strain of the Baraboo Syncline: Kinematic Implications 28 �11:40 a.m. – Fralick, P., and Pufahl, P.K. Oxygenation of the Archean Hydrosphere: Evidence from the Eagle Island Deltaic Complex 12:00 p.m. – 1:10 p.m.–LUNCH BREAK – POSTER SESSION and ILSG BOARD MEETING (by invitation) TECHNICAL SESSION II Session Chairs: Jill Peterman, Wisconsin Department of Transportation, Superior, WI Dave Dahl, MN Dept. Natural Resources, Lands & Minerals Div., Hibbing, MN 1:10 p.m. – Metsaranta, R.T.*, and Fralick, P.W. Geochemistry and Petrography of Altered Basement Rocks Underlying the Middle Proterozoic Sibley Group 1:30 p.m. – Heggie, G.*, and Hollings, P. Multiple Intrusive Stages Associated with Keweenawan Rifting: The Leckie Stock, Seagull Intrusion, and Nipigon Sill. 1:50 p.m. – Richardson, A.*, and Hollings, P. A Geochemical Study of the Sills of the Nipigon Basin, Ontario 2:10 p.m. – Boerboom, T.J. Newly Recognized Diatreme Breccia Dikes on Lake Superior Near Two Harbors, Minnesota 2:30 p.m. – 2:55 p.m. COFFEE BREAK AND POSTER SESSION 2:55 p.m. – Hollings, P. Trace Element Geochemistry of the Osler Group Volcanics – Implications for Mid-Continent Rifting 3:15 p.m. – Hart, T.R. Geochemistry of the Proterozoic Intrusive Rocks of the Nipigon Embayment 3:35 p.m. – MacDonald, C.A. and Tremblay, E. Lake Nipigon Region Geoscience Initiative: Results of Bedrock Mapping in the Northern Part of the Western Nipigon Embayment, Northwestern Ontario, Canada 3:55 p.m. – Schneider, R.V. Depth Migration of Seismic Reflection Data: An Example for Lake Superior Studies Ballroom Must Be Empty by 4:30 p.m. for Banquet Setup. 6:00 p.m. ICE BREAKER – MIXER – CASH BAR 7:00 p.m. ANNUAL BANQUET AND AWARD PRESENTATION • • • Announcement of 51st Annual Meeting Location 2004 Goldich Award Presentation to Paul Weiblen 2004 Banquet Address Meeting participants who are not registered for the banquet are welcome to attend the banquet address. 29 �Friday May 7, 2004 8:00 a.m. – 8:05 a.m. INTRODUCTORY REMARKS Steven A. Hauck and Mark J. Severson, Co-Chairs TECHNICAL SESSION III Session Chairs: Jayne Englebert, MSA Professional Services, Baraboo, WI Douglas Hunter, Wallbridge Mining Company, Lively, Ontario, Canada 8:05 a.m. – Johnson, J.R.,* Hollings, P., and Kissin, S. Regional Geochemistry Surrounding the Norton Lake Cu-Ni-PGE Deposit, Uchi Subprovince, Ontario 8:25 a.m. – Rossell, D.M., and Coombes, S. The Geology of the Eagle Nickel-Copper Deposit: Marquette County, Michigan 8:45 a.m. – Mahin, R.A., Quigley, T.O., and Lynott, J.S. The Discovery and Geology of the L-K Massive Sulfide Deposit, Menominee County, MI 9:05 a.m. – Bornhorst, T.J., and Robinson, G.W. Precambrian Aged Supergene Alteration of Native Copper Deposits in the Keweenaw Peninsula, Michigan 9:25 a.m. – Severson, M.J., and Hauck, S.A. Whatever Happened to Those Cu-Ni Deposits? 9:45 a.m. – Shafer, P.L.,* and Ripley, E.M. Hydrogen Stable Isotopic Evidence for Hydrothermal Alteration and PGE Concentration Involving Meteoric Water in the Birch Lake Area, Duluth Complex, MN 10:05 a.m. - 10:30 a.m. COFFEE BREAK AND POSTER SESSION 10:30 a.m. – Hudak, G.J., Newkirk, T.T., Drexler, H., Odette, J.D., and Hocker, S.M. Neoarchean Peperites in the Vicinity of Fivemile Lake, Vermilion District, NE Minnesota 10:50 a.m. – Han, T.-M. Effect of Mineralogy on Processing of Low Grade Iron Ores From the Negaunee IronFormation on Marquette Range of the Lake Superior District 11:10 a.m. – Fosnacht, D., Iwasaki, I., and Bleifuss, R. Iron Nodule Research at the Natural Resources Research Institute, UMD 11:30 a.m. – Zanko, L.M., Oreskovich, J.A., and Niles, H.B. Taconite Aggregate Potential of Coarse Tailings from the Biwabik Iron Formation, With an Emphasis on Geology, Mineralogy, and Microscopy 11:50 a.m. – Larson, P.C., Regional Till Sampling in the Vermilion Greenstone Belt, Minnesota: Preliminary Results and Interpretations 30 �12:10 p.m. - 1:00 p.m. LUNCH BREAK – POSTERS REMOVED AFTER LUNCH SPECIAL TECHNICAL SESSION IV Department of Geological Sciences, University of Minnesota Duluth Fifty Years of Geological Contributions to Lake Superior Geology and Other Geological Areas 1:00 p.m. – Introductory Remarks on 50 years of Geology at University of Minnesota, Duluth: Penny Morton Session Chairs: Scott Wolter, American Petrographics Service Company, St. Paul, MN Wanda Taylor, University of Nevada at Las Vegas, Las Vegas, NV 1:05 p.m. – Ojakangas, R.W., and Ojakangas, G.W. Deposition of Paleoproterozoic Siliciclastics and Iron-Formation in a Tidally Influenced Shelf Environment, Animikie Basin, Lake Superior Region 1:25 p.m. – Breckenridge, A.* The Lake Superior Varve Stratigraphy and Implications for Eastern Lake Agassiz 14 Outflow From 10,700 to 8,900 YBP (9.5-8.0 C KA) 1:45 p.m. – Syverson, K.M. Origin of Pre-Wisconsinan Glacial Units in Northern Wisconsin Based on Lithologic Characteristics 2:05 p.m. – Jirsa, M.A. Mapping by the Minnesota Geological Survey in Support of Land-use and Water Planning on the Mesabi Iron Range 2:25 p.m. – Brown, T.R. Recent Geophysical and Geochemical Applications to Exploration Activities in Cripple Creek Mining District, Colorado 2:45 p.m. – 3:10 p.m. 3:10 p.m. the COFFEE BREAK AND POSTER SESSION Student Paper and Travel Awards 3:20 p.m. – Vervoort, J.D., and Wirth, K.R. Origin of the Rhyolites and Granophyres of the Midcontinent Rift, Northeast Minnesota 3:40 p.m. – Schmidt, S.Th., and Seifert, K. Ocean-Floor-Type-Alteration of Drilled MRS Volcanic Rocks in Iowa 4:00 p.m. – Davidson, D.M., Jr. Heller, Sims and Marsden: Mentors Extraordinaire 4:20 p.m. – Grant, J.A. Isocon Analysis: How to Make It Work for You 4:40 p.m. – Morton, R. Twenty-One Years in a Caldera: UMD Geology Students and Sturgeon Lake, Ontario 31 �5:30-7:30 p.m. Buffet at the Depot Sponsored by the UMD Dept. of Geological Sciences (All ILSG Registrants are invited) Saturday May 8, 2004 8:00 a.m. Field Trip 5: Classic Outcrops of Northeastern Minnesota. Field Trip Leaders: M. Jirsa (MGS), T. Boerboom (MGS), R. Ojakangas (UMD-Dept. Geol. Sci.), J. Miller (MGS), J. Green (UMD-Dept. Geol. Sci.), G.B. Morey (MGS), D. Peterson (NRRI), M. Severson (NRRI), R. Patelke (NRRI). 6:00 p.m. Overnight in Tower, MN at Fortune Bay Casino. 8:00 a.m. Field Trip 6: Glacial and Postglacial Landscape Evolution in the Glacial Lake Aitkin and Upham Basin, Northern Minnesota. Field Trip Leaders: L. Marlow, P. Larson, H. Mooers (UMD-Dept. Geol. Sci.). 6:00 p.m. Return of Trip to Radisson Hotel, Duluth Minnesota. 7:00 a.m. Field Trip 7: Economic Geology of Archean Gold Occurrences in the Vermilion District, Northeast of Soudan, Minnesota. Field Trip Leaders: D. Peterson (NRRI), R. Patelke (NRRI). 6:00 p.m. Return of Trip to Radisson Hotel, Duluth Minnesota. 8:00 a.m. Field Trip 8: Geology of the Western Contact of the Duluth Complex, Partridge River and South Kawishiwi Intrusions, Northeastern Minnesota. Field Trip Leaders: M. Severson (NRRI), J. Miller, Jr. (MGS). 6:00 p.m. Return of Trip to Radisson Hotel, Duluth Minnesota. Sunday May 9, 2004 8:00 a.m. Field Trip 5: Classic Outcrops of Northeastern Minnesota. Field Trip Leaders: M. Jirsa (MGS), T. Boerboom (MGS), R. Ojakangas (UMD-Dept. Geol. Sci.), J. Miller (MGS), J. Green (UMD-Dept. Geol. Sci.), G.B. Morey (MGS), D. Peterson (NRRI), M. Severson (NRRI), R. Patelke (NRRI). 6:00 p.m. Return of Trip to Radisson Hotel, Duluth Minnesota. 32 �POSTER PRESENTATIONS Boerboom, T.J. Bedrock Geologic Maps of the Two Harbors and Castle Danger 7.5-Minute Quadrangles, North Shore of Lake Superior, Minnesota Buchholz, T.W., Falster, A.U., and Simmons, Wm.B. A Greisen-like Mineral Assemblage from the Nine Mile Pluton, Marathon County, Wisconsin Cordua, W.S. Enigmatic 1300 – 1400 Ma Mafic Pluton from the Koss Pit, Marathon County, WI Drexler, H.L.*, Hudak, G.J., and Peterson, D.M. A Field and Laboratory Study to Evaluate the Genetic Relationships Between the Purvis Pluton and Volcanic Rocks and Volcanic-Associated Mineralization in the Vermilion District of NE Minnesota Erickson, M.L.*, and Barnes, R.J. Late Wisconsin Till and Arsenic Contamination in Upper Midwest Groundwater Fitzpatrick, F.A. Influence of Geologic Setting on Hydrogeomorphic Characteristics of Southern Lake Superior Tributaries Green, J.C., and Miller, J.D., Jr. The Geology of the Duluth Complex and the North Shore Volcanic Group Portrayed in New 7.5' Quadrangle Maps of the Duluth Metropolitan Area Hart, T.R., and Magyarosi, Z. Precambrian Geology and Mineralization of the Northern Black Sturgeon River area, Nipigon Embayment Hemming, S.R., and Roy, M. 40 Ar/39Ar Hornblende Evidence for Provenance of Ice Rafted Detritus in the North Atlantic: Implications for Tracking Past Changes in the Extent and Dynamics of Northern Hemisphere Ice Sheets Hoffman, A.T.*, Peterson, D.M., Patelke, R.L., and Hudak, G.J. Preliminary Petrography and Hydrothermal Alteration of the Soudan Mine Area, Vermilion District, Northeastern Minnesota Jirsa, M.A. Regional Compilations of Bedrock Geology in Northern Minnesota: The Vermilion, Ely, and Basswood Lake Quadrangles Kaukonen, R.J., and Alapieti, T.T. Platinum Mineralization at Drill Hole A4-11 of the Wetlegs Area of the Partridge River Intrusion, Duluth Complex, Northeast Minnesota 33 �Kean, Wm.F. Magnetic Susceptibility Anisotropy and Remanent Magnetism of Quartzite and Phyllite from Baraboo, Wisconsin Klawiter, B. Lithic Materials and Archaeology in the Western Lake Superior Region Larson, P.C., Mooers, H.D., and Marlow, L.M. Early Advance of the St. Louis Sublobe: A Revised Chronology of the Deglaciation of Northeastern Minnesota MacDonald, C.A., and Tremblay, E. Precambrian Geology of the South Armstrong–Gull Bay Area, Nipigon Embayment, Northwestern Ontario, Canada Maes, S., Tikoff, B., Brown, P., and Ferré, E. Magnetic Fabric Constraints on Magmatic Flow: Insizwa Sill, South Africa and the Sonju Lake Intrusion, Minnesota. Magee, A. Mining and Exploration Activities in Northwestern Ontario Mahin, R.A., Quigley, T.O., and Lynott, J.S. The Geology of the L-K Massive Sulfide Deposit, Menominee County, MI McSwiggen, P.L., and Morey, G.B. Mineral Chemistry and Stratigraphy of the Biwabik Iron Formation, Near the Virginia Horn, Mesabi Iron Range, Minnesota Mudrey, M.G., Jr., and Cannon, W.F. Status of Publicly Available Mid-Continent Reflection Seismic Data Patelke, R., and Severson, M. Duluth Complex Bulk Samples Patelke, R., Severson, M., and Peterson, D. Untested Targets in the Duluth Complex Peterson, D.M., and Patelke, R.L. The Proposed National Underground Science and Engineering Laboratory at the Soudan Mine, Northeastern Minnesota: A Geological Site Investigation Piercey, P., Schneider, D.A., and Holm, D.H. Petrotectonic Evolution of Paleoproterozoic Granitic Rocks Across the Central Penokean Orogen, Northern MI and WI Planavsky, N.*, and Bjornerud, M. Blowing in the Wind: The Copper Harbor Stromatolites Revisited Ruhanen, R.W. Geologic Reconnaissance of the Spaulding Mine Area, Cook County, Minnesota 34 �Schneider, R.V. Depth Migration of Seismic Reflection Data: An Example for Lake Superior Studies Stott, G.M. Close Proximity of Kimberlite Pipes to Diabase Dykes: Structural Controls and Predictiveness in the James Bay Lowlands, Ontario Trow, J. Dowsing Employs Classical Mechanics and Static Electricity to Locate SelfPotential Anomalies Inductively and Rapidly NOTE: Asterisk * denotes a student eligible for a Best Student Paper Award. 35 �ABSTRACTS 36 �BEDROCK GEOLOGIC MAPS OF THE TWO HARBORS AND CASTLE DANGER 7.5MINUTE QUADRANGLES, NORTH SHORE OF LAKE SUPERIOR, MINNESOTA BOERBOOM, Terrence J., Minnesota Geological Survey, boerb001@umn.edu Two recent quadrangle-scale geologic maps of an area adjacent to Lake Superior have been published by the Minnesota Geological Survey as part of the U.S. Geological Survey STATEMAP program. This ongoing mapping effort has resulted in five published quadrangle geologic maps in an area stretching from Duluth to Castle Danger (Boerboom and others, 2002a, b, 2003a, b; Fig. 1a). Work is currently in progress on a sixth geologic map (Split Rock Point); and another (Two Harbors NE) will be mapped in the coming year. Field mapping for all these maps was or will be conducted at a scale of 1:12,000, and map compilations are at 1:24,000. The North Shore is experiencing ever-increasing development of both commercial property and private residences, creating a concomitant demand on ground-water resources, which near Lake Superior come mainly from bedrock reservoirs, particularly layered volcanic flows and interflow sedimentary rocks. Development also brings an increased need for quality aggregate materials for both construction and shoreline preservation projects. Although some volcanic flows may be suitable for crushed-rock aggregate, the intrusive rocks are likely to provide the best source of this material. Thus, the goal of this mapping is to refine the stratigraphy of volcanic rocks in the southwest limb of the North Shore Volcanic Group, and to identify the extent, mineralogy, and relationships of intrusive rocks emplaced into the volcanic pile. This mapping will not only lay the groundwork for present and future resource demands, but also further our understanding of the geologic aspects of these rocks. 37 �Green (2002) subdivided volcanic rocks of the Keweenawan North Shore Volcanic Group into a series of informal lithostratigraphic units based on the relative thickness and composition of the volcanic flows or by areas separated by intervening intrusions. Several of these units were extended into the Two Harbors and Castle Danger quadrangles from the southwest (Fig. 1b). Two new lithostratigraphic units were added to those of Green (2002) based on this mapping⎯the Stewart River basalts and the Crow Creek lavas (Fig. 1b). The Stewart River basalts include several flows of diabasic-textured basaltic lavas and an ambiguous unit that has attributes of both a lava flow and an intrusion, interpreted as a shallow-level subvolcanic intrusion that breached the surface to form flows along its upper margin. The Crow Creek lavas are named for olivine tholeiitic and andesitic flows that outcrop mainly along Crow Creek. These lavas contrast with flows east of the Lafayette Bluff diabase and west of the Silver Creek diabase, implying that the intrusions have created a major disruption of the volcanic stratigraphy. Mapping has refined the shape and intrusive relationships of known intrusions, and has identified several new intrusions. Most noteworthy among these is the previously known but poorly understood Two Harbors intrusion, which has been shown to form a small, zoned, east-plunging, synform-shaped body. This intrusion grades from troctolitic diabase through poikilitic olivine gabbro to well-foliated intergranular gabbro, from the lowest exposed to the highest exposed portions of the body. Another smaller body of more massive olivine-rich ophitic olivine diabase may be related to the Two Harbors intrusion, but does not exhibit any consistent modal or textural layering. Of particular interest is the recognition of a diatreme-like breccia that cuts volcanic rocks near the mouth of Crow Creek (Boerboom, 2004). This diatreme contains clasts from less than 1 millimeter to 5 meters in size, in a matrix of zeolite- and chlorite-cemented rock flour. The clasts include a heterogeneous mixture of fine-grained porphyritic basalt, amygdaloidal to ophitic to intergranular basalt, and interflow sedimentary rocks. Fine-grained felty-textured prismatic ferromonzodiorite also occurs as intrusions into basalt adjacent to the diatreme, and as clasts in the diatreme, indicating a possible cogenetic relationship between the two. References Boerboom, T.J., 2004, Newly recognized diatreme breccia dikes on Lake Superior near Two Harbors, Minnesota [abs.]: Institute on Lake Superior Geology (this volume). Boerboom, T.J., Green, J.C., and Jirsa, M.A., 2002a, Bedrock geology of the French River and Lakewood quadrangles, St. Louis County, Minnesota: Minnesota Geological Survey Miscellaneous Map M-128, scale 1:24,000. ———2002b, Bedrock geology of the Knife River quadrangle, St. Louis and Lake Counties, Minnesota: Minnesota Geological Survey Miscellaneous Map M-129, scale 1:24,000. Boerboom T.J., Green, J.C., and Miller, J.D., Jr., 2003a, Bedrock geologic map of the Castle Danger quadrangle, Lake County Minnesota: Minnesota Geological Survey Miscellaneous Map M-140, scale 1:24,000. ———2003b, Bedrock geologic map of the Two Harbors quadrangle, Lake County Minnesota: Minnesota Geological Survey Miscellaneous Map M-139, scale 1:24,000. Green, J.C., 2002, Volcanic and sedimentary rocks of the Keweenawan Supergroup in northeastern Minnesota, Chapter 5 of Miller, J.D., Jr., Green, J.C., Severson, M.J., Chandler, V.W., Hauck, S.A., Peterson, D.M., and Wahl, T.E., 2002, Geology and mineral potential of the Duluth Complex and related rocks of northeastern Minnesota: Minnesota Geological Survey Report of Investigations 58, p. 94-105. Miller, J.D., Jr., Green, J.C., Severson, M.J., Chandler, V.W., and Peterson, D.M., 2002, Geologic map of the Duluth Complex and related rocks, Northeastern Minnesota: Minnesota Geological Survey Miscellaneous Map M-119, scale 1:200,000. Sandberg, A.E., 1938, Section across Keweenawan lava flows at Duluth, Minnesota: Geological Society of America Bulletin, v. 49, p. 795-830. Schwartz, G.M., and Sandberg, A.E., 1940, Rock series in diabase sills at Duluth, Minnesota: Geological Society of America Bulletin, v. 51, p. 1135-1172. 38 �NEWLY RECOGNIZED DIATREME BRECCIA DIKES ON LAKE SUPERIOR NEAR TWO HARBORS, MINNESOTA BOERBOOM, Terrence J., Minnesota Geological Survey, boerb001@umn.edu Recent mapping by the Minnesota Geological Survey during the 2002 and 2003 field seasons (see Boerboom, 2004) has identified two nearly identical diatreme-like breccias located about 15 kilometers apart, both of which intrude volcanic rocks of the North Shore Volcanic Group. One is located near the mouth of Crow Creek, 3 kilometers southwest of Castle Danger, and the other is located near the mouth of the Split Rock River. The diatremes contain clasts that range up to four meters in diameter. The clasts are composed of typical North Shore volcanic group rocks, including intergranular to ophitic basalt, porphyritic basalt, and minor interflow sedimentary rocks, as well as felty-textured prismatic monzodiorite that also occurs as intrusions into basalts adjacent to the diatremes. At both places the clasts are heavily replaced by zeolites (mainly laumontite) and chlorite, and are surrounded by a matrix of zeolites and chlorite mixed with rock flour. Irregularly distributed brown gossans that probably represent zones of pyritic matrix have also been identified at Crow Creek. The Crow Creek diatreme is the best exposed of the two diatremes, but outcrops are mainly accessed by water. Exposures on a shore-parallel high cliff wall and in cliffs of basalt that are cut by the breccia and protrude into the lake show the dike to be approximately 10 meters wide and vertical in orientation, with clasts up to 4 meters in size. At the shore the dike is oriented approximately east–west, but other scattered, low outcrops inland imply that the dike may have an overall 0.25 mile diameter ring-like structure or a very irregular strike direction. Monzodiorite associated with this diatreme is poorly exposed, and where visible contains abundant angular basalt clasts and small amygdules of chlorite and calcite. The same monzodiorite also occurs as clasts in the diatreme, thus it must have preceded the diatreme in timing but may have been closely associated with it. The Split Rock River diatreme is exposed just southeast of the river mouth as a 6-meter wide, northstriking, subvertical dike that truncates amygdule-layered tholeiitic basalts. This dike contains clasts of both intergranular and ophitic basalt up to 20 centimeters in diameter, and small clasts of interflow sedimentary rocks and ferromonzodiorite petrographically identical to that at Crow Creek. The latter also occurs alone in an outcrop near the diatreme. Narrow, dike-parallel, anastamosing zones of brecciation cut both basalt and ferromonzodiorite in the vicinity of the diatreme dike. In both cases, the brecciated texture, multiple clast varieties of North Shore volcanic group-related rocks and sharp cross-cutting contacts with adjacent volcanic rocks imply that the diatremes were emplaced as an explosive, gascharged intrusion that cut across the volcanic strata. The amygdaloidal and deuterically-altered Lafayette Bluff diabase occurs in close proximity to the Crow Creek diatreme (Boerboom and others, 2003), which may have provided a source of volatiles as it cooled. These diatremes are soft and easily eroded and thus unlikely to form significant outcrops inland, and they could easily be misidentified as a volcanic flow breccia. Careful examination of isolated or seemingly out of sequence flow breccias for disparate clast lithologies may reveal more of these diatreme dikes. REFERENCES Boerboom, T.J., 2004, Bedrock geologic maps of the Two Harbors and Castle Danger 7.5-minute quadrangles, North Shore of Lake Superior, Minnesota [abs.]: Institute on Lake Superior Geology (this volume). Boerboom, T.J., Green, J.C., and Miller, J.D., Jr., 2003, Bedrock geology of the Castle Danger quadrangle, Lake County, Minnesota: Minnesota Geological Survey Miscellaneous Map M-140, scale 1:24,000. 39 �Precambrian Aged Supergene Alteration of Native Copper Deposits in the Keweenaw Peninsula, Michigan BORNHORST, Theodore J., and ROBINSON, George W., A.E. Seaman Mineral Museum, Michigan Technological University, Houghton, MI 49931 The Keweenaw Peninsula within the Midcontinent Rift System is host to a world-class native copper mining district from which about 6 billion kg of refined copper was mined from 1845 to 1968. By far the principal economic minerals mined were native copper and native silver. Supergene alteration minerals occur irregularly throughout the district. The most abundant of these are cuprite, tenorite, malachite, and chrysocolla in close association with native copper. Less common are azurite and paramelaconite, though about fifty additional species are known (Table 1). These minerals typically occur as thin coatings on or replacing native copper, irregular thin coatings along fractures, and euhedral crystals in small pockets filling remaining pore space. For the most part supergene minerals are found near the surface (< 300 m) and are well below the current water table. As might be expected, sulfates are conspicuously uncommon, owing to the general absence of sulfide ores in the district. Likewise, the arsenates (e.g., annabergite, tyrolite, erythrite, etc.) are associated with the copper arsenide minerals domeykite and algodonite. One group, however, the chlorides (e.g., paratacamite, calumetite, etc.), may have formed by reaction with fossil brines, rather than strictly supergene means, as these minerals have been found in isolated areas 1375 m below surface with no visible means of connection to downward-moving meteoric waters. The rocks of the Midcontinent Rift System were deposited between roughly 1.1 and 1.0 Ga, and late in the evolution of the rift (about 1.05 Ga) the rift was subjected to regional compression resulting in reverse faulting, uplift, and sediment deposition. During this compression event, native copper was deposited from a large-scale hydrothermal system along with numerous other hydrothermal minerals. Uplift related to reverse faulting likely continued for some time after the formation of the native copper deposits, likely ending about 1.0 Ga. The rift rocks of the Keweenaw Peninsula were subjected to erosion. If enough cover was removed, the native copper could have been sufficiently near the surface to be exposed to oxygenated groundwater, which would form supergene minerals. Erosion ended by the end of Precambrian time, when the rift rocks were unconformably overlain by Paleozoic sediments, which still cover major portions of the rift. These sediments sheltered the rift rocks of the Keweenaw Peninsula from weathering and erosion. The Paleozoic sediments were removed by Pleistocene glaciers, again making supergene alteration possible. Since the last glacial retreat it is probable that the water table has not been significantly lower than it is today. In turn, Pleistocene supergene alteration should be more or less restricted to above the current water table. Because most observed supergene alteration is below the water table, it is unlikely that it formed since the glaciers removed the Paleozoic cover. Thus, supergene alteration must have occurred during/near the end of the protracted period of erosion in late Precambrian time. The copper deposits had to be reasonably near the surface at that time for supergene alteration to occur. While the Pleistocene glaciers removed significant thickness of Paleozoic cover they could not have removed any significant thickness of rift rocks, else the supergene altered zones would have been removed too. Therefore, the current surface of the Keweenaw Peninsula is likely near the same stratigraphic/erosional level that was present when the Keweenawan rocks were buried by Paleozoic sediments. 40 �acanthite annabergite anthonyite ardennite ? atacamite azurite brochantite buttgenbachite calcite calumetite carbonate-cyanotrichite chalconatronite chrysocolla connellite covellite crednerite cuprite dioptase erythrite gerhardtite goethite guerinite gypsum halite humboldtine ? hydromagnesite kaolinite langite lavendulan likasite malachite manganite mirabilite montmorillonite moolooite ? nantokite olivenite paramelaconite paratacamite pharmacolite picropharmacolite plancheite posnjakite pseudomalachite rauenthalite spertiniite tenorite tyrolite vaterite veszelyite vladimirite whewellite ? unknown Ca-Cl mineral unknown Cu-Cl minerals unknown Cu-Ca-Cl mineral Table 1. Supergene minerals found or reported from the Keweenaw native copper deposits. 41 �THE LAKE SUPERIOR VARVE STRATIGRAPHY AND IMPLICATIONS FOR EASTERN LAKE AGASSIZ OUTFLOW FROM 10,700 TO 8,900 CAL YBP (9.5 - 8.0 14C KA) BRECKENRIDGE, Andy, Large Lakes Observatory, University of Minnesota Duluth, 10 University Drive, 109 RLB, Duluth, MN 55812-2496, brec0027@d.umn.edu Glaciolacustrine rhythmites from Lake Superior record the regional recession of the Laurentide Ice Sheet (LIS) from 10,700 to 8,900 cal ybp (ca. 9.5-8.0 14C ka). LIS retreat from Superior opened eastern Lake Agassiz outlets so that the rhythmites reflect the combined impacts of sediment-laden meltwater and Lake Agassiz discharge. Using sediment cores retrieved from Lake Superior, I present rhythmite stratigraphies, a time series analysis of the thickness measurements, and high-resolution inorganic carbonate data to demonstrate that this is an annual record (varved). The varve thickness records primarily document regional ice margin dynamics: thick varve sequences at 9,100 cal ybp (~8.1 14C ka) and 10,400-10,200 cal ybp (~9.29.0 14C ka) record two periods of moraine formation (the Nakina and Nipigon). General varve cessation is associated with the circumvention of Lake Agassiz and glacial meltwater into Lake Ojibway at 9,040 cal ybp (~8.1 14C ka), although adjacent to meltwater inlets, rhythmic sedimentation persisted for another 200 years. Positively identifying Lake Agassiz catastrophic discharge events remains speculative but seems feasible. The initial influx of Lake Agassiz water is expected at around 10,600 cal ybp (~9.4 14C ka), but at this time, most of eastern and northern Lake Superior was covered by ice. Three sets of thick-thin varves in western Lake Superior perhaps record influxes of Lake Agassiz at around 10,630, 10,600, and 10,570 cal ybp (~9.4 14C ka). Varve formation in Superior coincides with high lake levels in Lake Huron, suggesting that high lake levels in Huron correspond to periods of high Agassiz and/or meltwater flow into Lake Superior. 42 �Recent Geophysical and Geochemical Applications to Exploration Activities in the Cripple Creek Mining District, Colorado BROWN, Timothy R., Cripple Creek and Victor Gold Mining Company, P.O. Box 191, Victor, CO 80863, tbrown@anglogoldna.com Approximately 23 million ounces of gold have been produced from underground and surface operations since gold was discovered in the Cripple Creek Mining District in 1891. This total includes nearly 2 million ounces produced by Cripple Creek and Victor Gold Mining Company (CC&V) over the past 10 years. Gold has been produced from numerous veins in a 30 MA alkaline diatreme complex and is strongly associated with intense potassic alteration. Current production is mining low-grade disseminated haloes around the major historic producers from two open pits and the gold is recovered from a heap leach facility. This rate of production, and future production, in a mature mining district could not take place without an aggressive, ongoing exploration program that utilizes every available tool. Airborne geophysical surveys conducted in 1999 included magnetics, resistivity, and radiometrics. The magnetic survey clearly outlines the diatreme and shows numerous geological, structural, and cultural features inside the diatreme while contributing to the understanding of the alteration. Resistivity has given a better understanding of the zones of clay, potassic alteration, and possibly water. All of these suggest the location of structural features. The radiometric survey, and especially K, outlines large zones of alteration, however this is strongly influenced by historical and recent disturbances as well as the leach pad. IP and CSAMT surveys were initiated in 2001 and the results were encouraging enough to launch a much larger survey in 2002 that covered 37 line miles. The density of data allowed us to model and display the information in several different ways that include plans, sections, and 3D shells. CC&V utilizes a survey tool that captures oriented joint and fracture information with a down-hole camera. This tool captures important geotechnical data as well as structural orientations that can be cross-referenced to assay data. The geochemical relationships between Au and Te and the potassic alteration have long been known in the district. Recent studies have shown a consistent relationship between gold and other elements (As, Hg, Sb, and V) and have suggested high-grade gold always occurs with strong potassic alteration although strong potassic alteration does not always indicate zones of high-grade gold. Application of the knowledge gained from a better understanding of the district’s geology, alteration, and structure has led to focused, efficient drilling programs. The results of the exploration programs have continued to add to the operations as mid-year 2003 reserves stand at 4.2 million ounces and production is scheduled to continue through 2013. 43 �A GREISEN-LIKE MINERAL ASSEMBLAGE FROM THE NINE MILE PLUTON, MARATHON COUNTY, WISCONSIN BUCHHOLZ, Thomas W., 1140 12th Street North, Wisconsin Rapids, Wisconsin 54494, FALSTER, Alexander U., and SIMMONS, Wm.B., Department of Geology and Geophysics, University of New Orleans, New Orleans, Louisiana 70148. The Nine Mile pluton is the youngest and most silicic of the four known intrusive centers of the approximately 1.5 Ga Wausau complex, exposed in Marathon County, Wisconsin. Mineralization in this epizonal pluton is often varied and complex, though frequently restricted to small localized environments in pegmatitic veins, aplites, and miarolitic granite. Recently a greisen-like mineral assemblage was identified in the Maguire weathered granite quarry, located approximately ¼ mile west of the Ladick East (or Charneski) quarry in the south central portion of the pluton. Quarrying here has intersected several small aplite-pegmatite dikes ranging in thickness from approximately 2” (5 cm) to about 15” (40 cm). These consist of layered banded aplite, commonly with thin 1-3” thick pegmatitic cores, and locally exhibit a highly peraluminous composition that is unusual in the predominantly alkalic Nine Mile granite. Due to the rapid progress of pit operations and ongoing reclamation work, most dikes could not be studied in their original position, but one briefly exposed gently dipping subhorizontal dike was observed in situ. Piles of discarded aplite-pegmatite boulders indicate the probable locations of additional dikes, possibly as many as three based upon varying characteristics. Most dikes were probably roughly vertically oriented, as adjacent pit walls show no signs of the dikes. Much material was recovered from piles of mingled boulders; sample characteristics generally allow attribution to one of the surmised four dikes. Exotic mineralization is often present in both the aplite and pegmatitic portions, but is concentrated along and adjacent to aplite-pegmatite contacts and along thin discordant mica-rich veinlets cutting across visible banding or layering. Late-stage mineralization in these dikes, generally confined to the vicinity of the pegmatitic cores, shows mineralization indicative of a greisen-like environment. Minerals identified to date include topaz (19-20% F content) as masses intergrown with albite and other minerals and as tiny clear crystals to 0.4 mm. Ferberite/hübnerite is found as well-formed dark red-brown to black crystals to 1.5 mm on and in albite and quartz. Most crystals have a high Mn content, but some portions of crystals are Mn dominant and are therefore hübnerite. Cassiterite, though less common than ferberite/hübnerite, has been found as dark red-brown crystals and masses to 3 mm. It appears that these represent the first reports of topaz, ferberite and hübnerite from in-situ occurrences in the Wausau complex, and indeed from the state of Wisconsin. Cassiterite has been observed in trace amounts from several other sites within the Nine Mile Pluton, but its relative abundance at this site is highly unusual. Monazite- (Ce) is common as clear to translucent yellow-orange crystals up to 4.5 mm in size. Columbite-group minerals are common as well-formed crystals to approximately 4 mm, and are ferrocolumbite with significant Mn and Ta. Some crystals have W-contents of over 12%, making them tungstenian columbite-tantalite. Zircon is locally very abundant, and is Hfrich. Xenotime is sparse, and appears to show significant enrichment in HREE. Other minerals 44 �noted include pyrite, chalcopyrite, barite (excellent clear platelets), an unidentified bright blue Cu sulfide, ilmenite, quartz, microcline, albite, siderophyllite, muscovite and possibly zinnwaldite. Rare phases include tiny inclusions of stolzite/raspite in ferberite, microlite, a Bi mineral forming minute tabular crystals, a beam-sensitive W mineral, an ilmenorutile like mineral, a grayite-like Th phosphate and silvery black crystals of a Nb-dominant ixiolite-like mineral with octahedral morphology. Interestingly, considering the abundance of fluorite at other Nine Mile Pluton sites, fluorite is much less common here. Nonetheless, the high F content of topaz and associated micas indicates that these were very F-rich systems. The association of topaz, cassiterite and ferberite, and the highly peraluminous nature of the mineralization indicate that a greisen-like environment prevailed in the latter stages of crystallization of these dikes. To the knowledge of the authors this is the first observation of such an environment in the Nine Mile pluton, in the Wausau Complex, and probably in the state of Wisconsin. 45 �Promontory Tectonics of the Penokean Orogen in Minnesota: A Gravity and Magnetic Perspective CHANDLER, V.W., BOERBOOM, Terrence J., and JIRSA, Mark A., Minnesota Geological Survey, chand004@umn.edu The sharp southward bend of the Penokean orogen in central Minnesota and possible continuation southwest into Iowa along the Spirit Lake trend (Anderson and Black, 1983; Van Schmus and others, 1993) have been cited as evidence for a promontory in the pre-collisional margin of the Superior Province craton (Schulz and Sims, 1993). Recent geologic investigations in this area have clarified the structure of both the orogen and the proposed promontory. Owing to a lack of bedrock exposure and drill holes, these investigations have relied to varying degrees on geophysical data. Of particular importance have been the high quality gravity and aeromagnetic databases in Minnesota (Chandler, 1991; Chandler and Schaap, 1991) and Wisconsin (Daniels and Snyder, 2002). Gravity and magnetic data have guided recent re-interpretations of the high-grade gneissic rocks in the Minnesota River Valley subprovince, which forms the core of the proposed promontory. On the basis of distinctive anomaly signatures, Southwick and Chandler (1996) divided the subprovince into 4 blocks bounded by three major east- to northeast-striking shear zones, which most likely formed during late Archean accretion of the Minnesota River Valley rocks onto the Superior craton. These shear zones, which are inferred from geophysical models and seismic data to have a moderately steep north dip (Southwick and Chandler, 1996), were likely reactivated during the roughly north–south convergence of the Penokean orogen. On a broad scale, the gravity and magnetic signatures of the Minnesota River Valley subprovince differ significantly from those associated with the Archean gneissic rocks of the Marshfield terrane in Wisconsin. This supports the view that the two Archean gneiss terranes are unrelated, and were most likely brought together during events related to the Penokean orogeny (Schulz and others, 1993). Geologic mapping supported by geophysical data reveals that significant changes in the structure of the Penokean orogen occur near the proposed promontory. Derivative enhanced gravity and magnetic data indicate that the structural grain of the orogen changes from northeast–southwest to nearly north–south (Boerboom and others, 1995; Jirsa and Chandler, 1997), and neither external zone fold-and-thrust belts nor foreland basin deposits appear to extend appreciably south of lat 45°15’N. Part of the internal zone of the orogen includes syntectonic granitic and metavolcanic rocks that are similar to those of the Penokean magmatic terranes of northwestern Wisconsin, but a large proportion of the internal zone is comprised of post-orogenic granitic rocks (Jirsa and Chandler, 1997). In fact, these post-orogenic granites, which are collectively referred to as the east-central Minnesota batholith (Holm and others, in press) are interpreted to constitute the dominant part of the orogen south of lat 45°15’N. In that area, the orogen is characterized by a broad magnetic low, the source of which is tentatively interpreted by geophysical modeling to represent non-magnetic, metasedimentary rocks that occur at a depth of 5 to 15 kilometers beneath Paleoproterozoic granitic rocks. Gravity and magnetic signatures indicate a somewhat complicated structure for the orogen in southern Minnesota. The orogen is truncated near lat 44°45’N. along a fault bounded block of Minnesota River Valley subprovince rocks. Both the orogen and Minnesota River Valley rocks are covered to the east by rocks of the Mesoproterozoic Midcontinent Rift System, but south of lat 44°15’N., rocks of the orogen are interpreted to re-emerge from the Midcontinent Rift System and extend southwest along the Spirit Lake trend. A broad magnetic low, combined with the drilling data from Minnesota (Southwick, 1994) and Iowa (Van Schmus and others, 1993), indicate that the geology along this part of the Spirit Lake trend may be similar to the internal zone of the orogen in east-central Minnesota. In conclusion, recent geologic interpretations in central and south-central Minnesota have helped refine our understanding of the effects of the large continental promontory with the western margin of the 46 �Penokean orogen. In fact, some of the changes in orogen structure may be explainable by the promontory. For example, pre-existing crustal weaknesses within the promontory may have enhanced thrusting, sedimentation, igneous activity, and crustal thickening during Penokean convergence. Increased crustal thickening near the promontory, in the area now occupied by the east-central Minnesota batholith, could have led to the removal of foreland fold-and-thrust belts and foreland basin deposits, and to increased melt generation of the lower crust to produce the post-orogenic granites. REFERENCES Anderson, R.R., and Black, R.A., 1983, Early Proterozoic development of the southern Archean boundary of the Superior Province in the Lake Superior region [abs.]: Geological Society of America Abstracts with Programs, v. 15, no. 6, p. 515. Boerboom, T.J., Setterholm, D.R., and Chandler, V.W., 1995, Bedrock geology, pl. 2 of Meyer, G.N., project manager, Geologic atlas of Stearns County Minnesota: Minnesota Geological Survey County Atlas C-10, scales 1:100,000 and 1:200,000. Chandler, V.W., 1991, Aeromagnetic anomaly map of Minnesota: Minnesota Geological Survey State Map S-17, scale 1:500,000. Chandler, V.W., and Schaap, B.D., 1991, Bouguer gravity anomaly map of Minnesota: Minnesota Geological Survey State Map S-16, scale 1:500,000. Daniels, D.L., and Snyder, S.L., 2002, Wisconsin gravity and aeromagnetic maps and data: A web site for distribution of data: U.S. Geological Survey Open File Report 02-493 <http://pubs.usgs.gov/of/2002/of02-493/index.htm>. Holm D.K., Van Schmus, W.R., MacNeil, L.C., Boerboom, T.J., Schweitzer, D., and Schneider, D., in press, U-Pb zircon geochronology of Paleoproterozoic plutons from the northern mid-continent, U.S.A.: Evidence for subduction flip and continued convergence after geon 18 Penokean orogenesis: Geological Society of America Bulletin. Jirsa, M.A., and Chandler, V.W., 1997, Scientific test drilling and mapping in east-central Minnesota, 1994-1995: Summary of lithologic results: Minnesota Geological Survey Information Circular 42, 105 p. Schulz, K.J., Sims, P.K., and Morey, G.B., 1993, Tectonic synthesis, the Lake Superior region and TransHudson orogen, in Reed, J.C., Jr., Bickford, M.E., Houston, R.S., Link, P.K., Rankin, D.W., Sims, P.K., and Van Schmus, W.R., eds., Geology of North America: Precambrian: Conterminous U.S.: Boulder, Colo., Geological Society of America, v. C-2, p. 60-64. Southwick, D.L., 1994, Assorted geochronologic studies of Precambrian terranes in Minnesota: A potpourri of timely information, in Southwick, D.L., ed., Short contributions to the geology of Minnesota: Minnesota Geological Survey Report of Investigations 43, p. 1-19. Southwick, D.L., and Chandler, V.W., 1996, Block and shear zone architecture of the Minnesota River Valley Subprovince: Implications for late Archean accretionary tectonics: Canadian Journal of Earth Sciences, v. 33, p. 831-847. Van Schmus, W.R., Bickford, M., and Condie K., 1993, Early Proterozoic crustal evolution, in Reed, J.C., Jr., Bickford, M.E., Houston, R.S., Link, P.K., Rankin, D.W., Sims, P.K., and Van Schmus, W.R., eds., Geology of North America: Precambrian: Conterminous U.S.: Boulder, Colo., Geological Society of America, v. C-2, p. 279-281. 47 �Enigmatic 1300 – 1400 Ma Mafic Pluton from the Koss Pit, Marathon County, WI CORDUA, William S., Dept. Plant and Earth Science, University of Wisconsin - River Falls, 10 South Third Street, River Falls, WI 54022, william.s.cordua@uwrf.edu In late Fall, 2002, an unusual body of mela-diorite cutting granite was found by mineral collector Tom Buchholz in a newly excavated area of the Red Rock quarry #510 (A.K.A. Koss Pit), on the east side of County O, SW 1/4 sec 2 T27N R6E, SW of Wausau, Marathon County, WI. The quarry is dominantly in the 1520 –1480 Ma Nine Mile granite (Buchholz, et. al., 2000). The unusual rock is exposed as rubble in a teardrop shaped area approximately 2 meters wide by 15 meters long, trending N55oE. This rock contains spectacular euhedral twinned crystals of plagioclase up to 20 cm. long. It has chilled margins against the granite and contains granite xenoliths. It is cross-cut by thin pinkish diorite dikes less than a centimeter wide. Samples were collected for thin section work, major and minor trace element analysis and radiometric dating. Study of 8 thin sections revealed the pluton is a mela-diorite consisting of 7 – 20 % plagioclase phenocrysts in a matrix of medium to fine -grained hornblende (20- 24%), biotite (27 - 37%), titanite (3-4%) and felsic material (22 -28%). The felsic material is an equigranular mosaic consisting mostly of oligoclase (about An 14). The hornblende and biotite occasionally form clots of coarser crystals. No feldspathoids, olivine or pyroxenes were found. The plagioclase phenocrysts were rounded and embayed, suggestions partial resorption. Their compositions were andesine (about An 43) but showed zoning on the rims and along cleavages to oligoclase. The phenocrysts had numerous inclusions of biotite and hornblende identical to that found in the groundmass. This suggests that the plagioclase crystals are not xenocrysts. Chemical analyses were done of 2 samples: WSC-03-01 was from near the contact with the granite. WCS-O3-02 is from the center of the body. Both samples are nepheline normative (WSC-03-01 ne = 0.63; WSC-03-02 ne = 3.41) and olivine normative (WSC-03-01 ol = 9.16 WSc-03-02 ol = 10.46). The less undersaturated nature of WSC-03-01 may be due to contamination by the granite country rock. These rocks are similar chemically to lamprophyres. Some of their major element trends fall within the shoshonite fields (Joplin, 1968). Mineralogically, however, the rocks are distinct from typical lamprophyres in the conspicuous plagioclase phenocrysts and lack of modal pyroxene or olivine (Rock, 1991). Trace element chemistry of these two samples is consistent with trends from shonshonitic and alkalic rocks formed in mid-plate regions (Pierce, 1982). Spider gram plots show the Koss Pit mela-diorite is enriched in both compatible and incompatible lithophile elements relative to MORB (figure 1). Its pattern resembles that of lamprophyres, such as the calc-alkaline lamprophyre series (Pierce, 1982, Rock, 1991). REE distribution shows a negative slope and enrichment in all REEs relative to Chengwatana volcanic rocks (Wirth, et al., 1997) and local Penokean granites. They are inconsistent with a Keweenawan body contaminated with granitic basement. They are consistent with the partial melting of a metasomatically enriched lithospheric mantle. A possible source of enrichment could be volatile- rich material subducted during the Penokean orogeny. K-Ar ages were determined by Activation Labs Ltd. Argon was determined by isotope dilution procedure on noble gas mass spectrometry. K concentrations were determined by ICP. The whole age measured was 1307.2 +/- 41 Ma. A biotite separate was determined to have an age of 1410.8 +/- 47 Ma. These ages are unique for central Wisconsin, which had shown a gap in igneous activity between the Nine-Mile granite at 1520 - 1480 Ma, and Keweenawan events at 1100 Ma. The ages are consistent with the field data, in that the mela-diorite clearly cross-cuts the Nine-Mile 48 �Granite but is chemically and mineralogically dissimilar to younger Keweenawan bodies. Unless its radiometric age has been reset due to uplift, the Koss Pit mela-diorite pluton represents a newly discovered igneous event in central Wisconsin. Fieldwork by the author has found other thin, highly altered dikes of mafic to lamprophyric character cutting older granites elsewhere in central Wisconsin. Their altered character make petrographic and radiometric work difficult. One may speculate that these are related in age to the Koss Pit mela-diorite. The small size, easily eroded character, and extensive glacial cover make the extent and relationships of such mafic igneous rocks difficult to determine. Trace element Spidergram 1000 100 WSC-03-01 10 WSC-03-02 Av. Calc-Alk Lamp 1 Sr K2O Rb Ba Th Ta Nb Ce P2O5 Zr Hf Sm TiO2 Y Yb Sc Cr 0.1 Trace element Buchholz, T.W., A.U. Falster and W.B. Simmons, 2000, “Ta, Nb, U, Y and REE Minerals of the Koss Quarry, Marathon County, Wisconsin” [abstract], 26th Rochester Mineralogical Symposium, Rocks and Minerals, vol. 75, p. 170-171. Joplin, J.A., 1968, “The Shoshonite Association: a review”, Geological Society of Australia, vol. 15 #2, p. 275-294. Pierce, J.A., 1982, “Trace element characteristics of lavas from destructive plate boundaries” in Andesites: Orogenic andesites and related rocks edited by R.S. Thorpe, John Wiley and Sons Pub., p. 525-548. Rock, N.M.S., 1991, Lamprophyres, New York, Van Nostrand Reinhold, 285 p. Wirth, K; J.D. Vervoort and Z.J. Naiman, 1997, “The Chengwatana Volcanics, Wisconsin and Minnesota: petrogenesis of the southernmost volcanic rocks exposed in the Midcontinent Rift”, Canadian Journal of earth Sciences, vol. 34, p. 536-548. 49 �Heller, Sims and Marsden: Mentors Extraordinaire DAVIDSON, Donald M., Jr., P.O. Box 2571, Tubac, AZ 85646 In considering the measure of my “contributions to the science”, particularly as related to UMD, it became apparent that three men played essential roles in this pilgrim’s progress. Robert L. Heller was instrumental in building an outstanding geoscience department at UMD. Basically he hired people, including myself, who were committed to effective teaching as well as research. But above all, he set the pattern for hiring people largely based on “how well we got along” and then “what they did”. This premise served me well in building departments at both UTEP and NIU. Bob was also highly committed to teaching himself and thus was not afraid to ask considerable of his department. I distinctly remember a 27 contact hour quarter my first year in harness! However, he was equally quick to encourage educational innovation and that led to what I consider an outstanding series of team taught courses and course sequences: Earth Materials (integrated mineralogy-petrology); Earth Structure (integrated sedimentationtectonics); Geology of North America; and Precambrian Geology to name a few. Although more difficult to set in place under the semester system, I tended to encourage such thinking at other schools and the team-teaching process served me well at Exxon Research. Finally, through his activities at AGI Bob helped me truly realize that “the whole was indeed bigger than the sum of the parts” and thus I worked diligently at getting AGU back under the AGI umbrella during my tenure at GSA, I believe for the betterment of the science. Paul K Sims is well known to this Institute. His professional work represents to me the essence of doing “good science”. He was a patient reviewer, particularly for neophytes, and thus influenced my approach to graduate student thesis supervision as well as “in-house” publications at Exxon. It was a real pleasure to work for him summers under the sponsorship of the Minnesota Geological Survey mapping in the Boundary Waters with outstanding assistants and colleagues such as Paul Weiblen. While he demonstrated considerable administrative skill as Survey Head, I was fortunate to see such talent in action again during his tenure as SEG President and President of the Economic Geology Publishing Company. This outstanding role model of organization stood me in good stead both serving as director of graduate studies at UMD, but in preparing for and carrying out the first graduate program review. Ralph W. Marsden, as well as helping found the ILSG, was the consummate Department Chair. He was infinitely patient and delegated frequently and well. More importantly, once he gave you a responsibility, he left you alone to work on it, although always available for advice. He also gave young faculty license to develop and grow - in my case organizing informal departmental sessions in 1969 on a new paradigm for how the earth works: Plate Tectonics. Yet I believe Ralph will best be remembered for his service to the science through society work. He was extremely active both in SEG and AIME and encouraged young faculty to join and participate in societies of their interest. Under his tutelage I became the Business Manager for Economic Geology, and later Treasurer of SEG. I am truly pleased SEG named its distinguished service medal after him. None could be more deserving. Happy Fiftieth Birthday UMD Geology and ILSG! 50 �THE VAN HISE ARMY AND OTHER PIONEERS OF LAKE SUPERIOR GEOLOGY DOTT, R.H., Jr., Department of Geology & Geophysics, University of Wisconsin, Madison, WI 53706 Sir William Logan, first Director of the Canadian Geological Survey (1842-1869), initiated investigations of Precambrian rocks. He coined Laurentian for the complex granitic and gneissic rocks of southern Ontario and adjacent Quebec and he assumed that these represented the original continental crust. The Algoman granite and overlying Huronian sedimentary series were soon named north of Lake Huron. These three names were thought to represent universal Precambrian subdivisions for many years. The first comprehensive surveys south of Lake Superior were initiated by Congress to investigate mineral deposits. The first two were led by David Dale Owen in 1839-40 to the lead mining district of the upper Mississippi Valley and in 1848-49 farther north to Lake Superior. In 1850-51 J.W. Foster and J.D. Whitney surveyed northern Michigan and adjacent Wisconsin, where copper and iron deposits were known. Minnesota, Wisconsin, and Michigan funded state surveys during the 1860s and 1870s, but these were parochial and uneven in quality. Most important were surveys under N.H. Winchell in Minnesota, T.C. Chamberlin in Wisconsin, and T.B. Brooks and R.J. Pumpelly in northern Michigan. For the Tenth National Census of the United States, Congress mandated that the U.S. Geological Survey catalogue the nation’s mineral resources. In 1880 several university geologists, including T.C. Chamberlin and Roland D. Irving of Wisconsin, were recruited to help accomplish this formidable task. At the conclusion of the census, Wisconsin’s Irving suggested that an integrated geological investigation of the Precambrian of the Lake Superior region was needed to facilitate the understanding and exploitation of the iron ranges. U.S. Geological Survey Director J.W. Powell agreed, and in 1882 created a Lake Superior Division to be located at Madison with Irving in charge. The first of nine large USGS Monographs to be published by the Division was Irving’s Copper-Bearing Rocks of Lake Superior (1883). In this he recognized the Lake Superior syncline and presented petrographic analyses of varied Keweenawan rocks, an early application of that important, new technique. In 1888 Irving died suddenly, so his young assistant, Charles R. Van Hise, immediately became both Director of the Division and Professor of Geology. The program went forward at a fast pace with a small army of young geologists fanning out across the different iron ranges. Four more Monographs and two Bulletins appeared during the 1890s. In 1903, Van Hise was chosen President of the University of Wisconsin, so his protégée, Charles K. Leith, took over both of his mentor’s former offices. Leith’s own Mesabi Range Monograph (1903) and four others plus one Bulletin were published under his direction. Besides an overarching synthesis of all of the work of the army, which was published in 1911 (Monograph 52), Van Hise and Leith devoted much attention to the development of universal principles for deciphering complex structures and metamorphism in terms of fundamental mechanics and chemistry. To cope with the scattered nature of rock exposures in a recently glaciated region of complex geology, the USGS group honed techniques for determining the relations between visible outcrop-scale (mesoscopic) and very obscure larger-scale (macroscopic) structures. Slaty cleavage and drag folds were employed early as valuable tools for such analysis, and in 1910 William O. Hotchkiss, a student of the Van Hise-Leith school (and about-to-be Wisconsin State Geologist), recognized the value of cross bedding and graded bedding for determining ‘way up.’ These fundamental insights gained by the Van Hise army and ground-breaking textbooks by Leith of structural geology (1913), metamorphic geology (1915; 51 �with his protégée Warren J. Mead), and economic geology (1921) thrust the University of Wisconsin’s Department of Geology into international prominence. Soon many students came from Canada, China, Japan, and Britain for postgraduate work in the ‘Wisconsin School of Precambrian Geology.’ The largest contingent was from Canada after 1910 when Director R.W. Brock of the Geological Survey of Canada adopted the policy that survey geologists henceforth must have the Ph.D. degree. The flow from the north to Wisconsin and other U.S. universities continued until the 1960s when more Canadian institutions began granting the Ph.D. By 1900 there was a need to reconcile some Canadian and U.S. interpretations of the major divisions of the Precambrian rocks of the Lake Superior region. Of particular note was a discrepancy in the Rainey Lake area along the Minnesota-Ontario border, where Andrew C. Lawson had inferred in 1887 that the oldest rocks were sediments of the Coutchiching formation, but U.S. geologists believed that the Keewatin volcanic complex was older and that the Coutchiching was equivalent to the younger Knife Lake series in Minnesota. In 1905 an international committee of survey geologists from both countries reviewed the evidence and favored the U.S. interpretation. In response, Lawson restudied the area in 1911, but stubbornly reaffirmed his original belief in spite of the fact that his field assistant, J.D. Trueman, a PhD student of Leith’s, showed him the value of cross bedding for determining ‘way up,’ which should have led recalcitrant Lawson to see his error. It was not until 1925 that Frank F. Grout of Minnesota disproved Lawson definitively using both graded bedding and cross bedding. The Minnesota-Ontario border region also became the burial ground of the long-standing dogma that Laurentian granites and gneisses represented the original crust of North America, for here the Keewatin volcanic complex now claimed that title. By this time the commonly accepted divisions of the Lake Superior Precambrian record had become Archean (including Keewatin, Algoman and Huronian) and Proterozoic (including Animikie and Keweenawan). By the mid-twentieth Century, the major stratigraphic divisions of the region were established and isotopic dating was beginning at last to provide a sound basis for long-range correlations. A.O. Nier and S.S. Goldich at the University of Minnesota were especially important in applying the new techniques to the Precambrian of this region, which allowed the recognition and dating of several additional tectonic and metamorphic events. Meanwhile, Francis J. Pettijohn had pioneered the study of Precambrian sedimentary rocks with his classic Archean Sedimentation (1943) and many subsequent studies with his University of Chicago graduate students. Stanley A. Tyler’s discovery in 1953 of the Gunflint fossils on the north shore of Lake Superior and Preston Cloud investigations while at the University of Minnesota in the 1960s revolutionized thinking about Precambrian life. Meanwhile the study of the region was greatly enhanced by the widespread application of geophysical techniques such as aeromagnetic surveys and geochemical studies. Finally, since 1970 plate tectonics has revolutionized our understanding of the evolution of the Lake Superior region. 52 �A Field and Laboratory Study to Evaluate the Genetic Relationships Between the Purvis Pluton and Volcanic Rocks and Volcanic-Associated Mineralization in the Vermilion District of NE Minnesota DREXLER, H.L.*, HUDAK, G.J., Geology Department, University of Wisconsin Oshkosh, 800 Algoma Blvd., Oshkosh, WI 54901; drexlh92@uwosh.edu PETERSON, D.M., Natural Resources Research Institute, 5013 Miller Trunk Highway, Duluth, MN 55811 The Purvis Pluton is an east-west trending, moderate- sized (~3km3), sill-like multiphase dioritic to tonalitic intrusion with a strike length of 5.7 km and a thickness, which ranges from 100-1200 meters (Peterson, 2001). This intrusion occurs near the base of the eastern part of the Ely Greenstone – Lower Member (Peterson and Jirsa, 1999; Jirsa et al., 2001). Peterson (2001) has suggested that the Purvis Pluton represents a felsic, synvolcanic sill-like subvolcanic intrusion that may have been the heat engine, which drove subseafloor hydrothermal activity, which produced VMS-like Cu-Zn mineralization at the Eagles Nest and Purvis Road prospects. The evidence for this interpretation is based on the local presence of an east-west oriented D2 foliation within the Purvis Pluton, the lack of a significant contact aureole adjacent to the intrusion, and the intimate relationship between the uppermost margins of the pluton and intense, semi-conformable quartz + epidote alteration zones. Volcanic rocks in the Ely Greenstone – Lower Member consistently contain the D2 foliation, which is constrained by age dates to have occurred during regional deformation between 2674 and 2683 Ma (Boerboom and Zartman, 1993; Peterson et al., 2001). We have conducted detailed field mapping, petrographic and lithogeochemical studies to further evaluate the spatial, mineralogical, and chemical characteristics of the Purvis Pluton. Field mapping, supported by subsequent petrographic studies, indicates that the Purvis Pluton contains several distinct phases. These include: 1) xenolithic hornblende diorite; 2) xenolithic hornblende tonalite; 3) xenolithic leucotonalite; 4) leucotonalite and trondhjemite; and 5) leucotonalite dikes. Paragenetic relationships between these phases have been determined in the field based and by petrography based on cross-cutting relationships and the xenolith contents of the various phases. Angular, coarse-grained gabbro/diorite lapilli, which have rare earth element characteristics similar to the other phases of the pluton (Figure 1a), are common in the xenolithic hornblende tonalite and xenolithic leucotonalite phases, and appear to represent an early product of Purvis Pluton crystallization. The xenolithic hornblende diorite, xenolithic hornblende tonalite, and xenolithic leucotonalite commonly contain basalt-andesite lapilli, epidote + quartz-altered basalt-andesite lapilli, and lapilli and blocks of oxide facies iron formation. These three xenolithic phases are intruded by the main phase of the intrusion, leucotonalite/trondhjemite. Leucotonalite dikes are a minor phase of the intrusion, and when present, consistently cut through the other plutonic phases. A sample of the hornblende tonalite has been submitted for geochronological analysis, and we are anxiously awaiting the results. Preliminary lithogeochemical evaluations indicate that the Purvis Pluton is calc-alkalic (Figure 1b). The various phases of the intrusion are classified as tonalite and trondhjemite using O’Connors normativebased granitic rock classification scheme (Figure 1c). Based on trace element characteristics, all phases of the Purvis Pluton were formed in a volcanic arc setting (Figure 1d), which is consistent with the geochemical affinity of the volcanic strata in the Ely Greenstone – Lower Member (Hudak et al., 2002). Recent studies by Galley (2003) have evaluated the physical and chemical characteristics of synvolcanic intrusions spatially and temporally associated with VMS deposits in Canada and Scandinavia. We are currently completing our evaluation of the lithogeochemical features of the Purvis Pluton, and our comparison of these features to VMS-associated synvolcanic intrusions associated with VMS deposits. 53 �Figure 1. a) REE diagram illustrating trends associated with Purvis Pluton phases, gabbro/diorite xenoliths, and amphibolite xenoliths; b) normative alkali - total iron – magnesium tertiary plot (after Irvine and Baragar, 1971); c) normative feldspar tertiary plot for the Purvis Pluton (after O’Connor, 1965); d) Rb – (Y + Nb) discriminant diagram for the Purvis Pluton (after Pearce et al., 1984). References Boerboom, T. J., and Zartman, R. E., 1993, Geology, geochemistry, and geochronology of the central Giants Range batholith, northeastern Minnesota: Canadian Journal of Earth Sciences, v. 30, p. 2510-2522.Boerboom and Zartman, 1993 Galley, A., 2003, Composite synvolcanic intrusions associated with Precambrian VMS-related hydrothermal systems: Mineralium Deposita, v. 38, p. 443-473. Hudak, G. J., Heine, J., Newkirk, T., Odette, J., and Hauck, S., 2002. Comparative geology, stratigraphy, and lithogeochemistry of the Five Mile Lake, Quartz Hill, and Skeleton Lake VMS occurrences, Vermilion District, NE Minnesota: NRRI Technical Report NRRI/TR-2002/03, 390 pages. Jirsa, M. A., Boerboom, T. J., and Peterson, D. M., 2001, Bedrock geological map of the Eagles Nest Quadrangle, St. Louis County, Minnesota: Minnesota Geological Survey Misc. Map Series M-114. O’Connor, J. T., 1965, A classification for quartz-rich igneous rocks based on feldspar ratios: USGS Professional Paper 1965:B79-B84. Pearce, J. A., Harris, N. B. W., and Tindle, A. G., 1984, Trace element discrimination diagrams for the tectonic interpretation of granitic rocks: Journal of Petrology, v. 25, p. 956-983. Peterson, D. M., 2001, Development of Archean lode-gold and massive sulfide deposit exploration models using geographic information system applications: targeting mineral exploration in northeastern Minnesota from analysis of analog Canadian mining camps: unpublished Ph. D. dissertation, University of Minnesota, Duluth, Minnesota, 503 p. Peterson, D. M., Gallup, C., Jirsa, M. A., and Davis, D. W., 2001, Correlation of Archean assemblages across the U.S.- Canadian border: Phase I geochronology: 47th Annual Meeting, Institute on Lake Superior Geology, Proceedings Volume 47, Part 1 – Programs and Abstracts, p. 77-78. Peterson, D. M., and Jirsa, M. A., 1999, Bedrock Geological Map and Mineral Exploration Data, Western Vermilion District, St. Louis and Lake Counties, Northeastern Minnesota: Minnesota Geological Survey Miscellaneous Map Series M-98, scale 1:48,000. 54 �Late Wisconsin Till and Arsenic Contamination in Upper Midwest Groundwater ERICKSON, Melinda L.*(Water Resources Sciences), and BARNES, Randal J., (Civil Engineering), University of Minnesota, 500 Pillsbury Dr. SE, Minneapolis, MN 55455, eric0984@umn.edu Exposure to arsenic, a recognized human carcinogen, is a widespread public health problem, with more than 150 million people worldwide estimated to be exposed to unsafe levels of arsenic from their drinking water. To reduce arsenic exposure from drinking water, the US Environmental Protection Agency recently adopted a new, more protective arsenic drinking water standard, 10 µg/l. All public water systems must comply with the new arsenic standard by January 2006. In the upper Midwest, arsenic in ground water is a widespread, naturally occurring contamination problem regionally impacting both public and private drinking water wells. Hundreds of upper Midwest public water systems serving over a million people are affected by the change in the arsenic standard. Additionally, in Minnesota alone, 150,000 – 250,000 people are estimated to obtain drinking water from private wells with arsenic concentrations exceeding 10 µg/l. Private well owners are not forced to comply with federal drinking water standards. Figure 1 illustrates that groundwater arsenic concentrations in excess of 10 µg/l are associated with the lateral extent of northwest-sourced late Wisconsin sediment. Statistical analysis supports the visual observation: 10.7% of public water systems located within the footprint of the Late Wisconsin till exceed 10 µg/l, and only 2% of public water systems outside the footprint exceed 10 µg/l. Our research results indicate that the elevated arsenic concentrations in upper Midwest groundwater are not primarily due to high arsenic concentrations in Late Wisconsin till. Sediment analyses indicate that Late Wisconsin sediment in western Minnesota does not have particularly high arsenic concentrations, and water arsenic and sediment arsenic concentrations measured in our research are not correlated (Figure 2). We hypothesize that the specific physical characteristics of the Late Wisconsin till, such as its fine-grained matrix, entrained organic carbon, and active anaerobic biological activity, create the geochemical environment favorable to a regional-scale mobilization of arsenic via desorption. In western Minnesota aquifer sediments, we measured that 0.5 – 0.7 mg/Kg of the total arsenic is adsorbed arsenic. Adsorbed arsenic is labile and can be readily desorbed, especially in suboxic and reduced aquifers. 55 �# S S # S # # S S # S # S # S # S # S # S # S # # S S # S # S # S # S # S # S # S # S # S # S # S # S # S # S # S # S # # S S # S # S # S # S # S # S # S # S # S # S # S # S # S #S S # S# # S # S # S # S # # # S S S # S # S # S # S # S # S # North Dakota S # S # S # S # S # S # S # S # S # S # S # S # S # S # S # S # S # S # S # S# # S S # S # S # # S S # S # S # S # S # # S # S S # # S S # S # S # S # S # S # S # S # S # S # S # S # S # # S S # S # S # # S S # S # S # # S S # # S S # S # S # S # S # S # S # S # S # S # S # S # S # # S S # # S S # S # # S S # S # S # S # S # S # S # S # S # S # SS# # S S # S# # S# # S S# # S S # S# # S # # S S S S# # S S # S # # S S# S# S # S # S# # S# # S# ## S # S# S# S # S S S# S S# # S S# S# # S S # # S S# # S# S# # SS # S S # S# # S # S S S # # S # S # S # S # S # S # S # S # S # S # # S S # S # S # S# # S S # S # S # S # S # S # S # S # S # S # S # S # S # ## S S S # S # S # S # # S S # S # S # S # S # S # S # S # S # 75 0 75 S # S # # S S # S # S # S # S # S # S # S # S # S # S # S # S # S # S # S # # S S # # S S # S # S # S # # S # S S # S # S # S # # S S # S # S # S # # S # S S # S # S # S # S # S # S # S # S # S # S # S # S # S # S # S # S # S # S # S # S # S # S # S # S # S # # S S # S # S # # S S # # S S # S # # S S # S # S # S # S # S # # S S # # S S # S # S # S # S # S # # S S # S # ##S S # S S # S # # S # S # S # S # S S # # S S # S # S # S # S # # S S # S # S # S # S # S # S # S # S # # S S # S # S # S # S # S # S # S # S # S # S # S # S # # S S # # S # S S # S # S # S # S # S # # S # S S # S # S # S # # S # S S # S # S # S# # S S ## S S # S # S # S # S # ##S # S S # S ##S#S S # S S # S # # S S # S # S # S # # S S # S # S # S # S # S # S # S # # S # S # S S # S # S # S # S # S # S # S # # S S # # S S # S # S # S # S # S # S # S # S # S # S # S # # S S # # S # S S # S # S # S # S # # S S # # S # S S # S # S # S # S # # S # S # S # S S # S # S # S # S # S # S # S # S # S # S # S # S # # S # S S # S # # S # S # S S # S # S # S # S # # S S # S # S # S # S # S # S # S # S # S # S # S # S # S # S # S # S # # S S # # S S # S # S # S # S # # S S # # S # S S # S # S # S # S # S # S # S # S # S # # S S # S # # S S # S # S # S # S # S # # S # S S # # S S # S # S # S # S # S # S # S # S # S # S # S # S # S # S # S # S # # S S # # S S # S # # S S # S # # S ## S S # S # S # S Iowa S # S # S # S # S # S # S # # S S # S # S # S # S # S # S # S # S # S # S # S # S # # S S # S # S # S # # S S # S # S # S # S # S # S # # S S # S # S # S # # S S # S # S # S # S # # S S # S # S # S # S # S # S # # # #S S S # S # #S S S # S # S # S # # S S # S # S # S # S # # S # S S # S # S # # S S # # S # S S # S # S # S # # S S # S # S # # S S # S # S # # S S # # S ## S S S # S # S # # S S # S # S # S # S # S # # S S # S # S # S # S # S # S # S # S # S # S # S # # S S # S # S # S # S ## S S # # S S # S # S # S # S # S # S # S # S # S # S # S # S # S # S # S # S # S # S # S # S # S # S # S # S # S # S # S # S # S # S # # S S # S # S # S # S # S # # S S # S # S # S # S # S # S # S # S # # S # S # S # #S S #S S # S # # S S # S # S # S # S # S # S # S # S # S # # S S # S ## S S # S # # S S # S # S # S # S # S # S # S # S # S # S # S # S # S # S # S # # S S #S # S # S # S # S # S # ## S S S # S # S # S# # S S # S # S # S # S # S # S # S # S # S # S # S # # S S # S # S S # # S # S # S # S # S # S # S # S # S # # S S # S # S # S # S # S # S S # # S # S # Arsenic Concentration 0 - 10 ug/l 10 - 20 ug/l # 20 - 50 ug/l S Late Wisconsin Till S # # S S # S # S # S # S # # S S # S# # S# ## S S S# S S # S # S # S # S # # S S # S # S # S# # S # S S # S # # S S# # S S# # S S # S # S # # S S # S # S # S # S # S # # S S # S # S # S # S # S # S # # S S # S # # S # S# S S # S # S # # S S # S # S # S # S # S # S # # S S # # S S # S # # S S # # S # S S # S # S # S # S # S # 150 Miles S # S # S # S # S # # S S # S # S # S # S # # S # S S # S # S # S # S # S # S # S # S # S # S # # S S # S # S ## S S # S # S # S # S# # S# S# S # # S S S # S # S # S # S # S # # S S # S # S # S # S # # S # S # S S # S # S # S # S # S # S # S ## S S # S # S # S # S# # S# S # S S# S# # S# # S# # S S S S# S# # S S # S # S# S# # S# S S# # S S# S S# S # S# S# # S # S # S # S # S # S # S # S # S # S # S # S # # S S # S # # S S # S # S # S # S # S # S # S # S # S # # S S # # S # S S # # S S # S # S # S# # S S # S # S # S # S # S # S # S # S # S # S # S # S # S # S # S # S # S # S # S # S # ## S S S # S # S # # S S # S # S # S # # S S # S # S # S # S # S# # S S # S # S # S # S # S # S # S # S # S # S # S # S # S # ## S S # S# S S # S # S # S # S # # S S # S # S # S # S S# # S # S # SS # S# ## S S# S # ## S S S # S # S # S # S # S # S # S # S # S # S # S # S # S # S # S # S # S # S # S # S # S # S # # S S # S # S # S # S # S # S # S # S # # S S # S # S # S # S # ## S S S # S# # S # S # S S # S# S # # S S # S# # S S ## S S# # S# S S # S# # S# S S # S # S # S # S # S # S # S # S # S # # S S # S # # S S # S # S # S # S # # S S # S # S # # S S # S # S # S # S # S # # S S # S # S # S S# # S# S # S # S # S # S# # S # S S S S# # S# # S # S # S # # S# S# S# # S # S S # S# S S# S S S S # S# # S# S S# # S # S# S# # S# # S # S # S # # S# # S# S S # S# # S# # S S# # S S S# S SS # S # S S# # S S S # S# # S# S# # S # S# S# S# S # # S# S # S# S S# S S# # S S# # S# S# S# # S# S # S SS # S# # S# # S# S S S S # S# S # S # # S S# S# # S # # S# S# S# S# # S# S# S# SS # S# # S S# S # S# S# # S S # S # # S S# # S # S# S # S S# S# S# S# # S SS # S# # S S# # S # S # # S S# # S# S# S S # S # S# # S# S S# # S S# # S# S # # S# S # # S # S S # # S S S# # S# # S# S # S S # S# S # S# S S# # S # # S S# # S S# S# S# S# S # S# S # S# # S# # S# S S# S# S# S # S # S S # S# # S# S# S# # S ## S # # S# # S# # S S# S# S S # S# # S S S S # S# S# S# S# S # S# # S # S # # S# S S # S S # S # S S # S S S # S # S# # S# # S S # S # # S# S# S# S S # # S S S S# # S S# # S# # S # S # S# # S S# S# S # S # # S S# S S # S S# # S # S# # SS# S# S S # S # S# # S# S # # S# # S# S# S# # S # S# S # S S S# S S# # S # S# S S# # S# S# S # S S # S # S # S # S# # S S# S# S # S# # S S # S # S# # S S # # S # S # S S# # S S # # S S# # S S # S # S# # S # S # S S # S # S # S # S # S # S S # # S # S # S # #S S # S # S # S # S # S # S # S # S # S # S # S # S # S # S # S # S # S # S # S # S # S # # S S # S # #S S # S # S # # S S # S # S # S S # # S # S # S # S # S# # S S # S # S S S # # ## S S# # S# S# S# # S S S S ## S # S # S # S# # S# # S S S # S # S S # # S # S # S # S # S # S # S # S # S# ## S S S # S# # S S # S # S # S # S # S # S # S # # S S # S # S # S # S # S # S# # S S # S # ##S S S # # S# S # S S # S # S# # S S# # S# S# S S# # S S ## S S ## S ## S S # S S# # S S # S # S # S # S # # S S # S # S # S # N S # S S# # # S S # # S S # S # S # S# # S S # # S S # S # S # S # S # S # S # S # S # S # S # S S # S# # S# # S S # S S # # S # # S S # S # S # S # S # S # S # S # S # S # S # # S S # S # S# # S S # S # S # S # S# # S# S S # # S # S S S # # S # S # S # S # S # S # S # ## S SS # S # S # S # # S S # S # S # S# # S # S S # # S S # ## S S S # S # S # S # S # S # S # S # # S S # # S S # S # S # # S S # S # S # S # S # S S # # S # S S # # S# S # S # S # S # S # S #S#S #S#S # S # S # S # S # S # S # # S S # S # S # S # S# # S S # S # S # S # S # S # S # S S# # S # S # S # S # S # S # S # S # S # S # S # S # # S S # S # S# # S S # # S S # S # S # S ## S S # S # S # S # S # S # S # # S S # S # S # S # S # S # South Dakota S # S # S # S # ## S S S # S # S # S S # # S # S # S # S # S # S # S # S # S # S # S # S # S # S # # S # S S # S # S # S # # S ## S S S ## S S # S # S # # S S # S # S # S # S # S # S # # S S # S # S # S # S # S# # S S # S # S # S # S # S # S # S # S # S # S # S # S # S # S # S # S # S# # S S # S # S # S # S # S # S # S# # S# S S # S # S# # S S # S # S # S# # # S S S # S # Minnesota S # S # S # # S S # S # S # S # S # S # S # S # S # # S S # S # S # S # S # S # S # S # S # S # S # S # S # S # S # S # S# S S# # # S S # S # S # S # ## S S S # S # S # S # S ## S S # S # S# # S # S # S S # S # S # # S # S S # S # S # S # S # S # S # S # # S S # S # S # S # S ## S # S ## S S S # ## S S S # S# # S S # S # S ## S # S S # S # S # S # S # # S S # S # S # S # S # S # S # S # # S S # S # S # S # S # S # S# S # # SS S # # S # # S S # S # S # S # S # S # S # S # S # S # S # ## S S S # S # S # S # S # # S S # S # S # S # S # S # # S S # S # S # S # S # # S ##S S # S S # S # S # # S # S S # S # S # S # S # S # S # S # # S S # S # S # S # S # S # S # # S S # S # S # S # S # # S S # S # S# # S S # S# # # S S S # # S S # S # S # S # S # S # S # # S S # S # S # S # S S # # S # S # S # # S S # S # S # S # S # S # S # S # # S S # S # S # S# # S S # S # S # S # # S S # S# # S S # S # # S # S S # S # S # S # S # S # S # S # S # S # S # S # # S S # S # S # S # S # S # S # S # S # S # S # ## S SS # S # S # S # S # S # S # S # S # S # S # S # S # S # S # S # S # S # # S S # S # S # S # # S # S S# # S S S # S# # S# # S # S S # # S S # # S S # S # S # S # S # S # S # S S # ## S S # S # S # S # S # S # S# # S S # S# # S S S ## S S# # S# S# # S S # S # S # S # S # # S S # S # S # S # # S S # S # S # S # S # # S S # S # S # S # S # S # S # S # S # S # S # # S S # S # S # # S S # S # # S S # Figure 1 – Arsenic concentrations in upper Midwest public water systems Figure 2 – Measured arsenic concentrations in water and sediment collected from western Minnesota. 56 �INFLUENCE OF GEOLOGIC SETTING ON HYDROGEOMORPHIC CHARACTERISTICS OF SOUTHERN LAKE SUPERIOR TRIBUTARIES FITZPATRICK, Faith A., U.S. Geological Survey, 8505 Research Way, Middleton, WI 53562, fafitzpa@usgs.gov The U.S. Geological Survey has conducted assessments of historical and current geomorphic, sediment, and flooding characteristics for several Lake Superior tributaries in the Duluth, Minnesota and Bayfield County, Wisconsin areas. These assessments were done to determine historical natural and human-caused alterations in aquatic habitat and to provide base line data for stream restoration activities. For streams with little or no bedrock control, such as those in the Bayfield County area, historical geomorphic responses to clear-cut logging and burning in the late 1800s and subsequent agriculture in the early 1900s included channel incision and lateral migration in upstream reaches and aggradation, widening, and lateral migration in downstream reaches (Fitzpatrick et al., 1999). However, these geomorphic responses to changes in land cover were dependent on composition of glacial deposits, type of glacial or glaciolacustrine landforms, spatial position within the watershed, and relative timing of large floods. Geomorphic responses to increased runoff and sediment inputs were manifested during extreme floods that occurred one to two decades after maximum agricultural activity (Fitzpatrick and Knox, 2000). For streams with bedrock control, such as those in the Duluth area, the main geomorphic response to land clearing, such as urban sprawl, is channel widening. The major source of sediment in most of the southern Lake Superior tributaries has been and continues to be from channels down-cutting through relict glacial lake shorelines. Longitudinal profiles of the tributaries are a reflection of a combination of glacial and glacio-lacustrine landforms and bedrock topography (fig. 1). Slopes are steep where streams intersect glacial lake shorelines and (or) bedrock near the surface. Longitudinal profiles are a useful reconnaissance tool for identifying stream reaches prone to erosion or sedimentation. Inflection points on the longitudinal profiles represent reaches with slope transitions. These transitional reaches tend to be the most sensitive to changes in water and sediment inputs. 1,500 Miller Creek, Duluth, MN 1,400 ALTITUDE, IN FEET 1,300 1,200 Cranberry River, Herbster, WI 1,100 1,000 900 800 700 North Fish Creek, Ashland, WI 600 25 20 15 10 5 0 RIVER MILE FROM MOUTH Figure 1. Longitudinal profiles for three Lake Superior tributaries. REFERENCES Fitzpatrick, F.A., and Knox, J.C., 2000, Spatial and Temporal Sensitivity of Hydrogeomorphic Response and Recovery to Deforestation, Agriculture, and Floods: Physical Geography 21(2): 89-108. Fitzpatrick, F.A., Knox, J.C., and Whitman, H.E., 1999, Effects of Historical Land-Cover Changes on Flooding and Sedimentation, North Fish Creek, Wisconsin: U.S. Geological Survey Water-Resources Investigations Report 99-4083, 12 p. 57 �IRON NODULE RESEARCH AT THE NATURAL RESOURCES RESEARCH INSTITUTE, UMD FOSNACHT, Donald R., Center for Applied Research and Technology Development, Natural Resources Research Institute, University of Minnesota Duluth, Duluth, MN IWASAKI, Iwao, and BLEIFUSS, Rodney, Coleraine Minerals Research Laboratory, Natural Resources Research Institute, University of Minnesota Duluth, Coleraine, MN Synopsis A program jointly funded by the Economic Development Administration and the University of Minnesota Permanent University Trust Fund has been underway at the Coleraine Minerals Research Laboratory over the last two years. During this period, significant research and development has taken place using a variety of new furnace capabilities to test the responsiveness of iron ore taconite concentrates to reduction and smelting under a variety of test conditions. During the coarse of the investigation, over 1150 tests were undertaken using a laboratory tube furnace, these were supplemented by over 200 tests from a 2-stage laboratory box furnace, and finally by dozens of test from a 3-stage pilot-scale linear hearth furnace. During the program, the conditions for producing satisfactory iron nodules with low sulfur, gangue, and tramp impurity levels were elucidated. A variety of reductants, slag fluidizers, and iron ore mixtures were employed during the test program. Laboratory Tube Furnace Tests The test program was initiated using a tube furnace (see Figure 1) with a 2” dia. x 48” long mullite tube, which takes 1” wide x 4” long and 1” high graphite boat, to screen the test conditions for use in laboratory box and pilot plant linear hearth furnaces. Major parameters investigated included such raw materials as: (1) taconite concentrates with different levels of silica content as well as pellet plant wastes and screened pellet fines, (2) different carbonaceous reductants including Eastern anthracite, low-, medium- and high-volatile bituminous and Western sub-bituminous coals as well as their carbonized char and coke, and (3) different types of additives, such as balling binders and some specific additives for slag fusion temperature reduction and iron nugget sulfur control. Furnace operating conditions included temperature and time at temperature, furnace atmosphere, hearth layer materials, iron nugget and slag chemistries as well as iron nugget size. Environmental issues of concern are slag disposal and/or utilization and effluent emission of mercury, NOX, SOX and particulate matter. Figure 1: Laboratory Tube Furnace In the tube furnace, over 1150 different conditions have been tested. Test results demonstrated that larger-sized iron nuggets can be routinely produced by feeding dry raw material mixtures without prior agglomeration. Taconite concentrates with different levels of silica indicated that magnetic concentrates with 6% SiO2 produced metallic iron nuggets more readily than a more expensively produced super-concentrate of 2% SiO2. Pellet plant wastes and screened pellet fines produced satisfactory iron nuggets, but consisting mainly of hematite, these raw materials appeared to require somewhat different conditions. Laboratory Box Furnace Tests A laboratory, electrically-heated box furnace (see Figure 2), having two 12”x12”x12” heating chambers with the two chambers capable of controlling temperatures up to 1450°C (2642°F) independently, and which accepts a 5” wide x 6” long x 1-1/2” high graphite tray was designed and constructed during the project. Over 220 different conditions have been tested in the box furnace, confirming the results obtained in the tube furnace for both dry balled feed and a feed without prior agglomeration. In the box furnace, a major emphasis was placed in developing 58 �methods to produce larger-sized iron nuggets by feeding dry raw material mixtures in an attempt to circumvent costly balling and drying steps. A series of different size iron nuggets were produced, ranging from 5/15” to 2-1/2” (7 to 65 mm) in size. Figure 2: Laboratory Box Furnace Pilot-plant Linear Hearth Furnace Tests (Rotary Hearth Simulator) The natural gas-fired pilot-scale linear hearth furnace simulator has been installed and commissioned. The furnace is a forty-foot long iron reduction furnace (see Figure 3), consisting of three individual heating zones and a final cooling section. Sample trays are conveyed through the furnace by a hydraulically driven walking beam system. Zones are controlled individually according to temperature, pressure and feed rate, making this furnace capable of simulating several reduced iron processes and operating conditions. An Allen Bradley PLC micro logic controller coupled to an Automation-Direct PLC for the walking beam mechanism controls the furnace through a user-friendly PC interface. The PLC control system regulates individual zone burners to manage zone temperatures. A pair of 450,000 BTU/hr natural gas fired burners heats zones one and two. Zone one is rated for a continuous operating temperature of 2000 oF, while zone two can be continuously operated up to 2400 oF. Zone three is fired by a pair of 1 Million BTU/hr burners that were required to achieve the operating temperatures of 2600 oF in reasonable time to complete testing. Each zone has an individual exhaust duct and control damper to regulate pressure in that zone. A manually controlled exhaust fan damper is also installed to reduce the capacity of the exhaust fan, and allow the individual duct control dampers to manipulate pressures to desired set-points. Reducing the burner air, to operate the burners sub-stoichiometric, and operating zone pressures positive is required to reduce oxygen levels to 0.0% and provide acceptable furnace atmospheres for iron reduction. Figure 3: Pilot Scale Linear Hearth Furnace (Rotary Hearth Simulator) Major differences in the test conditions from laboratory electric furnaces were the low CO/CO2 ratio and high turbulence of the furnace gas and the sample pallets acting as an unexpectedly large heat sink. Research work focused on careful adjustment in the amount of coal addition, and on the type and amount of additives in order to minimize the generation of micro nuggets. The Linear Hearth Furnace has routinely been used to test a variety of the test variables shown to be important from the box furnace and tube furnace tests. It is possible to make various size iron nuggets at this scale that have low amounts of micro-nuggets and which have low levels of undesirable tramp elements. The furnace is extremely useful for testing a multiplicity of test parameters in a very short period of time. 59 �OXYGENATION OF THE ARCHEAN HYDROSPHERE: EVIDENCE FROM THE EAGLE ISLAND DELTAIC COMPLEX FRALICK, Philip, Department of Geology, Lakehead University, Thunder Bay, ON, Canada, P7B 5E1, philip.fralick@lakeheadu.ca PUFAHL, Peir K., Department of Geological Sciences and Geological Engineering, Queens University, Kingston, ON, Canada, K7L 3N6, pufahl@geol.queensu.ca The Eagle Island Group is located in southern Uchi Subprovince, Canadian Shield, at the west end of Lake St. Joseph. It overlies 2713 Ma volcanic rocks and is deformed by an event, which probably occurred prior to 2702 Ma (Stott and Corfu 1991). Outcrop along the shores of Eagle Island is excellent and provides a rare opportunity to document an Early Precambrian depositional system including abundant iron formation. The lowermost 35 m of section contains three coarse-grained parasequences separated by assemblages of graded sandstone beds and iron formation (IF) (Fig. 1). The IF consists of three types: (a) dominantly magnetite-rich sediment with mm- to cm-scale, graded or ungraded siltstone interbeds: (b) cm-scale graded to sharply bounded siltstone layers either contiguous or separated by mm-thick laminae of magnetite-rich sediment: (c) sandstone beds in places separated by magnetiterich intervals. The lowermost coarse-grained parasequence consists of graded sandstones and conglomerates separated by a-type IF units. The second parasequence contains: graded sandstones and conglomerates separated by magnetite; graded sandstone lenses surrounded by magnetite; crossstratified sandstones with magnetite drapes on reactivation surfaces; low angle, laterally accreting sandstone and conglomerate packages with internal magnetite laminae; multistory conglomerates with internal magnetite drapes; and ripple laminated sandstones in a-type IF with mm-thick magnetite laminae draping avalanche surfaces in ripple trains. The upper parasequence is composed of cross-stratified, coarse-grained sandstones interlayered with conglomeratic lenses. This is sharply overlain by 73 m of b-type, gradational to a-type, IF. A 182 m thick succession of graded, medium-grained sandstone beds overly the IF and these are succeeded upwards by 67 m of trough cross-stratified, coarse-grained sandstones. Next is a 60 m thick sandstone-conglomerate assemblage consisting of sharp-sided, nongraded laterally extensive, thin conglomerate lenses interlayered with well-sorted medium-grained sandstones with internal, shallowly inclined pebble stringers. Approximately 50% of the clasts are IF. This assemblage is overlain by a thin package of turbidites capped by a-type IF. 60 �The Eagle Island Group was previously considered a deep-water submarine fan deposit (Meyn and Palonen 1980, Berger 1981). The lithofacies associations present and their architectural organization make this unlikely. The thick succession of graded beds is interpreted as shallow-water storm deposits and the trough cross-stratified sandstones represent either nearshore sands, a distributary mouth bar complex or braided fluvial channels. The overlying conglomerate-sandstone unit consists of layers characteristic of foreshore beach deposits interlayered with fluvial mouth gravel bars. The 400 m thick, coarsening upwards sequence represents a wave modified delta. Thirty-five meters of strata underlying the coarsening-upwards delta is also progradational with three parasequences building from subaqueous (lower) to strandline (middle) to braided fluvial (upper). The parasequences are separated by IF developed on flooding surfaces. The most interesting features exist in the middle (strandline) parasequence. Here, IF was deposited at periods of low stream discharge in the very proximal distributary mouth environment. Magnetite laminae drape all scales of reactivation surfaces developed in this proximal nearshore setting. In contrast the 73 m thick IF was deposited on the delta top during a major flooding event and represents a portion of the transgressive and highstand systems tract (Fig. 2) where chemical sedimentation kept pace with relative sealevel rise. The accumulation of IF only in the nearshore of this depositional system limits possible precipitation mechanisms. IF accumulation models relying on relatively constant Fe precipitation in the world ocean combined with siliciclastic starvation are not compatible with data presented here. Freshwater influx into the nearshore, and resultant increase in pH, may have been responsible for iron precipitation but accompanying fresh water dilution of marine waters makes this unlikely. Photo-synthetically induced oxygenation of the shallow nearshore is the probable cause of iron precipitation. Berger, B.R. 1981. Stratigraphy of the west Lake St. Joseph greenstone terrain, northwestern Ontario. Unpub. M.Sc. Thesis, Lakehead University, 117p. Meyn, H.D. and Palonen, P.A. 1980. Stratigraphy of an Archean submarine fan. Precambrian Research, Vol. 12, 257-285. Stott, G.M. and Corfu, F. 1991. Uchi Subprovince. In: Geology of Ontario. Ont. Geol. Sur. Spec. Vol. 4, Pt. 1, 145-238. 61 �Isocon Analysis: How To Make It Work For You. GRANT, James A., Department of Geological Sciences, University of Minnesota Duluth, MN 55812 Isocon analysis (Grant, 1986) is a simple and effective means of quantitatively estimating changes in mass or volume or concentrations in mass transfer. The method has been applied to such diverse phenomena as hydrothermal alteration, replacement, migmatites, shear zones, paleosols, silcretes, sedimentary exhalative deposits and fumarolic deposits. It may be accomplished graphically by plotting an altered composition (CiA) against an original composition (CiO) with no significant manipulation of the data. Species that have remained immobile in the process define the isocon, which is a straight line through the origin. Data points falling above the isocon represent gain, and those below represent loss, of the corresponding chemical species, and the slope of the isocon gives the mass change in the process. It is critical to obtain as close an approximation to the original rock composition as possible, since that rock no longer exists. Sampling the altered rock is generally less problematic, even if the alteration is zoned. Given zonation or general heterogeneity of the rocks, judicious sampling and averaging of samples is necessary. Fortunately it is painless to try different combinations and arrive at a reasonable compromise. Scaling should be important only in producing a satisfactory isocon diagram to portray the model in question. If the slope of the isocon is based on CiA/CiO values, scaling cannot affect the results because the scale factor cancels out. Scaling can however affect the perception of the results especially if points are crowded close to the origin. The choice of immobile species can be determined by inspection of a well-constructed isocon diagram, by inspection of CiA/CiO values, by statistical methods like that of Baumgartner and Olsen (1995), or by plotting pairs of species like Cail and Cline (2001). In any case the geochemical characteristics of the species and of the process involved need to be considered thoughtfully. Characterization of an isocon based on immobile species (as opposed to constant mass, volume or predetermined species) devolves to defining a slope for the isocon. This may be done graphically, by a least squares method of linear regression, or by averaging the slopes for the immobile species. Commonly there is some range within which reasonable isocons could be chosen. Data points that lie close to a chosen isocon within such ranges would correspond to small gains and losses, and not much significance should be placed on them. Data points far from the range of possible isocons will not be affected significantly by the minutiae of the choice of isocon. Log-log plots do not add anything to the analysis, except the possibility of confusion, and should be avoided. 62 �RFERENCES Baumgartner, L. P. and Olsen, S. N., 1995. A least-squares approach to mass transport calculations using the isocon method. Economic Geology, 90, 1261-1270. Cail, T. L., and Cline, J. S., 2001. Alteration associated with gold deposition at the Getchell Carlin-type gold deposit, North-central Nevada. Economic Geology, 96, 1343-1359. Grant, J. A., 1986. The isocon diagram - a simple solution to Gresens' equation for metasomatic alteration. Economic Geology, 81, 1976-1982. 63 �THE GEOLOGY OF THE DULUTH COMPLEX AND THE NORTH SHORE VOLCANIC GROUP PORTRAYED IN NEW 7.5' QUADRANGLE MAPS OF THE DULUTH METROPOLITAN AREA GREEN, J.C., Department of Geological Sciences, University of Minnesota Duluth, Duluth, MN 55812 (jgreen@d.umn.edu) MILLER, J.D., Jr., Minnesota Geological Survey, c/o Dept. of Geological Sciences, University of Minnesota, Duluth, MN 55812 The most current bedrock geologic map of the Duluth area is the 40 year old map by R.B. Taylor (1964), which was the first detailed-scale (1:24,000), full color map of Precambrian bedrock geology published by the Minnesota Geological Survey. This map, which built on the earlier field studies of Grout (1918) and Schwartz (1949), served as a companion to MGS Bulletin 44 and focussed mainly on the geology and petrology of the Duluth Complex. Taylor's map divided the complex into two major series, the layered series and the anorthositic series, and several subordinate units. The volcanic rocks of the North Shore Volcanic Group (NSVG), which compose the hanging wall and part of the footwall of the Duluth Complex, were not subdivided, but the major mafic sills that intrude the hanging wall volcanic rocks were delineated. The first author (Green) has conducted reconnaissance mapping in the Duluth area since 1960, focussing mostly on the volcanic rocks of the Duluth Quadrangle. In 1992, the Minnesota Geological Survey received funding from the Minnesota Minerals Coordinating Committee to conduct detailed mapping in nine quadrangles encompassing the Duluth metropolitan area. Approximately five months of intense field mapping resulted in the production of a 1:48,000-scale open-file map (Miller, Green and Chandler, 1993). We have conducted intermittent mapping over the past 11 years, which has continued to improve our understanding of the Duluth area. These field data are currently being digitally compiled into new 1:24,000-scale maps for the Duluth, Duluth Heights, and West Duluth quadrangles and parts of the Esko and Adolph quadrangles. Preliminary versions of these maps will be displayed as a poster presentation. One of the most important contributions of these new maps is their detailed delineation of the igneous stratigraphy of the layered series. As Taylor (1964) recognized, the layered series at Duluth (DLS) is a well-differentiated, 3- to 4.5-km-thick, moderately east-dipping, sheet-like mafic layered intrusion. Our mapping has subdivided the DLS into six major zones and various subzones on the basis of dominant cumulate rock types. A 150-300m-thick basal contact zone is composed of coarse-grained, taxitic olivine gabbro and augite troctolite. This is overlain by a 300-600m thick zone of complexly layered cumulate rocks including feldspathic dunite, oxide peridotite, melatroctolite, augite troctolite and olivine gabbro that comprise the melanocratic zone. These rock types commonly define several macrocyclic subzones grading from dunite/melatroctolite upward to augite troctolite/olivine gabbro. However, in many areas, melatroctolite transgresses augite troctolite. The structural complexities of this zone are interpreted to represent the effects of multiple intrusions during the early inflation stage of the DLS magma chamber. The next zone up is the troctolite zone. It is 700-1200m thick, consists mostly of homogeneous foliated troctolitic cumulates. The cyclic zone forms the medial section of the DLS and is characterized by cyclical variations in cumulus mineralogy between troctolitic and gabbroic cumulates. At least four major troctolite-gabbro macrocycle subzones are delineated within the well-exposed southern extent of the cyclic zone. Miller and Ripley (1996) suggested that the cyclicity formed by pressure fluctuations attending magma venting episodes. The persistent occurrence of gabbroic cumulates defines the next unit, the 600m- to 1700m-thick gabbro zone. Gabbroic cumulates, in turn, grade upward into nonfoliated (noncumulate) apatitic quartz ferromonzodiorite, which composes most of the 50m- to 200m-thick upper contact zone. This quartz ferromonzodiorite complexly mixes with a fine-grained biotitic ilmenite ferrodiorite, which forms the "chilled" DLS contact with anorthositic series rocks. A couple of small bodies of melanogranophyre, which irregularly cut through the anorthositic series, probably represent the uppermost differentiate of the DLS. This igneous stratigraphy, which is complimented by cryptic 64 �layering of cumulus mineral compositions, implies that the DLS formed by bottom-up, open-system fractional crystallization of a moderately evolved, olivine tholeiitic magma. The structurally and lithologically complex anorthositic series (AS), which caps the layered series, is subdivided into four units: 1) a troctolitic anorthosite unit that fringes the lower part of the series; 2) an ophitic olivine leucogabbro unit that occurs mainly as inclusions in the upper part of the layered series; 3) a plagioclase-phyric gabbro unit that occurs along the upper contact; and 4) a main unit of undifferentiated gabbroic anorthosite that comprises 90% of the AS. Although their physical relations clearly indicate that the DLS intruded the AS, precise U/Pb zircon dating (Paces and Miller, 1993) shows essentially identical ages of 1099 Ma for both series. A more complete picture of geologic structure in the Duluth area is also portrayed by these new maps. Much of the area is cut by ENE to ESE-trending faults. With the exception of the fault zone exposed in Stewart Creek, these faults are speculative and inferred from topography, aeromagnetic data, and geologic offset. One of the more enigmatic structural features of the area is an antiform-synform duplex defined by foliation and layering in the Spirit Mountain area (West Duluth quadrangle). The limb between these fold structures is near vertical and their N-S fold axes are doubly plunging. By their orientation, they do not appear to be related to faulting. Perhaps the folds developed by collapse of the cumulate pile overlying a feeder zone. Another major improvement on the geologic picture of the Duluth area is in the subdivision of the North Shore Volcanic Group and related hypabyssal intrusions, which form the Duluth Complex hanging wall. The AS intruded normal-polarity lavas of the NSVG, of which approximately 2445 m form the section within the Duluth quadrangle. These volcanic rocks are intruded by the 600m thick Endion sill near the middle, the lensing Northland sheet in the upper part, and the Lester River sill at the top, plus two minor diabasic intrusions along with several late basaltic dikes. Several distinctive and mappable volcanic and sedimentary units within this section include five large felsic flows that constitute 37% of the sequence (Green and Fitz, 1993). From lowest to highest, these are the City Hall icelandite, the Congdon Park rhyolite, the 40th Ave. East icelandite (dated at 1098.4+/-1.9Ma, Davis and Green, 1997), the 42nd Ave. East rhyolite, and the Lester Park icelandite. The lowermost lavas are contact-metamorphosed by the Duluth Complex to pyroxene-hornfels to hornblende-hornfels facies; the remainder show greenschist and laumontite-prehnite-pumpellyite assemblages due to burial metamorphism (Schmidt, 1993). References Davis, D.W, and Green, J.C., 1997, Geochronology of the North American Midcontinent rift in western Lake Superior and implications for its geodynamic evolution. Canadian Journal of Earth Science 34, p. 476-488. Green, J.C., and Fitz, T.J.III, 1993, Extensive felsic lavas and rheoignimbrites in the Keweenawan Midcontinent Rift plateau volcanics, Minnesota: petrographic and field recognition. Journal of Volcanology and Geothermal Research 54, p. 177196. Grout, F.F., 1918, Internal structures of igneous rocks; their significance and origin with special reference to the Duluth Gabbro. Journal of Geology 26, 439-458 Miller, J.D., Jr., Green, J.C., & Chandler, V.W., 1993, Preliminary geologic map of the Duluth area, St. Louis County, Minnesota. Minnesota Geological Survey Open-file Report 93-2, scale 1:48,000 Miller, J.D., Jr., and Ripley, E.M., 1996, Layered intrusions of the Duluth Complex, Minnesota, USA. In Cawthorne, R.G., ed., Layered Intrusions: Amsterdam, Elsevier Science, p. 257-301. Paces, J.B., and Miller, J.D., Jr., 1993, Precise U-Pb ages of Duluth Complex and related mafic intrusions, northeastern Minnesota: Geochronological insights to physical, petrogenetic, paleomagnetic, and tectonomagmatic processes associated with the 1.1 Ga Midcontinent Rift System. Journal of Geophysical Research 98, No B8, p. 13,997-14,013. Schmidt, S.Th., 1993, Regional and local patterns of low-grade metamorphism in the North Shore Volcanic Group, Minnesota, USA. Journal of Metamorphic Geology 11, p. 401-414. Schwartz, G.M., 1949, The geology of the Duluth metropolitan area. Minnesota Geological Survey Bulletin 33, 136p. Taylor, R. B., 1964, Geology of the Duluth Gabbro Complex near Duluth, Minnesota. Minnesota Geological Survey Bulletin 44, 63 pp. 65 �EFFECT OF MINERALOGY ON PROCESSING OF LOW GRADE IRON ORES FROM THE NEGAUNEE IRON-FORMATION ON MARQUETTE RANGE OF THE LAKE SUPERIOR DISTRICT HAN, Tsu-Ming, Senior Research Scientist (Retired), Cleveland-Cliffs Inc., Ishpeming, Michigan, USA During the past half-century, Cleveland-Cliffs has investigated and processed three types of lowgrade iron ores from the Negaunee Iron-Formation on the Marquette Range of the Lake Superior District. The three ore types are: (1) Specular hematite ore of medium metamorphic grade with the principal gangue of chert and locally some sericite, garnet, epidote and grunerite. (2) Magnetite ore of low metamorphic grade with the principal gangue of chert, siderite, ankerite, stilpnomelane, minnesotaite and some clastics. (3) Oxidized magnetite ore in which martite is the principal ore mineral. Ultrafine-grained hematite, microplaty hematite, goethite and earthy hematite are locally present in substantial quantities. Chert and clastic quartz are the principal gangue with local distribution of some gypsum and clay minerals (kaolin, dickite, and montmorillonite). Some minor minerals in the above ores have caused problems in the concentration process and concentrate grade control either in plant practice or from the laboratory testing. Others have caused the physical and chemical quality of the final pellet product. This paper reports the mode of occurrence of these minerals and their negative effects affecting the plant operation and the quality of the pellet product. I – Mineralogy affecting the process of concentration A – Laboratory data showed that gypsum causes total flocculation during desliming due to the release of calcium ions into solution. It prevents the rejection of slimes from flotation feed. This minimizes the selectivity of amine flotation resulting in lower the weight and iron unit recoveries as a result. B– Montmorillonite absorbs amine killing froth leading the catastrophic failure in separating ore minerals from gangue. It can easily be detected by a simple procedure referred to as “Shake Test”, or by analyzing MgO content of the crude ore before processing, i.e., in most cases, the concentrate grade is determined by the MgO content of the crude ore. II – Ore mineralogy that can affect concentrate grade A – Ultrafine-grained magnetite is typically present in the iron-formation adjacent to chloritized basic dikes and sills. The magnetite may represent as much as 40% of the ironformation. However, its grain size is generally finer than 5 microns and it is practically impossible to produce a magnetic concentrate with an acceptable grade by any feasible mechanical means from this type of material. B – Ultrafine-grained hematite occurs as irregular grains and microplates of a few microns or less finely disseminated in chert. Such a hematite and chert relationship has been referred to as 66 �“Hematitic Chert”. It is the host of martite and is considered as waste, which cannot be rejected by the magnetic oxide conversion process (MOC) but can be partially removed by the amine flotation. III – Mineralogy that can affect pellet physical quality Graphite can be rejected during desliming and flotation. However, some of it is entrapped in the magnetic concentrate for palletizing. It causes internal fusion of pellets due to the differential rate of heat transfer and oxygen diffusion toward center of the pellets. This leads to the development of concentric cracking in the pellets and consequently lowers the physical quality of the pellets during transfer. The resulting structural weakness in the pellets can be minimized by the addition of hematite to the balling feed to enhance oxygen availability IV – Mineralogy that can affect pellet chemical quality A – Phosphorus in the oxidized ore occurs as apatite, which has been designated as P1, and as an impurity in goethite and dove-tailed hematite, as P2. Most of the P1 can be rejected during the desliming and flotation stages, whereas the P2 increases with the increase of iron in the concentrate. In order to produce an acceptable final product containing less than 0.03% P from some of the highly oxidized ore, a substantial amount of these ore minerals has to be rejected by high intensity magnetic separation. B – Titanium is present as rutile in some specular hematite. It is practically impossible to separate from its specular hematite host by any known mechanical means. Consequently, it reports with the iron in the concentrate from the specular hematite. C – Stilpnomelane and minnesotaite contain the potassium and sodium. These constituents are a detriment to blast furnace refractory. Most of these minerals are rejected during magnetic separation and flotation. Some of them are entrapped in the magnetite fines as a result of magnetic flocculation. Generally, the alkaline content in the pellets has not been a major problem. Specular hematite concentrate is no longer produced. Oxide ore containing montmorillonite or gypsum remain to be successfully processed. Magnetite iron-formation adjacent to the intrusives has been considered as “waste” and removed by selective mining. 67 �Geochemistry of the Proterozoic Intrusive Rocks of the Nipigon Embayment HART, T.R., Precambrian Geoscience Section, Ontario Geological Survey, 933 Ramsey Lake Road, Sudbury, Ontario P3E 6B5 (tom.hart@ndm.gov.on.ca) The Nipigon Embayment is an approximately 19 000 km2 area of Proterozoic igneous and sedimentary rocks centred on Lake Nipigon, north of Lake Superior and approximately 110 km northeast of Thunder Bay. There are three geochemically distinct Proterozoic intrusive rock types in the Nipigon Embayment, the southern ultramafic intrusions, the Kitto-Jackfish intrusions and the Nipigon Sill Complex (Hart, 2003). The southern ultramafic intrusions consist of the Disraeli, Seagull-Leckie, and Hele intrusions located in the area between Lake Nipigon and Lake Superior. These intrusions are composed of a pyroxene peridotite core with irregular olivine gabbro zones along their margins, and intrude the rocks of the Archean Quetico Subprovince and the Proterozoic Sibley Group. Their present geometry is sill-like, but all three intrusions are composed predominantly of cumulate wehrlite and lherzolite and may represent the remnants of large bodies. The intrusions have calc-alkaline affinities with [La/Yb]mn (mantle normalized) ratios of 5.3 to 18.53 and have weakly depleted Th and little to no Nb anomalies ([Th/Yb]mn ratios of 0.78 to 1.1). The broad range in composition is probably a result of a combination of igneous processes within the magma chambers and assimilation of country rock. Evidence of assimilation is most evident in small, irregular monzogabbro pods that are geochemically similar to the surrounding olivine gabbro but have higher K2O contents. All three intrusions have REE and HFSE ratios that are comparable to ocean island basalts as has been noted for the Seagull Intrusion by Heggie and Hollings (2004). The Kitto-Jackfish intrusions range from an approximately 750 m thick sill-like body at Kitto to an approximately 50 m thick sill at Jackfish Island, English Bay area (MacDonald, 2004), and sills up to a few metres thick at Kama Hill, Nipigon Bay of Lake Superior. The Kitto Intrusion is composed of a pyroxene peridotite core with an irregular olivine gabbro border zone comparable to the southern peridotites (Hart et al., 2002). These sills intrude the rocks of the Quetico and Wabigoon subprovinces and the Sibley Group. The Kitto-Jackfish sills have calc-alkaline affinities with [La/Yb]mn ratios of 6.3 to 10.7, weak Th depletion and weak negative Nb anomalies ([Th/Nb] mn ratios of 1.1 to 1.8) and rare earth element (REE) and high field strength element (HFSE) contents similar to the southern peridotites. The 68 �trend of these intrusions on a La/Sm - Gd/Yb diagram could be a result of either a higher degree of assimilation than the southern peridotites or an indication of a different magma source. The presence of platinum group element (PGE) mineralization in the Seagull and Kitto intrusions suggests that differences in geochemistry are not a useful tool in area selection during exploration. A series of generally flat-lying to shallow-dipping diabase sills of the Nipigon Sill Complex ranging from a few metres to greater than 100 m in thickness intrude both the southern ultramafic intrusions and the Kitto intrusion. The 1109 Ma sills (Davis and Sutcliffe, 1985) have tholeiitic affinities with [La/Yb]mn ratios of 1.61 to 3.29 and moderate negative Nb anomalies ([Th/Nb]mn ratios of 1.8-3.1). Although the sills probably formed as a result of multiple injections of magma, geochemistry suggests that many of the sills are single cooling units. There is geochemical evidence of assimilation of the country rock, which is supported by field relationships. The effects of assimilation are most evident in the chilled margins, although sills of similar thickness appear to display variability in composition suggesting that the degree of assimilation depends on the composition of the country rock. The Nipigon diabase sills have lower TiO2 (0.87 to 2.0 wt.%), Zr/Y (4.2 to 2.7) and [La/Yb]mn ratios than the Logan sills (TiO2: 3.45 to 3.79 wt.%; Zr/Y: 5.5 to 7.7; [La/Yb]mn: 6.5 to 7.8) located south of Thunder Bay. The [La/Yb]mn ratios of the Logan sills are comparable to the ultramafic intrusions of the Nipigon Embayment, but their REE and HFSE contents are about 3 times higher than the intrusions. Similar geographic related geochemical variations have been observed in some flood basalt provinces (e.g., Mantovani et al. 1985). References Davis, D.W. and Sutcliffe, R.H. 1985. U-Pb ages from the Nipigon plate and northern Lake Superior; Geological Society of America Bulletin, v.96, p.1572-1579. Hart, T.R. 2003. Keweenawan Mafic and Ultramafic Intrusive Rocks of the Lake Nipigon and Crystal Lake areas, northwestern Ontario; in Part 1: Programs and Abstracts, Institute on Lake Superior Geology, Proceedings Volume 49; Iron Mountain, Michigan, May 7-11, 2003. Hart, T.R., terMeer, M. and Jolette, C. 2002. Precambrian Geology of Kitto, Eva, Summers, Dorothea and Sandra Townships, Beardmore Area, Northwestern Ontario. Ontario Geological Survey, Open File Report 6095, 206p. MacDonald, C.A. 2004. Precambrian geology of the south Armstrong-Gull Bay area, Nipigon Embayment, northwestern Ontario; Ontario Geological Survey, Open File Report 6136, 42p Mantovani, M.S.M., Marques, L.S., de Sousa, M.A., Civetta, L., Atalla, L. and Innocenti, F. 1985. Trace element and strontium isotopic constraints on the origin and evolution of Parana continental flood basalts of Santa Catarina State (southern Brazil); Journal of Petrology, v.26, p.187-209. 69 �Precambrian Geology and Mineralization of the Northern Black Sturgeon River area, Nipigon Embayment HART, T.R., and MAGYAROSI, Z., Precambrian Geoscience Section, Ontario Geological Survey, 933 Ramsey Lake Road, Sudbury, Ontario P3E 6B5 (tom.hart@ndm.gov.on.ca) A 1:50 000 scale bedrock mapping project in the northern Black Sturgeon River area was conducted to investigate the regional geological setting of the platinum group element (PGE) bearing mafic to ultramafic intrusion in the Seagull Lake area, in the southern portion of the Nipigon Embayment (Hart and Magyarosi, 2004). The Nipigon Embayment is an approximately 19 000 km2 area of Proterozoic igneous and sedimentary rocks centred on Lake Nipigon, north of Lake Superior. This mapping was completed by the Ontario Geological Survey as part of its commitment of in-kind support to the Lake Nipigon Region Geoscience Initiative (LNRGI). The LNRGI is a geoscience-based geological data acquisition and compilation program operated by the Ontario Prospectors Association (OPA) and funded through an agreement with the Northern Ontario Heritage Fund Corporation (NOHFC). The LNRGI also includes partnerships with the private sector, Lakehead University and communities in the Lake Nipigon area. The initiative also includes airborne magnetic and radiometric surveys, ground gravity surveys, and targeted surficial geochemical and geochronological studies. The north Black Sturgeon 280000 River map area is located approximately 110 km northeast of Thunder Bay and south of Lake Nipigon, and is underlain by 5600000 metamorphosed and deformed Archean volcanic and sedimentary rocks of the southern Wabigoon Subprovince and metamorphosed feldspathic wackes and siltstones of the Quetico Subprovince. Sedimentary rocks of the relatively flat-lying 1340 Ma Sibley Group (Franklin, 1978), consisting of conglomerates, sandstones, LLaakkee mudstones, siltstones, limestone, N Niippiiggoonn unconformably overlie the Archean rocks. Proterozoic mafic to ultramafic intrusions in the Disraeli Lake and the Seagull–Leckie lakes areas intrude the Quetico Subprovince and Sibley Group. Both intrusions are composed of a pyroxene peridotite core with an irregular olivine gabbro zones along the margin. A series of undulating, generally flat-lying to shallow-dipping 1109 Ma diabase sills of the Nipigon Sill Complex 5400000 (Davis and Sutcliffe, 1985) intrude 430000 all other rock units in the map area. The Black Sturgeon fault zone consists of a series of north and northwest-trending faults which form an asymmetric basin or half-graben. Less prominent northeasttrending faults probably represent reactivation of structures in the Archean basement rocks. 70 �The location of alteration and the ultramafic intrusions appear to be controlled by the distribution of faults within the Black Sturgeon fault zone. The Disraeli and Seagull ultramafic intrusions occur along the same series of north trending faults that appear to correlate with north-trending structures in the northern Gull Bay area about 80 km to the north. A parallel series of north-trending faults about 25 km to the east hosts the Hele ultramafic intrusion. The most significant PGE mineralization in the Seagull Intrusion was intersected at or near the basal contact of the peridotite with metasedimentary rocks of the Quetico Subprovince. The mineralization is interpreted by Heggie and Hollings (2004) to be magmatic, and formed as a result of sulphur saturation of the magma during initial stages of emplacement. Biotite is ubiquitous in the ultramafic intrusions, but textural evidence is unclear as to whether the biotite is a primary igneous mineral. Preliminary microprobe analyses from the Disraeli Intrusion indicates that biotite may contain up to 5 wt.% Cl, which is similar to the high Cl and F contents reported in biotite associated with PGE minerals in the Coldwell Complex (Watkinson and Ohnenstetter, 1992). The ultramafic intrusions are also cut by the faults suggesting a later reactivation. Metre to tens of metre wide zones of intense hematization occur in along these faults in the Seagull intrusion, and a 40 m thick interval in one drill hole is reported to contain a sylvite rich brine. One sample from the brine rich interval has 3.4 ppm Pt and 1.2 ppm Pd along with elevated Cu and K2O contents suggesting that late fluids could remobilize, and possibly concentrate, the PGEs. Further work is required to understand the timing of this late alteration and the metallogenic significance. References Davis, D.W. and Sutcliffe, R.H. 1985. U-Pb ages from the Nipigon plate and northern Lake Superior; Geological Society of America Bulletin, v.96, p.1572-1579. Franklin, J.M. 1978. The Sibley Group, Ontario; in Rubidium-strontium isochron age studies, report 2; ed. R.K. Wanless and W.D. Loveridge; Geological Survey of Canada, Paper 77-14, p.31-34. Hart, T.R. and Magyarosi, Z. 2004. Precambrian Geology of the northern Black Sturgeon River and Disraeli Lake Area, Nipigon Embayment, northwest Ontario; Ontario Geological Survey Open File Report 6138, 56 p. Heggie, G.J., and Hollings, P., 2004. Controls on PGE Mineralization in the Seagull Intrusion, Northwestern Ontario; Geological Association of Canada-Mineralogical Association of Canada, Joint Annual Meeting, St. Catharines 2004, Program with Abstracts. Watkinson, D.H. and Ohnenstetter, D. 1992. Hydrothermal origin of platinum-group mineralization in the Two Duck Lake Intrusion, Coldwell Complex, northwestern Ontario; Canadian Mineralogist, v.30, p.121-136. 71 �Multiple Intrusive Stages Associated with Keweenawan Rifting: The Leckie Stock, Seagull Intrusion, and Nipigon Sill HEGGIE*, G., and HOLLINGS, P., Department of Geology, Lakehead University, 955 Oliver Rd., Thunder Bay, Ontario, P7B 5E1, Canada; gheggie@lakeheadu.ca Igneous activity related to Keweenawan Rifting (ca. 1108 Ma, Davis and Green, 1997) has produced a wide spectrum of lithologies and numerous igneous suites (Osler Volcanics, North Shore Volcanics, Mamainse Point Volcanics, Duluth Complex, Logan Sills, Nipigon Sills, Coldwell Complex, English Bay Complex, Eva Kitto Intrusion, Seagull Intrusion, Leckie Stock). Found on the periphery of Lake Superior and Lake Nipigon these igneous bodies have been studied for 95 years (first mapped in Canada by Wilson 1910), as work further expands our understanding of the magmatic history, the more complex igneous relationships become. Rift related intrusive rocks outcrop extensively around Lake Nipigon (Figure 1). The most abundant intrusions in this region are the Nipigon Sills (Sutcliffe 1986, Hart and McDonald 2003). Other igneous bodies have been identified in the process of PGE, Cu and Ni exploration. These intrusive bodies, including the Seagull Intrusion and Leckie Stock, although not as expansive as the Nipigon Sills still play an integral part in the development of a unified petrogenetic model. Figure 1. Location of intrusive, extrusive, and sedimentary rocks associated with the Keweenawan Rifting event. Modified after Sutcliffe, 1991. Contact relationships between the three intrusive suites (Leckie Stock, Seagull Intrusion, and Nipigon Sill) are not yet fully understood. Chill margins on a Nipigon Sill crosscutting the Leckie Stock have been identified in drill core, establishing that the Nipigon Sill post dates the 72 �Leckie Stock. Age relationships between the Seagull Intrusion and Nipigon Sill are still unknown, as is the relationship between Seagull Intrusion and Leckie Stock. Lithologically, geochemically, and mineralogically it is possible to distinguish between the three bodies. The Leckie Stock is characterized by ultramafic lithologies, with rare earth element plots similar to ocean island basalt with (La/Sm)n values of 1.01-5.21 and (Gd/Yb)n of 1.82-3.73. Mineralogically the Leckie Stock is dominated by olivine with an average composition of Fo82. This compares to the mafic lithologies (olivine gabbro - gabbro norites) of the Nipigon Sills with (La/Sm)n of 1.51-1.61 and (Gd/Yb)n values of 1.46-1.49. Olivine mineralogy in the Nipigon Sill varies more than in the Leckie Stock, and has an average olivine composition of Fo50. Lithologically the Seagull Intrusion, displays the greatest variation, varying from olivine gabbros, - gabbros to granophyres. Olivine analysed from this body has an average composition of Fo67. Mineralogical and geochemical data suggest that the Leckie Stock is the most primitive magma of the three intrusive suites. The Seagull Intrusion and Nipigon Sills are similar in terms of mineralogy and petrology in that they display overlapping olivine compositions, but REE data (Hart 2002) suggests that the Seagull Intrusion is more closely related to the ultramafic Leckie Stock, if a cross cutting relationship exists between the two (Seagull Intrusion crossing Leckie Stock). The Leckie Stock could not be a feeder zone for either the Seagull Intrusion or the Nipigon Sill, but a feeder for some yet unidentified igneous body higher up in stratigraphy. Davis, D.W., and Green, J.C., 1997. Geochronology of the North American Midcontinent rift in western Lake Superior and implications for its geodynamic evolution. Canadian Journal of Earth Sciences. V.34, p. 476-488. Hart, T., 2002, Keweenawan Mafic and Ultramafic Intrusive Rocks on the Lake Nipigon and Crystal Lake areas, northwestern Ontario, in Institute on Lake Superior Geology, Proceedings Volume 49, Part 1 –Programs and Abstracts, p. 21-22. Hart, T., and MacDonald C.A., 2003. Lake Nipigon Region Geoscience Initiative. Proterozoic and Archean Geology of the South-Central and North areas of the Western Nipigon Embayment. Ontario Geological Survey, Summary of Field work and other Activities. Open File Report 6120. Sutcliffe, R.H., 1991. Proterozoic Geology of the Lake Superior area, in Geology of Ontario, Ontario Geological Survey, Special Volume 4, Part 1, p. 627-658. Sutcliffe, R.H., 1986. The Petrology, Mineral Chemistry and Tectonics of Proterozoic rift-related igneous rocks at Lake Nipigon, Ontario. Unpublished PhD. Thesis, The University of Western Ontario, London, Ontario. Wilson, A.W., 1910, Geology of the Nipigon Basin, Ontario. Memoir No.1 Canada Department of Mines, 152 p. 73 �40 Ar/39Ar Hornblende Evidence for Provenance of Ice Rafted Detritus in the North Atlantic: Implications for Tracking Past Changes in the Extent and Dynamics of Northern Hemisphere Ice Sheets HEMMING, Sidney R., and ROY, Martin, Lamont-Doherty Earth Observatory of Columbia University, Rt. 9W, Palisades, NY 10964 The concentration and provenance of terrigenous sand grains from North Atlantic sediment cores from pelagic environments provide important constrains on the dynamics of former Northern Hemisphere ice sheets. The association of this ice rafted detritus (IRD) signal with proxy records for climate conditions in the North Atlantic, brings additional constraints on ice sheet dynamics in a paleoclimate context. Studies at proximal locations identify configuration changes in specific ice sheets, while studies of cores in the open ocean can yield a history of variation where relative timing of iceberg discharges from different source regions as constrained by simple stratigraphic principles. An example is the case of the Laurentide ice sheet (LIS) where the distinctive variations in age provinces underlying the LIS from south to north can be used to constrain its extent and ice stream activity during the last glacial cycle. 40Ar/39Ar hornblende data from IRD indicate the ice reached Grenville and Appalachian provinces along the margin after about 30 kyr (e.g., and the Last Glacial Maximum, LGM). The increase in flux of IRD at the LGM is coincident with the increase in southeastern LIS provenance components. The last glacial cycle was punctuated by Heinrich events, massive discharges of icebergs from the Hudson Strait ice stream. The general trend in LIS development and identification of major ice stream events that are captured by the marine sediment record show the potential power of this approach for understanding the evolution of ice sheets in general. This approach can be applied throughout the Pleistocene to understand the temporal and spatial development of large volume ice sheets and the transition to the 100-ky cycle that dominated the past 700 kyrs. We seek to expand the studies both geographically and through the Pleistocene. 74 �PRELIMINARY PETROGRAPHY AND HYDROTHERMAL ALTERATION OF THE SOUDAN MINE AREA, VERMILION DISTRICT, NORTHESTERN MINNESOTA HOFFMAN, A.T.*, Dept. of Geosciences, University of Minnesota, Duluth, hoff0578@d.umn.edu PETERSON, D.M., PATELKE, R.L., Economic Geology Group, Natural Resources Research Institute, University of Minnesota Duluth, 5013 Miller Trunk Highway, Duluth MN 55811 HUDAK, G.J., Geology Department, University of Wisconsin Oshkosh, Oshkosh, WI The Ely Greenstone of the western Vermilion District is a lithologic and structurally diverse setting located in the southern extension of the Wawa Subprovince of the Superior Province of the Canadian Shield. The Wawa Subprovince is the host for a significant number of mineral deposits and showings, most notably lode gold and volcanogenic massive sulfides (VMS) (Williams et al., 1991). In the last decade, there has been a significant effort put forth to document areas in the Vermilion district that seem geologically and mineralogically compatible for hosting these deposits. This work includes reconnaissance mapping in the eastern Murray shear zone for mesothermal gold mineralization (Peterson, 2001; Peterson and Patelke, in prep.) and the re-evaluation of the Fivemile Lake, Purvis Lake, Eagles Nest, Skeleton Lake, and Needleboy Lake VMS prospects (Peterson, 2001; Hudak et al., 2002a; Hudak et al., 2002b). In the summer of 2003 mapping for a National Underground Science and Engineering Laboratory (NUSEL) was completed near the Soudan Mine in northeastern Minnesota (Peterson and Patelke, 2003). This work revealed localized lode gold and volcanogenic massive sulfide type alteration. This alteration may correlate with alteration located in the adjacent Fivemile Lake Prospect (Hudak et al., 2002b) and Murray Gold Prospect (Peterson, 2001). The goal of this project is to better understand the volcanic stratigraphy, and syn- and post hydrothermal alteration near the Soudan Mine. Eighty thin sections were analyzed to defined primary syn-volcanic alteration assemblages in the Soudan Mine area. Classification of mineral assemblages followed Hudak et al. (2002b) in effort to establish consistent hydrothermal mineral alteration nomenclature across the Vermilion District. Four mineral assemblages dominate the area: 1) Epidote + Quartz + Actinolite ± Chlorite; 2) Epidote + Quartz ± Chlorite; 3) Mottle Epidote + Quartz ± Actinolite ± Chlorite ± Albite (Epidosites); and 4) localized and lesser amounts of Garnet + Magnetite. Alteration assemblages 1 (Epidote + Quartz + Actinolite ± Chlorite) and 2 (Epidote + Quartz ± Chlorite) likely represent early-formed, semi-conformable zones associated with down welling seawater. Alteration assemblages 3 (Mottle Epidote + Quartz ± Actinolite ± Chlorite ± Albite (Epidosites)) and 4 (localized Garnet + Magnetite) appear to represent hydrothermal fluid upflow zones that may be proximal to syn-volcanic structures (Harper, 1999; Gibson et al., 1999). These results suggest that volcanogenic massive sulfide targets may be present near the Soudan Mine. Petrographic analysis is ongoing and a detailed field analysis during summer 2004 will better constrain these relationships. 75 �References Harper, G.D., 1999, Structural Styles of Hydrothermal Discharge in Ophiolite/Sea-Floor Systems: Reviews in Economic Geology v. 8, p. 53-73 Hovis, S. T., 2001, Physical Volcanology and Hydrothermal Alteration of the Archean Volcanic Rocks at the Eagles Nest Volcanogenic Massive Sulphide Prospect, Northern Minnesota. Unpublished M.S. Thesis, University of Minnesota Duluth, Duluth, Minnesota, 102 p. Hudak, G.J., Heine J., Hocker, S.M., Hauck, S., 2002a, Geologic Mapping of the Needleboy Lake-Six Mile Lake Area, Northeastern Minnesota: A Summary of Volcanogenic Massive Sulfide Potential. Report of Investigations NRRI/RI-2002/14. Hudak, G.J., Heine, J., Newkirk, T., Odette, J., and Hauck, S., 2002b. Comparative Geology, Stratigraphy, and Litho-Geochemistry of the Five Mile Lake, Quartz Hill, and Skeleton Lake VMS Occurrences, Vermilion District, NE Minnesota. NRRI Technical Report NRRI/PR-2002/03, 390 p. Peterson, D.M., Patelke, R. L., 2003 National Underground Science and Engineering Laboratory (NUSEL): Geologic Site Investigation for the Soudan Mine, Northeastern Minnesota. NRRI Technical Report NRRI/TR-2003/29, 87 p. Peterson, D.M., 2001 Development of Archean lode gold and massive sulfide exploration models using Geographic Information System applications: Targeting mineral exploration in northeastern Minnesota from analysis of analog Canadian mining camps: Unpublished Ph.D. dissertation, University of Minnesota Minneapolis, 502 p. Peterson, D.M., and Patelke, R.L., in Prep, Neo-Archean gold mineralization in the Mud Creek area, Northern St. Louis County, Minnesota: Natural Resources Research Institute, University of Minnesota Duluth. Williams, H.R., Stott, G.M., Heather, K.B., Muir, T.L., and Sage, R.P., 1991, Wawa Subprovince, in Thurston, P.C., Williams, H.R., Sutcliffe, R.H., and Stott, G.M., eds., Geology of Ontario: Ontario Geological Survey Special Volume 4, Part 1, p. 485-539. 76 �Trace Element Geochemistry of the Osler Group Volcanics – Implications for Mid-Continent Rifting HOLLINGS, Pete, Department of Geology, Lakehead University, 955 Oliver Rd., Thunder Bay, Ontario, P7B 5E1, Canada; peter.hollings@lakeheadu.ca To date three major Proterozoic events have been recognized on the northern margins of Lake Superior (Sutcliffe, 1991); 1) the Paleoproterozoic Animikie Group sediments (~1.86 Ga), 2) ~1.54 Ga Mesoproterozoic anorogenic granites and Sibley Group sediments, 3) Mesoproterozoic rifting at ~1.11 to 1.09 Ga during which the Keweenawan Supergroup was deposited. The Osler Group volcanics are found towards the base of the Keweenawan Supergroup. The Osler Group volcanics comprise a bimodal sequence of basalts and less abundant rhyolites that are well exposed on a series of islands off Rosport on the northern shore of Lake Superior and also as sparse outcrop on the Slate Islands off Terrace Bay (Fig. 1). The Osler Group has been described as a thick sequence of tholeiitic flood basalts with up to 2800m exposed on the Black Bay Peninsula (Sutcliffe, 1991). The majority of the sequence comprises magnetically reversed Lower Keweenawan flows with a small section of magnetically normal flows at the top of the sequence (Halls, 1974). Davis and Sutcliffe (1985) have reported U-Pb ages of 1107.5 +4/-2 Ma for a rhyolite from the base of the sequence and 1097.6 ±3.7 Ma for a rhyolite towards the top. Figure 1. Location of the intrusive, extrusive and sedimentary rocks associated with Keweenawan Rifting. Modified after Sutcliffe (1991). 77 �Detailed sampling traverses were undertaken on Wilson and Vein islands in the summer of 2002, in order to investigate geochemical variations within the Osler Group. Exposure on the two islands is excellent, beginning at the northern end of the islands with a basal conglomerate that includes abundant clasts of Sibley sediments. The conglomerate is strongly heterolithic and indicates an approximately northward flow direction. The volcanic units comprise numerous flows ranging from a few centimeters to a few metres in thickness. Individual flows are frequently marked by rubbly flow tops or ropey, pahoehoe textures, while thicker flows may show well developed columnar jointing (Fig. 2). Figure 2. A) Columnar basalts within the Osler Group on Simpson Island. B) Pahoehoe texture in thin basalt flow on Wilson Island. SiO2 and MgO contents of the Osler Group volcanics on Wilson and Vein Islands range from 4754 wt. % and 5-15% respectively, consistent with data from earlier studies. Basalts are characterized by weak to moderate LREE enrichment (La/Smn = 1-5), weakly fractionated HREE (Gd/Ybn = 2-4) and display primitive mantle normalised patterns comparable to modern Ocean Island Basalts. Preliminary examination of REE data for the Group suggests that the La/Smn ratio, a good indicator of crustal contamination, increases towards the top of the sequence (ranging from ~1.5 near the base to ~5 near the top). References Davis, D. and Sutcliffe, R., 1985. U-Pb ages from the Nipigon plate and northern Lake Superior. Geological Society of America Bulletin, 96, 1572-1579. Halls, H. C., 1974. A paleomagnetic reversal in the Osler volcanic group, northern Lake Superior. Canadian Journal of Earth Sciences, 11, 1200-1207. Sutcliffe, R., 1991. Proterozoic geology of the Lake Superior area. In. Geology of Ontario, Ontario Geological Survey, Special Volume 4, Part 1. 627-660. 78 �The Influence of Radiometric Dating for Unraveling the Precambrian Geologic History of the Lake Superior Region HOLM, Daniel K., Dept. of Geology, Kent State University, Kent, OH 44242, dholm@kent.edu VAN SCHMUS, R.W., Dept. of Geology, Univ. of Kansas, Lawrence, KS 66045 SCHNEIDER, D.A., Dept. of Geological Sciences, Ohio University, Athens, OH 44701 The paucity of biostratigraphic controls in Precambrian rocks has long made radiometric dating of primary importance for unraveling the complex geologic history in the Lake Superior region (Goldich, 1968). The first ILSG meeting in 1955 occurred very close to the time of initiation of a radiometric dating program by S.S. Goldich and A.O Nier in 1956. Subsequent geochronologic investigations laid the theoretical and practical foundation upon which current radiometric studies are expanding. Thus the tremendous influence of geochronologic studies in this region, only briefly summarized here, has been well chronicled at ILSG meetings over the past 50 years. Pioneering studies in K-Ar, Rb-Sr, and U-Pb dating. Early studies by Goldich et al. (1961, 1970), Aldrich et al. (1965), and Peterman (1966) were pioneering applications of radiometric dating which provided a broad-brush means of correlation (based on age rather than on degree of metamorphism and deformation) and contributed to the formation of a world-wide time scale for the Precambrian (Goldich, 1968), flatteringly referred to by some as “Goldich’s time scale”. The early results represented a significant breakthrough in Precambrian geology, yet proved difficult to interpret as co-existing minerals gave different ages for the same decay scheme. Comparative mineral studies by Aldrich et al. (1965) and Hanson and Gast (1967) led to the recognition of metamorphic effects on various isotopic systems (especially K-Ar and Rb-Sr). For instance, Van Schmus et al. (1975a) used Rb/Sr age data to document the existence of a widespread but poorly understood low-grade 1650 Ma metamorphic event in Wisconsin. The 2700 Ma age of the greenstone-granite belts in Minnesota and southern Ontario was documented early on by whole-rock Rb-Sr ages (Jahn and Murthy, 1975), K-Ar, and U-Pb ages (Peterman et al., 1972). The large analytical uncertainty in these data, however, precluded their use for resolving the time of important, short-lived, geological events (plutonism, deformations) that occurred during their formation and accretion. Likewise, the errors on initial U-Pb zircon ages on Mid-continent Rift rocks would not allow for differentiation of magmatic pulses, but simply suggested “a sharp pulse of igneous activity” at 1115+15 Ma (Silver and Green, 1963). Early U-Pb zircon work in the Minnesota River Valley temporarily produced some of the world’s oldest dated rocks (Catanzaro, 1963; Goldich et al., 1970; Goldich and Hedge, 1974), and clearly demonstrated that K-Ar and Rb-Sr mineral ages reflect younger metamorphic events. For instance, using K-Ar and Rb-Sr ages, Goldich et al. (1961) first bracketed the Penokean orogeny as having occurred between 1800 and 1600 Ma. Similarly young K-Ar biotite ages (compared to U-Pb zircon ages from the same rock) from Precambrian shields and orogenic belts worldwide led to the concept of a ‘metamorphic veil’ (Armstrong, 1966) which reflects younger overprinting events (common in Precambrian terranes) and obscures the age of older rock forming events. Modern U-Pb dating (bulk aliquot to single crystal to spot dating). In the 1970’s and 1980’s, advances in conventional U-Pb zircon analyses (Krogh, 1973, 1982) allowed geochronologists to see through the ‘metamorphic veil’ and firmly established the age spectrum of igneous activity in the region (Silver and Green, 1972; Van Schmus et al., 1975b; Van Schmus, 1976; 1980). For instance, the age of the Penokean orogeny was definitively bracketed between 1870-1830 Ma by Van Schmus (1976, 1980), who first invoked the plate tectonic concept of a southern magmatic arc colliding with a northern passive margin. Archean age gneisses (Marshfield terrane) were dated south of the Penokean magmatic arc rocks (Van Schmus and Anderson, 1977) and Early Archean ages were obtained from gneiss dome rocks north of the Niagara fault zone (Peterman et al., 1980). The greatly improved accuracy in U-Pb zircon dating has allowed researchers (Boerboom and Zartman, 1993; Corfu and Stott, 1986, 1998; Davis et al., 1989; Zaleski et al., 1999; Ayers et al., 2002) to document the time of short-lived magmatic and deformational events commonly involved in the 79 �formation of late Archean granite–greenstone belts. Enough high precision data has been obtained (i.e., Shebandowan, Vermillion, and Manitouwadge) to suggest correlation of volcanic assemblages and their subsequent deformation along 600 km of strike (Peterson et al., 2001). New U-Pb single-crystal zircon studies continue to refine the earlier plutonic ages, which were obtained on mg-size fractions. Post-Penokean “1760 Ma” plutonism (Sims et al., 1989) is now known to have actually occurred in southeast younging pulses at ca. 1800, 1775, and 1750 Ma, possibly reflecting flip in subduction polarity and slab-rollback of Yavapai-age oceanic lithosphere (Holm et al., 2004). The Penokean orogenic belt twice formed the source region for generation of crustal-melt batholiths; first at ca. 1775 Ma with intrusion of the East-central Minnesota batholith (Holm et al., 2004) and again at 1470 Ma in central Wisconsin (Van Schmus et al., 1975). The new single crystal results show that the Eastcentral Minnesota batholith was emplaced over a ca. 20 m.y. duration (Holm et al., 2004; Keatts et al., 2004), whereas Wolf River magmatism was relatively short-lived (with nine different phases intruded over a <5 m.y. interval; Dewane and Van Schmus, 2003). New important U-Pb zircon results have also been obtained from volcanic rocks over the last decade or so (see Van Schmus and Hinze, 1985 for a summary of earlier age data). High precision U-Pb geochronology on the volcanics of the Midcontinent Rift system indicate rapid eruption over a relatively short duration (1108-1094 Ma; Davis and Paces, 1990; Paces and Miller, 1993; Davis and Green, 1997; Zartman et al., 1997). The great volume of magma generated over this short time span and the limited degree of extension strongly favor a mantle plume origin. New geochronology on interlayered volcanics within the Marquette Range Supergroup yield essentially identical ages of 1875 Ma for the Hemlock (Schneider et al., 2002) and Gunflint (Fralick et al., 2002) Formations. The revised age constraining the timing of deposition of the Supergroup across the Animikie basin suggests these sediments were laid down coeval with arc formation to the south and supports the hypothesis of Hoffman (1987), who first proposed that the iron formations are syn-Penokean foredeep deposits. Conventional single crystal and SHRIMP U-Pb dating of detrital zircons (Van Wyck, 1995; Holm et al., 1998; Medaris et al., 2003) finally resolved the controversy over the maximum age of the Baraboo Quartzite and similar red quartzites in northern Wisconsin and Minnesota (<1750 Ma). A completely different geochronologic database described next provided firm constraints on the minimum age of quartzite deposition (>1650 Ma). Ar-Ar thermochronology. Thermochronology (the study of the time-temperature evolution of rocks) was born from the realization than many mineral-isotopic systems could be used to determine the time of cooling of a terrain through a series of predictable temperatures. Because an intimate relationship exists between the thermal and tectonic processes operating during orogenesis and subsequent events, reconstructing the thermal history of a region ultimately aids in constraining its tectonic evolution. Thermochronologic data from the region was initially dominated by the Rb/Sr method on biotite (Peterman and Sims, 1988). In the 1990’s, application of the Ar-Ar incremental heating technique on hornblende, muscovite, and biotite yielded considerable information bearing on the Proterozoic thermal history of the southern Lake Superior region (Holm and Lux, 1996, 1998; Schneider et al., 1996; Holm et al., 1998a; Romano et al., 2000). Especially important was the proposal that a separate, perhaps widespread, geon 17 amphibolite facies metamorphic event occurred after the Penokean orogeny, followed by an episode of rapid crustal exhumation (Holm et al., 1998a). Additionally, the widespread geographic distribution of basement Ar/Ar biotite ages serendipitously provided a key minimum age constraint (ca. 1630 Ma) on the overlying Proterozoic red quartzites and led to a greater appreciation of the role of younger tectonism (i.e. Mazatzal deformation) in the region (Holm et al., 1998b). New minerals, new techniques, and new directions. Rapid advances in technology (allowing higher precision, increased mass and spatial resolution, and in situ capabilities) and the application of new chronometers (monazite and xenotime) are now verifying earlier hypotheses for widespread tectonothermal events following Penokean orogenesis. Recent results of U-Pb monazite dating using both ion and electron microprobe techniques now recognize distinct metamorphic pulses at 1835, 1800, and 1770 Ma – thermal pulses which can be directly tied to known magmatic events (Schneider et al., 2004). New U-Pb xenotime ages (Vanelli et al., 2003, and in progress) from coarse sandstone/conglomerate beds 80 �of the Marquette Range Supergroup identify a widespread 1790-1760 Ma fluid flow event – an event that may have been ultimately responsible for forming the high-grade iron ore deposits in this region (Morey, 1999). Recent single crystal Ar-Ar dating of fine-grained, low-temperature minerals within the Baraboo Interval Quartzites (Medaris et al., 2003) has documented a much younger, but apparently even more vast hydrothermal fluid system generated by Mesoproterozoic plutonism. Finally, Ar-ion laser dating results reveal significant age gradients (~200 to 500 m.y.) in coarse muscovite from basement samples interpreted to signify partial resetting by fluids during both Mazatzal orogenesis and Mesoproterozoic magmatism (McKenzie, 2004; Rose, 2004). In addition to direct dating of metamorphism and fluid flow, geochronology is now being used to put absolute time (not simply time constraints) on important deformation features in the Lake Superior region. The age of the Mazatzal tectonic front in northwest Wisconsin is dated by the age of reset biotite in basement beneath the deformed quartzites. The Malmo Structural discontinuity in Minnesota and the Flambeau Flow fault in Wisconsin are now thought to be geon 17 exhumation structures (formed during orogenic collapse) on the basis of differing metamorphic ages across these faults (McKenzie et al., 2003; Schneider et al., 2004). Current monazite work on tectonite samples of the Niagara fault zone (Rose, 2004) and the Eau Pleine shear zone (Loofboro, 2005) should provide direct time constraints on their formation (Williams and Jercinovic, 2002). Beginning this month we anticipate the publication of a large number of new ages in just the next few years – in terms of raw numbers, perhaps more than has been published in the Lake Superior region in the entire past 50 years! For instance, Van Wyck and Martin (2004) exploit the relatively fast LA-ICP-MS technique to report over 200 U-Pb detrital zircon ages from the Baraboo and Hamilton Mounds quartzites. Geochronologic work accepted and in progress (Schneider et al., 2004, 2005; Holm et al., 2004, 2005; Vanelli et al., in progress; Bickford et al., in progress; McKenzie, 2004; Rose, 2004; Keatts, 2004, Loofboro, 2005; Schmitz and Bowring, in progress; Medaris et al., in progress; et al. that we may be unaware of) will certainly continue to refine our knowledge of the Precambrian geologic history of this region and very likely yield surprises which can not be anticipated. Aldrich, L.T., Davis, G.L., and James, H.L., 1965, Ages of some minerals from metamorphic and igneous rocks near Iron Mountain, Michigan: Journal of Petrology, 6, 445-472. Armstrong, R.L., 1966, K-Ar dating of plutonic and volcanic rocks in orogenic belts. In O.A. Schaeffer and J. Zahringer, eds., Potassium argon dating, 117-131. Springer-Verlag, New York, 234 p. Ayer, J., Amelin, Y., Corfu, F., Kamo, S., Ketchum, J., Kwok, K., and Marquis, R., 2002: Evolution of the southern Abitibi greenstone belt based on U-Pb geochronology; autochthonous volcanic construction followed by plutonism, regional deformation and sedimentation: Precambrian Research, 115, 63-95. Boerboom, T.J., and Zartman, R.E., 1993, Geology, geochemistry, and geochronology of the central Giants Range batholith, northeastern Minnesota: Canadian Journal of Earth Sciences, v. 30, p. 2510-2522. Catanzaro, E.J., 1963, Zircon ages in southwestern Minnesota: Journal of Geophysical Research, v. 68, p. 20452048. Corfu, F., and Stott, G.M., 1986, U-Pb age for late magmatism and regional deformation in the Shebandowan Belt, Superior Province, Canada: Canadian Journal of Earth Sciences, 23, 1075-1082. Corfu, F., and Stott, G.M., 1998, Shebandowan greenstone belt, western Superior Province: U-Pb ages, tectonic implications, and correlations: Geological Society of America Bulletin, 110, 1467-1484. Davis, D.W., and Green, J.C. 1997, Geochronology of the North American Midcontinent Rift in western Lake Superior and implications for its geodynamic evolution: Canadian Journal of Earth Sciences, 34, 476-488. Davis, D.W., and Paces, 1990, Time resolution of geologic events on the Keweenaw Peninsula and implications for the development of the Midcontinent rift system: Earth and Planetary Science Letters, 97, 54-64. Davis, D.W., Poulsen, K.H., and Kamo, S.L., 1989, New insights into Archean crustal development from geochronology in the Rainy Lake area, Superior Province, Canada: Journal of Geology, 97, 379-398. Dewane, T.J., and Van Schmus, W.R., 2003, Detailed U-Pb geochronology of the Wolf River batholith, northcentral Wisconsin: Evidence for a short-lived magmatic event ca. 1470 Ma: Geological Society of America Abstracts, 37, 92. Fralick, P., Davis, D., and Kissin, S., 2002, The age of the Gunflint Formation, Ontario, Canada: single zircon U-Pb age determinations from reworked volcanic ash: Canadian Journal of Earth Sciences, 39, 1085-1091. Goldich, S.S., Nier, A.O., Baadsgaard, H., Hoffman, J.H., Krueger, H.W., 1961, The Precambrian Geology and geochronology of Minnesota, Minnesota Geology Survey Bulletin 41, 193 p. 81 �Goldich, S.S., Hedge, C.E., and Stern, T.W., 1970, Age of the Morton and Montevideo gneisses and related rocks, southwestern Minnesota: Geological Society of America Bulletin, 81, 3671-3696. Goldich, S.S., 1968, Geochronology in the Lake Superior region: Canadian Journal of Earth Sciences, 5, 715-724. Goldich, S.S., and Hedge, C.E., 1974, 3800-Myr granitic gneiss in south-western Minnesota: Nature. 252, 467-468. Hanson, G.N., and Gast, P.W., 1967, Kinetic studies in contact metamorphic zones: Geochim. Cosmochim. Acta, 31, 1119-1153. Hoffman, P., 1987, Early Proterozoic foredeeps, foredeep magmatism and Superior-type iron formations of the Canadian shield. In Proterozoic lithospheric evolution. Edited by A. Kroner, American Geophysical Union Geodynamics Series, 17, 85-98. Holm, D.K., and Lux, D., 1996, Core complex model proposed for gneiss dome development during collapse of the Paleoproterozoic Penokean orogen, Minnesota: Geology, 24, 343-346. Holm, D.K, and Lux, D., 1998, Depth of emplacement and tilting of the Middle Proterozoic (1470 Ma) Wolf River batholith, Wisconsin. Ar-Ar thermochronologic constraints: Canadian Journal of Earth Science, 35, 1143-1151. Holm, D., Darrah, K., and Lux, D., 1998a, Evidence for widespread ~1760 Ma metamorphism and rapid crustal stabilization of the Early Proterozoic Penokean orogen, Minnesota: American Journal of Science, 298, 60-81. Holm, D., Schneider, D., and Coath, C., 1998b, Age and deformation of Early Proterozoic quartzites in the southern Lake Superior region: Implications for extent of foreland deformation during final assembly of Laurentia: Geology, 26, 907-910. Holm, D.K., Van Schmus, W.R., MacNeill, L., Boerboom, T., Schweitzer, D., and Schneider, D., 2004, U-Pb zircon geochronology of Paleoproterozoic plutons from the northern mid-continent, U.S.A.: Evidence for subduction flip and continued convergence after geon 18 Penokean orogenesis: Geological Society of America Bulletin, in press. Jahn, B.M., and Murthy, V.R., 1975, Rb-Sr ages of the Archean rocks from the Vermilion district, northeastern Minnesota: Geochimica et Cosmochimica Acta, 39, 1679-1689. Keatts, M., Holm, D., Jirsa, M., and Boerboom, T., 2004, Generation of a 1790-1770 Ma continental arc batholith in east-central Minnesota: Compass, v. 82 (in press). Krogh, T. E., 1973, A low contamination method for hydrothermal decomposition of zircon and extraction of U and Pb for isotopic age determinations: Geochimica et Cosmochimica Acta, 37, 485-494. Krogh, T.E., 1982, Improved accuracy of U-Pb zircon ages by the creation of more concordant systems using an air abrasion technique: Geochim. Cosmochim. Acta, 46, 637-649. Loofboro, J., 2005, Timing and nature of Proterozoic poly-metamorphism in central Wisconsin: M.S. thesis, Kent State University, Kent, OH (in progress). McKenzie, M.M., 2004, Age pattern and nature of Paleoproterozoic metamorphism of the internal zone of the Penokean orogen, east-central Minnesota: M.S. thesis, Kent State University, Kent, OH, 105 p. McKenzie, M.M., Holm, D.K., Schneider, D.A., and Jercinovic, M.J., 2003, Results and implications of monazite geochronology from the western Penokean orogen, Minnesota: Geological Society of America Abstracts with Programs, 35, 272. Medaris, G., Singer, B.S., Dott, R.H., Naymark, A., Johnson, C.M., and Schott, R.C., 2002, Late Paleoproterozoic climate, tectonics and metamorphism in the southern Lake Superior region and Proto-North America: Evidence from Baraboo interval quartzite: Journal of Geology, 111, 243-257. Morey, G.B., 1999, High-grade iron ore deposits of the Mesabi Range, Minnesota – Product of a continental scale Proterozoic ground-water flow system: Economic Geology, 94, 133-142. Paces, J.B., and Miller, J.D., Jr., 1993, Precise U-Pb ages of Duluth Complex and related mafic intrusions, northeastern Minnesota: Geochronological insights to physical, petrogenetic, paleomagnetic and tectonomagmatic processes associated with the 1.1. Ga Midcontinent Rift system: Journal of Geophysical Research, 98, 13997-14013. Peterman, Z.E., 1966, Rb-Sr dating of Middle Precambrian metasedimentary rocks, Minnesota: Bulletin of the Geological Society of America, 77, 1031-1044. Peterman, Z.E., and Goldich, S.S., Hedge, C.E., and Yardley, D.H., 1972, Geochronology of the Rainy Lake region, Minnesota-Ontario, in Doe, B.R., and Smith, D.K., eds., Studies in Mineralogy and Precambrian Geology (John W. Gruner Volume): Geological Society of America Memoir 135, 193-215. Peterman, Z.E., and Sims, P.K., 1988, The Goodman Swell: A lithospheric flexure caused by crustal loading along the Midcontinent Rift System: Tectonics, 7, 1077-1090. Peterman, Z., Zartman, R., and Sims, P., 1980, Tonalitic gneiss of early Archean age from northern Michigan: Geological Society of America Special Paper 182, 125-138. Peterson, D.M., Gallup, C., Jirsa, M.A., and Davis, D., 2001, Correlation of Archean assemblages across the U.S.Canadian border: Phase I Geochronology: ILSG Abstracts, 47, 77-78. 82 �Romano, D., Holm, D., and Foland, K., 2000, Determining the extent and nature of Mazatzal-related overprinting of the Penokean orogenic belt in the southern Lake Superior region, north-central USA: Precambrian Research, 104, 25-46. Rose, S., 2004, The age and extent of metamorphism within the Paleoproterozoic Penokean orogen, northern Wisconsin and Michigan: M.S. thesis, Ohio University, Athens, OH, 105 p. Schneider, D., Holm, D., and Lux, D., 1996, On the origin of Early Proterozoic gneiss domes and metamorphic nodes, northern Michigan: Canadian Journal of Earth Sciences, 33, 1053-1063. Schneider, D., Bickford, M., Cannon, W., Shulz, K., and Hamilton, M., 2002, Age of volcanic rocks and syndepositional iron formations, Marquette Range Supergroup: implications for the tectonic setting of Paleoproterozoic iron formations of the Lake Superior region: Canadian Journal of Earth Sciences, 39, 999-1012. Schneider, D., Holm, D.K., O’Boyle, C., Hamilton, M., and Jercinovic, M., 2004, Paleoproterozoic development of a gneiss dome corridor in the southern Lake Superior region, U.S.A.: Geological Society of America Special Paper (in press). Silver, L.T., and Green, J.C., 1963, Zircon ages for Middle Precambrian rocks of the Lake Superior region: Trans. Am. Geophysical Union, 44, 107. Sims, P.K., Van Schmus, W.R., Schulz, K.J., and Peterman, Z.E., 1989, Tectonostratigraphic evolution of the Early Proterozoic Wisconsin Magmatic Terranes of the Penokean orogen: Canadian Journal of Earth Sciences, 26, 2145-2158. Vallini, D.A., et al., 2003, Using xenotime U-Pb geochronology to unravel the history of Proterozoic sedimentary basins: a study in Western Australia and the Lake Superior Region: ILSG abstr, 49, 79-80. Van Schmus, W.R., 1976, Early and Middle Proterozoic history of the Great Lakes area, North America. Royal Society of London Philosophical Transactions, 280, 605-628. Van Schmus, W.R., 1980, Chronology of igneous rocks associated with the Penokean orogeny in WI. In Morey, G., and Hanson, G., (eds.) Selected studies of Archean gneisses and lower Proterozoic rocks, southern Canadian Shield. Geological Society of America Special Paper, 182, 159-168. Van Schmus, W.R., Thurman, E.M., and Peterman, Z.E., 1975a, Geology and Rb-Sr chronology of middle Precambrian rocks in eastern and central Wisconsin: Geol. Society of America Bulletin, 86, 1255-1265. Van Schmus, W.R., Medaris, L.G., and Banks, P.O., 1975b, Geology and age of the Wolf River batholith, Wisconsin: Geological Society of America Bulletin, 86, 907-914. Van Schmus, W.R., and Anderson, J.L., 1977, Gneiss and migmatite of Archean age in the Precambrian basement of central Wisconsin: Geology, 5, 45-48. Van Schmus, W. R., and Hinze, W. J., 1985, The Midcontinent Rift System. Annual Reviews Earth Planetary Sciences, 13, 345-383. Van Wyck, N., 1995, Major and trace element, common Pb, Sm-Nd, and zircon geochronology constraints on petrogenesis and tectonic setting of pre- and Early Proterozoic rocks in Wisconsin: Ph.D. thesis, University of Wisconsin-Madison, 280 p. Van Wyck, N., and Martin, N., 2004, Detrital zircon ages from Paleoproterozoic Quartzites: Measured by laser – ablation ICP-MS: Journal of Geology (in press). Williams, M.L. and Jercinovic, M.J., 2002, Microprobe monazite geochronology: putting absolute time into microstructural analysis. Journal of Structural Geology, 24, 1013-1028. Zaleski, E., van Breemen, O., and Peterson, V.L., 1999, Geological evolution of the Manitouwadge greenstone belt and Wawa-Quetico subprovince boundary, Superior Province, Ontario, constrained by U-Pb zircon dates of supracrustal and plutonic rocks: Canadian Journal of Earth Sciences, 36, 945-966. Zartman, R.E., Nicholoson, S.W., Cannon, W.F., and Morey, G.B., 1997, U-Th-Pb zircon ages of some Keweenawan Supergroup rocks from the southern shore of Lake Superior: Canadian Journal of Earth Sciences, 34, 549-561. 83 �NEOARCHEAN PEPERITES IN THE VICINITY OF FIVEMILE LAKE, VERMILION DISTRICT, NE MINNESOTA HUDAK, G. J., NEWKIRK, T. T., DREXLER, H., ODETTE, J. D., and HOCKER, S. M., Department of Geology, University of Wisconsin Oshkosh, 800 Algoma Blvd., Oshkosh, WI 54901, hudak@uwosh.edu The Ely Greenstone – Lower Member in the vicinity of Fivemile Lake contains a well-studied sequence of ~2722 Ma, more or less east-west striking, steeply north-dipping and north-facing, arc-associated submarine basalt-andesite pillow lavas, tuffs and lapilli tuffs, rhyodacite to rhyolite tuffs, lapilli tuffs, and lavas, and synvolcanic diabase and diorite sills and dikes (Peterson et al., 2001; Hudak et al., 2002). Volcanic facies mapping at 1:5000 scale, supported by grants from the Natural Resources Research Institute (University of Minnesota Duluth), the University of Wisconsin Oshkosh, and the Minerals Diversification Plan of the Minnesota State Legislature, identified a northeast- trending zone of basalt - andesite tuffs, lapilli tuffs, and tuff-breccias which contain zones of northeast-trending coherent facies andesite–dacite that display pillowed, amoeboid, and commonly, jigsaw-puzzle fit morphologies. The southern extent of this zone occurs along a peninsula on the southwestern shoreline of Fivemile Lake. The northern extent of this zone extends approximately 150 meters north of the north-central shoreline of Fivemile Lake. Over the past year, extremely detailed volcanic facies mapping (1:50-1:100 scale), as well as petrographic and lithogeochemical studies, have been performed in an attempt to determine the genesis of these apparently genetically related coherentand volcaniclastic facies-bearing, northeast-trending zones. On the south shoreline of Fivemile Lake, the volcaniclastic facies is typically matrix-supported. The matrix consists of non-bedded basalt-andesite tuff, and locally contains amoeboid-shaped zones that contain up to 60% <1 mm quartz amygdules. Localized zones adjacent to northeast-striking coherent facies andesite–dacite comprise lapilli tuffs and tuff-breccias. Clasts in these deposits are commonly curviplanar to angular and jigsaw puzzle-fit in shape (Figure 1a), are moderately to highly vesicular (10-50%), have extremely finegrained margins, and locally contain <1-2 cm wide, apparently contact metamorphosed zones adjacent to their margins. These blocks and lapilli are compositionally similar to, more common adjacent to, and have their long axes aligned with, northeast-trending, sheet-like to pillow-shaped coherent facies andesite-dacite. The deposits on the north-central shoreline of Fivemile Lake have slightly different morphologies. A sharp, northsouth contact occurs between east-west striking, steeply north-dipping, bun- to mattress-shaped pillowed basalt-andesite and basalt-andesite tuffs and lapilli tuffs that comprise the base of a 700 meter wide, 200 meter thick, shallow submarine tuff cone (Hudak et al., in prep.). The tuffs and lapilli tuffs at this location are intruded by northeast-trending, synvolcanic, amoeboid (Figure 1b), pillow-like, and lobe-like zones of coherent-facies andesite-dacite which appear to have locally undergone in-situ fragmentation to produce localized lapilli tuffs and tuff-breccias that contain moderately to highly vesicular curviplanar, ameoboid, and blocky jigsaw puzzle-fit lapilli and blocks. These fragments have very fine-grained margins that are also rimmed by fine-grained, apparently contact metamorphosed zones. Locally, numerous thin (up to 1cm wide), parallel, highly vesicular zones occur within the volcaniclastic deposits that more or less mimic the orientations the margins of amoeboid coherent facies andesite–dacite or the margins of andesite-dacite blocks. The northeast-trending zones containing coherent and volcaniclastic facies are interpreted to comprise peperites with associated synvolcanic dikes. Peperites are fragmental rocks that form from the intimate mixing of hot magma with unconsolidated, typically wet sediments (Batiza and White, 2000; Schmidt and Schminke, 2000). They are common in submarine arc-related volcano-sedimentary sequences (Skilling et al., 2002), and commonly occur in proximity to synvolcanic fault zones. The interpretation that the volcaniclastic deposits represent peperites is based on the morphology of the lapilli and blocks which comprise the deposits, the consistent grain size variations from the margins to the centers of the lapilli and blocks, their spatial relationships adjacent to, and orientations parallel to, synvolcanic sheet-like to pillowed coherent facies andesite-dacite, and the presence of amygdules within the fine-grained tuffaceous matrix. The interpretation that the sheet-like to pillowed, coherent facies andesite-dacite represents dikes rather than lava flows is based on the northeast strike of the pillowed dikes (which is parallel to synvolcanic structures mapped in the Fivemile Lake region (Hudak et al., 2002)), the lack of consistent facing directions in the pillowed coherent 84 �facies, and the similarity in the chemical compositions of the coherent domains and the lapilli and blocks within the lapilli tuffs and tuff-breccias. The differences in the morphologies of the peperites on the southwestern and north-central shorelines of Fivemile Lake may represent their different levels of formation in the shallow sub-seafloor. Blocky peperites south of Fivemile Lake appear to have formed in lava flowconfined submarine aquifers located several hundred meters below the paleoseafloor, whereas more amoeboid peperites found north of Fivemile Lake appear to have formed near the seafloor within water-saturated submarine vent-fill deposits associated with a shallow submarine tuff cone volcano. Discordant zones of peperites can be used to identify synvolcanic fault zones that may be important in the exploration for volcanichosted massive sulfide deposits. Figure 1. Photographs of peperites deposits south (A) and north (B) of Fivemile Lake. References Batiza, R., and White, J. D. L., 2000, Submarine Lavas and Hyaloclastite, in Sigurdsson, H., 2000, Encyclopedia of Volcanoes: Academic Press, San Diego, California, p. 361-381. Hudak, G. J., Heine, J., Hocker, S., and Hauck, S. A., 2002, Geological mapping of the Needleboy Lake – Six Mile Lake area, northeastern Minnesota: a summary of volcanogenic massive sulfide potential: Natural Resources Research Institute Report of Investigation NRRI/RI – 2002/14, 16 p. Hudak, G. J., Heine, J., Newkirk, T. T., and Hocker, S. M., in prep. Comparative geology, stratigraphy, and lithogeochemistry of the Needleboy Lake to Sixmile Lake area, Vermilion District, NE Minnesota: University of Minnesota Permanent University Trust Fund Research Report. Peterson, D. M., 2001, Development of Archean lode-gold and massive sulfide deposit exploration models using geographic information system applications: targeting mineral exploration in northeastern Minnesota from analysis of analog Canadian Mining camps: unpublished Ph. D. dissertation, University of Minnesota, Duluth, Minnesota, 503 p. Peterson, D. M., Gallup, C., Jirsa, M. A., and Davis, D. W., Correlation of Archean assemblages across the U.S. – Canadian Border: phase I geochronology: ILSG Proceedings Volume 47, p. 77-78. Schmidt, R., and Schminke, H.-U., 2000, Seamounts and Island Building, in Sigurdsson, H., 2000, Encyclopedia of Volcanoes: Academic Press, San Diego, California, p. 383-402. Skilling, I. P., White, J. D. L., and McPhie, J., 2002, Peperite: a review of magma-sediment mingling: Journal of Volcanology and Geothermal Research, v. 114, p. 1-17. 85 �MAPPING BY THE MINNESOTA GEOLOGICAL SURVEY IN SUPPORT OF LANDUSE AND WATER PLANNING ON THE MESABI IRON RANGE JIRSA, Mark A., Minnesota Geological Survey, jirsa001@umn.edu This presentation describes two mapping projects on the Mesabi Iron Range underway by the Minnesota Geological Survey: 1) Hydrogeologic base maps of the Mesabi Iron Range—Funded by the Legislative Commission on Minnesota Resources; and 2) Bedrock and Quaternary geologic maps of the Mesabi Iron Range—Funded by the Minnesota Minerals Coordinating Committee. In recent years, a number of mining companies have been working with the University of Minnesota’s Department of Landscape Architecture on development concepts for the Mesabi Iron Range. Although not directly a part of those efforts, the Minnesota Geological Survey’s mapping projects are designed to provide technical data to address issues—primarily related to water—that require consideration prior to development. When mining and associated pumping ceases in any particular locality, water enters the mine from a variety of sources: rain and runoff, percolation through porous unconsolidated sediment layers, and flow through fractures and weathered zones in bedrock. The movement of ground water through these diverse materials is complex and poorly understood; however, it is clear that the boundary between the bedrock and overlying unconsolidated sediments is the single most important interface in the movement of ground water. Project 1, the hydrogeologic maps, addresses the location and shape of this hydrologically important interface. Some of this information for the western half of the Mesabi Range has already been published (Fig. 1; Jirsa and others, 2002; Lively and others, 2002). Project 2 will provide details about the lithologic content, structure, and water-bearing characteristics of the materials above and below that interface. Among other objectives, the bedrock geologic mapping is designed to identify other structures that may be important hydrologic interfaces, such as fractures, faults, and bedding surfaces. The bedrock mapping will modify and digitize the most recent existing map of the Mesabi Range compiled by a large group of scientists (Meineke and others, 1999). This will be compiled with other archived maps and new fieldwork. These efforts are reconnaissance in scope, and considerably more detail could be extracted from mine exposures, mining company records, and surface geologic mapping. Nevertheless, these projects will produce framework geologic maps and site-specific data in digital format that will be useful in resolving issues related to ground and surface waters, aggregate resource management, and land-use planning. They are intended to lay the groundwork for more detailed investigations into specific areas of future concern. 86 �Figure 1. Generalized geologic map of the Mesabi Iron Range showing the subcrop location of Paleoproterozoic Biwabik Iron Formation (gray) and Mesoproterozoic Duluth Complex, and various taconite mining operations (black; asterisk indicates inactive mine). Dashed polygons outline western and eastern map areas. None of these projects would be possible without the contributions of drill hole and geologic data and insight from members of the Minnesota Department of Natural Resources, the Natural Resources Research Institute, and most particularly, the mining companies. REFERENCES Jirsa, M.A., Setterholm, D.R., Bloomgren, B.A., and Lively, R.S., 2002, Bedrock topographic and depth to bedrock maps of the western half of the Mesabi Iron Range, northern Minnesota: Minnesota Geological Survey Miscellaneous Map M-126, scale 1:100,000. Lively, R.S., Morey, G.B., and Bauer, E.J., 2002, One hundred years of mining: Alterations to the physical and cultural geography of the western half of the Mesabi Iron Range, northern Minnesota: Minnesota Geological Survey Miscellaneous Map M-118; 4 pls., scale 1:100,000. Meineke, D.G., Buchheit, R.L., Dahlberg, E.H., Morey, G.B., and Warren, L.E., comps., 1999 Geologic map of the Mesabi Iron Range, Minnesota (2nd ed.): Hibbing, Minn., Mesabi Range Geological Society, scale 1:62,500. 87 �REGIONAL COMPILATIONS OF BEDROCK GEOLOGY IN NORTHEASTERN MINNESOTA: THE VERMILION, ELY, AND BASSWOOD LAKE QUADRANGLES JIRSA, Mark A., Minnesota Geological Survey, jirsa001@umn.edu Compilations of geologic mapping, although not typically portraying new field information in great detail, serve the important functions of providing regional mapping consistency, framework for various lithologic and geochemical surveys, and regional guidance for exploration and environmental issues. With this in mind, several regional bedrock geologic compilations at scale 1:100,000 have recently been completed and are underway for areas in northeastern Minnesota (Fig. 1), funded in large part by the STATEMAP program of the U.S. Geological Survey. The Vermilion Lake 30' x 60' quadrangle was completed in 2003 (Jirsa and Boerboom, 2003), and is displayed and described here. The adjacent Ely and U.S. portion of Basswood Lake 30' x 60' quadrangles are slated for completion in 2004. Perhaps as important as the functions listed above, the new compilations integrate disparate analog mapping, including some from the late 1800s and early 1900s, into a lithostratigraphically consistent, digital (GIS) format. Figure 1. Generalized geologic map of northeastern Minnesota showing the location of 30' x 60' quadrangles. The Vermilion Lake quadrangle covers most of the exposed area of the Vermilion district of northeastern Minnesota that lies outside of the Boundary Waters Canoe Area Wilderness (BWCAW), and is thus open in the broad sense to mineral exploration and mining. The Vermilion district is a local designation applied to the portion of the Neoarchean Vermilion greenstone belt in which there has been mining activity in the past, primarily of highgrade iron ore. The quadrangle also covers the east end of the Mesabi Iron Range, a world-class mining district in Paleoproterozoic strata that for decades has been the principal economic force in this part of Minnesota. Nevertheless, there is interest in finding alternative industries for cities along the iron range and alternative commodities for a diversified mining industry. At the present time there are encouraging indications that one or more viable polymetallic mines may develop in the basal contact zone of the Mesoproterozoic Duluth Complex. The zone of prime exploration and development interest in this regard crosses the southeastern corner of the Vermilion Lake map sheet. For the first time, the Vermilion Lake compilation merges well-exposed Neoarchean rocks of the Tower–Soudan area with more scattered exposures to the west into a single structural and lithologic interpretation. The map highlights a large, regional anticlinal structure that is cored by the steeply dipping Tower–Soudan anticline (Fig. 2). Tracing this fold structure westward into sedimentary rocks of the Lake Vermilion Formation, it becomes a broad and complex nappe structure that extends at least 30 kilometers. The Vermilion greenstone belt is comparable in its geologic attributes to other Neoarchean belts in Canada that contains significant deposits of gold, copper, zinc, and other metals. This general analogy has been recognized for decades and has stimulated several waves of mineral 88 �exploration in the area. Although past exploration efforts have been substantial, they have not been exhaustive. A major handicap was the lack of detailed geologic mapping, a situation that has been largely corrected over the past 25 years through the efforts of the Minnesota Geological Survey and the exploration industry itself. Figure 2. Schematic geologic map of the Vermilion Lake 30' x 60' quadrangle (Jirsa and Boerboom, 2003) showing folds, faults, and stratigraphic facing in Archean strata. Archean intrusions are gray. Three generations of folds are shown: F1—solid; F2—long dash; F3—short dash. Open arrows indicate horizontal facing directions in steeply dipping supracrustal sequences and upright facing directions where bedding is shallower. Solid arrows indicate the direction of downward stratigraphic facing. The bold fault line is the boundary between the Quetico subprovince to the north, and the Wawa subprovince to the south. The regional compilations of mapping data at scale 1:100,000 may prove to be valuable tools for the next cycle of exploration, which inevitably will come when local and global economic conditions appropriately conjoin. The compilation effort underway for the Ely and U.S. portions of the Basswood Lake 30' x 60' quadrangles involves many of the same geologic entities as depicted on the Vermilion Lake sheet. Because it includes areas within the BWCAW, which are generally protected from exploration and mining, this map will serve a slightly different purpose from that of the Vermilion Lake map, by providing regional geologic context. This effort will pave the way for such products as a “geologic user-guide” to the BWCAW, which has been initiated by the Minnesota Geological Survey. REFERENCE Jirsa, M.A., and Boerboom, T.J., 2003, Bedrock geology of the Vermilion Lake 30’ x 60’ quadrangle, northeast Minnesota: Minnesota Geological Survey Miscellaneous Map M-141, scale 1:100,000. 89 �Douglass Houghton’s 1840 Field Excursion to Lake Superior JOHNSON, Allan M., Professor Emeritus, Department of Geological & Mining Engineering & Sciences, Michigan Technological University, Houghton, Michigan 49931 In 1840, as the first State Geologist of Michigan, Douglass Houghton was near the end of the first geological survey of the state. In 1837, when Michigan entered statehood, and 1838 he was involved with and oversaw the reconnaissance surveys of the southern peninsula. In 1839 the survey work progressed to the northern peninsula, along the north shores of Lakes Huron and Michigan. For 1840, the program was much more ambitious, for he and his assistants (Bela Hubbard and C.C. Douglass) would undertake a survey along the south shore of Lake Superior. Detroit businessman, Charles Penny, also accompanied the group. The party left Detroit near the end of May 1840 and through the spring and early summer made their way from Sault Ste. Marie westward along the south shore of Lake Superior in their flotilla consisting of a larger Mackinaw boat and several smaller craft. This survey resulted in the mapping of rocks exposed adjacent to the shore, with more detailed mapping along major streams and rivers flowing into the big lake. Special attention was given to mapping volcanic and sedimentary rocks of the Keweenaw Peninsula and taking samples of previously known locations of copper bearing rocks (copper oxide at Copper Harbor and native metal from the copper boulder on the Ontonagon River). At the end of July, Houghton’s assistants returned to southern Michigan to continue with ongoing geologic investigations including boring a salt well at Grand Rapids. Houghton remained on Lake Superior with his voyageurs through mid-September. When his assistants left from LaPointe on Madeline Island, Houghton continued reconnaissance mapping at Isle Royale, the Porcupine Mountains and Portage Lake, and more detailed work on the Black and Eagle Rivers. It was on the Eagle River where Houghton discovered numerous occurrences of native copper and the presence of native silver which gave him the confidence to express cautious optimism in the potential for copper mining on the Keweenaw Peninsula in his early 1841 report to the Michigan Legislature. Word of this report soon led to the US War Department establishing a land office at Copper Harbor to issue mining permits and ultimately to the first great mining rush in the United States. For 150 years the native copper district of the Keweenaw was active in supplying a growing nation and the world with high purity lake copper with over 12 billion pounds of production. It is of interest to note that the 1840 journals of Hubbard and Penny have been published, while Houghton’s 1840 geologic notes became ‘lost’. It was not until 1978 that the notes appeared at public auction in New York City advertised as “the notes of an early Michigan surveyor”, where they became the property of Central Michigan University. 90 �References Carter, James L., and Rankin, Ernest H., eds., 1970, North to Lake Superior, The Journal of Charles W. Penny, 1840, The John M. Longyear Research Library, Marquette, Michigan, 84 p. Cummings, John, September 14, 2000, personal communication in Mount Pleasant, Michigan regarding purchase of Douglass Houghton’s 1840 field notes in New York City in 1978. Fuller, George N., 1928, Geological Reports of Douglass Houghton, Michigan Historical Commission, Lansing, 700 p. Houghton, Douglass, 1840, Original Field Notes of 1840 Expedition to Lake Superior, Clarke Library, Central Michigan Univ., Mount Pleasant, MI 325 p. Merrill, George P, 1906, Contributions to the History of American Geology, Smithsonian Institution, Washington Government Printing Office, 733 p. Mason, Philip, P., ed., 1958, Schoolcraft’s 1832 Expedition to Lake Itasca, Michigan State University Press, East Lansing, 390 p. Peters, Bernard C., ed., 1983, Lake Superior Journal, Bela Hubbard’s Account of the 1840 Houghton Expedition, Northern Michigan University Press, Marquette, 113 p. Rintila, Edsel K., 1954, Douglass Houghton, Michigan’s Pioneer Geologist, Wayne University Press, Detroit, 119 p. Williams, Mentor L., ed., Schoolcraft’s 1821 Narrative Journal of Travels through the Northwestern Regions of the United States, Michigan State University Press, East Lansing, 1992, 520 p. 91 �REGIONAL GEOCHEMISTRY SURROUNDING THE NORTON LAKE Cu-Ni-PGE DEPOSIT, UCHI SUBPROVINCE, ONTARIO JOHNSON, J.R.*, HOLLINGS, P., and KISSIN, S., Department of Geology, Lakehead University, Thunder Bay, ON, P7B 5E1 The Norton Lake Cu-Ni-PGE deposit (delineated in 1981 as 944,000 tonnes at 0.72% Ni and 0.56% Cu) is located within the northern most unnamed assemblage of the Miminiska-Fort Hope Greenstone Belt approximately 50 km northeast of Fort Hope, northwest Ontario (Fig. 1). The deposit is hosted within a sheared amphibolite unit that is typically found at, but not limited to, the contact between an upper basalt and a lower sedimentary unit. Due to both its remote location and sparse outcrop only limited geological investigations have been undertaken within the belt to date. Consequently, the belt has been subdivided based on available regional stratigraphic and structural interpretations. Previous work by the Ontario Geological Survey has tentatively correlated the unnamed assemblage with the McGruer assemblage of the North Caribou, located to the west, based on a similarity of rock types and a pervasive aeromagnetic anomaly that extends between the two (Stott and Corfu, 1991). Figure 1: Uchi Subprovince, northwestern Ontario, study area outlined. A 12 km east-west by 6 km north-south block surrounding the Norton Lake Deposit has been mapped and sampled to allow characterization of the volcanic assemblages. In addition to field mapping, drill core left in the area by previous exploration programs was examined (covering an area of 20 km by 10 km). Samples selected to provide good areal coverage and minimal alteration were analysed by XRF and ICP-MS. Three suites can be recognised within the assemblage; Suite I basalts are characterized by weakly depleted to enriched LREE [(La/Sm)n=0.9-1.2] and weakly fractionated HREE [(Gb/Yb)n=1.1-1.2] in conjunction with flat to positive Nb anomalies. Suite II is characterized by LREE depleted basalts [(La/Sm)n=0.4-0.7] and unfractionated HREE [(Gb/Yb)n=0.9-1.1], while Suite III consists of basalts to dacites that are LREE enriched with weakly fractionated HREE [(La/Sm)n=2.6-4.7, (Gd/Yb)n=0.8-2.4] and pronounced negative Nb anomalies. 92 �Sm-Nd isotope work on select samples is currently underway with initial epsilon-Nd values indicating little to no crustal contamination of the samples. Preliminary interpretations suggest the Norton Lake area formed in a tectonic setting analogous to modern island arcs and is best compared with the Northern Pickle Assemblage of the Pickle Lake belt rather than the McGruer assemblage of the North Caribou terrane. Hollings P., 1998, Geochemistry of the Uchi Subprovince, northern Superior Province: and evaluation of the geodynamic evolution of the northern margin of the Superior Province ocean basin; Ph. D. thesis, University of Saskatchewan, Saskatoon, Saskatchewan, 229 p. Stott G. M. and Corfu F., 1991, Uchi Subprovince, in Geology of Ontario, Ontario Geological Survey Special Volume 4, Part 1. Young, M. D., 2003. New structural, geochronological, and geochemical constraints on the tectonic assembly of the Archean Pickle Lake greenstone belt, Uchi subprovince, western Superior Province; M. Sc. thesis, Queen’s University, Kingston, Ontario, 182 p. 93 �Platinum Mineralization at Drill Hole A4-11 of the Wetlegs Area of the Partridge River Intrusion, Duluth Complex, Northeast Minnesota KAUKONEN, R.J., and ALAPIETI, T.T., University of Oulu, Oulu, Finland Apparently either the more peculiar PGE mineralization at DU-15 of the South Kawishiwi Intrusion or the vast but low grade deposits of disseminated base-metal sulfides may have been the reason why, as it seems, the platinum potential of the Wetlegs area of the Partridge River Intrusion has almost been forgotten. The whole rock analyses from drill core A4-11 (Gladen, 1990) show significant PGE values (Fig.1), which undoubtedly warrant an investigation. Unfortunately the best parts of the drill core A4-11 have been previously used for analysis and hence material for thin sections was not available throughout the core. The cryptic variation paths of the main rock-forming silicates are presented in Fig. 1. Compared to data from drill core A4-14 (Kaukonen, 1994), the crystallization paths of olivine and pyroxenes show distinctive similarities. The general upward increasing trend of primitiveness is particularly evident in olivine. Plagioclase compositions on the other hand don’t really present any clear trends aside from perhaps a slight decrease down the drill hole in the lower half of the core. Dpeth in Drill Hole (m) 0 0 100 100 200 200 300 300 400 400 500 500 600 600 700 40 50 60 70 80 30 40 50 60 70 40 50 60 70 80 30 Plag An% Oliv Fo% Opx En% 40 Cpx En% 50 0 700 4000 8000 Pt+Pd+Au ppb Fig.1. Cryptic variation paths of the main rock-forming silicates and the determined concentrations of noble metals in drill hole A4-11. The best PGE values are found between 70-80 meters down hole. The highest Pt+Pd+Au value is about 7 ppm, of which Au accounts for just less than 1 ppm (Fig.1). Petrologically the mineralization seems to be a somewhat ’classic’ base-metal sulfide type PGE mineralization where the platinum-group minerals are mainly associated with disseminated base-metal sulfides, mainly chalcopyrite and pyrrhotite. The most significant difference to the classic or often referred to as orthomagmatic PGE mineralizations is probably related to the silicates rather than sulfides, as the host rock is essentially troctolite rather than orthopyroxenite. This feature, however, is well in accordance with the crystal mush theory of Miller and Weiblen (1990). 94 �As each mineralization has some unique characteristics, the A4-11 PGE mineralization also has its own signature. One of the most striking features is the notable occurrence of native copper, which is widely present. The grain size of copper is usually very small, yet it is readily distinguishable with an ore microscope using a relatively small magnification. The presence of native copper is possibly an indication of a reducing environment, and here it is mainly an alteration product of chalcopyrite. The platinum-group mineralogy of the A4-11 mineralization is also rather special. The most common PGMs are stannides and plumbates (Komppa, 1998). The minerals identified and analyzed for this investigation included atokite (Pd2Sn) and zvyagintsevite (Pd3Pb). However, as pointed out by Cawthorn et al. (2002), the platinum-group mineralogy of any given deposit is not necessarily a reflection of the primary processes involved in the enrichment of the PGE in a stratiform deposit, but rather a product of secondary processes that shape the mineralization further. References: Cawthorn, R.G., Lee, C.A., Schouwstra, R.P., and Mellowship, P., 2002, Relationship between PGE and PGM in the Bushveld Complex: Can. Min., Vol. 40, pp. 311-328. Gladen, L., 1990, Duluth Project: Report on 1989 Exploration in the Duluth Complex, Minnesota Department of Natural Resources, Internal Report, 11 p. Kaukonen, R.J., 1994, Cryptic Variation in the Partridge River Intrusion of the Duluth Complex, unpublished M.Sc thesis, University of Oulu, Finland, 66 p., (in Finnish with English Abstract). Komppa, U.E., 1998, Oxide, Sulphide and Platinum Mineralogy of the South Kawishiwi and Partridge River Intrusions of the Duluth Layered Intrusion Complex, Minnesota, U.S.A. M.Sc. thesis, University of Oulu, Finland, 104 p., (in Finnish), English version published as Natural Resources Research Institute, Report of Investigation in 2002, NRRI-RI2002/02 Miller, J.D., Jr., and Weiblen, P.W., 1990, Anorthositic Rocks of the Duluth Complex: Examples of Rocks Formed from Plagioclase Crystal Mush: Jour. Petrol., Vol. 31, Part 2, pp. 295339. 95 �MAGNETIC SUSCEPTIBILITY ANISOTROPY AND REMANENT MAGNETISM OF QUARTZITE AND PHYLLITE FROM BARABOO WISCONSIN KEAN, William F., Department of Geosciences, UW-Milwaukee, P.O. Box 413, Milwaukee WI 53201, wkean@uwm.edu The Baraboo quartzite and the associated phyllite are paleomagnetically well behaved rocks, with single magnetic directions carried by hematite, but with different directions for the rock types. The magnetism in the quartzite is associated with single domain hematite grains, is pre-folding, and is consistent with an ~1760 Ma age of formation (Kean and Mercer, 1986). The phyllite is dominated by multidomain hematite, (Kelly and Kean 2001), and although the magnetic directions are internally consistent at any one site, they are scattered between sites both before and after a fold test. The presence of multidomain hematite grains (up to 100 µ) suggests the remanence was developed during metamorphism which could have occurred during the folding in the region, or from fluids introduced at a later time when the radiometric ages were reset (Medaris et al., 2003). In an attempt to better understand these differences in magnetic directions, a large block of rock that contained quartzite and phyllite was collected from the south limb of the Baraboo Syncline at an outcrop on Highway 12. A series of 2.5-cm. diameter cores were drilled from each of the layers for thermal demagnetization and anisotropy of magnetic susceptibility (AMS) measurements. The results presented in Figure 1 show that the phyllite has higher values of AMS (P`) than the quartzite, and the magnetic grains are more oblate in shape (T) compared to the quartzite. 1 0.8 Quartzite 0.6 SHAPE T Phyllite 0.4 0.2 0 1 1.1 1.2 1.3 1.4 1.5 -0.2 -0.4 Anisotropy P' Figure 1. Anisotropy of Magnetic Susceptibility (AMS) P’ versus shape factor T for samples from the Baraboo region. T values below zero are prolate in shape, values near zero are neutral, and values above zero are oblate in shape. The phyllite shows large values of anisotropy and is strongly oblate. The quartzite is close to neutral in shape and of lower anisotropy. 96 �The comparison between remanent magnetic directions and AMS ellipsoid axes for the two rock types is presented in Figure 2. The magnetic direction for the phyllite is perpendicular to the minimum anisotropy axis and is rotated toward the bedding plane. The magnetic direction for the quartzite appears to be unrelated to the susceptibility anisotropy. Figure 2: Comparison of paleomagnetic directions and AMS for quartzite and phyllite samples at Highway 12 outcrop. It appears that the disparity in the magnetic directions in the phyllite zone is related to the amount of local strain that occurred during the metamorphism and formation of the Baraboo syncline, and not related to later fluid injection associated with the Wolf River batholith intrusive event. Limited AMS results from other phyllite sites in the region provide similar results. References: Kean, W.F. and Mercer, D., 1986, Preliminary Paleomagnetic Study of the Baraboo Quartzite, Wisconsin, Geoscience Wisconsin, Vol. 10, p 46-53. Kean, W.F. and Kelly, C., 2001, Rock Magnetic Studies of Phyllite Layers from Baraboo Interval Rocks in Wisconsin, Abstracts with Programs, GSA Annual Meeting, 33, p. A143. Medaris, L.G., Singer, B.S., Dott, Jr., R.H., Naymark, A., Johnson, C.M., and Schott, R.C., 2003, Late Paleoproterozoic Climate and Tectonics in Southern Lake Superior Region and Proto-North America: Evidence from Baraboo Interval Quartzites. Journal of Geology, Vol. 111, p 243-257. 97 �Lithic Materials and Archaeology in the Western Lake Superior Region KLAWITER, Brian, Superior National Forest, Duluth, Minnesota 55808, USA The most prevalent and enduring artifacts left behind by prehistoric cultures are those made of stone. The study of these cultural material remains shows that prehistoric people were very perceptive and discerning “geologists” when it came to choosing the stone materials that they would use. The available lithic materials had a broad range of useful properties that were to be carefully considered when choosing the raw material for a particular tool or purpose. Prehistoric people developed a keen eye for the desired physical properties of stone, and they knew where to get it. One enduring legacy from these prehistoric and early historic people is in the form of place-names such as Gunflint Lake and Knife Lake; both translated from the earlier Ojibwe names (Upham, 1920), and both of which have subsequently passed their names along to major geologic features: the Gunflint Iron Formation and the Knife Lake Group metavolcanics and metasediments. This presentation will display and describe many of the geologic materials and their prehistoric uses as discovered by archaeologists working in the western Lake Superior region. In addition to studying prehistoric cultures, it is often equally interesting to study the modern archaeologists who study the ancient cultures. Most archaeologists are students of the Social Sciences whose occupation requires them to acquire a basic working knowledge of geology. This geologic education is often acquired in the field or in the lab by peer interaction, rather than in the classroom by professional geologists. As a result, the field of archaeology has in many ways developed its own sub-culture of geology, which is best displayed in the naming systems applied to the geologic materials recovered from archaeological excavations. This ad hoc (and locally territorial) nomenclature is often confusing to archaeologists and bewildering to geologists. For those interested in the overlap of geology and archaeology, this presentation outlines the archaeological nomenclature applied to geologic formations and materials in the western Lake Superior region, and highlights the efforts of this author and others to “reform” the archaeological nomenclature to more generally conform to geologic standards. Keywords: archaeology, lithics, Gunflint, Knife Lake, nomenclature, Superior National Forest Upham, W., 1920, Minnesota Geographic Names: Their Origin and Historic Significance: Minnesota Historical Society, Saint Paul, Minnesota. 98 �REGIONAL TILL SAMPLING IN THE VERMILION GREENSTONE BELT, MINNESOTA: PRELIMINARY RESULTS AND INTERPRETATIONS LARSON, P.C., Department of Geological Sciences, University of Minnesota, Duluth, MN 55812, plarson2@d.umn.edu A project of regional till sampling was undertaken over the Vermilion greenstone belt during the 2001 and 2003 field seasons. Samples were collected to provide coverage of ~1 sample per 3 km2 in the area between Tower and Ely, MN. The silt+clay fraction (<63µm) of B- and Chorizon till samples was analyzed for gold, platinum, and palladium by fire assay and for 47 major- and trace-elements by ICP-MS and ICP-AES. The regional sampling program provides information on the background concentrations of various elements in till, as well as the presence and location of anomalous gold and base metal indicator concentrations. In conjunction with the sampling, observations on the character and distribution of glacial sediments overlying the greenstone belt were made to provide a framework for interpretation of the till geochemical data set. The study area records a simple record of Quaternary events. Till cover is generally thin and discontinuous over the study area, with the exception of the Vermilion and Wahlsten moraines. Essentially all glacial sediments were deposited during the final retreat of ice from the study area (the Vermilion Phase). Moraine orientations indicate ice was flowing at 180° to the Wahlsten moraine, and 195° to the slightly younger Vermilion moraine. Elements in till associated with the granite-gneiss Vermilion granitic complex to the north of the greenstone belt (Be, K, Rb, Ba) show a systematic decrease in concentration along glacial flowlines south of the Vermilion fault (the contact between the granitic complex and greenstone belt). This demonstrates that the composition of till overlying the greenstone is overwhelmingly a function of physical transport by glacial action. Till overlying the greenstone is therefore a mixture of material transported from the Vermilion granitic complex and material eroded from the greenstone belt; quantification of this mixing trend indicates a mean transport length of ~8 km for till-forming material. The till sampling program has clearly identified a number of areas with anomalous precious and base metal concentrations. Highlights include a number of samples with >50 ppb gold, including one sample with 940 ppb gold. Copper values up to 314 ppm, zinc values up to 368 ppm, and platinum values of up to 8 ppb were also reported. Higher density follow-up sampling is recommended to more clearly define and determine the significance of anomalies, as well as determine the location of potential source rocks. The results of this survey clearly demonstrate the utility of till compositional surveys for exploration in the Vermilion greenstone belt, as well as nearby areas with a similar glacial geological setting. 99 �EARLY ADVANCE OF THE ST. LOUIS SUBLOBE: A REVISED CHRONOLOGY OF THE DEGLACIATION OF NORTHEASTERN MINNESOTA LARSON, P.C., MOOERS, H.D., and MARLOW, L.M., Department of Geological Sciences, University of Minnesota, Duluth, MN 55812, plarson2@d.umn.edu The general retreat of the Laurentide Ice Sheet (LIS) from Minnesota during the Late Wisconsin was characterized by a fluctuating boundary between ice originating in the Keewatin and Labradoran accumulation centers. Recent investigations into the glacial geology of central and northern Minnesota have newly recognized stratigraphic relationships prompting revision of the deglacial chronology. A prominent event during deglaciation was the advance of the Keewatin-provenance St. Louis Sublobe (Alborn phase) from the Red River Valley across northern Minnesota into the area vacated by the retreating Labradoran-provenance Rainy Lobe. This advance has previously assigned a relatively late age (~12 ka) and correlated with post-Vermilion phase margins of the Rainy Lobe, implying that ice-free conditions existed between the Rainy Lobe and the Giant’s Range at the time of the advance. However, the absence of Keewatin till north of the Giant's Range despite the presence of such till at the crest of the Giant's Range, combined with evidence for abundant stagnant Rainy Lobe ice south of the Giant’s Range, suggests the St. Louis Sublobe advance occurred while active Rainy Lobe ice was present immediately north of the Giant's Range. A newly identified Rainy Lobe ice margin confirms this relationship; this margin is probably correlative with the previously described Allen moraine. We refer to the phase of the Rainy Lobe responsible for its formation as the Northofnashwauk phase. The relationships above indicate that the Alborn phase occurred significantly earlier than previously believed. Retreat of the St. Louis Sublobe from its Alborn phase maximum occurred by stagnation and wastage of a large mass of ice. The next prominent recessional moraine formed at the suture between active and stagnant ice in southern Beltrami County (Rabideau moraine). Here, ice-contact meltwater channels emanated outward from the ice margin, terminating as outwash fans at the edge of the stagnant ice. The Rabideau moraine is correlative with the post-Northofnashwauk Big Rice phase and moraine of the Rainy Lobe. Much of the meltwater drained into Glacial Lake Sucre, a western extension of Glacial Lakes Aitkin and Upham II. Sucre drained after abandonment of the Hellwig Creek outlet of Upham II. The Rainy and St. Louis Sublobes retreated from the Big Rice and Rabideau moraines to the Vermilion and Big Stone(?) moraines, respectively. These newly recognized stratigraphic relationships indicate that the St. Louis Sublobe advanced immediately after recession of the Rainy Lobe. Consequently, Glacial Lakes Aitkin-Upham I were much shorter lived, and Aitkin and Upham II much longer lived, than previously believed. 100 �Figure 1. Ice margin positions during Northofnashwauk and Alborn Phases, ca. 13.5 kyr BP. Figure 2. Ice margin positions during Big Rice Phase, ca. 13 kyr BP. Figure 3. Ice margin positions during Vermilion Phase, ca. 12.5 kyr BP. 101 �Lake Nipigon Region Geoscience Initiative: Results of Bedrock Mapping in the Northern Part of the Western Nipigon Embayment, Northwestern Ontario, Canada MacDONALD, C.A. and TREMLAY, E. Precambrian Geoscience Section, Ontario Geological Survey, Ministry of Northern Development and Mines, Sudbury, Ontario, Canada, P3E 6B5 As part of the Lake Nipigon Regional Geoscience Initiative (LNRGI), a 2-year, 1:50 000 scale mapping program was begun in 2003 to better understand the geology of the western Nipigon Embayment. This talk presents results based on mapping of an area of roughly 1200 km2 during the 2003 field season, and focuses on Proterozoic rocks in the map area (Fig. 1) (MacDonald 2004; MacDonald et al. 2004a, 2004b). This project is funded by the Northern Ontario Heritage Fund Corporation (NOHFC) through the Ontario Prospectors Association. The 2003 map area is located approximately 190 km north of Thunder Bay and is partially bordered by the shore of Lake Nipigon on its east margin (Fig. 1, 2). Rocks of both the Superior and Southern provinces occur in the map area and include Archean rocks of the volcanic-plutonic central Wabigoon Subprovince that are disconformably overlain by Mesoproterozoic sedimentary rocks of the Sibley Group, all of which are intruded by Mesoproterozoic mafic igneous rocks. Archean rocks consist dominantly of variably foliated to gneissic, felsic to intermediate, granitoid rocks and mafic to felsic metavolcanic rocks. A 30 metre thick flatlying succession of mafic volcanic pillowed flows occurs in the northern part of the map area. The undeformed nature of these flows, combined with the well-preserved Figure 1. Key map showing the location of the nature of relatively delicate features such as hyaloclastite 2003 map area. suggests that these rocks may be Proterozoic rather than Archean in age. If so, they would be the first Proterozoic mafic volcanic rocks reported this far north of the Midcontinent Rift. Alternatively, they could represent a previously unrecognized greenstone belt within the Superior Province. Pre-Keweenawan rocks include anorogenic igneous and associated metavolcanic rocks of the English Bay complex and sedimentary rocks of the Sibley Group. The English Bay complex (~1540 Ma, Davis and Sutcliffe 1985) consists mainly of massive quartz and feldspar crystal tuffs with a variety of fragment types suggesting an extrusive, volcanic origin for most of the complex. Sibley Group clastic and chemical sedimentary rocks are few, and a combination of paleotopography on the Archean surface as well as the erosional level of the overlying diabase sills probably controls their distribution. At least one olivine gabbro sill, referred to as the Jackfish Island sill, intrudes the English Bay complex. The Jackfish Island sill has geochemical affinities (Fig. 3) with the Kitto peridotite intrusion located on the east side of the Nipigon Embayment (Hart 2003). Both the Jackfish Island and Kitto peridotite are roughly coeval with the ~1110 Ma Nipigon diabase sills (Davis and Sutcliffe, 1985). Nipigon diabase sills intrude and overlie all previously noted rock types and are part of the 1.11 to 1.09 billionyear-old Midcontinent Rift. The Nipigon sills are generally massive, medium-grained, intergranular-textured and gabbroic in composition with local variations including ophitic and poikilitic textured diabase, oikocrystic diabase and magnetite-rich to locally glomeroporphyritic magnetite phases. Coarse-grained pods, veins and/or monzogabbroic phases also occur within the diabase and could represent a late magmatic phases of the sills or assimilation of Sibley Group sedimentary rocks, or both (Hart and Magyarosi, 2004). The diabase sills intrude and typically overlie all other rock units. The diabase sills are tentatively subdivided into 2 types: 1) The Inspiration sills, located in the northern part of the map area, which have higher trace element ratios (Fig. 3) and normal 102 �remnant magnetization than typical Nipigon sills, and 2) Sills located in the southern part of the map area that are reversely polarized and which have lower trace element ratios. This southern group of sills are grouped with the typical Nipigon sills (Fig. 3). A series of subparallel north- and northwest-trending faults that occur within the Black Sturgeon Fault corridor may be related to the formation of the Midcontinent Rift (Fig. 2). These faults may also in part control the location of Archean inliers. Vertical displacement on both fault sets range from 200 to 400 metres. Figure 2. General geology of south Armstrong–Gull Bay area Figure 3. La/Sm versus Gd/Yb for samples from the English Bay complex, Jackfish Island Sill, Nipigon sills and Inspiration sills. References Davis, D.W. and Sutcliffe, R.H. 1985. U-Pb ages from the Nipigon plate and northern Lake Superior; Geological Society of America Bulletin, v.96, p.1572-1579. Hart, T.R. 2003. Keweenawan mafic and ultramafic intrusive rocks of the Lake Nipigon and Crystal Lake areas, northwestern Ontario; in Programs and Abstracts, Proceedings of the Institute on Lake Superior Geology, v.49, Pt. 1, p.21-22. Hart, T.R. and Magyarosi, Z. 2004. Precambrian geology of the northern Black Sturgeon River and Disraeli Lake area, Nipigon Embayment, northwestern Ontario; Ontario Geological Survey, Open File Report 6138, 56p. MacDonald, C.A. 2004. Precambrian Geology of the South Armstrong-Gull Bay area, Nipigon Embayment, Northwestern Ontario; Ontario Geological Survey Open File Report 6136, 42p. MacDonald, C.A., terMeer, M., Lepage, L., Prefontaine, S. and Tremblay, E. 2004a. Precambrian Geology of the Waweig-Wabinosh Lakes area, western Nipigon Embayment, Northwestern Ontario; Ontario Geological Survey, Preliminary Map P.3536, scale 1:50,000. MacDonald, C.A., terMeer, Lepage, L., Prefontaine, S. and Tremblay, E. 2004b. Precambrian Geology of the English Bay-Havoc Lake area, western Nipigon Embayment, Northwestern Ontario; Ontario Geological Survey, Preliminary Map P.3537, scale 1:50,000. 103 �Precambrian Geology of the South Armstrong–Gull Bay Area, Nipigon Embayment, Northwestern Ontario, Canada MacDONALD, C.A., and TREMBLAY, E. Precambrian Geoscience Section, Ontario Geological Survey Ministry of Northern Development and Mines, Sudbury, Ontario, Canada, P3E 6B5 As part of the Lake Nipigon Regional Geoscience Initiative (LNRGI), a 2-year, 1:50 000 scale mapping program was begun in 2003 to better understand the geology of the western Nipigon Embayment. As part of LNRGI, this study mapped an area of roughly 1200 km2 during the 2003 field season (MacDonald 2004; MacDonald et al. 2004a, 2004b). The project was funded by the Northern Ontario Heritage Fund Corporation (NOHFC) through the Ontario Prospectors Association. This poster presentation highlights some of the preliminary results of this mapping program. The south Armstrong–Gull Bay area is located approximately 190 km north of Thunder Bay and is partially bordered by the shore of Lake Nipigon on its east margin. Rocks of both the Superior and Southern provinces occur in the map area and include Archean rocks of the volcanic-plutonic central Wabigoon Subprovince that are disconformably overlain by Mesoproterozoic sedimentary rocks of the Sibley Group, all of which are intruded by Mesoproterozoic mafic igneous rocks. Archean rocks consist dominantly of variably foliated to gneissic, felsic to intermediate, granitoid rocks and mafic to felsic metavolcanic rocks. A 30 metre thick flat-lying succession of mafic volcanic pillowed flows occurs in the northern part of the map area. The undeformed nature of these flows, combined with the well-preserved nature of relatively delicate features such as hyaloclastite suggests that these rocks may be Proterozoic rather than Archean in age. If so, they would be the first Proterozoic mafic volcanic rocks reported this far north of the Midcontinent Rift. Alternatively, they could represent a previously unrecognized greenstone belt within the Superior Province. Pre-Keweenawan rocks include anorogenic igneous and associated metavolcanic rocks of the English Bay complex and sedimentary rocks of the Sibley Group. The English Bay complex (~1540 Ma, Davis and Sutcliffe 1985) consists mainly of massive quartz and feldspar crystal tuffs with a variety of fragment types suggesting an extrusive, volcanic origin for most of the complex. Sibley Group clastic and chemical sedimentary rocks are few, and their distribution is controlled by a combination of original paleotopography on the Archean basement as well as the erosional level of the overlying diabase sills. At least one olivine gabbro sill, referred as the Jackfish Island sill, intrudes the English Bay complex. The Jackfish Island sill has geochemical affinities with the Kitto peridotite intrusion located on the east side of the Nipigon Embayment (Hart 2003). Both the Jackfish Island and Kitto peridotite are roughly coeval with the ~1110 Ma Nipigon diabase sills. Nipigon diabase sills intrude and overlie all previously noted rock types and are part of the 1.11 to 1.09 billion-year-old Midcontinent Rift. The Nipigon sills are generally massive, medium-grained, intergranular-textured and gabbroic in composition with local variations including ophitic and poikilitic textured diabase, oikocrystic diabase and magnetite-rich to locally glomeroporphyritic magnetite phases. Coarse-grained pods, veins and/or monzogabbroic phases also occur within the diabase and could represent a late magmatic phases of the sills or assimilation of Sibley Group sedimentary rocks, or both (Hart and Magyarosi, 2004). The diabase sills intrude and typically overlie all other rock units. The diabase sills are tentatively subdivided into 2 types: 1) The Inspiration sills, located in the northern part of the map area, which have higher trace element ratios and normal remnant magnetization than typical Nipigon sills, and 2) Sills located in the southern part of the map area that are reversely polarized and which have lower trace element ratios. This southern group of sills are grouped with the typical Nipigon sills. 104 �Several northwest- and north-trending faults are prominent in the map area. Northwest-trending faults appear to correlate with structures in the central Wabigoon Subprovince and may control the distribution of Archean inliers. A series of subparallel north-trending faults, which include the Black Sturgeon fault, may represent faults related to the formation of the Midcontinent Rift. The vertical displacement on both fault sets range from 200 to 400 metres. The mineral potential within the map area consists of previously undocumented areas of Archean mafic and felsic metavolcanic rocks that may hold potential for Pb-Cu-Zn volcanogenic massive sulphide (VMS) deposits. Two areas of brittle-ductile deformation within the metavolcanic rocks may also hold potential for shear zone-hosted gold deposits. The mafic to ultramafic portions of an Archean sanukitoid multiphase intrusion should be investigated for platinum group element potential, since gabbroic to pyroxenitic rocks with disseminated chalcopyrite, pyrrhotite and pyrite from the Roaring River Complex have returned assays up to 2.1 g/t Pt+Pd+Au (Schnieders et al. 2002). Cr-Ni-Cu-platinum group element potential exists in both Proterozoic mafic to ultramafic bodies within the map area. Several areas within the Nipigon Embayment may have potential to host iron oxide-copper-gold (i.e., Olympic Dam type) deposits, particularly the English Bay complex. References Davis, D.W. and Sutcliffe, R.H. 1985. U-Pb ages from the Nipigon plate and northern Lake Superior; Geological Society of America Bulletin, v.96, p.1572-1579. Hart, T.R. 2003. Keweenawan mafic and ultramafic intrusive rocks of the Lake Nipigon and Crystal Lake areas, northwestern Ontario; in Programs and Abstracts, Proceedings of the Institute on Lake Superior Geology, v.49, Pt. 1, p.21-22. Hart, T.R. and Magyarosi, Z. 2004. Precambrian geology of the northern Black Sturgeon River and Disraeli Lake area, Nipigon Embayment, northwestern Ontario; Ontario Geological Survey, Open File Report 6138, 56p. MacDonald, C.A. 2004. Precambrian Geology of the South Armstrong-Gull Bay area, Nipigon Embayment, Northwestern Ontario; Ontario Geological Survey Open File Report 6136, 42p. MacDonald, C.A., terMeer, M., Lepage, L., Prefontaine, S. and Tremblay, E. 2004a. Precambrian Geology of the Waweig-Wabinosh Lakes area, western Nipigon Embayment, Northwestern Ontario; Ontario Geological Survey, Preliminary Map P.3536, scale 1:50,000. MacDonald, C.A., terMeer, Lepage, L., Prefontaine, S. and Tremblay, E. 2004b. Precambrian Geology of the English Bay-Havoc Lake area, western Nipigon Embayment, Northwestern Ontario; Ontario Geological Survey, Preliminary Map P.3537, scale 1:50,000. Schnieders, B.R., Scott, J.F., Smyk, M.C., Parker, D.P. and O’Brien, M.S. 2002. Report of Activities 2001, Resident Geologist Program, Thunder Bay South Regional Resident Geologist Report: Thunder Bay South District; Ontario Geological Survey, Open File Report 6081, 45p. 105 �Magnetic Fabric Constraints on Magmatic Flow: Insizwa Sill, South Africa and the Sonju Lake Intrusion, Minnesota. MAES, Stephanie, TIKOFF, Basil, BROWN, Phil, Department of Geology and Geophysics, University of Wisconsin, Madison, Wisconsin 53706 FERRÉ, Eric, Department of Geology, Southern Illinois University, Carbondale, Illinois 62901 Layered mafic intrusions are an important aspect of plate tectonics, commonly related to large igneous provinces and potentially acting as conduits for continental flood basalts. Although they are the source for most of the world’s PGE (platinum group element) and Cr deposits, as well as important Cu and Ni reserves, a large degree of uncertainty exists as to how these systems evolve. Magnetic fabrics, which often closely relate to the mineral fabric, allow us to document magmatic structures and map out the direction(s) of flow within an intrusion. Magnetic fabrics are determined using anisotropy of magnetic susceptibility (AMS) analysis. Knowledge of flow direction may permit us to place constraints on the location of ore deposits as well as to test models of magmatic sulfide deposition. In addition, these techniques allow us to evaluate the importance of vertical cumulus processes versus horizontal particle flow in the formation of layering. When applied to the study of mafic intrusions, standard magnetic techniques such as low field AMS do not always provide a fabric that reflects the flow field. This is due to the complex magnetic behavior of mafic rocks. Mafic rocks often contain multiple magnetic carriers and magnetite domain sizes, which can negatively affect the AMS fabric. A new magnetic approach, high field AMS (HFAMS), has been used to separate these complex anisotropies. By applying HFAMS techniques the ferromagnetic (magnetite) and paramagnetic (mafic silicate) components of the anisotropy can be separated. Hysteresis properties are then used to identify the domain size of magnetite. Our approach is to compare magmatic fabrics in two intrusions with contrasting genetic histories. In a closed system, such as the Sonju Lake intrusion, petrologic models predict a gradual upward increase in magnetite. In contrast, open systems, where episodes of recharge, eruption and/or assimilation can occur, result in a multimodal distribution of magnetite. The Insizwa sill, South Africa represents a system open to magmatic recharge. Bulk magnetic susceptibility measurements of closely spaced samples from vertical borehole cores within the Insizwa sill have documented significant variation in magnetic properties with depth (see attached figure). Variation in the magnetic signal results from changes in concentration and/or mineralogy of the magnetic material. In addition, a strong correlation exists between petrology of particular layers and bulk susceptibility. Preliminary high field results show consistent high field slopes, indicating a constant paramagnetic contribution to the susceptibility. Hysteresis ratios indicate magnetite is predominantly pseudosingle- and multi-domain, with minor single domain in the lower portions of the sill. In the Sonju Lake intrusion, a more straightforward interpretation of the magnetic properties is expected due to the nearly closed system nature. The same magnetic techniques will be applied to Sonju Lake to fully describe the intrusion and provide insight to the various fabric forming processes occurring in open and closed systems. 106 �107 �MINING AND EXPLORATION ACTIVITY IN NORTHWESTERN ONTARIO MAGEE, Angelique, Ontario Geological Survey, Ministry of Northern Development and Mines, Suite B002, 435 James St. South, Thunder Bay, ON P7E 6S7 CANADA Northwestern Ontario experienced a significant upswing in mining and mineral exploration in 2003. Six mines produced a total of 1.8 million ounces of gold in 2003, approximately 70% of Ontario’s total. Gold producers included: Campbell Mine (Placer Dome (CLA) Ltd.); David Bell Mine (Teck Cominco Limited and Barrick Gold Corporation); Golden Giant Mine (Newmont Canada Limited); Musselwhite Mine (Placer Dome (CLA) Limited / Kinross Gold Corporation); Red Lake Mine (Goldcorp Inc.); and Williams Mine (Teck Cominco Limited and Barrick Gold Corporation). North American Palladium Ltd. produced 288 000 ounces of palladium and 24 000 ounces of platinum at its Lac des Iles Mine and recently announced it would develop an underground operation below its open pit mine. There are approximately 300 active exploration projects in the northwest, the vast majority of which are focused on gold. Areas receiving the most interest from exploration companies were, the Red Lake greenstone belt, Shoal Lake area, Dogpaw Lake area, Shebandowan greenstone belt, Fort Hope greenstone belt, Onaman-Tashota belt and the Pickle Lake greenstone belt. If metal prices continue their upward trend, northwestern Ontario may well experience levels of exploration activity not seen since the mid-1980s. 108 �THE DISCOVERY AND GEOLOGY OF THE L-K MASSIVE SULFIDE DEPOSIT, MENOMINEE COUNTY, MI MAHIN, Robert A., Aquila Resources Corp., Duluth, MN QUIGLEY, Thomas O., Minerals Processing Corp, Duluth, MN LYNOTT, Jeffrey S., Environmental Compliance Consultants, Inc, Rhinelander, WI. The L-K zinc-gold deposit is a recently discovered major volcanogenic massive sulfide (VMS) of the early Proterozoic Penokean volcanic belt. Several events led to the eventual drilling of discovery hole LK-2, (37 meters @ 9.15 % Zn and 5.85 grams/tonne Au) none of which were part of earlier Wisconsin VMS exploration efforts. Prior AEM surveys to the north, west, and south failed to include the immediate deposit area, an area that despite proximal outcrops of intensely sericite-pyrite-altered rhyolite tuffs, was mapped as granitic intrusives and Paleozoic cover. The discovery of L-K can be attributed to Harry Kleiman, a water-well driller who deepened a local camp owner’s water well, his partner Rich Lassen, who recognized the sphalerite-rich drill cuttings as a potential VMS and subsequently located a nearby outcropping gold-rich gossan, and Tom Quigley, who later joined the partnership and pinpointed a significant gravity/conductive anomaly that turned out to be the L-K deposit. A joint venture with American Copper and Nickel Company, a subsidiary of Inco, resulted in a drilling program of 71 holes for over 20,000 meters of core. The drilling outlined a significant zinc-gold rich VMS within what appears to be a major felsic center. Significant portions of the deposit contain consistent grades of zinc in excess of 10 percent. Gold grades with in massive sulfides range from 1 to 6 grams/tonne. Significant gold mineralization also occurs in proximal sulfide stringers (e.g., 4.2 meters @ 25.3 grams/tonne Au), and in peripheral silicified zones in rhyolite tuffs and QFP dikes (e.g., 12.5 meters @ 7.4 grams/tonne Au). The near-surface gossan averages approximately 16 grams/tonne Au. The stratigraphy of the deposit consists of a stacked series of quartz-feldspar rhyolite crystal tuffs, locally fragmental, with intermittent fine-grained ash-tuff horizons, overlain by fine-grained, laminated tuffaceous sediments. Mineralization occurs as massive (>80%) pyrite+sphalerite+chalopyrite+galena localized at two stratigraphic contacts. Host rocks are intensely sericitized and silicified quartz-feldspar rhyolite tuffs and tuffaceous sediments. Structurally, the deposit and surrounding host rocks have been folded into a west/southwest-plunging, south verging antiform. The deposit is located both in the core of the antiform, where it appears to be tectonically thickened, and in the limbs of the fold. Numerous syntectonic, west-southwest-striking, steeply dipping, quartz-feldspar dikes intrude proximal to the deposit. Drilling has traced the massive sulfide along strike for 700 meters with vertical projections of the deposit ranging from 50 to 270 meters wide. Down-plunge, massive mineralization has been traced to a depth of approximately 300 meters. The deposit remains open at depth and along strike. 109 �THE GEOLOGY OF THE L-K MASSIVE SULFIDE DEPOSIT, MENOMINEE COUNTY, MI MAHIN Robert A., Aquila Resources Corp., Duluth, MN QUIGLEY, Thomas O., Minerals Processing Corp, Duluth, MN LYNOTT, Jeffrey S., Environmental Compliance Consultants, Inc., Rhinelander, WI The L-K deposit is a newly discovered volcanogenic massive sulfide deposit in the Beecher Formation of the early Proterozoic Penokean volcanic belt in western Menominee County, Michigan. The major economic metals at L-K are zinc and gold, with locally high concentrations of silver and copper. Mineralization occurs as massive (greater than 80%) pyrite+sphalerite+chalcopyrite+galena localized at two stratigraphic contacts within a large felsic volcanic center dominated by intensely sericitized and silicified quartz-feldspar, rhyolite tuffs. The stratigraphy consists of a stacked series of quartz-feldspar rhyolite crystal tuffs, locally fragmental, with intermittent fine-grained ash-tuff horizons, overlain by fine-grained, laminated tuffaceous sediments. The main-zone massive sulfide is hosted by altered hanging wall and footwall rhyolite crystal tuffs that are visually identical, but readily distinguishable by wholerock geochemistry, e.g., ratios of Al and Ti (Cattalani 2003, Shriver 2003). Tuffaceous zone mineralization, while not as consistently thick as the main zone, contains impressive grades and is focused along the contact between hanging wall rhyolites and overlying tuffaceous sediments. The massive sulfides are enveloped by gold (and to a lesser extent copper) bearing stockwork stringer sulfides (10 to 80% sulfide) that grade into a disseminated pyritic halo. Structurally, the deposit and surrounding host rocks have been folded into a west-southwest-striking, southwest plunging, south verging asymmetric antiform. Tectonically thickened portions of the deposit occupy the core of the fold and large sections of mineralization are also found in the limbs. Numerous syntectonic, west-southwest striking, steeply dipping quartz-feldspar dikes intrude the deposit. Faulting has resulted in minor offsets. Drilling has traced the massive sulfide along strike for 700 meters, with vertical projections of the deposit ranging from 50 to 270 meters wide. Portions of the deposit sub-crop at the east-northeast up-plunge extension where an ironoxide-rich, precious metal-enriched gossan has developed. Down-plunge, massive mineralization has been traced to a vertical depth of approximately 300 meters and remains open. Gradewise, drill intercepts of greater than 10 meters in excess of 10% zinc are common. Gold grades with in massive sulfides range from 1 to 6 grams. Significant gold mineralization also occurs in proximal sulfide stringers (e.g., 4.2 meters @ 25.3 grams/tonne Au), and in peripheral silicified zones in rhyolite tuffs and QFP dikes (e.g., 12.5 meters @ 7.4 grams/tonne Au). Intercepts of the near-surface gossan average 3 meters thick and approximately 16 grams/tonne Au. References Cattalani, S., 2003, Lithochemistry and chemostratigraphy, Back 40 project, Michigan: INCO private report, 7p. Shriver, N.A., 2003, Michigan: Back 40 chemostratigraphy and deformation of the Back 40 massive sulfide based upon lithogeochemical interpretation: INCO private report, 6p. 110 �MINERAL CHEMISTRY AND STRATIGRAPHY OF THE BIWABIK IRON FORMATION, NEAR THE VIRGINIA HORN, MESABI IRON RANGE, MINNESOTA McSWIGGEN, Peter L., and MOREY, G.B., McSwiggen & Associates, P.A., 2855 Anthony Lane South, Suite B1, St. Anthony, MN (PMcS@McSwiggenAssoc.com; morey001@umn.edu) The mineralogy of the Biwabik Iron Formation changes dramatically from west to east as the formation nears the basal contact of the Duluth Complex. This reflects a contact metamorphism that took place with the emplacement of the igneous Duluth Complex. However, the mineralogy of the Biwabik Iron Formation also varies vertically through the stratigraphy of the unit. A number of detailed studies have been done on the mineralogy of the contact zone (Bonnichsen, 1975). This investigation focused on the western Mesabi Range through the characterization of the E.J. Longyear Drill Hole #1 (S1/2, SW1/4, SE1/4, sec 23, T57N, R18W), which penetrated the entire section of the Biwabik Iron Formation from the overlying Virginia Formation through to the underlying Pokegama Quartzite (Fig.1). The iron-formation has been subdivided into four broad stratigraphic units (Fig. 2), lower cherty, lower slaty, upper cherty, and upper slaty, and into four lateral mineralogical zones (1-4) that reflect the zonation resulting from the contact metamorphism. Zone 1, the westernmost zone and the one in which the Longyear drill hole is located, is characterized by quartz, magnetite, hematite, carbonates, talc, chamosite, greenalite, minnesotaite and stilpnomelane. Talc and minnesotaite are the Mg- and Fe-end members, respectively, of the talc group [Mg6Si8O20(OH)4 – Fe6Si8O20(OH)4]. Minnesotaite is the dominant end member in the Biwabik Iron Formation, and typically occurs as a fibrous mineral, though it is also found in a tabular form. Chamosite is a Fe-chlorite [(Fe, Al)6 (Si, Al)4O10(OH)8], and generally occurs as a platy mineral in granules within the iron-formation. These granules are sand size gains that are the result of the reworking of previously deposited materials, which reflects a higher energy depositional environment. Greenalite is the iron serpentine [Fe6Si4O10(OH)8]. It is reported generally as having a platy, lizardite-like structure, and in the iron-formation occurs in granules. Stilpnomelane [(K, Na, Ca)0.6(Fe, Mg)6Si8Al (O,OH)27.2-4H2O] is a sheet silicate, but in the iron-formation it can occur in either a platy form or in a fibrous form. The above-described silicates do not occur uniformly throughout the stratigraphic section. In the Longyear core, chamosite + stilpnomelane is the dominant silicate assemblage in the upper three units (upper slaty, upper cherty and lower slaty). The assemblages minnesotaite + stilpnomelane, minnesotaite + talc, and greenalite + minnesotaite are the main silicate assemblages in the lower cherty. The carbonates have a wide range of compositions and include calcite, dolomite-ankerite, siderite, and kutnahorite, the manganese equivalent of ankerite. Carbonates occur throughout the Biwabik Iron Formation, but become more dominant in the lower cherty interval. The manganese component of the carbonates varies greatly, ranging from less than 1 mole% MnCO3 to as much as 25 mole percent. Bonnichsen, B., 1975, Geology of the Biwabik Iron Formation, Dunka River area, Minnesota: Economic Geology, v. 70, no 2, p319-340. Jirsa, M.A., Miller, J.D., Jr., and Morey, G.B., 2004, Geology of the Biwabik Iron Formation and Duluth Complex, (in press). 111 �Figure 1. Simplified geologic map of the Mesabi Iron Range. The main geologic unit is the Biwabik Iron Formation (shown in gray) (after Jirsa and others (in press)). Figure 2. Stratigraphic section and mineralogy of the E.J Longyear Drill Hole #1. It was drilled as a long stratigraphic test hole and was finished in 1910. 112 �GEOCHRONOLOGY OF PRECAMBRIAN ROCKS IN CENTRAL WISCONSIN: A REVIEW AND NEW 40Ar/39Ar ANALYSES MEDARIS, Jr., Gordon and SINGER, Brad, Dept. of Geology & Geophysics, Univ. Wisconsin Madison, Madison, WI, 53706; medaris@geology.wisc.edu; bsinger@geology.wisc.edu Most of the Precambrian evolution of Wisconsin is recorded by basement rocks in the central part of the state. Reported here are new 40Ar/39Ar analyses of hornblende, muscovite, and microcline, which bear on the thermal history of this important area. Because this is the 50th meeting of ILSG, it seems appropriate to provide a selective review of geochronological investigations over the past half century and to place our new results in a historical context. Review The framework for a modern classification of Precambrian rocks in the Great Lakes region was provided in 1961 by the seminal work of Goldich et al., who analyzed a large number of igneous and metamorphic rocks by the K/Ar and Rb/Sr methods. A three-fold Precambrian division was proposed, with boundaries at 2.5 and 1.7 Ga, corresponding to the Algoman and Penokean orogenies, although it was recognized that the apparent K/Ar and Rb/Sr ages might reflect subsequent metamorphism. In 1975 Van Schmus et al. established an apparent Rb/Sr age of ~1.65 Ga for a wide variety of igneous and metamorphic rocks in central and eastern Wisconsin. The few available U/Pb zircon data for such rocks yielded protolith ages of 1.8-1.9 Ga, and it was suggested that a widespread, low-grade metamorphic event, whose origin was poorly understood, affected the western Great Lakes region at 1.65 Ga. Also in 1975, Van Schmus et al. recognized the Wolf River batholith as a major igneous component in Wisconsin and determined equivalent Rb/Sr whole rock and U/Pb zircon ages of 1468±34 and 1485±15 Ma, respectively. With the continued acquisition of U/Pb analyses of zircon in the 1970s and 1980s, the Marshfield terrane in central Wisconsin was shown to consist of Archean gneiss (2.87-2.52 Ga) intruded and overlain by a wide variety of granitic rocks and associated felsic to intermediate volcanic rocks, ranging in age from 1.89 to 1.82 Ga (Sims et al., 1989). In 1983 Dott suggested that folding of Baraboo Interval quartzites was the result of plate collision to the south at ~1.65 Ga, and this concept was expanded by Van Schmus et al. (1993), who related 1.65 Ga deformation and low-grade metamorphism in the Great Lakes region to emplacement of the Outer Tectonic Belt onto the southern margin of Laurentia during the Mazatzal Orogeny. In 1998 Holm et al. located the tectonic and thermal front of Mazatzal deformation in northern Wisconsin, based on the distribution of folded and flat-lying quartzites and cooling ages (Rb/Sr, K/Ar, 40Ar/39Ar) of mica in basement rocks, e.g. 1.75-1.70 Ga vs. <1.63 Ga. The position and nature of the Mazatzal front in Wisconsin was confirmed by Romano et al. (2000), who showed that micas from basement rocks outside the front yield 40Ar/39Ar plateau ages of 1.76-1.75 Ga, and those inside, 1.61-1.58 Ga. Five samples of hornblende from Archean and Paleoproterozoic rocks within the front yield 40Ar/39Ar plateau ages of 1830, 1796, 1782, 1733, and 1638 Ma, which are thought to represent partial to complete Mazatzal resetting. Subsequently, 40Ar/39Ar ages of 1.45-1.47 Ga were obtained for muscovite in Baraboo Interval quartzites, reflecting widespread, but stratigraphically localized, hydrothermal activity related to Wolf River magmatism (Medaris et al., 2003). Central Wisconsin Precambrian Rocks The basement in NE Wood and NW Portage counties consists predominantly of Archean gneiss and a variety of Paleoproterozoic igneous rocks, including tonalite, granodiorite, granite, and associated felsic to intermediate volcanic rocks. U/Pb zircon ages are ~2780 Ma for migmatitic gneiss at Linwood Quarry, and 1892, 1851, 1841, and 1824 Ma for different varieties of tonalite along the Wisconsin River (Sims et al., 1989; Van Wyck, 1995). Many of the igneous rocks have been deformed and recrystallized, exhibiting a range of foliated and lineated fabrics. Amphibolite layers in Archean gneiss at Conants Rapids yield a temperature of 665 ºC and amphibolite (metadiabase) dikes cutting foliated tonalite at Biron Dam give 700 ºC (calculated by the hornblendeplagioclase geothermometer at P = 4 kbar; Holland & Blundy, 1994). Laser step-heating yields plateau ages of 1672 Ma for hornblende in metadiabase at Biron Dam (Fig. 1), 1516 and 1533 Ma for hornblende from two samples of amphibolite at Conants Rapids (Fig. 2), 113 �1530 Ma for muscovite in low-grade schist from the Eau Pleine shear zone (Fig. 3), and 981 Ma for microcline in Wolf River granite and 897 Ma for microcline in Baxter Hollow granite (located in the Baraboo Range) (Fig. 4). We interpret the ages of hornblende at Conants Rapids, 3.9 miles from the Wolf River batholith, and muscovite in the EPSZ, 6.7 miles from the batholith, to represent partial resetting by the Wolf River thermal pulse. The age of hornblende at Biron Dam, 13.3 miles from the batholith, may also reflect partial resetting by Wolf River heating, although this age lies within the range for hornblende reported by Romano et al. (2000) and ascribed by them to Mazatzal disturbance. The closure temperature of microcline can be as low as 150 oC, thereby allowing for the possibility that it may record cooling of the craton in central Wisconsin, following 1.1-1.0 Ga Keweenawan rifting and magmatism. The Ar ages reported here seem to result from degassing in response to regional thermal events, rather than pervasive internal deformation and recrystallization (also observed by Romano et al., 2000). Thus, although there has been widespread disturbance of Rb/Sr and Ar isotopic systems in Wisconsin Precambrian basement, many rocks in central Wisconsin have preserved their Penokean structures, textures, and mineralogical compositions. References Dott (1983) GSA Mem. 160 129-141; Goldich et al. (1961) Minn. Geol. Sur. Bull 41; Holland & Blundy (1994) Contrib. Mineral. Petrol. 116 433-447; Holm, D. et al. (1998) Geology 26 907-910; Medaris et al. (2003) J. Geol. 111 243-257; Romano et al. (2000) Precam. Res. 104 25-46; Sims et al. (1989) Can. J. Earth Sci. 26 2145-2158; Van Schmus et al. (1975a) GSA Bull. 86 1255-1265; Van Schmus et al. (1975b) GSA Bull. 86 907-914; Van Schmus et al. (1993) GSA Geology of North America C-2 270-281; Van Wyck (1995) Ph.D. thesis, Univ. Wis.-Madison, 280 pp. 114 �Geochemistry and Petrography of Altered Basement Rocks Underlying the Middle Proterozoic Sibley Group METSARANTA, R.T.*, and FRALICK, P.W., Department of Geology, Lakehead University, 955 Oliver Rd., Thunder Bay, Ontario, P7B 5E1, Canada. rtmetsar@lakeheadu.ca The Sibley Group is a relatively thin Mesoproterozoic mixed carbonate-clastic succession deposited, at least in part, under restricted shallow marine or lacustrine conditions (Franklin et al., 1980; Cheadle, 1986; Rogala 2003). A diverse mixture of genetically distinct chemical sediments is preserved within various depositional sub-environments of the Sibley Basin. These include: dolomitic mudstones and sandstones, stromatolitic carbonates, calcretes and nodular gypsum/anhydrite. In addition to these chemical sediments, possible weathering profiles are developed in various underlying basement lithologies and at higher stratigraphic positions. Given the diversity of chemical sediment types and possible weathering profiles within the basin the potential exists to develop a detailed model for the hydrology and paleoenvironmental evolution of the Sibley Group. Weathering is an important control on the composition of clastic sediments (e.g. Nesbitt et al., 1996) and also restricted basin brines (Rosen, 1994). As a first step towards an overall model of the hydrology of the Sibley Basin, the purpose of this paper is to investigate the petrography and geochemistry of altered rocks at the unconformity between the Sibley Group and underlying Archean and Paleoproterozoic lithologies. To be of value in an analysis of overall basin hydrology and paleoenvironmental conditions, the relative importance of primary pedogenically induced geochemical changes vs. later diagenetic or hydrothermal effects must be addressed. Suites of samples were collected from 4 areas spanning a variety of basement lithological types. Altered Quetico sandstones and Neoarchean granite were sampled from drill core at variable depths below the Sibley Group contact. Altered and unaltered Paleoproterozoic black shales of the Rove Formation were sampled from outcrop as were Mesoproterozoic anorogenic granites and overlying pebbly sandstones. Polished thin sections were cut from each sample and analysed petrographically using both optical and scanning electron microscopy. Whole rock powders were obtained for each sample and were analysed at Lakehead University via ICP-AES for a selection of major and trace elements. Petrographic evidence such as the progressive destruction of plagioclase upwards in the profiles coupled with extensive development of Fe-Ti oxides along grain boundaries and cleavage planes in biotite and chlorite is consistent with a weathering profile. Pebbles in sandstones associated with the anorogenic granite profile are also strongly iron enriched containing up to 30% total iron suggesting a highly oxidizing atmosphere during pre-Sibley Group weathering conditions. The presence of authigenic, euhedral potassium feldspars and the potassium-rich nature of clay minerals in the altered horizons suggest secondary potassium enrichment. The presence of barite, flourite and sulphide mineralization near the Sibley Group contact with Neoarchean granites also reveals that hydrothermal alteration may have had an influence on primary pedogenic geochemical signatures. Preliminary assessment of the major element geochemistry using a simple alteration index (CIA) and A-CN-K diagrams (e.g. Nesbitt and Young, 1982; Nesbitt et al., 1996) also suggests that primary pedogenic alteration may have been effected by later potassium enrichment. 115 �Al2O3 0 10 100 90 20 80 30 70 40 60 50 50 60 40 70 30 Granite Quetico Rove 80 90 20 10 100 CaO+Na2O 0 0 10 20 30 40 50 60 70 80 90 100 K2O Figure 1. Altered samples from three profiles plotted as molar proportions Al, Ca+Na, and K (as oxides), showing divergence of observed alteration trends towards more K-rich compositions from those expected due to weathering (arrow) Figure 2. Left: backscatter SEM image of K-rich clay mineral aggregates associated with altered primary K-feldspar (altered Neoarchean granite) and right: altered biotite grains with extensive development of Fe and Ti oxides (altered Quetico metasediment). References Cheadle, B.A., 1986. Alluvial and playa sedimentation in the lower Keweenawan Sibley Group, Thunder Bay District, Ontario. Canadian Journal of Earth Sciences. 23:527-542 Franklin, J.M., McIlwaine, W.H., Poulsen, K.H., and Wanless, R.K., 1980. Stratigraphy and depositional setting of the Sibley Group, Thunder Bay District, Ontario, Canada. Canadian Journal of Earth Sciences. 17:633-651. Nesbitt, H.W., Young, G.M., 1982. Early Proterozoic climates and plate motions inferred from major element chemistry of lutuites. Nature. 299:715-717. Nesbitt, H.W., Young, G.M., McLennan, S.M. and Keays, R.R. 1996. Effects of chemical weathering and sorting on the petrogenesis of siliciclastic sediments, with implications for provenance studies. Journal of Geology. 104:525-542. Rogala, B., 2003. The Sibley Group: A lithostratigraphic, geochemical and Paleomagnetic study. Unpublished M.Sc. thesis, Lakehead University, Thunder Bay, Ontario, Canada. 254p. Rosen, M.R. 1994. The importance of groundwater in playas: a review of playa classification and the sedimentology of playas. In Rosen, M.R., ed., Paleoclimate and Basin Evolution of playa systems. Geological Society of America Special Paper 289. Boulder Co. pp. 1-18. 116 �N.H. Winchell's Study of the Keweenawan Supergroup Rocks of Northeastern Minnesota, 1872-1900 MILLER, James D., Jr., Minnesota Geological Survey, mille066@umn.edu In 1872, fourteen years after its admission to the Union, the state legislature of Minnesota granted an initial appropriation of one thousand dollars per year to the University of Minnesota to create a geological and natural history survey of the state. In July of that year, Newton Horace Winchell (1839-1914) was hired to lead this survey, a task to which he committed 28 years of his life. There is little debate as to the contribution Winchell made to our understanding of diverse aspects of Minnesota's geology, especially in light of the paucity of existing research. Much of the survey's observations and interpretations of Paleozoic and Quaternary geology still stand up today. However, Winchell's greatest difficulties came in his attempts to make sense of the "crystalline rocks" of northeast Minnesota. As he stated in the preface to the fourth volume of the Final Report: "Here [among the crystalline rocks] the geologist is deprived of his usual guides and guys, and finds himself floundering in a muddy sea of innumerable conflicting currents" (Winchell, 1899, p. xiv). This talk focuses on Winchell's struggles with deciphering the complexities of what is now known as the Keweenawan Supergroup in northeastern Minnesota. My interest in this topic began while researching the history of geologic mapping in the Duluth Complex (Miller and others, 2002). My characterizations and interpretations of Winchell's ideas in this presentation come from selected readings of the 24 annual reports of the Geological and Natural History Survey of Minnesota, the final two volumes of the Final Report (Winchell, 1899, 1900), and Geological and Natural History Survey of Minnesota Bulletins 1, 2, 6, and 8. From this still incomplete sampling of Winchell's prolific writing on the Keweenawan rocks, I have come to conclude that most of his ideas, which seem unconventional by today's standards, were based on paradigms that were accepted by many, if not a majority, of geologists in his day. In the late nineteenth century the principles of stratigraphy and sedimentology were already well established, but the science of igneous and metamorphic petrology was in its infancy. At that time, numerous different ideas about the origin of magmas, volcanic processes, and progressive metamorphism existed. There was no accepted conventional wisdom. Winchell took advantage of the new field of petrographic petrology, which saw widespread use and growth in the last half of the century. He did not, however, have the benefit of the knowledge gained by experimental petrology, which started to emerge just as the survey was being completed. At the beginning of the Survey, Winchell's views of Lake Superior geology were strongly influenced by the early federal survey of the region (Owen, 1852), as well as by reports of Canadian geologists and the preeminent geologists from his native New York and New England. Over the course of the survey, Winchell regularly compared his observations to those of his U.S. and Canadian colleagues, but more often than not, he seemed to go his own way with many of his interpretations of the crystalline rocks. In fact, he often disagreed with the interpretations of his fellow survey colleagues, many of whom were his relatives—Alexander Winchell (his brother), Horace V. Winchell (his son), and U.S. Grant (his brother-in-law). One of his more curious relationships was with R.D. Irving of the University of Wisconsin, and later of the U.S. Geological Survey. Following up on his work on the Keweenawan rocks of northwestern Wisconsin for the third Wisconsin Geological and Natural History Survey report in 1880, Irving published the first thorough summary of Keweenawan geology in the Lake Superior region in a U.S. Geological Survey monograph (Irving, 1883). In this report, Irving recognized the volcanic character of the mafic and felsic rocks of the shore, and the intrusive nature of the gabbros. It included a remarkably accurate map of the geology of Minnesota's North Shore, in which Irving estimated that the volcanic pile from Duluth to the Temperance River exceeds 18,000 feet, relatively close to current estimates of 28,000 feet (Miller and others, 2002, Chapter 5). Irving relied exclusively on his own fieldwork and gave only passing acknowledgement to the work of the Minnesota survey, then in its tenth year. Winchell, for his part, rarely cited Irving's work, and then commonly only to point out some inconsistency or discrepancy with his observations or interpretations. Winchell's displeasure with the growing influence and overreaching of the U.S. Geological Survey, perhaps triggered by Irving's work, prompted him to found and edit the American Geologist journal in 1888. The journal was meant to highlight North American geology, but regularly featured articles critical of the U.S. Geological Survey (Bain, 1916). Irving died the year of its initial publication. Some of the major aspects of Keweenawan geology that Winchell wrestled with over the course of the state survey were: Potsdam Sandstone—With a strong belief in uniformitarianism, Winchell consistently held to the notion that all red quartzose sandstone lying unconformably on crystalline rocks was equivalent to the Lower Cambrian Potsdam Sandstone of upstate New York and New England, which has a similar lithology and unconformable geologic setting. Despite their lack of fossils, Winchell opined that the Puckwunge, Nopeming, Fond du Lac, and Hinckley sandstones, and even the Sioux Quartzite, were all Potsdam equivalents. He suggested that the lava 117 �flows overlying the Puckwunge and Nopeming Sandstones and interlayered with stratigraphically higher sandstone units (such as the sandstone at Cutface Creek near Grand Marais) represented localized volcanism during what was generally a time of sandstone deposition, a period he termed the Manitou epoch. Red rock—Winchell also consistently believed that all granophyre and rhyolite were metamorphosed and fused sedimentary rocks—a commonly held view at the time. He considered the "granophyre range," which arcs through the central part of the Duluth Complex, as a raised ridge of Animikie sediments that were fused by the eruption of the gabbro (see below). Rhyolites were thought to be strongly metamorphosed sandstone interleaved with and metamorphosed by basalt flows. In Winchell's view, quartz and feldspar-phyric flows represented less severe metamorphism because phenocrysts of quartz and feldspar were considered to be preserved detrital grains. Basaltic lava flows—Early on, Winchell adopted J.G. Norwood's interpretation (Owen, 1952) that the basaltic lava flows of the North Shore were intrusive sills (flow interiors) into volcanic sediments (amygdaloidal tops). Midway through the survey he recognized the physical stratigraphy of basalt flows. Duluth Complex—Winchell variably characterized the Duluth Complex as "the great gabbro flood," "the crowning overflow," "the great gabbro outflow," "a basic eruptive," and "the gabbro eruption." From these and other descriptors, it is clear that he saw the gabbro as a great volcanic outpouring of basic magma that spilled out over (and metamorphosed) its Animikie rampart and flowed downslope toward the Lake Superior basin. The Beaver Bay Complex and the gabbros at Duluth represent the distal part of this great gabbro flood. Anorthosite inclusions—Winchell interpreted the anorthosite inclusions of the Beaver Bay Complex as earlierformed feldspathic gabbros of the Duluth Complex (what is now termed the anorthositic series) that were picked up by later surges of the great gabbro eruptive. This idea was commonly accepted until recently (see Stop 24 in Field Trip 5). Age of the gabbro—Winchell changed his interpretation of the age of the gabbro many times over the course of the survey. Based on interlayering of the gabbro with rocks he thought to be upper Keewatin (the Pewabik Quartzite, which is actually metamorphosed Pokegama Quartzite), he saw the gabbro as syn-Keewatin to preAnimikie. Until Lawson (1893) showed that the Logan sills are intrusive into the Animikie Group rocks, rather than interlayered as lava flows, Winchell saw them and the gabbro as syn-Animikie. In the end, Winchell believed the gabbro to be younger than the Animikie Group and older than the Puckwunge Sandstone and overlying lavas. Winchell called the epoch during which the gabbros were emplaced the Norian and later the Cabotian. Origin of the gabbro magma—Winchell does not speculate on the origin of the basic magma that formed the gabbro and related volcanics until the Final Report. Following the idea that all granites formed by fusion of siliceous sediments, he concluded that the gabbro formed by the melting of greenstone-derived sediments. He considered hornfels basalt inclusions, which he called muscavodyte, an intermediate stage of metamorphism of these basic sediments. In the end, Winchell was certain that the facts of his numerous and well recorded observations would hold up to future scrutiny, and unquestionably most have. He was admittedly less confident in his interpretations, however and speculated that new facts, "…not included in our field of observation, will in the future place different interpretations on those which we have attempted..." (Winchell, 1899, p. xiv). This has happened to be sure, but more significantly, the changes in our geologic paradigms and our greater understanding of igneous petrology have allowed those of us who follow in his footsteps to reinterpret his many detailed observations. REFERENCES Bain, H.F., 1916, N.H. Winchell and the American Geologist: Economic Geology, p. 51-62. Irving, R.D., 1883, The copper-bearing rocks of Lake Superior: U.S. Geological Survey Monograph 5, 464 p. Lawson, A.C., 1893, The laccolithic sills of the north-west coast of Lake Superior: Geological and Natural History Survey of Minnesota Bulletin 8, p. 24-48. Miller, J.D., Jr., Green, J.C., Severson, M.J., Chandler, V.W., Hauck, S.A., Peterson, D.M., and Wahl, T.E., 2002, Geology and mineral potential of the Duluth Complex and related rocks of northeastern Minnesota: Minnesota Geological Survey Report of Investigations 58, 207 p. Owen, D.D., 1852, Report on a geological survey of Wisconsin, Iowa, and Minnesota: Philadelphia, U.S. Department of the Treasury, 638 p. Winchell, N.H., 1899, The geology of Minnesota: Geological and Natural History Survey of Minnesota, Final Report, v. 4, 629 p., 100 pls. ———1900, The geology of Minnesota: Geological and Natural History Survey of Minnesota, Final Report, v. 5, 1025 p., 6 pls. 118 �Twenty-One Years in a Caldera: UMD Geology Students and Sturgeon Lake, Ontario MORTON, Ron, Department of Geological Sciences, University of Minnesota Duluth Over the past 20 years students from the University of Minnesota-Duluth have been involved in studying the Sturgeon Lake Caldera Complex located in northwestern Ontario. Their work, based on outcrop mapping, logging of more than 200,000 meters of diamond drill core, thin section, microprobe, and chemical studies has shown that the complex comprises a wellpreserved, north facing, moderately to steeply north-dipping, homoclinal sequence that is up to 30 km in strike length and contains more than 3000 m of subaerially and subaqueously deposited volcanic and sedimentary strata. The Pre-Caldera Sequence, worked on by Groves (1984)*and Heine (1985) contains subaerial to shallow subaqueous basalt to andesite lava flows, tuffs and lapilli-tuffs with subordinate rhyolite lava flows. The Early-caldera Sequence, worked on by Walker (1993), Hudak (1989), Beszenek (1992) and Drews (1990) along with Rog (1991) and Murphy (1994) comprises subaerially to subaqueously deposited polymict breccias and aphyric or quartz-phyric, rhyodacite-rhyolite tuffs with reworked tuffs and minor andesite to rhyolite lava flows. The Latecaldera Sequence, worked on by Jongewaard (1989) and Hudak (1996) contains syn-eruptive and reworked quartz- and plagioclase-phyric rhyodacite to rhyolite tuffs and lapilli-tuffs, and subaqueous basalt-andesite to rhyolite lava flows, domes, and cryptodomes. Volcanic-hosted massive sulfide deposits occur in the Early and Late Caldera Sequences. Synthesizing these studies, with additional contributions by Peterson (2001), provides a detailed picture of caldera development and associated massive sulfide formation and hydrothermal alteration. The work of the above geologist’s shows this piecemeal caldera complex formed upon a subaerial to shallow subaqueous basalt -andesite shield volcano with associated local fields of scoria and tuff cones. Caldera formation was characterized by more than a kilometer of collapse accompanied by voluminous pyroclastic eruptions, deposition of laterally extensive meso-and mega-breccias, minor effusive volcanism, and massive sulfide ore deposition with widespread hydrothermal alteration. Later stages of caldera development were dominated by submarine effusive volcanism and intracaldera sedimentation, with subordinate pyroclastic volcanism and ore deposition. The lithostratigraphic sequence, caldera diameter, and estimated eruption volumes, determined from geographic information system (GIS) analysis, are consistent with those that characterize modern ash flow caldera complexes. The Sturgeon Lake Caldera Complex illustrates the following: 1) The necessity of long term, detailed field and laboratory studies to understand complex volcanic systems. 2) That evolutionary and mineralizing processes associated with "ash flow" calderas have been remarkably similar since at least Neoarchean time. 3) That good students do very good work and make professors look great! * Year of degree or year started work at Sturgeon Lake 119 �Status of Publicly Available Mid-Continent Reflection Seismic Data MUDREY, M.G., Jr. Wisconsin Geological and Natural History Survey, 3817 Mineral Point Road, Madison, WI 53705 mgmudrey@wisc.edu CANNON, W.F., U.S. Geological Survey, National Center MS 954, Reston, VA 22092 wcannon@usgs.gov The Midcontinent Rift was identified by potential field and geologic studies in the 1950s. However, much of the detail of this largely buried structure was obscure except in a few well exposed areas around Lake Superior. Interest in frontier petroleum rose in the 1970s and the recognition of documented petroleum seeps from the Nonesuch Formation led to the acquisition and evaluation of industrial reflection seismic data. From 1978 to 1986 a series of seismic reflection profiles was obtained by a combination of academic (COCORP), petroleum company, and government (GLIMPCE) research programs. The U.S. Geological Survey and the Geological Survey of Canada acquired 536 line-km in Lake Superior, L.D. McGinnis and Argonne National Laboratory purchased 1,816 line-km in Lake Superior from Grant-Norpac, and A.B. Dickas University of Wisconsin-Superior negotiated the release of 1,336 line-km from Lake Superior south to Iowa from Petty-Ray/Geosource. The profiles provided access to a wealth of new details of the lateral and vertical extent of the rift and its internal structure and stratigraphy from Lake Superior to Kansas. Some of the major findings include: • Particularly significant was the discovery that 20 to 30 km of basalt flows and secondary syn-rift volcaniclastic and post-basalt sedimentary rock produced exceptionally strong and coherent reflections that enabled accurate estimates of the volumes of basalt. • Moho reflections recorded in Lake Superior over the rift range from 46 to 58 km in contrast to 36 to 42 km beneath the surrounding Great Lakes. This provides evidence of magmatic underplating and intrusions within the lower crust and upper mantle contemporaneous with crustal extension...in effect, the mantle was changed into crust by a decrease in seismic velocity. ! Individual basins within the Midcontinent Rift have been delineated by long reflection lines and cross lines -- clearly developed unconformities remove ambiguities of correlation among various volcanic sections within and between basins. Although individual seismic lines have been interpreted, the entire collection of lines, along with newly acquired gravity and magnetic data, have yet to be collectively used to refine our understanding of this 2,000 km rift. GLIMPCE data are available from Robin R. Warnken, National Geophysical Data Center, NOAA/NESDIS/NGDC/ Mail Code E/GC3, 325 Broadway, Boulder, CO USA 80305-3328. phone: (303) 4976338. Email: Robin.R.Warnken@noaa.gov Argonne National Laboratory/Grant-Norpac data are available from 120 �McGinnis, L.D., and Mudrey, M.G., Jr., 2003, Seismic reflection profiling and tectonic evolution of the Midcontinent Rift in Lake Superior: Wisconsin Geological and Natural History Survey Miscellaneous Report MP 91-2, 15 pl. 1 CD-ROM. Files on CD are in PDF format. Petty-Ray/Geosource data are available from Dickas, A.B. and Mudrey, M.G., Jr., 2002, Regional-Scale Geologic Interpretation of Seismic Reflection, Gravity, and Magnetic Profiles Collected along the Western Arm of the Midcontinent Rift System, Upper Peninsula of Michigan, Wisconsin, Minnesota and Iowa: Wisconsin Geological and Natural History Survey Open-file Report 2002-01, 1 CD-ROM. Files on CD are in HTML format. 1. Location of reflection seismic lines: GLIMPCE, heavy dashed; Grant/Norpac, light solid; Petty-Ray/Geosource, medium solid. 121 �“GOLD IS WHERE YOU FIND IT! SO IS Ag AND Cu AND Fe!” (THE OLD PROSPECTOR: GOLD RUSHES AND MINERAL PROSPECTING, 1848 TO 1900 IN WESTERN NORTH AMERICA AND THE LAKE SUPERIOR REGION) OJAKANGAS, Richard W. (a.k.a., The Old Prospector), University of Minnesota Duluth, Duluth, MN 55812, rojakang@d.umn.edu Gold has long provided a chance for the “little guy” to make a fortune. The “Old Prospector” relates factual and illustrative information about several gold rushes, beginning with the 1849 gold rush in California. (“Go West, young man, go West!”) Where did the 200,000 “Forty-Niners” come from? From everywhere! Because it took 11 months for the news to reach the east coast, people living on the Pacific Rim got there first. How many (how few?) hit it rich? Even Captain Sutter and the actual discoverer, Jim Marshall, died poor. The Comstock Lode in Nevada, “discovered” by Henry Comstock, led to the gold and silver rush of 1860, with many of the fortune-seekers crossing back over the Sierra Nevada with their donkeys. A group on their way to California in 1850 found gold in Colorado at the present site of Denver, but the rich California gold was their goal. There were several discoveries in Colorado over the next decades. It was the gold at Cripple Creek, discovered by cowboy Bob Womack in 1890 that really brought the prospectors in. Bob sold his claim for $300 -- $ 7.5 million came out of that gulch! Looking for gold, silver and copper in Montana attracted many prospectors in the ’60s and ‘70s. The copper ore was “so pure that it could be shipped to hell and back for smelting and still make a profit.” (Swansea, Wales, was the location of early smelters.) In 1876, the rush was to the Black hills for gold. General Custer had gone in to look for gold in 1874, and his favorable report brought in a horde of prospectors. All of this was in violation of the Fort Laramie Treaty of 1868. The Indians were embittered, and Custer was sent in to force the Indians back onto their reservations. In the Battle of the Little Big Horn on June 25, 1876, all 265 soldiers in 5 companies of the U.S. 7th Cavalry died. Meanwhile, what was going on in the Lake Superior region? Native copper had been discovered on the Keweenaw Peninsula by Douglas Houghton in 1840, and mining began soon after. Actually, the copper was “rediscovered” by Houghton, as “Old Copper Complex Indians” had been mining it from numerous pits on the peninsula and on Isle Royale for the previous 6000 years. Iron ore was discovered in the UP near Negaunee in 1844 by William Burt and his party, who were running a line using a sun compass and noticed a large deviation in the magnetic azimuth of a regular compass. Chief Manjekijik of the Chippewas led explorers to another outcrop of iron-formation the next year. Major ore shipments began in 1855. Ore in the Menominee district was discovered in 1845 and began production in 1877. Iron ore on the Gogebic was first noted in 1848 by A. Randall and Charles Whittlesey, but production didn’t begin until 1884. 122 �Gold was mined from the Ropes Mine in the Marquette area in the early 1880s, and sporadically thereafter. In 1868, silver was discovered at Silver Islet near Thunder Bay. In 1865, there was a gold rush to Lake Vermilion. Had it been based on a valid discovery of gold, or was the rush a ruse to generate business for suppliers? (There are no authentic reports of gold having been found there.) The gold activity in the Lake Vermilion area led to the 1865 discovery of iron ore by George Stuntz, a surveyor who had a trading post on Minnesota Point in Duluth... The first ore was shipped in 1882 from Soudan, and in a few years 5 mines were producing at Ely. Many men had crossed the Giants Range (the “Mis-sa-be” hills of the Indians) on their trek to Lake Vermilion (Ona-ma-sa-ga-i-gan, or the “lake of the beautiful sunset”) along the 84mileVermilion Trail surveyed and built by Stuntz Some, including Lewis Merritt of Duluth, noted the presence of magnetic iron-formation in the eastern Mesabi. However, it was not until 1890 when the Merritt brothers (sons of Lewis Merritt), with their concept of ore “basins” within the iron-formation, discovered the first high-grade soft ore at Mountain Iron and a year later at Biwabik. (These discoveries ended the fledging developments on the Gunflint Range.) Within a few years, mines reached 30 miles westward, discovered by Frank Hibbing, Archibald Chisholm, Erwin Eveleth, and others. Within 20 years, most of the Mesabi ore had been located. In 1904, 58 Mesabi mines produced more ore than the 78 mines of Michigan and the Vermilion district. Meanwhile, the search for gold continued wherever bedrock was exposed. In 1894, it was discovered in a quartz vein on Little American Island on Rainy Lake, and a mine was developed to a depth of 212 ft. This was Minnesota’s only legitimate gold mine, having produced $5600 worth of gold. Rainy Lake City grew quickly, and died almost as quickly. There were not many steam gravels on bedrock to be panned in this glaciated country, although to the north in Ontario, prospecting continued unabated. The news of the discovery of the Klondike gold in the Yukon Territory by George Carmack in 1896 reached the West Coast, and even Minnesota, in 1897. Several Minnesota prospectors joined 100,000 others who were heading north to Dawson. Perhaps 40,000 made it, maybe 20,000 prospected, and about 4,000 shared in the total gold find of $10,000,000 (an average of $2,500 each). The good stream beds were rapidly staked. In 1898 near Nome, Alaska, on the Bering Sea, 1,000 miles west of the Klondike, gold was discovered by the “Three Lucky Swedes” (Jafet Lindeberg, Eric Lindblom, and John Brynteson, all greenhorns) who became millionaires. Then gold was found in the beach sands of Nome in 1900, and the beaches became “the poor man’s paradise”. More than 23,000 people sailed there from Seattle, Portland, and San Francisco to get rich in one way or another. At the height of beach mining, 2,000 men, women and children were at work, and produced about $2,000,000 worth of gold, an average of $1,000 each. This was the last great placer gold stampede in North America, and really lasted for only the 3 months of the summer of 1900. 123 �Selected References Boyum, Burton H., 1977, The Saga of Iron Mining in Michigan’s Upper Peninsula: John M. Longyear Research Library, Marquette, Michigan, 48 p. Campbell, L.T., 1992, Skagway—a Legacy of Gold: Alaska Geographic, v. 19, # 1, 96 p. Clark, Henry W., 1930, History of Alaska: the Macmillan Company, N.Y., 208 p. Cole, Terrance, 1984, Nome: “City of the Golden Beaches”: Alaska Geographic, v. 11, #1, 183. Davis, E.W., 1964, Pioneering With Taconite: Minnesota Historical Society, 246 p. DeKruif, Paul, 1929, Seven Iron Men: Harcourt, Brace and Company, N.Y., 241 p. Emanuel, Richard P., 1997, The Golden Gamble: Alaska Geographic, v. 24, #2, 96 p. Green, William, 1963, The Bonanza West: University of Oklahoma Press, 430 p. McCourt, Edward, 1969, The Yukon and Northwest Territories: St. Martin Press, N.Y., 236 p. Morgan, Murray and Hegg, E.A., 1967, one Man’s Gold Rush—A Klondike Album: University of Washington Press, 213 p. Oliver Iron mining Company, 1912, Iron Industry of Minnesota: 48 p. Van Barnevald, Charles E., 1912, Iron mining in Minnesota: University of Minnesota, School of Mines Experiment Station, Bulletin No. 1, 214 p. Walker, David A., 1974, Lake Vermilion Gold Rush: Minnesota History, Minnesota Historical Society, Summer 1974, p. 43-54. Walker, David A., 1979, Iron Frontier—The Discovery and Early Development of Minnesota’s Three Ranges: Minnesota Historical Society Press, 315 p. Welbanks, Wallace P. and Woodbridge, Dwight E., 1905, Minnesota Iron Mines: Welbanks, Crandall and Co., Duluth, Minnesota, 46 p. 124 �DEPOSITION OF PALEOPROTEROZOIC SILICICLASTICS AND IRONFORMATION IN A TIDALLY INFLUENCED SHELF ENVIRONMENT, ANIMIKIE BASIN, LAKE SUPERIOR REGION OJAKANGAS, Richard W., University of Minnesota Duluth, Duluth, MN 55812, rojakang@d.umn.edu; OJAKANGAS, Gregory W., Drury University, Springfield, MO 65802; gojakang@drury.edu The Paleoproterozoic Animikie Basin is interpreted as a northward-migrating foreland basin situated north of the Penokean orogen. Basal siliciclastic units are the Pokegama Formation on the Mesabi Range in Minnesota, the Palms Formation on the Gogebic Range in Michigan-Wisconsin, and the Kakabeka Quartzite on the Gunflint Range in Ontario and adjacent Minnesota. The overlying iron-formations are the Biwabik, Ironwood, and Gunflint, respectively. The iron-formations of these three ranges are in turn overlain by the Virginia Formation, the Tyler and Copps Formations, and the Rove Formation, respectively. We interpret the siliciclastics and the iron-formations to have been deposited on the northern edge (i.e., the peripheral bulge and foreland) of the basin about 1900 Ma. Those in Michigan-Wisconsin were likely continuous with those farther north in Minnesota and Ontario prior to their separation by the development of the Mesoproterozoic Midcontinent Rift System at 1100 Ma. However, the units are likely diachronous, with those in Michigan and Wisconsin somewhat older than those in Minnesota and Ontario. They are interpreted to have been deposited on a shelf near a peneplaned surface on Archean rocks. The siliciclastics were deposited near shore and the iron-formations were deposited farther seaward. As the sea transgressed northward, the iron-formations were deposited upon the siliciclastics. Walther’s Law applies, with the vertical facies indicating the lateral facies. The siliciclastic formations consist of lower argillaceous members, middle members of argillite, siltstone, and sandstone, and upper members of mature sandstone (all gradational), interpreted to have been deposited, respectively, in upper tidal, middle tidal, and lower tidal (subtidal?) environments in a transgressing sea. The well-exposed Palms Formation exhibits abundant tidal evidence including bimodal-bipolar paleocurrent plots (N=250) for the formation as a whole and also for specific localities, tidal bedding (lenticular, wavy, and flaser), and minor flat-topped ripple marks and mudcracks. Also present in the middle member are thin sandtextured beds composed of iron silicates that were apparently transported shoreward into the siliciclastic zone. The Pokegama Formation is poorly exposed, but tidal evidence can be interpreted from limited exposures and a few drill cores. Sequences of thicker and thinner laminae in siltstone beds of the lower member are interpreted as evidence of the diurnal inequality that is an alternation in the heights of successive high tides in a twice-daily tidal environment. The diurnal inequality occurs when the moon is above or below Earth’s equatorial plane, because under these conditions any non-equatorial location will pass through different parts of the tidal deformation ellipsoid during each successive high tide. Ideally the diurnal equality disappears at the equator, and therefore our data are suggestive of a non-equatorial depositional location. Poorly exposed packets of progressively thinner and progressively thicker laminae may indicate neap and spring tidal cycles. These investigations are continuing, with a search for longer sequences of laminae in drill cores. 125 �The iron-formations have thick-bedded and granular (‘sandy”) members and thin-bedded and fine-grained (“muddy”) members. The former make up the lower and upper “cherty” members and the latter comprise the lower and upper “slaty” members. The granules are composed of iron oxides, iron silicates, iron carbonates, and chert, whereas the fine-grained units are made up largely of iron silicates and iron carbonates. It has commonly been thought that fine-grained precipitates of silica, iron carbonates and/or iron silicates formed on the shelf edge where upwelling waters supplied the iron and silica to a location below wave-base. Reworking of these fine-grained precipitates by tidal and/or storm currrents resulted in the formation of the granules. The granules were then transported into higher energy locations shoreward of the deeper shelf. The Ironwood Iron Formation is poorly exposed, whereas the Biwabik and Gunflint are well exposed. The Biwabik is exceptionally well exposed in taconite pits. In the Minorca Mine just northeast of Virginia, a paleocurrent plot of 102 cross-beds, including rare herringbone cross-beds, is strongly unimodal to the NNE, perpendicular to the paleogeographically determined shoreline, but with 10 % of the readings in the opposite sense. Therefore, flood tides were dominant. In some pits, such as at Minntac, channels of granular iron-formation are cut into the fine-grained and thinly bedded iron-formation. These are as wide as 1 km and 25 m deep, are oriented perpendicular to the paleogeographically determined shoreline, and are interpreted to be tidal channels in which granular sediment was transported seaward into the realm of fine-grained precipitates. A shallow water environment for the deposition of the granular members is supported by the rounded nature of the grains, the cross-bedding, and two major stromatolite horizons. Stromatolite columns in a bed that has since been mined away were all inclined at 30 degrees to the vertical, suggestive of an environment of deposition at about 30 degrees latitude. The vertical sequence of members—lower cherty, lower slaty, upper cherty, and upper slaty—is due to transgression, regression, and transgression. Selected References Morey, G.B., 2003, Paleoproterozoic Animikie Group, related rocks and associated iron-ore deposits in the Virginia Horn: in Jirsa, M.A. and Morey, G.B., eds., Contributions to the geology of the Virginia Horn Area, St. Louis County, Minnesota, Minnesota Geological Survey, Report of Investigations 53, p. 74-102. Ojakangas, R.W., 1983, Tidal deposits in the early Proterozoic basin of the Lake Superior region—The Palms and the Pokegama Formations: Evidence for subtidal-shelf deposition of Superior-type banded iron-formation: in Medaris, L.G., ed. Early Proterozoic geology of the Great Lakes region: Geological Society of America Memoir 160, p. 49-66. 126 �THREE-DIMENSIONAL GEOMETRY AND STRAIN OF THE BARABOO SYNCLINE: KINEMATIC IMPLICATIONS ORMAND, Carol J., Department of Geology, Wittenberg University, Springfield OH 45501, cormand@wittenberg.edu CZECK, Dyanna M., Department of Geosciences, University of Wisconsin - Milwaukee, P.O. Box 413, Milwaukee, WI 53201 INTRODUCTION Paleoproterozoic sedimentary rocks of the “Baraboo interval” were deposited on a stable cratonic margin with subdued topography, in a warm, humid climate, as evidenced by their physical and chemical maturity (e.g. Dott, 1983; Medaris et al., 2003). The southern deposits, including the Baraboo Quartzite and associated rocks, subsequently underwent both low-grade thermal metamorphism and simultaneous deformation during the Mazatzal orogeny, ~1650-1630 Ma (Holm et al., 1998; Romano et al., 2000). During this collisional event, the flat-lying marginal sediments were crumpled into tight, asymmetric, southward-verging folds. The foreland fold-and-thrust belt of this collision is preserved in isolated outcrops in southern Wisconsin including the Baraboo hills (LaBerge and Klasner, 1986). Approximately 40 kilometers long by 15 kilometers wide, the geometry of the Baraboo Syncline is strikingly three-dimensional. The fold axis trends approximately N80E. The northern limb of the fold is subvertical to slightly overturned; the southern limb dips around 35 degrees northward; the eastern termination plunges approximately 35 degrees westward; and the western termination plunges approximately 25 degrees eastward. DEFORMATION FEATURES Strain on the limbs of the Baraboo Syncline is as three-dimensional as the fold itself. Both limbs of the fold have axial planar phyllitic cleavage, refracted into quartzitic strata. Within the southern limb, however, where quartzite beds are sandwiched within phyllitic layers, threedimensional pinch-and-swell structures (“chocolate tablet boudinage”) show extension parallel to layering, both along strike and down dip. Strain data from quartz grain shapes also indicate three-dimensional strain, with extension either layer-parallel or layer-normal (McKiernan, 2002; Craddock, pers. comm.). In addition, slickensides on the southern limb of the fold indicate one paleostress direction, while slickensides on the northern limb show multiple paleostress solutions (Kirschner et al., 1989). KINEMATIC MODEL Both the fold geometry and the extension within the gently dipping limb of the syncline are consistent with formation in a top-to-the-south simple shear environment (Cambray, 1987). In such an environment, non-cylindrical fold trains would verge southward. In this model, the longer, north-dipping fold limbs are favorably oriented for localized layer-parallel extension, while the shorter, steeply dipping limbs rotate and shorten during deformation. The location of boudinage exclusively on the south limb is consistent with this model. The multiple paleostress directions on the north limb, inferred from slickensides (Kirschner et al., 1989), are also consistent with the rotation of the north limb explicit in the model. Therefore, this simple shear 127 �model is consistent with the majority of the field data. However, it is a two-dimensional model that does not account for the strongly three-dimensional fold geometry. To account for the threedimensional shape of the syncline, we invoke a component of non-plane strain. We envision a variation in degree of shearing along strike, resulting in extension along the fold axis. This model therefore could explain both the strong change in plunge along trend and the threedimensional boudinage within the southern limb of the Baraboo Syncline. We are analyzing microstructural data on both limbs of the fold to further evaluate this kinematic model. REFERENCES Cambray, F. W., 1987. The Baraboo syncline; the shape and refolding explained as a result of superposition of simple shear on a pre-existing fold. GSA Abstracts with Programs, 192. Dott, R. H., Jr., 1983. The Proterozoic red quartzite enigma in the north-central United States: resolved by plate collision? GSA Memoir 160, 129-141. Holm, D., Schneider, D., Coath, C. D., 1998. Age and deformation of Early Proterozoic quartzites in the southern Lake Superior region: implications for extent of foreland deformation during final assembly of Laurentia. Geology 26, 907–910. Kirschner, D., Pershing, J., Teyssier, C., 1989. Nature and kinematics of fault surfaces in the Baraboo Syncline (WI). GSA Abstracts with Programs, 17. LaBerge, G. L., Klasner, J. S.., 1986, Evidence for a major south-directed early Proterozoic thrust sheet in south central Wisconsin. GSA Abstracts with Programs, 664. McKiernan, A., 2002. Stress-strain analysis in Precambrian quartzites from Wisconsin: evidence for eastward continuation of the ca. 1650 Ma Mazatzal and Central Plains orogenies. Honors Paper, Macalester College, MN. Medaris, L. G. , Jr., Singer, B. S. , Dott, R. H. , Jr., Naymark, A., Johnson, C. M., Schott, R. C. , 2003. Late Paleoproterozoic Climate, Tectonics, and Metamorphism in the Southern Lake Superior Region and Proto–North America: Evidence from Baraboo Interval Quartzites. Journal of Geology 111, 243–257. Romano, D., Holm, D. K., Foland, K. A., 2000. Determining the extent and nature of Mazatzalrelated overprinting of the Penokean orogenic belt in the southern Lake Superior region, north-central USA. Precambrian Research 104, 25–46. 128 �DULUTH COMPLEX BULK SAMPLES PATELKE, Richard, and SEVERSON, Mark, Natural Resource Research Institute, University of Minnesota Duluth, Duluth Minnesota 55811, rpatelke@nrri.umn.edu, mseverso@nrri.umn.edu Since copper-nickel exploration began in the Duluth Complex with the first drill hole in 1951, there have been numerous bulk samples taken for metallurgical testing. Our current project is an attempt to develop a narrative history of this work. The project began for two reasons: 1) there is a perception that these bulk samples have usually returned metal grades lower than was expected by the pre-excavation testing; and 2) there was no consolidated listing for where data about these projects might be found. The issue of sample head grade in bulk samples being lower than expected is real, but is not documented well enough to discern an overall cause or to propose a solution beyond more rigorous outcrop stripping, mapping, and drilling before choosing a test site. Most sites have been located based on a single drill hole and as far as we can tell no sites have been rejected after a location has been chosen or once excavation began. There is probably a distinction between a geologist’s definition of a successful test and a metallurgist’s definition. A geologist’s definition of a successful bulk sample is one where the overall grade and mineralogy is what was predicted from assaying, drilling, or outcrop study (a “scientific success”). A metallurgist might define a successful bulk sample as one that represents, or is typical of, the bulk composition and the mineralogical ratios of the deposit, and therefore allows reliable conclusions to be drawn from testing certain steps in the beneficiation process (a “practical success”). The primary source of information for this study is company publications and records in files at MDNR and NRRI, little was found at other locations. Samples in the South Kawishiwi intrusion include: a small outcrop (and drill core?) sample by the USBM; two surface bulk samples from the INCO Spruce Road deposit; samples from the shaft and drift of the INCO Maturi deposit; large excavation and incidental exposure at the Dunka Pit iron mine (over 14 million tons of Duluth Complex material on the surface); and a small incidental exposure of Duluth Complex rock and massive-sulfide related to iron-formation stripping in the Peter Mitchell Taconite mine. Bulk samples at the Babbitt (Mesaba) deposit in the Partridge River intrusion include: work on one surface sample pit and multiple samples from the shaft and drift by AMAX; numerous drill core composites by AMAX; two test pits by Arimetco in the 1990s; one test pit by Teck Cominco in 2001; and a 50,000 ton pit planned by Teck Cominco in the near future. The Dunka Road (NorthMet) deposit had three samples at two locations by USS; a 1991 drill core composite from new large diameter holes by Nerco and Fleck; and a large pilot plant sample by PolyMet from reverse-circulation cuttings. The Longnose Oxide-bearing Ultramafic intrusion (OUI) had two samples taken from pits for beneficiation and process testing of the Fe-Ti oxides. Two complete drill holes in the Water Hen OUI were taken for process testing by the USBM in the 1980s. The major bulk samples are listed in Table 1, the references for the table are in the document below. Reference: Patelke R., and Severson M.J., in prep., 2004, A history of copper-nickel and titanium-oxide test pits, bulk samples, and related metallurgical testing in the Keweenawan Duluth Complex, northeastern Minnesota, Natural Resources Research Institute, Technical Report NRRI/TR-XX, ~100 pages. 129 �SOUTH KAWISHIWI INTRUSION Project Responsible party Year(s) Tonnage Comment Spruce Road USBM Source of sample uncertain, test work done uncertain No data found. INCO 3 holes drilled in 1953, report issued in 1955 19661,150 tons 1967 1974 10,000 tons INCO 1968 INCO 1968? Serpentine Reserve Mining Dunka Pit Erie / LTV Before 1989 1975 to 1998? Comment Grades Reference 0.43% Cu, Ni est. at 0.12% Various files in AMAX archive at MDNR INCO Maturi Grades Lab / bench tests on composite from 3 drill cores and / or outcrop samples? Reported head grade of 0.38% Cu, 0.14% Ni, 0.88% S Reference Grosh et al., 1955, USBM Report 5177 1974 INCO project description on file at MDNR in AMAX archive Pit along south side of Spruce Road, processed by INCO at Sudbury (?) Reported head grade of 0.47% Cu, 0.15% Ni, 1.08% S 1974 INCO project description on file at MDNR in AMAX archive 700 tons (?) Shaft at Maturi, sample sent to INCO lab at Sudbury (?) No data found. 1974 INCO project description on file at MDNR in AMAX archive Drift at Maturi, some drilling done from drift, but little information in NRRI or MDNR files. Assume some material must have been sent for Misc. files at MDNR and NRRI metallurgical tests. Uncertain tonnage An exposure of massive sulfide assumed to be similar or related to the Serpentine deposit is seen in the Peter Mitchell Mine. Exposed during Ruhanen, 2001 for MDNR, Severson South iron-formation stripping. Assayed by MDNR in 2001. Kawishiwi report 14-20 million tons in Stockpiles at Dunka Pit represent Duluth Complex material removed for 0.23% Cu, 0.09% Ni, 2.20% S are the approximate values from Files at MDNR, and Ron Graber at CCI stockpiles? iron ore mine development. exploration drilling. MDNR reports values of 0.29% CuO, 0.10% NiO (uncertain about whether these are oxide or sulfide assays) PARTRIDGE RIVER INTRUSION Project Responsible party Babbitt (Mesaba) AMAX At B1-341 deposit AMAX Dunka Road (NorthMet) deposit Year(s) Tonnage 1978 1976 AMAX 1976 Arimetco at B1-374 1994 Arimetco at B1-411 19951996 Teck Cominco at B1-321 2001 150 tons sent to CMRL, January 1996 5,000 Teck Cominco at B1-321 USS Bulk No 1 Future 50,000 1971(?) unknown tonnage, but small USS Bulk No 2 1971 USS Bulk No 3 1971 Fleck / Nerco 1990 PolyMet Composite 19982000 Longnose Fe-Ti oxide (OUI) 1,150 ton Surface pit in NE corner of deposit. Sample may actually have been taken excavation, 560 tons in South Kawishiwi intrusion, not Partridge River intrusion sent as sample Shaft samples listed as "disseminated." Some of this material used by MDNR for various leaching and ARD tests Drift samples listed as "massive" or "semi-massive." Some of this material used by MDNR for various leaching and ARD tests 200 tons excavated, Surface pit. Sample probably in weakly mineralized pegmatitic zone of sample split to 85 Unit 3 and 115 ton portions American Shield 1984 American Shield 1999 Surface pit. Sample in western part of deposit, location in Unit 1. Reasonably typical material. Various disseminated ore samples. Est. at 0.43% Cu, 0.13% Ni, Various files in AMAX archive at MDNR S unknown Various massive and semi-massive sulfide samples. Various files in AMAX archive at MDNR 0.22% Cu, 0.06% Ni, 0.52% S from blast holes; sorted sample had head grade of 0.30% Cu, 0.08% Ni, 0.63% S 0.61% Cu, 0.12% Ni, 1.02% S from blast holes; CMRL reports MDNR and NRRI files head grade at 0.36% Cu, 0.08% Ni, 0.76% S Surface pit at location drilled by Severson for Arimetco, in Unit 1, near Severson estimate 460 tons at 0.62% Cu center of north edge of deposit. Very typical material. Final sample much larger than 460 tons outlined by Severson. Planned surface pit, at same location as Teck Cominco B1-321. EAW approved by State in 2003 Surface pit near drill hole (26058) with mineralization only in top few feet. Drill hole 26058 grade from 8 to 20 ft. was 0.82% Cu, 0.20% Small pit, found by Zanko and Severson in 1995, no definitive records Ni, 1.21% S; below that hole is not mineralized for hundreds of available. feet; head grade of bulk sample was 0.39% Cu, 0.14% Ni, 0.50% S 300 tons Surface pit near drill hole 26105. Intended to intercept mineralization seen Expected grade based on ddh 26105 was 0.77% Cu, 0.28% in that hole. Material contaminated with hornfels, poor grade. Ni(?), 1.23% S; head grade of sample was 0.40% Cu, 0.13% Ni, 0.97% S 20 tons Surface pit near drill hole 26105. Re-entry of Bulk No 2 site to get material Expected grade based on ddh 26105 was 0.77% Cu, 0.28% not contaminated with hornfels Ni(?), 1.23% S; head grade of sample was 0.58% Cu, 0.22% Ni, 0.98% S 2 large diameter core PolyMet report states they have no records for this work, other than that it No data holes was done in 1991. Two large diameter holes and two smaller twins for submission to state. Nerco holes twin two existing USS drill holes. At least 37 tons Reverse circulation drilling composite from about 55(?) reverse circulation Head grade in 1999 SME/AIME presentation is 0.43% Cu, shipped to testing holes. Data not available on how many or which holes constituted the bulk 0.12% Ni, PolyMet has not published sulfur numbers. laboratory sample. Surface pit, sample sent to CMRL for process testing Surface pit, sample sent to CMRL for process testing Drilled in about 400 ft. of drill USBM samples to test reduction processes on Fe-Ti ore; with goal of Water Hen Fe-Ti Water Hen drill holes SL-27 and SL- 1975 core producing saleable or processable titanium slag product. Work done in Oxide (OUI) 28 1985 Table 1. Major bulk samples of the Duluth Complex. 130 MDNR and NRRI files Study concluded that a high TiO2 product could be made, but that concentration that removes iron is important. High MgO content is not mentioned as a processing issue Communication w/Teck Cominco and NRRI files EAW approved June, 2003 NRRI files NRRI files NRRI files PolyMet January 2000 Prospectus PolyMet press releases and 2001 pre-feasibility study CMRL reports in 1990s on projects, but ore sources for individual projects uncertain CMRL reports in 1990s on projects, but ore sources for individual projects uncertain Nafziger and Elger, 1987, USBM report; drill hole desc. in Ross, 1985 �UNTESTED TARGETS IN THE DULUTH COMPLEX PATELKE, Richard, SEVERSON, Mark, and PETERSON, Dean, Natural Resource Research Institute, University of Minnesota Duluth, 5013 Miller Trunk Highway, Duluth Minnesota 55811, rpatelke@nrri.umn.edu, mseverso@nrri.umn.edu, and dpeters1@nrri.umn.edu Introduction There are at least four, presently sub-economic, large, copper-nickel +/-PGE deposits defined along the western and northwestern margins of the Duluth Complex, as well as many smaller prospects (more than ten?). Development has been slowed by metallurgical problems and the perception of permitting difficulty. Exploration for more of the large low-grade deposits would seem unneeded until some of the known ones are developed. We present a few exploration ideas for less studied areas of the Duluth and Beaver Bay Complexes (with profuse apologies to all who may also have mentioned these in the past). We hope to encourage a discussion about smaller, higher-grade, targets. All of the targets listed here point to the need for detailed field mapping and integration of geophysical data. Remember that five hundred million tons of rock forms a cube about 1,750 feet on a side, and that a viable deposit can be relatively small. The Schroeder-Forest Center crustal ridge target Regional aeromagnetics and gravity data indicate that the Duluth Complex occupies two deep “bowls”. The separation between these two deep zones is the Schroeder-Forest Center crustal ridge. In general, mapped surface geology does not carry across this basement ridge zone. The presence of inclusions of Archean supracrustal rocks could also indicate that the base of the Complex is closer to the surface in this area (Boerboom, 1994). The Wilder Lake intrusion strikes parallel to the ridge and dips northeastward, also indicating that there is a division in the Complex. So, if one applies a model based on what we see for the copper-nickel-PGE deposits, i.e., most economic mineralization is close to the basal contact, then determining the depth to the basal contact along the ridge could open up areas for future exploration if the footwall is found to be reasonably shallow. Also, this area would probably be a much different structural regime than we see at the western and northwestern margins of the Duluth Complex. Cloquet Lake layered series This area is grossly similar to the situation along the Schroeder-Forest Center crustal ridge or the western margin. A group of three holes, drilled near the edge of this funnel-shaped intrusion in 1982, went to the base of the intrusion and hit massive sulfide with magnetite. PGE values were low and no further drilling was done, but scattered thin intercepts (3 ft.?) of about 0.5% copper were seen within 250 ft. of the surface. In this case, the footwall was older Keweenawan intrusive rocks. PGE in oxide-rich, pegmatitic, and other rocks The highest average value in the Complex for combined Pt + Pd + Au are in oxide-rich rocks, particularly those at Birch Lake. Pegmatitic zones, massive sulfides, anorthositic rocks, and massive chlorite also return higher than average values. However, these five rock types represent a small percentage of the over 52,000 feet of sample in Severson and Hauck (2003) that record assays for all three metals (troctolitic rocks make up about three fourths of the Pt + Pd + Au assay footage). These five minor rock types are not often mineralized, but when they are, the mineralization is copper-rich. Could there be larger, near-surface zones of these anomalous rock types? So far, localized copper-rich, semi-massive sulfides (some with high PGE values) have been documented at Dunka Road, Dunka Pit, on trend with the Siphon Fault, and at Skibo. Oxide-bearing Ultramafic Intrusions (OUIs) While the Fe-Ti rich OUIs are not particularly rich in sulfides or PGE, and have not yet proved economic as sources of titanium, they are still viable targets for chromium and vanadium oxides. There is less than 1,000 feet of assaying for these oxides available for the Complex (Severson and Hauck, 2003; Patelke 2003). The 131 �OUIs are enigmatic: the alignments of large OUIs in the Western Margin and Partridge River intrusions would indicate a relation to large and as yet undefined faults. Similar fault-related OUI are present south of the Babbitt deposit. However, information from drill core gives no hint to the geometric nature of the root zones of the OUIs. As the OUI formed along fault zones, often late in the crystallization history of the various intrusions, they may mark zones with potentially vigorous hydrothermal activity that could have concentrated PGE. For example, drill hole SL-19A at the Water Hen OUI has a thin platinum and chrome-bearing horizon that has had no known follow up work for PGE, or chromium and vanadium. INCO records show extremely high copper and nickel values, with widely varying ratios, near the Skibo OUI; again with little follow up. Overall, the OUIs may be worthy of attention beyond being a source of titanium. Structural targets Two major scissor-like faults that lie perpendicular to the line of the basal contact near the Babbitt and Dunka Road deposits are relatively unexplored. The Siphon Fault begins in the former LTV pit and extends some distance into the Complex. The Grano Fault starts in the Peter Mitchell taconite pit, passes through the Serpentine deposit, and lies along the border between the Partridge River intrusion and the South Kawishiwi intrusion. The Grano Fault is inferred to be a vent that formed high-grade copper-PGE enriched massive sulfide at the Local Boy ore zone of the Babbitt deposit. Both of these large faults cross mapped W-NW to E-SE trending faults passing though the Dunka Road deposit and to the south of the Babbitt deposit. The intersection of these systems has not been well examined either by drilling or field mapping. These fault intersections could present two types of targets: 1) massive sulfide in locations where space opened during faulting, especially in the footwall (a Sudbury or Local Boy model); and 2) pathways for altering and /or mineralizing fluids to intersect particular geologic horizons (such as in the Birch Lake model or postulated for the top of Unit 1 in the Partridge River intrusion). Voisey’s Bay targets Peterson’s discussion of “feeder zone sulfide mineralization” in Miller et al., (2002), points to the possibility of such a target south of the Spruce Road area (a.k.a. the Highway One Corridor area). There, the potential conduit between the Bald Eagle intrusion and the South Kawishiwi intrusion is confined below a large raft or pillar of earlier formed anorthosite. Mapping of assay copper-nickel grade and ratios indicates that the highest grades in the area may be in a channel or vent area below this raft. References Boerboom, T.J., 1994, Archean crustal xenoliths in a Keweenawan hypabyssal sill, northeastern Minnesota. White was right!: Institute on lake Superior Geology, 40th Annual Meeting, Houghton Mich., Proceedings, v. 40, Program and Abstracts, pt. 1, p. 5-6. Miller, J.D., Jr., Green, J.C., Severson, M.J., Chandler, V.W., Peterson, D.M., and Wahl, T.E., 2002, Geology and Mineral Potential of the Duluth Complex and related rocks of northeastern Minnesota, Minnesota Geological Survey Report of Investigations 58, 207 p., one CD-ROM. Patelke, R.L., 2003, Exploration drill hole lithology, geologic unit, copper-nickel assay, and location database for the Keweenawan Duluth Complex, northeastern Minnesota: Natural Resources Research Institute, University of Minnesota Duluth, Tech. Report., NRRI/TR-2003/21, 97 pages, 1 CD-ROM. Severson, M.J., and Hauck, S.A., 2003, Platinum-group elements (PGEs) and platinum-group minerals (PGMs) in the Duluth Complex: Natural Resources Research Institute, University of Minnesota Duluth, Technical Report, NRRI/TR-2003/37, 296 pages, 1 CD-ROM. 132 �THE PROPOSED NATIONAL UNDERGROUND SCIENCE AND ENGINEERINGLABORATORY AT THE SOUDAN MINE, NORTHEASTERN MINNESOTA: A GEOLOGICAL SITE INVESTIGATION PETERSON, Dean M., Natural Resources Research Institute, Duluth, MN, dpeters1@nrri.umn.edu PATELKE, Richard L., Natural Resources Research Institute, Duluth, MN, patelke@nrri.umn.edu In 2000, the National Science Foundation (NSF) convened a committee chaired by Dr. John Bahcall, of Princeton University, to evaluate the scientific justification for a national facility for deep underground science. The committee's charge was to evaluate the potential physics research that could b completed by the next generation of solar neutrino, double beta decay, proton decay, dark matter, and related background-sensitive experiments. In addition, the committee considered the possible relevance of such a facility to other disciplines, including geoscience, microbiology, materials development and technology, and monitoring nuclear tests. NSF received the recommendations of the Bahcall Report titled “Underground Science” in 2001 (available online at http://www.sns.ias.edu/~jnb/Laboratory/science.pdf). One of the results of the NSF-sponsored workshop on Neutrinos and Subterranean Science in 2002 was the June 2003 publication “EarthLab, A Subterranean Laboratory and Observatory to Study Microbial Life, Fluid Flow, and Rock Deformation”. This publication sets a framework for geological research that could be undertaken in a deep underground setting, and is available online at http://www.earthlab.org. Three unsolicited proposals to fund (each ~ $275 million) the development of a National Underground Science and Engineering Laboratory (NUSEL) were submitted to NSF, and include the University of Washington's Homestake Mine site at Lead, South Dakota (http://mocha.phys.washington. edu/nusel/proposal.html), the University of Minnesota's Soudan Mine site in northeastern Minnesota (http://www.sudan.umn.edu/NUSEL/), and the University of California Irvine's Mt. San Jacinto site near Palm Springs, California (http://www.ps.uci.edu/~SJNUSL/). On May 28, 2003, a NSF site panel report on developing a NUSEL concluded that the Homestake Mine in South Dakota was the most favorable. In addition, the panel considered the Soudan Mine a possible back up site for NUSEL, and that the San Jacinto site is not a viable NUSEL candidate. The evaluation criteria of each of the sites were partitioned into two broad categories: (1) geological suitability; and (2) relative costs. Geological suitability issues for the Soudan Mine included the uncertainty of the geology and rock mass conditions at depth. On June 2, 2003, Barrick Mining Company, the owner of the Homestake Mine, turned off the pumps and began flooding the deep portions of the Homestake mine, which consequently jeopardizes most of the earth science initiatives outlined in EarthLab. On February 6, 2004, the NSF returned without prejudice all of the unsolicited NUSEL proposals, and will soon publish a three-stage request for new NUSEL proposals, which will include: Stage 1 - develop a preliminary plan of research activities requiring deep underground access, to aggregate the plans into science modules, and to define the physical requirements needed for each module; Stage 2 - fund grants for conceptual planning of infrastructure as related to each site; and Stage 3 - fund grants for technical designs for the underground infrastructure, detailed geological characterization and environmental permitting, and development of management plans. Between mid April and mid June of 2003, geologists from the Economic Geology Group of the Natural Resources Research Institute, University of Minnesota Duluth completed detailed geologic mapping around the proposed NUSEL site at the Soudan Mine, and wrote a detailed report describing the results of the study (Peterson and Patelke, 2003). The geological report, geological maps, and GIS data files generated as a result of this work are available online at http://www.nrri.umn.edu/egg/. This poster presents the three plates that accompany the geological site investigation report of the suitability of the Soudan Mine area for hosting a NUSEL. Based on this recent detailed field mapping and interpretation, the geological and structural setting of the Soudan Mine is perfectly suited for hosting a NUSEL. In addition, a Soudan Mine NUSEL contains all the requirements outlined in the EarthLab document. The report by 133 �Peterson and Patelke (2003) outlines the geological suitability of the area for a NUSEL and an integrated EarthLab. The five major themes addressed in this report include: Bedrock Geology - The Neo-Archean bedrock geology of the Soudan Mine area is divided into five major lithostratigraphic units. These units include the: (1) Fivemile Lake sequence, moderate to shallowwater bimodal volcanic rocks; (2) Central Basalt sequence, deep-water tholeiitic basalts; (3) Upper Sequence, Algoma-type iron formation, tuff, and epiclastic rocks; (4) intrusive rocks, felsic porphyries, granodiorite, diorite, gabbro, and lamprophyre; and (5) sheared rocks, distinct curvilinear zones of chloritesericite-ankerite-pyrite schists. Structural Geology - The field area is divided into four main structural domains that include: (1) the Murray shear zone; (2) the Mine Trend shear zone; (3) the Linking Zone; and (4) the Collapsed Hinge Zone. These domains appear to be internally structurally coherent, and are separated from each other either by areas of relatively undeformed rocks or discrete sheared boundaries. NUSEL Site Selection - The geological criteria deemed most important for NUSEL construction include: (1) definition of a competent rock mass for excavation of large caverns at depths of 1,450 m and 2,500 m; (2) minimizing the occurrence of major lithologic contacts that would be encountered during construction of shafts, drifts, and the helical decline; and (3) minimizing the occurrence of major structural features in the area proposed for construction of the helical decline. A large area in the competent pillowed basalts of the Central Basalt sequence appears to meet all of the criteria for construction of the helical decline, and large laboratories could probably be excavated out of a large, highly indurated dioritic sill. Compatibility with EarthLab - One of the main requirements for EarthLab is a very large, instrumented rock volume and access to great depths. At Soudan, the volume of rock that can be reasonably be accessed for EarthLab research in a Soudan Mine NUSEL is approximately 30 km3. The scientific themes of study proposed for EarthLab are: (1) microbial life at depth; (2) the hydrologic cycle; (3) rock fracture and fluid flow; (4) rock-water chemistry; (5) deep seismic studies; and (6) geophysical imaging. The compatibility of a Soudan Mine NUSEL with each of these themes is favorable. Although the conceptual design plans for the Soudan Mine NUSEL requires relatively high-cost new construction at depth, the pristine nature of this geological environment is highly desirable for EarthLab research. In addition, the close proximity of the Soudan Mine NUSEL to the four structural domains minimizes the cost of drilling and drifting into these structural settings for EarthLab research. Outstanding Geological Research Opportunities - The geological and structural setting of the rocks within and adjacent to the proposed Soudan Mine NUSEL provides a unique opportunity for advances in several areas of earth science. Ideas on outstanding research opportunities include: (1) the structural control of lode-gold mineralization; (2) the hydrothermal alteration of subaqueous volcanic rocks and associated massive sulfide copper-zinc mineralization; (3) the origin of massive hematite ore bodies within Algomatype iron-formation; (4) the genetic evolution and temporal development of a Neo-Archean volcanic arc; (5) the Neo-Archean tectonic architecture of the southern Laurentian margin; (6) the Pleistocene hydrogeology of the Superior Craton; and (7) the permeability of crystalline bedrock. References Peterson, D.M and Patelke, R.L., 2003, National Underground Science and Engineering Laboratory (NUSEL); Geological site investigation for the Soudan Mine, northeastern Minnesota: Natural Resources Research Institute, Technical Report NRRI/TR-2003/29, 97 p., 3 plates, 1 cd-rom. 134 �PETROTECTONIC EVOLUTION OF PALEOPROTEROZOIC GRANITIC ROCKS ACROSS THE CENTRAL PENOKEAN OROGEN, NORTHERN MI & WI PIERCEY, P., SCHNEIDER, D.A., Department of Geological Sciences, Ohio University, Athens, OH 45701 USA HOLM, D.H., Department of Geology, Kent State University, Kent, OH 44242 USA Recent U-Pb single-crystal zircon geochronology of Paleoproterozoic post-Penokean granitic rocks of northern Michigan and Wisconsin, historically interpreted as an "anorogenic suite," has revealed a distinct age trend: magmatic pulses apparently migrated southward from ca. 1800 to 1750 Ma, after cessation of Penokean orogenesis (Holm et al., 2004; figure1). Yavapai-aged subduction slab rollback has recently been hypothesized to explain this magmatic pattern. In this model, the subducting slab steepens, and while depth of melting remains static, the locus of melting migrates trenchward (figure 2). Granitoid bodies intrude the Archean gneissic basement, Proterozoic metasedimentary marginal sequences, and an accreted juvenile arc (the Wisconsin Magmatic Terrane) across the breadth of the orogen. Nine samples from eight localities (the Radisson granite was sampled twice due to significant differences in mineralogy) were analyzed petrologically and geochemically, using major-, trace-, and rare-earth element analysis, to discriminate the tectonic setting into which emplacement occurred. Petrologic analysis shows a grain size decrease to the east. Major-element classification (K2O vs. SiO2) indicates a calcalkaline to shoshonite trend for all localities sampled, indicating subduction-related genesis. Nevertheless, trace element tectonic discrimination diagrams after Pearce et al. (1984) indicate a correlation to the local lithology rather than tectonic setting. That is, Humboldt and Montello granites, which intrude Archean gneissic basement, are classified as within-plate granite (WPG); Park Falls syenite, intruding Proterozoic metasedimentary sequences, is categorized as a collisional granite (COLG); and the remaining granites (Radisson, Lugerville, Jennings, Amberg, and Chequamegon) that intrude the accreted arc of the Wisconsin Magmatic Terrane are classed as volcanic arc granites (VAG). For this reason, caution must be exercised in using this technique, especially on single localities. A rare-earth element spidergram, normalized to chondritic values, shows the COLG as the most evolved and WPG as the least, highlighting relative continental crust evolution/component. In this study, the geochemical analyses did not illustrate an age or geographical trend as expected, but rather a correlation of source area and/or relative crustal contribution. Therefore, the suite is interpreted as products of subduction-induced melting across a variable source terrane. References: Holm, D.K., Van Schmus, W.R., MacNeill, L.C., Boerboom, T.J., Schweitzer, D. and Schneider, D.A., 2004, U-Pb zircon geochronology of Paleoproterozoic plutons from the northern midcontinent, U.S.A.: evidence for subduction flip and continued convergence after Geon 18 Penokean orogenesis: Geological Society of America Bulletin, in press. Pearce, J.A., Harris, N.B.W., Tindle, A.G., 1984, Trace Element Discrimination Diagrams for the Tectonic Interpretation of Granitic Rocks: Journal of Petrology, 25, 956983. 135 �136 �BLOWING IN THE WIND: THE COPPER HARBOR STROMATOLITES REVISITED PLANAVSKY*, Noah, and BJORNERUD, Marcia, Geology Department, Lawrence University, Appleton WI 54912 The Copper Harbor Conglomerate is the basal unit of the sediment-dominated upper part of the Keweenawan series. This sedimentary sequence was deposited within the central basin of the Mid-Continent Rift System beginning at approximately 1087 Ma. The coarse grain size, rounded clast shapes, low clay content, large trough cross bed sets, channel structures and ripple marks observed in the conglomerate are best explained by a prograding alluvial fan complex in an arid environment with rugged topography (Daniels, 1982). Locally, the conglomerate is matrixsupported, indicating that debris flows also contributed to its formation. The clasts within the conglomerate appear to have been derived exclusively from the underlying volcanic flows of the rift, suggesting that the basin was only a relative low within a topographically elevated region – probably a thermally supported high similar to the modern East African rift. All sedimentary features of the Copper Harbor Conglomerate point to a nonmarine depositional setting. In the upper part of the Copper Harbor Conglomerate, thin, discontinuous clayey layers with dessication cracks are interbedded with the coarse and thick conglomerate strata, suggesting that ephemeral playa lakes existed within the basin. Some of the lacustrine deposits contain finely laminated, hemispherical, calcareous stromatolitic structures. In many cases these structures drape around the upper surfaces of large boulders that are partly enclosed by clayey sediment. The external shape and fine internal layering of the hemispheroids as well as the presence of detrital sand grains on their inclined sides (indicating organic stabilization) all suggest that they are true biogenic stromatolites (Elmore, 1983). That is, the Copper Harbor stromatolites appear to record a terrestrial microbial community that established itself far above sea level in middle Proterozoic time. Most modern microbial lithifying mats are complex symbiotic communities of more than one genus (Stal, 2000), although there are modern freshwater stromatolites formed exclusively by cyanobacterial activity (Eggleston and Dean, 1976). The current paradigm is that the mucilaginous sheath excreted by cyanobacteria is essential for formation and lithification of the stromatolite structure. Whether the Copper Harbor stromatolites represent multi-genus communities or simple cyanobacterial mats, it is interesting to consider how the microbes might have found their way into a high, dry basin that had previously been the filled with ponded basaltic lavas. Most modern and fossil stromatolites occur in near-shore marine settings, and migrate over time via aqueous fragmentation or microbial mat bifurcation. The Copper Harbor Basin, however, was clearly high and isolated. The nearest continental margin is thought to have lain some 800 km away, beyond the Grenville front (Ojakangas et al., 2001). Paleocurrent directions and the absence of extrabasinal clasts in the conglomerate, furthermore, exclude the possibility of fluvial transport from another terrestrial community. We suggest, therefore, that the basin was colonized through akinete anemochory, or wind transport of dormant reproductive structures. Colonization by this means is consistent with the inferred wind patterns of the time. Localized aeolian dune deposits within the Copper Harbor 137 �conglomerate indicate paleo-wind directions that were orthogonal to fluvial paleocurrent directions, blowing from the southeast (in paleogeographic coordinates), the azimuth of the Grenville coast. This is consistent with the inferred paleolatitude of 20° N, which would have placed the Copper Harbor basin in a paleo-trade wind region (Taylor and Middleton, 1990), with prevailing winds blowing from the Grenville coast toward the Lake Superior region. Long distance aeolian transport of akinete structures is physically plausible. Cyanobacterial akinetes are on the order of 10µm in diameter (Lang and Whitton, 1973), and several recent studies have documented regional and even transoceanic transport of fine sediment (Prospero, 1999), spores (Josefsson, 2002) and pollen grains (Rogers and Levetin, 1998) of similar size. The stromatolites of the Copper Harbor Conglomerate are among the few known records of Proterozoic terrestrial biological communities, and they provide a glimpse of the early stages of colonization of a barren landscape. Aeolian dissemination of microbes and nutrients may have been an important mechanism of dispersal in the Precambrian biosphere. References: Daniels, P. A., Jr., 1982. Proterozoic sedimentary rocks: Oronto Group, Michigan- Wisconsin, in Wold, R.J., and Hinze W.J., eds., Geology and Tectonics of the Lake Superior Basin, GSA Memoir 156, 107-133. Elmore, R.D., 1983. Precambrian non-marine stromatolites in alluvial fan deposits, the Copper Harbor Conglomerate, Upper Michigan. Sedimentology, 30, 829-842. Eggleston, J.R. and Dean, W.E., 1976. Freshwater stromatolitic bioherms in Green Lake, New York. In Walter, M.R., ed., Stromatolites. Developments in Sedimentology, 20, Elsevier, Amsterdam, 479-488. Josefsson, H., 2002. Long Distance Dispersal in Wood Decaying Basidiomycetes (MS Thesis}: University of Umeå University, Umeå, Sweden. Lang, N.J. and Whitton B.A. 1973. Arrangement and structure of thylakoids. In Carr, N.G. and Whitton, B.A., eds., The Biology of Blue Green Algae. University of California Press: Berkeley, 66-79. Ojakangas, R., Morey, G.B., and Green, J.C., 2001. The Mesoproterozoic Mid-continent Rift System, Lake Superior region, USA. Sedimentary Geology, 141-142, 421-442. Prospero, J. 1999. Long range transport of mineral dust in the global atmosphere: Impacts of African dust on the environment of the Southeastern United States. Proceedings of the. National Academy of Sciences, 96, 3396-3403. Rogers, C.A. and Levetin, E.1998. Evidence of long distance transport of mountain cedar pollen into Tulsa, Oklahoma. International Journal of Biometeorology, 42, 65-72. Stal, L.J., 2000 Cyanobacterial mats and stromatolites, in Whitton, B.A., ed., Ecology of Cyanobacteria. Kluwer Academic, Dordrecht, 61-120. Taylor, I. and Middleton, G., 1990. Aeolian sandstones in the Copper Harbor Fm., late Proterozoic, Lake Superior basin, Canadian Journal of Earth Sciences, 27, 1339-47. 138 �A Geochemical Study of the Sills of the Nipigon Basin, Ontario RICHARDSON*, A., and HOLLINGS, P., Department of Geology, Lakehead University, 955 Oliver Rd., Thunder Bay, Ontario, P7B 5E1, Canada; ajrichar@lakeheadu.ca Introduction and Background The Nipigon Sills are a relatively flat-lying Proterozoic tholeiitic diabase sequence associated with the Keweenawan midcontinent rift (MCR) event centered on the Lake Superior region. The MCR was active 5540000N approximately 1100 My ago with published U-Pb zircon ages of 1108.8 +4/-2 Ma, and 1097.6 ±3.7 Ma from the Nipigon Sills and Osler volcanics respectively (Davis and Lake Sutcliffe, 1985). These sills are up to 200 5510000N Nipigon metres in thickness and dominate the geology of the Lake Nipigon basin. The sills currently cover an area of approximately 11 000 km2 representing a minimum volume of 10 000 km3 (Fig. 1; Sutcliffe, 1986). 5480000N Although related to the Logan sills found further south in the Thunder Bay area, they differ in rare earth geochemistry, mineralogy, and paleomagnetic character. First noted by Sir William Logan in a report to the crown in 5450000N 1863, the region was not mapped in detail until the first decade of the twentieth century Legend by Andrew Wilson, whose report in 1910 Nipigon Sill Metavolcanic Drill Hole Collar Scale N included an accurate representation of the Sibley Sediments Granitic Sample 0 20 Km English Bay sills, in addition to Archean geology and Metasediment 1537 +10/-2 Ma (Davis & Sutcliffe, 1985) limited geology of the Sibley Group Figure 1. Regional Geology with sample sediments. Wilson’s report brought to light locations the question of whether the sills represent an extrusive flood basalt sequence or a hypabyssal intrusive unit. The lack of extrusive characteristics (pillows, ropy flow tops, vesicles, etc.) as well as a billion years of erosion makes interpretation based on direct observation difficult. 6 7 10 11 4 15 3 18 1 19 22 24 25 167 149 62 160 119 120 42 124 63 70 89 35 134 90 92 85 31 77 97 69 10 Project This research is funded as part of the Lake Nipigon Regional Geoscience Initiative (LNRGI) in order to further the understanding of the Lake Nipigon region and promote mineral exploration and development through a public/private sector partnership. The aim of this study is to develop a model of sill emplacement using detailed whole rock and isotope geochemical data, as well as petrographic work and mineral chemistry, to develop a formational model for the sills. 139 �Preliminary Results Of the 170 outcrop samples and 530 diamond drill hole (DDH) samples collected in 2003 (Fig. 1), 80 have been analyzed using XRF, ICP-AES, and ICP-MS methods. Preliminary results point to the sills being a remarkably uniform sequence of olivine basalt with a pronounced negative Nb anomaly, 100 LREE enrichment and slightly fractionated HREE (Fig. 2, grey) with La/Smcn and Gd/Ybcn ratios for normal sill averaging 1.74 and 1.40 respectively. A geochemically distinct sill with Gd/Ybcn and La/Smcn 10 ratios of 3.64 and 13.3 respectively was found in the top of drill holes DDH3 and DDH5. This distinct signature was also observed in the basal unit of drill hole SW08-5 1 Th Nb La Ce Pr Nd Zr Hf Sm Eu Ti Gd Tb Dy Y Ho Er Tm Yb Lu Sc of the ultramafic portion of the Seagull intrusion. A Figure 2. REE profiles of three sill types. Type 1 (black), Type 2 third distinct sill, identified in (grey), Type 3 (dashed) two outcrop samples along the southern shore of Lake Nipigon was found to have La/Smcn, and Gd/Ybcn ratios of 6.46 and 1.89 respectively. Though petrographically indistinguishable, this geochemistry indicates that there were at least three magma sources for the sill complex, of which all possess a significant Nb anomaly indicative of crustal contamination References Davis, D.W., Sutcliffe, R.H. (1985) U-Pub ages from the Nipigon plate and northern Lake Superior. Geological Society of America Bulletin, v. 96, p.1572-1579. Heggie, G., Hollings, P. (2003) Lake Nipigon Region Geoscience Initiative. Petrology and Mineral Chemistry of the Seagull Intrusion. In: Summary of Fieldwork and other Activities 2003, Ontario Geological Survey, Open File Report 6120, p. 48-1 to 48-5. Sutcliffe, R.H (1986) The Petrology, Mineral Chemistry and Tectonics of Proterozoic Rift-Related Igneous Rocks at Lake Nipigon, Ontario. Unpublished PhD thesis, University of Western Ontario, Ontario. 253p. Wilson, A (1910) Geology of the Nipigon Basin, Ontario. Canada Department of Mines Geological Survey Branch Memoir No.1. 152p. 140 �THE GEOLOGY OF THE EAGLE NICKEL-COPPER DEPOSIT: MARQUETTE COUNTY, MICHIGAN ROSSELL, D.M., dean.rossell@kennecott.com, Kennecott Exploration Company, 10861 N. Mavinee Dr. #141, Oro Valley, AZ. 85737 COOMBES, S., Kennecott Canada Exploration Inc., #354-200 Granville Street, Vancouver, B.C. V6C 1S4 Kennecott’s discovery of the Eagle nickel-copper deposit in 2002 marked the culmination of more than a decade of exploration work by Kennecott in the Baraga Paleoproterozoic sedimentary basin. The discovery hole, YD02-02 completed in July 2002, intersected 84.2m of massive sulfide mineralization averaging 6.3% Ni and 4.0% Cu. The resource estimate for the Eagle deposit at the end of 2003 was 5 million tonnes at 3.68% Ni, 3.06% Cu and 0.1% Co. The Eagle deposit is hosted in the westernmost of two small peridotite bodies historically referred to as the Yellow Dog Peridotite. The Yellow Dog intrusions, which lack penetrative foliations and truncate Penokean tectonic fabrics in the surrounding meta-sediments, are believed to be Keweenawan in age (Klasner, et. al., 1979). The intrusions are mainly comprised of coarsegrained, variably serpentinized peridotite and feldspathic peridotite. A fine-grained, olivine poor phase is found along the margins of the intrusions and as xenoliths within the peridotite. Possible amygdules in the olivine poor phase(s) suggest a shallow level of intrusion. Three principal types of sulfide mineralization are recognized in the Eagle deposit: disseminated (blebby), semi-massive (matrix) and massive. Although the nickel contents of massive sulfides are relatively uniform throughout the deposit, copper contents vary significantly. Platinum group metals (PGM) and gold values are significantly higher in the copper rich massive sulfides. Copper rich veins and disseminations, with significant PGM and gold, in the surrounding meta-sediments may constitute a fourth type of ore. Massive and semi-massive sulfide ore types in the Eagle deposit are irregularly distributed. The contacts between different ore types are sharp and show little evidence of the gradation that might be expected if gravity driven accumulation of sulfides from an overlying, sulfide saturated, silicate magma was the principle mechanism of ore formation. Sequential emplacement of various mixtures of silicate and sulfide magma and cumulus minerals, derived from a lower stratified magma chamber, may provide a better model. Klasner, J.S., Snider, D.W., Cannon, W.F., and Slack, J.F., 1979. The Yellow Dog Peridotite and a possible buried igneous complex of lower Keweenawan age in the northern peninsula of Michigan. Geologic Survey of Michigan DNR report of investigation 24, 31 pp. 141 �Geologic Reconnaissance of the Spaulding Mine Area, Cook County, Minnesota RUHANEN, Richard W., 1746 Janet Park Dr. Hibbing, MN 55746 The Spaulding “mine” consists of a series of exploration pits, shafts and trenches constructed on a fissure vein at the east end of Spaulding Lake in northeastern Cook County, MN. William P. Spaulding prospected this area during the late 19th century, from about 1875 until the summer of 1897, with the target being silver mineralization. Silver was being mined in Ontario during this time at the Rabbit Mountain and Silver Mountain areas just 20 miles to the northeast in veins of a similar nature, as well as at Silver Islet near the Sibley Peninsula on the shore of Lake Superior. The Spaulding Lake area is remote, accessible only by canoe, and consists of east-striking hills and ridges with predominantly north-facing cliffs. Porphyritic diabase sills cap the hills and ridges while the low lands are occupied by lakes and swamps underlain by Rove formation sediments. The rocks dip 12 – 16 degrees to the south. Spaulding’s work exposed an east-striking vein on the south side of Spaulding Lake at the base of a north-facing cliff of Rove formation capped by a sill. The vein consists of a breccia of angular, porphyritic sill and Rove formation fragments cemented by quartz, calcite and perhaps barite. Vugs lined with drusy quartz crystals are common. Sparse pyrite is the only mineralization seen, no silver or other sulfide minerals have been observed. Dump piles near the pits and shafts consist almost entirely of this breccia vein material. During October 2003, two traverses were made by the author on the north shore of Crystal Lake 1 and 2 miles, respectively, to the west of the exposed vein. Rocks noted are porphyritic sill(s), granophyre, small basaltic dike-like bodies, and hornfelsed to partially melted blocks of Rove sediments. At each traverse location, a north-south fracture forms a 1 to 2 foot scarp facing west. Gabbroic rocks of the Duluth Complex crop out ¼ mile to the south, forming a low ridge on the southwest shore of Crystal Lake. Inclusions of Rove formation are common in the sills and in the Duluth Complex rocks. At the Spaulding “mine” location, the sill – Rove formation contact rises in elevation to the east while curving towards the south. The exploration pits were sunk along depressions thought at the time to be ancient mining features created by copper culture peoples. At the shaft, the last excavation on the vein to the east, the breccia consists entirely of Rove formation. On one dump pile near the eastern extent of the working, granophyre with quartz-filled fractures was found, indicating that granophyre occurs at some depth beneath the sill. The vein disappears under glacial drift to the east of the main shaft. At the southwest end of Spaulding Lake, an east-west striking zone of fault gouge cuts a sill of porphyritic diabase, indicating that the vein structure may continue further west of the Spaulding workings. 142 �OCEAN-FLOOR-TYPE-ALTERATION OF DRILLED MRS VOLCANIC ROCKS IN IOWA SCHMIDT, Susanne Th., Département de Minéralogie, Rue des Maraîchers 13, CH1205 Genève, Switzerland, susanne.schmidt@terre.unige.ch SEIFERT, Karl, Department of Geological & Atmospheric Sciences, Iowa State University, Ames, IA 50011, kseifert@iastate.edu In the Thor Group of the buried Midcontinent Rift System of Iowa well cuttings and cores of basalts and diabases were studied from five sites to determine the alteration pattern within a subsurface zone of 250 x 50 km (Fig. 1). The metamorphic assemblage, metamorphic grade, bulk rock composition and the chemical composition of the metamorphic minerals such as actinolite, pumpellyite, epidote, and chlorite, were determined. Equilibrium phase diagrams were calculated using the DOMINO-Theriak Software. At sites 3 and 5 the metamorphic assemblage is similar and contains the minerals pumpellyiteactinolite-chlorite (Mg-rich)-albite. However, at site 3 this assemblages is restricted to a thin alteration band along a vein and the rock is unaltered away from the vein, whereas at site 5 the rock is almost totally altered and relicts of the primary magmatic minerals, such as clinopyroxene or Ca-rich feldspar, are rarely observed in thin section. At site 4 the assemblage pumpellyitealbite-chlorite is present in a diabase. For site 2 chlorite and epidote were determined. Chlorites are present at all sites showing a wide range of composition (Fig. 2). Chlorite is Mg-rich in less altered units and Fe-rich in strongly altered units. Cross cutting relationships between these minerals imply the later formation of Fe-chlorites. The observed pattern points to greenschistfacies conditions in site 3 and 5 and probably higher temperatures at sites 2 and 1 (epidote-chlorite assemblage). The fact that alteration is focused along veins such as observed at site 3 indicates that infiltration of a fluid at elevated temperatures occurred at some stage of the alteration. For the assemblage amphibole-chlorite-albite-epidote in the pervasively altered diabase of site 5, an equilibrium diagram was calculated using the DOMINO-THERIAK Software (de Capitani. 1994). It restricts the assemblage to a temperature interval between 210 to 260 °C and a pressure of up to 3 kbar. The presence of pumpellyite in another sample of the same site and its upper temperature stability limit of ca. 250 °C at 3 kbar (Potel et al., 2002) are in agreement with the calculated P-T field. References Seifert, K.E. & Anderson, R.E. (1996) Geochemistry of buried Midcontinent Rift Volcanic rocks in Iowa, Data from well samples. Jour. Iowa Acad. Sci. 103, 63-73. De Capitani, C. (1994) Gleichgewichtsphasendiagramme: Theorie und Software: Beihefte zum European Journal of Mineralogy, v. 72. Jahestagung der Deutschen Mineralogischen Gesellschaft, p. 48. 143 �Potel, S., Schmidt, S.Th. & de Capitani, C. (2002) Composition of pumpellyite, epidote and chlorite from New Caledonia – How important are metamorphic grade and whole rock composition? Schweiz. Miner. Petrograph. Mitt. 82, 229-252 Fig. 1 Location of drill sites in the buried MCR in Iowa (after Seifert & Anderson, 1996) Fig. 2 Composition of chlorite in the Thor group 144 �Depth Migration of Seismic Reflection Data: An Example for Lake Superior Studies SCHNEIDER, Robert V., Energy Institute, University of Louisiana at Lafayette, P.O. Box 43612, Lafayette, LA 70504-3612, USA 2-D reflection seismic profiling is a useful geophysical tool for understanding geologic structures in the Earth’s subsurface. For example, it is the primary tool of choice in hydrocarbon exploration on a worldwide basis. A seismic section, under the right circumstances, can provide an accurate picture of geologic formations. The main differences between seismic and geologic sections are: 1) Seismic data are recorded and displayed in time, not depth; 2) Seismic reflections are caused primarily by velocity changes, which may (or may not) be coincident with geologic boundaries. A key process in preparing a seismic data set for interpretation is application of a concept called migration. This step moves seismic amplitudes from where they are recorded (i.e. at the receiver) to where the reflection actually occurs in the geologic section (Gray et al., 2001). Because seismic data are recorded in time, this requires an accurate understanding of the velocities in the subsurface, which carries the seismic wave field. Seismic time processing, however, depends on several assumptions to simplify complexities in seismic wave theory. Of fundamental importance is the presence of a horizontally smoothly varying velocity field. Where this assumption is violated, the resulting seismic profile is degraded below the velocity change. In other words, structures displayed in such sections are misplaced both horizontally and vertically. In extreme cases, even the edges of bodies with significantly different velocities than the surrounding country rock are difficult to image (Larner et al., 1989). Near-surface velocity changes, especially in marine acquisition, are relatively rare examples of this problem. Where they occur, the subsurface image may be degraded even after the application of time migration. An example is found at the Florida Escarpment in the eastern Gulf of Mexico (Figure 1a). Here the steep slope of the ocean bottom, which approaches 45◦ over a 2000m interval, creates a lateral step change in velocity from water to a rock column. To minimize the effects of this problem, careful velocity analysis must be performed in depth (Schneider et al., 2000). The resulting velocity model was used to migrate the seismic data, which were recorded in time, and to output an image in depth (Figure 1b). The depth of the water bottom of Lake Superior varies over short horizontal distances (Figure 2). This similarity to the Florida Escarpment indicates that a reflection profile acquired over portions of the lake may suffer similar effects. Resulting interpretations may therefore be error-prone. Experience suggests that careful velocity modeling in depth followed by depth migration will be required to maximize our understanding of crustal structure in this region. 145 �a b Figure 1. (a) Example of seismic mis-imaging due to time processing across the abrupt Florida Escarpment velocity change. (b) Depth migrated data showing improvement in the image of the water bottom and the subsurface image (data courtesy of TGS-NOPEC). Figure 2. Bathymetric profile showing rapid variation in depth in Lake Superior (Natural Resources Research Institute, 1998). Gray, S. H., Etgen, J., Dellinger, J, and Whitmore, D., 2001, Seismic migration problems and solutions: Geophysics, 66, 1622-1640. Larner, K., Beasley, C. J., and Lynn, W., 1989, In quest of the flank: Geophysics, 54, 701-717. Natural Resources Research Institute, 1998, Lake Superior Bathymetry Map, http://oden.nrri.umn.edu/lsgis/bathy.htm, accessed April 9, 2004. Schneider, R. V., Gordon, M. K., Sempere, J., Willacy, C., Hightower, S., and Scholz, S.F., 2000, Prestack depth imaging in the eastern Gulf of Mexico: The Leading Edge, 19, 1340-1343. 146 �WHATEVER HAPPENED TO THOSE Cu-Ni DEPOSITS? SEVERSON, Mark J., and HAUCK, Steven A., Natural Resources Research Institute, University of Minnesota Duluth Large resources of low-grade copper-nickel sulfide ore that locally contain anomalous Platinum Group Element (PGE) concentrations are well documented by drilling in the basal zones of the Partridge River and South Kawishiwi intrusions. At least nine subeconomic deposits have been delineated in the basal 100 to 300 meters of both intrusions. The mineralization consists predominantly of disseminated sulfides that collectively constitute over 4.4 billion tons of material averaging 0.66% Cu and 0.20% Ni (Listerud and Meineke, 1977). Serious exploration for Cu-Ni deposits at the base of the Duluth Complex (Complex) began about 13 km (8 miles) to the southeast of Ely, MN, in 1948, when strongly mineralized rocks were uncovered in an excavation used to build a forest service road (Spruce Road). Local prospector Fred S. Childers of Ely noted copper stains in the material and he, along with Roger V. Whiteside of Duluth, began searching along the basal contact in the vicinity of the Kawishiwi River. In 1951, they diamond drilled a 57 meter (188 feet) deep hole and intersected mineralized gabbro that averaged 0.36% Cu and 0.13% Ni. In 1952, both Bear Creek Mining Company (BMC) and the International Nickel Company (INCO) began intensive exploration efforts along a 61 km-long zone (38 miles) that coincided with the basal contact. INCO eventually picked up the Childers-Whiteside properties (Spruce Road and Maturi deposits); whereas, BMC concentrated most of their effort near the town of Babbitt (Babbitt and Serpentine deposits). By 1960, these exploration efforts indicated that large tonnages of disseminated Cu-Ni deposits were present along the basal contact. However, the low-grade nature of the deposits and the unavailability of state-owned mineral lands led to suspension of activities. In 1966, state mineral leases were offered by the Minnesota Department of Natural Resources (DNR) and were awarded to successful bidders. Since 1966, over 20 companies have been actively involved in exploration for Cu-Ni and Fe-Ti-V deposits along the basal contact of the Complex and over 1,700 holes totaling over 1.5 million feet of core have been drilled. During the early 1970s, the Spruce Road and Babbitt deposits came the closest to development. Mining plans were submitted, test shafts were sunk (one each at the Maturi and Babbitt deposits), surface bulk samples were collected (3 deposits), and various landuse and water-use permits were requested from State and Federal agencies. Many of these activities drew strong opposition from environmental groups and some state legislators. In 1974, the Environmental Quality Board required that a regional Environmental Impact Statement (EIS) be conducted prior to acceptance of any site-specific EIS mining-related proposals. The DNR discontinued lease sales of State lands (1974-1982) until completion of the regional EIS. However, by the time the regional EIS was submitted in 1979, development of the Cu-Ni deposits was put on hold by the mining industry due to weakened copper and nickel markets, smelter-related problems with cubanite in the copper concentrate, and other financial reasons. Enter the “PGE era.” During the early period of drilling (prior to 1980), all of the exploration companies recognized that the Cu-Ni deposits had some potential for hosting PGEs. Based on very limited sampling, the companies assumed that the typical Cu-Ni ore contained no more that a few hundred parts per billion (ppb) combined platinum and palladium. In 1985, the DNR and Minerals Resource Research Center (MRRC of the U of M) conducted a geochemical evaluation of portions of drill hole Du-15, from the Birch Lake area, and found significant values of 9 parts per million (ppm) combined Pt and Pd (Sabelin and Iwasaki, 1986). A short time later, Morton and Hauck (1987) compiled all of the known PGE data for the Complex and reported the presence of anomalous PGE values, often associated with high Cu values, at several other Cu-Ni deposits. These discoveries sparked renewed interest in the Cu-Ni deposits as potential polymetallic deposits (Miller et al., 2002; and references therein). Additional drill holes were sampled and 147 �analyzed for PGEs throughout the Duluth Complex, and as a result, significant PGEs were found at several more deposits. Some of the PGE-enriched zones were found to be “stratabound” in that they are correlative with certain units of the igneous stratigraphy as determined by Severson and Hauck (1990), for the Partridge River intrusion, and Severson (1994), for the South Kawishiwi intrusion. Still other PGE-enriched zones were found to be related to either localized structural conditions (Local Boy massive sulfide zone of the Babbitt deposit; Severson and Barnes, 1991) and/or combinations of stratigraphy and structure (Birch Lake). For example, four stratabound horizons, each containing generally 1.0 ppm Pd, have been documented at the Dunka Road deposit (Geerts, 1991) and appear to be related to magma mixing. A single stratabound PGE-enriched horizon is present at the Birch Lake PGE prospect and also appears to be related to magma mixing (albeit, the PGE-mineralization is also related to variably digested iron-formation inclusions). However, the PGE-horizon at Birch Lake is quite variable (thickness and PGE contents) and cases can also be made that favor a late hydrothermal origin and redistribution of PGE along a fault zone or an early magmatic origin based on proximity to a feeder zone along the same fault. At present, close proximity to a vent, along with local magma mixing, appears to have been the major factor in controlling the PGE tenor in the above cases (Hauck et al., in prep). Localized modification of the PGE content by a later hydrothermal event, while not ruled out, appears to have been of lesser importance. Enter the “hydromet era.” In the mid to late 1990s, the potential of developing the Cu-Ni deposits using hydrometallurgical techniques has once again sparked renewed interest in the Duluth Complex. PolyMet Mining Corporation has acquired the Dunka Road deposit (NorthMet deposit) and plans to use its patented PlatSol technique to recover Cu, Ni, Co, and PGE. Teck Cominco has leased the Babbitt deposit (Mesaba deposit) and plans to use its patented CESL (Cominco Engineering Services Laboratory) process to recover the same metals. If it can be proven that these processes are feasible and economical, the next phase (the “permitting era”) in developing the low-grade Cu-Ni deposits of Minnesota could begin in the near future. The “permitting era” is anticipated to span at least a 2.5-3.0-year interval wherein an Environmental Assessment Worksheet (EAW), EIS, and applications for eight mining-related permits would be submitted. References: Geerts, S.G., 1991, Geology, stratigraphy, and mineralization of the Dunka Road Cu-Ni prospect, northeastern Minnesota: Natural Resources Research Institute, University of Minnesota Duluth, Technical Report NRRI/TR-91-14, 63 p. Listerud, W.H., and Meineke, D.G., 1977, Mineral resources of a portion of the Duluth Complex and adjacent rocks in St. Louis and Lake Counties, northeastern Minnesota: Minnesota Department of Natural Resources, Hibbing, MN, Division of Minerals Report 93, 74 p. Morton, P., and Hauck, S.A., 1987, PGE, Au, and Ag contents of Cu-Ni sulfides found at the base of the Duluth Complex, northeastern Minnesota: Natural Resources Research Institute, University of Minnesota Duluth, Technical Report NRRI/GMIN-TR-87-04, 81 p. Miller, J.M., Jr., Green, J.C., Severson, M.J., Chandler, V.W., Hauck, S.A., and Peterson, D.M., 2002, Geology and mineral potential of the Duluth Complex and related rocks of northeastern Minnesota: Minnesota Geological Survey Report of Investigations 58, 207 p. Sabelin, T., and Iwasaki, I., 1986, Evaluation of platinum group metal occurrence in Duval 15 drill core from the Duluth Complex: Internal report, Minerals Resource Research Center, University of Minnesota, Minneapolis, MN, 23 p. 148 �Hydrogen Stable Isotopic Evidence for Hydrothermal Alteration and PGE Concentration Involving Meteoric Water in the Birch Lake Area, Duluth Complex, MN SHAFER, Paula L., and RIPLEY, Edward M., Department of Geological Sciences, Indiana University, Bloomington, IN 47405 The Birch Lake prospect, located along the western margin of the 1.1 Ga Duluth Complex, contains local concentrations of platinum group elements (PGEs) of up to 8 ppm. Footwall rocks in the area are the Early Proterozoic Biwabik Iron Formation and the Archean Giant's Range Batholith. Petrographic analyses indicate minor to extensive late stage alteration of the troctolitic sequence of the Duluth Complex in the Birch Lake area. Olivine has been converted to serpentine, plagioclase has been locally replaced by chlorite, albite and sericite, and pyroxene has been partially converted to a mixture of chlorite and amphibole. Previous studies, both mineralogic and isotopic, (Sabelin and Iwasaki, 1986, Sabelin, 1987, Marma, et al., 2002, Shafer and Ripley, 2002, and Shafer, et al., 2003) have noted that: 1) some, but not all, PGE mineralization is associated with Cr enrichment, 2) oxygen isotopic studies are not supportive of Biwabik Iron Formation assimilation as a major control on either Cr or PGE enrichment, and 3) Re-Os isotopic studies clearly indicate extensive involvement of crustally derived Os in the ore forming process. Due to the intensity of alteration in the Birch Lake area, hydrothermal fluid transport or concentration of PGEs has been proposed as a key factor in the enrichment process. Hydrogen isotopic studies (primarily involving serpentine and sericite) have been undertaken to accompany our previous isotopic measurements, and to aid in the assessment of the alteration process. δD values of serpentine (-87‰ to -96‰) and sericite (-79‰ to -84‰) are very similar to whole rock values found previously (-78‰ to -98‰). Assuming a temperature between ~200º and 350ºC for serpentinization (Allen and Seyfried, 2003), computed δD values for the water in equilibrium with serpentine and sericite range from -75‰ to -84‰. When compared to the average δD of fluid liberated from the Virginia Formation (-53‰), an origin from a metamorphic fluid is unlikely. Considering the suspected low temperature nature of the extensive alteration and low δ18O values of serpentinized oxide melatroctolites (2.35‰ to 3.39‰), a magmatic fluid is also considered unlikely. The δ18O value of water in equilibrium with serpentine at temperatures between 200º and 300ºC is in the range of -3‰ to 3‰. Although mixing between a magmatic fluid and a variously evolved meteoric water can not be ruled out (Fig. 1), we suggest that the geologic and isotopic data are more consistent with hydrothermal alteration involving a fluid of primarily meteoric origin. The water isotopic compositions could be attained via exchange with either igneous rocks of the Complex or with country rocks. The lack of evidence for widespread 18 O exchange in the country rocks suggests that fluid flow was dominantly via fractures, and that isotopic exchange occurred over long path lengths at low time-integrated water/rock ratios. This fluid has locally concentrated PGEs, possibly as a result of differential solubility and removal of previously present sulfide minerals. 149 �References 10 0 -10 -20 -30 -40 -50 -60 -70 -80 -90 W at e rL in e SMOW M et eo ric δ D(o/oo VSM OW ) Allen, Douglas E., and Seyfried Jr., W. E., 2003, Compositional controls on vent fluids from ultramafic hosted hydrothermal systems at mid-ocean ridges: An experimental study at 400ºC, 500 bars, Geochimica et Cosmochimica Acta, vol. 67, no. 8, p. 1531-1542. Marma, John C., Brown, Phil E., Hauck, Steve A., 2002, Magmatic and hydrothermal PGE mineralization of the Birch Lake Cu-Ni-PGE deposit of the South Kawishiwi Intrusion, Duluth Complex, Northeast MN, In: Geological Society of America, 2002 Annual Meeting: Abstracts with Programs, vol. 34, no. 6, p. 112. Sabelin, T., and Iwasaki, I., 1986, Evaluation of platinum group metal occurrence in Duval 15 drill core from the Duluth Complex: Minneapolis, Minerals Resources Research Center, University of Minnesota, Internal Report. Sabelin, T., 1987, Association of platinum deposits with chromium occurrences: An overview with Implications for the Duluth Complex, Skillings Mining Review, p. 4-7. Shafer, Paula L., and Ripley, Edward M., 2002, Stable isotopic studies of PGE mineralization in the Birch Lake area, South Kawishiwi Intrusion, Duluth Complex, MN, In: Geological Society of America, 2002 Annual Meeting: Abstracts with Programs, vol. 34, no. 6, p. 112. Shafer, Paula L., Ripley, Edward M., Li, Chusi, and Hauck, Steve A., 2003, Re-Os isotope Characteristics of PGE mineralization in the Birch Lake Area, South Kawishiwi Intrusion, Duluth Complex, MN, In: Geological Society of America, 2003 Annual Meeting: Abstracts with Programs, vol. 35, no. 6, p. 230. Magmatic Water Mafic igneous rocks H2O in equilibrium with serpentine mixing exchange -15 -10 -5 0 5 18 δ Ο (o/oo VSMOW) Figure 1. Isotopic values of water in equilibrium with serpentine in the Birch lake area, and potential mixing/exchange paths. 150 10 �SILVER THREADS AND GOLDEN NEEDLES: GEOLOGICAL MILESTONES IN NORTHWESTERN ONTARIO SMYK, Mark C., and MAGEE, Angelique, Ontario Geological Survey, Ministry of Northern Development and Mines, Suite B002, 435 James St. South, Thunder Bay, ON P7E 6S7 CANADA Northwestern Ontario has been the focus of much geological inquiry and noteworthy discoveries over the past 140 years, many of which put the region in a worldwide limelight and continue to attract research interest. Some of these geological milestones form the basis of this retrospective paper. Reconnaissance mapping and seminal works by pioneers such as Logan, Macfarlane, Bell, McKellar, Lawson and Wilson helped establish the fledgling Geological Survey of Canada in the mid- to late-19th and early 20th centuries and developed the basic framework of local Precambrian geology. The area was part of the first geologic map in Canada, Geology of Canada, in 1869. Earlier mineral discoveries in the lake Superior area, followed by the discovery of silver in the Thunder Bay District in 1868 at Silver Islet prompted not only detailed surveys of mineral deposits, but also the development of rudimentary mineral policy in Canada. Despite its short-lived (1870-1884) history, Silver Islet was host to a number of “firsts”, including the introduction of the Burleigh drill, the Frue Vanner and the first use in Canada of the diamond drill. The Thunder Bay silver district also attracted E.D. Ingall and Ontario Bureau of Mines geologists, including a young N.L. Bowen, who later attained international fame as an igneous petrologist and geochemist. Evidence of the oldest life in North America is found in the ca. 3.0 Ga stromatolites at Steep Rock Lake. The discovery by Lawson in 1911 of the pseudofossil Atikokania there, named and described by Walcott (1912), led to its hailing as the world’s oldest fossil. Despite the ensuing debate and the widespread ascription of Atikokania to inorganic processes, the region once again gained notoriety when Tyler and Barghoorn (1954) discovered the best-preserved and most diverse microfossil assemblage in North America in the Paleoproterozoic Gunflint Formation. At the time of their discovery, they were deemed the world’s oldest fossils, "the oldest structurally preserved organisms that clearly exhibit cellular differentiation and original carbon complexes which have yet been discovered in pre-Cambrian sediments". It was a benchmark, a monumental "first" in global paleontology. Several minerals’ type localities are found in northwestern Ontario. The discovery of the Hemlo gold deposit in the 1980’s near Marathon yielded criddleite (TlAg2Au3Sb10S10), vaughnite (TlHgSb4S7) and hemloite ((As,Sb)2(Ti,V,Fe,Al)12O23OH). Nisbite (NiSb2); and paracostibite (CoSbS) were discovered in drill core at Trout Bay, Mulcahy Township, in the Red Lake area. The secondary minerals romarchite (SnO) and hydroromarchite (Sn2+3O2(OH)2) were discovered on tin pannikins lost from a voyageur’s overturned canoe between 1801 and 1821, and found 4.5 m below the surface of the Winnipeg River at Boundary Falls, near Kenora. The discovery of these tin-bearing minerals is fittingly related to northwestern Ontario’s colourful history. REFERENCES Tyler, S.A. and Barghoorn, E.S. 1954. Occurrence of structurally preserved plants in Precambrian rocks of the Canadian Shield; Science, v.119, no.3096, p.606-608. Walcott, C.D. 1912. Notes on fossils from limestone of Steeprock series, Ontario, Canada; Geological Survey of Canada, Memoir 28, p.16-23. 151 �Late Paleoproterozoic Rhyolite-Quartzite Sequences in the Southwestern U.S.: Speculative Relationship to Rocks of the Baraboo Interval SOUTHWICK, D.L. (Minnesota Geological Survey (retired); davidsouthwick@earthlink.net) At least 14 mappable units of supermature quartz arenite (quartzite) occur within Proterozoic terranes in the southwestern U.S. These typically are hundreds of meters in thickness, contain relatively minor interbeds of conglomerate and aluminous shale, and quasi-conformably overlie thick sections of high-silica rhyolite and/or rhyolitic pyroclastic rocks (Williams, 2003). Sedimentological features suggest that the quartzite units were deposited in fluvial to shallow marine environments, the latter having been influenced locally by tidal currents (Soegaard and Eriksson, 1985). The rhyolitic rocks beneath the quartzites range in age between 1665 and 1710 Ma. Extrusion apparently peaked in two pulses, the earlier one about 1700 Ma and the later one about 1670 Ma. Various geochronological methods indicate that several of the quartzite units are no more than a few million years younger than the subjacent rhyolite. Thus, as a first approximation, the quartzite formations were deposited in the interval 1700-1660 Ma with apparent depositional maxima around 1700-1695 Ma and 1665-1660 Ma. The rhyolite-quartzite sequences rest unconformably on previously deformed and metamorphosed Proterozoic rocks, and have themselves been involved in one to three fabric-forming tectonothermal events (Williams, 1991; Williams and others, 1999). Although the deformational history of the rhyolite-quartzite sequences is complex and is the topic of continuing research and debate, there is general agreement that the older fabrics were imposed during one or more pulses of the ~1650 Ma Mazatzal orogeny. Some of the younger fabrics and preserved metamorphic assemblages developed during a 1400 Ma tectonothermal event that probably was related to "anorogenic" plutonism in the southern Rocky Mountains and the southern Midcontinent. There are striking temporal, sedimentological, geochemical, and petrographic similarities between the 1700-1660 Ma quartzites in the Southwest and the 1712-1630 Ma quartzites of the Baraboo interval in the Upper Midwest (Medaris and others, 2003). However, the nearly ubiquitous stratigraphic association of quartzite with slightly older rhyolite observed in the Southwest has not been documented in the Upper Midwest. Essentially undeformed rhyolite occurs locally below the basal unconformity of the Baraboo Quartzite in Wisconsin. Clasts of undeformed porphyritic rhyolite and devitrified rhyolite tuff occur very locally in the Sioux Quartzite of extreme southwestern Minnesota (Southwick and others, 1986; Southwick, 1994), and 19th-century drilling in northwestern Iowa reportedly intersected rhyolite units (poorly described) interbedded with and beneath basal strata of the Sioux (Beyer, 1893; 1897). These rhyolites are texturally pristine and unmetamorphosed, although the Sioux occurrences are metasomatically altered. They have been interpreted as extrusive equivalents of late Penokean plutonism (ca. 1770 Ma) (Southwick, 1994), but as yet there is no solid geochronological evidence of their actual crystallization age. If future geochronological investigations should demonstrate a significantly post-Penokean age for the rhyolites beneath quartzites of the Baraboo interval (say 1715-1700 Ma), the possibility of a tectonic connection between the Baraboo rocks and the rhyolite-quartzite sequences of the southwest would become much more tenable. Specifically, the documentation of pre-quartzite rhyolitic volcanism would strengthen the speculative hypothesis that the Sioux Quartzite and related units were deposited in fault-bounded depressions (Southwick and others, 1986) that 152 �originally were volcanically active graben-like basins. Such basins may have been a far-field response to crustal stretching associated with Yavapai and transitional Yavapai-Mazatzal tectonism. References cited: Beyer, S.W., 1893, Ancient lava flows in northwestern Iowa: Iowa Geological Survey Annual Report, v. 1, p. 163-169. Beyer, S.W., 1897, The Sioux Quartzite and certain associated rocks: Iowa Geological Survey Reports and Papers, v. 6, p. 69-112. Medaris, L.G., Singer, B.S., Dott, R.H., Jr., Naymark, A., Johnson, C.M., and Schott, R.C., 2003, Late Paleoproterozoic climate, tectonics, and metamorphism in the southern Lake Superior region and proto-North America: Evidence from Baraboo interval quartzites: Journal of Geology, v. 111, p. 243-257. Soegaard, K., and Eriksson, K.A., 1985, Evidence of tide, storm, and wave interaction on a Precambrian siliciclastic shelf: The 1,700 M.Y. Ortega Group, New Mexico: Journal of Sedimentary Petrology, v. 55, p. 672-684. Southwick, D.L., Morey, G.B., and Mossler, J.H., 1986, Fluvial origin of the Lower Proterozoic Sioux Quartzite, southwestern Minnesota: Geological Society of America Bulletin, v. 97, p. 1432-1441. Southwick, D.L., 1994, Assorted geochronologic studies of Precambrian terranes in Minnesota: A potpourri of timely information [with data contributed by Z.E. Peterman, L.W. Snee, and W.R. an Schmus], in Southwick, D.L. ed., Short contributions to the geology of Minnesota, 1994: Minnesota Geological Survey Report of Investigations 43, p. 1-19. Williams, M.L., 1991, Heterogeneous deformation in a ductile fold-thrust belt: The Proterozoic structural history of the Tusas Mountains, New Mexico: Geological Society of America Bulletin, v. 103, p. 171-188. Williams, M.L., 2003 [abs.], Proterozoic rhyolite-quartzite sequences of the Southwest: Syntectonic "cover" and stratigraphic breaks (~1695 and ~1660 Ma) between orogenic pulses: Geological Society of America Abstracts with Programs, v. 35, no.5, p. 42. Williams, M.L., Karlstrom, K.E., Lanzirotti, A., Read, A.S., Bishop, J.L., Lombardi, C.E., Pedrick, J.N., and Wingsted, M.B., 1999, New Mexico middle-crustal cross sections: 1.65-Ga macroscopic geometry, 1.4-Ga thermal structure, and continued problems in understanding crustal evolution: Rocky Mountain Geology, v. 34, p. 53-66. 153 �Close Proximity of Kimberlite Pipes to Diabase Dykes: Structural Controls and Predictiveness in the James Bay Lowlands, Ontario STOTT, G.M., Ontario Geological Survey, Sudbury, ON P3E 6B5, greg.stott@ndm.gov.on.ca In the northernmost region of Ontario, Paleozoic sedimentary rocks (Figure 1a) cover the Archean Superior Province to form the Hudson Bay (HBL) and James Bay (JBL) lowlands. Diamondiferous kimberlite pipes of Early Jurassic (circa 190 Ma) and Mesoproterozoic (circa 1100 Ma) age occur in two separate clusters in the James Bay Lowlands (Figure 1b). Early Jurassic kimberlite pipes, including the Victor diamond deposit of De Beers Canada Exploration Inc., are close to the Winisk Fault, a major Archean dextral transpressive fault. However, the presence of this fault by itself does not adequately account for the linear chain of these kimberlite pipes near the Victor deposit nor the more scattered distribution, farther west, of Mesoproterozoic “Kyle” kimberlite pipes. Not all of the Kyle intrusions lie close to the Winisk Fault. More significantly, there is a spatial association between Proterozoic diabase dykes and these two clusters of kimberlite pipes. A geological interpretation of regional aeromagnetic maps is being completed of the Precambrian basement underlying the Phanerozoic cover in the JBL and HBL. This analysis includes identification of the various Proterozoic diabase dyke swarms in that region. From this there is reason to suspect a correspondence between both of these kimberlite pipe clusters and two diabase dyke swarms. The Early Jurassic pipes mainly lie in a linear northwestward trend close to a Matachewan (ca. 2446 Ma) diabase dyke. This dyke is part of a parallel bundle of northwest-striking dykes across an approximately 20-kilometre width near the Winisk Fault. It is suggested here that deep crustal fractures associated with these dykes, arising from the giant Matachewan magmatic event, were reopened during subsequent episodes of displacement along the Winisk Fault. Over 90 km farther west, the 2121 Ma Marathon swarm forms an approx. 20 kilometre wide bundle of dykes trending northwards in the vicinity of the Kyle kimberlite pipes. Individual pipes lie close to aeromagnetic traces of the dykes. The occurrence of both sets of kimberlite pipes, close to but generally not on the Winisk Fault, implies the possibility that dyke-associated fracture swarms served as secondorder, extensional “splays” near this major fault and provided preferred emplacement pathways for pipe intrusions at least in the middle to upper crust. Similar observations have been made in the Lac de Gras area in the Slave Province where Paleoproterozoic dykes show a moderate to strong spatial association with kimberlite pipes (Wilkinson et al., 2001). In the context of this model, other areas of potential exploration interest include: 1) an area approximately 60-80 km farther east of the Victor deposit, where there is an overlap of another set of Matachewan and Marathon dyke bundles (see Figure 2) transected by the east-trending Winisk Fault, and where no kimberlite pipes have as yet been discovered; 2) 2) a set of aeromagnetic anomalies near a Marathon dyke 120 km east of Fort Hope; and 3) 3) an area that straddles the Manitoba – Ontario border near the Hudson Bay Lowlands where a set of reversely magnetised, north-striking dykes (and fractures?) occurs between the North Kenyon fault and the Winisk fault. This dyke swarm lies “up-ice” from an area of glacially deposited kimberlite indicator minerals found to the southwest (Stone 2001). These three areas might serve as exploration tests of this empirically apparent correlation between pipe intrusions and dyke and fracture swarms, especially in proximity to the Winisk Fault. It is to be expected that the aeromagnetic expression of the pipes might be masked by the presence of these dykes. This is a testable hypothesis and further research requires dating fracture materials in these diabase/fracture swarms and episodic movement along the Winisk Fault. The apparent correspondence between kimberlite pipe emplacements and geophysically traceable bundles of diabase dykes and accompanying fractures provides a potentially important structural control, especially where subjected to reactivated tensile stress near major transcurrent faults. 154 �References: Stone, D. 2001. A study of indicator minerals for kimberlite, base metals and gold: northern Superior Province of Ontario; Ontario Geological Survey, Open File Report 6066, 140p. Wilkinson, L., Kjarsgaard, B.A., LeCheminant, A.N. and Harris, J. 2001. Diabase dyke swarms in the Lac de Gras area, Northwest Territories, and their significance to kimberlite exploration: initial results; Geological Survey of Canada, Current Research 2001-C8, 17p. Figure 1a. Map of Ontario showing the location of the James Bay and Hudson Bay lowlands. The Winisk fault underlies the Phanerozoic cover rocks of the lowlands. Location of Figure 1b is outlined. ! 1a 1b Figure 1b. A map highlighting the distribution of diabase dyke swarms under the Phanerozoic cover rocks of the James Bay Lowlands and the spatial correlation with kimberlite pipes. Early Jurassic kimberlite pipes, the Attawapiskat kimberlites, including the Victor diamond deposit, concentrate in a train parallel to one dyke in a group of northwest-striking Matachewan (2446 Ma) diabase dykes and inferred associated fractures. Mesoproterozoic (1100 Ma) kimberlite pipes, the Kyle kimberlites, are spatially concentrated near individual diabase dykes in a group of north-striking Marathon (2110-2121 Ma) dykes. 155 �ORIGIN OF PRE-WISCONSINAN GLACIAL UNITS IN NORTHERN WISCONSIN BASED ON LITHOLOGIC CHARACTERISTICS SYVERSON, Kent M., syverskm@uwec.edu, Dept. of Geology, University of Wisconsin, Eau Claire, WI 54702 Till and outwash units deposited before the Wisconsinan Glaciation are found in weathered, isolated erosional remnants that are difficult to interpret. The goal of this paper is to obtain input from other geologists with regards to lithologic trends observed in pre-Wisconsinan till and outwash units in northern Wisconsin (Syverson and Johnson, 2001; Syverson, 2004). Pierce Fm. till in western Wisconsin and till of the Medford Mbr. (Marathon Fm.) in central Wisconsin are very dark gray to yellowish brown, silty, and calcareous (Table 1, Fig. 1). Potential carbonate sources include Hudson Bay and the Winnipeg Lowland. Baker and others (1987) proposed that a pre-Illinoian Des Moines Lobe from the Winnipeg Lowland deposited the Pierce and Medford tills during the same glacial event based on lithologic similarities, reversed paleomagnetic signatures, and boulder trains and till fabrics suggesting ice flow from the NW/NNW. Thornburg and others (2000) noted much higher kaolinite concentrations in Pierce till than in Marathon Fm. till (Table 1). Syverson and Johnson (2001) proposed four possible origins for the Pierce and Medford tills and suggested that the Pierce and Medford tills may have been deposited synchronously by different lobes flowing from the northwest. Question: Do different source areas exist along reasonable flow lines that would cause higher kaolinite values in western Wisconsin than in central Wisconsin? Table 1. Data for calcareous, pre-Wisconsinan till units (from Thornburg and others, 2000; Syverson, 2004). Mean values are reported (the carbonate ratio is for weight % coarse silt fraction; K=kaolinite; V=vermiculite; number of samples in parentheses). Till Unit Pierce Fm. Snd:Slt:Cl % 39:37:24 (41) Calc:Dolo 4.2:1 (5) %K 23.3 (13) V/K 0.5 (13) Edgar Mbr., Mar. Fm. 40:40:20 (283) 0.7:1 (105) 6.8 (3) 2.4 (3) Medford Mbr., Mar. Fm. 35:46:19 (26) 0.3:1 (8) 5.7 (2) 3.2 (2) The easterly extent of the Superior Lobe before the Wisconsinan Glaciation is also uncertain. Reddishbrown, sandy till of the River Falls Fm. unconformably overlies the Pierce till in western Wisconsin (Fig. 1). Syverson (2004) has mapped River Falls Fm. outwash in western Chippewa County that is up to 35 m thick, extremely eroded, and enriched in pedogenic clay to depths of 5 m below the land surface. This outwash commonly contains ice-proximal cobbles, boulders, and large Lake Superior agates. Late Wisconsinan outwash of the Chippewa Lobe in adjacent areas is cobble poor, is relatively unweathered, and rarely contains Lake Superior agates. It is proposed that the Superior Lobe flowed into western Chippewa County (farther east than previously thought) before the Wisconsinan Glaciation. Agate-rich outwash of the River Falls Fm. in Chippewa County might have been deposited in the interlobate junction between the Superior and Chippewa Lobes as the ice wasted from its maximum extent. Baker, R.W., Attig, J.W., Mode, W.N., Johnson, M.D., and Clayton, L., 1987, A major advance of the preIllinoian Des Moines Lobe: Geological Society of America Abstracts with Programs, v. 19, no. 4, p. 187. Clayton, L., Attig, J.W., Mickelson, D.M., and Johnson, M.D., 1992 (revised), Glaciation of Wisconsin: Wisconsin Geological and Natural History Survey Educational Series 36, 4 p. Syverson, K.M., and Johnson, M.D., 2001, Origin of the calcareous, pre-Wisconsinan Pierce and Marathon Formations, Wisconsin: Geological Society of America Abstracts with Programs, v. 33, no. 4, p. A18. 156 �Syverson, K.M., and Colgan, P.M., 2004, The Quaternary of Wisconsin: a review of stratigraphy and glaciation history, in Ehlers, J. and Gibbard, P.L., eds., Quaternary Glaciations -- Extent and Chronology, Part II: North America: Amsterdam, Elsevier Publishing, in press. Syverson, K.M., 2004, Pleistocene geology of Chippewa County, Wisconsin: Wisconsin Geological and Natural History Survey Bulletin, accepted pending revisions. Thornburg, K.L., Syverson, K.M., and Hooper, R.L., 2000, Clay mineralogy of till units in western Wisconsin: Geological Society of America Abstracts with Programs, v. 32, no. 7, p. A270. Figure 1. Pleistocene lithostratigraphic units of Wisconsin (from Syverson and Colgan, 2004; modified from Clayton and others, 1992). The Medford Mbr. of the Marathon Fm. (mentioned in the text) is found in the subsurface below the Edgar Mbr. of the Marathon Fm. 157 �DOWSING EMPLOYS CLASSICAL MECHANICS AND STATIC ELECTRICITY TO LOCATE SELF-POTENTIAL ANOMALIES INDUCTIVELY AND RAPIDLY TROW, Jim, Geological Sciences, Michigan State University, emeritus, 540 Lake Avenue #2, Hancock, Michigan 49930 At last year’s 49th ILSG I showed where dowsing in the Michigan Copper Country could identify SP anomalies associated with four new (-) ore targets, seven historic (-) lodes, three historic (-) fissure veins, and four major (+) faults. A few of these examples are here illustrated as geophysical profiles. This year I should like to show you how this procedures works. A French physicist and a Czech physicist independently ascribed the dowsing phenomenon to magnetics, but this cannot be because famous Russian dowsers could not detect the enormous Kursk magnetic anomaly. The two physicists elicited human dowsing response in magnetic fields caused by direct electric currents. The Czech thought that a head shield of low-reluctance metal blocked the magnetic stimulus (but of course the metal was also a low-resistance Faraday cage which blocked electrical fields.) My experiments with permanent magnets have drawn a complete blank; experiments with static electric charge producers have been a big success. Try them! Over the past 31 years of examining ore deposits in six states and one province, one learns that the linear forces of static electric attraction and repulsion interact with mechanical lever arm, torque, moment of inertia, kinetic energy, and power factors to enable many humans to detect SP anomalies with 3/16” – diameter bare low-fuming bronze welding rods of two configurations: for me, 1) the more sensitive two-pronged 6” x 15” U-rods identify gentle SP gradients (dv/dx), and repeated turnings indicate the electrical magnitude of the SP anomaly by iteration of gradients, whereas 2) the less sensitive single-pronged 6”x15” L-rods identify steep or vertical SP gradients over target boundaries. One needs both kinds. At waist level, with elbows against your sides hold the short rod segments vertically in your hands with the long segments horizontal at essentially the same altitude, free to rotate in horizontal planes, immune from gravity. Extend your hands in front of you at body width with your lower arms horizontal, and aim the horizontal long rod segments away from you, parallel to each other. This is the standard state. Point the horizontal segments in the direction of your traverse, which should be at more than 45 degrees mapwise from the strike of an anticipated anomalous mass. As you walk, keep your eyes straight ahead on the traverse. Head orientation is critical, as the twin sensors are in the brain, as demonstrated by Faraday cage masking of the head and by family members’ CT Scans after strokes which obliterated their dowsing skills. For most people, as a negative SP anomaly is approached each rod swings inwards 90 degrees. At each such turning record location, reset the rods to the standard state, and walk on, recording every 90 degree turning and its location. If you do not reset the rods to the standard state the rods cannot indicate additional small dv/dx increments, and you will forfeit valuable information concerning the magnitude of the anomaly. Eventually, you will encounter a point where each rod swings outwardly 90 degrees for a positive dv/dx, as you finally climb out of the SP electrical “valley”. These readings may spread over hundreds of feet with these rods, which through the sum of incremental gradients, give you an idea of total SP voltage (v) magnitude. 158 �To determine the precise location and width of the shallow part of the anomalous mass, rerun the traverse with the 6” x 15” L-shaped rods. The 90 degrees inward turning of each rod indicates the steep to vertical negative dv/dx of the negative SP anomaly. Record data, reset the rods to the standard state and traverse a short distance more until the 90 degree outward turning of each rod at the positive steep to vertical dv/dx, as you start to climb out of the negative SP “valley”. Trench or drill between these – and + turnings. While one’s head contains the twin “sensors”, one’s rods, arms, body, and legs constitute the “meter”. The static charge to attract or repel the positively charged rods’ ends emanates from one’s body and legs, when activated by an involuntary signal from one’s brain. These conclusions follow from Faraday cage masking of one’s waist-to-knee area (which kills the “meter”), or by one’s shuffling side-ways along a traverse while one’s “eyes-right” head aims along the traverse as usual. Mechanics calculations show that the two sensitive 6” x 15” U-rods require a power of .0064 Watts for both to turn 90 degrees, whereas the less sensitive 6” x 15” L-rods require a power of only .0008 Watts for the same 90 degrees rotation. However, these sensitive U-rods each rotate 90 degrees with half of the torque-causing linear electric force per prong that it takes to rotate each less sensitive L-rod 90 degrees. For simplest interpretation start every traverse on electrically neutral ground. It would take a week to illustrate all the caveats and intricacies of the dowsing art, and then no two of us would react in the same way unless we individually standardized the lengths of our rods over known SP anomalies. To avoid physiological differences among humans, eliminate the human components of the electrical circuits: Connect a 13- or 20-cm.-diameter hollow spun aluminum sphere (the sensor) to an insulated rod handle, and connect the sphere by a wire to a rugged battery-powered center-zero electrometer (the meter) which records millivolts, and observe induced total SP millivoltage, v (not dv/dx). However, use station spacing of five feet or less if you want to make a second derivative (curvature, d2v/dx2) analysis of the data. Thusly, an ancient art transfigures into science. Trow, J., 1992, Inductive electrostatic gradiometry (IESG) deciphers Keweenawan copper plumbing system, Soc. Mining, Metall. and Expl. Phoenix Meeting, Preprint 92-32, 22 p. 159 �ORIGIN OF THE RHYOLITES AND GRANOPHYRES OF THE MIDCONTINENT RIFT, NORTHEAST MINNESOTA VERVOORT, J.D., Department of Geology, Washington State University, Pullman, WA, 99164, vervoort@wsu.edu WIRTH, K.R., Geology Department, Macalester College, St. Paul, MN, 55105. Throughout Earth history continental rift volcanism has been characterized by voluminous outpourings of dominantly mafic magma. Rhyolites and other evolved compositions are occasionally erupted in these rifts—sometimes in significant proportions (e.g., Paraná)—but in most cases they are subordinate or absent. This is also generally true in the Midcontinent Rift (MCR) where magmatism is predominantly basaltic with subordinate rhyolite; intermediate compositions are rare. An exception to this is in northeastern Minnesota where the rhyolite and granitic intrusive complexes comprise a significant percentage (10-25%; Green and Fitz, 1993) of the magmatic volume. Here we present U-Pb zircon and Nd isotopic data from the rhyolites and granitic complexes in order to constrain the timing and origin of these evolved magmas in the context of the dynamic evolution of the rift. Most of the rhyolitic volcanism is contained within a few exceptionally large eruptive units, the largest of which may have exceeded 600 km3 in volume (Green and Fitz, 1993). The rhyolites are characterized by having large areal extent, large aspect ratios, and high-T mineral assemblages all indicative of high-temperature, superliquidus eruptions (Green and Fitz, 1993). The granitic complexes are of comparable size to the rhyolites and occur as tabular concordant intrusions (up to 35 km by 1 km) that consist dominantly of granitic compositions and exhibit granophyric textures. Although dominantly silicic, the granophyres have a wide range of compositions (e.g., 47-76 wt. % SiO2) and plot along linear trends on many variation diagrams. The major and trace element compositions of the rhyolites and the silicic portions of the granophyre complexes are broadly similar and it is tempting to think of the granophyres as rhyolite magmas that never reached the surface. The magmatism of the MCR in the northeast limb of the rift is divided into two main magmatic stages (Miller and Vervoort, 1996): an “early stage” (1108-1105 Ma) of reversed magnetic polarity and a “main stage” (1100-1094 Ma) of normal magnetic polarity (Figure 1). Previous U-Pb zircon geochronology on the rhyolites (Davis and Green, 1997) indicate that whereas a few rhyolitic units were erupted during the early magmatic stage, the majority of these units, including the most voluminous rhyolites, were erupted at 11001097 Ma during the later main stage Figure 1. Plot of U-Pb zircon ages of granophyres compared with stages of rift evolution proposed by Miller and of magmatism. The granophyre Vervoort (1996). complexes we examined have U-Pb 160 �zircon ages consistent with this chronology. The stratigraphically lowest complexes (Misquah Hills, Greenwood Lake) have reversed magnetic polarity and ages of 1106±6 Ma and 1106±3 Ma (2 σ SE), respectively. The southern complexes (Eagle Mountain, Pine Mountain) are higher in the stratigraphy, have normal magnetic polarity, and have ages of 1098±4 to 1095±4 Ma. The rhyolites and granophyres have Nd isotopic compositions that are related to magmatic stage (Figure 2). Compared with the mafic volcanic rocks of the rift (epsilon Nd 0 ± 2), the early-stage rhyolites have slightly negative initial epsilon Nd values (~-4) and the younger, more voluminous, main-stage rhyolites have highly negative initial epsilon Nd values (-10 to -15). A similar correlation exists in the granophyres. The early stage granophyres are isotopically homogenous with epsilon Nd values of 0 to –2. In contrast, the main stage granophyres have more highly negative initial epsilon Nd values (-3 to -8). Thus for both the rhyolites and the granophyres, the main stage magmas appear to have been more highly contaminated by older evolved crust than those of the early stage. Based on these isotopic and age constraints we propose the following scenario for the magmatic evolution of the MCR. During the early stage, rapid extension allowed magmas to migrate through the crust with minimal interaction. Melting higher Sm/Nd (mafic) material in the lower crust at this time may have generated small volumes of silicic melts with slightly negative epsilon Nd values. Reduced extension during the latent stage (1105-1100 Ma) led to ponding of magma near the base of the crust and widespread crustal heating. Renewed extension during the main magmatic stage led to increased magma migration through the crust; prolonged crustal heating and magma flux resulted in increased crustal melting. The main stage rhyolites and granophyres represent melts of older, more evolved (lower Sm/Nd) compositions (Animikie sediments, Archean TTGs) perhaps at Figure 2. Plot of epsilon Nd versus SiO2 values for North mid- to upper-crustal levels. Shore Volcanic Group (NSVG) rhyolites, and granophyres. tholeiites, References Cited Davis, D.W., and Green, J.C., 1997, Geochronology of the North American Midcontinent rift in western Lake Superior and implications for its geodynamic evolution: Can. J. Earth Sci., v. 34, p. 476-488. Green, J.C., and Fitz, T.J., 1993, Extensive felsic lavas and rheoignimbrites in the Keweenawan Midcontinent Rift plateau volcanics, Minnesota: petrographic and field recognition: Journal of Volcanology and Geothermal Res., v. 54, p. 177-196. Miller, J.D., Jr., and Vervoort, J.D., 1996, The latent magmatic stage of the Midcontinent Rift: A period of magmatic underplating and melting of the lower crust: 42nd Annual Meeting of the Institute of Lake Superior Geology, Cable, WI, Proceedings v. 42, p. 33-35. Vervoort, J. D., and Green, J.C., 1997, Origin of evolved magmas in the Midcontinent Rift system, northeast Minnesota: Nd-isotope evidence for melting of Archean crust: Can. J. Earth Sciences, v. 34, p. 521-535. 161 �Taconite Aggregate Potential of Coarse Tailings from the Biwabik Iron Formation, With an Emphasis on Geology, Mineralogy, and Microscopy ZANKO, Lawrence M., ORESKOVICH, Julie A., Economic Geology Group, Center for Applied Research and Technology Development, Natural Resources Research Institute, 5013 Miller Trunk Highway, Duluth, MN 55811 NILES, Harlan B.(retired), Coleraine Minerals Research Laboratory, Natural Resources Research Institute, One Gayley Avenue, Box 188,Coleraine MN 55722 A study by Zanko et al. (2003) was undertaken to assemble a body of technical data that could be used to better assess the potential of using a crushed taconite mining byproduct (coarse tailings) for more widespread construction aggregate purposes, primarily in roads and highways. Fundamental to the project was the collection and generation of geological and mineralogical data. The major Biwabik Iron Formation stratigraphic units from which the samples were derived were identified, and their relative contribution to each sample was quantified. An important part of the mineralogical assessment included X-ray diffraction (XRD) analyses and microscopic evaluation of the size and shape (morphological) characteristics of potentially respirable microscopic mineral particles and fragments. Quantitative mineralogy, based on XRD analyses, showed that the dominant mineral in all samples was quartz (55 to 60 percent), followed by much smaller amounts of iron oxides, carbonates, and silicates. Specialized microscopic analyses and testing performed by the RJ Lee Group, Monroeville, PA, on both pulverized (-200 mesh, or 0.075 mm) and as-is sample composites showed that no regulated asbestos minerals or amphibole minerals were present. A very small number of mineral cleavage fragments/mineral fibers were detected, but these were mostly minnesotaite, a silicate mineral common to the Biwabik Iron Formation. Amphibole minerals, absent in coarse tailings samples from the five western Mesabi Range taconite operations, were present in a single eastern Biwabik Iron Formation sample collected in 2003 for Lake County from the Cliffs Northshore operation in Silver Bay, MN. Importantly, the Superfund Method for the Determination of Releasable Asbestos in Soils and Bulk Materials, EPA 540-R-97-028 (1997), as modified by Berman and Kolk (2000) failed to generate any protocol fibers, i.e., fibers longer than 5mm and thinner than 0.5mm, from either the western coarse tailings samples or the single eastern Biwabik Iron Formation sample. The combined findings suggest coarse tailings and other taconite mining byproducts should be treated with the same common sense safety and industrial hygiene approach practiced for all mineralbased materials that have the potential to generate respirable dust. Overall, the project showed that: 1) a significant source of fine aggregate (coarse taconite tailings) is available at each of the taconite operations studied; 2) coarse tailings are suitable for use in road construction applications; 3) no amphibole or asbestos minerals were present in any of the tailings samples evaluated; and 4) low-cost transportation, workable distribution logistics, and market acceptance will be key for expanded use of taconite mining byproducts like coarse tailings in markets beyond northeastern Minnesota. Furthermore, making greater use of materials that have long been considered “waste” byproducts makes environmental sense, because doing so maximizes the utilization of resources that have already been mined and crushed, and it could reduce pressures to expand existing, or develop new, “natural” aggregate sources. Permitting of pit and quarry expansions and new aggregate mines has become more complex and difficult, both 162 �environmentally and socially, given the growing “not in my back yard” (NIMBY) reaction to such projects. Future research initiatives intend to compile and generate baseline technical information on the quality of potential higher-value aggregate products (e.g., Class A-type aggregate, concrete aggregate, railroad ballast) derived from the major stratigraphic units within the Biwabik Iron Formation. Because the Biwabik Iron Formation is not monolithic, the goal will be to map and identify units that are the best potential sources for various construction aggregate applications. Its major cherty and slaty members, while laterally persistent, have variable geological, mineralogical, physical, and chemical characteristics across the Mesabi Range. Reference: Zanko, L.M., Niles, H.B., and Oreskovich, J.A., 2004, Properties and Aggregate Potential of Coarse Taconite Tailings from Five Minnesota Taconite Operations: Minnesota Local Road Research Board, Final Report 2004-06, 294 p., and Natural Resources Research Institute, University of Minnesota Duluth, Technical Report, TR-20003/44/ 163 � https://digitalcollections.lakeheadu.ca/files/original/bf5768fd04d62dab530753479e5e73ac.pdf b74b74f1c621be41df0769e12085bd07 PDF Text Text 50TH ANNUAL MEETING INSTITUTE ON LAKE SUPERIOR GEOLOGY 50TH ANNUAL MEETING MAY 4-9, 2004 DULUTH, MINNESOTA HOSTED BY: STEVEN A. HAUCK AND MARK J. SEVERSON Co-Chairs NATURAL RESOURCES RESEARCH INSTITUTE Proceedings Volume 50 Part 2 – Field Trip Guidebook Compiled and edited by Mark J. Severson and Julie Heinz, NRRI Cover Photos: Upper left – Dick Ojakangas, Peter Jongewaard and John Arola at the United Taconite mine, MN (2004); Upper right – Hal James and trip participants near Champion, MI (1964); Bottom – Carl Dutton, Bill Cannon and Matt Walton, Northern MI (1975). �CONTENTS PROCEEDINGS VOLUME 50 PART 2—FIELD TRIPS Trip 1. Volcanic Stratigraphy, Hydrothermal Alteration, and VMS Potential of the Lower Ely Greenstone, Fivemile Lake to Sixmile Lake Area................................................ 1 Trip 2. Geologic Highlights of New Mapping in the Southwestern Sequence of the North Shore Volcanic Group and in the Beaver Bay Complex .......................................... 46 Trip 3. Late Wisconsinan Superior-Lobe Deposits in the Lake Superior Basin northeast of Duluth ...................................................................................................................... 86 Trip 4. Geology of the Eastern Mesabi Iron Range, Northeastern Minnesota ............... 99 Trip 5. Classic Outcrops of Northeastern Minnesota ................................................... 129 Trip 6. Glacial and Postglacial Landscape Evolution in the Glacial Lake Aitkin and Upham Basin, Northern Minnesota .................................................................................... 170 Trip 7. Economic Geology of Archean Gold Occurrences in the Vermilion District, northeast of Soudan, Minnesota............................................................................ 200 Trip 8. Geology and Mineralization of the Western Contact of the Duluth Complex, Partridge River and South Kawishiwi Intrusions, Northeastern Minnesota............ 227 �FIELD TRIP 1 VOLCANIC STRATIGRAPHY, HYDROTHERMAL ALTERATION, AND VMS POTENTIAL OF THE LOWER ELY GREENSTONE, FIVEMILE LAKE TO SIXMILE LAKE AREA George J. Hudak1, John Heine2, Mark Jirsa3 and Dean Peterson2 1 2 University of Wisconsin Oshkosh Natural Resources Research Institute, University of Minnesota – Duluth 3 Minnesota Geological Survey INTRODUCTION The Vermilion district of northeastern Minnesota contains one of the classic granite-greenstone terranes in the United States. This district comprises the south-central part of the Wawa subprovince of the Superior Province of the Canadian Shield, and has been broadly correlated with the Saganagons Assemblage of the Wawa subprovince in northwestern Ontario (Peterson et al., 2001; Peterson and Patelke, 2003). In Canada, the Wawa subprovince hosts numerous lode gold (e.g. the Hemlo and Renabie districts) and volcanic-hosted massive sulfide (VMS) orebodies (e.g. the Winston Lake, Willroy, Big Nama Creek, Willecho, and Geco deposits; Fyon et al., 1992). The Vermilion district is well known for its numerous, previously mined, massive hematitic iron ore deposits. These iron deposits were discovered in the early 1880s, and virtually all subsequent exploration efforts in the region were targeted on similar iron-formation hosted hematite deposits. However, the discovery of world-class ore deposits in Ontario (the Kidd Creek VMS deposit in 1964 and the Hemlo gold deposit in 1980) led to short periods of both base-metal and gold mineral exploration in the Vermilion district. To date, no lode gold and/or VMS orebodies have been discovered in the Vermilion district to date. This field trip will explore recent research efforts to better understand the potential for VMS mineralization within the Lower member of the Ely Greenstone (Lower Ely). Peterson and Patelke (2004, this volume) explore new research regarding the potential for lode gold mineralization within the Newton Belt of the Vermilion district. Since the mid-1990’s, the Minnesota Department of Natural Resources, the Minerals Diversification Plan of the Minnesota Legislature through the Minerals Coordinating Committee, the Permanent University Trust Fund of the University of Minnesota, the Natural Resources Research Institute (University of Minnesota Duluth), and the University of Wisconsin Oshkosh have provided funding to support a series of systematic studies to better understand the VMS potential of the Lower Ely. Early studies (Lawler and Riihilouma (1997); Hudak and Morton, 1999; Peterson and Jirsa, 1999a; Peterson, 2001) showed that numerous base metal anomalies suggestive of localized VMS mineralization exist in the soils, rocks, and lake sediments within this region. Beginning in 2000, research efforts regarding the VMS potential of the Lower Ely have been focused in an approximately two mile wide corridor extending from Skeleton Lake northward to Sixmile Lake (Newkirk et al., 2001a, 2001b; Odette et al., 2001a, 2001b; Hudak et al., 2002a, 2002b; Hocker et al., 2003; Hudak et al., in prep. a). This area was chosen for several reasons: 1) there are historical base metal prospects in the area; 2) lake sediment samples in the area contain the highest copper (Sixmile Lake) and zinc (Fivemile Lake) anomalies within the state of Minnesota (Peterson, 2001); 3) the area contains several untested geophysical anomalies that have orientations roughly parallel to the strike of the strata (Peterson, 2001); 4) the area contains regionally extensive quartz-epidote alteration zones (Peterson and Jirsa, 1999a, 1999b; Peterson, 2001) that may be related to ancient, potentially VMS depositproducing hydrothermal systems; and 5) the bulk of the area comprises state land, and is easily accessible. These research efforts have been multidisciplinary, and have included several months of detailed field Page 1 1 �mapping (1:50 to 1:5000 scale) for stratigraphy and metamorphosed hydrothermal alteration mineral assemblages, petrographic studies (600+ thin sections), whole rock lithogeochemical analyses (~200), xray diffraction studies and electron microprobe investigations. REGIONAL GEOLOGICAL SETTING Supracrustal rocks in the Vermilion district consist of volcanic-dominated stratigraphic sequences of the Wawa subprovince of the Superior Province of the Canadian Shield. Rocks of the Wawa subprovince in northern Minnesota are divided on the basis of stratigraphic and structural setting into: (1) the Soudan belt, to the south, and (2) the Newton belt, to the north (Jirsa et al., 1992; Southwick et al., 1998). The boundary between these contrasting structural panels can be traced geophysically across the width of Minnesota, and was designated informally as the Leech Lake structural discontinuity (Jirsa et al., 1992). In the region west and north of the Soudan Mine, the Leech Lake structural discontinuity occurs along the Mud Creek shear zone (Hudleston et al., 1988), small segments of the Vermilion and Wolf Lake faults (Sims and Southwick, 1985), and the Bear River fault (Jirsa et al., 1992). The Soudan belt contains large, broad folds involving calc-alkalic and tholeiitic volcanic strata overlain by, and locally interdigitated with, turbiditic rocks. In contrast, the Newton belt consists of elongate, northeast-trending, and mostly northward-younging volcanic and volcaniclastic sequences. Volcanic rocks of the Newton belt differ from those of the Soudan belt in containing locally abundant komatiitic flows and peridotitic sills. The two belts are fault-bounded, and the relationship between stratigraphic units within each belt is largely conformable, although faults obscure contacts locally. In its eastern extension, the Soudan belt is continuous with the Saganagons assemblage in Ontario and terminates against the Saganaga pluton and Northern Light Gneiss. The Newton belt extends discontinuously eastward into the Shebandowan District of Ontario to form the Greenwater and Burchell assemblages. Intrusive rocks in both belts vary from gabbroic and felsic porphyries demonstrably related to volcanism, to large plutons emplaced posttectonically. Both districts contain unconformable, Timiskaming-type sequences composed of calc-alkalic volcanic rocks, conglomerates, and finer grained sedimentary rocks. A simplified regional geological map of the Neo-Archean terranes of northeastern Minnesota and adjacent Ontario is presented in Figure 1-1. Figure 1-1. Simplified correlation map of Neoarchean assemblages across the U.S. - Canada border (modified from Peterson et al., 2001). Inset illustrates major subprovinces of the southwestern Superior Province. Page 2 2 �Lithostratigraphic units in the western Vermilion district include: (1) the Lower member, Soudan Iron Formation member, and Upper member (Upper Ely) of the Ely Greenstone, the Lake Vermilion Formation (including the informally named Britt and Gafvert Lake sequences), and the Knife Lake Group of the Soudan belt; (2) the Bass Lake sequence (Peterson and Jirsa, 1999a) and the Newton Lake Formation of the Newton belt; and, (3) syn- to post-tectonic granitoid intrusions of the Giants Range batholith, and a suite of post-tectonic alkalic stocks and plutons (Fig. 1-2). Contacts between the different units are typically conformable, although considerable overlap in time and space is documented between volcanic and sedimentary sequences (Southwick, 1993). Rock types associated with the lithostratigraphic units in the area are presented in Table 1-1. 560001 + + 4+4 —t++'.'+— 4 • • 4 + 4-- 4 + + + RI .4• - + + - 4 •t 4 + + + I 4: -Fl. -±---± "-4-+4, +)+ + * * + + + + '+ + +,--) * + + /+ + + * I 4 * + * + + + + -F' + +2+ *+ — + +-r. +j* + * + + -F' 4 1 * 4 -J-/ * + * -t>. 4 -•+ + ' + ++ -+ + .4 Late Intrusive Rocks * VMS Prospect in Lower Ely) t' + '' Newton Lake Formation + +y+ + t(+ + + 4., + + + -# + + + + + + • * 590000 -P 4 + SBG000 , KnifeLakeGroup LakeVermilion Formation :: Britt Sequence Gafvert Lake Sequence :' Upper Member Ely Greenstone , Vermilion Granitic Complex + Giants Range Batholith 550000 + 570000 yt Duluth complex (1.1 Ga) + 4 + +,I + + + , • + + +. 4 4 ÷ +-_ ,- + +/ + + +* +*++ + 4- +\. 7+ -r *t_[+- *4 * I- +•+ + + IA Soudan Iron Formation A Lower Member Ely Greenstone -- -- C Bass Lake Sequence Figure 1-2. Simplified lithostratigraphic map of the western Vermilion district with the location of VMS prospects in the Lower Member of the Ely Greenstone (from Peterson and Jirsa, 1998a). UTM Nad 83 coordinates in meters. Page 3 3 �Table 1-1. Lithostratigraphic units within the western Vermilion district (from Peterson and Jirsa, 1998a). Intrusive Rocks Late Intrusions Vermilion Granitic Complex Giants Range Batholith Supracrustal Rocks Newton Belt Newton Lake Formation Bass Lake Sequence Soudan Belt Knife Lake Group Lake Vermilion Formation Gafvert Lake Sequence Britt Sequence Upper Ely Greenstone Soudan Iron Formation Lower Ely Greenstone Plutons and stocks of syenite, monzonite, diorite, and lamprophyre Granite, schist, amphibolite, and schist-rich migmatite Granite, granodiorite, monzodiorite, and schist-rich migmatite Tholeiitic and komatiitic basalt flows, intrusions, and clastic strata Tholeiitic basalt lava flows, iron-formation, and felsic porphyries Graywacke, slate, conglomerate, & sheared equivalents Graywacke, slate, dacitic tuff, and minor conglomerate Dacitic to trachyandesitic lava flows, tuffs, and intrusions Tholeiitic basalt lava flows Tholeiitic basalt lava flows and iron-formation Layered cherty iron-formation, epiclastic rocks, and tuff Calc-alkalic & tholeiitic basalt-rhyolite lava flows, tuffs, epiclastic rocks and minor iron-formations The Lower Ely and Soudan Iron Formation (Morey et al., 1970) comprise the strata we will be investigating during this field trip. The Lower Ely consists dominantly of volcanic arc-associated, pillowed and massive basalt and andesite flows of calc-alkalic and tholeiitic composition (Fig. 1-3). Hypabyssal diabase, gabbro, and diorite sills, isolated dacite, rhyodacite, and rhyolite lava flows, domes, tuffs, lapilli tuffs, and tuff-breccias (Fig. 1-4), and local chemical, volcaniclastic and epiclastic sedimentary strata occur throughout the sequence. Pillows in the lowermost sections of the Lower Ely (named the Fivemile Lake sequence by Peterson and Patelke, 2003) typically are irregularly shaped and well-vesiculated, indicating moderate to shallow water depths of formation (Schulz, 1982; Peterson, 2001; Hudak et al., 2002a). Rare massive to bedded scoria deposits interstratified with the pillowed flows also indicate shallow subaqueous, and perhaps locally, subaerial volcanism (Peterson, 2001; Hudak et al., 2002a). Pillowed basaltic rocks in the uppermost parts of the Lower Ely (named the Central Basalt Sequence by Peterson and Patelke, 2003) typically are sparsely-vesiculated and ovoid, and scoria-rich primary and reworked volcaniclastic rocks are not prevalent (Hudak et al., 2002b; Hudak et al., in prep. a; Peterson and Patelke, 2003). These features suggest a general subsidence of the volcanic pile to deepwater conditions. Stratigraphically overlying the volcanic rocks of the Lower Ely is the Soudan Iron Formation, which consists dominantly of laminated Algoma-type iron-formation, with interstratified basalt lava flows and volcaniclastic and epiclastic strata derived from basaltic to dacitic volcanic strata. A gradational contact over several tens to hundreds of meters occurs between the underlying Lower Ely and the overlying Soudan Iron Formation member of the Ely Greenstone (Hudak et al., 2002b; Peterson and Patelke, 2003). In general, the exhalative nature of many of the rocks within the Soudan Iron Formation member represent deep-water chemical deposition throughout a period of quiescence, which began during the latest stages of volcanism associated with the Lower Ely. The stratigraphic thickness of the Soudan Iron Formation member varies from 50 to 3,000 meters, and averages approximately 700 meters. The thickest sections occur in the nose of the Tower-Soudan anticline (Fig. 1-2), and probably represent stratigraphy that is repeated by shearing and thickened by folding. The time period over which the Soudan Iron Formation was deposited is poorly constrained, as geochronological data is very limited within the Ely Greenstone. Nevertheless, the size (thickness and strike length) of the Soudan Iron Formation is much larger than typical Algoma-type iron-formations, and Page 4 4 �its formation probably occurred during a profound break in effusive and pyroclastic volcanism that was accompanied by a long-lived period of hydrothermal activity. The upper contact of the Soudan Iron Formation is more diverse; overlying stratigraphic units along strike include the Upper Ely, the Gafvert Lake Sequence, and the Lake Vermilion Formation. Figure 1-3. Lithogeochemical characteristics of mafic and intermediate volcanic and volcaniclastic rocks of the Lower member of the Ely Greenstone in the vicinities of Fivemile, Needleboy, and Sixmile Lakes (after Hudak et al., 2002a; Hudak et al., in prep. a). Figures 1-4a and 1-4b modified from Winchester and Floyd (1977), Figure 1-4c modified from Wood (1980), Figure 1-4d modified from Winchester and Floyd (1976), Figures 1-4e and 1-4f modified from Barrett and MacLean (1999). Page 5 5 �Figure 1-4. Lithogeochemical characteristics of felsic volcanic and volcaniclastic rocks of the Lower member of the Ely Greenstone in the vicinities of Fivemile, Needleboy, and Sixmile Lakes (after Hudak et al., 2002a; Hudak et al., in prep. a). Figures 1-5a and 1-5b modified from Winchester and Floyd (1977), Figure 1-5c modified from Pearce et al. (1984), Figure 1-5d modified from Harris et al. (1986), Figures 1-5e and 1-5f modified from Piercey et al. (2001) and Barrie et al. (1993). STRUCTURAL GEOLOGY Periods of generally N-S directed compression resulted in three major regional deformation events in the Neoarchean terranes of northern Minnesota. The earliest deformation event (D1) produced broad, locally recumbent folds within the Soudan belt and major fault zones throughout the region. In the Page 6 6 �Newton belt, D1 was accommodated by thrust imbrication of large crustal blocks, resulting in mainly northward stratigraphic facing. Field relationships indicate that uplift, faulting, and the deposition of Timiskaming-type clastic sedimentary sequences in local fault-bounded basins occurred late in D1 deformation (Jirsa, 2000). A large, map-scale structure related to D1 deformation in the western Vermilion district is the Tower-Soudan Anticline, which is a west-plunging anticline within which the axis and plunge changes orientation along strike from nearly vertical in basalts to shallow NE plunging in the western sedimentary rocks. Axial-planar cleavage associated with this early fold typically is lacking, although Bauer (1985), Hooper and Ojakangas (1971), Hudleston (1976), and Jirsa et al. (1992) have described early cleavage (S1) locally. A second deformation event (D2) associated with synchronous regional metamorphism resulted in foliation development and structures having largely dextral asymmetry. D2 is constrained in the Vermilion district to the time period 2674 to 2685 Ma (Boerboom and Zartman, 1993), and between about 2680 and 2685 Ma in the Shebandowan (Corfu and Stott, 1998). Because D2 deformation affected all of the supracrustal rocks in the area and is reasonably constrained by geochronology, the regional foliation (S2) can be used in the field to temporally relate other structural, intrusive, and deformation events. The relationship between S2 fabric and shear structures indicates that most shearing occurred relatively late in the D2 event. Major shearing that produced the Mud Creek and related shear zones (e.g., the Murray shear zone, Fig. 1-1) is attributed to the late stages of D2 dextral transpression. Structures related to the third deformation event (D3) include abundant NE- and NW-trending faults that dissect the stratigraphic assemblages. Named structures related to D3 include the NE-trending Waasa and Camp Rivard faults east of the Soudan Mine area, and the WNW-trending, crustal-scale Vermilion and related faults that form the Wawa-Quetico Subprovince boundary north of the Soudan Mine (Fig. 1-1). VMS PROSPECTS AND EXPLORATION HISTORY Since the mid-1860’s, numerous mineral exploration programs have been conducted in the Vermilion district. Most of these exploration programs focused on identifying minable deposits of massive hematitic iron ores, such as those mined between 1883 and 1962 in the Soudan Iron Formation member at the Soudan Mine. During the 1980s and early 1990s, subeconomic lode gold mineralization was discovered in close proximity to the east-west-trending Murray shear zone, which dissects the Lower Ely, and in close proximity to the Mud Creek shear zone, which separates the Soudan belt from the Newton belt to the north (Fig. 1-1). Four VMS prospects (Fig. 1-2) occur within the Lower Ely, and occur in close proximity upsection from a semiconformable quartz-epidote alteration zone that extends for at least 19km along strike in the north limb of the Tower-Soudan Anticline (Peterson, 2001). These include the Skeleton Lake prospect (drilled by Exxon, 1972), the Eagles Nest prospect (drilled by Newmont, 1988), the Fivemile Lake prospect (drilled by Teck, 1994), and the Purvis Road prospect (drilled by Rendrag, 1999). The stratigraphy, hydrothermal alteration, and mineralization associated with the Skeleton Lake, Eagles Nest, and Fivemile Lake prospects have been recently re-evaluated (Hudak and Morton, 1999; Hudak et al., 2002a; Hudak et al., 2002b). Detailed studies of the Fivemile Lake, Eagles Nest, and Skeleton Lake prospects indicate that copper-zinc sulfide mineralization occurs proximal to relatively narrow (10s of meters wide) disconformable zones of chlorite and/or sericite alteration within felsic volcanic and volcaniclastic rocks (Hudak and Morton, 1999; Hudak et al., 2003). Hudak et al. (2003) and Hudak et al., (in prep. a) have noted that these disconformable alteration zones and associated mineralization commonly occur near high concentrations of synvolcanic mafic dikes, suggesting that these disconformable hydrothermal alteration zones occurred within synvolcanic fault zones (c.f. Gibson et al., 1999). Page 7 7 �VMS-ASSOCIATED VOLCANIC AND HYDROTHERMAL ALTERATION PROCESSES The composition and distribution of hydrothermal alteration mineral assemblages in the Lower Ely (Table 1-2) is similar to that described in major lava-flow dominated VMS mining districts worldwide (e.g. the Noranda Camp, Quebec; Morton and Franklin, 1987; Franklin, 1996; Gibson et al., 1999; Hudak and Morton, 1999; Peterson, 2001; Hudak et al., 2002; Hudak et al., in prep. a). Results of recent studies (Peterson, 2001; Odette et al., 2001a, 2001b; Hudak et al., 2002; Hudak et al., in prep. a) indicate that not only are the compositions and geometries of the regional alteration mineral assemblages identical to those present in many lava flow dominated massive sulfide mining districts, but that detailed alteration mineral chemistries (Hocker et al., 2003) are also consistent with those associated with the VMS ore deposits in these mining camps. These two observations suggest that the processes that formed the alteration mineral assemblages in the Lower Ely were similar to those that formed equivalent alteration zones in well-established VMS mining camps. Thus, one of the most perplexing questions plaguing economic geologists is why economically significant VMS deposits have not yet been discovered in the Vermilion district. A general genetic model for the formation of VMS deposits and associated hydrothermal alteration zone, as recently presented by Franklin et al. (1998), requires convective metalliferous hydrothermal fluid generation in the sub-seafloor environment via heating of down-welling seawater and leaching of metals from the enclosing volcanic and sedimentary strata (Fig. 1-5). The size of a convective hydrothermal system is a function of the abundance of heat in the upper two kilometers of the sub-seafloor crust (Franklin, 1996; Franklin et al., 1998). The intrusion of hypabyssal synvolcanic dikes and/or sills into the shallow sub-seafloor may vigorously enhance the dynamics of convective hydrothermal cells (Campbell et al., 1981). On reaching a critical reaction temperature of ~ 350°C, sustained acid pH in the hydrothermal fluid (evolved fluid) is achieved, and metals are leached from the rocks into the evolved fluid via primary mineral breakdown by calcium metasomatism, silicification, and hydrolysis reactions (Seyfried et al., 1999). In basalt-dominated systems (such as that in the Lower Ely), leaching-related alteration of mafic "source" zones (lower semi-conformable alteration) forms a mineral assemblage composed of albite-epidote-zoisite/clinozoisite-actinolite-quartz. These zones are variably metal-depleted, and are characterized by patchy silicification and epidotization associated with areas metasomatically enriched in silica and calcium. In lava flow-dominated stratigraphic sequences, regionally confined discordant “pipe-like”, and more regionally extensive “semiconformable” alteration zones are present (Morton and Franklin, 1987). The “pipe-like” semi-conformable alteration zones are closely associated with zones of cross-stratal permeability (e.g. synvolcanic fault zones), and are characterized by well-defined vertically extensive alteration zones containing anomalous abundances of sericite, chlorite (both Fe- and Mg-rich varieties), actinolite/ferroactinolite, quartz, pyrite, and locally, chalcopyrite and/or pyrrhotite. Semiconformable alteration zones extend for several kilometers to tens of kilometers in the rocks stratigraphically beneath and adjacent to VMS mineralized horizons (Santaguida et al., 2002a; Santaguida et al., 2002b). In maficdominated volcanic environments, such alteration typically is associated with regional zones of spilitization (an alteration assemblage composed of albite + quartz + Mg-rich chlorite ± sericite), silicification (quartz ± albite), and epidote-quartz alteration (epidote + quartz ± actinolite ± carbonate) (Morton and Franklin, 1987; Gibson et al., 1999; Santaguida et al.. 2002a, Santaguida et al., 2002b). Regional semiconformable alteration zones in felsic rocks in VMS producing camps such as Noranda (Quebec) or Sturgeon Lake (Ontario), typically comprise extensive zones of spilitization, silicification, and sericitization (sericite + quartz ± Mg-rich chlorite) (Morton and Franklin, 1987; Gibson et al., 1999). Page 8 8 �Table 1-2. Greenschist facies metamorphosed hydrothermal alteration mineral assemblages recognized in the Lower Ely (Hudak et al., 2002a; Hudak et al., in prep. a). Alteration Mineral Assemblage No apparent alteration (unaltered) Least altered Silicified Quartz + Chlorite (chlorite > 15%) Epidote + Quartz ± Chlorite ± Albite (Epidote >10%, Actinolite <10%, Fe-chlorite <20%) Epidote + Quartz ± Chlorite ± Albite (Epidote >10%, Actinolite <10%, Fe-chlorite >20%) Albite + Quartz ± Epidote ± Actinolite ± Chlorite (Epidote <10%, Actionlite <10%) Secondary Plagioclase Feldspar ± Chlorite ± Sericite Biotite ± Fe-/Mg-chlorite Iron Oxide / Hematite Geometry Not applicable Semiconformable Semiconformable Semiconformable Semiconformable Semiconformable Semiconformable Semiconformable Semiconformable Epidote + Quartz + Actinolite ± Chlorite ± Albite (Epidote>10%, Actinolite > 10%) Mottled Epidote +Quartz ± Actinolite ± Chlorite ± Albite (“Patchy Epidosite”) Semi/Disconformable Semi/Disconformable Actinolite ± Fe-chlorite ± Epidote ± Albite (Actinolite >10%, Epidote <10%) Fe-chlorite + Sericite (Fe-chlorite >10%, Sericite >5%) Fe-chlorite + Sericite (Fe-chlorite >10%, Sericite<10%, Fe-chlorite + Sericite >25%) Fe-chlorite + Fe-carbonate ± Sericite ± Actinolite ± Epidote (Fe-chlorite >25%, Fecarbonate > 5%, Actinolite, Sericite, Epidote < 5%) Sericite ± Pyrophyllite ± Fe-chlorite (Sericite/Pyrophyllite >5%, Fe-chlorite <10%) Sericite ± Carbonate (Sericite > 5%, calcite/dolomite/ankerite present, chlorite absent) Mg-chlorite ± sericite Disconformable Disconformable Disconformable Disconformable Disconformable Disconformable Disconformable Chlorite + Fe-carbonate ± Sericite Sericite + Green Mica ± Carbonate Shear Zones Shear Zones Tourmaline + quartz Veins Semiconformable Both discordant and semiconformable alteration zones have been discovered in the Vermilion district (Table 1-2), and have been described by Hudak and Morton (1999), Peterson (2001), Odette et al. (2001), and Hudak et al. (2002a). Semiconformable alteration zones in the Lower Ely are dominated by mineral assemblages containing various proportions of quartz, epidote, zoisite/clinozoisite, Fe-chlorite, Mg-chlorite, actinolite, ferroactinolite, sericite/pyrophyllite, and albite. Odette et al. (2001a, 2001b) and Hudak et al. (2002a) have shown via mass balance analysis that semiconformable quartz + epidote ± actinolite ± albite ± chlorite alteration mineral assemblages in the Fivemile Lake area are metasomatically enriched in calcium and silica, and depleted in base metals (copper and zinc) by 50-90%. Pipe-like, northeast-trending disconformable alteration zones in the Lower Ely are largely composed of Fe-rich chlorite, sericite/pyrophyllite, actinolite and/or ferroactinolite. Pipe-like alteration zones that have been mapped up-section have, to date, not led to the discovery of economically significant VMS deposits, but have been instrumental in locating potential base metal sulfide-bearing stratigraphic horizons and localized chemical exhalites. The mineralogy (Hudak et al., 2002a) and chemical compositions of the alteration minerals (Hocker et al., 2003) in these disconformable zones are consistent with those associated with economic VMS deposits in both Canada and Scandinavia (c.f. Hannington et al., 2002). Page 9 9 �VMS Deposit Impermeable Silicified Zone Zoisite/Ciinozoisite 7/ \ ha/fr - Magmatic Water ' ÷ Si - Cu +ca -Zn +Na - Fe Reservoir Zone Epk Quartz —400t-— \ / / .\ / / — \Subvolcanic Intrusion — — - Figure 1-5. Simplified schematic model of a convective hydrothermal system associated with the formation of Noranda–type (Morton and Franklin, 1987) or lava-flow dominated-type (Gibson et al., 1999) VMS deposits (modified from Franklin , 1996). Water depth controls aspects of associated VMS deposit composition (metal ratios) and alteration assemblages (Franklin, 1986; Franklin, 1993). Field evidence from the recent studies in the Lower Ely (Peterson, 2001; Hudak et al., in press) indicates that both shallow and deep subaqueous environments were present in the Vermilion district, as represented by the Fivemile Lake and Central Basalt Sequences. Such environments are not only associated with base-metal VMS deposits, but may also contain precious metal-rich (e.g. gold, silver) VMS deposits (Sillitoe et al., 1996; Hannington et al., 1999). Thus, the Vermilion district, and in particular, the rocks within a few kilometers of the area we are investigating on this field trip, may contain VMS deposits with a variety of base- and precious metal compositions. Page 10 10 �FIELD TRIP STOPS – DAY 1 (MAY 4) Figure 1-6. Field trip stop locations for Day 1 of the Vermilion district field trip. STOP 1-1: ARCHEAN SOUDAN IRON FORMATION No hammering please! Location: (NE, NE, S. 27, T.62N., R.15W., NAD83 UTM 557120E, 5296660N) Description: This classic exposure of the Soudan Iron Formation (Fig. 1-6) lies on the north limb of the Tower-Soudan anticline, and at the stratigraphic top of the volcanic sequences known collectively as the Lower member of the Ely Greenstone—the focus of this field trip. In a general way, the upper kilometer or so of strata assigned to the Lower Ely displays an upward-stratigraphic progression marked by increasing numbers and thicknesses of iron-formation-rich units, and corresponding decreasing thicknesses of the interleaved basaltic flows. This represents a general cessation of volcanism over some time. It is interesting to observe the rhythmic microlaminations (1 mm or so thick) in various cherty beds exposed here and speculate about the paleoenvironment—that is, whether these represent daily heating/cooling cycles, tidal, climatic, annual, or some other repetitive influence in the depositional environment. What is known about iron-formation units in the Ely Greenstone is that their deposition occurred during periods of relative volcanic and tectonic quiescence by the slow, subaqueous “rain” of chemical precipitates. The Soudan marks an abrupt transition from a period of waning basaltic volcanism in comparatively deep water, to one of mixed, locally emergent volcanic and associated sedimentary deposition represented by exposures to the north and west. The latter include dacitic rocks of what is Page 11 11 �known as the Gafvert Lake sequence, and tuffaceous graywacke of the Lake Vermilion Formation. Whether the transition at Soudan represents a significant unconformity remains enigmatic. This exposure also represents a microcosm of deformation in the western Vermilion district. It displays two generations of close folding in delicate laminations of chert (creamy white), chert-hematite jasper (red), and magnetite-chert (black to silver-colored). The second generation of folds (F2) is tectonic in origin, having subvertical axial surfaces that trend eastward, and steeply plunging axes. Most display Z-asymmetry. The earlier folds (F0-1) appear to have been sharply refolded to produce complex interference patterns. Lundy (1985) studied folding at this locality and concluded that some of the apparent interference structures are the product of early-formed sheath folds that did not involve refolding by D2. The F1 structures are predominantly intrafolial, and exhibit a great variety of style and orientation; implying they formed by layer-parallel, soft-sediment slumping. Work by Hudleston (1976) and Jirsa et al. (1992) extends these types of observations to regional tectonic interpretations of an early (D1) folding that included the development of the Tower-Soudan anticline in rigid volcanic complexes, and associated large nappe structures in the more ductile marginal sedimentary strata, followed by D2 metamorphism and transpressive deformation. STOP 1-2: XENOLITHIC HORNBLENDE DIORITE, PURVIS PLUTON Location: (NE, SW, S. 30, T.62N., R.13W., NAD 83 UTM 571755E, 5296815N) Description: The Purvis pluton is an east-west trending, moderate-sized (~3km3), sill-like multiphase dioritic to tonalitic intrusion with a strike length of 5.7 km and a thickness that ranges from 100-1200 meters (Peterson, 2001). This intrusion occurs in the lower stratigraphic section of the north limb of the Tower-Soudan anticline (Peterson and Jirsa, 1999a; Jirsa et al., 2001). Recent work by Drexler and Hudak (in press) indicate that the intrusion has several phases, including 1) xenolithic hornblende diorite; 2) xenolithic hornblende tonalite; 3) xenolithic leucotonalite; 4) leucotonalite and trondhjemite; and 5) leucotonalite dikes (Fig. 1-7). Detailed field mapping by Peterson (2001), Hovis (2001) and Drexler and Hudak (in press) suggest that the Purvis pluton is a synvolcanic intrusion based on the following characteristics: 1) it lacks a contact metamorphic aureole; 2) its uppermost contact is proximally associated with intense, semiconformable quartz + epidote alteration zones; 3) D2 deformation fabrics occur in both the intrusion and the surrounding country rocks; and 4) early xenolithic diorite phases are cross-cut by thin, commonly D2-deformed dikes of younger tonalite and trondhjemite phases. Galley (2002) and Galley (2003) have indicated that these characteristics are key features of synvolcanic intrusions temporally associated with the genesis of many Precambrian VMS deposits. Peterson (2001) has suggested that the Purvis pluton may have been the heat source that drove hydrothermal systems that produced the Eagles Nest and Purvis Road VMS prospects. A sample of the leucotonalite phase has been submitted to Dr. Daniel Holm (Kent State University) for geochronological analysis, but this age is not yet available. Based on the presence of the D2 fabric in the pluton, U/Pb zircon dates of a D2-deformed felsic lava dome in the Lower Ely in the Fivemile Lake area, and a post-D2 quartz feldspar porphyry in the Newton Belt (Peterson et al., 2001), we anticipate an age between 2683 Ma and 2722 Ma for the Purvis pluton. This locale offers an opportunity to investigate the xenolithic hornblende diorite phase of the Purvis pluton. The outcrop adjacent to the road predominately contains four types of xenoliths: 1) dark green xenoliths of amygdaloidal (5-8%) basalt-andesite pillow lavas which locally have preserved selvedges and interpillow hyaloclastite, and are locally contact metamorphosed along their margins; 2) pale green epidote + quartz-altered basalt-andesite lava xenoliths that are up to 15 cm in diameter; 3) rare coarse-grained gabbro/diorite xenoliths up to 3 cm in diameter; and 4) rare <1-2 cm diameter subangular Page 12 12 �chert xenoliths. Large iron-formation xenoliths up to several meters in diameter, and amphibolite xenoliths up to several centimeters in diameter, may be observed in xenolithic hornblende tonalite outcrops located east of this location (NAD 83 UTM coordinates 0574920E, 5297600N). * - Hr ft / Figure 1-7. Xenolithic hornblende tonalite (A) and xenolithic hornblende diorite (B) phases of the Purvis pluton.. Iron-formation xenoliths present in outcrops east of here were likely derived from iron-formation horizons that occur immediately southwest of Purvis Lake. Basalt and altered basalt fragments also were derived from the surrounding Lower Ely. The presence of epidote-quartz altered mafic xenoliths suggests that this phase of the Purvis pluton stoped its way upward into an earlier-formed proximal zone of quartzepidote alteration formed from high temperature seawater-rock interaction (e.g. Galley, 2003). Amphibolite xenoliths are believed to represent contact metamorphosed basalt fragments based on petrographic similarities (Drexler and Hudak, in press). Drexler and Hudak (in press) have shown that coarse-grained gabbro/diorite fragments likely represent xenoliths of the earliest phases of the pluton. A short hike up to the top of the ridge allows investigation of a newly exposed (and still lichenfree) outcrop displaying the complicated textures between medium-grained diorite and xenoliths in this phase of the Purvis pluton. Collectively, six types of xenoliths comprise 55-60% of the intrusion at this location. These xenolith types include: 1) pale to dark green, subangular to subround basalt-andesite clasts which range from 1-30cm in diameter and make up 15-20% of the rock; 2) subround to subangular, coarse-grained gabbro/diorite xenoliths that are up to 20cm in diameter; 3) subround epidote + quartzaltered basalt-andesite xenoliths that are up to 20cm in diameter; 4) subangular, dark grayish-green finegrained diorite xenoliths which are up to 10cm in diameter; 5) dark green, coarse-grained, actinolite-rich amphibolite fragments up to 12 cm in diameter; and 6) rare pillow selvedge / interpillow hyaloclastite xenoliths which locally make up 1% of the unit. Moving east along the ridge, one can observe additional outcrops of xenolithic diorite. Locally (UTM NAD 83 coordinate 571798E, 5296828N) ENE-trending 10-20cm wide leucotonalite dikes cut through the xenolithic diorite phase, indicating the age relationships between these two units. Farther east along the ridge, the complicated contact between the Purvis pluton and the overlying basalt-andesite pillow lavas can be observed. These lavas contain patchy epidote + quartz alteration, and have locally been metamorphosed to hornfels immediately adjacent to the intrusion. Studies of ancient VMS deposits has documented that the deposits commonly occur in depressions on the paleo-seafloor (3rd-order basins) while modern deposits on the seafloor are found on high-standing structures, such as ridges. These differences are probably more apparent than real, in that Page 13 13 �the modern deposits are generally confined to the axial graben, or depression, of what are otherwise are high-standing structures. In addition, both ancient and modern deposits occur in areas of anomalously high heat flow, generally linked to synvolcanic intrusions beneath the hydrothermal systems. The recent mapping in the Purvis Road area has shown the presence of all of the attributes of typical VMS-forming hydrothermal systems. These attributes include a synvolcanic intrusive heat source (the Purvis pluton), a paleotopographic high-standing structure, VMS-style alteration mineral assemblages, and the presence of Cu and Zn-rich massive sulfide (recent logging in this area has exposed numerous angular boulders of massive sulfide in the basal till). The VMS attributes of the Purvis road area are presented in Figure 1-8. Figure 1-8. Simplified regional lithostratigraphic sequences draped on a 3D view (looking due west) of a residual field aeromagnetic anomaly map of the western Vermilion district (same map area as Fig. 1-2). The lower two photographs show massive sulfide boulders exposed north of the Purvis pluton. Page 14 14 �STOP 1-3. SILICIFIED FIVEMILE LAKE SEQUENCE PILLOW LAVAS / REGIONAL SEMICONFORMABLE ALTERATION Location: (SE, SE, S. 22, T.62N., R.14W., NAD83 UTM 567818E, 5297818N) Description: Geological mapping by Peterson (2001) has indicated the presence of a regional semiconformable quartz-epidote alteration zone extending for at least 19 km along strike within the Lower Ely along the north limb of the Tower-Soudan anticline. This type of alteration is a common feature in many Archean VMS camps (e.g. Noranda (Gibson, 1989) and Snow Lake (Skirrow and Franklin, 1994)), and is attributed to silica- and calcium-dumping that occurs in the deep, sub-seafloor as downwelling hydrothermal fluids are heated to temperatures in excess of 350°C (Franklin, 1986; Franklin, 1993). Semiconformable alteration zones associated with VMS systems are generally much larger in area than their associated mineralization, and therefore provide exploration geologists regional areas in which to concentrate more detailed, follow-up field mapping, geochemical studies, and geophysical surveys for identifying VMS targets. Semiconformable quartz-epidote alteration zones are commonly metal-depleted. Peterson (2001), Odette et al. (2001a, 2001b), and Hudak et al. (2002a) have shown that that quartz-epidote altered basalts within this regional semiconformable alteration zone are commonly depleted in base metals by as much as 50-90%. Peterson (2001) completed simplified mass balance calculations of Cu and Zn depletion associated with the regionally extensive quartz-epidote alteration zone within the Lower Ely, and this work reveals the importance of this alteration to the VMS mineral potential of this area. The surface expression of the quartz-epidote alteration is approximately 19 kilometers long, and averages approximately 1.5 kilometers in width. The area of this zone is on the order of 30.5 km2. Using Southwick et al. (1998) values for Cu and Zn of 59 and 115 ppm, and a mean density of the rocks equal to 2.8g/cm3, the total contained copper and zinc for various volumes of rock from the Lower Ely are calculated, and presented in the top of Table 1-3. These volumes include a 1.0 kilometer thick slab (volume = 30.5 km3), a 2.0 kilometer thick slab (volume = 61 km3), a 3.0 kilometer thick slab (volume = 91.5 km3), and a circular disk (volume = 591 km3). Percent leaching calculations for copper and zinc are presented in the lower portions of Table 1-3, with values of metal leached (in pounds) from the four calculated volumes of rock. The leaching models include 5%, 10%, 25%, and 50% metal leached from the rock. Given the patchy nature of this alteration, an estimate of somewhere between 10 and 25% metal leaching seems reasonable, as does the 91.5 km3 volume. Therefore, one can estimate that many billions of pounds of copper and zinc have been leached out of the volcanic rocks in the north limb of the Lower Ely Greenstone. The concentration of these base metals into specific sites by a VMS style hydrothermal system would have created significant tonnages of massive sulfide. This data clearly reflects the potential for VMS mineralization up-section from this zone. At this location we can observe part of the regionally extensive quartz-epidote alteration zone. The outcrop contains relatively undeformed bun- and mattress-shaped pillows. Interpillow hyaloclastite zones are generally pale to dark green in color, and are chlorite and/or actinolite-rich. Minor red-brown staining locally occurs in these zones, and is indicative of the presence of trace amounts of pyrite and/or chalcopyrite. Pillow selvedges commonly contain up to 10% round to oval, pipe-like quartz-epidote and/or actinolite chlorite amygdules. The cores of the pillows are typically pale green gray in color due to nearly wholesale replacement of the original igneous minerals by quartz and epidote. Page 15 15 �Table 1-3. Copper and zinc leaching calculations for the regional semiconformable quartz-epidote alteration zone present in the Lower Ely (Peterson, 2001). Volume (Km3) 30.5 11,084,920,000 21,606,200,000 61 22,169,840,000 43,212,400,000 91.5 33,254,760,000 64,818,600,000 591 214,793,040,000 418,664,400,000 5% Cu leached (lbs) 10% Cu leached (lbs) 25% Cu leached (lbs) 50% Cu leached (lbs) 554,246,000 1,108,492,000 2,771,230,000 5,542,460,000 1,108,492,000 2,216,984,000 5,542,460,000 11,084,920,000 1,662,738,000 3,325,476,000 8,313,690,000 16,627,380,000 10,739,652,000 21,479,304,000 53,698,260,000 107,396,520,000 5% Zn leached (lbs) 10% Zn leached (lbs) 25% Zn leached (lbs) 50% Zn leached (lbs) 1,080,310,000 2,160,620,000 5,401,550,000 10,803,100,000 2,160,620,000 4,321,240,000 10,803,100,000 21,606,200,000 3,240,930,000 6,481,860,000 16,204,650,000 32,409,300,000 20,933,220,000 41,866,440,000 104,666,100,000 209,322,200,000 Total Contained Cu (lbs) Total Contained Zn (lbs) STOP 1-4: WELL-PRESERVED PILLOW LAVAS, SOUTH OF FIVEMILE LAKE Location: (NE, SW, S. 29, T.62N., R.14W., NAD83 UTM 563195E, 5296660N) Description: The Fivemile Lake Prospect comprises an extremely well preserved, and locally intensely hydrothermally altered, bimodal package of basalt-andesite pillows lavas and coherant and volcaniclastic facies felsic metavolcanic strata which have locally been intruded by diabase and/or diorite synvolcanic sills and dikes. Recent geological studies at the Fivemile Lake Prospect have included detailed field mapping, diamond drill core relogging, petrographic, lithogeochemical, x-ray diffraction, and electron microprobe investigations (Hudak and Morton, 1999; Peterson, 2001; Newkirk et al., 200a, 2001b; Odette et al., 2001a, 2001b; Hudak et al., 2002a; Hocker et al. 2003). These studies were undertaken to a) better understand the geology (in particular, the physical volcanology) of these regions; b) identify and evaluate the composition and distribution of the metamorphosed hydrothermal alteration mineral assemblages that occur at each of these prospects; c) evaluate and compare the chemical compositions of alteration mineral phases to those found at VMS deposits of various ages in various parts of the Canadian Shield, the western United States, and Tasmania; and d) evaluate the potential for VMS and/or lode gold mineralization in these areas. Field mapping and diamond drill core relogging indicate that the Fivemile Lake Prospect comprises thirteen distinct types of strata that can be subdivided into six major lithological classes (Hudak et al., 2002a). These include: a) calc-alkaline and tholeiitic, mafic to intermediate volcanic and volcaniclastic rocks (basalt-andesite pillow lavas, pillow breccias, hyaloclastite deposits, tuff, lapilli tuffs and monogenic volcanic breccias); b) chemical sedimentary rocks (semi-massive sulfide exhalite); c) calc-alkaline to tholeiitic, intermediate to felsic volcanic and volcaniclastic rocks (massive quartz-phyric rhyodacite lava flows, and aphyric to quartz-phyric rhyodacite to rhyolite tuff, lapilli tuff, and tuff breccia deposits); d) synvolcanic intrusive rocks (diorite sill-dike complexes, diabase dikes and sills, and massive gabbro); e) post-volcanic intrusive rocks (feldspar porphyry dikes and sills and quartz-feldspar porphyry dikes); and f) post-volcanic schists (quartz-sericite-ankerite schists, chlorite schists, and quartz-sericite- Page 16 16 �Figure 1.9. Generalized geological map of the Fivemile Lake – Needleboy Lake – Sixmile Lake area (modified after Peterson and Jirsa (1999a), Jirsa et al. (2001), and Hudak et al. (2002a). Page 17 17 �green mica schists). Supracrustal strata at the prospect vary from east-west to southeast-northwest striking, dip steeply to the north, and are north-facing. Because of this geometry, the geological map of the area (Figure 1-9) essentially illustrates a cross-section through the Lower Ely crust. Volcanic and volcaniclastic rocks have chemical characteristics indicative of formation with an ancient volcanic arc setting (Hudak and Morton, 1999; Hudak et al., 2002a). At this stop, we will investigate two outcrops that display exceptionally well-preserved pillow lavas and associated interpillow hyaloclastite. Detailed analysis (Newkirk et al., 2001a, 2001b; Hudak et al., 2002a) indicates that the pillow lavas at Fivemile Lake are morphologically similarly to undeformed Cenozoic pillow lavas from New Zealand and Tasmania. The nomenclature used for describing pillow lavas is illustrated in Figure 1-10). Intiapiliow Cavity r— Coiicentdc Cooling Joints Piliow Bud (non sight to loft) Blocky HyalocJastite — Radial Cooling Joint Neck and Knob Pipe .anygdule — Seivedge Formerly Glassy L Amygdulssririow — inteipiliow Pillow Margin -lyaloclastito Figure 1-10. Nomenclature used for describing pillow lavas and associated hyaloclastite (after Cas and Wright (1987) and Gibson (1989). At the first outcrop (NAD 83 UTM coordinates 563195E, 5296660N) we can observe bun- to lens-shaped, quartz-epidote-actinolite-chlorite-altered basalt-andesite pillow lavas. The general strike of the pillow lavas at this location is approximately 085°. The pillows vary from 0.4-1.0 meters high and 0.5-2.0 meters long, and contain zones of chlorite-rich interpillow hyaloclastite that ranges from 0.5-3.0 cm wide. Local brownish-red sulfide staining may be observed in the interpillow hyaloclastite zones. The pillow selvedges vary from 1-6 cm wide, are commonly silicified and/or quartz-epidote altered, and contain approximately 15% 1-5mm oval to round, quartz ± carbonate filled amygdules. Multiple pillow rinds, separated by 4-8 cm, may be locally observed. Reentrant pillow crusts and apparent pillow buds at this location suggest flow from west to east. The cores of the pillows at this location contain up to 5% 25 cm rounded quartz amygdules, and are faintly plagioclase feldspar-phyric (3-5% <1mm tabular phenocrysts). Faint radial cooling joints are also locally preserved in several of the pillows on this outcrop. Page 18 18 �A second spectacular outcrop of well-preserved, east-west striking pillow lavas occurs approximately 30 meters to the east (NAD 83 UTM coordinates 563225E, 5296660N). Pillow morphology at this outcrop is quite variable, ranging from bun- and mattress-shaped to amoeboid. Topping directions based on pillow morphology are consistently north. Pillows here are typically 50-80 cm in height and 1-1.5 meters long, although pillows as small as 30 cm in diameter and up to 2 meters long may be locally observed. Pillows selvedges vary from 1-7 cm wide (average 2-3 cm) and contain 15-20%, 3-7 mm diameter, round quartz amygdules. Pillow cores generally contain 5-10% 3-10mm round to oval quartz amygdules. Several pillows on the western and north-central part of the outcrop contain multiple pillow rinds. A pillow displaying exceptionally well-preserved “neck and knob” structure may be observed on the east central part of the outcrop. Vesicle size and abundance in pillow lavas (McPhie et al., 1993 and references therein) may be used with other textural and facies characteristics to interpret pillow lavas erupted in “relatively shallow” (<1-2 km water depth) versus “relatively deep” (>2 km water depth) submarine environments. Multiple pillow rind structures are common features in pillow lavas erupted in “relatively shallow” water environments, and are formed by implosion and rupture of the pillow skin resulting from condensation of exsolved gases concentrated in the upper part of the pillow (Kawachi and Pringle, 1988). The relatively high vesicularity of the pillows, coupled with the presence of multiple rind structures, indicate that the pillow lavas in this part of the Lower Ely were formed in a relatively shallow submarine environment. STOP 1-5: PILLOW DIKES, PEPERITES, AND SYNVOLCANIC FAULTS, SW SHORE, FIVEMILE LAKE No hammering please! Location: (SW, NW, S29, T. 62N, R. 14W; NAD 83 UTM Coordinates 0563305E, 5296955N) Description: Peperite is defined as a breccia-like volcaniclastic deposit formed from the in-situ disintegration and mixing of magma or lava with wet, poorly consolidated sediment (Batiza and White, 2000; Schmidt and Schminke, 2000). Peperite is a common rock type in submarine arc-related volcano sedimentary sequences, and is associated with synvolcanic intrusions. It often occurs in phreatomagmatic vent filling deposits and along contacts between synvolcanic intrusions and poorly consolidated, wet, submarine sediments. Key components that aid in the identification of peperites include evidence of partial fluidization of the sediment, local contact metamorphism, and in some rare instances, vesiculation within the sediment (Skilling et al., 2002). In general, the end-member compositions in a peperite are the igneous component (a synvolcanic dike or sill, or a lava flow) and the sedimentary component. Igneous component domains in peperites vary from tabular to lobe-like to pillow-like, and can commonly have irregular, interconnected, fold like, and pod-like shapes. Mixing that results from quenching, hydromagmatic explosions, magma-sediment density contrasts, and/or mechanical stresses resulting from inflation or movement of magma, causes the igneous component of the peperite to be broken-up and dispersed within the wet sediment to form peperite (McPhie and Orth, 1999). Factors such as magma and/or sediment composition, magma injection velocities, volatile content of the magma, relative volumes of sediment and magma involved, volume of pore water heated, presence or absence of shock waves, and the confining pressure all influence the morphology of peperites. Juvenile clast morphologies in peperite are extremely variable, and may be irregular, blocky (commonly jigsaw-fit), pumiceous or scoriaceous, irregular (amoeboid), elongate, wispy, platy or ragged. It is not uncommon for mixed juvenile clast populations to be present within a single peperite deposit (Skilling et al., 2002). This stop encompasses a series of outcrops that occur on a small peninsula along the southwest shoreline of Fivemile Lake (informally and affectionately known as “Pike Point” based on the exceptionally large pike that can be caught from this shoreline). A generalized geological map of this Page 19 19 �area, which points out key features to observe at this stop, is illustrated in Figure 1-11. The area was originally mapped as a series of pillow lavas and felsic debris flow deposits (Peterson and Jirsa, 1999a; Peterson, 2001); however, if the pillow lavas represent a stratigraphic unit, they are oriented approximately 40°-45° to the strike of the supracrustal strata in this area, suggesting that either a) deposition occurred upon a steep paleotopographic surface (which is not supported by the pillow morphology); or b) a fold may be locally present (evidence for this is not currently supported by regional mapping). (V >1. Fivemile — 5296925 Coherant Pillows Fades Volcanidas& Fades LapllI T'fl / TuIT-Br.a X H1cooct 1ñofSonoatI Difiusa planar stralitpcaton a! deals SVl Ice and topping direct on of pillow SyTwolcanlc Fault 0 I cL) I Oulciop Locaa' 7] Approximate Trail 5 10 20 Lobon Figure 1-11. Geological map of the southwestern shoreline (“Pike Point”) area of Fivemile Lake (after Hudak et al., in prep. b). Detailed facies mapping at scales ranging from 1:50 to 1:100 by Hudak et al. (2002a) and Hudak et al. (in press) now suggests that “Pike Point” comprises a series of northeast-trending andesite-dacite pillowed dikes that intruded a deposit of wet, unconsolidated basalt-andesite tuff to form blocky to amoeboid peperites. Pillows may be formed within water-saturated hyaloclastite or sediments within the sub-seafloor provided that the adjacent rocks are poorly consolidated and saturated with water (McPhie et al., 1993 and references therein). The interpretation that the pillowed igneous domains represent dikes rather than pillowed lava flows is based on several characteristics of the dikes: 1) the strike of the pillows is northeast, whereas the strike of the volcanic strata in this region is general more or less east-west; 2) topping directions measured in the pillows are variable and inconsistent; 3) on the most northwestern of the outcrops, apophyses of the dikes can clearly be seen propagating to the north-northwest; 4) the Page 20 20 �chemical compositions of the pillow domains and the blocky to amoeboid fragments in the volcaniclastic deposits is identical; and 5) the trend of the pillows, when followed to the north shore of Fivemile Lake, leads to a series of chemically identical, northeast-trending dikes and associated peperite deposits that occur within the vent facies of a 700 meter (strike length) by 200 meter (height) tuff cone volcano mapped by Hudak et al. (in prep. a, in prep. b; we will see these deposits tomorrow at field trip Stop 1-9). The interpretation that the volcaniclastic deposits represent peperites is based on the following characteristics of the deposits: 1) at several locations along the point, blocky jigsaw puzzle-fit fragments indicate in-situ fragmentation of northeast-trending pillow dikes; 2) fragment shapes in the volcaniclastic deposits vary from amoeboid to blocky and jigsaw puzzle-fit, to curviplanar, all indicative of fragmentation by external water; 3) vesiculation is common within the matrix of the volcaniclastic deposits; and 4) the general trend of the long directions of the fragments is consistent with the strikes of the pillow dikes. Several textures that may be observed at this location are illustrated in Figure 1-12. Figure 1-12. Textures within peperites that occur along the southwestern shoreline of Fivemile Lake: 1-12a) northeast-trending pillow dikes on the northwest side of the point; 1-12b) fractured synvolcanic dike, west-central part of point; 1-12c) synvolcanic dike and blocky peperite with vesiculated sediments, south-central part of point; 112d) northeast-trending pillowed dikes, east-central part of point. Page 21 21 �STOP 1-6: EPIDOTE – QUARTZ ALTERED DIABASE SILLS AND DIKES, SOUTH OF FIVEMILE LAKE Location: (NE, SW, S.29, T.62N., R.14W., NAD 83 UTM 563515E, 5296610N) Description: This stop affords us the opportunity to investigate both synvolcanic and post-volcanic hydrothermal alteration in the Fivemile Lake area. Field, petrographic, x-ray diffraction, electron microprobe, and lithogeochemical studies have identified twelve distinctive metamorphosed hydrothermal alteration mineral assemblages at the Fivemile Lake prospect (Odette et al., 2001a, 2001b; Hudak et al., 2002a; Hocker et al., 2003). Synvolcanic, semi-conformable alteration assemblages have been identified on the basis of the modal percentages of the minerals epidote, actinolite, and chlorite, and include: a) epidote + quartz ± chlorite ± albite; b) epidote + quartz + chlorite ± albite; c) epidote + quartz + actinolite ± chlorite ± albite; and d) albite + quartz ± epidote ± actinolite. These quartz + epidote-rich alteration assemblages are interpreted to represent “seafloor metasomatism” associated with hydrothermal fluids that moved through the subaqueous rocks. Detailed mapping and lithogeochemical trends suggest that early, relatively low temperature hydrothermal alteration mineral assemblages (e.g., albite + quartz ± epidote ± actinolite) were later overprinted by higher temperature alteration mineral assemblages (e.g., epidote + quartz ± chlorite ± albite, epidote + quartz + chlorite ± albite, epidote + quartz + actinolite ± chlorite ± albite) as the volcanic pile was progressively buried by volcanism deeper below the seafloor. It is believed that the early, near seafloor environment, which was locally base metal enriched by VMSstyle mineralization, eventually became depleted in base metals from later, deep-seated hydrothermal circulation. Synvolcanic, disconformable alteration mineral assemblages are commonly proximal to synvolcanic fault zones and VMS-style mineralization at the prospect, and include: a) actinolite + quartz ± iron-rich chlorite ± epidote ± albite; b) iron-rich chlorite + sericite; c) iron-rich chlorite ± sericite ± ironcarbonate ± actinolite ± epidote; d) sericite ± iron-rich chlorite; and e) mottled epidote + quartz ± actinolite. These alteration zones likely represent areas of high temperature metasomatism associated with VMS mineralization at, or up-section from, the Fivemile Lake prospect. Post-volcanic hydrothermal alteration mineral assemblages at the prospect include: a) carbonate (ankerite, dolomite, or calcite); b) sericite + carbonate (ankerite, dolomite, or calcite); and c) sericite + green mica ± carbonate (ankerite, dolomite or calcite). The close association of structurally deformed rocks and these alteration zones, and the orientations of these alteration zones, suggest that these alteration mineral assemblages resulted from syntectonic hydrothermal processes associated with the D2 Murray Shear Zone deformational event. A hydrothermal alteration mineral assemblage map for the Fivemile Lake prospect is illustrated in Figure 113. The mottled epidote + quartz + actinolite alteration zone present in this outcrop is confined to a diabase dike-sill complex located immediately south of Fivemile Lake. This 400 meter by 500 meter disconformable to semiconformable alteration zone locally cross-cuts semiconformable alteration zones comprising the epidote + quartz ± chlorite ± secondary feldspar assemblage, the epidote + quartz + ironchlorite ± secondary feldspar assemblage, and the secondary feldspar + quartz ± epidote ± actinolite alteration assemblage. The mottled epidote + quartz + actinolite alteration zone is characterized by a dark green, actinolite and epidote-rich groundmass that contains discrete 0.1-2.0 meter diameter, round to lens-shaped masses containing anhedral granular epidote and zoisite intergrown with polygonal quartz. These rounded epidote-quartz-rich masses can easily be mistaken for individual pillow lavas; however, they can be distinguished from pillows because they lack abundant amygdules, and have no discrete pillow selvedges or interpillow hyaloclastite zones. Petrographic, x-ray, and electron microprobe analyses indicate the presence of iron-rich chlorite, iron-rich actinolite, pistacite and zoisite/clinozoisite within this assemblage (Odette et al., 2001a, 2001b; Hocker et al., 2003). Page 22 22 �Figure 1-13. Hydrothermal alteration map of the Fivemile Lake prospect (after Hudak et al., 2002a). The mineralogy, mineral compositions, and pronounced calcium enrichment and copper depletion that characterize the mottled epidote + quartz + actinolite alteration assemblage (Odette et al, 2001a, 2001b) are consistent with formation within a synvolcanic, semiconformable to disconformable alteration zone formed by high temperature, high fluid to rock ratio interactions deep within a sub-seafloor hydrothermal cell (c. f. Franklin, 1996; Seyfried et al., 1999). Similar clinozoisite/zoisite bearing alteration mineral assemblages described by Hannington et al. (2002) that occur down-section from the world-class VMS deposits in the Noranda mining camp in Quebec are believed to have formed from anomalous fluid flow at high water to rock ratios and high temperatures. Large zones of base metaldepleted epidosite in the Troodos ophiolite complex have been interpreted by Richardson et al. (1987) to represent deep-seated fossil reaction zones where metaliferous “black smoker” fluids are produced. The confinement of this alteration assemblage to the base of the northeast-trending diabase dike / sill complex, indicates that this alteration assemblage occurs in the deep subsurface of a northeast-trending synvolcanic structure that focused magma, as well as high temperature, perhaps base metal-rich hydrothermal fluids, up-section. Base metal exhalite mineralization occurs approximately 1 km northeast of this location (Stops 1-7 and 1-8, Fig. 1-13). An east-southeast – west-northwest-trending post-volcanic shear zone is present in the northcentral part of the outcrop. The orientation of the schistosity adjacent to the shear zone indicates a dextral sense of shear. The shear zone is one of several east-southeast – west-northwest trending shears that occur at the Fivemile Lake Prospect. Similarly oriented dextral shear zones mapped by Peterson and Patelke (2003) between the north edge of the Murray Shear Zone and the Mine Shear zone in Sections 25 and 26, T. 62N, R. 15 W (approximately 2-3 km west of this location) have been interpreted as Reidel R structures. Page 23 23 �STOP 1-7: ALTERED PILLOW LAVAS, BASE METAL EXHALITE, SCORIA LAPILLI TUFF, NE OF FIVEMILE LAKE Location: (SE, NE, S.29, T.62N., R.14W., NAD83 UTM 564260E, 5297175N) Description: A 40-meter long, east-northeast striking, <1-2 meter thick chert-pyrite-chlorite ± chalcopyrite exhalite horizon crops out at this location approximately 50 meters northeast of Fivemile Lake (Fig. 1-13). Although this unit is volumetrically insignificant within the Fivemile Lake area, its presence is extremely important in terms of understanding potentially ore forming processes in this part of the Lower Ely. A lithogeochemical analysis of the exhalite (Hudak et al., 2002a) indicates slightly elevated Cu (470-509 ppm) and Zn (66-135 ppm). D. M. Peterson (personal communication, 1996) first recognized this unit as being similar in morphology and mineralogy to chemical exhalites associated with, and locally hosting, volcanic-associated massive sulfide mineralization in the Archean basalts and andesites within the Noranda mining camp of Quebec, Canada. This exhalite horizon appears to be on strike with the northernmost of four untested EM conductors that have been identified within Fivemile Lake (Peterson, 2001; Peterson and Jirsa, 1999a). Extremely detailed mapping (1:120 scale) has been completed (Hudak et al., 2002a) to further evaluate the stratigraphic and structural controls on this exhalite deposit (Fig. 1-14). The exhalite is relatively easy to distinguish from its surrounding rocks based on its deep red-brown, gossan-like, sulfidestained weathered surface. When broken, the exhalite is composed of vaguely banded chert and chlorite that contains 5-10% disseminated to banded pyrite. Locally, anhedral disseminated chalcopyrite and locally, extremely fine-grained, finely-disseminated, honey- to dark brown sphalerite grains are present in trace amounts. Detailed mapping indicates that the exhalite unit separates epidote + quartz + actinolite ± chlorite-altered basalt-andesite pillow lavas from overlying iron-chlorite- and sericite-altered basaltandesite tuffs and lapilli tuffs. The exhalite unit stratigraphically and conformably overlies the pillow lavas, and its sharp basal contact illustrates how the chemical sediment draped over the pillow-dominated paleotopography of the seafloor at the time of deposition. Locally, exhalite deposits cut through the pillow lavas, replacing the formerly glassy interpillow hyaloclastite. This relationship suggests that the interpillow hyaloclastite zones represented areas of high permeability, and these regions were the locus of hydrothermal fluid migration upward to, and possibly within the immediate subsurface, of the paleoseafloor. These features are consistent with the interpretation that this represents a region of ventproximal hydrothermal activity. The contact between the exhalite and the overlying lapilli tuff and tuff deposits is also sharp. It is important to note that fragments of the exhalite have not been observed in the basal parts of these overlying volcaniclastic deposits. In addition, no soft sediment deformation has been observed that could be attributed to syndepositional tractional deformation associated with the sedimentation of the overlying volcaniclastic rocks. This suggests that the exhalite deposit was relatively competent at the time the overlying tuffs were deposited. Such field evidence, combined with the lack of intense quartz-epidoteactinolite ± chlorite alteration (which is so prevalent in the footwall pillow basalts) in the overlying tuffs, also suggests that the hydrothermal activity associated with the genesis of the exhalite deposit was completed by the time that the overlying volcaniclastic rocks were deposited. Three other features suggest that exhalite deposition was closely associated with a volcanic ventproximal setting. First, property-scale mapping at Fivemile Lake (Hudak et al., 2002a) clearly illustrates that a synvolcanic diabase intrusion (observed in the previous stop) cross-cuts the stratigraphy in the immediate vicinity of the exhalite deposit (Fig. 1-9). Second, detailed mapping clearly indicates that the exhalite unit is abruptly terminated at its western margin by north to northwest striking pillow dikes that are similar in morphology to the pillow dikes that occur in close association with the peperite deposits Page 24 24 �Figure 1-14. Detailed geological map of exhalite mineralization northeast of Fivemile Lake (from Hudak et al., 2002a). Note the stratigraphic positioning of the chemical exhalite horizon between basalt-andesite pillow lava and basalt-andesite lapilli tuff, suggesting a period of volcanic quiescence which was accompanied by hydrothermal activity prior to the deposition of the lapilli tuff unit. Also note that the western part of the exhalite is cut by pillowed basalt-andesite dikes, once again suggesting the presence of a synvolcanic structure. Note that all UTM coordinates on the diagram are in NAD 27 coordinates. Page 25 25 �along the southwestern shoreline of Fivemile Lake. The location of both the diabase dikes and the pillow dikes clearly indicates the local presence of a major synvolcanic structure. Thick interpillow hyaloclastite deposits in the vicinity of the exhalite also suggest a vent-proximal environment (Newkirk et al., 2001a, 2001b; Hudak et al., 2002a). In summary, semi-massive sulfide exhalite associated mineralization clearly has formed within a volcanic (and associated hydrothermal) vent-proximal environment at Fivemile Lake. Such environments are commonly associated with economic massive sulfide mineralization in other lava-flow dominated Archean volcanic settings, such as at Noranda, Quebec (Gibson, 1989; Gibson et al., 1999; Santaguida, 1999). STOP 1-8: RHYOLITE LAVA DOME, NE OF FIVEMILE LAKE Location: (SE, NE, S.29, T.62N., R.14W., NAD 83 UTM 564440E, 5297160N) Description: The first day of our field trip concludes with an investigation of a 200-meter long, 15-45 meter thick unit of quartz-phyric, rhyodacitic to rhyolite lava that occurs approximately 200 meters northeast of Fivemile Lake (Figs. 1-9 and 1-13). The U/Pb zircon age for this unit is 2722.6 ± 0.9 Ma (Peterson et al., 2001). This biscuit shaped, relatively thick mass of rhyodacitic to rhyolitic is morphologically similar to felsic lava domes and cryptodomes (Cas and Wright, 1987). The presence of quartz-phyric lava fragments in epiclastic deposits approximately 400 meters southeast of this location, as well as the presence of the overlying subaqueously deposited volcaniclastic sediments and intermediate to mafic lava flows, suggests that this unit was at least partially emergent as a subaqueous lava dome. The uppermost contact of this unit is not exposed in outcrop. Where exposed in drill core (diamond drill hole SXL-2), the massive quartz-phyric lava is interstratified with, and overlain by, 1-2 meters of felsic tuff, which in turn, is overlain by pillowed basalt-andesite lava flows. The basal contact of the unit is exposed in diamond drill holes SXL-2 and SXL-3. In SXL-2, the basal contact is represented by a 3-meter thick shear zone composed of quartz, carbonate, sericite and green mica (fuchsite or mariposite?). In SXL-3, the base of the unit is immediately underlain by a 2-meter thick quartz-feldspar porphyry dike that, in turn, is underlain by a shear zone composed of quartz-carbonate-sericite-chlorite schist. This shear zone locally contains 1-3%, 1-8mm wide veins and bands composed of red to redbrown sphalerite. The presence of this shear zone conservatively precludes using the pillowed basaltandesite lava flows as reliable bounding facies; however, the lack of evidence for extensive structural transposition of the felsic lavas, the extremely thick sequence of pillow lavas stratigraphically below the felsic lavas, and the presence to the southeast of submarine epiclastic strata with felsic lava fragments identical in composition to the dome, suggest that the felsic lavas were formed in a subaqueous environment. Drill core intersections of these lava flows are characterized by a massive to faintly amygdaloidal (up to 1% 5mm rounded gray quartz amygdules), pale gray (least altered) to pale yellow green (sericitized) aphanitic groundmass which contains 1-4% grayish blue to colorless euhedral square to subhedral, locally broken, <1-2.5mm quartz phenocrysts (Fig. 1-15a). Pale brown to honey-colored sphalerite veins are locally present in the drill core and range from <1-8cm in width (Figure 1-15b). Two types of veins are present: a) sphalerite veins which are associated with quartz and/or chlorite, which display no indication of structural deformation (in-situ sphalerite veins); and b) sphalerite veins which are associated with local domains of quartz-sericite-ankerite schist, and appear to have been formed by local remobilization of sphalerite along post-volcanic shear zones (structurally remobilized sphalerite veins). The presence of in-situ sphalerite veins, and the abundance of structurally remobilized sphalerite veins in the quartz-phyric lava flows relative to other units in the Fivemile Lake area, suggests that the original Page 26 26 �sphalerite mineralization in the Fivemile Lake area was synvolcanic and associated with the massive quartz-phyric lava flows. As seen in this exposure, the quartz-phyric lava flows contain an aphanitic, pale-gray to gray groundmass. These lavas contain 5-8% 1-3mm diameter subhedral to square euhedral quartz phenocrysts that are locally broken. Rare, 2-4mm subhedral to euhedral quartz glomerocrysts are locally present. Faint, pale gray <1-2mm tabular feldspar phenocrysts are also present, and comprise up to 5% of the rock. Petrographic analysis indicates that lavas are characterized by a very fine-grained quartzo-feldspathic groundmass and subhedral to euhedral quartz phenocrysts that are locally resorbed. Alteration minerals that occur in the groundmass include sericite, epidote, clinozoisite/zoisite, iron-carbonate and iron-rich chlorite. Also present on the southwest side of this outcrop is a northeast-trending, post-volcanic quartzfeldspar porphyry dike. Figure 1-15. Drill core appearance of unmineralized, sericite-altered rhyolite dome (A, SXL-2-173’) and silicified rhyolite dome cut by red-brown “honey-colored” sphalerite veins (B, SXL-2-280’). Modified from Hudak et al. (2002a). Scale bar units are centimeters. FIELD TRIP STOPS – DAY 2 (MAY 5) Figure 1-16. Locations of field trip stops 1-9, 1-10, and 1-11. Page 27 27 �STOP 1-9: FLUIDAL PEPERITES AND VOLCANIC VENT FACIES, NORTH SHORELINE OF FIVEMILE LAKE No hammering please! Location: (SE, NW, S.29, T.62N., R.14W., NAD 83 UTM 563590E, 5297215N). Note: We will be accessing the north side of Fivemile Lake via a private road. Obtain permission to use this road from people in the first house on the right as you turn onto this private drive. Description: Detailed (1:100 to 1:2000 scale) mapping by Hudak et al. (in prep. a) and Hudak (in press) has identified the paleo-vent of a relative small basalt-andesite tuff cone volcano immediately north of this location (Figs. 1-9 and 1-16). The vent facies here is well exposed in a series of outcrops along the north shoreline of Fivemile Lake, and is extremely complicated (Fig. 1-17a). At this location, we can observe steeply north dipping, east-west striking basalt-andesite pillow lavas that occur stratigraphically beneath the tuff cone, and the contact between the pillowed flows and the vent fill deposits, which are composed of exceptionally well preserved blocky to amoeboid peperites (Figs. 1-17 b and 1-17c). The contact between the pillowed flows and the vent fill deposits is interpreted to be a synvolcanic fault zone. Several jigsaw puzzle-fit, more or less in-situ pillow lava blocks can be observed within the vent fill deposits near this contact. The basalt-andesite tuff comprising the vent fill deposits have been intruded by a series of andesite-dacite dikes that are compositionally identical to the pillowed dikes observed southwest of this location at “Pike Point”. Interactions between the wet, unconsolidated vent fill tuffs and the dikes have produced an absolutely spectacular deposit of amoeboid peperite. The peperite displays several exceptional textures, including: 1) jigsaw puzzle-fit igneous component lapilli and blocks indicative of in-situ fragmentation; 2) local contact metamorphosed zones ranging from a few millimeters to a few centimeters in width immediately adjacent to the lapilli and blocks within the peperite; 3) local chilled margins on the peperite fragments indicating rapid quenching and fragmentation of the igneous component from interactions with relatively cool, wet, unconsolidated vent fill tuffs; 4) complicated amoeboid peperite, especially on the northeastern part of the outcrop; and 5) the presence of 1-2mm diameter, commonly quartz-filled vesicles within the vent fill tuffs. Also note the presence of 1-2 cm wide, several centimeter-long parallel bands containing high abundances (20-50%) of 1-2mm vesicles. These bands are generally more or less parallel with the margins of adjacent igneous component peperite fragments, but locally, these bands show no preferred directional relationship with the margins of nearby clasts. Petrographic observations (Hudak et al., in press; Hudak et al., in prep. b) indicate that these zones are composed of parallel bands of highly vesicular, locally plagioclase-phyric fragments that are compositionally identical to the coherent igneous component clasts in the peperite. The origin of the bands may be related to collapse of thin vapor films along the margin of the hot igneous component as occurs in laboratory simulations of peperite formation (Zimanowski and Buttner, 2002). The parallel bands in this outcrop may have formed when the margins of the igneous component shattered due to explosive interaction with external water as the vapor film collapsed. The parallel bands observed on the outcrop indicate that this process occurred periodically and continually. Such a process is consistent with the pulsating phreatic and phreatomagmatic eruptions that occur in shallow submarine environments. Page 28 28 �DETAILED GEOLOGICAL MAP FIVE MILE LAKE PEPERITE Pillow Basalt - Andesite Pepe.te - Igneous Componenl [j] Pepenle - Sedimentary Component [] Miyg.iuie-ric, banding Figure 1-17. Detailed geological map (A) of the vent facies of a basalt-andesite tuff cone volcano located north of Fivemile Lake. Photographs A and B illustrate amoeboid peperite and parallel, vesicle-rich zones present in the outcrop. Page 29 29 �STOP 1-10: CENTRAL BASALT SEQUENCE SHEET FLOWS, PILLOW LAVAS, AND PERLITIC HYALOCLASTITE, HILLTOP S OF HIGHWAY 169 Location: (SE, SW, S.19, T.62N., R.14W., NAD 83 UTM 56200E, 5297800N) Description: The Central Basalt sequence (Peterson and Patelke, 2003) comprises a steeply northdipping (75°- vertical), north-facing sequence of sparsely amygdaloidal pillowed and massive lava flows of basalt composition that are believed to be correlative with the tholeiitic Armstrong Lake volcanic sequence mapped by Jirsa et al. (2001) in the Eagles Nest quadrangle. Relative to massive and pillowed basalt and andesite flows in the Fivemile Lake sequence, Central Basalt sequence lavas flows are notably less amygdaloidal, and lack multiple pillow rind structures. In addition, the Central Basalt sequence lacks the thick sequences of scoriaceous basalt-andesite lapilli tuffs that are commonly interstratified with lava flows in the Fivemile Lake sequence. These characteristics of the Central Basalt sequence indicate eruption and deposition in a deeper submarine environment than the stratigraphically older Fivemile Lake sequence, and suggest overall increasing water depth during the temporal development of the Lower Ely. This field trip stop (Fig. 1-16) displays exceptional preservation of fine-scale volcanic textures that are characteristic of the Central Basalt sequence. The outcrop comprises two east-southeast striking massive basalt flows, ranging from at least five to nine meters in thickness, that are separated by a ten meter thick flow unit comprising pillows and pillow lobes (Fig. 1-18). Flow 1, at the southern part of the outcrop, is composed of a pale- to dark green, faintly feldspar-phyric (~10% 0.5-1 mm laths), sparsely amygdaloidal, basalt sheet flow that locally exhibits tortoise-shell jointing formed in response to contraction during cooling. The uppermost 10-40 cm of the coherent part of Flow 1 is generally silicified and epidotized. Petrographic observations (Hudak et al., in prep. b) indicate that this section of the flow also contains up to 70% <0.1 cm round spherulites. An irregular contact occurs between the coherent basalt flow and an overlying one- to two meter thick unit of dark green, exceptionally well-preserved perlitic in-situ hyaloclastite and associate self-peperite (c.f. Batiza and White, 2000). The hyaloclastite formed from non-explosive fracturing of the basalt glass developed on the flow top due to quenching by water, whereas the perlite formed following deposition by hydration of volcanic glass. Irregular, amoeboid apophyses of coherent basalt, ranging from 10-30 cm thick and up to 1.5 meters long, locally intrude into the hyaloclastite. These apophyses have pale green cores and dark green, very fine-grained margins which grade outward into in-situ, jigsaw-fit perlitic hyaloclastite. An irregular contact occurs between the hyaloclastite and Flow 2, which is composed of north-facing mattress- to bun-shaped pillow lavas and pillow lobes with numerous “neck and knob” structures. Individual pillows have well developed perlitic hyaloclastite margins that range from 1-4 cm in width. Pillow buds indicate propagation from east to west, suggesting the volcanic vent was located east of this location. A NNE-trending D3 normal fault with a 10 cm displacement occurs in this unit on the southeastern part of the outcrop. The coherent pillows and lobes are overlain by up to 2.5 meters of hyaloclastite breccia that contains 20-40% subround to subangular pale gray green basalt lapilli in a jigsaw puzzle-fit dark green perlitic hyaloclastite matrix. The upper contact of Flow 2 and the overlying basalt sheet flow (Flow 3) is irregular, and is marked by thin (1-8 cm thick), sheet-like basalt fragments that are up to 1.6 meters in length. These fragments locally appear to be isoclinally folded about an east-west-trending fold hinge. Although the genesis of this structure is currently not well understood, it may be due to syneruptive deformation of either thin slabs of hot, basal flow margin crust from the overlying flow, or thin injections of basalt magma into the hyaloclastite from either the underlying pillows or the overlying sheet flow. Flow 3 comprises an at least ten-meter thick pale green-gray, slightly feldspar-phyric, sparsely amygdaloidal sheet flow. Steep, NNE-trending west dipping D3 joints are well developed in this unit, as are lensshaped psuedo-pillows that are up to 50 cm in diameter. Page 30 30 �Figure 1-18. Detailed geological map of sheet flows, pillow lavas, hyaloclastite, and associated “self-peperite” at field trip stop 1-10. Page 31 31 �STOP 1-11: Location: RHYODACITE BLOCK AND ASH FLOW DEPOSITS, NORTH SHORELINE OF NEEDLEBOY LAKE (Optional Stop, NW, SW, S.21, T.62N., R.14W., NAD 83 UTM 564855E, 5298360N) This is an optional stop, as it requires a moderately strenuous 20-30 minute hike along a poorly maintained, easy to trip upon trail. Be extremely careful and watch for protruding boulders and cobbles on the trail. Description: A 50 meter-thick unit of quartz-phyric rhyolite tuff and lapilli tuff crops out in a series of several closely-spaced outcrops along the northwestern shoreline of Needleboy Lake (Fig. 1-16). The pale gray to green-gray matrix contains 1-3% subhedral to angular quartz phenocrysts and crystal shards, 10-15% 1-5 cm subangular to subround pumice lapilli, and locally, up to 15% 2-11 cm subround to subangular quartz-phyric rhyolite lava lapilli and bombs which locally display a crude jigsaw puzzle-fit. Both the pumice and the felsic lava clasts are locally crudely stratified. Pumice lapilli altered by epidote commonly occur as pale green fragments within the deposits. The central part of the outcrop contains a well-developed, east-west trending, steeply north-dipping shear zone. Boudinage locally occur in the rhyolite deposits within this shear zone. A 30-35 meter thick gabbro sill occurs immediately north of this shear zone. This unit is characterized by an equigranular medium gray-green to brownish-green color, with pale green epidote altered feldspar and deep green actinolite present. Petrographic observations (Hudak et al., in prep. a) indicate that the gabbro has a sub-ophitic texture. Locally, steeply-dipping northsouth-trending D3 joints and east-west-trending quartz epidote veins may be observed on the northeastern side of this series of outcrops. A large east-west-trending outcrop occurs approximately 40 meters northwest of the northern-most outcrop near the shoreline. The southernmost 5 meters of the outcrop comprises a mafic lapilli tuff that contains up to 5% subangular silicified mafic lapilli. This tuff is progressively deformed into dark green chlorite schist with a well-developed, east-west-trending, steeply south-dipping S2 foliation. The chlorite schist is in sharp contact with a massive, 3-12 meter-thick quartzand feldspar-phyric rhyodacite sill. The sill is overlain by a mafic lapilli tuff containing up to 25% subangular to subround, locally jigsaw puzzle-fit amygdaloidal basalt and scoria clasts. Felsic volcaniclastic deposits at the base of the outcrop are interpreted to represent a sequence of variably-altered rhyolite block and ash flow deposits. Block and ash flow deposits are unsorted deposits with an ash-matrix containing both monolithologic, low-vesicularity lava lapilli and blocks and pumice lapilli and blocks that may display normal or reverse coarse-tail grading (Cas and Wright, 1987; Freundt et al., 2000). The deposits are formed during the explosive collapse of lava domes, and can occur in either the subaerial or submarine environment (Hudak, 1996; Gibson et al., 1999). These deposits are believed to have been initially overlain by a series of basalt-andesite tuffs and lapilli tuffs; however, a synvolcanic gabbro sill intruded the contact between and subsequently separated these two units. Deformation that is concentrated along the contacts between this sill and the adjacent supracrustal strata is attributed to strain partitioning due to different rheological properties during the D2 deformation event. STOP 1-12: SYNVOLCANIC FAULT ZONE WITH “EPIDOSITES”, SE OF SIXMILE LAKE Location: (NE, SE, S.21, T.62N., R.14W., NAD 83 UTM 565860E, 5298535N) During the hike through the swampy area, be extremely careful to walk on areas with vegetation and tree roots. Description: The next several stops (1-12 through 1-17) represent a north-south section through the uppermost parts of the Lower Ely (Fig. 1-19). Basalt-andesite lava flows in this region vary from massive to pillowed, and are generally less amygdaloidal than the basalt-andesite lava flows in the southern part of the section near Fivemile Lake. The purpose of this stop is to investigate a northeast-trending, Page 32 32 �disconformable zone of intensely quartz + epidote ± actinolite altered pillow lavas (epidosites), and to observe one of the post-volcanic quartz-feldspar porphyry dikes that commonly occur within the volcanic sequence. Figure 1-19. Detailed geological map of the area southeast of Sixmile Lake. Field trip stop locations 1-12 through 1-17 are also illustrated on the map. The first outcrop we will investigate is composed of intensely epidote + quartz-altered basaltandesite pillows and lobes. The pillows may be difficult to see due to the intense synvolcanic hydrothermal alteration, but may be located by identifying actinolite ± chlorite-altered zones of interpillow hyaloclastite, as well as concentrated zones of 0.1-1.0 cm round to oval actinolite ± chloritefilled amygdules which occur within the pillow selvedges. Dark gray veins of magnetite with minor amounts of pyrite, chalcopyrite, and malachite up to 1 cm in width occur primarily within interpillow hyaloclastite zones, but also locally cross-cut the interiors of the pillows and lobes. The patchy pistachiogreen and pink coloration on the outcrop is due to the presence of pistacite epidote (green) and zoisiteclinozoisite (pale pink). Santaguida et al. (2002a, 2002b) indicate that epidote compositions within epidote-quartz altered rocks in the Noranda Volcanic Complex of Quebec are sensitive to small-scale variations in fluid:rock ratios within individual alteration zones due to primary permeability differences in the strata being altered. Hannington et al. (2002) note that within the Proterozoic Kristineberg VMS district of Sweden, zoisite-clinozoisite formation occurs in regions altered at relatively high fluid:rock ratios and high temperatures by acidic hydrothermal fluids. The second outcrop to observe occurs approximately 20 meters to the southwest of the first outcrop, and is located near the top of a prominent east-northeast trending ridge. Compositionally, the rock is identical to the first outcrop. Texturally, the rock is intensely brecciated, containing lapilli- to block-sized subangular fragments of intensely epidote + quartz-altered amygdaloidal basalt. Disconformable zones containing jigsaw-fit epidosite occur proximal to synvolcanic fault zones in the Josephine Ophiolite (Harper, 1999). Based on detailed mapping, the northeast trending, disconformable Page 33 33 �zone of epidosite comprising these outcrops has been interpreted by Hudak et al. (2002b) as being proximal to a synvolcanic fault zone. The third outcrop occurs approximately due north of the second outcrop visited. Exposed at this location is a relatively fresh quartz-feldspar porphyry dike. Similar quartz-feldspar porphyry dikes commonly occur throughout this region of the Vermilion district. Figure 1-20. Photographs of intensely epidote-altered basalt-andesite lava flows from the area southeast of Sixmile Lake. Photo A shows brecciated, intensely epidote–quartz altered pillow lavas. Photo B shows typical relationships between intense epidote alteration, stockwork quartz veins, magnetite stringers, and sulfide staining. STOP 1-13: SYNVOLCANIC FAULT ZONE WITH EPIDOSITES, SE OF SIXMILE LAKE Location: (SE, NE, S.21, T.62N., R.14W., NAD 83 UTM 565850E, 5298560N) Description: Several relatively small outcrops of intensely epidote + quartz ± actinolite ± chloritealtered basalt-andesite pillow lavas occur along the southwestern part of an east-west trending ridge at this location. These rocks are mineralogically similar to those investigated at the previous outcrop; however, despite their intense alteration, they display extremely well preserved primary volcanic textures. The pillows at this location are primarily bun-shaped, and range from approximately 1-1.5 meters in diameter. Interpillow hyaloclastite zones range from <1-2 cm in width, and are pale yellow green in color due to the presence of epidote, actinolite, and chlorite. Pillow selvedges and cores once again vary in color from pale green to pinkish green due to variable percentages of pistacite and clinozoisite/zoisite. The pillow selvedges and cores contain up to 5% 0.1-1.0 cm diameter round to oval quartz ± actinolite ± chlorite-filled amygdules. STOP 1-14: STRINGER COPPER MINERALIZATION IN BASALT–ANDESITE, AND SERICITE-ALTERED RHYODACITE TUFFS, SE OF SIXMILE LAKE Location: (SE, NE, S.21, T.62N., R.14W., NAD 83 UTM 565910E, 5298655N) Description: Another small group of outcrops occurs approximately 50 meters northeast of the previous outcrops investigated (Fig. 1-19). Stratigraphically, we are now positioned within the uppermost 100 to 200 meters of the Lower Ely. At this location, we can observe locally brecciated, strongly epidote + quartz-altered, and locally actinolite- and chlorite-altered basalt-andesite pillow lavas. Pillows at this outcrop are significantly smaller (generally approximately 0.5 meters in diameter) than those observed in the previous outcrop, suggesting that we are positioned near the top of a pillowed flow unit (Dimroth et Page 34 34 �al. (1978) and Staudigal and Schminke (1984) have shown that pillows generally decrease in size near the top of a pillowed unit, and attribute this to change in pillow size due to decreasing effusion rates as an individual eruption comes to an end). The outcrop also locally contains up to 5% dark gray stringer-like veins of magnetite with associated pyrite, chalcopyrite, malachite, and associated deep-red sulfide burn (Fig. 1-21a). These veinlets are commonly parallel to a series of quartz stockwork veins that trend approximately 080° and dip steeply to the north. Both the magnetite-sulfide veins and quartz stockwork veins are consistent with cooling of a high temperature, iron-, base metal-, and silica-rich hydrothermal fluid in the shallow seafloor, and may represent stringer mineralization that occurs immediately downsection from massive sulfide mineralization. Figure 1-21. Mineralization and alteration present at field trip stop 1-14. Photograph A illustrates malachite mineralization associated with magnetite-chalcopyrite veins within altered basalt pillow lavas. B shows sericitealtered felsic tuff deposits located immediately up-section from the altered mafic lavas in photograph A. The pillow lavas are immediately overlain by a 10-20 meter thick sequence of sparsely quartz and plagioclase-phyric rhyodacite tuffs (Fig. 21b). These volcaniclastic deposits typically are brownish-gray in color due to the presence of abundant sericite. Close-up observation of the unit reveals the presence of approximately 1% sub-1mm anhedral to subhedral quartz crystal chips, and 2-3% 1 mm diameter subhedral to euhedral tabular plagioclase feldspar phenocrysts. Rare pumice lapilli can be observed with careful observation; they range from 1-2 cm in diameter, are generally rounded to oval in shape, and contain up to 50% sub-1mm round vesicles (originally carbonate vesicles which have now been weathered-out based on petrographic observations by Hudak et al. (in prep. a)). The pumice lapilli in this outcrop increase in abundance from the base toward the top of the unit. Such inverse grading of pumice may be the result of subaerially erupted air fall deposited into the ocean, as large, cold pumice generally take longer to saturate and sink than small, cold pumice (Whitham and Sparks, 1986). This tuff horizon may represent the distal equivalent to fragmental felsic rocks mapped by Peterson and Patelke (2003) that occur stratigraphically below the Ely Greenstone – Soudan Member and the Soudan Mine. Sericite alteration is common in submarine felsic volcaniclastic rocks (Gibson et al., 1989), and may be associated with either vertically extensive discordant pipe-like alteration zones associated with hydrothermal upflow zones, or laterally extensive semiconformable alteration zones formed by extensive shallow seafloor seawater metasomatism of permeable submarine strata. More detailed mapping will be necessary to determine with certainty the geometry of the sericite alteration zone observed in this outcrop. The exposures of felsic tuff dive abruptly to the north into a swamp. Hand auger boring in this swamp (NAD 83 UTM location 0565938E, 5298671N) yielded dark black, organic-rich soil containing abundant, angular, variably weathered clasts of massive pyrite. Stringer copper mineralization, sericitealtered felsic tuffs, the presence of massive sulfide in the subsurface beneath the swamp, and the presence Page 35 35 �of rare sulfide lapilli in volcaniclastic deposits north of the swamp (seen in the next outcrop) suggests that the swamp may be underlain by a massive sulfide horizon (Hudak et al., 2002b). STOP 1-15: CHERT, BANDED IRON-FORMATION AND SEDIMENTARY STRATA, SE OF SIXMILE LAKE ASSOCIATED CLASTIC Location: (SE, NE, S.21, T.62 N., R.14W., NAD 83 UTM 565840E, 5298760N) Be extremely careful when walking on these outcrop surfaces and descending into the small valley immediately south of these outcrops, as they are commonly very slippery. Description: North of the swamp, a southeast-trending outcrop ridge comprises a sequence of volcaniclastic and chemical sedimentary strata (Fig. 1-19). The purpose of this stop is to observe the variety of interflow sedimentary rocks that occur in this upper part of the Lower Ely, to observe wellpreserved sedimentary textures, and to see further evidence for the presence of ancient hydrothermal activity southeast of Sixmile Lake. A series of small outcrops occurring along the northwestern part of the outcrop ridge comprises west-northwest striking, steeply north dipping 10-30 cm thick chemical exhalites (chert horizons and banded magnetite + chert ± jasper banded iron-formation horizons) are that are interbedded with 10-60 cm thick, well-stratified horizons of mudstones, wackes, and matrix-supported polymict diamictites. The base of the stratigraphic sequence occurs at the southern end of the outcrop, where a 20 cm thick magnetite-rich horizon of banded iron-formation occurs (Fig. 1-22a). This chemical sedimentary horizon is overlain by a several meter-thick sequence of interbedded, laminated to bedded, commonly normally graded, mudstones and polymict diamictites interpreted to have formed from submarine debris flows and turbidity currents. The polymict diamictites range from 10-60 cm thick, and contain up to 5% 1-2.5 cm lens-shaped chert clasts, 10-40% silicified or chlorite-altered mafic volcanic lapilli, and rare (<1%) <12cm sulfide-rich fragments. Locally, clasts within the diamictites are vaguely imbricated. Interbedded mudstone horizons are up to 40 cm thick, and locally display cross beds that indicate stratigraphic topping direction is north. Iron-formation horizons at this location indicate that low temperature exhalative hydrothermal activity was occurring in this part of the Lower Ely. It is interesting to note that these iron-formation horizons occur in the area that would be immediately up-section from the possible sulfide horizon within the swamp to the south. Several VMS horizons in similar volcanic sequences within Canada are capped by iron-formations (Franklin et al., 1981). Debris flows and/or turbidity currents that deposited the polymict diamictites and associated mudstones periodically interrupted periods of relatively lowtemperature hydrothermal activity that formed the iron-formation horizons. Clasts within the diamictites are similar to the volcanic and chemical sedimentary strata that occur in the immediate vicinity of the deposits based on detailed mapping (Hudak et al., in prep. a). Chert clasts within the diamictites were likely derived from the iron-formation horizons. Rare sulfide-rich fragments locally contained within the diamictites also suggest that VMS mineralization occurred on or near the paleoseafloor in the vicinity of the area that is now Sixmile Lake, supporting the interpretation that a massive sulfide horizon may be present beneath the swamp which separates the outcrops at this stop from those at the previous stop. Page 36 36 �_J\ \.a' Figure 1-22. Sedimentary strata in the uppermost parts of the Lower Ely. Figure 1-22a shows oxide-facies banded iron-formation and chert exhalites located up-section from altered tuffs seen at field trip stop 1-15. Figure 1-22b shows diamictites that contain abundant chert clasts and rare sulfide clasts. These deposits are also located stratigraphically up-section from the felsic tuffs seen at the previous stop. STOP 1-16: EPIDOTE-QUARTZ ALTERATION ON MARGIN OF DIABASE/GABBRO SILL, SE OF SIXMILE LAKE Location: (SE, NE, S.21, T.62N., R.14., NAD 83 UTM 565960E, 5298790N) The outcrop at this stop occurs on the Sixmile Lake Road. Be attentive for automobiles, trucks, and four-wheelers when observing this outcrop. Description: This relatively small (3 meters by 5 meters) outcrop exposes the northern margin of the east-west-trending gabbro-diorite sill that extends from at least southwest of Sixmile Lake to at least 500 meters east of this location (Fig. 1-19; Hudak et al., in prep.). The southern two-thirds of the outcrop comprises pale green to pinkish green, epidote- and clinozoisite/zoisite-altered subophitic gabbro which contains up to 1% 1-5mm quartz- and/or actinolite-filled amygdules. Numerous north-northeast, steeply west-dipping joints were developed during the regional D3 deformation. The uppermost one-third of the outcrop contains an in-situ hyaloclastite breccia comprising pale-to dark green angular, locally jigsaw puzzle-fit, iron chlorite + actinolite + zoisite/clinozoisite-altered gabbro lapilli in a pinkish-tan to tan matrix of sericite, epidote, and zoisite/clinozoisite (Fig. 1-23a). This outcrop illustrates, in part, the difficulty in determining hydrothermally altered flow top breccias from hyaloclastite breccias and/or peperites that form from intrusion of sills into wet, relatively unconsolidated sediments that occur within the shallow seafloor. The intense hydrothermal alteration that occurs at the northern margin of the outcrop indicates that high water:rock ratio, high temperature (>300°C) hydrothermal alteration was focused in the permeable, sill-marginal, hyaloclastite or peperite (?) breccia. Synvolcanic sills intruded into the shallow seafloor are important heat sources that drive hydrothermal circulation cells that form VMS deposits (Campbell et al., 1981). Sills such as the one exposed at this outcrop may have contributed significantly to the formation of Algoma-type banded ironformation within the overlying Soudan Iron Formation, and perhaps, VMS mineralization within the uppermost parts of the Lower Ely or the Soudan Iron Formation. Page 37 37 �Figure 1-23. Synvolcanic sills and banded iron-formations in the uppermost parts of the Lower Ely. Figure 1-23a shows the uppermost margin of a gabbro/diorite sill that has apparently intruded wet, unconsolidated sediments to form an extremely altered hyaloclastite or sill-marginal peperite. Figure 1-23b shows folded banded iron-formation horizons that occur approximately 10 meters up-section from the sill. STOP 1-17: BANDED IRON-FORMATION, NORTH OF SIXMILE LAKE ROAD Location: (SE, NE, S.21, T.62N., R.14W., NAD 83 UTM 565953E, 5298823N) Description: Two outcrops located within 30 meters north of the Sixmile Lake Road contain relatively thin (<1-2 meters) magnetite-chert horizons interbedded with mafic to intermediate composition volcaniclastic sedimentary strata, and illustrate features common to the uppermost parts of the Lower Ely. Based on detailed mapping by Peterson and Patelke (2003) and Hudak et al. (in prep. a), the uppermost 50-200 meters of the Lower Ely is transitional into the base of the Soudan Iron Formation. Basalt – andesite lava flows and volcaniclastic sedimentary strata decrease in abundance, whereas Algoma-type banded iron-formations become more common as one progresses up-section through this transition zone. This sequence records the change from a period of dominantly effusive submarine volcanism to a period marked by chemical sedimentation. The outcrop closest to the road contains strongly deformed magnetite-chert iron-formation interbedded with iron-chlorite-rich metasediments. Microfossils are locally present in the Vermilion district iron-formations, and hint at a biogenic contribution to their formation (LaBerge, 1973). Deformation has produced more or less north-northwest striking, steeply dipping beds. The deformation that occurs in these strata is not regionally observed, and is believed to be a local phenomenon resulting from syndepositional intrusion of the mafic sill observed in the previous stop. A later quartz-feldspar porphyry dike occurs at the northeastern end of this small outcrop. Note the localized sulfide staining along the contact between the intrusion and adjacent banded iron-formation. The second outcrop, located approximately 30 meters north of the road, contains poorly exposed mafic – intermediate volcaniclastic strata and associated banded iron-formation horizons. The best exposures of the banded iron-formations occur at the southeastern edge of the outcrop. At this location, the magnetite-chert iron-formations locally contain veins and stringers of malachite, along with up to 20% pale brown garnet (x-ray analysis performed by Hudak et al. (in prep. a) indicate that the garnet is andradite). The presence of malachite is indicative of the local high concentrations of copper within the uppermost parts of the Lower Ely. Similar copper mineralization within the Soudan Iron Formation has been identified by Peterson and Patelke (2003) in the 12th level of the Soudan Mine. Page 38 38 �REFERENCES Barrett, T. J. and MacLean, W. H., 1994, Chemostratigraphy and hydrothermal alteration in exploration for VHMS deposits in greenstones and younger volcanic rocks: in Lentz, D. R. (ed.), Alteration and alteration processes associated with ore-forming systems: Geological Association of Canada Short Course Notes, v. 11, p. 433-467. Barrett, T. J., and MacLean, W. H., 1999, Volcanic sequences, lithogeochemisty, and hydrothermal alteraton in some bimodal volcanic-associated massive sulfide systems: Reviews in Economic Geology, v. 8, p. 101-131. Barrie, C. T., Ludden, J. N., and Green, T. H., 1993, Geochemistry of volcanic rocks associated with CuZn and Ni-Cu deposits in the Abitibi subprovince: Economic Geology, v. 88, p. 1341-1358. Batiza, R., and White, J. D. L., 2000, Submarine lavas and hyaloclastite: in Sigurdsson, H., Encyclopedia of Volcanoes: Academic Press, San Diego, CA, p. 361-381. Bauer, R. L., 1985, Correlation of early recumbent and youger upright folding across the boundary between an Archean gneiss belt and greenstone terrane, northeastern Minnesota: Geology, v. 13, p. 657-660. Boerboom, T. J., and Zartman, R. E., 1993, Geology, geochemistry, and geochronology of the central Giants Range batholith, northeastern Minnesota: Canadian Journal of Earth Science, v. 30, p. 2510-2522. Campbell, I. H., Franklin, J. M., Gorton, M. P., Hart, T. R., and Scott, S. D., 1981, The role of synvolcanic sills in the generation of massive sulfide deposits: Economic Geology, v. 87, p. 511541. Cas, R. A. F., and Wright, J. V., 1987, Volcanic Successions: London, Allen and Unwin, 528 p. Corfu, F. and Stott, G. M., 1998, Shebandowan greenstone belt, western Superior Province: U-Pb ages, tectonic implications, and correlations: Geological Society of America Bulletin, v. 110, p. 14671484. Dimroth, E., Cousineau, P., Leduc, M., and Sanschagrin, Y., 1978, Structure and organization of Archean subaqueous basalt flows, Rouyn-Noranda area, Quebec, Canada: Canadian Journal of Earth Science, v. 15, p. 902-918. Drexler, H., and Hudak, G. J., and Peterson, in press, A field and laboratory study to evaluate the genetic relationships between the Purvis pluton and volcanic rocks and volcanic-associated mineralization in the Vermilion district of NE Minnesota: 50th Annual Meeting, Institute on Lake Superior Geology, Proceedings and Abstract Volume 50. Franklin, J. M., 1986, Volcanic associated massive sulfide deposits – an update: in Andrew, C. J., Crowe, R. W. A., Finlay, S., Pennell, W. M., and Pyne, J. F. (eds.), Geology and Genesis of Mineral Deposits in Ireland, Irish Association for Economic Geology, p. 49-69. Franklin, J. M., 1993, Volcanic-associated massive sulfide deposits: in Kirkham, R. V., Sinclair, W. D., and Thorpe, R. I. (eds.), Geology of Canadian Mineral Deposit Types: Geological Survey of Canada, no. 8., p. 158-183. Franklin, J. M., 1996, Volcanic-associated massive sulfide base metals; in Eckstrand, O. R., Sinclair, W. D., and Thorpe, R. I. (eds.), Geology of Canadian Mineral Deposit Types; Geological Survey of Canada, no. 8, p. 158-183. Page 39 39 �Franklin, J. M., Hannington, M. D., Jonasson, I. R., and Barrie, C. T., 1998, Arc-related volcanogenic massive sulfide deposits, in Metllogeny of Volcanic Arcs: British Columbia Geological Survey, Short Course Notes, Open File 1998-8, Section N. Franklin, J. M., Sangster, D. M., and Lydon, J. W., 1981, Volcanic associated massive sulfide deposits: Economic Geology 75th Anniversary Volume, p. 485-627. Freundt, A., Wilson, C. J. N., and Carey, S. N., 2000, Ignimbrites and block and ash flow deposits: in Sigurdsson, H., Encyclopedia of Volcanoes: Academic Press, San Diego, CA, p. 581-599. Fyon, J. A., Breaks, F. W., Heather, K. B., Jackson, S. L., Muir, T. L., Stott, G. M., and Thurston, P. W., 1992, Metallogeny of metallic mineral deposits in the Superior Province of Ontario: in Thurston, P. C., Williams, H. R., Sutcliffe, R. H., and Stott, G. M. (eds.), Geology of Ontario, Special Volume 4, Part 2, p. 1091-1176. Galley, A., 2002, Characteristics of composite subvolcanic intrusive complexes associated with Precambrian VMS districts: in Galley, A., Bailes, A., Hannington, M., Holk, G., Katsube, J., Parquette, F., Paradis, S., Santaguida, F., and Taylor, B., 2002, CAMIRO Project 94E07: Interrelationships between subvolcanic intrusions, large-scale alteration zones, and VMS deposits: Geologic Survey of Canada Open-File Report 94E07, p. 1-40. Galley, A., 2003, Composite synvolcanic intrusions associated with Precambrian VMS-related hydrothermal systems: Mineralium Deposita, v. 38, p. 443-473. Gibson, H. L., 1989, The Mine Sequence of the Central Noranda Volcanic Complex: Geology, Alteration, Massive Sulfide Deposits, and Volcanological Reconstruction: unpublished Ph. D. dissertation, Carleton University, Ottawa, Ontario, Canada, 800 p. Gibson, H. L., Morton, R. L., Hudak, G. J., 1999. Submarine volcanic processes, deposits and environments favorable for the location of volcanic-associated massive sulphide deposits: Reviews in Economic Geology, v 8, p. 13-51. Hannington, M. D., Kjarsgaard, I. M., Santaguida, F., and Cathles, L. M., 2002, Mineral-chemical studies of regional-scale hydrothermal alteration in the Central Blake River Group, Western Abitibi Subprovince: Part 1. Summary of results from the Noranda Volcanic Complex: Geologic Survey of Canada Open-File Report 94E07, p. 47-76. Hannington, M. D., Poulsen, K. H., Thompson, J. F. H., and Sillitoe, R. H., 1999, Volcnaogenic gold in the massive sulfide environment: Reviews in Economic Geology, v. 8, p. 325-356. Harper, G. D., 1999, Structural styles of hydrothermal discharge in ophiolite / sea-floor systems: Reviews in Economic Geology, v. 8, p. 53-73. Harris, N. B. W., Pearce, J. A., and Tindle, A. G., 1986, Geochemical characteristics of collision-zone magmatism: in Coward, M. P., and Reis, A. C. (eds.), Collision Tectonics, Special Publication of the Geological Society 19, p. 67-81. Hocker, S. M., Hudak, G. J., and Heine, J., 2003, Electron microprobe analysis of alteration mineralogy at the Archean Fivemile Lake volcanic-associated massive sulfide mineral prospect in the Vermilion district of northeastern Minnesota: Natural Resources Research Institute Report of Investigations NRRI/RI-2003/17, 49 p. Hooper, P., and Ojakangas, R., 1971, Multiple deformation in the Vermilion district, Minnesota: Canadian Journal of Earth Sciences, v. 8, p. 423-434. Page 40 40 �Hovis, S. T., 2001, Physical volcanology and hydrothermal alteration of the Archean volcanic rocks at the Eagles Nest volcanogenic massive sulfide prospect, northern Minnesota: unpublished M. S. thesis, University of Minnesota – Duluth, Duluth, Minnesota, 137 p. Hudak, G. J., 1996, The physical volcanology and hydrothermal alteration associated with late caldera volcanic and volcaniclastic rocks and volcanogenic massive sulfide deposits in the Sturgeon Lake region of northwestern Ontario, Canada: unpublished Ph. D. dissertation, University of Minnesota, Minneapolis, Minnesota, 463 p. Hudak, G. J., Heine, J., Newkirk, T., Odette, J., and Hauck, S., 2002a, Comparative geology, stratigraphy, and lithogeochemistry of the Fivemile Lake, Quartz Hill, and Skeleton Lake VMS occurrences, Vermilion district, NE Minnesota: A report to the Minerals Coordinating Committee, DNR, Minerals Division, State of Minnesota: Natural Resources Research Institute Technical Report NRRI/TR-2002/03, 390 pages. Hudak, G. J., Heine, J., Hocker, S. M., and Hauck, 2002b, Geological mapping of the Needleboy Lake – Sixmile Lake area, northeastern Minnesota: a summary of volcanogenic massive sulfide potential: Natural Resources Research Institute Report of Investigation NRRI/RI-2002/14, 15 p. Hudak, G. J., Heine, J., Newkirk, T. T., and Hocker, S., in prep. a, Comparative geology, stratigraphy, and lithogeochemistry of the Needleboy Lake to Sixmile Lake area, Vermilion district, NE Minnesota: Natural Resources Research Institute Technical Report. Hudak, G. J., and Morton, R. L., 1999, Mineral Potential Study, Minnesota Department of Natural Resources Project 326, Bedrock and Glacial Drift Mapping for VMS and Lode Gold Alteration in the Vermilion – Big Fork Greenstone Belt, Part A: Discussion of Lithology, Alteration, and Geochemistry at the Fivemile Lake, Eagles Nest, and Quartz Hill Prospects: Minnesota Department of Natural Resources Division of Minerals Project 326 Report, 136 p. Hudak, G. J., Morton, R. L., Franklin, J. M., and Peterson, D. M., 2003, Morphology, distribution, and estimated eruption volumes for intracaldera tuffs associated with volcanic-hosted massive sulfide deposits in the Archean Sturgeon Lake Caldera Complex, NW Ontario: American Geophysical Union Geophysical Monograph 40, Explosive Subaqueous Volcanism, p. 345-360. Hudak, G. J., Newkirk, T. T., Drexler, H., Odette, J., and Hocker, S. M., in press, Neoarchean peperites in the vicinity of Fivemile Lake, Vermilion district, NE Minnesota: 50th Annual Meeting, Institute on Lake Superior Geology, Proceedings and Abstract Volume 50. Hudak, G. J., Newkirk, T. T., Drexler, H., Hocker, S. M., Peterson, D. M., and Heine, J., in prep. b, Neoarchean peperites in the Fivemile Lake area of the Vermilion district, NE Minnesota. Hudleston, P.J., 1976, Early deformational history of Archean rocks in the Vermilion district, northeastern Minnesota: Canadian Journal of Earth Sciences, v. 13, p. 579-592. Hudleston, P. J., Schultz-Ela, D., and Southwick, D. L., 1988, Transpression in an Archean greenstone belt, northern Minnesota: Canadian Journal of Earth Sciences, v. 25, p. 10601068. Jirsa, M. A., 2000. The Midway sequence: a Timiskaming-type pull-apart basin deposit in the western Wawa subprovince, Minnesota: Canadian Journal of Earth Sciences, v. 37, p. 1-15. Jirsa, M. A., Boerboom, T. J., and Peterson, D. M., 2001, Bedrock geological map of the Eagles Nest Quadrangle, St. Louis County, Minnesota: Minnesota Geological Survey, Miscellaneous Map M-114, scale 1:24,000. Page 41 41 �Jirsa, M.A., Southwick, D.L., and Boerboom, T.J., 1992, Structural evolution of Archean rocks in the western Wawa subprovince, Minnesota: refolding of precleavage nappes during D2 transpression: Canadian Journal of Earth Sciences, v. 29, p. 2146-2155. Kawachi, Y., and Pringle, I. J., 1988, Multiple-rind structure in pillow lava as an indicator of shallow water: Bulletin of Volcanology, v. 50, p. 161-168. LaBerge, G. L., 1973, Possible biological origin of Precambrian iron-formations: Economic Geology, v. 68, p. 1098-1109. Lawler, T., and Riihiluoma, D., 1997, Minralized clast study, greenstone belt boulder tracing, Ely-Bigfork area, northern Minnesota, Township 60-65 north, Range 11-17 west: Minnesota Department of Natural Resources Division of Minerals Report 318, 41 p. Lundy, J.R., 1985, Clues to structural history in the minor folds of the Soudan Iron Formation, northeastern Minnesota: Unpublished M.S. thesis, University of Minnesota, Minneapolis, 144p. McPhie, J., Doyle, M., and Allen, R., 1993, Volcanic Textures – a guide to the interpretation of textures in volcanic rocks: Centre for Ore Deposit and Exploration Studies, University of Tasmania, 198 p. McPhie, J., and Orth, K., 1999, Peperite, pumice, and perlite in submarine volcanic successions: implications for VHMS minralisation: Proceedings of PACRIM’99, Bali, Indonesia, p. 643-648. Morey, G. B., Green, J. C., Ojankangas, R. W., and Sims, P. K., 1970, Stratigraphy of the lower Precambrian rocks in the Vermilion district, northeast Minnesota: Minnesota Geological Survey, Report of Investigations 14, 33 p. Morton, R. L., and Franklin, J. M., 1987, Two-fold classification of Archean volcanic-associated massive sulphide deposits: Economic Geology, v.82, p. 1057-1063. Newkirk, T., Hudak, G. J., and Hauck, S. A., 2001a, Preliminary lava flow morphology studies at the Fivemile Lake VMS prospect, Vermilion district, NE Minnesota: Implications for volcanic processes, volcanic paleoenvironments, and VMS exploration: Institute on Lake Superior Geology, 47th Annual Meeting, Proceedings Volume 47, Part 1- Program and Abstracts, p. 69-70. Newkirk, T., Hudak, G. J., and Hauck, S. A., 2001b, Preliminary lava flow morphology studies at the Fivemile Lake VMS prospect, Vermilion district, NE Minnesota: Implications for volcanic processes, volcanic paleoenvironments, and VMS exploration: Geological Society of America Abstracts and Programs Volume 33, No. 6, p. A-398. Odette, J. D., Hudak, G. J., Suszek, T., and Hauck, S. A., 2001a, Preliminary evaluation of hydrothermal alteration mineral assemblages and their relationship to VMS-style mineralization in the Fivemile Lake area of the Archean Vermilion Greenstone Belt, NE Minnesota: Institute on Lake Superior Geology, 47th Annual Meeting, Proceedings Volume 47, Part 1-Program and Abstracts, p. 75-76. Odette, J. D., Hudak, G. J., Suszek, T., and Hauck, S. A., 2001b, Preliminary evaluation of hydrothermal alteration mineral assemblages and their relationship to VMS-style mineralization in the Fivemile Lake area of the Archean Vermilion Greenstone Belt, NE Minnesota: Geological Society of America Abstracts and Programs Volume 33, No. 6, p. A-420. Pearce, J. A., Harris, N. B. W., and Tindle, A. G., 1984, Trace element discrimination diagrams for the tectonic interpretation of granitic rocks: Journal of Petrology, v. 25, p. 956-983. Page 42 42 �Peterson, D. M., 2001, Development of Archean lode-gold and massive sulfide deposit exploration models using geographic information system applications: targeting mineral exploration in northeastern Minnesota from analysis of analog Canadian mining camps: unpublished Ph. D. dissertation, University of Minnesota, Duluth, Minnesota, 503 p. Peterson, D. M., Gallup, C., Jirsa, M. A., and Davis, D. W., 2001, Correlation of Archean assemblages across the U.S.- Canadian border: Phase I geochronology: 47th Annual Meeting, Institute on Lake Superior Geology, Proceedings Volume 47, Part 1 – Programs and Abstracts, p. 77-78. Peterson, D. M., and Jirsa, M. A., 1999a, Bedrock Geological Map and Mineral Exploration Data, Western Vermilion district, St. Louis and Lake Counties, Northeastern Minnesota: Minnesota Geological Survey Miscellaneous Map Series M-98, scale 1:48,000. Peterson, D. M., and Jirsa, M. A., 1999b, Lode gold and massive sulfide prospects in the Archean western Vermilion district: Minnesota Exploration Association, Minnesota Exploration Conference, Field Trip Guidebook, 10 maps, 30 p. Peterson, D. M., and Patelke, R. L., 2003, National Underground Science and Engineering Laboratory (NUSEL): Geological site investigation for the Soudan Mine, Northeastern Minnesota: Natural Resources Research Institute Technical Report NRRI/TR-2003/29, 88 p. Peterson, D. M., and Patelke, R. 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L., (compiler), 1993, Bedrock geologic map of the Soudan-Bigfork area, northern Minnesota: Minnesota Geological Survey, Miscellaneous Map M-79, scale 1:100,000. Southwick, D. L., Boerboom, T. J., and Jirsa, M. A., 1998, Geologic setting and descriptive geochemistry of Archean supracrustal and hypabyssal rocks, Soudan-Bigfork area, northern Minnesota: implications for metallic mineral exploration: Minnesota Geological Survey, Report of Investigations 51, 69 p. Staudigal, H., and Schminke, H.U.-, 1984, The Pliocene seamount series of La Palma, Canary Islands: Journal of Geophysical Research, v. 89, p. 11195-11215. Whitham, A. G., and Sparks, R. S. J., 1986, Pumice: Bulletin of Volcanology, v.48 , p. 209-223. Williams, H. R., Stott, G. M., Heather, K. B., Muir, T. L., and Sage, R. P., 1991, Wawa Subprovince: in Thurston, P. C., Williams, H. R., Sutcliffe, R. H., and Stott, G. M. (eds.), Geology of Ontario, Special Volume 4, Part 1, p. 485-542. Winchester, J. A., and Floyd, P. A., 1976, Geochemical magma type discrimination; application to altered and metamorphosed basic igneous rocks: Earth and Planetary Science Letters, v. 28, p. 459-469. Winchester, J. A., and Floyd, P. A., 1977, Geochemical discrimination of different magma series and the differentiation products using immobile elements: Chemical Geology, v. 20, p. 325-343. Wood, D. A., 1980, The application of a Th-Hf-Ta diagram to problems of tectonomagmatic classification and to establishing the nature of crustal contamination of basaltic lavas of the British Tertiary Volcanic Province: Earth and Planetary Science Letters, v. 50, p. 11-30. Zimanowski, B., and Buttner, R., 2002, Dynamic mingling of magma and liquefied sediments: Journal of Volcanology and Geothermal Research, v. 114, p. 37-44. Page 44 44 �FIELD TRIP 2 Geologic Highlights of New Mapping in the Southwestern Sequence of the North Shore Volcanic Group and in the Beaver Bay Complex Leaders: Terry Boerboom, Jim Miller Minnesota Geological Survey, University of Minnesota and John Green Department of Geological Sciences, University of Minnesota Duluth Split Rock Lighthouse Point (Stop 2-8) Page 45 �FIELD TRIP 2 Geologic Highlights of New Mapping in the Southwestern Sequence of the North Shore Volcanic Group and in the Beaver Bay Complex by Terry Boerboom, Jim Miller Minnesota Geological Survey, University of Minnesota and John Green Department of Geological Sciences, University of Minnesota Duluth INTRODUCTION For the past 20 years, the Minnesota Geological Survey has been actively conducting detailed (1:24,000-scale) bedrock geologic mapping in northeastern Minnesota. This effort began in 1985 with a mapping project focussed on delineating the geology of the intrusive Beaver Bay Complex in the central part of the region. This eight-year project was partially supported by USGS's COGEOMAP program and resulted in publication of five geologic maps (Miller, 1988; Miller and others, 1989, 1993, 1994; Boerboom and Miller, 1994) covering ten 7.5' quadrangles (Fig. 1). More recently, geologic mapping in northeastern Minnesota has focused on the shoreline quadrangles between Duluth and Split Rock Point, where it joins up with the Beaver Bay mapping. This ongoing mapping, which began in 2001, has produced four geologic maps (Boerboom and others, 2002a, 2002b, 2003a, 2003b) with another currently in production (Fig. 2-1). Mapping in the Two Harbors NE quadrangle, scheduled for this coming field season, and publication of quadrangles of the Duluth metropolitan area later this year, will result in 1:24,000-scale coverage of mappable bedrock along the North Shore from Duluth to Tofte. Long-range plans are to continue to systematically map the shore to the Canadian border. Figure 2-1. North Shore 7.5' quadrangles mapped by the MGS through the USGS-sponsored COGEOMAP and STATEMAP programs. Page 46 �This field trip is intended to highlight some of the characteristic and more intriguing aspects of North Shore geology that the recent detailed mapping has revealed. Of course, there are many more interesting geologic features than we can show in two days. Hopefully, you will take advantage of the geologic maps that have been produced of this area to explore more of its fascinating geology. VOLCANIC AND SEDIMENTARY ROCKS OF THE SOUTHWESTERN SEQUENCE OF THE NORTH SHORE VOLCANIC GROUP by John Green This overview is a slightly modified expert from the MGS Report of Investigations 58, Chapter 5: "Volcanic and sedimentary rocks of the Keweenawan Supergroup in Northeastern Minnesota" by John Green (Miller and others, 2002). Magmatic activity related to the 1.1 Ga Midcontinent Rift produced a more than 10 kilometer thick edifice of lava flows and subvolcanic intrusions that are exposed along Minnesota's north shore of Lake Superior. The lava flows and minor sedimentary rocks are referred to as the North Shore Volcanic Group (Goldich and others, 1961) and the intrusive rocks are variably assigned to the Duluth Complex, the Beaver Bay Complex, and miscellaneous intrusions of the Midcontinent Rift Intrusive Supersuite (Fig. 2-3). Although previous publications have subdivided the North Shore Volcanic Group into informal volcanic suites and distinctive flows (Green, 1972, 1982), the 1:200,000-scale map (M-119, Miller and others, 2001) accompanying the report of Miller and others (2002) represents the first time that the North Shore Volcanic Group has been subdivided into formational entities on a geologic map. A brief description of the North Shore Volcanic Group and associated sedimentary formations of the Keweenawan Supergroup is given here to supplement the information provided on the geologic map about these formational units. Rock classification, recognition, and textures As a coherent tholeiitic compositional suite, the volcanic rocks of the North Shore Volcanic Group can be described using only a few rock names (Fig. 2-2). The most primitive rocks are olivine tholeiites, which form an iron-enrichment trend with further evolution. They display ophitic textures and pahoehoe surfaces nearly everywhere. Most olivine tholeiites are aphyric, but those that are porphyritic contain dominantly plagioclase phenocrysts, less commonly olivine. Transitional basalts contain somewhat higher alkalies and other incompatible elements than the olivine tholeiites, but generally not enough to classify them as alkalic. Their texture is typically intergranular and fine- to medium-grained. Porphyritic varieties generally contain small phenocrysts of plagioclase, olivine, clinopyroxene, and magnetite. The reversed-polarity Hovland lavas, however, are characterized by transitional basalts (grading to basaltic andesites) that contain abundant, large, tabular, plagioclase phenocrysts. Transitional basalt flow surfaces are generally smooth (pahoehoe), although a few show breccia tops. The basaltic andesites and andesites (greater than 52 percent SiO2) are tholeiitic, rather than calcalkaline; they show iron enrichment and contain only anhydrous ferromagnesian minerals. These rocks are typically fine-grained and intergranular to felty or pilotaxitic, and many contain small phenocrysts of plagioclase, olivine, clinopyroxene, and magnetite. The andesites generally weather to a red-brown color, and have flow-brecciated (aa) tops but not bases. Many flows that contain 50 to 55 percent silica show millimeter-scale oxidation lamination (Green, 1989) parallel to the base. A few highly iron-enriched flows, separable only by chemical analysis, can be called ferroandesites. Page 47 �Figure 2-2. AFM compositional diagram for the lavas of the North Shore Volcanic Group (modified from Green, 1982). The boundary between tholeiitic and calc-alkalic rocks is modified from Irvine and Barager (1971). FeO* = FeO + 0.9Fe2O3. Carmichael (1964) first used the name "icelandite" for rocks intermediate in character between andesites and rhyolites in the Tertiary lavas of eastern Iceland. They might be considered the tholeiitic equivalent of calc-alkaline dacite in orogenic suites. Other examples of these rocks have been described from the Galapagos (McBirney and Williams, 1969) and the Miocene of Nevada–Oregon (Wallace and others, 1980). Very large flows of similar composition in the Etendeka volcanics of Namibia have been referred to as quartz latites by Milner and others (1992). Icelandites in the North Shore Volcanic Group (Green and Fitz, 1993) are characterized chemically by SiO2 contents ranging from 60 to 68 percent, high FeO* (averaging 7 percent), K2O + Na2O values between 6.5 and 9 percent, a potassium/sodium atomic ratio of about 0.9, and an Mg number [Mg/(Mg + Fe) atomic] averaging 0.14. Petrographically, North Shore Volcanic Group icelandites grade continuously from the andesites to somewhat paler colors (brown or tan), but have a similar phenocryst assemblage. Quartz and alkali feldspar are common in the groundmass but never occur as phenocrysts. Flowtop features (crusty to coarsely brecciated) indicate that the icelandites were erupted as lavas. The rhyolites have higher silica and total alkali contents, and lower FeO than the icelandites. They are generally light gray, pink, or red. Several are very thick, extensive, and voluminous (up to several hundred cubic kilometers; Green and Fitz, 1993). Although most rhyolites are porphyritic (phenocrysts of quartz, alkali feldspar ± plagioclase, and altered fayalite ± ferroaugite), some lack quartz and alkali feldspar phenocrysts, and rare flows are aphyric. Groundmass textures are fine-grained holocrystalline, typically with a meshwork of platy quartz paramorphs after primary tridymite, which may show a flow structure. A "snowflake" texture is common, in which poikilitic quartz patches (coalesced ex-tridymite grains) enclose small, dusty alkali-feldspar grains. In quartz-phyric flows, these poikilitic quartz patches are in optical continuity with adjacent quartz phenocrysts (Green, 1990). Outcrop-scale flow structure, including folding, is common near flow tops and bases. In some flows, distinct fiamme, deformed to varying degrees, are recognizable. These imply an explosive eruption that produced a pyroclastic flow, which welded and remobilized to produce a rheoignimbrite. Page 48 �Structure and Lithostratigraphy As stated above, the Midcontinent Rift volcanic rocks and interbedded redbeds in northeastern Minnesota comprise the North Shore Volcanic Group (Goldich and others, 1961; Green, 1972, 1977, 1982; Basaltic Volcanism Study Project, 1981). In general, these rocks form an arcuate stack that is slightly tilted toward the southeast and forms the roof rocks into and under which the Duluth Complex and associated hypabyssal intrusions were emplaced. At the southwest end of the North Shore Volcanic Group near Duluth, the volcanic rocks strike north with a 10º to 20º easterly dip; at the northeast end at Grand Portage, the flows strike east–west with a 10º southerly dip (Fig. 2-3). Thus, traveling northeast along the Lake Superior shore northeast from Duluth, and southwest from Grand Portage, one encounters successively higher flows in the volcanic stratigraphy until the Tofte–Lutsen area in southern Cook County, where the highest exposed flows crop out. Exposure is generally excellent along the eroding lakeshore, and along the lower, high-gradient stretches of tributary streams, providing good control on the stratigraphy. A stack of volcanic rocks approximately 9.7-kilometers-thick has been measured in the “southwest limb” (Table 2.1), and another stack of volcanic rocks about 7.2-kilometers-thick has been measured in the “northeast limb” (See Table 5.2, Miller and others, 2002). This implies nearly continuous subsidence during the rifting process. The difference in stratigraphic thickness between the two limbs reflects major complications in the central area, which appears not to have subsided at the same rate as in the limbs, and into which many of the subvolcanic intrusions were emplaced. Except for the capping Schroeder–Lutsen basalt sequence, no stratigraphic unit can be traced from one limb to the other; each limb has its own stratigraphic column. To aid in the correlation of intrusive and extrusive rock units throughout the Midcontinent Rift system, their paleomagnetic polarity has been used. Nearly all of the igneous and sedimentary rocks associated with the Midcontinent Rift were formed either during an earlier, reversed-polarity interval or a succeeding normal-polarity interval. Thus, in each limb of the North Shore Volcanic Group, the lower stratigraphic units show reversed polarity, and the upper sequences show normal polarity. This polarity reversal forms the basis for distinguishing upper and lower sequences in the northeast and southwest limbs. U-Pb zircon dates demonstrate that the reversed-polarity magmatism occurred mainly in the time interval from 1108 to 1107 Ma; whereas, around the Lake Superior basin, normal-polarity magmatism occurred mainly in the interval from 1099 to 1094 Ma (for example Davis and Paces, 1990; Paces and Miller, 1993; Davis and Green, 1997). These two pulses were separated by a magmatically inactive time (at least in the upper crust), which appears to be expressed as a slight unconformity in the volcanic sequence on the north shore. However, because intrusions subsequently penetrated along this horizon in the North Shore Volcanic Group, this unconformity has not been recognized in outcrop. The Duluth Complex separates the upper and lower sequences of the southeastern limb (Fig. 2-3, Table 2.1). One other significant gap in the stratigraphic continuity of the North Shore Volcanic Group occurs near the stratigraphic top, where the Schroeder–Lutsen sequence overlies the upper units of the northeast and southwest sequences (Fig. 2-3, Table 2.1). In the northeast limb, southwest of Grand Marais (Fig. 2-3), the basal flow of the Schroeder–Lutsen sequence (Terrace Point basalt member) overlies a thick sandstone and siltstone unit (Cut Face Creek sandstone), which in turn conformably overlies the Good Harbor Bay andesites of the upper northeast sequence (See Table 5.2, Miller and others, 2002 for details). However, in the southwest limb, the basal Schroeder–Lutsen sequence flow overlies a thinner sandstone and conglomerate unit (the Little Marais conglomerate) that in turn rests in sharp angular unconformity atop structurally disturbed flows of the Belmore Bay lavas near Little Marais (Table 2.1). Furthermore, the gently dipping Schroeder basalts have not been penetrated by the abundant hypabyssal intrusions of the Beaver Bay Complex that complicate the underlying volcanic sequence in this mid-shore area (Green, 1992; Miller and others, 1993). Attempts to date the Schroeder–Lutsen sequence have been unsuccessful to this point. Page 49 �______ ______ ' MESOPROTEROZOIC (KEWEENAWAN) INTRUSIVE ROCKS Beaver Bay Complex and Felsic rocks Misc. Intrusions 1 Mafic rocks Mafic rocks Duluth Felsic rocks Complex NoRTH SHORE VOLCANIC GROUP PALEOPROTERZOIC RoveNirgin ia/Thomson Fm ' General attitude of volcanic rocks Gunflint/Bwabik Fe-Fm ARCH EAN I Southwest Lower 0 10 20 30 40 50 Kilometers Granitoid Intrusions Supracrustal Rocks Sequence Figure 2-3. Simplified geology of northeastern Minnesota showing the major sequences of the North Shore Volcanic Group (taken from Fig. 5.2, Miller and others, 2002). The five lithostratigraphic sequences comprising the two limbs of the North Shore Volcanic Group are further subdivided into informal formational units (Table 2-1). Some formational units are individual flows of distinctive lithology and/or substantial thickness and lateral extent. Most are suites of lava flows that have distinct lithologic characteristics or that are separated by intrusions. Some lava formations contain distinct flows or sedimentary rock units within an otherwise homogeneous package of lavas. Such units are given informal member rank (such as the Silver Beaver rhyolite member of the Baptism River lavas, Manitou transitional basalt member of the Schroeder basalts, and Indian Camp sandstone member of the Lutsen basalts). See Chapter 1 of RI58 (Miller and others, 2002) for more details on stratigraphic nomenclature of Keweenwan rock in northeastern Minnesota. Page 50 �Table 2-1. Generalized stratigraphy of the southwest limb of the North Shore Volcanic Group showing U/Pb ages (Davis and Green, 1997; Green and others, 2001). Positions of intrusions denote approximate stratigraphic level affected and not age of emplacement. Thickness(m) Lithostratigraphic units Lithologic character U/Pb ages 9735 945 Total section 150 Carlton Quarry lavas (fault bounded) Schroeder–Lutsen sequence (normal polarity) 900 Schroeder basalts <45 Little Marais conglomerate basalt, andesite, and rhyolite flows 1094.3±2.0 ophitic olivine tholeiite basalt flows; includes Manitou transitional basalt and Pork Bay breccia polymict volcanic conglomerate and sandstone angular unconformity 8275 Upper southwest sequence (normal polarity) 565 Bell Harbor lavas 100 Palisade Head rhyolite mostly quartz tholeiite basalt and basaltic andesite flows gray-pink, porphyritic rhyolite flow ~1096 Beaver Bay Complex 700 1096.6±1.7 mixed lavas, mostly basalt; includes Baptism River lavas 165-meter-thick Silver Beaver rhyolite 20 Silver Bay porphyritic basalt ophitic basalt flow with abundant large plagioclase phenocrysts 730 Gooseberry River basalts mixed basalt flows, mostly ophitic Lafayette Bluff, Silver Creek diabase intrusions 315 Two Harbors basalts 550 Larsmont basalts mixed aphyric basalt flows; quartz tholeiite flows at base ophitic olivine tholeiite flows Stony Point–Knife Island diabase sheet 1500 Sucker River basalts mixed basalt flows, mostly ophitic 1350 Lakewood lavas mostly basalt flows; rhyolite, icelandite, and ferroandesite at base Lester River diabase sill 1285 mixed basalt, andesite, icelandite, and rhyolite flows Lakeside lavas 1098.4±1.9 Endion diabase sill 1160 mixed basalts, andesites Leif Erickson Park lavas ~1099 Duluth Complex 370 Lower southwest sequence (reversed polarity) 370 Ely's Peak basalts porphyritic, diabasic, and ophitic basalts; pillowed and pyx-phyric basal flow >8 Nopeming Sandstone white to tan quartzite and conglomerate angular unconformity Thomson Formation (Paleoproterozoic) Page 51 �Physical volcanology The volcanic rocks of the Midcontinent Rift, including the North Shore Volcanic Group, represent one of the world’s oldest and best-preserved examples of plateau lavas. However, they are not typical in that they contain a greater thickness of flows and, in the North Shore Volcanic Group, a higher proportion of evolved compositions. They are similar physically and chemically to the Tertiary lavas that make up eastern Iceland (Sigvaldason, 1974; Green, 1977; Wood, 1978), and they formed similarly over a plume at another major rift. The rocks also resemble the late Tertiary and Quaternary volcanic rocks of the southern Snake River Plain, Idaho and southeastern Oregon, because of their interbedded basalts and large rhyolites (e.g., Bonnichsen and Kauffman, 1987; Manley, 1996). The basalts range in character from typical flood flows as voluminous as tens of cubic kilometers to more modest, “plains-type” flows (Greeley, 1982) and thin flow units less than a meter thick. At Duluth in the southwest limb, and Grand Portage in the northeast limb, the lowest flows in the volcanic sequences are pillowed, and thus inferred to have erupted subaqueously; however, nearly all of the other flows were erupted subaerially. The flows show different physical characteristics, closely tied to their chemical compositions and viscosities (Green, 1989; Green and Fitz, 1993). Olivine tholeiites, which dominate the North Shore Volcanic Group, all have pahoehoe surfaces, with or without ropy structures. Other physical characteristics of the various rock types were previously discussed in the “Rock classification, recognition, and textures” section of this guide. All of the flows ranging in composition from basalts to icelandites were erupted as lavas. The rhyolites are notable in their abundance relative to other plateau-lava sequences, their size (up to several hundred cubic kilometers), and extent (Green and Fitz, 1993). Several rhyolites show textural evidence of rheomorphic flow after eruption as ash-flow tuffs, though some were lavas. One of the largest, the Devil Track rhyolite in Cook County, which is as thick as 250 meters and can be traced for 40 kilometers along strike, has ambiguous features that make its mode of eruption difficult to discern; it may be a lava flow. Nearly all the icelandites and rhyolites show evidence of an unusually high temperature of eruption, such as magmatically crystallized groundmass tridymite. The evidently low viscosity of these large rhyolites is attributed to their high temperature, high iron and fluorine contents, and low oxidation state (Green and Fitz, 1993). Geochemistry and chemostratigraphy The North Shore Volcanic Group constitutes a subalkalic, tholeiitic suite that ranges continuously from rather primitive olivine tholeiite to rhyolite, and shows a strong iron-enrichment trend (Fig. 2-2; also Basaltic Volcanism Study Project, 1981; Brannon, 1984). However, relative abundances are strongly bimodal; basalts are greatly predominant, but rhyolites make up 10 to 25 percent of the section. The basalts show trace element and isotopic evidence of derivation mostly from a mantle plume (Nicholson and others, 1997), whereas most of the rhyolites include major contributions from partial melting of the Archean basement (Vervoort and Green, 1997). The most common basalt type, ophitic olivine tholeiite, is generally aluminum-rich (16 to 18 percent Al2O3); the most primitive flows have Mg numbers of about 0.65 to 0.68. The basal few flows in both limbs of the North Shore Volcanic Group have a unique geochemical and petrographic character. Typically they contain augite phenocrysts, are aluminum-poor, and are rich in both compatible (chromium and nickel) and incompatible elements (titanium, phosphorus, and lanthanum) with steep chondrite-normalized lanthanum/ytterbium ratios. This suggests derivation by relatively small-fraction melting of the initial plume head (Nicholson and others, 1997; Green, 1995). In general, there is little stratigraphic regularity of compositional change within the North Shore Volcanic Group, with the following exceptions. In the middle of the upper southwest sequence, there is a marked upward progression toward more primitive compositions through a 3.4-kilometer section from rhyolite east of the Lester River into a thick group of primitive olivine tholeiites in the Knife River–Two Page 52 �Harbors area (Brannon, 1984). This includes the Lakewood lavas, the Sucker River basalts, and the Larsmont basalts. In contrast, in the lower northeast sequence, the approximately 1-kilometer-thick basal Grand Portage lavas progress upsection from basalt to increasingly evolved compositions, ending with Red Rock rhyolite (Green, 1995). As mentioned above, the Schroeder–Lutsen sequence, the youngest in the North Shore Volcanic Group, is composed almost entirely of olivine tholeiites. All of the North Shore Volcanic Group has been affected to some degree by hydrothermal/burial metamorphism. The more permeable (fractured, vesicular) tops and bases of the flows have undergone considerable mineralogical change (deposition of amygdule minerals, alteration of primary minerals), but in many cases the massive flow interiors are remarkably little-altered. Where alteration has approached equilibrium, mineral assemblages range from lower greenschist facies at the base of the North Shore Volcanic Group to zeolite facies at the top (Schmidt, 1993; Schmidt and Robinson, 1997). Interflow Sedimentary Rocks Clastic redbed strata occur at many horizons within the North Shore Volcanic Group (Jirsa, 1984). They are lenticular and range in thickness from a few centimeters to about 100 meters. As these rocks are relatively soft and erodable compared to the adjacent volcanic flows, they are mostly covered and are exposed only along actively eroding sites such as streambeds and the lakeshore. They are predominantly red to brown, well sorted sandstone, with minor conglomerate, siltstone, and shale. Conglomerate beds are most abundant in the midshore area from Little Marais to Lutsen. Compositionally, these redbeds are mainly immature lithic arkose and feldspathic lithic arenite (see Fig. 5.3, Miller and others, 2002). The angular to subrounded clasts are mainly plagioclase, mafic to felsic volcanic rock fragments, clinopyroxene, and Fe-Ti oxides; devitrified or replaced volcanic ash particles and shards are present in a few beds. Quartz is uncommon to absent. The framework grains have been variably cemented with hematite, calcite, prehnite, and a variety of zeolites, depending on the local hydrothermal/burial/contact metamorphic conditions. In some places hydrothermal minerals have replaced many or most of the clasts. A few of these redbed units have thicknesses in excess of 25 meters. These include a crossbedded sandstone in Leif Erickson Park in Duluth (35 meters), which disconformably overlies an eroded basalt flow; the Little Marais conglomerate (and sandstone) exposed in the Manitou River area near Little Marais (as thick as 45 meters); the Indian Camp sandstone (68 meters) northeast of Lutsen; and the Cut Face Creek sandstone southwest of Grand Marais (100 meters), which can be traced for at least 4 kilometers along strike. Of these, the Little Marais and Cut Face Creek units occur at the base of the Schroeder–Lutsen basalt sequence. The sandstone in these units is typically planar- or cross-bedded, and some beds are ripple-marked or mud-cracked. The rocks are inferred to be dominantly fluvial, deposited by moderate-gradient, east- to southwest-flowing streams from sources nearly entirely within the subsiding Midcontinent rift basin (Jirsa, 1984). Many flow-top breccias of andesite and basalt with aa structure contain laminated red sandstone as a matrix because sand filtered down from the flow surface. Similarly, red, laminated sandstone and siltstone form clastic dikes or crevice-fillings a few centimeters wide in the upper parts of some lava flows. Page 53 �INTRUSIONS WITHIN THE SOUTHWESTERN SEQUENCE OF THE NSVG by Terry Boerboom Several hypabyssal sills and sheet-like intrusions occur within the 7-kilometer-thick section of volcanic rocks exposed near Lake Superior from Duluth to Split Rock Point. From lowest to highest in the section, these consist of the Endion Sill, the Northland sill, the Lester River Sill, the Stony Point diabase, the Silver Creek diabase, the Lafayette Bluff diabase, and the Split Rock intrusive felsite. These sheets are variably concordant to the volcanic strata, range from tens of meters to over 500 meters thick, and generally dip gently eastward. They commonly form prominent topographic highlands. This discussion will be limited to those sills visited by this field trip. For a more complete description, see Miller and others, 2002. Lester River diabase The Lester River diabase is named for the outcrops adjacent to the mouth of the Lester River (Schwartz and Sandberg, 1940). The diabase forms a prominent topographic high (Moose Mountain) that extends about 6.5 miles inland from Lake Superior. The diabase forms a sill some 400-m (1,300-feet) thick that dips an average of 19 degrees southeast, conformable with the dip of the surrounding volcanic rocks. The sill generally overlies basalt and underlies rhyolite, the latter of which probably formed a density barrier that trapped the more dense mafic magma as it was emplaced. The upper margin of the sill contains abundant intermediate to felsic rocks that form a continuous, mappable unit along the entire mapped length of the sill, in contrast to the lower margin which contains only thin and discontinuous pods of the hybrid felsic rocks. The hybrid cap rocks likely formed by partial melting of the overlying rhyolite by heat generated from the underplating sill. Jerde (1991) provides considerable geochemical, petrographic, and petrologic data on the Lester River Sill. Most of the Lester River diabase is a dark grayish-black, medium- to coarse-grained, massive to locally weakly porphyritic diabase. The diabase contains approximately 60% plagioclase, 13% intergranular to subophitic augite, 12% variably altered olivine, 0-4% orthopyroxene, 1-4% Fe-Ti oxides, 0-10% quartz and granophyre, 1-3% diktytaxitic chlorite, and less than one percent apatite, biotite, and hornblende. Quartz commonly contains wispy rutile needles. Silver Creek diabase The Silver Creek diabase is named for proximity to Silver Creek, near Silver Cliff, located about 4 miles northeast of Two Harbors. This diabase is composed almost entirely of medium-grained ophitic olivine diabase, with augite oikocrysts from 1 to 5 centimeters in diameter. It forms a subcordant to discordant subhorizontal sill-like intrusion, at least 60-m (200-feet thick), that forms a prominent highland projecting inland about 7 kilometers north-northeast of Lake Superior, and is exposed intermittently for several kilometers beyond. In the area of the Encampment River, the diabase is in subvertical contact with surrounding volcanic and earlier intrusive rocks; this may have been the feeder to the sill. The diabase is free of anorthosite inclusions and contains only rare xenoliths of volcanic rocks. Pope (1976) studied the Silver Creek diabase as part of Master’s thesis under the guidance of Dr. John Green. The Silver Cliff tunnel on Highway 61 cuts through this diabase. Lafayette Bluff diabase The Lafayette Bluff diabase is named after prominent exposures at Lafayette Bluff, forms prominent knobs near Lake Superior but is typically weathered to a brown crumbly grus. It is an irregular, discordant, sheet- to dike-like body composed of soft, dark greenish-black, amygdaloidal and porphyritic Page 54 �diabase, with local differentiated masses of coarse-grained to pegmatitic ferromonzodiorite inland from Lake Superior. The diabase contains locally abundant 1-3 meter diameter inclusions of anorthosite and scattered xenoliths of metamorphosed basalt. The Lafayette Tunnel on Highway 61 has been excavated through the Lafayette Bluff diabase. Split Rock intrusive felsite The Split Rock intrusive felsite (rhyolite) is a pink, fine-grained, weakly porphyritic, flow-banded rock that has a prominent shingle parting to it (hence: Split Rock River). At a given location, the rhyolite has all the physical attributes of a rhyolite flow, but detailed mapping shows that it forms a north-striking, 3.4 kilometer wide body that cuts north from Lake Superior across the stratigraphy of the surrounding volcanic rocks. The felsite forms cliffs on Lake Superior south of the Split Rock River, and in the Split Rock River and nearby streams forms small, sharp canyons. Field measurements show that the flow banding dips gently towards the central axis of the body, implying that the intrusion is keel-shaped. The lower margins of the rhyolite are intruded by, or commingled with, a dark gray, fine-grained ferrodiabase or ferrodiorite. This felsite is exposed in the Split Rock Point 7.5’ quadrangle, which is currently a work in progress as one of the USGS STATEMAP series of geologic maps to be published by the Minnesota Geological Survey. Due to time constraints, this field trip will not visit this unit. GEOLOGY OF THE BEAVER BAY COMPLEX by Jim Miller The Beaver Bay Complex (BBC) is a hypabyssal, multiple-intrusive igneous complex that was emplaced into the upper part of the NSVG over a 600-km2 area in northeastern Minnesota (Fig. 2-4). Much of this area was the focus of detailed bedrock mapping by the Minnesota Geological Survey between 1985 and 1992 (Miller, 1988; Miller and others, 1989, 1993a, 1994; Boerboom and Miller, 1994). Three general areas of the BBC, southern, northern, and eastern, are distinguished on the basis of distinctive rock types and intrusion form (Miller and Chandler, 1997). This field trip will investigate some of the units composing the southern and northern BBC. The relationship of BBC intrusions to other subvolcanic intrusions within the NSVG (Fig. 2-4) is unclear, because of poor exposure to the southwest and insufficient mapping to the northeast. Within the mapped area of the BBC, thirteen intrusive units have been identified that represent at least six major intrusive events (Miller and Chandler, 1997). Most intrusive activity forming the BBC occurred around 1096 Ma based on U-Pb dates of 1095.8±1.2 Ma for a Silver Bay intrusion, the youngest unit of the BBC, and 1096.1±0.8 Ma for the Sonju Lake intrusion (Paces and Miller, 1993). Whether activity overlapped the main stage of Duluth Complex magmatism at 1099 Ma is unknown, because attempts to date the oldest component of the BBC were not successful (Paces and Miller, 1993). The boundary between the BBC and Duluth Complex is generally marked by a northeast-trending keel-shaped intrusion in the northern BBC (Houghtaling Creek troctolite) that separates largely dike and sill intrusions of the BBC to the southeast from massive granophyric granite and extensive areas of structurally complex gabbroic anorthosite to the northwest that are typical of the roof zone of the Duluth Complex. Page 55 �Figure 2-4: Geology of the southern and northern Beaver Bay Complex showing the locations of Stops 8-16. After Miller and others (2001). Units labels are: nsb - NSVG basaltic volcanics; nss - NSVG Schroeder basalts; nsf - NSVG felsic volcanics; asa anorthositic series of the Duluth Complex; fs - felsic series of the Duluth Complex ; slid - Shoepack Lake inclusion-rich diorite; ccpd - Cabin Creek porphyritic diorite; hct Houghtaling Creek trocolite; blg - Blesner Lake diorite; llg - Lax Lake gabbro; frg Finland granophyre; frqm - Finland qtz ferromonzonite; slt - Sonju Lake troctolitic zone; slg - Sonju Lake gabbroic zone; brd Beaver River diabase; sbi - Silver Bay intrusions. See map M-119 for more details. Page 56 �The range of BBC parent magma compositions is similar to the olivine tholeiite and transitional basalt compositions that dominate the NSVG (Fig. 2-5A). Moreover, like the NSVG, the sequence of intrusion of BBC magmas generally involved progressively more primitive compositions. Compositional variations within the various intrusive units developed as a result of in situ magmatic differentiation (Fig. 2-5B), assimilation of footwall rocks, and/or composite intrusions of evolved magma from deeper staging chambers (Fig. 2-5C). The tightly clustered trend of BBC parent magma compositions evident on an AFM diagram (Fig. 2-5A) and the systematic variation of other elemental abundances suggest that all mafic BBC magmas evolved from a common olivine tholeiitic primary magma type. Such a primary composition, which is approximated by the most primitive, high-Al olivine tholeiites of the NSVG, is thought to have given rise to most Midcontinent Rift magmas, especially in later stages of magmatism (Green, 1982; Miller and Weiblen, 1990; Klewin and Shirey, 1992). That even the most primitive of the BBC intrusions, the Beaver River diabase, is significantly evolved from a primitive olivine tholeiite composition (Fig. 2-5A) indicates that all BBC parent magmas were generated in turn by magmatic differentiation of such a primary composition in deeper staging chambers. Petrologic modeling of some BBC intrusions and other hypabyssal bodies that intruded the NSVG (Jerde, 1991) suggests that most magmas experienced multistage, polybaric fractionation between their extraction from the mantle and their subvolcanic emplacement. Although the available radiometric ages do not indicate an overlap of magmatic activity between the BBC and the Duluth Complex (Paces and Miller, 1993), additional dates and more detailed petrologic studies may show that some Duluth Complex intrusions acted as the final levels of staging and differentiation of some BBC-bound magmas. The focus of emplacement of BBC intrusions appears to have migrated toward the rift axis and toward higher stratigraphic levels with time, perhaps reflecting plate drift and thickening of the volcanic pile. Over the exposed extent of the BBC, intrusion shapes appear to have been controlled by a shallow crustal ridge (Schroeder Forest Center Crustal Ridge) which trends northwest across the BBC. The presence of this buried crustal ridge is indicated by a pronounced saddle in the gravity high over northeastern Minnesota (Chandler, 1990) and the presence of Archean-like inclusions of granitic gneiss, biotite schist, metagraywacke and granodiorite in early intrusions over the gravity low (Boerboom, 1994). The broad network of dikes and sheets, characterizing the southern BBC, becomes tightly focused into a narrow zone of subparallel dikes in the northern portion of the BBC that is situated over the gravity minimum. The eastern BBC opens up again into thick sheet intrusions. Based on geologic, geochronologic, geophysical, and geochemical evidence, Miller and Chandler (1997) suggested that the BBC, particularly the youngest Beaver River diabase dike and sheet network, acted as a magma conduit and structural boundary to the formation and infilling of the western end of the Portage Lake Volcanic basin during the main to late stages of rift volcanism and graben formation. On the North Shore, these volcanic rocks are represented by the Schroeder-Lutsen basalts (Fig. 2-2). The second half of this trip will investigate seven intrusive units of the BBC and rocks comprising the roof zone of the Duluth Complex (Fig. 2-4). Stops 2-8 through 2-11 will investigate the composite intrusions of the Beaver River diabase and Silver Bay intrusions, the youngest intrusive components of the BBC. Stop 2-12 will visit typical exposures of the Finland granophyre. Stop 2-13 will traverse the middle cumulate units of the Sonju Lake Intrusion - the most completely differentiated intrusion exposed in the Midcontinent Rift system. Stop 2-14 will examine the units defining the northeastern limit of the Beaver Bay Complex - the Houghtaling Creek troctolite, Dam Five gabbronorite, and the Shoepack Lake inclusion-rich diorite. Finally, Stops 2-15 and 2-16 will view anorthositic and granophyric rocks that comprise the roof zone of the Duluth Complex. For more detailed information on these and other units of the Beaver Bay Complex see reports by Miller and Chandler (1997) and Miller and others (2002, Chapter 7) and the 1:24,000 bedrock geologic maps of the area (Miller, 1988; Miller and others, 1989, 1993, 1994; Boerboom and Miller, 1994). Page 57 �Figure 2-5: AFM diagrams of Beaver Bay Complex (BBC) intrusions. A) Plot of estimated parental magma compositions to various BBC intrusions (see Miller and Chandler, 1997 for unit descriptions and details) compared to major NSVG lava compositions: OT - olivine tholeiite, TB - transitional basalt, A - andesite, FA - ferroandesite, I icelandite, R - rhyolite (after Green, 1983). NSVG-pot is a primitive NSVG olivine tholeiite composition. B) Calculated liquid line of descent of the Sonju Lake intrusion through troctolitic (slmt-sld-slt), gabbroic (slg-slfgslad) and monzodiorite (slmd) intervals of the layered sequence. Also plotted are whole rock compositions of Finland granite (frg) and quartz ferromonzodiorite (frpm). C) Whole rock composition plots of Beaver River diabase (brd; ophitic margins and coarse subophitic interiors distinguished), Silver Bay intrusions (sbi; coarse marginal facies, layered ferrogabbroic cumulate interiors, and granophyric compositions distinguished), and composite intrusions from the northern BBC (nbbc). Sonju Lake intrusion differentiation trend (dashed line) is also shown. Page 58 �FIELD TRIP STOPS The general locations of all stops are shown on Figure 2-6. A more detailed location map is included with each stop description, with a base made at an appropriate scale from a portion of a 7.5’ quadrangle map. This should allow the return visitor to accurately locate the features for each stop. The UTM coordinates listed are all given in NAD83, with easting listed first and northing listed second. The regional setting of the various rock units are given in the introduction, and only facts pertinent to each specific stop are given below. Figure 2-6. Location map for stops for Field Trip 2. Page 59 �DAY 1 GEOLOGY OF THE SOUTHWESTERN SEQUENCE OF THE NORTH SHORE VOLCANIC GROUP FROM DULUTH TO SPLIT ROCK POINT Drive Highway 61 from Duluth towards Two Harbors. At the outskirts of Duluth, just after the Lester River, veer right onto Scenic Highway 61 for approximately one-half mile, then turn right on the road that leads to Kitchee Gammee park. Park near the northeast end of this road and walk down to lakeshore. STOP 2-1: Lester River Diabase in contact with rhyolite T.50N., R.13W., Sec. 4 Lakewood 7.5’ quadrangle. UTM: Start at SW 576929E, 5188417N; End at NE 577390E, 5188981N Highlights: Lester River diabase (lrd), hybrid granophyric rocks (lrf, lrg), rhyolite (nr); late diabase dikes (bdb), glacial striations. The Lester River Diabase is named for the outcrops adjacent to the mouth of the Lester River (Schwartz and Sandberg, 1940). The diabase sill dips southwest about 19 degrees, and forms a prominent topographic high (Moose Mountain) that extends about 6.5 miles inland from Lake Superior. This diabase is mostly intergranular in texture, but does locally exhibit ophitic textures, as seen at this stop. The dominantly intergranular to relatively fine ophitic (less than 1.5 centimeter) texture of the Lester River diabase contrasts with most other Keweenawan diabases such as the Silver Cliff and Beaver River diabases, which typically exhibit a coarse ophitic texture. This stop starts in the massive interior of the sill, and traverses northeast through increasingly felsic rocks that range from ferrodiorite to granite, and ends at a cliff of fine-grained chilled diabase that cuts the preceding rocks. Felsic rocks first show up as irregular felsic dikes that cut the diabase, but moving northeast towards the rhyolite not only do the felsic dikes increase in abundance, but the diabase itself becomes increasingly granophyric until it grades into dioritic rocks. The granophyric felsic hybrids blend into pink, fine-grained, porphyritic rhyolite, informally termed the Lakewood rhyolite (Green and Fitz, 1993). The exact contact between rhyolite and granophyric hybrid rocks is hard to pinpoint due to the similarity in textures between recrystallized rhyolite and the hybrid melts. Note the thin, shorelineparallel, fine-grained diabase dikes that cut the Lester River diabase. On a map scale, the granophyric hybrid phases of the diabase are thick and continuous along the upper sill margin, in contrast with the sill base where hybrid rocks are thin and discontinuous. The diabase sill is sandwiched between rhyolite in the hanging wall, and basalt in the footwall, indicating that the rhyolite acted as a density barrier that trapped and ponded the mafic magma beneath it. The irregularly mixed and distributed hybrid rocks that cap the Lester River diabase are likely due to mixing of remobilized (melted) rhyolite with the underlying mafic magma. Page 60 �--- Climb up bank , walk NE approximately 0.1 mile to small clearing on east side of highway, climb down to lakeshore, stop 2.2. Alternatively walk to next wayside, climb down, and walk back southwest along lakeshore to basalt/rhyolite contact.--- STOP 2-2: Flow contact between rhyolite and basalt of olivine tholeiite composition T.51N., R.13W., Sec. 34 Lakewood 7.51 quadrangle UTM: 577648E, 5189145N Highlights: Contorted flow-banded rhyolite (nr), contact of basalt (nbd) with rhyolite, ropy flow tops in olivine tholeiite (‘diabasic’-textured) basalt flows. Walk southeast to the pink-tinted rhyolite flow that exhibits highly contorted and folded flow banding. Rhyolite contains amygdules of calcite and minor fluorite (please don’t beat up the outcrop with hammers), and is capped by a thin, discontinuous layer of fine-grained sandstone. Move northeast over four basalt flows and observe flow features such as (bottom to top of flow) pipe vesicles, vesicle cylinders, amygdaloidal zones in upper portions of flows, and ropy pahoehoe upper surfaces. The pahoehoe crusts indicate a general southeast flow direction. These basalt flows are of weakly alkaline, transitional intermediate olivine tholeiite composition, with typical olivine tholeiite flow structures. On recently published 1:24,000 scale geologic maps (e.g. Boerboom and others, 2002a), flows such as this are classified as “diabasic-textured’ flows. Our field mapping has shown that the textures of the basalt flows does not always correspond to a unique chemical composition, but rather may have more to do with the amount of volatiles in the lava. Some of the most coarse-grained diabasic-textured basalt flows were mapped in the Sucker River upstream from Old North Shore Road. Despite being relatively thin flows (1-3 meters thick), they exhibit a medium- to coarsegrained felty diabasic texture. Some have a coarse pegmatitic zone located about one-third of the way down from the top of the flow, attributed to the concentration of volatiles in this part of the flow as cooling proceeded from the top and bottom. These coarse-grained flows also have unusually prominent pipe amygdules at the base overlain by a zone of bead-like pipe amygdules/vesicle cylinders up to one meter in length that end below the most coarse-grained part of the flow. The flows observed in stops 2-1 through 2-3 are all part of the Lakewood lavas (see table in introduction), a lithostratigraphic unit characterized by multiple thin ‘packages’ that range in composition from rhyolite to olivine tholeiite. Each flow package consists of multiple flows of like composition. Brannon (1984) conducted a detailed sampling regime of virtually every flow exposed along the shoreline from Duluth to Two Harbors, starting with the rhyolite just above the Lester River diabase. Her geochemistry verifies the mapped stratigraphy and shows that the most silicic rocks (rhyolite, icelandite, and andesite) occur at the base of the Lakewood lava sequence, whereas primitive tholeiitic basalts dominate the top of the sequence. Vervoort and Green (1997) have shown, through Nd isotopic studies, that the NSVG rhyolites are the product of melting of Archean crustal rocks by underplated primitive Page 61 �mafic magma, whereas icelandite and basalt are most likely derived directly from a mantle plume source. In their model, early volcanism (lower reversed sequence) tapped a mantle source with little crustal contamination. This was followed by a period of volcanic quiescence (the 1107 -1100 Ma ‘volcanic hiatus’) during which a mantle plume underplated and melted the crust, generating superheated felsic melts that were later erupted as rhyolite flows and rheoignimbrites, of unusually wide areal extent given their thickness (Green and Fitz, 1993) --- Climb up bank of small stream to wayside rest (this is the third wayside rest on Scenic Highway 61 past Brighton Beach Road), drive or walk approximately 0.3 miles northeast to wayside rest directly across from Old North Shore Cottages Resort, stop 2-3.--- STOP 2-3: Interflow sandstone between icelandite and basaltic andesite flows T.51N., R.13W., Sec. 34 Lakewood 7.51 quadrangle UTM: 578287E; 5189652N Highlights: Interflow sandstone above icelandite (ni), below basaltic andesite (nba) Park at wayside across from North Shore Cottages Area A: Slide down the embankment below wayside (over red clays of Glacial Lake Duluth) to outcrop of sandstone on shoreline. Sandstone is approximately 12-15 feet thick, planar and trough crossbedded. Jirsa (1984) reports the sand grains are predominantly plagioclase (44-53%) and mafic volcanic rock fragments (18-25%), with lesser quartz (1-4), opaques (2-8%), K-spar, felsic volcanic rock fragments, and mudstone fragments (less than 2% each). The sandstone is cemented by a matrix of calcite, zeolite, K-feldspar, and quartz. Crossbedding indicates an easterly paleocurrent direction. The sandstone overlies an icelandite flow which has a rubbly flow top (and unfortunately is quite inaccessible due to cliffs), and is overlain by a flow of basaltic andesite composition (will examine these at site B). The upper surface of this interflow sandstone contains curly molds and bits of baked-on chilled basalt from the overlying flow, which is now eroded away. This sandstone is typical of the thin interflow sedimentary rocks, which are immature, fine- to coarsegrained sediments that were deposited in fluvial and lacustrine environments, although some may interpret some of the bedding in this outcrop to be aeolian in nature. Overall, paleocurrent indicators for the interflow sandstones indicate a transport direction generally toward Lake Superior from a highland of both Keweenawan and pre-Keweenawan sources (Jirsa, 1984). ---Climb back up bank and move about 100 feet northeast and return to lakeshore outcrops.--- Page 62 �Area B: Basaltic andesite. The base of this flow sequence was observed at stop 2-3a. These flows are dark purplish-gray, fine-grained basaltic andesite, which locally have pipe vesicles at the base, and amygdule-rich upper parts that exhibit billowy lobate forms defined by concentrated amygdules. Flow tops are commonly brecciated. Some flows contain sparse plagioclase phenocrysts. Due to time constraints we will not progress up the shore, but the return visitor is encouraged to walk up the shore over at least eight more flows of this composition that are in turn overlain by ophitic basalt flows. Brannon (1984) classifies these flows as ferroandesite, but they are morphologically more similar to flows of basaltic composition. ---- Climb back up back to highway, back to cars. Continue northeast on the Scenic Highway approximately 8 miles to Alseth Road. Turn right on Alseth Road and follow around to a point where shoreline is close to road, park and walk to shore (Stony Point).--- STOP 2-4: Stony Point diabase T.51N., R.12W., Sec. 1 Knife River 7.5’ quadrangle UTM: 590326E; 5197791N Highlights: Stony Point diabase (spd) The diabase forms a sheet-like intrusion that strikes parallel to the shoreline and is discordant to the surrounding volcanic rocks. It is exposed in numerous outcrops between here and Knife River, a distance of nearly 3 miles. It is composed of coarsely ophitic olivine diabase with scattered thin pegmatitic segregations. The island offshore from Knife River forms the northeast-most outcrop of this diabase. The exposed thickness is estimated to be about 100 meters, but a positive aeromagnetic anomaly that corresponds to this diabase, and continues offshore beneath Lake Superior, implies that this diabase is part of a larger intrusive mass whose thickness is unknown. The diabase is chilled against adjacent volcanic rocks, and contains rare small anorthosite xenoliths (neither visible at this stop). ---Continue northeast on the Scenic Highway, to Highway 61 into Two Harbors. Continue through Two Harbors to the northern outskirts of town, turn right on 1st Street and continue south to the crest of the hill adjacent to the picnic grounds. Walk east to lakeshore.--- Page 63 �STOP 2-5: Two Harbors Town Park T.52N., R.10W., Sec. 6 Two Harbors 7.5’ quadrangle UTM: 601851E, 5208673N to 601847E, 5208132N Highlights: Basaltic flows of quartz tholeiite composition (ntb), rubbly flow tops, diabase dike (db) This sequence of quartz tholeiite basalt flows is part of the Two Harbors lithostratigraphic unit (see table in introduction). These flows are comprised of brownish-gray to gray, fine-grained, fresh intergranular basalt that typically exhibits a pronounced oxidation-lamination type of flow banding. The upper parts of these flows typically contain a thick and irregular section of rubbly aa rich in laumontite, and red siltstone is common as thin lenses and crack fillings in the flow tops. Walk south along the shoreline and observe the transition from massive, oxidation-laminated flow interiors to amygdaloidal, rubbly flow tops, and contacts with overlying flows. Each rocky point along this traverse corresponds to the massive, more resistant base of a flow that is underlain by a rubbly, easily eroded, flow top. A N28W striking diabase dike that cuts the basalt can be seen along the south side of the north-most point, but due to time constraints this field trip will not go there. This dike follows a set of closely spaced brittle fractures in the basalt. :---Continue northeast of Two Harbors on Highway 61 approximately 4.5 miles to the Silver Cliff Tunnel. Just past tunnel turn right into an informal parking area adjacent to highway.--*** TRAFFIC HAZARD ****** USE EXTREME CAUTION *** Page 64 �STOP 2-6: Silver Cliff Tunnel T.53N., R.10W., Sec. 15 and 22 Castle Danger 7.5’ quadrangle UTM: 606993E, 5213952N (park area) to 606755E, 5213486N Highlights: Silver Creek diabase (scd), contact with subjacent andesitic flows nca), fault The Silver Creek diabase forms an irregular subcordant, subhorizontal intrusion that is at least 60-m (200ft) thick. The diabase forms a prominent highland that projects inland several miles from Silver Cliff at Lake Superior. The Highway 61 tunnel has created excellent exposures of the contact between both the top and bottom of the diabase with adjacent volcanic rocks, and has exposed a north striking, 55-degree east dipping brittle fault that cuts the base of the diabase. The andesitic flows beneath the sill show a very irregular, rather chaotic flow contact, a rubbly flow top, vuggy quartz-lined stretched vesicles and amygdules of gray agates that have been recrystallized by contact metamorphism from the adjacent diabase. The margins of the diabase are marked by a mix of commingled fine-grained, strongly magnetic, dark gray diabasic rock and pink granophyre. The lower diabase contact strike is approximately N-S, 70 degrees west, and the upper contact (exposed at the south end of the tunnel) strikes N40E, 70 degrees northwest. Out on the old roadbed the diabase displays prominent columnar joints that plunge approximately 60-65 degrees east. From the north edge of the old roadbed, one can look back across the highway down the length of the brittle fault that cuts the base of the diabase. The fault is about 3 meters thick and filled with a mixture of pink zeolites and calcite-filled voids around altered diabase gouge. The old roadbed affords an excellent view of the Lake Superior coast. ----Continue northeast up Highway 61. The next tunnel is cut through the Lafayette Bluff diabase, a dark green, porphyritic, amygdaloidal diabase which bears distinct textural differences from the Silver Creek diabase, and that locally contains anorthosite inclusions up to 2 meters in diameter. As we drive past, note the thick cap of reddish-brown grus developed on top of the Lafayette Bluff diabase, which is typical of this unit. Just inland, the grus was formerly excavated for use as road surfacing material. We will see blocks of the Lafayette Bluff diabase at the parking area for the next stop.-----Continue past Lafayette tunnel, pass Gooseberry State Park. From Gooseberry River, go 3.8 miles to a pulloff on lakeward side of road approximately 300 feet before crossing the Split Rock River. Park at wayside and walk northeast to small point to gain access to shore.--- Page 65 �STOP 2-7: Split Rock River diatreme T.54N., R.8W., Sec. 7 Split Rock Point 7.5’ quadrangle UTM: 620570E, 5226484N to 620497 E, 5226229N Highlights: Split Rock Creek diatreme breccia (dt), brecciated basalt, basalt/andesite flow contact Outcrops to north along shore are of weakly to moderately brecciated ophitic basalt that has apparently been slightly disrupted by the adjacent diatreme dike. A small “island” just offshore of the biggest point here consists of dark gray, medium-grained, ferromonzodiorite that petrographically consists of felty plagioclase, prismatic augite, skeletal to blocky oxides, and red-dusted anhedralinterstitial K-feldspar. The edge of this outcrop nearest the shore shows a dramatic brecciated texture due to diatreme emplacement, and the cliff adjacent to that exposes the diatreme breccia proper. The best diatreme breccia is exposed further south along the beach. Here, the breccia contains visible clasts of massive ophitic basalt, fine-grained amygdaloidal basalt, and intergranular basalt that vary from sub-millimeter to 25 cm in diameter and are all strongly magnetic. Small fragments of interflow sedimentary rocks in the breccia have been noted in thin section. The zeolitic matrix varies from pink to pale green in color. At the south end of this breccia, one can observe the sharp, vertical contact between the diatreme and layered amygdaloidal basalt. The contact here strikes approximately N20W, but overall it is more or less north-south. A short distance south of the diatreme contact are vertical cliffs formed by the blocky jointing pattern of a dark gray, very hard and fresh basaltic andesite flow which overlies amygdule-layered flows that exhibit minor low-amplitude billowy surfaces. The flow contact can be observed southward down the beach to the next point out into the lake. The top of this andesitic flow may be visible across the bay to the north, where it is overlain by massive ophitic basalt. The diatreme exposed here is identical to another to the south, near Crow Creek, that is much more well exposed but unfortunately only accessible by water. There, the diatreme forms a vertical, 10 meter thick, cliff-forming dike that cuts ophitic basalt flows along the shoreline, and in some small outcrops inland. Although poorly constrained, the Crow Creek diatreme may be in the form of a ¼ mile diameter ring-like circular dike, or it may simply have an irregular, ‘wandering’ strike direction that varies from north-south to east-west. The Crow Creek diatreme is a heterolithic breccia that contains clasts of basalt up to 3 meters in length, and has irregular pyrite-rich pods within it. Like the diatreme here, the Crow Creek diatreme has prismatic ferromonzodiorite associated with it, which is itself brecciated, and contains varied types of basalt clasts as well as clasts of interflow sedimentary rocks. Page 66 �The varied types of basalts coupled with interflow sedimentary rocks that make up the clasts in both places demonstrate that the diatreme has cut through a substantial thickness of volcanic strata. Although prismatic ferromonzodiorite is apparently associated with the diatreme in some fashion, the abundance of zeolitic matrix mixed with rock flour implies that the diatremes were formed by a gaseous, volatile-rich explosive mechanism. The volatile source is not known. However, the Lafayette Bluff diabase, which occurs in close proximity to the Crow Creek diatreme, contains abundant zeolitic (mainly laumontite) amygdules, and overall exhibits moderately strong deuteric alteration, which implies that the magma may have been gas-charged. Thus in a highly speculative scenario, degassing during cooling of the Lafayette Bluff diabase may have led to a buildup of volatiles that subsequently exploded through the overlying basalts. Both the Crow Creek and Split Rock river diatreme form vertical dike-like bodies which brecciated clasts of ophitic and intergranular basalt, interflow sandstone and siltstone, fine-medium-grained ferrodioritic rocks, isolated unit quartz grains, and isolated blocky plagioclase grains. At this locality the clasts are generally less than 0.5 meter in diameter, but the diatreme near Crow Creek contains clasts of basalt as large as 4 meters in length. Medium-grained prismatic ferrodioritic intrusive rocks are exposed next to the diatreme dikes at both localities, and at both places the ferrodiorites are cut by and hence predate the diatreme dikes. ---Continue up Highway 61 to Split Rock Lighthouse State Park and History Center. Pull into park lot for the History center and proceed toward the lighthouse. To visit the lighthouse area (Area A) during summer tourist season, the history center charges a fee or requires Historical Society membership. A fee is not required to access the shoreline exposures at Area B. STOP 2-8: Split Rock Lighthouse Anorthosite T.55N., R.8W., Secs. 32 and 33 Split Rock Point NE 7.5' quadrangle UTM: Area A- 623690E, 5228678N Area B - 623625E, 5228665N Highlights: large anorthosite inclusions (anor), ophitic diabase (brd), lower chill, basaltic lava flow with silt-filled aa flow top (nsb) The Beaver River diabase is the most areally extensive intrusive phase of the entire BBC and is found in contact with most other BBC units. In the southern BBC (Fig. 2-4), it occurs as a series of dikes, sills, and sheets of ophitic olivine gabbro that grades into coarser and more subophitic to intergranular gabbro in the medial portions of thicker sheets. One of the most distinctive characteristics of the diabase is that it commonly hosts large (as much as several hundred meters in diameter), rounded to angular inclusions of nearly pure anorthosite. These inclusions, which locally are brecciated and recrystallized (Morrison and others, 1983), are particularly common in the upper and lower margins of the larger diabase sheets. As reported for this stop in the Field Trip 7 guidebook (stop 24), these inclusions have been the focus of geologic debate for over 150 years. Page 67 �Area A: Outcrops of fine-grained, ophitic olivine diabase with centimeter-wide augite oikocrysts, typical of the margins of Beaver River diabase, are exposed just northeast of the lighthouse atop a sheer 30-mhigh sea cliff. The diabase here forms a sill that dips gently (<15°) into the lake and whose basal contact with a basalt flow top is exposed around the base of the point. The diabase is a moderately evolved (mg#=57), high-Al, olivine tholeiite (Fig. 2-5, BRD margin). The prominent point just to the northeast (Rusty Point) is held up by a very large (~200 m) inclusion of medium-grained leucogranite lying at the base of the sill. The diabase is slightly chilled around this granite inclusion, which closely resembles the Finland granophyre (see Stop 2-12). Most of Split Rock Lighthouse Point is held up by a single, large (>35m), layered anorthosite inclusion. Around the base of the lighthouse, the inclusion displays meter-scale modal layering of coarsegrained granular (cataclastic?) anorthosite (>99% Pl) and noritic anorthosite (20% Opx [En70Fs28Wo2], 80% Pl [An60-80]; Morrison and others, 1983). The steeply dipping layers are cut by thin dikes of mediumgrained, granular augite leuconorite (An56, En73Fs24Wo3, En46Fs12Wo41, Morrison and others, 1983). .....Head down the tramway path to the lakeshore and carefully make way along base of slope toward lighthouse. PROCEED CAREFULLY OVER LARGE TALUS BOULDERS. Area B: To the southwest of the lighthouse along the shore, the base of the sill can be observed to conformably overlie an amygdaloidal flow top breccia with a matrix of horizontally bedded siltstone. The diabase here contains a variety of types and sizes of anorthosite inclusions, which stand out as unjointed masses within the highly jointed fine-grained diabase. The diabase is strongly chilled at the basal contact against the flow top, but shows no sign of chilling against the anorthosite inclusions. The variety of anorthosite types can be viewed in the talus blocks at the base of the slope. Looking to the northeast, one can see that the near-vertically, layered inclusion beneath the lighthouse extends to lake-level. This and other anorthosite inclusions hosted in the Beaver River diabase are different from most anorthositic series rocks of the Duluth Complex; the latter are rarely layered, more compositionally evolved, and rarely contain cumulus hypersthene. These inclusions are similar, however, to some anorthosite inclusions within the anorthositic series. The highly disordered structural state of plagioclase (Miller, unpublished data) and the absence of any discernable chill of the diabase against the anorthosite indicate that these inclusions were derived from a middle to lower crustal source. Isotopic and traceelement compositions of these crustal xenoliths suggest that they may be pre-Keweenawan in age (Morrison and others, 1983), but the data are overall ambiguous. Alternatively, if a plagioclase crystal mush origin for Duluth Complex anorthositic rocks is correct (Miller and Weiblen, 1990), a corollary of such a model is that significant amounts of Keweenawan anorthosite, generated by plagioclase flotation under high pressure, should have formed in the deep crust prior to BBC magmatism at 1096 Ma. Under deep crustal conditions, such plagioclase cumulates would probably be distinctive in texture and composition from their shallow crustal counterparts. Moreover, the ambiguous isotopic compositions of the inclusions may indicate that anorthosite-forming Keweenawan magmas were contaminated by older crust, rather than older anorthosite being contaminated by interaction with Keweewawan magmas, as concluded by Morrison and others (1983). Return to Duluth for the evening. DAY 2 Page 68 �GEOLOGY OF THE BEAVER BAY COMPLEX Drive Highway 61 from Duluth past Two Harbors to Lake Co Rd 3. Take this road approximately 25 miles. About 2.3 miles past the Silver Bay municipal airport, look for a prominent roadcut on the adjacent railroad grade on the north side of the road. Pull into gravel pullout. STOP 2-9: Fanning columnar joints in Beaver River Diabase dike/sill T.55N., R.8W., Sec. 9 Silver Bay 7.5' quadrangle UTM: 624590E, 5235865N Highlights: columnar jointed ophitic diabase (brd), anorthosite inclusion (dark outcrops), contaminated and inclusion-rich diabase (brid) The western and northern extent of the Beaver River diabase is marked by a 110-km-long dike (or dike set) across which vertical downward displacement of 1.5 to as much as 6 km on the southeastern (rift axis) side is indicated by offset of older geologic units (Miller and Chandler, 1997). The feature, which has a very pronounced aeromagnetic expression (Fig. 2-7), is termed the Finland tectono-magmatic discontinuity (FTMD). Within the concavity of the FTMD are several other large, often bifurcating dikes and large sheets dipping gently southeast. The complex of sheets holding up tabletop highlands in the southern BBC (Figs. 2-4 and 2-7) may be part of an originally continuous, nearly horizontal sheet that has locally been eroded through to expose volcanic rocks forming the footwall. The fanning pattern of columnar jointing exposed in this railroad cut through Bear Lake Ridge reflects the transition from the FTMD dike into a thick sub-horizontal sheet developed to the east of the ridge. The rock type here is a fine-grained ophitic olivine diabase. The larger railroad cut 150 m to the east reveals the irregular, well-jointed base of the diabase sheet overlying the amygdaloidal flow-top breccia of a deeply weathered ophitic basalt (CAUTION, OUTCROP FACE IS UNSTABLE). Abundant weathered anorthosite inclusions and some quartz- and feldspar-phyric rhyolite inclusions (similar to the Palisade rhyolite) are evident in the diabase. This diabase sheet holds up the extensive 120-m cliff visible across (south of) the Beaver River. Page 69 �Figure 2-7. Shaded-relief image of total magnetic field data over the southern Beaver Bay Complex and generalized geologic map (from M-119) at the same scale. FTMD - Finland Tectono-magmatic Discontinuity. Labelled intrusions of the BBC include the Cloquet Lake layered series (CLLS), the Houghtaling Creek troctolite (HCT), the Sonju Lake intrusion (SLI), the Finland granophyre (FG), the Lax Lake gabbro (LLG), the Blesner Lake diorite (BLD), the Beaver River diabase (BRD), and the Silver Bay intrusions (SBI). Duluth complex units include the anorthositic series (AS), the felsic series (FS), the Osier Lake intrusion (OLI), and the Greenwood Lake intrusion (GLI). North Shore Volcanic Group rocks are denoted as V. Solid lines denote inter-intrusion contacts; dashed lines denote intra-intrusion contacts. See M-119 for subunits of intrusions. Number labels are NAD 83-based UTM grid coordinates. Modified from Figure 7-2 (Miller and others, 2002). Two types of diabase are exposed in the upper ledge of the railroad cut, which is accessible from the east. The more common type is the same fine-grained ophitic olivine diabase observed in the dike, but here it contains scattered anorthosite inclusions and locally is plagioclase porphyritic. Exposed across the eastern half of the ledge, the ophitic diabase is found in sharp contact with a dense, black, aphanitic, intersertal diabase rich in quartz and feldspar xenocrysts, numerous small, blebby inclusions of felsite, and larger inclusions of anorthosite. The presence of anorthosite inclusions argues against it being a volcanic xenolith. Near the western end of the ledge, the ophitic diabase is noticeably chilled and columnar jointed adjacent to a sharp steep contact with the inclusion-rich diabase. In the center of the ledge, the inclusion-rich diabase is itself pseudo-columnar jointed near its sharp contact with the ophitic diabase, but the joints are not orthogonal to the contact. This inclusion-rich diabase is locally observed near the margins of Beaver River diabase intrusions throughout the BBC. It probably represents strong contamination of early anorthosite-bearing Beaver River magmas as they were emplaced into brittle conduits in the volcanic edifice. .... Continue east on Lake Co Rd 3 to junction with Co Rd 4. Turn right and proceed to junction with Highway 61 in Beaver Bay. Turn left, after crossing the Beaver River pull on to shoulder. Walk paths down to beach. Page 70 �STOP 2-10: Inclusion-rich Contact Zone of the Beaver River Diabase at Beaver Bay T.55N., R.8W., Sec. 12 Silver Bay 7.5' quadrangle UTM: 629115E, 5235420N to 629240E, 5235770N Stop 10 Highlights: porphyritic rhyolite inclusion (nspr), hornfels basalt inclusions (nsb) with granophyre ring dikes, anorthosite inclusions (black masses), inclusion-rich Beaver River diabase (brid) Exposed along shoreline outcrops on the north side of the Beaver River is a complex mix of rock types that is commonly characteristic of the basal? contact of the Beaver River diabase. Exposed in the first outcrop north of the Beaver River sandbar is hybrid mix of fine-grained diabase and irregular masses of felsic rock in various stages of mixing and assimilation. While some of the felsic material looks to be rounded irregular melted? inclusions in the diabase, some felsic material clearly occurs as dikes in the diabase. At the steep north end of this exposure is a quartz-feldspar porphyritic rhyolite inclusion that is very similar to the Palisade rhyolite, which holds up Palisade Head and Shovel Point several miles to the north of here. At the base of the steep north side of the outcrop, the rhyolite is in sharp contact with a fine-grained diabase. The diabase is riddled with irregular blebs of felsic material that likely represent melted fragments of the rhyolite inclusion. Wieland Island in the northern part of Beaver Bay is composed of a similar porphyritic rhyolite. The cliffs across the mouth of the river to the southeast are held up by large inclusions of aphyric flow-banded rhyolite and medium-grained massive granophyre. Progressing to the northeast, we cross a small outcrop of an epidotized fragmental mafic rock. This rock may be contaminated diabase or, as implied by similar appearing rock we shall see to the north, it is more likely a metamorphosed flow top breccia of a basalt inclusion. The next low outcrop is of deeply altered (green-tinted) diabase charged with similarly altered anorthosite inclusions. Coming on to a large expanse of semi-continuous outcrop along the rest of the shore, several rock types are observed. Most of the exposure is altered fine-grained diabase. Another prominent rock type is granophyre, which occurs both as irregular masses of varied size and as a curving network of granophyre dikes ranging from several centimeters to over a meter wide. In some areas, granophyre composes almost half of the exposure. In several locations, granophyre dikes are found encircling blocks of dense basaltic hornfels. The basaltic hornfels are sometimes only distinguishable from the fine-grained diabase by a very prominent orthogonal joint pattern and the ring of granophyre. In one block occupying a low spot in the outcrop, a flow contact between massive and flow breccia basalt is recognizable. These blocks of basalt flows were likely thermally metamorphosed by their incorporation into the diabase. The origin of the granophyre is less clear, however. Melting of rhyolite inclusions has evidently given rise to at least some of the granophyre, especially that occurring as irregular masses. However, given the mantling relationship of some granophyre ring dikes to the basaltic hornfels inclusions, is seems possible that some of the granophyre dikes were "sweated out" from the originally hydrated basalt inclusion. Alternatively, the Page 71 �ring dikes may represent rhyolite-derived felsic melts that simply intruded along contacts between the diabase and the basalt inclusions. Following the exposure further to the north, this mix of diabase, granophyre, and basalt abruptly gives way to diabase heavily charged with large anorthosite inclusions. At this point, we will head upslope to the highway and back toward the river. .... Continue along Highway 61 to the northeast past the North Shore taconite plant at Silver Bay and Tettegouche State Park. Proceed 3.0 miles past the junction with MN Highway 1 to a road cut across from (NW of) a Jehovah's Witness Hall. STOP 2-11: Silver Bay intrusions, Beaver River diabase and overturned lava flows T.56N., R.7W., Sec. 1 Illgen City 7.5' quadrangle UTM: A: 637890E, 5247155N B: 638150E, 5247660N C: 638421E, 5247980N Highlights: ferrogabbro layered intrusion (sblg), overturned lava flows (nsb), monzodioritic composite intrusions (sbg) into diabase (brd) containing anorthosite and basalt inclusions The Illgen City quadrangle contains some of the most complex geology exposed in the Keweenawan system (Miller and others, 1988). This complexity resulted from block faulting, displacement, and rotation of volcanic rocks caused by the dike and sill emplacement of the Beaver River diabase and later composite intrusions. The present level of exposure along the shoreline has cut into the footwall of a major sheet-like intrusion of diabase that holds up the highlands about 2 km in from the shore. This is perhaps the same sheet that the Beaver River cuts through near Stop 2-9. The footwall is highly dissected with a complex network of large (50-800m wide) diabase dikes and the intervening blocks of volcanic rocks have been significantly displaced and rotated into a variety of orientations (Fig. 2-8). Multiple composite intrusions of ferrogabbroic to intermediate magmas have produced a variety of intrusions hosted by the Beaver River diabase, which are collectively termed the Silver Bay intrusions. Three roadcuts along a one-and-a-half kilometer stretch of the northwest side of Highway 61 display some of the best examples of the magmatic and structural complexities attending the emplacement of the Beaver Bay Complex. Roadcut A: This roadcut exposes a nearly complete cross section through a small, zoned Silver Bay intrusion. This intrusion, termed the Jehovah body, has the form of a broad, shallow asymmetric synform that plunges about 15° to the east and measures about 450 m north to south. It is intrusive into the axial portion of a Beaver River diabase dike about 500-600 m wide, which dips steeply to the north. Page 72 �A B C Figure 2-8. Geologic cross-section of the shoreline in the vicinity of STOP 2-11 (From Miller and others, 1989). Unit abbreviations are: nsb- basalt; nsob-ophitic basalt; nsr2-rhyolite; nss-interflow sandstone; brd-Beaver River diabase; sbg-Silver Bay gabbro; sblg-Silver Bay laminated gabbro;, gr-granite inclusion. Approximate locations of roadcuts A, B, and C projected to the shore are shown. No vertical exaggeration. On either end of the roadcut west of Highway 61 (Fig. 2-9A) are exposures of a deeply weathered, varitextured but generally coarse-grained, nonfoliated apatitic ferromonzodiorite forming the margins of the intrusion (unit sbg). Toward the center of the roadcut, the ferromonzodiorite abruptly grades into a medium-grained, well-foliated, subprismatic ferrodiorite with poikilitic olivine (unit sbpg). The poikilitic olivine ferrodiorite is composed of about 50-55% prismatic to lath-shaped plagioclase (An45-15); 15-20% subprismatic and partially uralitized augite (En'62-42) and minor intergrowths of pigeonite (En'42-36); 5-10% subequant to bladed iron-titanium oxide; 5-15% subpoikilitic to poikilitic, altered olivine (<Fo48); and 515% granophryic mesostasis and trace apatite. Olivine is almost completely altered to a glassy black sheet silicate mineral, called hisingerite by Gehman (1957). In thin section, the hisingerite appears to be mostly dark-greenish-brown biotite, partially altered to chlorite, with some serpentine and iron oxide. The oxidation of iron oxide, which is especially common around the outer margin of the olivine oikocrysts, produces purplish coronas around the black clots. Variations in the abundance and size of olivine oikocrysts (1.5 to 5 cm across) impart a layering to the gabbro, which is parallel to plagioclase foliation. This internal structure defines an asymmetric synform whose axial plane projects through the northern half of the intrusion. Cryptic variations in the Mg/Mg+Fe contents of mafic minerals are noted upward through this sequence (Fig. 2-9A) and are suggestive of magmatic differentiation. We interpret the coarse-grained, decussate rocks to represent equilibrium crystallization of a stagnant margin around a small convecting core of fractionally crystallizing magma, which formed the foliated gabbro. The dikes of coarse-grained nonfoliated ferrodiorite internal to the zoned intrusion may represent late intrusions of parental magma or remobilization of interstitial magma from within the intrusion. Roadcut B: The next major roadcut to the northeast displays a series of basalt lava flow that have been overturned 125° from horizontal. These flows are part of a large (~1 x 2 km) block of basalts that is completely enclosed by intrusive rocks of the Beaver River diabase and Silver Bay intrusions (Fig. 2-8 and location map). The basalts range in composition from olivine tholeiites, with smooth upper flow surfaces and pipe amygdules at their base, to quartz tholeiites with brecciated (aa) flow tops (Fig. 2-9B). They range in thickness from 3 to 20 meters. Two interflow sandstone units occur beneath the thickest lava flows. These flows are part of the Bell Harbor lavas, the uppermost unit of the upper southwestern sequence of the NSVG (Table 2.1). Page 73 �Figure 2-9. Schematic diagrams of geologic relationships exposed along three roadcuts at STOP 2-11. Foliation development portrayed in Roadcut A by alignment of tick marks. Units: sbg- nonfoliated ferromonzodiorite; sbpg - foliated poikilitic olivine ferrodiorite; sblg - foliated intergranular (non-poikilitic) olivine ferrodiorite. Compositions of augite shown by En content (= MgO/(MgO+FeO), mole %). Roadcut C: A complex sequence of intrusive and inclusive relationships are exposed in the 70' high roadcut to the northeast (Fig. 2-9C). This is one of the tallest roadcuts on the North Shore. Starting at the southernmost end of the roadcut (0 pace) is a medium-grained ophitic olivine diabase with 2cm augite oikocrysts. The diabase gradually coarsens to where by 80 paces the oikocrysts are about 5 cm across. Beginning at about 40 paces, the diabase displays an intense oxidation/alteration that persists through about 200 paces, where it is in contact with hornfels basalt. Between 90 and 130 paces is a coarse grained anorthosite inclusion, which has near vertical contacts with the enclosing diabase and displays the same alteration as the diabase. This anorthosite holds up the crest of the hill that the roadcut traverses. On the north side of the inclusion, the diabase is more subophitic, with coarse (~2 cm) augite clots, and it contains granophyric patches. Progressing north, augite gradually becomes more prismatic and granophyre content increases to where by 160 paces the rock is a ferromonzodiorite typical of the marginal phases of Silver Bay intrusions. Between 170 and 175 paces, two steeply inclined granophyre dikes cut the ferromonzodiorite. At about 180 paces, a subophitic texture again is evident. This rock gradually becomes more ophitic and more medium-grained as a contact with hornfels basalt is approached at 200 paces. The northern contact of this basalt inclusion occurs at a low spot in the roadcut and is obscured by two shallow dipping granophyre dikes. The larger dike (~1.5m wide) cuts medium finegrained ophitic diabase, which contains another hornfels basalt inclusion near the base of the exposure at about 240 paces. The exposure from 240 to 295 paces is relatively unaltered, medium fine to mediumgrained diabase. Between 270 to 280 paces, near the base of the roadcut, is an odd inclusion of coarse- Page 74 �grained, subophitic leucogabbro with apophyses? of very fine, amygdaloidal mafic rock. The inclusion is mantled on its upper right margin by a thin rind of granophyre. The northernmost 10 paces of the roadcut leading to a gravel side road is hornfels basalt. The sequence of events interpreted from the rocks displayed in Roadcut C are: 1) intrusion of diabase dike carrying anorthosite inclusions from depth and incorporating locally derived basaltic wall rock. 2) composite intrusion of ferromonzodioritic magma into the semi-molten core of the diabase dike; 3) injection of granophyre dikes (possibly auto-intrusions of late-stage felsic melt segregated from the ferromonzodiorite); and 4) fluxing of oxidizing fluids through the central zone of the dike. --- Continue on Hwy. 61 to Lake Co. Hwy 6. Take this to MN Hwy 1 in Finland. Turn right on Hwy 1 about 1/4 mile and turn right on to Lake Co Hwy 7. Just past the Finland Community Center and just before the pavement ends, turn left on to the road to the site of a former USAF Radar Station. Take the paved road about 1.4 miles to gravel road crossing and pull out to the left.--- STOP 2-12: Finland granophyre and hybrid dikes T.57N., R.7W., Sec. 4 Finland 7.5' quadrangle UTM: 633180E, 5256520N Highlights: granophyric leucogranite (frg), locally with blebby mafic enclaves (dgh) Exposed over a 40-km2 area in the northwestern part of the southern BBC (Fig. 2-4) is a distinctive, oval-shaped mass of leucogranite and quartz ferromonzodiorite, termed the Finland Radar Station granophyre by Miller and others (1993), or simply the Finland granophyre. The main phase of the granophyre is a homogeneous, salmon-colored, micrographic leucogranite with abundant miarolitic cavities (unit frg, Fig. 2-4). To the north, this granitic phase, which contains less than 5% Fe-silicates and oxides, abruptly grades to a quartz ferromonzodiorite characterized by 5-20% prismatic, iron-rich pyroxene, amphibole, and locally olivine and 20-40% micrographic felsic matrix (unit frqm, Fig. 2-10). At this stop, the typical character of the granitic phase of the Finland granophyre is displayed in the roadcuts on either side of the road to the former USAF radar station (decommissioned in 1974). In the rubble at the north end of this roadcut, the medium-grained granophyre contains small rounded enclaves of fine-grained mafic rock. Some of the rubble blocks are composed completely of this finegrained rock. This occurrence is in line with what to the north is clearly a mafic to intermediate dike cutting the granophyre. This dike is part of an orthogonal network of dikes composed of heterogenous mixtures of mafic and felsic rock types that cut the Finland granite and the underlying Sonju Lake Page 75 �intrusion and that parallel the adjacent Beaver River diabase (BRD-SLI hybrid dikes in Fig. 2-10A). Miller and Chandler (1997) have interpreted these dikes to represent hybrid mixtures of Beaver River diabase magma and residual felsic melts in the upper Sonju Lake intrusion and overlying Finland granophyre. The textures displayed here are consistent with those resulting from two magma mixing, which would imply that the Finland granite was significantly molten when the mafic dikes were emplaced. The intrusive relationships of the Finland granophyre, the older Lax Lake gabbro along its southern margin (llg, Fig. 2-4), and the younger Beaver River diabase at its eastern extent (unit brd, Figs. 2-4 & 210A) are well-established by several exposures of sharp contacts. However the genetic relationship of the granophyre to the underlying Sonju Lake layered intrusion (Stop 13) along its gradational northern boundary (Fig. 2-10A) is more problematic. Stevenson (1974), noting aplitic granophyric dikes cutting the mafic cumulates of the Sonju Lake intrusion, considered the Finland granophyre to be intrusive into the Sonju Lake intrusion. However, mapping by Miller and others (1993) showed these aplite dikes to be phases of the late hybrid dikes (Fig. 2-10A) that cut the Sonju Lake intrusion and both phases of the Finland granophyre. Again, the termination of such a dike is thought to give rise to the mafic enclaves at this stop. Given the parallel zonation of the two phases of the granophyre with the strike of Sonju Lake cumulate units (Figs. 2-4 & 2-10; also see Miller and others, 1993a) and the generally smooth compositional variations across these units (Fig. 2-10B), a comagmatic relationship resulting from crystallization differentiation could be envisioned. Such an interpretation is inconsistent, however, with the large amount of granophyre relative to the layered mafic rocks apparent from the geologic map (Figs. 2-4 & 2-10). Modeling of gravity and aeromagnetic data across these units (Miller and others, 1990) confirms that the volume of granophyre is at least as great as the volume of underlying mafic rocks and thus is too great to be a differentiate of the layered intrusion. Also, preliminary Sm-Nd and Rb-Sr data indicate that the granophyre has an isotopic composition distinct from the mafic rocks and therefore could not have evolved from them (J. Vervoort, unpublished data). A more plausible interpretation is that the mafic magma that produced the Sonju Lake intrusion was trapped by the less dense Finland granophyre. This underplating resulted in partial melting of the granophyre and the development of a diffuse contact. Petrologic and isotopic studies are needed to determine the extent of assimilation across the mafic-felsic contact. --- Return downhill to Lake Co Rd 7. Turn left and proceed 5.6 miles to Sonju Lake Forest Rd. Take the Sonju Rd 3.1 miles to an area of low outcrops--- Page 76 �STOP 2-13: Sonju Lake Intrusion T.58N., R.7W., Sec. 27 Finland 7.5' quadrangle UTM: 633180E, 5256520N Highlights: cumulate stratigraphy of Pl+Ol (slt) -> Pl+Cpx+Ol (slg) -> Pl+Cpx+Ox+/-Ol (slfg) The Sonju Lake intrusion (SLI) is the most completely differentiated mafic layered intrusion recognized in the Keweenawan magmatic system (Stevenson, 1974; Weiblen, 1982). The intrusion occurs as a shallow (15-30°) south- to southeast-dipping, 1200-m-thick sheet of mafic cumulates underlying a granophyre body of similar thickness. The SLI is exposed in outcrop over an area extending about 3 km west from its abrupt truncation by the Beaver River diabase dike of the FTMD structure (Fig. 2-10A). However, it can be traced beneath glacial cover by its aeromagnetic signature for a strike length of about 15 km (Fig. 2-4). Above a basal contact zone of fine- to medium-grained melatroctolite (unit slmt) intrusive into older gabbroic rock, five map units within the SLI are distinguished by their cumulus mineralogy: Ol (unit sld)→ Pl+Ol (unit slt)→Pl+Cpx+Ol (unit slg)→Pl+Cpx+Ox±Ol (unit slfg)→Pl+Cpx+Ox+Ol+Ap (unit slad). At the upper contact with the overlying Finland granophyre is a complex unit (slmd) characterized by a cyclical loss of igneous lamination and enrichment in granophyre at the expense of mafic phases. This igneous stratigraphy is complimented by a smooth, logarithmic cryptic layering exemplified by decreasing mg# values of pyroxene (Fig. 2-10B). Taken together, these characteristics are consistent with formation of the SLI by closed-system fractional crystallization of a moderately evolved tholeiitic basaltic magma (Miller and Ripley, 1996). At this stop, we will traverse the middle cumulate units of the SLI. Exposed in low outcrops on either side of the Sonju Lake Forest Road is coarse-grained, moderately foliated, ophitic olivine gabbro typical of the upper part of the slt unit. It is a Pl+Ol cumulate with abundant (15-20%) augite oikocrysts up to 8 cm in diameter. Downsection from here, the slt unit is more typically an ophitic augite troctolite with olivine about twice as abundant as augite and the latter as 1- to 3-cm oikocrysts (Fig. 2-11). The increased mode and size of augite oikocrysts here presages the approaching cumulus arrival of augite. The arrival of cumulus augite is indicated by its abrupt change from ophitic to granular habit (Fig. 211), which can be observed in intermittent outcrop about 70 paces (~100 m) south of the road. This singular cumulus phase transition from Pl+Ol to Pl+Cpx+Ol is traceable across the entire exposure area of the SLI and serves as a useful datum horizon (Fig. 2-10). The slg unit is about 70 m thick and is typically composed of 60-65% plagioclase, 28-32% subprismatic augite, 5-10% olivine and 1% interstitial Fe-Ti oxide. The rock is consistently coarse-grained and well foliated. Continuing south across a low swamp, the outcrop exposed on the north face and crest of the next ridgeline is medium-grained, well foliated oxide gabbro of the slfg unit. The cumulus arrival of Fe-Ti oxide is defined by its granular habit and its increase in modal abundance to 7-10% (Fig. 2-11). Olivine is commonly in low abundance or absent. This unit is over 200m thick, and in its medial section hosts an 80m-thick interval enriched in PGE (Miller, 1999; Joslin, 2004). Page 77 �91 12 10" — • sidp SNA-li Slit //> Map Units 91 10 4730 sig —. frqm ? :-: e:itei//ii e METER frg . 800 slmd r l1d 600 . 400 n 200 -3- c: x+ slig fl Beaver River diahase -3- /23 BRD-Sl I hybrid dikes Slid • Augile Arrival Soaju Lake Intrusion 7i0hç sirwt olivine lerromonzodiorite si3d apatite ol dionte (PAP05543 slig oxide gtihhio (PAS) sig gahhro sit nociohte P0) slit dumte (0) stmt line inelutioctoliie (OP) Os < -200 (PA 0) —47 27' 30' sld t micrc,graphic granite quaii lenoinoniodiotile -400 8CpxQpx Finland Oranophyrc slmt S + . Western Profiles (1 &2) Eastern Profiles (3-5) harahboiclc 501) oaks SLI-1 Drill Core -600 Volcanic rocks 100 80 60 40 20 MgO/(MgO+FeO) Figure 2-10. A) Geology of the Sonju Lake intrusion and overlying Finland granophyre showing the locations of stops 12 and 13 (modified from Miller and others, 1993). B) Cryptic variation of MgO/(MgO+FeO) (mole %) in augite and orthopyroxene through the Sonju Lake intrusion and Finland granophyre (from Miller and Ripley, 1997). Figure 2-11. Textures of cumulate rocks from the middle units of the Sonju Lake intrusion. Light phase is plagioclase, outlined light gray phase is olivine, dark gray phase is augite, and black phase is Fe-Ti oxide. Page 78 0 �--- Return to Co Rd 7. Proceed north (to left) about 10 miles to Hoist Lake Rd (just past the Trestle Inn on Crooked Lake). Turn left and go 4.5 miles to junction with snowmobile trail heading to right-- STOP 2-14: Northwestern margin of the Beaver Bay Complex T.59N., R.7W., Sec. 12 Cabin Lake 7.5' quadrangle UTM: A - 638780E, 5274975N B - 638460E, 5274980N C - 638125E, 5274755N D - 638565E, 5275005N Highlights: Houghtaling Creek trocolite (hct); Dam Five gabbronorite (dfgn) with inclusion of gabbroic anorthosite (klga); Shoepack Lake inclusion-rich diorite (slid) This sequence of four exposure areas shows the major units comprising the northwestern margin of the Beaver Bay Complex (Miller and others, 1994). The first exposure (Area A) is of a medium coarsegrained, moderately foliated, layered troctolite cumulate with minor (<5%) ophitic augite forming the northwestern margin of the Houghtaling Creek troctolite (Figs. 2-4 and 2-12). The layering and foliation dip about 30º SE. This intrusion occurs as a 2-5 km wide, northeast-trending macrodike, which can be traced along strike for over 50 kilometer in outcrop and by its distinctive aeromagnetic signature (Fig. 27). Intermittent olivine layering and foliation define an asymmetric trough structure with its shorter limb on the southeast side (Fig. 2-12B). ---Following the snowmobile trail north of the road for about 100 m to a junction of trails. Take the trail to the left (west)--Pavement outcrops on the snowmobile trail and in a larger outcrop on the north side of the trail (Area B) are medium-grained, well-foliated gabbronorite cumulates of the Dam Five gabbronorite (dfgn, Fig. 2-12). The rock is composed of 50% plagioclase, 20% subprismatic augite, 27% subprismatic inverted pigeonite, and 3% subpoikilitic Fe-Ti oxide and would classify as a Pl+Cpx+IPig cumulate. Well-developed foliation dips about 27º SSE. This unit occurs exclusively along the northwestern margin of the Houghtaling Creek troctolite. Although a contact between the troctolite and gabbronorite is not observed and their internal structures are nearly conformable, the troctolite does show some fining toward the inferred contact and is considered to be intrusive into the gabbronorite. The very different cumulus mineralogies of the two units, which cannot be related by any conventional differentiation mechanism, is further evidence that these are distinct intrusive units (Fig. 2-12B). --- Continue along snowmobile trail to junction with main road. After crossing Hoist Creek bridge and meeting another road junction, take the trail to the south and then follow flags to Area C outcrops --- Page 79 �The exposures at the crest of this hill (Area C) are of coarse-grained gabbroic anorthosite, which occurs as a large inclusion in the Dam Five gabbronorite. The inclusion is composed of 90-95% moderately foliated plagioclase, 3-7% ophitic augite and 2-3% poikilitic oxide. It is mapped as an inclusion of the Katydid Lake gabbroic anorthosite (klga; see location map), but its ophitic texture is more like lithologies found in the deeper anorthositic series of the Duluth Complex (as, Fig. 2-4; olga, Fig. 212A). --- Return to road junction and continue west and north to clear cut area. Follow flags over crest of hill to outcrop ledge--NW SE A. B. Figure 2-12. Interpretive cross-sections through the northern Beaver Bay Complex from geologic maps by A) Boerboom and Miller (1994) and B) Miller and others (1994). Map unit abbreviations: nsf- felsic volcanics, slid - Shoepack Lake inclusion-rich diorite; slAi - Archean inclusions in slid; whgg - Whitefish Lake granophyre, felsic series of the Duluth Complex; olga, sclg, klga - phases of the anorthositic series of the Duluth Complex; dfgn - Dam Five gabbronorite; hct - Houghtaling Creek troctolite. Exposed in a 5' ledge on the western crest of the clear cut hill (Area D) is a typical exposure of the earliest intrusive unit of the Beaver Bay Complex - the Shoepack Lake inclusion-rich diorite (slid). This unit is composed of a heterogenous mix of aphanitic to very fine-grained diorite and inclusions of predominantly felsite (icelandite and K-feldspar-phyric rhyolite) and lesser amounts of basalt, gabbroic anorthosite, gabbro and locally Archean? rock types (granite, gneiss, amphibolite, schist). Inclusions range in size from single quartz xenocryts to blocks 50m across. Most inclusions exposed here are of felsic volcanic rocks irregularly mixed and partially assimilated into the diorite. However, at the northern end of the exposure, is an inclusion of a cross-bedded interflow sediment hornfels. The rock is composed of a granular mix of plagioclase, oxide and minor pyroxene, with oxide and plagioclase defining graded bedding. The pyroxene (~5-10%) is probably metamorphic. To the north, Archean xenoliths are common. These occurrence reinforce the interpretation that the pronounced gravity low in this area reflects a prominent southeast-trending basement ridge that divides the Keweenawan igneous rocks into two basins of intrusion and eruption (Boerboom, 1994; Miller and Chandler, 1997). The Shoepack Lake diorite is interpreted to be an intrusive breccia that was the first northeast-trending intrusion to breach this crustal ridge and intrude into a rhyolite-dominated part of the NSVG overlying the ridge (Fig. 2-12). This breach of the crustal ridge paved the way for subsequent intrusions, including the Dam Five gabbronorite and the Houghtaling Creek troctolite, to intrude along this same crustal weakness and thus create the composite grouping of northeast-trending intrusions that form the northern BBC (Figs. 2-4, 2-12). The presence of anorthositic series inclusions in this rock suggests that it may be one of the older intrusions in the greater Duluth Complex, perhaps correlative with early stage magmatism. Page 80 �--- Return east to Co Rd 7. Turn left and proceed to Forest Rd 170. Go right about 2.5 miles and then turn left on the secondary forest road to Whitefish Lake. Proceed about 4.0 miles to a gravel pit road on left. Park and walk about 150m south on the forest road to low outcrops on the west side of the road. --- STOP 2-15: Contact between the felsic and anorthositic series of the Duluth Complex T.60N., R.6W., Sec. 2 Wilson Lake 7.5' quadrangle UTM: 646050E, 5286185N Highlights: Contact between Whitefish Lake granophyre (whgg) and flow foliated gabbbroic anorthosite of the Outlaw Lake gabbroic anorthosite (olga). In the low pavement exposure, a sharp contact can be observed between medium-grained pink granophyre and medium-grained, swirly foliated, ophitic oxide gabbroic anorthosite. A bimodal grain size of well-foliated plagioclase in the gabbroic anorthosite imparts a trachytic texture to the rock. Several lines of evidence indicate that the gabbroic anorthosite is intrusive into the granophyre: 1) the gabbroic anorthosite shows a subtle decrease in grain size toward the contact whereas the granophyre show no change in texture as the contact is approached. Gabbroic anorthosite in gravel pit outcrops, about 50 m to the north, is considerably coarser grained than observed here. Two miles to the northeast, a more obvious chill of the gabbroic anorthosite against granophyre is noted. 2) well-developed, but irregular-oriented foliation in the gabbroic anorthosite appears to be concordant within a meter of the contact; and 3) felsic apophyses emanate from the granophyre and into the gabbroic anorthosite, probably caused by back veining of partially melted granophyre at the intrusive contact. This exposure provides rare field evidence for the older age of the felsic series relative to the anorthositic series of the Duluth Complex. This inferred age relationship was reaffirmed by U-Pb zircon dating, which yielded an 1109.6±4 Ma age for the Whitefish granophyre (Sandland and others, 2001) compared to 1099.1 and 1099.6 Ma ages for two anorthositic series samples dated by Paces and Miller (1993). The early stage emplacement of felsic magmas, which gave rise to the granophyre bodies that now dot the upper contact of the Duluth Complex (Fig. 2-3), helps explain the subsequent emplacement of the multiple, massive intrusions of the Duluth Complex. These felsic bodies probably acted as density traps that triggered underplating of first, ferrogabbroic magmas, creating the early gabbro series, then, plagioclase-phyric magmas (Fig.2-12A), creating the anorthositic series, and finally, aphyric mafic magmas, creating the many discreet intrusions of the layered series (Miller and Ripley, 1996; Miller and others, 2002). In the gravel pit are exposures of several varieties of anorthositic rocks that show complex lithologic and structural relationships typical of the anorthositic series (Miller and Weiblen, 1990). Page 81 �--- Return south to Forest Rd 170, then west to Co Rd 7. Proceed north (right) to Forest Rd 172 (Wanless Rd). Go left on 172 for about 2.9 miles to quarry entrance on right side of road (Permission required for entry) --- STOP 2-16: "Lake Superior Green"quarry T.60N., R.7W., Sec. 35 Silver Island Lake 7.5' quadrangle UTM: 636532E, 5278342N Highlights: Dimension stone quarry; porphyritic gabbroic anorthosite (klga); diabase dikes. Cold Spring Granite Company has been operating a dimension stone quarry at this site for the past 10 years. The rock is marketed as Lake Superior Green, but its geologic name is the Katydid Lake gabbroic anorthosite (Boerboom and Miller, 1994; Miller and others, 1994). The rock is a coarse-grained plagioclase-porphyritic gabbroic anorthosite and is composed of 60-70% large (2-3 cm), blocky plagioclase phenocrysts in a medium-grained matrix composed 65% plagioclase, 20% prismatic augite, 510% granophyric mesostasis, and 5-10% accessory phases of oxide, biotite, amphibole, and apatite. The subequant habit of the plagioclase precludes the development of a foliation, though locally some hint of alignment is evident. Locally, small (10-30 cm) rounded inclusions of coarse-grained anorthosite or granulated (tectonized) anorthosite are found. Along the southern wall of the quarry, the gabbroic anorthosite is cut by 10- to 50-m-wide dikes of fine-grained diabase. This rock is thought to be an offshoot from the main mass of the anorthositic series, which occurs about 2 kilometers to the north and is locally called the Outlaw Lake gabbroic anorthosite (Boerboom and Miller, 1994). END OF TRIP ---Continue west along Forest Road 172 10 miles to MN Hwy. 1. Turn left and proceed southeast to Hwy 61 at the shore. Turn right and proceed to Duluth--- Page 82 �References Basaltic Volcanism Study Project (BVSP), 1981, Pre-Tertiary continental flood basalts: in Basaltic Volcanism on the Terrestrial Planets, NY, Pergamon Press, p. 30-77 Boerboom, T.B., 1994, Archean crustal xenoliths in a Keweenawan hypabyssal sill, northeastern Minnesota. White was right!: Proceedings of the 40th Annual Institute on Lake Superior Geology, Program and Abstracts, p. 5-6. Boerboom, T.J., Green, J.C., and Jirsa, M.A., 2002a, Geologic map of the French River and Lakewood quadrangles, St. Louis County, Minnesota: Minnesota Geological Survey Miscellaneous Map M-128, scale 1:24,000 Boerboom, T.J., Green, J.C., and Jirsa, M.A., 2002b, Geologic map of the Knife River quadrangle, St. Louis and Lake Counties, Minnesota: Minnesota Geological Survey Miscellaneous Map M-129, scale 1:24,000 Boerboom, T.J., Green, J.C., and Miller, J.D., Jr., 2003a, Geologic map of the Two Harbors quadrangle, Lake County, Minnesota: Minnesota Geological Survey Miscellaneous Map M-139, scale 1:24,000 Boerboom, T.J., Green, J.C., and Miller, J.D., Jr., 2003b, Geologic map of the Castle Danger quadrangle, Lake County, Minnesota: Minnesota Geological Survey Miscellaneous Map M-140, scale 1:24,000 Boerboom, T. J., and Miller, J. D., Jr., 1994, Geologic map of the Silver Island Lake, Wilson lake, and western Toohey Lake quadrangles, Cook and Lake Counties, Minnesota: Minnesota Geological Survey Miscellaneous Map Series, Map M-81, scale 1:24,000 Bonnichsen, B. and Kauffman, 1987, Physical features of rhyolite lava flows in the Snake River Plain volcanic province, southwestern Idaho: in The Emplacement of Silicic Domes and Lava Flows, J. H. Fink, ed., p. 119145 Brannon, J.C., 1984. Geochemistry of successive lava flows of Keweenawan North Shore Volcanic Group: unpublished Ph.D. Thesis, Washington University, St. Louis, 212pp. Carmichael, I.S.E., 1964, The petrology of Thingmuli, a Tertiary volcano in eastern Iceland: Jounral of Petrology, v. 5, p. 435-460 Chandler, V.W., 1990, Geologic interpretation of gravity and magnetic data over the central part of the Duluth Complex, northeastern Minnesota: Economic Geology, v. 85, p. 816-829 Davis, D.W., and Green, J.C., 1997, Geochronology of the North American Midcontinent rift in western Lake Superior and implications for its geodynamic evolution: Canadian Journal of Earth Science, v. 34, p. 476-488 Davis, D. W. and Paces, J. B., 1990, Time resolution of geologic events on the Keweenaw Peninsula and implications for development of the Midcontinent Rift system: Earth and Planetary Science Letters, v. 97, p. 54-64. Gehman, H.M., Jr., 1957, The petrology of the Beaver Bay Complex, Lake County, Minnesota: unpublished Ph.D. dissertation, University of Minnesota, Minneapolis, 300p. Goldich, S.S., Nier, A.O., Baadsgaard, H., Hoffman, J.H., and Krueger, H.W., 1961, The Precambrian geology and geochronology of Minnesota: Minnesota Geological Survey Bulletin 41, 193 p. Greeley, R., 1982, The Snake River Plain, Idaho: Representative of a new category of volcanism: Journal of Geophysical Research, v. 87, N. B4, p. 2705-2712. Green, J.C., 1972, North Shore Volcanic Group, in Sims, P.K., and Morey, G.B., eds., Geology of Minnesota—A centennial volume: Minnesota Geological Survey, p. 294-332. Green, J.C., 1977, Keweenawan plateau volcanism in the Lake Superior region, in Baragar, W. R. A., Coleman, L. C., and Hall, J. M., eds., Geological Association of Canada Special Paper 16, p. 407-422. Green, J.C., 1982, Geologic Map Atlas of Minnesota, Two Harbors Sheet: Minnesota Geological Survey, scale 1:250,000. Green, J.C., 1989, Physical volcanology of mid-Proterozoic plateau lavas: The Keweenawan North Shore Volcanic Group, Minnesota: Geological Society of America Bulletin, v. 101, p. 486-500. Green, J.C., 1990, Primary tridymite crystallization and inferences from tridymite and quartz textures in high-T Keweenawan rhyolites and granophyres, Minnesota (abs.): Geological Soc. of America, Abstracts with Programs, v. 22, p. A289-290. Green, J.C., 1992, Geologic map of the north shore of Lake Superior, Lake and Cook Counties, Minnesota: Part 1. Little Marias to Tofte: Minnesota Geological Survey Miscellaneous Map Series, M-71, scale 1:24,000 Page 83 �Green, J.C., 1995, Chemostratigraphy at the fringe of the Midcontinent Rift System: The northeast limb of the North Shore Volcanic Group, Minnesota (ext. abs.): in Proceedings, Petrology and Metallogeny of Volcanic and Intrusive Rocks of the Midcontinent Rift System: 1995 IGCP Project 336 Field Conference and Symposium, p. 55-56 Green, J. C. and Fitz, T. J. III, 1993, Extensive felsic lavas and rheoignimbrites in the Keweenawan Midcontinent Rift plateau volcanics, Minnesota: petrographic and field recognition: Journal of Volcanology and Geothermal Research, v. 54, p. 177-196 Green, J.C., Davis, D.W., and Schmitz, M.D., 2001, Three new zircon dates for the Midcontinent Rift, North Shore, Minnesota: more data, more questions: 47th Institute on Lake Superior Geology, Proceedings and Abstracts, p. 29. Irvine, T.N., and Baragar, W.R.A., 1971, A guide to the chemical classification of the common volcanic rocks: Canadian Journal of Earth Sciences, v. 8, no. 5, p. 523-548. Jerde, E.A., 1991, Geochemistry and petrology of hypabyssal rocks associated with the Midcontinent rift, northeastern Minnesota: unpublished Ph.D. Thesis, University of California, Los Angeles, 305 pp. Jirsa, M. A., 1984, Interflow sedimentary rocks in the Keweenawan North Shore Volcanic Group, northeastern Minnesota: Minnesota Geological Survey Report of Investigations 30, 20 pp. Joslin, G.A., 2004, Stratiform Pd-Pt-Au mineralization in the Sonju Lake intrusion near Finland, Minnesota: unpublished M.S. Thesis, University of Minnesota Duluth. Klewin, K.W., and Shirey, S.B., 1992, The igneous petrology and magmatic evolution of the Midcontinent Rift System: Tectonophysics, v. 213, p. 33-40. Manley, C. R., 1996, Physical volcanology of a voluminous rhyolite lava flow: The Badlands lava, Owyhee Plateau, southwestern Idaho: Journal of Volcanology and Geothermal Research, v. 71, p. 129-153 McBirney, A.R., and Williams, H., 1969, Geology and petrology of the Galapagos Islands: Geological Soc. of America Memoir 118, 197p. Miller, J.D., Jr., 1988, Geologic map of the Split Rock Point NE and Silver Bay quadrangles, Lake County, Minnesota: Minnesota Geological Survey, Miscellaneous Map Series, M-68, scale 1:24,000 Miller, J.D., Jr., 1999, Geochemical evaluation of platinum group element (PGE) mineralization in the Sonju Lake intrusion, Finland, Minnesota: Minnesota Geological Survey Information Circular 44, 32 p. Miller, J.D., Jr., and Chandler, V.W., 1997, Geology, petrology, and tectonic significance of the Beaver Bay Complex, northeastern Minnesota: in Ojakangas, R.J., Dickas, A.B., Green, J.C., (eds.) Middle Proterozoic to Cambrian Rifting, Central North America: Geological Society of America Special Paper 312, p. 73-96. Miller, J.D., Jr., and Ripley, E.M., 1996, Layered intrusions of the Duluth Complex, Minnesota, USA: in Cawthorne, R.G., ed., Layered Intrusions: Amsterdam, Elsevier Science, p. 257-301 Miller, J.D., Jr., and Vervoort, J.D., 1996, The latent magmatic stage of the Midcontinent Rift: a period of magmatic underplating and melting of the lower crust: 42nd Annual Institute on Lake Superior Geology, Proceedings Volume, Part I – Program and Abstracts, p. 33-35 Miller, J.D., Jr. and Weiblen, P.W., 1990, Anorthositic rocks of the Duluth Complex: Examples of rocks formed from plagioclase crystal mush: Journal of Petrology 31, p. 295-339 Miller, J.D., Jr., Boerboom, T.B., and Jerde, E.A., 1994, Bedrock geologic map of the Cabin Lake and Cramer 7.5minute quadrangles, Lake and Cook Counties, Minnesota: Minnesota Geological Survey Miscellaneous Map Series, M-82, scale 1:24,000 Miller, J.D., Jr., Green, J.C., Boerboom, T.B., & Chandler, V.W., 1993, Geology of the Doyle Lake and Finland quadrangles, Lake County, Minnesota: Minnesota Geological Survey Miscellaneous Map Series M-72, scale 1:24,000 Miller, J.D., Jr., Green, J.C., and Boerboom, T.B., 1989, Geology of the Illgen City quadrangle, Lake County, Minnesota: Minnesota Geological Survey Miscellaneous Map Series, M-69, scale 1:24,000 Miller, J.D, Jr., Schaap, B.D., and Chandler, V.W., 1990, The Sonju Lake intrusion and associated Keweenawan rocks: geochemical and geophysical evidence of petrogenetic relationships: Proceedings of the 36th Annual Institute on Lake Superior Geology, Part 1. Abstracts, p. 66-68 Page 84 �Miller, J.D., Jr., Green, J.C., Severson, M.J., Chandler, V.W., and Peterson, D.E., 2001, Geologic map of the Duluth Complex and related rocks, northeastern Minnesota: Minnesota Geological Survey Miscellaneous Map Series, M-119, scale 1:200,000 Miller, J.D., Jr., Green, J.C., Severson, M.J., Chandler, V.W., Hauck, S.A., Peterson, D.M., Wahl, T.E., 2002, Geology and mineral potential of the Duluth Complex and related rocks of northeastern Minnesota: Minnesota Geological Survey Report of Investigations 58, 207 p. Milner, S.C., Duncan, A.R., and Ewart, A. , 1992, Quartz latite rheoignibrite flows of the Etendeka Formation, northwestern Namibia: Bulletin of Volcanology, v. 54, p. 200-219 Morrison, D.A., Ashwal, L.D., Phinney, W.C., Shih, C., and Wooden, J.L., 1983, Pre-Keweenawan anorthosite inclusions in the Keweenawan Beaver Bay and Duluth Complexes, northeastern Minnesota: Geological Society of America Bulletin, v. 94, p. 206-221. Nicholson, S. W., Shirey, S. B., Schulz, K. J., and Green, J. C., 1997, Rift-wide correlation of 1.1 Ga Midcontinent rift system basalts: implications for multiple mantle sources during rift development: Canadian Journal of Earth Science, v. 34, p. 504-520. Paces, J.B., and Miller, J.D., Jr., 1993, Precise U-Pb ages of Duluth Complex and related mafic intrusions, northeastern Minnesota: geochonological insights to physical, petrogenetic, paleomagnetic and tectonomagmatic processes associated with the 1.1 Ga Midcontinent rift system: Journal of Geophysical Research, v. 98, no.B8, p. 13,997-14,013. Pope, N.M., 1976, Petrology and structure of the Late Precambrian mafic sills east of Silver Creek, Lake County, Minnesota: Unpublished M.S. thesis, University of Minnesota Duluth, 157 p. Sandland, T.O., Wirth, K.R., Vervoort, J.D., Gehrels, G.E., Kennedy, B.C., and Harpp, K.S., 2001, Roles of fractional crystallization and assimilation in the production of Midcontinent rift granophyres: 47th Institute on Lake Superior Geology, Abstracts and Proceedings, p. 85-86. Schmidt, S. Th., 1993, Regional and local patterns of low-grade metamorphism in the North Shore Volcanic Group, Minnesota, USA: Journal of Metamorphic Geology, v. 11, p. 401-414. Schmidt, S. Th. And Robinson, D., 1997, Metamorphic grade and porosity and permeability controls on mafic phyllosilicate distributions in a regional zeolite to greenschist facies transition on the North Shore Volcanic Group, Minnesota: Geological Society of America Bulletin, v. 109, No. 6, p. 683-697. Schwartz, G.M., and Sandberg, A.E., 1940, Rock series in diabase sills at Duluth, Minnesota: Geological Society of America Bulletin, v. 51, p. 1135-1172. Sigvaldason, G. E., 1974, Basalts from the centre of the assumed Icelandic mantle plume: Journal of Petrology, v. 15, p. 497-524. Stevenson, R.J., 1974, A mafic layered intrusion of Keweenawan age near Finland, Minnesota: unpublished M.S. thesis, University of Minnesota Duluth, 160 pp. Vervoort, J. D. and Green, J. C., 1997, Origin of evolved magmas in the Midcontinent Rift System, northeast Minnesota: Nd-isotope evidence for melting of Archean crust: Canadian Journal of Earth Sciences, v. 34, p. 521-535. Wallace, A.B., Drexter, J.W., Grant, N.K., and Noble, D.C., 1980, Icelandite and aenigmatite-bearing pantellerite from the McDermitt caldera complex, Nevada-Oregon: Geology, v. 8, p. 380-384. Weiblen, P.W., 1982. Keweenawan intrusive igneous rocks. In: Wold, R.J. & Hinze, W.J. (eds.) Geology and tectonics of the Lake Superior Basin: Geological Society of America Memoir 156, 57-82. Wood, D. A., 1978, Major and trace element variations in the Tertiary lavas of eastern Iceland and their significance with respect to the Iceland geochemical anomaly: Journal of Petrology, v. 19, p. 393-436 Page 85 �FIELD TRIP 3 LATE WISCONSINAN SUPERIOR-LOBE DEPOSITS IN THE SUPERIOR BASIN NORTHEAST OF DULUTH Howard Hobbs Minnesota Geological Survey INTRODUCTION The recession of the Superior lobe was marked by many readvances. We will examine glacial striations and tills of the Superior lobe along the scenic North Shore of Lake Superior from Duluth to Two Harbors. The stratigraphy in this area will be tied to ice margins and events elsewhere, leading to a consistent glacial history. Each time the ice lobe retreated into the Superior basin, it created a glacial lake, and each subsequent readvance incorporated reddish-brown lake sediment. Each of these lakes is here considered to be a phase of glacial Lake Superior in a broad sense. Each readvance covered a smaller area and reached a lower elevation than the last, and deposited a finer-grained till than the previous one. STRATIGRAPHY Cromwell Formation The oldest glacial sediment exposed in these stops is a rocky, gravelly, reddish-brown (5YR 4/4) till. Its matrix texture is typically a loam, but some samples are extremely low in clay (Fig. 3-1). It is non-to-slightly calcareous, and is deeply leached where exposed at the surface, even where calcareous at depth. This till and associated meltwater sediment has been named the Cromwell Formation (Wright and others, 1970). The characteristic reddish color and abundant red and black clasts, which define the Superior provenance, are derived from the passage of the ice through the Superior basin, and are presumably absent from deposits up-ice from the basin. The till matrix derived its reddish color and some of its red clasts from pulverized red sedimentary rock from the floor of the basin: sandstone, siltstone, and shale. The other red and black rock fragments are primarily extrusive and intrusive igneous rocks from the northwestern lake shore: basalt, rhyolite, diabase, and gabbro. Black slate fragments from the Proterozoic Rove Formation are locally present. In most of its extent (down-ice from the basin), the Cromwell Formation contains many clasts other than those from the Superior basin: gray to black Proterozoic metamorphic clasts, Archean granite and greenstone, and Paleozoic carbonate. These clasts are mainly derived from older Quaternary sediment and local bedrock. Within the Superior basin, the clast assemblage in the Cromwell Formation in many places is dominated by Superior basin clasts. I call this assemblage a “hyper-Superior” assemblage, as opposed to the mixed Superior assemblage down-ice. Inasmuch as the ice itself did not originate inside the Superior basin, the scarcity of clasts from up-ice of the basin implies that the rate of bedrock erosion is much higher within the basin than outside, which explains why the basin formed in the first place. The standard grain size for clast counting and determining provenance is 1-2 millimeters (very coarse-grained sand), and this size is used unless otherwise specified. Barnum Formation The remainder of the glacial and glaciolacustrine sediment in the area is referred to as the Barnum Formation (Fig. 3-2). The Barnum Formation was originally defined to include clayey Page 86 �till overlying the Cromwell Formation (Wright and others, 1970). Hobbs (2002, 2003a, b) recognized three texturally distinct tills above the Cromwell Formation. The tills are overlain and separated in places by reddish lake and deltaic sediment, which ranges in texture from silt to clay (Fig. 3-1), and contains very little sand and almost no coarse-grained fragments. This sediment ranges from massive to laminated, and from grayish-brown to reddish-brown. More detail is provided in the stop descriptions. The individual tills contain inclusions of similar lake sediment in places. These tills and lacustrine sediments are to be included in a modified Barnum Formation (Johnson and others, unpub. data). Until this work is published, the member names will be used informally. Lakewood member The lowest till in the Barnum Formation is the Lakewood member. It is typically reddishbrown (5YR 4/3 to 3/4) noncalcareous silt loam (Fig. 3-1). Its average clay content is only a little more than that of the Cromwell Formation. Its proportion of coarse-grained fragments is typically less than that of the Cromwell till, but more than that of the other tills of the Barnum Formation. In contrast to the Cromwell Formation, large pebbles and boulders are not common. Most samples have a hyper-Superior clast assemblage in the 1-2 millimeter size fraction. A few samples have a small number of Paleozoic carbonate clasts. The till is relatively thin and patchy in the field trip area; it probably averages less than 2 meters in thickness. Moose Lake member The middle till in the Barnum Formation is the Moose Lake member. It is typically reddishbrown (5 to 2.5YR 5/3 to 4/4) calcareous clay loam to silty clay loam (Fig. 3-1). Coarse-grained fragments are sparser than in the brown silty till of the Lakewood member, and large rocks are rare. The typical clast assemblage is Superior, but most are not hyper-Superior. The Moose Lake Page 87 �member contains more clasts from outside the Superior basin (mostly granitic) than does the Lakewood member. Many samples contain secondary carbonate precipitated by soil processes, but fewer than half of the samples have primary carbonate clasts. The number of primary carbonate clasts is small, even in samples that appear to be quite calcareous, which suggests that the bulk of carbonate is in the finer grain sizes. The average thickness of the till in the field trip area is about 3 meters. Page 88 �Wrenshall member Laminated red and gray lacustrine silt and clay in the Nemadji lake plain was named the Wrenshall Formation by Wright and others (1970). It is stratigraphically above the Moose Lake member, and behind the Nickerson moraine at the margin of the Moose Lake member. I am redefining the Wrenshall Formation as a member of the Barnum Formation, because it is a part of the same stratigraphic package of glacial lake sediment and lake-influenced tills. This member has not been observed in the field trip area. Knife River member The upper till of the Barnum Formation is informally named the Knife River member. It is typically reddish-brown (2.5 YR 5/3 to 4/4) calcareous clay (Fig. 3-1), containing few coarsegrained fragments or large rocks. A rough field criterion for differentiating the Moose Lake and Knife River tills is the sound they give off to a shovel. The Moose Lake member goes “clink,” but the Knife River goes “clunk.” That is, almost every shovel thrust into the Moose Lake till encounters a pebble, but most shovel thrusts into the Knife River do not. Where the Knife River till overlies the till of the Moose Lake member, its color is commonly on the same color chip, but a little lighter and redder. The clast assemblage is commonly Superior, rarely hyper-Superior, and occasionally a mixed Superior-Winnipeg assemblage (the Winnipeg assemblage is found in tills deposited by ice that advanced through the Winnipeg lowland. It is characterized by common to abundant Paleozoic carbonate, granitic grains that are more common than dark grains, few red grains, and little to no Cretaceous shale). More than half of the samples contain primary carbonate grains, and many samples contain common to abundant secondary carbonate. Its average thickness is 3 to 4 meters, but appears to be absent in many places close to Lake Superior. Its clay texture is atypical for glacial till, which led Moss (1977) and Gross (1982) to interpret this till as massive glacial lake clay. GLACIAL HISTORY During the most recent glaciation, the field trip area was dominated by the activities of the Superior lobe, which advanced through the axis of the Superior basin from northeast to southwest as far south as the St. Croix moraine (Wright, 1972). The advance to the maximum, and the earlier retreatal phases, deposited till and associated sediments of the Cromwell Formation. Many retreatal or readvance ice margins have been recognized between the St. Croix moraine and the Superior basin (Mooers, 1988; Patterson, 2001), but only the most recent ones are discussed here. As long as the ice did not front a substantial glacial lake between advances, the texture of the till remained more or less the same: rocky loam to sandy loam. The first retreat into the Superior basin did not create a large continuous lake, but rather a set of small ice-marginal lakes trapped between the ice and the sides of the basin. Meltwater escaped by a series of ice-marginal channels, building ice-contact deltas of sand and gravel into ponds on its way out of the basin to the southwest (Stop 3-8). The next advance of the Superior lobe overrode these deltas and deposited a loamy Cromwell till that ends at the Mille Lacs–Highland moraine. The texture of this till does not reflect any large amount of overridden lacustrine sediment. An outwash plain graded to the Highland moraine buries the adjacent part of the Toimi drumlin field. It is graded to a set of channels that seems to end at the St. Louis River. The present day St. Louis River flows east and south, into the Superior basin, so meltwater flow from the Highland moraine maximum must have flowed west (reversed) into glacial Lake Upham I. The flowpath out of Lake Upham I is unknown; deposits of the St. Louis sublobe later covered this whole area (Fig. 3-2). As the ice receded from the Highland moraine, a set of meltwater channels was formed between the receding ice in the basin, and the higher ground to the northwest. These channels are discontinuous, and must have partly formed on the ice itself. Their general flow direction is to Page 89 �the southwest, and they probably exited the Superior basin at its southwestern corner, where bedrock elevations are the lowest. Deposits of subsequent readvances have since covered this area, but the bottom of the most recently used lake spillway is about 1,050 feet in elevation. Gravel in these channels is somewhat younger than the gravel in the ice-contact deltas, but is also included in the Cromwell Formation. Further retreat opened up a lake in the southwestern corner of the Superior basin that extended about as far northeast as Two Harbors. The advance that followed was named the Split Rock phase by Wright (1972). It spilled out of the basin and deposited a thin, reddish-brown (5YR) till, which I have correlated to the Lakewood member of the Barnum Formation. This advance extended well out of the Superior basin deep into Pine County, where it apparently formed the Split Rock, Askov-Lookout Tower, and Kerrick ice margins. This correlation is uncertain, and the till texture is not exactly the same in Pine County as in the field trip area, but till behind this set of margins is finer-grained than that of the earlier phases (Patterson, 2001). The Lakewood member does not exhibit a morphologically distinct ice margin in the field trip area. Its margin is recognized only by the change in texture of the surface till, from that typical of the Cromwell Formation to that typical of the Barnum Formation. This change occurs fairly consistently between 1,150 and 1,200 feet in elevation. All three till members of the Barnum Formation have fairly consistent margin elevations in the field trip area. The ice was confined in a steep-sided basin, so their margins are similar to bathtub rings. Theoretically, one would expect the margins to rise to the northeast, both to account for the down-ice slope of the glacier, and differential postglacial rebound. There is little evidence of this rise in the margin of the Lakewood member. This is partly because the data points on which it is based are widely separated, and partly because the mapped margin of the member is not necessarily the actual ice margin, but the margin of preserved deposits. A thin patchy till deposited on a sloping surface is subject to extensive erosion, both by waves and by sheet runoff. In addition, the area mapped so far is rather small, and the expected rise in ice margin is not great. Another retreat opened up a larger portion of glacial Lake Superior; it is unclear how much of the basin was ice-free at this time. Apparently, this lake accumulated a considerable amount of clay, because the advance that followed deposited the clayey Moose Lake member and built the Nickerson moraine at the southwestern margin of the basin. In the field trip area, the Moose Lake member was deposited up to about 1,100 to 1,150 feet in elevation. If the glacier were merely recycling its own clay, it is puzzling why the Moose Lake member is so much more clayey than the Lakewood member. Another puzzle is why the Moose Lake member is so calcareous compared to the Lakewood member. One possibility is a change in the nature of debris carried into the Superior basin from the central Laurentide Ice Sheet. For example, Mooers and Lehr (1997) proposed that the change from calcareous to noncalcareous debris carried by the Rainy lobe (in a broad sense) was correlated to the migration of the ice divide south of the Hudson Bay lowland, so that the Paleozoic carbonates in the lowland could no longer be transported south. The eastern boundary of these lowlands is up-ice from the Superior basin, and could have supplied some carbonate. In fact, a small number of Paleozoic dolomite grains are sporadically present in the otherwise noncalcareous Cromwell Formation and Lakewood member tills, so a Hudson Bay component is quite possible. However, the mechanics of how a reverse transition from noncalcareous to calcareous would work in this setting is difficult to envision. Another possibility is that glacial Lake Upham I drained into Lake Superior between the Split Rock and Nickerson advances. This lake may have been fed by meltwater from the calcareous Itasca or Koochiching lobes to the north, or even the incipient St. Louis sublobe. If so, some of the meltwater probably funneled down the St. Louis River to glacial Lake Superior. Fine-grained calcareous lake sediment was thus potentially available for entrainment into the Moose Lake till. Although the sediment carried down the St. Louis River should have been mostly brown and Page 90 �gray, there was abundant red clay deposited in the lake from the melting Superior lobe, and the red color tends to dominate in mixtures (the gray color is not the result of a pigment, but the lack of pigment). The later advance of the St. Louis sublobe filled the Aitkin-Upham basin and buried the deposits of Lake Upham I. This advance coincided more or less with the Nickerson moraine, as shown by diversion channels around the moraine that can be traced upstream to the St. Louis River (Wright and others, 1970). There is no way to be sure which of these channels were fed by outwash from the St. Louis sublobe, and which were fed by overflow from glacial Lake AitkinUpham. The general pattern is that the earlier, higher diversion channels are narrower, and presumably carried less water than the later, lower ones. One might speculate that the earlier diversion channels carried meltwater from the ice margin, and that the later ones carried water from the glacial lake. At times, Lake Aitkin-Upham was fed by overflow from Lake Koochiching (the eastern arm of Lake Agassiz) at its highest levels (Hobbs, 1983). Thus, a much larger flow of water was available than could have been generated by local melting in the St. Louis River watershed. The succeeding retreat first opened up a small ice-marginal lake in the southwestern corner of the basin, called glacial Lake Nemadji by Winchell (1899). This lake appears to have been small and fronted by ice at first—the rapid decline of its depositional surface from the proximal edge of the Nickerson moraine to Duluth can be most easily explained if the Superior lobe still occupied most of the basin. The outlet of Lake Nemadji was the Portage River channel, which cuts through the Nickerson moraine and joins a diversion channel of the St. Louis River at the town of Moose Lake. The bottom of the Portage River outlet is about 1,050 feet in elevation, but lakesmoothed topography and minor beach ridges can be recognized up to 1,080 feet. This does not mean that the water in the outlet channel was necessarily 30 feet deep; the higher wave-washed topography could have formed while the channel was being deepened. A great thickness of laminated glacial clay and silt (Wrenshall member) accumulated at this time, between the proximal side of the Nickerson moraine and the ice remaining in the basin. Further retreat of the ice uncovered the lower Brule outlet in Wisconsin, which lowered the level of the lake to about 1,020 feet and dried up the Portage outlet (Leverett, 1932). This lower level of the lake has been called glacial Lake Duluth, but I prefer to use Duluth and Nemadji as levels or phases of glacial Lake Superior, rather than giving every phase a separate lake name. A large outflow from glacial Lake Aitkin-Upham II came down the St. Louis River after the Superior lobe melted back from the Nickerson moraine. It washed a large area (about 10 square miles) down to bedrock, upstream from the Nemadji lake plain. Although this scouring event was extremely widespread, it did not expose any substantial area of bedrock below 1,050 feet in elevation, suggesting that the local base level was no lower than 1,050 at the time of the event. Subsequent stream erosion has incised a narrow valley into the bedrock below 950 feet in elevation, but this cutting seems to have been accomplished by long erosion of a much smaller stream graded to a much lower base level. Thus, the last major meltwater flood down the St. Louis River seems to have come during the short time that glacial Lake Superior stood at the Nemadji level. As the Superior lobe retreated, the lake declined in stages as lower outlets were uncovered, until the entire lake basin was ice-free. The water level was much lower than it is today (at least in the field trip area). As the ice retreated north of Lake Superior, Lake Agassiz spilled east into Lake Nipigon, into Lake Superior, and then out into Lake Huron (Clayton, 1983). A considerable amount of suspended sediment from glacial Lake Agassiz was deposited in the basin. Combined with the earlier sediment from Lake Aitkin-Upham, the Superior basin now had a considerable amount of clay-rich calcareous sediment to be entrained by the next glacial advance. Lake Superior remained ice-free for about 1,000 years, from 1100 to 1000 B.P. (Drexler and others, 1983). Page 91 �The last, or Marquette advance, filled the basin with ice again, depositing a stone-poor, very clayey 2.5YR till, which I have included in the Knife River member of the Barnum Formation. This till is much more clayey on average than the clayey Moose Lake member (Fig. 3-1); its matrix is more calcareous, and it contains more actual carbonate clasts. These differences are attributed mainly to incorporation of sediment from Lakes Agassiz and Aitkin-Upham. In the field trip area, the Knife River member extends up to a little less than 1,050 feet in elevation; it extends laterally over the Wrenshall member as far as the proximal side of the Nickerson moraine (Howard Mooers, unpub. data). The field trip takes place in the area mapped in the French River, Lakewood, Knife River, Two Harbors, and Castle Danger quadrangles (Fig. 3-3). I have recently mapped the surficial deposits of the first 4 quadrangles under the USGS STATEMAP program (Hobbs, 2002, 2003a, b). A surficial map of the Castle Danger quadrangle is in progress. I combined the knowledge gained from this mapping with earlier mapping and interpretations in the region to create this new interpretation of Superior lobe recessional history. Page 92 �FIELD TRIP STOPS 8:00 a.m. Leave Radisson Hotel, Duluth; get onto I-35/ Highway 61, heading northeast through Duluth. Just beyond the where US Highway 61 becomes a 4-lane expressway, turn right onto the Scenic North Shore Drive (County Road 61). Continue about 6 miles to the village of French River. Stop 3-1. Superior bluff cut at French River. French River Quad., T.51N., R. 12 W., Sec 19 NE corner; 583815E, 5194075N NAD83 UTMs This wave-cut bluff exposes about 25 feet of glacial sediment above basalt bedrock. The top of the bedrock is 3 to 4 feet above lake level. It has been broken up by weathering and wave action in most places, but there are some surfaces that have been smoothed by glacial abrasion. Striations strike northeast, almost parallel to the shore but a little more westerly. These striations were carved by the main flow of the Superior lobe through the Superior basin. Wherever striations are exposed by wave action along the shoreline, they have a similar orientation. The lower third of the cut is the Lakewood member of the Barnum Formation [(5) 28 63 9] over till of the Cromwell Formation [(18) 52 42 6]. Numbers in brackets represent individual texture samples: (gravel) sand, silt, and clay. Sand, silt, and clay are considered matrix, and their numbers add to 100 percent, rounded to the nearest 1 percent. The number in parentheses is the total of all fragments larger than 2 millimeters, and is expressed as a percent of the original sample: matrix plus coarse-grained fragments. Large rocks were avoided for the texture samples. Both tills are firm but not hard, with a platy structure parallel to the bluff face. The platy structure is probably a weathering phenomenon. These tills are a little less red than they usually appear—7.5 YR rather than 5YR. The Cromwell sample has a hyper-Superior grain assemblage; the Lakewood sample has a Superior assemblage with a trace of carbonate. The middle third of the bluff cut is red clayey till of the Moose Lake member: [(1) 13 29 58 and [(2) 19 30 51]. Its lower contact is flat and sharp. Both the middle and upper tills are fairly firm, with a strong angular blocky structure. The structure and consistency are the best way to distinguish in-place till from the soft structureless mudflow sediment that coats the bluff. Two samples of the Moose Lake member have Superior grain assemblage with a trace of carbonate. The upper third of the bluff is red clay till of the Knife River member: [(0.1) 4 22 74] and [(0.2) 2 26 72]. Both tills are reddish-brown (2.5 YR 5/4); the contact between them was not observed, but inferred from the texture of the samples. This till contains irregular, subhorizontal clay inclusions, which look grayish by contrast to the red till. They range from pinkish gray (7.5YR 6/2) to light brown (7.5YR 6/3). These inclusions are more calcareous than the red till; they are interpreted as incompletely digested clumps of Lake Agassiz-derived clay. The texture samples from this interval contain some of these clay inclusions, which explains why they are so poor in gravel and sand, and so rich in clay, even for till of the Knife River member. Each sample contains only a tiny number of 1-2 millimeter grains—one is a Winnipeg assemblage, one is a Superior-Winnipeg mixture. NEXT: Continue along the scenic drive about 4.5 miles. Turn right on a road leading to a scenic overlook. Park and scramble down the bluff. Notice how the stone wall has broken and dropped down in places where the red clay till it was built on has slumped. This bluff is actively retreating by wave action and slope failure. The stop is the bluff just across a small gully west of the scenic overlook. Page 93 �Stop 3-2. Superior bluff by overlook. Knife River Quad., T.51N., R.12W., Sec 2, SE of SW of NW; 5888830E, 5197725N NAD 83 UTMs The bluff is about 28 feet high, but only the upper half is exposed (unless a storm has washed the lower part since I saw it). The top of the exposed bluff is not at its original elevation. There are a few slump scarps hidden in the trees above the top, and their combined offset makes the top of the bluff 10 to 12 feet lower than the original surface. No bedrock is exposed at this site. The lowest part of the exposure is 4 feet of till of the Cromwell Formation [(5) 36 59 5] and [(14) 43 48 9]. This till is unusually low in clay, even for Cromwell till. It is calcareous, apparently protected from leaching by the calcareous tills above it. Both samples of Cromwell till contain hyper-Superior grain assemblages. Above the Cromwell till is a layer of brown silty till [(11) 17 59 24] only 2 feet thick, overlain by a foot of massive silt [(1) 7 73 20], which is similar in color and texture to the silty till, but lacks stones. The brown silty till is included in the Lakewood member of the Barnum Formation; the brown silt could also be included in the Lakewood member. It could either be massive lacustrine, or actual till that happens to contain few coarse-grained fragments. More digging may help us figure this out. Both are calcareous. Both contain hyper-Superior grain assemblages with no carbonate grains, but the 1-2 millimeter sample from the massive silt is very small. Above the massive silt is a layer of interbedded red (2.5YR 4/4) and gray (10YR 4/1) calcareous lacustrine clay just over a foot thick. A sample of the red clay is slightly more clayey [0.2) 3 15 82] than the gray [(0.7) 3 18 79], but the gray clay feels more slippery, possibly because of a higher content of expandable clays. Both have very small Superior grain assemblages. The main red and gray beds are about an inch thick, but there are red and gray micro-laminations within each bed. There are no silt beds, making it unlikely that these beds represent varves. The bedding is more or less horizontal, but not very regular. Beds pinch and swell; is this original, or were the beds deformed by overriding of the next glacier? There are numerous slickensided joints running through both the brown silt and the red and gray clay. Were these caused by overriding ice, or by modern slumping? The uppermost layer exposed in this bluff is about 2 feet of calcareous red clayey till [(5) 31 25 44] of the Moose Lake member. It is weak red (2.5 YR 4/2) in the lower part, and reddish brown (2.5YR 4/4) in the upper part. A sample has a Superior grain assemblage. Red clay till of the Knife River member is not exposed here, but it may be present at the site. The top of the exposure is at least 3 feet below the bluff top, and the bluff top itself is probably not the original surface. A soil boring taken along the Scenic Highway from a bluff about 20 feet higher than this one penetrated about 16 feet of red clay till over lacustrine sediment, with an intercalated contact. NEXT: Leave the parking lot, drive back north to the Scenic Highway, turn left and go west about 0.5 mile to the intersection of Homestead Road (County Road 42). Turn right and go north across the railroad tracks and the Highway 61 expressway, and turn left on Old North Shore Road (County Road 290). Proceed about 0.5 mile west into the Big Sucker Creek valley, and park by the bridge. Walk upstream about 0.3 mile, following the trail on the northeast side of the stream. The trail traverses a slumped stream cut. Stop 3-3. Big Sucker Creek cut. Knife River Quad., T.51N., R. 12W., Sec 4, SW of NE of SE of NE; 586740E, 5198325N NAD83 UTMs The creek has cut down to and into bedrock in this whole area. At this site the basal 2 feet of the stream cut is basalt. The base of the drift section is rocky till of the Cromwell Formation, about 4 feet thick. Color is dark reddish brown (5YR 3/2). The lower sample is gravelly and very low in clay [(31) 48 46 6]. The upper sample is more clayey but even more gravelly than the Page 94 �lower one [(37) 34 47 19]. The till is slightly calcareous, but the grain assemblage is hyperSuperior with no carbonate grains. The Cromwell till is overlain by about 9 feet of the Lakewood member; this is one of the thickest Lakewood layers exposed in the field trip area. The trail crosses the cut at the level of the Lakewood member. This till is dark reddish brown (5YR 3/2), slightly to moderately calcareous, less rocky than the Cromwell till, but much more so than the overlying till. The results of three texture samples were: [(12) 24 54 22], [(6) 16 50 34], and [(11) 17 51 32]. All samples have a hyper-Superior grain assemblage, with only one carbonate grain among the three. The Moose Lake member is not exposed here. The contact between the Lakewood member and the overlying Knife River member is above the trail, and is not exposed. What appears to be the contact is actually a slump plane. Till of the Knife River member is not well exposed, and only one sample was obtained [(1) 7 22 71]. It is reddish brown (2.5YR 5/4), slightly to moderately calcareous, and has a Superior grain assemblage, with a few carbonate grains and one grain of spherical frosted quartz derived from Paleozoic sandstone. NEXT: Return to the road, drive back to Homestead Road, and turn right (south). Turn left (east) on the Highway 61 expressway, and drive about 3.5 miles, cross the Knife River, and turn right at the first street leading to the town of Knife River. Turn right at the first intersection, by the school, and head back south and west to a rest area overlooking the river. Stop 3-4. Lunch at Knife River rest area. Knife River Quad, T.52N., R.11W., Sec 31, NE of SW of NW; 591965E, 5200050N NAD83 UTMs While eating lunch, we can observe the erosion along the Knife River, and attempts to control it. This stream, like most streams emptying into Lake Superior, is fairly short, with a steep gradient and a greatly fluctuating discharge. Most of the time the level is low, but snowmelt and big rainfalls can turn it into a roaring torrent. NEXT: Return to Highway 61. Drive about 10 miles northeast, through Two Harbors. About 2.5 miles northeast of Two Harbors turn left (northwest) onto Lake County Road 3. Drive up the hill, and down into the Silver Creek valley. Park where the road crosses Silver Creek, about 2 miles from the turnoff. Walk 200 feet west (upstream) along the creek to a cut on the outside of a meander bend. Stop 3-5. Silver Creek cut. Castle Danger Quad., T.53N., R. 10W., Sec 16, SE of NW of SW of SW; 604470E, 5213910N NAD83 UTMs This is a small cut, but it illustrates some things rarely seen in this area: a good exposure of postglacial stream channel and overbank sediment, and a layer of artificial fill. The total height of the cut is about 7 feet. It exposes a foot of red clay fill over alluvium (overbank and channel sediment) over red clay till of the Knife River member, over brown sandy till of the Cromwell Formation. The Cromwell till is reddish-brown (5YR 4/3), moderately calcareous, fairly hard and very pebbly [(10) 30 44 26]. Its grain assemblage is Superior, with some calcite rhombs. They all appear to be amygdule fragments. Even though the stream has only cut a few feet into the till, it has developed a continuous pavement of rocks on its bottom. The Cromwell till is overlain by clay till [(2) 10 27 63] of the Knife River member, with a fairly sharp, wavy contact. This till is reddish-brown, on the same color chip but slightly lighter and redder than the color of the Cromwell Formation. It is calcareous, with a medium to coarsegrained blocky structure. Its grain assemblage is hyper-Superior, with no carbonate grains. Page 95 �The overlying alluvium was not sampled. It consists of 1.5 to 2 feet of dirty gravel channel sediment, overlain by 1 to 1.5 feet of silt and fine-grained sand overbank sediment. There is a thin soil (possibly truncated) in the top of the overbank sediment. The gravel contains clasts up to boulder size, but large clasts are much less common in this layer than in the currently active channel sediment. The difference is that at the time the gravel was being deposited, the stream was still eroding the clay till; the stream is now eroding till of the Cromwell Formation, which has more and larger coarse-grained clasts. The uppermost layer here is a layer of red clay that I interpret as recent fill dirt. It is texturally indistinguishable from the red clay till of the Knife River member, and was probably excavated from that material. But it is out of order stratigraphically, being underlain by a soil developed in recent alluvium, and not itself having a soil cover. NEXT: Return to vehicle. Drive 0.75 mile uphill (northeast) and down into another small valley, a tributary of Silver Creek. Park near the double culvert. Walk downstream (south) 200 feet to a slumped cut on the outside of a meander. Stop 3-6. Tributary to Silver Creek. Castle Danger Quad., T.53N., R.10W., Sec 16, SW of SW of NE; 605195E, 5214645N NAD83 UTMs This cut is a series of slumps, so there is a mixture of good exposure and covered areas. The description is sort of a composite section. The base of the exposure is loamy till of the Cromwell Formation [(16) 39 34 27]. This texture is somewhat clayey for Cromwell till, but not unusual for inside the Superior basin. The till is slightly calcareous, unoxidized brown (7.5YR 4/2); it is not especially pebbly for Cromwell till. The grain assemblage is hyper-Superior; a large 1-2 millimeter sample contains one grain of dolomite. The Cromwell till is overlain by red clay till of the Knife River member. There is an inclusion of Cromwell till near the base of the clay till, and another several feet higher. It is not clear whether the inclusions were created by glacial erosion, or if they are related to slumping on this slope. Elsewhere on the slope is a contact between red clayey till of the Moose Lake member [(13) 31 30 39] and red clay till of the Knife River member, at a higher elevation than the contact between the Cromwell Formation and the Knife Lake member. This suggests that some or all of the contacts may have shifted downslope. Near the top of the cut is a contact between red clay till of the Knife River member and red lacustrine clay. Here the texture of the till is [(3) 4 24 72] and the lacustrine texture is [(0) 3 18 79]. There is scarcely any difference other than the number of coarse-grained fragments. The till has a small hyper-Superior grain assemblage with no carbonate rock fragments, though there is a grain of secondary carbonate. The lacustrine sample has a very small 1-2 millimeter fraction, half of which is secondary carbonate. NEXT: Return to vehicle and continue northeast and north about 2 miles to the intersection of Gun Club Road. Turn left (west) and follow the road 1 mile west, 0.5 mile south, and 2 more miles west. Turn right on Lake County 2; go 0.5 mile north and turn left (west) on Reeves Road, an unpaved township road. Go up the hill, under a power line, and stop in a clearing about 0.5 mile west of County Road 2. Stop 3-7. Striated bedrock. Two Harbors Quad., T.53N., R.11W., Sec 1, SE of SE of NW; 600155E, 5217670N NAD83 UTMs There are several small hornfels outcrops here, flush with the ground. They are striated northwest–southeast, about 90 degrees from the striations we saw earlier today. These striations reflect ice moving up and out of the Superior basin toward the Highland moraine. This is the Page 96 �general orientation of striations in the highlands. The landforms in this area tend to be streamlined northwest–southeast parallel to the striations. These landforms, mainly bedrock, but partly mantled by drift, are named the Highland Flutes (Wright, 1970). This hill is one of the southwesternmost of the flutes. They extend northeast inside the Highland moraine as far as Lutsen. NEXT: Return to Lake County Road 2; turn right and go south 2.5 miles; turn right on Lake County 12, and go 3 miles west and 2.5 miles south where it dead-ends on Lake County 11 (Valley Road). Turn right and travel 7 miles south and west to Homestead Road. Lake County Road 12 becomes St. Louis County Road 41 at the county line. County Road 41 ends at County Road 42, which turns and becomes Homestead Road. Turn left on Homestead Road, travel 1.3 miles south to the entrance of a gravel pit. Stop 3-8. Peterson Gravel Pit. Knife River Quad., T. 52N., R.12W., Sec 15, NE of SE of NW; 587620E, 5204895N NAD83 UTMs This pit is developed in one of the many ice-contact deltas that developed between the Superior lobe and the North Shore highlands. They occur in the elevation range of 1,150 to 1,210 feet, and have been mapped in the French River, Knife River, and Two Harbors quadrangles. They have not been observed east of the Two Harbors quadrangle. The general stratigraphy here is sand and gravel of the Cromwell Formation overlain by till of the Cromwell Formation overlain by till of the Lakewood member of the Barnum Formation. The section currently exposed may be different from the one described, due to continued mining. The stratified unit ranges from fine-grained sand to medium-grained gravel, moderately well sorted. The color of the finer beds is dark reddish-brown (5YR 3/4); the color of the coarsegrained beds is dominated by the individual rock particles, which are mostly red, black, and dark gray. The unit is non-to-slightly calcareous; two samples show hyper-Superior grain assemblages with no carbonate grains. The gravel is subangular to subrounded; it is more rounded than the gravel in the till, but not much. It does not appear to have been transported far by water. Depending on the orientation of the cut, the sand and gravel appears to have either trough crossbedding, or foreset bedding. On the south side of the pit, the foreset beds dip west. The sand and gravel delta is overlain by a noncalcareous loamy till [(4) 39 52 9], ranging from 3 to 8 feet thick. The contact is sharp and wavy. Some of the underlying beds are deformed and truncated, and there is a considerable amount of sand and gravel incorporated into the till in places. The till is hard and dense, with a coarse-grained platy structure; this suggests that it was deposited under the weight of a glacier, rather than as a mudflow deposit. The grain assemblage is hyper-Superior, with no carbonate grains. On the east side, there is a discontinuous layer of silty till [(3) 20 71 9] that overlies the Cromwell till and the delta sand and gravel. Where sampled, it overlies the delta with no intervening till. This is interpreted as till of the Lakewood member. It is noncalcareous, reddishbrown (5YR 4/4), and contains only a few stones. Its grain assemblage is hyper-Superior, with no carbonate grains. The uppermost layer at this site is a sandy, silty, unbedded deposit, 1 to 2 feet thick, interpreted as colluvium. It does not bury a soil, but the surface soil is developed in it. It must therefore not be much younger than the glacial sediments. NEXT: Return to Homestead Road, turn right, and travel south to the Highway 61 expressway; turn right to return south to Duluth. Page 97 �REFERENCES Clayton, L., 1983, Chronology of overflow to Lake Superior, in Teller, J.T., and Clayton, L., eds., Glacial Lake Agassiz: Geological Association of Canada, Special Paper 26, p. 291-307. Drexler, C.W., Farrand, W.R., and Hughes, J.D., 1983, Correlation of glacial lakes in the Superior basin with eastward discharge events from Lake Agassiz, in Teller, J.T., and Clayton, L., eds., Glacial Lake Agassiz: Geological Association of Canada, Special Paper 26, p. 309-329. Gross, L.B., 1982, The stratigraphy and lithology of the glaciogenic sediments of the Two Harbors area, northeastern Minnesota: Minneapolis, Minn., University of Minnesota, M.S. thesis, 151 p. Hobbs, H.C., 1983, Drainage relationships of glacial Lakes Aitkin and Upham and early Lake Agassiz in northeastern Minnesota, in Teller, J.T., and Clayton, L., eds., Glacial Lake Agassiz: Geological Association of Canada, Special Paper 26, p. 245-259. ———2002, Surficial geology of the French River and Lakewood quadrangles, St. Louis County, Minnesota: Minnesota Geological Survey Miscellaneous Map M-127, scale 1:24,000. ———2003a, Surficial geology of the Knife River quadrangle, St. Louis and Lake Counties, Minnesota: Minnesota Geological Survey Miscellaneous Map M-137, scale 1:24,000. ———2003b, Surficial geology of the Two Harbors quadrangle, Lake County, Minnesota: Minnesota Geological Survey Miscellaneous Map M-138, scale 1:24,000. Leverett, F., 1932, Quaternary geology of Minnesota and parts of adjacent states: U.S. Geological Survey Professional Paper 161, 149 p., 5 pls. Mooers, H.D., 1988, Quaternary history and ice dynamics of the late Wisconsin Rainy and Superior lobes, central Minnesota: Minneapolis, Minn., University of Minnesota, Ph.D. dissertation, 200 p. Mooers, H.D., and Lehr, J.D., 1997, Terrestrial record of Laurentide Ice Sheet reorganization during Heinrich events: Geology, v. 25, no. 11, p. 987-990. Moss, C.M., 1977, The surficial and environmental geology of the French River quadrangle, St. Louis County: University of Minnesota Duluth, M.S. thesis, 69 p. Patterson, C.J., 2001, Surficial geology, pl. 4 of Boerboom, T.J., project manager, Geologic atlas of Pine County, Minnesota: Minnesota Geological Survey County Atlas C-13, 7 pls., scale 1:100,000. Winchell, N.H., 1899, The geology of Carlton County, chapter 1 of Final report of the Minnesota Geological and Natural History Survey: Minnesota Geological and Natural History Survey, v. 4, 528 p. Wright, H.E., 1972, Quaternary history of Minnesota, in Sims, P.K., and Morey, G.B., eds., Geology of Minnesota: A centennial volume: Minnesota Geological Survey, p. 515-547. Wright, H.E., Mattson, L.A., and Thomas, J.A., 1970, Geology of the Cloquet quadrangle; Minnesota Geological Survey Geologic Map GM-3, 30 p., 1 pl. Page 98 �FIELD TRIP 4 Geology of the Eastern Mesabi Iron Range, Northeastern Minnesota by Richard W. Ojakangas Emeritus, Department of Geological Sciences, University of Minnesota Duluth Mark J. Severson Natural Resources Research Institute, University of Minnesota Duluth Peter K. Jongewaard United Taconite Mining Company John L. Arola Ispat Inland Mining Company Joel Thomas Evers Retired – LTV Mining Company and Douglas G. Halverson Northshore Mining SCALE N 0 5 0 10 10 20 15 20 MILES 30 40 KILOMETERS Babbitt Mesaba Location Map Virginia Mt. Iron ITASCA CO. Buhl Biwabik Virginia Horn Coleraine Grand Rapids ST. LOUIS CO. LAKE CO. Hibbing Keewatin Nashwauk Duluth C omplex Eveleth CASS CO. AITKIN CO. DULUTH CARLTON CO. ke ior La per Su Generalized map of the Mesabi Range (cross-hatched). Note Duluth Complex at east end. Page 99 �INTRODUCTION Iron-formation was described as early as 1866 by Henry Eames for rocks on what was to become the Mesabi Range. Several attempts were made by individuals on their way to the iron mines of the Vermilion Range to find ore on the Mesabi. However, it was not until November 16, 1890, that the first rich iron ore on the Mesabi Range was discovered by the Merritt brothers near what is now Mountain Iron, MN. In 1892, the first shipment from this mine was 4245 tons (White, 1954). Exploration for iron ore ensued and within the next few years, most of the productive parts of the Mesabi Range were discovered. The Mesabi Range is the largest iron range in the United States and is one of the largest in the world. It is 0.25 - 3.0 miles wide and 120 miles long (cover page). The Biwabik Iron Formation, as thick as 750 ft, in general dips gently to the southeast at an angle of about 7-15 degrees. The iron-formation, called taconite, typically contains 30-40% iron and 40-50% SiO2, plus other components (Morey, 1992). In numerous places along the length of the range, silica was leached out, thereby enriching the iron content to 55%+. These pockets became the highgrade natural ore mines; there were more than 500 individual mines prior to merging into larger mines as the ore between adjacent properties was removed. These were very important in making the United States an industrial giant, and were instrumental in providing raw material for WWI and WWII. As the high-grade ore was becoming depleted, the taconite process was developed. In 1967, taconite production exceeded natural ore production. Currently, six taconite plants are in production (Fig. 4-1). Babbitt Chisholm N Ispat-Inland Hibbing Taconite Minorca Pit Buhl 5 4 Keewatin Nashwauk MDDP-7 Butler Taconite (closed) 3 2 Calumet Cliffs-Erie Site (LTV closed) 6 Keewatin Tac Dunka Pit Iron Mine (closed) 12 Minntac 8 Ispat-Inland Virginia MDDP-5 Laurentian Pit United Taconite Evel 7 Hibbing 11 Biwabik eth Aurora MDDP-2 Coleraine Northshore 10 9 Hoyt Lakes 1 MDDP-8 Grand Rapids 0 187000E 192000E 600 197000E 6 202000E 12 18 207000E 24 Miles 217000E 212000E 222000E 227000E 232000E 600 Looking North 8 500 500 U.S. Mined Taconite Intervals 5 4 300 2 1 U.S. U.S. 200 100 10 6 400 Upper Slaty U.S. 3 Slaty Upper U.S. 400 U.S. U.S. U.C. U.S. U.C. Upper Slaty U.C. U.C. L.S. Lower Slaty U.C. L.S. 100 L.S. Lower Slaty L.S. L.S. 0 L.C. L.C. -100 Lower Cherty Lower Cherty L.C. L.C. L.C. Lower Cherty L.C. 300 U.S. 200 U.C. L.S. 12 U.S. U.C. Cherty Upper U.C. 11 U.C. Upper Cherty U.S. U.C. 0 9 7 L.C. L.C. L.C. -100 L.C. -200 -200 -300 Virginia Horn Area -300 Generalized Stratigraphic Sections -400 187000E 192000E 197000E 202000E 207000E ILSG - May, 1993 212000E 217000E 222000E 227000E -400 232000E Figure 4-1: Generalized map of the Mesabi Range showing taconite pits (black) and cities, and in the lower half, a longitudinal section of the Biwabik Iron Formation (compiled by Henry Djerlev, 1993). Mined taconite intervals are shown as black columns adjacent to sections. Modified from Morey, 1993. Page 100 �The name of Biwabik Iron Formation was chosen by Van Hise and Leith (1901, p. 356), “because the word Biwabik is the Chippewa word for a piece or fragment of iron.” The word taconite is also used in discussions pertaining to hard, unoxidized portions of the iron-formation. H.V. Winchell (1882, p. 135) originally called portions of the BIF “taconyte” because he thought the rocks correlated with lower Cambrian rocks in the Taconic Mountains in northern New England. Since that time, many geologists have used taconite in their descriptions of the ironformation and it has thus become firmly established. Perhaps a more proper definition for “taconite” is an economic term for iron-formation from which iron can be profitably extracted after fine-grinding, followed by magnetic separation and pelletizing (Morey, 1993). REGIONAL GEOLOGY The peneplaned Archean craton in the Lake Superior region formed a platform upon which a Paleoproterozoic continental margin assemblage was deposited in Minnesota, Michigan, and Wisconsin. Extension resulted in localized rifts that received thicker accumulations of sediments and volcanic rocks than did adjacent parts of the platform. Seas transgressed onto the continent one or more times and an ocean basin opened south of present-day Lake Superior. Island arcs that formed during southward subduction collided with the craton margin to the north as the ocean basin closed. A remnant of this oceanic crust is poorly preserved as a dismembered ophiolite sequence in Wisconsin (Schulz, 1987, 2003). The arc volcanics are preserved as the Wisconsin magmatic terranes. The collision resulted in a fold-and-thrust belt known as the Penokean orogen. To the north of the fold-and-thrust belt, a northward-migrating foreland basin—the Animikie basin—developed as the stacked thrusts weighed down the crust (Fig. 4-2). Thick turbidite successions were deposited along the basin axis, and terrigenous clastics and Lake Superior-type iron-formation were deposited on the shelf along the northern margin (i.e., the foreland or peripheral bulge) of the basin. See Ojakangas et al. (2001) and Severson et al. (2003) for more detailed summaries on Paleoproterozoic basin development in the Lake Superior region. The development of the Midcontinent Rift System (MRS) at 1.1 Ga severed the basin into northwestern and southeastern segments (Fig. 4-2). If the MRS rocks are removed from the geologic map, the different portions of the Animikie basin become contiguous and the fold-andthrust belt rocks of Minnesota and Wisconsin-Michigan become continuous (Fig. 4-3). Figure 4-4 is an interpretive cross-section of the Animikie basin during its formative stages, with sediments derived from the Archean basement to the north and from the fold-and-thrust belt to the south. The Paleoproterozoic supracrustal rocks in the northwestern segment, including east-central and northeastern Minnesota and the adjoining part of Ontario, are for the most part poorly exposed. However, mining of iron ore on the Mesabi and Cuyuna Ranges and continued mining of taconite on the Mesabi Range have resulted in excellent artificial exposures and an abundance of drill hole information. Geophysical surveys and stratigraphic test drilling by the Minnesota Geological Survey also have been major sources of information (e.g., Southwick et al., 1988). Animikie Group The Animikie Group unconformably overlies the Mille Lacs and North Range Groups to the south and the Archean basement to the north (Southwick and Morey, 1991). Magnetic data show North Range structures are present beneath Animikie strata to the east of the exposed North Range Group (Chandler, 1993). Page 101 �Figure 4-2: Generalized geologic map showing the distribution of Precambrian rocks and structural elements of the Lake Superior region, modified from Ojakangas 1994 and references therein (from Ojakangas, et al., 2001). The group consists of three conformable major formations on both the Mesabi and Gunflint ranges. The respective units on the two ranges are the Pokegama Formation and the Kakabeka Quartzite (the lowest units), the Biwabik and Gunflint Iron Formations (the middle units) and the Virginia and Rove Formations (the upper units, composed of graywacke and shale). The Thomson Formation in the northern part of east-central Minnesota is correlative with the Virginia and Rove Formations. The Biwabik and Gunflint are on strike with each other and were probably continuous prior to the intrusion of the Duluth Complex at about 1100 Ma. The Animikie Group in Minnesota-Ontario on the Mesabi and Gunflint ranges and the Baraga Group of Michigan-Wisconsin on the Gogebic range were both deposited in the Animikie foreland basin. The basal units comprised of siliciclastic sediment derived from the Archean basement, and the overlying iron-formation, were deposited in a shallow sea on the northern edge (i.e., the peripheral bulge or foreland) of the northward-migrating Animikie basin (e.g., Ojakangas, 1994). Additional details are provided below in the section titled, Environments of Deposition. The siliciclastic and iron-formation units are exposed on the Gogebic Range of northern Michigan and Wisconsin (Palms Quartzite and Ironwood Iron Formation), on the Mesabi Range of northern Minnesota (the Pokegama Formation and the Biwabik Iron Formation), and on the Gunflint range of northeasternmost Minnesota and Ontario (the Kakabeka Quartzite and the Page 102 �Figure 4-3: Schematic hypothesized paleogeography at the time of sedimentation of the Animikie Group turbidites that overlie shelf deposits in the Animikie basin. The rocks of the 1.1 Ga Midcontinent Rift System have been removed from the map, and Michigan and Wisconsin are thus positioned 60 miles closer to Minnesota-Ontario than they were after the formation of the Midcontinent Rift System. Arrows denote generalized transportation directions of sediment from major source areas. Compare with Fig. 4-2. Modified from Ojakangas (1994) and references included therein (from Ojakangas, et al., 2001). Gunflint Iron Formation), and are lithostratigraphic equivalents. They probably were continuous from south to north prior to development of the Midcontinent Rift System in Mesoproterozoic time. A consequence of this model is that they are diachronous, with the units in MichiganWisconsin (located about 60 miles to the south of the Mesabi range during deposition) thus somewhat older than those in Minnesota-Ontario. The thickest and uppermost units in the basin, essentially lithostratigraphic correlatives but probably differing somewhat in age, are the Michigamme, Tyler, and Copps Formations of the southeastern segment and the Thomson, Virginia and Rove Formations of the northwestern segment. These are typical turbidite-shale (flysch) sequences, with graded beds and intercalated muddy “rain-out” sediment. Figure 4-5 is a regional correlation chart of the aforementioned units, as well as others that cannot be discussed herein. Page 103 �Figure 4-4: Schematic cross-section depicting deposition of the Animikie Group turbidites that overlie shelf deposits in the Animikie basin, with sediment derived from both the north south. The southern area, the fold-and-thrust belt, comprises a complex assemblage including: 1. accreted Paleoproterozoic volcanic and plutonic rocks and volcanic rocks of the Wisconsin magmatic terranes; 2. accreted Archean miniplate terranes; 3. older Paleoproterozoic passive-margin sedimentary rocks and volcanic rocks produced during initial rifting of the continental margin, both scraped off the southward-subducting Archean Superior craton; and 4. recycled initial foredeep deposits, possibly including basal shallow water sandstones deposited in the transgressing sea of the northward-migrating foreland basin. The peripheral bulge comprises a source-rock assemblage of Archan granitic rocks and Archean volcanic-sedimentary (greenstone) belts. Scale is approximate. Compare with Fig. 4-3. Modified from Ojakangas (1994) and references included therein (from Ojakangas, et al., 2001). Ages Along the Mesabi Range, the Pokegama Formation rests unconformably on diabase dikes of the Kenora-Kabetogama dike swarm that gives a Rb-Sr isochron age of 2125 +/- 45 Ma (Southwick and Day, 1983; Beck, 1988) and this provides a maximum age for deposition of the Pokegama. A minimum age of 1930 +/- 25 Ma (Pb/Pb) for the Pokegama was obtained by Hemming et al. (1990) from quartz veins that cut the Pokegama. A U/Pb age on euhedral zircons from an ash layer in the lower Gunflint Iron Formation of Ontario is 1878 +/- 2 Ma (Fralich and Kissin, 1998; Fralick et al., 2002). A similar age of 1874 +/- 9 Ma was obtained on zircon from rhyolite in the Hemlock Formation that is adjacent to (and is interlayered with?) the Negaunee Iron Formation in the Marquette Range Supergroup of Michigan (Schneider et al., 2002). A zircon age from an ash layer near the base of the Virginia Formation is 1850 Ma (Hemming et al., 1996), and an age of 1821 +/-16 Ma has been obtained from an ash layer in the Rove Formation about 70 m above the Gunflint Iron Formation (Kissen et al., 2003). Several of these ages are shown on Figure 4-5. Page 104 �Gunflint Range Mesabi Range Cuyuna Range Emily District Gogebic Range Gogebic Range Menominee Range Baraga Basin Pokegama Fm Michigamme Fm Ironwood IF unconformity Palms Fm North Range Group Rabbit L. Fm 2125-1930 Ma deposition occurred sometime during this range Bijiki IF unconformity Goodrich Qtzite unconformity unconformity Negaunee IF Fence River IF Vulcan IF Siamo Slate Hemlock Volc. Hemlock Volc. unconformity Trout Lake Dolo Bad River Dolo Mille Lacs Group Sunday Qtzite Michigamme Fm Marquette District Lower Member Emperor Volcs Trommald IF Iron River/Crystal Falls Michigami Fm Mahnomen Fm 1870 Ma unconformity Mille Lacs Group Greenwood Iron-fm Thomson Fm unconformity Ajibik Qtzite Wewe Slate Kona Dolomite unconformity unconformity 1874 Ma Randville Dolo. Mesnard Qtzite Sturgeon Qtzite (Glen Township) (Denham Fm) Fern Creek Fm. Baraga Group Menominee Group Menominee Range Iron River/Crystal Falls Fortune Lake Slate Michigami Fm Stambaugh Fm Michigami Fm Goodrich Quartzite unconformity Negaunee Iron-fm Amasa Iron-fm Hemlock Volcs 1874 Ma unconformity Vulcan Iron-fm Siamo Slate Felch Fm Ajibik Quartzite Chocolay Group Marquette Range Supergroup Marquette Range unconformity Paint River Group Iron-formation Copps Fm Menominee Group Biwabik Fm Pokegama Qtzite Upper Member Tyler Fm Chocolay Group Gunflint IF 1878 Ma Kekabeka Qtzite 1850 Ma Virginia Fm Animikie Group 1821 Ma Virginia Fm Animikie Group Rove Fm Animikie Group Animikie Group Michigami Fm Hiawatha Graywacke unconformity Riverton Iron-fm Dunn Creek Slate Badwater Grnstn unconformity Randville Dolomite Kona Dolomite Sturgeon Quartzite Mesnard Quartzite Enchantment L. Fm Fern Creek Fm. detachment surface Figure 4-5: Generalized correlation chart of Paleoproterozoic strata in the Lake Superior region (after Morey and Southwick, 1995). Note that recently obtained age dates are shown for the Gunflint Formation, Mahnomen Formation, Hemlock Volcanics, and the Rove and Virginia Formations (see text for references). Also included is a correlation chart (lower right corner) of strata in Menominee, Iron RiverCrystal Falls and surrounding terranes (LaBerge et al., 2003 – includes changes to previous usage not yet officially adopted by the USGS). Iron-formations are shaded. Modified from Severson et al., 2003. Pokegama Formation The formation has long been called the Pokegama Quartzite, but because it contains appreciable argillite and siltstone, the name Pokegama Formation is more appropriate. It has been studied by several workers since it was named by Winchell (1893) for exposures at the western end of the Mesabi Range. Much of the previous work has been summarized by Morey (1972, 1973, 2003). Few natural exposures exist, as thick glacial drift generally covers the formation. Outcrops, roadcuts, and mine cuts occur at a few places along the length of the range, but most exposures are in the central portion of the range. A few drill holes have penetrated the entire formation. One is located just south of Eveleth (NE 1/4, NE1/4, Section 5, T. 57 N., R. 17 W.) and another is southwest of Mountain Iron (SE 1/4, SE 1/4, Section 8, T. 58 N., R. 18 W.); the thicknesses are 167 ft and 85 ft, respectively (Fig. 4-6). Three other drill cores, recently rediscovered, have not yet been studied. Numerous drill holes have penetrated only the upper few feet of the formation, as the drilling was generally undertaken in relation to iron ore exploration and development. The Pokegama is thin at the eastern end of the range and thickens to the western end where it may be more than 300 ft thick. The formation is composed of three main rock types—argillite, siltstone, and quartzite. The latter is generally a silica-cemented quartz sandstone, and is therefore an orthoquartzite rather than a metaquartzite. (Morey, 2003, has determined that mineralogical changes in the Pokegama and the Biwabik are the result of diagenesis rather than metamorphism, except at the eastern end of the range adjacent to the Duluth Complex.) These three rock types make up three gradational Page 105 �members-- lower, middle, and upper-- respectively, as shown in Figure 4-6. Minor thin conglomerates occur at the base of the formation, and seem to represent a weathered residuum on the surface of Archean rocks, perhaps reworked by fluvial processes. The Pokegama unconformably overlies Archean metavolcanic, metasedimentary, and plutonic rocks. There may be as much as 100 ft of relief on the Archean surface (Grout and Broderick, 1919), but the surface was, nevertheless, essentially a peneplain. Some Archean “knobs” were islands when the Pokegama was being deposited, and are present in the wooded areas between Eveleth and Virginia. The Pokegama-Biwabik contact is gradational, with some cherty horizons in the upper Pokegama. Various geologists have placed the contact at different stratigraphic levels. EVELETH M BIF 50 SANDSTONE, FINE-MEDIUM, SHALE MINOR CHERT SANDSTONE, COARSE 40 UPPER MEMBER SANDSTONE, FINE, SHALE MINOR MOUNTAIN IRON SANDSTONE, FINE M 30 SILTSTONE, SHALE 30 BIF SANDSTONES, THIN SANDSTONE, COARSE SANDSTONE, FINE MIDDLE MEMBER 20 20 SILTSTONE, SILTSTONE, SHALE SHALE SANDSTONES, THIN 10 10 SHALE, SILTSTONE, MINOR SHALE, SILTSTONE CONGLOMERATE 0 Archean 0 LOWER MEMBER Archean Figure 4-6: Measured sections from two drill holes that penetrate the entire Pokegama Formation. Dark shading represents shale, thin blank units represent siltstone, and dotted pattern represents sandstone. BIF is Biwabik Iron Formation. After Ojakangas (1983). Biwabik Iron Formation This is one of the world’s major iron-formations, and the largest in the United States. The formation is 200 to 750 ft thick and consists of four divisions as defined by Wolff (1917). These lithostratigraphic units, now informal members, are from the bottom up, the Lower Cherty, the Lower Slaty, the Upper Cherty, and the Upper Slaty. (These are miners’ terms, and do not indicate metamorphism.) The cherty members are dominantly granular (i.e., sand-textured), thick-bedded (several inches to several feet), and are largely composed of chert and iron oxides. The slaty members are dominantly fine-grained (i.e., mud-textured), thin-bedded (<1 inch) and Page 106 �composed mostly of iron silicate and iron carbonate with local chert beds. However, these two rock types are interbedded on all scales and are generally gradational. They contain about the same high quantities of silica, 42-47% (Morey, 1992). The Lower Slaty is not present at the far western end of the range. There are some diagnostic marker units within the formation. Two stromatolite-bearing intervals several feet thick are present, one at the base of the Lower Cherty and the other in the middle of the Upper Cherty. The black “intermediate slate” at the base of the Lower Slaty is reportedly an ash-fall tuff containing about 4 to 5.5 % aluminum oxide (Morey, 1992). At the top of the Upper Slaty are several feet of limestone and dolomite. Most of these marker units pinch out to zero in the vicinity of Nashwauk, about 40 mi from the west end of the range (Morey, 1992). Virginia Formation There are rare exposures of the Virginia in mines at the east end of the Mesabi Range where it has been metamorphosed by the mafic intrusions of the Mesoproterozoic Duluth Complex. Several holes drilled south of the range to study the underlying iron-formation have been drilled through the Pleistocene cover and have intersected as much as 1443-ft of the preserved lower part of the formation (Lucente and Morey, 1983). The lower portion of the formation in the drill holes is dominantly black shale. The upper portion of the drill core, while still dominantly shale, contains beds of siltstone and finegrained feldspathic graywacke comprising thickening- and coarsening-upward turbidite sequences. Ash-fall tuffs, cherty sideritic iron-formation, chert, and limestone are minor rock types low in the formation. The contact with the underlying Biwabik Iron Formation is gradational. The clastic rocks were largely derived from the Archean rocks to the north, with some contributions from lower Proterozoic rocks to the south (Lucente and Morey, 1983). The Virginia Formation is correlated with the Thomson Formation (Morey and Ojakangas, 1970) that is exposed 60 miles to the south in the vicinity of Carlton and Cloquet, and also with the Rove Formation in northeasternmost Minnesota and adjacent Ontario (Morey, 1967). Environments of Deposition, Animikie Group The Pokegama is interpreted to have been deposited in a tidally influenced shallow marine setting near the shoreline, having received clastics from the Archean basement to the north (Ojakangas, 1983). In this model of a transgressing sea, the lower (argillaceous) member was deposited at the shoreline in the upper tidal flat, the middle member of intercalated argillaceous and silty sediment was deposited seaward in the middle tidal flat, and the upper member of quartz sand was deposited still further seaward in a lower tidal flat/subtidal environment. This is illustrated in Figure 4-7. Walther’s Law is applicable here, with the vertical facies showing the relationships of the lateral facies. The lowermost Pokegama contains siltstone beds that contain alternating thicker and thinner laminae that have been interpreted as evidence of the diurnal inequality, and are being investigated further for possible clues to the Paleoproterozoic lunar orbit (G. Ojakangas, 1996). Page 107 �la nep e P in High Tide Low Tide NT ME DI SE Mud, Mud Silt, Sand Sand Sand Upper FA ES CI Middle Lower Shoal or Barriers TIDAL FLAT SUBTIDAL "Cherty" ironformation "Slaty" ironformation Shallower Pelagic mud, Turbidites Deeper SHELF SLOPE Figure 4-7: Sedimentation model showing lateral relationships of the siliciclastic tidal facies of the Pokegama Formation, the two main facies of the Biwabik Iron Formation, and the Virginia Formation (on the slope?). Thicknesses and geography not to scale. From Ojakangas (1983). The Biwabik is interpreted to have been deposited seaward of the Pokegama on a shallow marine, tidally dominated shelf (Figure 4-7). Precipitation of iron minerals including iron carbonate, iron silicate, silica, and perhaps some hematite, occurred on the outer shelf in waters below wave base, giving rise to the mud-textured (slaty) iron-formation. These minerals were likely related to upwelling waters from the deeper part of the basin. The two sand-textured members (Lower Cherty and Upper Cherty) formed in a shallowwater, high-energy environment, as indicated by stromatolites, cross-bedding, and rounded (locally oolitic) grains of iron minerals and chert. Shoreward-moving tidal currents (i.e., flood tides) and/or storms may have disrupted the mud-textured sediment (i.e., precipitates) and transported sand-sized aggregates into shallower water where they were altered by seafloor processes and early diagenetic processes. Thus these granules are “intraclasts” derived from within the basin. Shallow channels up to a mile wide and tens of feet deep were cut into the Lower Slaty member and filled with sand-textured grains of iron minerals and chert at Minntac where this is called the IBC unit (interbedded chert unit). These grains apparently were derived from shallow water and carried seaward into the deeper water environment in which the iron minerals were precipitating. Ebb-flow tidal currents are interpreted as the erosion and transportation agent. A plot of 102 cross-bed measurements in the Minorca Mine on the northeast edge of the Virginia Horn (Fig. 4-2) shows 90 % of the readings making a very prominent mode to the northnortheast and a minor broader mode to the south (Fig. 4-8). This distribution is interpreted as the product of a strong flood tide toward the paleogeographically determined northern shoreline and a much weaker ebb tide. Page 108 �N Figure 4-8: Paleocurrent rose diagram of 102 cross-bedded measurements from the Lower Cherty in the Minorca Mine. 102 A study of the orientations of stromatolite mounds in the stromatolite horizon within the Upper cherty member was conducted by Kevin Boerst (1999) as a UROP (Undergraduate Research Opportunity Project) at the University of Minnesota Duluth. His map is presented here as Fig. 4-9). A paleocurrent plot of mound elongation (Fig. 4- 9) is interpreted as the result of shore-normal tidal currents and shore-parallel longshore currents in shallow water. The repetition of the cherty and slaty members has long been interpreted as the result of transgression and regression (White, 1954). The Virginia Formation was deposited seaward of the iron-formation, probably in a slope-type environment (Fig. 4-7) where episodic turbidity currents deposited graded beds. Some volcanic ash falls evidently settled into the basin forming graded beds with a totally volcanic composition. The dominance of black, fissile shale suggests the “raining out” of clay (i.e., settling through the water column) and deposition in deep, anoxic water below wave base. Minor thin sandstone lenses were deposited by bottom currents (Lucente and Morey, 1983). N 12 N 10 50 70 70 Feet 50 12 90 90 110 110 130 130 10 10 12 10 12 K. Boerst, 1999 (Unpub.) K. Boerst, 1999 (Unpub.) 150 150 20 0 20 40 80 60 100 120 140 160 180 Feet Figure 4-9: Mapped stromatolite mounds in the Algal submember (I submember) in the Upper Cherty of the LTV 2E pit. The rose diagram represents the elongation of the mounds. From unpublished work by Kevin Boerst (1999). Page 109 �Mineralogy The detailed origins of the iron minerals are exceedingly complex and are beyond the scope of this introduction. It has to suffice here to say that Eh and pH are major controls on the stability of the various iron minerals in both the depositional and diagenetic environments, and in the easternmost Mesabi, in the metamorphic environment as well. Recrystallization and replacement of the granules during diagenesis has been extensive, and probably consisted of a number of discrete events. Earlier work on the oxidized taconites of the western Mesabi was accomplished by Bleifuss (1964). He showed that late hematite was developed by the oxidation and pseudomorphic replacement of magnetite octahedra, that layers of goethite were precipitated from solutions likely derived from the oxidation of siderite, and that some goethite formed by the oxidation of acicular iron silicate minerals. Some of the hematite inclusions and crystals in magnetite are similar to those illustrated by Han (1982). He proposed that much of the magnetite formed by the replacement of, and overgrowth on, pre-existing hematite that served as nuclei. Han further suggested that ionic diffusion of ferrous iron was a key process in the formation of the magnetite. Organic carbon may have acted as a reductant in this process. The nature of the major hydrologic events that removed the 40-60% of the silica and oxidized the iron minerals, thus forming the high-grade (natural) ore bodies, has long been debated. Were they descending cool meteoric waters or ascending hydrothermal waters related to igneous activity? Did this occur during the Cretaceous (the age of conglomerates composed of clasts of high-grade hematite), or prior to that time? Morey (1999) provided an excellent review of the arguments. He then proposed that a large-scale topography-driven hydrothermal groundwater system moved waters northward through the sands of the underlying Pokegama Formation, from the vicinity of the regional Penokean orogenic uplift in northern Wisconsin and east-central Minnesota, 40 to 80 miles to the south. Production Figures – Iron Ore and Taconite The annual amount of direct shipped and taconite produced are shown in Figure 4-10. Production and shipping of direct ore started in 1892 and rose steadily until 1953 when a maximum 76 million tons were produced in one year (note the precipitous drop in direct ore production corresponding to the Depression). At around 1955, there was a dramatic decrease in the amount of direct ore as the various mines became depleted. This also corresponds to the initial start-up of taconite mining, using a concentrating and pelletizing method developed by E.W. Davis of the University of Minnesota. Reserve Mining opened the first taconite operations in 1955 (Peter Mitchell Mine) and was shortly followed by Erie Mining in 1957 (old LTV site). Six more taconite operations were added in the 1960s, and by 1967, annual taconite production exceeded direct ore production. The mid-1980s marked a serious depression in the iron ore and steel industry that resulted in the closure of one operation (Butler Taconite) and the bankruptcies of two other taconite producers. More recently, LTV Steel and Eveleth Taconite have closed; Evtac has since reopened as United Taconite. Page 110 �80,000,000 TACONITE DIRECT ORE 70,000,000 TONS PRODUCED 60,000,000 50,000,000 40,000,000 30,000,000 20,000,000 10,000,000 18 92 18 97 19 02 19 07 19 12 19 17 19 22 19 27 19 32 19 37 19 42 19 47 19 52 19 57 19 62 19 67 19 72 19 77 19 82 19 87 19 92 19 97 20 02 0 YEAR Figure 4-10: Annual production figures for direct ore (includes all forms of direct ore) and taconite for the period 1892-2003. Data and graph from James Sellner, Minnesota Department of Natural Resources, Lands and Minerals Division, Hibbing, MN. What’s in a Name? (Those confusing iron-formation submembers!) As early as 1917, the Biwabik Iron Formation (BIF) has been informally broken down into four major lithostratigraphic members, or subdivisions, known as (from bottom to top): Lower Cherty, Lower Slaty, Upper Cherty, and Upper Slaty (Wolff, 1917). The cherty iron-formation members are generally thick-bedded and contain round grains (0.5-2.0 mm) of chert that are referred to as granules. These “cherty” members typically contain higher percentages of iron oxides (magnetite, hematite and/or goethite). In contrast, the “slaty” members are thin-bedded (0.5-3.0 mm thick beds) and very fine-grained. They are composed mostly of Fe-silicates and Fecarbonates. Both cherty and slaty iron-formation types are interlayered at all scales. However, one rock type often predominates in each of the four lithostratigraphic members, and are sonamed due to this dominance, i.e., thick-bedded cherty iron-formation is dominant in the cherty members, whereas thin-bedded iron-formation is dominant in the slaty members. The 1917 four-fold stratigraphy of a Lower and Upper Cherty and a Lower and Upper Slaty members is still used at each of currently operating (and inactive) taconite mines on the Mesabi Range. However, each of the mining companies further subdivides the BIF into several Page 111 �submembers based on bedding types (Fig. 4-11) and mineral assemblages. It is at this point that the BIF stratigraphy becomes very complicated and at times confusing. This is mainly due to the following reasons: • There are localized lateral facies changes between mines (and even within a single mine). Some mines reconcile these differences by splitting out numerous submembers (each with a distinct bedding type, texture, ore grade, and/or mineral assemblage), whereas, other mines lump many of these same differences within a single submember. • There are significant lateral facies changes over several miles between mines. For example a particular horizon may be massive-bedded at one location but is regularbedded a few miles away. This is particularly troublesome within the Upper Cherty member in the western 2/3rds of the Mesabi Range. • Not all mines use the same numbering system – some use abbreviations (LC for Lower Cherty, etc.) followed by a number (as in LC-5 at the top of the Lower Cherty). However, other mines use an alphabet system, devised by Gundersen and Schwartz (1962), starting with the A submember at the top of the Upper Slaty (in this system the top of the Lower Cherty corresponds to the R submember). And further still, another mine refers to the Lower Cherty as the number 1 unit and subdivides it into eight submembers, with 1-8 at the top of the Lower Cherty. • Some mines label downward in their numbering system, whereas other mines label upward in their numbering system. Textures associated with granular rocks Disseminated Diffuse Granules Mottled Patches Textures associated with laminated rocks Regular, Sharp Wavy/Irregular, Sharp Regular, Diffuse Wavy/Irregular, Diffuse Shaly Thin-bedded Figure 4-11: Textural characteristics of the Biwabik Iron Formation (modified from Pfleider et al., 1968, from a classification scheme developed by geologists of the Hanna Mining Company). Page 112 �The submember nomenclature that is used at each of the mines is summarized in Figure 412. It can readily be seen on this summary that any particular submember name changes nomenclature from one mine to the next. This is because there are few good marker horizons within the BIF, and even these can exhibit gradual lateral facies changes or pinch-and-swell relationships to each other. A few of the potential marker horizons within the BIF are presented below. • Top contact of the BIF with the Virginia Formation – In the eastern half of the Mesabi Range a carbonate horizon is present at the very top of the Upper Slaty and the contact between the BIF and Virginia Formation is easily recognized (Gruner, 1924). However to the west of Hibbing, the carbonate layer is absent and lenses of thin-bedded Fe-carbonate iron-formation are present in the Virginia Formation, and the top of the BIF is not easily discerned. • Submember I/Algal unit – a thin unit containing algal stromatolites and jasper-bearing intraformational conglomerate is present near the top of the Upper Cherty. This submember is easily recognized but is not present to the west of Hibbing. • Lower Slaty member – The Lower Slaty has a very-well defined “Intermediate Slate” (also referred to as the Q submember or Paint Rock in Fig. 4-12) at its base which is characterized by a black, carbon-rich, thin-bedded, slaty unit that commonly contains pyrite. This unit is readily evident at all of mines on the range. However, the upper contact of the Lower Slaty is “indefinite and a gradual change to other slaty phases takes place” … [which makes] … the dividing line between the two [Upper Cherty and Lower Slaty] somewhat arbitrary” (Gruner, 1924, p.20). The upper contact of the Lower Slaty is particularly troublesome in the Virginia Horn area. Gruner (1946, p. 45) included lenses of cherty and wavy-bedded taconite (referred to as the Interbedded Chert -- IBC unit at Minntac; Fig. 4-12) in the Lower Slaty, whereas White (1954) included these same units in the overlying Upper Cherty member. • Base of the BIF - The base of the Lower Cherty is generally characterized by thin-bedded iron-formation (also called the “red basal unit”) with localized algal stromatolite and basal conglomerate horizons. However, at many localities the base of the BIF exhibits a gradational contact with the underlying Pokegama Formation. In the Virginia Horn area the base of the BIF contains an iron-bearing sandstone (White, 1954) that some mines include with the iron-formation, whereas others lump this type of material with the Pokegama Formation. From the above description it is readily evident that there are few good marker horizons within the iron-formation; even the upper and lower contacts of the iron-formation are gradational and subject to various interpretations. The “Intermediate Slate” and the algal horizon in the Upper Cherty are the only easily recognizable marker units. However, even using these horizons as markers, one can see from Fig.4-12 that there are problems. Clearly, much additional work needs to be done in understanding how submembers at one mine correlate with submembers at an adjacent mine. These types of studies could inevitably be important in determining why ore grades, and waste rock characteristics, change between mines and even within a single mine. For example, some of the best ore-grade taconite corresponds to the wavy-bedded or irregular-bedded taconite present in both the Lower or Upper Cherty members. The sedimentary environment that produced this type of taconite ore has not been fully documented nor have any recent detailed sedimentological studies been attempted. A better understanding of the various sedimentological textures in the BIF could ultimately lead to an increased ability to better predict changes in ore grades as they relate to facies changes. Page 113 �"Eastern" Mesabi Range LTV (Cliffs-Erie) EVTAC (T-Bird So.) Upper Cherty United (T-Bird No.) LC-5 mass-bdd? LC-4 wavy-bdd LC-3 straight-bdd LC-2 thin-bdd LC-1 ss & congl Lower Cherty Ispat Inland (Minorca pit) upper Upper Cherty Algal MUC waste - mixed-bdd MUC - thick/mass-bdd LUC waste - thin-bdd LUC waste - irreg/mass-bdd LUC - reg-bdd LUC - wavy/thin-bdd LUC - slaty LS - thin-bdd er Intermediate Slate Low TLC - thick/thin-bdd TLC - mass congl TLC - irreg/mass-bdd BLC - wavy-bdd Footwall Lean - thin-bdd Footwall Ore - reg-bdd Footwall Taconite Slaty y Slat US-2 slaty pper US-1 thick & thin-bdd U UC-7 thick-bdd UC-6 thick-bdd Ispat Inland UC-5 algal/congl (Laurentian pit) UC-4 thick & thin-bdd US UC-3 mass-bdd UC-3 thick-bdd UC-2 thick & thin-bdd UC-2 reg/thin-bdd UC-1 thin-bdd UC-1 reg-bdd LS-3 slaty IF LS LS-2 thin-bdd Intermediate Slate Intermediate Slate LC-5B transition zone LC-6 thick-bdd LC-5A mass-bdd LC-5 irreg-bdd LC-4 wavy-bdd LC-4 wavy-bdd LC-3 reg-bdd LC-3 reg-bdd LC-2 thin-bdd LC-2 thin-bdd LC-1 sandstone & congl LC-1 ferrug seds & congl A - limestone B - vague-bdd C - thin-bdd D - thin & wavy-bdd E - mass-bdd F - thin-bdd G - wavy/reg-bdd H - thin/wavy-bdd I - algal/congl J - wavy-bdd K - wide-spaced wavy-bdd L - wavy-bdd M - reg-bdd O - wide-spaced wavy-bdd P - thin-bdd Q - carbonaceous IF R - thick-bdd S - vauge wavy-bdd T - wavy-bdd J - thin/reg-bdd V - thin-bdd W - algal/congl Northshore A - chert & marble B - chert & diopside C - thin-bdd Upper Slaty D - thin & wavy-bdd E - mass-bdd F - thin & wavy-bdd G - mass-bdd H- wavy-bdd I - algal/congl J - thick-bdd K- wavy-bdd L - wavy-bdd Upper Cherty M - thin/reg-bdd N - ?-bdd O - ?-bdd P - thick-bdd Lower Slaty Q - graph. arg. IF R - thick-bdd S - ?-bdd T - ?-bdd Lower Cherty U - reg-bdd? V - w/congl MUC = middle Upper Cherty LUC = lower Upper Cherty TLC = top of Lower Cherty BLC = bottom of Lower Cherty Virginia Horn Upper Cherty Upper Slaty Keewatin (National) & Butler US UC LS paint rock LC-1 thick-bdd LC-2 irreg-bdd LC-3 thick-bdd LC-4A Upper irreg-bdd LC-4A Middle thick-bdd LC-4A Lower wavy/thick/thin-bdd LC-4B irreg-bdd LC-4C Upper irreg-bdd LC-4C Middle laminated LC-4C Lower reg/thin-bdd LC-5A reg/thin-bdd LC-5B thin-bdd LC-6 ?-bdd jasp & thin-bdd thin-bdd congl UC Slaty Lower2-1 thin-bdd 1-8 reg-bdd 1-7 wavy-bdd 1-6 wavy-bdd 1-5 wavy-bdd 1-4 thin/wavy-bdd 1-3 even-bdd 8-3 slaty 1-2 mass-bdd 1-0 red basal slaty algal/congl Hibbtac (Buhl-Kinney) 2-1 thn-bdd 1-8 mass-bdd 1-7 wavy-bdd 1-6 wavy-bdd 1-5 mass-bdd 1-4 slaty 1-3 even-bdd 1-2 slaty 1-1 thin-bdd 1-0 congl Red Basal Lower Cherty Lower Slaty US UC-3 thick-bdd UC-2 thick-bdd UC-1 reg-bdd LS paint rock LC-5 thick/reg-bdd LC-4 wavy-bdd LC-4 wavy-bdd LC-2 reg-bdd LC-1B thin-bdd jasper thin-bdd algal/congl LC-1A Upper Slaty Coleraine area (USS) Dolomite Upper Slaty Upper Slaty - thin-bdd UC-16 - irreg/thin-bdd UC-15 algal/congl y er t UC-14 slaty Ch UC-13 thin-bdd r e p UC-12 congl w/algal frags Up UC-11 slaty LS-10 even-bdd LS-9 even/thick/mass-bdd LS-8 slaty LS-7 (IBC) wavy-bdd Ispat Inland LS-6 thin-bdd (Minorca pit) carbonaceous IF LC-5B thick-bdd LC-5 mass-bdd? LC-5A mass-bdd LC-4 wavy-bdd LC-4 wavy-bdd L LC-3 straight-bdd ow LC-3 wavy-bdd LC-2 thin-bdd er LC-2 even-bdd Ch LC-1 ss & congl LC-2 thick/mass-bdd ert LC-1 arg IF y LC-1 thin-bdd LC-1 algal/congl we rS lat y Hibbtac (Hibbing) Minntac Lo "Western" Mesabi Range Figure 4-12: Correlation chart of submembers, at each of the mines/areas within the Biwabik Iron Formation, as deciphered from published descriptions and mine handouts (modified from Zanko et al., 2001). All columns are hung on the base of the Lower Slaty (“Intermediate Slate”). It is important to note that this summary is preliminary as it has not been field-checked. No scale is implied and the true thickness of each submember is not portrayed. Bars to the left of the columns indicate mined taconite ore zones. Note that there are several consistent submembers within the Lower Cherty as opposed to very few laterally persistent submembers in the Upper Cherty. Page 114 �STOP DESCRIPTIONS Babbitt Hywy 21 Minn 135 Minn 169 4-10 4-11 Du nka Ro ad Embarrass Hywy 21 U.S. 53 nn Mi Minn 135 169 Du n oad ka R 4-9 T59N lut u R13W D Biwabik 4-6 Minn 169 T58N T57N Virginia 4-5 Gilbert 4-4A 4-4C 4-1 4-4B 4-2 Eveleth 4-3 Aurora 4-7 nn Mi lex p om C h R12W Hywy 110 135 Hoyt Lakes Minn 37 U.S. 53 R18W R17W R16W R15W R14W Figure 4-13: Locations of stops that will be visited on the field trip. Generalized contacts of the Biwabik Iron Formation, for the eastern half of the Mesabi Range, and Duluth Complex are shown. Note that in order to observe Stops 4-1, 4-2, and 4-3 in stratigraphic order, we will be back-tracking for short distances. STOP 4-1A: Pokegama/Archean Unconformity Location: On U.S. 53 in Eveleth, there is a stoplight at Grant/Industrial Avenue. Proceed northward past the stoplight for about 0.4 mi north to a gas station. Turn right and immediately turn left on the frontage road (Midway Drive). Drive past a church and past the first street on the right (Mesabi Drive). Watch for a low, small outcrop in the trees on the right, just a few feet off the road. Eveleth 7.5’ quadrangle, T.58N., R.17W, Sec 20, NW of SW of SE; 535445E, 5259520N (NAD83 UTMs) Description: This is the only easily accessible exposure of the unconformity. A close examination will reveal the presence of a thin smear of Pokegama conglomerate composed of schist and vein quartz clasts upon Archean schist with a near-vertical foliation. Note that the foliated schist clasts are flat and have a subhorizontal orientation. NO HAMMERING, PLEASE! STOP 4-1B: Argillaceous lower member of the Pokegama Formation Location: From stop 4-1A, CAREFULLY walk across both lanes of U.S. 53 to the long, roadcut on west side of highway. Eveleth 7.5’ quadrangle, T.58N., R.17W, Sec 20, NW of SW of SE; 535380E, 5259555N (NAD83 UTMs) Page 115 �Description: This cut is about 500 feet long and 5-10 ft high, and is the only exposure of this member. It consists largely of shale and siltstone with minor fine-grained sandstone. It has been interpreted as having been deposited in a low-energy upper tidal flat environment in a sea that transgressed onto the peneplaned surface of Archean rocks (Ojakangas, 1983). Minor channeling is common at the bases of the thicker sandstone beds, and at one spot, 0.5 m of section has been eroded. Small-scale cross-bedding is present in some siltstone beds, and elongated sole marks are visible on the bottoms of some sandstone and siltstone beds. A total of 57 of these paleocurrent indicators show that the currents were generally oriented in a north-south direction. A few concretions as large as 6 inches in diameter are present, as is soft-sediment deformation. Hemming et al. (1991) illustrated the soft-sediment folding and interpreted it as evidence that the Animikie basin was tectonically active during deposition of the Pokegama and the Biwabik. Alternatively, it is interpreted herein as soft-sediment slumping into tidal channels. Fine laminations and sequences of laminations in the sandstone beds have been interpreted as tidal rhythmites (G. Ojakangas, 1996). STOP 4-1C: Jaspillite on Archean metaconglomerate Location: From stop 4-1A, drive a long block northward to Merritt Drive. Turn right. About 100 ft farther, turn right on Mesabi Avenue. About another 100 ft farther, there is a fork in the street. Park on Mesabi Avenue and walk uphill on the street on the left to a broad, flat rock exposure in a driveway. Eveleth 7.5’ quadrangle, T.58N., R.17W., Sec 20, SW of SE (No. 7 Mesabi Lane); 535610E, 5259460N (NAD83 UTMs) Description: This is an excellent exposure of jaspillite resting unconformably on subvertical volcanogenic metaconglomerate. The outcrop is an estimated 30 to 40 ft topographically higher than stop 4-1A, and was also that much higher when the jaspillite was deposited. Is it an erosional remnant of basal Biwabik Iron Formation or is it a local chemical precipitate at the base of the Pokegama Formation? NO HAMMERING, PLEASE! NOTE: The middle member of the Pokegama Formation (a unit of intercalated beds of sandstone, siltstone, and argillite) was once poorly exposed in the flat area across the highway from the U.S. Hockey Hall of Fame. However, the best part of the poor exposure has since been covered by a frontage road. STOP 4-2: Upper member of the Pokegama Formation Location: Continue driving down Mesabi Drive to the frontage road (Midway Drive). Turn right and drive past stop 4-1A to a stop sign. Turn left to intersection with U.S. 53. Cross the northbound lane and turn left on highway. Drive south past stop 4-1B, past the Grant/Industrial Avenue stoplight, past the U.S. Hockey Hall of Fame on the right, and stop at the Rustic Rock Inn (you are now opposite a large roadcut on the east side of the highway). Walk across the highway, CAREFULLY! Eveleth 7.5’ quadrangle, T.58N., R.17W, Sec 32, E ½ of SE; 536055E, 5256775N (NAD83 UTMs) Description: This is the upper member of the Pokegama Formation, composed of silicacemented quartz sandstone. It is the rock type found immediately beneath the Biwabik Iron Formation; it was penetrated by countless drill holes during mining and exploration, and resulted in the formation being originally named the Pokegama Quartzite. Note the massive beds Page 116 �separated by thin beds of shale or siltstone. Silica cementation likely obscured some original cross-bedding. This member was interpreted by Ojakangas (1983) as having been deposited in a high-energy, lower tidal or subtidal environment. STOP 4-3: Lower Cherty member, Biwabik Iron Formation Location: Proceed south on U.S. 53 for 0.6 miles (passing over an overpass and past a long roadcut of iron-formation on the right ), to a left-turn lane. Make a U-turn and proceed north on the highway for about 0.2 miles to roadcut on the off-ramp for Highway 37 (right side of highway). Eveleth 7.5’ quadrangle, T.57N., R.17W, Sec 5, E ½ of NE of NE; 536230E, 5256285N (NAD83 UTMs) Description: Note that this member of the Biwabik Iron Formation overlies the sandy member of the Pokegama Formation of the last stop, and that both units dip gently to the southeast. Observe the thick wavy bedding, the trough cross-bedding, and the sandy texture of the iron minerals and chert grains. The cross-beds are best observed in this eastern roadcut, but are also present at both ends of the longer cut on the other side of the highway. Cross-bedding measurements (Fig. 4-16), although not definitive, are suggestive of a tidally-influenced marine environment. This, coupled with Walther’s law of succession of sedimentary facies (i.e., the facies observed vertically are also similarly related laterally), places the deposition of the ironformation seaward of the Pokegama Formation. N Figure 4-14: Rose diagram of 28 crossbedded measurements, mostly from the roadcut of Stop 4-3. 28 Stops 4-4A through 4-4C are at the Thunderbird North Mine of United Taconite (formerly Eveleth Taconite, or Evtac). Simplified stratigraphic submembers of the iron-formation, according to terminology used by Evtac, are portrayed in Figure 4-15. From stop 4-3, proceed north along U.S. 53 past stop 4-2 to the stoplight at Grant/Industrial Avenue. Turn left on Grant Avenue and follow the road past a cemetery to the entrance road to United Taconite (U-Tac). Page 117 �EVTAC Thunderbird South Virgina Fm 50' Upper Slaty US-2 Slaty silicates +/- irreg chert North 20' US-1 thick + thin BDD thick chert + thin BDD, cherty zones 20' Upper Upper Cherty UC-7 Thick BDD +/- slaty UC-6 170' UC-3 thick-BDD salt & pepper textu re 45' slaty wavy BDD salt & pepper 12' Footwall Lea n thin-B DD +/- graphite Footwall Ore Lower Cherty BLC 45' Bottom Lower Cherty LS-2 Thin BDD sil IF Vertical scale (in feet) K Lower Slaty LS Keweenawan Sill wide sp aced thin wavy beds L Wavy BDD w/ intraform rip ups M Reg BDD w/ wavy-straight BDD Thin BDD Silicate IF Algal 20-35' wide spaced wavy beds 85-130 ' 60' LC-4 wavy BDD cherty IF 55' LC-3 Reg BDD = thin beds o f chert & sil P LC-5A massive BDD w/ mottles +/- th in MGT bnds 45' LC-1 Ferrug con gl Graywacke ss = qtz grns in chl matrix Keweenawan Sill 10-14' carb clasts 65' Thin BDD Non-mag D Wavy BDD 2-6' E Sep t. cracks 13-20' F Thin & wavy-BDD Sep t. crack s 25-34' Mass BDD, MGT G granules, +/- thin BDD zones 10-20' Q carbonaceous 10-20' salt & pepper BDD w/ R Thick poor BDD/mott 45-95' LC-4 wavy BDD 4 5' LC-3 straight BDD w/ 4-5" chert bnds S Vague, wavy BDD +/- mott T Wavy BDD +/- mott Wavy BDD +/- congl K 30 -60' Thin-reg (Hem) LC-2 Thin BDD Silicate IF W LC-1 10' SS +/-congl+/-CH Upper Cherty Wav y BDD Silicate IF (minor congl) 9-2 0' Abundant MGT M (thin + reg BDD) 2-5' N Fayalite-q tz 6-17' O Fayalite-q tz Low MGT content MGT g ran ules 60' Thick BDD, green, MGT poor Lower Slaty P The most metamorph & reconstituted U Thin-reg BDD Thick + thin BDD 25-45' Thin BDD V + Arg + jasp 30' Algal / co ngl Upper Slaty 8-11' H Wavy BDD 2-5 ' I Algal/congl 15-24' Granule w/ pebb les J Thick BDD 30-47' L 50' LC-2 thin BDD = jasp, hem slaty, green silicates 26-43' C Thin BDD 40-80' 60' some salt & p epper not drilled or mined 130' 3-5 ' Int slate 15' LC-5B Transition Zone 50 Keweenawan? Sill 3-6 ' A Chert/marble 13-20' B Chert + Diop <5' Algal congl I Virginia Formation Virgina Fm 15-40' LC-5 irreg BDD cherty silicate IF Footwall Taconite Northshore H Thin wavy BDD O 145' thin-BDD rose-colored with depth Mass w/ septarian cracks, High Pho s (congl @ base) 30' Reg-BDD salt & pepper thin-BDD gray-colored Thin&wavy BDD +/- chert pebbles E J Wavy BDD, mott UC-1 Mott, Reg-BDD LS-3 Dark, slaty silicate IF int slate - graphite 25' LC-6 Thick BDD w/ irreg green sil layers 65' TACONITE ORE ir reg- to mass-BDD +/- mott 30' Lower Cherty Lower Slaty Mass congl pinkish TACONITE ORE Lower Cherty Thick- to thin- BDD 15' 0 UC-2 Reg/thin-BDD 30' 45' TLC Top Lower Cherty D 40-75' Green, wavy reg G BDD UC-2 Thick + th in BDD (ch ert/silicate) 40' Lower Slaty 0 50' 35' UC-1 Thin BDD Thin chert layers w/ MGT beds + wavy bnds LS thin-BDD black to dark green Thin BDD Thin BDD F +/- gran jasp beds TAC ORE wavy- to thin-BDD 90' C 25 35-50' TAC ORE Reg-BDD w/congl Vagu e BDD, Chert + Fe Sil 25-55' TAC ORE 40' Lo wer Upper Cherty UC-3 mass BDD, mott w/ irreg beds TACONITE ORE irreg- to massBDD & mott Upper Cherty Lower Upper Cherty Waste 50' ) Algal unit present but not described B 50 TACONITE ORE Thick + thin BDD cherty silicate thick- to mass-BDD congl w/dissem magnetite ( TAC ORE UC-4 35-55' A Limestone TACONITE ORE 50' Middle Upper Cherty thin-B DD slaty TACONITE Upper Cherty TACONITE ORE 65' 45' Virgina Fm UC-5 jasp/ algal/ congl w/ Mn! Mixed : thin-BDD, congl, mass BDD Vertical Scale (in feet) Middle Upper Cherty Waste Thick BDD pink carb motts Cliffs-Erie Site (old LTV) US Green to Grey Thin BDD, Non-magnetic SIPHON FAULT Algal <20' Upper Cherty 15' 25 Upper Slaty 50' TACONITE ORE TACONITE ORE >50' Ispat Inland Laurentian Pit TACONITE ORE EVTAC Thunderbird 26' GraphiticArgillaceous IF Q 11' R Thick BDD 8' S ? BDD/MGT rich 5' T Granules 10' U Reg BDD? 3' V Granule/qtzose Congl Lower Cherty Figure 4-15: Submember nomenclature for the Biwabik Iron Formation as used at the various taconite mines and idled mine sites that will be visited on this field trip. Modified from Plate II in Zanko et al., 2001. Note that the nomenclature portrayed here is preliminary in nature and future correlations of the various submembers used at the different mines still needs field checking and modification. The stratigraphic nomenclature is currently being revised for the Thunderbird North Mine by United Taconite, but was unavailable at press time and is not included in this figure. Page 118 �STOP 4-4A: Submember LC-3 near the base of the Lower Cherty Location: Northeast end of the Thunderbird North Mine. Eveleth 7.5’ quadrangle T.58N., R.17W., Sec 20 , 535290E, 5260255N (NAD 83) Description: The LC-3 submember (new U-Tac terminology or “footwall ore” in the old Evtac terminology) is characterized by regular-bedded and wavy-bedded cherty taconite wherein most of the magnetite is contained within dark-colored wavy (irregular) beds that locally show good pinch-and-swell relationships. This is the lowest unit mined at the Thunderbird North Mine and contains approximately 20-23% mag-Fe and 2% Davis Tube Si. The Auburn Fault can also be viewed at this locality. The fault zone consists of a 20-footwide zone of broken-up and highly oxidized vuggy rock. To the northwest is the Auburn Mine that was originally developed as an underground mine by the Minnesota Iron Company in 18941902. It was reopened as an open pit by the Oliver Iron Mining Company (a subsidiary of United States Steel Corp.) in 1951 and was essentially closed in the 1960s; scram operations continued intermittently until 1999. The mined ore was located along a main ore trough that coincides with the northwest-trending Auburn Fault. Mined material was obtained from the Upper Cherty and Lower Slaty members, and locally from the Lower Cherty member. Jim Small (personal communication to Peter Jongewaard) reported that he was unable to find any evidence of the Auburn Fault anywhere on the newly-scraped floor of the mine during the final scramming period prior to allowing the pit to fill with water. United Taconite is currently filling the mine with waste rock. STOP 4-4B: Submember LC-4 near the base of the Lower Cherty Location: Thunderbird North Mine. Eveleth 7.5’ quadrangle T.58N., R.17W., Sec 31, 533930E, 5257810N (NAD 83) Description: The LC-4 submember (BLC submember – old Evtac terminology) exemplifies typical wavy-bedded taconite (see Fig. 4-16 at end of this report) that is characteristic of much of the taconite ore of the Mesabi Range. This unit varies from the previous stop in that wavy-beds are dominant and locally exhibit cross-bedded features. At this stop the magnetite is in: 1. the wavy beds; 2. disseminated throughout the cherty bands; and 3. within mottles that are generally less than 1 cm in diameter and cored by Fe-carbonate (siderite). The LC-4 is 40-45-ft-thick and contains 20-27% mag-Fe and 1-2% Davis Tube Si. The LC-4 submember is easily recognized in drill core due to the wavy beds and a salt-and-pepper texture that is defined by disseminated magnetite. STOP 4-4C: Submembers LC-5 through LC-8 near the top of the Lower Cherty Location: Thunderbird North Mine. Eveleth 7.5’ quadrangle T.58N., R.17W., Sec 19; 533915E, 5259540N (NAD 83) Description: At the base of this pit exposure is the LC-5 submember (according to the new UTac terminology, or TLC in the old Evtac terminology) characterized by thick- and irregularbedded, mottled chert with 23-28% mag-Fe. The mottles are pink Fe-carbonate; they are not readily evident on fresh break but appear after a short weathering period. Overlying the LC-5 is a 1-1.5-ft-thick intraformational conglomerate (LC-6 submember – U-Tac terminology) that Page 119 �contains abundant red jasper fragments. The next overlying unit is the LC-7 submember (U-Tac terminology) characterized by thin magnetite-rich beds interlayered with green, Fe-silicatebearing, chert beds (1-6 inches thick). The LC-7 is ore with 20-25% mag-Fe, whereas, the overlying LC-8 submember, which physically resembles the LC-7, is waste as the thin beds no longer contain magnetite – rather Fe-silicates are dominant in the thin beds. This is the last stop at the Thunderbird North Mine. From here we will return to U.S. 53 and proceed about 1.5 miles north to a gated entrance on the right to the “Mineview in the Sky” – follow the signs to the overlook on top of a waste rock dump. Stop 4-5: Mineview in the Sky Overlook Location: Eveleth 7.5’ quadrangle, T.58N., R.17W., Sec 17, Ne of NW of SE; 535710E, 5261650N (NAD83 UTMs). Description: The open pit immediately below the overlook is the Rouchleau Mine that connects northward with additional mines. The Rouchleau Mine produced 52,000,000 tons of high-grade “natural ore” containing 50-55% iron from 1920 to 1976. This area is located on the “Virginia Horn” which is a large Z-shaped bend in the otherwise straight ENE trend of the Mesabi Range. Six miles to the northwest on the horizon is United States Steel’s Minntac taconite operation. Steam visible to the northeast of Virginia is from the Ispat Inland taconite plant. From the Mine View we will proceed to the Minorca Mine of Ispat Inland by driving north on U.S. 53 approximately 4 miles around the town of Virginia. About 1 mile north of the third stop light, make a right turn onto an unnamed gravel road (this road is 0.4 miles north of the road to the golf course). Follow this gravel road across 9th Ave. (paved) and continue to the Minorca mine gate. Stop 4-6 (optional): Cross-bedded LC-3 submember, Minorca Mine Location: Near the northwest of the Minorca Mine (UTM coordinates will be acquired at the site during the field trip). Description: Cross-bedding is exceptionally well exposed at one spot in this mine. Most crossbeds here indicate paleocurrents to the north, but one excellent herringbone cross-bedded set shows paleocurrent trends toward azimuth 0º (lower cross-bed) and azimuth 220º (upper crossbed). See Figure 4-8. If stop 4-6 is visited, we will cross the Laurentian Divide on private company mining roads to gain access to the Laurentian Mine of Ispat Inland. If stop 4-6 is not visited we will proceed southward on U.S. 53 from the Mineview overlook and head west on Highway 135 (about 3 miles) to the town of Gilbert. At the junction of highways135and 37, turn left and proceed north to the gated entrance to the Laurentian Mine of Ispat Inland. The stratigraphic terminology of submembers in the Laurentian Mine is portrayed on Figure 4-15. Page 120 �STOP 4-7A: Submember LC-5a and LC-5b at the top of the Lower Cherty Location: Laurentian Mine. Gilbert 7.5’ quadrangle T.58N., R.17W., Sec 24, NW of SE of NE; 542240E, 5260650N (NAD 83) Description: This stop picks up where we left off at the last stop at the Thunderbird North Mine. At this locality the LC-5a and LC-5b submembers are exposed. The LC-5a is a wavy-bedded taconite ore unit with pink to brown Fe-carbonate patches, lenses, and mottles. The overlying LC-5b submember consists of green Fe-silicate-rich granular cherty material. STOP 4-7B: Lower Slaty member and the “Intermediate Slate” at the base of the Lower Slaty Location: Laurentian Mine. Gilbert 7.5’ quadrangle T.58N., R.17W., Sec 24, NW of SE of NE; traverse from 542315E, 5260700N to 542485E, 5260840N (NAD 83) Description: The entire stratigraphic section of the Lower Slaty (130-ft-thick) can be viewed at this impressive face within the Laurentian Mine. The “Intermediate Slate,” at the base of the Lower Slaty, is characterized by thin-bedded, black, organic-rich slate that locally exhibits bright shiny graphitic surfaces with bedding-parallel slickensides. Pyrite is common to this submember and is present as both disseminated fine- to medium-grained cubes and as thin disks (marcasite?) along bedding planes. All of the Lower Slaty constitutes waste rock. Note that the name “slate” has been applied to all thin-bedded rocks in the BIF, but nearly every writer has pointed out that this term is a misnomer, because these rocks do not have the cleavage of a true slate but merely a parting parallel to bedding (White, 1954). Morey (1993) reported that the “Intermediate Slate” is an ash-fall tuff; however the senior author has yet to see any evidence of volcanic shards in thin-sections collected from this unit. STOP 4-7C: UC-1 submember at the base of the Upper Cherty Location: Laurentian Mine. Gilbert 7.5’ quadrangle T.58N., R.17W., Sec 24, SE of NE of NE; 542545E, 5260790N (NAD 83) Description: The UC-1 submember is a regular-bedded (1-2 inches straight/even beds) granular cherty unit that contains magnetite-rich bands, pink Fe-carbonate mottles, and local crossbedding. This material constitutes ore in that it contains 16-40% mag-Fe (the mag-Fe is extremely variable in this unit) and 2-4% Davis Tube Si. Localized pods of very Fe-rich taconite (up to 40% mag-Fe!) were present but have been recently mined out. STOP 4-7D: UC-2 submember at the middle of the Upper Cherty Location: Laurentian Mine. Gilbert 7.5’ quadrangle T.58N., R.17W., Sec 24, SE of NE of NE; 542590E, 5260740N (NAD 83) Description: This submember exhibits both regular-bedded and thin-bedded features and consists of both taconite ore zones (18-20% mag-Fe) and waste zones. At this particular site are numerous bedding-parallel quartz-carbonate veins with chlorite slickensides. The chlorite is Page 121 �particularly troublesome as it cannot be selectively removed from the blasted ore and ultimately “gums up” in the concentrator. Interbedded with the magnetite-rich beds are red-colored hematite-rich beds that appear to be primary – they are pervasive throughout the area and do not appear to be related to a later oxidation event that produced the direct shipping ores of the Mesabi Range. Also at this locality are localized red jasper beds and intraformational conglomerate lenses with red jasper fragments. STOP 4-7E: UC-3 submember at the top of the Upper Cherty Location: Laurentian Mine. Gilbert 7.5’ quadrangle T.58N., R.17W., Sec 24, SE of NE of NE; 542635E, 5260785N (NAD 83) Description: At this locality is a mixed thick-bedded, regular-bedded, and diffuse-bedded granular cherty unit with brown Fe-carbonate-rich beds (irregular to wispy appearance) as well as Fe-carbonate mottles and patches. The basal contact with the UC-2 submember is present at this locality and is marked by a seven-foot-thick thin-bedded zone at the base of the UC-3. A quartzcarbonate vein marks the contact. Within the middle of this unit is an algal stromatolite-bearing unit which will be viewed at the next stop in LTV pit 2E. This is the last stop at the Laurentian Mine. Return to the mine entrance (the one that is north of Gilbert), turn left on State Highway 135 and proceed west to Biwabik and Aurora. Follow Co. Road 110 through Aurora to Hoyt Lakes. At the stop sign in Hoyt Lakes take a left and proceed down Co. Road 666 (approximately 4-5 miles) to the guard shack near the office buildings at the Cliffs-Erie site (old LTV offices). After getting permission to enter the property, take an immediate right and follow this road about 3.5 miles to a T-intersection with the Dunka Road (private company road). Follow this road about 2 miles through a sharp right turn and a sharp left turn. At the last turn is a series of closed mining roads angling off to the south – walk down the road that points in the more southerly direction to the brow of the hill (Stop 4-8). The stratigraphic nomenclature for the Cliffs-Erie site is presented in Figure 4-15. STOP 4-8: Algal submember (I submember) near the top of the Upper Cherty Location: Cliffs-Erie site (old LTV Pit 2E). Allen 7.5’ quadrangle T.59N., R.14W., Sec 23, N1/2 of NW; 568202E, 5270625N (NAD 83). Access to this site is via the Dunka Road which is a private mining company road. Description: Algal structures were first described by Leith (1903) as “contorted bedding.” Grout and Broderick (1919) are the first who assigned an organic origin to them. The algal submember within the Upper Cherty consists of mounds of fossilized algal colonies that are separated by jasper-bearing intraformational conglomerate; both the algal and conglomerate units exhibit a combined thickness of 2-20 feet. This horizon occurs only in the eastern half of the range (not present west of Hibbing) and is only sporadically present between Hibbing and Chisholm. This locality is an excellent place to view a nearly horizontal portion of the iron-formation that contains abundant individual mounds of algal stromatolite. Stripping of glacial overburden in this area has revealed a dip slope the size of a football field that contains the stromatolite mounds Page 122 �(Graber, 1993). See Figure 4-9 in this field guide. Internally, the mounds are characterized by many individual columnar finger-like structures that are convex upward. The mounds protrude up through a thin veneer of the overlying thin- to wavy-bedded H submember. Studies of a nearby zone in this horizon showed that all the columnar stromatolites were inclined at 30 degrees to the vertical. Unfortunately, this particular site has been removed by mining activities. Stromatolite samples will be able to be collected at the extreme eastern edge of this exposure. Also at this locality the J and H submembers locally contain anthraxolite, which is an organic bitumen containing 95% or more carbon that is black with a vitreous luster and conchoidal fracture and resembles obsidian (Morey, 1994). Morey (1994) reported that anthraxolite is present throughout the iron-formation but it is most common beneath the carbon-rich “Intermediate Slate.” Furthermore, he suggested it formed via a mechanism of concentrating carbon from a mass-kill phenomenon, followed by later migration of a carbon-rich liquid to form the anthraxolite. After this site we will proceed eastward about 14 miles down the Dunka Road (through a locked gate) to the Peter Mitchell mine operated by Northshore Mining. The stratigraphic nomenclature of submembers in the Peter Mitchell Mine is portrayed on Figure 4-15. STOP 4-9: Submembers C, D (Upper Slaty), F, G, H, and I (Upper Cherty) Location: Peter Mitchell Mine. Babbitt 7.5’ quadrangle T.60N., R.13W., Sec 26, S ½ of NE. Several subunits of the Upper Cherty can be viewed within short walking distances at this particular stop (see descriptions and locations listed below). Description: Submembers G (wavy-bedded taconite ore), H (wavy-bedded taconite ore) and I (stromatolitebearing unit) at 578533E, 5278414N (NAD83 UTMs). The I submember is present at the base of the exposure and is overlain by the wavy-bedded H submember. At the top of H is a 0.5-1.0-ft-thick intraformational conglomerate that separates the H and G subunits (the G submember is actually present within the Lower Slaty according to Gundersen and Schwartz, 1962). Note that both H and G subunits constitute taconite ore and both are characterized by wavy-bedding. This same bedding characteristic was also evident in the taconite ore zones within the Lower Cherty that were seen earlier on this field trip. Note also that the bedding characteristics of the Upper Cherty at this locality are wavy rather than massive as at the Laurentian pit. Submember F with small septaria-like structures at 578857E, 5278440N (NAD83 UTMs) The F submember is thin- to wavy-bedded and locally contains small septaria-like structures that consist of whitish quartz-filled subvertical fractures in the granular cherty layers. Even though the F submember contains appreciable magnetite, it is classed as waste material because the magnetite is too fine to be economically concentrated. Submember F with small septaria-like structures and submember G with minor garnets (optional) at 578841E, 5278503N (NAD83 UTMs) Submember C (with Keweenawan sill) and submember D (optional) at 578730E, 5278206N (NAD83 UTMs) Both the C and D submembers are thin-bedded units of the Upper Slaty, however, the D submember is different in that it contains slightly thicker beds and lenses of chert. The “contact” Page 123 �between the C and D is exposed on this bench. A 20-ft-thick Keweenawan sill is also present at this stop (see below for geologic description) and is positioned about in the middle of the C submember. STOP 4-10: Submembers A, B, and C within the Upper Slaty, partially-melted Virginia Formation, two Keweenawan sills, and base of the Duluth Complex Location: Peter Mitchell Mine. Babbitt 7.5’ quadrangle T.60N., R.12W., Sec 16, W ½ of SW. Several subunits of the Upper Slaty, the Virginia Formation, and three Keweenawan intrusive rocks can be viewed within short walking distances at this particular stop (see descriptions and locations listed below). Description: Keweenawan Sill (“BIFSill”) within the C submember at 584051, 5280958N (NAD83 UTMs) A 2-18-ft-thick sill is present in the middle of the C submember at the Peter Mitchell and Dunka Pit areas, and within the J submember in the LTV 2E pit. The sill is generally fine- to mediumgrained with locally very coarse-grained plagioclase phenocrysts and polygonal jointing. A granoblastic texture is evident in thin-section indicating that the sill was emplaced in the early Keweenawan and was later metamorphosed by intrusion of the Duluth Complex. Hauck et al. (1997) noted that this sill is chemically similar to the Logan sills, to the northeast in the Rove Formation, and have informally called this sill a “Logan-type” sill. C submember at 584129E, 5281033N (NAD83 UTMs) The C submember is dominated by well-laminated, thin-bedded, slaty iron-formation containing magnetite, fayalite, ferrohypersthene, and chert. Submembers A, B, and C at 584193E, 5281142N (NAD83 UTMs) At the very top of the BIF is a 2-6-ft-thick chert and marble unit (A submember) that corresponds to the carbonate horizon that is present in only the eastern half of the Mesabi Range. This unit is locally absent in some areas (non-depositional unconformity) and extremely thick in other areas. The B submember is characterized by alternating chert and diopside bands up to one foot thick; marble layers are locally present. In some areas at this stop, pink granophyric veins locally cut the B submember. These veins exhibit pinch-and-swell relationships in that the veins thicken within the diopside bands and pinch in the chert bands. Keweenawan Sill (“VIRGSill”) at base of the Virginia Formation at 584226E, 5281159N (NAD83 UTMs) At the very base of the Virginia Formation is a 2-100-ft-thick sill that consists of a fine-grained, granoblastic, rock with varying amounts of plagioclase, clinopyroxene, orthopyroxene, hornblende, olivine, and biotite. The informal term of “Cr-bearing sill” was first used by Hauck et al. (1997) to highlight the relatively high chromium contents (600-1,200 ppm) that are characteristic of this sill. This sill exhibits two varieties: 1. a fine-grained, massive, gray-colored unit (this exposure) that is extremely difficult to distinguish from the hornfelsed Virginia Formation; and 2. a medium- to coarse-grained unit that is olivine- and/or hornblende-rich and is easily recognized. Page 124 �Partially-melted Virginia Formation in close proximity to the Duluth Complex at 584261E, 5280908N (NAD83 UTMs) In close proximity to the Duluth Complex, the well-bedded sediments of the Virginia Formation are typically transformed into a rock that at first appearance looks like an intrusive rock due to the presence of randomly oriented biotite. This rock is informally referred to as the “recrystallized unit” but is more properly classed as a diatexite (Sawyer, 1999). During emplacement of the Duluth Complex, the sediments of the Virginia Formation were heated, generating 20-40% pervasive partial melts, that literally enabled these rocks to flow in response to stresses that were applied during emplacement. All bedding planes are obliterated and what remains is a mediumgrained recrystallized rock that contains plagioclase, cordierite, orthopyroxene, and decussate biotite. Within this recrystallized matrix are blocks/boudins of more structurally competent siltstone and calc-silicate hornfels (originally limey layers). Basal contact of the Duluth Complex at 584266E, 5280874N (NAD83 UTMs) At this locality the basal contact of the South Kawishiwi intrusion (SKI) is irregular with localized “fingers” of the footwall Virginia Formation protruding upward into the intrusive rocks. Rocks of the SKI consist of weakly to moderately mineralized, fine- to medium-grained, ophitic augite troctolite to olivine gabbro. Cu-Ni values are unknown for this exposure. Return to Duluth via highways 21, 169, and U.S. 53. References Beck, J.W., 1988, Implications for Early Proterozoic tectonics and the origin of continental flood basalts, based on combined trace element and neodymium/strontium isotopic studies of mafic igneous rocks of the Penokean Lake Superior belt, Minnesota, Wisconsin, and Michigan: Unpublished Ph.D. Dissertation, University of Minnesota, 262 p. Boerst, K., 1999, Stromatolites in the LTV 2E pit, Mesabi Range, northeastern Minnesota: unpublished Undergraduate Research Opportunity Project (UROP), University of Minnesota Duluth. Chandler, V.W., 1993, Geophysical characteristics: in Sims, P.K., ed. (chap. 2) The Lake Superior region and TransHudson Orogen, Precambrian: Conterminous US: Geologic Society of America: The Geology of North America, v. C-2, p. 81-89. Fralick, P.W., and Kissin, S.A., 1998, The age and provenance of the Gunflint lapilli tuff [abs.]: 44th Annual Institute on Lake Superior Geology, Minneapolis, MN, 1998, v. 44, part 1, p. 66-67. Fralick, P.W., Davis, D.W., and Kissin, S.A., 2002, The age of the Gunflint Formation, Ontario, Canada: Single zircon U-Pb age determinations from reworked volcanic ash: Canadian Journal of Earth Science, v. 39, p. 1089-1091. Graber, R.G., 1993, Field trip guidebook (Trip 1) – LTV Steel Mining Company: 39th Annual Institute on Lake Superior Geology, Eveleth, MN, 1993, v. 39, part 2, p. 39-42 and 52-59. Grout, F.F., and Broderick, T.M., 1919, The magnetite deposits of the eastern Mesabi Range, Minnesota: Minnesota Geological Survey Bulletin, v. 44, 58 p. Gruner, J.W., 1924, Contributions to the Geology of the Mesabi Range: With special reference to the magnetites of the iron-bearing formation west of Mesaba: Minnesota Geological Survey Bulletin 19, 71 p. Page 125 �Gruner, J.W., 1946, The mineralogy and geology of the taconites and iron ores of the Mesabi Range, Minnesota: Office of the Commissioner Iron Range Resources and Rehabilitation, St. Paul, in cooperation with the Minnesota Geological Survey, 127 p. Gundersen, J.N., and Schwartz, G.M., 1962, The geology of the metamorphosed Biwabik Iron Formation, eastern Mesabi district, Minnesota: Minnesota Geological Survey Bulletin 43, 139 p. Han, T.M., 1982, Iron formations of Precambrian age: Hematite-magnetite relationships in some Proterozoic iron deposits – microscopic observations, in G.C. Amstutz and others, eds., Ore Genesis: The State of the Art: New York, Springer-Verlag, p. 451-459. Hauck, S.A., Severson, M.J., Zanko, L.M., Barnes, S.-J., Morton, P., Alminas, H., Foord, E.E., and Dahlberg, E.H., 1997, An overview of the geology and oxide, sulfide, and platinum-group element mineralization along the western and northern contacts of the Duluth Complex; in Ojakangas, R.W., Dickas, A.B., and Green, J.C., eds., Middle Proterozoic to Cambrian rifting, central North America: Boulder, Geological Society of America Special Paper 312, p. 137-185. Hemming S., McLennan, S.M., Hanson, G.N., and Krogstad, K.M., 1990, Pb isotope systematics in quartz [abs]: Eos (American Geophysical Union Transactions), v. 71, no. 17, p. 654-655. Hemming, S., Hanson, G.N., McLennan, S.M., and Sharp, W.D., 1991, Isoclinal slump-folds in the lower Pokegama Quartzite: Evidence for seismicity and slope instability during deposition of the Animikie Group [abs]: Abstracts and Proceedings, 37th Annual Institute on Lake Superior Geology, Eau Claire, WI, 1991, v. 37, part 1, p. 56-58. Hemming, S.R., McLennan, S.M., and Hanson, G.N., 1996, Geochemical source characteristics and diagenetic trends of the Virginia Formation, Mesabi Iron Range, Minnesota [abs]: 42nd Annual Institute of Lake Superior Geology, Cable, WI, 1996, v. 42, part 1, p. 13. Kissin, S.A., Vallini, D.A., Addison, W.D., and Brumpton, G.R., 2003, New zircon ages from the Gunflint and Rove Formations, northwestern Ontario [abs.]: 39th Annual Institute on Lake Superior Geology, Iron Mountain, MI, 2003, v. 49, part 1, p. 43-44. LaBerge, G.L., Cannon, W.F., Schulz, K.J., Klasner, J.S., and Ojakangas, R.W., 2003, Paleoproterozoic stratigraphy and tectonics along the Niagara suture zone, Michigan and Wisconsin: Field Trip Guidebook, 49th Annual Institute on Lake Superior Geology, Iron Mountain, MI, 2003, v. 49, part 2, p. 1-32. Leith, C.K., 1903, The Mesabi iron-bearing district of Minnesota: United States Geological Survey Monograph 43, 3163 p. Lucente, M.E., and Morey, G.B., 1983, Stratigraphy and sedimentology of the Lower Proterozoic Virginia Formation, northern Minnesota: Minnesota Geological Survey Report of Investigations 28, 28 p. Morey, G.B., 1967, Stratigraphy and sedimentology of the Middle Precambrian Rove formation in northwestern Minnesota: Journal of Sedimentary Petrology, v. 37, no. 4, p. 1154-1162. Morey, G.B., 1972, Mesabi Range: in Sims, P.K. and Morey, G.B., eds., Geology of Minnesota: A Centennial Volume, Minnesota Geological Survey, p. 204-217. Morey, G.B., 1973, Stratigraphic framework of Middle Precambrian rocks in Minnesota: in Young, G.M., ed., Huronian stratigraphy and sedimentation, Geological Association of Canada, Special Paper 12, p. 211-249. Morey, G.B., 1992, Chemical composition of the eastern Biwabik Iron Formation (Early Proterozoic), Mesabi Range, Minnesota: Economic Geology, v. 87, p. 1649-1658. Morey, G.B., 1993, Geology of the Mesabi Range: Field trip guidebook (Trip 1): 39th Annual Institute on Lake Superior Geology, Eveleth, MN, 1993, v. 39, part 2, p. 1-18. Morey, G.B., 1994, Anthraxolite in the Early Proterozoic Biwabik Iron Formation, Mesabi Range, northern Minnesota: in Southwick, D.L., ed.: Short Contributions to the Geology of Minnesota, 1994: Minnesota Geological Survey Report of Investigations 43, p. 39-47. Page 126 �Morey, G.B., 1999, High-grade iron ore deposits of the Mesabi range, Minnesota – Product of a continental-scale Proterozoic ground-water flow system: Economic Geology, v. 94, 133-142. Morey, G.B., 2003, Paleoproterozoic Animikie Group, related rocks, and associated iron-ore deposits in the Virginia horn: in Jirsa, M.A. and Morey, G.B., eds., Contributions to the geology of the Virginia horn area, St. Louis county, Minnesota: Minnesota Geological Survey Report of Investigations 53, p. 74-102. Morey, G.B., and Ojakangas, R.W., 1970, Sedimentology of the Middle Precambrian Thomson Formation, east-central Minnesota: Minnesota Geological Survey Report of Investigations 13, 32 p. Ojakangas, G.W., 1996, Cyclic tidal laminations in the Early Proterozoic Pokegama Formation: digital image analysis and computer modeling [abs.]: 42nd Annual Institute on Lake Superior Geology, 1996, v. 42, part 1, p. 44-45. Ojakangas, R.W., 1983, Tidal deposits in the early Proterozoic basin of the Lake Superior region – The Palms and the Pokegama Formations: Evidence for subtidal-shelf deposition of Superior-type banded iron-formation; in Medaris, L.D., Jr., ed., Early Proterozoic geology of the Great Lakes region: Geological Society of America, Memoir 160, p. 49-66. Ojakangas, R.W., 1994, Sedimentology and provenance of the Early Proterozoic Michigamme Formation and the Goodrich Quartzite, northern Michigan: Regional stratigraphic implications and suggest correlations: United States Geological Survey Bulletin 1904, 31 p. Ojakangas, R.W., Morey, G.B., and Southwick, D.L., 2001, Paleoproterozoic basin development and sedimentation in the Lake Superior region, North America: Sedimentary Geology 141-142, Elsevier Science B.V., p. 319-341. Pfleider, E.C., Morey, G.B., and Bleifuss, R.L., 1968, Mesabi deep drilling project: Progress report no. 1: in Mining Symposium, 29th Annual, and American Institute of Mining and Metallurgical Engineers, Minnesota Section, 41st Annual Meeting, Duluth, 1968 [Proceedings]: University of Minnesota, p. 52-92. Sawyer, E.W., 1997, Criteria for the recognition of partial melting: Physics and Chemistry of the Earth, v. 24, p. 269279. Schneider, D.A., Bickford, M.E., Cannon, W.F., Schulz, K.J., and Hamilton, M.A., 2002, Age of volcanic rocks and syndepositional iron formations, Marquette Range Supergroup: Implications for tectonic setting of Paleoproterozoic iron formations of the Lake Superior Region: Canadian Journal of Earth Sciences, v. 39, p. 999-1012. Schulz, K.J., 1987, An Early Proterozoic ophiolite in the Penokean orogen [abs]: Geologic Association of Canada Program Abstracts 12, p. 87. Schulz, K.J., 2003, A Paleoproterozoic suprasubduction zone ophiolite-island arc complex in northeastern Wisconsin [abs]: 49th Annual Institute on Lake Superior Geology, Iron Mountain, MI, 2003, v. 49, part 1, p. 71-72. Severson, M.J., Zanko, L.M., Hauck, S.A., and Oreskovich, J.A., 2003, Geology and SEDEX potential of Early Proterozoic rocks, east-central Minnesota; Natural Resources Research Institute, University of Minnesota Duluth, Technical Report NRRI/TR-2003/35, 160 p. Southwick, D.L., Morey, G.B., and McSwiggen, P.L., 1988, Geologic map (scale 1:250,000) of the Penokean orogen, central and eastern Minnesota, and accompanying text: Minnesota Geological Survey Report of Investigations 37, 25 p. Van Hise, C.R., and Leith, C.K., 1901, The Mesabi district: United States Geological Survey Annual Report, v. 21, part 3, p. 351-370. White, D.A., 1954, The stratigraphy and structure of the Mesabi Range, Minnesota: Minnesota Geological Survey Bulletin 38, 92 p. Winchell, N.H., 1882, The Potsdam sandstone: Minnesota Geological Survey Annual Report, v. 10, p. 123-136. Winchell, N.H., 1893, Twentieth annual report for the year 1891: Minnesota Geological Natural History Survey, 344 p. Page 127 �Wolff, J.F., 1917, Recent geologic developments on the Mesabi Iron Range, Minnesota: American Institute of Mining and Metallurgical Engineers, Transactions, v. 56, p. 229-257. Zanko, L.M., Severson, M.J., Oreskovich, J.A., Heine, J.H., Hauck, S.A., and Ojakangas, R.W., 2003, Oxidized taconite geological resources for a portion of the western Mesabi Range (west half of the Arcturus Mine to the east half of the Canisteo Mine), Itasca County, Minnesota – A GIS-based resource analysis for land-use planning: Natural Resources Research Institute, University of Minnesota Duluth, Technical Report NRRI/TR-2001/40, 85 p. Figure 4-16: Typical example of wavy-bedded taconite (also referred to as irregular-bedded taconite) that is mined from both the Upper Cherty and Lower Cherty members of the Biwabik Iron Formation on the Mesabi Range of northeastern Minnesota. Photo of the LC-4 submember at the Thunderbird North Mine of United Taconite. Page 128 �FIELD TRIP 5--CLASSIC OUTCROPS OF NORTHEASTERN MINNESOTA Co-leaders and contributors: Mark A. Jirsa1, Terrence J. Boerboom1, John C. Green2, James D. Miller, Jr. 1, G.B. Morey1, Richard W. Ojakangas2, and Dean M. Peterson3 1 Minnesota Geological Survey (staff and emeritus) University of Minnesota-Duluth (emeritus) 3 Natural Resources Research Institute 2 This manuscript has not been reviewed to conform to editorial standards of the Minnesota Geological Survey. INTRODUCTION We propose on this field trip to present the great diversity of Precambrian rock types in northeastern Minnesota using some of the most illustrative and accessible outcrops. We also hope to portray our present understanding of that geologic framework in the context of history— highlighting contrasts between “what we thought we knew” in the earlier years of geologic study, with “what we think we know now.” The trip will revisit many of the outcrops on which so many historical discussions, many of them heated, occurred. Geologic controversies were begun, and in some cases resolved, through discussions of the geologic relationships exhibited at some of these localities. This approach is not intended to criticize earlier works or workers; as each has contributed incrementally to the overall geologic picture. Geologic knowledge, like that in most sciences, is “vertical”— that is, each new iteration stands on the shoulders of previous efforts. Obviously, the trip visits only those places that are reasonably accessible from Duluth and from larger roads (Fig. 5.1). Figure 5.1 Generalized geologic map of northeastern Minnesota showing route of Field Trip #5. Page 129 �Although we consider many of these to be classic outcrops, it should also be noted that— because of access and location—these are only some of the classics; some of the most instructive outcrops are comparatively less accessible. It is likely that we have omitted some favorites, for which we apologize; however, many other fine outcrops can be found in field trip guide books in the accompanying references, including guides of the Institute on Lake Superior Geology, the Minnesota Geological Survey Guidebook Series, and the Geological Society of America (e.g., Biggs, 1987). HISTORICAL CONTEXT The Institute on Lake Superior Geology (ILSG) originated in Minnesota—as the “Lake Superior Institute”—with its first meeting held in Minneapolis in 1955, and has met the past 50 years in a variety of localities around the Great Lakes. Including this year’s meeting, the Institute has met in Minnesota a total of 13 times; five meetings were headquartered in the Twin Cities, six were held in Duluth, and two in more remote localities such as International Falls and Eveleth. Many, though apparently not all of those meetings, involved field trips demonstrating the diverse geology and mineral resources of the state. Unfortunately, the records of field trips during the earliest meetings are scant. Nevertheless, archives show that field trip topics fall into the following general geologic categories, listed geochronologically (with Minnesota meeting years in parentheses) below: Quaternary <1.75 Ma Twin Cities area (1976, 1998) Northern Minnesota (1979, 2004) Paleozoic <545 Ma Southeastern Minnesota (1976, 1979, 1998) Mesoproterozoic—1600-900 Ma North Shore Volcanic Group/Midcontinent rift (1971, 1979, 1989, 1998, 2004) Duluth Complex (1965, 1971, 1979, 1993, 2004) Paleoproterozoic—2500-1600 Ma St. Cloud “granite” district/Penokean orogen (1965, 1979, 1989, 1998) Virginia/Rove Formations (1963, 1971, 2004) Mesabi Iron Range/Biwabik Iron Formation (1963, 1971, 1979, 1993, 2004) Gunflint Iron Formation (1971) Archean—Neoarchean 2900-2500 Ma and Mesoarchean 3400-2900 Ma Vermilion and other greenstone belts (1971, 1979, 1989, 1993, 2004) Vermilion Granitic Complex/Quetico subprovince (1982, 2004) Minnesota River Valley gneiss terrane (1976, 1998) Although there apparently was no companion field trip for the first ILSG meeting in 1955; the “hot topics,” as judged from printed abstracts of that meeting, included the following: • Age, stratigraphic setting, origin, and lithologic subdivision of Lake Superior ironformation (presentations by Harold James, Robert Schmidt, and J.F. Wolff) • Composition and origin of iron ores; addressing competing theories on the creation of “natural ores” by rising hydrothermal vs. descending meteoric waters (Burton Boyum, Stanley Tyler, David White, N.K. Huber, Alan Broderick, Henry Lepp, Tsu Ming Han) • Geophysical characteristics of the “Lake Superior Syncline” (Edward Thiel, Harold Mooney, George Wollard, Lloyal Bacon) • Copper-nickel potential in Duluth gabbro, discovered in 1948 (Gerald Anderson and Donald Yardley) Not surprisingly, most of these same geological topics are important today, and are featured in the various presentations and field trips of this 50th anniversary meeting. Some of the more Page 130 �significant are represented by this field trip to the “classic” outcrops of northeastern Minnesota geology. Many of the controversies during early geologic study of the Lake Superior region involve attempts to correlate geologic units, and the consequent application of stratigraphic nomenclature. In Minnesota and adjacent Ontario, this type of controversy is typified by the debate surrounding the “Couchiching series” in the Rainy Lake area, and the stratigraphic and temporal relationships of Precambrian units in the region. Based on field work, largely in Canada, Lawson (1887) proposed that there was a sequence of sedimentary rocks older than Keewatin greenstone, and named these rocks the Couchiching series. Other workers, notably those with the U.S. Geological Survey, strongly disagreed. The question was so fundamental to understanding the regional geology that it was addressed by a special committee of geologists from the U.S. Geological Survey, Geological Survey of Canada, Michigan Geological Survey, and the Ontario Department of Mines, who visited field localities on both sides of the border. The result was a new model which was applied, rightly or wrongly, to the geology of other greenstone sequences. In retrospect, the controversies arose from the fact that geologists working in different areas observe or infer field relationships and attempt (as a natural consequence of human endeavor) to apply those relationships everywhere, including far afield from their immediate areas of knowledge— the “blind man and the elephant” syndrome. Furthermore, lacking geochronologic markers and dating methods, early workers applied temporal constraints based on generalized rock types; for example, implying that all volcanic rocks are “Keewatin,” all sedimentary rocks are either Seine (younger than Keewatin greenstone) or Couchiching (older than Keewatin greenstone), and recognizing two distinct periods of granitic rock emplacement as either Laurentian (pre-Seine) or Algoman (post-Seine). We now know from additional field work, advances in the understanding of depositional environments, and geochronologic studies that many periods of volcanism, sedimentation, and pluton emplacement have occurred. Much of what was known about the Precambrian geology in Minnesota by the 1950s—when the Institute on Lake Superior Geology (ILSG) was in its infancy—was the result of efforts by F.F. Grout, J.W. Gruner, G.M. Schwartz, and G.A. Thiel, all professors of geology at the University of Minnesota, and their graduate students working for the Minnesota Geological Survey. They summarized their views in a long paper entitled “Precambrian stratigraphy of Minnesota” (Grout and others, 1951). This publication served as backbone for a Geological Society of America field trip in 1956 (Schwartz and others, 1956). This was pioneering work that described major rock units and formalized their classification. It divided Precambrian time into a general three-fold classification scheme of Earlier, Medial, and Later—each Era separated by “great unconformities” in the rocks. The efforts established a geologic framework that was tested and refined by many workers, commonly reporting their results during the early years of the ILSG. For example, geochronologic and geologic studies in the 1960s established the Laurentian as an orogenic event, and much of the evidence for that was presented at ILSG meetings and field trips. FIELD TRIP FACTS The field stops include rocks ranging in age from Archean to Mesoproterozoic (Fig. 5.1 and Table 5-1). For the most part, the stops are presented in geographic rather than geochronologic order. Temporal settings can be deduced from the various figures, descriptions, and Table 5-1. Five topical areas are represented: 1) Virginia Horn—Archean and Paleoproterozoic (Stops 5-1 to 5-7) 2) Tower-Soudan—Archean (Stops 5-8 to 5-14) 3) Ely area—Archean (Stops 5-15 to 5-18) 4) North Shore and Duluth—Mesoproterozoic (Stops 5-19 to 5-25) 5) West of Duluth—Paleoproterozoic and Mesoproterozoic (5-26 to 5-28) Page 131 �TABLE 5-1—Stratigraphic and temporal classification of Precambrian rocks in northern Minnesota (after Sims, 1972). Ages are referenced in the text. Circles enclose the approximate chronostratigraphic position of field trip #5 stops. Considerably more stops appear in this guide than can reasonably be visited during a two-day trip. Other stops are included to provide a more thorough view of the regional geology and to facilitate self-led excursions. Some of these stops, as noted below, are described in detail in other field trip texts in this guide book, and not repeated here. Furthermore, much of the regional geologic framework is covered in the introductory material of those field trips, as noted below. The descriptions of many of the stops contain brief discussions of the “Historical Perspective,” providing the contrast between early and modern understanding of the geology. All UTM locations are given in NAD 83, Zone 15 coordinates. Section subdivisions read from smallest to largest quarter; e.g., “NW, SE, SW” should be read “NW quarter of the SE quarter of the SW quarter.” The small map insets showing stop locations are taken from USGS 7.5-minute topographic quadrangles listed with each stop. Page 132 �FIELD TRIP STOPS Virginia Horn area: Stops 5-1 to 5-7 (refer to Figures 5.2 and 5.3) Regional geologic context of the Archean and Paleoproterozoic rocks described below is reviewed in the introductory material to Field Trips#1, #4, and #7. Figure 5.2 Simplified geologic map of Vermilion Lake 30X60’ quadrangle (modified from Jirsa and Boerboom, 2003) showing location of field stops 5-1 to 5-13. Insets show location of additional figures. Page 133 �Figure 5.3 Generalized geologic map of the Virginia horn area (modified from Jirsa and others, 1998) showing details of field trip stops 5-1 to 5-7. Page 134 �STOP 5-1. Archean pillowed and massive greenstone Location: T.58N., R.17W., sec.23 NW, SE, SW; north edge of athletic fields, Gilbert Junior High School. Gilbert 7.5-minute quadrangle UTM: 539,820E/5,259,750N DESCRIPTION: Outcrop of pillowed and massive basalt is part of the Archean Mud Lake sequence, metamorphosed to low greenschist-grade. Pillow shapes indicate stratigraphic facing is to the northwest, which places this outcrop on the south side of a major D1 structure known as the Mud Lake syncline. Note also the presence locally of fractures filled with reddish jasper, presumably deposited in depressions on the rock surface by overstepping of Paleoproterozoic seas during deposition of the Biwabik Iron Formation. HISTORICAL PERSPECTIVE STOP 5-1: Early work by Gruner (1941) and later by Sutton (1963) interpreted the Archean volcanic and graywacke succession now known as the Mud Lake sequence as an anticline, based on few stratigraphic top indicators, and perhaps influenced by early discussions of the “Couchiching series” (Lawson, 1887) that placed metasedimentary rocks of the Rainy Lake area stratigraphically beneath “Keewatin” volcanic rocks. Detailed structural study by Jirsa and others, (1998) and Jirsa and Boerboom (2003) demonstrate that tholeiitic (Stop 5-1) and calcalkalic volcanic rocks and tholeiitic intrusions are conformably overlain by graywacke and slate (Stop 5-2). In detail, the succession forms a broad, twice-deformed syncline that has been segmented by faults of several generations. NEXT: Return to Highway 37, travel northwest to Hwy 135, thence west on 135 approximately 2.5 miles to Bourgin Road. Turn left (south) on Bourgin Road and continue about 0.4 mile to large cut on left (east) side of road (Stop 5-2). Page 135 �STOP 5-2. Archean graywacke and slate, intruded by quartzofeldspathic porphyry. Location: T.58N., R.17W., sec.21 SW, SW; road cuts on east side of the Bourgin Road. Eveleth 7.5-minute quadrangle. UTM: 536,311E/5,260,659N DESCRIPTION: Outcrops along this side of the road expose quartzofeldspathic porphyry (QFP) intruded into variably deformed graywacke, siltstone, and slate of the Mud Lake sequence. The sedimentary rocks here are moderately deformed, but much of that deformation is inferred to predate the main cleavage-forming event D2, and some may be soft-sediment in origin. The QFP is large and continuous to the east, but at this locality it appears to be segmented into a zone of multiple dikes. Both graywacke and QFP are intensely altered to some combination of iron-carbonate minerals (ankerite, ferroan dolomite) and sericite. Regionally, this style of alteration is commonly, though not always associated with QFP intrusions—presumably because the QFP remained more structurally rigid than the enclosing sedimentary rocks during the shear-related deformation event that accompanied alteration late in D2. Most gold mineralization in the area is closely allied to this alteration, yet this outcrop is surprisingly barren. HISTORICAL PERSPECTIVE STOP 5.2: One of the earliest gold discoveries in Minnesota was made by J.W. Gruner (in Grout, 1937) in a railroad cut not far from stop 5-2. The cut exposes graywacke intruded by quartzofeldspathic porphyry, having visible gold associated with small quartz veins. Despite several episodes of prospecting and systematic study of the region, no economic gold deposits have been discovered. NEXT: Follow Bourgin road to the south and west to a frontage road on the east side of Hwy 53. Turn north (right) on the frontage road and travel about 0.2 miles to first road to right, turn up-hill and continue to #7 Mesabi Lane (Stop 5-3). Page 136 �STOP 5-3. Archean conglomerate Private driveway! Location: T.58N., R.17W., sec.20 SW, SE, No. 7 Mesabi Lane; village of Midway. Eveleth 7.5-minute quadrangle. UTM: 535,713E/5,259,459N DESCRIPTION: Archean conglomerate and lithic sandstone that form the driveway here are part of the northeast-trending Midway sequence, containing these strata types locally interbedded with subaerially deposited, calc-alkalic (trachyandesitic) volcanic rocks. The sequence is inferred to have formed after earliest deformation (D1) of the enclosing graywacke and basaltic rocks of the Mud Lake sequence, but before the cleavage-forming D2 deformation that affected both sequences. The conglomerate contains clasts of basalt, graywacke, porphyritic trachyandesite, and quartzofeldspathic porphyry (QFP). This provenance indicates that the older Archean rocks of the Mud Lake sequence were intruded by QFP, deformed, and uplifted, to provide detritus to what was probably a successor or “pull-apart” basin developed along a major structure now occupied by the Pike River fault zone. Note also the presence of remnant skins of red jasper as at stop 5-1. HISTORICAL PERSPECTIVE: Midway sequence conglomerate has previously been interpreted as a basal sediment (Sutton, 1963), and as a proximal turbidite fan deposit (Levy, 1991), depositionally transitional with graywacke and slate of the Mud Lake sequence. Subsequent work (Jirsa, 2000) indicates that the conglomerate is part of a Timiskaming-type clastic and volcanic sequence that unconformably overlies the older volcanic strata. Deposition of the Midway sequence required uplift, subaerial erosion, continental volcanism, and deposition in isolated basins along a major structural break. Interestingly, Gruner, 1941, inferred that these rocks may be equivalent to similar units of conglomerate in the Knife Lake area, which are now also considered to represent successor-basin deposits that post-date deposition of older greenstone by as much as 30 million years (Corfu and Stott, 1998). The rocks share many attributes with other Timiskaming-type sequences, including the namesake Timiskaming Group near Timmins and the Shebandowan Group near Thunder Bay. The use of the term Timiskaming in this context is quite different from that of Goldich and others, (1961), who applied it as a system term to include the Seine, Knife Lake, and other presumably correlative metasedimentary units. NEXT: Return to frontage road paralleling Hwy 53; turn north and travel about 500 feet to low outcrop (Stop 5-4) on east side of road. Page 137 �STOP 5-4. Archean/Paleoproterozoic unconformity Location: T.58N., R.17W., sec.20 SW, SE; hamlet of Midway. Eveleth 7.5-minute quadrangle. UTM: 535,441E/5,259,520N DESCRIPTION: In the brush on the east side of the frontage road is a small exposure of Archean conglomerate, having nearly vertical foliation and lithologic content much like that at stop 5-3, capped by a thin and discontinuous “skin” of subhorizontally foliated conglomerate. The latter represents basal deposition of the Paleoproterozoic Pokegama Quartzite, the lowest of a tripartite sequence of formations that constitute the Animikie Group. Age dates are somewhat speculative; however, the Archean rocks of the various sequences in the horn probably are about 2.7 Ga (e.g., Peterson and others, 2001). Based on a date from tuffaceous rocks in the Gunflint Iron Formation (Fralick and others, 2002) that is inferred to be equivalent to the Biwabik Iron Formation, the Animikie Group is about 1.8 Ga. Thus, this unconformity represents a geological hiatus of approximately 900 million-years— almost twice that of all Phanerozoic time. The large road cut visible on the west side of Highway 53 is the argillaceous lower member of the Pokegama Quartzite. The road cut exposes shale, siltstone, and minor sandstone, which has been interpreted by Ojakangas (1993) as having been deposited in a low-energy upper tidal flat environment in a sea that peneplaned the Archean surface. Minor channeling is common at the base of thicker sandstone beds, and small-scale cross-bedding occurs in some siltstone beds. Local soft-sediment deformation may be the product of syn-depositional tectonism, or alternatively may represent localized collapse near tidal channels. HISTORICAL PERSPECTIVE STOPS 5-4 and 5-5: The Paleoproterozoic rocks exposed at Stops 5-4 and 5-5, and discussed at stop 5-6 were previously considered to represent a “geosynclinal sequence,” the precise tectonic mechanism of which was poorly understood. Work by a number of authors (notably Southwick and others, 1988) demonstrates that the tripartite formations exposed along the Mesabi Iron Range were deposited along the leading edge of a foredeep known as the Animikie basin that transgressed north over the Archean craton during the Penokean orogeny. In detail, deposition of basal quartzite (Pokegama), medial chemical (Biwabik) and upper turbiditic (Virginia) sediments represents a transgression of near-shore, shelf, and slope environments, respectively (Ojakangas, 1993). NEXT: Travel south on Highway 53 about 1.5 miles; stop on Highway and cross (carefully) to large outcrop on east side (Stop 5-5A) Page 138 �STOP 5-5. Paleoproterozoic Pokegama Quartzite (A) and Biwabik Iron Formation (B) Location: T.58N., R.17W., sec.32 SE, SE, and adjacent, junction of Highways 37 and 53. Eveleth 7.5-minute quadrangle. UTM: scattered outcrops extend from 535,956E/5,256,913N on the north (stop 5-5A), to 536,263E/5,256,200N on the south (stop 5-5B). DESCRIPTION 5-5A: This is the sandy, upper member of the Pokegama Quartzite. It is characterized by coarse grain size and massive beds as thick as 1.5 m. Massive beds are separated by thin beds of shale and siltstone. Ojakangas (1993) interpreted the deposition of this facies as within high-energy, lower tidal or subtidal environment. NEXT: Return to vehicle and continue south on Highway 53 past Highway 37. Turn around and drive north to large outcrop near the SE corner of the junction of Highways 53 and 37 (stop 5-5B) DESCRIPTION 5-5B: This exposure of gently southeast-dipping strata is part of the Lower Cherty member of the Biwabik Iron Formation. It overlies and is generally in transition with the Pokegama Quartzite at stop 5-5A. Notice that both formations have sandy textures and cross-bedding, implying a moderately high-energy depositional environment. The most significant difference between these two units is the abrupt change in sediment source from the extrabasinal quartz grains in the Pokegama, to recycled, chemically precipitated chert in the Biwabik. Measurements of crossbedding in the iron-formation are bimodal, implying deposition in a tidally influenced marine environment (Ojakangas, 1993). NEXT: Drive north on Highway 53 approximately 4 miles to entrance to Mineview overlook (Stop 56), just northwest of the junction of Highways 53 and 135. Follow driveway to overlook. Page 139 �STOP 5-6. Mineview in the Sky Overlook Location: T.58N., R.17W., sec.17 NW SE. North of the junction of hwys 53 and 135. Virginia 7.5-minute quadrangle. UTM: Top of overlook approximately 535,710E/5,261,650N DESCRIPTION: North from this overlook is a 3-mile-long complex of abandoned mining properties, known collectively as the Rouchleau mine; all developed within the Paleoproterozoic Biwabik Iron Formation. In detail, there were some 15 separately named mines within view that shipped ore during the period 1893-1986. All of them, and nearly 500 more along the 150-mile long Mesabi Iron Range, extracted oxidized (hematite- or goethite-rich) and leached iron-formation generally referred to as “natural ore.” The ore deposits here are localized along a set of fault zones (Fig. 5.3) that presumably provided the plumbing system for fluids that first oxidized the formation and produced permeability; and secondly, leached silica from the porous zones. Natural ores contained as much as 50 percent iron and less than 10 percent silica. By contrast, the mammoth open-pit mine in the distance to the northwest, US Steel’s Minntac mine, is developed in unoxidized, magnetite-rich ore containing about 30 percent iron, and 50 percent silica. This type of ore at Minntac, and five other open-pit mines currently in operation along the range, is the source of the iron concentrate known as taconite. The name taconite has also been applied generally to unoxidized iron-formation containing sufficient iron to be mined for a profit using today’s technology. HISTORICAL PERSPECTIVE STOP 5-6: Nearly 70 percent of the 3.6 billion metric tons of iron ore produced on the Mesabi range was extracted as natural ores. Although it has been generally accepted that these ores formed along fracture, bedding, and fault planes by processes of oxidation and leaching, the source of altering solutions has been the subject of considerable debate among economic geologists for nearly 70 years. Much of the literature and geologic observations on the issue are reviewed in Morey (2003). Many writers support the concept of descending meteoric waters to account for the dissolution of silica and oxidation of iron minerals. Others, including Gruner (1930) believed the geologic features were better explained by ascending hydrothermal solutions. Gruner’s theory failed to gain common acceptance, in part because no driving mechanism for such a hydrothermal system could be envisioned. The integration of Animikie Group strata into the tectonic context of the Penokean orogen in east-central Minnesota revived the theory of hydrothermal fluid flow within the Pokegama Quartzite and ultimately the iron-formation, as part of a continent-scale, gravity-driven ground-water system (Morey, 1999). The debate continues, fueled in part by the observation that no oxidized (and subsequently metamorphosed) iron-formation exists on the eastern-most Mesabi range that was metamorphosed by the Mesoproterozoic Duluth Complex. The precise origin of the structural bend in iron-formation known as the Virginia horn has long been questioned. It has been explained as a paired anticline-syncline vs. a modified warping Page 140 �around a fault-bounded horst (Morey, 2003). A topic for future research involves the extent to which vertical tectonism may have been operating during deposition of the iron-formation. NEXT: Return to Highway 53 and travel north through the city of Virginia to wayside rest approximately 2 miles north of town (Stop 5-7). STOP 5-7. Archean Giants Range batholith at “Confusion Hill,” Laurentian Divide Location: T.59N., R.17W., sec.19 SE, SE; wayside off Highway 53. Virginia 7.5-minute quadrangle. UTM: 534,337E/5,269,458N DESCRIPTION: Exposed near this wayside and in road cuts on both sides of the highway is an array of variably layered intrusions having both tonalitic (white) and dioritic (black) compositions. A cursory look shows intrusive relationships that conclusively demonstrate that diorite was emplaced into tonalite at one locality, and at another, tonalite was emplaced into diorite. In detail, all compositions intermediate between the two end members are also present locally. Although the dioritic component is abundant here, the bulk of the mapped unit is tonalitic. Emplacement of this unit, now known as the Lookout Mountain tonalite, probably involved some degree of magma mingling. Dikes of tonalite that cut the adjacent high-grade supracrustal rocks of the Minntac sequence contain metamorphic fabrics, yet little evidence of metamorphic origin can be seen in the interior of the body, implying it is syntectonic with respect to D2 deformation. U-Pb zircon dates (Boerboom and Zartman, 1993) of two components of the batholith exposed to the north bracket the age of D2 deformation between about 2674 and 2682 Ma. Exposures at Confusion Hill are a small part of the Giants Range batholith, which forms the core bedrock of the Laurentian (drainage) divide. The batholith is a 40-mile wide belt of intrusions that can be traced on geophysical maps and outcrop east to the Mesoproterozoic Duluth Complex, and west beyond the western border of Minnesota. It separates Archean supracrustal sequences in the Virginia horn from those of the Tower-Soudan area—making stratigraphic correlation between the two districts speculative. HISTORICAL PERSPECTIVE STOP 5-7: It was once generally thought that the mafic component of this mixed rock represented xenolithic rafts of subjacent amphibolite grade metavolcanic strata. In the process of regional mapping, Boerboom (in Jirsa and Boerboom, 2003) recognized that the intimately co-mingled tonalitic and mafic phases are the product of magma mixing. NEXT: Travel north on Highway 53 to the junction with Highway 169; follow the latter to the northeast approximately 28 miles to County Road 77. Turn left (northwest) on 77 and proceed about 0.5 mi. to Pike River (Stop 5.8). Page 141 �Tower-Soudan Area (refer to Figures 5.2 and 5.4) Much of the framework geology for the Vermilion district, including the Tower-Soudan area, is covered in the prelude to other trips in this guide, notably field trips #1 and #7. HISTORICAL PERSPECTIVE STOPS 5-8 to 5-18; Vermilion District The application of formal stratigraphic nomenclature to these rocks that are poorly constrained by incomplete exposure and scant geochronologic control produced considerable confusion over the years. For example, early workers considered all metabasaltic sequences equivalent, and applied the name “Ely Greenstone” to similar rocks exposed in a broad area of northern Minnesota. It is clear from subsequent mapping and geochronologic work that “greenstones” in the various belts are not all correlative. Use of the term continues today; but is restricted to specific sequences in the Ely and Tower-Soudan areas. In his publication of 1887, Lawson interpreted rocks of the International Falls area as depicting “Couchiching” sedimentary rocks to lie beneath “Keewatin” volcanic strata, and these interpretations were extended to explain stratigraphic relationships throughout much of Minnesota including the Vermilion district. Lawson’s criteria were based in part on stratigraphic younging in metasedimentary sequences. More recent interpretations recognize that these strata have experienced at least two deformations, the earliest of which (D1) involved inversion of large packages of strata into great thrust nappes prior to the major cleavage-forming event (D2). Thus, the boundaries between sedimentary and volcanic rocks in many areas are more structural than stratigraphic, and the use of younging directions in these strata requires detailed structural mapping to fully evaluate. In addition to structural mapping (e.g., Hudleston, 1976; Hudleston and others, 1988; Schultz-Ela and Hudleston, 1991; Jirsa and others, 1992), the study of geochemistry (e.g., Arth and Hanson, 1975; Schulz, 1980; Southwick and others, 1998) and U-Pb zircon geochronology (e.g., Boerboom and Zartman, 1993; Peterson and others, 2001) in Minnesota and adjacent Ontario are beginning to resolve some of the temporal issues. Much work remains in this endeavor. STOP 5-8. Archean graywacke at Pike River Dam Location: T.61N., R.16W., sec. 3, NW, SW; west side of County Road 77, on N side of river. [Note that Fortune Bay Casino—the overnight hotel—lies to the north off of CR 77]. Tower 7.5-minute quadrangle. UTM: 547,300E/5,293,340N HISTORICAL PERSPECTIVE STOP 5-8 Prior to about the 1950s, no depositional mechanism could satisfactorily explain the coincidence in graywacke of 1) coarse sand derived from a source many kilometers distant and having an altered clayey matrix; 2) interbedded black slate; and 3) the lack of evidence for reworking in shallow water (indicative of deposition below wave base). This was changed when the concept of turbidity currents was introduced to the geological profession by Kuenen and Migliorini (1950). Despite widespread publication on turbidites in more modern geologic Page 142 �Figure 5.4. Geologic map of the western Vermilion district (modified from Peterson and Jirsa, 1999), including the Tower-Soudan and Ely areas, and showing details of field trip stops 58 to 5-18. Page 143 �settings through the 1950s and 1960s, the facies model was not refined and applied to Archean and Proterozoic strata in the Lake Superior region until somewhat later (Morey, 1965; Ojakangas, 1966). NEXT: Return to Highway 169 and turn east. Continue approximately 1.7 miles to just east of the junction of 169 and County Road 526. STOP 5-9. Multiply folded Archean graywacke Location: T.61N., R.16W., sec. 2, NE, NE; south side of Highway 169 just east of CR 526. Tower 7.5-minute quadrangle. UTM: 550,050E/5,294,000N DESCRIPTION: This outcrop at the road and several smaller ones in the bush nearby show the superposition of two generations of folds in thin-bedded, well-graded graywacke of the Lake Vermilion Formation. The second-generation folds (F2) are associated with a regional axial plane cleavage in which sedimentary clasts are flattened. The earlier F1 folds have no associated cleavage and tend to be erratic in form, trend, and distribution. Folds display “eye” and “mushroom” shapes that locally are interpreted to be sheath folds (Hudleston and others, 1987). These characteristics are consistent with deformation of poorly lithified sediment. The superposition of deformation events is manifest in the transection of F1 folds by cleavage related to D2. In this area and to the west, one can find anticlinal synclines and synclinal anticlines, indicating stratigraphic inversion prior to D2 folding. HISTORICAL PERSPECTIVE STOP 5-9: The complex structure of the Vermilion district was poorly understood in the 1950s and 1960s. Subsequent structural study (Hooper and Ojakangas, 1971; Hudleston, 1976; Ojakangas and others, 1978; Jirsa and others, 1993) demonstrated two distinct periods of deformation: D1 that includes largely soft-sediment deformation represented at Stop 5-9, and a D2 transpressive deformation and metamorphic cleavage-forming event. Much of the early D1 deformation produced broad areas of down-facing strata formed by large thrust nappes (Jirsa and others, 1992). Prior to this recognition, there was much confusion about temporal relationships of individual volcanic and clastic sequences. NEXT: Continue east on Highway 169 approximately 0.7 mile to Stop5-10. Page 144 �STOP 5-10. [Optional] Archean dacitic tuff/ Paleoproterozoic or Mesoproterozoic diabase dike Location: T.61N., R.16W., sec. 1, SW, NE; Highway 169 road cut. Tower 7.5-minute quadrangle. UTM: 551,160E/5,293,960N DESCRIPTION: These road cuts expose outcrops of white, dacitic tuffaceous sedimentary rock, a component of the Lake Vermilion Formation. Regionally, the formation consists of all compositional gradations between what appears to be first-cycle tuff, tuffaceous graywacke, and mixed-source graywacke, interbedded on all scales. In a general way, the tuffaceous component increases in proportion to the east toward the Tower-Soudan anticline, presumably the source region of volcanic detritus. Rocks of the anticline are interpreted to represent the core of what was probably a large, composite volcanic shield complex, bordered by irregular basins composed of detritus shed from the shield, now represented by the Lake Vermilion Formation. The northeast-trending, steeply dipping, seven-meter wide diabase dike that cuts tuffaceous rocks has been the source of considerable debate. It’s petrographic (olivine-bearing) and geochemical (silica undersaturated) composition is similar to Mesoproterozoic dikes (Schmitz, 1994); yet it lies nearly along strike with, though east of, dikes of the Paleoproterozoic Kenora-Kabetogama dike swarm. NEXT: Continue east on Highway 169 approximately 1.5 miles to road cut. STOP 5-11 [Optional] Archean fragmental volcanic rocks Location: T.62N., R.15W., sec. 32, SW, SW; Highway 169 road cut, west edge village of Tower. Tower 7.5-minute quadrangle. UTM: 553,380E/5,294,430N DESCRIPTION: This outcrop consists of fragmental, variably reworked volcanic conglomerate and tuffaceous rocks of the Lake Vermilion Formation. The presence of this rock type demonstrates the Page 145 �eastward-increasing proximity to volcanic source rocks from stop 5-9 to here. The rock is composed of about 85-95 percent dacitic detritus, 3-5 percent gray clasts of graywacke, slate, and basaltic andesite, and a small percentage of magnetic and sulfidic fragments. Fragments range in size from a few millimeters to 20 cm. The generally poorly developed sorting and bedding, together with varied clast composition, implies a debris-flow origin. NEXT: Travel east on Highway 169, through the city of Tower, and continue east to the village of Soudan. Follow signs to left toward Soudan State Park for approximately 0.3 mi.—at this point, State Park entrance is on your left. Do not follow Park signs, but rather, continue on roadway turning toward the right and follow the road to junction about 0.4 mi. to east. Turn left and follow road for about 0.5 mi., more or less straight past the Soudan Fire Station and up the hill toward the back side of the Park and Stuntz Bay. Disembark at mine buildings and walk about 150 feet north and up-hill to outcrop on the right. STOP 5-12. Archean Soudan iron-formation member of Ely Greenstone No hammering please! Location: T.62N., R.15W., sec. 27, NE, NE; Soudan Mine State Park. Soudan 7.5-minute quadrangle. UTM: 557,120E/5,296,660N DESCRIPTION: This classic exposure of the Soudan iron-formation member of the Ely Greenstone lies on the north limb of the Tower-Soudan anticline, and at the stratigraphic top of the volcanic sequences known collectively as the Lower member of the Ely Greenstone. The outcrop displays two generations of tight folding in delicate laminae of chert (creamy white), chert-hematite jasper (red), and magnetite-chert (black to silver-colored). The second generation of folds (F2) is tectonic in origin, having subvertical axial surfaces that trend east, and steeply plunging axes. Most display Z-asymmetry. The earlier folds (F0-1) appear to have been sharply refolded to produce complex interference patterns. Lundy (1985) studied folding at this locality and concluded that some of the apparent interference structures are the product of early-formed sheath folds that did not involve refolding by D2. The F1 structures are predominantly intrafolial, and exhibit a great variety of style and orientation; implying they formed by layer-parallel, softsediment slumping. It is interesting to observe the rhythmic microlaminae (1 mm or so thick) in various cherty beds exposed here and speculate about the paleoenvironment—that is, whether these represent daily heating/cooling, tidal, climatic, annual, or some other repetitive influence in the depositional environment. What is known about units of iron-formation in the Ely Greenstone, of which there are many, is that deposition occurred during periods of relative volcanic and tectonic quiescence by the slow subaqueous “rain” of chemical precipitates. The deep excavations in this area are the early workings of the Soudan iron mine, the first in Minnesota. The mine produced about 16 mt of high-grade hematite ore (60-63 percent iron Page 146 �content) from 1884 until 1962, when the land was deeded to the State of Minnesota and converted to a park. Most of the production came from underground workings that began here in 1900, and which now can be visited on guided tours. The mine also houses an underground physics research facility at 2340 feet below the surface. A massive expansion of that facility is under consideration to create a national underground laboratory at considerably greater depths (Peterson and Patelke, 2003). NEXT: Return to vehicle and drive to east-bound Highway 169. Travel east approximately 7.5 miles to Mud Creek Road. The Highway follows in a general way, the strike of the nearly vertically dipping Soudan iron-formation, bounded by volcanic rocks of the upper member of the Ely Greenstone on the north and the lower member on the south. Turn north (left) on the Mud Creek Road and follow it for approximately 3.8 miles to Mud Creek. STOP 5-13. Mud Creek shear zone Location: T.62N., R.14W., sec. 5, SE, SE; Outcrop just northwest of Mud Creek near road. Chad Lake 7.5-minute quadrangle. UTM: 564,230E/5,302,800N DESCRIPTION: This outcrop shows highly strained rocks in the Mud Creek shear zone. The rock type is a quartz-iron carbonate-sericite schist, having quartz and tourmaline knots, abundant pyrite, and trace amounts of gold. Its protolith is unknown, because of the intense deformation, but could be any of several rock types in the region, including quartzofeldspathic porphyry, metavolcanic rock, or graywacke. The shear fabric trends east-northeast, and lineations plunge at shallow angles to the east. Development of this shear zone, which occupies most of the valley of Mud Creek, is a product of largely dextral transpressive deformation that has been partitioned into discrete zones, presumably late in D2 deformation. It is generally believed that gold-bearing mineralization was introduced during these later deformation events, and the Mud Creek shear zone and environs continue to attract considerable attention as a gold target (Field Trip #7). The Mud Creek shear is a broad, anastomosing zone that forms the boundary between rocks of the Ely Greenstone and Lake Vermilion Formation on the south, and volcanic and ironformation-bearing rocks known informally as the Bass Lake sequence on the north. The Bass Lake rocks may be equivalent to parts of the Newton Lake Formation exposed north of Ely, but a complex series of faults in the intervening area makes this correlation speculative. NEXT: Drive south from Mud Creek to first gravel trail to the west; turn west and proceed about 0.2 to gravel pit. Page 147 �STOP 5-14 [Optional] Archean graywacke and slate of Lake Vermilion Formation Location: T.62N., R.14W., sec. 8, NW, NE. Soudan 7.5-minute quadrangle. UTM: 564,100E/5,302,400N DESCRIPTION: This recently exposed outcrop of the Lake Vermilion Formation consists of siliceous slate having a 1-2 meter thick unit of thinly bedded tuffaceous graywacke. The slate carries a strong S2 cleavage and is cut by shears; both trending to the east-northeast. Bedding in the graywacke trends north-northeast and youngs to the southeast—this contrasts with the regional setting which strikes to the east-northeast and youngs to the north. The reason for this anomalous trend is unclear, but it may be the result of fault drag along the Mud Creek shear zone. NEXT: Return to Mud Creek Road, travel south to Highway 169, then turn east on 169 and continue approximately 12 miles to Ely. [Enroute, one might visit a spectacular outcrop of pillowed flows described in Field Trip #1, Stop 1-13; Hilltop S of Highway 169 at SE, SW, S19, T.62N, R14W, UTM:056200E, 5297800N]. Pass through Ely and continue approximately 1 mile east of town to junction of 169 and County Road 88; then proceed 0.3 mi farther east to road cut. Ely and vicinity (refer to Figures 5.1 and 5.4) Geologic framework and outcrop locations are shown on Green and Schulz, 1982. STOP 5-15 [Optional] Archean Ely Greenstone Location: T.63N., R.12W., sec. 25, NW, SW; Road cut on Highway 169 approximately 0.3 mi. east of junction with County Road 88 (Spaulding Bay Road). Ely 7.5-minute quadrangle. UTM: 588,350E/5,307,075N Page 148 �DESCRIPTION Pillowed basalt of the Ely Greenstone. Flows and complexly interlayered iron-formation in the area are strongly folded into anticlines and synclines striking predominantly to the northeast. Stratigraphic younging to the north can be established from pillow structures in this exposure and others nearby. High grade iron ore was mined from iron-formations in the noses or axes of many of the folds. The productive Zenith, Chandler, and Pioneer mines, for example, lie within one such fold, the Ely trough. NEXT: Return to junction of Highway 169 and County Road 88, turn north on 88 and travel approximately 2 miles to Echo Trail. Turn right (north) on Echo trail and proceed 0.3 miles north to road cut on west side of the road. STOP 5-16. Archean Newton Lake Formation— variolitic basalt Location: T.63N., R.12W., sec. 22, NE, NW; road cut on Echo Trail. Ely 7.5-minute quadrangle. UTM: 585,750E/5,309,360N DESCRIPTION This road cut exposes pillowed and variolitic flows and hyaloclastite breccia of the Newton Lake Formation. Pillow sizes vary from “normal” to “mattress”, and their shapes indicate younging to the south. The Newton Lake is separated from the Ely Greenstone to the south by a complex zone of faulting (Shagawa Lake and Sibley faults) developed within sedimentary rocks of the Knife Lake Group. Although relatively undeformed conglomerate and sedimentary rocks of the Knife Lake Group are exposed just a few miles to the east, they are typically so sheared and altered in this area as to obscure lithologic and sedimentary interpretations, and will not be visited. The Newton Lake Formation differs from the Ely in that the former contains abundant diabasic sills and rare iron-formation. In addition, lava flows of the Newton Lake typically have larger MgO and incompatible element contents than those of the Ely, and some are classed as komatiites (Schulz, 1980). The Newton Lake Formation (and possibly equivalent Bass Lake sequence) is considered to be the youngest Archean supracrustal sequence in the Vermilion district. Rocks having nearly identical composition and stratigraphic/structural setting occur in Itasca County some 80 kilometers to the west (Jirsa, 1990). NEXT: Continue north on Echo Trail for 0.8 mi. to outcrop 5-17A on left (west) side of road. Page 149 �STOP 5-17. Archean Newton Lake Formation— felsic tuff and mafic intrusions Location: T.63N., R.12W., sec. 15 SE, NW; road cuts on Echo Trail. Ely 7.5-minute quadrangle. UTM: 5-17A=585,775E/5,310,660N 5-17B=585,810E/5,310,700N DESCRIPTION: 5-17A Road cut on west side of Echo Trail is aphanitic to fine-grained, laminated, light-colored felsic tuff and probable reworked tuff, cut by diabase. Minor graded bedding indicates younging to the north; however, it is likely at this exposure that the tuff represents a large block rafted in diabasic intrusions. NEXT: Cross to east side of Echo Trail and walk north to first outcrop. 5-17B This road cut exposes layered metadiabase intruded by hornblende-pyroxene-biotitebearing lamprophyre; both presumed to be intrusions of the Newton Lake Formation. Lamprophyre is coarse- to very coarse-grained and contains inclusions of the diabase. Overall, the Newton Lake Formation contains abundant and locally differentiated sills that vary in composition from diabase and gabbro to pyroxenite and peridotite. NEXT: Return to vehicle and proceed north on Echo Trail, which winds around the east shore of Burntside Lake, for approximately 3.5 miles to junction with County road 803 (Passi Road). Turn left (west) on Passi Road and stop. STOP 5-18. Archean schist (metagraywacke), paragneiss, and trondhjemite of Quetico subprovince Location: T.63N., R.12W., sec. 8, SW, NW; outcrop in SW corner of junction Echo Trail and Passi road. Shagawa Lake 7.5-minute quadrangle. UTM: 581,660E/5,312,050N Page 150 �DESCRIPTION: About one mile south en route to this stop, we passed a sharp, narrow valley that marks the trace of the Burntside Lake Fault. The fault forms a major boundary between comparatively low (greenschist) grade rocks on the south that typify the Wawa subprovince, with high-grade (amphibolite) rocks of the Quetico subprovince on the north. Rocks here include biotite schist, migmatite, and trondhjemite, a part of what’s known as the Vermilion Granitic Complex. Despite the amphibolite grade of metamorphism, the schist retains some evidence of graded bedding locally that indicates a graywacke protolith. NEXT: Backtrack to Highway 169, turn west and continue to Highway 1 at the east side of Ely. Follow Highway 1 south toward the north shore of Lake Superior, a distance of approximately 50 miles. Though we will not stop, this route takes us out of the Archean Wawa subprovince, crossing parts of the Mesoproterozoic Keweenawan Supergroup, including the Duluth Complex and North Shore Volcanic Group. North shore and Duluth areas (refer to Figures 5.1 and 5.5) For regional framework geology, refer to introductory material to Field Trip #2. Figure 5.5 Geologic map of northeastern Minnesota (modified from Miller and others, 2002) showing field trip stops on the north shore and in the Duluth area Page 151 �STOP 5-19. Top of Mesoproterozoic Palisade rhyolite flow (North Shore Volcanic Group) Location: T.56N., R.7W., SEC. 11 NE, SW; 0.2 mi. N of Highway 61 on Highway 1. Illgen City 7.5-minute quadrangle. UTM: 636,600E/5,245,850N DESCRIPTION: Road cuts on the west side of Highway 1 expose the upper zone of the Palisade rhyolite, a very large and extensive porphyritic flow that is part of the North Shore Volcanic Group. Much of the flow, seen for example on Palisade Head and Shovel Point and the Hwy 61 cut just SW of the junction with Hwy 1, has the appearance of a normal lava flow, but features here at the top, and at the inaccessible base of the cliff at Palisade head, show clearly that it was erupted explosively. The hot ash settled and welded, and the resulting hot, devolatilized mass flowed as “reconstituted lava” or ignimbrite. This road cut in the rapidly chilled top part of the flow is made of flow-brecciated, flow-folded welded tuff; microscopic study reveals deformed shards and fiamme in some samples. (More obvious shards are visible in the chilled welded tuff at the flow’s base). Pneumatolytic or hydrothermal alteration has kaolinitized much of the feldspar at this locality. In exposures of the massive flow interior, flow-aligned platy quartz after tridymite is abundant in the groundmass, implying a high temperature of eruption (greater than 870 degrees C). HISTORICAL PERSPECTIVE: Little attention was paid to the rhyolites in the North Shore Volcanic Group (NSVG) in earlier accounts. In some of the earliest work by N.H. Winchell (1889), he attributed all north shore rhyolites to the process of melting of sedimentary rocks. More recently, the importance of these rocks has been increasingly recognized because of their abundance compared to intermediate compositions (bimodal tholeiitic suite), and the opportunity they present for geochronologic study (Goldich and others, 1961). With the further development of the U/Pb zircon dating method, many rhyolites have provided age calibration for magmatism in the Midcontinent Rift. The Palisade rhyolite, for instance, has been dated at 1098.6 ±1.7 my (Davis and Green, 1997). Whereas Bowen-inspired models of magma evolution assumed rhyolites such as this to be the products of crystal fractionation of the dominant basaltic parent, their high abundance in the NSVG, along with recent Sm/Nd analyses (Vervoort and Green, 1997) show this and many others to have been produced by partial melting of Archean basement. Finally, detailed field studies and petrography of this and other large felsic flows has indicated that they were erupted at unusually high temperatures for rhyolite, were highly mobile, and that many are rheoignimbrites (Green and Fitz, 1993). NEXT: Continue south on Highway 1 for 0.3 miles to Highway 61. Turn northeast (left) on 61 and drive approximately 14 miles to turn-in for Sugarloaf Cove Scientific and Natural Area. Walk to Sugarloaf Point. Page 152 �STOP 5-20. Mesoproterozoic basalt at Sugarloaf Cove Location: T.58N., R.5W., Sec. 29 NE, NE. Little Marais 7.5-minute quadrangle. UTM: outcrops begin about 652,020E/5,261,120N Note: This stop is on property of the Sugarloaf interpretive Center Association (a non-profit) and the State of Minnesota. The beach and point are part of a Scientific and Natural Area (MN DNR) established to preserve these features. Please do not use hammers, or remove samples of any kind. Thanks. DESCRIPTION: Many of the attributes of olivine tholeiite lava flows of the NSVG are well exposed on the beach, mainland shore, and point. Flows range from several tens of meters thick to thin flow units of a meter or less. Massive interiors are ophitic: each “ophite” is made of an augite oikocryst enclosing many small plagioclase tablets. Abundant tiny olivine grains occur with plagioclase between the ophites. Pipe amygdules are common in the flow bases, and small vesicle cylinders occur in the massive interior of the thick flow that caps the sequence (The Sugarloaf) on the point. These are all pahoehoe flows, and ropy surfaces are well displayed, as are columnar joints and red sandstone-filled fractures (“clastic dikes”) in the interiors. HISTORICAL PERSPECTIVE: Although considerable petrographic study and some geochemistry had been done on the basalts of the Cu-bearing lavas of the Keweenaw Peninsula of Michigan (e.g., Butler and Burbank, 1929; Broderick, 1935), the NSVG only began to receive such attention in the mid- to late 1960’s, as the world geochemistry community began to focus on basalts and their parent ultramafic rocks of the mantle. The evolution of the plate-tectonics paradigm soon provided a model for the raison d’etre for these basalts, and the concept of the Midcontinent Rift System was born (White, 1972; Green, 1977). Further attention to the physical and geochemical aspects of basalts has generated more data on the NSVG (e.g., Nicholson and others, 1997, and references therein); olivine tholeiites such as these are interpreted as being mainly mantle plume melts, with minor lithospheric contribution. NEXT: Return southwest on Highway 61 approximately 28 miles to entrance to Split Rock Lighthouse State Park. Turn into the park and walk to base of lighthouse. Note that traveling southwest through this western limb of the NSVG, one traverses down-stratigraphic section. Page 153 �STOP 5-21. Mesoproterozoic (Keweenawan) Beaver Bay Complex at Split Rock Lighthouse Location: T.55N., R.8W., Sec. 33 SW, SW; Split Rock Point Lighthouse History Center and State Park. Split Rock Point NE 7.5-minute quadrangle. UTM: base of lighthouse at 623,640E/5,228,680N DESCRIPTION 5-21A: Outcrops of fine-grained, ophitic olivine diabase of the Beaver River diabase, which hosts the majority of anorthosite inclusions from Split Rock to Grand Marais, are exposed just northeast of the lighthouse atop a sheer 30-m-high sea cliff. The centimeter-wide augite oikocrysts obvious here are typical of the lower portion of this diabase sill, which dips gently (<15°) into the lake. The prominent point just to the northeast (Rusty Point) is held up by a very large (>200 m) inclusion of medium-grained granophyric granite lying at the base of the sill. Making our way to the base of the lighthouse, we come upon a good exposure of the large anorthosite inclusion that holds up the entire sea cliff. The coarse-grained (± 1 cm) anorthosite here displays meter-scale modal layering of noritic anorthosite (20% En72 hypersthene; 80% An6080 plagioclase) and anorthosite (>99% Pl). This inclusion is altered and displays a moderate to severe cataclastic and granulated texture indicative of having been recrystallized and/or tectonized (Morrison and others, 1983). The steeply dipping layers are cut by thin dikes of medium-grained, igneous-textured augite leuconorite (Pl-An56; Opx-En75; Cpx-En66). DESCRIPTION 5-21B. Follow the footpath south to the pump house on the lakeshore. Here, black, massive basalt is exposed in wave-washed outcrops. The brecciated, amygdaloidal AA flow top of this basalt flow is exposed in the rubbly bluff to the northeast in the direction of the lighthouse. Laminated siltstone in the matrix of the flowtop dips gently toward the lake. Carefully scrambling over some large boulders of ophitic diabase to the northeast, we can view the inclusion-rich base of the diabase sill conformably overlying the basalt flow top. Note that the diabase is chilled against the basalt, but not against the anorthosite inclusions. The abundance of inclusions disrupts the development of regular columnar jointing in the diabase. Numerous boulders along the base of the cliff display the textural and mineralogical varieties of anorthosite inclusions present. Looking to the northeast, one can see that the vertically layered inclusion beneath the lighthouse extends to lake level. HISTORICAL PERSPECTIVE: Occurrences of nearly pure plagioclase rock holding up various points of high ground between Split Rock Point and Grand Marias have held a special fascination for Lake Superior geologists for over 150 years. These enormous (up to 500m across), light-colored, coarse-grained masses embedded in dark, fine-grained mafic rock were first recognized by J.G. Norwood in 1849 (Fig. 5.6) as part of the federal Owen Survey (Owen, 1852). During the initial state geological survey (1872-1900), N.H. Winchell noted the resemblance of the feldspar rock, as he called it, to the Rice Point Gabbro at Duluth (anorthositic series of the Duluth Complex). He Page 154 �suggested that the anorthosites were blocks plucked from older feldspathic phases of the Duluth gabbro by later outpourings of the great gabbro flood, which he fancied to be an enormous extrusive (Winchell, 1900). He noted that the inclusions became somewhat smaller and more dispersed toward the lake and interpreted this to be due to disaggregation as they traveled downslope (to the southeast) from their source. Midway through the survey, Winchell commissioned A.C. Lawson to study these masses in greater detail. Lawson (1893) concluded that the anorthosite represented the peaks of Archean mountains that where inundated and largely buried by outpouring of the great gabbro flood. The inclusion character evident in most anorthosite occurrences was attributed to spalling of large blocks from the mountain peaks. In the early 1900's the search for corundum in northern Minnesota followed well publicized discoveries of the mineral in Canada. In 1902, several property owners mistook the light green anorthosite on the north shore for corundum. They formed a company, attracted investors, built a plant complete with processing, storage, and transport facilities---all without ever analyzing the rock! The first sale of mined product was also the last when it was discovered that the rock contained no corundum, but instead is composed of the much softer feldspar mineral, anorthite. Despite the setback, the investors regrouped and eventually formed the Minnesota Mining and Manufacturing company (now 3M); demonstrating an important principal: the lessons learned from small failures sometimes lead to great successes. One of the most complete inventories of the anorthosites of the North Shore was reported in Minnesota Geological Survey Bulletin 28 "The Geology of the Anorthosites of the Minnesota Coast of Lake Superior" by Grout and Schwartz (1939). In this report, they documented most known anorthosite occurrences in six 1:31,500 scale township maps. In considering the origin of the anorthosite, Grout and Schwartz clearly recognized them as inclusions of pre-existing rock that were derived from a deeper crustal source and were transported in diabasic magma to their present site by virtue of their low density. They agreed with Winchell that the source was likely the anorthositic rocks of the Duluth Complex. Figure 5.6—Woodcut print from J.G. Norwood’s report on the geology of the north shore (in Owen 1852) showing massive anorthosite inclusions in well-jointed basalt. More detailed considerations of the petrographic and geochemical attributes of the anorthosite inclusions led Phinney (1968) to conclude that Duluth Complex gabbroic anorthosites were an unlikely source for the inclusions. The inclusions, which commonly show signs of severe recrystallization and cataclasis, were more plagioclase-rich (>95%), coarser-grained, and more anorthitic (An70-75) than most anorthositic rocks of the complex. Also, Duluth Complex anorthositic rocks rarely contain orthopyroxene, a common mafic phase in the inclusions. Instead, he speculated that the inclusions were derived from deeper anorthosite bodies in the mid- Page 155 �to lower crust. Proterozoic anorthosite massifs seemed an attractive source by their depth of occurrence and plagioclase-rich composition; however, massif anorthosites are less anorthitic (An45-55) than even Duluth Complex anorthositic rocks (An55-65) and tend to be strongly recrystallized. In a follow-up petrographic and geochemical (Rb-Sr, Sm-Nd, and REE) study (Morrison and others, 1983), Phinney and his coworkers uncovered evidence of crustal contamination in the anorthositic inclusions from a source older than 1.9 Ma. They concluded from this that the inclusions were derived from early Proterozoic anorthosite bodies formed in the lower crust. As a corollary to a model for the origin of plagioclase crystal mush parent magmas to the anorthositic series of the Duluth Complex, Miller and Weiblen (1990) speculated that these anorthositic inclusions may be Keweenawan in age. In their model, plagioclase-rich magmas were generated by ponding of mantle-derived melts in the lower crust. Under the high pressures of the lower crust, plagioclase will be significantly buoyant in mafic magma and would likely give rise to anorthositic cupolas in these deep magma chambers. Early lower crustal intrusions may have been contaminated by interaction with the lower crust and thus imparted crustal isotopic signatures into these early anorthosite cumulates. As rifting progressed and the lower crust was displaced, later magmas may have picked up these early Keweenawan anorthosites and transported them tens of kilometers into subvolcanic dikes and sills of the Beaver River diabase. NEXT: Return to Highway 61, turn southwest (left), and continue approximately 15 miles to Silver Cliff Tunnel. STOP 5-22 [Optional] Mesoproterozoic (Keweenawan) diabase and andesitic flows at Silver Cliff Tunnel Location: T.53N., R.10W., Sec. 15 and 22. Castle Danger 7.5-minute quadrangle. UTM: 606,993E/5,213,952N to 606,755E/5,213,486N; DESCRIPTION: The Silver Creek diabase is an irregular, subcordant, subhorizontal intrusion at least 200 feet thick. The diabase forms a prominent highland that projects inland several miles from Silver Cliff at Lake Superior. Excavation of the Highway 61 tunnel has created excellent exposures of the contact between volcanic rocks and both the top and bottom of the diabase, and has exposed a north striking, 55-degree east-dipping fault that cuts the base of the diabase. Refer to Field Trip 2, stop 2-6 for details. NEXT: Continue southwest on Highway 61 for approximately 30 miles. Near the City of Duluth, 61 becomes London Road; continue southwest on London Road. Do NOT turn onto Interstate Highway 35, but clock mileage and continue approximately 1.25 miles to parking area for Leif Ericson City Park near 12th Avenue East. Walk into the park and to the shoreline. Page 156 �STOP 5-23. Mesoproterozoic (Keweenawan) interflow sedimentary rocks at Leif Ericson Park Location: T.50N., R.14W., Sec. 23 SW. Duluth 7.5-Minute quadrangle. UTM: 570,050E/5,182,950N DESCRIPTION: This classic location exposes an estimated 110’ of interflow sandstone, lying on slightly eroded amygdaloidal flows of the gently southeast-dipping Leif Ericson Park Lavas. The sandstone is fine- to medium-grained, moderately well sorted, and derived almost totally from underlying and adjacent lava flows—no extrabasinal detritus has been detected (Jirsa, 1984). The presence of planar-tabular and trough cross-bedding, together with the lenticular distribution of interflow units, implies the strata represent occasional stream flow deposits in depressions on the evolving lava surfaces. This is one of many interflow sedimentary units, most of which are “red bed-like” in appearance (considered in the early works of N.H. Winchell as Potsdam equivalents). By contrast, this interflow lies very near the base of the North Shore Volcanic Group, and thus has experienced burial metamorphism to nearly greenschist facies—though it is possible that some of the elevated grade above the zeolite facies typical of rocks just to the northeast, is an aureole effect of the adjacent Endion and other diabasic sills. NEXT: Follow signs to Interstate Highway 35, travel southwest on 35 to Highway 53. Turn north on 53 (Piedmont Avenue) and continue about 1 mile to intersection with Skyline Parkway. Turn left (southwest) on Skyline and travel 0.4 mi. to crossing with 28th Ave. W; continue 0.2 mi. farther southwest on Skyline to outcrop on the right (Stop 5-24). STOP 5-24 [Optional] Mesoproterozoic Duluth Complex; Layered Series “Chill”, Granophyre, and Anorthositic Series Location : T50N, R14W, Sec 32, SW, SW; Skyline Parkway about 1/5 mi. SW of 28th Ave. Duluth Heights 7.5-minute quadrangle. UTM: 564,880E/5,179,640N Page 157 �DESCRIPTION: Exposed at the northeast end of this roadcut is a fine-grained mafic rock with intermingled granophyre that together cut coarse-grained olivine gabbroic anorthosite of the anorthositic series. Since early mapping by Grout in the Duluth area in 1911, the relationships displayed by this rather innocuous exposure has been critical in interpreting the intrusive history of the Duluth Complex. The distinct, but complexly intermingled domains of mafic and felsic rock displayed here and commonly observed in the upper parts of the Duluth Complex led Grout (1918c) to the interpretation that these rocks formed by liquid immiscibility. This idea was strongly at odds with the newly introduced notion of granite formation by differentiation of mafic magma touted by Bowen (1928) and led to years of debate between these two famous petrologists. Another significant feature displayed by this exposure of more parochial interest is the relationship between the fine-grained gabbro and the coarse-grained olivine gabbroic anorthosite. The fine-grained mafic rock exposed here can be traced up over the ridge to the west where it merges into the upper contact zone of Layered Series (see Green and Miller, this abstract volume for general summary of the geology of the Duluth Complex at Duluth). Grout and later Taylor (1964) saw this exposure as evidence that the anorthositic series had cooled considerably when the layered series was intruded and thus was considerably older. This paradigm was accepted by all subsequent workers on the Duluth Complex up through the 1990’s. Consequently, it came as something of a shock when high resolution U-Pb ages (Paces and Miller, 1993) revealed that the anorthositic series and the layered series were virtually identical in age (within 0.5 Ma relative to the 22 Ma span of Midcontinent Rift magmatic activity). This precipitated a major paradigm shift in the perception of the intrusive relationships between these two series here and throughout the Duluth Complex (Miller, 1992). A closer look at this layered series “chill” reveals that it is not a thermal quench of the Layered Series at Duluth (DLS) at all. This rock type is found at the contact with the anorthositic series throughout most of this area and has a remarkably homogeneous, evolved composition (MgO/(MgO+FeO) = ~ 37; see Table 2 in Miller and Ripley, 1996). In thin section, it is a subprismatic biotitic oxide ferrodiorite. Phase equilibrium modeling of its composition indicates that it should be in equilibrium with evolved compositions of augite, ilmenite and plagioclase phases that comprise gabbroic cumulates found in the cyclic zone and gabbro zones of the DLS. In sum, this rock is much too evolved to have produced the entire cumulate pile of the layered series. Rather than this being a thermal quench, Miller and Ripley (1996) have interpreted this rock to represent decompression quenching of an evolved, water-saturated layered series magma during venting at a time when the cyclic zone was crystallizing. Whereas decompression of less than water saturated magma will result in superheating and a suspension of crystallization (or at least a significant change in phase equilibrium), decompression under water saturated conditions will cause supercooling and quenching. This model fits nicely with the explanation for the cyclic zone with which this composition is apparently comagmatic (see Stop 25). How does this scenario of venting of a hydrous magma relate to the mafic-felsic duplex which so intrigued Grout? The lobate contacts between the irregular masses of medium-grained granophyre and the fine-grained ferrodiorite host clearly gives the appearance of two-magma mixing. Grout's (1918a) idea that these two magmas formed by silicate liquid immiscibility of hydrous mafic magmas in the roof zone of the Duluth Complex seems more plausible today than when he first proposed it. The concept of silicate liquid immiscibility, which had come to be totally disparaged during Grout's day, has regained some respectability as an plausible, albeit, uncommon petrologic process (Roedder, 1979). However, alternative explanations for this compositional dichotomy can be suggested. One is that these felsic magmas were derived from anatectic melting of various inclusions carried into the layered series chamber. Because of their high silica content and low density, these felsic melts did not readily mix or assimilate with mafic melt, but rather rose to the roof zone where they ponded beneath the anorthositic series cupola. Page 158 �During magma venting from the chamber, the felsic melts became entrained and irregularly mixed with the mafic magmas. While decompression under water saturated conditions caused rapid crystallization of the mafic magma, the felsic melt became irregularly entrapped in the quenched mafic host and cooled more slowly to a medium-grained texture. NEXT: Return to Interstate 35 and follow it southwest to exit for Thomson Hill Rest Area near the crest of the hill west of Duluth. Follow signs to rest area (Stop 5-25). STOP 5-25. Mesoproterozoic (Keweenawan) Duluth Complex at Duluth Location: T.49N., R.15W., Sec. 14 SE, NW; Thomson Hill Rest Area on Skyline Parkway. West Duluth 7.5-minute quadrangle. UTM: 560,700E/5,175,380N HISTORICAL PERSPECTIVE: The well-exposed gabbroic rocks forming the escarpment above the city of Duluth have long been recognized as the type section of the Duluth Complex. While early surveys recognized the presence of two distinct rock types in the Duluth area - normal gabbros and feldspathic gabbros (Winchell, 1900), Grout was the first to interpret the layered gabbros as a product of convection and magma differentiation (Grout, 1918a-c). Taylor (1964) produced the first detailed-scale (1:24,000) geologic map of the complex in the Duluth area wherein he distinguished the stratiform gabbro cumulates of the layered series from the older, structurally complex anorthositic series. He interpreted the structural complexity of the anorthositic series as having formed from multiple injections of a plagioclase crystal mush. He also recognized the differentiated character of the layered series and pointed out that it was basically similar to the Skaergaard Intrusion - the classic example of a well-differentiated intrusion formed by fractional crystallization of a tholeiitic magma (Wager and Deer, 1939). More recently, detailed mapping and petrologic studies in the Duluth area have added substantially to our understanding of emplacement and crystallization history of these two series here at the type locality of the Duluth Complex (Miller and Ripley, 1996, Miller and others, 2002). See Green and Miller, this abstract volume for more details about the geology of the Duluth Complex at Duluth. In two outcrops at this stop, we can view exposures that demonstrate the inclusion/intrusion relationship between of anorthositic and layered series rocks and that illustrate the macrocyclic nature of the cumulate rocks which characterizes the medial part of the Layered Series at Duluth, an interval called the cyclic zone. DESCRIPTION 5-25A: In the road cut north of the rest area parking lot is an exposure of intermittently layered, wellfoliated olivine oxide gabbro hosting several meter-sized, flattened inclusions of olivine anorthosite. The gabbro is a four-phase cumulate of plagioclase, augite, Fe-Ti oxide and olivine. This cumulate typifies the upper gabbroic parts of troctolite→gabbro macrocycles that Page 159 �characterize the cyclic zone. In this three-dimensional view, the anorthositic inclusions clearly have a pancake shape that is conformable to layering and foliation in the host gabbro. This may represent the original shape of the inclusions or it may indicate compaction of a partially molten blocks. In either case, the occurrence of anorthositic inclusions in layered series rocks is a ubiquitous feature throughout the Duluth Complex. That the opposite relationship is rarely if ever observed has reinforced the longstanding interpretation that the anorthositic series is older than layered series. However, high precision U-Pb dating (Paces and Miller, 1993) has shown that this age difference is less than 1 million years relative to the 20-million year magmatic history of the Midcontinent Rift. DESCRIPTION 5-25B: In the layered sequence of gabbroic rocks exposed along the 200-m-long roadcut below the observation deck (Fig. 5.7), changes in cumulus mineral assemblages are displayed that characterize the cyclic zone of the Duluth Layered Series. The approximately 1-km thick cyclic zone is composed of five to six major macrocycles, ranging in thickness between 50 and 200 m, within which troctolitic cumulates (Pl+Ol) grade upward into gabbroic cumulates (Pl+Cpx+FeOx±Ol). Boundaries between the macrocycles are defined by abrupt cumulate reversals back to troctolitic cumulates and are also commonly marked by the occurrence of anorthosite inclusions and microgabbro cumulates at the top of the lower cycle. This exposure traverses the boundary between the third and fourth macrocycles. Figure 5.7. Geology and cryptic variation of mineral compositions along Skyline Parkway road cut near Thompson Hill rest area, Stop 5-24B. View is to the north. Dip of lamination and layering is exaggerated; it averages about 20° to the east. Contacts between units are gradational over thicknesses of 10 cm to 1 m. Mineral composition parameters are An in plagioclase = CaO/(CaO+Na2O+K2O), En' in augite and Fo in olivine = MgO/(MgO+FeO); all in mole%. Cumulus rock codes (in parentheses) list abbreviations of minerals in decreasing order of abundance (P/p plagioclase, C/c-clinopyroxene (augite); F/f -Fe-Ti oxide; O/o-olivine; upper case = cumulus mineral, lower case = intercumulus minerals). Samples A-G are noted by dark circles. The west end of the road cut begins with a coarse-grained, moderately laminated, subophitic olivine gabbro, which locally is intergranular and elsewhere is leucocratic (sample A, Fig. 5.7). Augite in this rock is marginally cumulus but becomes definitely so quickly up-section where it consistently has an anhedral granular to subprismatic habit (sample B). Beyond a poorly exposed interval, this gabbro is interlayered with a 2-m-thick interval in which minor olivine becomes Page 160 �subpoikilitic and concentrated in layers (sample C). Another 3 m above this, the coarse gabbro passes into a medium- to medium fine-grained, well-laminated, subpoikilitic olivine-bearing oxide gabbro (samples D and D') which displays layering of olivine oikocryst concentration and elsewhere isomodal layers rich in Fe-Ti oxide and pyroxene. The very strong foliation and subhedral to euhedral habit of cumulus phases (plagioclase, pyroxene, and ilmenite) impart an adcumulate texture to this rock. Over a poorly exposed interval about 15 m long is an altered, coarse-grained, ophitic gabbroic anorthosite (sample E) that is texturally and mineralogically identical to rocks in the anorthositic series. At the beginning of the next well-exposed section of roadcut, several similar gabbroic anorthosite inclusions are found in a coarse-grained, subophitic to intergranular olivine gabbro (sample F), which gradually grades upward into a more consistently subophitic texture over the remainder of the roadcut (sample G). This rock type closely resembles that at the west end of the roadcut and indicates a downgrading in the cumulus status of pyroxene (and oxide?) and a reemergence of cumulus olivine. At first glance, a sensible interpretation of this cumulus regression is that it represents a magma recharge event. However, the cryptic variation of En and Fo across the cumulus regression exposed in this section (Fig. 5.7) is the reverse of what would be expected from magma recharge. An alternative explanation to magma recharge is that the textural and compositional variations across this interval reflect decompression of the chamber due to eruption to the surface. Decompression of a volatile-enriched magma would cause supercooling and multiple saturation of the magma and thereby explain the abrupt decreases in grain size and cumulus phase changes without much compositional variation. Magma expulsion through the roof of the layered series would also explain the occurrence of a gabbroic anorthosite inclusion at the cumulate regression. The hydrothermally altered nature of the gabbroic anorthosite is consistent with a volatile-rich environment in the anorthositic series cupola of the Duluth Layered Series magma chamber. The cumulus reversal to ophitic olivine gabbro without an increase in mg# could be explained by repressurization of a devolatilized magma. NEXT: Return to Interstate Highway 35 and travel southwest on it approximately 3 miles to Highway 13, Midway Road. Turn north on Midway road and continue 0.8 mi. to road to east (right). Follow road east approximately 0.2 mi., disembark and walk east to base of bluff. West of Duluth (refer to Figures 5.1, 5.5, and 5.8) STOP 5-26. Mesoproterozoic /Paleoproterozoic Unconformity Location: T.49N., R.15W., Sec. 17 SE, SW. Esko 7.5-minute quadrangle. UTM: 555,580E/5,174,380N Page 161 �DESCRIPTION: This area contains exposures showing the unconformable relationship between the Paleoproterozoic Thomson Formation (will see at Stop 5-28), and the Mesoproterozoic (Keweenawan) North Shore Volcanic Group. Scattered outcrops in the brushy area just west of the bluff are folded and metamorphosed feldspathic graywacke, siltstone, and mudstone or slate of the Thomson Formation. By contrast the Keweenawan strata exposed in the bluff have been little affected by tectonism since deposition, as shown by their gentle dip to the east. The unconformity is not exposed; but, inferring from the two sets of exposures, it appears to be an angular one. It represents a nearly 800 million-year hiatus, based on an age of roughly 1100 Ma for the Lakeside lavas northeast of here (Davis and Green, 1997) versus a date of about 1880 Ma for tuff interbedded with iron-formation in the Animikie Group, of which the Thomson Formation is a component (Fralick and others, 2002). The Keweenawan stratigraphic section in this area consists of a basal sedimentary unit, the Nopeming formation, which is conformably overlain by the Ely’s Peak basalts. The latter comprise the oldest volcanic strata of the North Shore Volcanic Group. The Nopeming consists of approximately 30 feet (10 m) of interbedded conglomerate and quartz arenite, with minor siltstone beds in the uppermost part of the unit. Much of the sandstone is medium- to coarsegrained, well-sorted and rounded, quartz arenite. The uppermost, silty parts of the Nopeming contain load casts and other structures indicating soft-sediment deformation. The overlying Ely’s Peak basalts locally contain well-developed pillow structures, indicating subaqueous deposition. Interestingly, a nearly identical stratigraphic sequence—the Puckwunge Formation—is observed 150 miles to the northeast near Grand Portage (Mattis, 1972). Together, these sequences are representative of a broad depositional and tectonic setting at the onset of Keweenawan deposition in this part of the Lake Superior region. HISTORICAL PERSPECTIVE: The stratigraphic position of the Nopeming at the base of the Keweenawan and its correlation with the Puckwunge Formation in the Grand Portage area and the Bessemer Quartzite in the Ironwood, Michigan area has long been accepted. However, a curious complication to this simple interpretation is presented by the 120 year old record of a 500' deep well drilled about 3 miles due south of this site. The log of the Short Line Park well, as reported by Winchell (1889), encountered sandstone and conglomerate, very similar in appearance to the Nopeming that was interlayered with basaltic lavas over a 140-foot interval. Surprisingly, the lower 84 feet of the hole is reported to be exclusively in basalt. This has led some to question whether the Nopeming is the basal unit or just an interflow sedimentary unit (Mattis, 1972). If the latter is correct, it implies a north-south fault along the base of the slope at this site. NEXT: Return to Interstate 35, cross under it, and continue south to join with Becks Road. Follow Becks Road southeast to Gary-New Duluth and Highway 23. Turn south (right) on 23 and follow it through town. At the south edge of town, Highway 23 turns west (right); follow it into the city of Fond du Lac. At the west edge of Fond du Lac, turn northwest (right) on Highway 210 and turn very shortly afterward to left into city park. Walk to northwest to edge of bluff (Stop 5-27). Page 162 �Figure 5.8. Geology and location of stops in the Fond du Lac, Jay Cooke State Park, and Thomson Dam areas (modified from Jirsa and Morey, 1987). STOP 5-27. Mesoproterozoic Fond du Lac Formation Location: T.48N., R.15W., sec. 6 SE, SE along west shore of St. Louis River near city park. Esko 7.5-minute quadrangle (SEE Fig. 5.8 for location). UTM: 554,670E/5,168,140N DESCRIPTION: The Fond du Lac Formation consists of nearly 800 feet of red sandstone, shale, and minor basal conglomerate, of which only a few hundred feet are exposed here along the lower St. Louis River. It is part of an accumulation of as much as 20,000 feet of clastic sediments deposited in the central Lake Superior region following Keweenawan volcanism. The Fond du Lac is considered to be equivalent to the Orienta Sandstone of the Bayfield Group in Wisconsin, and the Jacobsville Sandstone of Michigan. In this area (though not visible at this locality), the Fond du Lac unconformably overlies rocks of the Paleoproterozoic Thomson Formation, Ely’s Peak basalts, and the Duluth Complex (Morey, 1967). The sandstone consists of poorly sorted arkose to subarkose, containing clasts of quartz, chert, microcline, micas, and minor volcanic rocks; implying a source from both outside and inside of the Midcontinent rift. Depositional structures, primarily trough cross-bedding, indicate transport to the east. These sedimentary structures, and the presence of mud cracks and rain imprints, indicate fluvial deposition by streams that meandered across a broad alluvial plane (Morey and Ojakangas, 1982; see also papers in Ojakangas and others, 1997). NEXT: Return to northwest-bound Highway 210 and follow it for about 5 miles to entrance to Jay Cooke State Park. Turn in at main park building area on south side of 210. Page 163 �STOP 5-28, Location 5-28A Paleoproterozoic Thomson Formation Location 5-28A: T.48N., R.16W., Sec. 9 NW, SE; Jay Cooke State Park. Esko 7.5-minute quadrangle. UTM: 548,120/5,166,870N DESCRIPTION 5-28A: The walking bridge over the river south of the park buildings provides a vantage (depending on river level) to steeply dipping beds of graywacke, siltstone, and slate of the Thomson Formation. The Thomson is the upper stratigraphic unit of the Paleoproterozoic Animikie Group, presumably equivalent with the Virginia Formation discussed in stops 5-4, 5, and 6. Geochronologic data indicate that the Thomson Formation was deposited approximately 18701880 Ma (broadly inferred from Fralick and others, 2002), and was deformed during the Penokean orogeny (ca 1850 Ma). As shown in Figure 5.8, the Thomson is unconformably overlain by redbeds of the Mesoproterozoic Fond du Lac Formation, exposed discontinuously just to the east. The unconformity, marked by a basal quartz-pebble conglomerate, can be seen with some difficulty in the river bed at low-water levels near Oldenburg Point, and up Little Creek to the northeast. HISTORICAL PERSPECTIVE In the 1950’s, the Thomson Formation was considered by a number of authors (e.g., Grout and others, 1951) to be equivalent with the Knife Lake Group in northeastern Minnesota. The two rocks share many of the same structural and lithologic attributes. Most significantly, they both unconformably overlie Archean granitic rocks locally. For clarity, the Thomson is part of a sequence of strata that was known to unconformably overlie “Laurentian” granite. As compelling as this argument is, the Thomson is broadly equivalent to the Virginia Formation on the Mesabi range, with which continuity can now be established from geophysical and drill hole data, and the Rove Formation in the Gunflint district. Thus, the Thomson is now assigned as the uppermost unit of the Paleoproterozoic Animikie Group; and the Knife Lake is interpreted to have formed in part within a successor basin during latest Archean. NEXT: Return to Highway 210 and continue northwest approximately 1.6 miles to Thomson Dam. Page 164 �STOP 5-28, Location 5-28B Paleoproterozoic Thomson Formation T.48N., R.16W., sec. 5 SW SW; Thomson Dam. Cloquet 7.5-minute quadrangle. UTM: 545,610E/5,168,100N DESCRIPTION 5-28B: This is the type locality of the Thomson Formation, represented by approximately 650 feet of strata exposed between the dam north of Highway 210 and the RR bridge south of it. These exposures contain about equal proportions of graywacke, siltstone, and slate; metamorphosed to the greenschist facies. The formation contains abundant carbonate-rich concretions that locally are useful for delineating bedding in otherwise massive graywacke beds. Graywacke units range in thickness from 1 inch (2 cm) to 14 feet (4 m), and commonly display sedimentary structures indicative of turbidite deposition, included graded bedding, cross-bedding, sole marks, flute casts, and flame and ball structures (Morey and Ojakangas, 1970). Cross-bedding indicates flow to the south; though the trends of other structures imply more diverse and localized paleoslope directions. Structures in the Thomson Formation include gentle to open folds on varied scales, presumably related to deformation during the Penokean orogeny (Holst, 1984). The fold axes trend east, have vertical to steep south dips, and plunge gently east and west. A well developed axial-planar cleavage is present in the slaty beds, and concretions and mud chips are flattened in the plane of cleavage. The cleavage is deformed locally by kink bands. Quartz veins ranging in width from several cm to 3 meters are common in the formation. One of the largest, just north of the Highway 210 bridge, occupies an extensional fracture near the crest of a large anticline. Smaller veins are more contorted, and presumably were folded along with the adjacent rock. Several dikes of ophitic microgabbro ranging in width from a few inches to 200 feet (65 m) form a dike swarm that occupies northeast-trending joints (Fig. 5.8). The dikes are generally fine- to medium-grained and have chilled, fine-grained margins. Their precise age is unknown; however, their northeast trend and composition implies that they are related to the Mesoproterozoic Midcontinent rift. END OF TRIP REFERENCES Arth, J.G., and Hanson, G.N., 1975, Geochemistry and origin of the early Precambrian crust of northeastern Minnesota: Geochimica et Cosmochimica Acta 39:325-362. Biggs, D.L., ed., 1987, Centennial Field Guide Volume 3, Geological Society of America, North-Central Section; pages 47-73 describe various localities in Minnesota. Boerboom, T.J., and Zartman, R.E., 1993, Geology, geochemistry, and geochronology of the central Giants Range batholith, northeastern Minnesota: Canadian Journal of Earth Sciences 30:2510-2522. Page 165 �Borradaile, G.J., 1982, Tectonically deformed pillow lava as an indicator of bedding and way-up: Journal of Structural Geology, 4:469-479. Bowen, N.L., 1928, The evolution of igneous rocks: Princeton University Press, Princeton, 334 p. Broderick, T.M., 1935, Differentiation in lavas of the Michigan Keweenawan: Geological Society of America Bulletin 46:503-558. Butler, B.S., and Burbank, W.S., 1929, The copper deposits of Michigan: U.S. Geological Survey Professional Paper 144, 238 p. Cannon, W.F., 1992, The Midcontinent rift in the Lake Superior region with emphasis on its geodynamic evolution: Tectonophysics 213:41-48. Corfu, F., and Stott, G.M., 1998, Shebandowan greenstone belt, western Superior Province: U-Pb ages, tectonic implications, and correlations: Geological Society of America Bulletin 110:1467-1484. Davis, D.W., and Green, J.C., 1997, Geochronology of the North American Midcontinent rift in western Lake Superior and implications for its geodynamic evolution: Canadian Journal of Earth Sciences 34:476-488. Fralick, P., Davis, D.W., and Kissin, S.A., 2002, The age of the Gunflint Formation, Ontario, Canada: single zircon U-Pb age determinations from reworked volcanic ash: Canadian Journal of Earth Sciences 39:1085-1091. Goldich, S.S., Nier, A.O., Baadsgaard, H., Hoffman, J.H., and Krueger, H.W., 1961, The Precambrian geology and geochronology of Minnesota: Minnesota Geological Survey Bulletin 41, 193p. Green, J.C., 1977, Keweenawan plateau volcanism in the Lake Superior region, in Baragar, W.R.A.,ed., Volcanic regimes in Canada: Geological Association of Canada Special Paper 16, p. 407-422. Green, J.C., 1982, Geology of Keweenawan extrusive rocks, in Wold, R.J. & Hinze, W.J. (eds.) Geology and tectonics of the Lake Superior Basin. Geological Society of America Memoir 156, p. 47-56. Green, J.C., and Fitz, T.J.III., 1993, Extensive felsic lavas and rheoignimbrites in the Keweenawan Midcontinent Rift plateau volcanics, Minnesota: petrographic and field recognition: Journal of Volcanology and Geothermal Research 54:177-196. Green, J.C., and Miller, J.D., Jr., 2004, Geology of the Duluth Complex at Duluth as portrayed in new 7.5' geological maps. Abstracts and Proceedings of the 50th Institute on Lake Superior Geology. Green, J.C., and Schulz, K.J., 1982, Geologic map of the Ely quadrangle, St. Louis and Lake Counties, Minnesota: Minnesota Geological Survey Miscellaneous Map M-50, scale 1:24,000. Grout, F.F., 1918a, Internal structures of igneous rocks; their significance and origin with special reference to the Duluth Gabbro: Journal of Geology 26:439-458. Grout, F.F., 1918b, Two-phase convection in igneous magmas: Journal of Geology 26:481-499 Grout, F.F., 1918c, A type of igneous differentiation: Journal of Geology 26:626-58. Grout, F.F., 1937, Petrographic study of gold prospects of Minnesota: Economic Geology 37:56-68. Grout, F.F., Gruner, J.W., Schwartz, G.M., and Thiel, G.A., 1951, Precambrian stratigraphy of Minnesota: Geological Society of America Bulletin 62:1017-1078. Grout, F.F., and Schwartz, G.M, 1939, The geology of anorthosites of the Minnesota coast of Lake Superior: Minnesota Geological Survey Bulletin 28, 119 p. Gruner, J.W., 1930, Hydrothermal oxidation and leaching experiments; their bearing on the origin of Lake Superior hematite-limonite ores: Economic Geology 21:697-719, 837-867. Gruner, J.W., 1941, Structural geology of the Knife Lake area of northeastern Minnesota: Geological Society of America Bulletin 52:1577-1642. 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Page 166 �Hudleston, P.J., Schultz-Ela, D.D., and Southwick, D.L., 1988, Transpression in an Archean greenstone belt, northern Minnesota: Canadian Journal of Earth Sciences 25:1060-1068. Jirsa, M.A., 1984, Interflow sedimentary rocks in the Keweenawan North Shore Volcanic Group, northeastern Minnesota: MGS Report of Investigations 30, 20 p. Jirsa, M.A., 1990, Bedrock geologic map of northeastern Itasca County, Minnesota: Minnesota Geological Survey, Miscellaneous Map M-68, scale 1:48 000. Jirsa, M.A., 2000, The Midway sequence: A Timiskaming-type, pull-apart basin deposit in the western Wawa subprovince, Minnesota: Canadian Journal of Earth Sciences 37:1-15. Jirsa, M.A., and Boerboom, T.J., 2003, Bedrock geology of the Vermilion Lake 30’X60’ quadrangle, northeastern Minnesota: Minnesota Geological Survey, Miscellaneous Map M-141, scale 1:100,000. Jirsa, M.A., and Boerboom, T.J., 2003, Geology and mineralization of Archean bedrock in the Virginia horn: in Jirsa, M.A., and Morey, G.B., eds., Contributions to the geology of the Virginia horn area, St. Louis County, Minnesota: Minnesota Geological Survey Report of Investigations 53, p. 74-102. Jirsa, M.A., Boerboom, T.J., and McSwiggen, P.L., 1993, Geology of Archean greenstone-granite terrane in the Cook to Side Lake area: Field Trip 3 in Institute on Lake Superior Geology Proceedings, 39th Annual Meeting, Eveleth Minnesota, v. 39, Part 2, p. 97-128. Jirsa, M.A., Boerboom, T.J., and Morey, G.B., 1998, Bedrock geologic map of the Virginia Horn, Mesabi Iron Range, St. Louis County, Minnesota: Minnesota Geological Survey, Miscellaneous Map Series M-85, scale 1:48 000. Jirsa, M.A., and Boerboom, T.J., and Peterson, D.M., 2001, Bedrock Geologic Map of the Eagles Nest Quadrangle, St. Louis County, Minnesota: Minnesota Geological Survey Miscellaneous Map M-114, scale 1:24,000. Jirsa, M.A., and Morey, G.B., 1987, Jay Cooke State Park and Grandview areas: Evidence for a major Early Proterozoic-Middle Proterozoic unconformity in Minnesota: in Biggs, D.L., ed., Centennial Field Guide Volume 3, Geological Society of America, North-central Section; p.6772. Jirsa, M.A., Southwick, D.L., and Boerboom, T.J., 1992, Structural evolution of Archean rocks in the western Wawa subprovince, Minnesota: refolding of precleavage nappes during D2 transpression: Canadian Journal of Earth Sciences 29:2146-2155. Kuenen, P.H., and Migliorini, C., 1950, Turbidity currents as a cause of graded bedding: Journal of Geology, 58:91-127. Lawson, A.C., 1887, Geology of the Rainy Lake region: American Journal of Science 33:473-480. Lawson, A.C., 1893, The anorthosytes of the Minnesota coast of Lake Superior: Geological and Natural History Survey of Minnesota Bulletin 8, p. 1-23. 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Morey, G.B., and Ojakangas, R.W., 1970, Sedimentology of the Middle Precambrian Thomson Formation, east-central Minnesota: Minnesota Geological Survey Report of Investigations 13, 32 p. Morey, G.B., and Ojakangas, R.W., 1982, Keweenawan sedimentary rocks of eastern Minnesota and northwestern Wisconsin, in Wold, R.J., and Hinze, W.J., eds., Geology and tectonics of the Lake Superior basin: Geological Society of America Memoir 156, p. 135-146. Nicholson, S.W., Shirey, S.B., Schulz, K.J., and Green, J.C., 1997, Rift-wide correlation of 1.1 Ga Midcontinent rift system basalts: implications for multiple mantle sources during rift development; in Bornhorst, T.J., ed., Petrology and metallogeny of intraplate mafic and ultramafic magmatism: Canadian Journal of Earth Sciences 34:504-520. Ojakangas, R.W., 1966, Precambrian stratigraphy and structure of the Tower, Minnesota quadrangle (abs): Institute on Lake Superior Geology Proceedings, 12th Annual Meeting, Sault Ste. Marie, Michigan, Proceedings p. 17. Ojakangas, R.W., 1993, Pokegama Quartzite: in Institute on Lake Superior Geology Proceedings, 39th Annual Meeting, Eveleth Minnesota, v. 39, Part 2, p.19-21 and 46-48. Ojakangas, R.W., Dickas, A.B., and Green, J.C., 1997, Middle Proterozoic to Cambrian rifting, central north America: Geological Society of America Special Paper 312, 322 p. Ojakangas, R.W., Sims, P.K., and Hooper, P.R., 1978, Geologic map of the Tower quadrangle, St. Louis County, Minnesota: U.S. Geological Survey Geologic Quadrangle Map CQ-1457, scale 1:24,000. Owen, D.D., 1852, Report on a geological survey of Wisconsin, Iowa, and Minnesota: U.S. Department of the Treasury, Philadelphia, 638 p. Paces, J.B., and Miller, J.D., Jr., 1993, Precise U-Pb ages of Duluth Complex and related mafic intrusions, northeastern Minnesota: Geochonological insights to physical, petrogenetic, paleomagnetic and tectono-magmatic processes associated with the 1.1 Ga Midcontinent rift system: Journal of Geophysical Research 98:13,997-14,013. Peterson, D.M., Gallup, C., Jirsa, M.A., and Davis, D.W., 2001, Correlation of Archean assemblages across the U.S.-Canadian border: Phase I geochronology (abs): Institute on Lake Superior Geology, 47th Annual Meeting, Madison, Wisconsin, Proceedings v. 47, Part 1, p. 77-78. Peterson, D.M., and Jirsa, M.A., compilers, 1999, Bedrock geologic map and mineral exploration data, western Vermilion district, St. Louis and Lake Counties, northeastern Minnesota: Minnesota Geological Survey Miscellaneous Map M-98, scale 1:48,000. Peterson, D.M., and Patelke, R.L., 2003, National underground science and engineering laboratory (NUSEL): geological site investigation for the Soudan Mine, northeastern Minnesota: University of Minnesota Natural Resources Research Institute, Technical Report NRRI/TR-2003/29, 88p. Phinney, W.C., 1968, Anorthosite occurrences in Keweenawan rocks of northeastern Minnesota: in Isachsen, Y.W., ed., Origin of anorthosite and related rocks: Albany, New York. New York State Museum and Science Service, Memoir 18, p. 135-147. Roedder, E., 1979, Silicate liquid immiscibility in magmas. In Yoder, H.S., Jr., ed., The evolution of the igneous rocks. Princeton, New Jersey. Princeton University Press, p. 15-57. Schmitz, M.D., 1994, Origin and petrogenesis of the Early Proterozoic Kenora-Kabetogama mafic dike swarm: unpublished seniors thesis, Macalester College, 110 p. Schultz-Ela, D.D., and Hudleston, P.J., 1991, Strain in an Archean greenstone belt of Minnesota: Tectonophysics 190:233-268. Page 168 �Schulz, K.J., 1980, The magmatic evolution of the Vermilion greenstone belt, NE Minnesota: Precambrian Research 11:215-245. Schwartz, G.M., Goldich, S.S., Marsden, R.W., eds., 1956, Field Trip 1: Precambrian of northeastern Minnesota: GSA Guidebook Series, 235 p. Sims, P.K., 1972, History of geologic investigations: in Sims, P.K., and Morey, G.B., eds., Geology of Minnesota: A centennial volume: Minnesota Geological Survey, p. 21-26. Southwick, D.L., Boerboom, T.J., and Jirsa, M.A., 1998, Geologic setting and descriptive geochemistry of Archean supracrustal and hypabyssal rocks, Soudan-Bigfork area, northern Minnesota: Minnesota Geological Survey Report of Investigations 51, 69p. Southwick, D.L., Morey, G.B., and McSwiggen, P.L., 1988, Geologic map of the Penokean orogen, central and eastern Minnesota, and accompanying text: Minnesota Geological Survey Report of Investigations 37, 25p. Sutton, T.C., 1963, Geology of the Virginia horn area: Minneapolis, University of Minnesota, M.S. thesis, 97 p. Taylor, R. B., 1964, Geology of the Duluth Gabbro Complex near Duluth, Minnesota. Minnesota Geological Survey Bulletin 44, 63 p. Vervoort, J.D., and Green, J.C., 1997, Origin of evolved magmas in the Midcontinent rift system, northeast Minnesota: Nd-isotope evidence for melting of Archean crust: Canadian Journal of Earth Sciences 34:521-535. Wager, L.R., and Deer, W.A., 1939, Geological investigations in East Greenland, Part III. The petrology of the Skaergaard intrusion, Kangerdlugssuaq, East Greenland. Meddr. Gronland. 105, 352 p. Winchell, N.H., 1889, 18th Annual Report of the Minnesota Geological and Natural History Survey. Winchell, N.H., 1899, The Geology of Minnesota. Geological and Natural History Survey of Minnesota, Final Report v. 4, 629 p. Winchell, N.H., 1900, The Geology of Minnesota, Geological and Natural History Survey of Minnesota, Final Report v. 5, 1025 p. White, W.S., 1972, The base of the Upper Keweenawan, Michigan and Wisconsin: U.S. Geological Survey Bulletin 1354-F, 23 p. Page 169 �FIELD TRIP 6 GLACIAL AND POSTGLACIAL LANDSCAPE EVOLUTION IN THE GLACIAL LAKE AITKIN AND UPHAM BASIN, NORTHERN MINNESOTA Lisa Marlow; Phil Larson; Howard Mooers, Department of Geological Sciences, University of Minnesota - Duluth Glacial Lake Aitkin and Upham Road Log with numbered field trip stops, geographic markers and discussion sites: F: Farnum site, B: Baker Spider Creek site, and Hay Lake. Image from 30 meter Digital Elevation Model of Minnesota Page 170 �GLACIAL AND POSTGLACIAL LANDSCAPE EVOLUTION IN THE GLACIAL LAKE AITKIN AND UPHAM BASIN, NORTHERN MINNESOTA Lisa Marlow; Phil Larson; Howard Mooers, Department of Geological Sciences, University of Minnesota – Duluth INTRODUCTION Recent investigations into the glacial geology of northeastern Minnesota have considerably revised the glacial chronology. This field trip examines features (landforms and stratigraphy) of the Glacial Lakes Aitkin and Upham basins that record a complex sequence of events related to advance and retreat of the Laurentide Ice Sheet. Deglaciation and formation of glacial Lakes Aitkin and Upham were followed by drainage of the lakes and eolian activity on exposed lacustrine sediments. Glacial Lakes Aitkin and Upham occupied a basin bounded by the Giants Range to the north and moraines of the Superior and Rainy Lobes and St. Louis Sublobe to the south, east, and west; respectively. As the Rainy Lobe retreated during the Late Wisconsin, meltwater ponded in front of the ice forming proglacial Lakes Aitkin and Upham I. As the Rainy Lobe continued to retreat northeastward across the basin to a margin roughly coincident with the Giants Range, the St. Louis sublobe advanced into the basin (Fig. 6-1). Stagnation and melting of the St. Louis sublobe resulted in formation of Glacial Lakes Aitkin and Upham II (Hobbs 1983). Continued retreat of the Rainy Lobe northward from the Giants Range resulted in formation of Glacial Lakes Norwood and Koochiching, both of which drained southward into Aitkin and Upham II. The evolution of the lakes by a combination of downcutting of the outlets and isostatic rebound is recorded by a series of beaches, wave-cut scarps, and multiple outlets. Dune formation in the Glacial Lakes Aitkin and Upham II basin was strongly controlled by sediment availability. Dune clusters show a strong correlation with the presence of underlying fine-grained nearshore lacustrine sand. Dune formation was likely episodic, coinciding with periods of rapid lake level lowering and exposure of nearshore sands. Cessation of eolian activity resulted from more gradual stabilization of dunefields. Peaks in eolian activity are indicated at 9.8, 9.3 and 7.4 kyr BP (all dates Page 171 �given in C14 years BP) by the magnetic susceptibility record of Hay Lake, a small lake near the Glacial Lake Upham II shoreline (Figs. 6-2 and 6-3). These peaks in eolian activity may coincide with episodes of drainage of Upham II and Aitkin II. Figure 6-1. The Glacial Lake Aitkin and Upham basin. Beaches are noted by shaded polygons; dunes appear as black dots in the basin; boundaries and channels noted as black lines. Field trip stops will illustrate examples of the following: beach, dune, underflow fan, rhythmites, alluvial fan, Lake Upham sediments in Rainy lobe outwash and a wave-washed esker. Map is modified from Hobbs (1983). Page 172 �Figure 6-2. Location of Hay Lake. The lined region indicates the Lake Upham upland area; white polygons are dunes. (Vanduse 7.5’ USGS quadrangle) (gyttja) (marl) C14 Figure 6-3. Hay Lake sediment core (8.57m): 1. Lithology 2. Age-depth model 3. Magnetic susceptibility 4. Composition 5. Mass accumulation rate. Page 173 �The dunefields in the Glacial Lakes Aitkin and Upham II basin display similarity to other Quaternary eolian deposits throughout Minnesota and the Midwest (Figs. 6-4 and 6-5). Despite well over a century of research on Minnesota's glacial landscape, these paleodunefields have received relatively little attention. Although mentioned by Upham (1896), Winchell (1896), Hall and Sardeson (1898), Elftman (1898), Leverett and Sardeson (1919) and Leverett (1932), the first comprehensive work on Minnesota's eolian landscape was that of Cooper (1935, 1938). Figure 6-4. North American dune and loess distribution. (Brady and Weil, 2000) 96° 94° 92° 90° Conifer/ Hardwood 48° 4 Lake Aitkin and Upham basin 3 1 46° 2 Prairie Deciduous 44° 0 100km Figure 6-5. Location of sites in Minnesota associated with eolian sedimentation referenced in the text. 1) Hay Lake 2) Lake Ann 3) Elk Lake 4) Lake Winnibigoshish. Filled areas are prominent dune colonies. (Modified from Keen and Shane 1990) Page 174 �More recently, Grigal and others (1976) examined a dunefield exposed along the southeast shore of Lake Winnibigoshish (Fig. 6-5). They described several buried soil horizons, which yielded radiocarbon dates in the range of 7910 to at least 5040 yr BP suggesting episodic dune formation during the mid-Holocene The formation of these dunes was related to lake-level instability and episodic exposure of littoral areas to wind erosion during the mid-Holocene (Larson and Mooers 2003). The mid-Holocene climate in the upper Midwest was considerably warmer and drier than the modern climate (Webb et al. 1983; Bartlein et al. 1984; Dean et al. 1984; COHMAP 1988; Dean et al. 1996). The warmer, drier conditions resulted in an eastward shift of prairie ecotone (Fig. 6-5). Lower groundwater levels were accompanied by lake level lowering, particularly in groundwater-dominant closed-basin lakes and ponds, and increased fire frequency and vegetational stress locally resulted in landscape destabilization. Grigal and others (1976) speculated that the dunes of the Anoka Sand Plain may be midHolocene in age, an idea Keen and Shane (1990) explored in detail in their paleoenvironmental investigation of Ann Lake (Fig. 6-5). They concluded that there was a relatively continuous record of eolian activity throughout the mid-Holocene, a reversal of the ideas of earlier workers (Hall and Sardeson 1898; Cooper 1935). Keen and Shane’s (1990) whole-core magnetic susceptibility record from Ann Lake records increased silt and fine sand input to the lake from about 8.0 until 4.5 kyr BP with discrete peaks in clastic input at ca. 7.4, 5.8, and 4.9 kyr BP. However, it is difficult to distinguish whether this sediment was exported to the lake directly from active dunes on the shore, eroded from the shoreline due to lake level instability, or deposited suspended airborne sediment. Despite these ambiguities, they concluded that the increased clastic input to Ann Lake was due to landscape destabilization and widespread dune activity on the Anoka Sand Plain. The distinction between lake level lowering and landscape destabilization as triggers of eolian activity is subtle but important. Although the prairie ecotone shifted eastward during the mid-Holocene, this in itself did not create an environment conducive to widespread landscape destabilization. At present in the central Dakotas there are numerous locations with ample sediment availability, but no widespread dune formation because of the stabilizing vegetation of the prairie environment. Landscape destabilization and dune formation in the existing prairie Page 175 �environment occurs by excessive drying such as in the Nebraska Sand Hills (Winspear and Pye 1996). Viewed in this context, while Grigal and others (1976) obtained dates from paleosols buried by eolian events, the Keen and Shane (1990) and Dean (1997) magnetic susceptibility records may merely be a record of dryer, dustier conditions during the mid-Holocene rather than pervasive local eolian activity. Today the Glacial Lakes Aitkin and Upham basin is patchwork of small ‘islands’ occupied by upland vegetation formed on stabilized dunes. The ‘islands’ are interrupted by vast areas of peatland developed on the poorly drained, low-relief lakebed composed of fine-grained lacustrine sediment. Locally, scattered topographic highs are underlain by older glacial sediments predating formation of the lakes. STOP 6 – 1. Glacial Lake Duluth underflow fan. (NW¼ SW¼ Sec. 30, T48N, R15W, Carlton County, Frogner 7.5’ USGS quadrangle; 553728E, 5161950N, NAD83) This location preserves the record of several glacial events that affected the western Lake Superior region and provides insight into their relative chronologies. Here, red Glacial Lake Duluth clays are overlain by a subaqueous fan deposited by meltwater from Glacial Lake Aitkin and Upham II (Fig. 6-6). These in turn are overlain by Superior Lobe till deposited by of the Marquette advance. These relationships indicate meltwater drained from Glacial Lake Upham into Glacial Lake Duluth (Table 1) (Mooers and Lehr 1997; Clayton and Moran 1982; Wright 1972; Wright et al. 1973). During the last phase of Glacial Lakes Aitkin and Upham II, the two lakes were thought to have separated and drained through different outlets; Upham through the St. Louis River and Aitkin through the Mississippi River (Hobbs 1983). A digital elevation model (DEM) reconstruction correcting the basin for isostatic rebound confirms the separation of the two lakes (Marlow 2004). The Mississippi River outlet to Aitkin is a relatively narrow passage through collapsed ice-cored terrain. It is unlikely this underdeveloped outlet carried significant meltwater. Final drainage of Aitkin therefore occurred after significant meltwater contributions to the lake basins had ceased. Page 176 �Figure 6-6. Stop 6-1. Underflow fan at the mouth of the St. Louis River drainage in Glacial Lake Duluth basin. The sediments were deposited by meltwater from Glacial Lake Upham II. Page 177 �Table 6-1. The glacial chronology of northeastern Minnesota outlined resulted from a compilation of several resources (Mooers & Lehr, 1997; Larson (unpublished); Marlow, 2004; Bjork, 1990; Wright, 1972; Clayton & Moran, 1982; Hobbs, 1983; Fenton, 1983; Clayton, 1983; Lehr & Hobbs, 1992) Phase Moraine Lobe Glacial Lakes Other events C14 Date (kyr BP) drainage of Aitkin II Marquette Superior Vermilion Vermilion Big Rice Big Rice/ Wampus 9.9 Rainy Rainy Aitkin II Upham II Allen Rainy Alborn Culver St. Louis Split Rock Cloquet Superior ~11.7 12.0 St. Louis River outlet Inflow from Embarrass gap Us-Kab-WanKa/Chicken/ Hellwig/Birch/Spider outlets formation of Goodland esker Nickerson Nickerson Superior North of Nashwau k Duluth drainage of Upham II cessation of meltwater inflow to Aitkin and Upham II L. Duluth underflow fan Inflow from Prairie River ~13.0 Aitkin Upham I I Automba Sandy Lake Outing St. Croix St. Croix Rainy Rainy ~15.516 Rainy Page 178 �STOP 6 – 2. Hellwig Creek outlet and Glacial Lake Upham II basin overlook. (SE ¼ SE ¼ Sec. 34, T53N, R17W, St. Louis County, Canyon 7.5’ USGS quadrangle; 540174E, 5207618N, NAD83) This stop is near beaches and outlets that existed during the earliest phases of Glacial Lake Upham II, and provides a good overlook from the Upham shore into the basin (Fig. 6-7). Figure 6-7. Stop 6-2. Location of early outlets to Lake Upham; Triangle marks location of core taken by Baker (1965) containing marl. Circle indicates stop 2 site. Page 179 �Following stagnation of St. Louis Sublobe ice meltwater flowed through a combination of surface and englacial channels toward the ice margin then along the ice margin through a chain of small proglacial lakes. Among the earliest and highest outlets in the Upham basin from which these small lakes drained were the Us-Kab-Wan-Ka River (427 m; 1400’) and Chicken Creek (434 m; 1425’) channels. These channels drained to the southeast along the margin of the Superior Lobe eventually reaching the St. Croix River (Hobbs, 1983). Proglacial lakes and subglacial meltwater in the Aitkin basin drained southward through the Snake channel (381 m; 1250’) to the St. Croix River and perhaps southwest to the Mississippi River (378 m; 1240’) (Hobbs 1983). All of these outlets lie above the highest main beaches of Glacial Lakes Aitkin and Upham II, and the DEM correction for isostatic rebound indicates ice must have been present in the basin for them to function (Marlow 2004). Therefore they were likely associated with small proglacial lakes rather than the main stages of the lakes. After the St. Louis Sublobe advance, the margin of the Rainy Lobe retreated north of the Giants Range resulting in the ponding of water between the retreating ice and the Giants Range, forming Glacial Lake Norwood (Fig. 6-8) (Winchell 1901; Hobbs 1983). Glacial Lake Norwood drained south through the Embarrass Gap entering Glacial Lake Upham II at an elevation of 436 m (1450’) (Hobbs 1983). This was the first major meltwater inlet to Glacial Lakes Aitkin and Upham II. During this time a significant amount of stagnant ice remained in the basin, and it is possible that Aitkin and Upham were separated by stagnant ice along the Swan River Sill (Fig. 68). As the Rainy Lobe continued to retreat northward, Glacial Lake Norwood increased in extent. Downcutting in the Embarrass Gap lowered the level first to 436 m (1430’) and eventually to 427 m (1400’). This lower stage is known as Glacial Lake Koochiching (Nikiforoff 1947; Hobbs 1983; Lehr and Hobbs 1992; Leverett 1932). While Glacial Lake Norwood was in existence, the upper strandlines (411 to 421 m; 1350-1380’) in the extreme northeastern part of Glacial Lake Upham II formed. These levels of Upham likely correspond to outlets at Hellwig Creek (409 m; 1330’), Birch (406 m; 1320’), and Spider Creek (400 m; 1300’). A combination of isostatic rebound and downcutting eventually led Page 180 �to successive abandonment of the Hellwig Creek, Birch, and Spider Creek outlets and lake level drop. Baker (1965) reported a bulk radiocarbon date of 13,000±400 (W-1234) yr B.P from a sequence of lacustrine marl within the Spider Creek outlet (Fig. 6-7; and “s” in Fig. 6-8). The marl must post-date the cessation of drainage through the channel since marl formation requires shallow still water. Baker (1965) expressed concern that this date was too old due to possible contamination by lignite. However, this date is consistent with the other evidence presented in this guide. The Spider Creek date places the minimum age of Glacial Lakes Aitkin and Upham II, and therefore the maximum limit of the St. Louis Sublobe, prior to 13.0 kyr B.P. Figure 6-8. Significant features associated with the recession of the Rainy Lobe after the St. Louis sublobe advance. Glacial Lake Norwood (LN) extent is indicated by a dashed line. Page 181 �STOP 6 – 3. Wave-washed esker island (NE¼ NE¼ Sec. 1, T54N, R20W, St. Louis County, Toivola 7.5’ USGS quadrangle, 514367E, 5226982N, NAD83). There are many landforms within the Glacial Lakes Aitkin and Upham II basins that predate development of the lakes. This exposure is an example of an esker deposited during retreat of the Rainy Lobe that was later modified by waves. (Fig. 6-9). This esker and others like it became wave-washed “islands” once Glacial Lakes Aitkin and Upham I and II formed. Exposed at the base of the sequence are coarse gravels. The gravels contain abundant northeast-provenance material and locally derived mudstone and shale from the Paleoproterozoic Virginia Formation and perhaps younger Cretaceous strata. They were deposited by a beaded esker system during retreat of the Rainy Lobe. Overlying the gravels is a fine-grained till deposited by the St. Louis Sublobe. On top of the till is a sequence of nearshore sands and gravels. These presumably eroded from that portion of the esker rising above the level of Glacial Lake Upham II; the strandline formed at about 397 m (1200’) elevation. The uppermost portion of the sequence is a blanket of eolian sediment exported from the surrounding lake plain to the upland after final drainage of Upham. Figure 6-9. Stop 6-3. Wave-washed esker island in Glacial Lake Upham II. Page 182 �STOP 6 – 4. Rainy Lobe collapsed outwash, Glacial Lake Upham I sediments, and St. Louis Sublobe till (NE¼ SE¼ Sec. 15, T57N, R19W, St. Louis County, Kirk 7.5’ USGS quadrangle; 520373E, 5251907N, NAD83) The Glacial Lakes Aitkin and Upham basins were occupied by glacial lakes on two separate occasions during the Late Wisconsin glaciation. The retreat of the Rainy and Superior Lobes from their maximum positions formed a series of ice-cored recessional moraines bordering the lake basins to the south and west leading to ponding of water and formation of Glacial Lakes Aitkin and Upham I (Wright 1972; Hobbs 1983; Lehr and Hobbs 1992). The initial retreat of the Rainy Lobe from the Mille Lacs and Outing moraines (Mooers 1988) led to the formation of Aitkin I (Fig. 6-10). Continued retreat of the Rainy Lobe from the Sandy Lake moraine led to the formation of Upham I. Although the exact time of formation of Aitkin and Upham I is not known, it occurred after the Rainy Lobe retreated from the St. Croix moraine about 15.5 kyr B.P. (Clayton and Moran 1982; Mooers and Lehr 1997), and before the St. Louis Sublobe advanced into the Aitkin and Upham basins from the northwest. Exposed at the base of the sequence are steeply south-dipping foreset beds of a subaqueously deposited fan. These sediments are Rainy Lobe provenance, deposited along the southern margin of stagnant ice lying on the southern slope of the Giant’s Range, an area now characterized by collapsed ice-cored topography. The upper portion of the sequence is a St. Louis Sublobe till. Between the fan sediments and till are a number of elongate slabs of fine-grained lacustrine sediment derived from Glacial Lake Upham I. This lacustrine sediment was eroded from deeper water and thrust onto the fan during the advance of the St. Louis Sublobe (Figs. 6-11 and 6-12). The relationships visible in this exposure indicate that the St. Louis Sublobe advanced while a substantial amount of Rainy Lobe ice was still present south of the Giant’s Range. Page 183 �Figure 6-10. Prominent moraines in the Glacial Lakes Aitkin and Upham basin with some modern features included. Modified from Mooers (1988) and Lehr and Hobbs (1992). Figure 6-11. Subaqueously deposited Rainy Lobe outwash exposed in a gravel pit near Cherry, MN. Page 184 �Figure 6-12. St. Louis sublobe till containing Glacial Lake Upham I sediment. STOP 6 – 5. Eolian dunes. (SW¼ SW ¼ Sec. 31, T56N, R20W, St. Louis County, Riley 7.5’ USGS quadrangle, 504626E, 5237098N, NAD83) Exposed in the sand pit is a small (<2 m) dune composed of characteristic 4-φ sand (62.5 microns or 230 mesh). Most of the sand exposed in the pit is massive and structureless. However, relict cross bedding can be observed in small patches near the base of the sequence. Primary sedimentary structures in the upper portion of the exposure have been obliterated by bio and crioturbation. Clusters of eolian dunes are widely distributed throughout the Glacial Lakes Aitkin and Upham basins. They formed as Glacial Lakes Aitkin and Upham II incrementally drained, exposing areas of littoral sediment to wind erosion. Dune heights range from 1 to 5 meters and are composed of a characteristic fine to very fine grained sand (Marlow 2004). They occur as parabolic or longitudinal dunes, but are commonly distorted in morphology as a result of forming in a variable hydrologic environment (Fig. 6-13) (Bagnold 1941) There are a large number of longitudinal dunes and elongate clusters of dunes oriented in a NW-SE direction, suggesting they formed under prevailing NW winds (Fig. 14). Bagnold’s (1941) description of dunes indicates that they “tend to occur in belts or chains, whose direction coincides with that of the resultant long-period Page 185 �sand vector Q”, with Q being sand flow because of the sum of the strong and gentle wind directions, and the width of the belt at right angles to Q.” Figure 6-13. Distorted dunes in the northern end of Lake Aitkin basin showing a combination of crescentic and longitudinal dunes (Jacobson and Split Hand 7.5 minute USGS quadrangles). Page 186 �Figure 6-14. Trend in dune clusters indicating a NW-SE wind direction. Elongate polygons are beaches. Circles indicate stops 8, 9, and 10 sites. STOP 6 – 6. Glacial Lake Upham II Shoreline. (SE¼ SE¼ Sec. 33, T56N, R21W, St. Louis County, Silica 7.5’ USGS quadrangle, 499595E, 5236726N, NAD83) After the time of upper beach formation, Lake Upham experienced a drop in water level documented at Townline beach (411 m; 1350’) through the use of Ground Penetrating Radar (Fig. 6-15). The GPR results are interpreted as a down stepping of shoreline deposits (Fig. 6-16). The progradation of the bedform resulted in a constructional shoreline and indicates regression of the lake. The regression is an example of Forced Regression as discussed by Posamentier and Allen (1999). Forced regression takes place when there is a relative sea-level fall that progressively exposes the sea (or lake) floor, thereby causing the shoreline to migrate seaward (Posamentier and Allen 1999). Page 187 �Figure 6-15. Shoreline of Glacial Lake Upham II along Townline Road south of Hibbing. Shoreline indicated by black dotted line. Heavy solid line indicates where GPR data was collected (Silica & Riley 7.5 ‘ USGS quadrangle). Figure 6-16. Ground Penetrating Radar profile of Glacial Lake Upham II shoreline. Vertical data represents ~9 meter; horizontal data ~121 meters. (Data processing courtesy of Nigel Wattrus at Large Lakes Observatory, University of Minnesota-Duluth) Page 188 �STOP 6 – 7. Goodland Esker. (SE¼ NE¼ Sec. 9, T55N, R23W, Itasca County, Calumet 7.5’ USGS quadrangle, 479736E, 5234496N, NAD83) This stop is a gravel pit exposure in the Goodland esker, one of the most prominent glacial landforms in Itasca County. The location of the esker and details of its formation place important constraints on the timing of the St. Louis Sublobe advance and deposition of the Alborn drift (Fig. 6-17). The morphology of the esker system is best described by the model of Shreve (1985). The proximal (with respect to the Giants Range) segment is an ~600 m wide, 10 km long channel incised into bedrock and older drift (tunnel valley), occupied by a multicrested esker. The medial segment consists of a single broad-crested esker segment deposited in a 10 km long channel incised into the overlying ice. The distal component of the esker system is a supraglacial fan complex. The base of the subglacial channel drops from 428 m at the crest of the Giant’s Range to <400 m at a point 6 km downstream, then rising to 409 m over the next 4 km. Downstream of this point, the elevation of the top of the broad-crested esker rises 19 m over 10 km, from 434 to 455 m at the apex of the distal fan. The transition from a multi-crested to broad-crested esker is apparently triggered by an increase in the adverse slope up which the subglacial channel flowed. Multi-crested eskers form in areas of moderate upgradient flow as the channel tends to migrate laterally, rather than upward, in the ice, while broad-crested eskers form in areas of steeper upgradient flow due to freezing of the tunnel walls, a process favoring low, wide tunnel geometries (Shreve 1985). Lithologies in the multi-crested segment esker are dominantly Archean granitics and greenstones transported from north of the Giant’s Range. The broad-crested segment has a markedly different lithologic assemblage than the multi-crested segment. In addition to Archean lithologies, an abundance of Paleoproterozoic Animikie Basin lithologies are present including quartzite, sulfidic mudstones, iron formation, and pisolitic lateritic iron formation. The abundance of locally-derived Animikean lithologies indicates material in the broad-crested segment was deposited as incision of the Nchannel was taking place upstream. The broad-crested segment is therefore older than the multi-crested segment. The wide range of mean sizes of the various Animikean Page 189 �lithologies attests to the strong control of primary rock characteristics on particle size. Note in particular the abundance of Pokegama quartzite as large (~1 m) boulders and its paucity in smaller size fractions. Deposition of the distal fan occurred throughout the period the esker system was active. The initial phase was characterized by deposition of a supraglacial fan on stagnant ice. Fan deposits are identifiable up to 10 km from the fan apex, and cover in excess of 100 km2. The maximum elevation on the fan complex is about 477 m, indicating at least 20 m of ice was present above the outlet of the englacial channel at the fan apex. During later stages of the esker system, underlying stagnant ice melted collapsing the earliest deposited fan sediment. The final phase of fan formation was characterized by incision of the collapsed fan head down to about 450 m. The subglacial drainage system that deposited the esker was probably short-lived. It could not have formed before the St. Louis Sublobe occupied the area around Grand Rapids, blocking the natural southwesterly flow of meltwater from the watershed of the present-day Prairie River. Similarly, it could not have persisted after St. Louis Sublobe ice wasted away and the Prairie River began flowing into Glacial Lake Aitkin II. Consequently, it may have been active a few hundred years at most. Despite its short duration, the large size of the esker system – it is one of the largest in Minnesota – attests to an enormous discharge of meltwater responsible for its formation. Meltwater was gathered from an interlobate zone that existed to the north of the Giant’s Range between the St. Louis Sublobe and the Rainy Lobe. This interlobate area may have drained well in excess of 1000 km2 of the ice sheet. The elevation difference between the fan apex (477 m) and the surrounding (subglacial) landscape (400 m) indicate that a continuous cover of Rainy Lobe ice at least 75 m thick was present south of the Giant’s Range at the time of esker formation and advance of the St. Louis Sublobe. This argues strongly against the postulated ice-free zone between the northern margin of the St. Louis Sublobe and the southern margin of the Rainy Lobe. Previous workers have postulated a relatively late advance for the St. Louis Sublobe (ca. 11.7 kyr BP), correlating it with the Vermilion Phase (ca. 12.0 kyr BP), or an even later phase, of the Rainy Lobe (Wright 1972; Hobbs 1983). However, the presence of active Rainy Lobe ice just north of the Giant’s Range at the time of the Page 190 �advance of the St. Louis Sublobe and esker formation provides further evidence that the St. Louis Sublobe advanced at a significantly earlier date. Figure 6-17. Main features of the Goodland esker system. (Image from 30 m DEM of MN) Page 191 �STOP 6 – 8. Prairie River underflow fan in Glacial Lake Aitkin II. (NE¼ NE¼ Sec. 35, T53N, R24W, Itasca County, Jacobson 7.5’ USGS quadrangle, 473831E, 5209702N, NAD83) Glacial Lakes Aitkin and Upham II had two successive major meltwater inlets, the Embarrass Gap and the Prairie River. Inflow of the Prairie River into Aitkin II resulted in deposition of a large underflow fan extending 50 km from its apex (Hobbs 1983). The fan was later incised by the Mississippi River. The cutbank at this stop exposes ~9 m of sandy underflow fan sediments overlying a lacustrine clay (Fig. 6-18). Visible within the underflow sediments are several Bouma sequences. Outflow from Glacial Lake Koochiching into Glacial Lake Upham II through the Embarrass Gap ceased when a lower outlet opened north of Grand Rapids because of collapse of stagnant ice-cored terrain. Meltwater then flowed down the Prairie River into Glacial Lake Aitkin II, lowering the level of Koochiching from 427 to 411 m (1400’ to 1350’) (Hobbs 1983) The Prairie River entered Glacial Lake Aitkin II at an elevation of 396 m (1300’) (Fig. 6-1). Although it is not known exactly when the Embarrass Gap was abandoned, it must have occurred prior to a 10.2 kyr B.P. transition from predominantly clastic to organic lake sedimentation in Sabin Lake located in the Embarrass Gap (Björk 1988; Lehr and Hobbs 1992). Fenton (1983) suggests that the Prairie River outlet was initiated between 12.3 and 10.8 kyr B.P. based on the chronology of the Lake Agassiz basin to the west. Clayton (1983) suggests 11.5 kyr B.P. for the inception of the Prairie River outlet. The Prairie River inlet was abandoned once Glacial Lake Koochiching began to flow into Glacial Lake Climax. However, Glacial Lakes Aitkin and Upham II persisted after abandonment on the last meltwater inlet. Upham finally drained as the St. Louis River outlet was incised to its modern level. Hobbs (1983) indicates that water could have still been flowing into Aitkin after drainage of Upham by way of the Mississippi River, which has a prominent terrace at 389 m (1275’). Farnham and others (1964) obtained a date of 11,635 yr BP on a paleosol in the southwestern part of the Glacial Lake Aitkin II basin. This paleosol is overlain by a thin Page 192 �marl and 3 feet of clay, indicating Aitkin was in existence well after this time. A radiocarbon date of 10,000 yr BP was obtained from a marl from the Ball Bluff quadrangle in the northeastern part of the Aitkin basin (Hobbs 1983) suggests the lake persisted at least until this time. There are two alternative explanations explaining how the southwestern portion of the Glacial Lake Aitkin II basin was successively drained and re-inundated. The close similarity between the presumed initiation of the Prairie River inlet at 11.5 kyr BP (Clayton 1983) and the re-inundation of the southwestern part of the Glacial Lake Aitkin II basin at 11,635 yr BP suggests a causal relationship. Glacial Lake Aitkin II may have assumed a lower, stable level by ca. 11.6 kyr BP. The relatively rapid lowering of Glacial Lake Koochiching would have sent a surge of meltwater into the lake, resulting in a rise in lake level even if only temporarily. The lacustrine sediment overlying the Farnham (1964) paleosol was thus derived from the Prairie River inlet. The alternate explanation is that much of the Aitkin basin was drained through Glacial Lake Upham II by downcutting of the St. Louis River outlet. The Swan River Sill controlled the water level in the remaining lake. As isostatic rebound of the basin progressed, the sill on the northeastern side of the basin rose at a higher rate than the southwestern portion of the basin. Lake level transgression resulted in re-inundation of lake bottom exposed by drainage of Upham. Page 193 �Figure 6-18. Stop 6-8. Exposure of the Prairie River underflow fan at a Mississippi River cutbank. STOP 6 – 9. Rhythmite in Glacial Lake Aitkin II. (SW¼ NW¼ Sec. 4, T52N, R23W, Aitkin County, Jacobson 7.5’ USGS quadrangle, 479288E, 5207689N, NAD83) A rhythmite is overlain by cross-bedded sands, which is then overlain by underflow sediments. This is an interesting site that may document a dramatic inception of the Prairie River inlet into a basin that was previously depositing clays. Page 194 �STOP 6 – 10. Eolian dunes in Glacial Lake Upham II basin. (NW¼ NE¼ Sec. 18, T 52 N R 22 W, Aitkin County, Vanduse Lake 7.5’ USGS quadrangle, 486857E, 5204509N, NAD83) Exposed at this site are eolian sand dunes overlying lacustrine clay of Glacial Lake Upham II (Fig 6-19). Dunes in the Glacial Lakes Aitkin and Upham basins are most densely concentrated near the inlet of the Prairie River to the Aitkin basin and east of the Swan River Sill in the Upham basin (Fig. 6-14). The 4-φ mean grain size of the dunes sampled in these areas in the basin match that of sediments from the underflow fan sediments seen at Stop 8. These sediments have been mapped in the Aitkin and Itasca Soil Surveys (Nyberg 1987, 1999) as the Zimmerman, Cowhorn, and Wawina soil series, all composed of fine to very fine grained sands of lacustrine origin. From the inception of Glacial Lakes Aitkin and Upham II net flow of water was from Aitkin to Upham. The initiation of the Prairie River inlet greatly increased this discharge. The flow of water from Aitkin to Upham resulted in formation the Ball Bluff Spit (Marlow, 2004) extending eastward from the Swan River Sill (Fig. 6-19). The dense dune clusters east of the Swan River Sill in the Upham basin formed from sediment transported from the underflow fan. Page 195 �Figure 6-19. Location of the Ball Bluff spit located within the dashed line. Circle at stop 10 indicates where lacustrine clay is overlain by 1 m. of sand derived from the underflow fan. Triangle indicates site where lake clay is exposed at the surface. REFERENCES Arbogast, A.F., Wintle, A.G., Packman, S.C. 2001. Widespread middle Holocene dune formation in the eastern Upper Peninsula of Michigan and the relationship to climate and outlet-controlled lake level. Geology 30, 55-58. Bagnold, R.A. 1941. The Physics of Blown Sand and Desert Dunes. William Morrow & Company, 265 p. Baker, R.G. 1965. Late-glacial pollen and plant macrofossils from Spider Creek, So. St. Louis County, MN. Geological Society of America Bulletin 45, 645-665. Ballantine, J.W. 1991. Late-Wisconsin Stratigraphy and Glacial History of Southwestern St. Louis County, Minnesota. Unpublished Masters Thesis, University of Minnesota Duluth. 154 p. Bartlein, P.J., Webb, T., and Fleri, E. 1984. Holocene climatic change in the northern Midwest: Pollen derived estimates. Quaternary Research 22, 361-374 Björk, S. 1990. Late-Wisconsinan history North of Giants Range, northern Minnesota, inferred from complex stratigraphy. Quaternary Research 33, 18-36. Brady, N.C. and Weil, R.R., 2000, Elements of the Nature and Properties of Soils. 12th Edition, Prentice Hall, New Jersey. P.558. Page 196 �Clayton, L. 1983. Chronology of Lake Agassiz drainage to Lake Superior, in Teller, J.T., and Clayton, Lee, eds., Glacial Lake Agassiz: Geological Association of Canada Special Paper 26, 291-307. Clayton, L. and Moran, S.R. 1982. Chronology of late Wisconsinan glaciation in middle North America: Quaternary Science Reviews 1, 55-82. COHMAP Members. 1988. Climatic changes of the last 18,000 years: Observations and model simulations. Science 241,1043-1052. Cooper, W.S. 1935. The history of the Upper Mississippi River in late-Wisconsinan and post-glacial time. Minnesota Geological Survey Bulletin 26. Cooper, W.S., 1938, Ancient dunes of the upper Mississippi Valley as possible climatic indicators. American Meteorological Society Bulletin, v. 19, p. 193-204. Dean, W.E. 1997. Rates, timing, and cyclity of Holocene eolian activity in north-central United States: Evidence from varved lake sediments. Geology 25, 331-334. Dean, W.E. 1999. The carbon cycle and biogeochemical dynamics in lake sediments. Journal of Paleolimnology 21, 375-393. Dean, W.E., Ahlbrandt, T.S., Anderson, R.Y., Bradbury, J.P., 1996, Regional aridity in North America during the middle Holocene. The Holocene 6, 145-155. Dean, W. E., Bradbury, J.P., Anderson, R.Y., Barnosky, C.W. 1984. The variability of Holocene climate change: Evidence from varved lake sediments. Science 226, 1191-1194. Elftman,, A.H. 1898. The Geology of the Keweenawan area in northeastern Minnesota. The American Geologist 18, 225-226. Farnham, R.S., McAndrews, J.H., and Wright, H.E. 1964. A Late-Wisconsin buried soil near Aitkin, Minnesota, and its paleobotanical setting. American Journal of Science 262, 393-412. Farrand, W.R. and Drexler. 1985. Late-Wisconsinan and Holocene History of the Lake Superior Basin. in Karrow, Quaternary evolution of the Great Lakes. Geological Association of Canada Special Paper 30, 17-32. Fenton, M.M.(Moran, S.R.; Teller, J.T.; Clayton, Lee). 1983. Quaternary stratigraphy and history in the southern part of the Lake Agassiz basin, in Teller, J.T., and Clayton, Lee, eds., Glacial Lake Agassiz. Geological Association of Canada Special Paper 26, 49-74. Grigal, D.F., Severson, R.C., Golz, G.E. 1976. Evidence of eolian activity in north-central Minnesota 8,000 to 5,000 yr. ago. Geological Society of America Bulletin 87, 1251-1254. Hall and Sardeson, 1898, Eolian deposits of Eastern Minnesota. Bulletin of the Geological Society of America, v. 10, p. 349-360. Hobbs, H.C. 1983. Drainage relationships of Glacial Lakes Aitkin and Upham and early Lake Agassiz in northeastern Minnesota. In Teller, J.T. and Clayton, L., eds., Glacial Lake Agassiz. Geological Association of Canada Special Paper 26, 245-259. Keen, K.L., Shane, L.C.K, 1990, A continuous record of Holocene eolian activity and vegetation change at Lake Ann, east-central Minnesota. Geological Society of America Bulletin 102, 1646-1657. Larson, P.C., and Mooers, H.D. 2003. Holocene drainage evolution of the Mississippi Headwaters, Minnesota: implications for mid-Holocene eolian activity in the North American midcontinent. GSA Abstracts with Programs 35 (7). Lehr, J.D. and Hobbs, H. 1992. Field Trip Guidebook for the Glacial Geology of the Laurentian Divide Area, St. Louis and Lake Counties, Minnesota. Minnesota Geological Survey Guidebook Series 18. Leverett, F., with contributions by Sardeson, F.W. 1932. Quaternary Geology of Minnesota and Parts of Adjacent States. United States Geological Survey Professional Paper 161. Leverett, F. and Sardeson, F.W. 1919. Surface formations and agricultural conditions of north-eastern Minnesota. Minnesota Geological Survey Bulletin 13. Marlow, L. 2004. Late Glacial and Early Holocene history of the Glacial Lakes Aitkin and Upham basin, NorthCentral Minnesota: Implications for the timing of post-glacial eolian activity. Unpublished Masters Thesis, University of Minnesota Duluth, 82 p. Mooers, H.D. and Lehr, J.D. 1997. Terrestrial record of Laurentide ice sheet reorganization during Heinrich events. Geology 25, 987-990. Mooers, H.D. 1988. Quaternary history and ice dynamics of the late Wisconsin Rainy and Superior lobes, central Minnesota. Unpublished Doctoral Thesis, University of Minnesota, 200 p. Nikiforoff, C. 1947. The life history of Lake Agassiz: alternative interpretation. American Journal of Science 245, 205-239. Page 197 �Nyberg, P.R. 1985. Soil Survey of Itasca County, Minnesota. United States Department of Agriculture Soil Conservation Service, 197 p. Nyberg, P.R. 1999. Soil Survey of Aitkin County, Minnesota. United States Department of Agriculture Natural Resource Conservation Service. 163 p. Ojakangas, R.W. and Matsch, C.L., 1982, Minnesota’s Geology. University of Minnesota Press, 255 p. Posamentier, H.W. and Allen, G.P. 1999. Siliciclastic Sequence Stratigraphy-Concepts and Applications. SEPM Concepts in Sedimentology and Paleontology 7. Seppala, M. 1993. Climbing and falling sand dunes in Finnish Lapland. in Pye, K., ed., The Dynamics and Environmental Context of Aeolian Sedimentary Systems. Geological Society London. Shreve, R.L. 1985. Esker characteristics in terms of glacier physics, Katahdin esker system, Maine. Geological Society of America Bulletin 96, 639-646. Upham, W. 1896-1899. The geology of Aitkin County. in Minnesota Geological and Natural History Survey Final Report: The Geology of Minnesota 4, 25-54. Webb, T. III, Cushing, E.J., and Wright Jr., H.E., 1983, Holocene changes in the vegetation of the Midwest. In Wright Jr., H.E., ed., Late-Quaternary Environments of the United States: the Holocene, 109-127. Winchell, N.W. 1901. Glacial Lakes of Minnesota. Geological Society of America Bulletin 12, 109-128. Winchell, N.W. 1896-1899. The geology of the northern part of St. Louis County. in Minnesota Geological and Natural History Survey Final Report: The Geology of Minnesota 4, 222-265. Winspear, N.R. and Pye, K. 1996. Textural, geochemical and mineralogical evidence for the sources of Aeolian sand in central and southwestern Nebraska, U.S.A. Sedimentary Geology 101, 85-98. Wright, H.E. 1972. Quaternary history of Minnesota. in Sims, P.K., and Morey, G.B., eds., Geology of Minnesota: A Centennial Volume. Minnesota Geological Survey. Wright, H.E., Matsch, C.L. and Cushing, E.J. 1973. Superior and Des Moines Lobes. in Black, R.F., Goldthwait, R,P., and Willman, H.B., eds., The Wisconsinan Stage. Geological Society of America Memoir 136, 153-185. Road Log MILES Begin in Duluth, MN. 0-3 Interstate 35 south to Grand Avenue/MN 23 exit. 3-22 14 miles to County 4. East (left) 2 miles to railroad crossing. Stop 1 Glacial Lake Duluth underflow fan. 22-39 County 4 west ~12 miles to Interstate 35. 39-49 North on Interstate 35 ~12miles to MN 33. 49-69 North on MN 33 through Cloquet for ~18 miles to US 53. 69-73 North on US 53 for ~4 miles. Cloquet River Hellwig Creek Stop 2 Hellwig Creek outlet and Glacial Lake Upham II basin overlook. 73-84 North on US 53 for ~12 miles to County 52 (Arkola Road) at Cotton, MN. 84-99 West on County 52 for ~16 miles to County 5. 99-101 North on County 5 for ~2 miles to gravel pit on left. Stop 3 Wave-washed esker island (Toivola, MN). 101-115 North on County 5 from previous stop for ~13 miles to MN 37. 115-119 East on MN 37 for ~3.5 miles to County 25. 119-120 North on County 25 for ~1.5 miles to the gravel pit on the left. Stop 4 Rainy Lobe collapsed outwash, Glacial Lake Upham I sediments, and St. Louis Sublobe till (Cherry, MN). 120-121 South on County 25 to MN 37. 121-135 West on MN 37 for ~9.5 miles to County 57 (1st Avenue). Page 198 �135-140 South on County 57 for ~8 miles. Stop just before County 442 (Townline Road South). Stop 5 Eolian dunes. 140-140 South on County 57 to County 442 (Townline Road South). 140-144 West on County 442 for ~3 miles. Stop at gravel pit access road on north side. Stop 6 Glacial Lake Upham II Shoreline. 144-145 West on County 442 (Townline Road South) to MN 73. 145-145 North on MN 73 for ~0.5 miles to County 16. 145-156 West on County 16 for ~11 miles to County 20. 156-164 West on County 20 for 0.25 miles to MN 65. 164-168 North on MN 65 for ~8.5 miles to County 12. 168-169 West on County 12 for ~3.5 miles to County 70. 169-170 South on County 70 for ~1 mile to County 434. 170-170 South on County 434 for ~1 mile to gravel pit on right Stop 7 Goodland Esker. 170-175 Continue south on County 434 for ~5 miles to County 10. 175-176 West on County 10 for ~1.5 miles to County 71. 176-181 South on County 71 for ~4 miles to US 2. 181-181 Cross US 2 and continue for ~ 0.25 miles to County 441 (Bluebird Lane) 181-184 West on County 441 for ~2.5 miles to County 3 (River Road). 184-197 South on County 3 for ~2.5 miles to cutbank along Mississippi River on left. Stop 8 Prairie River Underflow fan in Glacial Lake Aitkin II. 197-200 Continue southbound on County 3 (River Road) for ~2 miles to Mississippi River Boat Landing Road on the left Stop 9 Rhythmite in Glacial Lake Aitkin II. 200-201 Return to County 3. 201-202 South on County 3 to MN 200. 202-203 East on MN 200 for 1.5 miles to MN 65. 203-203 North on MN 65 for 0.5 miles to MN 200. 203-208 East on MN 200 for ~4 miles to 154th Avenue. 208-208 North on 154th Avenue. Stop 10 Eolian dunes in Glacial Lake Upham II basin. To return to Duluth: 208-208 Return to MN 200. 208-213 East on MN 200 to US 2. 213-262 East on US 2 to Interstate 35. North on Interstate 35 to start point. Page 199 �FIELD TRIP 7 ECONOMIC GEOLOGY OF ARCHEAN GOLD OCCURRENCES IN THE VERMILION DISTRICT, NORTHEAST OF SOUDAN, MINNESOTA By Dean M. Peterson and Richard L. Patelke Natural Resources Research Institute, University of Minnesota Duluth INTRODUCTION A widespread area of gold mineralization occurs in numerous prospects east of Lake Vermilion, within the Vermilion greenstone belt of northeastern Minnesota. The mineralization occurs in rocks of the Neoarchean (~2.7 Ga) Bass Lake sequence (Peterson and Jirsa, 1999a) of the Wawa subprovince of the Canadian Shield. This zone of abundant gold mineralization is bounded to the south by the Mud Creek shear zone and to the north by the Vermilion fault (Fig. 7-1). The main access to these prospects is along the Mud Creek road (St. Louis County 38). A brief period of mineral exploration for lode-gold deposits in this immediate area of the Vermilion district occurred in the mid 1980s to early 1990s. These programs typically consisted of grid-based geologic mapping, bedrock sampling, ground geophysics, and the completion of soil geochemical surveys. Conversations with many of the people involved in gold exploration programs in the immediate field trip area (centered on Section 6, Township 62 North, Range 14 West), and compilation of all exploration data from the district as a whole (data from the terminated lease files of the Minnesota DNR), has led to the conclusion that interpretation of linear structural elements exposed in outcrops were not used in designing exploratory drilling plans in the field trip area. Therefore, many of the prospects discovered as a result of these exploration programs remain untested by drilling. The authors recently completed a project (Peterson and Patelke, 2004) consisting of detailed geologic and structural mapping within many of the known gold prospects in the field trip area, and will highlight some of the insights generated as a result of this work during the course of this one day field trip. This recent work consisted of detailed outcrop mapping (at scales ranging from 1:1,000 to 1:3,000) that was focused on structural (i.e. shear zones, lineations, intersecting foliations and small-scale folds), geological (i.e. contact relationships, competence contrasts), geochemical (i.e. gold assays, trace element characteristics), and alteration (Fe-bearing carbonate, sericite, pyrite, silicificaton) features within and around areas of gold mineralized exposures. Based on detailed mapping of features described above, the project's goal was to try to determine the location and orientation at depth of gold-rich mineralized zones exposed in outcrops. The mapped geological features were incorporated into the data compiled and described by Peterson (2001), and are available online as a 1:12,000 scale geological map, as well as ArcView GIS data files at http://www.nrri.umn.edu/egg/. Page 200 �Figure 7-1. Location, simplified geology, lode gold prospects, and field trip #7 stops. LODE GOLD ORE DEPOSIT MODEL The brief description of Archean lode-gold deposits that follows is presented as both a basic reference and also to highlight the important features of the model that will be seen during the field trip. Archean lode-gold deposits are one category of ore deposit classified as mesothermal lode-gold deposits (Hodgson, 1993). This deposit type has also been called orogenic gold (Groves et al., 2000), greenstone gold (Robert et al., 1991), Archean lode-gold, mesothermal gold-quartz veins, shear-hosted gold, low-sulfide gold-quartz veins (Berger, 1986b), lode-gold, Mother Lode veins (Bohlke and Kistler, 1986), and iron formation-hosted gold deposits (Berger, 1986a; McMillan, 1996; Rye and Rye, 1974; Fripp, 1976; Kerswill, 1993; Thorpe and Franklin, 1984; and Vielreicher et al., 1994). Whatever the name, they are a widespread group of epigenetic ore deposits that have formed in similar settings throughout geologic time. In general, the deposits form during Page 201 �compressional or transpressional deformation at convergent plate margins in accretionary or collisional orogens (Fig.7-2). They form over a large crustal-depth range (2 to 20 km) from deep-seated, low-salinity H2O-CO2 ± CH4 ± N2 ore fluids, with Au transported as reduced sulfur complexes. The ore fluids are believed to be generated during lower crustal metamorphism from dehydration reactions. Regional structures provide the main control on distribution of lode gold deposits and mining camps. In many terranes, first-order faults or shear zones appear to have controlled regional fluid flow, with greatest ore-fluid fluxes in, and adjacent to, subsidiary faults, shear zones and/or large folds. Highly competent and/or chemically reactive rocks are the most common hosts to the larger deposits. Gold deposition occurs late during the evolutionary history of the host terranes, normally within D3 or D4 in a D1-D4 deformation sequence. Absolute ages of mineralization support their late-kinematic timing, and, in general, suggest that deposits formed diachronously towards the end of the evolutionary history of hosting orogens. Figure 7-2. Generalized tectonic model for the formation of mesothermal gold deposits, after Groves et al., 2000. The late timing of lode-gold deposits is critical to geology-based exploration methods, and hence mineral potential evaluations for these deposits. The late timing is critical because of the present structural geometry of: (1) the deposits, (2) the mining camps, and (3) the enclosing geologic terranes are essentially all similar to the structural geometry during gold mineralization. Therefore the interpretation of bedrock geological maps and cross-sections can be used to discern the physical conditions that existed at the time of ore deposition. Exploration for mesothermal lode-gold deposits should incorporate various aspects of the ore deposit model into criteria that can vector into the most favorable areas for hosting such mineralization. The most fundamental characteristic of this class of deposit is the spatial association of the deposits to regional structures in metamorphic terranes. Zones of widespread carbonate alteration (adjacent to regional structures) should be identified and used to focus subsequent exploration. Within carbonate alteration zones, gold is typically only in areas containing quartz veins, silicification, and/or sericite alteration (with or without sulfides). Two general structural controls on the orientation of lode gold ore shoots include deflections and curvatures of shear zones, and where high strain zones intersect favorable geological elements (Poulsen and Robert, 1989). A generalized sequence of events associated with the formation of typical Archean mesothermal gold deposits is outlined below. The possible observation of many of these important features during the course of the field trip is highlighted by the bracketed, bold text. Page 202 �I. Deposition of Archean Supracrustal Strata (Volcanic and Sedimentary Rocks) II. Compression and Early (D1) Folding [stop 7-1] III. Renewed Compression and Transpression (D2) 1) Development of Major Crustal Shear Zones [stop 7-1] 2) Strain Partitioning and Development of Subsidiary Shear Zones [stop 7-3, 7-4] 3) Intrusion of Porphyritic Intrusions, Continued D2 Deformation [stop 7-2, 7-3 and 7-5] -Local Development of Competency Contrasts [stop 7-3, 7-5] 4) Lower Crustal Dehydration and Fluxing of CO2-rich Fluids up Structures - Fe-Carbonate Alteration Zones [stop 7-3, 7-4, 7-5] 5) Fluxing of Gold-Bearing Hydrothermal Fluids up Subsidiary Shear Zones, Latest D2 - Gold Mineralization Associated with: A) Quartz-Pyrite Veins [stop 7-2, 7-3, 7-4, and 7-5] B) Silicification with Pyrite [stop 7-4] C) Pyritization of Fe-Rich Host Rocks [stop 7-5] D) Quartz-Sericite-Pyrite Schists/Phyllites [stop 7-4] E) Contact Zones Between Rock Units [stop 7-5] IV. Erosion REGIONAL GEOLOGIC SETTING OF THE VERMILION DISTRICT The field trip area is located in the Neo-Archean (~2.7 Ga) Vermilion Greenstone Belt of the classic Vermilion district of northeastern Minnesota. Supracrustal rocks in the Vermilion district consist of volcanic-dominated stratigraphic sequences of the Wawa subprovince of the Superior Province of the Canadian Shield. Rocks of the Wawa subprovince in northern Minnesota are divided on the basis of stratigraphic and structural setting into: (1) the southern Soudan belt and (2) the northern Newton belt (Jirsa et al., 1992; Southwick et al., 1998). The boundary between these contrasting structural panels can be traced geophysically across the width of Minnesota, and was designated informally as the Leech Lake structural discontinuity (Jirsa et al., 1992). In the Vermilion district, the Leech Lake structural discontinuity occurs along the Mud Creek shear zone (Hudleston et al., 1988), small segments of the Vermilion and Wolf Lake faults (Sims and Southwick, 1985), and the Bear River fault (Jirsa et al., 1992). The Soudan belt contains large, broad folds involving calc-alkalic and tholeiitic volcanic strata overlain by, and locally interdigitated with, turbiditic rocks. In contrast, the Newton belt consists of elongate, east- to northeast-trending, and mostly northward-younging volcanic and volcaniclastic sequences. Volcanic rocks of the Newton belt differ from those of the Soudan belt in containing locally abundant komatiitic flows and peridotitic sills. The two belts are faultbounded, and the relationship between stratigraphic units within each belt is largely conformable, although faults obscure contacts locally. In its eastern extension, the Soudan belt is continuous with the Saganagons assemblage in Ontario and terminates against the Saganaga pluton and Northern Light Gneiss. The Newton belt extends discontinuously eastward into the Shebandowan District of Ontario to form the Greenwater and Burchell assemblages. Intrusive rocks in both belts vary from gabbroic and felsic porphyries, demonstrably related to volcanism, to large plutons emplaced post-tectonically. Both districts contain unconformable, Timiskaming- Page 203 �type sequences composed of calc-alkalic volcanic rocks, conglomerates, and finer grained sedimentary rocks. A simplified regional geological map of the Neo-Archean terranes of northeastern Minnesota and adjacent Ontario is presented in Figure 7-3. Figure 7-3. Simplified correlation map of Neo-Archean assemblages across the U.S. - Canada border, modified from Peterson et al. (2001). Inset shows major subprovinces of the southwestern Superior Province. Periods of generally N-S directed compression resulted in three major regional deformation events in the Neoarchean terranes of northern Minnesota. The earliest deformation event (D1) produced broad, locally recumbent folds within the Soudan belt and major fault zones throughout the region. In the Newton belt, D1 was accommodated by thrust imbrication of large crustal blocks, resulting in mainly northward stratigraphic facing. Field relationships indicate that uplift, faulting, and the deposition of Timiskaming-type clastic sequences in local faultbounded basins occurred late in D1 deformation (Jirsa, 2000). A large, map-scale structure related to D1 deformation in the Soudan Mine area is the Tower-Soudan Anticline, which is a west-plunging anticline within which the axis and plunge changes orientation along strike from nearly vertical in basalts to shallow NE plunging in the western sedimentary rocks. Axial-planar cleavage associated with this early fold typically is lacking, although Bauer (1985), Hooper and Ojakangas (1971), Hudleston (1976), and Jirsa et al. (1992) have described early cleavage (S1) locally. A second deformation event (D2) associated with synchronous regional metamorphism resulted in foliation development and structures having largely dextral asymmetry. D2 is constrained in the Vermilion district to the time period 2674 to 2685 Ma (Boerboom and Zartman, 1993), and between about 2680 and 2685 Ma in the Shebandowan (Corfu and Stott, 1998). Because D2 deformation affected all of the supracrustal rocks in the area and is reasonably constrained by geochronology, the regional foliation (S2) can be used in the field to Page 204 �relate other structural, intrusive, and deformation events. The relationship between S2 fabric and shear structures indicates that most shearing occurred relatively late in the D2 event. Major shearing that produced the Mud Creek and related shear zones is attributed to the late stages of D2 dextral transpression. Regional D2 strain patterns in the Vermilion district vary from north to south in the belt (Hudleston et al., 1988; Schultz-Ela and Hudleston, 1991). These patterns include flattening strains that occur to the north, near the present Vermilion Fault and constrictional strains to the south. The field trip area lies within the zone of flattening strain of Hudleston et al. (1988) and Schultz-Ela and Hudleston (1991). Schultz-Ela and Hudleston (1991) mathematically modeled the observed strain patterns as deformation paths that produced flattening strains (west plunging ë 1 axes) by dextral shear of the pre-existing constrictional strains (east plunging ë 1 axes). The linear E-W strain patterns and minor rotations about horizontal axes during the deformation, as described by Hudleston et al. (1988) and Schultz-Ela and Hudleston (1991), preclude early theories (Hooper and Ojakangas, 1971; and Hudleston, 1976) on the structural setting of the greenstone belt by infolding and shear off the flanks of rising granitic diapirs. An estimate of 50% north-south shortening across the belt is proposed by Schultz-Ela and Hudleston (1991), and their model favors an origin of the Vermilion district rocks at a convergent margin, most likely as a N-dipping subduction complex with shallow slab dip. The origin of the southern constrictional strains remains enigmatic. Structures related to the third deformation event (D3) include abundant NE- and NWtrending faults that dissect the stratigraphic assemblages. Named structures related to D3 include the NE-trending Waasa and Camp Rivard faults SSE of Ely, and the WNW-trending, crustalscale Vermilion and related faults that form the Wawa-Quetico Subprovince boundary immediately north of the field trip area. LOCAL GEOLOGIC SETTING; THE BASS LAKE SEQUENCE The informally named Bass Lake sequence (Peterson and Jirsa, 1999a) of the Newton Belt occurs in an east-west trending, fault-bounded panel that widens to the west. The sequence is bounded by segments of the Mud Creek and Shagawa shear zones, and the Bear River, Haley, Vermilion, Burntside Lake, and Wolf Lake faults (Fig. 7-4). The continuation of stratigraphic and geophysical trends from areas of excellent exposure (east of Lake Vermilion) into poorly exposed areas (to the west) have led to the inclusion of rocks of the informally named Cook sequence (Southwick, 1993; Southwick et al., 1998) in the Bass Lake sequence. The western portion of the sequence consists of linear belts of graywacke and basalt cut by late felsic to intermediate composition intrusions. East of Lake Vermilion, the geology of the Bass Lake sequence is dominated by six basic rock types, which include: (1) Tholeiitic pillowed basalt flows (see Fig. 7-4) interpreted to have formed in a deep-water setting based on volcanic textures; (2) Gabbro sills interpreted as synvolcanic in age due to their stratigraphic continuity and similar deformation as the enclosing pillowed basalts; (3) Felsic porphyries (feldspar porphyry and quartz-feldspar porphyry) interpreted to have intruded during late stages of D2 deformation based on field relationships and geochronology (quartz-feldspar porphyry from the Pac Man Pond prospect returned a 207Pb/206Pb age of 2683.0 +/- 1.4 Ma (Peterson et al., 2001)); (4) Algoma-type iron-formation; (5) Thinly- Page 205 �bedded argillite and siltstone; and (6) Sheared rocks, which are dominated by chlorite-rich schist, phyllite, and phyllonite. In addition, localized areas of fragmental felsic volcanic rocks occur stratigraphically below distinct iron-formation horizons. Regional and detailed geologic maps of the sequence are presented in Fig. 7-5. In the last twenty years, numerous gold prospects have been discovered in the eastern portion of the sequence (Fig. 7-1). These prospects generally fall into one of three categories; (1) auriferous quartz-carbonate-pyrite veins and sulfidized zones in iron-formation; (2) auriferous quartz-sericite-ankerite-pyrite schists; and (3) felsic intrusive-hosted auriferous quartz veins and stockworks. All of the prospects are found within areas of moderate to strong ironcarbonate alteration, with the best mineralization commonly found within sericitic alteration zones. Numerous equigranular and porphyritic felsic intrusions occur within the areas of alteration and gold mineralization, and are a good guide for locating mineralized structures. The gold mineralization is generally related to deformation in subsidiary structures associated with movement along the D2 Mud Creek shear zone. Geological and geochemical descriptions of many of the gold prospects have previously been given by Peterson and Jirsa (1999b). Figure 7-4. Jensen cation plot (Jensen, 1976) for volcanic and hypabyssal rocks of the Bass Lake sequence. Undoubtedly the most striking structural feature in the immediate study area is the juxtaposition of the Soudan and Newton belts along the Mud Creek shear zone. In addition, numerous east-northeast trending highly strained zones occur to the north of the Mud Creek shear zone and these subsidiary sheared zones host a majority of the gold prospects in this area of the Bass Lake sequence. A stereonet projection of planar and linear structural features within the field trip #7 area of the Bass Lake sequence is shown in Fig. 7-6. Page 206 �Figure 7-5. Regional to detailed geological maps of the Bass Lake sequence. Geology simplified from Peterson (2001) and Peterson and Patelke (2004). Page 207 �Figure 7-6. Stereonet projections of planar and linear structural features from the field trip area. GLACIAL HISTORY Late Pleistocene glacial deposits (Late-Wisconsin glaciation) in the Vermilion district are associated with the stepwise retreat of the Rainy Lobe of the Laurentide Ice Sheet, approximately 14,000 to 12,000 years ago. The repeated glaciations of the Pleistocene epoch modified the preexisting topography of northeastern Minnesota, i.e. the surface was scoured by glacial ice, exposing fresh bedrock, and new surficial materials were deposited following the retreat of the glaciers. During the retreat of the glacier, the margin of the ice-sheet blocked the natural drainage to the north, and pro-glacial lakes formed in front of this barrier (glacial lakes Norwood, Koochiching, and Agassiz). Subglacial streams left sinuous ridges of sorted sand and gravel (eskers), and delta/fan complexes formed where these streams exited the ice margin and entered the pro-glacial lakes. The field trip area lies within the scoured bedrock terrain of northeastern Minnesota, immediately north of the Vermilion Moraine. Regional and detailed digital elevation maps of the area are presented in Figure 7-7, and display the pronounced recent bedrock scouring of the area, especially along the Vermilion fault and Mud Creek shear zone. Late Pleistocene surficial deposits and landforms that unconformably overlie the Neoarchean bedrock in the field trip area include a thin veneer of basal till, local outwash deposits, and sinuous eskers. Page 208 �Figure 7.7. Regional (top) and local (bottom) digital elevation maps depicting superimposed glacial landforms. Grid values in the detailed map are UTM coordinates, in meters. The locations of field trip stops are depicted in the lower image. FIELD TRIP STOPS Stops for this field trip will include short traverses that visit a number of outcrops for each locality. The traverses are designed to highlight specific features of the lode-gold ore deposit model for each area, though time constraints preclude detailed analysis of each area. Page 209 �STOP 7-1: MUD CREEK SHEAR ZONE Location: (SE, SE, Sec. 5, T.62N., R.14W., NAD83 UTM 564200E, 5302800N) Description: The regional scale Mud Creek shear zone occupies the east-northeast trending valley of Mud Creek, which is clearly visible at this location. This shear zone separates rocks of the Newton Belt (here the Bass Lake sequence) to the north and rocks of the Soudan Belt (Gafvert Lake sequence and the Upper Ely Greenstone Formation) to the south. The Mud Creek shear zone is analogous with major faults (Destor-Porcupine fault) and “breaks” (Cadillac-Larder Lake break) of major lode-gold mining districts in Canada. Historic gold assays taken from rocks of the shear zone itself are essentially devoid of gold, as is the case for most major structures within Archean lode-gold mining camps. The short field trip traverse is located within the northern margin of the internal highly strained zone of the shear, and will visit outcrops of: (1) ankerite-sericite-quartz-green mica-pyrite schist with quartz and tourmaline knots, and (2) highly folded and compositionally banded phyllites with quartz veins (Fig. 7-8). A simplified geology and field trip traverse map of stop 7-1 is presented in Figure 7-9. Figure 7-8. Outcrop photographs of ankerite-sericite-quartz-green mica-pyrite schist (A and B), and highly folded and compositionally banded phyllites (C and D). Page 210 �Figure 7-9. Simplified geology and field trip traverse map of stop 7-1, geology from Peterson and Patelke, 2004. STOP 7-2: SECTION 6 GOLD PROSPECT Location: (SE, SE, Sec. 6, T.62N., R.14W., NAD83 UTM 561895E, 5303410N) Description: Gold mineralization within the Section 6 prospect is dominantly associated with quartz-pyrite veins and stockworks in feldspar ± quartz porphyry. The stockwork-style mineralization is generally not apparent until one takes a detailed look at the outcrops, then the thin quartz veining is seen seemingly everywhere. The highest-grade gold assays taken to date occur in areas of strong sulfide oxidation (sulfide burn) in the porphyry. Mineralization also occurs in sulfidized and epidote-altered basaltic rocks adjacent to the felsic porphyries, and may Page 211 �locally contain significant quantities of chalcopyrite. In addition to porphyry and basaltic rocks, thin dikes and sills of diorite, peridotite, and inclusion-rich lamprophyre will be observed during the field trip stop. Outcrop photographs and a geologic map of the Section 6 prospect area are presented in Figures 7-10 and 7-11, and a table of anomalous gold assays is given in Table 7-1. Figure 7-10. Outcrop photographs from the Section 6 prospect. (A) 1 Ft.-wide dioritic dike near a basalt-porphyry (with BIF inclusion) contact; (B) strong sulfide burn within feldspar porphyry; (C) stockwork quartzveins (black lines) and local sulfide burn within feldspar porphyry; and (D) sulfide burn in quartzveined feldspar porphyry. Table 7-1. Anomalous gold assays from the Section 6 prospect. Description Au (ppb) Siliceous, sericitic and strongly pyritic basalt Carbonatized quartz-feldspar porphyry with pyrite Carbonatized feldspar porphyry with pyrite and quartz veins Pyritic selvage about a 3' quartz vein in basalt Pyritic selvage about a 3' quartz vein in basalt Epidote-silica-hematite altered feldspar porphyry with pyrite-rich veins Page 212 1,460 1,360 1,135 940 890 860 �Description Au (ppb) Pyritic quartz-feldspar porphyry Chloritic feldspar porphyry with ankerite, 1-3% pyrite, and quartz-ankerite-pyrite veins Chlorite-epidote-silica altered basalt with pyrite and chalcopyrite Carbonatized quartz-feldspar porphyry with pyrite Chlorite-epidote-silica altered basalt with pyrite and chalcopyrite 855 840 790 780 445 Figure 7-11. Simplified geology and field trip traverse map of stop 7-2, geology from Peterson and Patelke, 2004. Page 213 �STOP 7-3: SECTION 6 EAST GOLD PROSPECT Location: (SE, SE, Sec. 6, T.62N., R.14W., NAD83 UTM 562840E, 5302905N) Description: Three features of the generalized Archean lode-gold ore deposit model are beautifully exposed along the traverse of this stop. These features include: (1) intense ironcarbonate alteration, (2) competency contrast and associated auriferous quartz veining, and (3) shear deformation. Anomalous gold was first discovered by soil sampling in this locality in 1988 by Chevron Resources. Gold mineralization is generally confined to quartz-pyrite veins in ironcarbonate altered feldspar-porphyry intrusive rocks. The felsic porphyries are generally located adjacent to linear zones of intense strain, and are believed to have intruded along these structural breaks during D2 deformation. Outcrop photographs and a geologic map of the Section 6 East prospect area are presented in Figures 7-12 and 7-13, and anomalous gold assays in Table 7-2. Figure 7-12. Outcrop photographs from the Section 6 East prospect. (A) iron-carbonate altered feldspar porphyry with quartz veins; (B) close-up of quartz-pyrite veins in carbonatized feldspar porphyry; (C) large quartz ± pyrite ± galena veins in massive iron carbonate; and (D) intense iron carbonate alteration Page 214 �Table 7-2. Anomalous gold assays from the Section 6 East prospect. Description 6" quartz vein in sheared feldspar porphyry Feldspar porphyry with ankerite, pyrite, and quartz veins Feldspar porphyry with ankerite, pyrite, and quartz veins Feldspar porphyry with local fracturing and shearing Feldspar porphyry with a rusty quartz-pyrite vein Ankerite-sericite altered basalt with pyrite Au (ppb) Description Au (ppb) 6,210 2,400 1,760 1,380 1,130 1,030 Soil Sample Soil Sample Soil Sample Soil Sample Soil Sample Soil Sample 1,520 622 615 294 170 101 Figure 7-13. Simplified geology and field trip traverse map of stop 7-3, geology from Peterson and Patelke, 2004. Page 215 �STOP 7-4: KERR MCGEE GOLD PROSPECT Location: (SE, SE, Sec. 31, T.63N., R.14W., NAD83 UTM 562480E, 5304310N) Description: The Kerr McGee gold prospect is hosted within an extensive zone of highly strained rocks, interpreted to be a subsidiary structure associated with the Mud Creek shear zone. Moderate to high-grade gold mineralization at the Kerr McGee prospect occurs within multiple thin (0.2 – 2.0 meter) zones of quartz-sericite-ankerite-pyrite ± green mica ± tourmaline schist hosted by an extensive zone of essentially gold-barren chlorite-rich schist. Thin and probably boudined iron-formation horizons occur locally in the chlorite-rich schist, and locally are strongly mineralized in this area. Mineralized zones locally contain extensive foliation and shear parallel quartz, ankerite, and/or quartz-ankerite veins, and may widen in zones of silicification. The style of gold mineralization exposed in the Kerr McGee prospect is similar to both the Clear Cut (~½ mile west) and Railroad Zone (1½ miles east) prospects. In fact, the sericitic zone that hosts the mineralization may have continuity to both of these other prospects. The field trip traverse will take us to numerous outcrops in the prospect area, and discussions will highlight the style of mineralization, possible continuity to other prospects, and shear deformation. Anomalous gold assays from the Kerr McGee prospect are presented in Table 7-3. Outcrop photographs and a geologic map of the prospect area are presented in Figures 7-14 and 7-15 respectively. Table 7-3. Anomalous gold assays from the Kerr McGee prospect. Description 1' wide zone of quartz-sericite-ankerite-pyrite tourmaline schist Quartz-pyrite-sericite knot in ankeritic sericite schist 1' wide zone of quartz-sericite-ankerite-pyrite tourmaline schist 1' wide zone of sericite-quartz-pyrite-ankerite phyllite 1' wide zone of sericite-quartz-pyrite-ankerite phyllite 1' wide zone of sericite-quartz-pyrite-ankerite phyllite 0.5' wide zone of sericite-quartz-pyrite-ankerite phyllite 1.1' wide zone of sericite-quartz-pyrite-ankerite phyllite Sericite-chlorite schist 0.33' wide zone of sericite-quartz-ankerite-pyrite phyllite 0.5' wide zone of sericite-quartz-ankerite-pyrite phyllite Road cut of siliceous quartz-sericite-pyrite schist with quartz veins 1.2' wide zone of sericite-quartz-pyrite-ankerite phyllite 1.1' wide zone of sericite-quartz-pyrite-ankerite phyllite Chlorite-sericite-ankerite schist with 10-20% pyrite Chlorite-quartz-ankerite schist with pyritic (5-10%) siliceous zones Chlorite-quartz-ankerite schist with pyritic (5-10%) siliceous zones Chlorite-quartz-ankerite schist with 1-5% pyrite Quartz-ankerite-pyrite (2-3%) vein Chlorite-sericite-ankerite schist with 10-20% pyrite Brecciated ankeritic-pyritic (5-10%) chert Sericite-chlorite-quartz-ankerite-pyrite (5%) schist Page 216 Au (ppb) DDH 8,010 5,030 4,991 4,660 4,410 3,430 2,770 2,740 2,440 1,675 1,140 980 695 685 1,980 RC-3 1,470 RC-3 1,040 RC-3 620 RC-3 613 RC-3 448 RC-3 369 RC-3 334 RC-3 Interval (ft) 1.0 3.0 4.0 7.0 1.0 1.0 2.0 2.0 �Figure 7-14. Outcrop photographs from the Kerr McGee prospect. (A) Road side outcrop of quartz-sericite-pyriteankerite-green mica-tourmaline schist; (B) minor northwest-trending fault offsetting highly foliated chloritic and sericitic schists; (C) close-up view of complex deformation fabric associated with quartz veins and knots; (D) channel samples taken across thin mineralized zones; (E) more channel samples taken across thin mineralized zones in sericite-rich schist, barren chlorite-rich schist at the bottom of the photograph; and (F) dextral shear fabrics in a mineralized zone at the east end of the outcrop area. Page 217 �Figure 7-15. Simplified geology and field trip traverse map of stop 7-4, geology from Peterson and Patelke, 2004. Three-dimensional visualization (Fig. 7-16) of the detailed lithological and structural mapping by Peterson and Patelke, (2004) within the Kerr McGee prospect area reveals important information that can be used to design drilling plans that significantly increase the chance of intersecting gold mineralization exposed in outcrop at the surface. For example, drill hole RC-3, which is located 100 meters east of the map presented in Figure 7-15, was drilled due north (at a dip of 45º) and targeted to intersect the mineralization exposed in outcrop at the Kerr McGee Page 218 �showing. Chevron Resources drilled this hole in 1987, at the western boundary of their lease property (the Kerr McGee prospect was then held by Kerr McGee). Detailed structural mapping in these outcrops reveals that the rocks within the mineralized zone have moderate to strong elongation and intersection (foliation and shear planes) lineations trending 60º and dipping northeast at 72º. The best interpretation of the down-dip orientation of the mineralized zone is this lineation trend and plunge, and drill hole RC-3 never intersected the mineralized zone. A three-dimensional view of these relationships is given in Figure 7-16. Figure 7-16. Three-dimensional view of the relationship between structural boundaries, the mineralized zone exposed on the surface at the Kerr McGee prospect, and drill hole RC-3. Upward extension to the surface of the two anomalous zones (> 1,000 ppb gold) intersected in hole RC-3 would place these zones in the black spruce and cedar swamp located south-southeast of the prospect. As briefly described in the preceding paragraphs, the sericitic-schist hosted style of mineralization at the Kerr McGee prospect is similar to the mineralization at both the Clear Cut and Railroad Zone prospects, and may form a continuous zone of anomalous to ore-grade gold mineralization over a strike length of > 2.5 miles. By analogy to many Canadian and Australian Archean lode gold deposits, the odds of discovering high-grade zones within this trend would be significantly increased if possible future exploration ventures utilized structural elements exposed in outcrop. A simplified geologic map encompassing the highly strained zone that hosts the Clear Cut, Kerr McGee, and Railroad Zone gold prospects is presented in Figure 7-17. In addition, the trend and plunge of measured lineations are given in both the plan map of Figure 717 and the underlying east-west cross-section. Although the field trip will not visit the Clear Cut Page 219 �and Railroad Zone prospects, anomalous gold assays from these associated prospects are presented in Tables 7-4 and 7-5 respectively. Figure 7-17. Highly simplified geologic and lineation map of the highly strained shear zone that hosts the Clear Cut, Kerr McGee, and Railroad Zone gold prospects. The total lengths of the lineation arrows depicted in the east-west cross-section (lower portion of the figure) are all equal, their apparent difference in length is related to their individual trend and plunge in relation to the view angle of the section. Table 7-4. Anomalous gold assays from the Clear Cut prospect. Description Au (ppb) DDH Interval (ft) 2' wide zone of quartz-sericite-pyrite schist Quartz-sericite-pyrite schist Quartz-sericite-pyrite schist Quartz-sericite-pyrite schist Quartz-ankerite vein with a sericite-pyrite selvage in ankerite-chlorite schist 1/2" wide quartz-pyrite-arsenopyrite vein Oxide-facies iron-formation with 10% pyrite and 5% arsenopyrite Quartz-sericite-pyrite schist Oxide-facies iron-formation with 1-2% cross-cutting pyrite Oxide-facies iron-formation with 10% pyrite and 5% arsenopyrite Chlorite-pyrite phyllite with quartz veining and 5% pyrite Chlorite phyllite with trace to 5% pyrite Chlorite-pyrite phyllite with quartz veining and 1% pyrite Chlorite-pyrite phyllite with quartz veining and 5% pyrite Chlorite-pyrite phyllite with quartz veining and 5% pyrite Page 220 22,000 7,100 2,940 1,970 1,970 598 590 568 440 402 1,510 715 550 528 471 RC-5 RC-5 RC-5 RC-5 RC-5 2.0 2.0 5.0 2.0 2.0 �Table 7-5. Anomalous gold assays from the Railroad Zone prospect. Description Grab sample from large boulder encased in the roots of an overturned tree Sericite-chlorite-ankerite-pyrite phyllite with quartz-ankerite-pyrite veins 4' Sericite-chlorite-ankerite-pyrite phyllite with quartz-ankerite-pyrite veins Chlorite-ankerite-pyrite schist Siliceous sericite schist with ankerite and pyrite Chlorites schist with pyrite and sericite Chlorite schist with pyrite and sericite Chlorite schist with pyrite and sericite Siliceous chlorite schist with pyrite Massive pyrite lens in sericite-ankerite schist Chlorite-ankerite-pyrite phyllite with quartz-ankerite veins Chlorite schist with pyrite and sericite 5' zone of very rusty and weathered, sericite-ankerite-quartz-pyrite phyllite Chlorite-ankerite phyllite with numerous quartz-ankerite-pyrite veins Sericite-quartz-ankerite-pyrite phyllite with 5% pyrite Quartz-sericite-pyrite phyllite with 5% pyrite Au (ppb) DDH Interval (ft) 37,324 17,100 13,623 3,110 2,670 2,410 970 960 960 776 705 620 605 777 V-2 1.5 713 V-4 1.8 591 V-1 6.0 STOP 7-5: PACMAN POND GOLD PROSPECT Location: (SE, SE, Sec. 6, T.62N., R.14W., NAD83 UTM 562225E, 5303780N) Description: The Pac Man Pond gold prospect was explored by Noranda in the late 1980s and early 1990s. They completed a quite extensive program that consisted of geological mapping, bedrock sampling, till prospecting, trenching, and drilling. Three rock types, that include pillowed basalt, iron-formation, and intrusions of feldspar ± quartz porphyry, dominate the prospect geology, with rare occurrences of argillaceous and graphitic sediments as well as carbonate facies iron-formation intersected in drill holes. Gold mineralization is hosted dominantly by brecciated, quartz-pyrite veined, and sulfidized iron-formation, with locally anomalous gold in sulfidized basalt and porphyry. The outcrops observed on the field trip will be concentrated on one of the areas that Noranda completed extensive trenching and gold assaying. Outcrop photographs from the Pac Man Pond gold prospect are given in Figure 7-18, and a geologic map of the Pac Man Pond gold prospect area is presented in Figure 7-19. Anomalous gold assays from bedrock exposures and Noranda drill hole intersections are given in Table 7-6. Page 221 �Figure 7-18. Outcrop photographs from the Pac Man Pond prospect. (A) Strongly iron-carbonate altered quartzfeldspar porphyry; (B) sheared and laminated pyrite and chlorite at the contact between foliated to sheared basalt and sulfidized iron-formation; (C) irregular contact between carbonatized quartzfeldspar porphyry and sulfidized iron-formation; and (D) strong sulfide burn on highly sulfidized iron-formation. Sawed samples of gold-bearing, pyritic iron-formation reveal one of the classic chemical models for the precipitation of gold out of hydrothermal solutions. In this model, when silica-saturated auriferous hydrothermal fluids (with gold carried by HS complexes) encounter a rock rich in FeO (such as Fe-tholeiitic basalt or iron-formation), quartz, pyrite and gold are precipitated out of solution. The classic chemical equation is presented below. 2HAu(HS)2 aq + ½O2 aq + 2FeO s ↔ Page 222 2FeS2 s + 2Au s + 3H2O aq �Figure 7-19. Simplified geology and field trip traverse map of stop 7-5, geology from Peterson and Patelke, 2004. Page 223 �Table 7-6. Anomalous gold assays from the Pac Man Pond prospect. Description Large angular boulder of pyrite-rich (5-50%) iron-formation Sulfidized iron-formation Siliceous, pyritic iron-formation with limonite Siliceous, pyritic iron-formation Sulfidized iron-formation Sulfidized iron-formation with quartz-pyrite veins Limonite stained iron-formation with 5-15% pyrite Sulfidized (10-70% pyrite) basalt Siliceous, pyritic iron-formation Iron-formation with trace pyrite Sulfidized iron-formation Laminated iron-formation with trace pyrite Pyrite-rich iron-formation near contact with quartz-feldspar porphyry Sulfidized iron-formation with 5-20% pyrite Quartz-feldspar porphyry with a rusty quartz vein Laminated iron-formation with trace pyrite 6' wide zone of sulfidized iron-formation with 3-10% pyrite Mineralized iron-formation with 5-15% pyrite Brecciated iron-formation with 5-20% pyrite in matrix Brecciated iron-formation with 5-20% pyrite in matrix Iron-formation with 1-2% pyrite in veinlets Brecciated iron-formation with quartz-pyrite (10%) veins Thin-bedded and folded iron-formation with 3% pyrite Brecciated iron-formation with chlorite-quartz-pyrite (5-10%) matrix Brecciated iron-formation with 5-10% pyrite Weakly brecciated iron-formation with 3-10% pyrite in matrix Fine-grained mafic dike Quartz-feldspar porphyry with trace pyrite Oxidized iron-formation with ankerite and 8% pyrite Au (ppb) 2,701 2,190 1,940 1,810 1,750 1,635 1,020 985 890 875 845 845 815 811 785 760 758 705 28,460 5,400 4,212 2,255 1,747 1,364 1,026 960 856 856 782 DDH Interval (ft) V89-1 V89-1 V-90-2 V-90-4 V-90-7 V-90-2 V-90-3 V89-1 V-90-4 V-90-4 V-90-3 2.0 1.7 3.5 2.0 1.8 1.8 3.2 2.3 1.0 1.0 2.0 REFERENCES Bauer, R.L., 1985, Correlation of early recumbent and younger upright folding across the boundary between an Archean gneiss belt and greenstone terrane, northeastern Minnesota: Geology, v. 13, p. 657-660. Berger, B. R., 1986a, Descriptive model of Homestake Au: in Mineral Deposit Models, Cox, D.P. and Singer, D.A., eds., U.S. Geological Survey, Bulletin 1693, p. 245- 247. Berger, B. R., 1986b, Descriptive model of low-sulphide Au-Quartz veins: in Mineral Deposit Models, Cox, D.P. and Singer, D.A., eds., U.S. Geological Survey, Bulletin 1693, p. 239-243. Page 224 �Boerboom, T.J., and Zartman, R.E., 1993, Geology, geochemistry, and geochronology of the central Giants Range batholith, northeastern Minnesota: Canadian Journal of Earth Sciences v. 30, p. 2510-2522. Bohlke, J.K. and Kistler, R.W., 1986, Rb-Sr, K-Ar and stable isotope evidence for the ages and sources of fluid components of gold-bearing quartz veins in the Northern Sierra Nevada Foothills Metamorphic Belt, Economic Geology, v. 81, p. 296- 422. Corfu, F., and Stott, G.M., 1998, Shebandowan greenstone belt, western Superior Province: U-Pb ages, tectonic implications, and correlations: Geological Society of America Bulletin, v. 110, p. 1467-1484. Fripp, R.E.P., 1976, Stratabound gold deposits in Archean banded iron-formation, Rhodesia; Economic Geology, v. 71, p. 58-75. Groves, D.I., Goldfarb, R.J., Knox-Robinson, C.M., Ojala, J., Gardoll, S., Yun, G.Y., and Holyland, P., 2000, Late-kinematic timing of lode-gold deposits and significance for computer-based exploration techniques with emphasis on the Yilgarn Block, Western Australia; Ore Geology Reviews, v. 17, Issues 1-2, Pages 1-38. Hodgson, C.J., 1993, Mesothermal lode-gold deposits: in Mineral Deposit Modeling. Kirkham, R.V., Sinclair, W.D., Thorpe, R.I., Duke, J.M. eds., Geological Survey of Canada, Special Paper 40, p. 635–678. Hooper, P., and Ojakangas, R., 1971, Multiple deformation in the Vermilion district, Minnesota: Canadian Journal of Earth Sciences, v. 8, p. 423-434. Hudleston, P.J. 1976, Early deformational history of Archean rocks in the Vermilion district, northeastern Minnesota: Canadian Journal of Earth Sciences, v. 13, p. 579-592. Hudleston, P.J., Schultz-Ela, D., and Southwick, D.L., 1988, Transpression in an Archean greenstone belt, northern Minnesota: Canadian Journal of Earth Sciences, v. 25, p. 1060-1068. Jensen, L.S., 1976, A new cation plot for classifying subalkalic volcanic rocks: Ontario Department of Mines, Miscellaneous Paper 66. Jirsa, M.A., 2000, The Midway sequence: a Timiskaming-type pull-apart basin deposit in the western Wawa subprovince, Minnesota: Canadian Journal of Earth Science, v. 37. p. 1-15. Jirsa, M.A., Southwick, D.L., and Boerboom, T.J., 1992, Structural evolution of Archean rocks in the western Wawa subprovince, Minnesota: Refolding of pre-cleavage nappes during D2 transpression: Canadian Journal of earth Sciences, v. 29, p. 2146-2155. Kerswill, J.A., 1993, Models for Iron-formation-hosted Gold Deposits: in Mineral Deposit Modeling, Kirkham, R.V., Sinclair, W.D., Thorpe, R.I. and Duke, J.M., eds., Geological Association of Canada, Special Paper 40, p. 171-200. McMillan, R.H., 1996, Iron formation-hosted Au, in Lefebure, D.V. and Hoy, T, eds., Selected British Columbia Mineral Deposit Profiles, Volume 2 - Metallic Deposits, British Columbia Ministry of Employment and Investment, Open File 1996-13, p. 63-66. Page 225 �Peterson, D.M., 2001, Development of Archean lode-gold and massive sulfide deposit exploration models using geographic information system applications: Targeting mineral exploration in northeastern Minnesota from analysis of analog Canadian mining camps: Unpublished Ph.D. thesis, University of Minnesota, 503 p. Peterson, D. M., and Jirsa, M.A., 1999a, Bedrock geologic map and mineral exploration data, western Vermilion district, St. Louis and Lake Counties, northeastern Minnesota: MGS Miscellaneous Map M-98, scale 1:48,000. Peterson, D. M., and Jirsa, M.A., 1999b, Lode gold and massive sulfide prospects in the Archean western Vermilion district; Minnesota Exploration Conference 1999, Field trip guidebook, 10 maps, 30 p. Peterson, D.M and Patelke, R.L., 2004, Bedrock Geology and Lode Gold Prospect Data Map of the Mud Creek Road Area, Northern St. Louis County, Minnesota: Natural Resources Research Institute, Map Series NRRI/MAP-2004-01. Peterson, D.M., Gallup, C., Jirsa, M.A., and Davis, D.W., 2001, Correlation of Archean assemblages across the U.S. - Canadian border; Phase I geochronology, abstract and oral presentation, Institute on Lake Superior Geology, 47th Annual Meeting, Thunder Bay, Ontario, v. 47. Poulsen, K.H., and Robert, F., 1989, Shear zones and gold: Practical examples from the southern Canadian Shield: in Bursnall, J.T. ed., Mineralization and Shear Zones, Geological Association of Canada, Short Course Notes Volume 6, p. 239-266. Robert, F., Sheahan, P.A., and Green, S.B., eds., 1991, Greenstone gold and crustal evolution: NUNA Conference Volume, Geological Association of Canada, Mineral Deposits Division. Rye, D. M. and Rye, R. O., 1974, Homestake Gold Mine, South Dakota: I. Stable Isotope Studies; Economic Geology, v. 69, p. 293-317. S Schulz-Ela, D.D., and Hudleston, P.J., 1991, Strain in an Archean greenstone belt of Minnesota: Tectonophysics, v. 190, p. 233-268. Sims, P.K., and Southwick, D.L., 1985, Geologic map of Archean rocks, western Vermilion district, northern Minnesota: U.S. Geological Survey, Miscellaneous Investigations Map I-1527, scale 1:48,000. Southwick, D.L., Boerboom, T.J., and Jirsa, M.A., 1998, Geologic setting and descriptive geochemistry of Archean supracrustal and hypabyssal rocks, Soudan-Bigfork area, northern Minnesota: Implications for metallic mineral exploration: Minnesota Geological Survey Report of Investigations 51, 69 p. Southwick, D.L., compiler, 1993, Bedrock geologic map of the Soudan-Bigfork area, northern Minnesota: Minnesota Geological Survey Miscellaneous Map M-79, scale 1:100,000. Thorpe, R.I and Franklin, J.M., 1984, Chemical-sediment-hosted Gold: in Canadian Mineral Deposit Types: A Geological Synopsis, Eckstrand, O.R., Editor, Economic Geology Report 36, Geological Survey of Canada, p. 29. Vielreicher, R.M., Groves, D.I., Ridley, J.R. and McNaughton, N.J., 1994, A Replacement Origin for the BIF-hosted Gold Deposit at Mt. Morgans, Yilgarn Block, W.A; Ore Geology Reviews, v. 9, p. 325-347. Page 226 �FIELD TRIP 8 Geology and Mineralization of the Western Contact of the Duluth Complex, Partridge River and South Kawishiwi Intrusions, Northeastern Minnesota Leaders: Mark Severson Natural Resources Research Institute, University of Minnesota Duluth and Jim Miller Minnesota Geological Survey, University of Minnesota Railroad-cut exposures in the Wetlegs area of the Partridge River Intrusion (Stop 8-3) Page 227 �FIELD TRIP 8 Geology and mineralization of the western contact of the Duluth Complex, Partridge River and South Kawishiwi intrusions, northeastern Minnesota by Mark Severson Natural Resources Research Institute, University of Minnesota Duluth and Jim Miller Minnesota Geological Survey, University of Minnesota INTRODUCTION The Duluth Complex and associated Keweenawan intrusions in northeastern Minnesota constitute one of the largest mafic intrusive complexes in the world, second only to the Bushveld 2 Complex of South Africa. These rocks cover an arcuate area of over 5,000 km (Fig. 8-1) and give rise to two strong gravity anomalies (+50 & +70 mgal) that imply intrusive roots to more than 13 kilometers depth (Allen and others, 1997). The intrusive rocks of northeastern Minnesota were emplaced into a comagmatic volcanic edifice during formation of the Midcontinent Rift between 1108 and 1086 Ma. The Keweenawan geology of northeastern Minnesota has been recently reinterpreted in a 1:200,000 scale geologic map (MGS Miscellaneous Map, M-119; Miller and others, 2001) and in a comprehensive report that focused on the geology and mineral potential of the Duluth Complex (MGS Report of Investigation, RI-58; Miller and others, 2002). The general description of the Duluth Complex given below is largely excerpted from that report. The Duluth Complex is physically defined as a more or less continuous mass of mafic to felsic plutonic rocks that extends in an arcuate fashion from Duluth to nearly Grand Portage (Fig. 8-1). It is bounded by a footwall of predominantly Paleoproterozoic and Archean rocks, a hanging wall of largely mafic volcanic rocks and hypabyssal intrusions, and internally, it contains scattered bodies of strongly recrystallized mafic volcanic and sedimentary hornfels. Defining the Duluth Complex more genetically, it is composed of multiple discrete intrusions of mafic to felsic tholeiitic magmas that were episodically emplaced into the base of a comagmatic volcanic edifice in two general stages - an early stage at about 1108 Ma and an main stage at 1099 Ma. Within the Duluth Complex, four general rock series are distinguished on the basis of age, dominant lithology, internal structure, and structural position. These are: Felsic Series – massive granophyric granite and smaller amounts of intermediate rock that occurs as a semicontinous mass of intrusions strung along the eastern and central roof zone of the complex and was emplaced during early stage magmatism (~1108 Ma). Early Gabbro Series – layered sequences of dominantly gabbroic cumulates that occur in two major intrusions along the northeastern contact of the Duluth Complex and were also emplaced during early stage magmatism (~1108 Ma) Anorthositic Series – a structurally complex suite of foliated, but rarely layered, plagioclase-rich gabbroic cumulates that was emplaced throughout the complex during main stage magmatism (~ 1099 Ma). Layered Series – a suite of stratiform troctolitic to ferrogabboic cumulates that comprise at least 11 variably-differentiated mafic layered intrusions and occurs mostly along the base of the Page 228 �Duluth Complex. These intrusions were emplaced during main stage magmatism, but generally after the anorthositic series. The Partridge River (PRI) and South Kawishiwi (SKI) intrusions, the focus of this field trip, occur along the northwestern margin of the Duluth Complex (Fig. 8-1) and are two of the earliestformed intrusions of the Layered Series. These two intrusions are most renown for hosting the largest tonnage of Cu-Ni sulfide ore in the world (Naldrett, 1997). The bedrock geology of the northwestern margin of the Duluth Complex, as portrayed on the regional geologic map of northeastern Minnesota (M-119; Miller and others, 2001), is shown in Figure 8-2. Detailed mapping in the Babbitt NE, Babbitt SE, and Babbitt SW quadrangles, which was conducted since the publication of M-119 (Miller, Severson, and Foose, 2002; and unpublished field mapping, Miller, 2002-03), has revealed a somewhat different picture of the geology that has yet to be incorporated into the regional map. Mapping in this area will continue this summer with the objective of producing 1:24,000-scale maps of all four of the Babbitt 7.5' quadrangles in the summer of 2005. Figure 8-1. Generalized geology of northeastern Minnesota showing the field trip area. Partridge River intrusion (PRI) and South Kawishiwi intrusion (SKI) are labeled. Page 229 �Figure 8-2. Geology of the northwestern margin of the Duluth Complex showing field stops for Field Trip 8 (see Miller and others, 2001 for more details). Geologic units: Agr - Giants Range granite, PbifBiwabik Iron Fm, Pvf - Virginia Fm, pri - Partridge R. intr., ski-South Kawishiwi intr., bei-Bald Eagle intr.; gltr-Greenwood Lake intr-troctolitic zone; glgb-Greenwood Lake intr, gabbroic zone; glfgGreenwood Lake intr, ferrogabbroic zone; mwgp-Mount Weber granophyre, asau-anorthositic series undifferentiated; asa-anorthositic series, anorthositic rocks; asg-anorthositic series, gabbroic rocks; nsv-NSVG undifferentiated; nsbh-NSVG basaltic hornfels; nssh-NSVG sedimentary hornfels. Page 230 �Figure 8-3. Location of copper-nickel sulfide deposits, Fe-Ti±V deposits, and other exploration areas along the western base of the Duluth Complex (from Miller and others, 2002; Fig. 2.3) Page 231 �Partridge River Intrusion The Partridge River intrusion (PRI, Bonnichsen, 1974) is perhaps one of the most well studied intrusions of the Duluth Complex because it hosts at least four sub-economic Cu-Ni deposits and at least seven potential Fe-Ti deposits. The PRI consists mainly of troctolitic cumulates that are exposed in an arc-shaped area that extends from the Waterhen Fe-Ti deposit area (T.57N., R.14W., Sec. 27) to the Babbitt Cu-Ni deposit (T.60N., R.12W., Secs 31-33; Fig. 83). Miller and Ripley (1996) estimate that the PRI is 2.5 km thick. The footwall of the PRI includes the Paleoproterozoic Virginia Formation (slate and graywacke), and to a lesser extent, the Biwabik Iron Formation. The top of the PRI is in complex contact with anorthositic rocks (unit asa, Fig. 8-2), gabbroic rocks (unit asg), mafic volcanic hornfels (unit nshb), and in one location, an unusual fine-grained and cross-bedded sedimentary hornfels (Colvin Creek hornfels of Bonnichsen, 1972; Patelke, 1996; unit nssh). This assemblage of anorthositic, gabbroic, and hornfelsic rocks are also present as large inclusions within the interior of the PRI (Severson and Miller, 1999) and are thought to represent earlier roof zone septa that were overplated and isolated by later injections of PRI magma. The lower 900 meters of the PRI is known in great detail from the abundance of exploration drill core. This marginal zone, consisting of varied troctolitic and gabbroic rock types, is subdivided into seven stratigraphic units (Severson, 1991; 1994; Severson and Hauck, 1990; 1997; Geerts, 1991) that can be correlated over a strike length of 24 km (Fig. 8-4). All of these igneous units generally exhibit shallow dips (10-20°) to the southeast. The stratigraphy shown in Figure 8-4 is based on the relogging of almost 700 drill holes, or 672,000 feet of drill core. The units of the Partridge River marginal zone are briefly described below starting at the base of the PRI. Units I and III will be viewed at Stop 8-3. For locations of ore deposit areas mentioned below, see Figure 8-3. Unit I - This lower unit consists of a heterogeneous mixture of ophitic troctolitic to gabbroic rocks that contain abundant inclusions of hornfelsic sedimentary footwall rocks and minor thin, discontinuous layers of melatroctolite and peridotite. It is the dominant sulfide-bearing member of the PRI. Noritic rocks are common at the basal contact and peripheral to sedimentary hornfels inclusions, probably due to contamination of the magma. An ultramafic interval, consisting of an oxide-bearing peridotite overlying an oxide-bearing pyroxenite, is present at the base of Unit I in areas where the PRI is in direct contact with the Biwabik Iron Formation (extreme southeastern portion of the Babbitt deposit). Unit II - This unit exhibits considerable variation from one Cu-Ni deposit to the next. At the Dunka Road and Babbitt deposits, Unit II consists of homogenous troctolitic rocks, with minor sulfide mineralization, and a fairly persistent basal ultramafic layer that separates Unit II from Unit I. The upper contact with Unit III is gradational at the Dunka Road deposit. At the Wetlegs deposit, Unit II is either 1) a single ultramafic layer immediately beneath Unit III, and/or 2) the Wetlegs Layered Interval (Fig. 8-3) which consists of repeated, thin cyclic units that internally grade upward from ultramafic rock to troctolite. Still farther to the west at the Wyman Creek deposit, Unit II consists of a single ultramafic horizon that separates sulfide-bearing and heterogeneous troctolitic rocks of Unit I from homogenous troctolitic rocks of Unit IV. Unit III – This unit consists of poikilitic leucotroctolite that commonly grades into poikilitic/ophitic augite troctolite. Because of its fine-grained texture and distinctive olivine oikocrysts that impart a mottled appearance, Unit III is a useful marker horizon, although it is absent from the Wyman Creek deposit and portions of the Babbitt deposit. Hornfelsed basalt inclusions, or roof rocks, are commonly associated with Unit III at the Dunka Road deposit. This relationship, and the highly gradational contact of Unit III Page 232 �with Unit II, suggest that Unit III may have formed as a roof cumulate during crystallization of Unit II. Unit IV - Homogenous ophitic augite troctolite that contains a local basal unit of ultramafic rock. Unit IV typically exhibits a highly gradational upper contact with Unit V. A cyclic sequence of alternating troctolitic and ultramafic layers, termed the Bathtub Layered Interval, is present in the Bathtub ore zone of the Babbitt deposit. Unit V – Unit V consists of homogenous, coarse-grained leucotroctolite. At the Wyman Creek deposit, drill hole relationships suggest that Unit V cuts downward into the lower units (Fig. 8-3). Units VI and VII - Each of these units consist of homogenous leucotroctolite that locally grades into ophitic augite troctolite; both also contain a fairly persistent ultramafic base. Several other similar units (Unit VIII and up) are present above these two units but they are not defined by drilling. OUI - Several late-stage pegmatitic plugs and vertical lenses of oxide-bearing ultramafic intrusions (OUI) intrude the troctolitic rocks of the PRI. The acronym OUI was first used by Severson and Hauck (1990) to designate cross-cutting pegmatitic bodies of peridotite, melatroctolite, melagabbro, and clinopyroxenite that contain a high percentage of coarsegrained oxides (15-100%). Known OUI bodies in the PRI, with Fe-Ti potential, occur at Section 17, Longnose, Longear, Wyman Creek, Section 22, Skibo, Skibo-South, and Waterhen. In all instances, the OUI are spatially arranged along linear trends suggesting that structural control was important to their genesis. In addition, the Longnose-LongearSection 17 group of OUIs are positioned over a window in the basal contact where the Biwabik Iron-Formation is the footwall rock. This relationship suggests a genetic link between assimilation of iron-formation at the basal contact and formation of OUI along a coincident fault zone. Figure 8-4. Generalized stratigraphy of the marginal zone of the Partridge River intrusion (modified from Severson, 1994). Stratigraphic relationships for the area between the Wyman Creek deposit and the Water Hen deposit are poorly understood and are not portrayed (taken from RI-58 figure 6.10). Page 233 �Attributes of the more heterogeneous units (I and II) near the base of the PRI are interpreted to indicate rapid magma replenishment in a progressively developing magma chamber, and magmatic contamination from assimilated footwall rocks. The more homogeneous upper units (IV-VII), each floored by a persistent ultramafic layer, were probably emplaced later in a welldeveloped magma chamber. The ultramafic layers in the upper units, and abundant ultramafic layers of the Wetlegs and Bathtub layered intervals, probably represent the inception of episodic magma injection that crystallized more primitive ultramafic layers before mixing with the resident magma. The contact zone between the PRI and South Kawishiwi Intrusion (SKI) is poorly exposed and poorly drilled (Fig. 8-2). All of the units of the PRI marginal zone, including even the upper units, become unrecognizable in the contact zone with the SKI and correlation of igneous units in one drill hole to a nearby drill hole is tenuous at best. Severson (1994) reasoned that the heterogeneous contact zone of the PRI originally formed at the contact with pre-Keweenawan footwall rocks, and that later emplacement of the SKI effectively removed the footwall portion and positioned SKI intrusive rocks up against PRI intrusive rocks. Complicating the picture of the contact zone is the coincident Grano fault (Fig. 8-16), which appears to have been repeatedly reactivated during, and after, emplacement of the PRI and SKI. The Grano fault may have also served as a feeder channel to the massive sulfides of the Local Boy ore zone at the Babbitt deposit (Fig. 8-15). More petrologic studies have been conducted on the PRI than any other intrusion in the Duluth Complex. These studies pertain to drill holes in the Babbitt deposit (see Miller and others, 2002 for references). Most of the studies pertain to a stratigraphic section intersected in one or a few drill holes that represent only a small fraction of the PRI magmatic system. Divergent progenetic interpretations have resulted from these studies and have been summarized by Miller and Ripley (1996). South Kawishiwi Intrusion The South Kawishiwi intrusion (SKI) of Green and others (1966) hosts at least five subeconomic Cu-Ni deposits and a potential PGE-Cu-Ni deposit (Fig. 8-2). The SKI is dominantly composed of troctolitic cumulates that are exposed in an 8- x 32-kilometer arcuate band. Footwall rocks include the Virginia Formation, in the Serpentine and Dunka Pit deposits, the Biwabik Iron Formation in the Dunka Pit and Birch Lake deposits, and the Archean Giants Range Batholith in the Dunka Pit deposit north to the Spruce Road deposit. The presence of Biwabik Iron Formation as inclusions as far north as the Spruce Road deposit indicates that the majority of Paleoproterozoic units were assimilated and removed from the footwall during emplacement of the SKI leaving the Giants Range Batholith as the dominant footwall rock type. Also present as inclusions in the Dunka Pit and Serpentine deposits, are mafic volcanic hornfels (probable North Shore Volcanic Group) and quartz sandstone hornfels (probably either the Puckwunge or Nopeming sandstones. Anorthositic rocks (unit asau Fig. 8-2) abut the SKI on the northeast and enclose a possible SKI feeder dike that extends farther northeast. To the east, the SKI is inferred to be in semi-conformable contact with the Bald Eagle Intrusion (unit bei; Fig. 8-2). However, based on their relative cross cutting relationships to the Greenwood Lake intrusion, it is clear that the Bald Eagle is younger than the SKI (Chandler, 1990; Miller and others, 2002). On the regional Duluth Complex map (M-119, Miller and others, 2001), the SKI is subdivided into five major map units. These are, from the base upward, 1. a basal contact zone that is a heterogeneous mix of sulfide-bearing troctolitic, gabbroic, and noritic rocks with abundant hornfels inclusions (unit skcz, M-119); 2. a thick unit of subophitic to ophitic augite troctolite (unit skat, M-119) that contains an internal ophitic olivine gabbro unit (unit skog, M-119) ; Page 234 �3. discontinuous and localized layers of poikilitic leucotroctolite (unit skpt, M-119); 4. a thick homogeneous sequence of ophitic troctolite (unit sktr, M-119) ; and 5. an uppermost thick sequence of homogeneous troctolite (unit skta, M-119) that contains numerous anorthositic layers (designated as unit skan where anorthositic layers are mapped in detail). Detailed mapping of the Babbitt NE 7.5' quadrangle in 2001 and 2002 and published as an MGS open-file map (Miller, Severson and Foose, 2002), has subdivided the southern part of the SKI into eight stratiform map units. Most of these units show considerable variation in thickness and some pinch out altogether. Moreover, whereas Foose and Cooper (1978) have interpreted most of the anorthositic rock occurrences in the upper part of the SKI to be conformable plagioclase cumulate layers interleaved within the largely troctolitic cumulates, we have interpreted most anorthositic rock occurrences to be inclusions. Severson (1994) and Zanko and others (1994) further subdivide the marginal zone of the SKI (including units skcz, skat, skog, and sktr, Fig. 8-2) into 17 different lithostratigraphic units (Fig. 8-5) that are present in over 180 drill holes over a strike length of 31 kilometers. Sulfide mineralization is confined to the BH, BAN, UW, and U3 units, and to a lesser extent the U1 and U2 units. Major marker horizons that are correlated in drill hole include three horizons with abundant cyclic ultramafic layers (U1, U2, and U3 units) and a pegmatite-bearing unit (PEG Unit) that was initially recognized by Foose (1984). A large anorthositic inclusion (> 1 km thick) is intersected in six deep drill holes in the Highway One corridor area (AN-G Unit in Fig. 8-5). Figure 8-5. Generalized stratigraphy of the marginal zone of the South Kawishiwi intrusion (modified from Severson, 1994; taken from RI-58 figure 6.12). The lowest units of the marginal zone (Fig. 8-5) are the most varied with respect to textures, rock types, and sulfide content. They are very unevenly distributed along the strike length of the SKI in a “compartmentalized” fashion, suggesting a complicated intrusive history. The lowest units were emplaced early into several restricted magma chambers via repeated and close-spaced magmatic pulses. The U1, U2, and U3 units (Fig. 8-5) represent periods of rapid and continuous magma injection that crystallized more primitive ultramafic layers before mixing with the resident magma. The U3 Unit is unique among the lower units in that it contains several massive Page 235 �oxide pods (titanomagnetite-rich) along its entire length. A spatial correspondence between the U3 Unit and footwall iron-formation suggests that most of the massive oxide pods are iron-rich “restite” produced by the magmatic digestion of iron-formation. The U3 Unit also contains the majority of the high PGE values that have been sampled to date within the SKI. The upper units of the SKI are more laterally continuous throughout the intrusion, though recent mapping in the Babbitt NE quadrangle shows significant variation in thickness and, in some cases, pinching out of these upper troctolitic units. Still, the generally greater lateral continuity and monotonous troctolitic composition of these upper units suggest that they crystallized in a more quiescent and open magmatic system characterized by widely-spaced, large volume magmatic pulses. The occurrence of abundant anorthositic inclusions, especially in the uppermost unit (Fig 8-2), implies that much of the growth of the SKI chamber was accomplished by emplacement of new magma between previous troctolitic injections and an anorthositic series hanging wall. Disseminated Cu-Ni Sulfide Mineralization in the PRI and SKI Large resources of low-grade copper-nickel sulfide ore that locally contain anomalous PGE concentrations are well documented by drilling in the basal zones of the Partridge River and South Kawishiwi intrusions. At least nine subeconomic deposits (Fig. 8-3) have been delineated in the basal 100 to 300 meters of both intrusions. The mineralization consists predominantly of disseminated sulfides that collectively constitute over 4.4 billion tons of material averaging 0.66% Cu and 0.20% Ni (Listerud and Meineke, 1977). Overall, the copper to nickel ratio averages 3.3:1; however, there are wide variations in the Cu:Ni ratio from one Cu-Ni deposit to another deposit and also internally within each of the deposits. PGE concentrations average about 10 ppm Pt+Pd (recalculated to 100% sulfide), but may range as high as 50 ppm Pt+Pd (recalculated to 100% sulfide) in associated stratabound zones, such as at the Dunka Road and Birch Lake deposits. The disseminated sulfide deposits are hosted by taxitic troctolitic to gabbroic rocks that contain abundant inclusions of footwall rock types. Within the Partridge River intrusion, the basal unit - Unit I of Severson and Hauck (1990; Fig. 8-4) hosts the vast majority of the disseminated sulfides. Similarly, mineralization within the South Kawishiwi intrusion is confined to the bottom-most units (Fig. 8-5) that include the following units: BH (basal heterogeneous); BAN (basal augite troctolite and norite); three ultramafic units (U1, U2, and U3); and UW (updip wedge). The disseminated sulfide minerals (dominantly pyrrhotite, chalcopyrite, cubanite, and pentlandite) occur as interstitial grains that make up between trace amounts and 10% of the rock by volume (visual estimation). Pyrrhotite is generally the dominant sulfide, especially closer to the basal contact. Although this mineralization type is categorized as being present within the basal portions of the intrusions, it is important to stress that the rock units do not always contain sulfides throughout their entire vertical section. Mineralized zones are independent of rock type and are typically extremely erratic in their spatial extent and ore grades. Zones that are barren of sulfides commonly “interfinger” with mineralized zones in a random pattern. This erratic pattern of mineralization, in part, mirrors the lithologic heterogeneity of the basal units. The only exception to this random mineralization pattern is the Maturi deposit, and its downdip extension (Maturi Extension; Peterson, 2001), where the uppermost portions of the BH Unit generally exhibit copper values in excess of 1.0% that gradually decrease with depth toward the basal contact. Contrasting with this heterogeneity of rock types and mineralization, some internal PGEbearing sulfide zones within the lower units of both intrusions exhibit a stratabound relationship to the igneous stratigraphic section. Examples include Dunka Road and Birch Lake (see discussion below). Page 236 �Basal Cu-Ni Massive Sulfide Mineralization In a few localized areas along the basal zones of the SKI and PRI, semi-massive to massive sulfide mineralization is present at the basal contact. In most cases, the massive to semi-massive sulfide is proximal to either sulfide-rich footwall rocks or structures such as faults and preComplex folds. Massive sulfide zones that are spatially related to sulfide-rich footwall rocks are intersected in scattered drill holes in the Babbitt, Serpentine, and Dunka Pit deposits (Severson and others (1994), Zanko and others (1994), and Severson (1994), respectively). All of these massive sulfides are pyrrhotite-rich (with generally <2% Cu) and are present at, or slightly above, the basal contact. In all cases, a pyrrhotite-rich member of the footwall Virginia Formation (BDD PO unit) is located at the basal contact and is situated up-dip of the massive sulfide occurrences. This relationship suggests that the BDD PO unit acted as a local sulfur source, which generated a Cu-poor, sulfide-rich melt that was gravitationally concentrated downdip, along the basal contact. The massive sulfide occurrence in the Local Boy ore zone of the Babbitt deposit (Fig. 8-3) is clearly structurally controlled. At this locality, the massive sulfide zones are Cu-rich (generally 5-25% Cu) and are situated along the axis of an anticline defined by the footwall rock units. The highest PGE values (11 ppm Pd and 8 ppm Pt) yet found within the Duluth Complex are associated with these structurally-controlled Cu-rich massive sulfides. The massive sulfides are almost exclusively hosted by the Virginia Formation, present as both inclusions above the basal contact and in the footwall rocks below the basal contact. These relationships, plus sulfide textures that are indicative of structural preparation, suggest that the massive sulfides were "injected" into the footwall rocks. Ripley (1986) and Severson and Barnes (1991) propose that an immiscible sulfide melt, formed in an auxiliary magma chamber at depth, was injected into structurally prepared zones in the footwall rocks along the anticline to form the Local Boy ores. Late movement of Cl-rich fluids, along the axis of the anticline, further redistributed and concentrated the PGEs (Severson and Barnes, 1991). Recent studies (Severson and Zanko, in prep.) indicate that there is an overall increase in the Cu-PGE content of the massive sulfide in an east-to-west direction (Fig. 8-6); this is perhaps the result of fractional crystallization of immiscible sulfide melt as it migrated into the footwall rocks. In this scenario, the north-south trending Grano fault is inferred to be a potential feeder zone. Structurally-controlled veins and irregular pods of massive sulfide are locally present within granitic footwall rocks immediately beneath the SKI. These occurrences are intersected in scattered holes that outline two northeast-trending belts (Fig. 8-7). The linearity of the belts suggests they are fault controlled. One of these belts crudely aligns with the Birch Lake fault zone which trends through the Birch Lake PGE prospect. The veins are moderately Cu-enriched due to fractional crystallization of the sulfide melt as it moved down through the footwall rocks (Bonnichsen and others, 1980; Severson, 1994). The occurrence of local massive sulfide veins near and below the basal contact of the Duluth Complex is an indication that larger, potentially economic footwall massive sulfide deposits may yet be found. In the Sudbury Complex, pooling of a monosulfide solid solution (mss) melt at the basal contact appears to be an important prerequisite to the injection of fractionated sulfide melts (Naldrett, 1997). Stratabound PGE Mineralization Most of the PGE-enriched zones in both the Partridge River and South Kawishiwi intrusions are stratabound in nature. These stratabound PGE horizons are intimately associated with the CuNi sulfide mineralization and with one or more ultramafic layers that indicate magma recharge events. Thus, their PGE-enrichment appears to be related to magma mixing. However, there are also indications that the PGE content in some of these horizons was locally modified by later Clrich hydrothermal solutions. Page 237 �231 2400E 3600E 2800E 3200E 4400E 4000E 211 3600S 3600S Axis of Bathtub Syncline 189 149 253 ? 197 4000S 144 217 4000S 230 ? ? ? A-4 228 ? 234 156 A-3 4400S A-5 121 4400S 154 A-6 ? A-2 158 ? U D ? SHAFT A-1 4800S 162 146 138 142 4800S 152 ? ? Axis of Local Boy Anticline ? ? ? 159 143 ? ? 124 B-3 5200S 133 U D B-1 161 132 B-1A B-2 B-2A 136 5200S B-5 B-4 B-3A 150 C-0 Kulas Fault ? ? ? C-1 119 C-1A ? ? D-5 D-4 D-3 D-2 130 160 ? C-2A 116 5600S ? C-2 D-1 ? ? 148 ? 5600S C-3 139 105 127 135 C-3A U C-4 D C-4A 2400E C-5 C-5A C-6 153 6000S 141 134 129 131 137 ? ? Grano Fault 163 140 120 N MASSIVE SULFIDE TYPES: 1. SEMI-CONTINUOUS MASSIVE SULFIDE HORIZONS ASSOCIATED WITH FOOTWALL ROCKS OR HORNFELS INCLUSIONS ABOVE THE BASAL CONTACT Pyrrhotite Dominant i.e. >85% of sulf. is PO Pyrrhotite Rich i.e. 50-85% of sulf. is PO Copper Rich (i.e. PO is 50%, Cu minerals 50%) SCALE 0 100 FT. 2. WIDELY SCATTERED PODS OF SEMIMASSIVE TO MASSIVE SULFIDE ASSOCIATED WITH EITHER HORNFELS INCLUSIONS OR TROCTOLITIC ROCKS (Pyrrhotite Dominant, >85% PO) UNDERGROUND DRIFT B-5 UNDERGROUND DRILL FAN 153 SURFACE DRILL HOLE Figure 8-6. Potential distribution of semi-massive to massive sulfide types, relative to the Grano fault and Local Boy anticlinal axis, at the Local Boy ore zone of the Babbitt deposit (from Severson and Zanko, in prep.; taken from RI-58, Figure 8.4). Page 238 �Figure 8-7. Linear distribution of massive sulfide, disseminated sulfide, and copper-rich veins in the Giants Range granitic footwall rocks beneath the South Kawishiwi intrusion (after Severson, 1994; taken from RI58, Figure 8.5). Stratabound PGE-enriched horizons, with low to moderate sulfide concentrations (0.05-1.0 wt.% S), are commonly associated with ultramafic layers in the Dunka Road, Babbitt, Wetlegs, and Birch Lake deposits (Fig. 8-3). Elevated Cu and PGE concentrations at the Dunka Road deposit occur at the extreme top of Unit I immediately beneath a laterally persistent ultramafic layer. This stratabound horizon (red horizon of Geerts, 1991, 1994) averages about 10 meters thick and contains an average of 1.0 ppm Pd+Pt. Recent work by Theriault and others (1997, 2000) suggests that the sulfur was largely derived from the mafic magma and that this stratabound horizon was formed as a result of magma mixing. Two similar stratabound PGEenriched horizons, related to laterally discontinuous ultramafic layers, occur toward the middle of Unit I at Dunka Road (orange and yellow horizons of Geerts, 1991; 1994). To the west of Dunka Road, the stratabound PGE horizon at the top of Unit I is also present at the Wetlegs and Wyman Creek deposits. There however, the overall Pd content in this horizon exhibits a definite decrease in an east-to-west direction suggesting that as the magma was intruded it became progressively impoverished with respect to PGE (Severson and Hauck, 1997; Theriault and others, 1997). Additional PGE-enriched stratabound horizons are situated much further above the basal contact in the Partridge River intrusion. These horizons are also often associated with ultramafic layers and are present at Dunka Road, Wetlegs and the Fish Lake area (Sassani, 1992; Severson, 1995). Another example of a PGE stratabound horizon is at the Birch Lake PGE prospect within the SKI. There, PGE contents as high as 9 ppm Pd+Pt, and Cr2O3 contents locally as high as 10 wt.%, are associated with a wide variety of rock types within the U3 Unit. The U3 Unit consists of alternating troctolitic and ultramafic layers in which variably sulfide-mineralized zones and discontinuous pods of Cr-bearing massive oxide both occur (Severson, 1994). The massive oxide pods are interpreted, based on empirical relationships, to have been produced by assimilation and partial melting of the Biwabik Iron Formation. This oxide-rich partial melt may have initially acted as a trap that concentrated Cr and Ti, and through further assimilation and contamination of Page 239 �the magma, may have led to precipitation of PGE. However, because the ultramafic layers of the U3 Unit are interpreted to record new influxes of more primitive magma (Severson, 1994), magma mixing may have played a more significant role in PGE mineralization. Furthermore, the presence of Cl-rich drops on the surface of drill core from the Birch Lake area suggests that a hydrothermal model of concentrating the PGE could also be invoked. A model involving ascending Cl-rich hydrothermal fluids, depicted in Figure 8-8 and similar to a model proposed by Boudreau and McCallum (1992), may have remobilized and further concentrated the PGE along the northeast-trending Birch Lake fault (Severson, 1994). A possible explanation, depicted in Figure 8-8, is that the Birch Lake area represents an area where there was a local increase in the amount of upward-moving Cl-rich solutions that were concentrated, or funneled, along the Birch Lake fault. Another explanation is that the Birch Lake Fault may have initially served as a subsidiary feeder zone to the South Kawishiwi intrusion (Hauck and others, in prep.). According to their model, uncontaminated PGE-enriched magmas were vented in the Birch Lake area. Upon mixing with the resident magma, which was contaminated due to interaction with the Biwabik Iron Formation, PGEs were deposited in zones of turbulent mixing. As the magma migrated away from the vent area (up-dip?) it became progressively impoverished with respect to PGEs. Figure 8-8. Schematic diagram showing the possible role that the Birch Lake fault may have played in funneling upward-moving Cl-rich solutions and the resultant reconcentration of significant magmatic PGE within the U3 Unit at the Birch Lake PGE area (modified from Severson, 1994; taken from RI-58, Figure 8.8). Page 240 �Oxide Ultramafic Intrusions (OUI) Exploratory drilling for Cu-Ni mineralization encountered several OUIs, that later were evaluated for their Fe-Ti±V potential. Many of the OUIs are expressed as aeromagnetic highs, commonly with an associated electromagnetic conductor, and thus they were initially drilled in search of conductive sulfide mineralization. At least thirteen OUIs have been intersected in drill holes along the basal contact of the Duluth Complex (Fig. 8-3). The OUIs are plugs or pipe-like bodies that commonly have irregular apophyses. They intrude troctolitic rocks of the Partridge River, Western Margin, and Boulder Lake intrusions. The Waterhen OUI appears to be rootless as defined by detailed drilling; the three-dimensional configurations of the other OUIs are unknown due to insufficient drilling. In general, the OUIs are spatially arranged along linear trends suggesting that structural control was important to their genesis. Almost all of the OUIs are cross-cutting. Rock types include coarse-grained to pegmatitic clinopyroxenite, dunite, peridotite, melatroctolite, and minor melagabbro; all rock types are oxide-bearing. Some OUIs exhibit a crude zonation from an olivine-rich core (dunite, peridotite, melatroctolite) to an outer clinopyroxenite margin, whereas others consist of only one dominant rock type. Oxide content is variable in the OUIs and ranges from 15% in disseminated zones to 100% in localized massive oxide zones. OUIs that contain thick intervals of massive oxide include Longnose (up to 30 meters thick; Linscheid, 1991) and Section 34 (up to 40 m thick; Severson, 1995). Titanomagnetite is dominant in some of the OUIs whereas ilmenite is dominant in other OUIs. Sulfide minerals (predominantly pyrrhotite) are ubiquitous in all the OUIs and range from trace amounts to 5% in disseminated zones to >70% in localized net-textured and massive sulfide zones, as at Waterhen, Boulder Lake South, and Fish Lake (Fig. 8-3). Page 241 �STOP DESCRIPTIONS STOP 8-1: Hornfels Virginia Formation, Duluth Complex Footwall at Linwood Lake Location: Approximately 300 feet southwest of the intersection of Linwood Lake Road and Reagan Road. Harris Lake 7.5’ quadrangle, T.56N., R.14W., Sec 22, NE of SE of SW; 567865E, 52407780N (NAD83) Description: Outcrops of the Virginia Formation at Linwood Lake show a progressive increase in the amount of deformation, metamorphism, and degree of partial melting towards the basal contact of the Duluth Complex (which based on limited drilling in this area exhibits a nearvertical cliff-like geometry). In this area, outcrops furthest from the contact consist of interbedded argillite and fine-grained distal graywacke (Bouma sequence B with minor C) that exhibit shallow dips of 15° to the southeast. However, slightly closer to the Complex, bedding dips increase to 40-60° to the northeast and small wisps (<5 mm) of partial melt are present along bedding planes. Still closer to the Complex (Stop 8-1) the grade of metamorphism and associated deformation progressively increase and at least two metamorphic varieties are superimposed on the original sedimentary package. Both of these metamorphic varieties are visible at this stop and consist of the following: Disrupted unit (Fig. 8-9)– In close proximity to the Complex the well-bedded sediments of the Virginia Formation are typically transformed into a highly deformed rock or metatexite (Sawyer, 1999). Textures that characterize this rock are bedding planes that are extremely chaotic and random in orientation due to small-scale folding, faulting, and brecciation. Superimposed on this chaotic pattern are abundant zones of partial melt that are also chaotic and folded. Albeit differences in grain size, the partial melts are composed of the same mineralogy as the surrounding sedimentary rocks (feldspar, quartz, orthopyroxene, cordierite, and biotite). Figure 8-9. Photograph of disrupted unit of metamorphosed and folded Virginia Formation with abundant partial melt lenses and wisps in close proximity to the Duluth Complex at Linwood Lake, MN. Page 242 �Recrystallized unit (Fig. 8-10)– This unit is a higher-grade metamorphic equivalent of the disrupted unit, and is properly classed as a diatexite (Sawyer, 1999). By contrast, rocks of the recrystallized unit were heated, generating 20-40% pervasive partial melts, which literally enabled the rocks to flow in response to stresses that were applied during emplacement of the Duluth Complex. All bedding planes are obliterated and what remains is a medium-grained recrystallized rock that contains plagioclase, cordierite, orthopyroxene, and decussate biotite. Within this recrystallized matrix are blocks/boudins of more structurally competent siltstone and calc-silicate hornfels (originally limey layers). Figure 8-10: Photograph of recrystallized unit of metamorphosed Virginia Formation in close proximity to the Duluth Complex at Linwood Lake, MN. STOP 8-2: Anorthositic Series, Duluth Complex, Skibo Vista Location: Roadcut on St. Louis Co. Highway 110, approx. 3.7 mi. north of Co. Hwy 16. Bird Lake 7.5' quadrangle; T.57N., R.13W., Sec 17, SE of NW; 574140E 5252806N (NAD83) Description: Exposed in roadcuts on either side of Co. 110 is an exposure of poikilitic troctolitic anorthosite that is a common lithology of the anorthositic series of the Duluth Complex. The rock varies in texture and modal mineralogy on a meter scale over the outcrops ranging from medium- to medium coarse in grain size, from subpoikilitic to poikilitic in olivine habit, and from 80 to 90% in plagioclase mode. Plagioclase foliation is locally well developed and varies in orientation throughout the exposures. Olivine oikocrysts range from 1 to 5 cm in diameter (larger ones on north side of exposures) and are locally concentrated in planes that parallel foliation and thereby impart a subtle layering. This exposure lies at the western extent of a large expanse of plagioclase-rich gabbroic rocks that comprise the Anorthositic Series of the Duluth Complex (Fig. 8-1). West of here, troctolitic cumulates of the Western Margin intrusion are inferred to occur (Figs. 8-1, 8-2). The lithologic characteristics and structural complexities of the Anorthositic Series, which are hinted at here, Page 243 �have lead many workers (Grout, 1918; Taylor, 1964; Miller and Weiblen, 1990) to conclude that these rocks formed from multiple injections of plagioclase-enriched mafic magmas (plagioclase crystal mushes) early in the main stage of Duluth Complex magmatism. The effectively identical ages of Anorthositic and Layered Series rocks (~1099Ma, Paces and Miller, 1993) implies that intrusion of normal (crystal-free) magmas, forming layered series intrusions like the Western Margin Intrusion, followed soon after the emplacement and crystallization of the Anorthositic Series. STOP 8-3a: Erie hornfels – mafic volcanic unit overlying the Virginia Formation, Erie/LTV RR Grade Location: Access via Dunka Road (private mining company road) approximately 5 miles west the LTV guard shack. Allen 7.5’ quadrangle, T.59N., R.13W., Sec 18, NW of SE of SW; 571815E 5271060N (NAD83) Description: Inclusions of hornfelsed basalt bodies are documented in many places in the Duluth Complex – the earliest detailed studies were by Kilburg (1972), for the Ely’s Peak basalts beneath the Complex near Duluth, MN, and Bonnichsen (1972), for several inclusions located within the Complex. The Erie hornfels was originally discussed by Bonnichsen (1972), and was more recently described in detail by Tyson (1976). Detailed geologic mapping of the area (Severson and Miller, 1999) indicates that the Erie hornfels directly overlies the Virginia Formation (based on the geology in surrounding drill holes) and is most likely situated near the base of the North Shore Volcanic Group in this area. The Erie hornfels is exposed in a 215-meter long railroad cut. Tyson (1976) described it as a series of basalt flows, dipping 55° to the southeast, that are characterized by fine-grained granoblastic rocks containing variable amounts of plagioclase, olivine, and augite with lesser amounts of hornblende and biotite. Relict amygdules (plagioclase- or augite-filled ovoids) and relict plagioclase phenocrysts are present in many places in the railroad cut but the amygdules appear to be more concentrated in the upper portions of the flows. Tyson (1976) also reports that biotite-rich layers are locally present in the exposures and that these layers were probably formed from either interflow sedimentary rocks or altered flow tops. STOP 8-3b: Marginal Units of the Partridge River Intrusion, Erie/LTV RR Grade Location: Erie/LTV RR Grade approximately 1/3 mile east of previous stop. Allen 7.5’ quadrangle, T.59N., R.13W., Sec 18, SE of SE, and Sec 19, SW of SW; traverse from 572430E, 5271135N to 572960E, 5271205N (NAD83) Description: The Wetlegs Cu-Ni deposit was initially drilled by Bear Creek Mining in 19581960 (referred to as the A4 grid) on the basis of electromagnetic conductors which were found to be related to graphitic portions of the footwall Virginia Formation. Some indications of Cu-Ni mineralization were found in the initial drilling and after acquiring state mineral leases in 1966 Bear Creek conducted some follow-up drilling. However, the Cu-Ni grades were low overall, and Bear Creek abandoned further mineral exploration endeavors in this area of the Complex. Exxon Minerals Corp. leased the same lands and conducted drilling programs in 1975 and 1979. They estimated that the Wetlegs deposit contained 38 million tons of material grading 0.29% Cu and 0.10% Ni using a cutoff grade of 0.15% Cu. Recent sampling for platinum group elements (PGE) indicates that there are at least three potential stratabound zones at Wetlegs (Severson and Hauck, 2003). Page 244 �A west to east traverse along the LTV railroad tracks will be conducted at this field stop. The traverse, approximately 0.5 miles long, will start at the basal contact and progress upwards through the igneous stratigraphy of the Partridge River intrusion. Outcrops of Units I and III will be viewed. A generalized geologic map of the Wetlegs area is shown in Figure 8-11. Detailed descriptions of the railroad cuts are listed below. Oxide Ultramafic Intrusion Troctolite (V) Augite Troctolite(IV) PoikiliticTroctolite (III) Melatroctolite (II) Contact Zone (I) EEl MaficVolanic H or n fe Is Virginia Formation Figure 8-11: Geology of the Partridge River Intrusion in the vicinity of the Wetlegs Cu-Ni deposit showing stops 8-3a (Erie hornfels) and 8-3b (Wetlegs deposit). Roman numerals correspond to stratigraphic units of Severson and Hauck (1990). Modified from Severson and Miller (1999). Feet (to the East) Description 0 ft. 100-110 ft. (left side of tracks) Railroad culvert – Longnose Creek Sulfide/gossan-cemented till consisting mostly of large boulders of a pyrrhotite- and graphite-rich member of the Virginia Formation (the BDD PO unit). Note the rounded granite cobbles beneath the BDD PO boulders. Drilling indicates that the BDD PO subcrops very close to this location. 337-355 ft. Very fine-grained (chilled) gabbronorite at basal contact with 60% (left side of tracks) plagioclase, 30% orthopyroxene, 5 % clinopyroxene, trace to 2 % biotite, and 3 % oxides. The outcrop contains well-assimilated “streaks” of Virginia Formation inclusions (very hard to see). 400-1025 ft. Unit I – taxitic medium- to coarse-grained ophitic augite troctolite (POcf) to (both sides of olivine gabbro (PcOf) with patches and lenses of augite-rich pegmatite. tracks) The outcrops are sulfide bearing with the sulfides unevenly distributed along patches, spots, lenses, and joint faces (at numerous orientations!). Trace amounts to 5% uralite due to pervasive deuteric alteration is present. 1245-1355 ft. Unit I – taxitic, pervasively uralitized, medium- to coarse-grained ophitic (two outcrops on olivine gabbro (PcOf) to augite troctolite (POcf) with trace to 1% sulfides. left side of tracks) Also present within these outcrops are very coarse-grained anorthosite inclusions that vary from 10 cm across to 3x5 meter blocks. The edges of the inclusions are sharp, and straight to highly lobate. Within the inclusions, the plagioclase foliation is subvertical and highly variable. Unit I – taxitic, medium- to coarse-grained ophitic augitic troctolite (POcf) 1385-1685 ft. (many outcrops on with abundant irregular pegmatitic patches and lenses. The pegmatites Page 245 �both sides tracks) of contain variable amounts of saussurized plagioclase, clinopyroxene, oxides, biotite, and uralite, with minor quartz, k-feldspar, graphic granite, and sulfides. Most of the sulfides are either within or adjacent to the pegmatites. Uralite is common throughout the outcrops as pervasive replacement products in irregular patches and along joints. 2355-2480 ft. Unit III – mottled, poikilitic/ophitic troctolite (Po(cf)) to augite troctolite (four outcrops on (Pocf). This is a major marker bed due to the presence of medium- to highboth sides of the density olivine oikocrysts up to 10 cm across. This unit is easily recognized tracks) in drill core due to the mottled texture, and the relatively finer-grained plagioclase (1-5 mm). Dunka Road and Babbitt Deposits As the bus proceeds to the next field stop, we will traverse across the southernmost limits of the Dunka Road deposit (originally drilled by United States Steel, now held by PolyMet Mining and called the NorthMet deposit) and the Babbitt deposit (originally drilled by Bear Creek and Amax, now held by Teck Cominco and called the Mesaba deposit). There is very little to see in the way of mineralized exposures for either of these deposits. However, one point to keep in mind is the immense size of these low-grade deposits. The Dunka Road/NorthMet deposit extends for about 3 miles along the road, and the Babbitt/Mesaba deposit extends for another 2.5 miles along the road (the deposits are separated by undrilled and untested area that is about 1 mile wide). STOP 8-4: Hornfels mafic volcanic inclusion and oxide ultramafic intrusions near the margin of the Partridge River Intrusion Location: Erie/LTV RR Grade approximately 2 miles west of the locked gate on the Dunka Road. Babbitt NE 7.5’ quadrangle T. 60N., R.13W., Sec 33.; 584510E, 5275715N (NAD83) Description: The Dunka Railroad hornfels is a large mafic volcanic inclusion located near the eastern margin of the Partridge River intrusion and just south of the Babbitt/Mesaba deposit. Outcrops and drill hole information indicates that the inclusion is about 900 x 1,500 meters across. The hornfels is a fine-grained, granoblastic to poikiloblastic basaltic hornfels that contains variable amounts of plagioclase, augite, hypersthene, inverted pigeonite, and olivine. Both massive and meta-amydaloidal varieties are present. In addition to the basaltic hornfels, several small bodies of late intrusive OUIs are also present in the railroad cuts. The abundance of OUIs at this locality is related to proximity to the north-trending Grano Fault, which may have served as a feeder vent for the massive sulfides at the Local Boy area of the Babbitt/Mesaba deposit. These OUIs, and a wide variety of granitic rocks, occur as lenses and bodies that cut the troctolitic rocks of the Partridge River intrusion. They are extremely common in drill holes, within a 400-580 meter wide zone, on the west side of the Grano Fault. The OUIs at this locality are characterized by medium- to coarse-grained clinopyroxenite with 75-80% augite, 0-15% olivine, <5% interstitial plagioclase, and 5-15% oxides (ilmenite is dominant). Contact relationships with the basaltic hornfels are sharp but highly irregular and lobate. Granitic dikes and veins, present within a NNE-trending zone, are also evident in the exposures. They are rarely observed in close proximity to the OUI, but where they are, the dikes crosscut the OUI. Page 246 �STOP 8-5: Cu-Ni sulfide mineralization, Spruce Road deposit, South Kawishiwi Intrusion Location: Barrow pit 200 feet west of Spruce Road (Forest Rd 181) approximately 3.5 miles north of Highway One. Bogberry Lake 7.5’ quadrangle, T.62N., R.11W., Sec 24, NE of SE of SW; 599295E, 5299010N (NAD83) Description: It all started here! Serious exploration for Cu-Ni deposits at the base of the Duluth Complex began somewhere near this site in 1948 when strongly mineralized and gossanous rocks were uncovered in an excavation into weathered gabbro rubble used to build the Spruce Road. Local prospector Fred S. Childers of Ely, MN, noted copper stains in the material and began searching the outcrops along the basal contact in the vicinity of the Kawishiwi River. Roger V. Whiteside of Duluth, MN, later joined him in further exploration. In 1951, they diamond drilled a 57 meter (188 feet) deep hole located several miles to the southwest of this site in what is now referred to as the Maturi deposit (Fig. 8-3). This hole intersected disseminated sulfides in gabbroic rock that averaged 0.36% Cu and 0.13% Ni (Watowich and others, 1981). In 1952, both Bear Creek Mining Company and the International Nickel Company (INCO) began intensive exploration efforts along a 61 km-long zone (38 miles) that coincided with the basal contact (an area stretching from south of the town of Hoyt Lakes northeastward to this site at Spruce Road). INCO eventually picked up the Childers-Whiteside properties and began drilling activities in 1954; whereas, Bear Creek concentrated most of their effort near the town of Babbitt and drilled several properties during 1957-1960. During this same period, the Minnesota Geological Survey, in cooperation with the U.S. Bureau of Mines, began an examination of the Maturi-Spruce Road area that culminated in the drilling of three holes in 1953. All of these exploration efforts indicated that large tonnage, but low grade, disseminated Cu-Ni deposits were present along the basal contact. In 1966, the Minnesota Department of Conservation adopted rules for state mineral leases. The leases were offered through the Department of Natural Resources (DNR) and were awarded to successful bidders. Since 1966, over 20 companies have been actively involved in exploration for Cu-Ni and Fe-Ti-V deposits along the basal contact of the Complex and over 1.700 holes totaling over 1.5 million feet of core have been drilled. In regards to the Spruce Road deposit, INCO drilled over 150 holes on the property at approximately 200-foot spacings. They calculated that the deposit contains 248 million tons of low-grade material averaging 0.46% Cu and 0.17% Ni. INCO collected at least two bulk samples from Spruce Road: 1) a 1,150 ton sample from several unknown small pits in 1966-67 (Watowich and others, 1981) and; 2) a 10,000 ton sample in 1974. It is uncertain if this barrow pit is one of the 1966-67 INCO bulk sample sites or if this pit was only used for road material. Rock types at this pit consist of sulfide-bearing, taxitic augite troctolite and olivine gabbro of the BH Unit (Basal Heterogeneous Unit) in the Marginal Zone of the South Kawishiwi intrusion. The BH Unit is approximately 360 meters thick (1,200 feet) at Spruce Road. Footwall rocks at Spruce Road consist dominantly of granitic rocks of the Archean Giants Range batholith; but in local areas the Biwabik Iron Formation is still preserved beneath the basal contact. At this locale, the pit is situated about 150 meters (480 feet) above the basal contact. Cu-Ni grades in the top of a nearby drill hole (34801) are 0.51-0.63% Cu and 0.15-0.17% Ni. Page 247 �Figure 8-12: Location map of Stop 8-5 at the Spruce Road Cu-Ni deposit. Two possible INCO bulk sample sites are shown (this stop included), as well as, the reclaimed location of a 10,000 ton bulk sample collected by INCO in 1974. STOP 8-6: Quarry exposure of homogeneous troctolite, South Kawishiwi Intrusion Location: Approx. 3.0 miles south of Spruce Road on Highway 1; follow old access road to abandoned quarry about 800m S of Highway 1. Bogberry Lake 7.5' quad; T.61N., R.11W., Sec 11, SE of NW; 597940E 5293550W (NAD83) Description: This abandoned quarry provides a 3-dimensional look at the remarkable homogeneity of troctolitic cumulates, which compose most the South Kawishiwi (and Partridge River) intrusion. The average rock type is a medium-grained, moderately foliated, augite-poor troctolite. Moderately aligned, cumulus plagioclase makes up 70-75% of the rock, though locally up to 80% plagioclase occurs and the rock would be classified as a leucotroctolite. Subhedral granular olivine composes 20-25% of the average rock, though here too, local olivine enrichment Page 248 �of up to 30% occurs in thin layers parallel to foliation. Interstitial augite and Fe-Ti oxide compose 3-7% of the rock. The textural and mineralogic homogeneity of the troctolitic cumulates composing the middle to upper sections of the SKI (and PRI), and displayed here, are matched by limited variation in mineral compositions of plagioclase, olivine and pyroxene. Phinney (1969) reported a range of plagioclase and olivine compositions in troctolitic units of SKI (excluding the marginal rocks) of An57-72 and Fo50-63, respectively. Similar results are displayed by unpublished microprobe data from troctolitic rocks from the Babbitt NE quadrangle, which indicate olivine compositions of Fo50-65 and augite compositions of En68-75. Many see this lithologic homogeneity and lack of significant cryptic variation as indicating that the SKI and PRI magma systems were open to frequent recharge of relatively primitive magma (Severson, 1994; Lee and Ripley, 1996; Miller and Ripley, 1996). New recharge events are commonly marked by the intermittent occurrences of olivine-rich (melatroctolite) intervals separating otherwise subtle differences in troctolite texture and mode (Severson, 1994). These melatroctolite intervals show a significant increase in An, Fo, and En compositions consistent with the recharge of a more primitive magma. An alternative explanation has been put forth by Chalokwu (Chalokwu and Grant, 1990; Chalokwu and others, 1993). He has suggested that this homogeneity is indicative of single stage emplacement of a viscous semi-crystallized olivine-plagioclase mush that experienced little in situ differentiation. However, his sampling routinely overlooked the melatroctolite intervals. STOP 8-7: Anorthositic inclusion? in troctolite, South Kawishiwi Intrusion Location: Road cut on Tomahawk Rd. about 7.5 miles west of Highway 1; Babbitt NE 7.5' quad; T.60N., R.11W., Sec 18, center of NE; 592355E 5282430W (NAD83) Description: Scattered throughout the entire sequence of monotonous troctolitic cumulates are masses of coarse- to medium-grained troctolitic anorthosite to olivine gabbroic anorthosite. In recent mapping of the Babbitt NE quadrangle (Miller, Severson and Foose, 2002), we (Miller and Severson) have consistently interpreted these anorthositic masses as inclusions. We believe that they represent pieces of the anorthositic series roof pendant that was upwardly displaced and dissaggregated with successive recharge events into the SKI magma chamber. In an earlier detailed field mapping of this mixed anorthosite-troctolite terrane, mainly to the northeast of here, Foose and Cooper (1978, 1981) interpreted many of these anorthositic bodies as comagmatic layers within the troctolite. They saw their elongate and conformable relationship with the internal structure of the enclosing troctolite as evidence that most of these bodies are lensoidal plagioclase cumulate intervals intermittently layered within the troctolite. They used the apparent offset of these layers as evidence for a complex fault pattern (Fig. 8-13). This stop along the Tomahawk road will examine one such example of a troctolitic anorthosite body within leucotroctolitic cumulates. This interval of the SKI is particularly rich in anorthosite bodies. The relationships displayed here are difficult to reconcile with either the Miller and others (2002) or the Foose and Cooper (1978,1981) interpretations. An irregularly shaped anorthosite block projects into the leucotroctolite and appears to cut across the foliation in the enclosing leucotroctolite (Fig. 8-13). Page 249 �Figure 8-13. Geologic map of the Harris Lake area, which is northeast of Stop 8-7 from by Foose and Cooper (1981). Map units are: 1 - augite troctolite, 2 - troctolite, 2a - ophitic augite troctolite layer, 2b - traceable anorthosite layer, 3 - anorthosite haAn.csgaLx ,!aa 44/ •i Page 250 Figure 8-14. Photo of road cut at Stop 8-7 showing an irregularly shaped troctolitic anorthosite mass in leucotroctolite. Foliation in the leucotroctolite is approximately parallel to the hammer. �STOP 8-8: Grano fault zone, Partridge River Intrusion (optional) Location: Small exposure north of Forest Rd 113, 100m east ; Babbitt SE 7.5' quad; T.59N., R.12W., Sec 16, NW of NW; 584486E 5272519W (NAD83) Description: The Grano fault is a major N-S trending structure that was first recognized in the subsurface by compiling exploration drill hole data related to the Babbitt and Serpentine deposit areas (Severson, 1994). As shown in Fig. 8-15, the fault creates a significant (~60m) displacement (down to the east) of the Duluth Complex footwall and affects both the Partridge River and the South Kawishiwi Intrusions. Drill holes into the fault zone in the southeastern portion of the Babbitt deposit shows that to the immediate west of the fault is a 400-580 meterwide (up to 2,000 feet) zone that contains abundant subvertical lenses of granophyre and OUI. To the north along the fault trace the zone with late subvertical lenses pinches down appreciably (not present at Serpentine) and the amount of motion along the fault diminishes as well, indicating that the fault is a “scissors-type” fault. The massive sulfides of the Local Boy ore zone of the Babbitt deposit have been inferred to have been “vented” from the Grano fault. The surface expression of the fault is a prominent linear valley that can be traced over 10 kilometers south from the basal contact (Fig. 8-16). This stop is in the axis of that valley. The rock types exposed on the margins of this valley are a complex mixture of augite leucotroctolite with poikilitic olivine, ophitic augite troctolite to olivine gabbro, poikilitic olivine gabbroic anorthosite, and locally granophyric gabbroic pegmatite. This assemblage represents a complex mix of anorthositic series inclusions and unmineralized marginal zone rocks of the Partridge River Intrusion. The granophyric gabbroic pegmatite is evidently related to a late, volatile-rich mafic magma intruded into Grano fault zone. In the small pavement exposure near the road, a medium-grained poikilitic augite leucotroctolite is cut by gabbroic pegmatite. Figure 8-15. Grayscale image of the footwall topography of the Partridge River and South Kawishiwi intrusions near their contact showing the subsurface expression of the Grano Fault (image generated by Dean Peterson) Page 251 �I•i-_• -- '-.• 2000 m Figure 8-16. Grayscale image of surface topography of the Partridge River and South Kawishiwi intrusions near their contact showing the surface expression of the Grano Fault. Lines show geologic contacts and faults taken from MGS Misc. Map M-119. SKI - South Kawishiwi intrusion; PRI - Partridge River intrusion; AS - anorthositic series; PG - "Powerline Gabbro" of Bonnichsen (1974); HB hornfels basalt; BIF - Biwabik Iron-formation; VF - Virginia Formation. STOP 8-9: Volcanic hornfels and plagioclase-phyric leucogabbro, Partridge River Intrusion Location: Roadcuts along Erie/LTV RR grade approx 1km west of crossing by Forest Rd 113 Babbitt SW 7.5' quad; T.59N., R.12W., Sec 18, SW of SW; 581500E 5271020W (NAD83) Description: Scattered throughout the homogeneous troctolites of the Partridge River intrusion are kilometer-scale inclusions that are composed of various mixtures of anorthositic rocks, volcanic hornfels and oxide gabbro (Fig. 8-2). This assemblage is thought to represent initial intrusions of anorthositic series magmas into the base of the volcanic pile during the main stage of Duluth Complex magmatism (~1099 Ma). The anorthositic rock lithologies, which dominate the Anorthositic Series throughout the Duluth Complex, are interpreted to have crystallized from plagioclase crystal mushes (evolved basaltic melts laden with suspended plagioclase crystals). However, in this area, these anorthositic rocks are locally intruded by oxide gabbro. Bonnichsen (1974b) speculated that the oxide gabbro, which he termed the Powerline Gabbro, may be a differentiate of the Partridge River intrusion. However, detailed mapping in the Allen quadrangle to the west (Severson and Miller, 1999) demonstrated that this gabbro is intruded by troctolitic rocks of the PRI. We consider the gabbro to be a plagioclase-poor component of the Anorthositic Series. In a roadside exposure on the forest road, we can see a typical example of the "Powerline Gabbro". It is a coarse-grained, non-foliated, subophitic olivine oxide gabbro composed of 55% plagioclase, 20% granular olivine, 15% subophitic augite, 10%anhedral Fe-Ti oxide, and trace amounts of hornblende and biotite. The mafic phases locally show incipient granoblastic Page 252 �recrystallization textures and plagioclase and augite display moderate clouding by the exsolution of oxide needles. Both features are indicative of thermal metamorphism. About 200 m through the woods to the north of the forest road, we come upon the Erie/LTV railroad grade. Exposed along a 500m-long road cut on both sides of the grade is a complex mixture of two general rock types. Most of the exposure is a very fine-grained, dense mafic volcanic hornfels that is sparsely plagioclase porphyritic. In thin section, the hornfels displays a perfect granoblastic texture (Fig. 8-17). In sharp to abrupt contact with this volcanic hornfels is a medium grained plagioclase porphyritic leucogabbro. In thin section (Fig. 8-17), the leucogabbro is composed of strongly zoned plagioclase phenocrysts, which show deep clouding by oxide needles, in a matrix of granoblastic-textured oxide melagabbro (40%Pl, 30% Aug, 30% Fe-Ti Ox). At the contacts between the hornfels and the leucogabbro (best seen on the upper surface of the northern roadcut), the plagioclase phenocrysts in the leucogabbro show a strong alignment parallel to a steep contact with the hornfels. One possible interpretation of this leucogabbro is that it represents a chilled intrusion of plagioclase crystal mush that was emplaced into the volcanic pile early in the emplacement of the anorthositic series. Subsequent intrusions of more voluminous anorthositic series magma and later layered series magma forming the Partridge River intrusion produced the strong thermal metamorphism now evident in both the mafic volcanic and the porphyritic leucogabbro. Figure 8-17. Photomicrographs of mafic volcanic hornfels and plagioclase-phyric leucogabbro observed at Stop 8-9. Page 253 �STOP 8-10: Cross-bedded Colvin Creek hornfels, Partridge River Intrusion Location: Approximately 0.5 miles south of where Forest Rd 113 crosses the south branch of the Partridge River and 520 meters (1700 feet) east along a flagged trail. Babbitt SW 7.5' quadrangle; T.59N., R.13W., Sec 25, NE of SW of SE; 580255E 5267943N (NAD83) Description: Magnetic basalt hornfels inclusions (most notably the Colvin Creek hornfels) within the Duluth Complex were first observed by Bonnichsen (1972) and first described in some detail by Tyson (1976). According to Tyson, the magnetic basalt flows of the Colvin Creek hornfels are characterized by fine-grained granoblastic rocks composed of plagioclase, augite, and magnetite with relict plagioclase- and augite-filled amygdules. Tyson (1976) noted a major difference between the magnetic basalts and the more common non-magnetic basalt inclusions (as in stops 8-3a and 8-4) and theorized that the magnetic basalts were derived from weathered and oxidized basalt flows that were subsequently metamorphosed by the Complex. Tyson’s work was of a reconnaissance nature and much more detailed work has since been completed on the Northern Colvin Creek Body by Patelke (1996). The Northern Colvin Creek Body is a large inclusion (2,500 X 800 meters), associated with a magnetic high, that has been rotated to near vertical and exhibits excellent stratigraphic tops to the northwest. Patelke (1996) subdivided the northern Colvin Creek Body into five mappeable units including two metavolcanic units, two intrusive gabbroic sill units, and a cross-bedded sedimentary unit. Within the metavolcanic units, each consisting of multiple basalt flows, Patelke (1996) identified several volcanic features that include: pipe amygdules, sheeted amygdules, and local convoluted flow bases. Figure 8-18. Photograph of cross-bedded “microgabbroic” sediment (X-BDD Unit) of the Northern Colvin Creek Body. Enigmatic cross-bedded sedimentary rocks, with near-vertical dips, were first discovered in the Northern Colvin Creek hornfels and reported by Severson and Hauck (1990). They mapped a X-BDD Unit that exhibited a strike length of over 1,600 meters and an exposed thickness of over 240 meters. Overall the cross-bedded rocks are gabbroic in composition and consist of very finegrained granoblastic concentrations of plagioclase, diopsidic augite, and magnetite with lessor amounts of ilmenite, orthopyroxene, and poikiloblastic pyroxene – the rocks do NOT contain Page 254 �quartz or biotite, nor a basal conglomeratic unit where it overlies magnetic basalt (Patelke, 1996). Because sedimentary-like features were found in the cross-bedded rocks, and in the overlying gabbroic rocks (both with near-vertical dips), Severson and Hauck (1990) postulated that the cross-bedded rocks were deposited via magmatic density currents (a concept they no longer believe in). More recent studies by Patelke (1996) suggests that these cross-bedded rocks were sedimentary and were most likely deposited in a restricted basin as an eolian sediment that was derived from a strictly basaltic terrain (thus no quartz). Whatever their origin, these rocks exhibit beautiful sedimentary structures that include: bedding, cross-bedding, density-graded modal layering, and scour and fill structures (Patelke, 1996). Patelke (1996) suggests that the crossbedded rocks of the Colvin Creek hornfels are similar to a thin sandstone unit near Phantom Lake, north of Two Harbors, MN. However, he also cautions that neither of these sedimentary units are analogous to any of the typical interflow sandstones of the North Shore Volcanic Group as described by Jirsa (1984). Cross-bedded sediments with a gabbroic composition have been found at six locations within the Duluth Complex (most recently shown on a map in Severson, 1995; and in Severson and Miller, 1999). The last stop of this field trip is at one of the more “easily” accessible crossbedded localities. At this locale, the cross-bedded sediments exhibit shallow dips to the northeast and only about 10 feet of stratigraphic section are exposed. The best exposures are present in the northern Colvin Creek Body which is located about two miles to the west of this stop in sections 27, 33, and 34, T.59N., R.13W. A more complete description of the units exposed at the northern body, and a thorough examination of their origin, can be found in Patelke (1996). Figure 8-19: Scanned polished thin section image and photomicrographs of X-BDD Unit of the Northern Colvin Creek Body. Page 255 �References Allen, D.J., Hinze, W.J., Dickas, A.B., and Mudrey, M.G., Jr., 1997, Integrated geophysical modeling of the North American Midcontinent Rift System: New interpretations for western Lake Superior, northwestern Wisconsin, and eastern Minnesota. In: Ojakangas, R.J., Dickas, A.B., Green, J.C., (eds.) Middle Proterozoic to Cambrian Rifting, Central North America: Geological Society of America Special Paper 312, p.47-72. Bonnichsen, B., 1972, Southern part of the Duluth Complex. In: Sims, P.K. & Morey, G.B. (eds.) Geology of Minnesota - A centennial volume. Minnesota Geological Survey, p. 361-388 Bonnichsen, B., 1974a. Copper and nickel resources in the Duluth Complex, northeastern Minnesota. Minnesota Geological Survey Information Circular 10, 24p. Bonnichsen, B., 1974b. Geology of the Ely-Hoyt Lakes district, northeastern Minnesota. Unpublished report by the Minnesota Geological Survey for the Minnesota Department of Natural Resources, 30 p. Bonnichsen, B., Fukui, L.M., and Chang, L.L.Y., 1980, Geologic setting, mineralogy, and geochemistry of magmatic sulfides, South Kawishiwi Intrusion, Duluth Complex, Minnesota: Proceedings, IAGOD Symposium, 5th Stuttgart, Germany, p. 545-565. Boudreau, A.E., and McCallum, I.S., 1992, Concentration of platinum group-elements by magmatic fluids in layered intrusions: Economic Geology, v. 87, p.1830-1848 Chalokwu, C.I. & Grant, N.K., 1990. Petrology of the Partridge River intrusion, Duluth Complex, Minnesota: I. Relationships between mineral compositions, density, and trapped liquid abundance. J. Petrology 31, 265-93. Chalokwu, C.I. & Grant, N.K., Ariskin, A.A., & Barmina, G.S., 1993., Simulation of primary phase relations and mineral compositions in the Partridge River intrusion, Duluth Complex, Minnesota: implications for the parent magma composition. Contrib. Mineral. Petrol. 114, 539-49. Chandler, V.W., 1990, Geologic interpretation of gravity and magnetic data over the central part of the Duluth Complex, northeastern Minnesota. Economic Geology, v. 85, p. 816-829 Foose, M.P., 1984, Drill logs and correlations within part of the South Kawishiwi intrusion, Duluth, Minnesota. U.S. Geological Survey Open-file Report 84-14, 230p. Foose, M.P., and Cooper, R.W., 1978, Preliminary geologic report on the Harris Lake area, northeastern Minnesota. U.S. Geological Survey Open-file Report 78-385, 24pp. with map, scale 1:12,000 Foose, M.P., and Cooper, R.W., 1981, Faulting and fracturing in part of the Duluth Complex, northeastern Minnesota. Canadian Journal of Earth Science, v. 18, p. 810-814. Geerts, S.D., 1991. Geology, stratigraphy, and mineralization of the Dunka Road Cu-Ni prospect, northeastern Minnesota. Natural Resources Research Institute, University of Minnesota, Duluth, Technical Report, NRRI/TR-91-14, 63p. Geerts, S.D., 1994, Petrography and geochemistry of a platinum group element-bearing horizon in the Dunka Road prospect, (Keweenawan) Duluth Complex, northeastern Minnesota: Unpubl. M.S. thesis, Univ. Minn., Duluth, 155 p. Green, J.C., Phinney, W.C., & Weiblen, P.W., 1966. Gabbro Lake quadrangle, Lake County, Minnesota. Minnesota Geological Survey Miscellaneous Map M-2, scale 1:24,000 Grout, F.F., 1918, Internal structures of igneous rocks; their significance and origin with special reference to the Duluth Gabbro. Journal of Geology 26, 439-458 Hauck, S.A., Miller, J.D., Jr., Severson, M.J., in prep., Petrographic, geochemical, and oxide, sulfide, and platinum-group mineral relationships between the PEG and U3 Units, Birch Lake area, South Kawishiwi intrusion, Duluth Complex, Minnesota: Natural Resources Research Institute, University of Minnesota, Duluth, Technical Report. Jirsa, M. A., 1984, Interflow sedimentary rocks in the Keweenawan North Shore Volcanic Group, northeastern Minnesota. Minnesota Geological Survey Report of Investigations 30, 20 pp. Kilburg, J.A., 1972, Petrology, structure, and correlation of the Upper Precambrian Ely's Peak basalt. Unpublished M.S. thesis, University of Minnesota, Duluth, 97 p. Lee, I., and Ripley, E.M., 1996, Mineralogic and stable isotopic studies of the South Kawishiwi intrusion, Spruce Road Area, Duluth Complex, Minnesota. Journal of Petrology, v. 37, p. 1437-1461. Page 256 �Linscheid, E.K., 1991, The petrology of the Longnose peridotite deposit and its relationship to the Duluth Complex: Unpubl. M.S. thesis, Univ. Minn., Duluth, 121 p. Listerud, W.H., and Meineke, D.G.., 1977, Mineral resources of a portion of the Duluth Complex and adjacent rocks in St. Louis and Lake Counties, northeastern Minnesota: Minnesota Department of Natural Resources, Division of Minerals, Report 93, 74p. Miller, J.D., Jr., and Ripley, E.M., 1996, Layered intrusions of the Duluth Complex, Minnesota, USA. In Cawthorne, R.G., ed., Layered Intrusions: Amsterdam, Elsevier Science, p. 257-301. Miller, J.D., Jr. and Weiblen, P.W., 1990, Anorthositic rocks of the Duluth Complex: Examples of rocks formed from plagioclase crystal mush. Journal of Petrology 31, p. 295-339. Miller, J.D., Jr., Green, J.C., Severson, M.J., Chandler, V.W., and Peterson, D.E., 2001, Geologic map of the Duluth Complex and related rocks, northeastern Minnesota. Minnesota Geological Survey Miscellaneous Map Series, M-119, scale 1:200,000 Miller, J.D., Jr., Severson, M.J., and Foose, M.P., 2002, Bedrock geologic map of the Babbitt NE 7.5' quadrangle, St. Louis and Lake Counties, Minnesota. Minnesota Geological Survey Open-file Map, scale 1:24,000 Miller, J.D., Jr., Green, J.C., Severson, M.J., Chandler, V.W., Hauck, S.A., Peterson, D.M., Wahl, T.E., 2002, Geology and mineral potential of the Duluth Complex and related rocks of northeastern Minnesota. Minnesota Geological Survey Report of Investigations 58, 207 p. Naldrett, A.J., 1997, Key factors in the genesis of Noril’sk, Sudbury, Jinchuan, Voisey’s Bay, and other world class Ni-Cu-PGE deposits: implications for exploration: Australian Journal of Earth Sciences, v. 44, p. 283-315. Paces, J.B., and Miller, J.D., Jr., 1993, Precise U-Pb ages of Duluth Complex and related mafic intrusions, northeastern Minnesota: geochonological insights to physical, petrogenetic, paleomagnetic and tectono-magmatic processes associated with the 1.1 Ga Midcontinent rift system: Journal of Geophysical Research, v. 98, no.B8, p. 13,997-14,013. Patelke, R.L., 1996, The Colvin Creek body, a metavolcanic and metasedimentary mafic inclusion in the Keweenawan Duluth Complex, northeastern Minnesota: Unpublished M.S. thesis, University of Minnesota, Duluth, 232 p. Peterson, D.M., 2001, Development of a conceptual model of Cu-Ni-PGE mineralization in a portion of the South Kawishiwi Intrusion, Duluth Complex, Minnesota: Laurentian University – Society of Economic Geologists, Second Annual PGE Workshop, Sudbury, Ontario. Phinney, W.C., 1969, The Duluth Complex in the Gabbro Lake quadrangle, Minnesota. Minnesota Geological Survey Report of Investigation 9, 20 p. Ripley, E.M., 1986, Origin and concentration mechanisms of copper and nickel in Duluth Complex sulfide zones – a dilemma: Economic Geology, v. 81, p. 974-978. Sassani, D.C., 1992, Petrologic and thermodynamic investigation of the aqueous transport of platinumgroup elements during alteration of mafic intrusive rocks: Unpubl. Ph.D. thesis, Washington Univ., St. Louis, MO, 2 vols., 952 p. Sawyer, E.W., 1996, Melt segregation and magma flow in migmatite: Implications for the generation of granite magmas: Earth Sciences, v.87, p. 85-94. Severson, M.J., 1991, Geology, mineralization, and geostatistics of the Minnamax/Babbitt Cu-Ni deposit (Local Boy area), Minnesota, Part I: Geology: Natural Resources Research Institute, University of Minnesota, Duluth, Technical Report NRRI/TR-91/13a, 96 p. (with plates) Severson, M.J., 1994, Igneous stratigraphy of the South Kawishiwi intrusion, Duluth Complex, northeastern Minnesota: Natural Resources Research Institute, University of Minnesota, Duluth, Technical Report NRRI/TR 93/34, 210 p. (with plates) Severson, M.J., 1995, Geology of the southern portion of the Duluth Complex: Natural Resources Research Institute, University of Minnesota-Duluth, Technical Report NRRI/TR 95/26, 185p. (with plates) Severson, M.J., and Barnes, R.J., 1991, Geology, mineralization, and geostatistics of the Minnamax/Babbitt Cu-Ni deposit (Local Boy area), Minnesota, Part II: Mineralization and geostatistics: Natural Resources Research Institute, University of Minnesota, Duluth, Technical Report NRRI/TR-91/13b, 221 p. Page 257 �Severson, M.J., and Hauck, S.A., 1990, Geology, geochemistry, and stratigraphy of a portion of the Partridge River intrusion: Natural Resources Research Institute, University of Minnesota-Duluth, Technical Report, NRRI/GMIN-TR-89-11, 236p. (with plates). Severson, M.J., and Hauck, S.A., 1997, Igneous stratigraphy and mineralization in the basal portion of the Partridge River intrusion, Duluth Complex, Allen Quadrangle, Minnesota: Natural Resources Research Institute, Univ. Minn., Duluth, Tech. Rept. NRRI/TR-97/19, 102 p. Severson, M.J., and Hauck, S.A., 2003, Platinum group elements (PGEs) and platinum group minerals (PGMs) in the Duluth Complex: Natural Resources Research Institute, Univ. Minn., Duluth, Tech. Rept. NRRI/TR-2003/37, 296p. Severson, M.J., and Miller, J.D., Jr., 1999, Bedrock geologic map of Allen quadrangle, St. Louis County, Minnesota: Minnesota Geological Survey Miscellaneous Map Series, M-91, scale 1:24,000 Severson, M.J., and Zanko, L.M., in prep., The Babbitt Cu-Ni deposit, Part D: Footwall hosted massive sulfide at the Local Boy ore zone (revisited): Natural Resources Research Institute, University of Minnesota, Duluth, Technical Report Severson, M.J., Patelke, R.L., Hauck, S.A., and Zanko, L.M., 1994, The Babbit copper-nickel deposit, Part B: structural datums: Natural Resources Research Institute, University of Minnesota, Duluth, Technical Report, NRRI/TR-94/21b, 48p. (with plates) Taylor, R. B., 1964. Geology of the Duluth Gabbro Complex near Duluth, Minnesota. Minnesota Geological Survey Bulletin 44, 63 pp. Theriault, R.D., Barnes, S.-J., and Severson, M.J., 1997, The influence of country-rock assimilation and silicate to sulfide ratios (R factor) on the genesis of the Dunka Road Cu-Ni-platinum-group element deposit, Duluth Complex, Minnesota: Canadian Journal of Earth Science, v. 34, p. 375-389. Theriault, R.D., Barnes, S.-J., and Severson, M.J., 2000, Origin of Cu-Ni-PGE sulfide mineralization in the Partridge River intrusion, Duluth Complex, Minnesota: Economic Geology, v. 95, p. 929-943. Tyson, R.M., 1976, The mineralogy and petrology of the Partridge River troctolite in the Babbitt-Hoyt Lakes region of the Duluth Complex, northeastern Minnesota. Unpublished Ph.D. dissertation, Cornell University, 179p. Watowich, S.N., Malcolm, J.B., and Parker, P.D., 1981, A review of the Duluth Gabbro Complex as a domestic source of critical and strategic metals. Society of Mining Engineers of AIME, preprint 81351, 9 p. Zanko, L.M., Severson, M.J., and Ripley, E.M., 1994, Geology and mineralization of the Serpentine copper-nickel deposit, Duluth Complex, Minnesota. Natural Resources Research Institute, University of Minnesota, Duluth, Technical Report, NRRI/GMIN-TR-93-52, 90p. Page 258 � Dublin Core The Dublin Core metadata element set is common to all Omeka records, including items, files, and collections. For more information see, http://dublincore.org/documents/dces/. Title A name given to the resource Institute on Lake Superior Geology Dublin Core The Dublin Core metadata element set is common to all Omeka records, including items, files, and collections. For more information see, http://dublincore.org/documents/dces/. Title A name given to the resource Institute on Lake Superior Geology: Proceedings, 2004 Description An account of the resource Institute on Lake Superior Geology. Duluth, Minnesota. May 4-9, 2004. Creator An entity primarily responsible for making the resource Institute on Lake Superior Geology Date A point or period of time associated with an event in the lifecycle of the resource 2004 Format The file format, physical medium, or dimensions of the resource PDF Language A language of the resource English